Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inducta...Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inductance’characteristic of MMC impedance.Research indicates that this characteristic interacting with the capacitive characteristics of an AC system is the cause of high frequency resonance(HFR)in the Yu-E HVDC project.As the current controller is one of the main factors that affects the MMC impedance,a compensation control to imitate the paralleled impedance at the point of common coupling(PCC)is proposed.Therefore,the structure and parameter design of the compensation controller are core to realizing HFR suppression.There are two potentially risky frequency ranges of HFRs(around 700 Hz and 1.8 kHz)in the studied AC system within 2.0 kHz.The core concept of HFR suppression is to make the phase angle of MMC impedance smaller than 90◦in the two risky frequency ranges according to impedance stability theory.Hence,the design parameters aim to coordinate the phase angle of MMC impedance in the two risky frequency ranges.In this paper,three types of compensation controller are studied to suppress HFRs,namely,first-order low pass filter(LPF),second-order LPF,and third-order band pass filter.The results of parameter design show that the first-order LPF cannot suppress both HFRs simultaneously.The second-order LPF can suppress both HFRs,however,it introduces a DC component into the current control loop.Therefore,a high pass filter is added to form the recommended third-order controller.All parameter ranges of the compensation controller are derived using analytical expressions.Finally,the correctness of the parameter design is proofed using time-domain simulations.展开更多
Introduction:This paper uses a dynamic voltage restorer(DVR)to improve the voltage quality from voltage sags.It is difficult to satisfy various of compensation quality and time of the voltage sag by using single compe...Introduction:This paper uses a dynamic voltage restorer(DVR)to improve the voltage quality from voltage sags.It is difficult to satisfy various of compensation quality and time of the voltage sag by using single compensation method.Furthermore,high-power consumption of the phase jump compensation increases the size and cost of a dynamic voltage restorer(DVR).Methods&Results:In order to improve the compensating efficiency of DVR,an optimized compensation strategy is proposed for voltage sag of micro-grid caused by interconnection and sensitive loads.The proposed compensation strategy increases the supporting time for long voltage sags.Discussion:Firstly,the power flow and the maximum compensation time of DVR are analyzed using three basic compensation strategies.Then,the phase jump is corrected by pre-sag compensation.And a quadratic transition curve,which involves the injected voltage phases of pre-sag strategy and minimum energy strategy,is used to transform pre-sag compensation to minimum energy compensation of DVR.Conclusions:The transition utilizes the storage system to reduce the rate of discharge.As a result,the proposed strategy increases the supporting time for long voltage sags.The analytical study shows that the presented method significantly increases compensation time of DVR.The simulation results performed by MATLAB/SIMULINK also confirm the effectiveness of the proposed method.展开更多
基金supported by the National Natural Science Foundation of China(No.U1866210).
文摘Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inductance’characteristic of MMC impedance.Research indicates that this characteristic interacting with the capacitive characteristics of an AC system is the cause of high frequency resonance(HFR)in the Yu-E HVDC project.As the current controller is one of the main factors that affects the MMC impedance,a compensation control to imitate the paralleled impedance at the point of common coupling(PCC)is proposed.Therefore,the structure and parameter design of the compensation controller are core to realizing HFR suppression.There are two potentially risky frequency ranges of HFRs(around 700 Hz and 1.8 kHz)in the studied AC system within 2.0 kHz.The core concept of HFR suppression is to make the phase angle of MMC impedance smaller than 90◦in the two risky frequency ranges according to impedance stability theory.Hence,the design parameters aim to coordinate the phase angle of MMC impedance in the two risky frequency ranges.In this paper,three types of compensation controller are studied to suppress HFRs,namely,first-order low pass filter(LPF),second-order LPF,and third-order band pass filter.The results of parameter design show that the first-order LPF cannot suppress both HFRs simultaneously.The second-order LPF can suppress both HFRs,however,it introduces a DC component into the current control loop.Therefore,a high pass filter is added to form the recommended third-order controller.All parameter ranges of the compensation controller are derived using analytical expressions.Finally,the correctness of the parameter design is proofed using time-domain simulations.
基金supported by National Nature Science Foundation under Grant 51477070,and the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘Introduction:This paper uses a dynamic voltage restorer(DVR)to improve the voltage quality from voltage sags.It is difficult to satisfy various of compensation quality and time of the voltage sag by using single compensation method.Furthermore,high-power consumption of the phase jump compensation increases the size and cost of a dynamic voltage restorer(DVR).Methods&Results:In order to improve the compensating efficiency of DVR,an optimized compensation strategy is proposed for voltage sag of micro-grid caused by interconnection and sensitive loads.The proposed compensation strategy increases the supporting time for long voltage sags.Discussion:Firstly,the power flow and the maximum compensation time of DVR are analyzed using three basic compensation strategies.Then,the phase jump is corrected by pre-sag compensation.And a quadratic transition curve,which involves the injected voltage phases of pre-sag strategy and minimum energy strategy,is used to transform pre-sag compensation to minimum energy compensation of DVR.Conclusions:The transition utilizes the storage system to reduce the rate of discharge.As a result,the proposed strategy increases the supporting time for long voltage sags.The analytical study shows that the presented method significantly increases compensation time of DVR.The simulation results performed by MATLAB/SIMULINK also confirm the effectiveness of the proposed method.
