Transactions of China Electrotechnical Society updated on April 19, 2024

Transactions of China Electrotechnical Society is a comprehensive academic journal in the field of electrical engineering sponsored by the China Electrotechnical Society, reporting international and domestic leading academic and scientific research achievements in basic theoretical research and engineering application. Ma Weiming, academician of the Chinese Academy of Engineering, is the director of the editorial board of the Journal and the editor-in-chief of the journal.

Research on the integrated control strategy of frequency modulation of battery energy storage cluster considering the time delay characteristics of thermal power

Authors: Xiao Jiajie, Li Peiqiang, Mao Zhiyu, Tu Chunming

Abstract:In this paper, a comprehensive control strategy for battery energy storage clusters to participate in grid frequency regulation is proposed, which can achieve better frequency control effect and safe and economic operation of battery energy storage clusters.

Firstly, in order to solve the problem of low frequency modulation accuracy caused by the response time delay characteristics of thermal power units, and even reverse misregulation under rapid load changes, a joint frequency modulation control model of battery energy storage and thermal power units based on all-pass filtering was proposed, and the model parameter design method was further proposed based on the spectrum analysis of the actual load disturbance data, so that the battery energy storage as a phase shifter to control the load disturbance phase was basically consistent with the output of thermal power units, which effectively improved the frequency modulation effect. Then, a SOC consistency control strategy based on the dynamic correction of power weights in the frequency modulation cycle and the sequential input of energy storage units is proposed, which solves the problem that the consistency iteration direction is opposite to the frequency modulation power response direction when the SOC difference is small, takes into account the SOC consistency maintenance and power response, and reduces the influence of frequent switching of energy storage units on its service life.

At the same time, considering that the battery energy storage needs to switch frequently in the frequency modulation process, the energy storage cluster group control mode is adopted to reduce the life loss of the energy storage cluster and improve the economy of energy storage frequency modulation. Finally, a regional power grid simulation model is built to verify the effectiveness of the proposed strategy.

Optimal scheduling of multi-microgrid cooperative game considering multiple uncertainties and electricity-carbon coupling trading

Authors: Dong Lei, Li Yang, Chen Sheng, Qiao Ji, Pu Tianjiao

Abstract:Under the background of carbon peaking and carbon neutrality, building a low-carbon energy system is an important direction and implementation path to achieve the goal of carbon peaking and carbon neutrality. In order to promote the local consumption of energy in multi-microgrid systems and the operation of low-carbon economy, this paper studies the cooperative operation of multi-microgrid systems and electricity-carbon coupling trading in uncertain environments.

Firstly, for each microgrid, a cogeneration operation mode coupled with a power-to-gas carbon capture system was constructed, and a low-carbon operation model of multi-energy microgrid was proposed based on the local carbon trading market and the tiered carbon trading mechanism. Secondly, considering the fact that there is uncertainty in both new energy power generation and electricity market prices, the methods of opportunity constraint and robust optimization are adopted to reduce the impact of uncertainty. On this basis, based on the Nash negotiation theory, a cooperative game model of multiple microgrid power-carbon coupling is established, and each microgrid entity can participate in the higher-level energy market and the local energy market at the same time to trade electricity and carbon emission allowances.

Finally, the non-convex cooperative game problem is decomposed into two linearly solvable subproblems, and the alternating direction multiplier method is used to solve the problem. Through the verification of examples, the proposed method can effectively improve the economic benefits of each microgrid and reduce carbon emissions.

A robust unit combination scheduling method for frequency safety constraint distribution considering the support characteristics of wind power and condenser

Authors: Jiang Yihang, Zhao Shuqiang, Wang Hui, Wang Yingshan

Abstract:In the process of energy transition, the frequency security of the power system is becoming increasingly prominent, and the existing dispatching methods are difficult to take into account the frequency security and wind power consumption requirements. Therefore, a robust composite scheduling method of frequency safety constraint distribution considering the support characteristics of wind power and condenser is proposed.

Firstly, based on the inertial control and power backup control mechanism, a modeling method for the frequency support characteristics of wind power under all wind conditions suitable for the dispatching model was proposed. Then, the frequency support characteristics of the synchronous condenser and the modified thermal power units with the ability of phase modulation conversion are analyzed and modeled, and they are unified into the system frequency response model, and the safety constraint set of the frequency dynamic process is extracted by alternating the time-frequency domain solution, and an improved piecewise linearization method is proposed to linearly transform the nonlinear term. Finally, based on the data-driven distributed robust optimization, the wind power uncertainty is modeled, and a two-stage distributed robust unit combination model embedded in the frequency safety constraint set is constructed, and the model is solved by the improved column and constraint generation algorithm.

The results show that the active substitution effect of the condenser has a positive effect on reducing the curtailment of wind and improving the rotational inertia level of the system, and considering the support characteristics of wind power and condenser in the scheduling framework can improve the economy while taking into account the frequency safety of the system.

Analysis of transient energy transfer and oscillation characteristics of doubly-fed wind turbines under nonlinear elastic coupling

Authors: Zhang Xiangyu, Huang Yongxuan, Fu Yuan

Abstract:Efficient transient energy transfer between new energy and synchronous generator sets is the key to suppress power oscillation in the new power system. In this paper, the coupling relationship between the virtual shafting system between the synchronous generator set and the doubly-fed wind turbine in virtual synchronous operation is analyzed. Secondly, through the nonlinear power coupling, the cubic stiffness is introduced to establish a dynamic model of the two-degree-of-freedom system with wind power under nonlinear elastic coupling. Based on the Hamiltonian principle, the transient energy transfer process of the grid-connected wind power system after the introduction of cubic stiffness is analyzed, the necessary conditions for complete energy transfer between units are deduced, and the nonlinear elastic coupling control strategy of doubly-fed wind turbines is proposed, and the optimal design of controller parameters is completed according to the obtained necessary conditions. Finally, a high-proportion simulation system for wind power is built to verify that the doubly-fed wind turbines can efficiently transfer transient energy under the proposed control method, and significantly improve their power oscillation suppression and frequency support capabilities.

Line protection method of three-terminal hybrid DC transmission system based on control and protection coordination

Authors: Dai Zhihui, Niu Baoyi, Li Tiecheng, Xi Xiaorui, Li Hangze

Abstract:The sensitive and reliable protection principle is of great significance for the safe operation of the multi-terminal hybrid DC transmission line system, and the existing line protection principle of the multi-terminal hybrid DC system is easily disturbed by transition resistance, noise and other factors, and mostly ignores the coordination and cooperation between the inverter control link. Therefore, a single-ended protection scheme for multi-terminal hybrid DC lines based on control features is proposed. Firstly, the fault area was identified by using the direction of the fault current. Secondly, based on the difference of inductance in the equivalent impedance loop under different fault conditions, the difference of the integral value of the control signal at different locations is analyzed, so as to construct the fault identification criterion in and out of the area, and the fault selection is carried out by using the ratio of the integral value of the positive and negative control signals. Finally, the simulation verification is carried out by PSCAD/EMTDC, and the results show that the proposed protection scheme can identify various faults reliably and sensitively, and has strong anti-interference and anti-transition resistance capabilities.

Analysis of transient characteristics of distributed condenser and study on the stability mechanism of transient power angle

Authors: Wang Tong, Wang Xiaotong, Han Zichang, Wang Zengping, Zhao Wei

Abstract:At present, the proportion of new energy is rising, and the distributed condenser can effectively suppress the transient overvoltage of the new energy machine end and improve the transmission capacity of new energy, but the condenser also has the risk of transient power angle instability in the process of power grid failure.

In view of the transient characteristics and power angle stability mechanism of distributed condensers, firstly, a time-scale transient analysis model of power angle of condensers was established to retain the voltage characteristics of new energy grid-connected points, and the interaction mechanism between the power angle of the condenser and the voltage of the new energy grid-connected points after fault clearance was analyzed based on the relationship between electrical quantity and phasor. Secondly, the process and causes of the secondary phase angle jump of the voltage at the new energy grid-connected point in the process of fault transience and fault steady-state are analyzed, and the influence mechanism of phase angle jump, transition resistance and new energy low voltage ride-through control strategy on the swing direction of the power angle of the condenser is clarified. Finally, based on the transient energy function, the influence of new energy output power, condenser capacity and transmission distance on the transient power angle stability of the condenser is analyzed, and the correctness of the proposed mechanism and analysis is verified in the improved IEEE39 node system.

Considering the power supply restoration strategy of multi-terminal flexible interconnected distribution network with synergy between transfer and reconstruction

Authors: Xu Yutao, Feng Qihui, Tan Zhukui, Zhang Chao, Yuan Xufeng

Abstract:The flexible interconnection device (FID) realizes the flexible interconnection between different feeders of the distribution network, and can realize the rapid restoration of power supply in the distribution network after the fault. In this paper, a two-stage power supply restoration strategy for multi-terminal flexible interconnected distribution network based on FID and network reconstruction is proposed, taking the four-terminal flexible interconnected distribution network with DC network as the research object.

Firstly, on the basis of analyzing the working principle of the FID operation mode, a FID smooth control structure with fast fault transfer and a VSG control strategy considering the synchronous grid-connected control of the switch are proposed to support the rapid power supply recovery of the first stage of FID after the fault. Then, by establishing and solving the global optimization model considering the capacity constraints of the contact switch and FID, the second-stage power supply recovery strategy combining FID and network reconstruction is obtained to recover the power loss load to a greater extent. Finally, PSCAD/MTDC simulation software was used to build a 58-node four-terminal flexible power distribution system with DC network for simulation verification. The results show that the power supply recovery strategy can not only realize the uninterrupted power transfer of part of the load, but also greatly improve the load recovery level through network reconstruction.

An active comprehensive load model considering distributed renewable energy horizontally

Authors: Lan Tiankai, Sun Huadong, Wang Qi, Zhao Bing

Abstract:The installed capacity of distributed new energy in China is increasing, which has become an important factor influencing the safety and stability of large power grids. The current distributed new energy modeling methods are not mature and are difficult to be used for the simulation and analysis of large power grids in engineering practice. To this end, this paper introduces the current situation of distributed new energy model in the analysis of China's large power grid, discusses the engineering requirements of distributed new energy equivalent model, puts forward the modeling idea of "active comprehensive load model with distributed new energy", proposes the model structure and parameter calculation method with the goal of large-scale engineering application, and introduces the specific case of the preliminary application of the proposed method in S Province, China. The application results show that the proposed active comprehensive load model can meet the needs of large power grid modeling and simulation analysis with a high proportion of distributed renewable energy, and has the potential for large-scale engineering application.

Comparative analysis of post-disaster recovery methods of distribution network considering the dependence characteristics of user load decision-making

Authors: Deng Rongnan, Song Meng, Gao Ciwei, Yan Xingyu, Bai Wenchao

Abstract:Distribution network failures caused by extreme weather, cyber attacks and other factors have a wide range of impacts and bad social impacts, and resilient distribution networks are the basic guarantee for economic development and people's livelihood. The results show that the load characteristics are closely related to the load recovery decision in the process of distribution network recovery, but most of the current studies do not fully consider this, and the user load behavior cannot be accurately quantified, and the distribution network often faces safety problems such as voltage and power flow overrun in the process of load recovery.

In view of this, this paper firstly analyzes the dependence characteristics and evolution mechanism of user load decision-making in the process of distribution network recovery from both objective and subjective perspectives, namely cold load pick-up (CLPU) and load profit-seeking, and uses data-driven and knowledge-driven methods to accurately quantify their operation characteristics, laying a foundation for distribution network load recovery. Secondly, two load recovery methods of distribution network considering the dependence characteristics of user decision-making are proposed, one is the two-layer optimization model of distribution network load recovery based on Karush-Kuhn-Tucher (KKT) conditional processing, and the other is the adaptive recovery model of distribution network based on time label sequence, so as to realize the rapid load recovery of distribution network taking into account the characteristics of user decision-dependence. Finally, based on the system function curve, the two methods are compared and analyzed by using the indicators such as maximum load loss, load interruption rate, and privacy exposure.

The results show that in the process of distribution network recovery, considering the load decision dependence characteristics can avoid safety problems such as voltage overrun in the process of distribution network load recovery, and improve the operation safety of distribution network. Compared with the two-layer model, the proposed adaptive model only takes 33% of the two-layer model to solve the problem while improving the degree of user privacy protection.

Grounding fault protection algorithm for active distribution network with small resistance based on phase difference

Authors: Li Jun, He Min, Huang Shoudao, Liu Jun, Liu Zhiyong

Abstract:After the large-scale distributed power generation is connected to the distribution network of the small resistance grounding system, the fault current changes significantly, and the single-phase grounding fault will be misoperated when the zero-sequence current protection method is used to remove the single-phase grounding fault. In order to solve the above problems, a grounding fault protection algorithm for active distribution network of small resistor grounding system based on the phase difference between phase voltage and zero sequence current was proposed. By establishing the structure and model of the electrical system of the distribution network grounding fault including multiple distributed generators, the phase relationship between the phase voltage and the zero sequence current at the fault time is theoretically deduced and calculated, and the phase difference interval of different grounding fault locations is analyzed, and the grounding fault is judged and protected according to the phase difference range.

The simulation results show that the method can reliably judge the grounding fault under the conditions of multiple transition resistances, different distribution of power supply access number and capacity, and various types of cable lengths, and the load fluctuation when the neutral point of the distribution network adopts the small resistance grounding system, and the DG neutral point is suitable for grounding and non-grounding methods.