The rapid development of modern power electronics technology promotes the insulated gate bipolar transistor （IGBT）wide range of applications in the AC motor drive，inverter，switching power supply and new energy industry. In the application process of IGBT，due to the complex and varied circuit topology and system conditions，the problem of gate waveform oscillation usually exists. How to understand the oscillation mechanism and suppress methods becomes the basis of IGBT security and stability application. According to the IGBT internal parasitic parameter structure and switching process，the IGBT gate turn-on oscillation，turn-off oscillation and short-circuit oscillation were introduced in detail，the mathematical model of the gate oscillation process and the oscillation of the radio frequency （RF）positive feedback oscillation （turn-off oscillation and short-circuit oscillation） were deduced. The corrective measures of adding negative feedback or decreasing the positive feedback gain were put forward. By improving the experiment of different oscillations，the effectiveness of the suppression measures was verified，and the stability and reliability of IGBT application were improved.

In view of the need to test the operation of power electronic equipment under various working conditions in the current new power system，a control strategy using linear auto-disturbance rejection technology was proposed to study the power grid simulator with line impedance simulation function. On this basis，in order to separate and control the harmonics，the improved filter bank was used to separate and filter the grid voltage to achieve the effect of independent impedance simulation and harmonic output. Simulation and experiments show that the proposed control strategy has good output effect.

High-frequency transformers are an essential component in series-resonant DC/DC converters，and their stable operation has a decisive impact on the reliability，efficiency，and power density of power supply systems. Nanocrystalline magnetic cores are widely used due to their advantages of high saturation magnetic flux，high magnetic permeability，low coercivity，and low high-frequency losses. In order to improve the power density of DC/DC converters，the leakage inductance of high-frequency transformers is commonly used as a resonant inductor to achieve the soft-switching characteristics of the switching devices. However，nanocrystalline alloys possess a high electrical conductivity，and when high-frequency leakage magnetic flux passes perpendicularly through the surface strip，it induces strong eddy currents，which could result in potential thermal issues，thereby compromising the stable and safe operation of the transformer and the system. An improved finite element simulation method for high-frequency transformers was proposed for determining the distribution characteristics of additional eddy current losses induced by high frequency leakage flux at large leakage inductance by building a three-dimensional model of nanocrystalline strips at the edge of the independent core，and its validity was verified by temperature rise experiments.

The rapid increase in the proportion of renewable energy in the East China Power Grid System and the continuous decline in the rotational inertia and frequency modulation resources in the system will pose a threat to the system's frequency immunity and stability. The existing research focuses on the development and application of renewable energy system inertia and primary frequency modulation technology，while there is less research on the medium and long-term development priorities of multiple renewable energy frequency response technologies such as wind power，photovoltaic，and energy storage. Therefore，a research on the evolution path of collaborative frequency modulation technology in the East China Power Grid System was proposed. Firstly，based on the disturbance events of the East China Power Grid over the years，the system's multi-source collaborative frequency response system was analyzed，and the influencing factors of various frequency modulation entities in the disturbance events were quantitatively analyzed by decision-making trial and evaluation laboratory（DEMATEL）model. Secondly，the development priority and optimal evolution path of collaborative frequency modulation technology in East China Power Grid were prospectively analyzed based on the weight distribution of influencing factors，providing a theoretical basis for the orderly development of renewable energy frequency modulation technology in East China Power Grid. This has consolidated the frequency security of the East China Power Grid under the high proportion of new energy feeds.

Aiming at the poor robustness and system vibration problem of asynchronous motors under the traditional sliding mode control，a variability coefficient power exponent reaching law （VCPERL） was proposed to dynamically change the control coefficients according to the position of the sliding mode surface，and the sliding mode controller was designed based on this reaching law. Firstly，according to the advantages of quick-power reaching law （QPRL） and the double-power reaching law （DPRL），which have different reaching rates at different positions of the sliding mode surface，meanwhile，the tanh（x）was used to replace the sign（x），and a variable coefficient was introduced into the reaching law. Secondly，the stability of the new reaching law was proved based on theoretical analysis and simulation. Finally，the VCPERL was applied to design the sliding mode controller according to the theory of vector control oriented by rotor magnetic chain and the dynamic mathematical model of asynchronous motor. The simulation results show that compared with the traditional PI control，QPRL and DPRL，VCPERL has strong immunity to load disturbances and fast recovery capability，which can effectively improve the dynamic response performance of the system.

A three-phase four-wire energy storage type low-voltage control device with the function of grid voltage unbalance compensation was designed. Firstly，a control method based on active voltage droop and constant power factor was introduced in detail to solve the problem of low voltage at the terminal of substation area power grid，which can compensate the low voltage at the terminal of substation area power grid. Secondly，a three-phase unbalance voltage compensation method based on negative sequence and zero sequence virtual impedance was proposed，which directly controls negative sequence and zero sequence voltage and omits the application of current sensor. Finally，a Matlab/Simulink simulation model and a 50 kW mid-point capacitor three-phase four-wire T-type three-level energy storage converter experiment platform were built，and the effectiveness of the proposed control scheme was verified through simulation and experiments.

The problem of AC train passing neutral section can be solved by ground's flexible passing neutral section method. However，for multisystem electric locomotives，the switching of power supply system in neutral zone is much more complicated，but there is little research at present. Based on the approach of vehicle switching combined with vehicle kinetic energy，a method to stabilize the DC-link voltage of multisystem electric locomotive in the process of power supply system switching was proposed，and selected the typical multisystem electric locomotive of certain model as the research object. Firstly，the traction drive system topology of the multisystem electric locomotive was introduced. Then，a power supply system switching method was designed for it. Finally，real-time simulation of the proposed power supply switching method was conducted on a hardware-in-the-loop experimental platform，and the good DC-link voltage stabilization effect of the proposed method was verified.

Accurately estimating the state of health （SOH）of lithium-ion batteries is crucial for optimizing energy storage systems' operation，management，and maintenance. Existing methods that extract health features from single-stage charging data fail to exploit battery aging information fully，leading to a suboptimal estimation accuracy. In addressing this issue，a SOH estimation method for energy storage systems based on the fusion of two-stage charging data for lithium-ion batteries was proposed. Combining health features from both constant voltage charging and relaxation stages，the proposed method effectively mines aging information embedded in two-stage charging data，thereby improving SOH estimation accuracy. Additionally，the introduced health feature combination does not require the use of constant current charging stage data，making it less affected by the uncertainty of charging start points and more adaptable to practical energy storage conditions. Experimental results demonstrate that the proposed health feature combination significantly outperforms single-stage feature combinations，with an average absolute error of 0.66%，mean squared error of 0.85%，and an average coefficient of determination of 0.97.

Thermal and magnetic protection circuit breakers provided short circuit protection by instantaneous tripping devices. In the magnetic field formed by the coil with current，the moving armature and stationary core overcomed the spring force and engage under the influence of electromagnetic force，thereby pushing the circuit breaker mechanism to operate and causing the product tripping. During the entire process，only when the electromagnetic force reaches a certain value could be the moving armature and stationary core reliably engage at the preset current value. In actual engineering design，in order to simplify the design and calculation process，issues such as magnetic leakage may be ignored. Therefore，the theoretical calculated magnetic attraction force，i.e. spring reaction force，will be smaller than the preset target. By analogy calculation method，it is possible to directly eliminate the influence of magnetic leakage and part manufacturing accuracy on the test results during the manufacturing process，and complete the design of the instantaneous release device once. Finally，practical application cases were used to illustrate how to accurately and quickly design an instantaneous release devices through a combination of theoretical calculations and experiments.

Taking the planar rotation mechanism as an example，a magnetic coupling wireless power transmission system was designed and studied from two perspectives：the spatial structure of the coils and the resonant compensation circuit. This system aimed to reduce the voltage fluctuations caused by significant changes in mutual inductance between the coils during rotation and ensure system stability. Regarding the spatial structure of the coils，four coils were fixed on a stationary plane at the transmitter end，while two coils were used at the receiver end and fixed on the plane of the rotation mechanism to ensure that they could induce a certain amount of current during rotation. For resonant circuit compensation，an LCC/S-type compensation network was adopted. The current at the transmitter end is only influenced by the compensating inductance and input voltage，further enhancing the coils' resistance to offset. This approach provides significant advantages in terms of power transmission and efficiency improvement. Finally，a simulation and experimental platform was established to validate the design. The experimental results demonstrated that using two receiver coils and the LCC/S topology resulted in improved output voltage，power，and efficiency while maintaining stability to a certain degree.