35 Motor testing | Tech focus It is possible to use in-vehicle sensors to measure power values, but they are usually low-cost and low-accuracy sensors that update at a slow rate to the CAN bus. Typically, this is not useful when collecting dynamic power data because the method lacks accuracy and does not provide any insight beyond the slow data rate. However, this is being addressed with a new generation of inmotor sensors (see below). Continuous sampling One way to address these challenges is to constantly record the PWM voltages and currents at up to 2 MS/s per channel with real-time calculations on a digital signal processor (DSP) built into the hardware. The DSP executes equations in real time including a unique cycle detect algorithm. The cycle detect algorithm digitally filters the phase A current, finds zero crossings, takes the time between two successive zero crossings and uses that time for RMS calculations. The DSP then calculates the RMS voltage, current, power and efficiency on the half-cycle basis. The real-time calculation of these values cuts down on post-processing time and gives the user instant feedback on the state of the system. The combination of recorded highsample-rate data and availability of equations provides traceability of power results, rather than a black box outcome. In addition, the equations are processed in real time, meaning that they can be transferred onto a CAN bus for correlation to outside systems Signal correlation Powertrain testing on the road is significantly different from testing in a lab because there is a high level of unpredictability in the test conditions. For example, to measure torque and speed in a lab, a torque and speed setting are input to a dynamometer and a measurement is made. To do the same test in a vehicle, it must be set to a fixed speed, but this will vary with wind, road conditions and elevation. Measuring a fixed torque in a vehicle requires the proper loading, which could mean finding a hill that is steep enough to hit the desired power point or going as far as hooking a trailer to the vehicle or loading the vehicle down with weights. In-vehicle testing is also used to find issues with performance or control. If the powertrain does not perform as expected under certain conditions, engineers will want to understand the causes of the failure and replicate them. To be able to properly understand these environmental issues, it is necessary to correlate measurements such as video, GPS, acceleration, CAN bus and others to the power values. These types of measurements will provide insight into pedal position, wheel angle and environmental conditions that affect the total vehicle performance. Fortunately, these measurements are often already made by vehicle engineers with existing DAQ systems. A system that measures dynamic power can start to introduce real-time power to the available channels measured for those engineers. The combination of dynamic power measurements with environmental data will provide a significant amount of data to improve vehicle performance. To achieve this, the cycle-based calculations are sent over the CAN bus for correlation to an existing DAQ system. The high-frequency data are stored locally, but information on the power, control and other variables is also transferred to CAN for correlation. This test set-up provides power data to groups performing structural, NVH and fatigue testing, but also provides high-frequency data with context to powertrain and control engineers. All the high-speed or cycle-based signals can be viewed live on a computer in the cabin providing the user with visual feedback on the state of the powertrain. E-Mobility Engineering | January/February 2026 The COBROS in-motor sensor board (Image: CTS)
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