Damping and Harmonic Control of DG Interfacing Power Converters

Abstract

A large number of renewable energy resources have been installed in the power distribution system in the form of distribution generation. To interconnect renewable energy resources to the utility power system, the power electronics converter is often used as an efficient interface of distributed generation units. However, the presence of power converters with high order LC or LCL filters also introduces many harmonic and resonance problems to power distribution systems. In addition, the growing application of distributed nonlinear loads further aggravates the harmonic distortions in the power distribution system.To solve these problems, this thesis discusses interfacing converter control method that actively mitigates the resonances and harmonics in power distribution systems. The first objective is to provide sufficient damping effect to distributed generation unit interfacing converter filters through improved inverter control. To realize this objective, this thesis conducts an in-depth investigation on resonances in both a single inverter and multiple parallel inverters. The virtual impedance based damping method is proposed to realize better control of interfacing converters. The second objective of this thesis is to compensate the impact of nonlinear loads in the low voltage distribution system through flexible operation of interfacing converters. In the scenario, the interfacing converter essentially works as a virtual harmonic filter. A number of power distribution system harmonic compensation methods are proposed. They aim to realize better power quality of future power electronics intensive power distribution systems.