Special Electrical Machinery (eBook)

Jigneshkumar P. Desai (Herausgeber)

eBook Download: EPUB

2024 | 1. Auflage
176 Seiten
Wiley (Verlag)
978-1-394-19389-9 (ISBN)

Infos

This book is a comprehensive guide to specialized motors, providing in-depth information on the operating principles, applications, and controls of various special electrical machines.

It covers a range of special machines, including switched reluctance motors, permanent magnet synchronous machines, brushless direct current motor, stepper motors, universal motors, and hysteresis motors. The book also addresses the issue of torque ripple. Much of the literature available today focuses solely on conventional motors and their controls, like induction motors, synchronous motors, PMDC motors, servo machines, and transformers. This book takes a broader view, addressing the growing trend toward specialized motors tailored to specific applications and new innovations in control and modification. It aims to offer comprehensive insights into these special machines by providing detailed information on their operating principles, applications, and controls.

This exciting new volume:

• Provides application-based examples of machines not covered in other books on special machines
• Provides context for the use of special machines used in electric vehicle technology
• Gives examples which are helpful for industry practices

Audience

Undergraduate students, post-graduate students, researchers, and industry professionals who study and use special machines

Jigneshkumar P. Desai, PhD, is an assistant professor at the U.V. Patel College of Engineering, Ganpat University in Mehsana, India. He has 11 years of teaching experience and holds one utility patent and one granted design. In addition, he has published three books and more then 15 research papers, adding a wealth of expertise to the content of this guide.

Textauszug

1
Brushless Direct Current Motor

Jitendra G. Jamnani

Department of Electrical Engineering School of Energy Technology, Pandit Deendayal Energy University, Raisan, Gandhinagar, Gujarat, India

Abstract

The development of permanent magnet materials with high magnetic energy product lead to the development of dc machines with Permanent magnet field excitation. A BLDC motor is a motor having stator similar to a synchronous motor and permanent magnets in the rotor, operates in self-controlled mode by the use of position sensors to detect rotor poles and an inverter for controlling the phase currents of stator winding.

In conventional dc motor, the commutator and brushes are needed, which are subjected to wear and require maintenance. In BLDC motor, the function of commutator and brushes are implemented by using semiconductor power switches and digital controllers and hence maintenance free motor can be released. This motor is called BLDC motor. The rotor position sensors and the semiconductor power switches in the inverter performs the role of the commutator and brushes of the conventional dc motor. A conventional dc motor has stationary field system which consists of field magnets. It produces magnetic field in the machine. The armature is rotating part and it is the rotor. The armature is free to rotate between the field poles and it is mounted on the shaft. The construction of BLDC motor is similar to the AC motor called Permanent Magnet Synchronous Motor (PMSM).

The brushless dc motors offer many advantages as compared to conventional dc motors. BLDC motors have small size rotor, high power density, low inertia, higher efficiency and requires lower maintenance. High speed and torque capability because of absence of commutator and brushes.

Presently BLDC motors are the significant contributors for the modern drive technology. They are used for a wide variety of applications in the fields of Electric vehicles, hybrid vehicles, robotics, computer disk drives, servo drives, DVD players, fans, washing machines, pumps, blowers, compressors, Industrial robots and CNC machine tools etc.

Keywords: Brushless DC motors, position sensors, permanent magnet, permanent magnet synchronous motor (PMSM), BLDC drive

1.1 Brushless DC (BLDC) Motors

A BLDC motor is a motor having stator similar to a synchronous motor and permanent magnets in the rotor, operating in self-controlled mode by the use of position sensors to detect rotor poles and an inverter for controlling the phase currents of stator winding.

In conventional dc motor, the commutator and brushes are needed, which are subjected to wear and require maintenance. In BLDC motor, the function of commutator and brushes are implemented by using semiconductor power switches and digital controllers and hence maintenance free motor can be released. This motor is called BLDC motor. The rotor position sensors and the semiconductor power switches in the inverter performs the role of the commutator and brushes of the conventional dc motor [1].

1.2 Construction of Brushless DC (BLDC) Motors

The construction of BLDC Motor is shown in Figure 1.1. A BLDC Motor has two main parts: A stator- stationary part and a rotor – a rotating part. The stator consists of stator core and 3-phase AC distributed winding. The windings are similar to those in synchronous motor.

The construction of modern BLDC motor is similar to the AC motor called PMSM. The construction of PMSM is the same as conventional synchronous motor, but the only difference is with the rotor. The rotor consists of permanent magnets to create field poles instead of wound field winding.

Figure 1.1 Construction of BLDC motor.

Instead of wound field for the rotor, permanent magnets are mounted for creating rotating magnetic field. Since no dc supply is needed for exciting the rotor poles, these motors are very simple, robust, reliable and low cost.

The PMSM are very reliable, brushless, robust and gives very fast response when compared to the conventional motors. It produces ripple free torque, lower noise and suitable for high-speed applications.

1.3 Brushless DC Motor Drive System

The main parts of a BLDC drive system are shown in the schematic block diagram of Figure 1.2. The drive motor has three elements: stator, a rotor carrying a permanent magnet excitation system and a non-contacting means of sensing rotor position (rotor position sensors).

For a 3 phase motor supplied from a six-step power conditioner, the operation of the system is as follows:

The control circuit receives information on the position of rotor from the position sensors. This is then translated into one of six current states as shown in Figure 1.4. Each current pulse produces an EMF in the stator which remain fixed in space for 600 electrical until the next current state. Once the rotor completes 60˚ electrical rotation, the phase currents are ideally switched instantaneously into the next state. This results in a step of armature emf of 60˚ in the direction of rotation. This process will be repeated six times per electrical revolution resulting in a discretely emf and continuous rotation.

Figure 1.2 Schematic block diagram of brushless DC drive system.

The BLDC motor operates in the same way as self-controlled synchronous motor. The semiconductor power switches in the inverter controls the motor current are commutated by the back emf of the motor.

Nowadays, the inverter which consists of semiconductor power switches such as IGBTs or MOSFETs are used. The ON and OFF states of power switches are controlled by the gate signals, that can be obtained from rotor position sensors.

Figure 1.3 shows an inverter configuration which is fed from dc source and used for a BLDC drive system. The turn-on and off instants for the power swithes are controlled by rotor position sensors such that the angle between the rotor and stator field is regulated at 90°. The waveforms of the stator phasecurrents are shown in Figure 1.4.

On every 600 electrical the inverter switches will be turned on, the power switches are given numbers in the sequence in which they are turned ON. If the inverter is suppled from a DC voltage (VSI), the PWM of the individual switches can provide the control of the motor phase current [2].

Figure 1.3 Brushless dc motor drive system.

Figure 1.4 Idealised stator phase currents.

1.4 Position Sensors

The position sensors can be used for detecting the position of the rotor poles and send logic codes to a commutation decoder and thereafter processing this code, the firing circuits of semiconductor power switches will activate for feeding the power to the stator winding of the driving motor. A unidirectional torque is produced due to the interaction between the permanent magnets of the rotor and currents flowing through the stator winding. A BLDC motor incorporating rotor position sensors [3]. Nowadays the following position sensors are used:

1. Optical Sensors
2. Hall Sensors or Magnetic field sensors

In case of optical sensors, a light source shines through a patterned disc which is attached to the shaft of rotor and a photodiode will detect the presence or absence of light. Both the light source and photodiode are stationary. The main advantage of these sensors is that the signal from the photodiode rises and falls quite abruptly and hence switching points are well defined. Also, the output signal is dc, so it does not require rectification or filtering.

Disadvantages of Optical Sensors are as follows:

1. High cost
2. They require a clean environment
3. The light source is liable to fail suddenly

In Hall sensors, the output signals from the Hall elements operate the semiconductor power switches to control the stator winding currents. These hall sensors are placed at intervals of 120° electrical to detect rotor magnetic poles. The position of permanent magnets attached to the rotor is sensed by hall effect sensors (Hall ICs). The advantage of magnetic field hall sensors are freedom from RFI, suitale for a wide range of operating conditions and high accuracy [4].

The rotor magnetic field can be sensed directly by hall elements (ICs) eliminating the need for any auxiliary magnets. The sensors must be located far enough from the stator winding to prevent the magnetic field generated by stator currents from interfering with their operation [5].

1.5 Features and Advantages of BLDC Motors

BLDC motors have the following advantages and special features as compared with conventional brushed dc motors and Synchronous motors:

• Due to the absence of commutator, brushes and field windings, the size of the rotor is small and the motor has high power density.
• The inertia is low and hence dynamic response is fast
• Due to the absence of wound field, No field copper loss and hence efficiency increases
• Elimination of brushes and slip rings, no sparking
• Requires less maintenance and lower maintenance cost
• The motor has very high speed and torque capability because of absence of commutator and brushes
• High torque to inertia ratio
• As the armature winding is stationary, the heat dissipation is better
• High efficiency and reliability
• Torque ripples are absent
• Produces low...

Produkt-Details

• Erscheint lt. Verlag: 28.6.2024
• Sprache: englisch
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 1-394-19389-0 / 1394193890
• ISBN-13: 978-1-394-19389-9 / 9781394193899