Jinyu Wen’s research while affiliated with Huazhong University of Science and Technology and other places

This paper proposes an energy-utilizing frequency support method for modular multilevel converter-based multiterminal high voltage direct current (MMC-MTDC) system to participate in the frequency regulation of connected AC grids. By coordinating the energy reserves in asynchronous AC grids as well as MMC capacitors, the proposed method achieves comprehensive frequency support performance adaptive to different load disturbance conditions. Firstly, a disturbance identification algorithm is developed to precisely recognize the load disturbance degree and location. Then, an inertia control is developed for minor load disturbances to offer inertia support by only using the MMC energy. For major load disturbances, the energy in both asynchronous AC grids and MMC capacitors is utilized to avoid severe frequency deviation. Furthermore, a supplementary DC voltage-energy control is designed to increase the MMC energy utilization, thereby improving the frequency support performance. Finally, the simulations in an MTDC system integrated with four asynchronous grids are carried out to verify the effectiveness and robustness of the proposed method.

Mid- and high-frequency resonance (MHFR) is highly likely to occur at the sending end of voltage source converter-based ultra-high voltage direct current (VSC-UHVDC) for large-scale renewable energy transmission. It is of great importance to investigate the resonance characteristics and the corresponding suppression strategies. Firstly, this paper introduces the overall control scheme of VSC-UHVDC for large-scale renewable energy transmission. Then, the impedance models of VSC under grid-forming control with AC voltage coordinated control are established. The mid- and high-frequency impedance characteristics of VSC-UHVDC are analyzed. The key factors affecting the impedance characteristics have been revealed, including the AC voltage control, the voltage feedforward, the inner current loop, the positive-sequence and negative-sequence independent control (PSNSIC), and the control delay. The MHFR characteristics at the sending-end system are analyzed in the whole operation process, including the black start and the normal power transmission operation. An integrated control scheme is proposed to address the MHFR problems. Finally, extensive case studies are conducted on a planned VSC-UHVDC project to verify the theoretical analysis.

This paper aims to promote the lifespan benefit of multiple battery energy storage (BES) in real-time scheduling. An effective real-time scheduling model is formulated with the proposed concept of multiple BES (MBES) comprehensive lifespan benefit, which makes a tradeoff between MBES short-term operation and long-term profits. Then, a novel piece-wise linear function (PLF) based continuous ADP (PLFC-ADP) algorithm is proposed to optimize the scheduling model under uncertainties. A new decomposed value function approximation method employing both BES state of charge and BES cumulative life loss is proposed to achieve high optimality and wide applicability. Combined with the difference-based decomposed slope update method to train the PLF slopes with empirical knowledge, the proposed PLFC-ADP algorithm can handle the increasing computation complexity of MBES scheduling and obtain the approximate optimality of stochastic real-time scheduling. Numerical analysis demonstrates the validity of the proposed scheduling model, and superior computation tractability and solution optimality of the proposed PLFC-ADP algorithm.

The frequency support capability of each wind turbine (WT) within a wind farm varies based on factors such as location, wind direction, operating conditions, and wake effect. To fully utilize the frequency support capability of a wind farm, output power should be allocated to each WT based on its individual states. This article proposes a distributed adaptive leaderless consensus control (DALC) scheme for wind farms to achieve fast frequency support. The leaderless consensus algorithm is utilized among WTs to exchange operating information with neighbors and ensure reasonable power allocation. Additionally, frequency regulation coefficients adaptively change to ensure safe WT operation. After the frequency support stage, a preset recovery control is proposed to alleviate the second frequency drop (SFD) during the restoration stage. Case studies are conducted based on a two-area power system using MATLAB/Simulink and opal-RT real-time simulation platforms. Simulation results demonstrate the effectiveness and universality of the proposed DALC control scheme in both over-frequency and under-frequency events. Furthermore, the proposed control is found to be more reliable than leader-follower consensus-based control in the event of communication failure.

The cascaded diode rectifier (DR)- MMC based HVDC system is recognized as a promising topology for integrating offshore wind farms. However, the capacity design of DR-MMC remains an unsolved challenge. This paper proposes a capacity design method based on operating region (OR) analysis. First, the analytical models of DR-MMC with V - F grid-forming (GFM) control are established, revealing its operating characteristics. Then, considering multiple constraints, the OR of DR-MMC is calculated. The impact of different MMC capacities on OR is analyzed, highlighting that a system with a low MMC capacity ratio may be incapable of covering its full active power range. Hence, a three-layer GFM control utilizing MMC DC voltage is proposed, enabling operation under a lower MMC capacity ratio. Then, an optimal MMC capacity ratio is determined by balancing the system stability margin and economic considerations. Finally, the effectiveness of the designed MMC capacity with the proposed three-layer GFM control is validated by stability analysis and simulations in PSCAD/EMTDC.