Voltage regulator

Abstract

To provide a voltage regulator that can bring about a suppression effect of three-phase unbalance while using a two-phase regulator transformer in order to avoid a large-sized device.SOLUTION: A voltage regulator comprises: a series transformer having secondary coils, each of which is connected serially to each of power distribution lines for distributing a three-phase AC voltage, and primary coils corresponding to the secondary coils; a regulator transformer having the secondary coils with taps; a tap switch having two-phase switches for switching the taps of the regulator transformer for each of the secondary coils; and a control unit for controlling the tap switch. The control unit determines a combination of taps so that an index value based on the deviation between each of the output-side three-phase AC voltages in the distribution line and a target voltage value becomes minimum among combinations of the multiple taps of the respective secondary coils of the regulator transformer and controls the tap switch so as to have the determined combination.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a voltage regulator. [Background technology]

[0002] It is necessary to maintain the grid voltage of the power distribution system within a set range. The main cause of fluctuations in the power distribution system voltage is fluctuations in the load of consumers. Other factors include fluctuations due to the power generation status of distributed power sources such as solar power generation. To suppress these fluctuations and maintain the voltage within the set range, step voltage regulators (SVRs) that switch taps and static voltage compensators (SVCs) that adjust the grid voltage by adjusting reactive power are used. Regarding SVRs, thyristor-type step voltage regulators (TVRs) that use thyristors to improve the responsiveness of tap switching are also used.

[0003] Patent documents 1 and 2 disclose a voltage regulating device that includes a series transformer with three phase secondary windings connected in series to a distribution line distributing three phase AC voltages, and a tapped regulating transformer connected in parallel to the distribution line, and adjusts the voltage on the secondary side to a target voltage. In such a voltage regulating device, a tap changer is provided between the primary winding of the series transformer and each tap of the secondary winding of the regulating transformer to switch the taps of the regulating transformer, and a control device adjusts the voltage applied from the regulating transformer to the series transformer to adjust the voltage of the distribution line.

[0004] In the voltage regulator described in Patent Document 1, the primary winding of the series transformer is configured in a Y (star) connection, the secondary side of the regulating transformer is configured in a V connection, and the control unit controls the taps for two phases.

[0005] In the voltage regulator described in Patent Document 2, the primary winding of the series transformer is configured in a delta (Δ) connection, and the secondary winding of the regulating transformer is configured in a Y connection. The control unit controls the taps for three phases to adjust the voltage imbalance of the three phases of the distribution line. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-085715 [Patent Document 2] Japanese Patent Publication No. 2019-080430 [Overview of the project] [Problems that the invention aims to solve]

[0007] As disclosed in Patent Document 1, controlling two-phase tap changers simultaneously can achieve cost reduction and compactness compared to using three-phase tap changers and regulating transformers as in Patent Document 2. However, the unbalance suppression effect seen in the configuration of Patent Document 2, which uses three-phase tap changers and regulating transformers, cannot be obtained.

[0008] This invention has been made in view of these circumstances, and aims to provide a voltage regulator that can suppress the imbalance of three phases while using a two-phase regulator transformer to avoid increasing the size of the device. [Means for solving the problem]

[0009] A voltage regulator according to one embodiment of the present disclosure is a series transformer having a secondary winding connected in series to each of the three-phase AC power distribution lines, and a primary winding corresponding to the secondary winding. An adjusting transformer having two primary windings connected in parallel between the first distribution line and the second distribution line and between the second distribution line and the third distribution line among the distribution lines, and tapped secondary windings corresponding to the two primary windings respectively; A tap changer having a two-phase switch provided between the primary winding of the series transformer and the secondary winding of the adjusting transformer and switching the taps for each of the secondary windings; and a control unit for controlling the tap changer, wherein the control unit is configured to: Among combinations of a plurality of taps of each secondary winding of the adjusting transformer, a combination of taps that minimizes an index value based on the deviation between each of the three-phase AC voltages on the output side of the distribution line and a target voltage value is determined, and the tap changer is controlled so as to be the determined combination.

[0010] In the voltage regulating device of the present disclosure, taps are selected so as to reduce the deviation from the target voltage value as a whole for the three-phase AC voltage.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to improve voltage imbalance while preventing the device from becoming large without configuring a structure that can individually transform three-phase AC voltages.

Brief Description of the Drawings

[0012] [Figure 1] It is a block diagram showing the configuration of the voltage regulating device of the present embodiment. [Figure 2] It is an image diagram of the vector relationship between the secondary-side voltage and the regulated voltage in the voltage regulating device. [Figure 3] It is an explanatory diagram of the rise and fall of the line voltage. [Figure 4] It is a chart showing the voltage characteristics for each tap. <00​​​​​​​​​

[0013] This disclosure will be described in detail with reference to drawings illustrating its embodiments. The following embodiments will describe the voltage regulator of this disclosure.

[0014] Figure 1 is a block diagram showing the configuration of the voltage regulator 1 of this embodiment. The voltage regulator 1 is connected to three distribution lines 1u, 1v, and 1w. Distribution lines 1u, 1v, and 1w are distribution lines that distribute AC voltages in U-phase, V-phase, and W-phase from the power source to the load (not shown). Hereinafter, the voltages of each phase on the primary side will be referred to as U1, V1, and W1, and the voltages of each phase on the secondary side will be referred to as U2, V2, and W2.

[0015] Voltage regulator 1 includes a series transformer 2, a regulating transformer 3, a tap changer 4, and a control unit 5, and is a device that adjusts the AC voltage distributed to distribution lines 1u, 1v, and 1w so that it reaches a target voltage on the secondary side. Voltage detectors 101 and 102 are provided on the primary and secondary sides of distribution lines 1u, 1v, and 1w to detect the line-to-line voltage of each phase of distribution lines 1u, 1v, and 1w. Voltage detectors 101 and 102 are connected to the control unit 5. Only voltage detector 102 may be provided.

[0016] The series transformer 2 includes secondary windings 212, 222, and 232 connected in series to distribution lines 1u, 1v, and 1w, respectively, and primary windings 211, 221, and 231 corresponding to the secondary windings 212, 222, and 232, respectively. Each of the primary windings 211, 221, and 231 is configured in a "Δ connection" where one end and the other end are connected to an adjacent primary winding 211, 221, and 231. The contact point between primary winding 211 corresponding to secondary winding 212 of distribution line 1u and primary winding 221 corresponding to secondary winding 222 of distribution line 1v is defined as N1. Similarly, the contact point between primary winding 221 corresponding to secondary winding 222 of distribution line 1v and primary winding 231 corresponding to secondary winding 232 of distribution line 1w is defined as N2. Let N3 be the contact between primary winding 231 and primary winding 221. Contact N1 is connected to the neutral point, and contacts N2 and N3 are connected to the switch group of the tap changer 4. The series transformer 2 is configured in a "Δ-Y connection". However, the connection of primary windings 211, 221, and 231 in the series transformer 2 for the voltage regulator 1 of this disclosure is not limited to a Δ connection.

[0017] The regulating transformer 3 includes a primary winding 311 connected in parallel between distribution line 1u and distribution line 1v, and a primary winding 321 connected in parallel between distribution line 1v and distribution line 1w. The two primary windings 311 and 321 are configured in a "V connection" that is commonly connected to distribution line 1v. The regulating transformer 3 also includes secondary windings 312 and 322, which correspond to the primary windings 311 and 321, respectively.

[0018] The secondary winding 312 of the regulating transformer 3 has contacts drawn from one end and the other end, and contacts drawn from a point that divides the secondary winding 312 into specific ratios. Some of the contacts are connected to the tap changer 4 via fuses F. Similarly, the secondary winding 322 has contacts drawn from one end and the other end, and contacts drawn from a point that divides the secondary winding into specific ratios. Some of the contacts are connected to the tap changer 4 via fuses F. In other words, the secondary windings 312 and 322 of the regulating transformer 3 are tapped windings that allow selection of the portion of the winding to be used (taps) via contacts drawn from three or more points, including one end, the other end, and a point that divides the secondary winding into specific ratios. Each contact is connected to the contacts N1 to N3 between the primary windings on the primary side of the series transformer 2 via the tap changer 4. Note that the point that divides the winding into specific ratios is not limited to one as shown in Figure 1, but may be two or more. In the example shown in Figure 1, the secondary windings 312 and 322 are provided with contacts drawn out from 2 / 3 of the way, and the secondary windings 312 and 322 can each be selected from three tap patterns: 1x, 1 / 3x, and 2 / 3x.

[0019] The tap changer 4 has six switches (thyristors) for two phases to switch the taps of the secondary windings 312 and 322 of the regulating transformer 3. Specifically, the tap changer 4 has switches ThA1, ThB1, ThC1, Th11, Th21, and Th31 on the secondary winding 312 side, and switches ThA2, ThB2, ThC2, Th12, Th22, and Th32 on the secondary winding 322 side.

[0020] One end of the secondary winding 312 of the regulating transformer 3 is connected to one end of switches ThA1 and Th11 via fuse F. The other end of the secondary winding 312 of the regulating transformer 3 is connected to one end of switches ThC1 and Th31 without using fuse F. The contacts drawn from the point where the winding of the secondary winding 312 of the regulating transformer 3 is divided into a specific ratio (2 / 3) are connected to one end of switches ThB1 and Th21 via fuse F.

[0021] Similarly, one end of the secondary winding 322 is connected to one end of switches ThA2 and Th12 via fuse F. The other end of the secondary winding 322 of the regulating transformer 3 is connected to one end of switches ThC2 and Th32 without using fuse F. The contacts drawn from the point where the winding of the secondary winding 322 of the regulating transformer 3 is divided into a specific ratio (2 / 3) are connected to one end of switches ThB2 and Th22 via fuse F.

[0022] The other ends of switches ThA1, ThB1, and ThC1 are all connected to the neutral point along with contact N1 of series transformer 2. The other ends of switches Th11, Th21, and Th31, one end of which is connected to the secondary winding 312 of regulating transformer 3, are all connected to contact N3 of series transformer 2. The other ends of switches Th12, Th22, and Th32, one end of which is connected to the secondary winding 322 of regulating transformer 3, are all connected to contact N2 of series transformer 2.

[0023] The regulating transformer 3 is connected to the distribution lines 1u, 1v, and 1w, as well as to the tap changer 4, using a "V connection," and is composed of a "VV connection."

[0024] Between the other ends of switches ThA1, ThB1, and ThC1 of the tap changer 4 and the other ends of Th11, Th21, and Th31, a series circuit of a current-limiting resistor R1 and a changeover switch ThS1 and an electromagnetic contactor MC1 are connected in parallel. Changeover switch ThS1 is used to connect and disconnect the current-limiting resistor R1 to the taps in order to bridge the gap between the taps via the current-limiting resistor R1 during the process of switching the taps by switches ThA1, ThB1, ThC1, Th11, Th21, and Th31. Electromagnetic contactor MC1 is used to prevent the primary side of the series transformer 2 from being left open when the operation of switching the taps by switches ThA1, ThB1, ThC1, Th11, Th21, Th31, and ThS1 is stopped. Similarly, for the switch on the secondary winding 322 side, the current-limiting resistor R2 and the changeover switch ThS2 are connected in series with the electromagnetic contactor MC2.

[0025] The switches ThA1, ThB1, ThC1, Th11, Th21, Th31, ThS1 and the electromagnetic contactor MC1 of the tap changer 4, and the switches ThA2, ThB2, ThC2, Th12, Th22, Th32, ThS2 and the electromagnetic contactor MC1 are controllable from the control unit 5. The tap changer 4 may be a direct switching type or an indirect switching type.

[0026] The control unit 5 is configured using logic circuits, FPGA (Field Programmable Gate Array), etc. Based on a pre-stored control program, the control unit 5 outputs control signals to the switches ThA1, ThB1, ThC1, Th11, Th21, Th31, ThS1, ThA2, ThB2, ThC2, Th12, Th22, Th32, and ThS2 of the regulating transformer 3. Using these control signals, the control unit 5 can adjust the voltage of the first to seventh taps for each of the two phases by combining the three taps and switches (igniting thyristors) described above. For example, as shown by the hatching and thick lines in Figure 2, by igniting switches Th11 and ThB1 of the tap changer 4 and switches Th12 and ThB2, the positive and negative signs can be reversed, using only a portion (2 / 3 times) of the secondary windings 312 and 322, resulting in a voltage of -2 / 3 times (see Figure 4, second tap).

[0027] Details of the control for adjusting the voltage by the voltage regulator 1 will be explained. Figure 2 is an illustrative diagram of the vector relationship between the secondary voltage and the regulated voltage in the voltage regulator 1. In Figure 2, the upper part shows the connection relationship between the series transformer 2 and the regulating transformer 3 in the voltage regulator 1. In Figure 2, the lower part shows an image of the voltage conversion vector corresponding to each connection relationship.

[0028] Figure 2 shows, on the left, the Y (star) connection of the secondary windings 212, 222, 232 of the series transformer 2 located on the primary side of the voltage regulator 1, and, in order to the right, the Δ connection of the primary windings 211, 221, 231 of the series transformer 2, the V connection of the secondary windings 312, 322 of the regulating transformer 3, and the V connection of the primary windings 311, 321. The connection between the contacts of the Δ connection of the primary windings 211, 221, 231 of the series transformer 2 and the V connection of the secondary windings 312, 322 of the regulating transformer 3 is switched by the tap changer 4 as shown by the arrows in the figure. Thus, the voltage regulator 1 of this embodiment is configured with a VV-Δ-Y connection when viewed from the input voltage (secondary side) to the regulating transformer 3.

[0029] As shown in the upper part of Figure 2, the regulating transformer 3 is VV connected and has no phase displacement. In the series transformer 2, the phase displacement is 30° due to the Δ-Y connection. With respect to the input voltage to the regulating transformer 3 (secondary voltage), the phase of the output voltage (primary voltage) of the series transformer 2 is shifted by +30° or -30°. Since the primary windings 211, 221, and 231 of the series transformer 2 are configured in a Δ connection, compared to a Y connection configuration, the third harmonic component of the excitation current flows through the Δ connection, suppressing oscillations in the neutral point potential of the secondary windings 212, 222, and 232, and the generation of the zero-sequence voltage V0.

[0030] As shown in the lower part of Figure 2, the AC voltages between potentials U2, V2, and W2 in the primary windings 311 and 321 of the regulating transformer 3 are represented by vectors Vvu1 and Vwv1. The magnitudes of vectors Vvu1 and Vwv1 correspond to the magnitudes of the line voltages. The angle between vectors Vvu1 and Vwv1 indicates the phase difference (30°) between the two AC voltages.

[0031] In contrast, the AC voltages in the secondary windings 312 and 322 of the regulating transformer 3 are represented by vectors Vvu2 and Vwv2. In Figure 2, v2 represents the potential near V2 of the selected tap, w2 the potential near W2, and u2 the potential near U2. The magnitudes of vectors Vvu2 and Vwv2 correspond to the magnitudes of the line voltages. As described above, the primary windings 311 and 321 and the secondary windings 312 and 322 of the regulating transformer 3 are connected in a V-V configuration. The two AC voltages output from the secondary windings 312 and 322 are transformed by multiplying the AC voltage of the primary windings 311 and 321 by the turns ratio corresponding to the selected tap. As shown in Figure 2, no phase difference occurs, and the angle between vectors Vvu2 and Vwv2 remains unchanged. However, since taps can be selected individually for each of the two phases, the magnitudes of vector Vvu2 and vector Vwv2 can be changed individually, as shown in Figure 2.

[0032] As described above, the primary windings 211, 221, and 231 of the series transformer 2 are delta-connected. Therefore, two AC voltages corresponding to vectors Vvu2 and Vwv2 are applied directly to each of the three primary windings 211, 221, and 231. The three AC voltages applied to the primary windings 211, 221, and 231 are represented by vectors Vsr, Vts, and Vrt. The AC voltage Vrt applied to primary winding 231 is equal to the difference between the voltage between any of the switches Th11, Th21, and Th31 of the tap changer 4 and any of the switches Th21, Th22, and Th32. The magnitudes of vectors Vsr, Vts, and Vrt are the RMS values ​​of the AC voltages applied to the primary windings 211, 221, and 231.

[0033] As described above, the secondary windings 212, 222, and 232 of the series transformer 2 are Y-connected. Since the primary windings 211, 221, and 231 are Delta-connected, the Delta-Y connection transforms the vectors Vsr, Vts, and Vrt in the primary windings 211, 221, and 231 (converted according to the turns ratio) into phase voltages ΔV, ΔW, and ΔU, respectively. The phase voltages ΔU, ΔV, and ΔW are superimposed on the primary voltages U1, V1, and W1. Here, the triangle formed by connecting the vectors of phase voltages ΔU, ΔV, and ΔW is not even similar in shape to the triangle formed by the vectors Vsr, Vts, and Vrt. In this way, the two-phase line voltages (Vvu2, Vwv2) adjusted by tap switching create a phase difference in the adjusted voltage output from the series transformer 2. Therefore, it directly affects not only the adjustment voltages of two phases (between U and VW), but also the adjustment voltages of all three phases, including the WU phase, which is not directly subject to adjustment.

[0034] Thus, although the regulating transformer 3 is configured to control two phases, it is also possible to control the non-regulated phase to some extent. Furthermore, the voltage regulating device 1 of this embodiment is advantageous because, due to the Δ-Y connection of the series transformer 2, the third harmonic caused by the excitation current recirculates within the Δ connection, so the neutral point does not oscillate, and there is no need for a 3-phase 3-legged iron core. The series transformer 2 is not limited to a Δ-Y connection, and if it is not a Δ-Y connection, it is not always necessary to set the transformation ratio considering the effect of the phase difference, as will be described later.

[0035] In this embodiment, the voltage regulator 1 is configured with a VV-Δ-Y connection. Therefore, the design of the transformer ratio is more important compared to the case of a VVYY connection that does not produce a phase difference (Patent Document 1 in the prior art) or the case where tap control is performed for all three phases (Patent Document 2 in the prior art). This is because the Δ-Y connection of the series transformer 2 causes a phase difference in the regulated voltage output from the series transformer 2.

[0036] Therefore, in the voltage regulator 1 of this embodiment, the relationship between the magnitude ΔE of the secondary winding voltage of the series transformer 2 and the magnitude V2 of the secondary line voltage (K = ΔE / V2) is set to satisfy equations (1) and (2). Specifically, ΔE is the magnitude of the AC voltage vectors ΔEu, ΔEv, ΔEw across the ends of the secondary windings 212, 222, 232 of the series transformer 2. Specifically, V2 is the magnitude of the secondary line voltages Vuv1, Vvw1, Vwu1 (primary line voltage of the regulator transformer 3). K1 is the transformation ratio during voltage boosting (first ratio K1), and K2 is the transformation ratio during voltage bucking (second ratio K2).

[0037]

number

[0038] The following explains equations (1) and (2) which represent the ranges of ΔE, V2, and the transformer ratio.

[0039] Figure 3 is an explanatory diagram of the rise and fall of line voltages. The AC voltages on the primary side of distribution lines 1u, 1v, and 1w are represented by vectors Eu1, Ev1, and Ew1, respectively. The AC voltages on the secondary side of distribution lines 1u, 1v, and 1w are represented by vectors Eu2, Ev2, and Ew2, respectively. The AC voltages across the ends of the secondary windings 212, 222, and 232 of series transformer 2 are represented by vectors ΔEu, ΔEv, and ΔEw.

[0040] When increasing the line voltage, vector Eu2 is represented as the sum of vectors Eu1 and ΔEu. Similarly, vector Ev2 is represented as the sum of vectors Ev1 and ΔEv. Vector Ew2 is represented as the sum of vectors Ew1 and ΔEw. The distance between the endpoints of the two vectors Eu2 and Ev2 represents the line voltage Vuv on the secondary side of distribution lines 1u and 1v. The endpoint of the vector is the tip of the arrow. The distance between the endpoints of the two vectors Ev2 and Ew2 represents the line voltage Vvw on the output side of the secondary line voltage of distribution lines 1v and 1w. The distance between the endpoints of the two vectors Ew2 and Eu2 represents the line voltage Vwu on the secondary side of distribution lines 1w and 1u.

[0041] The AC voltages in the distribution lines 1u, 1v, and 1w are three-phase balanced voltages. Furthermore, the magnitudes of the vectors ΔEu, ΔEv, and ΔEw are the same. Therefore, the triangle formed by vectors Eu1, Eu2, and ΔEu is the same as the triangle formed by vectors Ev1, Ev2, and ΔEv, and also the same as the triangle formed by vectors Ev1, Ev2, and ΔEv.

[0042] As mentioned above, with respect to series transformer 2, the primary windings 211, 221, and 231 are delta-connected, and the secondary windings 212, 222, and 232 are Y-connected. Therefore, the angles formed by vectors Eu2 and ΔEu, Ev2 and ΔEv, and Ew2 and ΔEw are 30 degrees.

[0043] In the following, the magnitudes of vectors Eu1, Ev1, and Ew1 are represented by E1. The magnitudes of vectors Eu2, Ev2, and Ew2 are represented by E2. The magnitude of vectors ΔEu, ΔEv, and ΔEw is ΔE. The magnitudes of the input line voltages Vuv, Vvw, and Vwu are represented by V1. The magnitudes of the output line voltages Vuv, Vvw, and Vwu are V2.

[0044] When increasing the line voltage, the following equation (3) holds true according to the Law of Cosines. E1 2 =E2 2 +ΔE 2 -2·E2·ΔE·cos30°…(3) The "·" indicates a product. ΔE = K·V² holds true. By substituting K·V² for ΔE in equation (2), we obtain equation (4) below. E1 2 =E2 2 +(K·V2) 2 -E2·K·V2·√3…(4)

[0045] As mentioned above, the AC voltages of the distribution lines 1u, 1v, and 1w are three-phase balanced voltages. Therefore, E1 = V1 / √3 and E2 = V2 / √3 hold true. Using these equations, by removing E1 and E2 from equation (4), we obtain equation (5) below. 3·K 2·V2 2 -3·K·V2 2 +V2 2 -V1 2 =0…(5)

[0046] (5)式は、Kに関する2次方程式である。解の公式を用いることによって、Kは下記の(6)式で表される。

[0047]

Number

[0048] Normally, V2 is much larger than ΔE. Therefore, K does not exceed 0.5. For this reason, the solution where K is 0.5 or more in the (6) formula is deleted. As a result, K is represented by the (7) formula.

[0049]

Number

[0050] <所謂 The minimum value of the primary tap voltage at which the line voltage on the output side is adjusted to the secondary rated voltage is represented by V min When represented by V c for the secondary rated voltage, the first ratio K1 is represented by the following (8) formula.

[0051]

Number

[0052] When a deviation of r (%) is allowed with respect to the voltage transformation ratio (= V1 / V2) of the line voltages on the input side and the output side (the allowable ratio r of the voltage transformation error), the voltage transformation ratio may be a value that is not less than (1 - (r / 100)) · V1 / V2 and not more than (1 + (r / 100)) · V1 / V2. Therefore, when a deviation of r (%) is allowed with respect to the voltage transformation ratio (= V1 / V2) of the line voltages on the input side and the output side, the first ratio K1 satisfies the above formula (1).

[0053] When the line voltage is reduced, as shown in the lower part of Figure 3, vector Eu2 is obtained by subtracting vector ΔEu from vector Eu1. Similarly, vector Ev2 is obtained by subtracting vector ΔEv from vector Ev1. Vector Ew2 is obtained by subtracting vector ΔEw from vector Ew1. In this case as well, the magnitudes of the three line voltages Vuv, Vvw, and Vwu are the same.

[0054] The triangle formed by vectors Eu1, Eu2, and ΔEu is the same as the triangle formed by vectors Ev1, Ev2, and ΔEv, and the same as the triangle formed by vectors Ev1, Ev2, and ΔEv. The angles formed by vectors Eu2 and ΔEu, Ev2 and ΔEv, and Ew2 and ΔEw are all 30 degrees.

[0055] When reducing the line voltage, the following equation (9) holds true according to the Law of Cosines. E1 2 =E2 2 +ΔE 2 -2·E2·ΔE·cos150°…(9) Since ΔE = K·V2 holds true, substituting K·V2 for ΔE in equation (9) yields equation (10) below. E1 2 =E2 2 +(K·V2) 2 +E2·K·V2·√3…(10)

[0056] As mentioned above, E1 = V1 / √3 and E2 = V2 / √3 hold true. By using these equations to remove E1 and E2 from equation (10), we obtain equation (11) below. 3·K 2 ·V2 2 +3·K·V2 2 +V2 2 -V1 2 =0…(11)

[0057] Equation (11) is a quadratic equation in K. Using the quadratic formula, K can be expressed by equation (12) below.

[0058]

number

[0059] Since K is a ratio, it cannot be a negative value. Therefore, we eliminate the solutions in equation (12) where K is a negative value. As a result, K is expressed in equation (13).

[0060]

number

[0061] The maximum value of the primary tap voltage at which the output line voltage is adjusted to the secondary rated voltage is V max It is expressed as such, and the secondary rated voltage is V c When expressed in this way, the second ratio K2 is represented by the following equation (14).

[0062]

number

[0063] If a deviation of r(%) is allowed in the transformation ratio (=V2 / V1) of the line voltages on the input and output sides, the second ratio K2 satisfies equation (2) above.

[0064] In the voltage regulator 1, ΔE and V2 are designed such that the second ratio K2 satisfies equation (2). Therefore, accurate voltage regulation with small errors is achieved when the primary tap voltage is at its maximum value. As mentioned above, the allowable ratio r for the voltage transformation error is, for example, 0.4.

[0065] When the first ratio K1 satisfies equation (1) and the second ratio K2 satisfies equation (2), even if the primary tap voltage is different from the minimum and maximum values, the deviation in the transformation ratio of the input and output line voltages is less than or equal to r(%).

[0066] During voltage boosting, for example, the minimum value V of the primary tap voltage minThe secondary rated voltage is set to 6300V, and the secondary rated voltage is V c Assuming that the voltage is 6600V and the allowable ratio r for the voltage transformation error is 0.4 (%), these values ​​are substituted into equation (1) and ΔE and V2 are designed to satisfy 0.0280 ≤ K1 ≤ 0.00331. When the first ratio K1 is 0.03055, the angles formed by vectors Eu1, Eu2, Ev1, Ev2, and Ew1, Ew2 are approximately 1.6 degrees, which is sufficiently small.

[0067] Also, when stepping down the voltage, for example, the maximum value of the primary tap voltage V max The secondary rated voltage is set to 6900V, and the secondary rated voltage is V c Assuming that the voltage is 6600V and the allowable ratio r for the voltage transformation error is 0.4 (%), these values ​​are substituted into equation (2) and ΔE and V2 are designed to satisfy 0.0273 ≤ K2 ≤ 0.00328. When the second ratio K2 is 0.03086, the angles formed by vectors Eu1, Eu2, Ev1, Ev2, and Ew1, Ew2 are approximately 1.4 degrees, which is sufficiently small.

[0068] In the voltage regulator 1 configured and set as described above, the control unit 15 can calculate how much the voltage will be increased or decreased when one of the multiple taps is selected. By setting the number of turns, etc., based on the above-described transformation ratios K1 and K2, it is possible to adjust all three phases by adjusting only two phases, while minimizing errors in the transformation ratio and phase fluctuations, thereby suppressing imbalance.

[0069] Figure 4 is a chart showing the voltage characteristics for each tap. In the example in Figure 4, the secondary rated voltage is 6600V, and the maximum value of the primary tap voltage is V. max Set to 6900V, and the minimum value of the primary tap voltage is V min The voltage is set to 6300V, and the voltage characteristics are shown for the configuration shown in Figure 1, where the number of taps is "7".

[0070] In the example setting in Figure 4, the transformation ratio of the regulating transformer 3 is set to 1 / 10, and each element is selected so that the transformation ratio K is 0.0030. In the example in Figure 4, the rated voltage of the secondary side is 6600V, so one of the following can be selected: ±660V (±1x), ±440V (±2 / 3x), ±220V (±1 / 3x), and ±0x. The first tap (-1x) can significantly reduce the voltage when the primary side voltage is high, the fourth tap (0x) allows the voltage to pass through as is, and the seventh tap (+1x) can significantly increase the voltage when the primary side voltage is low.

[0071] The "actual primary tap voltage" represents the primary voltage when the secondary voltage is rated at 6600V, assuming a transformation ratio K of 0.0030. The error in the transformation ratio is expressed as "(actual primary tap voltage - rated primary tap voltage) / rated secondary voltage". As shown in Figure 4, regardless of which tap is selected, there is sufficient margin for r = 0.4%. ΔE is the potential magnitude at the secondary windings 212, 222, and 232 of the series transformer 2, respectively. While it is desirable for the phase displacement due to the transformation to be small, calculations show that, as shown in Figure 4, it is sufficiently small, within 2° regardless of which tap is selected.

[0072] The control unit 5 of the voltage regulator 1, configured as described above, further stores a table showing the relationship between boost or buck voltage and taps, as shown in Figure 4. Based on this table, it selects two taps for the two phases and controls the tap changer 4 so that the secondary voltage becomes the target voltage (reference voltage, in this case 6600V). Through the process described below, the voltage regulator 1 can adjust the overall voltage of the three phases to suppress imbalance, even with a compact configuration using two tap changers 4. Figure 5 is a flowchart showing an example of the control process by the control unit 5.

[0073] The control unit 5 obtains the primary line voltages Vuv, Vvw, and Vwu of the distribution lines 1u, 1v, and 1w from the voltage detector 101 (step S1). From the obtained primary line voltages Vuv, Vvw, and Vwu, the control unit 5 provisionally determines the taps for each of the two phases of distribution lines 1u, 1v and distribution lines 1v, 1w based on the difference between the line voltages Vuv and Vvw of the two phases to be controlled and the target voltage (step S2). For example, if the line voltage Vuv is closest to 6300V, the control unit 5 sets the tap between distribution lines 1u, 1v to the 7th tap in order to boost the voltage to the target voltage of 6600V. At this time, for example, if the line voltage Vvw is closest to 6400V, the control unit 5 sets the tap between distribution lines 1v, 1w to the 6th tap in order to boost the voltage to the target voltage of 6600V.

[0074] The control unit 5 calculates the line-to-line voltages Vuv2, Vvw2, and Vwu2 on the secondary side of each phase after adjustment, assuming the provisionally determined tap (step S3). For each of the Vuv2, Vvw2, and Vwu2 calculated in step S3, the control unit 5 calculates the deviations ΔVuv, ΔVvw, and ΔVwu from the target voltage (step S4).

[0075] The control unit 5 calculates the standard deviation σ from the three-phase reference voltage based on the deviations ΔVuv, ΔVvw, and ΔVwu calculated in step S4, based on the following equation (15) (step S5).

[0076]

number

[0077] In step S6, the control unit 5 calculates the adjusted secondary line voltages Vuv2, Vvw2, and Vwu2 for each phase, assuming that an adjacent tap is selected for the tap provisionally determined in step S2. Similarly, the control unit 5 calculates the deviations from the target voltage ΔVuv, ΔVvw, and ΔVwu, and the standard deviation σ, for each of the Vuv2, Vvw2, and Vwu2 calculated in step S6 (step S7).

[0078] The control unit 5 determines the tap pattern that has the smallest standard deviation among the standard deviations σ calculated in steps S5 and S7 as the optimal tap (step S8). The control unit 5 outputs a control signal to the tap changer 4 to switch to the determined tap (step S9), and terminates the process.

[0079] By referring to a table to determine combinations, the process can be simplified as much as possible while suppressing imbalances.

[0080] The processing procedure shown in Figure 5 is also applicable to voltage regulators configured with VVYY connections that do not produce phase differences. In voltage regulators configured with VVYY connections, it is not necessary to consider the phase fluctuations and transformation errors shown in Figure 2-3, and a voltage adjustment table corresponding to the tap selection in the VVYY connection, as shown in Figure 4, can be used. In this case as well, the control unit similarly determines the tap from the voltage line voltage, calculates the standard deviation σ of equation (15) for several combinations of taps to be switched, and determines the tap combination that has the smallest standard deviation σ.

[0081] Figure 6 is an overview diagram of the control process. Figure 6A shows an example of adjusting the voltage of each phase when the taps for two phases are individually selected and controlled, as shown in this embodiment. Figure 6B shows an example of adjusting the voltage of each phase when, as a comparative example, the taps for two phases to be adjusted, rather than the entire three-phase system, are selected and controlled to reach the target voltage. The dashed line shows the target voltage, the dashed line shows the voltage value of each phase before adjustment, and the solid line shows the voltage value of each phase after adjustment.

[0082] Before adjustment, the line voltages Vuv2, Vvw2, and Vwu2 between the secondary distribution lines 1u, 1v, and 1w are 6500V, 6300V, and 6700V, respectively. In the voltage adjustment device 1 of this embodiment, the line voltages Vuv2, Vvw2, and Vwu2 after adjustment can be, for example, 6476V, 6612V, and 6678V, respectively. In the comparative example, the line voltages Vuv2, Vvw2, and Vwu2 after adjustment are, for example, 6500V, 6497V, and 6801V, respectively.

[0083] In the comparative example, the line voltages between distribution lines 1u and 1v, and between distribution lines 1v and 1w, which are subject to adjustment, are both brought closer to the target voltage. However, the line voltage between distribution lines 1w and 1u, which are not subject to adjustment, is even further from the target voltage than before adjustment. Thus, in a configuration that adjusts only two phases instead of three phases, if the line voltage between distribution lines 1w and 1u, which are subject to adjustment, is not midway between the line voltages between distribution lines 1u and 1v, and between distribution lines 1v and 1w, it is possible that the line voltage of the non-adjusted line will be further moved away from the target voltage.

[0084] In contrast, the voltage adjustment device 1 of this embodiment, as described above, can also adjust the line voltage between the non-adjustable distribution lines 1w and 1u. Furthermore, the control unit 5 determines the tap so that the standard deviation σ is minimized. Therefore, the voltage adjustment device 1 of this embodiment can also adjust the line voltage between the non-adjustable distribution lines 1w and 1u. Even if the effect of bringing the line voltage to be adjusted closer to the target value is lower than in the comparative example, voltage imbalance can be further improved, as shown in Figure 6.

[0085] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not in the sense described above, and all modifications within the sense and scope equivalent to the claims are intended.

[0086] Regarding the multiple claims described in the patent claims, they can be combined with each other regardless of the form of citation. The patent claims include multiple dependent claims that depend on multiple claims. The patent claims do not include multiple dependent claims that depend on multiple dependent claims, but multiple dependent claims that depend on multiple dependent claims may be included. [Explanation of Symbols]

[0087] 1. Voltage Regulator 1u,1v,1w distribution line 101,102 Voltage detector 2 Series transformers 211,221,231 Primary winding 212,222,232 Secondary winding 3. Regulating Transformer 311,321 Primary winding 312,322 Secondary winding 4 Tap changer ThA1, ThB1, ThC1, Th11, Th21, Th31, ThA2, ThB2, ThC2, Th12, Th22, Th32 switches 5. Control Unit

Claims

1. A series transformer having a secondary winding connected in series to each of the three-phase AC power distribution lines, and a primary winding corresponding to the secondary winding, A regulating transformer having two primary windings connected in parallel between the first and second distribution lines and between the second and third distribution lines, and a tapped secondary winding corresponding to each of the two primary windings, A tap changer is provided between the primary winding of the series transformer and the secondary winding of the regulating transformer, and has two-phase switches for switching the taps of the regulating transformer for each of the secondary windings, and Control unit for controlling the tap changer, Equipped with, The control unit determines, from among multiple tap combinations of each of the secondary windings of the regulating transformer, the combination that minimizes the index value, which is the standard deviation calculated from the deviation between each of the three phase AC voltages on the output side of the distribution line and the target voltage value, and controls the tap changer to achieve the determined combination. Voltage regulator.

2. The control unit further includes a storage unit that stores a tap to be selected according to the difference between the voltage value on the input side of the power distribution line and the target voltage value on the output side. The control unit, The line-to-line voltage values ​​of the first and second distribution lines, and the line-to-line voltage values ​​of the second and third distribution lines are detected. For each detected line voltage value, the taps for two phases are tentatively determined individually by referring to the memory unit. An index value is calculated based on the deviation between the AC voltage of each of the three phases on the output side when the provisionally determined tap combination is used, and the target voltage value. Determine the tap combination that has the smallest index value calculated for other tap combinations. The voltage regulator according to claim 1.

3. The control unit calculates the index value using the following formula: A voltage regulator according to claim 1 or 2. [Math 1] σ: Index value ΔVuv: Deviation between the target voltage value and the effective value of the AC voltage between the first and second distribution lines. ΔVvw: Deviation between the target voltage value and the effective value of the AC voltage between the second and third distribution lines. ΔVwu: Deviation between the target voltage value and the effective value of the AC voltage between the third and first distribution lines.

4. The primary winding of the aforementioned series transformer is delta-connected. The voltage regulator according to claim 1.

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