Study on high-efficiency arc direct-drive system based on beam oil pumping unit and dynamic performance

To shorten the surface transmission chain of conventional beam pumping units while improving compatibility between direct-drive actuation and the existing walking-beam structure, this study proposes an arc permanent-magnet synchronous motor (arc-PMSM) arranged along the walking-beam trajectory. The rotary motor–belt–gearbox–crank/linkage drive chain is replaced while the walking beam, horsehead, polished rod, and principal lifting geometry are retained. A two-dimensional (2D) equivalent linear-motor model is used for electromagnetic design and sequential parametric screening, followed by a three-dimensional (3D) arc model for numerical cross-checking of the principal electromagnetic quantities. Performance is further evaluated over a representative motor-side speed range of 0.28–0.70 m/s, and two dynamic pumping scenarios are investigated using a sequential electromagnetic–kinematic framework. After screening, the average thrust increases from 58.76 to 59.72 kN, the thrust ripple decreases from 26.7% to 12.6%, and the maximum flux density decreases from 1.92884 to 1.71113 T. The approximately equivalent 3D model gives an average thrust of 60.78 kN and a thrust ripple of 14.9%, with only a 1.77% difference in average thrust relative to the 2D design. Across 0.28–0.70 m/s, the calculated average thrust remains within 56.31–60.07 kN, total electromagnetic loss is 2.01–2.55 kW, and motor efficiency is 88.7%–94.4%; the rated power factor given in the 3D design data is 0.97. Under a scheme-level comparison reflecting the characteristic low average motor load factor of conventional beam-pumping operation, the conventional drive-chain efficiency is 44.16% and the arc-PMSM direct-drive efficiency is 87%, corresponding to a 42.84-percentage-point difference. The two dynamic scenarios yield average motor efficiencies of 71.33% and 82.18%, with the target-trajectory case showing better coordinated input/output power variation during low-load and acceleration/deceleration intervals. The results support the high-efficiency potential of trajectory-matched arc-PMSM direct drive while retaining the principal lifting structure and removing intermediate surface mechanical transmission stages.