In response to the existing problems of traditional diode based clamp type wind turbine inverters，a hybrid clamp type structure was introduced. Based on the analysis of its working principle，a method for switching the switch state and a vector optimization selection method that can avoid modulation waveform burr line voltage were proposed，achieving balanced control of clamp capacitor and DC bus capacitor voltage. A third-order low-pass filter method with initial angle calculation was proposed to optimize the virtual flux orientation control strategy for the control of hybrid clamp type rectifiers in the unit. A direct power tracking control method for rectifiers based on improved virtual flux orientation was also presented. Finally，simulation and experiments were conducted on the system，confirming the correctness and effectiveness of the proposed method.

The load of a submerged arc furnace has many advantages，such as large single-unit regulation capacity，good communication conditions，easy control，and low economic retrofitting，making it an important flexible regulation resource for the power grid.However，there is currently a lack of effective digital simulation methods for modeling submerged arc furnace systems and their regulation characteristics.A time-domain digital simulation model for the power supply system of an industrial submerged arc furnace was established，which included an electric furnace transformer，short network，furnace body，and reactive power compensation，based on the actual electrical operating conditions of the submerged arc furnace.The power regulation characteristics of the submerged arc furnace were determined by representing the electrode regulation link with the time-varying arc length calculated through the Newton downhill method.The equivalent time-varying resistance was obtained by solving the arc differential equation using the Runge-Kutta method，enabling simulation of the power regulation process of the submerged arc furnace.This was achieved by encapsulating it with a custom module and integrating it with the system model to realize time-domain digital simulation.It is applicable to both AC submerged arc furnace and various electrode control strategies，and can be widely used for simulating the load characteristics of submerged arc furnace，flexibility resource assessment，and as a simulation platform for participating in grid interaction research.

With the emergence of a large number of distributed power generations，various unbalanced and nonlinear loads are connected to the power grid，resulting in the distortion of the grid current，which brings adverse effects to both the power grid and electrical equipment. A multifunctional energy storage converter was proposed，which is capable of simultaneously realizing the compensation of reactive current，harmonic current and unbalanced current of the load. This converter used a phase-locked loop based on double second-order generalized integrators to generate the required phase angle and frequency，and at the same time obtained the amplitude of the positive sequence component of the voltage.The converter obtained the command current by obtaining the positive sequence component of the load current and performing coordinate transformation，and then controled through the difference between the command current and the output current of the inverter to track the command signal.Proportional resonant control was used to obtain three-phase current，and pulses were generated through three-dimensional space vector control to control the conduction of the switch tube. By comparing with traditional energy storage converters，digital and analog hybrid experimental results have proven the effectiveness and reliability of this scheme.

A backstepping error port-controlled Hamiltonian （EPH） controller based on a novel extended state observer （ESO） was designed to address the issues of insufficient rotor flux observation accuracy and slow system dynamic response in induction motor speed control. Firstly，an extended state observer was used to observe the rotor flux，expanding the change in rotor resistance in the model to a new state to improve the accuracy of rotor flux observation. Secondly，using the backstepping control method to obtain the balance point of the stator current of the EPH controller，designing a backstepping EPH controller can effectively improve the dynamic response ability of the EPH control. The experimental results demonstrate that the designed controller has better stability performance and faster response speed compared to the EPH controller.

The permanent magnet synchronous generator （PMSG） is prone to current overstep in unbalanced grid，which affects the reliability of grid-connected system. To solve this problem，low-voltage ride-throgh control strategy based on direct power control was proposed. In this strategy，the direct power inner loop was used to control the grid-side inverter，and the active power and reactive power instructions were divided into DC components and double frequency AC components. The reference values of the DC components of active power and reactive power were calculated on the premise of the low voltage traverse reactive power support and the current amplitude of the inverter. The reference values of the AC components of active power and reactive power were calculated according to three different control objectives according to the voltage and current of the junction point. Then the control loop was designed by the quasi-proportional resonant controller. Finally，a simulation model was built based on Matlab/Simulink，and the simulation results show that the proposed control strategy can improve the dynamic performance of the inverter and improve the operation ability of the grid-connected system under the unbalanced grid.

In order to further improve the output performance and efficiency of the converter，a grid-connected converter based on heterogeneous device mixing was proposed，referred to as heterogeneous grid-connected converter（HGCC）. The HGCC consists of two half-bridge modules based on SiC MOSFET devices，which are cross-connected by the commutation bridge arm based on Si IGBT devices. Furthermore，the HGCC modulation principle was given. The SiC MOSFET device works in the high-frequency switching state，while the Si IGBT device works in the low-frequency switching state，giving full play to the advantages of low switching loss of SiC devices and low on-state loss of Si devices. Then，the working mode of HGCC was analyzed in detail，and the control block diagram of HGCC and the internal voltage balancing strategy of capacitor were given. Finally，the effectiveness and feasibility of the proposed topology and control strategy was verified by simulation.

Accurate topology and line parameter information is the basis of state estimation and security control of distribution network. Affected by the performance of collection terminals and environmental factors，the measurement error of metering equipment often deviates from Gaussian distribution. Higher requirements are put forward for the robustness of topology and parameter identification model under non-Gaussian noise measurements.The mathematical optimization model of distribution network parameter identification was firstly constructed with the goal of minimizing power estimation error. In order to improve the performance of identification algorithm in complex error scenarios，the correntropy induced loss function was established，and an improved correntropy matching pursuit （CMP） algorithm was proposed based on half-quadratic optimization and noise filtering. Finally，the simulation analysis was carried out on IEEE 33- and 85-bus distribution system，and the test results show that the proposed method can correctly identify the topology and effectively estimate the line parameters in both Gaussian and non-Gaussian data noise scenarios.

In recent years，the use of microinverters has received a lot of attention as one of the viable methods for residential and commercial PV power conversion systems. Flyback inverters operating in current continuous conduction mode （CCM） have been widely studied for their low output ripple current，high efficiency，and low cost. However，its control duty cycle to output current transfer function has right-half-plane （RHP） zeros，which may cause system instability when the inverter is combined with a high-gain feedback controller. In addition，flyback CCM inverters are subject to grid time-varying voltage disturbances. As a result，the conventional control scheme leads to inaccurate output tracking. An interleaved flyback CCM microinverter iterative learning control （ILC）method was proposed to help the system output converge to the reference trajectory by utilizing the prediction term and the current learning term. Compared with the traditional PI control scheme，the system output globally converges to the reference trajectory without state disturbance，output noise and initial state error.

Under the large-scale renewable energy integrated with uncertain output characteristics，balancing the supply and demand within a local area becomes a new challenge.The long-distance transmission and consumption scheme is utilized for the sending-end grid to meet the requirements of renewable energy consumption.Within the constraints of thermal stability，dynamically improving the transmission lines' rating capacity has become a critical method for the sending-end power grid.However，due to the insufficient thermal stability calculation model，the existing improvement methods have the problems of significant evaluation deviation and narrow applicability in the practical application of the sending-end power system the improvement scheme usually needs to be customized and modified for specific line. In order to solve above issues，firstly，the influence of dust corona heating on the thermal stability transfer capacity at the sending end was analyzed，and an improved model of line thermal rating based on the dust effect was proposed. Furthermore，considering the uncertainty of the dust effect，a calculation method of dust effect control parameters based on fuzzy analysis was proposed，and the thermal rate capability calculation model was improved. Finally，combined with the meteorological forecast，a scheme for improving the thermal rating capacity of the renewable energy transmission power grid was constructed，which can be analyzed for multiple lines simultaneously. Via the practical engineering case of the Ningxia power grid and the power meteorological forecast data of China Electric Power Research Institute，the effectiveness and applicability of the improvement model of dust effect and the improvement scheme of multi-line thermal stability transmission capacity were verified.

The common-mode equivalent circuit model of the motor is the basis for analyzing the electric erosion of bearings，especially for analyzing the technical problems and experimental phenomena of shaft voltage and shaft current，among which the centralized equivalent model is an important calculation basis for the key index of bearing electric erosion that is bearing voltage ratio （BVR），which can be evaluated in the early stage of motor design. The accurate simulation calculation of the distributed capacitance parameters of the centralized equivalent model were studied in depth. Firstly，the simulation calculation and comparison of the two-dimensional single-slot and full-model motors were carried out. Secondly，the influence of the stator winding end and the rotor end ring on the stray capacitance was considered，and the three-dimensional motor model was simulated and calculated，and the more accurate distributed capacitance parameters were obtained through comparative study. Finally，the parameters of YQ190-14 type traction motor were taken as an example，and the simulation calculation results and test results were compared and analyzed，and the accuracy of the simulation calculation results was verified.