| DC distribution network does not have problems such as reactive power fluctuation,harmonic degradation,frequency fluctuation and synchronous oscillation.Compared with AC distribution network,DC distribution network has many advantages and is an effective way to absorb distributed power supply.As the core equipment of DC distribution network,the efficient and reliable operation of DC transformer is of great significance to DC distribution network.Existing DC transformers mostly adopt two-port topological structure,so it is necessary to equip several two-port DC transformers when carrying out multi-voltage grade energy conversion in DC distribution network.The joint operation of multiple DC transformers not only increases the frequency of energy conversion and construction cost,but also generates circulation between ports,which leads to the difficulty of coordinated control and the decrease of system stability.Using one multi-port DC transformer instead of several two-port DC transformers can effectively solve the above problems.In the topology of multi-port DC transformer,the Three Active Bridge(TAB)converter has high research value and application potential because of its advantages of electrical isolation,wide voltage range and flexible and controllable power flow direction.However,under the traditional Single Phase Shift(SPS)control,TAB converter has some problems,such as port power coupling,insufficient soft switching range and large current effective value,which affect the efficiency of the converter.This paper aims to improve the operation efficiency of TAB converter,and carries out the following research:(1)A power decoupling phase shift control strategy for TAB converter is proposed.When the TAB converter works under the control of SPS,there is power coupling between the same input or output ports,which increases the interaction between ports and reduces the response characteristics of the converter.Therefore,TAB internal power interaction mechanism of the converter are analyzed in detail,this paper proposes a power decoupling based on voltage square wave line overlap phase shifting control strategy,without reducing converter power range at the same time eliminates as input or output port of power coupling,eliminate the mutual influence between the ports,and is verified by simulation and experiment.(2)An optimal control strategy of Zero Voltage Switch(ZVS)for TAB converter based on power decoupling and phase shifting is proposed.The TAB converter has many freedom of control,so it is difficult to calculate the inductive current expression of each port.In this paper,the inductance current coefficient of the voltage square wave at each port is calculated.Combined with the superposition theorem,a simplified calculation model of the inductance current of the TAB converter under the control of Multi Phase Shift(MPS)is established,which reduces the difficulty of derivation of the inductance current expression.This paper describes the ZVS range of TAB converter under the control of SPS and power decoupling phase shift,and proposes a hybrid ZVS optimal control strategy within the full power range of TAB converter,which can effectively reduce the switching loss of the converter.It is verified by simulation and experiment.(3)A current RMS optimization strategy for TAB converter based on power decoupling phase shift control is proposed.In order to reduce the difficulty of deducing the current RMS expression of the TAB converter under MPS control,a high-frequency model of the TAB converter based on Fourier series is established in this paper,and the current RMS expression of the TAB converter is deduced under the high-frequency model.All kinds of mode combinations under the power decoupling phase shift control strategy are compared and analyzed,and the mode combination with the best effective current value is selected,and the optimal effective current value control strategy based on the mode selection is proposed.On this basis,a multi-objective optimization strategy is proposed,which can optimize the effective value of current while ensuring ZVS,and it is verified by simulation and experiment.(4)A laboratory prototype of 5k W TAB converter is developed.The design scheme of hardware power circuit and drive circuit is given,and the software implementation method of power decoupling phase shift control is proposed.The power decoupling,ZVS optimization and current RMS optimization strategies proposed above are verified by laboratory prototype. |
