Traction drives primarily operate with motor-inverter combinations that use the field weakening function for higher speeds. At these speeds, which often cover 2/3 of the entire speed range, the motor control of the inverter is based on the reliably available voltage, e.g., from the battery. Compared to classic control, we achieve an 8% higher peak power and simultaneously a 0.5% improved efficiency with the HighSpeedBoost function in practical applications.
During operation in the field weakening range, the limiting element is the voltage. Specifically, the phase voltage that we can generate with the inverter from the DC voltage, for example, from the battery. This DC voltage can also fluctuate dynamically, e.g., it drops noticeably if you draw a lot of power from the battery for an acceleration process. In real applications we thus have to deal with slow voltage fluctuations (charging state of the battery) as well as with very dynamic processes in the range of a few milliseconds.
In control engineering, therefore, a safety reserve must be built in between the theoretically producible maximum phase voltage for the motor and the actually generated phase voltage. With this safety reserve, you “waste” power and efficiency. However, without a safety reserve, you risk unplanned system shutdowns, which is unacceptable.
For our HighSpeedBoost function, we take advantage of the fast response of our FPGA-based control. This allows us to bring the voltage at the motor terminal closer to its calculated limit without risking a shutdown. In practical applications, we were able to increase the power by up to 8% and simultaneously improve the real overall efficiency by up to 0.5%.