Power delivery to a current source and reduction of voltage harmonics for inverters

In this paper, the load and/or grid connected to an inverter is modelled as the combination of voltage sources and current sources at harmonic frequencies. As a result, the system can be analysed at each individual frequency, which avoids the difficulty in defining the reactive power for a system with different frequencies because it is now defined at each individual frequency. Moreover, a droop control strategy is developed for systems delivering power to a constant current source, instead of a constant voltage source. This is then applied to develop a harmonic droop controller so that the right amount of harmonic voltage is added to the inverter reference voltage to compensate the harmonic voltage of the harmonic current dropped on the output impedance. This forces the output voltage at the individual harmonic frequency close to zero and improves the THD of the output voltage considerably. Simulation results are provided to demonstrate the excellent performance of the proposed strategy.