Drivers for EV adoption of higher battery voltages

Drivers for EV adoption of higher battery voltages

[Introduction]Many countries and regions are enacting legislation to increase the number of electric vehicles (EVs), with the goal of phasing out or eventually banning gasoline and diesel vehicles. While early adopters may buy cars for environmental benefits, a significant portion of the market is still concerned about the range limits and charging times of electric vehicles.

The automotive industry is facing the challenge of continually delivering innovative solutions that appeal to a wider audience, and this is driving the trend toward higher battery voltages. Currently, most passenger electric vehicles on the road use 400V batteries. Electric buses and electric trucks are 600V-class vehicles, and passenger cars are starting to use 800V batteries.

The introduction of the 800V system is a big step forward compared to the existing 400V system, and it is rolling out faster than many expected. What are the advantages of an 800V system? How can they help address some of the issues that have created barriers for consumers and slowed the rollout of electric vehicles?

How does an 800V battery affect vehicle design?

The core elements of a brushless DC motor are the rotor (usually permanent magnets or DC armature windings) that generates the DC magnetic field, and the stator containing the copper windings through which the AC current flows. Motion relies on the interaction of the rotor magnetic field with the rotating magnetic field created by time-controlled currents in the stator windings. At a given input power, as the motor operating voltage increases, the input RMS current decreases, and the stator winding copper losses also decrease. Losses are typically reduced by a factor of 4 using an 800V supply compared to a 400V supply. This provides an opportunity to reduce the wire diameter of the copper windings, both to reduce the overall volume and to improve packaging efficiency, making the motor smaller. The 800V system has the same lower current requirements, which reduces not only the motor copper losses, but also the losses in the overall system connector, resulting in weight, space and cost savings.

800V systems also typically move from silicon-based IGBTs to silicon carbide (SiC) MOSFETs. SiC devices offer higher switching speeds and therefore lower switching losses. This helps to increase the operating frequency, further reducing motor losses due to reduced harmonic currents.

The lighter weight improves handling and acceleration, which is valuable in the premium sports car market. Combined with reduced losses, the range directly related to the battery can be increased, thereby reducing vehicle-related costs. The freed space can be used to increase the size of the battery pack for increased range, or it can be allocated for increased passenger compartment space. Want a bigger trunk? Smaller motors also help with this. It’s worth noting that larger battery packs will also increase charging time, but 800V can take advantage of charging.

Reductions in weight, bulk and wear provide vehicle designers with options to balance cost, performance and range based on specific market segments. The reduction in cost makes the solution more accessible to the mid-range consumer market, not just high-performance vehicles.

Range is one of the key determinants when considering the switch to electric vehicles. For some, it’s a matter of convenience, hoping to make long journeys easier. For commercial vehicles, increased range means more efficient delivery routes, more time on the road, fewer vehicles covering the same area, and lower operating costs.

800V system reduces charging time

Charging time is a challenge for both consumers and commercial vehicles. For city drivers and commuters, overnight charging at home is usually sufficient. However, when planning a long trip, especially when the distance is beyond the vehicle’s range, it is also necessary to plan a route that will provide a charging station at the right time. While charging stations are often placed in nearby amenities, there may still be a queue, which is unacceptable. For commercial vehicles, the problem is more complicated, because returning to the site to charge, or leaving the vehicle idle for 90 minutes while charging on-site, can reduce productivity and directly impact a business’ bottom line.

How does the 800V system architecture help solve the puzzle? As we mentioned earlier, at the same power, doubling the voltage will cut the current in half. During charging, heat dissipation is a limitation on the charging cable as well as the car charger inlet and internal wiring. Upgrading from 400V to 800V can double the charging rate for the same loss. This has several benefits. The first benefit is very simple, and that is reduced charging time. If the charging power is doubled, the charging time will be cut in half, but the improvement is actually smaller. A less obvious benefit is the increased utilization of charging stations. If the dwell time of charging vehicles is halved, the number of vehicles that can use a given charger is doubled.

Porsche and Kia have launched new all-electric vehicles that are starting to approach the median range of a gasoline car and charging times closer to those of a quick stop and pick up at a gas station. The latest deployment of a range of charging stations has a maximum power rating of 400kW, which is more than enough for an 800V architecture.

Porsche’s all-electric sports car, the Taycan, has a range of 420 kilometers (260 miles). It uses an 800V battery architecture and can charge from 5% to 80% in just 22.5 minutes on a 300A (240kW) fast charging station. It’s still capable of using a 400V charging station, which takes about 90 minutes. Kia has announced the EV6 800V architecture car, which can be charged from 10% to 80% in 18 minutes, has a maximum power of 239kW, and can travel 480 kilometers (300 miles) in an extended-range version.

Fast-charging times are critical for commercial vehicles, which can use fast charging to extend operating hours and delay returning to the site for a full charge until the evening. Importantly, these faster charging times also comply with the 30- to 40-minute rest period mandated by many regions.

800V Architecture Adoption Faster Than Expected

The automotive market is adopting 800V architecture faster than initially expected. Porsche is leading the way, but it’s not just sports cars – Kia and several Chinese manufacturers now offer 800V cars. As is typical in the automotive market, innovation starts in high-end cars and slowly makes its way to the mass market as the technology becomes more affordable. The benefits of 800V systems include cost savings that the mid-range consumer market can take advantage of faster than initially thought.

As the automotive market adopts 800V architectures, we will undoubtedly see companies push the benefits of higher voltage systems further. These advantages continue to expand, so 900V and higher can further add to these advantages, driving even more improvements in range, weight, and charging time. Infrastructure will need to keep pace; new 400kW charging stations are already facilitating this direction.

Design Points for Power Solutions in 800V Systems

High-voltage connection subsystems in electric vehicles often require a high-voltage to low-voltage power supply. Stepping up to 800V requires higher isolation and voltage ratings.

Electric vehicle battery packs consist of many individual cells connected in a series/parallel combination. The operating voltage range of each single cell is 3.1V to 4.2V. For a nominal 800V system, there are approximately 198 cells in series with a total pack voltage of 610V to 835V. Due to the effect of the voltage rise during regenerative braking, the voltage is typically increased by 20V to 30V, bringing the maximum voltage to 865V. The switch inside the power supply must be rated significantly higher than this voltage. For a flyback converter, an additional 150V to 200V must be added to bring the switching stress to 1065V. Applying the usual 20% derating, a specification of at least 1.33kV can be obtained.

Another important design point is the need for low voltage startup, typically 30V to 40V. Vehicle safety systems need to be powered up first to ensure that all control electronics are functional before anything starts moving or could fail. Designing a power supply that operates from 30V to >900V can be challenging.

Innovative High Voltage Solutions from Power Integrations

Power Integrations (PI) has announced two new AEC-Q100 qualified, 1700V rated ICs, adding new members to its InnoSwitch™3-AQ product family. These two new devices address the above-mentioned design challenges for 800V systems, bringing a range of valuable capabilities to the automotive space and providing a pathway to higher voltages for future designs.

Drivers for EV adoption of higher battery voltages

Figure 1: InnoSwitch3-AQ 1700V device enables simple, reinforced insulation for automotive power

This simple flyback converter design integrates silicon carbide switches and primary and secondary controllers. The InnoSwitch3-AQ IC uses FluxLink™ for isolation, allowing the secondary controller to become the primary controller. This unusual architecture means that the secondary side decides when the primary switches, enabling synchronous rectification without the usual drawbacks (eg incorrect switching times), and responding to all faults.

Drivers for EV adoption of higher battery voltages

Figure 2: The 1700V rated InnoSwitch3-AQ requires no additional external components

The InnoSwitch3-AQ has a 30V start-up voltage, which is critical for powering up safety systems in automotive applications. Discrete solutions require additional components on the primary side to achieve 30V startup, which is quite costly. Each component connected to the high-voltage bus must be tested for multiple failure modes, so the high integration advantage of PI devices can save system cost, reducing test cases by up to 50%.

Reducing the number of components is critical for electric vehicles. Since there are fewer components, the failure rate due to the components themselves is reduced, and there are fewer solder joints for greater reliability. The savings in board area are even more significant, as this reduces weight and increases power density, freeing up more interior space, important advantages in the electric vehicle market.

The unique architecture of the InnoSwitch3-AQ IC allows it to be located on a safety barrier, a space normally unavailable on the PCB. In fact, it can be placed under the transformer. This design does not take up PCB space, which is of great significance to the design engineer.

Drivers for EV adoption of higher battery voltagesFigure 3: Scalability allows the same design to deliver different power levels with small changes

With very high output control accuracy, there is no need for additional DC-DC converters to generate more busbars – the device itself can provide. Thanks to the FluxLink architecture and its ±2% control accuracy, it only takes two switching cycles to go from zero load to full load and increase the output power from zero to maximum. This means that the output capacitance is also much smaller. With over 90% efficiency, heat dissipation is drastically reduced enough to eliminate external heat sinks. These features further reduce size, space, and component count, among other benefits.

No-load power consumption is usually not a critical parameter, but for EVs that are always connected to the battery, the battery can easily drain when the vehicle is parked for long periods of time. The new InnoSwitch3-AQ device has a no-load power consumption of less than 15mW, ensuring that passengers are not stranded at the airport when they return to their cars.

With the addition of new 50W and 70W output power devices, Power Integrations’ InnoSwitch3-AQ product family is now expanded to provide designs for 400V, 600V, 800V and higher bus voltages for electric vehicles.

Drivers for EV adoption of higher battery voltages

FIGURE 4: COMPLETE FAMILY OF DEVICES FOR 400V, 600V AND 800V SYSTEMS

For more information, visit: power.com.

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