Current controller for inverter bridge designed for grid-connected photovoltaic system

Abstract

A grid-connected photovoltaic system provides electrical energy to the power grid from power generated by a solar system. The first requirement in connecting to the power grid is converting the DC voltage generated by the photovoltaic cells to AC. This is achieved using a single-phase switch-mode inverter. The next requirements are that the output frequency matches that of the grid to which it is connected and its current is near sinusoidal. Power supply authorities set stringent standards that limit the amount of DC delivered to the grid and therefore the inverter must be controlled to minimise the DC content of the sinusoidal output. To produce this waveform, the inverter is operated in unipolar mode and controlled using sinusoidal pulse-width modulation. This task is performed by a current controller circuit that controls the inverter output current by regulating the inverter transistor switching using tolerance band control.