Scalar Control (V/f Control) of Variable Frequency Drive (VFD, variable speed drive, VSD) (part 3)
Continued from Scalar Control (V/f Control) of Variable Frequency Drive (VFD, variable speed drive, VSD) (part 1) , and Scalar Control (V/f Control) of Variable Frequency Drive (VFD, variable speed drive, VSD) (part 2) , we introduce two other ways to implement scalar control (v/f control) for variable speed drives (variable frequency drives): Space Vector Modulation PWM (SVMPWM) and SVMPWM with overmodulation.
Space Vector Modulation PWM (SVMPWM)
Space Vector Modulation PWM (SVMPWM) is based on the fact that three phase voltage vectors of the induction motor can be converted into a single rotating vector. Rotation of this space vector can be implemented by variable frequency drive (frequency converter) to generate 3 phase sine waves.
Scalar Control (V/f Control) Variable Frequency Drive:
The advantages of Space Vector Modulation PWM (SVMPWM) are less harmonic magnitude at the PWM switching frequency due to averaging, less memory requirement compared to sinusoidal PWM, etc. The disadvantages are not full utilization of the DC bus voltage, more calculation required, etc.
Space Vector Modulation PWM (SVMPWM) with overmodulation
Implementation of SVMPWM with overmodulation can generate a fundamental sine wave of amplitude greater than the DC bus level. The disadvantage of Space Vector Modulation PWM (SVMPWM) with overmodulation is complicated calculation, line-to-line waveforms are not "clean" and the THD increases, but still less than the THD of the six-step PWM method.
:-) The series of scalar control (v/f control) for adjustable frequency drive (frequency changer, frequency inverter) are complete now. We will introduce vector control and Direct Torque Control (DTC) for variable speed drive later.
