As the proportion of wind power in new-type power systems increases year by year, its dynamic characteristics, especially fault ride-through characteristics, have a significant impact on power systems. To accurately analyze the impact of large-scale wind power on power systems, it is necessary to construct a white-box model that can characterize the actual dynamic characteristics of wind turbine. The white-box model has numerous parameters with interactive effects, and current parameter identification methods cannot achieve identification of the entire DFIG's fault ride-through, inner and outer controller parameters, limiting parameters, and electrical parameters, especially the accurate identification of parameters insensitive to external characteristics. To solve these problems, this paper constructs a frequency domain universal model for DFIG under fault ride-through conditions, which includes the DFIG itself and all controllers. The parameters are divided into four categories for step-by-step identification, proposing a categorized and integrated step-by-step identification method. The accuracy of the frequency domain universal model is verified through comparison with a simulation model, and the correctness of the proposed categorized and integrated step-by-step parameter identification method is validated by comparing the identified values with the real values.

With the access of numerous distributed generations such as wind turbines, photovoltaic generators, and energy storage devices, the composition and operation mode of the power grid are becoming increasingly complex, and more uncertain factors affect the recovery of the isolated grid voltage. Aiming at the problem of optimal control of isolated grid voltage under uncertain factors, a voltage control method for isolated grid is proposed, based on long short-term memory neural network optimized by improved particle swarm optimization algorithm. Firstly, the relationship between the gain of the distributed power controller and the performance of the isolated grid controller is analyzed. Then, the particle swarm optimization algorithm is utilized to optimize the hyper-parameters such as the learning rate and neuron number of the long short-term memory neural network, so as to prevent the hyper-parameters from selecting training effect affecting network improperly. Finally, the optimized long short-term memory neural network is mapped to the relationship between the voltage deviation of the distributed generation and the controller gain, and a voltage optimization control model for the isolated grid is constructed. The simulation results show that the voltage of the distributed generation is stabilized at 1 after 0.92 s, which indicates that the proposed optimal control method improves the voltage level of the isolated grid, verifying the effectiveness of the method.

With the construction of new power system, high-capacity renewable energy sources including wind power are integrated into the power system, whose transient response characteristics have a significant impact on the safe and stable operation of both renewable energy sources and power system. Real-time simulation has become an effective method to study interaction between high-capacity renewable energy sources and power system because of its high accuracy and reliability, and precise wind turbine real-time simulation model is of great significance in research mentioned above. Therefore, the wind turbine control hardware in loop (CHIL) real-time simulation method is proposed in the paper, whose feasibility and accuracy are also verified by comparing simulation data from CHIL platform and on-site testing data. It’s further used in the analysis of large-scale offshore wind farm cluster and connected power system as a practical reference case.

When the regional power grid with a high proportion of new energy and small hydropower is operated in a passive isolated grid, the speed regulation parameters of internal small hydropower systems and the configurations for controlling and protecting new energy sources within isolated grids play a pivotal role in determining the stability of these isolated grids. Based on the typical cases of actual isolated power grid operation, this paper focuses on investigating the main characteristics affecting the frequency stability of the isolated grid, and constructs a typical simulation example for benchmarking multiple types of isolated grid operation scenarios; through multi-dimensional quantitative simulation comparison analysis, the proposed General principles for small hydropower grid coordination and new energy grid-related parameter optimization when regional power grids operate in isolated grids. The outcomes of this research provide substantial backing for the development of a comprehensive safety and stability control strategy tailored to the operation of isolated grids. Furthermore, these findings contribute significantly to the establishment of novel power systems and the assurance of dependable power provisioning within regional grid networks.

Aiming at the problems of system inertia reduction and frequency modulation capacity reduction caused by large-scale wind power replacing some traditional generators, a multi-time scale coordinated control strategy of doubly-fed wind turbines and traditional synchronous units jointly supporting the system frequency is proposed, so as to improve the system frequency stability and rationally utilize frequency modulation resources. According to the frequency modulation reserve capacity of traditional synchronous units and disturbance power, the system frequency modulation demand in different scenarios is analyzed, and the multi-time scale coordinated control strategy to actively support frequency of doubly-fed wind turbines is proposed. And based on the reserve capacity of traditional synchronous units, the frequency modulation dead zone value of doubly-fed wind turbines is designed, so that it can adaptively switch the inertia support and primary frequency regulation for different scenarios, and realize the full use of the frequency modulation reserve capacity of traditional synchronous units while giving full play to the rapid response ability of doubly-fed wind turbines. The frequency dynamic response characteristics of doubly-fed wind turbines with additional frequency active support control are analyzed, which further proves its superiority. Finally, the large-scale wind power grid-connected system simulation model is built based on RTLAB real-time digital simulation platform, which verifies the effectiveness of the control strategy in this paper.

Controlled islanding is an important measure to ensure the stability of power system and avoid widespread power outages. However, the traditional research methods based on single-objective optimization neglect the isolated network. To address this issue, a controlled islanding strategy considering the critical nodes in proposed in this paper. Firstly, based on the electrical connections and power flow distribution between nodes, an initial islanding surface is determined with the objective of minimizing power flow impact. Then, considering the electrical coupling connectivity of critical nodes, the final islanding scheme is selected within the neighborhood search space of the initial surface to enhance the stability of isolated subsystems after islanding. The proposed method is simulated and validated based on the 39-noded system, and the simulation results validate the effectiveness and superiority of the method.

When the regional power grid and the main network connection line trip, the regional power grid passively enters the isolated power grid operation. Due to the interaction of traditional unit primary frequency modulation (PFR), new energy control protection, and frequency and voltage control devices in the isolation power grid, it is difficult for traditional simulation calculation methods to accurately derive the stability evolution process of the isolated power grid. Therefore, dynamic real-time simulation methods are needed to accurately deduce the whole process of regional power grid from networking to isolated grid operation. This paper conducts in-depth research based on the case of passive isolated grid operation of power grid in a real area. Based on the constructed all-electromagnetic transient simulation model of all elements of the actual power grid, the whole process of the operation of the isolated network is inverted, and the action characteristics of each stage of the on-site accident are completely reproduced. Based on this case, the impact of new energy access on the stability of the isolated grid is carried out, the influence of the high voltage ride-through characteristics of the wind farm on the operation of the isolated grid is analyzed, and the operation strategy of increasing the proportion of new energy is conducive to reducing the frequency peak after the regional power grid passively enters the isolated grid, and the simulation verification is carried out. Based on the above research, this paper proposes a general method for dynamic analysis of isolated grid operation considering new energy access, which can be applied to guide the operation control plan for regional power grids.

Aiming at the shortcomings of traditional double closed-loop control strategy in grid-connected inverter control, such as inadequate performance in measuring the dynamic performance of inverter, ineffective suppression of harmonies, low steady-state accuracy and poor anti-interference ability, an improved compound current control algorithm based on double closed-loop control is proposed. Based on the double closed-loop current loop control and the repetitive control strategy, the repetitive controller is added to the current loop to ensure the stability and accuracy of the system. Simulation and experimental results show that the improved algorithm has high steady-state control accuracy, good dynamic performance and strong robustness.

The stability control system is an important means to ensure the safe and stable operation of the power system. In view of the shortcomings of the existing offline/real-time simulation test methods, a closed-loop simulation scheme based on virtual component technology is proposed. The virtual component technology of the stability control device is researched, and the virtualization method of the external hardware interface of the device is designed. On this basis, a closed-loop simulation framework of the stability control system under the offline/real-time simulation test environment is proposed. The functional logic of each component under the framework are analyzed. The calculation and feedback process of the entire closed-loop simulation system are analyzed in depth, which effectively solves the difficulty of simulation analysis and test verification of large-scale stability control system, providing a new method for the research and verification of stability control system strategy.

Due to the lack of generators at sending end in the early operation stage of the DXB UHVDC project, if it passively entered into island operation mode, the system will encounter harmonic instability and will cause a great risk to the steady operation. In previous projects, the common solution is to disconnect AC filters and block bipolar DC with a certain time delay when receiving island operation signal. However HVDC system may block valves, cut generation capacity or shed power by error when receiving false island operation signal. Therefore, the blocking strategy at low power under passive island mode has been improved. In DXB UHVDC project, the power on AC tie lines is used as criteria for island operation to prevent false action. The logic and realization of the control strategy are illustrated, then RTDS simulations are carried out and it is verified that by judging the power on AC tie lines, the system can effectively prevent from entering island mode by error. Finally, the field test proved that the proposed improved strategy will not cause rejecting of the existing “island blocking logic”. The proposed strategy can be a reference to other DC projects.

With the development of power electronics technology, the power system is now evolving into a new-generation power system dominated by renewable energy. Due to the physical limitations of power electronics, controller saturation is widely adopted in wind turbines and photovoltaics. In this paper, a nonlinear system model considering output saturation is proposed in the view of general dynamic systems. By defining saturation-activation vector L, all the saturations of the system are uniquely represented. Then, the proposed modeling method is applied to a voltage source converter (VSC) grid-connected system. Based on RTDS simulation, this paper revealed that a class of oscillations at a specific frequency are caused by the activation of the phase-locked loop (PLL) saturation. The frequency of the oscillation depends on the top and bottom boundaries of PLL saturation.

Rapid development of power electronics technology has boosted the development of clean energy to a new height, but also brought a series of power quality problems which even threat the stable operation of power grid. Resonance caused by grid-connected wind turbines and the lag problem of discrete control systems gradually intensify with the increase of number of grid-connected units. Thus, a grid friendly control methodology of direct-drive wind turbine is researched in this paper. Considering the delay of capacitor current feedback and discretization control system, a repetitive predictive control strategy is proposed to improve its stability and controllability, whose effectiveness is verified by simulation and physical test.

The sending end of HVDC in islanded operation mode is a weak AC system, the security and stability control (SSC) system is very important for the operation of the islanded system. In this paper, the SSC strategy of Xinsong-Dongfang HVDC under islanded mode is deeply analyzed, and the defects and risks of the SSC discrimination logic for the small islanded operation mode is exposed during the RTDS simulation tests, as a result, some of the generators cannot be cut off. In addition, Then the research of the action sequence of SSC reveals the improper time coordination between the small islanded mode signal and the cut-off command. Based on the above work, an optimized scheme to discriminate the small islanded operation mode is proposed, and the correctness and effectiveness are verified through the same RTDS tests. This new method has great significance in the SSC design and implementation in HVDC transmission project with similar techniques.

The frequency limit controller, or FLC, is an important measure for grid frequency stability control, and has been widely used in DC projects. DXB UHVDC project is faced with the problems of increasing frequency instability of the Yunnan power grid, as it runs asynchronously from the main grid, and the shortage of the opening unit in the initial stage of production. The configuration of FLC is very important. It analyzes two kinds of FLC control logic used in current DC project of China Southern Power Grid and compares the results of two kinds of control logic response through simulation test. The FLC configuration and parameter selection of DXB UHVDC are explained, and the response characteristics of FLC under the typical fault under the isolated islanding system are verified through simulation. And verify its function in DXB R TDS simulation platform as well as field test.

Security and stability control system (SSC) is an important guarantee for the safe operation of power grid, and for HVDC system modulation function is an important kind of stability control measures. Combined with Tianshengqiao-Guangzhou HVDC safety strategy transformation, RTDS simulation test is conducted. In allusion to the exposed defects about SSC handling with multiple DC power modulation orders and sequence coordination between SSC and pole control system, the handling way for the stability control device of Mawo converter station and control characteristics of DC power modulation for pole control system are analyzed in detail. An optimization method of control sequence coordination for stability control system and pole control system is proposed, and tested on the SSC test platform. Test results show the effectiveness of the proposed method, and meanwhile the significance for the design and implementation of SSC scheme of HVDC project with similar techniques.

直流在孤岛运行方式下送端为弱交流系统,安全稳定控制对电网的稳定运行十分重要.分析了新东直流输电处于孤岛方式运行下的控制策略,结合新东直流安稳控制策略的验证,开展了RTDS仿真试验,并针对试验中暴露出的现有稳控系统对小孤岛状态判别的缺陷,深入分析了稳控系统中电厂稳控装置动作的原理,提出了优化的小孤岛判别方法,并验证了该方法的有效性.所提方法对于稳控系统测试标准化具有重要的借鉴意义.

Due to the difference between MMC-HVDC and LCC-HVDC control characteristics and the mutual influence of parallel connection, its power modulation strategy is different from that of LCC-HVDC. Coordinated control strategy of parallel system of MMC-HVDC and LCC-HVDC is analyzed. The methods of power distribution, rate distribution and reactive power control of power limit function are described. Combined with RTDS simulation research of modulation function of Luxi back-to-back HVDC system, the control characteristics of power limitation function of the parallel system under the condition of AC fault at the rectifier side are analyzed in view of the exposed defects. The coordination method of the power limit function, the high voltage crossing control function and the rate distribution optimization is proposed. The simulation results show that the optimized parallel system can perform the power limiting function according to the correct timing and rate.