Step 9: Setting Up the Hyperdrive
Tsunami’s Hyperdrive system features high-frequency PWM drive for silent motor control along with load compensation (or back-emf) to improve low speed operation and maintain constant speed regardless of changes to the motor load.
The PWM frequency is fixed at 22.000Khz and there are no adjustments.
Tsunami uses back EMF and a PI control loop to sense and control motor speed. There are four CVs associated with the load compensation feature:
CV 10, Back EMF Cutout CV 209, Kp Coefficient CV 210, Ki Coefficient CV 212, BEMF Feedback Intensity
Control Loop Coefficients
Tsunami compensates for load changes by comparing the locomotive’s speed, as measured by the motor’s back-emf voltage, with the current throttle setting. When a difference is detected, the motor voltage is adjusted up or down so that locomotive speed stays constant. This is done using a P-I (proportional-integral) control loop that is tuned using two CVs:
CV 209, Kp, controls the Proportional gain of the control loop and compensates for dynamic changes in the motor load by applying a correction based on the difference between the throttle setting and the current motor speed. This CV may be set between 1 and 255. Higher values produce an increasing level of compensation. However, setting this value too high can lead to irregular and rough performance.
CV 210, Ki, controls the Integral gain of the control loop and compensates for static motor load by applying a correction based on the historical (or integral) difference between the throttle setting and the current motor speed. This CV may be set between 0 and 255. Higher values produce an increasing level of compensation and set the ‘snappiness’ of the control loop. However, setting this CV value too high can lead to oscillations in locomotive speed and we suggest you use the lowest possible setting that still provides optimal performance.
Note: Setting both Kp and Ki to zero will cause the motor to stop.
Tsunami Steam Sound User’s Guide