Research On The Simplified Electromagnetic Transient Equivalent Modeling And Efficient Simulation For Energy-Storage Based Electric Energy Router

The intermittent and random characteristics of distributed renewable energy bring challenges to the security and stability of the power system.Energy storage can be an effective solution to address the challenges such as voltage stability and harmonics of distributed renewable grid-connected system.Energy-storage based electric energy router(ES-EER)is widely used because it can transmit power in multiple directions and smooth power fluctuations quickly.The electromagnetic transient(EMT)works as an important tool for parameter design and system characteristic analysis of ES-EER.However,the simulation accuracy and efficiency are contradictory due to the complex topologies and various cascading modes of ES-EER.Therefore,the research on high precision and efficiency simulation technology of EER has important theoretical and engineering significance.Regarding the issue above,the main works of this paper are as follows:Firstly,a simplified EMT equivalent modeling method for multiple active bridge(MAB)type EER is proposed.The cascaded H-bridge(CHB)and dual active bridge(DAB)are equivalent by the switching function method and the generalized state average method respectively.And a four-port controlled voltage source equivalent circuit is constructed which can directly connect with the external topology.Then the simplified EMT equivalent modeling method is extended to MAB type EER to construct the dual-port equivalent circuit.The detailed model and simplified equivalent model of MAB type EER are established in the PSCAD/EMTDC,and the proposed model can achieve a speed increase of 2～3 orders of magnitude over the detailed model,with the maximum relative error less than 5%.Secondly,a simplified equivalent modeling method for ES-EER is proposed.The energy storage sub-module(ESS)discrete circuit model is added to the MAB model to construct the ES-EER simplified equivalent model with lithium battery as energy storage units.Then reserve the energy storage unit interfaces and analyze different pooling ports to construct the simplified equivalent model of hybrid energy storage type EER,whose ESS are compatible with lithium battery and supercapacitor(SC).Through the simulation in PSCAD/EMTDC,the simplified equivalent models of the ES-EER and hybrid energy storage type EER are verified to have good accuracy and acceleration effect.Finally,the efficient simulation of the simplified equivalent model is realized from two perspectives of parallel solution and stepwise expansion simulation.The submodules are used as the basic solving unit to divide the computing load,and multi-module parallel solving logic is combined with OpenMP technology to realize parallel simulation speed up of the model.Based on the interpolation prediction method,the average signals are generated by the zero-crossing prediction of the carrier and modulated wave.The simulation step size of is expanded while ensure the accuracy.The simulation result in PSCAD/EMTDC shows that the acceleration ratio of the test model is 2.7 times compared with the simplified equivalent model when PM number is 42,and the acceleration ratio continues to increase as the number of PMs changes.