(完整word版)Universal Bridge模块

Universal Bridge

-

Implement universal power converter with selectable topologies

and power electronic devices

Library

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:

Dialog Box and 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).

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Set the Snubber resistance R

s 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 resistive snubber.

In order to avoid numerical oscillations when your system is discretized, you need to

specify

Rs

and

Cs

snubber

values

for

diode

and

thyristor

bridges.

For

forced-commutated

devices

(GTO,

IGBT,

or

MOSFET),

the

bridge

operates

satisfactorily

with

purely

resistive

snubbers

as

long

as

firing

pulses

are

sent

to

switching devices.

If

firing

pulses

to

forced-commutated

devices

are

blocked,

only

antiparallel

diodes

operate,

and

the

bridge

operates

as

a

diode

rectifier.

In

this

condition

appropriate

values of Rs and Cs must also be used.

When the system is discretized, use the following formulas to compute approximate

values of Rs and Cs:

where

Pn = nominal power of single or three phase converter (V

A)

Vn = nominal line-to-line AC voltage (Vrms)

f = fundamental frequency (Hz)

Ts = sample time (s)

These Rs and Cs values are derived from the following two criteria:

The snubber leakage current at fundamental frequency is less than 0.1% of nominal

current when power electronic devices are not conducting.

The RC time constant of snubbers is higher than two times the sample time Ts.

These

Rs

and

Cs

values

that

guarantee

numerical

stability

of

the

discretized

bridge

can be different from actual values used in a physical circuit.

Power electronic device

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

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

the

power_sfavg

demo

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).

Lon

Internal

inductance,

in

henries

(H),

for

the

diode

or

the

thyristor

device.

When

the

bridge is discretized, the Lon parameter must be set to zero.

Forward voltage Vf