Instantaneous voltage measurement in PWM voltage source inverters

The use of pulse width modulated (PWM) inverters is nearly universal in industrial drives, making accurate voltage measurements problematic due to the switching nature of the applied phase voltage. Often, the applied phase voltage is reconstructed by using a combination of the DC link voltage and the commanded PWM duty cycle. Another approach is to apply a low-pass filter to the phase voltage to remove the high frequency PWM switching component, but leaving the fundamental component of interest. In this paper, a strategy for detecting the instantaneous phase voltage is presented. The approach consists of integrating the switched phase voltage over either a full, or half PWM cycle. The integrated signal is then converted to voltage by dividing by the integrating period. Implementation details of the proposed approach are outlined in the paper, and experimental results are used to compare the proposed technique with other methods of voltage measurement in terms of measurement accuracy and transient performance. The results will demonstrate the opportunity for improvements to any inverter-driven motor control system that relies on accurate terminal voltage measurement to estimate internal machine states.