A State-Space Based Model For Integration Of Battery Energy Storage Systems

With the trend of upgrading in power grid and energy sources, which power system is experiencing recently, renewable energy replacing fossil fuels while traditional electric grid converting to smart grid, power system is thereby stepping into a brand new, smarter, safer and more environmental friendly stage. Meanwhile, the requirements of power system’s operational security, reliability and economic efficiency are boosting relentlessly as well. Applications of Battery Energy Storage Systems(BESS) in the power grids will be expanded in the coming years due to factors such as promotion of the stability in power system and reduction of the costs of such systems. In a modern power network, Battery Energy Storage Systems can be optimally controlled for peak-load shaving and other ancillary services such as active and reactive power control, system balancing and loss reduction. However, all these “system-level” controls will depend on the capability of each individual BESS to independently control the active and reactive power injection/absorption at its connected bus, and to maintain the voltage of the DC link between its AC/DC and DC/DC converters. As a result, understanding the behavior and control requirements for the operation of the Battery Energy Storage System is necessary.In this paper, we firstly announced an equivalent model of battery energy storage system based on an active AC/DC rectifier and a bidirectional DC/DC converter, for providing the battery a capability of working in both charge and discharge modes. Meanwhile, by analyzing and calculating the equivalent circuits of active AC/DC rectifier and bidirectional DC/DC converter in their charge and discharge modes respectively, we can find the state space formulas thereby simulating the state space model of battery energy storage system in MATLAB/Simulink. Sliding mode control method and voltage oriented control method(VOC) are applied in the simulation, for controlling the system’s active/reactive power and DC link voltage, separately. Basic achievements of the simulation experiment are list below:(1) The battery energy storage system based on state space model can smoothly operate and auto-switch between its charge and discharge modes, under the action of auto control methods. The efficiency of a charge-discharge circuit can reach 86.4%. Meanwhile, the energy storage system’s active/reactive power and DC link voltage are all under perfect control.(2) In order to verify the accuracy and viability of the state space model which we proposed, detailed switching circuit model is used for simulating the same system. Comparing the simulation results of the two different models and we can get the results that state space model simulation can not only catch the average behavior accurately, but also achieve a much faster simulation speed.(3) Under the action of control systems, the battery energy storage system can achieve load shaving effectively for electricity users, thus reduce the pressure of electric grid and save utility cost.