Real-time simulation, implementation, and new structure of DTC for a photovoltaic water pumping system based on a DFIM

This paper presents a new structure an off-grid photovoltaic water pumping system based on a doubly fed induction motor (DFIM) driving a centrifugal pump. The proposed control scheme combines a variable step-size perturb-and-observe maximum power point tracking algorithm (VSS-P&O MPPT) with a conventional hysteresis-based direct torque control (DTC) strategy to ensure effective photovoltaic power extraction and robust motor-drive operation under varying irradiance conditions. The VSS-P&O MPPT adaptively adjusts the duty cycle of a DC-DC boost converter, enabling the photovoltaic generator to operate close to its maximum power point while reducing steady-state oscillations and improving tracking dynamics. On the drive side, the DFIM is controlled by a conventional six-sector DTC switching table implemented through a two-level voltage source inverter, providing fast torque and flux response suitable for variable-speed pumping applications. The performance of the overall system is first evaluated in MATLAB/Simulink under both step and time-varying irradiance profiles. The developed control algorithms are then implemented in real time using a dSPACE DS1104 platform. The experimental results show good agreement with the simulation results, confirming the consistency, effectiveness, and practical feasibility of the proposed approach for photovoltaic water pumping applications. Future work will focus on extended experimental investigations under real operating conditions and on the integration of intelligent control techniques to further improve the energy and hydraulic performance of the system.