Transformer parallel circuit

Abstract

The invention provides a transformer parallel circuit. The transformer parallel circuit comprises a first bus; a second bus bar; the number of the transformer main circuits is at least two, each transformer main circuit is provided with a transformer, the input ends of the transformers are electrically connected with the first bus, the first branch circuit is provided with a first thyristor, the input ends of the first thyristors are electrically connected with the output ends of the transformers, and the output ends of the first thyristors are electrically connected with the second bus; the second branch is provided with a second thyristor, the input end of the second thyristor is electrically connected with the output end of the transformer, and the output end of the second thyristor is electrically connected with the second bus. The problem that in the prior art, when transformer circuits work in parallel, energy is wasted is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer design, and in particular to a transformer parallel circuit. Background Art

[0002] With the popularization of frequency conversion technology, such as electric vehicles, charging piles have sprung up everywhere in recent years. For the current transformer public area, if no changes are made, transformer overload and overload will become the norm, and special places must be arranged for the centralized placement of power equipment. Transformers with different capacities running in parallel will generate circulating currents, resulting in energy waste. Summary of the invention

[0003] The main purpose of the present invention is to provide a transformer parallel circuit to solve the problem of energy waste when the transformer circuits in the prior art work in parallel.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a transformer parallel circuit is provided, comprising: a first bus; a second bus; a transformer main circuit, there are at least two transformer main circuits, each transformer main circuit is provided with a transformer, the input end of the transformer is electrically connected to the first bus, each transformer main circuit is correspondingly provided with a first branch and a second branch, the first branch and the second branch are arranged in parallel, the first branch is provided with a first thyristor, the input end of the first thyristor is electrically connected to the output end of the transformer, and the output end of the first thyristor is electrically connected to the second bus, the second branch is provided with a second thyristor, the input end of the second thyristor is electrically connected to the output end of the transformer, and the output end of the second thyristor is electrically connected to the second bus; the first thyristor is used to conduct the transformer main circuit and the second bus in the positive half cycle of the voltage, and the second thyristor is used to conduct the transformer main circuit and the second bus in the negative half cycle of the voltage.

[0005] Furthermore, the first thyristors corresponding to the main circuits of the transformers are turned on or off at the same time, and the second thyristors corresponding to the main circuits of the transformers are turned on or off at the same time.

[0006] Furthermore, when the first thyristors corresponding to the main circuits of each transformer are turned on at the same time in the positive half cycle of the voltage, the second thyristors corresponding to the main circuits of each transformer are turned off at the same time in the positive half cycle of the voltage; when the first thyristors corresponding to the main circuits of each transformer are turned off at the same time in the negative half cycle of the voltage, the second thyristors corresponding to the main circuits of each transformer are turned on at the same time.

[0007] Further, the voltage of the first bus is greater than the voltage of the second bus.

[0008] Furthermore, the capacity of the transformers on different transformer main circuits is different.

[0009] Furthermore, both the first thyristor and the second thyristor are fully controlled thyristors.

[0010] Furthermore, a plurality of user load branches are connected to the second busbar, and output ends of the user load branches are in a connection state of being conducted with power load devices.

[0011] Furthermore, a compensation capacitor is electrically connected between the second bus and the user load branch, and the compensation capacitor is used to absorb excess reactive power in the circuit.

[0012] Furthermore, a three-phase balanced inverter is provided on the user load branch, the input end of the three-phase balanced inverter is electrically connected to the output end of the compensation capacitor, and the output end of the three-phase balanced inverter is electrically connected to the power load device.

[0013] Furthermore, the electrical load device is a charging pile, and one charging pile is electrically connected to three-phase balanced inverters on multiple user load branches, so that the charging pile uses multiple transformers to work simultaneously.

[0014] By applying the technical solution of the present invention, by setting a first thyristor for conducting the transformer main circuit and the second busbar in the positive half cycle of the voltage, and setting a second thyristor for conducting the transformer main circuit and the second busbar in the negative half cycle of the voltage, the thyristor can accurately control the current flow when the transformer is operated in parallel, and by simultaneously turning on and off, the occurrence of current circulation can be eliminated. The technical solution of the present application effectively solves the problem of energy waste when the transformer circuit works in parallel in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0016] Figure 1 A circuit diagram of a transformer parallel circuit in the prior art is shown;

[0017] Figure 2 A circuit diagram showing a first embodiment of a transformer parallel circuit according to the present invention is shown;

[0018] Figure 3 A circuit diagram of an embodiment of a first thyristor and a second thyristor according to the present invention is shown;

[0019] Figure 4 A circuit diagram showing a second embodiment of a transformer parallel circuit according to the present invention is shown;

[0020] Figure 5 A circuit diagram showing a third embodiment of a transformer parallel circuit according to the present invention;

[0021] Figure 6 A schematic diagram of voltage waveforms when two parallel transformers according to the present invention are operated in parallel is shown.

[0022] The above drawings include the following reference numerals:

[0023] 100, first busbar;

[0024] 101, second busbar;

[0025] 2. Transformer main circuit;

[0026] 203. Transformer;

[0027] 204. Three-phase balanced inverter;

[0028] 205, second thyristor;

[0029] 206. Compensation capacitor;

[0030] 208, first thyristor;

[0031] 2012, knife switch; 2023, circuit breaker. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0034] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in a variety of different forms and should not be construed as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art. In the accompanying drawings, for the sake of clarity, the thickness of the layers and regions may be enlarged, and the same reference numerals are used to represent the same devices, and thus their descriptions will be omitted.

[0036] For example, a community has more than 1,000 households and 10 630kVA transformers, with one distribution cabinet for every two transformers (e.g. Figure 1 As shown in the figure, when the load is heavy, the knife switch 2012 and the circuit breaker 2023 are separated, and the two transformers operate independently. When the load is light, the knife switch 2012 and the circuit breaker 2023 are closed, and only one transformer operates. In the current public transformer area, reactive power loss, transformer loss table 315kVA transformer reaches the upper limit of power consumption 90720KW, power factor assessment standard 0.8, reactive transformer loss 7348KW, 8.9%. 2500kVA transformer reaches the upper limit of power consumption 1620000KW, power factor assessment standard 0.9, reactive transformer loss 133200KW, 8.22%; plus active power loss, the comprehensive loss is about 10%. Calculated based on the monthly transformer loss charge of 23 yuan / kVA for a dedicated transformer, the monthly loss of this community when under heavy load is 14,490 yuan for 10 630kVA transformers multiplied by 23 yuan. Assuming that this community has 17 buildings, there are 10 property managers and each person has an average monthly salary of 10,000 yuan, a total of 100,000 yuan. Assuming that each household has 100 square meters and the monthly property fee is 0.7 yuan / square meter, the total cost of 1,000 households is 70,000 yuan, and the property fee only accounts for about half of the loss of 10 630kVA transformers. Therefore, there is a problem of energy waste in the existing technology.

[0037] A public transformer area refers to a collection of transformers and related distribution equipment used to supply power to users within a certain range (such as residential, commercial or industrial areas) in the power system. In a public transformer area, one or more transformers are used to convert higher distribution voltages into lower consumption voltages in order to safely supply electricity to end users.

[0038] Combination Figures 1 to 6As shown, according to a specific embodiment of the present application, a transformer parallel circuit is provided, including: a first bus 100; a second bus 101; a transformer main circuit 2, at least two transformer main circuits 2, each transformer main circuit 2 is provided with a transformer 203, the input end of the transformer 203 is electrically connected to the first bus 100, each transformer main circuit 2 is correspondingly provided with a first branch and a second branch, the first branch and the second branch are arranged in parallel, the first branch is provided with a first thyristor 208, the input end of the first thyristor 208 is electrically connected to the transformer The output end of the transformer 203 is electrically connected, the output end of the first thyristor 208 is electrically connected to the second bus 101, the second branch is provided with a second thyristor 205, the input end of the second thyristor 205 is electrically connected to the output end of the transformer 203, and the output end of the second thyristor 205 is electrically connected to the adjacent second bus 101; the first thyristor 208 is used to turn on the transformer main circuit 2 and the second bus 101 in the positive half cycle of the voltage, and the second thyristor 205 is used to turn on the transformer main circuit 2 and the second bus 101 in the negative half cycle of the voltage.

[0039] By applying the technical solution of the present invention, by setting the first thyristor 208 to conduct the transformer main circuit 2 and the second bus 101 in the positive half cycle of the voltage, and setting the second thyristor 205 to conduct the transformer main circuit 2 and the second bus 101 in the negative half cycle of the voltage, the thyristor can accurately control the current flow when the transformer is operated in parallel, and by timely conduction and cutoff, the occurrence of circulating current can be eliminated. The first thyristor 208 is positive, the second thyristor 205 is negative, the positive thyristors of the same phase line of each transformer are simultaneously turned on and cut off, and the negative thyristors are simultaneously turned on and cut off. The technical solution of the present application effectively solves the problem of energy waste when the transformer circuits work in parallel in the prior art.

[0040] Transformer parallel operation refers to the operation mode in which the primary and secondary terminals of two or more transformers with the same polarity are connected to each other through the same busbar.

[0041] When two or more transformers of different capacities are operated in parallel, that is, their primary side (high voltage side) and secondary side (low voltage side) are connected through the same busbar, a circulating current will usually be generated between the transformers when light load or no load occurs. Circulating current is between the transformers in parallel, because their impedance is not completely matched, resulting in non-load current, i.e., circulating current, flowing between the transformers when the load is the same. This current cannot be effectively transmitted to the load, but also increases the loss of the power system, reduces efficiency, and may even damage the transformer itself.

[0042] As a switching device, power electronic fully controlled thyristors play a key role in applications where transformers are operated in parallel. Thyristors are semiconductor devices that can control their on and off states. In the present invention, fully controlled thyristors are used to accurately control the current flow when transformers are operated in parallel. By turning them on and off at the right time, the occurrence of circulating current can be eliminated. Figure 6 shows one of the three phases of the transformer output. The first thyristor is positive and the second thyristor is negative. The positive thyristors of the same phase line of each transformer are turned on and off at the same time, and the negative thyristors are turned on and off at the same time, to prevent the current from flowing directly between the transformers without passing through the load.

[0043] The use of this power electronic switch enables transformers of different capacities to run in parallel more efficiently, improving the overall efficiency and reliability of the power system while reducing the loss of transformer and reactive power. For large power systems, especially those that require high flexibility and high efficiency, such as residential areas, commercial areas or industrial areas, the application of this technology is of great significance. Through this technology, the power system can better adapt to load changes, optimize power distribution, and reduce energy waste, thereby achieving a more economical and environmentally friendly power supply.

[0044] The technical principle of using fully controlled thyristors as power electronic switches to achieve parallel operation of transformers without generating circulating currents involves the precise control of power electronic switches and the physical characteristics of parallel operation of transformers.

[0045] exist Figure 3 In the figure, we see a simplified circuit diagram of a single-phase power electronic switch, each phase consists of two fully controlled thyristors. Thyristor is a controllable semiconductor switch that can be controlled to switch between on and off states. This control is based on the polarity of the voltage:

[0046] When the line voltage is in the positive half cycle, the thyristor marked with "+" is turned on, and the thyristor marked with "-" is turned off. When the line voltage is in the negative half cycle, the situation is the opposite, the thyristor marked with "-" is turned on, and the thyristor marked with "+" is turned off.

[0047] This operation ensures that at any given moment, only the thyristor that matches the current voltage polarity is turned on, thereby controlling the current to flow only in the required direction. This precise control of the thyristors prevents current from circulating through parallel transformers when the same polarity is turned on.

[0048] exist Figure 6In the figure, we see the voltage waveforms on the secondary sides of the two transformers. In order to prevent circulating current, the output voltages of the two transformers must be synchronized, that is, the frequency is the same, the phase is the same, and the voltage amplitude is equal. Through the precise control of the power electronic switch, it can be ensured that when the transformers are in parallel operation, even if the transformer capacities are different, as long as the voltages they output are synchronized in time and phase, no circulating current will be formed between the secondary sides. The reasons why transformers that do not meet the parallel operation conditions generate circulating current are as follows: From the power triangle analysis, the transformer has reactive power in addition to active power. For active power, between different capacities, the voltage of the transformer with large capacity is higher than that of the transformer with small capacity when the load is light, and the active power voltage is equal under a certain load. For reactive power, the reactive power voltage of the transformer with large capacity is greater than that of the transformer with small capacity, thus generating circulating current. Therefore, transformers that do not meet the parallel operation conditions are not allowed to operate in parallel.

[0049] The control logic of the thyristor ensures that when the voltage is positive, the "+" thyristor is turned on, allowing current to pass; when the voltage is negative, the "-" thyristor is turned on, allowing current to flow in the opposite direction. This control mechanism can prevent current from flowing from one transformer to another without load, that is, avoiding the generation of circulating current. Figure 6 shows one of the three phases of the transformer output. The first thyristor is positive and the second thyristor is negative. The positive thyristors of the same phase line of each transformer are turned on and off at the same time, and the negative thyristors are turned on and off at the same time to prevent the occurrence of circulating current.

[0050] In short, fully controlled thyristors, as power electronic switches, ensure the synchronization of output voltage and the correct guidance of current when transformers are running in parallel through their precise control capabilities, thus technically achieving the goal of eliminating circulating current. This control method utilizes the fast response characteristics of thyristors, which can adjust the conduction state in real time according to the change of voltage polarity, effectively preventing the current from forming unnecessary circulating currents between transformers, and improving the efficiency and reliability of the power system.

[0051] In alternating current (AC), positive half-cycle and negative half-cycle are terms that describe the periodic characteristics of voltage or current over time. AC is different from direct current (DC), and its magnitude and direction change periodically, usually in the form of a sine wave. A complete sine wave cycle includes the process from zero point of the waveform to the next zero point, which can be divided into two half-cycles: positive half-cycle and negative half-cycle.

[0052] Positive half cycle: In a cycle of a sine wave, when the voltage or current value starts to rise from zero, reaches a peak value, and then drops back to zero, this part is called a positive half cycle. At this stage, the direction and magnitude of the voltage or current are both positive, that is, they are positive relative to the zero point. In the power system, the positive half cycle usually refers to the part of the cycle in the voltage or current waveform that is above the zero voltage line (or zero current line).

[0053] Negative half cycle: The other half of the sine wave starts from zero, the voltage or current value drops to the negative peak, and then rises back to zero. At this stage, the voltage or current value is negative, that is, they are negative relative to zero. The negative half cycle is symmetrical with the positive half cycle in time and shape, but the voltage or current has the opposite sign.

[0054] The definition of positive half-cycle and negative half-cycle is based on the periodicity and symmetry of AC, and each half-cycle occupies half of the sine wave period. In power electronic devices, such as thyristors, the time points for controlling their conduction and cutoff are usually related to the positive and negative half-cycles of AC. As a controllable switch, thyristors can decide when to turn on and when to turn off according to the signals of the positive and negative half-cycles, thereby achieving precise control of AC.

[0055] For example, in the above technical solution, when the line voltage is in the positive half cycle, the "+" thyristor is turned on, allowing current to flow; while the "-" thyristor is turned off, preventing the current from flowing in the opposite direction. When the voltage switches to the negative half cycle, the on and off states are reversed to ensure that the current flows correctly between the positive and negative half cycles and does not form a loop current between different transformers. This control mechanism is crucial for the stable operation of the power system.

[0056] Furthermore, knife switches and switches are key control devices in power systems, used to connect and disconnect circuits. Knife switches are mainly used as isolation devices, which can disconnect circuits under no load or low load conditions, while switches refer to air switches, oil switches, etc., which can operate under load and play a role in protecting circuits.

[0057] Transformers are one of the core devices of the power system, used to convert electricity between different voltage levels. They use the principle of electromagnetic induction to achieve efficient transmission of electricity by changing the voltage.

[0058] During peak power demand, multiple transformers can be operated in parallel to increase the system's power supply capacity, prevent overload, and ensure the stability and reliability of power supply. For example, in industrial sites, large commercial buildings, or residential areas, when power consumption exceeds the rated capacity of a single transformer, the parallel standby transformers can be started to meet the additional load demand.

[0059] Parallel operation allows the power system to flexibly adjust the power supply mode according to the actual load conditions. When a transformer fails or needs maintenance, other parallel transformers can continue to supply power, preventing power outages and improving the availability and flexibility of the power system.

[0060] When transmitting electricity over long distances, transformer loads running in parallel can average out the current density of the line, thereby reducing line losses.

[0061] Parallel operation can help balance the load of the power system, especially in a three-phase system. By adjusting the operating status of the parallel transformer, the current between different phases can be balanced, voltage fluctuations can be reduced, and power quality can be improved.

[0062] Parallel operation can enhance the redundancy of the power system. That is, when multiple transformers are connected in parallel, even if one or more transformers are out of operation, the system can still continue to supply power through the remaining transformers, thereby improving the safety and risk resistance of the system. When the power demand is low, parallel operation can start only one or more transformers with appropriate capacity to avoid using oversized transformers and causing inefficient operation. Through parallel operation, some transformers can be shut down to save energy and reduce operating costs.

[0063] After a single transformer fails or shuts down, the system can quickly restore power through other transformers running in parallel, reducing power outage time and improving service continuity. Some power systems may face sudden or seasonal high load demands (such as peak air conditioning usage in summer), and parallel operation can quickly respond to these demands and avoid the high cost of long-term investment in large-capacity transformers.

[0064] Transformers operating in parallel can improve the power factor of the system, reduce reactive power loss, and improve the efficiency of power transmission through internal or external reactive power compensation devices.

[0065] like Figure 3 The figure shows one phase of the power electronic switch (two fully controlled thyristors). As shown in the figure, when the voltage is positive, the first thyristor 208 is turned on at the same time and the second thyristor 205 is turned off at the same time. When the voltage is negative, the second thyristor 205 is turned on at the same time and the first thyristor 208 is turned off at the same time. The above scheme is adopted to make the frequency the same, and the voltage is as follows Figure 6 As shown in the figure, there will be no circulating current when the secondary sides are connected together. The inverter does not need to be specially designed, and the three-phase load will not change at any time due to the input of the inverter, but the addition of the inverter can share part of the load to reduce the impact of unbalanced load on the transformer. During normal operation and maintenance, attention should also be paid to adjusting the three-phase imbalance to meet the requirements of the regulations. The main function of the inverter is to buffer the voltage impact when the power electronic switch is turned on and off. The main function of the charging pile is charging, and the power electronic switch can also buffer the voltage impact when it is turned on and off.

[0066] Furthermore, the first thyristors 208 corresponding to each transformer main circuit 2 are turned on or off at the same time, and the second thyristors 205 corresponding to each transformer main circuit 2 are turned on or off at the same time.

[0067] In the power system, when two or more transformers with the same capacity and load parallel conditions are operated, ideally, they share the load current evenly in proportion to their capacity, without generating additional current flow between the transformers. However, when the capacity of the transformers running in parallel is not exactly the same, or their impedance characteristics are different, current flow, i.e., circulating current, may still occur between the transformers even under the same voltage and frequency conditions. Circulating current will not only increase the loss of the power system, but may also cause overheating or even damage to the transformer, so measures need to be taken to prevent it.

[0068] Thyristor is a semi-controlled or fully controlled power semiconductor device that can switch between the on and off states and is used to control the flow of current in high-power circuits. When using a fully controlled thyristor, it provides a method for accurately controlling the flow of current and can be turned on or off in a timely manner to adjust the direction of current flow according to the needs of the power system.

[0069] In transformers of different capacities running in parallel, power electronic fully controlled thyristors are used as switches to achieve the following functions:

[0070] 1. Precise control: In the positive half cycle of the voltage, the thyristor "+" will be turned on and the "-" will be turned off, and vice versa. This control is based on real-time voltage polarity, ensuring that current flows only when needed, reducing unnecessary current flow.

[0071] 2. Eliminate circulating current: Thyristors can quickly adjust their conduction state according to the voltage changes on the secondary side of the transformer, and can synchronize the voltage phase and size in real time even between transformers of different capacities. In this way, even if the capacity or impedance of the transformer is different, the precise control of the thyristor can ensure that no circulating current is generated, because circulating current is usually caused by mismatch of voltage phase or size.

[0072] 3. Dynamically balanced load: Fully controlled thyristors can dynamically increase or decrease the number of transformers according to changes in load, ensuring that the system operates in the most efficient and safest state.

[0073] 4. Improve power system efficiency: By eliminating circulating currents and dynamically balancing loads, a system with fully controlled thyristors as switches can reduce power losses, improve the overall efficiency of the power system, and also protect the transformer.

[0074] In summary, the use of power electronic fully controlled thyristors as switches can overcome the problem of circulating current between transformers of different capacities running in parallel, and ensure the stable operation and efficient utilization of the power system under various load conditions by accurately controlling the flow of current in the circuit. This method has important application value in the design of modern power systems, especially when it is necessary to flexibly adjust the power supply strategy to adapt to changing power demand.

[0075] Furthermore, when the first thyristors 208 corresponding to each transformer main circuit 2 are turned on at the same time in the positive half cycle of the voltage, the second thyristors 205 corresponding to each transformer main circuit 2 are cut off at the same time in the positive half cycle of the voltage; when the first thyristors 208 corresponding to each transformer main circuit 2 are cut off at the same time in the negative half cycle of the voltage, the second thyristors 205 corresponding to each transformer main circuit 2 are turned on at the same time.

[0076] Further, the voltage of the first bus 100 is greater than the voltage of the second bus 101 .

[0077] Furthermore, the capacity of the transformer 203 on different transformer main paths 2 is different.

[0078] Furthermore, both the first thyristor 208 and the second thyristor 205 are fully controlled thyristors.

[0079] Furthermore, a plurality of user load branches are connected to the second bus 101, and the output ends of the user load branches are in a connection state of being conducted with the power load devices.

[0080] like Figure 6 It shows how to control the conduction and cutoff of thyristors to ensure that the voltage phase and frequency on the secondary side are the same when transformers of different capacities are operated in parallel, thereby avoiding the generation of circulating current. Figure 4 There are two sine waves in the middle, representing the voltage waveform on the secondary side of the transformer, usually represented by U (voltage), and the horizontal axis represents time t. The phase and frequency of the two sine waves are designed to be consistent, which means that their peaks and troughs appear at the same time point and the time to complete a cycle is the same.

[0081] Furthermore, a compensation capacitor 206 is electrically connected between the second bus 101 and the user load branch, and the compensation capacitor 206 is used to absorb excess reactive power in the circuit.

[0082] Compensation capacitors are used to improve the power factor of power systems. They can absorb excess reactive power, reduce losses in power transmission, and improve the overall efficiency of power systems.

[0083] Furthermore, a three-phase balancing inverter 204 is provided on the user load branch, the input end of the three-phase balancing inverter 204 is electrically connected to the output end of the compensation capacitor 206, and the output end of the three-phase balancing inverter 204 is electrically connected to the power load device.

[0084] An inverter is a power electronic device that converts direct current (DC) into alternating current (AC). In a three-phase balanced power system, the inverter also has the function of regulating the current balance. It may be used to compensate for imbalances in the power grid and improve the quality of power, especially in places with a large number of irregular loads such as charging stations and data centers, and it can also buffer these relatively large power consumption shocks.

[0085] Inverters can adjust the balance of three-phase voltage and current in the power system, which is crucial for parallel operation of transformers. In a three-phase system, unbalanced loads can cause phase and amplitude differences in voltage and current, damaging the transformer or reducing system efficiency. The addition of inverters can balance this load and reduce the impact of unbalanced three-phase loads on transformers.

[0086] At the moment when power electronic switches (such as fully controlled thyristors) are switched, rapid changes in voltage or current may occur, which are called "shocks". The inverter can absorb these shocks through its built-in snubber circuit to prevent them from causing damage to the transformer or other power equipment. This buffering effect helps to protect the stability of the power system and the safety of the equipment.

[0087] The inverter can flexibly adapt to various load requirements, whether it is a fast-changing load such as a charging pile, or other stable power-consuming equipment. Through the control of the inverter, the output voltage and frequency can be adjusted to ensure synchronization with the power system, thereby meeting the needs of different power-consuming equipment.

[0088] Reactive power compensation devices can improve the power factor of the power system, reduce reactive power loss, and improve power transmission efficiency. At the same time, reactive power compensation devices can also filter out harmonics, reduce power noise, optimize power quality, and provide purer power for sensitive equipment.

[0089] In power systems involving new energy sources (such as solar and wind energy), inverters convert the direct current generated by renewable energy equipment into alternating current so that it can be easily connected to the power grid or used by homes and commercial facilities. This power conversion is a key step in achieving the effective use of renewable energy.

[0090] The role of the inverter is to provide smooth power transmission when the load changes or the power electronic switch is switched, avoiding unnecessary impact on the system while ensuring the quality and efficiency of the power. Especially in the application of charging piles, the inverter can also ensure the stable supply of power during fast charging, avoiding voltage fluctuations or system instability caused by instantaneous large load demands on the power grid.

[0091] Furthermore, the electrical load device is a charging pile, and one charging pile is electrically connected to three-phase balanced inverters 204 on multiple user load branches, so that the charging pile uses multiple transformers 203 to work simultaneously.

[0092] The charging pile is set at any point in the parallel transformer area. In addition to balancing the three-phase load, the inverter also has an energy storage function to buffer the irregular load changes of large power-consuming equipment.

[0093] In an optional embodiment, a thyristor control method is also provided to achieve parallel operation of transformers of different capacities while avoiding the generation of circulating current:

[0094] 1. Synchronous detection and control: The system should be equipped with synchronous detection equipment to monitor the voltage and phase of the secondary side of all transformers. The square wave of the fully controlled thyristor trigger voltage is strictly consistent with the frequency and phase of the AC voltage. When the voltage passes through zero, it is turned on and off at the same time, which is the basis for achieving parallel operation without circulating current.

[0095] 2. Thyristor trigger control:

[0096] Voltage positive half-cycle control: When the voltage enters the positive half-cycle, the system detects the zero-crossing positive half-cycle time period and immediately triggers all the fully controlled thyristors marked "+" to turn on, while the "-" thyristors remain in the cut-off state. In this way, the current only passes in the positive half-cycle, ensuring the positive transmission of the current.

[0097] Voltage negative half cycle control: When the voltage enters the negative half cycle, it crosses the zero point positive and negative cycle time period, immediately triggering all thyristors marked as "-" to conduct, while the "+" thyristors remain in the cut-off state. In this way, the transmission direction of the current in the negative half cycle can be controlled to prevent the formation of reverse current.

[0098] 3. Current monitoring and regulation: During the process of thyristor conduction and cutoff, the current flowing through the thyristor should be monitored in real time to ensure a smooth transition of the current and avoid excessive current shock. If a sudden change or abnormality in the current is detected, the trigger point of the thyristor should be adjusted in time to restore the stability of the current.

[0099] 4. Fault detection and protection: The system should include a fault detection mechanism. Once a fault is detected in any transformer or thyristor, the thyristor at the fault point will be disconnected immediately to prevent the fault from propagating in the parallel system. At the same time, the system can be switched to the spare thyristor or transformer to maintain continuous operation of the system.

[0100] 5. Intelligent switching mechanism: According to the change of load, the system should be able to intelligently switch the conduction state of the thyristor to realize the dynamic load distribution of the transformer. When the load is light, only one transformer can be operated to reduce energy consumption; when the load increases, the system triggers more thyristors to conduct and puts multiple transformers into operation to meet higher power demand.

[0101] Control Flow:

[0102] 1. Preparation before starting: Before starting the system, ensure that all thyristors are in the cut-off state, and at the same time, check whether the square wave of the fully-controlled thyristor trigger voltage is strictly consistent with the frequency and phase of the AC voltage.

[0103] 2. Thyristor state switching:

[0104] When the system detects that the voltage enters the positive half cycle, all "+" thyristors are immediately triggered to turn on.

[0105] When the system detects that the voltage enters the negative half cycle, all “-” thyristors are immediately triggered to turn on.

[0106] At the beginning of each half cycle, the system should once again confirm the synchronization of the fully controlled thyristor trigger voltage square wave and the AC voltage frequency and phase, ensuring accurate control of the thyristor.

[0107] 3. Monitoring and adjustment:

[0108] Monitor the current in real time. Once abnormal current is found, adjust the trigger point of the thyristor immediately and cut off the thyristor to protect the system if necessary.

[0109] 4. Fault handling and recovery:

[0110] When a fault is detected, the thyristor at the fault point is immediately disconnected to prevent the fault from propagating.

[0111] If there are spare thyristors or transformers, switch to the spare equipment quickly to ensure continuous operation of the system.

[0112] Through the above control method, the parallel operation of transformers of different capacities can be realized, and the generation of circulating current can be avoided through the precise control of thyristors, ensuring the stability and efficiency of the power system. This method is particularly suitable for scenarios where the power supply strategy needs to be flexibly adjusted to cope with changing power demand and parallel operation of transformers of different capacities.

[0113] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0114] In addition to the above, it should be noted that "one embodiment", "another embodiment", "embodiment", etc. mentioned in this specification refer to the specific features, structures or characteristics described in conjunction with the embodiment included in at least one embodiment generally described in this application. The same expression appearing in multiple places in the specification does not necessarily refer to the same embodiment. Further, when describing a specific feature, structure or characteristic in conjunction with any embodiment, it is claimed that the realization of such feature, structure or characteristic in conjunction with other embodiments also falls within the scope of the present invention.

[0115] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0116] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A transformer parallel circuit, characterized in that: include: A first busbar (100); A second busbar (101); A transformer main circuit (2), wherein there are at least two transformer main circuits (2), each transformer main circuit (2) is provided with a transformer (203), the input end of each transformer (203) is electrically connected to the first bus (100), each transformer main circuit (2) is correspondingly provided with a first branch and a second branch, the first branch and the second branch are arranged in parallel, the first branch is provided with a first thyristor (208), the input end of the first thyristor (208) is electrically connected to the output end of the transformer (203), the output end of the first thyristor (208) is electrically connected to the second bus (101), the second branch is provided with a second thyristor (205), the input end of the second thyristor (205) is electrically connected to the output end of the transformer (203), and the output end of the second thyristor (205) is electrically connected to the second bus (101); The first thyristor (208) is used to conduct the transformer main circuit (2) and the second bus (101) in the positive half cycle of voltage, and the second thyristor (205) is used to conduct the transformer main circuit (2) and the second bus (101) in the negative half cycle of voltage.

2. The transformer parallel circuit according to claim 1, characterized in that: The conduction direction of the first thyristor (208) is different from the conduction direction of the second thyristor (205), the conduction direction of the first thyristor (208) is positive, and the conduction direction of the second thyristor (205) is negative. A plurality of the first thyristors (208) under the same phase line of each transformer (203) are turned on or off at the same time, and a plurality of the second thyristors (205) under the same phase line of each transformer (203) are turned on or off at the same time.

3. The transformer parallel circuit according to claim 2, characterized in that: When the first thyristors (208) corresponding to each transformer main circuit (2) are simultaneously turned on in a positive half cycle of voltage, the second thyristors (205) corresponding to each transformer main circuit (2) are simultaneously turned off in a positive half cycle of voltage; when the first thyristors (208) corresponding to each transformer main circuit (2) are simultaneously turned off in a negative half cycle of voltage, the second thyristors (205) corresponding to each transformer main circuit (2) are simultaneously turned on.

4. The transformer parallel circuit according to any one of claims 1 to 3, characterized in that: The voltage of the first bus (100) is greater than the voltage of the second bus (101).

5. The transformer parallel circuit according to any one of claims 1 to 3, characterized in that: The capacity of the transformer (203) on different transformer main circuits (2) is different.

6. The transformer parallel circuit according to any one of claims 1 to 3, characterized in that: Both the first thyristor (208) and the second thyristor (205) are fully controlled thyristors.

7. The transformer parallel circuit according to any one of claims 1 to 3, characterized in that: The second busbar (101) is connected to a plurality of user load branches, and the output ends of the user load branches are in a connection state of being connected to power load devices.

8. The transformer parallel circuit according to claim 7, characterized in that: A compensation capacitor (206) is electrically connected between the second bus (101) and the user load branch, and the compensation capacitor (206) is used to absorb excess reactive power in the circuit.

9. The transformer parallel circuit according to claim 8, characterized in that: A three-phase balancing inverter (204) is provided on the user load branch, the input end of the three-phase balancing inverter (204) is electrically connected to the output end of the compensation capacitor (206), and the output end of the three-phase balancing inverter (204) is electrically connected to the power load device.

10. The transformer parallel circuit according to claim 9, characterized in that: The electrical load device is a charging pile, and one of the charging piles is electrically connected to a plurality of three-phase balancing inverters (204) on the user load branches, so that the charging pile uses a plurality of transformers (203) to work simultaneously.

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