FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A single phase Brushless Direct Current (BLDC) Motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr. Annie Besant Road, Worli, Mumbai -400 030, Maharashtra, India, an Indian Company


INVENTORS
Shenoy Purushotham Talachery and Nirody Jaishankar Sithanand of Crompton Greaves Global R&D Center (AMDTC), Kanjur Marg (East), Mumbai-400042, Maharashtra, India and Madhukar Bomall, SMQ No. 28/2, Tech Area, Air Force Station, Hakimpet, Secunderabad - 500001, Andhra Pradesh, India, all Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:


FIELD OF THE INVENTION
This invention relates to a single phase brushless direct current (BLDC) motor. This invention also relates to a method for optimally operating a single phase BLDC motor at its rated speed.
BACKGROUND OF INVENTION
A single phase BLDC motor comprises of a stator, a rotor and a hall sensor mounted in close proximity to the rotor and electrically connected to an input side of the control unit. The output side of the control unit is connected to stator windings. The hall sensor outputs hall signals to the control unit indicative of a magnetic pole position of the rotor. Based on the hall signals received from the hall sensor, the control unit alternatively excites the winding of the stator. Conventionally, a deviation in the order of even a few mechanical degrees in the position of the hall sensor results in a delay or advancement in the instance of generation of the hall signals. Consequently, the excitation of the stator windings is also delayed or advanced thereby affecting the speed of the motor being achieved. Therefore, the position of the hall sensor within the motor is of critical importance in a conventional single phase BLDC motor. Practically, during the assembly stage of the motor, a precise location of the hall sensor on the stator corresponding to the rated motor speed is determined by a trial and error method. In such a method, the hall sensor is first placed at an arbitrary position on the stator and a corresponding motor speed is checked. If the motor speed is not found to be equal to the rated motor speed, the hall sensor is deviated from its previous position and a corresponding motor speed is checked. Such a process is continued until the rated motor speed is achieved. The corresponding


position of the hall sensor is then locked. Such an iterative process of determining a location of the hall sensor corresponding to the rated motor speed is tedious, time consuming and requires skilled manpower. It is also important that the hall sensor remains fixed to its position at all times during transportation and operation of the motor. The above mentioned iterative process has to be repeated incase of even a minor deviation in the position of the hall sensor which will cause the rotor to rotate at a speed different than the rated motor speed. The rated motor speed generated out of such an iterative process also consumes more energy thereby increasing the operational cost of the motor.
OBJECTS OF INVENTION
An object of the invention is to provide a singly phase BLDC motor in which the position of the hall sensor on the stator is rendered Uncritical for achieving a rated motor speed.
Another object of the invention is provide a single phase BLDC motor in which the generated rated motor speed is also optimum speed which consumes less energy.
Another object of the invention is to provide a method for rendering the position of the hall sensor uncritical for achieving a rated motor speed.
Another object of the invention is to provide a method for operating a single phase BLDC motor in which the generated motor speed is also optimum speed which consumes less energy.

DETAILED DESCRIPTION OF THE INVENTION
In order to achieve the aforesaid and other objectives, according to the invention, a single phase BLDC motor is provided comprising of a control unit including an auxiliary controller electrically connected to a hall sensor at the input side thereof and to a main controller at the output side thereof. The hall sensor is mounted in the proximity of the rotor of the motor and the main controller is electrically connected to the stator windings of the motor. The auxiliary controller comprises of a time recording means for registering the outputting instance of each hall signal to the auxiliary controller from the hall sensor, a time differencing means for delaying or advancing the instance of outputting the hall signal from the auxiliary controller to the main controller for exciting the stator windings, a processor for calculating a time difference between two consecutive hall signals outputted from the hall sensor, deriving the speed of the motor based on the calculated time difference between two consecutive hall signals outputted from the hall sensor, comparing the derived motor speed with a rated motor speed, triggering the time differencing means based on the output of said comparison and outputting the delayed or advanced hall signal to the main controller and a memory means for storing the delaying or advancing time in outputting the hall signal from the auxiliary controller to the main controller wherein the stored delaying or advancing time corresponds to the rated motor speed.
In order to achieve the aforesaid and other objectives, according to the invention, a method for operating a single phase BLDC motor is provided comprising the steps of deriving a current motor speed based on the sensed time difference between the instance of outputting of two consecutive hall signals from the hall

sensor; comparing the derived motor speed with a rated motor speed to be achieved, iteratively delaying or advancing the instance of outputting the hall signals to a means for exciting the stator windings of the motor based on the comparison until said derived motor speed is equal to the rated motor speed; storing the advanced or delayed time in outputting the sensed hall signals corresponding to the rated motor speed and advancing or delaying the instance of outputting the hall signals to the means for exciting the stator windings as per the stored advancing or delaying time in a subsequent operation of the motor.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 illustrates a block diagram of single phase BLDC motor with a main controller and an auxiliary controller according to an embodiment of the invention.
Fig 1 illustrates a block diagram of a single phase BLDC motor 1 comprising of an auxiliary controller 2, a hall sensor 3 and a main controller 4. During the assembly stage of the motor, the auxiliary controller 2 is electrically connected to the hall sensor 3 on the input side and to the main controller 4 on the output side. The main controller 4 is further connected to stator windings of the motor 1 for electrically exciting it. The hall sensor 3 is mounted on the stator (not shown in fig) and outputs logic signals to the auxiliary controller 2 based on its position on the stator. The auxiliary controller 2 which is a pre-programmed microcontroller according to one embodiment of the invention comprises of a central processing unit 5, a non-volatile

memory 6 and two timers 7 & 8. The CPU 5 first calculates a time difference between two consecutive hall signals received from the hall sensor 3 using the first timer 7 and subsequently the motor speed based on the calculated time difference between two consecutive hail signals. The CPU 5 then compares the calculated motor speed with a rated motor speed to be achieved. If the calculated motor speed is not equal to the rated motor speed, the CPU 5 triggers the second timer 8 to generate a delay or advancement in the instance of outputting the hall signa.1 to the main controller 4. The CPU 5 then outputs the delayed or advanced hall signal to the main controller 4. The main controller 4 excites the stator windings of the motor 1 alternatively based on the logic level and the delayed or advanced hall signal received from the auxiliary controller 2. Excitation of the sfafor windings causes the motor 1 to rotate at a certain speed thereby triggering the hall sensor 3 to generate a hall signal. The above method is repeated iteratively without any shift in the position of the hall sensor until the derived motor speed is equal to the rated motor speed. Once the derived motor speed is equal to the rated motor speed, the corresponding delay or advancement in outputting the hall signal to the main controller 4 is saved in the non volatile memory 5. The position of the hall sensor is locked by means of screws thereafter. Henceforth, during the subsequent operation of the motor at the customer's end, the delay or advancement to be applied in outputting the hall signal from the auxiliary controller 2 to the main controller 4 is sourced from the non volatile memory thereby achieving a consistent rated motor speed during the operation of the motor 1.
According to the invention, the placement of the hall sensor on the stator is rendered uncritical thereby saving time and obviating the need of a skilled manpower during the assembly stage of the motor. The rated motor speed achieved in such a

motor is also optimum speed thereby consuming less power and reducing the operational costs of the motor.
The type of auxiliary controller and means within it performing various functions may vary. Although, a microcontroller with a memory and timer devices is depicted in the above described embodiment, there can be a controller, memory and time differencing means of different type and configuration.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the invention as defined.

We claim:
1. A single phase BLDC motor comprising a control including an auxiliary controller electrically connected to a hall sensor at the input side thereof and to a main controller at the output side thereof, the hall sensor being mounted in the proximity of the rotor of the motor, said main controller being electrically connected to the stator windings of said motor, said auxiliary controller comprising
• a time recording means for registering the outputting instance of each hall signal to the auxiliary controller from the hall sensor;
• a time differencing means for delaying or advancing the instance of outputting the hall signal from the auxiliary controller to the main controller for exciting the stator windings;
• a processor for calculating a time difference between two consecutive hall signals outputted from the hall sensor, deriving a speed of the motor based on the calculated time difference between two consecutive hall signals outputted from the hall sensor, comparing the derived motor speed with a rated motor speed, triggering the time differencing means based on the output of said comparison and outputting the delayed or advanced hall signal to the main controller;
• a memory means for storing the delaying or advancing time in outputting the hall signal from the auxilary controller to the main controller wherein said stored delaying or advancing time corresponds to the rated motor speed;

2. The BLDC motor as claimed in claim 1, wherein the time recording means and the time differencing means is a timer, memory means is a non-volatile memory, and the processor is a central processing unit (CPU).
3. A method for operating a single phase BLDC motor at the rated optimum speed, the method comprising

• deriving a current motor speed based on the time difference between the instance of outputting of two consecutive hall signals from the hall sensor;
• comparing the derived motor speed with a rated motor speed to be achieved;
• iteratively delaying or advancing the instance of inputting the hall signals to a means for exciting the stator windings of the motor based on said comparison until said derived motor speed is equal to the rated motor speed;
• storing the advanced or delayed time in inputting the hall signals corresponding to the rated motor speed to the said means;
• advancing or delaying the instance of inputting the hall signal to the said means as per the stored advancing or delaying time in a subsequent operation of the motor;
Dated this 23rd day of October 2008
(Prita Madan)
of Khaitan&Co
Agent for the Applicants