| With the development of new energy technology,photovoltaic power generation has become one of the main energy consumption forces in the new power system.Energy storage,as a key technology to improve energy utilization and power quality,has received widespread attention in recent years,and the bidirectional DC converter and related control technologies in energy storage systems are currently a hot topic of research.Bidirectional DC/DC converter is the core equipment to realize the energy exchange between the energy storage equipment and the DC bus,and can adjust the operation mode according to the voltage value of the DC bus to achieve voltage stabilization.In order to improve the power level of the system,interleaved parallel technology is introduced into the bidirectional DC/DC converter.However,at the same time,the number and volume of magnetic components required by the system will increase.Therefore,in order to improve the power density of the system and improve the performance of the converter,magnetic integration and reverse coupling technologies are applied to the interleaved bidirectional DC/DC converter.However,due to the increase of phase number,the difference of component parameters of each phase branch and the difference of equivalent resistance,inductance value and other parameters of the coupling inductance lead to power imbalance between phases,which increases the current stress of the heavy-load phase switch,thus affecting the performance of the converter and the stability of the system.Therefore,higher requirements are put forward for the control of DC converter of energy storage system based on coupling inductor.First of all,the topology of the coupled inductor flying capacitor bi-directional DC/DC converter(CIFCBDC)was studied.When CIFCBDC operates in Buck-Boost mode,there are14 different operating modes in the whole range of duty cycle.There are different mode combinations in different duty cycle regions.After the equivalent inductance of each mode in different regions is derived,the steady-state and transient performance of CIFCBDC and the flying capacitor bi-directional DC/DC converter(FCBDC)based on independent inductor are compared,verifying the performance advantages of CIFCBDC.Secondly,based on the working principle of CIFCBDC,the expressions of parameters such as inductor current ripple and flying capacitor voltage ripple are derived,and the current and voltage stresses of the switches are analyzed.In this way,devices such as inductors and capacitors are designed and power MOS tubes are selected,providing a reference for actual hardware design.At the same time,the coupled inductor is designed,and the magnetic circuit model of the inductor is analyzed after selecting the appropriate magnetic core.The parameters such as the coil turns,coil diameter,and air gap of the two-phase winding of the inductor are studied and designed.Thirdly,aiming at the problem of phase to phase power imbalance caused by differences in parameters such as the equivalent resistance and inductance value of the coupling inductor in CIFCBDC,based on the analysis of the converter’s operating principle,the mathematical model of the decoupled inductor current in CIFCBDC is derived,and a decoupled power balancing control strategy based on model predictive control(MPC)is proposed.The proposed strategy not only eliminates the design process of weight coefficients,but also achieves independent dynamic optimization of each control variable,reducing the computational load of the controller during multi-objective optimization,simplifying controller design while maintaining good control performance,and is suitable for energy storage system applications.Finally,a small experimental platform is built to carry out relevant experiments on the MPC-based decoupled power balancing control strategy proposed in this paper when CIFCBDC works in Buck-Boost mode.The experimental waveforms show the advantages of CIFCBDC performance and the effectiveness of the proposed control strategy. |
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