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.

The grid frequently exhibits weak grid characteristics because the impedance fluctuation range of the collector network is broad in high permeability distributed generation system. The coupling relationship between the phase-locked loop and the grid impedance leads to desynchronizing between the grid-following（GFL）converter and grid，which seriously threatens the stability of the system. However，the slow power response of grid-forming（GFM）converter is contradictory to the maximum power point tracking of source side，and the economy is poor. Consequently，in order to increase the grid-connected reliability of the system，some units are necessary to be configured flexibly，which will switch to the GFM mode. Concentrating on the grid-connected converters，a dual-mode adaptive flexible switching control strategy for distributed energy was proposed considering friendly interaction between grid and converters to maximize the utilization of new energy under the premise of system stability. The grid impedance identification algorithm based on non-characteristic harmonic injection was applied to sense the power grid strength，and the control strategy was adaptively switched according to the strength of the grid. Under the circumstance of robust grid，the constant power control method was adopted，which can quickly respond to the maximum power point instruction and improve the utilization rate of renewable energy. During the weak grid，converters flexibly switch to the virtual synchronous generator（VSG）control strategy to enhance inertia and damping support capabilities，realizing the friendly interaction between converters and grid. The proposed strategy enhances the robustness of grid-connected converters during the variation of grid strength，ensuring the stable operation of the system. The effectiveness of the proposed dual-mode control strategy was validated by PLECS simulation.

The micro-grid solves the problem that the intermittent and fluctuating power generation has adverse effects on the stable operation of the distribution network when the distributed generation is connected to the distribution network. In order to meet the economic operation of micro-grid under grid connected mode and improve power supply reliability，a micro-grid energy dispatching strategy based on peak-valley price and energy storage state of charge （SOC） was proposed. The strategy divided the whole day into three periods：peak，average and valley. During the real-time scheduling cycle，different scheduling strategies were applied based on different time interval and the SOC of energy storage. Reasonable energy storage charging and discharging penalty functions were designed in different time interval，and the maximum energy storage charging and discharging constraint factor was introduced to further improve the charging and discharging of the energy storage device. The minimum operating cost of micro-grid was took as the objective function and solved it through particle swarm optimization algorithm. The effectiveness of the strategy was verified by an example analysis.

To address the supply-demand imbalance caused by renewable energy intermittency and load fluctuations in islanded microgrids，a two-layer optimization-based dynamic time-of-use（TOU）pricing scheduling model was proposed，aiming to enhance economic efficiency and operational stability.First，a comprehensive microgrid system model was established，integrating wind，photovoltaic，energy storage，marine energy，and diesel generators，while introducing a dynamic TOU pricing mechanism to guide user load behavior for peak shaving and valley filling.Subsequently，a two-layer optimization framework was constructed：the upper layer adjusts load distribution via dynamic pricing，and the lower layer optimizes generation dispatch and energy storage strategies to minimize operational costs，effectively resolving the limitations of traditional single-layer optimization in handling complex nonlinear constraints. Case studies demonstrate that the proposed model significantly reduces reliance on diesel generators，enhances adaptability to renewable energy fluctuations，and optimizes operational costs.The findings provide theoretical support for low-carbon scheduling of islanded microgrids，balancing economic and reliability objectives，and offer practical insights for advancing energy transition in island regions.

As the penetration rate of new energy and power electronic equipment increases，the inertia and damping of the power system decrease，and the stability decreases.The grid-forming control technology builds a voltage source to support the stable operation of the large power grid through the converter，so as to play the role of rapid frequency and voltage regulation，increase inertia and short-circuit capacity support，and suppress broadband oscillation，so it has gradually attracted attention. Firstly，the differences between the grid-following converter and the grid-forming converter were compared，and the grid-forming control technology was more suitable for the new power system. Secondly，according to the four different control strategies of the grid-forming converter，the control mechanism of these strategies was analyzed in principle.Finally，by using the same initial parameters and simulating the influence of different control strategies on the power grid frequency after the power grid was disturbed by common disturbances，the superiority of VSG control strategy was verified，and the influence of VSG virtual moment of inertia and damping coefficient on the output frequency response of the system was discussed，which provides a reference for further in-depth research.

Accurate and efficient multi-load forecasting is of great significance for the operation control and scheduling of integrated energy system（IES），in order to improve the load forecasting effect，a integrated energy system load prediction model based on least absolute shrinkage and selection operator（LASSO）and LSTM-GRU neural network was proposed. Firstly，in order to solve the problem of complex data caused by meteorological factors in the integrated energy system，a big data selection and analysis algorithm based on LASSO was studied to select and analyze the meteorological factors to obtain an effective data set. Secondly，the long short-term memory（LSTM）neural network was used to predict the system load，and the preliminary prediction value was obtained. Subsequently，the gated recurrent unit（GRU）was used to construct the error compensation model，and the compensation value of the prediction error was obtained through the training and learning of the prediction error. Finally，by reconstructing the output of the two，a more ideal prediction result was obtained. Through the simulation of the example，the proposed prediction model has higher prediction accuracy than the traditional LSTM neural network prediction model and the LSTM model optimized by particle swarm optimizer（PSO）.

The traditional three-phase pulse width modulation（PWM）rectifier requires six power switches.Due to the shoot-through problem between two switches on the same bridge arm，the control difficulty is increased and overall system design becomes more complicated. A half-controlled three-phase PWM rectifier topology was used to achieve a three-phase rectifier. Only three power switches were used. The three switches were controlled by the same driving signal. The driving signal was generated by a dedicated controller，and the control circuit was simple. An experimental prototype was built using SiC MOSFETs as power switches. The experimental results show that the rectifier could operate at a higher switching frequency and the inductor and the capacitor are greatly reduced，thus the volume of the rectifierand the product cost are reduced，the conversion efficiency is improved and total harmonic distortion is low.

A brake unit based on IGCT was designed for different applications of frequency converter in industrial scenes，especially the medium voltage frequency conversion system without feedback function. IGCT was used as the main power device，and the parameters and characteristics of IGCT was analyzed. According to the common topology of NPC medium voltage inverter in the market，the matching circuit of brake unit was designed，and the working principle of the system was described. In terms of device loss，the junction temperature of the power device was evaluated，and the water cooling circuit and the press assembly structure were designed. In order not to affect the midpoint balance of the DC bus voltage，an independent software control method was designed.Finally，the medium voltage brake unit designed has been applied to the occasion of rolling metal composite material in the indμstrial field，which confirmed the feasibility of the design scheme.

With the rapid development of the society and economy and the accelerated construction of new power systems，flexible interconnection has gradually become an important technical means for upgrading the structure and enhancing the flexible regulation ability of distribution network. A power coordinated control strategy for engineering applications was proposed to address the power control requirements of multi-terminal flexible interconnection systems，including heavy-load limiting control for the rational power distribution when some feeder lines were heavy-loaded，and power balance control for power flow optimization distribution when all feeders were heavy-loaded. A flexible interconnection coordinated control device was developed based on the proposed strategy and applied to practical engineering. The case analysis based on the real load data and the measured data of the project verify that the proposed strategy can deal with different flexible interconnection scenarios with different load/power characteristics，effectively solve the problems of unbalanced feeder load and reverse PV power flow in the distribution network，and improve the power supply efficiency and security.

Space vector pulse width modulation（SVPWM）strategy is one of the key technologies for three-level inverters.However，conventional three-level SVPWM often experiences neutral point potential（NPP）oscillation and high switching loss when addressing the neutral point potential balancing issue.To tackle this challenge，firstly，the fundamental principles of the traditional nearest three vector（NTV）synthesis strategy and the virtual space vector pulse width modulation（VSVPWM）strategy were reviewed. And then，the drawbacks of the NTV approach based on the conventional region partitioning method was analyzed. A dynamic partitioning method was proposed to resolve the neutral point potential offset caused by conventional partitioning.Furthermore，to counteract the NPP oscillation of the NTV under high modulation，a strategy that employs a synthesis of four-effective voltage vectors was introduced. Compared to VSVPWM，the proposed strategy significantly reduced the inverter's switching loss.Ultimately，the effectiveness and superiority of the proposed algorithm were validated through experimental results.