A Control Strategy of Islanded Microgrid With Nonlinear Load for Harmonic Suppression

A control strategy of islanded microgrid is proposed in this paper against the harmonic circulation of the inverters and the Point of Common Coupling (PCC) voltage harmonic distortion of the microgrid caused by nonlinear load. The reference voltage of the inverter's outer voltage loop is given by the decoupling control of the fundamental and harmonic components. Virtual synchronous generator (VSG) is adopted in fundamental domain. In harmonic domain, adaptive harmonic compensation and harmonic virtual impedance are applied to obtain the harmonic components of the reference voltage of the outer voltage loop. The hybrid control strategy combining P control and repetitive control in parallel is adopted in the outer voltage loop. Multi-period repetitive control (MPRC) with fast repetitive control (FRC) is adopted to improve the tracking control performance of the main harmonic components of the given reference voltage. Fractional order delay approximated by Lagrange interpolation polynomial FIR filter is applied in MPRC for different repetitive control periods at the fixed sampling period. The output harmonic current of the inverters can be distributed autonomously according to the capacity of the inverters to suppress the harmonic circulation, and the suppression of the PCC voltage harmonic distortion is realized. Simulation based on Matlab/Simulink and hardware-in-loop(HIL) test are carried out, and the results show that the proposed control strategy is effective.