Electric vehicle fast charging: is it the antidote to “range anxiety”?

As the number of electric vehicles increases, there is a growing need for more energy-efficient charging infrastructure systems around the world. The reality is that the range and battery capacity of new electric vehicles are higher than those of their predecessors, so there is an urgent need to develop new fast DC charging solutions to meet the demands of fast charging. The reference designs provided by TI focus on topological considerations when designing power modules that are smart and efficient as part of a fast DC charging pile design.

Author: Doctor M

Since March this year, with the official war between Russia and Ukraine, the international fuel price has been soaring, hitting new highs repeatedly. Affected by this, new energy vehicles with good market conditions have attracted more attention from consumers. In fact, the emergence of electric vehicles (EVs) and hybrid electric vehicles (HEVs) is primarily driven by environmental concerns. However, unexpectedly, the large-scale regional energy crisis caused by regional conflicts can also become an incentive to affect the development of the new energy vehicle industry.

As a result, experts predict that in the next decade, the market performance of electric vehicles will become more prominent, and even the topic of current discussion is no longer whether electric vehicles will eventually take over the auto industry, but when. According to Wallbox’s survey data, almost all respondents believe that electric vehicles will dominate the automotive market by 2030-2040.

When buying a car, why not an electric car?

From the perspective of environmental protection and intelligence, electric vehicles should be the first choice for buying a car. However, this is not the case. Because it is generally believed that: first, electric vehicles do not have much competitive advantage in price; second, there are problems such as insufficient number of commonly used AC piles and too long charging time, the charging process is time-consuming and laborious, and the cruising range has not reached the general level expectations.

Electric vehicle fast charging: is it the antidote to “range anxiety”?
Figure 1: Comparison of charging time from household sockets to ultra-high-power charging piles (Source: Infineon)

This will all be a thing of the past as charging infrastructure continues to be built, fast chargers are developed, and high power density batteries are used. The adoption of new materials and technologies has further improved the capacity and power density of electric vehicle batteries, and today’s lithium-ion batteries have a capacity seven times that of lead-acid batteries of the same size. According to the forecast of Grand View Research, the global electric vehicle charging infrastructure market size is 15 billion US dollars in 2020, and its compound annual growth rate is expected to reach 33.4% from 2021 to 2028. Among them, the market penetration rate of electric vehicle charging equipment in commercial places is significantly higher than that in residential places. With the popularity of electric vehicles, the number of fast charging piles and even smart charging stations that are conducive to energy optimization will also increase significantly.

Evolving Fast Charging Solutions

Fast, economical, safe and reliable are important considerations that electric vehicle charging solutions must take into account. When designing DC charging piles for electric vehicles, these conditions are often met: increase output power and shorten charging time; increase power density within the set size of the charging station; improve efficiency by increasing load and reducing power consumption; reducing per watt Design cost of electrical energy. Therefore, design engineers must overcome the following technical challenges:

One is power consumption and heat dissipation. True fast charging should allow the battery to be charged at up to 350kW. Based on this calculation, an efficiency of 97% means a power loss of 9kW. Powering an electric vehicle at a specified high power level creates significant losses and high temperatures that can cause damage to the device.

The second is the balance between battery size and charging current. Infineon has calculated that when charging the car battery, taking the BMW i3 car as an example, since 2016, its battery capacity has been 95Ah. If a 100Ah battery is charged continuously at a current of 100A, it will theoretically take an hour to fully charge. At the current normal voltage of 400V, it takes about 40kW of charging power to charge a 100Ah battery in one hour. This is only the power required for a battery life of about 200 kilometers, and it cannot be regarded as a real fast charge. If the charging time is to be further shortened, the charging current must be increased, and the modification of any parameter of the charging pile requires various trade-offs.

The third is the safety issue of high power output. The Consolidated Charging Standard (CCS) allows output voltages higher than 500V, so it should only be performed by trained professionals, and has high material and technical requirements for a uniform charging plug.

Faced with these challenges, semiconductor technology is the key to making electric vehicle fast charging more convenient, economical and sustainable.

Power topology of TI electric vehicle charging pile

As the number of electric vehicles increases, there is a growing need for more energy-efficient charging infrastructure systems around the world. The reality is that the range and battery capacity of new electric vehicles are higher than those of their predecessors, so there is an urgent need to develop new fast DC charging solutions to meet the demands of fast charging. The reference designs provided by TI focus on topological considerations when designing power modules that are smart and efficient as part of a fast DC charging pile design.

Figure 2 is a typical block diagram of a DC charging pile. Given that stacking converters inside the vehicle makes the vehicle bulky, these stacked converters are often placed outside the vehicle as part of the EV charging pile. The charging pile is directly connected to the vehicle battery through the on-board charger. The DC charging pile is an L3 charger that can handle extremely high power in the range of 120 to 240kW. The L3 charger typically charges the battery to 80% state of charge (SoC) within 30 minutes. To achieve this high power level, TI uses stackable modular power converters.

Electric vehicle fast charging: is it the antidote to “range anxiety”?
Figure 2: Typical block diagram of a DC charging pile (Image source: TI)

As shown in Figure 2, the power module in the DC charging pile consists of an AC/DC power stage and a DC/DC power stage integrated in the charging pile. Each converter is associated with its power stage, which consists of power switches and gate drivers, current and voltage sensing, and a controller. Figure 3 is a system-level block diagram of an electric vehicle charging pile power module obtained from TI’s Electric Vehicle Charging Station Power Modules webpage. On the input side, it has three-phase AC power, which is connected to the AC/DC power stage. The module converts the incoming AC voltage to a fixed DC voltage of about 800 V, which is used as the input for the DC/DC power stage. In addition, the gate driver that drives the power stage MOSFETs is also part of the power stage. Each power stage has a separate controller responsible for processing the analog signal and providing fast control action. In addition to this, there are different temperature sensing modules, CAN, Ethernet and RS-485 interfaces, as well as isolated and non-isolated DC/DC converters for powering auxiliary circuits such as fans for cooling radiators, isolation amplifiers, etc. .

Electric vehicle fast charging: is it the antidote to “range anxiety”?
Figure 3: System-level block diagram of the electric vehicle charging pile power module (Source: TI)

As mentioned earlier, DC charging piles require high-power converters to charge to 80% state of charge within 30 minutes. These fast charging applications require modular power converters that can be paralleled to meet different power levels for fast charging. Energy density and system efficiency are the most important parameters for fast charging piles. If we could double the power output for the same size, that would be a huge cost saving and would help with fast charging.

For a given application, higher system efficiency means lower losses and smaller heat sink solutions. TI’s reference designs take this into consideration. The AC/DC stage (also known as the PFC stage) is the first power conversion stage of the electric vehicle charging station, which converts the input AC power (380C415VAC) from the grid into a stable DC link voltage of around 800V. PFC stage is very important to maintain sinusoidal input current, usually THD Infineon ultra-fast DC charging system

If the energy conversion efficiency reaches 99% or more, cooling becomes relatively simple. Infineon sees modern power chips as the key to this. These chips now have levels of efficiency unimaginable just a few years ago. The high-performance silicon carbide (SiC) modules developed by Infineon have already established their place in the solar industry, an industry that also requires high performance. Now, Infineon is applying these high-efficiency circuits to the field of electric vehicles. The goal of high-power charging systems is to shorten charging times to the point where electric vehicles are comparable to gasoline-powered vehicles. With a high-power DC charging system of up to 350kW, it takes about 7 minutes to charge for a range of 200 kilometers. This efficient, fast and easy-to-use charging method will help eliminate people’s “range anxiety”. Charging stations with Infineon technology reduce the charging time from three hours to a few minutes.

For 50kW to 350kW DC EV chargers, a common strategy employed in this power category is to use power modules rather than discrete devices. IGBT-based solutions feature EconoPACK and EconoDUAL for Vienna rectifiers and AFEs as well as AC-DC conversion, typically operating at around 20 kHz. The CoolSiC Easy module enables the AC-DC converter stage to operate at around 40kHz to 50kHz. CoolSiC is also the device of choice for the DC-DC stage, enabling higher switching frequencies to reduce overall system size and achieve higher efficiency.

Among them, Infineon EconoDUAL3 series products can support 600V / 650V / 1200V and 1700V voltage levels, and the complete current range from 100A to 900A. Combined with the latest generation of TRENCHSTOP IGBT7 technology, the module extends the current rating of the 1200V product family from 600A up to 900A. The symmetrical design of the modules enables optimized current sharing between the IGBT half-bridges in parallel operation.

Electric vehicle fast charging: is it the antidote to “range anxiety”?
Figure 4: EconoDUAL 3 with TRENCHSTOP IGBT7 (Image credit: Infineon)

For converters using CoolSiC MOSFETs, the increased switching frequency can lead to significant reductions in magnetic component volume and weight by up to 25%, significantly reducing application cost. The optimized IMZA65R027M1H CoolSiC MOSFET 650V excels in achieving the lowest application losses and highest operational reliability. This SiC MOSFET is available in a TO247 4-pin package, which reduces the effect of parasitic source inductance of the gate circuit, resulting in faster switching and improved efficiency.

Four innovative technologies make electric vehicle charging more powerful

Fast charging, connected cars and smart charging are several key technologies that have accelerated the adoption of electric vehicles around the world in recent years. Next, what other major innovations will further promote the development of the electric vehicle market? After careful analysis, we believe that the following technologies will have the largest impact on the mass adoption of electric vehicles and will reshape the electric vehicle market in the coming years.

• Bidirectional charging technology

The latest trend in automotive technology is the vehicle-to-grid (V2G) concept, which allows energy to flow from the battery to the grid to maintain grid stability when the vehicle is parked or not in use. This is also a popular bidirectional charging technology in the industry.

Compared with traditional one-way chargers, two-way charging is a major breakthrough in car charging technology. In the past, this technology has only been used in specific pilot projects due to its high cost and bulk. After a series of technological improvements, bidirectional chargers are now cheaper, smaller and more efficient. With bidirectional charging technology, the battery of an electric vehicle will be transformed into a point of energy storage, benefiting EV drivers and even utility companies. In fact, electric vehicles could eventually become a key component of a decarbonized grid. In Wallbox’s Electric Vehicle Impact Survey, 75 percent of respondents said they approve of the technology’s promise. It seems that two-way charging is still in its infancy, and its potential will increase as the technology improves.

• Improved battery technology

Battery technology has improved significantly over the past decade and prices have fallen sharply, with lithium-ion battery prices falling by about 85% between 2010 and 2018. However, battery technology still needs further improvement, with the goal of equipping cheaper electric vehicle models with better range. Among them, the ratio of battery efficiency to cost is the key.

Most electric vehicles today use lithium-ion batteries. Higher-energy-density, safer, and lower-cost batteries are more likely to eliminate range anxiety about electric vehicles. In the process, solid-state batteries that can effectively extend life and cruising range have begun to enter the electric vehicle market. Compared with the 6-year life of lithium-ion batteries, the average life of solid-state batteries is about 10 years or more. With the addition of hydrogen fuel cells, it is impossible to judge which battery will ultimately stand out in the application, but as long as it can bring more capacity, greater range and lower price, the electric vehicle industry will benefit from this and further increase its market share.

• Smart charging technology

The idea behind smart charging is simple, all aspects of its definition boil down to energy consumption. The ultimate goal of smart charging is to optimize energy usage while charging electric vehicles. To achieve this, unlike traditional (or non-smart) chargers, smart charging requires digital communication and data exchange with the EV itself, charging stations and energy suppliers, and it is this way of working and charging that has earned the “smart” “title. The overall effect of smart charging is to “fill up” electric vehicles in a cheaper, more energy-efficient, sustainable way, while helping to extend battery life.

• Automobile manufacturing technology

Improved battery technology is a key step in increasing the demand for electric vehicles, and electric vehicle manufacturing technology is also an important part of making the public willing to choose electric vehicles. In short, economies of scale, incremental improvements, and major innovations in production technology are critical for the auto industry to keep up with the rapidly growing demand for electric vehicles.

Companies such as Tesla have demonstrated that electric vehicles can gradually replace traditional fossil fuel-powered vehicles in the coming decades. Electric vehicles are taking over the auto industry thanks to innovative technology, and improved battery technology will make electric vehicles cheaper and more attractive than gasoline-powered vehicles.

According to a report by the International Energy Agency (IEA), electric vehicle (EV) sales in the first quarter of 2021 increased by about 140% year-on-year. The transition to electric vehicles seems inevitable as governments work to meet the Sustainable Development Goals and the auto industry plans to invest more than $330 billion by 2025 to advance vehicle electrification.

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