Director of Business Development, Peter Vaughan Power Integrations
Many countries and regions are enacting legislation to increase the number of electric vehicles (EVs), with the goal of phasing out or eventually banning the use of gasoline and diesel vehicles. While early adopters may buy cars for environmental benefits, there are still a significant number of people in the market who are still concerned about the range limitations and charging time of electric vehicles.
The automotive industry is constantly challenged to deliver innovative solutions that appeal to a wider audience, which is driving the trend of increasing battery voltage. Currently, most passenger electric vehicles on the road use 400V batteries. Electric buses and electric trucks are 600V class vehicles, and passenger cars are beginning to use 800V batteries.
The rollout of the 800V system is a big step forward compared to the existing 400V system, and it will be launched faster than many people expected. What are the advantages of an 800V system? How can they help address some of the issues that pose barriers to consumers and slow the spread of electric vehicles?
How does an 800V battery affect vehicle design?
The core elements of a brushless DC motor are a rotor (usually a permanent magnet or DC armature winding) that generates a DC magnetic field and a stator containing a copper winding (from which AC current passes). Motion relies on the interaction of the rotor magnetic field with the rotating magnetic field generated by the time-controlled current in the stator windings. At a given input power, as the motor operating voltage increases, the input RMS current decreases, and so does the copper loss of the stator winding. Using an 800V supply typically reduces losses by a factor of 4 compared to a 400V supply. This provides the opportunity to reduce the wire diameter of the copper windings, both reducing the total volume and improving packaging efficiency, making the motor smaller. The 800V system has the same low current requirements, which not only reduces the copper loss of the motor, but also reduces the loss of the entire system wiring, resulting in weight, space and cost savings.
800V systems also typically switch from silicon-based IGBTs to silicon carbide (SiC) MOSFETs. SiC devices provide 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 high-end sports car market. This, combined with reduced losses, increases the range directly related to the battery, thereby reducing vehicle-related costs. The freed space can be used to increase the size of the battery pack to increase range, or can be allocated to increased passenger compartment space. Want a bigger trunk? Smaller motors also help with this. It is worth noting that a larger battery pack will also increase charging time, but 800V can play a charging advantage.
The reduction in weight, volume and loss gives vehicle designers the option to balance cost, performance and range based on specific market segments. The reduction in cost makes the solution more acceptable to the mid-range consumer market, not just high-performance vehicles.
When considering a shift to electric vehicles, range is one of the key determinants. For some, it's a matter of convenience and hopefully makes long-distance travel easier. For commercial vehicles, increased range means more efficient distribution routes, more time on the road, fewer vehicles covering the same area, and lower operating costs.
The 800V system reduces charging time
Charging time is a challenge for both consumers and commercial vehicles. For city drivers and commuters, charging overnight at home is usually sufficient. However, when planning a long trip, especially if the distance exceeds the vehicle's range, it is also necessary to plan a route that will provide charging stations at the right time. While charging piles are usually placed in nearby amenities, it is unacceptable that there may still be a queue to wait. For commercial vehicles, the problem is even more complicated, because returning to the site to charge, or leaving the vehicle idle for 90 minutes while charging in the field, reduces productivity and directly affects the profits of the enterprise.
How does the 800V system architecture help solve the problem? As we mentioned earlier, doubling the voltage at the same power halves the current. During charging, heat dissipation is a limitation on the charging cable as well as the inlet and internal wiring of the car charger. Upgrading from 400V to 800V doubles the charging rate with the same loss. This has several benefits. The first benefit is very simple, which is to reduce charging time. If the charging power is doubled, the charging time will be reduced by half, but the improvement is actually smaller. The less obvious benefit is the increased utilization of charging stations. If the dwell time of a charging vehicle is halved, the number of vehicles that can use a given charger is doubled.
Porsche and Kia have launched new all-electric vehicles, whose range is beginning to approach the median of gasoline vehicles and charging times closer to the time it takes to quickly stop and pick up goods while refueling at a gas station. The newly deployed series of charging stations has a maximum power rating of 400kW, which is more than enough for the 800V architecture.
Porsche's all-electric sports car, the Taycan, has a range of 420 km (260 mph). It uses an 800V battery architecture to charge from 5% to 80% in just 22.5 minutes on a 300A (240kW) fast charging station. It is still capable of using a 400V charging station, which takes about 90 minutes. Kia has announced the launch of the EV6 800V architecture car, which is charged from 10% to 80% in 18 minutes, has a maximum power of 239 kW, and the extended range version can travel 480 kilometers (300 miles).
Fast charging times are critical for commercial vehicles, as they can extend their working hours with fast charging and postpone the time to return to the depot for full charging until the evening. Importantly, these faster charging times also meet the 30 to 40 minute breaks mandated by many regions.
The adoption of the 800V architecture is faster than expected
The adoption of the 800V architecture in the automotive market is faster than initially expected. Porsche leads 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 with high-end cars and slowly enters the mass market as technology becomes more affordable. The benefits of an 800V system include cost savings, which can be leveraged by the mid-tier consumer market faster than initially thought.
As the automotive market adopts 800V architectures, we will undoubtedly see companies further promote the benefits of higher voltage systems. These benefits are constantly expanding, so 900V and higher voltages can further increase these benefits and even drive improvements in range, weight and charging time. Infrastructure will need to keep pace; new 400kW charging stations are already driving that 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. Increasing to 800V requires higher isolation and voltage ratings.
Electric vehicle battery packs consist of a number of single cells connected in series/parallel combinations. Each cell battery operates from 3.1V to 4.2V. For a nominal 800V system, there are approximately 198 batteries in series with a total battery pack voltage of 610V to 835V. Due to the effect of the voltage increase during regenerative braking, the voltage from 20V to 30V is usually increased, bringing the maximum voltage to 865V. The rating of the internal switch of the power supply must be significantly higher than this voltage. For flyback converters, an additional voltage of 150V to 200V must be added to the switch stress to 1065V. Apply the usual 20% derating to get a specification of at least 1.33kV.
Another important design point is the need for low voltage start-up, typically 30V to 40V. Vehicle safety systems need to be powered on first to ensure that all control electronics are functioning before anything starts to move or a failure is likely. Designing a power supply that operates from 30V to >900V can be challenging.
Innovative high-voltage solutions from Power Integrations
Power Integrations (PI) has released two new AEC-Q100-compliant ICs rated at 1700V, adding a new addition to its InnoSwitch3-AQ product family. These two new devices address these design challenges faced by 800V systems, bringing a range of valuable features to the automotive sector and providing a pathway to higher voltages for future designs.
Figure 1: The InnoSwitch3-AQ 1700V device enables a simple, reinforced insulation automotive power supply
This simple flyback converter design integrates a silicon carbide switch and primary and secondary controllers. The InnoSwitch3-AQ IC is isolated using FluxLink, allowing the secondary controller to become the master controller. This unusual architecture means that the secondary side decides when to perform primary switching operations, implements synchronous rectification without the usual drawbacks (e.g., incorrect switching times), and can respond to all faults.
Figure 2: InnoSwitch3-AQ rated at 1700V 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 the addition of additional components on the primary side to achieve 30V start-up, which is quite costly. Each component connected to a high-voltage bus must be tested against multiple failure modes, so the high integration benefits of PI devices can save system costs and reduce test cases by up to 50%.
Reducing the number of components is crucial for electric vehicles. With fewer components, the failure rate due to the components themselves is reduced, and there are fewer solder joints and higher reliability. The savings in board area are even more significant, as this reduces weight and increases power density, freeing up more interior space, which are important advantages in the eviction market.
The unique architecture of the InnoSwitch3-AQ IC allows it to be located on a safety barrier, which is a space that is not normally available on PCBs. In fact, it can be placed under the transformer. This design does not take up PCB space, which is significant for design engineers.
Figure 3: Scalability allows the same design to deliver different power levels with small variations
Due to the very high output control accuracy, no additional DC-DC converter is required to generate more busbars- the device itself can provide. Thanks to the FluxLink architecture and ±2% control accuracy, it only takes two switching cycles to go from zero load to full load and increase output power from zero to maximum. This means that the output capacitance is also much smaller. With an efficiency of more than 90%, heat dissipation is significantly reduced, enough to eliminate the need for external heat sinks. These features further reduce size, space, and component count, among other benefits.
No-load power consumption is usually not a key parameter, but for electric vehicles that are always connected to the battery, the battery can easily drain after a vehicle is parked for a long time. The new InnoSwitch3-AQ device consumes less than 15mW of no-load power, ensuring that passengers don't run aground there when they return to their car at the airport.
With the addition of new 50W and 70W output power devices, Power Integrations' InnoSwitch3-AQ product family is now even richer, offering bus voltage designs for electric vehicles at 400V, 600V, 800V and higher.
Figure 4: Complete device family for 400V, 600V, and 800V systems