voltage regulator

Abstract

To provide a voltage regulator capable of switching the connection destination of a terminal of a primary winding in a short period of time.SOLUTION: In a voltage regulator 1, multiple secondary windings 32 in multiple series transformers 3u and 3v are arranged in the middle of multiple distribution lines U and V, respectively. Using multiple switch circuits, a switching unit 5 switches a tap, among multiple taps T1, T2, and T3 connected to a single winding 40, to be electrically connected to each of multiple specific terminals in terminals of multiple primary windings 31 of the multiple series transformers 3u and 3v. In the switch circuit, a second semiconductor switch is connected in series to a first semiconductor switch. A first diode and a second diode are connected between both ends of the first semiconductor switch and the second semiconductor switch, respectively. The cathodes or anodes of the first diode and the second diode are connected to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a voltage regulator. [Background technology]

[0002] Patent Document 1 discloses a configuration for adjusting the effective value of the AC voltage between two distribution lines. In this configuration, a tap winding to which multiple taps are connected is connected between the two distribution lines. The effective value of the AC voltage between two of the multiple taps is adjusted according to the effective value of the AC voltage between the two distribution lines. Two transformers, each having a primary winding and a secondary winding, are arranged. Each of the two secondary windings is arranged midway between the two distribution lines.

[0003] Each terminal of the two primary windings is electrically connected to one of multiple taps. Therefore, the AC voltage between the two taps is applied to both ends of each of the two primary windings. As a result, the two secondary windings increase or decrease the effective value of the AC voltage between the two input distribution lines, and output the AC voltage with the increased or decreased effective value via the two output distribution lines. A switch switches the connection destination of each of two specific terminals of the two primary windings. The increase or decrease in the effective value depends on the two AC voltages applied to the two primary windings. The increase or decrease in the effective value depends on the two AC voltages applied to the two primary windings. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-187374 Summary of the Invention [Problem to be solved by the invention]

[0005] Regarding Patent Document 1, when the period from when the switching of the connection destination of a specific terminal starts to when the switching is completed is taken into consideration, it is preferable that the period required for the switching of the connection destination be short.

[0006] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a voltage regulator that can switch the connection destination of a specific terminal in a short period of time. [Means for solving the problem]

[0007] A voltage adjustment device according to one aspect of the present disclosure is a voltage adjustment device that adjusts an effective value of an AC voltage, and includes one or more tap windings to which multiple taps are connected, multiple transformers having primary and secondary windings, and a switch that switches taps electrically connected to multiple specific terminals of multiple primary windings of the multiple transformers among the multiple taps connected to the one or more tap windings, wherein the effective value of the AC voltage between two of the multiple taps connected to the tap winding is adjusted according to the effective value of the AC voltage between two distribution lines among multiple distribution lines, and the multiple taps Each of the multiple secondary windings of the multiple transformers is arranged midway along the multiple distribution lines, and the switch has multiple switch circuits that switch between a conducting state in which current can flow and a blocking state in which current flow is blocked, and each switch circuit has a first semiconductor switch, a second semiconductor switch connected in series with the first semiconductor switch, a first diode connected across both ends of the first semiconductor switch, and a second diode connected across both ends of the second semiconductor switch, and the cathodes or anodes of the first diode and the second diode are connected to each other.

[0008] In the above embodiment, the state of the switch circuit is switched to a conducting state by switching on the first semiconductor switch and the second semiconductor switch. The state of the switch circuit is switched to a blocking state by switching off the first semiconductor switch and the second semiconductor switch. Therefore, compared to when multiple mechanical relays are used to switch the connection destination of a specific terminal, the switch can switch the connection destination of the specific terminal in a short period of time.

[0009] In a voltage regulator according to one embodiment of the present disclosure, the switch has a resistor, and the multiple switch circuits include multiple tap switch circuits connected to each of multiple taps connected to the one or more tap windings, and a series switch circuit connected in series to the resistor, and at least two of the multiple tap switch circuits are connected to each of the multiple specific terminals, and a series circuit including the resistor and the series switch circuit is connected between two of the multiple specific terminals.

[0010] In the above embodiment, for example, after the state of the series switch circuit is switched to a conducting state, the state of one tap switch circuit connected to the specific terminal is switched to a blocking state. After the state of the other tap switch circuit connected to the specific terminal is switched to a conducting state, the state of the series switch circuit is switched to a blocking state. In this way, the connection destination of the two specific terminals connected to the series circuit is switched without interrupting the connection between them.

[0011] In a voltage adjustment device according to one embodiment of the present disclosure, the switch includes a determination unit that determines whether the gradient of the AC voltage between two taps connected to one tap winding is 0 degrees, and a switching circuit that switches the states of the plurality of switch circuits to the conductive state or the cut-off state, and the switching circuit switches the state of the series switch circuit from the cut-off state to the conductive state when the determination unit determines that the gradient is 0 degrees.

[0012] In the above embodiment, the primary winding and secondary winding of the transformer are wound around a core. The core is made of a magnetic material. When two taps connected to one tap winding are connected to two terminals of the primary winding, respectively, and the gradient of the AC voltage between the two taps is 0 degrees, the residual magnetic flux remaining in the core of the transformer is 0 [Wb]. The switching circuit switches the state of the series switch circuit to a conducting state at the timing when the gradient of the AC voltage is 0 degrees. Therefore, when the switching circuit switches the state of the series switch circuit to a cut-off state, the magnetic flux in the core is unlikely to exceed the saturation magnetic flux. As a result, there is little possibility that an excessive current will flow through the primary winding.

[0013] In a voltage regulator according to one embodiment of the present disclosure, the first semiconductor switch and the second semiconductor switch are IGBTs (Insulated Gate Bipolar Transistors), the emitters or collectors of the first semiconductor switch and the second semiconductor switch are connected to each other, and the cathodes of the first diode and the second diode are connected to the collectors of the first semiconductor switch and the second semiconductor switch.

[0014] In the above aspect, the first semiconductor switch and the second semiconductor switch are IGBTs. When an IGBT is in the on state, current can flow from the collector to the emitter. However, current does not flow from the emitter to the collector. The collectors or emitters of the first semiconductor switch and the second semiconductor switch are connected to each other, and a first diode and a second diode are connected between both ends of the first semiconductor switch and the second semiconductor switch, respectively. Therefore, when the first semiconductor switch and the second semiconductor switch are on, an AC current flows through the switch circuit.

[0015] In a voltage adjustment device according to one embodiment of the present disclosure, the first semiconductor switch and the second semiconductor switch are MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), the sources or drains of the first semiconductor switch and the second semiconductor switch are connected to each other, the first diode is a parasitic diode of the first semiconductor switch, and the second diode is a parasitic diode of the second semiconductor switch.

[0016] In the above aspect, the first semiconductor switch and the second semiconductor switch are MOSFETs. When a MOSFET is in the on state, current flows bidirectionally through the drain and the source. A parasitic diode is connected between both ends of each of the first semiconductor switch and the second semiconductor switch. Therefore, even when the first semiconductor switch is off, current can flow through the first diode. Even when the second semiconductor switch is off, current can flow through the second diode. The cathodes or anodes of the first diode and the second diode are connected to each other. Therefore, when the first semiconductor switch and the second semiconductor switch are off, no current flows through the first diode or the second diode. [Effects of the Invention]

[0017] According to the above aspect, the connection destination of the specific terminal can be switched in a short period of time. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a circuit diagram of a voltage regulator according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing the main configuration of a switch; [Figure 3] FIG. 10 is an explanatory diagram of a decrease in the effective value of an AC voltage. [Figure 4] 1 is a diagram showing the operation of two series transformers. [Figure 5] FIG. 3 is a circuit diagram of a first switch circuit. [Figure 6] 10 is a timing chart showing the outputs of an output transformer, a differentiating circuit, and a detection circuit. [Figure 7] 10 is a flowchart showing a procedure of a switching process. [Figure 8] FIG. 10 is a circuit diagram of a voltage regulator according to a second embodiment. [Figure 9] FIG. 2 is a block diagram showing the main configuration of a switch; [Figure 10] FIG. 10 is a circuit diagram of a voltage adjusting device according to a third embodiment. [Figure 11] FIG. 2 is a block diagram showing the main configuration of a switch; DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below with reference to the drawings showing embodiments thereof. (Embodiment 1) FIG. 1 is a circuit diagram of a voltage regulator 1 according to a first embodiment. An AC power source 2 is connected between two distribution lines U and V. The AC power source 2 is, for example, a substation. The AC power source 2 outputs an AC voltage to the voltage regulator 1 via the two distribution lines U and V. The voltage regulator 1 outputs the AC voltage via the two distribution lines U and V and a neutral line Q. The voltage regulator 1 adjusts the effective value of the AC voltage between the output distribution lines U and V according to the effective value of the AC voltage between the input distribution lines U and V. The effective value of the AC voltage between the distribution line U and the neutral line Q and the effective value of the AC voltage between the distribution line V and the neutral line Q are half of the effective value of the AC voltage between the output distribution lines U and V.

[0020] The voltage regulator 1 includes two series transformers 3u and 3v, a regulating transformer 4, a switch 5, and a measurement transformer 6. Each of the series transformers 3u and 3v includes an annular core 30, a primary winding 31, and a secondary winding 32. The core 30 is made of a magnetic material. The primary winding 31 and the secondary winding 32 are wound around the core 30. The regulating transformer 4 includes an auto-winding 40. The auto-winding 40 is wound around a core (not shown). Three taps T1, T2, and T3 are connected to the auto-winding 40. The tap T1 and T3 are connected to two terminals of the auto-winding 40, respectively. The tap T2 and one terminal of the neutral conductor Q are connected midway through the auto-winding 40. The measurement transformer 6 includes a primary winding 61 and a secondary winding 62. The primary winding 61 and the secondary winding 62 are wound around a common core.

[0021] The secondary windings 32 of the series transformers 3u and 3v are arranged midway through the respective distribution lines U and V. One terminal of the secondary winding 32 of each of the series transformers 3u and 3v is connected to the input distribution lines U and V. The other terminal of the secondary winding 32 of each of the series transformers 3u and 3v is connected to the output distribution lines U and V. An auto-winding 40 is connected between the output distribution lines U and V. Taps T1 and T3 are located on the distribution line U and V side, respectively. A switch 5 is connected to the three taps T1, T2, and T3. For the auto-winding 40, the number of turns from one terminal to the neutral conductor Q is the same as the number of turns from the other terminal to the neutral conductor Q.

[0022] The first and second terminals of the primary winding 31 of the series transformer 3u are connected to the first and second terminals of the primary winding 31 of the series transformer 3v, respectively. Hereinafter, the connection node between the two first terminals will be referred to as the first node. The connection node between the two second terminals will be referred to as the second node. The switch 5 is further connected to the first and second nodes. In FIG. 1, the first and second nodes are located on the right and left sides, respectively. The primary winding 61 of the measurement transformer 6 is connected between the output distribution lines U and V. The two terminals of the secondary winding 62 are connected to the switch 5.

[0023] The first and second nodes are each electrically connected to one of three taps T1, T2, and T3. The first and second terminals of the primary winding 31 function as specific terminals. The selector 5 switches the tap among the three taps T1, T2, and T3 to which the first and second nodes are electrically connected, i.e., the connection destination of each of the first and second nodes. The effective value of the AC voltage between two of the three taps T1, T2, and T3 is adjusted according to the effective value of the AC voltage between the output distribution lines U and V. When the first and second nodes are each connected to two different taps, the AC voltage between the two connected taps is applied to both ends of the primary winding 31 of each of the series transformers 3u and 3v. The auto-winding 40 functions as a tap winding.

[0024] The effective value of the AC voltage between the two taps of the single winding 40 is expressed as the product of the effective value of the AC voltage between the output distribution lines U and V and the turns ratio of the single winding 40. The turns ratio of the single winding 40 is (number of turns between the two taps) / (number of turns of the single winding 40). The greater the number of turns between the two taps, the greater the effective value of the AC voltage between the two taps.

[0025] The secondary winding 32 of the series transformers 3u, 3v adjusts the effective value of the AC voltage between the output distribution lines U, V according to the effective value of the AC voltage between the input distribution lines U, V and the AC voltage output from the two taps of the single winding 40. The AC voltage output from the single winding 40 varies depending on the connection destination of the first node and the second node. If the connection destination of the first node and the second node is the same, the single winding 40 does not output AC voltage from the two taps.

[0026] The AC voltage between the output distribution lines U and V is applied to both ends of the primary winding 61 of the measurement transformer 6. The secondary winding 62 outputs the AC voltage to the switch 5. The effective value of the AC voltage output by the secondary winding 62 is expressed as the product of the effective value of the AC voltage between the output distribution lines U and V and the turns ratio of the primary winding 61 and the secondary winding 62. The turns ratio is (number of turns of the secondary winding 62) / (number of turns of the primary winding 61). The turns ratio is a constant value. Therefore, the effective value of the AC voltage output by the secondary winding 62 indicates the effective value of the AC voltage between the output distribution lines U and V.

[0027] The switch 5 switches the connection destination of each of the first and second nodes according to the effective value of the AC voltage between the output-side distribution lines U and V. This adjusts the effective value of the AC voltage between the output-side distribution lines U and V to a value within a predetermined tolerance range. Note that the effective value of the AC voltage input from the AC power source 2 to the voltage adjustment device 1 fluctuates. In this case, the effective value of the AC voltage between the output-side distribution lines U and V also fluctuates. For this reason, it is necessary to adjust the effective value of the AC voltage between the output-side distribution lines U and V.

[0028] FIG. 2 is a block diagram showing the main configuration of the switch 5. The switch 5 includes an assembly 50, a series switch circuit 51, and a resistor 52. The assembly 50 includes three first switch circuits A1, A2, and A3 and three second switch circuits B1, B2, and B3. Hereinafter, any integer from 1, 2, and 3 will be referred to as i. The integer i may be any of 1, 2, and 3. The first switch circuit Ai and the second switch circuit Bi are each connected to a tap Ti and function as a tap switch circuit.

[0029] Each of the three first switch circuits A1, A2, and A3 is further connected to a first node. Each of the three second switch circuits B1, B2, and B3 is further connected to a second node. The series switch circuit 51 is connected in series with a resistor 52. The series circuit including the series switch circuit 51 and the resistor 52 is connected between the first node and the second node.

[0030] The switch 5 further includes a control unit 53 and a switching circuit 54. The control unit 53 is connected to the switching circuit 54. The series switch circuit 51, the first switch circuit Ai, and the second switch circuit Bi each have a conducting state in which current can flow, and a blocking state in which current flow is blocked. The control unit 53 instructs the switching circuit 54 to switch the states of the series switch circuit 51, the first switch circuits A1, A2, A3, and the second switch circuits B1, B2, B3 to either the conducting state or the blocking state.

[0031] Among the series switch circuit 51, the first switch circuits A1, A2, A3, and the second switch circuits B1, B2, B3, when only the first switch circuit A1 and the second switch circuit B3 are in a conducting state, the secondary windings 32 of the two series transformers 3u, 3v increase the effective value of the AC voltage between the output distribution lines U and V to a value higher than the effective value of the AC voltage between the input distribution lines U and V.

[0032] The voltage of the distribution line U, whose reference potential is the potential of the distribution line V, is denoted as Vs. In FIG. 2, the dashed arrow indicates the direction of current flow when the polarity of the voltage Vs is positive and only the first switch circuit A1 and the second switch circuit B3 are conducting. The current flows through the tap T1, the first switch circuit A1, and the first node in this order. In each of the two primary windings 31, the current flows through the first node and the second node in this order. The current flows through the second node, the second switch circuit B3, and the tap T3 in this order.

[0033] In each of the series transformers 3u and 3v, when a current flows through the primary winding 31, an induced electromotive force is generated in the secondary winding 32. Since a common AC voltage is applied to both ends of each of the two primary windings 31, the voltages of the two induced electromotive forces are the same. Figure 2 shows the polarities of the voltages of the two induced electromotive forces. The absolute value of the voltage of the induced electromotive force is denoted as ΔV.

[0034] When current flows from the first node to the second node in the primary winding 31 of the series transformer 3u, the secondary winding 32 adjusts the potential of the output distribution line U to a potential ΔV higher than the potential of the input distribution line U. When current flows from the first node to the second node in the primary winding 31 of the series transformer 3v, the secondary winding 32 adjusts the potential of the output distribution line V to a potential ΔV lower than the potential of the input distribution line U. Therefore, when the polarity of the voltage Vs is positive, the voltage between the output distribution lines U and V is adjusted to (Vs + (2 ΔV)), which is higher than the voltage Vs. "·" represents a product.

[0035] When only the first switch circuit A1 and the second switch circuit B3 are in the conducting state and the polarity of the voltage Vs is negative, the direction of the current shown in FIG. 2 is reversed. The polarities of the voltages of the two induced electromotive forces are also reversed. The current flows in the order of tap T3, second switch circuit B3, and the second node. In each of the two primary windings 31, the current flows in the order of the second node and the first node. The current flows in the order of the first node, first switch circuit A1, and tap T1.

[0036] In the primary winding 31 of the series transformer 3u, when a current flows from the second node to the first node, the secondary winding 32 adjusts the potential of the output-side distribution line U to a potential ΔV lower than the potential of the input-side distribution line U. In the primary winding 31 of the series transformer 3v, when a current flows from the second node to the first node, the secondary winding 32 adjusts the potential of the output-side distribution line V to a potential ΔV higher than the potential of the input-side distribution line U. Therefore, when the polarity of the voltage Vs is negative, the voltage between the output-side distribution lines U and V is adjusted to (Vs - (2 ΔV)), which is lower than the voltage Vs.

[0037] From the above, when only the first switch circuit A1 and the second switch circuit B3 are in the conducting state, the effective value (amplitude) of the AC voltage between the output distribution lines U and V is adjusted to a value higher than the effective value (amplitude) of the AC voltage between the input distribution lines U and V.

[0038] Among the series switch circuit 51, the first switch circuits A1, A2, A3, and the second switch circuits B1, B2, B3, when only the first switch circuit A3 and the second switch circuit B1 are in a conducting state, the secondary windings 32 of the two series transformers 3u, 3v reduce the effective value of the AC voltage between the output distribution lines U and V to a value lower than the effective value of the AC voltage between the input distribution lines U and V.

[0039] FIG. 3 is an explanatory diagram of a decrease in the effective value of an AC voltage. In FIG. 3, the dashed arrow indicates the direction of current flow when the polarity of the voltage Vs is positive when only the first switch circuit A3 and the second switch circuit B1 are in the conductive state. The polarities of the voltages of the two induced electromotive forces are also shown. When only the first switch circuit A3 and the second switch circuit B1 are in the conductive state, the current flows in the order of tap T1, second switch circuit B1, and the second node. In each of the two primary windings 31, the current flows in the order of the second node and the first node. The current flows in the order of the first node, first switch circuit A3, and tap T3.

[0040] In each of the two primary windings 31, a current flows from the first node to the second node. Therefore, when the polarity of the voltage Vs is positive, the two secondary windings 32 adjust the voltage between the output distribution lines U and V to (Vs - (2 ΔV)). The voltage between the output distribution lines U and V is lower than the voltage Vs.

[0041] When only the first switch circuit A3 and the second switch circuit B1 are in the conducting state and the polarity of the voltage Vs is negative, the direction of the current shown in FIG. 2 is reversed. The polarities of the voltages of the two induced electromotive forces are also reversed. The current flows in the order of tap T3, first switch circuit A3, and first node. In each of the two primary windings 31, the current flows in the order of the first node and second node. The current flows in the order of the second node, second switch circuit B1, and tap T1.

[0042] In each of the two primary windings 31, a current flows from the second node to the first node. Therefore, when the polarity of the voltage Vs is negative, the two secondary windings 32 regulate the voltage between the output distribution lines U and V to (Vs + (2·ΔV)). The voltage between the output distribution lines U and V is higher than the voltage Vs.

[0043] From the above, when only the first switch circuit A3 and the second switch circuit B1 are in the conducting state, the effective value of the AC voltage between the output distribution lines U and V is adjusted to a value lower than the effective value of the AC voltage between the input distribution lines U and V.

[0044] Fig. 4 is a diagram showing the operation of the two series transformers 3u and 3v. Fig. 4 shows the relationship between the combination of the first switch circuit and the second switch circuit in the conducting state and the operation of the two secondary windings 32 of the two series transformers 3u and 3v. As described above, when only the first switch circuit A1 and the second switch circuit B3 are in the conducting state, the two secondary windings 32 increase the effective value of the AC voltage between the input distribution lines U and V.

[0045] When only the first switch circuit A2 and the second switch circuit B3 are in the conducting state, or when only the first switch circuit A1 and the second switch circuit B2 are in the conducting state, the direction of the current is the same as the direction of the current when only the first switch circuit A1 and the second switch circuit B3 are in the conducting state. Therefore, the two secondary windings 32 increase the effective value of the AC voltage between the input distribution lines U and V.

[0046] The increase in the effective value is greater as the effective value of the AC voltage applied to both ends of each of the two primary windings 31 is greater. For the single winding 40, the number of turns between taps T1 and T3 is greater than the number of turns between taps T2 and T3. Therefore, the effective value of the AC voltage between taps T1 and T3 is greater than the effective value of the AC voltage between taps T2 and T3. For the single winding 40, the number of turns between taps T2 and T3 is greater than the number of turns between taps T1 and T2. Therefore, the effective value of the AC voltage between taps T2 and T3 is greater than the effective value of the AC voltage between taps T1 and T2.

[0047] When only the first switch circuit Ai and the second switch circuit Bi are in the conducting state, the first node and the second node are connected to the same node. Therefore, the single winding 40 does not output an AC voltage to the two primary windings 31. The effective value of the AC voltage between the output distribution lines U and V is substantially the same as the effective value of the AC voltage between the input distribution lines U and V. The integer i is any integer between 1, 2, and 3.

[0048] As described above, when only the first switch circuit A3 and the second switch circuit B1 are in the conducting state, the two secondary windings 32 reduce the effective value of the AC voltage between the input-side distribution lines U and V. When only the first switch circuit A3 and the second switch circuit B2 are in the conducting state, or when only the first switch circuit A2 and the second switch circuit B1 are in the conducting state, the direction of the current is the same as the direction of the current when only the first switch circuit A3 and the second switch circuit B1 are in the conducting state. Therefore, the two secondary windings 32 reduce the effective value of the AC voltage between the input-side distribution lines U and V.

[0049] The extent of the drop in the effective value of the AC voltage between the output distribution lines U and V increases as the effective values of the AC voltages applied to both ends of the two primary windings 31 increase. As described above, the effective value of the AC voltage between taps T1 and T3 is greater than the effective value of the AC voltage between taps T2 and T3. The effective value of the AC voltage between taps T2 and T3 is greater than the effective value of the AC voltage between taps T1 and T2.

[0050] As shown in FIG. 2, two terminals of the secondary winding 62 of the measurement transformer 6 are connected to the control unit 53 of the switch 5. As described above, the effective value of the AC voltage output from the secondary winding 62 represents the effective value of the AC voltage between the output distribution lines U and V. The control unit 53 switches the switch circuits that are in a conducting state among the first switch circuits A1, A2, A3 and the second switch circuits B1, B2, B3, depending on the effective value of the AC voltage between the output distribution lines U and V. By performing this switching, the control unit 53 adjusts the effective value of the AC voltage between the output distribution lines U and V to a value within a predetermined allowable range.

[0051] FIG. 5 is a circuit diagram of the first switch circuit A1. The configurations of the series switch circuit 51, the first switch circuits A2 and A3, and the second switch circuits B1, B2, and B3 are similar to those of the first switch circuit A1. Therefore, a description of these configurations will be omitted. The first switch circuit A1 has a first semiconductor switch G1, a second semiconductor switch G2, a first diode D1, and a second diode D2. FIG. 5 shows four examples of the first switch circuit A1. The first semiconductor switch G1 and the second semiconductor switch G2 are the same type. The second semiconductor switch G2 is connected in series with the first semiconductor switch G1.

[0052] In a first example of the first switch circuit A1, the first semiconductor switch G1 and the second semiconductor switch G2 are IGBTs (Insulated Gate Bipolar Transistors). The emitter of the first semiconductor switch G1 is connected to the emitter of the second semiconductor switch G2. The cathode and anode of the first diode D1 are connected to the collector and emitter of the first semiconductor switch G1, respectively. The cathode and anode of the second diode D2 are connected to the collector and emitter of the second semiconductor switch G2, respectively. Therefore, the anode of the first diode D1 is connected to the anode of the second diode D2. The gates of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the switching circuit 54. The collectors of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the first node and the tap T1, respectively.

[0053] The switching circuit 54 switches the first semiconductor switch G1 and the second semiconductor switch G2 on or off by adjusting the voltages of the two gates, the reference potential of which is ground potential. When the switching circuit 54 increases the voltages of the two gates, the first semiconductor switch G1 and the second semiconductor switch G2 are switched on. When the first semiconductor switch G1 and the second semiconductor switch G2 are in the on state, current can flow from the collector to the emitter in that order. In the first semiconductor switch G1 and the second semiconductor switch G2, current does not flow from the emitter to the collector in that order.

[0054] When the first semiconductor switch G1 and the second semiconductor switch G2 are on, the first switch circuit A1 is in a conducting state. A current input to the collector of the first semiconductor switch G1 flows through the first semiconductor switch G1 and the second diode D2 in this order, as indicated by the solid arrow. A current input to the collector of the second semiconductor switch G2 flows through the second semiconductor switch G2 and the first diode D1 in this order, as indicated by the dashed arrow. An AC current flows through the first switch circuit A1.

[0055] When the switching circuit 54 reduces the voltages of the two gates, the first semiconductor switch G1 and the second semiconductor switch G2 are switched off. When the first semiconductor switch G1 and the second semiconductor switch G2 are in the off state, no current flows through the collector and the emitter. When the first semiconductor switch G1 and the second semiconductor switch G2 are in the off state, the state of the first switch circuit A1 is the cutoff state. No current flows through the collectors of the first semiconductor switch G1 and the second semiconductor switch G2.

[0056] In the second example of the first switch circuit A1, the first semiconductor switch G1 and the second semiconductor switch G2 are IGBTs. The collector of the first semiconductor switch G1 is connected to the collector of the second semiconductor switch G2. The first diode D1 and the second diode D2 are connected in the same manner as in the first example. Therefore, the cathode of the first diode D1 is connected to the cathode of the second diode D2. The gates of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the switching circuit 54. The emitters of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the tap T1 and the first node, respectively.

[0057] When the switching circuit 54 switches on the first semiconductor switch G1 and the second semiconductor switch G2, the state of the first switch circuit A1 switches to the conducting state. The current input to the emitter of the second semiconductor switch G2 flows in this order through the second diode D2 and the first semiconductor switch G1, as indicated by the solid arrow. The current input to the emitter of the first semiconductor switch G1 flows in this order through the first diode D1 and the second semiconductor switch G2, as indicated by the dashed arrow. The AC current flows via the first switch circuit A1.

[0058] When the switching circuit 54 switches the first semiconductor switch G1 and the second semiconductor switch G2 off, the state of the first switch circuit A1 switches to the cut-off state, and no current flows through the emitters of the first semiconductor switch G1 and the second semiconductor switch G2.

[0059] In the third example of the first switch circuit A1, the first semiconductor switch G1 and the second semiconductor switch G2 are N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). The source of the first semiconductor switch G1 is connected to the source of the second semiconductor switch G2. The first diode D1 is a parasitic diode of the first semiconductor switch G1. The cathode and anode of the first diode D1 are connected to the drain and source of the first semiconductor switch G1, respectively.

[0060] Similarly, the second diode D2 is a parasitic diode of the second semiconductor switch G2. The cathode and anode of the second diode D2 are connected to the drain and source of the second semiconductor switch G2, respectively. Therefore, the anode of the first diode D1 is connected to the anode of the second diode D2. The gates of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the switching circuit 54. The drains of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the first node and the tap T1, respectively.

[0061] As in the first example, the switching circuit 54 switches the first semiconductor switch G1 and the second semiconductor switch G2 on or off. When the first semiconductor switch G1 and the second semiconductor switch G2 are in the on state, current can flow in both directions through the drain and source. When the first semiconductor switch G1 and the second semiconductor switch G2 are on, the first switch circuit A1 is in a conducting state. In this state, current flows in both directions through the first semiconductor switch G1 and the second semiconductor switch G2, as indicated by the solid and dashed arrows. No current flows through the first diode D1 or the second diode D2.

[0062] When the first semiconductor switch G1 and the second semiconductor switch G2 are off, the first switch circuit A1 is in a cutoff state, in which no current flows through the drains of the first semiconductor switch G1 and the second semiconductor switch G2.

[0063] As described above, the first diode D1 (parasitic diode) is connected between the drain and source of the first semiconductor switch G1. Therefore, even when the first semiconductor switch G1 is off, a current can flow through the first diode D1. As described above, the second diode D2 (parasitic diode) is connected between the drain and source of the second semiconductor switch G2. Therefore, even when the second semiconductor switch G2 is off, a current can flow through the second diode D2. However, in the first switch circuit A1, the anodes of the first diode D1 and the second diode D2 are connected to each other. Therefore, when the first semiconductor switch G1 and the second semiconductor switch G2 are off, no current flows through the first diode D1 or the second diode D2.

[0064] In the fourth example of the first switch circuit A1, the first semiconductor switch G1 and the second semiconductor switch G2 are N-channel MOSFETs. The drain of the first semiconductor switch G1 is connected to the drain of the second semiconductor switch G2. The first diode D1 and the second diode D2 are parasitic diodes of the first semiconductor switch G1 and the second semiconductor switch G2, respectively. The first diode D1 and the second diode D2 are connected in the same manner as in the third example. Therefore, the cathode of the first diode D1 is connected to the cathode of the second diode D2. The gates of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the switching circuit 54. The sources of the first semiconductor switch G1 and the second semiconductor switch G2 are connected to the tap T1 and the first node, respectively.

[0065] When the switching circuit 54 switches the first semiconductor switch G1 and the second semiconductor switch G2 on, the state of the first switch circuit A1 switches to the conducting state. In this case, current flows in both directions through the first semiconductor switch G1 and the second semiconductor switch G2, as indicated by the solid and dashed arrows. No current flows through the first diode D1 or the second diode D2. When the switching circuit 54 switches the first semiconductor switch G1 and the second semiconductor switch G2 off, the state of the first switch circuit A1 switches to the blocking state. In this case, no current flows through the sources of the first semiconductor switch G1 and the second semiconductor switch G2. Because the cathodes of the first diode D1 and the second diode D2 are connected to each other, no current flows through the first diode D1 or the second diode D2.

[0066] In each of the third and fourth examples of the first switch circuit A1, the first semiconductor switch G1 and the second semiconductor switch G2 may be P-channel MOSFETs. In this case, the cathode and anode of the first diode D1 are connected to the source and drain of the first semiconductor switch G1. Similarly, the cathode and anode of the second diode D2 are connected to the source and drain of the second semiconductor switch G2. The switching circuit 54 turns on the first semiconductor switch G1 and the second semiconductor switch G2 by lowering the gate voltage. The switching circuit 54 turns off the first semiconductor switch G1 and the second semiconductor switch G2 by raising the gate voltage.

[0067] In the first and second examples, the first semiconductor switch G1 and the second semiconductor switch G2 may each be a bipolar transistor other than an IGBT. For example, instead of an IGBT, a bipolar transistor having a collector, an emitter, and a base may be used. In this case, the base corresponds to the gate. In the third and fourth examples, the first semiconductor switch G1 and the second semiconductor switch G2 may each be an FET other than a MOSFET.

[0068] One or both of the connection destinations of the switch circuit different from the first switch circuit A1 are different from one or both of the connection destinations of the first switch circuit A1. As described above, the second switch circuit B2 is connected to tap T2 and the second node. The series switch circuit 51 is connected between the first node or the second node and resistor 52.

[0069] As shown in FIG. 2, the switch 5 further includes an output transformer 55, a differentiating circuit 56, and a detecting circuit 57. The output transformer 55 includes a primary winding 55f and a secondary winding 55r. The primary winding 55f and the secondary winding 55r are wound around, for example, an annular core. Two terminals of the primary winding 55f are connected to taps T1 and T2, respectively. Two terminals of the secondary winding 55r are connected to the differentiating circuit 56, respectively. The differentiating circuit 56 is further connected to the detecting circuit 57, which is further connected to the control unit 53.

[0070] FIG. 6 is a timing chart showing the outputs of the output transformer 55, the differentiation circuit 56, and the detection circuit 57. The vertical and horizontal axes of each output represent voltage and time, respectively. The output of the output transformer 55 is an AC voltage output from the secondary winding 55r to the differentiation circuit 56. The phase of the AC voltage output from the secondary winding 55r matches the phase of the AC voltage applied across the primary winding 55f, i.e., the AC voltage between taps T1 and T2 of the single winding 40. When the output of the output transformer 55 is compared with the AC voltage between taps T1 and T2, only the effective value differs. In the example of FIG. 6, the effective value (amplitude) of the AC voltage is stable.

[0071] The phase of the AC voltage between taps T1 and T2 matches the phase of the AC voltage between any two taps among taps T1, T2, and T3. Therefore, the taps to which the two terminals of the primary winding 55f of the output transformer 55 are connected are not limited to taps T1 and T2. For example, the two terminals of the primary winding 55f may be connected to taps T2 and T3. Hereinafter, the AC voltages output to the switch 5 from the two taps connected to the auto-winding 40 will be referred to as the output of the auto-winding 40.

[0072] The differentiating circuit 56 outputs a voltage proportional to the output of the output transformer 55, i.e., the output of the single winding 40. Therefore, when the slope of the output of the single winding 40 is 0 degrees, the output of the differentiating circuit 56 is 0 [V]. The detecting circuit 57 outputs a high-level voltage or a low-level voltage to the control unit 53. The detecting circuit 57 switches the output voltage to a high-level voltage or a low-level voltage every time the output of the differentiating circuit 56 becomes 0 [V]. The switching from a low-level voltage to a high-level voltage and the switching from a high-level voltage to a low-level voltage indicate that the slope of the output of the single winding 40 is 0 degrees.

[0073] The control unit 53 is, for example, a microcomputer. The control unit 53 has a processing element that executes processing, for example, a CPU (Central Processing Unit). A computer program is stored in the control unit 53. The processing element of the control unit 53 executes the computer program to perform a switching process that switches the connection destination of the first node and the second node.

[0074] 7 is a flowchart showing the procedure of the switching process. In the switching process, the control unit 53 first determines whether or not to switch the connection destination of both or one of the first and second nodes based on the effective value of the AC voltage between the output-side distribution lines U and V (step S1). When the control unit 53 determines not to change the connection destination (S1: NO), it executes step S1 again and waits until the timing to switch the connection destination arrives.

[0075] When the control unit 53 determines that the connection destination should be switched (S1: YES), it determines whether the slope of the output of the single winding 40 is 0 degrees based on the output voltage of the detection circuit 57 (step S2). The control unit 53 functions as a determination unit. When the control unit 53 determines that the slope is not 0 degrees (S2: NO), it executes step S2 again and waits until the slope of the output of the single winding 40 becomes 0 degrees.

[0076] When the control unit 53 determines that the tilt is 0 degrees (S2: YES), it instructs the switching circuit 54 to switch the state of the series switch circuit 51 from the cut-off state to the conduction state (step S3). Next, the control unit 53 instructs the switching circuit 54 to switch the states of the first switch circuits A1, A2, A3 and the second switch circuits B1, B2, B3 that are in the conduction state to the cut-off state (step S4).

[0077] Immediately after the control unit 53 executes step S4, all of the first switch circuits A1, A2, A3 and all of the second switch circuits B1, B2, B3 are in the cutoff state. However, since the series switch circuit 51 is in the conducting state, the connection between the first node and the second node is not cut off.

[0078] After executing step S4, the control unit 53 selects the first switch circuits and second switch circuits to be switched to the conducting state from among the three first switch circuits A1, A2, and A3 and the three second switch circuits B1, B2, and B3 (step S5). Next, the control unit 53 instructs the switching circuit 54 to switch the states of the first switch circuits and second switch circuits selected in step S5 from the blocking state to the conducting state (step S6). Next, the control unit 53 instructs the switching circuit 54 to switch the state of the series switch circuit 51 from the conducting state to the blocking state (step S7).

[0079] This switches the tap among taps T1, T2, and T3 to which the first node and the second node are connected. As a result, the AC voltage applied to both ends of the primary winding 31 of each of series transformers 3u and 3v changes, and the effective value of the AC voltage between the output distribution lines U and V changes. After executing step S7, control unit 53 executes the switching process again.

[0080] As described above, in each of the series switch circuit 51, the first switch circuits A1, A2, A3, and the second switch circuits B1, B2, B3 of the voltage regulator 1, the switching circuit 54 switches the state between a conducting state and a blocking state by switching the first semiconductor switch G1 and the second semiconductor switch G2 on or off. Therefore, compared to when multiple mechanical relays are used to switch the connection destinations of the first node and the second node, the switch 5 can switch the connection destinations of the first node and the second node in a short period of time. Therefore, the power consumed by the switch 5 is small.

[0081] After switching the state of the series switch circuit 51 to a conducting state, the switching circuit 54 switches the states of the first switch circuit and the second switch circuit connected to the first node and the second node, respectively, to a cutoff state. After switching the states of the first switch circuit and the second switch circuit to a conducting state, the switching circuit 54 switches the state of the series switch circuit 51 to a cutoff state. This switches the connection destination of at least one of the first node and the second node without cutting off the connection between the first node and the second node. Because the connection between the first node and the second node is not cut off, there is little chance that the voltage between the first node and the second node will rise to an abnormally high voltage due to the induced electromotive forces of the two primary windings 31.

[0082] In each of the series transformers 3u and 3v, when the gradient of the AC voltage applied from the single winding 40 to both ends of the primary winding 31 is 0 degrees, the residual magnetic flux remaining in the core 30 is 0 [Wb]. The switching circuit 54 switches the state of the series switch circuit 51 from the cut-off state to the conduction state at the timing when the gradient of the output of the single winding 40 is 0 degrees. Therefore, when the switching circuit 54 switches the state of the series switch circuit 51 from the conduction state to the cut-off state, the magnetic flux in the core 30 of each of the series transformers 3u and 3v changes from 0 [Wb]. Therefore, in each of the series transformers 3u and 3v, the magnetic flux in the core 30 is unlikely to exceed the saturation magnetic flux.

[0083] While the magnetic flux of the core 30 exceeds the saturation magnetic flux, the impedance of the two primary windings 31 is extremely low. As a result, an excessive current flows through each of the two primary windings 31. As described above, in the voltage regulator 1, the magnetic flux of each of the two cores 30 is unlikely to exceed the saturation magnetic flux. Therefore, the possibility of an excessive current flowing through the primary winding 31 is low.

[0084] If the period from when the switching circuit 54 switches the state of the series switch circuit 51 from the interrupted state to the conducting state until when the switching circuit 54 returns the state of the series switch circuit 51 to the interrupted state is short, the magnetic flux of the core 30 is unlikely to exceed the saturation magnetic flux. Therefore, if this period is short, the control unit 53 may omit execution of step S3 of the switching process. In this case, the switch 5 does not need to include the output transformer 55, the differentiating circuit 56, and the detection circuit 57.

[0085] (Embodiment 2) In the first embodiment, the number of distribution lines is two. However, the number of distribution lines is not limited to two and may be three. The following describes the differences between embodiment 2 and embodiment 1. Except for the configuration described below, the other configurations are common to embodiment 1, and therefore the same reference numerals as in embodiment 1 are used for the components common to embodiment 1, and the description thereof will be omitted.

[0086] FIG. 8 is a circuit diagram of a voltage regulator 1 according to a second embodiment. In the second embodiment, in addition to distribution lines U and V, a distribution line W is connected to an AC power supply 2. The AC power supply 2 outputs three AC voltages to the voltage regulator 1 via three distribution lines U, V, and W. The three AC voltages are the AC voltage between the distribution lines U and V, the AC voltage between the distribution lines V and W, and the AC voltage of the distribution lines U and W. The effective values of the three AC voltages are substantially the same. The phase of the first AC voltage is shifted by 120 degrees from the phase of the second AC voltage. The phase of the second AC voltage is shifted by 120 degrees from the phase of the third AC voltage.

[0087] The voltage regulator 1 has a series transformer 3w in addition to the two series transformers 3u and 3v. The series transformer 3w has a configuration similar to that of the series transformer 3u. The secondary winding 32 of the series transformer 3w is located midway along the distribution line W. The AC power source 2 and one terminal of the secondary winding 32 of the series transformer 3w are connected to the input distribution line W. The other terminal of the secondary winding 32 of the series transformer 3w is connected to the output distribution line W. The secondary windings 32 of the three series transformers 3u, 3v, and 3w adjust the effective values of the three AC voltages related to the output distribution lines U, V, and W. If the effective values of the three AC voltages of the input distribution lines U, V, and W change, the effective values of the three AC voltages of the output distribution lines U, V, and W also change.

[0088] The voltage regulator 1 further includes two regulating transformers 4a and 4b. Each of the regulating transformers 4a and 4b includes a primary winding 41 and a secondary winding 42. The primary winding 41 and the secondary winding 42 are wound around, for example, an annular core. The primary winding 41 of the regulating transformer 4a is connected between the distribution lines U and V. The primary winding 41 of the regulating transformer 4b is connected between the distribution lines V and W. The two primary windings 41 are connected in a V-connection. Three taps T1, T2, and T3 are connected to the secondary windings 42 of each of the regulating transformers 4a and 4b. Each secondary winding 42 functions as a tap winding.

[0089] Each of the regulating transformers 4a and 4b outputs an AC voltage from two taps connected to the secondary winding 42. The effective value of this AC voltage is expressed as the product of the effective value of the AC voltage applied across the primary winding 41 and the turns ratio. Here, the turns ratio is expressed as (the number of turns between the two taps) / (the number of turns of the primary winding 41). Therefore, the greater the number of turns between the two taps, the greater the effective value of the AC voltage between the two taps. The AC voltage between the output distribution lines U and V is applied across the primary winding 41 of the regulating transformer 4a. The AC voltage between the output distribution lines V and W is applied across the primary winding 41 of the regulating transformer 4b. The phase of the AC voltage between taps T1 and T2 matches the phase of the AC voltage between any two taps among taps T1, T2, and T3.

[0090] The voltage regulating device 1 has three measurement transformers 6a and 6b configured similarly to the measurement transformer 6 of the first embodiment. The primary winding 61 of the measurement transformer 6a is connected between the distribution lines U and V. The primary winding 61 of the measurement transformer 6b is connected between the distribution lines V and W. The secondary winding 62 of the measurement transformer 6a outputs an AC voltage whose effective value is proportional to the effective value of the AC voltage between the distribution lines U and V. The secondary winding 62 of the measurement transformer 6b outputs an AC voltage whose effective value is proportional to the effective value of the AC voltage between the distribution lines V and W.

[0091] 9 is a block diagram showing the configuration of the main parts of the switch 5. The switch 5 has two assemblies 50a and 50b configured similarly to the assembly 50 of the first embodiment. The assembly 50a, like the assembly 50 of the first embodiment, is connected to three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4a. The assembly 50b, like the assembly 50 of the first embodiment, is connected to three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4b.

[0092] One terminal of each of the three primary windings 31 functions as a specific terminal. The specific terminal of the primary winding 31 of the series transformer 3u is connected to the first switch circuits A1, A2, and A3 of the assembly 50a. The specific terminal of the primary winding 31 of the series transformer 3v is connected to the second switch circuits B1, B2, and B3 of the assembly 50a and the first switch circuits A1, A2, and A3 of the assembly 50b. The specific terminal of the primary winding 31 of the series transformer 3w is connected to the second switch circuits B1, B2, and B3 of the assembly 50b. The other terminal of one primary winding 31 is connected to the other terminals of the remaining two primary windings. The three primary windings 31 are connected in a Y-connection.

[0093] The selector 5 further includes two series switch circuits 51a, 51b and two resistors 52a, 52b. Each of the series switch circuits 51a, 51b has the same configuration as the series switch circuit 51 of the first embodiment. The series switch circuit 51a is connected in series to a resistor 52a. This series circuit is connected between specific terminals of the primary windings 31 of the series transformers 3u, 3v. The series switch circuit 51b is connected in series to a resistor 52b. This series circuit is connected between specific terminals of the primary windings 31 of the series transformers 3v, 3w.

[0094] The switch 5 further includes a control unit 53, a switching circuit 54, output transformers 55a and 55b, differentiation circuits 56a and 56b, and detection circuits 57a and 57b. Each of the output transformers 55a and 55b is configured similarly to the output transformer 55 of the first embodiment. The primary winding 55f of the output transformer 55a is connected between two taps connected to the primary winding 41 of the regulating transformer 4a. The primary winding 55f of the output transformer 55b is connected between two taps connected to the primary winding 41 of the regulating transformer 4b. The output transformer 55a, differentiation circuit 56a, and detection circuit 57a are connected in the same manner as the output transformer 55, differentiation circuit 56, and detection circuit 57. The output transformer 55b, differentiation circuit 56b, and detection circuit 57b are connected in the same manner as the output transformer 55, differentiation circuit 56, and detection circuit 57.

[0095] Output transformer 55a, differentiating circuit 56a, and detecting circuit 57a function in the same manner as output transformer 55, differentiating circuit 56, and detecting circuit 57. Output transformer 55b, differentiating circuit 56b, and detecting circuit 57b function in the same manner as output transformer 55, differentiating circuit 56, and detecting circuit 57. Two terminals of secondary winding 62 of each of three measuring transformers 6a, 6b, and 6c are connected to control unit 53.

[0096] As in the first embodiment, the control unit 53 instructs the switching circuit 54 to switch the states of the three first switch circuits A1, A2, and A3 and the three second switch circuits B1, B2, and B3 included in the assembly 50a and the state of the series switch circuit 51a. This switches the taps connected to the specific terminals of the primary windings 31 of the two series transformers 3u and 3v among the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4a. In this switching process, the control unit 53 determines whether to switch the connection destination of one or both of the two specific terminals based on, for example, the effective value of the AC voltage between the output distribution lines U and V. Furthermore, the control unit 53 determines whether the gradient of the AC voltage output from the secondary winding 42 of the regulating transformer 4a is 0 degrees.

[0097] As in the first embodiment, the control unit 53 instructs the switching circuit 54 to switch the states of the three first switch circuits A1, A2, and A3 and the three second switch circuits B1, B2, and B3 included in the assembly 50b and the state of the series switch circuit 51b. This switches the taps connected to the specific terminals of the primary windings 31 of the two series transformers 3v and 3w among the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4b. In this switching process, the control unit 53 determines whether to switch the connection destination of one or both of the two specific terminals based on, for example, the effective value of the AC voltage between the output distribution lines U and W. Furthermore, the control unit 53 determines whether the gradient of the AC voltage output from the secondary winding 42 of the regulating transformer 4b is 0 degrees.

[0098] When the switching circuit 54 performs the two switching operations described above, the AC voltages applied to both ends of each of the three primary windings 31 change, and the effective values of the three AC voltages for the output distribution lines U, V, and W are adjusted. In the voltage regulator 1 of the second embodiment, as in the first embodiment, the switch 5 can switch the connection destinations of the three specific terminals in a short period of time. The connection destination of at least one of the three specific terminals is switched without interrupting the connection between two of the three specific terminals. There is little possibility that an excessive current will flow through the primary winding 31 of one of the series transformers 3u, 3v, and 3w.

[0099] (Embodiment 3) In the second embodiment, the number of regulating transformers is 2. However, the number of regulating transformers may be 3. The following describes the differences between embodiment 3 and embodiment 2. Except for the configuration described below, the other configurations are common to embodiment 2, and therefore the same reference numerals as in embodiment 2 are used for the components common to embodiment 2, and the description thereof will be omitted.

[0100] FIG. 10 is a block diagram showing the configuration of the main parts of a voltage regulator 1 according to the third embodiment. Compared to the second embodiment, the voltage regulator 1 further includes a regulating transformer 4c configured similarly to the regulating transformer 4a. A primary winding 41 of the regulating transformer 4c is connected between the distribution lines U and W. The three primary windings 41 are delta-connected. An AC voltage between the output distribution lines U and W is applied to both ends of the primary winding 41 of the regulating transformer 4c. Three taps T1, T2, and T3 are connected to a secondary winding 42 of the regulating transformer 4c. The secondary windings of the three regulating transformers 4a, 4b, and 4c each function as a tap winding.

[0101] FIG. 11 is a block diagram showing the main configuration of the switch 5. Compared to the second embodiment, the switch 5 further includes an assembly 50c configured similarly to the assembly 50 of the first embodiment. One terminal of each of the three primary windings 31 functions as a specific terminal. The other terminal of the primary winding 31 of the series transformer 3u is connected to a specific terminal of the primary winding 31 of the series transformer 3w. The other terminal of the primary winding 31 of the series transformer 3v is connected to a specific terminal of the primary winding 31 of the series transformer 3u. The other terminal of the primary winding 31 of the series transformer 3w is connected to a specific terminal of the primary winding 31 of the series transformer 3v. The three primary windings 31 are connected in a Y-connection. Similar to the assembly 50a of the second embodiment, the assembly 50c is connected to three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4c.

[0102] A specific terminal of the primary winding 31 of the series transformer 3w is connected to the first switch circuits A1, A2, and A3 of the assembly 50a. A specific terminal of the primary winding 31 of the series transformer 3v is connected to the first switch circuits A1, A2, and A3 of the assembly 50b. A specific terminal of the primary winding 31 of the series transformer 3u is connected to the first switch circuits A1, A2, and A3 of the assembly 50c. A series circuit including a series switch circuit 51a and a resistor 52a is connected between specific terminals of the primary windings 31 of the series transformers 3v and 3w. A series circuit including a series switch circuit 51b and a resistor 52b is connected between specific terminals of the primary windings 31 of the series transformers 3u and 3v. Three second switch circuits B1, B2, and B3 are connected to the connection terminals of each of the assemblies 50a, 50b, and 50c. The connection terminal of the assembly 50a is connected to the connection terminals of the assemblies 50b and 50c.

[0103] In the third embodiment, the control unit 53 executes the switching process, for example, as follows. The control unit 53 repeatedly determines whether to switch the connection destination of at least one of the three specific terminals based on the effective value of the AC voltage between the output distribution lines U and V and the effective value of the AC voltage between the output distribution lines U and W. When the control unit 53 determines to switch the connection destination, it instructs the switching circuit 54 to switch the states of the two series switch circuits 51a and 51b to the cutoff state. Next, the control unit 53 instructs the switching circuit 54 to switch the states of the switch circuits that are in the conducting state among the nine first switch circuits A1, A2, and A3 and the nine second switch circuits B1, B2, and B3 included in the assemblies 50a, 50b, and 50c to the cutoff state.

[0104] Next, the control unit 53 instructs the switching circuit 54 to switch the states of six of the nine first switch circuits A1, A2, A3 and nine second switch circuits B1, B2, B3 in the assemblies 50a, 50b, 50c to the conducting state. This switches the connection destination of at least one specific terminal. Finally, the control unit 53 instructs the switching circuit 54 to switch the states of the two series switch circuits 51a, 51b to the blocking state, thereby completing the switching process. Thereafter, the control unit 53 executes the switching process again.

[0105] When the control unit 53 executes the switching process, the AC voltages applied to both ends of each of the three primary windings 31 change, and the effective values of the three AC voltages for the output distribution lines U, V, and W are adjusted. In the voltage regulator 1 of the third embodiment, similarly to the second embodiment, the switch 5 can switch the connection destinations of the three specific terminals in a short period of time. The connection destination of at least one of the three specific terminals is switched without interrupting the connection between any two of the three specific terminals.

[0106] In the third embodiment, the control unit 53 may switch the state of the series switch circuit 51a from the cutoff state to the conduction state when the gradient of the AC voltage between the two taps Ti of the regulating transformers 4a and 4b is 0 degree. As described in the description of the first embodiment, the integer i may be 1, 2, or 3. Similarly, the control unit 53 may switch the state of the series switch circuit 51a from the cutoff state to the conduction state when the gradient of the AC voltage between the two taps T1 of the regulating transformers 4b and 4c is 0 degree.

[0107] In the first to third embodiments, the number of taps provided in the tap winding is not limited to three and may be two or four or more. For each of the assemblies 50, 50a, 50b, and 50c, the number of first switch circuits is the same as the number of taps connected to one tap winding. The number of second switch circuits is also the same as the number of taps connected to one tap winding.

[0108] The technical features (constituent elements) described in the first to third embodiments can be combined with each other, and by combining them, new technical features can be formed. The disclosed embodiments 1 to 3 are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the meaning described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0109] 1 voltage regulator, 3u, 3v, 3w series transformer, 31 primary winding, 32 secondary winding, 40 single winding (tap winding), 42 secondary winding (tap winding), 5 switch, 51, 51a, 51b series switch circuit, 52, 52a, 52b resistor, 53 control unit (judgment unit), 54 switching circuit, A1, A2, A3 first switch circuit, B1, B2, B3 second switch circuit, D1 first diode, D2 second diode, G1 first semiconductor switch, G2 second semiconductor switch, T1, T2, T3 tap, U, V, W distribution line

Claims

1. A voltage regulator that adjusts the effective value of an AC voltage, one or more tap windings to which a plurality of taps are connected; a plurality of transformers having primary and secondary windings; a selector for selecting a tap to be electrically connected to each of a plurality of specific terminals among a plurality of terminals of a plurality of primary windings of the plurality of transformers, among a plurality of taps connected to the one or a plurality of tap windings; Equipped with an effective value of an AC voltage between two of the plurality of taps connected to the tap winding is adjusted according to an effective value of an AC voltage between two of the plurality of distribution lines; a plurality of secondary windings of the plurality of transformers are respectively arranged midway through the plurality of distribution lines; The switch has a plurality of switch circuits whose states are switched between a conducting state in which current can flow and a blocking state in which current flow is blocked, Each switch circuit is a first semiconductor switch; a second semiconductor switch connected in series with the first semiconductor switch; a first diode connected across the first semiconductor switch; a second diode connected across the second semiconductor switch; and the cathodes or anodes of the first diode and the second diode are connected to each other; The switch has a resistor; The plurality of switch circuits include: a plurality of tap switch circuits connected to a plurality of taps respectively connected to the one or more tap windings; a series switch circuit connected in series with the resistor; Including, At least two of the plurality of tap switch circuits are connected to each of the plurality of specific terminals, a series circuit including the resistor and the series switch circuit is connected between two of the plurality of specific terminals; The switch is a determination unit that determines whether or not a gradient of an AC voltage between two taps connected to one tap winding is 0 degrees; a switching circuit that switches the states of the plurality of switch circuits to the conducting state or the blocking state; and The switching circuit comprises: When the determining unit determines that the inclination is 0 degrees, the state of the series switch circuit is switched from the cut-off state to the conduction state. Voltage regulator.

2. the first semiconductor switch and the second semiconductor switch are IGBTs, the emitters or collectors of the first semiconductor switch and the second semiconductor switch are connected to each other; The cathodes of the first and second diodes are connected to the collectors of the first and second semiconductor switches, respectively. The voltage regulator of claim 1 .

3. the first semiconductor switch and the second semiconductor switch are MOSFETs; the sources or drains of the first semiconductor switch and the second semiconductor switch are connected to each other; the first diode is a parasitic diode of the first semiconductor switch, The second diode is a parasitic diode of the second semiconductor switch. The voltage regulator of claim 1 .

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