Machine Terminals Research Articles

Channel Efficiency with Security Enhancement for Remote Condition Monitoring of Multi Machine System Using Hybrid Huffman Coding

This paper presents a novel scheme of remote condition monitoring of multi machine system where a secured and coded data of induction machine with different parameters is communicated between a state-of-the-art dedicated hardware Units (DHU) installed at the machine terminal and a centralized PC based machine data management (MDM) software. The DHUs are built for acquisition of different parameters from the respective machines, and hence are placed at their nearby panels in order to acquire different parameters cost effectively during their running condition. The MDM software collects these data through a communication channel where all the DHUs are networked using RS485 protocol. Before transmitting, the parameter’s related data is modified with the adoption of differential pulse coded modulation (DPCM) and Huffman coding technique. It is further encrypted with a private key where different keys are used for different DHUs. In this way a data security scheme is adopted during its passage through the communication channel in order to avoid any third party attack into the channel. The hybrid mode of DPCM and Huffman coding is chosen to reduce the data packet length. A MATLAB based simulation and its practical implementation using DHUs at three machine terminals (one healthy three phase, one healthy single phase and one faulty three phase machine) proves its efficacy and usefulness for condition based maintenance of multi machine system. The data at the central control room are decrypted and decoded using MDM software. In this work it is observed that Chanel efficiency with respect to different parameter measurements has been increased very much.

Performance Evaluation of Eleven-Phase Induction Machine with Different PWM Techniques

Multiphase induction machines are used extensively in low and medium voltage (MV) drives. In MV drives, power switches have a limitation associated with switching frequency. This paper is a comparative study of the eleven-phase induction machine’s performance when used as a prototype and fed sinusoidal pulse-width-modulation (SPWM) with a low switching frequency, selective harmonic elimination (SHE), and single pulse modulation (SPM) techniques. The comparison depends on voltage/frequency controls for the same phase of voltage applied on the machine terminals for all previous techniques. The comparative study covers torque ripple, stator and harmonic currents, and motor efficiency.

Power Electronics Control of an Energy Regenerative Mechatronic Damper

This paper presents the development of a power electronics controller for a proof-of-concept energy regenerative damper in vehicular applications. The damper consists of an efficient motion conversion mechanism to convert translational base vibration into reciprocating rotary motion, a brushless three-phase permanent-magnet rotary machine, and a three-phase power converter. A power electronics boost controller is developed to capture the generated electrical power and store it into a battery that allows overcoming kinematic nonlinearities in the motion conversion stage. To this end, a sliding-mode controller that can enforce a resistive behavior across the terminals of the rotary machine by regulating the converter's input current in real time is presented. Through the proposed approach, the mechanical damping coefficient of the system can be controlled, on demand, with an energy regenerative function. The performance of the developed system is evaluated under sinusoidal excitation inputs and transient conditions when operating with a damping coefficient of 650 $\hbox{N}\cdot\hbox{s/m} $ synthesized through power electronics and control. Experimental results that evaluate the performance of the proposed energy regenerative damper are presented.

Parameter Extraction of a PM Machine Employing 3D Finite Element Analysis Tools for Model Predictive Control Schemes

This paper introduces a permanent magnet (PM) machine model accounting for saturation effects and non-sinusoidal electromotive force (EMF) employed in model predictive control schemes. The procedure of the model parameters determination is based on the three dimensional finite element analysis (FEA) considering saturation and cross-coupling effects. The conventional equivalent circuit model is subject to modifications so as to incorporate data derived from FEA enabling the model predictive control strategies to obtain proper actions for the converter operation based on the accurate prediction of the machine performance. The regeneration of the n-order harmonic components of the non-sinusoidal EMF is attained by combining methods of superposition and approximation estimating the output voltage at the machine terminals for different loading and speed. Developed model simulation results have been validated by experiments performed on an inset PM machine prototype.

Energy Regenerative Suspension Using an Algebraic Screw Linkage Mechanism

This paper presents the development of a novel energy-regenerative suspension mechanism. The system consists of a mass-spring unit coupled with an algebraic screw kinematic pair, a rotary permanent magnet synchronous generator (PMSG), and a three-phase boost charger connected to a battery. The algebraic screw converts the translational vibration into a reciprocating rotary motion which drives the PMSG through a planetary gearhead. A pulse-width-modulated three-phase boost converter is then used to convert the energy generated by the rotary machine into battery charge. To this end, a control and switching algorithm is utilized that makes the battery appear as a pseudo-resistor across the terminals of the rotary machine. Introducing this pseudo-resistive characteristic across the machine produces the same effect as mechanical damping with an energy regenerative function. The design and analysis of the regenerative suspension mechanism are presented by considering the dynamics of the electromechanical device, parameters of the suspension system, and the base excitation input profile. Experimental results are presented that evaluate performance of the proposed regenerative damper on a small-scale suspension system, which demonstrate the feasibility of building energy-regenerative dampers.

A Novel Neuro Fuzzy Based Control Strategy for Variable Speed Wind Energy Conversion System

— This article describes a novel control strategy of a stand-alone Self-Excited Induction Generator (SEIG) driven by a variable speed wind turbine. The conventional Wind Energy Conversion System (WECS) controller is restructured by using a Current Controlled Voltage Source Inverter (CC-VSI) with an Electronic Load Controller (ELC) is connected in parallel with the main consumer load to the AC terminals of the induction machine. The proposed control strategy has Neuro-Fuzzy Logic Controller (NFLC) and Hysteresis Current Controller (HCC) to extract the maximum available energy from the wind turbine as well as to regulate the generator terminal voltage simultaneously against wind speed and main load variation. The control parameters are derived according to steady state characteristics of the proposed system. The proposed system is modelled and simulated with the help of SimPower Systems block sets in MATLAB

Investigation of the Rotor Demagnetization Characteristics of Interior PM Synchronous Machines During Fault Conditions

This paper investigates the transient magnetic behavior of an interior permanent-magnet (IPM) synchronous machine following a large transient current caused by a fault condition. A combination of finite-element (FE) analysis and numerical integration of the machine equations is used to calculate the currents resulting from a symmetrical three-phase short-circuit fault at the machine terminals, including magnetic saturation effects. FE analysis is further used to simulate the magnetic behavior of the machine when subjected to the fault currents, with a particular focus on the propagation of the demagnetizing MMF throughout the conductive laminations as well as the conductive PM material. Eddy currents induced in the laminations and magnet material are shown to impede the progression of the demagnetizing MMF. However, the transient analysis illustrates the manner in which the fault currents ultimately trigger the onset of irreversible demagnetization of significant portions of the rotor magnets in the analyzed machine. The transient demagnetization analysis method is extended to investigate the influence of several key design variables, including machine operating temperature and segmentation of the rotor magnets.

A Space Vector PWM With Common-Mode Voltage Elimination for Open-End Winding Five-Phase Drives With a Single DC Supply

Open-end winding three-phase drive topologies have been extensively investigated in the last two decades. In the majority of cases supply of the inverters at the two sides of the winding is provided from isolated dc sources. Recently, studies related to multiphase open-end winding drives have also been conducted, using isolated dc sources at the two winding sides. This paper investigates for the first time a five-phase open-end winding configuration, which is obtained by connecting a two-level five-phase inverter at each side of the stator winding, with both inverters supplied from a common dc source. In such a configuration it is essential to eliminate the common-mode voltage (CMV) that is inevitably created by usual PWM techniques. Based on the vector space decomposition (VSD), the switching states that create zero CMV are identified and plotted. A space vector pattern with large redundancy of switching states is obtained. Suitable space vectors are then selected to realize the required voltage reference at the machine terminals with zero CMV. The large number of redundant states enables some freedom in the choice of switching states to impress these space vectors. Out of numerous possibilities, two particular switching sequences are chosen for further investigation. Both are implemented in an experimental setup, and the results are presented and discussed.

Wind Energy Conversion System for Rural Application

This paper presents the use of induction generator with suitable control strategy for use as standalone wind energy conversion system. This may find application in remote rural areas where extension of 11 kV feeder may not be feasible due to physical terrain and where drawing of line may not be economically viable if loads are dispersed over wide area. This Induction machine is driven from a prim em over which is usually a wind turbine. The stator terminals of the induction machine is connected to a voltage source converter. The voltage source converter (VSC) is a three level diode clamped VSC. The terminals of the converter are connected to a capacitor and a battery. The battery is initially charged to 12 V and provides initial magnetisation for the Induction Generator. The terminals of the stator are also connected to an induction motor represented by RL load. Control strategy has been developed to keep the DC voltage constant irrespective of variation of load and rotor speeds. The total harmonic distortion in the line voltage of the induction machine is ensured to be within limits by employing three level converter. The proposed system is mathematically modelled using SIMULINK/MATLAB. The simulated results validate the theory studied.

Efficient voltage regulation scheme for three‐phase self‐excited induction generator feeding single‐phase load in remote locations

This study presents analysis, design and implementation of a microcontroller based electronic load controller (ELC) for efficient voltage regulation of a three-phase self-excited induction generator (SEIG) feeding single-phase loads in remote locations. The proposed ELC has an uncontrolled rectifier, a filtering capacitor, an insulated gate bipolar transistor switch and a series dump load. The pulse-width modulation (PWM) pulses with appropriate duty cycle are generated using the dsPIC30F6010 microcontroller. The duty ratio is determined based on the closed-loop control scheme which decides the amount of power diverted to the dump load. The proposed SEIG–ELC system demonstrates an effective power switching between the main load and the dump load thereby providing an efficient voltage regulation at the machine terminals. The controller is modelled in Matlab/Simulink and the simulated results are validated by experimental results.

Application of Load Compensation in Voltage Controllers of Large Generators in the Polish Power Grid

The Automatic Voltage Regulator normally controls the generator stator terminal voltage. Load compensation is used to control the voltage which is representative of the voltage at a point either within or external to the generator. In the Polish Power Grid (PPG) compensation is ready to use in every AVR of a large generator, but it is utilized only in the case of generators operating at the same medium voltage buses. It is similar as in most European Power Grids. The compensator regulating the voltage at a point beyond the machine terminals has significant advantages in comparison to the slower secondary Voltage and Reactive Power Control System (ARNE)1 . The compensation stiffens the EHV grid, which leads to improved voltage quality in the distribution grid. This effect may be particularly important in the context of the dynamic development of wind and solar energy.

FPGA-Based Dynamic Reconfiguration of Sliding Mode Current Controllers for Synchronous Machines

This paper presents the concept of dynamic reconfiguration between two sliding mode current controllers for synchronous motor drives. The first one is a Direct Sliding Mode (DSM) current controller, which is based on a switching table synthesized via sliding mode theory. The second one is an Indirect Sliding Mode (ISM) current controller that computes a reference voltage vector via sliding mode theory. The computed reference voltage is then applied to the terminals of the synchronous machine through a Pulse Width Modulation (PWM) process. This item studies and discusses the reconfiguration criteria and presents the main interest of using FPGA digital solutions for dynamic reconfiguration process implementation between the two sliding mode current controllers. Numerous experimental results are presented in order to confirm the interest and performances of the proposed reconfigurable sliding mode current controller.

Impact of speed ripple on the back‐emf waveform of permanent magnet synchronous machines

Permanent magnet synchronous machines are frequently used in industry because of their high efficiency and favourable dynamic properties. Mechanical limitations and design considerations cause several harmonics in the flux and back-emf of these machines. The back-emf harmonics can be measured on the machine terminals if no stator current is present and the neutral point is accessible. The measured harmonics can then be included in a mathematical model of the machine. This measurement is often done for a constant speed. However, when a speed ripple is present, several new harmonics are introduced in the flux and back-emf. Although the existence of this phenomenon is intuitively clear, it has not yet been investigated in detail and no method exists to calculate these additional harmonics. Nevertheless, the impact of a speed ripple on the back-emf can become significant in some applications. Therefore in this study, a mathematical model is presented, which allows one to accurately calculate the additional back-emf harmonics in the presence of speed ripples. Also, it provides more insight in the interaction between speed ripples and harmonics. The mathematical model is extensively validated by means of simulations and experiments.

A Boost-Type Power Converter for Energy-Regenerative Damping

This paper presents the development of an energy-regenerative damper consisting of a mass-spring system coupled with a permanent-magnet dc machine, power electronics converter, and a battery. The vibration energy induced in the mass-spring system is converted into battery charge through the dc machine and a power electronics controller. The latter is a pulse-width-modulated boost-type converter, which enforces a pseudoresistive behavior between its input terminals through a feedback control scheme developed in this study. Introducing this pseudoresistive behavior across the input terminals of the dc machine produces the same effect as a mechanical damper but with an energy-regenerative function. The dynamics of the mass-spring system coupled with the linear machine are used to obtain a condition for extracting maximum electric power from mechanical vibrations. Experimental results are presented that demonstrate the performance of the regenerative damper using a small-scale suspension system test bed.

PERFORMANCE ANALYSIS OF AFPM GENERATOR DIRECT DRIVEN WIND TURBINE WITH STORAGE SYSTEM

Direct-drive type with no acceleration rare and the windmill blades attached to the disc surface of Axial Flux Permanent Magnet generator (AFPM) realizes simple structure and omission of central dynamic transformation achieves very high energy conversion efficiency of the generator. The generator itself consists of two magnets rotors that return together directly coupled to the blades. In this research study, one magnet rotor is on each side of the stator and each magnet rotor contains 16 Neodymim-Iron-Boron (NdFeB). The stator contains 12 coils wound with copper wire and cast into plastic resin, in line with and between the paths of each magnet. The AFPM generator direct drive wind turbine converts the mechanical energy by the rotating shaft as the wind pushing 3 wooden blades into 3-phase alternating current (AC) electricity that varies in frequency. In order to get this generated power into a battery bank, three-phase bridge rectifier is connected to the three terminals of the machine. The alternator will start 48 volt charging batteries system at about 140 rpm in 4m/s wind speed and reach rated output of 1.8 kW at 375 rpm in 10m/s wind speed. This machine is specially designed for battery charging and it’s probably quite useful and cost effective for remote locations that are not connected to the national grids where conventional methods of energy supply are expensive or impractical.

A new control strategy for a stand-alone self-excited induction generator driven by a variable speed wind turbine

This paper presents a new control strategy of a stand-alone self-excited induction generator (SEIG) driven by a variable speed wind turbine. The proposed system consists of a three phase squirrel-cage induction machine connected to a wind turbine through a step-up gear box. A current controlled voltage source inverter (CC–VSI) with an electronic load controller (ELC) is connected in parallel with the main consumer load to the AC terminals of the induction machine. The proposed control strategy is based on fuzzy logic control principles which enhance the dynamic performance of the proposed system. Three fuzzy logic PI controllers and one hysteresis current controller (HCC) are used to extract the maximum available energy from the wind turbine as well as to regulate the generator terminal voltage simultaneously against wind speed and main load variations. However, in order to extract the maximum available energy from the turbine over a wide range of wind speeds, the captured energy is limited due to electrical constraints. Therefore the control strategy proposed three modes of control operation. The steady state characteristics of the proposed system are obtained and examined in order to design the required control parameters. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results demonstrate the effectiveness of the proposed control strategy.

An Interconnected Adaptive Observer for PMS Motors

Abstract Controlling electrical drives without mechanical sensors at the machine shaft has several benefits e.g. low cost and high reliability. To avoid these sensors, state observers must be resorted to get the required information using only measured voltages and currents at the machine terminals. In this paper we are considering the problem of estimating mechanical state variables in permanent magnet synchronous motor driven by back-to-back rectifier-inverter (AC/DC/AC IGBT-based PWM converter). Only the electrical variables are supposed to be accessible to measurements. A sensorless interconnected adaptive observer of the high-gain type is designed to get online estimates of the rotor position and speed as well as the machine load torque. Parameter adaptation is resorted because the stator resistor is not supposed to be known. The observer convergence is formally analyzed and illustrated by simulation. This theoretical result is confirmed by simulations which, besides, show that the observer convergence is quite robust with respect to motor parameters uncertainties.

Analyzing the Magnetic Flux Linkage Characteristics of Alternating Current Rotating Machines by Experimental Method

The magnetically nonlinear behavior of electric alternating current rotating machines is characterized by current dependent magnetic flux linkage characteristics. In this work, the impacts of iron core saturation, iron core saliency, permanent magnets, and squirrel cage in the rotor design on the machines' behavior, and the respective flux linkage characteristics in forms of hysteresis loops is analyzed. The analysis is based on experimental data by utilizing a stator with two phase-windings that produce magnetomotive forces displaced by electrical 90 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> , enabling the direct evaluation of flux linkages by measurement of the windings' voltage and current on the machine terminals. Five rotors of different electromagnetic construction and manufactured from equal materials have been tested in combination with the aforementioned stator. Thus, induction machines, synchronous reluctance machines, permanent-magnet synchronous machines, and their hybrid types are incorporated in the analysis. The work provides a deeper insight into the magnetically nonlinear behavior of the aforementioned machines, which is not available in the current literature.

Starting scheme for load commutated inverter-fed wound field synchronous machine using an auxiliary low-power voltage source inverter

Conventional thyristor-based load commutated inverter (LCI)-fed wound field synchronous machine operates only above a minimum speed that is necessary to develop enough back emf to ensure commutation. The drive is started and brought up to a speed of around 10–15% by a complex ‘dc link current pulsing’ technique. During this process, the drive have problems such as pulsating torque, insufficient average starting torque, longer starting time, etc. In this regard a simple starting and low-speed operation scheme, by employing an auxiliary low-power voltage source inverter (VSI) between the LCI and the machine terminals, is presented in this study. The drive is started and brought up to a low speed of around 15% using the VSI alone with field oriented control. The complete control is then smoothly and dynamically transferred to the conventional LCI control. After the control transfer, the VSI is turned off and physically disconnected from the main circuit. The advantages of this scheme are smooth starting, complete control of torque and flux at starting and low speeds, less starting time, stable operation, etc. The voltage rating of the required VSI is very low of the order of 10–15%, whereas the current rating is dependent on the starting torque requirement of the load. The experimental results from a 15.8 hp LCI-fed wound field synchronous machine are given to demonstrate the scheme.

An Interconnected Observer for Wind Synchronous Generator

Controlling electrical drives without mechanical sensors at the machine shaft has several benefits e.g. low cost and high reliability. To avoid these sensors, state observers must be resorted to get the required information using only measured voltages and currents at the machine terminals. In this paper we are considering the problem of estimating mechanical state variables in permanent magnet synchronous generators driven by wind turbines through AC/DC rectifiers and DC/AC inverters. Only the electrical variables are supposed to be accessible to measurements. Then a sensorless interconnected adaptive observer of the high-gain type is designed to get online estimates of the rotor position and speed as well as the load torque. Parameter adaptation is resorted because the load torque and stator resistor are not supposed to be known. The observer convergence is formally analyzed and illustrated by simulation. This theoretical result is confirmed by simulations which, besides, show that the observer convergence is quite robust with respect to wind speed (or load torque) and machine parameters uncertainties.