DC-Bus Hybrid Energy Storage Devices Cooperation Control Strategy for Stand-Alone Inverter under Imbalance Load

In a small capacity low voltage renewable energy source (RES) distribution network, there are the increased likelihood of significant load imbalance between phases and the inevitable inherent intermittency in RES. Under this condition, for a stand-alone voltage-source inverter, appropriated inverter strategy would suppress negative-sequence voltage. However the DC-Bus ripple voltage could be observed. Thus even harmonic and odd harmonic voltages in DC-Bus and AC-Bus can be introduced, respectively, and the power qualify is deteriorated subsequently. In this paper, a hybrid energy storage devices (ESD) cooperation control strategy for eliminating the amplitude of DC Bus ripple voltage is proposed. Based on system model, the expression of DC-Bus ripple voltage is deduced. Additional, a notch filter based on Goertzel algorithms is adapted to realize hybrid ESDs reference signal extracting. Moreover, a ripple voltage feedforward control loop is placed in ultracapacitor (UC) ESD to eliminate DC-Bus voltage ripple. The design approach of the control strategy is discussed in detail. The feasibility and effectiveness of the control strategy are validated by simulation and experimental results.