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Integrated EV motor-inverter frees 7 litres of space

21 October, 2014

Siemens has developed an integrated motor and inverter for electric vehicles which, it says, will save space and weight, and cut costs. The key to the development is the use of a single water-based cooling system for both components, ensuring that the inverter's power electronics don't get too hot despite being next to the motor, and avoiding the need to reduce the drive’s output or service life.

Because range is an important requirement for electric vehicles, car-makers strive to reduce EV weights. This was also a key aim of the engineers who developed the Sivetec MSA 3300 integrated drive. By integrating the inverter with the motor, only one housing is needed and 6–7 litres of extra space are created, which can be used to accommodate components such as chargers. Integration also eliminates the costs of cabling between the motor and the inverter, and reduces the number of assembly steps needed to build a vehicle. 

One problem that the Siemens engineers encountered when they were developing the new drive was the heat generated by the motor. At high temperatures, the output of IGBT modules – which convert the battery's DC output into AC to power the motor – has to be limited, and EV inverters usually incorporate their own water cooling system.

In the integrated motor-inverter, the coolest water flows first around thermally sensitive components such as the IGBT modules and the intermediate circuit capacitor, after which it moves into the motor's cooling jacket. The flow is designed to create a “water screen” between the inverter electronics and the motor, thermally isolating them from each other.

Siemens' integrated motor-inverter will save space in electric vehicles

Another important element in the integrated drive are the robust power modules that use Semikron’s SkiN bonding technology to make connections to the surface of the semiconductor chips without needing bonding wires. As thermal loads fluctuate, the electrical contact points between chips and bonding wires can become a weak point in semiconductor components.

Siemens says it has demonstrated the integrated motor-inverter under laboratory conditions using typical load curves and operating conditions for EV motors.




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