An Active Harmonic Grid-Connecting Current Suppression Strategy for Hierarchical Control Based Microgrid
摘要
Given that the droop controlled inverters based grid-connected microgrid (DCIGC-MG) presents low equivalent output impedance when connecting to the grid, the grid-connecting current (GCC) is distorted easily by the harmonic voltage components at the point of common coupling (PCC), and results in the increase of THDn of GCC. An active harmonic GCC suppression strategy for DCGC-MG based on hierarchical theory was proposed in this paper. Firstly, the voltage error between bus of DCGC-MG and PCC of grid was transferred to dq frame by the Park transformation. Then, an additional compensator consisting of multiple resonant voltage regulators was added into the secondary control to generate the harmonic voltage reference for inverters in the primary level. PI and multiple resonant controllers were adopted as voltage controller in the original primary level to improve the voltage tracking performance of inverter. As a result, the voltage difference between the PCC and system bus decreased, and the GCC is purified. The proposed control strategy not only reduces the steady-state hormonic current injected into the grid by the microgrid, but also suppressed the harmonic inrush currents when the microgrid connects to the distorted grid for protecting inverter. Finally, the simulation and experimental results from scaled-down laboratory prototype have verified the proposed control strategy.