Scenario-based design for variable frequency drive irrigation pumping stations

Pumping stations in pressurised irrigation headworks are commonly selected from a single unfavourable duty point, although real operation is governed by multiple recurrent flow–head scenarios. This can cause oversizing, poor variable frequency drive (VFD) controllability and insufficient suction-side reliability. This study develops a reproducible design-stage workflow for selecting pumps and pumping configurations able to satisfy all expected scenarios within practical hydraulic and operational constraints. The workflow was applied to three commercial irrigation installations comprising 34 operating scenarios. Manufacturer head, efficiency and Net Positive Suction Head (NPSH) curves were represented using shape-preserving Piecewise Cubic Hermite Interpolating Polynomials (PCHIP). For each candidate pump and configuration, the required operating frequency was obtained by curve inversion within a 30–50 Hz envelope. Single-pump, two-pump parallel and two-pump series configurations were compared using catalogue-domain compatibility, frequency feasibility, commissioning guardrails, a scenario-summed power index and NPSH-margin screening. Single-duty-point sizing was insufficient to ensure multi-scenario feasibility. The selected configurations were two 65-160/150 pumps in parallel for Case A, two 80-400/300 pumps in series for Case B and one 150-400/750 pump for Case C. NPSH screening excluded two discharge-feasible candidates, and eight retained configurations required low-frequency guardrails. The proposed workflow links irrigation demand variability, catalogue-based pump behaviour, VFD limits, pumping architecture and suction feasibility into a single decision-support procedure. It improves pump-selection robustness and helps avoid configurations that are valid for one duty point but unsuitable under real multi-scenario irrigation operation, while retaining transparent, reproducible calculations suitable for design review, commissioning support and robust future energy assessment.