A new PWM pulse modification procedure of DC bus current detection for noise adaptation

Methods to detect DC bus current in order to reconstruct three-phase currents have a well-known problem of short DC pulse duration. To expand the pulse duration, several pulse width modulation (PWM) modification techniques have been proposed. The "Half Pulse Shift (HPS) method is very promising because it has both robustness against detection errors that occur due to current ripple and low acoustic noise. In general, a common-mode noise current permeates the DC bus current and causes detection errors, so the duration of a pulse expanded by PWM modification method is longer than the decay time of the common-mode noise. This decay time is dependent on the electrical environment, especially power supply cable from the inverter to the motor. Although the pulse duration to avoid common-mode noise can be estimated, another problem may arise; the pulse duration may be limited by the controllable range of the output voltage. We propose a new PWM modification method to ease the limit of the pulse duration. Numerical analysis confirmed that this method can expand the operation area in which current is detectable. Experimental results indicated that the proposed method offers stable operation and robustness against noise caused by the electrical environment.