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B.1.1 Servo configuration

The servo configuration is the default configuration for the drive, allowing the motor control system to operate as a torque controller, a velocity controller or a position controller. This configuration comprises 3 nested control loops; a current control loop, a velocity control loop and a position control loop, as shown in Figure 51.

The universal encoder interface reads rotor position from the encoder and estimates velocity. The commutation block uses the position to calculate the electrical angle of the rotor. The current sensor system measures U and V phase currents. These are fed into a current conversion block that converts them into quantities representing torque producing and magnetizing currents (the ’vector’ currents which are locked to the rotor).

In the current control loop, a current demand and the final measured current values form the inputs to a PI (Proportional, Integral) control system. This control system generates a set of voltage demands that are fed into a PWM (pulse-width modulation) block. The PWM block uses the space-vector modulation method to convert these voltage demands into a sequence of U, V and W phase switching signals, which are applied to the output bridge of the drive. The PWM block uses the measured DC bus voltage to compensate for variations in supply voltage.

The torque controller converts a torque demand into a current demand and compensates for various load non-linearities. A 2-stage notch or low-pass filter allows the effects of load compliance to be reduced. To avoid motor damage, a user-defined application current limit is also applied, as well as individual positive and negative torque limits.

In the velocity control loop, a velocity demand and measured velocity form the inputs to a PI control system. The output of the control system is a torque demand which, when the drive is operating as a velocity controller, forms the input to the current control loop.

Finally, in the position control loop, a position demand and measured position form the inputs to a PID (Proportional, Integral, Differential) control system incorporating velocity feedback, velocity feed-forward and acceleration feed-forward. The output of the position control system is a velocity demand which, when the drive is operating as a position controller, forms the input to the velocity control loop.

B-2 Control System

MN1942

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Baldor E100 manual Servo configuration