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30 May 2025, Volume 23 Issue 3
  

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    Special Issue on Analysis and Control of Power Quality in New Power Systems
  • Editors’ Letter for the Special Issue on Analysis and Control of Power Quality in New Power Systems
    ZHUO Fang, ZHU Mingxing, TU Chunming, GENG Hua
    2025, 23(3): 1-3. https://doi.org/10.13234/j.issn.2095-2805.2025.3.1
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  • Modeling and Stability Analysis of Multiple Grid- connected-converter System Based on Harmonic State Space
    WAN Yuxi, LI Yin, LIN Shunfu
    2025, 23(3): 4-14. https://doi.org/10.13234/j.issn.2095-2805.2025.3.4
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    To address the power quality issues in a multiple grid-connected-converter system (MGCCS) for renewable energy, the series and parallel models of MGCCS are established at first based on the harmonic state space (HSS) method. The HSS models account for high-frequency components during the switching process, with its internal Toeplitz matrix effectively capturing the harmonic coupling within the converters. Based on the series and parallel HSS models of MGCCS, a virtual resistor is introduced to improve the model, and the impact of grid impedance is considered to simulate the multi-converter grid-connected system. In addition, the harmonic stability of this system is investigated by analyzing the eigenvalues of the state matrix. The influences of main circuit and controller parameters on the harmonic instability are analyzed in depth, and the oscillation frequencies in harmonic instability modes are predicted. Simulation results based on MATLAB/Simulink and RT-LAB experimental results validate the accuracy of the improved HSS models and the harmonic stability analysis.
  • Voltage Compensation Control for Dynamic Voltage Restorer Based on Cascaded H-bridge Converter
    TANG Xuqing, MA Junpeng, XIAO Xianyong
    2025, 23(3): 15-24. https://doi.org/10.13234/j.issn.2095-2805.2025.3.15
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    Voltage sag is one of the main power quality problems, and dynamic voltage restorers (DVRs) provide an effective solution. Since the traditional DVRs are unsuitable for medium-voltage applications, a high-voltage direct-connect DVR based on a cascaded H-bridge multilevel converter is introduced. To enhance the response speed and compensation accuracy of the system, a dq-axis decoupling strategy for the AC voltage compensation control of DVR is proposed. Meanwhile, a carrier phase shifted pulse width modulation strategy with voltage offset injection is also employed to balance the DC-side capacitor voltage of the cascaded H-bridge, thus ensuring the safety and stability of the system. Finally, the proposed DVR and the corresponding control algorithm are modeled and simulated by MATLAB/Simulink, demonstrating the effectiveness and feasibility of the approach.
  • Multi-APF Parallel System and Current Sharing Method Based on Integrated Energy and Information Transmission
    SU Minchao, ZOU Jie, WANG Lei, GUO Qin, ZHOU Lei
    2025, 23(3): 25-35. https://doi.org/10.13234/j.issn.2095-2805.2025.3.25
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    Due to the intermittency of distributed generations and frequent fluctuations in non-linear loads in microgrids, significant changes in harmonic energy will occur. Although multiple parallel active power filters (APFs) can be used to effectively mitigate harmonics in microgrids, the parallel operation will result in circulating currents due to uneven compensation currents among the APFs, leading to increased system losses. To address this issue, a current-sharing control method based on the integrated transmission technology for electric energy information is proposed. With the incorporation of information modulation at the power modulation stage of an inverter, the transmission of key information is realized while the converting the electric energy, thereby enabling current-sharing control of the parallel system. Compared with the traditional centralized and master-slave control methods, the proposed method eliminates the need for additional communication equipment and lines, enhancing the system’s reliability, flexibility and scalability. The results of a simulation experiment based on RT-LAB validate the feasibility and effectiveness of the proposed current-sharing control method.
  • Utility Harmonic Impedance Estimation Method Considering Time-varying Characteristics of Background Harmonics
    WANG Xiaoming, ZHENG Hao, ZHAO Wenguang, WEN Yi, ZHU Mingxing, DING Tong
    2025, 23(3): 36-46. https://doi.org/10.13234/j.issn.2095-2805.2025.3.36
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    An accurate estimation of utility harmonic impedance is the key to harmonic source determination. Most of the existing methods are based on the premise that the background harmonics keep constant or fluctuate smoothly. However, the background harmonic voltage or utility harmonic impedance generally exhibits unsmooth fluctuation patterns in the novel power system, and there are even abrupt changes in some time sections, which leads to large calculation errors in the existing methods. To solve this problem, an estimation method for utility harmonic impedance considering the time-varying characteristics of background harmonics is proposed. First, this method identifies multiple abrupt change points of background harmonics by means of the binary sliding T maximum, and the measured harmonic data at a point of common coupling (PCC) is divided into several intervals of continuous unsmooth fluctuation accordingly. Then, with the consideration of the small var- iation of background harmonics between adjacent sampling points, utility harmonic impedance estimation is carried out based on the principle of comprehensive minimum fluctuation within each data interval, and the matrix sparse technique is introduced to reduce the computational time complexity. Finally, simulations and field data are adopted to conduct a comparative analysis, and results indicate that compared with the existing methods, the proposed method can more accurately estimate the utility harmonic impedance and demonstrate a higher computational efficiency.
  • Multi-harmonic Source Tracing Method Based on Multi-band Impedance Comparison
    DING Yi, WANG Yu, HE Zhen, NIAN Heng, ZHANG Junxing
    2025, 23(3): 47-55. https://doi.org/10.13234/j.issn.2095-2805.2025.3.47
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    With the continuous improvement of the degree of electronification in a power system, the proportion of harmonics in the system increases significantly. An accurate tracing of the source of harmonic disturbance is crucial for evaluating the influencing factors for power quality and providing important support for targeted control of harmonics. However, there are challenges in the large-scale harmonic tracing of power grids as follows. The sampling time of harmonic data of each power quality monitoring equipment is not synchronized, resulting in low time-domain accuracy and low effectiveness of the monitoring data. Through the calculation and analysis of the source tracing process, the amplification of errors will affect the quantitative results and source tracing effect. In a multi-harmonic source system, complex in multi-band impedance will affect the accurate traceability of a single disturbance source at a specific frequency. To solve the above problems, a harmonic state estimation method based on the time scale datum of different nodes is used to synchronously screen the monitoring data. With a focus on the complexity in the multi-band impedance characteristics, a multi-harmonic source tracing method based on multi-band impedance comparison at the same node is proposed. Through a comparison of the impedance results in multi-band at the same node, the potential harmonic source nodes can be effectively identified, and the harmonic force contribution of each node is calculated to quantitatively characterize its harmonic contribution. Finally, a simulation example of a multi-harmonic source power system including multiple new energy stations is established, and results fully verify the effectiveness of the proposed theoretical method.
  • Frequency Restoration Control Strategy for Islanded Microgrid with Inaccurate Feeder Impedance Based on Small-AC-signal Injection
    HU Xuekai, MENG Liang, YIN Yilin, LI Lei, WANG Haixu, LEI Wanjun
    2025, 23(3): 56-66. https://doi.org/10.13234/j.issn.2095-2805.2025.3.56
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    With the “Dual-carbon” strategy proposed in China, the microgrid composed of distributed generations has become an effective way to solve the energy crisis and environmental pollution problems. To improve the power quality of a microgrid system, frequency restoration control is usually added to distributed generations to compensate for the frequency deviation caused by changes in load. It is necessary to obtain the information about accurate feeder impedance when calculating the load terminal frequency, so as to reduce the reliance of the system on high-speed communication. However, this is often difficult to be guaranteed in practical engineering, thus leading to the difference of power distribution among distributed generations and eventually deteriorating the frequency stability of the system. To solve these problems, the mechanism of an unstable system caused by the inaccurate feeder impedance is analyzed, and it is pointed out that the calculation error of load terminal frequency is the basic cause of power distribution difference among distributed generations. On this basis, a frequency restoration control strategy based on small-AC-signal injection is proposed. By adding an additional small-AC-signal to the output voltage from each distributed generation, a droop relationship between the injected small-AC-signal frequency and the calculated value of load terminal frequency is established, and the active power of the small signal is used to compensate for the calculated deviation of load terminal frequency caused by the inaccurate feeder impedance, so as to realize the compensation for frequency deviation while maintaining the power sharing of the system. To illustrate the application scope of this control strategy, the differential-mode small-signal model of a typical microgrid system is established, and the design method for related parameters is discussed. Finally, the effectiveness of the proposed method was verified by a hardware-in-the-loop experiment.
  • Harmonic/inter-harmonic Detection Method Based on ISGMD and TLS-ESPRIT
    ZHOU Hang, GUO Cheng
    2025, 23(3): 67-75. https://doi.org/10.13234/j.issn.2095-2805.2025.3.67
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    In response to the problem that the extraction accuracy of existing harmonic detection methods is easily affected by noises, a novel harmonic detection method based on iteration symplectic geometry mode decomposition combined with total least squares and estimation of signal parameters with rotation invariant technique (TLS-ESPRIT) is proposed. First, the initial symplectic geometric components are obtained by constructing a trace matrix of harmonic signals and combining the matrix transformation. Second, based on dynamic time warping, the initial symplectic geometric components with a high similarity are linearly combined, and the residual components are eliminated. Third, the normalized mean absolute error is calculated to obtain the independent harmonic components. Finally, the TLS-ESPRIT algorithm is used to obtain the parameters of different harmonic and inter-harmonic components. Through an analysis of simulation and measured data, the superiority of the proposed method when it is applied in harmonic and inter-harmonic analysis under a noisy environment is verified.
  • Status Quo and Prospects of Researches on Load Equivalent Impedance Parameters in Nonlinear Load Analysis
    ZHANG Yi, KANG Yanyi, ZHENG Zonghua
    2025, 23(3): 76-85. https://doi.org/10.13234/j.issn.2095-2805.2025.3.76
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    With the rapid development of new energy and power electronics technologies, the proportion of nonlinear loads in power systems is increasingly growing, leading to more severe power quality issues in power grid. The identification of load equivalent impedance parameters is one of the important methods for analyzing the characteristics of nonlinear loads. The status quo of researches on the load equivalent impedance parameter technology and its application fields is systematically sorted out, and the research directions and application trends in the future are forecasted. First, the basic principle for load equivalent impedance parameters is elaborated upon. Second, the existing load equivalent impedance parameter identification methods are analyzed, and the accuracy, applicable scope, advantages and disadvantages of different parameter identification methods are pointed out. Third, the applications of load equivalent impedance parameters in harmonic analysis and instantaneous reactive power calculation are reviewed. Finally, further research directions for load equivalent impedance parameters are discussed, and the prospects for extended applications beyond the fields at present are given.
  • Research on Hybrid Active Power Filtering Technology for Low-voltage DC Power Supply System
    LI Jianbiao, LUO Yongju, CHEN Yong, WU Hongyuan, KANG Fangrui, ZHUO Fang
    2025, 23(3): 86-95. https://doi.org/10.13234/j.issn.2095-2805.2025.3.86
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    With the advancement of the construction of photovoltaic, energy storage, DC and flexibility, the problem of harmonics in a low-voltage DC (LVDC) power supply system has received widespread attention. Compared with those of an AC system, the characteristics of a DC system are that the power supply and load are more decentralized, the proportion of power electronic equipment is higher, and the AC-DC coupling effect caused by interface converters is strong. Therefore, the problem of harmonics in the DC system indicates that both the low- and high-frequency harmonic peak-to-peak values may be high, and thus the classic harmonic analysis and control methods for the AC system are not completely applicable. To this end, the main harmonic sources for the LVDC power supply system are analyzed, and the mechanism and characteristics of the DC bus voltage harmonic problem caused by DC sources and load are revealed. Accordingly, a hybrid active power filtering harmonic voltage control technology is proposed for the harmonic sources of a broadband and decentralized DC system, which achieves the control of harmonics in the case of uncertain disturbance location and high- and low-frequency mixing, thus improving the power quality level of the LVDC power supply system. Finally, simulation results prove the effectiveness of the proposed scheme.
  • Research on Wideband Harmonic Resonance Assessment of Distribution Network with Grid-connected Converter
    YANG Shuo, XU Zheheng, TAO Shun, XU Yonghai
    2025, 23(3): 96-105. https://doi.org/10.13234/j.issn.2095-2805.2025.3.96
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    In the context of a high-proportion of new energy integration into the distribution network, the interaction between a grid-connected converter and background disturbances increases the risk of harmonic resonance due to the emission of primary and secondary harmonics over a wide frequency band. Therefore, an indiscriminate risk-domain assessment method considering the severity of secondary harmonics and a temporal harmonic risk assessment method are proposed. First, based on the harmonic amplification factor, the severity indexes of harmonic amplification and secondary harmonics are defined, and the risk of harmonic resonance in all the nodes and branches of the distribution network across the entire frequency band is evaluated through indiscriminate sweep injection. Second, considering the temporal characteristics of actual harmonic sources and taking into account the superposition of primary and secondary harmonics, a risk level matrix containing three dimensions of over-limit probability, over-limit severity and continuous over-limit probability is constructed to quantify the temporal over-voltage and over-current risks of the distribution network. Finally, the feasibility of the proposed method was verified through a test case and an actual engineering case.
  • Offshore Wind Power Grid-connected Power Quality Improvement Technology Based on High-voltage Active Resonance Suppressor
    XU Qunwei, PAN Xing, XIONG Hongtao, HUANG Xiaoming, ZHU Feibai, MA Zhiquan
    2025, 23(3): 106-115. https://doi.org/10.13234/j.issn.2095-2805.2025.3.106
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    To solve the resonance problem in grid-connected offshore wind power delivered by long-distance AC submarine cables, the typical equipment models are established at first, and the resonant mechanism is analyzed by taking into account the capacitance-reactance characteristics of submarine cables. On this basis, a resonance suppression technology for offshore wind power based on high-voltage active resonance suppressor (HARS) is proposed. A two-stage transformation structure consisting of a Buck transformer and a H-bridge cascade valve bank is adopted to realize reliable grid-connection at 220 kV high-voltage level. According to the impedance reshaping theory, a resonant damping control strategy based on the feedback of resonant component of grid-side current is designed, and the feasible region analysis method for the damping coefficient and band-pass center frequency is also given. Finally, the feasibility and effectiveness of the proposed technology are verified by simulations and engineering practice.
  • Mechanism Analysis of DC-side Voltage Dip of PV Inverters After Fault Recovery at Sending End of Large-scale PV Base Transmission via VSC-HVDC
    SHEN Shuhao, ZHONG Qing, FENG Junjie, LI Haifeng, WANG Longjun, WANG Gang
    2025, 23(3): 116-125. https://doi.org/10.13234/j.issn.2095-2805.2025.3.116
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    There are extensive ranges and long electrical distances in the sending-end system of the large-scale photovoltaic (PV) base transmission by VSC-HVDC. A voltage dip will occur on the DC side of PV inverters after the short-circuit fault recovery at the sending-end, which is a new power quality problem the new power system faces. Aimed at this issue, the impact of the balance between output powers from PV arrays and inverters on the DC-side voltage is analyzed at first, and the voltage-power characteristics of PV arrays and the output power characteristics of inverters under different control strategies are mainly taken into consideration. Second, four kinds of operating conditions for inverters are formulated according to the operating point of PV arrays and the control strategies for PV inverters, and the evolution characteristics of DC-side voltage of inverters under each operating condition are also analyzed. It is revealed the mechanism is combined effects of movements of the operation point of PV arrays and the changes of control strategies of the inverter because of the power imbalance during the fault recovery. Finally, simu- lations are performed, and results verify the correctness of the mechanism analysis.
  • Harmonic Emission Mechanism and Suppression Strategy for Three-level Converter in Three-phase-four-wire System: Analysis of Neutral-point Voltage Fluctuations and Switching Dead-time
    LAI Zhenhong, YANG Zebin, YI Hao, MU Xiaobin, LIU Yang, LIU Wenbin
    2025, 23(3): 126-137. https://doi.org/10.13234/j.issn.2095-2805.2025.3.126
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    The neutral-point clamped (NPC) three-level converter is extensively used in low-voltage distribution networks with distributed energy resources. In a three-phase-four-wire system, the DC bus neutral-point (NP) of a three-phase converter is commonly connected to the N-wire, creating a zero-sequence current path in the system. This configuration leads to output voltage distortions caused by DC NP voltage fluctuations and switching dead-time, and further causes harmonic emission from the converter itself. First, the coupling relationship between NP voltage fluctuations and output current is analyzed, laying a foundation for establishing a quantitative model of NP voltage fluctuations. Based on this model, an active filtering circuit control system for DC bus is designed to suppress both the NP voltage fluctuations and the induced harmonics. Then, the influence of switching dead-time under various operating conditions of the three-phase converter is investigated. A quantitative relationship between the switching dead-time and output voltage distortions is derived, guiding the design of a modulation wave compensation strategy for mitigating the harmonic emission caused by switching dead-time. Finally, simulation models and an experimental platform were developed to reproduce the harmonic emission issues of the three-phase converter, and results validated the effectiveness of the proposed scheme.
  • Topological Structure of Multi-functional Active-type Arc Suppression Device Based on Heterogeneous Unit and Its Control Strategy
    LIU Hongwen, QIAN Xinjun, GUO Qi, CHEN Rao, SHI Congxin, HUANG Jisheng
    2025, 23(3): 138-151. https://doi.org/10.13234/j.issn.2095-2805.2025.3.138
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    The high-quality control of a single-phase grounding fault is important for supporting the safe operation of novel distribution network. However, the existing active-type arc suppression devices (AASDs) have some common problems, such as single function and high cost. To address these issues, a topological structure of AASD based on heterogeneous unit (HU-AASD) and its control strategy are proposed. First, the fourth arm is used to provide voltage support for the virtual neutral point of the HU-AASD, and the withstand voltage requirement of three-phase arms are reduced to the phase voltage, thus reducing the cost and volume of AASDs. Second, the capacitive and inductive reactive power compensation capabilities can be provided by the proposed scheme, and the HU-AASD can continuously provide reactive power compensation for the power grid after the single-phase grounding fault occurs, thus providing uninterrupted voltage support for the distribution network. Finally, simulation and experimental results demonstrate the validity and feasibility of the proposed topology and its control strategy.
  • Frequency Support Strategy for Grid-forming Virtual Synchronization PV-storage Grid-connected System
    LIU Yang, LIN Yingming, YU Da, LI Fengneng, HUAN Jiafei, ZHU Honglu
    2025, 23(3): 152-161. https://doi.org/10.13234/j.issn.2095-2805.2025.3.152
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    The accurate assessment of system frequency modulation requirements and the alleviation of contradiction between steady-state output and dynamic regulation of PV-storage grid-connected units are crucial for realizing the rapid frequency support in grid-forming virtual synchronization PV-storage grid-connected systems. First, a model of a grid-forming virtual synchronization PV-storage grid-connected system is built, and the coupling characteristics among multiple control objectives are analyzed. Second, the traditional grid-forming control is improved based on the damping compensation principle to boost the steady-state control accuracy of PV-storage units. On this basis, frequency security early warning and the controller’s dynamic performance constraints are utilized to quantitatively evaluate the grid-forming control parameters, and a frequency support strategy for the grid-forming virtual synchronization PV-storage grid-connected system is proposed. Finally, a simulation system is constructed, and results verify that the PV-storage grid-connected units can swiftly support the system frequency and remarkably enhance the system frequency security under the proposed control strategy.
  • Control Strategy for Enhancing Voltage Quality in Distribution Network by Orderly Charging Based on Equivalent Mapping Theory
    NING Zhihao, WANG Xiaoyuan, ZHU Jiran, XIAO Hui, ZENG Linjun
    2025, 23(3): 162-172. https://doi.org/10.13234/j.issn.2095-2805.2025.3.162
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    The widespread adoption of electric vehicles (EVs) has significantly accelerated the electrical transition of transportation, which brings challenges to distribution network such as “peak-on-peak” demand and deterioration of power quality. Moreover, the power and traffic systems belong to two different operators, so it is difficult to perform centralized optimization. To address these issues, a novel non-iterative coordinated optimization method for power-traffic based on the equivalent mapping theory is proposed. First, a decoupled framework for power-traffic incorporating the power at charging stations is established, and the optimal operation model of distribution network is transformed into a piecewise cost function with boundary charging station power and the corresponding equivalent constraint sets, thereby achieving the decoupled and coordinated optimization of power-traffic systems. Second, by exploiting the intrinsic relationship between boundary cost functions and nodal electricity prices, an optimized charging strategy for EVs which incorporates price signals is put forward, so as to alleviate the overload issues in distribution network. Finally, the effectiveness of the proposed method is validated through a case study, and results also demonstrate that the orderly charging strategy can effectively guide the EV charging behavior and improve the voltage quality.
  • Research on Multi-mode Control Strategy for Hybrid Flexible Interconnection Device in Terms of Power Flow Control and Power Quality Management
    XIONG Liying, YANG Zebin, YI Hao, MU Xiaobin, XU Weiwei, NING Xin
    2025, 23(3): 173-183. https://doi.org/10.13234/j.issn.2095-2805.2025.3.173
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    Hybrid flexible interconnection devices (FIDs) combine the advantages of power electronics technology and electromagnetic interconnection devices in terms of regulation accuracy, overload capacity and economy, which have been favored in engineering applications. Aimed at the problems of power flow control and background harmonics in a hybrid FID under the condition of steady-state interconnection of power grid, as well as the problem of load voltage deviation and harmonic voltage under the condition of power-loss switching, the line power flow and harmonic distribution characteristics under these two operating conditions are analyzed, and the corresponding power flow control and multi-mode power quality management strategies are put forward. In addition, the feasibility of the proposed strategies is verified by simulation results.
  • Power Quality Control Strategy for Microgrid Cluster Based on Ultra-short-term Power Quality Assessment
    SHI Hongtao, SUO Zhongmei, MENG Xinxin, ZHANG Bai, ZHU Jiahao
    2025, 23(3): 184-195. https://doi.org/10.13234/j.issn.2095-2805.2025.3.184
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    To realize the effective control of power quality (PQ) in microgrid cluster (MGC) by means of PQ assessment of MGC and the cooperation with multiple converters, a novel strategy for MGC based on ultra-short-term PQ assessment is proposed. First, an ultra-short-term PQ assessment method is employed to evaluate and locate the PQ problems in MGC in real time. Then, according to the positioning results, a distributed consensus algorithm is utilized to coordinate the control of multiple converters, thus achieving the PQ task allocation and governance. After the completion of governance, the assessment and verification are performed again to ensure the governance effect and further form a closed-loop governance system at the level of MGC. Finally, the results of an example show that compared with the traditional method, the proposed strategy can realize the closed-loop control of PQ problems from the perspectives of identification, assessment and governance at the level of MGC while effectively reducing the harmonic distortion rate, thereby realizing the effective assessment and governance of PQ in MGC.
  • Optimal Regulation Method for Distribution Network Clustering Considering Voltage Governance Potential of Heterogeneous Distributed Photovoltaics
    LAN Zheng, YANG Chunzhi, TAN Renyu, HE Dong, YI Bo, YU Xi
    2025, 23(3): 196-207. https://doi.org/10.13234/j.issn.2095-2805.2025.3.196
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    With the increasing penetration rate of distributed photovoltaics in distribution network, the problems of photovoltaic power backflow and voltage overrun are becoming more and more serious. Meanwhile, the distribution network is faced with different control methods and regulation potentials of photovoltaic, which makes the heterogeneous photovoltaics difficult to coordinate and further affects the regulation and operation of distribution network. Therefore, an optimal regulation method for distribution network clustering (DNC) considering the voltage governance potential of heterogeneous distributed photovoltaics (HDPV) is proposed. First, to solve the problem of node voltage overrun under a scenario of the integration of high-penetration distributed photovoltaics, a DNC partitioning method considering voltage deviation sensitivity is proposed by combining the voltage deviation, power balance and node coupling degree. Second, the active and reactive power regulation characteristics of HDPV are analyzed, and a regulation model in different operation modes is established. Furthermore, based on the synchronous alter- nating direction method of multipliers, an optimal regulation method for DNC considering the voltage governance potential of HDPV is developed with an objective of minimizing the comprehensive operating cost and voltage deviation. Finally, an improved IEEE 33-node distribution network is used as an example to verify the effectiveness of the proposed optimization model, and results show that the proposed strategy realizes an efficient control of HDPV, and it can guarantee an economic operation of distribution network while improving its voltage level.
  • Optimal Configuration Method for Energy Storage Taking into Account Lifetime Losses and Demand Response
    LI Longjie, LI Meng’en, LU Yong, XU Xianfeng, BAI Xinhe, LU Wanqi
    2025, 23(3): 208-219. https://doi.org/10.13234/j.issn.2095-2805.2025.3.208
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    Aimed at the issue of self-healing and coregulation of distributed energy storage in multi-energy distribution networks under fault, three key aspects are studied, i.e., improving the state estimation accuracy of energy storage batteries, fully utilizing the potential of demand-side load response, and reducing the lifetime losses of energy storage and the system’s operation costs. On this basis, an optimal configuration method for energy storage taking into account lifetime losses and demand response is proposed, which can reduce the lifetime losses of energy storage and the system’s operation costs while realizing the adaptive regulation of states of the energy storage system. First, a recalibration step is added to improve the extended Kalman filter algorithm, and the estimator is allowed to bypass ineffective updates in the meantime, so as to ensure a precise state estimation of energy storage batteries. Second, a demand response model based on price elasticity and behavioral correlation is constructed to optimize the load curves through a dual-effect of price signals and incentive fees. Finally, a mixed-integer linear programming model for energy storage configuration is developed to incorporate the costs of battery lifetime losses, and a demand response model is used to adjust load while integrating the incentive fees into the daily operation cost. Based on the real-time, dynamic and high-precision estimation results, the approach adaptively refines parameters such as the battery lifetime losses and the depth of discharge, as well as the lower and upper bounds of state-of-charge constraints. The analysis results of a case study demonstrate that compared with other models, the proposed model can significantly reduce the lifetime losses of energy storage and the system’s daily operation costs.
  • Two-layer Master-slave Game Harmonic Trading Model with PV Inverters Participating in Distribution Networks
    WANG Qing, ZHANG Huaying, LI Jingyi, WANG Ying
    2025, 23(3): 220-227. https://doi.org/10.13234/j.issn.2095-2805.2025.3.220
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    With the access of power electronic equipment to distribution networks, the harmonic problem therein is becoming increasingly serious. Photovoltaic (PV) inverters are topologically homologous with active filters, which have the capability of controllable harmonic management. However, the application of PV inverters for harmonic management involves multiple entities of interest, more independence is granted to PV users in terms of pricing, and there is still a lack of trading models that account for harmonic management. First, the concept of a harmonic management aggregator is proposed, which is involved in harmonic management trading as a third party and thus realizes a unified constraint on the random pricing behaviors of multiple PV user. Second, a two-layer master-slave game harmonic management trading model with the participation of three parties is formulated, in which a price game between the harmonic management aggregator and harmonic source users is realized in the upper layer and a price game between the aggregator and PV users is performed in the lower layer. Finally, the proposed method is verified by an IEEE 13-node system, and simulation results show that the established model has an obvious harmonic management effect and different parties have significant benefits, which can effectively incentivize the three parties to participate in the management.
    • DC-DC Converters
  • Operation Mode Analysis of Wide-input LLC Resonant Converter with Voltage Doubling Rectifier
    XIONG Lan, GAO Yingfei, SONG Jia, LIU Lin
    2025, 23(3): 228-237. https://doi.org/10.13234/j.issn.2095-2805.2025.3.228
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    Resonant converters with a wide input range are much in demand in energy storage and new energy systems. When the voltage gain characteristics of an LLC resonant converter are calculated using the operation mode analysis (OMA) method, it is often assumed in previous studies that the circuit under phase shift control is in discontinuous conduction mode, resulting in significant errors in the gain analysis result of a converter which is in continuous conduction mode. On the basis, an OMA calculation method for an LLC resonant converter with a voltage doubling rectifier is proposed to identify the two modes. First, the criterion for determining whether the converter operates in continuous or discontinuous conduction mode is obtained through the modal analysis. Then, the normalized calculation models of these two modes are derived by OMA, and the calculation results and the criterion are used to verify the actual mode. Finally, a comparison among the calculated, simulated and experimental voltage gain curves under different conditions indicates the effectiveness of the proposed method. This method is more applicable to LLC converters in possible continuous mode, improves the accuracy of the gain analysis and is helpful for parameter design.
  • Research on Carrier Modulation of Three-level Bidirectional DC Converter Based on Neutral Point Shift
    FENG Yangzhou, YANG Xu, ZHANG Haiping, LI Huiyong
    2025, 23(3): 238-244. https://doi.org/10.13234/j.issn.2095-2805.2025.3.238
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    When a three-level bidirectional DC converter is under carrier modulation, the switching between its forward and reverse operations is not smooth and the dynamic response is slow, which will easily cause harmonics in the resonant circuit. To solve these problems, a carrier modulation method for the three-level bidirectional DC converter based on neutral point shift is proposed. The working principle for the bidirectional DC converter is analyzed. Based on the principle of neutral point shift, the phase angle mode of three-phase output voltage from the converter is adjusted. On the basis of constant switching frequency, the neutral point shift voltage with different amplitude modulation ratios is calculated. According to the actual fault state, the shift between adjacent carriers in the same phase unit is rectified, and the carrier phase shift pulse width modulation is used to modulate the carrier of the three-level bidirectional DC converter. Simulation results show that the proposed modulation method can effectively control the output waveform of the three-level bidirectional DC converter. When the converter operates normally, the amplitude modulation ratio is greater than 1.0, the phase voltage is saturated, and the modu- lation signal is overshoot.
  • Design of DC Modular Multilevel Converter for Interconnection of HVDC Networks with Different Line Topologies
    YOU Shihong, ZHOU Jun, CHENG Hua, MENG Zhongli, WANG Meng
    2025, 23(3): 245-256. https://doi.org/10.13234/j.issn.2095-2805.2025.3.245
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    DC-DC converters are key devices for realizing the interconnection of high voltage direct current (HVDC) networks with different voltage levels and line topologies. Owing to their advantages such as increasing the controllability of power grid and enhancing the power flow control, voltage regulation and fault blocking capabilities of power grid, DC-DC converters have become one of the research hotspots with the gradual construction of novel power systems, among which the DC modular multilevel converter (DC-MMC) is an effective and non-isolated method for interconnecting HVDC systems with the same line topology. However, DC systems in practice often have large differences in voltage levels and line topologies. In this paper, a novel control strategy for a flexible DC-MMC is proposed, which can realize the interconnection of HVDC systems with different line topologies, such as bipolar and symmetric monopolar interconnection. First, the characteristics of different line topologies in a HVDC transmission system are introduced in detail. Then, a mathematical model including variable transformation is established for the novel DC-MMC, and a control method based on an average bridge arm model and simplified DC grid is put forward. Finally, the simulation results in MATLAB/Simulink show that the proposed method can guarantee the normal operation of DC-MMC in both the normal and degraded modes.
  • Switched-coupled-inductor Soft-switching Converter for Fuel Cell
    HONG Junzhe, LUO Peng, LIU Mingxin, YANG Yanxia
    2025, 23(3): 257-268. https://doi.org/10.13234/j.issn.2095-2805.2025.3.257
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A soft-switching high step-up converter based on switched-coupled-inductor is proposed to improve its voltage gain and efficiency for the applications of fuel cell. The switched-coupled-inductor and switched capacitor are utilized to achieve a high voltage gain under an appropriate duty cycle, and an active clamp circuit is used to reduce the voltage stress of power switches and recycle the energy of leakage inductor. All the power switches achieve zero voltage switching. In addition, the number of components is less, the power loss is reduced, and the efficiency and power density are improved. The operation principle and steady-state analysis are also introduced in detail. Finally, a 250 W experimental prototype was fabricated to verify the performance. Results show that the measured maximum and full-load efficiencies were 97.4 % and 96.1 %, respectively.
    • DC-AC Inverters
  • Impedance Remodeling Method for Improving Passivity of Grid-connected Inverters
    XU Hailiang, ZHANG Weijie, LIN Hongbin
    2025, 23(3): 269-279. https://doi.org/10.13234/j.issn.2095-2805.2025.3.269
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    As the interface between a new energy power generation system and power grid, inverters play an important role. However, the stable operation of the system may be threatened by the changes in grid impedance in a weak grid environment, interaction between parallel inverters and delay in the control system. Under this background, a novel virtual impedance remodeling strategy based on the passivity theory and traditional proportional voltage feedforward is proposed, which can eliminate the non-passive region below the Nyquist frequency and keep the inverter output impedance phase within [-90°, 90°]. The results of numerical examples show that the proposed scheme can keep a good stability of the inverter parallel system under changes in grid impedance, number of inverters and parameters.
  • Delay Compensation Strategy for Widening Effective Damping Zone of LCL Grid-connected Inverter
    ZHANG Xueyi, ZHANG Dong, LI Shengqing
    2025, 23(3): 280-289. https://doi.org/10.13234/j.issn.2095-2805.2025.3.280
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In an LCL grid-connected inverter system under digital control, the control delay reduces the performance of a capacitive current feedback active damping method for suppressing resonance peaks, i.e., the effective damping zone is only 0-fs/6 (where fs is the sampling frequency), which seriously affects the system stability. Aimed at this problem, a delay compensation strategy is proposed. First, a delay compensation link is added to the forward path to increase the system boundary frequency. Then, the stable conditions for the system after compensation are deduced according to the stability criterion. Finally, the capacitive current feedback coefficient is designed under the new stable conditions. The analysis results show that the proposed strategy can widen the effective damping zone to 0-0.4fs, thereby expanding the selection range of the filter resonant frequency fr, reducing the inverter’s design cost and improving the system’s adaptability to a wide range of grid impedance changes. Simulation and experimental results show that the proposed strategy widens the stable operation zone of the system and improves its poor stability when the resonant frequency fr is equal to or more than fs/6 under the weak grid.
    • AC-DC Converters
  • Fast Algorithm for Space Vector Modulation of VIENNA Rectifier
    JIANG Yuchang, JIANG Yunhao, YUAN Lei, XU Anfei
    2025, 23(3): 290-298. https://doi.org/10.13234/j.issn.2095-2805.2025.3.290
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Since the traditional algorithm for the space vector modulation (SVM) of a VIENNA rectifier is computationally intensive, complicated and difficult to implement digitally, a fast algorithm for implementing the SVM of the VIENNA rectifier is proposed in this paper. This algorithm does not require coordinate transformation, avoids a large number of root square and trigonometric operations, and only requires simple logic judgment and addition and subtraction operations to quickly determine the duty cycle of a three-phase drive signal, which is easy to implement digitally and saves the time resources of DSP. In addition, a neutral point voltage control strategy is redesigned accordingly. Finally, the effectiveness of the proposed fast algorithm was verified by MATLAB simulations and experiments conducted on a hardware platform.
    • Modeling and Control
  • Reduced-order Modeling Method for Grid-connected DFIG System Based on Singular Perturbation Theory
    XU Hailiang, CHEN Xiangyu, WU Han
    2025, 23(3): 299-308. https://doi.org/10.13234/j.issn.2095-2805.2025.3.299
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The detailed model of a grid-connected doubly-fed induction generator (DFIG) system has character- ristics such as a high order and nonlinearity, which brings great difficulties to system stability analysis and fault ride-through control. Although there have been many studies on the dimensionality reduction method for grid-connected DFIG system model, the number of model dimension is still high. A reduced-order modeling method based on the singular perturbation theory is proposed. First, the 12th-order detailed model of grid-connected DFIG system under weak grid is established, and its state space model is obtained by linearization. Then, based on the singular perturbation reduced-order theory and participation factor analysis, the state variables of the state space model are divided into multiple time scales, so as to separate the speed variables and deduce the 4th-order model of the system. A comparison of eigenvalues before and after the order reduction shows that the 4th-order model can well reflect the dominant dynamic characteristics of the full-order model while accurately reflecting the stability of grid-connected wind turbines under weak grid. Simulation and experimental results verify the accuracy of the reduced-order method as well as the effectiveness of the reduced-order model in stability analysis.
    • Renewable Energy System
  • Current-voltage Measurement Methods for Solar Cells and Their Applications: A Review
    YAN Youkang, XIAO Wenbo, ZHOU Heng, LI Ao, SUN Xueqin, WU Huaming
    2025, 23(3): 309-317. https://doi.org/10.13234/j.issn.2095-2805.2025.3.309
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The current-voltage (I-V) characteristics of solar cells are an important means to accurately evaluate their performance and diagnose their faults. In this context, five kinds of I-V measurement methods for solar cells (e.g., variable resistance load method, electronic load method, DC-DC converter load method, four-quadrant power supply method and capacitive load method) proposed in recent years are systematically summarized, and their advantages and disadvantages are pointed out. Then, the applications of these I-V measurement methods in extracting the cell parameters and diagnosing the aging of cells and components, partial shading, dust accumulation and short-circuit faults are analyzed. Finally, the development trend of I-V measurement methods for solar cells in the future is prospected, and it is predicted that the DC-DC converter load method and capacitive load method will be the mainstream methods for measuring the current-voltage characteristics.
    • Power System
  • Restoration Method for Limited Risk Power Supply in Distribution System Based on Cloud-edge Collaboration with User-side Microgrid Group
    SHI Zhixiong, ZHANG Zhiquan, LI Zhenkun, YANG Xiu, LIU Jinsong
    2025, 23(3): 318-329. https://doi.org/10.13234/j.issn.2095-2805.2025.3.318
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    With the steady advancement of the Dual-carbon goal in China, more and more user-side microgrids which mainly include renewable energy sources are being connected to the distribution system, which makes the operating modes and methods of distribution system change greatly. In particular, when a distribution system failure occurs, how to efficiently use these microgrids to provide active power support for the distribution system will be one of the key factors that promote the regional autonomy capability and the safe and reliable operation level of a novel distribution system. However, the existing distribution automation level cannot meet the demand of massive user-side grid-connected microgrids which participate in the active power support in real time. In addition, the uncertainties in renewable energy sources and loads in microgrids pose a challenge to the power supply restoration in the distribution system. Based on the emergence of cloud-edge collaboration architecture and taking into account the advantage of edge computing, a limited risk power supply restoration method considering uncertainties in renewable energy sources and loads in microgrid group is proposed in this paper, in which the risk is modeled and characterized by conditional value-at-risk. First, the power supply restoration architecture of distribution system with microgrid group based on the cloud-edge collaboration technology is put forward, and a support power model of microgrid is established. Second, with the goal of minimizing the cost of central cloud power supply restoration and maximizing the profit of edge cloud microgrid operator, an optimization model of power supply restoration is established, in which each edge cloud microgrid operator can make power supply restoration decisions independently, and the central cloud makes overall arrangements to ensure that the risk constraints on the whole system are satisfied. Finally, through simulation analysis, results show that the proposed method can effectively restore power at a smaller risk index while maximally reducing the power supply restoration cost, and it can well improve the profit of microgrid operators. Moreover, it is also proved that the cloud-edge collaboration technology can improve the flexibility of power supply restoration and effectively reduce the computational burden.
  • Smooth Switching Control of Microgrid Modes Based on Improved Linear Quadratic Regulator
    ZHU Chaoqun, SHEN Jie, LI Jie, ZHANG Xiaoming, MA Jun
    2025, 23(3): 330-342. https://doi.org/10.13234/j.issn.2095-2805.2025.3.330
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    With more and more microgrids (MGs) connected to power system, their operation control technology has become one of the key technologies to improve the utilization of renewable energy sources (RESs). However, when an MG switches between grid-connected and islanding operation modes, problems such as large voltage and frequency fluctuations will occur due to uncertainties in RESs output and the inconsistency of voltage, frequency and phase angle in the two operation modes. On this basis, a smooth switching control method of MG modes based on linear quadratic regulator (LQR) is proposed to reduce the drastic fluctuations of MG-related parameters during the mode switching. The proposed method uses the traditional LQR method and the state feedback theory to establish a smooth regulation model. Then, a smooth LQR based on a 2-DOF structure and its parameter selection principle are designed to minimize the transient changes in MG-related parameters during the mode switching. Finally, the simulation analysis and experimental results validated the effectiveness and superiority of the proposed method. Compared with other methods, the novel method can effectively reduce the overshoot percentage of MG-related parameters by about 22% and shorten the time of MG voltage and frequency oscillations by about 13%. In addition, it is easy to implement, and it has good compatibility with the common double-loop PI control.
    • Electric Machine System and Control
  • Dual-model-based Recursive Least Squares Online Identification of Electrical Parameters of Permanent Magnet Synchronous Linear Motor
    BAO Mingkun, ZHOU Yangzhong
    2025, 23(3): 343-353. https://doi.org/10.13234/j.issn.2095-2805.2025.3.343
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To realize a high-precision online identification of multiple electrical parameters of a permanent magnet synchronous linear motor (PMSLM), a dual-model-based recursive least squares online identification algorithm for electrical parameters is proposed in this paper. First, according to the dq-axis voltage equation of the motor, the first model for identifying the stator resistance and permanent magnet flux linkage and the second model for identifying the q-axis inductance and d-axis inductance are established, respectively, and the two identification models are combined cyclically. Second, based on the dual-model structure, the recursive least squares algorithm is used to realize the online identification of electrical parameters, and a piecewise variable forgetting factor with saturation characteristics is proposed for the characteristics of a large number of dynamic processes during the operation of PMSLM. Meanwhile, the error voltage caused by the power switch non-ideal factor is compensated, which further improves the identification accuracy. Finally, simulation and experimental results prove the effectiveness of the identification algorithm, indicating that it has advantages such as a fast convergence speed, a high accuracy of identification results, and applicability under multiple working conditions.
    • Battery and Energy Storage
  • Review of Analysis and Improvement Trend of New Energy Vehicle Power Battery Safety Issues
    SHU Junhao, WU Xiaohua, YANG Jialuo, XU Xin
    2025, 23(3): 354-362. https://doi.org/10.13234/j.issn.2095-2805.2025.3.354
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    New energy vehicles are the main direction for the transformation and development of automobile industry in China, and their safety issues have also attracted the attention from the whole society. To study the safety issues of new energy vehicle power battery, statistics of new energy vehicle accidents which have been publicly disclosed over the past six years are collected in this paper, and the corresponding vehicle models and fire causes are analyzed. The mechanisms of safety accidents such as battery overcharge, overdischarge, internal and external short-circuit faults, extrusion and collision, and thermal runaway are described. The characteristic parameters of battery thermal runaway are summarized. Based on the operating data, the variation in the characteristic parameters of one accident car when it was on fire is analyzed. Finally, some solutions to the existing issues of new energy vehicles are given, and the battery models and intelligent algorithms which are established on the basis of big data are introduced in detail, providing a basis for power battery fault diagnosis in the future.
  • State-of-charge Estimation Based on BP-Multi-timescale UKF Optimization Algorithm
    BAI Junqi, XIAN Yanhua
    2025, 23(3): 363-372. https://doi.org/10.13234/j.issn.2095-2805.2025.3.363
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Aimed at the problem that the state-of-charge(SOC) of batteries estimated by a combination algorithm is not ideal when there exits deviation from the initial value, a BP-multi-timescale unscented Kalman filter(UKF) optimization algorithm is proposed in this paper, which applies the multi-timescale theory to the combination algorithm. First, the multi-timescale UKF is used to preliminarily estimate the SOC value. Then, a BP model is constructed to train the data generated by the filtering algorithm, and the self-learning and adaptive capability of the BP algorithm is used to compensate and further reduce the error. The multi-timescale extended Kalman filter(EKF) modeling can not only reduce the SOC estimation error caused by changes in parameters, but also provide reliable data for error compensation, thus improving the model’s generalization capability and reducing the data dependence by the data-driven part. Simulation results show that the proposed algorithm depends on less data, and it outperforms other algorithms in terms of estimation accuracy, generalization capability and robustness. The root mean square error and mean absolute error are less than 1%, and the maximum absolute error is about 1%.
Volume 23 Issue 3
30 May 2025
Supervised by:
China Association for Science and Technology
Sponsored by:
China Power Supply Society
National Ocean Technology Center
Edited by: Editorial Department of JOURNAL OF POWER SUPPLY
Distribution in China: Local Post Offices or Online subscription
Editor-in-Chief: Jiaxin Han
Acting Editor-in-Chief: Xinbo Ruan
Co-Editor-in-Chief: Xiong Du and Wu Chen
Editorial Manager: Guozhen Chen
CN: 12-1420/TM
ISSN: 2095-2805
Postal Code in China: 6-273
International Postal Code: BM8665
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