Interleaved Sigma-Delta Current Sense for Improved Direct Torque Control of PMSM
Motor control is a prominent aspect of many industry applications. Although field-oriented control (FOC) is an established concept in industrial drives, direct torque control (DTC) can offer simpler implementation and faster dynamics. Existing literature focuses on evaluating hybrid DTC techniques on FPGA-DSP sets to achieve the desired speed and precision through the FPGA, while the DSP allows more complex control routines for the motor control. Controllers with ARM architecture on the other hand lack the necessary speed on the sensing chain for precise and fast-responding DTC controls. This paper evaluates DTC on an ARM microcontroller and uses external interleaved delta-sigma analog-to-digital converters (ADCs) for fast high-precision current sensing, which is crucial for an effective DTC. We present an interleaved current sensing approach with < 4 µs update rate, which the state of the art could at best achieve through an expensive FPGA. Additionally, the ARM architecture offers a low-cost alternative to existing FPGA systems. The solution scales well and can be extrapolated to achieve even higher update rates. The simulation in MATLAB/Simulink and measurements on the real motor and electronics hardware demonstrate the performance of the solution.
