Current-enhanced harmonic generator control method and system based on virtual impedance

Abstract

This invention provides a control method and system for a current-enhanced harmonic generator based on virtual impedance, belonging to the field of electrified track technology. The harmonic generator uses a virtual impedance controller and a current controller to inject pure, single-frequency harmonic current into the traction network within the range of 100-5000 Hz. The harmonic generator is connected to the traction network via the primary winding of a single-winding step-down transformer, and the secondary winding is connected to a reactor and a cascade converter to form a loop. The virtual impedance controller forms a negative inductor in the form of a differentiator to eliminate the effect of transformer leakage reactance increasing with frequency, ensuring that harmonic current can pass through the transformer and be injected into the traction network. This invention can significantly enhance the injection capability of harmonic current, improve the accuracy of measuring impedance-frequency characteristics, and accurately obtain the harmonic impedance characteristics of the traction network.

Description

Technical Field

[0001] The present invention relates to the technical field of electrified rails, and in particular to a virtual impedance-based current enhancement harmonic generator control method and system. Background Art

[0002] Since the commissioning of AC-DC-AC trains and electric locomotives (hereinafter collectively referred to as locomotives), harmonic resonance between the traction power supply system and the locomotive caused by high-order harmonic currents has occurred frequently. These resonances can cause the catenary arrester to burn out and explode, or the roof arrester to burn out and the spark gap to break down. This often leads to the tripping of the substation feeder, resulting in the serious consequence of service interruption. Research has shown that this high-order harmonic resonance phenomenon is a train-grid electrical matching problem, related to both the harmonic spectrum characteristics of the locomotive current and the harmonic impedance frequency characteristics of the traction power supply system, resulting from the interaction between the two. Therefore, understanding the harmonic impedance characteristics of the traction power supply system and clarifying the resonant frequency distribution of the traction power supply system are of guiding significance for the joint commissioning and testing of new railways, the commissioning of new locomotives, and the operation and maintenance of existing lines.

[0003] Based on the concept of active harmonic injection, existing technology has developed a railway traction power supply system impedance frequency characteristic test device that can be tested directly on the railway traction network. The test device can inject pure, single-frequency harmonic current into the traction network in the range of 100-5000Hz, detect the voltage and current waveforms on the traction network side, perform Fourier analysis to calculate the voltage and current at the test frequency, and use interharmonic interpolation and frequency sweep algorithms to obtain impedance frequency characteristic information across the entire set test frequency range.

[0004] However, as the test frequency increases, the transformer leakage reactance increases, preventing harmonic currents from passing through the transformer. This results in smaller harmonic currents injected into the traction power supply system and larger impedance measurement errors. Increasing the device capacity can improve harmonic current injection capability, but this increases costs. Summary of the Invention

[0005] The object of the present invention is to provide a current-enhanced harmonic generator control method and system based on virtual impedance, which configures controller parameters, introduces virtual impedance, offsets transformer leakage reactance, significantly enhances the injection capability of harmonic current, and improves the measurement accuracy of the impedance frequency characteristic testing device, so as to solve at least one technical problem existing in the above-mentioned background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In one aspect, the present invention provides a method for controlling a current-enhanced harmonic generator based on virtual impedance, wherein the harmonic generator includes a step-down transformer, a cascade converter, and a converter reactor; the primary winding of the step-down transformer is connected in series with a traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter; the method includes:

[0008] Collect the capacitor voltage of each module unit of the converter;

[0009] Calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0010] Based on the current inner loop active current given value and the current sampling value, the power control modulation wave is calculated;

[0011] Based on the harmonic modulation wave superimposed on the power control modulation wave, a harmonic current is obtained.

[0012] Preferably, the error between the collected sum of the capacitor voltages of each module unit of the converter and the sum of the given values of the capacitor voltages of each module unit of the converter passes through a PI controller and is synchronized through a phase-locked loop to be used as the given active current value of the current inner loop.

[0013] Preferably, the error between the active current set value of the current inner loop and the current sampling value is used as the input of the current controller; the output of the current controller is then summed with the voltage feedforward compensation, and the result is output as the power control modulation wave.

[0014] Preferably, the output voltage on the AC side of the converter is decomposed by fast Fourier transform to obtain the hth harmonic amplitude, and the difference between the hth harmonic amplitude and the given value of the amplitude of the hth harmonic voltage is used as the input of the PI controller; the output of the PI controller is multiplied by the hth harmonic angular frequency to obtain the hth harmonic modulation wave reference.

[0015] Preferably, the method further includes adopting a modulation wave fine-tuning amount superposition method to perform voltage equalization control.

[0016] Preferably, the module unit capacitor voltage sampling value is compared with the module capacitor voltage reference value, and the error signal is multiplied by the converter current sign after passing through the PI controller to obtain a voltage-equalizing control modulation wave; when the actual value of the module unit capacitor voltage is lower than the reference value, the capacitor of the corresponding module unit absorbs active power from the power supply, and the capacitor voltage rises; conversely, when the actual value of the module unit capacitor voltage is higher than the reference value, the corresponding capacitor releases active power to the power supply, and the capacitor voltage drops, thereby realizing capacitor voltage balancing regulation between modules.

[0017] In a second aspect, the present invention provides a current-enhanced harmonic generator control system based on virtual impedance, wherein the harmonic generator includes a step-down transformer, a cascade converter, and a converter reactor; the primary winding of the step-down transformer is connected in series with the traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter; the control system includes:

[0018] The acquisition module is used to collect the capacitor voltage of each module unit of the converter;

[0019] A first calculation module is used to calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0020] The second calculation module is used to calculate the power control modulation wave based on the difference between the active current given value of the current inner loop and the current sampling value;

[0021] The modulation module is used to obtain the harmonic current based on the harmonic modulation wave superimposed on the power control modulation wave.

[0022] In a third aspect, the present invention provides a non-transitory computer-readable storage medium, which is used to store computer instructions. When the computer instructions are executed by a processor, the current-enhanced harmonic generator control method based on virtual impedance as described above is implemented.

[0023] In a fourth aspect, the present invention provides a computer program product, comprising a computer program, wherein when the computer program is run on one or more processors, the computer program is used to implement the current enhanced harmonic generator control method based on virtual impedance as described above.

[0024] In a fifth aspect, the present invention provides an electronic device comprising: a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to execute instructions for implementing the virtual impedance-based current enhanced harmonic generator control method as described above.

[0025] Beneficial effects of the present invention:

[0026] By configuring controller parameters and introducing virtual impedance to offset transformer leakage reactance, the harmonic current injection capability can be significantly enhanced, improving the accuracy of impedance-frequency characteristic measurement without increasing costs. Three modes are implemented: Mode 1 adds a low-pass filter to remove harmonic current components in the current feedback loop, initially increasing the harmonic current value and making it suitable for low-frequency scenarios. Mode 2 uses a VI controller in the harmonic current feedback loop as a differentiator to compensate for transformer leakage reactance, significantly increasing the harmonic current value. At high frequencies, sufficient harmonic current is still generated to ensure test accuracy, essentially meeting testing requirements across a wide frequency range. Mode 3, building on Mode 2, simultaneously compensates for transformer leakage reactance and converter front-end impedance, improving harmonic current generation capability. This is suitable for higher frequencies and situations where harmonic current generation capability is still insufficient after compensation in Mode 2. Manual parameter configuration greatly enhances applicability and flexibility across a wide frequency range. VI controllers can be designed for different current controllers, providing high flexibility and adaptability to a wide range of current controllers.

[0027] Additional advantages of the present invention will be more clearly given in the following description or learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a schematic diagram of the structure of a cascaded H-bridge type traction network impedance test harmonic generator according to an embodiment of the present invention.

[0030] Figure 2 This is a simplified schematic diagram of a cascaded H-bridge traction network impedance test harmonic generator according to an embodiment of the present invention.

[0031] Figure 3 This is a voltage control principle diagram according to an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of the current inner loop control principle described in an embodiment of the present invention.

[0033] Figure 5 This is a schematic diagram of the harmonic control loop according to an embodiment of the present invention.

[0034] Figure 6 This is a schematic diagram of the capacitor voltage balancing control principle according to an embodiment of the present invention.

[0035] Figure 7 This is a schematic diagram of the overall control principle of the harmonic impedance measurement device according to an embodiment of the present invention.

[0036] Figure 8 This is a block diagram of the overall control model of the harmonic impedance measurement device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and are not to be construed as limiting the present invention.

[0038] Those skilled in the art will understand that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0039] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0040] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a," "an," "said," and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.

[0041] In the description of this specification, reference to the terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and integrate different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless otherwise inconsistent.

[0042] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings. However, the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0043] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0044] Example 1

[0045] This embodiment 1 provides a current-enhanced harmonic generator control system based on virtual impedance. The harmonic generator includes a step-down transformer, a cascade converter, and a converter reactor. The primary winding of the step-down transformer is connected in series with the traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter. The embodiment 1 is characterized by including:

[0046] The acquisition module is used to collect the capacitor voltage of each module unit of the converter;

[0047] A first calculation module is used to calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0048] The second calculation module is used to calculate the power control modulation wave based on the difference between the active current given value of the current inner loop and the current sampling value;

[0049] The modulation module is used to obtain the harmonic current based on the harmonic modulation wave superimposed on the power control modulation wave.

[0050] In this embodiment 1, a virtual impedance-based current enhancement harmonic generator control method is implemented using the above-mentioned system. The harmonic generator includes a step-down transformer, a cascade converter, and a converter reactor. The primary winding of the step-down transformer is connected in series with the traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter. The method includes:

[0051] Collect the capacitor voltage of each module unit of the converter;

[0052] Calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0053] Based on the current inner loop active current given value and the current sampling value, the power control modulation wave is calculated;

[0054] Based on the harmonic modulation wave superimposed on the power control modulation wave, a harmonic current is obtained.

[0055] The error between the sum of the capacitor voltages of each module unit of the converter and the sum of the given values of the capacitor voltages of each module unit of the converter is passed through a PI controller and synchronized through a phase-locked loop to be used as the given active current value of the current inner loop.

[0056] The error between the active current setting value of the current inner loop and the current sampling value is used as the input of the current controller; the output of the current controller is then summed with the voltage feedforward compensation, and the result is output as the power control modulation wave.

[0057] The output voltage on the AC side of the converter is decomposed by fast Fourier transform to obtain the hth harmonic amplitude. The difference between the hth harmonic amplitude and the hth harmonic voltage amplitude is used as the input of the PI controller; the PI controller output is multiplied by the hth harmonic angular frequency to obtain the hth harmonic modulation wave reference.

[0058] The system also uses a modulation wave fine-tuning superposition method for voltage balancing control: a small modulation wave is superimposed on each module's main modulation wave to adjust the phase or amplitude of the submodule's modulation wave, changing the submodule's AC output, adjusting the submodule's absorbed active energy, and balancing the submodule's capacitor voltage. This method is suitable for carrier phase-shift modulation and offers simple and effective control.

[0059] The module unit capacitor voltage sampling value is compared with the module capacitor voltage reference value. The error signal is multiplied by the converter current sign after passing through the PI controller to obtain the voltage-sharing control modulation wave. When the actual value of the module unit capacitor voltage is lower than the reference value, the capacitor of the corresponding module unit absorbs active power from the power supply and the capacitor voltage increases. Conversely, when the actual value of the module unit capacitor voltage is higher than the reference value, the corresponding capacitor releases active power to the power supply and the capacitor voltage decreases, thus achieving capacitor voltage balancing and regulation between modules.

[0060] Example 2

[0061] In this embodiment 2, a current enhancement type harmonic generator control method based on virtual impedance is provided, such as Figure 1 As shown in the figure, the cascaded H-bridge traction network impedance test harmonic generator (abbreviated as harmonic generator) consists of the following parts: step-down transformer TP, cascade converter HG, converter reactor L c The primary winding of the step-down transformer TP is connected in series with the traction network, and the secondary main winding of the step-down transformer TP is connected to the traction network through the converter reactor L. c The cascade converter HG is connected to provide a power supply voltage for the cascade converter HG.

[0062] In this embodiment 2, to simplify the analysis, the equivalent impedance Ze of the traction power supply system is converted to the secondary side of the transformer as Zs, and the leakage inductance of the primary winding of the transformer is converted to the secondary winding side and combined with the leakage inductance of the secondary winding as LT. Figure 1 The device topology shown can be equivalent to Figure 2 The circuit structure is shown.

[0063] The control system adopts a hierarchical control method, namely the top-level active power control, the second-level harmonic generation control, and the third-level voltage balancing control. Figure 2 Direction of each variable.

[0064] Top-level power control enables the converter to absorb a certain amount of fundamental active power from the grid, balance its own losses, and store energy in the capacitor as a source of energy for emitting harmonics. Figure 3 As shown in the figure, the error between the sum of the capacitor voltages of each module unit of the converter and the given value passes through the PI controller and is synchronized through the phase locked loop (PLL) to serve as the active current given by the current inner loop.

[0065] Figure 4 This is the top-level power control current inner loop structure, where the error between the current setting and the current sampling value is used as the input of the current controller w(s). The controller output is The result is then summed with the voltage feedforward compensation, and the result is output as the power control modulation wave. Voltage feedforward compensation can suppress disturbances in the control power supply voltage. The current controller w(s) can be a proportional regulator, a proportional-integral regulator, a proportional resonant regulator, a quasi-proportional resonant regulator, or other devices. Figure 4 In, K PWM is the equivalent gain of the bridge, u c is the output voltage of the converter bridge port.

[0066] The two-layer harmonic control structure is as follows Figure 5 As shown in the figure Indicates that the amplitude of the hth harmonic voltage is given, and the AC side output voltage of the converter is u c The hth harmonic amplitude is obtained by Fast Fourier Transform (FFT) decomposition and the difference between it and the given value is used as the input of the PI controller. The controller output is multiplied by the hth harmonic angular frequency. Get the hth harmonic modulation wave reference The harmonic modulation wave is modulated by the converter to generate the harmonic voltage of the required frequency, which is applied to the system impedance to generate the harmonic current i h , injected into the traction power supply system. Considering that the control parameter design of the top-level power control current loop is affected by the system impedance, the harmonic control loop design does not use the harmonic reference as the input of the current loop controller. Instead, it is directly superimposed on the current loop output, that is, the total modulation wave, which is beneficial to improving system stability.

[0067] The capacitor voltages of each module must be balanced to ensure the normal operation of the system. Figure 6 As shown in Figure 1, three-layer voltage-balancing control uses a modulation wave fine-tuning superposition method: a small modulation wave is superimposed on the main modulation wave of each module to adjust the phase or amplitude of the modulation wave of the submodule, changing the AC output of the submodule, adjusting the active energy absorbed by the submodule, and balancing the capacitor voltage of the submodule. This method is suitable for carrier phase-shift modulation, has simple and effective control, and has been widely researched and applied.

[0068] Module capacitor voltage sampling value u dck With reference value By comparison, the error signal is multiplied by the converter current sign after passing through the PI controller to obtain the voltage control modulation wave. When the actual value of the module unit capacitor voltage is lower than the reference value, the capacitor of the corresponding module unit absorbs active power from the power supply, and the capacitor voltage increases; conversely, when the actual value of the module unit capacitor voltage is higher than the reference value, the corresponding capacitor releases active power to the power supply, and the capacitor voltage decreases, achieving balanced adjustment of the capacitor voltage between modules and stabilizing it near the reference value. The complete control strategy of the traction power supply system harmonic impedance test device with a single-phase cascade H-bridge structure is as follows: Figure 7 shown.

[0069] according to Figure 7 You can get Figure 8 The control model of the harmonic impedance measurement device is shown.

[0070] according to Figure 8 The output current expression is obtained:

[0071]

[0072] Assume that the relationship of the harmonic current outer loop is:

[0073] I h =Y s V s +G ref I ref +G1I1+Y h V h (2)

[0074] According to formula (1), we can get

[0075]

[0076] From the above, we can see that H si It only appears in the denominator of each formula in (3), so it can be designed by H si , so that the denominator is reduced, the harmonic current can be increased. Among them, Z s Represents the equivalent impedance of the traction power supply system; Z c Represents the front-end impedance of the converter; Z TRepresents the transformer leakage reactance, i.e. Z T =X T =sL T ;H pwm Represents the equivalent gain of the bridge, which is equivalent to 1; H ci Represents the transfer function of the current controller, using the proportional regulator H ci =K p ;H si is the transfer function of the harmonic current feedback loop, representing the VI controller in this embodiment.

[0077] In summary, the denominator expression is transformed into

[0078] D=Z s +Z c +sL T +K p H si (4)

[0079] The optimization goal in this embodiment 2 is to make D as small as possible.

[0080] In order to improve the harmonic current emission capability, the harmonic current sampling signal can be filtered through a low-pass filter and then fed back to the top power control current loop to block the harmonic current feedback path. si =0, D=Z s +Z c +sL T , which increases the harmonic current value to a certain extent, corresponding to Mode 1 in Example 2.

[0081] Since the transformer leakage reactance is a frequency-varying parameter, consider designing a suitable VI controller H si , used to offset the transformer leakage reactance, so

[0082] sL T +K p H si =0 (5)

[0083] get:

[0084]

[0085] Therefore, a VI controller is set in the form of a differentiator in the harmonic current feedback loop, namely H si = -sK, where The compensation for the transformer leakage reactance is completed, corresponding to Mode 2 of this embodiment.

[0086] According to formula (4), compensating the transformer leakage reactance and the converter front-end impedance can further improve the harmonic current generation capability. Here, only the frequency-varying component of the converter front-end impedance is considered, i.e., Z c=sL c ,make

[0087] sL c +sL T +K p H si =0 (7)

[0088] get:

[0089]

[0090] Overcompensation is completed, and the harmonic current injection capability is further improved, corresponding to mode 3 of this embodiment.

[0091] The above process is based on the current controller using a proportional regulator, namely H ci =K p In fact, the current controller H ci Proportional regulator, proportional integral regulator, proportional resonant regulator, quasi-proportional resonant regulator, etc. can be used, all of which are within the scope of protection of this patent. The following design takes the more complex quasi-proportional resonant regulator as an example. When the current controller uses other regulators, the design process is similar, and the VI controller H si All have the same form.

[0092] When using a quasi-proportional resonant regulator, The denominator expression is now transformed into:

[0093]

[0094] The optimization goal of the present invention is to make D as small as possible.

[0095] In mode 1, the harmonic current sampling signal is filtered through a low-pass filter and then fed back to the top power control current loop to block the harmonic current feedback path. At this time, the VI controller H si =0, the harmonic current value can be increased.

[0096] Mode 2 aims to offset the transformer leakage reactance by designing the VI controller.

[0097]

[0098] get:

[0099]

[0100] Refer to the parameter setting of general quasi-proportional resonant regulator: K p =15,K r =2000,ω i =π,ω r=50×2π, in the wide frequency range, equation (11) can be fitted by equation (12)

[0101]

[0102] Therefore, a VI controller is set in the form of a proportional differentiator in the harmonic current feedback loop, namely H si = -sK1+K2, where The compensation for the transformer leakage reactance is completed, corresponding to Mode 2 of this embodiment.

[0103] Mode 3 aims to offset the transformer leakage reactance and converter front-end impedance through VI controller design, making

[0104]

[0105] get:

[0106]

[0107] This completes the design of the three modes of the VI controller when using a quasi-proportional resonant regulator.

[0108] Similarly, when the current controller uses other regulators, the design process is similar, and the VI controller has the same form, both using the proportional differentiator H si =-sK1+K2.

[0109] Example 3

[0110] Embodiment 3 of the present invention provides a non-transitory computer-readable storage medium for storing computer instructions. When the computer instructions are executed by a processor, a virtual impedance-based current-enhanced harmonic generator control method is implemented. The harmonic generator includes a step-down transformer, a cascade converter, and a converter reactor. The primary winding of the step-down transformer is connected in series with the traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter. The method includes:

[0111] Collect the capacitor voltage of each module unit of the converter;

[0112] Calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0113] Based on the current inner loop active current given value and the current sampling value, the power control modulation wave is calculated;

[0114] Based on the harmonic modulation wave superimposed on the power control modulation wave, a harmonic current is obtained.

[0115] Example 4

[0116] Embodiment 4 of the present invention provides a computer program (product), including a computer program. When the computer program is executed on one or more processors, it is used to implement a virtual impedance-based current enhancement harmonic generator control method, wherein the harmonic generator includes a step-down transformer, a cascade converter, and a converter reactor; the primary winding of the step-down transformer is connected in series with the traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter; the method includes:

[0117] Collect the capacitor voltage of each module unit of the converter;

[0118] Calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0119] Based on the current inner loop active current given value and the current sampling value, the power control modulation wave is calculated;

[0120] Based on the harmonic modulation wave superimposed on the power control modulation wave, a harmonic current is obtained.

[0121] Example 5

[0122] Embodiment 5 of the present invention provides an electronic device, comprising: a processor, a memory, and a computer program; wherein the processor is connected to the memory, and the computer program is stored in the memory. When the electronic device is running, the processor executes the computer program stored in the memory to cause the electronic device to execute instructions for implementing a method for controlling a current-enhanced harmonic generator based on virtual impedance, wherein the harmonic generator comprises a step-down transformer, a cascade converter, and a converter reactor; the primary winding of the step-down transformer is connected in series with a traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter; the method comprises:

[0123] Collect the capacitor voltage of each module unit of the converter;

[0124] Calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter;

[0125] Based on the current inner loop active current given value and the current sampling value, the power control modulation wave is calculated;

[0126] Based on the harmonic modulation wave superimposed on the power control modulation wave, a harmonic current is obtained.

[0127] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0128] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0129] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0130] These computer program instructions can also be loaded onto a computer or other programmable data processing device, and a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide the functions for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0131] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solutions disclosed in the present invention without the need for creative work should be included in the scope of protection of the present invention.

Claims

1. A method for controlling a current-enhanced harmonic generator based on virtual impedance, wherein the harmonic generator comprises a step-down transformer, a cascade converter, and a converter reactor; the primary winding of the step-down transformer is connected in series with the traction network, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter; characterized in that: include: Collect the capacitor voltage of each module unit of the converter; Calculate the current inner loop active current given value based on the collected capacitor voltage of each module unit of the converter; The error between the sum of the capacitor voltages of each module unit of the converter and the sum of the given values of the capacitor voltages of each module unit of the converter is passed through a PI controller and synchronized through a phase-locked loop to be used as the active current given value of the current inner loop; Based on the current inner loop active current given value and the current sampling value, the power control modulation wave is calculated; Based on the harmonic modulation wave superimposed on the power control modulation wave, a harmonic current is obtained.

2. The virtual impedance-based current-enhanced harmonic generator control method according to claim 1, characterized in that: The error between the sum of the capacitor voltages of each module unit of the converter and the sum of the given values of the capacitor voltages of each module unit of the converter is passed through a PI controller and synchronized through a phase-locked loop to be used as the given active current value of the current inner loop.

3. The virtual impedance-based current-enhanced harmonic generator control method according to claim 1, characterized in that: The difference between the active current set value of the current inner loop and the current sampling value is used as the input of the current controller; the output of the current controller is then summed with the voltage feedforward compensation, and the result is output as the power control modulation wave.

4. The virtual impedance-based current-enhanced harmonic generator control method according to claim 3, characterized in that: The output voltage on the AC side of the converter is decomposed by fast Fourier transform to obtain the hth harmonic amplitude. The difference between the hth harmonic amplitude and the hth harmonic voltage amplitude is used as the input of the PI controller; the PI controller output is multiplied by the hth harmonic angular frequency to obtain the hth harmonic modulation wave reference.

5. The virtual impedance-based current-enhanced harmonic generator control method according to claim 1, characterized in that: It also includes voltage equalization control using a modulation wave fine-tuning amount superposition method.

6. The virtual impedance-based current enhancement harmonic generator control method according to claim 5, characterized in that: The module unit capacitor voltage sampling value is compared with the module capacitor voltage reference value. The error signal is multiplied by the converter current sign after passing through the PI controller to obtain the voltage-sharing control modulation wave. When the actual value of the module unit capacitor voltage is lower than the reference value, the capacitor of the corresponding module unit absorbs active power from the power supply and the capacitor voltage increases. Conversely, when the actual value of the module unit capacitor voltage is higher than the reference value, the corresponding capacitor releases active power to the power supply and the capacitor voltage decreases, thus achieving capacitor voltage balancing and regulation between modules.

7. A current-enhanced harmonic generator control system based on virtual impedance, the harmonic generator comprising a step-down transformer, a cascade converter, and a converter reactor; the primary winding of the step-down transformer is connected in series with the traction grid, and the secondary main winding of the step-down transformer is connected to the cascade converter via the converter reactor to provide a power supply voltage for the cascade converter; characterized in that: include: The acquisition module is used to collect the capacitor voltage of each module unit of the converter; A first calculation module is configured to calculate a current inner loop active current set value based on the collected capacitor voltages of each module unit of the converter; the error between the sum of the collected capacitor voltages of each module unit of the converter and the sum of the capacitor voltage set values of each module unit of the converter is passed through a PI controller and synchronized through a phase-locked loop to be used as the current inner loop active current set value; The second calculation module is used to calculate the power control modulation wave based on the difference between the active current given value of the current inner loop and the current sampling value; The modulation module is used to obtain the harmonic current based on the harmonic modulation wave superimposed on the power control modulation wave.

8. A non-transitory computer-readable storage medium, characterized in that The non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by the processor, the virtual impedance-based current-enhanced harmonic generator control method according to any one of claims 1 to 6 is implemented.

9. A computer program product, characterized in that The invention comprises a computer program, which is used to implement the virtual impedance-based current enhanced harmonic generator control method according to any one of claims 1 to 6 when the computer program is run on one or more processors.

10. An electronic device, characterized in that: include: A processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to execute instructions for implementing the virtual impedance-based current enhanced harmonic generator control method according to any one of claims 1 to 6.

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