Theoretical prediction and experimental verification of light-load instability in a 11-kW open-loop induction motor drive

This paper presents the small-signal stability analysis of an 11-kW open-loop inverter-fed induction motor drive, including the effect of inverter dead-time. The analysis is carried out using an improved small-signal model of the drive that has been reported in literature recently, and is used to demonstrate small-signal instability in a higher-power-level motor. Through small-signal stability analysis, the region of oscillatory behaviour is identified on the voltage versus frequency plane (V–f plane), considering no-load. These predictions using the improved model are also compared against predictions of a standard model of an inverter-fed induction motor including dead-time effect. The oscillatory behaviour of the 11-kW motor drive is also studied through extensive time-domain numerical simulations and actual measurements over wide ranges of operating conditions. Both the simulation and experimental results confirm the validity of the predictions by the improved analytical model. Further, these results establish that the analysis is valid for both sine-triangle pulse-width modulation (PWM) and conventional space vector PWM.     

Eighteen-sided polygonal voltage space-vector-based PWM control for an induction motor drive

An inverter scheme with 18-sided polygonal voltage space-vector structure is proposed for induction motor drive applications. An open-end winding configuration is used for the drive scheme. The motor is fed from one end with a conventional two-level inverter and from the other end with a three-level inverter, realised by cascading two conventional two-level inverters. The inverters are fed with asymmetrical DC-link voltages. A simple linear PWM control scheme up to 18-step mode is proposed, based only on the motor reference phase amplitudes. The proposed scheme gives an increased modulation range with the elimination of the 5th, 7th, 11th and 13th-order harmonics, for the entire modulation range, when compared with any conventional schemes. The absence of low-order harmonics gives nearly sinusoidal currents throughout the modulation range, and makes PWM control of voltage very simple, with low inverter switching frequencies, especially in the extreme modulation range.     

Modeling of Eddy-Current Loss of Electrical Machines and Transformers Operated by Pulsewidth-Modulated Inverters

Pulsewidth-modulated (PWM) inverters are used more and more to operate electrical machines and to interface renewable energy systems with the utility grid. However, there are abundant high-frequency harmonics in the output voltage of a PWM inverter, which increase the iron losses and result in derating of the machine or transformer connected to them. Predicting the iron losses caused by the PWM supply is critical for the design of electrical machines and transformers operated by PWM inverters. These losses are primarily attributed to eddy-current loss caused by the PWM supply. In this paper, after analyzing the harmonic components of PWM voltage, we derive the effects of different parameters of PWM switching on the eddy-current loss. We compare the iron losses modeled with the proposed analytical methods on a three-phase transformer, a dc motor, and an induction motor with the results of time-stepping finite-element analysis and experiments. We provide detailed equations for the prediction of iron losses. These equations can be directly applied in the design and control of PWM converters and electric motors to improve energy efficiency in electrical machines and transformers operated from PWM converters.      

A General Model for Investigating the Effects of the Frequency Converter on the Magnetic Iron Losses of a Squirrel-Cage Induction Motor

We present a comprehensive analysis of iron losses in an inverter-fed induction motor. We performed experimental and numerical investigations to assess the additional losses produced by a pulsewidth modulated (PWM) supply compared to a sinusoidal supply. We developed an iron-loss model, called the hybrid model, and incorporated it into a two-dimensional (2-D) finite-element method (FEM) to investigate the losses. The model predicts the $Bhbox{-}H$ loops and the ensuing iron losses. We also used a traditional iron-loss model based on the statistical theory for the sake of comparison. We solved the nonlinear dynamic equations of the FEM by the fixed-point method and the Crank-Nicolson time-stepping scheme. We found the hybrid model to be fairly accurate in reproducing the iron losses obtained experimentally on a squirrel-cage induction motor operated under several different conditions. The numerical analysis also provided interesting results regarding the role of the PWM supply in characterizing the behavior and distribution of iron losses in the geometry of the motor.      

Five-leg inverter PWM technique for reduced switch count two-motor constant power applications

Industrial applications often require a number of variable speed electric drives. In the majority of cases, these multi-motor drive systems require independent control of individual motors. Over the past decade, research efforts have been made to reduce the number of power electronic devices required in multi-motor drive systems in order to reduce the overall complexity and hence cost of the drive. It has been shown recently that it is possible to independently control two three-phase induction machines using a five-leg voltage source inverter (VSI) as the supply, with one inverter leg being common to both machines. The existing pulse-width modulation (PWM) methods for this supply topology either limit the amount of DC bus voltage available to each machine or lead to uneven and increased switching frequency across five legs of the VSI. A new PWM method that effectively utilises the standard three-phase modulators in conjunction with appropriate modifications to generate modulation signals for all five legs of the VSI is presented. It enables an arbitrary distribution of the available DC bus voltage between the two machines. The considered supply topology, when utilised in conjunction with the developed PWM technique, is well suited to constant power applications such as centre-driven winders. Verification of the developed modulation method and its applicability to winder systems are demonstrated by experimental testing that includes both steady state and transient operation.     

Model reference adaptive control-based adaptive current control scheme of a PM synchronous motor with an improved servo performance

A model reference adaptive control (MRAC)-based current control scheme of a PM synchronous motor with an improved servo performance is presented. Although the predictive current control is known to give ideal transient and steady-state responses among various PWM inverter-fed current control schemes for a PM synchronous motor, its steady-state response may be degraded under the motor parameter variations. To overcome such a limitation, the disturbances caused by the parameter variations will be estimated using an MRAC technique and compensated by a feedforward manner. Thus, the steady-state control performance can be effectively improved, while retaining its good dynamic performance. The proposed control scheme does not require the measurement of the phase voltage unlike the conventional disturbance estimation scheme using observer. This can be an effective way considering the phase voltage contains much harmonics as well as noise. The asymptotic stability of the overall system is proved and the adaptation laws are derived by the Lyapunov stability theory. The proposed scheme is implemented using DSP TMS320C31 and the effectiveness is verified through the comparative simulations and experiments.     

A nine-level hybrid symmetric cascaded multilevel converter for induction motor drive

A nine-level hybrid symmetric cascaded multilevel converter (MLC) fed induction motor drive is proposed in this paper. The proposed converter is capable of producing nine output voltage levels by using the same number of power cells as that of conventional five-level symmetric cascaded H-bridge converter. Each phase in this configuration consists of one five-level transistor-clamped H-Bridge (TCHB) power cell and one three-level H-bridge power cell with equal dc link voltages, and they are connected in cascade. Due to cascade connection and equal dc link voltage, the power shared by each power cell is nearly equal. Near-equal power sharing enables the feature of improving input current quality by using an appropriate phase-shifting multi-winding transformer at the converter input. In this paper, the operation of the converter is explained using staircase and hybrid multi-carrier sine PWM techniques. Further, a detailed analysis for the variations in the dc link capacitor voltages and the dc link mid-point voltage in TCHB power cell is carried out, and the analytical expressions thus obtained are presented. The performance of proposed system is analysed by simulating a 500 hp induction motor drive system in MATLAB/Simulink environment. A laboratory prototype is also developed to validate the claims experimentally.     

A neurofuzzy application for AC motor drives monitoring system

Currently industrial applications require suitable monitoring systems able to identify any decrease in efficiency resulting in economic losses. This paper shows that the information coming from a general purpose monitoring system can be usefully exploited to realize a sensorless instrument for the monitoring of an ac motor drive, and can be fed to a diagnostic tool for providing useful risk coefficients. The method is based on digital processing of the line signals acquired by means of a virtual instrument. The employed wavelet algorithms have been implemented within a Matlab environment, and risk coefficients are generated by means of suitable neurofuzzy algorithms.     

A Single-phase Spindle Motor Design for DVD Application

1. IntroductionA spindle motor applied for DVD drive is usually designed with three phases, radial winding andradial air-gap type. Because of the phase coznxnutation of this motor without using the commutator andtriggered by an electronic controller, it is called asDC brushless motorll'2]. The construction of this DCbrushless spindle motor with three phase colltroller isshown as Fig.l. Recedely, a new type, single phaseDC brushless spindle motor, which has been developed in our laboratory,…     

Analytical closed-form investigation of pwm inverter induction motor drive performance under dc bus voltage pulsation

The voltage unbalance conditions at the input rectifier stage of the AC?DC?AC rectifier-inverter fed induction motor drive is analysed. This unbalance can cause significant voltage harmonic of twice the line frequency 2f1 in the DC bus. This voltage ripple can have a degrading effect on the induction-machine performance characteristics. The authors present an analytical closed-form mathematical model and analysis of the impact of DC bus ripple voltage of the three-phase voltage source inverter with the space-vector PWM on the induction machine phase voltages, currents and torque pulsations. The analytical expressions for the voltage and current space vectors as a function of the DC bus voltage pulsation are derived. Using superposition, the separate parts of the motor currents can be determined. From the current space vectors, the torque behaviour is estimated, again as a function of DC link voltage pulsation. Next, it is shown that the DC link voltage ripple components may cause large torque pulsation. The proposed analytical method is based on the mixed p?z approach, enabling presentation of the results in lucid and closed form. To verify the effectiveness of the proposed analytical model, experimental results based on laboratory setup were obtained.     

Application of Wind Energy Conversion Systemsfor the Production of Electrical Energy at the Northeast of Brazil

The stead-state analysis of wind energy conversion system, consisting on windmill, synchronous generator, transmission line and induction motor driving a centrifugal pump is developed. The performance of the system operating at variable speed with a flux control is examined using mathematical models and digital simulation. The control scheme is proposed and tested in a laboratory and test center to compare field results with simulation results.     

Predictive-space vector PWM current control method for asymmetrical dual three-phase induction motor drives

The interest in multiphase drives has re-emerged in the last decade, being the asymmetrical dual threephase induction motor drive one of the most popular options. Predictive control techniques, already implemented in three-phase drives, have been recently adapted to the multiphase case. Schemes proposed so far have demonstrated high performance at the expenses of a higher degree of computational cost and illdefined switching frequency. In this study, a predictive space vector PWM (SVPWM) current control technique with fixed switching frequency is proposed for asymmetrical dual three-phase AC drives. Fast torque and current response are achieved similar to those obtained using conventional predictive current control techniques. Electrical noise suppression is favoured as in PWM current control methods. Experimental results are provided to examine the benefits of the proposed control method.     

Efficiency of Model Induction Motor Using Various Non-Oriented Electrical Steels

1. IntroductionThe total performance of inverter power supplieshas improved drastically as a result of the development of colltrol methods, higher performance in semiconductors, and higher speed, higher integration, andlower cost in integrated circuits, making it possible touse the inverter drive method in a wide range of rotating machinery which requires smaller size and/or variable speed drives. In line with these trends, magneticloss under nonsinusoidal waveform excitation, including lower …     

Oil free turbo-compressors for CO2 refrigeration applications

Feasibility of replacing oil-lubricated compressing equipment in CO₂ based refrigeration systems with oil-free turbo-machinery is assessed. Presented concept enables efficient compression for systems ranging from 0.1 to 5 MW of cooling capacity, provided that the operating pressures are low, i.e. 30/10 bar. Performance of the systems with higher operating pressures, i.e. 77/30 bar is penalized in wide range of capacities due to the excessive windage losses, especially pronounced in the systems with cooling capacities lower than 1 MW. In some cases, possibility of using longer motor should be analyzed. This may require special strategies for rotordynamic issues or driving each impeller with separately mounted motor. It is observed that optimal specific speed of the compressor stage does not always result in optimal overall performance. The trade-off between aerodynamic efficiency and non-stage losses must be found.     

Synchronised carrier-based SVPWM signal generation scheme for the entire modulation range extending up to six-step mode using the sampled amplitudes of reference phase voltages

The issues in synchronised implementation of space vector-based pulse width modulation (SVPWM) signal generation are addressed on a conventional DSP platform. With the present day digital signal processors (DSPs) with clock over 10 MHz, it is possible to include additional tasks for synchronisation in the interrupt service routine (ISR). Also, the task of the synchronisation can be easily accommodated within the same ISR without disturbing the time critical pulse width modulation (PWM) operation. The authors systematically present the additional software requirements to determine the time period proportional to the half carrier switching time interval that is required for the synchronisation. First, the DSP implementation of the conventional multi-level SVPWM based on the sampled amplitudes of reference voltages is presented and then the additional requirements to maintain the PWM in synchronisation are discussed. The simulation results as well as experimental results are presented for a five-level PWM signal generation. A five-level inverter configuration, using a 1.5 kW open-end winding induction motor drive, is used for experimentally verifying the SVPWM     

An Improved Magnetic Equivalent Circuit Model for Iron-Core Linear Permanent-Magnet Synchronous Motors

The aim of this work is to establish an accurate yet simple method for predicting flux density distribution and iron losses in linear permanent-magnet synchronous motors (LPMSMs) for iterative design procedures. For this purpose, an improved magnetic equivalent circuit for calculation of the teeth and yoke flux densities in the LPMSMs is presented. The magnetic saturation of iron core is considered by nonlinear elements and an iterative procedure is used to update these elements. The armature reaction is also taken into account in the modeling by flux sources located on the teeth of motors. These sources are time dependent and can model every winding configuration. The relative motion between the motor primary and secondary is considered by wisely designing air gap elements simplifying the permeance network construction and preventing permeance matrix distortion during primary motion. Flux densities in different load conditions are calculated by means of the proposed model. The effects of saturation and armature reaction on the flux density distribution are shown in detail. Using these flux densities, iron losses in the motor are examined and its variations versus motor parameters are then studied. All results obtained by proposed model are verified by finite-element method based on an extensive analysis.     

Modelling and analysis of an open-loop induction motor drive incorporating the effect of inverter dead-time

The objective of this paper is to study the influence of inverter dead-time on steady as well as dynamic operation of an open-loop induction motor drive fed from a voltage source inverter (VSI). Towards this goal, this paper presents a systematic derivation of a dynamic model for an inverter-fed induction motor, incorporating the effect of inverter dead-time, in the synchronously revolving dq reference frame. Simulation results based on this dynamic model bring out the impact of inverter dead-time on both the transient response and steady-state operation of the motor drive. For the purpose of steady-state analysis, the dynamic model of the motor drive is used to derive a steady-state model, which is found to be non-linear. The steady-state model shows that the impact of dead-time can be seen as an additional resistance in the stator circuit, whose value depends on the stator current. Towards precise evaluation of this dead-time equivalent resistance, an analytical expression is proposed for the same in terms of inverter dead-time, switching frequency, modulation index and load impedance. The notion of dead-time equivalent resistance is shown to simplify the solution of the non-linear steady-state model. The analytically evaluated steady-state solutions are validated through numerical simulations and experiments.     

交流伺服电机直驱液压机传动系统研究综述

交流伺服电机直驱液压机相比传统液压机,具有低速锻冲、快速空程向下及快速回程的特点,其交流伺服电机直驱的传动方式可有效减少滑块上行和下行的时间,大大提高液压机工作速度。介绍了国内外交流伺服电机直驱液压机传动系统的研究现状,提出了一种无油泵交流伺服电机直驱新型液压机传动方式,介绍了该新型液压机传动系统的构成及工作原理,并提出了研制该无油泵交流伺服电机直驱新型液压机所需要解决的科学问题。     

Development of a novel ultrasonic motor resonator using topology optimization

The use of topology optimization in the design of a novel stator for an ultrasonic motor (USM) is investigated. The design challenge is to produce a stator, with two resonant modes whose frequencies are in a ratio of 1:2. When driven together, these modes result in a contact point trajectory in a figure of eight shape. As a result, only one electronic amplifier is required to drive the proposed device. In contrast traditional travelling wave USM, with elliptical contact point trajectories, require two modes with equal resonant frequencies to be driven 90° out of phase, and therefore require two amplifiers, one for each mode. To achieve a suitable stator design, a slightly unconventional topology optimization problem formulation is proposed, in which the objective function is to minimize the amount of material with intermediate density, while satisfying a constraint related to the frequency ratio of selected resonant modes. The planar design produced using the optimization procedure was refined using a detailed three dimensional finite element analysis. A prototype of the proposed stator design was manufactured and experimentally characterized. Scanning laser vibrometry measurements from two positions were used to measure the figure of-eight motion. Finally, the stator was fitted with a preloaded slider to form a simple linear motor demonstrator which was characterized experimentally. The prototype motor produced a slider speed of 14 mm/s reversibly and a maximum force of 50 mN.     

Calculation of no-load induction motor core losses using therate-dependent Preisach model

In this paper the authors present a two-step algorithm for predicting the core losses in an electrical machine. As a first step, the flux patterns in the cross section of the machine are calculated by using a time stepped two-dimensional finite element (FE) model, neglecting hysteresis and eddy currents in the laminated core. The second step consists in enforcing the calculated tooth and yoke flux waveforms to a one-dimensional FE lamination model in which the variation along the thickness of the induction and of the induced eddy currents is considered. The hysteretic behavior of the ferromagnetic material is taken into account by, means of a rate-dependent Preisach model. The outlined procedure is applied to a 3 kW squirrel-cage induction motor with either open or closed rotor slots, the former yielding elevated flux harmonics. Computation results and measurements at no-load (phase currents, stator tooth flux, and total iron losses) are compared