A global asymptotical stable control scheme for a Hexverter in fractional frequency transmission systems

Meng, Yongqing; Zou, Yichao; Huixuan, Li; Yu, Jie; Wang, Xifan

doi:10.1007/s40565-019-0549-y

Cited by 10 publications

(6 citation statements)

References 23 publications

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“…For a detailed introduction of each part, refer to [14]. Different from [6], after a full consideration of the frequency leakage component between each branch, this paper decouples them into IF and FF components and further considers the specific sequential component [28,29]. The FF side circuit equations of the Y-MMC system under the dq coordinate axis are ( 1) and ( 2), which is also the decoupling model of the FF system and it only contains FF components.…”

Section: Dynamic Decoupling Mathematical Model Of Y-mmcmentioning

confidence: 99%

Structure optimization based on phase‐locked loop and controller parameters optimization of Y‐connected modular multi‐level converter for fractional frequency offshore wind power system under weak grid

Meng

Jia

et al. 2022

IET Generation Trans & Dist

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Based on a practical long‐distance large‐capacity transmission engineering case, the small‐signal stability of fractional frequency transmission system (FFTS) with Y‐connected modular multi‐level converter (Y‐MMC) is mainly researched in this paper. Different from the previous control strategies of Y‐MMC, this paper establishes a frequency decoupling mathematical model and proposes the decoupling control strategies. Then, the small‐signal model of the Y‐MMC system is obtained. Considering the existence of phase locked loop (PLL) will deteriorate the stability of the system under weak grid, this paper applies the short‐circuit ratio (SCR) for analysis and proposed a new structure of PLL, called phase‐shifted PLL (PS‐PLL), to improve the small‐signal stability of the system. In addition, for better stability and dynamic response performance of the closed‐loop control system, this paper proposes a new parameter optimization objective function for parameters adjustment. Controller parameters optimization is conducted by using the particle swarm optimization (PSO) algorithm and stability evaluation of the system is conducted based on the eigenvalue distribution. Finally, the feasibility and superiority of the proposed strategies and optimization are verified in MATLAB/ Simulink.

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Section: Dynamic Decoupling Mathematical Model Of Y-mmcmentioning

confidence: 99%

Structure optimization based on phase‐locked loop and controller parameters optimization of Y‐connected modular multi‐level converter for fractional frequency offshore wind power system under weak grid

Meng

Jia

et al. 2022

IET Generation Trans & Dist

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“…In [8]- [10], based on the statespace model, a frequency-decoupled branch current control model in the dq reference frame was presented, and the operating principle and characteristic waveforms were verified with a simulation and experimental prototype. To solve the problems of difficulty in tuning proportional-integral (PI) parameters to ensure global stability, a global asymptotical stable control scheme of Hexverter based on the IDA-PBC methodology was presented in [11].…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, branch voltage-balancing control and circulating current suppression control are important for the steady-state operation of the Hexverter. Regulating the modulation ratio in a small range is a conventional method to realize voltage balancing for multilevel converters [11]. Compensating for branch power differs by superimposing common-mode voltages on the neutral points, and injecting circulating current is another solution to this problem [13], [14].…”

Section: Introductionmentioning

confidence: 99%

Branch Voltage Balancing Control Strategy Based on the Transfer Power Model by Zero-Sequence Circulating Current for the Hexverter

Yang

Qian

et al. 2022

IEEE Access

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This paper proposes a novel branch voltage-balancing control strategy for a hexagonal converter (Hexverter). First, the state-space model based on the double-dq transformation is analyzed in-depth along with the necessary basic mathematical derivation, and the active/reactive power control model in the dq reference frame for the Hexverter is proposed. Second, a zero-sequence double-loop network consisting of a Y-loop and a Hex-loop circulating current was established. This study proposes a method to suppress the Y-loop circulating current by connecting a capacitor at the neutral point. We then establish a novel branch voltage-balancing control strategy based on the transfer power model. The essence of the proposed control strategy is to control the charging and discharging states of each submodule via the zero-sequence voltages and the Hex-loop circulating current to regulate the power transfer between adjacent submodules and branches, thereby effectively ensuring the dynamic balance of the DC voltages of the submodules. The branch voltage-balancing control model and power control model proposed in this paper are based on zero-sequence and positive-sequence networks, respectively. The relative independence of the positive-and zero-sequence networks leads to decoupling of the branch voltage-balancing control model and the power control model; thus, the respective control objectives can be achieved by adjusting the respective control variables independently. It has a stronger adaptability to diverse power grid operating parameters. Finally, the validity and correctness of the mathematical model and control strategy proposed in this study are verified using MATLAB/Simulink.INDEX TERMS Hexverter, double-dq transformation, the zero-sequence double-loop network, the transfer power model, the voltage balancing control, circulating current suppression.

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“…Additionally, there are many internal circulating current paths in M3C. The suppression of circulating currents is a major challenge in the design of M3C controllers [17]. Another AC-AC converter named Hexverter is proposed in [18].…”

Section: Introductionmentioning

confidence: 99%

Grid integration and fault ride‐through of fractional frequency offshore wind power system based on Y‐connected modular multilevel converter

Meng

Jia

et al. 2022

IET Generation Trans & Dist

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Fractional frequency transmission is a promising solution to offshore wind power integration. This paper proposes a new grid integration scheme of fractional frequency offshore wind power system (FFOWPS) based on Y-connected modular multilevel converter (Y-MMC). To get better power quality, a novel Y-MMC modelling and control method considering frequency leakage is presented. Besides, in order to achieve satisfactory fault ride-through (FRT) performance for FFOWPS, this paper proposes a novel FRT strategy. The strategy makes use of the onshore grid voltage and offshore grid frequency droop control to coordinately control the power of Y-MMC and wind turbines. This strategy achieves power balance on both sides of Y-MMC through coordinated control, thereby suppressing the increase of DC capacitor voltage during faults. It is also able to support the grid by injecting reactive power during voltage sags. Additionally, a new pitch angle control algorithm is designed to keep the balance between input mechanical power and output active power of wind turbines during FRT, avoiding the rapid rise of rotor speed. The simulation results in MATLAB/Simulink demonstrate good performance of FFOWPS during wind speed variations and validate the effectiveness of the proposed frequency leakage suppression strategy and FRT strategy.

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A global asymptotical stable control scheme for a Hexverter in fractional frequency transmission systems

Cited by 10 publications

References 23 publications

Structure optimization based on phase‐locked loop and controller parameters optimization of Y‐connected modular multi‐level converter for fractional frequency offshore wind power system under weak grid

Structure optimization based on phase‐locked loop and controller parameters optimization of Y‐connected modular multi‐level converter for fractional frequency offshore wind power system under weak grid

Branch Voltage Balancing Control Strategy Based on the Transfer Power Model by Zero-Sequence Circulating Current for the Hexverter

Grid integration and fault ride‐through of fractional frequency offshore wind power system based on Y‐connected modular multilevel converter

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