Research On Storage Battery Feedback Diacharging Of Grid-connected Inverter

Storage Battery discharging experiment is an essential method which tests the battery capacity, deals with electrode active material hardens and the passivation of plate, and prevents the storage battery becoming invalid in the early age. At present, there are mainly two methods, resistor and phase-controlled active inverter discharging devices. However, the former wastes energy and is bad in the dynamic response, While the latter polluted the harmonic heavily to grid and it has poor reliability. Both of them cannot meet the relevant requirements. Based on some projects as background, this paper aims to design a new discharge device which can come over these defects, and research deeply on the later of grid-connected inverter.First, the paper introduces the background and significance of this research, demonstrates the applications and the main content of this research. It determines to use three-phase full bridge inverter with LCL filter as the structure of the main circuit . Analyzing LCL filter and establishing the transfer function. On the basis, It establishes two mathematical models about the main circuit is established in the three-phase static coordinate system and the two-phase rotating coordinate system. Using the voltage and current loop control scheme to solve the voltage and current coupling in the two-phase dq rotating coordinate system.Next, the author gives a detailed analysis of inner and outer rings in the control system, according to the system performance designing for typeâ… andâ…¡system separately, used to guide PI parameter settings. Adopting the theory of the instantaneous reactive power theory of software lock method, which is not only lock-effective and can be reduced the grid voltage distortion on the impact of phase-locked loop. It analyses deeply in the quality of grid-connected current, pointing out the defects of the switch dead and the influence of the bus voltage on the grid-connected current, as the basis of selecting the dead time and the bus voltage. Researcher adopts the fixed switching frequency of SVPWM and analyzes its algorithm deeply, besides builds the simulink model in the simulink environment.Then, the researcher studies the islanding effection usually existing in the grid-connected inverter, and puts forward islanding protection strategy which combine the active and passive methods. The active method is injecting the disturbance current which is low of the amplitude and frequency into the q-axis of the two-phase rotating coordinate system. This method has no impact on the quality of the grid-connected current, the non-detection zone is small and it can detect the Islanding phenomenon effectively. Finally, a systematic simulative model based on the above research is established, which is used to do detailed simulation study on phase-locked loop, control algorithm and islanding detection. According to the system requirements, the research calculates the relevant experimental parameters and designs an experimental sample. The comparation between the experiments and simulation verifies the correctness of theoretical analysis.