Research On Reactive Circulating Current Suppression Method For Parallel Inverters System In The Microgrid

With the increasingly serious energy crisis,environmental pollution and climate change issues,distributed power generation has become one of the development trends of power system in the future due to the less pollution,high efficiency and small loss of power transmission line.In order to coordinate the contradiction between the distributed power supply and the grid,the microgrid is proposed to integrate the advantages of various types of distributed power generation and improve the utilization of renewable energy.The inverter is taken as the interface of the micro power source to connect to the microgrid,therefore,the multiple parallel inverters are formed in the microgrid.There are many control methods to realize the parallel operation of multiple inverters,where,the droop control method is paid attention owing to high degree of redundancy,no communication,no geographical restriction,reasonable power distribution,etc.In this paper,two single-phase full-bridge parallel inverter systems with droop control is used as the research object.By designing the parameters of voltage control and current control,the equivalent impedance is guaranteed to be inductive and the power is decoupled.On this basis,the reason of the circulating current is analyzed for the traditional droop control method,and it is found that the mismatch between the equivalent impedance and the capacity can not cause the active circulation,but can cause the reactive circulation.In order to resolve this problem,the existing reactive suppression method based on reactive power control integrator structure can effectively suppress the reactive circulation,but it reduces the rapidity of the system.A reactive circulating method based on correction of both droop coefficient and no-load point voltage on line is researched in this paper.The analysis shows that the reactive power circulating suppression can be achieved by increasing the droop coefficient of reactive power or reducing the no-load voltage.The reactive droop coefficient and the no-load point voltage of the improved method are corrected according to the change of reactive power,so as to realize the effective restraint of reactive power circulating current,and the stability and rapidity of the system are still good.At the same time,the synchronous control method based on the SPWM synchronous modulation restrains the circulation current between the parallel inverter systems too.In order to verify the control method,the simulation model is built by PSIM software,and the experimental platform with two single-phase full-bridge parallel inverters is also set up.Simulation and experimental results verify the feasibility and effectiveness of the system control scheme.