Harmonic voltage compensation with power electronic grid regulator based on symmetrical components

Abstract

The number of decentralized generation units (e.g., wind and solar energy) and loads (e.g., heat pumps and EV-chargers) in the electrical distribution grid are increasing. Most of these sources and loads are coupled by power electronic converters to the main grid. In the low voltage distribution grid level, single-phase or three-phase devices with a neutral connection can lead to harmonics at zero sequence component. Compensation of the zero sequence component requires a grid regulator with a neutral line connection and a suitable control methodology. Consequently, a power electronic inverter with split dc-link capacitors with a neutral connection is considered in this paper. The device is modelled in the symmetrical component (SC) domain and differentiated to each individual harmonic order. The transformation from the time to frequency domain is based on the heterodyne dq-transformation and the SC domain. This results in a decoupling of the control parts in terms of harmonic frequency and the sequence components (positive, negative, zero sequence). Moreover, the coupling of dq-components of the system is compensated by individual resistance to reactance ratios (R/X) decoupling terms. The validation in simulation and a real hardware test shows the strength of the control approach.