Documentation

Current Controller (DC)

Implement PI current controller model for DC machine

Library

Electric Drives/Fundamental Drives

Description

The Current Controller (DC) block models a PI current controller for use with a DC machine. The block has multiple instances, depending on the DC drive type (chopper DC drive or thyristor-based DC drive) and operating quadrants (one-, two-, or four-quadrant). It has two operating modes to represent a detailed or an average-value current controller.

Detailed Mode

The figure shows the models of the detailed Current Controller (DC) block for one-, two-, and four-quadrant chopper DC drives, respectively.

The inputs of the DC current controller block are the current reference (in pu) and the armature current flowing through the motor. The current reference is typically provided by a speed or torque controller. The armature current input is filtered by a first-order low-pass filter.

The duty cycle of the chopper is computed with a PI regulator. The duty cycle is compared with a fixed frequency sawtooth carrier signal to obtain the required gate pulses (PWM) for the chopper devices (IGBT 1 and IGBT 2). The figure shows PWM signal generation for a two-quadrant chopper DC drive.

Average Model

The Average Current Controller (DC) model is normally used with average-value DC chopper models where the high-frequency switching actions of the power switches are not represented.

The Average Current Controller (DC) block is similar to the detailed model. However, there is no PWM signal generation. The output of the Average Current Controller (DC) block is the duty cycle of the IGBTs. For a two-quadrant operation, two duty cycles are computed for IGBT 1 and IGBT 2. For a four-quadrant operation, two duty cycles are computed for IGBT 1 and IGBT 4 and for IGBT2 and IGBT 3.

Current Controller (DC) for Chopper DC Drives

For chopper DC drives, the block outputs actual pulses (detailed mode) or duty cycle (average mode) for the DC chopper.

Current Controller (DC) for Thyristor-Based DC Drives

For thyristor-based DC drives, the Current Controller (DC) block outputs the firing angle for the thyristor bridge converter. The figure shows the models for a two-quadrant and four-quadrant thyristor-based DC drive.

A PI regulator computes the appropriate firing angle for the thyristor bridge. For two-quadrant operation, a feed-forward term is added to the firing angle to compensate for nonlinearities appearing during discontinuous conduction.

For four-quadrant thyristor-based drives, the DC current controller outputs two firing angles (Alpha_1 and Alpha_2) for the two antiparalleled thyristor bridges. The sum of the firing angles is 180 degrees at all times. This setting ensures opposite average voltages at each converter DC output terminal and maintains identical average voltages at the DC motor armature.

Parameters

Drive type

Specify the drive type to use:

  • Chopper based (default)

  • Rectifier based

Model detail level

Select between the detailed and the average-value model. This parameter is available only when the Drive type parameter is set to Chopper based.

Select one of these values:

  • Detailed (default)

  • Average

Number of quadrants

Specify the number of operating quadrants to use. Select between 1, 2, and 4.

The default value is 2.

Power (VA)

Base power in volt amperes of the DC machine, typically equivalent to the nominal power. The default value is 5*746.

Voltage (V)

Base voltage in volts of the DC machine, typically equivalent to the nominal voltage. The default value is 240.

Proportional

The PI controller proportional gain. The default value is 2.

Integral

The PI controller integral gain. The default value is 200.

Low-pass filter cutoff frequency (Hz)

The cutoff frequency, in hertz, of the low-pass filter used to filter the armature current measurement. The default value is 500.

Switching frequency (Hz)

The switching frequency, in hertz, of the DC chopper. This parameter is available only when the DC drive type parameter is set to Chopper based and the Detail level parameter is set to Detailed.

The default value is 5e3.

Firing angle limits

The lower and upper limits of the firing angle, in degrees. This parameter is available only when the Drive type parameter is set to Rectifier based. The default value is [20, 160].

Controller sample time (s)

The current controller sampling time, in seconds. The sampling time must be a multiple of the simulation time step. The default value is 20e-6.

Network sample time (s)

The time step used for the simulation, in seconds. The default value is 1e-6.

Inputs and Outputs

la

The measured armature current (A).

la*(pu)

Armature current reference in per-unit, typically provided by a speed/torque controller.

d_i

Armature current reference error (difference between the reference and the actual machine current).

la*

Armature current reference (A).

Pulse

PWM pulse signal required by the one-quadrant DC chopper. This port is visible only when the Drive type parameter is set to Chopper based, the Model detail level parameter is set to Detailed, and the Number of quadrants parameter is set to 1.

Pulses

PWM pulse signal required by the two-quadrant DC chopper or the four-quadrant DC chopper. This port is visible only when the Drive type parameter is set to Chopper based, the Model detail level parameter is set to Detailed, and the Number of quadrants parameter is set to 2 or 4.

Dcycle

Duty cycle required by the one-quadrant DC chopper. This port is visible only when the Drive type parameter is set to Chopper based, the Model detail level parameter is set to Average, and the Number of quadrants parameter is set to 1.

Dcycles

The duty cycles required by the two-quadrant DC chopper or the four-quadrant DC chopper. This port is visible only when the Drive type parameter is set to Chopper based, the Model detail level parameter is set to Average, and the Number of quadrants parameter is set to 2 or 4.

Alpha

The firing angle required by the one-quadrant thyristor bridge or the two-quadrant thyristor bridge converter. This port is visible only when the Drive type parameter is set to Thyristor based and the Number of quadrants parameter is set to 1 or 2.

Alpha_1

The firing angle required by the first antiparalleled thyristor bridge in a four-quadrant DC drive. This port is visible only when the Drive type parameter is set to Thyristor based and the Number of quadrants parameter is set to 4.

Alpha_2

The firing angle required by the second antiparalleled thyristor bridge in a four-quadrant DC drive. This port is visible only when the Drive type parameter is set to Thyristor based and the Number of quadrants parameter is set to 4.

Examples

The Current Controller (DC) block is used in the DC1 to DC7 blocks from the Electric Drives library.

References

[1] Bose, B. K. Modern Power Electronics and AC Drives, NJ: Prentice-Hall, 2002.

Introduced in R2015b

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