Design and simulation of reactive power control and SVG in photovoltaic project booster station

Abstract

With the large-scale integration of photovoltaic power generation into the grid, voltage stability has become an increasingly important issue. Due to the fluctuations in photovoltaic output and the growing proportion of renewable energy sources, photovoltaic grid-connected systems may cause voltage fluctuations and power quality problems. In particular, grid faults may lead to voltage sags, which can affect the safe and stable operation of the power system. Therefore, it is necessary to study voltage variation characteristics and reactive power compensation methods in photovoltaic grid-connected systems.

In this study, MATLAB/Simulink was used to develop a simplified equivalent model for analysing the voltage behaviour of a photovoltaic booster station. Instead of modelling the detailed photovoltaic generation units, the grid-connected side of the photovoltaic station was represented by an equivalent three-phase source, so that the study could focus on the voltage response and the influence of the SVG branch. Since the equivalent point of common coupling is located at the three-phase source in this simplified model, the voltage response was evaluated at the AC bus at the measurement point instead. Different operating conditions were simulated, including normal operation and a three-phase-toground fault. The model mainly consisted of an equivalent three-phase source, a transmission line, a transformer, a three-phase voltage and current measurement module, an SVG branch, and a fault branch. The voltage characteristics of the system under normal and fault conditions were then analysed and compared.

The voltage characteristics were first evaluated under normal operating conditions. The simulation results showed that the three-phase voltage at the AC bus at the measurement point remained balanced and stable, and the waveform maintained a sinusoidal shape. This indicates that the simplified system operated in a stable condition under normal operation. A three-phase-to-ground fault was then introduced to analyse the voltage response during a disturbance. The results showed that the voltage at the AC bus at the measurement point decreased rapidly after the fault occurred. After the fault was cleared, the voltage gradually recovered to a stable level.

To evaluate the voltage sag more clearly, the RMS value of the three-phase voltage at the AC bus at the measurement point was calculated. The RMS voltage curves were used to compare the voltage response under compensated and uncompensated conditions, because they show the depth, duration, and recovery process of the voltage sag more clearly than instantaneous three-phase waveforms. The comparison shows that, without SVG compensation, the bus voltage is directly affected by the fault and recovers after the fault is cleared. When the SVG branch is included, the voltage response changes because the compensation branch participates in the transient process and modifies the reactive power exchange of the system.

The simulation results show that MATLAB/Simulink is suitable for analysing the influence of grid disturbances on voltage behaviour in the simplified photovoltaic booster station model. The results also indicate that the SVG branch can affect the dynamic voltage response by participating in reactive power exchange during normal and fault conditions. Therefore, this study provides a basic simulation-based analysis of voltage behaviour and reactive power compensation in a photovoltaic booster station.