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Transformer-less string PV inverter is getting more and more widely utilized due to its higher efficiency, smaller volume and weight. However, without the galvanic isolation, the leakage current limitation and operation safety became the key issues of transformer-less inverters. This paper simplifies the leakage current generation circuit model and presents a leakage current estimation method both...
This paper presents a surrogate-model-based optimization of a doubly-fed induction generator (DFIG) machine winding design for maximizing power yield. Based on site-specific wind profile data and the machine's previous operational performance, the DFIG's stator and rotor windings are optimized to match the maximum efficiency with operating conditions for rewinding purposes. The particle swarm optimization-based...
The increasing wind power penetration brings new challenge for wind turbine to provide Low Voltage Ride-Through (LVRT) capability. Doubly Fed Induction Generator (DFIG) has been widely used in wind turbines; due to its cost-effective partially power rated of the converter and Variable-Speed Constant-Frequency (VSCF) operation. However, the DFIG system has two poorly damped poles and is sensitive to...
With the high penetration of distributed generations (DG) in low voltage (LV) distribution network, some power quality problems, such as harmonic impacts due to power electronics converters, are unavoidable. This paper analyzes the harmonic influence caused by DG inverters to the connection points and to other nodes in the network. The LV distribution network model with DG inverters is established...
The voltage stability of power system would be deteriorated with the steady increase of wind energy penetration, considering the large variation range of power output from wind farms. The capacity of the power system in integrating wind power is investigated in this paper. Model of grid-connected wind farm is firstly introduced, and the influence of large-scale wind farms on power system static voltage...
In this paper, models of distributed generations and distribution network are built in MATLAB and simulation results under several cases are given. An equivalent mathematical model at access point of distributed generation is built, based on which, the propagation mechanisms of harmonics produced by distributed generations in distribution network is analyzed. It is concluded that THDi may be no more...
Along with the enlargement of capability of Wind-turbine generator, the influence of wind power on grid transient stability is more and more obvious. This paper investigates the influence of reactive power compensation to transient stability of fixed speed induction generator (FSIG) and doubly-fed induction generator (DFIG). Firstly, the models of two kinds of wind turbines are introduced and the...
Base on the analysis of multi Distributed Generators (DG) paralleled with different droop control characteristics in smart grid, this paper points out that the difference of droop control characteristics would lead to the DGs' output power allocation unbalanced, and furthermore, may cause some of the DGs overload or even shutting down before the smart grid load reaches the maximum generating capacity...
This paper sets up a simplified model of microgrid, which consist of wind power, PV, energy storage and loads. The distributed sources in the microgrid are controlled using different strategies: PV and wind power are controlled in PQ control mode; while energy storage controlled in PQ mode during grid- connected operation, and in droop control mode when the microgrid is switched to the islanding operation...
Due to the “Hard Drive” technique implemented by the integrated Gate-Unit, “Integrated Gate-Commutated thyristor” (IGCT) has lots of outstanding features and becomes the best choices of medium voltage applications. In three level NPC IGCT converter, because of the complex commutation transient process, the IGCT works in different conditions such as anti-parallel diode forward recovery, reverse recovery,...
With the individual capacity of wind power generation system increasing, the demand for high power grid-connected converters is growing, which is usually limited by the available semiconductor technology. One solution is multiple lower power units connected in parallel. LCL filters can provide much better ripple and harmonic attenuation. Therefore, they are more suitable for high power conversion...
This paper focuses on a control method for microsources which can work as AC voltage sources, instead of AC current sources. The microsources can not only provide AC power in grid-connected mode, but also control the frequency and voltage for the microgrid load in island mode. By using the voltage and frequency droop control method, the microsources can realize the “plug-and-play” concept: share the...
With the individual capacity of wind power generation system increasing, the demand for high power grid-connected converters is growing, which is usually limited by the available semiconductor technology. One solution is multiple lower power units connected in parallel. In this paper, direct parallel and interleaved parallel are analyzed and compared. Then it focuses on two parallel interleaved converters...
Due to the large surface of the PV generator, its stray capacity with respect to the ground reaches values that can be quite high. When no transformer is used in a grid-connected PV system, common-mode current, which caused by the common mode voltage, can flow through the stray capacitance between the PV array and the ground. It is quite harmful to the body safety and PV system. In order to avoid...
A design algorithm for grid-side LCL-filter of three-phase voltage source PWM rectifier is presented, which allows to use reduced values of inductance, improve system dynamic performance and reduce cost compared to traditional L-filter. These advantages are even more attractive in medium and high power applications. In this paper, the design criterion and calculation procedures are introduced in detail...
Voltage unbalance in a three-phase system causes performance deterioration of PWM rectifier. Recently, much attention has been paid to the control strategies under such unbalanced operating conditions. However, the detecting of the fundamental positive and negative sequence components with high precision and fast dynamic response is the precondition to guarantee the control effectiveness. In this...
According to the operational principle of SVPWM and considering the characteristics of digital implement, this paper presents a novel algorithm of SVPWM harmonic analysis. This algorithm gives the expression of phase voltage harmonics through Fourier analysis, which provides the guidance for the filter design and motor control. To verify the algorithm, a three-phase voltage source inverter controlled...
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