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Fault Ride-Through Capability Enhancement of PV System with Voltage Support Control Strategy  [PDF]
Dehui Zeng, Gang Wang, Guoqing Pan, Haifeng Li
Open Journal of Applied Sciences (OJAppS) , 2013, DOI: 10.4236/ojapps.2013.32B006
Abstract: With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV system is controlled to keep grid connected, as well as inject reactive current to grid when fault occurs. The mathematical model of PV system is established and the fault characteristic is studied with respect to the control strategy. By analyzing the effect of reactive power supplied by the PV system to the point of common coupling (PCC) voltage, this paper proposes an adaptive voltage support control strategy to enhance the fault ride-through capability of PV system. The control strategy fully utilizes the PV system’s capability of voltage support and takes the safety of equipment into account as well. At last, the proposed control strategy is verified by simulation.
Cascaded Multilevel Inverter for PV Cell Application Using PIC Microcontroller  [PDF]
International Journal of Innovative Technology and Exploring Engineering , 2013,
Abstract: The PV power generation have low efficiency due to the various constrains. This paper gives a new proposed method to improve the performance of the PV system. The PV cell is connected to boost chopper and Multi-Level Inverter (MLI). In order to improve the efficiency and for making the power generation available to the grid MLI is employed. MLI have emerged as attractive high power medium voltage converter to reduce harmonic component in the output current due to filter. In the proposed MLI there are 2-H bridge inverters to achieve the 5-level output voltage. A SPWM technique is used to generate the PWM signal for boost chopper inverter switches. Boost chopper is connected between the PV array and MLI. The purpose of boost chopper is to step-up the voltage and to produce continuous current to MLI. The simulation results are validated for the improvement in the PV cell system. The hardware is implemented with boost chopper and multilevel inverter. The PIC microcontroller is used to generate the PWM signal for boost chopper and inverter switches. Boost chopper output is fed to multilevel inverter and the stepped wave is obtained. The results obtained through simulation are verified with hardware results obtained.
Naval Approach for Grid Connected PV Inverters Using PID Controller
R. Sivakumar,T. Rajamanikandan
International Journal of Electrical and Power Engineering , 2012, DOI: 10.3923/ijepe.2011.214.223
Abstract: The DC/AC inverters are used in grid-connected PV energy production systems as the power processing interface between the PV energy source and the electric grid. The energy injected into the electric grid by the PV installation depends on the amount of power extracted from the PV power source and the efficient processing of this power by the DC/AC inverter. In this study, two new methods are presented for the optimal design of a PV inverter power section, output filter and MPPT control strategy. The influences of the electric grid regulations and standards as well as the PV array operational characteristics on the design of grid-connected PV inverters have been considered. The proposed methods have been applied for the optimal design of PV inverters installed at various sites in Europe. The simulation results verify that the proposed optimization techniques enable the maximization of the PV energy injected into the electric grid thus, serving as a tool to gain more energy by the optimized PV installation.
The Study of Optimal Structure and Value of Dump Resistance in Direct-Drive Permanent Magnet Synchronous Generators  [PDF]
Jun Jia, Jie Zhao, Dichen Liu, Chen Cheng, Jun Wang, Linge Qi
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.24044
Abstract: This paper studied the direct-drive permanent magnet synchronous machine (permanent magnet synchronous generator, PMSG) Chopper optimal topology and resistance value. Compared the different Chopper circuit low voltage ride-through capability in the same grid fault conditions in simulation. This paper computes the dump resistance ceiling according to the power electronic devices and over-current capability. Obtaining the dump resistance low limit according to the temperature resistance allows, and calculating the optimal value by drop voltage in the DC-Bus during the fault. The feasibility of the proposed algorithm is verified by simulation results.
A Fuzzy Logic Controller to Increase Fault Ride-Through Capability of Variable Speed Wind Turbines  [PDF]
Geev Mokryani,Pierluigi Siano,Antonio Piccolo,Vito Calderaro
Applied Computational Intelligence and Soft Computing , 2012, DOI: 10.1155/2012/405314
Abstract: A fuzzy controller for improving Fault Ride-Through (FRT) capability of Variable Speed Wind Turbines (WTs) equipped with Doubly Fed Induction Generator (DFIG) is presented. The controller is designed in order to compensate the voltage at the Point of Common Coupling (PCC) by regulating the reactive and active power generated by WTs. The performances of the controller are evaluated in some case studies considering a different number of wind farms in different locations. Simulations, carried out on a real 37-bus Italian weak distribution system, confirmed that the proposed controller can enhance the FRT capability in many cases. 1. Introduction Wind turbines (WTs) are typically located in remote and rural areas. In these areas, the feeders are long and operated at a medium voltage level characterized by a high R/X ratio and unbalanced voltage situations. Furthermore, weak grids are usually referred to have a “low short-circuit level” or “low fault level.” In a weak network a change in the real and reactive power can cause a considerable change in the voltage. The impact relies on the strength of the network and the output power of the WTs [1]. Integration of WTs into weak grids can cause the steady-state voltage level to go outside of its acceptable limit. Therefore, it can limit the exploitation of wind energy resources. Another constraint is related to the effect of the power generated by WTs on the voltage quality. Voltage level limitations and accurate control systems are required to control the voltage variations as well as to improve the voltage quality [2], and variable speed WTs can be used as reactive power sources for voltage control. In recent times, many researches have been carried out in this field. A proportional-integral- (PI-) based control algorithm to control the reactive power produced by WTs has been proposed in [3]. In [4], the authors have proposed a mathematical model of the Doubly Fed Induction Generator (DFIG) for the analysis of active and reactive power performances of a wind farm (WF). In [5], the relation between reactive and active power to maintain the DFIG’s operation inside the maximum rotor and stator currents has been studied. In [6], the authors have proposed a fuzzy controller to manage the operation of a Flywheel Energy Storage System (ESS) connected to the DC bus. Recently, the penetration of WTs into the grids increased, and the performance of the WTs under faults has became an important issue, especially for DFIGs. Several grid codes prescribed, in fact, that WTs should remain connected to the network during and
Experimental Investigation on Ride through Capability of Closed Loop Controlled Matrix Converter Fed Cage Drive
Joshi R,Gupta R,Wadhwani A
IETE Technical Review , 2007,
Abstract: Three phase matrix converters have received considerable attention in recent years because they may become a good alternative to voltage-source inverter pulse width-modulation (VSI-PWM) converters. In fact, the matrix converter provides bidirectional power flow, sinusoidal input/output waveforms, and controllable input power factor. Furthermore, the matrix converter allows a compact design due to the lack of dc-link capacitors for energy storage. The matrix converters are more sensitive to input power disturbances than conventional PWM voltage source inverters due to the absence of dc-link. With the rapid increase of adjustable speed drives (ASDs) in commercial and industrial facilities, the susceptibility of ASDs under power disturbances such as sags, swells, transients and short term power interruption (STPI) has become more important issue. A matrix converter laboratory prototype of 250 VA, 230 V capacity has been developed with the embedded PWM VSI part, to investigate the ride through capability. The ride through approach has been shown to maintain the rotor flux and keep synchronization between the motor and matrix converter during momentary power interruption. It has been shown that by regenerating the mechanical energy stored in load inertia and transferring it to dc-link capacitor within the embedded PWM VSI part, successful ride-through operation is accomplished. The duration of the ride-through operation depends on initial motor shaft speed level, load torque type and load inertia and so the approach is more effective for applications with sufficient load inertia. The ride-through capability has been achieved by the minimal addition of hardware and software into the matrix converter.
A Novel Wind Turbine Concept Based on an Electromagnetic Coupler and the Study of Its Fault Ride-through Capability  [PDF]
Rui You,Braulio Barahona,Jianyun Chai,Nicolaos A. Cutululis
Energies , 2013, DOI: 10.3390/en6116120
Abstract: This paper presents a novel type of variable speed wind turbine with a new drive train different from the variable speed wind turbine commonly used nowadays. In this concept, a synchronous generator is directly coupled with the grid, therefore, the wind turbine transient overload capability and grid voltage support capability can be significantly improved. An electromagnetic coupling speed regulating device (EMCD) is used to connect the gearbox high speed shaft and synchronous generator rotor shaft, transmitting torque to the synchronous generator, while decoupling the gearbox side and the synchronous generator, so the synchronous generator torque oscillations during a grid fault are not transmitted to the gearbox. The EMCD is composed of an electromagnetic coupler and a one quadrant operation converter with reduced capability and low cost. A control strategy for the new wind turbine is proposed and a 2 MW wind turbine model is built to study the wind turbine fault ride-through capability. An integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to study its fault ride-through capability and the impact on the structural loads during grid three phase and two phase short circuit faults.
Fault Ride through Capability Improvement of Wind Turbine Based DFIG Considering an Optimized Crowbar Along with STATCOM under Grid Fault Condition  [cached]
Alireza Zohoori,Ahad Kazemi,Rouhollah Shafaie
Research Journal of Applied Sciences, Engineering and Technology , 2013,
Abstract: Grid disturbances, especially grid faults, have very unfavorable effect on the performance of wind turbine based Doubly Fed Induction Generator (DFIG). In this study active and reactive powers control of DFIG with STATCOM has been carried out to improve Fault Ride Through (FRT) capability of a wind turbine. In order to excel improvement of the DFIG behavior under grid fault disturbances, an optimized crowbar protection method is also considered together with STATCOM. The optimized protection crowbar resistance is achieved through Analytical Hierarchy Process (AHP) algorithm. Simulations results illustrate that an optimized crowbar protection method along with STATCOM has improved the stability of wind farm and provide grid code requirement compared with that of methods without using the optimized crowbar resistance.
Power Electronics for PV-Based Communal Grids  [PDF]
Nicholas Opiyo
Smart Grid and Renewable Energy (SGRE) , 2016, DOI: 10.4236/sgre.2016.72004
Abstract: In this paper power electronics used in PV power generation systems have been reviewed and modelled. PV systems need converters for maximum power point tracking, power conditioning, voltage step-up/down as necessary, and for storage charge-controlling. Inverters are needed for AC loads and for utility grid interfacing. The four basic DC-DC converters commonly used with PV systems have been reviewed and modelled. Different DC-AC inverter types and operational architectures have also been reviewed with the two-stage DC-AC inverter, with the point of common coupling (PCC) at the inverter input, suggested as the most cost-effective and efficient architecture for PV-based communal grids. This is because only one inverter is used for the entire system as opposed to an inverter for every module string, resulting in higher efficiencies, low cost, and low harmonic distortions when compared to systems with PCC at AC terminal. The aim of power conversion/inversion is to extract maximum power possible from the PV system and where necessary, to invert it at close to 100% as possible. Highlight: 1) DC-DC converters are necessary for power conditioning in PV systems; 2) DC-AC inverters are necessary for AC loads and for utility grid interfacing; 3) DC-AC inverters are also used to control the PV systems when grid connected; 4) Best inverter configuration cost-effectively and efficiently allows easy system modifications.
Study on Fault and Isolated Condition in Two Circuit Configurations of PV-ESS Hybrid System  [PDF]
Myo Htaik,Ryoichi Hara,Hiroyuki Kita
ISRN Renewable Energy , 2012, DOI: 10.5402/2012/863813
Abstract: Most photovoltaic (PV) generation systems are connected with a utility grid and recognized as supplemental generation resources; but in some applications such as microgrid concept, a PV system works as a main resource. To improve the availability of PV systems, technological development for higher less output fluctuation in normal condition, higher fault tolerance in fault occurrence, and power demand and supply balancing in isolated condition are required. For these reasons, hybridization of a PV system and an energy storage system (ESS) would become an important technology in the future. This paper presented two kinds of circuit models, conventional “ac-connected PV-ESS,” and proposed “dc-connected PV-ESS” in which ESS is inserted at the dc-side of PV system. This paper also investigated dc-link voltage controlled by dc-dc converter of ESS in dc-connected PV-ESS and suitable control systems are also discussed normal, during fault occurrence and isolated operation. 1. Introduction Recent R&Ds on photovoltaic (PV) generation systems and related technologies and expectation as a solution for the global warming issue accelerate PV installations in the world. PV generation systems have been installed in small-scaled application such as residential sector and in very large-scaled application such as Mega-Watt class PV power plant. However, PV generation output is generally intermittent and unstable since it strongly depends on the external environmental condition such as solar radiation level and ambient temperature. Since most of PV systems are operated with a grid interconnection, fluctuations in PV output may disturb the stable power system operation and deteriorate the power quality. In some applications such as microgrid concept, a PV system works as a main source. In order to investigate the above concerns, the New Energy and Industrial Technology Development Organization (NEDO) of Japan promoted two demonstration projects in Japan [1]. In those projects, effects of concentrated PV installations at a residential area and interconnection of a MW-class PV power plant were investigated. Application of energy storage systems (ESSs) such as lead-acid battery and/or Sodium Sulfur (NAS) battery were also developed to improve stability and controllability of PV systems. For example, a method for suppressing the output fluctuation of PV system using NAS battery system was proposed and investigated in [2]. Furthermore, in [3], the ESS capacity required for suppressing PV output fluctuation was evaluated. A usual PV-ESS hybrid system adopts the circuit
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