Test methods for battery powertrain technology and internal combustion engine powertrain technology

Battery powertrain technology and internal combustion engine (ICE) powertrain technology are fundamentally different. Therefore, the two technologies require a series of very different processes and test methods. When these two technologies are merged into hybrid vehicles (seamless integration), test time and cost are likely to increase significantly.

ICE is a complete physical test. The test content is combustion machinery, pressure, temperature, fluid, mechanical connection and power transmission, exhaust control, etc., through turbochargers and superchargers and other methods to improve the explosion efficiency or energy of the combustion chamber, Convert linear piston motion into rotational torque, and use a flywheel to balance energy output.

The electric powertrain is entirely electrical testing, testing power electronics and switching frequency, voltage and current, induction and back electromotive force; battery capacity, discharge rate, thermal management of inverters and converters, and regenerative power regulation; electric motors /The phase angle of the generator and the geometry of the laminate, as well as the position of the magnet and the flux lines.

When the two technologies are combined into a hybrid power system in various ways, integration tests are required, including control schemes, state diagrams and rules that manage the interaction between ICE and electronic components to ensure that the system can work in all driving conditions and scenarios Respond appropriately.

Hybrid vehicles (any combination) are more complex than any ICE or pure electric vehicle (BEV). 

Figure 1. Various combination structures between traditional internal combustion engine powertrain and pure electric powertrain.

Increasingly complex systems contain more components, which means that the probability of failure has increased. For the test engineer, this is 1 + 1 >> 2. They must not only perform traditional ICE tests, but also perform new and more demanding subsystem tests on electric power systems. Test engineers must also design extensive integrated test coverage to ensure that the two technologies work seamlessly together to provide the efficiency, performance, and driving experience expected in hybrid vehicle design.

Meet the testing needs of hybrid electric vehicles

Electric powertrain components are driving more complex testing requirements. Testing tools are constantly being developed to keep up with the pace of changes in requirements. Test engineers must also keep up with the ever-evolving technology in order to meet the changes in the testing requirements of the automotive industry due to high-speed innovation and the introduction of new technologies. The following are some of the new test requirements introduced by electric powertrain components, as well as the continuous improvement and improvement of test tools that can meet these requirements.

Higher fidelity and more complex modeling

Compared with ICE, the response speed of motors and inverters is faster, and they exhibit a high degree of non-linearity in their working range. The control signal from the ECU is very fast (2-20kHZ), and the dedicated motor model needs to run at a speed 100 times higher (200kHz to 2MHz) in order to accurately represent the system in hardware-in-the-loop (HIL) testing. If it is used on a processor-based real-time system for ICE HIL, this cannot be achieved efficiently. Therefore, test system providers such as NI are developing FPGA-based simulation tools to run models created with dedicated electronic modeling tools at the required microsecond cycle rate. Subaru has successfully implemented such a system, and the test time is greatly shortened, only 1/20 of the estimated time required for equivalent testing on the dynamometer.

Power level test

Usually, the ECU and inverter are packaged together, making it very difficult to test the signal level (-10 to 10V and a few mA). It is much more convenient to test under full power, sourcing and sinking actual current than disassembling the components for testing. However, this means testing at power levels up to 200 kilowatts. Such a large power level requires the use of special equipment and power supplies that can provide channel isolation, which can absorb and provide such a large-scale dynamic load. For example, the terminal inverter developed by the NI alliance company Loccioni for the Magneti Marelli inverter of the Ferrari hybrid sports car Transformer test platform.

Battery module/battery pack verification

Batteries, especially high-capacity plug-in hybrid batteries, must be analyzed separately at the unit, module, and battery pack level. The battery cells form a battery pack in series/parallel. The voltage range that needs to be tested is as high as 0-800V and the measurement accuracy requirements relative to the common mode voltage are very high. These tests may be very difficult (or very expensive).

Figure 2. Battery pack architecture (cell, module, battery pack) and required voltage level measurement range

The battery pack actually has its own ECU, which is the battery management system (BMS). Not only does it need to perform component-level tests on the simulated battery pack (for example, using the BMS test solution developed by the NI consortium Bloomy), it runs on it Control algorithms and functions also need to be tested on the actual battery pack at the subsystem level. These tests take place in a hot cell, because the battery's operating characteristics are very dependent on temperature. The test includes two aspects of characteristic analysis and durability test, because the attributes of battery pack performance are the charging/discharging behavior and the cycle time during the entire life cycle and under various temperature conditions (the battery pack is normally used under various climatic conditions). duration). In order to complete the test in an acceptable time and have statistical significance, car manufacturers are testing many (tens to hundreds) of battery packs in parallel. Efficiently managing these test devices, the generated data, and ensuring the traceability of the data and the confidence in the validity of the test data require special design of test automation, system management and data management tools for this purpose.

Integration Testing

If car manufacturers can only rely on laboratory or road/track testing for physical verification testing, it is unrealistic to ensure that the test can cover all expected use cases and working conditions, because it will be very expensive and time-consuming. In order to solve this problem, test engineers are trying to enhance data testing during system integration testing through HIL testing. HIL testing is based on simulation between physical verification and confirmation testing. In system integration testing, various parts of the system can be simulated according to the components or behaviors to be verified. Having a flexible test environment and architecture can support various combinations of simulated and actual components, thereby significantly reducing test time, while providing extensive test coverage, and increasing confidence in system-level performance and reliability

heart.

Figure 3. Standardization on a platform that supports various combinations of real and simulated system components can significantly improve test efficiency and equipment reuse rates. 

Why don't automakers make pure electric vehicles?

It can be said that the performance of the electric powertrain is more superior, and its advantages include higher performance, faster response, lower noise, zero emissions, low maintenance and driving costs, safer and simpler (less mobile components And failure points), and it also provides design engineers with exciting freedom to play, because electric vehicles remove or greatly simplify complex and expensive heavy-duty components, such as internal combustion engines and related belt drive systems, exhaust and catalytic conversion And gearbox. These components are replaced by smaller components, have a higher power/weight ratio, and allow more flexible placement. The problem is that the pure electric drivetrain is too expensive (to a large extent only depends on one component: the battery pack).

However, automakers must meet the various efficiency and emission requirements of various governments for automobiles, and they believe that electrification has attractive performance advantages. Therefore, they decided to decompose and integrate the powertrain technology in various interesting ways, and strive to give ICE vehicles some advantages of electric vehicles. But they must still avoid insisting on using large enough battery packs to make pure electric vehicles, because battery costs are expected to continue to fall.

The good news is that we are rapidly achieving this goal and are investing heavily in battery technology innovation, which is not only a demand in the automotive sector, but also a demand for consumer technology (such as mobile phones). The battery performance/cost curve gives us great hope, the annual cost reduction is as high as double digits, and there is no sign of slowing down.

Figure 4. Battery pack price/KWh continues to decline, and it is approaching the threshold of US$100/KWh that the mass market is willing to accept pure electric vehicles.

On the other hand, the problem with automakers turning to hybrid vehicles is that hybrid vehicles not only do not reduce the complexity of the car, but increase the complexity of the car. The hybrid power system contains more components, so there are more possible points of failure. In addition, hybrid vehicles also need to solve the thorny problem of integrating two different power system technologies. Managing this integration requires components as well as more software and control methods.

Keep up with the pace of innovation

Automakers’ active development of hybrid vehicles is to a large extent to meet the government’s requirements for vehicle fuel efficiency and emission levels. At the same time, they are also facing the need to provide attractive electrified products within the same time period as their competitors. (Identified as a strong consumer demand) pressure. These factors have accelerated the timetable for electric vehicle development and put greater pressure on test engineers to complete more tests on more complex systems in a shorter time to ensure the safety of these hybrid vehicle designs. Performance, reliability and high performance. Fortunately, the speed of development of test platform tools and technology just happens to be able to catch up with the speed of innovation in the general automotive industry. The automotive test team must take full advantage of these advancements to meet the growing needs of its organization and automotive project team.