Improved P-f/Q-V and P-V/Q-f droop controllers for parallel distributed generation inverters in AC microgrid
Sustainable cities and society
Distributed generation inverters are generally operated in parallel with P-f/Q-V and P-V/Q-f droop control strategies. Due to mismatched resistive and inductive line impedance, power sharing and output voltage of the parallel DG inverters deviate from the reference value. This leads to instability in the microgrid system. Adding virtual resistors and virtual inductors in the control loop of droop controllers improve the power sharing and stability of operation. But, this leads to voltage drop.
... herefore, an improved P-f/Q-V and P-V/Q-f droop control is proposed. Simulation results demonstrate that the proposed control and the selection of parameters enhance the output voltage of inverters. 2 based on active and reactive power droop control is proposed , . Wireless control includes droop control , , reverse droop control , hierarchical droop control , improved droop control , ,  and virtual power droop control , among others. Droop control in a microgrid has a broad application prospects, as it does not require physical communication links and easy to achieve plug and play operation  . The traditional P-f/Q-V droop control and P-V/Q-f droop control as the research background, the main research is summarized on the following aspects: Droop decoupling control strategy  , droop coefficient self-tuning optimization algorithm  , virtual impedance control ,  . In an inductive line environment, droop control can achieve better results. But, mostly for microgrid voltage level of 10 kV the line impedance is resistive, thus affects the droop control performance. The use of traditional droop control method makes it difficult to achieve precise power sharing and circulation suppression  . A variety of improved droop control methods are proposed. In ,  an improved droop control is proposed by designing control parameters, so that the inverter output impedance is always inductive. However, this method has a limited range of effective output impedance adjustment. In , by adding differential links in the traditional droop control equation, the power sharing of the parallel DG inverter is quickly stabilized. But this leads to harmonic amplification and output voltage distortion. Virtual impedance method ,  ,  is adopted for parallel DG inverters to improve power sharing under different line conditions. However, virtual impedance does not completely eliminate the influence of line impedance and increases the voltage drop. In an actual microgrid system, differences in parameters and line impedance, makes active and reactive powers not completely decoupled, thus affecting the accuracy of the droop controllers.