Reactive Power Injection Strategies for Single-Phase Photovoltaic Systems Considering Grid Requirements

As the development and installation of photovoltaic (PV) systems are still growing at an exceptionally rapid pace, relevant grid integration policies are going to change consequently in order to accept more PV systems in the grid. The next-generation PV systems will play an even more active role like what the conventional power plants do today in the grid regulation participation. Requirements of ancillary services like low-voltage ride-through (LVRT) associated with reactive current injection and voltage support through reactive power control have been in effectiveness in some countries, e.g., Germany and Italy. Those advanced features can be provided by next-generation PV systems and will be enhanced in the future to ensure an even efficient and reliable utilization of PV systems. In light of this, reactive power injection (RPI) strategies for single-phase PV systems are explored in this paper. The RPI possibilities are as follows: 1) constant average active power control; 2) constant active current control; 3) constant peak current control; and 4) thermal optimized control strategy. All those strategies comply with the currently active grid codes but are with different objectives. The proposed RPI strategies are demonstrated first by simulations and also tested experimentally on a 1-kW singe-phase grid-connected system in LVRT operation mode. Those results show the effectiveness and feasibilities of the proposed strategies with reactive power control during LVRT operation. The design and implementation considerations for the characterized RPI strategies are also discussed.