A medium voltage distribution network flexible interconnection switch topology structure and control method

Abstract

The present invention belongs to the technical field of power electronic converters and discloses a medium-voltage distribution network flexible interconnection switch topology and control method. The medium-voltage distribution network flexible interconnection switch topology provided by the present invention includes three connected reactors L1, three connected reactors L3, two chain-type STATCOMs, two three-phase isolation transformers, two three-phase LC filters, two three-phase inverter circuits, and a DC port. Back-to-back three-phase converters are introduced at the ends of the chain-type STATCOMs of two feeders. Through the back-to-back three-phase converters, active power flow mutualization between the two medium-voltage chain-type STATCOMs, that is, between two different feeders, can be achieved. The present invention can achieve DC capacitor voltage balancing of the chain-type STATCOM submodules of the two feeders. Compared with the BTB-VSC commonly used in existing medium-voltage distribution network flexible interconnection demonstration projects, this solution has lower cost, simpler topology, easier control, and does not need to consider the active and reactive power decoupling issues between interconnected feeders, making it easy to promote and apply on a large scale.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and in particular relates to a flexible interconnection switch topology structure and a control method for a medium-voltage distribution network. Background Art

[0002] With the increasing penetration of distributed energy resources, the large-scale integration of electric vehicles, and the diversification of user loads, the operation and dispatch of distribution networks have become increasingly complex, posing significant challenges in power quality, feeder operation, and protection design. Replacing mechanical tie switches with fully controllable Flexible Interconnect Switches (FIS) enables a regular "soft connection" in the distribution network, significantly enhancing its flexible regulation capabilities. During normal operation, the FIS provides continuous active power regulation and reactive power support, achieving feeder load balancing, alleviating network congestion, and managing voltage quality. In the event of a distribution network fault, the FIS provides fault isolation, power flow transfer, and power restoration.

[0003] Back-to-back voltage source converters (BTB-VSCs) are commonly used in existing demonstration projects for flexible interconnection of medium-voltage distribution networks. These solutions primarily include two-level VSCs, three-level VSCs, and MMCs. These solutions suffer from high costs, bulky design, and are difficult to implement on a large scale.

[0004] Currently, medium-voltage distribution networks are often equipped with reactive power compensation equipment, such as static synchronous compensators (STATCOMs). By optimizing the topology of existing medium-voltage chain STATCOMs, back-to-back three-phase converters are introduced at the ends of the STATCOMs on each of the two feeders. These back-to-back three-phase converters enable active power flow coordination between the two STATCOMs, meaning two different feeders. The reactive power between the two feeders can be self-regulated by the STATCOMs on each feeder, eliminating the need to consider active and reactive power decoupling between interconnected feeders. This solution, which only requires topological optimization of the reactive power compensation equipment in the existing medium-voltage distribution network, achieves active power flow coordination between different feeders. It is low-cost, has a simple topology, is easy to control, and is readily adaptable for large-scale deployment.

[0005] Through the above analysis, the problems and defects of the existing technology are as follows:

[0006] The back-to-back voltage source converter solution used in the medium-voltage distribution network flexible interconnection demonstration project is costly, bulky, and not easy to promote and apply on a large scale. Summary of the Invention

[0007] In response to the problems existing in the prior art, the present invention provides a medium-voltage distribution network flexible interconnection switch topology structure and control method.

[0008] The present invention is implemented as follows: a medium voltage distribution network flexible interconnection switch topology structure includes:

[0009] Three connected reactors L1, three connected reactors L3, two chain-type STATCOMs, two three-phase isolation transformers, two three-phase LC filters, two three-phase inverter circuits and one DC port;

[0010] Three connected reactors L1 and three connected reactors L3 are used to suppress high-order harmonics and ensure the sinusoidal nature of the grid-connected current;

[0011] Two chain-type STATCOMs for reactive power compensation of the two feeders;

[0012] Two three-phase isolation transformers for isolation between high-voltage and low-voltage sides;

[0013] Two three-phase LC filters are used to filter the higher harmonics of the two three-phase inverter circuits;

[0014] Two three-phase inverter circuits share a DC port, forming a back-to-back three-phase converter structure for mutual assistance of active power flow between the two feeders;

[0015] The flexible interconnection switch of the medium-voltage distribution network increases the number of interconnected feeders by increasing the number of chained STATCOMs and back-to-back three-phase converters.

[0016] Furthermore, the chain STATCOM1 control unit includes:

[0017] Synchronous Rotating Phase-Locked Loop (SRF-PLL) controller, used to calculate the real-time phase of the power grid;

[0018] The first Park controller is used to obtain the current i in the two-phase synchronous rotating coordinate system sd1 、i sq1 ;

[0019] A first proportional-integral controller is used to control the active current of the chain STATCOM1;

[0020] The second proportional integral controller is used to control the reactive current of the chain STATCOM1;

[0021] The third proportional-integral controller is used to realize the global voltage balancing control function of the DC voltage of the neutron modules in the chain STATCOM1;

[0022] A first anti-Park controller is used to obtain a modulation voltage in a three-phase stationary coordinate system;

[0023] A fourth proportional-integral controller, used to implement part of the inter-phase equalization control of the DC voltage of the neutron modules in the chained STATCOM1;

[0024] A fifth proportional-integral controller, used to implement part of the inter-phase equalization control of the DC voltage of the sub-modules in the chained STATCOM1;

[0025] A sixth proportional-integral controller, configured to implement a DC voltage intra-phase equalization control function for the neutron modules in the chained STATCOM1;

[0026] The first SPWM controller is used to realize the generation of a driving signal for each IGBT switch tube in each sub-module of each phase in the chain STATCOM1.

[0027] Furthermore, the three-phase inverter circuit 1 control unit includes:

[0028] The second Park controller is used to obtain the current u of the three-phase inverter circuit 1 in the two-phase synchronous rotating coordinate system id1 、u i q 1 ;

[0029] a seventh proportional-integral controller, configured to implement an active power control function of the three-phase inverter circuit 1;

[0030] an eighth proportional-integral controller, configured to implement a d-axis voltage control function of the three-phase inverter circuit 1;

[0031] a ninth proportional-integral controller, configured to implement a q-axis voltage control function of the three-phase inverter circuit 1;

[0032] A second anti-Park controller is used to obtain a modulation voltage of the three-phase inverter circuit 1 in a three-phase stationary coordinate system;

[0033] A first active damping controller, configured to implement active damping of the three-phase inverter circuit 1;

[0034] The second SPWM controller is used to generate driving signals for six IGBT switches in the three-phase inverter circuit 1 .

[0035] Furthermore, the three-phase inverter circuit 2 control unit includes:

[0036] The third Park controller is used to obtain the current u of the three-phase inverter circuit 2 in the two-phase synchronous rotating coordinate system id2 、u i q 2 ;

[0037] a tenth proportional-integral controller, configured to realize the function of controlling the DC voltage of the three-phase inverter circuit 2 to be constant;

[0038] an eleventh proportional-integral controller, configured to implement a d-axis voltage control function of the three-phase inverter circuit 2;

[0039] a twelfth proportional-integral controller, configured to implement a q-axis voltage control function of the three-phase inverter circuit 2;

[0040] a third anti-Park controller, configured to obtain a modulation voltage of the three-phase inverter circuit 2 in a three-phase stationary coordinate system;

[0041] A second active damping controller, used to implement active damping of the three-phase inverter circuit 2;

[0042] The third SPWM controller is used to generate driving signals for the six IGBT switches in the three-phase inverter circuit 2.

[0043] Another object of the present invention is to provide a control method of a chain STATCOM1 based on the medium voltage distribution network flexible interconnection switch topology structure, comprising the following steps:

[0044] (1) The phase information ω1t of the 10 kV AC feeder 1 of the power grid is obtained by SRF-PLL; the voltage and current of the 10 kV AC feeder 1 of the power grid are transformed by PARK, and the voltage and current of the two-phase synchronous rotating coordinate system are obtained;

[0045] (2) Sum the DC side voltages of the three-phase submodules in the chain STATCOM1 and divide it by 1 / 3n to obtain the average DC side voltage of all submodules U Hd1 ; Set the voltage reference value U of the global voltage control Hd1 * Subtract the actual value U Hd1 The difference is input into the third proportional integral controller, and the output is the d-axis current reference value i sd1 *;

[0046] (3) Set the reference value U of the phase-to-phase voltage control Hd2 *The average value of the DC side voltage of each phase sub-module is subtracted respectively, and the difference is input into the fourth proportional integral controller; the d-axis current of the chain STATCOM1 is subtracted from the output value of the fourth proportional integral controller of each phase, and the difference of the three phases is input into the fifth proportional integral controller. The output value of the fifth proportional integral controller is respectively added to cosω1t, cos(ω1t-2π / 3), and cos(ω1t+2π / 3) to obtain the modulation voltage that needs to be superimposed on each phase, redistribute the active power between phases, and realize the phase-to-phase voltage balance of the neutron module in the chain STATCOM1;

[0047] (4) Subtract the reference value of the three-phase intra-phase voltage balancing control from the DC side voltage of each submodule of each phase of the chain STATCOM1, and input the difference into the sixth proportional integral controller. The output of the sixth proportional integral controller is multiplied by sinω1t, sin(ω1t-2π / 3), and sin(ω1t+2π / 3) respectively to obtain the reactive vector that needs to be superimposed on the modulation voltage of each submodule of each phase in the chain STATCOM1, redistribute the intra-phase active power, and realize the intra-phase voltage balance of the submodules in the chain STATCOM1;

[0048] (5) The d-axis current reference value i of the chain STATCOM1 is sd1 * Actual value of d-axis current i of chained STATCOM1 sd1 Subtract the difference, input the first proportional integral controller, and after current decoupling control and grid voltage feedforward, obtain the reference value of the d-axis modulation voltage; the q-axis current reference value i of the chain STATCOM1 is sq1 *The actual value of the q-axis current i of the chain STATCOM1 sq1 Subtract the difference, and input it into the second proportional-integral controller. After current decoupling control and grid voltage feedforward, the reference value of the q-axis modulation voltage is obtained.

[0049] (6) The final modulation voltage u of the chain STATCOM1 ma1 ,u mb1 ,u mc1 , through the first SPWM controller, a PWM wave is generated by carrier phase shift modulation to control the IGBT switch tube of each phase and each sub-module in the chain STATCOM1.

[0050] Another object of the present invention is to provide a control method for a three-phase inverter circuit 1 based on the medium voltage distribution network flexible interconnection switch topology structure, comprising the following steps:

[0051] 1) The three-phase voltage on the filter capacitor side of the three-phase inverter circuit 1 is subjected to PARK transformation to obtain the voltage in the two-phase synchronous rotating coordinate system;

[0052] 2) Subtract the reference value of the active power transmitted by the three-phase inverter circuit 1 from the actual value of the active power transmitted by the three-phase inverter circuit 1, and input the difference into the seventh proportional integral controller, and output the reference value u of the q-axis voltage in the three-phase inverter circuit 1 iq1 *;

[0053] 3) The reference value u of the d-axis voltage in the three-phase inverter circuit 1 is id1 *The actual value of d-axis voltage u id1 subtracting each other, and inputting the difference into an eighth proportional-integral controller, the output value of which is a reference value of the d-axis modulation voltage;

[0054] 4) The reference value u of the q-axis voltage in the three-phase inverter circuit 1 is iq1 *The actual value of the q-axis voltage u iq1 subtracting each other, and inputting the difference into a ninth proportional-integral controller, the output value of which is a reference value of the q-axis modulation voltage;

[0055] 5) The filter capacitor current i C1a 、i C1b 、i C1c Multiply by the damping coefficient K to get the modulation voltage of the active damping part;

[0056] 6) The final modulation voltage u of the three-phase inverter circuit 1 im1a ,u im1b ,u im1c The second SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 1.

[0057] Another object of the present invention is to provide a control method for a three-phase inverter circuit 2 based on the medium voltage distribution network flexible interconnection switch topology structure, comprising the following steps:

[0058] (a) The three-phase voltage on the filter capacitor side of the three-phase inverter circuit 2 is subjected to PARK transformation to obtain the voltage in the two-phase synchronous rotating coordinate system;

[0059] (b) The actual value of the DC side voltage of the three-phase inverter circuit 2 is U DC The reference value U of the DC side voltage of the three-phase inverter circuit 2 DC * is subtracted, and the difference is input into the tenth proportional integral controller. The output value of the tenth proportional integral controller is the reference value u of the q-axis voltage in the three-phase inverter circuit 2. iq2 *;

[0060] (c) The reference value u of the d-axis voltage in the three-phase inverter circuit 2 is id2 *The actual value of d-axis voltage u id2 Subtracting each other, the difference is input into the eleventh proportional-integral controller, and the output value of the eleventh proportional-integral controller is the reference value of the d-axis modulation voltage;

[0061] (d) The reference value u of the q-axis voltage in the three-phase inverter circuit 2 is iq2 *The actual value of the q-axis voltage u iq2 Subtracting them, the difference is input into a twelfth proportional-integral controller, and the output value of the twelfth proportional-integral controller is a reference value of the q-axis modulation voltage;

[0062] (e) The filter capacitor current i C2a 、i C2b 、i C2cMultiply by the damping coefficient K to get the modulation voltage of the active damping part;

[0063] (f) The final modulation voltage u of the three-phase inverter circuit 2 im2a ,u im2b ,u im2c , a third SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 2.

[0064] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0065] First, the present invention provides a flexible interconnected switch topology for a medium-voltage distribution network. This topology optimizes existing medium-voltage chain STATCOMs and introduces back-to-back three-phase converters at the ends of the medium-voltage chain STATCOMs of two feeders. These back-to-back three-phase converters enable the mutual assistance of active power flows between the two medium-voltage chain STATCOMs, i.e., between two different feeders. The reactive power between the two different feeders can be self-regulated by the medium-voltage chain STATCOMs of their respective feeders, without having to consider the decoupling of active and reactive power between interconnected feeders. This solution only requires topology optimization of the reactive compensation equipment of the existing medium-voltage distribution network to achieve the mutual assistance of active power flows between different feeders. This solution is low-cost, has a simple topology, is easy to control, and is readily applicable on a large scale.

[0066] The significant technological advancements brought about by the flexible interconnection switch control method for medium-voltage distribution networks proposed in this invention include:

[0067] 1) Fully utilizing the reactive power compensation equipment of the medium-voltage distribution network: This method optimizes the topology of the reactive power compensation equipment of the existing medium-voltage distribution network, so that the reactive power compensation equipment between the two feeders has partial active power mutual assistance capability.

[0068] 2) Improved efficiency: Compared with the back-to-back voltage source converter commonly used in existing medium-voltage distribution network flexible interconnection demonstration projects, this method has a simpler topology and fewer components.

[0069] 3) Improved system response speed: This method can quickly respond to grid changes through SRF-PLL and efficient Park transform and inverse transform algorithms.

[0070] 4) Improved stability of the device: This method can effectively stabilize the DC voltage of the chain STATCOM submodules through three-layer voltage balancing control of the DC voltage of the chain STATCOM submodules, thereby improving the stability of the device.

[0071] In summary, this control method not only fully utilizes the reactive compensation equipment of the medium-voltage distribution network, but also improves efficiency, increases the response speed of the system, and improves the stability of the device.

[0072] Second, the flexible interconnection switch topology for medium-voltage distribution networks provided by this invention includes multiple key components, such as a connecting reactor, a chain-type STATCOM, an isolation transformer, an LC filter, an inverter circuit, and a DC port. Through the rational configuration and interconnection of these components, flexible interconnection and power flow control in the medium-voltage distribution network are achieved.

[0073] The connecting reactor connects the grid's 10kV AC feeder to the chain-type STATCOM, forming a flexible bridge that facilitates power flow regulation and control. The chain-type STATCOM, consisting of cascaded H-bridge converters, monitors and controls the grid's current and voltage to adjust the power factor and compensate for reactive power.

[0074] The isolation transformer and LC filter are used to process the voltage and current of the power grid and ensure stable power transmission. The inverter circuit is responsible for converting the power of the DC port into AC power for use in the power grid.

[0075] In addition, the present invention also provides a control block diagram, which realizes accurate control of power factor and reactive power by performing PARK transformation on the current of the chain STATCOM and adjusting the control voltage.

[0076] Through this flexible interconnected switch topology structure of the medium-voltage distribution network, the present invention effectively solves the power flow control problem of the medium-voltage distribution network in the existing technology, realizes the flexible operation and stable power supply of the power system, and brings significant technological progress to the power field.

[0077] Third, as auxiliary evidence for the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0078] (1) The technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0079] The present invention provides a flexible interconnected switch topology for a medium-voltage distribution network. This topology optimizes existing medium-voltage chain STATCOMs and introduces back-to-back three-phase converters at the ends of the medium-voltage chain STATCOMs of two feeders. These back-to-back three-phase converters enable active power flow coordination between the two medium-voltage chain STATCOMs, i.e., between two different feeders. The reactive power between the two different feeders can be self-regulated by the medium-voltage chain STATCOMs of their respective feeders, without having to consider active and reactive power decoupling between interconnected feeders. This solution requires only topological optimization of the reactive power compensation equipment of the existing medium-voltage distribution network to achieve active power flow coordination between different feeders. It offers low cost, a simple topology, ease of control, and is readily applicable on a large scale, providing a novel solution for flexible interconnected switches.

[0080] (2) The technical solution of the present invention overcomes technical prejudice:

[0081] In existing demonstration projects for flexible interconnection of medium-voltage distribution networks, the commonly used back-to-back voltage source converters mainly include: two-level VSC back-to-back, three-level VSC back-to-back, and MMC back-to-back. These solutions have the disadvantages of high cost, bulky size, and difficulty in large-scale promotion and application. How to reduce the cost and size of flexible interconnection switches for medium-voltage distribution networks is a technical difficulty that needs to be solved for flexible interconnection switches for medium-voltage distribution networks. The present invention optimizes the topology of existing medium-voltage chain STATCOMs and introduces back-to-back three-phase converters at the ends of the medium-voltage chain STATCOMs of each of the two feeders. Through the back-to-back three-phase converters, the active power flow between the two medium-voltage chain STATCOMs, that is, the two different feeders, can be realized. The reactive power between the two different feeders can be self-regulated by the medium-voltage chain STATCOMs of each feeder, and there is no need to consider the active and reactive power decoupling issues between the interconnected feeders. In comparison, the present invention has a lower cost, a simpler topology, is easier to control, and is easier to promote and apply on a large scale, providing a new approach for flexible interconnection switches for medium-voltage distribution networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 This is a topological diagram of a flexible interconnection switch for a medium-voltage distribution network provided by an embodiment of the present invention;

[0083] Figure 2 This is a general control block diagram of the chain STATCOM1 provided by an embodiment of the present invention;

[0084] Figure 3 This is a block diagram of the global voltage-sharing control of the chained STATCOM1 submodule provided in an embodiment of the present invention;

[0085] Figure 4 This is a block diagram of the inter-phase voltage sharing control of the chained STATCOM1 submodule provided in an embodiment of the present invention;

[0086] Figure 5 This is a block diagram of the intra-phase voltage sharing control of the chained STATCOM1 submodule provided in an embodiment of the present invention;

[0087] Figure 6 This is an overall control block diagram of a three-phase inverter circuit 1 provided in an embodiment of the present invention;

[0088] Figure 7 This is an overall control block diagram of a three-phase inverter circuit 2 provided in an embodiment of the present invention;

[0089] Figure 8 This is a grid-connected current waveform diagram of a chained STATCOM1 provided in an embodiment of the present invention;

[0090] Figure 9 1 is a total DC side voltage waveform diagram of each phase submodule of the chained STATCOM1 provided in an embodiment of the present invention;

[0091] Figure 10 : is a waveform diagram of active power transmitted by the three-phase inverter circuit 1 provided in an embodiment of the present invention;

[0092] Figure 11 This is a grid-connected current waveform diagram of a chained STATCOM2 provided in an embodiment of the present invention;

[0093] Figure 12 This is a waveform diagram of the total DC side voltage of each phase submodule of the chained STATCOM2 provided in an embodiment of the present invention;

[0094] Figure 13 1 is a DC side voltage waveform diagram of a three-phase inverter circuit 2 provided in an embodiment of the present invention;

[0095] Figure 14 This is a flow chart of a control method for a three-phase inverter circuit 1 based on the medium-voltage distribution network flexible interconnected switch topology structure provided by an embodiment of the present invention;

[0096] In the figure: 1. 10kV AC feeder 1 of the power grid; 2. Chain STATCOM 1; 3. Three-phase isolation transformer 1; 4. Three-phase LC filter 1; 5. Three-phase inverter circuit 1; 6. DC capacitor CDC; 7. Three-phase inverter circuit 2; 8. Three-phase LC filter 2; 9. Three-phase isolation transformer 2; 10. Chain STATCOM 2; 11. 10kV AC feeder 2 of the power grid. DETAILED DESCRIPTION

[0097] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0098] like Figure 1 As shown, the medium voltage distribution network flexible interconnection switch topology provided by the embodiment of the present invention includes: three connected reactors L1, three connected reactors L3, two chain STATCOMs, two three-phase isolation transformers, two three-phase LC filters, two three-phase inverter circuits and a DC port U DC ;

[0099] One end of the reactor L1 is connected to the 10kV AC feeder 1 of the power grid, and the other end is connected to the chain STATCOM 1; one end of the reactor L2 is connected to the 10kV AC feeder 2 of the power grid, and the other end is connected to the chain STATCOM 2;

[0100] The chain STATCOM1 includes three cascaded H-bridge converters H1N (N = A, B, C, representing the three phases A, B, and C); the cascaded H-bridge converter in the chain STATCOM1 includes n H-bridge submodules H1N1 to H1Nn, where n can be determined according to the actual design scheme; the H-bridge submodule includes a DC side capacitor C Hd And two bridge arms containing two IGBTs (a total of 4 IGBTs); in the cascaded H-bridge converter of each phase of the chain STATCOM1, one end of the AC side of H1N1 is connected to the 10kV AC feeder 1 of the grid through the connecting inductor L1, and the other end is connected to the AC side of H1N2; one end of the AC side of H1N2 is connected to the AC side of H1N1, and the other end is connected to the AC side of H1N3. Similarly, H1N3~H1N n-1 Connection method: H1N n The AC side of the H1N n-1 The other side is connected to the three-phase isolation transformer 1;

[0101] The chain STATCOM2 includes three cascaded H-bridge converters H2N (N = A, B, C, representing the three phases A, B, and C); the cascaded H-bridge converter in the chain STATCOM2 includes n H-bridge submodules H2N1 to H2Nn, where n can be determined according to the actual design scheme; in the cascaded H-bridge converter of each phase of the chain STATCOM2, one end of the AC side of H2N1 is connected to the 10kV AC feeder 2 of the power grid through the connecting inductor L2, and the other end is connected to the AC side of H2N2; one end of the AC side of H2N2 is connected to the AC side of H2N1, and the other end is connected to the AC side of H2N3. Similarly, H2N3 to H2Nn n-1 Connection method: H2N n One end of the AC side is connected to H2N n-1 The other side is connected to the three-phase isolation transformer 2;

[0102] A three-phase isolation transformer 1, one end of which is connected to the chain STATCOM 1, and the other end of which is connected to the three-phase LC filter 1; a three-phase isolation transformer 2, one end of which is connected to the chain STATCOM 2, and the other end of which is connected to the three-phase LC filter 2;

[0103] A three-phase LC filter 1, one end of which is connected to a three-phase isolation transformer 1, and the other end of which is connected to a three-phase inverter circuit 1; a three-phase LC filter 2, one end of which is connected to a three-phase isolation transformer 2, and the other end of which is connected to a three-phase inverter circuit 2;

[0104] The three-phase inverter circuit 1 includes six IGBT switches (Q1 to Q6). The switches Q1 and Q2 form a bridge arm of phase A. The source of Q1 is connected to the drain of Q2, and the drain of Q1 is connected to the DC side U DC The positive electrode of Q2 is connected to the DC side U DC The switch tubes Q3 and Q4 form the B-phase bridge arm, the source of Q3 is connected to the drain of Q4, and the drain of Q3 is connected to the DC side U DC The positive electrode of Q4 is connected to the DC side U DC The negative electrode of the switch tube Q5 and Q6 form the C phase bridge arm, the source of Q5 is connected to the drain of Q6, and the DC side of the drain of Q5 is U DC The positive electrode of Q6 is connected to the DC side U DC The negative pole is connected;

[0105] The three-phase inverter circuit 2 includes six IGBT switches (Q7 to Q 12 ); The switch tubes Q7 and Q8 form the A-phase bridge arm, the source of Q7 is connected to the drain of Q8, and the drain of Q7 is connected to the DC side U DC The positive electrode of Q8 is connected to the DC side U DC The negative pole of the switch tube Q9 is connected to Q 10 Forming the B phase bridge arm, the source of Q9 and Q 10 The drain of Q9 is connected to the DC side U DC The positive pole is connected to Q 10 The source and DC side U DC The negative pole of the switch tube Q 11 With Q 12 Forming the C phase bridge arm, Q 11 The source and Q 12 The drain of 11 The drain DC side U DC The positive pole is connected to Q 12 The source and DC side U DC The negative pole is connected;

[0106] The three-phase inverter circuit 1 and the three-phase inverter circuit 2 share the DC side U DC, forming a back-to-back three-phase converter structure, realizing the function of mutual assistance of active power flow between the grid 10kV AC feeder 1 and the grid 10kV AC feeder 2;

[0107] The medium voltage distribution network flexible interconnection switch can increase the number of interconnected feeders by increasing the number of chain STATCOMs and back-to-back three-phase converters;

[0108] In the main circuit topology, the three-phase voltage of the 10kV AC feeder 1 of the power grid is: sa1 、u sb1 、u sc1 , the three-phase current is: i sa1 、i sb1 、i sc1 ; The three-phase voltage on the filter capacitor side of the three-phase inverter circuit 1 is: u ia1 、u ib1 、u ic1 The three-phase current of the three-phase inverter circuit 1 current filter capacitor is: i C1a 、i C1b 、i C1c ; The DC side capacitor voltage of the three-phase inverter circuit is U DC ; The three-phase voltage of the 10kV AC feeder 2 of the power grid is: u sa2 、u sb2 、u sc2 , the three-phase current is: i sa2 、i sb2 、i sc2 ; The three-phase voltage on the filter capacitor side of the three-phase inverter circuit 2 is: u ia2 、u ib2 、u ic2 The three-phase current of the filter capacitor in the three-phase inverter circuit is: C2a 、i C2b 、i C2c .

[0109] When the medium-voltage distribution network flexible interconnected switch topology structure provided by the embodiment of the present invention is in operation, two chain STATCOM devices on two different feeders are used to compensate for the reactive power of their respective feeders. The two chain STATCOMs are connected by a back-to-back three-phase converter, and the back-to-back three-phase converter is used to realize the mutual assistance of the active power flow between the two chain STATCOMs, that is, the two feeders.

[0110] Figure 2 The overall control block diagram of the chain STATCOM1 provided by the present invention includes the following steps:

[0111] The three-phase current i of the chain STATCOM1 sa1 、i sb1 、i sc1Perform PARK transformation to obtain the current i in the two-phase synchronous rotating coordinate system sd1 、i sq1 ;

[0112] The d-axis current reference value i of the chain STATCOM1 is sd1 * Actual value of d-axis current i of chained STATCOM1 sd1 Subtract, and the difference is input into the first proportional integral controller, the actual value of the q-axis current i of the chain STATCOM1 sq1 The product of the angular velocity ω1 and the connected reactor L1 minus the output of the first proportional integral controller, plus the d-axis voltage value u of the 10kV AC feeder 1 of the power grid sd1 , get the reference value of d-axis modulation voltage; set the q-axis current reference value i of chain STATCOM1 sq1 *The actual value of the q-axis current i of the chain STATCOM1 sq1 Subtract, and the difference is input into the second proportional integral controller, the q-axis voltage value u of the 10kV AC feeder 1 of the power grid sq1 Subtract the actual value of the d-axis current i of the chain STATCOM1 sd1 The product of the angular velocity ω1 and the connected reactor L1 is subtracted from the output of the second proportional-integral controller to obtain the reference value of the q-axis modulation voltage;

[0113] Modulation voltage u of current control output in chain STATCOM1 a1 ,u b1 ,u c1 The modulation voltage u superimposed on the phase-to-phase voltage control Ba1 、u Bb1 、u Bc1 and the reactive power vector u output by the phase voltage balancing control Ca1 、u Cb1 、u Cc1 Add together to get the final modulation voltage u of the chain STATCOM1 ma1 ,u mb1 ,u mc1 , through the first SPWM controller, a PWM wave is generated by carrier phase shift modulation to control the IGBT switch tube of each phase and each sub-module in the chain STATCOM1.

[0114] The flexible interconnected switching topology for medium-voltage distribution networks provided by the present invention primarily operates based on a chained STATCOM (static var compensator) and back-to-back three-phase converters to achieve active power flow coordination and reactive power compensation between power grids. The following is a detailed explanation of its operating principle:

[0115] 1. System composition

[0116] Chain STATCOM: It consists of multiple cascaded H-bridge converters. Each H-bridge converter contains an H-bridge sub-module, which contains a DC side capacitor and two bridge arms containing two IGBTs.

[0117] Back-to-back three-phase converter: It consists of two three-phase inverter circuits, sharing a DC side UDC to achieve active power exchange between the two feeders.

[0118] Other components: including connection reactors, three-phase isolation transformers, three-phase LC filters, etc., used for connection to the power grid, isolation and filtering.

[0119] 2. Working Principle

[0120] 2.1 Working Principle of Chain STATCOM

[0121] Reactive power compensation: The chain STATCOM dynamically compensates for the reactive power required by the system by controlling its output current so that its phase difference with the system voltage is 90 degrees.

[0122] Current control: The three-phase current of the chained STATCOM is transformed by PARK to obtain the current in a two-phase synchronous rotating coordinate system. The d-axis and q-axis currents are adjusted by PI (proportional-integral) controllers to achieve precise current control.

[0123] Voltage modulation: The final modulated voltage is obtained based on the modulated voltage output by the current control and the modulated voltage output by the voltage-sharing control. A PWM wave is generated by the SPWM (sine pulse width modulation) controller to control the IGBT switches in the H-bridge submodule to achieve voltage modulation.

[0124] 2.2 Working principle of back-to-back three-phase converter

[0125] Active power exchange: Two three-phase inverter circuits are used to exchange active power between the two feeders. The power flow between the two feeders is regulated by controlling the on / off state of the IGBT switches.

[0126] DC-side voltage control: Since two three-phase inverter circuits share a single DC-side UDC, it is necessary to maintain the stability of the UDC. The DC-side voltage is regulated by controlling the IGBT switches in the inverter circuit.

[0127] 2.3 System Operation

[0128] When the system is operating, the two chain-type STATCOMs each provide reactive power compensation for its respective feeder. Simultaneously, active power is exchanged between the two feeders via back-to-back three-phase converters. This enables flexible interconnection between power grids, improving their stability and flexibility.

[0129] 3. Scalability

[0130] * By increasing the number of chained STATCOMs and back-to-back three-phase converters, the number of interconnected feeders can be expanded, further improving the flexibility and reliability of the system.

[0131] In summary, the flexible interconnection switch topology structure of the medium-voltage distribution network provided by the embodiment of the present invention realizes flexible interconnection between power grids and flexible power exchange through the combination of chain STATCOM and back-to-back three-phase converters, providing an effective means for the stable operation and optimization of the distribution network.

[0132] Figure 3 The global voltage-sharing control block diagram of the chained STATCOM1 submodule provided by the present invention includes the following steps:

[0133] Sum the DC side voltages of all submodules in each phase of the chain STATCOM1 to obtain the total DC side voltage of the three-phase submodule U A1-HdΣ , U B1-HdΣ , U C1-HdΣ , sum up the three-phase total submodule DC side voltage and divide it by 1 / 3n to get the average value of all submodule DC side voltage U Hd1 ;

[0134] The reference value of the DC side voltage of all submodules, that is, the voltage reference value U of the global voltage balancing control Hd1 * The voltage reference value U of the global voltage balancing control can be determined according to the actual design of the chain STATCOM. Hd1 * Subtract the actual value U Hd1 The difference is input into the third proportional integral controller, and the output is the d-axis current reference value i of the chain STATCOM1. sd1 *.

[0135] Figure 4 The block diagram of the interphase voltage sharing control of the chained STATCOM1 submodule provided by the present invention includes the following steps:

[0136] The total three-phase submodule DC side voltage U A1-HdΣ , U B1-HdΣ , U C1-HdΣ , divided by the number of submodules per phase n to obtain the average DC side voltage of each phase submodule U A1-Hd , U B1-Hd , U C1-Hd , reference value U for phase-to-phase voltage control Hd2 *=(U A1-Hd +U B1-Hd +U C1-Hd ) / 3;

[0137] Will U Hd2 *Respectively with the average value of DC side voltage of each phase submodule UA1-Hd , U B1-Hd , U C1-Hd The difference is input into the fourth proportional integral controller. sd1 The three-phase difference is subtracted from the output value of the fourth proportional-integral controller of each phase, and the difference is input into the fifth proportional-integral controller. The output value of the fifth proportional-integral controller is respectively added to cosω1t, cos(ω1t-2π / 3), and cos(ω1t+2π / 3) to obtain the modulation voltage that needs to be superimposed on each phase, redistribute the active power between phases, and realize the phase-to-phase voltage balance of the neutron module in the chain STATCOM1;

[0138] Figure 5 The present invention provides a block diagram of the intra-phase voltage sharing control of the chained STATCOM1 submodule, which includes the following steps:

[0139] The reference values ​​for the three-phase intra-phase voltage balancing control are the average value of the DC side voltage of the three-phase submodules U A1-Hd , U B1-Hd , U C1-Hd , will U A1-Hd , U B1-Hd , U C1-Hd The DC link voltage U of each submodule per phase of the chained STATCOM1 A1-Hdx , U B1-Hdx , U C1-Hdx Subtract the difference, and input the sixth proportional-integral controller. The output of the sixth proportional-integral controller is multiplied by sinω1t, sin(ω1t-2π / 3), and sin(ω1t+2π / 3) respectively to obtain the reactive vector that needs to be superimposed on the modulated voltage of each sub-module of each phase in the chain STATCOM1, redistribute the active power within the phase, and achieve voltage balance within the sub-module phase of the chain STATCOM1;

[0140] Figure 6 This is the overall control block diagram of the three-phase inverter circuit 1 provided by the present invention, which includes the following steps:

[0141] Three-phase voltage u on the filter capacitor side of three-phase inverter circuit 1 ia1 、u ib1 、u ic1 Perform PARK transformation to obtain the voltage u in the two-phase synchronous rotating coordinate system id1 、u iq1 The reference value P1* of the active power transmitted by the three-phase inverter circuit 1 is subtracted from the actual value P1 of the active power transmitted by the three-phase inverter circuit 1, and the difference is input to the seventh proportional integral controller. The output value of the seventh proportional integral controller is the reference value u of the q-axis voltage in the three-phase inverter circuit 1. iq1 *;

[0142] Reference value u of d-axis voltage in three-phase inverter circuit 1 id1 *The actual value of d-axis voltage u id1 The difference is input into the eighth proportional integral controller, and the output value of the eighth proportional integral controller is the reference value of the d-axis modulation voltage; the reference value u of the q-axis voltage in the three-phase inverter circuit 1 is iq1 *The actual value of the q-axis voltage u iq1 Subtract the difference, and input the ninth proportional integral controller. The output value of the ninth proportional integral controller is the reference value of the q-axis modulation voltage. C1a 、i C1b 、i C1c Multiply by the damping coefficient K to get the modulation voltage of the active damping part;

[0143] Modulation voltage u of three-phase inverter circuit 1 voltage control im1a1 ,u im1b1 ,u im1c1 , respectively added to the modulation voltage of the active damping part to obtain the final modulation voltage u of the three-phase inverter circuit 1 im1a ,u im1b ,u im1c The second SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 1.

[0144] Figure 7 This is the overall control block diagram of the three-phase inverter circuit 2 provided by the present invention, which includes the following steps:

[0145] Three-phase voltage u on the filter capacitor side of three-phase inverter circuit 2 ia12 、u ib2 、u ic2 Perform PARK transformation to obtain the voltage u in the two-phase synchronous rotating coordinate system id2 、u iq2 ; Actual value of DC side voltage of three-phase inverter circuit 2 U DC The reference value U of the DC side voltage of the three-phase inverter circuit 2 DC * is subtracted, and the difference is input into the tenth proportional integral controller. The output value of the tenth proportional integral controller is the reference value u of the q-axis voltage in the three-phase inverter circuit 2. iq2 *;

[0146] Reference value u of d-axis voltage in three-phase inverter circuit 2 id2 *The actual value of d-axis voltage u id2 The difference is input into the eleventh proportional integral controller, and the output value of the eleventh proportional integral controller is the reference value of the d-axis modulation voltage; the reference value u of the q-axis voltage in the three-phase inverter circuit 2 is iq2 *The actual value of the q-axis voltage u iq2Subtract, and the difference is input into the twelfth proportional integral controller, the output value of the twelfth proportional integral controller is the reference value of the q-axis modulation voltage; the filter capacitor current i C2a 、i C2b 、i C2c Multiply by the damping coefficient K to get the modulation voltage of the active damping part;

[0147] Modulation voltage u of three-phase inverter circuit 2 voltage control im2a2 ,u im2b2 ,u im2c2 , respectively added to the modulation voltage of the active damping part to obtain the final modulation voltage u of the three-phase inverter circuit 2 im2a ,u im2b ,u im2c , a third SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 2.

[0148] The present invention builds a simulation model of a flexible interconnection switch for a medium-voltage distribution network on a MATLAB / Simulink simulation experimental platform. The frequency of the 10kV AC feeder 1 of the power grid is 50Hz, and the initial phase of phase A is 0; the connected inductor L1 = 13mH; the chain STATCOM 1 uses 12 H-bridge submodules per phase, the switching frequency of each submodule is 500Hz, the DC voltage reference value of the submodule capacitor is 800V, the submodule capacitor is 5.6mF, and the rated capacity of the chain STATCOM 1 is ±1Mvar; the rated capacity of the three-phase isolation transformer 1 is 38kVA, the frequency is 50HZ, and the turns ratio is 1:1; the filter inductor L2 of the three-phase LC filter 1 is 1.73mH, and the filter capacitor C1 is 76.7μF; the switching frequency of the three-phase inverter circuit 1 is 12.8kHz, and the active power transmitted by the three-phase inverter circuit 1 is set to 30kW; the three-phase inverter The DC side capacitance of the circuit is 10mF, and the DC side capacitance reference value is 800V; the frequency of the 10kV AC feeder 2 of the power grid is 50Hz, and the initial phase of phase A is 0; the connected inductor L3 = 13mH; the chain STATCOM2 uses 12 H-bridge submodules per phase, each submodule switching frequency is 500Hz, the submodule capacitor DC voltage reference value is 800V, the submodule capacitance is 5.6mF, and the rated capacity of the chain STATCOM2 is ±1Mvar; the three-phase isolation transformer 2 has a rated capacity of 38kVA, a frequency of 50HZ, and a turns ratio of 1:1; the filter inductor L4 of the three-phase LC filter 2 is 1.73mH, and the filter capacitor C2 is 76.7μF; the switching frequency of the three-phase inverter circuit 2 is 12.8kHz. The simulation results are as follows Figures 8 to 13 shown.

[0149] Figure 8This is a grid-connected current waveform of the chain-type STATCOM1 in the medium-voltage distribution network flexible interconnection switch device provided by an embodiment of the present invention. At this time, the reactive current is about 81A. The chain-type STATCOM1 operates at a rated capacity of 1Mvar. The reactive current has good sinusoidality and the current THD is 0.62%.

[0150] Figure 9 This is a waveform diagram of the total DC side voltage of each phase submodule of the chain STATCOM1 provided by an embodiment of the present invention. It can be seen that the total DC side voltage of each phase submodule of the chain STATCOM1 can be maintained at about 800*12=9600V, and the phase voltage is balanced;

[0151] Figure 10 This is the active power waveform transmitted by the three-phase inverter circuit 1 provided in the embodiment of the present invention. It can be seen that the active power transmitted by the three-phase inverter circuit 1 is basically maintained at a set value of about 30kW.

[0152] Figure 11 This is a grid-connected current waveform of the chain-type STATCOM2 in the medium-voltage distribution network flexible interconnection switch device provided by an embodiment of the present invention. At this time, the reactive current is about 81A. The chain-type STATCOM2 operates at a rated capacity of 1Mvar. The reactive current has good sinusoidality and the current THD is 0.73%.

[0153] Figure 12 This is a waveform diagram of the total DC side voltage of each phase submodule of the chained STATCOM2 provided by an embodiment of the present invention. It can be seen that the total DC side voltage of each phase submodule of the chained STATCOM2 can be maintained at about 9600V, and the phase voltage is balanced;

[0154] Figure 13 2 is a DC side voltage waveform of the three-phase inverter circuit 2 provided by an embodiment of the present invention. It can be seen that the DC side voltage of the three-phase inverter circuit 2 is basically maintained at a set value of about 800V.

[0155] The present invention provides a medium voltage distribution network flexible interconnection switch topology structure and control method, comprising: three connected reactors L1, three connected reactors L3, two chain STATCOMs, two three-phase isolation transformers, two three-phase LC filters, two three-phase inverter circuits and a DC port;

[0156] Another object of the present invention is to provide a control method of a chain STATCOM1 based on the medium voltage distribution network flexible interconnection switch topology structure, comprising the following steps:

[0157] (1) The phase information ω1t of the 10 kV AC feeder 1 of the power grid is obtained by SRF-PLL; the voltage and current of the 10 kV AC feeder 1 of the power grid are transformed by PARK, and the voltage and current of the two-phase synchronous rotating coordinate system are obtained;

[0158] (2) Sum the DC side voltages of the three-phase submodules in the chain STATCOM1 and divide it by 1 / 3n to obtain the average DC side voltage of all submodules U Hd1 ; Set the voltage reference value U of the global voltage control Hd1 * Subtract the actual value U Hd1 The difference is input into the third proportional integral controller, and the output is the d-axis current reference value i sd1 *;

[0159] (3) Set the reference value U of the phase-to-phase voltage control Hd2 *The average value of the DC side voltage of each phase sub-module is subtracted respectively, and the difference is input into the fourth proportional integral controller; the d-axis current of the chain STATCOM1 is subtracted from the output value of the fourth proportional integral controller of each phase, and the difference of the three phases is input into the fifth proportional integral controller. The output value of the fifth proportional integral controller is respectively added to cosω1t, cos(ω1t-2π / 3), and cos(ω1t+2π / 3) to obtain the modulation voltage that needs to be superimposed on each phase, redistribute the active power between phases, and realize the phase-to-phase voltage balance of the neutron module in the chain STATCOM1;

[0160] (4) Subtract the reference value of the three-phase intra-phase voltage balancing control from the DC side voltage of each submodule of each phase of the chain STATCOM1, and input the difference into the sixth proportional integral controller. The output of the sixth proportional integral controller is multiplied by sinω1t, sin(ω1t-2π / 3), and sin(ω1t+2π / 3) respectively to obtain the reactive vector that needs to be superimposed on the modulation voltage of each submodule of each phase in the chain STATCOM1, redistribute the intra-phase active power, and realize the intra-phase voltage balance of the submodules in the chain STATCOM1;

[0161] (5) The d-axis current reference value i of the chain STATCOM1 is sd1 * Actual value of d-axis current i of chained STATCOM1 sd1 Subtract the difference, input the first proportional integral controller, and after current decoupling control and grid voltage feedforward, obtain the reference value of the d-axis modulation voltage; the q-axis current reference value i of the chain STATCOM1 is sq1 *The actual value of the q-axis current i of the chain STATCOM1 sq1 Subtract the difference, and input it into the second proportional-integral controller. After current decoupling control and grid voltage feedforward, the reference value of the q-axis modulation voltage is obtained.

[0162] (6) The final modulation voltage u of the chain STATCOM1 ma1 ,u mb1 ,u mc1, through the first SPWM controller, a PWM wave is generated by carrier phase shift modulation to control the IGBT switch tube of each phase and each sub-module in the chain STATCOM1.

[0163] like Figure 14 As shown, another object of the present invention is to provide a control method for a three-phase inverter circuit 1 based on the medium voltage distribution network flexible interconnection switch topology structure, comprising the following steps:

[0164] S101, performing PARK transformation on the three-phase voltage on the filter capacitor side of the three-phase inverter circuit 1 to obtain the voltage in a two-phase synchronous rotating coordinate system;

[0165] S102, subtract the reference value of the active power transmitted by the three-phase inverter circuit 1 from the actual value of the active power transmitted by the three-phase inverter circuit 1, and input the difference into the seventh proportional integral controller, and output the reference value u of the q-axis voltage in the three-phase inverter circuit 1 iq1 *;

[0166] S103, the reference value u of the d-axis voltage in the three-phase inverter circuit 1 is id1 *The actual value of d-axis voltage u id1 subtracting each other, and inputting the difference into an eighth proportional-integral controller, the output value of which is a reference value of the d-axis modulation voltage;

[0167] S104, the reference value u of the q-axis voltage in the three-phase inverter circuit 1 is iq1 *The actual value of the q-axis voltage u iq1 subtracting each other, and inputting the difference into a ninth proportional-integral controller, the output value of which is a reference value of the q-axis modulation voltage;

[0168] S105, the filter capacitor current i C1a 、i C1b 、i C1c Multiply by the damping coefficient K to get the modulation voltage of the active damping part;

[0169] S106, the final modulation voltage u of the three-phase inverter circuit 1 im1a ,u im1b ,u im1c The second SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 1.

[0170] Another object of the present invention is to provide a control method for a three-phase inverter circuit 2 based on the medium voltage distribution network flexible interconnection switch topology structure, comprising the following steps:

[0171] (a) The three-phase voltage on the filter capacitor side of the three-phase inverter circuit 2 is subjected to PARK transformation to obtain the voltage in the two-phase synchronous rotating coordinate system;

[0172] (b) The actual value of the DC side voltage of the three-phase inverter circuit 2 is U DC The reference value U of the DC side voltage of the three-phase inverter circuit 2 DC * is subtracted, and the difference is input into the tenth proportional integral controller. The output value of the tenth proportional integral controller is the reference value u of the q-axis voltage in the three-phase inverter circuit 2. iq2 *;

[0173] (c) The reference value u of the d-axis voltage in the three-phase inverter circuit 2 is id2 *The actual value of d-axis voltage u id2 Subtracting each other, the difference is input into the eleventh proportional-integral controller, and the output value of the eleventh proportional-integral controller is the reference value of the d-axis modulation voltage;

[0174] (d) The reference value u of the q-axis voltage in the three-phase inverter circuit 2 is iq2 *The actual value of the q-axis voltage u iq2 Subtracting them, the difference is input into a twelfth proportional-integral controller, and the output value of the twelfth proportional-integral controller is a reference value of the q-axis modulation voltage;

[0175] (e) The filter capacitor current i C2a 、i C2b 、i C2c Multiply by the damping coefficient K to get the modulation voltage of the active damping part;

[0176] (f) The final modulation voltage u of the three-phase inverter circuit 2 im2a ,u im2b ,u im2c , a third SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 2.

[0177] The present invention uses two chain STATCOM devices on two different feeders to compensate for the reactive power of their respective feeders. The two chain STATCOMs are connected by a back-to-back three-phase converter, and the back-to-back three-phase converter realizes the mutual assistance of the active power flow between the two feeders.

[0178] Existing demonstration projects for flexible interconnection of medium-voltage distribution networks generally employ full-power back-to-back voltage source converters, with back-to-back MMCs being a typical example. Furthermore, medium-voltage distribution networks are often equipped with reactive power compensation equipment such as STATCOMs. The integration of a large number of power electronic devices increases the size and cost of medium-voltage distribution network construction.

[0179] The present invention optimizes the topology of the existing medium-voltage chain STATCOM and introduces back-to-back three-phase converters at the ends of the medium-voltage chain STATCOMs of the two feeders. Through the back-to-back three-phase converters, the two medium-voltage chain STATCOMs, that is, the active power flow mutual assistance between the two different feeders can be achieved. The reactive power between the two different feeders can be self-regulated by the medium-voltage chain STATCOMs of the respective feeders, and there is no need to consider the active and reactive power decoupling problem between the interconnected feeders.

[0180] Compared with the current solution that requires medium-voltage distribution networks to be equipped with two sets of devices, namely flexible interconnection switches and reactive power compensation equipment, the present invention uses a single set of equipment to achieve reactive power compensation of feeders and flexible interconnection between feeders. It has lower costs, smaller required volume, simpler topology, easier control, and is easy to promote and apply on a large scale, providing a new idea for flexible interconnection switches in medium-voltage distribution networks.

[0181] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A medium voltage distribution network flexible interconnection switch topology structure, characterized in that: include: three connected reactors L1, three connected reactors L3, a chain STATCOM1, a chain STATCOM2, a three-phase isolation transformer 1, a three-phase isolation transformer 2, a three-phase LC filter 1, a three-phase LC filter 2, a three-phase inverter circuit 1, a three-phase inverter circuit 2, and a DC port; Three connected reactors L1 and three connected reactors L3 are used to suppress high-order harmonics and ensure the sinusoidal nature of the grid-connected current; A chain STATCOM1 and a chain STATCOM2 are used for reactive power compensation of a 10 kV AC feeder 1 and a 10 kV AC feeder 2 of the power grid; A three-phase isolation transformer 1 and a three-phase isolation transformer 2 are used for isolating a high-voltage side chain STATCOM 1 and a low-voltage side three-phase LC filter 1, and a high-voltage side chain STATCOM 2 and a low-voltage side three-phase LC filter 2; A three-phase LC filter 1 and a three-phase LC filter 2 are used to filter high-order harmonics of the three-phase inverter circuit 1 and the three-phase inverter circuit 2; A three-phase inverter circuit 1 and a three-phase inverter circuit 2 share a DC port, forming a back-to-back three-phase converter structure for mutual assistance of active power flow between a 10kV AC feeder 1 of the power grid and a 10kV AC feeder 2 of the power grid; A 10 kV AC feeder 1 of the power grid is connected to the head ends of three connected reactors L1, the ends of the three connected reactors L1 are connected to the head end of a chain STATCOM 1, the end of the chain STATCOM 1 is connected to the primary side of a three-phase isolation transformer 1, the secondary side of the three-phase isolation transformer 1 is connected to the head end of a three-phase LC filter 1, the end of the three-phase LC filter 1 is connected to the AC side of a three-phase inverter circuit 1, and the DC side of the three-phase inverter circuit 1 is connected to the DC side of a three-phase inverter circuit 2; The grid 10kV AC feeder 2 is connected to the head ends of three connected reactors L2, the ends of the three connected reactors L2 are connected to the head end of the chain STATCOM 2, the end of the chain STATCOM 2 is connected to the primary side of the three-phase isolation transformer 2, the secondary side of the three-phase isolation transformer 2 is connected to the head end of the three-phase LC filter 2, and the end of the three-phase LC filter 2 is connected to the AC side of the three-phase inverter circuit 2; The flexible interconnection switch of the medium-voltage distribution network increases the number of interconnected feeders by increasing the number of chained STATCOMs and back-to-back three-phase converters.

2. The medium voltage distribution network flexible interconnection switch topology structure according to claim 1, characterized in that: The chain STATCOM1 control unit comprises: The synchronous rotating phase-locked loop (SRF-PLL) controller has the AC voltage of the 10kV AC feeder 1 of the power grid as input and is used to calculate the real-time phase of the power grid. The output is connected to the first, second, and third Park controllers and the first, second, and third Anti-Park controllers. The first Park controller, whose input is the three-phase current of the chain STATCOM1 and the real-time phase output of the synchronous rotating phase-locked loop SRF-PLL controller, is used to obtain the current i in the two-phase synchronous rotating coordinate system. sd1 、i sq1 , the output is connected to the first and second proportional integral controllers; The first proportional integral controller, the input is the actual value of active current i sd1 and active current reference value i sd1 *, used to realize the control of the active current of the chain STATCOM1, and the output is connected to the first anti-Park controller; The second proportional integral controller, the input is the actual value of reactive current i sq1 and reactive current reference value i sq1 *, used to realize the control of reactive current of chain STATCOM1, and the output is connected to the first anti-Park controller; The third proportional integral controller, whose input is the average value U of the DC side voltage of all submodules in the chain STATCOM1 Hd1 And the voltage reference value U of the global voltage balancing control Hd1 *, used to realize the global voltage balancing control function of the DC voltage of the neutron module in the chain STATCOM1, and the output is the active current reference value i sd1 *; The first anti-Park controller, whose input is the output of the first proportional-integral controller, the second proportional-integral controller and the real-time phase of the synchronous rotating phase-locked loop SRF-PLL controller output, is used to obtain the modulation voltage u in the three-phase stationary coordinate system. a1 ,u b1 ,u c1 , the output is connected to the first SPWM controller; The fourth proportional integral controller, whose input is the average value of the DC side voltage of each phase submodule and the reference value U of the phase voltage control Hd2 *, used to realize part of the function of DC voltage phase-to-phase equalization control of the neutron module in the chain STATCOM1, and the output is connected to the fifth proportional-integral controller; The fifth proportional integral controller, whose input is the output of the fourth proportional integral controller and the actual value of active current i sd1 , used to realize part of the function of interphase equalization control of DC voltage of submodule in chain STATCOM1, and the output is connected to the first SPWM controller; a sixth proportional-integral controller, whose input is the DC side voltage of each submodule of each phase of the chained STATCOM1 and the reference value of the intra-phase voltage equalization control of the chained STATCOM1, and is used to implement the intra-phase DC voltage equalization control function of the submodules in the chained STATCOM1, and whose output is connected to the first SPWM controller; The first SPWM controller, whose input is the output of the first anti-Park controller, the output of the fifth proportional-integral controller and the output of the sixth proportional-integral controller, is used to generate a drive signal for each IGBT switch tube in each sub-module of each phase in the chain STATCOM1.

3. The medium voltage distribution network flexible interconnection switch topology structure according to claim 1, characterized in that: The three-phase inverter circuit 1 control unit includes: The second Park controller has the three-phase voltage u on the filter capacitor side of the three-phase inverter circuit 1 as input. ia1 、u ib1 、u ic1 The real-time phase of the synchronous rotating phase-locked loop SRF-PLL controller output is used to obtain the current u of the three-phase inverter circuit 1 in the two-phase synchronous rotating coordinate system. id1 、u iq1 , the output is connected to the eighth and ninth proportional integral controllers; The seventh proportional integral controller has the input of the actual value P1 of the active power transmitted by the three-phase inverter circuit 1 and the reference value P1* of the active power transmitted by the three-phase inverter circuit 1, which is used to realize the active power control function of the three-phase inverter circuit 1, and the output u iq1 *Access to the ninth proportional integral controller; The eighth proportional integral controller, the input is the reference value u of the d-axis voltage id1 * and the output u of the second Park controller id1 , used to realize the d-axis voltage control function of the three-phase inverter circuit 1, and the output is connected to the second anti-Park controller; The ninth proportional-integral controller, whose input is the output u of the seventh proportional-integral controller iq1 * and the output u of the second Park controller iq1 , used to realize the q-axis voltage control function of the three-phase inverter circuit 1, and the output is connected to the second anti-Park controller; The second anti-Park controller has the output of the eighth proportional-integral controller and the output of the ninth proportional-integral controller as input, and is used to obtain the modulation voltage of the three-phase inverter circuit 1 in the three-phase stationary coordinate system, and the output is connected to the second SPWM controller; The first active damping controller, the input is the filter capacitor current i C1a 、i C1b 、i C1c , used to realize active damping of the three-phase inverter circuit 1, and the output is connected to the second SPWM controller; The second SPWM controller, whose input is the output of the second anti-Park controller and the output of the first active damping controller, is used to generate driving signals for the six IGBT switch tubes in the three-phase inverter circuit 1.

4. The medium voltage distribution network flexible interconnection switch topology structure according to claim 1, characterized in that: The three-phase inverter circuit 2 control unit includes: The third Park controller, the input quantity is the three-phase voltage u on the filter capacitor side of the three-phase inverter circuit 2 ia2 、u ib2 、u ic2 The real-time phase of the synchronous rotating phase-locked loop SRF-PLL controller output is used to obtain the current u of the three-phase inverter circuit 2 in the two-phase synchronous rotating coordinate system. id2 、u iq2 , the output quantity is connected to the eleventh and twelfth proportional integral controllers; The tenth proportional integral controller, the input is the actual value U of the DC side voltage of the three-phase inverter circuit 2 DC The reference value U of the DC side voltage of the three-phase inverter circuit 2 DC *, used to realize the function of controlling the DC voltage constant of the three-phase inverter circuit 2, the output u iq2 *Access to the twelfth proportional integral controller; The eleventh proportional-integral controller, the input is the reference value u of the d-axis voltage id2 * and the output u of the third Park controller id2 , used to realize the d-axis voltage control function of the three-phase inverter circuit 2, and the output is connected to the third anti-Park controller; The twelfth proportional-integral controller, whose input is the output u of the tenth proportional-integral controller iq2 * and the output u of the third Park controller iq2 , used to realize the q-axis voltage control function of the three-phase inverter circuit 2, and the output is connected to the third anti-Park controller; The third anti-Park controller has the output of the eleventh proportional-integral controller and the output of the twelfth proportional-integral controller as input, and is used to obtain the modulation voltage of the three-phase inverter circuit 2 in the three-phase stationary coordinate system, and the output is connected to the third SPWM controller; The second active damping controller has the filter capacitor current i as input. C2a 、i C2b 、i C2c , used to realize active damping of the three-phase inverter circuit 2, and the output is connected to the third SPWM controller; The third SPWM controller, whose input is the output of the third anti-Park controller and the output of the second active damping controller, is used to generate driving signals for the six IGBT switches in the three-phase inverter circuit 2.

5. A control method for the chain STATCOM1 of the medium voltage distribution network flexible interconnection switch topology structure according to claim 1, characterized in that: The control method of the chain STATCOM1 includes the following steps: (1) The three-phase voltage of the 10kV AC feeder 1 of the power grid is passed through the SRF-PLL to obtain the phase information ω1t; the three-phase current of the chain STATCOM1 is passed through the first Park controller to obtain the current i in the two-phase synchronous rotating coordinate system sd1 、i sq1 ; (2) Sum the DC side voltages of the three-phase submodules in the chain STATCOM1 and multiply it by 1 / 3n to obtain the average value U of the DC side voltages of all submodules Hd1 ; Set the voltage reference value U of the global voltage control Hd1 * Subtract the actual value U Hd1 The difference is input into the third proportional integral controller, and the output is the d-axis current reference value i sd1 *; (3) Set the reference value U of the phase-to-phase voltage control Hd2 *The average value of the DC side voltage of each phase sub-module is subtracted respectively, and the difference is input into the fourth proportional integral controller; the d-axis current of the chain STATCOM1 is subtracted from the output value of the fourth proportional integral controller of each phase, and the difference of the three phases is input into the fifth proportional integral controller. The output value of the fifth proportional integral controller is respectively added to cosω1t, cos(ω1t-2π / 3), and cos(ω1t+2π / 3) to obtain the modulation voltage that needs to be superimposed on each phase, redistribute the active power between phases, and realize the phase-to-phase voltage balance of the neutron module in the chain STATCOM1; (4) Subtract the reference value of the three-phase intra-phase voltage balancing control from the DC side voltage of each submodule of each phase of the chain STATCOM1, and input the difference into the sixth proportional integral controller. The output of the sixth proportional integral controller is multiplied by sinω1t, sin(ω1t-2π / 3), and sin(ω1t+2π / 3) respectively to obtain the reactive vector that needs to be superimposed on the modulation voltage of each submodule of each phase in the chain STATCOM1, redistribute the intra-phase active power, and realize the intra-phase voltage balance of the submodules in the chain STATCOM1; (5) The d-axis current reference value i of the chain STATCOM1 is sd1 * Actual value of d-axis current i of chained STATCOM1 sd1 Subtract the difference, input the first proportional integral controller, and after current decoupling control and grid voltage feedforward, obtain the reference value of the d-axis modulation voltage; the q-axis current reference value i of the chain STATCOM1 is sq1 *The actual value of the q-axis current i of the chain STATCOM1 sq1 Subtract the difference, and input it into the second proportional-integral controller. After current decoupling control and grid voltage feedforward, the reference value of the q-axis modulation voltage is obtained. (6) The reference values ​​of the d-axis and q-axis modulation voltages of the chain STATCOM1 are input into the first anti-Park controller to obtain the modulation voltage u ma1 ,u mb1 ,u mc1 , through the first SPWM controller, a PWM wave is generated by carrier phase shift modulation to control the IGBT switch tube of each phase and each sub-module in the chain STATCOM1.

6. A control method for a three-phase inverter circuit 1 based on the medium voltage distribution network flexible interconnection switch topology structure according to claim 1, characterized in that: The control method of the three-phase inverter circuit 1 comprises the following steps: 1) The three-phase voltage on the filter capacitor side of the three-phase inverter circuit 1 passes through the second Park controller to obtain the voltage u in the two-phase synchronous rotating coordinate system id1 、u iq1 ; 2) Subtract the reference value of the active power transmitted by the three-phase inverter circuit 1 from the actual value of the active power transmitted by the three-phase inverter circuit 1, and input the difference into the seventh proportional integral controller, and output the reference value u of the q-axis voltage in the three-phase inverter circuit 1 iq1 *; 3) The reference value u of the d-axis voltage in the three-phase inverter circuit 1 is id1 *The actual value of d-axis voltage u id1 subtracting each other, and inputting the difference into an eighth proportional-integral controller, the output value of which is a reference value of the d-axis modulation voltage; 4) The reference value u of the q-axis voltage in the three-phase inverter circuit 1 is iq1 *The actual value of the q-axis voltage u iq1 subtracting each other, and inputting the difference into a ninth proportional-integral controller, the output value of which is a reference value of the q-axis modulation voltage; 5) The filter capacitor current i C1a 、i C1b 、i C1c inputting a first active damping controller to obtain a modulation voltage of the active damping part; 6) The reference values ​​of the d-axis and q-axis modulation voltages of the three-phase inverter circuit 1 are input into the second anti-Park controller to obtain the modulation voltage u im1a ,u im1b ,u im1c The second SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 1.

7. A control method for a three-phase inverter circuit 2 based on the medium voltage distribution network flexible interconnection switch topology structure according to claim 1, characterized in that: The control method of the three-phase inverter circuit 2 includes the following steps: (a) Input the three-phase voltage on the filter capacitor side of the three-phase inverter circuit 2 into the second Park controller to obtain the voltage u in the two-phase synchronous rotating coordinate system id2 、u iq2 ; (b) The actual value of the DC side voltage of the three-phase inverter circuit 2 is U DC The reference value U of the DC side voltage of the three-phase inverter circuit 2 DC * is subtracted, and the difference is input into the tenth proportional integral controller. The output value of the tenth proportional integral controller is the reference value u of the q-axis voltage in the three-phase inverter circuit 2. iq2 *; (c) The reference value u of the d-axis voltage in the three-phase inverter circuit 2 is id2 *The actual value of d-axis voltage u id2 Subtracting each other, the difference is input into the eleventh proportional-integral controller, and the output value of the eleventh proportional-integral controller is the reference value of the d-axis modulation voltage; (d) The reference value u of the q-axis voltage in the three-phase inverter circuit 2 is iq2 *The actual value of the q-axis voltage u iq2 Subtracting them, the difference is input into a twelfth proportional-integral controller, and the output value of the twelfth proportional-integral controller is a reference value of the q-axis modulation voltage; (e) The filter capacitor current i C2a 、i C2b 、i C2c inputting the second active damping controller to obtain a modulation voltage of the active damping part; (f) The reference values ​​of the d-axis and q-axis modulation voltages of the three-phase inverter circuit 2 are input into the third anti-Park controller to obtain the modulation voltage u im2a ,u im2b ,u im2c , a third SPWM controller generates a PWM wave to control the six IGBT switches in the three-phase inverter circuit 2.

Images