Based on the working principles of the three-phase PWM and the inverter described in Sec. 2.2, it is known
that the amplitude of the equivalent sinusoidal voltage applied to the machine stator is limited to half of
the DC-link voltage. This fact can be modeled as a voltage limiter as shown in Fig. 5.4. What’s more, in
this project, the amplitude of modulation voltage is expected to be smaller than the half of the DC-link
voltage because the inverter will output a constant voltage if the magnitude of the modulation voltage is
larger than half DC-link voltage. This can be achieved by adding a voltage limiter in the current controller.
For example, the DC link voltage is 60V , then the peak value of the phase voltage is set to be within ±28V .
As the scaling constantK of the Clark and the Inv.Clark transformationsmentioned in Sec. 2.3.1 will make
sure that k~uss
k equals to the peak value of ua, ub or uc and Park and Inv. Park transformations will never
change the vector length. Due to this fact the voltage limiter in d − q coordinate is set to 28V .