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101
Basic MPC Vector Control Loop
The function we are controlling is liquid flow from the pump, and the variable being controlled by the MPC Vector is
motor speed. This control must be based on some type of feedback, in this case a flow meter measuring liquid flow
rate.
Feedback and Error
Feedback is critical in control systems. The feedback lets the controller know the actual flow rate being output by the
pump at all times. Utilizing the feedback, the control system is able to determine the error which can be defined as the
difference between the expected flow rate and the actual flow rate. The PID controller acts on the error, manipulating
the process variable being controlled (in the case of the MPC Vector, motor speed) in order to bring the process
closer to the set point, thereby eliminating the error.
The PID controller does not act on the actual flow rate being reported by the flow meter, it acts on the error between
the actual flow rate, and the desired set point, it’s goal being to eliminate the error between the two as much as
possible.
Sampling Rate
In the digital world the control loop is run at some base period which is called the sampling rate, Ts. After the initial
command is given the control system waits for this period of time and then samples the output, compares it to the set
point, and makes motor speed adjustments. After the same period of time expires again, it samples the flow rate again
and compares it to the expected flow rate and adjusts. This continues as long as the pump is running. Like many other
options for the MPC Vector, this is a configurable setting. The sampling rate of the MPC Vector should be at least
twice as fast as the sampling rate of the flow sensor.
PID Control
System
Pulsafeeder
Pump
Requested
Flow Rate
Output
Flow
Flow
Meter
1
2
3
5
4
1 Requested flow rate from the user
Motor speed command from the control system
Flow output from the pump
Flow measurement from the flow meter
Flow output from flow meter
2
3
4
5
Содержание Pulsafeeder MPC Vector
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