Introdution to Brushless motor controller and Brushed controller system

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1. Differences between Brushless motor and Brushed motor

1.1 By name: brushed motor include carbon brush while brushless motor not.

1.2 By construction: The brushed motor rotates the silicon steel coil winding, the magnet is fixed and does not rotate, the brushless motor rotates the magnet, and the silicon steel coil winding is fixed and does not rotate.
1.3 By wiring: the brushless motor is connected to the positive and negative power supply, and the brushless motor is the U V W three-wire connection. The brushless motor with sensor will also include a five-core signal wire.(Hall sensor wire)

2. Advantages and disadvantages of brushed motor and brushless motor

The advantages of brushless motor is not only raise the reliability but also reduce noise and electrical interference associated with carbon brush rectification.
Brushed motors are primarily voltage controlled, however,the reliance on electronic commutation of brushless DC motors gives engineers the opportunity to manage rotor position, speed, acceleration, as well as motor output torque, efficiency, and other parameters with greater precision, to meet specific application requirements.

2.1 Advantages for brushed motor

2.2.1 The motor structure is simple and the related process is mature.
2.2.2 Motor running fluently with great starting/braking effect.
2.2.3 Fast response to electromagnetic force and large starting torque
2.2.4 Only need to control voltage to control the speed, tech requirement of controller is easy.

2.2 Disadvantages of brushed motor

2.2.1 The friction sound of the carbon brush is loud, and the commutator loss is large

2.2.2 The efficiency is low, the inactive power is converted into heat energy, the motor is easy to heat up and the service life is short.

2.2.3 It is contact converter, sparks will be generated during the commutation process, which will interfere with the power grid.

2.2.4 Due to the low efficiency, the output energy converted from the same input power is smaller.

2.2.5 It can only work continuously for about 5000 hours, the normal service life is 2-3 years, the service life is lower than brushless motor.

2.3 Advantages of brushless motor

2.3.1 With lower contact spark and electromagnetic interference

2.3.2 Lower noise and smooth operation

2.3.3 No consumable contact parts, long service life, can work continuously for about 20,000 hours, and the normal service life is 7-10 years

2.3.4 Without the carbonization problem to brush and commutator, no need for maintenance.

2.3.5 Use three phase drive circuit to control and avoid sudden unintended acceleration.

2.3.6 The efficiency of the brushless motor can reach more than 85%, and the efficiency of the brushed motor is about 55%, so the brushless system is more energy-saving.

2.4 Disadvantages of brushless motors

2.4.1 The winding of the brushless motor is a three-phase connection, and the motor design is more complicated

2.4.2 The control algorithm has high technical requirements and the drive circuit is complex.

2.4.3 The cost of brushless controller is higher than brushed controller.

2.4.4 High requirements for phase detection accuracy and motor mass production equipment.

3. How brushed and brushless motors work

3.1 Working principle of brushed motor

3.1.1 The main structure of a brushed motor is stator + rotor + carbon brush, which obtains rotational torque through the rotating magnetic field, thereby outputting kinetic energy. The brushes are constantly in contact and friction with the commutator, and play the role of conduction and commutation during rotation.

3.1.2 The brushed motor adopts mechanical commutation, the magnetic pole (magnet) does not move, and the coil rotates. When the motor is working, the coil and the commutator rotate, the magnet and the carbon brush are fixed and do not rotate, the alternation of the coil current direction is accomplished by the commutator and brush that rotate with the motor.

3.1.3 In the brushed motor, the process is to arrange the two power input ends of each group of coils into a ring in turn, and separate them with insulating materials to form a cylinder-like thing, which is connected to the motor shaft. As a whole, the power supply passes through two small columns (carbon brushes) made of carbon elements. Under the action of spring pressure, from two specific fixed positions, press the two points on the upper coil power input ring cylinder to give a group of coil energized.

3.1.4 As the motor rotates, different coils or different two poles of the same coil are energized at different times, so that the NS pole of the magnetic field generated by the coil and the NS pole of the closest permanent magnet stator have a suitable angle difference, and the magnetic field is opposite to phase. Suction and repulsion of the magnetic force drive the motor to rotate. The carbon electrode slides on the coil terminal, like brushing on the surface of the object, so it is called "carbon brush".

3.1.5 The friction between the carbon brush and the rotor will cause a loss on carbon brush, which needs to be replaced regularly. The on-off between the carbon brush and the coil terminal is alternated, and electrical sparks will occur, thus generating electromagnetic waves to interfere with electronic equipment.

3.2 Working principle of brushless motor

3.2.1 In the brushless motor, the commutation work is handed over to the control circuit in the controller, which is generally a Hall sensor and electronic commutator. (encoder technology will be used for more precise requirements)

3.2.2 The brushless motor adopts electronic commutation, the coil does not move and the magnet rotates. The brushless motor uses a set of electronic equipment to sense the position of the magnetic pole of the permanent magnet through the Hall element. According to this perception, the electronic circuit is used to switch the direction of the current in the coil in time to ensure that the magnetic force in the correct direction is generated to drive the motor, eliminating the disadvantages of brushed motors.

3.2.3 The above circuits are brushless motor controllers. The brushless motor controller can also realize some functions that the brushed motor cannot, such as adjusting the power switching angle, braking the motor to reverse the motor, or locking the motor.

3.2.4 The brushless DC motor consists of a motor body and a driver (controller), and is a typical mechatronic product. Since the brushless DC motor operates in a self-controlled manner, it does not require additional starting windings on the rotor like a synchronous motor started under variable frequency speed regulation, nor does it cause oscillation and loss of step when the load suddenly changes.

4. Speed regulation difference between brushed motor and brushless motor

In fact, the control of the two motors is through voltage regulation. It is only because the brushless DC adopts electronic commutation, so it can only be realized by digital control, while the brushed DC is commutated through carbon brushes, using traditional analog circuits such as SCR to control, which is relatively simple.

4.1 The speed regulation process of the brushed motor is to adjust the level of power supply voltage to the motor. The adjusted voltage and current are converted by commutators and brushes to change the strength of the magnetic field generated by the electrodes, to achieve the purpose of changing speed. This process is called variable voltage speed regulation.

4.2 The brushless motor speed regulation process is that the voltage of the motor's power supply remains, and the control signal of the drive circuit is changed by the microprocessor, and then the switching rate of the high-power MOS tube is changed to realize the change of the speed. This process is called variable frequency speed regulation.

5. Brushless motor control principle

5.1 To control a brushless DC motor, the rotor position must first be known. The controller uses this information to coordinate the power supply to the rotor coils in relation to the magnetic field to ensure that the motor provides the required response, including maintaining speed, accelerating, decelerating, changing direction, reduce or increase torque, emergency stop, or other responses, depending on application and operating conditions.

5.2 The rotor position can be detected directly by using a sensor or encoder located on the rotor shaft. There are many types of encoders, roughly divided into relative position and absolute position; there are also various types of sensing technologies, such as magnetic coil resolvers, or Hall effect, optical or capacitive sensors. Any of these types of technologies may be suitable for a given use case, depending on requirements such as resolution, durability, or cost.

5.3 Sensorless control is a feasible alternative that utilizes the computing ability of existing microcontrollers to calculate the rotor position by measuring the back EMF in each rotor winding. No encoder is required, which can save material costs, simplify assembly and improving reliability. Field Oriented Control (FOC) decomposes the rotor current into D and Q-axis components, which simplifies the control challenge because the DC value changes slowly. Combined with this control method, the rotor position can be detected without a sensor, which is very suitable for applications where cost and reliability are more important than accuracy.

6. DC brushless driver (generally referred as controller in the fitness equipment industry)

6.1 Motor drive control is to control the rotation or stop of the motor, as well as the speed of rotation. The motor drive control part is also called electronic speed controller

6.2 An electronic driver is also required outside the brushless motor. This driver is a brushless motor controller. It changes the direction of the current inside the fixed coil at any time to ensure that the force between it and the permanent magnet is mutually exclusive and attractive, so that the coil current commutation action has been exchanged and repeated, and the rotation of the motor rotor (magnet) can be continued.

6.3 To make a brushed motor rotate, directly supply the DC power to the positive and negative stages of the motor, and the motor can rotate by itself. The brushless motor must have a controller to convert the DC power into three-phase AC power and transmit it to supply the brushless motor.
6.4 From the perspective of the motor power source, the power source of the brushed motor is direct current, and the power source of the brushless motor is three-phase alternating current.

6.5 Three-phase alternating current is a form of transmission of electricity, referred as three-phase electricity. It is a power supply composed of three alternating voltages with the same frequency, amplitude, and phase difference of 120 degrees. The voltage waveform of three-phase electricity is as follows:

6.6 Brushless controller, the input is single-phase alternating current, a high voltage DC is rectified through a high voltage bridge rectifier and a high voltage filter capacitor. This high voltage DC is supplied to the main power supply of the full-bridge drive circuit. When the controller MCU performs commutation and transmits a small signal to the control terminal of the full-bridge drive circuit, the full-bridge circuit will convert the small signal into a large high-voltage DC signal and supply to the motor coil windings, so the current will always change the flow direction, which is called electronic commutation.

6.7 The MCU in the controller will output the PWM signal to each phase according to the speed command issued by the upper control electronic meter. The positive pulse width of the PWM signal determines the output voltage, matching the PWM frequency and the timing that each phase of UVW turns from LO to HI (tangential angle), to control the speed and steering of the motor, which is the principle of brushless electronic commutation.

6.8 When the drive motor is running, there are 3 groups of MOS tubes in the full-bridge circuit of the controller. Each group of 2 MOS tubes controls the positive output and the negative output. When the positive output is used, the negative output is not output, and vice versa, which forms the AC, and the three groups of MOS FET all operate as above.

6.9 When choosing a power MOSFET in a full-bridge circuit, the design engineer must consider factors such as the required voltage and current ratings, switching speed, switch and conduction losses. The gate driver must also be able to quickly charge and discharge the gate capacitance of the MOSFET to ensure fast switching to the maximum frequency required by the application. In the early days, this full-bridge driver circuit was based on six discrete MOSFETs components and surrounding components. Now, due to the development of integration technology, high-power full-bridge circuits all use IPM modular full-bridge driver modules. All parts of this full-bridge circuit are integrated into one wafer, and then the wafer is packaged into a module through the packaging process. The protection circuit of the full-bridge MOS FET is designed in the chip, and its protection response is fast, so it greatly reduces the probability of damage to the full-bridge drive circuit components during the operation of the brushless controller product.

6.10 Talking about PSoC 3 Architecture Diagram
The PSoC 3 architecture has rich brushless DC motor control functions, multiple PWM function blocks, and monitoring and communication functions.

6.11 Take MCP8024 as an example
The MCP8024 integrates important features such as three voltage ratings, and half-bridge drivers up to 12V and 0.5A (with shoot-through protection and independent input control for high-side and low-side MOSFETs), and one step-down power converter for a microcontroller. There are also three operational amplifiers for phase current monitoring and rotor position detection, an overcurrent comparator, two level converters, and 5V&12V 20mA LDO regulators. Additional built-in protection features include under- and over-voltage lockout, short-circuit protection, and thermal shutdown. These extensive features are packed into a small 40-pin 5mm x 5mm QFN or 48-pin 7mm x 7mm TQFP package.

The MPC8024 is a highly integrated power module designed to control the gate of an external MOSFET, to control the power supply to a brushless DC motor.

7. Summary

Brushless DC motors have rapidly grown into the first choice for motor types due to its high reliability, versatility, low noise and electrical interference, and ease of use. It can be controlled by lightweight magnetic field oriented control strategy through lower-cost microcontroller or programable Soc, with or without rotor position sensors. The PSoC 3 controller, combined with the appropriate power modules and power switches, integrates advanced motor management and monitoring function circuits, which can be used in Fitness Equipment Industry, which is a field that requires high-tech electromechanical integration. With the maturity of the brushless motor production process and the refinement of the control technology algorithm, the brushless system has become the trend of the treadmill drive system.