PLL Regulation Control Loop

Introduction

PLL bandwidth is used to calculate the feedback gain for the controller's phase-locked loop, PLL: Pll Kp and PLL Ki. The PLL tracks the sensorless angular position of the motor for motor modelling flux frequency calculation. It controls the output frequency.

As PLL bandwidth increases, the lock time decreases. Basically, the higher the bandwidth the faster the PLL can adjust the output frequency. The faster it can adjust the frequency, the faster it can lock.

A side effect of higher PLL bandwidth is that the PLL is harder to control, unstable. It might over-adjust, increasing output noise, audible noise, vibrations and jitter. In some cases, if the PLL bandwidth is low enough, then the jitter on the reference clock will be removed. But if the PLL bandwidth is too high, then the incoming jitter can be passed to the output or even amplified.

Tuning

Bandwidth tuning

If experiencing jitter, try adjusting by increments of 100 up and down, up to 500.

Higher electrical frequency motors or motors where RPM can change rapidly can often benefit from values 300 or higher in order to prevent instantaneous phase over current faults. Motors such as geared hubs or mid-drive motors.

Lower electrical frequency motors or motors where RPM changes more slowly, such as direct drive hubs can often tolerate lower values.

PLL damping will affect Kp. Increasing PLL damping will increase the PLL bandwidth auto-calculated PLL Kp factor.

Manual tuning

Though not recommended, if PLL bandwidth and PLL damping are set to zero, you can manually set PLL Kp and PLL Ki, but instead of PLL Kp and PLL Ki, you set PLL Kp old and PLL Ki old.

Tunning effects when increasing a parameter independently:

Parameter	Rise Time	Overshoot	Settling time	Steady-State error	Stability
PLL Kp	Decrease	Increase	Small Change	Decrease	Degrade
PLL Ki	Decrease	Increase	Increase	Eliminate	Degrade