Nonsinusoidal Supply Research Articles

Power Properties of Four-Wire Systems at Nonsinusoidal Supply Voltage

Powers of three-phase aggregates of single-phase static linear loads supplied with a nonsinusoidal voltage are the subject of this paper. It is demonstrated in this paper that the supply current of such systems with a nonsinusoidal voltage can be decomposed into six mutually orthogonal components associated with distinctive physical phenomena in the load, two of which do not exist at a sinusoidal voltage. Such decomposition enables evaluation of contribution of these phenomena to the supply-current rms value increase and the power factor decline. A power equation and definitions of powers in such systems in the presence of voltage harmonics are proposed. This paper shows that all powers can be expressed in terms of load parameters, which can be identified by a measurement at the load terminals.

Determination of the magnetic losses in laminated cores under pulse width modulation voltage supply

In the laminated ferromagnetic cores employed in transformers and electrical machines energy losses occur resulting in a warming effect and efficiency decrease. Normally, manufacturers only provide iron losses data when a sinusoidal voltage supply is applied, but the actual operating characteristics of electrical machines include non-sinusoidal supplies, in particular pulse-width modulation (PWM). This information can be experimentally obtained, but only measuring systems that have function generators with arbitrarily programmable waveforms allow measurements in the presence of higher harmonics. Therefore, having an analytical tool to obtain the most accurate estimation of the magnetic losses is of great interest in addressing the design of electric machines. This paper validates an analytical-expression-based procedure, which delivers results with acceptable accuracy under all operating conditions for the estimation of losses in laminated cores. In addition, it investigates the influence of the modulation amplitude and the switching frequency of the PWM signals in the magnetic losses of soft magnetic materials. For this purpose, non-oriented fully processed electrical steel strips have been measured in a commercial AC permeameter using a single strip tester.

A Distributed Magnetic Circuit Approach to Analysis of Multiphase Induction Machines With Nonsinusoidal Supply

A 15-phase induction machine supplied by voltages with third-order harmonic injection has nonsinusoidal magnetomotive forces distribution. This paper introduces a distributed magnetic circuit approach to perform magnetic circuit calculations in order to determine the magnetizing inductance for both the fundamental and third-harmonic component. The proposed approach divides the half-pole or one-pole machine model into a large number of fan-shaped sectors. The air-gap flux densities for all sectors are then solved iteratively. The fundamental and third-harmonic inductances are extracted via Fourier analysis of air-gap flux density distribution. Calculated fundamental and third-order harmonic inductances are compared with those obtained from no-load tests of a 15-phase prototype induction machine. The good agreement between calculated and experimental results verifies the accuracy of the presented method.

Steady state performance analysis of multi-phase induction motor with non-sinusoidal supply

Electromagnetic performance analysis is the very foundation for electric machine design optimization. Thus, the research on performance evaluation methods for multi-phase induction machines with non-sinusoidal supply is of great theoretical value and practical importance, as such process is much more complicated than traditional methods developed for three-phase induction machines. The fundamental and third harmonic equivalent circuits are employed as design tools for induction machines supplied by non-sinusoidal voltages with third harmonic injection. Considering that the air-gap flux density is asymmetrical, extended distributed magnetic circuit approach(EDMCA) is used to calculate the fundamental and third harmonic EMFs. The performance of the induction machine is finally determined by calculating quantities such as the fundamental and third harmonic currents in steady state through 3 layers of iterations. Particularly, the inner-layer iteration that calculates the air-gap magnetic flux and the middle-layer iteration that determines the magnetizing current is quite different from the traditional performance analysis approach for three-phase induction machines. The proposed method is applied to a prototype fifteen-phase induction machine with non-sinusoidal supply. Close agreement between the calculated and experimental results at various working conditions indicates the high accuracy of the proposed method.

Analysis of a Doubly Fed Induction Motor in Electric Drives of Pumping Stations

The investigation of a doubly fed induction motor in electric drives of pumping stations is conducted in this paper. The effect of non-sinusoidal rotor supply is considered in the analysis as well. The current total harmonic distortion (THD) is evaluated with respect to the selected voltage modulation in a thyristor frequency converter (TFC) as well as on motor duty cycle. A novel method of reactive power regulation with constant rotor current I2=I2н=constant is proposed. It is shown that the proposed method considerably improves motor performance in the whole operation range. The proposed analytical method is verified with laboratory measurements.

Detailed comparative study regarding different formulae of predicting the iron losses in a machine excited by non-sinusoidal supply

Variable-speed drives in any machine provide an accurate control and high-energy efficiency. More and more often machines are excited by non-sinusoidal voltages. Predicting the amount of iron losses in non-sinusoidal excitation is important. The paper aims to achieve accurate efficiency estimation by presenting a new modified calculation method to predict the iron losses. In a switched reluctance motor, the iron losses can't be ignored, it has considered value. This paper presents conventional and modified Steinmetz formulae for the estimation of the iron losses. The conventional Steinmetz formula consists of three terms: hysteresis, eddy current and anomalous losses. The equations of hysteresis and eddy current losses depend mainly on the value of the peak flux density. The reason to modify the Steinmetz formula is to avoid the need of knowing the peak flux density and the anomalous losses in accurate figures. The paper also explains and clarifies the methods of using both the conventional as well as the modified Steinmetz formulae in accurate calculation of the iron losses in different sections of the magnetic circuit. For both formulae, a comparison is made between the distributions of the iron losses in different parts of the magnetic circuit and the efficiencies.

Real-time implementation of PI and fuzzy logic controllers based shunt active filter control strategies for power quality improvement

Instantaneous active and reactive power (p–q) and current (Id–Iq) control strategies for extracting the three-phase reference currents for shunt active power filters are compared, evaluating their performance under different source voltage conditions with PI and fuzzy logic controllers in MATLAB/Simulink environment and also implemented using Real-Time Digital Simulator Hardware (RTDS Hardware). When the supply voltages are balanced and sinusoidal, then all control strategies with both controllers converge to the same compensation characteristics. However, when the supply voltages are distorted and/or un-balanced sinusoidal, these control strategies result in different degrees of compensation in harmonics. The p–q control strategy unable to yield an adequate solution when source voltages are not ideal. Extensive simulations are carried out with PI as well as fuzzy logic controller for both p–q and Id–Iq control strategies by considering different voltage conditions and adequate results were presented. On owing Id–Iq method with fuzzy logic controller gives away an out-standing performance under balanced, un-balanced and non-sinusoidal supply conditions. The detailed simulation and RTDS Hardware results are included.

DSP based adaptive hysteresis-band current controlled active filter for power quality conditioning under non-sinusoidal supply voltages

The use of non-linear loads critically affects the quality of supply by drawing harmonic currents and reactive power from the electrical distribution system. Active power filters are the most viable solution for solving such power quality problems in compliance with the harmonic standards. This article presents a digital signal processor (DSP) based fundamental-tuned-filter (FTF) algorithm for elimination of harmonics and reactive power compensation under distorted voltage without the use of conventional phase-locked-loop or low-pass filter blocks. FTF offers easy tracking of fundamental or selected frequency component from the contaminated signal. The limitation of fixed band hysteresis control i.e. variable switching frequency is resolved at some extent by generating switching pattern of active power filter switches using adaptive hysteresis-band control strategy. The bandwidth of hysteresis-band changes according to the slope of the reference current, modulation frequency, supply voltage and DC-capacitor voltage which give nearly constant switching frequency. Reference current signal is generated using DC-bus energy balance without sensing the load or filter current, hence, offers easy implementation using DSP with less sensor count. To prove the viability of proposed controller, first it is realized in MATLAB-Simulink environment, and subsequently a laboratory prototype is developed based on TMS320F28335, 32-bit floating-point DSP to show the effectiveness of the proposed strategy.

The Use of the Instantaneous-Reactive-Power Signature Analysis for Rotor-Cage-Fault Diagnostics in Three-Phase Induction Motors

In this paper, a new detection technique based on the instantaneous-reactive-power signature analysis is proposed for the diagnosis of rotor-cage faults (RCFs) in operating three-phase induction motors (IMs). This technique has been tested through the simulation of two different IMs using a mathematical model based on the winding-function approach. In order to demonstrate the capability of the proposed tool for rotor-condition monitoring, these simulations are complemented by the experimental results obtained from two IMs with several faulty rotors, powered from sinusoidal and nonsinusoidal supply voltages. The results obtained by the fast-Fourier-transform algorithm and the Welch method show the merits of the proposed approach for the detection of RCFs. A suitable fault-severity factor is also proposed as an indicator of the motor condition. Moreover, the inductive reactive effect of RCFs is underlined to demonstrate the effectiveness and convenience of this new technique for the diagnosis of RCFs in three-phase IMs.

Determination of aggregated load power consumption, under non-sinusoidal supply using an improved load model

The harmonic content of supply voltage results in additional power losses and hence increases the load power consumption. The role of the power quality equipments on the power consumption without using an accurate model cannot be determined, too. In this paper, an improved model for aggregated loads proposed, which estimates the effects of voltage harmonics on the power consumption. The distinguished aspect of the proposed model is its parameters identification method which is based on the practical techniques, such as employing a capacitor bank or varying dummy loads in steps. The proposed model has been verified by the comparison of measured and simulated results.

Effects of pulse-width-modulated supply voltage on eddy currents in the form-wound stator winding of a cage induction motor

The eddy currents of a form-wound multi-conductor stator winding because of the non-sinusoidal supply voltage in a cage induction motor are studied. The time and space dependence of the field, circuit variables and the motion of the rotor are modelled with the time-discretised finite-element analysis. A pulse-width-modulated voltage is used to supply the motor. The eddy-current loss distribution of the stator bars and the total eddy-current losses are studied. The radial distance of the stator bars from the air gap is re-emphasised as a design parameter because of its effect on the losses and the hot spots. The means for minimising the losses and avoiding the local hot spots are studied.

Identification of Flux Density Harmonics and Resulting Iron Losses in Induction Machines With Nonsinusoidal Supplies

Accurate prediction of iron losses in electrical machines requires detailed information of flux density waveforms in the iron. In the case of an induction machine operating at partial load, many supply cycles must be modeled to obtain accurate flux density waveforms on the rotor. This may be particularly troublesome when nonsinusoidal supplies are used and many small time steps are required. This paper presents an approach to predict rotor flux density harmonics with data from a finite-element model of a single supply cycle. Using this approach, the influence of particular harmonics on total iron loss can be extracted. Predicted rotor losses are compared with those obtained using direct calculation of losses from time-stepped data and with test measurement.

A DSP Based Optimal Algorithm for Shunt Active Filter Under Nonsinusoidal Supply and Unbalanced Load Conditions

The use of power electronic circuits in a wide range of applications has resulted in distorted current waveforms in the power system. This results in nonsinusoidal voltage drops across the transformers and transmission line impedances, resulting in a nonsinusoidal voltage supply at the point of common coupling. Asymmetrical distribution of large, 1-phi loads further complicates the issue by causing imbalance in the line currents of the 3-phi system. Not only should this imbalance be compensated, other parameters, such as the current total harmonic distortion and the power factor should also be maintained as per the norms. However, the requirements of harmonic free current waveforms and good power factor, under nonsinusoidal voltage conditions, are contradictory to each other. Under these conditions, an optimum performance is the best one can achieve. This paper proposes a new scheme for balancing the currents and obtaining the best compromise between the power factor and current distortion under nonsinusoidal voltage conditions. The technique does not use p-q theory and does not require sequence transformation for power calculations, even though the current is unbalanced. All the details of this work are presented

A Unity-Power-Factor Converter Using the Synchronous-Reference-Frame-Based Hysteresis Current Control

In this paper, a high-performance unity-power-factor rectifier-inverter structure is presented. A synchronous-reference-frame-based hysteresis current control as inner loop and dc-link voltage control as outer loop are adopted for the front-end converter. With the proposed control algorithm, the converter draws high-quality sinusoidal supply currents and maintains good dc-link-voltage regulation under wide load variation, and even under unbalanced and nonsinusoidal supply voltage conditions. Theoretical results of its analysis are verified initially through digital simulation. Finally, experimental results of a 1-kVA laboratory prototype system confirm the feasibility of the proposed technique

Modeling and Characterization of Induction Motor Internal Faults Using Finite-Element and Discrete Wavelet Transforms

This paper examines the behavior of a three-phase induction motors with internal fault conditions under sinusoidal and nonsinusoidal supply voltages. This includes two types of faults, rotor broken bar and stator faults. Early detection and diagnosis of these faults are desirable for condition assessment, maintenance schedule, and improved operational efficiency of induction motors. The terminal behavior of the induction motor was investigated by coupling the induction motor transient finite-element (FE) model and external electric circuit. Such a model would allow the efficient representation of the induction machine with internal faults. A discrete wavelet transform (DWT) was then used to extract the different harmonic components of the stator currents. The key advantages of the DWT are its ability to provide a local representation (in both time and frequency) of the current signal for normal and faulty modes, and its applicability to nonstationary signals

06/00798 A research survey of induction motor operation with non-sinusoidal supply wave forms: Singh, G. K. Electric Power Systems Research, 2005, 75, (2–3), 200–213.

06/00798 A research survey of induction motor operation with non-sinusoidal supply wave forms: Singh, G. K. Electric Power Systems Research, 2005, 75, (2–3), 200–213.

Application considerations for class-1 div-2 inverter-fed motors

Application considerations for fixed-speed motors utilized in hazardous locations are not new to the electrical community and have been discussed previously and are relatively well known in the petroleum industry. Documented guidelines for these applications are currently established, are primarily centered on motor-temperature-rise limitations and the use of nonsparking fans in class-1 division-2/zone-2 locations. However, there are additional considerations when motors and their associated loads are on inverter supply. Items such as the effect on motor temperature rise when operating at reduced speeds for units without independently powered blowers, the effect of nonsinusoidal supply at the motor terminals on motor temperature rise as well as rotor voltage related phenomenon are relevant items. This paper identifies and provides guidelines particular to inverter-fed applications for class-1 division-2 installations.

A Novel, DSP Based Algorithm for Optimizing the Harmonics and Reactive Power Under Non-Sinusoidal Supply Voltage Conditions

This paper presents a simple control algorithm for a shunt active filter for compensation of harmonics and reactive power under nonsinusoidal supply voltage conditions. Under nonsinusoidal supply conditions, any attempt to achieve unity power factor results in a nonsinusoidal current, which increases the total harmonic distortion (THD). On the other hand, attempt at getting harmonic free current may not yield unity power factor because of the harmonics present in the voltage waveform. The proposed algorithm optimizes this trade-off using the Lagrange multiplier technique and achieves the best compromise. It does not employ the normally used p-q theory and is applicable to both single phase and three phase systems. With the proposed technique, it is possible to obtain an optimized power factor satisfying the specified THD limit. The algorithm has been tested under various supply and load conditions using MATLAB simulations and validated with an experimental prototype based on DSP TMS320LF2407A.

A research survey of induction motor operation with non-sinusoidal supply wave forms

The developments in the power electronics field have lead to an ever-increasing use of static switching devices to control the torque and speed of ac motors. Invariably, the output voltage and current waveforms of these devices contain numerous harmonics and these harmonics have detrimental effects on the motor performance in form of derating and torque pulsation, especially at low speed. The order and magnitude of these harmonics depend on the design as well as nature of load being supplied. The extensive research has been underway for a long time in order to assess the effects these harmonics have on induction motor performance, and to investigate the various issues related to the use of induction motor to improve the drive performance and reduce the losses. This paper, therefore, presents a comprehensive review of research and developments in the induction motor operation with non-sinusoidal supply waveforms since its inception. Attempts are made to highlight the current and future issues involved in the development of induction motor drive technology to impart good dynamic stability with improved performance. A list of 167 research publications on the subject is also appended for a quick reference.

Maximum power throughput in the multiphase brushless DC generator

An advanced control technique for maximum power throughput of the multiphase brushless DC (BLDC) generator is presented. In a generator of given rating the weight and size of the system affect the fuel consumption of the generation system directly, especially in vehicle applications. Therefore maximum power density is one of the most important issues in a stand-alone power generation system. A BLDC generator itself has high power density from the machine point of view and additional increases by special control means can be expected. Conventional rectification methods cannot achieve the maximum power possible because of nonoptimal current waveforms. An optimal control scheme to maximise power density and minimise machine size and weight in a multiphase, nonsinusoidal power supply system is proposed, incorporated into a control system, and verified by simulation and experimental work.