Documentation

Chopper

Implement DC chopper model for DC motor drives

Library

Electric Drives/Fundamental Drives

Description

The Chopper block models a standard half-bridge (one leg, two IGBTs) or full-bridge (two legs, four IGBTs) converter model. It has two operating modes to represent a detailed or an average-value chopper.

Each operating mode has multiple instances depending on the DC motor drive type (two- or four-quadrant operation).

Detailed Mode

In detailed mode, the block is modeled by a Universal Bridge block configured as a half-bridge (one arm) or full-bridge (two arms) IGBT converter. The half-bridge IGBT converter model is used for one- or two-quadrant DC drives. The full-bridge converter model is for four-quadrant DC drives.

Average Mode

Average mode is used for fast simulations, where the high frequency switching actions of the switches is not required. The Chopper block implements an average-value half-bridge or full-bridge IGBT converter model. The average-value model can be one of these types:

  • Half-bridge, one-, or two-quadrant DC drive — The converter is composed of one controlled current source on the DC source side and one controlled voltage source on the motor side, as shown in the figure.

    The current source allows the representation of the average input current value following this equation:

    Iin = αIout

    where α is the duty cycle value of IGBT 1 and Iout the armature current value.

    For one-quadrant DC drives, when Iout ≤ 0,

    Iin = Iout

    The voltage source on the motor side represents the average voltage value following this equation:

    Vout = αVin

    For one-quadrant DC drives, when Iout ≤ 0,

    Vout = Vin

    with Vin being the input voltage.

  • Full-bridge, four-quadrant DC drive — This model is similar to the half-bridge, two-quadrant DC drive model, with the only difference being in the expressions of the average input current and output voltage, as shown in the figure.

    The average input current and output voltage are given by, respectively:

Iin = (2α – 1)Iout

Vout = (2α – 1)Vin

with α being the duty cycle value of IGBT 1 and IGBT 4.

Parameters

Mode detail level

Specify the model detail level to use:

  • Detailed (default)

  • Average

Number of quadrants

Select from these operating quadrants:

  • 1 — One quadrant

  • 2 — Two quadrants (default)

  • 4 — Four quadrants

Snubber resistance Rs (Ohms)

The value of the snubber resistance of the rectifier. When you set the Model detail level parameter to Detailed, this parameter is visible only when you set the Number of quadrants parameter to 4. When you set the Model detail level parameter to Average, this parameter is visible only when you set the Number of quadrants parameter to 2 or 4. The default value is 10e3.

Snubber capacitance Cs (F)

The value of the snubber capacitance of the rectifier, in farad. The default value is inf.

Resistance Ron (Ohms):

Internal resistance of the selected device, in ohms. The default value is 1e-3.

Forward voltages (V) [Vf, Vd]

Forward voltages, in volts, of the forced-commutated devices (IGBT, MOSFET, or GTO) and of the antiparallel diodes. The default value is [1.3,1.3].

Fail time and tail time (s) [Tf, Tt]

Fall time Tf and tail time Tt, in seconds, for the GTO or the IGBT devices. The default value is [0,0].

Sample Time

The sample time of the shopper, in seconds. The default value is 2e-6.

Inputs and Outputs

g

The gate input for the controlled switch devices. Pulses are sent to upper and lower switches of the half- or full-bridge converter. This port is visible only when you set the Model detail level parameter to Detailed.

Duty Cycle

The duty cycles required by IGBT 1 and IGBT 2 of a half-bridge converter. This port is visible only when you set the Model detail level parameter to Average and the Number of quadrants parameter to 1 or 2.

Duty Cycles

The duty cycles required by IGBT 1 and 4 and IGBT 2 and 3 of the full-bridge converter. This port is visible only when you set the Model detail level parameter to Average and the Number of quadrants parameter to 4.

+

The positive terminal on the DC source side.

-

The negative terminal on the DC source side.

A

The bridge-converter output terminals on the motor side.

B

The bridge-converter output terminals on the motor side. This port is visible only when you set the Number of quadrants parameter to 4.

Examples

The Chopper block is used in the DC5, DC6, and 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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