| With the development of power electronic technology,the development direction of modern power electronic converter has become high-frequency,modular and intelligent.At the same time,under the background of carbon neutralization,high efficiency has also become an important development goal of modern power electronics technology.As a typical power electronic converter,LCC resonant converter is widely used in the fields of industry,medical treatment,military and scientific research because of its soft switching,primary and secondary side isolation and the ability to take advantage of the parasitic parameters of the transformer.However,LCC resonant converter is still within the technical scope of traditional power electronic converter now,which is difficult to meet the technical requirements of high-performance high-voltage LCC converter in practical applications.The traditional control method is limited by the closed-loop control bandwidth,which is difficult to achieve a fast and smooth dynamic response.The LCC converters have the characteristics of low light load efficiency,it limits the realization of high efficiency of converters.The high-voltage application of LCC converters brings great challenges.High voltage increases the difficulty and cost of high-voltage circuits significantly.High-voltage output overshoot will have a significant negative impact on the insulation of power supplies.Therefore,this paper studies dynamic performance optimization,high efficiency and high-voltage application technologies of high-performance high-voltage LCC resonant converter.Firstly,the optimal dynamic performance is an important research content of LCC resonant converter.Although a lot of research and innovation in closed-loop control has been carried out on LCC converters,it is still difficult to break through the limitation of closed-loop bandwidth.If the converter can predict the target steady-state according to external changes,the dynamic performance of LCC converters can be significantly improved.However,the LCC converter is a third-order model,and its calculation complexity is high.It is difficult to solve it quickly because of the limited calculation ability of the controller.Based on the simplified state trajectory,this paper obtains the coordinates of each point on the steady-state trajectory completely through the circuit relationship,to obtain a simpler steady-state equation.To solve the equation,a two-point method based on piecewise approximate linearization is proposed.When a change of load occurs,this method can quickly and accurately calculate the target steady-state on the general controller according to the sampling and instructions.The time of the two-point method calculated by the controller is within 2.3 μs,and the fast steady-state prediction is realized,which can meet the control requirements of the converter.Under the condition that the target steady-state and the current steady-state are known,the optimal trajectory switching between different steady-states is established based on the simplified state trajectory.The calculation time of the optimal trajectory switching controller is within 2.0 μs.Finally,the experimental results show that this method realizes the optimal dynamic response under load change.Compared with the traditional method,the voltage fluctuation is reduced by more than 80% and the response time is reduced by more than 90%.Secondly,high efficiency is particularly important for high-power and long-time LCC converters,which can effectively reduce the power cost and carbon emission.However,due to the high working frequency under light load and the existence of a reactive power circuit by the parallel resonant capacitor,the light-load efficiency of the LCC converter is low.In this paper,the variable structure control method of the LCC converter is proposed.The working mode of LCC converter is divided into full-bridge working mode and half-bridge working mode through the inverter bridge.LCC converter can change the working mode according to the characteristics of different modes to ensure the efficiency of the full load range.To ensure the smooth switching of different modes,the state trajectory sub-modes of half-bridge LCC converter are established.On this basis,the coordinates of steady-state points are established completely from the perspective of electrical characteristics,and its steady-state prediction equation is established.The solution ability of the two-point method on a half-bridge LCC converter is verified.Under the condition that the current mode steady-state and the target mode steady-state are known,the optimal topology switching based on the two-point method is established.Finally,the experimental results show that the switching process is smooth and fast,and efficiency within the full load range of the converter is significantly improved.Thirdly,the light load optimization control method has the characteristics of low ripple and high efficiency.However,with the lightest load decreasing,the LCC converter’s efficiency with variable structure control is much better than the traditional one.However,it still is limited by the high switching frequency and reactive current loop under LCC gain characteristics.Therefore,in applications with high ripple requirements,burst mode is more popular because of its simple control and the advantages of being not limited by gain characteristics.However,as the load decreases,the working frequency of the traditional burst mode decreases continuously,and finally enters the audible frequency range to produce noise.The noise problem seriously limits the application of burst mode.At the same time,due to the energy storage effect of the resonant circuit,the switching logic of burst mode needs to be optimized to avoid the oscillation of the resonant circuit during burst off time.To solve the above problems,an adaptive multi-modal burst mode control method is established in this paper.Based on the simplified state trajectory,four burst modes are established to avoid the oscillation of the resonant circuit.According to the characteristics of different modes,an adaptive burst mode control method is established.In different load ranges,different burst modes can be used according to their characteristics to avoid the working frequency of burst mode entering the audible frequency range.Finally,experiments verify the effectiveness of the above algorithm and avoid the generation of audible noise.Finally,the modular LCC resonant converter can reduce the output voltage range of a single module,which is convenient for the selection of high-voltage devices and circuit design.At the same time,it has the advantage of modularization and is the preferred topology of the high-voltage DC converter.However,because the parameters between modules are inconsistent,it will lead to the difficult problem of voltage-sharing,which significantly reduces the reliability of the converter and limits the high-voltage application of modular LCC resonant converter.To solve this problem,a modular LCC parameter design method with the given parameters’ deviation is proposed in this paper.The device deviation of the main parameters of the circuit between modules is considered so that the gain gap between different modules is controllable.Further,at the control level,the voltage-sharing control method of the asymmetric duty cycle is proposed.The voltage sharing is realized by controlling the asymmetric duty cycle of each module and changing the gain of each module.The small-signal model of modular high voltage LCC converter with voltage doubling rectifier under asymmetric duty cycle control is established and its stability is analyzed.Compared with the existing methods,this method does not need to add additional hardware,and will not lose the soft-switching characteristics under heavy load conditions.Aiming at the requirements of a fast start without overshoot for the high-voltage application of LCC converter,this paper analyzes the requirements for control parameters in the start-up process and the nonlinear gain of LCC.Based on this,a piecewise control parameter look-up table is established through the fuzzy algorithm to control the start-up of the converter,which realizes the fast start without overshoot.Compared with the traditional method,the speed of start-up without overshoot of high-voltage power supply has been significantly improved.In addition,the traditional high voltage LCC converter is limited by traditional power devices,so it is difficult to realize a high switching frequency.The use of Si C MOSFETs can improve its switching frequency and ensure better dynamic and steady-state characteristics.In this paper,the application technology of Si C MOSFET for LCC converter is studied.Aiming at the crosstalk problem,a comprehensive modeling analysis is carried out,and two paths and three interference sources are summarized.On this basis,combined with the characteristics of LCC converter,a simple and effective crosstalk suppression method with gate parallel diodes is established.Finally,the effectiveness of the above crosstalk analysis and suppression methods is verified by experiments.To sum up,aiming at the high-performance dynamic response requirements of LCC resonant converter,this paper establishes the prediction model of LCC converter and gives a fast solution algorithm.Through the optimal state trajectory switching,the dynamic response performance of resonant converter is significantly improved.According to the demand for high performance and high efficiency of LCC converter,a variable structure control method is proposed in this paper,which significantly improves the light load efficiency of the converter and realizes the optimal dynamic response of topology switching;An adaptive multimodal burst mode based on simplified state trajectory is established,which effectively solves the noise pollution problem of burst mode.Aiming at the challenges brought by high-voltage application,this paper puts forward the asymmetric duty cycle voltage sharing control method and the LCC parameter design method considering parameter deviation,which solves the problems of voltage sharing and parameter design of modular high-voltage LCC converter;a start-up control method based on the fuzzy algorithm is proposed to solve the problem of the fast start-up without overshoot of high-voltage LCC converter;the crosstalk problem affecting the reliability of Si C MOSFET inverter module of high-voltage LCC converter is comprehensively analyzed,and the suppression method is proposed to improve the reliability of high-frequency high-voltage LCC converter. |
