Research On Control Strategies For Inverter In Three-phase Power Conditioning System Of Battery Energy Storage System

With the rapid development of energy storage technology, energy storage system withpower conditioning system as the interface device, can accept rational management fromthe power sector and play the role of load shifting in the power system; when the grid isout of electric power, the energy storage system can provide stable and reliable powersupply for local loads. Inverters are the most critical power electronic conversion devicesin power conditioning system. In this paper, research on control strategies for invertersoperating in various modes is clearly performed.While power conditioning system is working in grid mode, in order to reduce systemsize and improve high frequency harmonics suppression ability, LCL filter is often used toachieve these goals. In this paper, comparative study of the passive damping and activedamping of the resonant peak suppression strategies is presented; as for the LCL energystorage system single-loop control, operating characteristics analysis of grid-side inductorcurrent control and inverter-side inductor current control is presented; in order to solve thelower bandwidth and poor current waveform quality of single-loop control, this paperemployees filter capacitor current inner loop and grid current outer loop control scheme,in fact analyzed the inner filter capacitor equivalent parallel to the damping effect of thefilter capacitor is preferably suppressed third-order resonance peak LCL type system andin the frequency domain, the detailed design of the controller parameters is presented.When the grid breaks down, power conditioning systems need to work in an islandedoperation mode. In this paper, a capacitor voltage and inductor current double loop controlmethod for islanded operation is employed, the equivalent damping analysis uses theprinciple of double-loop control of damping a detailed derivation and analysis; Whendesigning the controller parameters, energy storage power conditioning system fordetailed mathematical modeling is firstly established, loop control parameter designmethod is given: through control block transformation, the inner loop is equivalent to adamping part of the system under no-load and load conditions, better steady statecharacteristics and dynamic response speed are guaranteed, simulation and experimentalresults verify the stability of the three-phase energy storage systems, dynamic characteristics and better output waveform quality.In large-scale battery energy storage system, to facilitate the expansion of thecapacity of the energy storage system, battery energy storage power conditioning systemsoften need to run in parallel operation. When the inverters operate in standalone mode, theparallelled system will allocate power reference to each PCS module. When using separateAC,DC bus of the parallel program bus, the state of charge of the battery side there aredifferences, the traditional common UPS modules in parallel control scheme is no longerapplicable, an power allocation scheme based on storage capacity and state of charge(SOC) is designed, allocating different power different commands based on the SOC ofthe storage modules in parallel, in order to take full advantage of the total capacity of theparallel system.