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Yandong Chen
College of Electrical and Information Engineering, Hunan University, Changsha, China

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Journal article
Published: 28 July 2021 in IEEE Transactions on Industrial Electronics
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When the control parameters and operating conditions remain unchanged, it is usually believed that the admittance characteristic of grid-connected inverter is time-invariant. However, considering the effect of frequency-coupling, an abnormal phenomenon is observed in the admittance measurement of the grid-connected inverter: the phase of the off-diagonal elements Y12 and Y21 in the admittance matrix is always changed with time, which presents a time-varying admittance characteristic. To explore this phenomenon, the theoretical analyses based on the traditional frequency-coupling admittance measurement method are made. Because the initial phase of the signal cannot be obtained from FFT in experiments and the disturbance frequency and coupling frequency are different, the phase difference between the two frequency components changes with time. However, the influence is not considered in the traditional frequency-coupling admittance measurement method, which makes the measurement results exhibit the confusing time-varying characteristic. The phenomenon is defined as pseudo-time-varying admittance characteristic in this letter. To accurately measure the admittance characteristic of the grid-connected inverter, a frequency-coupling admittance measurement method based on phase correction is proposed, which corrects the phase of disturbance frequency components and coupling frequency components. Finally, the effectiveness of the proposed measurement method is verified by experiments.

ACS Style

Zhiwei Xie; Wenhua Wu; Yandong Chen; Josep M. Guerrero. Pseudo-Time-Varying Admittance Characteristic of Grid-Connected Inverter and Its Corrected Admittance Measurement Method. IEEE Transactions on Industrial Electronics 2021, PP, 1 -1.

AMA Style

Zhiwei Xie, Wenhua Wu, Yandong Chen, Josep M. Guerrero. Pseudo-Time-Varying Admittance Characteristic of Grid-Connected Inverter and Its Corrected Admittance Measurement Method. IEEE Transactions on Industrial Electronics. 2021; PP (99):1-1.

Chicago/Turabian Style

Zhiwei Xie; Wenhua Wu; Yandong Chen; Josep M. Guerrero. 2021. "Pseudo-Time-Varying Admittance Characteristic of Grid-Connected Inverter and Its Corrected Admittance Measurement Method." IEEE Transactions on Industrial Electronics PP, no. 99: 1-1.

Journal article
Published: 29 June 2021 in IEEE Access
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This paper intends to comparatively study the stabilities of grid-connected inverters with three closely related controllers: quasi-proportional resonance (quasi-PR), proportional integral (PI), and proportional resonance (PR) under the weak grid. Firstly, considering the influence of frequency coupling characteristic, a frequency coupling admittance model of quasi-PR controlled inverter is established. Then, the admittance characteristics of the quasi-PR, PI and PR controlled inverters are compared. Admittance characteristics of the PI and PR controlled inverters are similar while the quasi-PR controlled inverter is quite different: the amplitude of the quasi-PR controlled inverter is larger than that of the PI controlled inverter and the phase difference between the two inverters is obvious in the mid-high frequency areas, which are mainly caused by the resonance bandwidth of the quasi-PR controller. Furthermore, the stabilities of the quasi-PR, PI and PR controlled inverters are analyzed. The stabilities of the PI and PR controlled inverters are similar but the quasi-PR controlled inverter is more sensitive to weak grid and high inverter output power. To achieve the same system stability, the voltage outer-loop bandwidth of the quasi-PR controlled inverter should be designed narrower than that of the PI and PR controlled inverters. Finally, experiments verify the correctness of the analyses.

ACS Style

Zhiwei Xie; Yandong Chen; Wenhua Wu; Yichao Wang; Wenlan Gong; Josep M. Guerrero. Frequency Coupling Admittance Modeling of Quasi-PR Controlled Inverter and its Stability Comparative Analysis Under the Weak Grid. IEEE Access 2021, PP, 1 -1.

AMA Style

Zhiwei Xie, Yandong Chen, Wenhua Wu, Yichao Wang, Wenlan Gong, Josep M. Guerrero. Frequency Coupling Admittance Modeling of Quasi-PR Controlled Inverter and its Stability Comparative Analysis Under the Weak Grid. IEEE Access. 2021; PP (99):1-1.

Chicago/Turabian Style

Zhiwei Xie; Yandong Chen; Wenhua Wu; Yichao Wang; Wenlan Gong; Josep M. Guerrero. 2021. "Frequency Coupling Admittance Modeling of Quasi-PR Controlled Inverter and its Stability Comparative Analysis Under the Weak Grid." IEEE Access PP, no. 99: 1-1.

Journal article
Published: 25 May 2021 in IEEE Access
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LLC resonant DC-DC converter has been widely used in high power density and high efficiency applications. Pulse frequency modulation (PFM) is commonly applied due to its wide soft-switching range. In some special cases, phase shift modulation (PSM) is applied to widen voltage regulation range, improve light-load efficiency, or implement a soft start-up process. Because LLC is with 2 control degrees of freedom (2DOFs), switching frequency and duty ratio, a unified analysis and optimization for LLC with 2DOFs is desired. This paper makes an effort to present a unified time domain operation stage trajectories (OSTs) analysis of LLC. On this basis, a unified numerical optimization method is proposed with arbitrarily designed optimization objectives. With the proposed optimization method, the optimized LLC with 2DOFs is with better performance compared to conventional PFM and PSM, which is verified by the experimental results.

ACS Style

Ziheng Xiao; Zhixing He; Yong Ning; Hongliang Wang; An Luo; Yandong Chen; Junling Chen. Optimization of LLC Resonant Converter With Two Degrees of Freedom Based on Operation Stage Trajectory Analysis. IEEE Access 2021, 9, 79629 -79642.

AMA Style

Ziheng Xiao, Zhixing He, Yong Ning, Hongliang Wang, An Luo, Yandong Chen, Junling Chen. Optimization of LLC Resonant Converter With Two Degrees of Freedom Based on Operation Stage Trajectory Analysis. IEEE Access. 2021; 9 (99):79629-79642.

Chicago/Turabian Style

Ziheng Xiao; Zhixing He; Yong Ning; Hongliang Wang; An Luo; Yandong Chen; Junling Chen. 2021. "Optimization of LLC Resonant Converter With Two Degrees of Freedom Based on Operation Stage Trajectory Analysis." IEEE Access 9, no. 99: 79629-79642.

Journal article
Published: 14 May 2021 in Energies
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In the series-compensated grid-connected system (SCGCS), there is an impedance interaction between the inverter impedance and the grid impedance that is prone to cause resonance in the SCGCS. In this paper, firstly, considering the effects of the phase-locked loop (PLL), current-loop, and frequency coupling, the broadband impedance model of the SCGCS is established. The stability of the SCGCS is analyzed by the impedance-based Nyquist stability criterion. It is found from the stability analysis that the impedance interaction between the inverter impedance and the grid impedance is the leading cause of the resonance. An impedance reshaping based resonance suppression method is proposed to suppress the resonance. The phase characteristics of the inverter equivalent output impedance are reshaped from the perspective of impedance. The phase margin at the intersection frequency of the inverter impedance and the grid impedance is improved. The proposed resonance suppression approach mainly consists of reshaping the current loop impedance and the novel phase-locked loop impedance. Finally, simulations and experiments are used to verify the feasibility of the resonance analysis and the effectiveness of the proposed control strategy.

ACS Style

Haining Wang; Yandong Chen; Wenhua Wu; Shuhan Liao; Zili Wang; Gaoxiang Li; Zhiwei Xie; Jian Guo. Impedance Reshaping Control Strategy for Improving Resonance Suppression Performance of a Series-Compensated Grid-Connected System. Energies 2021, 14, 2844 .

AMA Style

Haining Wang, Yandong Chen, Wenhua Wu, Shuhan Liao, Zili Wang, Gaoxiang Li, Zhiwei Xie, Jian Guo. Impedance Reshaping Control Strategy for Improving Resonance Suppression Performance of a Series-Compensated Grid-Connected System. Energies. 2021; 14 (10):2844.

Chicago/Turabian Style

Haining Wang; Yandong Chen; Wenhua Wu; Shuhan Liao; Zili Wang; Gaoxiang Li; Zhiwei Xie; Jian Guo. 2021. "Impedance Reshaping Control Strategy for Improving Resonance Suppression Performance of a Series-Compensated Grid-Connected System." Energies 14, no. 10: 2844.

Journal article
Published: 05 May 2021 in IEEE Transactions on Industrial Electronics
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Virtual Synchronous Machines (VSMs)-based high voltage DC (HVDC) systems enhance the inertia of the power system. However, the dynamic interactions between the VSM-based rectifier station, the inverter station, and the grid could induce the system oscillation, which has been investigated in this paper. At first, the hybrid AC/DC impedance models of the VSMs considering the coupling between the AC and DC dynamics are proposed. Then, the relationships between the DC impedance, dq-frame impedance, and the hybrid AC/DC impedance are presented. It is found that the DC impedance of the VSM-based inverter station and the d-d channel impedance of the dq-frame impedance of the rectifier station behave as negative resistors in the low-frequency range. Moreover, a five-dimension impedance stability criterion based on the hybrid AC/DC impedance and generalized inverse Nyquist criterion is proposed to assess the system stability. The analysis results show that the low-frequency oscillation occurs when the grid SCR of the rectifier station is small. Finally, the simulation and experimental results verify the impedance models and the stability criterion.

ACS Style

Jian Guo; Yandong Chen; Shuhan Liao; Wenhua Wu; Xiangyu Wang; Josep M. Guerrero. Low-Frequency Oscillation Analysis of VSMs-Based VSC-HVDC Systems Based on the Five-Dimension Impedance Stability Criterion. IEEE Transactions on Industrial Electronics 2021, PP, 1 -1.

AMA Style

Jian Guo, Yandong Chen, Shuhan Liao, Wenhua Wu, Xiangyu Wang, Josep M. Guerrero. Low-Frequency Oscillation Analysis of VSMs-Based VSC-HVDC Systems Based on the Five-Dimension Impedance Stability Criterion. IEEE Transactions on Industrial Electronics. 2021; PP (99):1-1.

Chicago/Turabian Style

Jian Guo; Yandong Chen; Shuhan Liao; Wenhua Wu; Xiangyu Wang; Josep M. Guerrero. 2021. "Low-Frequency Oscillation Analysis of VSMs-Based VSC-HVDC Systems Based on the Five-Dimension Impedance Stability Criterion." IEEE Transactions on Industrial Electronics PP, no. 99: 1-1.

Journal article
Published: 03 May 2021 in IEEE Transactions on Industrial Electronics
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Source-side virtual synchronous machines (VSG) and load-side virtual synchronous machines (LVSM) are gradually utilized together in the microgrid to provide virtual inertia and damping. However, instability occurs in the islanded microgrid system due to the interaction dynamics between the VSG and the LVSM, which has been investigated in this paper. At first, the dq-frame impedance models of the VSG and the LVSM are established and compared. It is revealed that the d-d channel impedance of LVSM behaves the negative resistor with a V-type magnitude in the low-frequency range, which easily interacts with the d-d channel impedance of the VSG and leads to instability of the system. Thus, the inductor current feedforward control and the additional voltage feedback control are proposed for the VSG to reshape its impedance. It diminishes the impedance magnitude and generates the active impedance of the VSG. In this way, the low-frequency interaction between the VSG and the LVSM can be mitigated. Besides, the proposed control preserves the dynamic performance of the system. Finally, simulations and experiments verify the effectiveness of stability analyses and the proposed suppression method.

ACS Style

Jian Guo; Yandong Chen; Shuhan Liao; Wenhua Wu; Leming Zhou; Zhiwei Xie; Xiangyu Wang. Analysis and Mitigation of Low-Frequency Interactions Between the Source and Load Virtual Synchronous Machine in an Islanded Microgrid. IEEE Transactions on Industrial Electronics 2021, PP, 1 -1.

AMA Style

Jian Guo, Yandong Chen, Shuhan Liao, Wenhua Wu, Leming Zhou, Zhiwei Xie, Xiangyu Wang. Analysis and Mitigation of Low-Frequency Interactions Between the Source and Load Virtual Synchronous Machine in an Islanded Microgrid. IEEE Transactions on Industrial Electronics. 2021; PP (99):1-1.

Chicago/Turabian Style

Jian Guo; Yandong Chen; Shuhan Liao; Wenhua Wu; Leming Zhou; Zhiwei Xie; Xiangyu Wang. 2021. "Analysis and Mitigation of Low-Frequency Interactions Between the Source and Load Virtual Synchronous Machine in an Islanded Microgrid." IEEE Transactions on Industrial Electronics PP, no. 99: 1-1.

Journal article
Published: 31 March 2021 in IEEE Transactions on Power Electronics
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In recent years, the virtual synchronous generator (VSG) concept has been widely studied to integrate renewable energy sources. However, instability occurs due to the implementation of the dc-link voltage controllers under the weak grid, and its mechanism remains unclear, which is investigated in this paper. At first, the wideband dq-frame impedance models of the VSGs with the dc-link voltage controllers for two cases are established. Then, the stability analyses of the VSGs are compared based on these impedance models. It is revealed that the interaction dynamics between the dc-link voltage loop and the active loop lead to the negative resistor behavior of the q-q channel impedances for both VSGs, which induces the emerging oscillations of the system in a weak grid. Besides, as a useful design guideline, the parameter design of the VSGs is proposed to enhance the system stability. Finally, experimental results obtained from a 100kW prototype system show good agreement with simulated results, validating the impedance models and theoretical analysis.

ACS Style

Jian Guo; Yandong Chen; Lei Wang; Wenhua Wu; Xiangyu Wang; Zhikang Shuai; Josep M Guerrero. Impedance Analysis and Stabilization of Virtual Synchronous Generators With Different DC-Link Voltage Controllers Under Weak Grid. IEEE Transactions on Power Electronics 2021, 36, 11397 -11408.

AMA Style

Jian Guo, Yandong Chen, Lei Wang, Wenhua Wu, Xiangyu Wang, Zhikang Shuai, Josep M Guerrero. Impedance Analysis and Stabilization of Virtual Synchronous Generators With Different DC-Link Voltage Controllers Under Weak Grid. IEEE Transactions on Power Electronics. 2021; 36 (10):11397-11408.

Chicago/Turabian Style

Jian Guo; Yandong Chen; Lei Wang; Wenhua Wu; Xiangyu Wang; Zhikang Shuai; Josep M Guerrero. 2021. "Impedance Analysis and Stabilization of Virtual Synchronous Generators With Different DC-Link Voltage Controllers Under Weak Grid." IEEE Transactions on Power Electronics 36, no. 10: 11397-11408.

Journal article
Published: 17 March 2021 in IEEE Transactions on Power Systems
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Due to impedance interaction, the sub-synchronous resonance (SSR) issue of the renewable energy generation (REG) system connected to weak grid has recently become prominent. Firstly, the mechanism and characteristics of the SSR occurring in the REG system under weak grid are analyzed based on the impedance method. With the decline of grid stiffness, the REG system can easily cause SSR owing to the impedance interaction between the inductive grid impedance and the capacitive REG system impedance in the low frequency range. To suppress this SSR, an inertia phase locked loop (IPLL) is proposed, which can optimize the impedance of the REG system in the low frequency range. According to the impedance based SSR analysis, the REG system with the proposed IPLL can hardly cause SSR under weak grid. Moreover, the mechanism, characteristics and design method of the proposed IPLL is introduced in detail. By using the proposed IPLL, the SSR issue of the REG system under weak grid can be effectively solved. Finally, the theoretical analysis and the proposed mitigation method of SSR are validated with the simulation and experimental study

ACS Style

Gaoxiang Li; Yandong Chen; An Luo; Yichao Wang. An Inertia Phase Locked Loop for Suppressing Sub-Synchronous Resonance of Renewable Energy Generation System Under Weak Grid. IEEE Transactions on Power Systems 2021, 36, 4621 -4631.

AMA Style

Gaoxiang Li, Yandong Chen, An Luo, Yichao Wang. An Inertia Phase Locked Loop for Suppressing Sub-Synchronous Resonance of Renewable Energy Generation System Under Weak Grid. IEEE Transactions on Power Systems. 2021; 36 (5):4621-4631.

Chicago/Turabian Style

Gaoxiang Li; Yandong Chen; An Luo; Yichao Wang. 2021. "An Inertia Phase Locked Loop for Suppressing Sub-Synchronous Resonance of Renewable Energy Generation System Under Weak Grid." IEEE Transactions on Power Systems 36, no. 5: 4621-4631.

Journal article
Published: 21 December 2020 in IEEE Transactions on Industrial Electronics
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It tends to cause system oscillation when the inverter with a phase-locked loop based on proportional integral controller (PI-PLL) is connected to the weak grid. To improve the oscillation suppression ability of the grid-connected inverter, a linear active disturbance rejection controller is applied to PLL (LADRC-PLL). Considering the influence of linear extended state observer, voltage outer-loop, current inner-loop and frequency coupling, the admittance model of the grid-connected inverter with LADRC-PLL is established. Based on the established admittance model and the generalized Nyquist criterion, the system stabilities of the grid-connected inverters with LADRC-PLL and PI-PLL are compared. The comparison results indicate that the grid-connected inverter with LADRC-PLL has better adaptability to the weak grid and shows a certain ability to suppress the sub- and super-synchronous oscillation. Then, the influence of the control parameters of LADRC-PLL on the system stability is studied. It is found that the system keeps stable when the control parameter of LADRC-PLL is changed in a relatively wide range, which indicates LADRC-PLL has good robustness. Furthermore, the dynamic performances of the grid-connected inverters with LADRC-PLL and PI-PLL are analyzed. It is revealed that the grid-connected inverter with LADRC-PLL has better dynamic performance. Finally, the correctness of the analysis is verified by experiments.

ACS Style

Zhiwei Xie; Yandong Chen; Wenhua Wu; Wenlan Gong; Leming Zhou; Xiaoping Zhou; Josep M. Guerrero. Admittance Modeling and Stability Analysis of Grid-Connected Inverter with LADRC-PLL. IEEE Transactions on Industrial Electronics 2020, PP, 1 -1.

AMA Style

Zhiwei Xie, Yandong Chen, Wenhua Wu, Wenlan Gong, Leming Zhou, Xiaoping Zhou, Josep M. Guerrero. Admittance Modeling and Stability Analysis of Grid-Connected Inverter with LADRC-PLL. IEEE Transactions on Industrial Electronics. 2020; PP (99):1-1.

Chicago/Turabian Style

Zhiwei Xie; Yandong Chen; Wenhua Wu; Wenlan Gong; Leming Zhou; Xiaoping Zhou; Josep M. Guerrero. 2020. "Admittance Modeling and Stability Analysis of Grid-Connected Inverter with LADRC-PLL." IEEE Transactions on Industrial Electronics PP, no. 99: 1-1.

Journal article
Published: 09 October 2020 in Applied Sciences
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This article proposes a topology of the secondary reconfigurable inverter and the corresponding fault-tolerant control strategy. When the secondary reconfigurable inverter is operating normally, its topology structure is the TPSS circuit. When the power semiconductor devices in the inverter are faulty, the inverter circuit needs to be reconfigured. After removing the faulty power semiconductor devices, the remaining power semiconductor devices and the DC side powers are reconstructed as the TPFS structure to keep the system running normally. This article also proposes a switch-pulse-resetting algorithm. This paper adopts the control strategy connecting the constant-voltage, constant-frequency control method with the switch pulse resetting algorithm. It need not change the control algorithm when the proposed reconfigurable inverter is transformed from the normal running state into the faulty running state. The inverter dependability is greatly improved. Finally, the feasibility and effectiveness of the proposed second reconfigurable inverter topology and control strategy are verified by simulation and experiment.

ACS Style

Yan Li; Peng Xiang; Yandong Chen. A Secondary Reconfigurable Inverter and Its Control Strategy. Applied Sciences 2020, 10, 7021 .

AMA Style

Yan Li, Peng Xiang, Yandong Chen. A Secondary Reconfigurable Inverter and Its Control Strategy. Applied Sciences. 2020; 10 (20):7021.

Chicago/Turabian Style

Yan Li; Peng Xiang; Yandong Chen. 2020. "A Secondary Reconfigurable Inverter and Its Control Strategy." Applied Sciences 10, no. 20: 7021.

Journal article
Published: 30 September 2020 in IEEE Journal of Emerging and Selected Topics in Power Electronics
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For the wind farm connected to line-commutated converter based high-voltage direct-current (LCC HVDC) and weak grid at sending end, sub-synchronous resonance (SSR) is prone to occur due to the impedance interactions among wind farm, weak grid and LCC HVDC. Firstly, the mechanism and characteristics of this SSR are analyzed based on impedance method. With the increase of the output power for wind farm or the decrease of the transmission power for LCC HVDC, the wind farm tends to cause SSR. Moreover, with the decline of the grid stiffness at sending end, the studied system easily causes SSR. Then, a wideband harmonic voltage feedforward control strategy of static synchronous compensator (STATCOM) is proposed to suppress this SSR. For the proposed damping controller of SSR, a constant voltage amplitude based harmonic extraction method is designed without using filter. The harmonic extraction error of the proposed strategy is a constant |Vn-Vr|, which is induced by the difference between the constant voltage amplitude Vn and actual voltage amplitude Vr. By the theoretical analysis and simulation, this constant error |Vn-Vr| can be automatically counteracted by the PI controller of STATCOM. Finally, experimental results verify the validity of the proposed strategy.

ACS Style

Gaoxiang Li; Yandong Chen; An Luo; Xuan Liu. Wideband Harmonic Voltage Feedforward Control Strategy of STATCOM for Mitigating Subsynchronous Resonance in Wind Farm Connected to Weak Grid and LCC HVDC. IEEE Journal of Emerging and Selected Topics in Power Electronics 2020, 9, 4546 -4557.

AMA Style

Gaoxiang Li, Yandong Chen, An Luo, Xuan Liu. Wideband Harmonic Voltage Feedforward Control Strategy of STATCOM for Mitigating Subsynchronous Resonance in Wind Farm Connected to Weak Grid and LCC HVDC. IEEE Journal of Emerging and Selected Topics in Power Electronics. 2020; 9 (4):4546-4557.

Chicago/Turabian Style

Gaoxiang Li; Yandong Chen; An Luo; Xuan Liu. 2020. "Wideband Harmonic Voltage Feedforward Control Strategy of STATCOM for Mitigating Subsynchronous Resonance in Wind Farm Connected to Weak Grid and LCC HVDC." IEEE Journal of Emerging and Selected Topics in Power Electronics 9, no. 4: 4546-4557.

Journal article
Published: 19 August 2020 in IEEE Transactions on Power Delivery
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In a line-commutated converter based high-voltage direct-current (LCC-HVDC) system, the inverter control system usually includes constant extinction angle (CEA) controller, constant current (CC) controller, current error controller (CEC), and voltage-dependent current order limiter (VDCOL). However, the interaction influence of multiple controllers may cause repetitive commutation failure (CF). For this purpose, this paper deeply investigates the mechanism and influencing factors of repetitive CF caused by controller interaction. It is found that the lower limit value of CEA controller can affect the control switching process and thus the probability of repetitive CF. Besides, the minimum gamma measurement (MGM) unit prevents the system from acquiring the real extinction angle in time, which results in the DC current fluctuation during the recovery process. Moreover, the probability of control-induced repetitive CF is much higher when the HVDC inverter is connected to a weak AC system or the AC fault is not serious but not cleared in time. Based on the above analyses, an improved control method is proposed for recovery performance improvement, which is mainly realized by modifying the lower and upper limits of the CEA controller during recovery. Finally, the simulation and experimental results verify the theoretical analyses and the proposed control method.

ACS Style

Lerong Hong; Xiaoping Zhou; Yifeng Liu; Haitao Xia; Hanhang Yin; Yandong Chen; Leming Zhou; Qianming Xu. Analysis and Improvement of the Multiple Controller Interaction in LCC-HVDC for Mitigating Repetitive Commutation Failure. IEEE Transactions on Power Delivery 2020, 36, 1982 -1991.

AMA Style

Lerong Hong, Xiaoping Zhou, Yifeng Liu, Haitao Xia, Hanhang Yin, Yandong Chen, Leming Zhou, Qianming Xu. Analysis and Improvement of the Multiple Controller Interaction in LCC-HVDC for Mitigating Repetitive Commutation Failure. IEEE Transactions on Power Delivery. 2020; 36 (4):1982-1991.

Chicago/Turabian Style

Lerong Hong; Xiaoping Zhou; Yifeng Liu; Haitao Xia; Hanhang Yin; Yandong Chen; Leming Zhou; Qianming Xu. 2020. "Analysis and Improvement of the Multiple Controller Interaction in LCC-HVDC for Mitigating Repetitive Commutation Failure." IEEE Transactions on Power Delivery 36, no. 4: 1982-1991.

Journal article
Published: 06 August 2020 in IEEE Transactions on Industrial Electronics
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Direct power control (DPC) has been widely used in grid-connected inverters. Firstly, considering the effects of phase-locked loop (PLL), voltage outer-loop, power inner-loop, control delay, and frequency coupling, a broadband admittance model of the grid-connected inverter with DPC is established. The admittance characteristics of grid-connected inverters with DPC and closed-loop current control (CCC) are compared and analyzed. Due to the different inner-loop control objects, the components produced by the power calculation in DPC and the Park's transformation in CCC cause the admittance differences between the grid-connected inverters with DPC and CCC. Then, the effects of grid impedance, output power and control parameters on system stability are analyzed. It is revealed that the stability of the grid-connected inverter with DPC is very sensitive to grid impedance and easily affected by output power and inner-loop bandwidth, while the grid-connected inverter with CCC has a better adaptability to weak grid, high output power and inner-loop bandwidth. Moreover, the PLL bandwidth has little effect on the stability of the grid-connected inverter with DPC, but has a great impact on the stability of the grid-connected inverter with CCC when the inverter is connected to weak grid. Finally, the correctness of the analysis is verified by experiments.

ACS Style

Zhiwei Xie; Wenhua Wu; Yandong Chen; Wenlan Gong. Admittance-Based Stability Comparative Analysis of Grid-Connected Inverters With Direct Power Control and Closed-Loop Current Control. IEEE Transactions on Industrial Electronics 2020, 68, 8333 -8344.

AMA Style

Zhiwei Xie, Wenhua Wu, Yandong Chen, Wenlan Gong. Admittance-Based Stability Comparative Analysis of Grid-Connected Inverters With Direct Power Control and Closed-Loop Current Control. IEEE Transactions on Industrial Electronics. 2020; 68 (9):8333-8344.

Chicago/Turabian Style

Zhiwei Xie; Wenhua Wu; Yandong Chen; Wenlan Gong. 2020. "Admittance-Based Stability Comparative Analysis of Grid-Connected Inverters With Direct Power Control and Closed-Loop Current Control." IEEE Transactions on Industrial Electronics 68, no. 9: 8333-8344.

Journal article
Published: 08 June 2020 in IEEE Transactions on Power Electronics
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For VSG, the voltage-controlled harmonic-suppression-method will seriously deteriorate the magnitude of inrush fault current in the moment of grid symmetrical fault, because the suppression effects of harmonic current and inrush fault current are mutually constrained from the perspective of its output impedance. For this issue, a harmonic current and inrush fault current coordinated suppression method is proposed to achieve both good results of harmonic current suppression in normal grid and inrush fault current limitation in fault grid, which mainly includes a passive branch, an active branch and an improved VSG control. The passive branch is installed between PCC and grid to introduce an additional voltage variable. Meanwhile, with the proper feed-forward of PCC voltage and additional voltage, the active branch increases the mid/high frequency impedance viewed from grid fault point to VSG, and decreases harmonic impedance viewed from PCC to VSG. Then, not only transient inrush fault current is limited, but also harmonic current introduced from nonlinear load is mostly absorbed. Moreover, the improved VSG control is used to limit steady-state fundamental frequency fault current. Therefore, the contradictory between harmonic current and inrush fault current suppression for VSG is well solved. Finally, the experiment results validate the proposed control method.

ACS Style

Leming Zhou; Siyi Liu; Yandong Chen; Weilang Yi; Shuke Wang; Xiaoping Zhou; Wenhua Wu; Jie Zhou; Chan Xiao; Aoyang Liu. Harmonic Current and Inrush Fault Current Coordinated Suppression Method for VSG Under Non-ideal Grid Condition. IEEE Transactions on Power Electronics 2020, 36, 1030 -1042.

AMA Style

Leming Zhou, Siyi Liu, Yandong Chen, Weilang Yi, Shuke Wang, Xiaoping Zhou, Wenhua Wu, Jie Zhou, Chan Xiao, Aoyang Liu. Harmonic Current and Inrush Fault Current Coordinated Suppression Method for VSG Under Non-ideal Grid Condition. IEEE Transactions on Power Electronics. 2020; 36 (1):1030-1042.

Chicago/Turabian Style

Leming Zhou; Siyi Liu; Yandong Chen; Weilang Yi; Shuke Wang; Xiaoping Zhou; Wenhua Wu; Jie Zhou; Chan Xiao; Aoyang Liu. 2020. "Harmonic Current and Inrush Fault Current Coordinated Suppression Method for VSG Under Non-ideal Grid Condition." IEEE Transactions on Power Electronics 36, no. 1: 1030-1042.

Journal article
Published: 27 May 2020 in IEEE Transactions on Industrial Electronics
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In current power system, the conversion between DC and AC is widely existing and dc side harmonic problem is prominent. To suppress the second-harmonic current (SHC) at the dc side of single-stage single-phase inverter, a dc hybrid active power filter (DC-HAPF) structure is presented, which composes of bidirectional dc-dc circuit based active power filter and CL passive filter. Here, the CL passive filter is used to mitigate the high frequency harmonics and the active power filter is applied to compensate the low frequency harmonic current. Meanwhile, the influence of filter parameters on harmonic suppression is analyzed based on the average switching model. In addition, for the control of the DC-HAPF, a nonlinear unified controller via feedback linearization is proposed, where the voltage and current dual-loop control is converted to a single-loop control of energy. By analyzing the control system stability and DC-HAPF's performance, appropriate control parameters are selected. To verify the feasibility of the proposed topology and control strategy, a 500W single-stage single-phase inverter with the DC-HAPF is built and a good performance of dc side harmonic suppression has been achieved.

ACS Style

Gaoxiang Li; An Luo; Zhixing He; Fu Jun Ma; Yandong Chen; Wenhua Wu; Zhen Zhu; Josep M. Guerrero. A DC Hybrid Active Power Filter and Its Nonlinear Unified Controller Using Feedback Linearization. IEEE Transactions on Industrial Electronics 2020, 68, 5788 -5798.

AMA Style

Gaoxiang Li, An Luo, Zhixing He, Fu Jun Ma, Yandong Chen, Wenhua Wu, Zhen Zhu, Josep M. Guerrero. A DC Hybrid Active Power Filter and Its Nonlinear Unified Controller Using Feedback Linearization. IEEE Transactions on Industrial Electronics. 2020; 68 (7):5788-5798.

Chicago/Turabian Style

Gaoxiang Li; An Luo; Zhixing He; Fu Jun Ma; Yandong Chen; Wenhua Wu; Zhen Zhu; Josep M. Guerrero. 2020. "A DC Hybrid Active Power Filter and Its Nonlinear Unified Controller Using Feedback Linearization." IEEE Transactions on Industrial Electronics 68, no. 7: 5788-5798.

Journal article
Published: 19 May 2020 in IEEE Transactions on Power Electronics
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Load converters with inertial support are used to enhance the system inertia. However, these converters may fail to operate stably in the weak grid. In this paper, sequence impedance modeling and stability comparison analysis are proposed for the load virtual synchronous machine (LVSM) and the load converter with virtual inertia control (LCVIC). Firstly, the universal sequence impedance formulas are derived by considering dc-link voltage dynamics and frequency-coupling effects. Then, the precise sequence impedance models are built for impedance characteristics analysis of LVSM and LCVIC. The analysis shows that the positive-sequence impedance of LVSM is generally inductive in the middle-frequency band, which is basically consistent with the grid impedance. In contrast, the positive-sequence impedance of LCVIC is negative-resistive-capacitive (i.e., phase angle is between -180° and -90°) in the middle-frequency band, which may lead to harmonic oscillation in the weak grid. Furthermore, the effects of grid impedance, load power, and other control parameters on the stability are analyzed for the two load converters based on the derived model and Nyquist stability criterion. The analysis results reveal that LVSM has better stability than LCVIC in the weak grid. Finally, the experimental results validate the correctness of the theoretical analyses.

ACS Style

Yifeng Liu; Xiaoping Zhou; Yandong Chen; Leming Zhou; Lei Wang; Wenhua Wu. Sequence Impedance Modeling and Stability Analysis for Load Converters With Inertial Support. IEEE Transactions on Power Electronics 2020, 35, 13031 -13041.

AMA Style

Yifeng Liu, Xiaoping Zhou, Yandong Chen, Leming Zhou, Lei Wang, Wenhua Wu. Sequence Impedance Modeling and Stability Analysis for Load Converters With Inertial Support. IEEE Transactions on Power Electronics. 2020; 35 (12):13031-13041.

Chicago/Turabian Style

Yifeng Liu; Xiaoping Zhou; Yandong Chen; Leming Zhou; Lei Wang; Wenhua Wu. 2020. "Sequence Impedance Modeling and Stability Analysis for Load Converters With Inertial Support." IEEE Transactions on Power Electronics 35, no. 12: 13031-13041.

Journal article
Published: 23 April 2020 in IEEE Journal of Emerging and Selected Topics in Power Electronics
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The load-side virtual synchronous machine (LVSM) enables the load to actively participate in the grid regulation, but it might still induce oscillations in weak grid. Considering the dclink voltage controller, power loops, ac voltage and current loops, the control delay and sampling filters, the wideband dq-frame impedance model of the LVSM is first established. And it is found that Zdd exhibits negative resistor impedance within 10 Hz. In addition, the dq-frame impedance of the LVSM is approximately inductive above 10 Hz. Then, using the dq-frame impedance-based approach, the comparative study shows that the smaller the proportional gain and integral gain of the dc-link voltage controller are, the more stable the conventional voltage source rectifier (VSR) is in weak grid. However, the larger the proportional gain is and the smaller the integral gain is, the more stable the LVSM is in weak grid. Furthermore, the voltage feedforward decreases the stability margin of the VSR in weak grid, while the virtual moment of inertia J and the damping gain Dp affect the stability of the LVSM. And the smaller J and Dp are, the more stable the LVSM is in weak grid. Finally, simulations and experimental results verify the impedance model and the stability analysis.

ACS Style

Jian Guo; Yandong Chen; Wenhua Wu; Xiangyu Wang; Zhiwei Xie; Lu Xie; Zhikang Shuai. Wideband dq-Frame Impedance Modeling of Load-Side Virtual Synchronous Machine and Its Stability Analysis in Comparison With Conventional PWM Rectifier in Weak Grid. IEEE Journal of Emerging and Selected Topics in Power Electronics 2020, 9, 2440 -2451.

AMA Style

Jian Guo, Yandong Chen, Wenhua Wu, Xiangyu Wang, Zhiwei Xie, Lu Xie, Zhikang Shuai. Wideband dq-Frame Impedance Modeling of Load-Side Virtual Synchronous Machine and Its Stability Analysis in Comparison With Conventional PWM Rectifier in Weak Grid. IEEE Journal of Emerging and Selected Topics in Power Electronics. 2020; 9 (2):2440-2451.

Chicago/Turabian Style

Jian Guo; Yandong Chen; Wenhua Wu; Xiangyu Wang; Zhiwei Xie; Lu Xie; Zhikang Shuai. 2020. "Wideband dq-Frame Impedance Modeling of Load-Side Virtual Synchronous Machine and Its Stability Analysis in Comparison With Conventional PWM Rectifier in Weak Grid." IEEE Journal of Emerging and Selected Topics in Power Electronics 9, no. 2: 2440-2451.

Journal article
Published: 17 April 2020 in IEEE Transactions on Industrial Electronics
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Load converter operating in the weak grid potentially suffers harmonic oscillation problem due to the impedance interaction. In this paper, considering DC-link voltage dynamics and frequency-coupling effects, the precise sequence impedance models are derived for the traditional load converter (TLC) and the load virtual synchronous machine (LVSM). Based on the derived models, their sequence impedance characteristics are analyzed and compared. The analysis shows that the positive-sequence impedance of the LVSM is generally inductive in the middle- and low-frequency bands, which is basically consistent with the grid impedance characteristics. In contrast, the positive-sequence impedance of the TLC is negative-resistive-capacitive (i.e., phase angle is between -180° and -90°) in the middle- and low-frequency bands, and its amplitude-frequency curve is easy to intersect with the amplitude-frequency curve of the grid impedance, which may lead to harmonic oscillation in the weak grid. Furthermore, based on the derived model and Nyquist stability criterion, the effects of the grid impedance and load power on the stability are analyzed for TLC and LVSM, which indicates that the LVSM has better stability in the weak grid than the TLC. Finally, the experimental results validate the correctness of the theoretical analyses.

ACS Style

Yifeng Liu; Xiaoping Zhou; Haoqi Yu; Lerong Hong; Haitao Xia; Hanhang Yin; Yandong Chen; Leming Zhou; Wenhua Wu. Sequence Impedance Modeling and Stability Assessment for Load Converters in Weak Grids. IEEE Transactions on Industrial Electronics 2020, 68, 4056 -4067.

AMA Style

Yifeng Liu, Xiaoping Zhou, Haoqi Yu, Lerong Hong, Haitao Xia, Hanhang Yin, Yandong Chen, Leming Zhou, Wenhua Wu. Sequence Impedance Modeling and Stability Assessment for Load Converters in Weak Grids. IEEE Transactions on Industrial Electronics. 2020; 68 (5):4056-4067.

Chicago/Turabian Style

Yifeng Liu; Xiaoping Zhou; Haoqi Yu; Lerong Hong; Haitao Xia; Hanhang Yin; Yandong Chen; Leming Zhou; Wenhua Wu. 2020. "Sequence Impedance Modeling and Stability Assessment for Load Converters in Weak Grids." IEEE Transactions on Industrial Electronics 68, no. 5: 4056-4067.

Journal article
Published: 14 April 2020 in IEEE Journal of Emerging and Selected Topics in Power Electronics
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Phase-locked loop (PLL) and grid impedance are easy to negatively affect the stability of the gridconnected inverter system and even cause the system oscillation. In order to suppress this oscillation, a stability enhancing voltage feed-forward inverter control method is proposed to reduce the effects of the PLL and the grid impedance. Then, considering the effects of the frequency coupling characteristic, the admittance model of the gridconnected inverter with the proposed stability enhancing control method is established, and the admittance characteristic and system stability of the inverters with the traditional control method and the proposed stability enhancing control method are compared and analyzed. Analysis results indicate that the proposed stability enhancing control method improves the system stability in different short-circuit ratio (SCR) conditions. What’s more, the system with the proposed stability enhancing control method keeps stable under a relative larger PLL bandwidth, while the system with the traditional control method oscillates. Finally, the effectiveness of the proposed stability enhancing control method is verified by experiments.

ACS Style

Zhiwei Xie; Yandong Chen; Wenhua Wu; Wenlan Gong; Josep M. Guerrero. Stability Enhancing Voltage Feed-Forward Inverter Control Method to Reduce the Effects of Phase-Locked Loop and Grid Impedance. IEEE Journal of Emerging and Selected Topics in Power Electronics 2020, 9, 3000 -3009.

AMA Style

Zhiwei Xie, Yandong Chen, Wenhua Wu, Wenlan Gong, Josep M. Guerrero. Stability Enhancing Voltage Feed-Forward Inverter Control Method to Reduce the Effects of Phase-Locked Loop and Grid Impedance. IEEE Journal of Emerging and Selected Topics in Power Electronics. 2020; 9 (3):3000-3009.

Chicago/Turabian Style

Zhiwei Xie; Yandong Chen; Wenhua Wu; Wenlan Gong; Josep M. Guerrero. 2020. "Stability Enhancing Voltage Feed-Forward Inverter Control Method to Reduce the Effects of Phase-Locked Loop and Grid Impedance." IEEE Journal of Emerging and Selected Topics in Power Electronics 9, no. 3: 3000-3009.

Journal article
Published: 03 March 2020 in IEEE Transactions on Power Electronics
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Analogizing the sub-synchronous resonance (SSR) phenomenon of the series-compensated grid-connected system based on synchronous generator, the virtual synchronous generator (VSG) also has the low-frequency oscillation problem owing to the impedance interaction between VSG and series-compensated network. Stability of the series-compensated grid-connected system controlled by VSG is analyzed by the impedance-based Nyquist stability criterion. Due to the inductive impedance of VSG, VSG is easy to couple with the series-compensated network in the low-frequency areas, which can lead to the SSR. With the increase of the series compensation level, the stability of VSG becomes worse and the induced oscillation frequency becomes higher. Therefore, a mod-ulation signal feedforward active damping control strategy with time delay compensation is proposed to suppress this SSR, which directly feeds the active-damping control signal to the PWM modulator for reshaping the output impedance of VSG from the inductance to the resistance-inductance. Moreover, a value range of virtual resistance is given with considering the influence on the regular operation of VSG. Finally, simulation and experimental results verify the correctness of the SSR analysis and the feasibility of the proposed active-damping control strategy.

ACS Style

Gaoxiang Li; Yandong Chen; An Luo; Zhixing He; Haining Wang; Zhen Zhu; Wenhua Wu; Leming Zhou. Analysis and Mitigation of Subsynchronous Resonance in Series-Compensated Grid-Connected System Controlled by a Virtual Synchronous Generator. IEEE Transactions on Power Electronics 2020, 35, 11096 -11107.

AMA Style

Gaoxiang Li, Yandong Chen, An Luo, Zhixing He, Haining Wang, Zhen Zhu, Wenhua Wu, Leming Zhou. Analysis and Mitigation of Subsynchronous Resonance in Series-Compensated Grid-Connected System Controlled by a Virtual Synchronous Generator. IEEE Transactions on Power Electronics. 2020; 35 (10):11096-11107.

Chicago/Turabian Style

Gaoxiang Li; Yandong Chen; An Luo; Zhixing He; Haining Wang; Zhen Zhu; Wenhua Wu; Leming Zhou. 2020. "Analysis and Mitigation of Subsynchronous Resonance in Series-Compensated Grid-Connected System Controlled by a Virtual Synchronous Generator." IEEE Transactions on Power Electronics 35, no. 10: 11096-11107.