Harmonic losses in LCI-fed synchronous motors

Load-commutated inverters produce considerable current harmonies, which can cause losses and heating inside the machine. As drive outputs increase, it is important to be able to accurately predict not only the magnitude of these losses, but also the precise location of the losses within the motor. Recent experience and modern calculation techniques have shown that the effects of these losses in large motors can be quite dramatic. If not considered at the design stage, they can lead to high-temperature hot spots. These potential hot spots need eliminating to prevent surface temperatures in excess of gas ignition temperatures and also possible early machine failure. New detailed calculations have been performed which allowed a novel technique to be determined to reduce these losses and allow larger ratings of drives to be safely engineered.     

Asynchronous induction roller motors

Problems of designing special modifications of roller induction motors of ARM2P type for variable-frequency electric drives have been considered. Motor designs, energy indices, and adjustment properties are presented.     

STS and induction motors

Industrial plants with a high amount of induction motor load can run into problems following short interruptions of the supply or voltage sags. After the voltage has recovered, the high current drawn by the motors can cause voltage collapse. The case study presented in this article shows that the static transfer switch (STS) can provide a solution to this problem by transferring the loads to an alternative healthy supply within some milliseconds from the occurrence of the disturbance. However, this case study has also shown that the time needed for transferring the load is dependent on the type of disturbance and the instant when it occurs, and the transfer time is, in general, higher with an induction motor load, as compared with static load. For plants with a high percentage of motor load, a specific performance study should be carried out to assess if the installation of the STS actually improves the power quality for the plant.     

一种改进的电动机静态聚合方法

电动机参数是电力系统电压稳定、暂态稳定的关键因素之一.在基于统计综合法的负荷建模中,如何提高电动机参数的聚合精度是重要课题.针对传统电动机聚合方法没有考虑聚合前每台电动机稳态滑差的不足,提出了一种改进的电动机的静态聚合方法.该方法首先根据聚合前各电动机的惯性时间常数、暂态电抗、转子回路时间常数、临界滑差定义了一个电动机的特性指标,并按照该指标对电动机进行分组.然后将每组中的电动机根据其稳态等值电路转化为3种阻抗并联的形式,在对3种阻抗分别聚合后再还原为一台电动机稳态等值电路.算例表明该方法能够有效提高仿真精度.     

Online condition monitoring of induction motors

Condition monitoring of induction motors is a process that may be used to great advantage in mining and other industrial applications. The early detection of motor winding deterioration prior to a complete failure provides an opportunity for maintenance to be performed on a scheduled routine without the loss of production time. Presented in this paper is a theoretical and experimental analysis of a voltage mismatch technique that may be used in operating situations to monitor the health of induction motor windings. It extends previous work in this area by demonstrating the robust nature of the monitoring process not only under conditions of power supply unbalance but also in situations where motor construction imperfections exist and mechanical loads are unpredictable. A suggested procedure for application of this condition monitoring process in industrial situations is also included.     

Capacitor braking of double-cage induction motors

Capacitor braking relies on the self-excitation process and represents a well-established technique of braking of single-cage induction machines. However, there appear to be no papers on the capacitor braking of double-cage induction motors. Since the self-excitation process constitutes the basis of capacitor braking, a correct representation must include the effects of main flux saturation in the induction machine model used. The paper first summarises the mathematical model of a saturated double-cage induction machine and then presents experimental results together with results of a comprehensive simulation study. Both symmetrical three-phase and asymmetrical single-phase capacitor braking techniques are considered. The results are shown for two different double-cage induction machines. The experimental and simulation results are found to be in good agreement.     

Condition monitoring of slip-ring induction motors

A technique for real-time condition monitoring of slip-ring induction motors is presented. The proposed method utilizes on-line sensing and analysis of the rotor current to assess the integrity of the motor. The theoretical basis for this approach is presented; the results of an experimental investigation are given. The paper is concluded with a discussion of the efficacy of the proposed method in industrial power systems.     

异步电机弱磁区转矩最大化策略

异步电机工作在弱磁区时,转矩随着转速的升高急剧下降,在转子磁场定向系统中,充分利用电机和逆变器的最大电压、电流限制,无需d轴电流控制器,通过调节q轴分量,稳定高速失步状态,实现弱磁区转矩最大化。异步电机在电压极限状态遇到干扰时,通过旋转定子电压矢量产生动态电压边缘,提高系统的瞬态响应。当异步电机运行在弱磁区,铁损增大,影响电机的磁链水平和转矩输出,引入铁损补偿机制,确保弱磁区的转矩最大化。仿真和实验证明,该控制系统能实现异步电机弱磁区转矩最大化,且具有很强的鲁棒性。     

Vector-controlled induction motors using neural network

Slip-frequency vector control generally is used for variable speed induction motor drives due to its excellent response characteristics. However, it is sensitive to the variation of motor parameters since the flux current and slip-frequency commands are computed using the motor parameters. As a result, the system performance will be degraded if the controller parameters do not match the motor parameters. The authors propose a new approach of vector control in which quick responses and system robustness are obtained concurrently by the learning capabilities of neural network. In the newly developed method, controller parameters are learned in real time at medium and high speeds. Using these learned parameters, the low-speed performance of the controller can also be improved greatly. This paper describes the theoretical analysis, simulation and experimental results of the proposed method.     

Saturation model for squirrel-cage induction motors

An induction motor model which includes stator leakage reactance saturation, rotor leakage reactance saturation and magnetizing reactance saturation is presented. This improved model is based on experimental data from 96 motors. The power range of the motors is between 11 and 90 kW. The effects on the torque–speed and current–speed curves of each kind of saturation have been studied. In addition, the parameters of magnetizing reactance saturation and stator leakage reactance saturation have been studied for each motor, and an average value and its dispersion for each parameter are given. This model is considerably more accurate than other models. In particular, it explains the significant differences between theoretical and experimental torque–speed curves in the braking regime (s > 1).     

Development of embodiments of variable-frequency induction motors

Experience accumulated at the Scientific-Research Design Technological Institute of the Electric Machine Industry (NIPTIEM, JSC) in the field of developing variable-frequency induction motors for different applications is generalized. A design approach in which a basic induction motor is supplemented (depending on the motor function) by add-on modules is described. When used in combination with one another, these modules yield all of the necessary embodiments. Thus, both the peculiarities of the power supply from a frequency converter and the requirements of concrete consumers in regards to operating modes, design, and function are taken into account in the process of motor development.     

Performance prediction of shaded pole induction motors

The authors present an analysis for evaluating the performance characteristics of reluctance-augmented shaded pole motors. The proposed model is based on the d-q axis technique and is valid for steady-state and dynamic conditions. An efficient method of predicting the steady-state operating characteristics of the triac-controlled shaded pole motor is presented. This method calculates the currents and average torque as a function of conduction and control angles of the triac. The effect of critical parameters on the motor performance is investigated. Simulated results are compared with experimental values of a two-pole single phase test induction motor     

Adaptive non-linear speed control of induction motors

In this paper we present two adaptive non-linear speed control algorithms for induction motors. They employ input-output linearization techniques for the motor model in the stator fixed reference frame. The first control algorithm directly tracks speed and rotor flux. The second is designed using torque and rotor flux tracking and is extended for speed control. A key point is that this algorithm ensures exact current limitation in the known parameter case. The adaptation based on Lyapunov design can cope with rotor and stator resistance variations. Significant simulations using sampled controllers are presented emphasizing adaptation and current limitation effects.