Direct torque control of a permanent magnet synchronous machine for hybrid hydraulic excavator

Abstract

A hybrid power train system (HPTS) is considered as a promising technology to improve the efficiency of excavators. In the hybrid hydraulic excavator, due to the drastic changes in the load, ultra-capacitors are employed to realise fast charge and discharge. Accordingly, a wide change of the DC voltage will happen. When the DC voltage is small, the maximum torque that the electric machine can output will be limited. The electric machine cannot fully compensate for the engine torque. Therefore, a novel direct torque control (DTC) is proposed for a permanent magnet synchronous machine (PMSM) in HPTS to reduce the influence of DC voltage on the maximum output torque of the PMSM. In this study, the mutual influence between the torque of the PMSM and DC voltage is analysed. The traditional DTC is briefly introduced. A novel DTC for the PMSM is presented. To validate the performance of the novel DTC, simulations and experiments are carried out. The results demonstrate that the proposed DTC can reduce the effect of DC voltage variation on the maximum output torque of the PMSM. Moreover, working points of the engine in HPTS can be better stabilised.