Types of electric motor motors and their characteristics

The electric vehicle motor converts the electrical energy of the power source into mechanical energy, through the transmission or directly drives the wheels and working devices. What are the types of electric motor motors? What are the characteristics of each?

Basic introduction of electric vehicle motor

Motor: Refers to all machines that convert mechanical energy into electrical energy and electrical energy into mechanical energy. Specifically refers to generators, electric machines, and electric motors.

Electric motor: A motor, commonly known as a motor, is an electrical device that converts electrical energy into mechanical energy and can use mechanical energy to generate kinetic energy to drive other devices.

Since electric vehicles use power batteries as the vehicle-mounted energy source, their capacity is limited. In order to extend the driving range as much as possible, most of the drive systems use energy feedback technology, that is, the kinetic energy of the wheel loss through the controller during vehicle braking. Feedback is made to the battery and the motor is in a generating state, delivering the emitted electricity to the battery. Therefore, the driver of an electric car should be called a motor, not the motor we are used to calling. For example, the double stator magnetic suspension composite rotor motor used by Zhongda Qingshan can convert electrical energy into mechanical energy and mechanical energy into electrical energy.

Electric vehicle motor type and its characteristics

Motor classification

In addition to the power generation function, the electric motor of the electric car mainly functions as an electric motor, so we classify it by electric motor: (only for simple classification)

1, according to the type of working power: can be divided into DC motor and AC motor.

DC:

According to the structure and working principle, it can be divided into: brushless DC motor and brushed DC motor.

It can also be divided into permanent magnet DC motor and electromagnetic DC motor.

The permanent magnet DC motor is further divided into rare earth, ferrite and AlNiCo permanent magnet DC motors.

Electromagnetic DC motors are further divided into series-excited, shunt-excited, separately excited and compound-excited DC motors according to the excitation mode.

AC motors can be divided into: single-phase motors and three-phase motors

2, according to the structure and working principle: can be divided into DC motor, asynchronous motor, synchronous motor.

The rotor speed of an asynchronous motor is always slightly lower than the synchronous speed of the rotating magnetic field.

The rotor speed of the synchronous motor is always kept at the synchronous speed regardless of the load.

3. According to the purpose, there are drive motor and control motor.

4. According to the running speed, there is high speed motor, low speed motor, constant speed motor and speed regulating motor.

Low-speed motors are further classified into gear reduction motors, electromagnetic reduction motors, torque motors, and claw-pole synchronous motors.

Electric car motor working principle

1, AC motor

The single-phase asynchronous motor separates the single-phase alternating current into another alternating current with a phase difference of 90 degrees by capacitive phase shifting. The two phases of alternating current are respectively fed into two or four sets of motor coil windings, and a rotating magnetic field is formed in the motor. The rotating magnetic field generates an induced current in the rotor of the motor, and the magnetic field generated by the induced current is opposite to the direction of the rotating magnetic field, and is rotated by the magnetic field. Push-pull enters the rotating state. Since the rotor must cut the magnetic lines of force to generate the induced current, the rotor speed must be lower than the rotating magnetic speed, so it is called an asynchronous motor.

The three-phase asynchronous motor does not have to be phase-shifted by the capacitor, and it has three-phase alternating current with a difference of 120 degrees, so the generated rotating magnetic field is more uniform and more efficient.

The magnetic field of the permanent magnet synchronous AC motor is generated by a permanent magnet, and the rotor coil is powered by a brush. The speed and the alternating current frequency are in multiple (fractional) relationships (depending on the number of windings of the rotor coil), so it is called synchronous motor.

The rotor coil is powered by a brush, and the stator generates a rotating magnetic field through the coil winding. The series and parallel relationship of the rotor coil and the stator coil are respectively called series excitation and parallel excitation motors.

2, DC motor

The DC motor has two parts: a stator and a rotor. The stator has magnetic poles (winding or permanent magnet). The rotor has windings. After energization, a magnetic field (magnetic pole) is formed on the rotor, and an angle exists between the stator and the magnetic pole of the rotor. The motor is rotated by mutual attraction of a fixed rotor magnetic field (between the N pole and the S pole). By changing the position of the brush, the angle of the stator pole can be changed (assuming the starting point of the magnetic pole of the stator, the magnetic pole of the rotor is on the other side, and the direction of the magnetic pole of the rotor pointing to the pole of the stator is the direction of rotation of the motor) The direction of the motor thus changes the direction of rotation of the motor.

Electric vehicle motor structure

1. Permanent magnet DC motor:

It consists of a stator pole, a rotor, a brush, a casing, and the like.

The stator poles are made of permanent magnets (permanent magnets) and are made of ferrite, aluminium-nickel-cobalt, neodymium-iron-boron or the like. According to its structural form, it can be divided into cylindrical type and tile type.

The rotor is generally laminated with silicon steel sheets, and the enameled wire is wound between the two slots of the rotor core (three slots have three windings), and the joints are respectively welded to the metal piece of the commutator.

Brush is a conductive component connecting the power supply and the rotor winding. The brush of the permanent magnet motor uses a single metal sheet or a metal graphite brush or an electrochemical graphite brush.

2, brushless DC motor:

It consists of a permanent magnet rotor, a multi-pole winding stator, a position sensor, and the like.

Brushless DC motors are characterized by brushless, semiconductor switching devices (such as Hall elements) for electronic commutation, that is, electronic switching devices replace traditional contact commutators and brushes. It has the advantages of high reliability, no commutation spark, and low mechanical noise.

The position sensor commutates the current of the stator winding in a certain order according to the change of the position of the rotor (detects the position of the rotor pole relative to the stator winding, and generates a position sensing signal at the determined position, which is processed by the signal conversion circuit. Control the power switch circuit to switch the winding current according to a certain logic relationship).

Position sensors are available in magnetic, photoelectric and electromagnetic types.

A brushless DC motor using a magnetic sensitive position sensor, the magnetic sensing element (such as a Hall element, a magnetic sensitive diode, a magnetically sensitive diode, a magnetoresistor or an ASIC) is mounted on the stator assembly. To detect the change of the magnetic field generated when the permanent magnet and the rotor rotate. Multi-purpose electric vehicles are Hall elements.

A brushless DC motor using a photoelectric position sensor has a photoelectric sensor device arranged at a certain position on the stator assembly, and a light shielding plate is mounted on the rotor, and the light source is a light emitting diode or a small light bulb. When the rotor rotates, the photosensitive components on the stator will intermittently generate pulse signals at a certain frequency due to the action of the visor.

Using electromagnetic position sensor brushless dc motor, is in the electromagnetic sensors are installed on the stator component parts (such as the coupling transformer, close to switch, LC resonance circuit, etc.), when the permanent magnet rotor position changes, electromagnetic effect will make the electromagnetic sensor produces high frequency modulation signal (the amplitude changes with the rotor position).

The operating voltage of the stator windings is provided by an electronic switching circuit controlled by the position sensor output.

Electric vehicle motor characteristics

The drive motor for electric vehicles is different from conventional industrial motors. The drive motor of an electric vehicle usually requires frequent start/stop, acceleration/deceleration, high torque required for low speed or climbing, low torque required for high speed running, and large shift range. Industrial motors are usually optimized at rated operating points. Therefore, electric vehicle drive motors are unique and should be classified separately.

Electric vehicle motor requirements

They have special requirements in terms of load requirements, technical performance and working environment:

1. The electric vehicle drive motor needs 4-5 times overload to meet the requirements of short-term acceleration or climbing; industrial motors only require 2 times overload.

2. The maximum speed of electric vehicles is required to reach 4-5 times of the basic speed when cruising on the road, while industrial motors only need to reach constant power, which is twice the basic speed.

3. Electric vehicle drive motor needs to be designed according to the driving style of the model and the driver, and the industrial motor only needs to be designed according to the typical working mode.

4. Electric vehicle drive motor requires high power density (generally required to reach 1kw / kg) and good efficiency map (high efficiency in a wide range of speed and torque range), which can reduce vehicle weight To extend the driving range; industrial motors generally consider power density, efficiency and cost, and optimize efficiency near the rated operating point.

5. Electric vehicle drive motors require high controllability, high steady-state accuracy, and good dynamic performance; industrial motors have only one specific performance requirement.

6. The electric vehicle drive motor is installed on the motor vehicle with small space and working in harsh environments such as high temperature, bad weather and frequent vibration. Industrial motors usually work in a fixed position.

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