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Modified LCL (MLCL) filter can be employed in a transformerless PV grid-connected inverter for leakage current reduction without any modifications in the modulation technique and inverter topology. However, MLCL filter requires a damping scheme, either passive or active, to avoid possible instability in the grid connection. The use of passive damping in the MLCL filter causes additional power losses...
PV Grid-connected inverters must fulfill the standards specifications of current harmonics injected to the grid. In order to satisfy these grid requirements, passive filters are connected between the inverter and the grid. This paper compares the response characteristic of the traditional inductive (L) filter with the inductive-capacitive-inductive (LCL) filter. It is shown that the increasing the...
Grid-connected current source inverter (CSI) employs CL-filter to meet the harmonic limitations set by IEEE 519-1992 and IEEE 1547-2008. However, parameter design for the CL-filter is rarely studied and no formalized approaches are followed. Therefore, this paper identifies the limitations in designing CL-filters for a single-phase grid-connected CSI and presents a complete design procedure which...
This paper presents a theoretical analysis and simulation for the design and implementation of a Second Order Generalized Integrator - Frequency Locked Loop (SOGI-FLL) aimed at synchronization and fault detection when connecting an inverter to the utility grid. Such an inverter is implemented in a Highly-Efficient-and-Reliable- Inverter-Concept (HERIC) topology. The two main aims of this work are:...
Recently the technology of WPT (Wireless Power Transfer) has received much attention on the new charging way of electric vehicle (EV). In the combination of the WPT and EV application, one of the key points is to keep the whole system operating under the high efficiency conditions. Considering the request of battery priority, this paper proposes a strategy of the maximum efficiency point tracking...
The number of photovoltaic distributed generators introduced into electricity distribution systems is increasing worldwide. Safety measures must be taken for the correct operation of these new distributed generators so as to prevent uncontrolled and undesired power injections into the grid and possible damages to equipment and personnel. This paper describes an anti-islanding detection method used...
In this paper, a current controller for an inverter connected to the grid through an LCL filter is proposed. Unlike classical active damping schemes, it is proposed to implement the controller by measuring the injected current only. It can be done irrespectively of the filter resonance frequency. In addition, it is possible to place the closed-loop poles of the system in an arbitrary way. The controller...
Second and third-order passive filters (LC and LCL) are interesting filters used for grid-connected inverters. Due to the stability problems of this filter regarding resonance frequency, additional damping resistor suggested for an LCL filter. However, the resistor value has a considerable impact on the response of the filter, voltage and current harmonic distortion and system power loss. In this...
In this paper, a hierarchical control system based on a novel autonomous current sharing controller for grid-connected microgrids (MGs) is presented. A three-level hierarchical control system is implemented to guarantee the power sharing performance among voltage controlled parallel inverters, while providing the required active and reactive power to the utility grid. A communication link is used...
The grid-feeding voltage controlled inverter (GF-VCI) based on droop control is vulnerable to the harmonic voltages of the utility grid. Because of the equivalent impedance of system is small, the slight distorted grid voltage will result in the harmonic component increasing of GF-VCI output currents. Therefore, the reason of generation of distorted grid-feeding current of GF-VCI under the distorted...
LCL-type filters are widely used in grid-connected voltage source inverters, since it provides switching ripples reduction with lower cost and weight than the L-type counterpart. However, the inclusion of LCL-filters in voltage source inverters complicates the current control design regarding system stability issues; because an inherent resonance peak appears due to zero impedance at that resonance...
This paper proposes an electrolytic capacitor-less bi-directional EV charger for V2G and V2H operation. The dc-dc converter stage of the proposed EV charger is a non-regulating series resonant converter (SRC) which can be designed with minimum voltage and current rating and always achieves ZCS turn ON and OFF. The unified inner loop of the proposed control block provides seamless mode transfer for...
Solving a short mileage and a long charging time is indispensable to putting electrical vehicles (EVs) on the full-scale market. A moving wireless power transfer (WPT) system is one of the effective solutions, because it can feed electric power to moving EVs. This paper proposes a moving WPT system consisting of several stationary ground-side (primary) coils and a moving vehicle-side (secondary) coil...
This paper presents a fast passive islanding detection method based on virtual phase-shift between the real voltage seen at the point of common coupling and its created image in a Microgrid. The proposed algorithm consists of extracting the positive and negative sequences of the voltage at this point using a second order generalized integrator in two-way; to synchronize properly the system with the...
This paper presents a novel prototype of a timesharing frequency doubler principle-based current-fed zero current soft-switching (ZCS) high frequency resonant (HF-R) inverter for inductive power transfer (IPT) systems. The newly-proposed ZCS HF-R inverter is suitable for producing a higher frequency resonant current with switching power loss reduction by using a middle-class switching frequency insulated-gate-bipolar-power...
With increasing penetration of grid-connected photovoltaic (PV) power generation in distribution network, the equivalent impedance of the distribution network and the distribution capacitance of the interconnection cables are changed. The changed impedance network may be excited by the harmonic current of inverters or the harmonics of the grid voltage, which will affect the power quality and stable...
Resonant converters have gained popularity for a variety of applications due to their ability to provide soft switching conditions and high power density. Controlling these converters is complex because of their non-linear behavior and high frequency resonant tank. Controllers are often designed by using small-signal models, which are limited to operating around a quiescent point. However, the small-signal...
The combination of coupled inductors (CIs) and LCL filters can be a filter configuration to achieve high power density for high current applications. Frequency characteristics (i.e., resonance phenomenon) are changed according to the filter configuration and feedback currents (i.e., inverter-side or grid-side current) for current control loops. Therefore, stability analysis should be performed to...
By utilizing next-gen wide band-gap (WBG) devices, such as GaN and SiC, at high switching frequency in a single-phase Quasi-Z-Source PV inverter (qZSI), the impedance network can be significantly reduced. Although, the reduced qZS impedance network will decrease cost and improved power density, it will also result in frequency resonance that will introduce oscillations in the capacitor voltage and...
Instabilities due to mutual interactions among converters and inverters are sometimes observed. The Lyapunov-based, or an energy-based control is useful to assure stability of parallel-connected power converters. This paper investigates why the Lyapunov-based method can stabilize the system even when linear methods fail in stabilization due to a large line impedance. The analysis is based on the impedance...
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