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Yiqi Liu
College of Mechanical and Electrical Engineering, Northeast Forestry University, Harbin, China

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Original article
Published: 18 August 2021 in Journal of Power Electronics
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A hybrid modular multilevel converter (HMMC) topology based on a bidirectional diode clamp circuit is proposed in this paper. The proposed topology ensures that the voltages at the ends of the capacitance between the two leads of each sub-module in the same phase are clamped to be equal to each other through the diode clamp circuit. The balancing process through the diode clamp circuit is bidirectional, which is only achieved by the diode clamp circuit. This topology has two advantages when compared with the traditional voltage balance control method. First, the framework used for controlling the entire structure is simplified while the link controlling the voltage balance is eliminated. Second, the control schemes used for the voltage balance are simplified, and the number of the corresponding high-frequency voltage sensors is reduced. Hence, the complexity of the system control is decreased, and communication is realized more easily. When compared with other voltage balancing circuits, the proposed circuit achieves bidirectional equalization and reduces the usage of the inductors. Then, the hardware cost is reduced. Finally, the feasibility of the proposed converter is verified by simulation results given in MATLAB/Simulink.

ACS Style

Yiqi Liu; Yanchao Liu; Yonglin Jin; Jianlong Chen. Novel submodule voltage balancing topology for hybrid modular multilevel converters. Journal of Power Electronics 2021, 1 -11.

AMA Style

Yiqi Liu, Yanchao Liu, Yonglin Jin, Jianlong Chen. Novel submodule voltage balancing topology for hybrid modular multilevel converters. Journal of Power Electronics. 2021; ():1-11.

Chicago/Turabian Style

Yiqi Liu; Yanchao Liu; Yonglin Jin; Jianlong Chen. 2021. "Novel submodule voltage balancing topology for hybrid modular multilevel converters." Journal of Power Electronics , no. : 1-11.

Journal article
Published: 01 April 2021 in International Journal of Electrical Power & Energy Systems
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Emerging nanogrids are expected to play a significant role in managing the ever-increasing distributed renewable energy sources and battery storage. And if nanogrids can supply fully-charged batteries (FBs) to a battery swapping station (BSS), it will help establish a novel renewable-energy-to-vehicle system. Following such an idea, this paper considers multiple nanogrids with a BSS as a battery swapping-charging system (BSCS), in which trucks collect FBs from individual nanogrids to the BSS to serve electric vehicles (EVs). In this way, the BSCS can bring together a local range of energy carriers to enhance energy supply cleanliness and promote transportation electrification. The system-level operation framework of the BSCS is introduced, and then a joint optimal scheduling model of it is established based on several effective progressing technologies. The model is formulated based on the mixed-integer linear programming (MILP) and solved by a heuristic method involving Exhaustive Search and Genetic Algorithm. Case studies demonstrate the effectiveness of the employed approach, and they also illustrate the potential benefits of BSCS applications in exploring local energy trading, market mechanisms, and business models.

ACS Style

Mingfei Ban; Zhanpeng Zhang; Chengyu Li; Zhenjie Li; Yiqi Liu. Optimal scheduling for electric vehicle battery swapping-charging system based on nanogrids. International Journal of Electrical Power & Energy Systems 2021, 130, 106967 .

AMA Style

Mingfei Ban, Zhanpeng Zhang, Chengyu Li, Zhenjie Li, Yiqi Liu. Optimal scheduling for electric vehicle battery swapping-charging system based on nanogrids. International Journal of Electrical Power & Energy Systems. 2021; 130 ():106967.

Chicago/Turabian Style

Mingfei Ban; Zhanpeng Zhang; Chengyu Li; Zhenjie Li; Yiqi Liu. 2021. "Optimal scheduling for electric vehicle battery swapping-charging system based on nanogrids." International Journal of Electrical Power & Energy Systems 130, no. : 106967.

Original article
Published: 13 November 2020 in Journal of Power Electronics
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With the rapid development of DC transmission technology, DC circuit breakers, the key equipment for DC fault handling, have become a research hotspot of scholars. This paper proposes a novel hybrid DC circuit breaker topology to improve the shortcomings of traditional hybrid DC circuit breakers. Traditional hybrid DC circuit breakers use too many IGBTs, which results in a large volume and a high cost. The main innovation of this topology is the use of a mechanical switch in series in a solid-state branch, which withstands most of the voltage. An oscillating circuit is in parallel on the mechanical switch, which can generate reverse current to reduce the current flowing through the mechanical switch to zero, to achieve arc free breaking. The feasibility of the proposed topology is verified based on a PSCAD simulation platform. It should serve as a valuable reference for the design of DC distribution systems and DC breakers.

ACS Style

Yiqi Liu; Tian Xia; Deqing Li. Hybrid DC circuit breaker based on oscillation circuit. Journal of Power Electronics 2020, 21, 214 -223.

AMA Style

Yiqi Liu, Tian Xia, Deqing Li. Hybrid DC circuit breaker based on oscillation circuit. Journal of Power Electronics. 2020; 21 (1):214-223.

Chicago/Turabian Style

Yiqi Liu; Tian Xia; Deqing Li. 2020. "Hybrid DC circuit breaker based on oscillation circuit." Journal of Power Electronics 21, no. 1: 214-223.

Journal article
Published: 27 July 2018 in Energies
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In this paper, a new constant-frequency quasi-resonant converter is proposed. Compared with the traditional LLC converter, the proposed converter can effectively reduce the range of the operating frequency. The output voltage is changed to adjust the reactance of the resonant cavity. The proposed converter has a better loss factor. To verify the theoretical analysis and soft-switching condition, a 250 W, 100 V output prototype was built and compared with the full-bridge LLC converter. Analysis and experimental results verify that a smaller operating frequency range and volume of the transformers, a soft-switching condition, and a higher overall efficiency are achieved with the proposed converter.

ACS Style

Tianyu Zhu; Jianze Wang; Yanchao Ji; Yiqi Liu. A Novel High Efficiency Quasi-Resonant Converter. Energies 2018, 11, 1961 .

AMA Style

Tianyu Zhu, Jianze Wang, Yanchao Ji, Yiqi Liu. A Novel High Efficiency Quasi-Resonant Converter. Energies. 2018; 11 (8):1961.

Chicago/Turabian Style

Tianyu Zhu; Jianze Wang; Yanchao Ji; Yiqi Liu. 2018. "A Novel High Efficiency Quasi-Resonant Converter." Energies 11, no. 8: 1961.

Journal article
Published: 28 May 2018 in Energies
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The average switching model of modular multilevel converter (MMC) is built in this paper when the hot reserved strategy is adopted as a fault-tolerant control. When the MMC SM faults, the rest of the SMs cannot support the DC-link voltage, which results in interruption of the inverter. To tackle this issue, a novel fault-tolerant control strategy is proposed to bypass the SM under fault and re-regulate the SM capacitor voltage and carrier phase-shift angle to maintain the main components of circulating current, and reduce the Total Harmonic Distortion (THD) of grid connected current to enable the stable operation of the photovoltaic inverter. The maximum power tracking control is improved to solve the problem of long restoration time when faults occur, based on a constant voltage startup method combined with a fix-step incremental conductance method. Simulations in MATLAB/Simulink and experimental results have verified the feasibility and effectiveness of the proposed control strategy.

ACS Style

Yiqi Liu; Danhua Li; Yu Jin; Qingbo Wang; Wenlong Song. Research on Unbalance Fault-Tolerant Control Strategy of Modular Multilevel Photovoltaic Grid-Connected Inverter. Energies 2018, 11, 1368 .

AMA Style

Yiqi Liu, Danhua Li, Yu Jin, Qingbo Wang, Wenlong Song. Research on Unbalance Fault-Tolerant Control Strategy of Modular Multilevel Photovoltaic Grid-Connected Inverter. Energies. 2018; 11 (6):1368.

Chicago/Turabian Style

Yiqi Liu; Danhua Li; Yu Jin; Qingbo Wang; Wenlong Song. 2018. "Research on Unbalance Fault-Tolerant Control Strategy of Modular Multilevel Photovoltaic Grid-Connected Inverter." Energies 11, no. 6: 1368.

Journal article
Published: 02 February 2018 in Energies
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In this paper, a two-stage battery energy storage system (BESS) is implemented to enhance the operation condition of conventional battery storage systems in a microgrid. Particularly, the designed BESS is composed of two stages, i.e., Stage I: integration of dispersed energy storage units (ESUs) using parallel DC/DC converters, and Stage II: aggregated ESUs in grid-connected operation. Different from a conventional BESS consisting of a battery management system (BMS) and power conditioning system (PCS), the developed two-stage architecture enables additional operation and control flexibility in balancing the state-of-charge (SoC) of each ESU and ensures the guaranteed small-signal stability, especially in extremely weak grid conditions. The above benefits are achieved by separating the control functions between the two stages. In Stage I, a localized power sharing scheme based on the SoC of each particular ESU is developed to manage the SoC and avoid over-charge or over-discharge issues; on the other hand, in Stage II, an additional virtual impedance loop is implemented in the grid-interactive DC/AC inverters to enhance the stability margin with multiple parallel-connected inverters integrating at the point of common coupling (PCC) simultaneously. A simulation model based on MATLAB/Simulink is established, and simulation results verify the effectiveness of the proposed BESS architecture and the corresponding control diagram.

ACS Style

Bing Xie; Yiqi Liu; Yanchao Ji; Jianze Wang. Two-Stage Battery Energy Storage System (BESS) in AC Microgrids with Balanced State-of-Charge and Guaranteed Small-Signal Stability. Energies 2018, 11, 322 .

AMA Style

Bing Xie, Yiqi Liu, Yanchao Ji, Jianze Wang. Two-Stage Battery Energy Storage System (BESS) in AC Microgrids with Balanced State-of-Charge and Guaranteed Small-Signal Stability. Energies. 2018; 11 (2):322.

Chicago/Turabian Style

Bing Xie; Yiqi Liu; Yanchao Ji; Jianze Wang. 2018. "Two-Stage Battery Energy Storage System (BESS) in AC Microgrids with Balanced State-of-Charge and Guaranteed Small-Signal Stability." Energies 11, no. 2: 322.

Journal article
Published: 29 April 2015 in Energies
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The rational power sharing among different interface converters should be determined by the converter capacity. In order to guarantee that each converter operates at the ideal condition, considering the radial and mesh configuration, a modified strategy for load power sharing accuracy enhancement in droop-controlled DC microgrid is proposed in this paper. Two compensating terms which include averaging output power control and averaging DC voltage control of neighboring converters are employed. Since only the information of the neighboring converter is used, the complexity of the communication network can be reduced. The rational distribution of load power for different line resistance conditions is realized by using modified droop control that can be regarded as a distributed approach. Low bandwidth communication is used for exchanging sampled information between different converters. The feasibility and effectiveness of the proposed method for different network configurations and line resistances under different communication delay is analyzed in detail. Simulation results derived from a DC microgrid with three converters is implemented in MATLAB/Simulink to verify the proposed approach. Experimental results from a 3 × 10 kW prototype also show the performance of the proposed modified droop control scheme.

ACS Style

Yiqi Liu; Jianze Wang; Ningning Li; Yu Fu; Yanchao Ji. Enhanced Load Power Sharing Accuracy in Droop-Controlled DC Microgrids with Both Mesh and Radial Configurations. Energies 2015, 8, 3591 -3605.

AMA Style

Yiqi Liu, Jianze Wang, Ningning Li, Yu Fu, Yanchao Ji. Enhanced Load Power Sharing Accuracy in Droop-Controlled DC Microgrids with Both Mesh and Radial Configurations. Energies. 2015; 8 (5):3591-3605.

Chicago/Turabian Style

Yiqi Liu; Jianze Wang; Ningning Li; Yu Fu; Yanchao Ji. 2015. "Enhanced Load Power Sharing Accuracy in Droop-Controlled DC Microgrids with Both Mesh and Radial Configurations." Energies 8, no. 5: 3591-3605.