Research on dynamic characteristics of a multi-motor electric driving system caused by parasitic power

To reduce greenhouse gas emissions in dealing with climate change, replacing fuel vehicles with electric vehicles (EVs) is one of the most effective measures. The multi-motor electric drive system (MMEDS), which is widely used in EVs, is driven by two or more permanent magnet synchronous motors (PMSM) by parallel shaft gear set (PSGS). Due to the action of forced synchronization of PSGS, once there is a rotational speed difference ( increment V) be-tween PMSMs, this will break the balance of output power between PMSMs and cause the increase in output power of some PMSMs while others decrease or even become nega-tive, and eventually generate parasitic power. Parasitic power in MMEDS is bound to cause an auto excitation vi-bration and a variation in dynamic characteristics of MMEDS. Therefore, in this paper, an electro-mechanical coupled dynamic model of MMEDS is set up, including a dynamic model of PSGS and a dynamic model of PMSM. Then, the affect of the forced synchronization action of PSGS on the dynamic characteristic of MMEDS is investi-gated under different increment V. The results show that under the action of the forced synchronization of PSGS, the output power of the PMSM with a fast speed (or a slow speed) in-crease (or decreases) with the increasing of increment V, and when increment V <= 5 rpm, the increment rate or decrement rate of the out-put power of PMSM is obviously greater than that when increment V>5 rpm. Meanwhile, increment V has a significant effect on the nonlinearity of the vibration of the wheel, which increases first and then decreases with increment V increases. The dominated frequencies of dynamic meshing force (DMF) of gear pair do not change with increment V, but their contributions to the ampli-tude of the DMF change with increment V. Moreover, the modulation frequencies also appear in the spectrum of the DMF, but their contributions to the amplitude of the DMF are signifi-cantly less than that of the dominated frequencies.