With the increasing proportion of renewable energy generation into the power grid, more challenges are coming to the safe and stable operation of the powersystem. In order to keep the balance in energy market, system...
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Shielding failure of lightning is the key problem for safe operation of transmission lines. Using Electro-geometry Method to simulate the process of shielding failure, large currents hit a conducting wire hardly, howe...
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Lightning is a major cause of power interruptions in power transmission lines. Nowadays the Leader Progression Model is an advanced method to evaluate the shielding failure probability of transmission lines. Calculati...
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As an essential direction of agricultural development in the future, the energy demand for facility agriculture varies significantly in different seasons. In this paper, an integrated energy network structure for inde...
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Polyethylene is a major kind of internal insulating material. This paper measured the space charge phenomenon in low-density polyethylene (LDPE) by the pulsed electro-acoustic (PEA) method and observed the space charg...
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Polyethylene is a major kind of internal insulating material. This paper measured the space charge phenomenon in low-density polyethylene (LDPE) by the pulsed electro-acoustic (PEA) method and observed the space charge packet. This research got the LDPE films of different morphology by different annealing rate and discussed the effect of morphology and electrical field stress changing on space charge packet's moving velocity. The research shows that morphology of LDPE affects the velocity of space charge packet remarkably;bigger crystallinity results in lower velocity of space charge packet. The intensity of electrical field has little affection to the velocity. The average mobility of different crystallinity under different electric field was calculated. The relationship between crystallinity and mobility was found. The results further demonstrate there are inherent relationships among higher crystallinity, more space charge accumulation, lower mobility and deeper trap depth. Lower mobility and deeper trap depth have a monotone relationship.
The ultra-short-term prediction of photovoltaic powersystem is of great significance to the safe operation of powersystem. However, the daily and annual periodicity of solar radiation brings strong non-stationary to...
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ISBN:
(数字)9789881563903
ISBN:
(纸本)9781728165233
The ultra-short-term prediction of photovoltaic powersystem is of great significance to the safe operation of powersystem. However, the daily and annual periodicity of solar radiation brings strong non-stationary to the photovoltaic power series, which makes it difficult to predict the photovoltaic power series. In order to overcome the problem that the detailed clear sky model relies on a large number of plant parameters, this paper proposes a prediction algorithm based on a modified clear sky model. Firstly, historical data and geographical location of a certain site are utilized to build a modified clear sky model, then the theoretical clear sky power curve fitted by the modified clear sky model are divided by the actual historical power output to get a stabilized time series, finally the method of "online update" is adopted to forecast PV plant power output in the ultra-short-term time horizon (0-4 h). The test results of a photovoltaic power station in Ningxia show that the proposed model can reduce the prediction error of the 4th hour to about 3%.
Paralleling SiC MOSFETs is a popular way to increase the current capacity. However, due to asymmetric layout, device parameter mismatch and other factors, imbalanced switching or dynamic current is observed among the ...
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ISBN:
(数字)9781728158266
ISBN:
(纸本)9781728158273
Paralleling SiC MOSFETs is a popular way to increase the current capacity. However, due to asymmetric layout, device parameter mismatch and other factors, imbalanced switching or dynamic current is observed among the paralleled switches in multi-device paralleling application which results in unequal switching loss, challenging the security and reliability of the system. In this paper, a common-mode choke in the gate loop is proposed and analyzed to suppress the imbalanced switching current induced by asymmetric layout in a half-bridge configuration with a Kelvin-source connection. The mechanism of the proposed method is comprehensively investigated to show that though the common-mode choke is placed in the gate loop, it can also mitigate the imbalanced current caused by asymmetric power loop. And it also shows that only the leakage inductance of the choke is seen in the gate loop and thus the switching speed is not expected to be influenced. The proposed method can be easily extended to multi-device paralleling application and the switching transients is hardly influenced by the common-mode choke. simulation and experimental results are presented to verify the proposed method.
In order to reduce the randomness and fluctuation of wind power, numerical weather prediction is usually used to forecast powergeneration. Due to the redundancy of numerical weather prediction factors, dimensionality...
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The strong coupling of electricity and heat of combined heat and power (CHP) unit in cold season results in the loss of flexibility, which may cause massive wind power curtailment if they are in the same system. This ...
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In this work, we are interested in space charge dynamics characteristics in the low-density polyethylene(LDPE) nanocomposite mixed with some mass fraction of inorganic nanofillers. Different with all previous qualitat...
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In this work, we are interested in space charge dynamics characteristics in the low-density polyethylene(LDPE) nanocomposite mixed with some mass fraction of inorganic nanofillers. Different with all previous qualitatively theoretical works, numerical simulation based on the bipolar charge transport model was performed to systematically investigate the influence of trap depth, trap concentration, and injection barrier height on the space charge and electric field distributions under DC external electric field of 100 k V/mm. Our simulation results showed that increasing the trap depth would severely distort the electric field distribution at the balanced status with the highest and lowest electric field of 119 k V/mm and 47 k V/mm, respectively. Due to the introduction of nanofillers, more deep traps were created and blocked the space charge movement, capturing most of space charge in the vicinity of the electrode and largely declining the local electric field further. In addition, our theoretical analysis also showed both the high permittivity and low local electric field contributed to the increase of injection barrier height. Once the injection barrier height surpassed 1.25 e V, there was almost no charge that could overcome the injection barrier. At last, a mechanism of space charge suppression in the LDPE nanocomposite was presented.
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