Power converter

Abstract

To provide a power converter which can suppress increase of size and cost and detect generation of a phase loss without requiring a large number of multi-phase detection circuits.SOLUTION: A power converter 1, which allows detection of a phase loss without requiring a large number of multi-phase detection circuits, includes: a multi-phase electric transformer 3 for transforming an AC power to a multiphase AC power; a rectification unit 4 for transforming the multiphase AC power to a DC power; and a phase loss detection unit 100 for detecting generation of a phase loss on the basis of an input voltage supplied to the multi-phase electric transformer and an output voltage of the rectification unit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power conversion device.

Background Art

[0002] A power conversion device converts an AC voltage into a DC voltage using a polyphase transformer and a rectifier. When a phase loss occurs in the polyphase transformer, the ripple component of the DC output voltage increases. If the operation is continued with the phase loss, the current flowing to the phases other than the phase where the phase loss has occurred increases, and damage to the diodes in the rectifier circuit may occur.

[0003] Regarding power conversion devices, there is known a technique that enables generation of DC power without using an AC / DC converter and further enables miniaturization of a polyphase transformer (see, for example, Patent Document 1). According to this technique, the polyphase transformer has a first winding that constitutes a primary winding and windings that generate four different three-phase phases of the second to fifth windings that constitute a secondary winding, and all the windings are wound around a common iron core. The second to fifth windings are all star-connected, and the third winding is wound around the iron core with 0.73 times the number of turns of the second winding and with its polarity reversed with respect to the second winding. The neutral points of the second and third windings are connected to each other. The fourth and fifth windings are branched and generated from a common predetermined portion in the middle of the second winding. Each of the second to fifth windings outputs three-phase power of different phases, and outputs a polyphase AC voltage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a power conversion device, when one-phase open phase occurs in the output circuit of a polyphase transformer or in a rectifier section, the ripple of the DC output voltage from the rectifier section is missing by one, and an excessive current flows through the other phases to compensate for the missing phase. For this reason, in the power conversion device, there are cases where a diode generates heat and is damaged or the circuit generates heat. Regarding the method for detecting an open phase, a wiring circuit breaker for a single-phase three-wire circuit with neutral line open phase protection is known. When an open phase occurs, the voltage division balance between the neutral line and the voltage phase is disrupted by the influence of the load in a wiring circuit breaker with neutral line open phase protection. Therefore, it is detected when the voltage between one of the voltage phases and the neutral line exceeds a certain threshold value.

[0006] If a method for detecting an open phase by a wiring circuit breaker with neutral line open phase protection is applied to a power conversion device equipped with a polyphase transformer, since the phase voltages for 12 phases need to be detected, a large number of detection circuits are required, leading to an increase in size and cost. An object of the present invention is to provide a power conversion device capable of detecting the occurrence of an open phase.

Means for Solving the Problem

[0007] (1) One aspect of the present invention is a power conversion device including a polyphase transformer that converts AC power into polyphase AC power, a rectifier section that converts the polyphase AC power into DC power, and an open phase detection section that detects the occurrence of an open phase based on the input voltage supplied to the polyphase transformer and the output voltage of the rectifier section. (2) One aspect of the present invention is the power conversion device according to (1) above, wherein the open phase detection section detects the occurrence of an open phase based on the ratio of the input voltage and the output voltage. (3) One aspect of the present invention is the power conversion device according to (1) above, wherein the open phase detection section derives a first value based on the three-phase phase voltages input to the polyphase transformer, derives a second value based on the output voltages corresponding to the three-phase phase voltages, a derivation section that derives the ratio of the first value and the second value, and a determination section that determines whether or not an open phase has occurred based on the ratio derived by the derivation section and a threshold value. (4) One aspect of the present invention is the power conversion device described in (3) above, wherein the derivation unit derives the first value every predetermined period based on the three-phase line-to-line voltages input to the polyphase transformer, and derives the second value every predetermined period based on the output voltages corresponding to the three-phase line-to-line voltages of the predetermined period, and derives the ratio of the first value to the second value every predetermined period. (5) One aspect of the present invention is the power conversion device described in (4) above, wherein the predetermined period is an integral multiple of a half cycle of the input voltage. (6) One aspect of the present invention is the power conversion device described in (3) or (4) above, wherein the first value and the second value are average values. (7) One aspect of the present invention is the power conversion device described in (3) or (4) above, wherein the first value and the second value are effective values. (8) One aspect of the present invention is the power conversion device described in (3) above, further comprising a circuit breaker that interrupts the AC power input to the polyphase transformer, and a drive unit that operates the circuit breaker when a phase loss is determined to have occurred by the determination unit. (9) One aspect of the present invention is the power conversion device described in (3) above, further comprising an alarm unit that sounds an alarm when a phase loss is determined to have occurred by the determination unit.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a power conversion device capable of detecting the occurrence of a phase loss.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 5B

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Figure 8A

Figure 8B

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Figure 10A

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Figure 11

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Figure 13A

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Figure 14A

Figure 14B

Embodiment for Carrying Out the Invention

[0010] Next, the power conversion device of the present embodiment will be described with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the following embodiments. In all the drawings for explaining the embodiments, those having the same function are denoted by the same reference numerals, and repeated explanations are omitted. In addition, "based on XX" as used in the present application means "based on at least XX", and includes cases where it is based on another element in addition to XX. Further, "based on XX" is not limited to the case where XX is directly used, and includes cases where it is based on something obtained by performing operations or processing on XX. "XX" is an arbitrary element (for example, arbitrary information).

[0011] (Embodiment) (Power Conversion Device) FIG. 1 is a schematic configuration diagram showing an example of the power conversion device 1 according to the present embodiment. The power conversion device 1 includes a polyphase transformer 3 that converts AC power into polyphase AC power, a rectifying unit 4 that converts polyphase AC power into DC power, a phase failure detection unit 100 that detects the occurrence of a phase failure based on the input voltage supplied to the polyphase transformer 3 and the output voltage of the rectifying unit 4, and a circuit breaker 2 that shuts off the voltage input to the polyphase transformer 3 when the phase failure detection unit 100 detects the occurrence of a phase failure.

[0012] An example of the power conversion device 1 receives 6600V high-voltage three-phase AC power from a high-voltage three-phase power source, converts it into low-voltage AC power with a specific voltage such as 380V, and then converts the low-voltage AC power into DC power for output. Hereinafter, an example of the case where high-voltage three-phase AC power is input to the power conversion device 1 will be described, but it is not limited to this example. For example, it can also be applied when low-voltage three-phase AC power is input to the power conversion device 1. An example of the polyphase transformer 3 is a 12-phase transformer. The 12-phase transformer outputs a low-voltage 12-phase voltage. The polyphase transformer 3 has a three-phase AC terminal on the input side and a polyphase AC terminal on the output side.

[0013] FIG. 2 is a diagram showing an example of the specific configuration of the 12-phase transformer 3. As shown in FIG. 2, the 12-phase transformer 3 includes a first winding 11 that constitutes the primary winding L1 and four windings (second winding 12, third winding 13, fourth winding 14, fifth winding 15) that constitute the secondary winding L2. Each winding has three winding portions (11a~11c, 12a~12c, 13a~13c, 14a~14c, 15a~15c) corresponding to the input three-phase power.

[0014] The first winding 11 is delta-connected, and high-voltage three-phase AC power is connected to three terminals (Rin, Sin, Tin). The second to fifth windings 12, 13, 14, 15 are all star-connected. However, the fourth winding 14 and the fifth winding 15 are not in a complete star connection. Hereinafter, the three phases will be described as the R phase, S phase, and T phase. Note that the first winding 11 may also be star-connected.

[0015] The secondary side of the 12-phase transformer 3 has output terminals R1, S1, T1 of the second winding 12, output terminals R2, S2, T2 of the third winding 13, output terminals R3, S3, T3 of the fourth winding 14, and output terminals R4, S4, T4 of the fifth winding 15, and has a total of 12 terminals. The neutral points Q of the star connection of the second winding 12 and the third winding 13 are connected to each other, and the third winding 13 is wound around the iron core 8 so that its polarity is reversed with respect to the second winding 12. Further, the fourth winding 14 and the fifth winding 15 are formed by branching from the same point in the middle of the third winding 13, and the fourth winding 14 and the fifth winding 15 share the neutral point Q of the third winding 13.

[0016] The fourth winding 14 and the fifth winding 15 are wound around the iron core 8 as follows. First, each phase of the fourth winding 14 is wound as follows. The R-phase winding 14a is branched and drawn out from the middle of the R-phase winding 13a of the third winding 13 and wound around the leg core 8c common to the primary-side T phase. And the tip is the output terminal T3. The S-phase winding 14b is branched and drawn out from the middle of the S-phase winding 13b of the third winding 13 and wound around the leg core 8a common to the R phase of the first winding 11 (or the R phase of the second winding 12). And the tip is the output terminal R3. Also, the T-phase winding 14c is branched and drawn out from the middle of the T-phase winding 13c of the third winding 13 and wound around the leg core 8b common to the primary-side S phase. And the tip is the output terminal S3.

[0017] Each phase of the fifth winding 15 is wound as follows. The R-phase winding 15a is branched and drawn out from the middle of the R-phase winding 13a of the third winding 13, which is the same part as the fourth winding 14, and wound around the leg core 8b common to the S phase of the first winding 11 (or the S phase of the second winding 12). And the tip is the output terminal S4. The S-phase winding 15b is branched and drawn out from the middle of the S-phase winding 13b of the third winding 13, which is the same part as the fourth winding 14, and wound around the leg core 8c common to the T phase of the first winding 11 (or the T phase of the second winding 12). And the tip is the output terminal T4. Also, the T-phase winding 15c is branched and drawn out from the middle of the T-phase winding 13c of the third winding 13, which is the same part as the fourth winding 14, and wound around the leg core 8a common to the R phase of the first winding 11 (or the R phase of the second winding 12). And the tip is the output terminal R4.

[0018] Figure 3 is a vector explanatory diagram of each winding of the secondary winding L2 of the 12-phase transformer 3. Figure 3 shows each phase with reference to the R1 phase of the second winding 12. As shown in this Figure 3, the three windings 12a, 12b, and 12c of the second winding 12 output voltages with a phase difference of 120 degrees each from the output terminals R1, S1, and T1, similar to the three-phase power input. And the phases of the windings 13a, 13b, and 13c of the third winding 13 show polarities opposite to those of the second winding 12, and the phases of the output terminals R2, S2, and T2 have a phase difference of 180 degrees with respect to the respective phases of R1, S1, and T1 of the second winding 12. Incidentally, the number of turns of the third winding 13 with respect to the second winding 12 is 0.73 times (√3 - 1 times).

[0019] Also, the phases of the output terminals R3, S3, and T3 of the windings 14a, 14b, and 14c drawn from the third winding 13 of the fourth winding 14 generate voltages in the same phase as the respective phases of the second winding 12. Furthermore, the phases of the output terminals R4, S4, and T4 of the windings 15a, 15b, and 15c drawn from the third winding 13 of the fifth winding 15 generate voltages in the same phase as the corresponding output terminals R1, S1, and T1 of the respective phases of the second winding 12, similar to the fourth winding 14. Returning to Figure 1, the explanation continues.

[0020] An example of the rectifier section 4 is composed of including four three-phase full-wave rectifier circuits 4-1 to 4-4. The four three-phase full-wave rectifier circuits 4-1 to 4-4 generate a set of DC output voltages. The three-phase full-wave rectifier 4-1 includes six diodes. The cathodes of three of the six diodes are connected to the positive-side DC circuit 4-1P, and the anodes of the other three diodes are connected to the negative-side DC circuit 4-1N. Also, the anodes of the three diodes and the cathodes of the other three diodes are respectively connected. The output terminals R1, S1, and T1 of the second winding 12 of the polyphase transformer 3 are respectively connected to the three connection points. The three-phase voltages of the three-phase output voltages input from the output terminals R1, S1, and T1 of the polyphase transformer 3 to the three-phase full-wave rectifier 4-1 are respectively rectified by the six diodes.

[0021] The three-phase full-wave rectifier 4-2 includes six diodes. The cathodes of three of the six diodes are connected to the positive-side DC circuit 4-2P, and the anodes of the other three diodes are connected to the negative-side DC circuit 4-2N. Also, the anodes of three diodes and the cathodes of the other three diodes are respectively connected. The output terminals R2, S2, T2 of the third winding 13 of the polyphase transformer 3 are connected to the three connection points respectively. The three-phase voltages of the three-phase output voltage input from the output terminals R2, S2, T2 of the polyphase transformer 3 to the three-phase full-wave rectifier 4-2 are respectively rectified by the six diodes.

[0022] The three-phase full-wave rectifier 4-3 includes six diodes. The cathodes of three of the six diodes are connected to the positive-side DC circuit 4-3P, and the anodes of the other three diodes are connected to the negative-side DC circuit 4-3N. Also, the anodes of three diodes and the cathodes of the other three diodes are respectively connected. The output terminals R3, S3, T3 of the fourth winding 14 of the polyphase transformer 3 are connected to the three connection points respectively. The three-phase voltages of the three-phase output voltage input from the output terminals R3, S3, T3 of the polyphase transformer 3 to the three-phase full-wave rectifier 4-3 are respectively rectified by the six diodes.

[0023] The three-phase full-wave rectifier 4-4 includes six diodes. The cathodes of three of the six diodes are connected to the positive-side DC circuit 4-4P, and the anodes of the other three diodes are connected to the negative-side DC circuit 4-4N. Also, the anodes of three diodes and the cathodes of the other three diodes are respectively connected. The output terminals R4, S4, T4 of the fifth winding 15 of the polyphase transformer 3 are connected to the three connection points respectively. The three-phase voltages of the three-phase output voltage input from the output terminals R4, S4, T4 of the polyphase transformer 3 to the three-phase full-wave rectifier 4-4 are respectively rectified by the six diodes. The three-phase full-wave rectifier 4-1, the three-phase full-wave rectifier 4-2, the three-phase full-wave rectifier 4-3, and the three-phase full-wave rectifier 4-4 are connected in parallel with each other.

[0024] A set of DC output voltages generated by each of the four three-phase full-wave rectifier circuits 4-1 to 3-phase full-wave rectifier 4-4 is output to a DC circuit M1 including two output lines and input to the phase loss detection unit 100. The phase loss detection unit 100 includes a first inter-phase voltage detection unit 101, a second inter-phase voltage detection unit 102, a third inter-phase voltage detection unit 103, a voltage detection unit 104, a derivation unit 105, a determination unit 106, and a drive unit 107.

[0025] The first inter-phase voltage detection unit 101 is connected to the Rin terminal and the Sin terminal among the three terminals (Rin, Sin, Tin) of the polyphase transformer 3 to which high-voltage three-phase AC power is connected. The first inter-phase voltage detection unit 101 detects the inter-phase voltage between the Rin terminal and the Sin terminal (hereinafter referred to as the "first inter-phase voltage"). The second inter-phase voltage detection unit 102 is connected to the Sin terminal and the Tin terminal among the three terminals (Rin, Sin, Tin) of the polyphase transformer 3 to which high-voltage three-phase AC power is connected. The second inter-phase voltage detection unit 102 detects the inter-phase voltage between the Sin terminal and the Tin terminal (hereinafter referred to as the "second inter-phase voltage"). The third inter-phase voltage detection unit 103 is connected to the Rin terminal and the Tin terminal among the three terminals (Rin, Sin, Tin) of the polyphase transformer 3 to which high-voltage three-phase AC power is connected. The third inter-phase voltage detection unit 103 detects the inter-phase voltage between the Rin terminal and the Tin terminal (hereinafter referred to as the "third inter-phase voltage").

[0026] The voltage detection unit 104 is connected to the DC circuit M1 and detects the voltage waveform between the DC circuits M1. For example, the voltage detection unit 104 detects the voltage waveform of the DC circuit M1 in the same period as one period of the high-voltage three-phase AC power in which the first inter-phase voltage detection unit 101, the second inter-phase voltage detection unit 102, and the third inter-phase voltage detection unit 103 respectively detect the first inter-phase voltage, the second inter-phase voltage, and the third inter-phase voltage.

[0027] FIG. 4 is a diagram showing an example of the voltage waveform detected by the voltage detection unit 104. In FIG. 4, the horizontal axis represents time [s], and the vertical axis represents the output voltage [V]. For example, the voltage detection unit 104 detects the full-wave rectified waveform of the low-voltage 12-phase output from the 12-phase transformer. The full-wave rectified waveform becomes the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. The full-wave rectified waveform is not constant, and minute voltage fluctuations occur. The magnitude of this voltage fluctuation is called the ripple voltage. In the example shown in FIG. 4, the power supply frequency is 50 Hz, and the power supply voltage is 269 Vrms. The voltage detection unit 104 detects a voltage that outputs 380 V in DC from the voltage waveform.

[0028] FIGS. 5A and 5B are diagrams showing an example of the voltage waveform detected by the voltage detection unit 104. In FIGS. 5A and 5B, the horizontal axis represents time [s], and the vertical axis represents the output voltage [V]. FIG. 5A is an enlarged view of part A of FIG. 4. FIG. 5B shows an example of the voltage waveform detected by the voltage detection unit 104 when a phase failure occurs. As shown in FIG. 5B, when a phase failure occurs, a portion where the voltage waveform detected by the voltage detection unit 104 decreases at a predetermined period can be seen. As shown in FIGS. 5A and 5B, it can be seen that the voltage waveform detected by the voltage detection unit 104 changes periodically. In the example shown in FIGS. 5A and 5B, the period is 0.7 ms. Returning to FIG. 1, the description will be continued.

[0029] The derivation unit 105 is connected to the first inter-phase voltage detection unit 101, the second inter-phase voltage detection unit 102, the third inter-phase voltage detection unit 103, and the voltage detection unit 104. The derivation unit 105 acquires information indicating the first inter-phase voltage value from the first inter-phase voltage detection unit 101, acquires information indicating the second inter-phase voltage value from the second inter-phase voltage detection unit 102, acquires information indicating the third inter-phase voltage value from the third inter-phase voltage detection unit 103, and acquires the voltage waveform between the DC circuits M1 from the voltage detection unit 104.

[0030] The derivation unit 105 derives the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage based on the information indicating the acquired first-phase voltage value, the information indicating the second-phase voltage value, and the information indicating the third-phase voltage value. Hereinafter, as an example, the case where the derivation unit 105 derives the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage for each cycle of the input voltage will be continued to be described.

[0031] Specifically, the first-phase voltage detection unit 101 detects the first-phase voltage until one cycle of the input voltage for which the average value is derived, for example, with a measurement period of 0.1 ms. The derivation unit 105 acquires the first-phase voltage value 0.1 ms after the first-phase voltage detection unit 101 detects (measures) the first-phase voltage. Thereafter, the derivation unit 105 acquires the first-phase voltage value every 0.1 ms until one cycle of the input voltage for which the average value is derived elapses. After one cycle of the input voltage has elapsed, the derivation unit 105 derives the first-phase voltage value for one cycle based on the acquired first-phase voltage value by the formula (1-1). First-phase voltage value for one cycle = √(Sum of squared values of the first-phase voltage values acquired during one cycle / Number of measurement times × Measurement period) (1-1)

[0032] The second-phase voltage detection unit 102 detects the second-phase voltage until one cycle of the input voltage for which the average value is derived, for example, with a measurement period of 0.1 ms. The derivation unit 105 acquires the second-phase voltage value 0.1 ms after the second-phase voltage detection unit 102 detects (measures) the second-phase voltage. Thereafter, the derivation unit 105 acquires the second-phase voltage value every 0.1 ms until one cycle of the input voltage for which the average value is derived elapses. After one cycle of the input voltage has elapsed, the derivation unit 105 derives the second-phase voltage value for one cycle based on the acquired second-phase voltage value by the formula (1-2). Second-phase voltage value for one cycle = √(Sum of squared values of the second-phase voltage values acquired during one cycle / Number of measurement times × Measurement period) (1-2)

[0033] The third-phase voltage detection unit 103 detects the third-phase voltage until one cycle of the input voltage for deriving the average value, for example, at a measurement period of 0.1 ms. The derivation unit 105 acquires the third-phase voltage value 0.1 ms after the third-phase voltage detection unit 103 detects (measures) the third-phase voltage. Thereafter, the derivation unit 105 acquires the third-phase voltage value every 0.1 ms until one cycle of the input voltage for deriving the average value elapses. After one cycle of the input voltage has elapsed, the derivation unit 105 derives the third-phase voltage value for one cycle based on the acquired third-phase voltage values by Equation (1-3). Third-phase voltage value for one cycle = √(Sum of squared values of third-phase voltage values acquired during one cycle / Number of measurements × Measurement period) (1-3)

[0034] The derivation unit 105 derives the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle by Equation (2). Average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle = (First-phase voltage value for one cycle + Second-phase voltage value for one cycle + Third-phase voltage value for one cycle) / 3 (2)

[0035] Further, the derivation unit 105 derives, for example, the average value of the voltage for one cycle based on the voltage waveform between the DC circuits M1 acquired during one cycle of the input voltage. Hereinafter, as an example, the case where the derivation unit 105 derives the average value of the voltage between the DC circuits M1 every cycle will be continued to be described.

[0036] Specifically, the period during which one diode of the rectifying unit 4 is conducting is set as one measurement range. The voltage detection unit 104 detects (measures) the output voltage until one cycle for deriving the average value, for example, at a measurement period of 0.1 ms. Here, the measurement periods in which the first-phase voltage detection unit 101, the second-phase voltage detection unit 102, and the third-phase voltage detection unit 103 detect the first-phase voltage, the second-phase voltage, and the second-phase voltage, respectively, may be different from the measurement period in which the voltage detection unit 104 detects (measures) the output voltage. The derivation unit 105 acquires the output voltage value 0.1 ms after the voltage detection unit 101 detects (measures) the output voltage. Thereafter, the derivation unit 105 acquires the output voltage value every 0.1 ms until one cycle for deriving the average value elapses. When one cycle elapses, the acquisition of one set of measurement values ends. The derivation unit 105 derives the average value of the output voltage for one cycle according to Equation (3). Average value of the output voltage for one cycle = Sum of the output voltage values acquired during one cycle / Number of measurements × Measurement period (3)

[0037] The derivation unit 105 compares the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle with the average value of the output voltage for one cycle. For example, the derivation unit 105 derives the ratio of the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle to the average value of the output voltage for one cycle according to Equation (4). Ratio of the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle to the average value of the output voltage for one cycle = Average value of the output voltage for one cycle / (Average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle) (4) In the normal state where no phase loss occurs, for example, for the three-phase AC power of 200 V input to the polyphase transformer 3, the ratio of the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle to the average value of the output voltage for one cycle, which results in a DC power output of 380 V, is determined by the turns ratio of the polyphase transformer 3. Therefore, in this embodiment, as an example, the ratio of the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle to the average value of the output voltage for one cycle is set as the threshold value.

[0038] The determination unit 106 acquires information indicating the ratio of the average values of the first-phase voltage, second-phase voltage, and third-phase voltage for one cycle to the average value of the output voltage for one cycle in the normal state from the derivation unit 105. The determination unit 106 sets the acquired ratio as the threshold value based on the information indicating the ratio in the normal state. The determination unit 106 determines whether the ratio of the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage of one cycle acquired later to the average value of the output voltage of one cycle is greater than or equal to a set threshold value, based on the information indicating the ratio and the information indicating the set threshold value. When the ratio is greater than or equal to the threshold value, the determination unit 106 determines that it is normal. When the determination unit 106 determines that it is normal, it outputs a low-level signal to the driving unit 107. When the ratio is less than the threshold value, the determination unit 106 determines that a phase failure has occurred. When the determination unit 106 determines that a phase failure has occurred, it outputs a cutoff signal, for example, a high-level signal, to the driving unit 107 to cut off the voltage input to the polyphase transformer 3.

[0039] Based on the signal output by the determination unit 106, the driving unit 107 cuts off the voltage input to the polyphase transformer 3 in the cutoff unit 2. When a high-level signal is input from the determination unit 106, the driving unit 107 cuts off the voltage input to the polyphase transformer 3 in the cutoff unit 2. When a low-level signal is input from the determination unit 106, the driving unit 107 does not cut off the voltage input to the polyphase transformer 3 in the cutoff unit 2. An example of the cutoff unit 2 is an electric vacuum circuit breaker (VCB) or a shunt type miniature circuit breaker (MCB). The electric vacuum circuit breaker is used when the input voltage is high, and the shunt type MCB is used when the input voltage is low.

[0040] The first-phase voltage detection unit 101, the second-phase voltage detection unit 102, the third-phase voltage detection unit 103, the voltage detection unit 104, the derivation unit 105, the determination unit 106, and the driving unit 107 are realized, for example, by a hardware processor such as a central processing unit (CPU) executing a computer program (software) stored in a storage unit (not shown). Further, some or all of these functional units may be implemented by hardware (including circuitry), such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), GPU (Graphics Processing Unit), or may be implemented by cooperation between software and hardware.

[0041] (Operation of Power Conversion Device 1) FIG. 6 is a flowchart showing an example of the operation of the power conversion device 1 according to the present embodiment. With reference to FIG. 6, the operation of the phase loss detection unit 100 will be mainly described. Here, as an example, the operation after the determination unit 106 sets the ratio between the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage in one cycle in the normal state and the average value of the output voltage in one cycle as a threshold value will be described. (Step S1-1) The first-phase voltage detection unit 101 detects the first-phase voltage for one cycle. The second-phase voltage detection unit 102 detects the second-phase voltage for one cycle. The third-phase voltage detection unit 103 detects the third-phase voltage for one cycle. (Step S2-1) The voltage detection unit 104 detects the voltage waveform between the DC circuits M1 for one cycle.

[0042] (Step S3-1) The derivation unit 105 acquires information indicating the first-phase voltage value for one cycle from the first-phase voltage detection unit 101, acquires information indicating the second-phase voltage value for one cycle from the second-phase voltage detection unit 102, and acquires information indicating the third-phase voltage value for one cycle from the third-phase voltage detection unit 103. The derivation unit 105 derives the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage in one cycle.

[0043] (Step S4-1) The derivation unit 105 derives the average value of the output voltage for one cycle between the DC circuits M1. (Step S5-1) The derivation unit 105 derives the ratio of the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage in one cycle to the average value of the output voltage in one cycle.

[0044] (Step S6-1) The determination unit 106 acquires information indicating the ratio of the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage in one cycle to the average value of the output voltage in one cycle from the derivation unit 105. The determination unit 106 determines whether the information indicating the acquired ratio is equal to or greater than a threshold value. (Step S7-1) When the ratio is equal to or greater than the threshold value, the determination unit 106 determines that it is normal. In this case, the process proceeds to step S1-1.

[0045] (Step S8-1) When the ratio is less than the threshold value, the determination unit 106 determines that a phase failure has occurred. (Step S9-1) When the determination unit 106 determines that a phase failure has occurred, it outputs a cutoff signal to the drive unit 107 to cutoff the voltage input to the polyphase transformer 3 by the cutoff unit 2. When the drive unit 107 receives the cutoff signal from the determination unit 106, it causes the cutoff unit 2 to cutoff the voltage input to the polyphase transformer 3.

[0046] The simulation results of the output waveform when a phase failure occurs in the power conversion device 1 will be described. FIG. 7 is a diagram showing an example of the circuit configuration of the polyphase transformer 3 and the rectifier unit 4 of the power conversion device 1 used in the simulation. FIG. 7 shows an example of the circuit configuration when no phase failure occurs (when it is normal).

[0047] FIGS. 8A and 8B are diagrams showing the simulation results in an example of the circuit configuration without a phase failure in the power conversion device 1 according to the present embodiment. FIG. 8A shows the waveform of the input voltage for one cycle. In FIG. 8A, the horizontal axis represents time [s], and the vertical axis represents the input voltage [V]. The power supply frequency is 50 Hz, and the power supply voltage is 200 Vrms. Figure 8B shows the waveform of the output voltage corresponding to one cycle of the input voltage. In Figure 8B, the horizontal axis represents time [s], and the vertical axis represents the input voltage [V]. The waveform of the output voltage is the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. The waveform of the output voltage is a voltage with a DC output of 380V.

[0048] Figure 9 is a diagram showing an example of the circuit configuration of the polyphase transformer 3 and the rectifier section 4 of the power conversion device 1 used in the simulation. Figure 9 shows an example of the circuit configuration when a phase loss occurs. One of the plurality of diodes included in the rectifier section 4 has failed and is in an open state. That is, one phase is missing.

[0049] Figures 10A and 10B are diagrams showing the simulation results in an example of the circuit configuration in which a phase loss has occurred in the power conversion device 1 according to the present embodiment. Figure 10A shows the waveform of the input voltage for one cycle. In Figure 10A, the horizontal axis represents time [s], and the vertical axis represents the input voltage [V]. The power supply frequency is 50 Hz, and the power supply voltage is 200 Vrms. Figure 10B shows the waveform of the output voltage corresponding to one cycle of the input voltage. In Figure 10B, the horizontal axis represents time [s], and the vertical axis represents the output voltage [V]. The waveform of the output voltage is the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. The waveform of the output voltage is a voltage with a DC output of 380V. Since a phase loss has occurred, a decrease in the output voltage ("D" in Figure 10B) can be observed.

[0050] When one of the diodes at a position different from the position shown in Figure 9 has an open failure, one phase is missing and the output waveform is the same. However, the position where a decrease in the DC output is observed is different. Therefore, it is possible to detect in which phase a phase loss has occurred.

[0051] (Example 1) Example 1 of the power conversion device 1 will be described. (1) Conditions A 12-phase transformer is used as the polyphase transformer 3. The power supply frequency is 50 Hz, the input voltage is three-phase three-wire AC 200 V, and the output voltage is DC 380 V.

[0052] (2) Measurement method The first inter-phase voltage detection unit 101, the second inter-phase voltage detection unit 102, and the third inter-phase voltage detection unit 103 detect the first inter-phase voltage, the second inter-phase voltage, and the third inter-phase voltage of one cycle, respectively. The voltage detection unit 104 detects the output voltage of the same one cycle as that detected by the first inter-phase voltage detection unit 101, the second inter-phase voltage detection unit 102, and the third inter-phase voltage detection unit 103.

[0053] The derivation unit 105 derives the first inter-phase voltage value of one cycle, the second inter-phase voltage value of one cycle, and the third inter-phase voltage value of one cycle from the sampling of one cycle. The derivation unit 105 derives the average value of the first inter-phase voltage, the second inter-phase voltage, and the third inter-phase voltage of one cycle from the first inter-phase voltage value of one cycle, the second inter-phase voltage value of one cycle, and the third inter-phase voltage value of one cycle. In addition, the derivation unit 105 derives the average value of the output voltage of one cycle from the output voltage values acquired during one cycle. For example, let the first inter-phase voltage value Vin1 of one cycle be 200 V, the second inter-phase voltage value Vin2 of one cycle be 200 V, and the third inter-phase voltage value Vin3 of one cycle be 200 V. The derivation unit 105 derives the average value of the first inter-phase voltage value Vin1 of one cycle, the second inter-phase voltage value Vin2 of one cycle, and the third inter-phase voltage value Vin3 of one cycle, and sets the derived average value as the input voltage value Vin (A1). Input voltage value Vin = (first inter-phase voltage value Vin1 of one cycle + second inter-phase voltage value Vin2 of one cycle + third inter-phase voltage value Vin3 of one cycle) / 3 = 200 V (A1)

[0054] Since the output side is a DC voltage, the detection location is one place. The derivation unit 105 derives the average value of the output voltage of one cycle from the output voltage values acquired during one cycle, and sets the derived average value of the output voltage of one cycle as the output voltage value Vout. When it is normal, it is (B1). Output voltage value Vout = 380 V (B1) The derivation unit 105 compares the input voltage value Vin with the output voltage value Vout. Specifically, the derivation unit 105 derives the ratio of the output voltage value Vout to the input voltage value Vin. Output voltage value Vout / Input voltage value Vin = (B1) / (A1) = 1.9

[0055] For example, in the normal state where no phase loss occurs, when the input voltage value Vin is AC200V, the ratio at which the output voltage value Vout becomes DC380V is determined by the number of turns of the transformer (polyphase transformer 3). Therefore, the determination unit 106 sets this ratio as the determination value (threshold value). The determination unit 106 determines that a phase loss has occurred when the ratio is less than 1.9 which is the determination value.

[0056] When a phase loss occurs, the output voltage value Vout decreases, so the ratio of the output voltage value Vout to the input voltage value Vin decreases. Suppose that as a result of simulation, the output voltage value Vout becomes 379V when one phase is missing (in the abnormal case). Output voltage value Vout = 379V (C1)

[0057] The determination unit 106 determines that a phase loss has occurred when the ratio of the output voltage value Vout to the input voltage value Vin falls below the determination value. Output voltage value Vout / Input voltage value Vin = (C1) / (A1) = 1.89 < Determination value (1.9) When the determination unit 106 determines that a phase loss has occurred, it outputs a cut-off signal to the drive unit 107. When a cut-off signal is input from the determination unit 106, the drive unit 107 causes the cut-off unit 2 to cut off the voltage input to the polyphase transformer 3. Alternatively, an alarm device (not shown) may be connected to the determination unit 106. When the determination unit 106 determines that a phase loss has occurred, it may cause the alarm device to issue an alarm.

[0058] (Example 2) Example 2 of the power conversion device 1 will be described. (1) Conditions A 12-phase transformer is used as the polyphase transformer 3. The power supply frequency is set to 50 Hz, the input voltage is three-phase three-wire AC 200 V, and the output voltage is DC 380 V.

[0059] (2) Measurement method The first inter-phase voltage detection unit 101, the second inter-phase voltage detection unit 102, and the third inter-phase voltage detection unit 103 detect the first inter-phase voltage, the second inter-phase voltage, and the third inter-phase voltage in one cycle, respectively. The voltage detection unit 104 detects the output voltage in the same one cycle as that detected by the first inter-phase voltage detection unit 101, the second inter-phase voltage detection unit 102, and the third inter-phase voltage detection unit 103. However, the voltage detection unit 104 detects the output voltage in one cycle every 1 / 8 cycle.

[0060] The derivation unit 105 derives the first inter-phase voltage value in one cycle, the second inter-phase voltage value in one cycle, and the third inter-phase voltage value in one cycle from the sampling in one cycle. The derivation unit 105 derives the average value of the first inter-phase voltage, the second inter-phase voltage, and the third inter-phase voltage in one cycle from the first inter-phase voltage value in one cycle, the second inter-phase voltage value in one cycle, and the third inter-phase voltage value in one cycle. Also, the derivation unit 105 derives the average value of the output voltage in 1 / 8 cycle from the output voltage values obtained during 1 / 8 cycle. For example, let the first inter-phase voltage value Vin1 in one cycle be 200 V, the second inter-phase voltage value Vin2 in one cycle be 200 V, and the third inter-phase voltage value Vin3 in one cycle be 200 V. The derivation unit 105 derives the average value of the first inter-phase voltage value Vin1 in one cycle, the second inter-phase voltage value Vin2 in one cycle, and the third inter-phase voltage value Vin3 in one cycle, and sets the derived average value as the input voltage value Vin (A2). Input voltage value Vin = (First inter-phase voltage value Vin1 in one cycle + Second inter-phase voltage value Vin2 in one cycle + Third inter-phase voltage value Vin3 in one cycle) / 3 = 200 V (A2)

[0061] Since the output side is a DC voltage, there is only one detection point. The derivation unit 105 derives the average value of the output voltage for each 1 / 8 cycle from the output voltage values acquired every 1 / 8 cycle, and sets the derived average values of the output voltage for each 1 / 8 cycle as the output voltage values Vout1 to Vout8 from the output voltage value Vout1 respectively. FIG. 11 is a diagram showing an example of the output voltage detected by the power conversion device 1 according to the present embodiment. FIG. 11 shows an example of the simulation result of the voltage values when the average values of the DC voltage measured every 1 / 8 cycle are set as the output voltage values Vout1 to Vout8. According to FIG. 11, it can be seen that among the output voltage values Vout1 to Vout8, the waveforms of the output voltage values Vout3 and Vout7 are depressed compared to the other output voltage values due to the influence of phase loss.

[0062] The derivation unit 105 compares the input voltage value Vin with each of the output voltage values Vout1 to Vout8. Specifically, the derivation unit 105 derives the ratio of each of the output voltage values Vout1 to Vout8 to the input voltage value Vin. The ratio for the output voltage value Vout1 with no depressed waveform is shown below. Output voltage value Vout1 / Input voltage value Vin = 1.9 ≥ Determination value (1.9) The same applies to the output voltage values Vout2, Vout4 to Vout6, and Vout8 with no depressed waveform.

[0063] The ratios for the output voltage values Vout3 and Vout7 with depressed waveforms due to the influence of phase loss are shown below. Vout3 / Vin = 1.88 < Determination value (1.9) Vout7 / Vin = 1.88 < Determination value (1.9) By deriving the ratio using the DC voltage measured every 1 / 8 cycle, the ratio becomes lower than when measured in one cycle where phase loss occurs, so the detection accuracy can be improved.

[0064] Also, as shown in FIG. 11, it can be seen that when one phase is open, the output waveform drops twice within one cycle. The determination unit 105 may detect that the output waveform drops multiple times within one cycle, for example, from the number of times the ratio is less than the determination value. For example, when the output waveform drops only once within one cycle, the determination unit 105 may determine that it is a false detection and no open phase has occurred. By configuring in this way, the detection accuracy can be further improved.

[0065] In the above-described embodiment, the case where the derivation unit 105 derives the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage and the average value of the output voltage within one cycle has been described, but it is not limited to this example. For example, the derivation unit 105 may derive the effective value of the first-phase voltage, the second-phase voltage, and the third-phase voltage and the effective value of the output voltage within one cycle.

[0066] In the above-described embodiment, the case where a 12-phase transformer is applied as an example of the polyphase transformer 3 has been described, but it is not limited to this example. For example, a 3-phase transformer, a 6-phase transformer, a 9-phase transformer, or a 24-phase transformer may be applied to the polyphase transformer 3. FIG. 12 is a schematic configuration diagram showing another example of the power conversion device 1 according to the present embodiment. For example, when a 6-phase transformer is applied to the polyphase transformer 3, the polyphase transformer 3 may be configured to include a three-phase transformer 3-1 and a three-phase transformer 3-2.

[0067] An example of the three-phase transformer 3-1 has a delta connection on the primary side and a delta connection on the secondary side. An example of the three-phase transformer 3-2 has a delta connection on the primary side and a star connection on the secondary side. Instead of the three-phase transformer 3-1 or the three-phase transformer 3-2, a three-phase transformer with a star connection on the primary side (high voltage side) and a delta connection on the secondary side (low voltage side) may be used.

[0068] An example of the power conversion device 1 in this case will be described. (1) Conditions A 9-phase transformer is used as the polyphase transformer 3. The power supply frequency is set to 50 Hz, the input voltage is three-phase three-wire AC 200 V, the output is 270 Vrms, and the output voltage after rectification is DC 380 V.

[0069] (2) Measurement method The first-phase voltage detection unit 101, the second-phase voltage detection unit 102, and the third-phase voltage detection unit 103 detect the first-phase voltage, the second-phase voltage, and the third-phase voltage of one cycle, respectively. The voltage detection unit 104 detects the output voltage of the same one cycle as that detected by the first-phase voltage detection unit 101, the second-phase voltage detection unit 102, and the third-phase voltage detection unit 103.

[0070] The derivation unit 105 derives the first-phase voltage value of one cycle, the second-phase voltage value of one cycle, and the third-phase voltage value of one cycle from the sampling of one cycle. The derivation unit 105 derives the average value of the first-phase voltage, the second-phase voltage, and the third-phase voltage of one cycle from the first-phase voltage value of one cycle, the second-phase voltage value of one cycle, and the third-phase voltage value of one cycle. In addition, the derivation unit 105 derives the average value of the output voltage of one cycle from the output voltage values acquired during one cycle. For example, let the first-phase voltage value Vin1 of one cycle be 200 V, the second-phase voltage value Vin2 of one cycle be 200 V, and the third-phase voltage value Vin3 of one cycle be 200 V. The derivation unit 105 derives the average value of the first-phase voltage value Vin1 of one cycle, the second-phase voltage value Vin2 of one cycle, and the third-phase voltage value Vin3 of one cycle, and sets the derived average value as the input voltage value Vin (A3). Input voltage value Vin = (first-phase voltage value Vin1 of one cycle + second-phase voltage value Vin2 of one cycle + third-phase voltage value Vin3 of one cycle) / 3 = 200 V (A3)

[0071] Since the output side is a DC voltage, the detection location is one place. The derivation unit 105 derives the average value of the output voltage of one cycle from the output voltage values acquired during one cycle, and sets the derived average value of the output voltage of one cycle as the output voltage value Vout. When it is normal, it is (B3). Output voltage value Vout = 380 V (B3) The derivation unit 105 compares the input voltage value Vin and the output voltage value Vout. Specifically, the derivation unit 105 derives the ratio of the output voltage value Vout to the input voltage value Vin. Output voltage value Vout / Input voltage value Vin = (B3) / (A3) = 1.9 The determination unit 106 sets this ratio as a determination value (threshold value). When the ratio is less than the determination value of 1.9, the determination unit 106 determines that a phase loss has occurred.

[0072] FIG. 13A and FIG. 13B are diagrams showing simulation results in an example of a circuit configuration in which no phase loss occurs in the power conversion device 1 according to the present embodiment. FIG. 13A shows the waveform of the input voltage for one cycle. The power supply frequency is 50 Hz, and the power supply voltage is 200 Vrms. FIG. 13B shows the waveform of the output voltage corresponding to the input voltage for one cycle. The waveform of the output voltage is the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. The output voltage Vout is 380 V. Output voltage value Vout = 380 V (C3)

[0073] When the ratio of the output voltage value Vout to the input voltage value Vin is lower than the determination value, the determination unit 106 determines that a phase loss has occurred. Output voltage value Vout / Input voltage value Vin = (C3) / (A3) = 1.9 ≥ determination value (1.9) Since the ratio of the output voltage value Vout to the input voltage value Vin is not lower than the determination value, the determination unit 106 determines that no phase loss has occurred.

[0074] FIG. 14A and FIG. 14B are diagrams showing simulation results in an example of a circuit configuration in which a phase loss occurs in the power conversion device 1 according to the present embodiment. FIG. 14A shows the waveform of the input voltage for one cycle. The power supply frequency is 50 Hz, and the power supply voltage is 200 Vrms. FIG. 14B shows the waveform of the output voltage corresponding to one cycle of the input voltage. The waveform of the output voltage becomes the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. Since a phase failure has occurred, a decrease in the output voltage can be observed in the waveform of the output voltage.

[0075] The derivation unit 105 calculates the input voltage value and the output voltage value from the sampling for one cycle. Since the output voltage value decreases when a phase failure occurs, the ratio of the output voltage value to the input voltage value decreases. Suppose that, in the case where one phase is missing (abnormal), the output voltage value Vout becomes 379V according to the simulation result. Vout = 379V (C3)

[0076] When the ratio of the output voltage value to the input voltage value falls below the determination value, the determination unit 106 determines that a phase failure has occurred. Output voltage value Vout / Input voltage value Vin = (C3) / (A3) = 1.89 < Determination value (1.9) Since the ratio of the output voltage value to the input voltage value has fallen below the determination value, the determination unit 106 determines that a phase failure has occurred. In this case, the determination unit 106 outputs a cut-off signal to the drive unit 107. When the cut-off signal is input from the determination unit 106, the drive unit 107 cuts off the voltage input to the polyphase transformer 3 in the cut-off unit 2. Alternatively, an alarm device (not shown) may be connected to the determination unit 106. When the determination unit 106 determines that a phase failure has occurred, it may cause the alarm device to issue an alarm.

[0077] In the above-described embodiment, the case where the voltage input to the polyphase transformer 3 is cut off in the cut-off unit 2 has been described, but the present invention is not limited to this example. For example, the cut-off unit 2 may be provided between the polyphase transformer 3 and the rectification unit 4 to cut off the polyphase AC power supplied from the polyphase transformer 3 to the rectification unit 4. Further, the cut-off unit 2 may be provided after the rectification unit 4 to cut off the DC power output from the rectification unit 4.

[0078] In the foregoing embodiments, the case where the derivation unit 105 derives the average value of the output voltage for each cycle of the input voltage has been described, but the present invention is not limited to this example. For example, the derivation unit 105 may derive the average value of the voltage for each half cycle of the input voltage, or may derive the average value of the voltage for every two cycles, or may derive the average value of the voltage for every three cycles, or may derive the average value of the voltage for every four or more cycles. The derivation unit 105 may derive the average value of the voltage for every integer multiple of the half cycle of the input voltage. The cycle in which the derivation unit 105 derives the average value of the voltage can be changed as appropriate.

[0079] In the foregoing embodiments, the case where the voltage input to the polyphase transformer 3 is cut off when the phase failure detection unit 100 detects the occurrence of a phase failure has been described, but the present invention is not limited to this example. For example, instead of the circuit breaker 2, or together with the circuit breaker 2, an alarm unit that sounds an alarm may be provided. For example, the alarm unit may be driven using a relay contact or the like. By configuring in this way, when it is determined that a phase failure has occurred, notification can be made, so that, for example, the operator of the power conversion device 1 can take corresponding measures.

[0080] According to the power conversion device 1 according to the present embodiment, a polyphase transformer 3 that converts AC power into polyphase AC power, a rectification unit 4 that converts polyphase AC power into DC power, and a phase failure detection unit 100 that detects the occurrence of a phase failure based on the input voltage supplied to the polyphase transformer 3 and the output voltage of the rectification unit 4 are provided. By configuring in this way, since it is possible to detect the occurrence of a phase failure based on the input voltage supplied to the polyphase transformer 3 and the output voltage of the rectification unit 4, the size of the power conversion device 1 can be reduced compared to the case of using a circuit breaker for wiring with neutral line phase failure protection, and the occurrence of a phase failure can be detected. For example, it is possible to detect the occurrence of a phase failure due to a poor contact, disconnection, or diode breakage of the rectification unit 4 between the polyphase transformer 3 and the rectification unit 4 based on the input voltage supplied to the polyphase transformer 3 and the output voltage of the rectification unit 4.

[0081] Also, in the power conversion device 1, the phase failure detection unit 100 detects the occurrence of a phase failure based on the ratio between the input voltage and the output voltage. By configuring in this way, since it is possible to detect the occurrence of a phase failure based on the ratio between the input voltage and the output voltage, the size of the power conversion device 1 can be reduced compared to the case of using a circuit breaker for wiring with neutral line phase failure protection, and the occurrence of a phase failure can be detected.

[0082] Also, in the power conversion device 1, the phase failure detection unit 100 derives a first value based on the three-phase line-to-line voltages input to the polyphase transformer 3, and derives a second value based on the output voltages corresponding to the three-phase line-to-line voltages, and includes a derivation unit 105 that derives the ratio between the first value and the second value, and a determination unit 106 that determines whether or not a phase failure has occurred based on the ratio derived by the derivation unit 105 and a threshold value. By configuring in this way, the phase failure detection unit 100 can derive a first value based on the three-phase line-to-line voltages, derive a second value based on the output voltages, and derive the ratio from the derived first value and second value, so that it is possible to detect the occurrence of a phase failure by comparing with the threshold value.

[0083] Also, in the power conversion device 1, the derivation unit 105 derives a first value every predetermined period based on the three-phase line-to-line voltages input to the polyphase transformer 3, and derives a second value every predetermined period based on the output voltages corresponding to the three-phase line-to-line voltages of the predetermined period, and derives the ratio between the first value and the second value every predetermined period. By configuring in this way, since the ratio between the first value and the second value can be derived every predetermined period, it is possible to determine whether or not a phase failure has occurred every predetermined period by comparing with the threshold value.

[0084] Also, in the power conversion device 1, the predetermined period is an integer multiple of the half cycle of the input voltage. By configuring in this way, since the ratio between the first value and the second value can be derived every integer multiple of the half cycle of the input voltage, it is possible to determine whether or not a phase failure has occurred every predetermined period by comparing with the threshold value.

[0085] Also, in the power conversion device 1, the first value and the second value are average values. By configuring in this way, the phase loss detection unit 100 can derive the average value of the three-phase line voltages based on the three-phase line voltages, derive the average value of the output voltage based on the output voltage, and derive a ratio from the derived average value of the three-phase line voltages and the average value of the output voltage. Therefore, it is possible to detect that a phase loss has occurred by comparing with a threshold value.

[0086] Also, in the power conversion device 1, the first value and the second value are effective values. By configuring in this way, the phase loss detection unit 100 can derive the effective value of the three-phase line voltages based on the three-phase line voltages, derive the effective value of the output voltage based on the output voltage, and derive a ratio from the derived effective value of the three-phase line voltages and the effective value of the output voltage. Therefore, it is possible to detect that a phase loss has occurred by comparing with a threshold value.

[0087] Also, the power conversion device 1 further includes a circuit breaker 2 that shuts off the AC power input to the polyphase transformer 3, and a drive unit 107 that operates the circuit breaker when the determination unit 106 determines that a phase loss has occurred. By configuring in this way, when it is determined that a phase loss has occurred, the AC power supplied to the polyphase transformer 3 can be shut off, so safety can be ensured.

[0088] Also, the power conversion device 1 further includes an alarm unit (not shown) that sounds an alarm when the determination unit 106 determines that a phase loss has occurred. By configuring in this way, when it is determined that a phase loss has occurred, an alarm can be sounded. Therefore, it is possible to notify the surroundings that a phase loss has occurred.

[0089] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention are also included. For example, a computer program for realizing the function of the phase failure detection unit 100 of the power conversion device 1 described above may be recorded on a computer-readable recording medium, and the computer program recorded on this recording medium may be read into a computer system and executed. Here, the "computer system" may include hardware such as an OS and peripheral devices.

[0090] Further, the "computer-readable recording medium" refers to a writable non-volatile memory such as a flexible disk, a magneto-optical disk, a ROM, a flash memory, a portable medium such as a DVD (Digital Versatile Disc), a storage device such as a hard disk built into a computer system, etc. Furthermore, the "computer-readable recording medium" also includes a volatile memory (for example, DRAM (Dynamic Random Access Memory)) inside a computer system that becomes a server or a client when a computer program is transmitted via a network such as the Internet or a communication line such as a telephone line, and holds the program for a certain period of time.

[0091] Also, the above program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Also, the above program may be for realizing a part of the functions described above. Furthermore, it may be a so-called difference file (difference program) that can realize the functions described above in combination with a program already recorded in a computer system.

Explanation of Reference Numerals

[0092] 1... Power conversion device, 2... Circuit breaker, 3... Polyphase transformer, 4... Rectifier section, 100... Open-phase detection section, 101... First-phase voltage detection section, 102... Second-phase voltage detection section, 103... Third-phase voltage detection section, 104... Voltage detection section, 105... Derivation section, 106... Judgment section, 107... Driving section

Claims

1. A polyphase transformer that converts AC power into polyphase AC power, a rectifier that converts the polyphase AC power into DC power, and a phase loss detection unit that detects the occurrence of a phase loss based on the input voltage supplied to the polyphase transformer and the output voltage of the rectifier A power conversion device comprising:

2. The power conversion device according to claim 1, wherein the phase loss detection unit detects the occurrence of a phase loss based on a ratio between the input voltage and the output voltage.

3. The phase loss detection unit derives a first value based on the three-phase line-to-line voltages input to the polyphase transformer, and derives a second value based on the output voltages corresponding to the three-phase line-to-line voltages, and derives a ratio between the first value and the second value; a derivation unit, and a determination unit that determines whether or not a phase loss has occurred based on the ratio derived by the derivation unit and a threshold value. The power conversion device according to claim 1, comprising:

4. The derivation unit derives the first value every predetermined period based on the three-phase line-to-line voltages input to the polyphase transformer, and derives the second value every predetermined period based on the output voltages corresponding to the three-phase line-to-line voltages of the predetermined period, and derives a ratio between the first value and the second value every predetermined period. The power conversion device according to claim 3.

5. The power conversion device according to claim 4, wherein the predetermined period is an integer multiple of a half cycle of the input voltage.

6. The power conversion device according to claim 3 or claim 4, wherein the first value and the second value are average values.

7. The power conversion device according to claim 3 or claim 4, wherein the first value and the second value are effective values.

8. A circuit breaker that interrupts the AC power input to the polyphase transformer, and a drive unit that operates the circuit breaker when it is determined by the determination unit that a phase loss has occurred. The power conversion device according to claim 3, further comprising:

9. The power conversion device according to claim 3, further comprising an alarm unit that sounds an alarm when it is determined by the determination unit that a phase loss has occurred. ​

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