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A reliable islanding detection method is one of the most important function of a well designed inverter based distributed generation (DG) system. Active islanding detection methods have negligible non-detection zone, but they bring some power quality issues to the network. In this paper an islanding detection method which addresses constant current inverter based DGs is introduced. It has both high...
The dynamic voltage restorer, with its excellent dynamic capabilities, when installed between the supply and a critical load feeder, can compensate for voltage sag/swells, restoring line voltage to its nominal value within few milliseconds and hence avoiding any power disruption to the load. A new topology based on Z-source inverter is presented in order to enhance the voltage restoration property...
Proliferation of the voltage-sensitive loads in the distribution systems has made the voltage quality an important issue. The main factors considering the voltage quality are the voltage sags and voltage swells. There are many available solutions to improve voltage quality. In the past years, application of the power-electronic based devices known as custom power devices have developed an interesting...
In this paper novel voltage mitigation method is introduced to protect sensitive loads due to under voltage or by over current. It will be able to compensate voltage sags on critical loads dynamically. It consists of voltage source inverter, injection transformer, filter and energy storage device. The efficiency of the mitigation method depends on the efficiency of the control techniques involved...
The Inter-Line Dynamic Voltage Restorer (IDVR) consists of several voltage source inverters connected to different independent distribution feeders with common dc bus. When one of the inverters compensates for voltage sag that appears in its feeder (voltage control mode), the other inverters pump the required power into the dc bus (power control mode). Each inverter will have both voltage and power...
Distributed power generation systems (DPGS) are based on the grid-converters as interface between the source and the grid. They require a control strategy is designed in order to guarantee system stability and reliability. The effect of converter outages should be properly studied as well as the effect of power quality disturbances. The aim of this paper is to provide a comprehensive analysis of these...
Effect of a new parameter of voltage sag, i.e., phase angle jump, on invertors for PV System was surveyed by newly developed Voltage Sag Generator. The generator can reproduce actual voltage sags recorded past, and artificial voltage sag with controlled phase angle jump. It consists of PC, D/A converter and power amplifier. A program generating wave form of sag has been developed and improved considering...
This paper proposes a new topology of Z-source based cascaded multilevel inverter. In this topology the output voltage is not limited to DC voltage source similar to traditional cascade multilevel inverter and can be increased with Z network shoot-through state control. Besides, it is more reliable against short circuit. Performance of suggested topology in the closed-loop control scheme is described...
As the wind power penetration is increasing rapidly into the power grid, modern gird codes require the wind turbines (WTs) to possess the low voltage ride-through (LVRT) capability. In order to evaluate the performance of a WT under grid fault conditions, a voltage sag generator (VSG) is needed to simulate all kinds of grid faults. This paper investigates a three-phase programmable VSG based on a...
The performance of the Grid Connected Inverters (GCIs) (like windmill and large central PV converters) is extremely important related to stable and safety operation of a "Smart Grid" SG. These inverters' control features not only cover the renewable energy conversion and active power feeding into the utility grid but furthermore they cover the helping of the grid voltage stabilization, supporting...
In this paper an UPQC (Unified Power Quality Conditioner) with a FLFB (Four-Leg Full-Bridge) inverter used as a Shunt Active Filter is presented. The UPQC works in a three-phase four-wire electrical system in order to compensate for nonlinear and asymmetrical loads, and disturbances in the power supply voltage. For the generation of reference currents for the FLFB the instantaneous power theory in...
This paper researches the intrinsic relationship between inter-harmonics and typical voltage fluctuations of which the enveloping line is sine wave, it analyses the effects to voltage fluctuations of inter-harmonics of different frequencies, including a single inter-harmonic and a pair of inter-harmonics. In this paper, experiments of voltage fluctuations production and compensation are all carried...
In this paper, a new type of controller is proposed for series connected PV inverter for grid voltage compensation. The inverter operates during the day time as an active power compensator as well as load voltage regulator under grid voltage sag, swell or even under normal condition. The compensating voltage provided by the inverter is added vectorially in series with the grid voltage in such a way...
In this paper, the main circuit structure with series dynamic voltage restorer (DVR) and shunt active power filter (APF) of unified power quality conditioner (UPQC) is taken as the research object. According to its fundament component of steady-state equivalent circuit the phasor representation in voltage changing is shown. The optimum angle voltage injection of DVR is proposed by the principle of...
Three-phase currents of STATCOM with conventional control strategy will be unbalanced and distorted when the STATCOM operates at the condition of non-ideal grid voltages. Special attention was paid to the influence of grid voltage quality on STATCOM current and a new control strategy was presented to counteract the influence in this paper. The unbalance and non-sine distortion of grid voltage causes...
Voltage disturbances specially voltage sags can cause significant problems and losses for electricity users. Dynamic voltage restorer (DVR) is a series compensator device that can hold load voltage partially isolated from grid side disturbances. A DVR based-on matrix converter topology is proposed in this paper. A control algorithm using d-q transformation is introduced to generate the reference voltages...
The current source inverter (CSI) is preferred to interface a renewable source such photovoltaics (PV) to the AC power grid because it can provide smooth current source in the DC side, which fits to the PV behaviour and also steps-up the voltage from DC side to AC side, which allows smaller and safer DC voltage levels to be used. However, the CSI has the problem that during an AC grid fault, it cannot...
This paper proposes a combined synchronization method for full scale converter of wind turbine (WT) aiming to ride trough balanced and unbalanced voltage dips due grid faults. A Kalman filter synchronization (KFS), capable extract the positive and negative sequence grid voltages, is designed to have a fast response to voltage disturbances. Then, a synchronous reference frame phase locked loop (SRF-PLL)...
In this paper, a new control strategy for a low cost series connected single phase PV module inverter is introduced that delivers full PV power (at MPPT) to the load together with voltage compensation. The inverter operates during the day time as an active power compensator as well as load voltage regulator under grid voltage sag, swell or even under normal condition. The compensating voltage provided...
This paper presents the digital control scheme of a single phase uninterruptible power supply (UPS). In order to obtain fast response in the current control, the authors propose the digital control scheme based on the instantaneous values. The inverter of the UPS is connected to the load in parallel to reduce the loss of the UPS. The controller is constructed by a DSP. The control schemes in all of...
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