PWM INVERTER FED INDUCTION MOTORS LOSSES EVALUATION

ABSTRACT

In this paper the authors deal with the problems concerning the steady state losses evaluation in medium power industrial induction motors supplied by PWM inverter. They present a method based on the no-load and short circuit tests. This technique seems to be very useful for the good obtained results and because it is quite similar to the standard no-load and short circuit tests used with sinusoidal voltage supply.

The method is based on some simple hypothesis that have been verified during the experimental tests by means of mathematical models. As a consequence, it is possible to compare the no-load and the short circuit tests under sinusoidal and PWM inverter supply considering the same rms fundamental voltage.

The method has been applied to a 7.5 kW induction motor supplied by a prototype PWM Voltage Source Inverter (VSI) modulated with a ramp comparison technique at a 1 kHz switching frequency.

The obtained results could be utilized in order to define some design criteria and the derating for standard induction motors supplied by PWM inverters.     

LOSS ITEMS EVALUATION IN INDUCTION MOTORS FED By SIX-STEP VSI

ABSTRACT

At present time, induction motors are widely supplied from several types of solid-state adjustable voltage-frequency controllers with a wide range of operating features. However, in any case, the motor has to be derated for the harmonic effects due to the non-sinusoidal nature of the supply voltage. The authors propose a simple method based on the no-load and short circuit test in order to get the useful machine parameters to adopt in equivalent circuit model for the losses evaluation. Complete experimental results are reported and the comparison between six-step and sinusoidal supplies are summarized.     

DETERMINATION OF IRON AND STRAY LOAD LOSSES IN INDUCTION MOTORS USING A THERMOMETRIC METHOD

Abstract

In an induction motor, losses in the magnetic materials account for 10% to 20% of total losses. The iron loss effectively reduces both the output capability and possibly the life span of the machine. To limit these undesirable effects a prior requirement is to accurately assess the iron losses, and understand their nature and, ideally, their spatial location. An experimental method for determining the iron and stray load losses is presented. The test motor is a 3 phase, 4 pole, 4 KW induction motor which was heavily instrumented with thermocouples to map the loss distribution.     

PERFORMANCE ANALYSIS OF LOAD COMMUTATED INVERTER FED CAGE INDUCTION MOTOR DRIVE

ABSTRACT

An approach, to analyse the performance of a variable speed cage induction motor drive fed from load commutated inverter (LCI), is presented. Induction motor with an appropriate capacitor across its stator terminals constitutes the load on the inverter. A fully controlled bridge converter, supplied by a variable dc voltage source, commutated with the back emf of the motor, acts as an inverter. An algorithm to compute the motor performance, is developed using equivalent circuit representation of the system. Strategies for the selection of control variables, in order to achieve the desired speed range for satisfactory performance of the drive are given. The performance of a 3-hp, cage induction motor fed from LCI is computed, using the developed algorithm for wide range of speed; and is verfied experimentally.     

DESIGN OPTIMIZATION OF CURRENT SOURCE INVERTER FED SQUIRREL CAGE INDUCTION MOTOR

ABSTRACT

This paper deals with the design optimization of current source inverter (CSI) fed squirrel cage induction motor. For this a set of ten independent variables is selected and seven objective functions are considered namely, the active material cost, operating cost, a mixed objective function of the active material cost and operating cost, torque pulsations, voltage across commutating capacitor, maximum commutation time of CSI and an integrated objective function. To visualize extreme performance for a particular objective function, the design is optimized considering only one objective function at a time. Finally an integrated objective function is proposed which is formed as a combination of all other objective functions with suitable weighting factors to suit optimum design for a particular application. In the task of design optimization the desired thermal, starting and normal operating performance are optimally met by imposing twelve suitable constraints. In this investigation the Sequential Unconstrained Minimization Technique (SUMT) with interior penalty function approach is used to optimize the design. In this method, Rosenbrock's method is used to achieve unconstrained minimization. The optimized design results of a 7.5 kW, delta connected CSI fed cage motor are given and discussed in detail.     

电动机节能模糊控制器

为提高感应电动机的运行效率，本文提出了电动机节能模糊控制器的实现策略，设计了电动机调压节能模糊器和调频节能模糊控制器原型。它的基本原理是，在保护负载需求的前提下，通过控制电动机的定子电压或频率，最大限度地减少其输入功率，以实现节电运行。模糊控制器的输入变量是定子电流及其变化率，输出变量是定子电压或与频率对应的ＰＷＭ脉冲序列。本文所提出的节能模糊控制器的特点是成本低，鲁棒性强，模糊推理和ＰＷＭ脉冲序     

CONCEPT OF BUILT-IN RELIABILITY IN THE DESIGN OF LARGE INDUCTION MOTORS

ABSTRACT

In recent years, the reliability study of the equipment has been given vital importance alongwith the other studies. In this paper, an attempt is made to construct the reliability model of a large induction motor in order to predict the reliability, with the knowledge of realistic failure data. Since the author is not aware of any failure data, the prediction is based on some realistic failure data. However, in this paper the basic concepts are laid down, to ensure reliability goal of each component in the design stage. It is also emphasised here, the effect of supply conditions, ambient and malfunctioning of accessories in induction motor on its reliability goal. The method of attack is based on Markov model, by judiciously choosing ‘Available’ states and ‘Failed’ states. This method affords better realisation of failure modes and possible decisions to improve the same. The theory of reliability is presented in short, in order to make the ideas presented in this paper, more clear. A numerical example is presented at the end, to elucidate the theory presented here.     

NUMERICAL TREATMENT OF TRANSVERSE EDGE EFFECTS IN LINEAR INDUCTION MOTORS

Abstract

A 3-dimensional-field analysis is presented for the treatment of finite-width effects in linear induction motors (LIM). Account is taken of the effects of stator fringing and rotor-end-portion leakage. The model allows for a finite iron height and width, an arbitrary lateral secondary displacement, and the secondary iron width different from the primary iron width. The method used involves numerical solution of difference equations for the magnetic vector potential as well as a scalar potential. The performance such as thrust, real and reactive power are obtained from the vector potential, and the induced primary voltage. An equivalent circuit with a secondary leakage reactance and modified finite-width correction factors is proposed.     

MICROCONTROLLER BASED ONLINE IDENTIFICATION OF VARIABLE PARAMETERS IN INDUCTION MOTORS

ABSTRACT

On-line identification of machine parameters has been a challenge in induction drives for the achievement of high performance operation of machines with variable parameters. Conventional recursive or iterative algorithms, in most cases, are not applicable because of computing time limitations and convergence problems. In addressing the issue of obtaining operating-condition dependent parameters in transportation linear induction motors (LIMs), this work proposes a microcontroller based on-line scheme, which is conceptually simple and operationally stable, for identification of key variable parameters, namely magnetizing inductance and secondary resistance, in induction motors. The algorithm is derived from the terminal equivalent impedance, and uniqueness is verified. A new algorithm for calculating Arctg(x) when x ≈ 1 is also derived to facilitate the real-time operations of microprocessor-based systems. The effectiveness of this new scheme is demonstrated by experimental results.     

OPTIMIZATION OF DUAL SPEED INDUCTION MOTORS

ABSTRACT

Design optimization of single-winding dual speed and double-winding dual-speed three phase induction motors is attempted. The choice of independent variables and the specification of the performance requirements for these two types of motors are discussed. The formation of an objective function end the various steps involved in the minimization process are explained. It has been shown that comprehensive computer programs can be developed to design optimum dual speed motors of any pole ratio with any stator coil span and winding connection.     

异步电动机定子绕组匝间短路故障检测方法研究

基于多回路数学模型，对异步电动机定子绕组匝间短路故障瞬变过程做了数字仿真，并完成了相关实验。通过分析仿真与实验结果，对各种故障特征量的灵敏度与可靠性进行探讨，指出定子负序视在阻抗是最可靠兼具良好灵敏度的定子绕组匝间短路故障特征量。以此为基础，提出了一种异步电动机定子绕组匝间短路故障检测新方法，该方法以定子负序视在阻抗滤波值作为匝间短路故障特征量，并应用神经网络技术根据电机当前运行参数确定适当的故障检测阈值。实验结果表明，该方法是正确可行的。     

TRANSIENT PERFORMANCE OF A GROUP OF INDUCTION MOTORS

ABSTRACT

The paper develops the non-linear differential equations which describe the transient behaviour of a group of parallel-connected induction motors, either when fed from a stiff supply or when the supply is weak and the machine behaviour is interactive. A digital-computer solution of these equations provides a numerical prediction of the transient currents, voltages, torques and speeds of a laboratory-scale group of motors, in close agreement with experimentally-obtained results.     

A COMPANION CIRCUIT MODEL OF INDUCTION MOTORS

ABSTRACT

The theory of a companion circuit model of the induction motor is presented. The model comprises an independent current source in parallel with a constant resistance. Accuracy of problem solutions is the same as that obtained from conventional models, but the time of solution is much shorter. This stems from the combined consideration given to the problem formulation and its solution. A companion circuit model can include extra sets of machine coils such as those needed to represent deep-bar effects. Conventional motor models are adequate for single-machine, transient studies. It is for multi-machine studies that the companion circuit concept provides advantages for formulation and solution.     

EXPERIMENTAL INVESTIGATIONS ON STARTING OF INVERTER FED CAGE MOTOR

Abstract

Starting and low speed operation of an inverter fed cage motor is considered, which is not possible with load commutated inverter (LCI) fed induction motor due to lack of sufficient induced emf in the stator winding at zero and low speeds. To overcome this drawback of starting with LCI, three starting schemes are developed. Principle of operation of these schemes is described. Experimental performance of all the three schemes are discussed and their comparative features are also given     

MEASUREMENTS OF IRON LOSSES IN SINGLE-/PHASE SQUIRREL CAGE MOTORS

ABSTRACT

To determine the iron losses of a shaded pole motor, the authors have removed the shading ring, thus obtaining a single phase motor of particular characteristics. Using Veinott's method, they first obtained 60 Watts under normal conditions, that is to say, 30 Watts per kilogram of lamination. To check this value, they tried to set up two other methods, which are the object of the present paper. In both methods, the motor is represented by the equivalent circuit of a single phase-motor without iron losses, in parallel with a constant resistance which absorbs a power equal to the iron losses (which are thus assumed constant).

The first method is based on some geometrical properties of the impedance diagram of a single phase motor. The second method is analytical. A modification of Veinott's method is then presented to explain the results.     

瞬时功率分解算法在感应电机定子故障诊断中的应用

分析了电压不平衡、电压及负载的动态变化在故障负序电流检测中的表现；揭示了电机的负序感抗受电机自身固有不对称，铁磁饱和程度以及转子漏抗、转子几何静偏心的影响而非常数；提出了一种基于瞬时功率分解算法(IPDT)的感应电机定子线圈故障诊断方法，导出了故障负序电流的近似表达式：利用该方法可消除非故障因素产生负序电流的影响。实验结果证实，电机在不同条件下运行时，用该方法检测定子线圈故障，均可提高故障识别的精度。     

一种新型的级联型逆变器PWM信号随机分配方法研究

级联型逆变器具有开关冗余和隔离直流电源冗余.该文提出采用随机分配的方法来均衡开关和电源的利用率.当控制器给出输出电平后,电源和开关器件的工作状态是由两个随机函数决定的.随机函数具有均匀分布特性,可以由线性同余法来实现.当输出波形正负对称时,逆变器的每个单元处于工作状态的概率是相同的.随着逆变器工作时间的延长,各单元的利用率自然趋于相同.仿真和实验结果证明了该方法的可行性.     

高压异步电机转子绕组故障诊断系统的研究

采用定子稳态电流与起动电流相结合的分析方法诊断异步电机转子绕组故障中 ,通过频率细化和自适应滤波技术 ,大大提高了基于电机稳态电流故障诊断的分辨能力和实用性 ;通过对电机定子起动电流时频分析 ,提出采用起动电流中特定频率分量诊断故障的新方法 ,大大提高了电机轻微故障时故障诊断的准确性。根据分析结果研制出了实用可靠的大型异步电机转子绕组故障诊断系统。     

ANALYSIS AND CONTROL OF TORQUE PULSATIONS IN CURRENT FED INDUCTION MOTOR DRIVES

ABSTRACT

Three types of feedback compensation schemes are described which can be used to reduce the torque pulsations which normally occur when induction machines are supplied from a current source inverter. The approach is verified both by a detailed computer simulation and also by test results from an actual system. Limitations of the method near zero slip frequency (no load) is discussed and a means suggested for elimination of the problem.     

DC BRAKING CHARACTERISTICS OF DOUBLE-SIDED LINEAR INDUCTION MOTORS

ABSTRACT

An analysis of dc braking performance of linear induction motors is presented. Specific phenomena such as longitudinal end-effects and transverse edge-effects are taken into account. Computed results are compared with test results available for the dc braking characteristics of the existing largest double-sided linear induction motor.