Under the dual carbon background of AC and DC hybrid power grids have the new feature of "strong HVDC and weak AC system" and power electronization， in order to effectively reduce the risk of large-scale power outages in power grid，it is necessary to build a secure and reliable comprehensive defense system to ensure the stable operation of the power system. Based on the traditional three defense lines in China，the objectives and design principles of the UHV AC and DC power grid security defense system that adapt to the dual carbon background of China's power grid were determined，and designed the overall structure of the UHV AC/DC power grid security defense system，main functions and specific configuration schemes.

The traditional ultra high speed permanent magnet synchronous motor（PMSM）driver uses PWM equivalent sine voltage output，which leads to severe motor heating due to large harmonics，and it cannot be used in situations where the input voltage changes over a large range，such as fuel cells. To reduce the heat generated by the motor and further expand its application scenarios，a new sine wave voltage output inverter based on three-phase DC/DC converter was proposed，a 120 kr/min ultra high speed PMSM was successfully driven. The experimental results show that the output voltage harmonics of the three-phase sine wave voltage output inverter are lower than those of traditional inverters，which reduces the heat generation of the motor under high speed conditions and has practical engineering application value.

The primary side feedback can stabilize the output voltage，and improve the service life of the equipment without using the secondary winding detection error signal. The topology of active filter and the improved method of primary side feedback were adopted. The performance of active EMI filter topologies was analyzed from insertion loss and equivalent circuit，the active filter with voltage sampling and current compensation was adopted. Through describing the mechanism of primary-side feedback of sampling knee point voltage，the small signal modeling of the converter in discontinuous current mode（DCM） was carried out，and the compensation network was designed to ensure the stability. The simulation and experimental results show that the active EMI filter can effectively replace the traditional filtering method，and the original side feedback method can detect and correct the output voltage fluctuation to ensure the voltage stability.

The VPX power standard is currently the most compatible military embedded computer standard internationally， and its modules can stably power multiple different functional modules in the chassis. A VPX power board based on VITA46 and VITA62 standards was designed. The design architecture， ideas， and functions of the 6U structure power supply board were mainly introduced. The circuit characteristics of hardware protection， slow start， acquisition， and DCDC module power supply were analyzed. The software working mode， management process， and external structure design were described. Maxwell thermal simulation was used to analyze the working status of the board in high temperature environments. Finally， the stability and reliability of the board's power on timing were tested through experiments， and load stability and voltage stability under load. Through the research and development of software and hardware， the proposed design has accumulated some experience in terms of autonomous hardware design， software adaptation， and other aspects.

A method for establishing edge triggered pulse control switch state time was proposed to address the divergence of floating capacitor voltage and DC capacitor midpoint voltage in a 5-level active neutral point clamped（ANPC-5L）inverter using the space vector pulse width（SVPWM）algorithm in the g-h coordinate system. The fluctuation of floating capacitor voltage and the offset of DC side capacitor voltage were reduced. The principle that the fluctuation of the floating capacitor current causes the voltage deviation of the floating capacitor was used. Based on the principle that the same level is output under different switch states，and different switch states cause the current direction of the floating capacitor to be opposite，within a complete cycle，the floating capacitor current cancels out each other，reducing the voltage fluctuation of the floating capacitor. An active power flow model was established to balance the midpoint voltage of the DC side capacitor by reducing the voltage fluctuation of the floating capacitor. Finally，by building a simulation platform and comparing the capacitor voltage balance of ANPC-5L before and after the application of the proposed method，the validity of the method was verified.

Based on the principle of magnetic coupling resonance technology， a bilateral LCC topology compensation network parameter design method was adopted. Firstly， the mathematical model of the main circuit of the bilateral LCC topology was analyzed， and the inductance ratio of the coil self-inductance and the series compensation inductance was set.Then， by writing an M file and building a Simulink simulation platform， according to the relationship between inductance ratio and efficiency， found the optimal efficiency point. Finally， a all-SiC MOSFET device system experimental platform was built for verification. The experimental results show that the efficiency of the coupling mechanism can be maintained at about 95% and the maximum efficiency of the system is more than 92.5% in the range of full power offset by setting the appropriate inductance ratio， which proves that the compensation network parameter design method is effective.

Aiming at the adverse effects of large-scale electric vehicle charging load on the distribution network，based on vehicle to grid（V2G）technology，a V2G reactive dispatching strategy combining the non-dominated sorting genetic algorithm and the local optimization of global objectives algorithm was proposed. The superstructure was based on the ordered charging strategy of electric vehicles based on the non-dominating ranking genetic algorithm，and the standard deviation of the user's starting charging time distribution was optimized with load mean square deviation，charging cost and voltage offset rate as the target，and the starting charging parameters that meet the needs of users were obtained. The sub-architecture was a local optimization algorithm for global targets，which optimizes the amount of reactive power compensation with voltage offset rate as the target for vehicles that can provide reactive power compensation. Finally，taking the IEEE100 node system as an example to simulate，it was found that this method can provide charging station operators with better load peak-valley difference，charging cost，voltage quality and other charging methods，and the hierarchical scheduling strategy can better ensure the safety and economy of the power grid compared with the single-layer scheduling strategy.

Aiming at the problems of high investment cost，low efficiency of electrolyzer operation and high fluctuation of power input in the new energy electrolytic water to hydrogen microgrid system，the scenery hydrogen production capacity configuration scheme with the installation cost of microgrid equipment and the comprehensive optimization index of the system consisting of load hydrogen deficiency rate and power abandonment rate as the objective function and the power regulation method for achieving maximum hydrogen production efficiency based on the characteristic curve of electrolyzer efficiency was proposed. The battery was selected to supplement the electrolyzer according to the fluctuation of the power of the scenery generation，and the elitist non-dominated sorting genetic algorithm（NSGA-Ⅱ）was written to solve the capacity configuration of each device in the system，and the multi-objective particle swarm optimization（MOPSO）was used to perform the maximum efficiency power regulation of the electrolyzer. In comparison to the scenery complementary hydrogen generation scheme，the capacity configuration model achieved a lower overall optimization index with a similar installation cost. After power regulation，the average electrolyzer input power fluctuation rate and electrolyzer efficiency decreased by 58.37% and 37.54%，respectively，which significantly improved the system stability and energy utilization.

To enhance the economic and operational flexibility of accompanying energy storage facilities in new energy power stations，as well as to improve the stability of supplying electricity directly to large users and the grid-friendliness of large-scale new energy power stations，a two-stage robust configuration and optimized operation strategy for hybrid energy storage on the generation side was proposed. In the first stage，based on the empirical mode decomposition and Hilbert-Huang transform of demand power signals，considering the investment cost of energy storage and the supply-demand requirements of new energy power stations and grid integration，a robust configuration model for various types of energy storage units in the hybrid system was constructed. In the second stage，with the first-stage optimized configuration as a constraint，an optimization model for the operation of hybrid energy storage was developed with the objective of reducing net load fluctuations while meeting the power supply requirements of the power station and grid integration.The effectiveness and competitiveness of the proposed models and strategies were demonstrated through case studies using actual wind power and load data from a certain province，providing technical support and decision-making references for the coordinated development of new energy power stations and energy storage.

Unbalanced grid voltage will affect the normal grid connection operation of the wind energy conversion system（WECS），resulting in fluctuations in system output power and distortion of output current. In addition，in the actual permanent magnet synchronous wind power system，there may be uncertainties in the network side circuit parameters due to changes in ambient temperature and detection errors. If the parameter changes，the performance of traditional control methods will decline. Based on this，a model-free adaptive control（MFAC）scheme based on grey prediction was proposed to alleviate the performance degradation problem caused by parameter uncertainty and make the control system have better anti-interference ability. Furthermore，three independent control methods were adopted to solve the problem of grid connected output power fluctuation and current distortion under unbalanced grid voltage. The simulation results show that the proposed control strategy not only has good static and dynamic performance under nominal parameters，but also improves the robustness of the system when the grid side inductance changes，which verifies the superiority of the proposed scheme.

To address the issue of transient overvoltage at the sending end of the wind farm caused by faults in conventional high-voltage direct current systems system，the impact mechanism of DC faults on transient voltage changes at the sending end was analyzed. It was discovered that the reactive power surplus of the AC system after the fault was the root cause of the sudden voltage rise. To address this，a reactive power coordination control strategy based on distributed synchronous condensers and doubly fed induction generators（DFIG） was proposed. A distributed synchronous condenser was installed at the grid-connected bus of the wind farm to stabilize the grid-connected voltage and improve the low-voltage or high-voltage ride-through capability of the wind farm using its unique reactive power regulation characteristics. During various severe fault scenarios in the DC system，the DFIG participated in reactive power regulation by changing the reactive power reference value，and improved system voltage during the fault period with the distributed synchronous condenser. The DFIG wind farm was controlled to exit reactive power regulation during steady-state after the fault，to ensure economic operation after fault recovery. Simulation results using PSCAD software demonstrate that the proposed reactive power coordination control strategy effectively suppress transient voltage variations of the wind farm after faults，improving the reliability and economy of the wind farm，particularly during commutation failure and direct current blocking in the system.

The multi-source monitoring data of switchgear contains rich equipment operating status information，and analyzing it can achieve switchgear fault diagnosis. A fault diagnosis method for switchgear based on SMOTE-SSA-CNN was proposed. Firstly，based on monitoring data such as switchgear voltage，current，and temperature and humidity，the synthetic minority over-sampling technique（SMOTE） algorithm was used to expand the original dataset，solving the problem of severe imbalance between positive and negative samples in the original dataset. Then，the sparrow search algorithm（SSA） was introduced to optimize the hyperparameters of convolutional neural networks（CNN），such as the size and number of convolutional kernels，the number of fully connected layer neurons，and the learning rate，in order to improve the accuracy of the model's fault diagnosis results. Finally，the performance of the established SMOTE-SSA-CNN model was evaluated through example analysis，verifying the effectiveness of the proposed method for switchgear fault diagnosis. Compared with traditional fault diagnosis methods，the proposed method has better convergence and higher accuracy.

The main circuit faults of the four-quadrant rectifier and the corresponding influences were analyzed and summarized，focusing on the analysis of the voltage and current parameter equations in the pre-charging process of the intermediate DC link，and the estimation method of the converter input current and the intermediate DC link voltage was proposed. The estimated parameters were compared with the actual detection results，and the corresponding fault detection can be carried out by using the performance of different faults in the pre-charging process. Through simulation and experiment，different faults were simulated and analyzed，and the results show that the fault detection method proposed is effective and feasible.