Novel four-quadrant variable impedance and its application

The variable impedance can be applied in many fields of power system. A novel four-quadrant variable impedance based on voltage-sourced inverter control is proposed in the study. The schematic diagram of the novel variable impedance is presented, and its principle and transient characteristic are addressed. The system stability of the variable impedance when it is connected in series with a resistive and inductive load is described. Based on the developed variable impedance, a novel shunt power quality controller (SPQC) is proposed. In the SPQC, the fundamental equivalent impedance of the primary winding is a variable impedance, which can be used to compensate the fundamental reactive power. The equivalent impedance of the primary winding for nth order harmonics is short-circuit impedance, which is very low impedance and the harmonics produced by loads will be short-circuited in primary winding. The control strategy is also analysed. Two sets of single-phase prototypes have been constructed. One is for the demonstration of the variable impedance, the other is for the demonstration of the SPQC. The validity of the novel variable impedance and the SPQC has also been verified through experimental results.