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.     

High-Performance Vector-Controlled AC Motor Drives: Applications and New Technologies

A high-performance ac motor control has been developed by employing the vector control concept. Its versatility has been proven through the six years of experience in applications to pinch roll drives of continuous casting plants, machine tool spindle drives, and other drive systems in industry. Equivalent torque characteristics are achieved with ac motors compared to dc motors without direct detection of the magnetic flux. The effect of rotor temperature on the torque characteristics has been compensated to a satisfactory level in actual industrial use by various means. Servo drives, both synchronous motor and induction motor types, have been introduced. The test results show that the performance of ac servo drives is equivalent or superior to that of the PWM-controlled dc servo drives. Furthermore, an example of the direct-drive servo is described, where an ultra-low speed high-torque motor and an ultra-high resolution position sensor play key roles. In addition, the possibility of a more sophisticated servo drive exploiting modern control theory is suggested.     

Solid-State AC Drives: New Reliability for Packaging Equipment

Today's low cost variable frequency inverter drives combined with standard three-phase ac motors, eliminate downtime and maintenance of mechanical speed changers, dc motor armatures, and brushes. Advances in power semi-conductor technology makes the ac drive cost competitive with traditional variable speed drives.     

Induction Motors for Variable Frequency Power Supplies

Characteristics of variable frequency power supplies are compared, including sine wave, six-step square wave, and pulse width modulated (PWM) types. The effects of the complex voltage waveforms and variable frequency supplies on motor efficiency, heating, torque, winding stresses, and low speed pulsating torques are described. Possibilities for customizing induction motors for use with variable speed drives are considered.     

Pulsewidth Modulated Inverter Motor Drives with Improved Modulation

The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.     

感应电机压频比调节的模糊节能控制

根据三相感应电机的等效电路，推导出电机的损耗和输出功率与压频比之间的关系，提出了压频比调节的节能控制方法。考虑电机不同负载时损耗曲线的变化持点，引入基于电机转速和输入功率的比例算子，对电机输入功率的变化进行量化；电机稳态运行时进行模糊自寻优控制，动态调速时进行较高的恒压频比控制，提高了电机的效率并保持了一定的动态响应特性。仿真结果验证了运行控制方案的可行性和有效性。     

Using corona inception voltage for motor evaluation

Failures of the interturn insulation system of induction motors fed by PWM variable speed controllers have plagued the industry since the introduction of fast-switching, IGBT-based drives. The majority of these failures are attributed to high voltage stresses imposed upon the motor by the drive. Here, the author describes how the corona inception voltage can be used for evaluating the state of variable speed induction motor drive insulation     

Two-phase induction motor drives

This article starts with a presentation of the mathematical model for an asymmetrical two-phase induction motor drives (TPIM). This is followed by an analysis of TPIM behavior under variable frequency supply, with the running capacitor placed or removed from the circuit. This article attempts mainly to investigate the reasons for the lack of variable-speed drives. Consequently, the aptitude of the TPIMs for operating at variable speed is to be estimated and the suitable power electronic topologies identified. The most common form of a typical two-phase machine is the permanent split-capacitor motor (PSCM), usually recognized as the single-phase induction machine.     

A quantative approach to estimate the life expectancy of motorinsulation systems

Electric motors represent the largest single load in most power systems. With continuing increase in nonlinear loads, the effects of harmonic contents of power systems on various components is becoming more important. This paper is concerned with the effects of power system harmonics and voltage unbalance on the useful life of electric motors. A simple equivalent circuit is used to calculate the additional heat losses caused by supply distortions. A lumped-parameter thermal network is proposed to calculate the resulting heat distribution within the machine. An Arrhenius chart is then used to estimate motor insulation remaining life. The proposed approach is used to determine the effect of supply harmonics and voltage unbalance on the useful life of a three phase induction motor and the results are verified experimentally     

基于变压恒频的电梯电机软起动器谐波分析与补偿

电梯设备中的感应电机通常采用三相六支反并联晶闸管为驱动装置的软起动器来实现电机软起动和能耗降低。在晶闸管强迫换流作用下,定子电压和电流产生大量谐波,会给电机带来损耗甚至影响电梯运行。针对这一问题,以晶闸管驱动感应电机系统为研究对象,建立了该对象的电路数学模型,采用变压恒频(VVCF)模式,计算了各次谐波频谱特性,设计了新的补偿控制律。计算结果和补偿结果通过计算机仿真加以验证,最终试验证明这一方法是有效的。     

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.     

Design and Application of a Solid-State AC Motor Starter

This paper will explore the design, application, and field operating experience of the first complete line of 25-1000 hp solid-state ac motor starters. The contents are as follows: 1) the basic requirements of ac motor starting; 2) power circuitry?a brief review of solid-state; 3) a complete solid-state ac motor starter with provision for reduced voltage starting; 4) application problems, advantages and disadvantages of solid-state; 5) the ``hybrid' motor starter; 6) new dimensions for squirrel-cage motors using solid-state control; 7) limited range speed control using variable voltage, fixed frequency; 8) the universal replacement. Is it practical?     

A MODIFIED EQUIVALENT CIRCUIT FOR THREE-PHASE INDUCTION MOTORS WITH BALANCED NONSINUSOIDAL VOLTAGE SOURCE

Abstract

In this paper, the equivalent circuit model of a three-phase induction motor with balanced nonsinusoidal voltage waveform is solved by the experimental test of a 3-phase, 3-hp induction motor with a variable voltage, variable frequency (VVVF) voltage source. The parameters are calculated by analyzing the test results with statistical methods.

The performance of an induction motor with nonsinusoidal voltage source is calculated by the computer simulation based on the circuit model derived. The simulation results are compared with the laboratory test to verify the accuracy of the equivalent circuit model.     

标量控制的感应电机高效节能运行的实现

从感应电机高效节能运行出发,依据三相感应电机的等效电路推导出电机高效率运行的供电条件,揭示了电机高效率运行时电机输出的转速和负载转矩与输入的电源电压和频率之间存在的确定关系.在此基础上,提出实现电机高效节能运行的标量控制方案,并通过与恒压频比控制方式运行效率的比较及控制系统转速调节和转矩变化过渡过程的仿真实例,验证了电机高效节能控制运行方案的可行性.     

Aspects of voltage responses of induction motor loads

In this paper, the voltage dynamics of induction motor loads up to some ten seconds are discussed in terms of a linearized model. It is generally recognized that the dynamics of a power system load mainly originate from the induction motor dynamics constituting the load. Aspects of the voltage dynamics of induction motors are analyzed with respect to machine constants. The results show that small and medium-sized induction motors have dynamics that can be well approximated at the first order, thus partly accounting for the fact that most feeders indicate first-order dynamics     

感应电机非线性输出反馈控制变频调速系统

针对以定子电压为控制量的交流感应电机调速系统存在的系统结构复杂、实时计算量大的缺点,提出了一种感应电机的非线性输出反馈控制变频调速方法。该方法依据感应电机的降阶模型,采用非线性输出反馈控制技术设计外环转速与磁链控制器,以滞环比较器作为内环电流跟踪控制器,直接产生PWM信号控制电压源逆变器,驱动感应电机运行,实现了对光滑转速参考信号的渐近跟踪。仿真结果表明该系统不仅具有快速的动态响应性能,而且对负载扰动具有较强的鲁棒性。     

Experimental High-Frequency Parameter Identification of AC Electrical Motors

In order to predict conducted electromagnetic interference in inverter-motor drive systems, high-frequency (HF) motor models are requested and the involved parameters have to be available. In previous studies, the authors have presented an accurate HF model for induction motors and they have defined the procedures to identify the model parameters. In this paper, these results are extended to several types and sizes of industrial ac motors such as induction, synchronous reluctance (without interior permanent magnets), and brushless motors. The model parameter-identification procedure has been improved, and it is based on a least-squares data fitting applied to the measured magnitude and phase-frequency-response curves of the phase-to-ground and the phase-to-neutral impedances. The aim of this paper is to provide quick indications to select the suitable values of the HF model parameters, with reference to the size and type of the ac motor, to evaluate the HF voltage and current components in inverted-fed ac motor systems     

Performance analysis of a reluctance synchronous motor under abnormal operating conditions

In recent years, the application of reluctance synchronous motors to ac drives has been gaining importance. In this paper, the performance of such motors under abnormal operating conditions (such as voltage unbalance) is analyzed and compared to their performance under normal conditions by means of motor current signature analysis. In order to permit an objective comparison of the simulation and experimental results, the influence of the supply time harmonics and constructional asymmetries of the machine is also considered. Detailed mathematical proofs are provided to support the results. Such analysis will be helpful for understanding and identifying stator inter-turn faults unambiguously. To the best knowledge of the authors, such an analysis has not been carried out previously.     

Rotor temperature estimation of squirrel-cage induction motors by means of a combined scheme of parameter estimation and a thermal equivalent model

This paper deals with a rotor temperature estimation scheme for fan-cooled mains-fed squirrel-cage induction motors. The proposed technique combines a rotor resistance estimation method with a thermal equivalent circuit. Usually, rotor resistance estimation works quite well under rated load conditions. By contrast, if the motor is slightly loaded, rotor resistance estimation becomes inaccurate due to the small slip. Therefore, rotor temperature estimation under low-load conditions may be estimated by a thermal equivalent model. In order to determine the rotor resistance and, thus, rotor temperature accurately, several machine parameters have to be obtained in advance. Load tests provide the leakage reactance and the iron losses of the induct machine. The stator resistance has to be measured separately. The parameters of the thermal equivalent model are a thermal resistance and a thermal capacitance. These parameters are derived from a heating test, where the reference temperature is provided from the parameter model in the time domain. This lumped thermal parameter model is based on the assumption that the total rotor temperature increase is caused by the total sum of the losses in the induction machine. Measuring results of a 1.5-kW and an 18.5-kW four-pole low-voltage motor and a 210-kW four-pole high-voltage motor are presented and compared.     

Slip power recovery system stability

A slip power recovery configuration provides an attractive alternative for variable speed drives and generating systems, due to its improved efficiency and low power converter rating. The core component is the doubly-excited machine. First, the authors present a stability analysis of the doubly-excited machine with open-loop voltage control and open-loop current control in the rotor circuit. Possibilities of open-loop control are analyzed. Second, they present a unified model of a high-performance slip power recovery system composed of a field-orientation controlled doubly-excited machine, power converters and a DC bus in the rotor circuit. The stability of this composite system represented by a model is studied. Of special interest is when the system functions as a variable-speed motor drive system or as a variable-speed constant-frequency generating system