A DC motor is an electric motor whose power is provided by a constant current. If necessary, get a high-torque engine with a relatively low speed. Structurally, Inrunners is simpler due to the fact that the fixed stator can serve as a housing. It can be mounted fasteners. In the case of Outrunners, the entire outer part rotates. Engine mounting is carried out for a fixed axis or stator parts. In the case of a motor-wheel, the fastening is carried out by the fixed axis of the stator, wires lead to the stator through a hollow axis of which less than 0.5 mm.
- 1 Types of electric motors
2 Brushless DC motor. General information and device design
- 2.1 Stator
- 2.2 Rotor
- 2.3 DPR
- 2.4 Control system
- 3 Principle of operation
- 4 Engine control
- 5 Advantages and disadvantages
- 6 Three-phase brushless DC motor
- 7 Conclusion
Types of electric motors
The following types of DC motors exist:
- excited by permanent magnets;
- with a series connection of the armature and excitation windings;
- with parallel connection of the armature and excitation windings;
- with a mixed mix of armature and field windings;
- valve motor (brushless DC motor), made using a closed system; in this type the motor uses an inverter (power semiconductor converter), a coordinate converter and a DPR (position sensor rotor).
AC motor called alternating current powered electric motor. The following types of AC motors exist:
- hysteresis motor;
- valve jet engine;
- asynchronous electric motor with a rotor rotation frequency different from the rotation frequency of the magnetic field generated by the voltage;
- synchronous motor with a rotor rotation frequency coinciding with the rotation frequency of the magnetic field generated by the voltage.
There is also a UCD (universal collector motor) with function of an operating mode both on variable, and on a direct current.
Another type of engine is stepper motor with a finite number of rotor positions. The specified specified position of the rotor is fixed by applying power to the necessary windings. When removing the supply voltage from one winding and its transfer to another, the process of moving to another position occurs.
An AC motor powered by an industrial network usually does not allow reaching speeds of more than three thousand revolutions per minute. For this reason, if you need to get higher frequencies, a collector motor is used, additional advantages of which is lightness and compactness while maintaining the necessary power.
Sometimes they also use a special transmission mechanism called a multiplier, which changes the kinematic parameters of the device to the required technical parameters. The collector nodes sometimes occupy up to half the space of the entire engine, so the AC motors reduce in size and make it lighter in weight by using a frequency converter, and sometimes due to the presence of a network with increased frequency to 400 Hz.
The resource of any asynchronous AC motor is noticeably higher than the collector one. It is determined insulation condition of the windings and bearings. A synchronous motor with an inverter and a rotor position sensor is considered electronic analog of the classic collector engine supporting operation by direct current.
Brushless DC motor. General information and device design
The brushless DC motor is also called a three-phase valve motor. It is a synchronous device whose principle of operation is based on a self-synchronized frequency regulation, due to which there is a vector control (starting from the rotor position) of the magnetic field the stator.
Controllers of electric motors of this type are often powered by constant voltage, which is why they got their name. In the technical English literature, a valve motor is called a PMSM or BLDC.
Brushless electric motor was created primarily to optimize the lany dc electric motor generally. The executive mechanism of such a device (especially a high-speed microdrive with precise positioning) put very high demands.
This, perhaps, led to the use of such specific DC devices, brushless three-phase motors, also called BDPT. By design, they are almost identical to synchronous AC motors, where the rotation of the magnetic rotor occurs in a normal laminated stator in the presence of three-phase windings, and the number of revolutions depends on the voltage and load the stator. Based on the determined coordinates of the rotor, switching of different stator windings occurs.
Brushless DC motors can exist without any separate sensors, however, sometimes they are present on the rotor, for example, a Hall sensor. If the device works without an additional sensor, then stator windings function as a locking element. Then the current arises due to the rotation of the magnet, when in the stator winding the rotor induces an emf.
If one of the windings is turned off, the signal that was induced will be measured and further processed, however, such a principle of operation is impossible without a signal processing professor. But for the reverse or braking of such an electric motor the bridge circuit is not needed - it will be enough to feed in the reverse sequence control pulses to the stator windings.
In the VD (valve engine), an inductor in the form of a permanent magnet is located on the rotor, and the anchor winding is on the stator. Based on the position of the rotor, power supply voltage of all windings is formed electric motor. When used in such structures, a collector will perform its function in a valve motor in a semiconductor switch.
The main difference between the synchronous and valve motors is the self-synchronization of the latter using DPR, which determines the proportional frequency of rotation of the rotor and the field.
Most often, the brushless DC motor is used in the following areas:
- freezing or refrigeration equipment (compressors);
- electric drive;
- air heating, air conditioning or ventilation systems.
This device has a classic design and resembles the same device asynchronous machine. The composition includes copper core (laid on the perimeter of the grooves), which determines the number of phases, and the body. Usually, the sine and cosine phases are enough for rotation and self-starting; however, often the valve motor creates a three-phase and even four-phase one.
Electric motors with a back electromotive force by the type of laying turns on the stator winding are divided into two types:
- trapezoidal shape.
In the corresponding types of motor, the electric phase current also varies according to the method of feeding sinusoidally or trapezoidally.
Usually the rotor is made of permanent magnets with the number of pairs of poles from two to eight, which, in turn, alternate from north to south or vice versa.
The most common and cheap for the manufacture of the rotor are ferrite magnets, but their disadvantage is low magnetic inductiontherefore, devices created from alloys of various rare-earth elements are now replacing such material, because they can provide a high level of magnetic induction, which, in turn, reduces the size rotor.
The rotor position sensor provides feedback. According to the principle of operation, the device is divided into the following subspecies:
- Hall effect sensor.
The latter type has received the greatest popularity due to its almost absolute inertialess properties and the ability to get rid of the position of the rotor from the delay in the feedback channels.
The control system consists of power switches, sometimes also thyristors or power transistors, including an insulated gate, leading to the collection of a current inverter or a voltage inverter. The process of managing these keys is implemented most often. by using a microcontroller, requiring to control the engine a huge number of computational operations.
Principle of operation
The operation of the engine is that the controller commutes a certain number of stator windings in such a way that the vector of the magnetic fields of the rotor and stator are orthogonal. Using PWM (Pulse Width Modulation) the controller controls the current flowing through the motor and adjusts the torque affecting the rotor. The direction of this effective moment determines the angle mark between the vectors. Electrical degrees are used in the calculations.
Switching should be done in such a way that Ф0 (rotor excitation flow) is kept constant with respect to the armature flow. In the interaction of such excitation and the flow of the armature, a torque M is formed, which tends to turn the rotor and in parallel to ensure the coincidence of the excitation and the flow of the armature. However, during the rotation of the rotor, different windings are switched under the influence of the rotor position sensor, as a result of which the flow of the armature turns in the direction of the next step.
In such a situation, the resulting vector shifts and becomes fixed with respect to the rotor flow, which, in turn, creates the necessary moment on the motor shaft.
The controller of the brushless DC motor makes the regulation of the moment acting on the rotor, changing the value of the pulse-width modulation. Switching is controlled and carried out by electronics, unlike a conventional brushless DC motor. Also common are control systems that implement pulse-width modulation and pulse-width control algorithms for the workflow.
Vector driven engines provide the widest range of known ranges for controlling your own speed. Regulation of this speed, as well as maintaining the flux linkage at the required level, occurs due to the frequency converter.
A feature of electric drive control based on vector control is the presence of controlled coordinates. They are in a fixed system and converted to rotating, allocating a constant value proportional to the parameters of the vector being controlled, due to which a control action is formed, and then a reverse transition.
Despite all the advantages of such a system, it is accompanied by a disadvantage in the form of the complexity of controlling the device for controlling the speed in a wide range.
Advantages and disadvantages
Nowadays, in many industries, this type of engine is in great demand, because the brushless DC motor combines almost all the best qualities of contactless and other types engines.
Indisputable advantages of a valve motor are:
- a wide range of changes in speed and ease of regulation;
- energy performance is incredibly high - efficiency is more than 90%;
- safety when using in a hostile environment or in explosive places;
- overload capacity is extremely high;
- when operating in motor overload mode, low overheating is observed;
- the absence of maintenance-requiring components (in a conventional valve motor);
- positioning accuracy;
- dynamics and high speed;
- starting moment is very large;
- possibility of use in different modes (motor and generator);
- high reliability;
- long service life;
- no sliding contacts;
- high work resource.
Despite significant positive moments, in brushless DC motor There are also a few drawbacks:
- the use of expensive materials in the rotor design, in particular, permanent magnets, leads to a high cost of the device;
- the resource of electronic nodes is limited;
- the collector wears out quickly enough, which limits the service life of the device;
- collector brush units require periodic preventive maintenance (in a brushless DC motor);
- The motor has a complex control system for the average man.
Based on the foregoing and the underdevelopment of modern electronics in the region, many still consider it appropriate to use a conventional asynchronous motor with a frequency converter.
Three-phase brushless DC motor
This type of engine has excellent performance, especially when performing control through position sensors. If the moment of resistance varies or is completely unknown, as well as when higher starting torque control with sensor is used. If the sensor is not used (as a rule, in fans), the control allows you to do without a wired connection.
Features of control of a three-phase brushless motor without a sensor according to the position:
- the location of the rotor is determined using a differential ADC (analog-to-digital converter);
- current overload is also determined using an ADC (analog-to-digital converter) or analog comparator;
- speed adjustment is performed using PWM channels connected to the lower drivers;
- AT90PWM3 and ATmega64 are considered as recommended microcontrollers;
- Supported communication interfaces (communication interfaces) are UART, SPI and TWI.
Management features three-phase brushless motor with a sensor by position using the example of a Hall sensor:
- speed adjustment is performed using PWM channels connected to the lower drivers;
- the output of each of the Hall sensors is connected to the corresponding I / O line of the microcontroller, which is configured during state changes to generate interrupts;
- supported communication interfaces (communication interfaces) are UART, SPI and TWI;
- current overload is determined using an ADC (analog-to-digital converter) or analog comparator.
Brushless DC motor has many advantages and will be a worthy choice for use as a specialist, and a simple man in the street.