Stepper and brushless DC motor characteristics and control
The stepping motor can be used as a special motor for control, and it is widely used in various open loop control by virtue of its lack of accumulated error. The accuracy of a general stepper motor is 3-5% of the step angle and does not accumulate. The stepper motor torque will decrease as the speed increases. The stepper motor can run normally at low speed, but if it is higher than a certain speed, it cannot be started, accompanied by howling.
When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction, called the "step angle", and its rotation is step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve the purpose of accurate positioning. At the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, thereby achieving the purpose of speed regulation.
Stepper motors include reactive, permanent magnet, hybrid, and single-phase stepper motors. The reactive stepping motor is generally three-phase, and can realize a large torque output. The step angle is generally 1.5 degrees, but the noise and vibration are large. The rotor of the reactive stepping motor is made of a soft magnetic material, and the stator has a multi-phase excitation winding, and the torque is generated by the change of the magnetic permeability.
Hybrid stepper motors are a combination of permanent magnets and reactive. It is divided into two phases and five phases: the two-phase step angle is generally 1.8 degrees. The five-phase step angle is generally 0.72 degrees.
Brushless DC motor
Brushless DC motor has excellent linear mechanical characteristics, wide speed range, large starting torque, simple control method, electronic commutation instead of mechanical commutation, no wear, spark, greatly reduced noise, etc. Features.
The brushless DC motor consists of a motor body and a driver, and is a typical mechatronic product. A brushless motor is a motor without a brush and a commutator, and is also called a commutatorless motor. As early as the birth of the motor in the 19th century, the practical motor produced was the brushless form, that is, the AC squirrel-cage asynchronous motor, which has been widely used. However, asynchronous motors have many insurmountable drawbacks, resulting in slow development of motor technology. Transistors were born in the middle of the last century, and DC brushless motors using transistor commutating circuits instead of brushes and commutators have emerged. This new type of brushless motor is called an electronically commutated DC motor, which overcomes the shortcomings of the first generation of brushless motors.
The stator windings of the brushless DC motor are mostly made into a three-phase symmetrical star connection method, which is very similar to the three-phase asynchronous motor. The rotor of the motor has a magnetized permanent magnet. In order to detect the polarity of the rotor of the motor, a position sensor is mounted in the motor. The driver is composed of power electronics and integrated circuits. Its function is to accept the start, stop and brake signals of the motor to control the start, stop and brake of the motor; to accept the position sensor signal and the forward and reverse signals to control the inverter. The on/off of each power tube of the bridge generates continuous torque; the speed command and the speed feedback signal are accepted to control and adjust the speed; provide protection and display, and the like.
DC motors have fast response, large starting torque, and can provide rated torque from zero to rated speed. However, the advantages of DC motors are also its disadvantages, because DC motors must produce constant rotation under rated load. For the performance of the moment, the armature magnetic field and the rotor magnetic field must be maintained at 90°, which is through the carbon brush and the commutator. Carbon brushes and commutators generate sparks and toner when the motor rotates. In addition to damage to the components, the use is also limited.
AC motors do not have carbon brushes and commutators. They are maintenance-free, rugged, and widely used. However, to achieve the equivalent performance of DC motors, complex control technology can be used. Today's semiconductors are developing rapidly and the power component switching frequency is much faster, improving the performance of the drive motor. The speed of the microprocessor is also faster and faster, and the AC motor control can be placed in a rotating two-axis rectangular coordinate system, and the AC motor's current component in two axes can be appropriately controlled to achieve similar DC motor control and is equivalent to the DC motor. performance.
Reprinted from the network