STPS1L60 datasheet(20/34 Pages) STMICROELECTRONICS

20 / 34 page

Firmware implementation

AN3151

20/34

Doc ID 17051 Rev 1

In the PI algorithm, the error is first computed, and based on this, the variation of the duty

cycle is calculated according to the equation, to reach and maintain the target average

current.

PI parameters tuning

In order to perform a working average current regulation, it is fundamental to choose the

right PI parameters depending on the system's bandwidth.

Unfortunately, to get the best PI parameters, there isn't a general procedure to follow and

the fastest way to tune them is trial and error.

However, please note that, besides making the closed loop system stable, the KP and KI

parameters can also compensate the non-linearity introduced into the system.

PI algorithm

An easy and efficient PI controller is implemented. The algorithm uses an anti Wind-Up

effect. This methodology allows the freezing of the integral action when the error signal is

out of working range. In this way, it's possible to improve the dynamic of the current loop. In

Figure 11

, below, the diagram of the PI regulator is shown:

Figure 11.

PI standard controller with anti-saturation control

The C code is shown here:

/*****************************************************************

* Function Name

: PID_Regulator_FIRST_STRING

* Description

: Compute the PI output for the current loop

regulation.

* Input

: none

* Output

: s16

* Return

: None

*****************************************************************/

s16 PID_Regulator_First(PI_ControllerTYPEDEF *PID, u16

Current_String_Input)

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