Brushless DC electric motor
A brushless DC electric motor (BLDC), also known as an electronically commutated motor, is a
The construction of a brushless motor system is typically similar to a
The advantages of a brushless motor over
Background
An electric motor develops torque by keeping the magnetic fields of the rotor (the rotating part of the machine) and the stator (the fixed part of the machine) misaligned. One or both sets of magnets are electromagnets, made of a coil of wire wound around an iron core. DC running through the wire winding creates the magnetic field, providing the power that runs the motor. The misalignment generates a torque that tries to realign the fields. As the rotor moves, and the fields come into alignment, it is necessary to move either the rotor's or stator's field to maintain the misalignment and continue to generate torque and movement. The device that moves the fields based on the position of the rotor is called a commutator.[4][5][6]
Brush commutator
In brushed motors this is done with a rotary switch on the motor's shaft called a commutator.[4][6][5] It consists of a rotating cylinder or disc divided into multiple metal contact segments on the rotor. The segments are connected to conductor windings on the rotor. Two or more stationary contacts called brushes, made of a soft conductor such as graphite, press against the commutator, making sliding electrical contact with successive segments as the rotor turns. The brushes selectively provide electric current to the windings. As the rotor rotates, the commutator selects different windings and the directional current is applied to a given winding such that the rotor's magnetic field remains misaligned with the stator and creates a torque in one direction.
Disadvantages of commutator
The commutator has disadvantages that has led to a decline in use of brushed motors. These disadvantages are:[4][6][5]
- The friction of the brushes sliding along the rotating commutator segments causes power losses that can be significant in a low power motor.
- The soft brush material wears down due to friction, creating dust, and eventually the brushes must be replaced. This makes commutated motors unsuitable for low particulate or sealed applications like hard diskmotors, and for applications that require maintenance-free operation.
- The electrical resistance of the sliding brush contact causes a voltage drop in the motor circuit called brush drop, which consumes energy.
- The repeated abrupt switching of the current through the electronic noise, which can cause electromagnetic interferencein nearby microelectronic circuits.
During the last hundred years, high-power DC brushed motors, once the mainstay of industry, were replaced by alternating current (AC) synchronous motors. Today, brushed motors are used only in low power applications or where only DC is available, but the above drawbacks limit their use even in these applications.
Brushless solution
In brushless DC motors, an electronic
Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases.[7] Some limitations of brushed motors can be overcome by brushless motors; they include higher efficiency and lower susceptibility to mechanical wear. These benefits come at the cost of potentially less rugged, more complex, and more expensive control electronics.
A typical brushless motor has permanent magnets that rotate around a fixed
Brushless motors offer several advantages over brushed DC motors, including high torque to weight ratio, increased efficiency producing more torque per watt, increased reliability, reduced noise, longer lifetime by eliminating brush and commutator erosion, elimination of ionizing sparks from the commutator, and an overall reduction of electromagnetic interference (EMI). With no windings on the rotor, they are not subjected to centrifugal forces, and because the windings are supported by the housing, they can be cooled by conduction, requiring no airflow inside the motor for cooling. This in turn means that the motor's internals can be entirely enclosed and protected from dirt or other foreign matter.
Brushless motor commutation can be implemented in software using a
The maximum power that can be applied to a brushless motor is limited almost exclusively by heat;[citation needed] too much heat weakens the magnets and damages the windings' insulation.
When converting electricity into mechanical power, brushless motors are more efficient than brushed motors primarily due to the absence of brushes, which reduces mechanical energy loss due to friction. The enhanced efficiency is greatest in the no-load and low-load regions of the motor's performance curve.[8]
Environments and requirements in which manufacturers use brushless-type DC motors include maintenance-free operation, high speeds, and operation where sparking is hazardous (i.e. explosive environments) or could affect electronically sensitive equipment.
The construction of a brushless motor resembles a stepper motor, but the motors have important differences due to differences in implementation and operation. While stepper motors are frequently stopped with the rotor in a defined angular position, a brushless motor is usually intended to produce continuous rotation. Both motor types may have a rotor position sensor for internal feedback. Both a stepper motor and a well-designed brushless motor can hold finite torque at zero RPM.
Controller implementations
Because the controller implements the traditional brushes' functionality it needs to know the rotor's orientation relative to the stator coils. This is automatic in a brushed motor due to the fixed geometry of the rotor shaft and brushes. Some designs use Hall effect sensors or a rotary encoder to directly measure the rotor's position. Others measure the back-EMF in the undriven coils to infer the rotor position, eliminating the need for separate Hall effect sensors. These are therefore often called sensorless controllers.
Controllers that sense rotor position based on back-EMF have extra challenges in initiating motion because no back-EMF is produced when the rotor is stationary. This is usually accomplished by beginning rotation from an arbitrary phase, and then skipping to the correct phase if it is found to be wrong. This can cause the motor to run backwards briefly, adding even more complexity to the startup sequence. Other sensorless controllers are capable of measuring winding saturation caused by the position of the magnets to infer the rotor position.[9]
A typical controller contains three polarity-reversible outputs controlled by a logic circuit. Simple controllers employ comparators working from the orientation sensors to determine when the output phase should be advanced. More advanced controllers employ a microcontroller to manage acceleration, control motor speed and fine-tune efficiency.
Two key performance parameters of brushless DC motors are the motor constants (torque constant) and (back-EMF constant, also known as speed constant ).[10]
Variations in construction
Brushless motors can be constructed in several different physical configurations. In the conventional inrunner configuration, the permanent magnets are part of the rotor. Three stator windings surround the rotor. In the external-rotor outrunner configuration, the radial relationship between the coils and magnets is reversed; the stator coils form the center (core) of the motor, while the permanent magnets spin within an overhanging rotor that surrounds the core. Outrunners typically have more poles, set up in triplets to maintain the three groups of windings, and have a higher torque at low RPMs. In the flat axial flux type, used where there are space or shape constraints, stator and rotor plates are mounted face to face. In all brushless motors, the coils are stationary.
There are two common electrical winding configurations; the delta configuration connects three windings to each other in a triangle-like circuit, and power is applied at each of the connections. The wye (Y-shaped) configuration, sometimes called a star winding, connects all of the windings to a central point, and power is applied to the remaining end of each winding. A motor with windings in delta configuration gives low torque at low speed but can give higher top speed. Wye configuration gives high torque at low speed, but not as high top speed. The wye winding is normally more efficient. Delta-connected windings can allow high-frequency parasitic electrical currents to circulate entirely within the motor. A Wye-connected winding does not contain a closed loop in which parasitic currents can flow, preventing such losses. Aside from the higher impedance of the wye configuration, from a controller standpoint, the two winding configurations can be treated exactly the same.[11]
Applications
Brushless motors fulfill many functions originally performed by brushed DC motors, but cost and control complexity prevents brushless motors from replacing brushed motors completely in the lowest-cost areas. Nevertheless, brushless motors have come to dominate many applications, particularly devices such as computer
Transport
Brushless motors are found in electric vehicles, hybrid vehicles, personal transporters, and electric aircraft.[14] Most electric bicycles use brushless motors that are sometimes built into the wheel hub itself, with the stator fixed solidly to the axle and the magnets attached to and rotating with the wheel.[15] The same principle is applied in self-balancing scooter wheels. Most electrically powered radio-controlled models use brushless motors because of their high efficiency.
Cordless tools
Brushless motors are found in many modern cordless tools, including some string trimmers, leaf blowers, saws (circular and reciprocating), and drills/drivers. The weight and efficiency advantages of brushless over brushed motors are more important to handheld, battery-powered tools than to large, stationary tools plugged into an AC outlet.
Heating and ventilation
There is a trend in the heating, ventilation, and air conditioning (HVAC) and refrigeration industries to use brushless motors instead of various types of AC motors. The most significant reason to switch to a brushless motor is a reduction in power required to operate them versus a typical AC motor.[16] In addition to the brushless motor's higher efficiency, HVAC systems, especially those featuring variable-speed or load modulation, use brushless motors to give the built-in microprocessor continuous control over cooling and airflow.[17]
Industrial engineering
The application of brushless DC motors within
Brushless motors are commonly used as pump, fan and spindle drives in adjustable or variable speed applications as they are capable of developing high torque with good speed response. In addition, they can be easily automated for remote control. Due to their construction, they have good thermal characteristics and high energy efficiency.[19] To obtain a variable speed response, brushless motors operate in an electromechanical system that includes an electronic motor controller and a rotor position feedback sensor.[20] Brushless DC motors are widely used as servomotors for machine tool servo drives. Servomotors are used for mechanical displacement, positioning or precision motion control. DC stepper motors can also be used as servomotors; however, since they are operated with open loop control, they typically exhibit torque pulsations.[21]
Brushless motors are used in industrial positioning and actuation applications.
Aeromodelling
Brushless motors have become a popular motor choice for
Legal restrictions for the use of combustion engine driven model aircraft in some countries,[citation needed] most often due to potential for noise pollution—even with purpose-designed mufflers for almost all model engines being available over the most recent decades—have also supported the shift to high-power electric systems.
Radio-controlled cars
Their popularity has also risen in the
Brushless motors are capable of producing more torque and have a faster peak rotational speed compared to nitro- or gasoline-powered engines. Nitro engines peak at around 46,800 r/min and 2.2 kilowatts (3.0 hp), while a smaller brushless motor can reach 50,000 r/min and 3.7 kilowatts (5.0 hp). Larger brushless RC motors can reach upwards of 10 kilowatts (13 hp) and 28,000 r/min to power one-fifth-scale models.[26]
See also
References
- ^ Control differences between ac induction motor and brushless dc motor? – Electrical Engineering Stack Exchange. electronics.stackexchange.com (2019-12-20). Retrieved on 2019-12-26.
- ^ "What is a BLDC Motor in a Washing Machine?". Dumb Little Man. Retrieved 11 June 2019.
- ^ T.G. Wilson, P.H. Trickey, "D.C. Machine. With Solid State Commutation", AIEE paper I. CP62-1372, October 7, 1962
- ^ ISBN 978-1420076875.
- ^ ISBN 085296921X.
- ^ ISBN 978-1118188361.
- ISBN 978-0-07-048289-0.
- ^ "Brushless DC Motor vs. AC Motor vs. Brushed Motor?". Retrieved 2021-04-29.
- ISBN 979-8-3503-0439-8. Retrieved 2023-12-23.
- ^ Brushless Motor Kv Constant Explained[permanent dead link]. Learningrc.com (2015-07-29). Retrieved on 2019-12-26.
- ^ "Delta vs Wye phase connections". Retrieved 2021-11-01.
- ^ "Vinyl Turntable Drive Techniques". 2 November 2019. Retrieved 2021-12-02.
- ^ "What is a Thruster?". Blue Robotics. Retrieved 2024-01-12.
- ^ "Custom axial flux permanent magnet BLDC". Turncircles. Archived from the original on 24 November 2020. Retrieved 23 November 2020.
- ^ "home page". .ebikekit.
- ^ ECMs and HVAC Systems. Thomasnet.com. Retrieved on 2019-12-26.
- ^ "Reliance Electric GV3000 Drive 30V4160 | Automation Industrial". 30v4160.com. Retrieved 2023-12-23.
- ^ a b "Brushless DC Motors Used in Industrial Applications". Ohio Electric Motors. 2012. Archived from the original on November 4, 2012.
- ^ Ohio Electric Motors. DC Motor Protection. Ohio Electric Motors. 2011. Archived January 26, 2012, at the Wayback Machine
- ISBN 978-0-07-059630-6.
- ISBN 978-0-521-56688-9.
- ISBN 978-0-07-048289-0.
- ISBN 978-0-412-55770-5.
- ISBN 978-0-08-094752-5.
- ^ Bobby Bernstein (15 January 2015). "Top 4 Fastest RC Cars for Sale in the World". heavy.com. Retrieved 2 February 2015.
As far as THE fastest RC car available for sale is concerned, it is the Traxxas XO-1 Supercar. The XO-1 hits 100mph, with proper LiPos batteries.
The maker's product specifications indicate the usage of a "Traxxas Big Block brushless motor" - ^ Maning, Jayric (2022-08-20). "Brushed vs. Brushless Motors: What's the Difference, and What's Best?". MUO. Retrieved 2023-12-23.
Further reading
- Jacek F. Gieras; Mitchell Wing (2002), Permanent magnet motor technology: design and applications, CRC Press, ISBN 9780824743949
- Krishnan Ramu (2009), Permanent Magnet Synchronous and Brushless DC Motors, CRC Press, ISBN 9781420014235
- Howard E. Jordan (1994), Energy-efficient electric motors and their applications, Springer, ISBN 9780306446986
- Bobby A. Bassham (2003), An Evaluation of Electric Motors for Ship Propulsion, Naval Postgraduate School, archived from the original on April 8, 2013
- Duane Hanselman (2012), Brushless Motors: Magnetic Design, Performance, and Control, E-Man Press, ISBN 9780982692615
External links
- How Motors Work (brushed and brushless RC airplane motors) at the Wayback Machine (archived 2013-10-02)
- BLDC Motor Fan Advantages And Disadvantages at the Wayback Machine (archived 2022-01-17)
- Animation of BLDC Motor in different commutation (Block, Star, Sinus (sine) & Sensorless) – compared to stepper motors at the Wayback Machine (archived 2020-02-05) Flash
- Electric Drives – Brushless DC / AC and Reluctance Motors with useful diagrams
- How Brushless Motor and ESC Work – Video explanation how Brushless DC Motor works, plus how to control one with an Arduino micro-controller.