A Novel Control Strategy for Zig-Zag Transformer Supported Three-Phase Four-Wire UPQC

In this paper a novel control strategy has been proposed for the mitigation of different power quality(PQ) problems using a zig-zag supported three-phase four-wire(3P-4W) UPQC. The UPQC is realized using two readily available back to back connected three-leg voltage source inverters (VSIs) to a common DC link capacitor. To extract the fundamental source voltages as reference signals for series APF, a zero crossing detector and the ‘sample and hold circuits’ are used, while I CosΦ theory is used for the control of Shunt APF. The performance of the implemented control algorithm is evaluated in terms of power-factor correction; load balancing, source neutral current mitigation and mitigation of voltage and current harmonics for different combinations of linear and non-linear loads. In this control strategy of UPQC, to reduce the effect of computational dealy the current/voltage control is applied over the fundamental supply currents/voltages instead of fast changing APFs currents/voltages. Moreover, in a transformer supported 3P-4W UPQC, there is no need for sensing the load/shunt APF neutral current, hence numbers of required current sensors are reduced. MATLAB/Simulink based simulation results are presented, which support the functionality of the UPQC.