Patent Publication Number: US-2015061553-A1

Title: Apparatus and method for detecting back electro-motive force in sensorless motor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2013-0105612 filed on Sep. 3, 2013, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an apparatus and a method for detecting back electro-motive force in a sensorless motor. 
     2. Description of the Related Art 
     In general, in order to achieve miniaturization and cost reductions in motor control devices, a sensorless driving scheme is commonly being used so as to reduce the amount of required sensor components, such as a hall sensor and a current sensor. 
     Typically, in a motor operating in a sensorless driving fashion (sensorless motor), a back electro-motive force (EMF) voltage is used to detect a rotation rate of the motor. 
     However, such aback EMF voltage is proportional to the rotation rate in a motor, and thus has large variations, according to the rotation rate of the motor. 
     Therefore, in existing sensorless motors, motors are driven at a low speed during an initial driving period, and thus, a level of a back EMF voltage is too low to be accurately detected. 
     Patent Document 1 below relates to a circuit for compensating for detection in a motor at a low speed but does not disclose any feature to solve the problem of detecting a back EMF voltage during an initial driving period in a sensorless motor. 
     RELATED ART DOCUMENT 
     (Utility Model Document 1) Korean Utility Model Publication No. 1991-0019071 
     SUMMARY 
     An aspect of the present invention provides an apparatus and a method capable of accurately detecting back electro-motive force (EMF) in a sensorless motor using a back EMF voltage even during an initial driving period by way of performing an amplification mode in which a back electro-motive force (EMF) voltage is amplified during the initial driving period, and performing a bypass mode in which a back EMF voltage bypasses an amplification path during a normal mode after the initial driving period. 
     According to an aspect of the present invention, there is provided an apparatus for detecting a back EMF in a motor, the apparatus including: a mode selecting unit selecting between an amplification mode and a bypass mode when power is on; a back EMF amplifying unit amplifying a back EMF voltage from the motor during an initial driving time if the amplification mode is selected by the mode selecting unit, and allowing the back EMF voltage to bypass it after the initial driving period if the bypass mode is selected by the mode selecting unit; and a zero-crossing detecting unit detecting a zero-crossing of an output signal from the back EMF amplifying unit, wherein the back EMF amplifying unit amplifies the back EMF voltage to a level detectable by the zero-crossing unit or higher. 
     The back EMF amplifying unit may amplify the back EMF voltages in three phases input through first, second and third output terminals of a three-phase motor or allow them to bypass it. 
     The mode selecting unit may generate a mode selection signal including a first mode selection signal having a high level during the initial driving period and having a low level after the initial driving period, and a second mode selection signal inverted from the first mode selection signal. 
     According to another aspect of the present invention, there is provided an apparatus for detecting back electro-motive force (EMF) in a motor, including: a mode selecting unit providing a mode selection signal for selecting between an amplification mode and a bypass mode when power is on; a back electro-motive force (EMF) amplifying unit amplifying a back EMF voltage from the motor during an initial driving period, and allowing the back EMF voltage to bypass it after the initial driving period according to the mode selection signal; and a zero-crossing detecting unit detecting a zero-crossing of an output signal from the back EMF amplifying unit, wherein the back EMF amplifying unit amplifies the back EMF voltage to a level detectable by the zero-crossing unit or higher during the initial driving period with a gradually decreasing amplification gain. 
     The mode selection signal may include first and second mode selection signal, and the mode selecting unit may include: a mode-selection-signal generating unit generating the first mode selection signal having a high level during the initial driving period and having a low level after the initial driving period, and an inverter inverting the first mode selection signal to provide the second mode selection signal. 
     The mode-selection-signal generating unit may include a power-on-reset (POR) circuit unit generating a POR signal for resetting an internal register using the first mode selection signal when power is on. 
     According to another aspect of the present invention, there is provided an apparatus for detecting back electro-motive force (EMF) in a motor, the apparatus including: a mode selecting unit providing a mode selection signal including a first mode selection signal having a high level during an initial driving period and having a low level after the initial driving period, and a second mode selection signal inverted from the first mode selection signal; a back EMF amplifying unit amplifying a back EMF voltage from the motor during the initial driving period according to the first and second mode selection signals, and allowing the back EMF voltage to bypass it after the initial driving period according to the first and second mode selection signals; and a zero-crossing detecting unit detecting a zero-crossing of an output signal from the back EMF amplifying unit, wherein the mode selecting unit generates the first mode selection signal using a power-on-reset (POR) signal for resetting an internal register when power is on and wherein the back EMF amplifying unit amplifies the back EMF voltage to a level detectable by the zero-crossing unit or higher. 
     The back EMF amplifying unit may include: an amplification-path circuit unit completed during the initial driving period to amplify the back EMF voltage from the motor; and a bypass-path circuit unit completed after the initial driving period to allow the back EMF voltage from the motor to bypass the amplification-path circuit unit. 
     The amplification-path circuit unit may include at least one switch and an amplifier connected between an input node and an output node of the back EMF amplifier, wherein the at least one switch is switched on during the initial driving period. 
     The amplification-path circuit unit may include a bypass switch connected between an input node and an output node of the back EMF amplifier and the switch is switched on after the initial driving period. 
     According to another aspect of the present invention, there is provided a method for detecting back electro-motive force (EMF) in a motor, the method including: determining, by a mode selecting unit, whether an initial driving period has elapsed when power is on; amplifying, by a back EMF amplifying unit, a back EMF voltage from the motor if it is determined that the initial driving period has not elapsed; allowing, by the back EMF amplifying unit, the back EMF voltage to bypass it if it is determined that the initial driving period has elapsed; and detecting a zero-crossing of the amplified EMF voltage or the bypassing EMF voltage, wherein the back EMF amplifying unit amplifies the EMF voltage to a level detectable by a zero-crossing detecting unit or higher. 
     According to another aspect of the present invention, there is provided a method for detecting back electro-motive force (EMF) in a motor, the method including: determining, by a mode selecting unit, whether an initial driving period has elapsed when power is on, to thereby generate a mode selection signal including a first mode selection signal having a high level and a second mode selection signal having a low level if the initial driving period has not elapsed, and to generate the mode selection signal having the first mode selection signal having a low level and the second mode selection signal having a high level after the initial driving period; amplifying, by a back EMF amplifying unit, a back EMF voltage from the motor according to the first and second mode selection signals if it is determined that the initial driving period has not elapsed; allowing, by the back EMF amplifying unit, the back EMF voltage to bypass it according to the first and second mode selection signals if it is determined that the initial driving period has elapsed; and detecting a zero-crossing of the amplified EMF voltage or the bypassing EMF voltage, wherein the back EMF amplifying unit amplifies the EMF voltage to a level detectable by a zero-crossing detecting unit or higher during the initial driving period with a gradually decreasing amplification gain. 
     The amplifying of the back EMF voltage may include amplifying the back EMF voltage from the motor by an amplification-path circuit unit of the back EMF amplifying unit, the amplification-path circuit unit being completed during the initial driving period. 
     The allowing of the back EMF voltage to bypass may include allowing the back EMF voltage from the motor to bypass it through a bypass-path circuit unit of the back EMF amplifying unit, the bypass-path circuit unit being completed after the initial driving period. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of an apparatus for detecting back electro-motive force (EMF) in a sensorless motor according to an embodiment of the present invention; 
         FIG. 2  is a block diagram of the apparatus for detecting a back EMF in a sensorless three-phase motor according to the embodiment of the present invention; 
         FIG. 3  is a diagram illustrating the mode selecting unit  100  according to the embodiment of the present invention; 
         FIG. 4  is a detailed diagram of the back EMF amplifying unit and the zero-crossing detecting unit according to the embodiment of the invention; 
         FIG. 5  is a diagram showing an implementation of the back EMF amplifying unit according to the embodiment of the present invention; 
         FIG. 6  is a diagram showing another implementation of the back EMF amplifying unit according to the embodiment of the present invention; 
         FIG. 7  is a diagram illustrating the operation of the amplifying mode according to the embodiment of the present invention; 
         FIG. 8  is a diagram illustrating the operation of the bypass mode according to the embodiment of the present invention; 
         FIG. 9  is a first timing chart of principal voltages and signals according to the embodiment of the present invention; 
         FIG. 10  is a second timing chart of principal voltages and signals according to the embodiment of the present invention; and 
         FIG. 11  is a flowchart illustrating a method for detecting a back EMF in a sensorless motor according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Throughout the drawings, the same or like reference numerals will be used to designate the same or like elements. 
       FIG. 1  is a block diagram of an apparatus for detecting back electro-motive force (EMF) of a sensorless motor according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the sensorless motor apparatus to which the embodiment of the present invention is applied may include a motor control unit  10 , a motor driving unit  20  and a motor  30 . 
     The motor control unit  10  may provide a control signal SC to the motor driving unit  20  for driving the motor  30 . 
     The motor driving unit  20  may provide a motor driving signal SD to the motor  30  according to the control signal SC from the motor control unit  10 . 
     Then, the motor  30  may operate according to the driving signal SD from the motor driving unit  20 . 
     The apparatus for detecting a back EMF according to the embodiment of the present invention, which may be applied to the sensorless motor apparatus, may include a mode selecting unit  100 , a back electro-motive force amplifying unit  200 , and a zero-crossing detecting unit  300 . 
     The mode selecting unit  100  may select between an amplification mode and a bypass mode based on an initial driving period T1 when power is on. 
     For example, the amplification mode may be selected during the initial driving period T1 and the bypass mode may be selected after the initial driving period T1. 
     If the amplification mode is selected by the mode selecting unit  100 , the back EMF amplifying unit  200  may amplify a back EMF voltage V bemf  from the motor during the initial driving period T1 to provide it to the zero-crossing detecting unit  300 . Here, the back EMF amplifying unit  200  may amplify the back EMF voltage V bemf  to a level detectable by the zero-crossing detecting unit  300  or higher. 
     For example, the back EMF amplifying unit  200  may amplify the back EMF voltage V bemf  with a constant gain or with a gradually decreasing gain. If the back EMF amplifying unit  200  includes a variable-gain amplifier, it may amplify the back EMF voltage V bemf  with a gradually decreasing gain. 
     Further, if the bypass mode is selected by the mode selecting unit  100 , the back EMF amplifying unit  200  may allow the back EMF voltage V bemf  to bypass it toward the zero-crossing detecting unit  300  after the initial driving period T1. 
     The zero-crossing detecting unit  300  may detect a zero-crossing from an output signal S 200  from the back EMF amplifying unit  200 . 
     For example, the zero-crossing detecting unit  300  may determine whether there is a zero-crossing based on a level of the output signal S 200  from the back EMF amplifying unit  200 , to provide the motor control unit  10  with a signal in the form of a pulse. 
       FIG. 2  is a block diagram of the apparatus for detecting a back EMF in a sensorless three-phase motor according to the embodiment of the present invention. Referring to  FIG. 2 , the motor driving unit  20  provides the three-phase motor  30  with driving signals in three phases SD-U, SD-V and SD-W, to drive the three-phase motor  30 . 
     Here, the back EMF amplifying unit  200  may amplify back EMF voltages V bemf -u, V bemf -v and V bemf -w in three phases input through the first to third output terminals TU, TV and TW of the three-phase motor  30 , respectively, or may allow them to bypass it. 
       FIG. 3  is a diagram illustrating the mode selecting unit  100  according to the embodiment of the present invention. 
     Referring to  FIG. 3 , the mode selecting unit  100  may generate a mode selection signal SW including a first mode selection signal SW 1  having a high level during the initial driving period T1 and having a low level after the initial driving period T1, and a second mode selection signal SW 2  inverted from the first mode selection signal SW 1 . 
     As an exemplary implementation, the mode selecting unit  100  may include a mode-selection-signal generating unit  110  and an inverter  120 . 
     The mode-selection-signal generating unit  110  may generate the first mode selection signal SW 1  having a high level during the initial driving period T1 and having a low level after the initial driving period T1. 
     For example, the mode selecting unit  100  may include a power-on-reset (POR) circuit unit, which provides a power-on-reset (POR) signal for resetting an internal register when power is on. The mode selecting unit  100  may generate the first mode selection signal SW 1  using the POR signal. By using the POR circuit unit, it is not necessary to design a separate circuit to thereby simplify the design and reduce the manufacturing cost. 
     The inverter  120  may invert the first mode selection signal SW 1  to provide the second mode selection signal SW 2 . 
       FIG. 4  is a detailed diagram of the back EMF amplifying unit and the zero-crossing detecting unit according to the embodiment of the invention. 
     Referring to  FIG. 4 , the back EMF amplifying unit  200  may include an amplification-path circuit part  210  and a bypass-path circuit part  220 . 
     The amplification-path circuit part  210  may be completed during the initial driving period T1 to amplify a back EMF voltage from the motor. 
     The bypass-path circuit part  220  may be completed after the initial driving period T1 to allow a back EMF voltage from the motor to flow therethrough. 
     As an exemplary implementation, as shown in  FIG. 4 , the amplification-path circuit part  210  may include a first switch  211 , an amplifier  212  and a second switch  213  between an input node NI and an output node NO. 
     The first and second switches  211  and  213  may be switched on during the initial driving period T1. At this time, the amplifier  212  becomes operable, so that it may amplify a back EMF voltage from the motor. 
     Here, at least one of the first and second switches  211  and  213  maybe included between the input node NI and the output node NO of the back EMF amplifying unit  200 . 
     Further, the bypass-path circuit part  220  may include a bypass switch  221  connected between the input node NI and the output node NO of the back EMF amplifying unit  200 . 
     The bypass switch  221  may be switched on after the initial driving period T1, to allow a back EMF voltage from the motor to flow through the bypass-path circuit part  220 . 
     Further, the zero-crossing detecting unit  300  may include a comparator COM that has a non-inverted input terminal to receive the output signal S 200  from the back EMF amplifying unit  200 , an inverted input terminal to receive a reference voltage Vref, and an output terminal. 
     The comparator COM may output a high-level signal to the output terminal if the output signal S 200  is higher than the reference voltage Vref and may output a low-level signal to the output terminal if the output signal S 200  is not higher than the reference voltage Vref. 
       FIG. 5  is a diagram showing an implementation of the back EMF amplifying unit according to the embodiment of the present invention. 
     Referring to  FIG. 5 , the first and second switches  211  and  213  of the amplification-path circuit part  210  may be made up of first and second NMOS transistors NMOS 1  and NMOS 2 , respectively. 
     In addition, the bypass switch  221  of the amplification-path circuit part  210  may be made up of a third NMOS transistor NMOS 3 . 
     The first and second NMOS transistors NMOS 1  and NMOS 2  may be switched on according to the first mode selection signal SW 1  having a high level and may be switched off according to the first mode selection signal SW 1  having a low level. 
     In addition, the third NMOS transistor NMOS 3  may be switched off according to the second mode selection signal SW 2  having a low level and may be switched on according to the second mode selection signal SW 2  having a high level. 
       FIG. 6  is a diagram showing another implementation of the back EMF amplifying unit according to the embodiment of the present invention. 
     Referring to  FIG. 6 , the first and second switches  211  and  213  of the amplification-path circuit part  210  may be made up of first and second transmission gates TMG 1  and TMG 2 , respectively. 
     In addition, the bypass switch  221  of the bypass-path circuit part  220  may be made up of a third transmission gate TMG 3 . 
     The first transmission gate TMG 1  may include a first NMOS transistor (NMOS 1 ) to receive the first mode selection signal SW 1 , and a first PMOS transistor (PMOS 1 ) to receive the second mode selection signal SW 2 . 
     The second transmission gate TMG 2  may include a second NMOS transistor (NMOS 2 ) to receive the first mode selection signal SW 1 , and a second PMOS transistor (PMOS 2 ) to receive the second mode selection signal SW 2 . 
     The third transmission gate TMG 3  may include a third PMOS transistor (PMOS 3 ) to receive the first mode selection signal SW 1 , and a third NMOS transistor (NMOS 3 ) to receive the second mode selection signal SW 2 . 
     The first and second transmission gates TMG 1  and TMG 2  may be switched on during the initial driving period T1 according to the first mode selection signal SW 1  having a high level and the second mode selection signal SW 2  having a low level, and may be switched off after the initial driving period T1 according to the first mode selection signal SW 1  having a low level and the second mode selection signal SW 2  having a high level. 
     The third transmission gate TMG 3  may be switched off during the initial driving period T1 according to the first mode selection signal SW 1  having a high level and the second mode selection signal SW 2  having a low level, and may be switched on after the initial driving period T1 according to the first mode selection signal SW 1  having a low level and the second mode selection signal SW 2  having a high level. 
       FIG. 7  is a diagram illustrating the operation of the amplification mode according to the embodiment of the present invention. 
     Referring to  FIGS. 1 to 7 , since the first and second switches  211  and  213  of the amplification-path circuit part  210  is switched on according to the mode selection signal SW during the initial driving period T1, the back EMF amplifying unit  200  is operated in the amplification mode, such that the amplifier  212  of the amplification-path circuit part  210  becomes operable, to thereby amplify a back EMF voltage form the motor. 
       FIG. 8  is a diagram illustrating the operation of the bypass mode according to the embodiment of the present invention. 
     Referring to  FIGS. 1 to 8 , since the bypass switch  221  of the bypass-path circuit part  220  is switched on according to the mode selection signal SW after the initial driving period T1, the back EMF amplifying unit  200  is operated in the bypass mode, such that the bypass-path circuit part  220  may bypass a back EMF voltage from the motor through the bypass-path. 
     For example, after the initial driving period T1, the amplitude of the back EMF voltage is sufficiently high to be processed in the zero-crossing detecting unit and thus does not need to be amplified. 
       FIG. 9  is a first timing chart of principal voltages and signals according to the embodiment of the present invention.  FIG. 10  is a second timing chart of principal voltages and signals according to the embodiment of the present invention. 
     Referring to  FIGS. 1 to 9 , the mode selecting unit  100  is supplied with a supply voltage V dd  when power is on. At this time, a back EMF voltage V bemf  from by the motor  30  also increases gradually. 
     The first mode selection signal SW 1  has a high level during a predetermined initial driving period T1. For example, the first mode selection signal SW 1  may be a power on reset (POR) signal for resetting an internal register when power is on. 
     The second mode selection signal SW 2 , inverted from the first mode selection signal SW 1 , has an opposite level to the first mode selection signal SW 1 . 
     The signal S 200  output from the back EMF amplifying unit  200  has a level, obtained by amplifying the back EMF voltage V bemf  with a constant amplification gain, and has the same level with the back EMF voltage V bemf  after the initial driving period T1. 
     Further, the zero-crossing detecting unit  300  may provide the motor control unit  10  with a signal in the form of a pulse which has a high level if the level of the signal S 200  output from the back EMF amplifying unit  200  is higher than the reference voltage Vref and has a low level otherwise. The motor control unit  10  may control the operation of the motor based on the signal from the zero-crossing detecting unit  300 . 
     Now, description will be made referring to  FIGS. 1 to 10 .  FIG. 10  is different from  FIG. 9  in that the amplifier  212  has a constant amplification gain in  FIG. 9  whereas the amplifier  212  has a gradually decreasing amplification gain in  FIG. 10 . 
     That is, the back EMF amplifying unit  200  may amplify the back EMF voltage V bemf  to a level detectable by the zero-crossing detecting unit  300  or higher by using the gradually decreasing amplification gain during the initial driving period T1. 
       FIG. 11  is a flowchart illustrating a method for detecting back EMF in a sensorless motor according to an embodiment of the present invention. 
     The method for detecting back EMF in a sensorless motor according to the embodiment of the present invention will be described with reference to  FIGS. 1 to 11 . 
     In describing the method for detecting back EMF in a sensorless motor according to the embodiment of the present invention, the above descriptions with reference to  FIGS. 1 to 10  are equally applied, and thus the same descriptions will not be repeated. 
     Firstly, in operation S 100 , whether the initial driving period T1 has elapsed when power is on is determined by the mode selecting unit  100 . 
     As an example, the mode selecting unit  100  determines whether the initial driving period T1 has elapsed when power is on, such that it may generate the mode selection signal SW having the first mode selection signal SW 1  having a high level and the second mode selection signal SW 2  having a low level if the initial driving period T1 has not elapsed, and may generate the mode selection signal SW having the first mode selection signal SW 1  having a low level and the second mode selection signal SW 2  having a high level after the initial driving period T1. 
     Then, in operation S 200 , if the initial driving period T1 has not elapsed, the back EMF amplifying unit  200  may amplify a back EMF voltage from the motor according to the first and second selection signals SW 1  and SW 2 . 
     Here, the back EMF amplifying unit  200  may amplify the back EMF voltage V bemf  to a level detectable by the zero-crossing detecting unit  300  or higher. 
     For example, in operation S 200 , the amplification-path circuit part  210  of the back EMF amplifying unit  200  may be completed during the initial driving period T1 to amplify a back EMF voltage from the motor. 
     Incidentally, the back EMF amplifying unit  200  may also amplify the back EMF voltage V bemf  to a level detectable by the zero-crossing detecting unit  300  or higher by using the gradually decreasing amplification gain during the initial driving period T1. 
     Then, in operation S 300 , if the initial driving period T1 has elapsed, the back EMF amplifying unit  200  may allow a back EMF voltage from the motor to bypass it according to the first and second selection signals SW 1  and SW 2 . 
     For example, in operation S 300 , the bypass-path circuit part  220  of the back EMF amplifying unit  200  may be completed after the initial driving period T1 to allow a back EMF voltage from the motor to flow therethrough. 
     Finally, in operation S 400 , a zero-crossing of the back EMF voltage, which may have been amplified or have bypassed the amplification-path circuit unit, may be detected. 
     As above, according to the embodiments of the present invention, back electro-motive force can be accurately detected in a sensorless motor using a back EMF voltage, even during an initial driving period by way of performing an amplification mode in which a back EMF voltage is amplified during the initial driving period, and performing a bypass mode in which a back EMF voltage bypasses an amplification path during a normal mode after the initial driving period. 
     In particular, the problem relating to a level in a low speed operation at the time of start-up can be simply overcome by way of using a power on reset (POR) signal provided for resetting an internal register when power is on in a POR circuit part, so that a motor can operate stably even at the time of start-up. 
     While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.