Research On Power Synchronization Control Strategy Of Single-phase Grid Forming Inverter

With the development of renewable energy power generation technology,single-phase inverters are widely used in the distributed generation of medium and small power levels.Compared with the grid following control method using current control,the Grid Forming Inverter(GFI)using the voltage control method can achieve fast power tracking and provide inertial support for the power system,which is a more potential single-phase distributed power supply interface.In order to ensure good transient synchronization stability and dynamic characteristics of single-phase GFI in a complex grid environment,problems such as filtering of double-frequency ripple during single-phase operation of GFI,transient synchronization stability of single-phase GFI under sudden change of grid operating conditions(i.e.large disturbance),and optimization of dynamic characteristics of single-phase GFI after the dispatch reference power is changed are studied in this paper(1)The working principle of single-phase GFI is introduced at first,the mathematical model of voltage and current control of GFI is established,and the voltage and current double inner loop control structure of GFI is reasonably designed;Secondly,according to the GFI equivalent circuit model and the line transmission theory,the small-signal modeling method is used to analyze and compare the existing GFI power synchronization control strategies;Finally,problems of existing strategies that need to be solved urgently in the aspects of ripple filtering,transient synchronous stability control and dynamic characteristic optimization are explained,which lays the foundation for the following theories.(2)Aiming at the problem of transient synchronization instability of single-phase GFI under the sudden change of grid operating conditions,a transient synchronization stabilization strategy considering double frequency ripple filtering is proposed.Firstly,the influence of power control parameters and double frequency ripple of power on the GFI transient synchronization stability is analyzed,then the notch filter is used to filter the double frequency ripple of power without changing the GFI operating characteristics in the strategy;On this basis,the power angle curve of GFI is analyzed,and the critical condition of transient synchronous instability is given,then the system can be guaranteed to recover synchronous stability after transient instability through the coordinated adaptive adjustment of inertia and damping parameters;Finally,The correctness of the strategy is verified by theoretical analysis and simulation.(3)Aiming at the overshoot and oscillation of single-phase GFI output power and frequency,an optimization strategy of power loop dynamic characteristics based on inertial adaptation is proposed.Compared with the existing strategies,this strategy does not introduce noise;and does not constrain the adaptive adjustment range of inertia.Firstly,the output characteristics and operation mechanism of GFI are analyzed,and the corresponding relationship between the deviation of GFI virtual output power and reference power and the frequency change rate is explained;Then,the inertial adaptive selection function is constructed by using power deviation and frequency deviation,and the output dynamic characteristics of GFI are improved through the adaptive adjustment of inertial parameters.Finally,the correctness of the strategy is theoretically analyzed by using Lyapulov’s theorem and verified.(4)Firstly,a single-phase GFI hardware experimental platform is built;Secondly,then the feasibility of the transient synchronization control strategy considering the double frequency ripple filtering and the dynamic characteristic optimization strategy proposed in this paper is verified by experiments.