Motores Eléctricos · Arranque de motores de indução • Directo • Estrela-triângulo • Soft-starter • Variador electrónico de velocidade . Automação Industrial Motores

1 Automação Industrial

© Lino Marques 2015

Motores Eléctricos

Lino Marques

Versão de 21/04/2015



Conteúdo

• Introdução • Principais tipos de motores

• Motores DC com escovas • Motores de indução • Motores DC sem escovas • Motores de passo

• Comando e controlo • Variadores e contactores • Servomotores

• Eixos motorizados e controlo motriz • Máquinas de CNC e células flexíveis de fabrico



Referências

• Motors and Drives - A Practical Technology Guide (ISA 2003)

• Electric Motor Controls, Ninth Edition (Delmar 2010) • Electric Motors and Drives - Fundamentals, Types, and

Applications, 3rd Ed (Elsevier 2006)

4 Automação Industrial Motores Eléctricos


Electric Motors

• An electric motor is a power conversion device. It converts electrical power to mechanical power. Input to the motor is in the form of voltage and current, and the output is mechanical torque and speed. The key physical phenomenon in this conversion process is different for different motors.

• The torque generation, that is the electrical energy to mechanical energy conversion process, in any electric motor can be viewed as a result of the interaction of two magnetic flux density vectors: one generated by the stator (Bs) and one generated by the rotor (Br).

• Tm = K ⋅ Br ⋅ Bs ⋅ sin(𝜃𝜃rs)



Force production



Motoring and braking operation



Generic variable-speed drive system



Power density of electrical machines



Motores DC com escovas

• In the case of DC motors, there are two magnetic fields. In brush-type DC motors, one of the magnetic fields is due to the current through the armature winding on the rotor, and the other magnetic field is due to the permanent magnets in the stator (or due to field excitation of the stator winding if electromagnets are used instead of permanent magnets). In the case of brushless DC motors, the roles of rotor and stator are swapped.



DC motor operating principles





Torque as a function of the angular position of the rotor



Components of a brush-type DC motor



Cross-section of a DC Motor

http://kbreee.blogspot.pt/2013/11/magnetization-curve-of-dc-generator.html



Permanent magnet DC motor and curve



Series wound DC motor circuit and curve



Shunt wound DC motor and curve



Speed-controlled d.c. motor drive



Motores de indução

• In the case of AC motors, the first magnetic field is setup by the excitation current on the stator. This magnetic field in turn induces a voltage in the rotor conductors by Faraday’s induction principle. The induced voltage at the rotor conductors results in current which in turn sets up its own magnetic field, which is the second magnetic field. The torque is produced by the interaction of the two magnetic fields.



Induction motor elements

http://machinedesign.com/motorsdrives/difference-between-ac-induction-permanent-magnet-and-servomotor-technologies



Squirrel cage rotor



Flux rotation

Current is induced in the rotor’s conducting bars, and associated magnetic fields interact with those of the stator. This causes the rotor to follow the field generated by the stator, to rotate the output shaft.



Stator windings of an AC induction motor

(a) two-pole (P = 2) configuration, (b) four-pole (P = 4) configuration, (c) six-pole (P = 6) configuration.



Typical torque–speed curves



Speed control of cage motor by stator voltage variation

(a) low-resistance rotor, (b) high-resistance rotor



Torque-speed performance in steady-state under various control methods



Arranque de motores de indução

• Directo • Estrela-triângulo • Soft-starter • Variador electrónico de velocidade



Esquema de arranque directo com arrancador motor e contactor



Motor torque and inrush current (line starting)



Arranque directo: características e aplicações

• Binário inicial de arranque: 0,6 a 1,5 Mn. • Corrente inicial de arranque: 4 a 8 In. • Duração média do arranque: 2 a 3 s. Aplicações: • Motores até 4kW. • Máquinas pequenas que possam arrancar a plena carga,

sem problemas mecânicos: Rolamentos, correias, etc. • Bombas, Ventiladores.



Vantagens e inconvenientes

• Arrancador de esquema simples.

• Custo reduzido. • Binário de arranque elevado

comparativamente a outros arranques com contactores.

• Pico de intensidade muito elevado (a rede deve suportar este pico).

• Arranque brusco, golpe mecânico.

• Risco de roturas

• Maior desgaste dos rolamentos, transmissões a correias ou correntes.



Reducing the starting current Primary Resistor or Reactance • Uses series reactance or resistance to reduce the current during the first

seconds. After a preset time interval, the motor is connected directly across the line.

Auto Transformer • Uses an auto transformer to directly reduce voltage and the current for the

first few seconds. After a preset time interval, the motor is connected directly across the line.

Wye–Delta • Applies the voltage across the Y connection to reduce the current during the

first few seconds. After a preset time interval, the motor is connected in delta mode permitting full current.

Part–Winding • Uses a motor design that has two separate winding circuits. Upon starting,

only one winding circuit is engaged and current is reduced. After a preset time interval, the full winding of the motor is connected directly across the line.



Arranque estrela-triângulo



Arranque estrela-triângulo

Estrela: KM2, KM1 Triângulo: KM2, KM3



Curvas

Intensidade em triângulo

Intensidade em estrela

Binário em triângulo

Binário em estrela



Características e aplicações

• Binário inicial de arranque: 0,2 a 0,5 Mn • Corrente inicial de arranque: 1,3 a 2,6 In • Duração média do arranque: 3 a 7 s Aplicações : • Máquinas de arranque em vazio:

Ventiladores e bombas centrífugas de potência reduzida. • Máquinas-ferramenta. • Máquinas para madeira, etc..



Vantagens e inconvenientes

• Arrancador relativamente económico

• Boa relação binário/intensidade • Redução da corrente de

arranque

• Binário de arranque reduzido • Corte da alimentação durante a

transição (transitórios) • Ligação ao motor a 6 cabos • Sem possibilidade de regulação



Current regulation in AC motor phases by a field oriented vector control (FOVC) drive



Motores DC sem escovas



Cross section of the interior type PM (straight magnet) synchronous motor



Cross section of the surface-mounted type PM synchronous motor



Cross section of the inset type PM synchronous motor



Rotor cross section of the 4-pole (V-shaped) IPM motor



Permanent Magnetic Materials • Alnico which is an aluminum (Al)-nickel (Ni)-cobalt (Co) (“AlNiCo”)

mixture. • Ceramic (hard ferrite) magnetic materials which consists of strontium,

barium ferritite mixtures. • Samarium cobalt (samarium and cobalt mixtures, SmCo5,

Sm2Co17). • Neodymium (neodymium, iron, and boron are the main mixture

components with small amounts of other compounds). The ideal mixture is Nd2Fe14B1.



Evolution of PM materials



Performance Comparison of IPM and Induction Motors



Stepper vs. Brushless



Linear motors



Linear motors



Linear motor elements





Motores de Passo



Motores de passo

• Stepper motors (permanent magnet (PM) type) work on basically the same principle as brushless DC motors, except that the stator winding distribution is different. A given stator excitation state defines a stable rotor position as a result of the attraction between electromagnetic poles of the stator and permanent magnets of the rotor. The rotor moves to minimize the magnetic reluctance. At a stable rotor position of a step motor, two magnetic fields are parallel.



Características

• Brushless – Stepper motors are brushless. The commutator and brushes of conventional motors are some of the most failure-prone components, and they create electrical arcs that are undesirable or dangerous in some environments.

• Load Independent – Stepper motors will turn at a set speed regardless of load as long as the load does not exceed the torque rating for the motor.

• Open Loop Positioning – Stepper motors move in quantified increments or steps. As long as the motor runs within its torque specification, the position of the shaft is known at all times without the need for a feedback mechanism.

• Holding Torque – Stepper motors are able to hold the shaft stationary.

• Excellent response to start-up, stopping and reverse.



Tipos de motores de passo



Motores de relutância variável (MRV)

http://en.wikipedia.org/wiki/Reluctance_motor



Enrolamento de uma fase de um MRV

ΘS = 360o/NS ΘR = 360o/NR ΘST = ΘR - ΘS where: ΘS = stator angle, ΘR = Rotor angle, ΘST = step angle NS = number stator poles, NP = number rotor poles



Summary: variable reluctance stepper motor • The rotor is a soft iron cylinder with salient (protruding) poles. • This is the least complex, most inexpensive stepper motor. • The only type stepper with no detent torque in hand rotation of a de-energized motor shaft. • Large step angle • A lead screw is often mounted to the shaft for linear stepping motion.



Motor de passo de imanes permanentes



Comando bipolar e unipolar



Comando em passo completo



Meio-passo



Constituição de um motor de imanes permanentes

Summary: permanent magnet stepper motor • The rotor is a permanent magnet, often a ferrite sleeve magnetized with numerous poles. • Can-stack construction provides numerous poles from a single coil with interleaved fingers of soft iron. • Large to moderate step angle. • Often used in computer printers to advance paper



Motor de passo híbrido

This motor is termed a hybrid because it uses elements of both variable reluctance and permanent-magnet-rotor step motors.



Constituição



Rotação do motor híbrido

Summary: hybrid stepper motor • The step angle is smaller than variable reluctance or permanent magnet steppers. • The rotor is a permanent magnet with fine teeth. North and south teeth are offset by half a tooth for a smaller step angle. • The stator poles have matching fine teeth of the same pitch as the rotor. • The stator windings are divided into no less than two phases. • The poles of one stator windings are offset by a quarter tooth for an even smaller step angle.



Modos de comando

• Wave Drive (1 phase on) • Full Step Drive (2 phases on) • Half Step Drive (1 & 2 phases on) • Microstepping (Continuously varying motor currents)

Documents

Motores Eléctricos · Arranque de motores de indução • Directo • Estrela-triângulo • Soft-starter • Variador electrónico de velocidade . Automação Industrial Motores