Power converter

Abstract

To provide a power conversion device capable of suppressing generation of cyclic current.SOLUTION: A power conversion device includes: N (N is an integer of 2 or more) AC / DC conversion circuits; a first diode group having N diodes; and a second diode group having the N diodes. In the N AC / DC conversion circuits, an AC end is connected in parallel to an AC power supply, and AC current outputted from the AC power supply is converted into DC current. An anode of each diode of the first diode group is connected to a DC end on a high potential side of the N AC / DC conversion circuits, and a cathode of each diode of the first diode group is connected in parallel to the high potential end of an auxiliary load. A cathode of each diode of the second diode group is connected to a DC end on a low potential side of the N AC / DC conversion circuits, and an anode of each diode of the second diode group is connected in parallel to a low potential end of the auxiliary load.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device.

Background Art

[0002] Conventionally, in order to continue operation even if a failure occurs in one system, a power conversion device including rectifiers of a plurality of systems has been used. For example, as a power conversion device including two rectifiers of two systems, there is a power conversion device including two diode rectifiers connected in parallel to one AC power source. Here, in order to determine the potential from the ground, each rectifier is grounded with a low resistance, for example, at the DC terminal on the low potential side, the DC terminal on the high potential side, or the two-divided neutral point of the DC capacitor of each rectifier.

[0003] However, in the case of the power conversion device grounded as described above, due to the difference in I-V characteristics between the two diode rectifiers of the two systems, for example, variations in characteristics such as the voltage drop Vf and the on-resistance Ron of the diodes included in each diode rectifier, a circulating current flows through the ground. As a phenomenon, it occurs as a differential current due to the increase and decrease of the main current. As a result, the load of the diode rectifier is biased, the loss of one system increases, the voltage drop Vf further decreases due to the temperature rise, and the load is further biased, and the bias of the load is increased by such positive feedback. Finally, compared with the case where there is no variation in characteristics, the loss of one system significantly increases, and in the worst case, thermal breakdown may occur.

[0004] Further, for example, when the lower arm of the diode of one system is open-destroyed while the DC terminals on the low potential side of the two diode rectifiers of the two systems are each grounded, the total current of the two systems concentrates on the diode of the lower arm of the other healthy system. Therefore, a detector for detecting such a failure is required, which is a factor for cost increase. Furthermore, an increase in the current flowing causes an increase in the loss of the rectifier, and thermal breakdown may occur.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-232599 [Patent Document 2] Japanese Patent Publication No. 2022-87330 [Patent Document 3] Patent No. 5362139 [Patent Document 4] Patent No. 6999480 [Overview of the project] [Problems that the invention aims to solve]

[0006] Embodiments of the present invention provide a power conversion device that can suppress the generation of circulating current. [Means for solving the problem]

[0007] The power converter according to this embodiment comprises N (where N is an integer of 2 or more) AC-DC conversion circuits, a first diode group having N diodes, and a second diode group having N diodes. The AC terminals of the N AC-DC conversion circuits are connected in parallel to an AC power source, and the AC current output from the AC power source is converted into DC current. The anode of each diode in the first diode group is connected to the DC terminal on the high-potential side of the N AC-DC conversion circuits, and the cathode of each diode in the first diode group is connected in parallel to the high-potential terminal of an auxiliary load. The cathode of each diode in the second diode group is connected to the DC terminal on the low-potential side of the N AC-DC conversion circuits, and the anode of each diode in the second diode group is connected in parallel to the low-potential terminal of the auxiliary load. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing the circuit configuration of a power conversion device according to the first embodiment. [Figure 2] This diagram shows the circuit configuration of a power converter according to the first embodiment, where the device is grounded at a first grounding position and one grounding capacitor is provided. [Figure 3] This diagram shows the circuit configuration in a power converter according to the first embodiment, where the device is grounded at the second grounding position and one grounding capacitor is provided. [Figure 4] A diagram showing the circuit configuration of the power conversion device according to the second embodiment. [Figure 5] A diagram showing the circuit configuration of a power conversion device according to the third embodiment. [Figure 6] A diagram showing the circuit configuration of the power conversion device according to the fourth embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. These embodiments are not intended to limit the present invention. The drawings are schematic or conceptual, and the proportions of each part may not necessarily be the same as those of actual objects. In the specification and drawings, elements similar to those described above are denoted by the same reference numerals with respect to previously shown drawings, and detailed explanations are omitted as appropriate.

[0010] (First Embodiment) Figure 1 is a diagram showing the circuit configuration of the power converter 1 according to the first embodiment. The power converter 1 according to this embodiment includes a plurality of power converters connected in parallel to a single AC power source. That is, the power converter 1 according to this embodiment includes a plurality of power converters, and as shown in Figure 1, includes diode rectifiers DR1, DR2, DC reactors L1, L2, smoothing capacitors C1, C2, diodes D11, D12, D21, D22, and ground capacitors GC1, GC2. Note that the number of diode rectifiers in the power converter 1 is not limited to two, but may be any number such as three, four, etc. Also, the number of diode rectifiers in the plurality of power converters may be the same or different.

[0011] Furthermore, the power conversion device 1 according to this embodiment includes two power systems. The first power system is composed of a diode rectifier DR1, a DC reactor L1, a smoothing capacitor C1, and the wiring between them, and the second power system is composed of a diode rectifier DR2, a DC reactor L2, a smoothing capacitor C2, and the wiring between them.

[0012] As shown in Figure 1, the power converter 1 is connected to an AC power supply PS. In this embodiment, the AC power supply PS is a three-phase AC power supply. Alternatively, a single-phase AC power supply or a multi-phase AC power supply with four or more phases may be used as the AC power supply PS.

[0013] Diode rectifiers DR1 and DR2 are connected in parallel to the AC power supply PS and convert the AC current output from the AC power supply PS into DC current. In this embodiment, diode rectifiers DR1 and DR2 each convert three-phase AC current into DC current. As shown in Figure 1, the AC terminal A1 of diode rectifier DR1 is connected to the AC power supply PS. The AC terminal A2 of diode rectifier DR2 is connected in parallel to the AC power supply PS with the AC terminal A1 of diode rectifier DR1. When a single-phase AC power supply or a multi-phase AC power supply is used as the AC power supply PS, diode rectifiers DR1 and DR2 that convert single-phase AC current or multi-phase AC current into DC current are used, respectively. Diode rectifiers DR1 and DR2 are examples of AC-DC conversion circuits.

[0014] Furthermore, a circuit breaker, contactor, etc., may be provided between the AC power supply PS and the AC terminal A1 of the diode rectifier DR1. The same applies between the AC power supply PS and the AC terminal A2 of the diode rectifier DR2.

[0015] The DC reactors L1 and L2 are choke reactors for suppressing noise such as harmonics contained in the DC current output from the diode rectifiers DR1 and DR2. As shown in FIG. 1, one end of the DC reactor L1 is connected to the high-potential side DC terminal P1 of the diode rectifier DR1. Similarly, one end of the DC reactor L2 is connected to the high-potential side DC terminal P2 of the diode rectifier DR2.

[0016] The smoothing capacitors C1 and C2 are DC capacitors for smoothing the DC current output from the diode rectifiers DR1 and DR2. As shown in FIG. 1, one end of the smoothing capacitor C1 is connected to the other end of the DC reactor L1, and through this DC reactor L1, it is connected to the high-potential side DC terminal P1 of the diode rectifier DR1. The other end of the smoothing capacitor C1 is connected to the low-potential side DC terminal N1 of the diode rectifier DR1. Similarly, one end of the smoothing capacitor C2 is connected to the other end of the DC reactor L2, and through this DC reactor L2, it is connected to the high-potential side DC terminal P2 of the diode rectifier DR2. The other end of the smoothing capacitor C2 is connected to the low-potential side DC terminal N2 of the diode rectifier DR2.

[0017] Although it will be described in detail later, when a load such as a voltage-type inverter is connected as the main load to the DC terminals of the diode rectifiers DR1 and DR2, by providing the smoothing capacitors C1 and C2, the input voltage of the voltage-type inverter can be stabilized.

[0018] The DC reactor L1 and the smoothing capacitor C1 constitute a first filter circuit for stabilizing the output of the diode rectifier DR1. Similarly, the DC reactor L2 and the smoothing capacitor C2 constitute a second filter circuit for stabilizing the output of the diode rectifier DR2.

[0019] Note that the configurations of the first filter circuit and the second filter circuit are not limited to those described above and are arbitrary. For example, in the first filter circuit, a DC reactor directly connected to the DC terminal N1 on the low potential side of the diode rectifier DR1 may be provided. Alternatively, in the first filter circuit, a two-winding reactor may be provided in which the DC terminal P1 on the high potential side and the DC terminal N1 on the low potential side of the diode rectifier DR1 and both ends of the smoothing capacitor C1 are respectively connected. The same applies to the second filter circuit.

[0020] Diodes D11, D12, D21, and D22 rectify the DC current output from diode rectifiers DR1 and DR2.

[0021] The anode of diode D11 is connected to the other end of DC reactor L1, and through this DC reactor L1, it is connected to the DC terminal P1 on the high potential side of diode rectifier DR1. Similarly, the anode of diode D12 is connected to the other end of DC reactor L2, and through this DC reactor L2, it is connected to the DC terminal P2 on the high potential side of diode rectifier DR2. The cathodes of diode D11 and diode D12 are connected to each other and are connected in parallel to the high potential end Pel of the auxiliary load EL to be described later. That is, diodes D11 and D12 are connected in inverse series with each other in the direction of supplying power from diode rectifiers DR1 and DR2 to the auxiliary load EL. Diodes D11 and D12 constitute the first diode group in the power conversion device 1 according to this embodiment.

[0022] The cathode of diode D21 is connected to the low-potential DC terminal N1 of diode rectifier DR1. Similarly, the cathode of diode D22 is connected to the low-potential DC terminal N2 of diode rectifier DR2. The anodes of diode D21 and diode D22 are connected to each other and are connected in parallel to the low-potential terminal Nel of the auxiliary load EL. In other words, diodes D21 and D22 are connected in reverse series to each other in the direction of supplying power from diode rectifiers DR1 and DR2 to the auxiliary load EL. Diodes D21 and D22 constitute the second diode group in the power conversion device 1 according to this embodiment.

[0023] Although shown as an open terminal in Figure 1, the anode of diode D11 is connected to the high-potential DC terminal of the first main load, which is the main load of the inverter, and the cathode of diode D21 is connected to the low-potential DC terminal of the first main load. Similarly, the anode of diode D12 is connected to the high-potential DC terminal of the second main load, which is the main load of the inverter, and the cathode of diode D22 is connected to the low-potential DC terminal of the second main load. However, the first and second main loads are provided to be electrically isolated from each other.

[0024] The auxiliary load EL is a load provided across the cathodes of diodes D11 and D12 and the anodes of diodes D21 and D22. DC current flows from the cathodes of diodes D11 and D12 to the anodes of diodes D21 and D22 through the auxiliary load EL. As a result, the high-potential DC terminals P1 and P2 of diode rectifiers DR1 and DR2 and the low-potential DC terminals N1 and N2 of diode rectifiers DR1 and DR2 are connected via diodes D11, D12, D21, D22 and the auxiliary load EL, allowing diode rectifiers DR1 and DR2 to be grounded at a common position. The impedance of the auxiliary load EL may be greater than the impedances of the first and second main loads described above. Furthermore, the auxiliary load EL may be, for example, a circuit consisting of a single resistor or some kind of control circuit.

[0025] Grounding capacitors GC1 and GC2 are provided to ground the power converter 1 at grounding position GND3, which will be described later. Grounding capacitors GC1 and GC2 also stabilize the input voltage of the auxiliary load EL. As shown in Figure 1, one end of grounding capacitor GC1 is connected to the cathodes of diodes D11 and D12, i.e., the high-potential terminal Pel of the auxiliary load EL. One end of grounding capacitor GC2 is connected to the anodes of diodes D21 and D22, i.e., the low-potential terminal Nel of the auxiliary load EL. The other ends of grounding capacitor GC1 and grounding capacitor GC2 are connected to each other and grounded at grounding position GND3. Grounding capacitors GC1 and GC2 constitute the capacitive circuit in the power converter 1 according to this embodiment. However, in the power converter 1 according to this embodiment, grounding may be performed at grounding position GND1 or grounding position GND2 instead of grounding position GND3 as shown in Figure 1.

[0026] In this embodiment, power is supplied to the auxiliary load EL and ground capacitors GC1 and GC2 from the DC terminals P1 and N1 of diode rectifier DR1 via diodes D11 and D21, and power is supplied to the diode rectifier DR2 from the DC terminals P2 and N2 via diodes D12 and D22.

[0027] In the power converter 1 according to this embodiment, the high-potential DC terminals P1 and P2 of diode rectifiers DR1 and DR2 are not grounded between them and the anodes of diodes D11 and D12 in the first diode group. Also, the low-potential DC terminals N1 and N2 of diode rectifiers DR1 and DR2 are not grounded between them and the cathodes of diodes D21 and D22 in the second diode group. That is, as shown in Figure 1, the high-potential DC terminal P1 of diode rectifier DR1 and DC reactor L1, the inside of DC reactor L1, the DC reactor L1 and the anode of diode D11, the high-potential DC terminal P2 of diode rectifier DR2 and DC reactor L2, the inside of DC reactor L2, and the DC reactor L2 and the anode of diode D12 are not grounded. Furthermore, the connection between the low-potential DC terminal N1 of diode rectifier DR1 and the cathode of diode D21, and the connection between the low-potential DC terminal N2 of diode rectifier DR2 and the cathode of diode D22, are not grounded.

[0028] On the other hand, as described above, the power converter 1 according to this embodiment is grounded at one of the following locations: grounding position GND1, grounding position GND2, and grounding position GND3 shown in Figure 1. More specifically, when the power converter 1 is grounded at grounding position GND1, the cathodes of diodes D11 and D12, i.e., the high-potential terminals Pel of the auxiliary load EL, are grounded. When the power converter 1 is grounded at grounding position GND2, the anodes of diodes D21 and D22, i.e., the low-potential terminals Nel of the auxiliary load EL, are grounded. When the power converter 1 is grounded at grounding position GND3, the other end of grounding capacitor GC1 and the other end of grounding capacitor GC2 are grounded.

[0029] In this embodiment, when the power converter 1 is grounded at the grounding position GND3, the grounding capacitors GC1 and GC2 have the same capacitance. In this case, the power converter 1 is grounded at the neutral point of the two-voltage division between the cathodes of diodes D11 and D12 and the anodes of diodes D21 and D22. However, the capacitances of grounding capacitor GC1 and grounding capacitor GC2 may be different from each other, as long as they can be considered substantially the same.

[0030] Furthermore, if the power converter 1 is grounded at ground position GND1 or ground position GND2, the ground capacitors GC1 and GC2 do not need to be provided. Alternatively, as shown in Figures 2 and 3, instead of providing two ground capacitors GC1 and GC2, one ground capacitor GC may be provided. Figure 2 is a diagram showing the circuit configuration of the power converter 1 according to this embodiment when it is grounded at ground position GND1, which is the first ground position, and one ground capacitor GC is provided. Figure 3 is a diagram showing the circuit configuration of the power converter 1 according to this embodiment when it is grounded at ground position GND2, which is the second ground position, and one ground capacitor GC is provided.

[0031] Furthermore, although not shown in Figure 1, grounding may be performed at any of the grounding positions GND1, GND2, or GND3 using a low-resistance resistor, i.e., a resistor with a low resistance value. For example, when grounding position GND1 with a low-resistance resistor, one end of the resistor is connected to the high-potential terminal Pel of the auxiliary load EL, and the other end of the resistor is grounded.

[0032] Next, we will explain how the power converter 1 configured as described above suppresses the generation of circulating current, divided into two cases: (1) when the characteristics of diode rectifiers DR1 and DR2 are matched, and (2) when the characteristics of diode rectifiers DR1 and DR2 are not matched. Hereinafter, the characteristics of diode rectifiers DR1 and DR2 refer to the voltage drop Vf and conduction resistance Ron.Very farsighted, the voltage drop Vf and conduction resistance Ron will also be referred to as "impedance".

[0033] (1) When the characteristics of diode rectifiers DR1 and DR2 are matched In this case, the auxiliary load EL is powered by both systems, namely the diode rectifiers DR1 and DR2. As a result, the four diodes D11, D12, D21, and D22 become conductive.

[0034] Although it might seem that a circulating current would flow because the four diodes D11, D12, D21, and D22 are in a conductive state, a circulating current does not occur because, under the assumption, the characteristics of the diode rectifiers DR1 and DR2 are matched.

[0035] (2) When the characteristics of diode rectifiers DR1 and DR2 are not matched As an example, let's consider the case where the impedance of diode rectifier DR2 is smaller than the impedance of diode rectifier DR1.

[0036] In this case, the auxiliary load EL is supplied with power from the diode rectifier DR2, which has a lower impedance, via diodes D12 and D22. Therefore, of the four diodes D11, D12, D21, and D22, diodes D12 and D22 become conductive, while diodes D11 and D21 do not.

[0037] In this case, it appears that the circulating current flows from the diode rectifier DR1, which has a high impedance, to the diode rectifier DR2, which has a low impedance. For example, it appears that the circulating current flows in the following order: from the AC terminal A1 of diode rectifier DR1, to the low-potential DC terminal N1 of diode rectifier DR1, from the cathode to the anode of diode D21, from the anode to the cathode of diode D22, to the low-potential DC terminal N2 of diode rectifier DR2, to the AC terminal A2 of diode rectifier DR2, and finally to the AC terminal A1 of diode rectifier DR1.

[0038] However, since diode D21 in the high-impedance path is not conducting, no current flows backward from the cathode to the anode of diode D21. Even if diode D21 were conducting with a small current, it would cease to conduct before a current equivalent to the current flowing through the auxiliary load EL could flow through it. Therefore, no circulating current occurs in the above path. The same applies to the other paths; since none of the diodes in the path are conducting, no circulating current occurs.

[0039] Similarly, if the impedance of diode rectifier DR1 is smaller than the impedance of diode rectifier DR2, or if there are variations in characteristics other than the voltage drop Vf and conduction resistance Ron, circulating current will not occur.

[0040] As explained above, in the power converter 1 according to the first embodiment, no circulating current flows in either case (1) or (2). More specifically, for a circulating current to flow in the power converter 1, the conditions of variations in the characteristics of the diode rectifiers DR1 and DR2 and the condition that the four diodes D11, D12, D21, and D22 are in a conductive state must be met simultaneously. However, in the power converter 1 according to this embodiment, these conditions are mutually exclusive and cannot be met simultaneously. Therefore, the power converter 1 according to this embodiment can suppress the generation of circulating current.

[0041] In the case of (2) above, a reverse voltage is applied to diodes D11 and D21 that are not conducting, and the diode rectifier DR1, which has a large voltage drop Vf and conduction resistance Ron, will experience an increase in potential relative to ground, i.e., ground potential. However, the potential increase in this case is only to the extent of the difference in forward voltage drops across the diodes between the two systems. That is, it is only to the extent of the difference between the voltage drop across diode D11 and the voltage drop across diode D12, and the difference between the voltage drop across diode D21 and the voltage drop across diode D22, so this potential increase does not pose a major problem.

[0042] Furthermore, in the case of a power converter where, as in the conventional method, the DC terminal N1 on the low-potential side of diode rectifier DR1 and the DC terminal N2 on the low-potential side of diode rectifier DR2 are grounded with low resistance, the DC terminal N1 on the low-potential side of diode rectifier DR1 and the DC terminal N2 on the low-potential side of diode rectifier DR2 conduct through their grounding, and a circulating current is generated through the ground. For example, if the voltage drop Vf and conduction resistance Ron of diode rectifier DR2 are lower than the voltage drop Vf and conduction resistance Ron of diode rectifier DR1, the current that flows from the DC terminal N2 on the low-potential side of diode rectifier DR2 through the AC terminal A2 of diode rectifier DR2, the AC terminal A1 of diode rectifier DR1, and the DC terminal N1 on the low-potential side of diode rectifier DR1 will flow back to the DC terminal N2 on the low-potential side of diode rectifier DR2 through the ground.

[0043] In contrast, as described above, in the power converter 1 according to this embodiment, the DC terminals P1 and P2 on the high-potential side of the diode rectifiers DR1 and DR2 are not grounded between the cathodes of each diode D11 and D12 in the first diode group, and the DC terminals N1 and N2 on the low-potential side of the diode rectifiers DR1 and DR2 are not grounded between the anodes of each diode D21 and D22 in the second diode group. Therefore, circulating current via grounding can also be suppressed.

[0044] Furthermore, if the DC terminals N1 and N2 on the low-potential side of the diode rectifiers DR1 and DR2, the DC terminals P1 and P2 on the high-potential side, or the neutral points of the two-voltage divider smoothing capacitors C1 and C2, are grounded as in the conventional method, it is necessary to provide a resistor with a high resistance value for grounding to prepare for current in the event of a fault. This results in the diode rectifiers DR1 and DR2 having a potential difference to ground, which presents a problem.

[0045] On the other hand, according to the power converter 1 of this embodiment, there is no need to provide a resistor with a high resistance value to ground, so it is possible to suppress the diode rectifiers DR1 and DR2 from having a potential difference to ground.

[0046] (Second Embodiment) A second embodiment of the power converter 1 will be described, which includes a PWM converter instead of the diode rectifier in the power converter 1 of the first embodiment described above. That is, the power converter 1 of this embodiment includes converters in a plurality of power converters. Figure 4 is a diagram showing the circuit configuration of the power converter 1 of the second embodiment. As shown in Figure 4, the power converter 1 of this embodiment includes PWM converters CNV1 and CNV2 instead of the diode rectifiers DR1 and DR2 of the first embodiment described above. In addition, AC reactors AL1 and AL2 are included instead of DC reactors L1 and L2. The following description will focus on the differences between the power converter 1 of this embodiment and the first embodiment.

[0047] The AC reactors AL1 and AL2 suppress noise such as harmonics contained in the AC current output from the AC power supply PS. As shown in Figure 4, one end of AC reactor AL1 is connected to the AC power supply PS. One end of AC reactor AL2 is connected to the AC power supply PS in parallel with AC reactor AL1.

[0048] PWM converters CNV1 and CNV2, like diode rectifiers DR1 and DR2, are rectifiers that convert AC current output from an AC power supply PS into DC current. The other end of AC reactor AL1 is connected to the AC terminal A1 of PWM converter CNV1. The other end of AC reactor AL2 is connected to the AC terminal A2 of PWM converter CNV2. PWM converters CNV1 and CNV2 are examples of AC-DC conversion circuits.

[0049] Furthermore, as shown in Figure 4, the smoothing capacitor C1 is provided across the high-potential DC terminal P1 and the low-potential DC terminal N1 of the PWM converter CNV1. The smoothing capacitor C2 is provided across the high-potential DC terminal P2 and the low-potential DC terminal N2 of the PWM converter CNV2.

[0050] The power converter 1 according to this embodiment comprises two power systems. The first power system is composed of an AC reactor AL1, a PWM converter CNV1, a smoothing capacitor C1, and the wiring between them, while the second power system is composed of an AC reactor AL2, a PWM converter CNV2, a smoothing capacitor C2, and the wiring between them.

[0051] In this embodiment, power is supplied to the auxiliary load EL and ground capacitors GC1 and GC2 from the DC terminals P1 and N1 of the PWM converter CNV1 via diodes D11 and D21, and power is supplied to the PWM converter CNV2 from the DC terminals P2 and N2 via diodes D12 and D22.

[0052] Similar to the first embodiment, in this embodiment, the power converter 1 has no grounding between the high-potential DC terminals P1 and P2 of the PWM converters CNV1 and CNV2 and the anodes of the diodes D11 and D12 of the first diode group. Also, the low-potential DC terminals N1 and N2 of the PWM converters CNV1 and CNV2 and the cathodes of the diodes D21 and D22 of the second diode group are not grounded. That is, as shown in Figure 4, the connection between the high-potential DC terminal P1 of the PWM converter CNV1 and the anode of diode D11, and the connection between the high-potential DC terminal P2 of the PWM converter CNV2 and the anode of diode D12 are not grounded. Also, the connection between the low-potential DC terminal N1 of the PWM converter CNV1 and the cathode of diode D21, and the connection between the low-potential DC terminal N2 of the PWM converter CNV2 and the cathode of diode D22 are not grounded.

[0053] On the other hand, similar to the first embodiment, the power converter 1 according to this embodiment is grounded at one of the following locations: grounding position GND1, grounding position GND2, and grounding position GND3 shown in Figure 4.

[0054] As explained above, the power converter 1 according to the second embodiment, which uses PWM converters CNV1 and CNV2 as AC-DC conversion circuits, can also suppress the generation of circulating currents in the same way as the power converter 1 according to the first embodiment described above. More specifically, in the power converter 1 according to this embodiment, the condition in which there are variations in the characteristics such as the impedance of the PWM converters CNV1 and CNV2 and the condition in which the four diodes D11, D12, D21, and D22 are in a conducting state are mutually exclusive, and these conditions cannot be satisfied at the same time. Therefore, the power converter 1 according to this embodiment can suppress the generation of circulating currents.

[0055] Furthermore, according to the power conversion device 1 of this embodiment, by providing PWM converters CNV1 and CNV2 as AC-DC conversion circuits, the AC-DC conversion circuits can be actively controlled. Therefore, compared to the case where diode rectifiers DR1 and DR2 are used as in the first embodiment described above, the power factor can be improved and harmonics can be further suppressed.

[0056] Furthermore, when controlling a PWM converter that takes a three-phase AC power supply as input, typically, the current of two phases is detected, and the remaining phase is estimated by assuming that the total current of the three phases is zero, thereby reducing the number of sensors and lowering the cost of the equipment. However, if there is variation in the impedance between the two PWM converter systems, circulating current may flow, causing the assumption that the total current of the three phases is zero to fail. For example, circulating current may occur in a phase where no sensor is installed. Therefore, it becomes necessary to increase the number of current sensors to detect all three phases of current, or to change the mounting phase of the current sensors between the two systems. If the mounting phase of the current sensors is changed between the two systems, for example, current sensors must be installed on the U and V phases in PWM converter CNV1, and on the V and W phases in PWM converter CNV2. This increases the cost of sensors and the man-hours required for sensor replacement and control development.

[0057] On the other hand, according to the power conversion device 1 of this embodiment, since no circulating current is generated, the assumption that the total current is 0 can be maintained for the PWM converter that takes a three-phase AC power supply as input. Therefore, the cost of sensors and the costs of maintenance and control development can be reduced.

[0058] (Third embodiment) The number of AC-DC conversion circuits in the power converter 1 is not limited to two. Below, a third embodiment will be described in which the power converter 1 according to the first embodiment has N diode rectifiers (where N is an integer of 2 or more). That is, the power converter 1 according to this embodiment has N rectifier systems. It is also possible to have N PWM converters in the power converter 1 according to the second embodiment.

[0059] Figure 5 is a diagram showing the circuit configuration of the power converter 1 according to this embodiment. As shown in Figure 5, the power converter 1 according to this embodiment comprises N diode rectifiers DR1, DR2, ..., DRN, N DC reactors L1, L2, ..., LN, N smoothing capacitors C1, C2, ..., CN, N diodes D11, D12, ..., D1N, N diodes D21, D22, ..., D2N, and grounding capacitors GC1, GC2. Details of the AC power supply PS, DC reactors L1, L2, ..., LN, smoothing capacitors C1, C2, ..., CN, and grounding capacitors GC1, GC2 are the same as in the first embodiment described above, so their explanation is omitted.

[0060] As shown in Figure 5, the AC terminals A1, A2, ..., AN of the diode rectifiers DR1, DR2, ..., DRN are connected in parallel to the AC power supply PS. Each of the diode rectifiers DR1, DR2, ..., DRN is an example of an AC-DC conversion circuit.

[0061] The power converter 1 according to this embodiment comprises N power systems. A first power system is formed by a diode rectifier DR1, a DC reactor L1, a smoothing capacitor C1, and the wiring between them; a second power system is formed by a diode rectifier DR2, a DC reactor L2, a smoothing capacitor C2, and the wiring between them; ..., the nth power system is formed by a diode rectifier DRN, a DC reactor LN, a smoothing capacitor CN, and the wiring between them.

[0062] The first diode group in the power converter 1 according to this embodiment is composed of N diodes D11, D12, ..., D1N. As shown in Figure 5, the anode of each diode D11, D12, ..., D1N in the first diode group is connected to the high-potential DC terminals P1, P2, ..., PN of the diode rectifiers DR1, DR2, ..., DRN, respectively, via DC reactors L1, L2, ..., LN. The cathode of each diode D11, D12, ..., D1N in the first diode group is connected in parallel to the high-potential terminal Pel of the auxiliary load EL.

[0063] Furthermore, the second diode group in the power converter 1 according to this embodiment is composed of N diodes D21, D22, ..., D2N. As shown in Figure 5, the cathodes of each diode D21, D22, ..., D2N in the second diode group are connected to the DC terminals N1, N2, ..., NN on the low-potential side of the diode rectifiers DR1, DR2, ..., DRN, respectively. The anodes of each diode D21, D22, ..., D2N in the second diode group are connected in parallel to the low-potential terminal Nel of the auxiliary load EL, respectively.

[0064] In this embodiment, power is supplied to the auxiliary load EL and ground capacitors GC1 and GC2 from the DC terminals P1 and N1 of diode rectifier DR1 via diodes D11 and D21, from the DC terminals P2 and N2 of diode rectifier DR2 via diodes D12 and D22, ..., and from the DC terminals PN and NN of diode rectifier DRN via diodes D1N and D2N.

[0065] Similar to the first embodiment, in the power converter 1 according to this embodiment, the high-potential DC terminals P1, P2, ..., PN of the diode rectifiers DR1, DR2, ..., DRN and the anodes of each diode D11, D12, ..., D1N in the first diode group are not grounded. Also, the low-potential DC terminals N1, N2, ..., NN of the diode rectifiers DR1, DR2, ..., DRN and the cathodes of each diode D21, D22, ..., D2N in the second diode group are not grounded.

[0066] Furthermore, similar to the first embodiment, the power converter 1 according to this embodiment is grounded at one of the following locations: grounding position GND1, grounding position GND2, and grounding position GND3, as shown in Figure 5.

[0067] As explained above, the power converter 1 according to this embodiment, which is equipped with N diode rectifiers DR1, DR2, ..., DRN, can also suppress the generation of circulating current, similar to the first embodiment. More specifically, the condition that there is variation in the characteristics of any two diode rectifiers and the condition that the four diodes connected to these two diode rectifiers are in a conducting state cannot be met simultaneously. More specifically, for any i and j, where i and j are mutually distinct integers between 1 and N, the condition that there is variation in the characteristics such as the impedance of the diode rectifiers DRi and DRj and the condition that the four diodes D1i, D1j, D2i, and D2j are in a conducting state are mutually exclusive, and these conditions cannot be met simultaneously. Therefore, the power converter 1 according to this embodiment can suppress the generation of circulating current.

[0068] (Fourth Embodiment) A specific application example of the power converter 1 according to the first embodiment will be described as a fourth embodiment. Figure 6 is a diagram showing the circuit configuration of the power converter 1 according to the fourth embodiment. In the example shown in Figure 6, the power converter 1 according to the first embodiment is connected to two inverters INV1 and INV2, contactors CNT11, CNT12, CNT21, and CNT22, voltage sensors VS1 and VS2, current sensors IS1 and IS2, and a motor 10. In this embodiment, the auxiliary load EL is the control circuit 20. The differences from the first embodiment will be described below.

[0069] Inverters INV1 and INV2 convert DC current to AC current to drive the motor 10. In this embodiment, inverters INV1 and INV2 convert DC current to three-phase AC current. Inverters INV1 and INV2 may also convert DC current to single-phase AC current or multi-phase AC current with four or more phases. Inverters INV1 and INV2 are examples of DC-AC conversion circuits.

[0070] Furthermore, in this embodiment, inverters INV1 and INV2 are voltage-type inverters. The smoothing capacitors C1 and C2 are provided across the high-potential DC terminals Pinv1 and Pinv2 and the low-potential DC terminals Ninv1 and Ninv2 of inverters INV1 and INV2, respectively. By providing the smoothing capacitors C1 and C2, the input voltage of inverters INV1 and INV2, which are voltage-type inverters, can be stabilized. Note that inverters INV1 and INV2 may also be current-type inverters.

[0071] Furthermore, inverters INV1 and INV2 are the main loads of the power converter 1, respectively. In this embodiment, inverter INV1 is the first main load, and inverter INV2 is the second main load.

[0072] The anodes of diodes D11 and D12 in the first diode group of power converter 1 are connected to the high-potential DC terminals Pinv1 and Pinv2 of inverters INV1 and INV2, respectively. More specifically, as shown in Figure 6, the anode of diode D11 is connected to the high-potential DC terminal Pinv1 of inverter INV1. The anode of diode D12 is connected to the high-potential DC terminal Pinv2 of inverter INV2.

[0073] Furthermore, the cathodes of diodes D21 and D22 in the second diode group of power converter 1 are connected to the DC terminals Ninv1 and Ninv2 on the low-potential side of inverters INV1 and INV2, respectively. More specifically, as shown in Figure 6, the cathode of diode D21 is connected to the DC terminal Ninv1 on the low-potential side of inverter INV1. The cathode of diode D22 is connected to the DC terminal Ninv2 on the low-potential side of inverter INV2.

[0074] Two power systems are formed when the power converter 1 is connected to inverters INV1 and INV2. Specifically, the first power system is formed by the diode rectifier DR1, DC reactor L1, smoothing capacitor C1, inverter INV1, and the wiring between them, and the second power system is formed by the diode rectifier DR2, DC reactor L2, smoothing capacitor C2, inverter INV2, and the wiring between them.

[0075] In this embodiment, the motor 10 is driven by a three-phase alternating current. The motor 10 is a two-winding motor having a first winding and a second winding. The first and second windings are electrically insulated from each other. The motor 10 may also be driven by a single-phase alternating current or a multi-phase alternating current of four or more phases. Furthermore, if the power converter 1 is equipped with three or more diode rectifiers, the motor 10 may be a multi-winding motor having three or more windings.

[0076] The first winding of motor 10 is connected to the AC terminal Ainov1 of inverter INV1 via contactor CNT21 and is driven by the AC current generated by inverter INV1. The second winding of motor 10 is connected to the AC terminal Ainov2 of inverter INV2 via contactor CNT22 and is driven by the AC current generated by inverter INV2. In other words, the AC current output from the AC power supply PS is converted to DC current by diode rectifiers DR1 and DR2, respectively, and these DC currents are converted to AC current by inverters INV1 and INV2, respectively, and these AC currents drive each winding of motor 10.

[0077] Voltage sensor VS1 detects the voltage across smoothing capacitor C1. Voltage sensor VS2 detects the voltage across smoothing capacitor C2.

[0078] Current sensor IS1 detects the current flowing through the first winding of motor 10. Current sensor IS2 detects the current flowing through the second winding of motor 10.

[0079] The control circuit 20 controls inverters INV1 and INV2. As shown in Figure 6, the control circuit 20 receives voltage detection signals from voltage sensors VS1 and VS2, and current detection signals from current sensors IS1 and IS2, respectively. Based on the voltage values ​​of smoothing capacitors C1 and C2 detected by voltage sensors VS1 and VS2, and the current values ​​flowing through the first and second windings of motor 10 detected by current sensors IS1 and IS2, respectively, the control circuit 20 performs calculations, for example, for vector control and generates a control signal. The generated control signal is output to inverters INV1 and INV2 to control them.

[0080] The control circuit 20 may also be a control power supply circuit. In this case, the control power supply circuit may be an isolated type or a non-isolated type. Furthermore, the control circuit 20 may be redundant. That is, multiple control circuits 20 may be provided and configured so that if one fails, the other will compensate for it.

[0081] Furthermore, the control circuit 20 may accept, in addition to or instead of, the values ​​of the voltage sensors VS1, VS2 and current sensors IS1, IS2 as inputs to the control circuit 20. For example, the values ​​of the sensors that detect the voltage of each winding of the motor 10, or the values ​​of the sensors that detect the output voltage or output current of the AC power supply PS, may be accepted as inputs to the control circuit 20 in addition to the values ​​of the voltage sensors VS1, VS2 and current sensors IS1, IS2.

[0082] Contactors CNT11, CNT12, CNT21, and CNT22 electrically disconnect a power system in the event of a fault in that system. Each of the contactors CNT11, CNT12, CNT21, and CNT22 is an example of a disconnection circuit, such as a relay or a semiconductor switch. A circuit breaker may be installed instead of contactor CNT11. The same applies to contactors CNT12, CNT21, and CNT22.

[0083] The contactor CNT11 is installed between the AC power supply PS and the diode rectifier DR1. If a fault occurs anywhere in the first power system, the contactor CNT11 disconnects the first power system from the AC power supply PS. In other words, if a fault occurs at any point in the diode rectifier DR1, DC reactor L1, smoothing capacitor C1, inverter INV1, or the wiring between them, the first power system will be disconnected.

[0084] The contactor CNT12 is installed between the AC power supply PS and the diode rectifier DR2. If a fault occurs at any point in the second power system, the contactor CNT12 will disconnect the second power system from the AC power supply PS. In other words, if a fault occurs at any point in the diode rectifier DR2, DC reactor L2, smoothing capacitor C2, inverter INV2, or the wiring between them that constitute the second power system, the contactor CNT12 will disconnect the second power system.

[0085] The contactor CNT21 is installed between the inverter INV1 and the first winding of the motor 10. If a fault occurs anywhere in the first power system, the contactor CNT21 disconnects the first power system from the first winding of the motor 10.

[0086] The contactor CNT22 is installed between the inverter INV2 and the second winding of the motor 10. If a fault occurs anywhere in the second power system, the contactor CNT22 disconnects the second power system from the second winding of the motor 10.

[0087] In this embodiment, if a fault occurs in any part of the first power system, contactors CNT11 and CNT21 simultaneously disconnect the first power system from the AC power supply PS and the first winding of the motor 10. However, it is also possible to disconnect only one of contactors CNT11 or CNT21. Similarly, in this embodiment, if a fault occurs in any part of the second power system, contactors CNT12 and CNT22 simultaneously disconnect the second power system from the AC power supply PS and the second winding of the motor 10. However, it is also possible to disconnect only one of contactors CNT12 or CNT22.

[0088] In this embodiment, contactors CNT11, CNT12, CNT21, and CNT22 are each controlled by the control circuit 20. At least one of the contactors CNT11, CNT12, CNT21, and CNT22 may be controlled by a control circuit other than the control circuit 20 (not shown).

[0089] Furthermore, in this embodiment, the control circuit 20 detects faults in the first and second power systems based on the values ​​of the voltage sensors VS1 and VS2 and the current sensors IS1 and IS2. However, it may also detect faults by additionally using values ​​input from other sensors.

[0090] As described above, the power converter 1 according to the fourth embodiment makes it possible to configure a drive system for the motor 10 in which the generation of circulating current is suppressed. Furthermore, even if a failure occurs in a power system, the motor can continue to operate in a healthy successor state by disconnecting the power system using contactors CNT11, CNT12, CNT21, and CNT22.

[0091] Furthermore, as mentioned above, the control circuit 20 can be replaced with a control power supply circuit. When using the power converter 1 connected to the control power supply circuit instead of a conventional power converter, the actual increase in cost is only about the cost of diodes D11, D12, D21, and D22. Therefore, a power converter with suppressed circulating current can be provided at a low cost.

[0092] In addition, the power conversion device 1 according to this embodiment may include PWM converters CNV1 and CNV2 instead of diode rectifiers DR1 and DR2. In this case, the control circuit 20 may control the PWM converters CNV1 and CNV2 in addition to the inverters INV1 and INV2 and contactors CNT11, CNT12, CNT21, and CNT22.

[0093] Furthermore, although the power converter 1 according to this embodiment includes two diode rectifiers DR1 and DR2, it may also include N diode rectifiers DR1, DR2, ..., DRN, as in the third embodiment described above. In this case, the power converter 1 may include N inverters, each with a high-potential DC terminal connected to the anode of each diode D11, D12, ..., D1N of the first diode group, and a low-potential DC terminal connected to the cathode of each diode D21, D22, ..., D2N of the second diode group. In this case, the control circuit 20 may control these N inverters.

[0094] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0095] 1. Power converter 10 motors 20 Control circuits AL1, AL2 AC reactor C1, C2, CN Smoothing Capacitors CNV1, CNV2 PWM converter D11, D12, D1N, D21, D22, D2N diodes DR1, DR2, DRN Diode Rectifiers EL auxiliary load GC1, GC2 Ground Capacitors GND1,GND2,GND3 Grounding position INV1, INV2 Inverter IS1, IS2 current sensors L1, L2, LN DC reactor VS1, VS2 Voltage Sensors

Claims

1. N AC-DC conversion circuits (where N is an integer of 2 or more) have their AC terminals connected in parallel to an AC power source and convert the AC current output from the AC power source into DC current, A first diode group having N diodes, wherein the anode of each diode in the first diode group is connected to the high-potential DC terminal of the N AC-DC conversion circuits, and the cathode of each diode in the first diode group is connected in parallel to the high-potential terminal of an auxiliary load, A second diode group having N diodes, wherein the cathode of each diode in the second diode group is connected to the DC terminal on the low-potential side of the N AC-DC conversion circuits, and the anode of each diode in the second diode group is connected in parallel to the low-potential terminal of the auxiliary load, A capacitive circuit having one end connected to the cathode of each diode in the first diode group and the other end connected to the anode of each diode in the second diode group, In addition to being equipped, The capacitive circuit is, A first ground capacitor, with one end connected to the cathode of each diode in the first group of diodes and the other end grounded, A second ground capacitor, with one end connected to the anode of each diode in the second group of diodes and the other end grounded, A power conversion device equipped with the following features.

2. N AC-DC conversion circuits (where N is an integer of 2 or more) whose AC terminals are connected in parallel to an AC power source, and which convert the AC current output from the AC power source into DC current, A first diode group having N diodes, wherein the anode of each diode in the first diode group is connected to the high-potential DC terminal of the N AC-DC conversion circuits, and the cathode of each diode in the first diode group is connected in parallel to the high-potential terminal of an auxiliary load, A second diode group having N diodes, wherein the cathode of each diode in the second diode group is connected to the DC terminal on the low-potential side of the N AC-DC conversion circuits, and the anode of each diode in the second diode group is connected in parallel to the low-potential terminal of the auxiliary load, In addition to being equipped, The anode of each diode in the first diode group is connected to the high-potential DC terminal of N DC-to-AC converter circuits that convert DC current to AC current. The cathode of each diode in the second diode group is connected to the DC terminal on the low-potential side of the N DC-AC conversion circuits, The auxiliary load is a power conversion device, which is a control circuit that controls the N DC-AC conversion circuits.

3. The power conversion device according to claim 1 or claim 2, wherein the cathode of each diode in the first diode group, or the anode of each diode in the second diode group, is grounded.

4. The power conversion device according to claim 2, further comprising a capacitive circuit, one end of which is connected to the cathode of each diode of the first diode group and the other end of which is connected to the anode of each diode of the second diode group.

5. The N DC-AC conversion circuits are voltage-type inverters. The power conversion device according to claim 1, claim 2, or claim 4, further comprising N smoothing capacitors provided across the high-potential DC end and the low-potential DC end of each DC-AC conversion circuit.

6. The power conversion device according to claim 1, claim 2, or claim 4, wherein the N AC-DC conversion circuits are diode rectifiers or PWM converters.

7. The power conversion device according to claim 1, claim 2, or claim 4, wherein the DC terminal on the high-potential side of each AC-DC conversion circuit and the anode of each diode in the first diode group, and the DC terminal on the low-potential side of each AC-DC conversion circuit and the cathode of each diode in the second diode group are not grounded.

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