Power measurements in adjustable speed drives

Modern power meters and analyzers were tested to determine their accuracy with various nonsinusoidal waveforms applied. The meters were subjected to waveforms that are characteristic to the three most common fractional and integral horsepower adjustable speed drive (ASD) technologies, namely, PWM induction, brushless dc, and switched-reluctance drives. Fourier transform analysis of the distorted ASD waveforms was performed. The obtained measurement results show that the output power of ASD's for brushless dc and switched-reluctance technology was not measured with acceptable accuracy by any of the tested meters. Possible reasons for meter inaccuracies and suggestions for performance improvement are presented. Conclusions on the present state of ASD electric power measurements and recommendations for further research are given.