AN2388 datasheet(14/54 Pages) STMICROELECTRONICS

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Vector control of AC induction machines

AN2388

14/54

2.3

Block diagram of the vector control

The basic scheme of torque control with IFOC is shown below:

Figure 11.

Block diagram of I.F.O.C.

Two phase currents go into some transformation module (Clarke and Park). The projection

outputs of the Clark block are indicated with isα and isβ. These two components of the

current provide the input of the Park transformation that gives the current in the d,q rotating

reference frame aligned with the rotor flux vector. The exact rotor flux angular position (θλr)

is necessary to calculate the two components ids and iqs. The ids and iqs components are

compared to the references idref (the flux reference) and iqref (the torque reference). The

torque command iqref is the output of the speed regulator. The flux command idref indicates

the right rotor flux command for every speed reference within the nominal value. The current

regulator outputs are Vdref and Vqref . They are processed into the inverse Park

transformation. The outputs of this are Vαref and Vβref, which are the components of the

stator vector voltage in the α,β orthogonal reference frame. These are the inputs of the

Space Vector PWM. The outputs of this block are the gate signals that drive the inverter.

The main block of the vector control is the Current Model block. This block needs the rotor

resistance and rotor inductance as parameters and knowledge of these, with the highest

accuracy, greatly affects the performance of the control.

2.4

The current model (rotor flux estimator)

Knowledge of the rotor flux space vector magnitude and position are key for the AC

induction motor vector control. Knowing the rotor magnetic angular position allows to

establish, in fact, the rotational co-ordinate system (d, q). .

The current model consists of implementing the following two equations of the motor in the

d-q reference frame:

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