Study On A High Gain Bidirectional Dc-DC Cuk Converter And Its Nonlinear Control Strategy

In recent years,due to the shortage of fossil energy,distributed power generation systems based on renewable energy such as photovoltaic power generation system and fuel cell system have been developed rapidly.Bidirectional DC-DC converter is essential for distributed power generation systems,which connects a variety of renewable energy sources with energy storage cells such as batteries or supercapacitors.What’s more,it is widely used in uninterruptible power supply,electric vehicles,power supplies for aeronautics and astronautics or other new applications.The high efficiency,low ripple,high voltage gain topology and its control robustness and stability of the converters will be the development trend.Due to the strong nonlinearity of power electronic circuits,the traditional feedback control uses linearization processing,which is difficult to achieve global stability.It is difficult to obtain the accurate model for some high dimensional and complex power electronic systems,so satisfactory control effect can’t be achieved.It has important theoretical value and practical significance to carry out the study on the high efficiency and low ripple topologies,excellent nonlinear control strategies of the high gain bidirectional DC-DC converters.(1)A high gain bidirectional Cuk circuit with zero ripple is proposed,which is characterized with simple structure,zero ripple,low voltage stress of semiconductor power devices,high voltage gain.The operating principles and operating process of the proposed circuit are respectively analyzed.Then the characteristics of the proposed circuit were analyzed in detail,including voltage gain characteristics,main parameters and the voltage or current stress characteristics of semiconductor devices.Then the circuit’s key parameters are designed.On the base of these,the influence of scalable cell on the gain and stress characteristics of circuit is analyzed further,where the parametric relationship between them was deduced.All above are verfied by simulation and experimental results.And then,the dynamics modeling based on energy balance is adopted for the proposed circuit.The EL models of the high gain bidirectional Cuk with zero ripple are constructed in ideal condition.In this modeling method,the circuit system is regarded as a whole,and the kinetic energy,potential energy and other energy functions are used to describe the system,so that the dynamics problems of non free particle system with ideal constraints can be solved,and the solving process is greatly simplified.It overcomes the limitations of traditional modeling,such as only for some specific circuits or states,or medium and low frequency circuits,or small signal circuit analysis.It can be reserved the nonlinear information of the proposed high gain bidirectional converter with the characteristics of universal and systematic.(2)The passivity-based controller of the proposed high gain bidirectional Cuk with scalable switched-capacitor gain cell is designed based on ideal El models,in order to adapt to the occasions that often encounter large signal disturbances such as starting process,sudden load change,power fluctuation.However,the typical passive based control will cause large steady-state error because of the model error and disturbance of the system.A passivity-based control based on linear active disturbance rejection is proposed.The inductance current reference is generated by linear active disturbance rejection control to compensate the steady-state error caused by internal circuit loss and disturbance.The simulation and prototype experimental results have been obtained to show that the improved passivity-based control strategy solves the contradiction between rapidity and overshoot,reduces the steady state error,and has strong robustness and wide range stability.(3)In order to simplify the high gain circuit structure for high power applications,a tapped inductor using reverse coupling high gain bidirectional Cuk is proposed for high power applications in this paper,where the voltage gain of the converter is broadened effectively by introducing reverse coupling tapped inductor.The operating process of the proposed circuit,voltage gain characteristics and the voltage or current stress characteristics of semiconductor devices were analyzed in detail.The relationship between voltage gain and duty cycle and turn ratio of tap inductor is derived,and the optimal turn ratio of tapped inductor based on the optimum efficiency is given,when the converter operates in step-up or step-down.Computer simulation and prototypes were designed to verify the validity of the theoretical analysis of the proposed circuit.(4)A active soft-switching of the high gain bidirectional DC-DC converter is proposed.When it operates in step-up or step down,the resonant network realizes zero voltage switching of the main switch and the soft switching of the auxiliary switch,which consists of two auxiliary switches,two capacitors and one inductor.The objective is to improve the overall efficiency of the converter and enhance reliability.Taking the tapped inductor high gain bidirectional Cuk as an example,the operating principle and operating process,voltage gain characteristics and voltage or current stress characteristics of the proposed soft-switching circuit are analyzed in detail based on the circuit operate in step-up and step-down mode.The key parameters of soft switching network are designed and the corresponding soft-switching conditions is derived.A comparison between soft and hard switching bidirectional converter is deployed in simulation and experimental results.(5)In order to achieve excellent control of the high dimension and uncertainty of some high gain bidirectional DC-DC circuit,a TSK fuzzy control strategy with voltage feedforward was proposed,which is applied to the tapped inductor high gain bidirectional Cuk circuit with reverse coupling tap inductor.The proposed TSK fuzzy control strategy simplifies the fuzzy reasoning process,which uses 0-order TSK fuzzy controller,and reduces the number of rules required further.And then,In order to improve the steady-state accuracy of the converter,the membership function with nonlinear funtion in the universe is selected to achieve robust control.In addition,when the input voltage and output load change,the dynamic performance of the converter is improved by introducing voltage feedforward control and changing output scale factor dynamically.Computer simulation and experimental results were obtained to verify the validity of the proposed strategy.