Documentation

Universal Bridge

Implement universal power converter with selectable topologies and power electronic devices

Library

Fundamental Blocks/Power Electronics

Description

The Universal Bridge block implements a universal three-phase power converter that consists of up to six power switches connected in a bridge configuration. The type of power switch and converter configuration are selectable from the dialog box.

The Universal Bridge block allows simulation of converters using both naturally commutated (or line-commutated) power electronic devices (diodes or thyristors) and forced-commutated devices (GTO, IGBT, MOSFET).

The Universal Bridge block is the basic block for building two-level voltage-sourced converters (VSC).

The device numbering is different if the power electronic devices are naturally commutated or forced-commutated. For a naturally commutated three-phase converter (diode and thyristor), numbering follows the natural order of commutation:

For the case of a two-phase diode or thyristor bridge, and for any other bridge configuration, the order of commutation is the following:

GTO-Diode bridge:

IGBT-Diode bridge:

MOSFET-Diode and Ideal Switch bridges:

Parameters

Number of bridge arms

Set to 1 or 2 to get a single-phase converter (two or four switching devices). Set to 3 to get a three-phase converter connected in Graetz bridge configuration (six switching devices). Default is 3.

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Default is 1e5. Set the Snubber resistance Rs parameter to inf to eliminate the snubbers from the model.

Snubber capacitance Cs

The snubber capacitance, in farads (F). Default is inf. Set the Snubber capacitance Cs parameter to 0 to eliminate the snubbers, or to inf to get a resistive snubber.

When you are using the continuous solver you can eliminate snubbers in all power electronic devices if you select the Disable snubbers in switching devices option in the Preference tab of the Powergui block

When your system is discretized, you can simulate power electronic devices with virtually no snubbers by specifying purely resistive snubbers with a very large resistance, thus producing negligible leakage currents. The bridge operates satisfactorily with purely resistive snubbers.

Power electronic device

Select the type of power electronic device to use in the bridge. Default is Thyristors.

When you select Switching-function based VSC, a switching-function voltage source converter type equivalent model is used, where switches are replaced by two voltage sources on the AC side and a current source on the DC side. This model uses the same firing pulses as for other power electronic devices and it correctly represents harmonics normally generated by the bridge.

When you select Average-model based VSC, an average-model type of voltage source converter is used to represent the power-electronic switches. Unlike the other power electronic devices, this model uses the reference signals (uref) representing the average voltages generated at the ABC terminals of the bridge. This model does not represent harmonics. It can be used with larger sample times while preserving the average voltage dynamics.

See power_sfavg for an example comparing these two models to an Universal Bridge block using IGBT/Diode device.

Ron

Internal resistance of the selected device, in ohms (Ω). Default is 1e-3.

Lon

Internal inductance, in henries (H), for the diode or the thyristor device. Default is 0. When the bridge is discretized, the Lon parameter must be set to zero.

Forward voltage Vf

This parameter is available only when the selected Power electronic device is Diodes or Thyristors.

Forward voltage, in volts (V), across the device when it is conducting. Default is 0.

Forward voltages [Device Vf, Diode Vfd]

This parameter is available when the selected Power electronic device is GTO/Diodes or IGBT/Diodes.

Forward voltages, in volts (V), of the forced-commutated devices (GTO, MOSFET, or IGBT) and of the antiparallel diodes. Default is [ 0 0 ].

Measurements

Default is None.

Select Device voltages to measure the voltages across the six power electronic device terminals.

Select Device currents to measure the currents flowing through the six power electronic devices. If antiparallel diodes are used, the measured current is the total current in the forced-commutated device (GTO, MOSFET, or IGBT) and in the antiparallel diode. A positive current therefore indicates a current flowing in the forced-commutated device and a negative current indicates a current flowing in the diode. If snubber devices are defined, the measured currents are the ones flowing through the power electronic devices only.

Select UAB UBC UCA UDC voltages to measure the terminal voltages (AC and DC) of the Universal Bridge block.

Select All voltages and currents to measure all voltages and currents defined for the Universal Bridge block.

Place a Multimeter block in your model to display the selected measurements during the simulation. In the Available Measurements menu of the Multimeter block, the measurement is identified by a label followed by the block name.

Measurement

Label

Device voltages

Usw1:

Branch current

Isw1:

Terminal voltages

Uab:

Inputs and Outputs

g

The gate input for the controlled switch devices. The pulse ordering in the vector of the gate signals corresponds to the switch number indicated in the six circuits shown in the Description section. For the diode and thyristor bridges, the pulse ordering corresponds to the natural order of commutation. For all other forced-commutated switches, pulses are sent to upper and lower switches of phases A, B, and C.

Topology

Pulse Vector of Input g

one arm

[Q1,Q2]

two arms

[Q1,Q2,Q3,Q4]

three arms

[Q1,Q2,Q3,Q4,Q5,Q6]

Examples

The power_ACDCAC_Converter example illustrates the use of one Universal Bridge block in an ac/dc/ac converter to model a diode rectifier feeding an IGBT inverter through a DC link.

Introduced before R2006a

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