For a long time, DC motors have good linear speed regulation characteristics, simple control functions, higher efficiency and excellent characteristics. Therefore, DC motors are widely used for speed control. Especially with the development of computers in the field of human control, as well as high switching frequency, control of second-generation power semiconductor devices (GTR, GTO, MOST, IGBT, etc.), pulse width modulation (PWM) is more and more commonly used.
Speed control mechanisms are suitable for many situations, such as controlling the motion of robotic vehicles, the motion of motors in paper mills, and the motion of motors in elevators that use different types of DC motors. The DC motor control method is done manually by the worker or by using any automatic control tool. This seems to be the opposite of the speed limit, which must be the opposite of the natural change in speed because of changes in shaft load.
What are the control methods of DC motors?
There are three main control modes of DC motor: flux control mode, voltage control mode and armature resistance control mode.
1. Magnetic flux control mode: In the magnetic flux control mode, a varistor (variable resistor) is connected in series with the excitation winding. The purpose of this element is to increase the series resistance of the coil, which reduces the flux and thus increases the speed of the motor.
2. Voltage regulation method: The variable regulation method is usually used for parallel DC motors. Similarly, there are two ways to achieve voltage regulation control: connecting a parallel field and a fixed excitation voltage with different voltages to the armature (which may also be referred to as multi-voltage control).
3. Armature resistance control method: The armature resistance is controlled according to the principle that the speed of the DC motor is proportional to the back EMF. In this way, when the power supply voltage and armature resistance remain unchanged, the speed of the motor is proportional to the armature current.
Types of control signals for DC motors
The control signal types of DC motors are divided into digital version and analog version. The main difference between digital DC motor control signals and their analog variants is that the former includes microcontroller (MCU)-based hardware and firmware.
Some DC motor controller types can receive feedback from the motor, detect errors and correct them so that the value is in line with the set point. They are called closed loop or feedback controllers. Also, an open loop or no feedback controller can work without affecting the situation even if a fault occurs because it won't detect it. Controllers for DC motors can be found in simple systems that do not require automatic control.
Open-loop and closed-loop systems are the basic concepts of control theory. Depending on the requirements or complexity of the electronics, control systems can be implemented with or without feedback. For example, a stepper motor can be run with an open loop controller. A servo DC motor controller for precise positioning in high performance applications is a closed loop system.
