1  component clarkeinv "Inverse Clarke transform";
 2  description """The inverse Clarke transform can be used rotate a 
 3  vector quantity and then translate it from Cartesian coordinate
 4  system to a three phase system (three components 120 degrees apart).""";
 5  see_also """\\fBclarke2\\fR and \\fBclarke3\\fR for the forward transform.""";
 6  pin in float x;
 7  pin in float y "cartesian components of input";
 8  pin in float h "homopolar component of input (usually zero)";
 9  pin in float theta "rotation angle: 0.00 to 1.00 = 0 to 360 degrees";
10  pin out float a;
11  pin out float b;
12  pin out float c "three phase output vector";
13  function _;
14  license "GPL";
15  ;;
16  #include <rtapi_math.h>
17  
18  /* for the details, google "clarke transform", or see section 3 of
19     http://focus.ti.com/lit/an/bpra048/bpra048.pdf and/or appendix B of
20     http://www.esat.kuleuven.be/electa/publications/fulltexts/pub_1610.pdf
21  */
22  
23  #define K1 (0.500000000000000)  /* 1/2       */
24  #define K2 (0.866025403784439)  /* sqrt(3)/2 */
25  #define K3 (0.707106781186547)  /* 1/sqrt(2) */
26  #define rev2rad (6.283185308)   /* 2 * pi */
27  
28  FUNCTION(_) {
29      double xr, yr, rads, costheta, sintheta;
30  
31      // rotate it
32      rads = theta * rev2rad;
33      costheta = cos(rads);
34      sintheta = sin(rads);
35      xr = x * costheta - y * sintheta;
36      yr = x * sintheta + y * costheta;
37  
38      /* transform to three phase */
39      a =  xr +  K3*h;
40      b = -K1*xr + K2*yr + K3*h;
41      c = -K1*xr - K2*yr + K3*h;
42  }