At present，the traditional passive filter in on-board charger（OBC） has poor low-frequency performance，an active feedback loop was added to the traditional on-board charger passive filter，a design method of on-board charger electromagnetic interference（EMI） hybrid filter based on current sensing and current injection（CSCI） was proposed，and the structure，analysis and feedback loop design process of on-board charger hybrid filter were given.The experimental results show that compared with the existing on-board charger passive filter scheme，the new EMI filter scheme proposed has greatly improved the results of conduction test and radiation test.

Aiming at the challenge of demand response uncertainty to the safe and economical operation of integrated energy system，a cooperative optimal scheduling model of multi-region integrated energy system considering thermal pipe network transmission and demand response was proposed. Firstly，the energy transmission model of heat network was modeled in fine detail. Secondly，the demand response strategy was adopted for the comprehensive load，and the information gap decision theory was adopted to deal with the output uncertainty of renewable energy. Finally，the day-ahead operation scheduling scheme of the integrated energy system was proposed with the minimum dispatching cost and carbon emission penalty as the optimization objective，and various constraints were considered comprehensively. An example analysis proves that the proposed model can improve the economy of the system and the ability to absorb renewable energy.

Due to the wide control bandwidth of the shunt active power filter（SAPF），the resonance problem of the LCL output filter has become a key problem of the SAPF. To solve the resonance problem of the LCL filter，a novel damping method based on active damping circuit was proposed to achieve the damping effect without affecting the SAPF control. The proposed method was based on an auxiliary converter connected in series with the capacitor branch of LCL filter. In the auxiliary converter，the resonant current was detected and injected inversely as the reference signal of the converter，to achieve the damping effect on the resonant current. The stability of the proposed method was carried out through the frequency response analysis，and compared with the traditional method，which proved the theoretical feasibility of the proposed method. Finally，the effectiveness of the proposed method was verified by the experimental results，and it has better switching harmonic suppression effect compared with the traditional passive damping method.

The energy flow analysis method with both high precision and high computational efficiency is a basic tool to simulate the operation and analyze the interaction between the thermal and electric coupling systems. The traditional iterative numerical method is slow in computation，poor in computability for large-scale problems，and can only obtain the value of the state variable in discrete time series. Moreover，the traditional numerical method to solve electric power flow is not compatible with that to solve the dynamic flow of the heat network，so the alternating iterative solution is often adopted in the dynamic energy flow analysis，which makes the error spread in the iterative process. To solve the above problems，a dynamic energy flow analysis method was proposed based on holomorphic embedding for integrated electricity and heating systems. Through recursive calculation，the continuous analytic function of system state variable with respect to time was obtained. In the calculation process，the solution of electric power system and heating system was obtained jointly. The simulation results show that the maximum error between the algorithm and the Matlab solver is less than 3%，and the calculation speed is increased by more than 30%. Moreover，the algorithm can calculate the system state at any time in the dynamic process according to the holomorphic function.

A rotor position detection strategy based on virtual neutral point was proposed to realize position sensorless control of BLDC motor. Through the three-phase terminal voltage with the same value of three resistances star connection to construct a virtual neutral point，the relationship between the virtual neutral point voltage and commutation time of BLDC motor was analyzed. A conclusion was drawed that the moment when the virtual neutral point voltage through the DC bus midpoint is the zero-crossing time of the back electromotive force （BEMF），and the operation of the motor in each state，the effectiveness of zero-crossing signal of BEMF was further analyzed. The scheme was further verified by experiments，and the output of zero-crossing signal was realized by comparator. Compared with the conventional terminal voltage detection method，the system reduced two comparison detection circuits and has no phase shift. Experimental results show that the position of zero-crossing signal can be accurately determined by using this strategy，and the phase error caused by traditional BEMF method can be avoided.

Under digital control，the inner current loop of the LC-type inverter is affected by the control delay，which leads to the weakening of its active damping effect. Increasing the sampling control frequency can effectively reduce the negative influence of digital control delay. Furthermore，in order to suppress the high order harmonic disturbance caused by strongly nonlinear load，multiple resonant controllers are needed in the outer voltage loop. For reducing the time complexity of the outer voltage loop and increasing the quantity of the controlled harmonics，an optimal sampling digital control strategy was proposed for the current and voltage double loop control of the LC-type inverter. Specifically，the inner current loop was set to the double sampling control frequency and the outer voltage loop was set to the single sampling control frequency. The optimal sampling digital control strategy enhance the suppression ability of nonlinear load disturbance and reduce the total harmonic distortion of the output voltage while maintaining the stability margin of the inner current loop. Finally，the feasibility and effectiveness of the proposed optimal sampling digital control strategy were verified by experiments.

In order to solve the problems of high subjective misjudgment rate and low efficiency in manual hand touch and auscultation methods for acoustic quality detection of micro motors，while taking into account the accuracy of detection results and the fast construction of detection models，a small sample machine learning detection method was proposed. Based on the physical model of micro motor transmission chain，multi-dimensional acoustic fault features were extracted，particle swarm optimization was used to optimize the core parameters of support vector machine，a small sample learning method，so as to improve the accuracy of model discrimination.The experimental results show that this method can effectively distinguish abnormal vibration and sound of micro motors，with an accuracy rate of over 95%.

The integrated energy system contains adjustable resources and flexible operating modes，which to a certain extent play a supporting role in the power grid and assist in optimizing its operation. Based on this，an optimal operation model of integrated energy system considering support capacity to power grid was proposed. Firstly，the electric-heat integrated energy system（EHIES）was considered as the research object and the EHIES model was established. Secondly，considering the expected support demand of external power grid and aiming at meeting the expected support demand of external power grid，the optimal operation model of EHIES was established. Considering the complexity of the model，the Bacterial Colony Chemotaxis optimization algorithm was used to solve it. Finally，an integrated energy system in northern China was considered as an example and the effectiveness of the proposed model was verified. By adjusting the flexible operation of the EHIES，it can effectively meet the expected support needs of the external power grid and play an external support role.

Active power filters（APF）are widely used for dynamic compensation of power system harmonic. However，under weak grid conditions，the interaction between APF，nonlinear loads and grid impedance can easily lead to the stability issue of harmonic oscillation around the compensation frequency，resulting in the fault of harmonic compensation and further deterioration of the system's power quality. Through small-signal modelling of the loop，the harmonic oscillation mechanism in APF system under weak grid conditions was revealed，and an active damping scheme based on inductor current feedback was proposed to suppress harmonic oscillation according to the conclusion of stability analysis，which ensures the stable harmonic compensation capability of APF under weak grid conditions. The effectiveness of the proposed scheme was verified by PLECS time-domain simulations and hardware platform experiments.

In order to optimize the current stress of dual active bridge（DAB）converter，an improved dual phase shift （IDPS）modulation was proposed based on the traditional dual phase shift （DPS）modulation. Firstly，the working principle of IDPS modulation was introduced，its steady-state working characteristics were analyzed，and the mathematical model of current stress on transmission power was established. Then，the optimal value of current stress of IDPS modulation was obtained by using Lagrange multiplier method，and compared with traditional single phase shift（SPS） and DPS modulation methods. Finally，an experimental platform was built to verify the effectiveness of the proposed control strategy in optimizing current stress，meanwhile，the efficiency of the converter was improved.