Abstract:
A motor driving system for driving an induction motor with a rotation frequency detector. The induction motor drives a load, and the rotation frequency detector detects a rotation frequency of the induction motor. The motor driving system includes a variable speed driving unit and an inverter control unit. The variable speed driving unit is connected to the induction motor and has a capacitance at output. The variable speed driving unit rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency, and drives the induction motor with the second 3-phase AC power. The inverter control unit generates a frequency instruction and a temporary current instruction based on the detected rotation frequency and a rotation frequency instruction at least. Then, the inverter control unit corrects the temporary current instruction based on at least one of first correction depending on a value of the capacitance and second correction depending on a predetermined frequency component of the temporary current instruction to produce a current instruction, and controls the variable speed driving unit based on the frequency instruction and the current instruction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inverter control apparatus which is used for variable speed drive of a rotary machine, and a motor driving system using the same. 
     2. Description of the Related Art 
     FIG. 1 is a block diagram showing the circuit structure of a motor driving system using a conventional inverter control apparatus. A method of changing the frequency of 3-phase AC (alternating current) power Acc supplied to an induction motor is known as one method of controlling rotation speed of the induction motor. The conventional motor driving system is composed of a 3-phase AC power supply  50 , an inverter control unit  20 , a variable speed driving unit  60 , and an induction motor  11  with a rotation frequency detecting unit  12  for a load. The variable speed driving unit  60  is composed of a rectifier  61  and an inverter  62 . The variable speed driving unit  60  is used to control the rotation frequency of the induction motor. 
     The 3-phase AC power supply  50  supplies 3-phase AC power with a constant frequency (60 Hz) to the variable speed driving unit  60 . The variable speed driving unit  60  is composed of a rectifying unit  61  and a current type inverter  62 . The rectifying unit  61  rectifies the 3-phase AC power into DC power in response to a rectifier current instruction signal Id* from the inverter control unit  20 . The current type inverter  62  inverts the DC power into 3-phase AC power Acc in response to an inverter frequency instruction signal fe* from the inverter control unit  20 . Thus, the variable speed driving unit  60  controls the frequency of the 3-phase AC power Acc. The 3-phase AC power Acc is supplied to the multi-polar induction motor  11 . 
     The inverter control unit  20  is composed of converters  21  and  22 , adders  23  and  26 , a speed control section  24 , a slide calculating section  25 , and a current calculating section  27 . 
     For slide frequency control, a rotation frequency of the multi-polar induction motor  11  (the number of poles is p) is detected by the rotation frequency detecting unit  12  such as an encoder and a signal form indicative of the detected rotation frequency is supplied to the converter  22  of the inverter control unit  20 . The converter  22  converts the detected rotation frequency signal form into a 2-pole conversion detected rotation frequency signal fr 2  which is supplied to the adders  23  and  26 . A multi-polar rotation frequency instruction signal form* is supplied to the converter  21  from the outside, and the converter  21  converts the multi-polar rotation frequency instruction signal form* into a 2-pole conversion rotation frequency instruction signal fr 2 *, which is supplied to the adder  23 . 
     The adder  23  subtracts the 2-pole conversion detected rotation frequency signal fr 2  from the 2-pole conversion rotation frequency instruction signal fr 2 *, and supplies the subtracting result to the speed control unit  22 . The speed control unit  22  generates a 2-pole conversion torque instruction signal T 2 * from the subtracting result, and supplies to the current calculating section  27  and the slide calculating section  25 . The current calculating section  27  calculates the rectifier current instruction signal Id* from the 2-pole conversion torque instruction signal T 2 * and supplies to the rectifying unit  61  of the variable speed driving unit  60 . 
     The slide calculating section  25  calculates a slide frequency instruction signal Fs* from the 2-pole conversion torque instruction signal T 2 *. The adder  26  adds the slide frequency instruction signal Fs* and the 2-pole conversion detected rotation frequency signal fr 2  to produce the inverter frequency instruction signal fe*, which is supplied to the current type inverter  62  of the variable speed driving unit  60 . 
     In conjunction with the above description, an inverter control apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-69880). In this reference, an inverter inputs DC power from a DC power supply through a filter capacitor which is provided on the input side of the inverter, and supplies AC power with a variable voltage and a variable frequency to an AC motor to drive the AC motor. A voltage increase suppressing torque instruction correcting section of the inverter control apparatus inputs a capacitor DC voltage applied to the filter capacitor and an operation torque instruction, and outputs a first torque instruction to reduce regenerative torque for suppressing the increase of the DC voltage when the DC voltage increases. A change rate limiting section of the inverter control apparatus limits the change rate of the first torque instruction to output a second torque instruction. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an inverter control apparatus in which the stationary characteristics (such as effective values of voltage and current) of an inverter can be improved, and a motor driving system using the inverter control apparatus. 
     In an aspect of the present invention, a motor driving system for driving an induction motor with a rotation frequency detector, wherein the induction motor drives a load, and the rotation frequency detector detects a rotation frequency of the induction motor, includes a variable speed driving unit, and an inverter control unit. The variable speed driving unit is connected to the induction motor and has a capacitance at output. The variable speed driving unit rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency, and drives the induction motor with the second 3-phase AC power. The inverter control unit generates a frequency instruction and a temporary current instruction based on the detected rotation frequency and a rotation frequency instruction at least. Then, the inverter control unit corrects the temporary current instruction based on at least one of first correction depending on the capacitance and second correction depending on a predetermined frequency component of the temporary current instruction to produce a current instruction, and controls the variable speed driving unit based on the frequency instruction and the current instruction. 
     The variable speed driving unit may include a rectifying unit and a current type inverter. The rectifying unit rectifies the first 3-phase AC power in response to the current instruction to produce the DC power. The current type inverter has the capacitance at the output, and inverter converts the DC power into the second 3-phase AC power with the frequency in response to the frequency instruction. 
     Also, the inverter control unit may include a first correcting section which corrects the temporary current instruction for current flowing into the capacitance in the first correction to produce the current instruction. In this case, the first correcting section may correct the temporary current instruction based on a first correction factor to produce the current instruction. The first correction factor is determined based on the capacitor, a self-inductance of a stator of the induction motor stator, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor rotor, and slide. 
     Also, the inverter control unit may include a second correcting section which corrects the temporary current instruction based on a second correction factor in the second correction to produce the current instruction, wherein the second correction factor is determined such that the predetermined frequency component is set to a predetermined value. 
     Also, the inverter control unit may include a first correcting section and a second correcting section. The first correcting section corrects the temporary current instruction for current flowing into the capacitance in the first correction to produce a next temporary current instruction. The second correcting section which corrects the next temporary current instruction based on a second correction factor in the second correction to produce the current instruction, wherein the second correction factor is determined such that the predetermined frequency component is set to a predetermined value. In this case, the first correcting section may correct the temporary current instruction based on a first correction factor to produce the next temporary current instruction. The first correction factor is determined based on the capacitor, a self-inductance of a stator of the induction motor stator, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor rotor, and slide. 
     In another aspect of the present invention, an inverter control apparatus is for controlling a variable speed driving unit which rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency to drive an induction motor. The inverter control apparatus include a frequency instructing section and a current instructing section. The frequency instructing section generates a torque instruction based on a rotation frequency of the induction motor and a rotation frequency instruction at least and controls the frequency of the second 3-phase AC power based on the torque instruction and the rotation frequency of the induction motor. The current instructing section generates a temporary current instruction from the torque instruction, corrects the temporary current instruction based on a capacitance and an impedance of the induction motor, and controls the variable speed driving unit based on the corrected current instruction, the variable speed driving unit having the capacitance at output connected to the induction motor. In this case, the current instructing section may further correct the corrected current instruction such that a predetermined frequency component of the corrected current instruction is set to a predetermined value. 
     In still another aspect of the present invention, an inverter control apparatus outputs a control signal to a variable speed driving apparatus which drives an induction motor in a variable speed in response to the control signal. The inverter control apparatus includes a control signal generating section which generates the control signal based on a capacitance at an output terminal set of the variable speed driving apparatus which is connected to the induction motor at the output terminal set. 
     The control signal is determined based on parameters associated with a rotor and a stator of the induction motor. 
     Also, the control signal satisfies the following equation: 
     
       
         
           Idc*=Kc·Id*  
         
       
     
     where 
     Idc*: the control signal, 
     Id*: an auxiliary control signal to be outputted as the control signal when the capacitance is not considered, 
     Kc: a coefficient Kc determined based on a self-inductance of a stator of the induction motor, a mutual inductance between the stator and a rotor of the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor, and a slide quantity. 
     Also, the control signal generating section may generate the control signal to compensate for a capacitor current flowing into the capacitance. 
     Also, the control signal generating section generates the control signal based on a frequency instruction signal to instruct a frequency of an output of the variable speed driving apparatus, a self-inductance of a stator of the induction motor, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor, a slide quantity of the induction motor, in addition to the capacitance. 
     In yet still another aspect of the present invention, an inverter control apparatus outputs a control signal to a variable speed driving apparatus which drives an induction motor in a variable speed in response to the control signal. The inverter control apparatus includes a control signal generating section which generates the control signal based on a frequency component contained in an input signal and a remaining frequency components of the input signal. In this case, the control signal generating section multiplies the input signal and a reciprocal of a ratio of the frequency component to the input signal and generates the control signal based on the multiplication result. 
     In further another aspect of the present invention, an inverter control apparatus outputs a control signal to a variable speed driving apparatus which drives an induction motor in a variable speed in response to the control signal. The inverter control apparatus includes a capacitor correction signal generating section and a control signal generating section. The capacitor correction signal generating section generates a capacitor correction signal based on a capacitance connected with an output terminal set of the variable speed driving apparatus. The control signal generating section generates the control signal based on an inverter frequency component contained in the capacitor correction signal and a remaining frequency component of the capacitor correction signal other than the inverter frequency component. 
     In a still further another aspect of the present invention, a motor driving system includes a variable speed driving apparatus which supplies an AC control power generated based on a control signal to an AC motor to drive the AC motor in variable speed, and an inverter control apparatus which outputs the control signal to the variable speed driving apparatus. The variable speed driving apparatus includes a rectification section which rectifies AC power to generate DC power; and an inverter section which generates the AC control power from the generated DC power. The inverter control apparatus generates the control signal based on a capacitance connected with an output terminal set of the variable speed driving apparatus, an inverter frequency component of an input signal and a remaining frequency component of the input signal other than the inverter frequency component, and outputs the control signal to the rectification section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the circuit structure of a motor driving system using a conventional inverter control apparatus; 
     FIG. 2 is a block diagram showing the circuit structure of a motor driving system using an inverter control apparatus according to an embodiment of the present invention; 
     FIG. 3 is a block diagram showing the circuit structure of a variable speed driving unit used in the motor driving system according to the embodiment of the present invention; 
     FIG. 4 is a secondary side conversion equivalent circuit of an induction motor and the inverter control apparatus according to the embodiment of the present invention; and 
     FIG. 5 is an equivalent circuit obtained by simplifying the equivalent circuit shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a motor driving system using an inverter control apparatus of the present invention will be described with reference to the attached drawings. 
     FIG. 2 is a block diagram showing the circuit structure of a motor driving system using an inverter control apparatus according to an embodiment of the present invention. The motor driving system is composed of a 3-phase AC power supply  50 , an inverter control unit  20 , a variable speed driving unit  60 , a multi-polar induction motor  11  of p poles for a load, and a rotation frequency detecting unit  12  attached to the motor  11 . 
     The 3-phase AC power supply  50  supplies 3-phase AC power with a constant frequency (60 Hz) to the variable speed driving unit  60 . The variable speed driving unit  60  is used to control the rotation frequency of the induction motor  11 . 
     As shown in FIG. 3, the variable speed driving unit  60  is composed of a rectifying unit  61  and a current type inverter  62 . The rectifying unit  61  is composed of a 3-phase bridge type rectifier of group of devices  61   a  such as a thyristor, and a control unit. The control unit in the rectifying unit  61  controls the turn-on timing of each of the devices  61   a  in response to a signal indicative of a rectifier current instruction Idcp* from the inverter control unit  20 . The current type inverter is composed of DC reactors (smoothing reactor)  62   a  connected to the 3-phase bridge type rectifier, a group of self turn-off type devices  62   b  such as GTOs (gate turn-off thyristor) connected to the reactors  62   a , a group of capacitors  62   c  connected to the group of self turn-off type devices  62   b , and a control unit. The group of capacitors  62   c  is provided at the output of the current type inverter  62 . The control unit in the inverter  62  controls the turn-on timing of each of the self turn-off type devices  62   b  in response to a signal indicative of a rectifier current instruction Idcp* from the inverter control unit  20 . 
     The rectifier  61  rectifies the 3-phase AC power with a constant frequency (60 Hz) from a 3-phase AC power supply  50  into DC power in response to the rectifier current instruction signal Idcp* from the inverter control unit  20 . The current type inverter  62  inverts the DC power into 3-phase AC power Acc in response to the inverter frequency instruction signal fe* from the inverter control unit  20 . Also, the current type inverter  62  changes the frequency of the 3-phase AC power Acc to control the rotation frequency of the induction motor  11 . Thus, the variable speed driving unit  60  controls the frequency of the 3-phase AC power Acc. The 3-phase AC power Acc is supplied to the multi-polar induction motor  11 . The rotation frequency of the multi-polar induction motor  11  is detected by the rotation frequency detecting unit  12  such as an encoder and generates a multi-polar detected rotation frequency signal form, which is supplied to the inverter control unit  20 . 
     The inverter control unit  20  is composed of converters  21  and  22 , adders  23  and  26 , a speed control section  24 , a slide calculating section  25 , a current calculating section  27 , and a correcting section  70  of a capacitor correcting section  71  and a PWM correcting section  72 . A multi-polar rotation frequency instruction signal form* is supplied to the converter  21  from the outside. 
     The converter  22  converts the detected rotation frequency signal form into a signal indicative of 2-pole conversion detected rotation frequency fr 2  which is supplied to the adders  23  and  26 . Also, the converter  21  converts the multi-polar rotation frequency instruction signal form* into a signal indicative of 2-pole conversion rotation frequency instruction fr 2 *, which is supplied to the adder  23 . 
     A 2-pole motor model is generally used in the inverter control unit  20 . Here, for the simple description, the detected rotation frequency and the rotation frequency instruction signal are converted to have a 2-pole motor format. The 2-pole detected rotation frequency signal form and the 2-pole rotation frequency instruction signal form* are obtained from the following equations (1) and (2). 
     
       
           fr   2 = frm ×( p/ 2)  (1)  
       
     
     
       
           fr   2 *= frm *×( p/ 2)  (2)  
       
     
     where 
     p is the number of poles, 
     fr 2  is a 2-pole detected rotation frequency [Hz], form is a multi-polar detected rotation frequency [Hz], 
     fr 2 * is a 2-pole rotation frequency instruction signal [Hz], and 
     form* is a multi-polar rotation frequency instruction signal [Hz]. 
     The adder  23  subtracts the 2-pole conversion detected rotation frequency signal fr 2  from the 2-pole conversion rotation frequency instruction signal fr 2 *, and supplies the subtracting result to the speed control unit  22 . The speed control unit  22  is a PI controller, and the gain is previously determined in accordance with a specification. The speed control unit  22  generates a 2-pole conversion torque instruction signal T 2 * from the subtracting result using the following equation (3), and supplies to the current calculating section  27  and the slide calculating section  25 . 
     
       
           T   2 *= Kp ×(1+1/( sTI ))×( fr   2 *− fr   2 )  (3)  
       
     
     where 
     T 2 * is the 2 pole torque instruction signal [Nm], 
     Kp is a P gain of the PI controller [Nm/Hz], 
     TI is an I gain of the PI controller [sec], and 
     s is a Laplace transformation operator. 
     The slide calculating section  25  calculates a slide frequency instruction signal Fs* from the 2-pole conversion torque instruction signal T 2 *. If a total magnetic flux linkage number effective value Φr on the side of the rotor of the induction motor  11  and a resistance Rr on the side of the rotor of the induction motor  11  are known, the slide calculating section  23  determines a slide frequency instruction value fs* from the following equation (4). 
     
       
           fs *=( Rr×T   2 *)/(Φ r   2 ×2π)  (4)  
       
     
     where 
     fs* is a slide frequency instruction signal [Hz], 
     Rr is the resistance on the side of the induction motor rotor [Ω], 
     Φr is the total magnetic flux linkage effective value on the side of the induction motor rotor [Wb×T], and 
     T 2 * is a 2-pole motor conversion torque [Nm]. 
     The adder  26  adds the slide frequency instruction signal Fs* and the 2-pole conversion detected rotation frequency signal fr 2  to produce the inverter frequency instruction signal fe*, which is supplied to the current type inverter  62  of the variable speed driving unit  60 . 
     The inverter frequency instruction signal fe* determined from the following equation (5) is sent to the current type inverter  62  of the variable speed driving unit  60  and is used for the control of switches. 
     
       
           fe*=fr   2 + fs*   (5)  
       
     
     where 
     fe* is an inverter frequency instruction [Hz], and 
     fr 2  is a 2-pole detected rotation frequency [Hz]. 
     The current calculating section  27  calculates the rectifier current instruction signal Id* from the 2-pole conversion torque instruction signal T 2 * and supplies to the correcting section  70 . In the current calculating section  25 , the calculation of the following equations (6) and (7) is carried out. 
     
       
           Ii *=( Lrr/M )×((Φ r/Lrr ) 2 +( T   2 */ Φr ) 2 ) 1/2   (6)  
       
     
     
       
           Id *=(π/3{square root over ( )}2)× Ii*   (7)  
       
     
     where 
     Ii* is an inverter current effective value instruction [A], 
     Id* is a rectifier current instruction [A], 
     Lrr is a self-inductance on the side of the induction motor rotor [H], and 
     M is a mutual inductance between the stator and the rotor in the induction motor [H]. 
     In the conventional inverter control unit  20  shown in FIG. 1, the control has been carried out without noticing the effect of the capacitors  62   c  at the output of the current type inverter  62  shown in FIG.  2 . Also, the inverter  62  is generally operated in accordance with PWM (pulse width modulation). Therefore, the current waveform includes other frequency components in addition an inverter frequency component. 
     In this embodiment, the correcting section  70  carries out correction calculation to consider the effect of the capacitors at the output of the current type inverter  62  and the effect of PWM. The control is carried out based on the calculation result. As shown in FIG. 3, in the inverter control unit  90 , the capacitor correcting section  71  and the PWM correcting section  72  are provided in back of the current calculating section  25  in series in the order. 
     The capacitor correction section  71  generates and outputs a capacitor correction rectifier current instruction signal Idc* from the rectifier current instruction signal Id* supplied from the current calculating section  25  to the PWM correcting section  72 . The PWM correcting section  72  generates and outputs the correction rectifier current instruction signal Idcp* from the capacitor correction rectifier current instruction signal Idc* to the rectifying unit  61  of the variable speed driving unit  60 . 
     (1) The Capacitor Correcting Section  71   
     First, the capacitor correction will be described. Originally, the capacitor  62   c  with a small capacitance is selected for the inverter  62 . Therefore, it would be considered that the capacitor has no effect in the feedback system. In actuality, the effect of the capacitor  62   c  has been fully ignored. However, for the purpose of the more precious control of the stationary characteristics, it is important to consider the capacitor effect even in the feedback system. FIG. 4 is a secondary side conversion equivalent circuit of the induction motor  11  and the variable speed driving unit  60  with the effect of the capacitor  62   c  provided on the output of the inverter  62 . FIG. 5 is a diagram showing an equivalent circuit when the equivalent circuit shown in FIG. 4 is more simplified. 
     Because there are the DC reactors  62   a  in front of the current type inverter  62 , the impedance of the current type inverter  62  from the output side is large and the current type inverter  62  functions as a current source of an inverter current effective value Ii (M/Lrr). 
     In the equivalent circuit of FIG. 4, capacitor impedance Zc and induction motor impedance ZL are determined based on the following equations (8) and (9). 
     
       
           Zc= 1/( jωeC ( M/Lrr ) 2 )  (8)  
       
     
     
       
           ZL=Rs ( M/Lrr ) 2   +jωe ( LssLrr   2   /M   2   −Lrr )+( jωeLrr·Rr/S )/( jωeLrr+Rr/S )  (9)  
       
     
     It would be found from the equivalent circuit shown in FIG. 5 that it is sufficient to correct for the inverter current flowing into the capacitor impedance Zc. The current effective value obtained by subtracting the capacitor current effective value (Ic(M/Lrr)) flowing into the capacitor impedance Zc from the inverter current effective value (Ii(M/Lrr)) in the inverter  62  is supplied as the primary current effective value (I1(M/Lrr)) to the induction motor  11 . It is sufficient to consider a correction factor Kc [no dimension] as the capacitor correction when this effect is calculated using the following equation (10). 
     
       
           Idc*=Kc×Id*   (10)  
       
     
     where 
     Id*: a rectifier current instruction signal [A], 
     Idc*: a rectifier current instruction signal after the correction [A], and 
     Kc: a correction factor. 
     The correction factor Kc is represented by the following equation (11). 
     
       
           Kc =(( k 1− k 2) 2   +k 3 2 ) 1/2   (11)  
       
     
     where 
     k1=1−ωe 2 ·C(Lss−M 2 /Lrr), 
     k2=(ωe 2 ·C(Rr/S) 2 ·M 2 /Lrr)/((ωe·Lrr) 2 +(Rr/S) 2 ) 
     k3=ωe·C·Rs+(ωe 3 ·C(Rr/S)M 2 )/((ωe·Lrr) 2 +(Rr/S) 2 ), 
     ωe: inverter angular frequency (=fe*×2π) [rad/s], 
     C: a capacitance of the capacitors [F], 
     Lss: a self-inductance on the side of the induction motor stator [H], 
     M: a mutual inductance between the stator and rotor in the induction motor [H], 
     Lrr: self-inductance on the side of the induction motor rotor [H], 
     Rs: resistance on the side of the induction motor stator [Ω], 
     Rr: resistance on the side of the induction motor rotor [Ω], and 
     S: slide [no dimension]. 
     Also, seen from the above equation (11), the correction factor Kc could be rewritten by the following equation (12), when the capacitance is represented by C, if A, B, and D are appropriately selected. 
     
       
           Kc=D   1/2 {1−( AC+BC   2 )} 1/2   (12)  
       
     
     In this case, when capacitance C is enough small, 
     
       
           Kc=D   1/2 (1−(½)( AC+BC   2 ))  (13)  
       
     
     (2) PWM Correcting Section  72   
     Because the inverter is generally operated in a PWM (pulse width modulation) mode, the current waveform contains a basic inverter frequency component and other frequency components. Therefore, it is possible to carry out correction of the control of the basic frequency component in the PWM mode by using the following equation (14), if a reciprocal of the ratio of the basic inverter frequency component is used as a correction factor Kp. For example, the reciprocal is 1/0.9 when the ratio of the basic inverter frequency component is 90%. 
     
       
           Idcp*=Kp×Idc*   (14)  
       
     
     where 
     Kp: PWM correction factor [no dimension], and 
     Idcp*: current instruction signal after the correction [A] 
     It should be noted that both of the capacitor correction and the PWM correction are described. However, instead of carrying out both, either one may be carried out. The inverter control unit  90  may be composed of both of the capacitor correcting section  71  and the PWM correcting section  72  or may be composed of either of the capacitor correcting section  71  or the PWM correcting section  72 . When only the capacitor correction is carried out, the rectifier current instruction signal Idc* is outputted from the capacitor correcting section  71  to the rectifier  61 , just as it is. When only the PWM correction is carried out, the current instruction signal Id* is outputted from the current calculating section  25  to the PWM correcting section  72 . A product of the current instruction signal Id* and the above correction factor Kp is outputted to the rectifier  61  as the rectifier current instruction signal Idcp*. 
     By carrying out this control, the stationary characteristics of the inverter, i.e., the effective value of the voltage or current can be improved. 
     According to the inverter control apparatus of the present invention, the stationary characteristics can be improved, because the effect of the output stage of the inverter is considered.