Research On Stability Of Small Signals In Optical Storage AC And DC Microgrid Based On Impedance Model

Dual bus microgrid has gradually become one of the main power supply architectures for residential buildings and intelligent buildings due to its advantages such as reliable power supply,high load matching and flexible access to medium and low voltage distribution network.Stability analysis is an important problem in its design.In this paper,the impedance models of each converter in the optical storage AC and DC microgrids operating off-grid are established by means of the state-average modeling method.According to the integrated equivalent impedance model of AC and DC microgrids,the impedance characteristics of the changer and the load supply stability under various operating modes are studied.Firstly,the impedance models of each converter in the microgrid are established according to the traditional state-space modeling method,the generalized state-space average modeling method and the DQ domain state-space modeling method.Then,each unit is divided into two equivalent impedance models according to the control mode:1)Davinian equivalent model:constant voltage and constant frequency control of energy storage DC/AC inverter circuit,droop control of energy storage DC/DC circuit;2)Norton equivalent model:dual active bridge circuit for power control,photovoltaic Boost circuit for Maximum power point tracking(MPPT)and DC/AC inverter circuit.The two equivalent impedance models are the basis of the following research.The two equivalent impedance models are the basis of the following research.Secondly,the model building,impedance characteristic analysis and load power supply stability of the dual-bus DC micro grid under various operation modes are studied.From the perspective of impedance analysis,four impedance models are established according to the source and charge attributes of each converter under different operating modes of the system,and the influence of different modes,micro-source and load impedance characteristics on the stability of micro-grid small signals is studied by analyzing the Bode diagram of input and output impedance of the system and the impedance Bynaquist curve.Three passive schemes are compared to improving the load power supply stability of the system.The stability analysis of cascaded small signals is verified by simulation and experiment.Finally,the operation control and stability analysis of AC coupling power supply system is studied.Considering the load increase and decrease,the energy storage equilibrium output and the limitation of the State of Charge(Soc),the energy storage Soc equilibrium algorithm and the design steps of the system coordination control are given.The influence of each control loop parameter on the stability of the system is analyzed,and the influence law of control parameters on the stability of the system is analyzed by generalized Nyquist judgment,and the theoretical guidance of system parameter design is provided.A simulation platform was established to verify the Soc balance algorithm,system coordination control and three working conditions of energy storage battery.The results show that the system can switch operating modes independently according to the coordinated control strategy,can balance output according to the energy storage Soc equalization algorithm,and can prove the correctness of the analysis of generalized Nyquist criterion according to different working conditions.