Power converter

Abstract

To provide a power converter for detecting generation of a phase loss.SOLUTION: The power converter includes: a multi-phase voltage converter for converting an AC power to a multi-phase AC power; a rectification unit for converting the multi-phase AC power to a DC power; and a phase loss detection unit for detecting generation of a phase loss on the basis of the 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 uses a polyphase transformer and a rectifier to convert an AC voltage into a DC voltage. When a phase failure occurs in the polyphase transformer, the ripple component of the DC output voltage increases. If the operation continues with the phase failure, the current flowing to the phases other than the phase where the phase failure has occurred increases, and damage to the diodes in the rectifier circuit may occur.

[0003] Regarding a power conversion device, a technique is known 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, high-voltage three-phase AC power is converted into 12-phase low-voltage AC by a 12-phase transformer, and the low-voltage AC power of each output phase is converted into DC power by a rectifier circuit that performs full-wave rectification and then output. The 12-phase transformer has a secondary winding composed of second to fifth windings, all of which are star-connected, the neutral points of the second and third windings are connected to each other, the fourth and fifth windings are branched from a common predetermined position in the middle of the third winding, each of the second to fifth windings outputs a three-phase voltage with a different phase, and a 12-phase AC voltage is output. The common neutral point Q of the secondary winding L2 is grounded via a lightning arrester.

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 a single-phase open phase occurs in the output circuit of a polyphase transformer or in the rectifying section, the ripple of the DC output voltage from the rectifying 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 the diode generates heat and is damaged or the circuit generates heat. Regarding the method of detecting an open phase, a circuit breaker for wiring 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 phases is disrupted by the influence of the load in a circuit breaker for wiring with neutral-line open-phase protection, and it is detected when the voltage between one of the voltage phases and the neutral line exceeds a certain threshold value. If a method of detecting an open phase by a circuit breaker for wiring 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 Problems

[0006] (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 rectifying 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 output voltage of the rectifying 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 a decrease in 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 includes an average value derivation section that derives an average value of the output voltage based on the output voltage of the rectifying section, a threshold value derivation section that derives a threshold value based on the average value derived by the average value derivation section, and a determination section that determines whether or not an open phase has occurred based on the output voltage of the rectifying section and the threshold value. (4) One aspect of the present invention is the power conversion device described in (3) above, wherein the threshold derivation unit derives the threshold by reducing the voltage from the average value of the output voltage. (5) One aspect of the present invention is the power conversion device described in (3) above, further comprising a circuit breaker that shuts off the AC power input to the polyphase transformer, and a drive unit that operates the circuit breaker when the determination unit determines that a phase loss has occurred. (6) 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 the determination unit determines that a phase loss has occurred.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a power conversion device that can detect the occurrence of a phase loss.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiment for Carrying Out the Invention

[0009] 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. Also, "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 arithmetic operations or processing on XX. "XX" is an arbitrary element (for example, arbitrary information).

[0010] (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 rectifier section 4 that converts the polyphase AC power into DC power, a phase failure detection section 100 that detects the occurrence of a phase failure based on the output voltage of the rectifier section 4, and a circuit breaker 2 that shuts off the voltage input to the polyphase transformer 3 when the phase failure detection section 100 detects the occurrence of a phase failure.

[0011] 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 converted low-voltage AC power into DC power for output. Hereinafter, 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 three-phase AC terminals on the input side and polyphase AC terminals on the output side.

[0012] FIGS. 2 to 3 are diagrams 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 to 11c, 12a to 12c, 13a to 13c, 14a to 14c, 15a to 15c) corresponding to the input three-phase power.

[0013] 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, and 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.

[0014] 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.

[0015] 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 is wound around the leg iron core 8b common to the primary side S-phase. And the tip is the output terminal R3. 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 is wound around the leg iron 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 S3. 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 is wound around the leg iron core 8a common to the primary side R-phase. And the tip is the output terminal T3.

[0016] 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 at the same position as the fourth winding 14, and is wound around the leg iron 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 R4. The S-phase winding 15b is branched and drawn out from the middle of the S-phase winding 13b of the third winding 13 at the same position as the fourth winding 14, and is wound around the leg iron 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 S4. 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 at the same position as the fourth winding 14, and is wound around the leg iron 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 T4.

[0017] Figure 3 is a vector explanatory diagram of each winding of the secondary winding L2, showing each phase based on the R1 phase of the second winding 12. As shown in this Figure 3, the three-phase 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 each phase 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).

[0018] 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 each phase of the second winding 12. Further, 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 each phase of the second winding 12, similar to the fourth winding 14. Hereinafter, as an example of the polyphase transformer 3, the 12-phase transformer will be described continuously. Returning to Figure 1, the description will be continued.

[0019] An example of the rectifying unit 4 is configured to include four three-phase full-wave rectifying circuits. The four three-phase full-wave rectifying circuits generate a set of DC output voltages. The set of DC output voltages generated by the four three-phase full-wave rectifying circuits 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 voltage detection unit 101, an average value derivation unit 102, a voltage level adjustment unit 103, a comparison unit 104, a signal holding unit 105, a holding release unit 106, and a driving unit 107.

[0020] The voltage detection unit 101 is connected to the DC circuit M1 and detects the voltage waveform between the DC circuits M1. FIG. 4 is a diagram showing an example of the voltage waveform detected by the voltage detection unit 101. For example, the voltage detection unit 101 detects the full-wave rectified waveform of the low-voltage 12-phase output from the 12-phase transformer. The full-wave rectified waveform is 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 101 detects a voltage that outputs 380 V DC from the voltage waveform. When a phase failure occurs, the DC output power decreases to less than the threshold value.

[0021] FIGS. 5A and 5B are diagrams showing an example of the voltage waveform detected by the voltage detection unit 101. FIG. 5A is an enlarged view of part A in FIG. 4. FIG. 5B shows an example of the voltage waveform detected by the voltage detection unit 101 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 101 decreases at a predetermined period can be seen. As shown in FIGS. 5A and 5B, it can be understood that the voltage waveform detected by the voltage detection unit 101 changes periodically. In the example shown in FIGS. 5A and 5B, the period is 0.7 ms. Returning to FIG. 1, the description will continue.

[0022] The average value derivation unit 102 is connected to the voltage detection unit 101. The average value derivation unit 102 derives the average value of the voltage values based on the voltage detected by the voltage detection unit 101. The average value derivation unit 102 derives, for example, the average value of the voltage for at least one period (for example, 0.7 ms). Hereinafter, as an example, the case where the average value derivation unit 102 derives the average value of the voltage every one period will be continued with the description. Specifically, the period during which one diode of the rectifying unit 4 is conducting is defined as one measurement range. The voltage detection unit 101 detects (measures) the output voltage up to 0.7 ms, which is the period for deriving the average value, at a measurement period of 0.1 ms. The average value derivation unit 102 acquires the voltage value 0.1 ms after the voltage detection unit 101 detects (measures) the output voltage. Thereafter, the average value derivation unit 102 acquires the voltage value every 0.1 ms until 0.7 ms, which is the period for deriving the average value, elapses. When 0.7 ms has elapsed, the acquisition of one measurement value is completed. The average value derivation unit 102 derives the average value of the voltage according to Equation (1). Average value of voltage = Sum of measurement values / Number of measurements × Measurement period (1)

[0023] The voltage level adjustment unit 103 is connected to the average value derivation unit 102. The voltage level adjustment unit 103 acquires the average value of the voltage values from the average value derivation unit 102, and obtains the voltage threshold by reducing the voltage level of the acquired average value of the voltage values. For example, the voltage level adjustment unit 103 obtains the voltage threshold by reducing the voltage level of the average value of the voltage by about 10% to 40%. Also, the voltage level adjustment unit 103 may obtain the voltage threshold by reducing the voltage level of the average value of the voltage by about 10% to 30%. Thereby, even when the AC voltage input to the polyphase transformer 3 fluctuates and the DC output voltage from the rectifying unit 4 fluctuates, the threshold value fluctuates in accordance with the fluctuation. Therefore, compared with the case where the threshold value is fixed, the detection accuracy of open phase can be improved. Here, as an example, the case where the voltage level adjustment unit 103 obtains the voltage threshold by reducing the voltage level of the average value of the voltage by 20% will be continued to be described.

[0024] The comparison unit 104 is connected to the voltage detection unit 101 and the voltage level adjustment unit 103. The comparison unit 104 acquires a voltage value from the voltage detection unit 101 and acquires a voltage threshold value from the voltage level adjustment unit 103. Here, the voltage value acquired by the comparison unit 104 is detected by the voltage detection unit 101 after the measurement value used for deriving the voltage threshold value. For example, the voltage value acquired by the comparison unit 104 may be detected by the voltage detection unit 101 immediately after the measurement value used for deriving the voltage threshold value. The comparison unit 104 compares the acquired voltage value with the voltage threshold value, and outputs a high-level signal to the signal holding unit 105 when the voltage value is less than the voltage threshold value, and outputs a low-level signal to the signal holding unit 105 when the voltage value is greater than or equal to the voltage threshold value. For example, when a voltage waveform as shown in FIG. 5A is obtained, since the voltage value is greater than or equal to the voltage threshold value, the comparison unit 104 outputs a low-level signal (for example, "0") to the signal holding unit 105. Also, for example, when a voltage waveform as shown in FIG. 5B is obtained, since the voltage value is less than the voltage threshold value, the comparison unit 104 outputs a high-level signal (for example, "1") to the signal holding unit 105.

[0025] The signal holding unit 105 performs signal holding processing. The signal holding processing will be described. The signal holding unit 105 acquires the signal output by the comparison unit 104. When the acquired signal is a low-level signal, the signal holding unit 105 outputs a low-level signal. Also, when the acquired signal is a high-level signal, the signal holding unit 105 outputs a high-level signal. Thereafter, the signal holding unit 105 holds the output of the high-level signal regardless of whether a low-level signal or a high-level signal is acquired.

[0026] The holding release unit 106 causes the signal holding unit 105 to release the holding of a signal (high-level signal). When causing the signal holding unit 105 to release the holding of a signal, the holding release unit 106 outputs a high-level signal to the signal holding unit 105. When the signal holding unit 105 outputs a high-level signal and a low-level signal is input from the hold release unit 106, the signal holding unit 105 maintains the output of the high-level signal. Also, when the signal holding unit 105 outputs a high-level signal, a high-level signal is input from the hold release unit 106, and after the signal holding unit 105 is caused to release the signal holding, if a low-level signal is acquired from the comparison unit 104, a low-level signal is output. This concludes the description of the signal holding process.

[0027] The drive unit 107 shuts off the voltage input to the polyphase transformer 3 in the cutoff unit 2 based on the signal output by the signal holding unit 105. When a high-level signal is input from the signal holding unit 105, the drive unit 107 shuts off the voltage input to the polyphase transformer 3 in the cutoff unit 2, and when a low-level signal is input from the signal holding unit 105, the drive unit 107 does not shut 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 MCB (Miniature Circuit Breaker). 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.

[0028] The voltage detection unit 101, the average value derivation unit 102, the voltage level adjustment unit 103, the comparison unit 104, the signal holding unit 105, the hold release unit 106, and the drive unit 107 are realized, for example, by a hardware processor such as a CPU (Central Processing Unit) 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.

[0029] FIG. 6 is a circuit diagram showing an example of the phase loss detection unit 100 of the power conversion device 1 according to the present embodiment. With reference to FIG. 6, a case where the phase loss detection unit 100 is realized by an electric circuit will be described. An example of the voltage detection unit 101 is a resistor voltage division circuit, which includes a resistor R1 and a resistor R2. The resistor R1 and the resistor R2 are connected in series, and a DC circuit M1 is connected to both ends thereof. The negative side of the DC circuit M1 is grounded. The voltage detection unit 101 divides the voltage supplied between the series-connected resistor R1 and resistor R2 at a predetermined ratio. By adjusting the resistor R1 and the resistor R2, the output voltage V1out of the voltage division circuit is adjusted. The voltage detection unit 101 supplies the output voltage V1out to the average value derivation unit 102.

[0030] An example of the average value derivation unit 102 is an integration circuit, which includes a resistor R3, a capacitor C1, and an operational amplifier OP. The output voltage V1out of the voltage detection unit 101 is supplied as an input voltage V2in to the average value derivation unit 102. The voltage detection unit 101 obtains an output voltage V2out by time-integrating the input voltage V2in and supplies it to the voltage level adjustment unit 103. For example, the voltage detection unit 101 derives the average value of the voltage by time-integrating the input voltage V2in during the period for deriving the average value.

[0031] An example of the voltage level adjustment unit 103 is a resistor voltage division circuit, which includes a resistor R4 and a resistor R5. The resistor R4 and the resistor R5 are connected in series. At one end, the output voltage V2out is supplied as the input voltage V3in by the average value derivation unit 102, and the other end is grounded. The voltage level adjustment unit 103 divides the voltage supplied between the series-connected resistor R4 and resistor R5 at a predetermined ratio. By adjusting the resistor R4 and the resistor R5, the output voltage V3out of the resistor voltage division circuit is adjusted to be a voltage (voltage threshold) that reduces the voltage level of the input voltage V3in.

[0032] An example of the comparison unit 104 is a comparator. The output voltage V1out of the voltage detection unit 101 is supplied to the minus input terminal, and the output voltage V3out of the voltage level adjustment unit 103 is supplied to the plus input terminal. When the output voltage V3out is higher than the output voltage V1out, the comparison unit 104 outputs a high-level signal. When the output voltage V3out is less than the output voltage V1out, the comparison unit 104 outputs a low-level signal. When a phase loss occurs, the output voltage V1out of the voltage detection unit 101 decreases, so the output voltage V3out becomes higher than the output voltage V1out. Therefore, when a phase loss occurs, the comparison unit 104 outputs a high-level signal to the signal holding unit 105. After that, since the output voltage V3out becomes less than the output voltage V1out, the comparison unit 104 outputs a low-level signal to the signal holding unit 105.

[0033] An example of the signal holding unit 105 is an RS flip-flop circuit, which includes two NOR gates. A low-level signal is supplied from the hold release unit 106 to the reset (R). The high-level signal output by the comparison unit 104 is supplied to the set (S). When a high-level signal is supplied to the set, the signal holding unit 105 supplies a high-level signal to the drive unit 107. After that, the signal holding unit 105 holds the high-level signal even when a low-level signal or a high-level signal is supplied to the set from the comparison unit 104. Also, when the signal holding unit 105 is outputting a high-level signal and a low-level signal is supplied from the hold release unit 106 to the reset (R), the output of the high-level signal is maintained. Further, when the signal holding unit 105 is outputting a high-level signal and a high-level signal is supplied from the hold release unit 106 to the reset (R), the signal holding is released. When a low-level signal is supplied from the comparison unit 104 to the set (S), the low-level signal is supplied to the drive unit 107.

[0034] The hold release unit 106 includes a resistor R8, a NOT circuit NOT, a capacitor C2, and a switch SW. When the switch SW is off, a voltage is supplied from a power source (not shown) to the input terminal of the NOT circuit NOT, so a low-level signal is supplied to the reset (R) of the signal holding unit 105. When the switch SW is on, the input terminal of the NOT circuit NOT is grounded, so a high-level signal is supplied to the reset (R) of the signal holding unit 105.

[0035] The drive unit 107 includes a transistor TR, resistors R6, R7, a diode DI, and a cutoff machine drive power supply V7. Resistor 6 is connected to the base of the transistor TR and R7, and the signal holding unit 105 is connected to one end. When a high-level signal is supplied from the signal holding unit 105 to the drive unit 107 and the base voltage exceeds the on-voltage between the base and emitter, the transistor TR turns on. The collector current is adjusted by adjusting the base current with the resistor R6.

[0036] An example of the transistor TR is a bipolar transistor, and the emitter is grounded. The output voltage of the signal holding unit 105 is supplied to the base. When a low-level signal is supplied from the signal holding unit 105 to the drive unit 107 and the base voltage is less than the on-voltage between the base and emitter of the transistor TR, the transistor TR is off. Since the collector current does not flow because the transistor TR is off, no current flows through the external cutoff circuit of the circuit breaker 2 connected to the drive unit 107, and the circuit breaker 2 is not driven. When a high-level signal is supplied from the signal holding unit 105 to the drive unit 107 and the base voltage of the transistor TR exceeds the on-voltage between the base and emitter, the transistor TR turns on. When the transistor TR turns on, a collector current flows, and the cutoff driver power supply V7 is supplied to the external cutoff circuit of the circuit breaker 2 connected to the drive unit 107, and the circuit breaker 2 is driven.

[0037] (Operation of the power conversion device 1) FIG. 7 is a flowchart showing an example of the operation of the power conversion device 1 according to the present embodiment. With reference to FIG. 7, the operation of the phase failure detection unit 100 will be mainly described. (Step S1-1) The voltage detection unit 101 detects one set of DC output voltages of the rectifying unit 4 and supplies them to the average value derivation unit 102. (Step S2-1) The average value derivation unit 102 derives the average value of the voltage based on the voltage supplied by the voltage detection unit 101.

[0038] (Step S3-1) The voltage level adjustment unit 103 acquires the average value of the voltage from the average value derivation unit 102. The voltage level adjustment unit 103 obtains the voltage threshold by reducing the voltage level of the average value of the voltage based on the acquired average value of the voltage. (Step S4-1) The comparison unit 104 acquires the voltage value from the voltage detection unit 101 and acquires the voltage threshold from the voltage level adjustment unit 103. The comparison unit 104 compares the acquired voltage value with the voltage threshold, outputs a high-level signal to the signal holding unit 105 when the voltage value is less than the voltage threshold, and outputs a low-level signal to the signal holding unit 105 when the voltage value is greater than or equal to the voltage threshold.

[0039] (Step S5-1) The signal holding unit 105 performs signal holding processing. The processing flow of the signal holding processing will be described later. (Step S6-1) When a high-level signal is input from the signal holding unit 105, the drive 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 signal holding unit 105, the drive unit 107 does not cut off the voltage input to the polyphase transformer 3 in the cutoff unit 2.

[0040] FIG. 8 is a flowchart showing an example of the operation of the power conversion device 1 according to the present embodiment. With reference to FIG. 8, the signal holding process will be described. As an example, the case where the signal holding unit 105 has acquired a low-level signal from the hold release unit 106 will be described. (Step S1-2) The signal holding unit 105 acquires a signal from the comparison unit 104. (Step S2-2) The signal holding unit 105 determines whether the acquired signal is a low-level signal. (Step S3-2) When the acquired signal is a low-level signal, the signal holding unit 105 outputs a low-level signal. Then, it returns to step S1-2.

[0041] (Step S4-2) When the acquired signal is not a low-level signal, that is, when it is a high-level signal, the signal holding unit 105 outputs a high-level signal. (Step S5-2) The signal holding unit 105 acquires a signal (high-level signal or low-level signal) from the comparison unit 104.

[0042] (Step S6-2) The signal holding unit 105 holds the output of the high-level signal. (Step S7-2) When the signal holding unit 105 is outputting a high-level signal, it determines whether it has acquired a signal from the hold release unit 106. If it has not acquired a signal, it returns to step S5-2.

[0043] (Step S8-2) When the signal holding unit 105 is outputting a high-level signal and acquires a signal from the hold release unit 106, it determines whether the acquired signal is a low-level signal. (Step S9-2) When the acquired signal of the signal holding unit 105 is at a low level, it maintains the output of the high-level signal. Then, it proceeds to step S5-2. (Step S10-2) When the acquired signal of the signal holding unit 105 is not at a low level, that is, when it is a high-level signal, it releases the signal hold. Then, it proceeds to step S1-2.

[0044] The simulation results of the output waveform when a phase loss occurs in the power conversion device 1 will be described. FIG. 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. FIG. 9 shows an example of the circuit configuration when no phase loss occurs (when it is normal). FIG. 10 is a diagram showing the simulation results in an example of the circuit configuration when no phase loss occurs. The power supply frequency is 50 Hz and the power supply voltage is 269 Vrms. The DC output voltage waveform is the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. The DC output voltage waveform is a voltage that outputs 380 V DC.

[0045] FIG. 11 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. FIG. 11 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. FIG. 12 is a diagram showing the simulation results in an example of the circuit configuration when a phase loss occurs. The power supply frequency is 50 Hz and the power supply voltage is 269 Vrms. The DC output voltage waveform is the waveform of the ripple voltage obtained by rectifying the AC voltage with a diode. It is a voltage that outputs 380 V DC. Since a phase loss has occurred, a decrease in the DC output (''D'' in FIG. 12) can be seen. When one of the diodes at a position different from the position shown in FIG. 11 has an open failure, one phase is missing and the output waveform is the same. However, the position of the DC output drop is different. Therefore, it is possible to detect when a phase loss occurs in any phase.

[0046] In the above-described embodiment, as an example of the polyphase transformer 3, the case where a 12-phase transformer is applied has been described, but it is not limited to this example. For example, a 3-phase transformer may be applied to the polyphase transformer 3, a 6-phase transformer may be applied, or a 24-phase transformer may be applied. FIG. 13 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 3-1. 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 having a star connection on the primary side (high voltage side) and a delta connection on the secondary side (low voltage side) may be used.

[0047] In the above-described embodiment, the case where the blocking unit 2 blocks the voltage input to the polyphase transformer 3 has been described, but it is not limited to this example. For example, the blocking unit 2 may be provided between the polyphase transformer 3 and the rectifying unit 4 to block the polyphase AC power supplied from the polyphase transformer 3 to the rectifying unit 4. Further, the blocking unit 2 may be provided after the rectifying unit 4 to block the DC power output from the rectifying unit 4. In the above-described embodiment, the case where the average value derivation unit 102 derives the average value of the voltage every one cycle (for example, 0.7 ms) has been described, but it is not limited to this example. For example, the average value derivation unit 102 may derive the average value of the voltage every two cycles, every three cycles, or every four or more cycles. The cycle at which the average value derivation unit 102 derives the average value of the voltage can be changed as appropriate.

[0048] In the above-described embodiment, 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, a relay contact or the like may be used to drive the alarm unit. By configuring in this way, when it is determined that a phase failure has occurred, it is possible to notify, for example, the operator of the power conversion device 1 to take corresponding measures. Thereafter, the operator of the power conversion device 1 can reset the signal holding unit 105 by turning on the switch SW of the holding release unit 106.

[0049] According to the power conversion device 1 according to the present embodiment, there are provided a polyphase transformer 3 that converts AC power into polyphase AC power, a rectifying unit 4 that converts the polyphase AC power 3 into DC power, and a phase failure detection unit 100 that detects the occurrence of a phase failure based on the output voltage of the rectifying unit 4. By configuring in this way, since it is possible to detect the occurrence of a phase failure based on the output voltage of the rectifying unit 4, the size of the power conversion device 1 can be reduced compared to the case of using a wiring circuit breaker with neutral line phase failure protection, while being able to detect the occurrence of a phase failure. For example, it is possible to detect the occurrence of a phase failure based on the output voltage of the rectifying unit 4 due to a poor contact, disconnection, or diode breakage in the rectifying unit 4 between the polyphase transformer 3 and the rectifying unit 4.

[0050] Also, in the power conversion device 1, the phase failure detection unit 100 detects the occurrence of a phase failure based on a decrease in the output voltage. By configuring in this way, since it is possible to detect the occurrence of a phase failure based on a decrease in the output voltage of the rectifying unit 4, the size of the power conversion device 1 can be reduced compared to the case of using a wiring circuit breaker with neutral line phase failure protection, while being able to detect the occurrence of a phase failure.

[0051] Also, in the power conversion device 1, the phase failure detection unit 100 includes an average value derivation unit 102 that derives the average value of the output voltage based on the output voltage of the rectification unit 4, a voltage level adjustment unit 103 as a threshold value derivation unit that derives a threshold value based on the average value derived by the average value derivation unit 102, and a comparison unit 104 as a determination unit that determines whether a phase failure has occurred based on the output voltage of the rectification unit 4 and the threshold value. By configuring in this way, the average value of the output voltage of the rectification unit 4 can be derived, and the threshold value can be derived based on the derived average value. Therefore, it is possible to determine whether the output voltage of the rectification unit 4 has decreased by comparing it with the threshold value. For this reason, it is possible to detect that a phase failure has occurred. The power conversion device 1 has a DC output voltage that also varies in conjunction with fluctuations in the input voltage (for example, the system voltage). Also, the DC output voltage varies depending on the power consumption of the load (not shown). By deriving the average value of the output voltage of the rectification unit 4, it is possible to derive the voltage threshold value according to these fluctuations. Therefore, compared with the case where the threshold value is a fixed value, it is possible to accurately detect that a phase failure has occurred.

[0052] Also, in the power conversion device 1, the threshold value derivation unit derives the threshold value by reducing the voltage from the average value of the output voltage. By configuring in this way, the threshold value can be derived. Therefore, it is possible to determine whether the output voltage of the rectification unit 4 has decreased by comparing it with the threshold value. For this reason, it is possible to detect that a phase failure has occurred.

[0053] 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 it is determined by the determination unit that a phase failure has occurred. By configuring in this way, when it is determined that a phase failure has occurred, the AC power supplied to the polyphase transformer 3 can be shut off, so safety can be ensured.

[0054] Further, in the power conversion device 1, when it is determined by the determination unit that a phase failure has occurred, an alarm unit that sounds an alarm is further provided. By configuring it in this way, when it is determined that a phase failure has occurred, an alarm can be sounded. Therefore, it is possible to notify the surroundings that a phase failure has occurred.

[0055] 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. 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), and a storage device such as a hard disk built into a computer system. 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 that holds the program for a certain period of time. 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. Further, the program may be for realizing a part of the functions described above. Furthermore, it may be a so-called differential file (differential program) that can realize the functions described above in combination with a program already recorded in a computer system.

Explanation of Signs

[0056] 1... Power conversion device, 2... Circuit breaker, 3... Polyphase transformer, 4... Rectifier section, 100... Open-phase detection section, 101... Voltage detection section, 102... Average value derivation section, 103... Voltage level adjustment section, 104... Comparison section, 105... Signal holding section, 106... Holding release section, 107... Drive 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 failure detection unit that detects the occurrence of a phase failure based on the output voltage of the rectifier. A power conversion device comprising the above.

2. The power conversion device according to claim 1, wherein the phase failure detection unit detects the occurrence of a phase failure based on a decrease in the output voltage.

3. The phase failure detection unit includes an average value derivation unit that derives an average value of the output voltage based on the output voltage of the rectifier, a threshold value derivation unit that derives a threshold value based on the average value derived by the average value derivation unit, and a determination unit that determines whether a phase failure has occurred based on the output voltage of the rectifier and the threshold value. The power conversion device according to claim 1, comprising the above.

4. The power conversion device according to claim 3, wherein the threshold value derivation unit derives the threshold value by reducing the voltage from the average value of the output voltage.

5. 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 failure has occurred. The power conversion device according to claim 3, further comprising the above.

6. 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 failure has occurred. The power conversion device according to claim 3, further comprising the above.

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