PH12018000166A1

PH12018000166A1 - Motor control apparatus

Info

Publication number: PH12018000166A1
Application number: PH12018000166A
Authority: PH
Inventors: Yuji Ide; Masahisa Koyama; Masakazu Sakai; Toshio Hiraide
Original assignee: Sanyo Electric Co
Priority date: 2017-06-14
Filing date: 2018-06-14
Publication date: 2019-12-11
Also published as: CN109088577A; TW201905474A; JP2019004603A

Abstract

A motor control apparatus is provided which does not shut down a system immediately even if current that is regenerated to a power supply exceeds a threshold during regeneration of power and, as a result, can operate a motor continuously even if imbalance occurs in a three-phase power supply. A motor control apparatus includes: a converter configured to convert three-phase AC power into direct current; an inverter connected to the converter and a motor, the inverter being configured to drive the motor; and a control circuit configured to control the converter, and the control circuit includes a maximum phase current value detection unit configured to detect a maximum value of a phase current, and a threshold comparison unit configured to compare the detected maximum value of the phase current with a threshold, and controls the converter in such a manner as to adjust a phase-to-phase voltage between two phases where current is flowing to zero upon the threshold comparison unit detecting that the maximum value of the phase current has reached a current limit threshold during regeneration of power.

Description

A control unit of the converter 7 includes a phase detection circuit 27 that = detects the phases of the three-phase AC power supply, a current limit control unit 25, a pus powering/regeneration determination unit 31, and a gate signal generation unit 33 that : generates a gate signal of the transistor 21. “ @

The powering/regeneration determination unit 31 determines the operating @ state of the motor on the basis of, for example, a voltage of a direct current unit of the pd converter 7 or the direction of direct current. Moreover, during powering operation, the gate of the transistor configuring the converter is turned off. Three-phase full-wave rectification is performed from the three-phase AC power supply 5 through, for example, a diode 7a-1-2 connected in parallel to, for example, a transistor 7a-1-1.

Consequently, power is supplied to the inverter 11. During regenerative operation, a transistor on an upper arm side of a phase having the largest voltage and a transistor of a lower arm of a phase having the smallest voltage are turned on in a 120° section on the basis of the phases of the three-phase AC power supply detected by the phase detection circuit 27 as in Fig. 5S. Consequently, current flows through each phase to return direct current power to the power supply.

The current limit control unit 25 includes a maximum phase current value detection unit 25-1 that detects the maximum value of the phase current, a threshold comparison unit 25-2 that compares the detected maximum phase current value with a threshold, and a transistor (switching element) selection unit 25-3 that selects a transistor to be turned off.

When the threshold comparison unit 25-2 detects that the maximum value of the phase current has reached a current limit threshold during regeneration of power, the regenerative resistor 17 is turned on. At the same time, the transistor selection unit

@ o - : 3 25-3 selectively turns off only an upper transistor in one of two phases where current is , flowing. The upper transistor in the phase where current is flowing is then turned off = through the gate signal generation unit 33. Consequently, current regenerated to the ps

AC power supply S is reduced. Moreover, regenerative power that cannot be : regenerated to the AC power supply 5 is absorbed by resistor regeneration. When the “ maximum value of the phase current is reduced to a current limit lifting threshold during ® the regeneration of power, the transistor that has been off is turned on. At the same 0 time, the regenerative resistor 17 is turned off. Consequently, the power supply current is controlled to between the current limit threshold and the current limit lifting threshold.

In the event of, for example, a power supply imbalance, the current of a specific phase increases. Hence, when the current of the phase reaches the current limit threshold, the current to be regenerated to the AC power supply § is limited.

Current that cannot be regenerated to the AC power supply 5 is then absorbed by the regenerative resistor 17. In this manner, even in the event of a power supply imbalance, it becomes possible to continue operation without shutting down the system due to overcurrent.

Moreover, regenerative power that cannot be regenerated to the AC power supply 5 is absorbed by the regenerative resistor 17. Hence, it is possible to prevent the flow of excess current when, for example, the transistor 7a-1-1 of the converter 7 is turned on again by a voltage of a smoothing unit becoming excessive while limiting the current to be regenerated to the power supply.

Moreover, only an upper transistor in one of two phases where current is flowing is turned off. Hence, a phase-to-phase voltage generated while being off is reduced to 1/2 as compared to a case where the transistors are turned off in all the

> - phases. The phase-to-phase voltage is generated by forcibly turning off the current > flowing through the ACL 15 by, for example, the transistor 7a-1-1. ©

Figs. 2A to 2C are diagrams illustrating an example of the circuit operation of > the converter 7. In an example described below, an upper transistor in the R-phase and o alower transistor in the S-phase are on as in Fig. 2A. Moreover, a current I1 flows = + from the upper transistor in the R-phase through the R-phase of the ACL 15 to the @ power supply. Furthermore, a current 12 flows from the S-phase of the ACL 15 to the e lower transistor in the S-phase. If the current increases in this state and reach the ® current limit threshold, when both of the upper transistor in the R-phase and the lower transistor in the S-phase are turned off, a lower diode in the R-phase is turned on (a current 13) as in Fig. 2B, and the potential of V1 becomes -VDC. On the other hand, an upper diode in the S-phase is turned on. As a result, the potential of V2 becomes +VDC (a current 14). Figs. 3A and 3B are diagrams illustrating time dependency of the phase-to-phase voltage, that is, a signal waveform. Hence, a voltage change of 2 x

VDC occurs in the phase-to-phase voltage between the R-phase and the S-phase as in

Fig. 3A.

When the current that has been reduced by turning off the transistors reaches the current limit lifting threshold, the upper transistor in the R-phase and the lower transistor in the S-phase are turned on again. Consequently, the potential of V1 becomes +VDC. The potential of V2 becomes —-VDC. Asa result, a voltage change of 2 x VDC occurs. When the current increases and reaches again the current limit threshold, the upper transistor in the R-phase and the lower transistor in the S-phase are turned off. Such a fluctuation in phase-to-phase voltage is prevented by an interphase capacitor C for noise filtering provided to a power input unit. However, at the same time, a large ripple current flows through the interphase capacitor C.

~ 0.

For example, a film capacitor is usually used for the interface capacitor for — noise filtering. When the effective value of the ripple current exceeds a permissible = ripple current of the capacitor, the interphase capacitor is damaged. | ~

In contrast, if the maximum phase current value reaches the current limit : threshold, when only an upper transistor in a phase is turned off, the fluctuation amount hy of a phase-to-phase voltage can be reduced. For example, as in Fig. 2A, the upper a transistor in the R-phase and the lower transistor in the S-phase are on; accordingly, @ current flows from the upper transistor in the R-phase through the R-phase of the ACL 15 to the power supply. Furthermore, if current flows from the S-phase of the ACL 15 to the lower transistor in the S-phase, only the upper transistor in the R-phase is turned off (a current 15) as in Fig. 2C. The lower diode is turned on in the R-phase. The potential of V1 becomes ~VDC. On the other hand, the lower transistor remains on in the S-phase. The potential of V2 remains at -VDC. Hence, the phase-to-phase voltage between the R-phase and the S-phase becomes 0 V. As in Fig. 3B, only a voltage change of VDC occurs. "Moreover, voltage applied to the ACL is reduced to 172. - Hence, a reduction in current also becomes gentle. When the current is reduced and reaches the threshold, the upper transistor in the R-phase is turned on again. Hence, the current is regenerated to the power supply. A phase-to-phase voltage waveform at this point in time is generated as many as the number of times that the voltage change of VDC reaches the current limit threshold as in Fig. 3B. In this manner, when only an upper gate is turned off in a phase during the current limitation, the fluctuation of the phase-to-phase voltage is reduced to 1/2. Consequently, it is possible to reduce the number of times required to limit current. Furthermore, noise leaking to the power supply side through the ACL is also reduced. Consequently, the ripple current of the

© ® ~ interphase capacitor can also be reduced. As a result, it becomes possible to prevent a * ro reduction in the life of the interphase capacitor and improve the reliability of the motor @ control apparatus. The gate that is turned off may not be of an upper transistor in a © phase. In other words, the gate of a transistor in one of two phases that are on is h simply required to be turned off. o

As described above, according to the embodiment, when the maximum value © of a phase current reaches the current limit threshold during regeneration of power in o ) the motor control apparatus that regenerates power, only a transistor in one of two - phases that are on is turned off. Consequently, it is possible to limit current and meanwhile absorb regenerative power that cannot be regenerated to the power supply with resistor regeneration.

Consequently, according to the motor control apparatus provided, even if current that is regenerated to the power supply exceeds the threshold during the regeneration of power, the system is not immediately shut down. As a result, even if imbalance occurs in the three-phase power supply, the operation can be continued. At the same time, power supply noise can also be reduced.

In the above embodiment, the configurations and the like are not limited to those illustrated in the accompanying drawings. The motor control apparatus according to the above embodiment can be modified as appropriate within the scope that does not impair the effects of the present invention. In addition, the above embodiment can be modified as appropriate and carried out as long as the modification does not depart from the scope of the object of the present invention.

Moreover, each component of the present invention can be freely selected.

Moreover, the technical scope of the present invention also includes an embodiment including the selected components.

> —

The motor control apparatus according to the present invention may be the > following first to fifth motor control apparatuses: >

The first motor control apparatus is characterized by including: a converter 0 configured to convert three-phase AC power into direct current; an inverter connected to o the converter and a motor, the inverter being configured to drive the motor; and a « control circuit configured to control the converter, wherein the control circuit includes a @ o maximum phase current value detection unit configured to detect a maximum value of a = phase current, and a threshold comparison unit configured to compare the detected “ maximum value of the phase current with a threshold, and performs the control in such a manner as to adjust a phase-to-phase voltage between two phases where current is flowing to zero upon the threshold comparison unit detecting that the maximum value of the phase current has reached a current limit threshold during regeneration of power.

The second motor control apparatus is the first motor control apparatus characterized by further including a regenerative resistor on an output side of the converter, wherein the control circuit turns on the regenerative resistor upon the threshold comparison unit detecting that the maximum value of the phase current has reached the current limit threshold during the regeneration of power. . The third motor control apparatus is the first or second motor control apparatus characterized in that the converter includes a three-phase bridge circuit of six switching elements and diodes, and the control circuit includes a switching element selection unit configured to select any of the switching elements, and performs the control in such a manner as to turn off the switching element selected by the switching element selection unit.

The fourth motor control apparatus is the first or second motor control apparatus characterized in that the control circuit further includes: a phase detection n circuit configured to detect the phases of the three-phase AC power; a current limit @ ho control unit; a powering/regeneration determination unit; and a gate signal generation © unit configured to generate a gate signal of the switching element. *

The fifth motor control apparatus is the first or second motor control apparatus ~ characterized in that the control circuit performs the control in such a manner as to turn o on the switching elements in the phase having the largest voltage and the phase having 2 the smallest voltage among the phases of the three-phase AC power during regenerative & operation. "

The foregoing detailed description has been presented for the purposes of illustration and description. Many modifications and variations are possible in light of the above teaching. It is not intended to be exhaustive or to limit the subject matter described herein to the precise form disclosed. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily ’ 15 limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims appended hereto.

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MOTOR CONTROL APPARATUS 2

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BACKGROUND

’ be 1. Technical Field - ul

The present invention relates to a motor control apparatus. or oD © “Le faa] 2. Description of the Related Art on be

A motor control apparatus is configured of, for example, a converter and an inverter.

When the powering operation of a motor is performed, the converter converts

AC power into direct current power. The inverter then convers direct current power into AC power and drives the motor.

When the regenerative operation of the motor is performed, the inverter converts AC power generated by the motor into direct current power, and the converter converts direct current power into AC power to regenerate the power to a power supply.

As a method for controlling the converter, there is a control method in which, in a case of, for example, a three-phase power supply, a transistor is switched at each 120° section of a phase of the power supply to return power to the power supply.

Fig. 4 is a circuit diagram illustrating an example of the configuration of such a motor control apparatus. A motor control circuit X included in the motor control apparatus includes an AC reactor 115, a converter including a three-phase bridge circuit, a phase detection circuit 127, and a gate signal generation unit 133. The three-phase bridge circuit includes, for example, six parallel-connected pairs (107a-1 to 107¢c-2) of converter transistors and rectifier diodes. A nodal point of each pair is connected to a three-phase AC power supply 105 through the AC reactor 115. The phase detection

@ o circuit 127 detects the phases of the three-phase AC power supply. The gate signal > generation unit 133 generates a gate signal of the transistor. a

When the powering operation of a motor 103 is performed, a gate of a oe transistor 107a-1-1 included in the parallel-connected circuit 107a-1 of the transistor ~ and the diode included in a converter 107 is off. Moreover, three-phase full-wave - rectification is performed from the three-phase AC power supply 105 through a diode ® 107a-1-2 connected in parallel to the transistor 107a-1-1. Consequently, electric power ® is supplied to an inverter 111. ”

When the regenerative operation of the motor 103 is performed, the gate of the transistor 107a-1-1 is turned on, as illustrated in Fig. 5, on the basis of the phases of the three-phase AC power supply detected by the phase detection circuit 127.

Consequently, electric current flows through two phases to return the direct current power to the power supply. A section where the transistor 107a-1-1 is on is a 120° section where the power supply voltage of each phase is higher than the power supply 15. voltages of the other phases in the upper side of a phase, and is a 120° section where the power supply voltage of each phase is lower than the power supply voltages of the other phases in the lower side of a phase.

An example where overcurrent is prevented under control of such a converter 107 is disclosed in JP-A-10-239360.

An overcurrent detection circuit having the following features is described in

JP-A-10-239360. In the overcurrent detection circuit, a converter that controls regeneration of power includes current direction detection means for detecting the current direction of an input current of the converter, and current characteristic comparison means for comparing the current characteristic of the input current of the converter with a comparison value for detecting overcurrent to detect overcurrent. The

@ i comparison value of the current characteristic comparison means is changed on the > basis of the current direction of the current detected by the current direction detection > means. The change of the comparison value allows the detection of overcurrent with > hr the comparison value according to the current direction.

Moreover, a power regeneration converter having the following features is o described in 1P-A-2009-201333. The power regeneration converter includes a > switching circuit that switches excess power generated on a three-phase load side to = regenerate it to a three-phase power supply system, a current detector that detects the ” magnitude and direction of each phase current flowing between the three-phase power supply system and the switching circuit, and a control unit. When the current value detected by the current detector is equal to or greater than a predetermined value, the control unit outputs an instruction to sequentially turn off a plurality of switching elements configuring the switching circuit to a drive circuit of the switching element, with a predetermined time difference, starting with a switching element corresponding to a phase having the lowest current value of the phase currents detected by the current detector.

However, when overcurrent is detected in the circuit of JP-A-10-239360, the system is shut down. In such a method of JP-A-10-239360, the detection of overcurrent leads to a system shutdown. Hence, for example, if an imbalance occurs in the three-phase power supply, a current of a specific phase becomes excessive, which may lead to an instantaneous system shutdown. The system shutdown reduces the availability rate of a machine. Hence, it is better to reduce the frequency of system shutdowns as much as possible.

However, in the method of JP-A-10-239360, the operation of the system cannot be continued in the event of overcurrent.

> 0 :

Moreover, in JP-A-2009-201333, switching circuit protection in the event of : the occurrence of abnormal overcurrent is achieved in such a manner as to enable a © reduction in the capacity of a snubber capacitor by preventing an increase in the ” . terminal voltage of the snubber capacitor which prevents the surge voltage of a ~

S transistor included in the converter. Hence, the value of a current flowing from the = switching circuit toward the three-phase AC power supply is monitored. When o abnormal overcurrent equal to or greater than a protection level flows, the switching elements are sequentially turned off with the predetermined time difference, starting with a switching element corresponding to a phase having the lowest current value among the phase currents, instead of turning off all the switching elements configuring the switching circuit at once. Consequently, the capacity of the snubber capacitor can be reduced. However, as in the method of JP-A-10-239360, the operation of the system cannot be continued in the event of overcurrent.

In this manner, the methods for controlling a converter of a motor control apparatus of JP-A-10-239360 and JP-A-2009-201333 result in shutting down the system when the overcurrent protection works during regeneration. Hence, the operation of the system cannot be continued.

SUMMARY

The present invention has been made to improve such a problem. An object of the present invention is to provide a motor control apparatus that does not shut down a system immediately even if current to be regenerated to a power supply exceeds a threshold during regeneration of power, and can operate a motor continuously irrespective of imbalance occurring in a three-phase power supply. :

In addition, an object of the present invention is to provide a motor control

@ > 3 apparatus that can reduce power supply noise. : ¥ ha

According to one aspect of the present invention, a motor control apparatus is at provided which includes: a converter configured to convert three-phase AC power into > : - direct current; an inverter connected to the converter and a motor, the inverter being w= configured to drive the motor; and a control circuit configured to control the converter, wherein the control circuit includes a maximum phase current value detection unit @ configured to detect a maximum value of a phase current, and a threshold comparison o wt unit configured to compare the detected maximum value of the phase current with a threshold, and controls the converter in such a manner as to adjust a phase-to-phase voltage between two phases where current is flowing to zero upon the threshold comparison unit detecting that the maximum value of the phase current has reached a current limit threshold during regeneration of power. i

According to the motor control apparatus, it is possible to limit current by turning off only a switching element in one of two phases that are on when the maximum value of the phase current has reached the current limit threshold during the regeneration of power, and meanwhile absorb regenerative power that cannot be regenerated to the power supply with resistor regeneration.

Furthermore, according to the motor control apparatus, even if current to be regenerated to the power supply exceeds the threshold during the regeneration of power, the system is not immediately shut down. Moreover, even if imbalance occurs in the three-phase power supply, it is possible to continuously operate the motor. At the same time, it is also possible to reduce power supply noise.

Furthermore, it is preferable that a regenerative resistor be included onan output side of the converter, and the control circuit turn on the regenerative resistor upon the threshold comparison unit detecting that the maximum value of the phase current has reached the current limit threshold during the regeneration of power. 7 ro

It is preferable that the converter include a three-phase bridge circuit having six © switching elements and diodes, and the control circuit include a switching element —- selection unit configured to select any of the switching elements, and control the = converter in such a manner as to turn off the switching element selected by the - switching element selection unit. 2

It is preferable that the control circuit further include: a phase detection circuit o . ££ configured to detect the phases of the three-phase AC power; a current limit control unit; a powering/regeneration determination unit; and a gate signal generation unit configured to generate a gate signal of the switching element.

The control circuit may control the converter in such a manner as to turn on the switching elements in the phase having the largest voltage and the phase having the smallest voltage among the phases of the three-phase AC power during the regeneration of power.

According to the present invention, even if current to be regenerated to a power supply exceeds a threshold during regeneration of power in the operation of a motor, a system is not immediately shut down. As a result, even if imbalance occurs in the three-phase power supply, it is possible to continuously operate the motor. In addition, it is possible to reduce power supply noise.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a circuit diagram illustrating an example of the configuration of a motor control apparatus according to one embodiment;

Figs. 2A to 2C are diagrams illustrating an example of the circuit operation of a converter;

a

Figs. 3A and 3B are diagrams illustrating time dependency of a phase-to-phase oy voltage, and are diagrams illustrating a signal waveform; -

Fig. 4 is a circuit diagram illustrating an example of the configuration of a - general motor control apparatus; and :

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DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the : disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

A motor control apparatus according to one embodiment of the present invention is described in detail hereinafter with reference to the drawings.

Fig. 1 is a circuit diagram illustrating an example of the configuration of the motor control apparatus according to the embodiment. As illustrated in Fig. 1, a motor control apparatus 1 according to the embodiment includes an AC reactor 15 connected to, for example, a three-phase AC power supply 5, a converter 7 connected to an output of the AC reactor 15, a regenerative resistor 17 connected to an output of the converter 7, a transistor (a switching element such as a semiconductor switch) 21 that drives the regenerative resistor 17, a smoothing capacitor 23, an inverter 11, and a control system circuit described below. A motor 3 is driven by the output of the inverter 11. The converter 7 is configured of, for example, a three-phase bridge circuit including six

Claims

1. = Amotor control apparatus comprising: @ a converter configured to convert three-phase AC power into direct current; » an inverter connected to the converter and a motor, the inverter being o configured to drive the motor; and = a control circuit configured to control the converter, wherein @ the control circuit - includes a maximum phase current value detection unit configured to = detect a maximum value of a phase current, and a threshold comparison unit configured to compare the detected maximum value of the phase current with a threshold, and controls the converter in such a manner as to adjust a phase-to-phase voltage between two phases where current is flowing to zero upon the threshold comparison unit detecting that the maximum value of the phase current has reached a current limit threshold during regeneration of power.

:

2. The motor control apparatus according to claim 1, further comprising a regenerative resistor on an output side of the converter, wherein the control circuit turns on the regenerative resistor upon the threshold comparison unit detecting that the maximum value of the phase current has reached the current limit threshold during the regeneration of power.

3. The motor control apparatus according to claim 1 or 2, wherein the converter includes a three-phase bridge circuit having six switching elements and diodes, and i : the control circuit .

© . [an] includes a switching element selection unit configured to select any of *® the switching elements, and @ controls the converter in such a manner as to turn off the switching oe element selected by the switching element selection unit. o | 0 4, The motor control apparatus according to claim 1 or 2, wherein 2 the control circuit further includes: @ a phase detection circuit configured to detect the phases of the © three-phase AC power; a current limit control unit; a powering/regeneration determination unit; and a gate signal generation unit configured to generate a gate signal of the switching element.

5. The motor control apparatus according to claim 1 or 2, wherein the control circuit controls the converter in such a manner as to turn on the switching elements in the phase having the largest voltage and the phase having the smallest voltage among the phases of the three-phase AC power during regenerative operation.