SimPowerSystems

Modeling the DC Drive

Open the psbdrive model and save this model 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 with blocks from 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 here:

Figure 2-12: 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 the DC Machine block and use the Look under mask item 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 K_E.

The field circuit is represented by an RL circuit.

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

Set the DC machine parameters to the desired values by using the dialog box of the DC Machine block.

You implement the load torque-speed characteristic using 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 10 mH inductor (Ls) is connected in series with the DC motor to smooth out the armature current. The constant excitation is implemented by the connection of 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.

Chopper-Fed DC Motor Drive

Simulation of the DC Drive