A method for reducing the coherent Rayleigh noise (CRN) in a Rayleigh and Brillouin (RB) self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR) system using phase shift keying (PSK) pulse encoding is proposed and verified experimentally. A phase modulator and an electro-optic modulator driven by the same arbitrary function generator perform PSK pulse encoding modulation on the signal, and the traces obtained by PSK encoded pulses with different encoding patterns are superposed and averaged to reduce the CRN. The experimental results show that, in the case of 10,000 times average to eliminate other random noise effects, after using PSK pulse encoding, the amplitude fluctuation and signal-to-noise ratio at the fiber end of the RB self-heterodyne detection BOTDR sensing system are reduced by 1.12 dB and improved by 3.01 dB, respectively. In addition, the measurement accuracy and measurement stability of the Brillouin frequency shift and temperature are effectively improved. The proposed method offers a robust solution for reducing the CRN in the RB self-heterodyne detection BOTDR sensing system, facilitating high-precision and long-distance sensing capabilities.

Existing liner power flow (LPF) models do not consider the non-smooth constraint characteristics of the voltage source converter (VSC) and on-load tap changer (OLTC) that contain operation limit and dead zones, which limits its application. Thus, a three-phase LPF model for distribution networks is proposed, which considers non-smooth constraint characteristics. Firstly, smoothing functions are used to effectively fit the non-smooth constraint characteristics, resulting in control functions that are continuous and differentiable. Then, based on the first-order Taylor series expansion, the three-phase power flow equations are physically linearized, and the terms to compensate errors are obtained through the partial least squares (PLS) method. Compared with the model without considering the non-smooth constraints, the three-phase LPF model considering the non-smooth constraints can accurately represent the operating characteristics of the VSC and the OLTC in the actual distribution network, thus providing more reliable power flow calculation results. Based on a typical 42-node distribution network, the proposed model is compared and analyzed against other LPF models. The results indicate that the proposed model has the ability to handle non-smooth constraints, with higher computational accuracy compared to existing data-physical hybrid driven models.