(19)
(11)EP 3 703 249 A1

(12)EUROPEAN PATENT APPLICATION
published in accordance with Art. 153(4) EPC

(43)Date of publication:
02.09.2020 Bulletin 2020/36

(21)Application number: 18871235.0

(22)Date of filing:  27.06.2018
(51)International Patent Classification (IPC): 
H02P 27/06(2006.01)
H02M 7/48(2007.01)
(86)International application number:
PCT/JP2018/024350
(87)International publication number:
WO 2019/082441 (02.05.2019 Gazette  2019/18)
(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(30)Priority: 24.10.2017 JP 2017205000

(71)Applicant: Hitachi Industrial Equipment Systems Co., Ltd.
Tokyo 101-0022 (JP)

(72)Inventors:
  • TOBARI, Kazuaki
    Tokyo 100-8280 (JP)
  • IWAJI, Yoshitaka
    Tokyo 100-8280 (JP)
  • HADINATA, Agnes
    Tokyo 100-8280 (JP)
  • NAKAMURA, Atsuhiko
    Tokyo 101-0022 (JP)
  • ONUMA, Yusaku
    Tokyo 101-0022 (JP)
  • SUGIMOTO, Takuya
    Tokyo 101-0022 (JP)

(74)Representative: Mewburn Ellis LLP 
Aurora Building Counterslip
Bristol BS1 6BX
Bristol BS1 6BX (GB)

  


(54)POWER CONVERSION DEVICE AND CONTROLLING METHOD THEREFOR


(57) In acceleration and deceleration operations of a motor, a problem has been posed in that a power converter gets into overcurrent or overvoltage when an inertia moment value of a machine mounted to the motor is large. In order to solve the above problem, provided is a power conversion device that controls a DC voltage, an output frequency, and an output current of a power converter that drives the motor. The power conversion device has a frequency command correction calculation unit that automatically adjusts a frequency command, and is configured to automatically adjust the frequency command such that the power converter does not get into overvoltage or overcurrent during acceleration and deceleration operations of the motor.




Description

Technical Field



[0001] The present invention relates to a control method for a stable operation of a motor without causing overcurrent and overvoltage of the power conversion device in an actual operation of a V/f control and a vector control in which a ratio of an output voltage V and an output frequency f of a power conversion device which drives a motor, or in an automatic tuning in which an inertia moment value of a machine attached to the motor is automatically measured before the actual operation.

Background Art



[0002] As a background art of this technical field, there is disclosed PTL 1. In PTL 1, when an output current of the power conversion device exceeds the current limit value, a voltage command value is corrected on the basis of a voltage limit value in proportion to an exceeding amount, and an acceleration of a frequency command is corrected at the same time so as not to cause a power converter to reach overcurrent.

Citation List


Patent Literature



[0003] PTL 1: JP 2002-34289 A

Summary of Invention


Technical Problem



[0004] However, in the technique of PTL 1, the regenerative energy returns to the power conversion device at the time of the regeneration operation where the frequency command decelerates. Therefore, a DC voltage is increased. As a result, it is not considered that the power converter gets into overvoltage.

[0005] In an acceleration (power running) operation where the frequency of the motor and the polarity of torque are same and a deceleration (regeneration) operation where the frequency of the motor and the polarity of torque are different, there is a need to prevent that the power converter does not fall into overcurrent and overvoltage.

Solution to Problem



[0006]  The invention has been made in view of the background art and the problem. As an example, there is provided a power conversion device which controls a DC voltage, an output frequency, and an output current of a power converter which drives a motor. The power conversion device includes a frequency command correction calculation unit which automatically adjusts a frequency command. The frequency command is automatically adjusted such that the power converter does not fall into overvoltage and overcurrent in an acceleration/deceleration operation of the motor.

Advantageous Effects of Invention



[0007] According to the invention, there is provided a power conversion device and a control method thereof which can realize the acceleration/deceleration operation such that a power conversion device does not get into overcurrent and overvoltage by automatically adjusting a frequency command even in a case where an inertia moment value of the machine attached to a motor is large.

Brief Description of Drawings



[0008] 

[FIG. 1] FIG. 1 is a diagram illustrating a configuration of the power conversion device in a first embodiment.

[FIG. 2] FIG. 2 is a diagram illustrating acceleration operation characteristics in a case where the related art is used.

[FIG. 3] FIG. 3 is a diagram illustrating a configuration of a frequency correction calculation unit in the first embodiment.

[FIG. 4] FIG. 4 is a diagram illustrating the acceleration operation characteristics in the first embodiment.

[FIG. 5] FIG. 5 is a diagram illustrating a deceleration operation characteristic in the first embodiment.

[FIG. 6] FIG. 6 is a diagram illustrating other acceleration operation characteristics in the first embodiment.

[FIG. 7] FIG. 7 is a diagram illustrating a configuration for checking presentation in the first embodiment.

[FIG. 8] FIG. 8 is a diagram illustrating a configuration of the power conversion device in a second embodiment.

[FIG. 9] FIG. 9 is a diagram illustrating a configuration of the power conversion device in a third embodiment.

[FIG. 10] FIG. 10 is a diagram illustrating a configuration of the power conversion device in a fourth embodiment.

[FIG. 11] FIG. 11 is a diagram illustrating a configuration of the power conversion device in a fifth embodiment.


Description of Embodiments



[0009] Hereinafter, embodiments of the invention will be described using the drawings.

First Embodiment



[0010] FIG. 1 is a diagram illustrating a configuration of the power conversion device in this embodiment. In FIG. 1, an induction motor 1 generates a magnetic flux generated by the current of a magnetic flux axis component (d axis), and torque generated by the current of a torque axis component (q axis) perpendicular to the magnetic flux axis. A power converter 2 outputs the voltage values in proportion to voltage command values vu*, vu*, and vu* of the three-phase AC current, and varies an output voltage and an output frequency of the induction motor 1. A DC power source 2a supplies a DC voltage to the power converter 2.

[0011] A current detector 3 outputs detection values iuc, ivc, and iwc of the three-phase AC currents iu, iv, and iw of the induction motor 1, or may detect two phases (for example, u-phase and w-phase) out of three phases of the induction motor 1 to obtain the v-phase current as iv = - (iu + iw) from the AC condition (iu + iv + iw = 0) .

[0012] A DC voltage detector 4 outputs the DC voltage EDC of the power converter 2. A coordinates transformation unit 5 outputs the current detection values idc and iqc of d and q axes from the detection values iuc, ivc, and iwc of the three-phase AC currents and a phase calculation value θdc. A frequency command correction calculation unit 6 outputs new frequency command ωr** calculated on the basis of a frequency command ωr*, the DC voltage EDC of the power converter, and the current detection values idc and iqc of dc axis and qc axis. A V/f control calculation unit 7 outputs a voltage command value vqc* of q axis in proportion to the new frequency command ωr** and vdc* which is zero.

[0013] A phase calculation unit 8 integrates the new frequency command ωr** to output the phase calculation value θdc. A coordinates transformation unit 9 outputs the voltage command values vu*, vv*, and vw* of the three-phase AC current from voltage command values vdc* and vqc* of dc axis and qc axis and the phase calculation value θdc.

[0014] First, the description will be given about a basic operation of a V/f control system in a case where the frequency command correction calculation unit 6 of this embodiment is not used.

[0015] The V/f control calculation unit 7 outputs the voltage command value vqc* of qc axis and the voltage command value vdc* of dc axis which is zero according to Expression (1) using the frequency command ωr* and the DC voltage EDC.
[Math. 1]



[0016] Herein, ωr_max is a maximum frequency.

[0017] In Expression (1), a setting value EDC* of the DC voltage may be used instead of the DC voltage EDC.

[0018] In the phase calculation unit 8, the phase calculation value θdc of the magnetic flux axis of the induction motor 1 is calculated according to Expression (2).
[Math. 2]



[0019] Next, the description will be given about a control characteristic when the frequency command correction calculation unit 6 is not used in a case where the inertia moment value of a machine attached to the induction motor 1 is large. The upper and lower drawings of FIG. 2 illustrate actual frequency and current characteristics when the induction motor 1 accelerates (power running) operation. In the upper drawing of FIG. 2, the frequency command ωr* of a ramp shape is applied from 0 to 100% from Point (A) to Point (B) while a frequency ωr of the induction motor 1 is stopped. An output current i1c of the power converter 2 illustrated in the lower drawing of FIG. 2 reaches an overcurrent level determined from current withstand (maximum current) of a semiconductor switching element of the power converter 2 at Point (C) and, at this time point, is not possible to drive the induction motor 1.

[0020] In this way, in a case where the inertia moment value of the machine attached to the induction motor 1 is large, the power conversion device falls to an overcurrent and easily becomes inoperable.

[0021] Therefore, the problem can be improved if the frequency command correction calculation unit 6 according to this embodiment is employed. Hereinafter, this embodiment will be described.

[0022] Hereinbelow, the description will be given about control characteristics in a case where the frequency command correction calculation unit 6 according to this embodiment is employed.

[0023] FIG. 3 illustrates a configuration of the frequency command correction calculation unit 6 in this embodiment. In FIG. 3, 6a1 indicates a constant EDClmt which is a predetermined voltage value. 6a2 indicates a subtraction unit and receives the constant EDClmt of 6a1 and the DC voltage EDC. 6a3 indicates a current command limit calculation unit, and outputs Δi1lmt* of Expression (3) according to a proportional integral control.
[Math. 3]



[0024] Herein, Kpv is a proportional gain, and Kiv is an integral gain.

[0025] The upper limit of the integration is limited to "0". In addition, 6a4 indicates a constant of "0". A switch changeover unit 6a5 outputs "0" of 6a4 when the induction motor 1 accelerates, and outputs Δi1lmt* of 6a3 when being decelerated.

[0026] An output current calculation unit 6a7 is provided to calculate the output current i1c according to Expression (4) from the current detection values idc and iqc of dc axis and qc axis.
[Math. 4]



[0027]  6a8 indicates an addition unit which receives the constant i1lmt of 6a6 and the output of the switch changeover unit 6a5 and outputs a current limit value i1lmt* which is the addition value.

[0028] The current limit value i1lmt* varies according to Expression (5) in the acceleration (power running) operation.
[Math. 5]



[0029] In the deceleration (regeneration) operation, the output follows Expression (6).
[Math. 6]



[0030] 6a9 indicates a subtraction unit, and receives the current limit value i1lmt* and the output current i1c. 6a10 indicates a frequency command limit calculation unit, and outputs a frequency correction amount Δωr* of Expression (7) according to the proportional integral control.
[Math. 7]



[0031] Herein, Kpf is a proportional gain, Kfi is an integral gain, and the upper limit of the integral unit is limited to "0".

[0032] 6a11 indicates an addition unit, and outputs the new frequency command ωr** of Expression (8).
[Math. 8]



[0033] In other words, the frequency command correction calculation unit 6 corrects a predetermined current value i1lmt such that the DC voltage EDC approaches the predetermined voltage value EDClmt, and controls an output frequency ωr** such that the output current i1c approaches the corrected current value i1lmt*.

[0034] FIG. 4 illustrates the frequency and current characteristics according to this embodiment. (the condition used in FIG. 2 is set). Comparing the acceleration (power running) characteristics illustrated in FIGS. 2 and 4, the effects are apparent. Since FIG. 4 illustrates the acceleration characteristics, the switch changeover unit 6a5 in FIG. 3 outputs "0", and the output current i1c is limited at the predetermined current value i1lmt. In other words, the output current i1c illustrated in the lower drawing of FIG. 4 is limited to the predetermined current value i1lmt from Point (D). In other words, the output current i1c is controlled to approach the predetermined current value i1lmt. In addition, the actual frequency ωr of the induction motor 1 accelerates to follow the new frequency command ωr**, and a stable V/f control can be realized.

[0035] In the DC power source 2a of FIG. 1, the DC voltage EDC is supplied from a commercial three-phase AC power source by a diode rectifying operation in the power converter 2. If the induction motor 1 accelerates, the DC voltage EDC is once lowered. However, power is continuously supplied from the three-phase AC power source. Therefore, the DC voltage EDC is not significantly lowered in the acceleration (power running) operation. Therefore, the output current is limited to the predetermined current value i1lmt in this embodiment.

[0036] However, the power is not possible to be returned to the three-phase AC power source in the deceleration (regeneration) operation. Therefore, "Δi1lmt*" of the switch changeover unit 6a5 in FIG. 3 is selected to set the limit of the output current i1c to the current value i1lmt* which is corrected according to Expression (6).

[0037] Next, FIG. 5 illustrates the frequency and current characteristics when the induction motor 1 decelerates (regeneration) operation. In the upper drawing of FIG. 5, the frequency command ωr* of a ramp shape is applied from 100% to 0 from Point (E) to Point (F). The output current i1c illustrated in the middle of FIG. 5 is limited to the predetermined current value i1lmt at Point (G). In addition, the DC voltage EDC illustrated in the lower drawing of FIG. 5 is limited to the predetermined voltage value EDClmt from Point (H) so as to limit the output current i1c to the current value i1lmt* which is corrected according to Expression (6). In other words, in a case where the DC voltage EDC is larger than the predetermined voltage value EDClmt, the predetermined current value i1lmt is corrected, and the output current i1c is controlled to approach a predetermined current value i1lmt*.

[0038] In addition, the frequency correction amount Δωr* according to Expression (7) is calculated in the frequency command limit calculation unit 6a10 of FIG. 3. However, as illustrated in FIG. 6, the calculation of Expression (7) may start from a time point (D) when the output current i1c becomes larger than the corrected current value i1lmt*. In this case, overshoot is generated as illustrated in region L of the same drawing.

[0039] In this way, with this embodiment, it is possible to realize a stable operation such that the DC voltage EDC of the power converter 2 and the output current i1c do not fall into overvoltage and overcurrent regardless of the acceleration operation and the deceleration operation.

[0040] Further, the predetermined voltage value EDClmt and the predetermined current value i1lmt are automatically set using a circuit constant, a rated frequency, a rated voltage, and a rated current of the motor which are set in an inner memory of a microcomputer mounted in the power conversion device including the power converter 2. In addition, the predetermined voltage value EDClmt and the predetermined current value i1lmt may be set using a maximum voltage and a maximum current of a switching semiconductor element of the power converter 2.

[0041] Herein, the description will be given using FIG. 7 about a correction method in a case where this embodiment is employed. As illustrated in FIG. 7, a DC voltage detector 22 and the current detector 23 are attached to the power conversion device 21 which drives the induction motor 1, and an encoder 24 is attached to a shaft of the induction motor 1.

[0042] In the calculation unit 25 of the output current, the three-phase current values (iu, iv, and iw) which are the outputs of the current detector 23 and a position θ which is the output of the encoder are input, and the output current i1c is calculated. An observation unit 26 of the waveform of each unit observes the waveforms of the DC voltage EDC and the output current i1c. For example, in a case where the induction motor 1 is in the deceleration operation, it can be seen clearly from the characteristics at Point G (limitation at the predetermined current value), Point H (limitation at the predetermined voltage value), and Point I (the corrected current value) illustrated in FIG. 5.

[0043] In addition, in a case where the encoder is not attached, the maximum value of the three-phase current values (iu, iv, and iw) may be set to i1c.

[0044] As described above, this embodiment is possible to provide the power conversion device and the control method thereof which can realize the acceleration/deceleration operation such that the power converter does not get into overcurrent and overvoltage by automatically adjusting the frequency command even in a case where the inertia moment value of the machine attached to the motor is large.

Second Embodiment



[0045] FIG. 8 is a diagram illustrating a configuration of the power conversion device in this embodiment. In the first embodiment, the induction motor 1 is subjected to the V/f control. However, the description in this embodiment will be given about an automatic tuning in which the inertia moment value of the machine attached to the induction motor 1 is measured as a base of the control of FIG. 1.

[0046] In FIG. 8, the same function as that of FIG. 1 is attached with the same symbol, and the description is omitted. In FIG. 8, a difference from FIG. 1 is that an inertia moment calculation unit 27 is provided.

[0047] The inertia moment calculation unit 27 receives the new frequency command ωr** which is the output of the frequency command correction calculation unit 6 and the current detection values idc and iqc of dc axis and qc axis. An average torque τm_Power-Running of a section ((A) to (J) in FIG. 4) of the acceleration (power running) operation and an average torque τm_Regeneration of a section ((E) from (H) in FIG. 5) of the deceleration (regeneration) operation are calculated by Expression (9) in the inertia moment calculation unit 27. For example, an estimation value J^ of an inertia moment J is calculated by Expression (10) using time Δt and speed Δω in FIG. 4.
[Math. 9]


[Math. 10]



[0048] Further, the estimation value J^ may be used in gain calculation of a speed control which is employed in a third embodiment.

[0049] In addition, the control of FIG. 1 may be performed by the automatic tuning in which the measurement of the circuit constant of the motor is performed.

Third Embodiment



[0050] FIG. 9 is a diagram illustrating a configuration of the power conversion device in this embodiment. In the first embodiment, the induction motor 1 is subjected to the V/f control. However, in this embodiment, the speed control, a current control, and a vector control are calculated without using an encoder (speed sensor).

[0051] In FIG. 9, the same function as that of FIG. 1 is attached with the same symbol, and the description is omitted. In FIG. 9, a difference from FIG. 1 is that a feed-back control calculation unit 10 and a frequency estimation calculation unit 11 are included.

[0052] The feed-back control calculation unit 10 receives the new frequency command ωr** which is the output of the frequency command correction calculation unit 6, the current detection values idc and iqc of dc axis and qc axis, a frequency estimation value ωr^, and an output frequency ω1*. In the feed-back control calculation unit 10, the feed-back control of the speed control, the current control, and the vector control is calculated.

[0053] A current command value id* of d axis is a predetermined value, and causes a secondary magnetic flux ϕ2d of d axis in the induction motor 1.

[0054] The speed control calculates a current command value iq* of q axis according to Expression (11) by the proportional integral control such that the frequency estimation value ωr^ follows the new frequency command ωr**.
[Math. 11]



[0055] Herein, Ksp is a proportional gain of the speed control, and Ksi is an integral gain of the speed control.

[0056] The vector control calculates voltage reference values vdc* and vqc* according to Expression (12) using the current command values id* and iq* of d axis and q axis, circuit constants (R1, Lσ, M, and L2) of the induction motor 1, and a secondary magnetic flux command value ϕ2d* and an output frequency ω.' of d axis.
[Math. 12]



[0057] Herein, Tacr is a constant when the current control delays, R1 is a primary resistance value, Lσ is a leaking inductance value, M is a mutual inductance value, and L2 is a secondary inductance value.

[0058] The current control calculates voltage correction values Δvdc* and Δvqc* of d axis and q axis according to Expression (13) by the proportional integral control such that the current detection values idc and iqc follow the current command values id* and iq* of d axis and q axis.
[Math. 13]



[0059] Herein, Kpd is a proportional gain of the current control of d axis, Kid is an integral gain of the current control of d axis, Kpq is the proportional gain of the current control of q axis, and Kiq is an integral gain of the current control of q axis.

[0060] Further, voltage command values vdc** and vdc** of dc axis and qc axis are calculated according to Expression (14) .
[Math. 14]



[0061]  In the frequency estimation calculation unit 11, the frequency estimation value ωr^ and the output frequency ω1* of the induction motor 1 are calculated according to Expression (15).
[Math. 15]



[0062] Herein, R2'* is a primary conversion value of a secondary resistance, Tobs is an observer time constant, and T2 is a secondary time constant value.

[0063] In this embodiment, even if the speed control, the current control, and the vector control are calculated instead of the V/f control, it is possible to realize a stable operation that the DC voltage EDC and the output current i1c of the power converter 2 do not get into overvoltage and overcurrent.

[0064] Further, the frequency estimation value ωr^ is calculated in this embodiment. However, in a case where an encoder is provided in the induction motor 1, a frequency detection value ωr may be detected. In such a case, the current value iq* of q axis according to Expression (16) is calculated to calculate the output frequency ω1* according to Expression (17).
[Math. 16]


[Math. 17]



[0065] The voltage reference values vdc* and vqc* may be calculated by Expression (12) using the output frequency ω1*.

[0066] In this way, according to the invention, even in a method for calculating the speed control, the current control, and the vector control, it is possible to realize a stable operation that the DC voltage EDC and the output current i1c of the power converter 2 do not get into overvoltage and overcurrent regardless of the existence of an encoder (speed sensor).

[0067] In addition, the inertia moment calculation unit 27 illustrated in the second embodiment may be provided as a base of the control of this embodiment, or may be realized by the automatic tuning where the circuit constant of the motor is measured.

Fourth Embodiment



[0068] FIG. 10 is a diagram illustrating a configuration of the power converter in this embodiment. In the first embodiment, the induction motor 1 is subjected to the V/f control. However, this embodiment relates to a method for calculating the speed control, the current control, and the vector control of a synchronous motor.

[0069] In FIG. 10, the same function as that of FIG. 1 is attached with the same symbol, and the description is omitted. In FIG. 10, a difference from FIG. 1 is that a control target is a synchronous motor 12 of a permanent magnetic type, and a feed-back control calculation unit 13 and a frequency estimation calculation unit 14 are included.

[0070] The feed-back control calculation unit 13 receives the new frequency command ωr** which is the output of the frequency command correction calculation unit 6, the current detection values idc and iqc of dc axis and qc axis, and a frequency estimation value ωr^. In the feed-back control calculation unit 13, the feed-back control of the speed control, the current control, and the vector control is calculated. The current command value id* of d axis is "0" or a negative value.

[0071] The speed control calculates a current command value iq* of q axis according to Expression (9) such that the frequency estimation value ωr^ follows the new frequency command ωr**.

[0072] The vector control calculates the voltage reference values vdc* and vqc* according to Expression (18) using the current command values id* and iq* of d axis and q axis, the circuit constants (R, Ld, Lq, and Ke) and the frequency estimation value ωr^ of the synchronous motor 12.
[Math. 18]



[0073]  Herein, R is a winding resistance value, Ld is an inductance value of d axis, Lq is an inductance value of q axis, and Ke is an induction voltage coefficient.

[0074] The current control calculates the voltage correction values ΔVdc* and Δvqc* of dc axis and qc axis according to Expression (19) such that the current detection values idc and iqc follow the current command values id* and iq* of d axis and q axis.
[Math. 19]



[0075] Further, the voltage command values vdc** and vdc** are calculated according to Expression (20).
[Math. 20]



[0076] In the frequency estimation calculation unit 14, the frequency estimation value ωr^ of the synchronous motor 12 is calculated according to Expression (21).
[Math. 21]



[0077] Herein, Δθc is an estimation value of a phase error between a control axis (dc-qc axis) and a magnetic axis (d-q axis), Kppll is a proportional gain of speed estimation, and Kipll is an integral gain of speed estimation.

[0078] As described in this embodiment, even if the synchronous motor is applied instead of the induction motor, and the speed control, the current control, and the vector control are calculated, it is possible to realize a stable operation that the DC voltage EDC and the output current i1c of the power converter 2 do not get into overvoltage and overcurrent.

[0079] Further, the frequency estimation value ωr^ is calculated in this embodiment. However, in a case where an encoder is provided in the synchronous motor 12, a frequency detection value ωr may be detected. In such a case, the current value iq* of q axis according to Expression (22), and the voltage reference values vdc* and vqc* according to Expression (23) are calculated.
[Math. 22]


[Math. 23]



[0080] In addition, the synchronous motor of this embodiment is a permanent magnet type in which a permanent magnetic is embedded, but may be a synchronous reluctance motor which does not use a permanent magnetic.

[0081] Further, the second embodiment may be applied as a base of the control of this embodiment.

Fifth Embodiment



[0082] FIG. 11 is a diagram illustrating a configuration of the power converter in this embodiment. This embodiment is an example which is applied to an induction motor drive system.

[0083] In FIG. 11, the components 5 to 9 are the same as those of FIG. 1. The induction motor 1 of the component of FIG. 1 is driven by the power conversion device 17. In the power conversion device 17, the components 5 to 9 of FIG. 1 are mounted as software components 17a, and the components 2, 2a, 3, and 4 of FIG. 1 are mounted hardware components. A predetermined voltage value 15 and a predetermined current value 16 in the software component 17a may be set by a digital operator 17b of the power conversion device 17 and a host device such as a personal computer 18, a tablet 19, and a smart phone 20 which are external machines of the power conversion device 17.

[0084] If this embodiment is applied to the induction motor drive system, it is possible to realize a stable operation while preventing overcurrent and overvoltage even if the inertia moment value of the machine is large.

[0085] In addition, the predetermined voltage value 15 and the predetermined current value 16 may be set on a programmable logic controller (PLC) which is a host device and a local area network (LAN) connected to a computer.

[0086] Further, this embodiment has been described using the first embodiment, but may be applied to the second to fourth embodiments.

[0087] In the third and fourth embodiments, the voltage correction values Δvdc* and Δvqc* are created from the current command values id* and iq* and the current detection values idc and iqc, and the voltage correction values and the voltage reference value of the vector control are added. However, there may be used a vector control method in which medium current command values id** and iq** in Expression (24) for calculating the vector control are created as the current command values id* and iq* from the current detection values idc and iqc, and the voltage command values vdc** and vqc** of dc axis and qc axis are calculated according to Expression (25) using the output frequency ω1* and the circuit constant of the induction motor 1 and Expression (26) using the frequency estimation value ωr^ and the circuit constant of the synchronous motor 12.
[Math. 24]


[Math. 25]


[Math. 26]



[0088] In addition, there may be applied a vector control method in which the voltage command values vdc** and vqc** of dc axis and qc axis are calculated according to Expression (27) using a current command id* of d axis, the current detection value iqc of qc axis, the new frequency command ωr** and the circuit constant of the synchronous motor 12, and Expression (28) using the circuit constant of the synchronous motor 12.
[Math. 27]


[Math. 28]



[0089] Further, in the first to fourth embodiments, a Si (silicon) semiconductor element or a wide-band gap semiconductor element such as a SiC (silicon carbide) and a GaN (gallium nitride) may be employed as a switching element of the power converter 2.

Reference Signs List



[0090] 
1
induction motor
2
power converter
2a
DC power source
3
current detector
4 DC
voltage detector
5
coordinates transformation unit
6
frequency command correction calculation unit
7 V/f
control calculation unit
8
phase calculation unit
9
coordinates transformation unit
10, 13
feed-back control calculation unit
11, 14
frequency estimation calculation unit
15
predetermined voltage value
16
predetermined current value
17
power conversion device
17a
software of power converter
17b
digital operator of power converter
18
personal computer
19
tablet
20
smart phone
ωr*
frequency command
ωr**
new frequency command
id*
current command value of d axis
iq*
current command value of q axis
idc
current detection value of d axis
iqc
current detection value of q axis
ωr
actual frequency of motor
ωr^
frequency estimation value of motor



Claims

1. A power conversion device which controls a DC voltage, an output frequency, and an output current of a power converter which drives a motor, the power conversion device comprising a frequency command correction calculation unit which automatically adjusts a frequency command,
wherein the frequency command is automatically adjusted such that the power converter does not get into overvoltage and overcurrent in an acceleration/deceleration operation of the motor.
 
2. The power conversion device according to claim 1, wherein the frequency command correction calculation unit corrects a predetermined current value such that the DC voltage approaches a predetermined voltage value, and controls the output frequency such that the output current approaches the corrected current value.
 
3. The power conversion device according to claim 2,
wherein, in a power running mode where a frequency of the motor and a polarity of torque are same, the output frequency is controlled such that the output current approaches the predetermined current value, or
wherein, in a case where the output current becomes larger than the predetermined current value, the output frequency is controlled.
 
4. The power conversion device according to claim 2,
wherein, in a case where the DC voltage becomes larger than the predetermined voltage value in a regeneration mode where a frequency of the motor and a polarity of torque are different, the predetermined current value is corrected and the output frequency is controlled such that the output current approaches the corrected current value, or
wherein, in a case where the output current becomes larger than the predetermined current value, the output frequency is controlled.
 
5. The power conversion device according to any one of claims 1 to 4,
wherein the motor is an induction motor, and
wherein an automatic tuning, a V/f control, a speed-senseless vector control, or a speed-sensor vector control are performed in an actual operation to measure a circuit constant and an inertia moment value of the motor.
 
6. The power conversion device according to any one of claims 1 to 4,
wherein the motor is a synchronous motor, and
wherein an automatic tuning, a position-senseless vector control, or a position-sensor vector control are performed in an actual operation to measure a circuit constant and an inertia moment value of the motor.
 
7. The power conversion device according to any one of claims 2 to 4, wherein the predetermined voltage value and the predetermined current value are automatically set using a circuit constant, a rated frequency, a rated voltage, and a rated current of the motor which are set in an inner memory of a microcomputer mounted in the power conversion device which includes the power converter.
 
8. The power conversion device according to any one of claims 2 to 4, wherein the predetermined voltage value and the predetermined current value are set using a maximum voltage and a maximum current of a switching semiconductor element of the power converter.
 
9. The power conversion device according to any one of claims 2 to 4, wherein the predetermined voltage value and the predetermined current value are set by an outside of the power conversion device.
 
10.  The power conversion device according to claim 9, wherein the outside of the power conversion device is a personal computer, a tablet, or a smart phone which is an external device.
 
11. The power conversion device according to claim 9, wherein the outside of the power conversion device is a programmable logic controller which is a host device, a local area network which is connected to a computer, or a field bus of the power conversion device.
 
12. A control method for a power conversion device which controls a DC voltage, an output frequency, and an output current of a power converter which drives a motor, the method comprising automatically controlling a frequency command to prevent the power converter from getting into overvoltage and overcurrent in an acceleration/deceleration operation of the motor.
 
13. The control method for the power conversion device according to claim 12, wherein a predetermined current value is corrected such that the DC voltage approaches a predetermined voltage value, and the output frequency is controlled such that the output current approaches the corrected current value.
 
14. The control method for the power conversion device according to claim 13,
wherein, in a power running mode where a frequency of the motor and a polarity of torque are same, the output frequency is controlled such that the output current approaches the predetermined current value, or
wherein, in a case where the output current becomes larger than the predetermined current value, the output frequency is controlled.
 
15. The control method for the power conversion device according to claim 13,
wherein, in a case where the DC voltage becomes larger than the predetermined voltage value in a regeneration mode where a frequency of the motor and a polarity of torque are different, the predetermined current value is corrected and the output frequency is controlled such that the output current approaches the corrected current value, or
wherein, in a case where the output current becomes larger than the predetermined current value, the output frequency is controlled.
 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Patent documents cited in the description