Resesrch On The Key Technologies Of Microgrid Inverter

With the growing energy crisis and environmental pollution problems,distributed generation with the advantages of clean and efficient,flexible installation and low cost has been developing rapidly.In order to solve problems occurred in connection distributed powers with the Grid directly under high permeability,the concept of microgrid which can make full use of distributed generation's potential of distributed generation is proposed.Most of distributed powers and energy storage devices in the microgrid are connected to the common bus through the inverter,so the form of multiple inverters working in parallel is common and research of the control technologies of inverters in microgrid is vital.As the non-interconnection control method has high redundancy and reliability,it will become the development trend of multiple inverters' control technology.In this paper,the modeling and analysis of the voltage-inverter used in the distributed power are carried out firestly.Then the parallel inverters' model is established and the circulating current between parallel inverters is defined and analyzed.Besides,the traditional power droop control principle and design method are analyzed in detail.It is pointed out that the difference of the equivalent output impedance of the inverter will cause the circulating current in the system when microgrid is working in off-grid,which will affect the control target of current sharing,and for traditional power droop control's deviating regulation characteristics,it may lead to serious low bus voltage amplitude and frequency problem in the case of unplanned heavy-duty,affecting system performance.For the problems above,according to the characteristics of the circulating current and power output of parallel inverters,this paper proposes an idea of indirect current sharing,and designs an inverter control system with synchronous generator characteristics to realize the control idea.It realizes the decoupling and accurate control of the equivalent voltage source's voltage and the equivalent output impedance of the inverter.The phase-locked loop can well control the frequency and phase of the equivalent voltage source and make it has the basic function of simulating the synchronous generator.Morever,the inverter has the function of frequency self-synchronization.Based on the mentioned characteristics above,this method realizes the function of simulating the frequency-active power and amplitude-reactive power of the synchronous generator,and indirectly realizes the parallel power inverters without the power loop and has the ability of circulating current suppression.In addition,by designing secondary voltage regulation control,it can eliminate the deviation of bus voltage and frequency.Finally,the simulation of the single inverter working in the grid connected and off-grid modes as well as the simulation of parallel inverters under the same capacity and different capacities are carried out to verify the feasibility and effectiveness of the proposed control strategy.