Feature

How to ensure precision measurements when evaluating electric motor and drive efficiency

Electric motors consume around 45 percent of electrical energy worldwide, a statistic set to increase rapidly with the ramp-up of electric vehicle (EV) sales. Measuring and verifying the efficiency of both motors and inverters (motor drives) is therefore an increasingly critical task. However, to detect small changes in efficiency, it is advisable to take advantage of a high-precision power analyser.

05/11/2024 11:08:11

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Among the signals generated by an inverter is the pulse-width modulated (PWM) voltage, which controls motor torque. The bandwidth required to measure a PWM signal depends on the duty cycle, which means it is easier to consider a square wave.

However, to capture the amplitude of a square wave correctly (up to 99.95 percent), engineers need a frequency response of at least 400 times the switching frequency. So, if the switching frequency is 20kHz, a bandwidth of 8MHz is necessary.

There are similar requirements for achieving the precise measurement of current and electrical power, although the effect on motor current when fed from an inverter is triangular, as it cannot respond fast enough to follow the square.

To minimise the error of bandwidth limitation in line with power meter accuracy, a bandwidth of at least seven times the switching frequency is necessary, according to the characteristics of a triangular waveform, while including the complete signal needs a bandwidth of up to 25 times the switching frequency. Again, using the example of 20kHz switching frequency, the bandwidth required to include all signal components is 500kHz.

Today’s electric motors are already working at efficiencies of 95 percent and better, so improving efficiency is a challenging but critical ambition for manufacturers.

Read the full article in DPA's November 2024 issue

Written By Sophia Bell

Sophia Bell is the Group Editor of DPA, Connectivity, and PBSI. She joined the team in 2020 as Assistant Editor after achieving a First-Class Honours BA in English Literature and Film Studies from the University of East Anglia. In her current role, she leads the editorial strategy, driving digital growth and ensuring each title continues to deliver trusted, relevant insight for engineering and manufacturing professionals.