Harmonic Resonance Analysis of Voltage/Current Controlled Hybrid Systems at High Penetration of Renewable Energy Sources

With the continuous large-scale access of renewable energy, the penetration rate continues to rise, which reduces the short-circuit ratio of the system. Existing current-controlled inverters (CCI) are widely used in grid-connected power generation systems for renewable energy sources. Voltage controlled inverters (VCI) are gradually being introduced to form multi-inverter hybrid operation mode systems because of their ability to guarantee sufficient stability margins even at very low short-circuit ratios. The complex grid-connected environment brings more severe challenges to the inverter and system stability. Therefore, this paper mainly studies the mechanism and characteristics of the harmonic resonance of the multi-inverter hybrid operating mode system, and analyzes the harmonic characteristics of carrier interleaving at high frequencies. Firstly, the equivalent small-signal impedance models of a single CCI and VCI are established respectively, and the small-signal impedance model of the hybrid operation mode is established in parallel from the grid connection point. On this basis, the frequency dividing filter function is introduced to adjust the impedance model of the hybrid operation mode inverter. The output frequency characteristics of CCI and VCI are analyzed separately to obtain their harmonic resonance interaction characteristics. Finally, four 20kW CCI and VCI hybrid parallel physical test platforms were built to verify the obtained harmonic resonance characteristics.