Performance Of Synchronous Machine Research Articles

IMPROVEMENT OF THE ENERGY PERFORMANCE OF ASYMMETRIC EXCITORS OF SYNCHRONOUS MACHINES IN VOLTAGE FORCING MODES

The main mode of operation of synchronous machines in electric drives of industrial plants is the mode in which a static load moment close to the nominal is applied to the shaft. If the synchronous machine works as a generator, when consumers of comparable power are connected to the stator to stabilize the output voltage of the generator, forcing of the excitation voltage is applied by influencing the control angles of the thyristors of the controlled rectifier. In the nominal mode, the control angles of the thyristors of the exciter are significant, which makes it possible to ensure a sufficient multiplicity of the voltage during forcing. But with significant thyristor opening angles, the controlled rectifier consumes significant reactive power, which reduces the power factor of the rectifier bridge. In addition, forcing the excitation voltage is necessary for synchronous motors when a significant load is applied to the shaft and when voltage drops in the power supply network.
 It is widely used to connect capacitors in parallel to the windings of the power transformer, or to use two zero diodes that are connected in series and connected to the output of the exciter to improve its energy performance. A significant improvement in the power factor can be achieved by using forced capacitive switching nodes. However, the improvement of energy indicators by turning on zero diodes and capacitors leads to a significant change in the harmonic composition of the excitation voltage. In the work, a research of the harmonic composition of the excitation voltage of synchronous machines with asymmetric bridge rectifiers using artificial commutation circuits was carried out. 
 To research the harmonic composition, experimentally obtained dependences of the forced excitation voltage, which are decomposed into a trigonometric series, are used. Calculated amplitude spectra of the excitation voltage during natural and forced switching of thyristors. The above calculations show that the coefficient of ripples of the output voltage of the thyristor exciter when using a rectifier with forced commutation is more than two times less (5.4 %) than the coefficient of ripples of the output voltage of a rectifier with natural commutation (11.2 %). The conducted experiments and the results of their analysis proved the expediency of using the developed exciter with forced capacitive commutation.

DTC Based on Five-level SVM with Balancing Strategy of Sensorless DSSM

This paper presents a direct torque control based on multilevel space vector modulation of a double star synchronous machine operating without speed sensor. Each star of the machine is supplied by a five-level diodeclamped inverter. This topology of multilevel inverters represents one of the most interesting solutions to increase voltage and power levels and to achieve high quality voltage waveforms. However, a very important issue in using diode-clamped inverters is the ability to guarantee the stability of the DC-link capacitor voltages. To overcome this problem the multilevel space vector modulation equipped by a balancing strategy is proposed to suppress the unbalance of DC-link capacitor voltages. For achieving high performances control of the multiphase drive, the proposed control method needs accurate information about rotor position and rotor speed. To this end, they are estimated by using Luenberger observer.

Some aspects of comparing the operational properties of synchronous machines with a conventional and two mutually shifted excitation windings

A comparative analysis of the operational properties of traditional and two-valve synchronous machines with a rotor, having a reciprocating axis, excited from independent regulated DC sources, is generalized. On the basis of research, it has been shown that the use of a control quadrature excitation winding significantly improves the performance of synchronous machines at low costs for its manufacture. The authors have shown a significant improvement in the performance of machines with different operating modes based on the results of theoretical and experimental studies carried out on synchronous machines with a rotating axis of magnetic saturation, attached to various designs of quadrature excitation winding. It has been recognized that neglecting magnetic saturation in performance calculations for synchronous machines leads to significant estimation errors properties of the studied machine. In addition, the advantages of synchronous machines with sine-cosine field winding are shown. With an insignificant complication of the manufacturing technology, it opens the way to solving the problem of creating energy-saving turbine generators, which have a property that is very important for the practice of operation, i.e. an almost unchanged (sinusoidal) shape of the resulting magnetic field in the air gap of the machine within the allowable range of load variation under steady-state symmetric modes.

MANAGE THE EXCITATION CONTOUR OF AN AUTONOMOUS SYNCHRONOUS GENERATOR WITH SHORT CIRCUITS IN THE STATOR

The actual scientific problem is solved in the work, which consists in development, theoretical and experimental researches of devices which provide reduction of negative consequences at short circuits in a stator of synchronous machines.The most difficult mode of operation of synchronous machines is internal short circuits in the stator, which leads to the destruction of the windings, and in some cases — the burning of steel. Moreover the current of the excitation winding induces emf, which feeds the point k.z. To reduce the effects of k.z. it is necessary to reduce the excitation current that determines the magnetic field.Despite the relative short-livedness, k.z. lead to power failure, but also adversely affects the operation of adjacent, especially loaded electrical receivers and, in addition, can cause failure of the excitation system SG.Therefore, the urgent technical task is to develop devices that ensure the reliability of the elimination of short-circuits in the stator of the synchronous generator.Comparative analysis of the obtained expressions shows that the inclusion of electrical capacity contributes to a more intense change in the current of the OZ.It is proved that a significant amount of time and the presence of soothing circuits SG do not allow to intensively dampen the magnetic field.The experiments confirmed the feasibility of using the developed device in the modes of damping the magnetic field of the synchronous generator and identified the advantages over existing devices.

Effects of clock deviations on the performance of microgrids based on virtual synchronous generators

An inverter-based microgrid is a small-scale power network governed by a distributed control system. In this system, the nodes are the digital controllers of the power inverters, normally located at separate points within the microgrid. A relevant issue is that these controllers operate at different frequencies due to inherent clock deviations in the local hardware oscillators. This paper evaluates the effects of these clock deviations on the performance of microgrids equipped with inverters that emulate the operation of synchronous machines. A systematic procedure is presented to derive steady-state expressions of the inverter active power and microgrid frequency as a function of clock drift rates. This procedure is applied to swing and governor equations of the virtual synchronous generators, revealing the mechanism that allows clock drifts to be absorbed, making their presence negligible. In addition, it allows recognising the controllers that should never be implemented in a distributed control system, since they cause an unsatisfactory behaviour that can even lead to a blackout in the microgrid. Therefore, the relevance of this study is the identification of the control schemes that are most sensitive to clock drifts, which makes it easier to choose the most suitable control implementation for a particular application. Furthermore, technical guidelines are reported to help researchers on developing control solutions more robust to clock drifts. In this study, the theoretical results are validated by experimental tests in a laboratory microgrid.

Synchronous machine performance under geomagnetic disturbances

Synchronous machine performance under geomagnetic disturbances

Anisotropic layer model theory applied to synchronous machine analysis

This study demonstrates the application of layer model theory to the analysis of synchronous machines. The derivation of the model from Maxwell's equations is briefly described. With the use of steady-state equations and terminal operation information, a methodology is established, and the synchronous machine operation is modelled. Two case examples are then analysed. It is shown that the layer model methodology can be applied to synchronous machines with promising results.

Damping Enhancement for SMIB Power System Equipped with LQR Tuned via Analytical Approach

Among several aspects of stability of synchronous machine operation, an important aspect is the mode of ‘small perturbation stability’ referred to as steady-state, dynamic or conditional stability. Attention has been increasing on the effect of excitation control in damping small-frequency rotor oscillations which characterize the phenomena of dynamic stability. In particular, it has been found useful and practical to incorporate stabilizing signals derived from speed and/or terminal frequency and/or power superposed on the normal voltage error signal of automatic voltage regulators to provide an additional damping to these oscillations. Conventionally, the lead–lag power system stabilizer (CPSS) is employed to supplement stabilizing signal to normal voltage error signal for damping these rotor oscillations of small frequency typically ranges from 0.2 to 3.5 Hz. In recent years, researchers have been proposing linear quadratic regulator (LQR) to replace CPSS for damping these small-frequency rotor oscillations. In this paper, an ‘algebraic approach’ derived from the relationship between algebraic Riccati equation and Lagrange multiplier optimization technique is proposed to tune LQR. The performance of single-machine infinite-bus power system equipped with LQR tuned via the proposed analytical method has been tested in MATLAB/Simulink® environment.

Ferroresonance modes of operation of synchronous machines

Purpose. It is proposed to use the method of sensitivity of variable models to the initial conditions for the calculation of ferroresonance modes of operation of saturated electric machines. Methodology. The calculation algorithms are based on Newton's iterative formula. The initial values of the variables determine the area of attraction of stable or unstable modes. Results. The results are illustrated by an example of the analysis of one of the most difficult modes of operation - two-phase switching on the capacity of a synchronous generator at the breakage of the third phase. Originality. The originality of the method is the ability to determine all the stable and unstable modes, as well as the self-excitation zone of the synchronous generator. Practical value. The method is universal and can be used to investigate resonance phenomena in any circle using steel.

Experimental study of the field in the gap of synchronous machine with the use of sinusoidal turns

The paper deals with experimental study of the gap of a synchronous machine with using sinusoidal turns. The characteristics of a three-phase short circuit and the current dependence of the winding excitation are presented. Static modes of operation of synchronous machines in the stationary state of the rotor by supplying the stator and rotor windings with a direct current conducted by means of sinusoidal and cosine-shaped turns with respect to the transverse axis established in the air gap on the rotor surface along the longitudinal and transverse axes, respectively.

Analysis and Exploitation of the Star-Point Voltage of Synchronous Machines for Sensorless Operation

In the field of sensorless drive of synchronous machines (SMs), many techniques have been proposed that can be applied successfully in most applications. Nevertheless, these techniques rely on the measurement of the phase currents to extract the rotor position information. In the particular case of low-power machines, the application of such techniques is challenging due to the limited bandwidth of the available current sensors. An alternative is offered by those techniques that exploit the star-point voltage rather than phase currents. This work aims at providing a model of the dynamic behavior of the star-point voltage and presenting a technique for extracting the rotor electrical position needed for sensorless operation of SMs. Two different circuitries for measuring the star-point voltage are also presented and then compared. The presented mathematical analysis and the measurement methods are validated both numerically and experimentally on a test machine.

Design and Analysis of Virtual Synchronous Machines in Inductive and Resistive Weak Grids

The term Virtual Synchronous Machine (VSM) commonly refers to the emulation of synchronous machines operation by using power electronics converters. However, a wider application of this control technique is still pending on further refinement of its design aspects and digital implementation. In this paper, a systematic approach to design the VSM parameters is introduced. First, a simplified third-order small-signal model of a VSM based on the conventional model of synchronous generators is developed. Unlike the existing works published in literature, the proposed model takes into account the effects of inductive and resistive weak grids. The model is then used to design the controller parameters by appropriately placing the poles of the closed-loop system. VSM robustness is studied for weak grids dominated by either inductance or resistance, and the aspects of digital control implementation are addressed. All the control system features and improvements were tested on a 15 kW prototype of a battery-supported VSM connected to a weak grid.

A Systematic Study on the Effects of Dimensional and Materials Tolerances on Permanent Magnet Synchronous Machines Based on the IEEE Std 1812

In the process of designing and manufacturing an electrical machine, a systematic study of dimensional and material tolerances is of the utmost importance. This paper proposes a systematic method by which the effect of design specification variations on permanent magnet (PM) synchronous machine performance may be identified and quantified. The method combines design of experiments techniques, open-circuit and short-circuit physical measurements, and virtual test simulations conducted based on the recently approved IEEE Std 1812 testing guide. Three case studies, two provided by a spoke-type PM radial field machine configuration, in two designs with different electromagnetic loading, and an axial flux PM machine are discussed. It is shown that based on the output performance, out of specification tolerances for magnet remanence, steel grade, as well as dimensional variables, and stator to rotor eccentricity, may be identified under certain conditions. It is also exemplified that the ratings, magnetic loading, and configuration of the machine play critical roles and should be thoroughly considered as part of the studies.

Simulation and testing of single-supply back-to-back high-power synchronous machines

Of a special concern is the steady state and dynamic single-supply back-to-back operation of synchronous machines. This issue is of theoretical and practical interest in the field of electrical machines, especially high power, and there are no detailed references in the literature. The recoverable character of operation is fundamental. The dynamical process produced by coupling together of the two machines to network is analyzed. Important information regarding electromechanical stresses is obtained by simulation. The proposed test method at rated load is experimentally validated. It is quite appropriate for high-power machines, comparing with other methods. This study considerably increases the test capacity of limited power test bench.

Tesla's Contribution to Electric Machine Analysis

In the late 1920s, R. H. Park published a change of variables that provided a means of analyzing the performance of synchronous machines. He transformed the stator variables to substitute variables that eliminated the rotor-position-dependent terms from the self- and mutual inductances. This transformation has become the bedrock of machine analysis and simulation; however, Park's derivation involves a maze of three-phase trigonometric identities with generator action and we are left searching for a more concise analytical development. In this paper, a direct connection is established between Tesla's rotating magnetic field and reference frame theory. In particular, an analytical basis for the change of variables is established from the expression of Tesla's rotating magnetic field combined with an expression that relates stationary and rotating coordinates. This leads directly to reference frame theory and an array of transformations that yield the same advantages as Park's transformation. It shows that all transformations used in the analysis of power systems, electric machines, and drive systems have a common origin. Also, the magnetic poles can be analytically located during transient operation and on a phasor diagram during steady-state operation, thereby providing a vivid visualization of machine and drive operation.

Loss of excitation of synchronous generator

Abstract This paper presents results of study of loss-of-excitation phenomena simulations. Loss of excitation is a very common fault in synchronous machine operating and can be caused by short circuit of the field winding, unexpected field breaker open or loss-of-excitation relay mal-operation. According to the statistic [1], the generator failure due to loss-of-excitation accounts for 69% of all generator failures. There has been concern over possible incorrect operation of the relay when operating the generator in the under-excited region, during stable transient swings and during major system disturbances. This article can serve as inputs for system operators in preparation of operation area or protection relaying area.

Efficient operation of anisotropic synchronous machines for wind energy systems

This paper presents an analytical solution for the Maximum-Torque-per-Ampere (MTPA) operation of synchronous machines (SM) with anisotropy and magnetic cross-coupling for the application in wind turbine systems and airborne wind energy systems. For a given reference torque, the analytical MTPA solution provides the optimal stator current references which produce the desired torque while minimizing the stator copper losses. From an implementation point of view, the proposed analytical method is appealing in terms of its fast online computation (compared to classical numerical methods) and its efficiency enhancement of the electrical drive system. The efficiency of the analytical MTPA operation, with and without consideration of cross-coupling, is compared to the conventional method with zero direct current.

Modelling and Simulation of Static Excitation System in Synchronous Machine Operation and Investigation of Shaft Voltage

Static excitation system (SES) has been implemented in a specially designed synchronous machine installed in a testing laboratory. This is a large capacity single machine operated in dual mode (i.e., motor or generator) with the help of static sources. It is well known that bearings of the rotating machines are vulnerable to the effects of the shaft voltages caused by the static sources. Shaft voltage is the prime concern for this special machine too due to SES. To find out the exact cause of the shaft voltage, SES of this machine has been modelled with Power Systems software. Various waveforms drawn from the model are validated through computer simulations and actual laboratory tests. Sources of shaft voltages are also analysed thereafter with the FFT analysis of the rotor voltage and current waveforms.

Integrating VSCs to Weak Grids by Nonlinear Power Damping Controller With Self-Synchronization Capability

This paper presents a new control topology to enable effective integration of voltage source converters (VSCs) in weak grids. The controller has two main parts. The first part is a linear power-damping and synchronizing controller which automatically synchronizes a VSC to a grid by providing damping and synchronizing power components, and enables effective full power injection even under very weak grid conditions. The controller adopts cascaded angle, frequency and power loops for frequency and angle regulation. The controller emulates the dynamic performance of synchronous machines, which eases grid integration and provides a virtual inertia control framework for VSCs to damp power and frequency oscillations. Although the linear controller offers stable and smooth operation in many cases, it cannot ensure system stability in weak grids, where sudden large disturbances rapidly drift system dynamics to the nonlinear region. To overcome this difficulty, a supplementary nonlinear controller is developed to assist the linear controller and enhance system performance under large-signal nonlinear disturbances, such as self-synchronization, disturbances in grid frequency and angle, high power injection in very weak grids and fault-ride-through conditions.

Simulation of Static Frequency Converter for Synchronous Machine Operation and Investigation of Shaft Voltage

Simulation of Static Frequency Converter for Synchronous Machine Operation and Investigation of Shaft Voltage