Power converter

Abstract

To evaluate whether or not, when an unbalance occurs in a three-phase AC input from a three-phase AC power supply, an unbalance factor of the three-phase AC is equal to or higher than a predetermined value larger than 0.SOLUTION: A power conversion device (1) is provided with a capacitor voltage measurement part (16) that measures a voltage of a capacitor (14), and an unbalance factor evaluation part (17) that evaluates whether or not an unbalance factor of a three-phase AC is equal to or higher than a predetermined value larger than 0 by determining the presence / absence of the phenomenon that the number of times of charging of the capacitor (14) during a half period of a three-phase AC power supply (2) becomes one is determined on the basis of a voltage measured by the capacitor voltage measurement part (16).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a power conversion device including a rectifier circuit that rectifies three-phase alternating current input from a three-phase alternating current power supply into direct current and outputs the direct current.

Background Art

[0002] Patent Document 1 discloses a power conversion device including a rectifier circuit that rectifies three-phase alternating current input from a three-phase alternating current power supply into direct current and outputs the direct current, a capacitor connected between two output terminals of the rectifier circuit, a voltage detector that measures the voltage of the capacitor, a frequency detection unit that detects the ripple frequency of a ripple component included in the voltage measured by the voltage detector, a determination unit that determines that there is a power supply imbalance when the detected ripple frequency is not a reference frequency, and a cutoff unit that cuts off the power supply to a load when the duration of the state determined to have a power supply imbalance exceeds a predetermined time.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a power conversion device such as Patent Document 1, when an imbalance occurs in the three-phase alternating current input from a three-phase alternating current power supply, there is a demand to evaluate whether the imbalance rate of the three-phase alternating current is greater than or equal to a predetermined value greater than 0.

[0005] For example, if an imbalance occurs, even if the unbalance rate is low, the ripple frequency will deviate from the reference frequency, and in Patent Document 1, the power supply to the load will be cut off. However, even if an imbalance occurs, if the unbalance rate is low, there may be no problem in continuing to supply power to the load as usual. In such cases, it is desirable to evaluate whether the unbalance rate is greater than a predetermined value greater than 0 in order to determine whether or not to cut off the power supply to the load.

[0006] This disclosure has been made in view of the above, and aims to enable evaluation of whether the unbalance rate of the three-phase AC input from a three-phase AC power source is greater than or equal to a predetermined value greater than 0 when an unbalance occurs in the three-phase AC power source. More specifically, it aims to enable determination of whether the unbalance rate is high, such that the capacitor is charged and discharged only once in half a cycle of the three-phase AC power source, or low, such that the capacitor is charged and discharged twice. [Means for solving the problem]

[0007] The first embodiment is a power converter comprising a rectifier circuit (11) that rectifies and outputs three-phase AC power input from a three-phase AC power supply (2) into DC power, and a capacitor (14) connected between the two output terminals of the rectifier circuit (11), characterized in that it comprises a physical quantity measuring unit (16, 18, 20) that measures a predetermined physical quantity, and an unbalance rate evaluation unit (17) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0 by determining, based on the physical quantity measured by the physical quantity measuring unit (16, 18, 20), whether or not a phenomenon caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11) is caused by current flowing through only two predetermined input lines of the rectifier circuit (11) for at least half a cycle of the three-phase AC power supply (2).

[0008] In the first embodiment, if the unbalance rate evaluation unit (17) determines that the phenomenon is present, it evaluates that the unbalance rate of the three-phase AC is greater than or equal to the predetermined value which is greater than 0, while if it determines that the phenomenon is absent, it evaluates that the unbalance rate of the three-phase AC is less than the predetermined value which is less than 0.

[0009] The second aspect is that, in the first aspect, the phenomenon is caused by current flowing only through two predetermined input lines of the rectifier circuit (11) for at least one cycle of the three-phase AC power supply (2).

[0010] In the second embodiment, even when imbalance occurs and the average input voltage of the rectifier circuit (11) is not zero, it is easier to correctly evaluate whether the imbalance rate is above a predetermined value.

[0011] In a third embodiment, the capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier circuit (11) in the first or second embodiment.

[0012] In the third embodiment, the capacitance of the capacitor (14) can be reduced to a degree that allows for pulsation of the output voltage of the rectifier circuit (11). Therefore, the capacitor (14) can be made smaller.

[0013] The fourth aspect is that, in any one of the first to third aspects, the physical quantity includes the current of one or more input lines (L1 to L3) of the three input lines (L1 to L3) of the rectifier circuit (11).

[0014] The fifth aspect is that in any one of the first to third aspects, the physical quantity includes at least one of the current flowing through the rectifier element (11D) constituting the rectifier circuit (11) and the voltage generated in the rectifier element (11D) as a result of the current flowing through the rectifier element (11D).

[0015] The sixth aspect is that, in any one of the first to third aspects, the physical quantity includes at least one of the output voltage and output current of the rectifier circuit (11).

[0016] The seventh aspect is that in any one of the first to third aspects, the physical quantity includes at least one of the voltage and current of the capacitor (14).

[0017] The eighth aspect is, in the seventh aspect, the unbalance rate evaluation unit (17) includes a charge / discharge count calculation unit (17b) that calculates the number of times at least one of charging and discharging of the capacitor (14) during a predetermined period based on a physical quantity measured by the physical quantity measuring unit (16), and an evaluation unit (17c) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0 based on the number calculated by the charge / discharge count calculation unit (17b).

[0018] In the eighth embodiment, the physical quantity measuring unit (16) only needs to measure at least one of the voltage and current of the capacitor (14) as a physical quantity, so the configuration of the physical quantity measuring unit (16) can be simplified compared to the case where the three-phase voltage or current input to the rectifier circuit (11) is measured.

[0019] The ninth aspect is the eighth aspect, wherein the predetermined period is half a cycle or longer of the three-phase AC power supply (2).

[0020] When an imbalance occurs in the three-phase AC input to the rectifier circuit (11), the number of charge-discharge cycles per half-cycle of the three-phase AC power supply (2) differs depending on whether the unbalance ratio is less than a predetermined value greater than 0, or whether the unbalance ratio is greater than or equal to the predetermined value, such as in the case of a phase loss. In the ninth embodiment, the charge-discharge cycle calculation unit (17b) calculates the number of charge and discharge cycles of the capacitor (14) during a period of half a cycle or longer of the three-phase AC power supply (2), so it is possible to accurately evaluate whether the unbalance ratio is greater than or equal to a predetermined value greater than 0.

[0021] Aspect 10 is, in Aspect 7, the imbalance rate evaluation unit (17) includes a period calculation unit (17d) that calculates at least one of the lengths of the charging periods of consecutive capacitors (14), the discharging periods of consecutive capacitors (14), and the charge-discharge periods of consecutive pairs of capacitors (14) based on the physical quantity measured by the physical quantity measurement unit (16); and an evaluation unit (17c) that evaluates whether or not the imbalance rate of the three-phase alternating current is greater than or equal to a predetermined value greater than 0 based on at least one length calculated by the period calculation unit (17d).

[0022] In Aspect 10, since the physical quantity measurement unit (16) may measure at least one of the voltage and current of the capacitor (14) as the physical quantity, the configuration of the physical quantity measurement unit (16) can be simplified compared to the case of measuring the three-phase voltage or current input to the rectifier circuit (11).

[0023] Aspect 11 is a power conversion device including a rectifier circuit (11) that rectifies three-phase alternating current input from a three-phase alternating current power source (2) into direct current and outputs it, and a capacitor (14) connected between two output terminals of the rectifier circuit (11), characterized by including an imbalance rate evaluation unit (17) that evaluates whether or not the imbalance rate of the three-phase alternating current is greater than or equal to a predetermined value greater than 0 based on at least one of the current flowing through the input lines (L1 to L3) of the rectifier circuit (11), the current flowing through the rectifying elements (11D) constituting the rectifier circuit (11), the voltage generated in the rectifying elements (11D) due to the flow of current through the rectifying elements (11D), the output voltage of the rectifier circuit (11), the output current of the rectifier circuit (11), the voltage of the capacitor (14), and the current of the capacitor (14).

Brief Description of Drawings

[0024] [Figure 1] FIG. 1 is a block diagram showing the configuration of a power conversion device according to Embodiment 1 of the present disclosure. [Figure 2]FIG. 2 shows, in order from the top, the timing charts of the capacitor voltage and the line voltage of the three-phase AC for the case where no imbalance occurs in the three-phase AC input from the three-phase AC power supply when the power supply voltage is 200 V, the case where an imbalance occurs with an imbalance rate less than a predetermined value greater than 0, and the case where a phase failure occurs. [Figure 3] FIG. 3 is a flowchart for explaining the evaluation operation of the imbalance rate. [Figure 4] FIG. 4 is a diagram corresponding to FIG. 1 of Embodiment 2. [Figure 5] FIG. 5 is a diagram corresponding to FIG. 1 of Embodiment 3. [Figure 6] FIG. 6 is a diagram corresponding to FIG. 1 of Embodiment 4.

MODE FOR CARRYING OUT THE INVENTION

[0025] Embodiments of the present disclosure will be described in detail based on the drawings. Note that the following embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or its uses.

[0026] 《Embodiment 1》 FIG. 1 shows a power conversion device (1) according to Embodiment 1 of the present disclosure. This power conversion device (1) converts the input AC supplied from a three-phase AC power supply (2) into AC having a desired frequency and a desired voltage and supplies it to an electric motor (3).

[0027] The power conversion device (1) includes a rectifier circuit (11), an inverter (12), a reactor (13), a capacitor (14), a PWM controller (15), a capacitor voltage measurement unit (16) as a physical quantity measurement unit, and an imbalance rate evaluation unit (17).

[0028] The rectifier circuit (11) rectifies the three-phase AC power input from the three-phase AC power supply (2) via three input lines (L1~L3) into DC power and outputs it to the first and second output terminals (11a, 11b). More specifically, the rectifier circuit (11) is a full-wave rectifier circuit. The rectifier circuit (11) has six diodes (11D) as rectifying elements connected in a bridge configuration. These diodes (11D) have their cathodes facing the first output terminal (11a) and their anodes facing the second output terminal (11b).

[0029] The inverter (12) converts the DC output from the rectifier circuit (11) into three-phase AC by switching operation and supplies it to the motor (3). More specifically, the inverter (12) has six switching elements (12S) and six freewheeling diodes (12D). The six switching elements (12S) are connected in a bridge configuration. More specifically, the inverter (12) has three switching legs connected between its first and second input nodes (12a, 12b). Each switching leg consists of two switching elements (12S) connected in series.

[0030] In each of the three switching legs, the midpoint between the upper arm switching element (12S) and the lower arm switching element (12S) is connected to the respective phase coils (u-phase, v-phase, and w-phase coils) of the motor (3). Each switching element (12S) is connected in antiparallel to a freewheeling diode (12D).

[0031] One end of the reactor (13) is connected to the first output terminal (11a) of the rectifier circuit (11), and the other end of the reactor (13) is connected to the first input node (12a) of the inverse converter (12).

[0032] The capacitor (14) is connected between the first and second output terminals (11a, 11b) of the rectifier circuit (11). More specifically, the capacitor (14) is connected between the first and second input nodes (12a, 12b) of the inverse converter (12).

[0033] The capacitance of the capacitor (14) is set so that it can hardly smooth the output voltage of the rectifier circuit (11), but can suppress the ripple voltage caused by the switching operation of the inverter (12). The ripple voltage suppressed here is the voltage fluctuation in the switching element (12S) according to the switching frequency.

[0034] In short, the capacitance of capacitor (14) is set to tolerate pulsations in the output voltage of the rectifier circuit (11) and to absorb voltage fluctuations between the first and second input nodes (12a, 12b) (DC side nodes) of the inverter (12) caused by switching operation. More specifically, the capacitance of capacitor (14) is set to suppress the voltage fluctuation of capacitor (14) during the switching period to less than 1 / 10 of the average value of the capacitor (14) voltage. In this way, the capacitance of capacitor (14) can be reduced to a degree that tolerates pulsations in the output voltage of the rectifier circuit (11), thus allowing capacitor (14) to be miniaturized.

[0035] Here, the switching period is the period during which the switching element (12S) repeatedly switches on and off. In this embodiment 1, since the switching element (12S) is controlled by PWM control, the switching period is the carrier period of the carrier wave.

[0036] Conventionally, electrolytic capacitors are sometimes used as smoothing capacitors to smooth the output voltage of the rectifier circuit (11). On the other hand, the capacitance value of the capacitor (14) in this embodiment is approximately 0.01 to 0.1 times that of this smoothing capacitor. As an example, the capacitor (14) is made of a film capacitor.

[0037] Therefore, the voltage across capacitor (14) experiences pulsations caused by the frequency of the input AC supplied from the three-phase AC power supply (2). Since the three-phase AC power supply (2) is a three-phase power supply, the frequency of the pulsations caused by the frequency of the three-phase AC power supply (2) is six times the frequency of the three-phase AC power supply (2).

[0038] The capacitor (14) and the inductance component between the three-phase AC power supply (2) and the capacitor (14) constitute an LC filter. The inductance component includes the reactor (13).

[0039] The PWM controller (15) outputs a control signal to the inverter (12) to control the switching operation of each switching element (12S). The PWM controller (15) controls the inverter (12) to rotate the motor (3) at a desired rotational speed. Specifically, the PWM controller (15) performs PWM control to control multiple switching elements (12S) using switching signals corresponding to the comparison result between the modulated wave of each phase and a predetermined triangular wave carrier wave. Specifically, if the modulated wave is greater than the carrier wave, the switching element (12S) of the upper arm is turned on and the switching element (12S) of the lower arm is turned off, while if the modulated wave is less than the carrier wave, the switching element (12S) of the upper arm is turned off and the switching element (12S) of the lower arm is turned on.

[0040] The capacitor voltage measuring unit (16) measures the voltage of the capacitor (14) as a predetermined physical quantity.

[0041] The unbalance rate evaluation unit (17) includes an unbalance detection unit (17a), a charge cycle calculation unit (17b) which is a charge / discharge cycle calculation unit, and an evaluation unit (17c). The functions of the unbalance rate evaluation unit (17) are realized by a microcomputer or the like.

[0042] The unbalance detection unit (17a) determines whether or not there is an imbalance in the three-phase AC power input from the three-phase AC power supply (2) to the rectifier circuit (11), based on the voltage of the capacitor (14) measured by the capacitor voltage measurement unit (16). Specifically, the unbalance detection unit (17a) determines that there is no imbalance in the three-phase AC power if the pulsation frequency of the voltage pulsation of the capacitor (14) is six times the frequency of the three-phase AC power supply (2). This pulsation is caused by the frequency of the input AC supplied from the three-phase AC power supply (2). On the other hand, the unbalance detection unit (17a) determines that there is an imbalance in the three-phase AC power if the pulsation frequency is not six times the frequency of the three-phase AC power supply (2).

[0043] In Figure 2, the solid line represents the voltage across capacitor (14), the dashed line represents the line-to-line voltage of input lines (L1, L2), the dashed line represents the line-to-line voltage of input lines (L2, L3), and the double-dotted line represents the line-to-line voltage of input lines (L3, L1). As shown in the top graph of Figure 2, when there is no imbalance in the three-phase AC, the pulsation frequency of the voltage across capacitor (14) is six times the frequency of the three-phase AC power supply (2). On the other hand, as shown in the middle and bottom graphs of Figure 2, when there is an imbalance in the three-phase AC, the pulsation frequency is twice the frequency of the three-phase AC power supply (2). Therefore, the imbalance detection unit (17a) can determine whether or not there is an imbalance in the three-phase AC by determining whether or not the pulsation frequency of the voltage across capacitor (14) is six times the frequency of the three-phase AC power supply (2).

[0044] The charge cycle calculation unit (17b) calculates the number of charges of the capacitor (14) during half a cycle of the three-phase AC power supply (2) based on the voltage of the capacitor (14) measured by the capacitor voltage measurement unit (16). The number of charges can be calculated by differentiating the voltage of the capacitor (14) measured by the capacitor voltage measurement unit (16), identifying the sign of the derivative (whether it is positive or negative), and the inflection point of the voltage.

[0045] When the unbalance detection unit (17a) determines that an unbalance has occurred in the three-phase AC, the evaluation unit (17c) evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on the number of times calculated by the charging cycle calculation unit (17b). Specifically, if the number of times calculated by the charging cycle calculation unit (17b) is 2, the evaluation unit (17c) evaluates that the unbalance rate is less than the predetermined value. On the other hand, if the number of times calculated by the charging cycle calculation unit (17b) is 1, the evaluation unit (17c) evaluates that the unbalance rate is greater than or equal to the predetermined value. If the evaluation unit (17c) evaluates that the unbalance rate is greater than or equal to the predetermined value, it stops the switching operation of the switching element (12S) of the inverter (12) by controlling the PWM controller (15). On the other hand, in other cases, the evaluation unit (17c) has the PWM controller (15) continue PWM control.

[0046] In Figure 2, the symbol H represents a half-cycle of the three-phase AC power supply (2). As shown in the central graph of Figure 2, if unbalance occurs but the unbalance rate is less than a predetermined value greater than 0, the capacitor (14) will be charged twice during a half-cycle of the three-phase AC power supply (2). On the other hand, as shown in the bottom graph of Figure 2, if one of the three phases is out of phase, i.e., if the unbalance rate is greater than or equal to the predetermined value, the capacitor (14) will be charged once during a half-cycle of the three-phase AC power supply (2). The evaluation unit (17c) can evaluate whether the unbalance rate is less than a predetermined value greater than 0 or greater than or equal to the predetermined value by determining whether the number of times calculated by the charging count calculation unit (17b) is 2 or 1.

[0047] As described above, the power converter (1) repeatedly performs the unbalance rate evaluation operation shown in Figure 3 at predetermined intervals while supplying power to the electric motor (3).

[0048] In this evaluation operation, first, in (S101), the unbalance detection unit (17a) determines whether or not there is an imbalance in the three-phase AC input from the three-phase AC power supply (2) to the rectifier circuit (11) based on the voltage of the capacitor (14) measured by the capacitor voltage measurement unit (16). Specifically, if the pulsation frequency of the voltage of the capacitor (14) is six times the frequency of the three-phase AC power supply (2), the unbalance detection unit (17a) determines that there is no imbalance in the three-phase AC, and the process proceeds to (S102). On the other hand, if the pulsation frequency is not six times the frequency of the three-phase AC power supply (2), the unbalance detection unit (17a) determines that there is an imbalance in the three-phase AC, and the process proceeds to (S103).

[0049] In (S102), the evaluation unit (17c) instructs the PWM controller (15) to continue PWM control.

[0050] In (S103), the evaluation unit (17c) evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on the number of times the capacitor (14) is charged during half a cycle of the three-phase AC power supply (2) calculated by the charge count calculation unit (17b). Specifically, if the number calculated by the charge count calculation unit (17b) is 2, the evaluation unit (17c) evaluates that the unbalance rate is less than the predetermined value, and the process proceeds to (S102). On the other hand, if the number calculated by the charge count calculation unit (17b) is 1, the evaluation unit (17c) evaluates that the unbalance rate is greater than or equal to the predetermined value, and the process proceeds to (S104).

[0051] In (S104), the evaluation unit (17c) instructs the PWM controller (15) to stop the switching operation of the switching element (12S) of the inverter (12).

[0052] Thus, in this embodiment 1, the charge count calculation unit (17b) and evaluation unit (17c) of the unbalance rate evaluation unit (17) evaluate whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, by determining whether or not the phenomenon of the capacitor (14) being charged once during half a cycle of the three-phase AC power supply (2) is present, based on the voltage of the capacitor (14) measured by the capacitor voltage measurement unit (16). In other words, if the unbalance rate evaluation unit (17) determines that the phenomenon is present, it evaluates that the unbalance rate of the three-phase AC is greater than or equal to the predetermined value, while if it determines that the phenomenon is not present, it evaluates that the unbalance rate of the three-phase AC is less than the predetermined value. Here, the phenomenon in which the capacitor (14) is charged only once during half a cycle of the three-phase AC power supply (2) is a phenomenon caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11), specifically when current flows through only two predetermined input lines (L1 to L3) of the rectifier circuit (11) for more than half a cycle of the three-phase AC power supply (2).

[0053] Therefore, in this embodiment 1, even if an imbalance occurs in the three-phase AC of the three-phase AC power supply (2), as long as the imbalance rate is less than a predetermined value greater than 0, the power converter (1) can continue to supply power without abnormal shutdown.

[0054] Furthermore, since the voltage of the capacitor (14) is used to calculate the number of charging cycles of the capacitor (14), and it is not necessary to measure the three-phase voltage or current input to the rectifier circuit (11), the configuration of the power converter (1) can be simplified.

[0055] When an imbalance occurs in the three-phase AC input to the rectifier circuit (11), the number of charge / discharge cycles per half-cycle of the three-phase AC power supply (2) differs depending on whether the unbalance ratio is less than a predetermined value greater than 0, or whether the unbalance ratio is greater than or equal to the predetermined value, such as in the case of a phase loss. In this embodiment 1, the charge cycle calculation unit (17b) calculates the number of charges of the capacitor (14) during a period of half a cycle or longer of the three-phase AC power supply (2), so it is possible to accurately evaluate whether the unbalance ratio is greater than or equal to a predetermined value greater than 0.

[0056] Furthermore, in this embodiment 1, the capacitance of the capacitor (14) is set to be small enough to allow pulsation of the output voltage of the rectifier circuit (11). Therefore, even when the load on the motor (3) is small, the waveform of the voltage across the capacitor (14) changes significantly depending on whether the unbalance rate is above the predetermined value. This makes it easy to determine whether or not the phenomenon of the capacitor (14) being charged only once occurs.

[0057] Embodiment 2 Figure 4 shows a power converter (1) according to Embodiment 2 of the present disclosure. In Embodiment 2, the unbalance rate evaluation unit (17) has a period calculation unit (17d) instead of a charge cycle calculation unit (17b).

[0058] The period calculation unit (17d) calculates the length of the charge-discharge period of a consecutive pair of capacitors (14) based on the voltage of the capacitors (14) measured by the capacitor voltage measurement unit (16). The length of the charge-discharge period of a consecutive pair of capacitors (14) is the interval between the timings in which the voltage reaches its maximum value. Therefore, the length of the charge-discharge period of a consecutive pair of capacitors (14) can be calculated by differentiating the voltage measured by the capacitor voltage measurement unit (16), identifying the timing in which the voltage reaches its maximum value, and determining the interval between those timings. Alternatively, the length of the charge-discharge period of a consecutive pair of capacitors (14) can also be calculated by identifying the timing in which the voltage reaches its minimum value and determining the interval between those timings.

[0059] The evaluation unit (17c) evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on the period calculated by the period calculation unit (17d). Specifically, if the period calculated by the period calculation unit (17d) is shorter than the predetermined period, the evaluation unit (17c) evaluates that the unbalance rate is less than the predetermined value. On the other hand, if the period calculated by the period calculation unit (17d) is longer than or equal to the predetermined period, the evaluation unit (17c) evaluates that the unbalance rate is greater than or equal to the predetermined value.

[0060] As shown in Figure 2, when a phase loss occurs, the length of the charge-discharge period of a consecutive pair of capacitors (14) is longer compared to when the unbalance ratio is less than a predetermined value greater than 0. Therefore, the evaluation unit (17c) can evaluate whether the unbalance ratio of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on whether the period calculated by the period calculation unit (17d) is greater than or equal to the predetermined period.

[0061] Since the other components are the same as in Embodiment 1, the same reference numerals are used for the same components, and their detailed descriptions are omitted.

[0062] Embodiment 3 Figure 5 shows a power converter (1) according to Embodiment 3 of the present disclosure. In Embodiment 3, the power converter (1) is not provided with a reactor (13). Therefore, the voltage of the capacitor (14) measured by the capacitor voltage measuring unit (16) becomes the output voltage of the rectifier circuit (11). In addition, the power converter (1) is further provided with a DC current measuring unit (18). This DC current measuring unit (18) measures the output current of the rectifier circuit (11) as a predetermined physical quantity. The capacitor voltage measuring unit (16) and the DC current measuring unit (18) constitute a physical quantity measuring unit.

[0063] Furthermore, the unbalance rate evaluation unit (17) is further equipped with a power calculation unit (17e). This power calculation unit (17e) calculates the output power of the rectifier circuit (11) based on the voltage measured by the capacitor voltage measurement unit (16) and the current measured by the DC current measurement unit (18).

[0064] The charge cycle calculation unit (17b) calculates the number of times the capacitor (14) is charged during half a cycle of the three-phase AC power supply (2) based on the output power output by the power calculation unit (17e).

[0065] These power calculation unit (17e) and charge cycle calculation unit (17b) together constitute a charge / discharge cycle calculation unit that calculates the number of times the capacitor (14) is charged during half a cycle of the three-phase AC power supply (2) based on the voltage measured by the capacitor voltage measurement unit (16) and the current measured by the DC current measurement unit (18).

[0066] Since the other components are the same as in Embodiment 1, the same reference numerals are used for the same components, and their detailed descriptions are omitted.

[0067] Embodiment 4 Figure 6 shows a power converter (1) according to Embodiment 4 of the present disclosure. In Embodiment 4, the power converter (1) is equipped with a physical quantity measuring unit (20) instead of a capacitor voltage measuring unit (16). This physical quantity measuring unit (20) measures the current flowing through the three input lines (L1 to L3) of the rectifier circuit (11).

[0068] The unbalance rate evaluation unit (17) determines, based on the current measured by the physical quantity measurement unit (20), whether the current of one of the three input lines (L1 to L3) has been zero for a predetermined period of time or longer. Specifically, the unbalance rate evaluation unit (17) determines whether the number of input lines (L1 to L3) with a current of zero for a predetermined period of time or longer is one, or a number other than one (0, 2, or 3). The predetermined period is set to half a cycle or longer of the three-phase AC power supply (2). If the current of one of the three input lines (L1 to L3) has been zero for a predetermined period of time or longer, the unbalance rate is evaluated as being greater than a predetermined value greater than zero, and the PWM controller (15) stops the switching operation of the switching element (12S) of the inverter (12). On the other hand, if current flows through all three input lines (L1 to L3) at least once during the predetermined period, the unbalance rate is evaluated as being equal to or greater than the predetermined value, and the PWM controller (15) is instructed to continue PWM control. The unbalance rate evaluation unit (17) repeatedly performs this unbalance rate evaluation operation at predetermined timings.

[0069] Thus, in this embodiment 4, the unbalance rate evaluation unit (17) evaluates whether the unbalance rate of the three-phase AC is greater than a predetermined value greater than 0 by determining, based on the currents of the three input lines (L1 to L3), whether or not the current of one of the three input lines (L1 to L3) is 0 for a predetermined period of time or longer. Here, the phenomenon in which the current of one of the three input lines (L1 to L3) is 0 for a predetermined period of time or longer is caused by current flowing only through two predetermined input lines of the rectifier circuit (11) for half a cycle or more of the three-phase AC power supply (2).

[0070] Since the other components are the same as in Embodiment 1, the same reference numerals are used for the same components, and their detailed descriptions are omitted.

[0071] Embodiment 5 In this embodiment 5, the physical quantity measuring unit (20) measures the current flowing through the diodes (11D) that make up the rectifier circuit (11), instead of the current flowing through the three input lines (L1 to L3) of the rectifier circuit (11). Specifically, the physical quantity measuring unit (20) measures the current flowing through each of the three upper arm diodes (11D) that make up the rectifier circuit (11).

[0072] The unbalance rate evaluation unit (17) determines, based on the current measured by the physical quantity measurement unit (20), whether the current of one of the three input lines (L1 to L3) has been zero for a predetermined period of time or longer. This predetermined period is also set to be half a cycle or longer of the three-phase AC power supply (2).

[0073] Since the other components are the same as in Embodiment 4, a detailed explanation will be omitted.

[0074] Modified form of Embodiment 5 In the above embodiment 5, the physical quantity measuring unit (20) measured the current flowing through the three upper arm diodes (11D) constituting the rectifier circuit (11) instead of the current flowing through the three input lines (L1 to L3) of the rectifier circuit (11). However, the voltage of the three upper arm diodes (11D) may also be measured. A voltage is generated in the diode (11D) when current flows through it, and the voltage of the diode (11D) reflects the conduction state of the diode (11D). Therefore, the unbalance rate evaluation unit (17) may determine, based on the voltage of the diode (11D), whether the current in one of the three input lines (L1 to L3) has been 0 for a predetermined period of time or longer.

[0075] Alternatively, the unbalance rate evaluation unit (17) may calculate the power consumption of the diodes (11D) based on the voltage and current of the three upper arm diodes (11D) constituting the rectifier circuit (11), and determine, based on said power consumption, whether the current of one of the three input lines (L1 to L3) has been zero for a predetermined period of time or longer.

[0076] Alternatively, the physical quantity measuring unit (20) may measure at least one of the current and voltage of the three lower arm diodes (11D) constituting the rectifier circuit (11), instead of measuring at least one of the current and voltage of the three upper arm diodes (11D) constituting the rectifier circuit (11).

[0077] Furthermore, the physical quantity measuring unit (20) may measure the current flowing through one or two input lines (L1~L3) of the rectifier circuit (11) and the current or voltage of the diode (11D) on the upper or lower arm corresponding to the remaining input line (L1~L3). The unbalance rate evaluation unit (17) may then determine, based on the current flowing through one or two input lines (L1~L3) of the rectifier circuit (11) and the current or voltage of the diode (11D) on the upper or lower arm corresponding to the remaining input line (L1~L3), whether the current of one of the three input lines (L1~L3) has been zero for a predetermined period of time or longer.

[0078] In the above embodiment 1, the unbalance rate evaluation unit (17) calculated the number of charging cycles based on the voltage of the capacitor (14). However, the unbalance rate evaluation unit (17) may also calculate the number of charging cycles based on the current of the capacitor (14), or by calculating the power of the capacitor (14) based on the voltage and current of the capacitor (14).

[0079] Furthermore, in embodiments 1 and 3 described above, the charge cycle calculation unit (17b) calculated the number of times the capacitor (14) was charged. However, instead of calculating the number of charges, the unit may calculate the number of discharges or the number of charge-discharge cycles.

[0080] Furthermore, in embodiments 1 and 3 described above, the charging cycle calculation unit (17b) calculates the number of times the capacitor (14) is charged during half a cycle of the three-phase AC power supply (2). However, it is also possible to calculate the number of times the capacitor (14) is charged during other periods of time longer than half a cycle of the three-phase AC power supply (2). For example, it is possible to calculate the number of times the capacitor (14) is charged during one cycle of the three-phase AC power supply (2).

[0081] Furthermore, in the above embodiment 2, the period calculation unit (17d) calculated the length of the charge-discharge period of a continuous pair of capacitors (14), but instead, it may calculate the charging period of a continuous pair of capacitors (14) or the discharge period of a continuous pair of capacitors (14). Alternatively, the period calculation unit (17d) may calculate two or more of the charge-discharge period of a continuous pair of capacitors (14), the charging period of a continuous pair of capacitors (14), and the discharge period of a continuous pair of capacitors (14).

[0082] Furthermore, in the above embodiment 3, the unbalance rate evaluation unit (17) calculated the number of charging cycles based on both the output voltage and output current of the rectifier circuit (11), but it may also be done based on either one of them.

[0083] In the above embodiment 3, the reactor (13) was not provided on the output side of the rectifier circuit (11), but it may be provided in the same manner as in embodiment 1.

[0084] Furthermore, in the above embodiment 3, the output voltage of the rectifier circuit (11) and the voltage of the capacitor (14) are the same, so the number of charging cycles of the capacitor (14) may be calculated based on the output voltage of the rectifier circuit (11).

[0085] Furthermore, in the above embodiment 1, the reactor (13) is provided on the output side of the rectifier circuit (11). However, if the inductance value of the reactor (13) is such that it does not interfere with the calculation of the number of charging cycles of the capacitor (14) based on the output voltage of the rectifier circuit (11), the number of charging cycles of the capacitor (14) may be calculated based on the output voltage of the rectifier circuit (11).

[0086] In embodiments 1 and 3 described above, the output current of the rectifier circuit (11) is approximately the same as the charging current of the capacitor (14), so the number of charging cycles of the capacitor (14) may be calculated based on the output current of the rectifier circuit (11).

[0087] Furthermore, in embodiments 1 to 5 described above, the unbalance rate evaluation unit (17) determined whether or not a phenomenon occurred caused by current flowing only through two predetermined input lines of the rectifier circuit (11) over half a cycle of the three-phase AC power supply (2). However, with this method, the unbalance rate evaluation unit (17) may not be able to make a correct evaluation if the average of the input voltages of the rectifier circuit (11) is not zero (for example, if the maximum voltage of the absolute value waveform of the positive input voltage and the maximum voltage of the absolute value waveform of the negative input voltage are different). For example, if the waveform of one half-cycle and the waveform of the other half-cycle of the absolute value waveform of the input voltage during one cycle are different, and despite the low unbalance rate, no current flows through one input line in one half-cycle, but current flows through two predetermined input lines in the other half-cycle, the unbalance rate evaluation unit (17) is highly likely to be unable to make a correct evaluation. Therefore, in order to perform a correct evaluation even when the average of the input voltages of the rectifier circuit (11) is not zero, the unbalance rate evaluation unit (17) may be configured to determine whether or not a phenomenon occurs caused by current flowing only through two predetermined input lines of the rectifier circuit (11) for one or more cycles of the three-phase AC power supply (2). For example, in embodiments 4 and 5 above, the unbalance rate evaluation unit (17) may be configured to monitor the current measured by the physical quantity measurement unit (20) for one cycle of the three-phase AC power supply (2).

[0088] Furthermore, in embodiments 1 to 5 described above, when the unbalance detection unit (17a) determines that an unbalance has occurred in the three-phase AC based on the pulsation frequency of the voltage of the capacitor (14), the evaluation unit (17c) evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0. However, the unbalance detection unit (17a) may be omitted, and the evaluation unit (17c) may always evaluate whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0.

[0089] While embodiments and modifications have been described above, it will be understood that a variety of changes in form and details are possible without departing from the spirit and scope of the claims. Furthermore, these embodiments and modifications may be combined or substituted as appropriate, as long as they do not impair the functions covered by this disclosure. [Industrial applicability]

[0090] As described above, this disclosure is useful as a power converter equipped with a rectifier circuit that rectifies a three-phase AC input from a three-phase AC power source into DC and outputs it. [Explanation of symbols]

[0091] 1. Power converter 2 Three-phase AC power supply 11 Rectifier circuit 11D Diode (Rectifier) 11a First output terminal 11b Second output terminal 14 Capacitors 16. Capacitor voltage measurement section (physical quantity measurement section) 17. Unequilibrium rate evaluation unit 17b Charging cycle calculation unit (charge / discharge cycle calculation unit) 17c Evaluation Department 17d Period calculation part 18 DC current measurement section (physical quantity measurement section) 20 Physical quantity measurement section L1~L3 Input Lines

Claims

1. A rectifier circuit (11) that rectifies the three-phase AC power input from a three-phase AC power supply (2) into DC and outputs it, A capacitor (14) connected between the two output terminals (11a, 11b) of the rectifier circuit (11) and In the power conversion device provided, A physical quantity measuring unit (16, 18, 20) for measuring the voltage of the capacitor (14), The system includes an unbalance rate evaluation unit (17) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than zero, by determining, based on the voltage of the capacitor (14) measured by the physical quantity measuring unit (16, 18, 20), whether or not a phenomenon caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11) is caused by current flowing through only two predetermined input lines of the rectifier circuit (11) for at least half a cycle of the three-phase AC power supply (2), among the phenomena caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11), The capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier circuit (11), The aforementioned unequilibrium rate evaluation unit (17) A charge / discharge cycle calculation unit (17b) calculates the number of times the capacitor (14) is charged and discharged during a predetermined period by differentiating the voltage of the capacitor (14) measured by the physical quantity measuring unit (16), A power conversion device characterized by having an evaluation unit (17c) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on the number of charge / discharge cycles calculated by the charge / discharge cycle calculation unit (17b).

2. A rectifier circuit (11) that rectifies the three-phase AC power input from a three-phase AC power supply (2) into DC and outputs it, A capacitor (14) connected between the two output terminals (11a, 11b) of the rectifier circuit (11) and In the power conversion device provided, A physical quantity measuring unit (16, 18, 20) for measuring the current of the capacitor (14), The system includes an unbalance rate evaluation unit (17) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than zero, by determining, based on the current of the capacitor (14) measured by the physical quantity measuring unit (16, 18, 20), whether or not a phenomenon caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11) is caused by current flowing through only two predetermined input lines of the rectifier circuit (11) for at least half a cycle of the three-phase AC power supply (2), among the phenomena caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11), The capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier circuit (11), The aforementioned unequilibrium rate evaluation unit (17) A charge / discharge cycle calculation unit (17b) calculates the number of times the capacitor (14) is charged and discharged during a predetermined period, based on the current of the capacitor (14) measured by the physical quantity measuring unit (16), A power conversion device characterized by having an evaluation unit (17c) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on the number of charge / discharge cycles calculated by the charge / discharge cycle calculation unit (17b).

3. In the power conversion device according to claim 1 or 2, The power conversion device is characterized in that the aforementioned phenomenon is caused by current flowing only through two predetermined input lines of the rectifier circuit (11) for at least one cycle of the three-phase AC power supply (2).

4. In the power conversion device according to claim 1 or 2, The power conversion device is characterized in that the predetermined period is half a cycle or more of the three-phase AC power supply (2).

5. A rectifier circuit (11) that rectifies the three-phase AC input from a three-phase AC power supply (2) into DC and outputs it, A capacitor (14) connected between the two output terminals (11a, 11b) of the rectifier circuit (11) and In the power conversion device provided, A physical quantity measuring unit (16, 18, 20) for measuring the voltage of the capacitor (14), The system includes an unbalance rate evaluation unit (17) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than zero, by determining, based on the voltage of the capacitor (14) measured by the physical quantity measuring unit (16, 18, 20), whether or not a phenomenon caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11) is caused by current flowing through only two predetermined input lines of the rectifier circuit (11) for at least half a cycle of the three-phase AC power supply (2), among the phenomena caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11), The capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier circuit (11), The aforementioned unequilibrium rate evaluation unit (17) A period calculation unit (17d) calculates the length of at least one of the following: a continuous charging period of the capacitor (14), a continuous discharge period of the capacitor (14), and a continuous charge-discharge period of a set of capacitors (14), by differentiating the voltage of the capacitor (14) measured by the physical quantity measuring unit (16), A power conversion device characterized by having an evaluation unit (17c) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on at least one length calculated by the period calculation unit (17d).

6. A rectifier circuit (11) that rectifies the three-phase AC input from a three-phase AC power supply (2) into DC and outputs it, A capacitor (14) connected between the two output terminals (11a, 11b) of the rectifier circuit (11) and In the power conversion device provided, A physical quantity measuring unit (16, 18, 20) for measuring the current of the capacitor (14), The system includes an unbalance rate evaluation unit (17) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than zero, by determining, based on the current of the capacitor (14) measured by the physical quantity measuring unit (16, 18, 20), whether or not a phenomenon caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11) is caused by current flowing through only two predetermined input lines of the rectifier circuit (11) for at least half a cycle of the three-phase AC power supply (2), among the phenomena caused by current flowing through at least two of the three input lines (L1 to L3) of the rectifier circuit (11), The capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier circuit (11), The aforementioned unequilibrium rate evaluation unit (17) A period calculation unit (17d) calculates the length of at least one of the following lengths based on the current of the capacitor (14) measured by the physical quantity measuring unit (16): a continuous charging period of the capacitor (14), a continuous discharge period of the capacitor (14), and a continuous charge-discharge period of a set of capacitors (14). A power conversion device characterized by having an evaluation unit (17c) that evaluates whether the unbalance rate of the three-phase AC is greater than or equal to a predetermined value greater than 0, based on at least one length calculated by the period calculation unit (17d).

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