PLL-less single stage grid-connected photovoltaic inverter with rapid maximum power point tracking

• A grid-connected PV inverter is designed without using any PLL circuitry.
• The PV system performs rapid MPPT and good current shaping with two control loops.
• Only four power switches achieve three output levels, MPPT and grid interface.

This paper presents a systematic way of designing control scheme for a grid-connected photovoltaic (PV) inverter featuring rapid maximum power point tracking (MPPT) and grid current shaping without using any phase-locked loop (PLL) circuitry. A simple integral controller has been designed for the tracking of the maximum power point of a PV array based on the extremum seeking control method to provide a reference PV output current for the grid interface. For the grid-connected inverter, two current loop controllers have been designed. One of the current loop controllers is designed to shape the inverter output current while the other current control loop is to follow the reference received from the maximum power point tracking algorithm and to provide a reference inverter output current for the PV inverter without largely disturbing the maximum power point of the PV array. Four power switches are used to achieve three output levels and MPPT. Moreover, it is unnecessary to use any energy storage such as rechargeable battery. Experimental results are included to demonstrate the effectiveness of the tracking and control scheme.