HM is one of the richest regions in new energy resources, which are wind and solar resources, and coal resources. Relying on the perfect electric transmission channel in Northwest China, HM has accelerated the construction of 10 million kW coal power base, 10 million wind power base kW and a 1 million kW solar thermal energy production demonstration base; and built the largest wind and fire transmission HVDC base in China. The development of wind power technology in HM reached 75.498 million kW, accounting for 62.9 percent of the total technology development in northwest China. In terms of solar energy resources, HM enjoys 3170-3380 hours of sunshine throughout the year and is one of the sunniest regions in China. Although the HM power grid offers such great advantages in the development of new energy, the large-scale grid connection and long-distance transmission of the new energy raises concerns about the safety of the HM power grid. Therefore, the security and stability of the HM power grid has become the focus of our research.
Electrical system security is a characteristic of the electrical system in the process of operation, which reflects the ability of the system to continue supplying energy to users with the required parameters after experiencing possible disturbances1.2. Although most countries adopt “security first” as a policy to guide the operation of the power system, some countries even elevate the power system as a national strategic defense system.3.4even so, power outages still occur from time to time, indicating that the capacity of current electrical systems is still not adequate to deal with emergencies5.6.
At present, with the continuous development of China’s electrical system and interconnection scale, Chinese electricity workers have built a strong and stable protection and control system based on three lines of defense to ensure stable operation, which ensures the stability of the power grid and the quality of power supplied to users, to a large extent. So much is said, power outage accidents in large areas are almost impossible to happen in China. The first line of defense relies on the reliable and fast action of the relay protection elements, to ensure that the system can restore stable operation over time and supply power normally in the event of a single fault. Gradually, the second line of defense includes a series of emergency control measures, which can ensure stable operation of the system at low cost, after experiencing an unlikely but severe disturbance. Key measurements include mechanical chopping, load chopping, local splitting and DC modulation. In engineering practice, the control framework of “offline pre-decision and real-time matching” is often used to form a large number of contingency control strategy tables of expected faults in the offline phase. The importance of the third line of defense is that when the system encounters rare serious faults and can no longer maintain stable operation, it should prevent system collapse and minimize load loss, i.e. a reasonable disconnect. However, there is no mature scientific connection between the three lines of defense at present. These lines of defense are still event-driven and act progressively according to the evolution of events.
With the rapid development of the national economy and the increasing improvement of the living standards of the people, the people’s demand for and dependence on electricity are becoming greater and, as a result, the power supply reliability requirements are becoming increasingly stringent.7.8. Admittedly, due to the impact of the natural environment, the production of new energy has a certain random and intermittent character. For example, when wind power is connected to the power grid, the security and stability of the power grid will be affected by the characteristics of wind power, the installed capacity of wind power, the scale of the power system wind turbine connected to the power grid, the structure and layout of the power supply. , and load characteristics, etc. In addition, the installed capacity of new energy affects the frequency stability of the system, thereby affecting the power quality of the power grid and the normal operation of certain frequency-sensitive loads. In addition, the new energy has small inertia support, large output uncertainty, low frequency regulation ability and damping characteristics, which leads to the growing problem of the stability of the system frequency. When the new energy loses its output due to power shutdown or blockage, the frequency of the power system will be reduced, especially when the penetration level of the new energy is high, which will directly affect the system frequency stability. Therefore, the new energy itself cannot provide reactive power compensation to the system, so it worsens the voltage level, reduces the system power quality, and affects the system voltage stability. In addition, the new energy is a source of interference for the power system, however, when the system fails and the fault is not eliminated in time, transient voltage instability will occur. All these issues require more technical attention for the safe and stable operation of the new energy supply system.9,10,11. The modern power system has gradually developed into a large-scale complex system with the characteristics of multi-level structure, multi-time scale, multiple control parameters, dynamic, real-time, non-linearity, openness, extended area, uncertainty, non-autonomy and sociality. economy12,13,14. Therefore, the level of security of an electrical system is difficult to characterize using a single index. However, traditional security scans, whether static security scans8,15,16,17 or dynamic security analysis18,19,20,21,22, usually can only analyze one aspect of power system security, which is certainly not enough to describe the security of the power system as a whole. Therefore, it is only through a comprehensive, multi-level and multi-angle analysis of all aspects of the system, including the randomness and fuzziness of components, loads and external conditions, using ‘a comprehensive assessment method, which we can obtain an objective and comprehensive understanding of the security of the electrical system23.
The so-called complete evaluation refers to the objective, fair and reasonable evaluation of the different aspects of the object evaluated. Its core includes the index system of the evaluated object and the selected evaluation method24. Currently, Multi-Criteria Decision-Making Method (MCDM) is a powerful tool widely used for global assessment, such as Analytical Hierarchy Process (AHP)23,24,25,26,27entropy weight (EW)25,26,27,28cloud method (CM)24.28gray relation analysis (GRA)29analytical network process (ANP)30,31,32Decision support testing and evaluation laboratory (DEMETEL)31,32,33,34,35Više-Kriterijumska Optimizacija I Kompromisno Rešenje (VIKOR)33,34,35,36,37,38,39and technique of order of preference by similarity to the ideal solution (TOPSIS)28,36,37,38,39 evaluation method based on the theory of proof. These MCDM assessment methods are currently used for indicator ranking, risk identification and assessment, cross-country sustainability assessment, economic assessment, social assessment, environmental protection, technical assessment and other issues. However, it has hardly ever been used in electrical system safety assessment. In addition, SWOT analysis with internal (Sstrengths and Oweaknesses) and external factors (Oopportunities and Threats) is also a powerful tool, helping to reveal different strategies for decision-makers and participants40. SWOT analysis is widely used in future foresight in different fields, but is not sufficient for decision making. Alternatively, MCDM methods can be helpful in overcoming this problem41,42,43,44,45,46which are used to make based on a pairwise comparison of criteria and alternatives43. For this reason, one of the MCDM – AHP methods is used for SWOT analysis in this study. The AHP SWOT-fuzzy was used to carry out the strategic selection of renewable energy resources for Pakistan47. Meanwhile, the integrated SWOT-AHP and Fuzzy-TOPSIS approach was used to assess sustainable energy planning strategies in Pakistan.48. Nevertheless, there is not a single study that uses the SWOT-AHP approach to evaluate and select the optimal improvement strategy for power system operational safety prospective.
In this study, the proposed SWOT-fuzzy AHP-MARCOS methodology is used for the evaluation of the safety perspective of power system operation and the study of strategic advantages in a case study of the HM power grid in the North West. from China. The obtained results are compared with the VIKOR and TOPSIS methods to validate the proposed integrated SWOT-fuzzy AHP method and the measurement of alternatives and ranking according to the compromise solution methodology (MARCOS)39.