Preston Ernst / Mbed OS mirror_actuator_VT

-data logging revision

Dependencies:   FastPWM

Lib_Misc/IIR_filter.cpp@2:92c25cb669f4, 2021-08-24 (annotated)

Committer:
ernstpre
Date:
Tue Aug 24 08:51:13 2021 +0000
Revision:
2:92c25cb669f4
Parent:
0:d2e117716219 
Publish Commit 24/8/21

Who changed what in which revision?

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altb2 0:d2e117716219 1 #include "IIR_filter.h"
altb2 0:d2e117716219 2 #include "mbed.h"
altb2 0:d2e117716219 3 using namespace std;
altb2 0:d2e117716219 4
altb2 0:d2e117716219 5 /*
altb2 0:d2e117716219 6 IIR filter implemention for the following filter types:
altb2 0:d2e117716219 7 init for: first order differentiatior: G(s) = s/(T*s + 1)
altb2 0:d2e117716219 8 first order lowpass with gain G(s) = K/(T*s + 1)
altb2 0:d2e117716219 9 second order lowpass with gain G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0*w0)
altb2 0:d2e117716219 10 nth order, with arbitrary values
altb2 0:d2e117716219 11 the billinear transformation is used for s -> z
altb2 0:d2e117716219 12 reseting the filter only makes sence for static signals, whatch out if you're using the differnetiator
altb2 0:d2e117716219 13 */
altb2 0:d2e117716219 14
altb2 0:d2e117716219 15 // G(s) = s/(T*s + 1)
altb2 0:d2e117716219 16 IIR_filter::IIR_filter(float T, float Ts){
altb2 0:d2e117716219 17
altb2 0:d2e117716219 18 // filter orders
altb2 0:d2e117716219 19 nb = 1; // Filter Order
altb2 0:d2e117716219 20 na = 1; // Filter Order
altb2 0:d2e117716219 21
altb2 0:d2e117716219 22 // filter coefficients
altb2 0:d2e117716219 23 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 24 A = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 25 B[0] = 2.0/(2.0*(double)T + (double)Ts);
altb2 0:d2e117716219 26 B[1] = -B[0];
altb2 0:d2e117716219 27 A[0] = -(2.0*(double)T - (double)Ts)/(2.0*(double)T + (double)Ts);
altb2 0:d2e117716219 28
altb2 0:d2e117716219 29 // signal arrays
altb2 0:d2e117716219 30 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 31 yk = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 32 uk[0]= uk[1] = 0.0;
altb2 0:d2e117716219 33 yk[0] = 0.0;
altb2 0:d2e117716219 34
altb2 0:d2e117716219 35 // dc-gain
altb2 0:d2e117716219 36 this->K = 0.0;
altb2 0:d2e117716219 37 }
altb2 0:d2e117716219 38
altb2 0:d2e117716219 39 // G(s) = K/(T*s + 1)
altb2 0:d2e117716219 40 IIR_filter::IIR_filter(float T, float Ts, float K){
altb2 0:d2e117716219 41
altb2 0:d2e117716219 42 // filter orders
altb2 0:d2e117716219 43 nb = 1; // Filter Order
altb2 0:d2e117716219 44 na = 1; // Filter Order
altb2 0:d2e117716219 45
altb2 0:d2e117716219 46 // filter coefficients
altb2 0:d2e117716219 47 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 48 A = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 49 B[0] = (double)Ts/((double)Ts + 2.0*(double)T);
altb2 0:d2e117716219 50 B[1] = B[0];
altb2 0:d2e117716219 51 A[0] = ((double)Ts - 2.0*(double)T)/((double)Ts + 2.0*(double)T);
altb2 0:d2e117716219 52
altb2 0:d2e117716219 53 // signal arrays
altb2 0:d2e117716219 54 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 55 yk = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 56 uk[0]= uk[1] = 0.0;
altb2 0:d2e117716219 57 yk[0] = 0.0;
altb2 0:d2e117716219 58
altb2 0:d2e117716219 59 // dc-gain
altb2 0:d2e117716219 60 this->K = (double)K;
altb2 0:d2e117716219 61 }
altb2 0:d2e117716219 62
altb2 0:d2e117716219 63 // G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0^2)
altb2 0:d2e117716219 64 IIR_filter::IIR_filter(float w0, float D, float Ts, float K){
altb2 0:d2e117716219 65
altb2 0:d2e117716219 66 // filter orders
altb2 0:d2e117716219 67 nb = 2; // Filter Order
altb2 0:d2e117716219 68 na = 2; // Filter Order
altb2 0:d2e117716219 69
altb2 0:d2e117716219 70 // filter coefficients
altb2 0:d2e117716219 71 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 72 A = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 73 double k0 = (double)Ts*(double)Ts*(double)w0*(double)w0;
altb2 0:d2e117716219 74 double k1 = 4.0*(double)D*(double)Ts*(double)w0;
altb2 0:d2e117716219 75 double k2 = k0 + k1 + 4.0;
altb2 0:d2e117716219 76 B[0] = (double)K*k0/k2;
altb2 0:d2e117716219 77 B[1] = 2.0*B[0];
altb2 0:d2e117716219 78 B[2] = B[0];
altb2 0:d2e117716219 79 A[0] = (2.0*k0 - 8.0)/k2;
altb2 0:d2e117716219 80 A[1] = (k0 - k1 + 4.0)/k2;
altb2 0:d2e117716219 81
altb2 0:d2e117716219 82 // signal arrays
altb2 0:d2e117716219 83 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 84 yk = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 85 uk[0]= uk[1] = uk[2] = 0.0;
altb2 0:d2e117716219 86 yk[0] = yk[1] = 0.0;
altb2 0:d2e117716219 87
altb2 0:d2e117716219 88 // dc-gain
altb2 0:d2e117716219 89 this->K = (double)K;
altb2 0:d2e117716219 90 }
altb2 0:d2e117716219 91
altb2 0:d2e117716219 92 IIR_filter::IIR_filter(float *b, float *a, int nb_, int na_){
altb2 0:d2e117716219 93
altb2 0:d2e117716219 94 // filter orders
altb2 0:d2e117716219 95 this->nb = nb_-1; // Filter Order
altb2 0:d2e117716219 96 this->na = na_; // Filter Order
altb2 0:d2e117716219 97
altb2 0:d2e117716219 98 // filter coefficients
altb2 0:d2e117716219 99 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 100 A = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 101 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:d2e117716219 102 yk = (double*)malloc(na*sizeof(double));
altb2 0:d2e117716219 103
altb2 0:d2e117716219 104 for(int k=0;k<=nb;k++){
altb2 0:d2e117716219 105 B[k]=b[k];
altb2 0:d2e117716219 106 uk[k]=0.0;
altb2 0:d2e117716219 107 }
altb2 0:d2e117716219 108 for(int k=0;k<na;k++){
altb2 0:d2e117716219 109 A[k] = a[k];
altb2 0:d2e117716219 110 yk[k] = 0.0;
altb2 0:d2e117716219 111 }
altb2 0:d2e117716219 112
altb2 0:d2e117716219 113 // dc-gain
altb2 0:d2e117716219 114 this->K = 1.0;
altb2 0:d2e117716219 115 }
altb2 0:d2e117716219 116
altb2 0:d2e117716219 117
altb2 0:d2e117716219 118 IIR_filter::~IIR_filter() {}
altb2 0:d2e117716219 119
altb2 0:d2e117716219 120 void IIR_filter::reset(float val) {
altb2 0:d2e117716219 121 for(int k=0;k < nb;k++)
altb2 0:d2e117716219 122 uk[k] = (double)val;
altb2 0:d2e117716219 123 for(int k=0;k < na;k++)
altb2 0:d2e117716219 124 yk[k] = (double)val*K;
altb2 0:d2e117716219 125
altb2 0:d2e117716219 126 }
altb2 0:d2e117716219 127
altb2 0:d2e117716219 128 /*
altb2 0:d2e117716219 129 the filter is operating as follows:
altb2 0:d2e117716219 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)
altb2 0:d2e117716219 131 y(n) = B[0]*u(k) + B[1]*u(k-1) + ... + B[nb]*u(k-nb) + ...
altb2 0:d2e117716219 132 - A[0]*y(k-1) - A[1]*y(k-2) - ... - A[na]*y(n-na)
altb2 0:d2e117716219 133 */
altb2 0:d2e117716219 134 float IIR_filter::filter(double input){
altb2 0:d2e117716219 135 for(int k = nb;k > 0;k--) // shift input values back
altb2 0:d2e117716219 136 uk[k] = uk[k-1];
altb2 0:d2e117716219 137 uk[0] = input;
altb2 0:d2e117716219 138 double ret = 0.0;
altb2 0:d2e117716219 139 for(int k = 0;k <= nb;k++)
altb2 0:d2e117716219 140 ret += B[k] * uk[k];
altb2 0:d2e117716219 141 for(int k = 0;k < na;k++)
altb2 0:d2e117716219 142 ret -= A[k] * yk[k];
altb2 0:d2e117716219 143 for(int k = na;k > 1;k--)
altb2 0:d2e117716219 144 yk[k-1] = yk[k-2];
altb2 0:d2e117716219 145 yk[0] = ret;
altb2 0:d2e117716219 146 return (float)ret;
altb2 0:d2e117716219 147 }
altb2 0:d2e117716219 148