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.

Fault detection is quite important for discrete event systems. We investigate K-codiagnosability of Petri nets in this paper under the framework that some local sites monitor the operation of the system using their own masks. They exchange information with a coordinator while do not communicate with each other. A fault is detected when there exists a site can diagnose it. We recall the notion of Modified Verifier Nets (MVNs), and prove that K-codiagnosability can be verified looking at some special cycles in the reachability or coverability graph of the MVN. In particular, the proposed approach is available for bounded and unbounded nets. Finally, we give an algorithm to compute the minimum value of K.

In order to solve the problem that the dual Mach Zehnder (M-Z) interferometer system is easily affected by external environmental noise, a data signal-processing scheme based on Hilbert–Huang transform (HHT) is proposed to achieve high-precision location with distributed optical fibers. The polarization compensation module has a built-in dual Sagnac interferometer system which is used to stabilize the polarization state of the Sagnac interferometer. The eigenmode function is obtained by empirical mode decomposition of the received two optical signals, and then the Hilbert spectrum is obtained by superimposing the Hilbert transform, so that the high-similarity curve caused by the vibration signal can be clearly and intuitively extracted. The optical signal information can be calculated based on the cross-correlation and delay estimation algorithm to accurately obtain the vibration position information. The experimental results show that the positioning accuracy can reach ±11 m, with a sensing fiber length of 15 km and a sampling rate of 10 MHz. It is proven that the distributed optical fiber sensing technology based on the dual Sagnac interferometer system has high practical application value.