component clarkeinv "Inverse Clarke transform";
description """The inverse Clarke transform can be used rotate a 
vector quantity and then translate it from Cartesian coordinate
system to a three phase system (three components 120 degrees apart).""";
see_also """\\fBclarke2\\fR and \\fBclarke3\\fR for the forward transform.""";
pin in float x;
pin in float y "cartesian components of input";
pin in float h "homopolar component of input (usually zero)";
pin in float theta "rotation angle: 0.00 to 1.00 = 0 to 360 degrees";
pin out float a;
pin out float b;
pin out float c "three phase output vector";
function _;
license "GPL";
;;
#include <rtapi_math.h>

/* for the details, google "clarke transform", or see section 3 of
   http://focus.ti.com/lit/an/bpra048/bpra048.pdf and/or appendix B of
   http://www.esat.kuleuven.be/electa/publications/fulltexts/pub_1610.pdf
*/

#define K1 (0.500000000000000)  /* 1/2       */
#define K2 (0.866025403784439)  /* sqrt(3)/2 */
#define K3 (0.707106781186547)  /* 1/sqrt(2) */
#define rev2rad (6.283185308)   /* 2 * pi */

FUNCTION(_) {
    double xr, yr, rads, costheta, sintheta;

    // rotate it
    rads = theta * rev2rad;
    costheta = cos(rads);
    sintheta = sin(rads);
    xr = x * costheta - y * sintheta;
    yr = x * sintheta + y * costheta;

    /* transform to three phase */
    a =  xr +  K3*h;
    b = -K1*xr + K2*yr + K3*h;
    c = -K1*xr - K2*yr + K3*h;
}