Transcript Diodes with RL loads. Freewheeling

Diodes with RL loads. Freewheeling
Assume ideal diode (zero reverse
rocvery time, zero voltage drop)
An antiparallel diode known as the
freewheeling diode must be
connected across the load to provide
a path for the inductive current to
flow.
Diode rectifiers
Learn performance parameters of rectifiers and
power converters
Study effects of load inductance on load current
D1
D2
Vs
L
R
First neglect the freewheeling
diode
The diode current is found using the
Laplace transform method:
Note that the diode conduction time is
longer than half-period
The waveform is nonsinusoidal but periodic.
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Now with the freewheeling diode
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Recommended reading
Chapter 1
● Sections 2.10-2.13 and examples in those sections, the rest are optional)
● Sections 3.1 to 3.3, example 3.2
●
Single phase full wave rectifier
Full wave rectifier with centre tapped transformer
Full wave bridge rectifier
Single phase full wave rectifier with large
inductive load
Single phase full wave rectifier with RL load
T/2
For a steady state solution, require i0(0)= i0(T)=I0. Then
I0>0 guarantees that the current flows continuously.
Load, source and diode currents (E=10V).
Download Matlab code fwr.m, (also requires fun_fwr.m).
Load, source and diode currents (E=0.6Vm)
E=10 V
E=120 V
Load voltage
Source voltage
Load current
Conclusion
●
An inductive load can make load current flow
continuously if voltage ratio is below the critical
value
●
E=0 guarantees continuous current
●
If L=0, any E>0 will cause current interruptions
●
References: Section 3.4 and examples in that
section
Three phase bridge rectifier
(Note 30 deg phase shift).
-p/6
p/6
0
Performance:
Single phase rectifier
3 phase rectifier
3phase rectifiers with RL load
E
Condition for continuous load current
Largest critical value of the
EMF ratio is substantially
higher (95.5% vs 63.6%)