Hybrid modular multilevel converter (MMC) combines the advantages of half-bridge sub-module and full-bridge sub-module, and has a good application prospect. Compared with the half-bridge MMC, the charging process of hybrid MMC has changed a lot due to the addition of full-bridge sub-modules. Firstly, this paper studies and analyzes the charging characteristics of sub-modules in the case with and without transmission lines. It is found that there are some problems such as under-voltage of half-bridge sub-modules and over-voltage of full-bridge sub-modules during the uncontrolled charging period. Then, a corresponding charging strategy is proposed to prevent the above problems. A real simulation model is established in PSCAD/EMTDC. Through the simulation research in different sub-module proportion, the results verify the correctness of theoretical analysis and the feasiblity of the charging strategy.

Modular multilevel converter (MMC) technology is favored by academia and industry for high-power power conversion. A low-voltage small-current prototype of a re-configurable multi-function full-bridge MMC type test apparatus was developed. Firstly,the principle of MMC topology is demonstrated and the components of the small power prototype are described. Secondly, operating conditions of a full power system is simulated by this low-power prototype. At last, this low-power prototype is tested in experiment. The testing results verify the prototype.

Valve hall is the most important building of converter station, it is necessary to adopt effective seismic damping technology to control the seismic response of valve hall in high intensity area. Firstly, the structure and energy dissipation mechanism of buckling-restrained brace are introduced, and the energy dissipation scheme of buckling-restrained brace in the high intensity region of the valve hall structure is proposed. Then, the effect of different energy dissipation and shock absorption schemes for the valve hall structure under 9 degree frequent earthquake and 9 degree rare earthquake are compared and analyzed. The results show that the vibration mode and basic frequency of the valve hall structure with buckling support have not changed greatly; under the frequent earthquake, the seismic responses of the valve hall structure under each scheme are relatively close, and buckling-restrained braces have not yielded, which is equivalent to the ordinary steel support, providing the lateral stiffness; under the rare earthquake, the valve hall structure with buckling-restrained braces replaced has greatly reduced the seismic response, and the energy dissipation and damping effect of buckling-restrained braces is good.

In the neutral point grounding system, in order to suppress the subsynchronous resonance that may occur between the mechanical and electrical systems, a blocking filter is connected between the neutral point of the transformer high voltage winding and the ground. Due to the connection of the blocking filter, the voltage of the transformer’s neutral point to ground changes. Especially when a fault occurs, the surge in the voltage of the transformer’s neutral point may affect the insulation. Based on the actual data of the 500 kV booster station and blocking filter of the Tuoketuo Power Plant, a PSCAD/EMTDC simulation model is established. The simulation discovers the over-voltage law of the blocking filter zero-order reactor at different compensation levels and different ground faults. A method of suppressing the current flowing through the transformer neutral point through a zero-order reactor is proposed, and the zero-order reactor is obtained. The design value of the compensation degree of the filter and the configuration method of the insulation protection of the blocking filter are pointed out.

The transmission characteristics of electromagnetic pulses in cable are of great significance for off-line and on-line fault location of most traveling waves as well as detection and location of local discharge. Transmission loss occurs when pulses pass through a crosslinked polyethylene (XLPE) cable. Because different waveforms have different component parameters, wave propagation characteristics such as attenuation and propagation velocity will change accordingly. In order to obtain the propagation characteristics of different pulses in cables, a method based on the cable frequency domain model combined with the vector fitting method is proposed to obtain the propagation characteristics of electromagnetic pulses in cables on the premise of considering the skin effect of conductor core and the frequency variation characteristics of semiconductor layer. Based on this method, the propagation characteristics of different kinds of electromagnetic pulse waves are studied and analyzed, and the validity and accuracy of this method are verified by comparing with the improved J-Marti model in the traditional simulation software ATP-EMTP. Finally, based on genetic algorithm, the parameters of cable semiconductor layer are inversed, and a nondestructive extraction method for semiconductor layer parameters is proposed.

Aiming at the requirement of on-site partial discharge ultra-high frequency (UHF) signal detection, to solve the problem of large size of traditional Archimedes spiral antenna for partial discharge detection, a miniaturized Archimedes wide-band planar spiral antenna is designed by using a new sine wave loading mode in which the amplitude increases linearly with the amplitude angle. The radiation principle of Archimedes plane spiral antenna is analyzed, the structure parameters of miniaturized antenna are determined, and the port parameters and radiation performance of antenna are studied by simulation and measurement. The results indicate that the antenna has ultra wide band characteristics, the return loss is less than-10 dB in the frequency band of 700~3 000 MHz, and the maximum gain is not less than 5 dB in the frequency band of 500~3 000 MHz, which meets the requirements of partial discharge detection antenna. In the laboratory, the partial discharge test is simulated and the test performance of the miniaturized antenna is compared with that of the other two large gain antennas, the results show that the designed antenna has good detection performance and the advantage of small size is more suitable for partial discharge field detection of electrical equipment with complex structure.

The section constrains could make an impact on the calculating efficiency and results of the spot market clearing. At present, the pre-warning methods of transmission capacity constraints generally focus on deterministic scenarios through artificial experience. The operation mode of power system could be more complicated under spot market. To enhance the compatibility and comprehensiveness of section constrains in spot market clearing, this paper proposes a pre-warning idea of transmission capacity constraints based on Monte Carlo method to handle the uncertainty of the prediction error from renewable energy, load, and power plant bidding, which can effectively evaluate the safety margin/risk degree of transmission capacity constraints. On this basis, considering that Monte Carlo method needs to solve a large number of samples, which the computational burden is huge, this paper further proposes a fast algorithm for transmission capacity constraints pre-warning based on deep learning technology. The algorithm directly solves all the samples generated by Monte Carlo by function mapping. The samples can be calculated by the proposed algorithm in seconds. Finally, the effectiveness of the proposed method is verified in the IEEE 118 standard test system with renewable energy sources.

Due to its good reliability, direct-driven wind turbines (WTs) are increasing used in new wind farms, especially in offshore wind farms. With the increasing use of direct-driven WTs, a new type of sub-synchronous oscillation problems related to direct-driven WTs has occurred when connected to weak AC grid. Several studies have tried to analyze these oscillation problems, but most of them used the impedance method from the circuit equivalent perspective. Actually, the circuit equivalent and mechanical equivalent can be transformed to each other. To understand the sub-synchronous oscillation problems related with direct-driven WTs from the perspective of mechanical equivalent, this paper verifies that the dynamic interactions between the DC-link voltage control loop and the phase-locked loop (PLL) are the same as the two-masses shaft model based on the motion equation method, and proposes a quantitative method to evaluate direct-driven WT’s intrinsic mode characteristics in sub-synchronous range. Results are all verified in MATLAB/Simulink. In addition to impedance method, this paper provides another modal perspective to understand sub-synchronous oscillation problems related to direct-driven WTs.

In order to accurately capture the impact factors of the equipment reliability parameters, such as geographical region, outage liability reasons, and available repair resources, an accurate model of reliability parameters is proposed for equipment of distribution network in this paper. Firstly, with the historical data categorized according to the outage liability reasons and the proposed refined modeling standards, an accurate failure rate model of equipment is established. Then, according to the actual workflow of fault repair adopted by the grid operator, an accurate repair time model of distribution network equipment is established. Finally, the reliability assessment of medium-voltage distribution network is performed with the reliability parameter model and the the block algorithm. Case studies on an actual distribution network show that compared with the traditional parameter model, the proposed parameter model can obtain specific reliability parameters according to the characteristics of the equipment. The results of reliability evaluation of distribution network are more consistent with the statistical level of system reliability, and have higher reference value for the identification of critical components.

Dispersed wind farm access to the distribution network with high penetration may cause problems such as over-voltage and overcurrent. This paper presents a method for determining maximum allowable capacity of dispersed wind farm. Firstly, based on the voltage and current constraints, the calculation method of the maximum allowable capacity of distributed wind farm is introduced. Then, the grid configuration optimization model and its multi-objective optimization algorithm are studied. The PG&E 69 node example is used to verify the feasibility and effectiveness of the algorithm. The maximum allowable capacity change normalization index is used to evaluate the meshed operation of the distribution network, and the results prove that the meshed network is conducive to improve the allowable penetration level.

The study is conducted to compare economy of centralized photovoltaic power in western China and distributed photovoltaic power in eastern China. The generation cost compositions are first analyzed. Then the cost per kWh models of photovoltaic power, including generation cost model and comprehensive cost model, are established based on levelized cost of energy(LCOE). The generation cost model contains construction cost, maintenance and operation cost, financial cost, depreciable cost and tax cost. The comprehensive cost model is obtained by considering additional simplified transmission cost. Quantitative analysis on economy of these two kinds of photovoltaic power is compared. Based on the proposed models and parameters, the generation cost of centralized photovoltaic power in western China is lower than that of distributed photovoltaic power in eastern China regardless of transmission cost. The comprehensive cost of centralized photovoltaic power in western China is close to that of distributed photovoltaic power in eastern China considering transmission cost.

The regional unified electricity spot market plays an important role in promoting the optimized allocation of power resources in a wider range and promoting the cross-regional consumption of renewable energy. Based on the Southern China Regional Electricity Market, building a unified electricity spot market in the Guangdong-Hong Kong-Macao Greater Bay Area will play an important role in optimizing the power structure of Hong Kong and Macau, reducing electricity costs in the Greater Bay Area, and improving the reliability of Hong Kong and Macau power system operations. However, there are huge differences in the economic, legal, and administrative systems of the Greater Bay Area, which determines that current power resources cannot completely flow freely in the Greater Bay Area. It is quite difficult to directly build a unified electricity market in the Greater Bay Area. This paper takes the unified electricity spot market as the research object. Firstly, it compares and analyzes the characteristics of typical foreign regional market models and the adaptability to the Greater Bay Area spot market. Secondly, based on the status quo of the Greater Bay Area, the market model and construction path of the unified electricity spot market in the Greater Bay Area are proposed, and a mathematical model and solution of market clearing in the initial stage, decentralized coordination stage, and unified stage are proposed.