New PQ theory for power quality improvement using modular multilevel converter based UPFC system

Abstract

The source current harmonics reduction techniques were found to be unpredictable and disparity under different loading conditions. The presence of uncertainity issue in harmonics elimination is due to nonlinear loads. Filters can be used to eliminate the harmonics and power quality issues. But these filters are not cost effective to provide dynamic performance under various loading conditions. The target of this paper is to minimize source current harmonics with optimum voltage stability under different loading conditions. A new Unified Power Flow controller is developed whose series compensator is replaced by modular multilevel converter to achieve high modular level with reduced harmonics and fast current limiting during the fault short circuit and shunt compensator is replaced with four switches and one capacitor combination to achieve the twin benefit of more reliable power system and good voltage stability for different loadings. DDSRF (Decoupled Double Synchronous Reference Frame) theory is utilized in the proposed converter for generating the reference current from the AC supply. DDSRF theory generates sinusoidal harmonics with the opposite phase to the load current. The UPFC can suck or injects the responsive power in the PCC. After DDSRF theory, hysteresis controller is used to produce PWM pulse for the shunt and series compensator. The proposed DDSRF theory is compared with existing dq theory to show its effectiveness in terms of THD analysis. The PI and fuzzy logic methodology is utilized to control the capacitor DC rail voltage. The proposed approach is simulated using Matlab under various loading condition and hardware is developed using Spartan 6E FPGA Controller.