JP2000269044A - Voltage control device in powder distribution system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a voltage share of each phase of a multiple transformer equal and reduce exciting current, without generating lower-order harmonics in distribution lines from a voltage control device. SOLUTION: In a multiple transformer, where AC side coils are connected in series by zigzag-connections and Y-connections and DC side coils are connected by Δ-connections, secondary voltage outputs in parallel are connected to a multiple three-phase bridge transformer 4, to supply AC voltage with different phases to the three-phase bridge transformer. In response to these phase lags, by controlling the three-phase bridge transformer unit for phase advance, low- higher order harmonics are not generated in a distribution lines system. Furthermore, end surfaces of a main core leg of the multiple transformer 3 are processed to form a gap with steps on a joining surface with a yoke. Consequently, irregularities in voltage shared by the DC side is eliminated, the exciting current is reduced, and abnormal current due to exciting rush current is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage control device for a distribution system including a multiplex transformer for taking measures against abnormal voltage and harmonics and a multiplex three-phase bridge converter using switching elements.

[0002]

2. Description of the Related Art FIG. 10 shows a conventional technique for controlling the voltage of a distribution line using a reactive power compensator. 31 is a substation, 32 is a distribution line, 33 is a load, 34 and 38 are capacitors, 35 and 39 are reactors, 36 is a transformer, 37 is a bus, 40A and 40B are thyristors, 41 is a reactive power compensator, 42 is The filter 43 is a connection point of the reactive power compensator 41 to the distribution line 32.

[0003] Load 3 from substation 31 via distribution line 32
3 for power. The load 33 varies with the season, day, and time. Slow voltage fluctuations are dealt with by the condenser 34 and the reactor 35 connected to the distribution line 32. Sudden voltage fluctuations are dealt with by a reactor 39 and a capacitor 38 connected via antiparallel thyristors 40A and 40B in a reactive power compensator 41 connected to the distribution line 32.

Based on the leading reactive power of the capacitor 38 via the transformer 36, the amount of delayed reactive power supplied to the reactor 39 via the transformer 36 is adjusted based on the phase of the ignition pulse to the thyristors 40A and 40B which are reverse-parallelized. By controlling, the voltage of the connection point 43 to the distribution line was kept constant. In this control, third and higher harmonics are generated. Therefore, filter 4
Is connected to the bus to absorb higher harmonics and prevent higher harmonics from being output to the distribution line 32.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a voltage control apparatus for a distribution system having a multiple transformer and a multiple three-phase bridge converter that do not require a filter for absorbing low-order harmonics. And The present invention also provides a multi-transformer that eliminates irregularities in the shared voltage of each stage, suppresses the occurrence of an abnormal voltage caused by an abnormal excitation current of the multi-transformer when the three-phase bridge converter is activated, and performs three-phase bridge conversion. IGBT (Insulated Gate Bipolar mode Transisi
(ter: insulated gate bipolar mode transistor) It is intended to prevent the breakage of the switching element such as the transistor.

[0006]

In order to achieve the above object, a voltage control apparatus for a power distribution system according to the present invention has a structure in which an AC-side winding (primary side) is connected in series by a staggered connection and a Y connection, and Side (secondary side) windings are Δ-connected, and these DC side windings are
By connecting to the phase bridge converter, supplying the AC voltage to the three-phase bridge converter with the phase shifted, returning these phases to the original state, and controlling the phases of the three-phase bridge converters,
A step-like gap is formed to prevent low-order harmonics from being generated on the AC side and to eliminate irregularities in output voltage during steady-state operation in the iron core of each stage of the multiple transformer, thereby suppressing an inrush current due to excitation.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the voltage control device according to the present invention. 1 is a distribution line, 2 is a circuit breaker, 3 is a three-stage staggered / Δ connection transformer, one stage of a Y-connection / Δ connection transformer is a 4-core multiple transformer, and 4 is a parallel output of each of the multiple transformers 3. A multiplexed three-phase bridge converter composed of four self-excited three-phase bridge converter units 4a, 4b, 4c, and 4d composed of connected switching elements, and 5 was connected to the multiplexed three-phase bridge converter. A capacitor, 6 is an arithmetic and control unit for controlling the phase of each three-phase bridge converter, 7 is provided in the arithmetic and control unit,
This is a sequence unit that controls the start and stop of the voltage control device.
8 is a transformer for detecting the voltage of the distribution line 1, 9 is a transformer for detecting the input side voltage of the multiplex transformer 3, and 10 is a capacitor 5.
, 11 is a current limiting resistor, 12 is a discharge resistor, and 13 and 14 are switches.

FIG. 2 is an example of a connection diagram of the multiple transformer 3 used in the embodiment of FIG. For the AC side winding, the first stage is Y-connected,
The fourth to fourth stages are in a staggered connection, and the terminals U, V, and W in the fourth stage are connected to a distribution line having a line voltage of 6600 V. The DC side windings are four Δ windings corresponding to the input windings of each stage, and each output terminal (u1, v1, w1), (u2, v2, w2), (u
3, v3, w3) and (u4, v4, w4) are 3
It is connected for each phase bridge converter.

FIG. 3 shows an AC side voltage of the multiplex transformer 3 of FIG.
It is a vector diagram of a DC side voltage. The sign at the end of each vector represents the voltage at the winding terminal in FIG. The absolute value of the voltage of the AC winding of each stage is equal, and the phase is different by 15 ° due to the staggered connection. Phase voltage of the second stage (U2
−U1) is the first-stage terminal voltage U1 (= first-stage phase voltage)
The number of turns of the staggered connection is determined so that the absolute value becomes equal to that of the staggered connection by 15 °. Similarly, the phase voltages of the third and fourth stages are staggered so that the phase voltages of the third and fourth stages are equal in absolute value to the phase voltages of the second and third stages and are delayed by 15 °. The number of turns is determined.

[0010] The transformers at each stage connect phase windings (U-U3-U2-U1) and (V-V
3-V2-V1) and (W-W3-W2-W1) are in phase. The DC side output voltage is 3 volts to the AC side line voltage (UV, VW, WU) because the DC side winding is Δ-connected.
The line voltages have a phase delay of 0 °, 45 °, 60 °, and 75 °. For example, the UV side voltage of the AC side voltage is the DC side voltage uv
Lead by 30 ° from the inter-voltage.

FIG. 4 shows a self-excited three-phase bridge converter unit of a multiplexed three-phase bridge power converter. S1 to S6 are switching elements arranged in a three-phase bridge,
This is an example using a T element. U1, V1, and W1 are voltages connected to the output terminal of the DC side Δ winding of the multiple transformer,
P and N are capacitor connection terminals P 'and N' are output connection terminals of other three-phase bridge converter units. Arithmetic and control unit 6
Controls the conduction phase of the switching elements S1 to S6 based on the input of the distribution line voltage signal from the transformer 8 to maintain the distribution line voltage constant. D1 to D6 are rectifying elements for preventing reverse voltage and for charging the capacitor 4.

The operation of the present invention will be described with reference to an embodiment. When a start signal is given to the voltage control device 15, the sequence section 7 turns on the circuit breaker 2, connects the voltage control device 15 to the distribution line 1, and charges the capacitor 5 via the current limiting resistor 11. When the voltage value of the capacitor 5 becomes equal to the distribution line voltage value, the start-up operation of the sequence unit 7 ends, and the arithmetic control unit 6 starts voltage adjustment. The arithmetic and control unit 6 is a multiplex 3
The switching element of each unit of the phase bridge converter 4 has a gate.
And outputs the control signals to the second, third, and fourth three-phase bridge converter units 4b, 4c, and 4d based on the secondary side of the first three-phase bridge converter unit 4a. 15 each
A square wave AC voltage delayed by 30 °, 30 °, and 45 ° is generated. The phase of the square wave AC voltage of each three-phase bridge converter unit is matched by the AC side winding of the multiplex transformer 3 and synthesized to obtain an internal voltage having a voltage waveform close to a sine wave. These voltage waveforms are shown in FIG.

The voltage control device shown in FIG.
In each stage, the input windings are connected in series by 15 ° phase lead connection, and the three-phase bridge converters 4 are 24 pulse number converters, each of which operates with a delay of 15 °, and This is an example of canceling the phase. A description will be given of harmonic reduction in a case where m m three-phase bridge converters (pulse number 6m) are operated with a phase shift of π / (3m) and coupled with a multiple transformer canceling the phase difference between each. .

The three-phase square wave output voltage waveform of the three-phase bridge converter is expanded into a Fourier series as shown in the following equations (1), (2) and (3).

[0015]

(Equation 1)

From this expansion equation, the fundamental wave is a symmetric three-phase voltage,
The harmonics in the 2m + 1 = 3p order are a, b, and c homologous phase voltages (for zero phase), and the harmonics in the 2m + 1 = 3p + 1 order are symmetric three-phase voltages (positive phase voltages) having the same phase rotation as the fundamental wave. Minute), 2
It can be seen that the harmonic at the time of m + 1 = 3p + 2nd order is a symmetrical three-phase voltage (a negative-phase component) having a phase rotation opposite to that of the fundamental wave.
(Where m and p are integers)

Since the connection of the primary winding of the multiplex transformer according to the present invention is a Y connection without a neutral point, a zero-phase current does not flow, and the 2m + 1 = 3p-order third harmonic and its multiples are used. There are no harmonics. 2m + 1 = 3p + 1,2m
+ 1 = 3p + 2 can be easily expressed as 6r + 1,6r-1 (where r is an integer). Therefore, the harmonic component flowing through the primary winding of the multiplex transformer of the present invention can be expressed by the following equation (4). n = 6r ± 1 (4)

The fundamental component of the second three-phase bridge converter operated with a delay of π / (3 m) is the first three-phase bridge converter with respect to the first three-phase bridge converter having no voltage phase. Although it is delayed by π / (3m) with respect to the fundamental wave component of the converter, it advances by π / (3m) by the staggered transformer, so that it becomes in-phase on the AC side.

On the other hand, there is a delay of n × π / (3m) with respect to the n-th harmonic component of the output voltage of the second three-phase bridge converter. n
= 6r + 1, the positive-phase harmonic component is advanced by π / (3m) by the zigzag transformer. Therefore, on the AC side, the following equation (5) is applied to the n-th harmonic component of the first three-phase bridge converter. Will be delayed by

[0020]

(Equation 2)

Since the anti-phase harmonic component represented by n = 6r-1 is delayed by π / (3m) by the staggered transformer, on the AC side, the n-th harmonic component of the first three-phase bridge converter is reduced. Therefore, it is delayed by the following equation (6).

[0022]

(Equation 3)

As described above, the output voltage of the three-phase bridge converter shifted by π / (3m) has the same fundamental wave component on the AC side, and the n = 6r ± 1st harmonic component is (2π / 3m).・ R
Due to this, the sum of the phase differences of the voltage harmonic components generated by the m units of three-phase bridge converters is given by the following equation (7).

[0024]

(Equation 4)

When (2π / 3m) · r is 2π or an integer multiple of 2π, that is, in the case of the following equation (8), the harmonic components are in phase, and the harmonic components at each stage of the multiplex transformer are added. In other cases, the voltage vector to which the harmonic components are added becomes a closed polygon, and no harmonic appears on the AC side of the multiple transformer.

[0026]

(Equation 5)

That is, only the harmonic of the r = mk order component exists, and in the converter having the pulse number of 6 m, the harmonic of the following equation (9) is included in the AC output. n = (6m) K ± 1 (K is an integer) (9)

In the embodiment of FIG. 2, the harmonics appearing on the AC side at m = 4 are the harmonics of the order of the following equation (10), that is, 23, 2
5, 47, 49 ... The next harmonic. n = (6 × 4) K ± 1 (K is an integer) (10)

Next, a description will be given of how to prevent the output voltages of the multiple transformers 3 from being irregular and to suppress the inrush current. FIG. 7 shows a core structure of a three-phase transformer used in each stage of the multiple transformer. Reference numeral 21 denotes an AC side winding, 22 denotes a DC side winding, 23 denotes a core main leg having both end faces processed into a stepped surface protruding from the center, 24a denotes an upper yoke, and 24b denotes a lower yoke. Iron and 25 are step-like (stepped) gap portions formed between the joining surfaces of the yoke and the main leg iron core. The central gap and the peripheral gap formed differently, and the central gap 25a is a short gap and a peripheral gap 25b formed at the joint surface between the central protruding portion of the end face of the iron core main leg and the yoke. Denotes a long gap around the central protrusion. A magnetic insulator, for example, a glass epoxy laminate (FRP) is sandwiched in a gap portion 5 formed between the upper and lower yoke and the main leg iron core.

FIG. 7 shows a magnetic flux path near the gap 25. The solid line 26a is the magnetic flux during steady operation, and the dotted line 26b is the magnetic flux when an inrush current occurs. The magnetic flux 26a during steady operation passes through the central gap 25a having a low excitation impedance. When the multiple three-phase bridge converter is turned on, an excessively large magnetic flux 26b flows due to the inrush current from the steady state operation, and the central protruding portion on the end face of the iron core main leg portion is saturated to increase the magnetic resistance. Then, the magnetic flux also starts to pass through the peripheral gap 25b around the central protruding portion of the end face of the iron core main leg, and the magnetic flux 26b passes through the gap portion 25 on the entire end face of the main leg iron core.

The excitation impedance during steady operation is determined by the excitation impedance of the central gap 25a.
When the phase bridge converter is turned on, the exciting rush current is suppressed by the exciting impedance of the peripheral gap 25b. In the conventional planar gap, the gap length was set large to suppress the inrush current, so that the excitation impedance during the steady operation was larger than necessary. The stepped gap shown in FIG. 7 has a structure corresponding to the central gap 25a having a small gap length acting during steady operation and the peripheral gap 25b having a large gap length acting when an inrush exciting current is generated. Since the excitation impedance during steady operation is determined by the gap length of the central gap 25a, the excitation impedance can be reduced to a minimum. Therefore, the transformer is small and efficient.

FIG. 8 is a magnetic equivalent circuit of one stage of the transformer. Ea, Eb, and Ec are the magnetomotive forces of each phase, R1 is the excitation impedance of the iron core main leg 23, R2 is the excitation impedance of the yoke 24a and the yoke 24b, and Rg1 and Rg2 are the central gap 25a and the outer gap 25b, respectively. The excitation impedance, φa, φb, φc, are the magnetic flux of each phase.
R1, R2≪Rg1, Rg2, and Rg1 <Rg2. Equivalently, when exciting rush current occurs, gap exciting impedance Rg2 becomes effective. Since the magnetic flux of the magnetic circuit is determined by the excitation impedance of the gap 25, the excitation current of each stage of the multiplex transformer becomes the same by making the gap 25 the same structure, and the shared voltage of each stage on the DC side and the DC side is equal. become.

Although there may be theoretically one gap portion 25 per iron core main leg portion, if the gap length is increased, fringing occurs in which a part of the magnetic flux does not pass through the gap and leaks to the yoke, resulting in efficiency. Therefore, as shown in FIG. 6, it is preferable to install a plurality of iron core main legs such as upper and lower portions so that the gap length does not exceed a predetermined length. The exciting impedance of the iron core can be changed by changing the shape and length of the gap.

The voltage control of the distribution system by the voltage control device of the present invention will be described. The arithmetic and control unit 6 supplies a conduction control signal to the switching element of the three-phase bridge converter 4, synchronizes the power distribution system and the three-phase bridge converter, and changes the phase difference between the distribution line voltage and the internal voltage. The distribution line voltage is kept constant by controlling the phase of the internal voltage. When the phase of the internal voltage is changed, a difference voltage between the distribution line voltage and the internal voltage is applied to the multiple transformer 3, and thereby a leading and lagging current flows. When the distribution line voltage is low, the voltage control device supplies the leading reactive power to the distribution line, and when the distribution line voltage is high, supplies the delayed reactive power to the distribution line to keep the distribution line voltage constant. These situations are illustrated in FIG. When the voltage control device is stopped, the sequence unit 7 stops the multiplex three-phase bridge converter 4, the circuit breaker 2 is opened, the switch 14 is closed, and the capacitor 5 is discharged.

[0035]

As described in detail above, the voltage control device of the present invention does not generate low-order harmonics, can absorb low-order harmonics present in the distribution line, and can output the multiple transformers. Irregularity of voltage, reduction of exciting current during steady operation, and suppression of exciting rush current can be achieved. In addition, since the excitation impedance required for each transformer in the multiple transformer can be adjusted by adjusting the gap shape and gap length of the main leg iron core, the degree of freedom in transformer design is expanded, and more appropriate economical design is possible. Thus, downsizing and cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram illustrating a connection example of a multiple transformer.

FIG. 3 is a diagram showing a vector diagram of a multiple transformer.

FIG. 4 is a diagram illustrating an example of a circuit for each three-phase bridge converter.

FIG. 5 is a diagram illustrating an AC voltage of a multiple three-phase bridge converter.

FIG. 6 is a diagram illustrating an example of an iron core structure of a multiple transformer.

FIG. 7 is a diagram showing a magnetic flux in a stepped gap portion.

FIG. 8 is a diagram showing a magnetic equivalent circuit of an iron core having a stepped gap portion.

FIG. 9 is a diagram illustrating voltage adjustment of a power distribution system.

FIG. 10 is a diagram showing a conventional voltage control technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Distribution line 2 Circuit breaker 3 Multiple transformer 4 Multiple 3 phase bridge converter 5 Capacitor 6 Arithmetic controller 7 Sequence part 15 Voltage controller 21 AC side winding 22 DC side winding 23 Iron core main leg part 24a, 24b Yoke 25 Gap 25a Central gap 25b Peripheral gap 26a Magnetic flux (during steady operation) 26b Magnetic flux (during exciting current inrush)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiichi Yoshii 4-33 Komachi, Naka-ku, Hiroshima City, Hiroshima Prefecture Inside Chugoku Electric Power Co., Inc. (72) Inventor Shunji 4-4-2 Oshu, Minami-ku, Hiroshima City, Hiroshima Prefecture No. China Electric Manufacturing Co., Ltd. (72) Inventor Hidenori Kuramoto 4-4-2 Oshu, Minami-ku, Hiroshima City, Hiroshima Prefecture China Electric Manufacturing Co., Ltd. (72) Inventor Akihisa Yamaji Minami-ku, Hiroshima City, Hiroshima Prefecture 4-4-2, Chuo, China Electric Manufacturing Co., Ltd.

Claims (2)

[Claims] 1. A gap that suppresses an abnormal voltage at the time of an inrush current by exciting the DC side winding voltage between the joint surfaces of the iron core main leg portion and the yoke of each stage to form a gap. A multiple transformer in which the windings are connected in a plurality of stages in a staggered connection and the DC side winding of each stage is a Δ connection, and a plurality of three-phase bridge converters respectively connected to the Δ connection of each stage; A voltage control device for a distribution line, comprising: a capacitor connected in parallel to a plurality of three-phase bridge converters configured by switching elements; and an arithmetic control device that provides a conduction signal of the switching elements, wherein the voltage control device includes a plurality of staggered connections. A voltage control device for a distribution system, wherein an AC output of each three-phase bridge converter is delayed by a phase displacement amount to synchronize with an AC voltage. 2. The gap according to claim 1, wherein both end faces of the iron core main leg are formed in a stepped shape with a central portion protruding, and a magnetic insulator is interposed between the yoke and the iron core main leg. A voltage control device for a distribution system, characterized in that: