A strategy for improving reliability of field-oriented controlledinduction motor drives

Although design of induction motor drives employing field-oriented control has reached a relatively mature state, relatively little effort has been expended on improving the reliability of these drives. A new, improved induction motor drive topology and control strategy are proposed that allow for continuous, disturbance-free operation of the drive even with complete loss of one leg of the inverter or motor phase. A complete analysis and computer simulation of the control and circuit concepts is included     

一种新颖的用于六相感应电机调速系统的空间矢量PWM方法

基于三相调速系统中传统的空间矢量理论和统一电压调制技术,本文提出了一种新颖的用于六相感应电机调速系统的空间矢量SVPWM方法.该方法有效地抑制了电压源逆变器供电的六相感应电机中定子谐波电流,提高了直流母线电压利用率,且易于实现,执行速度快,极易推广到以三相组为子集的多相感应电机调速系统PWM控制中.本文给出了这种SVPWM方法具体的实现思路,通过数字仿真和实验结果将它与传统的SPWM和SVPWM方法做了深入的分析和比较研究,研究结果验证了该算法的有效性,它具有谐波电流最小和实现简单的突出优点,在多相PWM逆变器控制中有广阔的应用前景.     

TEST PROCEDURE FOR VERY HIGH SPEED SPINDLE MOTORS

Abstract

In the last ten years, the new power electronic devices and the new control techniques have allowed to open new application fields for adjustable speed/torque electrical drives. Although the traditional dc drives keep still the market supremacy, the new ac drives have performance really attractive and some additional benefits due to the machine structure and to the maintenance costs. Usually, ac drives use induction or brushless motors and the power amplifiers are driven by variable voltage/frequency in order to obtain variable speed. The authors deal with induction motors fed by non conventional supplies at very high frequency. In order to evaluate the total motor losses and the single items, a test bench with a synchronous machine capable to work up to 2 kHz with sinusoidal output voltage has been set up. As a consequence, an induction motor equivalent circuit with parameters depending on the frequency has been proposed. Today, the empirical procedure is that to use for high frequency applications shelf motors derated of a factor 10 to 20 % in order to keep into account the extra harmonic losses. On the other hand, the authors propose to design ‘ad hoc’ the motors for six-steps continuous operation in order to get about the same efficiency of standard motors. The new proposed motor equivalent circuit together with the test procedure seem to be a practical tool in order to aid the new motor design.     

MRAS-based sensorless control of a vector controlled five-phase induction motor drive

Multi-phase ac motor drives are nowadays considered for various applications, due to numerous advantages that they offer when compared to their three-phase counterparts. In principle, control methods for multi-phase machines are the same as for three-phase machines. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information of the rotor speed is extracted from measured stator currents and voltages at motor terminals. Vector controlled drives require estimating the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open-loop estimators and closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. This paper analyses operation of an open-loop and model reference adaptive system (MRAS)-based sensorless control of vector controlled five-phase induction machine with current control in the stationary reference frame. The MRAS-based sensorless operation of a three-phase induction machine is well established and the same principle is extended in this paper for an IRFOC five-phase induction machine. Performance, obtainable with hysteresis current control, is illustrated for a number of operating conditions on the basis of simulation results. Full decoupling of rotor flux control and torque control is realised. Dynamics, achievable with a five-phase vector controlled induction machine, are shown to be essentially identical to those obtainable with a three-phase induction machine. Experimental verification is also provided.     

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.     

Lower speed range drive for sensorless vector controlled induction machines with stator voltage offset compensation method

The vector control method is widely used for induction machine drives. Recently, sensorless vector control for induction machines has been investigated and proposed. The speed range for the drives is limited to about 1:100 in industry. The main reason for this limitation is the inaccuracy of stator voltage measurement. The lower the rotor speed is, the lower the stator voltage. Therefore, it is difficult to detect the stator voltage accurately in the lower speed region, and difficult to control motor speed and motor torque precisely. This paper presents a method of improving the lower speed performance of sensorless vector controlled induction machine drives using offset compensation of stator voltage. The offset is compensated by using the fluctuation of the estimated rotor flux. The validity of the proposed method is verified by experimentation. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 79–86, 2000     

变频调速异步电动机效率优化控制的研究进展

异步电动机运行于额定工作点附近时效率较高,轻载运行时其效率会明显下降.优化变频调速异步电动机的效率对于节约能源、系统自身冷却和控制环境污染具有重要意义.总结近年来变频调速异步电动机效率优化控制策略的研究现状,包括基于模型的最优励磁控制、最小输入功率在线搜索法和最小定子电流控制等,分析了各种效率优化控制策略的性能和优缺点,指出变频调速异步电机效率优化研究的发展方向,并给出考虑电机动态响应的效率优化控制研究结果.     

A new direct torque control strategy for the minimization of common-mode emissions

This paper presents a new direct torque control (DTC) algorithm for induction machine drives capable of reducing the common-mode conducted emissions of the drive. It is based on the application of only odd or only even voltage vectors in each sector in which the stator flux lies. In the work, after an overview of the generation of common-mode emissions of inverter fed drives and the most employed techniques for their minimization, a simplified equivalent circuit of the common-mode path has been identified to be used in numerical simulation on the basis of experimental measurements. Then, the new DTC technique has been described and applied to an induction machine drive, both in numerical simulation and experimentally on a suitably developed test setup. Finally, results are presented and compared to those obtained with the classic DTC technique. It has been shown that this methodology is able to reduce the common-mode voltage repetition rate, and therefore the resulting common-mode currents in comparison with the classic DTC in a frequency range of about tens of kilohertz. Finally the analysis of the impact of both control techniques in terms of the current absorbed by the grid has been performed.     

A NEW STATISTICAL DISTRIBUTION FUNCTION SENSITIVE TO RENEWABLE ENERGY SYSTEMS

ABSTRACT

Although design of the variable reluctance (switched reluctance( type of synchronous machine has experienced intense activity in recent years, relatively little effort has been expended on improving the torque capability of the synchronous reluctance type of motor drive. Based on the analysis presented in this paper, it appears that substantial improvements can be made in the design of such motor drives resulting in performance characteristics which match or, indeed, perhaps even exceed that of the induction machine.     

基于DSP的感应电机参数辨识

感应电机高性能交流调速方法中,电机参数的准确性严重影响着电机控制系统的控制品质。该文基于感应电机的数字控制平台,利用自身固有资源,向电机注入脉冲电压和阶跃直流电流激励,然后检测定子电流或电压响应,通过曲线拟合的方法得到部分电机参数。在介绍原理的基础上,介绍了硬件电路的设计,最后进行了仿真和实验研究,结果表明该辨识方案具有较高的精度。     

Modeling and analysis of a wide-speed-range induction motor drivebased on electronic pole changing

It has been previously demonstrated that an induction machine drive with contactorless pole changing can be achieved by reversing the current directions of certain stator coil groups. This paper compares the power and torque capability of this type of induction motor drive with conventional four-pole and two-pole induction machine drives. Based on the technique of vector space decomposition, the machine coupled-circuit model is transformed into a reference frame model. As a result of this transformation, the coupled coil group variables can be replaced by equivalent decoupled four-pole and two-pole dqO variables. This reference frame model facilitates the analysis and control of the machine drive, especially during transients, such as the pole-changing transition     

Rotor resistance adaptation for sensorless vector-controlled induction machines

The vector control method is widely used for induction motor drives. In these applications, a rotational transducer such as a shaft encoder is used. A rotational transducer, however, cannot be mounted in some cases, such as motor drives in a hostile environment or high-speed motor drives. Several sensorless vector-controlled induction machine drive methods have been proposed. These methods have the disadvantage that rotor resistance variation causes errors in the estimation of the motor speed. It is difficult to estimate the motor speed and the rotor resistance simultaneously, because the equivalent rotor resistance is the ratio of the rotor resistance to the slip at steady state. Therefore, we have proposed a method of simultaneously estimating the motor speed and the rotor resistance of an induction motor by superimposing ac components on the field current command. This paper presents a modified method of the rotor resistance adaptation. The validity of the proposed method is verified by experiments. © 1998 Scripta Technica, Electr Eng Jpn, 125(2): 65–72, 1998     

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.     

Five-level GTO inverters for large induction motor drives

The development of large induction motor drives with low torque ripple and fast dynamic response for new or retrofit applications has been limited by the device ratings and problems of series connections. This paper investigates the use of a five-level GTO voltage-sourced inverter for large induction motor drives. The advantages of such a drive are that single GTO thyristors may be used at each level, thereby avoiding the need for series connection of the thyristors. The thyristors are well protected from overvoltages by the clamping action of the DC supply capacitors. The disadvantages are that each DC level requires a separate supply, four in the case of the five-level inverter, and that the devices are not equally loaded. This paper reviews the basic operation of the five-level inverter and possible PWM voltage/frequency control techniques for the specific application of induction motor drives. The simulation results clearly show the unequal loading of the devices and the need for independent voltage supplies for the five levels. It is shown that a combination of several PWM techniques offers the best solution for the drives application. The conclusions indicate that large induction motors with ratings up to 22 MVA, 7.46 kV may be supplied by the five-level inverter using available 4.5 kV, 3.0 kA GTO thyristors. The recommended supply for such an inverter with full regenerative operation over the complete speed range is four, four-quadrant converters in a quasi-24-pulse configuration     

An efficient braking method for controlled AC drives with a dioderectifier front end

Standard pulsewidth-modulated inverter-fed induction motor drives employ a diode rectifier bridge to supply AC power from the utility to the DC link. Although a diode rectifier is the most cost-effective solution, it does not permit reversing the power flow. This prohibits operating the machine in the regenerative braking mode for active deceleration. An innovative control method substitutes conventional hardware, such as an active front-end rectifier or a chopper controlled braking resistor in the DC-link circuit, by additional software that is implemented in the standard microprocessor control. The control algorithm maximizes the power losses in the machine and in the inverter. It enables regenerative braking operation of the induction motor at high torque. The algorithm conserves the high dynamic performance of a vector-controlled drive system     

A VARIABLE VOLTAGE AND FREQUENCY SCHEME TO OPTIMIZE THE EFFICIENCY OF A WIND-DRIVEN INDUCTION GENERATOR

ABSTRACT

The most recent approaches to harness energy from the wind utilizing induction generators has been made possible by advances in induction motor control using power electronic drives. The freedom in adjusting terminal voltage or current, and frequency al lows operation of the induction machine to fit any desired characteristic. The purpose of this paper is to propose a scheme using this technology to convert wind energy to electricity at maximum wind turbine power and induction generator efficiency. The Electromagnetic Transients Program (EMTP) is used to simulate the control of the induction generator. Simulation results show that this system operates as predicted in a stable fashion at the desired operating point.     

Calculation of Electric Drives with Electric Machines of Unconventional Design

The design procedure for electric drives operating in a zone of large overloads or having the motor with unconventional rotor design is presented. The calculation of the magnetic system is based on the finite-element method. In addition, the settings for the phase currents come from the control system. To reduce the time of calculation, an algorithm for parallelizing the calculations by the criterion of maximum acceleration was developed. A determination of the possibilities of design procedures depending on the number of processors and the nature of the problem to be solved is presented. It is shown that, if an electric drive has small overloads and they are in the tolerance zone, then it is more appropriate to give a preference to simplified design models and the parameters of an electric machine can be replaced by lumped ones. If an asynchronous electric drive operates with larger overloads (with an impact character of the torque of resistance or when frequent starting-brake operating modes with relatively large dynamic torque), it is appropriate to use refined design procedures. Electric drives with a complicated configuration of the magnetic system—for example, drives with a synchronous reluctance machine—require taking the distributed nature of the motor magnetic system into account. Moreover, there are electric-drive operating modes in the zone of large overloads by torque and with angles β < 30°, when higher demands are placed on the initial data of the design model.     

Modeling of induction machines including stator and rotor slot effects

Three-phase as well as single-phase induction machines form the backbone of a substantial portion of the adjustable-speed drives' applications. Among the current estimation techniques available for speed-sensorless induction motor drives, speed measurement based on rotor or principal slot harmonics (RSH or PSH) detection in machine line current happens to be a prominent one. In practice, two predominant RSH can be seen. The present paper attempts to investigate the effect of slot permeance on the production of RSH. Simulation studies on a small motor but with a popular stator, rotor slot, and pole combination suggest that their effect is less significant compared to rotor space harmonics effect. Also, out of the two aforementioned RSH, the cause of the less significant slot harmonic is shown to be the negative-sequence-current-induced reverse rotating field. Voltage unbalances and constructional imperfections can cause negative-sequence current even in a healthy machine. Thus, although the less significant RSH is absent in the simulated line current of an idealized machine running from a balanced supply, it can be detected in an actual machine.     

A field orientation scheme for current-fed induction motor drivesbased on the torque angle closed-loop control

A novel field orientation scheme for current-fed induction motor drives is presented. The scheme is based on the closed-loop control of the torque angle and has the merits of being simple in implementation and insensitive to rotor resistance variations. The limits of previous field orientation schemes are reviewed. The torque angle control scheme is then formulated, and its application to induction motor (IM) drives fed by either current source inverters or current-controlled PWM inverters is illustrated. As an example, a current source inverter induction motor drive incorporating the scheme is designed, and its performance, which has been tested by simulation, is given