Research On A Direct Control Strategy For Unified Power Quality Conditioner (UPQC)

With the progress of industrialization, power load and grid structure of thedistribution network are increasingly complex and diverse, various power qualityproblems exists in the same distribution system or the same user at the same time.Therefore, unified power quality conditioner (UPQC) which can compensate differentkinds of power quality problems becomes research focus. The device cansimultaneously meet the requirements of grid and users on voltage and current quality,so it has great research value.The research object of this paper is three-phase three-wire with none neutral lineUPQC, on the basis of analyzing it’s topology, the mathematical model is established.In order to design the control system of UPQC, the fundamental wave equivalentcircuit under steady operation is deduced and the power flow character is analyzed.The traditional UPQC control strategy usually takes the voltage and currentcompensation variable as the control objective. Voltage fluctuation, current harmonicand reactive component are calculated through detection algorithm, which work as thecommand signal, and guide output signal of UPQC. A direct control strategy forUPQC which takes grid current and load voltage as control objective is proposed, thecomplicated detection of voltage and current distortion is left out. The trackingcontrolling method of direct control strategy is studied, the current hysteresis voltagespace vector control is adopted in parallel compensation unit and the voltage spacevector control is adopted in serial compensation unit. Feasibility and validity of theproposed control strategy is verified through simulation and experiments.Based on the One-cycle Control Strategy (OCC) applied to active power filter(APF), this paper proposes UPQC One-cycle Control Strategy. By Deducing its OCCmodel, the implementation method is obtained. The reduction of switching loss isachieved by combining with space vector, which improves OCC strategy for parallelcompensation unit. The validity of the strategy is testified through simulating.