Self-balancing intelligent transformer and control method thereof

Abstract

The application discloses a self-balancing intelligent transformer and a control method thereof, and belongs to the technical field of intelligent control of transformers. The self-balancing intelligent transformer comprises an electromagnetic transformer, a three-phase power regulating device and a controller. The electromagnetic transformer comprises three-phase core columns, a high-voltage winding, a low-voltage main winding and a built-in coupling winding. The three-phase power regulating device comprises three bidirectional power converters. The alternating current side of each bidirectional power converter is electrically connected with one built-in coupling winding. The direct current sides of the bidirectional power converters are connected with each other to form an internal direct current bus. The input end of the controller is connected with a sensor group. The three-phase power regulating device is used for power extraction and injection of the low-voltage main winding, three-phase balance is realized, and the problem that an external power electronic regulating device needs to be additionally arranged when the prior art regulates and controls three-phase imbalance, resulting in high regulation and control cost and high regulation and control difficulty, can be solved.

Description

Technical Field

[0001] This application belongs to the field of intelligent transformer control technology, specifically relating to a self-balancing intelligent transformer and its control method. Background Technology

[0002] Distribution transformers are core assets in power distribution networks, and their operating status directly affects power supply reliability and grid economy. With the widespread integration of single-phase high-density loads such as distributed photovoltaic systems and electric vehicle charging stations, distribution transformers face increasingly severe three-phase imbalance problems. Unbalanced operation of distribution transformers increases transformer losses, reduces operating efficiency, and can lead to overheating, reduced lifespan, or even direct burnout under single-phase overload conditions. This seriously threatens the reliable, safe, and economical operation of the power distribution network.

[0003] Traditional distribution transformers can only perform voltage transformation and electrical isolation, lacking active functions such as dynamic regulation, status interaction, and power quality management. To solve the three-phase imbalance problem, additional power electronic regulating devices need to be installed outside the distribution transformer, resulting in a complex system, large footprint, high cost, and difficulty in coordination, increasing system size and operating costs. Moreover, current technology can only handle unidirectional power flow from the grid to the three-phase load, or switching between different power sources, and lacks the ability to build an interphase active power circulation path independent of the external load path inside the distribution transformer. Summary of the Invention

[0004] This application proposes a self-balancing smart transformer and its control method, which can solve the problem that existing technologies require the external installation of power electronic regulating devices when regulating three-phase imbalance, resulting in high regulation costs and high regulation difficulty.

[0005] The first aspect of this application provides a self-balancing smart transformer, comprising: an electromagnetic transformer, a three-phase power regulation device, and a controller. The electromagnetic transformer includes a three-phase core column, a high-voltage winding, a low-voltage main winding, and an internal coupling winding. The three-phase power regulating device includes three bidirectional power converters. The AC side of each bidirectional power converter is electrically connected to one of the built-in coupling windings, and the DC sides of the bidirectional power converters are interconnected to form an internal DC bus. The three-phase power regulating device is built into the electromagnetic transformer. The input terminal of the controller is connected to the sensor group, which is used to collect electrical and temperature data of the low-voltage main winding. The output terminal of the controller is connected to the bidirectional power converter.

[0006] The above scheme incorporates an additional three-phase power regulation device and a controller within the electromagnetic transformer. The three-phase power regulation device features a corresponding bidirectional power converter for each of the three phases. Each bidirectional power converter is electrically connected to its corresponding built-in coupling winding, regulating the power of the low-voltage main winding through electromagnetic induction. This enables timely and precise control of three-phase load imbalances. The controller uses a sensor array to monitor the electromagnetic transformer's temperature changes and three-phase load conditions. It can also control the built-in coupling winding to form a closed-loop active power circulation current within the transformer, independent of the external load power path, providing support for dynamically adjusting the equivalent load distribution of the low-voltage main winding. Because both the three-phase power regulation device and the controller are integrated within the electromagnetic transformer, power regulation can be achieved without the need for external power electronic regulation devices, effectively reducing the difficulty of regulation and enabling timely three-phase self-balancing of the transformer.

[0007] In one possible implementation of the first aspect, the high-voltage winding and the low-voltage main winding are respectively wound on the core column of each phase; each built-in coupling winding is coaxially wound with the low-voltage main winding of the corresponding phase on the same core column to share the main magnetic circuit; the rated voltage of the built-in coupling winding is lower than the rated voltage of the low-voltage main winding of the corresponding phase.

[0008] The above scheme allows the three-phase power regulation device to extract or inject active power from the main magnetic circuit without loss by sharing the same iron core column with the built-in coupling winding and the low-voltage main winding. This eliminates the need to connect other transformers from the outside, greatly reducing the size and cost of transformer regulation and also reducing the difficulty of regulation.

[0009] In one possible implementation of the first aspect, for the coaxially wound built-in coupling winding and the low-voltage main winding, the number of turns of the built-in coupling winding ranges from 1 / 10 to 1 / 4 of the number of turns of the low-voltage main winding.

[0010] The above scheme sets the number of turns of the built-in coupling winding to be lower than the number of turns of the low-voltage main winding of the corresponding phase, so as to ensure that the rated voltage of the built-in coupling winding is lower than the rated voltage of the low-voltage main winding of the corresponding phase.

[0011] In one possible implementation of the first aspect, the bidirectional power converter adopts a single-phase H-bridge topology, and the bidirectional power converter is connected in parallel with a supporting capacitor through a common DC bus to form the internal DC bus.

[0012] In one possible implementation of the first aspect, the controller further includes a digital twin lifetime prediction module; the digital twin lifetime prediction module is trained using historical load data and historical temperature data of the electromagnetic transformer to construct a mapping relationship between the three-phase load imbalance and the insulation lifetime loss of the low-voltage main winding.

[0013] The above scheme uses the constructed mapping relationship to predict the current insulation life of the low-voltage main winding based on the existing three-phase load imbalance, and uses the predicted life loss rate as a correction factor to dynamically adjust the control mode of the self-balancing smart transformer.

[0014] A second aspect of this application provides a control method for a self-balancing smart transformer, the method comprising: The current data collected from the low-voltage side of the balanced smart transformer, as well as the temperature data on the low-voltage main winding side, are used to calculate the current three-phase current negative sequence component and winding temperature difference. Based on the negative sequence components of the three-phase current, the winding temperature difference, and the preset constraints, the power regulation command of the three-phase power regulation device is constructed with the goal of minimizing the preset objective function. Based on the power regulation command, the low-voltage main winding is extracted and injected with power through the three-phase power regulation device.

[0015] The above scheme calculates the power to be injected or extracted into each phase's low-voltage main winding based on collected current and temperature data, aiming to achieve three-phase balance. Then, it calculates the corresponding power regulation command with the optimization objectives of minimizing the negative sequence component of the three-phase current and minimizing the winding temperature difference. Reducing the negative sequence component of the three-phase current effectively reduces three-phase load imbalance, and reducing the winding temperature difference effectively extends the insulation life of the low-voltage main winding, indirectly increasing the transformer's lifespan. The obtained power regulation command allows for adjustment of the proportion of power drawn from the grid by each phase's low-voltage main winding solely through internal circulating current, achieving dynamic balance of the three-phase current and extending the transformer's lifespan.

[0016] In one possible implementation of the second aspect, based on the negative sequence components of the three-phase current, the winding temperature difference, and preset constraints, a power regulation command for the three-phase power regulation device is constructed with the objective of minimizing a preset objective function, specifically as follows: The objective function is constructed with the optimization objectives of minimizing the negative sequence component of the three-phase current and minimizing the winding temperature difference. Based on the constraints, and with the objective function as the goal, the power extraction and injection quantities of the low-voltage main winding in each phase of the three-phase power regulation device are solved to obtain the power regulation command. The extracted power and injected power are both referred to as transfer power.

[0017] The above scheme takes minimizing the negative sequence component of the three-phase current and balancing the temperature of the three-phase low-voltage main winding as the synergistic optimization objectives, providing theoretical support for generating power regulation commands that can reduce the three-phase imbalance and the aging rate of transformer insulation.

[0018] In one possible implementation of the second aspect, the constraint condition restricts the sum of all said transferred power to zero, and any said transferred power is less than or equal to the maximum power that the bidirectional power converter can carry.

[0019] In one possible implementation of the second aspect, based on the power regulation command, power is extracted and injected into the low-voltage main winding through the three-phase power regulation device, specifically as follows: For any corresponding low-voltage main winding, if the power adjustment command is greater than 0, the corresponding bidirectional power converter is switched to inverter mode. In inverter mode, power is drawn from the internal DC bus to inject power into the low-voltage main winding. For any corresponding low-voltage main winding, if the power adjustment command is less than 0, the corresponding bidirectional power converter is switched to rectification mode. In rectification mode, power is drawn from the low-voltage main winding to inject power into the internal DC bus.

[0020] The power extraction and injection in the above scheme are achieved through the internal DC bus inside the self-balancing smart transformer. Therefore, this power extraction / injection process does not change the total input power and total output power of the self-balancing smart transformer. The three-phase imbalance can be reduced simply by adjusting the power distribution ratio between the low-voltage main windings of each phase, which effectively reduces the adjustment difficulty and cost.

[0021] In one possible implementation of the second aspect, the power injection process and the power extraction process are synchronized in time so that the instantaneous net power on the internal DC bus is always 0.

[0022] The above scheme ensures that the instantaneous net power on the internal DC bus does not fluctuate too much by simultaneously injecting and extracting power into the low-voltage main windings of different phases, thereby maintaining the stable operation of the self-balancing smart transformer. Attached Figure Description

[0023] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is an overall structural diagram of a self-balancing smart transformer provided in one embodiment of this application; Figure 2 This is an electrical topology diagram of a self-balancing smart transformer provided in one embodiment of this application; Figure 3 This is a flowchart illustrating a control method for a self-balancing smart transformer according to an embodiment of this application. Figure 4 This is a comparison diagram of the three-phase current waveforms of a control method for a self-balancing smart transformer provided in an embodiment of this application; Figure 5 This is a comparison diagram of the temperature rise curves of the low-voltage main winding of a control method for a self-balancing smart transformer provided in an embodiment of this application. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0027] First Embodiment Transformers in power distribution networks utilize the principle of electromagnetic induction to change AC voltage. Three-phase load imbalance can cause uneven thermal stress, accelerated insulation aging, and wasted capacity in the transformer. Therefore, regulating three-phase imbalance is crucial for transformers. However, current solutions typically connect the regulating device externally to the transformer rather than deeply integrating it within the transformer itself. This results in a large footprint and high equipment cost for transformer + power electronic regulating device combinations, increasing the cost and difficulty of three-phase imbalance regulation. Furthermore, the influence of the excitation current generated by electromagnetic induction is not considered during transformer balancing control. Small deviations caused by the excitation current can affect control accuracy, leading to unsatisfactory regulation results.

[0028] like Figure 1 As shown, to address the problem that existing technologies require the external installation of power electronic regulating devices when controlling three-phase imbalance, resulting in high control costs and difficulties, Figure 1This is an overall structural diagram of a self-balancing smart transformer provided in an embodiment of this application. The self-balancing smart transformer provided in this embodiment includes an electromagnetic transformer, a three-phase power regulation device, and a controller.

[0029] Unlike existing technologies, this application introduces a three-phase power regulation device and controller into the electromagnetic transformer, forming a self-balancing smart transformer that can regulate three-phase loads without connecting to external regulation equipment. Furthermore, the three-phase power regulation device is built into the electromagnetic transformer. Compared to existing technologies that typically connect power electronic regulation devices externally to the transformer, this application's embodiment has a smaller system footprint during regulation, thus requiring less cost and offering more convenient control.

[0030] The self-balancing intelligent transformer includes an electromagnetic transformer, a three-phase power regulation device, and a controller. The electromagnetic transformer comprises three-phase core columns, a high-voltage winding, a low-voltage main winding, and an internal coupling winding. The high-voltage winding and the low-voltage main winding are wound on the core columns of each phase, respectively. The three-phase power regulation device includes three bidirectional power converters (also known as bidirectional AC / DC converters, where AC stands for alternating current and DC for direct current). The AC side of each bidirectional power converter is electrically connected to one of the internal coupling windings, and the DC sides of the bidirectional power converters are interconnected to form a DC bus. The input terminal of the controller is connected to a sensor group, which is used to collect electrical and temperature data; the output terminal of the controller is connected to the bidirectional power converters.

[0031] like Figure 1 As shown, AX, BY, and CZ are the high-voltage windings; temperature sensors are deployed on the low-voltage main windings, and Ta, Tb, and Tc are the low-voltage main winding temperatures of phases a, b, and c, respectively; Ia, Ib, and Ic are the current three-phase currents of phases a, b, and c, respectively, collected by the current measuring device; a', b', and c' are the electrical connections between the built-in coupling winding and the bidirectional power converter.

[0032] The innovation of this application embodiment lies in that each of the built-in coupling windings and the corresponding phase's low-voltage main winding are coaxially wound on the same iron core column, sharing the main magnetic circuit. In this way, the three-phase power regulation device only needs to extract and inject power inside the self-balancing smart transformer to reduce the three-phase imbalance without changing the total input power and total output power of the self-balancing smart transformer, thus achieving the optimization of the transformer's own operating state without connecting to external devices.

[0033] The built-in coupling winding shares the same core magnetic circuit with the low-voltage main winding, thus enabling energy coupling through electromagnetic induction rather than electrical connection.

[0034] Because the electrical connection path between the built-in coupling winding and the bidirectional power converter is completely built into the self-balancing smart transformer, there is no need for exposed wiring terminals, which effectively reduces the control cost.

[0035] Furthermore, the high-voltage winding, the low-voltage main winding, and the three-phase core columns together constitute the main magnetic circuit, undertaking more than 95% of the load power transmission. The built-in coupling winding, the three-phase power regulation device, and the DC bus together constitute the balance regulation channel, which can regulate a small amount of active power (usually less than 5% of the rated capacity of the self-balancing smart transformer) inside the self-balancing smart transformer. Active power can be extracted or injected from the main magnetic circuit without loss through the balance regulation channel, without the need for external electrical interfaces.

[0036] In addition, the number of turns of the built-in coupling winding is lower than the number of turns of the low-voltage main winding of the corresponding phase, so as to ensure that the rated voltage of the built-in coupling winding is lower than the rated voltage of the low-voltage main winding of the corresponding phase.

[0037] Optionally, in this embodiment, for the coaxially wound built-in coupling winding and the low-voltage main winding, the number of turns of the built-in coupling winding is between 1 / 10 and 1 / 4 of the number of turns of the low-voltage main winding. With this turn count setting, the operating voltage range of the built-in coupling winding is between 1 / 10Ue and 1 / 4Ue, and the operating voltage range of the internal DC bus is between 200V and 500V.

[0038] Furthermore, the bidirectional power converter adopts a single-phase H-bridge topology. The bidirectional power converter is connected in parallel with a supporting capacitor via a common DC bus to form the internal DC bus. The controller also includes a digital twin lifetime prediction module; this module is trained using historical load and temperature data from the electromagnetic transformer to construct a mapping relationship between the three-phase load imbalance and the insulation lifetime loss of the low-voltage main winding. This mapping relationship can predict the insulation lifetime loss rate of the low-voltage main winding, and the insulation lifetime loss rate can be used as a weighting factor to dynamically adjust the control mode of the self-balancing smart transformer.

[0039] Therefore, the self-balancing smart transformer provided in this application not only enables precise three-phase control at low cost and high efficiency to achieve three-phase balance, but also balances the temperature difference between the low-voltage main windings, stabilizing the winding temperature difference within a set threshold, thus preventing excessively rapid insulation life loss due to excessive temperature differences. In contrast, existing technologies only aim to achieve three-phase load balance when controlling transformers, neglecting the transformer's overall operating status. Consequently, they do not address issues such as uneven thermal stress, accelerated insulation aging, and hidden capacity waste caused by three-phase load asymmetry. Therefore, compared to existing technologies, this application's embodiment can reduce the risk of insulation aging while achieving three-phase load balance.

[0040] Figure 2 This is an electrical topology diagram provided in an embodiment of this application, illustrating the above-described single-phase H-bridge topology. The IGBT is an insulated-gate bipolar transistor, and the bidirectional power converter is connected to a common DC bus. Figure 2 The supporting capacitors are connected in parallel to form the internal DC bus.

[0041] Second Embodiment like Figure 3 As shown, Figure 3 This is a flowchart illustrating a control method for a self-balancing smart transformer according to an embodiment of this application. The control method for the self-balancing smart transformer provided in this embodiment includes steps S1 to S3, which are detailed below: Step S1: Collect current data on the low-voltage side of the self-balancing smart transformer and temperature data on the low-voltage main winding side to calculate the current three-phase current negative sequence component and winding temperature difference.

[0042] First, the three-phase current on the low-voltage side of the self-balancing smart transformer is collected, along with the three-phase voltage on the low-voltage side and the current temperature on the low-voltage main winding side.

[0043] Then, the current winding temperature difference is calculated using the difference between the current temperature and the preset maximum temperature; the negative sequence component of the current three-phase current is calculated using the three-phase current. The negative sequence component of the three-phase current can be used to quantify the degree of three-phase imbalance of the transformer.

[0044] Step S2: Based on the negative sequence components of the three-phase current, the winding temperature difference, and the preset constraints, construct the power regulation command of the three-phase power regulation device with the goal of minimizing the preset objective function.

[0045] This application's embodiments use "minimizing three-phase current imbalance" and "balancing the temperature change of the three-phase low-voltage side main winding (i.e., minimizing the winding temperature difference)" as synergistic optimization objectives. Therefore, an objective function is constructed based on the negative sequence components of the three-phase current and the winding temperature difference. "Balancing the temperature change of the three-phase low-voltage side main winding" protects the transformer's insulation, ensuring that the insulation performance is not reduced due to excessive temperature. "Minimizing three-phase current imbalance" achieves three-phase load balancing in the transformer. Therefore, through this objective function, while achieving three-phase load balancing, the unevenness of thermal stress in the transformer body can be reduced, thus ensuring safe operation and extending the transformer's service life.

[0046] The specific expression for the objective function is: ; Where J is the collaborative optimization objective, I2 is the negative sequence component of the three-phase current, and T max To preset the maximum temperature, Tavg The average temperature of the low-voltage main winding. All of these are weighting coefficients that are dynamically adjusted based on the insulation life curve of the self-balancing smart transformer.

[0047] The relationship between the negative sequence component of the three-phase current and the power regulation command can be expressed by the following formula: ; P cyc = ( P load,a + P a )×( P load,b + P b )+ ( P load,b + P b )×( P load,c + P c )+ ( P load,c + P c )×( P load,a + P a ); in, i For any one of the three phases a, b, and c, P i for i The corresponding transfer power, i =a or b or c; Pload,i For self-balancing smart transformers on the load side i Phase power, k It is 1 / (Uph), where Uph is the effective value of the phase voltage. P cyc This is the cycle power.

[0048] Solving the objective function is essentially solving for the power extraction and injection quantities of the low-voltage main winding in each phase of the three-phase power regulation device, in order to obtain the power regulation command. Here, both the extracted power and the injected power are referred to as transfer power.

[0049] The relationship between the winding temperature difference and the power adjustment command can be expressed by the following formula: ; ; ; in, T i for i Corresponding winding temperature, i =a or b or c, T amb For ambient temperature, To take into account the overall thermal resistance coefficient, T avg This represents the average temperature of the low-voltage main winding.

[0050] Therefore, the specific expression of the above objective function can also be transformed into: ; In addition, the weighting coefficient It is dynamically adjusted based on the thermal risk index, and the mapping relationship between the thermal risk index and the three-phase load imbalance and the insulation life loss of the low-voltage main winding is also relevant. The expression for the weighting coefficient and the thermal risk index is as follows: ; ; in, T risk As a thermal risk indicator, It is a constant. T limit This is the upper limit of the temperature that the low-voltage main winding can withstand.

[0051] When calculating the power that can be injected / extracted by the three-phase power regulation device by minimizing the objective function, the calculation process is monitored according to preset constraints to obtain a more accurate and realistic transfer power for each corresponding phase.

[0052] The process of constructing the constraint conditions is as follows: The transferred power of the three-phase power regulation device is extracted from the collected electrical data. This transferred power is actually the amount of power extracted or injected by the bidirectional power converter from each phase of the main magnetic circuit. Extracting or injecting power essentially adjusts the power distribution ratio among the low-voltage main windings of each phase; it does not change the total input power or total output power of the self-balancing smart transformer. For example, if the power extracted from phase a is 10W, then the total power injected into phases b and c is 10W, so the sum of the transferred power of the three phases is always 0. Therefore, the specific expression of the constraint conditions is: ; ; in, P a , P b , P c These represent the transfer power of phases a, b, and c, respectively. P i for i Phase transfer power, i =a or b or c; P rated This is the maximum power that a three-phase power regulation device can handle.

[0053] i If the phase transfer power is greater than 0, it indicates that the three-phase power regulation device is functioning correctly. i Power is injected into the low-voltage main winding of the phase. i If the phase transfer power is less than 0, it indicates that the three-phase power regulation device is in operation. i Power is extracted from the low-voltage main winding of the phase.

[0054] Step S3: Based on the power regulation command, the low-voltage main winding is extracted and injected with power through the three-phase power regulation device.

[0055] According to the power regulation command of each phase, the three bidirectional power converters of the three-phase power regulation device are controlled to perform power injection or extraction operations.

[0056] Specifically, if i If the power regulation command for a phase is greater than 0, the three-phase power regulation device is switched to inverter mode. In inverter mode, power is drawn from the internal DC bus to supply the self-balancing smart transformer. i Power is injected into the low-voltage main winding of the phase; if i If the power regulation command for a phase is less than 0, the three-phase power regulation device will be switched to rectification mode. In rectification mode, from i The low-voltage main winding of the phase draws power to feed into the internal DC bus.

[0057] The power injection and extraction processes are synchronized in time to ensure that the instantaneous net power on the internal DC bus is always zero. The internal DC bus serves only as a power routing and buffer node and does not perform long-term energy storage functions.

[0058] Moreover, the above control method maintains the total power supplied by the low-voltage main winding to the load constant during the operation of the self-balancing smart transformer. It only adjusts the proportion of power obtained by the low-voltage side winding of each phase from the grid side through internal circulating current to achieve dynamic balance of the three-phase current.

[0059] Figure 4 This is a comparison diagram of three-phase current waveforms provided in the embodiments of this application. The horizontal axis represents the operating time of the self-balancing smart transformer, and the vertical axis represents the three-phase current of the self-balancing smart transformer. The yellow curve represents the current of phase A, the green curve represents the current of phase B, and the red curve represents the current of phase C. The control method provided in the embodiments of this application is used to regulate the three-phase load of the self-balancing smart transformer when the operating time is 0.49s. Therefore, it is possible to... Figure 4 It can be seen that before 0.49s, the three-phase currents were significantly different in magnitude, indicating a serious load imbalance. After 0.49s, the magnitudes of the three-phase currents were close, and the self-balancing smart transformer achieved three-phase load balancing.

[0060] Figure 5 This is a comparison chart of the temperature rise curves of the low-voltage main winding provided in this application embodiment. The horizontal axis represents the operating time of the self-balancing smart transformer, and the vertical axis represents the hot spot temperature of the low-voltage main winding. The black curve represents the hot spot temperature change of the low-voltage main winding in phase A, the red curve represents the hot spot temperature change of the low-voltage main winding in phase B, and the blue curve represents the hot spot temperature change of the low-voltage main winding in phase C. The control method provided in this application embodiment is used to regulate the three-phase load of the self-balancing smart transformer at an operating time of 14 minutes, thus enabling... Figure 5 The data shows that the hot spot temperatures of the three-phase low-voltage main windings were very different 14 minutes ago, but gradually became the same after 14 minutes, and the temperature difference decreased, indicating that the self-balancing smart transformer achieved three-phase load balancing.

[0061] Implementing the embodiments of this application has the following beneficial effects: In this embodiment, a three-phase power regulation device and a controller are additionally installed inside the electromagnetic transformer. The three-phase power regulation device has a corresponding bidirectional power converter for each of the three phases. Each bidirectional power converter is electrically connected to a corresponding built-in coupling winding, and regulates the power of the low-voltage main winding through electromagnetic induction, thereby achieving timely and precise control of three-phase load imbalance. The controller uses a sensor array to promptly detect temperature changes and three-phase load conditions of the electromagnetic transformer, and can control the built-in coupling winding to form a closed-loop active power circulation current inside the transformer, independent of the external load power path, providing support for dynamically adjusting the equivalent load distribution of the low-voltage main winding. Because both the three-phase power regulation device and the controller are deployed within the electromagnetic transformer, power regulation can be achieved without the need for additional power electronic regulation devices installed outside the transformer, effectively reducing the difficulty of regulation and enabling timely three-phase self-balancing of the transformer.

[0062] Third Embodiment To demonstrate the technical effects achievable by the above-described method embodiments, this application uses a standard three-phase oil-immersed distribution transformer (rated capacity 800kVA, voltage combination 10kV / 0.4kV) as the electromagnetic transformer. An internal coupling winding is added to the three-phase core columns, closely attached to the low-voltage main winding (rated voltage 400V). The rated voltage of this winding is designed to be 100V, and the rated current is designed to be 10% of the electromagnetic transformer's rated current (approximately 115A), thus constructing a self-balancing intelligent transformer. The internal coupling winding uses the same insulation class as the low-voltage main winding, but with a smaller conductor cross-section to save material costs.

[0063] The three bidirectional power converters employ a single-phase H-bridge back-to-back topology, using 600V / 200A IGBT modules (Insulated Gate Bipolar Transistors). The DC sides of these bidirectional power converters are connected in parallel to form an internal DC bus within the self-balancing smart transformer. The internal DC bus capacitor is designed to support 10ms instantaneous power fluctuations (using an electrolytic capacitor bank with a total capacity of 20mF). The AC sides of the three bidirectional power converters are directly connected to the output terminals of their respective built-in coupling windings via the shortest copper busbar path. All connection points are located inside the self-balancing smart transformer enclosure, with no exposed wiring.

[0064] The controller uses a TMS320F28379D dual-core DSP as the main control chip. It monitors the hot spot temperature of the three-phase low-voltage main winding in real time through a fiber optic temperature measurement system and monitors the three-phase current through Hall current sensors. The controller embeds the aforementioned optimized control model and digital twin lifetime prediction algorithm.

[0065] This application embodiment designs a typical operating condition: On a summer afternoon, a distribution transformer in an 800kVA residential community experienced severe three-phase imbalance due to concentrated air conditioning load. The measured data obtained by the sensors included A-phase current of 580A (overload), B-phase current of 450A (moderate), and C-phase current of 360A (light load); the winding temperatures were 82℃ for A-phase, 71℃ for B-phase, and 63℃ for C-phase.

[0066] Based on the above data, the three-phase load power is as follows: Assuming a power factor of 0.95, a line voltage of 400V, the load power of phase A is 127kW, the load power of phase B is 99kW, and the load power of phase C is 79kW.

[0067] Therefore, the total three-phase power is 305kW, with a balance target of approximately 101.7kW per phase.

[0068] The method described above is used to calculate the required increase / decrease in current for each phase: Phase A needs to reduce current → Power needs to be injected into Phase A: ΔP_a_inject = 127 - 101.7 = 25.3kW.

[0069] Phase B requires increased current → power needs to be extracted from phase B: ΔP_b_extract = 101.7 - 99 = 2.7kW.

[0070] Phase C requires increased current → power needs to be extracted from phase C: ΔP_c_extract = 101.7 - 79 =≈22.6kW.

[0071] The above calculation results are consistent with the total power injected into phase A being equal to the total power extracted from phases B and C.

[0072] Then, the power transfer path is determined. First, the power should flow from phases B and C to phase A. Therefore: Main path (C→A): 22.6 kW is extracted from phase C and injected into phase A; Auxiliary path (B→A): 2.7 kW is extracted from phase B and injected into phase A; According to the above power transfer path, the bidirectional power converter connected to the built-in coupling winding of phase C operates in rectification mode, taking 22.6 kW of active power from the low-voltage main winding of phase C and converting it into DC power to be sent to the internal DC bus. The bidirectional power converter connected to the built-in coupling winding of phase A operates in inverter mode, taking 22.6 kW from the internal DC bus and converting it into AC power to supplement the low-voltage main winding of phase A. The bidirectional power converter connected to the built-in coupling winding of phase B operates in rectification mode, taking 2.7 kW from the low-voltage main winding of phase B and sending it to the internal DC bus. The other bidirectional power converter connected to the built-in coupling winding of phase A operates in inverter mode, taking 2.7 kW from the internal DC bus to supplement the low-voltage main winding of phase A.

[0073] During power extraction and injection, the internal DC bus voltage is maintained at 400V, and the instantaneous net power between the three bidirectional power converters and the internal DC bus is always zero.

[0074] The final operating results are as follows: Phase A receives 25.3 kW of internal power injection → Power drawn from the grid is reduced by 25.3 kW → Current drops from 580A to 465A; Phase B is depleted by 2.7 kW → This is equivalent to adding an additional 2.7 kW internal load → The power drawn from the grid increases by 2.7 kW → The current increases from 450A to 465A; Phase C is drawn 22.6 kW → Power drawn from the grid increases by 22.6 kW → Current rises from 360A to 465A.

[0075] The three-phase current is dynamically balanced to around 465A, and the imbalance is reduced to below 1.5%.

[0076] Electrical balance effect: The three-phase current stabilizes at 465A±8A within 1 second, and the imbalance is reduced to 1.5%.

[0077] Thermal balance effect: After 15 minutes, the temperature of the three-phase winding tends to be balanced and stabilizes at 73℃ ±2℃.

[0078] Asset gain effect: Under this operating condition, the transformer's equivalent capacity is increased by about 22%, and its lifespan is expected to be extended by 1.8 times.

[0079] The experimental data above show that, by considering the excitation current to compensate for the base power, the embodiments of this application significantly improve the control accuracy and thermal balance effect without increasing the hardware cost, making them particularly suitable for scenarios such as precision manufacturing and data centers with extremely high power quality requirements.

[0080] Fourth embodiment Furthermore, in order to implement the cloud-edge collaborative transmission optimization system for pose data corresponding to the above method embodiments and achieve the corresponding functions and technical effects, this application embodiment provides a control system for a self-balancing smart transformer. For ease of explanation, only the parts related to this embodiment are shown. The control system for a self-balancing smart transformer provided in this application embodiment includes: The transformer status calculation module 201 is used to collect the current data on the low-voltage side of the self-balancing smart transformer, as well as the temperature data on the low-voltage main winding side, in order to calculate the current three-phase current negative sequence component and winding temperature difference.

[0081] First, the three-phase current on the low-voltage side of the self-balancing smart transformer is collected, along with the three-phase voltage on the low-voltage side and the current temperature on the low-voltage main winding side.

[0082] Then, the current winding temperature difference is calculated using the difference between the current temperature and the preset maximum temperature; the negative sequence component of the current three-phase current is calculated using the three-phase current. The negative sequence component of the three-phase current can be used to quantify the degree of three-phase imbalance of the transformer.

[0083] The power regulation command generation module 202 is used to construct the power regulation command of the three-phase power regulation device based on the negative sequence component of the three-phase current, the winding temperature difference and the preset constraints, with the goal of minimizing the preset objective function.

[0084] This application's embodiments use "minimizing three-phase current imbalance" and "balancing the temperature change of the three-phase low-voltage side main winding (i.e., minimizing the winding temperature difference)" as synergistic optimization objectives. Therefore, an objective function is constructed based on the negative sequence components of the three-phase current and the winding temperature difference. "Balancing the temperature change of the three-phase low-voltage side main winding" protects the transformer's insulation, ensuring that the insulation performance is not reduced due to excessive temperature. "Minimizing three-phase current imbalance" achieves three-phase load balancing in the transformer. Therefore, through this objective function, while achieving three-phase load balancing, the unevenness of thermal stress in the transformer body can be reduced, thus ensuring safe operation and extending the transformer's service life.

[0085] The specific expression for the objective function is: ; Where J is the collaborative optimization objective, I2 is the negative sequence component of the three-phase current, and T max To preset the maximum temperature, Tavg The average temperature of the low-voltage main winding. All of these are weighting coefficients that are dynamically adjusted based on the insulation life curve of the self-balancing smart transformer.

[0086] The relationship between the negative sequence component of the three-phase current and the power regulation command can be expressed by the following formula: ; P cyc = ( P load,a + P a )×( P load,b + P b )+ ( P load,b + P b )×( P load,c + P c )+ ( P load,c + P c )×( P load,a + P a ); in, i For any one of the three phases a, b, and c, P i for i Corresponding transfer power, i =a or b or c; P load,i For self-balancing smart transformers on the load side i Phase power, k It is 1 / (Uph), where Uph is the effective value of the phase voltage. P cyc This is the cycle power.

[0087] Solving the objective function is essentially solving for the power extraction and injection quantities of the low-voltage main winding in each phase of the three-phase power regulation device, in order to obtain the power regulation command. Here, both the extracted power and the injected power are referred to as transfer power.

[0088] The relationship between the winding temperature difference and the power adjustment command can be expressed by the following formula: ; ; ; in, T i for i Corresponding winding temperature, i =a or b or c, T amb For ambient temperature, To take into account the overall thermal resistance coefficient, T avg This represents the average temperature of the low-voltage main winding.

[0089] Therefore, the specific expression of the above objective function can also be transformed into: ; In addition, the weighting coefficient It is dynamically adjusted based on the thermal risk index, and the mapping relationship between the thermal risk index and the three-phase load imbalance and the insulation life loss of the low-voltage main winding is also relevant. The expression for the weighting coefficient and the thermal risk index is as follows: ; ; in, T risk As a thermal risk indicator, It is a constant. T limit This is the upper limit of the temperature that the low-voltage main winding can withstand.

[0090] When calculating the power that can be injected / extracted by the three-phase power regulation device by minimizing the objective function, the calculation process is monitored according to preset constraints to obtain a more accurate and realistic transfer power for each corresponding phase.

[0091] The process of constructing the constraint conditions is as follows: The transferred power of the three-phase power regulation device is extracted from the collected electrical data. This transferred power is actually the amount of power extracted or injected by the bidirectional power converter from each phase of the main magnetic circuit. Extracting or injecting power essentially adjusts the power distribution ratio among the low-voltage main windings of each phase; it does not change the total input power or total output power of the self-balancing smart transformer. For example, if the power extracted from phase a is 10W, then the total power injected into phases b and c is 10W, so the sum of the transferred power of the three phases is always 0. Therefore, the specific expression of the constraint conditions is: ; ; in, P a , P b , P c These represent the transfer power of phases a, b, and c, respectively. P i for i Phase transfer power, i =a or b or c; P ratedThis is the maximum power that a three-phase power regulation device can handle.

[0092] i If the phase transfer power is greater than 0, it indicates that the three-phase power regulation device is functioning correctly. i Power is injected into the low-voltage main winding of the phase. i If the phase transfer power is less than 0, it indicates that the three-phase power regulation device is in operation. i Power is extracted from the low-voltage main winding of the phase.

[0093] The power scheduling module 203 is used to extract and inject power into the low-voltage main winding through the three-phase power regulation device based on the power regulation command.

[0094] According to the power regulation command of each phase, the three bidirectional power converters of the three-phase power regulation device are controlled to perform power injection or extraction operations.

[0095] Specifically, if i If the power regulation command for a phase is greater than 0, the three-phase power regulation device is switched to inverter mode. In inverter mode, power is drawn from the internal DC bus to supply the self-balancing smart transformer. i Power is injected into the low-voltage main winding of the phase; if i If the power regulation command for a phase is less than 0, the three-phase power regulation device will be switched to rectification mode. In rectification mode, from i The low-voltage main winding of the phase draws power to feed into the internal DC bus.

[0096] The power injection and extraction processes are synchronized in time to ensure that the instantaneous net power on the internal DC bus is always zero. The internal DC bus serves only as a power routing and buffer node and does not perform long-term energy storage functions.

[0097] Moreover, the above control method maintains the total power supplied by the low-voltage main winding to the load constant during the operation of the self-balancing smart transformer. It only adjusts the proportion of power obtained by the low-voltage side winding of each phase from the grid side through internal circulating current to achieve dynamic balance of the three-phase current.

[0098] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. In particular, it should be noted that any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A self-balancing intelligent transformer, characterized in that, include: Electromagnetic transformers, three-phase power regulating devices and controllers; The electromagnetic transformer includes a three-phase core column, a high-voltage winding, a low-voltage main winding, and an internal coupling winding. The three-phase power regulating device includes three bidirectional power converters. The AC side of each bidirectional power converter is electrically connected to one of the built-in coupling windings, and the DC sides of the bidirectional power converters are interconnected to form an internal DC bus. The three-phase power regulating device is built into the electromagnetic transformer. The input terminal of the controller is connected to the sensor group, which is used to collect electrical and temperature data of the low-voltage main winding. The output terminal of the controller is connected to the bidirectional power converter.

2. The self-balancing smart transformer according to claim 1, characterized in that, The high-voltage winding and the low-voltage main winding are respectively wound on the core column of each phase; each built-in coupling winding is coaxially wound with the low-voltage main winding of the corresponding phase on the same core column to share the main magnetic circuit; the rated voltage of the built-in coupling winding is lower than the rated voltage of the low-voltage main winding of the corresponding phase.

3. The self-balancing smart transformer according to claim 2, characterized in that, For the coaxially wound built-in coupling winding and the low-voltage main winding, the number of turns of the built-in coupling winding ranges from 1 / 10 to 1 / 4 of the number of turns of the low-voltage main winding.

4. The self-balancing intelligent transformer according to claim 1, characterized in that, The bidirectional power converter adopts a single-phase H-bridge topology. The bidirectional power converter is connected in parallel with the supporting capacitor through a common DC bus to form the internal DC bus.

5. The self-balancing intelligent transformer according to claim 1, characterized in that, The controller also includes a digital twin lifetime prediction module; the digital twin lifetime prediction module is trained using the historical load data and historical temperature data of the electromagnetic transformer to construct a mapping relationship between the three-phase load imbalance and the insulation lifetime loss of the low-voltage main winding.

6. A control method for a self-balancing smart transformer according to any one of claims 1 to 5, characterized in that, include: The current data collected from the low-voltage side of the balanced smart transformer, as well as the temperature data on the low-voltage main winding side, are used to calculate the current three-phase current negative sequence component and winding temperature difference. Based on the negative sequence components of the three-phase current, the winding temperature difference, and the preset constraints, the power regulation command of the three-phase power regulation device is constructed with the goal of minimizing the preset objective function. Based on the power regulation command, the low-voltage main winding is extracted and injected with power through the three-phase power regulation device.

7. The control method for a self-balancing intelligent transformer according to claim 6, characterized in that, Based on the negative sequence components of the three-phase current, the winding temperature difference, and preset constraints, the power regulation command of the three-phase power regulation device is constructed with the objective of minimizing a preset objective function. Specifically: The objective function is constructed with the optimization objectives of minimizing the negative sequence component of the three-phase current and minimizing the winding temperature difference. Based on the constraints, and with the objective function as the goal, the power extraction and injection quantities of the low-voltage main winding in each phase of the three-phase power regulation device are solved to obtain the power regulation command. The extracted power and injected power are both referred to as transfer power.

8. The control method for a self-balancing intelligent transformer according to claim 7, characterized in that, The constraint condition restricts the sum of all the transferred power to zero, and any of the transferred power is less than or equal to the maximum power that the bidirectional power converter can carry.

9. The control method for a self-balancing intelligent transformer according to claim 6, characterized in that, Based on the power regulation command, the three-phase power regulation device extracts and injects power into the low-voltage main winding, specifically as follows: For any corresponding low-voltage main winding, if the power adjustment command is greater than 0, the corresponding bidirectional power converter is switched to inverter mode. In inverter mode, power is drawn from the internal DC bus to inject power into the low-voltage main winding. For any corresponding low-voltage main winding, if the power adjustment command is less than 0, the corresponding bidirectional power converter is switched to rectification mode. In rectification mode, power is drawn from the low-voltage main winding to inject power into the internal DC bus.

10. The control method for a self-balancing intelligent transformer according to claim 9, characterized in that, The power injection and power extraction processes are synchronized in time to ensure that the instantaneous net power on the internal DC bus is always 0.

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