February/March 2021

20 INDUSTRY NEWS Issue 1 2021 Power Electronics Europe www.power-mag.com engineers designing and evaluating EPS in a single unit. Torque generated by steering wheel operation is transmitted to torsion bar, rack and pinion gears. These forces are detected by the torque sensor and transmitted to the ECU. ECU applies current (power assist amount) to assist motor according to torque and vehicle speed. To develop and evaluate EPS systems, it is necessary to monitor and record a large number of signals, such as sensor (vehicle speed, torque, torsion, rack axial tension, battery power) signals (often voltage output via amplifier), three-phase motor current, voltage, and rotation amount, as well as power assist amount (CAN data) calculated by ECU. In addition, since continuous recording of about 10 to 20 minutes is required, long memory is also required. The DL950 can simultaneously record voltage, current, and CAN data over a long period of time using a multi-channel, real-time calculation function to calculate and display torque and steering angle. In addition, it is possible to calculate the rotation angle of the assist motor from the encoder output, and to record vibration and sound at the same time, so that the EPS system can be evaluated in an integrated manner. Evaluation of ECU and inverter/motor Inverter and motor controlled by ECUs in electric vehicles (EV) require even higher levels of control and responsiveness (Figure 4). In addition to confirming the operation of the control program, it is becoming increasingly important to comprehensively measure the control program instructions and the actual operation of the inverter/motor, and to evaluate their behavior, responsiveness or validity. In order to perform these evaluations, the CAN / CAN FD data from the ECU, the battery output, the internal control and output voltage/current of the inverter, and the torque / rotation speed of the motor must be integrated and measured. In waveform measurement of high voltage or large current, there is a possibility of short circuit, electric shock accident or damage of the measuring instrument caused by insulation failure, wrong wiring, over-input, etc. In order to prevent such accidents, it is important that the measurement instrument has an isolated input. The ScopeCorder offers a variety of isolated input modules, including up to 1000 V input modules. Voltage and current of various motors and control systems, motor rotation speed, battery voltage fluctuation, vibration, noise, temperature, strain, etc. may be measured simultaneously. The DL950 has a maximum of 32 channels, and a 5- unit synchronization provides up to 160 channels. High-speed sampling is required to understand sudden voltage fluctuations in inverters and batteries. The DL950 is capable of sampling up to 200 MS/s. You can also set a different sample rate for each channel, reducing the amount of data combined with slower sample channels such as temperature. The in-vehicle serial bus data of CAN / CAN FD, LIN, SENT can be displayed by trend. For example, vehicle speed data on CAN FD can be measured simultaneously with sensor outputs such as voltage and current of motor drive, motor speed, temperature and vibration. The CAN/CAN FD bus data and related waveforms can be viewed on the same screen. For example, an ignition switch ON/OFF signal, a CAN FD signal corresponding to that command, and pressure signals can be checked on the same screen to verify the correlation between them. Synchronous measurements A motor/inverter evaluation bench system incorporates equipment such as a power meter and a waveform measurement instrument. Generally, when acquiring the evaluation data, it is necessary to collect data from each instrument, and, commonly, a data collection system is designed. For example, a power meter obtains measured data including DC voltage, DC current, and DC power that are input from a battery to an inverter, and three-phase AC voltage, AC current, active power, frequency, and power factor that are output from the inverter to a motor—all at a data update rate of one second. A waveform measurement instrument such as an oscilloscope performs high-speed data acquisition at 1 or 10 MS/s to capture the carrier frequency of the inverter more accurately. It saves both power data and waveform data as a series of evaluation data to create a report that is based on the evaluation results. Power data may be transferred and saved to a PC from a power meter at a data update rate of one second or 100 ms. Since the size of a single item of numerical data is about four bytes, the data volume is small and the data transfer time is unlikely to be a problem even when acquiring 32 items of data, such as inverter input/output voltage, current or power, by a PC. On the other hand, when three-phase inverter waveforms are transferred and saved to a PC from a waveform measurement instrument at a sample rate of 10 MS/s, there are six waveforms of voltage and current signals and it is necessary to transfer a large amount of data, 60 MB/s. Where the amount of waveform data is too large to transfer to a PC within a given time, the data may be saved in the waveform measurement instrument and transferred to the PC after the measurement to continue an evaluation test. However, the data transfer may take several minutes instead of several seconds, during which the evaluation test is interrupted. Since the data is acquired from the power meter and the waveform measurement instrument separately, it is necessary, at least, to match the Figure 4: In ECU and inverter/motor evaluation the DL950 captures and displays numerous variable