JP2012151959A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter that can exactly detect a change in the voltage amplitude of an AC power supply and thus can determine abnormality of a power voltage with a low-cost and small configuration.SOLUTION: The power converter includes a voltage derivation section (20) that derives a power voltage index of an AC power supply (2) at every predetermined timing synchronizing with a power voltage phase of the AC power supply (2).

Description

  The present invention relates to a power conversion device.

  2. Description of the Related Art Conventionally, there is known a power conversion device including a converter unit that rectifies AC power of an AC power source and an inverter unit that converts the output of the converter unit into AC power having a predetermined frequency.

  Some power converters of this type are provided with an abnormality detection means for detecting an abnormality in the power supply voltage (for example, an instantaneous voltage drop) in order to protect the inverter unit and the like. Specifically, for example, in Patent Document 1, a detector is provided on the input power line via a transformer. In the power converter of the same document, the input voltage of the converter unit is detected by this detector. In the power conversion device, when the detected value is equal to or less than a predetermined value, it is determined that the instantaneous voltage has dropped.

Japanese Patent Laid-Open No. 3-27793

  As disclosed in Patent Document 1, the detection of the voltage of the input power supply line using a transformer causes an increase in the size of the device and an increase in the device cost. Also, the DC signal obtained by rectifying and smoothing the input power supply is used as the AC power supply voltage amplitude. If this power supply voltage amplitude falls below a predetermined reference value or exceeds a predetermined reference value, it is determined that the AC power supply is abnormal. It is also possible to do. However, in such a system, a voltage drop abnormality is erroneously detected in a rectifier circuit that does not have a capacitor capacity capable of smoothing fluctuations in the power supply voltage waveform, such as a so-called capacitorless inverter. In addition, when direct current signal filtering is performed so as not to be affected by voltage fluctuation during energization, there is a problem that control of the power converter becomes unstable due to delay in detection. As described above, it may be impossible to distinguish whether the decrease or increase in the DC signal is caused by some abnormality or the periodic voltage fluctuation of the power supply voltage amplitude at the normal time. For this reason, the problem that the voltage abnormality of AC power supply cannot be detected correctly arises.

  The present invention has been made in view of the above points, and an object of the present invention is to provide power conversion that can accurately detect a change in the voltage amplitude of an AC power supply using an inexpensive and small configuration, and thus can determine abnormality of the power supply voltage. Is to provide a device.

  The first invention has a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz), and the input AC power (2) power is supplied to the switching elements (Su, Sv, Sw, Sx, A power conversion device that converts AC power of a predetermined frequency by a switching operation of (Sy, Sz) and supplies the AC power to a load (3) is an object. The power converter includes a voltage deriving unit (20) for deriving a power supply voltage index of the AC power supply (2) at every predetermined timing synchronized with the power supply voltage phase of the AC power supply (2). Features.

  In the first invention, the voltage deriving unit (20) derives an index indicating the power supply voltage of the AC power supply (2) (hereinafter referred to as a power supply voltage index). The voltage deriving unit (20) of the present invention appropriately derives the power supply voltage index at a timing synchronized with the power supply voltage phase of the AC power supply (2). As a result, it is possible to reliably and promptly detect a change in the power supply voltage during an abnormality or the like without being affected by periodic fluctuations in the power supply voltage of the AC power supply (2). Further, since a change in the power supply voltage of the AC power supply (2) can be detected with a relatively simple configuration, the power conversion device can be reduced in size and cost.

  According to a second invention, in the first invention, a converter unit (11) connected to the AC power source (2) to rectify AC power of the AC power source (2), and the plurality of switching elements (Su, Sv) , Sw, Sx, Sy, Sz), and the switching power of the switching element (Su, Sv, Sw, Sx, Sy, Sz) changes the output power of the converter unit (11) to AC power of a predetermined frequency. DC link having an inverter part (13) for conversion and a capacitor (14) connected between the converter part (11) and the inverter part (13) and outputting pulsating DC voltage to the inverter part (13) The voltage derivation unit (20) includes a DC link voltage detection unit (21) that detects a DC voltage of the DC link unit (12), and the DC link voltage detection unit (21 ) To derive an index indicating the power supply voltage of the AC power supply (2) based on the detection voltage detected by It is characterized by that.

  In the second invention, the capacitance of the capacitor (14) is set to be relatively small so that the output voltage from the capacitor (14) pulsates. That is, the power conversion device of the present invention is configured in a so-called capacitor-less system. In the present invention, the DC voltage of the DC link unit (12) is detected by the DC link voltage detection unit (21). Based on the detected voltage, an index indicating the power supply voltage of the AC power supply (2) is appropriately derived at a timing synchronized with the power supply voltage phase of the AC power supply (2).

  According to a third invention, in the first invention, the plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) are provided, and the AC power of the AC power source (2) is supplied to the switching elements (Su, Sv). , Sw, Sx, Sy, Sz) includes a matrix converter unit (40) that converts the AC power into a predetermined frequency by switching operation, and the voltage deriving unit (20) converts the AC power of the AC power source (2) A rectifying unit (42) for rectifying and a DC voltage detecting unit (43) for detecting a DC voltage rectified by the rectifying unit (42), based on a detection voltage detected by the DC voltage detecting unit (43) Thus, an index indicating the power supply voltage of the AC power supply (2) is derived.

  The power conversion device of the third invention is configured in a matrix converter system. In the voltage deriving unit (), the AC power of the AC power source (2) is rectified by the rectifying unit (42), and the DC voltage after rectification is detected by the DC voltage detecting unit (43). Based on the detected voltage, an index indicating the power supply voltage of the AC power supply (2) is appropriately derived at a timing synchronized with the power supply voltage phase of the AC power supply (2).

  In a fourth aspect based on the first aspect, the voltage deriving section (20) has a power supply voltage detecting section for detecting the power supply voltage of the AC power supply (2), and the detected voltage detected by the power supply voltage detecting section. An index indicating the power supply voltage of the AC power supply (2) is derived based on the above.

  In the fourth invention, the index indicating the power supply voltage of the AC power supply (2) is directly detected by the power supply voltage detection section of the voltage deriving section (20).

  In a fifth aspect based on any one of the second to fourth aspects, the voltage deriving unit (20) determines the average value or effective value of the detection voltage of the voltage deriving unit (20) in a predetermined period. It is derived as an index indicating the power supply voltage.

  In the fifth invention, a power supply voltage index is obtained by an average value or an effective value of the detection voltage of the voltage deriving unit (20) in a predetermined period, and this power supply voltage index is calculated from the power supply voltage phase of the AC power supply (2). It is derived at the timing of synchronization. By using the average value and effective value of the detection voltage during a predetermined period in this way, it is less susceptible to the steep noise of the power supply voltage of the AC power supply (2), and changes in the power supply voltage during abnormal conditions etc. It can be detected reliably.

  According to a sixth aspect of the present invention, in the second or third aspect, the voltage deriving unit (20) determines the power supply voltage of the AC power source (2) when the number of phases of the AC power source (2) is n. An average value or an effective value of the detection voltage of the voltage deriving unit (20) in a 1 / (2 × n) cycle is derived as an index indicating the power supply voltage.

  In the sixth invention, the average value and effective value of the detection voltage are calculated for each 1 / (2 × n) period of the power supply voltage (where n is the number of phases of the AC power supply (2)). In this calculation period, the peak of the power supply voltage straddles. For this reason, for example, when there is an abnormality, a decrease or increase in the power supply voltage index becomes significant.

  In a seventh aspect based on the second or third aspect, the voltage deriving unit (20) has a power supply voltage of the AC power source (2) when the number of phases of the AC power source (2) is n. An average value or an effective value of the detection voltage of the voltage deriving unit (20) in a 1 / (4 × n) cycle is derived as an index indicating the power supply voltage.

  In the seventh invention, the average value and the effective value of the detection voltage are calculated for each 1 / (4 × n) period of the power supply voltage (where n is the number of phases of the AC power supply (2)). Thereby, abnormality determination etc. can be performed with comparatively quick responsiveness.

  According to the present invention, since the power supply voltage index of the AC power supply (2) is derived at every predetermined timing synchronized with the power supply voltage phase of the AC power supply (2), it is not affected by the periodic fluctuation of the power supply voltage. Thus, it is possible to reliably detect a change in the power supply voltage during an abnormality or the like. Thereby, for example, abnormalities such as an instantaneous voltage drop and a steep voltage rise can be detected quickly and reliably. In addition, since the configuration of the power converter is simplified, the cost and size of the power converter can be reduced.

  In the second invention, since the power supply voltage index is derived based on the DC voltage (DC link voltage) of the DC link section (12), the change in the power supply voltage can be reliably and promptly changed with a relatively simple and inexpensive configuration. Can be detected.

  According to the third aspect of the present invention, in the matrix converter type power converter, a change in the power supply voltage can be reliably and promptly detected with a relatively simple and inexpensive configuration.

  In the fifth invention, an average value or an effective value of the detection voltage is calculated in a predetermined period, and the result is used as a power supply voltage index. Accordingly, it is possible to make an abnormality determination while alleviating the influence of a steep voltage fluctuation such as noise.

  Particularly, in the sixth invention, the period during which the power supply voltage index is calculated is 1 / (2 × n) period (n is the number of phases of the AC power supply (2)) of the power supply voltage of the AC power supply (2). Yes. As a result, when there is an abnormality or the like, a decrease or increase in the power supply voltage index becomes significant, so that the accuracy of abnormality determination can be further improved. In addition, since the power supply voltage index can be accurately obtained in any timing calculation period, abnormality determination or the like can be performed with relatively quick response.

  In the seventh invention, the period during which the power supply voltage index is calculated is 1 / (4 × n) period (n is the number of phases of the AC power supply (2)) of the power supply voltage of the AC power supply (2). Therefore, the abnormality determination can be performed with a relatively fast response.

FIG. 1 is a schematic circuit diagram of a power converter according to an embodiment. FIG. 2 is a time chart for explaining the detection operation of the instantaneous voltage drop according to the embodiment. FIG. 2 (A) shows the waveform of the power supply voltage of the AC power supply, and FIG. 2C shows a waveform of the DC link voltage, FIG. 2C shows a section for obtaining the average value of the DC link voltage, and FIG. 2D shows the calculated voltage average value. Is shown. FIG. 3 is a time chart for explaining the detection operation of the instantaneous voltage drop according to the first modification. FIG. 3A shows the waveform of the power supply voltage of the AC power supply, and FIG. Shows the waveform of the DC link voltage, FIG. 3C shows a section for obtaining the average value of the DC link voltage, and FIG. 3D shows the calculated voltage average. Value. FIG. 4 is a time chart for explaining the detection operation of the instantaneous voltage drop according to the modification 2. FIG. 4A shows the waveform of the power supply voltage of the AC power supply, and FIG. Shows the waveform of the DC link voltage, FIG. 4C shows a section for obtaining the average value of the DC link voltage, and FIG. 4D shows the calculated voltage average. Value. FIG. 5 is a time chart for explaining the detection operation of the instantaneous voltage drop according to the modification 3. FIG. 5 (A) shows the waveform of the power supply voltage of the AC power supply, and FIG. Shows the waveform of the DC link voltage, FIG. 5 (C) shows the time when the DC link voltage is derived, and FIG. 5 (D) shows the derived voltage value. is there. FIG. 6 is a time chart for explaining the detection operation of the instantaneous voltage drop according to the modified example 4. FIG. 6A shows the waveform of the power supply voltage of the AC power supply. Shows the waveform of the DC link voltage, FIG. 6 (C) shows the time when the DC link voltage is derived, and FIG. 6 (D) shows the derived voltage value. is there. FIG. 7 is a schematic circuit diagram of the power conversion apparatus according to the first embodiment. FIG. 8 is a schematic circuit diagram of a power conversion apparatus according to another second embodiment. FIG. 9 is a schematic circuit diagram of a power conversion apparatus according to another third embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

  A schematic configuration of a power converter (1) according to an embodiment of the present invention is shown in FIG. The power conversion device (1) includes a converter circuit (11) (converter unit), a DC link unit (12), and an inverter circuit (13) (inverter unit). ) Is converted into electric power of a predetermined frequency and supplied to the three-phase AC motor (3). The three-phase AC motor (3) is, for example, for driving a compressor provided in a refrigerant circuit of an air conditioner, and constitutes a load of the power conversion device (1).

  The converter circuit (11) is connected to the AC power source (2) and configured to rectify AC power. In this converter circuit (11), a bridge circuit (full-wave rectifier circuit) in which a plurality (four in this embodiment) of rectifier diodes (D1 to D4) are connected in a bridge shape is connected to the AC power source (2). Are connected to each other. Thereby, the AC voltage of the AC power source (2) is full-wave rectified by the bridge circuit of the rectifier diodes (D1 to D4). The reactor (16) is connected to the converter circuit (11).

  The DC link section (12) is provided between the output side of the converter circuit (11) and the input side of the inverter circuit (13). The DC link part (12) is provided with a capacitor (14). The capacitor (14) is constituted by, for example, a film capacitor, and a ripple voltage (voltage) generated when a switching element (Su, Sv, Sw, Sx, Sy, Sz) described later of the inverter circuit (13) performs a switching operation. It is configured to have a capacitance capable of smoothing only (variation). That is, the capacitor (14) is a small-capacitance capacitor that does not have a capacitance that smoothes the voltage rectified by the converter circuit (11) (voltage fluctuation caused by the power supply voltage). Therefore, in the single-phase AC power source (2), the DC voltage of the DC link unit (12) (hereinafter referred to as DC link voltage) pulsates at twice the frequency of the power source frequency, and the maximum voltage is the minimum voltage. More than twice.

  The inverter circuit (13) is connected in parallel to the DC link section (12) on the output side of the converter circuit (11). The inverter circuit (13) is formed by bridge-connecting a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) (for example, six in the case of a three-phase alternating current). That is, the inverter circuit (13) includes three switching legs in which two switching elements are connected in series with each other. In each switching leg, the upper arm switching elements (Su, Sv, Sw) and the lower arm The midpoints of the switching elements (Sx, Sy, Sz) are connected to the coils (3a, 3b, 3c) of the respective phases of the three-phase AC motor (3).

  The inverter circuit (13) converts the DC voltage into a three-phase AC voltage by the on / off operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplies it to the three-phase AC motor (3). Is configured to do. In this embodiment, a free-wheeling diode (Du, Dv, Dw, Dx, Dy, Dz) is connected in antiparallel to each of the switching elements (Su, Sv, Sw, Sx, Sy, Sz). Yes.

  The power conversion device (1) of the present embodiment includes a voltage deriving unit (20) for deriving an index indicating the power supply voltage of the AC power supply (2), and a power supply voltage derived by the voltage deriving unit (20). And an abnormality determination unit (25) for detecting an abnormality in the voltage of the AC power source (2) based on the index indicating The abnormality determination unit (25) of the present embodiment is configured to detect an instantaneous voltage drop (also referred to as “instantaneous drop” for short) of the AC power supply (2) caused by a power failure or the like.

  More specifically, the voltage deriving unit (20) of the present embodiment includes a DC link voltage detecting unit (21) and a calculating unit (23). The DC link voltage detection unit (21) is configured to detect a voltage (that is, a DC link voltage Vdc) applied to the capacitor (14) of the DC link unit (12).

  The computing unit (23) of the present embodiment calculates an average value for the DC link voltage every predetermined period. Specifically, in the present embodiment, an average value Vdcave is calculated for each predetermined section T with respect to the DC link voltage (see FIG. 2B) detected by the DC link voltage detector (21). In the present embodiment, the length of the section T is the same as the half cycle of the power supply voltage of the AC power supply (2). The start timing of this section T corresponds to the phase of about 0 ° and about 180 ° of the power supply voltage of the AC power source (2). In the calculation unit (23), the average value Vdcave of the DC link voltage Vdc in this section T is calculated by the following equation (1).

  The abnormality determination unit (25) detects an instantaneous voltage drop of the AC power supply (2) based on the average value Vdcave for each section T obtained as described above. The abnormality determination unit (25) detects an instantaneous voltage drop of the AC power supply (2) based on a change in the average value Vdcave at every predetermined timing synchronized with the power supply voltage phase of the AC power supply (2). The phase of the power supply voltage of the AC power supply (2) is detected by using a zero cross detection circuit that detects a zero cross of the power supply voltage waveform that is an AC waveform. The power supply voltage phase can also be obtained based on a change in the power supply voltage waveform.

  The power conversion device (1) includes an inverter control unit (17) that outputs control signals of switching elements (Su, Sv, Sw, Sx, Sy, Sz) of the inverter circuit (13). The inverter control unit (17) is configured to be able to change the speed of the motor (3) by outputting a gate signal corresponding to the speed command of the motor (3) to the inverter circuit (13). The inverter control unit (17) of the present embodiment is provided with a speed limiting unit (30) that limits the speed of the motor (3) to a predetermined speed when the instantaneous voltage drop described above is detected.

−Voltage detection operation−
The detection operation of the instantaneous voltage drop as described above will be described in more detail with reference to FIG.

  In the AC power supply (2) of the power conversion device (1), the waveform of the power supply voltage is substantially sinusoidal as shown in FIG. On the other hand, the capacitor (14) described above is a small-capacitance capacitor that does not have a capacitance that smoothes the voltage rectified by the converter circuit (11). For this reason, the DC link voltage of the DC link section (12) has a waveform with a relatively large fluctuation period corresponding to the power supply voltage phase of the AC power supply (2), for example, as shown in FIG. .

  During the operation of the power conversion device (1), the average value Vdcave of the DC link voltage for each section T is detected as described above. The abnormality determination unit (25) compares the average value Vdcave for each section T before and after every 1/2 cycle timing synchronized with the power supply voltage phase. That is, the timing of this comparison is the same as the end timing of each section T.

  For example, assuming that the average value derived in the latest section T1 is Vdcave1, and the voltage average value derived in the immediately preceding section T2 is Vdcave2, the abnormality determination unit (25) reduces the average value for these sections. (That is, Vdcave1-Vdcave2) is calculated gradually.

  Assume that the AC power supply (2) is momentarily lowered due to lightning strikes or the like during the operation of the power conversion device (1). In this case, the power supply voltage of the AC power supply (2) is reduced due to the occurrence of a sag (see FIG. 2A), and the average value Vdcave derived by the voltage deriving unit (20) is also associated with this. It becomes smaller (see FIG. 2B). In such a period, the average value Vdcave calculated for each section T by the abnormality determination unit (25) is instantaneously reduced (see FIG. 2D). In the example of FIG. 2D, the average value Vdcave is greatly reduced immediately after the half cycle of the power supply voltage of the AC power supply (2) has elapsed after the instantaneous voltage drop has occurred. In this way, the decrease change amount of the average value Vdcave (for example, the voltage drop amount ΔV shown in FIG. 2D) increases, and when this voltage drop amount ΔV becomes larger than a preset set value, the instantaneous voltage A signal indicating the occurrence of the decrease is output to the inverter control unit (17) and the like.

  When the instantaneous voltage drop signal is output to the inverter controller (17), the speed limiter (30) outputs a speed limit value ωlim for limiting the motor speed to the inverter circuit (13). This speed limit value ωlim is calculated by the following equation (2), for example.

  Here, Vdcave is an average value of the DC link voltage at the timing when the instantaneous voltage drop is detected, φa is a motor induced voltage constant, and k is a speed limit value calculation constant (0 ≦ k ≦ 1). In this way, by limiting the speed of the motor (3) when the instantaneous voltage drops, the operation can be continued at the minimum motor speed that can be controlled in accordance with the power supply voltage. Therefore, the operation of the motor (3) can be stably continued even when the instantaneous voltage drops. In particular, since the capacitor (14) of the present embodiment has a relatively small capacity, when the instantaneous voltage drop occurs, the change in the DC link voltage also becomes steep. For this reason, for example, even if phase control is performed in response to a voltage drop by advancing the current phase, the phase control may not be in time for changes in the DC link voltage, which may lead to instability and step-out. However, such a problem can be prevented in advance by quickly detecting the instantaneous voltage drop and limiting the speed of the motor (3) as described above. If it is determined that the unstable step-out cannot be prevented even if the speed is limited, the operation of the motor (3) is stopped, and after the power supply voltage is restored, the malfunction can be prevented.

-Effect of the embodiment-
According to the embodiment, the instantaneous drop of the AC power supply (2) is detected based on the decrease change of the DC link voltage at each timing synchronized with the power supply voltage phase of the AC power supply (2). Therefore, even if the DC link voltage fluctuates periodically due to the power supply voltage of the AC power supply (2), it is determined whether or not there is an instantaneous voltage drop without being affected by such periodic voltage fluctuations. it can. Therefore, it is possible to prevent erroneous determination of instantaneous voltage drop during normal operation, and thus the reliability of the power conversion device (1) can be improved. In addition, since the DC link voltage detected by the DC link voltage detector (21) is used, the instantaneous voltage can be reduced by a relatively simple and inexpensive configuration (for example, a configuration in which a resistance voltage dividing circuit is used to input to the microcomputer AD input). The decrease can be accurately detected.

  Moreover, in the said embodiment, since the capacity | capacitance of a capacitor | condenser (14) is achieved, size reduction of a power converter device (1) and by extension, cost reduction can be achieved. On the other hand, when the capacitance of the capacitor (14) is reduced and the so-called capacitorless inverter method is adopted, the DC link voltage cannot be sufficiently smoothed. For this reason, in the power conversion device (1), the DC link voltage greatly fluctuates even during normal operation. However, in the above embodiment, since the DC link voltage is derived in synchronization with the power supply voltage phase of the AC power supply (2), the voltage drop is not greatly affected by such a large fluctuation of the DC link voltage. It can be detected.

  Moreover, in the said embodiment, for every timing which synchronizes with the power supply voltage phase of AC power supply (2), the average value of DC link voltage in a predetermined area is derived | led-out, and AC power supply ( 2) The instantaneous voltage drop is detected. By using the voltage average value in such a predetermined section, the instantaneous drop can be detected while further mitigating the influence of the periodic voltage fluctuation of the DC link voltage.

  Furthermore, in the said embodiment, the area T which detects DC link voltage is a half cycle of the power supply voltage of AC power supply (2). In this section T, since the peak of the power supply voltage always crosses, when the instantaneous voltage drop occurs, the decrease change of the derived voltage average value becomes remarkable. For this reason, the accuracy of detection of instantaneous voltage drop can be further improved.

<< Modification of Embodiment >>
In the said embodiment, it is good also as a structure of the following modifications.

<Modification 1>
In the example shown in FIG. 3, the length of the section T is the same as the half cycle of the power supply voltage of the AC power supply (2), and the start timing of the section T is 90 ° of the power supply voltage of the AC power supply (2). And 270 ° phase. Even in this way, the instantaneous drop can be detected based on the decrease change of the average voltage value derived for each section T.

<Modification 2>
In the example shown in FIG. 4, the length of the section T is the same as the quarter cycle of the power supply voltage of the AC power supply (2), and the start timing of the section T is the power supply voltage of the AC power supply (2). Corresponding to phases of 0 °, 90 °, 180 °, and 270 °. Even in this case, the instantaneous drop can be detected based on the decrease change of the average voltage value derived for each section T.

<Modification 3>
In the example shown in FIG. 5, the length of the section T is the same as the half cycle of the power supply voltage of the AC power supply (2), and the start timing of the section T is the power supply voltage of the AC power supply (2). It corresponds to the phase every 1/8 period. Even in this case, the instantaneous drop can be detected based on the decrease change of the average voltage value derived for each section T. That is, regardless of the specific phase, if the length of the section T is the same as the half cycle of the power supply voltage, the instantaneous value can be reduced as in the above embodiment, regardless of the phase at any phase. Can be detected.

<Modification 4>
In the example illustrated in FIG. 6, the DC link voltage Va ′ is derived at the time point ta ′ synchronized with the power supply voltage phase of the AC power supply (2). That is, in this example, the average value of the DC link voltage in the predetermined period is not derived. Then, the abnormality determination unit (25) compares the DC link voltage derived at each time point ta ′ before and after, and detects an instantaneous voltage drop when the drop amount of the DC link voltage becomes greater than a predetermined value. When the DC link voltage is derived at predetermined time points ta ′ in this way, the DC link voltage is derived at a time close to the phase of about 90 ° and 270 ° of the power source voltage of the AC power source (2). good.

<< Other Embodiments >>
About the said embodiment, it is good also as the following structures.

  In the above embodiment, the average value for each predetermined section T is calculated by the above equation (1) for the DC link voltage detected by the DC link voltage detector (21). However, during this period T, the effective value of the DC link voltage Vdc may be derived by the following equation (3) by the calculation unit (23).

  The abnormality determination unit (25) compares the effective values for each period T calculated by the above equation (3), and determines that an instantaneous voltage drop occurs when the change amount of these effective values exceeds a predetermined value. Also good. Further, when the instantaneous voltage drop is detected in this way, the speed limiter (30) outputs the speed limit value ωlim obtained by the following equation (4) to the motor (3).

  Thereby, as described above, the operation of the motor (3) can be continued even under a condition where an instantaneous voltage drop occurs.

  Furthermore, in order to further improve the determination accuracy of the instantaneous voltage drop, the power conversion device (1) may be configured as shown in FIG. 7 (other embodiment 1). In this example, an input current detection unit (22) is provided as the voltage deriving unit (20). Further, a voltage correction unit (23a) and a basic waveform width calculation unit (23b) are added to the calculation unit (23) of FIG. In the power conversion device (1) shown in FIG. 7, the DC link voltage is adjusted so that the DC link voltage detected by the DC link voltage detector (21) approaches the absolute value of the actual power supply voltage of the AC power supply (2). Vdc is corrected by the following equation (5).

  In the above equation (5), Vdc ′ is the corrected DC link voltage and can be said to be an estimated value of the power supply voltage of the AC power supply (2). lin is the input current of the reactor (16) detected by the input current detector (22), and Vdc is the DC link voltage detected by the DC link voltage detector (21). L is the inductance of the reactor (16), and Vf (lin) is a voltage drop in the forward direction with respect to the current lin of one rectifier diode (D). By this formula, the power supply voltage of the AC power supply (2) can be estimated in consideration of the voltage drop of the rectifier diode (D) and the voltage drop of the reactor (16). Further, the fundamental waveform calculation unit (23b) calculates the fundamental wave amplitude by FFT for the corrected Vdc.

  Based on the calculated value (DC link voltage correction value) obtained as described above, the average value and effective value for each period T described above can be obtained, and the instantaneous voltage drop can be detected based on these changes. . Even when an instantaneous voltage drop is detected in this manner, the speed of the motor (3) may be limited in the same manner as described above.

  Moreover, the abnormality determination part (25) of the said embodiment has detected the instantaneous voltage drop of the power supply voltage of AC power supply (2) based on the decrease change of the calculated value computed by the calculating part (23). However, the AC power supply at the time of abnormality (for example, when a device with a large power capacity sharing the power supply is stopped in a power supply system with high impedance) based on the rising change of the calculated value calculated by the calculation unit (23) It is also possible to detect a sharp rise in power supply voltage in (2).

  Moreover, in the said embodiment, although single phase alternating current power supply (2) is used as alternating current power supply, it is not restricted to this, You may use alternating current power supply of three phase alternating current. In the three-phase AC power source, the cycle of the DC link voltage is 1/3 of the cycle of the single-phase AC power source (2). Therefore, in the three-phase AC power supply, the section T described above may be set to 1/6 period of the power supply voltage. Thereby, in the single-phase alternating current power supply (2), it is possible to obtain the same effect as in the case where the section T is set to ½ cycle of the power supply voltage. Further, in the three-phase AC power supply, the space T described above is set to 1/12 period of the power supply voltage, so that in the single-phase AC power supply (2), the section T is set to 1/4 period of the power supply voltage. The effect of this can be obtained. In other words, the period T in which the effective value and average value of the DC link voltage are calculated is 1 / (2 × n) of the power supply voltage of the AC power supply (2), where n is the number of phases of the AC power supply (2). ) Period, or 1 / (4 × n) period of the power supply voltage.

  Moreover, in the said embodiment, the parameter | index which shows the power supply voltage of AC power supply (2) is derived | led-out based on the detection voltage detected by the DC link voltage detection part (21). However, a power supply voltage detection unit that directly detects the power supply voltage of the AC power supply (2) is provided, and an index indicating the power supply voltage of the AC power supply is derived based on the detection voltage detected by the power supply voltage detection unit. May be.

  Moreover, in the said embodiment, it is what is called a capacitor-less type power converter device. However, you may employ | adopt the power converter device which has a matrix converter part (40) as shown, for example in FIG.8 and FIG.9.

  The example of FIG. 8 (other example 2) is a matrix converter type power converter using a single-phase AC power source (2). The matrix converter unit (40) has a plurality of switching elements (Sru, Srv, Srw, Ssu, Ssv, Ssw), and converts the AC power of the AC power source (2) to the switching elements (Sru, Srv, Srw, Ssu, Ssv, Ssw) is converted into AC power having a predetermined frequency by the switching operation. In the power supply deriving unit (20) in the example of FIG. 8, the rectifier circuit (rectifier unit (42)) connected in parallel to the smoothing capacitor (41) and the DC voltage rectified by the rectifier circuit (42) are received. And a DC voltage detector (43) for detection. The rectifier circuit (42) is a bridge circuit (full-wave rectifier circuit) in which rectifier diodes (D5 to D8) are connected in a bridge shape. Also in the example of FIG. 8, as in the above embodiment, an index indicating the power supply voltage of the AC power supply (2) is derived based on the voltage detected by the DC voltage detection unit (43). Abnormality determination such as a momentary drop can be made based on the change.

  The example (other example 3) shown in FIG. 9 is a matrix converter type power converter using a three-phase AC power source (2). The matrix converter section (40) has a plurality of switching elements (Sru, Srv, Srw, Ssu, Ssv, Ssw, Stu, Stv, Stw), and converts the AC power of the AC power source (2) into the switching elements (Sru, Srv, Srw, Ssu, Ssv, Ssw, Stu, Stv, and Stw) are converted into AC power having a predetermined frequency by the switching operation. 9 includes a rectifier circuit (rectifier unit (42)) connected in parallel to the smoothing capacitors (41a, 41b, 41c) and after rectification by the rectifier circuit (42). And a DC voltage detection unit (43) for detecting the DC voltage. The rectifier circuit (42) is a bridge circuit (full-wave rectifier circuit) in which rectifier diodes (D5 to D10) are connected in a bridge shape. Also in the example of FIG. 9, as in the above embodiment, an index indicating the power supply voltage of the AC power supply (2) is derived based on the voltage detected by the DC voltage detection unit (43), and the power supply voltage index Abnormality determination such as a momentary drop can be made based on the change.

  Further, in the matrix converter type power converter as shown in FIG. 8 or FIG. 9, a power supply voltage detection unit for directly detecting the power supply voltage of the AC power supply (2) is provided, and the power supply voltage detection unit detects the power supply voltage. An index indicating the power supply voltage of the AC power supply may be derived based on the detected voltage.

  As described above, the present invention is useful for a power converter.

1 Power converter
2 AC power supply
3 Motor (load)
11 Converter circuit
12 DC link
13 Inverter circuit
14 capacitors
20 Voltage deriving unit
21 DC link voltage detector
25 Abnormality judgment section
40 Matrix converter
42 Rectifier
43 DC voltage detector

Claims (7)

Having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz), switching the switching element (Su, Sv, Sw, Sx, Sy, Sz) with the input power of the AC power supply (2) A power conversion device that converts AC power of a predetermined frequency by operation and supplies it to a load (3),
A power converter comprising a voltage deriving unit (20) for deriving a power supply voltage index of the AC power supply (2) at every predetermined timing synchronized with the power supply voltage phase of the AC power supply (2). In claim 1,
A converter unit (11) connected to the AC power source (2) to rectify AC power of the AC power source (2) and the plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) An inverter unit (13) for converting the output power of the converter unit (11) into AC power of a predetermined frequency by a switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz), and a capacitor (14 A DC link unit (12) connected between the converter unit (11) and the inverter unit (13) and outputting a pulsating DC voltage to the inverter unit (13),
The voltage deriving unit (20) has a DC link voltage detection unit (21) for detecting a DC voltage of the DC link unit (12), and is based on a detection voltage detected by the DC link voltage detection unit (21). A power conversion device characterized in that an index indicating the power supply voltage of the AC power supply (2) is derived. In claim 1,
The switching operation of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) having the plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and the AC power of the AC power source (2). A matrix converter (40) for converting into AC power of a predetermined frequency by
The voltage deriving unit (20) includes a rectifying unit (42) that rectifies AC power of the AC power source (2), and a DC voltage detecting unit (43) that detects a DC voltage rectified by the rectifying unit (42). And an index indicating the power supply voltage of the AC power supply (2) is derived based on the detection voltage detected by the DC voltage detection section (43). In claim 1,
The voltage deriving unit (20) includes a power supply voltage detection unit that detects a power supply voltage of the AC power supply (2), and the power supply voltage of the AC power supply (2) based on the detection voltage detected by the power supply voltage detection unit The power converter characterized by deriving the parameter | index which shows. In any one of Claims 2 thru | or 4,
The voltage derivation unit (20) derives an average value or an effective value of detection voltages of the voltage derivation unit (20) during a predetermined period as an index indicating the power supply voltage. In claim 2 or 3,
The voltage deriving unit (20) has the voltage deriving unit (1/2 × n) period of the power source voltage of the AC power source (2), where n is the number of phases of the AC power source (2). 20) A power conversion device, wherein the average value or the effective value of the detected voltages is derived as an index indicating the power supply voltage. In claim 2 or 3,
The voltage deriving unit (20) is configured to provide the voltage deriving unit (1) in a 1 / (4 × n) cycle of the power supply voltage of the AC power supply (2), where n is the number of phases of the AC power supply (2). 20) A power conversion device, wherein the average value or the effective value of the detected voltages is derived as an index indicating the power supply voltage.

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