Modular Multi-Port Converter Voltage Balancing Topology and Voltage Matching Control for Battery-Swapping Stations
Battery-swapping stations offer an alternative charging service,significantly reducing charging duration.As the number and charging power of electric vehicles continue to rise,these stations require connection to a medium-voltage grid to expand capacity.However,the traditional solution entails numerous converters and two power conversion stages,resulting in significant device costs and power loss.This paper proposes a single-stage modular multi-port converter with voltage balancing for Battery-Swapping Stations.By integrating just one power converter stage,this approach effectively lowers equipment costs and minimizes power losses.Additionally,a voltage balancing circuit and a voltage matching(VM)control strategy are proposed to address power mismatch issues arising from state-of-charge differences.The sub-module utilizes a phase-shifted full-bridge(PSFB)configuration to regulate charging power by adjusting the phase-shift angle of the drive signals between the two main bridge arms.The input side of the PSFB is linked in series to the MVDC bus,while the output side serves as a distinct charging port for connecting to the power battery.This configuration ensures only one power conversion stage from the MVDC bus to the charging port.This paper introduces LC balance branches at the input side of adjacent modules to solve series voltage mismatch,thereby conserving active devices.Mismatched power transfers between two sub-modules while the PSFB ensures continuous battery charging.The two switches of the leading leg of each submodule are multiplexed and continue to operate in the zero-voltage switching(ZVS)state.Furthermore,this paper proposes a voltage matching(VM)control strategy.Based on the battery voltage,the corresponding input voltage of each module is adjusted proportionally,aligning more closely with the battery voltage.Compared to traditional voltage equalization control methods,this approach broadens the charging voltage range of the converter and reduces battery charging current ripples.Simulation results demonstrate that the converter output current consistently aligns with the reference value,even when the reference value changes.When the port voltages of batteries 1 to 5 are 650,700,800,850,and 900 V,respectively,the submodule effectively maintains input voltages at 833,897,1 026,1 090,and 1 154 V through the VM control.Notably,the VM control successfully charges the 970 V battery,a task unachievable with traditional voltage equalization control due to insufficient power output.When concurrently charging a 600 V battery,the current ripple reduces from 5.5 A with the conventional control to 3.3 A with the VM control.The experimental results demonstrate that the switches can still operate in the ZVS state.The following conclusions can be drawn.The proposed LC voltage balance structure eliminates the need for additional switches,thereby reducing hardware costs.With only one stage of power conversion and switches capable of ZVS,the converter enhances efficiency.By controlling both the intra-module and inter-module phase-shift angles of the converter,battery charging control and submodule VM control can be realized simultaneously.The proposed VM control strategy makes the input voltage match the battery voltage,thereby broadening the charging voltage range of the converter and reducing battery charging current ripples.With the VM control,each module's input voltage reference value is proportionally distributed based on the battery voltage,which has a rather simplistic selection process.Future research will focus on the flexible voltage reference selection for each port.
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