Decoupled control of PWM active-front rectifiers using only DC bus sensing

Abstract

Active front-end rectifiers based on pulse-width modulated voltage source rectifiers (PWM-VSR) are becoming the preferred topology for implementing high performance AC/DC voltage power supplies. This is due to the fact that the input AC current is fully controllable, both in amplitude and distortion, and in phase: close to unity power factor can be obtained. However, in high performance applications, a second order filter is usually introduced on the AC side to reduce the high frequency current injection into the distribution system. To avoid the use of damping resistors, active damping is used. This requires measurement of the filter capacitor voltages, in addition to sensing of the supply currents, the AC supply voltage synchronization, DC voltage for output control and DC current for protection purposes. As a result, a large number of sensors is required and the overall reliability is thus reduced. This paper proposes a complete scheme based on virtual sensors that synthesize the required AC currents and voltages without the need for measuring them. It uses the information provided by DC current and DC voltage sensors in combination with a linear reduced order state observer and a linear parameter identification algorithm. In addition, the scheme handles the nonlinearities inherent in the model of the PWM-VSR. As a result, at least four sensors can be eliminated, while the control strategy maintains an excellent performance. The paper includes a complete formulation of the virtual sensor based algorithm and its application to control the reactive power and the DC voltage of the PWM voltage source rectifier. Simulated and experimental results on a 2 kVA digital signal processor-controlled prototype confirm the validity of the theoretical considerations.