Hybrid distributed power flow controller topological structure and control method thereof

Abstract

The invention discloses a hybrid distributed power flow controller topological structure and a control method thereof. The topological structure comprises a distribution network Sen transformer DST and a distributed static synchronous series compensator DSSC. The distribution network Sen transformer DST comprises a three-phase double-winding transformer and an on-load tap changer group; each phase of the three-phase double-winding transformer comprises a main winding and a secondary winding, the high-voltage end of the three-phase main winding is connected with the head end of the three-phase distribution line, the low-voltage end of the three-phase main winding is in star connection, and the neutral point of the three-phase main winding is grounded; the on-load voltage regulation switch group comprises six on-load voltage regulation switches which are respectively configured on the low-voltage side of the three-phase main winding and the three-phase secondary winding and provide three-phase first compensation voltage in a cross series connection mode; a distributed static synchronous series compensator DSSC provides a three-phase second compensation voltage; and the three-phase first compensation voltage and the three-phase second compensation voltage are superposed to synthesize a three-phase compensation voltage, and the three-phase compensation voltage is injected into a three-phase distribution line through a three-phase isolation transformer. The invention provides a series hybrid topology consisting of a DST (Digital Subscriber Terminal) and a DSSC (Digital Subscriber Subscriber Center).

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flexible alternating current transmission system of power system, and particularly relates to a hybrid distributed power flow controller topology structure and a control method thereof. BACKGROUND

[0002] With large-scale grid connection of distributed photovoltaic, energy storage and other new energy equipment, the distribution network is facing the severe challenge of random fluctuations on both sides of the source and load. The existing regulation technology presents three technical faults in response to dynamic disturbance: the traditional mechanical on-load tap changer (OLTC) relies on mechanical switching of the tap changer to achieve voltage regulation, with a delay of more than 5 seconds and a coarse step voltage regulation step (about 1.25-2.5%), which cannot suppress millisecond-level voltage fluctuations and lacks phase regulation capability, resulting in continuous deterioration of line congestion problems caused by new energy fluctuations. Although the unified power flow controller (UPFC) has dynamic regulation capability, it is subject to the ultra-high cost (about 3-5 times the cost of traditional solutions) caused by the full-capacity configuration of the converter, the efficiency decay (usually less than 92%) caused by IGBT on-state loss, and the reliability risk caused by cumulative damage to power devices, which is in a dilemma of "excessive performance and insufficient economy" in the distribution network scenario.

[0003] The hybrid architecture of OLTC and UPFC that has appeared in recent years tries to compromise, but it has a systematic defect because it retains the parallel side converter (STATCOM) of UPFC - the redundant parallel structure not only significantly increases the device volume and material cost, but also causes the unit capacity cost to rise to several times the level of the pure mechanical solution due to the additional configuration of filter circuits and protection devices on the parallel side. In addition, the strong coupling characteristics of the parallel side converter and the line inductance force the system to bear a non-negligible circulating current loss for a long time, which doubles the cost of heat dissipation and operation and maintenance compared to the single series structure. The coordination difficulty of the time-varying characteristics of mechanical and electronic devices further leads to a dramatic increase in the complexity of the control module and a significant reduction in system stability margin. Especially in 10kV medium voltage distribution networks, the existing technology system exposes the dual contradictions of fragmented regulation performance and multiplied operation risks: new energy fluctuations can make the probability of transient overvoltage reach more than twice that of traditional power grids, and the line congestion rate increases by more than 15%, while device selection is forced to make a difficult choice between "slow response and cheap solution" and "cost is too high and precise system", which seriously restricts the accommodation capacity of high penetration rate of new energy.

[0004] In summary, there are three core defects in existing voltage regulation technologies: the pure mechanical scheme (such as OLTC) relies on mechanical switch switching, the response time is more than 5 seconds, and only the voltage amplitude can be adjusted, which cannot meet the rapid voltage disturbance and phase compensation demand of new energy fluctuation scene; the all-electronic scheme (such as UPFC) has millisecond multi-dimensional regulation capability, but it must be configured with STATCOM parallel converter, which causes more than 5% of the circulating current loss of the system, and significantly increases the cost of equipment; the hybrid scheme (such as OLTC+STATCOM) needs to be additionally configured with reactor and filter due to the parallel structure, which increases the complexity of the system, and the control timing conflict of mechanical and electronic devices easily causes transient oscillation risk.

[0005] Therefore, there is an urgent need for a topology structure with fast dynamic response, high economy and low loss to solve the coordination problem of mechanical and electronic devices. SUMMARY

[0006] In view of the defects of the prior art, the present application provides a hybrid distributed power flow controller topology structure and a control method thereof, which synchronously solves the above problems through the hybrid distributed power flow controller topology structure (distribution network Sen transformer + distributed static synchronous series compensator): the distribution network Sen transformer mechanical unit realizes large deviation step voltage regulation, the distributed static synchronous series compensator electronic module provides millisecond dynamic compensation and phase regulation capability, and the STATCOM parallel branch is avoided to eliminate circulating current loss; the control method adopts a cooperative control mechanism to solve the timing conflict of mechanical and electronic devices, significantly reduces the equipment cost and transient risk, and realizes the comprehensive optimization of response speed, regulation dimension and energy efficiency.

[0007] The first aspect of the present application provides a hybrid distributed power flow controller topology structure, comprising: a distribution network Sen transformer DST and a distributed static synchronous series compensator DSSC; The distribution network Sen transformer DST comprises a three-phase double-winding transformer and an on-load voltage regulating switch group; each phase of the three-phase double-winding transformer comprises a primary winding and a secondary winding, the high-voltage ends of the three-phase primary windings are respectively connected to the first ends of the three-phase distribution lines, and the low-voltage ends of the three-phase primary windings are star-connected and the neutral points are grounded; the on-load voltage regulating switch group comprises six on-load voltage regulating switches, which are respectively arranged at the low-voltage sides of the three-phase primary windings and the three-phase secondary windings; wherein the A-phase primary winding and the B-phase secondary winding are connected in series by the corresponding two on-load voltage regulating switches to provide the C-phase first compensation voltage , the B-phase primary winding and the C-phase secondary winding are connected in series by the corresponding two on-load voltage regulating switches to provide the A-phase first compensation voltage , and the C-phase primary winding and the A-phase secondary winding are connected in series by the corresponding two on-load voltage regulating switches to provide the B-phase first compensation voltage ; The three distributed static synchronous compensators DSSCs are modular chain H-bridge cascaded structures, respectively A-phase chain H-bridge cascaded DSSC, B-phase chain H-bridge cascaded DSSC and C-phase chain H-bridge cascaded DSSC, and respectively provide A-phase second compensation voltage , B-phase second compensation voltage and C-phase second compensation voltage ; A-phase first compensation voltage , B-phase first compensation voltage and C-phase first compensation voltage are superimposed with A-phase second compensation voltage , B-phase second compensation voltage and C-phase second compensation voltage respectively, to synthesize three-phase compensation voltage , and , and are injected into three-phase distribution lines through a three-phase isolation transformer.

[0008] In some embodiments, the voltage-regulating sections of the three-phase main winding and the three-phase secondary winding are led out to the common end of the corresponding on-load voltage regulating switch, and the tap end of the on-load voltage regulating switch is connected to the gear selection contact array of the corresponding voltage-regulating section; wherein the A-phase main winding and the corresponding on-load voltage regulating switch K1 provide series compensation voltage ; the B-phase main winding and the corresponding on-load voltage regulating switch K2 provide series compensation voltage ; the C-phase main winding and the corresponding on-load voltage regulating switch K3 provide series compensation voltage ; the A-phase secondary winding and the corresponding on-load voltage regulating switch K4 provide series compensation voltage ; the B-phase secondary winding and the corresponding on-load voltage regulating switch K5 provide series compensation voltage ; the C-phase secondary winding and the corresponding on-load voltage regulating switch K6 provide series compensation voltage ; and series compensation voltage and series compensation voltage are combined to form A-phase first compensation voltage , series compensation voltage and series compensation voltage are combined to form B-phase first compensation voltage , and series compensation voltage and series compensation voltage are combined to form C-phase first compensation voltage .

[0009] In some embodiments, series compensation voltage and series compensation voltage The first compensation voltage of the B phase is As follows:

[0010] In the formula, And The gear; The B phase voltage; The C phase voltage; The first compensation voltage of the B phase And the first compensation voltage of the C phase Similarly; By adjusting the corresponding And The combination of the amplitude and phase of the corresponding first compensation voltage of the phase is controlled.

[0011] In some embodiments, the on-load voltage regulating switch is switched to the tap to select different gears in the ±m level range; When m is 2, the gear step U step Is 5%, the gear .

[0012] In some embodiments, the single-phase dynamic compensation radius of the distributed static synchronous series compensator DSSC is:

[0013] In the formula, The single-phase second compensation voltage; The rated voltage of the distribution network line.

[0014] In some embodiments, the continuous adjustable compensation range is composed of a circular domain with each discrete compensation point of the distribution network Sen transformer DST as the center and a radius of 2.89%U N , which satisfies:

[0015] In the formula, The amplitude of the three-phase compensation voltage phasor; The corresponding phase discrete compensation point.

[0016] In some embodiments, the first end of the A-phase chain-type cascaded H-bridge DSSC is connected to the common end of the on-load voltage regulating switch of the C-phase secondary winding, forming an A-phase series compensation line, and the common end of the B-phase main winding on-load voltage regulating switch and the second end of the A-phase chain-type cascaded H-bridge DSSC provide the A-phase compensation voltage . The first end of the B-phase chain cascade H-bridge DSSC is connected to the common end of the A-phase secondary winding on-load tap-changer to form a B-phase series compensation circuit, and the common end of the C-phase main winding on-load tap-changer and the second end of the B-phase chain cascade H-bridge DSSC provide the B-phase compensation voltage. ; The first end of the C-phase chain cascade H-bridge DSSC is connected to the common end of the B-phase secondary winding on-load tap-changer to form a C-phase series compensation circuit, and the common end of the A-phase main winding on-load tap-changer and the second end of the C-phase chain cascade H-bridge DSSC provide the C-phase compensation voltage. .

[0017] In some embodiments, each cascade module of the distributed static synchronous series compensator DSSC includes an energy storage module, an H-bridge converter, and an LC filter; each cascade module can independently output three basic states through the IGBT switching of the H-bridge: forward DC voltage +U dc , zero level or reverse DC voltage-U dc ; After several cascade modules are cascaded, they are connected to the series compensation circuit via a bypass switch, and a continuously adjustable dynamic compensation voltage is generated through the cascade topology.

[0018] In some embodiments, when the number of cascaded modules is 3, the output state combination forms 7 discrete levels: -3U dc 、-2U dc 、-U dc ,0,+U dc 、+2U dc and +3U dc ,The multi-level structure generates a step-shaped pseudo-sine wave through pulse width modulation.

[0019] According to a second aspect of the present invention, there is provided a control method, which is applied to the hybrid distributed power flow controller topology structure described in any one of the first inventions, the method comprising: Detect voltage fluctuation amplitude; Determine whether the voltage fluctuation amplitude exceeds the single-phase dynamic compensation radius of the distributed static synchronous series compensator DSSC; If not, closed-loop continuous regulation is performed through the distributed static synchronous series compensator DSSC; If so, coarse adjustment is performed through the distribution network Sen transformer DST, and the voltage step correction is achieved through the mechanical tap switching of the on-load tap changer group. During the switching transition period of the mechanical action of the distribution network Sen transformer DST, the distributed static synchronous series compensator DSSC does not operate; after the switching transition period ends, the voltage fluctuation amplitude continues to be detected and judgment continues.

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects: The present application successfully solves the core contradiction that economy, energy efficiency and response speed are difficult to balance in dynamic power flow control of distribution network through innovative hybrid distributed power flow controller topology combined with cooperative control mechanism: 1) Abandoning the traditional parallel side converter (STATCOM), through the cooperative design of DSSC modular chain structure and micro energy storage, the UPFC compensation effect is retained while the device structure is greatly simplified. Combined with the pure series architecture, the filter circuit and redundant protection device are omitted, which significantly reduces the material cost and floor area.

[0021] 2) Through the cooperative adjustment of the fundamental voltage of DST and the dynamic fine adjustment of DSSC, while ensuring a wide range of voltage compensation capability, the power electronic devices only need to handle small capacity dynamic components, and the overall efficiency and reliability are significantly better than the traditional hybrid scheme.

[0022] 3) The coupling effect of parallel device and line inductance is completely avoided in series structure, which fundamentally suppresses the circulating loss, and at the same time, through the steady-state-dynamic task decomposition control strategy, the coordinated operation of mechanical and electronic devices is realized, and the system stability margin and dynamic response speed are simultaneously improved.

[0023] Compared with the prior art, the present scheme realizes the dynamic performance close to all power electronic devices at a cost close to conventional regulating devices, especially in high proportion of new energy access scene, effectively alleviating the voltage fluctuation and line congestion problem, providing a new generation of power flow control solution with practicability and economy for distribution network. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A topology diagram of a hybrid distributed power flow controller is provided for the embodiments of the present application; Figure 2 A small-capacity chain-type cascaded H-bridge DSSC topology diagram is provided for the embodiments of the present application; Figure 3 A phase voltage compensation phasor diagram of phase A is provided for the embodiments of the present application; Figure 4 A simplified schematic diagram of a distribution system is provided for the embodiments of the present application; Figure 5 A voltage phasor diagram of a distribution system is provided for the embodiments of the present application; Figure 6 An active power compensation range diagram of a hybrid distributed power flow controller is provided for the embodiments of the present application; Figure 7 A reactive power compensation range diagram of a hybrid distributed power flow controller is provided for the embodiments of the present application; Figure 8 A flow chart of a hybrid distributed power flow controller steady-state-dynamic task decomposition mechanism is provided for embodiments of the present application. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of the present application.

[0026] Obviously, the accompanying drawings in the following description are only some examples or embodiments of the present application, and for those of ordinary skill in the art, the present application can be applied to other similar scenarios without creative efforts based on these drawings. In addition, it can be understood that although the efforts made in this development process can be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some designs, manufacturing or production changes based on the technical content disclosed in the present application are only routine technical means and should not be understood as insufficient disclosure of the present application.

[0027] In the present application, the phrase "embodiments" means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in the present application can be combined with other embodiments without conflict.

[0028] Unless otherwise defined, technical terms and scientific terms used in the present application shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "a", "an", "one", "this", and similar referents in the context of describing the application are to be construed to be inclusive, not exclusive. For example, the use of the term "comprises", "comprising", "containing", "having" and the like are inclusive, not exclusive. The process, method, system, product, or apparatus that comprises a list of steps or modules (units) is not limited to the listed steps or units, but can also comprise additional steps or units not listed, or can also comprise other steps or units inherent to such process, method, product, or apparatus. The terms "connected", "coupled", and "linked" and the like, unless otherwise defined, are not limited to physical or mechanical connections or couplings, but can include electrical connections, whether direct or indirect. The term "plurality" refers to two or more. The term "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, "A and / or B" can mean that A exists alone, A and B exist together, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects. The terms "first", "second", "third", and the like are merely used to distinguish similar objects, and do not represent a specific order of the objects.

[0029] The present application provides a hybrid distributed power flow controller topology structure suitable for medium and low voltage distribution network and a control method thereof, which is particularly suitable for solving the dynamic power flow regulation problem in the high proportion of new energy access scenario.

[0030] The hybrid distributed power flow controller topology structure provided by the present application is shown in Figure 1 The structure breaks through the technical contradiction between dynamic response speed, regulation accuracy and economic benefit of traditional equipment through the innovative combination of mechanical voltage regulating device and power electronic compensation device. The specific technical scheme is as follows: a series hybrid topology composed of distribution Sen transformer (DST) and distributed static synchronous series compensator (DSSC) is constructed. The distribution Sen transformer DST is designed by cooperating three-phase double-winding transformer and on-load voltage regulating switch group, the main winding adopts star connection neutral point grounding structure, the main winding low voltage side and the secondary winding are both configured with on-load voltage regulating switch group, the main winding voltage regulating section adopts self-coupling transformer design, the tapping can be switched in the range of ±m level, and the reconfigurable fundamental voltage compensation network is formed by cross series connection. The distributed static synchronous series compensator DSSC adopts modular chain H bridge cascade structure, as shown in Figure 2As shown, each power module integrates a voltage-stabilized micro-energy storage unit, a full-controlled H-bridge converter and an LC filter, and generates a continuously adjustable dynamic compensation voltage through a cascaded topology. The outputs of the DST and the DSSC are connected in series through an isolation transformer and injected into the distribution line, forming a composite voltage compensation mechanism.

[0031] The distribution Sen transformer DST is based on step voltage regulation of the on-load voltage regulating switch group, and achieves coarse adjustment of the fundamental voltage amplitude through mechanical contact switching. The compensation step length is determined by the transformer winding tap ratio. The distributed static synchronous series compensator DSSC is based on the fast switching capability of power electronic devices, and achieves continuous fine adjustment of the compensation voltage phase and amplitude through pulse width modulation technology. The output voltages of the distribution Sen transformer DST and the distributed static synchronous series compensator DSSC form a combination of discrete point sets and continuous domains in the vector space, as shown in Figure 3 As shown, the hybrid topology has both large-capacity fundamental compensation capability and precise suppression of dynamic disturbances.

[0032] The control method of the present application is based on the series complementary characteristics of the DST and the DSSC, and achieves collaborative regulation through steady-state and dynamic task decomposition: when the line voltage / current deviation exceeds the instantaneous adjustment range of the DSSC, the DST tap changer is triggered to reset the compensation reference point. The DSSC then generates a dynamic compensation voltage based on closed-loop feedback, and the amplitude is limited to 50% of the difference between adjacent DST tap levels to maintain efficient operation. During the tap changer switching process, the DSSC instruction update is temporarily frozen to avoid transient conflicts, and the dynamic compensation is restored according to the real-time deviation signal after the mechanical action is completed. The control flow can be realized through a proportional-integral controller, and the parameters are adjusted according to the impedance characteristics of the cascaded modules.

[0033] The embodiments of the present application take a 10kV distribution line as the implementation scenario, Figure 1 As shown, the simplified topology structure diagram of the hybrid distributed power flow controller connected to the line.

[0034] The distribution network Sen transformer DST is mainly composed of a three-phase double-winding transformer and a load regulating switch. Each phase of the three-phase double-winding transformer includes a main winding (winding a1, b1, c1) and a secondary winding (winding a2, b2, c2). The high-voltage end of the input side of the main winding is connected to the first end of the three-phase distribution line, and the other end is star-connected and grounded at the neutral point. The low-voltage side of the main winding is the regulating section, which has multiple tap-off taps. The regulating sections of the three-phase main winding and the three-phase secondary winding lead to the common end of the corresponding load regulating switch (K1, K2, K3, K4, K5, K6), and the tap end of the load regulating switch is connected to the corresponding regulating section of the regulating section. Each load regulating switch can selectively access different regulating points (such as ±10%, ±5%, 0%) on the corresponding main winding or secondary winding regulating section. The common end connection point serves as the reference point for the compensation voltage output of the phase. The main winding regulating section (a1, b1, c1) adopts a self-coupling transformer design, and the two sets of load regulating switches can be switched within ±m levels. The three-phase main winding is connected to the distribution line in parallel, and its input is the voltage at the first end of the distribution line before compensation.

[0035] The series compensation voltages provided by windings a1, b1, c1, a2, b2, c2 in DST are respectively denoted as . Among them, winding b1 and winding c2 are connected in series by load regulating switches K2 and K6 to provide the A-phase compensation voltage of DST, winding c1 and winding a2 are connected in series by load regulating switches K3 and K4 to provide the B-phase compensation voltage of DST, and winding a1 and winding b2 are provided by load regulating switches K1 and K5 to provide the C-phase compensation voltage of DST. Since , and are symmetrical in three phases, only the A-phase compensation voltage compensation principle of DST is analyzed. The A-phase compensation voltage is generated by the cross connection of the main winding B-phase tap section and the secondary winding C-phase , satisfying the relationship:

[0036] wherein the adjustment range of DST is ±10%U N , U N is the rated voltage of the distribution line 10kV, the tap-off tap is configured in ±2 levels (step U step is 5%), and the amplitude and phase joint control of the compensation voltage is realized by adjusting the combination of k1 and k2. For example, when k1=+10% and k2=−10%, substitute into the three-phase balance condition U sA +U sB+U sC =0 can be obtained:

[0037] At this time, the leading A-phase 90°, amplitude 17.3%U sA The orthogonal compensation component is generated.

[0038] The DSSC has three, which are the A-phase chain cascade H-bridge DSSC, the B-phase chain cascade H-bridge DSSC and the C-phase chain cascade H-bridge DSSC, which are used to provide the A-phase second compensation voltage , the B-phase second compensation voltage and the C-phase second compensation voltage . As Figure 1 shown, the A-phase main winding and its on-load voltage regulating switch, the B-phase secondary winding and its on-load voltage regulating switch, and the C-phase chain cascade H-bridge DSSC are connected in series to form a C-phase series compensation circuit, and the output end of the C-phase chain cascade H-bridge DSSC and the common end of the on-load voltage regulating switch of the A-phase main winding provide the C-phase compensation voltage, and are injected into the distribution line through the isolation transformer; the other two are similar.

[0039] Each DSSC adopts a modular structure of chain H-bridge cascade, and when the number of cascade modules is 3, the topological structure is as shown in Figure 2 . Among them, each cascade module is composed of a micro energy storage module containing voltage stabilization, an H-bridge converter and an LC filter, and is connected to the series compensation circuit by a bypass switch after cascade. In the level generation mechanism, each module of the DSSC can independently output three basic states: forward direct current voltage (+U dc ), zero level or reverse direct current voltage (-U dc ) through the IGBT switching of the H-bridge. When the three modules are connected in series, the output state combination forms seven discrete levels (-3U dc , -2U dc , -U dc , 0, +U dc , +2U dc , +3U dc ), and the multi-level structure generates a stepped pseudo-sine wave through pulse width modulation. The single-phase dynamic compensation radius of the DSSC (i.e. the maximum compensation phase voltage amplitude that can be provided) is designed as:

[0040] This parameter ensures the DSSC can cover the transition area between any adjacent DST gears. According to the ratio of the number of cascaded modules to the rated voltage of 10 kV line, each H-bridge module is configured with a super capacitor energy storage unit with rated voltage of 200 V on its DC side. This voltage value is determined based on the compensation requirement: three H-bridge modules in series need to provide a maximum compensation of 289 V phase voltage, which corresponds to an effective value of 96.3 V for a single module. After peak conversion (136 V) and modulation ratio constraint (0.85), the theoretical requirement on the DC side is 160 V. A standard voltage grade of 200 V is selected to leave a design margin of 25%.

[0041] Compensation voltage generated by DST Residual voltage generated by DSSC on the series side Superimposed, synthesized compensation voltage , which is injected into the distribution line through a three-phase isolation transformer. With the discrete compensation points (diamond markers) of DST as the center and a circular domain with a radius of 2.89%U N constituting a continuously adjustable compensation range, the following conditions are met:

[0042] The line A-phase output voltage phasor diagram after compensation is shown in Figure 3 , and the A-phase line head voltage after compensation is shown in . The compensation voltage phasor that can be output by DST is a discrete point on the diamond, which performs step voltage regulation; the compensation voltage phasor that can be provided by DSSC containing voltage stabilization micro energy storage is a small circle with all discrete points as the center and any point within the circle. The superimposition of the two voltage phasors outputs a continuously adjustable voltage phasor that combines the point compensation of DST and the surface compensation of DSSC.

[0043] When the line voltage fluctuates, DST achieves coarse adjustment of ±10%U N through tap switching, and DSSC performs dynamic fine adjustment within a range of ±2.89%U N . Taking a voltage drop of 8% as an example, DST switches to the -2 gear to output -10% compensation, and DSSC subsequently compensates for the +2% residual deviation, resulting in a final voltage error of less than 0.5%.

[0044] When the hybrid distributed power flow controller is put into operation in the distribution system, it can be approximately regarded as a controllable voltage source with adjustable amplitude and phase. Figure 4 and Figure 5 are the simplified schematic diagram and voltage phasor diagram of the distribution system after the access device. The two ends of the distribution line are simplified as ideal single-machine infinite systems, ignoring resistance and capacitance, and the equivalent reactance is (taken as 1.0 p.u. in this embodiment), and the current flowing through the series part of the compensator is represented as . The system head voltage before compensation is , and the phase is , the system end voltage is , the phase lags the head-end voltage (taken as in this embodiment). , the compensation voltage phasor provided by the distributed high-voltage hybrid power flow controller has an amplitude of and a phase of . The compensated system head-end voltage phasor is expressed as , and the voltage phase difference between the head and tail ends of the power distribution system is .

[0045] After the hybrid distributed power flow controller is connected to the power distribution system, the active and reactive power at the tail end of the system is:

[0046] Before the connecting device, the active and reactive power at the tail end of the system are respectively:

[0047] From the above two formulas, the active and reactive power compensation amounts provided by the hybrid distributed power flow controller are respectively:

[0048] According to the above formula, the active power and reactive power compensation range diagram of the hybrid distributed power flow controller is shown in Figure 6 and Figure 7 . As can be seen from the diagram, the compensation range of active power and reactive power in this embodiment is .

[0049] The cooperative regulation process realizes the timing decoupling of mechanical and electronic components through magnetic isolation signal transmission, and the steady-state-dynamic task decomposition mechanism is shown in Figure 8 : when the voltage fluctuation amplitude exceeds ±2.89% of the rated voltage (V ), the system preferentially triggers the DST (on-load tap changer) for coarse adjustment, and realizes stepwise correction of voltage through mechanical tap switching; for fine fluctuations within the range of ±2.89%, the DSSC implements closed-loop continuous adjustment through the power electronic converter, achieving millisecond-level accurate compensation. In particular, during the switching transition period of the DST mechanical action (about 2-5s), the DSSC will automatically freeze the adjustment instruction, maintaining the current output state unchanged, which can not only avoid the timing conflict between mechanical contact switching and electronic regulation, but also ensure the seamless connection of the compensation process. This strategy divides the action threshold and isolates the time window, so that the slow large-range adjustment of mechanical devices and the fast fine control of electronic devices form a complement, and the overall response speed is more than 3 times faster than the traditional OLTC (on-load tap changer transformer).

[0050] The hybrid distributed power flow controller topology completely eliminates the circulating current loss of the traditional STATCOM parallel branch through a pure series architecture, and theoretical calculations show that the line transmission capacity is improved:

[0051] wherein θ is in the range of 0° to 90°. In the θ = 45° working condition, the active and reactive compensation amount synchronously reaches 9.1% of the reference capacity, which is significantly better than the single amplitude adjustment capability of the mechanical OLTC.

[0052] In summary, the application successfully solves the core contradiction of economic efficiency and response speed in the dynamic power flow control of distribution networks through the innovative hybrid distributed power flow controller topology combined with the cooperative control mechanism: 1) Abandoning the traditional parallel side converter (STATCOM), the UPFC compensation effect is retained while the device structure is greatly simplified through the cooperative design of the DSSC modular chain structure and the micro energy storage. Combined with the pure series architecture, the filter circuit and redundant protection device are omitted, which significantly reduces the material cost and floor area.

[0053] 2) Through the cooperative adjustment of the fundamental voltage of the DST and the dynamic fine adjustment of the DSSC, the power electronic devices only need to handle small capacity dynamic components while ensuring a wide range of voltage compensation capability, and the overall efficiency and reliability are significantly better than the traditional hybrid scheme.

[0054] 3) The series structure completely avoids the coupling effect of the parallel device and the line inductance, which effectively suppresses the circulating current loss, and at the same time, through the steady-state and dynamic task decomposition control strategy, the mechanical and electronic devices are coordinated to operate, and the system stability margin and dynamic response speed are simultaneously improved.

[0055] Compared with the prior art, the application realizes the dynamic performance close to the all-power electronic device at a cost close to the conventional regulation device, effectively alleviates the voltage fluctuation and line congestion problem in the high proportion of new energy access scene, and provides a new generation of power flow control solution with practicality and economy for distribution networks.

[0056] It should be noted that each technical feature of the above-described embodiments can be combined arbitrarily, and in order to make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not exist contradictory, it should be considered as the scope of the present application. In addition, according to the needs of implementation, each step / component described in the present application can be split into more steps / components, or two or more steps / components or part of the operation of the steps / components can be combined into a new step / component to achieve the purpose of the present application.

[0057] Those skilled in the art will easily understand that the above-mentioned embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the patent scope of the application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A hybrid distributed power flow controller topology, characterized in that: include: Distribution network Sen transformer DST and distributed static synchronous series compensator DSSC; The distribution network Sen transformer DST includes a three-phase double-winding transformer and an on-load tap-changing switch group; each phase of the three-phase double-winding transformer includes a main winding and a secondary winding, the high-voltage end of the three-phase main winding is connected to the head end of the three-phase distribution line respectively, and the low-voltage end of the three-phase main winding is star-connected and the neutral point is grounded; the on-load tap-changing switch group includes six on-load tap-changing switches, which are respectively configured on the low-voltage side of the three-phase main winding and the three-phase secondary winding; among them, the A-phase main winding and the B-phase secondary winding are connected in series by the corresponding two on-load tap-changing switches to provide the first compensation voltage of the C-phase The B-phase main winding and the C-phase secondary winding are connected in series by two corresponding on-load tap-changers to provide the first compensation voltage of the A-phase The C-phase main winding and the A-phase secondary winding are connected in series by two corresponding on-load tap-changers to provide the first compensation voltage of the B-phase ; There are three distributed static synchronous series compensators (DSSCs) with a modular chain H-bridge cascade structure, namely, A-phase chain cascade H-bridge DSSC, B-phase chain cascade H-bridge DSSC and C-phase chain cascade H-bridge DSSC, and they provide the second compensation voltage for A-phase respectively. , B phase second compensation voltage and the second compensation voltage of phase C ; Phase A first compensation voltage , Phase B first compensation voltage and the first compensation voltage of phase C Respectively with the second compensation voltage of phase A , B phase second compensation voltage and the second compensation voltage of phase C Superposition, synthesis of three-phase compensation voltage 、 and , and injected into the three-phase distribution line through a three-phase isolation transformer.

2. The hybrid distributed power flow controller topology according to claim 1, characterized in that: The voltage regulating sections of the three-phase main winding and the three-phase secondary winding are connected to the common terminals of the corresponding on-load tap-changing switches, and the tap terminals of the on-load tap-changing switches are connected to the gear selection contact arrays of the corresponding voltage regulating sections; Among them, the A-phase main winding and its corresponding on-load tap-changing switch K1 provide series compensation voltage The B-phase main winding and its corresponding on-load tap-changer K2 provide series compensation voltage The C-phase main winding and its corresponding on-load tap-changer K3 provide series compensation voltage The A-phase secondary winding and its corresponding on-load tap-changer K4 provide series compensation voltage The B-phase secondary winding and its corresponding on-load tap-changer K5 provide series compensation voltage The C-phase secondary winding and its corresponding on-load tap-changer K6 provide series compensation voltage ; And series compensation voltage and series compensation voltage The first compensation voltage of phase A is synthesized in series , series compensation voltage and series compensation voltage The first compensation voltage of phase B is synthesized in series , series compensation voltage and series compensation voltage The first compensation voltage of phase C is synthesized in series .

3. The hybrid distributed power flow controller topology according to claim 2, characterized in that: Series compensation voltage and series compensation voltage The first compensation voltage of phase A is synthesized in series as follows: Where, and For the gear position; is the B phase voltage; is the C phase voltage; Phase B first compensation voltage and the first compensation voltage of phase C Similarly; By adjusting the corresponding and The combination of realizes the amplitude and phase joint control of the first compensation voltage of the corresponding phase.

4. The hybrid distributed power flow controller topology structure according to claim 3 is characterized in that: The on-load tap-changer switches on and off the tap within the range of ±m to select different gears; When m is 2, the gear step length is U step When it is 5%, the gear .

5. The hybrid distributed power flow controller topology structure according to claim 4, characterized in that: The single-phase dynamic compensation radius of the distributed static synchronous series compensator DSSC is: Where, is the single-phase second compensation voltage; Rated voltage of the distribution network line.

6. The hybrid distributed power flow controller topology structure according to claim 5, characterized in that: With the discrete compensation points of the distribution network Sen transformer DST as the center and a radius of 2.89%U N The circular domain of constitutes a continuously adjustable compensation range, satisfying: Where, is the three-phase compensation voltage phasor amplitude; is the corresponding phase discrete compensation point.

7. The hybrid distributed power flow controller topology structure according to claim 2, characterized in that: The first end of the A-phase chain cascade H-bridge DSSC is connected to the common end of the C-phase secondary winding on-load tap-changer to form an A-phase series compensation circuit, and the common end of the B-phase main winding on-load tap-changer and the second end of the A-phase chain cascade H-bridge DSSC provide the A-phase compensation voltage. ; The first end of the B-phase chain cascade H-bridge DSSC is connected to the common end of the A-phase secondary winding on-load tap-changer to form a B-phase series compensation circuit, and the common end of the C-phase main winding on-load tap-changer and the second end of the B-phase chain cascade H-bridge DSSC provide the B-phase compensation voltage. ; The first end of the C-phase chain cascade H-bridge DSSC is connected to the common end of the B-phase secondary winding on-load tap-changer to form a C-phase series compensation circuit, and the common end of the A-phase main winding on-load tap-changer and the second end of the C-phase chain cascade H-bridge DSSC provide the C-phase compensation voltage. .

8. The hybrid distributed power flow controller topology structure according to claim 7, characterized in that: Each cascade module of the distributed static synchronous series compensator DSSC includes an energy storage module, an H-bridge converter and an LC filter; each cascade module can independently output three basic states through the IGBT switching of the H-bridge: forward DC voltage +U dc , zero level or reverse DC voltage-U dc ; After several cascade modules are cascaded, they are connected to the series compensation circuit via a bypass switch, and a continuously adjustable dynamic compensation voltage is generated through the cascade topology.

9. The hybrid distributed power flow controller topology structure according to claim 8, characterized in that: When the number of cascaded modules is 3, the output state combination forms 7 discrete levels: -3U dc 、-2U dc 、-U dc ,0,+U dc 、+2U dc and +3U dc ,The multi-level structure generates a step-shaped pseudo-sine wave through pulse width modulation.

10. A control method, characterized in that: Applied to the hybrid distributed power flow controller topology structure according to any one of claims 1 to 9, the method comprises: Detect voltage fluctuation amplitude; Determine whether the voltage fluctuation amplitude exceeds the single-phase dynamic compensation radius of the distributed static synchronous series compensator DSSC; If not, closed-loop continuous regulation is performed through the distributed static synchronous series compensator DSSC; If so, coarse adjustment is performed through the distribution network Sen transformer DST, and the voltage step correction is achieved through the mechanical tap switching of the on-load tap changer group. During the switching transition period of the mechanical action of the distribution network Sen transformer DST, the distributed static synchronous series compensator DSSC does not operate; after the switching transition period ends, the voltage fluctuation amplitude continues to be detected and judgment continues.

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