Boost function for VP600 inverter
The challenge of traction drives: starting torque
For traction drives, it is always a challenge to produce maximum torque from a standstill. The reason is because most of the power during starting is required for only one motor phase. This is mainly noticeable in the following situations:
- Starting with inclines (on a hill)
- Starting with obstacles (curb, pothole)
- A considerably overdimensioned drive for special cases → Cost disadvantage
- An additional coupling for starting → Cost disadvantage
- Use of the ARADEX boost function
The common solution to current control for power electronics is pulse width modulation (PWM) realized with MOSFETs or IGBTs. For larger electric motors of approx. 50 kW and up, this usually comprises three IGBT modules, one per motor phase. These modules share the power in normal operation. However, this is not physically possible during starting and with an electric rotational frequency of less than 1 Hz. Furthermore, the torque basically depends on only one MOSFET or IGBT, which is why the maximum available torque is reduced to 1/3.
The limiting factor of an IGBT is basically its operating temperature. One the one hand, the temperature is not proportional to the current, and on the other hand, the mass of the installed silicon also causes a time delay in the temperature increase. In addition, simply measuring the temperature via a sensor is too imprecise, since for design reasons, the sensor is located at a point in the IGBT that does not have the highest temperature – and there is a time delay here too.
For this reason, an IGBT is normally operated in a mode that does not fully utilize its power.
This is where the ARADEX boost function comes in. A very precise simulation model for semiconductor temperature measurement that ARADEX has continuously improved through years of experience in developing power electronics makes it possible to draw up to 20% more current from an IGBT during starting.
The boost function allows a high power during starting, even with smaller and thus more economical IGBTs. The implemented semiconductor simulation model for calculating the IGBT temperatures prevents the IGBT from overheating and prevents the lifetime of the inverter from decreasing.