High-voltage battery simulator and test systems critical for EV and HEV development

Systems essential for conducting research and development, performance and durability testingon electrical vehicles and hybrid/electric vehicles.

In response to this critical need, technology is being developed that can be used for high voltage battery testing. The testing system subjects the battery to the same charge/discharge profile as it would encounter in an actual vehicle on an actual road course.

With these systems, during regenerative modes, absorbed power is regenerated back to the AC mains instead of being dissipated as waste heat, which is common practice among previous generation testing systems. This highly efficient method provides much greater power efficiency and measurably reduces overall operating costs.

The technology uses an inverter system to convert high voltage three phase AC power to very stable DC voltages. This is a complex technology, especially if done in a regenerative fashion. To provide a high voltage DC source that can also absorb power, you need high power high frequency switching, using very high quality components. The system also needs to provide very good filtering to provide the stable DC voltage required.

For example, SAKOR has developed a new HEV battery test and simulation system that precisely controls DC voltages up to 1000 volts or more. The system switches seamlessly and precisely from powering to regenerating modes.

In addition to providing precise testing, the technology is extremely (approximately 95 percent) energy efficient. Absorbed power is placed back on the AC mains to be re-used or re-sold to the power company. The system can actually cause the electric meter to run backwards, reducing the electricity bill and wasting little or no heat energy. This results in significant savings in total testing costs.

A typical HV Battery test system would include:

  • A high-voltage regenerative DC power supply. If the system is just being used to test a battery, this power supply hooks up directly to the battery being tested.

  • A DynoLAB EM test cell supervisory system, attached by Ethernet to the power supply, and serving as a command to the battery testing system. The DynoLAB EM can be configured to perform any charge/discharge for road load cycle required.

  • External instrumentation, depending upon what the system is being used for. Examples include a bank of thermocouples and pressure transducers.

In addition, high voltage battery systems may be equipped with a separate smart battery charging device; if so, the DynoLAB EM system can also communicate with and control this device.

Technology used in a variety of testing scenarios

There are three different types of battery testing conducted as part of new product engineering: research and development, performance, and durability. The same basic equipment is needed to conduct all three types of testing, though there are a few significant differences.

R&D testing by its very nature comes with a plethora of unknowns. In addition, R&D systems are usually more expensive because they tend to have more data acquisition/data logging capabilities. With R&D systems, engineers may be designing high-voltage batteries within a particular range, not knowing exactly what the maximum voltage, current, and/or dynamic performance will be. In this case, care must be taken not to underestimate the size of the testing equipment, which should be built with high enough voltage, current, and power capacity to test the biggest battery that can reasonably be expected to build within the next few years.

For example, SAKOR was recently asked to develop a 120 kW system, which was sized up to 150 kW so it would have a sufficient margin for safety and growth. The customer had begun its R&D efforts testing 80 and 120 kW batteries, but before the testing system design had been completed they had gone to larger devices (155kW), and by the time the system was built and installed they were testing a 220 kW device. Unfortunately, running too close or over the system design can severely limit the system’s lifespan.

Performance testing systems are similar to those used for R&D, but may be somewhat less complicated because engineers typically have a much better idea of the highest voltage, current, and power requirements, and know much more about what kind of speed response will be needed. They also tend to require somewhat less instrumentation.

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