Coordinated Multi-Objective Optimization for Multiple Trade-Offs in Pumped Outage Condition of Pumped Storage System

The transient process of pumped storage system (PSS) experienced pump mode, turbine mode and switching mode in pumped outage condition, spanning hump zone and S-shaped region. The conflicting dynamic indicators make it difficult to meet the requirements of the transient process. How to specify optimal operating strategies and improve the reliability of PSS in the pumped outage condition has become a key issue. This problem is addressed in this work based on coordinated multi-objective optimization, and three stages are included: nonlinear modeling, strategy optimization and decision making. A trade-off is embodied in each stage. Firstly, the real-time accurate equivalent circuit model is applied for PSS. The spatiotemporal discrete analysis is presented to enable the trade-off between computing efficiency and model accuracy in stage 1. Then, the neighborhood-search chaotic mutation multi-objective gravitational search algorithm, integrating multiple constraints, is performed to solve the Pareto front. It achieves the trade-off between algorithm convergence and searching diversity in stage 2. Further, fuzzy analytic hierarchy process is innovatively introduced to select the most compatible solution, which comprehensively considers the quantitative and qualitative factors. It accomplishes the trade-off in conflicting objectives and indicators in stage 3. Compared with the on-site operation in pumped outage condition, the maximum reversing speed decreased from 545 rpm to 161.45 rpm, the maximum water pressure of volute can be reduced by 4.55%, and the minimum draft tube pressure can be improved by 6.94%. The coordinated multi-objective optimization provides a novel technical guidance for the safe and stable operation of PSS.