Sunt Srianthumrong

Comparisons in circuit configuration and filtering performance between hybrid and pure shunt active filters

This paper deals with a hybrid shunt active filter for harmonic compensation of a three-phase diode rectifier in a 480-V adjustable-speed drive system. The hybrid filter is formed by a three-phase single-tuned current LC filter for the 7-th harmonic frequency and a small-rated three-phase voltage-source PWM inverter. Computer simulation is carried out to compare the hybrid filter with a pure shunt active filter in terms of circuit configuration and filtering performance. The simulation results indicate effectiveness and viability of the hybrid filter. In addition, theoretical analysis confirms the validity of the simulation results.

Stability analysis of a series active filter integrated with a double-series diode rectifier

This paper deals with a harmonic current-free AC/DC power conversion system which is characterized by the integration of a small-rated series active filter with a large-rated double-series diode rectifier. The stability of the active filter based on feedback control is discussed theoretically, taking into account delay time in the control circuit. As a result, it is revealed that the delay time may produce a bad effect on stability, especially when the power conversion system is installed on a stiff power system with low system inductance. The authors propose a viable way of reducing the effect of delay time on the system stability. Analysis in the frequency domain enables us to know how much the system stability is improved in terms of gain and phase margins. A switching-ripple filter is designed to obtain good filtering performance without affecting the system stability. Experimental results obtained from a 20 kW laboratory system verify the validity of the developed theory, and confirm the viability and effectiveness of the proposed control circuit.

A medium-voltage transformerless AC/DC power conversion system consisting of a diode rectifier and a shunt hybrid filter

This paper proposes a 3.3-kV transformerless AC-to-DC power conversion system consisting of a three-phase six-pulse diode rectifier and a shunt hybrid filter. The hybrid filter is formed by a single tuned LC filter per phase and a small-rated three-phase active filter, which are directly connected in series without any matching transformer. The required rating of the active filter is much smaller than that of a conventional standalone active filter. In addition, no additional switching-ripple filter is required for the hybrid filter because the LC filter functions not only as a tuned filter around the 7th-harmonic frequency but also as a switching-ripple filter around 10 kHz. Experimental results obtained from a 200-V, 5-kW laboratory system and simulation results of a 3.3-kV, 300-kW system confirm the validity and effectiveness of the system.