Ruprecht Altenburger / Cntrlol_Lib

My Controller Library

IIR_filter.cpp@1:bf62e74fbcf3, 2018-09-28 (annotated)

Committer:
altb
Date:
Fri Sep 28 09:01:42 2018 +0000
Revision:
1:bf62e74fbcf3
Parent:
0:e2a7d7f91e49 
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Who changed what in which revision?

UserRevisionLine numberNew contents of line
altb 0:e2a7d7f91e49 1 #include "IIR_filter.h"
altb 0:e2a7d7f91e49 2 #include "mbed.h"
altb 0:e2a7d7f91e49 3 using namespace std;
altb 0:e2a7d7f91e49 4
altb 0:e2a7d7f91e49 5 /*
altb 0:e2a7d7f91e49 6 IIR filter implemention for the following filter types:
altb 0:e2a7d7f91e49 7 init for: first order differentiatior: G(s) = s/(T*s + 1)
altb 0:e2a7d7f91e49 8 first order lowpass with gain G(s) = K/(T*s + 1)
altb 0:e2a7d7f91e49 9 second order lowpass with gain G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0*w0)
altb 0:e2a7d7f91e49 10 nth order, with arbitrary values
altb 0:e2a7d7f91e49 11 the billinear transformation is used for s -> z
altb 0:e2a7d7f91e49 12 reseting the filter only makes sence for static signals, whatch out if you're using the differnetiator
altb 0:e2a7d7f91e49 13 */
altb 0:e2a7d7f91e49 14
altb 0:e2a7d7f91e49 15 // G(s) = s/(T*s + 1)
altb 0:e2a7d7f91e49 16 IIR_filter::IIR_filter(float T, float Ts){
altb 0:e2a7d7f91e49 17
altb 0:e2a7d7f91e49 18 // filter orders
altb 0:e2a7d7f91e49 19 nb = 1; // Filter Order
altb 0:e2a7d7f91e49 20 na = 1; // Filter Order
altb 0:e2a7d7f91e49 21
altb 0:e2a7d7f91e49 22 // filter coefficients
altb 0:e2a7d7f91e49 23 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 24 A = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 25 B[0] = 2.0/(2.0*(double)T + (double)Ts);
altb 0:e2a7d7f91e49 26 B[1] = -B[0];
altb 0:e2a7d7f91e49 27 A[0] = -(2.0*(double)T - (double)Ts)/(2.0*(double)T + (double)Ts);
altb 0:e2a7d7f91e49 28
altb 0:e2a7d7f91e49 29 // signal arrays
altb 0:e2a7d7f91e49 30 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 31 yk = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 32 uk[0]= uk[1] = 0.0;
altb 0:e2a7d7f91e49 33 yk[0] = 0.0;
altb 0:e2a7d7f91e49 34
altb 0:e2a7d7f91e49 35 // dc-gain
altb 0:e2a7d7f91e49 36 this->K = 0.0;
altb 0:e2a7d7f91e49 37 }
altb 0:e2a7d7f91e49 38
altb 0:e2a7d7f91e49 39 // G(s) = K/(T*s + 1)
altb 0:e2a7d7f91e49 40 IIR_filter::IIR_filter(float T, float Ts, float K){
altb 0:e2a7d7f91e49 41
altb 0:e2a7d7f91e49 42 // filter orders
altb 0:e2a7d7f91e49 43 nb = 1; // Filter Order
altb 0:e2a7d7f91e49 44 na = 1; // Filter Order
altb 0:e2a7d7f91e49 45
altb 0:e2a7d7f91e49 46 // filter coefficients
altb 0:e2a7d7f91e49 47 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 48 A = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 49 B[0] = (double)Ts/((double)Ts + 2.0*(double)T);
altb 0:e2a7d7f91e49 50 B[1] = B[0];
altb 0:e2a7d7f91e49 51 A[0] = ((double)Ts - 2.0*(double)T)/((double)Ts + 2.0*(double)T);
altb 0:e2a7d7f91e49 52
altb 0:e2a7d7f91e49 53 // signal arrays
altb 0:e2a7d7f91e49 54 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 55 yk = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 56 uk[0]= uk[1] = 0.0;
altb 0:e2a7d7f91e49 57 yk[0] = 0.0;
altb 0:e2a7d7f91e49 58
altb 0:e2a7d7f91e49 59 // dc-gain
altb 0:e2a7d7f91e49 60 this->K = (double)K;
altb 0:e2a7d7f91e49 61 }
altb 0:e2a7d7f91e49 62
altb 0:e2a7d7f91e49 63 // G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0^2)
altb 0:e2a7d7f91e49 64 IIR_filter::IIR_filter(float w0, float D, float Ts, float K){
altb 0:e2a7d7f91e49 65
altb 0:e2a7d7f91e49 66 // filter orders
altb 0:e2a7d7f91e49 67 nb = 2; // Filter Order
altb 0:e2a7d7f91e49 68 na = 2; // Filter Order
altb 0:e2a7d7f91e49 69
altb 0:e2a7d7f91e49 70 // filter coefficients
altb 0:e2a7d7f91e49 71 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 72 A = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 73 double k0 = (double)Ts*(double)Ts*(double)w0*(double)w0;
altb 0:e2a7d7f91e49 74 double k1 = 4.0*(double)D*(double)Ts*(double)w0;
altb 0:e2a7d7f91e49 75 double k2 = k0 + k1 + 4.0;
altb 0:e2a7d7f91e49 76 B[0] = (double)K*k0/k2;
altb 0:e2a7d7f91e49 77 B[1] = 2.0*B[0];
altb 0:e2a7d7f91e49 78 B[2] = B[0];
altb 0:e2a7d7f91e49 79 A[0] = (2.0*k0 - 8.0)/k2;
altb 0:e2a7d7f91e49 80 A[1] = (k0 - k1 + 4.0)/k2;
altb 0:e2a7d7f91e49 81
altb 0:e2a7d7f91e49 82 // signal arrays
altb 0:e2a7d7f91e49 83 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 84 yk = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 85 uk[0]= uk[1] = uk[2] = 0.0;
altb 0:e2a7d7f91e49 86 yk[0] = yk[1] = 0.0;
altb 0:e2a7d7f91e49 87
altb 0:e2a7d7f91e49 88 // dc-gain
altb 0:e2a7d7f91e49 89 this->K = (double)K;
altb 0:e2a7d7f91e49 90 }
altb 0:e2a7d7f91e49 91
altb 0:e2a7d7f91e49 92 IIR_filter::IIR_filter(float *b, float *a, int nb_, int na_){
altb 0:e2a7d7f91e49 93
altb 0:e2a7d7f91e49 94 // filter orders
altb 0:e2a7d7f91e49 95 this->nb = nb_-1; // Filter Order
altb 0:e2a7d7f91e49 96 this->na = na_; // Filter Order
altb 0:e2a7d7f91e49 97
altb 0:e2a7d7f91e49 98 // filter coefficients
altb 0:e2a7d7f91e49 99 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 100 A = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 101 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:e2a7d7f91e49 102 yk = (double*)malloc(na*sizeof(double));
altb 0:e2a7d7f91e49 103
altb 0:e2a7d7f91e49 104 for(int k=0;k<=nb;k++){
altb 0:e2a7d7f91e49 105 B[k]=b[k];
altb 0:e2a7d7f91e49 106 uk[k]=0.0;
altb 0:e2a7d7f91e49 107 }
altb 0:e2a7d7f91e49 108 for(int k=0;k<na;k++){
altb 0:e2a7d7f91e49 109 A[k] = a[k];
altb 0:e2a7d7f91e49 110 yk[k] = 0.0;
altb 0:e2a7d7f91e49 111 }
altb 0:e2a7d7f91e49 112
altb 0:e2a7d7f91e49 113 // dc-gain
altb 0:e2a7d7f91e49 114 this->K = 1.0;
altb 0:e2a7d7f91e49 115 }
altb 0:e2a7d7f91e49 116
altb 0:e2a7d7f91e49 117
altb 0:e2a7d7f91e49 118 IIR_filter::~IIR_filter() {}
altb 0:e2a7d7f91e49 119
altb 0:e2a7d7f91e49 120 void IIR_filter::reset(float val) {
altb 0:e2a7d7f91e49 121 for(int k=0;k < nb;k++)
altb 0:e2a7d7f91e49 122 uk[k] = (double)val;
altb 0:e2a7d7f91e49 123 for(int k=0;k < na;k++)
altb 0:e2a7d7f91e49 124 yk[k] = (double)val*K;
altb 0:e2a7d7f91e49 125
altb 0:e2a7d7f91e49 126 }
altb 0:e2a7d7f91e49 127
altb 0:e2a7d7f91e49 128 /*
altb 0:e2a7d7f91e49 129 the filter is operating as follows:
altb 0:e2a7d7f91e49 130 (B[0] + B[1]*z^-1 + ... + B[nb]*z^-nb)*U(z) = (1 + A[0]*z^-1 + ... + A[na-1]*z^-na))*Y(z)
altb 0:e2a7d7f91e49 131 y(n) = B[0]*u(k) + B[1]*u(k-1) + ... + B[nb]*u(k-nb) + ...
altb 0:e2a7d7f91e49 132 - A[0]*y(k-1) - A[1]*y(k-2) - ... - A[na]*y(n-na)
altb 0:e2a7d7f91e49 133 */
altb 0:e2a7d7f91e49 134 float IIR_filter::filter(double input){
altb 0:e2a7d7f91e49 135 for(int k = nb;k > 0;k--) // shift input values back
altb 0:e2a7d7f91e49 136 uk[k] = uk[k-1];
altb 0:e2a7d7f91e49 137 uk[0] = input;
altb 0:e2a7d7f91e49 138 double ret = 0.0;
altb 0:e2a7d7f91e49 139 for(int k = 0;k <= nb;k++)
altb 0:e2a7d7f91e49 140 ret += B[k] * uk[k];
altb 0:e2a7d7f91e49 141 for(int k = 0;k < na;k++)
altb 0:e2a7d7f91e49 142 ret -= A[k] * yk[k];
altb 0:e2a7d7f91e49 143 for(int k = na;k > 1;k--)
altb 0:e2a7d7f91e49 144 yk[k-1] = yk[k-2];
altb 0:e2a7d7f91e49 145 yk[0] = ret;
altb 0:e2a7d7f91e49 146 return (float)ret;
altb 0:e2a7d7f91e49 147 }