Transcript Class notes
ECE 1750 Power Electronics Conversion Theory Week 0 Power Electronics • ECE 1750 - Power Electronics Conversion Theory Tuesdays and Thursdays from 2:30 pm to 3:45 pm Professor: Alexis Kwasinski (Benedum Hall 1229, [email protected], Ph: 412-383-6744). Course Home Page: http://www.pitt.edu/~akwasins/ECE1750Spr17.html Office Hours: Mondays from 3 pm to 5 pm and Tuesdays from 1:30 pm to 2:30 pm, or by appointment. TAs: Joseph Petti ([email protected]), office hours: Tuesdays and Thursdays from 11:00 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 % • 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 (82% > grade ≥ 77%), • B- (77% > grade ≥ 72%), • C+ (72% > grade ≥ 67%), • C (67% > grade ≥ 62%), • C- (62% > grade ≥ 57%), • D+ (57% > grade ≥ 52%), • D (52% > grade ≥ 47%), • D- (47% > grade ≥ 40%), • F (40% > grade), 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. • 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: • 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 midterms. • Missing exams make-up: • There are no make-up exams except on well justified reasons. Hence, 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-bycase basis. Power Electronics (date indicates the Monday of the corresponding week) • Week 0 (Jan. 2) Introduction. Course description and overview • Week 1 (Jan. 9) Basic circuit components. Resistors, capacitors, indictors and power electronic switches. •Week 2 (Jan. 16) Waveforms, power and energy, power electronic circuits analysis and performance metrics. • Week 3 (Jan. 23) ac to dc power conversion: Rectifiers • Week 4 (Jan. 30) dc to dc power conversion: Converters • Week 5 (Feb. 6) dc to dc power conversion: Converters • Week 6 (Feb. 13) dc to dc power conversion: Converters dc to ac power conversion: Inverters • Week 7 (Feb. 20): dc to ac power conversion: Inverters 1st Midterm on Thursday (up to and including dc-dc converters) Power Electronics • Week 8 (Feb. 27): dc to ac power conversion: Inverters ac to ac power conversion: example based on a light dimmer • Week 9 (March 6): Spring Recess. • Week 10 (March 13): Fundamentals of controls • Week 11 (March 20): Application of power electronics in photovoltaic applications. •Week 12 (March 27): Application of power electronics in photovoltaic applications. Application of power electronics in motor drives. •Week 13 (April 3): Application of power electronics in motor drives. •Week 14 (April 10): Reliable design 2nd Midterm on Thursday •Week 15 (April 17) Thermal design Power Electronics 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: • Circuits • Controls • Devices • Systems Power Electronics • Applications: - Low power (few Watts) to very high power (MWatts). - Static energy conversion and electromechanical energy conversion. • Industries (few examples): - IT and communications - Renewable and alternative energy - Utilities - Automotive - Consumer electronics Power electronics basic concepts • Types of interfaces: • dc-dc: dc-dc converter • ac-dc: rectifier • dc-ac: inverter • ac-ac: cycloconverter (used less often) • Power electronic converters components: • Semiconductor switches: • Diodes • MOSFETs • IGBTs Diode • SCRs • Energy storage elements • Inductors • Capacitors • Other components: • Transformer IGBT • Control circuit MOSFET SCR 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 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) • 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 antiparallel and 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 associated 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 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: L C Power electronics basic concepts • dc-dc converters • Buck converter Vo DE • Boost converter E Vo 1 D • Buck-boost converter DE Vo 1 D Power electronics basic concepts • Rectifiers v v v t t Rectifier Filter t Power electronics basic concepts • Inverters • dc to ac conversion • 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 conversion • 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 conversion • Several control techniques. The simplest technique is square wave modulation (seen below). •The most widespread control technique is Pulse-Width-Modulation (PWM). Power Electronics - Applications Pump Application: Adjustable Flow rate Bad news – inefficient! Equivalent to reducing the output voltage of a DBR with a series resistor Payback in energy savings is about 1 year • 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 singlephase applications? But a three-phase motor is 95% efficient, compared to 80% Some 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 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 • with ASDs, the air conditioner speed is lowered with demand, so that there are fewer start-ups each day • The system efficiency is improved by ~30 percent Source: Ned Mohan’s power electronics book Power Electronics - Applications Homes • Most modern loads at homes, such as computers and TVs, are powered through power electronic circuits • Other applications in homes: solar power, wind power, electric vehicles. WIND GENERATOR PV MODULES LED LIGHTS (DC) MAIN DC BUS REFRIGERATOR (LOAD) ENERGY STORAGE ELECTRIC VEHICLE AIR CONDITIONER FUEL CELL EPA 430-F-97-028 Power Electronics - Applications Photovoltaic (PV) systems (solar power) • Grid-tied systems (inverter on PV side) • 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. Power Electronics - Applications Power Electronics Has Made Wind Farms Possible The choices used to be • Use an efficient induction generator, which has very poor power factor, or • use a synchronous generator, but constantly fight to synchronize the 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 the max power speed, and use power electronics to “trick” the wind generator into producing grid-frequency output. Power Electronics - Applications Power 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.