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Closed-loop Control of Motor Applications in Multisim

NI Employee (retired)

Hello Circuit Designers,

Machine applications require knowledge of a wide range of system components and parameters. The modeling and simulation of these parameters are not easy tasks, at the same time, they remain very critical to the accuracy of the design.

These designs usually involve an analog plant of the power electronics switching components. In addition, to accurately control the switching of IGBTs or MOSFETs, a preliminary controller behavior needs to be simulated. Finally, the load of the system, such as a motor, needs to be modeled based on specific physical parameters.

Below is a sample Multisim design of a DC motor driver with closed loop control showing how you can evaluate all these aspects of the design performance within a single simulation environment.

The design could also be found in the Multisim samples folder under the Machines sub-folder.

The design includes accurate models of the following components:

1. A 3-phase signal generator, modeling the grid input.


2. A 3-phase diode bridge rectifier with parametrizable voltage drops and on/off resistances.


3. An H-bridge network of four transistor-diodes (basic IGBTs)  to drive the motor. Components are also parametrizable to account for electrical behavior.


4. Models of a DC machine and a speed encoder to simulate the load effect based on physical parameters of the motor and to provide an input speed to a closed loop controller.


5. Partial Integral (PI) controller block that reads the speed input and provide control signals to a Pulse Width Modulator (PWM) that drives the switching of the IGBTs.


All these components are provided in the master database of Multisim 12.0 and can be the building blocks of your power electronics system. Parameters such as the transient current through the motor, the speed settling, the control signal levels, and the ripples on the DC link of this system could be evaluated running a transient simulation of the circuit shown below. Simply drag and drop it into your Multisim design sheet.


Entire circuit design in Multisim, drag and drop into your Multisim design environment to load.        


Motor speed settling to 4000 rpm, then getting stepped down to 3500 rpm using the PI closed loop control block in Multisim