Research on Active Power Filters with Energy Feedback Capability for Characteristic Load of Beam Pumping Units

Beam pumping units are predominantly used for onshore oil extraction worldwide, and to enhance operational efficiency and enable flexible stroke adjustment, these units typically employ frequency converter-driven motors. However, conventional frequency converters with uncontrolled rectification introduce harmonic distortion into the power grid, compromising power quality. Furthermore, beam pumping units represent typical potential energy loads, where the driving motor experiences power regeneration during the downstroke. Since diode rectifiers cannot feed this regenerated energy back to the grid, brake resistors are required to dissipate excess energy, resulting in power wastage. This study investigates an active power filter with energy feedback capability to address both harmonic control and energy recovery. During motor-driven operation, the active power filter suppresses harmonic currents generated by nonlinear loads, thereby improving grid power quality. In contrast, during power regeneration, the filter switches to grid-connected inverter mode, feeding energy back to the power grid. To ensure optimal control performance in both operational modes, the system employs hysteresis current detection for voltage loop control and repetitive sliding mode control for current loop regulation, utilizing Space Vector Pulse Width Modulation (SVPWM) for modulation. Simulation results demonstrate that this closed-loop controlled three-phase active power filter effectively achieves both harmonic filtering and energy feedback functions, with smooth transitions between operational modes.