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The stochasticity of photovoltaic (PV) generation output makes it necessary to smooth the output using other flexible power sources to realize the scale development of PV power. Small cascade hydropower stations (SCHSs) are also widely distributed in space, like PV generation. Therefore, it is proposed to utilize the regulation capability of SCHSs to complement PV generation. Targeting the maximization of the utilization rate of outgoing lines (utilization rate for short) of the system, the minimization of the curtailment rate, and the maximization of the minimum output within a time frame, a model for exploring the capability of SCHSs for regulating PV generation was established and solved by a hierarchical optimization method. By taking two small hydropower stations (the Mupo and Yangjiawan stations) on the Fabian River with a total installed capacity of 105 MW and the surrounding PV power source in China's Sichuan Province as examples, it was found that SCHSs can regulate a certain level of PV generation through the combined operation of cascade reservoirs and reduce the fluctuations and stochasticity of the PV generation output. The results have far-reaching significance on the large-scale development of PV generation. [ABSTRACT FROM AUTHOR]

The central Tibet AC interconnection project (CTAIP), which connects the Tibet power grid and the Sichuan power grid through a long distance transmission line of more than 1400 km, has a significant problem of voltage regulation. In order to improve the voltage regulation performance, six sets of ±60 Mvar static VAR compensators (SVC) were installed in the CTAIP. However, the SVCs may lead to electromagnetic oscillation below 50 Hz while improving voltage regulation capability. In this paper, the electromagnetic oscillation modes and the sensitivity of control parameters of SVC are analyzed. Then, the characteristics and influencing factors of the oscillation are discussed. It was found that there is an inherent electromagnetic oscillation mode below 50 Hz in the ultra-long distance transmission system. The employ of SVCs weaken the damping of this mode. Large proportional gain and integral gain (PI) parameters of SVCs can improve the voltage regulation performance, but weaken the electromagnetic oscillation mode damping. Therefore, a suppression method based on SVC PI parameters optimization is proposed to damp the oscillation. The essential of this method is to use the rising time of voltage response and setting time of SVCs as performance indicators of voltage regulation, and take the damping level of the electromagnetic oscillation mode as the performance index of SVC electromagnetic oscillation suppression ability. Combining the two indicators to form a comprehensive optimization index function, an intelligent optimization algorithm is applied. The process of SVC parameter optimization and the steps of multi-SVC parameter optimization in large power grids is proposed. Finally, PSCAD and real-time digital simulation (RTDS) simulation results verified the correctness of the proposed method. The optimization strategy was applied to CTAIP. The artificial grounding short circuit experimental results proved the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]