Dynamic Modeling and Simulation of Transmotor Based Series-Parallel HEV Applied to Toyota Prius

2004

Abstract— Pollution and limited fossil fuels are the critical issues that lead HEVs to emerge. Nowadays new designs and topologies of HEVs are suggesting and developing. In this paper we have dynamically modeled and simulated a new structure of series-parallel HEV based on a special machine named Transmotor and applied it to Toyota Prius 2004. In This structure, generator and planetary gear in common series-parallel HEV structure are replaced with a Transmotor resulting in a simpler HEV structure. Transmotor performs as a speed coupler between ICE and wheels. Performance of this structure has been compared with those given in DOE reports for Toyota Prius 2004.

Keywords; Transmotor; Hybrid Electric Vehicle (HEV); Series-Parallel; Simulation;

I. INTRODUCTION In recent decades dozens of papers about HEVs have been

published. The main goal in HEV design is to increase the efficiency of ICE and use the wasted part of energy as much as possible. One of the first industrialized HEVs was Toyota Prius and after that various HEVs have been presented and even industrialized from Toyota Corporation and other vehicle manufactures. Toyota Prius has series-parallel topology. In normal series-parallel HEV, there is a planetary gear which provides speed coupling between Internal Combustion Engine (ICE) and vehicle wheels. The planetary gear is a mechanical device and has some drawbacks like decreasing vehicle efficiency and also increasing the car’s overall cost. In this paper we simulate a new structure of series-parallel HEV, which has no planetary gear and a Transmotor will be replaced with planetary gear and generator. The idea is based on [1] and here in this paper we simulate it in MATLAB Simulink and compare the results with US Department of Energy (DOE) report [2].

II. COMPONENTS MODELS

A. Transmotor Static Model: Transmotor is an electric motor with a

floating stator which forms a double-rotor machine with stator as outer rotor and traditional rotor as inner rotor. Through the air gap, electric power converts into mechanical power as

shown in Figure 1.The stator electrical frequency in Transmotor is the relative speed of rotor (as inner rotor) to stator(as outer rotor). According to the action and reaction effects, in steady state rotor and stator torques are the same.

The speed relationship can be expressed as

e r sω ω ω= − (1)

ωr and ωs are outer and inner rotor speeds respectively and

ωe is the inner rotor (rotor) relative speed to the outer rotor (stator) and it is indeed the electrical frequency of stator windings. In steady state the torque relationship can be expressed as

es ms er mrT T T T= = − = − (2)

Figure 1. Transmotor used as a speed coupler [1]

Dynamic Model: For simulation purposes, dynamic model of Transmotor have been used. The dynamic model of Transmotor is same as common synchronous PM machine but it has one extra mechanical equation for stator rotation. Equations (3)-(9) show this model.

( )qsqs s qs r s ds

dv R i p

dtψ

ω ω ψ= + + − (3)

( )dsds s ds r s qs

dv R i pdtψ ω ω ψ= + − − (4)

Hiva Nasiri Ahmad Radan Abbas Ghayebloo Kiarash Ahi

Faculty of Electrical and Computer Engineering K.N.T University of Technology

Tehran, Iran

Hiva.nasiri@gmail.com Radan@kntu.ac.ir Abbas_ghayebloo@ee.kntu.ac.ir ahi@kiarash-ahi.com

978-1-4244-8782-0/11/$26.00 ©2011 IEEE

qs qs qsL iψ = (5)

ds m ds dsL iψ ψ= + (6)

3 ( ( ) )2es er qs m ds qs ds qsT T p i L L i iψ= − = + − (7)

ses ms s s s

dT T J Bdtω ω= + + (8)

rer mr r r r

dT T J Bdtω ω= + + (9)

B. ICE Model

The ICE model is based on Toyota Prius 2004[3]. The model uses a look-up table for its speed-torque characteristic and according to its throttle and speed the output torque will be defined. The look-up table is presented in Figure 2[3].

Figure 2. ICE look-up table

B. Energy Management This is the heart of the vehicle, subsystem which most of

the decisions are made in it. Energy management decides which part should provide torque and how much torque should be provided. In braking mode it decides whether the motor could provide the whole negative torque and act as a generator or mechanical brake should be used. Most of the decisions are based on SOC and speed of the vehicle.

III. TOPOLOGY OF TRANSMOTOR BASED HEV The topology we have used in this paper is shown in Figure

3 [1]. The Engine power through Transmotor transfers to wheels and combined with traction motor, provides the moving force. The Transmotor acts as a speed coupler and the gears which connect it to differential, act as a torque coupler. The

whole system acts as a torque-speed coupler which decouples simultaneous speed and torque of engine from required speed and torque on wheels. Therefore this topology results in a series-parallel vehicle [1].

Figure 3. New topology of series-parallel HEVs with Transmotor

IV. OPERATING MODES This vehicle operates in several modes. We describe them

through a start - stop drive cycle.

In starting and low speeds, only traction motor provides propelling torque. In this mode the engine is off and Transmotor provides no electric energy.

When vehicle reaches a specific speed (20 km/h), or when the battery’s state of charge (SOC) comes down to a specific amount (50 percent), the engine starts and Transmotor acts as a speed coupler. It transfers engine power to differential. In this mode whenever the SOC of battery gets lowered the Transmotor recharges it.

In braking mode, traction motor acts as a generator and recharges the battery. If braking needs more negative torque and the traction motor could not provide it, a mechanical brake will provide the rest and act as an emergency brake.

V. SIMULINK MODEL The Simulink model has been shown in Figure 4. This

model is based on MATLAB HEV model [4]. It consists of six main blocks; Energy management, Battery and DC-DC converter, ICE, Transmotor, Motor and Vehicle Dynamics. Specifications for this model are based on DOE report of Toyota Prius 2004 and a brief list of them has been presented in TABLE I~III [2].

The 'Ts' parameter used in this model is set to 6e-5 by the Model Properties Callbacks

Energy ManagementSubsystem

ICE

Motor

Vehicle Dynamics

Hybrid Electric Vehicle (HEV) Power Train Using Battery Model

Power Subsystem

Transmotor

1

Car Speed km/h

Discrete,Ts = 6e-005 s.

pow ergui

Wice

Wmot

Tgen

Vg

Wgen

Igen

ICEMotor

v

SpSns1

v

SpSen2

T

SIm/SDL1

[Th_ICE]

[Wgen]

[Tgen]

[Tbrk]

[Tmot]

[Batt]

[Igen]

[Wmot]

[Imot]

[DC_CTL]

[Wice]

[Wmot]

Torque

[T mot]

[Batt]

[Wmot]

Power

[Wgen]

[Tgen]

[Imot]

[Igen]

Vg

[Tbrk]

[Wmot]

[Wice]

[Th_ICE]

Vm

[DC_CTL]

[Wice]

Accelerator

Batt

Wmot

Wgen

Wice

Tmot

Tgen

Tbrk

Th_ICE

DC_CTL

Car

2

Road Angle

1

Accelerator

Accelerator

Electrical Power (Motor, Generator, Battery )

Driv e torque (ref erence, measured)

Car speed (km/h)Car speed (km/h)

Figure 4. Simulink model for series parallel HEV with Transmotor

TABLE I. SIMULATION SPECIFICATIONS

Subassembly Specifications

Description Value

Traction motor Power 50 kW

Machine type 4 pole pairs PMSM

Maximum torque 400 Nm

Transmotor Power 30 kW

Machine type 1pole pairs PMSM Maximum torque 130 Nm

ICE Power 57 kW

Maximum torque 115 Nm at 4200rpm

Vehicle Dynamic Mass 1325 kg

Frontal area 2.57 m^2

TABLE II. TRANSMOTOR PARAMETERS

Parameter Value

Lds 0.635 mH Lqs 0.635 mH Rs 0.05 Ohm

TABLE III. TRACTION MOTOR PARAMETERS

Parameter Value

Lds 1.598 mH Lqs 2.057 mH Rs 0.0065 Ohm

VI. SIMULATION RESULTS To verify this model and simulation results, we have used

US DOE report for Toyota Prius 2004 as a reference. In Figure 5 the Drive power (5-a), ICE generated power (5-b), generator and battery output power (5-c) and hybrid indicator (5-d) has been shown. During time intervals that drive power gets negative values, the ICE will produce no power. In braking

mode, the battery gets the maximum acceptable power through traction motor (which acts as a generator) and the rest will be wasted through mechanical brake. Battery SOC and the charging process in braking mode have been showed in Figure 6. In Figure 7, the model output of vehicle speed is compared to related figure of DOE report. The digitized one is DOE result and the smooth one is our model result. There are some minor differences but mainly our model’s output is similar to DOE output.

a)

0 10 20 30 40 50 60-5

0

5x 10

4 Drive Power(Reference, Measured)(W)

0 10 20 30 40 50 60

0

2

4

x 104 ICE Power(Reference, Measured)(W)

0 10 20 30 40 50 60

-2

0

2

x 104 Generator Power, Battery Power

0 10 20 30 40 50 600

0.5

1

Hybrid Mode

b)

c)

d)

Figure 5. a) Drive power, b) ICE power, c) generator and batteri power, and d) hybrid mode indicator

a)

0 10 20 30 40 50 6055

56

57

58

59

60

61

Time(s)

SOC(%) Transmotor based HEV

b)

0 10 20 30 40 50 6059

60

61

62

63

64

Time (s)

SOC(%) Planetary Gear (Simple Generator)

Figure 6. Battery State of Charge (SOC) a) With Transmotor b) With usual generator

0 10 20 30 40 50 600

10

20

30

40

50

60

70

80

Time(s)

Vehicle Speed(km/h)

Figure 7. Vehicle speed (km/h); the digitized one is DOE result and the smooth one is proposed model results

VII. CONCLUSION In this paper we have dynamically modeled and simulated a

new series-parallel HEV topology based on a special machine named Transmotor in MATLAB Simulink. Applying the new

structure to the parameters of Toyota Prius 2004, its performance indices are then compared with those given in DOE report for Toyota Prius 2004. Compared to the real Prius 2004 results published in DOE report, the results are similar and topology could be treated as a replacement for generator and planetary gear to enhance the vehicle performance and simplicity. The main drawback of the proposed topology, when compared with the usual generator based topology, is a few percents larger variation in battery SOC as Fig. 6 depicts it.

REFERENCES [1] M. Ehsani, Y. Gao and A. Emadi “Modern Electric, Hybrid Electric,

and Fuel Cell Vehicles: Fundamentals, Theory, and Design” SE, CRC Press, 2010, pp. 141-150.

[2] U. S. Dept. Energy, “Evaluation of 2004 Toyota Prius Hybrid Electric Drive System”Tech. Rep. ORNL/TM- 2006/423, May 2006. [Online] Available at: http://inspire.ornl.gov/OriginalDocument/f38948a5-d6a2- 4f80-8cc9-34b77e3862a3

[3] K. Muta, M. Yamazaki and J.Tokieda, “Development of New-Generation Hybrid System THS II – Drastic improvement of Power Performance and Fuel Economy” Tech. paper series, 2004-01-0064, Detroit, MI, March 8-11, 2004

[4] MATLAB Simulink Software,” Hybrid Electric Vehicle model” Version 2008 and 2009