An Electro-Hydraulic Hybrid Drive Swing System for Excavators with Operating Condition-Based Speed Control Strategy

Excavator swing systems typically suffer from significant throttling losses and braking energy waste during frequent acceleration and deceleration, resulting in low energy efficiency. To address these issues, an electro-hydraulic hybrid drive swing system for excavators (E-HHDSS) combining electric and hydraulic drives is proposed. The E-HHDSS employs a permanent magnet synchronous motor (PMSM) and a hydraulic pump/motor in parallel to drive the swing system. The PMSM provides fast response and precise motion control, while the pump/motor cooperates with a hydraulic accumulator to regulate system power and recover braking energy. During braking, the braking energy is converted into hydraulic energy and stored in the accumulator. During subsequent acceleration, the stored energy is released to assist the PMSM, thereby reducing electrical power demand. Furthermore, a speed control strategy based on operating condition identification is developed to coordinate the two power sources. The strategy integrates adaptive PMSM control with hydraulic system operation to achieve stable speed tracking and effective braking energy recovery under different operating conditions. Experimental results demonstrate satisfactory dynamic performance, with a maximum braking energy recovery efficiency of 57.6% and a 40.8% reduction in overall energy consumption.