Power Quality Enhancement of Distributed Network fed with Renewable Energy Sources based on Interfacing Inverter

Abstract

transformer for connecting to loads or utility in order to exchange power. Model and dynamic of each of this part may have influence in system operation. But here for simplification it is considered that DC side of the units has sufficient storage and considered as a constant DC source. Hence only DC-AC inverter modeling and control investigated in this paper. A circuit model of a three-phase DC to AC inverter with LC output filter is further described in Fig 1. The system consists of a DC voltage source (Vdc), a three-phase PWM inverter, an output filter (Lf and C with considering parasitic resistance of filter-Rf). Sometimes a transformer may be used for stepping up the output voltage and hence Lf can be transformer inductance. The carrier-based PWM technique fulfils such a requirement as it defines the on and off states of the switches of one leg of a VSI by comparing a modulating signal Vc (desired ac output voltage) and a triangular waveform V D (carrier signal). In practice, when Vc > V D the switch S. is on and the switch is off; similarly, when Vc < V D the switch S. is off and the switch is ON. The PWM technique allows an ac output voltage to be generated that tracks a given modulating signal. Fig 1. PWM interfacing inverter A special case is the SPWM technique (the modulating signal is a sinusoidal) that provides in the linear region an ac output voltage that varies linearly as a function of the modulation index and the harmonics are at well-defined frequencies and amplitudes. These features simplify the design of filtering components.