Abstract:
A conventional apparatus with the above operation, includes a torque ripple due to harmonic wave components included in the detected fundamental wave of current frequency of the detected apparatus for controlling rotation speed, switching dead time and the like and accordingly, harmonic wave components are included in the induced voltage. Therefore, a ripple is generated in an estimated-calculated rotation speed and accordingly, precise speed control was not possible. Also, it was difficult to handle the apparatus by using an encoder and hole-sensor of the rotor position detection unit. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for controlling rotation speed of a synchronous reluctance motor, including a position estimation unit for controlling rotation speed of the synchronous reluctance motor by estimating the flux angle of the rotor and rotation speed of the rotor according to the low speed or high speed region, and the apparatus can control the motor in the high speed area or low speed area, stabilize the transient state generated in the process that the motor is converted from the low speed area to the high speed area and show stable speed control performance, thus to perform more precise speed control.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an apparatus for controlling rotation speed of a synchronous reluctance motor and particularly, to an apparatus for controlling rotation speed of a synchronous reluctance motor capable of controlling rotation speed and torque of a motor by detecting input voltage and input current of a synchronous reluctance motor and estimating speed and flux angle of a rotor, without using a sensor for detecting rotor position.  
           [0003]    2. Description of the Background Art  
           [0004]    Generally, for a conventional apparatus for controlling rotation speed of a synchronous reluctance motor, information of speed or flux of a motor is necessary in case of performing an instantaneous torque control and accordingly, sensors such as a tachometer, generator, resolver or pulse encoder to abstract the information of speed or flux of a motor.  
           [0005]    However, since it is difficult to handle the above sensors, the sensors are very sensitive for noise and increase cost, recently, much researches about sensorless vector control method capable of controlling speed and torque without revising the speed according to the second resistance change of a motor have been conducted actively in overseas advanced enterprises.  
           [0006]    [0006]FIG. 1 is a block diagram showing structure of a conventional apparatus for controlling rotation speed of a synchronous reluctance motor and as shown in the drawing, the conventional apparatus for controlling rotation speed of a synchronous reluctance motor includes a first comparator  11  for outputting speed error after comparing a speed reference value ω r   *  and real rotor speed value ω r , a speed control unit  12  for outputting electric current i qs   *  for reference torque after performing Pl control for compensating the outputted speed error, a second comparator  13  for outputting current error after comparing the current for reference torque i qs   *  and current for real torque i qs , a flux reference generation unit  14  for referring the flux and outputting flux reference value λ d   *  according to the real speed ω r , a flux control unit  15  for outputting a current for reference flux i ds   *  after performing Pl control receiving the above outputted flux reference value λ d   *  a third comparator  16  for outputting a corresponding current error by comparing the electric current for the reference flux i ds   *  and current for real flux i ds , a current control unit  17  for outputting voltage V ds   *  for reference flux and voltage V qs   *  for reference torque according to an output current of the second comparator  13  and third comparator  16 , a three phase voltage generation unit  18  for receiving the voltage V ds   *  for reference flux, voltage V qs   * , for reference torque and the real flux angle θ from the integrator  22 , converting into three phase voltages Vas, Vbs and Vcs of the fixed coordinate system and outputting the voltages, an inverter unit  19  for rotating the synchronous reluctance motor  20  by applying the three phase voltages Vas, Vbs and Vcs of the three phase voltage generation unit  18 , a rotor position detection unit  21  for yielding the real speed by detecting rotation speed of the synchronous reluctance motor, an integrator  22  for yielding the real flux angle by integrating the real speed ω r  and a coordinate conversion unit  23  for receiving the two phase electric currents ias and ics detected in rotating the synchronous reluctance motor  20 , converting the currents into the current i ds  for real flux and current i qs  for real torque and outputting the converted currents.  
           [0007]    Here, operation principle of the conventional apparatus for controlling rotation speed of a synchronous reluctance motor with reference to the accompanied drawings is as follows.  
           [0008]    First, the first comparator  11  outputs speed error to the speed control unit  12  after comparing a speed reference value ω r   *  and real rotor speed value ω r  detected from the rotor position detection unit  18  in rotating the synchronous reluctance motor  17 . Then, the speed control unit  12  outputs electric current i qs   *  for reference torque after performing Pl control for compensating the outputted speed error.  
           [0009]    On the other hand, the flux reference generation unit  14  generates and outputs the flux reference value λ d   *  to the flux control unit  15  and the flux control unit  15  outputs the current i ds   *  for reference flux to third comparator  16  after performing Pl control by receiving the above outputted flux reference value λ d   *  .  
           [0010]    The third comparator  16  outputs the corresponding current error to the current control unit  17  by comparing the electric current i ds   *  for the reference flux generated and outputted according to the outputted flux reference value λ d   *  and current i ds  for real flux outputted to the coordinate conversion unit  20 . Then, the current control unit  17  generates the voltage V ds   *  for reference flux and voltage V qs   *  for reference torque, which are respectively D-axis voltage and Q-axis voltage by receiving the current errors outputted from the second comparator  13  and third comparator  16  and outputs the voltages to the three phase voltage generation unit  15 .  
           [0011]    Here, a formula for yielding the voltage V ds   *  for reference flux and voltage V qs   *  for reference torque is as follows:  
           [0012]    Formula 1 
                     V   d     =         R   s          i   d       +       L   d                 i   d            t         -       ω   e          L   q          i   q                       V   q     =         R   s          i   q       +       L   d                 i   q            t         -       ω   e          L   d          i   d                       Formula                 1                               
 
           [0013]    Here, V d , V q  are respectively components of D-axis and Q-axis of voltage, i d , i q  are respectively components of the D-axis and Q-axis of current, R s  is resistance of stator side and L d , L q  are inductances of the D-axis and Q-axis.  
           [0014]    Then, the three phase voltage generation unit  18  generates three phase voltages Vas, Vbs and Vcs of the fixed coordinate system using the voltage V ds   *  for reference flux, voltage V qs   *  for reference torque and the real flux angle θ from the integrator  22  and applies the voltages into the inverter unit  19  and the inverter unit  19  applying the three phase voltages Vas, Vbs and Vcs into the synchronous reluctance motor  20 .  
           [0015]    At this time, the rotor position detection unit  21  for detecting the rotor position of the synchronous reluctance motor  20  outputs the real rotation speed of the detected motor into the first comparator  11  and the integrator  22 . Then, the integrator  22  yields the flux angle (θ) corresponding to the real position of the rotor by integrating the real speed and outputs the angle into the coordinate conversion unit  23  and three phase voltage generation unit  18 .  
           [0016]    Therefore, the conventional synchronous reluctance motor controls rotation speed of the motor by repeatedly performing the above process.  
           [0017]    However, the conventional apparatus with the above operation, includes a torque ripple due to harmonic wave components included in the detected fundamental wave of current frequency, switching dead time and the like and accordingly, harmonic wave components are included in the induced voltage. Therefore, a ripple is generated in an estimated-calculated rotation speed and accordingly, precise speed control was not possible. Also, it was difficult to handle the apparatus by using an encoder and hall-sensor of the rotor position detection unit.  
           [0018]    Also, the conventional apparatus for controlling rotation speed of a synchronous reluctance motor has problems that the cost increases due to using a costly rotor position detection unit and low speed control can not be smoothly done in spite of excellent high speed control.  
         SUMMARY OF THE INVENTION  
         [0019]    Therefore, the object of the present invention is to control a low speed area and high speed area separately to maintain precision of speed control according to variation of load in sensorless speed control for detecting rotor position of a synchronous reluctance motor.  
           [0020]    Another object of the present invention is to provide an apparatus for controlling rotation speed of a synchronous reluctance motor capable of accurately controlling rotation speed of a motor where detection of a rotor position such as in a compressor in a refrigerator and air conditioner is difficult by enabling linear control of the inductance variation according to current change using magnetic modeling of the motor.  
           [0021]    To achieve these and other advantages in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for controlling rotation speed of a synchronous reluctance motor, including a first comparator for outputting speed error after comparing a speed reference value and real rotor speed value of a synchronous motor, a speed control unit for outputting electric current for reference torque after performing Pl control for compensating the outputted speed error, a second comparator for outputting current error after comparing the outputted electric current for reference torque and electric current for real torque, a flux reference generation unit for generating and outputting flux reference value, a third comparator for outputting flux error after receiving the above outputted flux reference value and comparing the flux reference value and real flux value, a flux control unit for outputting voltage for reference flux of the synchronous coordinate system after performing Pl control receiving the above outputted flux error, a current control unit for generating and outputting voltage for reference torque after receiving the current error outputted from the second comparator, a synchronization/fixed coordinate conversion unit for receiving the above voltage for reference flux, voltage for reference torque and flux angles showing the real position of a rotor estimated in the high speed and low speed areas of the synchronous reluctance motor, converting the two voltages in the synchronous coordinate system into two voltages in the fixed coordinate system and outputting the voltages, a three phase voltage generation unit for converting the outputted two voltages of the fixed coordinate system into three phase voltages and outputting the voltages, an inverter unit for inverting the outputted three phase voltages and then outputting a three phase electric currents for driving the synchronous reluctance motor, a synchronous reluctance motor which is driven by being received the outputted three phase currents, a fixed/synchronization coordinate conversion unit for detecting two phase currents among the three phase currents outputted to the synchronous reluctance motor and then outputting the currents to the second and third comparators and a flux observer, the flux observer for receiving the outputted two phase currents and the two voltages of the fixed coordinate system outputted from the synchronization/fixed coordinate conversion unit and then outputting the corresponding flux, a position estimation unit for estimating the flux angle of the rotor for high speed control of the motor and rotation speed of the rotor using the outputted flux, a low speed control unit for receiving the flux angle and rotation speed, and then estimating the flux angle of the rotor for low speed control of the motor and outputting the angle to the synchronization/fixed coordinate conversion unit and a transient state stabilization unit for stabilizing a transient state which is generated according to the low speed control and speed control algorithm.  
           [0022]    The foregoing and other, features, aspects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0024]    In the drawings:  
         [0025]    [0025]FIG. 1 is a block diagram showing structure of a conventional apparatus for controlling rotation speed of a synchronous reluctance motor;  
         [0026]    [0026]FIG. 2 is a block diagram showing structure of a synchronous reluctance motor in accordance with the present invention; and  
         [0027]    [0027]FIG. 3 is a characteristic graph which illustrates variation of flux which is varied in accordance with variation of current applied into a synchronous reluctance motor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0029]    Hereinafter, preferred embodiments of an apparatus for controlling rotation speed of a synchronous reluctance motor, capable of controlling a low speed area and high speed area separately to maintain precision of speed control according to variation of load without using a hall sensor or encoder for detecting speed and position of a synchronous reluctance motor and accurately controlling rotation speed of a motor where detection of a rotor position such as in a compressor in a refrigerator and air conditioner is difficult by enabling linear control of the inductance variation according to current change will be described in detail with reference to FIG. 2.  
         [0030]    [0030]FIG. 2 is a block diagram showing structure of a synchronous reluctance motor in accordance with the present invention.  
         [0031]    As shown in the drawing, the apparatus for controlling rotation speed of a synchronous reluctance motor in accordance with the present invention includes a first comparator  31  for outputting speed error after comparing a speed reference value and real rotor speed value of a synchronous motor, a speed control unit  32  for outputting electric current for reference torque after performing Pl control for compensating the outputted speed error, a second comparator  33  for outputting current error after comparing the outputted electric current for reference torque and electric current for real torque, a flux reference generation unit  34  for generating and outputting flux reference value, a third comparator  35  for outputting flux error after receiving the above outputted flux reference value and comparing the flux reference value and real flux value, a flux control unit  36  for outputting voltage for reference flux of the synchronous coordinate system after performing Pl control by receiving the above outputted flux error, a current control unit  37  for generating and outputting voltage for reference torque by receiving the current error outputted from the second comparator  33 , a synchronization/fixed coordinate conversion unit  38  for receiving the above voltage for reference flux, voltage for reference torque and flux angles showing the real position of a rotor estimated in the high speed and low speed areas of the synchronous reluctance motor, converting the two voltages in the synchronous coordinate system into two voltages in the fixed coordinate system and then outputting the voltages, a three phase voltage generation unit  39  for converting the outputted two voltages of the fixed coordinate system into three phase voltages and outputting the voltages, an inverter unit  40  for inverting the outputted three phase voltages and then outputting a three phase electric currents for driving the synchronous reluctance motor, a synchronous reluctance motor  41  which is driven by being received the outputted three phase currents, a fixed/synchronization coordinate conversion unit  42  for detecting two phase currents among the three phase currents outputted to the synchronous reluctance motor  41  and then outputting the currents to the second and third comparators  33  and  36  and a flux observer  43 , the flux observer  43  receiving the outputted two phase currents and the two voltages of the fixed coordinate system outputted from the synchronization/fixed coordinate conversion unit  39 , for outputting the corresponding flux, a position estimation unit  45  for estimating the flux angle of the rotor for high speed control of the motor and rotation speed of the rotor using the outputted flux, a low speed control unit  44  receiving the flux angle and rotation speed, for estimating the flux angle of the rotor for low speed control of the motor and outputting the angle to the synchronization/fixed coordinate conversion unit  39  and a transient state stabilization unit  44 - 1  for stabilizing a transient state which is generated according to the low speed control and speed control algorithm.  
         [0032]    Here, the flux observer  43  includes a flux conversion unit  43 a receiving the two phase currents i dq  outputted from the fixed/synchronization coordinate conversion unit  42 , for outputting the estimated flux {tilde over (λ dq )} according to the synchronous coordinate system, a synchronization/fixed flux conversion unit  43   b  for converting the estimated flux {tilde over (λ dq )} according to the synchronization coordination system into an estimated flux {tilde over (λ αβ )} in the fixed coordinate system using the flux angle {tilde over (θ)} which is position information outputted from the position estimation unit  45  for high speed control and outputting the flux value, a first comparator unit  43   d  for comparing the voltage V αβ  of the fixed coordinate system outputted from the synchronization/fixed coordinate conversion unit  39  and the voltage corresponding to a multiplied value of the two phase currents i dq  and resistance R at the stator side and outputting the corresponding voltage error, that is, an induced voltage e αβ , a first integrator  43   f  for yielding the real flux {circumflex over (λ αβ )} and outputting the flux after integrating the outputted induced voltage e αβ , a sixth comparator unit  43   c  for yielding difference between the estimated flux {tilde over (λ αβ )} of the fixed coordinate system outputted from the synchronization/fixed flux conversion unit  43   b  and the real flux {circumflex over (λ αβ )} outputted from the first integrator  43   f  and outputting the difference, a gain generation unit  43   g  for generating and outputting a gain value to reduce the difference between the outputted two fluxes, that is, the flux error Δλ αβ  and a position estimation unit  45  receiving the real flux {circumflex over (λ αβ )} outputted form the first integrator  43   f  and the estimated flux {tilde over (λ dq )} outputted from the flux conversion unit  43   a , for yielding the flux angle {tilde over (θ)} for estimating the rotor position of the synchronous reluctance motor  41  and outputting the angle.  
         [0033]    Also, the low speed control unit  44  includes a signal injection unit  44   a  for inputting a predetermined signal to a flux of a D-axis and obtaining the difference Δλ q  between the flux value of a Q-axis which is finally observed in the synchronous reluctance motor and flux value of the Q-axis which was initially estimated, in the low speed area of the synchronous reluctance motor or in an initial driving; a high pass filter  44   b  for performing filtering to remove signals of the direct current DC component among signals outputted from the signal injection unit  44   a  and outputting the resultant; a demodulation unit  44   c  for receiving, demodulating the resultant and outputting the signal of the DC component; a low pass filter  44   d  for performing filtering to generate a signal of complete DC component, by removing erroneous components among the signals of the DC component and outputting the signal of the DC component; a Pl control unit  44   e  for performing Pl control of the signal of the DC component and obtaining speed information according to low speed control of a motor; a second integrator  44   f  for performing integration by receiving the speed information and obtaining position information according to the low speed control of the motor; and a switching unit  44 - 1   b  for receiving the position information and outputting the information to the synchronization/fixed coordinate conversion unit  38 .  
         [0034]    Also, the transient state stabilization unit  44 - 1  includes a speed ratio adjustment unit  44 - 1   a  for comparing the rotation speed {tilde over (ω n )} of the rotor which was estimated in the position estimation unit  45  in case of controlling the motor at high speed and outputted and the rotation speed {circumflex over (ω)} of the rotor which was estimated and outputted to the Pl control unit  44   e  in case of controlling the motor at low speed, in gear controlling of the motor, determining whether the motor is controlled at high or low speed, and stabilizing a transient state which is generated in the motor by having an overlapping region in case of converting from the high speed area to low speed area or from the low speed area to high speed area; a second integrator  44   f  for outputting the speed information which was inputted from the speed ratio adjustment unit  44 - 1   a ; and a switching unit  44 - 1   b  for switching to control the motor at low or high speed by receiving the speed information and then outputting the speed information sin {circumflex over (θ)}, cos {circumflex over (θ)} according to the low speed control or the speed information sin {tilde over (θ)}, cos {tilde over (θ)} according to the high speed control respectively to the synchronization/fixed coordinate conversion unit  38 .  
         [0035]    The operation of the apparatus for controlling rotation speed of a synchronous reluctance motor in accordance with the present invention with the above composition will be described in detail.  
         [0036]    First, the first comparator  31  compares the speed reference value ω n   *  and real rotor speed value {tilde over (ω n )} detected in the position estimation unit  45  and outputs speed error into the speed control unit  32  and the speed control unit  32  outputs electric current i q   *  for reference torque after performing Pl control for compensating the outputted speed error. Then, the second comparator unit  33  outputs current error to the current control unit  37  after comparing the outputted electric current i q   *  for reference torque outputted from the speed control unit  32  and electric current i q  for real torque outputted from the fixed/synchronization coordinate conversion unit  42 . The current control unit  37  generates and outputs voltage V qs   *  for reference torque, which is a Q-axis voltage into the synchronization/fixed coordinate conversion unit  38 , receiving the current error outputted from the second comparator  33 .  
         [0037]    On the other hand, the flux reference generation unit  34  generates and outputs the flux reference value λ d   *  into the second comparator  35  and the second comparator  35  outputs flux error into the flux control unit  36  after comparing the flux reference value λ d   *  and real flux value outputted from the fixed/synchronization coordinate conversion unit  42 . Then, the flux control unit  36  outputs voltage V ds   *  for reference flux, which is a D-axis voltage after performing Pl control by receiving the above outputted flux error.  
         [0038]    Later, the synchronization/fixed coordinate conversion unit  38  receives a sine value and cosine value to the flux angles {tilde over (θ)} and {circumflex over (θ)} showing the voltage V d   *  for reference flux, voltage V q   *  for reference torque and the real position of the rotor estimated in the high speed and low speed areas, converts the two voltages in the synchronous coordinate system into two voltages V d   *  and V q   *  in the fixed coordinate system and outputs the voltages into the three phase voltage generation unit  38 .  
         [0039]    Later, the three phase voltage generation unit  39  applies the three phase voltages Vas, Vbs and Vcs into the inverter unit  40  and the inverter unit  40  inverts the outputted three phase voltages Vas, Vbs and Vcs, applies the three phase electric currents for driving motor into the synchronous reluctance motor  41  and drives the motor. The fixed/synchronization coordinate conversion unit  42  detects two phase currents i dq  among the applied three phase current and then outputs the currents to the second and third comparators units  33  and  36  and the flux conversion unit  43   a.    
         [0040]    Then, the process that synchronous reluctance motor  41  performs speed control by estimating the rotor position of the synchronous reluctance motor  41  in high speed or low speed control will be described as follows.  
         [0041]    First, the flux observer  43  for performing high speed control of the synchronous reluctance motor  41  will be described as follows.  
         [0042]    The flux conversion unit  43   a  receives the two phase currents i dq  outputted from the fixed/synchronization coordinate conversion unit  42  and outputs the estimated flux {tilde over (λ dq )} according to the synchronous coordinate system into the position estimation unit  45 . At this time, FIG. 3 is a characteristic graph showing variation of flux which is varied in accordance with variation of current to yield the estimated flux {tilde over (λ dq )}.  
         [0043]    [0043]FIG. 3 is a characteristic graph which illustrates variation of flux which is varied in accordance with variation of current applied into a synchronous reluctance motor and the graph is used to form a lookup table with the flux value measured according to the variation amount of two currents.  
         [0044]    Later, the synchronization/fixed flux conversion unit  43   b  converts the estimated flux {tilde over (λ dq )} according to the synchronization coordination system into an estimated flux {tilde over (λ αβ )} in the fixed coordinate system using the flux angle {tilde over (θ)} which is position information outputted from the position estimation unit  45  and outputs the flux value into the sixth comparator unit  43   c.    
         [0045]    On the other hand, the first comparator unit  43   d  for comparing the voltage V αβ  of the fixed coordinate system outputted from the synchronization/fixed coordinate conversion unit  38  and the voltage corresponding to the multiplied value of the two phase currents i dq  and resistance R at the stator side and outputting the corresponding voltage error, that is, an induced voltage e αβ  into the first integrator  43   f  and the first integrator  43   c  yields the real flux {circumflex over (λ αβ )} and outputting the flux after integrating the outputted induced voltage e αβ . Then, the sixth comparator  43   c  unit yields difference between the estimated flux {tilde over (λ αβ )} of the fixed coordinate system outputted from the synchronization/fixed flux conversion unit  43   b  and the real flux {circumflex over (λ αβ )} outputted from the first integrator  43   c  and outputs the difference into the gain generation unit  43   g  and the gain generation unit  43   g  for generating and outputs a gain value to reduce the difference between the outputted two fluxes, that is, the flux error Δλ αβ  into the fifth comparator unit  43   e.    
         [0046]    Later, the position estimation unit  45  receives the real flux {circumflex over (λ αβ )} and the estimated flux {tilde over (λ dq )} and yields the flux angle {tilde over (θ)} for estimating the rotor position of the synchronous reluctance motor  41  and outputs the corresponding sine value and cosine value into the synchronization/fixed coordinate conversion unit  38 , thus to perform high speed control of the synchronous reluctance motor.  
         [0047]    At this time, a formula for obtaining the sine value and cosine value corresponding to the flux angle {tilde over (θ)} using the real flux {circumflex over (λ αβ )} and estimated flux {circumflex over (λ dq )} is as follows.  
         [0048]    Formula 2  
                 sin        θ   ~       =           λ   ~     dq     ⋀       λ   ~     αβ         λ   2         ,       cos        θ   ~       =           λ   ~     dq     ×       λ   ~     αβ         λ   2                 Formula                 2                               
 
         [0049]    Here, {tilde over (θ)} designates the rotation angle of the estimated rotor, {tilde over (λ dq )} designates the flux estimated according to the synchronous coordinate system, {circumflex over (λ αβ )} designates the flux measured according to the fixed coordinate system, dq designates the signal in the synchronous coordinate system and αβ designates the signal in the fixed coordinate system, respectively.  
         [0050]    Then, the operation of the low speed control unit  44  for performing low speed control of the synchronous reluctance motor  41  will be described as follows.  
         [0051]    Since the voltage component has a relatively small value in the low speed region, a voltage error such as dead-time and the like is occurred. Therefore, there occurs a problem in estimating the position only by high speed control of the motor. Therefore, to solve the above problem, a position estimating loop using signal input in the low speed region of the motor is used.  
         [0052]    In the low speed region of the motor or in case of initially driving the motor, the signal injection unit  44 a obtains difference value Δλ q  between the flux value of the Q-axis, which is finally observed in the synchronous reluctance motor and the flux value which was initially estimated by inputting a predetermined signal into the flux of D-axis. The predetermined signal is a preference value which was yielded through experiments and in case there is no difference value Δλ q , that is, the difference value between the observed flux value of the Q-axis and the s estimated flux value of the Q-axis is “0”, it means that there is no error in the low speed control of the motor.  
         [0053]    However, when the difference value is occurred, a flux angle {circumflex over (θ)} which is a position component appropriate for low speed control through a series of control processes to compensate the difference. Then, the high pass filter  44   b  performs filtering to remove signals of the DC component among the signals outputted from the signal injection unit  44   a  and outputs the resultant value to the demodulation unit  44   c . The demodulation unit  44   c  receives the resultant value, performs demodulation and outputs the signal of the DC component again. The low pass filter  44   d  removes erroneous components, performs filtering to generate a signal of a complete DC component and outputs the signal to the Pl control unit  44   e . Then, the Pl control unit  44   e  performs Pl control about the generated signal of the DC component and obtains an estimated speed {circumflex over (ω)} which is speed information according to low speed control of the motor. The second integrator  44   f  receives the estimated speed {circumflex over (ω)} and performs integration and then obtains an estimated flux angle {tilde over (θ)} which is position information according to low speed control of the motor. The estimated flux angle θ is outputted to the synchronization/fixed coordinate conversion unit  38  through a switching unit  44 - 1   b  which will be described in the following paragraphs.  
         [0054]    As a result, the low speed control unit  44  performs stable speed controlling at low speed by having the difference of flux value of Q-axis as ‘0’, in case of a low speed region of the motor and initial driving of the motor.  
         [0055]    Then, the operation of the transient state stabilization unit  44 - 1  for preventing the state that the increased amount of the voltage/current applied into the whole system of the motor is rapidly increased and stably performing high speed or low speed gear controlling of the motor, when the synchronous reluctance motor  41  is converted from the low speed region to high speed region or from the high speed region to low speed region, that is, when the motor is gear controlled will be described as follows.  
         [0056]    First, in case of gear controlling of the motor speed, the speed ratio adjustment unit  44 - 1   a  compares the rotation speed {tilde over (ω n )} of the rotor, which is outputted from the position estimating unit  45  by being estimated in case of high speed control and the rotation speed {circumflex over (ω)} of the rotor, which is outputted to the Pl control unit  44   e  by being estimated in case of low speed control and determines whether low speed or high speed control will be performed. Also, the transient state stabilization unit  44 - 1  stabilizes transient state generated in the motor, by having the overlapped region, in converting from the low speed region to high speed region or from the high speed region to low speed region.  
         [0057]    The second integrator  44   f  integrates the speed information which is inputted from the speed ratio adjustment unit  44 - 1   a  and outputs to the switching unit  44 - 1   b . The switching unit  44 - 1   b  receives the speed information, performs switching for low or high speed controlling of the motor and outputs the speed information sin {circumflex over (θ)}, cos {circumflex over (θ)} according to low speed control and the speed information sin {tilde over (θ)}, cos {tilde over (θ)} according to the high speed control respectively to the synchronization/fixed coordinate conversion unit  38 .  
         [0058]    As described above in detail, the synchronous reluctance motor in accordance with the present invention controls rotation speed of the rotor without a position detection sensor of the motor by separating the low speed area and high speed area to maintain accuracy of the speed control according to variation of the load.  
         [0059]    Also, the apparatus for controlling rotation speed of the synchronous reluctance motor in accordance with the present invention controls the motor in the high speed area or low speed area, stabilizes the transient state generated in the process that the motor is converted from the low speed area to the high speed area and shows stable speed control performance, thus to perform more precise speed control.  
         [0060]    Also, the present invention can control the rotation speed of the motor at a position where it is difficult to detect the rotor such as a compressor of a refrigerator and air conditioner by enabling linear control of the inductance which varies according to current variation using a magnetic modeling.  
         [0061]    As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.