Control and dynamic analysis of a BLDC-based pico-pump hydro energy storage system in a utility-interactive wind-based AC/DC microgrid

Abstract

This study presents a novel integration of a variable-speed Brushless DC (BLDC) machine within a pico-Pump Hydro Energy Storage (pPHES) system, integrated into a utility-interactive wind-based AC/DC microgrid. The Third-Order Field-Oriented Sliding Mode Control (TOFOSMC) interfaced with a 3-level Neutral Point Clamp (NPC) converter is employed for efficient regulation of the variable-speed pPHES (VS-pPHES) system under fluctuating wind and grid load conditions focusing on transitions between pumping, generating, and disconnecting modes. The Maximum Power Point Tracking (MPPT) is employed for both VS-pPHES reversible pump-turbine and wind energy to maximize extraction efficiency. The performance evaluations demonstrate notable improvements: the TOFOSMC exhibits lower rotor speed standard deviation (STD) during transition, compared to conventional field-oriented control with proportional-integral controller (FOC-PI) in both Case 1 (1.8188 vs. 2.4587) and Case 3 (1.6106 vs. 1.8427), highlighting its enhanced ability to minimize speed fluctuations. Additionally, TOFOSMC outperforms FOC-PI in transient response, achieving faster peak time (0.0464 s vs. 0.0570 s), reduced overshoot (34.37 % vs. 52.27 %), and lower RMSE (6.1590 vs. 6.9527), which collectively ensures improved tracking accuracy. Moreover, the system's operational efficiency exceeds 60 % in both pumping and generating modes, with total harmonic distortion maintained below 5 %, ensuring compliance with IEEE-519 standards. These results are simulated in MATLAB/Simulink, and experimental validation in laboratory prototype confirms its effectiveness and practicality.