Charged is hosting a virtual conference on EV engineering this week that’s free to attend. The conference includes live webinar sessions with interactive Q&As and on-demand webinars.
Just like the content Charged brings you every day, conference topics will span the entire EV engineering supply chain and ecosystem including motor and power electronics design and manufacturing, cell development, battery systems, testing, powertrains, thermal management, circuit protection, wire and cable, EMI/EMC and more.
The California Public Utilities Commission (CPUC) has unanimously approved Southern California Edison’s (SCE) Charge Ready 2 program, a $437-million EV infrastructure program that will support the deployment of up to 38,000 new charging stations across Southern California over the next four years.
SCE says Charge Ready 2, which builds on the $22-million Charge Ready program that was approved in 2014, is the largest single utility EVSE project in the country.
One major goal of Charge Ready 2 is to increase access to EV charging in important but underserved locations such as apartment complexes and workplaces.
Highlights of the program include:
Make-ready infrastructure for charging stations at workplaces and multi-unit dwellings; turnkey infrastructure solutions for charging stations at multi-unit dwellings; and rebates to ensure newly constructed buildings are EV-ready
Commitments to serve disadvantaged communities, including a 50 percent target for make-ready infrastructure; a 100 percent target for turnkey solutions; and a 30 percent target for new construction rebates
$14.5 million for education and outreach efforts
According to the Sierra Club, regulators around the US have approved some $2.1 billion in utility-driven EV infrastructure programs to date. These investments include more than $1 billion in California, as well as a $701-million program approved in July by New York regulators that will be split among the state’s electric utilities.
Tesla is increasing its focus on perfecting its manufacturing process. As Zachary Shahan writes in a recent CleanTechnica article, “the machine that builds the machine” just may be Elon Musk’s favorite phrase these days.
In fact, Musk expects Tesla’s manufacturing prowess to give it an edge over other EV-makers. “Tesla’s long-term competitive advantage will be manufacturing,” he told Shahan. Of course, some critics would consider that a bold statement, considering the piles of bad publicity Tesla has gotten over reports of poor build quality in the past.
Shahan notes that there is “much less industry derision regarding Tesla’s manufacturing experience than there used to be. However, “the world still doesn’t understand how disruptive Tesla will be when it comes to manufacturing innovation.”
Shahan points out that some of the widespread media tropes about Tesla’s struggles with manufacturing may be overstated. In a recent CleanTechnica interview, Peter Mertens, a former exec at Audi, VW, Volvo, and Jaguar Land Rover, said he knew exactly what Tesla was going through during its Production Hell phase, and that he saw it as an unavoidable part of the process for any automaker that ramps up production of a new model—not the existential disaster that was depicted in the press.
Shahan also explains that Tesla’s bad experience with too much and too-hasty automation during the Model 3 ramp has not caused the company to back off on automation altogether. On the contrary, Tesla is “continuously looking for opportunities to automate more of the production process.” In a 2019 interview, President of Automotive Jerome Guillen told Shahan that Elon wanted production line engineers to find at least a couple of improvements per week to make production more efficient.
Some may be surprised to learn that many of the efficiency improvements have to do with software systems at Tesla’s factories. Tesla’s focus on software in its vehicles is well known, and is often cited as one of the company’s main competitive advantages over legacy automakers. However, software is a key part of the machine that builds the machine as well.
Remember that Musk’s original background is in engineering. “Vast majority of what I do every day is hardcore engineering across many disciplines,” he told Shahan. “I’m chief engineer at both SpaceX and Tesla. That would be a more accurate title than CEO.”
Aspiring engineers know this, and that’s surely part of the reason that the companies are so attractive to top engineering students. As Benzinga reports, in a recent survey, engineering students ranked Tesla as the most attractive employer in the US, and SpaceX as #2.
Amazon made a splash in the EV world last September when it ordered 100,000 electric delivery vans from EV startup Rivian. Now the company says it will buy an additional 1,800 electric vans from Mercedes-Benz.
The order includes 1,200 large eSprinter electric vans and 600 medium-size eVito electric vans. It represents Mercedes-Benz Vans’ largest order of EVs to date.
Amazon’s Delivery Service Partners will have access to the new fleet in Europe this year.
Mercedes-Benz’s eSprinter, the electric version of its popular Sprinter van, has a battery capacity of 55 kWh, and delivers an estimated range of 150 kilometers with a maximum payload of 900 kilograms. Safety features include active brake assist, reverse camera and blind spot assist.
The mid-size eVito sports a 41.4 kWh battery pack, an 84 kW electric motor, and a range of around 150 km.
“With the eVito and the eSprinter, we have electric vehicles in our portfolio [that are] ideally suited for the requirements of the courier, express, and parcel-service industry for goods delivery on the so-called ‘last mile’ in terms of their equipment and range,” said Marcus Breitschwerdt, head of Mercedes-Benz Vans. “They show that local emission-free driving, convincing performance, comfort and low operating costs can be combined perfectly.”
Mercedes-Benz chose this occasion to announce that it has joined The Climate Pledge, which calls on signatories to be net zero-carbon across their businesses by 2040. The company is evaluating ways to remove carbon from its entire value chain, from development to the supplier network, and to power its EVs with renewable energy.
“We welcome the bold leadership demonstrated by Mercedes-Benz by signing up to The Climate Pledge and committing to ambitious action to address climate change. We need continued innovation and partnership from auto manufacturers like Mercedes-Benz to decarbonize the transportation sector and tackle the climate crisis,” said Amazon CEO Jeff Bezos.
Researchers at the Karlsruhe Institute of Technology (KIT) and Jilin University have investigated a promising anode material for future high-performance batteries: lithium lanthanum titanate with a perovskite crystal structure (LLTO). As the team reported in Nature Communications, LLTO can improve battery energy density, power density, charging rate, safety and cycle life without requiring a particle size decrease from micro to nano scale.
Anodes of lithium-ion batteries consist of a current collector and an active material—usually graphite—that stores energy in the form of chemical bonds. However, negative electrodes made of graphite have a low charging rate, and are associated with safety issues. Among the alternatives, lithium titanate oxide (LTO) has already been commercialized. Negative electrodes with LTO present a higher charging rate and are considered to be safer than those made of graphite, but they tend to have a lower energy density.
Schematic representation of the perovskite crystal structure of lithium lanthanum titanate. (Illustration: Fei Du/Jilin University)
According to the study, which was led by Professor Helmut Ehrenberg, LLTO anodes have a lower electrode potential compared to commercialized LTO anodes, which allows for a higher cell voltage and a higher capacity. “Cell voltage and storage capacity ultimately determine the energy density of a battery,” explains Ehrenberg. “In the future, LLTO anodes might be used to build particularly safe high-performance cells with long cycle life.”
To improve the charging rate, it is common practice to reduce the particle size of the electrode material from micro to nano scale. The study shows that even particles of a few micrometers in size in LLTOs with a perovskite structure feature a higher power density and a better charging rate than LTO nanoparticles. “Thanks to the larger particles, LLTO basically enables simpler and more cost-effective electrode manufacturing processes,” says Ehrenberg.
Charging time is the Achilles’ heel of EVs. Much faster refueling could be enabled by boosting the voltage of an EV’s battery system from the 400 volts used by most current models.
The Porsche Taycan uses an 800-volt battery architecture, which means the current can be cut in half, so wires can be lighter and thinner. According to Porsche, at the Taycan’s maximum charging power of 270 kilowatts, the battery can be charged from 5% to 80% of capacity in about 20 minutes.
GM says its upcoming Hummer EV will also use an 800-volt system.
Now Kia says it will introduce an 800-volt battery system on a new crossover-like EV that will be launched in 2021. The company said in January that the new model will have “around 300 miles” of range and offer a “sub-20-minute recharge time.”
Automakers’ EV efforts will remain focused on Europe for the near future, so it could be some time before the new faster-charging Kia is available in the US. A Kia spokesperson told Electrek that the company’s electric priority is Europe, and that its US EV sales would continue to be limited, for various reasons. However, the company has said that pure EVs will make up 20% of its US sales by 2026.
Electrek’s Bradley Berman notes that Kia is currently selling EVs in only 13 or so US states, and that it sold no more than 2,000 EVs in the US in 2019, so the company’s predictions should be sprinkled with a grain or two of (lithium) salt.
Be that as it may, an increase to 800 volts is clearly the future. As EV ranges push past 400 miles, and charging networks are starting to roll out 350 kW fast chargers, system voltages will have to be cranked up to keep pace.
Lonestar Specialty Vehicles has partnered with Los Angeles-based In-Charge Energy to offer customers turnkey energy and charging solutions for fleet conversion to EVs.
Texas-based Lonestar is a supplier of fully electric remanufactured commercial vehicles. The company has deployed more than 3,000 Class 8 trucks and tractors. Its mission is to provide an alternative to internal combustion-powered terminal tractors (tractors that serve ports, logistics centers and industrial facilities). Observing the amount of downtime customers were encountering with Tier 4 emissions equipment was the driving force behind the development of Lonestar SV’s Reman line of electric terminal tractors. The company deployed its first electric T22 in November, 2019.
Together with In-Charge Energy, Lonestar will now offer end-to-end turnkey solutions that include EV charging infrastructure as a service.
“When electrifying a fleet, our customers have new operational and budgetary considerations to make, that often require an innovative solution,” said Lonestar General Manager Blake Yazel. “It is critical that we provide solutions for any obstacle our customers might face in their sustainability goals. Our mission is to provide zero-emission solutions that are hassle-free, value-added, every time, for every customer. Our partnership with In-Charge Energy allows us to provide a turnkey solution and ultimately make the transition to zero emissions seamless for fleets.”
Q&A with Giovanni Bertolino, Head of E-Mobility at Enel X
Some of the most compelling stories in the EV world these days have to do with charging. For an individual EV driver, charging may seem like a simple matter—plug in your car in the evening, and it’s ready to drive in the morning—and that’s part of the appeal of driving electric. However, behind the plug, there’s a complex ecosystem that’s still taking shape, and it’s full of challenges and opportunities for automakers, infrastructure providers and electric utilities.
Fleet operators are learning that they need help to manage charging in order to maximize the benefits from going electric, and utilities are discovering that EVs present a valuable new resource to make grids run more smoothly and to ease the integration of renewable energy. The opportunities are especially rich for companies offering products and services that make all the pieces of the green puzzle work together. One of the fastest-growing firms in this space is Enel X, a North American subsidiary of the Enel Group, a multinational power company headquartered in Italy.
Enel X is involved in several different sectors of the clean energy ecosystem, and it offers a broad range of solutions to help both individuals and commercial customers electrify their transport operations and optimize their energy usage. Enel acquired the innovative EV charger manufacturer eMotorWerks in 2017, and folded it into the Enel X brand in 2019. eMotorWerks was a pioneer in smart charging, distributed energy storage and vehicle-to-grid services, and now Enel X is taking these concepts to the next level.
Charged recently spoke with Giovanni Bertolino, Head of E-Mobility at Enel X, and here’s what he had to say.
Charged: You provided over 200 electric buses, along with charging infrastructure, to Santiago, Chile in 2019. Tell us about that.
Giovanni Bertolino: Our ideal is to provide a full turnkey solution to our customers, the city of Santiago and the other cities we’ve been working with. We provide bus route analysis to understand which routes are best suited for electric buses. We then select the buses with the right characteristics to optimally convert those routes. We buy the buses, and we provide the charging infrastructure and set up the depots for the buses to be charged at night or during the day, whenever they are idle. Then we deploy the software to optimize the fleet management, the routes, and the charging of those buses. We also size the charging infrastructure for those depots. Everything is bundled into a turnkey service for cities.
We procure the buses, and in the case of Santiago, we deployed several hundred BYD electric buses and charging infrastructure.
When possible, we can also provide energy services, which means leveraging the bus batteries and Enel X smart chargers to provide flexibility to the grid in the form of demand response or, in the more advanced cases, we can also provide full V2G integration, where you can use the batteries to give back energy to the grid. We have a number of pilots already implementing V2G, and that’s definitely a part of our solution. There are still very few instances where that is becoming a reality, but we are ready to offer that as well.
Charged: Is this kind of turnkey service something that transit agencies are using in the US, or are they typically trying to find the electrification solutions themselves?
Giovanni Bertolino: In the United States there are at least two, or maybe more, relevant markets when we talk about public transportation. There are transit buses and there are school buses. Transit buses are usually managed by transit authorities. School buses are sometimes operated by private companies, but in many cases, cities and school districts own the buses.
There are about 100,000 transit buses across North America, and there are more than 480,000 school buses. Those buses are well suited to be substituted with electric buses. When it comes to transit buses, the penetration is already quite significant globally, because it makes economic sense today.
We believe that our solution might accelerate the transition to e-buses, providing an easier or less capital-intensive up-front solution for transit authorities, especially in this period of budget cuts and reductions due to COVID. We believe that, rather than them putting the money up front, or entering a financial lease, a solution of a fleet-as-a-service might be appealing. We have recently started bringing this solution to the United States.
When it comes to school buses, the economics are more challenging. The cost difference between a conventional diesel bus and an electric bus is significantly higher. It’s expensive, regardless of how it is powered, so there is a missing finance issue, which is being solved through grants.
Some school districts and municipalities are willing to push for electrification of their school bus fleets because they are aware of the environmental benefits that they bring, but that investment can be more challenging, getting that funding. With our solution, we can provide easier access to electric buses, because we can package a turnkey solution and the benefits of participating in energy markets. In North America, there are several markets where packaging the solutions can also include the value of energy services that we are able to monetize, and that can make for a better deal for the customer. For electric school buses, this is especially relevant, because they spend much of the day idle, so they can be connected to provide grid services.
Charged: Why is the economic case so much different for school buses than it is for transit buses?
Giovanni Bertolino: Basically, it’s just that the battery pack is expensive. The cost of batteries is going down year after year, but it’s still a very significant cost of acquiring the bus. The fact is that the rest of the bus—the vehicle, the wheels and the rest for the school bus is pretty cheap. When you add the battery pack and the electric transmission, the cost of a school bus goes from a range of $85,000 to $100,000 for a conventional bus to the $350,000 range for an electric school bus, so it’s three times more expensive.
When it comes to transit buses, first of all, they’re much bigger than school buses, they are more sophisticated, and they have better design and features. The hardware of the bus, regardless of the drivetrain, is rather expensive, so when you add the battery pack, the percentage increase from a conventional bus to an electric bus is smaller. And if you couple that with the fact that the transit buses are driving many more miles than school buses, and driving electric saves money for every mile that you travel, transit buses have a business case advantage.
Charged: Tell us about your charging hardware, particularly your JuiceBox line.
Giovanni Bertolino: What we are providing to our customers is a smart charging solution. It’s a solution because it’s hardware, software and services, depending on the customer. And it is smart because our chargers are connected to WiFi and the electric grid. JuiceNet, our Internet of Things software platform, connects all of our chargers, and enables a number of services. We provide a number of energy services for dozens of utilities, and also independently participate in energy markets.
We have a line of hardware products. The core product is what we call JuiceBox, which is a smart charger for EV drivers. It’s a Level 2 charger, and we have different power levels. Our lineup ranges from 32-amp to 40-amp to 48-amp products. We also have JuicePump, a 50 kW DC fast charger for public and commercial use.
The Level 2 chargers are single-phase, 240-volt smart home appliances that you can install in your garage or in a parking lot, or that can be mounted on our mounting solutions. These boxes can be configured and managed through an app on your phone, and there is also a dashboard available through the web, through which you can access all the connectivity of the box. You can manage your settings and you can monitor your energy consumption, how much you are spending for driving your car, and other things.
The commercial version, our JuiceBox Pro, has an identification mechanism. Our JuiceNet Enterprise dashboard allows commercial customers to manage multiple charging ports and multiple locations, and so forth. The smart features allow the chargers to participate in utility programs that provide active and passive strategies like demand response or time-of-use rates.
In fact, we are partnering with more than 30 utilities in North America. We provide energy services, like enabling time-of-use rates, demand response, collecting behavioral charging data, and so on. We have very good use cases with Seattle City Light, Puget Sound Energy, Sonoma Clean Power, Hawaiian Electric, Platte River Power Authority and many others.
We also provide services directly to grid operators. For instance, in California, we’ve aggregated thousands of our smart chargers, which together make about 68 megawatts of load. And we can manage that load as if it were a virtual battery, by participating in CAISO markets. The value we create by providing the flexibility of those chargers to the grid, we give back to our EV drivers through JuicePoints, a charging rewards program.
This is a rewards program for customers to keep their JuiceBox chargers connected to WiFi, so that they can participate in this program. And it translates into actual money that our customers get back by providing flexibility to the grid. Whenever there is a peak load in California, the CAISO [California Independent System Operator, which manages the grid] can dispatch a signal to reduce consumption to our JuiceBox chargers. So instead of charging the electric cars at full power, we will reduce [power to] all the smart chargers, or some of the chargers, depending on the settings that each customer has set on their phones. We can reduce the load and provide demand response service.
Another smart feature that we provide to our customers is what we call JuiceNet Green. This is a feature that the customer can activate, which keeps track of the generation mix at any moment in time in each grid. We know the carbon intensity of the electrons that are coming into the grid at any given moment, and we can optimize the charging of your car during the time available.
Let’s say you plug in your car when you get home and you set on your phone that you need the car in the morning—that gives us about 11 or 12 hours to charge the car. And we know, given the state of charge, that you will need a smaller number of hours to completely charge your car. We can play with that flexibility, trying to optimize the moment when you charge so that we can minimize the carbon intensity of the electricity that goes into your car. So, you’re driving a bit cleaner than if you were just adding a charger, and that’s something that more environmentally conscious customers really appreciate.
Charged: What are the main customer segments that you’re serving?
Giovanni Bertolino: We’ve historically served the residential market, and we have thousands of smart chargers in homes across North America—many in California, which correlates with EV adoption. This year, we expanded our product line to serve commercial customers, which is an area where we are planning to grow significantly.
In North America, 80 percent of charging happens at home, so we will continue to see demand for smart home chargers. However, this market is closely tied to EV sales, and we also expect to see significant acceleration in the amount of commercial EV infrastructure that will be installed at the workplace, in commercial spaces and with fleets. The more connected electric vehicles there are, the more value we can extract for all stakeholders to save money, through grid services.
One of a coming wave of low-volume luxury plug-in hybrid SUVs, the 2020 BMW X3 xDrive 30e offers 18 miles of electric range—and the ability to use it in the real world.
The 2020 BMW X3 xDrive 30e is the first conventional plug-in hybrid model from BMW that’s actually worth plugging in. It’s one of a growing number of sedan and utility models from the German maker to be offered in the States with optional plug-in hybrid powertrains, following a few earlier models that simply didn’t justify making the effort.
On the outside, the X3 PHEV is indistinguishable from any standard X3. New for 2018, this generation of the “compact crossover utility”—or “Sport Activity Vehicle” as BMW tends to dub it—has grown considerably from earlier versions. It’s now longer and wider, with a longer wheelbase, than the first X5 crossover launched in 2000, though it’s incrementally lower.
The plug-in hybrid X3 is powered by a 2.0-liter turbocharged 4-cylinder engine that drives all four wheels through an 8-speed automatic transmission. Combined output of the engine plus the 80 kW (107 hp) electric motor is 252 hp and 310 lb-ft of torque. It’s EPA-rated at 18 miles of electric range. Once the 12 kWh battery is depleted, the heavy SUV operates as a conventional hybrid, with a combined fuel economy rating of 24 mpg—versus a higher 26 mpg combined for the same X3 without the plug.
A plug-in hybrid version of the larger X5 utility will join the X3 for 2021. Compared to the plug-in X5’s previous generation, which was BMW’s first-ever SUV with a plug, it has a more powerful engine (a 389 hp turbocharged 3.0-liter inline 6 replaces the previous 308 hp 2.0-liter turbo 4) and a far larger battery (24 kWh vs 9 kWh). That gives it 30 miles of EPA-rated range rather than the previous 14 miles. The new, larger battery has as much capacity as the one in the 2014 BMW i3.
Both plug-in crossovers are tuned more for performance than for green credentials—the X5 45e sports a 0-60 acceleration time of 5.3 seconds and a towing capacity of up to 7,200 pounds. Both the X3 we tested and the 2021 X5 are built at BMW’s plant in Spartanburg, South Carolina.
Why plug it in?
Prior to the current generation, BMW’s plug-in hybrids had small batteries and electric motors that only powered the car under light loads. The earliest ones—we drove a 2016 BMW 330e and a prototype 2016 X5 xDrive 40e—were so sensitive that even a whiff of uphill slope could cause the engine to flip on.
The current X3 xDrive 30e, on the other hand, automatically starts in Max eDrive (all-electric) mode if the battery has been charged. Absent emergencies or lead-foot driving, it will stay there for more or less its EPA-rated 18 miles of electric range. That’s enough to do all or most of your local trips on electricity, and plug it in once you return home. And it’s an incentive for drivers to plug in for smooth, quiet, uninterrupted electric travel without the engine flipping on.
As befits a performance SUV, of course, when you floor it, both parts of the powertrain kick in and it takes off like a scalded cat (or at least a scalded cat that weighs 4,600 pounds).
That’s not the case for another luxury plug-in hybrid SUV, the 2020 Volvo XC90 T8, which, with three rows of seats, is considerably larger. On major hills and at highway speeds, its 11.6 kWh battery and 65 kW (88 hp) electric motor weren’t always enough to sustain the 5,400-pound SUV’s speed.
We put 244 miles on the plug-in BMW X3 over several days, in a combination of highway travel and around-town errands. We plugged the car in to recharge five times, giving us a total of 78 electric-only miles in Max ePower mode. (The math may be confusing because we didn’t fully discharge the pack on all of those runs.)
At the end, the trip computer said 95.7 of the 244 miles were covered on electric power. That’s a bit deceptive, as it includes electric-only miles covered as a regular hybrid once the battery had been depleted. But the trip computer also indicated a combined gas-and-electric average of 47.2 mpg, which is stellar for an SUV of this size—and we’d only used three eighths of the tank of gas to do that.
Adventurous gives way to conservative
BMW was the most adventurous of German makers in electric cars 10 years ago, but it hit the Reset button hard on its electrification efforts in 2016. A new CEO set the goal of stemming the flow of red ink from early experiments in EVs, and rolling out models that would meet stiffer carbon-emission rules at lower cost. The current range of models reflects that change, of course.
BMW’s first EV was the technically advanced i3, a small hatchback with a carbon-fiber-reinforced plastic body shell. It delivered 81 miles of rated range, and offered an optional tiny two-cylinder range-extending engine that gave it another 70 miles or so. The combination made sense for European drivers living in crowded cities, but its small size, peculiar styling, limited range, and starting price above $40,000 limited its sales in the US.
Here, BMW buyers want SUVs and sedans, not city cars or hatchbacks. Despite multiple range increases—the current EPA rating is 153 miles—over seven model years, BMW has sold fewer than 45,000 i3s in the US.
Total US sales of its various conventional plug-in hybrid models are roughly equivalent. Over five years, these have included versions of the 3, 5, and 7 Series sedans, and the X5. None of BMW’s various plug-in hybrid models have reached the 20,000-plus annual sales of the now-deceased Chevrolet Volt in its heyday. The highest one-year sales for its two best-selling PHEVs were 8,600 530e sedans (in 2018) and 6,000 X5 25e SUVs (in 2016).
BMW, however, has no fewer than five plug-in hybrids on tap for 2021. The list for the coming model year includes: the 3 Series sedan (330e, with or without xDrive AWD); 5 Series sedan (545e xDrive); X2 transverse-engine crossover (X2 xDrive 25e, not yet confirmed by the company); the X3 xDrive 30e we tested; and the larger X5 xDrive 45e. The company also sells a plug-in hybrid version of the Mini Cooper Countryman small crossover utility vehicle (whose underpinnings the X2 shares), which is rated at 18 miles of electric range.
PHEVs: compliance cars for the EU
Those plug-in models, most of which will likely sell in modest volumes, underscore BMW’s commitment to electrification before its new all-electric models—the i4 that will compete with the Tesla Model 3, and its flagship iNext luxury SUV—hit showrooms in the next few years.
It’s important to understand that plug-in hybrids serve an important function in Europe, where rules for reducing tailpipe emissions of carbon dioxide really started to bite this year. And a change in legislation has improved the electric range of all those PHEVs.
Over the last two years, the European Union has switched from using the outmoded and wildly overoptimistic New European Drive Cycle (NEDC) tests to the more stringent Worldwide Harmonized Light Vehicles Test Procedure (WLTP), which requires lab tests to be backed up by on-the-road tests of real-world emissions and energy use. WLTP still produces more optimistic electric ranges than the test cycles used by the US EPA, but its results are considered closer to reality for European driving conditions.
Finally, European carbon-emission rules now give credit to plug-in hybrids only if their WLTP tested range is at least 50 km (31 miles). That’s why the latest round of BMW and other makes’ plug-in hybrids have far larger battery packs and ranges up to double the previous numbers.
BMW is hardly an outlier
The policy of offering longer electric ranges in a wider range of PHEVs is hardly limited to BMW. Its German rivals Audi and Mercedes-Benz, Britain’s Jaguar Land Rover, and the Chinese-owned Volvo of Sweden are all introducing more sedan, wagon and hatchback models with plugs, as well as the SUVs that dominate in North America.
While most of these models are likely to sell in quite low numbers, together they will add up. They’ll also introduce more luxury buyers to vehicles with plugs. And now, they’re more pleasant—meaning more consistently electric—to drive.
It’s usually one of the first objections cited by EV naysayers: batteries can’t or won’t be recycled, and they contain hazardous materials that will end up in landfills. In fact, no such sinister scenario is likely—most of the components of Li-ion batteries are valuable, and it’s quite feasible, technically and economically, to recycle them. Several auto OEMs, research institutes and other industry players around the world are developing systems to do just that.
However, it is fair to say that it’s early days for battery recycling, and that there is much work to do to build a recycling regimen that will be able to handle the volume once substantial numbers of vehicles are electrified. Charged spoke with Li-Cycle’s Co-Founder, President and CEO, Ajay Kochhar, who explained what his company is doing to build a sustainable battery recycling ecosystem.
Ajay Kochhar, a chemical engineer, and Tim Johnson, a mechanical engineer and Chartered Financial Analyst, founded Li-Cycle (pronounced LIE-cycle) in 2016. “We come from the lithium industry,” Kochhar told Charged. “We used to work for companies that produced lithium chemicals that go into cathodes, cells and, ultimately, battery packs. Way at the other end of the supply chain—mining and refining, particularly the refining piece.”
Kochhar chatted with Charged about the company’s history, its unique system for collecting and processing materials, and the future of the battery recycling ecosystem.
Charged: What inspired you to start Li-Cycle?
Ajay Kochhar: We were leading a practice, a consultancy, essentially consulting with companies to build large chemical plants. And we’d be asked as lithium consultants and experts to look into these looming questions: “How environmentally friendly are batteries? And what’s going to happen to all these batteries?” It was very opaque, hard to figure out what was happening. Sometimes you can’t even figure out who is dealing with the batteries. So, we didn’t find very satisfying answers.
It’s all about critical material supply—supply of lithium and nickel and cobalt to go back into batteries. We’d be asked, what’s actually happening to all these batteries, at end of life? Is there really some sort of recovery of these materials to go back into batteries? And again—this is now four or five years ago—it was very opaque, unclear. Most of the time we concluded, for some materials like lithium, there really wasn’t any recycling happening to process that material back into lithium-ion batteries.
Charged: So, all of the batteries used in laptops and phones, there’s not been much material recovery?
Ajay Kochhar: No, not so much has been recovered. I’d say the general approach has been reuse. It’s typically either mom-and-pops or individuals that are—in the case of laptop batteries—taking them apart, and selling the cells. There’s a lot of that that happens.
Or, if it’s large quantities, it usually is a waste approach. You have these generalized “recyclers” that deal with those batteries. They often thermally treat them—they’re burning off plastic and electrolyte in the batteries and are not really focused on the material recovery. It’s mainly the cobalt, the nickel and the copper that they can get via that method, but that’s usually it. Lithium is burned off, or it goes into a waste fraction. Other components, like plastics, electrolytes, graphite, they’re all essentially burned off, typically. It’s not usually overtly apparent—you have to dig in and understand. Our team has been to a lot of these facilities, and that’s usually the case—it’s usually a waste approach, not resource recovery, and not very efficient.
Charged: So, you guys came along to fix that.
Ajay Kochhar: Exactly. We launched the company in 2016, after a couple of years of intense R&D. Instead of a thermal process, what we do is a mechanical and chemical process. It’s two steps. Both are patented, owned by the company. We handle all types of lithium-ion batteries, from laptop and cellphone batteries all the way up to EV batteries. There’s not a large quantity of end-of-life EV batteries yet, but we’re starting to see some here and there.
In the first step, we basically size-reduce the batteries. It’s a shredding process, which may not sound that spectacular, but it’s really all about safety—how do you do that without risk of fire or a thermal event?
In the second step, we take those physically separated materials, and we reprocess that intermediate material to recover battery-grade end chemicals—lithium, nickel, cobalt—that are suitable to go back into cathodes again. Overall, it’s 95% recovery, and the materials that we make are equivalent grade, if not better, to mined and refined materials, and very competitive in terms of price with virgin materials.
At a high level, this is very different from what’s been happening in the industry to date. Materials don’t actually go back to the lithium-ion battery supply chain, they go to some other lower-quality use, typically. So, ours is a completely different approach.
We’ve had a couple of years of R&D, and now we’re in the commercial operations and building phase.
Charged: Would you say this is analogous to the process for recycling lead-acid batteries, in which they reuse the materials?
Ajay Kochhar: Yeah, that’s where we’re trying to get to. Lithium-ion is quite a bit more complex, obviously, than lead-acid. With lead-acid, you have a few different types, but on the whole it’s pretty homogenous. The complication with lithium-ion—and this is why there’s the need for innovation—is that there are so many different types. It keeps on getting innovated, keeps on changing year-on-year. You have different chemistries, different flavors, different form factors. It doesn’t end. So, that’s the challenge. How do you get a process that’s agnostic, and at the same time is going to be economic no matter what, on a mixed basis? That’s been our mantra from the start—to ensure that you can take any lithium-ion battery in a mixed fashion and ensure it’s scalable. And now, we’re operating at commercial scale and on the verge of expanding internationally.
Charged: You said step one is to safely shred the batteries. Can you tell me a little bit about how you do that safely? Do you fully discharge them?
Ajay Kochhar: It’s a Hub-and-Spoke model, like a wheel. The Spokes are the decentralized satellite sites that do the shredding, and the Hub is the refining, the chemical process.
A big problem in this industry has been logistics. If I’m an automotive company, and I have a battery I have to get rid of, if I have to pay somebody to take care of the battery, that’s a big issue. Because you have to pay quite a bit to ship these heavy batteries any distance. So, the solution to that is our Spokes. We get close to the source. Modular, scalable plants, low-footprint, almost “Lego-built” facilities. That’s how we set it up for them, regionally deploying these sites to get batteries close to the source, convert into not-a-battery and then ship that intermediate material, which is now safe, can’t catch fire, and is cheaper and easier to ship in bulk.
Charged: I know there’s a lot of regulations around shipping lithium-ion, so this gets you around that, I imagine.
Ajay Kochhar: It does. So, how to deal with this safely? We’re essentially shredding in such a way that there’s no access to oxygen. There’s a variety of ways to do that—we do it in a particular way, it’s patented. But from a safety standpoint, it’s not only the actual processing, but there’s a lot of standard operating procedures and health and safety requirements around storage, logistics, handling. We’ve had to develop a lot of this safety stack of approaches.
Charged: When you have a barrel of your shredded material, what is handling that like? Are there any special precautions you have to take with the shredded stuff?
Ajay Kochhar:Handling the shred products is way easier. It’s basically mixed metals—quite inert. At the Spokes you get batteries going in, any type, minimal dismantling. Mixed small and large, one stream, one process. And coming out the other end we have separated plastics, copper, aluminum. And the key fraction, which is the most valuable, is the cathode and the anode in the battery. The cathode always contains lithium, and potentially nickel, cobalt, other metals. And the anode is usually graphite.
So, that cathode/anode mixture, that’s the most valuable. All that’s inert, not a big deal to be shipping that around relative to batteries. There are some key regulatory aspects you have to ensure that are met, but way easier than batteries. That black powder is the feed to our Hub process, the refining process.
Charged: So then, at that step you use chemical processes?
Ajay Kochhar: That cathode/anode material, we recover everything in it: graphite; lithium, you recover that as a lithium chemical; cobalt, you recover that as a cobalt chemical; nickel, as a nickel chemical, and so on. There are about eight different products from our hub facility.
In the first step, it’s a lot about safety and automation. In the second step, it’s mainly about dealing with the variability. You get such a large variation of different types of lithium-ion batteries. You have types that are really high cobalt, types that are really high nickel. So, that’s the difficulty and the innovation that we’ve now had to deal with.
Around the world you have a lot of [variation]. In China, for example, you have a lot of refineries that are taking this cathode/anode material and recovering cobalt and nickel. But the interesting thing is that they don’t usually recover lithium. There is basically no commercial, battery-grade, lithium chemical recovery from any facility around the world. You have a lot of people that are doing bench-scale work, pilot work. But the reality is, in the market there’s no one who’s actually getting the lithium out of a lithium-ion battery, which is very ironic.
We do. We actually get the lithium, in a battery grade, out of lithium-ion batteries. And I think we’re the only facility in the world that can do that. So, it’s another key differentiator of what we’re doing.
Charged: Is that just due to the market cost of lithium?
Ajay Kochhar: I think it’s two things. If you rewind about 10 years, lithium prices were way lower than they are today. So that’s probably part of it. I think the second is that this industry is on the precipice of turning from a niche business with low volumes into one that’s going to have quite high volumes in the future. It’s going to take some time to get there, but if you still have these old, inefficient, generalized processes, you’re losing out on a lot of the material in those batteries that can be recovered.
Charged: When a battery dies or loses capacity, it’s largely due to side chemical reactions that are unwanted and build-up or damage to the interfaces of the electrodes, etc. But all the originally materials are still present, so your process separates those and starts from scratch, correct?
Ajay Kochhar: Yes, exactly. The way the batteries usually die is through these side, or parasitic, reactions. And usually it’s a physical change or morphological change within the battery. There’s a number of ways that batteries can die, but commonly you have, call it lithium inventory, it ends up in parts of the battery that it shouldn’t be, it gets locked up in these side products, so you lose the ion, which is basically the thing shuttling back and forth to create the charge. Over time, the inventory of that changes. That’s actually the most common way that the battery dies. So, you lose your capacity because the “runner” got stuck somewhere, or a few of the “runners” got stuck in some other places and now you can’t use them to create electrical charge.
It’s a location or a form change that’s happened in the actual physical form. We go back to the fundamental building blocks. The actual lithium is still there, it’s just in a different form. We’re basically going back to the fundamental atoms, then we’re rebuilding those chemicals that are reused in a lithium-ion battery.
Charged: You’re entering a new phase now, into a commercial process. Can you tell me where you are now and where you’re headed next?
Ajay Kochhar: Right now, we’re the largest recycler of lithium-ion batteries in North America. In pretty quick order that’s become the case. We have an existing facility in Ontario, which grew out of our R&D center and is now a commercial facility—North America Commercial Spoke 1. And we have a second facility (North America Commercial Spoke 2) that we’re building in Rochester, New York in the old Eastman Kodak business park, which has now turned into a hub of activity for cleantech, which will be live later in 2020.
Where we’re going is twofold: we’ll continue to grow in North America. And, outside North America, what we’re doing is partnering up via joint ventures. Our philosophy behind that is that this is a very regional market, the nuances are very regional, regulations are very regional. In every region of the world it’s going to have a different approach, so you really do need regional partners to help you get to speed at scale.
Charged: In terms of a business model, are you buying the used batteries, or are they paying you to process them?
Ajay Kochhar: It really depends on the type of battery, and the region around the world. In some regions there’s a norm that groups pay for batteries and in other regions it’s the norm that it’s a service. Within that there’s variability, because some batteries have a lot of valuable materials, and some don’t. But from a high level, if you talk to any vehicle manufacturer, anybody that has batteries that will need to be recycled in the future, what they want is for this not to be a liability. They want it to be either zero-cost or even, ideally, a value. That’s why we started this company, in large part, was a customer need. It’s basically folks saying, “Why are we paying for this? Isn’t there a lot of valuable material in here? Why hasn’t there been an innovation to solve this?”
As the scale gets there in the next five to ten years, we believe we can transform that norm and make it clearer. Is this a cost? Is it net zero? It’s a bit immature today, but in the medium and long term, our objective is to change that into a clear economic position.
Charged: Are you currently selling the raw materials on the open market?
Ajay Kochhar: We actually do commercially sell a lot of our materials back to the market today. It is a very rigorous process to qualify the material, convince people of its quality. Usually, you start with a small sample and then you get to a medium-size sample and then a larger sample, and that’s the thing that basically leads, ultimately, to a contract. That takes a long time. And we’ve progressed to that for a lot of the materials that we produce. We’re delivering materials under contract to groups that make battery materials that go back into batteries again.
Where I’d love to see us go in the next, say, three to five years—and this isn’t quite there yet in the market—is the circular economy model. Say you get battery materials from a certain manufacturer and you recover the materials out of that, then you integrate that right back into the same manufacturer’s supply chain or a few suppliers’ supply chains. We’re getting there, we can definitely enable that, but that’s going to be a medium-term reality.
Charged: In terms of the quality of the materials that are the product, in most cases it’s identical to the virgin material? How do you quantify that for people for graphite, for example?
Ajay Kochhar: Yes. There are a variety of nuances as it relates to the quality of lithium and nickel and cobalt. And in graphite, for example, these are almost tailored, specialty chemicals. You have a specific customer, they’re going to want a little bit less of this and a little bit more of that, etc. There’s a generalized specification that you can work to, but the reality is that when you actually engage with specific groups they’ll say, “Actually, we want a little bit less of that.” And, “Oh, that’s too high.” We’re talking about levels of parts per million—very, very small levels of materials. So, we’ve gone through that qualification with a variety of groups for lithium and nickel and cobalt.
We make lithium carbonate and nickel sulfate and cobalt sulfate. That’s gone very well, and it just takes iteration. Being in the market, having materials to market, iterating the physical properties of that specification, etc.
Lithium, for example, that goes to a cathode manufacturer, it has to meet a certain spec. There are certain impurity sensitivities, and you have to be below those thresholds. So, we supply to meet that spec and then they would use that lithium in making a new cathode. That’s one example where it integrates back into the supply chain.
There are, however, parts of the battery where it’s tougher and it’s going to cost a lot and maybe it’s not worth it, or there are difficulties, and graphite is one of those examples. So, we make the graphite, say technical grade or concentrate material, that can go back to other applications of graphite, like electrodes or pencils, whatever it might be. But graphite is very sensitive. It’s down to the physical properties of it. You have different types of graphite—synthetic, natural. We are getting the complete mix of all that. In one stream, we get synthetic, mixed, this size, that size, etc.
So in theory, yes, you could go back to a graphite battery-grade product, sure. But there’s some strategic decisions where we’ve looked at it and tried a variety of things, and we just said, “No. There’s not as much net value.”
It’s a big step up not to be burning graphite, which has been the norm to date. We’re giving back to the economy, that’s important. But there are some technical realities. You can’t be taking this mixed feed in and getting a perfect graphite product. There’s some situations where we are trading back into the battery supply chain, and there’s others where it’s more difficult and the priority is to get it back to the economy through other markets.
Charged: There are regulations that mandate the amount of lead-acid batteries that have to be recycled. Do you see that becoming the norm for lithium-ion as well?
Ajay Kochhar: Yes. If you had asked me about maybe 12 months ago, I think it was much more unclear. But we’ve seen a lot of movement, even in the last year, from jurisdictions such as China, Europe, certain states in the US, provinces in Canada. There’s an emerging theme of two things. One is, there is an emerging priority of who is responsible for the battery at end of life. And that’s been a big question. Who is going to deal with this and who’s responsible? In the case of China, it’s been made very clear that it is the automotive manufacturer that is responsible for the battery’s end of life.
Second, it’s about recovery. Typically, if you have regulations on recycling, they do mandate some level of recovery. For example, in Europe to date, the mandated recovery for lithium-ion batteries has been 50%. But there is an upcoming renewal of that regulatory framework that will likely push that number up. And that’s the same theme around the world. We see a lot of different regulations that are stipulating recoveries that are way above 50%, typically 70%, 80%, even 85% plus. And that’s really interesting because on the one hand, as a recycler that can achieve that, that’s great. That’s locking in a lot of acceleration for us. However, we have to be a bit careful about the staging. In some parts of the world that solution may be available, in other parts not. And so, I think that’s typically the place that the automotive companies are trying to plug in and make sure that it’s not being introduced prematurely. That it’s being staged in the right way so that the solutions are available in the market to meet those requirements.
Charged: What about the copper and aluminum and the plastics? Is that stuff easily mechanically separated out in the grinding phase?
Ajay Kochhar: Exactly. It’s all automated, we use physical properties to separate that out, no thermal processing, we don’t burn anything off. Then we put them into the standard copper, aluminum, plastic recycling supply chain.
Charged: What are the next steps for you? Are you guys looking for customers? Are you looking for partners? If someone in China or Europe wanted to license your technology, would you do that?
Ajay Kochhar: Generally speaking, yes, that’s what we’re doing. The intent is not maybe so much via licensing. I think there’s a lot of, say, younger companies in this space where that’s what their business model is. And now the reality is that, to put it very plainly, you have to do it. You have to show that what you’re doing is working at commercial scale before somebody else is going to take the risk and license it.
Just to sum up, let me say this. From a consumer perspective about EVs, I think there’s been a lot of questions about, “What are the end-of-life recycling solutions out there? Are they economically viable?” I just want to say it loud and clear: There are solutions today, and they’re here. And this “end-of-lifecycle problem” with lithium-ion batteries and EVs, it’s not a problem. It’s taken innovation to figure it out, but the reality is, it can be done. All that needs to happen is that we continue to scale up to meet the market need over time.
There are solutions there, and that’s important for not only consumers to know, but government stakeholders and OEMs themselves. The whole supply chain, the whole ecosystem, really needs to have that awareness. Because in the absence of that, there is this clear, countercurrent narrative which homes in on [the lack of sustainable and economic recycling solutions for lithium-ion batteries], and it’s actually wrong.
Charged: You hear a similar thing with the long tailpipe argument. People say, “You know, these things are fueled by coal.” And, “What are we going to do with all the batteries?” is the next thing they say, and my response is, those are both solved.
Ajay Kochhar: Exactly. And they’re not solutions that will be here in the future. They’re here today.
For years, we’ve been hearing about an EV technology that promises to be a game-changers: Vehicle-to-Grid (V2G) bidirectional charging. My recent work with one V2G charger developer, Fermata Energy, has convinced me that V2G has found its proverbial killer app: load peak shaving for commercial/industrial energy customers. This article is going to concentrate on the technical aspects of bidirectional chargers, but understanding why the added headache of bidirectional operation is worth the price paid never hurts. Larger commercial/industrial energy customers are charged not only for the total energy in kWh consumed each month, as all customers are, but are also assessed a penalty for the peak power demanded over a given sampling interval (typically 15 to 30 minutes), as well as a penalty if their average power factor is too high (or a discount if it’s low). For example, my local utility, TECO, assesses a demand charge of $11.03/kW for the average power drawn over any given 30-minute period, so a facility that draws 10 kW most of the time but spikes to an average of 50 kW for at least 30 minutes would be assessed a penalty of $551.50! This is called demand billing, and the idea behind it is to encourage larger energy consumers to take steps to flatten out their load profiles and/or improve their average power factors, so the utility doesn’t have to spend so much on upgrading the grid. A bidirectional DC fast charger that can detect when a peak load comes online and switch from charging to inverting can shave off at least some of that peak demand, and that does rather shift the economics of installing one at a facility from merely being a nice gesture (or even just a token nod towards “being green”) to one that is strongly compelling.
Two other critical requirements for bidirectional chargers are that they must be galvanically isolated from the AC mains, and they must immediately cease operating as an inverter upon loss of power (in other words, they can’t be used as a standby generator or UPS). That last is also known (somewhat more infamously) as the “anti-islanding” provision, whose questionable rationale is to protect utility workers from being electrocuted from a power source at the load end backfeeding onto the mains (despite the fact that utility workers are trained to treat all wires as hot until bonded to earth ground, and to wear gloves when handling them). Another common regulatory requirement is that the charger operate at very close to unity power factor (that is, it must employ Power Factor Correction, or PFC), but this functionality more or less comes for free in any charger that is bidirectional. In fact, not only can a bidirectional charger source back to the grid at near unity power factor, it can also correct bad power factor to some extent, at least for the loads downstream, and some utilities will even pay you for doing so.
There are a myriad of different circuit arrangements that could be used to make an isolated bidirectional charger which meet the above criteria, but for the sake of brevity I’m going to concentrate on just two approaches: a 3-phase active rectifier/inverter front end (i.e. the mains-side converter) coupled to a bidirectional buck/boost converter back end (i.e. the EV-side converter), and with isolation either provided by (1) a conventional mains-frequency transformer or by (2) inserting a high-frequency DC-DC converter in between the DC link that would otherwise directly join the other two converters (e.g. between C4 and C5 in Fig. 1). The main reason for choosing this topology is that it is pretty much the simplest one for a bidirectional EV charger that can perform power factor correction over a wide range of EV traction battery voltage relative to that of the mains. Referring to Fig. 1, the three voltage sources on the far left, V1-V3, represent the 3-phase AC mains (wired in wye, though they could be wired in delta with no functional difference), while the battery symbol on the far right, V4, represents the EV traction battery. MOSFETs M1-M6, along with inductors L4-L6, operate as a 3-phase boost converter when in charging mode, and a buck converter in discharging mode, and as long as the DC link voltage (buffered by reservoir capacitors C4 and C5) is higher than the peak voltage of the AC mains, near unity power factor can be achieved. MOSFETs M7 and M8, along with inductor L7, comprise a bidirectional DC-DC converter that can operate as a buck when M7 is modulated and M8 is freewheeling, or as a boost when M8 is modulated and M7 is freewheeling. Those of you paying close attention will have noted that L1-L3 have yet to be mentioned. These inductors—more commonly referred to as line reactors in this position—are inevitably required to meet surge and electromagnetic compatibility (EMC) requirements, so they are typically purchased ready-made as pre-approved components.
That just leaves the proverbial elephant in the room, which is providing galvanic isolation between the mains and the EV, and the only practical way of doing that is with a transformer. As mentioned above, this could be a mains-frequency (and likely 3-phase) type inserted in between the bidirectional charger and its connection to the mains, or a high-frequency (HF) ferrite type inserted in between the other two converters. The biggest upsides to the mains-frequency transformer are that it will be very robust and almost certainly pre-approved as meeting worldwide safety standards, so incorporating one into the charger can make getting through safety agency testing much easier overall. Furthermore, isolation on the mains side also allows a much simpler circuit to be used for the bidirectional charger (basically the one shown in Fig. 1). The biggest downside is that the size and weight of a transformer go up as operating frequency goes down. For example, a commercially available mains isolation transformer rated for 15 kVA (or 15 kW at unity power factor) will weigh about 90 kg (200 lb), and come in a cabinet approximately 0.5 m (20 in) on a side, while a 12.5 kW/200 kHz ferrite transformer I recently designed fits in the palm of the hand and weighs about 1 kg (2.2 lb). There is an equally dramatic difference in price between both transformers, too—the mains version costs $1,100, while the ferrite one can be built in modest quantities (~100 units) for less than $100. However, the mains transformer will provide bidirectional isolation right out of the box, and can be easily wired in between an existing non-isolated charger with little or no effect on the latter’s operation. In contrast, the ferrite transformer will need a whole bunch of switches and the support circuitry to drive them to operate at HF, and all of this has to be inserted into the DC link between the AC-DC active rectifier/inverter on the mains side and the DC-DC buck/boost converter on the EV side. Hence, it has to be designed into the charger from the get-go, and since every HF ferrite transformer is bespoke, all of the burden of meeting safety agency requirements will then fall upon the charger OEM (or the magnetics design firm subcontracted for the job). All of this narrows the price differential between the two approaches, or outright inverts it, and that’s not even factoring in the much higher development effort and regulatory burden when going the HF ferrite transformer route.
Things get really interesting in bidirectional charger design when you consider all the support circuitry needed to use a HF ferrite transformer for isolation, as the circuits that do the active rectification/inversion (on the AC side) and buck/boost DC-DC conversion (on the EV side) are relatively straightforward. The simplest approach is to use identical full bridges on each side of the transformer, which are driven synchronously with a duty cycle just under 50% so that little filtering is required (see Fig. 2). This allows energy to flow in either direction at any time, effectively making it a transformer that operates on DC. In fact, an electromechanical version of this circuit—with relays replacing the semiconductor switches used today—was employed to supply HV to the vacuum tubes in early car radios. This topology is formally known as the synchronous bidirectional full-bridge, but it is more commonly referred to as a DC transformer, because that is effectively what it is. Applying PWM to this topology is notoriously difficult (because the input and output can flip sides at any time), but operating at a fixed duty means there is no way to limit overcurrent except by totally shutting down all of the switches simultaneously. Also, the leakage inductance of the transformer and the output capacitances of the switches can exact a hefty penalty on efficiency and reliability, limiting the allowable switching frequency as power goes up (right when you need it most).
There are numerous circuit variations that address some or even all of the aforementioned downsides—adding either passive or “lossless” snubbers is the most obvious—but a particularly compelling option is to make use of the transformer leakage inductance as part of a series resonant network by inserting a calculated amount of capacitance (and, optionally, additional inductance) in series with each side of the transformer, then driving the bridge switches with a fixed duty cycle at the resultant resonant frequency (see Fig. 3). This changes the shape of the current waveform from squarish to sinusoidal, which dramatically reduces switching losses, and it also absorbs any other stray inductances (besides transformer leakage) into the series resonant networks, eliminating the need for snubbers and allowing much higher-frequency operation. There are two downsides to series resonant operation: output can only be regulated by varying the frequency so it still can’t limit overcurrent when operated at a fixed duty cycle; and the stability of the resonant frequency depends on the value of components (and strays) not drifting too much with time and temperature. Both of these issues have prevented wider adoption of this topology, but DC fast chargers are expensive and relatively low-volume products, so having to tweak the frequency on a per-unit basis isn’t quite so painful as it would be for, say, a Level 1 charger.
