Multi-winding grading reactor applied to urbanization cable distributed capacitance compensation

Abstract

The invention belongs to the technical field of urbanization cable distributed capacitance compensation, and discloses a multi-winding grading reactor applied to urbanization cable distributed capacitance compensation, which comprises a multi-winding transformer, a passive series / parallel coarse tuning reactor shunt, an active inversion fine tuning reactor shunt and a controller, the multi-winding transformer comprises a primary winding and N secondary windings, and N is greater than or equal to 3; two ends of the primary winding are connected in series in a power grid cable line; the M secondary windings and the corresponding M bidirectional thyristors are connected in series or / and in parallel to form a passive series / parallel coarse tuning reactor shunt, and M is less than N; the active inversion fine adjustment reactor shunt comprises a single-phase full-bridge conversion circuit, and the alternating current side of the single-phase full-bridge conversion circuit is connected with any one of the residual N-M secondary windings in the multi-winding transformer; and the controller controls the coarse adjustment and fine adjustment reactor shunt to perform coarse adjustment and fine adjustment on the system output inductive impedance so as to perform on-demand compensation on the impedance of the distributed capacitor, and the compensation precision and the power grid electric energy quality can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed capacitance compensation of urbanized cables, and more specifically, relates to a multi-winding graded reactor used for distributed capacitance compensation of urbanized cables. Background Art

[0002] With the advancement of the urbanization process of the power grid and the continuous access of new power electronic devices, the industrial functions corresponding to the transmission lines in the urbanized power grid are intensive and the actual working environment is complex. Therefore, overhead lines are gradually transformed into underground cables. The increase in the underground cable rate plays a key role in the urbanization process, but the excessively high cable rate will lead to an increase in the capacitance value of the distributed capacitance (mainly the cable distributed capacitance) in the equivalent circuit of the power grid system. The increase in the capacitive nature of the circuit will cause the voltage at the end of the power grid or near the concentrated area of ​​urban cables to increase abnormally, and the current waveform will suddenly become disordered, thereby reducing the power quality of the power grid.

[0003] At present, the suppression and compensation methods for capacitive electrical coupling parameters in urban power grid cable construction are limited to the selection of cable materials and the various electromagnetic shielding methods used by the cables themselves. That is, the suppression and control methods for the distributed capacitance of power grid cables mostly rely on the characteristics of the power grid cable materials themselves, thereby making electrical improvements to cable-dense areas at the source. However, in actual engineering applications, on the one hand, factors such as weather, temperature, and electromagnetic noise generated by new urban construction will affect the characteristics of the cable materials themselves, causing the characteristics of the cable materials themselves to change, thereby affecting the suppression and compensation effects, and failing to guarantee the quality of power grid electricity; on the other hand, the characteristics of the cable materials themselves are fixed during planning and construction, and cannot be adjusted and improved according to actual application needs. Summary of the invention

[0004] In response to the above defects or improvement needs of the prior art, the present invention provides a multi-winding graded inductor for compensating the distributed capacitance of urban cables. Its purpose is to compensate for the distributed capacitance of urban cables according to actual application requirements and to improve the compensation accuracy to improve the power quality of the power grid.

[0005] To achieve the above object, according to a first aspect of the present invention, there is provided a multi-winding tiered reactor for use in urbanized cable distributed capacitance compensation, comprising: a multi-winding transformer, a passive series / parallel coarse-adjusting reactor shunt, an active inverter fine-adjusting reactor shunt and a controller;

[0006] The multi-winding transformer includes a primary winding and N secondary windings, N≥3; both ends of the primary winding are connected in series in the power grid cable line; M secondary windings and corresponding M bidirectional thyristors are connected in series or / and in parallel to form the passive series / parallel coarse adjustment reactor shunt, M<N; the active inverter fine adjustment reactor shunt includes a single-phase full-bridge conversion circuit, the AC side of which is connected to any secondary winding of the remaining NM secondary windings in the multi-winding transformer;

[0007] The controller is used to control the switching states of M bidirectional thyristors to control the number k of inductive reactance circuits composed of secondary windings and corresponding bidirectional thyristors put into operation in the passive series / parallel coarse adjustment reactor branch, thereby step-by-step adjusting the inductive impedance value output by the primary winding, so that the inductive impedance value is roughly matched with the cable distributed capacitance impedance, 0≤k≤M;

[0008] The controller is also used to generate a control signal to control the on and off of the switch tube of the full-bridge conversion circuit, so as to control the output voltage and current of the AC side of the full-bridge conversion circuit, and then continuously adjust the inductive impedance value after rough matching, so that the inductive impedance value after continuous adjustment is completely matched with the cable distributed capacitance impedance, thereby realizing compensation for the cable distributed capacitance.

[0009] Furthermore, a voltage stabilizing capacitor C is connected in parallel to the DC side of the full-bridge conversion circuit.

[0010] Furthermore, the multi-winding transformer operates in a linear region.

[0011] Furthermore, the full-bridge conversion circuit is composed of an IGBT switch T 1 -T 4 constitute.

[0012] According to a second aspect of the present invention, a control method for a multi-winding tiered reactor for urbanized cable distributed capacitance compensation is provided, which acts on a controller in the multi-winding tiered reactor according to any one of the first aspects, and the control method comprises:

[0013] By controlling the switching states of M bidirectional thyristors, the number k of inductive reactance circuits composed of secondary windings and corresponding bidirectional thyristors put into operation in the passive series / parallel coarse-adjusting reactor branch is controlled, and then the inductive impedance value output by the primary winding is adjusted in a step-by-step manner, so that the inductive impedance value is roughly matched with the cable distributed capacitance impedance, 0≤k≤M;

[0014] A control signal is generated to control the on and off of the switch tube of the full-bridge conversion circuit to control the output voltage and current of the AC side of the full-bridge conversion circuit, and then the inductive impedance value after rough matching is continuously adjusted so that the inductive impedance value after continuous adjustment is completely matched with the cable distributed capacitance impedance, thereby realizing compensation for the cable distributed capacitance.

[0015] Furthermore, during the coarse matching process, the voltage and current equations satisfied by the multi-winding transformer are:

[0016] U 1 =jw(I 1 L 1 +(I 21 M 21 +I 22 M 22 …+I 2k M 2k ))

[0017] Where U 1 ,I 1 Respectively represent the equivalent output voltage and equivalent output current of the primary winding, U 1 / I 1 Used to characterize the inductive impedance of the primary winding output; L 1 I is the self-inductance of the primary winding; 21 ,I 22 ,…,I 2k They represent the current in the secondary winding corresponding to the k inductive reactance circuits put into operation; M 21 、M 22 , …, M 2k They represent the mutual inductances of the k secondary windings corresponding to the k inductive reactance circuits put into operation; j represents the sign of the imaginary part of the inductance, and w is the preset electrical angular frequency;

[0018] Based on the voltage-current equation satisfied by the multi-winding transformer in the rough matching process, the switching states of the M bidirectional thyristors are controlled to control the number k of inductive reactance circuits composed of the secondary winding and the corresponding bidirectional thyristors put into operation in the passive series / parallel coarse adjustment reactor branch, thereby controlling the inductive impedance value U output by the primary winding. 1 / I 1 Perform step-by-step adjustment to make the inductive impedance value U 1 / I 1 Roughly match the impedance of the cable distributed capacitance.

[0019] Furthermore, when k>0, during the continuous adjustment of the inductive impedance value after rough matching, the voltage and current equation satisfied by the multi-winding transformer is:

[0020] U 1 =jw(I1 L 1 +(I 21 M 21 +I 22 M 22 …+I 2k M 2k )+I 3 M 3 )

[0021] In the formula, I 3 、M 3 They respectively represent the secondary winding current and the secondary winding mutual inductance connected to the active inverter fine-tuning reactor branch;

[0022] Based on the voltage-current equation satisfied by the multi-winding transformer and the number k of inductive reactance loops determined after rough matching during the continuous adjustment of the inductive impedance value after rough matching, the duty cycle of the control signal is changed; the on-off of the switch tube of the full-bridge conversion circuit is controlled by the changed duty cycle of the control signal to control the output voltage and current of the AC side of the full-bridge conversion circuit, thereby adjusting the inductive impedance value U after rough matching. 1 / I 1 Continuously adjust so that the inductive impedance value after continuous adjustment U 1 / I 1 It completely matches the impedance of the cable distributed capacitance to achieve compensation for the cable distributed capacitance.

[0023] Furthermore, when k=0, the inductive impedance value after the rough matching is the current output impedance value of the primary winding; during the continuous adjustment of the output impedance value of the primary winding, the voltage-current equation satisfied by the multi-winding transformer is:

[0024] U 1 =jw(I 1 L 1 +I 3 M 3 )

[0025] In the formula, I 3 、M 3 They respectively represent the secondary winding current and the secondary winding mutual inductance connected to the active inverter fine-tuning reactor branch;

[0026] Based on the voltage-current equation satisfied by the multi-winding transformer, the duty cycle of the control signal is changed; the on-off of the switch tube of the full-bridge conversion circuit is controlled by the changed duty cycle of the control signal to control the output voltage and current of the AC side of the full-bridge conversion circuit, thereby adjusting the output impedance value U of the primary winding. 1 / I 1 Continuously adjust so that the inductive impedance value after continuous adjustment U 1 / I1 It completely matches the impedance of the cable distributed capacitance to achieve compensation for the cable distributed capacitance.

[0027] Furthermore, L 1 、M 21 、M 22 , …, M 2k , and M 3 The initial value of is determined by the short-circuit impedance method, which includes:

[0028] During the rough matching process, the short-circuit impedance Z of the primary winding of the multi-winding transformer is detected. 1 ; During the continuous adjustment of the inductive impedance value after the rough matching, the short-circuit impedance Z of the primary winding of the multi-winding transformer is detected 3 ; where k>0;

[0029] When k=0, the inductive impedance value after the rough matching is the output impedance value of the current primary winding, and the short-circuit impedance Z of the primary winding of the multi-winding transformer is detected during the continuous adjustment of the output impedance value of the primary winding. 2 ;

[0030] According to Z 1 , Z 2 , Z 3 With L 1 、M 2 、M 3 The initial value of L satisfies the relationship between 1 、M 2 、M 3 ; wherein the relationship is:

[0031]

[0032] Where M 2 M 21 、M 22 , …, M 2k The equivalent mutual inductance.

[0033] According to a third aspect of the present invention, there is provided a controller comprising a computer readable storage medium and a processor;

[0034] The computer-readable storage medium is used to store executable instructions;

[0035] The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the control method described in any one of the second aspects.

[0036] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0037] (1) The multi-winding graded reactor of the present invention adopts multiple windings on the secondary side of the transformer. By adopting a graded adjustable control strategy on the secondary side of the transformer, a coarse adjustment plus fine adjustment method is used to compensate for the complex distributed capacitance caused by the high urban cabling rate on demand, and the compensation accuracy is improved, thereby improving the power quality of the power grid. Specifically, the primary winding of the transformer is connected in series in the power grid cable line. The current in the power grid cable passes through the primary winding, which will generate induced potential and current in multiple secondary windings. Through the designed passive series / parallel coarse adjustment reactor shunt, the output impedance of the primary winding is made inductive, and the switching states of M bidirectional thyristors are controlled to control the number of inductive reactance circuits composed of each secondary winding and the corresponding bidirectional thyristor put into operation in the passive series / parallel coarse adjustment reactor shunt, thereby realizing a step-by-step coarse adjustment of the inductive impedance of the primary winding output, so that the inductive impedance value output by the system is in line with the impedance of the distributed capacitance of the cable. On this basis, the control signal is used to control the on and off of the IGBT switch of the active inverter fine-tuning reactor shunt to control the output voltage and current on the AC side of the full-bridge conversion circuit, thereby realizing continuous fine adjustment of the output inductive impedance of the system after coarse matching. In this way, the roughly required system output inductive impedance is quickly determined through step-by-step coarse adjustment, and then precise cable distributed capacitance compensation is further performed through continuous adjustment, realizing adjustable on-demand compensation with fast dynamic response speed. In addition, the coarse-to-fine graded adjustable control strategy also improves the compensation accuracy and the power quality of the power grid.

[0038] (2) The distributed capacitance to be suppressed and compensated does not participate in the design of the multi-winding graded reactor of the present invention, which reduces the difficulty of compensation control and allows the output inductive impedance of the entire equivalent circuit to be regulated according to actual conditions.

[0039] (3) Both the passive series / parallel coarse-adjusting reactor shunt and the active inverter fine-adjusting reactor shunt affect the output inductive impedance of the primary winding through the secondary winding of the transformer, thereby compensating for the electrical parameters of the capacitive nature of the grid cable, and achieving electrical isolation through the transformer to ensure the reliability of the multi-winding graded reactor. In addition, the use of AC excitation of the transformer greatly reduces the original problems of high noise and high harmonics.

[0040] (4) Preferably, a voltage stabilizing capacitor C is connected in parallel to the DC side of the full-bridge conversion circuit to ensure voltage stability on the DC side of the full-bridge conversion circuit.

[0041] (5) Preferably, the high-performance transformer composed of multiple windings of the present invention operates in the linear region, and the system working flux is smaller than the working flux of the traditional transformer. The DC excitation component generated thereby is smaller, the system working noise is lower, and the device can withstand a higher voltage, which can enable the cable lines and power transmission equipment to operate in a higher voltage level area. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a circuit structure diagram of a multi-winding graded reactor used for compensation of distributed capacitance of urbanized cables in an embodiment of the present invention;

[0043] Figure 2 1 is a structural diagram of a passive series / parallel coarse adjustment reactor shunt circuit in an embodiment of the present invention;

[0044] Figure 3 The active inverter fine-tuning reactor shunt circuit structure diagram in the embodiment of the present invention;

[0045] Figure 4 It is an equivalent circuit diagram of a transformer in a continuously adjustable reactor in an embodiment of the present invention.

[0046] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0047] 1-Multi-winding transformer, 2-Passive series / parallel coarse-adjustment reactor shunt, 3-Active inverter fine-adjustment reactor shunt. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] Example 1

[0050] like Figure 1-Figure 3 As shown, the multi-winding graded reactor used for urban cable distributed capacitance compensation in the embodiment of the present invention mainly includes: a multi-winding transformer 1, a passive series / parallel coarse adjustment reactor branch 2, an active inverter fine adjustment reactor branch 3 and a controller.

[0051] The multi-winding transformer 1 includes a primary winding and N secondary windings, N≥3; both ends of the primary winding are connected in series in the power grid cable line, and the M secondary windings in the multi-winding transformer 1 and the corresponding M bidirectional thyristors constitute a passive series / parallel coarse adjustment reactor branch 2, M<N; wherein each bidirectional thyristor and its corresponding secondary winding form a series, parallel or series-parallel relationship, and the reactance circuit formed by each secondary winding and the corresponding bidirectional thyristor is inductive. In the embodiment of the present invention, the multi-winding transformer 1 is a high-performance multi-winding transformer. Figure 2 As shown in the figure, the passive series / parallel coarse adjustment reactor shunt circuit structure diagram when M=3 is shown. 21 -M 23They represent the mutual inductance of the three secondary windings, S 21 -S 23 They represent the bidirectional thyristors corresponding to the three secondary windings respectively.

[0052] Active inverter fine-tuning reactor branch 3 includes an IGBT switch T 1 -T 4 The full-bridge conversion circuit is a single-phase full-bridge conversion circuit; the AC side of the full-bridge conversion circuit is connected to any one of the remaining NM secondary windings in the multi-winding transformer 1. Preferably, a voltage stabilizing capacitor C is connected in parallel to the DC side of the full-bridge conversion circuit to ensure the voltage stability of the DC side of the full-bridge conversion circuit. Figure 3 As shown, the circuit structure diagram of the active inverter fine-tuning reactor shunt is shown. Figure 3 M 3 Represents the mutual inductance of the secondary winding connected to the active inverter fine-tuning reactor branch.

[0053] The controller is used to control the switching states of M bidirectional thyristors to control the number k of inductive reactance circuits composed of each secondary winding and the corresponding bidirectional thyristor put into operation in the passive series / parallel coarse adjustment reactor branch 2, thereby realizing a step-by-step adjustment of the inductive impedance output by the primary winding, so that the inductive impedance value output by the primary winding is roughly matched with the cable distributed capacitance impedance, 0≤k≤M; wherein, M secondary windings and the corresponding M bidirectional thyristors constitute M inductive reactance circuits.

[0054] The controller is also used to generate a control signal to control the on and off of the IGBT switch to control the output voltage and current on the AC side of the full-bridge conversion circuit, thereby realizing continuous adjustment of the output inductive impedance of the primary winding obtained after step-by-step adjustment, so that the output inductive impedance after continuous adjustment is completely matched with the impedance of the cable distributed capacitance, thereby realizing compensation for the cable distributed capacitance; wherein, the impedance of the cable distributed capacitance is obtained based on the existing power quality parameter detection method, and the power quality parameter detection method detects the capacitive electrical parameters of the power grid cable line connected in series at both ends of the primary winding to obtain the impedance of the cable distributed capacitance. In the embodiment of the present invention, the power grid cable line to which the multi-winding stepped inductor is connected is equivalent to a transmission cable line independent of other power grid cable lines, that is, each power grid cable line is connected in parallel, and the equivalent capacitance in parallel is the cable distributed capacitance in the embodiment of the present invention, including distributed stray capacitance and line coupling capacitance.

[0055] Due to the safety requirements of users and enterprises during the specific implementation of the project, the multi-winding graded adjustable reactor in the embodiment of the present invention is connected in series at the easy-to-install connection point of the original cable line.

[0056] As a preferred implementation method, the high-performance multi-winding transformer in the embodiment of the present invention operates in the linear region, the system working flux is smaller than the working flux of the traditional transformer, the DC excitation component generated is smaller, the system working noise is lower, and the device can withstand a higher voltage, which can enable cable lines and power transmission equipment to operate in a higher voltage level area.

[0057] As a preferred implementation, the multi-winding graded inductor used for urban cable distributed capacitance compensation in the embodiment of the present invention also includes a current sensor for detecting the equivalent output current of the primary winding and the current in the secondary winding.

[0058] like Figure 1 As shown, the secondary side of the multi-winding transformer 1 is a multi-winding parallel / series structure. The high-performance transformer in the multi-winding stepped reactor includes three windings with different functions: the primary winding L 1 , forming the M secondary windings L of the passive series / parallel coarse-tuning reactor branch 2 2 , and the secondary winding L connected to the active inverter fine-tuning reactor branch 3 3 . Primary winding L 1 Although it is electrically isolated from the secondary winding, it can be regarded as electrically connected through the equivalent circuit. 2 The number of inductive reactance circuits on the secondary winding L 3 Modulation strategy of the connected IGBT power electronic switch: each secondary winding L 2 Each corresponding branch (i.e., inductive reactance loop) is controlled by a corresponding bidirectional thyristor. For each branch, the working state is either working or isolated from the system. By controlling the number of inductive reactance loops put into operation, the step-by-step coarse adjustment of the system output inductive impedance can be achieved, thereby achieving a coarse matching of the system output inductive impedance and the impedance of the cable distributed capacitance; the secondary winding L 3 The connected inverter controls the current and voltage output on the AC side, thereby achieving fine adjustment of the primary side output reactance value. The two work together to make the multi-winding graded continuously adjustable reactor continuously adjustable, thereby matching the impedance of the cable distributed capacitance.

[0059] Based on the above-mentioned multi-winding stepped reactor, the specific control scheme of the present invention is as follows.

[0060] The transformer windings in the multi-winding cascaded reactor in the embodiment of the present invention are converted to:

[0061] U 1 =I 1 r 1 +jw(I 1 L 1 +(I21 M 21 +I 22 M 22 …+I 2k M 2k )+I 3 M 3 ) (1)

[0062] Among them, U 1 Indicates the equivalent output voltage of the primary side of the multi-winding transformer, I 1 Indicates the equivalent output current of the primary side of the multi-winding transformer, U 1 / I 1 It is used to characterize the value of the inductive impedance of the primary output of the current multi-winding transformer; r 1 is the equivalent resistance of the multi-winding transformer, j represents the symbol of the imaginary part of the inductance; I 21 ,I 22 ,…,I 2k They represent the current in the secondary winding corresponding to the k inductive reactance circuits put into operation, 0≤k≤M; M 21 、M 22 , …, M 2k They represent the mutual inductances of the k secondary windings corresponding to the k inductive reactance circuits put into operation; I 3 M represents the loop current of the active inverter fine-tuning reactor branch 3, that is, the current in the secondary winding connected to the active inverter fine-tuning reactor branch; 3 Indicates the secondary winding L connected to the active inverter fine-tuning reactor branch 3 3 Mutual inductance is related to the output voltage and current on the AC side of the active inverter fine-tuning reactor shunt; w is the electrical angular frequency preset by the system.

[0063] In this transformer, r 1 Relatively small, r can be ignored 1 The impact of , so there are:

[0064] U 1 =jw(I 1 L 1 +(I 21 M 21 +I 22 M 22 …+I 2k M 2k )+I 3 M 3 ) (2)

[0065] The multi-winding stepped reactor in the embodiment of the present invention will operate in three different modes depending on the conduction conditions of the conduction switch tubes (including bidirectional thyristors and IGBT switches) on the secondary side of the transformer.

[0066] Working mode 1: using M secondary windings L constituting passive series / parallel coarse-tuning reactor shunts separately 2 , that is, the output voltage of the AC side of the full-bridge conversion circuit is controlled to be 0, and only the passive series / parallel coarse adjustment reactor works in shunt. At this time, the secondary winding L 3 When not put into operation in the power grid, the voltage and current equations satisfied by the multi-winding transformer are:

[0067] U 1 =jw(I 1 L 1 +(I 21 M 21 +I 22 M 22 …+I 2k M 2k )) (3)

[0068] Based on the voltage-current equation and the current equivalent output current I detected by the current sensor, 1 The secondary winding current I corresponding to the inductive reactance circuit currently in operation 21 ,I 22 ,…,I 2k , adjust the number of inductive reactance circuits k required to be put into operation to change the output inductive impedance value U of the primary winding 1 / I 1 The size of the primary winding output inductive impedance value U 1 / I 1 The impedance of the cable distributed capacitance is roughly matched; wherein the impedance of the cable distributed capacitance is determined based on the power quality parameter detection method, M 21 、M 22 , …, M 2k Determined by short-circuit impedance method. In other embodiments, M 21 、M 22 , …, M 2k They can also be equal to reduce the calculation complexity. 1 / I 1 When the impedance is roughly matched with the cable distributed capacitance, the optimal number k of inductive reactance circuits put into operation of the current multi-winding graded reactor can be determined.

[0069] At this time, the reactor in the embodiment of the present invention realizes the rough regulation of the capacitive abnormality in the cable line. Since the power electronic device under the control mode at this time is only used as a judgment transformer M secondary windings L 2Whether each branch is connected to the grid is controlled. Therefore, under this condition, the reactor can only achieve step-by-step coarse adjustment. Although it is a coarse adjustment, the impedance of the cable distributed capacitance is roughly matched, which improves the capacitance under complex coupling conditions of the cables in the grid.

[0070] Working mode 2, transformer secondary winding L 3 Used alone, that is, to control the bidirectional thyristor S 2 All are disconnected, and only the active inverter fine-tuning reactor shunt works. When the distributed capacitance of the cable is very small, for example, the inductive impedance value of the primary winding output corresponding to only one running inductive reactance circuit is also much greater than the impedance value of the distributed capacitance of the cable. In this case, the number of inductive reactance circuits selected to be put into operation is 0, that is, only the active inverter fine-tuning reactor shunt works. At this time, the voltage and current equation satisfied by the multi-winding transformer is:

[0071] U 1 =jw(I 1 L 1 +I 3 M 3 ) (4)

[0072] Based on the voltage-current equation, the current equivalent output current I of the primary winding detected by the current sensor is 1 , and the current I in the secondary winding connected to the current active inverter fine-tuning reactor shunt 3 , change the duty cycle of the controller control signal to change the voltage and current output on the AC side of the full-bridge converter circuit, and through feedback control (the voltage and current output on the AC side will affect the current M 3 The value of the output inductive impedance of the primary winding is U 1 / I 1 The impedance of the cable distributed capacitance is completely matched, that is, the output inductive impedance value of the primary winding is U 1 / I 1 is the inductive impedance value required for compensation, which matches the impedance of the cable distributed capacitance. Since the output voltage and current on the AC side change continuously, M 3 It also changes continuously. When the output inductive impedance value of the primary winding is U 1 / I 1 When the impedance of the cable distributed capacitance is matched, the optimal parameter M of the current multi-winding graded reactor can be determined. 3 , M 3 The initial value of I 21 ,I 22 ,…,I 2k Similarly, determined by the short-circuit impedance method.

[0073] At this time, the reactor realizes the fine control (continuous adjustment) of the capacitive anomaly in the cable line. In this control mode, the power electronic devices can realize stepless adjustment, that is, by controlling the output current and output voltage of the inverter, the voltage fluctuation, harmonics, power factor, loss and other power quality problems caused by the complex coupling capacitance of the cable in the power system can be carefully compensated and improved.

[0074] Working mode three, first put into operation the passive series / parallel coarse adjustment reactor shunt, and then put into operation the active inverter fine adjustment reactor shunt, that is, firstly use the passive series / parallel coarse adjustment reactor shunt to roughly match the system output inductive impedance with the distributed capacitance impedance, and then use the active inverter fine adjustment reactor shunt to continuously adjust the current system output inductive impedance on the basis of the current system output inductive impedance, so that the current system output inductive impedance is completely matched with the impedance of the cable distributed capacitance; at this time, the voltage and current equation satisfied by the multi-winding transformer is:

[0075] U 1 =jw(I 1 L 1 +(I 21 M 21 +I 22 M 22 …+I 2k M 2k )+I 3 M 3 ) (5)

[0076] The voltage-current equation is consistent with formula (2). In the actual control, the duty cycle of the control signal is first controlled to make the output voltage on the AC side of the full-bridge conversion circuit 0. At this time, only the passive series / parallel coarse adjustment reactor shunt works. Based on the voltage-current equation satisfied by the multi-winding transformer at this time, that is, formula (3), and the current equivalent output current I of the primary winding detected by the current sensor, 1 The secondary winding current I corresponding to the inductive reactance circuit currently in operation 21 ,I 22 ,…,I 2k , adjust the number of inductive reactance circuits k required to be put into operation to change the output inductive impedance value U of the primary winding 1 / I 1 The size of the primary winding output inductive impedance value U 1 / I 1 Coarse matching of the impedance with the cable distributed capacitance; based on the number of inductive reactance circuits k put into operation determined during coarse matching, the voltage-current equation satisfied by the multi-winding transformer after the active inverter fine-tuning reactor branch is put into operation, that is, formula (5), and the current primary winding equivalent output current I detected by the current sensor1 and the current I in the secondary winding connected to the current active inverter fine-tuning reactor branch 3 , change the duty cycle of the controller control signal to change the voltage and current output on the AC side of the full-bridge conversion circuit, and make the output inductive impedance value U of the primary winding through feedback control 1 / I 1 By fully matching the impedance of the cable distributed capacitance, the influence of the cable distributed capacitance can be compensated and the load capacitance of the system can be weakened.

[0077] At this time, it is equivalent to the coordinated use of working mode 1 and working mode 2. By adopting reasonable control strategies and joint adjustment methods, the power grid system can carry out compensation control and adjustment on a wider range of power quality problems caused by inevitable capacitive anomalies in cables, with more timely dynamic response speed and more reliable adjustment accuracy.

[0078] In the embodiment of the present invention, the short-circuit impedance method is used to determine the self-inductance L of the primary winding. 1 , the k inductive reactance circuits put into operation correspond to the k secondary winding mutual inductance M 21 、M 22 , …, M 2k , and the secondary winding mutual inductance M connected to the active inverter fine-tuning reactor branch 3 3 The initial value of .

[0079] After analysis, it can be known that the multi-stage graded continuously adjustable reactor is equivalent to a three-winding transformer in the working mode, and the equivalent circuit diagram of the three-winding transformer can be drawn, as shown in Figure 4 As shown, Figure 4 In the equation, Xm represents the equivalent excitation reactance on the secondary side, S 2 Indicates the equivalent switch tube of the inductive reactance circuit put into operation, M 2 Indicates the equivalent mutual inductance of the secondary winding corresponding to the inductive reactance circuit put into operation. In working mode 2, the equivalent circuit is equivalent to the T-type equivalent circuit of a two-winding transformer.

[0080] The equivalent electrical parameters (mutual inductance M) of the reactor in the embodiment of the present invention are different in each working mode, so the control parameters in different working modes will also be different. The effect of theoretical analysis can be achieved through actual design and short-circuit testing. For high-performance transformers, the excitation impedance is large, so it can be regarded as an open circuit when performing equivalent analysis.

[0081]

[0082] In the formula, Z 1 -Z 3 Respectively represent the short-circuit impedance of the primary side of the transformer in working modes one to three;

[0083] The equivalent transformations of the above formula are:

[0084]

[0085] L can be determined by formulas (6) and (7): 1 、M 2 、M 3 The initial value of M 2 M 21 、M 22 , …, M 2k Then, through the coarse adjustment and fine adjustment control of the output inductive impedance of the above system, the output inductive impedance value U of the primary winding is achieved. 1 / I 1 The impedance size of the cable distributed capacitance is roughly matched and finally completely matched to determine the optimal parameters of the current multi-winding cascaded reactor, including the number k of inductive reactance circuits put into operation in the passive series / parallel coarse-adjustment reactor branch, and the secondary winding mutual inductance M connected to the active inverter fine-adjustment reactor branch 3. 3 . By designing reasonable electrical parameters and control parameters, it is possible to achieve a low-cost, high-reliability and efficient solution to a series of abnormal electrical state problems of complex coupled capacitive electrical states of urban cables. It is a multifunctional and superior performance specific implementation plan for power management.

[0086] The multi-winding graded reactor of the present invention adopts multiple windings on the secondary side of the transformer. By adopting a graded adjustable control strategy on the secondary side of the transformer, a coarse adjustment plus fine adjustment method is used to compensate on demand for the complex distributed capacitance caused by the complex layout cables built underground in the urban power grid system, and the compensation accuracy is improved, and the power quality of the power grid is improved. Specifically, the primary winding of the transformer is connected in series in the power grid cable line. The current in the power grid cable passes through the primary winding, which will generate induced potential and current in multiple secondary windings. Through the designed passive series / parallel coarse adjustment reactor shunt, the output impedance of the primary winding is made inductive, and the switching states of M bidirectional thyristors are controlled to control the number of inductive reactance circuits composed of each secondary winding and the corresponding bidirectional thyristor put into operation in the passive series / parallel coarse adjustment reactor shunt, thereby realizing a step-by-step coarse adjustment of the inductive impedance output of the primary winding, so that the inductive impedance value output by the system is adjusted with the distributed capacitance impedance of the cable. On this basis, the control signal is used to control the on and off of the IGBT switch of the active inverter fine-tuning reactor shunt to control the output voltage and current on the AC side of the full-bridge conversion circuit, thereby realizing continuous fine adjustment of the output inductive impedance of the system after coarse matching. In this way, the roughly required system output inductive impedance is quickly determined through step-by-step coarse adjustment, and then precise cable distributed capacitance compensation is further performed through continuous adjustment, realizing adjustable on-demand compensation with fast dynamic response speed. In addition, the coarse-to-fine graded adjustable control strategy also improves the compensation accuracy and the power quality of the power grid.

[0087] The distributed capacitance to be suppressed and compensated does not participate in the design of the multi-winding graded reactor of the present invention, which reduces the difficulty of controlling the compensation and allows the output inductive impedance of the entire equivalent circuit to be regulated according to actual conditions.

[0088] Passive series / parallel coarse-adjusting reactor branch 2 and active inverter fine-adjusting reactor branch 3 both affect the output inductive impedance of the primary winding through the secondary winding of the transformer, thereby compensating for the electrical parameters of the capacitive nature of the grid cable, and achieving electrical isolation through the transformer to ensure the reliability of the multi-winding graded reactor. In addition, the use of AC excitation of the transformer greatly reduces the original problems of high noise and high harmonics.

[0089] Example 2

[0090] An embodiment of the present invention provides a controller, including a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above control method when executing the computer program.

[0091] The relevant technical solutions are the same as above and will not be described again here.

[0092] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-winding graded reactor used for urban cable distributed capacitance compensation, characterized in that: include: Multi-winding transformer, passive series / parallel coarse-tuning reactor shunt, active inverter fine-tuning reactor shunt and controller; The multi-winding transformer includes a primary winding and N secondary windings, N≥3; both ends of the primary winding are connected in series in the power grid cable line; M secondary windings and corresponding M bidirectional thyristors are connected in series or / and in parallel to form the passive series / parallel coarse adjustment reactor shunt, M<N; the active inverter fine adjustment reactor shunt includes a single-phase full-bridge conversion circuit, the AC side of which is connected to any secondary winding of the remaining NM secondary windings in the multi-winding transformer; The controller is used to control the switching states of M bidirectional thyristors to control the number k of inductive reactance circuits composed of secondary windings and corresponding bidirectional thyristors put into operation in the passive series / parallel coarse adjustment reactor branch, thereby step-by-step adjusting the inductive impedance value output by the primary winding, so that the inductive impedance value is roughly matched with the cable distributed capacitance impedance, 0≤k≤M; The controller is also used to generate a control signal to control the on and off of the switch tube of the full-bridge conversion circuit, so as to control the output voltage and current of the AC side of the full-bridge conversion circuit, and then continuously adjust the inductive impedance value after rough matching, so that the inductive impedance value after continuous adjustment is completely matched with the cable distributed capacitance impedance, thereby realizing compensation for the cable distributed capacitance.

2. The multi-winding stepped reactor according to claim 1, characterized in that: A voltage stabilizing capacitor C is connected in parallel to the DC side of the full-bridge conversion circuit.

3. The multi-winding stepped reactor according to claim 1 or 2, characterized in that: The multi-winding transformer operates in a linear region.

4. The multi-winding stepped reactor according to claim 3, characterized in that: The full-bridge conversion circuit is composed of IGBT switches T1-T4.

5. A control method for a multi-winding graded reactor applied to urban cable distributed capacitance compensation, characterized in that: A controller acting on a multi-winding cascaded reactor according to any one of claims 1 to 4, wherein the control method comprises: By controlling the switching states of M bidirectional thyristors, the number k of inductive reactance circuits composed of secondary windings and corresponding bidirectional thyristors put into operation in the passive series / parallel coarse-adjusting reactor branch is controlled, and then the inductive impedance value output by the primary winding is adjusted in a step-by-step manner, so that the inductive impedance value is roughly matched with the cable distributed capacitance impedance, 0≤k≤M; A control signal is generated to control the on and off of the switch tube of the full-bridge conversion circuit to control the output voltage and current of the AC side of the full-bridge conversion circuit, and then the inductive impedance value after rough matching is continuously adjusted so that the inductive impedance value after continuous adjustment is completely matched with the cable distributed capacitance impedance, thereby realizing compensation for the cable distributed capacitance.

6. The control method according to claim 5, characterized in that: During the rough matching process, the voltage and current equations satisfied by the multi-winding transformer are: U1=jw(I1L1+(I 21 M 21 +I 22 M 22 …+I 2k M 2k )) Wherein, U1 and I1 represent the equivalent output voltage and equivalent output current of the primary winding respectively, U1 / I1 is used to characterize the inductive impedance of the primary winding output; L1 is the self-inductance of the primary winding; I 21 ,I 22 ,…,I 2k They represent the current in the secondary winding corresponding to the k inductive reactance circuits put into operation; M 21 、M 22 , …, M 2k They represent the mutual inductances of the k secondary windings corresponding to the k inductive reactance circuits put into operation; j represents the sign of the imaginary part of the inductance, and w is the preset electrical angular frequency; Based on the voltage-current equation satisfied by the multi-winding transformer during the coarse matching process, the switching states of the M bidirectional thyristors are controlled to control the number k of inductive reactance circuits composed of the secondary winding and the corresponding bidirectional thyristors put into operation in the passive series / parallel coarse adjustment reactor branch, and then the inductive impedance value U1 / I1 output by the primary winding is adjusted in a step-by-step manner to make the inductive impedance value U1 / I1 coarsely matched with the cable distributed capacitance impedance.

7. The control method according to claim 6, characterized in that: When k>0, during the continuous adjustment of the inductive impedance value after rough matching, the voltage and current equation satisfied by the multi-winding transformer is: U1=jw(I1L1+(I 21 M 21 +I 22 M 22 …+I 2k M 2k )+I3M3) In the formula, I3 and M3 represent the secondary winding current and the secondary winding mutual inductance connected to the active inverter fine-tuning reactor branch respectively; Based on the voltage-current equation satisfied by the multi-winding transformer and the number k of inductive reactance loops determined after rough matching during the continuous adjustment of the inductive impedance value after rough matching, the duty cycle of the control signal is changed; the on-off of the switch tube of the full-bridge conversion circuit is controlled by the changed duty cycle of the control signal to control the output voltage and current of the AC side of the full-bridge conversion circuit, and then the inductive impedance value U1 / I1 after rough matching is continuously adjusted so that the continuously adjusted inductive impedance value U1 / I1 is completely matched with the cable distributed capacitance impedance, thereby realizing compensation for the cable distributed capacitance.

8. The control method according to claim 6, characterized in that: When k=0, the inductive impedance value after the rough matching is the current output impedance value of the primary winding; during the continuous adjustment of the output impedance value of the primary winding, the voltage and current equation satisfied by the multi-winding transformer is: U1=jw(I1L1+I3M3) In the formula, I3 and M3 represent the secondary winding current and the secondary winding mutual inductance connected to the active inverter fine-tuning reactor branch respectively; Based on the voltage-current equation satisfied by the multi-winding transformer, the duty cycle of the control signal is changed; the on-off of the switch tube of the full-bridge conversion circuit is controlled by the changed duty cycle of the control signal to control the output voltage and current on the AC side of the full-bridge conversion circuit, and then the output impedance value U1 / I1 of the primary winding is continuously adjusted so that the continuously adjusted inductive impedance value U1 / I1 is completely matched with the cable distributed capacitance impedance, thereby realizing compensation for the cable distributed capacitance.

9. The control method according to claim 7 or 8, characterized in that: L1, M 21 、M 22 , …, M 2k , and the initial value of M3 is determined by the short-circuit impedance method, including: In the coarse matching process, the short-circuit impedance Z1 of the primary winding of the multi-winding transformer is detected; in the process of continuously adjusting the inductive impedance value after the coarse matching, the short-circuit impedance Z3 of the primary winding of the multi-winding transformer is detected; wherein k>0; When k=0, the inductive impedance value after the rough matching is the current output impedance value of the primary winding, and the short-circuit impedance Z2 of the primary winding of the multi-winding transformer is detected during the continuous adjustment of the output impedance value of the primary winding; L1, M2, M3 are determined according to the relationship between Z1, Z2, Z3 and the initial values ​​of L1, M2, M3; wherein the relationship is: Where M2 is M 21 、M 22 , …, M 2k The equivalent mutual inductance.

10. A controller, characterized in that: comprising a computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the control method described in any one of claims 5-9.

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