372

circuits, each fed by an input voltage phase-shifted by 30° against each other feeding a

commonDC-bus

.

Examples of diode/thyristor bridge rectifiers

The operation of the rectifier circuits is examined in detail below, using the B2 circuit of

a single-phase, sinusoidal AC voltage at the input. For this purpose, the circuit of

o the left is extended by the line impedance L

N

. The load on the DC side is

replaced by a current source. For initial consideration L

N

= 0H and no effective capacity

in the path is to be present. In the next step, the analysis is then extended gradually to

L

N

> 0H and taking intoaccount a smoothing capacitor.

In

(taking into account an ohmic resistance in the load circuit) an

(taking into account a current source as a load, such as a sufficiently large inductance in

the load circuit) the voltage and current curves are plotted for L

N

= 0H. For the mains

current i

N

(

ω

t) it follows:

( )

( )

( )

( )

( )

V0 t

u

V0 t

u

with

with

t

i

t

i

t

i

N

N

d

d

N

<ω

>ω

ω−

ω

=ω

Due to the lack of inductance in the commutation path the current transfer of D

1

and D

4

toD

3

andD

2

occurs instantly. For the ideal open circuit DC voltageU

di(B2)

it follows:

( )

( ) ( )

N

N

0

N

2Bdi

U90.0 U2 2 t dt

sin U2 1

U

⋅

=

π

⋅

=ω ω ⋅

⋅

π

=

∫

π

If L

N

is now assumed to be larger than 0H, the current can not instantaneously

commutate from D

1

and D

4

to D

3

and D

2

, but requires a certain minimum time

(commutation time).

2

TheB12 circuit is set upwithin three-phasemains bymeans of an intermediary transformer, inwhich oneoutput

side is wired in delta and the other in star. Applications of this circuit are in the upper power range, such as in

wind turbines.

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