Predicting Inverter-Induced Harmonic Loss by Improved Harmonic Injection

This letter presents an improved harmonic injection method for determination of inverter-induced harmonic power loss across a range of induction motors rated at 1.1, 7.5, 15, and 30 kW. Techniques to obtain the necessary experimental precision and repeatability are investigated in detail. The harmonic injection method allows the machine to be tested under normal operating conditions while a range of selected harmonics are superimposed on the fundamental frequency of the pulse width modulation (PWM) waveform. This technique is validated by direct loss measurement using a specially built calorimeter capable of detecting power loss as low as a few watts in induction motors of up to 30 kW. Comparisons of segregated losses by IEEE 112 method B for the machines operating on sinusoidal and inverter-fed supplies show a good correlation between high frequency PWM harmonic loss and core loss. Core loss is not a constant proportion of total loss for any machine and neither is harmonic loss independent of machine design.