Documentation

DC Bus

Implement DC bus model that includes resistive braking chopper

Library

Electric Drives/Fundamental Drives

Description

The DC Bus block has two operating modes. The most common mode implements a capacitive DC bus with a proportional controller. The braking resistance is switched based on activation and shutdown voltages, which you supply as parameters. For the second operating mode, a smoothing inductor is added to the DC bus to filter out high-current harmonics generally present in six-step motor drives. A resistive braking chopper is modeled in both cases.

Capacitive DC Bus with Proportional Control

In this mode, the DC bus voltage is maintained within a range determined by the activation and shutdown voltages. As shown in the figure, the braking chopper is activated when the bus voltage reaches the upper limit of the hysteresis band. When the bus voltage reaches the lower limit of the hysteresis band, the braking chopper shuts down.

LC DC Bus for Six-Step Induction Motor Drive

In this mode, the DC bus voltage is kept as constant as possible. A thyristor rectifier ahead of the DC bus regulates the DC bus voltage. When the rectifier is close to its operating limits, the braking chopper further regulates the DC bus voltage. The smoothing inductor filters the current harmonics content generated by the thyristor rectifier.

Parameters

Bus type

Specify the bus type to use:

  • Capacitive (generic) (default)

  • LC (for six-step drive)

Bus capacitance (F)

DC bus capacitance (F). The default value is 2000e-6.

Bus inductance (H)

DC bus inductance (H). This parameter is required and available only when the Bus type parameter is set to LC (for six-step drive). The default value is 1e-3.

Set initial bus voltage

Select to specify an initial voltage for the DC bus capacitor. Otherwise, the voltage is initialized at zero. The default value is cleared.

Initial bus voltage (V)

Initial bus voltage, in volts. This parameter is required and available only when the Set initial bus voltage check box is selected. The default value is 600.

Resistance (ohms)

The braking resistance, in ohms. The default value is 8.

Frequency (Hz)

The frequency at which the braking resistance is switched on and off, in hertz. The default value is 4000.

Activation voltage (V)

The voltage at which the braking chopper is enabled, in volts. This value must be greater than or equal to the shutdown voltage. This parameter is required and available only when the Bus type parameter is set to Capacitive (generic). The default value is 320.

Shutdown voltage (V)

The voltage at which the braking chopper is disabled, in volts. Use a value less than or equal to the activation voltage. This parameter is required and available only when the Bus type parameter is set to Capacitive (generic). The default value is 310.

Inputs and Outputs

P_chop

Duty cycle of the braking chopper, typically provided by a DC bus voltage controller. This input is visible only when the Bus type parameter is set to LC (for six-step drive).

Brak_crtl

This binary signal enables (1) or disables (0) the braking chopper. This input is visible only when the Bus type parameter is set to LC (for six-step drive).

in+

The positive input port. It is usually connected to the positive output port of the rectifier.

in-

The negative input port. It is usually connected to the negative output port of the rectifier.

Meas

A vector containing these measurement signals:

  • I rectifier (A): the current entering the DC bus on the rectifier side

  • V rectifier (V): the voltage across the DC bus on the rectifier side. This signal is present only in the output vector when the Bus type parameter is set to LC (for six-step drive).

  • I bus (A): the current exiting the DC bus on the inverter side.

  • V bus (V): the voltage across the DC bus on the inverter side. If the Bus type parameter is set to Capacitive (generic), this voltage is also the rectifier-side voltage.

Out+

The positive output port. It is usually connected to the positive input port of the inverter.

Out-

The negative output port. It is usually connected to the negative input port of the inverter. Note that the in– and Out– ports are exactly the same electrical node.

Examples

The DC Bus block is used in the AC1 and AC3 blocks in 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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