CN104934974A - A Controllable Phase Shifter with Short Circuit Current Limiting Function - Google Patents

Abstract

The invention provides a controllable phase shifter with a short-circuit current limiting function. The controllable phase shifter comprises an exciting transformer, a booster transformer and a thyristor voltage regulator circuit; the low-voltage end of a primary side winding in the booster transformer is the input end of the controllable phase shifter while the high-voltage end of the primary side winding in the booster transformer is the output end of the controllable phase shifter; the primary side winding consists of two winding sections connected in series; a secondary side winding of the exciting transformer consists of three winding sections connected in series; and the input end of the thyristor voltage regulator circuit is connected with the secondary side winding of the exciting transformer while the output end of the thyristor voltage regulator circuit is connected with the high-voltage end of the primary side winding of the booster transformer. Compared to the prior art, the controllable phase shifter with the short-circuit current limiting function provided by the invention can rapidly change phase angles and limit short-circuit current, and achieves an important protective effect on safe operation of power grids in malfunction states.

Description

A Controllable Phase Shifter with Short Circuit Current Limiting Function

technical field

The invention relates to the field of electric current system transmission control, in particular to a controllable phase shifter with short-circuit current limiting function.

Background technique

Phase shifter (phase shift transformer, PST) is also called phase angle regulator (phase angle regulator, PAR), which is an effective means to control the power transmission flow. The phase or amplitude of the point voltage, so as to control the steady-state power flow or voltage of the transmission line, realize the rational distribution of line transmission power, improve the transmission capacity of key sections, and reduce transmission costs. The early PSTs used mechanical voltage regulation. With the rapid development of power electronics technology, a thyristor controlled phase shift transformer (TCPST) using thyristor voltage regulation appeared. The controllable phase shifter based on thyristor voltage regulation has the following advantages:

①: The thyristor can operate continuously and frequently, and can avoid expensive daily maintenance costs of mechanical voltage regulating equipment;

②: Thyristor voltage regulation speed is much faster than mechanical voltage regulation, which can meet the fast control requirements of power system.

Therefore, it is necessary to provide a controllable phase shifter with a short-circuit current limiting function to deal with system transient and dynamic problems, such as improving transient stability, reducing cross-currents that cause tie-line out-of-step, and suppressing post-fault Switch overload, damping oscillation, etc. caused by sudden increase in line power.

Contents of the invention

In order to meet the needs of the prior art, the invention provides a controllable phase shifter with short-circuit current limiting function.

Technical scheme of the present invention is:

Preferably, the controllable phase shifter includes an excitation transformer, a boost transformer and a thyristor voltage regulating circuit;

The low-voltage end of the primary side winding in the booster transformer is the input end of the controllable phase shifter, and the high-voltage end is the output end of the controllable phase shifter; the primary side winding is composed of two sections of winding in series, and the two sections The connection point of the winding is provided with an intermediate tap, and the intermediate tap is connected to the high-voltage end of the primary winding in the excitation transformer; the secondary winding of the excitation transformer is composed of three windings in series;

The input end of the thyristor voltage regulating circuit is connected to the secondary side winding of the excitation transformer, and the output end is connected to the high voltage end of the primary side winding in the booster transformer.

Preferably, both the primary side winding and the secondary side winding of the excitation transformer are Y0 connected _; the secondary side winding of the booster transformer is Δ connected;

Preferably, the primary winding of the excitation transformer is connected by Δ, and the secondary winding is connected by Y0 _; the secondary winding of the booster transformer is connected by Y0 or Y _;

Preferably, the primary side winding of the excitation transformer includes an A-phase winding, a B-phase winding, and a C-phase winding, and the intermediate tap of the booster transformer includes an A-phase intermediate tap, a B-phase intermediate tap, and a C-phase intermediate tap; the excitation transformer The connection methods between the primary side winding in the medium and the primary side winding in the step-up transformer include:

The high-voltage end of the A-phase winding is connected to the middle tap of the A-phase;

The high-voltage end of the B-phase winding is connected to the B-phase center tap;

The high-voltage end of the C-phase winding is connected to the C-phase center tap;

Preferably, the thyristor voltage regulating circuit includes a first thyristor voltage regulating circuit, a second thyristor voltage regulating circuit and a third thyristor voltage regulating circuit;

The input end of the first thyristor voltage regulating circuit is connected to the A-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the C-phase winding of the secondary side winding in the booster transformer;

The input end of the second thyristor voltage regulating circuit is connected to the B-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the A-phase winding of the secondary side winding in the booster transformer;

The input end of the third thyristor voltage regulating circuit is connected to the C-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the B-phase winding of the secondary side winding in the booster transformer;

Preferably, the first thyristor voltage regulating circuit, the second thyristor voltage regulating circuit and the third thyristor voltage regulating circuit all include a first full bridge circuit, a second full bridge circuit and a third full bridge circuit connected in series in sequence;

The input end of the first full bridge circuit is connected to both ends of the first section winding of the secondary side winding in the excitation transformer;

The input end of the second full bridge circuit is connected to both ends of the second segment winding of the secondary side winding in the excitation transformer;

The input end of the third full bridge circuit is connected to both ends of the third segment winding of the secondary side winding in the excitation transformer;

Preferably, each bridge arm of the first full bridge circuit is composed of a thyristors connected in series, each bridge arm of the second full bridge circuit is composed of b thyristors connected in series, and each bridge arm of the third full bridge circuit is composed of b thyristors connected in series. A bridge arm is composed of c thyristors connected in series, a:b:c=1:3:9;

The ratio of the number of turns n1 of the first winding, the number of turns n2 of the second winding, and the number of turns n3 of the third winding is n1:n2:n3=1:3:9;

Preferably, the working states of the secondary side winding in the excitation transformer include 27 working states;

The working state of the first section of winding includes forwardly connecting the secondary winding of the booster transformer, reversely connecting the secondary winding of the boosting transformer and not connecting the secondary winding of the boosting transformer;

The working state of the second section of winding includes forwardly connecting the secondary winding of the booster transformer, reversely connecting the secondary winding of the boosting transformer and not connecting the secondary winding of the boosting transformer;

The working state of the third section winding includes the secondary side winding of the booster transformer being connected in series in forward direction, the secondary side winding of the boosting transformer being connected in series in reverse direction and the secondary side winding of the boosting transformer not being connected in series.

Compared with the closest prior art, the excellent effect of the present invention is:

1. A controllable phase shifter with a short-circuit current limiting function provided by the present invention can improve the operation mode of the existing AC power grid, increase the transmission capacity of the key sections of the existing grid, and ease the construction of power transmission and transformation projects in the load center area It can control the voltage while balancing the power flow of the power grid, and improve the stability of the system. It can also solve related problems in the distribution network when used in the distribution network. The quality of grid power supply is of great significance;

2. A controllable phase shifter with a short-circuit current limiting function provided by the present invention can quickly change the phase angle, limit the short-circuit current, and play an important role in protecting the safe operation of the power grid in a fault state;

3. A controllable phase shifter with a short-circuit current limiting function provided by the present invention uses a thyristor control circuit instead of a load tap to form a thyristor-controlled phase shifter: on the one hand, the thyristor can operate continuously and frequently, and can Exempt from the expensive daily maintenance costs of mechanical voltage regulation equipment; on the other hand, the thyristor voltage regulation speed is much faster than mechanical voltage regulation, which can meet the rapid control requirements of the power system;

4. A controllable phase shifter with a short-circuit current limiting function provided by the present invention can be used to deal with system transient and dynamic problems, such as improving transient stability, alleviating crossing currents that lead to tie-line out-of-step, suppressing Switch overload, damping oscillation, etc. caused by sudden increase in line power after a fault.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1: A schematic diagram of a controllable phase shifter connected to a power transmission system in an embodiment of the present invention;

Figure 2: A schematic diagram of the phase angle relationship after the controllable phase shifter is connected to the power transmission system in the embodiment of the present invention;

Fig. 3: Topological structure diagram of a controllable phase shifter with a short-circuit current limiting function in an embodiment of the present invention;

Fig. 4: SCR voltage regulating circuit diagram in the embodiment of the present invention;

Figure 5: Schematic diagram of the primary and secondary side voltage phasor relationship of the excitation transformer in the embodiment of the present invention;

Fig. 6: The phasor relationship of the input and output voltages of the controllable phase shifter in the embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

The present invention provides a controllable phase shifter with a short-circuit current limiting function, which can not only adjust the active power transmitted on the transmission line, but also limit the short-circuit current of the transmission line. In the case of a short-circuit fault in the transmission system, It can quickly change the phase angle to achieve the effect of limiting short-circuit current.

The active power transmitted by the line in the transmission system is:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; L</span>}}}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, δ is the phase angle difference between the voltage at the sending end S and the receiving end L shown in Figure 1, σ is the phase angle difference between U _sl and U _s after the phase shift by the phase shifter, U _S is the voltage at the sending end, U _L is Terminal voltage, U _sl is the voltage after phase shift, X _SL is the line impedance. It can be seen from formula (1) that the change of σ can greatly affect the active power transmitted by the line.

The phase shifter controls the injection of voltage ΔU into the line to change the phase angle of the voltage on both sides of the phase shifter, thereby changing the phase angle difference between the head and the end of the transmission line to achieve the purpose of controlling the power flow. Its phase angle relationship is shown in Figure 2.

The embodiment of controllable phase shifter among the present invention is shown in Figure 3, specifically:

The controllable phase shifter includes an excitation transformer (Excitation Transformer, ET), a booster transformer (Booster Transformer, BT) and a thyristor voltage regulating circuit. in,

1. Booster transformer

(1) The primary side winding of the booster transformer

The low-voltage end of the primary winding is the input end of the controllable phase shifter, and the high-voltage end is the output end of the controllable phase shifter;

The primary side winding is composed of two sections of winding in series, and the connection point of the two sections of winding is provided with a middle tap, which is connected to the high-voltage end of the primary side winding in the excitation transformer; the middle tap includes A-phase middle tap, B-phase middle tap and C Phase center tap.

As shown in Figure 3, the A-phase winding of the primary side winding includes winding B1a and winding B2a in series, and the A-phase center tap set at the connection end of the two is connected to the high-voltage end of the primary side winding E1a in the excitation transformer, and the other end of winding B1a is the input terminal SA of the controllable phase shifter, and the other end of the winding B2a is the output terminal LA of the controllable phase shifter;

The B-phase winding of the primary side winding includes winding B1b and winding B2b connected in series, and the B-phase center tap set at the connection end of the two is connected to the high-voltage end of the primary side winding E1b in the excitation transformer, and the other end of winding B1b is a controllable phase shifter The input terminal SB of the winding B2b is the output terminal LB of the controllable phase shifter at the other end of the winding B2b;

The C-phase winding of the primary side winding includes winding B1c and winding B2c in series, and the C-phase center tap set at the connection end of the two is connected to the high-voltage end of the primary side winding E1c in the excitation transformer, and the other end of winding B1c is a controllable phase shifter The input terminal SC of the winding B2c is the output terminal LC of the controllable phase shifter.

The potentials induced on the two windings in the primary winding are equal, that is in:

The winding ratio n _B of the step-up transformer is:

n _B ＝N _B3 /N _B1 ＝N _B3 /N _B2 (2)

Among them, N _B1 is the number of turns of one section of winding on the primary side of the booster transformer, N _B2 is the number of turns of the other section of winding on the primary side of the booster transformer, and N _B3 is the number of turns of the secondary side winding of the booster transformer.

The winding ratio n _T of the excitation transformer is:

n _T ＝(N _E1 /TN _T )＝(U _E1 /U _T ) (3)

Among them, T=±1,±2,...±3, N _E1 is the number of turns of the primary winding of the excitation transformer, N _T is the number of winding turns corresponding to the unit step difference voltage of the secondary side of the excitation transformer, U _E1 is the number of turns of the excitation transformer Change the voltage of the primary side winding, U _T is the equivalent output voltage of the secondary side of the excitation transformer.

If the primary and secondary sides of the excitation transformer are star-connected, the three-phase voltage phasors are shown in Figure 4, where, is the voltage phasor of the primary side winding of the excitation transformer, is the equivalent output voltage phasor of the secondary side of the excitation transformer.

With reference to the phasor position in Figure 4, combined with the transformation ratio of the excitation transformer, the phasor relationship between the input and output voltages of the phase shifter can be obtained as shown in Figure 5, where, is the voltage phasor at the input side of the phase shifter; is the voltage phasor at the output side of the phase shifter; is the voltage phasor at the connection between the intermediate tap point of the booster transformer and the primary side winding of the excitation transformer; is the voltage phasor on the primary side segment winding of the step-up transformer; φ is the phase shift angle of the phase shifter.

It can be obtained that the phase shift angle φ satisfies the following relationship:

The "T"-shaped equivalent circuit with an ideal transformer is used for analysis, and the voltage relationship between the sending end S and the receiving end L of the phase shifter is as follows:

where the equivalent impedance $Z_{eq}=2Z_{B1}+\frac{12}{{\left({\mathrm{no}}_T{\mathrm{no}}_B\right)}^2+3}(Z_{\mathrm{E.}1}+{\mathrm{no}}_T^2{Z}_T+\frac{1}{3}{\mathrm{no}}_T^2{Z}_{B3});$

Z _E1 is the equivalent impedance of the primary side of the excitation transformer, Z _T is the equivalent impedance of the secondary side of the excitation transformer, Z _B1 is the equivalent impedance of a section of winding on the primary side of the booster transformer, and Z _B3 is the equivalent impedance of the secondary side of the booster transformer .

When the leakage reactance of each winding of the phase shifter is considered, the phase shifter can be equivalent to an ideal phase shifter connected in series with an impedance, as shown in Figure 1, where X _SL is the line impedance, is the voltage phasor at the output side of the controllable phase shifter. Therefore, in the case of a short circuit in the line, the thyristor can act quickly, change the phase angle, and use Z _eq and X _SL to effectively limit the short circuit current.

In this embodiment, although the leakage reactance and loss of the phase shifter body will have a great impact on the power transmission system, the phase shift angle of the phase shifter will reduce the voltage drop of leakage reactance and loss, and the output voltage will only be lower than the input voltage. The phase angle changes and the amplitude does not change.

(2) The secondary side winding of the booster transformer

As shown in FIG. 3 , the secondary side winding includes a winding B3a, a winding B3b and a winding B3c.

2. Excitation transformer

(1) The primary side winding of the excitation transformer

The primary side winding includes an A-phase winding, a B-phase winding and a C-phase winding.

The connection methods between the primary side winding of the excitation transformer of the booster transformer and the primary side winding of the booster transformer include:

The high-voltage end of the A-phase winding is connected to the middle tap of the A-phase; the high-voltage end of the B-phase winding is connected to the B-phase middle tap; the high-voltage end of the C-phase winding is connected to the C-phase middle tap.

As shown in FIG. 3 , the A-phase winding is the winding E1a, the B-phase winding is the winding E1b, and the C-phase winding is the winding E1c.

(2) The secondary side winding of the excitation transformer

The secondary side winding consists of three sections of winding connected in series.

As shown in Figure 3, the A-phase winding of the secondary side winding is composed of the first winding E2a, the second winding E3a and the third winding E4a in series, and the B-phase winding of the secondary winding is composed of the first winding E2b , the second section winding E3b and the third section winding E4b are sequentially connected in series, and the C-phase winding of the secondary side winding is composed of the first section winding E2c, the second section winding E3c and the third section winding E4c in sequence.

3. Thyristor voltage regulating circuit

The input end of the circuit is connected with the secondary side winding of the excitation transformer, and the output end is connected with the high voltage end of the primary side winding in the step-up transformer. The thyristor voltage regulating circuit includes a first thyristor voltage regulating circuit, a second thyristor voltage regulating circuit and a third thyristor voltage regulating circuit, wherein:

①: The input end of the first thyristor voltage regulating circuit is connected to the A-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the C-phase winding of the secondary side winding in the booster transformer. As shown in FIG. 3 , the input ends are respectively connected to the first segment winding E2a, the second segment winding E3a and the third segment winding E4a, and the output end is connected to the winding B3c.

②: The input end of the second thyristor voltage regulating circuit is connected to the B-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the A-phase winding of the secondary side winding in the booster transformer. As shown in FIG. 3 , the input ends are respectively connected to the first segment winding E2b, the second segment winding E3b and the third segment winding E4b, and the output end is connected to the winding B3a.

③: The input end of the third thyristor voltage regulating circuit is connected to the C-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the B-phase winding of the secondary side winding in the booster transformer. As shown in FIG. 3 , the input ends are respectively connected to the first segment winding E2c, the second segment winding E3c and the third segment winding E4c, and the output end is connected to the winding B3b.

The first thyristor voltage regulating circuit, the second thyristor voltage regulating circuit and the third thyristor voltage regulating circuit all include the first full bridge circuit, the second full bridge circuit and the third full bridge circuit connected in series in sequence, wherein:

①: The input end of the first full bridge circuit is connected to the two ends of the first winding of the secondary side winding in the excitation transformer, and each bridge arm of the first full bridge circuit is composed of a thyristors connected in series.

In this embodiment, a=1. As shown in FIG. 3 , the first full bridge circuit includes bridge arm 1 , bridge arm 2 , bridge arm 3 and bridge arm 4 .

②: The input end of the second full bridge circuit is connected to the two ends of the second section winding of the secondary side winding in the excitation transformer, and each bridge arm of the second full bridge circuit is composed of b thyristors connected in series.

In this embodiment, a=3. As shown in FIG. 3 , the second full bridge circuit includes bridge arm 5 , bridge arm 6 , bridge arm 7 and bridge arm 8 .

③: The input end of the third full bridge circuit is connected to both ends of the third section winding of the secondary side winding in the excitation transformer, and each bridge arm of the third full bridge circuit is composed of c thyristors connected in series.

In this embodiment, a=9. As shown in FIG. 3 , the third full bridge circuit includes a bridge arm 9 , a bridge arm 10 , a bridge arm 11 and a bridge arm 12 .

In this embodiment, a:b:c=1:3:9, the ratio of the number of turns n1 of the first winding, the number of turns n2 of the second winding, and the number of turns n3 of the third winding is n1: n2:n3=1:3:9.

In this embodiment, the working state of the secondary side winding in the excitation transformer includes 27 working states, wherein the working state of each segment winding is:

①: The working state of the first winding, including the secondary side winding connected in series with the booster transformer, the secondary side winding connected in series with the booster transformer in reverse, and the secondary side winding not connected in series with the booster transformer.

As shown in Figure 3, when bridge arm 1 and bridge arm 4 are turned on and the others are cut off, the E2 winding is forwardly connected in series with the winding B3c; when bridge arm 2 and bridge arm 3 are turned on and the others are cut off, the E2 winding is reversed connected in series to winding B3c; when bridge arm 1 and bridge arm 2 are turned on, and the others are cut off, the E2 winding is not connected in series to winding B3c; when bridge arm 3 and bridge arm 4 are turned on, and the others are cut off, the E2 winding is not connected in series in winding B3c.

②: The working state of the second winding, including the secondary side winding connected in series with the booster transformer in forward direction, the secondary side winding connected in series with the booster transformer in reverse and the secondary side winding not connected in series with the booster transformer.

③: The working state of the third winding, including the secondary side winding connected in series with the booster transformer, the secondary side winding connected in series with the booster transformer in reverse, and the secondary side winding not connected in series with the booster transformer.

In this embodiment, the connection modes of the excitation transformer and the booster transformer mainly include:

①: Both the primary winding and the secondary winding of the excitation transformer are connected by Y ₀ , and the secondary winding of the booster transformer is connected by Δ.

②: The primary side winding of the excitation transformer is Δ connected, the secondary side winding is Y ₀ connected, and the secondary side winding of the booster transformer is Y ₀ connected.

③: The primary side winding of the excitation transformer is Δ connected, the secondary side winding is Y ₀ connected, and the secondary side winding of the booster transformer is Y connected.

Finally, it should be noted that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

Claims (8)

1. A controllable phase shifter with short-circuit current limiting function, characterized in that, said controllable phase shifter comprises an excitation transformer, a booster transformer and a thyristor voltage regulating circuit; The low-voltage end of the primary side winding in the booster transformer is the input end of the controllable phase shifter, and the high-voltage end is the output end of the controllable phase shifter; the primary side winding is composed of two sections of winding in series, and the two sections The connection point of the winding is provided with an intermediate tap, and the intermediate tap is connected to the high-voltage end of the primary winding in the excitation transformer; the secondary winding of the excitation transformer is composed of three windings in series; The input end of the thyristor voltage regulating circuit is connected to the secondary side winding of the excitation transformer, and the output end is connected to the high voltage end of the primary side winding in the booster transformer. 2. controllable phase shifter as claimed in claim 1, is characterized in that, the primary winding of described excitation transformer and the secondary winding are Y ₀ connection; The secondary winding of described step-up transformer is Δ connect. 3. controllable phase shifter as claimed in claim 1, is characterized in that, the primary side winding of described excitation transformer is Δ connection, and secondary side winding is Y ₀ connection; The secondary side winding of described step-up transformer It is Y ₀ connection or Y connection. 4. The controllable phase shifter as claimed in claim 1, wherein the primary side winding of the excitation transformer comprises an A-phase winding, a B-phase winding and a C-phase winding, and the center tap of the step-up transformer comprises an A Phase mid-tap, B-phase mid-tap and C-phase mid-tap; the connections between the primary side winding in the excitation transformer and the primary side winding in the booster transformer include: The high-voltage end of the A-phase winding is connected to the middle tap of the A-phase; The high-voltage end of the B-phase winding is connected to the B-phase center tap; The high voltage end of the C-phase winding is connected to the C-phase center tap. 5. The controllable phase shifter according to claim 1, wherein the thyristor voltage regulating circuit comprises a first thyristor voltage regulating circuit, a second thyristor voltage regulating circuit and a third thyristor voltage regulating circuit; The input end of the first thyristor voltage regulating circuit is connected to the A-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the C-phase winding of the secondary side winding in the booster transformer; The input end of the second thyristor voltage regulating circuit is connected to the B-phase winding of the secondary side winding in the excitation transformer, and the output end is connected to the A-phase winding of the secondary side winding in the booster transformer; The input end of the third thyristor voltage regulating circuit is connected to the C-phase winding of the secondary winding in the excitation transformer, and the output end is connected to the B-phase winding of the secondary winding in the boosting transformer. 6. The controllable phase shifter as claimed in claim 5, wherein the first thyristor voltage regulating circuit, the second thyristor voltage regulating circuit and the third thyristor voltage regulating circuit all comprise first full bridges connected in series in sequence circuit, a second full bridge circuit and a third full bridge circuit; The input end of the first full bridge circuit is connected to both ends of the first section winding of the secondary side winding in the excitation transformer; The input end of the second full bridge circuit is connected to both ends of the second segment winding of the secondary side winding in the excitation transformer; The input end of the third full bridge circuit is connected to both ends of the third segment winding of the secondary side winding in the excitation transformer. 7. The controllable phase shifter as claimed in claim 6, wherein each bridge arm of the first full bridge circuit is composed of a thyristors connected in series, each bridge arm of the second full bridge circuit It is composed of b thyristors connected in series, each bridge arm of the third full bridge circuit is composed of c thyristors connected in series, a:b:c=1:3:9; The ratio of the number of turns n1 of the first winding, the number of turns n2 of the second winding, and the number of turns n3 of the third winding is n1:n2:n3=1:3:9. 8. The controllable phase shifter as claimed in claim 6, wherein the working state of the secondary side winding in the excitation transformer comprises 27 working states; The working state of the first section of winding includes forwardly connecting the secondary winding of the booster transformer, reversely connecting the secondary winding of the boosting transformer and not connecting the secondary winding of the boosting transformer; The working state of the second section of winding includes forwardly connecting the secondary winding of the booster transformer, reversely connecting the secondary winding of the boosting transformer and not connecting the secondary winding of the boosting transformer; The working state of the third section winding includes the secondary side winding of the booster transformer being connected in series in forward direction, the secondary side winding of the boosting transformer being connected in series in reverse direction and the secondary side winding of the boosting transformer not being connected in series.