PWM Brushless Servo-Current and Velocity Feedback

Category: Toolbox > eDrives > eMotors (Legacy) > Controllers > PWM Control

Inputs:

•      inhibit: Disables amplifier output for a control voltage less than 0.3 V (logic low).

•      tach: Provides the measured shaft velocity.

•      current limit: Limits load current according to the specified current limit.

Outputs:

•      motor a: PWM control signal.

•      motor b: PWM control signal.

•      motor c: PWM control signal.

Description: The PWM Brushless Servo-Current and Velocity Feedback block simulates a brushless PWM servo amplifier used to control the velocity of a brushless DC motor. The control logic provides a transformation that decodes Hall sensed motor shaft position and direction to stator field commutation (six-step control). An inhibit control is provided to disable amplifier output for voltage input less than 0.3 V (logic low). All three-phase voltages are provided with full PWM control (0 – 100%). A value of 100% represents no modulation. This allows variable speed control. Control of the PWM is accomplished through cascaded loops.

The inner loop is current feedback control. Current sense is fed back through a current sense (resistor) or transconductance gain. The controller for the current loop is PI; you can specify integral and proportional gains. The PI output is clamped between 0 and 100% modulation to prevent control windup.

The outer loop is velocity feedback control. A tachometer voltage input provides the measured shaft velocity that is converted to engineering units (rad/sec) by the tach sensitivity and compared against the reference velocity input (rad/sec). The controller is PI; you can specify integral and proportional gains. The PI output is clamped by the current limit control that limits the current loop reference.

Current Loop Integral Gain: Indicates the current loop PI controller integral gain. This parameter typically sets the steady-state tracking accuracy of the current control.

Current Loop Proportional Gain: Indicates the current loop PI controller proportional gain. This parameter typically sets the speed (bandwidth) of the current control.

PWM Frequency: Sets the carrier frequency for the PWM. Note that the reciprocal of the simulation step size (simulation frequency) must be equal to or greater than the carrier frequency to perform a proper simulation.

Supply Voltage: Specifies the voltage level for PWM pulses. A positive voltage produces clockwise rotation of the motor. A negative voltage produces counterclockwise rotation.

Tachometer sensitivity: Lets you rescale tachometer readings from V to rad/sec. For example, if the known tachometer sensitivity is 200 V/rad/sec, enter this number to scale the reading back to rad/sec.

Transconductance Gain: Sets the current to voltage gain of the current controller.

Velocity Loop Integral Gain: Indicates the velocity loop PI controller integral gain. This parameter typically sets the steady-state tracking accuracy of the speed control.

Velocity Loop Proportional Gain: Indicates the velocity loop PI controller proportional gain. This parameter typically sets the speed (bandwidth) of the velocity control.