Research On Droop Control Strategy For Parallel System Of High Frequency Link Matrix Converter

The High Frequency Link Matrix Converter(HFLMC)has the advantages of compact structure,two-way energy flow and light weight.In recent years,it has been mainly used in new energy power generation,power transmission and other fields.HFLMC is composed of matrix converter and high frequency transformer.In large-capacity,high-safety occasions,multiple HFLMCs are combined into a parallel system.As a control strategy without communication,droop control has become a research hotspot of HFLMC parallel system control technology.In this thesis,HFLMC with symmetrical topology is used as the basic unit,and the droop control strategy of the parallel system is deeply studied.The modulation strategy of the converter is the basis of the system control strategy.Aiming at the problem of high output voltage and current harmonic content caused by HFLMC commutation,a de-re-coupling vector modulation strategy is proposed.Using the 12-sector division method to obtain the space vector modulation signal from the αβ coordinate plane.Using the polarity selection signal,the converter composed of bidirectional controllable switches can be decomposed into two groups of single-phase controllable switching converters,which optimizes the logical combination of the space vector modulation signal and the polarity selection signal.This strategy can reduce the difficulty of commutation,thereby reducing the HFLMC output voltage and current harmonic content,and ultimately improving the output power quality.The simulation results verify the correctness and effectiveness of the proposed modulation strategy.Aiming at the problems of low power distribution accuracy and voltage sag in HFLMC parallel system,a droop control strategy of virtual resistance and bus voltage regulation is proposed.This strategy introduces a virtual resistance in the power main loop to compensate for the difference in line impedance,and can improve the accuracy of HFLMC output power sharing.The introduction of the bus voltage regulation link can modify the voltage control equation parameters in the droop control loop to reduce the amplitude of the AC bus voltage drop,thereby ensuring the stability of the HFLMC parallel system.The simulation results verify that the proposed control strategy can effectively suppress the drop of the bus voltage and improve the power distribution accuracy of the parallel system.Aiming at the problem of unbalanced output power distribution of HFLMC due to the unequal impedance parameters of each output line,a droop control strategy of adaptive virtual impedance is proposed.This strategy introduces adaptive virtual impedance to reshape the equivalent output impedance of HFLMC.The adaptive adjustment of virtual impedance can be realized by using local power information and power factor.Furthermore,the load power is distributed in proportion to the capacity through the fine-tuning compensation link of droop control,so as to improve the stability and reliability of the HFLMC parallel system.The control strategy is verified by simulation,which is correct and effective,and can be extended to other voltage source converter parallel systems.