Optimal Allocation of Curtailment Levels of PV Power Output in Different Regions in Consideration of Reduction of Aggregated Fluctuations

Due to the high penetration of photovoltaic power generation system (PV) anticipated in the future, the curtailment of PV power output becomes crucial, not only to maintain supply-demand balance but also to preserve an adequate capacity for the frequency control. When the curtailment level (CL) of the aggregated PV power output is determined in a day-ahead unit commitment (UC) scheduling, different CL should be applied to different regions with distinctive weather modes in the power system area so that the fluctuations of aggregated PV power output are minimized. The objective of this study is to optimally allocate the CL to each region based on the short-term forecasting of the weather modes so that the hourly maximum fluctuation of the aggregated PV power output (MFagg) is minimized as long as the aggregated average power output (Avgagg) becomes the same as the scheduled value in UC. Based on the past observations of PV power output, the proposed method employs relations between the regions’ MF and CL (MF-CL patterns), and relations between the regions’ Avg and CL (Avg-CL patterns) for several typical weather modes. Thus, a specific MF-CL pattern and Avg-CL pattern are determined for each region based on the short-term forecasting of the weather mode, and the CL optimization is proceeded by using these patterns. The proposed methods are tested by using the time-series of PV power output at 61 observation points in the central region of Japan for one year. As a result, it is demonstrated that merely acknowledging the weather mode of each region enabled the proposed methods to reduce MFagg significantly and these results are practically similar to the method where perfect short-term forecasting of PV power output was utilized in the entire year

Autonomous Dual Active Power-frequency Control in Power System with Small-scale Photovoltaic Power Generation

Active power control of the photovoltaic (PV) power generation system is a promising solution to regulate frequency fluctuation in a power system with high penetration of renewable energy. This paper proposes an autonomous active power control of a small-scale PV system for supporting the inertial response of synchronous generators and power-frequency control. In the proposed control approach, an effective grid frequency regulation scheme is realized using slow- and fast-frequency responses. A low-pass filter based frequency measurement is used for slow-frequency response, while direct frequency measurement is used for fast-frequency response. The designed dual droop characteristic-based control is shaped to achieve a smooth transition between slow- and fast-frequency responses. The performance of the proposed control approach is demonstrated for serious disturbance scenarios, i. e., considerable power-load imbalance and generation trip. In the power-load imbalance test scenario, the proposed control approach works properly within the normal frequency deviation region even when the frequency deviation exceeds that region occasionally. In the generation trip test, the frequency deviation is mitigated quickly, and the employed droop control is smoothly transferred from the slow- to fast-frequency responses