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The overall system consists of components that are devel-oped in parallel by different suppliers or development de-partments. Such components for the HV electrical system include electric motor, battery, inverter, on-board charger, electric heater, or DC / DC converter.High-voltage-safe shunts inside the CSM HV breakout modules (HV BM) were installed in each phase of the three-phase synchronous machine with a rated output of 43 kW (Figure 2). The currents to be measured ranged up to ± 90 A. In addition, the three external conductor voltages were measured. The battery voltage was 480 V. The engine was operated in various load situations on the test bench by varying the speed and the torque.

The ChallengeThe inverter operates at a frequency of 24 kHz (41.6 μs), so that a time resolution of the measured values of a few mi-croseconds is necessary to correctly capture the short PWM voltage pulses at low loads (Figure 2 and 3).

The fast acquisition and analysis of voltage and current waveforms is a recurring application in the development of the elec-tric powertrain, as the efficiency of the drive is critical to the success of the overall system. In this application example, a real measurement setup is described in which voltages and currents from a three-phase, inductively excited synchronous machine are measured and analyzed in real-time. The measurement is done with HV breakout modules from CSM and re-corded with the measurement software vMeasure exp (Figure 1), where also a precise parallel real-time calculation of fre-quency and power is done. All graphics show data measured at the test bench with 1 μs time resolution.

Vector Measurement Tools Applications

Fast Measurement of Current, Voltage and Power for the Electric Power Train

Figure 1: Measuring set-up with electric machine and three HV BM 1.1

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The SolutionA perfectly tuned tool chain consisting of HV-safe mea-surement modules, ECU measuring technology and soft-ware for synchronized online data acquisition and data analysis during the driving test is being used.vMeasure exp was used for the data recording, because vMeasure exp allows the synchronous acquisition of XCP on Ethernet incoming measurement data of more than 40 MS/s (mega samples per second).Figure 4 shows the three outer conductor voltages and the three conductor currents of the electric machine, each re-corded at a sampling rate of 1 MS/s. Figure 5 shows in a detailed view the exact measurement of current and volt-age due to the high resolution of 1MS/s. The time synchro-nization of the various measurement channels is in the mi-crosecond range and can best be done via PTP (Precision Time Protocol, IEEE 1588), so that the analysis of the effi-

ciencies or performance calculations during the test drive can be done with high accuracy.A central component of the power measurement is the de-termination of the electrical speed or the rotational fre-quency. Simple methods of detecting the zero crossing provide unstable results due to the transients in the cur-rent signal. Therefore, an integration over several periods is necessary. The model-based prediction approach imple-mented in vMeasure exp combines high dynamics with high stability. Thus, the instantaneous power can be precisely calculated both with strong speed gradients and with con-stant speed ratios.The calculation of the frequency (Figure 6) as well as power is done precisely and online, in sync with the measured data.Due to the high temporal resolution of the measured data and synchronization in the microsecond range of the six measurements, it is additionally possible to verify the val-ues of the models used in the development of the power-train. Likewise, unwanted effects or errors can be detected with this measuring system.

Figure 4: Current and voltage curves of all three phases (at 2000 rpm and 37 Nm)

Figure 5: Detailed view of the three pulse width modula-tion voltage curves and three phase currents

Figure 3: Detailed view of the voltage pulses of one phase Figure 2: Voltage and current characteristics of 1 phase of the 3-phase E-Motor (at 4500 rpm and 37 Nm)

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The Advantages > Innovative, fast, precise and flexible measurement for the validation and verification of HV electrical systems in the laboratory and on road tests > The eMobility Analyzer is included in vMeasure exp and CANape > Like all measuring modules from CSM, the BM modules are small, robust and designed for direct mounting in the vehicle. There is no need to equip the vehicle with addi-tional current sensors, long measurement cables, and gauges. This not only saves time and reduces risk, but also shortens the measuring chain and improves the quality of the measurement. > Synchronous recording of all signals, including ECU signals or vehicle bus signals

Figure 6: Current and calculated electrical frequency

> The power of the vMeasure exp measurement software makes it easy to perform complex mathematical opera-tions on measurement channels in real-time during the measurement. Thus, in addition to the recording of the directly measured signals, filtered signals or derivation of signals can also be visualized and recorded synchro-nously. They can even act as a trigger signal. > The user can easily and accurately measure the current and voltage dynamics in the on-board network and at the HV components and gets immediate feedback during road testing, which makes the verification and a subsequent deeper analysis much more efficient. > The measurement configuration can be easily applied to the data logger vMeasure log. No laptop is necessary during test drives. > Seamless, automated analysis and representation of the measurement data through the Vector vSignalyzer soft-ware tool and direct transmission and secure storage of measurement data in the Vector measurement data management system vMDM