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29th July 2016, 09:03 #1
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 Jul 2016
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LMD18200 Pin8 Sensing
Hej,
i am using a H Bridge (LMD18200) for controlling a DC Motor. Therefore i am using the Pin8 Current Sensing Output and a simple PIcontroller. My problem is that i just can measure the abs value of the motor current, if i get the datasheet right. Does anyone know how to get the real signum of the current?
I tried to just take the signum of the desired current which i apply to the motor controller, but when i am using a sinusoidal input i get problems at the zero crossing.
My controller code at the moment looks like this (i am using matlab/simulink and a dspace box CP1103)
Code:Dir_x ... direction bit for HBridge UMx....Voltage for DC motor which is later on converted into a PWM Signal (0..1) > (0..12)V e1I.... Error for integral value of PI Controller reset...to reset the controller errors when starting the simulation/measurement AntiWindUp....freeze the integral value when reaching the maximum voltage IMx_d...desired current IMx....measured current par...parameterfile function [UMx,Dir_X] = PICurrentControl(resetI,IMx_d,IMx,AntiWind,par) persistent e1I if isempty(e1I) e1I=0; end persistent e1 if isempty(e1) e1=0; end persistent Ux if isempty(Ux) Ux=0; end if (resetI) e1I=0; end %Calculate Control Deviation e1=abs(IMx_d)abs(IMx); %1..AntiWindup on, 0..of if(AntiWind) if (Ux < 12 && Ux > 12) e1I=e1I+0.01*e1; else e1I=e1I; end else e1I=e1I+0.01*e1; end if(IMx_d == 0) Ux = 0; e1I = 0; else Ux = par(1)*e1 + par(2)*e1I; end UMx = abs(Ux); if (sign(IMx_d) >=0) Dir_X = false; else Dir_X = true; end
My strategie know was to control the abs value of the error (IMx_dIMx) and take the signum of the desired current as the direction bit of the HBridge. Furthermore i just set the output voltage as zero when the desired current is zero. But this step results in problems.Last edited by KlausST; 29th July 2016 at 09:21. Reason: added code tags

29th July 2016, 09:03
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