With the rapid development of the society and economy and the accelerated construction of new power systems，flexible interconnection has gradually become an important technical means for upgrading the structure and enhancing the flexible regulation ability of distribution network. A power coordinated control strategy for engineering applications was proposed to address the power control requirements of multi-terminal flexible interconnection systems，including heavy-load limiting control for the rational power distribution when some feeder lines were heavy-loaded，and power balance control for power flow optimization distribution when all feeders were heavy-loaded. A flexible interconnection coordinated control device was developed based on the proposed strategy and applied to practical engineering. The case analysis based on the real load data and the measured data of the project verify that the proposed strategy can deal with different flexible interconnection scenarios with different load/power characteristics，effectively solve the problems of unbalanced feeder load and reverse PV power flow in the distribution network，and improve the power supply efficiency and security.

A dual active bridge （DAB） DC-DC converter voltage control strategy based on double-integral sliding mode control was proposed，which can obtain good control effect under the condition that the model accuracy requirements are low and the controller design process is simple. Firstly，the reduced-order model of the converter was established based on the single-phase shift modulation mode. Then，the output voltage controller of the converter was designed by using the double-integral sliding mode control theory. The design process introduced the time domain analysis method to analyze the sliding surface coefficients. Finally，simulation and experimental results show the effectiveness of the proposed control strategy.

The telecommunication power supply applied in 5G base stations can save energy consumption by reducing the output voltage when the equipment works in standby state. Nevertheless，frequent and rapid output voltage regulating of the converters is challenging. To solve this problem，the concept of partial power conversion was adopted in the design of power supply converters. A partial voltage regulating circuit was added at the output side of the converter，and fast output voltage regulating was realized with control of outer voltage loop，inner current loop，load current feedforward and output voltage feedforward loop. At the same time，higher energy conversion efficiency was guaranteed. A 1 kW DC/DC converter was built and verified the effectiveness of the proposed topology and control strategy.

Aiming at the problem that the ripple content of current and voltage in cycloconverter speed control system is large and the ripple period is time-varying， the real-time sampling value is not suited for feeding back to the speed control system directly，a variable period mean sampling algorithm was proposed. Firstly，the algorithm took the interval time of trigger pulse of cycloconverter power device as the mean period to calculate the meanvalue of actual current and voltage. Secondly，the phase lag angle caused by the mean period was calculated according to the real-time frequency and mean period of current and voltage. Finally，the lag compensation and interpolation operation were carried out according to the phase lag angle. More ideal voltage and current feedback values were obtained for speed control system. Compared with the average sampling method，this algorithm is more suitable for the time-varying ripple period of cycloconverter conversion，and it eliminate the sampling lag and improve the performance and stability of the speed control system.

Up to now，the distribution network planning project optimization method rarely considered the impact of the speed of load growth on the power supply efficiency of the project and the year when the project is selected，and rarely considered the urgency，technical benefit and economic benefit of the project at the same time. Therefore，the optimal model for medium and low voltage distribution network planning projects was established with the goal of maximizing technical and economic benefits. According to the urgency of the project，the technical benefits of the project were rewarded and punished. In order to measure the annual change rate of the power supply benefits of the project，the differential weight method was used to obtain the five-year comprehensive level of power supply benefits after the project was put into operation. An improved multi-objective particle swarm algorithm solution model was proposed，and a series of project combination schemes with mutually advantageous objectives were obtained，and the optimal project combination scheme was obtained by multi-level screening of the project combination scheme set according to the target preference of the power supply enterprise. Taking the distribution network planning project database in a certain region as an example，it show that the proposed model can better consider the change of power supply efficiency and the urgency of the project，and achieve multi-regional and multi-objective comprehensive improvement.

With the continuous promotion of the "double carbon" strategy，the reformation of China's electricity market has entered a new stage，but the overall construction of the electricity market is still in the primary stage，and there is an urgent need to develop a scientific and feasible regulatory prevention strategy. An iterative model of "evolution game—optimized clearing" was established between regulators and risky subjects. A library of market risk and profit indicators was formed. And the risk prevention strategy was quantitatively constructed for the electricity market. The evolutionary stabilization strategy and market risk changes in the process of continuous game interaction between the two participants was explored. Iterative simulations base on real data，the simulation results show that when the market risk is high，after limited rounds of evolutionary game，the regulatory prevention strategy can reduce the degree of transaction risk，which verifies the effectiveness of the regulatory prevention strategy. The proposed method can provide theoretical support for the formulation of electricity market regulatory strategy.

DC high current comprehensive characteristic test device is used to detect the released characteristics of DC low-voltage electrical overcurrent protection electrical device，which is used in low-voltage electrical industry for DC products for long time delay，short time delay，instantaneous tripping test and short circuit test. With the wide application of DC low-voltage electrical products in non-ferrous metallurgy，chlor-alkali chemical industry，low-voltage power distribution，DC transmission and distribution，new energy and railway applications，the DC high current comprehensive characteristic test device used for DC electrical product testing needs to be traced regularly to ensure that it can meet the accuracy requirements of the test detection capability. In the field of measurement calibration，the present situation of relevant calibration methods was analyzed，and the research direction of calibration methods of this test device was reviewed. According to the corresponding product of the test device and the national standard，a new calibration parameter was proposed. Aiming at the calibration problem of the DC high-current device，the measurement method of optical fiber current sensor was proposed，so as to evaluate the uncertainty of the data generated.

In view of the lack of flexibility in the input and exit of the current metal sheath loop suppression device for high voltage cables，the problems such as excessive induced voltage of the sheath and excessive power loss were not considered when determining the suppression impedance value，a loop suppression device was designed which could dynamically input or exit the loop suppression impedance of the sheath according to the field conditions. Firstly，the structure and operation flow of the suppression device was described. Then，the variation characteristics of sheath circulation，induced voltage and sheath loss when the suppression impedance was pure resistance，pure inductance and combined resistance inductance were analysed. On this basis，an optimization model was established to solve the optimal impedance value which can minimize the power loss when meeting the requirements of sheath circulation and induced voltage. Based on the optimal impedance value，the parameters of thyristors and other components were configured. The results show that the proposed method can obtain the optimal value of cable suppression impedance that meets the engineering requirements，and achieve a good circulation suppression effect.

Permanent magnet synchronous motors play an important role in industrial automation， automotive， aerospace， household appliances， and other fields due to their high efficiency， high power density， good torque performance， and ease of control. However， in the field of electrical transmission， it is not only necessary to accurately control its operating status， but also to have complex industrial communication and human-machine interfaces. Traditional electrical drives mostly use proportional integral components for speed control， which may lead to integrator saturation issues， resulting in slower integration response after disturbance disappears. Complex industrial communication and human-machine interfaces require a large amount of chip resources and chip IO， resulting in high control costs. By improving the traditional proportional integrator and introducing output feedforward control， the response delay caused by integrator saturation was solved. By improving the external communication protocol and external human-machine interface hardware circuit， it solved the problem of resource and IO occupation that traditional transmission system design can only solve by increasing the number of chips. The improved system can complete all functions on a single chip 280039C DSP. Due to the absence of inter chip communication， the communication speed and response speed is greatly improved， and the on-site use is good.

The semi-bridgeless dual Boost power factor correction（PFC） circuit can obtain higher conversion efficiency without increasing common mode noise，but the return current of the input AC terminal produces additional losses on the introduced diodes，which reduces the conversion efficiency. The replacement of diodes with MOS transistors was investigated. The MOS transistor was with very low impedance when turned on to short-circuit the MOS transister（or its body diode） and the inductor branch in parallel. Most of the return current was flowed through the introduced MOS transistor，the conduction loss was reduced and the conversion efficiency was improved. At the same time，a low impedance path was provided for the common mode noise through the MOS transistor and its body diode，and the commonmode noise level was not changed. The working process and design criteria of the circuit were given，and the correctness of the analysis was verified by circuit simulation. Finally，a 1.5 kW principle prototype was developed，in which it was verified that the circuit can further improve the conversion efficiency.