Week 5 DC-to-DC Converters 1. Functional Block Diagram of DC-DC Converter System Unregulated dc...
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Week 5 DC-to-DC Converters 1. Functional Block Diagram of DC-DC Converter System Unregulated dc voltage obtained by rectifying the line voltage, and therefore
Functional Block Diagram of DC-DC Converter System Unregulated
dc voltage obtained by rectifying the line voltage, and therefore
will fluctuate with line voltage magnitude Controlled dc output at
a desired voltage level
Slide 3
Control of DC-DC Converters In a dc-dc converter: Average
output dc voltage must be controlled to equal a desired level.
Utilizes one or more switches to transform dc from one level to
another. The average output voltage is controlled by controlling
the switch on and off durations (t on and t off ). Lets consider
the following switch-mode dc-dc converter: Average output dc
voltage V o depends on t on and t off. Switching is done at a
constant frequency with switching time period T s. This method is
called pulse-width modulation (PWM) in which the duty ratio D is
varied to control V o, where D=t on /T s
Slide 4
Control of DC-DC Converters (contd) The switch control signal,
which controls the on and off states of the switch, is generated by
comparing a signal level control voltage v control with a
repetitive waveform. The switching frequency is the frequency of
the sawtooth waveform with a constant peak. The duty ratio D can be
expressed as
Slide 5
Static dc switch based on a fully controlled semiconductor
power switch 5
Slide 6
Voltage and current waveforms in a static dc switch 6
Slide 7
SCR-based static dc switch with a resonant commutating circuit
7
Slide 8
Sub-circuit of an SCR-based static dc switch 8
Slide 9
Voltage and current waveforms in an SCR-based static dc switch
9
Slide 10
Step-down chopper: (a) block diagram, (b) equivalent circuit
for the dc output voltage and current 10
Slide 11
Equivalent circuits of the first- quadrant chopper: (a) state 1
(b) state 0 11
Slide 12
First-quadrant chopper 12
Slide 13
Example waveforms of output voltage and current in a first-
quadrant chopper 13
Slide 14
Single cycle of the output voltage and current in a first-
quadrant chopper 14
Slide 15
Current ripple in a chopper as a function of the magnitude
control ratio and switching frequency 15
Slide 16
Second-quadrant chopper 16
Slide 17
Equivalent circuits of a second- quadrant chopper: (a) state 1
(b) state 0 17
Slide 18
Waveforms of output voltage and current in a second- quadrant
chopper 18
Slide 19
First-and-second-quadrant chopper 19
Slide 20
Waveforms of output voltage and current in a first-and-
second-quadrant chopper 20
Slide 21
First-and-fourth-quadrant chopper 21
Slide 22
Equivalent circuits of a first-and- fourth-quadrant chopper
operating in the fourth-quadrant: (a) state 2 (b) state 0 22
Slide 23
Waveforms of output voltage and current in a first-and-
fourth-quadrant chopper 23
Slide 24
Four-quadrant chopper 24
Slide 25
25
Slide 26
Allowable ranges of the magnitude control ratio in step-down
choppers 26
Slide 27
Waveforms of the output voltage and input current in a step-up
chopper (d = 0.75) 27
Slide 28
Typical supply system of a chopper 28
Slide 29
dc drive with a chopper with a braking resistor 29