Patent Description:
As a control method for an induction motor in regenerative operation, a method is described as in Patent Literature <NUM>, in which a frequency or voltage is corrected so that a q-axis secondary magnetic flux has a negative value in regenerative operation for preventing torque from being decreased due to a change in the magnetic flux and hence the shortage of torque is reduced.

<CIT> describes a controller for an induction motor that carries out estimation calculation of the magnetic flux, electric current and speed of the motor using the current and voltage of the induction motor, and uses the speed estimation value calculated to variable speed-control the motor by vector control through a power converter.

In the method of Patent Literature <NUM>, the q-axis secondary magnetic flux is controlled to have a negative value in regenerative operation, and hence robustness is secured. However, the state of vector control is out of an ideal state (the q-axis secondary magnetic flux = <NUM>). Thus, a problem arises in that in regenerative operation in a low-speed range, control performances to velocity command values are degraded.

An object of the present invention is to provide a power converter that can achieve highly accurate velocity control performances even in regenerative operation in a low-speed range.

A power conversion device according to the present invention is set out in claim <NUM>. A method for controlling a power conversion device according to the present invention is set out in claim <NUM>.

According to the present invention, stable, highly accurate velocity control performances can be provided even in regenerative operation in a low-speed range. Problems, configurations, and effects other than ones described above will be apparent from the description of embodiments below.

In the following, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited by these embodiments, the scope of protection is defined in the appended claims.

Moreover, in all the drawings for explaining the present invention, components having the same functions are designated the same reference numerals and signs, and overlapping description is sometimes omitted.

<FIG> is a block diagram of a power conversion device according to an embodiment.

An induction motor <NUM> generates torque by magnetic flux generated by the electric current of a magnetic flux axis (a d-axis) component and the electric current of a torque axis (a q-axis) component orthogonal to the magnetic flux axis.

A power converter <NUM> outputs voltage values proportional to output voltage command values Vu*, Vv*, and Vw* of three-phase alternating currents, and varies the output voltage values and the rotational frequency value of the induction motor <NUM>.

A direct current power supply 2a supplies a direct current voltage to the power converter <NUM>.

A current detector <NUM> outputs detected values Iuc, Ivc, and Iwc of three-phase alternating currents Iu, Iv, and Iw of the induction motor <NUM>. The current detector <NUM> may be configured in which the current detector <NUM> detects the line currents of the U-phase and the W-phase, for example, which are two phases of the three-phase induction motor <NUM>, and the line current of the V-phase is found as Iv = - (Iu + Iw) from the alternating current conditions (Iu + Iv + Iw = <NUM>).

A coordinate conversion unit <NUM> (a current vector component detecting unit) outputs detected current values Idc and Iqc of the d-axis (the magnetic flux component) and the q-axis (the torque component) based on the detected values Iuc, Ivc, and Iwc of the three-phase alternating currents Iu, Iv, and Iw and a phase estimation value θdc.

The velocity estimation operation unit <NUM> outputs a velocity estimation value ωr^ of the induction motor <NUM> based on a d-axis current command value Id*, a q-axis voltage command value Vqc**, the q-axis detected current value Iqc, an output frequency value ω<NUM>*, and electric constants (R<NUM>, R<NUM>', M, L<NUM>, and φ2d*) of the induction motor <NUM>.

A slip frequency operation unit <NUM> outputs a slip frequency value ωs* of the induction motor <NUM> based on the d-axis current command value Id*, a q-axis current command value Iq*, and a secondary electric constant T<NUM> of the induction motor <NUM>.

In a constant torque range, the d-axis current command value Id* is typically constantly controlled, and the magnetic flux Φ is constant as well. Thus, the slip frequency operation unit <NUM> operates and outputs the slip frequency value ωs* of the induction motor <NUM> based on the q-axis current command value Iq*. In a constant output range, the d-axis current command value Id* is variably controlled with respect to the number of revolutions, and the magnetic flux Φ is variable as well. Thus, the slip frequency operation unit <NUM> operates and outputs the slip frequency value ωs* of the induction motor <NUM> based on the d-axis current command value Id* and the q-axis current command value Iq*.

An adding unit <NUM> (an output frequency operation unit) outputs the output frequency value ω<NUM>*, which is the additional value of the velocity estimation value ωr^ and the slip frequency command value ωs*.

A phase estimation operation unit <NUM> integrates the output frequency value ω<NUM>*, and outputs the phase estimation value θdc.

A velocity command adjustment operation unit <NUM> outputs an adjustment value Δωr* of the velocity command based on the output frequency value ω<NUM>* and ω<NUM>* _lvl, which is a velocity command adjustment start level <NUM> for a velocity command value ωr*.

A subtracting unit <NUM> outputs a new velocity command value ωr**, which is a subtraction value between a velocity command value ωr*, which is supplied from a higher unit, and the adjustment value Δωr* for the velocity command.

A d-axis current command setting unit <NUM> outputs the d-axis current command value Id* of a positive polarity.

A velocity control operation unit <NUM> outputs the q-axis current command value Iq* based on a deviation ((ωr** - ωr^) between the new velocity command value ωr** and the velocity estimation value ωr^.

A vector control operation unit <NUM> outputs a d-axis voltage command value Vdc* and a q-axis voltage command value Vqc* based on the electric constants (R<NUM>, Lσ, M, and L<NUM>) of the induction motor <NUM>, the current command values Id* and Iq*, and the output frequency value ω<NUM>*.

A d-axis current control operation unit <NUM> (a current control operation unit) controls a d-axis current vector component value according to the d-axis current command value Id*, and outputs a d-axis voltage correction value ΔVd* based on a deviation (Id* - Idc) between the d-axis current command value Id* and the detected current value Idc.

A q-axis current control operation unit <NUM> (a current control operation unit) controls a q-axis current vector component value according to the q-axis current command value Iq*, and outputs a q-axis voltage correction value ΔVq* based on a deviation (Iq* - Iqc) between the q-axis current command value Iq* and the detected current value Iqc.

An adding unit <NUM> outputs Vdc**, which is an additional value of the d-axis voltage command value Vdc* and the d-axis voltage correction value ΔVd*.

An adding unit <NUM> outputs Vqc**, which is an additional value of the q-axis voltage command value Vqc* and the q-axis voltage correction value ΔVq*.

A coordinate conversion unit <NUM> outputs the three-phase alternating current voltage command values Vu*, Vv*, and Vw* based on the voltage command values Vdc** and Vqc** and the phase estimation value θdc.

First, the basic operation of a velocity sensorless control method in the case without using the velocity command adjustment operation unit <NUM>, which is a feature of the embodiment, will be described.

The d-axis current command setting unit <NUM> outputs the current command value Id*, which is necessary to generate the d-axis secondary magnetic flux φ2d of the induction motor <NUM>. In the velocity control operation unit <NUM>, the q-axis current command value Iq* is operated according to an arithmetic operation expressed in Expression <NUM> so that the velocity estimation value ωr^ is matched with the velocity command value ωr*. In Expression <NUM>, KpASR is the proportional gain of velocity control, and KiASR is the integral gain of velocity control. [Expression <NUM>] <MAT>.

In the vector control operation unit <NUM>, the voltage command values Vdc* and Vqc* expressed in Expression <NUM> are operated using the d-axis current command value Id*, the q-axis current command value Iq*, the electric constants (R<NUM>, Lσ, M, and L<NUM>) of the induction motor <NUM>, the d-axis secondary magnetic flux command value φ2d*, and the output frequency value ω<NUM>*. In Expression <NUM>, TACR is a current control delay time constant, R<NUM> is a primary resistance value, Lσ is a leakage inductance value, M is a mutual inductance value, and L<NUM> is a secondary inductance value. [Expression <NUM>] <MAT>.

To the d-axis current control operation unit <NUM>, the d-axis current command value Id* and the detected current value Idc are inputted. To the q-axis current control operation unit <NUM>, the q-axis current command value Iq* and the detected current value Iqc are inputted.

Here, according to Expression <NUM>, the arithmetic operation of (proportion + integral) is performed on the current command values Id* and Iq* so that the detected current values Idc and Iqc of the components are followed, and the d-axis and the q-axis voltage correction values ΔVd* and ΔVq* are outputted. In Expression <NUM>, KpdACR is the proportional gain of d-axis electric current control, KidACR is the integral gain of d-axis electric current control, KpqACR is the proportional gain of q-axis electric current control, and KiqACR is the integral gain of q-axis electric current control. [Expression <NUM>] <MAT>.

In the adding units <NUM> and <NUM>, the voltage command values Vdc** and Vqc** expressed in Expression <NUM> are operated to control the output of the power converter <NUM>. [Expression <NUM>] <MAT>.

In the velocity estimation operation unit <NUM>, the velocity of the induction motor <NUM> is estimated according to Expression <NUM>. In this velocity estimation arithmetic operation, the q-axis induced voltage value is estimated using a disturbance observer, and divided by a magnetic flux coefficient, and hence ωr^ is extracted. In Expression <NUM>, R<NUM>' is the primary reduced value of a secondary resistance value, and Tobs is a velocity estimation delay time constant set to the disturbance observer. [Expression <NUM>] <MAT>.

In the slip frequency operation unit <NUM>, the slip frequency command value ωs* of the induction motor <NUM> is operated according to Expression <NUM>. In Expression <NUM>, T<NUM> is a secondary time constant value. [Expression <NUM>] <MAT>.

In the adding unit <NUM>, the output frequency value ω<NUM>* expressed in Expression <NUM> is operated using the velocity estimation value ωr^ and the slip frequency command value ωs*. [Expression <NUM>] <MAT>.

In the phase estimation operation unit <NUM>, the magnetic flux axis position θdc of the induction motor <NUM> is estimated according to Expression <NUM>. [Expression <NUM>] <MAT>.

Based on the estimated position θdc used for control, a sensorless control arithmetic operation is executed. The description above is the basic operation.

In the following, control performances will be described in the case of using the velocity command adjustment operation unit <NUM>, which is a feature of the embodiment.

<FIG> is load performances in the case of using Patent Literature <NUM>. In the state in which the velocity of the induction motor <NUM> is controlled at <NUM>% of a rated speed, ramp regenerative torque τL is given up to -<NUM>%. From <FIG>, a q-axis secondary magnetic flux φ2q in the inside of the induction motor <NUM> is generated on the negative side, and the d-axis the secondary magnetic flux φ2d is increased on the positive side. The output frequency value ω<NUM>* is finally zero. After point A shown in <FIG>, the output frequency value ω<NUM>* is diverged in the positive direction. In other words, in regenerative operation in the low-speed range, there is a problem in that velocity control performances are degraded.

When the velocity command adjustment operation unit <NUM>, which is a feature of the embodiment, is used, these velocity control performances can be improved. In the following, this will be described.

<FIG> is a flowchart of a velocity command adjustment arithmetic operation method according to the embodiment.

In a determination process <NUM>, the output frequency value ω<NUM>* is compared with a constant value (ω<NUM>*_lvl). In the case where ω<NUM>* is smaller than ω<NUM>*_lvl, in an arithmetic operation process <NUM>, a deviation (ω<NUM>* - ω<NUM>*_lvl)is multiplied by a gain Gain, and Δωr*(i) is operated according to Expression <NUM>. [Expression <NUM>] <MAT>.

On the other hand, in the case where ω<NUM>* is greater than ω<NUM>*_lvl, Δωr*(i) = <NUM> in the arithmetic operation process <NUM>.

In an arithmetic operation process <NUM>, Δωr*(ii) is operated according to Expression <NUM> using Δωr*(i) and an operated value Δωr*(i-<NUM>), which is the previous operated value. [Expression <NUM>] <MAT>.

In a subsequent arithmetic operation process <NUM>, Δωr*(ii) is restricted according to Expression <NUM> using a positive-side value that is zero and a negative-side value that is a negative constant value Δωr*min. For Δωr*min, for example, a value only has to be set, which corresponds to a slip frequency value generated at the maximum torque. [Expression <NUM>] <MAT>.

This operated value Δωr*(ii) is outputted as the adjustment amount Δωr* of the velocity command value.

The load performances according to the embodiment are shown in <FIG>, to which the load conditions used in <FIG> are set. From <FIG> and <FIG>, with the comparison of the load characteristics disclosed in <FIG> and <FIG>, in the case of control using the velocity command adjustment operation unit <NUM>, which is a feature of the embodiment, stability is noticeable in all the generated torque, frequency, and secondary magnetic flux of the induction motor, clearly showing the effects of the velocity command adjustment operation unit <NUM>.

In the embodiment, Δωr* is operated so that the output frequency value ω<NUM>* is matched with the adjustment level ω<NUM>*_lvl of the velocity command value. Thus, it is revealed that ω<NUM>* is stationarily matched with ω<NUM>*_lvl.

To the velocity command value ωr* that is <NUM>% before adjusted, the new velocity command value ωr** is (<NUM> + ω<NUM>*_lvl)%. The induction motor <NUM> is driven under velocity control so that the velocity estimation value ωr^ follows the new velocity command value ωr**. More highly accurate velocity control can be implemented, compared with <FIG>, which shows the previously existing performances. Here, the velocity corresponds to ω<NUM>*_lvl = <NUM>%. This value is involved in a setting error ΔR<NUM> of the primary resistance value of the induction motor <NUM> and error voltage values in performing dead time compensation for switching devices configuring the power converter.

When the set values are matched with the actual values, the velocity corresponding to ω<NUM>*_lvl = <NUM>% is sufficient. However, for example, ω<NUM>*_lvl is set corresponding to the velocity in a range of <NUM> to <NUM>%, or <NUM>% or less in advance taking into account of the setting errors, more stable driving can be implemented. The value of ω<NUM>*_lvl is one example, and any values can be used.

As described above, in the case where the output frequency value is the constant value or less, the velocity command value of the induction motor is controlled so that the output frequency value is matched with the constant value. Thus, the stability of the generated torque, frequency, and secondary magnetic flux of the induction motor can be improved. Here, in the case where the output frequency value is the constant value or less, the velocity command value of the induction motor may be controlled so that the output frequency value is the constant value or more. Control is conducted so that the output frequency value is matched with the constant value. Thus, a possibility of exceeding the number of revolutions, which is desired to be constant, can be reduced, even in the case where torque is changed.

Here, switching devices configuring the power converter may be silicon (Si) semiconductor devices or may be wide-band gap semiconductor devices, such as silicon carbide (SiC) and gallium nitride (GaN).

<FIG> is a block diagram of a power converter according to a second embodiment. In the first embodiment, the velocity command value ωr* is adjusted based on the output value of the velocity command adjustment operation unit <NUM>. However, the embodiment is a method that adjusts the velocity estimation value ωr^. In <FIG>, components <NUM> to <NUM>, <NUM> to <NUM>, and 2a are the same as the components in <FIG>.

An adding unit <NUM>' outputs a new velocity estimation value ωr^^, which is an additional value of the velocity estimation value ωr^ and the velocity command adjustment value Δωr*, which are operated. In a velocity control operation unit <NUM>, the q-axis current command value Iq* is operated so that the velocity estimation value ωr^^ is matched with the velocity command value ωr*.

In other words, the velocity estimation value is adjusted instead of the velocity command value. This also allows highly accurate velocity control to be implemented similarly to the first embodiment, obtaining similar effects.

<FIG> is a block diagram of a power converter according to a third embodiment. In the first embodiment, the velocity command value ωr* is adjusted based on the output value of the velocity command adjustment operation unit <NUM> in powering/regenerative operation. However, the embodiment is a method that adjusts the velocity command value ωr* only in regenerative operation. In <FIG>, components <NUM> to <NUM>, and 2a are the same as the components in <FIG>.

A regeneration determination operation unit <NUM> receives the q-axis current command value Iq* and the velocity estimation value ωr^. When Iq* and ωr^ have the same signs, the regeneration determination operation unit <NUM> determines that operation is powering operation, and outputs "<NUM>", whereas when Iq* and ωr^ have different signs, the regeneration determination operation unit <NUM> determines that operation is regenerative operation, and outputs "<NUM>".

A method may be possible in which after the q-axis detected current value Iqc and the velocity estimation value ωr^ are inputted to the regeneration determination operation unit <NUM>, when Iqc and ωr^ have the same signs, the regeneration determination operation unit <NUM> determines that operation is powering operation, and outputs "<NUM>", whereas when Iqc and ωr^ have different signs, the regeneration determination operation unit <NUM> determines that operation is regenerative operation, and outputs "<NUM>".

A multiplying unit <NUM> receives the adjustment value Δωr* of the velocity command and "<NUM>" or "<NUM>", which is the output signal of the regeneration determination operation unit <NUM>. In other words, in powering operation, the velocity command value ωr* is not adjusted. The velocity command value ωr* is adjusted only in regenerative operation.

The velocity command value is adjusted only in regenerative operation. This also allows highly accurate velocity control to be implemented.

<FIG> is a block diagram of a power converter according to a fourth embodiment. In the first embodiment, the velocity command adjustment operation unit <NUM> outputs the velocity command adjustment value Δωr* based on the output frequency value ω<NUM>* and the adjustment start level ω<NUM>*_lvl of the velocity command value ωr*. However, in the embodiment, the adjustment start level of the velocity command value ωr* is set to two levels (ω<NUM>*_lvl1 and ω<NUM>*_lvl2). For example, the value of <NUM>% of the rated speed is set to ω<NUM>*_lvl1, and the value of <NUM>% of the rated speed is set to ω<NUM>*_lv12. In <FIG>, components <NUM> to <NUM>, <NUM> to <NUM>, and 2a are the same as the components in <FIG>.

<NUM>' denotes the adjustment start level of the velocity command value ωr*, to which two levels (ω<NUM>*_lvl1 and ω<NUM>*_lvl2) are set.

In a velocity command adjustment operation unit <NUM>', first, the adjustment start level of the velocity command value ωr* is set to the first level (ω<NUM>*_lvl1) for actual operation. As a result, in the case where torque is short or an overcurrent trip occurs, the setting of the adjustment start level of the velocity command value ωr* is automatically changed to the second level (ω<NUM>*_lvl2) at the subsequent arithmetic operation timing.

With this configuration, the adjustment start levels of the optimum velocity command value ωr* can be set. In the embodiment, the number of levels is two levels. However, a plurality of levels may be prepared. In this manner, a plurality of adjustment start levels is set to the velocity command value ωr*, and hence stable, highly accurate velocity control can be implemented in any states of load torque (the level or slope of torque).

<FIG> is a block diagram of a power converter according to a fifth embodiment. The embodiment is applied to an induction motor drive system. In <FIG>, components <NUM> to <NUM> and 2a are the same as the components in <FIG>.

An induction motor <NUM>, which is the component in <FIG>, is driven by a power conversion device <NUM>. On the power conversion device <NUM>, the components <NUM> to <NUM> and 2a in <FIG> are mounted as software and hardware.

A configuration may be possible in which the value of the velocity command adjustment start level (ω<NUM>*_lvl)can be set through higher devices, such as a digital operator 22b of the power conversion device <NUM>, a personal computer <NUM>, and a tablet <NUM>.

When the embodiment is applied to the induction motor drive system, highly accurate velocity control performances can be implemented. The embodiment is disclosed using the first embodiment. However, the embodiment may be disclosed using the second to the fourth embodiments.

<FIG> is a block diagram of a power converter according to a sixth embodiment. The embodiment is applied to a higher controller that gives velocity command values to a power converter. In <FIG>, components <NUM> to <NUM>, <NUM> to <NUM>, and 2a are the same as the components in <FIG>.

A velocity command value (ωr**' is a new velocity command value operated on the higher controller side. A configuration may be possible in which the output frequency value ω<NUM>* operated inside the power conversion device is returned to the higher controller, a velocity command value adjustment arithmetic operation is performed on the higher controller side, and a new velocity command value ωr**' is given to the power conversion device. Higher devices in this case are a PLC (Programmable Logic Controller) and a program operating function in the inside of the power conversion device, for example.

The configurations of the embodiment can also implement highly accurate velocity control similarly to the first embodiment.

In the first to the sixth embodiments so far, the arithmetic operation expressed in Expression <NUM> is performed, in which the voltage correction values ΔVd* and ΔVq* are generated based on the current command values Id* and Iq* and the detected current values Idc and Iqc and then the voltage correction values are added to the voltage command values for vector control. This is also applicable to a control method below.

Claim 1:
A power conversion device (<NUM>) comprising:
a velocity estimation operation unit (<NUM>) configured to output a velocity estimation value of an induction motor (<NUM>);
an output frequency operation unit (<NUM>) configured to output an output frequency value that is an additional value of the velocity estimation value and a slip frequency value of the induction motor; and
a velocity command adjustment operation unit (<NUM>, <NUM>') configured to control a velocity command value or the velocity estimation value of the induction motor (<NUM>) according to an adjustment value so that the output frequency value is a constant value or more when the output frequency value is the constant value or less;
characterized in that the adjustment value is operated according to the deviation between the output frequency value and a velocity command adjustment start level value (<NUM>), which is the constant value, as multiplied by a gain, in case the output frequency value is smaller than the velocity command adjustment start level value (<NUM>), and
that the adjustment value is zero in case the output frequency value is greater than the velocity command adjustment start level value (<NUM>).