SINGLE-SIDED ISOLATION TRANSFORMER FLEXIBLE CONNECTION POINT SYSTEM FOR GROUNDED NEUTRAL LOW VOLTAGE DISTRIBUTION NETWORKS

Abstract

This invention relates to a soft open point (SOP) system for providing controlled power transfer between different feeders in grounded neutral low-voltage distribution networks. The system is located between distribution transformer - 1 (1) and distribution transformer - 2 (2) feeding two feeders and includes an I / O isolation transformer (3), LCL filter 1 (4), AC / DC converter (5), DC coupling capacitor-1 (6) and DC coupling capacitor-2 (7), DC / AC converter (8), LCL filter 2 (9), SSI controller 1 (10), SSI controller 2 (11), power analyzer 1 (12), power analyzer 2 (13) and central control unit (14) located on the first terminal side. The ε / Y isolation transformer (3) eliminates loop currents through ground by disconnecting the galvanic link between the neutral points of the two distribution transformers (1, 2). This makes it possible to use residual current devices safely in the system. Active and reactive power flow between feeders is controlled via the AC / DC converter (5) and DC / AC converter (8), while LCL filters (4, 9) filter out harmonic components and DC coupling capacitors (6, 7) provide energy buffering. Data measured by power analyzers (12, 13) are processed by the central control unit (14) to create a power transfer reference. The invention offers a safe, compact, and cost-effective SOP solution for grounded neutral low-voltage networks through the use of a single-sided isolation transformer, ensuring continuous and controlled power flow between feeders.

Description

1 TARIFF FOR GROUNDED NEUTRAL LOW VOLTAGE DISTRIBUTION NETWORKS SINGLE-SIDED ISOLATION TRANSFORMER FLEXIBLE CONNECTION POINT SYSTEM TECHNICAL FIELD This invention relates to the field of electrical energy distribution systems and power electronics. Furthermore... Specifically, the invention is applicable to low-voltage distribution networks with grounded neutrals, in different A 10-point system for ensuring controlled active and reactive power transfer between feeders. It is related to the soft open point (SOP) system. The invention relates to the interconnection of low-voltage feeders supplied by two separate distribution transformers. Based on the AC / DC / AC conversion principle, it enables controlled connection. power electronics converters, filter structures, control units and 15 on one side It is a system that includes a positioned isolation transformer. In this context, the invention relates to the operation of electricity distribution networks, load balancing, and power. flow control, reactive power compensation, grid safety, and galvanic isolation. It also includes sub-technical areas such as techniques. 20 STATE OF THE ART In traditional low-voltage distribution networks, a normally open circuit is used between two feeders. There is a Normally Open Point (NOP). At this point, there is a circuit breaker. Two networks can be connected via this method, but this direct connection does not provide power. It offers no control over the flow. The circuit breaker is either open or closed. It is in the closed position; controlled power transfer cannot be performed at intermediate values. (Figure 1). In the literature, flexible junction point (SOP) devices operate on the AC / DC / AC conversion principle. using a back-to-back voltage source converter topology This has offered a solution to this problem. However, current studies largely focus on medium voltage. 2 (OG) focused on applications, and the SOP device on both terminal sides A coupling transformer is installed. These transformers ensure both voltage level matching. It provides both thermal insulation and galvanic isolation (Figure 2). Although some transformerless SOP solutions have been proposed at the low voltage level, these 5 The solutions are designed for systems where the neutral point is not grounded. Türkiye and In low-voltage distribution systems in many European countries, the distribution transformer neutral It is grounded at this point. The network, which has two grounded neutrals, is used for power electronics. when connected to each other via a converter without galvanic isolation, 10 through ground both mains frequency (50 Hz) and switching source. High-frequency loop currents are generated. These loop currents have low impedance. It can reach high values ​​and residual current devices are a true ground. It disables the system by triggering it without any leakage. This is the AG SOP. integrating residual current protection into the devices and thus ensuring the safety of the system. This makes its operation impossible. 15 The technical framework outlined above is also supported by patent documents. For example... CN112202173A – “Medium-voltage bus flexible interconnection power distribution In the "network system" document, it is stated that two medium-voltage busbars operate in reverse parallel. The converter structure and the use of phase-shifting transformers on both sides are clearly evident in 20 This document describes the SOP / flexible interconnection approach, particularly in the context of the medium. This shows that it is designed with a voltage level and transformer architecture. The same The document describes power modules with phase-shifted transformers on both sides of the converter. It is stated that it is powered. Therefore, the solution in question is a grounded neutral LV. 25 directly relevant in terms of cost, volume and protection coordination in networks It does not offer any instruction. Similarly, CN113783197A – “Power distribution network flexible In the document "interconnection device and control method thereof", traditional AC / DC bidirectional converter and mechanical 30 on an interconnection switch structure. Controlled power between bus or feeder is achieved by integrating an interconnection switch. It is explained that the flow was ensured. The document states that the mechanical switch was initially... it is normally kept open and power flows through the converter during normal operation. 3 It shows that control has been carried out. However, this patent is more about the network. It focuses on business topology and interconnection logic, two separate from connecting a grounded neutral low-voltage network without galvanic isolation the effect of generated ground loop currents and their coordination with residual current relays It does not offer a specific solution in terms of its impact. 5 For the control layer, CN110148954B – “A SOP-Based Distribution The "Network Control Method" document specifies the DC bus for converters on the SOP side. voltage control, active / reactive current targets, DQ / ABC conversions, and load. It describes control principles such as compensating for imbalances. This document, 10 SOP demonstrates its ability to precisely manage active and reactive power flow. This is important in terms of its scope. However, the document is essentially about the control method; in LV systems directly galvanically connected between grounded neutrals physical solution to eliminate the resulting 50 Hz and high frequency loop currents It does not offer instruction on topology. In other words, power flow control 15 While it is being taught, a safe low-voltage connection architecture compatible with RCDs is not being taught. In terms of low-voltage solutions, CN112350311A – “Multipurpose flexible interconnection device suitable for common zero line low-voltage power The "distribution system" is noteworthy. In this document, 20 systems sharing a common DC bus are described. between numerous single-phase converters and common neutral low-voltage systems Flexible connectivity is anticipated; additionally, there is a lot of information available in the background of the document. Most ported devices are suitable for three-phase symmetrical LV systems. This is stated. However, the same document describes its structure as a shared DC bus and It is defined via reactors; clearly with a one-way isolation transformer 25 A safety mechanism based on breaking the galvanic connection between two grounded neutrals. It does not teach architecture. Therefore, this solution is for common neutral LV systems. While important in this context, the physical aspect of loop current flowing through the ground... the circuit is cut off and the associated residual current protection devices are safely installed at both ends. This does not completely solve the problem of usability. 30 Moreover, CN117240062A – “A common-mode circulating current suppression “method for flexible interconnection devices in low-voltage distribution networks” 4 document, common-mode leakage current in transformerless LV flexible connection devices and explicitly acknowledges the existence of the common-mode circulating current problem. The document states that transformerless isolation structures can be more efficient and compact. However, these structures have a common mode leakage current problem; and as a solution... Suppression of the common mode voltage spectrum with SVPWM-based control 5 This document suggests addressing the technical aspects of the problem indicated in your user text. This confirms its reality. However, the solution proposed here does not control the problem. The strategy is to reduce; galvanic between two grounded neutral networks Describe a topology that physically eliminates the current path by providing isolation. In other words, the problem is recognized; however, the protection relays are not being activated. A compact AG SOP that eliminates false triggering at the structural level. Its architecture is not being revealed. From a conservation perspective, US20040156155A1 – “Residual current The document "device with double grounded neutral fault detection" also mentions grounded 15 In neutral systems, additional neutral-to-ground connections directly affect RCD behavior. The document reveals that it has an effect. The document states that the feed neutral is connected to the ground. In typical TN installations, a second neutral-to-ground occurs on the load side. the connection creates a "double grounded neutral fault" and the current is to ground / neutral It is explained that the RCD detection can be affected by being divided along the path. This patent 20 This is not related to the SOP; however, it relates to the conservation engineering aspect of your problem. It strongly supports: additional connections in grounded neutral systems. And loop currents can directly disrupt leakage current protection. This means that... not only does it control power flow, but it is also compatible with the protection scheme. This indicates the need for an AG-SOP topology. 25 When this patent family and similar documents are considered together, they demonstrate the advancements in the art as known. In this case, there appear to be two main trends: the first trend is SOP / flexible The interconnection function is mostly performed at the medium voltage level, with transformers or This is achieved with larger structures containing phase-shifted transformers; the second trend is 30 They propose transformerless or insulation-free solutions at the low voltage level, but this It completely eliminates common mode / leakage / loop current problems. It cannot handle it. In particular, the LV distribution network with two grounded neutrals. in connecting them, on the one hand, bidirectional active / reactive power control is provided. On the other hand, a loop originating from 50 Hz and switching frequency through the ground. structural prevention of currents and the use of RCDs at both terminals a clear and direct solution doctrine in making it possible in the current technology It appears that it is not present. 5 DEFINITION OF INVENTION The present invention is a solution for two distribution networks in low-voltage distribution networks with grounded neutrals. a flexible coupling placed between transformers and providing controlled power transfer 10 It presents a point of view (SOP) system. The technical aspects of the invention are specified in Clause 3. The fundamental solution it offers to the problems is that the SOP device is only on one terminal side. This is an isolation transformer installation with a delta / star (Δ / Y) connection type. An isolation transformer connects the galvanic current between the neutral points of two distribution transformers. cutting through the ground, both low-frequency (50 Hz) and high-frequency 15 Hz waves are generated. It eliminates frequency-related (switching frequency-induced) loop currents. Placing the isolation transformer on only one side saves both cost and physical space. Sufficient galvanic current to interrupt the loop current path while minimizing its size. It provides insulation. By eliminating loop currents, both outputs of the SOP device A residual current device (RCD) can also be installed at the terminal. Thus, any In the event of a ground fault, the system can be safely shut down. The system includes the following elements, starting from the output of the first distribution transformer: (Figure 3): Δ / Y isolation transformer, LCL filter (Figure 4), AC / DC converter (Figure 5), 25 DC junction capacitor, DC / AC converter (Figure 5), LCL filter (Figure 4) and secondary Distribution transformer connection. AC / DC converter, checks the DC connection voltage. by regulating active power transfer, in addition to the reactive power set value. It can perform reactive power compensation depending on the DC / AC connection. The converter will then follow the active and reactive power reference values ​​by 30. He is working. 6 The instantaneous power of distribution transformers is measured using power analyzers (Figure 6) and The active power transfer reference is automatically determined by the power difference between the transformers. They are manufactured. Converters are Digital System Processor (DSP) based controllers. While controlled by the SPWM method, communication and data are provided throughout the system. Management is provided via an embedded computer-based central control unit. 5 (Figure 7). Measurements from power analyzers, power reference values ​​and transfer. The power data obtained is recorded in a database on this unit. The advantages of this invention over the existing technology are as follows: With a single-sided isolation transformer. Thanks to the prevention of loop currents, 10 in LV networks with grounded neutrals Secure SOP operation becomes possible. KAR to both output terminals. (Residual Current Device, RCD) can be installed on the existing low voltage It ensures full compliance with network safety standards. Transformer on both sides. Achieves lower cost and more compact design compared to solutions that place other materials. The flow of active and reactive power between feeders is continuous, precise and automated. 15 Control is ensured. Thanks to the load balancing function, distribution transformers Overloading is prevented. REFERENCE LIST 1 Distribution transformer - 1 2 Distribution transformers - 2 3 Δ / Y Isolation transformer 4 LCL filters 1 AC / DC converter 25 6 DC junction capacitors-1 7 DC junction capacitors-2 8 DC / AC converters 9 LCL filters 2 SSI controller 1 30 11 SSI controller 2 12 Power Analyzer 1 13 Power Analyzer 2 7 14 Central control unit BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: 5 located between two feeders in a conventional low-voltage distribution network. Schematic showing the connection structure of a normally open point (NOP) circuit breaker. Representative view. Figure 2: Coupling transformer used at medium voltage level, with coupling on both terminal sides. Flexible connection point (SOP) with back-to-back converter located A representative schematic diagram showing the general structure of the system. 10 Figure 3: Low-voltage SOP containing a single-sided Δ / Y isolation transformer, which is the subject of the invention. A general block diagram representing the system. Figure 4: Representative illustration showing the structure of the LCL filter used within the SOP system. schematic circuit diagram Figure 5: Three-level (3-level NPC) AC / DC and DC / AC 15 used in the SOP system. A schematic representation of the converter topology. Figure 6: Power used to measure the instantaneous power values ​​of distribution transformers. A representative block diagram showing the location of the analyzers within the system. Figure 7: Central control unit, communication infrastructure, and data management structure. A representative system architecture diagram showing the system architecture. 20 EXPLANATION OF THE INVENTION The invention may be defined briefly below without imposing a restrictive effect. It is explained through elements; 25 The Roles and Technical Functions of the Elements Distribution transformer - 1 (1): Obtaining low voltage (400V) from medium voltage network It enables this and feeds the first feeder. 30 Distribution transformer - 2 (2): Obtaining low voltage (400V) from medium voltage network It enables this and feeds the second feeder. 8 Δ / Y Isolation transformer (3): It is placed on the first terminal side of the SOP device. Thanks to the Delta / Star connection group, the connection between the neutral points of two distribution transformers is established. By disconnecting the galvanic link, it eliminates loop currents that form through the ground. removes. 5 LCL filter 1 (4): Switching source on the AC side of the AC / DC converter It filters out harmonics. AC / DC converter (5): It has a three-level NPC topology. DC junction voltage 10 It regulates active power transfer by controlling it and provides reactive power compensation. It is driven using the SPWM method, based on a DSP (Digital Spectroscopic Control). DC coupling capacitor-1 (6): AC / DC converter (5) to DC / AC converter (8) It provides energy buffering between them. 15 DC coupling capacitor-2 (7): AC / DC converter (5) to DC / AC converter (8) It provides energy buffering between them. DC / AC converter (8): It has a three-level NPC topology. Active power and reactive 20 It follows power reference values ​​and is driven by a DSP-based SPWM method. LCL filter 2 (9): Switching source on the AC side of the DC / AC converter It filters out harmonics. SSI controller 1 (10): AC / DC converter (5) Vdc + Q external loop and dq current internal loop It performs loop control. SSI controller 2 (11): DC / AC converter (8) P + Q outer loop and dq current inner loop It performs cycle control. 30 Power analyzer 1 (12): Measures the instantaneous power values ​​of distribution transformer - 1 (1). 9 Power analyzer 2 (13): Measures the instantaneous power values ​​of distribution transformer - 2 (2). Central control unit (14): It is based on an embedded computer. Power between two transformers It calculates the difference, generates a Pref, and coordinates communication across the system. During system operation, firstly Δ / Y Isolation transformer (3), Distribution transformer - 1 By disconnecting the galvanic link between the neutral points of (1) and Distribution transformer - 2 (2). It eliminates ground loop currents (A). This prevents loop currents. and residual current devices can be safely connected to both output terminals of the SOP device. It becomes possible to establish it (B). 10 After this isolation is provided, the AC / DC converter (5), DC connection It performs active power transfer between two feeders by controlling the voltage (C). At the time of the AC / DC converter (5), depending on the set reactive power set value It performs reactive power compensation on the first feeder side (D). 15 After power transfer is established via the DC junction stage, the DC / AC converter (8), by monitoring the active power and reactive power reference values ​​on the second feeder side It provides controlled power output (E). In this process, Power Analyzer 1 (12) and Power Analyzer 2 (13) are used to analyze the Distribution transformer, respectively. - By measuring the instantaneous power values ​​of transformer - 1 (1) and distribution transformer - 2 (2), this data is sent to the Central transmits to control unit (14) (F). The central control unit (14) uses this measurement data to determine the power between the two transformers. It calculates the difference and determines the active power transfer reference according to the relationship Pref = (P₁ − P₂) / 2. It produces it automatically (G). On the other hand, LCL filter 1 (4) and LCL filter 2 (9) originate from the converters. By filtering out switching harmonics, it injects clean sinusoidal current into the grid. 30 It enables (H). The entire system is controlled by SSI controller 1 (10) and SSI controller 2 (11). dq is implemented with dual closed-loop control in the reference frame and the converter Switching signals are generated by the SPWM method (I). In the configuration suitable for the invention, the low 5 supplied by two distribution transformers (1, 2) An SOP device is placed between the voltage feeders. The first of the SOP device... A Δ / Y isolation transformer (3) is connected to the terminal side. This isolation transformer, The delta side is connected to the first feeder, and the star side is connected to the internal circuit of the SOP device. Thanks to the Delta connection, the first distribution transformer (1) neutral point and the SOP internal circuit The galvanic link between them is broken, and the loop that can form through the ground is 10 The path of the currents is eliminated. This allows both outputs of the SOP device to function correctly. Residual current devices can also be installed at the terminal, and any actual ground connection is possible. In the event of a leak, the system can be safely deactivated. Insulation The output of the transformer (3) passes through an LCL filter (4) into the three-level NPC topology It is connected to the AC / DC converter (5). The AC / DC converter (5) is the first SSI 15 It is controlled by the controller (10). DC junction voltage in the outer loop. (Vdc) and reactive power (Q) error signals are passed through PI controllers to determine the dq axis current. References are being produced, and in the inner loop, DQ current controllers detect current errors. It processes and generates voltage reference signals. The PLL block processes the mains voltage. It provides synchronization for the dq transformation by determining the phase angle (θ). (20 obtained) The obtained voltage references are passed through the dq / abc transformation and fed to the SPWM modulator. Transmission takes place and converter switching signals are generated. The DC output of the AC / DC converter (5) is connected to the DC coupling capacitors (6,7). Capacitors provide energy buffering between the two converters, DC 25 This contributes to maintaining voltage level stability. The other aspect of the DC connection... On the side, there is a DC / AC converter (8) in a three-level NPC topology. This converter is controlled by the second SSI controller (11). External In the loop, active power (P) and reactive power (Q) references are passed through PI controllers. dq current references are generated, current control is performed in the internal loop, and 30 SPWM signals are generated. 11 The output of the DC / AC converter (8) passes through an LCL filter (9) and a residual current relay. It is connected to the second distribution transformer (2) via. At the system level, Instantaneous power values ​​of distribution transformers 1 and 2 are determined by means of power analyzers (12, 13). It is measured. These measurement data are transmitted to the central control unit (14). Central The control unit (14) calculates the active power difference between the two transformers, and the active power is 5 The transfer reference is automatically determined according to the formula Pref = (P₁ − P₂) / 2. It produces this reference value together with measurements from power analyzers. The data is sent to the controllers (10, 11). The data on the central control unit (14) the base power analyzer's measurement values, reference values, and transfer It records the power data obtained, thus enabling retrospective analysis of the system and 10 It is made possible to monitor.

Claims

12 REQUESTS 1. This invention is a distribution transformer - 1 (1) and distribution transformer - 2 (2) feeding two feeders. unilateral for low-voltage distribution networks containing grounded neutrals It is an isolation transformer flexible connection point system, and its feature is; 5 • the distribution transformers in question (distribution transformer - 1 (1) and distribution transformer - positioned between 2 (2)) and placed on the first terminal side Δ / Y Isolation transformer (3), • LCL filter 1 (4) connected to the output of the aforementioned Δ / Y Isolation transformer (3), • 10 three-level NPC topology connected to the output of the LCL filter 1 (4) AC / DC converter (5), • DC coupling capacitor-1 (6) connected with the aforementioned AC / DC converter (5) and DC junction capacitor-2 (7), • three-level NPC associated with the DC junction capacitors (6, 7) DC / AC converter with topology (8), 15 • LCL filter 2 (9) connected to the output of the aforementioned DC / AC converter (8), • SSI controller 1 (10) which controls the AC / DC converter (5), • SSI controller 2 (11) which controls the aforementioned DC / AC converter (8), • measuring the instantaneous power values ​​of distribution transformer - 1 (1) and distribution transformer - 2 (2) Power analyzer 1 (12) and Power analyzer 2 (13), 20 • active power with data obtained from the power analyzers (12, 13) Generates transfer references and coordinates system communication. Central control unit (14) It includes. 25 2. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is; two 30 by disconnecting the galvanic link between the neutral points of the distribution transformer (1, 2) to eliminate loop currents that form through the ground It includes a structured Δ / Y Isolation transformer (3). 13 3. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is; AC It is configured to filter out harmonics caused by switching on that side. It contains LCL filter 1 (4). 5 4. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its characteristic is; DC By controlling the junction voltage, it regulates active power transfer and reactive power 10 AC / DC with a three-level NPC topology to provide compensation. It contains a converter (5).

5. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. For grounded neutral low voltage distribution networks containing transformer - 2 (2) 15 It is a flexible connection point system with a single-sided isolation transformer, its characteristic feature is; energy DC junction capacitor-1 (6) and DC responsible for providing buffering It contains coupling capacitor-2 (7).

6. Distribution transformer - 1 (1) and distribution 20 feeding the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is; active three configured to track power and reactive power reference values It includes a DC / AC converter (8) with a multi-level NPC topology.

7. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is; DC / AC filtering out switching-induced harmonics on the AC side of the converter It is to include LCL filter 2 (9) structured in such a way. 30 14 8. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is AC / DC. (5) Control of the converter's Vdc and Q external loop and dq current internal loop. It includes the SSI controller 1 (10) configured to perform 5.

9. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is; DC / AC 10 The converter's (8) control of the P and Q outer loop and dq current inner loop It includes the SSI controller 2 (11) configured to perform this.

10. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. for grounded neutral low voltage distribution networks containing transformer - 2 (2) It is a flexible connection point system with a single-sided isolation transformer, and its feature is; distribution 15 transformer - 1 (1) and distribution transformer - 2 (2) are responsible for measuring instantaneous power values. It includes Power Analyzer 1 (12) and Power Analyzer 2 (13).

11. Distribution transformer - 1 (1) and distribution that feeds the two feeders mentioned in Claim 1. For grounded neutral low voltage distribution networks containing transformer - 2 (2) 20 It is a flexible connection point system with a single-sided isolation transformer, and its feature is; two Active power transfer by calculating the power difference between distribution transformers (1, 2). to generate the reference and coordinate system communication It includes a structured central control unit (14). 30 35

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