UZ Workshop - Variable Speed Drives: Switching Techniques, Waveforms and EMI


On May 26th 2022, the ESR 9 (Douglas Nascimento) presented a workshop titled “Variable Speed Drives: Switching Techniques, Waveforms and EMI” (Fig. 1) for the mechanical engineering students of the University of Zielona Gora.

About switching technique, it went over the power switching techniques especially scalar control using SPWM (switching PWM), divided in: (1) thirty minutes of theoretical explanation and (2) thirty minutes of practical activities, covering parameterization, time-domain analysis of inverter’s output waveform, frequency-domain of trapezoidal waveform switching from IGBTs and how to use filters to improve the harmonics contents in terms of EMC.

In the occasion the ESR showed the importance to be aware of time-domain and frequency-domain techniques of electrical signal analysis (Fig. 2) as preventive maintenance for variable speed drives (VSDs). The setup (Fig.2) was composed by an 1kW inverter and squirrel cage induction motor 1hp. 

The output voltage waveform of the inverter is shown in Fig. 2.

During the demonstration of the testbench, the parameters of the controller was changed such as modulating frequency and switching frequency (Fig. 4 and Fig. 5)

After demonstration of time-domain analysis, the FFT spectral components in the garbage band (9-150 khz) was presented. The students also would follow the amplitude and frequencies according to the parameters variation. 

Finally, some take-home messages about inverter disposal (clean and ventilated environment), preventive maintenance and audible noise mitigation.

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