Power System Blockset    
Universal Bridge

Implement a universal three-phase bridge converter with selectable configuration and power switch type.

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Power Electronics

Description

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

Diode bridges:

Thyristor bridges:

GTO-Diode bridges:

MOSFET-Diode bridges:

IGBT-Diode bridges:

Ideal switch bridge:

Dialog Box and Parameters

Port configuration
Set to ABC as input terminals to connect the A,B, and C phases of the bridge to the input ports one, two, and three of the Universal Bridge block. The DC + and - terminals will be connected at outputs one and two.
Set to ABC as output terminals to connect the A,B, and C phases of the bridge to the output ports one, two, and three of the Universal Bridge block. The DC + and - terminals will be connected at outputs one and two.
Snubber resistance Rs
The snubber resistance, in ohms (). Set the Snubber resistance Rs parameter to inf to eliminate the snubbers from the model.
Snubber capacitance Cs
The snubber capacitance, in farads (F). Set the Snubber capacitance Cs parameter to 0 to eliminate the snubbers, or to inf to get a purely resistive snubber.
Power electronic device
Select the type of power electronic device to use in the bridge.
Ron (Ohms)
Internal resistance of the selected device, in ohms ().
Lon (H)
Internal inductance, in henries (H), for the Diode, the Thyristor, or the MOSFET device.
[Tf (s), Tt (s)]
Fall time Tf and tail time Tt, in seconds (s), for the GTO or the IGBT devices.
Measurements
Select Device voltages to measure the voltage across the six power electronic device terminals.
Select Device currents to measure the current flowing through the six power electronic devices. If the snubber devices are defined, the measured currents are the one 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 Measurement listbox of the Multimeter block, the measurement will be identified by a label followed by the block name.

Measurement

Label

Device voltages

uSw1: , uSw2: ,uSw3: ,uSw4: ,uSw5: ,uSw6:

Branch current

iSw1: , iSw2: , iSw3: , iSw4: , iSw5: , iSw6:

Terminal voltages

uAB: , uBC:, uCA: , uDC:

Inputs and Outputs

The bridge configuration is selectable so that the inputs and outputs depend on the configuration chosen:

Except for the case of diode bridge, the Pulses input accepts a Simulink-compatible vectorized gating signal containing six pulse trains. The gating signals are sent to the power switches according to the number shown in the diagrams above.

Assumptions and Limitations

Universal Bridge blocks can be discretized to be used in a discrete time step simulation specified by the Discrete System block. In this case, the internal commutation logic of the Universal Bridge takes care of the commutation between the power switches and the diodes in the converter legs.

Example

This example illustrates the use of two Universal Bridge blocks in an ac-ac converter consisting of a rectifier feeding an IGBT inverter through a dc link. The inverter is pulse-width modulated (PWM) to produce a three-phase variable-voltage variable-frequency sinusoidal voltage to the load. In this example the inverter chopping frequency is 2000 Hz and the modulation frequency is 50 Hz.

The IGBT inverter is controlled in closed loop with a PI regulator in order to maintain a 1 p.u. voltage (380 Vrms, 50 Hz) at the load terminals.

A multimeter block is used to observe commutation of currents between diodes 1 and 3 in the diode bridge and between IGBT/Diodes switches 1 and 2 in the IGBT bridge.

.The circuit is available in the psbbridges.mdl demo.

Start simulation. After a transient period of approximately 70 ms, the system reaches a steady state. Observe voltage waveforms at DC bus, inverter output and load on Scope1. The harmonics generated by the inverter around multiples of 2 kHz are filtered by the LC filter. As expected the peak value of the load voltage is 537 V (380 V rms).

In steady state the mean value of the modulation index is m=0.77 and the mean value of the DC voltage is 780 V. The fundamental component of 50 Hz voltage buried in the chopped inverter voltage is therefore:

Vab= 780 V * 0.612 * 0.80 = 382 V rms

Observe diode currents on trace 1of Scope2, showing commutation from diode 1 to diode 3. Also observe on trace 2 currents in switches 1 and 2 of the IGBT/Diode bridge (upper and lower switches connected to phase A). These two currents are complementary. A positive current indicates a current flowing in the IGBT, whereas a negative current indicates a current flowing in the anti parallel diode.

See Also
Diode, GTO, Ideal Switch, IGBT, MOSFET, Thyristor


 Thyristor Voltage Measurement