Advantage supply: KLEINWACHTER electrostatic tester imported from Germany

Advantage supply: KLEINWACHTER electrostatic tester imported from GermanyEFM022 CPS

Advantage supply: KLEINWACHTER electrostatic tester imported from GermanyEFM022 CPS

Jiangsu Qiucheng Electromechanical Co., Ltd

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Jiangsu Qiucheng Electromechanical Co., Ltd. is a modern enterprise that integrates research and development, engineering, sales, and technical services. It is a competitive equipment supplier in the field of automation in China. The company mainly deals in industrial automation products such as mechatronics equipment, high-precision analytical and testing instruments, environmental and new energy industrial equipment, and electric tools from developed countries such as Europe, America, Japan, and South Korea.

The excitation method of a DC motor refers to the problem of how to supply power to the excitation winding, generate excitation magnetic flux potential, and establish the main magnetic field. According to different excitation methods, DC motors can be divided into the following types.

separately excited

The excitation winding is not connected to the armature winding, and a DC motor powered by other DC power sources is called a separately excited DC motor. The wiring is shown in Figure 1 (a). In Figure 1, M represents an electric motor, and if it is a generator, it is represented by G. Permanent magnet DC motor can also be regarded as a separately excited DC motor.

And encourage

The excitation winding of the parallel excited DC motor is connected in parallel with the armature winding. As a parallel excitation generator, the terminal voltage generated by the motor itself supplies power to the excitation winding; As a parallel excited motor, the excitation winding and armature share the same power source, which is equivalent in performance to a separately excited DC motor.

String excitation

After the excitation winding of the series excited DC motor is connected in series with the armature winding, it is then connected to the DC power supply. The excitation current of this DC motor is the armature current.

Re excitation

A compound excited DC motor has two excitation windings, parallel excitation and series excitation. If the direction of the magnetic flux generated by the series excitation winding is the same as that of the magnetic flux generated by the parallel excitation winding, it is called integral compound excitation. If two magnetic flux potentials have opposite directions, it is called differential excitation.

DC motors with different excitation methods have different characteristics. In general, the main excitation methods for DC motors are parallel excitation, series excitation, and compound excitation, while the main excitation methods for DC generators are separate excitation, parallel excitation, and compound excitation.

Permanent magnet editing and broadcasting

A permanent magnet DC motor is also composed of stator magnetic poles, rotor, brushes, housing, etc. The stator magnetic poles are made of permanent magnets (magnetic steel) made of materials such as ferrite, aluminum nickel cobalt, neodymium iron boron, etc. According to its structural form, it can be divided into several types such as cylindrical and tile shaped. The electricity used in record players is mostly cylindrical magnets, while the electric motors used in power tools and automotive appliances mostly use specialized block magnets.

The rotor is generally made of stacked silicon steel sheets, which has fewer slots than the rotor of an electromagnetic DC motor. Most low-power motors used in video recorders have 3 slots, while higher end ones have 5 or 7 slots. The enameled wire is wound between the two slots of the rotor core (three slots means there are three windings), and its joints are welded to the metal plates of the commutator. Electric brush is a conductive component that connects the power supply and rotor winding, and has two properties: conductivity and wear resistance. The brushes of permanent magnet motors use single metal sheets or metal graphite brushes, as well as electrochemical graphite brushes.

The permanent magnet DC motor used in the recorder adopts electronic speed stabilization circuit or centrifugal speed stabilization device.

Brushless DC editing and broadcasting

Brushless DC motors use semiconductor switching devices to achieve electronic commutation, replacing traditional contact commutators and brushes with electronic switching devices. It has the advantages of high reliability, no commutation sparks, and low mechanical noise, and is widely used in high-end recording stands, video recorders, electronic instruments, and automated office equipment.

A brushless DC motor consists of a permanent magnet rotor, a multi pole winding stator, a position sensor, and other components. bit

According to the change in rotor position, the sensor converts the current of the stator winding in a certain order (i.e. detects the position of the rotor magnetic pole relative to the stator winding and generates a position sensing signal at a determined position, which is processed by the signal conversion circuit to control the power switch circuit and switch the winding current according to a certain logical relationship). The working voltage of the stator winding is provided by an electronic switch circuit controlled by the output of the position sensor.

There are three types of position sensors: magnetic sensitive, photoelectric, and electromagnetic. A brushless DC motor using a magnetic sensitive position sensor, whose magnetic sensing devices (such as Hall elements, magnetic sensitive diodes, magnetic sensitive polarizing tubes, magnetic sensitive resistors, or dedicated integrated circuits) are mounted on the stator assembly to detect changes in the magnetic field generated by the rotation of the permanent magnet and rotor.

A brushless DC motor using photoelectric position sensors is equipped with photoelectric sensor devices at certain positions on the stator components, a light shielding plate is installed on the rotor, and the light source is a light-emitting diode or a small light bulb. When the rotor rotates, due to the effect of the shading plate, the photosensitive components on the stator will intermittently generate pulse signals at a certain frequency.

The brushless DC motor using electromagnetic position sensors is equipped with electromagnetic sensor components (such as coupling transformers, proximity switches, LC resonant circuits, etc.) on the stator components. When the position of the permanent magnet rotor changes, the electromagnetic effect will cause the electromagnetic sensor to generate high-frequency modulation signals (whose amplitude varies with the rotor position).

*Sex

DC motors have fast response, large starting torque, and the ability to provide rated torque from zero speed to rated speed. However, the advantages of DC motors are also their disadvantages, because in order to generate constant torque under rated load, the armature magnetic field and rotor magnetic field must be maintained at a constant 90 ° angle, which requires the use of carbon brushes and rectifiers. Carbon brushes and rectifiers generate sparks and carbon powder when the motor rotates, which not only causes component damage, but also limits their usage. AC motors do not have carbon brushes or rectifiers, are maintenance free, sturdy, and widely used. However, to achieve performance equivalent to DC motors in terms of characteristics, complex control technology is required. The rapid development of semiconductors nowadays has greatly accelerated the switching frequency of power components, improving the performance of drive motors. The speed of microprocessors is also increasing, which can realize the control of AC motors in a rotating two axis orthogonal coordinate system, and appropriately control the current components of AC motors in both axes, achieving similar performance to DC motor control and comparable to DC motors.

In addition, many microprocessors have incorporated the necessary functions for controlling motors into chips, and their size is becoming smaller and smaller; Such as analog-to-digital converters (ADCs), pulse width modulators (PWM), etc. A brushless DC motor is an application that electronically controls the commutation of an AC motor to achieve characteristics similar to those of a DC motor without any missing components in the DC motor mechanism. [1]

control structure

DC brushless motor is a type of synchronous motor, which means that the speed of the motor rotor is affected by the speed of the rotating magnetic field of the motor stator and the number of rotor poles (p):

n=120．f / p。 When the number of rotor poles is fixed, changing the frequency of the stator rotating magnetic field can change the speed of the rotor. DC brushless motor is a synchronous motor with electronic control (driver), which controls the frequency of the stator rotating magnetic field and feeds back the speed of the motor rotor to the control center for repeated correction, in order to achieve a way that is close to the characteristics of a DC motor. That is to say, brushless DC motors can still control the rotor of the motor to maintain a certain speed within the rated load range when the load changes.

The DC brushless driver includes a power supply unit and a control unit. The power supply unit provides three-phase power to the motor, and the control unit converts the input power frequency according to demand.

The power supply unit can directly input DC power (usually 24V) or AC power (110v/220V). If the input is AC power, it needs to be converted to DC through a converter first. Whether it is direct current input or alternating current input, before entering the motor coil, the direct current voltage must be converted from the inverter to a three-phase voltage to drive the motor. Inverters are generally composed of six power transistors (q1~q6) divided into upper arms (q1, q3, q5)/lower arms (q2, q4, q6) connected to motors as switches that control the flow through the motor coils. The control department provides PWM (Pulse Width Modulation) to determine the frequency of power transistor switching and the timing of inverter commutation. DC brushless motors are generally intended for speed control where the speed can remain stable at the set value without significant changes when the load changes. Therefore, the motor is equipped with a Hall sensor that can sense the magnetic field, which serves as a closed-loop control for speed and also as a phase sequence control

The basis for the system. But this is only used as speed control and cannot be used as positioning control.

Control Theory

To make the motor rotate, the control unit must determine the order of turning on (or off) the power transistors in the inverter based on the position of the motor rotor sensed by the Hall sensor, and then follow the stator winding to make the current flow through the motor coil in sequence, generating a forward (or reverse) rotating magnetic field and interacting with the rotor magnet, so as to make the motor rotate clockwise/counterclockwise. When the motor rotor rotates to the position where another set of signals is sensed by the Hall sensor, the control unit turns on the next set of power transistors, so that the cyclic motor can continue to rotate in the same direction until the control unit decides to stop the motor rotor and turn off the power transistors (or only turn on the lower arm power transistors); If the motor rotor is to be reversed, the order of power transistor activation is reversed.

Fixed magnetic field brushless motor

A typical brushless DC motor is essentially a servo motor, consisting of a synchronous motor and a driver, and is a variable frequency speed regulation motor. The brushless DC motor with variable voltage speed regulation is a true brushless DC motor, which is composed of a stator and a rotor. The stator is composed of an iron core, and the coil adopts a "forward reverse forward reverse..." winding, thereby generating a fixed magnetic field of N-S group. The rotor is composed of a cylindrical magnet (with a shaft in the middle) or an electromagnet and a collector ring. This brushless DC motor can generate torque, but cannot control direction. Anyway, this motor is a very meaningful invention. When used as a DC generator, the present invention can generate continuous amplitude DC current, thereby avoiding the use of filtering capacitors. The rotor can be permanent magnet, brushed excitation, or brushless excitation. When used as a large motor, this motor will generate self inductance and requires the use of protective devices.

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