The trajectory tracking approach-a new method for minimum distortion PWM in dynamic high-power drives

The requirements for high-performance pulse width modulation (PWM) at low switching frequency are defined. It is shown that the conversion of a continuous reference signal into a discrete switching sequence normally creates a modulation error at dynamic operation. This error is detected in an optical synchronous modulator using the steady-state current trajectory as a reference track in the transient state. A tracking controller eliminates the tracking error by modifying the switching pattern in real time. A parameter identification scheme enables the identification of the instantaneous fundamental current and the implementation of fast current regulators. Oscillograms from a 30-kW model drive demonstrate the high quality in forms of dynamic performance and minimum harmonic distortion obtained with a three-level inverter at only 200 Hz switching frequency.<>