UHV three-terminal hybrid DC power distribution is flexible, compared with the conventional two-terminal DC power, the interaction between power regulation and AC system is complex. How to reasonably distribute the three-terminal DC power will directly affect the safe and stable operation of the integrated power grid. In order to solve this practical problem, taking the world’s first UHV three-terminal hybrid DC—±800 kV Kunliulong DC project under construction as an example, this paper analyzes the power distribution requirements in the normal DC operation, pole (valve group) fault and power emergency control scenarios in the first time, summarizes the basic principles of three-terminal UHVDC in combination with the actual operation of the China Southern Power Grid(CSG), and proposes the UHV three-terminal hybrid DC power distribution schemes in various typical scenarios. All the principles and schemes have realized the flexibility of UHV three-terminal hybrid DC power distribution, and can reduce the power loss of UHVDC as much as possible, improve the interaction between AC and DC, and promote the safety and stablity of the main network of the integrated power grid.

When turning on a thyristor valve, the AC system current, stray capacitance current, damping branch current, valve arrester current, and other currents are coupled to each other, which determines the opening process of the thyristor together. When turning off a thyristor valve, the reverse recovery process, short-circuit impedance of transformer, and damping branch parameters determine the thyristor turn-off voltage together. Based on PSCAD/EMTCD, this paper builds a thyristor valve electromagnetic transient simulation model to study the influencing factors and time-varying mechanism of the voltage and current of switching process of thyristor valve. The result shows the saturation reactor and damping resistance play important roles in suppressing the open current of capacitor, and the short-circuit impedance has a greater effect on the commutation overshoot. Studying the influencing factors of the switching process of the thyristor valve has certain guiding significance for parameter selection and device design in engineering design.

As a result of prosperous development of HVDC transmission, multiple HVDC sending systems have been transmitting power through identical AC tunnels. These tunnels are thus turned into junction areas, interconnecting with multiple HVDC sending systems. Their existed regional security and stability control system strategies are no longer compatible with changed system operation characteristics and issues. Worse still, strategy actions might even introduce risks into operation. To solve such dilemma, this paper produces analysis on operation risk of junction areas of multiple HVDC sending system, proposing a method of region security and stability control system design for these areas according to operation issues. This method has been practically applied in security and stability control system transformation in Huangping area in Yunnan province. The design is proved to be effective for coping with operation risks and it is also suitable to be referred in security and stability control design projects for similar areas.

In order to study the influence of DC power grid structure changes on power flow transfer and explore how to design a DC grid with better power transfer characteristics, the DC distribution coefficient is used to quickly calculate the power flow increment and load rate of the other lines when one line is disconnected. Power distribution entropy is used to measure the distribution of load rate of the DC grid. Power transfer entropy is used to reflect the influence of power flow transfer of the other lines in the grid. The structural eigenvalue is used to measure the DC line characteristics. A±400 kV five-terminal MMC-MTDC system is established in PSCAD/EMTDC, and simulation results show that power distribution entropy of the grid decreases with the increase of the structural eigenvalue; The power transfer entropy of the line connecting to the power supply and the load is relatively high. After adding a line connecting to the power supply and the load, the power transfer entropy of the DC line in the grid generally has different degrees of reduction. It is concluded that in the design of the DC grid structure, priority is given to erecting the DC line connecting the power supply with the load, that can effectively reduce the power distribution entropy of the DC grid and the power transfer entropy of the DC line. So that the DC grid has better power flow transfer characteristics.

Voltage sourced converter-high voltage direct current (VSC-HVDC) transmission has been widely applied all over the world owing to its unique advantages. Converter valve is the key equipment of VSCs, its losses are significant to the economically operation of VSC stations. Analysis and accurate measurement of the losses can make great contribution to efficiency optimization, devices selection and thermal design, etc. This paper investigates the losses measurement technology of power electronics equipment and surveys the academic research at home and abroad of the double pulse method, electrical method and thermal method for losses measurement. It comes up with three test schemes for measuring losses of VSC sub-modules respectively, the schemes include measuring method, test circuit design, equipment selection, software platform and its control method, test procedure, uncertainty and loss estimation method. In the physical test platform, tests based on three schemes are carried out, the uncertainty of tests results is analyzed. This paper provides reference for measuring losses of VSC sub-modules in practical projects.

Load aggregator (LA) is an important measure to integrate distributed load side resources and realize “source-load” interaction, which has flexible demand side response capability. In order to take the influence of its economic dispatch on the power flow of the distribution network into consideration, a two-layer optimal dispatch of distribution network considering load aggregator is established in this paper. By performing second-order cone relaxation on the power flow equation, the original mixed integer nonlinear programming problem is transformed into a second-order cone programming (SOCP) model, which reduces the difficulty of solving the problem and improves the efficiency of the solution. The simulation results of the improved 33-node distribution network verify the feasibility and applicability of the proposed method.

New energy generation exhibits intermittent /volatility, and the theoretical study of power system planning, operation and control based on uncertainties using point estimation method is the current research hotspot. This paper focuses on the three-point estimaten method, which is commonly used in the calculation of probabilistic load flow in power systems in recent years, to carry out an improved study, and proposes an improved three-point estimate method for probabilistic load flow calculation. In order to overcome the problem of insufficient tail accuracy of the three-point estimation method, the method is calculated by adding a combination of normally distributed tail points and combining with the three-point estimation method, and the correlation input variables are processed by Nataf transformation and Cholesky decomposition. The Cornish-Fisher series is fitted to obtain the probability distribution function. The IEEE14 node and IEEE33 node systems were tested, and the results verify the correctness of the improved three-point estimate probabilistic load flow algorithm.

Effective short circuit ratio and critical effective short circuit ratio are common indicators for quantitative evaluation of the static voltage stability margin of a single-infeed LCC-HVDC system, but these indicators can not reflect the change of the static voltage stability of the system after STATCOM is fed in. This paper linearises STATCOM near the operating point based on the same dynamic response characteristics to small disturbances, equivalent the system containing STATCOM to a single-infeed system, specifically discusses the influence of STATCOM on the system structure parameters and state parameters combing the control mode of STATCOM in the equivalent single-infeed system and clarifies the mechanism by which STATCOM increases the static voltage stability margin of the system. Theoretical analysis and electromagnetic transient simulation results show that the static voltage stability margin of the system containing STATCOM can be accurately evaluated by comparing the relative sizes of ESCR and CESCR in the equivalent single-infeed system.

As an energy substitution analysis and prediction tool with flexible parameter structure, long-range energy alternatives planning system(LEAP)can provide strong support and guidance for guiding the work of electricity sub-stitution, and it has been widely used in a variety of energy planning and environmental analysis. Aiming at the basic application demand of accurate parameters of LEAP model, this paper proposes a specific parameter classification prediction method. First, a targeted data structure is established, and the parameters that need to be input into the LEAP model are divided into general parameters and scenario parameters according to the uncertainty of their development. Secondly, improved GM(1,1) model, an improved gray model based on background values and initial conditions, is used to predict the general parameters. Thirdly, a Gray-Monte Carlo model is proposed to predict scenario parameters and their occurrence probability. Finally, the correctness of the parameter classification and the parameter prediction model are verified by example analysis, and it is proved that the co-application of the two prediction methods improves the accuracy of the parameters and further improves the accuracy of the electric energy substitution prediction.

The paper aims to investigate the influence of typhoon on the design wind speed in Guangdong coastal area, and to develop technological process for improving wind zone atlas for transmission line. An optimization method based on the YanMeng typhoon wind field model and Poisson-Gumbel distribution is proposed. Based on the historical maximum wind speed data and design wind speed results of 23 coastal stations in Guangdong, the performance of the typhoon wind field model is verified. The results indicate that typhoon is the main source of maximum wind speed in coastal areas of Guangdong. The consistent temporal variation of the maximum wind speed are shown between simulation and observation data, with the mean absolute error (MAE) of 0~2 m/s. Compared with wind zone atlas of design wind speed for coastal power grid of Guangdong, similar spatial distribution characteristics are reproduced by typhoon wind field model with higher spatial resolution. It is reasonable to apply typhoon wind field model in wind zone atlas distribution simulation and optimization in coastal areas.

In order to analyze the temperature distribution of circuit breaker tulip contact, thermal field simulation model for tulip contact is built combined with the electromagnetic-stress-thermal coupled finite element simulation and virtual material method which models the contact resistance characteristics of tulip contact. The temperature rise characteristic of tulip contacts under rated current condition and short-circuit condition is analyzed with the model. Results show that virtual material method can describe the shrinkage resistance and additional resistance at the end of the contact finger simultaneously, and is capable to simulate the partial high temperature of the contact interface. Then, the influence of spring pressure and pressure uniformity on the thermal field of tulip contact is analyzed. Results show that the decrease of spring pressure and the imbalance of contact finger pressure may lead to the increase of the temperature rise of the tulip contact. The proposed method can be used as a reference for the design and the overheating analysis of tulip contact.

Based on the existing research achievement of submarine cables, the research status of submarine cables at home and abroad is summarized. Taking the XLPE insulation submarine cables as example, this paper systematically summarized the research achievements including the state monitoring and integrated online monitoring systems of submarine cables; the calculation and analysis of submarine cables ampacity, temperature field and energy loss; the construction of the theoretical models of submarine cable designs; the mechanics and load analysis; and the studies on electromagnetic performance and laying technology. The causes of existing problems are analyzed, and improvement measures and suggestions are put forward from the aspects of the structure and process designs of submarine cables, the fault monitoring technologies for operation and maintenance, the laying technology, the simplification and optimization of theoretical analysis models of mechanics and load, electromagnetic field performance, ampacity and temperature field.