The distributed power sources in microgrid possesses randomness and volatility, voltage and current fluctuations can be observed, which affects the stable operation of the connected cascaded converters. The three-level Buck/Boost bidirectional converter (3LBBC) connected with the off-grid three-phase voltage source inverter VSI (Voltage Source Inverter) is discussed in this paper to inspect the influence of system parameter on the stability of cascaded converters. In response to the instability and oscillation of inverters caused by voltage fluctuations, based on impedance criteria, a linear feedforward compensator is proposed to optimize the control strategy and adjust the output impedance of the 3LBBC side, and hence improve the stability of the system.