| Renewable energy is characterized by randomness,intermittentness and volatility.Large-scale grid connection of renewable energy will seriously affect power quality.Energy storage technology effectively compensates for the shortage of renewable energy in grid-connected power generation.As an important device for DC-AC conversion between energy storage system and power grid,energy storage converter has been studied more and more extensively.Aiming at the requirements of large-scale energy storage development,a cascaded AC high-frequency link bidirectional converter topology is proposed in this dissertation,and the key technologies of the circuit are studied.The topology of single-phase cascaded high-frequency link converter is first analyzed in this dissertation.Combined with the characteristics of cascaded multilevel topology and high-frequency link topology,the integrated modulation strategy is proposed based on the principle of harmonic optimization.Each high-frequency chain adopts a decoupling modulation strategy.The cascaded chains are implemented by carrier phase shift SPWM method.On this basis,the parameters of the main circuit of the 5MW/35 kV energy storage converter are designed to complete the selection of key components.The energy storage system has two modes,independent operation and grid-connected operation.The mathematical models and the control methods of the converters in these two modes are studied respectively in this dissertation.When operating independently,a dual-loop control method based on voltage and current feedback is adopted.The simulation results show that the system has better load capacity and dynamic response capability.When operating with the grid,the quasi-PR control is adopted.Compared with traditional PI control,quasi-PR control can achieve no static tracking and harmonic suppression.Redundant control is an important research direction for cascaded multilevel topology.When the energy storage batteries fail,a hybrid energy storage system can be formed by disconnecting the battery connection switches.In this dissertation,the stable working range of the hybrid energy storage system is obtained by vector analysis.A control method based on voltage source converter and current source converter is proposed.The simulation results show that the control method can achieve system power allocation and improve system stability.Due to the inconsistency of active power absorbed and consumed by chain,the batterySOC and capacitor voltage will be unbalanced.According to the power balance condition,several balance control methods are analyzed,which are the balance control method of changing the amplitude of the output voltage,changing the phase of the output voltage,and changing the amplitude and phase of the output voltage.The performances of different methods are compared by simulation.On this basis,a hardware-in-the-loop simulation test platform for single-phase cascaded high-frequency energy storage system based on RT-LAB is built,and hardware circuits including conditioning circuit,control circuit,digital-to-analog conversion circuit and voltage conversion circuit are designed.The experimental results fully verify the correctness of the proposed control method.In this dissertation,the key technologies of single-phase cascaded high-frequency link bidirectional energy storage converter are studied.The dissertation lays a foundation for the realization of high efficiency and large capacity energy storage development,and has important engineering application value. |
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