Patent Publication Number: US-7898199-B2

Title: Controller for motor

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     This application claims the priority of JP Application No. 2007-097969, filed Apr. 4, 2007, the entire specification, claims and drawings of which are incorporated herewith by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a controller for an electric motor of an axial air-gap type. 
     2. Description of the Related Art 
     The electric motor of the axial air-gap type having a rotor having a permanent magnet, two stators arranged on both sides of the rotor in a rotation axis direction of the rotor, and an armature winding mounted to each stator is formerly known (e.g., see Japanese Patent Laid-Open No. H10 (1998)-271784, Japanese Patent Laid-Open No. 2001-136721, and Japanese Patent Laid-Open No. H6 (1994)-245458). In accordance with such an electric motor of the axial air-gap type, relatively high output torque can be generated while the axial length of the rotor of the electric motor is shortened. 
     Meanwhile, when an electric motor of an axial air-gap type operates in a low torque and low speed operating state where an output torque and a rotating speed of the rotor are small, a variation in the output torque tends to appear remarkably. Then, when such an electric motor is installed in a hybrid vehicle or an electric vehicle as the driving power source for the vehicle, a car body will vibrate due to a variation in the output torque of the electric motor (so-called torque ripple) when the vehicle starts moving. 
     Therefore, it is desirable to suppress a variation in the output torque of the electric motor in the low torque and low speed operating state. 
     However, the techniques disclosed in the above-stated Japanese Patent Laid-Open No. H10 (1998)-271784 and Japanese Patent Laid-Open No. 2001-136721 do not provide a countermeasure for suppressing a variation in the output torque of the electric motor. 
     In the technique disclosed in Japanese Patent Laid-Open No. H6 (1994)-245458, in order to suppress a variation in the output torque of the electric motor, an installation position of an armature winding to one stator is displaced from an installation position of an armature winding to the other stator in the circumferential direction of the stators (the direction around the axis center of the rotor). Alternatively, a position of a permanent magnet mounted to one face of the rotor in the axis direction is displaced in the circumferential direction of the rotor from a position of a permanent magnet mounted to the other face. According to the technique disclosed in this Japanese Patent Laid-Open No. H6 (1994)-245458, a variation in the output torque can be suppressed irrespective of the operating state of the electric motor. 
     The technique disclosed in this Japanese Patent Laid-Open No. H6 (1994)-245458, however, has a problem that, as compared with the case where the armature windings are installed at the same position for both stators or where the permanent magnets are mounted at the same position for both faces of the rotor, the maximum torque that the electric motor can output is decreased, or the energy efficiency of the electric motor is decreased. 
     SUMMARY OF THE INVENTION 
     The present invention has been made with a view of the aforesaid background, and it is an object of the invention to provide a controller for an electric motor capable of operating the electric motor so as to suppress a variation in output torque only in an operating state where the variation in output torque of the electric motor is to be suppressed, and enhance the output torque and the energy efficiency of the electric motor sufficiently in the other operating states. 
     In order to fulfill the above-stated object, a controller for an electric motor of the present invention is adapted to control an electric motor of an axial air-gap type including: a rotor including a permanent magnet; two stators provided on both sides of the rotor in a direction of a rotation axis center; and an armature winding mounted to each stator. The controller includes an electric current conduction control means which controls electric currents supplied to the armature windings of the stators, the electric current control means setting, in a predetermined operating state of the electric motor, a phase difference between an electric current supplied to an armature winding of one of the stators and an electric current supplied to an armature winding of the other stator so as to suppress a variation in an output torque of the electric motor, and supplying electric currents having the phase difference to the armature windings of the stators (a first invention). 
     According to such a first invention, in the predetermined operating state of the electric motor, a phase difference between an electric current supplied to an armature winding of one of the stators and an electric current supplied to an armature winding of the other stator enables to suppress a variation in output torque of the electric motor. That is, a variation in output torque of the electric motor can be suppressed by the electric control of the electric current supplied to the armature winding of each stator of the electric motor without the need of a special mechanism. In this case, by limiting the operating state of controlling in order to set a phase difference between an electric current supplied to an armature winding of one of the stators and an electric current supplied to an armature winding of the other stator to the predetermined operating state as stated above, the electric current supplied to the armature winding of each stator of the electric motor can be controlled so as to enhance the output torque and the energy efficiency of the electric motor sufficiently in the operating states other than the predetermined operating state. 
     Thus, according to the first invention, it is possible to operate the electric motor so as to suppress a variation in output torque only in a predetermined operating state where the variation in output torque of the electric motor is to be suppressed, and enhance the output torque and the energy efficiency of the electric motor sufficiently in the other operating states. 
     In the above first invention, preferably the predetermined operating state includes at least a low torque and low speed operating state in which a request value of the output torque of the electric motor is a predetermined value or lower and a rotating speed of the electric motor is a predetermined value or lower (a second invention). Thereby, in a low torque and low speed operating state where a variation in output torque of the electric motor tends to appear remarkably, such a variation in output torque can be suppressed appropriately. Especially, in the case where such an electric motor is installed in a hybrid vehicle or an electric vehicle as the driving power source for the vehicle, vibration of a car body can be suppressed effectively when the vehicle starts moving for example. 
     In the first invention or the second invention, preferably the electric current control means controls electric currents supplied to the armature windings of the stators so that, in an operating state other than the predetermined operating state of the electric motor, an electric current supplied to the armature winding of the one of the stators and an electric current supplied to the armature winding of the other stator are in a same phase (a third invention). 
     Thereby, in an operating state other than the predetermined operating state of the electric motor, the maximum value of the torque that the electric motor can output is enhanced, while securing a high energy efficiency of the electric motor. 
     In the first invention to the third invention, preferably the two stators have a substantially same magnetic circuit cross section (a fourth invention). That is, in the electric motor of axial air-gap type, magnetic flux by permanent magnets and magnetic flux by the electric currents supplied to the armature windings form a closed circuit between two stators. Therefore, if the stators have different magnetic circuit cross sections from each other, the maximum magnetic flux that is allowed to pass through both of the stators (the magnetic flux generating the magnetic flux saturation) will be limited to a stator having a smaller magnetic circuit cross section between the stators, thus making the magnetic flux obtained smaller than the maximum magnetic flux that can pass through the stator having a larger magnetic circuit cross section. This causes a decrease in the maximum torque that the electric motor can output. On the other hand, by making the two stators have a substantially same magnetic circuit cross section, the maximum magnetic flux in accordance with the magnetic circuit cross section is allowed to pass through the both stators. As a result, the magnetic path of each stator can be used most effectively, thus enhancing the maximum torque that the electric motor can output. 
     Incidentally, the two stators having a substantially same magnetic circuit cross section permits not only the case where their magnetic circuit cross sections equal to each other in a strict sense, but also the case where the magnetic circuit cross sections of both stators equal to each other substantially. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the schematic configuration of a vehicle to which an electric motor according to one embodiment is installed; 
         FIGS. 2(   a ) and ( b ) are perspective views in an assembled state and a disassembled state of an electric motor in one embodiment, respectively, illustrating a configuration of a rotor and stators of the electric motor; 
         FIG. 3  is a block diagram illustrating a functional configuration of a controller of an electric motor in one embodiment; and 
         FIG. 4  is a graph illustrating an exemplary change over time of the output torque of an electric motor in a low torque and low speed operating state. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the present invention will be explained with reference to  FIGS. 1 to 4 . 
     First, the schematic construction of a vehicle mounting an electric motor of this embodiment will be explained with reference to  FIG. 1 .  FIG. 1  shows the schematic construction of the vehicle. 
     The vehicle  1  of this embodiment is a hybrid vehicle of a parallel type, and has an internal combustion engine (engine)  2  as a main propulsive force generating source of the vehicle  1 , and also has an electric motor  3  as an auxiliary propulsive force generating source of the vehicle  1 . The electric motor  3  is an electric motor of an axial air-gap type having a rotor  11  and two stators  12   a ,  12   b , although the electric motor  3  will be described later. A resolver  14  as a rotation angle detecting means for detecting a rotation angle of the rotor  11  of the electric motor  3  is arranged in the electric motor  3 . 
     An output shaft  2   a  of the internal combustion engine  2  is coaxially directly connected to a rotating shaft  3   a  rotatable integrally with the rotor  11  of the electric motor  3 . The output shaft  2   a  of the internal combustion engine  2  and the rotating shaft  3   a  of the electric motor  3  may be also connected through a power transmitting mechanism such as a speed reducer or the like. The output shaft  2   a  and the rotating shaft  3   a  are connected to the input side of a transmission  5  through a clutch  4 . An output side of the transmission  5  is connected to drive wheels  7 ,  7  of the vehicle  1  through a differential gear unit  6 . 
     In this vehicle  1 , output torque of the internal combustion engine  2 , or torque provided by adding output torque (power torque) of the electric motor  3  to this output torque is transmitted to the drive wheels  7 ,  7  as propulsive force of the vehicle  1  through the clutch  4 , the transmission  5  and the differential gear unit  6 . Thus, running of the vehicle  1  is performed. The electric motor  3  can also perform a regenerative operation in which the electric motor  3  generates electricity by kinetic energy of the vehicle  1  transmitted from the drive wheels  7 ,  7  side to the electric motor  3  and this electric power generation energy is charged to an unillustrated storage battery as an electric source of the electric motor  3 . Regenerative torque generated by the electric motor  3  during this regenerative operation functions as braking force of the vehicle  1 . 
     Further, the vehicle  1  has a controller  8  for performing operation control of the electric motor  3 . A detection value θm_s of the rotation angle of the rotor  11  is inputted from the above resolver  14  to this controller  8 . A torque command value Tr_c as a request value of the output torque of the electric motor  3  is also inputted to the controller  8 . The torque command value Tr_c is determined by an unillustrated vehicle operation controller performing centralized operation control of the vehicle  1  in accordance with a manipulation amount of an accelerator pedal of the vehicle  1 , a manipulation amount of a brake pedal, a vehicle speed or the like. The controller  8  controls a conducting electric current of each of armature windings of the stators  12   a ,  12   b  so as to generate the output torque of torque command value Tr_c in the electric motor  3 . In the present embodiment, the torque command value Tr_c is set at a positive value when the electric motor  3  is to carry out the power running operation, while being set at a negative value when the electric motor  3  is to carry out the regenerative operation. 
       FIGS. 2(   a ) and  2 ( b ) are perspective views showing the structure of the rotor  11  of the electric motor  3 , and the stators  12   a ,  12   b .  FIG. 2(   a ) shows the rotor  11  and the stators  12   a ,  12   b  in an assembled state of the electric motor  3 .  FIG. 2(   b ) shows the rotor  11  and the stators  12   a ,  12   b  in a disassembled state of the electric motor  3 . 
     The rotor  11  is constructed from a frame body  14  formed by a non-magnetic material, and a plurality of permanent magnets  15  assembled into this frame body  14 . The frame body  14  is constructed by integrally forming a base body  16  of a disk shape, a circular ring-shaped body  17  spaced from an outer circumferential face of this base body  16  in a diametrical direction and coaxially arranged around the base body  16 , and a plurality of partition plates  18  connecting these base body  16  and ring-shaped body  17 . As shown by a virtual line in  FIG. 2(   a ), the rotating shaft  3   a  is coaxially attached to the base body  16 . 
     The plurality of partition plates  18  are radially extended between the outer circumferential face of the base body  16  and an inner circumferential face of the ring-shaped body  17 , and are arrayed at an equal angle interval around the axis of the rotor  11 . In each space surrounded by the outer circumferential face of the base body  16 , the inner circumferential face of the ring-shaped body  17 , and the partition plates  18 ,  18  adjacent to each other in the circumferential direction of the rotor  11 , the permanent magnet  15  of the same shape as this space (fan plate shape) is fitted. Thus, the plurality of permanent magnets  15  are arrayed at an equal angle interval around the axis of the rotor  11  between the base body  16  and the ring-shaped body  17 . 
     Each permanent magnet  15  is a magnet in which one face in its thickness direction (the axial direction of the rotor  11 ) is the north pole and the other face is the south pole. As described in each permanent magnet  15  of  FIG. 2(   b ), the permanent magnets  15 ,  15  adjacent to each other in the circumferential direction of the rotor  11  are set such that their magnetic poles of faces of the same side in the thickness direction are different from each other. In other words, the plurality of permanent magnets  15  arranged in the rotor  11  are arrayed such that the orientations (orientations in the axial direction of the rotor  11 ) of magnetic fluxes of the permanent magnets  15 ,  15  adjacent in the circumferential direction of the rotor  11  are mutually reverse. In the illustrated example, the number of permanent magnets  15  is 8, and a number of pole-pairs of the rotor  11  is 4. 
     Additionally, the permanent magnets may be also arrayed respectively separately on one face side and the other face side of the axial direction of the rotor  11 . 
     The stators  12   a ,  12   b  have the same construction. As shown in  FIG. 2(   b ), a plurality of teeth  20  respectively projected in the axial direction of ring-shaped base body  19  from one face among both end faces in the axial direction of the base body  19  are arrayed at an equal angle interval around the axis of the base body  19 . The base body  19  and the teeth  20  are integrally formed by a magnetic material. In the illustrated example, the numbers of teeth  20  of the stators  12   a ,  12   b  are respectively 24. 
     In the stators  12   a ,  12   b , an unillustrated armature winding is mounted to a slot  21   a  as a groove between the teeth  20 ,  20  adjacent to each other in the circumferential direction, so as to accommodate the armature winding in the slot  21   a . In this embodiment, the armature winding mounted to each of the stators  12   a ,  12   b  have three phases (U-phase, V-phase and W-phase). Further, the armature winding in the stator  12   a  and the armature winding in the stator  12   b  are mutually mounted in the same manner. For example, when the armature winding of each phase of the stator  12   a  is seen in the axial direction of the stator  12   a , this armature winding is mounted to the stator  12   a  such that a winding loop in number equal to the number of permanent magnets  15  of the rotor  11  is formed at an equal angle interval in the circumferential direction of the stator  12   a . The armature winding of the stator  12   b  side is also similarly mounted. 
     As shown in  FIG. 2(   a ), the stators  12   a ,  12   b  are arranged coaxially with the rotor  11  on both sides of the axial direction of the rotor  11  in an assembled state of the electric motor  3  so as to sandwich the rotor  11  between the stators  12   a ,  12   b , and are fixed to an unillustrated housing of the electric motor  3 . In this case, tip faces of the tooth  20  of the stator  12   a  and the tooth  20  of the stator  12   b  are opposed in proximity to the rotor  11 . Further, in this embodiment, the stators  12   a ,  12   b  are assembled into the electric motor  3  such that the position (an angular position around the axis) of each tooth  20  of the stator  12   a  and the position (an angular position around the axis) of each tooth  20  of the stator  12   b  are conformed when the electric motor  3  is seen in the axial direction of the rotor  11  in the assembled state of the electric motor  3 . Namely, the individual tooth  20  of the stator  12   a  and the individual tooth  20  of the stator  12   b  are arranged in direct opposing positions in the axial direction of the rotor  11 . The armature winding of each phase of the stator  12   a  and the armature winding of the stator  12   b  of the same phase as this armature winding are mounted to the stators  12   a ,  12   b  such that the winding loop of the armature winding of the stator  12   a  and the winding loop of the armature winding of the stator  12   b  are opposed to each other in the axial direction of the rotor  11  for each phase (such that the winding loop of the stator  12   a  side and the winding loop of the stator  12   b  side are mutually located in the same angular position when these armature windings are seen in the axial direction of the rotor  11 ). Accordingly, when the electric current of the same phase is conducted to the armature winding of each phase of the stator  12   a  and the armature winding of the stator  12   b  of the same phase as this armature winding, a magnetic flux generated by the armature winding of the stator  12   a  and a magnetic flux generated by the armature winding of the stator  12   b  attain a state mutually strengthened to its maximum extent in the axial direction of the rotor  11  for each phase. In this embodiment, the stators  12   a ,  12   b  have the same structure, and the respective sections thereof have the same dimensions. Accordingly, magnetic circuit cross sections (cross sections of magnetic paths) for each phase of the stators  12   a ,  12   b  are mutually the same. 
     Next, the construction of the controller  8  will be explained in detail with reference to  FIG. 3 .  FIG. 3  is a block diagram showing the functional construction of the controller  8 . The controller  8  is constructed by an electronic circuit unit including a microcomputer and the like. In the following explanation, as shown in  FIG. 3 , reference numeral  13   a  is given to the armature winding of each phase mounted to the stator  12   a , and reference numeral  13   b  is given to the armature winding of each phase mounted to the stator  12   b.    
     First, the summary of control processing of the electric motor  3  using the controller  8  will be explained. In this embodiment, conducting electric currents (phase electric currents) of the armature windings  13   a ,  13   b  of each phase of the stators  12   a ,  12   b  of the electric motor  3  are controlled by so-called d-q vector control. Namely, the controller  8  converts the armature windings  13   a ,  13   a ,  13   a  of the three phases of the stator  12   a , and the armature windings  13   b ,  13   b ,  13   b  of the three phases of the stator  12   b  into equivalent circuits in a d-q coordinate system of a two-phase direct current, and treats these armature windings. The equivalent circuits corresponding to the stators  12   a ,  12   b  respectively have an armature winding on a d-axis (hereinafter called a d-axis armature winding), and an armature winding on a q-axis (hereinafter called a q-axis armature winding). The d-q coordinate system is a rotating coordinate system in which a field magnet direction provided by the permanent magnet  15  of the rotor  11  is the d-axis, and a direction perpendicular to the d-axis is the q-axis and this rotating coordinate system is rotated integrally with the rotor  11  of the electric motor  3 . 
     The controller  8  then controls the respective phase electric currents of the armature windings  13   a ,  13   b  of the stators  12   a ,  12   b  of the electric motor  3  such that the torque of torque command value Tr_c given from the exterior is outputted from the rotating shaft  3   a  of the electric motor  3 . In this case, in the present embodiment, except for a predetermined operating state of the electric motor  3 , a phase electric current of the armature winding  13   a  of the stator  12   a  and a phase electric current of the armature winding  13   b  of the stator  12   b  for each phase are mutually in the same phase. On the other hand, in the predetermined operating state of the electric motor  3 , a phase electric current of the armature winding  13   a  of the stator  12   a  and a phase electric current of the armature winding  13   b  of the stator  12   b  are shifted by a predetermined phase difference for all of the phases. In the present embodiment, the predetermined operating state is a low torque and low speed operating state where the output torque of the electric motor  3  is a low torque and the rotating speed of the rotor  11  of the electric motor  3  is a low speed. 
     In order to carry out the above-stated control, the controller  8  of the present embodiment includes, as the functional configuration, an electric current command determining section  21 , a first electric current control section  22   a  and a second electric current control section  22   b . The electric current command determining section  21  determines a d-axis electric current command value Id_c that is a command value of an electric current for the d-axis armature winding (hereinafter called a d-axis electric current) and a q-axis electric current command value Iq_c that is a command value of an electric current for the q-axis armature winding (hereinafter called a q-axis electric current) for the stators  12   a  and  12   b . The first electric current control section  22   a  controls the respective phase electric current of the armature winding  13   a  of the stator  12   a  in accordance with the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c. The second electric current control section  22   b  controls a respective phase electric current of the armature winding  13   b  of the stator  12   b  in accordance with the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c. In the present embodiment, the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c are common to both of the stators  12   a  and  12   b.    
     The controller  8  further includes a skew command determining section  23 , a rotor speed calculating section  24  and an angle correcting section  25 . The skew command determining section  23  determines a skew command sk_c that is a command value of a phase difference between a phase electric current of the armature winding  13   a  of the stator  12   a  and a phase electric current of the armature winding  13   b  of the stator  12   b . The rotor speed calculating section  24  calculates a rotating angular velocity ωm_s of the rotor  11  by differentiating a rotating angle θm_s of the rotor  11  detected by the resolver  14  (hereinafter called a rotor angle detected value θm_s). The angle correcting section  25  corrects the rotor angle detected value θm_s in accordance with the skew command sk_c determined by the skew command determining section  23 . In the present embodiment, the rotating angular velocity ωm_s calculated by the rotor speed calculating section  24  is an angular velocity of the mechanical angle of the rotor  11 , which may be converted into an angular velocity of the electric angle of the rotor  11  by multiplying the number of pole-pairs of the rotor  11  thereto. 
     Incidentally, in the present embodiment, the skew command determining section  23 , the angle correcting section  25 , the first electric current control section  22   a  and the second electric current control section  22   b  constitute an electric current conducting control means of the present invention. 
     The processing by a respective functional section of the above-stated controller  8  is carried out sequentially on a predetermined control processing cycle as follows. 
     To the skew command determining section  23 , the torque command value Tr_c fed from the outside to the controller  8  and the rotating angular velocity ωm_s of the rotor  11  calculated by the rotor speed calculating section  24  (hereinafter called a rotor angular velocity ωm_s) are input sequentially. Then, based on these input values, the skew command determining section  23  judges whether the electric motor  3  is in the above-stated low torque and low speed operating state or not, and sequentially determines the skew command sk_c based on the judgment result. 
     In this case, according to the present embodiment, if an absolute value (magnitude) of the torque command value Tr_c is a predetermined value or lower and the rotor angular velocity ωm_s is a predetermined value or lower, the skew command determining section  23  judges that the electric motor  3  is in the low torque and low speed operating state. Then, if the electric motor  3  is not in the low torque and low speed operating state, the skew command determining section  23  sets sk_c=0. Setting sk_c=0 means that a phase electric current of the armature winding  13   a  of the stator  12   a  and a phase electric current of the armature winding  13   b  of the stator  12   b  are in the same phase for each phase (a phase difference of the phase electric current for each phase is set at 0). 
     On the other hand, if the electric motor  3  is in the low torque and low speed operating state, the skew command determining section  23  sets the skew command sk_c at a predetermine value (≠0). Assuming that an angular interval between the adjacent teeth  20  and  20  of each of the stators  12   a  and  12   b  (a difference in angular position between the adjacent teeth  20  and  20 ) is θtt, the predetermined value of the present embodiment is a half value of the angle interval θtt. More specifically, in the present embodiment, since the number of the teeth  20  in each of the stators  12   a  and  12   b  is 24, θtt=360/24=15 [deg]. Note that since the number of pole-pairs of the rotor  11  is 4 in the present embodiment, when θtt is converted into an electrical angle, it will be 15×4=60 [deg]. Therefore, when the electric motor  3  is in the low torque and low speed operating state, the skew command sk_c is set at 15/2=7.5 [deg] in terms of the mechanical angle (30 [deg] in terms of the electric angle). In this way, setting sk_c at a predetermined value not being 0 means that a phase electric current of the armature winding  13   a  of the stator  12   a  and a phase electric current of the armature winding  13   b  of the stator  12   b  have a phase difference equal to the value sk_c for each phase. 
     Incidentally, judgment as to whether the electric motor  3  is in the low torque and low speed operating state or not may be, for example, conducted as follows. That is, in the vicinity of an origin of a coordinates plane including the torque command value Tr_c and the rotor angular velocity ωm_s as two components, a predetermined region (a region such as a circle, a triangle or a quadrangle) including the origin is set. Then, based on as to whether a point (Tr_c, ωm_s) determined by the values of the torque command value Tr_c and the rotor angular velocity ωm_s exists within the predetermined region or not, judgment may be made as to whether the electric motor  3  is in the low torque and low speed operating state or not. 
     To the angle correcting section  25 , the rotor angle detected value θm_s and the skew command sk_c determined by the skew command determining section  23  are input sequentially. Then, the angle correcting section  25  adds the skew command sk_c to the rotor angle detected value θm_s, thus correcting θm_s to determine a corrected rotating angle θm_s′ one by one. Alternatively, the corrected rotating angle θm_s′ may be determined by subtracting the skew command sk_c from the rotor angle detected value θm_s. 
     To the electric current command determining section  21 , the torque command value Tr_c, the rotor angular velocity ωm_s, and the skew command sk_c determined by the skew command determining section  23  are input sequentially. Then, the electric current command determining section  21  determines the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c from these input values in accordance with a predetermined map. In this case, when sk_c=0, the q-axis electric current command value Iq_c is basically determined at a value proportional to the torque command value Tr_c. The d-axis electric current command value Id_c is determined so that the magnitude of the resultant vector of a voltage of the d-axis armature winding (hereinafter called a d-axis voltage) and a voltage of the q-axis armature winding (hereinafter called a q-axis voltage) determined based on the q-axis electric current command value Iq_c, the d-axis electric current command value Id_c, and the rotor angular velocity ωm_s does not exceed a predetermined value determined corresponding to a power supply voltage of the electric motor  3 . When sk_c≠0, the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c are determined at values obtained by correcting the d-axis electric current command value and the q-axis electric current command value when sk_c=0. The reason is as follows. That is, when sk_c≠0, a phase difference corresponding to the value of the skew command sk_c occurs for any phase between a phase electric current of the armature winding  13   a  of the stator  12   a  and a phase electric current of the armature winding  13   b  of the stator  12   b . Therefore, even when the d-axis electric current command value and the q-axis electric current command value are the same as those in the case of sk_c=0, the output torque of the electric motor  3  will be different from that in the case of sk_c=0. 
     The first electric current control section  22   a  includes electric current sensors  26   a  and  27   a , and a dq conversion section  29   a . The electric current sensors  26   a  and  27   a  serve as an electric current detection means that detects a respective phase electric current of two phases out of the three-phase armature windings  13   a ,  13   a , and  13   a  of the stator  12   a , e.g., the armature windings  13   a  and  13   a  in U-phase and W-phase. The dq conversion section  29   a  calculates, from an electric current detected value Iu_s 1  of the U-phase armature winding  13   a  and an electric current detected value Iw_s 1  of the W-phase armature winding  13   a  of the stator  12   a  that are obtained by letting the outputs from these electric current sensors  26   a  and  27   a  pass through a BP filter  28   a , a d-axis electric current detected value Id_s 1  and a q-axis electric current detected value Iq_s 1  that are detected values (estimation values) of the d-axis electric current and the q-axis electric current on the stator  12   a  side. The BP filter  28   a  is a filter having a band-pass property for removing noise components from the outputs of the electric current sensors  26   a  and  27   a.    
     The dq conversion section  29   a  calculates the d-axis electric current detected value Id_s 1  and the q-axis electric current detected value Iq_s 1  by coordinate transformating the electric current detected value Iu_s 1  of the U-phase armature winding  13   a , the electric current detected value Iw_s 1  of the W-phase armature winding  13   a  of the stator  12   a  and an electric current detected value Iv_s 1  (=−Iu_s 1 −Iw_s 1 ) of the V-phase armature winding  13   a  that can be calculated from these values based on the electrical angle θe of the rotor  11  by the following expression (1): 
     
       
         
           
             [ 
             
               Expression 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     
                       [ 
                       
                         
                           
                             Id_s1 
                           
                         
                         
                           
                             Iq_s1 
                           
                         
                       
                       ] 
                     
                     = 
                     
                       
                         
                           2 
                           3 
                         
                       
                       · 
                       
                         A 
                         ⁡ 
                         
                           ( 
                           
                             θ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             e 
                           
                           ) 
                         
                       
                       · 
                       
                         [ 
                         
                           
                             
                               Iu_s1 
                             
                           
                           
                             
                               Iv_s1 
                             
                           
                           
                             
                               Iw_s1 
                             
                           
                         
                         ] 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       where 
                       ⁢ 
                       
                           
                       
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                     = 
                     
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                               cos 
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                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     
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                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Herein, in the case where an instantaneous value of an actual respective phase electric current of the armature winding  13   a  of the stator  12   a  is controlled in accordance with the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c (controlling to a command value for each phase electric current specified by Id_c, Iq_c and an actual rotating angle of the rotor  11  (rotating phase in the dq coordinate system)), the value of the electric angle θe used for the calculation on the right side of the expression (1) may be set at an electric angle of the rotor  11  (=θm_s×the number of pole-pairs of the rotor  11 ) corresponding to the electric current rotor angle detected value θm_s. 
     In the present embodiment, however, the first electric current control section  22   a  controls the respective phase electric current of the armature winding  13   a  of the stator  12   a  so that the actual phase electric current of the armature winding  13   a  of the stator  12   a  agrees with a value obtained by displacing a command value of the phase electric current of the armature winding  13   a  of the stator  12   a  corresponding to the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c by the phase difference of the above-stated skew command sk_c. Therefore, to the dq conversion section  29   a  of the first electric current control section  22   a , the corrected rotating angle θm_s′ (=θm_s+sk_c) is input from the angle correcting section  25 . Then, the dq conversion section  29   a  uses, as the value θe in the expression (1), the value obtained by converting the above-stated corrected rotating angle θm_s′ into an electric angle (=θm_s′×the number of pole-pairs of the rotor  11 ) to calculate the d-axis electric current detected value Id_s 1  and the q-axis electric current detected value Iq_s 1 . In other words, the dq conversion section  29   a  regards the corrected rotating angle θm_s′ as the actual rotation angle of the rotor  11  to calculate the d-axis electric current detected value Id_s 1  and the q-axis electric current detected value Iq_s 1 . 
     The first electric current control section  22   a  further includes a computing section  30   a , a computing section  31   a , PI control sections  32   a ,  33   a  and a non-interference control section  34   a . The computing section  30   a  determines a deviation ΔId 1  (=Id_c−Id_s 1 ) between the d-axis electric current command value Id_c and the d-axis electric current detected value Id_s 1 . The computing section  31   a  determines a deviation ΔIq 1  (=Iq_c−Iq_s 1 ) between the q-axis electric current command value Iq_c and the q-axis electric current detected value Iq_s 1 . The PI control sections  32   a ,  33   a  calculate a basic command value Vd 1 _c 1  of the d-axis voltage and a basic command value Vq 1 _c 1  of the q-axis voltage, respectively, so as to eliminate the deviations ΔId 1  and ΔIq 1  (bring them closer to 0) by a PI control law (proportion/integration control law) as a feedback control law. The non-interference control section  34   a  determines a correction amount Vd 2 _c 1  of the d-axis voltage and a correction amount Vq 2 _c 1  of the q-axis voltage for canceling a speed electromotive force that is mutual interference between the d-axis and the q-axis. The non-interference control section  34   a  calculates the correction amount Vd 2 _c 1  on the d-axis side from the q-axis electric current command value Iq_c and the rotor angular velocity ωm_s, and calculates the correction amount Vq 2 _c 1  on the q-axis side from the d-axis electric current command value Id_c and the rotor angular velocity ωm_S. 
     The first electric current control section  22   a  further includes a computing section  35   a , a computing section  36   a , a three-phase conversion section  37   a , and a power drive unit (PDU)  38   a . The computing section  35   a  determines a final d-axis voltage command value Vd_c 1  by adding the correction amount Vd 2 _c 1  to the above-stated basic command value Vd 1 _c 1  of the d-axis voltage. The computing section  36   a  determines a final q-axis voltage command value Vq_c 1  by adding the correction amount Vq 2 _c 1  to the above-stated basic command value Vq 1 _c 1  of the q-axis voltage. The three-phase conversion section  37   a  determines phase voltage command values Vu_c 1 , Vv_c 1 , and Vw_c 1  of the armature winding  13   a  in U-phase, V-phase and W-phase, respectively, of the stator  12   a  from these d-axis voltage command value Vd_c 1  and q-axis voltage command value Vq_c 1 . The PDU  38   a  conducts electric current to the respective phase armature windings of the stator  12   a  in accordance with these phase voltage command values Vu_c 1 , Vv_c 1 , and Vw_c 1 . Although not illustrated in detail, the PDU  38   a  is a circuit unit including an inverter circuit (not illustrated) connected with a capacitor (not illustrated) as a power source of the electric motor  3 , which controls ON/OFF of a switching element of the inverter circuit by PWM control, thus controlling the conducting of electric current between the respective phase armature windings  13   a  of the stator  12   a  and the capacitor. 
     The three-phase conversion section  37   a  calculates the above-stated phase voltage command values Vu_c 1 , Vv_c 1 , and Vw_c 1  by coordinate transforming the d-axis voltage command value Vd_c 1  and q-axis voltage command value Vq_c 1  by the following expression (2) in accordance with the electric angle θe of the rotor  11 . Herein, A(θe) T  in the expression (2) is a transposed matrix of the matrix A(θe) defined in the description following the above expression (1): 
     
       
         
           
             [ 
             
               Expression 
               ⁢ 
               
                   
               
               ⁢ 
               2 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             Vu_c 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       
                         
                           
                             Vv_c 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       
                         
                           Vw_c1 
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         2 
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                         ⁡ 
                         
                           ( 
                           
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                       T 
                     
                     · 
                     
                       [ 
                       
                         
                           
                             Vd_c1 
                           
                         
                         
                           
                             Vq_c1 
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     In this case, according to the present embodiment as stated above, the first electric current control section  22   a  controls a respective phase electric current of the armature winding  13   a  of the stator  12   a  so that the actual phase electric current of the armature winding  13   a  of the stator  12   a  agrees with a value obtained by displacing a command value of the phase electric current of the armature winding  13   a  of the stator  12   a  corresponding to the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c by the phase difference of the above-stated skew command sk_c. Therefore, to the three-phase conversion section  37   a  of the first electric current control section  22   a , a corrected rotating angle θm_s′ (=θm_s+sk_c) is input from the angle correcting section  25 . Then, similarly to the case of the dq conversion section  29   a , the three-phase conversion section  37   a  uses, as the value θe in the expression (2), the value obtained by converting the above-stated corrected rotating angle θm_s′ into an electric angle (=θm_s′×the number of pole-pairs of the rotor  11 ) to calculate the phase voltage command values Vu_c 1 , Vv_c 1 , and Vw_c 1 . In other words, the three-phase conversion section  37   a  regards the corrected rotating angle θm_s′ as the actual rotation angle of the rotor  11  to calculate the phase voltage command values Vu_c 1 , Vv_c 1 , and Vw_c 1 . 
     As a result of the control processing by the respective functional sections of the first electric current control section  22   a  as stated above, the respective phase electric current of the armature winding  13   a  of the stator  12   a  is controlled to agree with a value obtained by displacing a command value of the respective phase electric current of the armature winding  13   a  of the stator  12   a  corresponding to the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c (a command value of the respective phase electric current specified in accordance with Id_c and Iq_c when the value of the electric angle θe of the rotor  11  is made to agree with the value obtained by multiplying the rotor angle detected value θm_s by the number of pole-pairs of the rotor  11 ) by the phase difference of the above-stated skew command sk_c. 
     Similarly to the first electric current control section  22   a , the second electric current control section  22   b  includes electric current sensors  26   b  and  27   b , and a dq conversion section  29   b . The electric current sensors  26   b  and  27   b  detect phase electric currents of the armature windings  13   b  and  13   b  in two phases (in the present embodiment, U-phase and W-phase) of the stator  12   b . The dq conversion section  29   b  calculates, from an electric current detected value Iu_s 2  of the U-phase armature winding  13   b  and an electric current detected value Iw_s 2  of the W-phase armature winding  13   b  of the stator  12   b  that are obtained by letting the outputs from these electric current sensors  26   b  and  27   b  pass through a BP filter  28   b , a d-axis electric current detected value Id_s 2  and a q-axis electric current detected value Iq_s 2  on the stator  12   b  side. In this case, the dq conversion section  29   b  calculates the d-axis electric current detected value Id_s 2  and the q-axis electric current detected value Iq_s 2  by the expression in which the Id_s 1  and Iq_s 1  on the left side of the above expression (1) are replaced with Id_s 2  and Iq_s 2 , respectively, and Iu_s 1 , Ivs_ 1 , and Iw_s 1  on the right side of the expression (1) are replaced with Iu_s 2 , Iv_s 2  (=−Iu_s 2 −Iw_s 2 ), and Iw_s 2 , respectively. Note that to the dq conversion section  29   b  of the second electric current control section  22   b , the rotor angle detected value θm_s is input as it is. Then, the dq conversion section  29   b  uses, as the value of the electric angle θe of the rotor  11 , a value obtained by converting the rotor angle detected value θm_s as it is into an electric angle (=θm_s×the number of pole-pairs of the rotor  11 ) to calculate the d-axis electric current detected value Id_s 2  and the q-axis electric current detected value Iq_s 2 . 
     Similarly to the first electric current control section  22   a , the second electric current control section  22   b  further includes a computing section  30   b , a computing section  31   b , PI control sections  32   b ,  33   b  and a non-interference control section  34   b . The computing sections  30   b  and  31   b  determine a deviation ΔId 2  (=Id_c−Id_s 2 ) between the d-axis electric current command value Id_c and the d-axis electric current detected value Id_s 2 , and a deviation ΔIq 2  (=Iq_c−Iq_s 2 ) between the q-axis electric current command value Iq_c and the q-axis electric current detected value Iq_s 2 . The PI control sections  32   a ,  33   a  calculate a basic command value Vd 1 _c 2  of the d-axis voltage and a basic command value Vq 1 _c 2  of the q-axis voltage, respectively, so as to eliminate the deviations ΔId 2  and ΔIq 2  (bring them closer to 0) by a PI control law as a feedback control law. The non-interference control section  34   b  determines a correction amount Vd 2 _c 2  of the d-axis voltage and a correction amount Vq 2 _c 2  of the q-axis voltage for canceling a speed electromotive force that is mutual interference between the d-axis and the q-axis. The non-interference control section  34   b  calculates the correction amount Vd 2 _c 2  on the d-axis side from the q-axis electric current command value Iq_c and the rotor angular velocity ωm_s, and calculates the correction amount Vq 2 _c 2  on the q-axis side from the d-axis electric current command value Id_c and the rotor angular velocity ωm_s. In this case, in the present embodiment, since the armature winding  13   a  of the stator  12   a  and the armature winding  13   b  of the stator  12   b  have substantially the same specifications, and their d-axis electric current command value Id_c and q-axis electric current command value Iq_c also equal to each other, the correction amounts Vd 2 _c 2  and Vq 2 _c 2  calculated by the non-interference control section  34   b  equal to the correction amounts Vd 2 _c 1  and Vq 2 _c 1 , respectively, calculated by the non-interference control section  34   a  of the first electric current control section  22   a . Therefore, the correction amounts calculated by any one of the non-interference control sections  34   a  and  34   b  may be shared by the first electric current control section  22   a  and the second electric current control section  22   b.    
     Similarly to the first electric current control section  22   a , the second electric current control section  22   b  further includes a computing section  35   b , a computing section  36   b , a three-phase conversion section  37   b , and a power drive unit (PDU)  38   b . The computing section  35   b  determines a final d-axis voltage command value Vd_c 2  by adding the correction amount Vd 2 _c 2  to the above-stated basic command value Vd 1 _c 2  of the d-axis voltage. The computing section  36   b  determines a final q-axis voltage command value Vq_c 2  by adding the correction amount Vq 2 _c 2  to the above-stated basic command value Vq 1 _c 2  of the q-axis voltage. The three-phase conversion section  37   b  determines phase voltage command values Vu_c 2 , Vv_c 2 , and Vw_c 2  of the armature windings in U-phase, V-phase and W-phase, respectively, of the stator  12   b  from these d-axis voltage command value Vd_c 2  and q-axis voltage command value Vq_c 2 . The PDU  38   b  conducts electric current to the respective phase armature windings  13   b  of the stator  12   b  in accordance with these phase voltage command values Vu_c 2 , Vv_c 2 , and Vw_c 2 . Similarly to the PDU  38   a  of the first electric current control section  22   a , the PDU  38   b  controls the conducting of electric current between the respective phase armature windings  13   b  of the stator  12   b  and the capacitor by PWM control of the inverter circuit. 
     In this case, the three-phase conversion section  37   b  of the second electric current control section  22   b  calculates the phase voltage command values Vu_c 2 , Vv_c 2 , and Vw_c 2  by the expression in which Vu_c 1 , Vv_c 1 , and Vw_c 1  on the left side of the above expression (2) are replaced with Vu_c 2 , Vv_c 2 , and Vw_c 2 , respectively, and Vd_c 1  and Vq_c 1  on the right side of the expression (2) are replaced with Vd_c 2  and Vq_c 2 , respectively. Note that to the three-phase conversion section  37   b , the rotor angle detected value θm_s is input as it is. Then, the three-phase conversion section  37   b  uses, as the value of the electric angle θe of the rotor  11 , a value obtained by converting the rotor angle detected value θm_s as it is into an electric angle (=θm_s×the number of pole-pairs of the rotor  11 ) to calculate the phase voltage command values Vu_c 2 , Vv_c 2 , and Vw_c 2 . 
     As a result of the control processing by the respective functional sections of the second electric current control section  22   b  as stated above, a respective phase electric current of the armature winding  13   b  of the stator  12   b  is controlled to agree with a command value of the respective phase electric current of the armature winding  13   b  of the stator  12   b  corresponding to the d-axis electric current command value Id_c and the q-axis electric current command value Iq_c (a command value of the respective phase electric current specified in accordance with Id_c and Iq_c when the value of the electric angle θe of the rotor  11  is made to agree with the value obtained by multiplying the rotor angle detected value θm_s by the number of pole-pairs of the rotor  11 ). 
     Thus, in the operating state of the electric motor  3  where sk_c≠0, i.e., in the state of a low torque and low speed operating state, the respective phase electric currents of the stator  12   a  and the respective phases electric current of the stator  12   b  are controlled to have a phase difference of the skew command sk_c for each phase. 
     As a result, in the low torque and low speed operating state of the electric motor  3 , a variation in output torque of the electric motor  3  can be suppressed. Herein, the graph a in a solid line of  FIG. 4  illustrates an example (Example) of a change over time of the actual output torque of the electric motor  3  when the operation of the electric motor  3  in a low torque and low speed operating state is controlled using the controller  8  of the present embodiment. In this case, the torque command value Tr_c and the rotating speed of the rotor  11  are kept constant. The graph b in a chain double-dashed line of  FIG. 4  illustrates an example of (Comparative example) of a change over time of the actual output torque of the electric motor  3  when the skew command sk_c is forcibly kept at 0, where the torque command value Tr_c and rotating speed are the same as those in the graph a. A variation width Δ 1  of the output torque of the electric motor  3  in Example is smaller than a variation width Δ 2  of the output torque of the electric motor  3  in Comparative example. In this way, according to the controller  8  of the present embodiment, a variation in the output torque of the electric motor  3  in a low torque and low speed operating state can be appropriately suppressed. 
     On the other hand, when the electric motor  3  is not in the low torque and low speed operating state, the skew command sk_c is set at 0 (since θm_s′=θm_s). Therefore, the electric angle θe of the rotor  11  that is used for each computation by the dq conversion section  29   a  and the three-phase conversion section  37   a  of the first electric current control section  22   a  agrees with the electric angle θe of the rotor  11  that is used for each computation by the dq conversion section  29   b  and the three-phase conversion section  37   b  of the second electric current control section  22   b . Therefore, a respective phase electric current of the armature winding  13   a  of the stator  12   a  and a respective phase electric current of the armature winding  13   b  of the stator  12   b  are in the same phase. As a result, the magnetic flux generated by the armature windings  13   a  in V-phase, U-phase, and W-phase of the stator  12   a  in the axis center direction of the rotor  11  and the magnetic flux generated by the armature windings  13   b  in V-phase, U-phase, and W-phase of the stator  12   b  in the axis center direction of the rotor  11  will be mutually reinforced to a maximum extent. Therefore, in the operating state of the electric motor  3  other than the low torque and low speed operating state, the electric motor  3  can be operated with a high energy efficiency (with a decreased energy loss), or the output torque of the electric motor  3  can be made a high torque. 
     Further, in the present embodiment, the stators  12   a  and  12   b  have the same magnetic circuit cross section, and therefore the maximum magnetic flux is allowed to pass through the stators  12   a  and  12   b  in accordance with their magnetic circuit cross section. As a result, the maximum value of the output torque of the electric motor  3  can be enhanced. 
     In the above-described embodiment, out of the first electric current control section  22   a  and the second electric current control section  22   b , the first electric current control section  22   a  uses the corrected rotating angle θm_s′ to carry out the operations by the dq conversion section  29   a  and the three-phase conversion section  37   a . Instead, the first electric current control section  22   a  may use the rotor angle detected value θm_s as it is to carry out the operations by the dq conversion section  29   a  and the three-phase conversion section  37   a , whereas the second electric current control section  22   b  uses the corrected rotating angle θm_s′ to carry out the operations by the dq conversion section  29   b  and the three-phase conversion section  37   b.    
     Alternatively, the skew command sk_c is multiplied by α (0&lt;α&lt;1), which is added to the rotor angle detected value θm_s. Then, the resultant is set as a first corrected rotating angle (=θm_s+α·sk_c). And the skew command sk_c is multiplied by (1−α), which is subtracted from the rotor angle detected value θm_s. Then, the resultant is set as a second corrected rotating angle (=θm_s−(1−α)·sk_c). The first electric current control section  22   a  may use any one of the first corrected rotating angle and the second corrected rotating angle to carry out the operations by the dq conversion section  29   a  and the three-phase conversion section  37   a , whereas the second electric current control section  22   b  may use the other to carry out the operations by the dq conversion section  29   b  and the three-phase conversion section  37   b.    
     In the present embodiment, the electric motor  3  operates with the skew command sk_c not being 0 only in the low torque and low speed operating state. However, the electric motor  3  may operate with the skew command sk_c not being 0 in the operating state other than this as needed. 
     The present embodiment has been exemplified as the electric motor  3  being installed in a parallel type hybrid vehicle  1 . However, the electric motor  3  may be installed an electric vehicle or a series type hybrid vehicle as the driving power source.