Recently, the high frequency resonance problems of modular multilevel converter based high voltage direct current (MMC-HVDC) take place frequently, which have seriously threatened the stability of power systems. As the actual system network topology and operation modes change frequently, the high frequency resonance characteristics with the high frequency bandwidth of MMC-HVDC are complex, which bring challenges to the suppression of the high frequency resonance of MMC-HVDC. In order to improve performance of the suppression strategy of high frequency resonance in the case of multiple operating modes, firstly, the impedance characteristics of the system are established. Then the defects of different suppression strategies are analyzed. Based on the above research, a high frequency resonance suppression strategy based on an adaptive band-stop filter is proposed in this paper. By adjusting the number and parameters of additional band-stop filters, the strategy effectively solves the variable problem of high frequency resonance under different operation modes of AC power system and has strong adaptability. Finally, the effectiveness of the proposed suppression strategy is verified through PSCAD electromagnetic transient simulations.

The valve body loss of the modular multilevel converter （MMC） is relatively large, and the refined electromagnetic transient simulation of the MMC based high voltage direct current （MMC-HVDC） requires more accurate simulation of the valve body loss for system efficiency study. Aiming at the problems of virtua losses caused by the use of equivalent models in existing MMC-HVDC electromagnetic transient simulation, a MMC-HVDC electromagnetic transient modeling method with valve body loss based on current injection method is proposed, which includes accurate automatic calculation of valve body losses under different operating conditions using the finite sampling method. Referring to the calculation results, the current injection method is used to compensate for losses in the modeling and dynamic tracking and simulation of converter valve losses are realized. Finally, the accuracy of the proposed method is verified by constructing a MMC-HVDC electromagnetic transient simulation model in PSCAD. The research results can be used to accurately simulate MMC-HVDC electromagnetic transient modeling with valve body losses, and further research on loss reduction measures can be carried out through simulation.

Traveling wave protection is widely used as the main protection in DC lines. However, as a single-ended protection, traveling wave protection has the disadvantages of high maloperation and poor resistance to transition resistance. Based on the analysis of the propagation characteristics of traveling wave in DC transmission system, according to the different change directions of transient current traveling wave in internal and external faults, a longitudinal directional protection based on the transient current traveling wave mutation for LCC-MMC hybrid bipolar DC transmission system is proposed in this paper. If the mutation directions of transient current traveling waves on both sides are the same during the fault, it is an internal fault, otherwise it is an external fault. The simulation results of PSCAD and MATLAB show that the protection can quickly and accurately identify the faults under different fault types, different fault resistances and different fault location distance, so it has certain practicability.

At present, the voltage source coverter-based high voltage direct current （VSC-HVDC） transmission technology is usually adopted to access large-capacity offshore wind power to the power grid. A symmetical monopole wiring scheme is adopted for the offshore DC project currently in operation. Although the symmetrical bipolar scheme has a higher initial investment, its high reliability can improve the power generation profit in the operation stage. Based on the scale of 2 GW offshore wind power VSC-HVDC transmission, this study compares the design of symmetrical monopole system and symmetrical bipolar system. Two schemes for the layout and structural design of offshore converter station platform are proposed, and the initial construction investments and full life cycle profits of the two schemes are calculated. The results show that the symmetrical monopole scheme has economic advantages in whole life cycle economy compared with the symmetrical bipolar scheme.

The mechanical DC circuit breaker based on LC oscillating commutation can suppress the breaking arc, reliably remove the faulty line, and ensure the safe operation of the system. In order to analyze the influence of topological parameters of mechanical DC circuit breaker on its breaking, based on the principle of artificial zero-crossing arc suppression, a simulation model of DC circuit breaker is built in MATLAB/Simulink, and the effect of arc suppression under different models is analyzed. On this basis, the arc suppression simulation is carried out for the topology parameters of the circuit breaker under different commutation modes, and the influence of controllable parameters and uncontrollable parameters on the arcing duration is discussed. The simulation results show that in forced oscillation and self-excited oscillation commutation modes, controllable parameters have different effects on arcing duration, and uncontrollable parameters such as arc time constant and arc heat dissipation power have the same effect on arcing duration. This research results can provide effective reference for the design of arc suppression topology for DC circuit breakers.

To ensure the construction of the new power system, the impact of power electronic equipment harmonics on main network is analysed. Three main characteristics of harmonics of the main network are analysed: massive distributed harmonic source access, amplification effect of line capacitance on harmonics and long-distance propagation of harmonics. The above factors overlap with each other, causing the current main network to generally exceed the standard. On the basis of following the recognized source control of "who pollutes, who treats", this paper explores the harmonic control of the main network, analyses the advantages and disadvantages of different control measures from the mechanism and case. The scheme of "who suffers, who treats" to implement terminal control is suggested at present and comprehensive harmonic control measures should be considered from the source, region power grid and the newly built main grid stations in the long run.

With the development of new power systems and the increasing proportion of gas turbine units, coordinating power and natural gas systems is critical to sustainable energy supply and energy transition. Firstly, the research work on coordination mechanism design under information interaction environment of gas market and power market and multi-time scale trading decisions of market entities are reviewed, and the coordination mechanism practices in foreign countries from the perspective of market transaction modes and operating organizations are introduced. Then the market risk and response experience caused by natural gas supply shortage in extreme weather is analyzed based on abnormal electricity price events abroad, and the key problems of market coordination mechanism during the development of domestic gas and power markets are summarized. Finally, some suggestions adapting to the actual domestic situation on the coordination mechanism of the energy market are put forward, which include improving gas-power price transmission and compensation mechanism, strengthening diversified competition of natural gas market, improving information exchange and emergency management capacity between gas-power systems.

In order to solve the problem of voltage exceeding limits in the distribution network caused by a high proportion of renewable energy intergration, as well as the difficulty of balancing bidirectional voltage regulation and loss reduction optimization with existing voltage regulation methods, a series-connected double rotating phase shift transformer (DRPST) regulator based on the principle of phase synthesis is proposed, This regulator has the characteristics of bidirectional voltage regulation, high reliability and low cost. Firstly, the topology, working principle and equivalent circuit of DRPST are introduced and its simplified circuit model is established. On this basis, the causes of voltage exceeding limits are analyzed and an active distribution network model containing DRPST is constructed. Secondly, a real-time rolling two-layer optimization strategy based on DRPST is proposed. The inner-layer model is solved using a multi-objective particle swarm algorithm to minimize voltage deviation and line loss, and the optimal compromise solution of the Pareto solution set of the inner-layer model is determined by the fuzzy affiliation function method. According to the optimal compromise solution of the inner-layer model, the outer-layer model achieves undifferentiated control of the DRPST output rotor angle using the double-closed-loop PI regulation. Finally, simulation analysis is carried out by MATLAB/Simulink to verify the correctness and effectiveness of the proposed topology and control method.

With the implementation of the national carbon trading market policy, in order to fully tap the low carbon emission reduction capacity of the regional integrated energy system (RIES) and improve the economic interaction benefits of the multi-regional integrated energy system's access to the active distribution network (ADN), the regional integrated energy system alliance considering flexible resources and low-carbon interaction structure is proposed to participate in the optimal dispatching strategy for distribution network peak shaving. A master-slave game model with active distribution network as the main body and regional integrated energy system alliance as the slave body is established. The main body formulates time-of-use electricity pricing strategies with the goal of maximizing interaction benefits, while the subordinate members achieve multi-energy sharing through interconnection lines. Considering the carbon trading system, the objective is to minimize the combined cost of energy supply and carbon trading, responding to the main body's electricity pricing strategy. A cooperative game optimization model for the multi-regional integrated energy system is established. Flexible resource applications including demand response, energy storage and electric vehicles are introduced, cooperating with carbon capture electric-to-gas coupling units to optimize the low-carbon energy supply strategy of each system within the alliance, and meet the alliance's load demand. Based on Nash bargaining theory, the cooperative benefits among alliance members are distributed. The proposed strategy can effectively reduce the carbon emissions of the regional integrated energy system and ensure the economic benefits of master-slave interaction, as demonstrated through the numerical example.

Aiming at the practical problem that substations are prone to encounter unmanned aerial vehicle （UAV） intrusion, an improved anti UAV target detection method is proposed based on YOLOv5. Firstly, a four scale features fusion structure is proposed by improving the original model structure of YOLOv5 to enhance the detection capability of small-scale objects. Secondly, the C3 module in the original model is introduced into the Transformer encoder to improve the learning ability of small target feature information. Finally, the convolution channel attention module is integrated into the network, focusing on the learning of the target area to improve the representation ability of the model for features. The test results show that the overall recognition rate of the improved model is 90.2%, the average accuracy is 89.5%, and the forward reasoning speed is 160 frames per second. In addition, compared with other existing frontier algorithms, the overall performance of this method is better, and it can better meet the real-time detection requirements of anti UAV in substations.

Open-loop mode resonance theory is the research result to explain the mechanism of power system oscillation caused by wind power integration in which the reliability of the off-line time-domain simulation results based on the average model in the theoretical research is questionable. Firstly, to improve the reliability of engineering guidance for the theory, based on hardware in the loop (HIL) simulation, a phisical experimental platform is established. Secondly, a small signal model of the grid-connected system of doubly-fed induction generator (DFIG) wind farm is built, and a general method of open-loop mode analysis is proposed to assess the oscillation risk of the system. Finally, two examples are used to analyze and experiment the phenomenon of open-loop mode resonance. It is concluded that the experiment results are consistent with the results of open-loop mode analysis. Under the condition of open-loop mode resonance, the stability of power system decreases. The residue method can accurately predict the closed-loop mode of the system, and the reasonable tuning of parameters can reduce the impact of open-loop mode resonance.

Since the battery state of charge (SOC) cannot be measured directly, and the traditional SOC estimation methods have low accuracy. To improve the SOC estimation accuracy of lithium-ion batteries, this paper compares the effects of different deep-learning network models applied to SOC estimation and proposes a SOC estimation method for lithium-ion batteries based on the DRSN-CW-LSTM network. The method is based on long-short-term memory (LSTM) and deep residual shrinkage networks with channel-wise thresholds (DRSN-CW), using the data information of lithium-ion battery voltage, current, temperature, and capacity extracted in the deep residual shrinkage networks, and the time series data trends are further fitted by LSTM to achieve the prediction of SOC of lithium-ion battery during its service life. In the residual shrinkage module of the DRSN-CW network, an adaptive noise data processing function can be implemented to eliminate the negative impact of lithium-ion battery data stream quality on SOC prediction. In this paper, the proposed network is trained using the lithium-ion battery public dataset and the prediction effects of three neural network models on the two datasets are compared. The experimental results show that the MAE and RMSE of the deep learning model proposed in this paper are controlled within 5% of the average value on both public datasets, and have better noise immunity and prediction performance with high estimation accuracy compared with the other three deep learning models.

To comprehensively consider the interests of the supply side and demand side of the microgrid, a hierarchical optimization model of the microgrid is established. The upper layer optimizes the load curve with the net load cost and electricity consumption satisfaction as the goal, and the lower layer optimizes the output of each unit with the operating cost and environmental cost as the goal. And the sparrow search algorithm （SSA） is selected to solve the complex optimization problem. Aiming at the problem that SSA is prone to fall into local optimum, an improved sparrow search algorithm （ISSA） is proposed which improves the finder search mode and adds the mutation and greedy strategies. And adding the non-dominant sorting and roulette method into ISSA to improve it to the multi-objective algorithm. The example results show that a 10% transferable load ratio can reconcile the microgrid's interests of both supply and demand sides. Comparing the iterative results of ISSA with SSA, particle swarm optimization, chicken swarm optimization, and grey wolf optimizer proves that ISSA has a good optimization effect and stability.

In order to explore the performance difference of XLPE insulation materials for high-voltage cables at home and abroad, 220 kV domestic and imported cable insulation slice samples are prepared, and the molecular weight, melting and crystallization characteristics, cross-linking by-product content, short-time breakdown characteristics and long-time breakdown characteristics of the two insulation materials are compared. The experimental results show that the molecular structure, crystallinity, melting temperature and by-product content of domestic 220 kV XLPE cable insulation are not significantly different from those of imported insulation materials. The Weibull distribution characteristics of short breakdown field strength of two kinds of insulation materials are analyzed. It is found that the breakdown field strength of domestic XLPE insulation materials is higher than that of imported insulation materials at 30~50 ℃, while when the temperature exceeds 70 ℃, the breakdown field strength of domestic XLPE insulation materials decreases significantly and is lower than that of imported insulation materials, and the dispersion of breakdown field strength of domestic XLPE insulation materials is higher. The breakdown times of two kinds of insulating materials under five electric fields at 70 ℃ are analyzed. The direct relationship between breakdown electric field and time is analyzed by using the inverse power model, and the results show that the life indexes of domestic and imported 220 kV insulating materials are 19.3 and 19.5 respectively. The research results provide theoretical and experimental support for the development and application of domestic XLPE insulation.

The influences of pressure are not considered when testing the conductivity of semiconducting water-blocking buffer layer of HV cable. The surface resistance characteristics of buffer layer under different pressure are studied. Firstly, the surface resistance of buffer layer are tested, the statistical characteristics of which are explained through microstructure characteristics and nano-filler conductive mechanism. By applying loads of different weights on the surface resistance test electrode and the buffer layer between the electrodes, the relationship between the resistance value of the buffer layer and the external pressure is studied. Based on n-order resistance network and difference equations, the surface resistance model of buffer layer under pressure is established. The microscopic piezoresistive property of buffer layer and the simulation calculations of its model are used to analyze the characteristics of surface resistance test and the change law under different pressure. The results are helpful to understand the conductive characteristics of the buffer layer of HV cable under real operating pressure.