mohan

Ned Mohan, Amit Jain, Philip JoseUniversity of Minnesota

and

Raja AyyanarArizona State University

Teaching Utility Applications of

Power Electronics in a First

Course on Power Systems

2

Outline

Importance of teaching power electronics in a power systems course

Description of proposed approach consisting of four segments Functional aspects of power electronics Power device capabilities and Power Electronic

Structures Role of power electronics in utility applications Details of the power electronics structures

3

Control Center

Micro-Turbine Hospital Commercial

Building

Fuel Cell Smart House Performance

Building

Combined Heat and PowerPlant (CHP)FactoryCommercial BuildingHouseApartment Building

Wind Power Plants Village Commercial

Building

Central PowerStation Solar Power Plants

CHP House

Importance

Increasing applications of Power Electronic Equipment in Power Systems Availability of high power

semiconductor devices Decentralized renewable

energy generation sources Increased power transfer

with existing transmissionsystem

Effective control of power flow needed in a deregulated environment

Norms for Power quality Future Power System

4

Approach

Top Down approach consisting of four segments Function of power electronics as an interface, and the

listing of utility applications requiring power electronics interface (1 lecture)

Power device capabilities and the resulting structures of power electronic interfaces to exploit them (1 lecture)

Importance and the role of power electronic interfaces in various applications (2 lectures)

Discussion of power electronics interface in appropriate detail (3 lectures)

5

Segment 1: Function of Power Electronics in Utility Applications

Enabling technology providing interface between two (ac/dc) electrical systems

E.g. Interconnection of two asynchronous ac systems dc to ac conversion is required to connect fuel cells

or photovoltaics to the utility grid

Converter

Controller

Source Load

6

Segment 1: Listing of Power Electronic Applications

Distributed generation (DG) Renewable resources (wind and photovoltaic) Fuel cells and micro-turbines Storage: batteries, super-conducting magnetic energy

storage, flywheels

Power electronics loads: Adjustable speed drives Power quality solutions

Dual feeders Uninterruptible power supplies Dynamic voltage restorers

Transmission and distribution (T&D) High voltage dc (HVDC) and medium voltage dc Flexible AC Transmission Systems (FACTS): Shunt and

Series compensation, and the unified power flow controller

7

Segment 2: Power Device Capabilities & Resulting Power Electronic Structures

Power Semiconductor Devices and their Capabilities Polarity of voltage blocked and direction of current

conduction Switching speeds and power ratings

IGBT MOSFET

Thyristor IGCT

101 102 103 104

102

104

106

108

Thy

rist

or

IGBT

MOSFET

Pow

er (

VA

)

Switching Frequency (Hz)

IGCT

8

Segment 2: Structure of Power Electronic Systems

Voltage-Link Systems Transistors and diodes that

can block voltage of only one polarity

Current-Link Systems higher power bipolar voltage-

blocking capabilities of thyristors

Solid State Switches bidirectional voltage blocking

and current conduction

AC1 AC2

AC1 AC2

9

Segment 3: Role of Power Electronics in Important Utility Applications

Distributed Generation (DG) ApplicationsPower electronic interface depends on the source characteristics

AC

DC

DC

AC

Wound rotorInduction Generator

Generator-sideConverter

Grid-sideConverter

WindTurbine

IsolatedDC-DC

Converter

PWMConverter

Max. Power-point Tracker

Utility1f

Wind Power Generation with Doubly Fed Induction Motors

Photo-voltaics Interface

10

Segment 3: Role of Power Electronics in Important Utility Applications

Power Electronic Loads: Adjustable Speed Drives

Controller

Motor

Utility

Rectifier

Switch-modeConverter

11

Segment 3: Role of Power Electronics in Important Utility Applications

Power Quality Solutions for voltage distortion unbalances voltage sags and swells power outages

Load

Feeder 1

Feeder 2

Dual Feeders

Power ElectronicInterface

Load

Dynamic Voltage Restorers (DVR)

Uninterruptible Power Supplies

Rectifier Inverter FilterCriticalLoad

EnergyStorage

12

Segment 3: Role of Power Electronics in Important Utility Applications

Transmission and Distribution: DC Transmission most flexible solution for connection of two ac

systems

AC1 AC2

HVDC

AC1 AC2

MVDC

13

Segment 3: Role of Power Electronics in Important Utility Applications

Transmission and Distribution: Flexible AC Transmission Systems (FACTS)

1 2 sinE E

PX

1E

2E

3E

+- 3E1E 2E

Shuntconverter

Seriesconverter

I

Shunt and Series Compensation

Series Compensation

Shunt Compensation

Utility

STATCOM

jX

14

Segment 4: Discussion of Power Electronics Interface

Fundamental concepts for understanding the operation of the power electronic structures voltage-link systems current link systems solid state switches

15

Voltage-Link Systems

Unifying approach: Power-Pole Building Block building block of all

voltage-link systems

AC1 AC2

dAi

Av

Ai

dV

controlv1 or 0Aq

A sd T+

-

+

-

PWM

Voltageport Current

port

16

Voltage-Link Systems

Power conversion using Pulse Width Modulation (PWM) Power reversal with reversal of current direction

Averaged conversion

dAi

Av

Ai

dV

controlv1 or 0Aq

A sd T+

-

+

-

PWM

Voltageport Current

port

Av

t

dVAv

AsdT

sT

onA d A d

s

Tv V d V

T

17

Voltage-Link Systems

Averaged Representation of Power Pole Average quantities are of main interest

dAi

Av

Ai

dV

controlv

A sd T+

-

+

-

PWM

1: Ad

dAi

Av

Ai

dV

controlv1 or 0Aq

A sd T+

-

+

-

PWM

Voltage

portCurrent

port

( ) ( )A A dv t d t V

( ) ( ) ( )dA A Ai t d t i t

18

Voltage-Link Systems

Synthesis of AC voltages voltage to be synthesized

duty ratio needed

dc side current

Ai

t0

v

dV

dV

2

0 t

Av

I

( ) sin2d

AN

Vv t V t

1sin

2Ad d t

1( ) sin ( )

2

1 ˆsin sin( )2

1 ˆ cos sin( ) cos(2 )2

dA ai t d t i t

d t I t

I d t d t

19

Voltage-Link Systems

Implementation of bi-positional switch

AidV

+

-

Aq

Aq

1A Aq q

dAi

Av

Ai

dV

1 or 0Aq

A sd T+

-

+

-

20

Current-Link Systems

Exclusively thyristor based

One of (T1, T2, T3) and (T2, T4, T6)conduct at a time

Average dc voltage controlled by ‘firing angle’

Power flow reversed by reversing voltage polarity

AC1 AC2

3 2 3cosd LL c dV V L I

ai

bi

cidv

+

-

dI

1T

3T

5T

4T

6T

2T

cL

bL

aL

21

Solid State Switch

Can conduct current in both directions Turn-on or off in an ac circuit in one-half of a line-

frequency cycle

22

Conclusion

Teaching utility applications of power electronics in a power systems course is very important

A top down approach, starting with functional aspects and going to implementation details is suggested

Topics outlined in the four segment proposed structure will introduce students to future practices and technologies in power engineering

The proposed structure may be adapted based on individual preferences