In order to improve the robust stability of the grid-connected inverter of wind power or photovoltaic power generation while connected to a weak power-grid, the robust model of grid-connected inverter under weak power-grid is established, and the influence mechanism of power-grid impedance and voltage distortion on the stability and current quality of grid-connected inverter is analyzed. On this basis, an adaptive robust H_∞ control method is proposed, in which there is no need to online measure the power-grid impedance, and the control parameters do not change with the change of the power-grid impedance. Then, the calculation method of each reference quantity and the design method of control parameters are introduced. Finally, an experimental platform is built, and the correctness and effectiveness of the theoretical analysis and the proposed control method are verified by experiments. Compared with other control methods, the adaptive robust H_∞ control method realizes the stability of the system when the power-grid impedance varies in a wide range, which optimally restrains the power-grid voltage distortion and improves the quality of grid-connected current.

To address the challenges of real-time insulation monitoring and accurate partial discharge (PD) location in cable joints. A distributed Optical Fiber sensing system with polarization compensation module is established to detect the ultrasonic signal of partial discharge. The locating range of optical time-domain reflectometer (Φ-OTDR) is analyzed, and a variance variable mathematical model based on Rayleigh scattering coherent light signals is established to denote weak ultrasonic characteristic signals of partial discharge in cable joints. The polarizing beam splitter (PBS) is devised in the Φ-OTDR detection circuit to improves the stability of polarization states. Four Optical Fiber ring sensors are wound on the cable joint to locate and detect the partial discharge point of the cable joint. Then, the signal characteristics of partial discharge measured by electrical measurement method and Optical Fiber acoustic measurement method are compered, and the positions of four Optical Fiber ring sensors are calibrated based on piezoelectric sensors. It shows that when the test fiber length is 600m or 1125m respectively, the locating deviation is less than 1.9m, which is verified a high accuracy of Optical Fiber sensing system in detecting partial discharge. It provides a feasible monitoring method for real-time sensing of insulation status of transmission equipment.

The coordinated use of electricity and a heat energy system can effectively improve the energy structure during winter heating in the northern part of China and improve the environmental pollution problem. In this paper, an economic scheduling model of an electric–thermal integrated energy system, including a wind turbine, regenerative electric boiler, solar heat collection system, biomass boiler, ground source heat pump and battery is proposed, and a biomass boiler was selected as the auxiliary heat source of the solar heat collection system. A mixed integer linear programming model was established to take the operating cost of the whole system as the target. A day-ahead optimization scheduling strategy considering the demand side response and improving new energy consumption is proposed. In order to verify the influence of the coordinated utilization of the flexible load and energy storage equipment on the optimal scheduling in the model built, three scenarios were set up. Scenario 3 contains energy storage and a flexible load. Compared with scenario 1, the total cost of scenario 3 was reduced by 51.5%, and the abandonment cost of wind energy was reduced by 43.3%. The use of a flexible load and energy storage can effectively reduce the cost and improve new energy consumption. By increasing the capacity of the energy-storage device, the wind power is completely absorbed, but the operation and maintenance cost is increased, so the capacity of energy storage equipment is allocated reasonably according to the actual situation.