Research On Dc Injection Mechanism And Suppression Strategy Of MMC-BESS

Direct grid-connected MMC-BESS converter will introduce dc component into grid current due to the influences of inconsistency of battery voltage,mismatched driving signal,inconsistency of switching characteristics and current detection error.IEEE std1547-2003 requires that the dc component injected into the power grid by power electronic devices shall not exceed 0.5% of the rated current.Based on the analysis of the battery MMC-BESS topological structure and power control of the system,the influences of battery voltage inconsistency,drive signal mismatch,switching characteristics inconsistency and SOC balance strategy selection on the dc component of MMC-BESS network side current are derived in detail from the perspective of open loop.At the same time,based on the power closed-loop control,through the analysis of the control structure of the closed-loop,the influence of introducing dc interference into the forward channel and feedback channel of the current control loop on the output current is deduced.Then,two of the most commonly used suppression strategies for dc component of network current--feedback control suppression strategies based on current detection and voltage detection are introduced.The two strategies are improved,analyzed and compared based on this design,and the feasibility of the suppression strategies is verified in the simulation system.After that,this paper designs the structure of the laboratory prototype system based on the comprehensive control strategy and system topology.The power submodule control board are also designed and introduced,and relevant performance tests on its main functional modules are performed to verify the rationality of the submodule power control board design.Finally,the communication mode used in this design is introduced,and relevant tests are conducted to verify the feasibility of the communication mode.