Research On Design And Control Of T-Type Three-Level Converter For Micro-Grid Energy Storage

Micro-grid is a single controllable micro grid which is consist of micro power, energy storage unit, load unit, energy conversion unit, related monitoring and protecting devices. Not only can the micro-grid work in-grid, but also it can work off-grid, which can realize power supply diver sification, high reliability and high performance requirements in efficient and economical way. From the perspective of power dispatching, micro-grid can cut off the connection with the external network quickly and safely and reliably. Micro-grid can access into off-grid operating state when micro-grid internal or external system is fault. When micro-grid works off-grid, the storage unit plays a vital role on improving the power supply reliability of micro-grid in order to ensure the voltage and the frequency of the micro-grid load unit.Compared with traditional diode clamped three level circuit, T-type three-level circuit topology has low harmonic, high efficiency and low conduction loss. T-type three-level has been more and more attention and application at home and abroad. The main circuit topology of T-type three level converter is T-type three-level circuit topology. In order to realize the bidirectional flow of energy, the T-type three-level circuit topology is applied in the micro-grid energy storage system. The main research contents are below.Firstly, the working principle of the T-type three-level circuit topology is analyzed, and the main circuit of micro-grid energy storage converter is designed based on T-type three-level topology. The abc coordinates and dq coordinates mathematical model of T-type three level micro grid energy storage converter are established, which works in-grid status and off-grid state.Secondly, the controlling strategies of grid connected discharge status and off-grid state are introduced. When micro-grid energy storage converter is working in-grid connected discharge status, the outer ring of the PQ grid operation control strategy of current control loop is introduced. While micro-grid energy storage converter is working off-grid state, the outer ring of the V/f control strategy of current control loop is used.Thirdly, the simulations of the grid connected discharge status and the off-grid state are built in MATLAB. In order to achieve the goal of reducing the output harmonic and maintaining the balance of neutral point voltage, the Space Vector Pulse Width Modulation(SVPWM) is used.Finally, the hardware and software of the T-type three-level micro-grid energy storage converter are designed. Hardware design includes control platform construction with TMS320F28335+SPARTAN6 as main control chip, design of power supply module, design of analog sampling conditioning circuit, design of drive circuit. Software includes main program, Analog Digital(AD) sampling compiling program, Software Phase Locked Loop(SPLL) program, SVPWM program. Experimental results are consistent with the simulation waveform, which can verify the correctness of the proposed method comprehensively.