Views:0 Author:Site Editor Publish Time: 2021-09-24 Origin:Site
DC motors have existed for nearly 200 years, and a series of improvements were made at that time. Recently, brushless DC motors have become more and more popular, but for many applications, brushed DC motors are still the right choice. Brushed motors are low cost and easy to drive, so they are still a popular choice. How to drive a DC motor?
Working principle of DC motor
Drive circuit of brushed motor
Back to the basics, the basic principle of the motor is of course to convert electrical energy into motion. It is achieved through the interaction between magnets, and the interaction between magnets is usually produced by passing current through wires bound around the ferrite core. The current flowing through the wire creates a second magnetic field. This interacts with the main magnetic field to produce a reaction force that moves part of the motor, usually rotating the motor around the axis.
Braking is a phenomenon that reduces the speed of a DC motor drive. When braking, the DC motor driver is used as a generator. It produces a negative sequence torque, which is opposite to the motion of the drive. The braking of DC motor drives is mainly divided into three types. That is, the regenerative braking, the dynamic braking and plugging.
In principle, as mentioned above, a brushed motor does not require an external controller, because the change of the magnetic field polarity is achieved by the brush, which creates and breaks the electrical path through the winding, thereby achieving continuous in one direction Spin.
For some applications, this is sufficient. However, if we want to be able to change the speed of the motor or reverse the direction of rotation, we need a drive circuit. This can be as simple as reversing the direction of the current to make the motor rotate in the opposite direction.
To change the speed, we can use a voltage divider to change the voltage-the speed is proportional to the voltage. However, reducing the voltage in this way is very inefficient, because the voltage divider does not reduce the total current flowing. In order to overcome this problem, pulse width modulation (PWM) is usually used, which needs to quickly turn off and on the current to reduce the "average" voltage on the motor.
In order to limit the starting current, a specially designed variable resistor is often connected in series in the armature circuit. In the starting process, as the speed continues to rise, each segment resistance is short-circuited step by step in time to limit the starting current to a certain allowable value. This kind of starting method is called series resistance starting, which is widely used in various medium and small DC motors. However, due to the large energy consumption during the starting process, it is not suitable for motors that are frequently started and medium and large DC motors. But for some special needs, such as city trams are often started, in order to simplify equipment, reduce weight and facilitate operation and maintenance, usually series resistance starting method is used.
For a DC motor with a larger capacity, it is usually started with a reduced voltage. That is, a separate adjustable voltage DC power supply supplies power to the motor armature.
Brushed DC motors may not seem as attractive as brushless motors, but they provide reliable, proven performance and require less complex drive circuits—to minimize overall cost.
Choosing the right motor for any given application depends on the specific requirements of that application. Is it necessary to precisely control the position of the motor, the brushless motor provides smoothness of movement, or can a simpler and lower cost brush alternative provide a better solution? Is it important to avoid the wear and maintenance that a brushless motor can provide, or is the application's motor running so rarely that deterioration of the brushes and commutator is a low priority issue?
If the application cannot prove that the functions provided by the brushless motor have higher cost and complexity, then the brushed DC motor, coupled with the correct drive circuit design, can still provide a very attractive solution.