Railway Carriage BLDC fan

CT Group Of Institutions Registration no: - 1282728 (4 th semester) EEE

Railway Carriage BLDC

Fan

1Electrical And Electronic EngineeringBachelor of technology (B. Tech)


Railway Carriage BLDC Fan(With Sensor)



TYEPS OF FANS:-

>CONVENTIONAL FANS (WITH BRUSSH)

1) A.C FANS

2) D.C FANS >ADVANCE ELECTRONIC BLDC FANS (WITHOUT BRUSSLESS)

1) BLDC with Sensor

2) BLDC without Sensor



In BLDC and Conventional Fans we use DC MOTOR:-

So what is DC MOTOR?

DC MOTOR:-

Introduction:-

Almost every mechanical movement that we see around us is accomplished by an electric motor. Electric machines are a means of converting energy. Motors take electrical energy and produce mechanical energy.Electric motors are used to power hundreds of devices we use in everyday life. Or

we can say that dc motor is an electrical instrument.

In these fig. parts of DC motor:-



1) Stator

2) Rotor

3) Commutator

4) Brushes

5) Axis

6) Field Magnets

MAIN PARTS OF DC MOTOR:-



EXPLANATON:-



1) CARBON BRUSH: - A brushed DC motor is an internally commutated electric motor designed to be run from a direct current power source. A brush is a device conducts current between stationary wires and moving parts, most commonly in a rotating shaft. Typical applications include electric motor, alternator and electric generator.

2) ARMATURE: - The power-producing component of an alternator, generator, dynamo or motor. In a DC machine, the main field is produced by field coils. In both the generating and motoring modes, the armature carries current and a magnetic field is established, which is called the armature flux. The effect of armature flux on the main field is called the armature reaction.

The armature reaction:-

1. Demagnetizes the main field, and2. Cross magnetizes the main field.

3) COMMUTATOR: - A commutator is the moving part of rotary electrical switches in certain types of electrical generator that periodically reverses the current direction between the rotor and the external circuits. The rotating switches that contacts the brushes of a DC motor. The commutator maintains DC when the rotation of the armature switches the polarity of the conductor.

Construction of DC MOTOR:-



DC motors consist of one set of coils, called armature winding, inside another set of coils or a set of permanent magnets, called the stator. Applying a voltage to the coils produces a torque in the armature, resulting in motion.

1) Stator:-=>The stator is the stationary outside part of a motor.=>The stator of a permanent magnet dc motor is composed of two or more permanent magnet pole pieces.=>The magnetic field can alternatively be created by an electromagnet. In this case, a DC coil (fieldWinding) is wound around a magnetic material that forms part of the stator.

2) Rotor:-=>The rotor is the inner part which rotates. =>The rotor is composed of windings (called armature windings) which are connected to the externalCircuit through a mechanical commutator.Both stator and rotor are made of ferromagnetic materials. The two are separated by air-gap.

3) Winding:-A winding is made up of series or parallel connection of coils.a) Armature winding - The winding through which the voltage is applied or induced.b) Field winding - The winding through which a current is passed to produce flux (for

the electromagnet)Windings are usually made of copper.

Principle of operation DC MOTOR:-



Consider a coil in a magnetic field of flux density (B) .When the two ends of the coil are connected across a DC voltage source, current I flow through it. A force is exerted on the coil as a result of the interaction of magnetic field and electric current. The force on the two sides of the coil is such that the coil starts to move in the direction of force.In an actual DC motor, several such coils are wound on the rotor, all of which experience force,Resulting in rotation. The greater the current in the wire, or the greater the magnetic field, the faster the wire moves because of the greater force created.

Induced voltage in the armature winding of DC motor:-



At the same time this torque is being produced, the conductors are moving in a magnetic field. AtDifferent positions, the flux linked with it changes, which causes an electromotive force (emf) to be induced (e = d/dt) This voltage is in opposition to the voltage that causes current flow through the conductor and is referred to as a counter-voltage or back emf.

BRUSSHLESS DC MOTOR FAN:-



BLDC FAN MOTOR:-

Introduction:-



Conventional dc motors are highly efficient and their characteristics make them suitable for use as servomotors. However, their only drawback is that they need a commutator and brushes which are subject to wear and require maintenance. When the functions of commutator and brushes were implemented by solid-state switches, maintenance-free motors were realized. These motors are now known as brushless dc motors.

BLOCK DIAGRAM OF BLDC FANS:-



EXPLAIN:-

Brushless DC electric motor (BLDC motors, BL motors) also known as electronically commutated motors (ECMs, EC motors) are synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC electric signal to drive the motor (AC, alternating current, does not imply a sinusoidal waveform but rather a bi-directional current with no restriction on waveform); additional sensors and electronics control the

inverter output amplitude and waveform (and therefore percent of DC bus usage/efficiency) and frequency (i.e. rotor speed).

Construction of BLDC FAN:-



The construction of modern brushless motors is very similar to the ac motor, known as the permanent magnet synchronous motor. Illustrates the structure of a typical Three-phase brushless dc motor. The stator windings are similar to those in a polyphone Ac motor and the rotor is composed of one or more permanent magnets. Brushless dcMotors are different from ac synchronous motors in that the former incorporates some Means to detect the rotor position (or magnetic poles) to produce signals to control the Electronic switches. The most common position/pole sensor is the Hall element, but some motors use optical sensors.

BLDC fans can be classified as :-

1) BLDC fans with sensor



2) BLDC fans without sensor

1) BLDC fans with sensor:-

2) BLDC fans without sensor:-

Brushless vs. brushed motors

Brushed DC motors have been in commercial use since 1886.Brushless motors, on the other hand, did not become commercially viable until 1962.



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 a lower susceptibility of the commutator assembly 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 which rotate and a fixed armature, eliminating problems associated with connecting current to the moving armature. An electronic controller replaces the brush/commutator assembly of the brushed DC motor, which continually switches the phase to the windings to keep the motor turning. The controller performs similar timed power distribution by using a solid-state circuit rather than the brush/commutator system.

Brushless motors offer several advantages over brushed DC motors, including more torque per weight, more torque per watt (increased efficiency), increased reliability, reduced noise, longer lifetime (no brush and commutator erosion), elimination of ionizing sparks from the commutator, and 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 microcontroller or computer, or may alternatively be implemented in analogue hardware or digital firmware using an FPGA. Commutation with electronics instead of brushes allows for greater flexibility and capabilities not available with brushed DC motors, including speed limiting, "micro stepped" operation for slow and/or fine motion control, and a holding torque when stationary.

The maximum power that can be applied to a brushless motor is limited almost exclusively by heat; too much of which weakens the magnets, and may damage the winding's insulation.

A brushless motor's main disadvantage is higher cost, which arises from two issues.



>Firstly, brushless motors require complex electronic speed controllers (ESCs) to run. In contrast, brushed DC motors can be regulated by a comparatively simple controller, such as a rheostat (variable resistor). However, this reduces efficiency because power is wasted in the rheostat.

>Secondly, some practical uses have not been well developed in the commercial sector. For example, in the radio control (RC) hobby arena, brushless motors are often hand-wound while brushed motors are usually machine-wound.

Applications

1>Brushless motors are more efficient at converting electricity into mechanical power than brushed motors.

2>This improvement is largely due to the brushless motor's velocity being determined by the frequency at which the electricity is switched, not the voltage.

3>Additional gains are due to the absence of brushes, alleviating loss due to friction.



4>The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve.

5>Under high mechanical loads, brushless motors and high-quality brushed motors are comparable in efficiency.

6>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.

Controller implementations

Because the controller must direct the rotor rotation, the controller requires some means of determining the rotor's orientation/position (relative to the stator coils.) Some designs use Hall Effect sensors or a rotary encoder to directly measure the rotor's position. Others measure the back EMF in the un driven coils to infer the rotor position, eliminating the need for separate Hall Effect sensors, and therefore are often called sensor less controllers.

A typical controller contains 3 bi-directional outputs (i.e. frequency controlled three phase output), which are controlled by a logic circuit. Simple controllers employ comparators to determine when the output phase should be advanced, while more



advanced controllers employ a microcontroller to manage acceleration, control speed and fine-tune efficiency.

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 briefly backwards, adding even more complexity to the startup sequence. Other sensors less controllers are capable of measuring winding saturation caused by the position of the magnets to infer the rotor position.

Variations in construction

Schematic for delta and wyes winding styles. (This image does not illustrate the motor's inductive and generator-like properties)


http://en.wikipedia.org/wiki/File:Wye-delta.svg


Brushless motors can be constructed in several different physical configurations: In the 'conventional' (also known as in runner) configuration, the permanent magnets are part of the rotor. Three stator windings surround the rotor. In the out runner (or external-rotor) 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 which surrounds the core. The flat or axial flux type, used where there are space or shape limitations, uses stator and rotor plates, mounted face to face. Out runners typically have more poles, set up in triplets to maintain the three groups of windings, and have a higher torque at low RPMs. In all brushless motors, the coils are stationary.

There are two common electrical winding configurations; the delta configuration connects three windings to each other (series circuits) in a triangle-like circuit, and power is applied at each of the connections. The Wyes (Y-shaped) configuration, sometimes called a star winding, connects all of the windings to a central point (parallel circuits) 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. Wyes configuration gives high torque at low speed, but not as high top speed.

Although efficiency is greatly affected by the motor's construction, the Wyes winding is normally more efficient. In delta-connected windings, half voltage is applied across the windings adjacent to the driven lead (compared to the winding directly between the driven leads), increasing resistive losses. In addition, windings can allow high-frequency parasitic electrical currents to circulate entirely within the motor. A Wyes-connected winding does not contain a closed loop in which parasitic currents can flow, preventing such losses.

From a controller standpoint, the two styles of windings are treated exactly the same, although some less expensive controllers are designed to read voltage from the common center of the Wyes winding.



Motor control power supplies

Main articles:

>Inverter (electrical) and

>Variable-frequency drive

Typical brushless motors are permanent magnet synchronous AC motors, combined with sensor electronics (detecting rotor position) and an AC signal generator (Inverter) driven by a DC supply. Typical brushless inverters use a switched power supply pulse width modulation to generate an AC drive signal. Various terms are



used to refer to the inverters/electronic control systems, including "Vector Drives", and "VVVF drives" (variable voltage variable frequency).

The four poles on the stator of a two-phase brushless motor. This is part of a computer cooling fan; the rotor has been removed.

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 hard drives and CD/DVD players. Small cooling fans in electronic equipment are powered exclusively by brushless motors. They can be found in cordless power tools where the increased efficiency of the motor leads to longer periods of use before the battery needs to be charged. Low speed, low power brushless motors are used in direct-drive turntables for gramophone records.

Main Applications

1) Transport

High power brushless motors are found in electric vehicles and hybrid vehicles. These motors are essentially AC synchronous motors with permanent magnet rotors. The Subway Scooter and Beatrix Maxi-Scooter use brushless technology.

A number of 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.2) Heating and ventilations

There is a trend in the 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 the dramatic reduction in power required to operate them versus a typical AC motor. While shaded-pole and permanent split capacitor motors once dominated as the fan motor of choice, many fans are now run using a brushless motor. Some fans use brushless motors also in order to increase overall system efficiency.

In addition to the brushless motor's higher efficiency, certain HVAC systems (especially those featuring variable-speed and/or load modulation) use brushless motors because the built-in microprocessor allows for programmability, better control over airflow, and serial communication.

3) Industrial engineering

The application of brushless DC motors within industrial engineering primarily focuses on manufacturing engineering or industrial automation design. In manufacturing, brushless motors are primarily used for motion control, positioning or actuation systems.

Brushless motors are ideally suited for manufacturing applications because of their high power density, good speed-torque characteristics, high efficiency and wide speed ranges and low maintenance. The most common uses of brushless DC motors in industrial engineering are linear motors. Servomotors, actuators for industrial robots, extruder drive motors and feed drives for CNC machine tools.

4) Motion control systems

Brushless motors are commonly used as pump, fan and spindle drives in adjustable or variable speed applications. They can develop 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. 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.

Brushless dc motors are widely used as servomotors for machine tool servo drives. Servomotors are used for mechanical displacement, positioning or precision motion control. In the past DC stepper motors were used as servomotors; however, since



they are operate with open loop control, they typically exhibit torque pulsations. Brushless dc motors are more suitable as servomotors since their precise motion is based upon a closed loop control system that provides tightly controlled and stable operation.

5) Positioning and actuation systems

Brushless motors are used in industrial positioning and actuation applications. For assembly robots, brushless stepper or servo motors are used to position a part for assembly or a tool for a manufacturing process, such as welding or painting. Brushless motors can also be used to drive linear actuators.

Actuators that produce linear motion are called linear motors. The advantage of linear motors is that they can produce linear motion without the need of a transmission system, such as a ball-and-lead screw, rack-and-pinion, cam, gears or belts that would be necessary for rotary motors. Transmission systems are known to introduce less responsiveness and reduced accuracy. Direct drive, brushless DC linear motors consist of a slotted stator with magnetic teeth and a moving actuator, which has permanent magnets and coil windings. To obtain linear motion, a motor controller excites the coil windings in the actuator causing an interaction of the magnetic fields resulting in linear motion.

6) Model engineering

A microprocessor-controlled BLDC motor powering a micro radio-controlled airplane. This external rotor motor weighs 5 grams, consumes approximately 11 watts and produces thrust of more than twice the weight of the plane.

Brushless motors are a popular motor choice for model aircraft including helicopters. Their favorable power-to-weight ratios and large range of available sizes, from under 5 gram to large motors rated at thousands of watts, have revolutionized the market for electric-powered model flight, displacing virtually all brushed electric motors. They have also encouraged a growth of simple, lightweight electric model aircraft, rather than the previous internal combustion engines



powering larger and heavier models. The large power-to-weight ratio of modern batteries and brushless motors allows models to ascend vertically, rather than climb gradually. The low noise and lack of mess compared to small glow fuel internal combustion engines that are used is another reason for their popularity.

Legal restrictions for the use of combustion engine driven model aircraft in some countries have also supported the shift to high-power electric systems.

7) Radio controlled cars

Their popularity has also risen in the radio controlled car sector. Brushless motors have been legal in North American RC car racing in accordance to ROAR since 2006. These motors provide a great amount of power to RC racers and if paired with appropriate gearing and high-discharge Li-Po (Lithium Polymer) batteries, these cars can achieve speeds of up to 100 miles per hour (161 km/h).

Why use brushless DC motors (advantages/disadvantages)?

Brushless DC motors are synchronous motors suitable for use as a simple means of controlling permanent drives (e.g. ABS pumps, EHPS pumps, fuel pumps or cooling fans). This type of 3-, 4- or 5-phase brushless DC motor will increasingly replace brushed DC motors. Brushed DC motors require maintenance, e.g. to service coal brushes and commutator. Another major problem with a brushed DC machine is the possibility of brush burnout in the event of an overload or stall condition.



Functional principle of a brushless DC motor

A three-phase brushless DC motor with two pole pairs. The rotation of the electrical field (vector) has to be applied twice as fast as the desired mechanical speed of the brushless DC motor. The three coils of the stator are split into two groups of coils (A, B, C and A’, B’, C’). As you can see in Figure 1, coils A and C are energized and coil B is not energized. A 0° to 180° rotation will be shown in detail in section 2.1 to explain the setting of the appropriate switches of the B6 bridge pattern, the appropriate voltages relating to the coils, and the energized coils of the motor with the suitable rotor position between 0° and 180° mechanical.



Brushless DC Motors wiring diagrams

The wiring diagrams for a 3-pole armature (stator) Brushless DC Motors

The wiring diagrams for a 6-pole armature Brushless DC Motors


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Brushless DC Motors Animation

Brushless DC motors are referred to by many aliases: brushless permanent magnet, permanent magnet ac motors, permanent magnet synchronous motors ect. The confusion arises because a brushless dc motor does not directly operate off a dc voltage source. However, as we shall see, the basic principle of operation is similar to a dc motor.


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Brushless DC Motors

EXPLAIN :-

DC brushless motors are similar in performance and application to brush-type DC motors. Both have a speed vs. torque curve which is linear or nearly linear. The motors differ, however, in construction and method of commutation. A brush-type permanent magnet DC motor usually consists of an outer permanent magnet field and an inner rotating armature. A DC brushless motor has a wound stator, a permanent magnet rotor assembly, and internal or external devices to sense rotor position. The sensing devices provide signals for electronically switching (commutating) the stator windings in the proper sequence to maintain rotation of the magnet assembly. The rotor assembly may be internal or external to the stator in a DC brushless motor. The combination of an inner permanent magnet rotor and outer windings offers the advantages of lower rotor inertia and more efficient heat dissipation than DC brush-type construction. The elimination of brushes reduces maintenance, increases life and reliability, and reduces noise and EMI generation.



DC Brushless Motor Control Block Diagram


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Brushless DC Motor driver circuit

1>Closed Loop Brushless DC Motor Control With the MC33033 Using the MC33039 driver circuitThe MC33033 is a high performance second generation, limited feature, monolithic brushless dc motor controller which has evolved from ON Semiconductor's full featured MC33034 and MC33035 controllers. It contains all of the active functions required for the implementation of open loop, three or four phase motor control. The device consists of a rotor position decoder for proper commutation sequencing, temperature compensated reference capable of supplying sensor power, frequency programmable saw tooth oscillator, fully accessible error amplifier, pulse width modulator comparator, three open collector top drivers, and three high current totem pole bottomdrivers ideally suited for driving power MOSFETs. Unlike its predecessors, it does not feature separate drive circuit supply and ground pins, brake input, or fault output signal.

2>THREE-PHASE BRUSHLESS DC MOTOR driver circuitThe L6235 is a DMOS Fully Integrated Three-Phase Motor Driver with Over current Protection. Realized in Multi Power-BCD technology, the devicecombines isolated DMOS Power Transistors with CMOS and bipolar circuits on the same chip. The device includes all the circuitry needed to drive athree-phase BLDC motor including: a three-phase DMOS Bridge, a constant off time PWM Current Controller and the decoding logic for single ended hallsensors that generates the required sequence for the power stage.

3>3-Phase Full-Wave PWM Driver for Sensor less brushless Motors driver circuitThe TB6588FG is a three-phase full-wave PWM driver for sensor less brushless DC (BLDC) motors. It controls rotation speed by changing the PWM duty cycle, based on the voltage of an analog control input.



Procedure For

manufacturing Brushless dc fan

(BLDC with sensor)

a) Inner housing body cover



b) Drilling shop/ Hole tapping machine



c) Powder coating machine



d) Heating oven(300 degree Celsius)



e) Press section



(In stator press under the fan body)



f) High voltage testing room (winding test)



g) Assembly section



h) ELECTRICAL testing room (with the help of voltage control

rectifier machine)



i) Dust cover section



j) Top bottom covering section



k) Guard and blade assembly section



Advance technology

Microcontroller for Variable Speed

BLDC Fan ControlSystem

Introduction



Portable, feature rich, high-performance and compact in size are typical trends of most electronic Products. The amount of heat generated by such electronic products, such as notebook Computers, is a growing problem. Use of cooling fan remains the most common and efficient Way of preventing electronics equipment from overheating. Microcontroller (MCU) based, intelligent, variable-speed control, brushless DC (BLDC) fans are Needed in order to fulfill the rapidly changing electronics products specification. Variable speed Control, low acoustic noise, reliability, long lifetime, low power consumption, protection features, Easy to maintain/upgrade and communication interface capability are the characteristics of flashMCU based BLDC.This article describes variable speed control algorithms of BLDC fan, which include methods for Acoustic noise reduction, power consumption consideration, locks detection and automatic restart, Thermal shunt down and communication interface

Different between DC Fan and BLDC fan



The physical appearance of conventional and BLDC fans are basically the same. Both of these fans operate on the same principle to convert the electrical energy to the mechanical motion.The fan is rotated when a dc voltage is applied to its terminals. The speed of the fan depends on the applied voltage across the terminals. The significant difference between the conventional and BLDC fans is in their internalConstruction. Both fan systems require the commutation that allows the direction of current flowing through the fan windings to reverse every 180o of rotation.In the conventional DC fan system, the stator of the permanent magnet is composed of two or more permanent magnet pole pieces and the rotor is composed of windings that are connected toa mechanical brush (commutator). The opposite polarities of the energized winding and the stator magnet attract the rotor and the rotor will rotate until it is aligned with the stator. Just asthe rotor reaches alignment, the brushes move across the commutator contacts and energize the next winding. As a result the fan rotor is rotated continuously.The BLDC fan however is a rotating electric machine in which the stator is a classic two-phase stator and the rotor has surface-mounted permanent magnets. In this respect, the BLDC fan is equivalent to a reverse-conventional DC fan; the current polarity is altered by the electricalcommutator instead of mechanical brushes.Due to the polarity reversal performed by transistors / FETs switching in synchronization with the rotor position, a Hall Effect sensor is used to sense the actual rotor position.

Construction of BLDC Need for an Intelligent BLDC fan



The conventional DC fan has a higher inertia due to the bulky rotor coils, while the BLDC fan has a lighter rotor due to its permanent magnets. The BLDC fan has a higher efficiency as more energy can be transferred to the load because of the lighter rotor. The BLDC fan uses the electrical commutation and does not have some of the problems experienced by the conventional DC fan, such as mechanical wear of commutator brushes, sparking and electromagnetic interference (EMI) induced by its rotation.An intelligent variable speed control BLDC fan system is becoming widely used because it is can be easily reconfigured to meet the fast changing requirements of modern electronic products, and includes enhanced features such as lock detection, automatic restart, and automatic thermal shunt down.

Speed Control in BLDC Fan

There are Fixed and Variable speed control BLDC fan.

1. Fixed Speed Control in BLDC fan



Hall-effect sensor with External or Built-in Driver is used in fixed speed control fan;

a) Three-pin Hall sensor with external driverIn this method, the single output latching Hall-effect sensor with external transistors / FETs is used. The sensor is commonly used in the BLDC fan because it senses both positive and negative magnetic fields of the BLDC fan for electrical commutation. The sensor includes an on chip Hall voltage generator for magnetic sensing, a comparator that amplifies the Hall voltageand a Schmitt trigger to provide switching hysteresis for noise rejection, and open-collector output. The sensor detects the polarity of the magnetic field generated by the permanent magnets on the rotor and provides information about the position of the rotor. This information is using to trigger the external transistors / FETs ON / OFF. As the transistors are operated the BLDC fan will rotate continuously and the speed depends on the supplied voltage.

b) Hall sensor with built-in drivers

This type of the implementation is the enhancement version of the three-pin Hall

sensor with external drive. The Hall sensor not only includes on-chip Hall amplify

circuitry as three-pin Hall sensor, but also two complementary outputs for two-

phase BLDC fan’s coil driving and some additional features such as auto lock shutdown and auto restart.

Many BLDC fan manufacturer use this type of implementation. The advantage of this implementation is more PCB board space is available for additional external components and the fan will be more reliable due to built-in basic protection features included on chip.

The disadvantage of this type of implementation is its drive capability. Due to the limited package spacing, the output drive capability will be limited to use of the smaller or lower rating BLDC fans. Typically the maximum output current should be limited to 20mA.



2. Variable Speed Control in BLDC fanThere are External and Internal approaches for variable speed control in BLDC fan; The external approach is connecting one external transistor / FET in series of the BLDC fan (high side / low side) to control the supply voltage across the fan by (c) linear regulator, (d) DCDC regulator or (e) pulse-width modulation (PWM) driving method. The speed of the BLDC fanis direct proportion to the supply voltage.The internal approach is using the build-in internal transistors / FETs inside the BLDC fan. Change the speed by (f) ASIC solution or (g) MCU solution

a) Linear Regulation driving method in external approachThe speed of the DC or BLDC fan can be changed by the applied voltage across the fan. The DC voltage across the fan is adjusted by using a traditional linear regulator. Figure 4a and 4b shows the low-side and high-side configurations. The major problem in this method is the heat dissipation of the passive component and the narrower controllable speed range.When the fan is operating in the zero or full speed, the passive component is either fully off in zero speed or fully on in full speed. So under this condition, all the power is transferred to the BLDC fan. And it implies no power dissipation in the passive component. But when the BLDC fan is not in zero or full speed, part of the power will be dissipated in the passive component. Sothe efficiency in the is method is questionable.

b) DC-DC Regulation driving method in external approachDue to the drawback in the linear regulation method, some designers use DC-DC regulation instead. The main idea of this drive method is to use the switching mode power supply to change the supply voltage of the fan. In this method the head dissipation effect is eliminated but the efficiency is also needed to be considered.

Since it is impossible to reach 100% efficiency in DC-DC switching power supply, the overall efficiency of the fan will be reduced to around 5 – 25% loss in DC-DC switching mode regulation. But compare with the linear regulation, the overall efficiency is higher and it depends on the regulated voltage. Comparing to linear regulation method lower the regulated supply voltage will lower the power loss. The disadvantage in this method is the higher system cost, high frequency noise and circuit complexity.



c) PWM drive method in external approach

The PWM driving methods was introduced to overcome the efficiency problem in the linear and DC-DC regulations. The speed of the BLDC fan is controlled by the duty cycle of fixed PWM signal that applied to the external switching device (transistor / FET). The speed of the fan is direct proportional with duty cycle of the PWM. Increase the percentage in duty cycle of the PWM signal will increase the speed of the fan. But one important consideration in this method isthe choice of PWM frequency. Higher PWM frequency will cause the malfunction of the internal commutation circuit inside the fan. Lower PWM frequency will cause the fan oscillate. So the popular value of PWM frequency is the major consideration in this method. Typically the PWM frequency is around 30 - 150Hz to avoid the mentioned problems. Due to the PWM frequency is falling into the audible range of human ear, the acoustic noise will be occurred when the fan is running. As a result, some additional component needs to add to eliminate this effect.

Advantage of this method:-1) No heat dissipation.2) Low efficient problems in the linear regulation.3) Low cost.4) Improve the performance. 5) Protection features.

d) ASIC Solution

In ASIC solution, all features, speed control method and hardware configuration pin had been defined and fixed. The advantage of this method is easier to implement but the disadvantage is lack of flexibility. The ASIC semiconductor manufacturer to design the ASIC controller to fit for some particular fan control application with some pre-defined speed control algorithm and some feature for protection and other purposes. When ASIC



solution was introduced, most of the ASIC controller is to control the energizing off time to adjust the speed of BLDC fan.

Advantages of ASCI solution:-1) Easier to implement. 2) All the features are pre-defined.

Disadvantage:- ASIC solution is lack of flexibility

e) MCU Solution

Recently, the cost of microcontrollers has decreased, causing many BLDC fan manufacturers to start using microcontrollers in their products.There are many speed control algorithms that can be adopted in the MCU solution. The typical variable speed control methods are i) phase on/off time delay and ii) PWM control.The flexibility of the MCU allows many features to be easily implemented with changes of the firmware. Thus, in this paper we limit our discussion to the configuration of two types of closed loop speed control, their advantages and disadvantages and design / implementation consideration issues.

i. Phase on/off delay time control method in internal approachThe phase on/off delay time method in internal approach is to adjust the off time at phases witching. The rotation speed can be adjusted by the length of the off time. The off time is inversely proportional to the energy provided to the fan. That is, the longer the off time, the less energy is supplied to the stator coils, which results in a lower speed of the fan. The basic principle of this method is similar to the PWM method. Both



methods change the ratio of the on/off time to change the energy that is applied to the winding coil. But the accuracy, current ripple, noise level may vary between these two methods.

ii. PWM control method in internal approachDue to some drawbacks of the phase on/off delay time control method, the PWM control method can provide higher accuracy and lower acoustic noise level. The hardware configuration/connection of this control method is same as phase on/off delay time control method but the drive control mechanism is different. The speed is controlled by changing the duty cycle of the PWM, instead of changing the off-time period.In this method, the speed is controlled by the duty cycle of the PWM that drives two winding coils in the BLDC fan independently. The two winding coils are turned on alternately but the voltage of the coil is controlled by the duty cycle of the PWM drive signal. The PWM frequency is a major design consideration. The PWM frequency can be chosen to be between 18 kHz to 60KHz typically.

Conclusion

There are many different implementation methods for fan control from as simple as using a Hall sensor plus two transistors to drive the fixed speed BLDC fan. Various implementation methods from fixed speed to variable speed control, from external approach to internal approach havebeen described.



The intelligent BLDC fan can provide sophisticated speed control algorithms, high efficiency, low acoustic noise, low power consumption, low standby power consumption, and intelligent system protection features for both electrical and mechanical protection and interface communications.

ASIC and MCU internal approaches are becoming more popular solution for the intelligent variable speed BLDC fan control. The MCU solution has the advantage of flexibility. Many manufacturers have started to use MCUs in their products, particularly for customized fans.Therefore a low cost, low pin count, high precision built-in oscillator (e.g. ICS), high resolution ADC and high resolution PWM modulator / generator MCU is suitable for future BLDC fan products. The Rescale MC9S08QD4 is an example of an MCU that meets these requirements.It is a low cost 8-bit, 8-pin count MCU and it also includes a +/-2% built-in oscillator, 10-bit ADC module, and two 16-bit timer / PWM modulators. All of these features are well suited for BLDC fan applications.


Documents

Railway Carriage BLDC fan