With the increasing penetration of renewable energy in power systems, integrated wind-solar-storage (WPS) power plants have become a critical component of modern power grids. However, due to the complex interactions among multiple power electronic devices within these plants, stability challenges such as voltage oscillations and temporary overvoltage have emerged. This study establishes a comprehensive WPS station model, incorporating wind turbines, photovoltaic systems, static var generators (SVGs), and energy storage systems. Then the coordination and optimization of control characteristics among these devices are investigated. To address the issue of multi-device control incoordination during operation, the paper proposes a coordinated optimization framework based on differentiated control and response-priority hierarchy. The effectiveness of this method is validated through large-scale grid simulation. The results demonstrate that rational coordination strategies and parameter optimization can significantly improve the transient response characteristics of WPS stations, thereby enhancing grid stability.

Active splitting control, as an emergency control measure, serves as a critical line of defense for the safe and stable operation of power systems. Active splitting control serves as an effective control strategy to contain disturbance spread, block cascading failure paths, and mitigate outage impacts. Therefore, identifying an optimal splitting boundary is pivotal to proactive islanding control. Based on the COI (Center of Inertia) coordinate system equations for multi-machine systems, a branch transient energy function model is established for power systems. This model characterizes the transient evolution trends of power systems from the perspective of system transient energy. The proposed method assesses power system stability by evaluating each branch's capability to absorb generator rotor kinetic energy. Branches that can withstand transient energy after system disturbances are identified as candidate splitting boundaries for proactive islanding. Validation Analysis was conducted on the transient energy function distribution characteristics of regional branches in the EPRI 8-machine 36-bus system following disturbances. Simulation results demonstrate the effectiveness of the proposed method.

With the advancement of the new power system and accelerated development of renewable energy, its randomness, intermittency, its randomness, intermittence and volatility will lead to the complexity and variability of power system operation mode. At the same time, with the rapid development of UHVDC and the continuous improvement of AC/DC grid coupling, the traditional grid pre-control stability limits method is difficult to adapt to the complex and changeable characteristics of the new power system mode and the demand for new energy transmission and accommodation. Therefore, it is urgent to carry out multilevel transmission sections stability limit modeling research. This paper, taking the XJ outgoing section, HeY section and HX section as the research object, based on the simplified model of Northwest China Power Grid, clarifies the relationship between the dynamic reactive power characteristics of lines and new energy and the initial power of the section, and then derives mathematical representations of the initial power of section and the voltage fluctuation of the nodes, which provides a simplified analytical method for the grid dispatching and operation.

Forced power oscillation differs from traditional weak damping power oscillation. Sustained periodic disturbances can trigger forced power oscillations in power systems. From their generation mechanism to their oscillation characteristics, forced power oscillations differ significantly from classical weakly damped free oscillations. The energy characteristics of forced power oscillations from the perspective of kinetic-potential energy conversion are analyzed. First, the dynamic response mechanism of the power system under persistent periodic disturbances is analyzed, then the rotor angular kinetic and potential energies of a disturbed power system are defined, response characteristics of the generator rotor angle under the action of a forced disturbance source are analyzed from the point of view of energy conversion, energy variations corresponding to generator rotor angles at different frequencies of forced oscillation source are compared, Finally, the operating characteristics of the power system at three energy resonance states are analyzed on the basis of the kinetic-potential energy conversion mechanism.

Accurate load forecasting is crucial for the safe and stable operation of power systems. In order to further improve the accuracy of load forecasting, an improved iTransformer ultra-short-term load forecasting method based on decomposition-reconstruction is proposed. Firstly, the load data is decomposed using time varying filtering-empirical mode decomposition (TVF-EMD) to obtain several intrinsic mode functions (IMFs). The IMF components are then reorganized based on their entropy values using sample entropy (SE). Secondly, the iTransformer neural network is improved by introducing a stand alone attention (SAA) mechanism to replace the self-attention mechanism in the iTransformer encoder, which effectively enhances the model's ability to capture the dependencies of different variables. Finally, the restructured components are input into the improved iTransformer for prediction, and the obtained results are superimposed to obtain the final prediction value. The actual active load dataset of 220kV substations in a region of China is taken as an example for validation and comparison with the existing mainstream models, and the results show that the prediction method adopted in this paper has better prediction performance.

With the rapid growth of intermittent renewable energy and converter based devices, power systems have seen significant decrease in system inertia and deteriorating system dynamic performance. To address this issue, many studies have been carried out on methods and techniques for the asynchronous resources to provide active system support, such as fast frequency response (FFR). This paper presents a systematically review on the state of the art research progresses on the FFR. Firstly, an amplitude-phase motion equation based modelling method which is suitable for the analysis of electromechanical transient is introduced. Then, focusing on a typical scenario that including both synchronous and asynchronous sources, a comprehensive analysis for the system frequency dynamics is presented. Based on that, different kinds of FFR techniques are summarized in detail, which contains the basic principles, merits and demerits and the scope of application. Moreover, several suggestions are given for the further development of FFR technique.

随着"十四五"新能源布局向中东部倾斜,中东部的新能源发展速度高于西部、北部地区,对受端电网新能源承载能力的研究变得越来越迫切.文中针对华东受端电网,提出了一种评估新能源承载规模上限的方法.该方法依托中国电科院研发的生产模拟软件,统筹直流规模、弃电率、交流断面限制、储能应用等因素,在满足电力电量平衡、调峰平衡等约束前提,优化求解各类电源开发规模,求得受调峰约束的新能源发展上限;依托综合仿真试验研究系统(Power?system?department-bonneville?power?adminis-tration,?PSD-BPA),兼顾直流规模、直流功率敏感性,在满足单一直流功率缺额不触发低频减载、第一级安全稳定标准等约束条件,利用时序仿真法求得受频率稳定、电压稳定约束的新能源发展上限;通过比较论证,提出制约华东电网新能源规划发展的主要影响因素、承载规模和应对措施.

Energy storage is an effective means to ensure the consumption of renewable energy and the supply to power consumers in the new power system, which will be widely applied. As energy storage is also a kind of power electronic equipment, its low/high voltage ride through (LVRT/HVRT) transient characteristics will have positive or negative impacts on the safety of power grid, especially on the transient stability and temporary overvoltage (TOV) problems. In order to make full use of the flexible regulation ability of energy storage and make it play a positive role to the safety of power grid, this paper sorted out the typical power transmission mode of large scale renewable energy bases in China and constructed a typical model of wind-solar-thermal-storage combined system. On this basis, the principle of the influence of the LVRT/HVRT transient characteristics of the energy storage on the transient stability of the sending end system and the TOV of renewable energy generation unit is analyzed. Then, the optimization direction of the key control parameters for LVRT/HVRT of energy storage was studied through simulation by PSD-BPA. Finally, the differentiated technical requirements were proposed.

With the increasing proportion of wind power capacity into the grid, it is brought about a serious of questions to the security and stability of the power system. In particular, the low voltage ride through (LVRT) ability of wind turbine when the grid voltage sag is the extensive research of the problem at present. This paper firstly clarifies the control switching logic of the wind farm during the grid fault ride-through process and analyzes the transient active and reactive power output characteristics of the wind turbine during the LVRT and recovery process in detail. Secondly, the mechanism of transient overvoltage of wind farm low penetration process deterioration system is discussed. On this basis, the simulation models of DFIG, SVG and energy storage equipment are established, and the PSD-BPA electromechanical transient simulation model of each equipment is built to study the influence of model control parameters on its dynamic characteristics.

新能源的快速发展,给系统带来调峰困难、抗扰动能力下降等问题.为了支撑新能源合理规划建议,亟需评估电网能承载的新能源上限.该文结合西北电网能源结构和网架特点,梳理新能源开发和直流外送规模研究的思路框架;推导考虑频率安全约束的高比例新能源系统指标,包括一次调频容量与稳态频率偏差、频率响应特性与暂态频率偏差和直流送出规模与系统惯量指标;建立基于生产模拟结果的频率安全仿真算法.结合"十四五"规划边界条件,研究提出西北电网新能源开发及直流外送建议规模,验证了该文所提方法的有效性和工程实用性.

Recently, the increasing penetration of the renewable energy generation, i.e., inverter-based resources (IBRs), is challenging the grid operation. Besides, static var generators (SVGs), due to its high flexibility and controllability, have been widely-used in renewable energy generation for providing voltage support. However, the strong interaction among grid-following IBRs and SVGs may cause serious small signal stability issues, especially in weak grids. To ensure the secure operation of modern power systems, it is important to analyze the small signal stability of grid-tied IBRs with SVGs. This paper proposes a short-circuit ratio (SCR) based method for quantifying small signal stability of a single-IBR infinite-bus system (SIIBS) with a SVG located at arbitrary bus, in which SCR is a metric for quantifying small signal stability of a SIIBS from the viewpoint of grid strength. Furthermore, the key factors for the impact of a SVG on the stability of a SIIBS are investigated from the viewpoint of grid strength. Simulation results based on MATLAB/Simulink verifies the efficacy of the proposed SCR- based method.

分析现有含新能源系统频率模型进行仿真验证,发现其在部分工况下误差较大.通过在现有模型基础上增加原动机限幅环节,区分系统有效调差比例系数与有效惯量比例系数,提出了考虑限幅环节含新能源系统频率模型与简化聚合模型.通过典型系统算例表明,所提2种模型在不同新能源接入比例与类型下均有较好拟合预测效果,能够反映系统整体惯量和一次调频特性.通过实际含直流电源与新能源共同馈入电网算例表明,所提简化聚合模型可准确地反映系统频率变化情况,具有工程应用价值.

With the development of renewable energy resources, the modern power systems are integrated with large-scale inverter-based resources (IBRs). However, it has been pointed out that the increasing number or capacities of IBRs can deteriorate the small signal stability of a multi-infeed power electronic system (MIPES). This indicates that the small signal stability is one key factor that limits the grid-accommodable capacity (GAC) of IBRs in a MIPES. Therefore, it is of great value to deal with the GAC issue of IBRs with small signal stability constraints. However, this issue is still unsolved due to that the dynamic of a large-scale MIPES is too complex. To deal with this issue, this paper proposes a semi-definite programming (SDP)-based method. In the proposed method, we use GSCR, a ratio for quantifying small signal stability from the viewpoint of grid strength, as the small signal stability constraint. Since the GSCR is a static value, which avoids constructing the system’s detailed model for small signal stability analysis, the proposed SDP-based method can be suitable for a large-scale MIPES. The efficacy of the proposed SDP is demonstrated on a 39-bus test system.

With increasing inverter-based resources taking place of the traditional synchronous generators, system inertia and primary frequency regulation capability are declining. The fast frequency response (FFR) from inverter-based resources proves to be an important mitigation option in maintaining grid security during low inertia and insufficient primary frequency capacity conditions. However, the inconsistent understanding of FFR is still confusing and unsettled. There have been practical needs for clear definition and performance requirements of FFR from inverter-based resources for further study and application. Aiming at the above problems, the system needs for FFR are analyzed in depth firstly. Then through the review of the existing usage of FFR, the recommended definition is given and the impact mechanism on frequency of FFR from inverter-based resources is studied. Finally, the performance requirements of FFR are clarified and the application effects are further verified.

The inertia response and primary frequency regulation capability of synchronous grids are declining owing to the increasing penetration of inverter-based resources. The fast frequency response (FFR) of inverter-based resources is an important mitigation option for maintaining grid security under the conditions of low inertia and insufficient primary frequency response capability. However, the understanding and technical characteristics of the FFR of inverter-based resources are still unclear. Aiming at solving the aforementioned problems, this paper proposes a definition for FFR based on the impact mechanism of FFR on system frequency. The performance requirements of FFR are clarified. Then, the effects of FFR on system frequency characteristics are further analyzed based on steady-state frequency deviation, the initial rate of change of frequency, and the maximum transient frequency deviation. Finally, the system requirements for FFR and its application effects are verified by simulating an actual bulk power grid, providing technical support for subsequent engineering application.

With the increase of the capacity of wind power, the pressure of frequency modulation by conventional synchronous generator gradually aggravates and wind farm to provide frequency modulation become a concern in the power industry. Wind turbine's inertial control is one of the ways to provide frequency modulation, which will release the rotational inertia through additional controls. But the frequency response performance of inertial frequency modulation by wind turbine under different wind power penetration levels is not fully studied at present. Therefore, this paper firstly discusses the wind turbine active power characteristics and simulation model based on reserve power frequency modulation and inertial control frequency modulation, and then carried out simulations to analyses the response of wind turbine with inertial control in frequency decline event, at last, frequency response of power system based on three types of frequency modulation under wind power penetration levels between 5%∼50% is analyzed in detail, include conventional reserve power frequency modulation, inertial frequency modulation, and the combined frequency modulation. The case study shows that inertial frequency modulation performance are various under different wind power penetrations, it has good effect on the grid frequency nadir under relatively low wind penetration levels, but not in the high wind power penetration levels, in high penetration levels the combined frequency modulation can be adopted to reduce the inertial control's negative impact.

As the penetration of renewable energy increases continuously,the inertia of synchronous power grid and the ability of primary frequency regulation are declining.If renewable energy power generators adopt the virtual synchronous generator (VSG)technology,they can make due contributions to slow down the rate of system frequency variation and reduce the system frequency deviation under the impact of large power shortage.Aiming at the current situation of unclear functional orientation of inertia support and primary frequency regulation in the research on VSG,it is urgent to define the functional orientation demand of both inertia support and primary frequency regulation of VSG in its application in the large power grid.Firstly,this paper analyzes the inertia support function of VSG and its physical meaning.Then the expression formula of inertia support power of VSG is deduced.Secondly,the distinction between the inertial support function and the primary frequency regulation function of VSG is analyzed in detail.Thirdly,this paper simulates and analyzes the roles of the VSG using different control functions in the dynamic characteristic of system frequency changing caused by power imbalance in the large-scale synchronous grid.Finally,it is pointed out that,in a large synchronous power grid,the impact brought by reduction of primary frequency regulation ability is more serious than that brought by the decrease of system inertia.The power system needs the continuous power support of VSG for the primary frequency regulation more than short-term inertia support power.

Short-circuit current level is an important symbol for the strength of power grid.Excessive short circuit current will threaten the safety and stability of the power grid,so the short circuit current control is an important part of the grid planning and operation.The paper analyzes the relationship between the short circuit current and system safety and stability,and proposes the short circuit current control requirements for multi-infeed DC receiving power grid based on the average difference between the short circuit ratio and the multi-infeed short circuit ratio,as well as the preliminary site selection for new DC substation in future multi-infeed DC receiving power grid.Taking the East China power grid planning as an example,the feasibility of the research results is verified.

As the penetration of RES (renewable energy sources) in large scale grid increases continuously, the inertia support capability and primary frequency regulation of synchronous power grid are both declining. A decrease in inertia is problematic because it negatively influences the dynamic characteristic of the system’s frequency. But its concrete impact is still not clearly distinguished from that caused by the decline of primary frequency regulation. Aiming at the above problem, firstly, the inertia support capability and its physical meaning of synchronous generator are analyzed in depth, and the expression formula of inertia support power of synchronous generator is deduced. Secondly, the distinction between the inertia support capability and primary frequency regulation of synchronous generator is analyzed in detail. Thirdly, the respective impacts of the inertia support and of the primary regulation on the dynamic characteristic of system frequency during power shortage disturbances in large scale synchronous grid are simulated and analyzed. Finally, all the study above points to a conclusion that the large synchronous power grids with increasing penetration of RES require more relatively continuous power support of the primary frequency regulation than the short term inertia support, because the impact brought by the decrease of system inertia support is less serious than that brought by reduction of primary frequency regulation ability in large scale power grid.

Saturated load is city's maximum affordable load, which is very important for urban development planning. As the power grid matures, the short-circuit current gradually becomes the key factor affecting the security of power grid, it is urgent to analysis the saturated load based on grid technology constraint of short-circuit current. In the paper, firstly, the regular pattern of power supply partition is put forward. Secondly, the typical partition structure model is extracted and the relationship between the model parameters and the actual power supply is deduced. Furthermore, a new method of calculating the saturated load level of power grid is proposed with the consideration of different partition structures and different power supply growth modes. Finally, the saturated load of an actual grid is calculated and the accuracy and effectiveness of the method is verified.