TIDUF67 April 2024
Figure 3-6 summarizes the basic scheme of torque control with FOC:
Two motor phase currents are measured. These measurements feed the Clarke transformation module. The outputs of this projection are designated isα and isβ. These two components of the current are the inputs of the Park transformation that gives the current in the d,q rotating reference frame. The isd and isq components are compared to the references isdref (the flux reference component) and isqref (the torque reference component). At this point, this control structure shows an interesting advantage: the control structure can be used to control either synchronous or induction machines by simply changing the flux reference and obtaining rotor flux position. As in synchronous permanent magnet a motor, the rotor flux is fixed determined by the magnets; there is no need to create one. Hence, when controlling a PMSM, isdref is set to zero. As an AC induction motor needs a rotor flux creation to operate, the flux reference must not be zero. This conveniently solves one of the major drawbacks of the classic control structures: the portability from asynchronous to synchronous drives. The torque command isqref can be the output of the speed regulator when we use a speed FOC. The outputs of the current regulators are Vsdref and Vsqref; these are applied to the inverse Park transformation. The outputs of this projection are Vsαref and Vsβref which are the components of the stator vector voltage in the (α, β) stationary orthogonal reference frame. These are the inputs of the Space Vector PWM. The outputs of this block are the signals that drive the inverter. Note that both Park and inverse Park transformations need the rotor flux position. Obtaining this rotor flux position depends on the AC machine type (synchronous or asynchronous machine).