Power System Blockset    

Modeling the DC Drive

Open the psbdcdrive.mdl file of the powerlib library by typing psbdcdrive in MATLAB command window. A circuit diagram titled psbdcdrive will appear. Before running the example, save this circuit as case2.mdl in your working directory so that you can make further modifications without altering the original file.

The drive system diagram is built using electrical blocks contained in the powerlib library combined with Simulink blocks. Voltage Measurement and Current Measurement blocks are used as the interface between the two block types. The system diagram is shown in Figure 2-13.

Figure 2-13: DC Motor Drive Using Power System Blockset (psbdcdrive.mdl)

The DC motor represented by the DC Machine block is modeled in two separate parts: electrical and mechanical. To view the Simulink model of the DC motor, click on the DC Machine block and use the LookUnderMask command in the Edit menu.

The armature circuit is represented by an RL circuit in series with a controlled voltage source, the value of which is KE.

The field circuit is represented by an RL circuit.

The mechanical part is represented by Simulink blocks, which implement the following equation:

The DC machine parameters are set to the desired values by using the dialog mask of the DC Machine block.

The load torque-speed characteristic can be implemented by a Simulink Fcn block.

The motor used in this case study is a separately excited 5 HP/240 V DC motor having the following parameters: Ra = 0.5 , La = 10 mH, KE =1.23 V/(rad/s), KT = 1.23 N.m/A.

A 10mH inductor (Ls) is connected in series with the DC motor to smooth out the armature current. The constant excitation is implemented by connecting a DC Voltage Source block to the field winding.

The required trigger signal for the GTO thyristor is generated by a hysteresis current controller, which forces the motor current to follow the reference within +h/2 and -h/2 limits (h is the hysteresis band).

The current controller is a masked block that contains:

The speed control loop uses a proportional-integral controller, which is implemented by Simulink blocks:


 Description of the Drive System Simulation of the DC Drive