Research On High Performance Control Strategy Of High Frequency Link-matrix Converter

With the implementation of a series of national support policies and the rapid development of new-energy technologies,the market share of electric vehicles(EVs)is steadily expanding.Compared with traditional fuel vehicles,electric vehicles have the advantages of environmental protection and high energy efficiency,but they also face the trouble of "Range anxiety".The key way to solve this problem is to adopt high-power DC charging system which can improve charging rate.In addition,the dual properties of load and energy storage of EVs provide a new way to solve the demand of "Peak load cutting and valley filling" of grid,and charging piles are the key facilities to realize the interaction between electric vehicles and grid(V2G).Therefore,the research of high-power DC charging system that can support bidirectional operation is of great significance to the development of EVs.The traditional DC charging topology adopts the two-level structure of AC/DC plus a DC/DC,which makes the system inefficient and requires a large DC bus capacitor in the middle,thus reducing the power density of the system.The AC/DC class usually uses a Vienna rectifier,which does not support bidirectional operation.High frequency chain matrix converter(HFLMC)is a single-stage power conversion topology composed of input and output filters,matrix converters,high frequency transformers and H-bridge converters.It has the advantages of high energy density,isolation between grid side and load side,and support bidirectional operation.It is suitable for the application of high power DC charging system.This paper studies the application of HFLMC in high-power DC bidirectional charging system,and the main achievements are as follows:1.The working principle of HFLMC is introduced in detail,and its basic mathematical models in abc coordinate system,αβ coordinate system and dq coordinate system are derived.In this paper,the basic principle of space vector pulse width modulation(SVPWM)strategy of matrix converter is introduced in detail,the mathematical models of vector synthesis in αβcoordinate system and dq coordinate system are derived respectively.MATLAB\Simulink’s simulation and experiment verify the effectiveness of the two modulation strategies.A comparative analysis of the two modulation strategies is given.2.Aiming at the problem that high frequency transformers are prone to magnetic bias under the traditional six-section SVPWM modulation strategy,the basic principle of magnetic bias is analyzed from the aspects of vector modulation.On this basis,a three-effective vector SVPWM modulation strategy based on switch timing design is studied,and the vector synthesis model of the proposed modulation strategy in αβ coordinate system is given.The effectiveness of the proposed strategy in transformer bias suppression is verified by simulation and experiment.3.When HFLMC is applied to DC charging system,it faces the comprehensive performance requirements of power quality on the grid side,wide output range and fast dynamic response on the battery side.In addition,it also suffers from difficulties in precise modeling and parameter setting.Therefore,a deadbeat-predictive control strategy based on direct power is studied.The prediction model of the reference current vector is established,and the corresponding control strategy is designed based on it.The proposed control strategy has the advantages of wide current range and fast response speed on the battery side,high power quality on the power grid side.In addition,it has the advantages of no PLL,no complex coordinate transformation,no inner loop parameter setting and low sensitivity to system parameter disturbance.The effectiveness of the proposed control strategy is verified by simulation and experiment.4.An HFLMC bidirectional modulation and control strategy was studied for V2G operation of charging system.The basic principle of HFLMC power bidirectional flow is analyzed,and a modulation strategy of "Three effective vector SVPWM of matrix converter+phase shift modulation of H-bridge"is proposed.The power direction control is realized by controlling the phase of the voltage on the secondary side of the transformer relative to the primary side.Based on the proposed modulation strategy and direct power-deadbeat control,a cooperative control strategy of "Predictive reference current vector+phase shift angle" was studied,so that HFLMC could meet the comprehensive performance requirements of battery side and power grid side in rectifier and inverter state.The effectiveness of the proposed modulation and control strategy is verified by simulation.