Enhanced Energy Delivery for Solar PV Distributed Generators at Voltage Sags

Distributed generator of renewable energy (DGRE) requires ancillary services for protection against disturbances in the grid system. Hence, a current limiting property is crucial for the DGRE to achieve self-protection. However, such property would reduce the generated power that corresponds to optimum current injection. In order to overcome this shortcoming, this paper proposes an enhanced DGRE that features decoupled active and reactive power delivery as well as low voltage ride-through (LVRT) strategy. An improved DGRE power delivery system is achieved by employing an auto-correction droop control scheme. By taking into account the droop slope parameters, the system adjusts the reference voltage based on the power value computed from the measured voltage and current. Active and reactive power are consequently delivered proportionally, while the voltage at the point of common coupling (PCC) is maintained despite a voltage sag. In addition, the LVRT strategy which involves three modes namely Constant Average Active Power Control (CAAPC), Constant Active Current Control (CACC), and Constant Peak Current Control (CPCC) would ensure that the grid code requirements are met and the DGRE would remain connected to the grid during a voltage sag. By generating the necessary active and reactive power, the grid voltage can be satisfactorily restored. In the event of a grid fault, the combination of the proposed auto-correction droop control scheme and LVRT strategy would enhance power delivery and increase voltage stability. The DGRE prototype has been developed and experimental tests have been conducted for validation purposes. Both strategies have been practically implemented by the DGRE with satisfactory performance achieved.