ET3380 Principles and Methods of Electric Power Conversion David Morrisson MS,MBA Week 1

CONTENTS 1.Principles and Methods of Electric Power Conversion 2.Semiconductor Power Switches 3.Supplementary Components and Systems 4.AC-to-DC Converters 5.AC-to-AC Converters 6.DC-to-DC Converters 7.DC-to-AC Converters 8.Switching Power Supplies 9.Power Electronics and Clean Energy 2

Principles and Methods of Electric Power Conversion 3

The Power Grid From Generation to the Home

The Basics Every power grid in the U.S. has a few essential components. These components include the following: A source: the power plant A transmission system A hub: the substation A distribution system A user: the home or business 5

The Source: The Power Plant Essentially, there are only a few ways to generate AC electricity. For the vast majority of electricity in the U.S. a fuel (coal, natural gas, a nuclear reaction) is used to create electricity. In addition, solar, wind and hydroelectric methods are used to generate electricity. 6

The Heart: The Steam Turbine Once a fuel has created sufficient heat, steam is created. Pressure from the steam is used to rotate the steam turbine. The turbine has magnets attached to the end. These magnets rotate within coils, thus generating an AC signal. 7

8 Electrical Generation: Coal, Natural Gas, & Diesel

Relevant Links uclearplants.htmhttp:// uclearplants.htm om/learningpower/powerinfo_5.aspxhttp:// om/learningpower/powerinfo_5.aspx 9

Nuclear Generation 10

Transmission and Distribution Once produced, electricity must be distributed. The main device used to achieve this is the transformer. Transformers convert AC voltages. Step-up transformers convert from low to high voltages. Step-down transformers convert from high to low voltages. 11

Transmission and Distribution Power plant transformers step up voltages to reach substations and are sent at approximately 550kV. Once at the substation, transformers are used to step down voltages to approximately 13kV. These 13kV voltages are sent via distribution lines to your neighborhood home or business. Once in the neighborhood, transformers are used (on poles or set on the ground) to step down the electrical voltage to 120/

Transmission and Distribution From the power plant, via transmission lines to the substation. From the substation, via distribution lines to the home. All through the use of the transformer. 13

The Entire System 14

Power Electronics Power electronics is the application of electronic apparatus for the control and conversion of electric power. Also to design, control, computation and integration of nonlinear, time varying energy processing electronic systems The first high power electronic devices were mercury-arc tubes. In modern systems the conversion is performed with semiconductor switching devices such as diodes, thyristors and transistors

Mercury-arc Tube

Types of electric power conversion 17

Generic power converter 18

AC input voltage waveform 19

Output voltage and current waveforms in the generic rectifier 20

Output voltage and current waveforms in the generic inverter 21

Configurations of power electronic converters: (a) current-source (b) voltage-source 22

Total Harmonic Distortion, or THD Measurement of the harmonic distortion Defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. Measurement is most commonly defined as the ratio of the RMS amplitude of a set of higher harmonic frequencies to the RMS amplitude of the first harmonic, or fundamental Harmonic distortion adds overtones that are whole number multiples of a wave's frequencies

Decomposition of the output voltage waveform in the generic rectifier 24

Decomposition of the output voltage waveform in the generic inverter 25

Decomposition of the output current waveform in the generic inverter 26

Input current waveform and Its fundamental component in the generic inverter 27

Resistive control schemes: (a) rheostatic control, (b) potentiometric control 28

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Output voltage and current waveforms in the generic chopper 30

Output voltage and current waveforms in the generic chopper: switching frequency twice as high as in the previous figure 31

RL load circuit 32

Fragments of output voltage and current waveforms in a generic PWM ac voltage controller 33

Single-pulse diode rectifier 34

Output voltage and current waveforms in the single-pulse diode rectifier with an R load 35

Output voltage and current waveforms in the single-pulse diode rectifier with an RL load 36

Single-pulse diode rectifier with a free-wheeling diode 37 What are the possible types of loads and what are the effects of each?

Output voltage and current waveforms in the single-pulse diode rectifier with a freewheeling diode and an RL load 38

Single-pulse diode rectifier with an output capacitor 39

Output voltage and current waveforms in the single-pulse diode rectifier with an output capacitor and an RL load 40

Two-pulse diode rectifier 41

Cycloconverter 42

Timing diagram of switches in the generic cycloconverter 43

Output voltage waveform in the generic cycloconverter 44

Cycloconverter for three- phase alternating current 45

Block diagram of a dc power supply. Rectifier Circuits

Half-wave Rectifier

Input and output waveforms. Rectifier Circuits Full-wave rectifier utilizing a transformer with a center-tapped secondary winding

Input and output waveforms. Rectifier Circuits Bridge Rectifier PIV = V s V DO 

Voltage and current waveforms in the peak rectifier circuit with CR  T. The diode is assumed ideal. Rectifier Circuits With A Filter Capacitor

Rectifier Circuits Diode – Applications

52 Pulse-width Modulation

53 Pulse-width modulation (PWM) is a modulation technique that controls the width of the pulse based on modulator signal. Main use is to allow the control of the power supplied to electrical devices. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load. The PWM switching frequency has to be much higher than what would affect the load (the device that uses the power. Typically switching has to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies.

54 The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on and power is being transferred to the load, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.

Chapter 155 Pulse Width Modulated Step- Down Converter Circuit Schematic

Output voltage and current waveforms in the generic PWM rectifier 56

Output voltage and current waveforms in a (a) generic PWM rectifier (b) generic PWM ac voltage controller 57

Control characteristics of (a) generic PWM rectifier (b) generic PWM ac voltage controller 58

Harmonic spectra of output voltage in (a) generic PWM rectifier (b) generic PWM ac voltage controller (N = 24) 59

Output voltage and current waveforms in the generic PWM inverter (a) M = 1 (b) M =