Voltage source converter（VSC） connected to weak AC power grid has the risk of small disturbance instability. Under the traditional control strategy，VSC has to reduce output power to maintain stable operation. In order to improve the stability of the weak grid connected VSC system，first established a universal analysis model for revealing the stability mechanism of weak grid connected VSC based on the AC voltage outer loop，and revealed the influence of the coupling characteristics among the phaselocked loop （PLL） and the VSC outer loop control on system stability. On this basis，a parameter adaptive control strategy for virtual parallel point was proposed. The detailed switch model of VSC in the PSCAD/EMTDC environment verifies the effectiveness of the proposed control method.

In order to study the distribution of magnetic field and temperature field of dry-type transformer iron core more accurately，analyze the influence of different excitation on the magnetic field loss and hot spot temperature rise of dry-type transformer core，firstly，Maxwell was used to calculate the transient magnetic field distribution of dry-type transformer，and the loss of the iron core under no-load condition was obtained. On this basis，a three-dimensional dry-type transformer magnetic field-temperature field coupling calculation method was proposed. The magnetic field loss was coupled to Fluent as the heat source of temperature field calculation，and the fluid structure coupling method was used to calculate the temperature field distribution of dry-type transformer. Finally，based on the above method，the magnetic field and temperature field of transformer core under harmonic action were calculated，and the influence of harmonic on core loss and temperature rise of dry-type transformer was analyzed，which provides a reference for the monitoring of the temperature rise about the transformer core under harmonics.

Aiming at ultra-low frequency oscillation in power system caused by hydraulic turbine governing system，an additional damping control strategy for governing side was developed. Firstly，according to the damping torque method，the negative damping generated by the hydraulic turbine governing system was regarded as the main reason for the ultra-low frequency oscillation of the power system. Secondly，the damping torque coefficient expression of the speed regulation system was derived，which proves that the coefficient is closely related to the time constant of water hammer effect and the PID parameters of the governor. Besides，based on the additional damping control strategy，the positive damping compensation was introduced in the speed control side of the system. The grey wolf optimization（GWO） algorithm was applied to optimize the PID parameters to further improve the damping characteristics of the system. Finally，simulation verification in a single-machine system and a four-machine two-area system was executed through Matlab/Simulink. The results illustrate that the proposed control strategy can significantly enhance the damping characteristics of the speed control system and effectively suppress ultra-low frequency oscillation.

The process automation control system L2 of an aluminum zinc plating production line was explored.In response to potential production faults on the production line，a process data control module of the process automation control system was provided. Through the analysis of process data，the fault location of the strip steel or production line was analyzed. Finally，a quick method for finding the fault location was provided. The actual operation shows that this method is stable，reliable，and meets the control needs of actual production.

In high-precision applications，the control accuracy of the servo system is extremely high required. The control precision of the servo system depends largely on the precision of the feedback measurement. Position and speed feedback accuracy can be improved by increasing the absolute accuracy of the encoder，and it is not sensitive to external interference，while the current sampling link is more sensitive to switching noise，which will cause torque fluctuation and reduce the control precision of the servo system. Based on the principle of high-precision current sampling in servo system，the influence of switching noise on current control accuracy was studied. An SINC3 filter structure with continuous output and a method to improve the steady-state current control accuracy were proposed. The experimental results show that the method has obvious effect on restraining the current fluctuation caused by switching noise，and has strong engineering guiding significance.

The motor actuator used in circuit breaker has the advantages of simple structure，small dispersal of action and strong controllability，which provides the possibility for the switch contact of circuit breaker to follow the preset reference curve. The traditional control method can not adjust the parameters according to the movement process of circuit breaker switch contact，and the following is poor，and the intelligent control algorithm is complicated in calculation，affects the rapidity of control system，and is extremely difficult to implement in engineering. A piecewise pseudo-differential control strategy was presented，which avoids direct differentiation of the controlled variables and has the ability of fast dynamic response and anti-interference. Meanwhile，the control system parameters were given according to the segmented environment to ensure the following accuracy. The control strategy model was established for simulation analysis，and the 126 kV circuit breaker motor actuator control system was developed for experimental verification. The simulation and experimental results show the effectiveness of the control strategy.

A quasi-resonant Flyback（QR-Flyback） converter with 65 W output was designed. The valley switching principle and the switching loss reduction mechanism of QR-Flyback were analyzed，the frequency and loss characteristics of the system under different working conditions were compared，and the advantages and disadvantages of frequency conversion control were summarized. Combined with the frequency hopping control function of the NCP1380 controller，the hardware circuit parameters of each part of the system were designed and the efficiency of the system was effectively improved. Finally，the feasibility of theoretical analysis and parameter design were verified by simulation and experiment.

Aiming at the problems of three-phase load imbalance，power quality degradation and harmonic dispersion in current electronic power distribution system，a comprehensive power quality control scheme with fast dynamic response and small output harmonic was proposed，which includes comprehensive control mode and compound repeat control strategy. By example analysis，it is found that harmonic content decreases before and after compensation in a specific subharmonic compensation mode. After the unbalanced grid compensation，the current distortion was eliminated and the voltage and current were in the same phase，which indicates the effectiveness of the comprehensive management. In the experimental verification，the continuous output of 25 kW inductive reactive power to 25 kW capacitive reactive power was realized，the requirements of reactive power regulation -100%~100% in the technical index was met，and the deviation between the output power and the command value was only 0.49%，the requirements of less than 3% in the technical index were met. In addition，the compensated three-phase grid current THD was reduced to 4.7%，after unbalance compensation treatment，the unbalance degree was reduced to 1.4%，which shows the effectiveness of the device in the treatment of three-phase load unbalance，power quality degradation and harmonic dispersion.

In order to effectively manage the grid short-circuit current overrun problem，optimization decision-making evaluation method of short-circuit current limitation scheme based on hybrid decision model considering asymmetric closeness was designed. Considering the relevant influence of the short-circuit current limiting measures of the power grid，a four-level evaluation index system considering short-circuit current，static safety，transient stability and implementation cost was established，eight three-level evaluation index factors were simplified and analyzed，and the decision evaluation results were divided further. An improved DEMATEL+ANP index weight assignment method for balancing the interaction relationship between indexes was proposed，and a hybrid decision-making model for the optimization decision evaluation of the short-circuit current limitation scheme of power grid was established by further considering asymmetric closeness，priority and cloud theory. Combined with simulation example based on PSASP，the effectiveness of the proposed optimization decision evaluation method was verified. This method can better balance the evaluation indexes，fully consider the fuzziness and randomness in the optimization decision evaluation，not only can realize the evaluation of multiple schemes，but also can realize the evaluation of its own scheme，and improve the accuracy and applicability of the optimization decision evaluation of the short-circuit current limit scheme of the power grid.

As a new type of compressor，linear compressor has the advantages of high efficiency，small volume，low noise and little vibration. However，in order to give full play to its advantages of high efficiency，it is necessary to control the driving frequency to track its mechanical resonance frequency. According to this characteristic，a frequency tracking control algorithm of linear oscillation motor based on second-order generalized integrator （SOGI） and double correlation phase detection algorithm was proposed. Compared with the frequency tracking control algorithm based on the average value of stroke-current product （ASCP），the control algorithm has the advantages of fast dynamic response and stable operation under variable working conditions，enhances the suppression effect of external interference and improves the stability of the control system. Simulation and experiments show that the proposed control algorithm can quickly track the natural frequency of the motor，which verifies the rationality and effectiveness of the theory.