To have a highly efficient traction invertor system, both hardware and software have to be optimized. Besides gate drivers, one of the key component is the MCU. In addition to having the accurate position, current and voltage sensing, a fast control loop has a big influence on the torque signal. Torque ripple can lead to the speed oscillations, noises and vibrations.

In this reference design, a 20kHz PWM switching frequency is used to control the XM3 SiC power modules. To achieve a higher control performance, FOC and SVPWM algorithm are called every 25us, which means that the PWM duty is updated at 40kHz. As the TI MCU (for example F280039C and AM263P) has a trigonometric math unit (TMU) to accelerate the trigonometric function calculation, the central processing unit (CPU) load can be kept at a lower percentage.

TI MCU supports software resolver-to-digital conversion (RDC). To improve the CPU load performance, F280039C can use Control Law Accelerator (CLA) to execute the RDC algorithm. CLA is an independent, fully-programmable, 32-bit floating-point math processor that brings concurrent control-loop execution to the C28x family.

In the motor control software, to control the motor at highest efficiency point, MTPA (Maximum Torque Per Ampere) and MTPV (Maximum Torque Per Voltage) are implemented using a lookup table. The most efficient work points are stored in the constant data. The software gets the appropriate direct (d) and quadrature (q) stator current commands according to torque, electrical speed and DC bus voltage. MTPA and MTPV are shown in Figure 2-3.

Figure 2-3 MTPA and MTPV Curves