Flexible parallel operation method for passive transformer and hybrid transformer

Abstract

According to the flexible parallel operation method for the passive transformer and the hybrid transformer, the passive transformer and the hybrid transformer integrated with the power electronic converter are operated in parallel, system capacity expansion is achieved on the basis that an original transformer is not replaced, and the transformation cost is remarkably reduced. The method is characterized in that the hybrid transformer realizes reactive power dynamic compensation, load harmonic suppression and distribution of active power according to capacity proportion through control of the power electronic converter, so that the electric energy quality of a passive transformer in a parallel system is improved, winding harmonic stress and loss are reduced, and the service life of equipment is prolonged. Aiming at the urgent demand on power supply capacity improvement in industrial power distribution system capacity expansion reconstruction and new energy high-permeability scenes, the method solves the problems of high cost and long period caused by transformer replacement in a traditional capacity expansion scheme, and overcomes the problem of uneven current distribution caused by impedance difference of parallel branches; and the method can be suitable for scenes sensitive to land occupation and strict in electric energy quality requirements, such as urban high-density power distribution networks and industrial parks.

Description

Technical Field

[0001] The invention of this application is applicable to the field of stable power supply for medium - voltage distribution networks. It can be used for the flexible expansion of transformer capacity in scenarios such as distribution networks. It is a method for the parallel operation of a passive transformer that takes into account reactive power support and harmonic suppression and a hybrid transformer integrated with a power - electronic module. Background Art

[0002] With the rapid development of power - electronic technology, the number of non - linear loads in medium - voltage distribution networks is increasing day by day. These loads will generate a large amount of harmonic currents, resulting in the distortion of the grid voltage waveform and affecting the power quality. At the same time, the demand for the expansion of distribution networks is also continuously increasing. The traditional method of transformer expansion often requires a large investment and a long construction period, and it is difficult to flexibly adapt to different load changes. In addition, the flow of reactive power in the power grid will also affect the voltage stability and transmission efficiency of the system. At present, the passive expansion scheme mainly realizes expansion by paralleling multiple power - frequency transformers. However, limited by the physical impedance difference, it is difficult to suppress the parallel circulating current, and the static turns - ratio adjustment cannot adapt to dynamic load changes. Traditional passive transformers have high reliability but fixed regulation ability, while pure power - electronic solutions are dynamically controllable but lack economy. With the wide application of new power - electronic equipment in traditional distribution networks, the hybrid transformer composed of traditional power - frequency transformers and power - electronic converters plays an important role in improving the reliability and flexibility of the system. The present invention realizes more efficient and flexible power transmission and distribution by paralleling a passive transformer and a hybrid transformer. It combines the simple reliability of the passive transformer and the flexibility of the hybrid transformer, and can meet the expansion demand of the distribution network, effectively compensate for reactive power and harmonics, and improve the stability and power quality of the system without significantly increasing costs and complexity. Summary of the Invention

[0003] The present invention proposes a flexible parallel operation method for a passive transformer and a hybrid transformer. By paralleling a passive transformer and a modular power - electronic transformer, it realizes flexible capacity expansion, reactive - power and harmonic suppression, and the distribution of load active current according to capacity. The passive transformer serves as the main channel for fundamental - wave active - power transmission, and the hybrid transformer provides dynamic compensation and capacity - expansion capabilities.

[0004] The object of the present invention is achieved through the following technical solutions: Measure the secondary - side voltage of the traditional power - frequency transformer according to the voltage sensor described in claim 1 , the DC - bus voltage and the low - voltage load - side voltage ; according to the current sensor described in claim 1, measure the output current of the parallel converter , the output current of the series converter , the output current of the series filter Hybrid transformer branch current and load current ; The controller obtains a power distribution coefficient β according to the capacities of the passive transformer and the traditional transformer in the hybrid transformer branch; The controller is also used to measure the load current , extract the fundamental component through a sliding discrete Fourier transformer (SDFT) to obtain the fundamental active component of the load current and the fundamental reactive component of the load current ; Based on the obtained fundamental active component of the load current and the power distribution coefficient β, combined with the fundamental reactive component of the load current , obtain the fundamental current reference that the series converter needs to introduce ; The controller is also used to measure the load current , extract the harmonic component through a sliding discrete Fourier transformer (SDFT) to obtain the harmonic current reference that the series converter needs to introduce ; Based on the obtained fundamental current reference and harmonic current reference of the series converter, combined with the output current of the series filter and the output current of the series converter , obtain the modulation wave of the series converter through a current double closed-loop controller ; Based on the set DC bus reference voltage , combined with the DC bus voltage measured through a low-pass filter (LPF) , obtain the active current reference that the parallel converter needs to compensate through a voltage closed-loop controller ; The controller is also used to measure the hybrid transformer branch current , extract the fundamental component through a sliding discrete Fourier transformer (SDFT) to obtain the fundamental active component of the branch current and the fundamental reactive component of the branch current ; Based on the obtained fundamental reactive component of the branch current , combined with the obtained active current reference , obtain the fundamental current reference that the parallel converter needs to compensate ; The controller is also used to measure the hybrid transformer branch current , the harmonic component extraction is carried out by sliding the discrete Fourier transformer (SDFT) to obtain the harmonic component reference to be compensated by the shunt converter. ; Based on the obtained fundamental current reference of the shunt converter and the harmonic component reference , combined with the output current of the shunt converter , the modulation wave of the shunt converter is determined through the current controller. ; Based on the obtained modulation wave , the control signals of the series converter and the shunt converter are obtained through the sine pulse width modulator.

[0005] Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are 1. By applying the technical solution proposed by the present invention, the capacity of the passive transformer can be flexibly expanded. Only new hybrid transformer modules need to be added, which reduces the equipment cost and solves the problems of high cost and long cycle caused by replacing the transformer in traditional capacity expansion.

[0006] 2. The structure of the traditional hybrid transformer is fixed, and most systems are complex and costly. The present invention adopts a modular architecture, supports multi-machine parallel connection and flexible expansion of power levels. New modules do not require manual parameter adjustment, and the failure of a single module does not affect the operation of the overall system. At the same time, through the integrated design, the equipment cost is reduced.

[0007] 3. The parallel operation method of the passive transformer and the hybrid transformer proposed by the present invention can achieve harmonic and reactive power combined governance and load dynamic current sharing, and is applicable to industrial scenarios with strict requirements for reliability and power quality, such as data center power supply and port onshore power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is the electrical connection structure of the parallel device of the passive transformer and the hybrid transformer provided by the embodiment of the present invention; Figure 2 is the schematic diagram of the full process implementation flow of the control of the parallel device of the passive transformer and the hybrid transformer provided by the embodiment of the present invention; Figure 3 is the block diagram of the series and parallel side converter controllers of the hybrid transformer provided by the embodiment of the present invention; Figure 4 is the schematic diagram of the control algorithm flow of the hybrid transformer provided by the embodiment of the present invention; Figure 5 , 6 , 7 are the simulation operation effect diagrams of the parallel device of the passive transformer and the hybrid transformer provided by the embodiment of the present invention; Figure 8It is a schematic diagram of the module of the parallel operation method of the passive transformer and the hybrid transformer provided by the embodiment of the present invention; Figure 9 It is a schematic diagram of a flexible parallel operation method of a passive transformer and a hybrid transformer provided by an embodiment of the present invention. Detailed implementation manners

[0009] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. The specific operation methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of the present application, "at least one" means one or more, where "a plurality" means two or more. In view of this, in the embodiments of the present application, "a plurality" can also be understood as "at least two". "And / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " generally represents an "or" relationship between the associated objects before and after, unless otherwise specified. In addition, it should be understood that in the description of the present application, words such as "first" and "second" are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0010] A flexible parallel operation method of a passive transformer and a hybrid transformer includes the following steps: Please refer to Figure 1 , the electrical connection structure of the parallel device of the passive transformer and the hybrid transformer, including: a passive transformer, a controller, a traditional power frequency transformer, a parallel converter, a series converter, a filter, a series isolation transformer, a current sensor, and a voltage sensor; The primary coil of the passive transformer is connected to the 10 kV medium-voltage power grid, the secondary coil is connected to the 400 V low-voltage busbar, the primary coil of the traditional transformer in the hybrid transformer branch is connected to the medium-voltage power grid, the secondary coil is connected in series with the series isolation transformer, and then connected to the low-voltage side load.

[0011] Please refer to Figure 2 , the schematic diagram of the whole control process implementation of the parallel device of the passive transformer and the hybrid transformer, including: Step S201: Measure the secondary voltage of the traditional power frequency transformer, the DC bus voltage and the low-voltage load side voltage according to the voltage sensor; measure the output current of the parallel converter and the output current of the series converter according to the current sensor, the output current of the series filter The branch current of the hybrid transformer and the load current ; Please refer to Figure 3 , the series and parallel side converter controller block diagram of the hybrid transformer provided by the embodiment of the present invention includes: Step S202: The controller is further configured to measure the load current , and through the sliding discrete Fourier transform (SDFT), extract the fundamental component to obtain the fundamental active component of the load current and the fundamental reactive component of the load current ; Step S203: Based on the obtained fundamental active component of the load current and the power distribution coefficient β, combined with the fundamental reactive component of the load current , obtain the fundamental current reference that the series converter needs to introduce , including the following steps: ; In the formula, , is the coordinate transformation matrix from dq to abc.

[0012] Step S204: The controller extracts the harmonic components of the load current, that is, through the harmonic extractor , obtain the harmonic current reference that the series converter needs to introduce , as shown in the following formula: ; In the formula, represents the bandwidth at the center frequency of the controller, represents the fundamental angular frequency of the system, represents the harmonic order, taking 3, 5, 7, 9, 11, 13 times.

[0013] Step S205: Based on the obtained fundamental current reference and harmonic current reference of the series converter, combined with the output current of the series filter and the output current of the series converter, through the current double closed-loop controller, obtain the modulation wave of the series converter; ; In the formula, represents the proportional coefficient of the proportional resonance controller, represents the resonance coefficient of the controller. represents the bandwidth at the center frequency of the controller represents the fundamental angular frequency of the system represents the harmonic order, taking values of 1, 3, 5, 7, 9, 11, 13 represents the proportionality coefficient

[0014] Step S206: The controller, based on the set DC bus reference voltage , combined with the DC bus voltage measured through a low-pass filter (LPF) , obtains the reference active current to be compensated for the parallel converter through a voltage closed-loop controller , as shown in the following formula ; In the formula is a proportional-integral controller

[0015] Step S207: The controller, based on the obtained fundamental reactive component of the branch current , combined with the obtained reference active current and the parallel-side phase reference obtained by the phase-locked loop , obtains the reference fundamental current to be compensated for the parallel converter , as shown in the following formula ; In the formula , is the coordinate transformation matrix from dq to abc

[0016] Step S208: The controller is used to measure the branch current of the hybrid transformer , and through a sliding discrete Fourier transformer (SDFT), extracts the harmonic components to obtain the reference harmonic components to be compensated for the parallel converter , as shown in the following formula ; In the formula, it is the same as the series-side harmonic extractor , represents the bandwidth at the center frequency of the controller represents the fundamental angular frequency of the system represents the harmonic order, taking values of 3, 5, 7, 9, 11, 13

[0017] Step S209: The controller, based on the obtained reference fundamental current and the reference harmonic components of the parallel converter, combined with the output current of the parallel converter, determines the modulation wave of the parallel converter through a current controller, including the following steps ; In the formula, represents the proportional coefficient of the proportional resonant controller, represents the resonant coefficient of the controller. represents the bandwidth at the center frequency of the controller, represents the fundamental angular frequency of the system, represents the harmonic order, taking 1, 3, 5, 7, 9, 11, 13 times.

[0018] Step S210: Based on the obtained modulation waves of the series converter and the parallel converter, the controller obtains the control signals of the series and parallel power circuits through the sine pulse width modulator.

[0019] Figure 5 、 6 is the simulation operation effect diagram of the parallel device of the passive transformer and the hybrid transformer provided by the embodiment of the present invention. It is characterized in that the capacity ratio of the passive transformer to the hybrid transformer is 1:1, that is, β = 0.5. The simulation is carried out under three working conditions. Working condition 1: 15kW pure resistive load, Figure 5 (a) is the output power of the hybrid transformer branch and the passive transformer branch under a 15kW resistive load. It can be seen that in the face of a 15kW load, when the traditional control is used without applying the parallel control method proposed by the present invention from 0 to 0.05s, due to the impedance difference in the line, the passive transformer branch undertakes about 8kW of load power. At 0.05s, by switching the control mode, under the power distribution control of the parallel operation mode, the uniform distribution of the power of the two branches is completed within less than 2ms; Figure 5 (b)and Figure 5 (c)are the waveform diagrams of the voltage and current on the secondary side of the hybrid transformer. Figure 5 (d)and Figure 5 (e)are the output currents of the passive transformer and the hybrid transformer branch. Under a pure resistive load, through the control method, the magnitudes and phases of the currents of the two branches are the same. Working condition 2 is a 64kW and 20kVar resistive-inductive load, Figure 6 (a) and (b) are the active power and reactive power output by the passive transformer and the hybrid transformer respectively. At 0.2s, by switching the control mode, under the power distribution control of the parallel operation mode, the active power is evenly divided, and the reactive power is transferred from the passive transformer branch to the hybrid transformer branch. Figure 6 (c) and (d) are the output currents of the passive transformer and the hybrid transformer branch. At 0.2s, through the control switching, it can be seen that the reactive current is transferred from the passive transformer branch to the hybrid transformer branch. Figure 6 (e), it can also be seen that at 0.2s, the voltage and current of the passive transformer branch are in phase, and it operates at a unity power factor. Working condition three: under a non-linear load, Figure 7(a) and (b) are the active power and reactive power output by the passive transformer and the hybrid transformer respectively. Under the power control of operating condition 2, harmonic control is added at 0.35 s. Figure 7 (c) and (d) are the output current of the passive transformer branch and the output current of the hybrid transformer branch.

[0020] In summary, a flexible parallel operation method of a passive transformer and a hybrid transformer proposed by the present invention is practical and feasible. The control scheme can achieve the functions of accurately compensating harmonics and reactive power, and at the same time has the function of active power sharing of fundamental current. While taking into account the passive capacity expansion, the stability of the system is increased.

[0021] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention. The above specific embodiments are only illustrative and not restrictive. Without departing from the spirit of the present invention and the scope protected by the claims, those of ordinary skill in the art can make many specific transformations in various forms under the inspiration of the present invention, and these all belong to the protection scope of the present invention.

[0022] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0023] The embodiment module is as Figure 8 shown. A flexible parallel operation method of a passive transformer and a hybrid transformer includes: A first acquisition module 801, configured to acquire the secondary side voltage of the traditional power frequency transformer, the DC bus voltage, the load voltage, the converter output current, the filter output current, the branch current, and the load current according to the sensor; A first determination module 802, configured to determine the power distribution coefficient β according to the capacities of the traditional transformers in the passive transformer and hybrid transformer branches; A second determination module 803, configured to measure the load current, extract the fundamental component, obtain the fundamental active component and fundamental reactive component of the load current, and determine the fundamental current reference that the series converter needs to introduce according to the power distribution coefficient β; A third determination module 804, configured to measure the load current, extract the harmonic component, and determine the harmonic current reference that the series converter needs to introduce; A fourth determination module 805, configured to determine the modulation wave of the series converter according to the fundamental current reference and harmonic current reference that the series converter needs to introduce; A second acquisition module 806, configured to obtain the switching signal of the series power converter through sine pulse width modulation according to the modulation wave voltage of the fourth determination module 705; A fifth determination module 807, configured to determine a reference active current to be compensated by the parallel converter according to the obtained DC bus voltage through a low-pass filter and voltage closed-loop control; A sixth determination module 808, configured to obtain a fundamental active component and a fundamental reactive component of the branch current according to the obtained branch current of the hybrid transformer through a fundamental wave extractor, and determine a reference fundamental current to be compensated by the parallel converter in combination with the obtained reference active current; A seventh determination module 809, configured to determine a reference harmonic current to be compensated by the parallel converter according to the obtained branch current of the hybrid transformer through a harmonic extractor; An eighth determination module 810, configured to determine a voltage reference of the parallel converter according to the fourth determination module 806, the fifth determination module 807, and the sixth determination module 808, and determine a modulation wave voltage of the parallel converter through the current closed-loop controller; A third acquisition module 811, configured to obtain a switching signal of the parallel power converter through sine pulse width modulation according to the modulation wave voltage determined by the seventh determination module 809.

[0024] Figure 9 It is a schematic diagram of a flexible parallel operation method of a passive transformer and a hybrid transformer provided by an embodiment of the present invention.

[0025] The schematic diagram of the parallel device of the hybrid transformer is as Figure 9 shown, including: a converter 901, a controller 902, a memory 903, and a computer program 904 stored in the memory 903 and operable on the controller 902. When the controller 902 executes the computer program 804, the steps in the embodiment of the above resonance suppression method are implemented, such as Figure 2 the steps S201 to S208 shown. Alternatively, when the controller 902 executes the computer program 904, the powers of the above-mentioned modules / units in the embodiment are implemented, such as Figure 8 the functions of the modules 801 to 810 shown.

[0026] Exemplarily, the computer program 904 can be divided into one or more modules / units, which are stored in the memory 903 and executed by the controller 902 to complete the embodiments of the present invention. The one or more modules / units can be a series of computer program instruction segments capable of completing specific functions, and these instruction segments are used to describe the execution process of the computer program 904 in the hybrid transformer system device 9. For example, the computer program 904 can be divided into a first acquisition module, a first determination module, a second determination module, a third determination module, a second acquisition module, a fourth determination module, a fifth determination module, a sixth determination module, a seventh determination module, and a third acquisition module. The functions of each module are as follows: The first acquisition module is configured to acquire the secondary side voltage of the traditional power frequency transformer, the DC bus voltage, the load voltage, the converter output current, the branch current, and the load current according to the sensor; The first determination module is configured to determine the harmonic current reference for series converter compensation according to the load current and the secondary side voltage of the traditional power frequency transformer; The second determination module is configured to obtain the current data that the series converter needs to compensate according to the fundamental component of the load current, and determine the fundamental current reference output by the series converter; The third determination module is configured to determine the current reference required by the series converter according to the first determination module and the second determination module, and determine the modulation wave voltage of the series converter through a current closed-loop controller; The second acquisition module is configured to obtain the switching signal of the series power converter through sinusoidal pulse width modulation according to the modulation wave voltage of the third determination module; The fourth determination module is configured to determine the DC active component current reference of the parallel converter through a low-pass filter and voltage closed-loop control according to the obtained DC bus voltage; The fifth determination module is configured to determine the harmonic current reference that the parallel converter needs to compensate through a harmonic extractor according to the obtained branch current of the hybrid transformer; The sixth determination module is configured to determine the reactive current reference that the parallel converter needs to compensate through a reactive power extractor according to the obtained branch current of the hybrid transformer; The seventh determination module is configured to determine the voltage reference of the parallel converter according to the fourth determination module, the fifth determination module, and the sixth determination module, and determine the modulation wave voltage of the parallel converter through the current closed-loop controller; The third acquisition module is configured to obtain the switching signal of the parallel power converter through sinusoidal pulse width modulation according to the modulation wave voltage determined by the seventh determination module.

[0027] The parallel operation method of the passive transformer and the hybrid transformer may include, but is not limited to, a converter 901, a controller 902, and a memory 903. Those skilled in the art can understand that Figure 9 These are merely examples of the hybrid transformer device and do not constitute a limitation on the hybrid transformer device. It may include more or fewer components than those shown in the figure, or combine certain components, or have different components. For example, the life evaluation terminal device of the power transformer may further include input / output devices, network access devices, buses, etc.

[0028] The so-called controller 902 may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0029] The memory 903 may be an internal storage unit of the parallel operation device 9 of the passive transformer and the hybrid transformer, such as an external memory circuit of the hybrid transformer device 9. For example, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the hybrid transformer device 9. Further, the memory 903 may also include both the internal storage unit of the hybrid transformer device 9 and external storage devices. The memory 903 is used to store the computer program and other programs and data required by the hybrid transformer device 9. The memory 903 may be used to temporarily store the data that has been output or is to be output.

[0030] Those skilled in the art can clearly understand that, for the convenience and conciseness of description, only the above-mentioned division of each functional unit and module is used as an example. In actual applications, the above functions can be allocated to different functional units and modules according to needs, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction and do not limit the protection scope of this application. The specific working process of the units and modules in the above system can refer to the corresponding process in the foregoing method embodiment and will not be elaborated here.

[0031] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For the parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0032] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or by a combination of computer software and electronic hardware. Whether these functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0033] In the embodiments provided by the present invention, it should be understood that the disclosed device / terminal device and method can be implemented in other ways. For example, the device / terminal device embodiments described above are merely illustrative. For example, the division of the above-mentioned module or unit is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection can be through some interfaces. The indirect coupling or communication connection of the device or unit can be in an electrical, mechanical or other form.

[0034] The unit described as a separated component may or may not be physically separated, and the component displayed as a unit may or may not be a physical unit, that is, it can be located in one place, or can be distributed to multiple network units. Some of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0035] In addition, in each embodiment of the present invention, each functional unit can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0036] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, all or part of the processes in the above-described embodiment methods of the present invention can also be completed by instructing relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-described various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the content included in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0037] The above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A flexible parallel operation method for a passive transformer and a hybrid transformer, characterized in that, Comprising: A passive transformer, a controller, a traditional power frequency transformer, a parallel converter, a series converter, a filter, a series isolation transformer, a current sensor, and a voltage sensor; The primary coil of the passive transformer is connected to the medium voltage grid, and the secondary coil is connected to the low voltage side bus. The hybrid transformer includes a traditional power frequency transformer, a series-parallel converter, a filter, and a series isolation transformer; the primary coil of the traditional power frequency transformer is connected to the medium voltage grid, and the secondary coil is connected to the first end of the first current sensor. The second end of the first current sensor is connected to one end of the primary coil of the series isolation transformer, and the other end is connected to the low voltage side load. The first end of the second current sensor is connected to the filter inductor of the parallel converter, and the second end is connected to the first end of the parallel converter. The second end of the parallel converter is connected to the first end of the series converter. The second end of the series converter is connected to the first end of the third current sensor. The second end of the second current sensor is connected to the first end of the filter. The second end of the filter is connected to the first end of the fourth current sensor. The second end of the fourth current sensor is connected to the secondary coil of the series isolation transformer. The first end of the fifth current sensor is connected to the low voltage side bus, and the second end is connected to the load; the voltage sensors are respectively installed on the output side of the secondary coil of the traditional power frequency transformer, the DC bus, and the low voltage side load.

2. A flexible parallel operation method for a passive transformer and a hybrid transformer, characterized in that, Comprising: The voltage sensor according to claim 1 measures the secondary side voltage of a traditional power frequency transformer , the DC bus voltage and the low-voltage load side voltage ; The output current of the parallel converter measured by the current sensor according to claim 1 , the output current of the series converter , the output current of the series filter , the branch current of the hybrid transformer and the load current ; The controller is configured to receive the voltage and current information measured by the above sensors, and based on the measured load voltage , load current and the branch current of the hybrid transformer , and obtain the load power and , the output power of the passive transformer branch and , as well as the output power of the hybrid transformer branch and , and select one of them as the power observable; The controller obtains the power distribution coefficient β according to the capacities of the traditional transformers in the passive transformer and the hybrid transformer branches; The controller is also used to measure the load current , and through a sliding discrete Fourier transformer (SDFT), the fundamental component is extracted to obtain the fundamental active component of the load current and the fundamental reactive component of the load current ; The controller, based on the obtained fundamental active component of the load current and the power distribution coefficient β, combines with the fundamental reactive component of the load current , to obtain the fundamental current reference that the series converter needs to introduce ; The controller is further configured to measure the load current , and extract harmonic components through a sliding discrete Fourier transformer (SDFT) to obtain the harmonic current reference that the series converter needs to introduce ; The controller, based on the obtained fundamental current reference and harmonic current reference of the series converter , combines the output current of the series filter and the output current of the series converter , and through a current dual closed-loop controller, obtains the modulation wave of the series converter ; ​ The controller, based on the set DC bus reference voltage , combines with the DC bus voltage measured through a low-pass filter (LPF) , and obtains the reference active current to be compensated for the parallel converter through a voltage closed-loop controller ; The controller is also used to measure the branch current of the hybrid transformer , and extract the fundamental component through a sliding discrete Fourier transformer (SDFT) to obtain the fundamental active component of the branch current and the fundamental reactive component of the branch current ; The controller, based on the obtained fundamental reactive component of the branch current , combines with the obtained reference active current to obtain the reference fundamental current that the shunt converter needs to compensate ; The controller is also used to measure the branch current of the hybrid transformer and extract the harmonic components through a sliding discrete Fourier transformer (SDFT) to obtain the harmonic component reference to be compensated by the parallel converter ; The controller determines the modulation wave of the parallel converter through a current controller based on the obtained fundamental current reference and harmonic component reference of the parallel converter and in combination with the output current of the parallel converter. Harmonic component reference ; By combining the output current of the parallel converter, the modulation wave of the parallel converter is determined through a current controller based on the obtained fundamental current reference and harmonic component reference of the parallel converter. ; The controller, based on the obtained modulation wave , obtains the control signals of the series converter and the parallel converter through the sine pulse width modulator.

3. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that The controller determines the power distribution coefficient β based on the capacity of the passive transformer and the capacity of the traditional transformer in the hybrid transformer branch , as shown in the following formula:

4. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that, The controller, based on the obtained fundamental active component of the load current and the power distribution coefficient β, combines the fundamental reactive component of the load current , and through the low-voltage side voltage phase obtained by the phase-locked loop , performs coordinate transformation to obtain the fundamental current reference that needs to be introduced by the series converter , as shown in the following formula: ； In the formula, , is the coordinate transformation matrix from dq to abc.

5. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that, The controller extracts the harmonic components of the load current, i.e., through a harmonic extractor , and obtains the harmonic current reference that the series converter needs to introduce , as shown in the following formula: ； In the formula, represents the bandwidth at the center frequency of the controller, represents the fundamental angular frequency of the system, represents the harmonic order, taking the 3rd, 5th, 7th, 9th, 11th, and 13th orders.

6. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that, The controller is based on the DC bus reference voltage , combines the measured DC bus voltage , and obtains the reference active current to be compensated for the parallel converter through a voltage closed-loop controller , as shown in the following formula: ； In the formula, is a proportional-integral controller.

7. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that The controller, based on the obtained fundamental reactive component of the branch current , combines the obtained reference active current and the phase reference of the shunt side obtained by the phase-locked loop to obtain the reference fundamental current that the shunt converter needs to compensate , as shown in the following formula: ； In the formula, , is the coordinate transformation matrix from dq to abc.

8. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that The controller is used to measure the branch current of the hybrid transformer , and through a sliding discrete Fourier transformer (SDFT), harmonic component extraction is performed to obtain the harmonic component reference to be compensated by the parallel converter , as shown in the following formula: ； In the formula, it is the same as the series-side harmonic extractor and represents the bandwidth at the center frequency of the controller, represents the fundamental angular frequency of the system, represents the harmonic order, taking the 3rd, 5th, 7th, 9th, 11th, and 13th orders.

9. A flexible parallel operation method for a passive transformer and a hybrid transformer according to claim 2, characterized in that Based on the obtained current references of the series converter and the parallel converter, the modulation wave voltages of the series converter and the parallel converter are obtained, and through the sine pulse width modulator, the control signals of the series and parallel power circuits are obtained.

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