Abstract:
Disclosed is a single-phase switched reluctance motor (SRM) driving apparatus and method which enables a high-speed and high-efficiency SRM and can minimize the switching frequency of elements for driving the SRM. The SRM driving apparatus includes a smoothing circuit section for smoothing an input power supply, a motor driving section for receiving a voltage smoothed by the smoothing circuit section and supplying the voltage to a motor in accordance with a control signal, a plurality of sensors for sensing a rotating speed and a phase of the motor, and a microcomputer for receiving one selected among signals sensed by the plurality of sensors and outputting the control signal for controlling the motor driving section.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an apparatus and method of driving a single-phase switched reluctance motor, and more particularly to a single-phase switched reluctance motor (SRM) driving apparatus and method which enables a high-speed and high-efficiency SRM by employing a plurality of sensors, and which can minimize the switching frequency of elements constituting an SRM driving section.  
           [0003]    2. Description of the Related Art  
           [0004]    A switched reluctance motor (SRM) is a specific type motor combined with a switching control device, wherein both its stator and rotor have a protruded pole type structure, and there exists no winding or permanent magnet of any type on the rotor part, enabling the SRM to have a very simple structure.  
           [0005]    Since the SRM has a very simple structure, it has advantages in productivity. Also, it has a good starting characteristic and a great torque, while it requires little maintenance and repair such as a periodic exchange of brushes and so forth. Also, the structure of its driving apparatus Ls simplified in comparison to an induction motor driven by an inverter, and it has superior characteristics in torque per volume, efficiency, rating of the converter, etc.  
           [0006]    Due to such superior characteristics, the SRM has been increasingly used in various fields in many countries.  
           [0007]    [0007]FIG. 1 is a block diagram of a conventional single-phase SRM driving apparatus.  
           [0008]    Referring to FIG. 1, the conventional single-phase SRM driving apparatus comprises a smoothing circuit section  102  for smoothing an AC current applied from a commercial AC power supply  101  to a DC voltage, a microcomputer  106 , a motor driving section  103  for receiving the DC voltage supplied from the smoothing circuit section  102  and a control signal outputted from the microcomputer  106 , and driving a motor  104  accordingly, and a Hall sensor  105  for detecting the position and speed of the motor  104 , and outputting a detection signal to the microcomputer  106 .  
           [0009]    The operation of the conventional single-phase SRM driving apparatus as constructed above will be explained in detail with reference to FIG. 1.  
           [0010]    The smoothing circuit section  102  smoothes the input voltage of the commercial power supply  101 . The smoothed voltage is supplied to the motor driving section  103 , and the motor driving section  103  supplies the voltage to the motor  104  in accordance with the control signal from the microcomputer  106 .  
           [0011]    Then, the Hall sensor  105  detects the rotating speed and phase of the motor  104  to generate a detection signal, and the microcomputer  106  controls the motor driving section  103  in accordance with the signal generated by and received from the Hall sensor  105 , so that the motor driving section  103  controls the voltage supplied to the motor  104 .  
           [0012]    [0012]FIG. 2 is a view illustrating the construction of the conventional single-phase SRM and motor driving section.  
           [0013]    Referring to FIG. 2, the conventional single-phase SRM motor  300  is a single-phase 6/6-pole SRM composed of a stator  207 , a rotor  208 , a magnet  209  for position detection, and a parking magnet  210 .  
           [0014]    The conventional SRM driving section  200  comprises a DC link capacitor  201  for smoothing the AC power supply and outputting a smoothed DC voltage, upper and lower switching elements  202  and  203 , connected in parallel to the DC link capacitor  210 , for being turned on/off in accordance with a gate driving signal from a switching driving section (not illustrated) which rotates the motor in a forward or backward direction in accordance with a rotor position signal of the SRM, a first diode  204  connected to motor windings  206  for generating a torque according to an on/off operation of the upper and lower switching elements  202  and  203 , one terminal of the upper switching element  202 , and one terminal of the lower switching element  203 , and a second diode  205  connected between the other terminal of the upper switching element  202  and the other terminal of the lower switching element  203 .  
           [0015]    The operation of the conventional single-phase SRM as constructed above will be explained in detail.  
           [0016]    First, if the AC power supply is applied, the DC link capacitor  201  smoothes it to a DC voltage. This smoothed DC voltage is supplied to the motor windings  206  in accordance with the switching operation of the upper and lower switching elements  202  and  203 .  
           [0017]    Specifically, the upper and lower switching elements  202  and  203  are turned on according to the position of the rotor  208  and the stator  207  of the SRM, and this causes a current path is formed through the DC link capacitor  201 , upper switching element  202 , motor windings  206 , and lower switching element  203 . Accordingly, a voltage is excited in the motor windings  206 , a magnetic force is generated from the stator  207 , and thus the SRM rotates by the magnetic force acting on the rotor  208 .  
           [0018]    If the upper and lower switching elements  202  and  203  are simultaneously turned off as the SRM rotates, a phase current being applied to the motor windings  206  is eliminated through the first diode  204 , motor windings  206 , second diode  205 , and DC link capacitor  201 .  
           [0019]    As described above, the conventional SRM is driven by supplying or intercepting the voltage to the motor in accordance with the on/off operation of the upper and lower switching elements  203  and  204  which constitute the motor driving section.  
           [0020]    Here, the control signal applied to the upper and lower switching elements  202  and  203  is generated by detecting the rotating speed and the phase of the motor through the Hall sensor as shown in FIG. 1, and the microcomputer pulse-width-modulates the output signal of the Hall sensor and controls the on/off operation of the upper and lower switching elements  202  and  203  in accordance with a duty ratio of pulse width modulation (PWM).  
           [0021]    [0021]FIG. 3 is a graph illustrating an inductance profile according to the phase change of the conventional single-phase SRM.  
           [0022]    Hereinafter, the voltage supplying operation of the motor driving section to the motor will be explained in detail with reference to FIGS. 2 and 3.  
           [0023]    According to the SRM having the structure as shown in FIG. 2, when a protruded pole part  207 - 1  of the stator  207  and a protruded pole part  208 - 1  of the rotor  208  are in an alignment state, the inductance of the SRM becomes greatest, while when they are in a misalignment state, the inductance becomes smallest.  
           [0024]    Also, in the case of the conventional SRM having the 6/6-pole structure, the maximum point and the minimum point of inductance alternately appear every phase of 30°.  
           [0025]    In order to drive the SRM, the Hall sensor (not illustrated) detects the position of the rotor  207 , generates and outputs the control signal to the microcomputer when a position a of the rotor  207  moves to a position b or b′ of the stator  208 , i.e., at the time point when the inductance increases. Then, the microcomputer generates the control signal, and supplies the current to the motor windings  206  by controlling the motor driving section to supply the voltage.  
           [0026]    [0026]FIGS. 4 a  and  4   b  are views illustrating a normal parking position and an abnormal position of the single-phase SRM.  
           [0027]    When the SRM is stopped, it is parked by mutual attraction acting between an N pole of a parking magnet  401   a  and an S pole of a magnet  404   a  fixed to a rotor  402   a , and between an S pole of the parking magnet  401   a  and an N pole of the magnet  404   a , respectively, as shown in FIG. 4 a , and thus a normal parking state of the SRM is maintained for the next rotation.  
           [0028]    However, as occasion requires, when a rotor  402   b  is stopped, the SRM may be parked by mutual repulsion acting between an N pole of a magnet  404   b  fixed to the rotor  402   b  and an N pole of a parking magnet  401   b , and between an S pole of the magnet  404   b  and an S pole of the parking magnet  401   b , respectively, and this causes the SRM to be in an abnormal parking state.  
           [0029]    As described above, the conventional single-phase SRM has the following problems:  
           [0030]    First, in spite of the increase of voltage applied to the motor, the increasing speed of current is slower than that of the voltage, and thus it is difficult to use the conventional SRM for a product that requires a high-speed rotation.  
           [0031]    Second, in the conventional high-speed SRM, the switching loss occurs in the upper and lower switching elements due to frequent switching operations since the switching elements are controlled by the adjustment of the PWM duty ratio from a Low speed to a high speed, and this causes electromagnetic waves to be greatly generated.  
           [0032]    Third, in the case that the rotor of the motor is in the abnormal parking position, the rotor may not rotate further or may operate unstably even if any current flows to the stator for the further rotation of the motor.  
         SUMMARY OF THE INVENTION  
         [0033]    Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and a first object of the present invention is to provide a single-phase switched reluctance motor (SRM) driving apparatus and method which enables a high-speed and high-efficiency SRM by driving the SRM with a start sensor and an operation sensor separately provided.  
           [0034]    It is a second object of the present invention to provide a single-phase SRM driving method which can minimize the switching frequency of elements for driving the SRM.  
           [0035]    It is a third object of the present invention to provide a single-phase SRM driving method which can stably drive the SRM by preventing an abnormal parking of the SRM.  
           [0036]    In order to achieve the above objects, according to the present invention, there is provided a single-phase SRM driving apparatus comprising a smoothing circuit section for smoothing an input power supply, a motor driving section for receiving a voltage smoothed by the smoothing circuit section and supplying the voltage to a motor in accordance with a control signal, a plurality of sensors for sensing a rotating speed and a phase of the motor, and a microcomputer for receiving one selected among signals sensed by the plurality of sensors, and outputting the control signal for controlling the motor driving section.  
           [0037]    In another aspect of the present invention, there is provided a single-phase SRM driving method comprising the steps of (a) sensing a rotating speed and a phase of a motor through a plurality of sensors and producing sensed signals, (b) selecting one among the plurality of sensors, receiving the sensed signal produced from the selected sensor, and producing a control signal for controlling a voltage supplied to the motor, (c) detecting the rotating speed of the motor, and comparing the sensed rotating speed with a reference speed determined by a system, and (d) selecting another sensor if the sensed rotating speed of the motor is faster than the reference speed as a result of comparison at step (c), and producing a control signal for controlling the voltage supplied to the motor in accordance with the sensed signal produced from the selected sensor.  
           [0038]    In still another aspect of the present invention, there is provided a single-phase SRM driving method comprising the steps of (a) initially aligning a rotor and a stator of a motor when a power supply is inputted, (b) waiting for a predetermined time after the rotor and the stator of the motor are aligned at step (a), (c) applying a secession pulse for an initial start of the motor after the predetermined time elapses, (d) receiving a signal produced from a first sensor, and increasing a rotating speed of the motor started at step (c) by adjusting a duty ratio of pulse width modulation (PWM) of the signal, (e) comparing the rotating speed of the motor with a reference speed determined by a system, and (f) if the rotating speed of the motor is faster than the reference speed as a result of comparison, receiving a signal produced from a second sensor, and controlling the rotating speed of the motor in a dwell time.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiment thereof with reference to the attached drawings in which:  
         [0040]    [0040]FIG. 1 is a block diagram of the conventional single-phase SRM driving apparatus;  
         [0041]    [0041]FIG. 2 is a view illustrating the construction of the conventional single-phase SRM and motor driving section;  
         [0042]    [0042]FIG. 3 is a graph illustrating an inductance profile according to the phase change of the conventional single-phase SRM;  
         [0043]    [0043]FIGS. 4 a  and  4   b  are views illustrating a normal parking position and an abnormal position of the single-phase SRM.  
         [0044]    [0044]FIG. 5 is a block diagram of the single-phase SRM driving apparatus according to the present invention;  
         [0045]    [0045]FIG. 6 is a view illustrating the inductance change in accordance with the phase change of the single-phase SRM and signals produced from the start sensor and the operation sensor according to the present invention;  
         [0046]    [0046]FIGS. 7 a  and  7   b  are sectional views of the single-phase SRM and the permanent magnet part according to the present invention;  
         [0047]    [0047]FIG. 8 is a flowchart illustrating the method of driving the single-phase SRM driving apparatus having the construction as shown in FIG. 5 according to the present invention; and  
         [0048]    [0048]FIG. 9 is a graph explaining the single-phase SRM driving method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0049]    Reference will now be made in greater detail to the preferred embodiment of the present invention with reference to the accompanying drawings.  
         [0050]    [0050]FIG. 5 is a block diagram of the single-phase SRM driving apparatus according to the present invention.  
         [0051]    Referring to FIG. 5, the single-phase SRM driving apparatus according to the present invention comprises a smoothing circuit section  502  for smoothing an AC voltage supplied from a commercial AC power supply  501  to a DC voltage, a microcomputer  507 , a motor driving section  503  for receiving the DC voltage supplied from the smoothing circuit section  502  and a control signal from the microcomputer  507  and driving a motor  504  accordingly, a start sensor  505  and an operation sensor  506  for detecting a rotating speed and a phase of the motor  504  and outputting detected signals to the microcomputer  507 .  
         [0052]    Hereinafter, the operation of the single-phase SRM driving apparatus according to the present invention will be explained in detail with reference to FIG. 5.  
         [0053]    First, the smoothing circuit section  502  smoothes the input AC power supply  501 , and supplies the smoothed voltage to the motor driving section  503 . The motor driving section  503  supplies the voltage to the motor  504  in accordance with the control signal outputted from the microcomputer  507 .  
         [0054]    Thereafter, the start sensor  505  and the operation sensor  506  detect the rotating speed and the phase of the motor  404  and output corresponding sensed signals. At this time, the start sensor  505  and the operation sensor  506  detect different phases of the rotor. Specifically, the operation sensor  506  detects the phase preceding the strat sensor  506 .  
         [0055]    The sensed signals produced from the start sensor  505  and the operation sensor  506  are inputted to the microcomputer  507 . At an initial start of the motor, the microcomputer  507  selects the signal outputted from the start sensor  505 , and produces the control signal for controlling the motor driving section  503 .  
         [0056]    As described above, if the motor driving section  503  is driven by the signal detected by the start sensor  505 , it causes trouble in the product that rotates at a high speed due to the problem of the current increase supplied to the motor windings (not illustrated). Thus, the microcomputer  507  selects the signal produced from the start sensor  505  as its input at the initial start of the motor  504 , and produces the control signal for controlling the motor driving section  503 .  
         [0057]    If the motor speed exceeds the predetermined reference speed, the microcomputer  507  selects the signal produced from the operation sensor  506  as its input, and outputs the control signal for controlling the motor driving section  503 .  
         [0058]    [0058]FIG. 6 is a view illustrating the inductance change in accordance with the phase change of the single-phase SRM and signals produced from the start sensor and the operation sensor according to the present invention.  
         [0059]    Hereinafter, the operation of the single-phase SRM driving apparatus according to the present invention will be explained in detail with reference to FIGS. 5 and 6.  
         [0060]    The inductance becomes lowest when the protruded pole part of the rotor and the protruded pole part of the stator are accurately in a misalignment state. At the time point when the inductance becomes increased, the motor driving section supplies the voltage to the motor to flow the current to the motor windings.  
         [0061]    The start sensor  505  adopted in the single-phase SRM driving apparatus according to the present invention detects the phase where the inductance starts to increase and produces the detected signal, and the operation sensor  506  detects the phase that precedes the phase detected by the start sensor  505 .  
         [0062]    As described above, the start sensor  505  and the operation sensor  506  detect the rotating speed and the phase of the motor and produce the detected signals to the microcomputer  507 . The microcomputer  507  selects one of the detected signals produced from the two sensors  505  and  506  as its input in accordance with the rotating speed of the motor  504 , and outputs the control signal to the motor driving section  503 .  
         [0063]    In selecting the signals produced from the start sensor  505  and the operation sensor  506 , the microcomputer  507  selects the signal of the start sensor  505  if the RPM of the SRM is in the range of 1,000 RPM˜2,000 RPM, while it selects the signal of the operation sensor  506  if the RPM of the SRM exceeds the above range.  
         [0064]    [0064]FIGS. 7 a  and  7   b  are sectional views of the single-phase SRM and the permanent magnet part according to the present invention. In FIG. 7 a , the reference numeral ‘ 701 ’ denotes a magnet for position detection, ‘ 702 ’ a parking magnet, ‘ 703 ’ an operation sensor, and ‘ 704 ’ a start sensor.  
         [0065]    [0065]FIG. 8 is a flowchart illustrating the method of driving the single-phase SRM driving apparatus having the construction as shown in FIG. 5 according to the present invention.  
         [0066]    Referring to FIGS. 5 and 8, the single-phase SRM driving method according to the present invention will be explained in detail.  
         [0067]    If the power supply is turned on to drive the single-phase SRM (step  801 ), the initial alignment is performed (step  802 ). The reason for performing the initial alignment is that there exists a point where the torque is zero due to the characteristic of the magnet fixed to the rotor of the SRM. In other words, it is to solve the problem of the abnormal parking due to the repulsion between the parking magnet and the magnet fixed to the rotor.  
         [0068]    As a method for the initial alignment, the current is momentarily supplied to the motor windings by outputting a number of small pulses to the upper and lower switching elements of the motor driving section  503 .  
         [0069]    After the initial alignment is completed at step  802 , a predetermined waiting time is given so that the rotor moves to the normal parking position as shown in FIG. 4 b  (step  803 ). In the embodiment of the present invention, the waiting time is determined to be about one second.  
         [0070]    If the rotor is positioned to the normal parking position as above, a big pulse (secession pulse), i.e., a large amount of current is applied to the motor windings so that the rotor can secedes from the parking position (step  804 ).  
         [0071]    If the secession pulse is applied to the motor driving section  503  as described above and an instantaneous torque is generated, the rotor starts to rotate. Then, the rotating speed of the rotor is gradually increased by performing the PWM of a small duty and then continuously increasing the duty ratio of the PWM (step  805 ).  
         [0072]    Here, the PWM duty ratio is determined by the following equation.  
               D   ratio     =       T   on         T   on     +     T   off                 [Equation 1]                               
 
         [0073]    In equation 1, D ratio  represents a duty ratio, T on  a time period where the upper and lower switching elements of the motor driving section having the construction as shown in FIG. 2 are turned on, T off  a time period where the upper and lower switching elements are turned off. As shown in Equation 1, since the value of the denominator is constant, the duty ratio is determined by the value of the numerator T on .  
         [0074]    Accordingly, the increase of the duty ratio corresponds to the lengthening of the ‘turned-on’ time of the upper and lower switching elements, and this means that a much more current flows to the motor windings and the rotor rotates more rapidly.  
         [0075]    Also, the above-described PWM is performed in a period taken from a rising edge of the start sensor to a falling edge thereof.  
         [0076]    Then, the rotating speed and the phase of the motor is detected using the start sensor, and the detected rotating speed is compared with the reference speed determined by the system (step  806 ).  
         [0077]    If the detected rotating speed of the motor is faster than the reference speed as a result of comparison at step  806 , the base of commutation is changed from the start sensor to the operation sensor, and a dwell time control is performed, while if the detected rotating speed is slower than the reference speed, the process of adjusting the PWM duty ratio is continuously performed.  
         [0078]    The dwell time control is performed in a manner that the current is supplied or cut off at a time for a time determined by the microcomputer instead of turning on or off the switching elements according to the PWM duty ratio. In comparison to the PWM, the dwell time control greatly reduces the number of switching operations of the switching elements of the motor driving section.  
         [0079]    Here, the dwell time control is used if the next value can be estimated by the previously read value. The reason why the base of commutation is changed from the start sensor to the operation sensor during the dwell time control is that it is difficult to estimate the next value from the previously read value due to the frequent RPM change in the event that the start sensor is the base of commutation.  
         [0080]    Thereafter, if the external power supply is turned off (step  808 ), it is judged whether the external power supply is turned on again (step  809 ).  
         [0081]    If the external power supply is not turned on again as a result of judgement at step  809 , the SRM drive is terminated (step  811 ), while if it is judged that the external power supply is turned on again at step  809 , it is judged whether the motor is kept to rotate (step  810 ).  
         [0082]    If it is judged that the motor is stopped at step  810 , the process is fed back to step  802 , and the above-described steps including the initial alignment are repeatedly performed, while if it is judged that the motor is not stopped, the process is directly fed back to step  805 , and the above-described steps are repeatedly performed since the steps  802 ,  803 , and  804  are not required any further.  
         [0083]    [0083]FIG. 9 is a graph illustrating the single-phase SRM driving method according to the present invention as described above.  
         [0084]    While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that other modifications thereof may be made without departing from the scope of the invention. Thus, the invention should not be limited to the disclosed embodiment, but should be defined by the scope of the appended claims and their equivalents.