An electric motor (English: Electric machinery, commonly known as a "motor") is an electromagnetic device that converts or transmits electrical energy based on the law of electromagnetic induction. It is represented by the letter M in circuit diagrams (D in older standards). Its main function is to generate driving torque, serving as a power source for electrical appliances or various machines. A generator is represented by the letter G in circuit diagrams. Its main function is to convert mechanical energy into electrical energy; currently, the most common method is to use heat energy, water energy, etc., to drive the generator rotor to generate electricity.
Category 1
1. According to the type of power supply: motors can be divided into DC motors and AC motors.
1) DC motors can be classified into brushless DC motors and brushed DC motors according to their structure and working principle.
Brushed DC motors can be classified into two types: permanent magnet DC motors and electromagnetic DC motors.
Electromagnetic DC motors can be classified into: series-wound DC motors, shunt-wound DC motors, separately excited DC motors, and compound-wound DC motors.
Permanent magnet DC motors can be classified into three types: rare earth permanent magnet DC motors, ferrite permanent magnet DC motors, and AlNiCo permanent magnet DC motors.
2) AC motors can be further divided into single-phase motors and three-phase motors.
2. According to structure and working principle, motors can be divided into DC motors, asynchronous motors, and synchronous motors.
1) Synchronous motors can be classified as: permanent magnet synchronous motors, reluctance synchronous motors, and hysteresis synchronous motors.
2) Asynchronous motors can be divided into: induction motors and AC commutator motors.
Induction motors can be classified as: three-phase asynchronous motors, single-phase asynchronous motors, and shaded-pole asynchronous motors, etc.
AC commutator motors can be classified as: single-phase series motors, AC/DC universal motors, and repulsion motors.
3. According to the starting and running methods, single-phase asynchronous motors can be divided into: capacitor-start single-phase asynchronous motors, capacitor-run single-phase asynchronous motors, capacitor-start-run single-phase asynchronous motors, and split-phase single-phase asynchronous motors.
4. According to their purpose, electric motors can be divided into drive motors and control motors.
1) Electric motors for driving can be divided into: electric motors for power tools (including tools for drilling, polishing, grinding, grooving, cutting, and reaming), electric motors for household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric shavers, etc.), and electric motors for other general-purpose small mechanical equipment (including various small machine tools, small machinery, medical devices, electronic instruments, etc.).
2) Control motors are further divided into stepper motors and servo motors, etc.
5. According to the rotor structure, induction motors can be divided into: squirrel-cage induction motors (formerly known as squirrel-cage asynchronous motors) and wound-rotor induction motors (formerly known as wound-rotor asynchronous motors).
6. According to operating speed, motors can be classified as: high-speed motors, low-speed motors, constant-speed motors, and variable-speed motors. Low-speed motors are further divided into geared motors, electromagnetic geared motors, torque motors, and claw-pole synchronous motors, etc.
In addition to being classified into stepped constant speed motors, stepless constant speed motors, stepped variable speed motors, and stepless variable speed motors, speed-regulating motors can also be classified into electromagnetic speed-regulating motors, DC speed-regulating motors, PWM frequency conversion speed-regulating motors, and switched reluctance speed-regulating motors.
The rotor speed of an asynchronous motor is always slightly lower than the synchronous speed of the rotating magnetic field.
The rotor speed of a synchronous motor remains constant regardless of the load.
2 DC type
The working principle of a DC generator is to convert the alternating electromotive force induced in the armature coil...
The principle is that the commutation effect of the commutator and the brushes is used to convert the current into a DC electromotive force when it is drawn from the brush end.
The direction of the induced electromotive force is determined by the right-hand rule (the magnetic field lines point to the palm, the thumb points to the direction of the conductor's motion, and the other four fingers point to the direction of the induced electromotive force in the conductor).
Working principle
The direction of the force on a conductor is determined by the left-hand rule. This pair of electromagnetic forces creates a torque acting on the armature, which is called electromagnetic torque in a rotating electrical machine. The direction of the torque is counterclockwise, attempting to make the armature rotate counterclockwise. If this electromagnetic torque can overcome the resistive torque on the armature (such as the resistive torque caused by friction and other load torques), the armature can rotate counterclockwise.
DC motors are electric motors that operate on DC working voltage and are widely used in radios, video recorders, DVD players, electric shavers, hair dryers, electronic watches, toys, etc.
3 Electromagnetic
An electromagnetic DC motor consists of stator poles, rotor (armature), commutator (commonly known as rectifier), brushes, housing, bearings, etc.
The stator poles (main poles) of an electromagnetic DC motor consist of an iron core and excitation windings. Based on their excitation (formerly known as magnetization) method, they can be further classified into series-wound DC motors, shunt-wound DC motors, separately excited DC motors, and compound-wound DC motors. Due to the different excitation methods, the magnetic flux of the stator poles (generated by energizing the excitation coils of the stator poles) also differs.
In a series-wound DC motor, the excitation winding and rotor winding are connected in series via brushes and a commutator. The excitation current is proportional to the armature current, and the stator flux increases with the increase of the excitation current. The torque is approximately proportional to the square of the armature current, and the speed decreases rapidly with the increase of torque or current. Its starting torque can reach more than 5 times the rated torque, and its short-term overload torque can reach more than 4 times the rated torque. The speed variation rate is large, and the no-load speed is very high (generally, it is not allowed to operate under no-load conditions). Speed regulation can be achieved by connecting an external resistor in series (or in parallel) with the series winding, or by switching the parallel connection of the series winding.
In a shunt-wound DC motor, the excitation winding is connected in parallel with the rotor winding. Its excitation current is relatively constant, and the starting torque is proportional to the armature current, which is approximately 2.5 times the rated current. The speed decreases slightly with increasing current and torque, and the short-term overload torque is 1.5 times the rated torque. The speed variation rate is small, ranging from 5% to 15%. Speed can be adjusted by using constant power to weaken the magnetic field.
In a separately excited DC motor, the excitation winding is powered by an independent excitation power supply, and its excitation current is relatively constant. The starting torque is proportional to the armature current. The speed variation is also 5%~15%. The speed can be increased by weakening the magnetic field and maintaining constant power, or the speed can be decreased by reducing the voltage of the rotor winding.
In addition to the shunt winding, the stator poles of a compound-wound DC motor also have a series winding (with fewer turns) connected in series with the rotor winding. The magnetic flux generated by the series winding is in the same direction as that of the main winding. The starting torque is approximately four times the rated torque, and the short-term overload torque is approximately 3.5 times the rated torque. The speed variation rate is 25%~30% (related to the series winding). The speed can be adjusted by weakening the magnetic field strength.
The commutator segments are made of alloy materials such as silver-copper and cadmium-copper, molded from high-strength plastic. The brushes slide in contact with the commutator, providing armature current to the rotor windings. Electromagnetic DC motors typically use metal-graphite brushes or electrographite brushes. The rotor core is made of laminated silicon steel sheets, typically with 12 slots, containing 12 sets of armature windings. These windings are connected in series and then individually connected to the 12 commutator segments.
4 DC motors
The excitation method of a DC motor refers to how the excitation winding is powered to generate an excitation magnetomotive force to establish the main magnetic field. Based on different excitation methods, DC motors can be classified into the following types.
He encouraged
A DC motor in which the field winding and armature winding are not connected, but the field winding is powered by another DC power source, is called a separately excited DC motor, and the wiring diagram is shown in Figure 1.23(a). In the figure, M represents a motor, and G represents a generator. Permanent magnet DC motors can also be regarded as separately excited DC motors.
And encourage
In a shunt-wound DC motor, the field winding is connected in parallel with the armature winding. As a shunt-wound generator,
The excitation winding is powered by the terminal voltage generated by the motor itself; as a shunt-wound motor, the excitation winding and the armature share the same power supply, and in terms of performance, they are the same as separately excited DC motors.
Series excitation
In a series-wound DC motor, the field winding and armature winding are connected in series and then connected to a DC power supply. The field current of this type of DC motor is the armature current.
Reinforcement
A compound-wound DC motor has two excitation windings: a shunt winding and a series winding. If the magnetomotive force (MF) generated by the series winding is in the same direction as that generated by the shunt winding, it is called cumulative compound excitation. If the two MFs are in opposite directions, it is called differential compound excitation.
DC motors with different excitation methods have different characteristics. Generally, the main excitation methods for DC motors are shunt-wound, series-wound, and compound-wound, while the main excitation methods for DC generators are separately excited, shunt-wound, and compound-wound.
5 permanent magnet type
Permanent magnet DC motors also consist of stator poles, rotor, brushes, and housing. The stator poles use permanent magnets (permanent steel), made of materials such as ferrite, AlNiCo, and NdFeB. Based on their structural form, they can be divided into several types, including cylindrical and block-type. Most motors used in VCRs and players use cylindrical magnets, while motors used in power tools and automotive electrical appliances mostly use block-type magnets.
The rotor is generally made of laminated silicon steel sheets, and has fewer slots than the rotor of an electromagnetic DC motor. Most low-power motors used in VCRs and players have 3 slots, while higher-end models have 5 or 7 slots. Enameled wire is wound between two slots of the rotor core (three slots means three windings), and each joint is welded to the commutator's metal plates. Brushes are conductive components that connect the power supply to the rotor windings, possessing both conductivity and wear resistance. Permanent magnet motors use single-element metal sheets, metal-graphite brushes, or electrographite brushes.
The permanent magnet DC motor used in the recorder employs an electronic speed stabilization circuit or a centrifugal speed stabilization device.
6 brushless DC
Brushless DC motors use semiconductor switching devices to achieve electronic commutation, replacing traditional contact commutators and brushes with electronic switching devices. They offer advantages such as high reliability, no commutation sparks, and low mechanical noise, and are widely used in high-end tape recorders, video recorders, electronic instruments, and automated office equipment.
A brushless DC motor consists of a permanent magnet rotor, a multi-pole winding stator, and a position sensor. The position sensor, based on changes in rotor position, commutates the current in the stator windings in a specific sequence (i.e., it detects the position of the rotor poles relative to the stator windings, generates a position sensing signal at a defined position, processes the signal through a signal conversion circuit, and then controls the power switching circuit to switch the winding current according to a specific logic). The operating voltage of the stator windings is provided by an electronic switching circuit controlled by the position sensor output.
Position sensors come in three types: magnetic, photoelectric, and electromagnetic. In a brushless DC motor that uses a magnetic position sensor, the magnetic sensor element (such as a Hall element, magnetic diode, magnetic transistor, magnetoresistive element, or dedicated integrated circuit) is mounted on the stator assembly to detect changes in the magnetic field generated by the permanent magnet and the rotor during rotation.
A brushless DC motor employing photoelectric position sensors has photoelectric sensor components positioned at specific locations on the stator assembly, and a light-shielding plate mounted on the rotor. The light source is a light-emitting diode or a small bulb. As the rotor rotates, due to the effect of the light-shielding plate, the photosensitive components on the stator will intermittently generate pulse signals at a certain frequency.
A brushless DC motor that uses an electromagnetic position sensor has an electromagnetic sensor component (such as a coupling transformer, proximity switch, LC resonant circuit, etc.) installed on the stator assembly. When the position of the permanent magnet rotor changes, the electromagnetic effect will cause the electromagnetic sensor to generate a high-frequency modulation signal (the amplitude of which changes with the rotor position).
Superiority
DC motors have the characteristics of fast response and large starting torque.
DC motors offer rated torque from zero speed to rated speed, but this advantage is also their disadvantage. To generate constant torque under rated load, the armature and rotor magnetic fields must maintain a constant 90° angle, requiring carbon brushes and a commutator. These brushes and commutators generate sparks and carbon dust during motor rotation, potentially damaging components and limiting their applications. AC motors, on the other hand, are brushless, robust, and widely applicable, but achieving DC-like performance requires complex control techniques. Rapid advancements in semiconductor technology have significantly increased the switching frequency of power components, improving drive motor performance. Microprocessors are also becoming increasingly faster, enabling AC motor control within a rotating two-axis orthogonal coordinate system. By appropriately controlling the current components of the AC motor along both axes, similar control methods to DC motors can be achieved, resulting in comparable performance.
Furthermore, many microprocessors now integrate the necessary motor control functions into individual chips, and their sizes are becoming increasingly smaller; examples include analog-to-digital converters (ADCs) and pulse-width modulators (PWM). A brushless DC motor is an application that uses electronic control to commutate an AC motor, achieving characteristics similar to a DC motor without the structural deficiencies of a DC motor.
control structure
A brushless DC motor is a type of synchronous motor, meaning that the rotor speed is affected by the speed of the rotating magnetic field of the stator and the number of rotor poles (p).
n=120. f/p. With a fixed number of rotor poles, changing the frequency of the stator rotating magnetic field can change the rotor speed. A brushless DC motor is essentially a synchronous motor with added electronic control (driver). This controls the frequency of the stator rotating magnetic field and feeds the rotor speed back to the control center for repeated correction, aiming to achieve characteristics close to a DC motor. In other words, a brushless DC motor can maintain a certain rotor speed within its rated load range even when the load changes.
A brushless DC driver includes a power supply section and a control section. The power supply section provides three-phase power to the motor, while the control section converts the input power frequency as needed.
The power supply can accept direct DC input (typically 24V) or AC input (110V/220V). If the input is AC, it must first be converted to DC by a converter. Regardless of whether the input is DC or AC, the DC voltage must be converted to a three-phase voltage by an inverter to drive the motor coils. The inverter typically consists of six power transistors (Q1-Q6), divided into upper arms (Q1, Q3, Q5) and lower arms (Q2, Q4, Q6), connected to the motor as switches controlling the flow through the motor coils. The control unit provides PWM (Pulse Width Modulation) to determine the switching frequency of the power transistors and the timing of inverter commutation. DC brushless motors generally require speed control that maintains a stable speed at a set value without significant fluctuations when the load changes. Therefore, the motor is equipped with a Hall sensor that senses the magnetic field, serving as a closed-loop speed control and also as a basis for phase sequence control. However, this is only used for speed control and cannot be used for positioning control.
Control Principles
To make the motor rotate, the control unit must determine the sequence of power transistors in the inverter based on the position of the motor rotor sensed by the Hall sensor and the stator windings. This causes current to flow sequentially through the motor coils, generating a clockwise (or counterclockwise) rotating magnetic field that interacts with the rotor's magnets, thus making the motor rotate clockwise or counterclockwise. When the motor rotor rotates to a position where the Hall sensor senses another set of signals, the control unit activates the next set of power transistors. This cycle continues, allowing the motor to rotate in the same direction until the control unit decides to stop the motor rotor by turning off the power transistors (or only turning on the lower arm power transistors); to reverse the motor rotor's direction, the power transistor activation sequence is reversed.
7 asynchronous motors
I. AC asynchronous motor
AC asynchronous motors are motors that operate on AC voltage and are widely used in household appliances such as electric fans, refrigerators, washing machines, air conditioners, hair dryers, vacuum cleaners, range hoods, dishwashers, electric sewing machines, and food processing machines, as well as various power tools and small electromechanical equipment.
AC asynchronous motors are divided into induction motors and AC commutator motors. Induction motors are further divided into single-phase asynchronous motors, AC/DC universal motors, and repulsion motors.
An asynchronous motor is one where the rotor speed is less than the speed of the rotating magnetic field. It is essentially the same as an induction motor. The formula is: s = (ns - n) / ns, where s is the slip rate.
ns is the magnetic field speed, and n is the rotor speed.
Basic principle:
1. When a three-phase asynchronous motor is connected to a three-phase AC power supply, the three-phase stator windings generate a three-phase magnetomotive force (stator rotating magnetomotive force) through which three-phase symmetrical current flows, and a rotating magnetic field is generated.
2. The rotating magnetic field has a relative cutting motion with the rotor conductor. According to the principle of electromagnetic induction, the rotor conductor generates an induced electromotive force and an induced current.
3. According to the law of electromagnetic force, the current-carrying rotor conductor is subjected to electromagnetic force in the magnetic field, forming electromagnetic torque, which drives the rotor to rotate. When the motor shaft is loaded with mechanical load, it outputs mechanical energy.
An asynchronous motor is an AC motor whose speed under load is not a constant ratio to the frequency of the connected power grid. It varies with the load size. The greater the load torque, the lower the rotor speed. Asynchronous motors include induction motors, doubly-fed asynchronous motors, and AC commutator motors. Induction motors are the most widely used, and in cases where this will not cause misunderstanding or confusion, they are generally referred to as asynchronous motors.
The stator winding of a typical asynchronous motor is connected to the AC power grid, while the rotor winding does not require connection to any other power source. Therefore, it boasts advantages such as simple structure, ease of manufacturing, use, and maintenance, reliable operation, small size, and low cost. Asynchronous motors have high operating efficiency and good working characteristics, operating at near constant speed from no-load to full-load, meeting the transmission requirements of most industrial and agricultural machinery. Asynchronous motors are also easy to derive into various protection types to adapt to different environmental conditions. However, when an asynchronous motor is running, it must draw reactive excitation power from the power grid, which degrades the power factor of the grid. Therefore, synchronous motors are often used for driving high-power, low-speed machinery such as ball mills and compressors. Because the speed of an asynchronous motor has a certain slip relationship with the speed of its rotating magnetic field, its speed regulation performance is relatively poor (except for AC commutator motors). For transportation machinery, rolling mills, large machine tools, printing and dyeing machinery, and papermaking machinery requiring a wider and smoother speed regulation range, DC motors are more economical and convenient. However, with the development of high-power electronic devices and AC speed control systems, the speed control performance and economy of asynchronous motors suitable for wide speed ranges are now comparable to those of DC motors.
II. Single-phase asynchronous motor
A single-phase asynchronous motor consists of a stator, rotor, bearings, housing, end covers, etc.
The stator consists of a frame and a core with windings. The core is made of silicon steel sheets that have been punched and stacked. Two sets of main windings (also called running windings) and auxiliary windings (also called starting windings) are embedded in the slots, spaced 90° apart electrically. The main windings are connected to an AC power supply, and the auxiliary windings are connected in series with a centrifugal switch S or a starting capacitor, running capacitor, etc., before being connected to the power supply.
The rotor is a cage-type cast aluminum rotor, which is made by stacking iron cores and then casting aluminum into the slots of the iron cores, and casting end rings together to short-circuit the rotor bars to form a squirrel cage shape.
Single-phase asynchronous motors are further divided into single-phase resistance-start asynchronous motors, single-phase capacitor-start asynchronous motors, single-phase capacitor-run asynchronous motors, and single-phase dual-capacitor asynchronous motors.
III. Three-phase asynchronous motor
The structure of a three-phase asynchronous motor is similar to that of a single-phase asynchronous motor. Three-phase windings (with three structures: single-layer chain type, single-layer concentric type, and single-layer cross type) are embedded in the stator core slots. After the stator windings are connected to a three-phase AC power supply, the rotating magnetic field generated by the winding current induces a current in the rotor conductors. Under the interaction of the induced current and the rotating magnetic field in the air gap, the rotor generates an electromagnetic rotor (i.e., an asynchronous rotor), causing the motor to rotate.
IV. Shaded-pole motor
Shaded-pole motors are the simplest type of single-phase AC motors, typically employing a squirrel-cage cast aluminum rotor with skewed slots. Based on the stator's external structure, they are further classified into salient-pole shaded-pole motors and non-salient-pole shaded-pole motors.
The stator core of a salient-pole shaded-pole motor is a square, rectangular, or circular magnetic field frame with protruding poles. Each pole has one or more auxiliary short-circuit copper rings, i.e., shaded-pole windings. The concentrated windings on the salient poles serve as the main windings.
The stator core of a salient-pole shaded-pole motor is the same as that of a conventional single-phase motor. Its stator windings are distributed windings, with the main windings located within the stator slots. The shaded-pole windings do not use short-circuit copper rings; instead, they are made of thicker enameled wire wound into distributed windings (which self-short-circuit after being connected in series) and embedded in the stator slots (approximately 2/3 of the total number of slots), serving as an auxiliary winding. The main windings and shaded-pole windings are spatially separated by a certain angle.
When the main winding of the shaded pole motor is energized, the shaded pole winding will also generate an induced current, causing the magnetic flux of the part of the stator magnetic pole covered by the shaded pole winding to rotate in the direction of the unshaded part towards the covered part.
V. Single-phase series motor
The stator of a single-phase series motor consists of a salient-pole core and a field winding, while the rotor consists of a non-salient-pole core, an armature winding, a commutator, and a shaft. The field winding and the armature winding form a series circuit through brushes and the commutator.
A single-phase series motor is a dual-purpose AC/DC motor, meaning it can operate on either AC or DC power.
8 synchronous motors
Synchronous motors, like induction motors, are commonly used AC motors. Their key characteristic is that during steady-state operation, the rotor speed and the grid frequency maintain a constant relationship: n = ns = 60f/p, where ns is the synchronous speed. If the grid frequency remains constant, the synchronous motor's speed in steady state is always constant and independent of the load. Synchronous motors are divided into synchronous generators and synchronous motors. Modern power plants primarily use synchronous motors in their AC motor systems.
Working principle
Establishment of the main magnetic field: A DC excitation current is passed through the excitation winding to establish an excitation magnetic field with alternating polarities, that is, to establish the main magnetic field.
Current-carrying conductor: The three-phase symmetrical armature winding acts as the power winding, becoming the carrier of induced electromotive force or induced current.
Cutting motion: The prime mover drives the rotor to rotate (inputting mechanical energy into the motor), and the excitation magnetic field with alternating polarities rotates with the shaft and sequentially cuts each phase of the stator winding (equivalent to the conductors of the winding cutting the excitation magnetic field in the opposite direction).
Generation of alternating electromotive force: Due to the relative cutting motion between the armature winding and the main magnetic field, a three-phase symmetrical alternating electromotive force with periodically changing magnitude and direction will be induced in the armature winding. AC power can then be provided through the leads.
Alternating polarity and symmetry: Due to the alternating polarities of the rotating magnetic field, the polarity of the induced electromotive force alternates; due to the symmetry of the armature winding, the three-phase symmetry of the induced electromotive force is guaranteed. [1]
I. AC Synchronous Motor
An AC synchronous motor is a constant-speed drive motor in which the rotor speed maintains a constant proportional relationship with the power supply frequency. It is widely used in electronic instruments, modern office equipment, textile machinery, and other fields.
II. Permanent Magnet Synchronous Motor
Permanent magnet synchronous motors belong to the category of asynchronous starting permanent magnet synchronous motors. Their magnetic field system consists of one or more permanent magnets, typically housed inside a cage-type rotor made of cast aluminum or welded copper bars, with the required number of permanent magnet poles installed. The stator structure is similar to that of an asynchronous motor.
When the stator winding is powered on, the motor starts and rotates according to the principle of asynchronous motor. When it accelerates to synchronous speed, the synchronous electromagnetic torque generated by the rotor permanent magnet field and the stator magnetic field (the electromagnetic torque generated by the rotor permanent magnet field and the magnetic reluctance torque generated by the stator magnetic field) pulls the rotor into synchronization, and the motor enters synchronous operation.
Reluctance synchronous motors, also known as reactive synchronous motors, are synchronous motors that generate reluctance torque by utilizing the unequal magnetic reluctance between the rotor's quadrature and direct axes. Their stator structure is similar to that of asynchronous motors, only the rotor structure is different.
III. Reluctance Synchronous Motor
Evolved from the co-cage asynchronous motor, the rotor also features cage-type cast aluminum windings to generate asynchronous starting torque. The rotor has reaction slots corresponding to the number of stator poles (only the salient pole portion functions, without excitation windings and permanent magnets) to generate reluctance synchronous torque. Based on the structure of the reaction slots, it can be divided into internal reaction rotors, external reaction rotors, and both internal and external reaction rotors. In external reaction rotors, the reaction slots are cut into the outer circumference of the rotor, making the air gap unequal in the direct and quadrature axes. Internal reaction rotors have internal grooves that obstruct magnetic flux in the quadrature axis direction, increasing reluctance. The combination of internal and external reaction rotors, with a significant difference between the direct and quadrature axes, results in a motor with greater force. Reluctance synchronous motors also come in various types, including single-phase capacitor-run, single-phase capacitor-start, and single-phase dual-capacitor types.
IV. Hysteresis Synchronous Motor
A hysteresis synchronous motor is a synchronous motor that operates by generating hysteresis torque using hysteresis materials. It is classified into internal rotor hysteresis synchronous motors, external rotor hysteresis synchronous motors, and single-phase shaded-pole hysteresis synchronous motors.
The rotor structure of the internal rotor hysteresis synchronous motor is salient pole type, and its appearance is a smooth cylinder. There are no windings on the rotor, but there is an effective ring layer made of hysteresis material on the outer circle of the iron core.
After the stator windings are powered on, the resulting rotating magnetic field causes the hysteresis rotor to generate asynchronous torque and start rotating, subsequently pulling itself into synchronous operation. During asynchronous operation, the stator rotating magnetic field repeatedly magnetizes the rotor at the slip frequency; during synchronous operation, the hysteresis material on the rotor is magnetized, creating permanent magnet poles, thus generating synchronous torque. The soft starter uses three anti-parallel thyristors as voltage regulators, connected between the power supply and the motor stator. This circuit resembles a three-phase fully controlled bridge rectifier circuit. When starting the motor with a soft starter, the thyristor output voltage gradually increases, and the motor gradually accelerates until the thyristors are fully conducting. The motor operates at its rated voltage mechanical characteristics, achieving smooth starting, reducing starting current, and avoiding overcurrent tripping. Once the motor reaches its rated speed, the starting process ends, and the soft starter automatically replaces the thyristors with a bypass contactor, providing the rated voltage for normal motor operation. This reduces thyristor heat loss, extends the soft starter's lifespan, improves its efficiency, and prevents harmonic pollution of the power grid. The soft starter also provides a soft stop function. The soft stop process is the opposite of the soft start process. The voltage gradually decreases and the speed gradually drops to zero, avoiding the torque shock caused by free stop.
9-speed geared motor
A geared motor is an integrated unit combining a speed reducer and a motor. This type of integrated unit is also commonly referred to as a geared motor. It is typically assembled and supplied as a complete set by specialized speed reducer manufacturers. Geared motors are widely used in industries such as steel and machinery. The advantages of using geared motors include simplified design and space saving.
1. The geared motor is manufactured in accordance with international technical requirements and has a high level of technological content.
2. Space-saving, reliable and durable, with high overload capacity and power up to 95KW or more.
3. Low energy consumption, superior performance, and reducer efficiency of over 95%.
4. Low vibration, low noise, high energy efficiency, made of high-quality steel, with a rigid cast iron housing and gear surfaces treated with high frequency heat treatment.
5. Precision machining ensures positioning accuracy. All of these factors contribute to the gear transmission assembly. The gear reducer motor is equipped with various motors, forming a mechatronics system that fully guarantees the product's quality characteristics.
6. The product adopts a serialized and modular design concept, which has a wide range of adaptability. This series of products has a wide variety of motor combinations, installation positions and structural schemes, and any speed and various structural forms can be selected according to actual needs.
Gear motor classification:
1. High-power geared motor
2. Coaxial helical gear reducer motor
3. Parallel shaft helical gear reducer motor
4. Spiral bevel gear reducer motor
5. YCJ series geared motors
Gear motors are widely used in the speed reduction transmission mechanisms of various general-purpose mechanical equipment in metallurgy, mining, hoisting, transportation, cement, construction, chemical, textile, printing and dyeing, and pharmaceutical industries.
10 variable frequency motors
Variable frequency technology actually utilizes the principles of motor control to control the motor through a so-called frequency converter. Motors used for this type of control are called variable frequency motors.
Common variable frequency motors include: three-phase asynchronous motors, DC brushless motors, AC brushless motors, and switched reluctance motors.
Control principle of variable frequency motor
The typical control strategies for variable frequency motors are: constant torque control at base speed, constant power control above base speed, and field weakening control in the ultra-high speed range.
Base speed: Because a motor generates back electromotive force (EMF) when it is running, and the magnitude of the back EMF is usually proportional to the rotational speed, the speed at which the motor reaches a certain speed is called the base speed, since the magnitude of the back EMF is the same as the magnitude of the applied voltage.
Constant torque control: The motor operates at constant torque at its base speed. In this mode, the motor's back electromotive force (EMF) E is directly proportional to its speed. Since the motor's output power is proportional to the product of its torque and speed, the motor power is directly proportional to its speed.
Constant power control: When the motor exceeds its base speed, the motor's back electromotive force is kept essentially constant by adjusting the motor's excitation current, thereby increasing the motor's speed. At this time, the motor's output power remains essentially constant, but the motor torque decreases inversely proportional to the speed.
Field weakening control: When the motor speed exceeds a certain value, the excitation current is already quite small and can basically not be adjusted further. At this time, the field weakening control stage is entered.
Speed regulation and control of electric motors is one of the fundamental technologies for various industrial and agricultural machinery, as well as office and household electrical equipment. With the remarkable development of power electronics and microelectronics technologies, AC speed regulation using a "dedicated variable frequency induction motor + frequency converter" is leading a revolutionary shift in the speed regulation field, replacing traditional methods, due to its superior performance and economic efficiency. Its benefits to various industries include: significantly improved automation and production efficiency; energy savings; increased product qualification rates and quality; correspondingly increased power system capacity; equipment miniaturization; and enhanced comfort. It is rapidly replacing traditional mechanical and DC speed regulation solutions.
Due to the special nature of variable frequency power supplies and the system's requirements for high-speed or low-speed operation and dynamic speed response, stringent requirements are placed on the electric motor, which is the main power source, bringing new challenges to the electric motor in terms of electromagnetics, structure, and insulation.
Applications of variable frequency motors
Variable frequency speed control has become the mainstream speed control solution and can be widely used in continuously variable transmissions in various industries.
Especially with the increasingly widespread application of frequency converters in the field of industrial control, the use of frequency converter motors has also become more and more widespread. It can be said that due to the superiority of frequency converter motors over ordinary motors in frequency control, we can easily see frequency converter motors wherever frequency converters are used.
11 linear motors
The traditional "rotary motor + ball screw" feed transmission method on machine tools, due to its structural limitations, struggles to achieve significant improvements in feed speed, acceleration, and rapid positioning accuracy, failing to meet the higher demands of ultra-high-speed cutting and ultra-precision machining for the servo performance of machine tool feed systems. Linear motors directly convert electrical energy into linear motion mechanical energy, eliminating the need for any intermediate conversion mechanisms. They offer advantages such as high starting thrust, high transmission rigidity, fast dynamic response, high positioning accuracy, and unrestricted stroke length. The biggest difference between using a linear motor for direct drive and the original rotary motor transmission in machine tool feed systems is the elimination of the mechanical transmission link between the motor and the worktable (slide), shortening the machine tool feed transmission chain to zero; hence, this transmission method is also known as "zero transmission." It is precisely this "zero transmission" method that brings performance indicators and advantages that the original rotary motor drive method could not achieve.
1. High-speed response
Because some mechanical transmission components with large response time constants (such as lead screws) are directly eliminated from the system, the dynamic response performance of the entire closed-loop control system is greatly improved, and the response is exceptionally sensitive and fast.
2. Accuracy
Linear drive systems eliminate transmission backlash and errors caused by mechanical mechanisms such as lead screws, and reduce tracking errors caused by transmission system lag during interpolation movements. By using linear position detection feedback control, the positioning accuracy of machine tools can be greatly improved.
3. High dynamic stiffness: Due to "direct drive", the motion lag caused by elastic deformation, friction and wear and backlash of intermediate transmission links is avoided during starting, speed change and reversal, and the transmission stiffness is also improved.
4. High speed and short acceleration/deceleration process
Since linear motors were initially used primarily in maglev trains (reaching speeds of up to 500 km/h), their application in machine tool feed drives to meet the maximum feed speed requirements for ultra-high-speed cutting (60–100 m/min or higher) is certainly not a problem. Due to the aforementioned "zero-transmission" high-speed response, the acceleration and deceleration processes are significantly shortened. This allows for instantaneous high-speed start-up and instantaneous precise stopping during high-speed operation. Higher accelerations can be achieved, typically 2–10 g (g = 9.8 m/s²), while the maximum acceleration of ball screw drives is generally only 0.1–0.5 g.
5. The stroke length is not limited. By connecting linear motors in series on the guide rail, the stroke length can be extended indefinitely.
6. Quiet and low-noise operation. Because the mechanical friction of components such as the transmission screw is eliminated, and the guide rail can be a rolling guide rail or a magnetic pad suspension guide rail (without mechanical contact), the noise during operation is greatly reduced.
7. High efficiency. Because there are no intermediate transmission links, energy loss due to mechanical friction is eliminated, greatly improving transmission efficiency.
