Mitigation of the Harmonic Injection in TCLC Part and Nonlinear Hysteresis PWM Control in Active Inverter Part of Thyristor Controlled LC-Coupling Hybrid Active Power Filter (TCLC-HAPF)

Abstract

In this chapter, two techniques are proposed to improve the performance and reduce the inverter loss of the thyristor controlled LC-coupled hybrid active power filter (TCLC-HAPF). Specifically, for the TCLC part, a design method is proposed to mitigate its self-harmonic injection of the thyristor pairs, which can improve the TCLC-HAPF performance for linear loading compensation. Compared with the traditional static var compensators (SVCs) like a fixed capacitor-thyristor controlled reactor (FC-TCR), which generates low order harmonic current, the proposed TCLC design method can significantly mitigate the injection of harmonic current. The design of the TCLC parameters is investigated with the considerations of its reactive power compensation range and harmonic current rejection. And, representative simulation and experimental results of the proposed three-phase three-wire TCLC are presented to show its effectiveness in dynamic reactive power compensation in comparison with the traditional FC-TCR. For active inverter part, the nonlinear pulse width modulation (PWM) control method is proposed to reduce the inverter loss of the TCLC-HAPF and keep the total harmonic distortion at an acceptable level. As the coupling TCLC impendence of the TCLC-HAPF can yield nonlinear compensating current, the quasi-linear and nonlinear regions are focused with special compensation characteristics under relatively low switching frequency. An approximated harmonic distortion (ATHD) index is proposed to reflect the THD in a simplified way, which results in speed up the TCLC-HAPF system response. A non-linear adaptive hysteresis band PWM controller is proposed for TCLC-HAPF to reduce switching loss. Finally, the performance of the nonlinear adaptive hysteresis band controller is verified by simulation results in comparison with the conventional hysteresis PWM.