Development and Application of
Virtual Power System Technology
Matthew Armstrong
School of Electrical, Electronic & Computer
Engineering
Matthew Armstrong
Presentation Contents
¾ Introduction to the Virtual Power System Concept
¾ Application areas of Virtual Power System
¾ Virtual Power System Developments at Newcastle University
¾ Summary
Matthew Armstrong
Virtual Power System Concept
What is the Virtual Power System?
¾ A real time, real power level emulation tool, designed to behave exactly
like a real power system.
¾ A fully controllable set of power electronics, which can be configured to
behave like an actual electrical power system. For example, an electrical
machine, a wind turbine, a fuel cell, or fully controllable voltage source.
¾ Based on an earlier concept developed at Newcastle University – The
Virtual Machine
Matthew Armstrong
Virtual Power System Concept
What is the Virtual Machine?
Take a conventional electric drive system:
Main components:
- Power electronic inverter.
- Electrical machine.
Consider the test procedure for a power electronic inverter manufacturer:
Problem 1: To fully test inverter, a full range of machines may be required.
¾ Costly, storage issues, down time during machine changeover
Problem 2: Safety concerns
¾ Motor is a mechanically moving component of the system.
Matthew Armstrong
Virtual Power System Concept
How does the Virtual Machine work?
¾ The Virtual Machine directly replaces
the actual motor.
¾ The Virtual Machine contains a real
time model of the motor. This is
programmed into a DSP and typically
sits alongside the control software.
¾ The model controls the Virtual
Machine power electronic hardware in
real time to behave in the same way as
the motor.
¾The inverter under test ‘believes’ it is
still connected to the motor. However,
it is actually connected to the Virtual
Machine.
Matthew Armstrong
INVERTER UNDER TEST
Hz
GRID
A
Virtual Power System Concept
Advantages of the Virtual Machine
¾ Flexibility. It can run any model
the user wants.
¾ Saves on space. No need for
multiple pieces of test kit. Lowers
maintenance cost.
¾ Very little down time. Emulated
machine can be changed in software.
¾ Safety Aspects. No mechanically
moving parts.
¾ Why limit the concept to machines?
The idea is applicable to any power
system Æ Virtual Power System (VPS)
Matthew Armstrong
INVERTER UNDER TEST
Hz
GRID
A
Virtual Power System Concept
Motor/ Generator Sets
(Virtual Machine)
Wind Turbine Systems
Virtual
Power
System
?
Network Emulation – Grid
Connected Applications
Matthew Armstrong
New and Novel
Applications
Application of Virtual Power System
Example 1: Wind turbine systems
Induction
Generator
Stator
Gear
box
Grid
Rotor
Inverter Under Test
Converter
Converter
AC
DC
DC
AC
Control
Application of VPS
Benefit
Emulation of Doubly Fed
Induction Generator
No need for real wind turbine
to be present Æ lab testing
Emulation of mechanical
elements - gear box etc
Repeatable testing:
programme with test data
Matthew Armstrong
Application of Virtual Power System
Example 2: Grid connected photovoltaic inverters
Application of VPS
Benefits
Emulation of Solar Array
24 hour testing.
Emulation of Supply Network
Repeatable tests – standardisation.
Fault conditions can be explored
Matthew Armstrong
Development of Virtual Power System
Newcastle University & NaREC*
Virtual
Power
System
System 1: Current Sink/Source
Motor/ Generator Sets
(Virtual Machine)
Wind Turbine Systems
Matthew Armstrong
System 2: Voltage Source
Network Emulation
Grid Connected Inverter
Applications
*The New and Renewable Energy Centre, Blyth, England, UK
Development of Virtual Power System
Five components to consider:
VPS power electronic
converter. Conventional three
phase inverter technology
Hz
VPS inductors.
To allow continuous current
flow between inverter systems
Current and voltage
measurement equipment.
VPS microprocessor
system.
High speed microprocessor
technology
Inverter Under Test.
Matthew Armstrong
VIRTUAL POWER SYSTEM
INVERTER
UNDER TEST
A
Power Electronic
Inverter
GRID
Voltage
Measure
DSP
Current
Measure
Power
System
Model
Current
Control
Development of Virtual Power System
VPS Power Electronic Converter system
4–quadrant commercial
drive system.
Two back-to-back 145kW
Control Techniques drive
units. Drive system rated
to 200A rms.
Challenge:
Higher power Æ Slower
switching semiconductors:
14kHz @ 15kW
3kHz @ 145kW
Matthew Armstrong
Development of Virtual Power System
VPS Power Electronic Converter system
¾ Front end inverter
modified for external DSP
control.
¾ Converter keeps
responsibility for system
monitoring, protection and
PWM signal generation.
¾ Custom interface, fibre
optic link:
- Galvanic isolation.
- Noise immunity.
Matthew Armstrong
Development of Virtual Power System
VPS Power Electronic Converter system
¾ Front end inverter
modified for external DSP
control.
¾ Converter keeps
responsibility for system
monitoring, protection and
PWM signal generation.
¾ Custom interface, fibre
optic link:
- Galvanic isolation.
- Noise immunity.
Matthew Armstrong
Development of Virtual Power System
VPS Inductors
Required to ensure continuous current
flows between the power electronic
systems
3–off 30mH tapped inductors
¾ Tapped at 5mH intervals
¾ Rated at 200A, 50Hz, 750V
Tapped inductors offer better control
options
Small inductor value = quicker
response, but higher current ripple
Large inductor value = slower
response, better current smoothing
Matthew Armstrong
Development of Virtual Power System
Measurement Hardware
Conventional Current Measurement
Inverter under test output current is
monitored and fed back to control system
Voltage Measurement
Problem with sampling voltage. Inverter
output voltage is a switching waveform
(PWM controlled).
Dedicated synchronous integrator
hardware is required to determine the
average inverter output voltage
Matthew Armstrong
Development of Virtual Power System
Measurement Hardware
Synchronous integrator
hardware connects across the
output terminals of the inverter
under test.
Determines average voltage
applied by inverter under test.
Measures average voltage
over the sampling period of
the Virtual Power System
Matthew Armstrong
Development of Virtual Power System
Software Development (dSPACE® DSP Platform)
Matlab/Simulink®
Real Time Workshop®; generate
real time simulation models for
dSPACE® DSP platform.
1
ids
1
i1s
2
2/3
Vds
i2s
3
iqs
In1
2
3/2
idr
In2
3
i3s
2/3 transform
Vqs
iqr
4
In3
Software Functions
3/2 transform
i1r1
5
Fds
2/3
Vdr
Fdr
i2r1
6
0
Fqs
Inputs from power electronics:
current and voltage measurements.
Constant
Vqr
i3r1
2/3 transform1
Fqr
Motor Model
7
ids
8
iqs
9
Run power system model: generate
current/voltage demands
idr
10
iqr
ids
iqs
trq
Current/voltage control – PI controller
idr
iqr
Torque
Outputs to power electronics: PWM
modulation signals
Matthew Armstrong
Development of Virtual Power System
Software Development (dSPACE® DSP Platform)
During emulation: use
dSPACE® ControlDesk®
software
Real time monitoring of
system variables
Real time control over
system variables
Matthew Armstrong
Operation of Virtual Power System
Inverter Under Test
4 – quadrant commercial drive system:
Two back-to-back Control Techniques
drive units.
Conventional control as supplied by
manufacturer, no modifications.
Matthew Armstrong
Operation of Virtual Power System
System Testing
100A peak sine wave. (30mH inductors)
Matthew Armstrong
Operation of Virtual Power System
System Testing
100A peak sine wave. (30mH inductors)
Matthew Armstrong
Summary of Virtual Power System
Practical Limitations
Power System Model Complexity – dependent on processing
speed. Solution: faster processors, parallel processing
Semiconductor switching rates – bandwidth. Possible problem when
emulating high power systems. Solution: alternative power converter
topologies – multilevel converters.
Matthew Armstrong
Summary of Virtual Power System
Matthew Armstrong
Summary of Virtual Power System
Matthew Armstrong
Summary of Virtual Power System
A real time, real power level emulation tool.
A controlled, power electronic replacement for any power system
Suited to a number of distributed generation applications
Matthew Armstrong
Summary
Matthew Armstrong
INVERTER
UNDER TEST
Hz
A
Power Electronic
Inverter
GRID
Voltage
Measure
DSP
Current
Measure
Power
System
Model
Matthew Armstrong
Current
Control