With the deepening of power electronicization in power system, grid-forming converters with voltage source characteristics will become conventional equipment in modern power systems. In order to conduct accurate and efficient control and operation analysis for power systems equipped with grid-forming equipment and to study their safety and stability characteristics, it is necessary to reduce the complexity of grid-forming converter model with strong nonlinear characteristics. Conventional simplification methods based on current loops and voltage control loops neglect the potential effect of inner loop control and line coupling impedance on the synchronous stability of the equipment. Ensuring the accuracy of stability analysis can be challenging in certain scenarios. Therefore, based on the existing order reduction methods, fully considering the small-signal characteristics of inner loop control and the influence of line coupling impedance, a series of improved simplified models are proposed. Moreover, the adaptability of each simplified model to frequency domain, eigenvalues, and time domain analysis is discussed. It turns out that there is no simplified model that can always maintain high accuracy in all scenarios. It is concluded that the simplification method needs to be changed according to the scenario. According to the analysis results, the relevant basis for selecting the simplified model of the converter and adjusting the control parameters is summarized.

The impedance inside weak current network is large, and when unbalanced loads are connected, it is unable to maintain the stability of its own voltage, resulting in three-phase voltage imbalance and output power fluctuations. Virtual synchronous generator (VSG) technology, as a grid-forming control, can provide support for voltage of the weak current network. However, under the connection of unbalanced loads, the VSG technology cannot maintain output voltage balance. To solve this problem, an improved VSG sequence decoupling control strategy is proposed. Firstly, the principle of three-phase imbalance and power fluctuation in VSG output voltage caused by unbalanced load connection is investigated. Secondly, a dual synchronous coordinate system decoupling (DDSRF) is adopted to separate the positive and negative sequence voltages of the power grid, and a positive and negative sequence control strategy is employed to control the negative sequence voltage component in dq rotating coordinate system. Finally, a VSG simulation model is built and the simulation results indicate that the proposed improved VSG sequential decoupling control strategy can suppress the unbalanced voltage output of the VSGs.

To address the frequency fluctuations and exceeding limits caused by load changes when wind hydrogen coupling system is connected to the weak current grid, a grid type virtual synchronous generator (VSG) moment of inertia self-adaptive control strategy based on dynamic feedback of hydrogen storage system pressure is proposed. Firstly, a physical simulation model of the grid type wind hydrogen coupling system is established, the closed-loop transfer function of active power is derived, and the influence of rotational inertia and damping coefficient on the power frequency oscillation characteristics of the system is analyzed. Then, considering the dynamic changes in pressure of the hydrogen storage system, the moment of inertia calculation is optimized in real time to ensure stable operation of the wind hydrogen coupling system under grid frequency fluctuations and load active power fluctuations. Finally, the strategy is validated using MATLAB/SIMULINK platform. The results show that, using the grid type self-adaptive method can accelerate the frequency recovery of the system, significantly improve the dynamic response ability of the system, and achieve stable operation of the wind hydrogen coupling system.

Under the “dual-carbon” background, in order to realize low-carbon emission and maximize wind power consumption of the microgrid system, an optimal scheduling strategy with a two-layer model of integrated energy system (IES) containing carbon capture power plant (CCPP) and power-to-gas (P2G) coupling and vehicle into the grid (V2G) is proposed. Firstly, at the low-carbon technology level, to address the problem that the CCPP and P2G equipment operate out of sync in time, a liquid storage tank is added as a CO₂ buffer station in the middle of the CCPP and the P2G equipment, and a mathematical model containing the CCPP, the P2G equipment and the gas turbine is established. Moreover, a laddered carbon transaction is established to impose low-carbon emission constraints on the IES. Secondly, in order to fully utilize the dual characteristics of EV load and energy storage, strategies are formulated to guide EV charging and discharging during wind abandonment hours and peak hours of the IES to carry out energy time shifting. Finally, at the level of economic efficiency, the integrated operating cost minimization is taken as the objective function, and MATLAB is used to invoke the GUROBI solver to solve the problem. By setting up different scenarios for comparison, the results show that the scheduling strategy can improve the level of microgrid wind power consumption while realizing the low-carbon economic operation of the system.

Integrated wind storage system, namely the wind power generation equipped with energy storage, has a black-start capability, which can be controlled to use the system as a black-start power source. On this basis, a black start program for the integrated wind storage system is developed based on a single wind turbine. Firstly, the energy storage device is started through grid-forming control, and to avoid the self-excitation generated by excitation inrush or resonance in the process of transformer input, the inertia link is added based on the original voltage-loop control to realize soft-start strategy. Then, the energy storage system establishes the AC frequency and voltage to realize restoration of the wind turbine generators and the loads. After the wind-storage integrated system is stably started, the electrical energy is transmitted to the 35 kV busbar through the main transformer and transmission line, to complete the black start process. Finally, a simulation model of the integrated wind-storage system is built on the PSCAD/EMTDC platform to validate the black-start scheme using the soft-start strategy, which keeps the voltage stable and the power balanced, and completes the start-up of the system, and at the same time suppresses the excitation inrush current effectively.

With the high proportion of new energy connected to power grid, multi-machine parallel coordinated control of energy storage inverter has become a key problem. Virtual synchronous generator (VSG) algorithm can provide damping, inertial support and stable voltage frequency for grid-forming energy storage system. However, the parallel synchronization, stability, state of charge (SOC) of each stack and impedance of each line should be considered in the coordinated control of parallel operation of multiple energy storage inverters. To solve this problem, a parallel mathematical model of energy storage inverter is established, the methods of reactive power allocation considering virtual impedance and active power allocation considering SOC are analyzed, and an improved VSG control strategy combining self-adaptive virtual impedance and SOC equalization is proposed. Finally, a model is built on the MATLAB/Simulink simulation platform, and the coordination control of each energy storage inverter is analyzed under the discharge condition with the all vanadium redox flow battery pack as the energy storage system. The validity of the improved VSG control strategy is verified, and the problem of over-discharge caused by voltage drop, reactive power and SOC difference caused by impedance difference is solved effectively, the utilization efficiency of the battery and the energy storage inverter is improved, and the life loss of the battery is reduced.

To address the problem of grid connection failure caused by low frequency and voltage stability in power system during pre-synchronization process of grid-forming converters, a pre-synchronization control strategy for grid-forming converters based on improved linear active disturbance rejection control (LADRC) is proposed. Firstly, the phase locked loop (PLL) control strategy is used to synchronize the phase and amplitude of the grid voltage with the feedback control of phase deviation, which can avoid the stability problems caused by low precision of the PLL and the slow response speed. On this basis, introducing LADRC in angular frequency output of the active frequency branch module can effectively suppress the frequency oscillation of the system, so as to ensure the normal pre-synchronization process of the grid-forming converter and realize successful grid-connection. Finally, on the MATLAB/Simulink simulation platform, a pre-synchronization control model for grid-forming converters based on improved LADRC is established verified through simulation. The results show that, the proposed strategy can effectively suppress the system frequency oscillations and accelerate the pre-synchronization process of the system, ensuring safe operation of the grid-forming converter and ultimately achieving successful grid connection. The simulation results verify the effectiveness of the proposed method.

To further improve the accuracy and reliability of transient stability assessment (TSA), a feature selection method (Powershap) based on the combination of statistics and Shapley values is proposed, and a power system transient stability assessment model is established. Firstly, the input feature set is constructed based on the steady-state components during the operation of the power system. Powershap is used to divide the dataset into multiple subsets for training, and key feature sets are selected. Then, multiple CatBoost models are trained using key feature sets and transient stability assessments are conduct to generate transient stability assessment models. Finally, simulation experiments are conducted on the New England 10-machine 39-node system and the New England 54-machine 118-node system with the addition of new energy generation, and evaluation results are provided. The experiments show that, in the 10-machine 39-node system in New England, using the Powershap feature selection method for classification can achieve an accuracy of 99.79%. On the improved New England 54-machine 118-node system, its accuracy can reach 99.49%, indicating that the method can effectively perform transient stability assessment of power systems. It is verified that the proposed TSA model has good robustness and generalization ability.

The use of grid-forming inverters for grid-connection of photovoltaic units is the key to stable operation of the new energy grid in desert and gobi. The conventional PV load-shedding operation is greatly affected by irradiance and inaccurate power retention. To solve these problems, a PV active standby control strategy based on grid-configuration inverter is proposed. Firstly, a PV grid-connected structure containing reference and backup arrays is designed. Secondly, based on the two-stage PV topology, an active backup control is introduced at the front stage DC/DC and a grid-forming control strategy is introduced at the back stage DC/AC to realize active participation of PV units in grid frequency regulation. The control strategy introduces a constant DC capacitor voltage control to maintain the DC voltage while enhancing the inertia characteristics of the PV unit. Finally, the PV small signal model of the grid-forming inverter is established, and the influence of DC capacitor value on the PV frequency response is analyzed through the root trajectory. The simulation results verify the correctness and feasibility of the proposed control strategy.

With the increasing proportion of new energy in power grid system, the domestic capacity of peak regulation, frequency regulation and voltage regulation is increasing, which greatly affects the flexibility of the power grid. In this regard, the focus is on analyzing and researching the related fields of grid-forming energy storage. Firstly, the technical characteristics of grid-following and grid-forming control are compared and analyzed, and the development status of grid-forming energy storage in Xinjiang is summarized. At the same time, a demonstration project of a grid-forming energy storage power station in Xinjiang is selected to test the low voltage ride-through, inertia response and damping characteristics, and a grid-connected test method for grid-forming energy storage power stations covering multi-level and full-scale scenarios is proposed. The test results can provide reference for grid-connected performance evaluation of grid-forming energy storage. Finally, the development of grid-forming energy storage in Xinjiang is predicted and analyzed, and the development advantages of grid-forming energy storage in new energy-rich areas are summarized.