| Environmental pollution and energy shortage are two major issues in our human society,and it is imminent to develop of clean and pollution-free energy.Fuel cell is one of the promising energy sources due to its high efficiency and non-pollution,and it has a very high value of applied research in the field of DC microgrid and electric vehicles.Due to the soft output characteristic and poor dynamic response of fuel cell,it usually needs to be assisted by energy storage equipment with better dynamic response.Supercapacitor has the characteristics of high power density and good dynamic response,which is suitable as the auxiliary energy storage equipment for fuel cell.In this paper,the fuel cell electric vehicle is used as the application background.Around the hybrid energy source system which is composed of fuel cell and supercapacitor,the research focuses on the wide voltage gain DC-DC converter for fuel cell power interface,bidirectional DC-DC converter with good dynamic response for supercapacitor power interface and power distribution control strategy for hybrid energy source system.Firstly,according to the boosting principle of traditional Boost DC-DC converter,combined with existing converters,four essential methods of improving the voltage gain of non-isolated DC-DC converter are summarized.According to three types of essential methods,three types of wide voltage gain range DC-DC converters that meet the requirements of fuel cell power interface converters are proposed.1.In order to solve the problem that the converter in the essential method of increasing the inductor charging time within one switching period has the narrow pulse PWM voltage of power semiconductor,a capacitor-clamped H-type DC-DC converter is constructed.The proposed converter has a wider voltage gain and a lower power switches conduction loss while solving the above problem.2.In order to solve the problems that the converter in the essential method of increasing the inductive charging voltage has the high inductor current and high voltage stress of power semiconductor,a DC-DC converter with input current divided by inductors and output voltage divided by capacitors is constructed.The proposed converter has higher voltage gain and conversion efficiency while solving the above problems.3.In order to solve the problem that the converter in the essential method of parallel input and series output has high voltage stress of power semiconductor or the input and output ports are not common grounds,a DC-DC converter with the common ground and the output capacitors in series is constructed to solve the above problem.In addition,the proposed converter has the advantages of high efficiency and reliability.The experimental prototypes of the DC-DC converters are made to verify the relevant characteristics.Secondly,according to the characteristics of low energy density and high power density of supercapacitors,a wide voltage gain bidirectional DC-DC converter with good dynamic response performance is proposed.The proposed converter can have a wider control bandwidth,thereby improving its dynamic response performance.In addition,the converter also has a wide voltage gain range.In order to interface a higher voltage DC bus,a bidirectional DC-DC converter with higher voltage gain is obtained by improving the output voltage side of the above converter.This converter retains the advantages of the above converter,while the power semiconductors and capacitors have lower voltage stress.Experimental prototypes of the above two converters were established for verification.Finally,in order to solve the problem that the real-time adjustment of the state of charge of the super capacitor and the steady-state voltage deviation of the DC bus can not be well considered in the droop-frequency power distribution control of the hybrid energy source system composed of the fuel cell and the super capacitor,and that the frequency division controller is not easy to design,a power distribution control strategy of the hybrid energy source system which is easy to implement is proposed.This control strategy can achieve power frequency division control between different energy sources without designing a frequency division controller.At the same time,the control method can also solve the problem of real-time adjustment of the state of charge of the supercapacitor and the deviation of the DC bus steady-state voltage.A simulation and experimental platform for a hybrid energy source system was established to verify the above characteristics. |
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