Testing Challenges for Electric Vehicle Powertrains
-Battery simulation and testing of V2G modules
The deadline for banning the sale of fuel vehicles in various countries throughout the world have been announced one by one, and the completion of net-zero carbon emissions are rapidly approach. It is critical to reduce reliance on fossil fuels as quickly as possible and promote electrification. As a result, governments have stepped up to promote the electric vehicle industry. However, the industry's new designs and innovations bring new testing challenges too. Electric vehicles contain approximately three times the number of power electronic components as gasoline vehicles, according to research. It usually has high-voltage and high-power characteristics. How can these components be efficiently tested and the electric propulsion system's dynamic performance verified? Engineers require thorough and competent solutions.
What is the EV Powertrain System?
Compared to typical gasoline vehicles, the EV Powertrain System is primarily made up of a power battery system, a drive motor, and a vehicle controller, which is referred to as a "three-electric system." The "three-electric system" is the key to electric vehicles and distinguishes them from gasoline-powered automobiles. The battery is the most crucial of the three systems. It has an impact on a car's range on a single charge, as well as the cost of production.
Gasoline automobiles, in essence, turn chemical energy into mechanical energy, whereas electric vehicle powertrains transfer electrical energy into mechanical energy. Because of the distinct operating principles, troubleshooting the power system of pure EV is wholly new and continually evolving. The debugging job mainly includes low-voltage system debugging, power-on and power-off debugging, high-voltage system joint debugging, charging debugging, and so on. The difficulties encountered in this procedure include, on the one hand, high-voltage and high-current wiring, as well as operational safety issues; on the other hand, if you use a real battery for testing, there are risks such as poor efficiency and battery explosion. As a result, using a high-performance battery simulator for testing is a good decision.
New testing challenges for fully electric powertrains
Fully electric car cruising range and charging time have always been critical issues for major EV manufacturers to overcome. Due to differences in materials and architectures, the characteristics of EV batteries will have different life, temperature, capacity, and discharge curves in practical operation. When debugging a system in the lab, it frequently requires a power supply to simulate the characteristics of a high-voltage battery pack and validate the logic performance of the VCU (vehicle controller unit). For example, in high-voltage debugging, power-on process debugging is primarily used to detect BMS, IPU, and DCDC pre-charging, switching of the working mode of high-voltage devices (such as switching from Standby mode to Work mode), and whether the entire vehicle's high-voltage interlock function is active. You need to check the power-on sequence of the VCU if a power-on failure occurs during the power-on process.
In addition, testing is also essential for regulatory compliance. There are many regulations in the United States and through the American Continent that require renewable energy systems to meet specific performance standards before they can be deployed. Testing ensures that these standards are met, and that the technology is safe for use. REXGEAR has all the tools you need to be able to test to these standards.
(1) The trend of higher voltage and power
The power and voltage levels of fully electric vehicle batteries are trending upwards from 300V/400Vdc to 800V/1000V/1200V. The high-voltage technology speeds up charging while also lowering the amount of space needed for internal wiring. As a result, when selecting a battery simulator, it is vital to take into account both the several voltage levels and the trend of increasing battery power. The IT6000C bidirectional DC power supply allows for a variety of power combinations. An IT6000C power supply cabinet ( see figure 1 ), can be used as four units of 90kW power supplies or as the one with a total power of 360kW. The IT6000C bidirectional DC power supply has a voltage range of up to 2250V. Its maximum power can be extended to 1152kW after connection in parallel.
(2) Fast switching between charge and discharge
The battery is constantly cycled between charging and discharging states when the vehicle accelerates and decelerates while it is running. To simulate the bidirectional flow of battery current, engineers normally use a power supply and an electronic load separately. The disadvantage of this test solution is that the response is not quick enough to strictly match the actual simulation criteria for EV batteries, regardless of whether the current is switched manually or through a program (the normal programming response time is roughly 50ms to 100ms). It should be noted that in a transient condition, the charging and discharging switching of real batteries is nearly complete. ITECH brings a different solution. It solves the above concerns by combining sourcing and sinking capabilities in one test instrument and enabling "seamless" switching
(3) Simulation of battery characteristics and BMS protocol compatibility
Currently, ternary lithium batteries and lithium iron phosphate batteries are the most common EV power batteries. Lately, BYD officially announced the launch of blade batteries, specifically super lithium iron phosphate, which has a better power density than ordinary lithium iron phosphate. Tesla is also gradually replacing the previous 21700 and 18650 cells with 4860.
The challenge of battery simulation is exacerbated by the ongoing iteration of EV batteries. Engineers need not only simulate the characteristic curve of existing batteries, but also the characteristics of new batteries whose characteristics are constantly evolving. The gasoline-electric hybrid system and the hydrogen fuel cell power system, on the other hand, are extensively used to improve the vehicle's cruising range. The energy management strategy for these vehicles (gasoline-electric, fuel cell-lithium ion battery) is an essential topic. In the test of them, the battery simulator must not only simulate the battery's "seamless" bi-directional flow, but also the battery's BMS function to communicate with PDUs, VCUs, etc.(figure 3)
(4) V2G (vehicle-to-grid) , V2H (vehicle-to-home)
Vehicle-to-grid (V2G) technology aids in climate change mitigation by allowing the energy system to balance more and more renewable energy. An electric vehicle can now be used as a huge home battery thanks to a new type of charger. Unlike traditional one-way EV chargers, bidirectional chargers can also discharge energy from an EV, allowing them to power a home and its appliances (known as vehicle-to-home or V2H) or feedback the electricity to the grid (vehicle-to- grid or V2G). In this case, the energy conversion efficiency, grid connectivity, and anti-islanding become typical testing challenges it brings.
How to Simulate an EV Battery Pack ?
When confronted with the above test challenges, just simulating the battery's bidirectional flow is insufficient. Internal resistance, ambient temperature, and depth of discharge all have an effect on the characteristic curve of an actual battery in use, which in turn influences the power performance and energy distribution strategy of the vehicle. As a result, when researching a power system, it cannot just evaluate its impact on the overall performance of the vehicle at ideal full voltage or a certain fixed voltage. The ITECH BSS2000 Pro battery simulator simulation software is designed special for EV powertrain research. Engineers can easily select the appropriate battery characteristic curves from the built-in types, such as lithium iron phosphate, ternary lithium, or nickel metal hydride and so on.
In reaction to the new EV batteries, such as the "blade battery," the BSS2000 Pro supports .mat file import function. You can create the battery mathematical model by MATLAB and then import it into BSS2000 Pro for simulation, or you can import the real measured characteristic curves. Further more, the BSS2000M provides up to 20 channels of battery simulation, user-defined BMS protocols, and CAN interface with external control systems. The BSS2000 not only satisfies today's needs, but also enables you easily cope with the automobile industry's ever-changing testing requirements.
How to test V2G modules ?
The primary power conversion modules that enable bidirectional energy flow between the grid and the automobile are the BOBC and V2G EV charger. We need to do various tests on the bidirectional electrical performance of AC-DC and DC-AC, such as grid-connection disturbance, phase angle jump, frequency disturbance, and harmonic injection, to assure dependable grid connection of BOBC and V2G EV charger.
V2G EV charger modules present a significant challenge to existing test solution, particularly when testing DC-AC inverter power conversion performance. When the V2G modules are operational, it must track signals of grid voltage, frequency, and phase angle in real time. The traditional test solution often use an AC power supply, an AC load, and a DC power supply. Among these, the AC power supply is to simulate the voltage and frequency of the power grid and to give a reference signal for the V2G module. The AC electronic load is to absorb the energy released by the power battery.
However, as the tests become more sophisticated, the shortcomings of this solution become more apparent. First, because the AC power supply and the AC load are two separate instruments, you must consider the order in which the two units are turned on and off during operation. If the AC load is powered off before the AC power supply, all of the inverter's energy will be poured into it, but it can’t absorb the energy, which will cause the damage of the AC power supply finally.
Test solution for V2G power module
Because the power grid may both absorb and sink energy, a grid simulator should also do. The IT7900 regenerative grid simulator is a full four quadrant power supply with 100 percent current sinking and sourcing capability. It can successfully complete the V2G EV charger and BOBC bidirectional performance verification tests. You only need to set the grid's voltage and frequency, and the IT7900 regenerative grid simulator will absorb or output power based on the DUT's current flow. Simultaneously, the absorbed energy will be fed back into the grid, with a feedback efficiency of up to 88 percent. There is no need to worry about how to coordinate and control two independent test instruments when only one unit IT7900 can perform all
In the application of V2G grid connection, it’s also necessary to do the islanding protection testing. When the power grid is turned off, the EV battery is not allowed to feed back power to the grid any more, and its power output should be cut off in less than 2 seconds. The IT7900 has built-in anti-islanding mode. To simulate nonlinear electrical loads, you can configure the parameters of R,L,C, or active/reactive power per phase. You don’t need to buy an extra RLC load at your design phase of product. A single unit of IT7900 can perform the functions of an RLC load, a power meter and a grid simulator. It largely reduces your cost by simplifying the test platform.
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