7 Dynamic Response and Robust Closed-Loop Control

While one can hope for good conditions, real-world systems always introduces periodic anomalies or disturbances. The motor current can be disturbed any of the following:

• SVPWM to OPP transition
• Changing number of OPP pulses
• Torque request change (driver input)

Closed loop and active control that address each of these cases are critical in realizing a complete and robust OPP design.

Because active control cannot be done by traditional FOC (Field-Oriented Control) alone, flux control is necessary. Flux control is highly complex and introduces three sub-challenges:

• Flux reference: what flux must be.
• Flux observer: actual flux. This is difficult because flux cannot be measured.
• Flux controller: corrective action and calculations to minimize flux error

TI has designed a flux controller to achieve robust, closed-loop control – which is highly computation-intensive and complex. C29 CPU addresses this with industry-leading real-time performance, showing more than 2.5x better performance versus other competitor MCUs in the traction inverter market (benchmarked by leading Automotive TIER1). The hardware-based TMU (Trigonometric Math Unit) feature significantly offloads specific math functions from the C29 CPU, helping further improve performance. The figure below showcases TI's OPP design validated for stable closed-loop control.