Objective With the increasing proportion of renewable energy integrated into the distribution network, along with advancements in energy storage technology, cloud energy storage (CES) provides a new approach for the future management of customer-side energy storage. Many decentralized energy storage resources exist on the consumer side of the distribution network, which exhibit high inactivity and present management challenges. The effective utilization of decentralized energy storage resources not only raises the consumption of renewable energy but also reduces the operating cost of the distribution network and enhances the utilization of inactive decentralized energy storage resources. Therefore, this study proposes a bi-level optimization scheduling method for the distribution network-cloud energy storage system while considering renewable energy uncertainties. Methods A multi-agent interaction structure of the distribution network with the CES system was established to analyze the characteristics of decentralized energy storage resources on the customer side of the distribution network. Specifically, a bi-level optimal scheduling model of the distribution network-cloud energy storage system was proposed by considering wind and solar uncertainties. With the objective of minimizing the operation cost of the distribution network, the upper-level model determined the optimal dispatching strategy of different generating units and the charging/discharging strategy of the CES system. Accordingly, the lower-level model aimed to maximize the benefit of the CES system by determining the detailed charging and discharging strategy of its customers while considering the operation constraints of the distribution network. Results and Discussions The validity of the proposed bi-level optimization scheduling method of the distribution network-cloud energy storage system under renewable energy uncertainties was verified through four numerical cases. The comparative analysis was conducted in terms of the load profile of the distribution network, the charging and discharging strategy of the CES system, and the operation cost of the distribution network. In Case 1, the optimal scheduling strategy of the distribution network-cloud energy storage system was obtained. The charging hours of the CES system were mainly from 01:00—05:00 and at 24:00, while the discharging hours were mainly from 12:00—14:00 and 18:00—20:00. The peak-to-valley load difference of the distribution network was 2.7 p.u., together with the total operating cost of ¥93 401.2. For the distribution network, the electricity purchasing cost from the upper-level grid was ¥46 542.6, the operation cost of the gas unit was ¥45 382.1, the charging/discharging cost paid to the CES operator was ¥3 187.5, and the charging revenue from the CES operator was ¥1 711.0. From the perspective of the CES system, the charging/discharging cost paid to EV customers was ¥399.1, the charging/discharging cost paid to UPS customers was ¥611.6,the compensation cost paid to load interruption customers was ¥562.2, and the charging revenue from EV customers was ¥2 037.0. As a result, the total revenue of the CES operator was ¥1 940.6. In Case 2, the CES system was not considered, and EV users performed uncontrolled charging. The UPS and load interruption customers were also not included. Compared to Case 1, the peak-to-valley load difference of the distribution grid increased to 3.4 p.u., with an increase of 25.9%. In addition, the total operating cost of Case 2 increased by 8.0%, and the electricity purchasing cost from the upper-level grid increased by 19.2%. Specifically, the charging cost of EV customers increased by 245.7%. Case 3 examined the influence of CES capacity by changing the number and capacity of CES customers. The CES capacity participating in the distribution network scheduling was adjusted to 75%, 50%, and 25% of its capacity in Case 1, respectively. It was concluded that the total operating cost of the distribution network decreased as the CES capacity increased. However, the peak-to-valley load difference of the distribution network appeared to increase inversely when the CES capacity reached 100%, because the charging loads of EV customers were shifted to the low valley hours. Hence, the charging of the CES system at 01:00 increased abruptly from 0.2 p.u. to 0.7 p.u. at the capacity of 75%, while the CES system did not charge at 06:00—07:00, which increased the peak-to-valley load difference. Therefore, it was concluded that the appropriate capacity of the CES system can smooth the peak-to-valley difference of the load profile when participating in the distribution network scheduling. In Case 4, the uncertainty of wind and solar power was considered. Taking the wind and solar power prediction curve of Case 1 as the base scenario, 5 typical wind and solar power output scenarios were generated by Monte Carlo sampling and simultaneous backward reduction. For Scenario 3, the wind power output increased from 21:00 to 23:00, and the excess wind power was consumed by the CES system through charging. For Scenario 5, the wind power output decreased at 02:00, and the CES system discharged power to meet the load demand of the distribution network, with the discharging power increasing from 0 to 0.5 p.u. Therefore, the CES system managed the fluctuation of wind and solar power by adjusting its charging and discharging power under the premise of satisfying the charging demand of CES customers, improving the flexibility and stability of system operation. The proposed bi-level optimization scheduling model of the distribution network-cloud energy storage system under renewable energy uncertainties effectively reduced the operation cost of the distribution network and the peak-to-valley difference of the load curve, while improving the economy and stability of the distribution network operation. In addition, by adjusting the charging and discharging strategies of the CES system, the distribution network maintained stable operation under the fluctuation of wind and solar power. Conclusions Numerical results demonstrate that the proposed cloud energy storage operation strategy effectively reduces the operational cost of the distribution network, mitigates peak-load differentials, and fosters a mutually beneficial relationship among the distribution network, cloud energy storage operators, and cloud energy storage users. In addition, using the flexible regulation capability of the cloud energy storage system, the stable operation of the distribution network can be maintained even under fluctuating renewable energy outputs such as wind and solar power.
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