Download 3. The time-frequency characteristic analysis of VFTO simulation

Research on experimental simulation and S transform time-frequency
characteristics analysis of VFTO
YANG ZHUANGZHUANG，XU JIANYUAN
School of Electrical Engineering, Shenyang University of Technology, Shenyang 110870, Liaoning, China
Abstract:
In this paper, experimental simulation research of VFTO electromagnetic interference source is done
for the experimental study of electromagnetic compatibility problems caused by VFTO, and the VFTO
simulation waveform is obtained. The analog experiment circuit is composed of high voltage equipments,
including impulse voltage generator, etc. The time-frequency characteristics of results waveform are
analyzed by using the S transform method. Research shows that the experimental simulation results meet
the requirements of frequency and amplitude characteristics of VFTO. Results waveform can be used as
VFTO electromagnetic interference sources for insulation experiments and electromagnetic compatibility
experiments in upcoming subject research. At the same time, the influence law of the parameters such as
inductor, capacitor and sharping clearance in VFTO experimental simulation is analyzed by the analog
circuit simulation model established.
1.
Introduction
VFTO of high frequency can produce electromagnetic interference to influence secondary equipments[1] by
the form of conduction or radiation, it is necessary to study VFTO. Due to actual VFTO is obtained hard, VFTO
simulated experiment is easy to implement and the repeatability is good. The study of VFTO is mainly around
perhaps the most large amplitude and harm to insulation of the VFTO in time domain. And the spectrum features
study of VFTO is less[2]. Therefore, the related research include the VFTO simulated experiment, time-frequency
characteristics of result wave and the influence factors of simulation experiment is studied in this paper.
2.
The experiment study system and results waveform
The VFTO simulated system and test system of the basic circuit adopted in this experimental design is
shown in figure 1. Voltage source of impulse voltage generator is equivalent to voltage of bus residual charge.
Load in the circuit is composed of resistance, inductance, capacitance, etc. The parameter value is determined in
accordance with the requirements of VFTO simulated experiment.
Impulse
voltage
generato
r
Steepenin
Steepenin
gg
clearance
clearance
Resistan Inductanc
Capacitance
ce
e
Insulation
bracket
VFTO waveform
simulation system
Fig.1
Resistan
ce
Test
system
High-voltage
resistancecapacitance divider
VFTO signal
output
Oscillosco
Oscillosco
pe
pe
220V~
UPS
220V~
Diagram of VFTO simulation and testing system
Fig.2
(a)
(b)
(c)
Diagram of VFTO simulated test equipment
The physical diagram of experiment equipment is shown in figure 2 Among them, the load capacitance is
shown in (a). Impulse voltage generator and spherical sharping clearance etc. is shown in (b). High-voltage
resistance-capacitance divider is shown in (c). The oscillation position of VFTO simulated waveforms on the
thunder electric wave can be adjusted by controlling the steepening clearance gap size.
The results waveform is shown in figure 3. Among them, the thunder electric wave is shown in figure (a).
VFTO simulated waveform is shown in (b). The waveform shows that function of sharping gap is well reflected
and high frequency oscillation wave is superimposed on the thunder electric wave, The theoretical characteristics
of VFTO experimental simulation is reflected.
Single-Sided Amplitude Spectrum of y(t)
1.5
X: 1.012e+07
Y: 1.25
X: 2.768e+07
Y: 1.133
|Y(f)|
1
X: 4.537e+07
Y: 0.6445
X: 7.902e+07
Y: 0.642
0.5
0
(a)
(b)
Fig.3 The output waveform of 3.5 cm peaking clearance
Fig.4
0
1
2
3
4
5
6
Frequency (Hz)
7
8
9
7
x 10
FFT analysis of VFTO simulation waveform
3.
The time-frequency characteristic analysis of VFTO simulation waveform
3.1
S transform method
VFTO waveform is a kind of non-stationary waveforms of randomness strong. S transform can retention
time and frequency information at the same time, reflect the local characteristics of signal frequency change over
time. And frequency resolution is better in low frequency band. Time resolution is better in high frequency band.
Therefore the method is widely used. S transform of VFTO output signal h(t) is defined as follows:

S  , f    h  t w  t   , f  e-j2πft dt

w t  , f  
3.2
f
2π
e

f 2  t 
2
(1)
2
(2)
Time-frequency characteristic Analysis of VFTO
To the requirement of VFTO, IEC60071-1 1993 recommended by front edge of steep wave front
overvoltage wave is 3~100 ns, superposition oscillation frequency is 0.3~100 MHZ. The FFT analysis of
amplitude frequency characteristics of VFTO simulated waveform is shown in figure 4. The main frequency
components are 10.12 MHz, 27.68 MHz, 45.37 MHz and 79.02 MHz, etc. Meet the characteristics requirements
of VFTO.
S transform results is shown in figure 5. Each frequency component of FFT analysis results exists in the S
transformation results figure and in different time domain. The VFTO the time-frequency characteristic analysis
is implemented and more intuitive. As shown, low frequency component of high amplitude continued
throughout the time domain. And the high frequency and low frequency component exist in about 4 us - 4.4 us at
the same time. The energy of the simulate VFTO is larger area in the area. High frequency oscillation wave
amplitude on thunder electric wave is decayed as time increases. As shown in the figure, the high frequency
component amplitude decay gradually disappeared in the blue area of the low amplitude. Results show the
effectiveness of S transform method, and the rationality of experimental simulation of VFTO waveform. Actual
VFTO amplitude-frequency characteristic requirements be met.
5
7
x 10
x 10
45
12
4.5
40
11
4
10
35
9
30
25
7
20
6
15
5
10
4
3
5
2
4
4.05
4.1
4.15 4.2
Time (s)
4.25
4.3
4.35
4.4
-6
x 10
Frequency (Hz)
Frequency (Hz)
3.5
8
3
2.5
2
1.5
1
0.5
0
0
1
2
3
4
Time (s)
5
6
7
8
-6
x 10
(a)
(b)
(c)
Fig.5 S transform analysis of VFTO waveform
4.
Fig.6 Simulation circuit model of VFTO waveform
Influence factors analysis of VFTO experimental simulation
VFTO simulated test circuit model is shown in figure 6. The influence law of inductance, capacitance and
sharping clearance, etc. is analyzed by model simulation in VFTO simulated experiment.
5.
Conciusion
The results show that the S transform method is suitable for time-frequency characteristic analysis of the
unsteady VFTO signal waveform. Waveform simulation results meet the VFTO waveform characteristics range
by the time-frequency characteristics analysis. Amplitude characteristics of results waveform can be changed by
adjusting the trigger voltage value of impulse voltage generator. Therefore, the output waveform of VFTO
experiment simulation system can be used as the VFTO interference sources for the related insulation and
electromagnetic compatibility experiments. At the same time, the influence law of the various factors in VFTO
experimental simulation are summarized through the simulation circuit model.
Keywords:
VFTO electromagnetic interference source, S transform, time-frequency characteristics, experimental simulation
Author’s brief introduction and contact information:
Yang Zhuang-zhuang(1987-). Doctor degree candidate of Electrical Engineering. His current research interest is the study of
electromagnetic compatibility and intelligent electrical apparatus. E-mail: [email protected]
Xu Jian-yuan(1962-). Professor of Electrical Engineering. His research interests include the analysis and control of the power
system, high voltage apparatus, overvoltage protection and high voltage and insulation technology.