Virginia Ivanov

Diagnosis system for power rectifiers using the tree of faults method

The static power converters are essential equipment for adapting the type and parameters of the electric energy, placed between sources and loads. During the exploitation of the static power converters, the experience of an expert is absolutely necessary for competitive operation. Minor faults or defects of this equipment can lead to ravaging effects. The most part of the monitoring and diagnosis systems are developed around expert systems. The paper deals with a diagnosis system dedicated to the power rectifiers using the tree of faults method. Based on the effects noted in the behavior of the power rectifiers, an expert system for the diagnosis and the functional testing was developed, by considering the abnormal comportments and the faults which determine these. For building the inference mechanism, the faults tree method applied to the converters was used. The database is comprehensive and takes into account the most frequent faults which occur during the converters operation. The designed expert system was developed by using the CLIPS 6.0 language. The diagnosis system of the bridge rectifier analyses and identifies the causes of the faults which occur during the operation and reduces the displayed results if two sets of values of the sources which determine the same answer differ by a single input. The paper presents the results of the system running and the conclusions resulted after the expert system was executed in order to qualitatively and quantitatively analyze the tree of faults corresponding to the considered equipment.

Short circuits faults diagnosis for the rectifier based on the analytic model method

The monitoring and diagnosis systems are needed to analyze the normal operation and maintenance of electrical systems. The approach is of interest because there are a lot of measuring points and a multitude of possible faults which can be analyzed. The method based on analytic models can be applied and the system behavior can be compared with normal operation of the system obtained as result of processing the mathematical model. The experience of an expert is absolutely necessary for the competitive operation of the static power converters. Ravaging effects can occur only if minor faults or failings appear in these equipment. The paper proposes a method of diagnosis which compares the waveforms in normal operation with the ones resulted from the analytic model when different types of power supply short circuits faults occur, applied to a variable DC drive supplied by a three-phase rectifier.

Diagnosis method for the elements of the three-phase rectifier supplying a variable DC drive

For the operation of the static power converters, the experience of an expert is absolutely necessary for competitive functioning. Minor faults or defects of these equipments can lead to ravaging effects. In this paper is proposed a diagnosis method based on the analytic model which investigates the output waveforms of a three-phase rectifier supplying a variable DC drive for two types of possible faults of the switches: interrupted and short circuit. For identifying the defective components, the waveforms corresponding for different faults are stored in an information database in order to be compared with the ones corresponding to normal operation.

Concerning the selectivity of the experimental device based on eddy currents for the metal waste separation

In this paper, a method for the identification and separation of the ferrous and non ferrous metal waste, as well as of their alloys, is described. For this purpose, the obtained results using an experimental device based on eddy currents are presented. One probe coil having an open magnetic circuit made from Mn Zn ferrite, U type is supplied with a high frequency sinusoidal AC voltage. The probe coil is located on the random nonferrous metal parts from copper and his alloy such as brass, on the aluminum and his alloy duralumin and also on the random ferrous metal parts from steel carbon, ferritic stainless steel and GO silicon steel. The probe coils impedance variation to changes in frequency and metal material type were determined by measuring the current when the voltage value was kept constant. The influence of material parameters, such as electrical conductivity for the nonferrous materials, and the magnetic permeability for the ferrous ones, over the depth penetration values of the eddy currents and therefore over the impedance values was highlighted. In contrast to other types of magnetic separators, where the metallic wastes are shredded, the presented method can be applied for the separation of metal scrap with various geometries and sizes.

On the experimental setup based on Eddy current meant to metallic parts identification

The metallic waste management, from industrial or household activities, is of great actuality. In this context, the sorting of the mixtures of metallic materials and the identification of the non-ferrous and ferrous metallic pieces is of high interest for operators in the field. This paper presents the results achieved using our experimental device based on eddy currents for ferrous and non-ferrous materials identification. The device allows the measurement of the current through a high-frequency probe coil, in different situations, as follows: the probe coil in the air, near ferrous and non-ferrous metallic parts. The device is able to identify types of metallic materials based on the changes of the coil impedance and consequently the changes of the measured currents at constant voltage amplitude, due to the magnetic field of the induced eddy currents. The changes of the coil electric impedance at high frequency supply voltage are due to the material properties, such as electrical conductivity and magnetic permeability.

Predictive Versus Vector Control Of The Induction Motor

The paper deals with the vector control and predictive control of the induction motor. For the vector control, the rotor flux oriented one is pointed out, with highlight on the voltage source inverter type. The influence of the most important parameter variations (e.g. stator resistance) is discussed. A simple (and practical) method for avoiding these influences is presented, based on proper simulation models. Following the basics of the predictive control, a simulation model for this type of command is presented, together with simulations results. Finally, the results are cross analysed and further actions are proposed the work continuation. INTRODUCTION On one hand, since the basic work concerning torque and field control due to Leonhard, Blaschke and their followers in the 1970s, the AC drives became a competitive technology with respect to the traditional one, based on DC drives. In rotating references, solidar with the rotor flux, stator flux or magnetizing flux respectively, there is an obvious decoupling between the two components of the stator current: while the direct component acts on the flux modulus only and produces the reactive component, the quadrature component generates the torque, being the active component. The two components of the stator current may be thus controlled independently and the flux and torque generation are thus decoupled, similarly to the DC motor. Due to results simplicity, the rotor flux orriented control has imposed almost as a standard. From here, two types of control were engineered. On one hand we have the direct control drives, where flux position and modulus are known while the reactive and active components of the stator current are computed in the proper reference frame using the set-point torque and flux. On the other hand we have the indirect control drives, where the slip frequency is computed and imposed without direct knowledge of the flux, while the reference system change from the flux-reference to stator-reference one is performed by integration of the sum of the motor speed and the speed corresponding to the computed slip (Casadei et al. 2002, Vas 1998). A very simple method for the toque control is also the Direct Torque Control (DTC), suited for electrical traction applications (Takahashi and Noguchi 1986, Baader et al. 1992, Ehsani et al. 1997, Faiz et al. 1999, Haddoun et al. 2007, Ivanov 2009, Ivanov 2010). On the other hand, the increased computational capabilities of the existing DSP allow the implementation of the predictive control at the level of the converters which induce the hybrid character of the overall control system of the drive. We infer that predictive control has established itself in the last 5-7 years as a very proficient form of controlling highly nonlinear and uncertain systems; moreover the most recent results show its applicability to fast processes among which drives and their converters have a central position (Seo et al. 2009, Prieur and Tarbouriech 2011, Geyer et al. 2008, Mariethoz et al. 2010, Geyer et al. 2009, Trabelsi et al. 2008, Shi et al. 2007, Rodriguez et al. 2007, Larrinaga et al. 2007, Richter et al. 2010, Almer et al. 2010). The paper will briefly present in the first section the basics of the vector control for the rotor flux oriented control for voltage source inverter, with highlight on the influence of the parameters variations on the drive performance. A simple method for reducing these influences will be discussed based on appropriated models. The basics of the predictive control will be presented in Section 2. Section 3 will analyse the predictive control applied to the induction motor, based also on a Simulink model. Finally, conclusions will be issued and ideas for continuation will be pointed out. VECTOR CONTROL OF INDUCTION MOTOR As stated above, the vector control strategy most often used is the rotor flux oriented one. The reasons reside in the simplicity of the expressions resulted from the rotor voltage equation which mainly gives the rotor flux speed and further, by integration, the rotor flux position, used at its turn for the transformation of the reference currents/voltages from the rotary frame to the stationary one. For the squirrel cage induction motor, the rotor voltages equation in terms of phasors is ( ) 0 r r r mr r r r r r d R i j P dt Ψ Ψ Ψ Ψ = + + ω − ω Ψ , (1) where Rr is the rotor resistance, r r i Ψ is the rotor current, m ω is the rotor flux speed, ω is the mechanical speed of the rotor and P is the number of pairs of poles. The Ψ subscript highlights that (1) is expressed in the rotary frame synchronous with the rotor flux r r Ψ Ψ . By assuming unsaturated operation (realistic hypothesis when the stator currents are precisely controlled), the rotor flux expressed in terms of magnetizing inductance Lm and rotor magnetizing current mr i is m r mr L i Ψ = ⋅ Consequently, (1) becomes ( ) 0 mr r m mr r m r r mr d i R i L j P i L dt Ψ = + + ω − ω ⋅ ⋅ . (2) The rotor current r r i Ψ , being immeasurable for the squirrel cage motor, is expressed in terms of the stator current s r i Ψ and the magnetizing one. By denoting the rotor time constant / r r r T L R = , (2) becomes ( ) mr r mr r r mr s r mr d i T i i j P T i dt Ψ + = − ω − ω , (3) Lr being the total rotor inductance which includes the leakages ( r m r L L Lσ = + ). By identifying the terms on each of the axes d, q, the following two expressions result which are the simplest among all the vector control types mr r sd mr d i T i i dt + = , (4) sq mr r r mr i P T i ω = ω + . (5) We notice from (4) that if the flux is kept constant ( ct. mr i = ), then = ct. sd mr i i = As the electromagnetic torque expressed in the rotor flux oriented frame is 2 3 2 m e sd sq r L t P i i L = ⋅ , (6) from (5) and (6) results that the slip speed (term 2 in (5)) is proportional with the torque and further, the mechanical characteristic of the induction motor are straight lines, quite similar to the DC motor. When the motor is supplied by a voltage source inverter, the necessary voltages are obtained by considering the stator voltages equation expressed in the same rotary frame synchronous with the rotor flux r r Ψ Ψ : s r r r s s m s r s r mr s r m s r r r d i di u R i L L dt dt j L i j L i Ψ Ψ Ψ Ψ

Controlled Switching - Solution For Reducing The Overvoltages At Commutation Of The Transport And Distribution Lines.

Recently, worldwide, the controlled switch became a technical solution for reducing the switching stress. After 90es, the number of equipment which uses the controlled switch fast increased, mainly due to the achieved performances. The controlled switching can be applied to any type of commutations. Now there are dedicated controllers which are used more often for the switching of the transport and distribution lines, of the small inductive loads, of the capacitors batteries, or the energizing the no load power transformers. The paper deals with the simulation of the commutation of a transportation line by using the distributed parameters model. The controlled switch of the line is compared with the uncontrolled one, highlighting the major differences in what concerns the stress. TRANSPORT AND DISTRIBUTION LINES SWITCH When the long lines are energized, undesired over voltages can be generated in the transport and distribution networks. These are caused by the propagation, reflection and refractions of electromagnetic waves, both in ramifications points and end of the lines. Such phenomenon both occur when the lines are quick re-energized after a disconnection. The cause of the over voltages in this case are the residual charges on the line. As will be seen, both the over voltages and their slopes determine important stress of the equipment insulation. When connected, at the end of the long lines over voltages can occur due to more causes. For lines shorter than 1500 km, the input impedance has capacitive character and the voltage drop on the equivalent inductive reactance of the system has the same sign with the supplying fem. Consequently, this voltage drop is added to the fem. Thus, the resulted overvoltage highly depends by the line length and by the short circuit power of the system. Another cause of the over voltages resides in the oscillations which occur when the initial repartition of the voltage across the line is replaced by the new repartition corresponding to the new steady state operation, after its connection. The stress of the insulation depends both by the amplitude of the overvoltage and by its shape, characterized by two parameters: rising duration and falling duration. (Gusa 2002). The mathematical models used to determine the over voltages can be more or less complex, depending on the characteristics of the studied commutation phenomenon. The long lines can be modeled by circuits with either uniform distributed parameters or concentrated parameters. The models can be single phase or three phase ones. The over voltages when a line is energized can be analytically estimated if two hypotheses are considered: the lines have no losses and all the three phases of the breaker are simultaneously connected. For the analytically evaluation of the over voltages at the line energizing with no residual charge on the line, the simplified diagram in Figure 1 can be considered. The equation specific to the equivalent electric system is: 1 1 s s di e u L dt = + ⋅ . (1) The equations specific to the uniform distributed long line model are: u i r i L x t ∂ ∂ − = ⋅ + ⋅ ∂ ∂ , (2) i u g u C x t ∂ ∂ − = ⋅ + ⋅ ∂ ∂ , (3) where: ⋅ es – the instantaneous value of the fem of the system; ⋅ u1 – instantaneous voltage at the front end of the long line; Proceedings 23rd European Conference on Modelling and Simulation ©ECMS Javier Otamendi, Andrzej Bargiela, Jose Luis Montes, Luis Miguel Doncel Pedrera (Editors) ISBN: 978-0-9553018-8-9 / ISBN: 978-0-9553018-9-6 (CD) Figure 1: Simplified Equivalent Diagram of a No Load Line when is Connected ⋅ i1 – the instantaneous value of the current at the front end of the long line; ⋅ Ls – the inductance of the supplying electric system; ⋅ u, i the voltage and the current in a point of the line; ⋅ r, L, g, C – the parameters of the line per length unit. By solving the equations (1-3), the voltage at the end of the line results:

Controlled switching for fault interruption in transport and distribution lines

The controlled switch became a technical solution for reducing the switching stress. The controlled switching can be applied to any type of commutations. There are now dedicated controllers which are used more often for the switching of the transport and distribution lines, of the small inductive loads, of the capacitors batteries, or for energizing the no load power transformers. The paper deals with the simulation of the commutation of a transportation line by using the distributed parameters model. The controlled switch for fault interruption in transport and distribution lines is compared with the uncontrolled one, highlighting the major differences in what concerns the stress. The primary objective of controlled short-circuit interruption is to restrict the arcing time of the circuit-breaker and thereby seek to reduce the electrical stress and wear on the interrupter.

Power supply short circuits faults diagnosis for the rectifier in a driving system

The paper applies the diagnosis method based on the analytic model by investigating the output waveforms of the currents and voltages specific to a rectifier in a driving system. The direction is interesting due to the multitude of the measuring points and large number of possible faults to be analyzed. The method based on analytic models can be applied and the system behavior can be compared with the results of the mathematical model which reproduces the system in normal operation. The fault simulated is grounding of power phases. The different types of power supply short circuits faults will cause more or less important oscillations of the currents and voltages. The consequences are corresponding, more or less severe and can lead to major damages. For identifying the fault, the waveforms corresponding to different faults are stored in an information database and compared with the ones corresponding to normal operation.

Diagnosis And Monitoring Of The PMSM Using The Analytical Model Method.

The paper applies the diagnosis method based on the analytic model by investigating the output waveforms of the currents, torque and speed specific to a PMSM driving system. Several faults are simulated: open phase, entire phase short circuit in two situations (with and without current measurement, short circuit before and after current sensor respectively) and current sensor fault (no reaction). Thanks to the described model, the method based on analytic models can be applied and the system behavior can be compared with the results of the mathematical model which reproduces the system in normal operation. For all types of faults, more or less important oscillations of the currents and output torque are noticed. The consequences are corresponding, more or less severe and can lead to major damages.