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FAST MOTOR -A new motor for EV-PartⅠ

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1001775694587191296


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Description


1.Background


The project FAST focuses on the development of a high performance traction drive with breakthrough metrics (kW/kg, kW/L, $/kW). In the early stages of this project extensive analysis is performed to identify the most appropriate machine technology. This document reports the findings of this work and is organised as follows. Section 2 describes the machine requirement, including the torque-speed characteristic, dc link voltage, available coolants as well as the target performance metrics. These numbers are compared to existing commercial EV traction motors. In Section 3, the choice of magnetic materials (hard and soft) is discussed, together with the cooling technologies. In Section 4, using a unique sizing environment the Interior Permanent Magnet (IPM), Permanent Magnet Assisted Synchronous Reluctance (PMaSynRel), and Induction Machines (IM) are compared in detail on various considerations including power density, efficiency and VA requirement for a range of pole numbers. Section 5 discusses the main outcomes from this work activity, and describes the next steps.


2.Machine requirement


The machine requirement is firstly described in this section. Consequently two selected commercial EV machines are reviewed for putting the target performance metrics in perspective.


2.1.Target Requirement


The machine target requirement is summarised in Table 2.1, corresponding to a high performance electric motor for an all-electric passenger car. The rated power is 80 kW, with the said power which needs to be achieved between 4000 and 16000 rpm, corresponding to a torque of 190 Nm at the base speed. The overall target power density is 20 kW/L in line with the APC next generation passenger car motor roadmaps [1], while the DC link is 800 V in line with the next generation trends [2]. Within the system both water and oil are available as coolants for the electrical machine thermal management.

 

A gear ratio of 14:1 is initially selected based on WLTC drive cycle. From Fig. 2.1, when the drive cycle is further examined, it is evident that over 50% of time is spent between 2000 rpm and 10000 rpm at low to intermediate loads.

2.2.Benchmark Machines


Three automotive benchmark machines, the JLR D8 (IPM), Nissan Leaf (IPM) and Tesla Model S (induction machine) are investigated for their characteristic properties, which set comparative baselines for the FAST machine.


Electric motor of JLR I-Pace is an IPM type synchronous motor with three layers of permanent magnets as shown in Fig. 2.2(a). It has a base speed of 3500 rpm and a maximum speed of 12000 rpm with 110 Nm and 30 Nm output torque respectively. In Fig. 2.2(b), induction motor


(IM) of Tesla Model S is shown. It has a base speed of 5000 rpm and a maximum speed of 15000 rpm with 180 Nm rated torque.

 

Specifications of the three machines are summarized in Table 2.2. While it is difficult to draw a perfectly fair comparison (for example the Nissan Leaf motor has a peak rating very similar to the continuous), it can be noted that the power density (kW/L) being targeted within FAST is ambitious and will translate to innovations in electromagnetic design, cooling and manufacturing.

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