Research On Synchronous And Circulating Current Control Of Parallel Inverters In PV Microgrid

In PV microgrid,the parallel operation of PV inverters can increase the redundancy of the system and improve the utilization of distributed PV energy.But in actual operation,the dispersion of inverter control clock,steady-state interference and dynamic fluctuation of load will affect the running performance of parallel system,so that the output voltages of multiple inverters running in parallel is not synchronized,resulting in circulating current.Circulating current will not only degrades micro-source output voltage quality,shortens the life of inverters,and may lead to micro-grid shocks or even collapse.Therefore,synchronization and circulation control of inverters parallel operation is an important research topic in photovoltaic microgrid.Firstly,this paper reviews the research progress of inverter parallel synchronous control,analyzes the running process of the parallel system,establishes the synchronous control model of the system based on triggering pulse,and deeply delve the effects of dispersion,steady state disturbance and dynamic fluctuation band of the clock.Secondly,aiming at the asynchronization problem caused by inverter clock dispersion,a wireless second base clock synchronization control method is proposed,and the controller design is carried out.The method realizes carrier synchronization by adjusting the frequency and phase of the carrier waves by using the second base clock pulse,and solves the problem of instantaneous circulating current caused by clock dispersing.Thirdly,a method of synchronous decision-making is proposed to solve the problem of sine-modulated wave asynchronization caused by steady-state disturbance and dynamic load fluctuation.A fuzzy power controller and a phase-synchronization controller based on second-base clock are designed.By synthesizing the output voltage amplitude,frequency and phase deviations in combination with the setting of the loop control target,the proposed switching control between the two controllers can achieve the synchronization of sinusoidal modulation wave.The synchronization control of the phase does not need interconnect wire,which ensures the real-time performance of the regulation process and improves the anti-jamming performance of the regulation process.At the same time,the switching control method not only achieves steady-state operation under the transient circulation of the effective suppression,but also ensures the output voltage quality during the voltage dynamic adjustment process so as to suppress the dynamic circulating current.Finally,based on the previous work,the Matlab simulation model of the control system is established,and the effectiveness of the synchronization control method is verified by the comparison of the simulation results.At last,by combined the theoretical analysis and simulation results,a parallel system experiment platform is built,the hardware circuit and software control program are designed.The experimental results verify the effectiveness of the proposed control method.