Generation of PWM for 2-level Inverter on Modern Microcontrollers: A Generic Algorithm Leveraging on Waveform Symmetry

The inherent symmetries and periodicity of signals based on sinusoidal functions are leveraged to develop a computationally efficient firmware algorithm for generating pulse width modulation (PWM) gating signals on a modern microcontroller for voltage source inverters (VSIs). This method involves creating PWM directly through firmware by utilizing scalar carrier comparison methods for various PWM schemes, including Sinusoidal PWM (SPWM), Third Harmonic Injection PWM (THIPWM), Space Vector PWM (SVPWM), and Discontinuous PWM (DPWM). By exploiting the symmetry and cyclic nature of reference signals, the novel approach allows for the reuse of calculations across different phases under steady-state conditions. Synchronizing the carrier wave period with the symmetries of the modulation reference signal further allows the use of quarter-wave symmetry to simplify pulse width calculations and reduce memory requirements. The algorithm also incorporates pipeline and pre-calculations of certain parameters to efficiently determine embedded timer counter values. Additionally, the firmware, written in ‘C’, supports dynamic switching between different modulation schemes. Practical results demonstrate the algorithm's effectiveness with a 3-phase 2-level VSI controlled by an ARM Cortex M4-based microcontroller equipped with a CORDIC trigonometric math unit.