WO2016088140A2

WO2016088140A2 - Fan motor and method for regulating speed of the same

Info

Publication number: WO2016088140A2
Application number: PCT/IN2015/050184
Authority: WO
Inventors: Prathamesh Bhagawat HAJARE; Azad Habib Ahmed CHOWDHARY; Om Prakash Ramchandra VERMA
Original assignee: Ram Ratna Electricals Ltd
Priority date: 2014-12-03
Filing date: 2015-12-02
Publication date: 2016-06-09
Also published as: WO2016088140A3

Abstract

In an implementation, the present specification provides a DC operated fan motor and a speed regulator system having: an H-bridge with four power transistors controlled with PWM signals and variable frequency commutation provided on each of the two diagonal pairs of the H-bridge power transistors; a DC voltage in the range 24 to 350 V DC derived from a main power supply; a micro controller based circuit to generate the PWM signals and the variable frequency commutation provided to the H-bridge power transistors to achieve a specified rotation speed of the fan motor; at least four drivers to provide the pulse width modulation signals to the H-bridge; and a circuit for monitoring a start sequence of the fan motor, the circuit causing the fan motor to shut down in case of a mechanical failure of a rotor of the fan motor.

Description

FAN MOTOR AND METHOD FOR REGULATING SPEED OF THE SAME

TECHNICAL FIELD

[0001] The present subject matter relates, in general, to motors used in fans and, in particular, to a DC brushiess fan motor and a method for regulating speed of the motor.

BACKGROUND

[0002] A direct current (DC) motor works on the principal that a current carrying conductor placed in a magnetic field experiences a torque and is caused to rotate. Reversing the direction of current in the conductor reverses the direction of rotation. Apart from AC single phase induction motors with split capacitor winding, DC motors with commutators and brushes capable of commutatmg the coil current and capable of running by using a direct current source are commonly used to operate fans. A DC motors with brushes requires frequent replacement of the motor brushes which suffer wear and tear caused by reverse electromagnetic force (emf) generated in the motor by reversing of the direction of current as the motor rotates. This brush deterioration causes the motor to fail over a period of time.

SUMMARY

[0003] This summary is provided to introduce concepts related to a DC brushiess fan motor and a method for regulating speed of the motor, and the concepts are further described below in the detailed description. This summary is neither intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter. [0004] In an implementation, a fan motor comprises: a circular stator assembly with a plurality of slots to hold a plurality of electrical windings interconnected to form one single electrical winding, a stator magnetic flux being generated when electrical current is passed through the electrical windings; a circular rotor assembly encircling the stator assembly, the rotor assembly comprising a plurality of permanent magnetic poles for generating a rotor magnetic flux, the permanent magnetic poles being fitted along an inside periphery of the circular rotor assembly facing the electrical windings of the stator assembly; and at least one sensor coupled with the stator assembly to sense an alignment of the stator and rotor magnetic fluxes, the sensor being adapted to provide a pulsing electrical signal to be used to regulate speed of the fan upon connection with a regulator circuit, a number of pulses provided by the sensor being equal to the number of rotor magnetic poles. A plurality of fan blades can be mounted to an outer periphery of the rotor.

[0005] In an implementation, the number of slots of the stator assembly range is between 16 and 24; and a number of permanent magnetic poles of the rotor is equal to the number of stator slots. Also, in an implementation the stator and rotor positions are exchanged, with the stator on the outside and rotor on the inside. The fan motor has an improved efficiency when compared to an AC fan motor.

[0006] in another implementation a fan motor speed regulator system is provided. The fan motor speed regulation system comprises: an H-bridge with four power transistors controlled with pulse width modulation signals and variable frequency commutation provided on each of the two diagonal pairs of the H-bridge power transistors; a DC voltage derived from a mam power supply through a step down and rectification process; an electronic micro controller based circuit to generate the pulse width modulation signals and the variable frequency commutation of the two diagonal pairs of the H-bridge power transistors, the micro controller based circuit controlling the four power transistors in the H-bridge to achieve a desired rotation speed of the fan motor; at least four drivers to connect the pulse width modulation signals generated by the electronic micro controller to the four power transistors in the H-bridge; and a circuit for monitoring a start sequence of the fan motor, the circuit causing the fan motor to shut down in case of a mechanical failure of a rotor of the fan motor. In an implementation, the DC voltage lies in the range of 24 to 350 Volts.

[0007] In an implementation, a method for controlling a speed regulator of a fan motor comprising a rotor, the movement of the rotor being controlled by an H-bridge circuit comprising four power transistors, is provided. : On a start command the appropriate diagonal pair transistors of the H- Bridge is switched ON for a brief period ranging from 2 to 6 seconds causing enough energy to flow and enable the initial movement to the Rotor. A sensor detects the movement of the rotor as a feedback signal and in case there is no movement detected on applying initial power via H-bridge , a lapse time of 2 to 6 seconds is applied for bringing the H-Bridge to a full off condition. After the lapse time, the H-Bridge is switched on once again and signal of the sensor is checked. If there is no movement detected, the lapse time of 2 to 10 seconds is again applied and this cycle is repeated till the movement on the Rotor is detected. ON repeated failed attempts spread over 6- 10 restart attempts the regulator is shut down with an error indications alarm. After the start command, and on detecting the direction of rotation and speed of the rotor movement through the feedback signal from the sensor, the feedback signal is used for controlling a set of four pulse width modulation signals to be applied to the H-bridge diagonal pair transistor gates and the commutation frequency to switch to the other diagonal pair of the H-bridge. In an implementation the method also comprises detecting a mechanical failure of the rotor and a over-current through an over-current sensor; and progressively shutting down the pulse width modulation signals by causing the fan motor to trip. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0009] Figure 1 shows a diagram of a fan motor stator and rotor assembly, in accordance with an embodiment of the present subject matter;

[0010] Figure 2 is a block diagram showing the power and speed regulation controls of the fan motor assembly, in accordance with an embodiment of the present subject matter;

[0011] Figure 3a, 3b, and 3c show the H-bridge circuit schematic and the scheme of pulse width modulation (PWM) based commutation control of H-bridge circuit for regulating the fan at start and run conditions with feedback speed regulation, in accordance with an embodiment of the present subject matter;

[0012] Figure 4 shows the gate drive signal positioning with respect to the commutation of the H-bridge and the stator coil voltage waveform and an implementation of protection of the fan motor from malfunction by current monitoring at start up as well during speed regulated running conditions, in accordance with an embodiment of the present subject matter;

[0013] Figure 5 shows a method to regulate the H-bridge from a start initiation to a speed back regulation mode through speed sensing and overload protection, in accordance with an embodiment of the present subject matter; and

[0014] Figure 6 illustrates a table comparing operation parameters of the fan motor assembly of the present specification to a conventional AC fan, in accordance with an embodiment of the present subject matter. DETAILED DESCRIPTION

[0015] Tins description deals with subject matter related to the use of a DC hrushJess motor that works by using electronic commutation principles. Such a fan motor comprises a rotor having permanent magnets and a stator having windings through which electrical current, controllable by electronic switches, flows. In order to determine a direction of current flow to cause the rotor to rotate in a desired direction and the point in time when the electronic switches should be commutated, it is essential to know the position of a rotor magnet with respect to a stator winding, or the flux alignment between the two. [0016] AC fans with a primary running winding and a second start-and-run winding with a series capacitor have been used for a long time. The second start-and- run winding is able to create a second coil current with a phase lead over the first coil current thus providing a simple method to generate two phase control to start and run the fan motor. This method makes the traditional AC fan motor a single phase AC motor. The fan speed is regulated by using a series resistance with the fan coils as implemented in a standard speed regulator or using a TRIAC known in art (or alternatively back to back SCRs known in art ) with a suitable control circuit to regulate the AC voltage applied to the fan so that the fan speed is dependent on the AC voltage applied after the regulator. A second type of fan motor that is used less frequently uses 3 phase BLDC motors ( Brushless DC motors ) with suitable PWM ( Pulse width Modulation) regulators in tandem with 3 individual half H-bridges with each half bridge having two transistor switches and thus forming a 6 transistor switch and effectively a three phase bridge and the control scheme involves producing a three phase PWM based inverter that powers the BLDC motor that has three windings and three magnetic field sensors to provide electronic signal assist for half bridge commutation. While these fan motors and fan control schemes have been used, the former using voltage based dual winding fans suffer from poor efficiency by^¬ way of watts per cubic meter air flow due to the use of dual coils of which the second coil that has the capacitor does not provide any useful torque and the latter scheme with three phase BLDC motors is very expensive due to the construction of BLDC motors with rare earth permanent magnets and the exhaustive controls through a 6 transistor three phase bridge to provide three phase inverter power to run the BLDC motor.

[0017] The present subject matter deals with a scheme that uses a single winding fan motor with ferrite based permanent magnets and powered with a H-bndge containing four transistor switches and a single sensor to aid commutation of the H- bndge diagonal pair transistor switches.

[0018] A suitable method of control to start and run the fan motor with closed loop speed regulation for the single magnetic field sensor is also part of the subject matter described herein.

[0019] In an implementation the present specification provides a fan motor having a single sensor for sensing the magnetic flux alignment between the rotor and the stator magnetic poles. The rotor comprises a MS ring mounted along an external surface for supporting a magnetic ring comprising permanent magnets equally distributed along the ring's circumference and facing the stator poles. Also, in an implementation, the stator comprises at least 16 poles created by single windings provided in equidistant slots made along an outer periphery of the stator facing the rotor magnets.

[0020] The operation of the fan motor in accordance with an implementation is controlled by a microcontroller or any other control circuit known in art. The fan motor of the present specification can be switched ON or OFF at any time, notwithstanding the position of the rotor and stator poles. The present specification also provides a fan motor which enables the fan to start from zero speed without a jerk. The microcontroller enables the fan motor to be operated smoothly and noiselessly at variable speeds under closed loop speed regulation. [0021] In an implementation the fan motor of the present specification operates on 24 to 350 V DC input voltage which is derived from a 230 v AC mains supply. The control regulator used with this implementation enables smooth start from zero speed and also monitors the presence of any unwanted restraining torque that could be the result of mechanical jamming of the rotor and the stator, and shut down the fan before any failure can happen to the electrical stator winding.

[0022] Figure 1 shows a stator and rotor diagram of a fan motor assembly, in accordance with an embodiment of the present subject matter. In an implementation, the present subject matter provides a DC brushless motor 100 comprising a rotor assembly 110 encircling a stator assembly 101. An outside periphery of the rotor assembly 110 is fitted with fan blades (not shown n Fig. 1). In an implementation, the stator assembly 101 is laminated.

[0023] The stator assembly 101 comprises a circular stator having a plurality of teeth 102 and slots 103 made in an outer peripheiy. In one implementation, the number of slots 103 in the outer periphery of the stator range from 16 to 24. In an implementation, as shown in Fig. 1 , stator assembly 101 comprises 16 teeth 102 and 16 slots 103. Each slot 103 occupies a portion of the 360 degrees angular circumference of the stator. In an implementation as shown in Figure 1 , each slot 103 occupies an angle 104 equal to 360/ 16 degrees measured from a concentric center 115 of the rotor and stator assemblies (110, 101 ). In other implementation, the angular width of each slot may be obtained by dividing 360 by the number of teeth or slots of the stator assembly. A uniform air gap 1 16 is provided between the stator assembly 101 and the rotor assembly 1 10. This gap has the magnetic fields set up by the permanent magnets in the rotor. [0024] Each stator slot comprises an electrical winding for carrying electrical current when connected to a electrical power source. In an implementation as shown in Fig. 1, each slot 103 comprises at least two legs of an electrical winding. In an implementation all the electric windings in the stator slots are interconnected to form a single electric winding. As shown in Fig. 1 electric current enters the stator windings at a point 105 and travels through a first leg 105a and a second leg 105b of a stator winding to a second leg 106b and then a first leg 106a of a second stator winding, and in this manner traverses all the legs of all the stator windings before exiting at an end point 107 of the stator windings.

[0025] In an implementation, the rotor assembly 110 comprises a circular rotor ring encircling the stator assembly; the circular rotor ring having an inner periphery facing the electric windings of the stator assembly 101, and an outer periphery facing away from the stator assembly 101 and fitted with fan blades (not shown in Fig. 1). In an implementation, as shown in Fig. 1, the rotor ring is an MS circular frame 111 which holds a plurality of permanent magnets along the inner periphery facing the stator assembly 101 and separated from each other in uniform machined recesses 114 are made in the inner periphery of the MS circular frame 111 for holding the permanent magnets. In an implementation, as shown in Fig. 1, 8 pairs of permanent magnets comprising north and south pole pairs are fitted along the inner periphery of the MS circular frame 111. A north pole 112 and corresponding south pole 113 of a pair of permanent magnets are placed in adjacent positions as shown in Figure 1, and this scheme is repeated along the inner periphery of the rotor. In one implementation the permanent magnets are ferrite magnets with field strength between 1400 and 1500 gauss.

[0026] Current flowing through the windings of the stator assembly 101 creates an inductive magnetic field. A magnetic sensor 108 is provided for sensing the alternating inductive magnetic field flux when the rotor that has alternating north (N) and south (S) poles rotates with respect to the stator. The sensor 108 senses the permanent magnet field strength and provides a HIGH (5V) signal when sensing the north pole flux and a LOW (0V) signal when sensing a south pole flux. Thus the sensor 108 electrical output is a set of pulses that has a period equal to the time taken for the alignment to happen with respect to the north and south poles on the rotor, and is thus indicative of the speed of the rotor. The electrical output of the sensor 108 is used to commutate the current in the stator winding. This commutation is enabled by a microcontroller driving a set of transistors in a H-bridge (not shown in Fig. 1), and causes current to flow in the windings of the stator assembly 101 in a direction such that the inductive magnetic field of the stator 101 repels the poles of the rotor assembly 1 10 causing the rotor assembly 110 to rotate in a desired direction. The microcontroller changes a direction of current flowing through windings of the stator assembly 101 based on a continuous feedback of the rotor and stator flux alignments received from the sensor 108 in order that the rotor assembly 110 rotates continuously. The mechanism of driving the H-bridge transistors from the microcontroller using the electrical signal output from the sensors will be fully described further in this document.

[0027] In an implementation the current supplied to the stator windings via an H bridge circuit. Pulse width modulation (PWM) technique is used to control switching of the H bridge circuit to generate a voltage in every commutation half cycle. The H bridge circuit control is described with reference to Figure 2. Figure~3a, 3b, and 3c provide the circuit details of the H-bridge and the PWM control at start and speed regulated closed loop operation of the fan motor.

[0028] Figure 2 is a block diagram showing the power regulation controls of the fan motor, in accordance with an embodiment of the present subject matter. In an implementation the fan is operated by using the main electrical supply line supplying a voltage of 110 to 230 V AC 201 which is converted to DC voltage lying in the range of 24 to 350 V depending upon a power (wattage) required to operate the fan and whether the switch mode regulator is operated in buck mode or boost mode. In an implementation, a switched mode regulator 203 is used in buck mode to convert 230V AC input 201 to a DC output voltage 204 ranging between 24 to 300 V DC which is fed to a synchronous inverter before being fed to stator windings 212 of the fan motor. In another implementation the switched mode regulator 203 is operated in boost mode to derive a DC voltage between 300 and 350 V DC and fed to the synchronous inverter. The selection of the buck or the boost mode in the switched mode regulator is made depending on the AC tine voltage used that could range from 1 10 V AC to 220 V AC. The mode selection is so made to ensure that the required DC voltage range of 24 to 350 V DC is achieved from the available line AC voltage.

[0029] A current sensor 217 monitors the current from the H-bridge to the fan motor stator coil and helps shut down of the H-bridge when an over-current is sensed.

[0030] In an implementation the synchronous inverter is an H bridge circuit 210 which is controlled by a microcontroller 220. The H bridge circuit 210 having 4 transistors (not shown in Fig. 2) works as a synchronous inverter to provide a variable frequency AC output PWM square wave 211 that is generated by controlling the H- bridge drive transistors by using pulse width modulation (PWM). The PWM controlled H-bridge circuit is described with reference to Figures 3a, 3b, and 3c.

[0031] Four gate control signals are required for controlling the respective gates of the four transistors of the H-bridge circuit 210. In an implementation, a drive circuit gate amplifier 215 provides gate control signals 215 a,b,c,d for controlling the H-bridge circuit 210. In one implementation, the drive circuit gate amplifier 215 includes at least a set of four drivers as a composite module that forms a known method for gating H-bridge transistors. The set off four drivers form a quad-gate drive level shifter known in the art for gating H-bridge transistors. The drive circuit gate amplifier 215, in turn is controlled by the microcontroller 220. In an implementation the microcontroller 220 is powered by the 24 to 350 V DC voltage output 204 after step down and regulation via a regulator control power supply circuit 225 that reduces the voltage to 3.5 V to 5 V DC as required by the microcontroller 220. [0032] in an implementation a user may control a speed of rotation of the fan rotor via a fan speed regulator (not shown in Fig. 2). The microcontroller 220 receives the user speed input 206 through the fan speed regulator. The microcontroller 220 also receives an input 216 from a sensor fitted in the fan motor for measuring rotor and stator flux alignments. The microcontroller 220 generates a switching control signal based on the user speed input 206 and the sensor input 216 which is fed to the driver circuit gate amplifier 215 for amplification and is then supplied to the H-bridge circuit 210 for powering the transistors of the H-bridge circuit 210. The output of the H-bridge circuit which is the variable frequency signal 211 is applied to the stator windings in order to achieve a desired speed of rotation of the fan rotor.

[0033] Figure 3a illustrates a schematic showing a circuit for controlling the H- bridge, according to an embodiment of the present specification. In one implementation, a switched mode regulator 303 steps down line voltage 301 of 230 V AC. The switched mode regulator 303 has features as known in the art with regulation for any line voltage between 100 to 220 v and in-built short circuit protection. The output DC voltage 305 of the switched mode regulator 303 in the implementation is 36 V DC and can be in any range between 24 to 350 V DC, depending on the wattage rating of the fan to be used with the H-bridge. The DC voltage serves as the DC power source to the H-bridge 306 that comprises two diagonal pair of MOSFETs ( Metal Oxide Semiconductor Field Effect Transistors ) 310, 31 1 , 312, and 313, with each diagonal pair containing two transistors. In one implementation the MOSFET pair comprising 310 and 311 are one diagonal pair and 312 and 313 are the other diagonal pair. These MOSFETs have gates 310a, 31 1 a, 312a, and 313a respectively using which the MOSFETs can be turned on to conduct electric current. The H-bridge output 316 is connected to the stator winding 315 of the fan motor. A current sensor 317 is used to detect any high current beyond the threshold flowing through the stator winding 315 due to an over load and conditions of mechanical jam of the rotor of the fan motor, in another implementation, the current sensor 317 can also be provided in the switched mode regulator 303 itself, instead of on the H-bndge return line.

[0034] While the implementation in Figure 3a shows use of MOSFETs to form the switching diagonal pair transistors, other implementations can use IGBTs (Insulated Gate Bipolar Transistors) or any other gate or base controlled transistor device or monolithic H-bridges integrated into a package and normally referred to in the art as Intelligent Power modules that can carry the rated current and work on the DC voltage applied to the H-bridge . [0035] Figure 3b illustrates waveforms showing the manner in which the MOSFET gates are controlled with PWM signals during the start of the fan motor. At the time of starting the motor marked as 'START' in Figure 3b, when the rotor is stationary, the gates 310a and 31 1a of one diagonal pair of MOSFETs are powered pushing a DC current of low value into the stator winding 315. The current is held low by using a minimal P WM 320 timing comprising of a ON time and a period. The ON time 321 is held between 10 to 15 % of the complete PWM period 323 as the minimal ON time. The OFF time 322 is the remaining part of the PWM period. The motor rotor movement response in the desired direction which is now fixed because winding current is in one selected direction as decided by the first diagonal pair transistors 310 and 31 1. The starting diagonal pair is kept gated with this PWM signal for a period of 2 - 6 sec as shown by 324 and switched OFF if no response from the sensor 108 is seen. Positive response is indicated by a LOW to HIGH or a HIGH to LOW⁷ transition of the signal 216a. This is repeated again after about 2 to 6 seconds for a re-start. This process is repeated till the fan motor is started. In cases of mechanical jamming of the rotor, and other similar instances, the fan motor may not start. When a sensor response displaying such instances is seen, the signal response would be a LOW to HIGH or a HIGH to low transition of the sensor signal indicating that the moving rotor is causing the change in the poles seen by the sensor on the fixed stator.

[0036] Once the response is seen by way of a LOW to HIGH or HIGH to LOW⁷ transition of the sensor 108 output, after a fixed delay 326, the gates of the complementary diagonal pair of MOSFETs are powered with a signal similar to the PWM 320. The further tracking of the sensor movement by way of a s witching from HIGH to LOW provides the point 327 to switch back the commutation of the diagonal pair 310 and 311 and the pair 312 and 313 is switched off. This is illustrated by the commutation waveform sho wn in Figure 3 b.

[0037] Figure 3c illustrates the PWM control once motion of the fan motor rotor is detected from the sensor. Once the continuity of this sensor signal 216a by way of repeating LOW to HIGH and HIGH to LOW⁷ switching is observed the PWM signal delay 326 at the leading edge of the switching of sensor signal 216a is adjusted to between 15 % to 25 % of the sensor half period signal time 328 and a tail time frame 329 created so that the diagonal pair in conduction is switched OFF prior to the sensor switching with a time period that is also 15 % to 25 % of the commutation period 328. The commutation with this continuous sensor signal monitoring is shown by the 'START-INITIATED' waveform in Figure 3b. Once the START INITIATED phase is passed, the PWM ON time 321 is increased progressively thereby increasing the current in the stator coil and the fan motor gains speed with this increased coil current. The sensor signal 216a now shows increasing speed by way of decreasing period 328.

[0038] The time period over which one cycle for the stator current control is the commutation period containing two half-periods 328. The PWM ON time 321 is now progressively increased keeping the PWM period constant. In one implementation this period is kept at 50 micro sec corresponding to a frequency of 25 Khz. This PWM frequency in an implementation can be between 20 to 30 Khz, As the PWM increase and the motor speed reaches the desired speed the PWM ON time is pet increasing and at higher speeds the ON time nears the 100 % mark of the PWM period 323.

[0039] Figure 3c illustrates current waveforms used for controlling the MOSFET gates with PWM signals as the PWM ON time approaches 100 %. The fan motor current increases in this phase and is dependent on the load due to the air blow created. The first waveform in Figure 3 c shows gating signals for LOW FAN SPEED and the second waveform shows the gating signals towards maximum speed. Beyond a speed that is more than about 60 to 75% range of the maximum speed the PWM signal is 100 % ON time 321 and so the PWM signal degenerates to a long pulse for each of the commutation half cycles with a lead and tail delay of 326 and 329 respectively. The sensor signal 216a which is also indicative of the fan speed is continuously used to provide commutation as well as move the PWM ON time from 100 % to lower values if a reduction in current in the fan stator coil is needed for speed regulation.

[0040] Figure 4 shows current and voltage waveforms under regulation from the H-bridge as applied to the stator coil. The commutation half cycles as detected from the sensor signal 216a provide the gate pulse to H-bridge at a typical speed regulation scenario with the PWM signal 342 applying the bridge voltage to the stator coil in each commutation half cycle. Since the rotor is under movement the stator develops a back EMF voltage over which the PWM H-bridge output voltage is applied. The back EMF voltage on the stator coil is shown as 340 and reverses direction as the coils pass under the moving north and south poles of the rotor. During the H-bridge turn on in each commutation half cycle the stator current increases depending on the inductance of the stator coil winding and the H-bridge voltage is greater than the back EMF 340. This increase is Smear since back EMF 340 tends to plateau out at higher voltages and the H-bridge PWM voltage is a constant. The current as sensed is compared to threshold in a suitable control circuit so that in case if the positive cycle current exceeds the setting 345a or the negative cycle current exceeds the threshold 345b, the H-bridge control PWM is disengaged during the remaining part of the commutation half cycle. The system thus would operate at a over-current limit set by the complementary thresholds 345a and 345b. [0041] Figure 5 shows a method of control and protection of the fan motor from possible malfunction during start up and during operation, in accordance with an embodiment of the present subject matter. In an implementation of the present specification, a sequence of checks and operational steps are maintained by a logic section of the control software in the microcontroller. [0042] The control method of the fan motor and the H-bridge is illustrated as a flow diagram 500 in Figure 5. At step 501 it is determined by a microcontroller if a start command has been initiated. At step 502 the specific diagonal pair of H-bridge transistor for the specific direction in which the fan motor is required to rotate is gated. The gating signal in step 502 is kept for a period of 1 to 2 sec and if a sensor response that monitors fan rotor rotation is not sensed, step 502 is halted and a first time out period of 2 to 6 seconds is initiated at step 503, after which step 502 is reinitiated. In case the sensor is not detected continuously for a number of time out periods that can vary from 5 to 10 counts of time out period of 2 to 6 seconds in the step 504, a trip is initiated and the fan control is locked out to protect the fan motor windings. If a sensor signal is detected after step 502, the control step moves to 505 where commutation of the H-bridge transistor pairs is initiated and PWM is kept at the minimal value. Next, control passes to step 505 where a comparison is made between user speed reference and sensor actual speed measurement and the PWM is progressively increased to 100 % if speed is not reached or is regulated downwards. This step 505 is the continuous running mode with speed regulation of the fan during which the monitoring of over current in the stator coil and appropriate reduction is PWM is initiated. During speed regulated running mode at step 505 if an over current is sensed at step 506, the PWM is tuned down at step 507 to reduce the applied voltage on the fan coil and speed regulation is compromised. If the over current sensing is continuous for a number of commutations half periods, the over current sense mode will push the control scheme PWM to lower and lower ON time and the PWM setting can go towards lower values wherein the torque is not sufficient to overcome the extraneous force that was causing the over current. Under this condition the sensor output at step 508 could disappear and the control method will this pass over to the initiating step 502 and held under repeated start attempts till a trip is initiated. This scheme thus provides a comprehensive of the stator coil for all malfunction of the fan motor mechanical assembly either in start or run mode.

[0043] The construction of the permanent magnet rotor and the H-bridge based DC voltage commutation of the stator current with no eddy current magnetic losses that is inherent in AC regulated fans leads to improved efficiency of this fan motor. Figure 6 illustrates Table 1 showing the improved efficiency of a fan motor of the present specification when compared to a AC regulated fan motor having a similar sweep. The wattage power per cubic unit of air blown is substantially higher for the fan detailed in this subject matter.

[0044] The present specification provides a DC brushless fan motor having a single sensor for sensing the flux alignments of rotor magnetic field. The operation of the fan motor is regulated by using a PWM controlled H-bridge causing a jerk free and noiseless operation even when the motor is starting from zero speed. In various implementations, the fan motor is provided with protection against damage in cases of mechanical jamming of the rotor. Further, in various implementations, the fan motor provides a rotor speed of three hundred and sixty five rotations per minute and is compatible with standard fan speed regulators.

[0045] Although the subject matter has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present subject matter as defined.

Claims

I/We claim:

I A fan motor, comprising:

a circular stator assembly (101) with a plurality of slots (103) to hold a plurality of electrical windings interconnected to form one single electrical winding ( 105a , 105b ..106b) , a stator magnetic flux being generated when electrical current is passed through the electrical windings; a circular rotor assembly (110) encircling the stator assembly (101), the rotor assembly comprising a plurality of permanent magnetic poles (112) , (113) generating a rotor magnetic flux, the plurality permanent magnetic poles being fitted along an inside periphery of the circular rotor assembly facing the electrical windings of the stator assembly;

at least one sensor (108) coupled with the stator assembly (101) to sense an alignment of the rotor magnetic fluxes, the sensor providing a pulsing electrical signal to be used to regulate speed of the fan upon connection with a regulator circuit , a number of pulses provided by the sensor being equal to the number of rotor magnetic poles (112), (113); and

a plurality of fan blades mounted to an outer periphery of the rotor.

2. The fan motor as claimed in claim 1, wherein the number of slots of the stator assembly (101) range between 16 and 24.

3. The fan motor as claimed in claim 1, wherein a number of permanent magnetic poles of the rotor ( 112), (1 13) is equal to the number of stator slots.

4. The fan motor as claimed in claim 1 , wherein the stator and rotor positions are exchanged, with the stator on the outside and rotor on the inside.

5. The fan motor as claimed in claim 1, having an improved efficiency when compared to an AC fan motor.

6. A fan motor speed regulator system comprising: a H-bridge (300) with four power transistors (310), (311), (312), and (313) controlled with pulse width modulation signals (310a), (311 a), (312a), and (313a) and variable frequency commutation provided on each of the two diagonal pairs of the H-bridge power transistors (310), (311) and (312),(313) respectively;

a DC voltage (305) derived from a mam power supply through a step down and rectification process (303) ;

an electronic micro controller (220) based circuit to generate the pulse width modulation signals (215a), (215b), (215c), and (215d) and the variable frequency commutation of the two diagonal pairs of the H-bridge power transistors (310), (311) and (312),(313) respectively, the micro controller based circuit controlling the four power transistors in the H-bridge (300) to achi eve a desired rotation speed of the fan motor;

at least a set of four drivers (215) to connect the pulse width modulation signals (215a), (215b), (215c), and (215d) generated by the electronic micro controller to transitively drive the gates of the four power transistors in the H-bridge as gate signals; and

a circuit comprising of the user speed input module (206), sensor speed signal monitoring module (216) and current sensor module (217) for monitoring a start sequence of the fan motor, the circuit causing the fan motor to shut down in case of a mechanical failure of a rotor of the fan motor.

7. The fan motor speed regulator system of claim 6 wherein the DC voltage lies in the range of 24 to 350 Volts DC.

8. A method for controlling a speed regulator of a fan motor comprising a rotor, the movement of the rotor being controlled by an H-bridge circuit comprising four power transistors, the method comprising:

detecting rotor movement on a start command through module (501) and switching the H-bridge through a gating module (502);

detecting a time out period ranging from 2 to 10 seconds through a time out counter module (504);

stopping the rotor movement on detection of the first time out period via the H-bridge circuit if the time out period ranging from 2 to 10 seconds is detected; causing the H-bridge circuit to start the rotor movement after a first time out period if the time out period ranging from 2 to 10 seconds is not detected;

shutting down the regulator with a trip signal in case rotor movement is not detected on the start command after a second time out period when the first time out has repeatedly elapsed after the start command; and

detecting the direction of rotation and speed of the rotor movement for providing a feedback signal using module (508) used for controlling the pulse width modulation signal and the commutation frequency generated through regulation module (505);

9. The method as claimed in claim 8 further comprising:

detecting a mechanical failure of the rotor and a over-current through an over-current sensor connected to a module (506) ; and progressively shutting down the pulse width modulation signals using a down regulation module (507) by causing the fan motor to trip through the sensor response module (508) and time out counter module (504) .