AN2388 datasheet(46/54 Pages) STMICROELECTRONICS

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Software design

AN2388

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The theoretical background explanations have already been handled and assuming that

the current model equations can be discretized as follows:

Take into consideration that all variables are in q1.15 format.

In the above equations, appear two constants:

where

= sampling time=PWM period

In the following code the constants are converted in the new numerical form:

void Calc_theta(void)

{

mul_q15_q15_q31(K_incr, q_Flux_Speed,&Theta_cm_tmp);

Teta_cm_new = (short)(Teta_cm_tmp>>16);

Theta_cm = Theta_cm+Theta_cm_new;

Theta_cm=Theta_cm+q_Mechanical_Rotor_Angle; //Rotor Flux Angle

Theta_cm=Theta_cm+q_Mechanical_Rotor_Position

}

************************************************************************************

**************************End Calc Teta calculation*

************************************************************************************

************************

4.6.4

Generation of sine and cosine values

In order to generate sine and cosine values, a sine table and indirect addressing mode have

been implemented. In order to have the best performance in term of position accuracy and

the used memory minimization, this table contains 28=256 values to represent the [0;2π]

range. The above computed position (16-bit integer value) therefore needs to be shifted 8

positions to the right. This new position (8-bit integer value) is used as a pointer (Index_Sin

or Index_Cos) to access this table. The outputs of the table are the Sin_Teta_cm and

Cos_Teta_cm value represented in Q1.15 format.

The following figure below shows how the sine value calculation is handled:

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