As an indispensable part of the electricity market architecture, the spot market is the key to the coordination of market transaction and system operation security. In this paper, two major models, the incremental optimization and integrated optimization model, are studied. The differences between the two models in the treatment of power grid constraints, transaction delivery mode,the priority level and optimization result are analyzed. Examples are presented to illustrate the differences of dispatching result and total generation cost with incremental optimization and integrated power optimization. For the typical international clearing mode of spot market, including the Bid/Offer based balanced market mechnism of the UK and the intergated power optimization mode of USA, comparisons are conducted. Finally, based on the comparison of incremental and integrated optimization, the paper puts forward suggestions for the development and construction of China’s power spot market.

In the context of low-carbon economy and Energy Internet, the integrated electric power and natural gas system (IEGS) is an effective carrier to achieve regional resource optimization configuration and new energy consumption. This paper proposes an IEGS optimal scheduling model that takes into account the synergy between power-to-gas and carbon capture. By introducing a carbon capture power plant-electric gas-to-gas system synergistic utilization framework, the captured high-concentration carbon dioxide (CO₂) is used as a raw material power-generating equipment, and it is proposed that the use of gas storage devices to solve the CO₂ capture and utilization time is not matching questions. Aiming at the strong non-convex nonlinearity of the model, the model is transformed into a mixed integer second-order cone programming model by piecewise linearization and second-order cone relaxation. Finally, the improved continuous cone optimization method is used to ensure the strictness of relaxation. The simulation results show that the proposed model reduces the carbon emission and the amount of abandoned wind, and realizes the low carbon economy operation of IEGS, and the proposed algorithm can effectively improve the efficiency of the solution.

AC-DC hybrid half-wavelength system is an effective way to solve energy-supplying along half-wavelength. When there is a short circuit fault on the AC bus of the DC station and the fault is not removed in time, voltage along the AC system will increase and lead to the action of over-voltage protection and exitance of DC system. The valve of DC system will be also subjected to the impact of over-current. This paper proposes a method of accessing current limiting module at the DC bus to stable DC voltage by limiting the rising speed of the fault current. This way enables the AC system to continue to power the DC system under fault condition and improves the fault-crossing capability of system. Finally, the effectiveness of the method is verified by simulation.

The frequency stability problem brought about by the asynchronous operation of the Southwest Power Grid is outstanding. The research results of the suppression of ultra-low frequency oscillations need to be further practiced in the actual power grid. This paper firstly summarizes the problem of ultra-low frequency oscillation, and points out that the root of ultra-low frequency oscillation lies in the control system of hydropower unit prime mover. Then the limitations of existing oscillation suppression measures are analyzed and the additional damping control method based on governor (GPSS) is proposed. The ultra-low frequency oscillation suppression method is based on the time-frequency analysis method, and the control parameters are set. The single-machine-loaded hydropower unit speed control system model is built in Simulink to verify the suppression effect of GPSS. Finally, the semi-physical simulation test platform is built and the ultra-low frequency oscillation suppression effect of GPSS is verified, which provides practical support for the application of GPSS in the actual power grid.

When high density and large capacity wind power is transmitted by HVAC/HVDC hybrid power grid, the interaction between them becomes more complicated. Large scale wind powers connecting to grid centrally haven’t be considered so far in the mechanism of AC tie-line power oscillation caused by commutation failure. Firstly accordingly the relationship between equivalent inertia of system and damping is researched, and the influence on damping made by large scale wind power connecting to grid centrally is quantified. On the basis, mechanism of AC tie-line power oscillation caused by commutation failure under the circumstance of large scale wind power connecting to grid centrally is first proposed. Fast algorithms for peak value and peak time calculation of power oscillation on AC tie-line after commutation failure are proposed. The mechanism and algorithms are verified by simulation analysis of a Chinese regional grid. It provides theory and technical basis for arranging operating schemes and control measures of interconnected power systems.

The small disturbance signal model of three permanent magnet direct-drive synchronous generators (PMSGs) connecting to the grid via VSC-HVDC is established. By calculating the eigenvalues, it is found that there are close sub-synchronous oscillation modes in the system. When the wind speed and other parameters of the PMSGs change slightly, the eigenvalues of these close sub-synchronous oscillation modes do not change much, but the participation factors of these close modes change greatly, which indicates that the dominant factors affecting the oscillation are sensitive to parameter changes.

There is good application prospect in the transmission and grid-connection of large-scale wind power and other renewable energy of VSC-HVDC transmission grid with overhead lines. Due to the rapid rise of DC current under DC line fault, DC circuit breaker with high speed and large capacity is generally used to isolate DC faults in the VSC-HVDC engineering. However, the manufacture of DC circuit breaker is difficult and costly, which hinders the development of DC grid. Then, VSC-HVDC transmission grid based on hybrid MMC and fast vacuum breaker is proposed. It makes full use of the control ability of hybrid MMC, it can ensure that the converter does not lock during the DC fault, so that the DC power grid can quickly and flexibly switch to a new operation state after the DC fault is cleared. The power interruption time of the DC grid is shortened, which can improve the utilization of the DC grid. At the same time, the fast vacuum breakers are installed in the DC line to replace the high-speed large-capacity DC circuit breaker, so as to reduce the construction cost of the DC grid. Finally, simulations based on PSCAD/EMTDC platform are executed to verify the correctness of this method.

The main function of DC reactor in the VSC-HVDC system is to suppress the rate of rise and peak value of the fault current, and to isolate the fault of the DC side with DC circuit breaker. The inductance value of DC reactor determines the operational safety and system stability of the inverter,it plays an important role in the excecution of control and protection strategy of the entire system. At present, there is no relevant design criteria and method of calculation for the parameters of the inductance value of DC reactor. For the different parameters of the VSC-HVDC system,it’s very important to search for a reasonable method for determining the inductance value of DC reactor. This paper analyzes the generation mechanism of short-circuit current of half-bridge converter,and the parameter value calculation is based on the typical case of medium voltage flexible DC. Double-ended VSC-HVDC system is bulit in PSCAD/EMTDC electromagnetic simulation software to verify the correctness of the design method by simulation.

Based on the switching characteristic of insulated gate bipolar transistor (IGBT), this paper proposes a structure and parameter design method of hybrid on-load tap changer for distribution transformer by adding an auxiliary switching circuit composed of IGBT and power diode to the mechanical on-load tap changer. The proposed structure leads power electronic switches in when the tap is switched, and realizes the on-load arcless adjustment of the distribution transformer tap by utilizing the switching performance of the power electronic switches. Finally, the simulation model of hybrid on-load tap changer for distribution transformer is built in MATLAB/Simulink, which verifies the feasibility of the proposed structure and parameter design method of hybrid on-load tap changer.

In order to solve the problems of poor effects in operation and maintenance training for smart substation, a simulation system of operation and maintenance based on augmented reality technology is introduced and implemented. Firstly, the differences between augmented reality (AR) and virtual reality (VR) are compared, and the design framework of operation and maintenance simulation system based on AR technology is proposed. Then, the 3D model base of each equipment scenario in substation is established by data preprocessing, hierarchical pattern recognition and image shape retrieval. The key technologies such as three-dimensional registration and tracking technology, virtual-real fusion technology and human-computer interaction are further introduced in smart substation. Finally, the above key technologies are integrated into the operation and maintenance simulation platform for smart substation. Practical training examples demonstrate that based on augmented reality technology and virtual reality scenario to simulate the operation, maintenance and repair of intelligent substation, a more realistic immersive virtual training environment is constructed for substation operation and maintenance personnel from both visual and tactile aspects, and the simulation effect is more realistic, effective and practical.

Improving the current divergence characteristics of tower foundation can effectively reduce the tower grounding resistance and reduce the cost of secondary artificial grounding. At present, the research on tower foundation grounding needs to be deepened. In this paper, the finite element simulation software COMSOL is used to build single-pile concrete foundation and multi-pile concrete foundation. Five kinds of resistance reduction methods for tower foundation are put forward based on flexible plane composite grounding material, including full-laying, lower-half-laying, upper-laying, middle-laying and lower-laying, and simulation test is carried out to verify the resistance reduction efficiency. The influences of applied radius, tower foundation depth and groundwater position on grounding resistance are studied. The influences of aquifer on current density distribution is compared, and the influences of three multi-pile resistance reduction schemes on ground potential and current density are also studied. The simulation results show that the resistance reduction efficiency can be improved by increasing the applied radius and the depth of tower foundation. The resistance reduction efficiencies of external application of pile-by-pile foundation from large to small are in the order of full application, lower half application, lower, middle and upper. The grounding resistance of foundation is reduced by aquifer, and the effect is obvious when the aquifer is close to the surface. When multi-pile foundation with higher voltage level adopts external application to reduce resistance, the efficiency of external application of ring wrap is higher than that of pile-by-pile application. The conclusions of this paper can provide reference for actual transmission line design and lightning protection grounding construction.

The distribution of power equipment in substation is concentrated and their shapes are complex. The whole distribution of power frequency electric field in substation is influenced by 500 kV switching field, transformers and reactors. Firstly, in order to simplify the calculation, 3D modeling of these large power equipment is carried out. Then Biosaval’s Law is applied to the calculation of power-frequency magnetic field, and then the distribution of power-frequency magnetic field around the large power equipment is calculated and analyzed. The results show that the power frequency magnetic fields in the 500 kV switching field area varies between 0.1 and 1.6 μT, the power frequency magnetic fields in the transformer area varies between 1 and 6 μT, and the power frequency magnetic fields in the reactor group varies between 0.1 and 4.5 mT, which is relatively large. The results can provide reference for optimizing the distribution of power frequency magnetic field in the design stage.