Control apparatus for AC rotary machine

A control controls starting of an AC rotary machine by calculating a resistance drop component, corresponding to a resistance drop of the AC rotary machine, based on a detection current, and adjusts angular frequency of an AC output voltage based on subtracting the resistance drop component from a voltage command, and, simultaneously, adjusting amplitude of the AC output voltage so that amplitude of an AC phase current may change in conformity with a predetermined function.

TECHNICAL FIELD

This invention relates to a control apparatus for an AC rotary machine wherein the AC rotary machine is controlled by employing a power inverter, and more particularly to a control apparatus for an AC rotary machine wherein a start control for starting the AC rotary machine in a free-run state or the like is performed.

BACKGROUND ART

In a control apparatus for an AC rotary machine wherein the variable speed control of the AC rotary machine is performed by a power inverter without employing any rotational angular velocity detector for the AC rotary machine, a cost and wiring which are required for the rotational angular velocity detector can be omitted. Since, however, the rotational angular velocity detector is not employed, the rotational velocity of the AC rotary machine cannot be known when the AC rotary machine starts in a free-run state, that is, in a state where the power inverter stops a power inversion operation and where the AC rotary machine is rotating at any desired rotational velocity, so that a stable start is difficult to be performed without generating large fluctuations in the torque and rotational velocity of the AC rotary machine.

A start method wherein an induction motor is started without employing any rotational angular velocity detector is disclosed in JP 63-77397A (Patent Document 1). In Patent Document 1, the instantaneous magnetic flux vector signal and instantaneous generation torque signal of the motor are calculated using switch state signals for commanding the respective phase output voltages of a power inverter, the voltage detection value of a DC voltage source and the current detection value of the motor, and three control flags are generated using the instantaneous magnetic flux vector signal and instantaneous generation torque signal of the motor. Owing to the combination of the three control flags, the switching state of the power inverter is designated so as to generate a voltage vector optimizing a torque response, the generation torque of the motor is controlled so as to follow up a command value, and a magnetic flux vector is controlled so as to depict an approximate circular locus, so that the induction motor is started from a free-run state. In the start control, the angular frequency of an AC voltage in the power inverter is set higher than the highest angular frequency which arises in a normal operation, and a switch4on the DC input side of the power inverter is thereafter closed to pull in the motor.

DISCLOSURE OF THE INVENTION

Problems that the Invention is to Solve

In Patent Document 1, the instantaneous magnetic flux vector signal of the induction motor is calculated on the basis of a primary terminal voltage vector value, a primary terminal current vector and a primary winding resistance in the induction motor, and a voltage command for the power inverter is corrected so that this instantaneous magnetic flux vector signal may hold a desired value. However, in a case where the induction motor is arranged, for example, outdoors, its temperature fluctuates greatly, and by way of example, it is below the freezing point in midwinter and exceeds 100° C. in the overload continuous operation of the induction motor. A control apparatus in Patent Document 1 starts the induction motor by correcting the voltage command for the power inverter so that the instantaneous magnetic vector signal of the induction motor may hold the desired value under the temperature change of the induction motor. With the temperature change of the induction motor, however, a large change arises also in the amplitude of an AC phase current flowing through the induction motor, to incur the drawback that the AC phase current enlarges at the time of the start. In the worst case, a situation where a protective function is actuated occurs to bring about a situation where the start of the induction motor cannot be effected. Moreover, in the control apparatus in Patent Document 1, the voltage command for the power inverter is corrected so that the instantaneous magnetic flux vector signal may hold the desired value, and hence, the disorder of the output torque of the induction motor arises at the time of the start on account of the delay of the correction, to incur the drawback that a shock and a rotation number fluctuation take place.

This invention consists in proposing a control apparatus for an AC rotary machine as improves such drawbacks and as can effect a stable start.

Means for Solving the Problems

A control apparatus for an AC rotary machine according to this invention including: control means for generating a voltage command on the basis of a current command, and for generating a switching command on the basis of the voltage command; a power inverter which generates an AC output voltage that has its amplitude and its angular frequency controlled on the basis of the switching command; at least one AC rotary machine which is connected to said power inverter; and a current detector which outputs a detection current on the basis of an AC phase current that flows from said power inverter to said AC rotary machine;

wherein: said control means is configured so as to perform controls including a start control for said AC rotary machine; said control means operates in the start control to calculate a resistance drop component corresponding to a resistance drop of said AC rotary machine on the basis of the detection current, and to adjust the angular frequency of the AC output voltage on the basis of a subtraction output obtained by subtracting the resistance drop component from the voltage command; and said control means simultaneously operates in the start control to adjust an amplitude of the AC output voltage so that an amplitude of the AC phase current may change in conformity with a predetermined function.

Advantages of the Invention

In the control apparatus for the AC rotary machine according to this invention, the control means operates in the start control to calculate the resistance drop component corresponding to the resistance drop of the AC rotary machine on the basis of the detection current, and to adjust the angular frequency of the AC output voltage on the basis of the subtraction output obtained by subtracting the resistance drop component from the voltage command, so that the angular frequency of the AC output command of the power inverter can be adjusted without involving a delay as in a prior-art control apparatus wherein a voltage command for a power inverter is corrected so that an instantaneous magnetic flux vector signal may hold a desired value, and simultaneously, the amplitude of the AC output voltage of the power inverter is adjusted so that the amplitude of the AC phase current flowing from the power inverter to the AC rotary machine may change in conformity with the predetermined function, so that even under the temperature change of the AC rotary machine, the large change of the amplitude of the AC phase current is suppressed, and the AC rotary machine can be stably started.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, several embodiments of this invention will be described with reference to the drawings.

FIG. 1is a block diagram showing Embodiment 1 of a control apparatus for an AC rotary machine according to this invention. The control apparatus for the AC rotary machine in Embodiment 1 includes a power inverter1, the AC rotary machine2, current detector3, and a control means10. The power inverter1is, for example, a three-phase power inverter, which performs the power inversion between a DC power and a three phase AC power. The power inverter1includes three-phase inversion circuits U, V and W which are connected to a DC power source in parallel with one another. As is well known, each of the inversion circuits U, V and W includes a pair of switches on a plus side and a minus side, and AC power feed lines1u,1vand1wof the three phases are connected between the pairs of switches of the respective inversion circuits.

The power inverter1is concretely configured as a three-phase power inverter of variable-voltage and variable-frequency type. This power inverter1receives switching commands Su*, Sv* and Sw* from the control means10, and when it inverts the DC power into the three-phase AC power, it generates the three-phase AC power having controlled output voltage and controlled angular frequency, on the basis of the switching commands Su*, Sv* and Sw*. The switching commands Su*, Sv* and Sw* are respectively fed to the inversion circuits of the U-phase, V-phase and W-phase, and they turn ON and OFF the pairs of switches of the respective inversion circuits in controlled phases.

In Embodiment 1, the AC rotary machine2is an AC induction machine2I, concretely an induction motor of the three phases, and it is connected to the power inverter1through the AC power feed lines1u,1vand1wof the three phases. The current detector3is arranged in, for example, the AC power feed lines1uand1v, and it generates a detection current idet on the basis of AC phase currents flowing from the power inverter1to the AC induction machine2I, that is, a U-phase current iu and a V-phase current iv. The detection current idet contains a U-phase detection current component iudet and a V-phase detection current component ivdet. The U-phase detection current component iudet corresponds to the U-phase current iu flowing through the U-phase AC power feed line1u, while the V-phase current component ivdet corresponds to the V-phase detection current iv flowing through the V-phase AC power feed line1v. In Embodiment 1, the AC rotary machine2is the AC induction machine2I, and hence, AC phase currents iu, iv and iw which flow from the power inverter1to the AC induction machine2I in the start period of the AC rotary machine become excitation currents for the AC induction machine2I.

The control means10includes voltage command generation means11, coordinate transformers31and32, and phase signal generation means40. The voltage command generation means11generates a voltage command v* on rotating two-axis coordinates which include a d-axis and a q-axis intersecting orthogonally. The voltage command v* contains a d-axis voltage command vd* and a q-axis voltage command vq*. The voltage command generation means11includes start current command means12, post-start current command means15, changeover means18, and a current controller20.

The start current command means12is used when the start control of the AC induction machine2I is performed by the control means10. At the time when the power inverter1stops a power inversion operation and when the AC induction machine2I is in a free-run state, the start control is used for starting the power inverter1and beginning the power inversion operation thereof, so as to start the AC induction machine2I by the power inverter1. This start control is executed in that period of the start period SP before an armature magnetic flux φ rises in the AC induction machine2I. The start period SP is concretely several tens milliseconds to several hundred milliseconds, and it is set at, for example, 100 milliseconds, namely 100 (msec) in Embodiment 1. The start current command means12generates a start current command i1* in the start period SP.

The start current command means12includes a function generator13and a band-pass filter14, and it generates the start current command i1*. The start current command i1* contains a d-axis start current command id1* and a q-axis start current command iq1*. The band-pass filter14is connected to the function generator13, and it generates the d-axis start current command id1*. The q-axis start current command iq1* is made, for example, zero in Embodiment 1, and iq1*=0 holds. The q-axis start current command iq1*=0 is given from outside.

The post-start current command means15is used instead of the start current command means12by changing-over the changeover means18after the completion of the start. The post-start current command means15generates a post-start current command i2*. The post-start current command i2* contains a d-axis current command id2* and a q-axis current command iq2*. The post-start current command means15has a d-axis current command unit16and a proportional gain multiplier17. The d-axis current command unit16generates the post-start d-axis current command id2*. The proportional gain multiplier17receives a torque command τ*, and it multiplies the torque command τ* by a proportional gain K, thereby to generate the q-axis current command iq2*. That is, iq2*=τ*×K holds.

The changeover means18performs changeover from the start current command means12to the post-start current command means15after the lapse of the start period SP. In the start period SP, the changeover means18feeds the start current command i1* as a current command I* from the start current command means12to the current controller20, and after the lapse of the start period SP, it feeds the current command i2* as the current command I* from the post-start current command means15to the current controller20. The changeover means18includes a d-axis changeover switch18dand a q-axis changeover switch18q. The d-axis changeover switch18dperforms the changeover between the d-axis start current command id1* and the post-start d-axis current command id2*. The q-axis changeover switch18qperforms the changeover between the q-axis start current command iq1* and the post-start q-axis current command iq2*. The changeover switches18dand18qare changed-over in interlocking with each other. In the start period SP, the changeover switch18dselects the d-axis start current command id1* and feeds this d-axis start current command id1* to the current controller20as a d-axis current command id*, while the changeover switch18qselects the q-axis start current command iq1* and feeds this q-axis start current command iq1* to the current controller20as a q-axis current command iq*. After the start period SP has lapsed, both the changeover switches18dand18qare changed-over, and the changeover switch18dselects the post-start d-axis current command id2* and feeds this d-axis current command id2* to the current controller20as the d-axis current command id*, while the changeover switch18qselects the post-start q-axis current command iq2* and feeds this q-axis current command iq2* to the current controller20as the q-axis current command iq*.

FIG. 2Ashows a stepped function command is* which is outputted from the function generator13of the start current command means12, whileFIG. 2Bexemplifies a filter function command if* which is outputted from the band-pass filter14on the basis of the stepped function command is*. In Embodiment 1, the filter function command if* is outputted as the d-axis start current command id1*. InFIGS. 2A and 2B, the axes of abscissas are a common time axis. The stepped function command is* from the function generator13is in a stepped waveform which rises at a time of 0.1 (second), but the filter function command if* which is outputted from the band-pass filter14decreases with the lapse of time. In Embodiment 1, the control range of the angular frequency of the AC induction machine2I has been set at 1 to 60 (Hz), and also the pass bandwidth of the band-pass filter14has been set at 1 to 60 (Hz) in conformity therewith.

In an apparatus in which the band-pass filter14is not used, the stepped function command is* from the function generator13is fed to the current controller20as the d-axis start current command id1*. However, in a case, for example, where the AC rotary machine2is the AC induction machine2I and where this AC induction machine2I is started, it suffices to command a voltage and a current which contain the rotational angular frequency component of the AC induction machine2I, and the AC induction machine2I can be started without feeding any frequency component other than the frequency necessary for the commands. With the stepped function command is* from the function generator13as shown inFIG. 2A, an amplitude becomes equal for all frequency bands, but the filter function command if* which is outputted from the band-pass filter14extracts only the frequency bandwidth necessary for the start, so that the current amplitude of the power inverter1can be suppressed smaller than in the apparatus in which the stepped function command is* from the function generator13is used as the d-axis start current command

In such a case where the current bearing capacity characteristic of the power inverter1is tolerant against a current generated in a short time, the d-axis start current command id1* of larger magnitude can be given by setting the filter function command if* from the band-pass filter14as the d-axis start current command id1*, than by setting the stepped function command is* from the function generator13as the d-axis start current command id1*, whereby the precision of the detection current idet to be obtained from the AC rotary machine2is enhanced more, and the precision of the calculation of the angular frequency ω by the phase signal generation means40can be enhanced more. In this manner, the band-pass filter14generates the filter function command if* with the unnecessary signal components cut, so that the AC rotary machine2can be efficiently started without feeding any wasteful current command component unnecessary for the start, in the start period SP.

Incidentally, although the function generator13has been described as generating the stepped function command is*, an M-series signal or a pseudo-noise signal utilizing a random number table can also be generated instead of the stepped function command is*. Also in this case, the band-pass filter passes only the frequency component necessary for the start and generates the filter function command if*, so that the start can be efficiently effected without feeding any wasteful current component for the start.

The coordinate transformer31is a coordinate transformer from the rotating two-axis coordinates which include the d-axis and q-axis intersecting orthogonally, into the three-phase time coordinates, and it receives the voltage command v* and generates the switching commands Su*, Sv* and Sw*. The switching commands Su*, Sv* and Sw* are fed to the power inverter1. The coordinate transformer32is a coordinate transformer from the three-phase time coordinates into the rotating two-axis coordinates which include the d-axis and q-axis intersecting orthogonally, and it receives the detection current idet from the current detector3and transforms them into detection currention the rotating two-axis coordinates which include the d-axis and q-axis intersecting orthogonally. The detection currention the rotating two-axis coordinates contains a d-axis detection current id and a q-axis detection current iq.

Both the d-axis detection current id and the q-axis detection current iq are fed to the current controller20of the voltage command generation means11. The current controller20receives the d-axis detection current id and q-axis detection current iq together with the d-axis current command id* and q-axis current command iq*, and it generates the d-axis voltage command vd* and q-axis voltage command vq* so as to equalize the d-axis detection current id to the d-axis current command id* and to equalize the q-axis detection current iq to the q-axis current command iq*.

As stated before, in the start period SP, the control means10uses the start current command means12, it generates the voltage command v* on the basis of the start current command i1* of the start current command means12, and it generates the switching commands Su*, Sv* and Sw* by the coordinate transformer31on the basis of the voltage command v*, so as to start the power inverter1. In this start period SP, the AC phase currents iu, iv and iw which flow from the power inverter1to the AC induction machine2I become the excitation currents for the AC induction machine2I, and the amplitude of the AC phase currents iu, iv and iw is determined by the start current command i1*. In the start current command i1*, the d-axis start current command id1* is set as the filter function command if* outputted from the band-pass filter14, and the q-axis current command iq1* is set at zero.

Letting “ia” denote the amplitude of the AC phase currents iu, iv and iw, the amplitude ia is expressed by the following formula (1):
ia=a×{(id*)2+(iq*)2}1/2(1)

In the start period SP, id1*=id* holds, and iq1*=iq*=0 holds, so that the amplitude ia becomes the following formula (2):
ia=a×id1*  (2)

In other words, the amplitude of the AC phase currents iu, iv and iw is determined by the d-axis start current command id1* as indicated by Formula (2). In a case where the AC rotary machine2such as the AC induction machine2I is arranged, for example, outdoors, its temperature fluctuates greatly, and by way of example, it is below the freezing point in midwinter and exceeds 100° C. in the overload continuous operation of the AC rotary machine2, so that the armature resistance R of the AC rotary machine2fluctuates greatly with the change of the temperature. In Embodiment 1, however, the amplitude of the AC phase currents iu, iv and iw is determined by the d-axis start current command id1* in the start period SP, thereby to perform a current control by the current controller20, so that the temperature change of the AC rotary machine2is not influential. In the start period SP, accordingly, the amplitude of the AC phase currents iu, iv and iw does not change greatly with the temperature change of the AC rotary machine2, a situation where a protective function operates does not occur, and the AC rotary machine2can be stably started.

Next, the phase signal generation means40will be described. This phase signal generation means40includes means41for calculating the resistance drop of the AC rotary machine2, subtraction means43, an integrator45, a divider46, and an integrator47. The resistance drop calculation means41includes a d-axis resistance drop calculator41d, and a q-axis resistance drop calculator41q. The d-axis resistance drop calculator41dis fed with the d-axis detection current id from the coordinate transformer32, and it multiplies this d-axis detection current id by the armature resistance R of the AC rotary machine2, thereby to output a d-axis resistance drop component (R×id). The q-axis resistance drop calculator41qis fed with the q-axis detection current iq from the coordinate transformer32, and it multiplies this q-axis detection current iq by the armature resistance R of the AC rotary machine2, thereby to output a q-axis resistance drop component (R×iq).

The subtraction means43includes a d-axis subtractor43d, and a q-axis subtractor43q. The d-axis subtractor43dis fed with the d-axis voltage command vd* from the current controller20, and with the d-axis resistance drop component (R×id) from the d-axis resistance drop calculator41d. This d-axis subtractor43dsubtracts the d-axis resistance drop component (R×id) from the d-axis voltage command vd*, thereby to deliver the subtraction output (vd*−R×id) between them. The q-axis subtractor43qis fed with the q-axis voltage command vq* from the current controller20, and with the q-axis resistance drop component (R×iq) from the q-axis resistance drop calculator41q. This q-axis subtractor43qsubtracts the q-axis resistance drop component (R×iq) from the q-axis voltage command vq*, thereby to deliver the subtraction output (vq*−R×iq) between them.

The integrator45is fed with the subtraction output (vd*−R×id) from the d-axis subtractor43d. The integrator45integrates this subtraction output (vd*−R×id), and delivers an integral output φd. This integral output φd corresponds to a d-axis component φd at the time when the armature magnetic flux φ of the AC rotary machine2is decomposed into the d-axis component φd and a q-axis component φq on the rotating two-axis coordinates which include the d-axis and q-axis intersecting orthogonally, and when the q-axis component φq is made zero. The divider46is fed with the subtraction output (vq*−R×iq) from the q-axis subtractor43q, and with the integral output φd from the integrator45. The divider46divides the subtraction output (vq*−R×iq) by the integral output φd, thereby to generate a division output ω. That is, the division output ω is expressed by the following formula (3):

This division output ω corresponds to the angular frequency ω of the AC output voltage which is outputted from the power inverter1when the q-axis component φq of the armature magnetic flux φ of the AC rotary machine2is made zero.

The integrator47is fed with the division output ω from the divider46, and it integrates this division output ω, thereby to generate a phase signal θ. This division output ω corresponds to the phase θ of the AC output voltage which is outputted from the power inverter1when the q-axis component φq of the armature magnetic flux φ of the AC rotary machine2is made zero. This phase signal θ is fed to the coordinate transformers31and32. Using the phase signal θ, the coordinate transformer31transforms the voltage command v* on the rotating two-axis coordinates which include the d- and q-axes intersecting orthogonally, into the switching commands Su*, Sv* and Sw* on the three-phase time coordinates, and using the phase signal θ, the coordinate transformer32transforms the detection currents iudet and ivdet on the three-phase time axis, into the detection currents id and iq on the d- and q-axes of the rotating two-axis coordinates which include the d- and q-axes intersecting orthogonally.

In this manner, in the phase signal generation means40, the d-axis resistance drop component (R×id) and q-axis resistance drop component (R×iq) of the AC rotary machine2are calculated on the basis of the detection current idet detected by the current detector3, the d-axis resistance drop component (R×id) and q-axis resistance drop component (R×iq) are respectively subtracted from the d-axis voltage command vd* and q-axis voltage command vq*, and the angular frequency ω of the AC phase currents iu, iv and iw flowing to the AC rotary machine2is calculated on the basis of the subtraction outputs (vd*−R×id) and (vq*−R×iq), so that the angular frequency of the AC output voltage to be outputted from the power inverter1can be adjusted so as to agree with the angular frequency of the AC phase currents iu, iv and iw flowing to the AC rotary machine.

The angular frequency ω which is calculated by the phase signal generation means40will be further described. In a case where the rotating two-axis coordinates which include the d-axis and q-axis intersecting orthogonally are rotating at any desired angular frequency ω, the d-axis component φd and q-axis component φq of the armature magnetic flux φ of the AC rotary machine2are expressed by the following formulas (4) and (5):
φd=∫(vd*−R×id+ω×φq)dt(4)
φq=∫(vq*−R×iq−ω×φd)dt(5)

Here, “vd*” and “vq*” denote the voltage commands on the rotating two-axis coordinates as are generated by the current controller20of the voltage command generation means11, and “id” and “iq” denote the detection currents obtained in such a way that the detection currents iudet and ivdet which correspond to the AC phase currents iu and iv flowing to the AC rotary machine2are transformed onto the rotating two-axis coordinates by the coordinate transformer32.

Besides, the output torque τm of the AC rotary machine2is expressed by the following formula (6):
τm=Pm×(φd×iq−φq×id)  (6)

Here, “Pm” denotes the number of pair poles of the AC rotary machine2.

In a case where the d-axis direction of the rotating two-axis coordinates and the direction of the armature magnetic flux φ are in agreement, the q-axis component φq of the armature magnetic flux φ becomes zero, and φq=0 holds. When φq=0 is therefore substituted into Formulas (4) and (5), respectively, the following formulas (7), (8) and (9) are obtained:
φd=∫(vd*−R×id)dt(7)
vq*−R×iq−ω×φd=0  (8)
ω=(vq*−R×iq)÷φd(9)

In other words, when the rotating two-axis coordinates which include the d- and q-axes intersecting orthogonally are rotated in synchronism with the angular frequency ω calculated in conformity with Formulas (7), (8) and (9), the d-axis direction of the rotating two-axis coordinates and the direction of the armature magnetic flux φ can be brought into agreement, and the q-axis component φq of the armature magnetic flux φ can be made zero, that is, φq=0 can be held.

The phase signal generation means40calculates the angular frequency ω in conformity with Formulas (7), (8) and (9). The d-axis subtractor43dcalculates (vd*−R×id) in Formula (7), and the integrator45calculates the d-axis component φd of the armature magnetic flux φ as is expressed by Formula (7). The q-axis subtractor43qcalculates (vq*−R×iq) in Formula (9), and the divider47calculates the angular frequency ω expressed by Formula (9). The phase signal θ is calculated on the basis of the angular frequency ω, and it controls the coordinate transforms of the coordinate transformers31and32. As a result, therefore, the rotating two-axis coordinates which include the d- and q-axes intersecting orthogonally are rotated in synchronism with the angular frequency ω calculated in conformity with Formula (9), the d-axis direction of the rotating two-axis coordinates and the direction of the armature magnetic flux φ can be brought into agreement, and the q-axis component φq of the armature magnetic flux φ can be made zero, that is, φq=0 can be held. The angular frequency of the AC output voltage to be outputted from the power inverter1is controlled so as to equalize to the rotational angular frequency of the rotating two-axis coordinates, in correspondence with the rotational angular frequency ω of the rotating two-axis coordinates, so that the angular frequency of the AC output voltage to be outputted from the power inverter1is adjusted so as to agree with the angular frequency of the AC phase currents iu, iv and iw flowing to the AC rotary machine.

In addition, in Embodiment 1, simultaneously with the control of the angular frequency of the AC output voltage to be outputted from the power inverter1, the start current command circuit12feeds the q-axis start current command iq1*=0 to the current controller20as the q-axis current command iq* in the start period SP. In the start period SP, accordingly, the command iq* is also made zero together with the component φq. That is, iq*=0 holds, and φq=0 holds. In the start period SP, therefore, (φd×iq−φq×id) in Formula (6) becomes zero, and the output torque τm of the AC rotary machine2becomes zero, that is, τm=0 is held.

As described above, in Embodiment 1, the angular frequency ω of the rotating two-axis coordinates is controlled by the phase signal θ for the coordinate transformers31and32, so that the angular frequency of the AC output voltage to be outputted from the power inverter1can be brought into agreement with the angular frequency of the AC phase currents iu, iv and iw flowing to the AC rotary machine2, without any delay. Simultaneously, in the start period SP, the output torque τm of the AC rotary machine2is made zero, and the AC rotary machine2in a free-run state is started, whereby the output torque of the AC rotary machine2is prevented from fluctuating in the start period SP, and the occurrences of a shock and a rotation number fluctuation in the AC rotary machine2can be suppressed. In the prior-art control apparatus disclosed in Patent Document 1, the angular frequency of the output voltage of the power inverter is corrected on the basis of the angular frequency ω, and hence, a shaft deviation arises due to the delay of the correction. In contrast, in Embodiment 1, the shaft deviation ascribable to the delay of the correction is eliminated, and the AC rotary machine2can be started with the shock and the rotation number fluctuation suppressed.

Besides, in Embodiment 1, the start current command i1* to be fed to the current controller20is afforded from the start current command circuit12irrespective of the armature resistance R of the AC rotary machine2, so as to determine the amplitude of the AC phase currents iu, iv and iw. Accordingly, even when the armature resistance R of the AC rotary machine2has changed depending upon the temperature condition of the AC rotary machine2, the start current command i1* is not influenced by the armature resistance R. Accordingly, even when the armature resistance R of the AC rotary machine2has changed with the temperature condition of the AC rotary machine2in the start period SP, the amplitude of the AC currents flowing to the AC rotary machine2does not fluctuate, with the result that the situation where the protective function for overcurrent protection or the like operates can be avoided in the start period SP, to effect a stable start.

Besides, in Embodiment 1, the start is effected in such a way that the q-axis start current command iq1* in the start period SP is held at zero by the start current command means12, and that the initial value of the q-axis voltage command vq* in the start period SP as is generated by the current controller20is made zero. In this case, at the start time point of the start period SP, iq1*=0 and vq*=0 hold. At the start time point of the start period SP, accordingly, also the subtraction output (vq*−R×iq) of the q-axis subtractor43qbecomes zero, and also the division output ω of the divider46becomes zero. In other words, the angular frequency ω becomes zero at the start time point of the start period SP, and this angular frequency ω rises with the lapse of the start period SP.

In the control apparatus disclosed in Patent Document 1, at the start time point of the start period, the angular frequency of the power inverter is set to be higher than the highest angular frequency which arises in the normal operation of the power inverter. At the start time point of the start period, therefore, the angular frequency of the power inverter needs to be set at the frequency higher than the highest angular frequency after it is set to be either plus or minus, with the result that a start response becomes different in accordance with the rotating direction of the AC rotary machine. In Embodiment 1, the start is performed by making the angular frequency ω of the power inverter1zero at the start time point of the start period SP, so that the stable start can be always effected irrespective of the rotating direction of the AC rotary machine2.

Incidentally, although the q-axis start current command iq1* is held at zero in the start period SP in Embodiment 1, a similar advantage can be obtained even when the q-axis start current command iq1* is held at a predetermined value other than zero in the start period SP. In this case, the d-axis component φd of the armature magnetic flux φ enlarges from zero with the increase of the d-axis start current command id1*, and the output torque τm of the AC rotary machine2enlarges with the increase of the d-axis component φd of the armature magnetic flux. In the start period SP, however, the d-axis start current command id1* enlarges from zero, with the result that also the output torque τm of the AC rotary machine2enlarges from zero, and the AC rotary machine2can be stably started with a large shock and a sudden rotation number fluctuation suppressed.

Embodiment 1 consists in starting the AC rotary machine2when the AC rotary machine2is in its free-run state, whereas Embodiment 2 consists in starting the AC rotary machine2when whether the AC rotary machine2is in its free-run state or its stop state cannot be discriminated. The control means10has the same configuration as in Embodiment 1, and it starts the power inverter1so as to start the AC rotary machine2. A start control at the time when the AC rotary machine2is in the free-run state is the same as in Embodiment 1, and also in a case where the AC rotary machine2is in the stop state, a stable start can be effected in the same manner as in Embodiment 1.

When the AC rotary machine2is in the stop state, the rotational angular frequency of the AC rotary machine2is zero at the start time point of the start period SP, and also the angular frequency ω calculated by the phase signal generation means40becomes zero, but with the start of the power inverter1, the armature magnetic flux φ of the AC rotary machine2rises gradually, and the stable start can be effected.

FIG. 3is a block diagram showing Embodiment 3 of a control apparatus for an AC rotary machine according to this invention. Embodiment 3 is such that the control means10in Embodiment 1 is replaced with control means10A, in which the start current command means12in Embodiment 1 is replaced with start current command means12A. In this start current command means12A, a band-pass filter14is removed, and a stepped function command is* is fed from the function generator13to the current controller20through the d-axis changeover switch18dof changeover means18as the d-axis start current command id1*. The others are the same in configuration as in Embodiment 1 or 2.

In Embodiment 3, the wasteful component of the start current command id1* cannot be cut by the band-pass filter14, but the same advantages as in Embodiment 1 or 2 can be obtained as to the others.

FIG. 4is a block diagram showing Embodiment 4 of a control apparatus for an AC rotary machine according to this invention. In Embodiment 4, a synchronous machine2S is used as the AC rotary machine2. This synchronous machine2S is concretely a three-phase synchronous motor by way of example.

Even when the AC rotary machine2is the synchronous machine2S, Formula (1) to Formula (9) hold similarly, so that the same start control as in Embodiment 1 can be basically performed also in Embodiment 4. In Embodiment 4, with the use of the synchronous machine2S, the control means10in Embodiment 1 is replaced with control means10B, in which the start current command means12in Embodiment 1 is replaced with start current command means12B. In this start current command means12B, the q-axis start current command iq1* is made zero, and also the d-axis start current command id1* is made zero, that is, id1*=0 holds, and this command id1*=0 is fed to the current controller20through the d-axis changeover switch18dof changeover means18. The q-axis start current command iq1*=0 is fed to the current controller20through the q-axis changeover switch18qof the changeover means in the same manner as in Embodiment 1. The others are the same in configuration as in Embodiment 1.

The AC rotary machine2is the induction machine2I in Embodiment 1, and for starting the induction machine2I which is in the free-run state, it is necessary to feed the voltage and current of the rotational angular velocity component to the induction machine2I. In case of starting the synchronous machine2S in its free-run state, however, an induced voltage caused by a rotor is generated in the synchronous machine2S, and hence, the voltage and current of the rotational angular velocity component need not be fed from the power inverter1, so that the d-axis start current command id1* is held at zero. In starting the synchronous machine2S, at the start time point of the start period SP thereof, AC phase currents iu, iv and iw flow so as to cancel out the induced voltage generated in the synchronous machine2S, in a very short time. In the same manner as in Embodiment 1, therefore, phase signal generation means40calculates the angular frequency ω on the basis of the AC phase currents iu, iv and iw, and the angular frequency of the AC output voltage of the power inverter1is controlled on the basis of the angular frequency ω. In Embodiment 4, the d-axis start current command id1* is made zero, whereby the synchronous machine2S can be efficiently started without feeding any wasteful current to the synchronous machine2S. Incidentally, although the q-axis start current command iq1* is made zero in the same manner as in Embodiment 1, it can also be made a predetermined value other than zero.

FIG. 5is a block diagram showing Embodiment 5 of a control apparatus for an AC rotary machine according to this invention. Also Embodiment 5 uses a synchronous machine2S as the AC rotary machine2, likewise to Embodiment 4.

In Embodiment 5, the control means10B in Embodiment 4 is replaced with control means10C, in which the start current command means12B in Embodiment 4 is replaced with start current command means12C. In the start current command means12C, a d-axis start current command unit19is used, and the d-axis start current command id1* is fed from this d-axis start current command unit19to the current controller20through the d-axis changeover switch18dof changeover means18. This d-axis start current command unit19is fed with an external command io=0 for establishing the d-axis start current command id1*=0, and an angular frequency ω from the divider46of phase signal generation means40. The others are the same in configuration as in Embodiment 4.

In a case where the absolute value of the angular frequency ω from the divider46is smaller than a predetermined value ωBASE, the d-axis start current command unit19brings the d-axis start current command id1* to zero on the basis of the external command io, that is, it establishes id1*=0. Besides, in a case where the absolute value of the angular frequency ω from the divider46is equal to or larger than the predetermined value ωBASE, the d-axis start current command unit19brings the d-axis start current command id1* to (A−B/ω) on the basis of the external command io.

These are expressed by the following formulas (10):
id1*=0(for |ω|<ωBASE)
id1*=A−B/ω(for |ω|≧ωBASE)  (10)

Owing to the use of this d-axis start current command unit19, when the absolute value of the angular frequency ω is smaller than ωBASE, the synchronous machine2S is efficiently started without feeding any wasteful current to the synchronous machine2S in order to start this synchronous machine2S, and when the absolute value of the angular frequency ω is equal to or larger than ωBASE, a magnetic flux weakening control is performed by setting (A−B/ω) at a negative value, whereby the voltage saturation of a power inverter1can be prevented. Incidentally, although the q-axis start current command iq1* is made zero in the same manner as in Embodiment 1, it can also be made a predetermined value other than zero.

FIG. 6is a block diagram showing Embodiment 6 of a control apparatus for an AC rotary machine according to this invention. Embodiment 6 is such that two AC rotary machines, concretely two induction machines2I1and2I2are connected to a power inverter1in parallel with each other. The induction machines2I1and2I2are three-phase induction motors whose ratings are equal to each other, and they are carried on, for example, an electric car so as to drive the electric car.

The induction machines2I1and2I2have armature resistances R which are equal to each other. Since these induction machines2I1and2I2are connected to the power inverter1in parallel to each other, the combined armature resistance thereof as seen from the power inverter1becomes (R/2). In Embodiment 6, the control means10in Embodiment 1 is replaced with control means10D, in which the phase signal generation means40in Embodiment 1 is replaced with phase signal generation means40D. This phase signal generation means40D has a resistance drop calculation circuit41D, which has a d-axis resistance drop calculator411dand a q-axis resistance drop calculator411q. The others are the same in configuration as in Embodiment 1.

The d-axis resistance drop calculator411dis fed with the d-axis detection current id from the coordinate transformer32, and it multiplies this d-axis detection current id by (R/2) so as to output a d-axis resistance drop {(R/2)×id}. The q-axis resistance drop calculator411qis fed with the q-axis detection current iq from the coordinate transformer32, and it multiplies this q-axis detection current iq by (R/2) so as to output a q-axis resistance drop {(R/2)×iq}. On the basis of the d-axis resistance drop and the q-axis resistance drop, the d-axis subtractor43ddelivers a subtraction output {vd*−(R/2)×id}, and the q-axis subtractor43qdelivers a subtraction output {vq*−(R/2)×iq}. Besides, the integrator45delivers an integral output ∫{vd*−(R/2)×id}dt, so that the division output ω of a divider46in Embodiment 6 becomes the following formula (11):
ω=∫{vd*−(R/2)×id}dt÷{vq*−(R/2)×iq}(11)

The phase signal generation means40D in Embodiment 6 calculates the angular frequency ω in conformity with Formula (11), and the angular frequency of the AC output voltage of the power inverter1is controlled so as to become equal to this angular frequency ω. Also in Embodiment 6, the two induction machines2I1and2I2in free-run states can be stably started in the same manner as in Embodiment 1. In a case where three or more induction machines are connected to the power inverter1in parallel, the multiplication coefficient in the resistance drop calculation circuit41D is adjusted in accordance with the number of the connected machines, whereby the three or more induction machines in free-run states can be stably started similarly.

FIG. 7is a block diagram showing Embodiment 7 of a control apparatus for an AC rotary machine according to this invention. Embodiment 7 is such that two AC rotary machines, concretely two synchronous machines2S1and2S2are connected to a power inverter1in parallel with each other. The synchronous machines2S1and2S2are, for example, three-phase synchronous motors whose ratings are equal to each other. With the use of the synchronous machines2S1and2S2, the control means10D in Embodiment 6 is replaced with control means10E, in which the start current command means12of the control means10D is replaced with start current command means12B. This start current command means12B is the same as in Embodiment 4. The others are the same in configuration as in Embodiment 6.

When, in starting the synchronous machines2S1and2S2which are in free-run states, the magnetic pole positions of the synchronous machines2S1and2S2have agreed, any circulating current does not flow between these synchronous machines2S1and2S2. If the synchronous machines2S1and2S2have no load in the case of starting the synchronous machines2S1and2S2which are in the free-run states, a state where the circulating current does not flow between these synchronous machines2S1and2S2is a stable state, and the synchronous machines2S1and2S2are started in this stable state. In this case, a combined armature resistance seen from the power inverter1becomes (R/2), and hence, the two synchronous machines2S1and2S2being in the free-run states can be stably started in the same manner as in Embodiment 4, by employing the same phase signal generation means40as in Embodiment 6. In a case where three or more synchronous machines are connected to the power inverter1in parallel, the multiplication coefficient in the resistance drop calculation circuit41D is adjusted in accordance with the number of the connected machines, whereby the three or more synchronous machines in free-run states can be stably started similarly.

INDUSTRIAL APPLICABILITY

A control apparatus for an AC rotary machine according to this invention is applied to a control apparatus for the AC rotary machine such as an induction machine or a synchronous machine.