Novel topological structure of thyristor control type phase-shifting transformer combined with cascaded H-bridge converter

Abstract

The invention provides a novel topological structure of a thyristor control type phase-shifting transformer combined with a cascaded H-bridge converter. The novel topological structure comprises a series transformer, a parallel transformer, a thyristor control circuit and a continuous regulation control circuit, the parallel transformer obtains voltage from a power grid line through the series transformer, according to a power grid line power control target, secondary side adjustable voltage is generated through the thyristor control circuit, coarse adjustment of phase-shifting voltage is achieved, the coarse adjustment is combined with output voltage of the continuous adjustment control circuit, and phase-shifting voltage with adjustable phase amplitude is generated. And the phase-shifting voltage is compensated into the power grid line through the series transformer, so that the power of the power grid line is adjusted to the target power. The method not only inherits the characteristics of quick adjustment and quick response of the traditional TCPST, but also overcomes the defect that the power of the traditional TCPST cannot be continuously adjusted, and realizes the quick and continuous adjustment of the active power flow of the line.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a novel topology of a phase-shifting transformer. Background Art

[0002] As the most typical FACTS device, the unified power flow controller (UPFC) has good effects in power flow regulation and load balancing. However, due to the large-scale use of high-power power electronic devices, the topology of UPFC is relatively complex, the cost is high, and the floor space requirement is large. In contrast, the thyristor controlled phase shifting transformer (TCPST), as a new type of flexible AC transmission equipment, has a simpler structure and higher economy. After research by many scholars at home and abroad, it has been proved that TCPST not only has the function of regulating the power flow of the power grid and improving the distribution of the power flow of the system like the traditional mechanical phase shifting transformer, but also has the characteristics of fast regulation and fast response.

[0003] The invention patent with publication number CN104934974A discloses a controllable phase shifter with short-circuit current limiting function, which discloses that the controllable phase shifter includes an excitation transformer, a boost transformer and a thyristor voltage regulating circuit;

[0004] The low-voltage end of the primary 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 winding is composed of two windings connected in series, and the connection point of the two windings 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 connected in series; the input end of the thyristor voltage regulating circuit is connected to the secondary winding of the excitation transformer, and the output end is connected to the high-voltage end of the primary winding in the booster transformer. This invention patent can quickly change the phase angle, limit the short-circuit current, and play an important protective role in the safe operation of the power grid under fault conditions.

[0005] However, TCPST does not have the ability of continuous regulation, there is a dead zone in power flow regulation, and it cannot fully regulate the power flow according to the power control target. Summary of the invention

[0006] In view of the technical problem that TCPST does not have the ability of continuous regulation and has a dead zone in power flow regulation, the present invention proposes a new topology structure of a thyristor controlled phase shifting transformer combined with a cascaded H-bridge converter (cascaded H-bridge converter-thyristor controlled phase shifting transformer, CHBC-TCPST). CHBC-TCPST connects a cascaded H-bridge converter in series on the secondary side of the excitation transformer, combines the output voltage of the cascaded H-bridge converter with the output voltage of the secondary side of the excitation transformer, and generates a continuously adjustable voltage as the phase shift compensation voltage of the series transformer. It not only inherits the characteristics of fast regulation and fast response of traditional TCPST, but also overcomes the disadvantage that traditional TCPST cannot continuously adjust power, thereby realizing fast and continuous regulation of line active power flow.

[0007] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A novel topology structure of a thyristor-controlled phase-shifting transformer combined with a cascaded H-bridge converter, characterized in that it comprises a series transformer, a parallel transformer, a thyristor control circuit and a cascaded H-bridge converter;

[0009] The parallel transformer obtains voltage from the power grid line through the series transformer, and generates a secondary-side adjustable voltage using a thyristor control circuit according to the power control target of the power grid line to achieve coarse adjustment of the phase-shift voltage, and combines it with the output voltage of the cascaded H-bridge converter to generate a phase-shift voltage with adjustable phase and amplitude, thereby achieving continuous adjustment of the phase-shift voltage, and compensates the phase-shift voltage to the power grid line through the series transformer, thereby adjusting the power of the power grid line to the target power.

[0010] The positive polarity end of the primary winding B1 of the series transformer is connected to the sending end S of the power grid line, and the negative polarity end of the primary winding B2 of the series transformer is connected to the receiving end L of the power grid line. The negative polarity end of the primary winding B1 and the positive polarity end of the primary winding B2 are star-connected with the parallel transformer through the neutral point; the series transformer obtains voltage from the power grid line through the sending end S and the receiving end L and performs phase-shift voltage compensation.

[0011] The primary winding E1 of the parallel transformer obtains voltage from the power grid line through the primary winding B1 and the primary winding B2 of the series transformer; the negative polarity end of the primary winding E1 of the parallel transformer is grounded; the secondary winding of the parallel transformer is connected to the secondary winding B3 of the series transformer through the positive polarity end of the thyristor control circuit, and the access mode of the secondary winding of the parallel transformer is controlled by the thyristor control circuit, so as to change the phase-shifting voltage to be injected into the power grid line by the phase-shifting transformer to realize coarse adjustment of the phase-shifting voltage.

[0012] The number of the series transformers is at least 3, and the series transformers are connected in a triangle; the number of the parallel transformers is at least 4.

[0013] The secondary winding of the parallel transformer is connected to the positive end of the cascaded H-bridge converter through the negative end of the thyristor control circuit, the negative end of the cascaded H-bridge converter is grounded, and the phase-shift voltage is further continuously adjusted through the cascaded H-bridge converter.

[0014] The thyristor control circuit comprises a plurality of thyristor circuits connected in sequence, and each thyristor circuit comprises four thyristor modules connected in reverse parallel.

[0015] The number of the thyristor circuits matches the number of the secondary windings of the parallel transformers, the connection sequence of the multiple thyristor circuits matches the secondary windings of the parallel transformers, and each thyristor circuit controls the access mode of the secondary winding of the corresponding parallel transformer.

[0016] The number of the cascaded H-bridge converters is at least 3, and the cascaded H-bridge converter includes multiple groups of H-bridge converter units, each group of H-bridge converter units includes four IGBT switch tubes equipped with reverse parallel freewheeling diodes and a DC capacitor; the forward conduction direction of the four IGBT switch tubes is consistent, and the forward conduction direction of the freewheeling diode is opposite to that of the IGBT switch tube.

[0017] The four IGBT switch tubes equipped with reverse parallel freewheeling diodes are respectively the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube. The first IGBT switch tube and the second IGBT switch tube constitute a bridge arm I, and the third IGBT switch tube and the fourth IGBT switch tube constitute a bridge arm II. Lines are respectively drawn from the middle points of the bridge arms I and II to connect with the external circuit of the H-bridge commutation unit. The bridge arms I, II and the DC capacitor are connected in parallel; the gates of the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube are all connected to the external PWM control circuit.

[0018] The number of secondary windings of the parallel transformer is at least 4; the access modes of the secondary windings of the parallel transformer include forward access, reverse access and no access.

[0019] Beneficial effects of the present invention:

[0020] Firstly, the CHBC-TCPST of the present invention not only inherits the fast adjustment and fast response characteristics of the traditional TCPST, but also overcomes the shortcoming that the traditional TCPST power cannot be continuously adjusted, thereby realizing fast and continuous adjustment of the line active power flow.

[0021] Secondly, since the response speed of thyristor operation is in the millisecond level, TCPST can be used not only for system steady-state regulation, but also for system transient regulation. Moreover, the response speed of CHBC is also in the millisecond level, so the two can be combined. When the system is subjected to a large disturbance, a certain control strategy can be used to adjust the phase shift angle, improve the stability of the initial swing in the transient process of the power system, and provide damping for subsequent oscillations.

[0022] Finally, for thyristor continuous regulation phase shifters that occupy a large area, have a complex control method and a high manufacturing cost, not only the cost of such continuous regulation phase shifters is reduced, the area occupied is reduced, but also the complexity of the voltage regulation circuit is reduced and the control method is simplified. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a topology diagram of a thyristor controlled phase shifting transformer combined with a cascaded H-bridge converter.

[0025] Figure 2 It is a topology diagram of a three-phase cascaded H-bridge converter.

[0026] Figure 3 It is the topology diagram of the C-phase thyristor control circuit.

[0027] Figure 4 2 is a simulation circuit diagram of an embodiment.

[0028] Figure 5 It is the active power curve of the power grid line installed with phase-shifting transformer.

[0029] Figure 6 It is the voltage curve across the phase-shifting transformer. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] A new topology of thyristor-controlled phase-shifting transformer combined with cascaded H-bridge converters, such as Figure 1 As shown:

[0033] It includes a series transformer, the series transformer is connected to a parallel transformer, the parallel transformer is connected to a thyristor control circuit, and the thyristor control circuit is respectively connected to the cascade H-bridge converter and the series transformer;

[0034] The parallel transformer obtains voltage from the power grid line through the series transformer, and according to the power control target of the power grid line, uses the thyristor control circuit to generate an adjustable secondary voltage to achieve coarse regulation of the phase-shift voltage, and combines with the output voltage of the continuous regulation control circuit to generate a phase-shift voltage with adjustable phase and amplitude, thereby achieving continuous regulation of the phase-shift voltage, and compensates the phase-shift voltage to the power grid line through the series transformer, thereby regulating the power of the power grid line to the target power.

[0035] The number of the series transformers is 3, corresponding to the three phases A, B, and C, namely series transformer BTa, series transformer BTb, and series transformer BTc; the series transformer is a three-winding transformer, adopts a Y / D connection method, and the secondary winding ratio of the series transformer is NB1:NB2=1:1.

[0036] The three series transformers have the same structure, such as Figure 1 Shown in the upper part.

[0037] The positive polarity end of the primary winding B1a of the series transformer BTa is connected to the sending end SA of the power grid line, and the negative polarity end of the primary winding B2a is connected to the receiving end LA of the power grid line. The negative polarity end of the primary winding B1a and the positive polarity end of the primary winding B2a are star-connected (Y-connected) with the primary winding E1a of the parallel transformer Eta through the neutral point; the series transformer BTa obtains voltage from the power grid line through the sending end SA and the receiving end LA and performs phase-shift voltage compensation.

[0038] The positive polarity end of the primary winding B1b of the series transformer BTb is connected to the power grid line sending end SB, and the negative polarity end of the primary winding B2b is connected to the power grid line receiving end LB. The negative polarity end of the primary winding B1b and the positive polarity end of the primary winding B2b are star-connected (Y-connected) with the primary winding E1b of the parallel transformer Etb through the neutral point. The series transformer BTb obtains voltage from the power grid line through the sending end SB and the receiving end LB and performs phase-shift voltage compensation.

[0039] The positive polarity end of the primary winding B1c of the series transformer BTc is connected to the power grid line sending end SC, and the negative polarity end of the primary winding B2c is connected to the power grid line receiving end LC. The negative polarity end of the primary winding B1c and the positive polarity end of the primary winding B2c are star-connected (Y-connected) with the primary winding E1c of the parallel transformer Etc through the neutral point. The series transformer BTc obtains voltage from the power grid line through the sending end SC and the receiving end LC and performs phase shift voltage compensation.

[0040] As shown in the figure, the secondary winding B3a of the series transformer BTa, the secondary winding B3b of the series transformer BTb and the secondary winding B3c of the series transformer BTc are connected in a triangle (D connection), and the end point a of the secondary winding B3a of the series transformer BTa is connected to the parallel transformer ETc through the thyristor control circuit C, and the end point a is also connected to the end point z, and the end point x is connected to the end point b; the end point b of the secondary winding B3b of the series transformer BTb is connected to the secondary side of the parallel transformer ETa through the thyristor control circuit A, and the end point y is connected to the end point c; the end point c of the secondary winding B3c of the series transformer BTc is connected to the secondary side of the parallel transformer ETb through the thyristor control circuit B.

[0041] The number of parallel transformers is 3, corresponding to the three phases A, B, and C, which are parallel transformer ETa, parallel transformer ETb, and parallel transformer ETc respectively; the number of parallel transformer windings can be determined according to the requirements of the phase shift angle adjustment range in the specific application scenario. Usually, the parallel transformer is a four-winding transformer with a Y / Y connection method; the secondary winding ratio of the parallel transformer is NE2:NE3:NE4=1:3:9. Figure 1 Shown in the lower part.

[0042] The three parallel transformers have the same structure, such as Figure 1 Shown in the lower part.

[0043] For the parallel transformer ETa: the primary winding E1a obtains voltage from the grid line through the primary windings B1a and B2a of the series transformer BTa; the negative polarity end of the primary winding E1a of the parallel transformer ETa is grounded;

[0044] The secondary windings E2a, E3a, and E4a of the parallel transformer ETa are connected to the secondary side B3a of the series transformer BTa through the positive polarity end of the thyristor control circuit A. The thyristor control circuit A controls the access mode of the secondary winding of the parallel transformer ETa, changes the phase-shifting voltage to be injected into the power grid by the phase-shifting transformer, and realizes the coarse adjustment of the phase-shifting voltage.

[0045] The secondary windings E2a, E3a, and E4a of the parallel transformer ETa are connected to the positive end of the cascaded H-bridge converter A through the negative end of the thyristor control circuit A. The negative end of the cascaded H-bridge converter A is grounded, and the phase-shift voltage is further continuously adjusted through the cascaded H-bridge converter A.

[0046] For the parallel transformer Etb: the primary winding E1b obtains voltage from the grid line through the primary windings B1b and B2b of the series transformer BTb; the negative polarity end of the primary winding E1b of the parallel transformer ETb is grounded;

[0047] The secondary windings E2b, E3b, and E4b of the parallel transformer ETb are connected to the secondary side B3b of the series transformer BTb through the positive polarity end of the thyristor control circuit B. The secondary winding access mode of the parallel transformer ETb is controlled by the thyristor control circuit B to change the phase-shifting voltage to be injected into the power grid line by the phase-shifting transformer, thereby realizing the coarse adjustment of the phase-shifting voltage.

[0048] The secondary windings E2b, E3b, and E4b of the parallel transformer ETb are connected to the positive end of the cascaded H-bridge converter B through the negative end of the thyristor control circuit B. The negative end of the cascaded H-bridge converter B is grounded, and the phase-shift voltage is further continuously adjusted through the cascaded H-bridge converter B.

[0049] For the parallel transformer Etc: the primary winding E1c obtains voltage from the grid line through the primary windings B1c and B2c of the series transformer BTc; the negative polarity end of the primary winding E1c of the parallel transformer ETc is grounded;

[0050] The secondary windings E2c, E3c and E4c of the parallel transformer ETc are connected to the secondary side B3c of the series transformer BTc through the positive polarity end of the thyristor control circuit C. The secondary winding access mode of the parallel transformer ETc is controlled by the thyristor control circuit C to change the phase-shifting voltage to be injected into the power grid line by the phase-shifting transformer, so as to realize the coarse adjustment of the phase-shifting voltage.

[0051] The secondary windings E2c, E3c and E4c of the parallel transformer ETc are connected to the positive end of the cascaded H-bridge converter C through the negative end of the thyristor control circuit C. The negative end of the cascaded H-bridge converter C is grounded. The phase-shift voltage is further continuously adjusted through the cascaded H-bridge converter C.

[0052] The thyristor control circuit comprises a thyristor control circuit A, a thyristor control circuit B and a thyristor control circuit C, which correspond to the three phases A, B and C respectively.

[0053] If the parallel transformer adopts a four-winding transformer and the secondary winding level ratio is 1:3:9, the corresponding thyristor control circuit is also divided into a 1:3:9 three-level thyristor circuit. Taking the thyristor control circuit C as an example, the thyristor control circuit C includes a 1-level thyristor circuit, a 3-level thyristor circuit and a 9-level thyristor circuit connected in sequence, and the connection sequence matches the secondary windings E2c, E3c, and E4c of the parallel transformer ETc;

[0054] Each thyristor circuit includes four thyristor modules connected in reverse parallel. Figure 3 As shown;

[0055] The 1-level thyristor circuit includes a first thyristor module, a second thyristor module, a fourth thyristor module and a fourth thyristor module; wherein the first thyristor module and the second thyristor module are connected in series to form a first bridge arm, the third thyristor module and the fourth thyristor module are connected in series to form a second bridge arm, and lines are respectively drawn from the midpoints of the first bridge arm and the second bridge arm to connect to the secondary winding E2c of the parallel transformer; the first thyristor module and the third thyristor module are connected to the end point a of the secondary winding B3a of the series transformer BTa, and the second thyristor module and the fourth thyristor module are connected to the input end of the 3-level thyristor circuit.

[0056] The 3-level thyristor circuit includes a fifth thyristor module, a sixth thyristor module, a seventh thyristor module and an eighth thyristor module; wherein the fifth thyristor module and the sixth thyristor module are connected in series to form a third bridge arm, the seventh thyristor module and the eighth thyristor module are connected in series to form a fourth bridge arm, and lines are respectively drawn from the midpoints of the third bridge arm and the fourth bridge arm to be connected to the secondary winding E3c of the parallel transformer; the input end of the fifth thyristor module and the input end of the seventh thyristor module are connected to form the input end of the 3-level thyristor circuit, which is connected to the second thyristor module and the fourth thyristor module, and the sixth thyristor module and the eighth thyristor module are connected to the input end of the 9-level thyristor circuit.

[0057] The 9-level thyristor circuit includes a ninth thyristor module, a tenth thyristor module, an eleventh thyristor module and a twelfth thyristor module; wherein the ninth thyristor module and the ninth thyristor module are connected in series to form a fifth bridge arm, the eleventh thyristor module and the twelfth thyristor module are connected in series to form a sixth bridge arm, and lines are respectively drawn from the midpoints of the fifth bridge arm and the sixth bridge arm to be connected to the secondary winding E4c of the parallel transformer; the input end of the ninth thyristor module and the input end of the eleventh thyristor module are connected to form the input end of the 9-level thyristor circuit to be connected to the sixth thyristor module and the eighth thyristor module, and the tenth thyristor module and the twelfth thyristor module are connected to the cascaded H-bridge converter C.

[0058] The 1-level thyristor circuit controls the access mode of the winding E2c, the 3-level thyristor circuit controls the access mode of the winding E3c, and the 9-level thyristor circuit controls the access mode of the winding E4c. The access modes include forward access, reverse access, and no access.

[0059] The thyristor module is controlled to be turned on and off by an external control signal; for the level 1 thyristor circuit, when the secondary winding E2c of the parallel transformer is controlled to be connected in the forward direction, the first thyristor module and the fourth thyristor module in the corresponding level 1 thyristor circuit are turned on; when the secondary winding E2c of the parallel transformer is controlled to be connected in the reverse direction, the second thyristor module and the third thyristor module in the corresponding level 1 thyristor control circuit are turned on; when the secondary winding E2c of the parallel transformer is not controlled to be connected, the first thyristor module and the second thyristor module in the corresponding level 3 thyristor control circuit are turned on or the third thyristor module and the fourth thyristor module are turned on.

[0060] For the 3-level thyristor circuit, when the secondary winding E3c of the controlled parallel transformer is connected in the forward direction, the fifth thyristor module and the eighth thyristor module in the corresponding 3-level thyristor circuit are turned on; when the secondary winding E3c of the controlled parallel transformer is connected in the reverse direction, the sixth thyristor module and the seventh thyristor module in the corresponding 3-level thyristor control circuit are turned on; when the secondary winding E3c of the controlled parallel transformer is not connected, the fifth thyristor module and the sixth thyristor module in the corresponding 3-level thyristor control circuit are turned on or the seventh thyristor module and the eighth thyristor module are turned on.

[0061] For the 9-level thyristor circuit, when the secondary winding E4c of the controlled parallel transformer is connected in the forward direction, the ninth thyristor module and the twelfth thyristor module in the corresponding 9-level thyristor circuit are turned on; when the secondary winding E2c of the controlled parallel transformer is connected in the reverse direction, the tenth thyristor module and the eleventh thyristor module in the corresponding 9-level thyristor control circuit are turned on; when the secondary winding E4c of the controlled parallel transformer is not connected, the ninth thyristor module and the tenth thyristor module in the corresponding 9-level thyristor control circuit are turned on or the eleventh thyristor module and the twelfth thyristor module are turned on.

[0062] By combining the three winding voltages on the secondary side of the parallel transformer ETc, 27 output voltages on the secondary side of the parallel transformer ETc can be formed. The structure and principle of the B phase and the C phase are the same as above.

[0063] The number of the cascaded H-bridge converters is 3, corresponding to the three phases A, B, and C, namely, the cascaded H-bridge converter A, the cascaded H-bridge converter B, and the cascaded H-bridge converter C.

[0064] Taking the cascaded H-bridge converter A as an example, the cascaded H-bridge converter A includes multiple groups of H-bridge converter units. The number of H-bridge converter units is determined according to the voltage regulation dead zone between the 27 output voltages of the above-mentioned parallel transformer and the output voltage of a single H-bridge converter unit. As long as the total voltage output by multiple groups of series-connected H-bridge converter units can cover the voltage regulation dead zone while considering a certain redundancy, it can be used. Each group of H-bridge commutation units includes four IGBT switch tubes equipped with reverse parallel freewheeling diodes and a DC capacitor; the four IGBT switch tubes equipped with reverse parallel freewheeling diodes are respectively the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube; the first IGBT switch tube and the second IGBT switch tube constitute bridge arm I, the third IGBT switch tube and the fourth IGBT switch tube constitute bridge arm II, and lines are respectively drawn from the middle points of bridge arm I and bridge arm II to connect with the external circuit of the H-bridge commutation unit, the four IGBT switch tubes have the same forward conduction direction, and the forward conduction direction of the freewheeling diode is opposite to that of the IGBT switch tube; bridge arm I, bridge arm II and the DC capacitor are connected in parallel.

[0065] The gates of the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube are all connected to an external PWM control circuit. The PWM control circuit uses a carrier phase-shift PWM technology to control the output voltage amplitude and phase of the H-bridge commutation unit. During the process, each H-bridge commutation unit shares a modulation wave, and the carrier phase difference between adjacent modules is 2π / N.

[0066] The carrier phase-shift PWM technology uses the difference between the actual line power and the reference power (grid line power control target) and the difference between the actual voltage of each capacitor inside the H-bridge and the reference voltage as the input of the controller of the PWM control circuit, and uses current feedforward decoupling control and capacitor voltage balancing control to obtain the modulation wave signal of each phase cascaded H-bridge converter. Then, through the PWM control circuit, the modulation wave is compared with the carrier to obtain the control signal of the IGBT switch tube inside the cascaded H-bridge converter of each phase, and the control signal is used to control the output voltage of the H-bridge converter unit, thereby realizing the control of the output voltage of the cascaded H-bridge converter.

[0067] Example 2

[0068] A new topology of a thyristor-controlled phase-shifting transformer combined with a cascaded H-bridge converter is proposed. The CHBC-TCPST is set to be installed in a 220kV line for power flow regulation. The series transformer is a three-winding transformer, which adopts a Y / D connection method. The transformation ratio of the secondary winding of the series transformer is NB1:NB2=1:1; the parallel transformer is a four-winding transformer, which adopts a Y / Y connection method. The transformation ratio of the secondary winding of the parallel transformer is NE2:NE3:NE4=1:3:9.

[0069] like Figure 2 As shown, the number of the cascaded H-bridge converters is 3, corresponding to the three phases A, B, and C, namely, the cascaded H-bridge converter A, the cascaded H-bridge converter B, and the cascaded H-bridge converter C.

[0070] Taking the cascaded H-bridge converter A as an example, the cascaded H-bridge converter A includes n=7 groups of H-bridge converter units. The number of H-bridge converter units is determined according to the voltage regulation dead zone between the 27 output voltages of the above-mentioned parallel transformer and the output voltage of a single H-bridge converter unit. As long as the total voltage output by multiple groups of H-bridge converter units in series can cover the voltage regulation dead zone under a certain redundancy, considering that the secondary side tap switch differential voltage of the parallel transformer is 5kV, the number of cascaded H-bridge converters per phase in CHBC is set to 7 (7*0.8>5), the maximum output voltage amplitude is 5.6kV, and there are 21 in total for three phases. Each group of H-bridge commutation units includes four IGBT switch tubes equipped with reverse parallel freewheeling diodes and a DC capacitor; the four IGBT switch tubes equipped with reverse parallel freewheeling diodes are respectively the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube; the first IGBT switch tube and the second IGBT switch tube constitute bridge arm I, the third IGBT switch tube and the fourth IGBT switch tube constitute bridge arm II, and lines are respectively drawn from the middle points of bridge arm I and bridge arm II to connect with the external circuit of the H-bridge commutation unit, the four IGBT switch tubes have the same forward conduction direction, and the forward conduction direction of the freewheeling diode is opposite to that of the IGBT switch tube; bridge arm I, bridge arm II and the DC capacitor are connected in parallel.

[0071] The gates of the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube are all connected to an external PWM control circuit. The PWM control circuit uses a carrier phase-shift PWM technology to control the output voltage amplitude and phase of the H-bridge commutation unit. During the process, each H-bridge commutation unit shares a modulation wave, and the carrier phase difference between adjacent modules is 2π / N.

[0072] The carrier phase-shift PWM technology uses the difference between the actual line power and the reference power (grid line power control target) and the difference between the actual voltage of each capacitor inside the H-bridge and the reference voltage as the input of the controller of the PWM control circuit, and uses current feedforward decoupling control and capacitor voltage balancing control to obtain the modulation wave signal of each phase cascaded H-bridge converter. Then, through the PWM control circuit, the modulation wave is compared with the carrier to obtain the control signal of the IGBT switch tube inside the cascaded H-bridge converter of each phase, and the control signal is used to control the output voltage of the H-bridge converter unit, thereby realizing the control of the output voltage of the cascaded H-bridge converter.

[0073] Figure 4The simulation circuit diagram of the embodiment is shown below. When the cascaded H-bridge converter is not put into operation, the phase shift angle of each stage of the thyristor control circuit is approximately ±0.812°, and the carrier frequency is 1kHz. Figure 5 It is the active power curve of the CHBC-TCPST installed line. After CHBC is put into use, the line power can be gradually adjusted to the set line power reference value; Figure 6 It is the voltage curve across CHBC-TCPST. The voltage and current output by CHBC are gradually adjusted by the controller until the line power and capacitor voltage are consistent with the reference value.

[0074] The power control target is set to 118kW, and the capacitor voltage reference value is 0.8kV. At 2s, the system is connected to CHBC-TCPST, and the thyristor control circuit gear is 0. Figure 5 It can be seen that the active power of the line is stable at 82kW, and the CHBC-TCPST end passes Figure 6 It can be seen that the voltage is stable at about 2.5kV. When 2.5, the thyristor control circuit adjusts the gear from 0 to 5 (the 1st winding on the secondary side of the parallel transformer is reversely connected, the 3rd winding is reversely connected, and the 9th winding is positively connected. 5 = 9-3-1). Figure 5 It can be seen that the line active power is adjusted from about 82kW to about 112kW. Figure 6 It can be seen that the voltage at the CHBC-TCPST end increases from 2.5kV to about 5kV. 4s ago, CHBC was in a locked state, and the system was working in a steady state. At 4s, CHBC was unlocked and put into the system for line power regulation. Figure 5 It can be seen that the line power is adjusted from about 112kW to about 116kW. Figure 6 It can be seen that the voltage at the CHBC-TCPST end increases from 5kV to about 6.25kV. At 6s, the CHBC has basically completed the line power regulation. Figure 6 It can be seen that the voltage at the CHBC-TCPST terminal is stable at around 6.25kV. Figure 5 It can be seen that the line active power is stable at around 118kW.

[0075] The other structures and principles are the same as those in Example 1.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel topology of a thyristor-controlled phase-shifting transformer combined with a cascaded H-bridge converter, characterized in that: It includes a series transformer, a parallel transformer, a thyristor control circuit and a cascade H-bridge converter; The parallel transformer obtains voltage from the power grid line through the series transformer, and generates a secondary-side adjustable voltage using a thyristor control circuit according to the power control target of the power grid line to achieve coarse adjustment of the phase-shift voltage, and combines it with the output voltage of the cascaded H-bridge converter to generate a phase-shift voltage with adjustable phase and amplitude, thereby achieving continuous adjustment of the phase-shift voltage, and compensates the phase-shift voltage to the power grid line through the series transformer, thereby adjusting the power of the power grid line to the target power.

2. The novel topological structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 1 is characterized in that: The positive polarity end of the primary winding B1 of the series transformer is connected to the sending end S of the power grid line, and the negative polarity end of the primary winding B2 of the series transformer is connected to the receiving end L of the power grid line. The negative polarity end of the primary winding B1 and the positive polarity end of the primary winding B2 are star-connected with the parallel transformer through the neutral point; the series transformer obtains voltage from the power grid line through the sending end S and the receiving end L and performs phase-shift voltage compensation.

3. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to any one of claims 1 to 3, characterized in that: The primary winding E1 of the parallel transformer obtains voltage from the power grid line through the primary winding B1 and the primary winding B2 of the series transformer; the negative polarity end of the primary winding E1 of the parallel transformer is grounded; the secondary winding of the parallel transformer is connected to the secondary winding B3 of the series transformer through the positive polarity end of the thyristor control circuit, and the access mode of the secondary winding of the parallel transformer is controlled by the thyristor control circuit, so as to change the phase-shifting voltage to be injected into the power grid line by the phase-shifting transformer to realize coarse adjustment of the phase-shifting voltage.

4. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 3 is characterized in that: The number of the series transformers is at least 3, and the series transformers are connected in a triangle; the number of the parallel transformers is at least 4.

5. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 4 is characterized in that: The secondary winding of the parallel transformer is connected to the positive end of the cascaded H-bridge converter through the negative end of the thyristor control circuit, the negative end of the cascaded H-bridge converter is grounded, and the phase-shift voltage is further continuously adjusted through the cascaded H-bridge converter.

6. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 1 or 5, characterized in that: The thyristor control circuit comprises a plurality of thyristor circuits connected in sequence, and each thyristor circuit comprises four thyristor modules connected in reverse parallel.

7. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 6 is characterized in that: The number of the thyristor circuits matches the number of the secondary windings of the parallel transformers, the connection sequence of the multiple thyristor circuits matches the secondary windings of the parallel transformers, and each thyristor circuit controls the access mode of the secondary winding of the corresponding parallel transformer.

8. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 7 is characterized in that: The number of the cascaded H-bridge converters is at least 3, and the cascaded H-bridge converter includes multiple groups of H-bridge converter units, each group of H-bridge converter units includes four IGBT switch tubes equipped with reverse parallel freewheeling diodes and a DC capacitor; the forward conduction direction of the four IGBT switch tubes is consistent, and the forward conduction direction of the freewheeling diode is opposite to that of the IGBT switch tube.

9. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 8 is characterized in that: The four IGBT switch tubes equipped with reverse parallel freewheeling diodes are respectively the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube. The first IGBT switch tube and the second IGBT switch tube constitute a bridge arm I, and the third IGBT switch tube and the fourth IGBT switch tube constitute a bridge arm II. Lines are respectively drawn from the middle points of the bridge arms I and II to connect with the external circuit of the H-bridge commutation unit. The bridge arm I, the bridge arm II and the DC capacitor are connected in parallel; the gates of the first IGBT switch tube, the second IGBT switch tube, the third IGBT switch tube and the fourth IGBT switch tube are all connected to the external PWM control circuit.

10. The novel topology structure of the thyristor-controlled phase-shifting transformer combined with the cascaded H-bridge converter according to claim 7, characterized in that: The number of secondary windings of the parallel transformer is at least 4; the access modes of the secondary windings of the parallel transformer include forward access, reverse access and no access.

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