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.

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%.

In traditional current protection，the effective value of current is compared with the setting value to identify the fault which is the typical protection scheme for the transmission lines of the power distribution systems. The current is calculated by the fast Fourier transform algorithm. As the calculation of the effective value of current requires a long time，the speed of the current quick break protection is reduced. In this regard，a fast current protection algorithm based on the discrete setting-value was presented to solve this problem. The main emphasis was placed on the construction of the discrete sequence of setting-value and the protection criterion. The protection startup criterion and action criterion were constructed based on comparisons between discrete sequence of setting-value and sampling-value of the current fault component. The operation characteristics and reliability of the fast current protection were analyzed. The performance of the novel fast current protection algorithm was compared with that of the conventional current protection through simulations based on PSCAD/EMTDC. The results verify that the novel fast current protection algorithm has good operation characteristics under different fault conditions.

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.

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.

To cope with the impact of electric vehicle（EV）charging loads on the power grid and achieve a balance of interests between the power grid，charging station and users，a customized charging strategy for EVs that takes dynamic electricity prices into consideration was proposed. Initially，the dynamic pricing mechanism was designed for charging station based on the needs of tripartite interests. Then，the optimization model with the lowest user charging cost and the lowest load fluctuation rate of power grid had been established to perfect the charging process of EV. Moreover，on the basis of the traditional artificial bee colony（ABC）algorithm，the adaptive normal attenuation coefficient was introduced to form the adaptive ABC algorithm and it was applied to solve the optimization model in order to obtain the customized ordered charging scheme. Furthermore，the charging process of each EV was optimized by combining the dynamic electricity pricing mechanism and EV customized charging method. Finally，based on Monte Carlo method，the charging situation of different number of electric vehicles under different charging modes was simulated. The simulation results show that the proposed method can significantly improve the load index of the power grid，ensure the revenue of charging station，reduce the charging costs of users，and achieve an all-win benefits between power grid，charging station and users.

In order to further improve the accuracy of fault identification of local abnormal factors in distribution network，a digital twin based fault identification simulation of local abnormal factors in distribution network was proposed. Through real-time acquisition of electrical parameters of distribution network operation and preprocessing，the fault feature matrix based on time series was extracted，and the multidimensional scaling （MDS）method was used to detect the abnormal physical nodes of distribution network from the reduced dimension fault features. Then，the fault section corresponding to the abnormal physical nodes was obtained according to the distribution network topology. Finally，the local abnormal factor value corresponding to each physical node was calculated with local outlier factor （LOF）algorithm，so as to obtain the fault diagnosis results and complete the accurate identification of distribution network faults. The simulation results show that the proposed method can achieve accurate identification of distribution network faults.

An adaptive active arc suppression method based on S-transform correlation degree for distribution network unidirectional grounding was proposed to effectively eliminate single-phase grounding fault arc in distribution network and improve power system stability. The time series data of zero-sequence current of distribution network lines were collected，the time-frequency information matrix of zero-sequence current through S-transformation was obtained，the correlation matrix of time-frequency information matrix between each line was calculated and obtained. Input the convolution neural network model，and output the single-phase grounding fault line selection results；the double closed-loop adaptive control method based on fuzzy quasi-PR and PI control was adopted in the fault line to inject zero-sequence current into the neutral point of the fault line of the distribution network，effectively control the phase and amplitude of the injected current，force the voltage value of the phase of the fault line of the distribution network to be 0，and complete the adaptive active arc suppression. The experimental results show that this method can effectively identify the single-phase grounding fault lines in the distribution network，realize the single-phase grounding adaptive active arc suppression，and complete the single-phase grounding adaptive active arc suppression work as soon as possible to ensure the safe and stable operation of the distribution network.

To solve the chaos problem of inverter in new energy generation system，a regulation scheme of H-bridge inverter based on active disturbance rejection control（ADRC） was proposed. Aiming at the phenomenon of poor steady-state and dynamic characteristics of inverters in chaotic state，a discrete model of the inverter was developed to control the chaos by establishing tracking differentiators，extended state observers，and state error feedback control laws. Through bifurcation diagram，folding diagram and simulation，the results show that the stability range of the H-bridge inverter based on ADRC control is expanded by 45% compared with the H-bridge inverter based on proportional control，which effectively suppresses the occurrence of chaos. It can be concluded that the control strategy can restrain the chaotic behavior of the system and broaden the stable working range of the system.

Aiming at the low voltage ride through（LVRT）problem of the combined grid-connected system with new energy-energy storage under the control of the grid-forming converter，an additional voltage limiter control scheme based on the traditional LVRT was proposed. Firstly，the shortcomings of the traditional LVRT strategy based on current limitation was analyzed. When the fault duration is long，only setting current limitation would easily lead to synchronization instability. Then，an improved LVRT strategy with additional voltage limiter was proposed to suppress the fault current under a longer time scale and improve the synchronization stability under the fault. Finally，a simulation model of new energy-energy storage combined grid system was built in Matlab/Simulink to validate the proposed scheme. The experimental results show that the proposed scheme can ensure that the new energy-energy storage combined grid-connected system not be taken off-grid during the three-phase symmetrical sag fault，and effectively improved the synchronization stability of the system during the fault.