This paper proposes a hierarchical control scheme for parallel grid-connected PV inverters with a common dc bus. Droop control and group coordination are implemented to achieve equal power sharing between inverters as...
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ISBN:
(纸本)9781849197588
This paper proposes a hierarchical control scheme for parallel grid-connected PV inverters with a common dc bus. Droop control and group coordination are implemented to achieve equal power sharing between inverters as well as zero steady-state error for dc voltage regulation. The implementation is specifically designed for distributed control to promote modularization and system reliability. Experimental results have verified that the proposed scheme is effective.
Large-scale, highly-concentrated wind power integrated into grids through long transmission lines will bring significant challenges to powersystem operation during steady-state and dynamic processes. Tremendous resea...
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ISBN:
(纸本)9781479977215
Large-scale, highly-concentrated wind power integrated into grids through long transmission lines will bring significant challenges to powersystem operation during steady-state and dynamic processes. Tremendous research has been conducted in this critical area. However, few, if any available testing systems have been established to meet the requirements of the research on different time-scales. The objective of this paper is to identify the functionality requirements of the testing systems for the comprehensive studies, which covers different time-scale problems of powersystems. For this purpose, the realistic Gansu power grids in China and wind farms in Jiuquan area are selected. As a typical power grid with large-scale highly-concentrated wind power integration by long-distance transmissions, the characteristics of the selected wind farms and power grid are discussed first. Two simplified systems are constructed associated with the major characteristics. The critical functionality requirements of the testing systems for different research purposes, i.e., system planning, operation, control, and protection, are identified. As the first step, this paper scopes the key requirements and, ultimately, a complete testing system is expected.
This study investigated the air-gap magnetic field distribution and inductance characteristics of a long primary sectional powered variable pole pitch linear induction motor (VPPLIM). A one-dimensional analytical mode...
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Due to the power electronic devices in doubly fed induction generators (DFIG), it is very time consuming to simulate the electromagnetic transients of DFIG using its detailed model. Thus it is necessary to have approp...
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ISBN:
(纸本)9781849197588
Due to the power electronic devices in doubly fed induction generators (DFIG), it is very time consuming to simulate the electromagnetic transients of DFIG using its detailed model. Thus it is necessary to have appropriately simplified model of DFIG that maintains desirable accuracy. In this paper, the piecewise averaged model of PWM converters is introduced and applied to the modelling of DFIG. The proposed model divides the simulation time interval into switching periods and recalculates the averaged state equations of PWM converters in each switching cycle. In addition, a predictorcorrector based EMTP algorithm is designed to iteratively solve the model. Instead of treating switching events at the time points when they happen, the new algorithm solves all the switching instants in a switching cycle at the same time, which avoids frequency modification of the system conductance matrix and speeds up EMT simulations of DFIG. simulation results of a single-machine infinity bus system with a DFIG show that the proposed model and algorithm can achieve satisfactory accuracy and efficiency.
The development of high voltage direct current (HVDC) grid is an effective approach to implement the large-scale long-distance power transmission, the large-scale renewable energy integration and accommodation, and th...
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The dynamic characteristics of space charge in nanocomposite of low-density polyethylene (LDPE) mixed with inorganic nano- fillers. Different from previous qualitatively theoretical works, we investigated the influenc...
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The dynamic characteristics of space charge in nanocomposite of low-density polyethylene (LDPE) mixed with inorganic nano- fillers. Different from previous qualitatively theoretical works, we investigated the influence of trap depth, trap volume charge density and injection barrier height on the space charge and the electric field distribution in the nanocomposite under a DC external electric field (100 MV/m) systematically and quantificationally, through numerical simulations based on a bipolar charge transport model. The simulation re- sults showed that, the increase of trap depth would severely distort the balanced electric field distribution with the highest and the lowest electric field of 119 MV/m and 47 MV/m, respectively. It is concluded that the introduction of nanofillers creates more deep traps, which would block space charges by capturing most of them in the vicinity of electrode and hence reduce the local electric field largely. Further theoretical analysis of the simulation indicates that both the high permittivity and the low local electric field of the nanocomposite contri- buted to the increase of injection barrier height, and almost no charge could overcome an injection barrier higher than 1.25 eV. At last, a mechanism of space charge suppression in the LDPE nanocomposite was presented.
Nowadays, the network mode of the most energy recovery power battery testing instruments adopts AC-microgrid, which has the drawbacks of low energy recovery efficiency, complicated power circuit topology, cumbersome o...
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Reactive power optimization with discrete control variables can be formulated as a mixed-integer nonlinear programming problem, which is a typical NP-hard problem in mathematics. This paper proposed a Gaussian penalty...
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Wireless power transfer (WPT) has been a research focus in recent decades. Based on magnetically-coupled resonant WPT (MCR-WPT), this paper made a comparison of two basic structures in MCR-WPT: the two-coil structure ...
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Wireless power transfer (WPT) has been a research focus in recent decades. Based on magnetically-coupled resonant WPT (MCR-WPT), this paper made a comparison of two basic structures in MCR-WPT: the two-coil structure and the four-coil structure. Their equivalent circuits were built. To illuminate the difference between these two structures, the input impedance, the transfer efficiency, and the load matching were studied and tested by experimental results. The conclusion is drawn that without reducing the transfer efficiency, the addition of the source coil and the load coil in the four-coil structure makes it easier to match the source and the load than the two-coil structure.
Purpose - A fast algorithm is proposed to calculate the lightning electromagnetic field over a perfectly conducting earth surface. Design/methodology/approach - The channel base current is approximated by a number of ...
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