Principles of Electric Machines and Power Electronicsli/slides/ch10 SLi.pdf• Switch mode power supply —Auto mobile electronics —Motor drive control circuits —computers —Chargers

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Power Converters, Renewable Energy, Smart Grid

Third Edition

P. C. Sen

Principles of Electric Machines

and

Power Electronics


Main contents

• Power ConvertersDC-DC

AC-DC

DC-AC

• Alternative energy

• Smart grid


• Controlled switch switches at fix frequency and duty ratio D

• For buck converter(step down converter): 𝑉𝑜𝑢𝑡

𝑉𝑖𝑛= 𝐷

• Current paths when switch is on and off

• Inductor current and output voltage

DC-DC converter- topology

Buck converter


• Switch mode power supply—Auto mobile electronics

—Motor drive control circuits

— computers

—Chargers

• Common voltage levels— 400V to 15V

—15V to 5V

—24V to 12V

—15V to 3V

DC-DC converter - Application


• Bridge rectifier is the simplest AC-DC circuit

• For positive half cycle, D1 and D2 conduct

• For negative half cycle, D3 and D4 conduct

AC-DC converter- topology


• The primary application of rectifiers is to derive DC power from an AC supply (AC to DC converter).

• Virtually all electronic devices require DC, so rectifiers are used inside the power supplies of virtually all consumer electronic devices.

• AC-DC converter is the first stage, DC-DC converter is the second stage

AC-DC converter- application


• Phase leg: Two switches connected in between DC bus voltage

• 2 phase legs for single phase load, 3 phase legs for 3 phase load

• Sinusoidal pulse width modulation

• Output voltage is fundamental frequency plus switching frequency

• Output current is usually sinusoidal

Inverter - topology


Introduction to Renewable energy

Nonrenewable sources: Fossil fuels: coal, oil, gas----limit, pollution…

Nuclear energy: safety issue

Renewable sources Hydroelectric: falling water turns turbines connected to generator

Solar: solar energy to electric energy

Wind: kinetic energy to mechanical energy to electric energy

Waves, tides, geothermal heat, Bio energy

Application ways

o Grid-connected

o Off-grid


Basics of solar energy (Wikipedia)

Solar cell: an electrical device that converts the energy of light into

electricity by photovoltaic effect—a physical and chemical phenomenon

Typical voltage: ~0.5V


Basics of solar energy (Wikipedia) Photovoltaic (PV) module Packaged assembly of typically 6x10 cell (series)

DC output voltage: e.g., 18V~45V

100~365W

Sunlight conversion rate: typical 20%

PV system One or multiple PV panels

Solar inverter

Battery

Solar tracer

Interconnection wiring

Life-time of solar moduleWithstand rain, hail, heavy snow load, cycles of

heat and cold

Electrical production for 10 ys at 90% rated power

25 years at 80%

Mono: 270W


Solar energy : cost and market


Wind energyMuch higher power capacity than solar energy

Denmark: 50% by 2030

US: 30% by 2030

Minority : stand-alone operation

Majority: grid-connected operation

Components of wind power systems


Grid-connected wind farmGenerator outputs 690V

Transformer increases 690V to 35 kV

Multiple wind turbines in parallel

Substation further step up by transformer to 230 kV


Wind Energy Conversion System -1

Squirrel-cage induction generator

Generator speed variation is very small

Wind turbine speed is adjusted through gear box and blade angle

MPP at rated wind speed. At other wind speeds, energy conversion is low.

Disadvantages: gear box, low efficiency at low speeds, power fluctuation

Advantages: simple, robust, inexpensive, reliable

Low-power and medium power application


Wind Energy Conversion System - 2 Wound rotor induction generator (WRIG)

Power converter is used to vary rotor resistance

Wind turbine speed is adjusted through gear box, blade angle

Motor efficiency can be adjusted using external resistor

Loss in external rotor resistance

Low- and medium- power


Wind Energy Conversion System - 3 Full capacity back-to-back AC-DC-AC power converters

Full speed range due to decoupled generator connection from grid

High power

Maximum power point tracking (MPPT) at different speeds


Smart GridDefinition: an electrical grid (Wikipedia) has: Two way communication technology through power lines

Smart meters, monitors

Smart appliances

Renewable energy resources

http://www.slideshare.net/RommuelP/rommuel-paragas-presentation-v3


Smart Grid

Benefits (https://www.smartgrid.gov/the_smart_grid/smart_grid.html)

More efficient transmission of electricity

Quicker restoration of electricity after power disturbances

Reduced operations and management cost

Reduced peak demand

Increased integration of large-scale renewable energy systems

Better integration of customer-owner generation systems

Improved security


Example 1 Magnetic circuit

Determine the flux density in the air gap of the magnetic circuit

shown below. The cross sectional area of all branches is 10 cm2

and 𝜇𝑟=50.


Example 2 - transformer

A single-phase 10kVA, 2200/220, 60 Hz transformer:

No-load test (HV winding open, VL = VL,rated = 220 V) IL =2.5A,PL =100W

Short-circuit test (LV winding shorted, IH = IH,rated = 4.55 A) VH =150V,PH =215W

(a.) Determine the approximate equivalent circuit parameters from the test data

(use the approximate equivalent circuit that includes core losses). Draw the

equivalent circuit for this transformer referred to the LV side.

(b.) Draw the equivalent circuit for this transformer referred to the HV side.

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Principles of Electric Machines and Power Electronicsli/slides/ch10 SLi.pdf• Switch mode power supply —Auto mobile electronics —Motor drive control circuits —computers —Chargers