Accelerate EV Battery Testing

Battery testing in general is the verification of a battery's safety, performance, and quality. Testing is important to ensure production quality and safety, to ensure proper performance in use. It is also important to verify the effectiveness of new developments and ensure improvements in safety, performance, and reliability. 

The two biggest areas are performance tests and characterizations. 

Performance tests include, for example, charge-discharge cycles, in which artificial aging is simulated to observe how fast and in what way batteries age. Another example would be drive cycles. For these tests, real-world current or power demands are recorded and used as test input. The goal is to understand how a newly developed battery behaves under known conditions and see if there is an improvement in performance. 

Characterization focuses on the parameters of a battery, which include tests for resistance, impedance, capacity, and thermal responses. These tests will be performed by using different stimuli and reading back the responses. For example, resistance and impedance. Classically, the stimulus is a current signal, and for resistance measurement, a DC current pulse is the most common method. For a defined period, a current pulse is active, and the voltage response is measured back. Based on the known current and the measured voltage, the internal resistance for DC could be calculated. This is known as Direct Current Internal Resistance (DCIR). Impedance measurements could be performed similarly, but instead of DC current, AC current is used. The impedance for a given frequency could be determined depending on the chosen frequency. If the fixed frequency is replaced by a sweep, the impedance measurement is considered as electrochemical impedance spectroscopy.  

For electrical tests, the following components are the main parts: A battery test system, a climatic or temperature chamber, measurement equipment, communication and Rest-Bus simulation, a conditioning unit, and safety equipment. 

The battery test system is a high-performing bidirectional power supply. It ensures communication with all other test components while handling the test scenarios and characterization tasks. Measurements are collected, and the test results are captured and prepared for analysis. 

Battery tests are always performed in a test chamber to ensure safe operation and allow thermal and climatic tests. The test chamber ensures safety via safety equipment, such as redundant temperature measurement, gas sensors and detecting systems, venting and burst disks, fire extinguishing systems, inerting, and mechanical safety systems. Different temperature profiles and conditions can easily be achieved to verify robust behavior under all conditions or to stress test the batteries under extreme conditions. A subpart of the temperature and climatic control is the replacement of the in-vehicle cooling system. For packs and some modules, it is necessary to have a cooling circuit present that replaces the car’s cooling system. This could not only be used to have a static operation, but temperature profiles could be programmed to simulate different scenarios and test cases.  

While the battery test system measures voltage and current during the test, additional measurements could be needed, such as temperature measurements, individual cell measurements, digital and analog input and output channels (IOs) to communicate and simulate behaviors, and digital higher-level communication with the BMS.  

From an integration point of view, packs and modules are built out of cells in parallel and series. With that given, the tests are performed on a much higher voltage and power level than with cells.  

 In addition, the integration of cells into modules and packs is adding components that need either to be tested or controlled to enable tests. The BMS plays the biggest role by adding a communication component to the tests. All tests need to be in alignment with the BMS, and so a constant communication stream is flowing between the test system and the BMS. The BMS not only takes care of balancing the cells to ensure even charge and discharge, but also controls the output contactors. Communication with the BMS should test and verify its reaction to certain conditions, but it is also necessary to ensure proper operation by running the tests. One example would be pre-charge: Before a pack test can start, the test system's and battery's voltages need to be matched. This is necessary to limit high balancing currents at the very beginning of a test, once the contactors are closed. The BMS system coordinates this. Only if the voltage at the contactors matches the internal battery voltage will the contactors close. 

Fast charging is one of the trends in the EV/EVSE sector. The batteries are only one part of the chain. A battery could support a given current for a given time. This could be verified and tested during performance tests. If the current is too high for too long a time, thermal effects could start, and permanent damage could be caused. The performance of batteries under higher charge currents could be improved by conditioning the cells prior to the charge event and keeping the temperature and thermal impact with cooling under control. But in general, fast charging is more challenging for the rest of the car chain, mainly for the plugs, cables, and contactors, as they need to be optimized for the current while keeping the weight and space at a tolerable level. 

Keysight provides a wide range of battery test systems, software, and services. The systems are highly flexible and offer a wide range of built-in functionalities.  

The cell test systems, for example, provide built-in Electrochemical Impedance Spectroscopy (EIS) measurement. This allows for the measurements to be performed without the need to rewire and use different test equipment. It could be part of a broader test cycle and automatically perform the measurements. This saves time, allowing for shorter times to gain more and deeper insights into the battery's behavior. 

In addition, module and pack test systems are designed to adapt to changing test needs, with additional fine current and voltage ranges to enable module tests with a pack test system and cell tests with a module test system. This boosts flexibility and allows for the creation of a versatile and reliable test laboratory. 

Offering a full turnkey solution could ensure a faster time to test. If desired, Keysight will take care of the planning and project management of the full laboratory, including all needed components. Delivery times and commissioning will be aligned to support the fastest possible ramp-up of the newly built battery test lab. This service is not fixed and can be adjusted to the individual needs and scope of the project.