Direct Current (DC) motor controllers are unique electronic components engineered to guide the functioning of direct current motors. Does each DC motor necessitate a controller? Certainly not. Let’s delve into which DC motors require controllers and for what intentions. This piece will dissect two classifications of DC motors: a Brushed DC (BDC) and a Brushless DC (BLDC) motor.
Understanding BDC and BLDC Motors and Controllers
To generate the rotation of a DC motor, you need to alter or commutate the current delivered to the motor and modify the polarity of the magnetic field formed around the motor’s wound part.
In a BDC motor, the current traverses through the rotor’s windings, while its stator can either contain windings (series, shunt, compound BDC motors) or permanent magnets (permanent magnet BDC motor). The movement of the motor relies on the interplay of the magnetic fields generated around these two components. Consequently, oppositely charged fields attract, and identically charged fields repel each other.
An essential component of a BDC motor is the commutator that alters the current’s polarity and applies it to the rotor’s windings through the electrical contacts known as brushes.
A BLDC motor also features a rotor and a stator, but in contrast to a brushed motor, the current travels through the windings of the stator. The rotor, composed of permanent magnets, can be positioned internally (inrunner BLDC motor) or externally (outrunner BLDC motor).
A BLDC motor lacks mechanical parts like a commutator or brushes, as the commutation here is an electronic process facilitated by a controller. By gauging the position of the rotor, the controller decides when to switch the current and which stator’s winding to energize. Hence, a controller is indispensable for the functioning of brushless motor controller.
Unique Features of Brushed and Brushless Motor Applications
Brushed and brushless DC motors boast pros and cons that dictate their application zones. For instance, a BLDC motor possesses a more compact and lighter design that does not compromise its efficacy. This accounts for its extensive usage in portable electronics and wireless devices of varying sizes.
A BLDC motor controller commutes current at a higher frequency than a mechanical commutator. This enables the motor to sustain a high torque and function smoothly at low and high velocities. Reliability and low maintenance are additional advantages of a BLDC motor. Its application scope can involve its use in the following:
- Electric vehicles
- Unmanned aerial vehicles (UAVs)
- Household electronics
- Industrial robots.
BDC motors have ceded to their brushless counterparts in certain applications. Indeed, mechanical commutation could be more efficient, often resulting in power losses. The sparks created during the current switching can induce high electronic noise. Moreover, brushes demand regular upkeep and replacement.
Developing a BDC Motor Controller
Before building a DC motor controller, you should delineate your technical specifications and select a specific type of device. The characteristics of the controller comprise but are not confined to:
Power Regulation
To modulate the velocity or torque, a BDC controller augments or reduces the power supplied to the motor. A linear voltage regulator allows a controller to apply a constant voltage throughout the motor’s working cycle.
This type of regulation is generally no longer employed in contemporary controllers as they primarily depend on a switching voltage regulator with pulse-width modulation (PWM). This method enables the controller to alter the voltage and current level by supplying it in pulses.
Control Type
Simplistic systems utilize a DC motor controller for regulating the motor’s functioning without receiving feedback. Thus, an open-loop controller cannot rectify the parameters of the motor. The opposite applies to a closed-loop DC motor controller that can acquire feedback from the motor and adjust its velocity, rotational direction, and other parameters as needed.
Developing a BLDC Motor Controller
A BLDC motor controller computes the current using transistors of a half-H bridge circuit. The number of transistors relies on the number of phases or windings energized by the controller. 3-phase brushless motor controllers (one of the most common configurations) require three half-H bridges, one high-side and one low-side switch for each phase.
Upon receiving MCU signals, the gate drivers open the transistors and supply the current to the stator’s windings. To switch between the phases, the controller needs to know the position of the rotor. There are two ways to detect it:
- install a position sensor and use its measurements
- sense back electromotive force (back EMF) that arises in the stator’s windings in tandem with the rotor’s motion.
Conclusion
DC motor controls have diverse working principles and design features. You can explore articles on Brushed Motor Controllers and Brushless Motor Controllers to learn more about them.
