| With the continuous improvement of material technology and rapid progress of industrial scale,the application scenarios of BESS(battery energy storage system)have been greatly expanded,it is playing an important auxiliary role in the power system increasingly.In the BESS-Grid connected system,the batteries are transformed by bidirectional energy storage converter,and then connected to the power grid at the common coupling point after harmonic filtering by filter.When the battery energy storage subsystem is connected to the grid,there would have the risk of internal resonance between the control system and the filter of the bi-directional energy storage converter,and the risk of external resonance between the control system and the complex power grid.The existence of both situations threatens the stable operation of the grid connected system.This paper selects the bi-directional energy storage converter which plays a important role in enhancing the stability of BESS-Grid system,conducts the research as follows:At firstly,this paper introduced the grid-connected structure of bi-directional energy storage converter and the control system structure of charge and discharge.According to the circuit equation of the system,the Derivation process of the circuit mathematical model is given step by step,and the small signal model of dq is obtained by applying small signal disturbance to the DC working point of dq mathematical model.Then,by using the functional relationship between the capacitor voltage and the AC side current of the converter in the small signal model,the open-loop impedance of the bi-directional energy storage converter is derived,and the current inner loop and three different outer loop controls are applied layer by layer.The impedance model of bi-directional energy storage converter under different control strategies is established.By convetring the transfer function to the typical system,this paper designed the inner current loop parameters subsequently.And based on the equivalent transfer function of the inner loop,the outer loop parameters with different strategies are designed under several bindwidth.In order to evaluate the parameters’ correctness and the stability in different power grid environments,this paper used both the generalized Nyquist stability criterion and the frequency response curve is used,and carried out simulation verification.At the end of this paper,the passivity of bi-directional energy storage converter is taken as the starting point to improve the stability,and the admittance passivity of bidirectional energy storage converter in AC/DC mode and DC/AC mode is analyzed.By studying the influence of control parameters on passivity,the control parameters are further optimized.The paper also enhances the passivity of the bi-directional energy storage converter by introducing capacitor voltage feedforward,and selects the optimal compensation coefficient for the three kinds of loop control in this paper,which broadens the passive range without changing the original dynamic performance indicators,and improves the grid-connected stability of the bi-directional energy storage converter. |
PDF Full Text Request