(A) study on observation and compensation of voltage distortion in PWM VSI for PM synchronous motor

Abstract

A pulse width modulated (PWM) voltage source inverter (VSI) is generally used to control a rotating machine. In the PWM VSI, there are voltage distortions or nonlinear gain between a voltage reference and a voltage applied to motor. These voltage distortions affect the machine performances such as current distortions, torque pulsations, instabilities of control system, and degradation of control performance. These voltage distortions are partly caused by the blanking time which is inevitable to prevent the shoot-through phenomenon. The other reasons are the inherent characteristics of the switching devices such as voltage drops, turn on/off time, and output voltage transition time. These non-ideal characteristics of the devices vary with the operating conditions such as the temperature, DC bus voltage, and phase current level. Generally, the blanking time is a small delay time in the gate signal of the turning-on devices, in order to avoid a shoot through phenomena. Therefore, the blanking time is a known value by the microprocessor or digital signal processor in which control signals are processed and calculated. However, the DC bus voltage error and non-ideal characteristics of power devices such as``the voltage drops, turn-on/off time, and output voltage transition time are not known. Up to now, various estimation methods using off-line manner have been proposed. These methods with off-line compensation, however, are difficult to compensate perfectly the time varying voltage distortion using these methods with off-line experiments. In some papers, on-line observing methods for the voltage distortion have been proposed. In these methods, expensive sensing hardware circuits are necessary or a phase delay exists between the real distortion voltage and the observed voltage, which originates from a low-pass filter of the observer. In this dissertation, real on-time voltage distortion observation methods without the phase delay and without any hardware circuit are...