This paper introduces a three-phase grid-connected inverter for commercial-scale photovoltaic systems. The circuit topology combines an electrolytic-capacitor-less and ac-inductorless active bridge with a parallel-connected PWM inverter acting as an instantaneous reactive power compensator. The active bridge, called a 120◦-conduction inverter, operates at the switching frequency equal to the grid frequency and outputs 120-degree rectangular currents, while the compensator eliminates the harmonic currents included in the rectangular currents. The main
advantage of this strategy is the reduction in size of the required ac inductor by a factor of four as well as the reduction of power losses in the switching devices. The theoretical analysis clearly shows that the compensator can synthesize a sinusoidal output current by controlling only instantaneous reactive power, thus eliminating the need for electrolytic capacitors. This paper also discusses the required dc capacitor and a current control delay in the compensator paying attention to practical applications. A 5-kW experimental setup validates the operating principle and the control method of the proposed inverter and exhibits an inverter efficiency as high as 99.2% with Si super-junction MOSFETs.
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