Multi-terminal hybrid ultra-high voltage direct current (UHVDC) transmission system provides a more flexible mode to meet the needs of longer distance and larger capacity renewable energy. In this paper, the hybrid system composed of the conventional UHVDC at the sending and the valve group series structure at the receiving is used. The RT-LAB real-time simulation model of bipolar hybrid system is built, the closed-loop connection with control and protection system is realized. The results verify the effectiveness of the closed-loop simulation model and the control and protection strategy. It can realize the verification of control and protection system function and dynamic performance of the hybrid system, and provide technical support for the application of multi-terminal hybrid UHVDC project.

The mechanism on frequency limit control (FLC) improving frequency stability is well analyzed, characteristics between reverse frequency differential model and integrated negative feedback model are studied, the operation of FLC on Yunnan asynchronous interconnection network is introduced with the proposal of FLC parameter optimization on Xinsong-Dongfang UHVDC Project, and finally the FLC malfunction and operation suggestion are put forward. The conclusions are: 1) FLC can well improve frequency stability of Yunnan Power Grid in case of generators tripping, heavy load disturbance and HVDC accident. 2) It causes neither constant transformer tap changing nor constant AC filter action. 3) Xinsong-Dongfang UHVDC FLC system owns a desired DC power modulation after FLC parameter optimization. 4) Reverse frequency differential model gains an advantage over integrated negative feedback model and deserves wide use.

The full chain test of VSC-HVDC valve control is an important method of validating the functional and dynamic performance of VSC-HVDC valve control system. In this paper, the full chain test scheme of VSC-HVDC valve control is put forward, which includes framework of valve control and of full chain test system, main simulation functions, test items design, etc. Firstly, the framework, features and multilayer connection relations of valve control are analyzed. Secondly, based on the features of valve control, the full chain test system including pulse distribution and power module control is proposed. Finally, the full chain test system is implemented on the real-time simulation platform. And the valve control applied in practical engineering is tested comprehensively. Meanwhile, the typical test results are analyzed, which shows that the proposed scheme and system of full chain test can meet the requirements of testing the functional and dynamic performance of VSC-HVDC valve control.

As the core device of power electronic converter, the reliability of IGBT power modules is currently the focus of academic and industrial circles. In this paper, based on the actual structure of IGBT module, an electrical-thermal-mechanical simulation model of IGBT module is constructed by means of finite element analysis software. Aiming at the problem of IGBT module bond wire failure, the effects of different bond wire materials and surface metallized layer materials on temperature and stress nephograms of IGBT module are researched. The simulation results show that there is a strong correlation between the selection of bond wire material and the temperature distribution inside the module, and the selection of metallized layer material has a strong correlation with the stress distribution inside the module. Therefore, the temperature and stress in the module can be greatly reduced by reasonably choosing the type of metallized layer material and the bond wire material, thereby it also can reduce the risk of bond line failure and improve the reliability of the module.

At present, most voltage source converters (VSC) in known VSC-HVDC projects adopt modular multi-level converter (MMC). Among the MMC sub-modules, half-bridge sub-module is most widely used. The high reliability of HVDC transmission system requires the construction of half-bridge sub-modules to adopt press-pack insulated gate bipolar transistor IGBT. In this paper, the electro-thermal coupling simulation of the press-pack IGBT half-bridge module MMC is carried out, and an electro-thermal coupling simulation method based on Foster thermal network is explored. The safe operation domain of MMC system is described from the perspective of thermal stability.

Optimizing the operation mode of the flexible interconnection device in the distribution network can improve the power supply reliability, and reasonable configuration of flexible interconnection device requires comprehensive consideration of equipment investment economy, power supply reliability and operation economy. In this paper, the operation configuration of flexible interconnection device is studied. Based on the average loss reduction rate of power load under the expected fault set, the distribution of flexible interconnection device is optimized, the distribution point that has great influence on power supply reliability is selected. Then, multi-objective fuzzy optimization is adopted to optimize the capacity of flexible interconnection device, based on the established objective function of minimum load loss and minimum distribution network loss. The approach degree of fuzzy optimization is taken to evaluate the optimal solution of multi-objective function. Moreover, the deterministic constraints of AC/DC power flow balance, and the uncertainty constraints of branch safety current and node voltage considering the power fluctuation of load and distributed generation are also included. Finally, based on the improved IEEE 33 node distribution network model, the operation configuration scheme proposed in this paper is verified and analyzed.

Featured with long distance, large capacity, extra high voltage and AC-DC interconnected operation, China Southern Power Grid is interconnected with surrounding areas and countries through multiple AC lines, and has complex operation characteristics. In combination with the operation practice of Southern China regional power system during recent years, the operation characteristics of complex AC-DC interconnected power grid is discussed in depth. This paper reveals the main security risks in the operation of Southern China regional power system, including: the prominent risk of single-cause common mode fault, the prominent stability problem caused by the primary and secondary equipment failure in the AC-DC close coupling scenario; and the security of main power grid caused by the stability problems of frequency and rotor angle seriously. On the basis of summarizing the stability control methods, this paper proposes to build the power system security and stability defense lines based on wide-area information, which will make the China Southern Power Grid more secure and stable in the future.

The unbalanced power caused by AC/DC faults in large power grid may cause local power grid to exceed the stability limit, or the voltage of key buses to exceed the voltage limit. In serious cases, it may lead to cascading faults or large-scale blackout. In order to accurately simulate the power flow distribution when the power grid transits to a steady state after faults and determine the validity of control strategy that controls the unsafe power fault, a rapid power flow calculation method after fault considering the automatic control strategy is proposed in this paper. According to the influence of automatic devices such as safety control system, system protection device, primary frequency modulation of generator, automatic generation control (AGC) and automatic voltage control (AVC) on the active and reactive power injection of grid nodes after AC/DC fault at different time scales, the action timing and strategy of various automatic devices are simulated to form the system power flow from fault occurrence to steady-state process, so as to determine the overload equipment, the stable section of power flow exceeding the limit and the key bus of voltage exceeding the limit, which provides a basis for the online control decision of large power grid. The effectiveness and practicability of the method are verified by the case analysis of the actual online data of power grid.

Conventional power supplies are replaced by DC system and local new energy gradually. Increasing the reactive power output of conventional power supply in advance will induce potential risk of steady state over voltage and the insufficient dynamic reactive power reserve. Therefore, a two-stage heuristic optimization method considering start-up measures is proposed to solve the transient voltage dip security preventive control model. In order to reduce the computing scale, faults are selected according to the weakest transient voltage bus and the measures are selected according to the performance-price ratio. The reactors/capacitors switching measures and reactive power adjustable units are searched with the reserved part of the reactive adjustable space. Then, the start-up unit measures and the balancing active power adjustable unit measures are searched if the transient voltage safety margin cannot be improved obviously. Combinatorial optimization and enumeration are adopted in parallel computation to improve computation efficiency. The effectiveness of the proposed method is verified by an example of an actual power grid.

The necessity of the construction of southern regional electricity market simulation system is deeply analyzed based on spot market reform practice. Then, this paper studies and designs the functional framework and corresponding implementation scheme of full-process electricity market simulation system from three aspects of system application scenario, system menu and system function, which adapt to multi-types, multi-varieties and multi-agents and conform to the actual situation of southern region. Research in this paper will provide strong technical support for the construction and development of spot market in southern region, and also provide valuable experience for the construction of other provincial electricity spot markets in China.

This paper summarizes the market coupling process in the European electricity markets, and introduces the price coupling of regions project which is the platform to calculate the electricity prices and cross-border power exchange among the European countries. The Pan-European Hybrid Electricity Market integration algorithm is studied. An explanation of different pricing models is given, these models are the local marginal price model, the available transmission capacity model and the flow-based market coupling model. Finally the characteristics of market coupling model are summarized, and the suggestions for the southern electricity spot market are proposed.

Affected by adjacent construction, the deformation, cracking, opening and leakage of joint of pipe-jacking tunnels are found out. The effects of nearby deep excavation (L/D_e≤0.75) on a pipe-jacking tunnel of high-voltage cables in Guangzhou are studied by numerical simulation method. Results show that vertical displacement of cable tunnel is obviously observed rather than lateral displacement. This might be attributed to the large stiffness of supporting system and large excavation depth. The radial deformation of cable tunnel is relatively small and can even be ignored. According to the current design scheme of retaining structure and the net distance between excavation site and tunnel (L=12 m), the displacement and radial deformation of pipe-jacking cable tunnel are controllable. However, when the net distance L reduces to 2~5 m, the uplift of cable tunnel may exceed the allowable limit.