Carrier-Based Variable Frequency PWM Technique for PMSM Drives to Achieve Dispersed Spectrum and Extended Low-Speed Operation Capability

Constant switching frequency pulse width modulation (PWM) schemes introduce harmonics in the inverter’s output voltage and current which are concentrated at frequencies close to the switching frequency and its multiples. This peaking in the current and voltage harmonic spectrum results in vibration and acoustic noise in AC motor drives. One way to alleviate these problems is by spreading the harmonic spectrum and reducing the magnitude of dominant harmonic components using variable switching frequency schemes. The key objective of this paper is to introduce a novel trapezoidal variation based variable frequency PWM switching strategy to spread out the harmonic spectrum, with reduced current THD even during no-load low-speed operation. This paper also proposes a modified switched DC cell inverter to achieve DC voltage control to enhance the THD reduction. The presented strategy achieves a maximum of 42.2\(\%\) reduction in low-speed THD compared to linear sub-cycle period variable frequency PWM, a 46\(\%\)reduction in dominant harmonics compared to conventional space vector PWM, and a dispersion index of 1.61, demonstrating its competency as a promising variable switching frequency scheme. The suggested techniques are simulated using MATLAB/Simulink on a vector-controlled Permanent Magnet Synchronous Motor (PMSM) drive and are validated experimentally on a 1.07 kW PMSM drive with a WAVECT-FPGA controller.