A sensorless brushless dc motor system

This paper describes a brushless dc motor system without position or speed sensor. The brushless motor consists of a permanent magnet synchronous motor and a voltage-source inverter capable of controlling the amplitude and frequency of voltage. The rectangular-shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage similarly to chopper control of dc motors. In this paper, two sensorless position detecting methods, i.e., an “indirect method” suited for the lower-speed range and a “direct method” suited for the higher-speed range are proposed. The combination of the two makes it possible to detect the rotor position over a wide-speed range. Furthermore, a speed-sen-sorless PLL control is proposed in applying the principle of the direct method. Experimental results obtained from a prototype brushless dc motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor also is discussed because it is impossible to detect the rotor position at a standstill.     

TORQUE CHARACTERISTICS OF A SELF-CONTROLLED SYNCHRONOUS MOTOR

ABSTRACT

This paper presents a study of the torque characteristics of a self-controlled synchronous motor drive in which motor terminal voltages are used for inverter synchronization. Torque control techniques for normal operation and for starting are considered. A control strategy which optimizes the motor power factor and torque is studied. Experimental results are given.     

Development of an Induction Machine Commutated Thyristor Inverter for Traction Drives

Several designs detailing the construction of brushless cage-rotor induction machines operating at unity or leading power factor at the 35-hp level have recently been published [1]-[3]. The experimental machine combines the torque characteristics of a conventional cage induction machine with the leading power-factor (PF) capability of an overexcited dc field synchronous condenser into one unit using a common cage rotor and a common stator core. The ability of this machine to naturally commutate a high-power current-source thyristor inverter is apparent without any need for capacitors. The preferred adjustable speed propulsion arrangement consists of a mains-fed phase-delay-rectifier (PDR), high-voltage dc link, and a current-source inverter powering a ten-pole traction motor with constant V/Hz control. The drive system provides continuously variable torque during motoring, and regenerative braking modes and specific details are given for a 150-hp cage-rotor traction motor and converter, capable of natural commutation up to 200 Hz, currently under development.     

Analysis of characteristics of half-wave rectified brushless synchronous motor with permanent magnets

Previously, the authors proposed a “half-wave rectified brushless synchronous motor” as a novel servomotor. The rotor winding emf of the motor is induced by the stator current mmf which rotates at synchronous speed and pulsates at bias frequency. The field excitation is produced by the field current obtained from rectifying the emf with a diode inserted into the field winding. To improve the power factor and the efficiency, they also proposed a new-type half-wave rectified brushless synchronous motor with permanent magnets. This paper analyzes the flux distribution and the torque characteristics of the new half-wave rectified brushless synchronous motor using the finite element method. The computed torque characteristics are confirmed with the experimental results. Furthermore, the steady-state characteristic equations are derived and the effect of the modulation function waveforms on the motor performance is investigated. The theory also is confirmed by the experiments.     

Current control of brushless dc motor based on a common dc signal for space operated vehicles

The objective of the paper is to build a simple current controlled modulation technique for brushless dc motors. In electric traction and most other applications, a wide range of speed and torque control of the electric motor is required. The dc machine fulfills these requirements, but it requires constant maintenance. In the brushless permanent magnet motors, they do not have brushes and so there will be lesser maintenance. Brushless dc motors are widely used in applications which require wide range of speed and torque control because of its low inertia, fast response, high reliability and less maintenance. This current controlled technique is based on the generation of quasi-square wave currents using only one controller for the three phases. The current control strategy uses a triangular carrier for the power transistors which is simpler and more accurate than any other options. The advantages of this technique are: (a) The stator currents are completely characterized by their maximum amplitude. (b) The three phases are controlled with the same dc component, and then the phase currents are kept at exactly the same magnitude I_max. (c) The dc link current measurement is not required. (d) Phase currents are kept balanced and phase over currents are eliminated.     

Low-Speed Drive of PWM-VSI-Fed Brushless Self-Excited Synchronous Motor

The brushless self-excited synchronous motor with halfwave rectified field circuits has been invented already by Nonaka. For the low-speed drive of the motor a new method of the voltage supply which superimposes a higher-order harmonic component on sinusoidal low-frequency voltage by a pulsewidth modulated (PWM) GTO inverter is presented. The amplitude and frequency of the fundamental component and those of the harmonic component are controlled independently by a microcomputer-based PWM strategy. It is confirmed from the experimental results that controllable brushless self-excitation and smooth low-speed operation without torque pulsation are achieved by the proposed scheme.     

Synchronous Motor Railcar Propulsion

Development of ac motor drives for rail transit car has centered on the induction motor with pulsewidth modulated (PWM) inverter control. Interest in the induction motor as a replace for the series dc traction motor stems from the simplicity of the squirrel cage rotor of the induction motor. In this article, the short-comings of PWM inverter-induction motor transit car drive are examined. It is shown that the synchronous, or brushless dc, motor drive can provide performance exceeding both the PWM inverter-induction motor and the conventional dc motor in the transit car application.     

A brushless three-phase synchronous motor using the armature winding as both load and DC excitation winding

This paper presents a new brushless three-phase synchronous motor which has no exciter. The technique applied to the motor provides an effective way for conventional brushless synchronous motors to simplify the system configuration. The stator of the motor is equipped with a double-star connected armature winding which has two neutral points. The rotor is a cylindrical one, which is equipped with a two-phase field winding. The field winding is connected with shaft-mounted rectifiers. A dc voltage is applied to the two neutral points of the armature winding to obtain the rotor excitation when the motor is operated at synchronous speed. At that time. the armature winding acts as a stator dc exciting winding while also acting as a load winding. In this paper the principle and characteristics of the motor are described. and the experimental results are shown. It is confirmed that with a 2-kW experimental machine, the proposed motor has good performance. For example, by adjusting the stator dc current, this motor power factor can easily be controlled within a wide range.     

INVESTIGATIONS ON DYNAMIC BEHAVIOR OF PERMANENT MAGNET BRUSHLESS DC MOTOR DRIVE

ABSTRACT

Permanent magnet brushless dc (PMBLDC) motors are increasingly being used in a wide range of applications such as machine tools, robotics and high precision servo applications. A comprehensive analysis which includes modeling and simulation of PMBLDC motor drive is presented in this paper. A mathematical model of the drive is developed with a view to studying the transient response of current controlled voltage source inverter (VSI) fed PMBLDC motor. The drive system consists of discrete PID(Proportional, integral plus derivative) speed controller, the reference current generator, the position sensor, an inverter and the motor. Each part of the drive system is modeled separately and then integrated to study the dynamic behavior of the drive system. The study also examines the effectiveness of the drive system during starting, load perturbation, speed reversal and dc link voltage fluctuation.     

Five-phase permanent-magnet motor drives

A five-phase brushless permanent-magnet (PM) motor is introduced. The proposed motor has concentrated windings such that the produced back electromotive force is almost trapezoidal. The motor is supplied with the combined sinusoidal plus third harmonic of currents. This motor, while generating the same average torque as an equivalent PM brushless dc motor (BLDC), overcomes its disadvantages. The motor equations are obtained in the d/sub 1/q/sub 1/d/sub 3/q/sub 3/0 rotating reference frame. Therefore, the so-called vector control is easily applicable to this kind of motors and the motor has the same controllability as a PM synchronous motor (PMSM). For presenting the superior performance of the proposed five-phase motor, its three and five-phase PMSM and BLDC counterparts are also analyzed. Finite element method is used for studying the flux density and calculating the developed static torque. Also, the developed torque is obtained using the mathematical model in the d-q reference frame. The average torque and the torque ripple for all cases are calculated and compared. Experimental results are in good agreement with the simulation results.     

Excitation Control of a Brushless Synchronous Motor

A simple system is presented for controlling the excitation of a brushless synchronous motor independently of the motor speed or load angle. The system comprises a pulsewidth modulated (PWM) inverter provided with controllable pulsenumber. Experimental measurements of the induced rotor excitation shows that a wide range of excitation control is obtainable by simply varying the pulsenumber of the output waveform of the inverter while keeping the fundamental frequency of the inverter unaltered. An approximate formula for the rotor current is also given which confirms the dependence of the rotor current upon the pulsenumber.     

180°导通方式无刷直流电机换相转矩脉动研究

无刷直流电机(BLDCM)换相转矩脉动一直是业界关注的问题,但仅限于120°导通模式。文章研究了180°导通模式无刷直流电机在换相期间的转矩脉动变化,并与120°导通方式转矩脉动进行了比较。理论分析和仿真结果表明:电机在低速区域,120°导通模式比180°导通模式转矩脉动变化小,而在高速区域,180°导通模式比120°导通模式转矩脉动变化小。研究结果为无刷直流电机换相转矩脉动抑制提供了一种新的控制策略。     

Temperature effects on torque production and efficiency of PMmotors using NdFeB magnets

Recent developments in high energy magnets have created widespread interest in the area of permanent magnet (PM) motors. The use of PM synchronous motors or brushless motors to replace conventional DC or induction type motors has not been as speedy as anticipated earlier. This paper deals with the temperature effects of PM motors using neodymium magnets on the torque production capability and on the efficiency of the motor. When PM motors are designed to operate in a wide temperature range, the reversible demagnetization of the neodymium magnets with temperature and the increase in winding resistance with temperature influence the maximum torque capability at rated speed and efficiency of the PM motor. The maximum torque at rated speed is limited due to the fixed DC link voltage of the inverter feeding the motor. In this paper, it is shown that over an operating range of -40°C to 150°C the maximum torque capability and efficiency of the motor can vary over a wide range. It is also shown that for certain designs, a near flat maximum torque versus temperature characteristic may be obtained. The major factors influencing these variations are identified. The discussion in this paper is concentrated on PM motors with a trapezoidal back EMF waveform. The idea could be extended to sinusoidal back EMF motors and to PM DC motors     

Indirect sensing for rotor flux position of permanent magnet ACmotors operating over a wide speed range

This paper describes an indirect sensing, or sensorless, method for rotor flux position for brushless permanent magnet (BPM) motors operating over a wide speed range, while keeping maximum torque per ampere and/or maximum efficiency capabilities. The method described is particularly applicable to trapezoidal back emf type of BPM motors. The typical trapezoidal waveform of the motor internal voltages (or back emf) contains a fundamental and higher order frequency harmonics. In particular, the third harmonic component is extracted from the stator phase voltages while the fundamental and other polyphase components are eliminated via a simple summation of the three phase voltages. The resulting third harmonic signal keeps a constant phase relationship with the rotor flux for any motor speed and load condition, and is practically free of noise that can be introduced by the inverter switching, making this a robust sensing method. In contrast with indirect sensing methods based on detection of the back-emf signal that require heavy filtering, the third harmonic signal needs only a small amount of filtering to eliminate the switching frequency and its side bands. As a result, the method described here is not sensitive to filtering delays, allowing the motor to achieve a good performance over a wide speed range. Motor starting is also superior with this method since the third harmonic signal can be detected and processed at lower speeds than for the conventional method of back-emf sensing     

A Current Source GTO Inverter with Sinusoidal Inputs and Outputs

With the application of gate turn-off thyristors (GTO's) and PWM control techniques, a current source inverter capable of producing sinusoidal input/output (I/O) voltages and currents has been developed. The sinusoidally modulated current is fed to the GTO's in the rectifier and inverter sections. The overvoltage-absorption capacitors connected to the ac input and output terminals function as a filter and, consequently, the waveforms of the input/output voltages and currents become sinusoidal. Because the PWM control utilizes the high-speed switching characteristics of the GTO's, the dc link current smoothing reactor and the overvoltage absorption capacitors are greatly reduced. The dc link voltage in the rectifier section is controlled to adjust the ac motor current. This is accomplished by using the firing angle shift method in conjunction with the method involving varying the width of the bypass gate pulses, which put the rectifier section into a bypass state. The current source GTO inverter is used to drive an 11-kW induction motor. As a result, excellent acceleration and deceleration characteristics are obtained, which verifies that the new current source inverter is quite suitable for driving an ac motor at variable speeds.     

无刷直流电动机控制方法的研究

对传统无刷直流电动机的控制方法进行了总结和分析,并在此基础上提出了一种新的最大转矩控制方法,这种方法可以为无刷直流电动机提高效率提供一定的参考.     

有效平滑无刷直流电机转矩的新方法

在无刷直流电机(Brushless DC Motor,简称BLDCM)数学模型的基础上,分析了传统PWM调制方式对BLDCM非导通相引起续流电流的原因,以及该续流电流导致非换相期间的电磁转矩脉动的现象.通过原理分析及数学推导,提出在三相逆变桥输入端加上前级直流变换器,以控制电机的新策略.该方法在理论上消除了BLDCM在非换相区内的转矩脉动,并且利用试验证明了该方法的有效性.     

基于Buck变换器的无刷直流电机转矩控制仿真

无刷直流电动机（BLDCM）存在转矩脉动的突出缺点，提出了一种基于直流环节电压控制和模糊PID控制器的新型混合控制策略，以抑制无刷直流电机的转矩脉。电路拓扑包含功率因数校正降压转换器和逆变器。降压转换器通过控制直流电路电压来降低换向转矩脉动，使用模糊PID控制器和脉冲宽度调制（PWM）技术的逆变器在导通区域提供适当的电流。 Buck变换器降低了通过控制直流环节电压换向转矩脉动，逆变器使用模糊PID和PWM技术提供导通区域的电流。该方法能够消除传导区转矩脉动,削弱换相区转矩脉动，仿真结果表明，该策略具有功率因数校正功能，可有效抑制转矩脉动，提升电机运行的鲁棒性。     

A Method for Determining the Field Shape Influence upon Parameters of a DC Micromotor

ABSTRACT

A method for determining the magnetic field shape influence upon the average values and ripple content in induced voltage, current and the electromagnetic torque of a dc micromotor is presented. The dc micromotor with three slots and six different field shapes is analyzed and described analytically. The analysis shows that by using a shape function X(θ) one can find the best motor performance, i.e., highest average values of torque and the lowest ripple component. Using this approach a rectangular magnetic field shape provides the optimum solution for a wide range of tolerances. With this waveform the motor has no ripple on the induced voltage and as a result the torque pulsation are eliminated.     

Direct torque control of brushless DC drives with reduced torque ripple

The application of direct torque control (DTC) to brushless ac drives has been investigated extensively. This paper describes its application to brushless dc drives, and highlights the essential differences in its implementation, as regards torque estimation and the representation of the inverter voltage space vectors. Simulated and experimental results are presented, and it is shown that, compared with conventional current control, DTC results in reduced torque ripple and a faster dynamic response.