Showing papers by "V. Fernao Pires published in 2015"

Detection of stator winding fault in induction motors using a motor square current signature analysis (MSCSA)

Abstract: In this paper the short-circuit fault inter-turn on the stator of an induction motor is analysed by an online diagnostic method. For the diagnostic method it is proposed the motor square current signature analysis (MSCSA). This method uses the results of spectral analysis of the instantaneous square stator current. The effects of stator square current spectrum are described and the related frequencies determined. This method is similar to the instantaneous power signature analysis, however has the advantage of just require one current sensor. Several simulation and experimental results are presented in order to illustrate the characteristics of the proposed method.

A PV panel simulator based on a two quadrant DC/DC power converter with a sliding mode controller

Abstract: The use of a solar photovoltaic (PV) panel simulator can be a valued tool for the design and evaluation of the several components of a photovoltaic system. This simulator is based on power electronic converter controlled in such a way that will behave as a PV panel. Thus, in this paper a PV panel simulator based on a two quadrant DC/DC power converter is proposed. This topology will allow to achieve fast responses, like suddenly changes in the irradiation and temperature. To control the power converter it will be used a fast and robust sliding mode controller. Therefore, with the proposed system I–V curve simulation of a PV panel is obtained. Experimental results from a laboratory prototype are presented in order to confirm the theoretical operation.

Fault detection and diagnosis in a PV grid-connected T-type three level inverter

Abstract: In grid-connected photovoltaic systems (PV) the inverter is a fundamental component. In fact, a fault in a switch of this power converter could result in an important system malfunction. Thus, fault detection and diagnosis of this fault type is fundamental to overcome this problem. This paper proposes a fault detection diagnosis for the T-type three level inverter. This inverter presents characteristics such as output voltage multilevel and good capability to work in fault tolerant mode. The proposed fault diagnosis method is based on the mass center of the voltage pattern. It is characterized by low computational requirements and not dependent of the load. Simulation results show the characteristics of the proposed method.

A control strategy for a grid-connected PV system with unbalanced loads compensation

Abstract: Photovoltaic systems plays an important role as a micro generators. These systems are normally near domestic loads that normally are unbalanced. Thus, a photovoltaic system that also compensates unbalanced loads is proposed. This system is implemented with a four leg voltage source inverter connected to the AC mains with accessible neutral. In order to control the AC currents a space vector based hysteresis controller in αβ0 coordinate system is used. A control algorithm that determines the references of the AC currents for compensate the load unbalance and transfer the generated by the photovoltaic panels is proposed. The performance of the proposed system is validated by several simulation tests. The obtained results show that the system can effectively transfer the energy from the photovoltaic panels and at the same time to compensate unbalanced loads.

A dual inverter topology controled by a voltage sliding mode in normal and fault operation

Abstract: Several multilevel inverters have been proposed and extensively studied. The main topologies are the neutral point clamped inverter, the flying capacitor inverter and the cascaded connection of bridge inverters. A modular recently proposed alternative is the dual inverter configuration. This topology requires only two classical three phase voltage source inverters. One of the characteristics of this dual inverter is the high number of redundant states of the ac voltages according to the available switching combinations. Therefore, the dual inverter topology presents interesting capabilities for fault-tolerant operation. In this work, it is proposed a new controller based on a sliding mode approach and α,β vector modulator, for normal and fault operation of the dual inverter. Some simulation studies are presented in order to verify the characteristics of the proposed methodology. A comparison with the NPC multilevel topology is also presented. From this comparison it is possible to confirm the advantages of the dual inverter topology with the proposed control structure in fault operation.

Double Three-phase Induction Machine Modeling for Internal Faults Simulation

Abstract: Multi-phase induction motors present excellent characteristics for faulty tolerant operation. Among them, six-phase induction motors, which are among the most used, exhibit two types of configuration: the double three-phase and the six-phase with single neutral. The double three-phase presents the advantage of reducing harmonics with its symmetric winding. This article presents a new modeling of the double three-phase induction machine for internal faults simulation. The developed model is composed by two sets of three-phase stator windings forming two stars. The model considers an arbitrary displacement (α) between stator stars, allowing the simulation of this type induction machines with different configurations, with 60° displacement used herein. The simulations of internal faults, such as stator windings or rotor faults, are both considered in the proposed model, allowing the machine study under abnormal conditions. The double three-phase induction machine model was fully implemented in real c...

Automating remote grid acceptance and energy services tests suited for large deployments of PV systems in active distribution networks

Abstract: The perspective of Smart Grid developments brings a picture with active distribution networks having many distributed resources such as PV connected to the grid through inverters. The challenge for this future is so complex that the Smart Grid Coordination Group (SG-CG) is already considering for standardization in the new Use-Case cluster "Connect and active actor to the grid", the high level use case "Managing generation connection to the grid". This is considered as emerging necessary functionality of the "Distribution management system", to be subject of CEN/CENELEC standardization. This paper presents enabling solutions for these requests and proposes solutions for Automated Remote Grid Acceptance and Energy Services Tests using new concepts for the Smart Meter and for the inverters design. Results to sustain the proposals are also sustained by a case of simulation for a Grid Acceptance test — Fault Ride Through with reactive power and for an Energy Services Test proving interphase simetrization service.

Multiobjective switching devices placement considering environmental constrains in distribution networks with distributed energy resources

Abstract: In the past years, the Electrical Utility Industry has been confronted with numerous challenges, which include amongst others, the widespread use of distributed energy resources and a public increase in environmental issues. By optimizing the location of switching devices on the electrical distribution system, an improvement in energy not supplied and in the use of distributed energy resources can be obtained. This work proposes the genetic evolutionary algorithm NSGA-II for the multiobjective optimal placement of the switching devices. A trade-off between the investment in switching devices, energy not supplied and greenhouse gas emissions is analyzed, in order to choose the optimal placement of switching devices in distribution electrical networks. The proposed method was tested with a Portuguese real distribution network. The obtained results are presented and discussed.

A modeling scheme for the Le Blanc transformer

Abstract: One of the major problems in power networks due to AC electrified railway systems is voltage and current unbalance. Several methods can be used for reducing these unbalancing problems. Several methods can be used for reducing these unbalancing problems, being one of the most used specially connected transformers. Several transformer connection schemes, including single-phase, V-V, Scott, and Le Blanc connections, are usually considered. The Le-Blanc transformer is a special winding connection transformer adopted for the single-phase power supply of electrified railway systems. This paper deals with a modeling scheme for the Le-Blanc transformer. Simulation and experimental results are presented in order to show the effectiveness of the proposed method.

A new teaching tool to enhance power quality assessment

Abstract: The study and assessment of Power Quality issues is nowadays a very important subject, particularly regarding Cyber-physical and Industrial Agents based systems, which are extremely sensitive to Power Quality disturbances. Giving students or engineers practical experience in this field requires a large investment from teaching institutions. This paper presents a laboratory device that emulates Power Quality disturbances in order to provide the required experimental expertize in the subject. It addresses limiting aspects such as harmonic distortion, flicker, sags, swells and transients. The developed system presents a good opportunity for technicians, even without deep knowledge on the field of power quality, to learn basic principles and be able to identify Power Quality events. Since the system is based on real data, represents a valuable approach giving trainees practical knowledge on the field.

Distributed energy resources and environmental optimization using a memetic algorithm

Abstract: In recent years the Electrical Utilities has been confronted with several challenges which include amongst others the widespread use of distributed energy resources and a public increase in environmental issues. By optimizing the location of switching devices on the electrical distribution system, an improvement in energy not supplied and in the availability of the distributed energy resources can be obtained thus reducing greenhouse gas emissions. This work proposes the Memetic evolutionary algorithm for the multiobjective optimal placement of the switching devices. A trade-off between the investment in equipment cost (EC), energy not supplied (ENS) and greenhouse gas emissions (GGER) is analyzed, in order to choose the optimal placement of switching devices in distribution electrical networks. The proposed method was tested with a Portuguese real distribution network. The obtained results are presented and discussed.