Improved current droop control strategy of parallel inverters for microgrid based on negative feedback of current

Abstract

In order to increase the current distribution accuracy of the system and restrain the system frequency fluctuation on the basis of reducing the control operation complexity, this paper proposes an improved current droop control strategy. The strategy can be described as follows: Firstly, a virtual negative inductance and a virtual resistance are introduced into the voltage and current double closed loop control to balance the output impedance of the inverter unit. Then an impedance ratio is introduced to solve the contradiction between the virtual complex impedance and potential drop. Finally, by introducing new current variables and using these current variables to form the negative feedback to the droop coefficient in the voltage equation in the droop control, the allocation of the active current and reactive current is implemented in terms of the inverter capacity, and the plug and play function of the inverter unit is realized in the low-voltage microgrid. A great number of simulation results show that by the strategy, the active and reactive currents output can be distributed in terms of the own capacities of the inverters in the system, the smooth operation of parallel inverters with the same or different capacities is ensured and the computational complexity is simplified.

Keywords

• Improving droop control
• New current variable
• Current distribution
• Virtual complex impedance