A multi-winding grading reactor applied to urbanization cable distribution capacitance compensation

Abstract

The application belongs to the technical field of urban cable distribution capacitance compensation, and discloses a multi-winding grading reactor applied to urban cable distribution capacitance compensation, which comprises a multi-winding transformer, a passive series / parallel coarse adjustment reactor branch, an active inversion fine adjustment reactor branch and a controller; the multi-winding transformer comprises a primary winding and N secondary windings, and N is greater than or equal to 3; the primary winding is connected in series at both ends in a 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 branch, and M is less than N; the active inversion fine adjustment reactor branch comprises a single-phase full-bridge conversion circuit, the AC side of which is connected with any one of the remaining N-M secondary windings in the multi-winding transformer; the controller controls the coarse adjustment and fine adjustment of the coarse adjustment and fine adjustment reactor branches on the inductive impedance of the system output, so as to compensate the impedance of the distribution capacitance as required, and the application can improve the compensation accuracy and power grid power quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of urbanization cable distribution capacitance compensation, and more particularly relates to a multi-winding grading reactor applied to urbanization cable distribution capacitance compensation. BACKGROUND

[0002] With the advancement of the urbanization process of the power grid and the continuous access of new power electronic devices, the transmission line in the urbanization power grid corresponds to an industrial function-intensive and complex actual working environment. Therefore, overhead lines gradually become underground cables. The increase of the underground cable rate plays a key role in the urbanization construction process, but too high cable rate will cause the capacitance value of the distributed capacitance (mainly cable distributed capacitance) in the equivalent circuit of the power grid system to increase, and the capacitive nature of the circuit will increase the voltage abnormally at the end of the power grid or near the urban cable concentration area, the current waveform will suddenly become disordered, and thus the power quality of the power grid will be reduced.

[0003] At present, the suppression and compensation method for the capacitive electrical coupling parameters existing in the cable construction of the urbanization power grid is limited to the selection of cable materials and the use of various electromagnetic shielding methods of the cable itself, that is, the suppression and control method for the power grid cable distributed capacitance depends on the characteristics of the power grid cable material itself, so as to improve the electrical properties of the cable concentration area from the source. However, in actual engineering applications, on the one hand, weather, temperature, and electromagnetic noise generated by new urban construction and other factors will affect the characteristics of the cable material itself, causing the characteristics of the cable material itself to change, thereby affecting the suppression and compensation effect and failing to guarantee the power quality of the power grid; on the other hand, the characteristics of the cable material itself are fixed in the planning and construction and cannot be adjusted and improved according to actual application requirements. SUMMARY

[0004] In view of the above defects or improvement needs of the prior art, the present application provides a multi-winding grading reactor applied to urbanization cable distribution capacitance compensation, which aims to compensate for the urbanization cable distribution capacitance according to actual application requirements and improve the compensation precision to improve the power quality of the power grid.

[0005] To achieve the above-mentioned purpose, according to the first aspect of the present application, a multi-winding grading reactor applied to urbanization cable distribution capacitance compensation is provided, comprising: a multi-winding transformer, a passive series / parallel coarse adjustment reactor branch, an active inverter fine adjustment reactor branch, and a controller.

[0006] The multi-winding transformer comprises a primary winding and N secondary windings, N≥3; two ends of the primary winding are connected in series in a power grid cable line; M of the secondary windings and corresponding M bidirectional thyristors form a passive series / parallel coarse regulation reactor branch through series connection or / and parallel connection, M

[0007] The controller is configured to control the number k of inductive reactance loops formed by the secondary windings and the corresponding bidirectional thyristors in operation in the passive series / parallel coarse regulation reactor branch by controlling the switching state of the M bidirectional thyristors, so as to stepwise adjust the inductive impedance value output by the primary winding, and to coarsely match the inductive impedance value with the cable distribution capacitance impedance, 0≤k≤M.

[0008] The controller is further configured to generate a control signal to control the on-off of the switching tubes of the full-bridge conversion circuit, so as to control the output voltage and current of the alternating current side of the full-bridge conversion circuit, and to continuously adjust the coarsely matched inductive impedance value, so as to completely match the continuously adjusted inductive impedance value with the cable distribution capacitance impedance, and to realize the compensation for the cable distribution capacitance.

[0009] Further, the direct current side of the full-bridge conversion circuit is connected in parallel with a voltage stabilizing capacitor C.

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

[0011] Further, the full-bridge conversion circuit is formed by IGBT switches T1-T4.

[0012] According to the second aspect of the present application, a control method of a multi-winding grading reactor applied to the compensation for urban cable distribution capacitance is provided, which is applied to the controller in the multi-winding grading reactor according to any one of the first aspect, and the control method comprises:

[0013] The number k of inductive reactance loops formed by the secondary windings and the corresponding bidirectional thyristors in operation in the passive series / parallel coarse regulation reactor branch is controlled by controlling the switching state of the M bidirectional thyristors, so as to stepwise adjust the inductive impedance value output by the primary winding, and to coarsely match the inductive impedance value with the cable distribution capacitance impedance, 0≤k≤M.

[0014] A control signal is generated to control the on-off of the switching tubes of the full-bridge conversion circuit, so as to control the output voltage and current of the alternating current side of the full-bridge conversion circuit, and to continuously adjust the coarsely matched inductive impedance value, so as to completely match the continuously adjusted inductive impedance value with the cable distribution capacitance impedance, and to realize the compensation for the cable distribution capacitance.

[0015] Further, in the rough matching process, the multi-winding transformer satisfies the voltage and current equation:

[0016] U1 = jw(I1L1 + (I 21 M 21 +I 22 M 22 …+I 2k M 2k )

[0017] wherein U1 and I1 represent the equivalent output voltage and the equivalent output current of the primary winding respectively, U1 / I1 is used to represent the inductive impedance of the output of the primary winding; L1 is the self-inductance of the primary winding; I 21 , I 22 , …, I 2k represent the currents in the k secondary windings corresponding to the k inductive reactive loops in operation; M 21 , M 22 , …, M 2k represent the mutual inductances of the k secondary windings corresponding to the k inductive reactive loops in operation; j represents the imaginary unit, and w is a preset electrical angular frequency.

[0018] Based on the voltage and 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 reactive loops in operation in the passive series / parallel rough tuning reactor branch composed of the secondary windings and the corresponding bidirectional thyristors, and then the inductive impedance value U1 / I1 of the output of the primary winding is adjusted in steps, so that the inductive impedance value U1 / I1 is roughly matched with the cable distributed capacitance impedance.

[0019] Further, when k>0, in the continuous adjustment process of the inductive impedance value after rough matching, the multi-winding transformer satisfies the voltage and current equation:

[0020] U1 = jw(I1L1 + (I 21 M 21 +I 22 M 22 …+I 2k M 2k )+I3M3)

[0021] wherein I3 and M3 represent the current in the secondary winding connected to the active inverter fine tuning reactor branch and the mutual inductance of the secondary winding, respectively.

[0022] The duty cycle of the control signal is changed based on the inductive impedance value after the rough matching, the voltage and current equation satisfied by the multi-winding transformer, and the number k of inductive reactance loops determined after the rough matching; the on-off of the switch tube of the full-bridge conversion circuit is controlled by the duty cycle of the changed control signal, 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 U1 / I1 after the rough matching, so that the inductive impedance value U1 / I1 after the continuous adjustment is completely matched with the cable distributed capacitance impedance, and the cable distributed capacitance compensation is realized.

[0023] Further, when k=0, the inductive impedance value after the rough matching is the output impedance value of the primary winding at present; 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:

[0024] U1=jw(I1L1+I3M3)

[0025] In the formula, I3 and M3 respectively represent the secondary winding current and the secondary winding mutual inductance connected with the active inverse variable reactance shunt;

[0026] The duty cycle of the control signal is changed based on the inductive impedance value after the rough matching, the voltage and current equation satisfied by the multi-winding transformer, and the number k of inductive reactance loops determined after the rough matching; the on-off of the switch tube of the full-bridge conversion circuit is controlled by the duty cycle of the changed control signal, 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 U1 / I1 after the rough matching, so that the inductive impedance value U1 / I1 after the continuous adjustment is completely matched with the cable distributed capacitance impedance, and the cable distributed capacitance compensation is realized.

[0027] Further, the initial values of L1, M 21 , M 22 , …, M 2k , and M3 are determined by the short-circuit impedance method, which specifically includes:

[0028] During the rough matching process, the short-circuit impedance Z1 of the primary winding of the multi-winding transformer is detected; during the continuous adjustment of the inductive impedance value after the rough matching, the short-circuit impedance Z3 of the primary winding of the multi-winding transformer is detected; wherein k>0;

[0029] When k=0, the inductive impedance value after the rough matching is the output impedance value of the primary winding at present, 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;

[0030] The initial values of L1, M2, and M3 are determined according to the relationship between Z1, Z2, Z3 and L1, M2, and M3; wherein the relationship is:

[0031]

[0032] In the formula, M2 is M 21 , M 22 , …, M 2k The equivalent mutual inductance of M

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

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

[0035] The processor is configured to read the executable instructions stored in the computer readable storage medium to perform the control method of any one of the second aspect.

[0036] Overall, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0037] (1) The multi-winding grading reactor of the present application adopts multi-winding on the secondary side of the transformer, and through the use of a grading adjustable control strategy on the secondary side of the transformer, the complex distributed capacitance brought by high urban cable ratio is compensated on demand in a coarse adjustment and fine adjustment manner, and the compensation accuracy and power grid power quality are improved. Specifically, the primary winding of the transformer is connected in series in the power grid cable line, and the current in the power grid cable passes through the primary winding to generate an induced potential and current in multiple secondary windings. By designing a passive series / parallel coarse adjustment reactor branch, the output impedance of the primary winding is inductive, the switching state of the M bidirectional thyristors is controlled to control the number of inductive reactance loops composed of each secondary winding and the corresponding bidirectional thyristor in the passive series / parallel coarse adjustment reactor branch, thereby realizing stepwise coarse adjustment of the inductive impedance output by the primary winding, and matching the inductive impedance value output by the system with the cable distributed capacitance impedance. On this basis, the on-off of the IGBT switch of the active inverter fine adjustment reactor branch is controlled by the control signal to control the output voltage and current of the full-bridge conversion circuit AC side, thereby realizing continuous fine adjustment of the inductive impedance output by the system after coarse matching. In this way, the approximate required inductive impedance output by the system is quickly determined through stepwise coarse adjustment, and further accurate cable distributed capacitance compensation is performed through continuous adjustment, realizing adjustable on-demand compensation, fast dynamic response speed, and improved compensation accuracy and power grid power quality through the grading adjustable control strategy.

[0038] (2) The distributed capacitance to be suppressed and compensated does not participate in the design of the multi-winding grading reactor of the present application, reducing the control difficulty of compensation, and the output inductive impedance of the entire equivalent circuit can be adjusted according to the actual situation.

[0039] (3) The passive series / parallel coarse adjustment reactor branch and the active inverter fine adjustment reactor branch both affect the output inductive impedance of the primary winding through the secondary winding of the transformer, and then compensate the electrical parameters of the capacitive property of the power cable, and the electrical isolation is realized through the transformer, thereby ensuring the reliability of the multi-winding grading reactor. Moreover, the AC excitation of the transformer greatly reduces the original problems of large noise, high harmonics and the like.

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

[0041] (5) As a preferred, the high-performance transformer composed of multiple windings of the present application works in a linear region, the system working magnetic flux is smaller than that of the traditional transformer, thereby generating less DC excitation component, the system working noise is lower, and the device working voltage is higher, which can make the cable line and power transmission equipment work in a higher voltage level area. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 FIG. 1 is a circuit structure diagram of a multi-winding grading reactor applied to urban cable distribution capacitor compensation in an embodiment of the present application;

[0043] Figure 2 FIG. 2 is a circuit structure diagram of a passive series / parallel coarse adjustment reactor branch in an embodiment of the present application;

[0044] Figure 3 FIG. 3 is a circuit structure diagram of an active inverter fine adjustment reactor branch in an embodiment of the present application;

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

[0046] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0047] 1 - multi-winding transformer, 2 - passive series / parallel coarse adjustment reactor branch, 3 - active inverter fine adjustment reactor branch. DETAILED DESCRIPTION

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

[0049] Embodiment 1

[0050] AsFigures 1-3 As shown, the multi-winding grading reactor applied to urban cable distribution capacitor compensation in the embodiment of the present application mainly comprises: a multi-winding transformer 1, a passive series / parallel coarse adjustment reactor branch 2, an active inverse fine adjustment reactor branch 3 and a controller.

[0051] The multi-winding transformer 1 comprises a primary winding and N secondary windings, N≥3; the two ends of the primary winding are connected in series in the power grid cable line, M secondary windings in the multi-winding transformer 1 and corresponding M bidirectional thyristors constitute the passive series / parallel coarse adjustment reactor branch 2, M Figure 2 As shown, the passive series / parallel coarse adjustment reactor branch circuit structure diagram when M=3 is shown in the figure, M 21 -M 23 respectively represent mutual inductances of the three secondary windings, S 21 -S 23 respectively represent bidirectional thyristors corresponding to the three secondary windings.

[0052] The active inverse fine adjustment reactor branch 3 comprises a full-bridge conversion circuit composed of IGBT switches T1-T4, i.e. a single-phase full-bridge conversion circuit; the alternating current side of the full-bridge conversion circuit is connected with any one of the remaining N-M secondary windings in the multi-winding transformer 1. Preferably, a voltage stabilizing capacitor C is connected in parallel with the direct current side of the full-bridge conversion circuit to ensure the voltage stability of the direct current side of the full-bridge conversion circuit. As shown, Figure 3 As shown, the circuit structure diagram of the active inverse fine adjustment reactor branch is shown in the figure, Figure 3 M3 in the figure represents the mutual inductance of the secondary winding connected with the active inverse fine adjustment reactor branch.

[0053] The controller is used to control the number k of inductive reactance loops composed of each secondary winding and corresponding bidirectional thyristor in the passive series / parallel coarse adjustment reactor branch 2 by controlling the switching state of the M bidirectional thyristors, so as to realize the stepwise adjustment of the inductive impedance output by the primary winding, and to make the inductive impedance value output by the primary winding and the cable distribution capacitor impedance to be coarsely matched, 0≤k≤M; wherein the M secondary windings and the corresponding M bidirectional thyristors constitute M inductive reactance loops.

[0054] The controller is further configured to generate a control signal to control the on-off of the IGBT switch, so as to control the output voltage and current of the full-bridge conversion circuit AC side, and then realize continuous adjustment of the inductive impedance of the output of the primary winding after the step adjustment, so that the inductive impedance of the output after the continuous adjustment is completely matched with the impedance of the cable distribution capacitance, and the cable distribution capacitance compensation is realized; wherein, the impedance of the cable distribution capacitance is obtained based on an existing power quality parameter detection method, and the power quality parameter detection method obtains the impedance of the cable distribution capacitance by detecting the capacitive electrical parameter of the power grid cable line connected in series at both ends of the primary winding. In the embodiment of the application, the power grid cable line connected with the multi-winding grading reactor is equivalent to a power transmission cable line independent of other power grid cable lines, that is, the power grid cable lines are connected in parallel, and the equivalent capacitance connected in parallel is the cable distribution capacitance in the embodiment of the application, including the distributed stray capacitance and the line coupling capacitance.

[0055] Due to the safety protection requirements of users and enterprises in the engineering implementation process, the multi-winding grading adjustable reactor in the embodiment of the application is connected in series at the easy-to-install connection point of the original cable line.

[0056] As a preferred implementation manner, the high-performance multi-winding transformer in the embodiment of the application works in the linear region, the system working magnetic flux is smaller than that of the traditional transformer, the generated direct-current excitation component is less, the system noise is lower, and the device working voltage is higher, so that the cable line and the power transmission equipment can work in a higher voltage level area.

[0057] As a preferred implementation manner, the multi-winding grading reactor applied to the urban cable distribution capacitance compensation in the embodiment of the application further comprises a current sensor for detecting the equivalent output current of the primary winding and the current in the secondary winding.

[0058] As Figure 1As 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 hierarchical reactor comprises three different functional windings: a primary winding L1, M secondary windings L2 constituting a passive series / parallel coarse adjustment reactor branch 2, and a secondary winding L3 connected with an active inverter fine adjustment reactor branch 3. The primary winding L1 is electrically isolated from the secondary winding, but can be regarded as having electrical connection through an equivalent circuit. By designing the number of inductive reactance loops acting on the M secondary windings L2 and the modulation strategy of the IGBT power electronic switch connected with the secondary winding L3: each branch corresponding to each secondary winding L2 (i.e. the inductive reactance loop) is controlled by the corresponding bidirectional thyristor, and 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 stepwise coarse adjustment of the inductive impedance of the system output can be realized, and then the coarse matching of the inductive impedance of the system output and the impedance of the cable distribution capacitance is realized. The secondary winding L3 controls the current and voltage of the alternating current side output through the connected inverter, thereby realizing the fine adjustment of the inductive value of the primary side output. The two work together and cooperate to make the multi-winding hierarchical continuously adjustable reactor continuously adjustable, and then matched with the impedance of the cable distribution capacitance.

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

[0060] The transformer winding in the multi-winding hierarchical reactor in the embodiment of the present application is converted, and then there are:

[0061] U1=I1r1+jw(I1L1+(I 21 M 21 +I 22 M 22 …+I 2k M 2k )+I3M3) (1)

[0062] Wherein, U1 represents the equivalent output voltage of the primary side of the multi-winding transformer, I1 represents the equivalent output current of the primary side of the multi-winding transformer, U1 / I1 is used to represent the size of the inductive impedance value of the current multi-winding transformer primary side output; r1 is the equivalent resistance of the multi-winding transformer, j represents the imaginary part symbol of inductance; I 21 , I 22 , …, I 2k respectively represent the currents in the secondary windings corresponding to the k inductive reactance loops put into operation, 0≤k≤M; M 21 , M 22 , …, M 2krespectively represent the k secondary winding mutual inductances corresponding to the k inductive reactance loops in operation; I3 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; M3 represents the secondary winding L3 mutual inductance connected to the active inverter fine-tuning reactor branch 3, which is related to the output voltage and current of the active inverter fine-tuning reactor branch AC side; w is the electrical angular frequency preset by the system.

[0063] In this transformer, r1 is relatively small, and the influence of r1 can be ignored, so:

[0064] U1 = jw(I1L1 + (I 21 M 21 +I 22 M 22 …+I 2k M 2k ) + I3M3) (2)

[0065] The conduction of the conducting switch tubes (including bidirectional thyristors and IGBT switches) on the secondary side of the transformer is different, which causes the multi-winding grading reactor in the embodiment of the application to work in three different modes.

[0066] Mode one: only the M secondary windings L2 constituting the passive series / parallel coarse-tuning reactor branch are used, that is, the output voltage of the full-bridge conversion circuit AC side is controlled to be 0, and only the passive series / parallel coarse-tuning reactor branch works, at this time, the secondary winding L3 is not put into operation in the power grid, and the voltage and current equation satisfied by the multi-winding transformer is:

[0067] U1 = jw(I1L1 + (I 21 M 21 +I 22 M 22 …+I 2k M 2k )) (3)

[0068] Based on the voltage and current equation, and the current sensor detected current equivalent output current I1 of the primary winding and the current I 21 , I 22 , …, I 2k of the secondary winding corresponding to the inductive reactance loop to be put into operation, the number k of inductive reactance loops to be put into operation is adjusted to change the size of the output inductive impedance value U1 / I1 of the primary winding, so that the output inductive impedance value U1 / I1 of the primary winding is coarsely matched with the impedance of the cable distribution capacitor; wherein the impedance of the cable distribution capacitor is determined based on the power quality parameter detection method, M 21 , M 22 , …, M 2k is determined by the short-circuit impedance method. In other embodiments, M21 , M 22 , …, M 2k Also can be equal, reduce the complexity of calculation. When the output inductive impedance value U1 / I1 of the primary winding and the impedance of the cable distribution capacitor are roughly matched, the optimal number of inductive reactance loops k of the current multi-winding grading reactor can be determined.

[0069] At this time, the reactor in the embodiment of the application realizes rough adjustment of the capacitive abnormality in the cable line. Since the power electronic device under the control mode only serves as control of whether each branch of the M secondary windings L2 of the transformer is connected to the power grid, the reactor can only realize stepwise rough adjustment under this mode. Although it is rough adjustment, the impedance of the cable distribution capacitor is roughly matched, and the capacitive abnormality in the complex coupling of the cable in the power grid is improved.

[0070] In the second working mode, the secondary winding L3 of the transformer is used alone, that is, the control of the bidirectional thyristor S2 is all turned off, and only the source inverter fine adjustment reactor branch works. When the distribution capacitor of the cable is very small, for example, the inductive impedance value of the output of the primary winding corresponding to the inductive reactance loop put into operation is much larger than the impedance value of the distribution capacitor of the cable. In this case, the number of inductive reactance loops put into operation is selected as 0, that is, only the source inverter fine adjustment reactor branch works. At this time, the voltage and current equation satisfied by the multi-winding transformer is:

[0071] U1 = jw(I1L1 + I3M3) (4)

[0072] Based on the voltage and current equation, the duty cycle of the controller control signal is changed to change the voltage and current output by the full-bridge conversion circuit on the AC side by detecting the current I1 equivalent to the output of the current primary winding and the current I3 in the secondary winding connected to the current source inverter fine adjustment reactor branch according to the current detected by the current sensor. Through feedback control (the voltage and current output on the AC side will affect the size of the current M3, and then affect the voltage and current output on the AC side at the current moment), the output inductive impedance value U1 / I1 of the primary winding is completely matched with the impedance of the cable distribution capacitor, that is, the output inductive impedance value U1 / I1 of the primary winding is the required inductive impedance value, which is matched with the impedance of the cable distribution capacitor. Since the voltage and current output on the AC side are continuously changed, M3 is also continuously changed. When the output inductive impedance value U1 / I1 of the primary winding is matched with the impedance of the cable distribution capacitor, the optimal parameter M3 of the current multi-winding grading reactor can be determined, and the initial value of M3 is I 21 , I 22 , …, I 2k Similarly, it is determined by the short-circuit impedance method.

[0073] At this point, the reactor realizes fine-tuning (continuous regulation) of capacitive anomalies in the cable line. In this control mode, power electronic devices can achieve stepless regulation, that is, by controlling the output current and output voltage of the inverter, it can finely compensate and improve power quality problems such as voltage fluctuations, harmonics, power factor, and losses caused by the complex coupling capacitance of the cable in the power system.

[0074] Operating mode three involves first activating the passive series / parallel coarse-adjustment reactor branch, followed by the active inverter fine-adjustment reactor branch. That is, the passive series / parallel coarse-adjustment reactor branch is used to coarsely match the system output inductive impedance with the distributed capacitance impedance. Based on the current system output inductive impedance, the active inverter fine-adjustment reactor branch continuously adjusts the current system output inductive impedance to ensure a perfect match between the current system output inductive impedance and the cable distributed capacitance impedance. At this point, the voltage-current equations satisfied by the multi-winding transformer are:

[0075] U1=jw(I1L1+(I 21 M 21 +I 22 M 22 …+I 2k M 2k (5)

[0076] The voltage and current equation is consistent with formula (2). In the actual control, the duty cycle of the control signal is first controlled so that the output voltage of the AC side of the full-bridge converter is 0. At this time, only the passive series / parallel coarse adjustment reactor works. Based on the voltage and current equation satisfied by the multi-winding transformer at this time, that is, formula (3), and the equivalent output current I1 of the current primary winding detected by the current sensor and the secondary winding current I corresponding to the inductive reactor circuit currently in operation, the voltage and current equation is calculated. 21 I 22 ... I 2k Adjust the number of inductive reactor circuits k to be put into operation to change the output inductive impedance value U1 / I1 of the primary winding, so that the output inductive impedance value U1 / I1 of the primary winding is coarsely matched with the impedance of the cable distributed capacitance; based on the number of inductive reactor circuits k determined during coarse matching, the voltage and current equation satisfied by the multi-winding transformer after the active inverter fine-tuning reactor branch is put into operation, i.e., formula (5), and the equivalent output current I1 of the current primary winding and the current I3 in the secondary winding connected to the current active inverter fine-tuning reactor branch detected by the current sensor, change the duty cycle of the controller control signal to change the voltage and current output of the AC side of the full-bridge converter circuit, and make the output inductive impedance value U1 / I1 of the primary winding completely matched with the impedance of the cable distributed capacitance through feedback control, so as to compensate for the influence of the cable distributed capacitance and weaken the load capacitance of the system.

[0077] At this time, the coordination of the working mode one and the working mode two is used together, reasonable control strategy and joint debugging mode are adopted, the power quality problem caused by the capacitive abnormality inevitably existing in the cable can be compensated and adjusted in a wider range, the dynamic response speed is more timely, and the adjustment precision is more reliable.

[0078] In the embodiment of the application, the self-inductance L1 of the primary winding is determined by using the short-circuit impedance method, the initial values of the mutual inductances M 21 、M 22 、…、M 2k corresponding to the k secondary windings of the k inductive reactance loops in operation, and the mutual inductance M3 connected with the shunt 3 of the active inverter fine-tuning reactance.

[0079] It can be analyzed that the multi-stage hierarchical continuously adjustable reactance in the working mode one is equivalent to a three-winding transformer, and the equivalent circuit diagram of the three-winding transformer can be drawn, as shown in Figure 4 , wherein Xm represents the equivalent excitation reactance on the secondary side, S2 represents the equivalent switch tube of the inductive reactance loop in operation, and M2 represents the equivalent mutual inductance of the secondary winding corresponding to the inductive reactance loop in operation. Figure 4 The equivalent electrical parameters (mutual inductance M) of the reactance in each working mode in the embodiment of the application are different, and therefore the control mode parameters in different working modes are also different.

[0080]

[0081]

[0082] In the formula, Z1-Z3 respectively represent the short-circuit impedance of the primary side of the transformer in the working mode one to three.

[0083] The equivalent transformation of the above formula is:

[0084]

[0085] The initial values of L1, M2, M3 can be determined through the formula (6) and (7), wherein M2 is M 21 、M 22 、…、M 2k ​The equivalent mutual inductance is obtained. Then, the coarse adjustment and fine adjustment control of the output inductive impedance size of the above system is realized, the output inductive impedance value U1 / I1 of the primary winding is matched with the impedance size of the cable distribution capacitor, and the coarse matching and final complete matching of the impedance size of the cable distribution capacitor are realized, so that the optimal parameters of the current multi-winding grading reactor are determined, including the number k of inductive reactance loops in the passive series / parallel coarse adjustment reactor shunt in operation, and the secondary winding mutual inductance M3 connected with the active inverter fine adjustment reactor shunt 3. After reasonable design of electrical parameters and control parameters, the abnormal series problems of the complex coupled capacitive electrical state of the urbanization cable can be solved at low cost and high reliability, and it is a multifunctional set with superior performance.

[0086] The multi-winding grading reactor of the application adopts multi-winding on the secondary side of the transformer, adopts a hierarchical adjustable control strategy on the secondary side of the transformer, adopts coarse adjustment and fine adjustment to compensate the complex distribution capacitor caused by the complex layout of the cable laid underground in the construction of the urbanization power grid system, and improves the compensation accuracy and 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, and an induced electromotive force and current are generated in the multiple secondary windings. The output impedance of the primary winding is inductive through the designed passive series / parallel coarse adjustment reactor shunt, the switching state of the M bidirectional thyristors is controlled to control the number of inductive reactance loops composed of each secondary winding and the corresponding bidirectional thyristor in the passive series / parallel coarse adjustment reactor shunt, and then the stepwise coarse adjustment of the output inductive impedance of the primary winding is realized, so that the inductive impedance value output by the system is matched with the impedance of the cable distribution capacitor. On this basis, the on-off of the IGBT switch of the active inverter fine adjustment reactor shunt is controlled by the control signal to control the output voltage and current of the full-bridge conversion circuit AC side, and then the output inductive impedance of the system after coarse matching is continuously and finely adjusted. In this way, the approximate required output inductive impedance of the system is quickly determined through stepwise coarse adjustment, and the cable distribution capacitor is further compensated accurately through continuous adjustment, realizing adjustable compensation on demand, fast dynamic response speed, and the hierarchical adjustable control strategy of coarse and fine adjustment also improves the compensation accuracy and the power quality of the power grid.

[0087] The distribution capacitor to be suppressed and compensated does not participate in the design of the multi-winding grading reactor of the application, which reduces the control difficulty of compensation, and the output inductive impedance of the entire equivalent circuit can be adjusted according to the actual situation.

[0088] The passive series / parallel coarse regulation reactor branch 2 and the active inverter fine regulation reactor branch 3 both affect the output inductive impedance of the primary winding through the secondary winding of the transformer, and then compensate the electrical parameters of the capacitive property of the power cable, the electrical isolation is realized through the transformer, and the reliability of the multi-winding stepped reactor is ensured. Moreover, the original problems such as large noise and high harmonics are greatly reduced by adopting the AC excitation of the transformer.

[0089] Embodiment 2

[0090] The embodiment of the present application provides a controller, comprising a memory and a processor, the memory stores a computer program, and the processor implements the steps of the control method when executing the computer program.

[0091] The related technical solutions are the same as above, and will not be repeated here.

[0092] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A multi-winding grading reactor applied to the capacitive compensation of urbanized cable distribution, characterized in that, It comprises: a multi-winding transformer, a passive series / parallel coarse adjustment reactor shunt, an active inverter fine adjustment reactor shunt and a controller; the multi-winding transformer comprises a primary winding and N secondary windings, N≥3; two ends of the primary winding are connected in series in a power grid cable line; M of the 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 comprises a single-phase full-bridge conversion circuit, whose AC side is connected with any one of the remaining N-M secondary windings in the multi-winding transformer; The controller is used for controlling the number of inductive reactance loops composed of secondary windings and corresponding bidirectional thyristors put into operation in the passive series / parallel coarse adjustment reactance shunt by controlling the switching state of M bidirectional thyristors , and then stepwise adjusting the inductive impedance value output by the primary winding, so as to coarsely match the inductive impedance value with the cable distribution capacitance impedance, M; the controller is further used to generate a control signal to control the on-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 coarse matching, so that the inductive impedance value after continuous adjustment is completely matched with the cable distributed capacitance impedance, and the cable distributed capacitance compensation is realized; the multi-winding transformer works in a linear region; During the continuous adjustment process of the rough-matched inductive impedance value, the multi-winding transformer satisfies the voltage and current equation: wherein, , respectively represent the equivalent output voltage and the equivalent output current of the primary winding, for characterizing the inductive impedance of the primary winding output; is the self-inductance of the primary winding; , , respectively represent the current in the secondary winding corresponding to the inductive reactance circuits put into operation; , , respectively represent the mutual inductance of the secondary windings corresponding to the inductive reactance circuits put into operation; represents the imaginary part of the inductance, is a preset electrical angular frequency; , respectively represent the secondary winding current and the secondary winding mutual inductance connected with the active inverter fine-tuning reactor shunt. Based on the continuous adjustment process of the inductive impedance value after the rough matching, the voltage and current equation satisfied by the multi-winding transformer, and the number of inductive reactance loops determined after the rough matching , the duty cycle of the control signal is changed; the on-off of the full-bridge conversion circuit switch tube is controlled by the changed duty cycle of the control signal, so as to control the output voltage and current of the full-bridge conversion circuit alternating current side, and then continuously adjust the inductive impedance value after the rough matching , so that the inductive impedance value after the continuous adjustment is completely matched with the cable distribution capacitance impedance, realizing the compensation of the cable distribution capacitance. In the rough matching process, the inductive impedance value is the output impedance value of the primary winding at the moment. During the continuous adjustment of the output impedance value of the primary winding, the multi-winding transformer satisfies the voltage and current equation: In the formula, , respectively represent the secondary winding current and the secondary winding mutual inductance connected with the active inverse fine-tuning reactor shunt. Based on the voltage and current equation satisfied by the multi-winding transformer, the duty cycle of the control signal is changed; the on-off of the full-bridge conversion circuit switch tube is controlled by the changed duty cycle of the control signal, so as to control the output voltage and current of the full-bridge conversion circuit AC side, and further control the output impedance value of the primary winding The continuous adjustment is carried out to make the inductive impedance value after the continuous adjustment Completely match with the cable distribution capacitance impedance, and realize the compensation of the cable distribution capacitance.

2. The multi-winding grading reactor of claim 1, wherein, the DC side of the full-bridge conversion circuit is connected in parallel with a voltage stabilizing capacitor C.

3. The multi-winding grading reactor of claim 1, wherein, The full-bridge conversion circuit is composed of IGBT switches T1-T4.

4. A control method for a multi-winding grading reactor applied to the capacitive compensation of urbanized cable distribution, characterized in that, The controller for the multi-winding grading reactor according to any one of claims 1-3, the control method comprises: By controlling the switch state of the M bidirectional thyristors, the number of inductive reactance loops composed of secondary windings and corresponding bidirectional thyristors in operation in the passive series / parallel coarse adjustment reactance shunt is controlled , and the inductive impedance value output by the primary winding is stepwise adjusted, so that the inductive impedance value is coarsely matched with the cable distribution capacitance impedance, M; generating a control signal to control the on-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 coarse matching, so that the inductive impedance value after continuous adjustment is completely matched with the cable distributed capacitance impedance, and the cable distributed capacitance compensation is realized.

5. The control method according to claim 4, characterized by In the coarse matching process, the multi-winding transformer satisfies the voltage and current equation: wherein , respectively denote the equivalent output voltage and the equivalent output current of the primary winding, characterizing the inductive impedance of the primary winding output; is the self-inductance of the primary winding; , , respectively denote the current in the secondary winding corresponding to the inductive reactance circuits put into operation; , , respectively denote the mutual inductance between the secondary windings corresponding to the inductive reactance circuits put into operation; denotes the imaginary unit, is a preset electrical angular frequency; Based on the voltage and current equation satisfied by the multi-winding transformer in the coarse matching process, the switching state of the M bidirectional thyristors is controlled to control the number of inductive reactance loops composed of secondary windings and corresponding bidirectional thyristors put into operation in the passive series / parallel coarse adjustment reactor shunt , and then the inductive impedance value / output by the primary winding is stepwise adjusted, so that the inductive impedance value / is coarsely matched with the cable distribution capacitance impedance.

6. The control method according to claim 4, characterized by , , , , and The initial values of the short-circuit impedance method are determined, in particular comprising: during the coarse matching process, detecting the short-circuit impedance of the primary winding of the multi-winding transformer during the continuous adjustment process of the inductive impedance value after coarse matching, detecting the short-circuit impedance of the primary winding of the multi-winding transformer ; wherein ; At the time, the rough matching inductive reactance value is the output impedance value of the primary winding at present, and the short-circuit impedance of the primary winding of the multi-winding transformer is detected in the continuous adjustment process of the output impedance value of the primary winding ; According to , , and , , the relationship determined between the initial values of , , ; wherein the relationship is: wherein is , ,..., mutual inductance.

7. A controller characterized by comprising: It comprises 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 according to any one of claims 4-6.

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