A direct current bus phase-to-phase energy equalization control method, device, system and medium

Abstract

The application discloses a DC bus inter-phase energy balance control method, device, system and medium, and belongs to the technical field of power electronic converter control. The method is as follows: three-phase DC bus voltages of a series converter are acquired, and three-phase DC bus average voltages are acquired; an additional fundamental frequency voltage instruction value is generated according to the deviation of the three-phase DC bus voltages and the three-phase DC bus average voltages; the additional fundamental frequency voltage instruction value is superimposed to an inherent output voltage instruction value of an energy balance module to generate a final modulation voltage; the energy balance module outputs the additional fundamental frequency voltage through the final modulation voltage, so that the additional fundamental frequency voltage and a zero sequence fundamental frequency current component in a circulating current actively injected by a parallel type cascaded full-bridge converter are power-interacted, and energy balance among the three-phase DC buses is realized. The application can reduce the hardware cost required in the DC bus inter-phase energy balance control process.

Description

Technical Field

[0001] This application relates to the field of power electronic converter control technology, and in particular to a method, device, system and medium for DC bus phase-to-phase energy balance control. Background Technology

[0002] The delta-connected series-parallel flexible interconnection device achieves overall energy balance of the DC bus through the interaction of the circulating current injected by the energy balance module and the parallel cascaded full-bridge converter. However, in actual engineering, due to factors such as the asymmetry of three-phase device parameters, the three-phase DC bus voltage may become unbalanced, leading to problems such as output voltage asymmetry and current distortion, affecting the stable operation of the device. Therefore, inter-phase energy balancing control of the three-phase DC bus is necessary.

[0003] Existing DC bus cluster balancing strategies achieve energy transfer between three-phase DC buses by superimposing an additional third-harmonic voltage component onto the inherent third-harmonic voltage of the energy balancing module. This additional component interacts with the third-harmonic component in the circulating current actively injected by the parallel-type cascaded full-bridge converter. However, in this method, both the superimposed voltage and the inherent output voltage are third harmonics, resulting in a significant increase in the peak output voltage of the energy balancing module. This increase in peak voltage necessitates higher voltage withstand ratings for power devices, thus increasing the size and cost of the device. Summary of the Invention

[0004] This application provides a method, device, system, and medium for DC bus phase-to-phase energy balance control, which can solve the problem of high hardware cost requirements of existing DC bus phase-to-phase energy balance control methods.

[0005] This application provides a DC bus phase-to-phase energy balancing control method in some embodiments, applied to a control system. The control system includes a series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balancing module; the control method includes: Obtain the three-phase DC bus voltage and the average three-phase DC bus voltage of the series converter; An additional base frequency voltage command value is generated based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage. The additional baseband voltage command value is superimposed on the inherent output voltage command value of the energy balance module to generate the final modulation voltage; The energy balance module outputs an additional base frequency voltage by controlling the final modulation voltage, so that the additional base frequency voltage interacts with the zero-sequence base frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance among the three-phase DC buses.

[0006] Compared to existing technologies, the above embodiments have the following advantages: By superimposing an additional fundamental frequency voltage on the inherent output voltage of the energy balance module, power interaction is achieved between the zero-sequence fundamental frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thus realizing energy balance among the three-phase DC buses. Compared to the existing technology's scheme of superimposing a third harmonic voltage of the same frequency, this application adopts a mixed superposition method of fundamental frequency additional voltage and inherent output voltage. Since the peak values ​​of voltage components of different frequencies will not superimpose in the same direction, the peak value of the output voltage of the energy balance module is effectively reduced, thereby improving the DC bus voltage utilization rate and reducing the requirements for the withstand voltage level of power devices and the overall cost of the device.

[0007] Further, the three-phase DC bus voltage includes: phase A DC bus voltage, phase B DC bus voltage, and phase C DC bus voltage; the step of generating an additional fundamental frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage includes: Calculate the first difference between the A-phase DC bus voltage and the average voltage of the three-phase DC bus, and the second difference between the B-phase DC bus voltage and the average voltage of the three-phase DC bus; The first difference and the second difference are respectively input into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the DC bus voltage of phase A and the second additional base frequency voltage command value corresponding to the DC bus voltage of phase B. Based on the sum of the first additional base frequency voltage command value and the second additional base frequency voltage command value, a third additional base frequency voltage command value corresponding to the C-phase DC bus voltage is generated.

[0008] Compared to existing technologies, the above embodiments have the following advantages: By comparing the DC bus voltages of phase A and phase B with the three-phase average voltage, the proportional-integral controller independently generates corresponding additional base frequency voltage command values, and the additional base frequency voltage command value of phase C is obtained by inverting the sum of the two phases. This method ensures that the sum of the three-phase additional base frequency voltage command values ​​is zero, making the total three-phase power generated by the interaction of the additional voltage and circulating current zero, thereby accurately realizing the energy redistribution among the three-phase DC buses without affecting the overall energy balance of the DC bus.

[0009] Further, the step of inputting the first difference and the second difference into the corresponding proportional-integral controllers to obtain the first additional base frequency voltage command value corresponding to the A-phase DC bus voltage and the second additional base frequency voltage command value corresponding to the B-phase DC bus voltage includes: The first difference is input into the first proportional-integral controller to obtain the first control output quantity; The second difference is input into the second proportional-integral controller to obtain the second control output. The first control output and the second control output are multiplied by the pre-constructed fundamental frequency sinusoidal signal to obtain the first AC quantity and the second AC quantity. Based on the sign of the zero-sequence fundamental frequency current component, the sign directions of the first AC quantity and the second AC quantity are determined to obtain the first additional fundamental frequency voltage command value and the second additional fundamental frequency voltage command value, respectively.

[0010] Compared to existing technologies, the above embodiments have the following advantages: By first processing the difference signal through a proportional-integral controller to obtain the control output, then multiplying it with a pre-constructed fundamental frequency sinusoidal signal to impart AC characteristics, and finally determining the voltage direction based on the sign of the zero-sequence fundamental frequency current component, an additional fundamental frequency voltage command value is generated step by step. This step-by-step processing method decouples amplitude adjustment, frequency assignment, and direction determination, allowing the parameters of each stage to be designed and optimized independently, thus improving the flexibility and accuracy of control. Simultaneously, determining the voltage direction based on the sign of the zero-sequence fundamental frequency current component ensures that the additional fundamental frequency voltage and the circulating current always generate the correct power interaction direction, guaranteeing the effectiveness of energy balance.

[0011] Furthermore, the process of constructing the fundamental frequency sinusoidal signal includes: Extract the phase and power frequency angular velocity from the zero-sequence fundamental frequency current component; The fundamental frequency sinusoidal signal is constructed based on the phase and the power frequency angular velocity.

[0012] Compared with existing technologies, the above embodiments have the following advantages: By extracting the phase and power frequency angular velocity from the zero-sequence fundamental frequency current component to construct a fundamental frequency sinusoidal signal, the phase of the additional fundamental frequency voltage is synchronized with the zero-sequence fundamental frequency current component in the circulating current. This phase synchronization mechanism ensures that a stable active power interaction can be generated between the additional fundamental frequency voltage and the zero-sequence fundamental frequency current component, avoiding power oscillations or reactive power circulation caused by phase deviation, and improving the stability and efficiency of energy balance control.

[0013] Further, the inherent output voltage command value is a fixed third harmonic voltage command value; the step of superimposing the additional baseband voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage includes: vector superimposing the additional baseband voltage command value and the inherent output voltage command value to obtain the final modulation voltage.

[0014] Compared with existing technologies, the above embodiments have the following advantages: By using mixed modulation of the fundamental frequency and its third harmonic, compared with the simultaneous superposition of the third harmonics in existing technologies, the peak value of the modulation voltage is effectively reduced, and the DC voltage utilization rate is improved. The vector superposition method ensures that the two voltage components are independently controllable and do not interfere with each other during the modulation process.

[0015] Further, the step of controlling the energy balance module to output an additional baseband voltage through the final modulation voltage, so that the additional baseband voltage interacts with the zero-sequence baseband current component in the circulating current actively injected by the parallel cascaded full-bridge converter, to achieve energy balance among the three-phase DC buses, includes: Based on the final modulation voltage, the energy balance module is controlled to output the additional base frequency voltage and the third harmonic voltage corresponding to the third harmonic voltage command value; The energy between the three-phase DC buses is distributed through power interaction between the additional fundamental frequency voltage and the zero-sequence fundamental frequency current component. The power interaction between the third harmonic voltage and the third harmonic current component in the circulating current actively injected by the parallel cascaded full-bridge converter is carried out to maintain the energy balance of the three-phase DC bus.

[0016] Compared with existing technologies, the above embodiments have the following advantages: Based on the final modulation voltage control, the energy balance module simultaneously outputs an additional fundamental frequency voltage and a third harmonic voltage. The additional fundamental frequency voltage interacts with the zero-sequence fundamental frequency current component to achieve energy redistribution among the three-phase DC buses, while the third harmonic voltage interacts with the third harmonic current component to maintain the overall energy balance of the three-phase DC buses. This application, through frequency decoupling, separates the inter-phase energy balance control from the overall energy balance control. The two control objectives are independently undertaken by different frequency components, avoiding mutual interference between control loops and improving system stability and control accuracy.

[0017] Another embodiment of this application provides a DC bus phase-to-phase energy balancing control device, applied to a control system, the control system including: a series converter and a parallel cascaded full-bridge converter, the series converter including an energy balancing module; the control device including: a data acquisition module, a first generation module, a second generation module and a control module; The acquisition module is used to acquire the three-phase DC bus voltage and the average three-phase DC bus voltage of the series converter. The first generation module is used to generate an additional base frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage. The second generation module is used to superimpose the additional baseband voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage; The control module is used to control the energy balance module to output an additional base frequency voltage through the final modulation voltage, so that the additional base frequency voltage interacts with the zero-sequence base frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance among the three-phase DC buses.

[0018] Further, the three-phase DC bus voltage includes: phase A DC bus voltage, phase B DC bus voltage, and phase C DC bus voltage; the first generation module includes: a first calculation unit, a second calculation unit, and a third calculation unit; the first generation module is used to generate an additional fundamental frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage, including: The first calculation unit is used to calculate a first difference between the A-phase DC bus voltage and the average voltage of the three-phase DC bus, and a second difference between the B-phase DC bus voltage and the average voltage of the three-phase DC bus; The second calculation unit is used to input the first difference and the second difference into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the DC bus voltage of phase A and the second additional base frequency voltage command value corresponding to the DC bus voltage of phase B. The third calculation unit is used to generate a third additional base frequency voltage command value corresponding to the C-phase DC bus voltage based on the sum of the first additional base frequency voltage command value and the second additional base frequency voltage command value.

[0019] Another embodiment of this application provides a DC bus phase-to-phase energy balance control system, including: a series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balance module, and the series converter and the parallel cascaded full-bridge converter are controlled by the steps of the DC bus phase-to-phase energy balance control method of this application.

[0020] Another embodiment of this application also provides a computer-readable storage medium item, including: a stored computer program, which, when the computer program is running, controls the device where the computer-readable storage medium is located to perform the steps of the DC bus phase-to-phase energy equalization control method of this application. Attached Figure Description

[0021] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating a DC bus phase-to-phase energy balance control method provided in some embodiments of this application; Figure 2 This is a schematic diagram of the structure of a DC bus phase-to-phase energy balancing control device provided in some embodiments of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0025] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0028] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0029] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0030] Existing DC bus cluster balancing strategies achieve energy transfer between three-phase DC buses by superimposing an additional third-harmonic voltage component onto the inherent third-harmonic voltage of the energy balancing module. This additional component interacts with the third-harmonic component in the circulating current actively injected by the parallel-type cascaded full-bridge converter. However, in this method, both the superimposed voltage and the inherent output voltage are third harmonics, resulting in a significant increase in the peak output voltage of the energy balancing module. This increase in peak voltage necessitates higher voltage withstand ratings for power devices, thus increasing the size and cost of the device.

[0031] Please refer to Figure 1 To address the issue of high hardware cost requirements in existing DC bus phase-to-phase energy balance control methods, this application provides a DC bus phase-to-phase energy balance control method applied to a control system. The control system includes a series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balance module.

[0032] Preferably, in some embodiments of this application, the control system is a delta-connected series-parallel flexible interconnection device, comprising a series converter and a parallel-type cascaded full-bridge converter. The series converter consists of a set of half-bridge sub-modules sharing a common DC bus, which can be divided into two categories according to their functions: one is a power flow regulation module, used to regulate the active and reactive power flow of the interconnection line; the other is an energy balance module, whose function is to output a fixed third-harmonic voltage, interacting with the circulating current injected into the parallel part to maintain the overall energy balance of the DC bus of the series converter. The parallel part adopts a delta-connected cascaded full-bridge converter, whose main functions include two aspects: first, providing reactive power compensation to the system; and second, actively injecting circulating current. The delta-connected series-parallel flexible interconnection device, through the working principle of series control and parallel support, establishes an energy interaction channel between the series and parallel parts through the energy balance module, enabling the device to achieve energy balance without the participation of feeder current, thereby possessing full-range operation capability under any operating conditions.

[0033] Furthermore, in some embodiments of this application, the control method includes the following steps S101 to S104: S101: Obtain the three-phase DC bus voltage and the average three-phase DC bus voltage of the series converter.

[0034] Understandably, in the actual operation of a delta-connected series-parallel flexible interconnection device, the parameters of the devices connected to the three-phase DC bus inevitably differ. The on-state voltage drop, switching losses, and leakage current of the DC-side capacitors in each phase are not entirely consistent. These factors can lead to deviations in the three-phase DC bus voltage, resulting in phase-to-phase energy imbalance. To achieve phase-to-phase energy balance control, it is first necessary to obtain the three-phase DC bus voltages of the series converter, namely, the A-phase DC bus voltage, the B-phase DC bus voltage, and the C-phase DC bus voltage. Based on this, the average voltage of the three-phase DC bus is calculated. This average voltage serves as the benchmark for subsequent calculations of phase voltage deviations, reflecting the overall level of the three-phase DC bus voltage. After obtaining the phase voltages and the average voltage, the degree of imbalance of each phase DC bus can be quantified by the difference between the phase voltage and the average value, providing input for the subsequent generation of the additional base frequency voltage command value.

[0035] S102: Generate an additional base frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage.

[0036] Further, in some embodiments of this application, the three-phase DC bus voltage includes: phase A DC bus voltage, phase B DC bus voltage, and phase C DC bus voltage; the step of generating an additional base frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage includes: Calculate the first difference between the A-phase DC bus voltage and the average voltage of the three-phase DC bus, and the second difference between the B-phase DC bus voltage and the average voltage of the three-phase DC bus; The first difference and the second difference are respectively input into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the DC bus voltage of phase A and the second additional base frequency voltage command value corresponding to the DC bus voltage of phase B. Based on the sum of the first additional base frequency voltage command value and the second additional base frequency voltage command value, a third additional base frequency voltage command value corresponding to the C-phase DC bus voltage is generated.

[0037] To achieve energy redistribution among the three-phase DC buses, corresponding additional baseband voltage command values ​​need to be generated based on the deviations of each phase DC bus voltage from the average voltage. Specifically, the difference between the A-phase DC bus voltage and the average voltage of the three-phase DC buses is first calculated to obtain the first difference; similarly, the difference between the B-phase DC bus voltage and the average voltage is calculated to obtain the second difference. The first and second differences are then fed into their respective proportional-integral controllers, which, through closed-loop regulation, output the first additional baseband voltage command value corresponding to A and the second additional baseband voltage command value corresponding to B, respectively. For phase C, its additional baseband voltage command value is not set by a separate controller; instead, the negative of the sum of the first and second additional baseband voltage command values ​​is directly taken as the third additional baseband voltage command value. The purpose of this processing is to ensure that the sum of the three-phase additional baseband voltage command values ​​is always zero, guaranteeing that the total three-phase power generated when the additional voltage interacts with the circulating current is zero. This ensures that energy is redistributed only among the three-phase DC buses and does not affect the overall energy balance of the series converter DC buses. Meanwhile, this approach, which involves independent closed-loop control of only two phases and derives the third phase from power constraint relationships, reduces the number of controllers and simplifies the control structure.

[0038] This application compares the DC bus voltages of phases A and B with the three-phase average voltage, and generates corresponding additional base frequency voltage command values ​​independently via a proportional-integral controller. The additional base frequency voltage command value for phase C is then obtained by inverting the sum of the two phase voltages. This method ensures that the sum of the three-phase additional base frequency voltage command values ​​is zero, resulting in zero total three-phase power generated by the interaction between the additional voltage and the circulating current. Therefore, it accurately achieves energy redistribution among the three-phase DC buses without affecting the overall energy balance of the DC bus.

[0039] Further, in some embodiments of this application, the step of inputting the first difference and the second difference into the corresponding proportional-integral controllers to obtain the first additional base frequency voltage command value corresponding to the A-phase DC bus voltage and the second additional base frequency voltage command value corresponding to the B-phase DC bus voltage includes: The first difference is input into the first proportional-integral controller to obtain the first control output quantity; The second difference is input into the second proportional-integral controller to obtain the second control output. The first control output and the second control output are multiplied by the pre-constructed fundamental frequency sinusoidal signal to obtain the first AC quantity and the second AC quantity. Based on the sign of the zero-sequence fundamental frequency current component, the sign directions of the first AC quantity and the second AC quantity are determined to obtain the first additional fundamental frequency voltage command value and the second additional fundamental frequency voltage command value, respectively.

[0040] In the output processing of the proportional-integral (PI) controller, it is not directly used as the final additional baseband voltage command value. Instead, it needs to be further endowed with baseband AC characteristics and the correct power interaction direction needs to be determined. Specifically, the first difference is fed into the first PI controller, generating a first control output quantity. This output quantity reflects the magnitude of the deviation of the A-phase DC bus voltage from the average voltage. Similarly, the second difference is processed by the second PI controller to generate a second control output quantity, reflecting the deviation magnitude of phase B. At this point, the control output quantity is still a DC quantity and cannot generate effective power interaction with the AC component in the circulating current. Therefore, the first and second control output quantities are multiplied by a pre-constructed baseband sinusoidal signal, respectively, to modulate them into power frequency AC quantities, obtaining the first and second AC quantities. After obtaining the AC quantities, their sign direction also needs to be determined to ensure that the additional voltage and circulating current generate a positive power transfer rather than reverse compensation. This section introduces a circulating current sign determination function. Based on the sign of the zero-sequence fundamental frequency current component in the circulating current actively injected by the parallel-type cascaded full-bridge converter, the sign directions of the first and second AC quantities are determined. If the sign is positive, the original direction is maintained; if the sign is negative, the direction is reversed. This ultimately forms the first and second additional fundamental frequency voltage command values, respectively. Through this step-by-step processing, the amplitude adjustment, frequency assignment, and direction determination stages are decoupled. The parameters of each stage can be independently tuned, facilitating engineering debugging. Simultaneously, it ensures that the additional fundamental frequency voltage and the zero-sequence fundamental frequency current component always generate the correct active power interaction.

[0041] This application generates an additional fundamental frequency voltage command value by first processing the difference signal through a proportional-integral controller to obtain the control output, then multiplying it by a pre-constructed fundamental frequency sinusoidal signal to impart AC characteristics, and finally determining the voltage direction based on the sign of the zero-sequence fundamental frequency current component. This step-by-step processing method decouples amplitude adjustment, frequency assignment, and direction determination, allowing for independent design and optimization of parameters in each stage, thus improving control flexibility and accuracy. Simultaneously, determining the voltage direction based on the sign of the zero-sequence fundamental frequency current component ensures that the additional fundamental frequency voltage and the circulating current always generate the correct power interaction direction, guaranteeing the effectiveness of energy balance.

[0042] Furthermore, in some embodiments of this application, the process of constructing the fundamental frequency sinusoidal signal includes: Extract the phase and power frequency angular velocity from the zero-sequence fundamental frequency current component; The fundamental frequency sinusoidal signal is constructed based on the phase and the power frequency angular velocity.

[0043] This application constructs a fundamental frequency sinusoidal signal by extracting the phase and power frequency angular velocity from the zero-sequence fundamental frequency current component, ensuring that the phase of the additional fundamental frequency voltage is synchronized with the zero-sequence fundamental frequency current component in the circulating current. This phase synchronization mechanism ensures stable active power interaction between the additional fundamental frequency voltage and the zero-sequence fundamental frequency current component, avoiding power oscillations or reactive circulating currents caused by phase deviation, and improving the stability and efficiency of energy balance control.

[0044] Specifically, in some embodiments of this application, the formula for calculating the additional base frequency voltage command value is as follows: ; in, This is the first additional base frequency voltage command value; This is the second additional base frequency voltage command value; This is the third additional base frequency voltage command value; The average voltage of the three-phase DC bus; This refers to the DC bus voltage of phase A. This refers to the DC bus voltage of phase B. This is the proportionality coefficient; The integral coefficient; It is the angular velocity at power frequency; The phase of the zero-sequence fundamental frequency current component; A function for determining the symbol of the fundamental frequency circulating current; For time.

[0045] S103: The additional baseband voltage command value is superimposed on the inherent output voltage command value of the energy balance module to generate the final modulation voltage.

[0046] Furthermore, in some embodiments of this application, the inherent output voltage command value is a fixed third harmonic voltage command value; the step of superimposing the additional baseband voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage includes: vector superimposing the additional baseband voltage command value and the inherent output voltage command value to obtain the final modulation voltage.

[0047] In a delta-connected series-parallel flexible interconnect device, the energy balancing module undertakes two voltage output tasks: first, it outputs a fixed third harmonic voltage to interact with the third harmonic circulating current injected by the parallel-type cascaded full-bridge converter, maintaining the overall energy balance of the DC bus; this fixed output is the inherent output voltage command value. Second, it outputs the aforementioned additional fundamental frequency voltage to interact with the zero-sequence fundamental frequency current component, realizing energy redistribution among the three-phase DC buses. The two voltage command values ​​are vector-superimposed in the modulation stage to obtain the final modulation voltage of the energy balancing module. The superimposed voltage waveform contains both fundamental frequency and third harmonic components, belonging to mixed modulation of different frequency components. Unlike existing schemes that superimpose an additional third harmonic voltage on top of the inherent output third harmonic voltage, this scheme adopts a superposition method combining the fundamental frequency and the third harmonic. Since the peak values ​​of the fundamental frequency and the third harmonic will not superimpose in the same direction at the same time, the peak value of the final modulation voltage is effectively reduced. This characteristic allows the modulation ratio of the energy balancing module to be optimized under the same DC bus voltage conditions, improving DC voltage utilization and reducing the requirements for the withstand voltage level of power devices.

[0048] This application employs hybrid modulation of the fundamental frequency and its third harmonic, which, compared to the prior art's simultaneous superposition of two third harmonics, effectively reduces the peak value of the modulation voltage and improves DC voltage utilization. The vector superposition method ensures that the two voltage components are independently controllable and do not interfere with each other during modulation.

[0049] S104: The energy balance module outputs an additional base frequency voltage by controlling the final modulation voltage, so that the additional base frequency voltage interacts with the zero-sequence base frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance between the three-phase DC buses.

[0050] Furthermore, in some embodiments of this application, the step of controlling the energy balance module to output an additional baseband voltage through the final modulation voltage, so that the additional baseband voltage interacts with the zero-sequence baseband current component in the circulating current actively injected by the parallel cascaded full-bridge converter to achieve energy balance among the three-phase DC buses, includes: Based on the final modulation voltage, the energy balance module is controlled to output the additional base frequency voltage and the third harmonic voltage corresponding to the third harmonic voltage command value; The energy between the three-phase DC buses is distributed through power interaction between the additional fundamental frequency voltage and the zero-sequence fundamental frequency current component. The power interaction between the third harmonic voltage and the third harmonic current component in the circulating current actively injected by the parallel cascaded full-bridge converter is carried out to maintain the energy balance of the three-phase DC bus.

[0051] After the energy balancing module outputs the final modulated voltage, its AC side voltage actually contains two frequency components: one is the fundamental frequency voltage component generated by the additional fundamental frequency voltage command value, and the other is the third harmonic voltage component generated by the inherent output voltage command value. These two components are physically output through the same energy balancing module, but they are decoupled from each other and perform their respective functions in terms of power interaction mechanism. The fundamental frequency voltage component interacts with the zero-sequence fundamental frequency current component in the circulating current actively injected by the parallel-type cascaded full-bridge converter. Since the sum of the three-phase additional fundamental frequency voltages is zero, the total distribution of this interaction power among the three phases is also zero. Therefore, without affecting the overall energy, energy can be transferred from the DC bus with a higher voltage to the DC bus with a lower voltage, realizing the redistribution of energy among the three-phase DC buses. Simultaneously, the third harmonic voltage component interacts with the third harmonic current component in the circulating current. This power interaction is superimposed in the same direction on the three phases, used to supplement or absorb the overall active power loss of the DC bus of the series converter, maintaining the overall energy balance of the three-phase DC bus. The two frequency components operate in parallel through different frequency channels, with phase-to-phase equalization control and overall energy balance control operating independently, achieving natural decoupling between control loops. This frequency decoupling method fully utilizes the existing third harmonic and fundamental frequency circulating current injection capabilities of the triangular series-parallel flexible interconnect device, eliminating the need for additional hardware circuitry or the injection of new circulating current components. While achieving phase-to-phase energy balance, it ensures the reliability and economy of the device.

[0052] Specifically, in some embodiments of this application, the power interaction structure can be represented as follows: ; in, This is the power applied to the A-phase DC bus by the additional fundamental frequency voltage; This is the power applied to the B-phase DC bus by the additional base frequency voltage; This is the power applied to the C-phase DC bus by the additional fundamental frequency voltage; This is the zero-sequence fundamental frequency current component.

[0053] This application uses a final modulation voltage control energy balance module to simultaneously output an additional fundamental frequency voltage and a third harmonic voltage. The additional fundamental frequency voltage interacts with the zero-sequence fundamental frequency current component to achieve energy redistribution among the three-phase DC buses, while the third harmonic voltage interacts with the third harmonic current component to maintain the overall energy balance of the three-phase DC buses. This application separates inter-phase energy balance control from overall energy balance control through frequency decoupling. The two control objectives are independently undertaken by different frequency components, avoiding mutual interference between control loops and improving system stability and control accuracy.

[0054] In summary, the DC bus phase-to-phase energy balancing control method provided in this application has the following advantages compared to the prior art: This application achieves energy balancing between the three-phase DC buses by superimposing an additional fundamental frequency voltage on the inherent output voltage of the energy balancing module, which interacts with the zero-sequence fundamental frequency current component in the circulating current actively injected by the parallel-type cascaded full-bridge converter. Compared to the prior art scheme of superimposing a third harmonic voltage of the same frequency, this application uses a mixed superposition of the fundamental frequency additional voltage and the inherent output voltage. Since the peak values ​​of voltage components of different frequencies do not superimpose in the same direction, the peak value of the output voltage of the energy balancing module is effectively reduced, thereby improving the DC bus voltage utilization rate and reducing the requirements for the withstand voltage level of power devices and the overall cost of the device.

[0055] like Figure 2 As shown, based on the above-described method embodiments, this application provides a DC bus phase-to-phase energy balancing control device for use in a control system. The control system includes a series converter and a parallel cascaded full-bridge converter. The series converter includes an energy balancing module. The control device includes an acquisition module 201, a first generation module 202, a second generation module 203, and a control module 204. The acquisition module 201 is used to acquire the three-phase DC bus voltage and the average three-phase DC bus voltage of the series converter. The first generation module 202 is used to generate an additional base frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage. The second generation module 203 is used to superimpose the additional base frequency voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage; The control module 204 is used to control the energy balance module to output an additional base frequency voltage through the final modulation voltage, so that the additional base frequency voltage interacts with the zero-sequence base frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance among the three-phase DC buses.

[0056] Further, in some embodiments of this application, the three-phase DC bus voltage includes: phase A DC bus voltage, phase B DC bus voltage, and phase C DC bus voltage; the first generation module 202 includes: a first calculation unit, a second calculation unit, and a third calculation unit; the first generation module 202 is used to generate an additional fundamental frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage, including: The first calculation unit is used to calculate a first difference between the A-phase DC bus voltage and the average voltage of the three-phase DC bus, and a second difference between the B-phase DC bus voltage and the average voltage of the three-phase DC bus; The second calculation unit is used to input the first difference and the second difference into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the DC bus voltage of phase A and the second additional base frequency voltage command value corresponding to the DC bus voltage of phase B. The third calculation unit is used to generate a third additional base frequency voltage command value corresponding to the C-phase DC bus voltage based on the sum of the first additional base frequency voltage command value and the second additional base frequency voltage command value.

[0057] Further, in some embodiments of this application, the second calculation unit is used to input the first difference and the second difference into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the A-phase DC bus voltage and the second additional base frequency voltage command value corresponding to the B-phase DC bus voltage, including: The first difference is input into the first proportional-integral controller to obtain the first control output quantity; The second difference is input into the second proportional-integral controller to obtain the second control output. The first control output and the second control output are multiplied by the pre-constructed fundamental frequency sinusoidal signal to obtain the first AC quantity and the second AC quantity. Based on the sign of the zero-sequence fundamental frequency current component, the sign directions of the first AC quantity and the second AC quantity are determined to obtain the first additional fundamental frequency voltage command value and the second additional fundamental frequency voltage command value, respectively.

[0058] Furthermore, in some embodiments of this application, the process of constructing the fundamental frequency sinusoidal signal includes: Extract the phase and power frequency angular velocity from the zero-sequence fundamental frequency current component; The fundamental frequency sinusoidal signal is constructed based on the phase and the power frequency angular velocity.

[0059] Furthermore, in some embodiments of this application, the inherent output voltage command value is a fixed third harmonic voltage command value; the second generation module 203 is used to superimpose the additional baseband voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage, including: vector superimposing the additional baseband voltage command value and the inherent output voltage command value to obtain the final modulation voltage.

[0060] Further, in some embodiments of this application, the control module 204 includes: a first control unit, a second control unit, and a third control unit; the control module 204 is used to control the energy balance module to output an additional baseband voltage through the final modulation voltage, so that the additional baseband voltage interacts with the zero-sequence baseband current component in the circulating current actively injected by the parallel cascaded full-bridge converter to achieve energy balance among the three-phase DC buses, including: The first control unit is configured to control the energy balance module to output the additional base frequency voltage and the third harmonic voltage corresponding to the third harmonic voltage command value based on the final modulation voltage; The second control unit is used to perform power interaction with the zero-sequence fundamental frequency current component through the additional fundamental frequency voltage to distribute the energy between the three-phase DC buses; The third control unit is used to perform power interaction with the third harmonic current component in the circulating current actively injected by the parallel cascaded full-bridge converter through the third harmonic voltage, so as to maintain the energy balance of the three-phase DC bus.

[0061] It is understood that the above-described device embodiments correspond to the method embodiments of this application, and can realize the DC bus phase-to-phase energy balance control method provided by any of the above-described method embodiments of this application.

[0062] It should be noted that the device embodiments described above are merely illustrative, and some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the device embodiments provided in this application, the connection relationships between modules indicate that they have communication connections, which can specifically be implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0063] In summary, the DC bus phase-to-phase energy balancing control device provided in this application has the following advantages compared to the prior art: This application achieves energy balancing between the three-phase DC buses by superimposing an additional fundamental frequency voltage on the inherent output voltage of the energy balancing module, which interacts with the zero-sequence fundamental frequency current component in the circulating current actively injected by the parallel-type cascaded full-bridge converter. Compared to the prior art scheme of superimposing a third harmonic voltage of the same frequency, this application uses a mixed superposition of the fundamental frequency additional voltage and the inherent output voltage. Since the peak values ​​of voltage components of different frequencies do not superimpose in the same direction, the peak value of the output voltage of the energy balancing module is effectively reduced, thereby improving the DC bus voltage utilization rate and reducing the requirements for the withstand voltage level of power devices and the overall cost of the device.

[0064] Based on the above embodiments of the DC bus phase-to-phase energy balance control method, another embodiment of this application provides a DC bus phase-to-phase energy balance control system, including: a series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balance module, and the series converter and the parallel cascaded full-bridge converter are controlled by the DC bus phase-to-phase energy balance control method of any embodiment of this application.

[0065] Based on the above embodiments of the DC bus phase-to-phase energy balance control method, another embodiment of this application provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the DC bus phase-to-phase energy balance control method of any embodiment of this application.

[0066] For example, in this embodiment, the computer program can be divided into one or more modules, which are stored in the memory and executed by the processor to complete this application. The one or more module units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in the terminal device.

[0067] The terminal device may be a desktop computer, laptop, handheld computer, or cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0068] The processor can be a Central Processing Unit (CPU), or 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. A general-purpose processor can be a microprocessor or any conventional processor. The processor is the control center of the terminal device, connecting all parts of the terminal device via various interfaces and lines.

[0069] Based on the above-described method embodiments, another embodiment of this application provides a computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to execute the DC bus phase-to-phase energy equalization control method described in any of the above-described method embodiments of this application.

[0070] The modules / units integrated in the device / terminal equipment, if implemented as software functional units and sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

Claims

1. A method for phase-to-phase energy balance control of a DC bus, characterized in that, The system is applied to a control system, which includes a series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balance module; the control method includes: Obtain the three-phase DC bus voltage and the average three-phase DC bus voltage of the series converter; An additional base frequency voltage command value is generated based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage. The additional baseband voltage command value is superimposed on the inherent output voltage command value of the energy balance module to generate the final modulation voltage; The energy balance module outputs an additional base frequency voltage by controlling the final modulation voltage, so that the additional base frequency voltage interacts with the zero-sequence base frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance among the three-phase DC buses.

2. The DC bus phase-to-phase energy balance control method as described in claim 1, characterized in that, The three-phase DC bus voltage includes: phase A DC bus voltage, phase B DC bus voltage, and phase C DC bus voltage; the step of generating an additional fundamental frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage includes: Calculate the first difference between the A-phase DC bus voltage and the average voltage of the three-phase DC bus, and the second difference between the B-phase DC bus voltage and the average voltage of the three-phase DC bus; The first difference and the second difference are respectively input into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the DC bus voltage of phase A and the second additional base frequency voltage command value corresponding to the DC bus voltage of phase B. Based on the sum of the first additional base frequency voltage command value and the second additional base frequency voltage command value, a third additional base frequency voltage command value corresponding to the C-phase DC bus voltage is generated.

3. The DC bus phase-to-phase energy balance control method as described in claim 2, characterized in that, The step of inputting the first difference and the second difference into the corresponding proportional-integral controllers to obtain the first additional base frequency voltage command value corresponding to the A-phase DC bus voltage and the second additional base frequency voltage command value corresponding to the B-phase DC bus voltage includes: The first difference is input into the first proportional-integral controller to obtain the first control output quantity; The second difference is input into the second proportional-integral controller to obtain the second control output. The first control output and the second control output are multiplied by the pre-constructed fundamental frequency sinusoidal signal to obtain the first AC quantity and the second AC quantity. Based on the sign of the zero-sequence fundamental frequency current component, the sign directions of the first AC quantity and the second AC quantity are determined to obtain the first additional fundamental frequency voltage command value and the second additional fundamental frequency voltage command value, respectively.

4. The DC bus phase-to-phase energy balance control method as described in claim 3, characterized in that, The process of constructing the fundamental frequency sinusoidal signal includes: Extract the phase and power frequency angular velocity from the zero-sequence fundamental frequency current component; The fundamental frequency sinusoidal signal is constructed based on the phase and the power frequency angular velocity.

5. The DC bus phase-to-phase energy balance control method as described in claim 1, characterized in that, The inherent output voltage command value is a fixed third harmonic voltage command value; the step of superimposing the additional baseband voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage includes: vector superimposing the additional baseband voltage command value and the inherent output voltage command value to obtain the final modulation voltage.

6. The DC bus phase-to-phase energy balance control method as described in claim 5, characterized in that, The step of controlling the energy balance module to output an additional baseband voltage through the final modulation voltage, so that the additional baseband voltage interacts with the zero-sequence baseband current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance among the three-phase DC buses, includes: Based on the final modulation voltage, the energy balance module is controlled to output the additional base frequency voltage and the third harmonic voltage corresponding to the third harmonic voltage command value; The energy between the three-phase DC buses is distributed through power interaction between the additional fundamental frequency voltage and the zero-sequence fundamental frequency current component. The power interaction between the third harmonic voltage and the third harmonic current component in the circulating current actively injected by the parallel cascaded full-bridge converter is carried out to maintain the energy balance of the three-phase DC bus.

7. A DC bus phase-to-phase energy balancing control device, characterized in that, The system is applied to a control system, which includes a series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balance module; the control device includes a data acquisition module, a first generation module, a second generation module, and a control module. The acquisition module is used to acquire the three-phase DC bus voltage and the average three-phase DC bus voltage of the series converter. The first generation module is used to generate an additional base frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage. The second generation module is used to superimpose the additional baseband voltage command value onto the inherent output voltage command value of the energy balance module to generate the final modulation voltage; The control module is used to control the energy balance module to output an additional base frequency voltage through the final modulation voltage, so that the additional base frequency voltage interacts with the zero-sequence base frequency current component in the circulating current actively injected by the parallel cascaded full-bridge converter, thereby achieving energy balance among the three-phase DC buses.

8. The DC bus phase-to-phase energy balancing control device as described in claim 7, characterized in that, The three-phase DC bus voltage includes: phase A DC bus voltage, phase B DC bus voltage, and phase C DC bus voltage; the first generation module includes: a first calculation unit, a second calculation unit, and a third calculation unit; the first generation module is used to generate an additional fundamental frequency voltage command value based on the deviation between the three-phase DC bus voltage and the average three-phase DC bus voltage, including: The first calculation unit is used to calculate a first difference between the A-phase DC bus voltage and the average voltage of the three-phase DC bus, and a second difference between the B-phase DC bus voltage and the average voltage of the three-phase DC bus; The second calculation unit is used to input the first difference and the second difference into the corresponding proportional-integral controller to obtain the first additional base frequency voltage command value corresponding to the DC bus voltage of phase A and the second additional base frequency voltage command value corresponding to the DC bus voltage of phase B. The third calculation unit is used to generate a third additional base frequency voltage command value corresponding to the C-phase DC bus voltage based on the sum of the first additional base frequency voltage command value and the second additional base frequency voltage command value.

9. A DC bus phase-to-phase energy balancing control system, characterized in that, include: A series converter and a parallel cascaded full-bridge converter, wherein the series converter includes an energy balance module, and the series converter and the parallel cascaded full-bridge converter are controlled by a DC bus phase-to-phase energy balance control method as described in any one of claims 1 to 6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein, when the computer program is executed, it controls the device containing the computer-readable storage medium to perform a DC bus phase-to-phase energy equalization control method as described in any one of claims 1 to 6.

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