AN2388 datasheet(9/54 Pages) STMICROELECTRONICS

9 / 54 page

AN2388

Vector control of AC induction machines

9/54

Vector control of AC induction machines

2.1

Introduction

The performance of an AC induction motor is strongly dependant on its control. The recent

advances of powerful microcontrollers with DSP functions has enhanced complex and real-

time algorithms. In particular, the use of a powerful microcontroller brings the following:

●

system cost reduction by an efficient control and right dimensioning power devices as

well

●

the removal of speed or position sensors by the implementation of sensorless

algorithms that need higher complexity calculations

●

a reduction of current harmonics using enhanced algorithms

●

a reduction in the number of look-up tables which reduces the amount of memory

required

●

real-time generation of torque and flux profiles and move trajectories, resulting in

better-performance

Thanks to the capability of such modern microcontrollers it is possible to implement

sophisticated controls like Vector Control.

Vector control refers not only to the magnitude but also to the phase of variables. Matrix and

vectors are used to represent the control quantities. This method takes into account not only

successive steady-states but real mathematical equations that describe the motor itself, so

that the obtained results have a better dynamic for torque variations in a wider speed range.

The Field Oriented Control (FOC) offers a solution to circumvent the need to solve high

order equations with a large number of variables and nonlinearities and achieve an efficient

control with high dynamic.

This approach needs more calculations than other standard control schemes and has the

following advantages:

●

full motor torque capability at low speed

●

better dynamic behavior

●

higher efficiency for each operation point in a wide speed range

●

decoupled control of torque and flux

●

short term overload capability

●

four quadrant operation

2.2

Theory on vector control

FOC involves controlling the components of the motor stator currents, represented by a

vector, in a rotating reference frame (with a d-q coordinate system). In a special reference

frame, the expression for the electromagnetic torque of the smooth-air-gap machine is

similar to the expression for the torque of the separately excited DC machine. In the case of

induction machines, the control is normally performed in a reference frame aligned to the

rotor flux space vector. To perform the alignment on a reference frame revolving with the

rotor flux requires information on the modulus and the space angle (position) of the rotor flux

AN2388 Datasheet(PDF) 9 Page - STMicroelectronics

AN2388 Datasheet(HTML) 9 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Datasheet Download

Link URL