Voltage and power control used to stabilise the distributed generation system for stand-alone or grid-connected operation

This study presents a control strategy for managing power delivered to, or absorbed from, the grid, independent of local load or grid characteristics. To achieve this objective, the strategy requires the use of three levels of control structures. The first is related to phase-locked loop and grid-tie algorithms, which are employed to minimise disturbances during the grid connection. The second, which produces voltages with reduced harmonics levels at the distributed generation (DG) terminals, comprises the cascade voltage and current control. The third structure is the active and reactive power control mechanisms, which uses the angle of displacement and the adjusting of the DG voltage amplitude to keep the power flow through the grid at a specific set-point, independent of local load characteristics. In addition, the power control structures have to operate in a decoupled operation mode, whereby the active power control has to be faster than the reactive power control, or vice versa. In terms of their physical structure, a passive LCL filter is used to connect the voltage source inverter to the grid. To verify the findings and observations discussed in this study, a set of simulations and experimental results are presented.