Research On Control Strategy Of Paralleled Three-phase Inverters

The technology of parallel inverters can realize the transformation of inverter power from traditional centralized power supply to distributed power supply mode,and further promote the development of inverter power to high power.In the control of parallel inverters,the problems of load sharing and circulating current suppression are mainly solved.The virtual synchronous generator technology is applied in parallel inverters,and the characteristics of its application are further studied in this paper.The basic principle of synchronous machine is analyzed in detail at first,including the electrical part,machinery part,speed regulating device and excitation device etc.To get the mathematical model of the synchronous generator,each part of the mathematical model is derived and combined.In this paper,the application of synchronous machine mathematical model in the control of single inverter power supply is studied,and the virtual synchronization control algorithm of inverter is obtained.What's more,the steady state characteristics and frequency modulation as well as voltage regulation characteristics of the virtual synchronous machine are verified.The key technology of inverter power supply in parallel is analyzed,and the definition of circulation as well as the main factors is introduced.The way that the output voltage,output impedance and load of inverter power supply effects on the circulation is studied.In view of that the output voltage of inverters must be pre-synchronized before been connected,the control algorithm of virtual synchronous machine based on the unlocking phase loop is studied.As a result,the traditional lock phase loop is eliminated and the control is simplified.Since the automatic current sharing characteristic and high frequency stability of the synchronous machine,virtual synchronous machine technology was applied to the control of inverter power supply in parallel,and the performance of virtual synchronous machine control can be improved.In order to guarantee steady and dynamic performance of the parallel inverter system,small signal modeling and its transfer function of virtual synchronous machine were obtained.According to the cutoff frequency and phase angle margin,the parameters of the active ring and reactive ring are designed,and according to the bode plots of the active ring and reactive ring,the feasibility of parameter design is verified.An experimental prototype of two parallel inverters is designed and constructed.The simulation and experimental results verify the feasibility and applicability of virtual synchronous generator technology used in parallel inverters.