Control method of three-phase decoupling series power flow regulation and control equipment

Abstract

According to the control method of the three-phase decoupling series connection type power flow regulation and control equipment, the equipment comprises a three-phase four-bridge-arm inverter and three single-phase transformers, the three-phase output end of the inverter is connected with the primary sides of the three transformers respectively, neutral points of the primary sides of the three transformers are connected with the zero line phase output end of the inverter, and the neutral points of the primary sides of the three transformers are connected with the zero line phase output end of the inverter. The secondary sides of the three transformers are respectively connected with a normally open switch, the normally open switches are connected in series on a power distribution network line connected with the two three-phase alternating current sources, when the normally open switches are kept in an off state, the power flow regulation and control equipment can carry out power flow regulation and control on A-end and B-end network sides formed by the two three-phase alternating current sources, and when the power flow regulation and control equipment does not work, the power flow regulation and control equipment can carry out power flow regulation and control on the A-end and B-end network sides. And the normally open switch is closed. The invention can effectively solve the problems that the traditional parallel power flow regulation and control equipment has strict requirements on the voltage resistance of devices, and the traditional series power flow regulation and control equipment cannot independently regulate and control the interphase power or has a large number of devices.

Description

Technical Field

[0001] The present invention relates to the technical field of power control, and in particular to a control method for three-phase decoupled series flow control equipment. Background Art

[0002] At present, with the increasing integration of renewable energy and electric vehicles into the distribution network, the power flow situation has become more and more complicated. The transformers of each distribution network will often fall into light or heavy load operation due to the uncertainty of distributed energy output and load switching, and the comprehensive loss of the transformer will increase, which poses a challenge to the high-quality and efficient operation of the distribution network. Traditional interconnecting switches or section switches cannot accurately control the power interaction between distribution networks. In contrast, the new power flow control equipment based on power electronics technology can quickly and accurately control its own power flow, thereby adjusting the power flow distribution of the distribution network, providing a promising way to solve the problem of accurate power flow in the distribution network. From the perspective of industrial applications, these advantages have made power flow control equipment based on power electronics technology increasingly popular.

[0003] At present, power flow control equipment can be divided into two categories: parallel type and series type. The parallel type is the most common structure at present, mainly back-to-back AC-DC-AC converters, such as Figure 1 As shown in Figure 1, this structure can realize the free flow of power between adjacent feeders and adjust the line voltage according to the corresponding control strategy, and can also limit the fault current to isolate the fault. However, the construction cost of this structure is high, the tolerance requirements of the devices are high, and the operating power consumption is large, resulting in relatively low efficiency.

[0004] In contrast, Figure 2 The series power flow control equipment shown, such as the static synchronous series compensator (SSSC), can achieve the same power flow control effect as the back-to-back converter. At the same time, while achieving the same power and voltage control, the cost and loss of the series type are lower, which means that the use of this structure is more cost-effective.

[0005] At present, the research on tandem type is mainly based on Figure 2 (a) SSSC three-phase full-bridge structure or Figure 2 (b) shows the SSSC three-phase H-bridge structure. However, the SSSC three-phase full-bridge structure cannot independently regulate the power between phases. The three-phase H-bridge structure has many components and high cost. How to ensure that the device size is further reduced, the system power utilization efficiency is improved, and the investment cost is reduced on the basis of achieving a good power flow control effect, while taking into account the independent control of each phase of the system, is a problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the problems that traditional parallel flow control equipment has strict requirements on the voltage resistance of devices and traditional series flow control equipment cannot independently control the power between phases or has a large number of devices, the present invention provides a control method for three-phase decoupled series flow control equipment.

[0007] In order to solve the above technical problems, the present invention adopts the following technical method: a three-phase decoupled series flow control equipment, including: a three-phase four-bridge arm inverter and three single-phase transformers, the three-phase output ends of the inverter are respectively connected to the primary sides of the three transformers, the neutral points of the three transformer primary sides are all connected to the zero-line phase output end of the inverter, and the secondary sides of the three transformers are respectively connected to a normally open switch, and the normally open switch is connected in series to a distribution network line connecting two three-phase AC sources. When the normally open switch remains in an open state, the flow control equipment can perform flow control on the A and B end network sides formed by the two three-phase AC sources. When the flow control equipment is not working, the normally open switch is closed.

[0008] Furthermore, the DC side power supply element of the inverter is a DC voltage source, and the filter element of the inverter includes a filter inductor L a , L b , L c , L n And filter capacitor C fa , C fb , C fc , filter inductors L are connected in series between the three-phase output terminals of the inverter and the primary sides of the three transformers. a , L b , L c , a filter inductor L is connected in series between the zero-line phase output terminal of the inverter and the neutral point of the primary side of the transformer n , filter capacitor C fa , C fb , C fc One end of the filter inductor L a , L b , L c The other end is connected to the neutral point of the primary side of the transformer.

[0009] As another aspect of the present invention, a control method for a three-phase decoupled series power flow control equipment comprises: Step S1, real-time monitoring of the output voltages of the distribution network A and B terminals and the power flow control equipment, and calculation of the amplitude and phase of each voltage; Step S2, calculating the reference output voltage of the power flow control equipment according to the power flow control target of the distribution network; Step S3, fitting the output voltage of the power flow control equipment to the reference output voltage through two voltage loops to obtain the PWM signal of the three-phase bridge arm of the inverter; Step S4, performing decoupling control on the fourth bridge arm of the inverter to obtain a PWM signal of the fourth bridge arm of the inverter.

[0010] Furthermore, in step S2, the reference output voltage of the power flow control equipment is calculated according to the grid-side injection power target value and the real-time detected grid-side output voltage, as shown in the following formula: (1) In the formula, are the amplitude and phase of the reference output voltage respectively; and are the impedance and phase of the distribution network line respectively; when the A-side of the distribution network injects power to the B-side, x is a, y is b, , are the target values ​​of active and reactive power injected from the A-side of the distribution network to the B-side of the distribution network, is the phase difference between the output voltage on the grid side of end A and the output voltage on the grid side of end B. When the grid side of end B of the distribution network injects power into the grid side of end A, x is b, y is a, , are the target values ​​of active and reactive power injected from the B-side of the distribution network to the A-side. The phase difference between the grid-side output voltage of terminal B and the grid-side output voltage of terminal A; They are the output voltages of the network side of terminals A and B respectively; They are the phases of the grid-side output voltages at terminals A and B respectively.

[0011] Furthermore, the step S3 includes: S301, the first voltage loop control: first adjust the output voltage amplitude of the equipment according to the power flow For reference output voltage amplitude Proportional integral feedback control is performed to obtain , combined with the reference output voltage phase get ; S302, second voltage loop control: the voltage obtained in step S301 is controlled according to the output voltage of the grid side at the end where the power is injected Proportional feedback control is performed to obtain a modulated wave, and then a third harmonic with the same amplitude as the modulated wave is injected; S303, comparing the voltage waveform obtained in step S302 with the triangular wave to obtain a PWM signal of the three-phase bridge arm of the inverter.

[0012] Preferably, step S4 comprises: S401, firstly perform the calculation on the result obtained in step S301 Perform three-phase summation and the actual output voltage amplitude of the power flow control equipment Sum the three phases, then take the difference between the two summed voltages, and then multiply by the inductance proportional coefficient k pn ,get ; S402, performing integral feedback control on the third harmonic to obtain ; S403, the result obtained in step S401 is and the one obtained in step S402 After addition, the PWM signal of the fourth bridge arm of the inverter is obtained by comparing with the triangular wave.

[0013] Preferably, the proportional control coefficient k used in step S3 and step S4 is p , integral control coefficient k i , inductance ratio coefficient k pn The relationship between them is as follows: (2) In the formula, They represent the filter inductances at the three-phase output terminals of the inverter. The values ​​of the three filter inductances are the same, all .

[0014] Compared with the prior art, the advantages of the present invention are as follows: (1) Compared with the back-to-back parallel type power flow control equipment, the three-phase decoupled series type power flow control equipment proposed in the present invention does not need to fully withstand the grid line voltage, and the voltage resistance level of the device is lower.

[0015] (2) Compared with the SSSC type three-phase bridge structure series type power flow control equipment topology, the three-phase decoupled series type power flow control equipment topology proposed in the present invention reduces the number of components by 33%, thereby greatly reducing the cost of the system.

[0016] (3) The three-phase decoupled series power flow control equipment proposed in the present invention can realize accurate and stable control of three-phase power under different grid amplitude and phase conditions, and provides a solution to the problems of three-phase imbalance in the substation area and light or heavy load of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a topological diagram of the traditional back-to-back parallel power flow control equipment connected to the power grid; Figure 2 It is a simplified topological diagram of a traditional series power flow control device connected to a power grid (wherein, (a) is a simplified topological diagram of a series power flow control device with a SSSC type three-phase full-bridge structure; (b) is a simplified topological diagram of a series power flow control device with a SSSC type three-phase H-bridge structure); Figure 3 A topological diagram of the three-phase decoupled series power flow control equipment involved in the present invention connected to a power grid; Figure 4 It is an A-phase circuit equivalent model of the power injected from the A-end grid side to the B-end grid side under the grid-connected working condition in the present invention; Figure 5 A block diagram of a control method for a three-phase decoupled series flow control device according to the present invention; Figure 6 A block diagram of the decoupling control of the fourth bridge arm in the control method of the three-phase decoupling series type power flow control equipment involved in the present invention; Figure 7 This is the topology diagram of the series power flow control equipment of the traditional SSSC type three-phase H-bridge structure; Figure 8 The three-phase active power transmission waveform under the simulation conditions of the three-phase decoupled series power flow control equipment (where (a) is the active power transmission waveform of phase a; (b) is the active power transmission waveform of phase b; (c) is the active power transmission waveform of phase c); Fig. 9 It is the voltage waveform diagram of the three-phase decoupled series power flow control equipment under simulation conditions (where (a) is the output voltage waveform diagram of the grid side of end A under simulation conditions; (b) is the output voltage waveform diagram of the grid side of end B under simulation conditions; (a) is the output voltage waveform diagram of the power flow control equipment under simulation conditions); Fig.10 It is the voltage waveform diagram of the three-phase decoupled series power flow control equipment under the three-phase asymmetric simulation condition (wherein, (a) is the output voltage waveform diagram of the grid side of end A under the three-phase asymmetric simulation condition; (b) is the output voltage waveform diagram of the grid side of end B under the three-phase asymmetric simulation condition; (a) is the output voltage waveform diagram of the power flow control equipment under the three-phase asymmetric simulation condition); Fig.11 The three-phase active power transmission waveform diagram under the three-phase voltage uneven simulation condition for the three-phase decoupled series power flow control equipment; Fig.12 It is the waveform of the current injected on the grid side of end A under the three-phase asymmetric simulation condition of the three-phase decoupled series power flow control equipment (where (a) is the waveform of the current injected on the grid side of phase a at end A, (b) is the waveform of the current injected on the grid side of phase b at end A, and (c) is the waveform of the current injected on the grid side of phase c at end A). DETAILED DESCRIPTION

[0018] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0019] like Figure 3As shown, the three-phase decoupled series power flow control equipment provided by the present invention includes: a three-phase four-bridge arm inverter and three single-phase transformers, the three-phase output ends of the inverter are respectively connected to the primary sides of the three transformers, the neutral points of the three primary sides of the transformers are all connected to the zero-line phase output end of the inverter, and the secondary sides of the three transformers are respectively connected to a normally open switch.

[0020] The power flow control equipment of the present invention is applied to a distribution network connected to two three-phase AC sources, wherein the two three-phase AC sources respectively constitute the A and B network sides of the distribution network. Figure 3 In, V gA (including V gA—a 、V gA—b 、V gA—c ) represents the three-phase AC source on the network side of end A, V gB (including V gB—a 、V gB—b 、V gB—c ) represents the three-phase AC source on the network side of terminal B, R g (including R gA—a , R gA—b , R gA—c , R gB—a , R gB—b , R gB—c ) and L g (including L gA—a , L gA—b , L gA—c , L gB—a , L gB—b , L gB—c ) represent the line impedance and inductance between the A and B end network sides, respectively. The flow control equipment is connected in series between the terminals of the distribution network through a normally open switch. Specifically, the normally open switch S1 is connected in series with the A phase line between the A and B end network sides of the distribution network, the normally open switch S2 is connected in series with the B phase line between the A and B end network sides of the distribution network, and the normally open switch S3 is connected in series with the C phase line between the A and B end network sides of the distribution network. When the normally open switch remains in the disconnected state, the flow control equipment can perform flow control on the A and B end network sides. When the flow control equipment is not working, the normally open switch is closed, and the flow control equipment is equivalent to a wire. The present invention enables the flow control equipment to independently adjust the phase-to-phase power by controlling the on and off of the three normally open switches and the switch tubes on the four bridge arms of the inverter.

[0021] We know that depending on the different power supply elements on the DC side of the inverter, if the DC side stability needs to be regulated, the calculation of active and reactive power output by the power flow control equipment needs to change. The present invention mainly realizes the power flow control on the grid side, and does not consider the voltage stabilization control on the DC side. Therefore, preferably, the present invention uses a DC voltage source as the power supply element on the DC side of the inverter. Figure 3 In, V dcIn order to make the inverter of the present invention have better filtering ability, the filter element of the inverter of the present invention is composed of a filter inductor L a , L b , L c , L n And filter capacitor C fa , C fb , C fc Composition, such as Figure 3 As shown, filter inductors L are connected in series between the three-phase output terminals of the inverter and the primary sides of the three transformers. a , L b , L c , a filter inductor L is connected in series between the zero-line phase output terminal of the inverter and the neutral point of the primary side of the transformer n , filter capacitor C fa , C fb , C fc One end of the filter inductor L a , L b , L c The other end is connected to the neutral point of the primary side of the transformer.

[0022] It is worth mentioning that the three-phase bridge arm control of the inverter combined with the fourth bridge arm neutral point voltage control can effectively solve the problem of three-phase voltage imbalance or waveform distortion caused by three-phase imbalance or nonlinear load. The fourth bridge arm of the inverter is connected in series with an inductor to eliminate the influence of the harmonics generated by the bridge arm on the three-phase voltage. At the same time, connecting the neutral point of the transformer to the fourth bridge arm can make the single-phase transformer work independently without interference from the other two phases.

[0023] The aforementioned power flow control equipment creates a power flow path between two three-phase AC voltage sources, which can be the power injection from the A-side grid to the B-side grid, or the power injection from the B-side grid to the A-side grid. For example, the output voltage amplitude of the A-side grid is greater than the output voltage amplitude of the B-side grid, which will result in a larger line voltage V l , and thus cause a significant line current to flow from the A-end grid side to the B-end grid side. The power flow control equipment will provide a reverse potential to offset the temporary drop in the output voltage on the B-end grid side, or the output voltage phase of the A-end grid side will lead the output voltage phase of the B-end grid side. In both cases, power will flow from the A-end grid side to the B-end grid side. Similarly, the conditions for the B-end grid side to inject power into the A-end grid side only need to be opposite.

[0024] The present invention takes phase A as an example, and the equivalent circuit model of the power flow control equipment for injecting power from the A-end grid side to the B-end grid side under the grid-connected working condition is as follows: Figure 4 As shown, the power flow control equipment is equivalent to a controlled voltage source V s , U s is its output voltage amplitude, φs is its output voltage phase, Z ax It represents the line impedance between the A-side network and the power flow control equipment, Z bx Indicates the line impedance between the B-side network and the power flow control equipment, U ga and φ ga They represent the output voltage amplitude and phase of the grid side at end A, U gb and φ gb Respectively represent the output voltage amplitude and phase of the grid side of terminal B, i ab Indicates the line current flowing from the A-side network to the B-side network. Figure 4 The equivalent circuit model shown in the figure can calculate the power transmission size of the power grid. The reactive power flows from the grid-side output voltage with high amplitude to the grid-side output voltage with low amplitude. The active power flows from the grid-side output voltage with advanced phase to the grid-side output voltage with lagging phase. When connected to the grid, the grid-side output active power flows from the high frequency to the low frequency. The power of each node in the distribution network under the grid-connected condition is calculated as follows.

[0025] First, based on the equivalent circuit model, we calculate: (3) Where U s and φ s are the output voltage amplitude and phase of the power flow control equipment respectively; Z represents the line impedance of the distribution network, including Z ax and Z bx ,φ z Indicates the impedance phase of the distribution network line; i ga Indicates the current injected from the A-side network to the B-side network.

[0026] Next, combined with formula (3), we can get the active power injected from the A-side network to the B-side network: for: (4) In the formula, It is the phase difference between the grid-side output voltage of end A and the grid-side output voltage of end B.

[0027] Then, combined with formula (3), the active power consumed by line impedance is obtained: for: (5) Finally, combining formula (4) and formula (5), we can get the active power transmitted between feeders through the power flow control equipment: for: (6) Combining the above formulas (1)-(4), we can derive the reference output voltage of the power flow control equipment: The expression is as follows: (1) In the formula, are the amplitude and phase of the reference output voltage respectively; and are the impedance and phase of the distribution network line respectively; when the A-side of the distribution network injects power to the B-side, x is a, y is b, , are the target values ​​of active and reactive power injected from the A-side of the distribution network to the B-side of the distribution network, is the phase difference between the output voltage on the grid side of end A and the output voltage on the grid side of end B. When the grid side of end B of the distribution network injects power into the grid side of end A, x is b, y is a, are the target values ​​of active and reactive power injected from the B-side of the distribution network to the A-side. The phase difference between the grid-side output voltage of terminal B and the grid-side output voltage of terminal A; They are the output voltages of the network side of terminals A and B respectively; They are the phases of the grid-side output voltages at terminals A and B respectively.

[0028] The three-phase decoupled series power flow control equipment provided by the present invention realizes voltage compensation on the grid side through a level compensation strategy to provide active support for the output, and the three-phase four-bridge arm inverter in the present invention adopts decoupling control to realize independent control of the three-phase power under any load condition, thereby improving the dynamic and static characteristics of the equipment. Therefore, the present invention also provides a control method for the three-phase decoupled series power flow control equipment, such as Figure 5 As shown, the method includes: Step S1: Real-time monitoring of the output voltage of the distribution network A and B terminals and the output voltage of the power flow control equipment ,calculate The amplitude and Phase ,as well as The amplitude and Phase , where i is a or b.

[0029] Step S2, calculating the reference output voltage of the power flow control equipment according to the grid-side injected power target value and the real-time detected grid-side output voltage, that is, formula (1).

[0030] Under ideal conditions, the grid-side output voltage at ends A and B of the distribution network remains stable. However, considering that grid drops may occur during actual operation, the dynamic fluctuations of the grid-side transmitted active power should be fully considered in actual application to set the grid-side injection power target value.

[0031] Step S3, fitting the output voltage of the power flow control equipment to the reference output voltage through two voltage loops to obtain the PWM signal of the three-phase bridge arm of the inverter.

[0032] S301, the first voltage loop control: first adjust the output voltage amplitude of the equipment according to the power flow For reference output voltage amplitude Proportional integral feedback control is performed to obtain , combined with the reference output voltage phase get .

[0033] S302, the second voltage loop control: according to the output voltage of the grid side at the end where the power is injected The step S301 obtained Proportional feedback control is performed to obtain a modulated wave, and then the third harmonic with the same amplitude as the modulated wave is injected.

[0034] S303, comparing the voltage waveform obtained in step S302 with the triangular wave to obtain a PWM signal of the three-phase bridge arm of the inverter.

[0035] Step S4, refer to Figure 6 The fourth bridge arm of the inverter is decoupled and controlled to obtain a PWM signal of the fourth bridge arm of the inverter.

[0036] S401, firstly perform the calculation on the result obtained in step S301 Perform three-phase summation and the actual output voltage amplitude of the power flow control equipment Sum the three phases, take the difference between the summed voltages, and then multiply by the inductance proportional coefficient k pn ,get ; S402, performing integral feedback control on the aforementioned third harmonic to obtain ; S403, the result obtained in step S401 is and the one obtained in step S402 After addition, the PWM signal of the fourth bridge arm of the inverter is obtained by comparing with the triangular wave.

[0037] The PWM generation method of the present invention adopts a method of comparing the modulation wave with the triangle wave. To improve the utilization rate of the DC bus voltage, a third harmonic with the same amplitude is injected into the modulation wave of the three-phase and neutral phase. The injected third harmonic is 0.15sin(3ωt).

[0038] Regarding the decoupling control of the present invention, the proportional control coefficient k used in step S3 and step S4 is p , integral control coefficient k i , inductance ratio coefficient k pnThe selection follows: (2) In the formula, They represent the filter inductances at the three-phase output terminals of the inverter. The values ​​of the three filter inductances are the same, all .

[0039] k p The larger the value, the smaller the equivalent inductance of each phase of the power flow control equipment. However, from the perspective of feedback control, k p Too large will cause vibration, so k p Choose moderate.

[0040] Under the condition that L is determined, k pn The larger the k is, the smaller the neutral line phase inductance is, which is not conducive to the protection of the phase and the elimination of harmonics; but pn The smaller the L n The larger it is, the stronger the coupling between phases.

[0041] Determine k p and k pn Then, we can get k by formula (2): i The selection range.

[0042] To further verify the stability and superiority of the three-phase decoupled series power flow control equipment proposed in the present invention, three schemes are compared below. ① Scheme 1: Based on the traditional four-bridge arm back-to-back power flow control device, such as Figure 1 As shown; ②Scheme 2: Based on the three-phase H-bridge SSSC structure device, such as Figure 7 As shown; ③ The present invention: Based on the three-phase decoupled series type power flow control equipment proposed by the present invention, as Figure 3 shown.

[0043] For the convenience of comparison and discussion, the above schemes are all carried out under the following conditions: the normal operating voltage amplitude of the AC side is 311V, the three-phase voltage phases differ by 120° in sequence, and the DC side voltage is stabilized at 800V; under the grid-connected condition, 15kW of active power is transmitted from the A-end network side to the B-end network side before 0.3 seconds, 30kW of active power is transmitted from the A-end network side to the B-end network side at 0.3-0.5 seconds, and 10kW of active power is transmitted from the B-end network side to the A-end network side after 0.5 seconds. The comparison table of the present invention and the existing scheme is as follows.

[0044] Table 1 Comparison between the present invention and existing solutions

[0045]

[0046] From the comparison results in Table 1, it can be seen that under the same working conditions, compared with Scheme 1, the present invention can compensate for voltage loss through a transformer, has stronger DC side voltage stability, lower requirements for device withstand voltage, fewer devices, and smaller volume; compared with Scheme 2, the present invention has stronger DC side voltage stability, fewer devices, less device loss, smaller system volume, and lower cost. Therefore, compared with the prior art, the present invention can significantly improve system stability and reduce the requirements and number of devices.

[0047] The present invention builds the three-phase decoupled power flow control equipment model proposed in the present invention in the MATLAB / Simulink simulation platform to verify the effectiveness and correctness of the control method proposed in the present invention. The simulation parameters are shown in Table 2.

[0048] Table 2 Simulation parameters

[0049]

[0050] In order to simulate the actual working state of the three-phase decoupled series power flow control equipment during operation and verify the effectiveness of the control method of the present invention, the present invention fully considers the dynamic fluctuation of the active power transmitted on the grid side and sets the dynamic transmission active power waveform as follows: Figure 8 As shown. In the simulation of grid-connected conditions within 0-0.3s, the three-phase load is uniform, and 15kW of active power is transmitted from the A-side grid to the B-side grid; at 0.3s, the voltage on the B-side grid drops temporarily, and the active power transmitted from the A-side grid to the B-side grid increases to 30kW. At 0.5s, the voltage on the B-side grid recovers, the voltage on the A-side grid drops temporarily, and 10kW of active power is transmitted from the B-side grid to the A-side grid. Fig. 9 Shown are the grid-side voltage and compensation voltage waveforms.

[0051] In addition, if Fig.10 As shown in the waveform diagram of grid-side voltage and supplementary voltage, the three-phase decoupled series power flow control equipment can flexibly adjust the output active power according to the current grid voltage conditions, such as Fig.11 As shown, when the amplitude and phase of the three-phase power grid are uneven, the output active power is also different, but it can compensate for the grid voltage. Fig.12 The waveform diagram shows the current injected from the A-end network side to the B-end network side.

[0052] The present invention proposes a control method for three-phase decoupled series type power flow control equipment, which provides a new way for the application of power flow control equipment. The present invention proposes a three-phase decoupled series type power flow control equipment that fully utilizes the decoupling control of the existing three-phase four-bridge arm inverter, and adopts voltage amplitude and phase control to perform voltage compensation on the grid side. The proposed control method can realize independent control of a single phase while realizing transmission of specified power size and direction, while reducing the withstand voltage requirements of the device and the number of devices, thereby improving the stability and economy of the system, and providing reliable guarantee for the stable operation of the three-phase decoupled series type power flow control equipment. In general, the equipment proposed by the present invention has strong engineering practicality, and provides important reference and reference for the engineering and practical application of future power flow control equipment.

[0053] It is worth noting that the present invention only analyzes a single device parameter as an example. The present invention can also be applied to power electronic devices of different types, capacities, and withstand voltage levels. When applied in actual engineering projects, the number and parameters of devices can be adjusted according to the actual situation of device selection.

[0054] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0055] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements have been omitted. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A control method for three-phase decoupled series power flow control equipment, characterized in that: The three-phase decoupled series type power flow control equipment includes a three-phase four-bridge arm inverter and three single-phase transformers. The three-phase output ends of the inverter are respectively connected to the primary sides of the three transformers, and the neutral points of the primary sides of the three transformers are all connected to the zero line phase output end of the inverter. The secondary sides of the three transformers are respectively connected to a normally open switch, and the normally open switch is connected in series to the distribution network line connecting the two three-phase AC sources. When the normally open switch remains in an open state, the power flow control equipment can perform power flow control on the A and B end network sides formed by the two three-phase AC sources. When the power flow control equipment is not working, the normally open switch is closed; The control method of the three-phase decoupled series type power flow control equipment includes: Step S1, real-time monitoring of the output voltages of the distribution network A and B terminals and the power flow control equipment, and calculation of the amplitude and phase of each voltage; Step S2, calculating the reference output voltage of the power flow control equipment according to the power flow control target of the distribution network, as follows: （1） In the formula, are the amplitude and phase of the reference output voltage respectively; and are the impedance and phase of the distribution network line respectively; when the A-side of the distribution network injects power to the B-side, x is a, y is b, , are the target values ​​of active and reactive power injected from the A-side of the distribution network to the B-side of the distribution network, is the phase difference between the output voltage on the grid side of end A and the output voltage on the grid side of end B. When the grid side of end B of the distribution network injects power into the grid side of end A, x is b, y is a, , are the target values ​​of active and reactive power injected from the B-side of the distribution network to the A-side. The phase difference between the grid-side output voltage at end B and the grid-side output voltage at end A; They are the output voltages of the network side of terminals A and B respectively; They are the phases of the grid-side output voltages at terminals A and B respectively; Step S3, fitting the output voltage of the power flow control equipment to the reference output voltage through two voltage loops to obtain the PWM signal of the three-phase bridge arm of the inverter; Step S4, performing decoupling control on the fourth bridge arm of the inverter to obtain a PWM signal of the fourth bridge arm of the inverter.

2. The control method of three-phase decoupled series power flow control equipment according to claim 1, characterized in that: The DC side power supply element of the inverter is a DC voltage source, and the filter element of the inverter includes a filter inductor L a , L b , L c , L n And filter capacitor C fa , C fb , C fc , filter inductors L are connected in series between the three-phase output terminals of the inverter and the primary sides of the three transformers. a , L b , L c , a filter inductor L is connected in series between the zero-line phase output terminal of the inverter and the neutral point of the primary side of the transformer n , filter capacitor C fa , C fb , C fc One end of the filter inductor L a , L b , L c The other end is connected to the neutral point of the primary side of the transformer.

3. The control method of three-phase decoupled series power flow control equipment according to claim 2, characterized in that: The step S3 comprises: S301, the first voltage loop control: first adjust the output voltage amplitude of the equipment according to the power flow For reference output voltage amplitude Proportional integral feedback control is performed to obtain , combined with the reference output voltage phase get ; S302, second voltage loop control: the voltage obtained in step S301 is controlled according to the output voltage of the grid side at the end where the power is injected Proportional feedback control is performed to obtain a modulated wave, and then a third harmonic with the same amplitude as the modulated wave is injected; S303, comparing the voltage waveform obtained in step S302 with the triangular wave to obtain a PWM signal of the three-phase bridge arm of the inverter.

4. The control method of three-phase decoupled series power flow control equipment according to claim 3, characterized in that: The step S4 comprises: S401, firstly perform the calculation on the result obtained in step S301 Perform three-phase summation and the actual output voltage amplitude of the power flow control equipment Sum the three phases, then take the difference between the two summed voltages, and then multiply by the inductance proportional coefficient k pn ,get ; S402, performing integral feedback control on the third harmonic to obtain ; S403, the result obtained in step S401 is and the one obtained in step S402 After addition, the PWM signal of the fourth bridge arm of the inverter is obtained by comparing with the triangular wave.

5. The control method of three-phase decoupled series power flow control equipment according to claim 4, characterized in that: The proportional control coefficient k used in step S3 and step S4 p , integral control coefficient k i , inductance ratio coefficient k pn The relationship between them is as follows: （2） In the formula, They represent the filter inductances at the three-phase output terminals of the inverter. The values ​​of the three filter inductances are the same, all .

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