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| Research on Power Characteristics of Full-Power Variable Speed Pumped Storage Units Based on Hydraulic-Mechanical-Electrical Modeling |
| Luan Yihang1,2, Zhang Yuanzhi1,2, Chuang Kaihsun1,2, Ding Lijie3,4, Sun Jianjun1,2 |
1. Hubei Key Laboratory of Power Equipment & System Security for Integrated Energy Wuhan University Wuhan 430072 China;
2. School of Electrical Engineering and Automation Wuhan University Wuhan 430072 China;
3. State Grid Sichuan Electric Power Research Institute Chengdu 610041 China;
4. Power Internet of Things Key Laboratory of Sichuan Province Chengdu 610041 China |
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Abstract As the most mature and most economical energy storage technology at present, pumped storage has become an important means to ensure the safe and stable operation of new power systems. Among them, full-power variable speed pumped storage units (Full-power VSPS) are the most potential due to their excellent comprehensive performance and gradually reducing costs. However, the current research on Full-power VSPS is still in its infancy. The complex physical process of hydraulic-mechanical-electrical coupling within the unit and the unit's ability to respond to grid dispatching instructions under different control strategies is not yet fully understood.
In response to the above problems, this paper carries out relevant research on the modeling and power characteristics analysis of Full-power VSPS. First, this paper uses the sub-module modeling method to establish the transfer function model of the water diversion system with double surge tanks, the characteristic curve model of the pump turbine, and the simplified model of the generator motor and full-power converter, and finally obtains the unit hydraulic-mechanical-electrical joint simulation model.
Subsequently, this paper summarizes the two most basic control strategies for Full-power VSPS, namely speed priority control and power priority control. On the basis of the unit characteristic curve, the movement trajectory of the unit's working point under pumping and generating conditions is given when the above two control strategies are used, and the changing rules of the unit'sspeed, electromagnetic power and guide vane opening are qualitatively analyzed.
When the speed priority control strategy is adopted, the speed of the unit quickly reaches the new steady state, while the electromagnetic power changes rapidly at first and then slowly. In the period of rapid change, the power undershoot will occur under generating condition, which must be suppressed. A feasible suppression method is to input the mechanical power of the pump turbine instead of the power grid dispatching instruction into the speed optimizer. However, the power overshoot may occur under pumping condition, which can be prevented by setting a reasonable proportion coefficient of the MSC.
When the power priority control strategy is adopted, the electromagnetic power of the unit quickly reaches the new steady state. However, due to the different forms of speed feedback, there are great differences between the operation characteristics of the unit under pumping and generating condition. Under the generating condition, due to the potential positive feedback of the speed, the unit will have two inherent phenomena: the speed undershoot and the guide vane overshoot. Thespeed undershoot brings the risk of instability to the unit, and the restraining method is to set reasonable governor PI parameters.
While under pumping condition, due to the negative feedback of the speed, the risk of instability of the unit is low, but the speed will change rapidly at the initial stage of the transition process, and the speed overshoot may occur. In this paper, an approximate formula for calculating the speed at the trajectory inflection point is given, and it is pointed out that whether the rotational speed overshoot occurs or not depends mainly on the design parameters of the unit and has little relationship with the control parameters.
Finally, this paper points out that the main reason for the difference of unit oscillation modes under the two control strategies is the different transfer path of water hammer effect. Combined with the above analysis, the power characteristics and the potential operational risk of the units utilizing the two basic control strategies under pumping and generating conditions are summarized.
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Received: 10 January 2024
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2025, Vol. 40 
