1. Teaching Utility Applications of
Power Electronics in a First
Course on Power Systems
Ned Mohan, Amit Jain, Philip Jose
University of Minnesota
and
Raja Ayyanar
Arizona State University

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
2

3. Importance
Increasing applications of Power Electronic
Equipment in Power Systems
Availability of high power Control Center
semiconductor devices Central Power
Solar Power Plants
Station
Decentralized renewable  CHP House
energy generation sources Combined Heat and Power Wind Power Plants
Plant (CHP)  Village
Increased power transfer Factory  Commercial
with existing transmission Commercial Building
House
Building
system Apartment Building
Micro-Turbine
Effective control of power Fuel Cell  Hospital
 Commercial
 Smart House
flow needed in a  Performance Building
deregulated environment Building
Norms for Power quality
Future Power System
3

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)
4

5. Segment 1: Function of Power
Electronics in Utility Applications
Converter
Source Load
Controller
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
5

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
6
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
108
Thyristor
Power (VA)
IGCT
106
Thyristor IGCT IGBT
104
102 MOSFET
101 102 103 104
IGBT MOSFET Switching Frequency (Hz)
7

8. Segment 2: Structure of Power
Electronic Systems
Voltage-Link Systems
Transistors and diodes that
can block voltage of only
one polarity AC1 AC2
Current-Link Systems
higher power bipolar voltage- AC1 AC2
blocking capabilities of thyristors
Solid State Switches
bidirectional voltage blocking
and current conduction
8

9. Segment 3: Role of Power Electronics in
Important Utility Applications
Distributed Generation (DG) Applications
Power electronic interface depends on the source
characteristics
Wound rotor
Induction Generator
Isolated
PWM
DC-DC
Converter
Converter
AC DC
Wind Utility
Turbine DC AC 1f
Max. Power-
Generator-side Grid-side point Tracker
Converter Converter
Wind Power Generation with Photo-voltaics Interface
Doubly Fed Induction Motors
9

10. Segment 3: Role of Power Electronics in
Important Utility Applications
Power Electronic Loads: Adjustable Speed Drives
Switch-mode
Utility Converter
Motor
Rectifier
Controller
10

11. Segment 3: Role of Power Electronics in
Important Utility Applications
Power Quality Solutions for
voltage distortion
unbalances Power Electronic Load
Interface
voltage sags and swells
power outages
Dynamic Voltage Restorers (DVR)
Feeder 1 Critical
Rectifier Inverter Filter
Load
Load
Energy
Feeder 2 Storage
Dual Feeders Uninterruptible Power Supplies
11

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 AC1 AC2
HVDC MVDC
12

13. Segment 3: Role of Power Electronics in
Important Utility Applications
Transmission and Distribution: Flexible AC E1 E2
P= sin δ
Transmission Systems (FACTS) X
Series Compensation
E2
E3
E1
E1 E3 E2
I - +
jX
Utility
STATCOM Series
Shunt
converter
converter
Shunt Compensation Shunt and Series Compensation 13

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
14

15. Voltage-Link Systems
Unifying approach: Power-Pole Building Block
building block of all
voltage-link systems
AC1 AC2
idA
+ iA
d A Ts
Voltage
Vd
port + Current
vA
- - port
q A = 1 or 0
vcontrol
PWM
15

16. Voltage-Link Systems
Power conversion using Pulse Width Modulation (PWM)
Power reversal with reversal of current direction
idA
+ iA
d A Ts
Voltage vA Vd
Vd vA
port + Current
vA t
port d ATs
- -
Ts
q A = 1 or 0
vcontrol
PWM
Ton
Averaged conversion vA = Vd = d AVd
Ts
16

17. Voltage-Link Systems
Averaged Representation of Power Pole
Average quantities are of main interest
idA idA
+ iA + iA
d A Ts d A Ts
Vd
Voltag
Vd +
e +
Current
vA vA
- port - port - -
q A = 1 or 0 1: d A
vcontrol
PWM vcontrol
PWM
v A (t ) = d A (t ) × d
V
idA (t ) = d A (t ) ×iA (t )
17

18. Voltage-Link Systems
Synthesis of AC voltages
vA
voltage to be synthesized Vd
Vd ¶
v AN (t ) = + ∆V sin ω t Vd ¶
∆v
2 2
duty ratio needed
0 ωt
1 ¶ iA
d A = + ∆d sin ω t
2 $
I
0 ωt
dc side current
1 ¶  φ
i dA (t ) =  + ∆d sin ω t ÷× a (t )
i
 2 
1 ¶  ˆ
=  + ∆d sin ω t ÷×I sin(ω t − φ )
2 
2
{
1ˆ ¶ ¶
}
= I ∆d cos φ + sin(ω t − φ ) − ∆d cos(2ω t − φ )
18

19. Voltage-Link Systems
Implementation of bi-positional switch
idA
+ qA
d A Ts iA +
iA
Vd
Vd -
+
vA
- - q′
A
q A = 1 or 0
q′ =1 −q A
A
19

20. Current-Link Systems
Exclusively thyristor based
AC1 AC2
T1
One of (T1, T2, T3) and (T2, T4, T6) T3
conduct at a time T5 +
ia
Average dc voltage controlled
by ‘firing angle’ La ib
vd Id
Lb
3 2 3 ic
Vd = VLL cos α − ω Lc I d
π π Lc T4
-
Power flow reversed by reversing T6
voltage polarity T2
20

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
21

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
22