Wayne McLachlan
Uses trigonometry to produce high quality 3 phase sinewave output waveworms on the PWM. Tested from 30 to 100Hz at 10kHz modulation. Changes frequency glitch free. Amplitude is scalable. Could be used as a basic invertor back-end. Not optimised for processor overhead, could be modified to use lookup tables if less accuracy required. Oscilloscope trace here: http://mbed.org/users/waynemcl/notebook/sine3-v2/
Diff: main.cpp
- Revision:
- 0:d040778370fc
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Sun Nov 28 22:39:32 2010 +0000
@@ -0,0 +1,61 @@
+#include "mbed.h"
+#include "stdio.h"
+
+#define PI 3.1416
+
+// License: You may copy or modify and re-use this code, but you MUST credit me:
+// Wayne McLachlan, www.embeddedengineering.co.nz
+// You may add your name to the author list if you have done significant modifications or improvements
+
+PwmOut chA(p21);
+PwmOut chB(p22);
+PwmOut chC(p23);
+
+Serial pc(USBTX, USBRX);
+Ticker sine3ticker;
+
+#define SINE3_PWM_FREQ 10000
+
+unsigned char sine3freq;
+float sine3mag;
+float sine3theta;
+
+void sine3tick() {
+ // offset PWM for bipolar: 0.5 => 0V
+ chA = 0.5 + (sine3mag * sinf(sine3theta) /2);
+ chB = 0.5 + (sine3mag * sinf(sine3theta + 2*PI /3)/2); // + 120 degrees
+ chC = 0.5 + (sine3mag * sinf(sine3theta + 2*PI*2/3)/2); // + 240 degrees => - 120 degrees
+
+ sine3theta += 2*PI / (SINE3_PWM_FREQ / sine3freq); // one cycle / steps per cycle
+ if (sine3theta >= 2*PI) {
+ sine3theta = 0;
+ }
+}
+
+
+void sine3_init() {
+ chA.period_us( 1000000 / SINE3_PWM_FREQ ); // period in uS. Common to all PWM
+ chA = 0.5;
+ chB = 0.5;
+ chC = 0.5;
+
+ sine3mag = 0.9; // prevent overmodulation
+ sine3freq = 55; // compromise between 50Hz and 60Hz
+ sine3theta = 0;
+ sine3ticker.attach_us(&sine3tick, (1000000 / SINE3_PWM_FREQ) ); // period in uS
+ //pc.printf("\n\r init ");
+}
+
+
+int main() {
+ sine3_init();
+ while (1) {
+ sine3freq++;
+ if (sine3freq > 100) {
+ sine3freq = 30;
+ pc.printf("\n\r");
+ }
+ wait(0.2);
+ pc.printf("%d ",sine3freq);
+ }
+}