Abstract
In this paper, a proposed control strategy is presented to improve the performance of the pulse width modulation (PWM) boost type rectifier when operating under different supply voltage conditions (balanced, unbalanced, and distorted three-phase supply voltages). The proposed control strategy is divided into two parts, the first part is voltage controller and the second part is current controller. In the voltage controller, Repetitive Controller (RC) is used to reduce the even order harmonics in the regulated output dc voltage so small output capacitor (filter) is used instead of large capacitor. RC also reduces the even order harmonics which appear in the reflected dc current (I MAX ), this leads to reduce the odd order harmonics which appear in the input currents. While in the current controller, Enhanced Phase Locked Loop (EPLL) technique is used to obtain sinusoidal and balanced three phases, to construct the reference currents, which are in phase with the fundamental supply voltages. Therefore, the supply-side power factor is kept close to unity. A proportional controller is used to give excellent tracking between the line and the reference currents. The complete system with the proposed control strategy are simulated using Matlab/Simulink. The results for the complete system using repetitive voltage controller are obtained and compared to the results of the system with the conventional voltage controller (Proportional-Integral (PI) controller connected in series with a Low Pass Filter (LPF)). The results with the repetitive controller show better response and stable operation in the steady state under different input voltage conditions, as well as in the transient response under changing the load condition. — Enhanced Phase Locked Loop,Repetitive Controller,Three-Phase PWM Boost Rectifier, Proportional-Integral controller. I. INTRODUCTION The boost type PWM rectifier has been increasingly employed in recent years since it offers the possibility of a low distortion line current withnear unity power factor for any load condition. Another advantage over traditional phase-controlled thyristor rectifiers is its capability for nearly instantaneous reversal of power flow. Unfortunately, the features of the PWM boost type rectifier are fully realized only when the supply three phase input voltages are balanced. It has been shown that unbalanced input voltages cause an abnormal second order harmonic at the dc output voltage, which reflects back to the input causing third-order harmonic current to flow. Next, the third-order harmonic current causes a fourth-order harmonic voltage on the dc bus, and so on. This results in the appearance of even harmonics at the dc output and odd harmonics in the input currents. An attempt was made to reduce low order harmonics at the input and the output of the PWM Boost Type Rectifier under unbalance input voltages [1]. The authors in [2] used two synchronous reference frames: a positive- sequence current regulated by a