On Insulation Detection And SOC Estimation Method Of Battery Pack In Micro-grid Energy Storage Power Station

Due to the existing insulation resistance detection methods can’t do real-time detection and the low accuracy problem of common State of Charge (SOC) estimation methods in the application of practical project, this paper presents an active insulation resistance detection method of battery pack (DC system) by taking the battery pack of energy storage power station as research object, meanwhile, a method for battery SOC estimation was designed, some research on battery management system (BMS) of energy storage power station was also promoted. The main work is as follows:(1) The overall design of energy storage power station was accomplished, which include in the connection type of battery pack, System configuration of the battery pack and the connection type of external energy unit. The battery management system of the energy storage power station which uses a hierarchical architecture was designed: local data sample unit, battery control unit, battery management unit and master control centre.(2) An active insulation detection method which injected low-frequency AC signal was proposed. And the method was partitioned into two detection levels:fault detection and insulation resistance calculation. Such as, the fault detection:measure the "measurement resistance" voltage, meanwhile, calculate the positive-negative parallel resistance value which is determined the insulation resistance fault status of the insulation resistance. Insulation resistance fault is detected after entering the insulation resistance calculation:disconnect the load circuit and the AC signal source, respectively, connected two resistors in parallel with positive and negative insulation resistance, meanwhile, two resistors terminal voltage is measured that the positive and negative insulation resistance values is calculated.Simulation results shows that the failure rate of false positives is less than2.15%of fault detection. In the paper, it has achieved a function of real-time detection in the insulation resistance detection by injecting the low-frequency AC signal. (3) A SOC adaptive estimation method was proposed based on Second-order equivalent circuit model. According to the battery charge-discharge characteristics, an second-order equivalent circuit model of battery charge-discharge was established, the forgetting factor recursive least squares algorithm is used to identify the model parameters, Which can estimate the open circuit voltage (OCV) of the battery charge-discharge, Also, the Gaussian filter is used to filter out the outlier data of OCV. Finally, The SOC is estimated in accordance with the mathematical relationship SOC-OCV. The simulation result which using analog condition data of micro-grid energy storage power station and MATLAB software show that the maximum error is10%.