| The large-scale application of distributed generation and smart grid has promoted the rapid development of energy storage technology. The energy storage system can be used to balance the fluctuating power of renewable energy generation, play the role of “load shifting” in power system, maintain the power balance and improve the power quality of micro-grid. As the interface device for energy storage carrier and power system, power conversion system(PCS) plays an important role in exchanging the energy between them. This thesis is dedicated to control strategies and parallel operation technologies of double-stage PCS.Firstly, based on the relationship of power balance and vector diagram of system voltage and current, the bi-directional converting principle of DC/DC converter on the battery side and DC/AC converter on the power system side are analyzed, respectively. The small-signal dynamic model of Buck/Boost converter is derived by state-space averaging and small disturbance method. According to the control objective, the mathematic model of diode-clamped three level converter under the grid-connected and island operating mode are derived, respectively.Then, the PCS control stategy is given, that is, the former-stage DC/DC converter is used to stabilize the DC-bus voltage, and the subsequent-stage DC/AC converter works as a voltage source or current source according to instruction. The double closed-loop control of DC/DC converter is studied. The control strategy of DC/AC converter under the grid-connected and island operating mode are analyzed, respectively. Because of the state variable of DC/AC converter in dq two-phase rotating coordinate is coupling and also affected by the grid voltage or load current, adopting control strategy of state feedback and grid voltage or load current feedforward decoupling method. The reason of neutral-point potential fluctuation in three level converter is analyzed. A simple and practical neutral-point potential balance control strategy is given on the basis of establishing the neutral-point potential fluctuation model. The experimental results verify the validity of the control strategies.Finally, the parallel operation technologies of PCS under island operating mode is studied. The master-slave mode control method of PCS parallel system is introduced. The relationship between the output power of PCS and the d/q axis component of the output voltage in parallel system is derived. The centralized control strategy based on the power error adjusting the d/q axis reference voltage is presented. The droop control strategy is given by the relationship between the output power and the output voltage radian frequency(phase) and amplitude of PCS. The simulation and experimental results show the effectiveness of the parallel operation technologies. |
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