Voltage stability enhancement Scheme using PV-reinforced Dynamic Voltage Restorer

Among the promising solutions proposed for the mitigation of the voltage instabilities is a series compensator known as Dynamic Voltage Restorers (DVR) due to its flexibility and cost effectiveness. Dynamic Voltage Restorer (DVR) also known as Static Synchronous Series Compensator (SSSC) is a series compensation technique used in the distribution and transmission system. The power flow through the supply line is regulated by controlling the equivalent impedance of the line. The output voltage of DVR is fully controlled and independent of the line current In conventional DVR, capacitors or supercapacitors are used at the DC-link as energy storage elements. However, due to the self-discharge rate and gradual voltage loss of capacitors and supercapacitors, the stored voltage drops linearly as the capacitor is discharging, thereby making the DVR not suitable for voltage stabilization following a prolonged disturbance. In this study, the DC-link of conventional DVR is reinforced with Photovoltaic (PV) and battery with aim to mitigate the devastating impact of symmetrical and unsymmetrical faults on the load voltage. Specifically, the PV-reinforced DVR is developed to mitigate voltage sags( and harmonics) caused by three phase symmetrical fault as well as unsymmetrical faults. In order to mitigate the harmonics generated due to the injection of compensation voltage, a filter is implemented to lessen the effect. To verify the performance of the developed PV-reinforced DVR, the system is designed in MATLAB/Simulink where a time-based simulation is carried out. It is established that the PV reinforcement to the DC-link has significantly improved the DVR response to the voltage sag at the PCC. Similarly, the filter designed has led to remarkable reduction in the THD. For the three phase fault, the load voltage is improved from the faulted condition of 20.18V to 319.36V by injecting a three phase voltage of 298.24V. The load voltage of 298.24V obtained represents 22.56% improvement on the voltage of 260.5V obtained using the technique of PID-DVR. For the DLG fault, the phase voltages are improved from faulted condition of 126.4V to 323.66V in both phases, which represents 12.77% improvement over those obtained using PID-DVR. The Total Harmonic Distortion obtained using PV-reinforced DVR in the two scenarios were reduced from 3.64% to 2.84% (21.98% reduction), 5.10% to 3.96% (22.35% reduction) for the three phase, double line-to-ground faults scenarios respectively.