A three-phase shared hybrid flexible distribution transformer and control method thereof

Abstract

A three-phase shared hybrid flexible distribution transformer and a control method thereof, the hybrid flexible distribution transformer comprises a transformer body, a full-bridge converter module, three series-side switching switches, and three parallel-side switching switches, the full-bridge converter module comprises a series converter and a parallel converter with the same structure, the series converter is connected to the three series-side switching switches, the three series-side switching switches are respectively connected to the A, B, and C phase windings of the voltage compensation winding in the transformer body, the parallel converter is connected to the three parallel-side switching switches, the three parallel-side switching switches are respectively connected to the A, B, and C phase windings of the current compensation winding in the transformer body. In application, by sharing a full-bridge converter module with the hybrid flexible distribution transformer, the purpose of achieving the highest compensation capacity utilization and the minimum distribution line loss can be achieved under the condition of limited converter compensation capacity, and the switching loss can be reduced to improve the reliability of the device.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical devices in power systems, and specifically relates to a three-phase shared hybrid flexible distribution transformer and a control method thereof, which is suitable for improving the device reliability and utilization rate of the converter, thereby improving the comprehensive power quality level of power supply and use. Background Art

[0002] As the core equipment for power conversion in all links of "transmission, transformation and distribution", electromagnetic power transformers have become the "backbone" equipment in the power system due to their high reliability and stable power transmission. However, they only have the function of mechanical segmented voltage regulation, which cannot meet the goals of rapid and continuous voltage regulation and complex power flow control, and cannot meet the requirements of new power systems for comprehensive power quality management. Power electronic devices have become an effective technical means to solve the problems of comprehensive power quality management and new energy grid-connected fluctuations, but pure power electronic equipment has low reliability, high power density application occasions require large construction investment, complex control circuits, and high operation and maintenance costs. For this reason, a flexible distribution transformer with an electromagnetic transformer as the main body and equipped with an AC / DC / AC converter was born, which has the advantages of high reliability of electromagnetic transformers and high flexibility in converter regulation.

[0003] Existing hybrid flexible distribution transformers all adopt topological structures such as three-phase three-bridge arms, three-phase four-bridge arms, and three-phase full-bridge, respectively using three bridge arms, four bridge arms, and six bridge arms. When only one phase of the three-phase load needs reactive power compensation, the three-phase load is unbalanced, and the voltage amplitude is adjusted, only one phase of the converter needs to work, and the other two phases are unloaded, resulting in large switching losses and relatively low device reliability. In addition, when a phase has large harmonics, large reactive power, and severe imbalance, due to the limited capacity of the converter (the converter capacity is generally 10%-50% of the transformer body), only limited single-phase compensation can be provided, that is, only one-third of the current corresponding to the converter capacity can be provided for the phase, and there is nothing to be done about the compensation current shortage of the phase. When a phase has very small reactive power and good three-phase balance, the converter cannot transfer the spare capacity of the phase to the other two phases with large reactive power and poor three-phase balance. There is a problem that the compensation capacity for reactive power compensation of each phase cannot be flexibly adjusted, and the converter utilization rate is poor. Summary of the invention

[0004] The object of the present invention is to provide a three-phase shared hybrid flexible distribution transformer and a control method thereof, which can improve the reliability and utilization of the converter device, in view of the above-mentioned problems existing in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a three-phase shared hybrid flexible distribution transformer, comprising a transformer body, wherein the transformer body comprises a main transformer module, a voltage compensation winding, and a current compensation winding;

[0007] The hybrid flexible distribution transformer also includes a full-bridge converter module, three series side switching switches, and three parallel side switching switches. The full-bridge converter module includes a series converter and a parallel converter. The series converter has the same structure as the parallel converter. The series converter is connected to the three series side switching switches, and the three series side switching switches are respectively connected to the A, B, and C phase windings of the voltage compensation winding. The parallel converter is connected to the three parallel side switching switches, and the three parallel side switching switches are respectively connected to the A, B, and C phase windings of the current compensation winding.

[0008] The parallel converter and the series converter each include a single-phase full-bridge power unit, and the single-phase full-bridge power unit has two bridge arms, and the bridge arm is composed of an IGBT half-bridge module.

[0009] The series-side switching switch and the parallel-side switching switch are both IGBT modules.

[0010] An energy storage capacitor is connected in parallel between each of the three series-side switching switches and the series converter, and the parallel converter and the series converter share a DC bus capacitor.

[0011] The voltage compensation winding and the current compensation winding are both connected to the secondary side of the main transformer module.

[0012] The voltage compensation winding and the current compensation winding are respectively connected to the primary side and the secondary side of the main transformer module.

[0013] In a second aspect, the present invention provides a control method for a three-phase shared hybrid flexible distribution transformer. The control method is based on the aforementioned three-phase shared hybrid flexible distribution transformer, and the control method includes:

[0014] Control methods include:

[0015] S1, determine whether single-phase compensation control or multi-phase compensation control is currently required, if it is single-phase compensation control, enter S2, if it is multi-phase compensation control, enter S3;

[0016] S2, controlling the series side switch and the parallel side switch corresponding to the one to be compensated to close, so as to realize the single-phase compensation at full power;

[0017] S3. Implement multi-phase compensation control through a comprehensive compensation strategy, wherein the comprehensive compensation strategy is specifically: control the corresponding series-side switching switches and parallel-side switching switches to be compensated to be closed, and distribute the compensation capacity of the three phases.

[0018] In S1, it is determined whether single-phase compensation control or multi-phase compensation control is currently required according to the following steps:

[0019] A1. Calculate the unit current loss reduction rate of reactive power compensation of the three phases under different compensation currents respectively;

[0020] A2. With the compensation current as the horizontal coordinate and the unit current loss rate as the vertical coordinate, draw the compensation current-unit current loss rate curve of the three phases in the same coordinate system; suppose that the three curves from top to bottom in the obtained curve graph are curve A, curve B, and curve C respectively. First, determine whether any point in curve A is higher than the highest point in curve B. If so, perform single-phase compensation control on the phase corresponding to curve A. If not, continue to determine whether any point in curve B is higher than the highest point in curve C. If so, perform multi-phase compensation control on the two phases corresponding to curves A and curve B. If not, perform multi-phase compensation control on the three phases.

[0021] In A1, the unit current loss reduction rate of reactive power compensation of three phases under different compensation currents is calculated according to the following formula:

[0022]

[0023]

[0024]

[0025] In the above formula, η Q Indicates the unit current loss rate of single-phase reactive power compensation; ΔP lQ Indicates the loss reduced by single-phase reactive power compensation; I Q Represents the reactive compensation current on a single phase, I Q ≤M·I, I represents the current of the transformer body, M represents the proportion of the full-bridge converter module capacity to the transformer body capacity; R represents the line resistance; cosφ 1 is the single-phase current power factor.

[0026] In S3, the compensation capacity of each phase is allocated according to the following steps:

[0027] B1. Calculate the total line loss reduction contribution rate under different compensation capacity allocations according to the following formula:

[0028]

[0029] p A +p B +p C =M;

[0030] In the above formula, ηtotal is the total line loss reduction contribution rate; η QA , η QB , η QC are the unit current loss reduction rates of reactive power compensation for phases A, B, and C respectively; p A 、p B 、p C They are the proportion of reactive power compensation capacity on phases A, B, and C to the transformer capacity. If a phase does not need reactive power compensation, the proportion of reactive power compensation capacity of the phase to the transformer capacity is 0.

[0031] B2. Select the maximum total line loss reduction contribution rate, and calculate the corresponding p value according to the maximum total line loss reduction contribution rate. A 、p B 、p C Allocate compensation capacity for the three phases.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. A three-phase shared hybrid flexible distribution transformer of the present invention comprises a transformer body, a full-bridge converter module, three series-side switching switches, and three parallel-side switching switches. The full-bridge converter module comprises a series converter and a parallel converter with the same structure. The series converter is connected to the three series-side switching switches, and the three series-side switching switches are respectively connected to the A, B, and C phase windings of the voltage compensation winding in the transformer body. The parallel converter is connected to the three parallel-side switching switches, and the three parallel-side switching switches are respectively connected to the A, B, and C phase windings of the current compensation winding in the transformer body. In application, the hybrid flexible distribution transformer shares a full-bridge converter module. The full-bridge converter module can be connected to any one phase of the transformer body for single-phase compensation control through the series-side switching switch and the parallel-side switching switch, and can also be connected to any one phase of the transformer body for single-phase compensation control. It provides functions such as voltage regulation, reactive power compensation, and three-phase load current imbalance compensation. It can also connect to two or three phases of the transformer body for multi-phase compensation control, and provide two or three phases with voltage regulation, reactive power compensation, and three-phase load current imbalance compensation. When compensating a certain phase, full power compensation can be achieved. When compensating two or three phases, its single-phase compensation capacity can still exceed the single-phase limit of the traditional converter, and the compensation capacity is stronger. Through this three-phase sharing strategy, the reactive power compensation capacity of each phase can be flexibly allocated. When the converter compensation capacity is limited, the purpose of achieving the highest compensation capacity utilization rate and the minimum distribution line loss is achieved, thereby improving the overall working efficiency of the hybrid flexible distribution transformer, and ultimately improving the power quality on the user side. In addition, since there is no no-load condition, the switching loss can be reduced and the device reliability can be improved. Therefore, the present invention can improve the compensation capacity utilization rate and device reliability of the converter.

[0034] 2. In a three-phase shared hybrid flexible distribution transformer of the present invention, the parallel converter and the series converter each include a single-phase full-bridge power unit, and the single-phase full-bridge power unit has two bridge arms, and the bridge arm is composed of an IGBT half-bridge module; in this design, a single single-phase full-bridge power unit with two bridge arms is used to replace the original three-phase three-bridge arm, four-bridge arm, six-bridge arm and other power units, which can save 30%, 50%, and 67% of the converter device cost in comparison. Therefore, the present invention can reduce the converter device cost.

[0035] 3. The present invention provides a control method for a three-phase shared hybrid flexible distribution transformer. The control method selects one of single-phase compensation control and multi-phase compensation control for compensation. The specific selection steps are: first, calculate the unit current loss rate of reactive compensation of the three phases under different compensation currents; then, take the compensation current as the horizontal coordinate and the unit current loss rate as the vertical coordinate, and draw the compensation current-unit current loss rate curve of the three phases in the same coordinate system. Suppose the three curves from top to bottom in the obtained curve graph are curve A, curve B, and curve C, first determine whether any point in curve A is higher than the highest point in curve B. If so, perform single-phase compensation control on one phase corresponding to curve A. If not, continue to determine whether any point in curve B is higher than the highest point in curve C. If so, perform multi-phase compensation control on the two phases corresponding to curve A and curve B. If not, perform multi-phase compensation control on the three phases. In application, the reactive compensation that reduces the line loss the most is preferentially selected from the single-phase compensation control and the multi-phase compensation control for reactive compensation, thereby achieving the effect of reducing line loss and improving device efficiency. Therefore, the present invention can achieve the effect of reducing line loss and improving device efficiency.

[0036] 4. In the control method of a three-phase shared hybrid flexible distribution transformer of the present invention, when using a comprehensive compensation strategy to realize multi-phase compensation control, it is necessary to reasonably allocate the compensation capacity of each phase. The compensation capacity allocation step is to first calculate the total line loss reduction contribution rate under different compensation capacity allocations, then select the maximum total line loss reduction contribution rate, and allocate the compensation capacity to the three phases according to the compensation capacity allocation method corresponding to the maximum total line loss reduction contribution rate, and finally achieve the effect of maximizing the reduction of line loss and optimizing the device efficiency. Therefore, the present invention can achieve the effect of maximizing the reduction of line loss and optimizing the device efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a topological structure diagram of the hybrid flexible transformer described in Example 1 of the present invention.

[0038] Figure 2 This is a curve graph obtained by plotting the hybrid flexible transformer described in Example 1 of the present invention in Test 1.

[0039] Figure 3 This is a curve graph obtained by plotting the hybrid flexible transformer described in Example 1 of the present invention in Test 2.

[0040] Figure 4 This is a topological structure diagram of the hybrid flexible transformer described in Example 2 of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with specific implementations and drawings.

[0042] Embodiment 1:

[0043] See also Figure 1 A three-phase shared hybrid flexible distribution transformer, comprising a transformer body, a full-bridge converter module, a series side switch, and a parallel side switch, wherein the transformer body comprises a main transformer module, a voltage compensation winding, and a current compensation winding, wherein the main transformer module is a double-winding main transformer module using a Δ / Y connection, wherein the secondary side thereof is connected to the voltage compensation winding and the current compensation winding, wherein the full-bridge converter module comprises a series converter and a parallel converter with the same structure, wherein the parallel converter and the series converter share a DC bus capacitor Ces, wherein the series converter is connected to three series side switches, wherein each of the series converter and the three series side switches is connected in parallel with an energy storage capacitor C 2 , the three series-side switching switches are respectively connected to the A, B, and C phase windings of the voltage compensation winding, the parallel converter is connected to the three parallel-side switching switches, and the three parallel-side switching switches are respectively connected to the A, B, and C phase windings of the current compensation winding. The parallel converter and the series converter each include a single-phase full-bridge power unit, and the single-phase full-bridge power unit has two bridge arms, and the bridge arm is composed of an IGBT half-bridge module. The series-side switching switch and the parallel-side switching switch are both IGBT modules;

[0044] In the above-mentioned hybrid flexible distribution transformer, the parallel converter is used to invert the amplitude and phase of the output current, and send the AC current to the parallel side switching switch, and then output the current with adjustable amplitude and phase to the secondary side of the main transformer module, thereby realizing reactive power compensation and three-phase imbalance compensation on the secondary side of the main transformer module; the series converter is used to invert the DC voltage across the energy storage capacitor into an AC voltage, and send the AC voltage to the series side switching switch, and then output the voltage with adjustable amplitude and phase to the primary side of the main transformer module, thereby completing flexible voltage regulation; through the series side switching switch, the single-phase AC voltage can be distributed to any one of the three phases of the main transformer module, and different single-phase AC voltages can be distributed to any two or even three phases in cooperation with the converter control program, realizing the use of a set of full-bridge converter modules to supply power to single-phase, two-phase or even three-phase.

[0045] The control method of the above three-phase shared hybrid flexible distribution transformer is specifically carried out according to the following steps:

[0046] S1. Determine whether single-phase compensation control or multi-phase compensation control is currently required. If it is single-phase compensation control, enter S2; if it is multi-phase compensation control, enter S3. Specifically, determine whether single-phase compensation control or multi-phase compensation control is currently required according to the following steps:

[0047] A1. Calculate the unit current loss reduction rate of three-phase reactive power compensation under different compensation currents according to the following formula:

[0048]

[0049]

[0050]

[0051] In the above formula, η Q Indicates the unit current loss rate of single-phase reactive power compensation; ΔP lQ Indicates the loss reduced by single-phase reactive power compensation; I Q Represents the reactive compensation current on a single phase, I Q ≤M·I, M·I represents the maximum compensation current; I represents the current of the transformer body, M represents the proportion of the full-bridge converter module capacity to the transformer body capacity; R represents the line resistance; cosφ 1 is the current power factor of the single phase;

[0052] A2. With the compensation current as the horizontal coordinate and the unit current loss rate as the vertical coordinate, draw the compensation current-unit current loss rate curve of the three phases in the same coordinate system; suppose that the three curves from top to bottom in the obtained curve graph are curve A, curve B, and curve C respectively, first determine whether any point in curve A is higher than the highest point in curve B, if so, perform single-phase compensation control on the phase corresponding to curve A, if not, continue to determine whether any point in curve B is higher than the highest point in curve C, if so, perform multi-phase compensation control on the two phases corresponding to curves A and curve B, if not, perform multi-phase compensation control on the three phases;

[0053] S2, controlling the series side switch and the parallel side switch corresponding to the one to be compensated to close, so as to realize the single-phase compensation at full power;

[0054] S3. Implement multi-phase compensation control through a comprehensive compensation strategy, wherein the comprehensive compensation strategy is specifically: control the corresponding series side switches and parallel side switches to be compensated to be closed, and distribute the compensation capacity of the three phases; or implement multi-phase compensation control through an intermittent rotation compensation strategy, wherein the intermittent rotation compensation strategy is specifically: rotate and close different corresponding series side switches and parallel side switches, and when any corresponding series side switch and parallel side switch are closed, the other corresponding series side switches and parallel side switches are disconnected;

[0055] When adopting the comprehensive compensation strategy, the compensation capacity of each phase is allocated according to the following steps:

[0056] B1. Calculate the total line loss reduction contribution rate under different compensation capacity allocations according to the following formula:

[0057]

[0058] p A +p B +p C =M;

[0059] In the above formula, η total is the total line loss reduction contribution rate; η QA , η QB , η QC are the unit current loss reduction rates of reactive power compensation for phases A, B, and C respectively; p A 、p B 、p C They are the proportion of reactive power compensation capacity on phases A, B, and C to the transformer capacity. If a phase does not need reactive power compensation, the proportion of reactive power compensation capacity of the phase to the transformer capacity is 0.

[0060] B2. Select the maximum total line loss reduction contribution rate, and calculate the corresponding p value according to the maximum total line loss reduction contribution rate. A 、p B 、p C Allocate compensation capacity for the three phases.

[0061] Performance Verification:

[0062] In order to verify the effectiveness of the control method described in the present invention, two tests were carried out on the hybrid flexible transformer described in the embodiment and the traditional hybrid flexible transformer; in the hybrid flexible transformer described in the embodiment, the current of the transformer body is 724.7A, the capacity of the full-bridge converter module accounts for 30% of the capacity of the transformer body, and the maximum compensation current is 30%*724.7A=217.4A; in the traditional hybrid flexible transformer, the current of the transformer body is 724A, the capacity of the full-bridge converter module accounts for 10% of the capacity of the transformer body, and the maximum compensation current is 10%*724.7A=72.4A.

[0063] Test 1:

[0064] Parameter settings: The current current of phase A is 724A, the power factor is 0.766, the current current of phase B is 506.8A, the power factor is 0.574, the current current of phase C is 217.2A, the power factor is 0.067; the line impedance is 0.0754 ohms;

[0065] (1) Hybrid flexible transformer described in the embodiment

[0066] The line loss reduction contribution rates of phase A, phase B, and phase C under different reactive compensation currents are calculated. The calculation results are shown in Table 1:

[0067] Table 1 Line loss reduction contribution rate of the hybrid flexible transformer in Example 1 under different reactive compensation currents

[0068]

[0069] The curve graph obtained according to Table 1 is as follows Figure 2 As shown by Figure 2 It can be seen that the reactive compensation current-line loss reduction contribution rate curves of phase A, phase B, and phase C correspond to curve A, curve B, and curve C respectively. The latter part of curve A is lower than the former part of curve B, and the overall position of curve B is higher than curve C. Therefore, it is necessary to perform multi-phase compensation control on the two phases corresponding to curve A and curve B (i.e., phase A and phase B). The total line loss reduction contribution rate of phase A and phase B under different compensation capacity allocations is calculated, and the maximum total line loss reduction contribution rate is 58.41W / A, and the final line loss reduction is 12686.21W; the compensation capacity allocation corresponding to the maximum total line loss reduction contribution rate is: phase A -21%, phase B -9%, that is, 152.04A is used for phase A reactive compensation, and 65.16A is used for phase B reactive compensation. Since all compensation capacity is used for reactive compensation, its compensation capacity utilization rate is 100%.

[0070] (2) Traditional hybrid flexible transformer

[0071] When the compensation reaches unity power factor 1, the reactive compensation currents required for phase A, phase B, and phase C are 627A, 344A, and 72.12A, respectively. Only the reactive compensation current required for phase C, 72.12A, is less than the maximum compensation current 72.4A. Therefore, the reactive compensation current of phase C is 72.12A, and the reactive compensation currents of phase A and phase B are both 72.4A. The line loss reduction contribution rates of phase A, phase B, and phase C under different reactive compensation currents are calculated, and the calculation results are shown in Table 2:

[0072] Table 2 Contribution rate of line loss reduction of traditional hybrid flexible transformer under different reactive compensation currents

[0073]

[0074] The total line loss reduction contribution rates of phase A, phase B, and phase C under different compensation capacity allocations were calculated respectively, and the maximum total line loss reduction contribution rate was obtained to be 49.67W / A; the final reduction in line loss was calculated to be 10790.16W.

[0075] (3) Comparison results

[0076] Under the same compensation capacity, compared with the traditional hybrid flexible distribution transformer, the hybrid flexible distribution transformer of the present invention using three phases sharing the same full-bridge converter can reduce the line loss by an additional 1896.05W.

[0077] Test 2:

[0078] Parameter settings: The current current of phase A is 506.8A, the power factor is 0.5, the current current of phase B is 217.2A, the power factor is 0.5, the current current of phase C is 217.2A, the power factor is 0.643; the line impedance is 0.0754 ohms;

[0079] (1) Hybrid flexible transformer described in the embodiment

[0080] The line loss reduction contribution rates of phase A, phase B, and phase C under different reactive compensation currents are calculated. The calculation results are shown in Table 3:

[0081] Table 3 Line loss reduction contribution rate of the hybrid flexible transformer under different reactive compensation currents described in the embodiment

[0082]

[0083]

[0084] The curve graph obtained according to Table 3 is as follows Figure 3 As shown by Figure 3It can be seen that the reactive compensation current-line loss reduction contribution rate curves of phase A, phase B, and phase C correspond to curve A, curve B, and curve C respectively. The overall position of curve A is higher than curve B. Therefore, single-phase compensation control is required for phase A, that is, all 217.2A is used for reactive compensation of phase A, and phases B and C are not compensated. The total line loss reduction contribution rate of single-phase compensation control of phase A is 49.81W / A. It is calculated that the line loss reduced by single-phase compensation control of phase A is 10818.6W.

[0085] (2) Traditional hybrid flexible transformer

[0086] Since the reactive compensation currents required for phase A, phase B, and phase C when compensated to unity power factor 1 are 438.9, 188.1A, and 166.38A, respectively, which are all less than the maximum compensation current of 72.4A, phase A, phase B, and phase C cannot be compensated to unity power factor 1; the line loss reduction contribution rates of phase A, phase B, and phase C under different reactive compensation currents are calculated, and the calculation results are shown in Table 4:

[0087] Table 4 Line loss reduction contribution rate of traditional hybrid flexible transformer under different reactive compensation currents

[0088]

[0089] The total line loss reduction contribution rate of phase A, phase B, and phase C under different compensation capacity allocations is calculated, and the maximum total line loss reduction contribution rate is 34.42W / A; the final reduction in line loss is calculated to be 7476.45W.

[0090] (3) Comparison results

[0091] Under the same compensation capacity, compared with the traditional hybrid flexible distribution transformer, the hybrid flexible distribution transformer of the present invention using three phases sharing the same full-bridge converter can reduce the line loss by an additional 3342.15W.

[0092] Embodiment 2:

[0093] The difference from Example 1 is that:

[0094] See also Figure 4 In the hybrid flexible distribution transformer of this embodiment, the primary side and the secondary side of the main transformer module are connected to the voltage compensation winding and the current compensation winding respectively.

Claims

1. A three-phase shared hybrid flexible distribution transformer, comprising a transformer body, wherein the transformer body comprises a main transformer module, a voltage compensation winding, and a current compensation winding, characterized in that: The hybrid flexible distribution transformer also includes a full-bridge converter module, three series side switching switches, and three parallel side switching switches. The full-bridge converter module includes a series converter and a parallel converter. The series converter has the same structure as the parallel converter. The parallel converter and the series converter each include a single-phase full-bridge power unit. The series converter is connected to the three series side switching switches, and the three series side switching switches are respectively connected to the A, B, and C phase windings of the voltage compensation winding. The parallel converter is connected to the three parallel side switching switches, and the three parallel side switching switches are respectively connected to the A, B, and C phase windings of the current compensation winding.

2. A three-phase shared hybrid flexible distribution transformer according to claim 1, characterized in that: The single-phase full-bridge power unit has two bridge arms, each of which is composed of an IGBT half-bridge module.

3. A three-phase shared hybrid flexible distribution transformer according to claim 1 or 2, characterized in that: The series-side switching switch and the parallel-side switching switch are both IGBT modules.

4. A three-phase shared hybrid flexible distribution transformer according to claim 1 or 2, characterized in that: An energy storage capacitor is connected in parallel between each of the three series-side switching switches and the series converter, and the parallel converter and the series converter share a DC bus capacitor.

5. A three-phase shared hybrid flexible distribution transformer according to claim 1 or 2, characterized in that: The voltage compensation winding and the current compensation winding are both connected to the secondary side of the main transformer module.

6. A three-phase shared hybrid flexible distribution transformer according to claim 1 or 2, characterized in that: The voltage compensation winding and the current compensation winding are respectively connected to the primary side and the secondary side of the main transformer module.

7. A control method for a three-phase shared hybrid flexible distribution transformer, characterized in that: The control method is based on the three-phase shared hybrid flexible distribution transformer according to claim 1, and the control method includes: S1, determine whether single-phase compensation control or multi-phase compensation control is currently required, if it is single-phase compensation control, enter S2, if it is multi-phase compensation control, enter S3; S2, controlling the series side switch and the parallel side switch corresponding to the one to be compensated to close, so as to realize the single-phase compensation at full power; S3. Implement multi-phase compensation control through a comprehensive compensation strategy, wherein the comprehensive compensation strategy is specifically: control the corresponding series-side switching switches and parallel-side switching switches to be compensated to be closed, and distribute the compensation capacity of the three phases.

8. The control method of a three-phase shared hybrid flexible distribution transformer according to claim 7, characterized in that: In S1, it is determined whether single-phase compensation control or multi-phase compensation control is currently required according to the following steps: A1. Calculate the unit current loss reduction rate of reactive power compensation of the three phases under different compensation currents respectively; A2. With the compensation current as the horizontal coordinate and the unit current loss rate as the vertical coordinate, draw the compensation current-unit current loss rate curve of the three phases in the same coordinate system; suppose that the three curves from top to bottom in the obtained curve graph are curve A, curve B, and curve C respectively. First, determine whether any point in curve A is higher than the highest point in curve B. If so, perform single-phase compensation control on the phase corresponding to curve A. If not, continue to determine whether any point in curve B is higher than the highest point in curve C. If so, perform multi-phase compensation control on the two phases corresponding to curves A and curve B. If not, perform multi-phase compensation control on the three phases.

9. The control method of a three-phase shared hybrid flexible distribution transformer according to claim 8, characterized in that: In A1, the unit current loss reduction rate of reactive power compensation of three phases under different compensation currents is calculated according to the following formula: In the above formula, η Q Indicates the unit current loss rate of single-phase reactive power compensation; ΔP lQ Indicates the loss reduced by single-phase reactive power compensation; I Q Represents the reactive compensation current on a single phase, I Q ≤M·I, I represents the current of the transformer body, M represents the proportion of the full-bridge converter module capacity to the transformer body capacity; R represents the line resistance; cosφ1 is the current power factor of the single phase.

10. A control method for a three-phase shared hybrid flexible distribution transformer according to any one of claims 7 to 9, characterized in that: In S3, the compensation capacity of each phase is allocated according to the following steps: B1. Calculate the total line loss reduction contribution rate under different compensation capacity allocations according to the following formula: p A +p B +p C =M; In the above formula, η total is the total line loss reduction contribution rate; η QA , η QB , η QC are the unit current loss reduction rates of reactive power compensation for phases A, B, and C respectively; p A 、p B 、p C They are the proportion of reactive power compensation capacity on phases A, B, and C to the transformer capacity. If a phase does not need reactive power compensation, the proportion of reactive power compensation capacity of the phase to the transformer capacity is 0. B2. Select the maximum total line loss reduction contribution rate, and calculate the corresponding p value according to the maximum total line loss reduction contribution rate. A 、p B 、p C Allocate compensation capacity for the three phases.

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