Abstract
This paper presents a constrained multi-objective optimisation scheme for a grid-connected voltage source converter operating under unbalanced voltage conditions in a three-phase three-wire system. The scheme is aimed at evaluating the converter reference currents required to supply all the power generated by the connected source to the grid, whilst simultaneously suppressing oscillations of both real and reactive powers. The trade-off between these two conflicting requirements is achieved by setting a single cost function with variable weightings. Two constraints are set to restrict the converter instantaneous phase current and maintain low DC-bus voltage percentage ripple. A genetic algorithm is applied to search for the optimal solution. Simulation results are presented and confirm the effectiveness of the proposed method.
Highlights
The rapid penetration of renewable energy sourced generators into the utility network has resulted in many grid-connected voltage source converters (VSCs) being connected to the distribution lines and load centres
The power ripples are formulated as a multi-objective optimisation problem (MOOP) and the decision variable, k is chosen based on the genetic algorithm (GA)
Simulation results have compared the operations of the proposed constrained optimised flexible power control (COFPC) with two other classical methods: the constant active power control (CAPC) and the balanced positive sequence control (BPSC)
Summary
The rapid penetration of renewable energy sourced generators into the utility network has resulted in many grid-connected voltage source converters (VSCs) being connected to the distribution lines and load centres. The two main objectives are to mitigate unbalanced voltages at the point of common connection (PCC) and to eliminate active and/or reactive power oscillations While the former relies on the injection of reactive currents using devices such as static voltage controllers [6], the latter relies on grid converter control and poses more challenges. The objective is to ensure that the grid connected inverter supplies the power from its renewable source to the grid, maintaining unity power factor whilst simultaneously dealing with the conflicting requirements of suppressing real and reactive power oscillations Under such a control law, the inverter should be able to ride through unbalanced grid faults.
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