Zero-impact hybrid flexible loop closing device and method

Abstract

The invention discloses a zero-impact hybrid flexible loop closing device and method, and relates to the field of power distribution network loop closing. The device comprises a measuring device, a control device, a three-phase multi-winding transformer, a plurality of thyristor switch groups and a plurality of full-control power electronic conversion circuits, in each phase of auxiliary winding, the two ends of the secondary winding provided with the tap and the tap are connected with a thyristor switch group, and the two ends of the secondary winding not provided with the tap are connected with a full-control power electronic conversion circuit; the two thyristor switch groups and the full-control power electronic conversion circuit are connected in series to form a three-phase voltage compensation circuit; two thyristor switch groups and one full-control power electronic conversion circuit in each phase voltage compensation circuit are respectively from three phases of the three-phase multi-winding transformer; and the control device controls the thyristor switch group and the full-control power electronic conversion circuit according to the voltage amplitudes and phases of the two feeder lines measured by the measuring device. According to the invention, voltage compensation of zero-impact compensation can be realized on the premise of saving cost.

Description

Technical Field

[0001] The present application relates to the field of distribution network loop closure, and in particular to a zero-impact hybrid flexible loop closure device and method. Background Art

[0002] The distribution network generally adopts the construction and operation mode of "closed-loop design, open-loop operation". However, the open-loop operation mode cannot avoid short-term power outages caused by switching operations, fault self-healing, etc., and it is difficult to meet the high-quality needs of important users for continuous power supply. If the closed-loop operation power supply method is forcibly adopted, the large closing-loop impact current will not only easily cause the line to trip due to overcurrent and cause the closing-loop operation failure, but also increase the operating loss. The inability of distribution network lines to reliably close the loop is a problem that has long plagued the operation of the power grid. To a certain extent, it has limited the further improvement of power supply reliability and operating efficiency, and has become a bottleneck restricting the high-quality development of the distribution network. Therefore, in order to reduce the closing-loop impact current and improve the reliability of power supply, there is an urgent need for a zero-impact flexible closing-loop technology for medium-voltage distribution networks to improve the flexibility of distribution network operation.

[0003] The closing devices based on phase-shifting transformers and voltage source converters are the two most representative types of closing technologies at present. The former has mature phase angle control technology and is the most widely used, while the latter can achieve independent control and other functions that the former does not have, and is the most universal. The phase-shifting transformer can only adjust the phase and does not have the zero-impact function; the closing device based on the voltage source converter can achieve zero impact, but the installation and operation costs are high. Neither of them can take into account both economy and performance. The Sen transformer based on a three-phase multi-winding transformer has low installation and operation costs and is an excellent choice. However, the traditional Sen transformer cannot achieve zero impact and needs to be improved. Summary of the invention

[0004] The purpose of the present application is to provide a zero-impact hybrid flexible loop closing device and method, which can achieve voltage compensation with zero-impact compensation while saving costs.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a zero-impact hybrid flexible loop closing device, comprising: a measuring device, a control device, a three-phase multi-winding transformer, a plurality of thyristor switch groups, and a plurality of fully-controlled power electronic conversion circuits; each auxiliary winding of the three-phase multi-winding transformer includes three secondary windings, and each of the two secondary windings in each auxiliary winding is provided with a tap. A thyristor switch group is connected between the two ends of the secondary winding provided with the tap and the tap; a fully-controlled power electronic conversion circuit is connected between the two ends of the secondary winding not provided with the tap; two thyristor switch groups and a fully-controlled power electronic conversion circuit are connected in series to form a three-phase voltage compensation circuit; the two thyristor switch groups and a fully-controlled power electronic conversion circuit in each phase voltage compensation circuit respectively come from three phases of the three-phase multi-winding transformer; the two ends of the A-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the A-phase line of the first feeder and the A-phase line of the second feeder; the two ends of the B-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the B-phase line of the first feeder and the B-phase line of the second feeder; the two ends of the C-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the C-phase line of the first feeder and the C-phase line of the second feeder; the three main windings of the three-phase multi-winding transformer are respectively connected to the three-phase lines of the first feeder in one-to-one correspondence; the measuring device is used to measure the voltage amplitude and voltage phase of the first feeder, and the voltage amplitude and voltage phase of the second feeder; the control device is used to generate the on-off control signal of each thyristor switch group and the modulation wave amplitude and modulation wave phase of each fully-controlled power electronic conversion circuit according to the voltage amplitude and voltage phase of the first feeder and the voltage amplitude and voltage phase of the second feeder, control the thyristor switch group according to the on-off control signal, and control the fully-controlled power electronic conversion circuit according to the modulation wave amplitude and modulation wave phase to perform zero-impact voltage compensation after loop closing operation.

[0007] In a second aspect, the present application provides a zero-impact hybrid flexible loop closing method, which is used for the zero-impact hybrid flexible loop closing device described above. The zero-impact hybrid flexible loop closing method includes:

[0008] Obtain the i-phase voltage vectors of the first feeder and the second feeder respectively; the voltage vector includes voltage amplitude and voltage phase; i is one of A, B, and C phases;

[0009] Determine the amplitude and phase of the total compensation voltage required for the i phase according to the i-phase voltage vectors of the first feeder and the second feeder;

[0010] Determine the phase of the i phase after being converted to the 0-120° region according to the phase of the total compensation voltage required for the i phase;

[0011] Calculate a first voltage intermediate value and a second voltage intermediate value according to the amplitude of the total compensation voltage required for the i phase and the phase of the i phase after being converted to the 0-120° region;

[0012] If the absolute value of the first intermediate voltage is less than or equal to 3 and the absolute value of the second intermediate voltage is less than or equal to 3, determine that the converted compensation voltage levels of the three electrical components connected in series in the i-phase voltage compensation circuit in the current flowing direction are equal to the first intermediate voltage, zero, and the second intermediate voltage; the three electrical components are two thyristor switch groups and a fully controlled power electronic conversion circuit; the converted compensation voltage level is the sub-compensation voltage level of the i-phase converted to the 0 - 120° region.

[0013] If the absolute value of the first intermediate voltage is greater than 3 or the absolute value of the second intermediate voltage is greater than 3, determine whether the phase of the i-phase converted to the 0 - 120° region belongs to (0, 60°].

[0014] When the phase of the i-phase converted to the 0 - 120° region belongs to (0, 60°], determine that the converted compensation voltage level of the first electrical component connected in series in the i-phase voltage compensation circuit in the current flowing direction is equal to 3, and calculate the converted compensation voltage levels of the other two electrical components in the i-phase voltage compensation circuit according to the amplitude and phase of the total compensation voltage required for the i-phase.

[0015] When the phase of the i-phase converted to the 0 - 120° region does not belong to (0, 60°], determine that the converted compensation voltage level of the second electrical component connected in series in the i-phase voltage compensation circuit in the current flowing direction is equal to 3, and calculate the converted compensation voltage levels of the other two electrical components in the i-phase voltage compensation circuit according to the amplitude and phase of the total compensation voltage required for the i-phase.

[0016] Obtain the compensation voltage level of the i-phase voltage compensation circuit according to the phase of the total compensation voltage required for the i-phase and the converted compensation voltage levels of the three electrical components in the i-phase voltage compensation circuit.

[0017] Determine the compensation voltage levels of the voltage compensation circuits for each phase other than the i-phase according to the compensation voltage level of the i-phase voltage compensation circuit.

[0018] Determine the amplitude and phase of the modulation wave of the fully controlled power electronic conversion circuit in the three-phase voltage compensation circuit according to the amplitude and phase of the total compensation voltage required for the i-phase, and the compensation voltage level of the i-phase voltage compensation circuit.

[0019] Control the thyristor switch group according to the compensation voltage level of each phase voltage compensation circuit, and control the fully controlled power electronic conversion circuit according to the modulation wave amplitude and the modulation wave phase to perform zero-impact voltage compensation after the closed-loop operation.

[0020] According to the specific embodiments provided in this application, this application has the following technical effects:

[0021] The present application provides a zero - impact hybrid flexible loop - closing device and method. For existing loop - closing devices based on phase - shifting transformers, if they need to simultaneously compensate for the amplitude and phase of the voltage, additional transformers need to be invested. However, the present application only requires one three - phase transformer, saving costs. Compared with loop - closing devices based on voltage - source converters with high equipment investment, the topological structure of the present application is lightweight and economical, also saving costs. Compared with the existing combination of Sen transformers and power electronic switches, the fully - controlled power electronic conversion circuit and the secondary winding with tap changers can output voltages with two opposite phases and three adjustable amplitude levels, and the fully - controlled power electronic circuit can output a flexible and adjustable voltage, realizing the zero - impact compensation function. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 Topological schematic diagram of a zero - impact hybrid flexible loop - closing device provided by an embodiment of the present application;

[0024] Figure 2 Topological schematic diagram of the secondary winding connected to the thyristor switch group provided by an embodiment of the present application;

[0025] Figure 3 Topological schematic diagram of the secondary winding connected to the fully - controlled power electronic conversion circuit provided by an embodiment of the present application;

[0026] Figure 4 Corresponding schematic diagram of compensation voltage levels provided by another embodiment of the present application;

[0027] Figure 5 Schematic diagram of the A - phase compensation range provided by an embodiment of the present application;

[0028] Figure 6 Flow schematic diagram of a zero - impact hybrid flexible loop - closing method provided by an embodiment of the present application;

[0029] Figure 7 Total logic block diagram of the control signal provided by another embodiment of the present application;

[0030] Figure 8 Calculation coordinate schematic diagram of the first voltage intermediate value and the second voltage intermediate value provided by an embodiment of the present application;

[0031] Figure 9Schematic diagram for calculating the conversion compensation voltage level when the phase of phase i after being converted to the 0-120° region in an embodiment of this application belongs to (0, 60°];

[0032] Figure 10 Schematic diagram for calculating the conversion compensation voltage level when the phase of phase i after being converted to the 0-120° region in an embodiment of this application does not belong to (0, 60°];

[0033] Figure 11 Logic block diagram for processing the A-phase partial compensation voltage level provided in an embodiment of this application;

[0034] Figure 12 Logic block diagram for calculating the thyristor conduction signal provided in an embodiment of this application;

[0035] Figure 13 Logic block diagram for calculating the modulation wave provided in an embodiment of this application;

[0036] Figure 14 Simulated voltage vector diagram provided in an embodiment of this application;

[0037] Figure 15 Schematic diagram of the current waveform after a traditional closed-loop device is put into operation provided in an embodiment of this application;

[0038] Figure 16 Schematic diagram of the current waveform after a hybrid flexible closed-loop device is put into operation provided in an embodiment of this application. Detailed implementation manners

[0039] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0040] To make the above objects, features, and advantages of this application more obvious and understandable, the following further details this application in conjunction with the accompanying drawings and specific implementation manners.

[0041] In an exemplary embodiment, as Figure 1 shown, a zero-impact hybrid flexible closed-loop device is provided, including: a measurement device, a control device, a three-phase multi-winding transformer, a plurality of thyristor switch groups, and a plurality of fully controlled power electronic conversion circuits.

[0042] Each auxiliary winding of the three-phase multi-winding transformer includes three secondary windings. One tap is provided for each of the two secondary windings in each phase of the auxiliary winding. A thyristor switch group is connected between the two ends of the secondary winding with a tap and the tap. A fully controlled power electronic conversion circuit is connected between the two ends of the secondary winding without a tap.

[0043] Two thyristor switch groups and a fully controlled power electronic conversion circuit are connected in series to form a three-phase voltage compensation circuit. The two thyristor switch groups and the fully controlled power electronic conversion circuit in each phase voltage compensation circuit respectively come from the three phases of the three-phase multi-winding transformer.

[0044] The two ends of the A-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the A-phase line of the first feeder and the A-phase line of the second feeder. The two ends of the B-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the B-phase line of the first feeder and the B-phase line of the second feeder. The two ends of the C-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the C-phase line of the first feeder and the C-phase line of the second feeder. The three main windings of the three-phase multi-winding transformer are respectively connected to the three-phase lines of the first feeder in one-to-one correspondence.

[0045] The measuring device is used to measure the voltage amplitude and voltage phase of the first feeder, and the voltage amplitude and voltage phase of the second feeder. The control device is used to generate the on-off control signal of each thyristor switch group and the modulation wave amplitude and modulation wave phase of each fully controlled power electronic conversion circuit according to the voltage amplitude and voltage phase of the first feeder and the voltage amplitude and voltage phase of the second feeder, control the thyristor switch group according to the on-off control signal, and control the fully controlled power electronic conversion circuit according to the modulation wave amplitude and modulation wave phase to perform zero-impulse voltage compensation after the closed-loop operation.

[0046] As an optional implementation mode, Figure 1 shows a specific structure of the zero-impulse hybrid flexible closed-loop device. As Figure 1As shown in the figure, a fully controlled power electronic conversion circuit in the A-phase auxiliary winding of a three-phase multi-winding transformer, a thyristor switch group in the B-phase auxiliary winding of the three-phase multi-winding transformer, and a thyristor switch group in the C-phase auxiliary winding of the three-phase multi-winding transformer are connected in series in sequence to form an A-phase voltage compensation circuit. A thyristor switch group in the A-phase auxiliary winding of the three-phase multi-winding transformer, a fully controlled power electronic conversion circuit in the B-phase auxiliary winding of the three-phase multi-winding transformer, and another thyristor switch group in the C-phase auxiliary winding of the three-phase multi-winding transformer are connected in series in sequence to form a B-phase voltage compensation circuit. Another thyristor switch group in the A-phase auxiliary winding of the three-phase multi-winding transformer, another thyristor switch group in the B-phase auxiliary winding of the three-phase multi-winding transformer, and a fully controlled power electronic conversion circuit in the C-phase auxiliary winding of the three-phase multi-winding transformer are connected in series in sequence to form a C-phase voltage compensation circuit. The A-phase of the first feeder is respectively connected to the A-phase main winding of the three-phase multi-winding transformer and the fully controlled power electronic conversion circuit in the A-phase auxiliary winding. The B-phase of the first feeder is respectively connected to the B-phase main winding of the three-phase multi-winding transformer and a thyristor switch group in the A-phase auxiliary winding. The C-phase of the first feeder is respectively connected to the C-phase main winding of the three-phase multi-winding transformer and another thyristor switch group in the A-phase auxiliary winding. One thyristor switch group in the C-phase auxiliary winding is connected to the A-phase of the second feeder. Another thyristor switch group in the C-phase auxiliary winding is connected to the B-phase of the second feeder. The fully controlled power electronic conversion circuit in the C-phase auxiliary winding is connected to the C-phase of the second feeder.

[0047] Figure 1 Serial number ① in the figure: Three-phase voltage source, three-phase voltages at the connection point of the first feeder (hereinafter simply referred to as feeder A). Serial number ②: Resistance and reactance, three-phase line impedance of feeder A. Serial number ③: Main windings of the three-phase transformer, which are the A, B, and C phases from top to bottom, perform voltage conversion, and provide appropriate AC low voltage for the circuits connected to the secondary windings. Serial number ④: Resistance and reactance, three-phase line impedance of the second feeder (feeder B). Serial number ⑤: Three-phase voltage source, three-phase voltages at the connection point of feeder B. Serial numbers ⑥, ⑦, ⑧: Auxiliary windings of the three-phase transformer. Serial number ⑥ is the A-phase auxiliary winding, which are the a1 secondary winding, a2 secondary winding, and a3 secondary winding from top to bottom. Serial number ⑦ is the B-phase auxiliary winding, which are the b1 secondary winding, b2 secondary winding, and b3 secondary winding from top to bottom. Serial number ⑧ is the C-phase secondary winding, which are the c1 secondary winding, c2 secondary winding, and c3 secondary winding from top to bottom. Among them, the six secondary windings a2, a3, b1, b3, c1, and c2 have an additional tap. Serial number ⑨, Fully controlled power electronic conversion circuit, used to output a controllable AC voltage. Serial numbers ⑩, The thyristor switch group, through the opening and closing coordination of six groups of antiparallel thyristor switches, has two choices for the phase of the output compensation voltage that are 180° out of phase with each other, one positive and one negative. The amplitude is determined by the number of turns of the secondary winding connected to the main circuit. Since there is an additional tap on the secondary winding connected to the thyristor switch group, there are three choices.

[0048] As an alternative implementation, the thyristor switch group includes: a first thyristor switch pair, a second thyristor switch pair, a third thyristor switch pair, a fourth thyristor switch pair, a fifth thyristor switch pair, and a sixth thyristor switch pair. The first thyristor switch pair and the fourth thyristor switch pair are connected in series; the midpoint of the series connection of the first thyristor switch pair and the fourth thyristor switch pair is connected to one end of the secondary winding. The second thyristor switch pair and the fifth thyristor switch pair are connected in series; the midpoint of the series connection of the second thyristor switch pair and the fifth thyristor switch pair is connected to the tap of the secondary winding. The third thyristor switch pair and the sixth thyristor switch pair are connected in series; the midpoint of the series connection of the third thyristor switch pair and the sixth thyristor switch pair is connected to the other end of the secondary winding. One end of the series connection of the first thyristor switch pair and the fourth thyristor switch pair, one end of the series connection of the second thyristor switch pair and the fifth thyristor switch pair, and one end of the series connection of the third thyristor switch pair and the sixth thyristor switch pair are all used as the input terminals of the thyristor switch group. The other end of the series connection of the first thyristor switch pair and the fourth thyristor switch pair, the other end of the series connection of the second thyristor switch pair and the fifth thyristor switch pair, and the other end of the series connection of the third thyristor switch pair and the sixth thyristor switch pair are all used as the output terminals of the thyristor switch group. The first thyristor switch pair, the second thyristor switch pair, the third thyristor switch pair, the fourth thyristor switch pair, the fifth thyristor switch pair, and the sixth thyristor switch pair all include two antiparallel thyristor switches; the control terminals of all thyristor switches are connected to the signal output terminal of the control device.

[0049] Figure 2 It is the topology diagram of the secondary winding connected to the thyristor switch group. Figure 2 In it, S1, S2, S3, S4, S5, S6 are the first thyristor switch pair, the second thyristor switch pair, the third thyristor switch pair, the fourth thyristor switch pair, the fifth thyristor switch pair, and the sixth thyristor switch pair in sequence. Two antiparallel thyristor switches are a group, sharing a control signal, allowing alternating current to pass through when conducting simultaneously; blocking alternating current from passing through when turning off simultaneously. Ⅰ, Ⅱ: Ports directly connected to the external main circuit, Ⅰ is the input terminal of the thyristor switch group, and Ⅱ is the output terminal of the thyristor switch group.

[0050] As an alternative implementation, the fully controlled power electronic conversion circuit includes: a first diode, a second diode, a first capacitor, a second capacitor, a first insulated gate bipolar transistor, a second insulated gate bipolar transistor, an inductor, and a third capacitor.

[0051] The anode of the first diode is respectively connected to the cathode of the second diode and one end of the secondary winding; the cathode of the first diode is respectively connected to one plate of the first capacitor and the drain of the first insulated gate bipolar transistor; the anode of the second diode is respectively connected to one plate of the second capacitor and the source of the second insulated gate bipolar transistor. The other plate of the first capacitor is connected to the other plate of the second capacitor, and the connection midpoint of the other plate of the first capacitor and the other plate of the second capacitor is connected to the other end of the secondary winding. The source of the first insulated gate bipolar transistor is respectively connected to the drain of the second insulated gate bipolar transistor and one end of the inductor. The other end of the inductor is connected to one plate of the third capacitor, and the other plate of the third capacitor is connected to the other end of the secondary winding. The connection point of the other end of the inductor and one plate of the third capacitor serves as the input end of the fully controlled power electronic conversion circuit, and the connection point of the other plate of the third capacitor and the other end of the secondary winding serves as the output end of the fully controlled power electronic conversion circuit. The gates of the first insulated gate bipolar transistor and the second insulated gate bipolar transistor are both connected to the signal output end of the control device.

[0052] Figure 3 It is a topological diagram of the secondary winding connected to the fully controlled power electronic conversion circuit. Figure 3 In the figure, D1 is the first diode, D2 is the second diode, and D1 and D2 perform half-wave rectification on the AC voltage on the secondary winding. C1 is the first capacitor, C2 is the second capacitor, and C1 and C2 store and release energy. T1 is the first insulated gate bipolar transistor, T2 is the second insulated gate bipolar transistor, and T1 and T2 invert the DC voltage into a controllable AC voltage. L is the inductor, C is the third capacitor, and L and C form an LC filter. The LC filter is used to filter out the switching harmonics generated by the power electronic devices, and the compensation voltage is connected in series to the main circuit through the capacitor C. Ⅰ, Ⅱ: Ports directly connected to the external main circuit. Ⅰ is the input end of the fully controlled power electronic conversion circuit, and Ⅱ is the output end of the fully controlled power electronic conversion circuit.

[0053] Each phase of the hybrid flexible closed-loop device realizes the zero-impact voltage compensation function by connecting three secondary windings in series. These three secondary windings come from phases A, B, and C respectively. Two of them are connected to power electronic switches at the back and can output AC voltages with two forward and reverse phases and three adjustable amplitudes; one is connected to a fully controlled power electronic conversion circuit at the back and can output a flexible and controllable AC voltage. The specific connection method of phase A is as follows: Port Ⅰ of the fully controlled power electronic conversion circuit in No. ⑨ is directly connected to the A-phase line of feeder A. Port Ⅱ of the fully controlled power electronic conversion circuit in No. ⑨ is connected to Port Ⅰ of the thyristor switch group in No. ⑩. Port Ⅱ of the thyristor switch group in No. ⑩ is connected to Port Ⅰ of the thyristor switch group, and Port Ⅰ of the Port Ⅱ of the thyristor switch group is directly connected to the A-phase line of feeder B, and the same applies to the other two phases.

[0054] As an alternative implementation, by controlling the opening and closing of the upper and lower three groups of thyristors, it can cooperate with the secondary winding with taps, and can achieve voltages with two opposite phases and three adjustable amplitudes at the output. The specific connection method is as Figure 2 shown. It can be seen that there is a tap in the secondary winding, which divides the number of turns of the secondary winding into two parts with a ratio of 1:2. In this way, through the three taps of the secondary winding, three different winding turns with a turn ratio of 1:2:3 can be obtained, so three different amplitudes can be obtained. And this thyristor switch can also achieve reverse connection and short circuit through other opening and closing combinations. Therefore, there are seven different compensated voltages with amplitudes and phases added together, called seven gears of +3, +2, +1, 0, -1, -2, -3. The relationship between the gears and the on-off of the thyristor switch is shown in Table 1, where conduction is represented by the number 1 and turn-off is represented by the number 0.

[0055] Table 1 Gear Switch Status Table

[0056] -3 -2 -1 0 +1 +2 +3 <![CDATA[S1]]> 0 0 0 1 1 0 1 <![CDATA[S2]]> 0 0 1 0 0 1 0 <![CDATA[S3]]> 1 1 0 0 0 0 0 <![CDATA[S4]]> 1 0 1 1 0 0 0 <![CDATA[S5]]> 0 1 0 0 1 0 0 <![CDATA[S6]]> 0 0 0 0 0 1 1

[0057] After knowing the relationship between the switch status and the gears, it is also necessary to know the relationship between the compensated voltage and the gears. First, take the case where the parts connected to the three secondary windings all use thyristor switches. Since the three partial compensated voltages are obtained from the three-phase transformer, they are in phase or 180° out of phase with the three-phase line voltage. Therefore, the compensated voltage can be mathematically divided. Taking phase A as an example, the relationship between the total compensated voltage and the three partial compensated voltages is as Figure 4 shown, where Vc is the voltage vector of feeder A, Vs is the voltage vector of feeder B, and Va, Vb, and Vc are the three partial compensated voltage vectors.

[0058] Since the three partial compensated voltages only have two opposite phases and there are only three choices for the amplitude, and including short circuit, only seven different compensated voltages can be provided in total. Therefore, its compensation range is composed of "points". The compensation range of phase A is as Figure 5 shown. It can be seen that when the parts connected to the three secondary windings all use thyristor switches, only the compensated voltage at fixed points can be output. If the required compensated voltage falls in the "gap" between points, there will still be a certain closed-loop impact current. Therefore, this is an inherent disadvantage of the combination of this type of thyristor switch and the Sen transformer.

[0059] In order to achieve zero impact, this application introduces a fully controlled power electronic conversion circuit, and the topology diagram connected to the secondary winding is as Figure 3As shown in the figure, the circuit is a simple AC-DC-AC system, which can realize flexible adjustment of the output voltage. Use this to replace one of the above thyristor switches. In this way, when the compensation voltage falls in the "gap", the generated voltage deviation can still be compensated by the fully controlled power electronic conversion circuit, thereby realizing the zero-impact function.

[0060] The advantages of the device of this application are as follows:

[0061] This application can solve the problem of excessive impact current generated when the voltage amplitude and phase difference on both sides of the line are relatively large during the loop closing operation. Compared with other solutions, if the loop closing device based on the phase-shifting transformer needs to have both voltage amplitude and phase compensation, another transformer needs to be invested, while this topology only requires one three-phase transformer; for a pure Sen transformer, simple voltage amplitude and phase compensation can be achieved, but the secondary winding cannot be reversely connected, resulting in too small a compensation range, while this topology can realize the reverse connection of the secondary winding, greatly increasing the compensation range; the combination of a Sen transformer and a power electronic switch can also realize the reverse connection of the secondary winding, but it cannot achieve zero-impact compensation, while this topology has the zero-impact compensation function; the loop closing device based on the voltage source converter also has the zero-impact compensation function, but its equipment investment is high, the volume is large, and the maintenance is difficult, while this topology is lightweight and economical.

[0062] The reason for the above advantages is:

[0063] The cooperation between the power electronic switch and the secondary winding with tap changers can output voltages with two opposite phases and three adjustable amplitude levels; the fully controlled power electronic circuit can output a flexible adjustable voltage. The combination of the two realizes the expansion of the compensation range and the zero-impact compensation function on the premise of saving costs and reducing volume as much as possible, achieving a balance between economy and performance compared with several existing loop closing technologies.

[0064] Based on the same inventive concept, the embodiment of this application also provides a zero-impact hybrid flexible loop closing method for the zero-impact hybrid flexible loop closing device involved above. The implementation solution provided by this method to solve the problem is similar to the implementation solution recorded in the above device. Therefore, the specific limitations in one or more zero-impact hybrid flexible loop closing method embodiments provided below can refer to the limitations on the zero-impact hybrid flexible loop closing method in the above text, and will not be repeated here.

[0065] In an exemplary embodiment, as Figure 6 shown, a zero-impact hybrid flexible loop closing method is provided, including the following steps 101 to step 112. Among them:

[0066] Step 101: Obtain the phase-i voltage vectors of the first feeder and the second feeder respectively; the voltage vectors include voltage amplitudes and voltage phases; the phase-i is one of phase A, phase B, and phase C.

[0067] Step 102: Determine the amplitude and phase of the total compensation voltage required for phase-i according to the phase-i voltage vectors of the first feeder and the second feeder.

[0068] Step 103: Determine the phase of phase-i after being converted to the 0-120° region according to the phase of the total compensation voltage required for phase-i.

[0069] Step 104: Calculate the first intermediate voltage value and the second intermediate voltage value according to the amplitude of the total compensation voltage required for phase-i and the phase of phase-i after being converted to the 0-120° region.

[0070] Step 105: If the absolute value of the first intermediate voltage value is less than or equal to 3, and the absolute value of the second intermediate voltage value is less than or equal to 3, determine that the converted compensation voltage grades of the three electrical components connected in series in the phase-i voltage compensation circuit in the current flowing direction are equal to the first intermediate voltage value, zero, and the second intermediate voltage value; the three electrical components are two thyristor switch groups and a fully controlled power electronic conversion circuit; the converted compensation voltage grade is the sub-compensation voltage grade of phase-i after being converted to the 0-120° region.

[0071] Step 106: If the absolute value of the first intermediate voltage value is greater than 3 or the absolute value of the second intermediate voltage value is greater than 3, determine whether the phase of phase-i after being converted to the 0-120° region belongs to (0, 60°].

[0072] Step 107: When the phase of phase-i after being converted to the 0-120° region belongs to (0, 60°], determine that the converted compensation voltage grade of the first electrical component connected in series in the phase-i voltage compensation circuit in the current flowing direction is equal to 3, and calculate the converted compensation voltage grades of the other two electrical components in the phase-i voltage compensation circuit according to the amplitude and phase of the total compensation voltage required for phase-i.

[0073] Step 108: When the phase of phase-i after being converted to the 0-120° region does not belong to (0, 60°], determine that the converted compensation voltage grade of the second electrical component connected in series in the phase-i voltage compensation circuit in the current flowing direction is equal to 3, and calculate the converted compensation voltage grades of the other two electrical components in the phase-i voltage compensation circuit according to the amplitude and phase of the total compensation voltage required for phase-i.

[0074] Step 109: Obtain the compensation voltage grade of the phase-i voltage compensation circuit according to the phase of the total compensation voltage required for phase-i and the converted compensation voltage grades of the three electrical components in the phase-i voltage compensation circuit.

[0075] Step 110: Determine the compensation voltage levels of the voltage compensation circuits for each phase other than phase i according to the compensation voltage level of the phase i voltage compensation circuit.

[0076] Step 111: Determine the amplitude and phase of the modulation wave of the fully controlled power electronic conversion circuit in the three-phase voltage compensation circuit according to the amplitude and phase of the total compensation voltage required for phase i, and the compensation voltage level of the phase i voltage compensation circuit.

[0077] Step 112: Control the thyristor switch group according to the compensation voltage level of each phase voltage compensation circuit, and control the fully controlled power electronic conversion circuit according to the modulation wave amplitude and the modulation wave phase to perform zero-impact voltage compensation after the closed-loop operation.

[0078] The on / off of the thyristor of the power electronic switch and the on / off of the IGBT of the fully controlled power electronic conversion circuit both require control signals. The overall logic block diagram of the control signals is as Figure 7 shown.

[0079] In another exemplary embodiment of the present application, the formulas for determining the amplitude and phase of the total compensation voltage required are:

[0080] V∠θ = Vc∠θc - Vs∠θs;

[0081] Wherein, V is the amplitude of the total compensation voltage required for phase i, θ is the phase of the total compensation voltage required for phase i, Vc is the amplitude of the phase i voltage of the first feeder, θc is the phase of the phase i voltage of the first feeder, Vs is the amplitude of the phase i voltage of the second feeder, and θs is the phase of the phase i voltage of the second feeder.

[0082] The formula for determining the phase after being converted to the 0 - 120° region is:

[0083]

[0084] Wherein, θ0 is the phase of phase i after being converted to the 0 - 120° region, and θ is the phase of the total compensation voltage required for phase i.

[0085] In another exemplary embodiment of the present application, as Figure 8 shown, the above step 104 may specifically include: establishing an A coordinate axis and a C coordinate axis; the included angle between the A coordinate axis and the C coordinate axis is 120°; decompose the amplitude of the total compensation voltage required for phase i onto the A coordinate axis and the C coordinate axis according to the phase of phase i after being converted to the 0 - 120° region, and determine the amplitude decomposed onto the A coordinate axis as the first intermediate voltage value, and the amplitude decomposed onto the C coordinate axis as the second intermediate voltage value. Figure 8 The B coordinate axis in has an included angle of 120° with both the A coordinate axis and the C coordinate axis.

[0086] In another exemplary embodiment of the present application, asFigure 9 As shown, when the phase of phase i after being converted to the 0 - 120° region belongs to (0, 60°], the calculation formulas for the converted compensation voltage levels of the other two electrical components in the phase i voltage compensation circuit are as follows:

[0087] Sb0sin(θ - 60°) = Sc0sin(120° - θ);

[0088] Sb0cos(θ - 60°) + Sc0cos(120° - θ) = V;

[0089] Wherein, Sb0 and Sc0 are respectively the converted compensation voltage levels of the other two electrical components in the phase i voltage compensation circuit, θ is the phase of the total compensation voltage required for phase i, and V is the amplitude of the total compensation voltage required for phase i. Figure 9 Lc in it is Sc0, and Lb is Sb0.

[0090] Such as Figure 10 As shown, when the phase of phase i after being converted to the 0 - 120° region does not belong to (0, 60°], the calculation formulas for the converted compensation voltage levels of the other two electrical components in the phase i voltage compensation circuit are as follows:

[0091] Sb0sin60° = Vsinθ;

[0092] Sb0cos60° - Vcosθ = Sc0.

[0093] Figure 10 La in it is Sa0.

[0094] In another exemplary embodiment of the present application, the above step 109 may specifically include:

[0095] If 0 < θ ≤ 120°, then make the compensation voltage levels of the three electrical components connected in series in sequence according to the current flow direction in the phase i voltage compensation circuit equal to Sa0, Sb0, and Sc0; wherein, Sa0, Sb0, and Sc0 are respectively the converted compensation voltage levels of the three electrical components connected in series in sequence according to the current flow direction in the phase i voltage compensation circuit.

[0096] If 120° < θ ≤ 240°, then make the compensation voltage levels of the three electrical components connected in series in sequence according to the current flow direction in the phase i voltage compensation circuit equal to Sb0, Sc0, and Sa0.

[0097] If 240° < θ ≤ 360°, then make the compensation voltage levels of the three electrical components connected in series in sequence according to the current flow direction in the phase i voltage compensation circuit equal to Sc0, Sa0, and Sb0.

[0098] In another exemplary embodiment of the present application, the determination formula for the compensation voltage level of each phase voltage compensation circuit other than phase i is:

[0099] S Bb = S Cc = S Aa ;

[0100] S Bc = S Ca = S Ab ;

[0101] S Ba = S Cb = S Ac ;

[0102] Wherein, S Aa , S Ab and S Ac are respectively the compensation voltage levels of three electrical components connected in series in sequence in the i-phase voltage compensation circuit, S Ba , S Bb and S Bc are respectively the compensation voltage levels of three electrical components connected in series in sequence in a voltage compensation circuit of a phase other than the i-phase, S Ca , S Cb and S Cc are respectively the compensation voltage levels of three electrical components connected in series in sequence in a voltage compensation circuit of another phase other than the i-phase.

[0103] In another exemplary embodiment of the present application, the above step 111 can be replaced by the following steps 201 to step 202:

[0104] Step 201: According to the amplitude and phase of the total compensation voltage required for the i-phase, and the compensation voltage level of the i-phase voltage compensation circuit, use the formula V A ∠θ A = V∠θ - S Ab ∠ - 120° - S Ac ∠120°, calculate the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the i-phase voltage compensation circuit; wherein, V A and θ A are respectively the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the i-phase voltage compensation circuit, V is the amplitude of the total compensation voltage required for the i-phase, θ is the phase of the total compensation voltage required for the i-phase, S Ab and S Ac are respectively the compensation voltage levels of two thyristor switch groups connected in series in sequence in the i-phase voltage compensation circuit.

[0105] Step 202: According to the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the i-phase voltage compensation circuit, use the formula V B ∠θ B = V A ∠θA -120° and V C ∠θ C = V A ∠θ A +120°, calculate the modulation wave amplitude and modulation wave phase of the full-controlled power electronic conversion circuit in each phase voltage compensation circuit except the i-phase; where, V B and θ B are respectively the modulation wave amplitude and modulation wave phase of the full-controlled power electronic conversion circuit in a phase voltage compensation circuit except the i-phase, V C and θ C are respectively the modulation wave amplitude and modulation wave phase of the full-controlled power electronic conversion circuit in another phase voltage compensation circuit except the i-phase.

[0106] Taking the A-phase partial compensation voltage gear in the device shown in Figure 1 as an example, first obtain the A-phase partial compensation voltage gear of a "point position" closest to the compensation voltage through mathematical processing. The logic block diagram of this part is as shown in Figure 11 . The partial compensation voltage gears of the BC two phases only change the order. The calculation of the thyristor conduction signals of these two phases is as shown in Figure 12 . Since a full-controlled power electronic conversion circuit replaces a thyristor switch group, if the modulation wave required for the full-controlled power electronic conversion circuit of this phase is to be obtained, subtract the partial compensation voltages of the other two phases from the total compensation voltage. The logic block diagram is as shown in Figure 13 . Then the i-phase mentioned above refers to the A-phase, one phase except the i-phase is the B-phase, and the other phase except the i-phase is the C-phase.

[0107] Taking the 10kV power grid as an example, set the voltage Vc of feeder A as the reference value 1∠0°, and the impedance on this side is 1 + j1.57Ω; set the voltage Vs of feeder B as 0.77∠-5°, and the impedance on this side is also 1 + j1.57Ω. The simulation voltage vector diagram is as shown in Figure 14 . It can be seen that it does not fall on the fixed "point position". Set the closing operation at 1s. The phase current waveforms of a traditional closing device in several cycles after the closing operation are as shown in Figure 15 , and the phase current waveforms of the hybrid flexible closing device proposed in this application in several cycles after the closing operation are as shown in Figure 16 .

[0108] When the compensation voltage does not fall on the fixed "point position", the hybrid flexible closing device can greatly reduce the amplitude of the impact current and has a good voltage compensation effect, while the traditional closing device has a relatively large closing impact current. Therefore, through comparison, it can be found that the hybrid flexible closing device of this application has the zero-impact compensation function.

[0109] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0110] Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A zero-impact hybrid flexible ring closing device, characterized in that: include: Measuring devices, control devices, three-phase multi-winding transformers, multiple thyristor switch groups and multiple fully controlled power electronic conversion circuits; Each phase auxiliary winding of the three-phase multi-winding transformer includes three secondary windings, and two secondary windings in each phase auxiliary winding are provided with a tap, and both ends of the secondary winding with the tap and the tap are connected to a thyristor switch group; and both ends of the secondary winding without the tap are connected to a fully controlled power electronic conversion circuit; Two thyristor switch groups and a fully controlled power electronic conversion circuit are connected in series to form a three-phase voltage compensation circuit; the two thyristor switch groups and the fully controlled power electronic conversion circuit in each phase voltage compensation circuit come from three phases of a three-phase multi-winding transformer respectively; Two ends of the A-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the A-phase line of the first feeder and the A-phase line of the second feeder; two ends of the B-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the B-phase line of the first feeder and the B-phase line of the second feeder; two ends of the C-phase voltage compensation circuit in the three-phase voltage compensation circuit are respectively connected to the C-phase line of the first feeder and the C-phase line of the second feeder; The three-phase main windings of the three-phase multi-winding transformer are connected to the three-phase lines of the first feeder in a one-to-one correspondence; The measuring device is used to measure the voltage amplitude and voltage phase of the first feeder, and the voltage amplitude and voltage phase of the second feeder; The control device is used to generate an on-off control signal for each thyristor switch group and a modulation wave amplitude and a modulation wave phase for each fully-controlled power electronic conversion circuit according to the voltage amplitude and voltage phase of the first feeder and the voltage amplitude and voltage phase of the second feeder, control the thyristor switch group according to the on-off control signal, and control the fully-controlled power electronic conversion circuit according to the modulation wave amplitude and the modulation wave phase, so as to perform zero-impact voltage compensation after the loop closing operation.

2. The zero-impact hybrid flexible ring closing device according to claim 1, characterized in that: The thyristor switch group includes: a first thyristor switch pair, a second thyristor switch pair, a third thyristor switch pair, a fourth thyristor switch pair, a fifth thyristor switch pair and a sixth thyristor switch pair; The first thyristor switch pair is connected in series with the fourth thyristor switch pair; the midpoint of the first thyristor switch pair and the fourth thyristor switch pair connected in series is connected to one end of the secondary winding; The second thyristor switch pair is connected in series with the fifth thyristor switch pair; the midpoint of the second thyristor switch pair and the fifth thyristor switch pair connected in series is connected to the tap of the secondary winding; The third thyristor switch pair is connected in series with the sixth thyristor switch pair; the midpoint of the third thyristor switch pair and the sixth thyristor switch pair connected in series is connected to the other end of the secondary winding; One end of the first thyristor switch pair connected in series with the fourth thyristor switch pair, one end of the second thyristor switch pair connected in series with the fifth thyristor switch pair, and one end of the third thyristor switch pair connected in series with the sixth thyristor switch pair all serve as input ends of the thyristor switch group; The other end of the first thyristor switch pair and the fourth thyristor switch pair connected in series, the other end of the second thyristor switch pair and the fifth thyristor switch pair connected in series, and the other end of the third thyristor switch pair and the sixth thyristor switch pair connected in series all serve as output ends of the thyristor switch group; The first thyristor switch pair, the second thyristor switch pair, the third thyristor switch pair, the fourth thyristor switch pair, the fifth thyristor switch pair and the sixth thyristor switch pair each include two anti-parallel thyristor switches; the control ends of all thyristor switches are connected to the signal output end of the control device.

3. The zero-impact hybrid flexible ring closing device according to claim 2, characterized in that: The tap divides the turns of the secondary winding into two sections, and the turns ratio of the two sections is 1:2; The compensation voltages output by the A-phase voltage compensation circuit, the B-phase voltage compensation circuit and the C-phase voltage compensation circuit have seven gears, including: -3 gear, -2 gear, -1 gear, 0 gear, +1 gear, +2 gear and +3 gear; The relationship between the seven gears and the on-off of the thyristor switch is: -3 gear: the first thyristor switch pair, the second thyristor switch pair, the fifth thyristor switch pair and the sixth thyristor switch pair are all turned off, and the third thyristor switch pair and the fourth thyristor switch pair are all turned on; -2 gear: the first thyristor switch pair, the second thyristor switch pair, the fourth thyristor switch pair and the sixth thyristor switch pair are all turned off, and the third thyristor switch pair and the fifth thyristor switch pair are all turned on; -1 gear: the first thyristor switch pair, the third thyristor switch pair, the fifth thyristor switch pair and the sixth thyristor switch pair are all turned off, and the second thyristor switch pair and the fourth thyristor switch pair are all turned on; 0 gear position: the second thyristor switch pair, the third thyristor switch pair, the fifth thyristor switch pair and the sixth thyristor switch pair are all turned off, and the first thyristor switch pair and the fourth thyristor switch pair are all turned on; +1 gear: the second thyristor switch pair, the third thyristor switch pair, the fourth thyristor switch pair and the sixth thyristor switch pair are all turned off, and the first thyristor switch pair and the fifth thyristor switch pair are all turned on; +2 gear: the first thyristor switch pair, the third thyristor switch pair, the fourth thyristor switch pair and the fifth thyristor switch pair are all turned off, and the second thyristor switch pair and the sixth thyristor switch pair are all turned on; +3 gear: the second thyristor switch pair, the third thyristor switch pair, the fourth thyristor switch pair and the fifth thyristor switch pair are all turned off, and the first thyristor switch pair and the sixth thyristor switch pair are both turned on.

4. The zero-impact hybrid flexible ring closing device according to claim 1, characterized in that: The fully controlled power electronic conversion circuit comprises: a first diode, a second diode, a first capacitor, a second capacitor, a first insulated gate bipolar transistor, a second insulated gate bipolar transistor, an inductor and a third capacitor; The anode of the first diode is connected to the cathode of the second diode and one end of the secondary winding respectively; the cathode of the first diode is connected to one plate of the first capacitor and the drain of the first insulated gate bipolar transistor respectively; the anode of the second diode is connected to one plate of the second capacitor and the source of the second insulated gate bipolar transistor respectively; The other electrode plate of the first capacitor is connected to the other electrode plate of the second capacitor, and the midpoint of the connection between the other electrode plate of the first capacitor and the other electrode plate of the second capacitor is connected to the other end of the secondary winding; The source of the first insulated gate bipolar transistor is connected to the drain of the second insulated gate bipolar transistor and one end of the inductor respectively; The other end of the inductor is connected to one plate of the third capacitor, and the other plate of the third capacitor is connected to the other end of the secondary winding; The connection point between the other end of the inductor and one plate of the third capacitor serves as the input end of the fully controlled power electronic conversion circuit, and the connection point between the other plate of the third capacitor and the other end of the secondary winding serves as the output end of the fully controlled power electronic conversion circuit; The gate of the first insulated gate bipolar transistor and the gate of the second insulated gate bipolar transistor are both connected to the signal output terminal of the control device.

5. A zero-impact hybrid flexible loop closing method, characterized in that: The zero-impact hybrid flexible loop closing method is used for the zero-impact hybrid flexible loop closing device according to any one of claims 1 to 4, and the zero-impact hybrid flexible loop closing method comprises: The i-phase voltage vectors of the first feeder and the second feeder are respectively obtained; the voltage vectors include voltage amplitude and voltage phase; the i-phase is one of the A-phase, the B-phase and the C-phase; Determine the amplitude and phase of the total compensation voltage required for the i-phase according to the i-phase voltage vector of the first feeder and the second feeder; According to the phase of the total compensation voltage required for phase i, determine the phase of phase i after being converted to the region of 0 to 120°; Calculate the first voltage intermediate value and the second voltage intermediate value according to the amplitude of the total compensation voltage required for the i-phase and the phase of the i-phase after being converted to the 0-120° region; If the absolute value of the first voltage intermediate value is less than or equal to 3, and the absolute value of the second voltage intermediate value is less than or equal to 3, then it is determined that the converted compensation voltage level of the three electrical components connected in series in the current flow direction in the i-phase voltage compensation circuit is equal to the first voltage intermediate value, zero, and the second voltage intermediate value; the three electrical components are two thyristor switch groups and a fully controlled power electronic conversion circuit; the converted compensation voltage level is the compensation voltage level after the i-phase is converted to the 0-120° region; If the absolute value of the first voltage intermediate value is greater than 3 or the absolute value of the second voltage intermediate value is greater than 3, it is determined whether the phase of the i phase after being converted to the 0-120° region belongs to (0,60°]; When the phase of the i-phase after being converted to the 0-120° region belongs to (0,60°], it is determined that the converted compensation voltage level of the first electrical component connected in series according to the current flow direction in the i-phase voltage compensation circuit is equal to 3, and according to the amplitude and phase of the total compensation voltage required for the i-phase, the converted compensation voltage levels of the other two electrical components in the i-phase voltage compensation circuit are calculated; When the phase of the i-phase after being converted to the 0-120° region does not belong to (0,60°], the converted compensation voltage level of the second electrical component connected in series according to the current flow direction in the i-phase voltage compensation circuit is determined to be equal to 3, and the converted compensation voltage levels of the other two electrical components in the i-phase voltage compensation circuit are calculated according to the amplitude and phase of the total compensation voltage required for the i-phase; Obtaining the compensation voltage level of the i-phase voltage compensation circuit according to the phase of the total compensation voltage required for the i-phase and the converted compensation voltage levels of the three electrical components in the i-phase voltage compensation circuit; According to the compensation voltage level of the i-phase voltage compensation circuit, determining the compensation voltage level of each phase voltage compensation circuit other than the i-phase; According to the amplitude and phase of the total compensation voltage required for phase i and the compensation voltage gear of the phase i voltage compensation circuit, the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the three-phase voltage compensation circuit are determined; The thyristor switch group is controlled according to the compensation voltage gear of each phase voltage compensation circuit, and the fully controlled power electronic conversion circuit is controlled according to the modulation wave amplitude and the modulation wave phase to perform zero-impact voltage compensation after the loop closing operation.

6. The zero-impact hybrid flexible loop closing method according to claim 5, characterized in that: The formula for determining the amplitude and phase of the required total compensation voltage is: V∠θ=Vc∠θc-Vs∠θs; Wherein, V is the amplitude of the total compensation voltage required for phase i, θ is the phase of the total compensation voltage required for phase i, Vc is the amplitude of the i-phase voltage of the first feeder, θc is the phase of the i-phase voltage of the first feeder, Vs is the amplitude of the i-phase voltage of the second feeder, θs is the phase of the i-phase voltage of the second feeder; The formula for determining the phase after conversion to the 0-120° region is: Wherein, θ0 is the phase of phase i after being converted to the region of 0 to 120°, and θ is the phase of the total compensation voltage required for phase i.

7. The zero-impact hybrid flexible loop closing method according to claim 5, characterized in that: When the phase of the i-phase after being converted to the 0-120° region belongs to (0,60°], the calculation formula for the converted compensation voltage level of the other two electrical components in the i-phase voltage compensation circuit is: Sb0sin(θ-60°)=Sc0sin(120°-θ); Sb0cos(θ-60°)+Sc0cos(120°-θ)=V; Where, Sb0 and Sc0 are the converted compensation voltage levels of the other two electrical components in the i-phase voltage compensation circuit, θ is the phase of the total compensation voltage required for the i-phase, and V is the amplitude of the total compensation voltage required for the i-phase; When the phase of the i-phase after being converted to the 0-120° region does not belong to (0,60°], the calculation formula for the converted compensation voltage level of the other two electrical components in the i-phase voltage compensation circuit is: Sb0sin60°=Vsinθ; Sb0cos60°-Vcosθ=Sc0.

8. The zero-impact hybrid flexible loop closing method according to claim 5, characterized in that: According to the phase of the total compensation voltage required for the i-phase and the converted compensation voltage levels of the three electrical components in the i-phase voltage compensation circuit, the compensation voltage level of the i-phase voltage compensation circuit is obtained, which specifically includes: If 0<θ≤120°, the compensation voltage levels of the three electrical components connected in series in the i-phase voltage compensation circuit according to the current flow direction are set to be equal to Sa0, Sb0 and Sc0; wherein Sa0, Sb0 and Sc0 are respectively the converted compensation voltage levels of the three electrical components connected in series in the i-phase voltage compensation circuit according to the current flow direction; If 120°<θ≤240°, the compensation voltage levels of the three electrical components connected in series in the i-phase voltage compensation circuit in the direction of current flow are set equal to Sb0, Sc0 and Sa0; If 240°<θ≤360°, the compensation voltage levels of the three electrical components connected in series in the i-phase voltage compensation circuit are set to be equal to Sc0, Sa0 and Sb0.

9. The zero-impact hybrid flexible loop closing method according to claim 5, characterized in that: The formula for determining the compensation voltage level of the voltage compensation circuit of each phase other than phase i is: S Bb =S Cc =S Aa ; S Bc =S Ca =S Ab ; S Ba =S Cb =S Ac ; In the formula, S Aa , S Ab and S Ac are the compensation voltage levels of the three electrical components connected in series in the i-phase voltage compensation circuit, S Ba , S Bb and S Bc are the compensation voltage levels of the three electrical components connected in series in the voltage compensation circuit of one phase other than phase i, S Ca , S Cb and S Cc They are respectively the compensation voltage levels of three electrical components connected in series in a voltage compensation circuit of another phase other than phase i.

10. The zero-impact hybrid flexible loop closing method according to claim 5, characterized in that: According to the amplitude and phase of the total compensation voltage required for phase i and the compensation voltage gear of the phase i voltage compensation circuit, the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the three-phase voltage compensation circuit are determined, specifically including: According to the amplitude and phase of the total compensation voltage required for phase i, and the compensation voltage level of the phase i voltage compensation circuit, the formula V A ∠θ A =V∠θ-S Ab ∠-120°-S Ac ∠120°, calculate the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the i-phase voltage compensation circuit; where V A and θ A are the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the i-phase voltage compensation circuit, V is the amplitude of the total compensation voltage required for the i-phase, θ is the phase of the total compensation voltage required for the i-phase, S Ab and S Ac They are respectively the compensation voltage levels of two thyristor switch groups connected in series in the i-phase voltage compensation circuit; According to the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the i-phase voltage compensation circuit, the formula V B ∠θ B =V A ∠θ A -120° and V C ∠θ C =V A ∠θ A +120°, calculate the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the voltage compensation circuit of each phase other than phase i; where V B and θ B are the modulation wave amplitude and modulation wave phase of the fully controlled power electronic conversion circuit in the voltage compensation circuit of one phase other than phase i, V C and θ C They are respectively the modulation wave amplitude and the modulation wave phase of the fully controlled power electronic conversion circuit in the voltage compensation circuit of another phase other than the i phase.

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