Research On DC Side Control Strategy Of Cascaded H-Bridge Energy Storage Converter

Renewable energy is intermittent and random,which will threaten the stability of the power system when connected to the grid in the form of distributed generation.The energy storage system can realize the real-time storage and release of energy,which plays the role of peak clipping and valley filling in the power system.Therefore,it can be used to improve the reliability of distributed power grid connection and achieve the balance between supply and demand of energy in the power grid.The energy storage system based on cascade H-bridge topology has the advantages of good output harmonic characteristics,high scalability,simple control and so on.By increasing the number of cascade modules,the high-voltage output of low-voltage devices can be realized,which can be used in high-voltage and high-power occasions.In this thesis,the balance control of in-phase DC-side voltage and inter-phase DC-side voltage of 10 k V cascade H-bridge energy storage converter is studied,which is prone to unbalanced DC-side voltage.Based on the topological structure of the cascade H-bridge energy storage converter,the working principle of the cascade H-bridge energy storage converter is analyzed,and the mathematical model of the converter is established.On this basis,the power conversion control of the cascade H-bridge energy storage converter is realized by using the carrier phase shift pulse width modulation(CPS-PWM)and power decoupling control.Aiming at the inconsistency of capacity and voltage of DC-side energy storage unit of cascade H-bridge energy storage converter,the balance control of in-phase DC-side voltage and inter-phase DC-side voltage are studied.In order to equalize the DC side voltage in the phase of the converter,an in-phase modular independent control strategy is studied.By analyzing the relation between the voltage and power of the DC side in the phase,the charging speed of the DC side energy storage module can be changed by changing the power distribution in the phase is pointed out.According to the voltage difference of the in-phase DC side energy storage unit,the in-phase power distribution coefficient is obtained.The power distribution coefficient is used to redistribute the in-phase power and change the charging and discharging speed of the DC-side energy storage unit,thus the voltage balance of the in-phase DC-side energy storage unit is realized.Simulation results verify the effectiveness of the in-phase modular independent control strategy.By injecting the maximum value of zero-sequence voltage or negative sequence current at the initial stage of equalization,the voltage equalization speed of the DC side of the phase is accelerated.and the traditional equalization strategy is switched in the later stage of equalization,to shorten the voltage equalization time of the DC side of the phase.In order to balance the DC voltage between the two phases of the converter,the control strategies of traditional zero-sequence voltage injection and negative sequence current injection are studied.Considering the long voltage equalization time under traditional zero-sequence voltage and negative sequence current injection method,based on this,by analyzing the relationship between voltage equalization time and injection voltage amplitude,the control strategy for rapid equalization of phase DC side voltage was studied.By injecting the maximum value of zero-sequence voltage or negative sequence current at the initial stage of equalization,and switching to the traditional equalization strategy at the later stage of equalization,the voltage at the DC side of the phase can reach equalization quickly and smoothly.The application of the two voltage equalization control strategies is compared and analyzed.The simulation results verify the effectiveness of the voltage equalization control strategy.Based on the Typhoon HIL experimental platform,the experimental verification is carried out,and the grid connection control experiment of cascade H-bridge energy storage converter,the single-pole frequency doubling CPS-PWM strategy experiment,the in-phase modular independent control experiment,the interphase traditional zero-sequence voltage injection method and the maximum zero-sequence voltage injection method experiment are completed.The correctness and effectiveness of the control strategy studied in this thesis are verified by experimental.There are 65 figures,17 tables and 85 references in this thesis.