Electric drive system technologies - Propulsion Systems for Hybrid Vehicles - page 281

according to Reference 9 is that the saliency ratio must be at least 9:1. This is, of
course, very difficult to achieve in practice due to the need for rotor iron bridges
and posts to secure the soft iron pole shoes over the magnets and not have issues
with rotor retention. The second design constraint for hybrid propulsion is that for
the buried magnet IPM to be immune to UCG will require that it be designed for
CPSR < 4. This means the lowest possible magnet flux that will suffice to meet
application design torque requirements. Otherwise, the IPM will have some speed
regime where an inverter shutdown may result in UCG output and consequent
overvoltage being imposed on the traction battery, other energy storage system, or
concerns with active device voltage ratings (aluminium electrolytics fall into this
category as well).

Example 4: The Camry Hybrid traction motor, MG1, is directly coupled to
the Camry wheels via a compound planetary, with stage 2 epicyclic gear E2 ratio
of k E2 ¼ 2.478. The total final drive ratio, g fd ¼ 3.542 and dynamic rolling radius,
r w ¼ 0.355 for the tyres. Assess the following:

(a) The vehicle speed, V , for which MG2 angular speed is 5,000 rpm.

(b) Given that MG2 open circuit voltage, U oc ¼ 150 V rms line-to-line, at 5,000 rpm,
determine the PM voltage constant for this IPM electric machine (i.e. use
(5.23)). MG2 is a P ¼ 8 poles, 3-phase IPM with Q ¼ 48 slot stator.

(c) What is the voltage of MG2 at vehicle WOT?

(d) Using data on the Camry MG2 magnets (IPM with single layer chevron
geometry, 145 ) L m ¼ 6.6 mm, g ¼ 0.73 mm and NdFeB with recoil per-
meability m r ¼ 1.05, calculate the airgap flux during static conditions.
Solution:

(a) For the single-mode eCVT with the stated gearing, and MG2 geared from
the driveline, the vehicle speed corresponding to MG2 angular speed n ¼
5,000 rpm is

r w w MG2
g fd k E2 ¼

0 Þ

3 : 542 ð 2 : 478 Þ ¼ 21 : 2m = s

: 355 ð 523 : 5

V ¼ ð 47 : 4m = h Þ

(b) This is a straight application of (5.1) and with care about units:

U oc phase
w e

p
2 w MG2 ¼ 4 ð 523 : 5 Þ¼ 2,094 rad = s

y m ¼ , w e ¼