| As an important means,energy storage can achieve high proportion of renewable energy in the power grid.It can smoothen the output power of renewable energy generation and improve the schedulability of renewable energy.The predicted cumulative installed capacity of electrochemical energy storage in 2020 will increase to 2GW,is about 15 times as large as that in 2015.As the scale of enegy storage generation becomes larger and larger,hundred MW-level electrochemical energy storage generation is an important development tendency in the future.In order to improve the operation performance of electrochemical energy storage generation,both the performance of energy storage elements and the performance of grid interface converter are supposed to be improved.For the purposes of improving the operation performance of large-scale battery energy storage system,this dissertation contributes to the optimized control strategies for hybrid cascaded battery energy storage converter.This dissertation compares common topologies of grid interface converter between large-scale battery energy storage and medium voltage power system.The characteristic of hybrid cascaded battery energy storage converter is also discussed.In the research of DC-DC stage in hybrid cascaded converter,the backflow power in DAB converter is studied,and three global minimum backflow power optimization methods are proposed.By comparing among these three optimized control strategies,the best control method can be determined.Then,non-active power transmission in DAB is analyzed,and the index of non-active power transmission time is proposed.Therefore,minimum non-active power transmission control can be derived.More than that,the limitation of backflow power optimization control is explained based on non-active power transmission in DAB.In the research of DC-DC+H-Bridge two-stages system,the advantages and disadvantages of traditional control methods are analyzed.Then,quantitative analysis of transient dc bias in DAB is given,and a current sensorless control strategy is proposed.By the estimation and control of output current and load current,the two-stage system can achieve excellent steady-state performance as well as excellent dynamic performance at the same time.Moreover,the dead-time effect on the proposed control strategy is analyzed,and a compensation method is also given.Several performance indexes are built to evaluate the closed-iuop performance of two-stage system with the proposed method.The parameter sensitivity analysis is also carried out.Finally,a parameter design method for designing the minimum dc-bus capacitance,which increases the practicability of proposed control strategies,is proposed.In the research of inner-phase power distribution control,flexible power distribution control strategies,which can control the transmission power of every H-Bridge independently,is proposed.Then,the output voltage of CHB under the maximum power unbalance distribution condition is derived,and the analytical calculation method is also derived for maximum power unbalance distribution.By comparing the proposed control strategy and traditional CPS-SPWM strategy,the proposed control strategy has significant advantages over power unbalance distribution ability and harmonic performance of output voltage.Finally,a SOC control method is designed based on proposed control strategy to enhance adaptive capacity of batteries.In the research of low voltage ride through under unbalanced grid voltage,the common control objectives are analyzed.Then,a flexible reference current calculation method is proposed,and the linear search path is derived.Based on the monotonic rules of common control objectives,a multi-objective coordination controller is proposed.Considering the limitation of peak current and average transmission power,a set of multi-objective coordination control strategies are given to enhance the flexibility of LVRT control.The practical engineering project which supports this research in dissertation is introduced.Series of key engineering problems in the development process of engineering equipment are summarized.Corresponding solutions to these problems are given.The feasibility of the topology,the validity and correctness of proposed control strategies are all verified by experimental results on the engineering prototype and equipment. |
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