DC Motors: Characteristics and BLDC
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Questions and Answers

Which of the characteristics listed are considered advantages of DC brush motors?

  • Low HP capacity
  • Speed control over a wide range is possible (correct)
  • Requires high expertise for maintenance
  • Expensive and not cost effective

BLDC motors rely on the Left Hand Rule for their operation.

False (B)

What design feature of BLDC motors addresses a primary disadvantage found in DC brush motors?

The absence of brushes.

Due to continuous friction, DC brush motors experience wear and tear on the brushes and the _________.

<p>commutator</p> Signup and view all the answers

What is a primary disadvantage of DC brush motors related to their operation?

<p>Frequent brush replacement (C)</p> Signup and view all the answers

Which component is essential for starting a DC motor to prevent a high inrush of current?

<p>Starter (C)</p> Signup and view all the answers

BLDC motors do not require a specialized motor driver circuit.

<p>False (B)</p> Signup and view all the answers

Match the motor type with its operational characteristic:

<p>DC Brush Motor = Requires Frequent Brush Replacement BLDC Motor = Relies on Attraction-Repulsion Principle</p> Signup and view all the answers

Two conductors carrying current in opposite directions are placed near each other. What will happen?

<p>They will attract each other. (C)</p> Signup and view all the answers

According to the interaction of magnetic fields around conductors, lines of force traveling in the same direction attract each other.

<p>False (B)</p> Signup and view all the answers

The Right Hand Thumb Rule is used to determine the direction of the magnetic ______ around a conductor carrying current.

<p>field</p> Signup and view all the answers

What does Fleming's Left Hand Rule primarily describe?

<p>Motoring action due to a conductor in a magnetic field (C)</p> Signup and view all the answers

Which of the following rules or laws describes the generating action?

<p>Fleming's Right Hand Rule (C)</p> Signup and view all the answers

Match the term with the corresponding description:

<p>Magnetic Permeability = Ability of a material to allow magnetic lines of force to pass through it</p> Signup and view all the answers

Magnetic permeability is a measure of a material's resistance to the formation of magnetic fields.

<p>False (B)</p> Signup and view all the answers

State the relationship between the direction of the thumb and fingers in the Right-Hand Thumb Rule.

<p>Thumb indicates current direction, fingers indicate magnetic field direction.</p> Signup and view all the answers

Lenz's law is related to the direction of ______ voltage.

<p>induced</p> Signup and view all the answers

Faraday's laws of electromagnetic induction are related to which process?

<p>The generation of voltage due to changing magnetic fields (D)</p> Signup and view all the answers

In a BLDC motor, what is the primary reason for using a Hall effect sensor?

<p>To detect the precise position of the rotor poles. (C)</p> Signup and view all the answers

The EMF generated in the Hall effect is parallel to the flow of electric current.

<p>False (B)</p> Signup and view all the answers

Briefly explain how a Hall effect sensor detects the presence of a magnetic field.

<p>By sensing the EMF generated when a current-carrying conductor is subjected to a perpendicular magnetic field.</p> Signup and view all the answers

In a BLDC motor, the rotor pole continuously chases the opposite pole of the ______.

<p>stator</p> Signup and view all the answers

What happens when a current-carrying conductor is subjected to a magnetic field perpendicular to the current flow?

<p>An EMF is generated at right angles to the path of the current. (A)</p> Signup and view all the answers

Absence of a magnetic field disables the Hall effect sensor.

<p>True (A)</p> Signup and view all the answers

In the context of a BLDC motor, what is the role of the motor driver circuit?

<p>To change the stator polarity at the correct moment. (A)</p> Signup and view all the answers

How does the Hall effect contribute to the operation of a BLDC motor?

<p>It provides information on the rotor position, which allows for synchronized switching of the stator electromagnets to maintain rotation.</p> Signup and view all the answers

What is the primary purpose of a driver circuit in a BLDC motor system?

<p>To control the polarity of the stator poles at the correct time. (A)</p> Signup and view all the answers

A deglitch circuit is primarily designed to amplify the incoming signal to improve signal strength.

<p>False (B)</p> Signup and view all the answers

In a BLDC motor system, what component is commonly used alongside the driver circuit to determine the rotor's position?

<p>Hall effect sensor</p> Signup and view all the answers

A _________ circuit is used to prevent temporary malfunctions or faults in equipment.

<p>deglitch</p> Signup and view all the answers

What is the main component used in a deglitch circuit design?

<p>Logic Gates (B)</p> Signup and view all the answers

What is the significance of knowing the rotor position in a BLDC motor?

<p>To change the polarity of the stator pole at the right time. (C)</p> Signup and view all the answers

The driver circuit's primary function is to regulate the voltage supplied to the motor, ensuring it remains constant regardless of load.

<p>False (B)</p> Signup and view all the answers

What type of signal is typically received by the delay block in a deglitch circuit?

<p>data signal</p> Signup and view all the answers

Which of the following methods can be used to control the speed of a servo motor?

<p>Both Armature voltage and Field (Flux) control (D)</p> Signup and view all the answers

Continuous rotation servos are mainly designed for precise positional control rather than continuous movement.

<p>False (B)</p> Signup and view all the answers

What type of gear mechanism do linear servos typically employ to convert circular motion into linear motion?

<p>rack and pinion</p> Signup and view all the answers

The device within a servo motor that is responsible for determining its accuracy and resolution is the ______.

<p>encoder</p> Signup and view all the answers

Servo motors are particularly well-suited for applications requiring:

<p>High torque at all speeds and rapid acceleration (C)</p> Signup and view all the answers

Match the servo motor type with its typical application:

<p>Continuous Rotation Servo = Robotics Linear Servo = Airplanes</p> Signup and view all the answers

What percentage of efficiency can servo motors approach at light loads?

<p>90% (D)</p> Signup and view all the answers

For short periods, servo motors can achieve how many times their rated torque?

<p>5-10 times (D)</p> Signup and view all the answers

In a hydraulic system, what is the primary function of an actuator?

<p>To convert hydraulic energy into mechanical motion or force. (B)</p> Signup and view all the answers

A spring is commonly used in hydraulic actuators to extend the piston rod.

<p>False (B)</p> Signup and view all the answers

What is the purpose of adding additives to the oil within a hydraulic actuator system?

<p>Improve lubrication, reduce wear, and prevent corrosion</p> Signup and view all the answers

A hydraulic system's _______ is used to store hydraulic fluid and maintain consistent pressure.

<p>reservoir</p> Signup and view all the answers

Which type of actuator is suitable for applications requiring circular or rotational motion?

<p>Rotary actuator (B)</p> Signup and view all the answers

The flow rate of oil in a hydraulic actuator has no impact on its speed of actuation

<p>False (B)</p> Signup and view all the answers

What does a decline in the hydraulic fluid level inside a reservoir typically indicate?

<p>Fluid Leak or System Malfunction (A)</p> Signup and view all the answers

How does the design of an actuator contribute to controlling speed?

<p>Variable Orifice To Regulate Flow</p> Signup and view all the answers

Pressure ports are used to _______ the flow of oil to the actuator.

<p>control</p> Signup and view all the answers

Match the term with its related association in the functionality of actuators:

<p>Actuation = Movement Conditioning = Optimization Spring = Reset Ports = Pressure</p> Signup and view all the answers

Flashcards

Magnetic Repulsion

Property where magnetic lines moving in the same direction push away from each other.

Magnetic Attraction

Property where magnetic lines moving in opposite directions pull towards each other.

Right Hand Thumb Rule

A rule using your right hand to determine the direction of either the current or the magnetic field around a conductor.

Fleming's Left Hand Rule

Determines the force on a current-carrying conductor in a magnetic field; relates force, field, and current direction.

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Faraday's Laws

Describes how a voltage is induced in a circuit due to a changing magnetic field.

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Lenz's Law

States that the direction of an induced current opposes the change that caused it.

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Magnetic Permeability (µ)

Property of a material describing how easily magnetic lines of force pass through it.

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Right Hand Grip Rule

A rule to determine field direction around a conductor.

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Fleming's Right Hand Rule

Determines the direction of induced current in a generator.

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Motoring Action

Action of converting electrical energy into mechanical energy using magnetic fields.

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BLDC Motor

Brushless DC motor where the rotor chases the stator's magnetic field.

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Motor Driver Circuit

A circuit that switches the polarity of the stator windings in a BLDC motor.

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Hall Effect Sensor

Device that detects the presence and polarity of a magnetic field.

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Hall Effect

A phenomenon where a voltage (EMF) is produced across a conductor when it is exposed to a magnetic field perpendicular to the current flow.

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Rotor

The part of the BLDC motor that rotates, containing permanent magnets.

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Stator

The stationary part of the BLDC motor with windings that create rotating magnetic field.

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Rotor Pole Chasing

The action of the rotor's magnetic poles constantly being attracted to the opposite poles generated by the stator windings.

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EMF

Electromotive Force: Voltage created by electromagnetic induction.

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BLDC Motor Driver Circuit

A circuit that controls the polarity switching of stator poles in a BLDC motor to ensure continuous rotor movement.

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Glitch

A sudden, temporary fault or malfunction in equipment.

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Deglitch Circuit

A circuit designed to remove or smooth out glitches from a signal.

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Delay Block in Deglitch Circuit

Utilizes logic gates to create a delayed version of the input signal, filtering out glitches.

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Hall Effect Sensor in BLDC Driver

Senses the rotor position to time the switching of stator poles in a BLDC motor.

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Driver Circuit

An electronic circuit that switches the stator poles in a BLDC motor.

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Why rotor position is important?

The position of the rotor should be known.

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Driver circuit

A circuit controlling the polarity switching of stator poles.

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Electrical & Magnetic Circuit Similarities

Both have a driving force (voltage/MMF), resistance (electrical/reluctance), and a flow (current/flux).

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Electrical & Magnetic Circuit Differences

Electrical circuits involve flow of electrons. Magnetic circuits involve establishment of magnetic flux in a magnetic core.

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Merits of DC Brush Motors

Wide speed control, high HP capacity, simple power supply, easy maintenance, and cost-effective.

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Demerits of DC Brush Motors

Brush wear, high maintenance, carbon particles, frequent brush replacement, voltage drop, starter needed, separate DC supply, noisy.

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Features of BLDC Motors

BLDC motors eliminate brush contact issues, use attraction-repulsion, may include Hall effect sensors, need specialized drivers, and are quiet.

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BLDC Motor Working Principle

Uses attraction and repulsion between magnetic poles (N and S) to generate motion.

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Hall Effect Sensors in BLDC motors

Sensors that detect the position of the rotor magnets, used for commutation in sensor-based BLDC motors.

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Specialized Motor Driver (BLDC)

A circuit required to properly energize the stator windings in the correct sequence, controlling the BLDC motor.

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Armature Voltage Control

Speed control achieved by varying the voltage supplied to the armature.

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Field (Flux) Control

Speed control achieved by altering the strength of the magnetic field.

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Continuous Rotation Servo

Rotates continuously, both clockwise and counterclockwise. Used in applications needing constant motion.

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Linear Servo

Servo motor with gears converting circular to back-and-forth motion.

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Precision Control

Precise command over position, velocity, and torque. High degree of accuracy and repeatability.

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High Torque

Servo motors maintain high turning force across all speeds.

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Fast Response Time

Servo motors can quickly change speeds.

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Wide Speed Range

Ability to function accurately at many velocities.

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Actuator

A device that controls the flow and rate of oil in a hydraulic system to direct actuation.

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Spring Reset

A component, often employing a spring, used to reset the actuator to its initial position.

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Pump

The component that supplies pressurized oil to the hydraulic system.

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Oil Additives

Substances added to hydraulic oil to improve its properties, such as viscosity and lubrication.

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Oil Reservoir

Part of hydraulic system storing the fluid.

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Controlling Actuation

The process of regulating the movement or force in a hydraulic system.

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Pressure Ports

Openings in hydraulic components that control the direction of fluid flow.

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Rotary Motors

A hydraulic device that converts fluid power into rotary motion.

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Variable Property

The ability to change or adjust a parameter, like speed, within a hydraulic system.

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Hydraulic Design

Refers to the overall layout and specifications of a hydraulic system.

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Study Notes

Basics of Magnetism

  • Basics of magnetism show a magnet with North and South Poles
  • Basics of magnetism show a thumb pointing in the direction of the fields and fingers curled showing the direction of current

Earth's magnetic properties

  • Poses questions about Earth's magnetic properties:
    • Why does Earth show magnetic properties?
    • Where is the magnetic North Pole?
    • Where is the magnetic axis?
    • Is the geographical axis same as the magnetic axis?
    • Are both axes matching?
    • What is the exact location of magnetic poles?
  • The Earth is a huge magnet with its magnetic North Pole located at its geographical South Pole, and vice versa

Origin of magnetism

  • Magnetism originates from electron spin
  • The number of unpaired electrons and their clockwise (CW) or counter-clockwise (CCW) spins are mainly responsible for Magnetism, along with the crystal structure

Properties of magnetic lines of force

  • Magnetic lines are invisible, imaginary lines, which have a somewhat elliptical shape and never cross each other
  • Magnetic lines form closed loops that are thought to travel from the North Pole of a bar magnet to the South Pole externally, and from the South Pole to the North Pole internally
  • Magnetic lines that are parallel and traveling in the same direction repel each other
  • Magnetic lines act like stretched rubber bands, trying to contract
  • Magnetic lines prefer a path of minimum reluctance

Orientation of magnetic flux

  • The orientation of magnetic Flux can be seen in varying configurations in a material, with vectors showing magnetic flux pointing different directions

Attraction or Repulsion

  • Attraction or Repulsion is a property of the direction of magnetic lines in a current conductor
  • Two conductors with magnetic lines traveling in the same direction repel each other
  • Two conductors with magnetic lines traveling in opposite direction attract each other

Right-hand thumb rule

  • The right-hand thumb rule relates the direction of current and magnetic field

Important Terms - Permeability

  • Magnetic Permeability (μ) signifies the property of a material to allow magnetic lines of force to pass through it, and has a unit of Henry per meter (H/meter)
  • Relative Permeability is a ratio for comparison with no units
  • A good ferromagnetic material is 800 to 1200X better than air

Important Terms - Magneto Motive Force (MMF)

  • Magneto Motive Force MMF (F) is analogous to EMF: F = (Number of Turns) x (Current through the turns)
  • The unit for MMF is Amp-Turns (or Amp)

Important Terms - Magnetic Flux Density

  • Magnetic Flux Density (B) equals Flux divided by Area, with Flux in Webers and Area in Square Meters, and magnetic Flux expressed in Teslas

Terms - Relationships in Magnetism

  • Flux = MMF / Reluctance or Amp x Turns / ((1/μ) x (l/a)), where:
    • MMF is Magnetomotive Force
    • μ is the permeability
    • l is is length
    • a is area
  • The earth is a huge magnet
  • H (Magnetic field strength) is a function of the Current I, and proportional to it

B-H Curve

  • The OD part of the B-H curve shows Retentivity or Residual Magnetism
  • The OG part of the B-H curve also shows Retentivity or Residual Magnetism
  • The letter H on the B-H curve shows the Magnetising Force

DC Motors

  • DC Motors have enclosures, use an armature, armature conductors, and operate using an external DC supply, which connects to the Commutator and Brushes to drive a Yoke, which has Field Windings and Poles.

DC Motor Commutators

  • DC Motor Commutators are divided into two halves called segments, are connected to brushes, which transfer DC power, and are practically equal to number of slots in the armature

DC Motor Parts

  • Armature and Shaft are visible
  • The Armature Winding connects to a Commutator
  • The Stator consists of Windings attached to Poles

Fleming's rules

  • Flemings right-hand thumb rule and Fleming's right-hand grip rule determines current flow
  • Flemings right-hand rule can be used for generating action

Fleming's Left Hand Rule

  • Fleming's left-hand rule for determining the direction of force in a motor using current, magnetic field The direction of rotation of a DC motor can be seen if the there is a Dense Flux present

DC motors rotation

  • Commutators provide unidirectional rotations
  • When a DOT goes from N to S, it shifts upon reaching S using the Commutator

DC Motor Concept and Equations

  • When a motor starts rotating, the conductors cut the main flux in the air gap.
  • This cutting of Flux gives rise to an EMF which has a generating action
  • This EMF opposes the cause to create it in terms of Lenz's Law
  • This EMF opposes the cause or Supply voltage V
  • This EMF is called Back EMF (Eb) or Counter EMF hence V = - Eb
  • V is the supply voltage and Eb is generated EMF
  • Equations can be generated based on parameters
  • Faradays Law is based on a Total Flux cut

Torque

  • Various equations can be determined for DC motors including Torque T
  • If a motor is loaded then Speed is reduced which causes Eb to be reduced and the Ia current increases

BLDC Motors

  • Brushless DC Motors: use Actuators and consists of a P Semiconductor Element, with Winding
  • Brushless DC motors have a range of speed control.
  • High HP capacity motors are accessible
  • Power and Starters requirements are sufficient
  • Maintenance requirements are sufficient
  • Inexpensive

Demerits of DC motors

  • Brushes cause continuous friction.
  • Commutator segments result in wear as well as tear
  • Increases cost associated with maintenance
  • Results in temperature issues as they produce particles of carbon at contact point of the brush
  • Requires in frequent changes
  • Results in voltage decreases where brushes are used
  • In-rush can burn them out. So they require starters
  • Requires separate power supply
  • Considered to be very noisy to operate

BLDC Motor Features

  • Overcomes the problem that arise due to the contact of the brush
  • Working is founded upon basic concepts
  • BLDC motors are compatible (hall effect) hall effect sensors
  • Motor driver requires specific circuitry
  • Quieter to operate and maintain
  • Compact with lighter weight ratio
  • Better software and electronic management system
  • Requires low upkeep

BLDC Motor - Working Principle

  • Brushless DC motors work by using electrical direct current. The parts are Stator and Rotor.
  • During movement the rotor becomes affected through the repelling force of the stator
  • Upon approach of the stator the pole switches off (excitement) from on stator segment to the next
  • Rotation results (constant cycle repeats with magnet and pole interactions)

BLDC Motor- Components

  • Motors require Driver circuit (modifies voltage polarities)
  • Motors use Halls effect sensors (used to locate sensor for correct locations)

BLDC Motor - Types

  • Motors exist in distinct varieties depending upon the intended application
  • Inner and outer type
  • Motors may be Sensor and sensor less

BLDC Motor - Features

  • Axial flux motors, flat or disk are known for their motor and rotor assembly style, generally used for applications that require more space

Components - Hall effect/ sensor

  • Side movement and hall sensor parts

Deglitch features

  • The removal of signal glitches; the removal of sudden, temporary faults of equipment

The Servo Motor System

  • Servo Motors operate using electricity and are used in systems within components including transistors

BLDC Applications

  • BLDC Motors are versatile, used for CNC Machines, Robotics, Automobiles and domestic applications

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Description

Explore the advantages and disadvantages of DC brush motors and BLDC motors. Understand the design features of BLDC motors that address the drawbacks of DC brush motors. Includes key concepts like the Left Hand Rule and Right Hand Thumb Rule.

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