Apparatus for a microinverter particularly suited for use in solar power installations

Abstract

A microinverter is disclosed for use in a solar power installation. The microinverter incorporates a voltage-to-current control loop that initially converts output current produced by a photovoltaic panel into a pulse width modulated output synchronized and phase-locked to the utility grid voltage. The duty cycle of that modulated output is specified by output power internally requested from the microinverter. This modulated output is converted into a full-wave rectified unipolar waveform that is converted, through a Commutator, into a bipolar AC output that is also phase-locked and synchronized to the grid voltage. The commutator uses an H-bridge composed of four FETs, with each of two diagonally-oriented pairs of these FETs being advantageously switched on substantially at zero-crossing points in the grid voltage. Switching these FETs during times of zero current and voltage, and switching each pair on for substantially an entire half-cycle of grid voltage reduces switching loss and power dissipation of the FETs and ensures that these FETs remain substantially unaffected by transients which might appear in the grid voltage.