| With semiconductor switching devices developed rapidly,various novel power generation methods and power loads are gradually entering people’s lives.Bidirectional DC-DC converters have the advantages of high power density per unit volume,small space occupation and good power quality,and are widely used in high-power applications.Taking isolated bidirectional DC-DC converter as the research object,this thesis proposes a combined modulation strategy and a new control strategy,aiming at improving the voltage and current dynamic characteristics of boost mode and buck mode,and improving the system stability.In order to realize the bidirectional flow of energy on both sides of the converter,a Bipolar&Phase-shifted modulation mode is proposed.Bipolar modulation is used in boost mode,phase-shifted modulation is used in Buck mode,and modulation mode is switched with different system modes.In the actual working environment,capacitance and inductance are fractional order,which has been supported and confirmed by a large number of scholars in recent years.In order to improve the control performance of DC-DC converter,a control strategy combining fractional order PIλDμ with fuzzy control is proposed in this thesis.In the non-linear system,fractional order PIλDμ is better than integer order PID control,and the fuzzy control can adjust the control parameters.Finally,a 5 kW converter hardware experimental platform is established for experimental verification.The main research work in this thesis is as follows:(1)Based on Bipolar&Phase-shifted modulation.In this thesis,the working principle of isolated bidirectional DC-DC converter under combined modulation mode is studied.Bipolar modulation is used to execute the boost mode of the converter,and phase shift modulation is used to execute the boost mode of the converter.The system states and theoretical waveforms of the converters under various modes are analyzed in detail.Then,a simulation model is constructed in Simulink to verify it.(2)Research and design of fractional-order modeling and fuzzy fractional-order PIλDμcontrol system.In order to improve the accuracy and authenticity of the system model,this thesis presents fractional order modeling of equivalent circuit in two operating modes of isolated bidirectional DC-DC converter.The equivalent inductance and capacitance in the circuit are constructed according to fractional order model,and the state average model of the converter system is established.Then,by combining fuzzy control with fractional order PIλDμ control,a fast response and good robustness fuzzy fractional order PIλDμ control strategy is proposed.It is applied to the voltage loop control of isolated bidirectional DC-DC converter,and a simulation model is built in Simulink to verify it.(3)Development of high-power experimental platform and analysis of experimental results.In this thesis,a 5 kW power experimental platform is developed,and the corresponding hardware circuit and software program are designed.Hardware circuits include:converter circuit,double closed-loop single-ended flyback power circuit,MC9S12XF128 control system circuit,driving circuit and sampling circuit.Software programs include:main program,ADC sampling program,fuzzy fractional PIλDμ algorithm,communication program,etc.Based on the experimental platform,experimental verification and analysis of experimental results are carried out.Experiments show that the designed fuzzy fractional order PIλDμ control system has better robustness and stability. |
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