The modular multilevel converter(MMC)has become a promising topology for widespread power converter applications.However,an evident circulating current flowing between the phases will increase system losses and compli...The modular multilevel converter(MMC)has become a promising topology for widespread power converter applications.However,an evident circulating current flowing between the phases will increase system losses and complicate the heatsink design.This paper proposes a novel hybrid model predictive control method for MMCs.This method utilizes an indirect structure MPC and a sorting algorithm to implement current tracking and capacitor voltages balancing,considerably resulting in reduced calculation burden.In addition,different from the conventional MPC solutions,we add a simple proportional-integral(PI)controller to suppress circulating current through modifying the submodule(SM)inserted number,which is parallel to the MPC loop.This hybrid control solution combines both advantages of MPC and linear control,evidently resulting in improved performance of circulating current.Finally,the MATLAB/Simulink results of an 11-level MMC system verify the effectiveness of the proposed solution.展开更多
Circulating currents in a microgrid increase the power loss of the microgrid, reduce the operational efficiency, as well as affect the power quality of the microgrid. The existing literature is seldom concerned with m...Circulating currents in a microgrid increase the power loss of the microgrid, reduce the operational efficiency, as well as affect the power quality of the microgrid. The existing literature is seldom concerned with methods to suppress the loop currents using fuzzy logic control. In this paper, a method based on fuzzy control of droop coefficients is proposed to suppress the circulating currents inside the microgrid.The method combines fuzzy control with droop control and can achieve the effect of suppressing the circulating currents by adaptively adjusting the droop coefficients to make the power distribution between each subgrid more balanced. To verify the proposed method, simulation is carried out in Matlab/Simulink environment, and the simulation results show that the proposed method is significantly better than the traditional proportional-integral control method. The circulating currents reduce from about 10 A to several nanoamperes, the bus voltage and frequency drops are significantly improved, and the total harmonic distortion rate of the output voltage reduces from 4.66% to 1.06%. In addition, the method used in this paper can be extended to be applied in multiple inverters connected in parallel, and the simulation results show that the method has a good effect on the suppression of circulating currents among multiple inverters.展开更多
A modular-parallel IPT system with multi-inverters is proposed to enhance power capacity and expansibility for primary power equipment.In order to balance the actual output power of each inverter,a control strategy is...A modular-parallel IPT system with multi-inverters is proposed to enhance power capacity and expansibility for primary power equipment.In order to balance the actual output power of each inverter,a control strategy is designed to minimize circulating-current and equalize output current.In the process of circulating current suppression,current could be decoupled into the following two parts through a d-q synchronous rotating frame:virtual active and reactive current.Then,the above two virtual current components can be adjusted by PWM and PPM.A close-loop control method based on master-slave scheme is proposed to improve the scalability for a practical IPT system,and an impedance matching and its ZCS method is proposed to avoid detuning caused by a change of the number of modules.Finally,an IPT experiment platform with 3-parallel modules is established to verify availability of the proposed control methods.As shown in the experiment,circulating current of the prototype can be reduced from 2.6 A to 0.3 A,and the difference of output power of each module is less than 1%when deviation of the input DC voltage,the delay of driving signals,and the resonant inductance is 10%,respectively.The overall efficiency of the modular IPT system is up to 92.5%at 3.3 kW.展开更多
The modular multilevel converter(MMC)has been a highly promising topology in the high-voltage direct-current(HVDC)transmission area,where each arm of the MMC may consist of hundreds of series-connected submodules and ...The modular multilevel converter(MMC)has been a highly promising topology in the high-voltage direct-current(HVDC)transmission area,where each arm of the MMC may consist of hundreds of series-connected submodules and an inductor.Due to its parameter inaccuracy,component aging,and so on,the component parameter in different arms of the MMC may be different,which may cause circulating current in the MMC-HVDC transmission system,and result in current deterioration,power losses,and electromagnetic interference,etc.In this paper,the circulating current suppressing(CCS)in the MMC-HVDC system,due to asymmetric arm impedance,is analyzed.Based on the mathematical analysis,a method of using an auxiliary circuit is proposed for the MMC to realize the CCS and improve the performance of the MMC-HVDC system.Simulation studies are conducted with PSCAD/EMTDC in the HVDC system,which confirms the feasibility of the proposed method.展开更多
用于中高压直流电网互联和隔离的模块化多电平直流变压器(modular multilevel DC transformer,MMDCT)在传输功率变化的过程中会出现电流欠阻尼振荡的问题,从而降低了装置的稳定性,因此文中对振荡抑制展开了研究。首先,通过差模和共模电...用于中高压直流电网互联和隔离的模块化多电平直流变压器(modular multilevel DC transformer,MMDCT)在传输功率变化的过程中会出现电流欠阻尼振荡的问题,从而降低了装置的稳定性,因此文中对振荡抑制展开了研究。首先,通过差模和共模电路中的振荡现象分析,并基于状态空间平均法建立数学模型,从而揭示了MMDCT中的电流振荡机理;进一步提出了一种基于共模和差模分离的电流振荡抑制方法,利用变副边交流侧电压占空比的方式实现漏感电流振荡的抑制,同时采用变桥臂电压占空比的方式进行环流电流振荡的抑制,并给出了相应控制器参数设计依据。最后,通过仿真和实验验证了所提控制方法的有效性,结果表明在基于共模和差模分离的振荡抑制方法下,MMDCT可以在功率变化过程中快速实现电流稳定,有利于提升装置稳定性。展开更多
基金This work was partially supported by the National Natural Science Foundation of China(11847104)General Program of National Natural Science Foundation of China(51977124)+2 种基金Shandong Natural Science Foundation(ZR2019QEE001)Natural Science Foundation of Jiangsu Province(BK20190204)National Distinguished Expert(Youth Talent)Program of China(31390089963058)。
文摘The modular multilevel converter(MMC)has become a promising topology for widespread power converter applications.However,an evident circulating current flowing between the phases will increase system losses and complicate the heatsink design.This paper proposes a novel hybrid model predictive control method for MMCs.This method utilizes an indirect structure MPC and a sorting algorithm to implement current tracking and capacitor voltages balancing,considerably resulting in reduced calculation burden.In addition,different from the conventional MPC solutions,we add a simple proportional-integral(PI)controller to suppress circulating current through modifying the submodule(SM)inserted number,which is parallel to the MPC loop.This hybrid control solution combines both advantages of MPC and linear control,evidently resulting in improved performance of circulating current.Finally,the MATLAB/Simulink results of an 11-level MMC system verify the effectiveness of the proposed solution.
基金Foundation items:National Natural Science Foundation of China(No.62303107)Fundamental Research Funds for the Central Universities,China(Nos.2232022G-09 and 2232021D-38)Shanghai Sailing Program,China(No.21YF1400100)。
文摘Circulating currents in a microgrid increase the power loss of the microgrid, reduce the operational efficiency, as well as affect the power quality of the microgrid. The existing literature is seldom concerned with methods to suppress the loop currents using fuzzy logic control. In this paper, a method based on fuzzy control of droop coefficients is proposed to suppress the circulating currents inside the microgrid.The method combines fuzzy control with droop control and can achieve the effect of suppressing the circulating currents by adaptively adjusting the droop coefficients to make the power distribution between each subgrid more balanced. To verify the proposed method, simulation is carried out in Matlab/Simulink environment, and the simulation results show that the proposed method is significantly better than the traditional proportional-integral control method. The circulating currents reduce from about 10 A to several nanoamperes, the bus voltage and frequency drops are significantly improved, and the total harmonic distortion rate of the output voltage reduces from 4.66% to 1.06%. In addition, the method used in this paper can be extended to be applied in multiple inverters connected in parallel, and the simulation results show that the method has a good effect on the suppression of circulating currents among multiple inverters.
文摘A modular-parallel IPT system with multi-inverters is proposed to enhance power capacity and expansibility for primary power equipment.In order to balance the actual output power of each inverter,a control strategy is designed to minimize circulating-current and equalize output current.In the process of circulating current suppression,current could be decoupled into the following two parts through a d-q synchronous rotating frame:virtual active and reactive current.Then,the above two virtual current components can be adjusted by PWM and PPM.A close-loop control method based on master-slave scheme is proposed to improve the scalability for a practical IPT system,and an impedance matching and its ZCS method is proposed to avoid detuning caused by a change of the number of modules.Finally,an IPT experiment platform with 3-parallel modules is established to verify availability of the proposed control methods.As shown in the experiment,circulating current of the prototype can be reduced from 2.6 A to 0.3 A,and the difference of output power of each module is less than 1%when deviation of the input DC voltage,the delay of driving signals,and the resonant inductance is 10%,respectively.The overall efficiency of the modular IPT system is up to 92.5%at 3.3 kW.
基金This work was supported by the Science and Technology Program of the State Grid Corporation of China(Grant No.5100-201999330A-0-0-00).
文摘The modular multilevel converter(MMC)has been a highly promising topology in the high-voltage direct-current(HVDC)transmission area,where each arm of the MMC may consist of hundreds of series-connected submodules and an inductor.Due to its parameter inaccuracy,component aging,and so on,the component parameter in different arms of the MMC may be different,which may cause circulating current in the MMC-HVDC transmission system,and result in current deterioration,power losses,and electromagnetic interference,etc.In this paper,the circulating current suppressing(CCS)in the MMC-HVDC system,due to asymmetric arm impedance,is analyzed.Based on the mathematical analysis,a method of using an auxiliary circuit is proposed for the MMC to realize the CCS and improve the performance of the MMC-HVDC system.Simulation studies are conducted with PSCAD/EMTDC in the HVDC system,which confirms the feasibility of the proposed method.
文摘用于中高压直流电网互联和隔离的模块化多电平直流变压器(modular multilevel DC transformer,MMDCT)在传输功率变化的过程中会出现电流欠阻尼振荡的问题,从而降低了装置的稳定性,因此文中对振荡抑制展开了研究。首先,通过差模和共模电路中的振荡现象分析,并基于状态空间平均法建立数学模型,从而揭示了MMDCT中的电流振荡机理;进一步提出了一种基于共模和差模分离的电流振荡抑制方法,利用变副边交流侧电压占空比的方式实现漏感电流振荡的抑制,同时采用变桥臂电压占空比的方式进行环流电流振荡的抑制,并给出了相应控制器参数设计依据。最后,通过仿真和实验验证了所提控制方法的有效性,结果表明在基于共模和差模分离的振荡抑制方法下,MMDCT可以在功率变化过程中快速实现电流稳定,有利于提升装置稳定性。
