To facilitate rapid analysis of the oscillation stability mechanism in modular multilevel converter-based high voltage direct current(MMC-HVDC)systems and streamline the simulation process for determining MMC impedanc...To facilitate rapid analysis of the oscillation stability mechanism in modular multilevel converter-based high voltage direct current(MMC-HVDC)systems and streamline the simulation process for determining MMC impedance characteristics,a simplified mathematical simulation model for MMC closed-loop impedance is developed using the harmonic state space method.This model considers various control strategies and includes both AC-side and DC-side impedance models.By applying a Nyquist criterion-based impedance analysis method,the stability mechanisms on the AC and DC sides of the MMC are examined.In addition,a data-driven oscillation stability analysis method is also proposed,leveraging a global sensitivity algorithm based on fast model results to identify key parameters influencing MMC oscillation stability.Based on sensitivity analysis results,a parameter adjustment strategy for oscillation suppression is proposed.The simulation results from the MATLAB/Simulinkbased MMC model validate the effectiveness of the proposed method.展开更多
Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion sys...Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion systems.However,due to the utilization of large amount of semiconductor devices,the reliability of MMCs becomes one of the severe challenges constraining their further development and applications.In this paper,common electrical faults of the MMC have been summarized and analyzed,including open-circuit switching faults,short-circuit switching faults,dc-bus short-circuit faults,and single line-to-ground faults on the ac side.A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted.In addition,fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented.All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated,which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.展开更多
Modular multilevel resonant converter is an promising candidate for high voltage applications since it has advantageous features,such as high efficiency,high voltage capability and easy fault-tolerant operation.Howeve...Modular multilevel resonant converter is an promising candidate for high voltage applications since it has advantageous features,such as high efficiency,high voltage capability and easy fault-tolerant operation.However,the inequality of arm inductance in practice will lead to imbalance between the upper and lower arm voltages,which will induce large ripples in the circulating current and a dc bias on the voltage generated by modular circuits.To compensate for the voltage imbalance,effects of arm duty cycle changes on arm voltages are discussed.An arm voltage balancing control method is proposed:adjust arm duty cycle according to arm voltage deviation in every switching cycle.Simulation and experimental results are presented to validate the theoretical analysis and the proposed control method.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
Solid state transformer(SST)can provide more advanced functionalities compared with conventional transformer,and has great potential in smart grid application.Recently,the SST with medium frequency(MF)isolation link a...Solid state transformer(SST)can provide more advanced functionalities compared with conventional transformer,and has great potential in smart grid application.Recently,the SST with medium frequency(MF)isolation link and magnetic integration feature has been proposed,which can reduce the system volume and thus increase the power density.However,the magnetic integration also introduces strong coupling between the line frequency(LF)and MF variables,which poses a great challenge on modeling and control issues.This paper proposes a modeling and control method for an SST with magnetic integration and mixed-frequency modulation.A mathematical model based on dual d-q references is deduced,and then a cascaded control system is designed according to the model.Parameters of the controller for the variables at one frequency are properly designed to avoid disturbance from the variables at the other frequency.The simulation and experimental results show good decoupling effect and satisfactory dynamics performance of the proposed control system.展开更多
A modular multilevel converter(MMC)integrated with split battery cells(BIMMCs)is proposed for the battery management system(BMS)and motor drive system.In order to reduce the switching losses,the state of charge(SOC)ba...A modular multilevel converter(MMC)integrated with split battery cells(BIMMCs)is proposed for the battery management system(BMS)and motor drive system.In order to reduce the switching losses,the state of charge(SOC)balancing strategy with a reduced switching-frequency(RSF)is proposed in this paper.The proposed RSF algorithm not only reduces the switching losses,but also features good balancing performance both in the unbalanced and balanced initial states.The results are verified by extensive simulations in MATLAB/Simulink surroundings.展开更多
This paper presents a new modular multilevel converter (MMC) topology. Compared to conventional multilevel converters, MMC has much lower switching frequency (50 Hz) resulting in lower switching losses, and consequent...This paper presents a new modular multilevel converter (MMC) topology. Compared to conventional multilevel converters, MMC has much lower switching frequency (50 Hz) resulting in lower switching losses, and consequently, lower total losses of the transmission system. The fundamental concept and the applied control scheme are introduced in detail. A modified multilevel fundamental switching modulation scheme adopting the multicarrier pulse width modulation concept is presented. A capacitor voltage balancing technique is proposed. With the established simulation model of the 11-level MMC, the modulation and balancing strategy presented are confirmed by MATLAB/SIMULINK simulations. The multicarrier pulse width modulation converter strategy enhances the fundamental output voltage and reduces total harmonic distortion. This new type of converter is suitable for high-voltage drive systems and power system applications such as high voltage dc (HVDC) transmission, reactive power compensation equipment and so on.展开更多
In this paper, a novel voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides the voltages of sub-module capacitors in each arm into several groups and the voltage balancing ...In this paper, a novel voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides the voltages of sub-module capacitors in each arm into several groups and the voltage balancing is based on these groups. The proposed method can save sorting time greatly compared with the conventional method. Simulation results on a MMC based three-phase inverter show validity of the proposed method.展开更多
The stop control strategy of modular multilevel converter based HVDC transmission system is proposed. This stop process is divided into stages of energy feedback and energy consumption. The DC voltage controller is co...The stop control strategy of modular multilevel converter based HVDC transmission system is proposed. This stop process is divided into stages of energy feedback and energy consumption. The DC voltage controller is coordinated to the used modules per phase when active power is transmitted prior to reactive power, so that the energy is fed back to the AC power grid connected to the converter station which uses the fixed dc voltage controller. In addition, in view of the different forms connected to the grid, specifically when the converter station supplies power for passive network, the passive converter station can take a certain auxiliary trigger strategy to make its maximum energy feedback to the grid. Finally, a simulation system of the MMC-HVDC system is constructed in Matlab/Simulink environment, and simulation results show that the proposed stop strategies are effective.展开更多
The fractional frequency transmission system is an emerging technology for long-distance wind power integration,and the modular multilevel matrix converter(M3C)is the keen equipment.Since the M3C directly connects two...The fractional frequency transmission system is an emerging technology for long-distance wind power integration,and the modular multilevel matrix converter(M3C)is the keen equipment.Since the M3C directly connects two ac grids with different frequencies,the external and internal harmonics have complex coupling relationships with a unique dual-fundamental-frequency spectrum,which has not been properly investigated due to a lack of an effective method.To address this issue,a novel harmonic state-space method is proposed to achieve comprehensive modelling of the harmonic dynamics of the M3C.Based on the principle of two-dimensional Fourier transform,the decomposition of the dual-fundamental-frequency harmonics is realized,and the multiplicative coupling between time-domain variables is modelled through double-layer convolution on the frequency domain.Besides,the general expression of the proposed method is provided,which highlights a modularized matrix with easy scalability to meet different truncation requirements.Then,the HSS model of M3C considering the close-loop control is established,based on which a panoramic harmonic coupling relationship between the system-and the low-frequency side is concluded.Finally,the M3C model and harmonic coupling relationship are validated by simulation tests conducted in MATLAB/Simulink environment.展开更多
Innovative dynamic models for the DC modular multilevel converter(DC-MMC)in rotating dq frame are presented in this paper,which are specifically designed to enhance converter design and stability analysis.Open-loop an...Innovative dynamic models for the DC modular multilevel converter(DC-MMC)in rotating dq frame are presented in this paper,which are specifically designed to enhance converter design and stability analysis.Open-loop and closed-loop models are developed using three dq frames,providing a detailed examination of the impact of 2^(nd)and 3^(rd)harmonic components on the model accuracy.A novel contribution of this paper is the integration of a 2^(nd)harmonic current suppression controller(SHCSC)within the closed-loop model,offering new insights into its effects on system stability.The DC-MMC model is further extended by coupling it with high-voltage direct current(HVDC)cables on each side,forming an interconnected system model that accurately represents a more authentic scenario for future DC grids.The proposed model is rigorously validated against PSCAD benchmark model,confirming their precision and reliability.The interconnected system model is then utilized to analyze the influence of cable length on system stability,demonstrating practical applications.The closed-loop model is subsequently employed for stability assessment of the interconnected system,showcasing its applicability in real-world scenarios.Additionally,a damping controller is designed using participation factor and residue approaches,offering a refined approach to oscillation damping and stability optimization.The effectiveness of the controller is evaluated through eigenvalue analysis,supported by simulation results,underscoring its potential for enhancing system stability.展开更多
Modular Multilevel Converters(MMC)have emerged as a key technology for medium-to high-voltage power conversion applications such as HVDC transmission,large-scale renewable integration,and flexible AC transmission syst...Modular Multilevel Converters(MMC)have emerged as a key technology for medium-to high-voltage power conversion applications such as HVDC transmission,large-scale renewable integration,and flexible AC transmission systems.Despite their superior performance and modularity,MMCs present complex control challenges due to their multi-level structure,numerous submodules,and circulating currents.This paper comprehensively reviews advanced control strategies developed for MMCs,including fundamental current and voltage balancing controls,sophisticated switching algorithms,and multifunctional approaches addressing harmonic suppression,power factor correction,and fault tolerance.Emphasis is placed on modern methods such as model predictive control,adaptive and robust controls that accommodate system nonlinearities and parameter uncertainties.Implementation aspects,including digital control hardware and the impact of control delays,are also discussed.The paper highlights recent advancements that improve system stability,efficiency,and reliability,thus facilitating MMC deployment in evolving power grids with high renewable penetration and stringent grid code requirements.展开更多
This paper develops a detailed equivalent model for modular multilevel converters with partially-integrated battery energy storage.The proposed model gains computational efficiency in two ways.Firstly,it markedly redu...This paper develops a detailed equivalent model for modular multilevel converters with partially-integrated battery energy storage.The proposed model gains computational efficiency in two ways.Firstly,it markedly reduces the large number of nodes in the conventional switching model of the converter,thereby shrinking the size of its admittance matrix.Secondly,it avoids computationally expensive re-triangularization of the admittance matrix during the normal operation of the converter and restricts it only to the rare occasions of converter blocking.Mathematical derivation of the model is carried out using differential equations of the converter.The computational efficiency and accuracy of the proposed model are confirmed by comparison of the results from its implementation in the PSCAD/EMTDC simulator against conventional detailed switching models and measurements from a single-phase scaleddown laboratory setup.This paper also shows a case study wherein a converter with partially-integrated batteries is included in the CIGRE B4-5 benchmark system.展开更多
Fault current limiting is a critical technology to en sure the safe operation of modular multilevel converter based multi-terminal direct current(MMC-MTDC)grids.This paper proposes a fault severity classification base...Fault current limiting is a critical technology to en sure the safe operation of modular multilevel converter based multi-terminal direct current(MMC-MTDC)grids.This paper proposes a fault severity classification based coordination con trol strategy of fault current limiter(FCL)and MMC for adap tive fault current limiting.The proposed strategy reduces the in vestment in FCL,and keeps the bus voltages of non-faulty lines at reasonable values.Firstly,a rapid fault circuit parameter esti mation(FCPE)method using initial fault current information is proposed.With this method,the fault distance and fault transi tion resistance can be quickly estimated,which are used for a quantitative indication of the fault severity.Subsequently,the coordination control strategy of FCL and MMC is proposed,in which the FCL action is prioritized,while the control of MMC is complementary for current limiting.Based on the proposed strategy,fault severity phase planes(FSPPs)are constructed to assess fault severity and calculate the activation time of FCL and voltage regulation factor of MMC.Therefore,the FCL acti vation and MMC control are matched to the fault severity.The effectiveness and advantages of the proposed strategy are vali dated by the simulations in PSCAD/EMTDC.展开更多
The most commonly used modulation for an isolated modular multilevel DC-DC converter(IMMDCC)is quasi-square-wave modulation(QSWM).However,in order to realize soft-switching,QSWM-IMMDCC usually needs to increase the ph...The most commonly used modulation for an isolated modular multilevel DC-DC converter(IMMDCC)is quasi-square-wave modulation(QSWM).However,in order to realize soft-switching,QSWM-IMMDCC usually needs to increase the phase-shifting angle or reduce the voltage amplitude ratio,which will not only increase the conduction loss but also require more passive components.This paper proposes an improved quasi-square-wave modulation(IQSWM),which generates ripple current through the non-complementary output of the upper and lower arms.Compared with QSWM-IMMDCC,the ripple current can make IQSWM-IMMDCC realize soft-switching under the conditions of a smaller phase-shifting angle and larger voltage amplitude ratio.The decrease of the phase-shifting angle can improve the power factor of the AC link and reduce the inductance in the AC link,and the increase of the voltage amplitude ratio can increase the fundamental wave voltage of the AC output and reduce the capacitance of the sub-module.In addition,IQSWM can also adjust the ripple current according to changes in output power,thereby broadening the range of soft-switching.Finally,the ripple currents generated by multiple parallel IQSWM-IMMDCCs can offset each other,thereby preventing any impact on the DC output.The simulation results prove the correctness and effectiveness of IQSWM.展开更多
Energy storage systems support electrical grid stability by enabling strategies to tackle issues,such as power fluctuations,low inertia,and insufficient damping.The present study proposes a battery energy storage syst...Energy storage systems support electrical grid stability by enabling strategies to tackle issues,such as power fluctuations,low inertia,and insufficient damping.The present study proposes a battery energy storage system based on a modular multilevel converter with multiplexed submodule arms(M-MMC-BESS)to reduce the number of switching devices while embedding DC short-circuit fault ride-through capability.Compared to the conventional two-stage half-bridge topology,the M-MMC-BESS retains the same number of switching devices but allows uninterrupted operation under DC short-circuit faults.In addition,compared to the two-stage full-bridge topology,the proposed topology reduces the number of switching devices by one-third.The control of the M-MMC-BESS is thoroughly investigated under both normal and DC short-circuit operating conditions.Simulation and experimental results are used to demonstrate the effectiveness of the proposed system and control approach.展开更多
This paper proposes a continuous control set model predictive control(CCS-MPC)algorithm of a modular multilevel matrix converter(M3C)for low-frequency AC transmission(LFAC),via which the offshore wind farm(OWF)is inte...This paper proposes a continuous control set model predictive control(CCS-MPC)algorithm of a modular multilevel matrix converter(M3C)for low-frequency AC transmission(LFAC),via which the offshore wind farm(OWF)is integrated.The M3C is operated with a 16.7 Hz frequency at the OWF side and a 50 Hz frequency at the onshore grid side.The balance of the capacitor voltages and the regulation of circulating currents in the M3C are performed using the proposed CCSMPC algorithm,which is based on the online solution of a cost function with constraints.Simulation and experimental work(with a 5 kW M3C prototype)are provided,showing the performance of the LFAC system to operate with symmetrical and asymmetrical voltage dips,active and reactive power steps,and optimal limitation of currents and voltages using constraints.Unlike previous publications,the predictive control system in this paper allows seamless operation under balanced and unbalanced conditions,for instance,during asymmetrical voltage dips.展开更多
基金National Natural Science Foundation of China(52307127)State Key Laboratory of Power System Operation and Control(SKLD23KZ07)。
文摘To facilitate rapid analysis of the oscillation stability mechanism in modular multilevel converter-based high voltage direct current(MMC-HVDC)systems and streamline the simulation process for determining MMC impedance characteristics,a simplified mathematical simulation model for MMC closed-loop impedance is developed using the harmonic state space method.This model considers various control strategies and includes both AC-side and DC-side impedance models.By applying a Nyquist criterion-based impedance analysis method,the stability mechanisms on the AC and DC sides of the MMC are examined.In addition,a data-driven oscillation stability analysis method is also proposed,leveraging a global sensitivity algorithm based on fast model results to identify key parameters influencing MMC oscillation stability.Based on sensitivity analysis results,a parameter adjustment strategy for oscillation suppression is proposed.The simulation results from the MATLAB/Simulinkbased MMC model validate the effectiveness of the proposed method.
文摘Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion systems.However,due to the utilization of large amount of semiconductor devices,the reliability of MMCs becomes one of the severe challenges constraining their further development and applications.In this paper,common electrical faults of the MMC have been summarized and analyzed,including open-circuit switching faults,short-circuit switching faults,dc-bus short-circuit faults,and single line-to-ground faults on the ac side.A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted.In addition,fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented.All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated,which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.
基金the National Key Research and Development Program of China(No.2016YFB0100603)National Natural Science Foundation of China(No.51877193)。
文摘Modular multilevel resonant converter is an promising candidate for high voltage applications since it has advantageous features,such as high efficiency,high voltage capability and easy fault-tolerant operation.However,the inequality of arm inductance in practice will lead to imbalance between the upper and lower arm voltages,which will induce large ripples in the circulating current and a dc bias on the voltage generated by modular circuits.To compensate for the voltage imbalance,effects of arm duty cycle changes on arm voltages are discussed.An arm voltage balancing control method is proposed:adjust arm duty cycle according to arm voltage deviation in every switching cycle.Simulation and experimental results are presented to validate the theoretical analysis and the proposed control method.
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the National Natural Science Foundation of China under Grant 51777085.
文摘Solid state transformer(SST)can provide more advanced functionalities compared with conventional transformer,and has great potential in smart grid application.Recently,the SST with medium frequency(MF)isolation link and magnetic integration feature has been proposed,which can reduce the system volume and thus increase the power density.However,the magnetic integration also introduces strong coupling between the line frequency(LF)and MF variables,which poses a great challenge on modeling and control issues.This paper proposes a modeling and control method for an SST with magnetic integration and mixed-frequency modulation.A mathematical model based on dual d-q references is deduced,and then a cascaded control system is designed according to the model.Parameters of the controller for the variables at one frequency are properly designed to avoid disturbance from the variables at the other frequency.The simulation and experimental results show good decoupling effect and satisfactory dynamics performance of the proposed control system.
文摘A modular multilevel converter(MMC)integrated with split battery cells(BIMMCs)is proposed for the battery management system(BMS)and motor drive system.In order to reduce the switching losses,the state of charge(SOC)balancing strategy with a reduced switching-frequency(RSF)is proposed in this paper.The proposed RSF algorithm not only reduces the switching losses,but also features good balancing performance both in the unbalanced and balanced initial states.The results are verified by extensive simulations in MATLAB/Simulink surroundings.
文摘This paper presents a new modular multilevel converter (MMC) topology. Compared to conventional multilevel converters, MMC has much lower switching frequency (50 Hz) resulting in lower switching losses, and consequently, lower total losses of the transmission system. The fundamental concept and the applied control scheme are introduced in detail. A modified multilevel fundamental switching modulation scheme adopting the multicarrier pulse width modulation concept is presented. A capacitor voltage balancing technique is proposed. With the established simulation model of the 11-level MMC, the modulation and balancing strategy presented are confirmed by MATLAB/SIMULINK simulations. The multicarrier pulse width modulation converter strategy enhances the fundamental output voltage and reduces total harmonic distortion. This new type of converter is suitable for high-voltage drive systems and power system applications such as high voltage dc (HVDC) transmission, reactive power compensation equipment and so on.
文摘In this paper, a novel voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides the voltages of sub-module capacitors in each arm into several groups and the voltage balancing is based on these groups. The proposed method can save sorting time greatly compared with the conventional method. Simulation results on a MMC based three-phase inverter show validity of the proposed method.
文摘The stop control strategy of modular multilevel converter based HVDC transmission system is proposed. This stop process is divided into stages of energy feedback and energy consumption. The DC voltage controller is coordinated to the used modules per phase when active power is transmitted prior to reactive power, so that the energy is fed back to the AC power grid connected to the converter station which uses the fixed dc voltage controller. In addition, in view of the different forms connected to the grid, specifically when the converter station supplies power for passive network, the passive converter station can take a certain auxiliary trigger strategy to make its maximum energy feedback to the grid. Finally, a simulation system of the MMC-HVDC system is constructed in Matlab/Simulink environment, and simulation results show that the proposed stop strategies are effective.
基金supported by the National Natural Science Foundation of China(52207103)in part by Basic and Appiled Basic Research Foundational of Guangdong Province(2020A1515111117).
文摘The fractional frequency transmission system is an emerging technology for long-distance wind power integration,and the modular multilevel matrix converter(M3C)is the keen equipment.Since the M3C directly connects two ac grids with different frequencies,the external and internal harmonics have complex coupling relationships with a unique dual-fundamental-frequency spectrum,which has not been properly investigated due to a lack of an effective method.To address this issue,a novel harmonic state-space method is proposed to achieve comprehensive modelling of the harmonic dynamics of the M3C.Based on the principle of two-dimensional Fourier transform,the decomposition of the dual-fundamental-frequency harmonics is realized,and the multiplicative coupling between time-domain variables is modelled through double-layer convolution on the frequency domain.Besides,the general expression of the proposed method is provided,which highlights a modularized matrix with easy scalability to meet different truncation requirements.Then,the HSS model of M3C considering the close-loop control is established,based on which a panoramic harmonic coupling relationship between the system-and the low-frequency side is concluded.Finally,the M3C model and harmonic coupling relationship are validated by simulation tests conducted in MATLAB/Simulink environment.
基金supported by Petrofac through the Petrofac Ph.D.Scholarship.
文摘Innovative dynamic models for the DC modular multilevel converter(DC-MMC)in rotating dq frame are presented in this paper,which are specifically designed to enhance converter design and stability analysis.Open-loop and closed-loop models are developed using three dq frames,providing a detailed examination of the impact of 2^(nd)and 3^(rd)harmonic components on the model accuracy.A novel contribution of this paper is the integration of a 2^(nd)harmonic current suppression controller(SHCSC)within the closed-loop model,offering new insights into its effects on system stability.The DC-MMC model is further extended by coupling it with high-voltage direct current(HVDC)cables on each side,forming an interconnected system model that accurately represents a more authentic scenario for future DC grids.The proposed model is rigorously validated against PSCAD benchmark model,confirming their precision and reliability.The interconnected system model is then utilized to analyze the influence of cable length on system stability,demonstrating practical applications.The closed-loop model is subsequently employed for stability assessment of the interconnected system,showcasing its applicability in real-world scenarios.Additionally,a damping controller is designed using participation factor and residue approaches,offering a refined approach to oscillation damping and stability optimization.The effectiveness of the controller is evaluated through eigenvalue analysis,supported by simulation results,underscoring its potential for enhancing system stability.
文摘Modular Multilevel Converters(MMC)have emerged as a key technology for medium-to high-voltage power conversion applications such as HVDC transmission,large-scale renewable integration,and flexible AC transmission systems.Despite their superior performance and modularity,MMCs present complex control challenges due to their multi-level structure,numerous submodules,and circulating currents.This paper comprehensively reviews advanced control strategies developed for MMCs,including fundamental current and voltage balancing controls,sophisticated switching algorithms,and multifunctional approaches addressing harmonic suppression,power factor correction,and fault tolerance.Emphasis is placed on modern methods such as model predictive control,adaptive and robust controls that accommodate system nonlinearities and parameter uncertainties.Implementation aspects,including digital control hardware and the impact of control delays,are also discussed.The paper highlights recent advancements that improve system stability,efficiency,and reliability,thus facilitating MMC deployment in evolving power grids with high renewable penetration and stringent grid code requirements.
基金supported in part by the Natural Sciences and Engineering Research Council(NSERC)of Canada,MITACS Accelerate,Manitoba Hydro,and by the University of Manitoba。
文摘This paper develops a detailed equivalent model for modular multilevel converters with partially-integrated battery energy storage.The proposed model gains computational efficiency in two ways.Firstly,it markedly reduces the large number of nodes in the conventional switching model of the converter,thereby shrinking the size of its admittance matrix.Secondly,it avoids computationally expensive re-triangularization of the admittance matrix during the normal operation of the converter and restricts it only to the rare occasions of converter blocking.Mathematical derivation of the model is carried out using differential equations of the converter.The computational efficiency and accuracy of the proposed model are confirmed by comparison of the results from its implementation in the PSCAD/EMTDC simulator against conventional detailed switching models and measurements from a single-phase scaleddown laboratory setup.This paper also shows a case study wherein a converter with partially-integrated batteries is included in the CIGRE B4-5 benchmark system.
基金supported in part by the National Natural Science Foundation of China(No.52207126)the Natural Science Foundation of Sichuan Province(No.2024NSFSC0869)the Joint Funds of the National Natural Science Foundation of China(No.U22B6006).
文摘Fault current limiting is a critical technology to en sure the safe operation of modular multilevel converter based multi-terminal direct current(MMC-MTDC)grids.This paper proposes a fault severity classification based coordination con trol strategy of fault current limiter(FCL)and MMC for adap tive fault current limiting.The proposed strategy reduces the in vestment in FCL,and keeps the bus voltages of non-faulty lines at reasonable values.Firstly,a rapid fault circuit parameter esti mation(FCPE)method using initial fault current information is proposed.With this method,the fault distance and fault transi tion resistance can be quickly estimated,which are used for a quantitative indication of the fault severity.Subsequently,the coordination control strategy of FCL and MMC is proposed,in which the FCL action is prioritized,while the control of MMC is complementary for current limiting.Based on the proposed strategy,fault severity phase planes(FSPPs)are constructed to assess fault severity and calculate the activation time of FCL and voltage regulation factor of MMC.Therefore,the FCL acti vation and MMC control are matched to the fault severity.The effectiveness and advantages of the proposed strategy are vali dated by the simulations in PSCAD/EMTDC.
文摘The most commonly used modulation for an isolated modular multilevel DC-DC converter(IMMDCC)is quasi-square-wave modulation(QSWM).However,in order to realize soft-switching,QSWM-IMMDCC usually needs to increase the phase-shifting angle or reduce the voltage amplitude ratio,which will not only increase the conduction loss but also require more passive components.This paper proposes an improved quasi-square-wave modulation(IQSWM),which generates ripple current through the non-complementary output of the upper and lower arms.Compared with QSWM-IMMDCC,the ripple current can make IQSWM-IMMDCC realize soft-switching under the conditions of a smaller phase-shifting angle and larger voltage amplitude ratio.The decrease of the phase-shifting angle can improve the power factor of the AC link and reduce the inductance in the AC link,and the increase of the voltage amplitude ratio can increase the fundamental wave voltage of the AC output and reduce the capacitance of the sub-module.In addition,IQSWM can also adjust the ripple current according to changes in output power,thereby broadening the range of soft-switching.Finally,the ripple currents generated by multiple parallel IQSWM-IMMDCCs can offset each other,thereby preventing any impact on the DC output.The simulation results prove the correctness and effectiveness of IQSWM.
基金supported by the National Natural Science Foundation of China(No.52277188)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province(No.22KJB470005).
文摘Energy storage systems support electrical grid stability by enabling strategies to tackle issues,such as power fluctuations,low inertia,and insufficient damping.The present study proposes a battery energy storage system based on a modular multilevel converter with multiplexed submodule arms(M-MMC-BESS)to reduce the number of switching devices while embedding DC short-circuit fault ride-through capability.Compared to the conventional two-stage half-bridge topology,the M-MMC-BESS retains the same number of switching devices but allows uninterrupted operation under DC short-circuit faults.In addition,compared to the two-stage full-bridge topology,the proposed topology reduces the number of switching devices by one-third.The control of the M-MMC-BESS is thoroughly investigated under both normal and DC short-circuit operating conditions.Simulation and experimental results are used to demonstrate the effectiveness of the proposed system and control approach.
基金supported by ANID BECAS/DOCTORADO NACIONAL 21230608supported by the Projects Fondecyt Nr.1221392,Anillo grant ATE230035,and Basal project FB0008(AC3E)supported by Fondecyt Nr.1230596 and Fondequip EQM200234.
文摘This paper proposes a continuous control set model predictive control(CCS-MPC)algorithm of a modular multilevel matrix converter(M3C)for low-frequency AC transmission(LFAC),via which the offshore wind farm(OWF)is integrated.The M3C is operated with a 16.7 Hz frequency at the OWF side and a 50 Hz frequency at the onshore grid side.The balance of the capacitor voltages and the regulation of circulating currents in the M3C are performed using the proposed CCSMPC algorithm,which is based on the online solution of a cost function with constraints.Simulation and experimental work(with a 5 kW M3C prototype)are provided,showing the performance of the LFAC system to operate with symmetrical and asymmetrical voltage dips,active and reactive power steps,and optimal limitation of currents and voltages using constraints.Unlike previous publications,the predictive control system in this paper allows seamless operation under balanced and unbalanced conditions,for instance,during asymmetrical voltage dips.
