A Three-Phase Grid-Connected Inverter Equipped With a Shunt Instantaneous Reactive Power Compensator

Abstract

This paper introduces a new three-phase grid-connected inverter for commercial-scale 10-50-kW photovoltaic systems installed on underutilized assets such as rooftops of office buildings. The circuit topology combines an inductorless active bridge with a parallel-connected PWM inverter behaving as an instantaneous reactive power compensator. The active bridge, referred to as 120°-conduction inverter, performs a fundamental-frequency switching and outputs a 120°-block-shaped current, while the instantaneous reactive power compensator suppresses the harmonic current included in the block-shaped current. The main advantage of this strategy is the size reduction of the required ac inductor by a factor of four as well as the reduction in switching device power losses. The theoretical analysis clearly shows that the compensator controls only instantaneous reactive power to synthesize a sinusoidal current, thus eliminating the need for an electrolytic capacitor. A 5-kW experimental setup validates the operating principle and control method of the proposed inverter, and exhibits an inverter efficiency as high as 98.8%.