ROLE OF TORQUE ANGLE IN INVERTER-FED INDUCTION MOTOR DRIVES

ABSTRACT

It is shown from the induction motor differential equations that changes in load torque, speed reference and torque angle are accompanied by a transient change in the speed of the air-gap mmf. The time constant associated with the torque angle change is different for a voltage source and a current source inverter-fed induction motor. This aspect throws light on the instability of current source inverter-fed induction motor on open loop operation. Evidently, the solution to overcome this instability is to use the torque angle for feedback control. It is proved that torque angle feedback alone is not sufficient for stabilization of the current source inverter-fed induction motor.     

AN ELECTROMECHANICAL NETWORK MODEL FOR FREQUENCY CONTROLLED INDUCTION MOTORS

ABSTRACT

An electromechanical network model valid for small values of slip under steady state and dynamic conditions is given for frequency controlled induction motors. The model has been developed using the perturbation equations in the synchronously rotating reference frame and neglecting stator resistance and stator transients. Bode plots of incremental transfer functions relating speed and load torque as well as speed and stator frequency under constant volts/Hz control mode obtained from the exact and approximate models are compared with those of the electromechanical network model. The usefulness of the model in steady state and dynamic studies is discussed     

风电变桨系统模型简化及运行特性比较

针对风电变桨驱动系统详细模型参数变量众多影响其仿真速度,而常规一阶简化模型又不能较好地反映其动态特性的问题,文中基于传递函数法,提出了一种兼顾特性和参数的改进简化传递函数模型。首先,论文阐述了电动变桨系统基本原理与结构,建立了基于笼型异步电动机驱动的转子磁链定向详细动态数学模型。其次,基于传递函数的方法,简化其速度环和转矩环,推导了兼顾变桨系统动态特性的改进简化模型,比较了其频率特性。最后,分别建立了详细、简化和改进简化的变桨系统模型,对其桨距角跟踪特性和抗负载能力进行了仿真比较,并搭建了变桨电机系统实验平台进行验证。结果表明,改进简化模型具有兼顾详细模型动态特性及一阶简化模型参数较少的特点,并归纳了不同模型可适用于的场合。     

CLOSED LOOP PERFORMANCE OF INDUCTION MOTORS WITH CONSTANT VOLTS/HERTZ CONTROL

ABSTRACT

Characteristics of a closed loop induction motor drive, supplied from a variable frequency voltage source, and operating under constant volts/hertz control are presented. The motor linearized equations in the synchronously rotating reference frame are used to analyse the drive dynamic performance. It is shown that this performance can be greatly improved by including a properly designed speed controller in the drive structure. Thus, the decrease in stability, associated with the open loop motor operation is eliminated and the resulting drive gives satisfactory performance over the entire input frequency range. The experimental results, which confirm the validity of the motor dynamic model are also included.     

异步电动机软起动过程中的振荡

针对异步电动机软起动过程中出现的电流、电磁转矩以及转速振荡问题,建立了其软起动通用仿真模型,分析了异步电动机软起动过程中引起振荡的影响因素及其产生原因,提出用控制关断角的方法,即以电流关断时刻为基准,在电机软起动过程中使关断角逐渐减小为零来抑制振荡。通过仿真验证了该控制方法的正确性,并在此基础上研制了基于关断角控制的异步电动机软起动装置并进行了样机试验,实验结果验证了理论分析的正确性。     

MICROCOMPUTER BASED EFFICIENT AUTOSYNCHRONOUS MOTOR DRIVE

ABSTRACT

The paper presents the development of a microcomputer based digital control system for the current source load-commutated inverter fed synchronous motor drive. The control system comprised two loops: (i) Fast acting dynamic speed and torque angle control loop to ensure the self synchronous operation of the drive system, disturbance rejection and robustness of the complete motor drive system. (ii) Slow acting quasi steady-state efficiency maximization loop that ensures that the drive load is met at minimum source power input.     

异步电机电流调节器PI参数整定及抗饱和研究

针对异步电动机电流环中存在的耦合问题,首先利用状态反馈方法对感应电机的状态空间方程进行解耦,给出了解耦之后的电机模型;给出了一种交流电动机电流环的PI调节器参数整定方法,对电流调节器进行了整定,并分析了调节器抗饱和问题,给出一种新型抗积分饱和控制器的设计方法.为验证该方法的有效性,利用Matlab仿真软件进行了仿真实验...     

变频调速在双电机同步传动中的应用

在许多大功率拖动系统中,双电机同步传动很好地解决了因单电机功率不足而出现的拖动问题。在两台电机同步拖动的过程中保持输出功率平衡,防止单电机过载而烧坏电机是双电机同步传动中最为核心的问题之一。针对基于刚性联接的双电机同步传动中的功率分配问题提出一种新的控制方案。采用主从控制方式对两台电机分别控制,主电机速度闭环,用基于状态观测器的无速度传感器矢量控制;从电机用直接转矩控制。使从电机转矩跟随主电机输出转矩,在同步传动中确保功率平衡。提出了双电机同步传动的Mat- lab模型搭建方法,并对整个控制系统进行了仿真,结果表明转矩跟踪精度高,系统动静态性能比较好。     

SPEED AND CURRENT CONTROL OF DC MOTOR IN CONTINUOUS CURRENT OPERATION

ABSTRACT

In this paper we present a non-linear rigurous model of a d.c. motor fed from single phase thyristor bridge. The current and speed control are realized by ; internal current loop with proportional controller and external speed loop with proportional-integral one without zero. This model has been linearised around a steady state operating point to study the behaviour of the system for small perturbations. Analytical formulas are given for the controller parameters for any desired response. A general method of simulation is presented to study the behaviour of the system, taking into account all the discontinuities which may be occur in such a system.     

ANALYSIS OF STATE FEEDBACK CONTROL OF CHOPPER DRIVEN SEPARATELY EXCITED D.C. MOTOR

ABSTRACT

Armature voltage control of d.c. motor speed to a set point in the face of large step torque changes can be treated as a regulation problem in linear system theory. By proper pole assignment, one can have complete control over the dynamics of the closed loop system. The control input comes out as a function of the states, motor speed and armature current respectively, and integral of the output (speed error). The paper deals with separately exicited d.c. motors fed from a thyrister chopper circuit controlled by the state feed back signal. Discontinuous mode of current conduction in the chopper gives rise to unwanted swings in the dynamic response of the system. The proposed approach models the system taking discontinuous mode of current conduction into account, obtains the feed-back constants and predicts the oscillations that may come into picture at low shaft torques. Also a time varying model in proposed and this gives the designer an insight into the working of the system and guides him in his choice of the feedback coefficients. The proposed regulation method has been tested on a laboratory model d.c. motor, and the experimental and the theoritically predicted response curves are found to be in agreement     

一种异步电动机矢量控制的转速辨识方法

提出了异步电动机无速度传感器矢量控制的一种新的转速辨识方法。将模型参考自适应方法和直接计算的方法相结合 ,具有一定的辨识速度和精度 ,解决了反电动势模型参考自适应方法在速度过零点辨识误差大以及瞬时无功模型参考自适应方法在转速给定为负阶跃时的转速不稳定问题。通过用多电平变频器对 2 2kW电动机进行转子磁场定向矢量控制实验 ,验证了该方法的正确性。     

TORQUE PRODUCTION IN ac MOTORS WITH CONSTANT CURRENT SUPPLY

ABSTRACT

Basic theory is presented concerning the production of torque in synchronous motors and induction motors under conditions of constant current supply. Simple methods are described for treating the effects of magnetic saturation, which are important at high currents. It is shown that, for a given stator current, a synchronous motor produces more torque than an induction motor, albeit with higher air-gap flux. Examples illustrate the variation, due to saturation, of the optimum torque angle of synchronous motors with cylindrical and salient rotors.     

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。     

SPEED AT BREAKDOWN TORQUE OF A SINGLE-PHASE INDUCTION MOTOR

ABSTRACT

The purpose of this paper is to present an “exact” analytical expression to calculate speed at breakdown torque and the breakdown torque of single-phase induction motors. From the theoretical expression for torque developed by a single-phase motor, a sixth order polynomial in speed at breakdown torque is obtained, and solved, using a well known method. A real root for per unit speed, i.e. the ratio of speed to the synchronous speed, that lies between 0 and 1 is selected and the actual breakdown torque is determined by substituting it in the torque equation. The breakdown torque, also termed as maximum torque, so obtained has been found to yield better correlation between the predicted and the tested results than the only existing empirical relation. Steps to calculate speed at maximum torque are also suggested. For an arbitrarily selected single-phase induction motor, a curve of speed at breakdown torque as a function of r₂/X is also included for the purposes of illustration and understanding.     

TORQUE VECTOR CONTROL (TVC) OF AXIALLY-LAMINATED ANISOTROPIC (ALA) ROTOR RELUCTANCE SYNCHRONOUS MOTORS

Abstract

Axially-laminated anisotropic (ALA) rotor reluctance synchronous motors (RSMs) have been proved recently capable of higher torque density, higher power factor and efficiency compared to their induction motor counterpart with the same stator. Vector current control systems have been proposed for such drives, based on maximum available torque constant current angle or minimum current for a given torque constant current angle or combined current-voltage control. In an effort to do away with the current controller limitations, especially in the high speed region, the paper proposes a torque vector control (TVC) system which is a direct stator flux and torque control through a table of optimum switchings in the voltage-source PWM inverter. A sliding mode speed controller is added. Extensive digital simulations are presented. They demonstrate the TVC fast response, wide speed range and load rejection performance.     

TORQUE VECTOR CONTROL (TVC) OF AXIALLY-LAMINATED ANISOTROPIC (ALA) ROTOR RELUCTANCE SYNCHRONOUS MOTORS

Abstract

Axially-laminated anisotropic (ALA) rotor reluctance synchronous motors (RSMs) have been proved recently capable of higher torque density, higher power factor and efficiency compared to their induction motor counterpart with the same stator. Vector current control systems have been proposed for such drives, based on maximum available torque constant current angle or minimum current for a given torque constant current angle or combined current-voltage control. In an effort to do away with the current controller limitations, especially in the high speed region, the paper proposes a torque vector control (TVC) system which is a direct stator flux and torque control through a table of optimum switchings in the voltage-source PWM inverter. A sliding mode speed controller is added. Extensive digital simulations are presented. They demonstrate the TVC fast response, wide speed range and load rejection performance.     

Suppression control of speed variation in an induction motor with fluctuating load by repetitive learning control

Induction motors are robust and inexpensive machines and are used widely for variable speed control because of the recent development of electronic technique. In the case where loads of the motors are compressors, pumps, and so on, the constant V/F control of the induction motors usually is employed because it is difficult to install speed sensors and accurate speed control is not required. In such loads, the rotational speed of the motors fluctuates considerably because the load torque is pulsated. When the frequency of the torque pulsation is close to the resonant frequency of the mechanical system, large vibration and acoustic noise are produced especially in the low-frequency region. This paper proposes a method to suppress the variation of the rotational speed of the V/F controlled induction motor with a fluctuated load by feedforward compensation using a timing sensor of 1 pulse/rev, considering that the load torque varies periodically. The feedforward data by a period for the compensation is obtained by the learning control based on the repetitive control in which the motor speed is controlled by periodically reflecting the past speed error on the present V/F input to the inverter. Effectiveness of the proposed method is confirmed by approximate analysis, simulations and experiments.     

A DSP-based modified slip energy recovery drive using a 12-pulse converter and shunt chopper for a speed control system of a wound rotor induction motor

This paper introduces a modified slip energy recovery drive system for speed control of a wound rotor induction motor offering improvement of drive performance, particularly line power factor and overall system efficiency. A 12-pulse line commutated thyristor converter operating in an inverter mode in conjunction with an additional IGBT shunt chopper is employed to transfer slip energy back to ac mains supply via three phase transformers. This approach offers motor speed control by varying the duty cycle of the chopper instead of changing the inverter firing angle. As a consequence, supply power factor can be improved. The servo state feedback designed by linear quadratic regulator (LQR) with observer is also included in order to keep motor speed to be constant over a certain range of operating conditions by using the estimated dc link current derived from motor speed. The advantage of this technique is absence of current transducers for current feedback control loop. The overall control system is implemented on DSP, DS1104’TMS320F240 controller board. Experimental results are illustrated in order to validate performance of the proposed system.