Overview and comparative study of two control strategies used in 3-phase grid-connected inverters for renewable systems

Abstract

In this paper, an overview of grid-connected renewable systems is presented, then two current-control strategies for 3-phase grid-connected inverters are analyzed: firstly, the well-known d–q control in the rotating synchronous reference frame (d–q axes) using Proportional Integral regulators is described, and secondly, the Proportional Resonant controller in the Stationary Reference Frame (αβ axes). In order to obtain a high efficiency of the system when the 3-phase utility grid voltages are affected by harmonic pollution, a Harmonic Compensator (HC) structure is used with the Proportional Resonant controller, this due to the ease way to compensate harmonics when a Proportional Resonant control is utilized instead of a d–q control. Then both control strategies (d–q control and PR + HC) are analyzed under harmonic pollution condition. For both strategies, a Positive Sequence Detector plus a Synchronous Reference Frame Phase-Look Loop (PSD + dqPLL) is used as the synchronization algorithm. After the study, it was observed that the PR controller provides a greater facility for carrying out the harmonic compensation process helping to fulfill with the international standards. A model of a grid-connected photovoltaic system with a nominal power of 10 kW is used to evaluate and compare the performance of the current-control strategies. For this, a Real-Time Digital Simulator (RTDS) platform is used.