Toyota Prius Study case

Toyota Prius Concept Building Operation Electrical machines

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

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

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

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

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

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

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

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

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.

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

The THS operation

The THS operation

The THS operation

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

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%,

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

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

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

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

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

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

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