Patent Description:
Examples of a highly efficient control method of an induction motor include Patent Document <NUM>. In Patent Document <NUM>, it is described that in a hydraulic unit, an excitation electric current according to vector control is forcibly changed in accordance with a discharge pressure of a hydraulic pump or torque of an induction motor, and an electric current of supply power with respect to the discharge pressure or the torque is minimized.

Then, it is described that a vector control unit determines a minimum value of a supply electric current of the induction motor that satisfies required torque corresponding to a torque instruction value and sets an excitation electric current instruction value such that the supply electric current with respect to the induction motor is minimized by providing a table relevant to a pressure and an electric current. Furthermore, Patent Document <NUM> discloses a drive control system for escalators and moving sidewalk systems, wherein the drive control system is composed of a microprocessor and uses a vector control method to control the induction motor so that a torque current command value output by a speed loop PI controller is filtered and input to the excitation current command arithmetic unit in order to adjust a final output excitation current command value Ids in real time according to the filtered torque current command value to minimize the total current of the induction motor.

<CIT>discloses a drive and control device for an induction motor comprising a torque electric current detection value and an excitation electric current detection value from an electric current flowing to the induction motor wherein an excitation current instruction equals a torque current command.

In Patent Document <NUM>, the minimum value of the supply electric current of the induction motor is determined on the basis of the torque instruction value, and the excitation electric current instruction value from an excitation electric current calculation unit. However, it is required that an electric current flowing to the motor is detected, and highly efficient control is performed such that the electric current is reduced on the basis of the detected electric current.

In addition, in Patent Document <NUM>, it is necessary to prepare a pressure/electric current table for each hydraulic unit, and such a control method is not capable of being applied to a general-purpose inverter not including the pressure/electric current table or the like.

An object of the present invention is to provide a power conversion device with highly efficient control properties.

The invention is defined in the independent Claims. Preferable embodiments are defined by the dependent claims.

According to the present invention, highly efficient control properties can be attained.

Hereinafter, examples will be described in detail by using the drawings.

<FIG> is a system configuration diagram including a power conversion device and an induction motor <NUM> that is an external device in Example <NUM>. The induction motor <NUM> generates torque by a magnetic flux that is generated by an excitation electric current of a magnetic flux axis (d axis) component, and a torque electric current of a torque axis (q axis) component orthogonal to the magnetic flux axis.

A power converter <NUM> includes a semiconductor element as a switching element. The power converter <NUM> inputs three-phase alternating-current voltage instruction values vu*, vv*, and vw*, and prepares and outputs voltage values proportional to the three-phase alternating-current voltage instruction values vu*, vv*, and vw*. An output voltage value and an output frequency value of the induction motor <NUM> are variable on the basis of the output of the power converter <NUM>. IGBT may be used as the switching element.

A direct-current power source <NUM> supplies a direct-current voltage to the power converter <NUM>.

An electric current detector <NUM> outputs iuc, ivc, and iwc that are detection values of three-phase alternating-current electric currents iu, iv, and iw of the induction motor <NUM>. The electric current detector <NUM> may detect two phases in three phases of the induction motor <NUM>, for example, may detect a u-phase line electric current and a w-phase line electric current, and may obtain v phase line electric current as iv =-(iu + iw) from an alternating-current condition (iu + iv + iw = <NUM>).

In this example, an example is described in which the electric current detector <NUM> is provided in the power conversion device, but the electric current detector <NUM> may be provided outside the power conversion device.

A control unit includes a coordinate conversion unit <NUM>, a V/f control calculation unit <NUM>, a voltage instruction correction calculation unit <NUM>, a phase calculation unit <NUM>, an addition unit <NUM>, and a coordinate conversion unit <NUM>, described below. Then, the control unit controls the power converter <NUM>.

The control unit includes a semiconductor integrated circuit (a calculation controller) such as a microcomputer or a digital signal processor (DSP).

Next, each constituent of the control unit which controls the power converter <NUM> will be described.

The coordinate conversion unit <NUM> calculates and outputs an electric current detection value idc of a d axis and an electric current detection value iqc of a q axis from the alternating-current electric current detection values iuc, ivc, and iwc of the three-phase alternating-current electric currents iu, iv, and iw, and a phase calculation value θdc.

The V/f control calculation unit <NUM> outputs a voltage instruction value vdc" of the d axis that is the value of zero, and a voltage instruction value vqc* of the q axis that is proportional to a frequency instruction value ωr*.

The voltage instruction correction calculation unit <NUM> outputs a voltage correction value Δvqc* of the q axis that is calculated on the basis of the electric current detection value iqc of the q axis and the electric current detection value idc of the d axis.

The phase calculation unit <NUM> outputs the phase calculation value θdc by integrating the frequency instruction value ωr*.

The addition unit <NUM> outputs a second voltage instruction value vqc** of the q axis by adding the voltage instruction value vqc* of the q axis and the voltage correction value Δvqc* of the q axis.

The coordinate conversion unit <NUM> outputs three-phase alternating-current voltage instruction values vu*, vv*, and vw* from the voltage instruction value vdc* of the d axis, the voltage instruction value vqc** of the q axis, and the phase calculation value θdc.

First, a basic operation of a V/f control method in a case of using the voltage instruction correction calculation unit <NUM> that is the characteristic of this example will be described.

In the V/f control calculation unit <NUM>, the voltage instruction value vqc* of the q axis is output in accordance with (Expression <NUM>) by using the voltage instruction value vdc* of the d axis that is the value of zero, the frequency instruction value ωr*, and a direct-current voltage EDC. [Expression <NUM>] <MAT>.

Here, ωr_max is a basilar angle frequency.

In the phase calculation unit <NUM>, a phase θdc of the magnetic flux axis of the induction motor <NUM> is calculated in accordance with (Expression <NUM>). [Expression <NUM>] <MAT>.

<FIG> is a diagram illustrating a function block of the voltage instruction correction calculation unit <NUM> in Example <NUM>.

In an absolute value calculation unit <NUM>, the electric current detection value iqc of the q axis is input, and an absolute value |iqc| of iqc is output.

In a subtraction unit <NUM>, the absolute value |iqc| of the iqc and the electric current detection value idc of the d axis are input, and an electric current deviation Δi is output.

The electric current deviation Δi when the absolute value |iqc| of the torque electric current detection value is greater than or equal to the excitation electric current detection value idc is input to a proportional calculation unit <NUM> having a constant of a proportional gain Kp and an integral calculation unit <NUM> having a constant of Ki. An output signal of the proportional calculation unit <NUM> and the integral calculation unit <NUM> is input to an addition unit <NUM>. As a result thereof, the correction value Δvqc* of the voltage instruction value vqc* of the q axis is calculated by calculation represented in (Expression <NUM>). As described above, control of correcting the voltage instruction value vqc* of the q axis is performed such that the electric current detection value idc of the d axis follows the absolute value of the electric current detection value iqc of the q axis. Here, Kp1 is a proportional gain, and Ki1 is an integral gain. [Expression <NUM>] <MAT>.

The principle that this example is highly efficient will be described. <FIG> is a diagram illustrating an electric current vector of the induction motor <NUM>. In a case where the direction of the magnetic flux that is generated by an excitation electric current id is the d axis, a direction π/<NUM> ahead thereof is the q axis that is the torque axis, and a phase angle between a motor electric current i<NUM> and the excitation electric current id is θi, the excitation electric current id and a torque electric current iq are given by Expression (<NUM>). Here, the motor electric current i<NUM> may be a peak value of any one of the alternating-current electric current detection values iuc, ivc, and iwc. [Expression <NUM>] <MAT>.

In (Expression <NUM>), when phase angle θi = π/<NUM>, the motor electric current i<NUM> is minimized by the relationship of (Expression <NUM>) at the same torque. [Expression <NUM>] <MAT>.

Torque τ of the induction motor <NUM> is given by (Expression <NUM>). [Expression <NUM>] <MAT>.

Here, Pm is the number of pole pairs (the value of <NUM>/<NUM> of the number of motor poles), M is mutual inductance, L<NUM> is secondary inductance, φ2d is a secondary magnetic flux of the d axis, and φ2q is a secondary magnetic flux of the q axis.

Here, an ideal condition of the magnetic flux in motor control is (Expression <NUM>), and
[Expression <NUM>] <MAT>
when (Expression <NUM>) is assigned to (Expression <NUM>), (Expression <NUM>) is obtained. [Expression <NUM>] <MAT>.

Further, when (Expression <NUM>) is assigned to (Expression <NUM>), (Expression <NUM>) that is a torque expression when the motor electric current is minimized is obtained. [Expression <NUM>] <MAT>.

In this example, in order to respond to both of a power running operation and a regenerative operation, an absolute value of the torque electric current iq is calculated, and the voltage instruction value vqc* of the q axis is corrected such that the excitation electric current id follows the absolute value of the torque electric current iq.

<FIG> is a diagram illustrating electric current control properties of Example <NUM> and a comparative example. <FIG> is a diagram illustrating electric current control properties of a state in which the voltage instruction correction calculation unit <NUM> is not operated by V/f control. <FIG> is a diagram illustrating electric current control properties of a state in which the voltage instruction correction calculation unit <NUM> is operated.

In both of <FIG>, lamp-shaped load torque starts to be applied from a point A in the drawing, the size of rated torque is obtained at a point B in the drawing, and rated torque is applied from the point B to the right. In a case where an electric current value of <FIG> is <NUM>%, an electric current value of <FIG> is <NUM>%, and thus, it is found that there is a reduction of approximately <NUM>%. The effects of this example are apparent.

In this example, the control unit performs the control of correcting the voltage instruction value vqc* of the q axis such that the electric current detection value idc of the d axis follows the absolute value of the electric current detection value iqc of the q axis, and thus, the electric current value is smaller and highly efficient electric current properties can be attained, compared to the electric current properties of the V/f control.

In addition, in this example, in the voltage instruction correction calculation unit <NUM>, the gain (Kp, Ki) of proportional calculation and integral calculation is a fixed value, but may be changed in accordance with the frequency instruction value ωr*, as illustrated in <FIG> is a diagram illustrating a modification example of Example <NUM>, and is a function block of a voltage instruction correction calculation unit 7a which changes the gain (Kp, Ki) of the proportional calculation and the integral calculation, in accordance with the frequency instruction value ωr*.

The voltage instruction correction calculation unit 7a in <FIG> is a modification example of the voltage instruction correction calculation unit <NUM> in <FIG>. In addition, 7a1 and 7a2 in <FIG> are identical to the absolute value calculation unit <NUM> and the subtraction unit <NUM> in <FIG>.

As illustrated in <FIG>, Δi that is a deviation between the absolute value |iqc| of the electric current detection value iqc of the q axis and the electric current detection value idc of the d axis is input to a proportional calculation unit 7a3 having the gain Kp1 of the proportional calculation that is changed in accordance with the size of the frequency instruction value ωr* and an integral calculation unit 7a4 having the gain Ki1 of the integral calculation that is changed in accordance with the size of the frequency instruction value ωr*. An output value of the proportional calculation unit 7a3 and an output value of the integral calculation unit 7a4 are added by an addition unit 7a5, and are output as a correction value Δvqc** of the voltage instruction value vqc* of the q axis.

In <FIG>, Kp1 and Ki1 are changed approximately in proportion to the size of the frequency instruction value ωr*, and thus, a mechanism in which the electric current detection value idc of the d axis follows the absolute value |iqc| of the electric current detection value iqc of the q axis is changed in accordance with a frequency. That is, in a low-velocity area to a high-velocity area, the stability of a feedback loop relevant to highly efficient control can be improved, and a motor electric current value can be minimized within a shorter period of time.

<FIG> is a diagram describing a verification method in a case of adopting this example. An electric current detector <NUM> is attached to a power conversion device <NUM> which drives the induction motor <NUM>, and an encoder <NUM> is attached to a shaft of the induction motor <NUM>.

The three-phase alternating-current electric current detection values (iuc, ivc, and iwc) that are the output of the electric current detector <NUM> and a position θ that is the output of the encoder are input to a calculation unit <NUM> of a vector electric current component, and the electric current detection value idc of the d axis and the electric current detection value iqc of the q axis of the vector electric current component are output.

In an observation unit <NUM> of the waveform of each unit, when the electric current detection value iqc of the q axis is greater than the electric current detection value idc of the d axis, as illustrated in <FIG>, it is apparent that this example is adopted insofar as the electric current detection value idc of the d axis follows the electric current detection value iqc of the q axis.

<FIG> is a diagram illustrating the configuration of a system including a power conversion device and the induction motor <NUM> Example <NUM>. In Example <NUM>, the absolute value of the torque electric current iq is calculated, and the excitation electric current id is allowed to follow the absolute value of the torque electric current iqc but in this example, an absolute value |Qc| of reactive power is allowed to follow an absolute value |Pc| of effective power.

In <FIG>, the induction motor <NUM>, the power converter <NUM>, the electric current detector <NUM>, the coordinate conversion unit <NUM>, the V/f control calculation unit <NUM>, the phase calculation unit <NUM>, the addition unit <NUM>, and the coordinate conversion unit <NUM> are identical to those in <FIG>. A voltage instruction correction calculation unit 7b included in the control unit outputs a correction value Δvqc*** of the voltage instruction value vqc* of the q axis, on the basis of the absolute value |Pc| of an effective power calculation value and an absolute value |Qc| of a reactive power calculation value.

<FIG> illustrates the configuration of the voltage instruction correction calculation unit 7b. 7b3 illustrates a proportional calculation unit. 7b4 illustrates an integral calculation unit. 7b5 illustrates the addition unit <NUM>. The voltage instruction value vqc** of the q axis and the electric current detection value iqc of the q axis are input to a multiplication unit 7b6, and an effective power calculation value Pc that is a multiplication value thereof is output. The effective power calculation value Pc that is the output of the multiplication unit 7b6 is input to an absolute value calculation unit 7b7, and the absolute value |Pc| of Pc is output.

The voltage instruction value vqc** of the q axis and the electric current detection value idc of the d axis are input to a multiplication unit 7b8, and a reactive power calculation value Qc that is a multiplication value thereof is output. The reactive power calculation value Qc that is the output of the multiplication unit 7b8 is input to an absolute value calculation unit 7b9, and the absolute value |Qc| of Qc is output.

In a subtraction unit 7b2, the absolute value |Pc| of Pc and the absolute value |Qc| of Qc are input, and a power deviation Δp is output. The power deviation Δp is input to the proportional calculation unit 7b3 having the constant of the proportional gain Kp and the integral calculation unit 7b4 having the constant of Ki, and an output signal thereof is input to the addition unit 7b5. The correction value Δvqc*** of the voltage instruction value vqc* of the q axis is calculated by calculation represented in (Expression <NUM>). [Expression <NUM>] <MAT>.

Here, Kp2 is a proportional gain, and Ki2 is an integral gain.

Here, the principle that this example is highly efficient will be described. When the voltage instruction value vdc* of the d axis = <NUM>, the effective power Pc that is calculated on a control axis is given by (Expression <NUM>). [Expression <NUM>] <MAT>.

The absolute value of the effective power Pc is (Expression <NUM>). [Expression <NUM>] <MAT>.

In addition, the reactive power Qc that is calculated on the control axis is given by (Expression <NUM>).

The absolute value of the reactive power Qc is (Expression <NUM>). [Expression <NUM>] <MAT>.

The voltage instruction value vqc* of the q axis is corrected by using |Pc| and |Q|. In a case where control is performed such that (Expression <NUM>) = (Expression <NUM>), the following expression is given.

As a result thereof, in Example <NUM>, idc (the electric current detection value of the d axis) = iqc (the electric current detection value of the q axis) is indirectly obtained, which is directly obtained in Example <NUM>, and thus, a highly efficient operation can be attained.

In Example <NUM>, as with the example of <FIG>, the gain Kp1 of the proportional calculation and the gain Ki1 of the integral calculation are changed approximately in proportion to the size of the frequency instruction value ωr*, and thus, in the low-velocity area to the high-velocity area, the stability of the feedback loop relevant to the highly efficient control can be improved, and the motor electric current value can be minimized within a shorter period of time.

<FIG> is a system configuration diagram including a power conversion device and an induction motor in Example <NUM>. In Example <NUM> and Example <NUM>, the induction motor <NUM> is subjected to the V/f control, but in Example <NUM>, the calculation of velocity control, electric current control, and vector control is performed.

In <FIG>, the induction motor <NUM>, the power converter <NUM>, the direct-current power source <NUM>, the electric current detector <NUM>, the coordinate conversion unit <NUM>, the phase calculation unit <NUM>, and the coordinate conversion unit <NUM> are identical to those in <FIG>.

The control unit includes the coordinate conversion unit <NUM>, the phase calculation unit <NUM>, the coordinate conversion unit <NUM>, a feedback control calculation unit <NUM>, an excitation electric current instruction calculation unit <NUM>, and a frequency estimation calculation unit <NUM>. Then, the control unit controls the power converter <NUM>.

The feedback control calculation unit <NUM> inputs a second excitation electric current instruction id**, the electric current detection value idc of the d axis, the electric current detection value iqc of the q axis, an estimation frequency ωr^, and an output frequency ω<NUM>*. In the feedback control calculation unit <NUM>, feedback control of the velocity control, the electric current control, and the vector control is calculated. The estimation frequency ωr^ is used as a velocity estimation value.

The second electric current instruction value id** of the d axis that is the second excitation electric current instruction is a variable value, and the secondary magnetic flux φ2d of the d axis that is variable is generated in the induction motor <NUM>.

In the velocity control, an electric current instruction value iq* of the q axis that is a torque electric current instruction is calculated in accordance with (Expression <NUM>) by the proportional control and the integral control such that the estimation frequency ωr^ follows the frequency instruction value ωr*.

Here, Ksp is a proportional gain in the velocity control, and Ksi is an integral gain in the velocity control.

In the vector control, the voltage instruction values vdc" and vqc* are calculated in accordance with (Expression <NUM>) by using the electric current instruction value id** of the d axis that is the second excitation electric current instruction, the electric current instruction value iq* of the q axis, an electric circuit constant (R<NUM>, Lσ, M, and L<NUM>) of the induction motor <NUM>, the secondary magnetic flux instruction value φ2d* of the d axis, and the output frequency ω<NUM>*. [Expression <NUM>] <MAT>.

Here, Tacr is a time constant corresponding to an electric current control delay, 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.

In the electric current control, a voltage correction value Δvdc of the d axis and a voltage correction value Δvqc of the q axis are calculated in accordance with (Expression <NUM>) by the proportional control and the integral control such that the electric current detection value idc of the d axis and the electric current detection value iqc of the q axis that are each component follow the second electric current instruction value id** of the d axis and the electric current instruction value iq* of the q axis. [Expression <NUM>] <MAT>.

Here, Kpd is a proportional gain of the d axis in the electric current control, Kid is an integral gain of the d axis in the electric current control, Kpq is a proportional gain of the q axis in the electric current control, and Kiq is an integral gain of the q axis in the electric current control.

Further, a voltage instruction value vqc** of the d axis and a voltage instruction value vqc** of the q axis are calculated in accordance with (Expression <NUM>).

<FIG> is a function block diagram of the excitation electric current instruction calculation unit <NUM>.

In an absolute value calculation unit <NUM>, the electric current instruction value iq* of the q axis is input, and an absolute value |iq*| of iq* is output. In an addition unit <NUM>, a first electric current instruction value iq* of the d axis and a correction electric current instruction Δid* are added, and the second electric current instruction value id** of the d axis is output.

In a subtraction unit <NUM>, the absolute value |iq*| of iq* and the second electric current instruction value id** of the d axis are input, and an electric current instruction deviation Δi* is output. The electric current instruction deviation Δi* is input to a proportional calculation unit <NUM> having a constant of a proportional gain Kp3 and an integral calculation unit <NUM> having a constant of Ki3, and an output signal thereof is input to an addition unit <NUM>.

In the addition unit <NUM>, the second electric current instruction value id** of the d axis is output by calculation represented in (Expression <NUM>).

In the frequency estimation calculation unit <NUM>, the velocity estimation value (the estimation frequency) ωr^ and the output frequency ω<NUM>* of the induction motor <NUM> are calculated by (Expression <NUM>). [Expression <NUM>] <MAT>.

Here, R* is an addition value of primary conversion of the primary resistance value and secondary resistance, Tobs is an observer time constant, and T<NUM> is a secondary time constant value.

Even in this example in which the velocity control, the electric current control, and the vector control are calculated instead of the V/f control, control is performed such that the second electric current instruction value id** of the d axis follows the absolute value of the electric current instruction value iq* of the q axis.

According to such control, a highly efficient operation can be attained. Note that, in this example, the velocity estimation value (the estimation frequency) ωr^ is calculated, but a velocity detection value ωr may be detected by attaching an encoder to the induction motor <NUM>.

<FIG> is a configuration diagram of an induction motor driving system including a power conversion device and the induction motor <NUM> in Example <NUM>.

In this example, this example is applied to the induction motor driving system.

In <FIG>, the induction motor <NUM> that is the constituent, the coordinate conversion unit <NUM>, the V/f control calculation unit <NUM>, the voltage instruction correction calculation unit <NUM>, the phase calculation unit <NUM>, the addition unit <NUM>, and the coordinate conversion unit <NUM> are identical to those in <FIG>.

The induction motor <NUM> that is the constituent of <FIG> is driven by the power conversion device <NUM>. In the power conversion device <NUM>, the coordinate conversion unit <NUM>, the V/f control calculation unit <NUM>, the voltage instruction correction calculation unit <NUM>, the phase calculation unit <NUM>, the addition unit <NUM>, and the coordinate conversion unit <NUM> of <FIG> are mounted as software 20a, and the power converter <NUM>, the direct-current power source <NUM>, and the electric current detector <NUM> of <FIG> are mounted as hardware.

In addition, the voltage instruction correction calculation unit <NUM> of the software 20a is capable of setting or changing a predetermined proportional gain <NUM> and a predetermined integral gain <NUM> by a higher-level device such as a digital operator 20b, a personal computer <NUM>, a tablet <NUM>, and a smart phone <NUM>.

In a case where this example is applied to the induction motor driving system, a highly efficient operation can be attained in the V/f control or velocity sensorless vector control. In addition, the proportional gain <NUM> that is a predetermined parameter and the integral gain <NUM> that is a predetermined parameter may be set on a programmable logic controller, a local area network that is connected to a computer, and a fieldbus of a control device.

Further, this example is disclosed by using Example <NUM>, but Example <NUM> or Example <NUM> may be used. In Example <NUM> and Example <NUM> described above, the V/f control is performed.

In Example <NUM>, the voltage correction values Δvdc and Δvqc are prepared from the second electric current instruction value id** of the d axis, the electric current instruction value iq* of the q axis, the electric current detection value idc of the d axis, and the electric current detection value iqc of the q axis, and calculation represented in (Expression <NUM>) for adding the voltage correction value and the voltage instruction value of the vector control is performed.

As another method, intermediate electric current instruction values id*** and iq** represented in (Expression <NUM>) that are used in vector control calculation are prepared from the second electric current instruction value id** of the d axis, the electric current instruction value iq* of the q axis, and the electric current detection values idc and iqc. Then, vector control calculation represented in (Expression <NUM>) may be performed by using the output frequency value ω<NUM>* and the electric circuit constant of the induction motor <NUM>. [Expression <NUM>] <MAT>.

Here, Kpd1 is a proportional gain of the d axis in the electric current control, Kid1 is an integral gain of the d axis in the electric current control, Kpq1 is a proportional gain of the q axis in the electric current control, Kiq1 is an integral gain of the q axis in the electric current control, Td is an electric time constant (Lσ/R) of the d axis, and Tq is an electric time constant (Lσ/R) of the q axis. [Expression <NUM>] <MAT>.

Alternatively, a voltage correction value Δvd_p* of a proportional calculation component of the d axis, a voltage correction value Δvd_i* of an integral calculation component of the d axis, a voltage correction value Δvq_p* of a proportional calculation component of the q axis, and a voltage correction value Δvg_i* of an integral calculation component of a q axis, which are used in the vector control calculation, are prepared from the second electric current instruction value id** of the d axis, the electric current instruction value iq* of the q axis, the electric current detection value idc of the d axis, and the electric current detection value iqc of the q axis by (Expression <NUM>). Then, vector control calculation represented in (Expression <NUM>) using the output frequency value ω<NUM>* and the electric circuit constant of the induction motor <NUM> may be performed. [Expression <NUM>] <MAT>.

Here, Kpd2 is a proportional gain of the d axis in the electric current control, Kid2 is an integral gain of the d axis in the electric current control, Kpq2 is a proportional gain of the q axis in the electric current control, and Kiq2 is an integral gain of the q axis in the electric current control. [Expression <NUM>]
<MAT>.

In addition, the calculation of an output frequency instruction value ω<NUM>** represented in (Expression <NUM>) and vector control calculation represented in (Expression <NUM>) may be performed by using the second electric current instruction value id** of the d axis, a primary delay signal iqctd of the electric current detection value iqc of the q axis, the frequency instruction value ωr*, and the electric circuit constant of the induction motor <NUM>. [Expression <NUM>]
<MAT>
[Expression <NUM>]
<MAT>.

Here, iqctd is a signal obtained by iqc passing through a primary delay filter.

In Example <NUM> to Example <NUM> described above, the frequency estimation calculation unit <NUM> calculates the estimation frequency ωr^ (the velocity estimation value) and the output frequency ω<NUM>*, in accordance with (Expression <NUM>), but electric current control and velocity estimation may be used together in q-axis electric current control. As represented in (Expression <NUM>), the velocity estimation value ωr^^ is calculated. [Expression <NUM>] <MAT>.

Here, Kpq3 is a proportional gain in the electric current control, and Kiq3 is an integral gain in the electric current control.

Further, the feedback control calculation unit <NUM> in Example <NUM> calculates the velocity estimation value, in accordance with (Expression <NUM>) or (Expression <NUM>), but the velocity detection value may be calculated from an encoder signal by attaching an encoder to the induction motor <NUM>.

Claim 1:
A power conversion device, comprising:
a power converter (<NUM>) including a switching element; and
a control unit (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) which controls the power converter (<NUM>),
wherein the control unit calculates a torque electric current detection value (Iqc) and an excitation electric current detection value (Idc) from an electric current flowing to an external device, calculates an absolute value of an effective power and a reactive power, characterized in that
when an absolute value of the effective power (IPcI) is greater than or equal to an absolute value of the reactive power (IQcI), performs control such that the absolute value of the reactive power follows the absolute value of the effective power.