unable to tune PID controller with matlab function block

I am trying to design controllers for 3-ph buck-type PWM rectifier. Attached is the model i am using to design the circuit. Inside the 'SVPWM' subsystem i am trying to design a current controller using PI block. The system plant model is a matlab function block. the code inside is given below. Basically, i am trying to generate a pwm waveform. Using a formula that takes input parameters as the 3 ph voltages and returns the duty cycle. using the duty cycle i create a certain kind of pwm pattern and return 1 or 0 to the 6 switches which produces dc current/voltage. using this dc current,Idc (feedback) i am trying to input to PI controller with its output going into the matlab function block. I get the error plant linearises to zero. can someone please help me tune this PI controller and teach me how???

Thanks a lot.....

if true

function [sector,sr,ss,st,s1,s2,s3,s4,s5,s6] = find_sector(t,angle,Van,Vbn,Vcn,Voref)

 persistent y1;          % store same duty values within the same sector
 persistent y2;          % store same duty values within the same sector
 persistent y3;          % store same duty values within the same sector
 persistent ctr;         % counter for number of sectors in total
 persistent n;           % number of the swithcing periods

 carr_freq = 396*50; 
 switching_period = 1/carr_freq;

if isempty(y1) y1 = 0; end if isempty(y2) y2 = 0; end if isempty(y3) y3 = 0; end

if isempty(ctr) ctr = 0; end

if isempty(n) n = 0; end

s1 = nan; s2 = nan; s3 = nan; s4 = nan; s5 = nan; s6 = nan;

sr = 0.2; ss = 0.2; st = 0.2; sector = nan;

if(angle >= 0 && angle < 30) sector = 0; elseif(angle >= 30 && angle < 60) sector = 1; elseif(angle >= 60 && angle < 90) sector = 2; elseif(angle >= 90 && angle < 120) sector = 3; elseif(angle >= 120 && angle < 150) sector = 4; elseif(angle >= 150 && angle < 180) sector = 5; elseif(angle >= 180 && angle < 210) sector = 6; elseif(angle >= 210 && angle < 240) sector = 7; elseif(angle >= 240 && angle < 270) sector = 8; elseif(angle >= 270 && angle < 300) sector = 9; elseif(angle >= 300 && angle < 330) sector = 10; elseif(angle >= 330 && angle < 360) sector = 11; end

% calculate preliminary duty once every swithcing period

if(t >= ctr*switching_period) y1 = (Voref*abs(Van))/(Van*Van + Vbn*Vbn + Vcn*Vcn); y2 = (Voref*abs(Vbn))/(Van*Van + Vbn*Vbn + Vcn*Vcn); y3 = (Voref*abs(Vcn))/(Van*Van + Vbn*Vbn + Vcn*Vcn); ctr = ctr + 1; end

if(sector == 0 sector == 6) %sector = -1, -1 is for sector calculating algorithm, just ignore it. sr = y1; ss = (1 - y3 + td); st = y3;

elseif(sector == 1 sector == 7) sr = y1; ss = (1 - y1 + td); st = y3;

elseif(sector == 2 sector == 8) sr = (1 - y2 + td); ss = y2; st = y3;

elseif(sector == 3 sector == 9) sr = (1 - y3 + td); ss = y2; st = y3;

elseif(sector == 4 sector == 10) sr = y1; ss = y2; st = (1 - y1 + td);

elseif(sector == 5 sector == 11) sr = y1; ss = y2; st = (1 - y2 + td);

end

% change duty ratio to ON time in seconds

on_time_sr = sr*(1/carr_freq); on_time_ss = ss*(1/carr_freq); on_time_st = st*(1/carr_freq);

% _______ % ___| h _v____

% h = hill and v = valley, swithching pattern generation for 6 switches for %each of 12 (0-11) sector % s1, s3, s5 -> odd/top switches % s2, s4, s6 -> even/bottom switches

if(sector == 0) s2 = 0; s3 = 0; s5 = 0; pattern = 'v'; [s1,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s6,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s4,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern);

elseif(sector == 1) s2 = 0; s4 = 0; s5 = 0; pattern = 'v'; [s1,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s6,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s3,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern);

elseif(sector == 2) s2 = 0; s4 = 0; s5 = 0; pattern = 'v'; [s3,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); [s6,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s1,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern);

elseif(sector == 3) s1 = 0; s4 = 0; s5 = 0; pattern = 'v'; [s3,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); [s6,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s2,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern);

elseif(sector == 4) s1 = 0; s4 = 0; s5 = 0; pattern = 'v'; [s2,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s3,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); pattern = 'h'; [s6,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern);

elseif(sector == 5) s1 = 0; s4 = 0; s6 = 0; pattern = 'v'; [s2,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s3,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); pattern = 'h'; [s5,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern);

elseif(sector == 6) s1 = 0; s4 = 0; s6 = 0; pattern = 'v'; [s2,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s5,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s3,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern);

elseif(sector == 7) s1 = 0; s3 = 0; s6 = 0; pattern = 'v'; [s2,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s5,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s4,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern);

elseif(sector == 8) s1 = 0; s3 = 0; s6 = 0; pattern = 'v'; [s4,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); [s5,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s2,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern);

elseif(sector == 9) s2 = 0; s3 = 0; s6 = 0; pattern = 'v'; [s4,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); [s5,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern); pattern = 'h'; [s1,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern);

elseif(sector == 10) s2 = 0; s3 = 0; s6 = 0; pattern = 'v'; [s1,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s4,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); pattern = 'h'; [s5,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern);

elseif(sector == 11) s2 = 0; s3 = 0; s5 = 0; pattern = 'v'; [s1,n] = SLO_switching(on_time_sr,carr_freq,t,n,pattern); [s4,n] = SLO_switching(on_time_ss,carr_freq,t,n,pattern); pattern = 'h'; [s6,n] = SLO_switching(on_time_st,carr_freq,t,n,pattern);

end

% Function = create symmetrical Switching Loss Optimised (SLO) pattern through %amplitude control every 1us

% Inputs = switch_output-> 1/0, n = same as ctr in the find_sector function, %count number of sectors % Outputs =

function [switch_output,n] = SLO_switching(on_time,carr_freq,t,n,pattern)

persistent amplitude; % output is zero if niether of conidtions match

if isempty(amplitude) amplitude = 0; end

% divide on time of phase a/s or b/r or c/t into half half_on_time = on_time/2; switching_period = (1/carr_freq);

if( (t >= n*switching_period) && (t < (n*switching_period + half_on_time))) if(pattern == 'v') amplitude = 1; elseif(pattern == 'h') amplitude = 0; end elseif( (t >= (n*switching_period + half_on_time)) && (t <= (((n+1)*switching_period) - half_on_time))) if(pattern == 'v') amplitude = 0; elseif(pattern == 'h') amplitude = 1; end elseif((t > (((n+1)*switching_period) - half_on_time)) && (t < (n+1)*switching_period)) if(pattern == 'v') amplitude = 1; elseif(pattern == 'h') amplitude = 0; end elseif(t >= (((n+1)*switching_period) - (1e-6))) % check and increment n (go to next switching period) one simulation time step ahead n = n + 1; end switch_output = amplitude;

end

Answer 1

[Arkadiy Turevskiy]

Take a look at this video and try to follow the shown approach. Step by step instructions are here .