Abstract:
The present invention relates to a method for detecting position of a BLDC (Brushless Direct Current) motor which is capable of decreasing position detecting errors by detecting accurately a crossing time point of a back electromotive force and reference potential by using. a phase voltage outputted from the BLDC motor regardless of an ON/OFF operation of a PWM (Pulse Width Modufation) signal inputted to the BLDC motor, accordingly the present invention can stably operate the BLDC motor, lower power consumption and noise of an equipment installed the BLDC motor stably operating.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a BLDC (Brushless Direct Current) motor, in particular to a method for detecting position of the BLDC motor which is capable of detecting position of a rotor of the BLDC motor when a phase voltage outputted from the BLDC motor is “0”. 
     2. Description of the Prior Art 
     FIG. 1 is a block diagram illustrating a construction of an apparatus for detecting position of a BLDC (Brushless Direct Current) motor according to the conventional technology. As depicted in FIG. 1, the apparatus comprises a position detecting pulse generation unit  11  outputting a position detecting pulse by being inputted a phase voltage generated when the BLDC motor operates and comparing it with a reference potential set in advance, a micro computer  12  controlling the BLDC motor in accordance with a position signal after recognizing an output of the position detecting pulse generation unit  11  as the position signal, its operation will now be described in detail with reference to FIG.  2 . 
     FIGS. 2A through 2C are wave form diagrams illustrating wave forms of the each output signal in FIG.  1 . 
     First, the BLDC motor controlled by a PWM (Pulse Width Modulation) signal generates a back electromotive force while operating. Herein, the phase voltage is equal to the back electromotive force of the BLDC motor  10  when the PWM signal applied to the BLDC motor  10  is in the ON state, the phase voltage is “0” when the PWM signal is in the OFF state and the phase voltage is generated as three phases and are separately inputted to the position detecting pulse generation unit  11 . The position detecting pulse generation unit  11  outputs the position detecting pulse by using the inputted three phases (Ref. FIG.  2 A). 
     The position detecting pulse generation unit  11  outputs the position detecting pulse to the micro computer  12  which is a “high potential” when the phase voltage is bigger than a reference potential Vf, or is a “low potential” when the phase voltage is smaller than the reference potential Vf. 
     After that, the micro computer  12  detects a time point when the position detecting pulse is became the “high potential” initially by an interrupt signal, determines the time point as a position detecting time point of the BLDC motor  10 , and operates the BLDC motor by controlling a driving unit (not shown) in accordance with the position detecting time point. 
     However, as depicted in FIG. 2C, in the apparatus for detecting position of the BLDC motor according to the conventional technology, when the phase voltage outputted from the motor is “0”, the position detecting pulse generation unit  11  can not detecting the time point when the back electromotive force is bigger than the reference potential, accordingly a position detecting error Δt occurs. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a method for detecting position of a BLDC (Brushless Direct Current) motor which is capable of detecting accurately a crossing time point of a back electromotive force and a reference potential by using a phase voltage outputted from the BLDC motor regardless of ON/OFF operation of a PWM (Pulse Width Modulation) signal inputted to the BLDC motor. 
     In order to achieve the object, the method of the present invention comprises a storing step storing the phase voltage outputted from the motor as a previous phase voltage with a detecting time detecting it when the phase voltage outputted from the motor is smaller than a reference potential set in advance, and a determining step determining a position detecting time point by using the stored detecting time after storing the phase voltage outputted from the motor as the present voltage when the phase voltage outputted from the motor is bigger than the reference potential set in advance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating a construction of an apparatus for detecting position of a BLDC motor according to the conventional technology. 
     FIGS. 2A through 2C are wave form diagrams illustrating wave forms of the each out signal. 
     FIG. 3 is a wave form diagram illustrating a method for detecting position of the BLDC motor according to the conventional technology. 
     FIG. 4 is a flow chart illustrating a method for detecting position of the BLDC motor according to the embodiment of the present invention. 
     FIG. 5 is a block diagram illustrating an apparatus for detecting position of the BLDC motor in FIG.  4 . 
     FIGS. 6A and 6B are wave form diagrams illustrating wave forms of input signals of a microcomputer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 4 is a flow chart illustrating a method for detecting position of a BLDC (Brushless Direct Current) motor according to the embodiment of the present invention. The method will now be described in detail. 
     First, when a phase voltage outputted from the motor is inputted S 1 , the phase voltage is compared with a reference potential Vf S 2 . 
     In the comparing step S 2 , when the phase voltage is smaller than the reference potential Vf, the phase voltage is stored as a previous voltage V 1  with a detecting time T 1  S 10 , and an after operation is performed S 9 . 
     In the comparing step S 2 , when the inputted phase voltage is bigger than the reference potential Vf, the inputted phase voltage is stored as a present phase voltage V 2  S 3 , and the difference between the reference potential Vf and the previous phase voltage V 1  is calculated S 4 . 
     After that, the difference between the stored present phase voltage V 2  and previous phase voltage V 1  is calculated S 5 . 
     The remainder of the S 5  is divided by the remainder of the S 4  S 6 . 
     After that, the value of the S 6  is multiplied by a PWM (Pulse Width Modulation) cycle of the phase voltage T S 7 . 
     A position detecting time point Tb is determined by adding the value of the S 7  to the detecting time T 1  detecting the inputted phase voltage, and the after operation is performed S 9 . 
     FIG. 5 is a block diagram illustrating an apparatus for detecting position of the BLDC motor in FIG. 4, its operation will now be described with reference to FIG.  6 . 
     FIGS. 6A and 6B are wave form diagrams illustrating wave forms of input signals of a microcomputer. 
     As depicted in FIG. 5, the microcomputer  51  comprised in FIG. 5 controls the BLDC motor  50  by detecting a position of a rotor of the BLDC motor  50  by comparing the phase voltage generated while the BLDC motor operates with the reference potential Vf set in advance, and its operation will now be described. 
     First, the BLDC motor  50  controlled in accordance with the PWM (Pulse width Modulation) signal generates a back electromotive force while operating. Herein, when the PWM signal applied to the BLDC motor is in the ON state, the back electromotive force of the BLDC motor  50  is equal to the phase voltage, when the PWM signal is in the OFF state, the phase voltage is “0” and is generated as three phases, and the three phases are separately inputted to the microcomputer (Ref. FIG.  6 A). 
     The microcomputer  51  adopts below Equation 1, 2 in order to determine a position detecting time point (Tb) after detecting position of the rotor of the BLDC motor  50  (Ref. FIG.  6 B). 
     
       
           T :( V   2 − V   1 )=( T b− T   1 ):( V f− V   1 )  [Equation 1] 
       
     
     
       
         
           
             
               
                 
                   Tb 
                   = 
                   
                     T1 
                     + 
                     
                       
                         
                           Vf 
                           - 
                           V1 
                         
                         
                           V2 
                           - 
                           V1 
                         
                       
                       × 
                       T 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
                 
         
             
         
      
     
     Herein, Tb is the position detecting time point, T 1  is the detecting time, Vf is the reference potential, V 1  is the previous phase voltage, V 2  is the present phase voltage, T is the cycle of the phase voltage outputted from the BLDC motor, the equations will now be described in detail. 
     The microcomputer  51  is inputted the phase voltage outputted from the BLDC motor  50  and converts it into a digital signal through a digital converter (not shown). 
     When the phase voltage converted into the digital signal is smaller than the reference potential Vf, it is regarded as the previous phase voltage V 1  and is stored on a memory (not shown) with the detecting time T 1 . 
     In addition, the microcomputer  51  repeatedly stores the previous phase voltage V 1  and detecting time T 1  until the phase voltage outputted from the BLDC motor  50  is bigger than the reference potential Vf. Herein, when the phase voltage converted into the digital signal is bigger than the reference potential Vf for the first time, it is stored on the memory (not shown) as the present phase voltage V 2 . 
     After that, difference between the reference potential Vf and previous phase voltage V 1  is calculated, and difference between the present phase voltage V 2  and previous phase voltage V 1  is calculated. 
     The remainder between the reference potential Vf and previous phase voltage V 1  is divided by the remainder between the present phase voltage V 2  and previous phase voltage V 1 , and the value is multiplied by the cycle of the PWM of the phase voltage. 
     After that, the multiplied value is added to the detecting time T 1 , thus the added value is the position detecting time point Tb. 
     As described above, the method for detecting the position of the BLDC motor of the present invention is capable of detecting more accurately the position of the rotor of the BLDC motor by detecting the position detecting time point Tb by being directly inputted the phase voltage outputted from BLDC motor on the microcomputer. 
     In addition, the method is capable of operating stably the BLDC motor by decreasing position detecting errors in detecting the rotor of the BLDC motor by using the phase voltage outputted from the BLDC motor. 
     The present invention is capable of decreasing power consumption of an equipment installed the BLDC motor operating stably. 
     In addition, the present invention is capable of preventing noise of an equipment installed the BLDC motor operating stably.