Due to the influence of line impedance

the conventional P-f and Q-V droop control cannot realize the target of accurate reactive power sharing proportional to their rated capacity and the output voltage amplitudes of all distributed generators(DGs)deviate from nominal voltage. The frequency cannot be maintained at the rated frequency value when load fluctuates. A secondary regulation strategy based on model predictive control(MPC)is proposed. By optimizing the frequency and voltage references of droop control

respectively

the frequency and average system voltage are always maintained at their respective nominal values. Meanwhile

the target of accurate reactive power sharing proportional to their rated capacity is realized and the output voltage amplitude deviation from nominal voltage is reduced. The state-space model of DG is discretized with a certain sampling period in this strategy. The control variables of frequency and voltage are obtained by rolling optimization and feedback correction and then added to P-f and Q-V primary controls

respectively

to realize the secondary regulation for frequency and voltage optimization. The number of proportional-integral(PI)control parameters decreases and the sensitivity to the system parameters is reduced. The MATLAB/Simulink simulation verifies that the proposed strategy has faster transient response characteristics and stronger robustness when load fluctuates compared with the PI based secondary regulation strategy.