Harmonic mitigation throughout a distribution system: a distributed-generator-based solution

The paper investigates the use of ancillary services from inverter-interfaced distributed generators (DGs) to achieve harmonic mitigation across a network. The approach is to include the functionality of a resistive active-power filter (R-APF) within several DGs. The R-APF provides adjustable damping at harmonic frequencies. In a realistic network, which has feeder sections of different characteristic impedances, it is impractical to damp with a single value of resistance. Instead, feeders are split into harmonic sections based on the standing waves of the highest-order harmonic, and DG ancillary services are called up for each section. Co-ordination of services from each DG is arranged through adaptation of the harmonic resistance according to target THD levels. The primary purpose of each DG is the supply of real power and this is respected through a further aspect of the resistance adaptation which reduces the harmonic duty of an individual DG if it approaches the apparent-power rating of the inverter. The harmonic VA required of the inverter is dependent on both the chosen harmonic resistance and the harmonic-voltage component present at the connection bus. The system is demonstrated through a simulation of an irregular feeder using Simulink and PLECS.