1. Toyota Prius
Study case

2. Toyota Prius
Concept
Building
Operation
Electrical machines

3. The Toyota Hybrid System
The Prius evolved from 1997 to 2000
In 2003 Toyota increases the motor output by 50% (THS II)
The THS transmission is indicated by the dotted outline

4. The Toyota Hybrid System
The system’s main elements are:
A power electronic unit
A main processor
HV battery
MG1 and MG2
Skid and break control unit

5. The Toyota Hybrid System
The hybrid transaxle
MG1, MG2 and the engine are on one axle
A planetary unit ensures coupling of the motors
A silent chain and a differential provide motion transition to the wheels

6. The Toyota Hybrid System
This system controls the state of charge (SOC)
The SRMs control and limit the current flow into and out from the battery
The target of the SOC is about 60% controlled by the battery ECU

7. The Toyota Hybrid System
The power electronic of the THS is composed of:
The boost converter
Two inverters (one for each machine)
DC-DC converter
AC converter

8. The Toyota Hybrid System
The DC-DC converter ensures the charging of the auxiliary low voltage battery of the machine
It has a H-bridge to invert the cc into high frequency ac
The transformer lower the ac voltage and rectify it to 12Vcc

9. The Toyota Hybrid System
The AC inverter ensures the ac for the air-conditioning compressor
This was introduced from 2004, changing the HV’s 201Vcc into 206Vac

10. The Toyota Hybrid System
The regenerative break system control
By this, the loss of kinetic force to heat and friction is diminished and transformed into electrical energy
Distribution of force balance

11. The Toyota Hybrid System
The assisted break system was implemented in 2004
Is senses the speed and the force on of the pedal when it is pushed and function of this, and of other sensor’s response it increases the hydraulic pressure.

12. The Toyota Hybrid System
The EPS system assists the steering based on:
Torque sensors
Data from additional sensors regarding the machine condition
A DC motor

13. The THS operation

14. The THS operation

15. The THS operation

16. The THS improvements Bus voltage 274V to 500V then to 650V
The torque is reduced and the speed is increased
Downsizing of the motor, reduced the motor weight, hence low center of gravity offering the possibility of mounting on one shaft the traction drive motor, the generator, the power distribution and the engine

17. The THS improvements Reducing the iron losses is mandatory
Losses were reduced with over 30%
10% due to improvement of reluctance torque
20% due to using high grade steel
5% due to design considerations
The efficiency of the motor is 95%,

18. The THS improvements
The THD of the air-gap flux density must be decreased as much as possible
The shape and the arrangement of the permanent magnets is crucial

19. The THS improvements
The bridge is used to ensure mechanical stress and supports the flux barrier
The bridge must be sized as small as possible
The number and size of the bridges reduces the mechanical stress predicted for the manufacturing process and other final stage issues

20. The THS improvements Experimental results of the 2005 motor design
Wise use of the reluctance torque

21. The THS improvements
The noise is due to the switching frequency that creates an AC field in the core of the inductor
Frequency over 20kHz is recommended to be used in HEVs
The phenomenon is called “magnetostriction” (the core expands and contracts)
More Si (from 4% to 6.5%) was added in the material for the core’s lamination

22. The THS improvements
The noise given also by the power switches, the machine housing and the vibration of different body parts, was diminished by countermeasures, noise absorbing and insulation materials applied to the body

23. Conclusions
The Toyota Prius has a complex system based on several sensors all operating together to fulfill the control of the vehicle’s behaviour
A lot of improvements were added to increase the benefits of using a Toyota designed HEV
The PMSM used for the Prius proved to fit all the requirements perfectly reaching the desired output power and torque
The optimal structure is achieved testing several permanent magnet arrangements, considering the solution to place them along the flux paths
Using 3 bridges proved to fulfill the requirement of low air-gap flux density THD
The noise due to switching and vibrations were reduced to a convenient target

24. Thank you for your attention !