Datasheet

12. PWM Modulation Technique
Among the various possibilities, a particular form of PWM modulation was chosen. In this modulation technique, the
voltages to be imposed are shifted in order to have in every moment one of the three phases of the motor connected to
the system ground. This allows reducing the commutations of the power bridge of one third, in respect to other
modulation techniques. In fact the phase that is connected to the system ground doesn’t require any commutation,
having the lower arm always on and the upper arm always off.
The method is based on the fact that, having no neutral connection, we are interested only in phase-to-phase voltages, or
in the voltage differences between the phases, not in the voltage level of the single phases. This allows us to add or
subtract an arbitrary quantity to the phase voltages, on condition that this quantity is the same for all the three phases.
So, obtained from the algorithm the three phase voltages requests, the minimum is chosen and it is subtracted to all the
three requests.
With this method, the applied voltage star centre is not at a fixed level, but it is moving.
Modulation Technique
The maximum phase-to-phase voltage that can be obtained (without distortion of the sinusoidal waveform) with this
method is equal to the DC Link voltage, as in other methods (like Space Vector Modulation).
VBUS