altb_pmic / Lib_Cntrl

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IIR_filter.cpp@0:d49418189c5c, 2019-03-04 (annotated)

Committer:
altb
Date:
Mon Mar 04 11:03:08 2019 +0000
Revision:
0:d49418189c5c
Child:
14:9184aa9fdac7
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altb 0:d49418189c5c 1 #include "IIR_filter.h"
altb 0:d49418189c5c 2 #include "mbed.h"
altb 0:d49418189c5c 3 using namespace std;
altb 0:d49418189c5c 4
altb 0:d49418189c5c 5 /*
altb 0:d49418189c5c 6 IIR filter implemention for the following filter types:
altb 0:d49418189c5c 7 init for: first order differentiatior: G(s) = s/(T*s + 1)
altb 0:d49418189c5c 8 first order lowpass with gain G(s) = K/(T*s + 1)
altb 0:d49418189c5c 9 second order lowpass with gain G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0*w0)
altb 0:d49418189c5c 10 nth order, with arbitrary values
altb 0:d49418189c5c 11 the billinear transformation is used for s -> z
altb 0:d49418189c5c 12 reseting the filter only makes sence for static signals, whatch out if you're using the differnetiator
altb 0:d49418189c5c 13 */
altb 0:d49418189c5c 14
altb 0:d49418189c5c 15 // G(s) = s/(T*s + 1)
altb 0:d49418189c5c 16 IIR_filter::IIR_filter(float T, float Ts){
altb 0:d49418189c5c 17
altb 0:d49418189c5c 18 // filter orders
altb 0:d49418189c5c 19 nb = 1; // Filter Order
altb 0:d49418189c5c 20 na = 1; // Filter Order
altb 0:d49418189c5c 21
altb 0:d49418189c5c 22 // filter coefficients
altb 0:d49418189c5c 23 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 24 A = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 25 B[0] = 2.0/(2.0*(double)T + (double)Ts);
altb 0:d49418189c5c 26 B[1] = -B[0];
altb 0:d49418189c5c 27 A[0] = -(2.0*(double)T - (double)Ts)/(2.0*(double)T + (double)Ts);
altb 0:d49418189c5c 28
altb 0:d49418189c5c 29 // signal arrays
altb 0:d49418189c5c 30 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 31 yk = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 32 uk[0]= uk[1] = 0.0;
altb 0:d49418189c5c 33 yk[0] = 0.0;
altb 0:d49418189c5c 34
altb 0:d49418189c5c 35 // dc-gain
altb 0:d49418189c5c 36 this->K = 0.0;
altb 0:d49418189c5c 37 }
altb 0:d49418189c5c 38
altb 0:d49418189c5c 39 // G(s) = K/(T*s + 1)
altb 0:d49418189c5c 40 IIR_filter::IIR_filter(float T, float Ts, float K){
altb 0:d49418189c5c 41
altb 0:d49418189c5c 42 // filter orders
altb 0:d49418189c5c 43 nb = 1; // Filter Order
altb 0:d49418189c5c 44 na = 1; // Filter Order
altb 0:d49418189c5c 45
altb 0:d49418189c5c 46 // filter coefficients
altb 0:d49418189c5c 47 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 48 A = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 49 B[0] = (double)Ts/((double)Ts + 2.0*(double)T);
altb 0:d49418189c5c 50 B[1] = B[0];
altb 0:d49418189c5c 51 A[0] = ((double)Ts - 2.0*(double)T)/((double)Ts + 2.0*(double)T);
altb 0:d49418189c5c 52
altb 0:d49418189c5c 53 // signal arrays
altb 0:d49418189c5c 54 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 55 yk = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 56 uk[0]= uk[1] = 0.0;
altb 0:d49418189c5c 57 yk[0] = 0.0;
altb 0:d49418189c5c 58
altb 0:d49418189c5c 59 // dc-gain
altb 0:d49418189c5c 60 this->K = (double)K;
altb 0:d49418189c5c 61 }
altb 0:d49418189c5c 62
altb 0:d49418189c5c 63 // G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0^2)
altb 0:d49418189c5c 64 IIR_filter::IIR_filter(float w0, float D, float Ts, float K){
altb 0:d49418189c5c 65
altb 0:d49418189c5c 66 // filter orders
altb 0:d49418189c5c 67 nb = 2; // Filter Order
altb 0:d49418189c5c 68 na = 2; // Filter Order
altb 0:d49418189c5c 69
altb 0:d49418189c5c 70 // filter coefficients
altb 0:d49418189c5c 71 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 72 A = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 73 double k0 = (double)Ts*(double)Ts*(double)w0*(double)w0;
altb 0:d49418189c5c 74 double k1 = 4.0*(double)D*(double)Ts*(double)w0;
altb 0:d49418189c5c 75 double k2 = k0 + k1 + 4.0;
altb 0:d49418189c5c 76 B[0] = (double)K*k0/k2;
altb 0:d49418189c5c 77 B[1] = 2.0*B[0];
altb 0:d49418189c5c 78 B[2] = B[0];
altb 0:d49418189c5c 79 A[0] = (2.0*k0 - 8.0)/k2;
altb 0:d49418189c5c 80 A[1] = (k0 - k1 + 4.0)/k2;
altb 0:d49418189c5c 81
altb 0:d49418189c5c 82 // signal arrays
altb 0:d49418189c5c 83 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 84 yk = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 85 uk[0]= uk[1] = uk[2] = 0.0;
altb 0:d49418189c5c 86 yk[0] = yk[1] = 0.0;
altb 0:d49418189c5c 87
altb 0:d49418189c5c 88 // dc-gain
altb 0:d49418189c5c 89 this->K = (double)K;
altb 0:d49418189c5c 90 }
altb 0:d49418189c5c 91
altb 0:d49418189c5c 92 IIR_filter::IIR_filter(float *b, float *a, int nb_, int na_){
altb 0:d49418189c5c 93
altb 0:d49418189c5c 94 // filter orders
altb 0:d49418189c5c 95 this->nb = nb_-1; // Filter Order
altb 0:d49418189c5c 96 this->na = na_; // Filter Order
altb 0:d49418189c5c 97
altb 0:d49418189c5c 98 // filter coefficients
altb 0:d49418189c5c 99 B = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 100 A = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 101 uk = (double*)malloc((nb+1)*sizeof(double));
altb 0:d49418189c5c 102 yk = (double*)malloc(na*sizeof(double));
altb 0:d49418189c5c 103
altb 0:d49418189c5c 104 for(int k=0;k<=nb;k++){
altb 0:d49418189c5c 105 B[k]=b[k];
altb 0:d49418189c5c 106 uk[k]=0.0;
altb 0:d49418189c5c 107 }
altb 0:d49418189c5c 108 for(int k=0;k<na;k++){
altb 0:d49418189c5c 109 A[k] = a[k];
altb 0:d49418189c5c 110 yk[k] = 0.0;
altb 0:d49418189c5c 111 }
altb 0:d49418189c5c 112
altb 0:d49418189c5c 113 // dc-gain
altb 0:d49418189c5c 114 this->K = 1.0;
altb 0:d49418189c5c 115 }
altb 0:d49418189c5c 116
altb 0:d49418189c5c 117
altb 0:d49418189c5c 118 IIR_filter::~IIR_filter() {}
altb 0:d49418189c5c 119
altb 0:d49418189c5c 120 void IIR_filter::reset(float val) {
altb 0:d49418189c5c 121 for(int k=0;k < nb;k++)
altb 0:d49418189c5c 122 uk[k] = (double)val;
altb 0:d49418189c5c 123 for(int k=0;k < na;k++)
altb 0:d49418189c5c 124 yk[k] = (double)val*K;
altb 0:d49418189c5c 125
altb 0:d49418189c5c 126 }
altb 0:d49418189c5c 127
altb 0:d49418189c5c 128 /*
altb 0:d49418189c5c 129 the filter is operating as follows:
altb 0:d49418189c5c 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:d49418189c5c 131 y(n) = B[0]*u(k) + B[1]*u(k-1) + ... + B[nb]*u(k-nb) + ...
altb 0:d49418189c5c 132 - A[0]*y(k-1) - A[1]*y(k-2) - ... - A[na]*y(n-na)
altb 0:d49418189c5c 133 */
altb 0:d49418189c5c 134 float IIR_filter::filter(double input){
altb 0:d49418189c5c 135 for(int k = nb;k > 0;k--) // shift input values back
altb 0:d49418189c5c 136 uk[k] = uk[k-1];
altb 0:d49418189c5c 137 uk[0] = input;
altb 0:d49418189c5c 138 double ret = 0.0;
altb 0:d49418189c5c 139 for(int k = 0;k <= nb;k++)
altb 0:d49418189c5c 140 ret += B[k] * uk[k];
altb 0:d49418189c5c 141 for(int k = 0;k < na;k++)
altb 0:d49418189c5c 142 ret -= A[k] * yk[k];
altb 0:d49418189c5c 143 for(int k = na;k > 1;k--)
altb 0:d49418189c5c 144 yk[k-1] = yk[k-2];
altb 0:d49418189c5c 145 yk[0] = ret;
altb 0:d49418189c5c 146 return (float)ret;
altb 0:d49418189c5c 147 }