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

Abstract

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 nextgeneration 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 singlephase PV systems are explored in this paper. The RPI possibilities are: a) constant average active power control, b) constant active current control, c) constant peak current control and d) 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 firstly by simulations and also tested experimentally on a 1 kW singe-phase gridconnected 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.

Photovoltaic-STATCOM with Low Voltage Ride through Strategy and Power Quality Enhancement in a Grid Integrated Wind-PV System

“…The instantaneous reactive power control method can develop power in stationary reference frames (αβ-Frame). Reactive power injection (RPI) control can be implemented by setting the active power (p) and the reactive power (q), followed by generating the reference grid current (i * sabc ) [11]. The whole control block diagram for instantaneous reactive power theory (P-Q control theory) is depicted in Figure 5.…”

“…Figure 1 depicts the voltage profiles that generating units must sustain according to various grid codes [9]. The injection demands of reactive power during sags to support grid stability that is required by the German Grid Code, the Italian Grid Code, and the Japanese Grid code [9][10][11], are shown in Figure 2. LVRT strategy can prevent inverter over-current and provide reactive power support for sag mitigation [7,9].…”

“…LVRT strategy can prevent inverter over-current and provide reactive power support for sag mitigation [7,9]. The various grid standards are mainly focused on power quality issues, frequency stability and voltage stability [10,11]. It is required that generating units should cease to energize local loads during a grid fault, for example voltage sag or frequency disturbance, which is known as anti-islanding protection [10,11].…”

“…The various grid standards are mainly focused on power quality issues, frequency stability and voltage stability [10,11]. It is required that generating units should cease to energize local loads during a grid fault, for example voltage sag or frequency disturbance, which is known as anti-islanding protection [10,11]. In normal operating conditions, PV-STATCOM will inject the reactive power that is demanded by the load on the grid integrated system; whereas, in abnormal operating conditions (i.e., grid fault conditions) as per the LVRT requirement, the shunt connected Voltage Source Converter (VSC)-based PV-STATCOM will inject reactive power to the grid, in addition to the reactive power demanded by the load and wind generators.…”

Low-Voltage Ride-Through Control Strategy for a Grid-Connected Energy Storage System

“…The LVRT control strategies researched recently comply with the LVRT requirement. In addition, these strategies focus on the additional operations that are effective and economical, which include the continuously stable operations with dynamic breakers in the WPG systems [26][27][28][29][30] and the maximum power generation with low voltages in the SEG systems [31][32][33]. These methods for additional operations are presented by considering the characteristics of the source type.…”