Flexible phase modulation and voltage regulation system and method based on back-to-back converter

Abstract

The invention relates to the technical field of power electronics, particularly provides a flexible phase modulation and voltage regulation system and method based on a back-to-back converter, and aims to solve the technical problem that continuous phase modulation and continuous voltage regulation cannot be realized in the prior art. Therefore, the flexible phase and voltage regulation system based on the back-to-back converter comprises a stepless voltage and phase regulation unit and a stepped voltage and phase regulation unit, a first input end of the step voltage-regulating and phase-regulating unit is connected with a power supply line of a three-phase power grid, and a first output end of the step voltage-regulating and phase-regulating unit is connected with an input end of the stepless voltage-regulating and phase-regulating unit; the output end of the stepless voltage regulation and phase modulation unit is connected with the second input end of the step voltage regulation and phase modulation unit; and the second output end of the stepped voltage-regulating and phase-regulating unit is connected with a load. Through coordination and cooperation of the stepless voltage and phase regulation unit and the stepped voltage and phase regulation unit, continuous phase shift regulation and voltage amplitude regulation can be realized.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a flexible phase-modulation and voltage-regulation system and method based on a back-to-back converter. Background Art

[0002] A double-core phase shifting transformer (PST) is a device used to adjust the phase angle difference between lines or different power networks in a power system. It can control the direction and magnitude of power flow by adjusting the phase, thereby optimizing the operation of the power grid. At present, most existing phase shifting transformer technologies use mechanical on-load tap changers, or use thyristors to replace mechanical on-load tap changers for on-load voltage regulation. In this way, the voltage can only be phase-adjusted according to fixed discrete steps, and continuous phase regulation cannot be achieved.

[0003] In the prior art, a dual-core symmetrical discrete controllable phase shifter is also proposed. The excitation unit and series unit of this dual-core PST use separate transformers, and the on-load voltage regulator is isolated from the system by means of the series transformer, so that it will not be directly affected by the system overvoltage and short-circuit current. However, this symmetrical phase-shifting transformer can only perform phase adjustment operations and cannot achieve voltage regulation functions; and although the asymmetrical phase-shifting transformer can perform voltage regulation, it still cannot achieve continuous voltage regulation.

[0004] Accordingly, the art needs a new phase and voltage regulation solution to solve the above problems. Summary of the invention

[0005] In order to overcome the above-mentioned defects, the present application is proposed to solve or at least partially solve the technical problem that the prior art cannot achieve continuous phase modulation and continuous voltage regulation.

[0006] In a first aspect, a flexible phase-modulation and voltage-regulation system based on a back-to-back converter is provided, wherein the flexible phase-modulation and voltage-regulation system comprises a stepless voltage-regulation and phase-modulation unit and a stepped voltage-regulation and phase-modulation unit; a first input end of the stepped voltage-regulation and phase-modulation unit is connected to a power supply line of a three-phase power grid, and a first output end is connected to an input end of the stepless voltage-regulation and phase-modulation unit; an output end of the stepless voltage-regulation and phase-modulation unit is connected to a second input end of the stepped voltage-regulation and phase-modulation unit; and a second output end of the stepped voltage-regulation and phase-modulation unit is connected to a load.

[0007] In a technical solution of the flexible phase-modulation and voltage-regulating system based on the back-to-back converter, the stepless voltage-regulating and phase-modulating unit includes a first tap switch, an excitation transformer and a back-to-back converter; one end of the primary winding of the excitation transformer is connected to the first output end of the step-modulating and phase-modulating unit, and the other end of the primary winding is grounded; the secondary side of the excitation transformer includes an isolation winding and a plurality of segmented windings, adjacent segmented windings are connected in series, and taps of the plurality of segmented windings are respectively connected to the first input end of the first tap switch; both ends of the isolation winding are connected to the input end of the back-to-back converter, and the output end of the back-to-back converter is connected to the second input end of the first tap switch; the output end of the first tap switch is connected to the second input end of the step-modulating and phase-modulating unit.

[0008] In a technical solution of the flexible phase-modulation and voltage-regulating system based on the back-to-back converter, the back-to-back converter includes an input module, a capacitor module and an output module; the input end of the input module is connected to the two ends of the secondary side isolation winding of the excitation transformer, and the output end is connected to the output module through the capacitor module; the output end of the output module is connected to the second input end of the first tap switch.

[0009] In a technical solution of the flexible phase-modulation and voltage-regulating system based on the back-to-back converter, the input module includes a first inductor and a rectifier module, the rectifier module includes a first bridge arm and a second bridge arm, the first bridge arm includes a first switch and a second switch connected in series, and the second bridge arm includes a third switch and a fourth switch connected in series; one end of the secondary side isolation winding of the excitation transformer is connected to the emitter of the third switch and the collector of the fourth switch through the first inductor, and the other end of the secondary side isolation winding is connected to the emitter of the first switch and the collector of the second switch; the collector of the first switch and the collector of the third switch are connected to one end of the capacitor module, and the emitter of the second switch and the emitter of the fourth switch are connected to the other end of the capacitor module.

[0010] In a technical solution of the flexible phase-modulation and voltage-regulating system based on the back-to-back converter, the output module includes an inverter module and a filter module, the inverter module includes a third bridge arm and a fourth bridge arm, the third bridge arm includes a fifth switch and a sixth switch connected in series, and the fourth bridge arm includes a seventh switch and an eighth switch connected in series; the filter module includes a second inductor and a filter capacitor; the emitter of the fifth switch is connected to the collector of the sixth switch and the input end of the second inductor, and the output end of the second inductor is connected to the second input end of the first tap switch through one end of the filter capacitor; the emitter of the seventh switch and the collector of the eighth switch are connected to the second input end of the first tap switch through the other end of the filter capacitor; one end of the capacitor module is connected to the collector of the fifth switch and the collector of the seventh switch, and the other end is connected to the emitter of the sixth switch and the emitter of the eighth switch.

[0011] In a technical solution of the flexible phase-modulation and voltage-regulating system based on the back-to-back converter, the number of the first tap switch, the excitation transformer, the back-to-back converter, and the plurality of segmented windings is at least three; the grounding end of each primary winding of the excitation transformer is connected and grounded; and the grounding end of each back-to-back converter is connected and grounded.

[0012] In a technical solution of the flexible phase-modulation and voltage-regulating system based on the back-to-back converter, the stepped voltage-regulating and phase-modulating unit includes a second tap switch and a series transformer; the input end of the primary winding of the series transformer is connected to the power supply line of the three-phase power grid, the taps of the primary winding are respectively connected to the input end of the second tap switch, and the output end of the primary winding is connected to the load; the input end of the secondary winding of the series transformer is connected to the output end of the first tap switch; and the output end of the second tap switch is connected to the input end of the excitation transformer.

[0013] In a technical solution of the above-mentioned flexible phase-modulation and voltage-regulating system based on back-to-back converters, the number of the series transformers is at least three, namely, a first series transformer, a second series transformer and a third series transformer; the output end of the secondary winding of the first series transformer is connected to the input end of the secondary winding of the second series transformer; the output end of the secondary winding of the second series transformer is connected to the input end of the secondary winding of the third series transformer; the output end of the secondary winding of the third series transformer is connected to the input end of the secondary winding of the first series transformer.

[0014] In a technical solution of the flexible phase-modulation and voltage-regulation system based on back-to-back converters, the number of the second tap changers is at least three; the first tap changer and the second tap changer are power electronic tap changers, mechanical switches or composite tap changers.

[0015] In a second aspect, a flexible phase-modulation and voltage regulation method is provided, and the method is performed based on the flexible phase-modulation and voltage regulation system based on the back-to-back converter described in any technical solution of the flexible phase-modulation and voltage regulation system of the back-to-back converter, and the method includes: obtaining a voltage regulation requirement, and the voltage regulation requirement includes a phase-modulation requirement, or a phase-modulation requirement and a voltage regulation requirement; determining whether the voltage regulation requirement is a phase-modulation requirement; if so, controlling the stepless voltage regulation and phase regulation unit to perform a phase-modulation operation on the input voltage based on the voltage regulation requirement; otherwise, controlling the stepless voltage regulation and phase regulation unit and the stepped voltage regulation and phase regulation unit to perform a voltage regulation operation and a phase regulation operation on the input voltage based on the voltage regulation requirement.

[0016] The above one or more technical solutions of the present application have at least one or more of the following beneficial effects:

[0017] The present application provides a flexible phase-modulation and voltage-regulating system based on a back-to-back converter, the flexible phase-modulation and voltage-regulating system comprising a stepless voltage-regulating and phase-modulating unit and a stepped voltage-regulating and phase-modulating unit; the first input end of the stepped voltage-regulating and phase-modulating unit is connected to the power supply line of the three-phase power grid, and the first output end is connected to the input end of the stepless voltage-regulating and phase-modulating unit; the output end of the stepless voltage-regulating and phase-modulating unit is connected to the second input end of the stepped voltage-regulating and phase-modulating unit; the second output end of the stepped voltage-regulating and phase-modulating unit is connected to the load. The present application realizes continuous voltage regulation and continuous phase modulation through coordinated control of the stepless voltage-regulating and phase-modulating unit and the stepped voltage-regulating and phase-modulating unit, and can realize fast and dynamic voltage regulation and phase modulation by utilizing the fast response characteristics of the back-to-back converter, thereby ensuring the stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The disclosure of the present application will become easier to understand with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present application. Among them:

[0019] Figure 1 is a main structural schematic diagram of a flexible phase-modulation and voltage-regulation system based on a back-to-back converter according to an embodiment of the present application;

[0020] Figure 2 is a main structural schematic diagram of a back-to-back converter according to an embodiment of the present application;

[0021] Figure 3 is a schematic diagram of a principle of an input module according to an embodiment of the present application;

[0022] Figure 4 is a schematic diagram of a principle of an output module according to an embodiment of the present application;

[0023] Figure 5 is a schematic diagram of the main structure of a power electronic tap changer according to an embodiment of the present application;

[0024] Figure 6 is a main structural schematic diagram of a mechanical tap changer according to an embodiment of the present application;

[0025] Figure 7 is a main structural schematic diagram of a composite tap changer according to an embodiment of the present application;

[0026] Figure 8 It is a schematic flow chart of main steps of a flexible phase and voltage regulation method according to an embodiment of the present application;

[0027] Fig. 9 It is a detailed step flow chart of a flexible phase and voltage regulation method according to an embodiment of the present application;

[0028] Fig.10 is a vector voltage schematic diagram of a second tap switch according to an embodiment of the present application;

[0029] Fig.11 is a vector voltage schematic diagram of a first tap switch and a back-to-back converter according to an embodiment of the present application.

[0030] Reference numerals:

[0031] 10: stepless voltage regulation and phase modulation unit; 11: first tap switch; 12: excitation transformer; 13: back-to-back converter; 20: stepless voltage regulation and phase modulation unit; 21: second tap switch; 22: series transformer; 221: first series transformer; 222: second series transformer; 223: third series transformer; 130: input module; 1301: first switch; 1302: second switch; 1303: third switch; 1304: fourth switch; 1305: first inductor; 131: capacitor module; 132: output module; 1321: fifth switch; 1322: sixth switch; 1323: seventh switch; 1324: eighth switch; 1325: second inductor; 1326: filter capacitor. DETAILED DESCRIPTION

[0032] Some embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the protection scope of the present application.

[0033] In the description of the present application, "module" and "processor" may include hardware, software or a combination of the two. A module may include hardware circuits, various suitable sensors, communication ports, memory, and may also include software parts, such as program code, or a combination of software and hardware. The processor may be a central processing unit, a microprocessor, an image processor, a digital signal processor or any other suitable processor. The processor has data and / or signal processing functions. The processor may be implemented in software, hardware or a combination of the two. Computer-readable storage media include any suitable medium that can store program code, such as a disk, a hard disk, an optical disk, a flash memory, a read-only memory, a random access memory, etc. The term "A and / or B" means all possible combinations of A and B, such as only A, only B or A and B. The term "at least one A or B" or "at least one of A and B" has a similar meaning to "A and / or B" and may include only A, only B or A and B. The singular terms "one" and "the" may also include plural forms.

[0034] The current phase-shifting transformer technology has certain limitations, which are mainly reflected in the following aspects: the existing phase-shifting transformer can only adjust the phase according to fixed discrete steps, and cannot achieve continuous phase adjustment. Symmetrical phase-shifting transformers can perform phase adjustment operations, but do not have voltage regulation functions. Although asymmetric phase-shifting transformers can adjust voltage, they still cannot achieve continuous voltage regulation.

[0035] To this end, the present application provides a flexible phase-modulation and voltage-regulating system based on a back-to-back converter, the flexible phase-modulation and voltage-regulating system comprising a stepless voltage-regulating and phase-modulating unit and a stepped voltage-regulating and phase-modulating unit; the first input end of the stepped voltage-regulating and phase-modulating unit is connected to the power supply line of the three-phase power grid, and the first output end is connected to the input end of the stepless voltage-regulating and phase-modulating unit; the output end of the stepless voltage-regulating and phase-modulating unit is connected to the second input end of the stepped voltage-regulating and phase-modulating unit; the second output end of the stepped voltage-regulating and phase-modulating unit is connected to the load. The present application can realize continuous voltage regulation and continuous phase modulation through coordinated control of the stepless voltage-regulating and phase-modulating unit and the stepped voltage-regulating and phase-modulating unit, and can realize fast and dynamic voltage regulation and phase modulation by utilizing the fast response characteristics of the back-to-back converter, thereby significantly improving the stability and reliability of the power system.

[0036] See attached Figure 1 , Figure 1 FIG. 1 is a schematic diagram of the main structure of a flexible phase-modulation and voltage-regulation system based on a back-to-back converter according to an embodiment of the present application. Figure 1As shown, in this embodiment, a flexible phase-modulation and voltage-regulation system based on a back-to-back converter is provided, wherein the flexible phase-modulation and voltage-regulation system comprises a stepless voltage-regulation and phase-modulation unit and a stepped voltage-regulation and phase-modulation unit; a first input end of the stepped voltage-regulation and phase-modulation unit is connected to a power supply line of a three-phase power grid, and a first output end is connected to an input end of the stepless voltage-regulation and phase-modulation unit; an output end of the stepless voltage-regulation and phase-modulation unit is connected to a second input end of the stepped voltage-regulation and phase-modulation unit; and a second output end of the stepped voltage-regulation and phase-modulation unit is connected to a load.

[0037] Specifically, the flexible phase-modulation and voltage-regulating system based on the back-to-back converter includes a stepless voltage-regulating and phase-modulating unit and a stepped voltage-regulating and phase-modulating unit, wherein the first input end of the stepped voltage-regulating and phase-modulating unit is connected to the power supply line of the three-phase power grid for receiving input voltage and current from the three-phase power grid, and the first output end of the stepped voltage-regulating and phase-modulating unit is connected to the input end of the stepless voltage-regulating and phase-modulating unit, and the input voltage is continuously voltage-regulated and continuously phase-modulated by coordinated control with the stepless voltage-regulating and phase-modulating unit, and finally the voltage after voltage-regulation and phase-modulation is output from the second output end of the stepped voltage-regulating and phase-modulating unit and provided to the load or fed back to the power grid.

[0038] In one embodiment, the stepless voltage regulation and phase modulation unit includes a first tap switch, an excitation transformer and a back-to-back converter; one end of the primary winding of the excitation transformer is connected to the first output end of the step-by-step voltage regulation and phase modulation unit, and the other end of the primary winding is grounded; the secondary side of the excitation transformer includes an isolation winding and a plurality of segmented windings, adjacent segmented windings are connected in series, and taps of the plurality of segmented windings are respectively connected to the first input end of the first tap switch; both ends of the isolation winding are connected to the input end of the back-to-back converter, and the output end of the back-to-back converter is connected to the second input end of the first tap switch; the output end of the first tap switch is connected to the second input end of the step-by-step voltage regulation and phase modulation unit.

[0039] Specifically, the stepless voltage regulation and phase modulation unit includes three identical excitation transformers, three identical first tap switches and three identical back-to-back converters. A first tap switch, an excitation transformer and a back-to-back converter are correspondingly arranged, and continuous voltage regulation and phase modulation can be achieved by controlling the first tap switch and the back-to-back converter. One end of the primary side winding of each excitation transformer is connected to the output end of the second tap switch of the stepless voltage regulation and phase modulation unit, and the other end of the primary side winding is connected to the other end of the primary side winding of the other two excitation transformers and then grounded.

[0040] The secondary side of the excitation transformer includes three segmented windings and one isolation winding. The three segmented windings are connected in series and are provided with four taps. The first tap switch includes four first input terminals. The four taps of the segmented windings are respectively connected to the four first input terminals of the first tap switch. Both ends of the isolation winding are connected to the input terminals of the back-to-back converter. By coordinating the control of the first tap switch and the back-to-back converter, continuous voltage regulation and phase regulation can be achieved.

[0041] See attached Figure 2 , Figure 2 is a schematic diagram of the main structure of a back-to-back converter according to an embodiment of the present application; Figure 2 As shown, in one embodiment, the back-to-back converter includes an input module, a capacitor module and an output module; the input end of the input module is connected to the two ends of the secondary side isolation winding of the excitation transformer, and the output end is connected to the output module through the capacitor module; the output end of the output module is connected to the second input end of the first tap switch.

[0042] Specifically, the back-to-back converter is a single-phase back-to-back circuit, including an input module, a capacitor module and an output module. The input module and the output module are decoupled by the capacitor module, so that the output voltage can be controlled to a compensation voltage with adjustable amplitude and phase angle.

[0043] In one embodiment, the input module includes a first inductor and a rectifier module, the rectifier module includes a first bridge arm and a second bridge arm, the first bridge arm includes a first switch and a second switch connected in series, and the second bridge arm includes a third switch and a fourth switch connected in series; one end of the secondary side isolation winding of the excitation transformer is connected to the emitter of the third switch and the collector of the fourth switch through the first inductor, and the other end of the secondary side isolation winding is connected to the emitter of the first switch and the collector of the second switch; the collector of the first switch and the collector of the third switch are connected to one end of the capacitor module, and the emitter of the second switch and the emitter of the fourth switch are connected to the other end of the capacitor module.

[0044] Specifically, the input module includes a first inductor and a rectifier module, the rectifier module includes four insulated gate bipolar transistor (IGBT) switch devices, the four switch devices form a rectifier bridge, the first bridge arm includes a first switch and a second switch connected in series, the second bridge arm includes a third switch and a fourth switch connected in series, the first bridge arm is connected to one end of the secondary side isolation winding of the excitation transformer, and the second bridge arm is connected to the other end of the secondary side isolation winding of the excitation transformer through the first inductor. The input module is used to rectify the input AC voltage into a stable DC voltage.

[0045] like Figure 3As shown in the figure, the input module uses the grid voltage phase as a phase-locked loop and adopts a double closed-loop control strategy to set the reference value u of the DC side voltage dc_ref With the actual value u dc After comparison, the error is obtained. After the error passes through the PI controller and is multiplied by the standard sinusoidal value (θ-sin), the reference value of the grid-connected inductor current is obtained. The reference value of the inductor current is compared with the actual value i L1 After comparison, the modulation signal is obtained through the PR controller, and then the PWM wave required by the switching device is obtained.

[0046] In one embodiment, the output module includes an inverter module and a filter module, the inverter module includes a third bridge arm and a fourth bridge arm, the third bridge arm includes a fifth switch and a sixth switch connected in series, and the fourth bridge arm includes a seventh switch and an eighth switch connected in series; the filter module includes a second inductor and a filter capacitor; the emitter of the fifth switch is connected to the collector of the sixth switch and the input end of the second inductor, and the output end of the second inductor is connected to the second input end of the first tap switch through one end of the filter capacitor; the emitter of the seventh switch and the collector of the eighth switch are connected to the second input end of the first tap switch through the other end of the filter capacitor; one end of the capacitor module is connected to the collector of the fifth switch and the collector of the seventh switch, and the other end is connected to the emitter of the sixth switch and the emitter of the eighth switch.

[0047] Specifically, the output module includes an inverter module and a filter module, the inverter module includes four insulated gate bipolar transistor (IGBT) switch devices, the four switch devices form an inverter bridge, the fifth bridge arm includes a fifth switch and a sixth switch connected in series, and the sixth bridge arm includes a seventh switch and an eighth switch connected in series. The filter module uses an LC filter for filtering, including a second inductor and a filter capacitor.

[0048] like Figure 4 As shown, the inverter module adopts dual closed-loop control, selecting the inductor current as the sampling value of the current inner loop and the output voltage as the sampling value of the voltage outer loop. c2 Through negative feedback and given voltage reference value u c2ref The comparison error value is processed by the PI controller as the reference value of the current inner loop and compared with the feedback inductor current i L2 In comparison, the comparison error is processed by the PI controller as a modulation signal, and is compared with the triangular carrier to generate an SPWM signal.

[0049] In one embodiment, the number of the first tap switch, the excitation transformer, the back-to-back converter, and the plurality of segmented windings is at least three; the grounding end of each primary winding of the excitation transformer is connected and grounded; and the grounding end of each back-to-back converter is connected and grounded.

[0050] In one embodiment, the stepped voltage and phase regulation unit includes a second tap switch and a series transformer; the input end of the primary winding of the series transformer is connected to the power supply line of the three-phase power grid, the taps of the primary winding are respectively connected to the input end of the second tap switch, and the output end of the primary winding is connected to the load; the input end of the secondary winding of the series transformer is connected to the output end of the first tap switch; the output end of the second tap switch is connected to the input end of the excitation transformer.

[0051] Specifically, the stepped voltage and phase modulation unit includes three second tap switches and three series transformers, one second tap switch and one series transformer are correspondingly arranged, the second tap switch includes three input terminals, the series transformer includes three taps, the three input terminals of the second tap switch are respectively connected to the three taps of the series transformer, and the output terminal of the second tap switch is connected to the primary winding input terminal of the corresponding excitation transformer. The second tap switch can realize discrete voltage and phase modulation by switching the taps. By combining the stepless voltage and phase modulation unit with the stepped voltage and phase modulation unit, a wider voltage and phase adjustment range can be covered.

[0052] In one embodiment, the number of the series transformers is at least three, namely, a first series transformer, a second series transformer and a third series transformer; the output end of the secondary winding of the first series transformer is connected to the input end of the secondary winding of the second series transformer; the output end of the secondary winding of the second series transformer is connected to the input end of the secondary winding of the third series transformer; the output end of the secondary winding of the third series transformer is connected to the input end of the secondary winding of the first series transformer.

[0053] Specifically, the output end of the secondary winding of the first series transformer is connected to the input end of the secondary winding of the second series transformer, the output end of the secondary winding of the second series transformer is connected to the input end of the secondary winding of the third series transformer, and the output end of the secondary winding of the third series transformer is connected to the input end of the secondary winding of the first series transformer, so that the first, second and third series transformers form a closed loop through their secondary windings.

[0054] In one embodiment, the number of the second tap changers is at least three; the first tap changer and the second tap changer are power electronic tap changers, mechanical switches or composite tap changers.

[0055] Specifically, the first tap switch and the second tap switch can be a power electronic tap switch, a mechanical switch or a composite tap switch. The structure of the power electronic tap switch is as follows: Figure 5 As shown in the figure, a single power electronic tap-changer consists of a pair of thyristors connected in anti-parallel. The power electronic tap-changer composed of thyristors is uniformly controlled by the control center. The voltage regulating winding is switched on and off by controlling the thyristor trigger pulse. The thyristor current is naturally turned off at zero point, and a trigger pulse is sent to the thyristor or the trigger pulse is stopped at zero point. The structure of the mechanical switch is shown in the figure. Figure 6 As shown, the structure of the composite tap changer is as follows Figure 7 shown.

[0056] See attached Figure 8 , Figure 8 1 is a flow chart of the main steps of the flexible phase and voltage regulation method according to an embodiment of the present application; Figure 8 As shown, the flexible phase and voltage regulation method in the embodiment of the present application mainly includes the following steps S101 to S104.

[0057] Step S101: obtaining a voltage regulation requirement, where the voltage regulation requirement includes a phase regulation requirement, or a phase regulation requirement and a voltage regulation requirement.

[0058] In this embodiment, the voltage regulation requirement may be a specific requirement for adjusting the grid voltage proposed by the user according to the actual needs of the power system operation, or it may be a voltage fluctuation caused by various factors, which requires voltage adjustment to meet specific operation requirements. Specifically, it includes phase adjustment requirements, or phase adjustment requirements and voltage regulation requirements.

[0059] Step S102: determining whether the voltage regulation requirement is a phase regulation requirement.

[0060] In this embodiment, it is determined whether the voltage regulation requirement is a separate phase adjustment requirement. If it is determined to be a separate phase adjustment requirement, the process proceeds to step S103. If not, it is a phase adjustment requirement and a voltage regulation requirement, the process proceeds to step S104.

[0061] Step S103: If yes, based on the voltage regulation requirement, controlling the stepless voltage and phase regulation unit to perform a phase regulation operation on the input voltage.

[0062] In this embodiment, if there is a separate phase adjustment requirement, the back-to-back converter and the first tap switch are controlled to perform a phase adjustment operation according to the required phase adjustment.

[0063] Specifically, determine whether the required adjustment phase is less than the preset adjustment range of the back-to-back converter. If so, only use the back-to-back converter for adjustment; otherwise, determine whether the required adjustment phase is equal to the preset phase adjustment gear corresponding to the first tap switch. If so, use the first tap switch for adjustment; otherwise, control the back-to-back converter and the first tap switch to cooperate to achieve phase adjustment, and the phase adjustment range of the first tap switch is larger than the phase adjustment range of the back-to-back converter. For example, the first tap switch can be controlled to achieve a large range of phase adjustment, and the back-to-back converter can be controlled to achieve a small range of phase adjustment to ensure accuracy.

[0064] Step S104: otherwise, based on the voltage regulation requirement, controlling the stepless voltage and phase regulation unit and the stepped voltage and phase regulation unit to perform voltage regulation and phase regulation operations on the input voltage.

[0065] In this embodiment, if the voltage regulation requirement includes voltage regulation requirement and phase adjustment requirement, it is necessary to control the first tap switch, the back-to-back converter and the second tap switch to perform voltage regulation and phase adjustment operations. Specifically, it is determined whether the required voltage regulation value is less than the preset adjustment range of the back-to-back converter. If so, the back-to-back converter is used for adjustment; if not, it is further determined whether the required voltage regulation range is equal to the preset voltage regulation gear corresponding to the second tap switch. If so, the second tap switch is used for adjustment; if not, the first tap switch and the back-to-back converter are used to achieve phase adjustment. The first tap switch achieves a large range of voltage regulation, and the back-to-back converter achieves a small range of voltage regulation to ensure accuracy. In this way, continuous phase adjustment can be achieved by controlling the coordination between the first tap switch, the second tap switch and the back-to-back converter; the second tap switch and the back-to-back converter can both achieve the voltage regulation function, and a larger voltage regulation range can be achieved through coordination. In this embodiment, the detailed steps of the flexible phase adjustment and voltage regulation method are as follows: Fig. 9 shown.

[0066] The flexible phase-adjusting and voltage-regulating system of the present application can realize continuous phase-shifting and voltage-amplitude regulation by setting two sets of tap-changers and back-to-back converters, and has multiple voltage-regulating modes, covering a wider phase-shifting and voltage-regulating range. Compared with the phase-adjusting and voltage-regulating scheme using both the "Sen" transformer (ST) and the unified power flow controller (UPFC), the structure is simpler and the cost is lower.

[0067] See attached Fig.10 , Fig.10 is a vector voltage schematic diagram of a second tap switch according to an embodiment of the present application; Fig.10As shown, V10, V20, and V30 are the primary input voltages of the phase-modulating and voltage-regulating system based on back-to-back transformers, that is, the voltages at the middle positions of the three-phase series windings A, B, and C respectively; V12, V23, and V31 are the voltages on the primary windings of the phase-modulating and voltage-regulating system based on back-to-back transformers, VSA and VLA are the starting and ending voltages of the line, and ΔV1 and ΔV2 are the compensation voltages of the phase-modulating and voltage-regulating system based on back-to-back transformers.

[0068] The phase-modulation and voltage-regulation system based on back-to-back transformers is equivalent to connecting an adjustable vector voltage in series in the line. Taking phase A as an example, Fig.10 As shown in Figure 1, two compensation voltages ΔV1 and ΔV2 are added between VSA and VLA. Fig.10 As shown in the left figure, when the tap of the second tap changer is in the middle position, the compensation voltages on the windings on both sides are equal, that is, ΔV1 = ΔV2. At this time, the voltage amplitude before and after phase modulation can be guaranteed to remain unchanged; Fig.10 As shown in the right figure, when the tap of the second tap changer is at the tap position on both sides, the compensation voltages on the windings on both sides are not equal, that is, ΔV1>ΔV2 or ΔV1<ΔV2. At this time, in addition to phase modulation, the second tap changer also realizes the voltage regulation function.

[0069] See attached Fig.11 , Fig.11 : is a vector voltage diagram of a first tap switch and a back-to-back converter according to an embodiment of the present application; a vector diagram of an adjustment range that can be achieved by the first tap switch and the back-to-back converter is as follows Fig.11 As shown, when only the first tap switch is used, discrete phase modulation can be achieved, that is, Fig.11 After adding the back-to-back converter, the first tap changer and the back-to-back converter can be coordinated to achieve continuous phase adjustment and small-range voltage regulation, such as Fig.11 Solid continuous arrow lines in .

[0070] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art can understand that in order to achieve the effect of the present application, different steps do not have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders. These adjusted schemes are equivalent to the technical schemes described in this application, and therefore will also fall within the scope of protection of this application.

[0071] It is understood by those skilled in the art that all or part of the processes in the method for implementing the above-mentioned embodiment of the present application can also be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable storage medium may include: any entity or device, medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium, etc. that can carry the computer program code.

[0072] So far, the technical solution of the present application has been described in conjunction with an embodiment shown in the accompanying drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present application.

Claims

1. A flexible phase-modulation and voltage-regulation system based on back-to-back converters, characterized in that: The flexible phase-modulation and voltage-regulation system comprises a stepless voltage-regulation and phase-modulation unit and a stepped voltage-regulation and phase-modulation unit; the first input end of the stepped voltage-regulation and phase-modulation unit is connected to the power supply line of the three-phase power grid, and the first output end is connected to the input end of the stepless voltage-regulation and phase-modulation unit; the output end of the stepless voltage-regulation and phase-modulation unit is connected to the second input end of the stepped voltage-regulation and phase-modulation unit; the second output end of the stepped voltage-regulation and phase-modulation unit is connected to the load.

2. The flexible phase-modulation and voltage-regulating system based on back-to-back converter according to claim 1 is characterized in that: The stepless voltage and phase regulation unit comprises a first tap switch, an excitation transformer and a back-to-back converter; One end of the primary winding of the excitation transformer is connected to the first output end of the step-by-step voltage and phase modulation unit, and the other end of the primary winding is grounded; The secondary side of the excitation transformer includes an isolation winding and a plurality of segmented windings, adjacent segmented windings are connected in series, and taps of the plurality of segmented windings are respectively connected to the first input end of the first tap switch; Both ends of the isolation winding are connected to the input end of the back-to-back converter, and the output end of the back-to-back converter is connected to the second input end of the first tap switch; The output end of the first tap switch is connected to the second input end of the stepped voltage and phase regulation unit.

3. The flexible phase-modulation and voltage-regulating system based on back-to-back converter according to claim 2 is characterized in that: The back-to-back converter includes an input module, a capacitor module and an output module; The input end of the input module is connected to the two ends of the secondary isolation winding of the excitation transformer, and the output end is connected to the output module through the capacitor module; The output end of the output module is connected to the second input end of the first tap changer.

4. The flexible phase-modulation and voltage-regulating system based on back-to-back converter according to claim 3 is characterized in that: The input module includes a first inductor and a rectifier module, the rectifier module includes a first bridge arm and a second bridge arm, the first bridge arm includes a first switch and a second switch connected in series, and the second bridge arm includes a third switch and a fourth switch connected in series; One end of the secondary side isolation winding of the excitation transformer is connected to the emitter of the third switch and the collector of the fourth switch through the first inductor, and the other end of the secondary side isolation winding is connected to the emitter of the first switch and the collector of the second switch; The collector of the first switch and the collector of the third switch are connected to one end of the capacitor module, and the emitter of the second switch and the emitter of the fourth switch are connected to the other end of the capacitor module.

5. The flexible phase-modulation and voltage-regulation system based on back-to-back converter according to claim 3 is characterized in that: The output module includes an inverter module and a filter module, the inverter module includes a third bridge arm and a fourth bridge arm, the third bridge arm includes a fifth switch and a sixth switch connected in series, and the fourth bridge arm includes a seventh switch and an eighth switch connected in series; the filter module includes a second inductor and a filter capacitor; The emitter of the fifth switch is connected to the collector of the sixth switch and the input end of the second inductor, and the output end of the second inductor is connected to the second input end of the first tap switch through one end of the filter capacitor; The emitter of the seventh switch and the collector of the eighth switch are connected to the second input end of the first tap switch through the other end of the filter capacitor; One end of the capacitor module is connected to the collector of the fifth switch and the collector of the seventh switch, and the other end of the capacitor module is connected to the emitter of the sixth switch and the emitter of the eighth switch.

6. The flexible phase-modulation and voltage-regulating system based on back-to-back converter according to claim 2 is characterized in that: The number of the first tap switch, the excitation transformer, the back-to-back converter, and the plurality of segmented windings is at least three; the grounding end of each primary winding of the excitation transformer is connected and grounded; and the grounding end of each back-to-back converter is connected and grounded.

7. The flexible phase-modulation and voltage-regulating system based on back-to-back converter according to claim 2 is characterized in that: The step-by-step voltage and phase regulation unit comprises a second tap switch and a series transformer; The input end of the primary winding of the series transformer is connected to the power supply line of the three-phase power grid, the taps of the primary winding are respectively connected to the input end of the second tap changer, and the output end of the primary winding is connected to the load; The input end of the secondary winding of the series transformer is connected to the output end of the first tap switch; The output end of the second tap switch is connected to the input end of the excitation transformer.

8. The flexible phase-modulation and voltage-regulation system based on back-to-back converters according to claim 7 is characterized in that: The number of the series transformers is at least three, namely a first series transformer, a second series transformer and a third series transformer; The output end of the secondary winding of the first series transformer is connected to the input end of the secondary winding of the second series transformer; The output end of the secondary winding of the second series transformer is connected to the input end of the secondary winding of the third series transformer; The output end of the secondary winding of the third series transformer is connected to the input end of the secondary winding of the first series transformer.

9. The flexible phase-modulation and voltage-regulation system based on back-to-back converters according to claim 7 is characterized in that: The number of the second tap changers is at least three; the first tap changer and the second tap changer are power electronic tap changers, mechanical switches or composite tap changers.

10. A flexible phase modulation and voltage regulation method, the method is performed based on the flexible phase modulation and voltage regulation system based on back-to-back converters according to any one of claims 1 to 9, characterized in that: The method comprises: Acquiring a voltage regulation requirement, where the voltage regulation requirement includes a phase modulation requirement, or a phase modulation requirement and a voltage regulation requirement; Determining whether the voltage regulation requirement is a phase modulation requirement; If yes, based on the voltage regulation requirement, controlling the stepless voltage and phase regulation unit to perform a phase regulation operation on the input voltage; Otherwise, based on the voltage regulation requirement, the stepless voltage and phase regulation unit and the stepped voltage and phase regulation unit are controlled to perform voltage regulation and phase regulation operations on the input voltage.

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