Optimization on the VFDs’ Operation for Pump Units

The third Huaiyin pumping station in the South-to-North Water Diversion Project aims to solve the problem of lack of water. In order to save on electricity while satisfying the required flow demand, the operation optimization problem of the third Huaiyin pumping station is investigated, with a mathematical model set up to simulate the optimal daily operation, in which the pump units can have variable speed. After analyzing the characteristics of the mathematical model, an improved dynamic programming algorithm is presented to decrease the dimensions of the operation optimization problem and save electricity cost, which enables us to perform a practical engineering application. After discretization of the optimization problem has been achieved, the number of operational schedule sequences could be reduced and optimal scheduling could be achieved to save electricity costs by power constraint, classified enumeration constraint, feasible combination constraint and flow demand constraint. Through research and analysis of the working of the third Huaiyin pumping station, optimal operational scheduling of multiple pump units with variable speed operation using variable frequency drive (VFD) can lessen the electricity tariff significantly compared with dynamic programming with the successive approximation method and decomposition/aggregation-dynamic programming method. The operational electricity tariff is reduced by 7.71% by the improved dynamic programming algorithm in comparison with the benchmark scheduling. Simulation results demonstrate that the cost efficiency comes from variable speed operation with VFD and flow demand transfer from the time periods when a high electricity tariff applies to time periods of a low electricity tariff based on the time-of-use electricity tariff.