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ITEC-AP.2017.8080841

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2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific)
Research on new type electric variable transmission
and its application in hybrid electric vehicle
Qiwei Xu, Xiaobiao Jiang, Meng Zhao
Shumei Cui, Xu Liu , Zhiyuan Wang
State Key Laboratory of Power Transmission
Equipment & System Security and New
Technology, Chongqing University
Chongqing, China
[email protected]
Harbin Institute of Technology
Harbin University
Harbin, China
[email protected]
Abstract?A new electric variable transmission in hybrid
electric vehicle is analyzed. The equivalent magnetic circuit and
finite element simulation model is established in this paper for
analysis of internal magnetic field coupling law. As for the strong
coupling relation in the internal magnetic field of electrical
transmission, magnetic flux-insulation ring is the electrical the
applied into the electric variable transmission in hybrid electric
vehicle, and its mathematical model is also built. Then, the
working modes of hybrid electric vehicle are analyzed. Power
output of engine and electric variable transmission is depended
on the power follower strategy. At last, the simulations and
experiments have verified that the electric variable transmission
can be used in hybrid electric vehicle, thus exploring a new way
for the study of hybrid electric vehicles.
Keywords?Electrical variable transmission; hybrid electrical
vehicle; magnetic field coupling; power follower strategy;
I.
INTRODUCTION
Professor Martin Hoeijmakers of Holland Dyer Fu Delft
University proposed electrical variable transmission in 2004
(Electric Variable, Transmission, EVT) concept, and its design
idea comes from the induction motor cascade speed control.
EVT has the advantages of fast dynamic response, high
mechanical integration, strong overload capacity, etc. Under
the condition of limited working space, it can make full use of
the space and volume of the motor to improve the
performance of the motor [1, 2]. In practical application, EVT
can be used as a new electronically controlled continuously
variable transmission device used in hybrid electric vehicle
(hybrid electric vehicle, HEV) [3], that is, its function is
equivalent to the TOYOTA Prius series hybrid vehicle
continuously variable transmission (continuously variable
transmission, CVT) Based on planetary gear. The reasonable
control of engine can guarantee the engine always works in
the zone of high EVT, which is of important significance to
improve the vehicle's power, fuel economy, and emission
reduction [4, 5].
At present, due to the specific characteristics of its
structure, there are still some problems in the design and
control of EVT. In the body design, there is no good way to
design EVT in large. Still internal and external motor are
separately designed in a traditional way, without considering
the magnetic coupling effect. So EVT will be split into inside
and outside the two induction motor design [6]. In the control
aspect, if still using the traditional mathematical model and
control strategy of motor for analysis, it is not only hard to
improve the performance of motor control through magnetic
coupling EVT, but also cause the output torque fluctuation,
severe fever and the efficiency of the system reduction [7].
In the light of the problem of EVT applied in HEV, a
model of equivalent circuit of EVT is established. By finite
element simulation and analysis on the internal magnetic field
distribution, this paper puts forward using magnetic fluxinsulation ring in EVT. Based on the working mode of EVT in
HEV, Power output of engine and electric variable
transmission is depended on the power follower strategy [8].
At last, the simulations and experiments have verified that the
electric variable transmission can be used in hybrid electric
vehicle, thus exploring a new way for the study of hybrid
electric vehicles.
II.
INTERNAL MAGNETIC FIELD DISTRIBUTION OF
ELECTRIC TRANSMISSION
A. Equivalent magnetic circuit model
The EVT architecture is shown in Fig.1, with two
mechanical ports and two electrical ports, comprised of the
inner rotor, the middle rotor squirrel cage structure and
independent double winding stator. The rotor winding in the
shaft receives three collector ring through the brush out. The
inner rotor named EM1, while the outer rotor named EM2.
It?s easy to analyze the EVT when splitting the inner
motor and the outer motor. It is shown in the Fig.1.
Fig.1 Split diagram of EVT
In order to study the coupling mechanism of the internal
magnetic field of EVT, the equivalent magnetic circuit is
established as shown in Fig.2.
This work is Project No. 51507021 supported by the National Natural
Science Foundation of China.
978-1-5386-2894-2/17/$31.00 �17 IEEE
978-1-5386-2894-2/17/$31.00 �17 IEEE
2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific)
Fig.2 Equivalent flux paths of the EVT
As is shown in Fig.2??1 is inner rotor yoke permeance
??2 is stator yoke permeance, ?o and ?i are inner and outer air
gap and adjacent alveolar permeance, ?c is outer rotor yoke
radial permeance??o?1 and ?o?2 are tangential permeance of
outer rotor yoke???1 is internal rotor winding flux???2 is
flux supplied by stator winding outward??o?1 is the flux of
the inner rotor winding and the outer rotor yoke tangential part
??o?2 is the flux of the stator winding and the tangential part
of the outer rotor yoke ?c is radial flux of outer rotor
winding[9]?
B. Analysis of internal magnetic field distribution
With the different working states of the motor, the angle
? between the inner rotor magnetic potential and the stator
magnetic potential will change continuously in the range from
0 degree to 360 degrees. Fig.3 shows that when the ? is
separately equal to 0 degree, 90 degrees, 180 degrees and 270
degrees of electrical angle and EVT internal and external
windings are introduced into the three-phase 30A current, the
finite element simulation results of the internal magnetic field
distribution are presented.
(a) IEM1=30A?IEM2=30A? ? =0�
(c) IEM1=30A?IEM2=30A? ? =180�
(d) IEM1=30A?IEM2=30A? ? =270�
Fig.3 Magnetic field distribution of the EVT
From the simulation results, when the ?=0 degree, the
majority of the EVT internal magnetic field is through the
outer rotor magnetic yoke, while the tangential flux is very
small, as shown in Fig.3 (a). At ?=180�, the external rotor
tangential flux is added and prone to saturation, as shown in
Fig. 3 (c). When the ? changes in the range from 0 degree to
180 degrees, or in the range from 180 degrees to 360 degrees,
as shown in Fig.3 (b) and 3 (d), the distribution of the EVT
magnetic circuit varies between the above two magnetic
states. When the ?=180 degrees, the outer rotor yoke center
tangential flux density reached 2.2T, and ?=0 degree, the outer
rotor yoke tangential flux density is less than 0.2T, however
the maximum radial magnetic flux density is only 0.6T.
Therefore, the ?=180 degrees, the outer rotor yoke is easy to
saturation.
III. INTERNAL MAGNETIC FIELD DISTRIBUTION OF VET
WITH MAGNETIC FLUX-INSULATION RING
A. Analysis Equivalent magnetic circuit model
?
Inner rotor magnetic potential F1 couples with inner
?
squirrel cage. Outer rotor magnetic potential F2 couples with
external squirrel cage [10]. The equivalent circuit is shown in
the Fig.4.
(b) IEM1=30A?IEM2=30A? ? =90�
Fig.4 Equivalent flux paths of the EVT with magnetic isolation
ring
2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific)
?c1 is the magnetic permeance between Inner rotor
winding and radial direction of external rotor yoke; ?c2 is the
magnetic permeance between stator winding and radial
direction of outer rotor yoke; ?c1 is the Radial flux between
outer rotor winding and Inner rotor winding; ?c2 is the Radial
flux between outer rotor winding and stator winding.
B. Analysis of internal magnetic field distribution
Included angle between inner rotor magnetic potential
?
?
F1 and outer rotor magnetic potential F2 is also changing in
the range of 0皛360�. As shown in the Fig.5, it is finite
element simulation results of internal magnetic field
distribution when the inner and outer windings are
respectively connected with the three-phase 30A current and
the electrical angles ? were 0�90�180� and 270�.
(d) IEM1=30A?IEM2=30A? ? =270�
Fig.5 Magnetic field distribution of the EVT with magnetic
isolation ring
As can be seen from Fig.5, because of magnetic fluxinsulation ring using inner rotor, magnetic circuits of internal
and external motor are isolated. If the radial size is the same as
in Fig.4, the outer rotor yoke is easy to be saturated.
IV. ANALYSIS OF OPERATING MODE BASED ON HYBRID
ELECTRIC VEHICLE
(a) IEM1=30A?IEM2=30A? ? =0�
EVT can get more energy conversion mode, it is very
suitable for the application of electromechanical energy
conversion in a wide variety of hybrid vehicles as a power
separation device. EVT can be used to replace the traditional
automobile CVT, starter, generator, clutch and other devices,
achieving the function of CVT. EVT is shown in Fig.6.
(b) IEM1=30A?IEM2=30A? ? =90�
Fig.6 HEV structure based on the EVT
(1) CVT mode
(c) IEM1=30A?IEM2=30A? ? =180�
The main working mode of the VET is the continuously
variable transmission (CVT) mode, which is traditional
vehicle CVT function. The mechanical energy output of the
engine PICE is divided into two parts. A part of the energy is
directly transferred to the stator of EM2 in the form of
electrical energy passed from EM1, through collector ring,
brush, rectifier, inverters. On the other hand, the other power
is in form of magnetic field passed to output shaft. It can be
shown in the equation (7).
PICE=PEM1+Pd
(7)
The electromagnetic torque of EM1 TEM1 is balanced with
the output torque of motor TICE. Thus, the power equations can
be expressed as follow:
2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific)
? PICE = TICE?ICE
?
? PEM1 = TEM1 (?ICE ? ?EM2 ) = TICE (?ICE ? ?EM2 )
?P = P ? P = T ?
? d
ICE
EM1
ICE EM2 = TEM1?EM2
(8)
The shaft output torque T2m of the outer rotor is a
combined torque of the inner motor and the outer motor .as
shown in equation (9):
T2m = TEM1 +
=
PEM1
?EM2
= TEM1 +
TEM1 (?ICE ? ?EM2 )
?EM2
TEM1?ICE
?EM2
(9)
According to equation (9), the EVT realizes the CVT
function of the traditional vehicle?and the transmission ratio
iEVT of the EVT can be defined?
iEVT
?
T
= ICE = 2m
?EM2 TEM1
(10)
The transmission ratio iEVT of the EVT can be
continuously. As a result, the powers of EM1 and EM2 can be
gotten?
1
?
? PEM1 = TEM1 (?EM2 ? ?ICE ) = TEM1?ICE ( i ? 1)
?
EVT
?
1
?P = T ?
)
EM2 EM2 = (T2m ? TEM1 )? EM2 = TEM1? ICE (1 ?
?? EM2
iEVT
(11)
As equation (5) implied, in CVT mode, the output
electromagnetic power of inner motor is equal to that of outer
motor when transmission ratio iEVT=2; compared with outer
motor, the inner motor will output higher torque and lower
speed when transmission ratio iEVT between 1~2; it is in
contrary when transmission ratio iEVT>2.
(2) Starter mode
It is free of starter that traditional vehicle installs when
hybrid vehicle has been installed EVT, the inner motor start
engine via the power that battery supplied. It is time to fuel
supply and ignition so that starting engine when the engine has
been dragged at relatively high speed by inner motor.
In auxiliary assist mode, vehicle is drive by the energy
that engine and battery supply together, so that the dynamic
performance is improved.
According to the above analysis about main working
mode, the summary of working states under each mode of
vehicle powertrain was shown in table 1.
Tab.1 Status of power-trains in different operation modes
Work mode
generator
Inner motor
Outer motor
Mechanical
braker
CVT mode
work
Electricity
generation
electromotion
stop
Starter mode
work
electromotion
stop
stop
Generation
mode
work
Electricity
generation
work
stop
Pure electric
mode
stop
stop
electromotion
stop
Regenerative
braking
mode
stop
stop
generating
stop
Auxiliary
assist mode
work
Electricity
generation
electromotion
stop
Reverse
mode
stop
stop
electromotion
stop
Mechanical
braking
mode
stop
stop
stop
work
Hybrid
braking
mode
stop
stop
Electricity
generation
work
V.
ANALYSIS OF POWER FOLLOWING CONTROL STRATEGY
The power follower management strategy is to adjust the
output of the engine according to the different requirements of
the load. According to the vehicle load demand and SOC of
battery, it is determined the engine operating points, the output
power of the engine for the difference between the load power
requirements and battery power output.
(3) Generation mode
In generation mode, the battery will be charged by inner
motor which is in generation mode. Under such condition, the
mechanical energy which output by engine will transform into
electric energy and store in battery, it can supply auxiliary
energy to the vehicle.
(4) Braking mode
If we use drum or dish type brakes during the braking,
the energy of braking will be wasted by fiction. Because of
electrical powertrain, the hybrid vehicle based on EVT can
work in feedback brake mode.
(5) Pure electric mode
In pure electric mode, the engine will be stopped and
EVT that battery supply will drive the vehicle solely. Under
such condition, the inner motor will stop and the outer motor
work in generation state.
(6) Auxiliary assist mode
Fig.7 The optimal operation curve of ICE
As is shown in the Fig.7, the engine is operating in
optimal working curve in the road, which is independent of
cycle. That is, the output of the engine can be different from
the wheels? speed and torque output. At this time, by adjusting
the EM2 output torque, it is compensated torque deviation ?T,
while by adjusting the EM1 output speed, it is compensated
speed deviation ?n. When the engine operating point
coincides with the wheel working point, the battery output
2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific)
power is zero. At the time, the transmission in the work
process is equivalent as a gear of ratio of 1.
According to the current load power demand and battery
SOC, by looking up in table the engine work in the current
state of the optimal operating speed is got. The optimal
transmission ratio iEVT of an electrical transmission can be
calculated according to follow equation.
iEVT = 0.377
rd ? ?ICE_opt
i0 ? VVHE
(12)
The power follower strategy is used to The HEV with the
EVT. In the 10.15 urban driving cycles the simulation results
shown in Fig.8. Because of the demand of low power, the
vehicle pure always work with electric driving mode, thus
EM2 providing the main power output. The engine mode stays
the zone of the low torque or closed. The torque of EM1 is
depended on the torque output of the engine, while the EM1
speed changes according to the change of the vehicle speed.
So the EM1 is constantly switching between the electric state
and the power generation state.
Fig.8 The simulation waveforms of 10.15 urban driving cycles
based on power following strategy
VI. EXPERIMENTAL STUDY
In the experiment, two induction motors simulate the
engine and traffic load, and simulation experiment platform is
shown in Fig.9. From left to right three motors respectively
simulate the engine motor EM0, EVT and traffic load motor
EM3. The 10.15 city conditions is applied in HEV with EVT
for experiment. Because the motor rated value is relatively
small, therefore, the actual rotational speed value is 0.5 times
than the calculated value of the torque control strategy and the
actual value of 0.25 times than the calculated value for the
control strategy.
Fig.9 The experiment bench
(a) The waveforms of speed
In this paper, the power follower strategy used in this
paper is used to configure the working points of the motor
simulated the engine and EVT. The experimental waveforms
are shown in Fig.10. From Fig.10, the control system is
designed in this paper can successfully complete the various
operation modes of HEV and torque and speed errors are
smaller compared with its target value given, thus verifying
the correctness that the EVT is applied in HEV.
(b) The waveforms of torque
(a) The waveforms of EM1 speed
(c) The waveforms of power
(d) The waveforms of SOC and battery power
(b) The waveforms of EM2 speed
2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific)
vehicle, thus exploring a new way for the study of hybrid
electric vehicles.
EVT, as a continuously variable transmission, realize that
change of transmission ratio the can be continuous. The
vehicle control strategy can ensure that the engine is always
working in high efficient area, which is of important
significance to improve the vehicle?s power, fuel economy,
and emission reduction.
REFERENCES
(c) The waveforms of EM1 torque
[1]
(d) The waveforms of EM2 torque
Fig.10 The experiment waveforms of 10.15 urban driving cycles
VII. CONCLUSION
This paper analyzes the application of EVT in HEV, the
equivalent magnetic circuit and Ansoft finite element
simulation can find the magnetic coupling law. Because of the
inner and outer magnetic field coupling, the inner and outer
motor mutual interference is serious. For the transmission of
magnetic field in the strong coupling relationship, a kind of
magnetic flux-insulation ring is applied into EVT and its
mathematical model is established. On the basis of the above
analysis, the working modes of the HEV based on EVT are
analyzed. Power output of engine and electric variable
transmission is depended on the power follower strategy. At
last, the simulations and experiments have verified that the
electric variable transmission can be used in hybrid electric
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