Current Controller (DC)
Implement PI current controller model for DC machine
Library
Simscape / Electrical / Specialized Power Systems / Electric Drives / Fundamental Drive Blocks
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, and4.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 basedand the Detail level parameter is set toDetailed.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
laThe measured armature current (A).
la*(pu)Armature current reference in per-unit, typically provided by a speed/torque controller.
d_iArmature current reference error (difference between the reference and the actual machine current).
la*Armature current reference (A).
PulsePWM 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 toDetailed, and the Number of quadrants parameter is set to1.PulsesPWM 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 toDetailed, and the Number of quadrants parameter is set to2or4.DcycleDuty 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 toAverage, and the Number of quadrants parameter is set to1.DcyclesThe 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 toAverage, and the Number of quadrants parameter is set to2or4.AlphaThe 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 basedand the Number of quadrants parameter is set to1or2.Alpha_1The 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 basedand the Number of quadrants parameter is set to4.Alpha_2The 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 basedand the Number of quadrants parameter is set to4.
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.
See Also
Bridge Firing Unit (AC) | Bridge Firing Unit (DC) | Current Controller (Brushless DC) | Direct Torque Controller | Field-Oriented Controller | Regulation Switch | Six-Step Generator | Space Vector Modulator | Speed Controller (AC) | Speed Controller (DC) | Speed Controller (Scalar Control) | Vector Controller (PMSM) | Vector Controller (WFSM) | Voltage Controller (DC Bus)