DQ transform based current controller for single-phase grid connected inverter

Abstract

In this paper, the design and simulation of a current controller for a grid connected inverter is implemented by using the synchronous reference frame conversion. The active power and the reactive power outputs of the inverter are controlled in the dq reference frame with the use of Proportional-Integral (PI) controllers. The measured grid current and grid voltage are used to generate an orthogonal signal pair with the use of Second Order Generalized Integrator with Phase-Locked Loop (SOGI PLL). According to the available standards for grid connected inverters, the unity power factor operation of the inverter is essential. In our design this is achieved by maintaining the reactive power reference of the controller at zero steady state value. The injected grid current is forced to be in phase with the grid voltage with the use of PLL. Also, a third order LCL output filter design is proposed in this paper to filter out the switching harmonics. The Matlab simulation results of the grid connected inverter are also included in this paper.