Download Real Time Simulation for Time-Varying Harmonic Distortion Analysis

Chapter 18
Real Time Simulation for TimeVarying Harmonic Distortion
Analysis: A Novel Approach
Y. Liu, and P. Ribeiro
18.1 - Introduction
A novel approach to time-varying harmonic distortion assessement based on real-time
(RT) hardware-in-the–loop (HIL) simulation is proposed. The sensitivity for power quality
deviations of a variable speed drive controller card was tested in the platform. The successful
experiment has contributed to the conceptive design of a universal power quality test bed,
which would have the function of testing the immunity of electric components and equipment
and the consequent impact on AC distribution systems.
Electromagnetic transient simulations or laboratory experiments are often used for
power quality studies. The results of different simulation programs could be different because
of the usage of different mathematic models. Also, the simulation results largely depend on the
accuracy and complexity of those models. On the other hand, the disadvantages of the
laboratory experiments are the high cost and the large amount of developing time. Also, the
power quality impact on power systems is hardly achieved due to the difficulties of connecting
a tested device to real power systems. To achieve better accuracy on the power quality studies
of large and complex power systems in an economic way, a novel power quality assessment
method based on a real time (RT) hardware-in-the-loop (HIL) simulator is proposed. Hardwarein-the-loop is an idea of simultaneous use of simulation and real equipment. Generally, a HIL
simulator is composed of a digital simulator, one or more hardware pieces under test, and their
analog and digital signal interfaces (e.g., high performance A/D and D/A cards).
18.2 Description of the RT-HIL Platform
A RT-HIL platform is currently being established at the Center for Advanced Power
Systems (CAPS) at Florida State University, Tallahassee, Florida. The platform has been designed
for research on NAVY all-electric ship power systems. Figure 18.1 shows the diagram of the RTHIL platform. The platform is composed of a digital simulator (RTDS TM), tested hardware, and
their interface (e.g., power amplifiers and transducers). The simulator can be used either as an
independent simulation system (e.g., no hardware in the loop), or with tested hardware. In
Figure 18.1, a real power electronic device is connected to the simulated power system through
D/A adaptors and power amplifiers. The supply current of the AC/DC converter is measured and
fed back into the system at the common coupling point through transducers and A/D adaptors.
In fact, any component (e.g., controllers of power electronic devices, and control and
protection equipment) in power systems could be tested in the platform.
DIGITAL SIMULATOR
D/A
AC loads
A/D
D/A
Voltage reference
A/D
D/A
Generation and
distribution systems
Current injection
A/D
DSP hardware
Ethernet
PC: GUI and real-time control
Current probe
Amplifier
Transducer
Amplifier
Transducer
Amplifier
Transducer
Power electronic device and its
controllers
TESTED HARDWARE AND ITS INTERFACE
Figure 18.1. Diagram of the RT-HIL platform at the CAPS, Tallahassee, FL
The distribution system of the US coast guard icebreaker “Healy” has been simulated in
real-time to demonstrate the simulator’s capabilities. Figure 18.2 shows a good agreement
between the complete software simulation results and the field measurements taken during
Healy’s commissioning trials in 1998.
HV Bus PT output voltage [V]
200
Phase A
Phase C
150
100
Measured
waveform
event at
05/13/00 22:13:12.64
50
0
Simulated
waveform
dt = 65 s
-50
-100
Phase B
-150
-200
22:13:12.640
t [h:m:s]
22:13:12.645
22:13:12.650
22:13:12.655
22:13:12.660
Figure 18.2. Measured AC bus voltage waveforms (broken gray lines) of US Coast Guard
icebreaker (all four cycloconverter bridges operating) compared to the simulated waveforms
(solid colored) using the digital simulator model (only one bridge of each of both cycloconverter
drives operating)
18.3 Sample Case: Testing the Sensitivity of a Thyristor Firing Board to Poor
Quality Power
An Enerpro FCOG 6100 three-phase thyristor firing board was tested in the platform for
its sensitivity to poor quality power. Also, the impact of its sensitivity on the DC load and the AC
distribution systems is considered. The schematic of the simulated AC distribution system is
shown in fig. 18.3.
.
Power grid
Distribution transformer
12.47 kV/480 V
VL-L=12.47 kV
6-pulse
thyristor rectifier
+
Industry
DC load
YY
Lline=0.05 p.u.
Rline=0.005 p.u.
LT=0.05 p.u.
RT=0.005 p.u.
RL=0.48 ohm
LL=1 mH
Firing pulse
board
Figure 18.3. Diagram of the simulated industrial distribution system and rectifier load (60 Hz,
power base = 833 kW)
To consider the application of the board on NAVY all-electric-ships, extreme
conditions (e.g., significant frequency change) are simulated in the test. Table 18.1 shows the
RT-HIL simulation results.
Table 18.1 The RT-HIL simulation results for the firing board
PQ phenomena
THD
Voltage sag
Simulation results

Tolerate THD up to 14.8% and higher

Tolerance has no impact on distribution systems

Tolerance depends on not only the time duration and
voltage reduction, but also phase shift

Frequency change 
Tolerance results in DC voltage drop or blackout
Tolerate system frequency from 30 Hz to 80 Hz
Figure 18.4 and Figure 18.5 show the single-phase voltage sag with and without any
phase shift and their impact on the DC output voltage of the rectifier. The sag with a phase shift
resulted in the reboot of the firing board. The reboot then resulted a 0.1 s DC blackout and
about 1.5 s transient process on both DC and AC systems. However, the sag without phase
shifts only resulted in a DC voltage drop. This finding can not be discovered by using traditional
laboratory tests (e.g., changing the amplitude of one phase voltage in a 3-phase vari AC).
Primary voltage (kV)
10
5
0
-5
-10
DC voltage (kV)
0.05
0.1
0.15
0.2
0.25
0.1
0.15
Time (s)
0.2
0.25
0.4
0.3
0.2
0.1
0
0.05
Primary voltage (kV)
Figure 18.4. Single-phase voltage sag (0.1 s duration, 40% voltage reduction, no phase shift) and
its impact on the rectifier DC output (delay angle  = 7)
10
5
0
-5
-10
DC voltage (kV)
0.05
0.1
0.15
0.2
0.25
0.1
0.15
Time (s)
0.2
0.25
0.4
0.3
0.2
0.1
0
0.05
Figure 18.5. Phase-shifted single-phase voltage sag (0.1 s duration, 40% voltage reduction) and
its impact on the rectifier DC output (delay angle  = 7)
The successful test leads to a design of a universal power quality test bed. Figure 18.6
shows the diagram of the universal power quality test bed. A universal interface is built to easily
connect any firing board. Test systems and power quality phenomena can be selected from the
existing ones in the digital simulator or self designed for a special purpose.
Digital simulator
Self designed
Test system N
Start
Test system 2
Test system 1
Selecting
Tested systems
Selecting PQ
phenomena
Frequency change
Print results
Voltage sag
THD
Firing board
Firing
pulses
Reference
voltages
Universal interface
(e.g., power amplifiers,
and transducers)
End
Figure 18.6. Diagram of universal power quality test bed
18.4 Conclusions and Future Work
A novel power quality assessment method was proposed. The method is applied in the
RT-HIL platform to test an industry firing board. The successful initial test results show that the
tested board can tolerate highly distorted voltages, significant sudden frequency change, and
three-phase voltage sags , but it cannot tolerate certain short-term phase-shifted single-phase
voltage sags. This result which could only be revealed through the proposed RT-HIL method is
helpful for future product improvements. The successful experiment has contributed to the
conceptual design of a universal power quality test bed, in which any kind sensitivity of power
quality deviation could be revealed.
18.5 References
[1] A. J. Grono, “Synchronizing Generators with HITL Simulation,” IEEE Computer Applications in
Power, Vol. 14, No. 4, October 2001, pp. 43-46.
[2] M. Steurer, S. Woodruff, “Real Time Digital Harmonic Modeling and Simulation: An
Advanced Tool for Understanding Power System Harmonics Mechanisms,” IEEE PES General
Meeting, Denver, USA, June 2004.