Line conditioning system with simple control strategy and fast dynamic response

Abstract

The performance and dynamic characteristics of a solid-state line conditioning system which simultaneously eliminates line current harmonics and compensates load power factor is presented and analysed. The line conditioning system is implemented with a pulsewidth modulated voltage-source inverter. Power factor compensation is achieved by controlling the magnitude and the phase angle (delta) of the transistorised PWM inverter output voltage. Fast response times are obtained by adjusting the amplitude of the PWM inverter output voltage through a modulation index control. The principal advantage of this scheme is that it can maintain a near unity mains overall power factor without sensing and computing the associated reactive power component. It can also substantially reduce the harmonic content of the line current when the load is nonlinear. A time domain model is derived and used to accurately predict dynamic behaviour, the stability region and to adjust system controllers. The transfer function of the line conditioning system for open-loop and closed-loop operation is derived. Experimental results confirm the operation characteristics obtained by computer simulation and mathematical analyses.