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Calculation of characteristics for 3⁃stage passive RC integrators
CHEN Chang⁃yu
(Department of Electrical Engineering, Tsinghua University, Beijing 100084, China)
Abstract: The voltage transfer function H(s) of the 3⁃stage passive RC integrator is provided. The calculating
method using Laplace transform for the characteristic of the integrator and the differentiating⁃integrating (D/ I)
measuring system is introduced. As an important part of the D/ I system, this integrator can be used for measuring
the lightning impulse voltage. A group of improved 3⁃stage RC integrator parameters and its characteristic calcula⁃
tion results are presented. The measuring error for the lightning impulse using this D/ I system with the 3⁃stage im⁃
proved RC integrator is extremely low. This improved 3⁃stage RC integrator can also be used to measure lightning
impulse current when it is combined with the Rogowski coil.
Key words: lightning impulse voltage measuring; differentiating⁃integrating (D/ I) measuring system; compensa⁃
ted RC integrator; voltage transfer function
Simulation and comparative study of three modulation strategies
and voltage balance control in modular multilevel converter
WU Xiao⁃kun1, WANG Kui1, WAN Lei1,2, ZHENG Ze⁃dong1, LI Yong⁃dong1,3
(1. State Key Lab of Control and Simulation of Power Systems and Generation Equipments, Department of
Electrical Engineering, Tsinghua University, Beijing 100084, China; 2. China Electric Power Research Institute,
Beijing 100192, China; 3. Department of Electrical Engineering, Xinjiang University, Urumqi 830046, China)
Abstract: As a novel multilevel topology, the modular multilevel converter (MMC) has been widely studied be⁃
cause of its application in HVDC. In this paper, the commonly used modulation strategies in MMC, carrier stacked
PWM, nearest level modulation, and carrier phase shifted PWM are introduced. To balance the capacitor voltage of
sub⁃module, several different capacitor voltage balancing algorithms are also analyzed. The carrier stacked PWM
has the highest switch frequency which leads to the best capacitor voltage balancing performance. The nearest level
modulation is easy to implement and the switching frequency can be restricted to a low rate. The carrier phase shif⁃
ted PWM has a fixed switching frequency. To compare the three modulation strategies, a 31⁃level simulation model
of MMC is built in PSCAD/ EMTDC. The three modulation strategies and capacitor voltage balancing algorithm are
realized in the simulation model. The performance of the capacitor voltage fluctuation, switching frequency, voltage
harmonics and other aspect of performance are compared. Key words: modular multilevel converter; carrier stacked PWM; nearest level modulation; carrier phase shifted
PWM; capacitor voltage balance
High⁃efficiency modification of Y⁃series induction motors
with low⁃harmonic winding
LI Juan, SHEN Jian⁃xin
(College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China)
Abstract: It is pointed out in the National Program of Electrical Machines Efficiency Enhancement that high⁃effi⁃
ciency modification of the existing induction motors is one of the important technique routes. In this paper, modifi⁃
cation of a conventional Y⁃series induction motor (22kW/ Y⁃180L⁃4) is taken as an example, of which the winding
is redesigned according to the low⁃harmonic winding theory. Finite element analysis shows that, compared with the
conventional motor, the low⁃harmonic⁃winding motor exhibits reduced harmonics in the airgap field, lower magnetic
and electric loads and hence slightly better over⁃load capability, higher efficiency over a wide load range, and high⁃
er starting torque but slightly lower starting current. The modification cost is low whilst the performance improve⁃
ment is effective.
Key words: induction motor; low⁃harmonic winding; high⁃efficiency modification
Stability improvements for closed⁃loop flux observer
of induction machine
HU Qing, WANG Kai
(1. Department of Applied Electronics, Shangqiu Polytechnic College, Shangqiu 476000, China;
2. College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China)
Abstract: Accurate flux estimation is essential in the speed sensorless vector control system of induction machine.
The reduced order flux observer (including the voltage mode and current mode flux observer) has the advantages of
both simple structure and reduced sensitivities of parameters. However, the pure voltage mode flux observer has the
integral problem whereas the pure current mode flux observer needs the speed information. The voltage and current
model based closed⁃loop flux observer combines the voltage mode and current mode flux observers together and ob⁃
tains good control performance with small parameter sensitivity but has some drawbacks in the stability characteris⁃
tics under the low⁃speed generation mode, thus the motor cannot run normally in this region. Based on the stability
analysis of the flux observer and the corresponding conditions, this paper proposes a reasonable method to eliminate
the unstable region. Both simulation and experimental results show validity and effectives of this proposed method.
Key words: induction machine; closed⁃loop flux observer; sensorless; stability analysis; low⁃speed generation
mode
Photovoltaic grid⁃connected power conditioning system
based on fuzzy sliding mode variable⁃structure control
JI Yan⁃e, SUN Yu⁃kun, CAI Ji⁃he
(Institute of Electrical and Information Engineering, Jiangsu University, Zhenjiang 212013, China)
Abstract: When integrated with the function of active power output, harmonic and reactive power compensation,
PV grid⁃connected power conditioning system (PVPCS) is helpful to improve power quality and efficiency of the
system. Its working principle and instantaneous reactive power theory are analyzed. Combination of grid⁃connected
current and current tracking is also discussed. PVPCS based on fuzzy sliding variable⁃structure control (FSMC) is
studied and the transient simulation in single machine infinite bus system is compared with traditional PI control.
Research results show that this system can effectively optimize the reactive and harmonic compensation while stabili⁃
zes the DC capacitor voltage and with better robustness and adaptability. Efficiency of the system is improved.
Key words: harmonic analysis; reactive power compensation; fuzzy sliding mode variable⁃structure control; PV
grid⁃connection
Influence evaluation method on power system frequency dynamics
by shedding large scale wind generation
CUI Yang1, LIU Jia2, ZHAO Bing3, YAN Gan⁃gui1
(1. School of Electrical Engineering, Northeast Dianli University, Jilin 132012, China;
2. Nanning Power Supply Bureau, Guangxi Power Grid Corporation, China Southern Power Grid,
Nanning 530031, China; 3. Changchun Power Supply Bureau, State Grid Jilinsheng Electric
Power Supply Company, Changchun 130012, China)
Abstract: The fluctuations of large⁃scale integrated wind power can destroy the balance of power supply and de⁃
mand of the power system so that the power system frequency would deviate over the limit. The traditional analysis
method of frequency dynamics based on step disturbance is no longer applicable since the small installed capacity of
wind turbine and the stochastic fluctuation characteristic of wind power. This paper has proposed a method taking
account of both the wind power characteristics and the frequency regulating model of power system, which focused
on the impact on frequency influenced by large scale integrated wind farms. The extreme condition of frequency dy⁃
namic process has been simulated and analyzed, caused by the all wind farms shedding in one integrated point at
the same time. Simulation results shows that the maximum shedding value of wind power is restricted by the permis⁃
sible deviation of frequency of the tested system. Key words: large⁃scale integrated wind power; wind power shedding; power system frequency; permissible devia⁃
tion of frequency
Thermo characteristics of Silicone rubber and its effects on operational
reliability of extra⁃high voltage cable accessories
FEI Yi⁃jun1, ZHANG Yun⁃xiao2, ZHOU Yuan⁃xiang2
(1. State Grid Jiangsu Electric Power Company, Nanjing 210000, China;
2. State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments,
Department of Electrical Engineering, Tsinghua University, Beijing 100084, China)
Abstract: With fast development of power cable, Silicone rubber (SIR), as an advanced internal insulating mate⁃
rial, has been widely used in high voltage cable accessories due to its excellent insulation and mechanical perform⁃
ance, but there is still a lot of insulation failure. It was reported that material aging properties are main reason
which influences the operational reliability of extra⁃high voltage cable accessories. In this paper, electrical tree ag⁃
ing characteristics was analyzed including the effects of temperature on electrical tree initiation voltage and tree
shape in SIR. It was found that the electrical tree initiation voltage was declined badly with the temperature rise.
And electrical tree shape transits from the branch tree and pine tree to bush tree. It was shown that there is thermo
destruction under cable operating temperature which causes bad influence on cable operational reliability. Long hys⁃
teresis characteristics of bush tree in SIR may become hidden danger of long⁃term operating cable accessories. The
difference of PE and SIR in temperature characteristics was discussed. It was considered that thermo destruction is
the main reason of the problem above and the lacking understand of SIR aging characteristics is the main reason of
frequent failure in high voltage cable accessories which causes insufficient allowance of architectural design of cable
accessories. .
Key words: cable accessories; silicone rubber; electrical tree; aging; thermo destruction
Precise planning for mid⁃voltage distribution network
based on load supply capability analysis
LI Fang1, XU Jian1, XIE Fang1, GUO Yin⁃chang2, LIU Hong2
(1. Tianjin Electric Power Design Institute, Tianjin 300400, China;
2. Key Laboratory of Smart Grid, Ministry of Education, Tianjin University, Tianjin 300072, China)
Abstract: A precise planning for mid⁃voltage distribution network based on load supply capability analysis was put
forward in this paper so as to fill a gap that was a deficiency in theoretical analysis when mid⁃voltage distribution
connection mode is selected in the traditional distribution network planning. Firstly, different interconnection “de⁃
grees” were compared based on the concept of load supply capability, and reasonable interval of interconnection
“degree” was given. Secondly, rational load supply framework was contributed based on that. Lastly, connection
scheme of mid⁃voltage feeder was put forward to the principle of full use in load supply capability. The effectiveness
and practicality were proved by analysis of an example. It also proved that the method in this paper was a good
guide in distribution network planning.
Key words: mid⁃voltage distribution network; distribution network plan; load supply capability; load supply
framework; connection mode
Numerical modeling of heat transfer performance
of ONAN distribution transformers
XU Zhi⁃ming1, WU Kai1, LI Xiu⁃yun2, LIU Qing3
(1. Energy and Power Engineering Institute, Northeast Dianli University, Jilin 132012, China;
2. EPRI of Jilin Electric Power Co. Ltd., Changchun 130021, China; 3. China National Water Resources &
Electric Power Materials & Equipment Co. Ltd., Beijing 100045, China)
Abstract: The thermal behaviour of ONAN distribution transformers has been numerically modeled using FLUENT
for obtaining the velocity distribution and temperature distribution of insulating oil. A simplified model has been de⁃
veloped according to the transformer entity data. Turbulence was modeled using the RNG k⁃ε turbulence model,
while 2⁃layer approach was adopted to deal with turbulence near the wall. The insulating oil flow and the thermal
distribution results inside transformer were presented. The devised model has been validated by comparing the nu⁃
merical results with the experimental ones. The conclusion provides theory basis for optimization design and fault
diagnosis of ONAN distribution transformers.
Key words: distribution transformer; numerical modeling; velocity distribution; temperature distribution
Application of amorphous alloy in motor
HAN Xue⁃yan, TONG Wen⁃ming, TANG Ren⁃yuan
(National Engineering Research Center for REPM Electrical Machines, Shenyang University of Technology,
Shenyang 110870, China)
Abstract: Through comparison of basic performance of amorphous alloy strip and cool⁃rolled silicon steel sheet by
domestic and Hitachi factory, it can be shown that amorphous alloy has excellent electromagnetic performances
(high permeability and low loss) as a novel soft magnetic material, which can significantly reduce motor’s iron
loss, improve the efficiency, has outstanding effect of energy⁃saving, and is especially suitable for high frequency
motor whose iron loss occupies the main part. In this paper, through reviewing on the research and development
process of amorphous alloy motor, the advantages and disadvantages and key applications in the future for amor⁃
phous alloy motor are summarized, and the direction of development is pointed out.
Key words: amorphous alloy; motor; application
Fault diagnosis of power electronic circuits based on mathematical morphology
based generalized fractal dimensions
SONG Ping⁃gang, ZHOU Jun
(College of Electrical and Electronic Engineering, East China Jiaotong University, Nanchang 330013, China)
Abstract: The fault detection and diagnosis of power electronic circuits can guarantee safe operation of power elec⁃
tronic devices. Considering the limitation of traditional fault diagnosis of power electronic circuits, this paper pres-
ents a new method based on mathematical morphology based generalized fractal dimensions. Combined with the
fractal geometry theory, this method extracts the fractal dimensions of different faults’ output waveforms as the fault
characteristics, and identifies them by Elman neural network. This paper takes a Buck circuit as the example and
analyzes its fault signals. The results show that compared with the traditional box⁃counting based generalized fractal
dimensions, the mathematical morphology based generalized fractal dimensions can distinguish Buck circuit signals
in different states more effectively. Besides, the calculation of mathematical morphology is simple and accurate for
it only involves addition, subtraction practice, and maximum and minimum operations. Thus, it provides a fast and
effective method for accurate fault diagnosis of power electronic circuits.
Key words: mathematical morphology; multi⁃fractal; generalized fractal dimensions; power electronic circuits;
fault diagnosis
Method study of on⁃line risk analysis for district grid
LUO Ya⁃di, LI Jing, CHEN Li⁃jie, LI Qiang, JIA Yu⁃pei
(China Electric Power Research Institute, Beijing 100192, China)
Abstract: In order to more accurately measure the running risks of the district power grid, this paper presents a
method of on⁃line risk analysis for district grid. The calculation of risk indicators uses the weighted fault probability
model of the overhead line which is based on equipment operating status and fuzzy theory, and the risk indicators
can reflect the influence of environmental factors. In this model, the proper membership function is adopted to de⁃
scribe the influence of lightning, wind speed, line ice and temperature, and the outage rate of overhead line, de⁃
rived from historical statistics, is amended. By making full use of operating experience of dispatchers, the fuzzy
membership function boundary conditions are determined. Therefore, the problem of lacking historical statistics is
solved. Based on this method, the power supply risk analysis software can be developed to calculate the online risk
indicators of district grid, and the simulation results for WSCC9 system verify the effectiveness of the method.
Key words: district grid; fault probability model; risk analysis; fuzzy theory
Study on monitoring system of electrification railway
harmonic based on ZigBee
TENG Zhi⁃jun, ZHANG Xiao⁃xu, LI Guo⁃qiang, ZHANG Fan, HE Xin
(Department of Information Engineering, Northeast Dianli University, Jilin 132012, China)
Abstract: Harmonic monitoring of electrified railway is of great significance. In view of the characteristics of har⁃
monic generation in electrified railway, this paper proposes a harmonic detection algorithm based on windowed FFT
and all⁃phase FFT. The simulation shows that the algorithm can guarantee the accuracy of amplitude, frequency
and phase of harmonic. The paper also proposes Zigbee⁃based harmonic monitoring system. The basic function of
the monitoring system is realized by designing system hardware and system software. Moreover, an actual harmonic
test is taken in a traction substation and the test results show that this monitoring system is feasible and has remark⁃
able field application significance.
Key words: all⁃phase; FFT; harmonic; ZigBee; monitoring
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