All About DC Motor Controllers What They Are and How They Work - JohnHau/mis GitHub Wiki
https://www.thomasnet.com/articles/instruments-controls/dc-motor-controllers/ https://www.thomasnet.com/articles/instruments-controls/ac-motor-controllers/
https://www.thomasnet.com/articles/instruments-controls/types-of-motor-controllers-and-drives/
https://www.thomasnet.com/articles/machinery-tools-supplies/types-of-dc-motors/
https://www.thomasnet.com/articles/machinery-tools-supplies/all-about-induction-motors-what-they-are-and-how-they-work/ https://www.thomasnet.com/articles/machinery-tools-supplies/synchronous-motors/ https://www.thomasnet.com/articles/machinery-tools-supplies/types-of-motors/
https://www.thomasnet.com/articles/machinery-tools-supplies/brushless-dc-motors/ https://www.thomasnet.com/articles/machinery-tools-supplies/stepper-motors/ https://www.thomasnet.com/articles/machinery-tools-supplies/stepper-motors-vs-servomotors/ DC motors are still relevant in modern industry, even though they are one of the oldest electric motor designs. How have they stood the test of time, especially against all the amazing new machines of the 21st century?
There are many potential answers to this question, but their good controllability is a major reason why DC motors have persisted. This simple machine transforms DC current into mechanical rotation, which can be controlled by simply changing the input voltage or reversing its leads. The elegance of DC motors has led to the production of many DC motor controllers, which are often simple in design and provide adequate performance for their cost. This article will take a look at some common DC motor controllers, how they work, and will discuss what the most popular applications are for these systems.
What are DC motor controllers? Simply put, a DC motor controller is any device that can manipulate the position, speed, or torque of a DC-powered motor. There are controllers for brushed DC motors, brushless DC motors, as well as universal motors, and they all allow operators to set desired motor behavior even though their mechanisms for doing so differ.
Our articles on shunt DC motors, series wound DC motors, and brushless DC motors provide detailed explanations on how DC machines function. To briefly summarize, the speed/torque curve of DC motors are inversely linear, meaning their torque proportionally decreases as the motor RPMs increase. This allows for easy control, as lowering the speed will increase the torque, and vice versa. Also, unlike some AC motors, DC motors are easily reversed by simply switching their leads so that the DC current runs in the opposite direction. DC motor controllers exploit these characteristics in unique ways, and this article will explore the most popular methods.
Types of DC motor controllers Below are some common methods of DC motor control. Note that these methods are not exhaustive and that DC motors can be controlled in many ways, including servo motor controllers (learn more in our article on servo motor controllers):
Direction Controller: H Bridge An H bridge circuit is one of the simplest methods to control a DC motor. Figure 1 below shows a simplified circuit diagram of the H Bridge:
There are four switches controlled in pairs (1 & 4, 2 & 3), and when either of these pairs are closed, they complete the circuit and power the motor. A 4 quadrant motor can, therefore, be made by pairing certain switches together, where the changing polarities will create different effects on the motor. In essence, this circuit is switching the leads of the DC motor, which will reverse its rotational direction on command. They are readily sold as chips and can be found in most microprocessor-based controllers, as the H Bridge can be scaled down with transistors to very small sizes.
Not only can H bridges reverse the motor direction, but they can also be used for speed control. If directional control is only desired, then the H bridge will be used as a so-called non-regenerative DC drive. However, more complexity can be added to create regenerative DC drives. Figure 2 shows a graph visualizing how regenerative drives work:
Most DC motors are slowed down by just cutting their power to the motor; regenerative drives include braking capabilities, where switching the polarities as the motor is running will cause deceleration. Quadrants 1 and 3 are considered “motoring” quadrants where the motor is providing acceleration in either direction, and is what non-regenerative drives control. Quadrants 2 and 4 are considered “braking” quadrants where the motor is decelerating and is what regenerative drives benefit from. When the motor speed is opposing the motor torque, the motor becomes a generator where its mechanical energy will drive a current back to the power source (known as “regenerative braking”). This feature reduces energy losses and can recharge the power source, effectively increasing the motor efficiency. Figure 3 shows the simplified circuit diagram for each quadrant, and how quadrants 2 and 4 send current back to the supply to regenerate energy:
When the motor decelerates, Ea (the voltage produced/used by the motor) is greater than the supply voltage (Va), and current will flow back into the power source. Regenerative braking is currently being researched in electric vehicles and other applications which need to maximize efficiency. This method not only creates DC motor control, but it also provides a clever way to lower power consumption.
Speed Controller: Pulse Width Modulation (PWM) PWM can be used in many kinds of motors, as is seen in our article on AC motor controllers. Essentially, PWM circuits vary the motor speed by simulating a reduction/increase in supply voltage. Adjustable speed drive controllers send periodic pulses to the motor, which, when combined with the smoothing effect caused by coil inductance, makes the motor act as if it is being powered by a lower/higher voltage. For example, if a 12 V motor is given a PWM signal that is high (12 V) for two-thirds of each period and low (0 V) for the remainder, the motor will effectively operate at two-thirds the full voltage, or 8 V. The percentage of voltage reduction, or the PWM “duty cycle”, will therefore change the speed of the motor. PWM is both easy and inexpensive to implement, and virtually any duty cycle can be chosen, allowing for almost continuous control of motor speed. PWM is often paired with H bridges to allow for both speed, direction, and braking control.
Armature Controller: Variable resistance Another way to affect DC motor speed is by varying the current fed through either the field coil or the armature. The speed of the output shaft will change when the current through these coils change, as its speed is proportional to the strength of the armature’s magnetic field (dictated by current). Variable resistors or rheostats in series with these coils can be used to alter the current, and therefore speed. Users can increase the resistance of the armature coil to decrease speed, or increase the stator resistance to increase it, all by regulating resistance. Note that this method introduces inefficiency into a motor, as increasing resistance means losing more energy to heat, and is why PWM is the preferred DC motor controller type.
Applications and Selection Criteria When considering the purchase of a DC motor controller, there are some key questions that should be answered by either your research or the supplier. DC motor controllers can be tricky to specify due to their diversity, so the question list below will be a robust tool when choosing one for your project. Be sure to find the most up to date information on the latest available technology by contacting your supplier, and use these questions to make informed choices:
What is the rated voltage range for the motor in use, and what parts of that range will it be using? Which type of control is desired (speed, torque, direction, or all three)? What type of motor is being controlled? What is the continuous current the controller can supply, and does it match with the motor’s continuous current consumption under load? Does the system have built-in overcurrent/thermal protection? When using microprocessor drives, what will be the control method (PWM, R/C, analog voltage, etc.)? Is software necessary? Do you need a dual-motor controller (one controller for two independent motors)? There are as many DC motor controllers available as are DC motors themselves; their variability is one of their strongest advantages. Their applications are also as numerous, as most designers benefit from some kind of user input to their DC motor. The fields of robotics, manufacturing, military applications, automobiles, and many more utilize DC motor controllers with great results. Depending upon how they are used, DC motor controllers can provide a simple means of control with good precision at an acceptable cost.
Summary This article presented an understanding of what DC motor controllers are and how they work. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.