PGT 320 Chapter 5 AC VOLTAGE CONTROLLERS converting
- Slides: 28
PGT 320 Chapter 5 AC VOLTAGE CONTROLLERS (converting ac to ac) Prepared by: Khairul Affendi Rosli, Msc Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
AC VOLTAGE CONTROLLERS Ac to ac Converters q INTRODUCTION q SINGLE-PHASE VOLTAGE CONTROLLERS q THREE-PHASE VOLTAGE CONTROLLERS q INDUCTION MOTOR SPEED CONTROL q STATIC VAR CONTROL Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
INTRODUCTION • AC VOLTAGE CONTROLLER……. …is a converter that controls the voltage, current and average power delivered to an AC load from an AC source. • Electronics switches connect and disconnect the source and the load at regular intervals. • Two typical switching scheme: • Phase control, switching takes place during every cycle of the source, in effect removing some of the source waveform before it reaches the load. • Integral-cycle control, whereby the source is connected and disconnected for several cycles at a time. • The phase-controlled ac voltage controller has several practical uses including light-dimmer circuits and speed control of induction motors. The input voltage source is ac, and the output is ac (although not sinusoidal), so the circuit is classified as an ac-ac converter. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 1 THE SINGLE-PHASE AC VOLTAGE CONTROLLER Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 1 THE SINGLE-PHASE AC VOLTAGE CONTROLLER Basic Operation • A basic single-phase voltage controller is shown in Fig. 51 a. The electronic switches are shown as parallel thyristors (SCRs). This SCR arrangement makes it possible to have current in either direction in the load. This SCR connection is called antiparallel or inverse parallel because the SCRs carry current in opposite directions. A triac is equivalent to the antiparallel SCRs. Other controlled switching devices can be used instead of SCRs. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 1 THE SINGLE-PHASE AC VOLTAGE CONTROLLER The principle of operation for a single-phase ac voltage controller using phase control is quite similar to that of the controlled halfwave rectifier of Sec. 3. 9. Here, load current contains both positive and negative half-cycles. An analysis identical to that done for the controlled half-wave rectifier can be done on a half cycle for the voltage controller. Then, by symmetry, the result can be extrapolated to describe the operation for the entire period. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 1 THE SINGLE-PHASE AC VOLTAGE CONTROLLER Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
RMS OUTPUT VOLTAGE Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Power Factor & Iscr Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 2 OUTPUT VOLTAGE VS. DELAY ANGLE Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 3 HARMONIC AMPLITUDES VS. DELAY ANGLE Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 4 SINGLE-PHASE CONTROLLER WITH AN R-L LOAD Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
The load current in each half cycle is the same as for a controlled half-wave rectifier: Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 6 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 7 a-b THREE-PHASE VOLTAGE CONTROLLERS Y-Connected Resistive Load Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
van for 0 < α < 60° (α = 30° shown) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 7 c Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 7 d-e van for 60° < α < 90° (α = 75° shown) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
van for 90° < α < 150° (α = 120° shown) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 8 OUTPUT VOLTAGE VS. DELAY ANGLE Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 9 Y-Connected R-L Load Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 10 Delta-Connected Resistive Load Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 11 INDUCTION MOTOR SPEED CONTROL Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5. 12 STATIC VAR CONTROL Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
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