A BLDC motor has a rotor with permanent magnets and a stator with windings. The brushes and commutator have been eliminated and the windings are connected to the control electronics. The control electronics replace the function of the commutator and energize the windings in a pattern that rotates around the stator. The energized stator winding leads the rotor magnet and switches just as the rotor aligns with the stator.
A BLDC motor does not operate directly off a DC voltage source. It has a rotor with permanent magnets, a stator with windings and commutation that is performed electronically. Typically, three Hall sensors are used to detect the rotor position and commutation is performed based on Hall sensor inputs. The motor is driven by rectangular or trapezoidal voltage strokes coupled with the given rotor position. The voltage strokes must be properly applied between the phases, so that the angle between the stator flux and the rotor flux is kept close to 90 to generate maximum torque. The position sensor required for the commutation can be very simple since only six pulses per revolution (in a three-phase machine) are required. Typically, the position feedback is implemented by using three Hall effect sensors aligned with the back EMF of the motor. In sensorless control, back EMF zero-crossing detection is used for commutation.
The ADC in PIC and AVR MCUs, or dsPIC DSCs samples the motor phase voltages. From these voltages, the CPU determines the rotor position and drives the motor control PWM module to generate trapezoidal output signals for the three-phase inverter circuit.
The history of the first brushless DC (BLDC) motor dates back to 1962. The implementation of this new type of electrical motor was made possible thanks to a transistor switch invented shortly before. Using electronics instead of a mechanical commutator with brushes was a breakthrough in electrical engineering at that time.
BLDC motors have found wide application in various industries - from computer hard drives to electric transport and industrial robots. In some fields, they have almost squeezed out brushed DC (BDC) motors. High performance and durability are among the major advantages of a brushless DC motor. Nevertheless, it will hardly edge out BDC motors completely as it is still a costly solution with a complex construction and control system.
A BLDC motor controller can perform the same functions and apply similar methods as a brushed DC motor controller. However, there are some conceptual differences in their arrangement and implementation. This article will shed light on the characteristics of a brushless DC motor controller, that is how it works, how it is built, and what it works best for.
A BLDC motor controller regulates the speed and torque of the motor; it can also start, stop, and reverse its rotation. To understand the working principles of the controller, let us start first with the construction of a brushless motor. Its major components comprise:
The key benefits of a brushless DC motor arise from its construction features. The electronic commutation provides improved current switching. It results in increased torque, effective speed control over a wide range, and thus better performance of the motor.
Of course, there are inexpensive low-power systems that do not need a programmable brushless DC motor controller with feedback. Here, the use of a BDC motor with a simple controller could make more sense. But if you still prioritize higher efficiency and durability over simplicity and cost-effectiveness, a brushless DC motor can be a viable option for your project.
A typical BLDC motor controller has a half-bridge or half-H bridge circuit. Unlike an H bridge, this circuit configuration has only two switches - one high-side and one low-side transistor.
Most brushless motors use two or three-phase power systems. So in a BLDC motor controller circuit diagram, this will look like two or three half-bridges (depending on the number of phases) with a pair of switches each.
The three-phase BLDC motor controller circuit includes six steps necessary to complete a full switching cycle (that is to energize all the three windings of the stator). By turning the high-side and low-side transistors on and off, the current flows through the stator windings in sequence.
Designing a BLDC motor controller, you can consider different approaches to current switching, including trapezoidal and sinusoidal commutation. The names of these methods relate to the signal waveforms.
As an option, you can employ hysteresis to control the operation of a BLDC motor. This method relates to the sinusoidal commutation too. It allows you to establish the upper and lower limits of the current supplied to the motor. As soon as the current reaches its upper or lower range, the transistor switches turn off or on respectively and change the average current using the law of sines.
You can implement a BLDC motor controller half-bridge as either an integrated circuit (IC) or as discrete components. This is one of the most common dilemmas you might face as you start figuring out how to design a BLDC motor controller.
A discrete circuit can be less reliable since the components should be assembled and soldered onto the board separately. A brushless DC motor controller IC has a smaller size, low production costs, and simplifies the design process. However, integrated circuits have power limitations. Above that, the failure of one component will lead to the replacement of the entire BLDC motor controller IC, not just this component.
For example, BLDC motor controllers used in power electronics deal with high current and voltage. They require a high switching frequency. Here, it will make sense to use discrete components, including external high power transistors, such as IGBT and GaN.
Position sensors offer a relatively simple detection method that you can implement without sophisticated control algorithms. However, their use complicates the arrangement and maintenance of the motor.
The sensorless method (back EMF measurement) can cut the cost of the bill of materials (BOM) and simplify your brushless DC motor controller design. The major challenge here is to make the rotor move first, since back EMF will not appear when the rotor is at rest. Thus, the controller will not receive the required information.
To measure the back EMF correctly, think through your brushless DC motor controller schematic as well as its software. You need to install current and voltage converters, add noise filters, and build digital signal processing (DSP) algorithms.
In most cases, the MCU of a closed-loop motor controller uses a proportional-integral-derivative (PID) algorithm. It is necessary for regulating the speed, torque, and other characteristics of the motor. For example, a PID algorithm can process the current speed, compare this value with the setpoint, and define the frequency of the output signals that should be applied to the motor to stabilize its speed.
Brushless DC motors have been in use for over fifty years. Their application area ranges from a small-sized consumer device to a complicated industrial automation system. The all-electronic control system increases torque, improves wide-range speed regulation, and enhances other characteristics of the motor.
Design of brushless DC motor controls can take resources and require unconventional engineering solutions at both hardware and software levels. If you need professional services or advice on how to make your own BLDC motor controller, feel free to contact us with your queries. We are ready to share our relevant experience in electronic design and firmware development.
A brushless DC electric motor, also known as an electronically commutated motor, is a synchronous motor using a direct current (DC) electric power supply. It uses an electronic controller to switch DC currents to the motor windings producing magnetic fields which effectively rotate in space and which the permanent magnet rotor follows. The controller adjusts the phase and amplitude of the DC current pulses to control the speed and torque of the motor. This control system is an alternative to the mechanical commutator (brushes) used in many conventional electric motors.
The construction of a brushless motor system is typically similar to a permanent magnet synchronous motor (PMSM), but can also be a switched reluctance motor, or an induction (asynchronous) motor. They may also use neodymium magnets and be outrunners (the stator is surrounded by the rotor), inrunners (the rotor is surrounded by the stator), or axial (the rotor and stator are flat and parallel).
The advantages of a brushless motor over brushed motors are high power-to-weight ratio, high speed, nearly instantaneous control of speed (rpm) and torque, high efficiency, and low maintenance. Brushless motors find applications in such places as computer peripherals (disk drives, printers), hand-held power tools, and vehicles ranging from model aircraft to automobiles. In modern washing machines, brushless DC motors have allowed replacement of rubber belts and gearboxes by a direct-drive design.
In brushless DC motors, an electronic servo system replaces the mechanical commutator contacts. An electronic sensor detects the angle of the rotor and controls semiconductor switches such as transistors which switch current through the windings, either reversing the direction of the current or, in some motors turning it off, at the correct angle so the electromagnets create torque in one direction. The elimination of the sliding contact allows brushless motors to have less friction and longer life; their working life is only limited by the lifetime of their bearings.
Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases. 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. 59ce067264