Electrical vehicles (EVs) pose a host of questions, challenges and problems for people seeking to put this breed of car on the road. OEMs’ engineers have one set of issues to tackle, and infrastructure planners quite another, while policymakers are busy assembling the puzzle pieces of renewable energy, EVs and the smart grid. If we consider EVs in isolation, which is easily done on paper but difficult in the real world, the biggest issues are charging time and infrastructure availability.
Architectures and Topologies for of Off-Board Chargers
By Baran Özbakir, Product Marketing Manager, and Gábor Manhertz, Sr. Development Engineer, Vincotech
These challenges will have to be mastered, for EVs are the future of transportation: As many as 120 million EVs could be up and running by 2030 , and the more EVs are on the road, the greater the collective eet’s appetite for energy. Today charging energy demand amounts to around 20 billion kilowatt-hours, with forecasts calling for it to rise to 100 billion kilowatt-hours by 2025 and 280 billion kilowatt- hours by 2030 . This is a tall order to ll – 2030 is just ten years down the road. More ef cient EV chargers could help meet rising en- ergy demands and deliver more power, faster. This article investigates various system architectures and topologies. It trains the spotlight on the DC-DC converters that are the heart of off-board chargers.
There are two main scenarios to ponder, public charging and home charging. Demand for each option varies by region. In view of China’s infrastructural constraints and densely populated cities, public charg- ing is likely to be the far more frequent application in that country. In much of the USA, in contrast, home charging will dominate because so many people live in single-family houses. Then there is the nature of the charging device to contemplate – is it to be a slow charger, a fast charger or a high-power charger?
Figure 1: EV charger power levels
Batteries’ charging periods range from 20 minutes to 20 hours, de- pending on the output power of the electrical vehicle charger (EVC). Take, for example, an EV with 27.2 kWh net battery capacity. A 3-kW residential charger replenishes this battery’s capacity from 0% to 80% in nine hours. A DC-DC off-board fast charger (Level 3) does this in less than 45 minutes.
Figure 2: Average EV charging time
Three main system architectures were on the market at the time of writing. A quick review of each follows.
Figure 3: System architectures
System architecture 1
This is the state-of-the-art system architecture for up to 350 kW. Composed of several units, it is modular. The power level and type
of power unit varies by regions. In China, for example, power units in the latest models of EV chargers are rated for 15 kW to 30 kW, and mainstream power units for 20 kW. Most are based on telecom power supplies with discrete components that still satisfy today’s expecta- tions for ef ciency and reliability. Europe presents an entirely different picture, where even 20 kW power units are based on power modules to meet reliability and ef ciency expectations and reduce manufactur- ing time. Much the same can be said of the USA.
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