Study On High Step-Up DC-DC Converter Topology Based On Coupled Inductor And Switched Capacitors

With the aggravation of the global energy crisis and environmental pollution,green and clean renewable energy such as solar energy and wind energy have been widely concerned by academia and industry.In the photovoltaic power generation system,how to efficiently convert the low-voltage DC power output from photovoltaic panels into high-voltage DC power,so that to invert the grid becomes the key technology of photovoltaic power generation.Therefore,in recent years,efficient and high voltage gain DC-DC converter has become one of the important research directions in academia.Based on the traditional coupled inductor converter,this paper proposes several integrated switched capacitor circuits and constructs a series of high step-up DC-DC converter topologies suitable for different scenarios.Firstly,three different methods of constructing voltage doubling circuits are proposed for double-winding coupled inductor converters,and a series of high step-up DC-DC converters are constructed respectively.The switched capacitor unit is extended to n,so that it can flexibly change the circuit structure to adapt to different application scenarios through voltage gain and voltage stress requirements.It can be known from the comparative analysis of similar converters proposed in recent years at home and abroad that under the premise of the same or even fewer number of components,the proposed converters can achieve higher voltage gain and lower voltage stress.So a low voltage level,low on resistance of power devices can be used to reduce the conduction loss and improve the operating efficiency of the converter.Secondly,on the basis of double-winding coupled inductor converter,the third winding is added to constitute a three winding coupled inductor converter.A series of high step-up DC-DC converters based on three-winding coupled inductor and switched capacitor are constructed by the same method as integrated switched capacitor circuits of the double-winding coupled inductor converter.A high power density and high step-up DC-DC converter based on the three-winding coupled inductor is proposed by remouldming the circuit topology based on the structure characteristics of the three-winding coupled inductor.And the pump generation capacitor unit is introduced into the converter to further improve the voltage gain.The comparative analysis shows that the proposed three-winding coupled inductor converters have higher voltage gain and lower voltage stress under the condition of fewer components.Thirdly,for the isolated high step-up application scenarios,based on the basic flyback converter,a variety of voltage multiplier circuit units are proposed,and a variety of active-clamp isolated high step-up DC-DC converters are constructed.The converters use the active clamp circuit to recycle the leakage energy,so that the main switch and the clamp switch can achieve zero voltage switching.Increasing the voltage doubling capacitors can not only increase the voltage gain and reduce the voltage stress of the power device,but also solve the problem of resonant voltage peak of the output diode and leakage inductor of the active-clamp flyback converter.When switch S is closed,the secondary side winding of the transformer transfers energy to the voltage doubling capacitor.Compared with the flyback converter,the utilization ratio of the transformer winding is improved and the power density of the converter is increased.Finally,for the application of low input current ripple,the coupled inductor converters based on Sepic that is cuttent input converter and symmetric/asymmetric interleaving coupled inductor converters are proposed.For the Sepic coupled inductor DC-DC converter applied in small and medium power scenarios,its input current continues the Sepic converter current continuity,with the characteristics of low input current ripple.With the introduction of the filter inductor,the magnetizing current of the coupled inductor is greatly reduced,and even the average magnetizing current of some circuit topologies is reduced to zero,so as to achieve the effect of bilateral excitation and improve the utilization rate of the magnetic core.Therefore,the volume of the coupled inductor can be reduced,and the power density and efficiency of the converter can be improved.As for the interleaving coupled inductor used in high-power and super-large voltage gain scenarios,it adopts the form of two-phase interleaved,and the rate of change of the leakage current of the two coupled inductors is effectively weakened at the input end,thus reducing the input current ripple.Combined with the structural characteristics of interleaving connection,the added switched capacitor circuits can increase the voltage gain,reduce the voltage stress of the power device to a greater extent.Meanwhile,the interleaving circuit can share the power,making it easily capable of high-power situations.A series of new topologies proposed above in this paper effectively solve the shortcomings of traditional DC-DC converter in high voltage gain conversion,and can be basically applied to various scenarios with different requirements.On the one hand,the voltage gain is improved to avoid the converter operating under the limit duty cycle;on the other hand,the voltage stress of the power devices are reduced,so the low voltage level and high performance devices can be used to improve the efficiency and reliability of the converters.A passive or active clamp circuit is used to recycle the leakage energy of the coupled inductor,which makes the switch realize zero current or zero voltage switching,and further reduce the converter loss.Compared with similar high step-up DC-DC converters proposed at home and abroad in recent years,the proposed converters can achieve higher voltage gain and lower voltage stress with relatively few components.