ECE 1750 Power Electronics Conversion Theory

W k 1Week 1

Power Electronics

• ECE 1750 - Power Electronics Conversion TheoryTuesdays and Thursdays from 2:30 pm to 3:45 pmTuesdays and Thursdays from 2:30 pm to 3:45 pm

Professor: Alexis Kwasinski (Benedum Hall 1229 akwasins@pitt edu Ph:Professor: Alexis Kwasinski (Benedum Hall 1229, akwasins@pitt.edu, Ph: 412-383-6744).

Course Home Page: http://www pitt edu/~akwasins/ECE1750Spr18 htmlCourse Home Page: http://www.pitt.edu/ akwasins/ECE1750Spr18.html

Office Hours: Tuesdays and Thursdays from 1:00 pm to 2:30 pm, or by appointment.pp

TAs: Thibaut Harzig (Benedum Hall 816, THH39@pitt.edu), office hours: Mondays from 10:00 am to 12:00 pm).

Prerequisites: ECE 0257 or COE 0257 and ECE 1552.

Power Electronics• Grading:• Homework: 25 %• Midterm Exam #1: 25 %• Midterm Exam #2: 25 %Midterm Exam #2: 25 %• Final Exam: 25 %

• Letter grades assignment: Grades will be assigned based on the following scale:• A+ (grade > 97%), • A (97% ≥ grade ≥ 92%), • A- (92% > grade ≥ 87%), • B+ (87% > grade ≥ 82%),B (87% grade ≥ 82%),• B (82% > grade ≥ 77%),• B- (77% > grade ≥ 72%),• C+ (72% > grade ≥ 67%),

C (67% > d ≥ 62%)• C (67% > grade ≥ 62%),• C- (62% > grade ≥ 57%),• D+ (57% > grade ≥ 52%),• D (52% > grade ≥ 47%),( g ),• D- (47% > grade ≥ 40%),• F (40% > grade),

• Homework:

Power Electronics• Homework:

• Homework will be assigned usually every week on Thursday and will usually (but not always) be due the immediately following Thursday in class. No late submissions will be accepted after the corresponding due day.submissions will be accepted after the corresponding due day.

• Two Midterms: • Topics included in each of these exams are indicated in the class schedule. One 8½ x 11” sheet of notes (both sides) is permitted.

• Final exam:Th f t f th fi l ill b d d i th t• The format of the final exam will be announced during the semester.

Possibilities include, but are not limited to, a take home exam or a comprehensive exam to which you can bring an 8½ x 11” sheet of notes in addition to those prepared for the midtermsaddition to those prepared for the midterms.

• Missing exams make-up:• There are no make-up exams except on well justified reasons. Hence, p p j ,accepting a reason for missing an exam as a valid one is at the sole discretion of the professor and each request for a make-up exam will be treated on a case-by-case basis.

(date indicates the Monday of the corresponding week)

Power Electronics(date indicates the Monday of the corresponding week)

• Week 1 (Jan. 8) Introduction. Course description and overview

•Week 2 (Jan 15)Basic circuit components Resistors capacitors indictors and•Week 2 (Jan. 15)Basic circuit components. Resistors, capacitors, indictors and power electronic switches.

•Week 3 (Jan. 22)Waveforms, power and energy, power electronic circuits analysis and performance metrics.

•Week 4 (Jan. 29) ac to dc power conversion: Rectifiers

W k 5 (J 5) d t d i C t•Week 5 (Jan. 5) dc to dc power conversion: Converters

•Week 6 (Feb. 12) dc to dc power conversion: Converters

•Week 7 (Feb 19) dc to dc power conversion: Converters•Week 7 (Feb. 19) dc to dc power conversion: Convertersdc to ac power conversion: Inverters

•Week 8 (Feb. 26) dc to ac power conversion: Inverters1st Midterm on Thursday (up to and including dc-dc converters)

Power Electronics

• Week 9 (March 5) Spring Recess.

•Week 10 (March 12) dc to ac power conversion: Inverters•Week 10 (March 12) dc to ac power conversion: Invertersac to ac power conversion: example based on a light dimmer

•Week 11 (March 19) Fundamentals of controlsWeek 11 (March 19) Fundamentals of controls

•Week 12 (March 26) Application of power electronics in photovoltaic systems.

•Week 13 (April 2) Application of power electronics in photovoltaic systems.Application of power electronics in motor drives.

•Week 14 (April 9) Application of power electronics in motor drives.2nd Midterm on Thursday

W k 15 (A il 16) R li bl d i•Week 15 (April 16) Reliable design

Power ElectronicsS h t i l t i ?So what is power electronics?:

• Power electronics involves the study of electronic systems, circuits and components to control the flow of electrical energy.

• Power electronic circuits involve the study of:Power electronic circuits involve the study of:• Circuits• Controls

D i• Devices• Systems

Power Electronics

• Applications:Low power (few Watts) to very high power (MWatts)- Low power (few Watts) to very high power (MWatts).

- Static energy conversion and electromechanical energyconversion.

• Industries (few examples):- IT and communications- Renewable and alternative energy- Utilities- AutomotiveAutomotive- Consumer electronics

Power electronics basic concepts

• Types of interfaces:• dc-dc: dc-dc converter• ac-dc: rectifier

d i t• dc-ac: inverter• ac-ac: cycloconverter (used less often)

• Power electronic converters components:• Power electronic converters components:• Semiconductor switches:

• Diodes• MOSFETsMOSFETs• IGBTs• SCRs

• Energy storage elements

Diode MOSFETgy g

• Inductors• Capacitors

• Other components:SCR• Transformer

• Control circuitIGBT SCR

Q ti Wh t l t i d i ?

Power Electronic switches•Question: What are power electronic devices?

•Answer: Fast switches that can handle high voltages and currents

• Question: Why do we need these fast switches?

•Answer: To efficiently convert AC to DC, DC to DC, or DC to AC, or toAnswer: To efficiently convert AC to DC, DC to DC, or DC to AC, or to efficiently control average power flow. (Efficiently usually means greater than 80% – 90%)

Rugged, reliable, efficient, long lived, but not very fast

Power Electronic switches

The ideal power electronic device is a perfect switch that• is fast − can open and close instantly (thus no switching losses), and at

a high rate (i e operating frequency)a high rate (i.e., operating frequency)

• when closed, can conduct any amount of current with no internal voltage drop (thus no conduction losses)

• when open, will conduct no current and can withstand any voltage without breakdown

• will be unidirectional or asymmetric (that is an inherent property of power electronic devices, and we can always place two switches in antiparalleland use blocking diodes to prevent backward conduction)

Power electronics basic concepts

• Energy storage• When analyzing the circuit, the state of each energy storage element contributes to the overall system’s state. Hence, there is one state variable

i t d t h t l tassociated to each energy storage element.

• In an electric circuit, energy is stored in two fields:• Electric fields (created by charges or variable magnetic fields and• Electric fields (created by charges or variable magnetic fields and related with a voltage difference between two points in the space)• Magnetic fields (created by magnetic dipoles or electric currents)

• Energy storage elements:• Capacitors: Inductors:

CL

C

• dc-dc converters

Power electronics basic concepts• dc-dc converters

• Buck converter

oV DE

E• Boost converter

1oEV

D

DEV

• Buck-boost converter

1oVD

Power electronics basic concepts

• Rectifiers

vv

t

v v

ttt

R tifi FiltRectifier Filter

Power electronics basic concepts

• Inverters

• dc to ac conversionS l t l t h i Th i l t t h i i• Several control techniques. The simplest technique is square wave

modulation (seen below).•The most widespread control technique is Pulse-Width-Modulation (PWM).

Power electronics basic concepts

• Inverters

• dc to ac conversionS l t l t h i Th i l t t h i i• Several control techniques. The simplest technique is square wave

modulation (seen below).•The most widespread control technique is Pulse-Width-Modulation (PWM).

Power electronics basic concepts

• Inverters

• dc to ac conversionS l t l t h i Th i l t t h i i• Several control techniques. The simplest technique is square wave

modulation (seen below).•The most widespread control technique is Pulse-Width-Modulation (PWM).

P A li ti Adj t bl Fl t

Power Electronics - Applications

Pump Application: Adjustable Flow rate

Bad news – inefficient!

Equivalent to reducing the output voltage of a DBR with a series resistor

P b k iPayback in energy savings is about 1 year

Fi d dj t bl d d i• Fixed versus adjustable speed drive

Source: Ned Mohan’s power electronics book

Power Electronics - Applications

Improving Energy Efficiency of Heat Pumps

How does inserting an adjustable speed drive save energy in single-h li ti ?phase applications?

Some losses

But a three-phase motor is 95% efficient, compared to 80% efficiency for a single-phase motorSome losses efficiency for a single phase motor

• Used in one out of three new homes in the U.S.Source: Ned Mohan’s power electronics book

Ai diti L A i t d ith ON/OFF C li

Power Electronics - Applications

Air conditioners: Loss Associated with ON/OFF Cycling

The big efficiency gain is here

• with conventional air conditioners, the first few minutes after start-up are very inefficient as the mechanical system reaches steady-state

i h ASD h i di i d i l d i h• with ASDs, the air conditioner speed is lowered with demand, so that there are fewer start-ups each day

Th t ffi i i i d b 30 t• The system efficiency is improved by ~30 percentSource: Ned Mohan’s power electronics book

HomesPower Electronics - Applications

Homes• Most modern loads at homes, such as computers and TVs, are powered through power electronic circuits

WIND GENERATOR

p g p• Other applications in homes: solar power, wind power, electric vehicles.

PV MODULESGENERATOR

MAIN DC BUSLED LIGHTS (DC)

ENERGY STORAGE

REFRIGERATOR (LOAD)

FUEL CELLAIR CONDITIONER EPA 430-F-97-028 ELECTRIC

VEHICLE

Power Electronics - Applications

• Grid-tied systems (inverter on PV side)

Photovoltaic (PV) systems (solar power)

y ( )

• Most widely used PV integration approach• Most widely used PV integration approach.• PV and home operation subject to grid operation: Due to IEEE 1547, the inverter cannot power the home when the grid is not present.

P El i H M d Wi d F

Power Electronics - Applications

Power Electronics Has Made Wind Farms Possible

Th h i d t bThe choices used to be

• Use an efficient induction generator,which has very poor power factor, ory p p

• use a synchronous generator,but constantly fight to synchronizethe turbine speed with the gridthe turbine speed with the grid.

Now,

• Either use a DC bus and inverter to decouple the generator and grid AC busses, or

Use a doubly fed induction motor operate the wind turbine at• Use a doubly-fed induction motor, operate the wind turbine at the max power speed, and use power electronics to “trick” the wind generator into producing grid-frequency output.

Power Electronics - Applications

P El i h l dPower Electronics has also made transportation electrification possible

• Power electronics are used for battery chargers and for driving electric motors in electric or hybrid electric vehicles.