In order to improve the compensation effect of LCL-type shunt active power filter，a frequency adaptive decimal delay repetitive control based on IIR filter was proposed. The resonance suppression loop of LCL was designed through root locus and the design result was used as a new control object for repetitive control. The IIR filter used could approximate the decimal delay caused by frequency changes，thereby matching the resonant frequency of repetitive control with the fundamental and harmonic frequencies of the power grid. The adaptive implementation diagram，the phase characteristics of the approximation part，and the design method of the compensator in sequence were presented. Finally，the stabilities of the system were analyzed. Simulation and experimental verification show that the proposed method can improve the steady-state tracking performance and THD of the system.

Modular multilevel matrix converter （M3C） is a multilevel topology that can directly realize AC-AC conversion，which has good application prospects in high-voltage transmission systems and DC distribution systems，but the existence of bridge-arm circulating channels inside the M3C leads to a very complex control structure. For this reason，a hierarchical system control strategy was proposed. First，the mathematical model of the M3C was derived based on the conventional double αβ0 coordinate transformation. Then，a dual-loop control structure consisting of an outer-loop and an inner-loop controller was employed in the M3C，which is usually employed in voltage source converters. In addition，in order to suppress the loop current component inside the system，a bridge arm energy equalization control strategy based on double αβ0 transform decoupling was proposed，through which the capacitive voltage control between the bridge arm and the bridge arm was realized by this control and carrier phase shift modulation. Ultimately，the simulation model and physical prototype were constructed，and the outcomes validated the viability of the proposed control strategy for the M3C system.

Since the compressed air energy storage system grid-connected inverter voltage is always influenced by voltage fluctuations of the power grid with little problem，for the sake of ameliorating the dynamic and stable performance of the DC bus voltage of the inverter on the side of the grid and the actual output power of the system in the compressed air energy storage expansion power generation system and reducing the fluctuations，second-order linear active disturbance rejection control （LADRC） technique was used in the voltage outer loop control，a new-style double closed loop control construction was formed. The mathematical model of the grid-connected converter of expansion power generation system was established，the operating principle of LADRC was researched，and the conventional PI control was contrasted with the control methods studied. The simulation results indicate that when make a contrast with the conventional control methods，the control methods designed can make the DC voltage enter the stable state more quickly，the total harmonic distortion （THD） of the grid-connected current becomes smaller，and has better disturbance immunity.

The electricity power price setting mechanism will be fundamentally reformed with the continuous advancement of a new round of electricity market-oriented reform. Presently，some provincial and regional power grid enterprises are facing the problem of large fluctuations in electricity prices，which is not conducive to the in-depth promotion of electricity marketization reform. Firstly，based on the partial least squares method，the agency power purchase price formation model was established. Then，the main factors affecting the fluctuation of power purchase price were analyzed，and the mechanism of the influence of power supply and consumption balance on the price change of different types of electricity consumption was clarified. In order to reduce the fluctuation of electricity purchase price，a multi-objective optimization model of agent electricity purchase was established with the constraint of power supply and consumption balance. The actual example results show that the model can realize the reasonable distribution of power consumption among different types of power sources in the process of agent power purchase，and effectively reduce the fluctuation of agent power purchase price.

With the increasing penetration of new energy equipment，while alleviating the environmental problems caused by fossil energy，it also increases the frequency instability of the system. Photovoltaic （PV）and other new energy equipment to participate in the grid frequency regulation is an effective way to improve the frequency stability of the power system.First，the basic principle of frequency response of synchronous machine was analyzed，the correspondence was determined which is between active output of PV power generation and primary frequency regulation and inertia response，and the virtual synchronous control strategy of PV power generation was formed.Then，based on the power-frequency correspondence relationship of primary frequency regulation，it gave the parameter adjustment method that directly corresponds to the frequency and the load shedding rate，and realized the function of primary frequency regulation. Once again，based on the inertia response minus the frequency-power correspondence relationship，it gave the inertia response minus the frequency-power correspondence relationship，which is the most effective way to improve frequency stability of power system. Once again，based on the correspondence between inertia response frequency reduction and power，the parameter setting method of inertia response load shedding rate was given，and the negative influence of inertia in the process of frequency restoration was avoided through the determination of application conditions of inertia response. Finally，the PV grid-connected model was constructed，which verified that the PV load shedding operation has the ability to participate in the frequency regulation of the power grid.

In order to solve the problem that the time-of-use price is not taken into account in the calculation of the peaking cost in the case of a large number of renewable energy sources，a method of calculating the peaking cost of power system with time-of-use price was proposed. First，the key scenarios of power grid peak regulation were obtained，and the technical cost characteristic boundaries of various peak regulation resources were determined. Second，according to typical daily new energy and load characteristics，taking the minimum total peaking cost of the power system as the objective function，taking into account the technical output of thermal power units，charging and discharging characteristics of energy storage，capacity of pumped storage power station and other constraints，and taking into account the time-of-sale price factor，a quantitative model of the peaking cost of the power system was established. Finally，through solving the model，the peak load balancing cost and unit output under the optimal scheme were obtained. The actual data of Ningxia Power Grid，the first provincial power grid whose output of new energy generation exceeds the entire regional power load，was taken as an example to verify the model. The results show that the model can effectively evaluate the peaking cost and unit output in the key scenarios of power grid peak regulation.

As the penetration rate of household distributed PV in China's low-voltage distribution network continues to increase，the power flow of the distribution network has changed，leading to more serious problems such as node voltage overruns and three-phase imbalance，which poses a serious threat to the safe and stable operation of the distribution network. For situations where the distribution network topology and line parameters are unknown，the traditional voltage control strategy based on power flow calculation is no longer applicable， a data-driven voltage coordination control strategy was proposed for low-voltage distribution networks with high household photovoltaics penetration. First，a linear approximation model of the low-voltage distribution network was established，and the least squares method was applied to fit the relationship between node power and voltage based on the historical operation data of the low-voltage distribution network. Then，the photovoltaic inverter and energy storage system were used as regulation measures to minimize the degree of node voltage over-limit，minimize the three-phase unbalance and minimize the amount of equipment regulation as the objective function. The improved multi-objective particle swarm algorithm was utilized to achieve voltage optimization control. Finally，the effectiveness of the proposed voltage coordination control strategy was verified by simulation comparison and analysis with other control strategies and methods，taking the 21-node low-voltage station as an example.

Voltage source converter （VSC） is prone to low-frequency oscillations of 10⁰~10¹ Hz when connected to weak AC power grids. The mechanism of improving the control strategy of VSC on the traditional inverter side to suppress low-frequency oscillations（LFO） in the AC power grid is to transfer the oscillations from the AC side to the DC side，which poses a risk of inducing instability in the DC system. An adaptive voltage power damping control strategy was designed that can suppress low-frequency oscillations in AC systems based on the adjustable output power of the interface converter of energy storage devices containing new energy storage stations. This strategy was based on a damping control loop embedded in the rectifier side VSC control system，which suppresses DC voltage oscillation by controlling the output power of the rectifier energy storage system，effectively solving the shortcomings of traditional inverter side VSC control strategies in transferring oscillations. Based on the analysis of small signal stability，the parameter design process of the virtual damping control link was provided. The simulation results in Matlab/Simulink environment verified the effectiveness of the proposed control strategy and the correctness of the parameter design process.

The islanding detection method is a necessary method for grid-connected PV systems，but，the current islanding detection method is prone to misjudgement when encountering grid operation states such as high-resistance short-circuit ground faults and large-capacity load casting. For this reason，an islanding detection method based on reactive power perturbation and featured kurtosis was proposed based on analyzing the difference between the power at the grid point in the islanding operation state and other grid operation states. The method firstly used the three-phase voltage amplitude offset rate at the grid point to realize the starting criterion of active reactive power injection in PV system. Then，the apparent power waveform at the grid point was obtained，and after the normalization operation was performed to obtain the normalized apparent power （NAP） waveform，variational modal decomposition algorithm was used to decompose NAP at 8 layers，and the time-frequency component at layer 5 was obtained as the feature detection component. And then the feature detection component was characterized by a featured kurtosis to achieve islanding detection. Finally，a typical PV grid-connected system was constructed using Matlab simulation platform，and the effectiveness of the proposed method was tested through the working conditions of islanding operation with different quality factor loads，different high-resistance short-circuit ground faults，large-capacity load switching，and lightning strike faults，and so on.

To address the complexities of transformer condition assessment indicators and the overreliance on expert judgment in the evaluation process，a novel method for fuzzy comprehensive assessment of transformer condition was introduced，which is based on gaming theory and an improved version of the D-S evidence theory. First，the analytic hierarchy process （AHP） and the Critic method was adopted to determine both the subjective and objective weights of the evaluation indicators. These weights are then combined using game theory，reducing the dependence on expert opinions in traditional weight determination methods. Second，instead of traditional membership functions，cloud models was employed to preserve the inherent uncertainty in fuzzy assessments. Finally，membership information at the project level was fused by using improved D-S evidence，eliminating paradoxical results that can occur when combining high-conflict evidence. Through the results of case studies，the method effectively assesses the transition probabilities of various transformer states.

With the wide application of solar photovoltaic panels，the detection of hidden dangers and faults of photovoltaic panels has become more and more important. In order to improve the inspection efficiency of photovoltaic panels and the accuracy of defect detection，a target detection algorithm based on attention mechanism was designed and a complete inspection scheme of photovoltaic panels combined with UAV technology was proposed. The method uses the high-resolution camera mounted on the UAV for image acquisition，and detects and identifies the defects of photovoltaic panels through the combination of the object detection of the attention mechanism and the UAV technology. The experimental results show that the proposed method has high accuracy and reliability in photovoltaic panel inspection，mean average accuracy （mAP） reaches 83.2%，F1 score is 84.5%，effectively improve the quality and effect of photovoltaic panel inspection，and has high practical value.