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
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
Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz...Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz while less on the low-frequency noise/drift. We use double resonance alignment magnetometers(DRAMs) to measure and suppress the low-frequency noise of a homemade current source(CS) board. The CS board noise level is suppressed by about 10 times in the range of 0.001-0.1 Hz and is reduced to 100 n A/√Hz at 0.001 Hz. The relative stability of CS board can reach2.2 × 10^(-8). In addition, the DRAM shows a better resolution and accuracy than a commercial 7.5-digit multimeter when measuring our homemade CS board. Further, by combining the DRAM with a double resonance orientation magnetometer,we may realize a low-noise CS in the 0.001-1000 Hz range.展开更多
Physiotherapeutic effects of infrared lasers have been proved in clinic.These infrared-based regulations of the bioelectrical activities can roughly be classied into enhancement and suppression of action potential(AP)...Physiotherapeutic effects of infrared lasers have been proved in clinic.These infrared-based regulations of the bioelectrical activities can roughly be classied into enhancement and suppression of action potential(AP),which are described by sodium(Na)and potassium(K)transmembrane current equations,named as Hodgkin and Huxley(HH)-model.The enhancement effect is able to evoke or strengthen the AP when infrared light is applied.Its corresponding mechanism is commonly ascribed to the changes of the cell membrane capacitance,which is transiently increased in response to the infrared radiation.The distinctive feature of the suppression effect is to inhibit or reduce the AP by the designed protocols of infrared radiation.However,its mechanism presents more complexity than that in enhancement cases.HH-model describes how the Na current determines the initial phase of AP.So,the enhancement and suppression of AP can be also ascribed to the regulations of the corresponding Na currents.Here,a continuous infrared light at the wavelength of 980 nm(CIS-980)was employed to stimulate a freshly isolated hippocampal neuron in vitro and a suppression effect on the Na currents of the neuron cell was observed.Both Na and K currents,which are named as whole cell currents,were simultaneously recorded with the cell membrane capacitance current by using a patch clamp combined with infrared irradiation.The results demonstrated that the CIS-980 was able to reversibly increase the capacitance currents,completely suppressed Na currents,but little changed K currents,which forms the steady outward whole cell currents and plays a major role on the AP repolarization.A conrmation experiment was designed and carried out by synchronizing tens of milliseconds of infrared stimulation on the same kinds of hippocampal neuron cells.After the blocked K channel,a reduction of Na current amplitude was still recorded.This proved that infrared suppression of Na current was irrelevant to K channel.A membrane capacitance mediation process was preliminarily proposed to explain the Na channel suppression process.展开更多
A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic so...A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic source-follower are proposed, which can overcome the drawbacks of the present techniques, such as sensitive to the non-uniformity of the QWIP materials, poor readout noise features, low frame frequency, limited injection efficiency and dynamic range, etc. The dummy is adopted to realize dark current suppression, while the cascode current mirror (with current ratio of 1:10) can increase charge sensitivity and reduce integration time. Through the novel CDS structure, the output waveform is boxcar, and the frame frequency is increased. Simulation results demonstrate that, in high background sense, the proposed DCS circuit can suppress the dark current, achieve good readout performance, such as low power consumption, high charge sensitivity, high resolution, large dynamic range, and insensitive to the non-uniformity of the QWIP materials.展开更多
Corona discharge suppression for high-voltage direct-current(HVDC)transmission lines at line terminals such as converter stations is a subject that requires attention.In this paper,a method based on a conductor covere...Corona discharge suppression for high-voltage direct-current(HVDC)transmission lines at line terminals such as converter stations is a subject that requires attention.In this paper,a method based on a conductor covered with dielectric film is proposed and implemented through a bench-scale setup.Compared with the bare conductor,the corona discharge suppression effect of the dielectric-film-covered conductor under positive polarity is studied from the composite field strength and ion current density using a line-plate experimental device.The influences of film thickness and film material on the corona discharge suppression effect are investigated.The charge accumulation and dissipation characteristics of different film materials are also studied.The results show that the conductor covered with dielectric film has excellent ability to inhibit corona discharge.The ground-level composite field strength of the conductor covered with dielectric film is lower than its nominal field strength,and its ion current density is at the nA m^(−2) level.The corona threshold voltage can be promoted by increasing the film thickness,but the ability to inhibit corona discharge becomes weak.The larger the surface electric field strength,the more charge accumulated,but the faster the charge dissipation rate.Compared with polyvinyl chloride film,cross-linked polyethylene film has stronger charge accumulation ability and slower charge dissipation rate,which can better restrain the corona discharge of HVDC transmission lines.展开更多
The negative-sequence voltage is often caused by the asymmetrical fault in the AC system,as well as the harmonics after the symmetrical fault at the AC side of inverter in line commutated converter based high-voltage ...The negative-sequence voltage is often caused by the asymmetrical fault in the AC system,as well as the harmonics after the symmetrical fault at the AC side of inverter in line commutated converter based high-voltage DC(LCC-HVDC).The negative-sequence voltage affects the phase-locked loop(PLL)and the inverter control,thus the inverter is vulnerable to the subsequent commutation failure(SCF).In this paper,the analytical expression of the negative-sequence voltage resulting from the symmetrical fault with the commutation voltage is derived using the switching function and Fourier decomposition.The analytical expressions of the outputs of the PLL and inverter control with respect to time are derived to quantify the contribution of the negative-sequence voltage to the SCF.To deal with the AC component of the input signals in the PLL and the inverter control due to the negative-sequence voltage,the existing proportional-integral controls of the PLL,constant current control,and constant extinction angle control are replaced by the linear active disturbance rejection control against the SCF.Simulation results verify the contributing factors to the SCF.The proposed control reduces the risk of SCF and improves the recovery speed of the system under different fault conditions.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
A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, t...A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, to the IGCT’s over-voltage sensitivity problem, a new technique of reducing the over-voltage is introduced, which releases the elect romantics energy of faulty line by a capacitive current branch to reduce the amplitude of over-voltage. Secondly, the principle of over-voltage suppression with current release branch is analyzed, and the overall control scheme of solid- state breaker is put forward. Finally, the simulation results also demonstrate its obvious effectiveness in over-voltage suppression after adding a current release branch into the SSB.展开更多
Neutral beam injection is one of the effective auxiliary heating methods in magnetic-confinementfusion experiments. In order to acquire the suppressor-grid current signal and avoid the grid being damaged by overheatin...Neutral beam injection is one of the effective auxiliary heating methods in magnetic-confinementfusion experiments. In order to acquire the suppressor-grid current signal and avoid the grid being damaged by overheating, a data acquisition and over-current protection system based on the PXI（PCI e Xtensions for Instrumentation） platform has been developed. The system consists of a current sensor, data acquisition module and over-current protection module. In the data acquisition module,the acquired data of one shot will be transferred in isolation and saved in a data-storage server in a txt file. It can also be recalled using NBWave for future analysis. The over-current protection module contains two modes： remote and local. This gives it the function of setting a threshold voltage remotely and locally, and the forbidden time of over-current protection also can be set by a host PC in remote mode. Experimental results demonstrate that the data acquisition and overcurrent protection system has the advantages of setting forbidden time and isolation transmission.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
为提高电网频率波动条件下并联型有源电力滤波器(shunt active power filters,SAPF)的补偿电流跟踪控制精度,有效抑制电网的谐波污染,提出一种具有变频适应性的重复控制策略。采用可调整采样频率的选择性重复控制器构建多采样率重复控...为提高电网频率波动条件下并联型有源电力滤波器(shunt active power filters,SAPF)的补偿电流跟踪控制精度,有效抑制电网的谐波污染,提出一种具有变频适应性的重复控制策略。采用可调整采样频率的选择性重复控制器构建多采样率重复控制系统,利用基于拉格朗日线性插值法的有限脉冲响应(FIR)滤波器将多采样率重复控制系统转换成具有统一采样频率的重复控制系统(frequency-adaptive uniform-rate selective repetitive control system,FUSRCS),通过跟随电网频率调整重复控制器延迟环节近似表达式系数的方法使FUSRCS能适应电网频率波动,设计了FUSRCS的补偿器,分析了FUSRCS的稳定性、收敛性和稳态误差,建立了三相SAPF的数学模型,依据实际数据设计了基于FUSRCS的补偿电流复合重复控制系统。仿真和实验结果表明:基于FUSRCS的SAPF能够在电网频率存在稳态偏差、电网频率动态变化和负载切换等情况下,保持较高的补偿电流跟踪精度和较好的补偿效果。与经典重复控制相比,FUSRCS在具有变频适应性的同时,减少了控制系统的计算负担,提高了系统的动态响应速度,解决了多采样率重复控制系统带来的问题。展开更多
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.
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Project supported by the National Natural Science Foundation of China (Grant Nos. 12174446 and 61671458)。
文摘Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz while less on the low-frequency noise/drift. We use double resonance alignment magnetometers(DRAMs) to measure and suppress the low-frequency noise of a homemade current source(CS) board. The CS board noise level is suppressed by about 10 times in the range of 0.001-0.1 Hz and is reduced to 100 n A/√Hz at 0.001 Hz. The relative stability of CS board can reach2.2 × 10^(-8). In addition, the DRAM shows a better resolution and accuracy than a commercial 7.5-digit multimeter when measuring our homemade CS board. Further, by combining the DRAM with a double resonance orientation magnetometer,we may realize a low-noise CS in the 0.001-1000 Hz range.
基金This study was financially supported by the National Natural Science Foundation of China(No.31370835)National Science and Technology Major Special Project on new drug innovation(No.2012ZX09503-001-003)funding from the Dalian University of Technology for the corresponding author(No.DUT21YG121).
文摘Physiotherapeutic effects of infrared lasers have been proved in clinic.These infrared-based regulations of the bioelectrical activities can roughly be classied into enhancement and suppression of action potential(AP),which are described by sodium(Na)and potassium(K)transmembrane current equations,named as Hodgkin and Huxley(HH)-model.The enhancement effect is able to evoke or strengthen the AP when infrared light is applied.Its corresponding mechanism is commonly ascribed to the changes of the cell membrane capacitance,which is transiently increased in response to the infrared radiation.The distinctive feature of the suppression effect is to inhibit or reduce the AP by the designed protocols of infrared radiation.However,its mechanism presents more complexity than that in enhancement cases.HH-model describes how the Na current determines the initial phase of AP.So,the enhancement and suppression of AP can be also ascribed to the regulations of the corresponding Na currents.Here,a continuous infrared light at the wavelength of 980 nm(CIS-980)was employed to stimulate a freshly isolated hippocampal neuron in vitro and a suppression effect on the Na currents of the neuron cell was observed.Both Na and K currents,which are named as whole cell currents,were simultaneously recorded with the cell membrane capacitance current by using a patch clamp combined with infrared irradiation.The results demonstrated that the CIS-980 was able to reversibly increase the capacitance currents,completely suppressed Na currents,but little changed K currents,which forms the steady outward whole cell currents and plays a major role on the AP repolarization.A conrmation experiment was designed and carried out by synchronizing tens of milliseconds of infrared stimulation on the same kinds of hippocampal neuron cells.After the blocked K channel,a reduction of Na current amplitude was still recorded.This proved that infrared suppression of Na current was irrelevant to K channel.A membrane capacitance mediation process was preliminarily proposed to explain the Na channel suppression process.
基金Supported by the National Natural Science Foundation of China(No.60077025)
文摘A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic source-follower are proposed, which can overcome the drawbacks of the present techniques, such as sensitive to the non-uniformity of the QWIP materials, poor readout noise features, low frame frequency, limited injection efficiency and dynamic range, etc. The dummy is adopted to realize dark current suppression, while the cascode current mirror (with current ratio of 1:10) can increase charge sensitivity and reduce integration time. Through the novel CDS structure, the output waveform is boxcar, and the frame frequency is increased. Simulation results demonstrate that, in high background sense, the proposed DCS circuit can suppress the dark current, achieve good readout performance, such as low power consumption, high charge sensitivity, high resolution, large dynamic range, and insensitive to the non-uniformity of the QWIP materials.
基金by State Grid Shandong Electric Power Company(52062618001M)。
文摘Corona discharge suppression for high-voltage direct-current(HVDC)transmission lines at line terminals such as converter stations is a subject that requires attention.In this paper,a method based on a conductor covered with dielectric film is proposed and implemented through a bench-scale setup.Compared with the bare conductor,the corona discharge suppression effect of the dielectric-film-covered conductor under positive polarity is studied from the composite field strength and ion current density using a line-plate experimental device.The influences of film thickness and film material on the corona discharge suppression effect are investigated.The charge accumulation and dissipation characteristics of different film materials are also studied.The results show that the conductor covered with dielectric film has excellent ability to inhibit corona discharge.The ground-level composite field strength of the conductor covered with dielectric film is lower than its nominal field strength,and its ion current density is at the nA m^(−2) level.The corona threshold voltage can be promoted by increasing the film thickness,but the ability to inhibit corona discharge becomes weak.The larger the surface electric field strength,the more charge accumulated,but the faster the charge dissipation rate.Compared with polyvinyl chloride film,cross-linked polyethylene film has stronger charge accumulation ability and slower charge dissipation rate,which can better restrain the corona discharge of HVDC transmission lines.
基金supported by National Natural Science Foundation of China(No.51877061).
文摘The negative-sequence voltage is often caused by the asymmetrical fault in the AC system,as well as the harmonics after the symmetrical fault at the AC side of inverter in line commutated converter based high-voltage DC(LCC-HVDC).The negative-sequence voltage affects the phase-locked loop(PLL)and the inverter control,thus the inverter is vulnerable to the subsequent commutation failure(SCF).In this paper,the analytical expression of the negative-sequence voltage resulting from the symmetrical fault with the commutation voltage is derived using the switching function and Fourier decomposition.The analytical expressions of the outputs of the PLL and inverter control with respect to time are derived to quantify the contribution of the negative-sequence voltage to the SCF.To deal with the AC component of the input signals in the PLL and the inverter control due to the negative-sequence voltage,the existing proportional-integral controls of the PLL,constant current control,and constant extinction angle control are replaced by the linear active disturbance rejection control against the SCF.Simulation results verify the contributing factors to the SCF.The proposed control reduces the risk of SCF and improves the recovery speed of the system under different fault conditions.
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.
文摘A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, to the IGCT’s over-voltage sensitivity problem, a new technique of reducing the over-voltage is introduced, which releases the elect romantics energy of faulty line by a capacitive current branch to reduce the amplitude of over-voltage. Secondly, the principle of over-voltage suppression with current release branch is analyzed, and the overall control scheme of solid- state breaker is put forward. Finally, the simulation results also demonstrate its obvious effectiveness in over-voltage suppression after adding a current release branch into the SSB.
基金supported by National Natural Science Foundation of China(No.11575240)Key Program of Research and Development of Hefei Science Center,CAS(grant 2016HSC-KPRD002)
文摘Neutral beam injection is one of the effective auxiliary heating methods in magnetic-confinementfusion experiments. In order to acquire the suppressor-grid current signal and avoid the grid being damaged by overheating, a data acquisition and over-current protection system based on the PXI（PCI e Xtensions for Instrumentation） platform has been developed. The system consists of a current sensor, data acquisition module and over-current protection module. In the data acquisition module,the acquired data of one shot will be transferred in isolation and saved in a data-storage server in a txt file. It can also be recalled using NBWave for future analysis. The over-current protection module contains two modes： remote and local. This gives it the function of setting a threshold voltage remotely and locally, and the forbidden time of over-current protection also can be set by a host PC in remote mode. Experimental results demonstrate that the data acquisition and overcurrent protection system has the advantages of setting forbidden time and isolation transmission.
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。
文摘为提高电网频率波动条件下并联型有源电力滤波器(shunt active power filters,SAPF)的补偿电流跟踪控制精度,有效抑制电网的谐波污染,提出一种具有变频适应性的重复控制策略。采用可调整采样频率的选择性重复控制器构建多采样率重复控制系统,利用基于拉格朗日线性插值法的有限脉冲响应(FIR)滤波器将多采样率重复控制系统转换成具有统一采样频率的重复控制系统(frequency-adaptive uniform-rate selective repetitive control system,FUSRCS),通过跟随电网频率调整重复控制器延迟环节近似表达式系数的方法使FUSRCS能适应电网频率波动,设计了FUSRCS的补偿器,分析了FUSRCS的稳定性、收敛性和稳态误差,建立了三相SAPF的数学模型,依据实际数据设计了基于FUSRCS的补偿电流复合重复控制系统。仿真和实验结果表明:基于FUSRCS的SAPF能够在电网频率存在稳态偏差、电网频率动态变化和负载切换等情况下,保持较高的补偿电流跟踪精度和较好的补偿效果。与经典重复控制相比,FUSRCS在具有变频适应性的同时,减少了控制系统的计算负担,提高了系统的动态响应速度,解决了多采样率重复控制系统带来的问题。
