A generalized synchronous optimal pulse width modulation method and system for new energy stations

Abstract

The present invention discloses a generalized synchronous optimal pulse width modulation method and system for new energy stations. The method obtains steady-state operating information of a converter cluster in a new energy station; constructs a coordinated power quality optimization modulation equation based on the steady-state operating information, and adds constraints to the coordinated power quality optimization modulation equation based on the fundamental volt-second characteristic and time sequence to obtain an optimization problem; solves the optimization problem using an optimization solver to obtain the optimal switching pulse switching sequence of the converter cluster at the ideal operating point; solves the optimization problem using a gradient descent algorithm to obtain a converter cluster pulse width modulation lookup table whose ideal operating point extends within a set modulation index range, and distributes it to each converter. Aiming at the harmonic pollution problem at low switching frequencies in high-power new energy stations, the method fully utilizes the additional control freedom provided by the converter cluster within the new energy station to significantly reduce the harmonic distortion of the injected current at the public grid connection point of the new energy station.

Description

Technical Field

[0001] The present invention relates to the field of grid connection technology, and in particular to a generalized synchronous optimal pulse width modulation method and system for new energy stations. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] With the rapid development of renewable energy, large-scale power conversion systems, such as high-power photovoltaic power plants and offshore wind farms, are increasingly playing a role in the energy sector. In these systems, power converters are the core equipment for efficient power conversion. To reduce losses and meet heat dissipation requirements, high-power power converters typically operate at low switching frequencies. However, this can lead to significant harmonic distortion in the output current and voltage, polluting the power grid, increasing filtering costs, and reducing overall system performance.

[0004] High-power grid-connected converter systems, limited by switching losses and system thermal limits, typically operate at low switching frequencies in industrial products. This results in significant switching nonlinearity and severe harmonic distortion, necessitating the use of bulky passive filtering equipment, resulting in large system sizes and high hardware costs.

[0005] Pulse-width modulation (PWM) technology is a key component of power converters. Existing PWM techniques, such as carrier modulation and space vector modulation, are prone to generating low-order harmonics at low switching frequencies. While programmed modulation can manage harmonics, existing research has largely focused on optimizing individual converters, overlooking the advantages of coordinated converter clusters. In practical large-scale power conversion systems, multiple power converters are often connected to the grid via a point of common coupling (PCC). Coordinated control of converter clusters is crucial to system performance. Therefore, developing a modulation technique that fully leverages the advantages of converter clusters and reduces harmonic distortion is urgent.

[0006] Programmed modulation technology is an effective method to solve power quality problems at low switching frequencies, but existing solutions generally focus on optimizing the power quality of a single converter. For the clustered distribution of converter systems within new energy stations, this method has limited optimization and faces insurmountable bottlenecks in improving the overall system performance. Summary of the Invention

[0007] In order to overcome the shortcomings of the above-mentioned existing technologies, the present invention provides a generalized synchronous optimal pulse width modulation method and system for new energy stations. It targets the harmonic pollution problem at low switching frequencies of high-power new energy stations, makes full use of the additional control freedom brought by the internal converter cluster of the new energy station, and achieves a significant reduction in the harmonic distortion of the injected current at the public grid connection point of the new energy station.

[0008] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0009] In a first aspect, the present invention provides a generalized synchronous optimal pulse width modulation method for new energy stations, comprising:

[0010] Obtain steady-state operation information of converter clusters in new energy stations;

[0011] Constructing a coordinated power quality optimization modulation equation based on the steady-state operation information, and adding constraints to the coordinated power quality optimization modulation equation based on the fundamental wave volt-second characteristic and time sequence to obtain an optimization problem;

[0012] Solving the optimization problem by an optimization solver to obtain an optimal switching pulse sequence of the converter cluster at an ideal operating point;

[0013] The optimization problem is solved by a gradient descent algorithm to obtain a pulse width modulation lookup table of a converter cluster in which an ideal operating point extends within a set modulation index range, and the table is distributed to each converter.

[0014] According to a further technical solution, the steady-state operation information includes modulation index, phase, and circuit parameters.

[0015] In a further technical solution, the collaborative power quality optimization modulation equation is expressed as:

[0016]

[0017] in, Represents the total harmonic distortion of the current, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the lumped harmonic current, represents the total number of subunits, Indicates the subunits Subharmonic current, represents the converter coefficient, Indicates the subunits Subharmonic voltage.

[0018] Further technical solution, the optimization problem is expressed as:

[0019]

[0020] in, represents the cost evaluation function, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the total number of subunits, represents the converter coefficient, Indicates the subunits Subharmonic voltage, Indicates the upper limit of harmonics considered, Indicates the first DC bus voltage, Indicates the DC bus voltage, represents the expected fundamental modulation depth of the first subunit, Indicates the The expected fundamental modulation depth of each subunit, Indicates the The first subunit The switching moment, Indicates the The first subunit The switching moment.

[0021] As a further technical solution, preferably, the optimization solver adopts a QP solver.

[0022] A further technical solution is to solve the optimization problem by using a gradient descent algorithm: by changing the expected fundamental modulation degree of the sub-unit, the optimization problem is extended and solved using a gradient descent algorithm.

[0023] A further technical solution is to distribute the converter cluster pulse width modulation lookup table to each converter through information interaction.

[0024] In a second aspect, the present invention provides a generalized synchronous optimal pulse width modulation system for new energy stations, comprising:

[0025] A data acquisition module is configured to: acquire steady-state operation information of a converter cluster in a new energy station;

[0026] a problem construction module configured to: construct a coordinated power quality optimization modulation equation based on the steady-state operation information, and add constraints to the coordinated power quality optimization modulation equation based on fundamental wave volt-second characteristics and time sequence to obtain an optimization problem;

[0027] A problem-solving module is configured to: solve the optimization problem by an optimization solver to obtain an optimal switch pulse switching sequence of the converter cluster at an ideal operating point;

[0028] The sequence extension module is configured to solve the optimization problem by a gradient descent algorithm, obtain a pulse width modulation lookup table of the converter cluster in which the ideal operating point is extended within a set modulation index range, and distribute the table to each converter.

[0029] In a third aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a generalized synchronous optimal pulse width modulation method for new energy stations as described in the first aspect.

[0030] In a fourth aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of a generalized synchronous optimal pulse width modulation method for new energy stations as described in the first aspect are implemented.

[0031] One or more of the above technical solutions have the following beneficial effects:

[0032] This method leverages the additional degrees of freedom offered by converter clusters. By analyzing the pulse-harmonic coupling mechanism within the station, it establishes a global optimization problem for power quality, thereby obtaining the optimal switching pulse sequence that minimizes harmonic pollution at the grid connection point of the renewable energy station. This method can significantly reduce the harmonic impact of renewable energy stations on the power grid.

[0033] The present invention can further improve the compatibility of new energy stations with the grid, reduce the size and capacity of filters, promote cost reduction and efficiency improvement of new energy conversion equipment, and promote the development of related industrial chains.

[0034] Compared with traditional methods, this solution fully utilizes the additional degrees of freedom offered by converter clusters in new energy stations, achieving reduced harmonic injection and contamination at the grid connection point (compared to traditional carrier modulation technology, at an extremely low switching frequency of 250 Hz, the total harmonic distortion of the four converter units can be reduced by 97%). The deployment of this solution can further improve the grid connection performance of new energy stations, reduce the size and capacity of filters, promote cost reduction and efficiency improvement of new energy conversion equipment, and promote the development of the related industrial chain. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 This is a flowchart of an implementation of a generalized synchronous optimal pulse width modulation method according to an embodiment of the present invention;

[0037] Figure 2 This is a simplified frequency domain model of the power converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0041] Example 1

[0042] This embodiment discloses a generalized synchronous optimal pulse width modulation method for new energy stations, which includes the following steps:

[0043] S1: Obtain the steady-state operation information of the converter cluster in the new energy station;

[0044] In this embodiment, a unified central control unit collects steady-state operating information from each converter in the new energy station, including modulation index, phase, and circuit parameters. This data is used to construct the optimization equation.

[0045] New energy stations such as Figure 1 As shown, a renewable energy power plant includes multiple power units (power converters). Each power unit is connected to a filter and a transformer in sequence through cables to a common connection point PCC. One end of the common connection point PCC is connected to the output end, and the other end is connected to a monitor.

[0046] S2: constructing a coordinated power quality optimization modulation equation based on the steady-state operation information, and adding constraints to the coordinated power quality optimization modulation equation based on the fundamental wave volt-second characteristic and time sequence to obtain an optimization problem;

[0047] In this embodiment, (1) Analysis of the converter harmonic pulse coupling mechanism

[0048] The purpose of harmonic programming modulation is to achieve the desired optimal harmonics using a limited number of switches. According to Fourier series theory, any periodic signal that satisfies the Dirichlet condition can be expanded into a series of sinusoidal functions with different frequencies, namely:

[0049]

[0050] in, is the fundamental frequency period, represents the harmonic order of decomposition, represents the total harmonic order, 、 are the Fourier coefficients, Indicates the moment, represents the switching pulse function. Therefore, if Figure 1 For the pulse sequence shown, its harmonic composition can be determined, namely:

[0051]

[0052] in, Indicates the fundamental angular frequency.

[0053] Since the quarter-symmetrical waveform has inherent DC component, even-order component, and cosine cancellation capabilities, the present invention adopts this symmetrical solution. That is, the coupling relationship between harmonic voltage and switching pulse can be converted to:

[0054]

[0055] in, is the order of switching moments, is the number of switching times within a quarter cycle, Indicates the DC bus voltage, Represents the switching pulse angle. According to the formula provided above, the relationship between the pulse sequence and voltage harmonics can be accurately established, providing a theoretical basis for subsequent harmonic optimization.

[0056] Figure 2 It is a simplified frequency domain model of power converter, which consists of grid harmonics, converter harmonics and harmonic reactance, among which, Indicates the power grid Sub-voltage harmonics, Indicates the motivation Subcurrent harmonics, Indicates the current generated by the converter Sub-voltage harmonics, represents the equivalent parasitic resistance of the circuit, Indicates The equivalent impedance of the system under subharmonics. According to the analysis, the harmonic current of the system under specific harmonic voltage excitation can be expressed as:

[0057]

[0058] in, represents the lumped harmonic current, represents harmonic voltage, is the harmonic order, is the fundamental frequency of the system, Indicates the inductive reactance of the line and filter, Indicates the parasitic resistance of the line and filter.

[0059] The total harmonic distortion of the system current is defined as:

[0060]

[0061] in, Represents the total harmonic distortion of the current, represents the lumped harmonic current, Indicates the fundamental current.

[0062] Since the system expects the fundamental current amplitude to be fixed under certain working conditions, the optimization of power quality can be simplified as follows:

[0063] .

[0064] However, the above optimization is limited to a single converter system and has limited effect on improving the setting performance of new energy stations. To fully utilize the additional degrees of freedom provided by the converter cluster within the station, the harmonic coupling relationship within the converter cluster was further derived.

[0065] (2) Constructing a coordinated power quality optimization modulation equation

[0066] The effect of current injection from a single converter on the common point can be deduced from Kirchhoff's law, namely:

[0067]

[0068] in, Indicates the The phase current of each sub-unit, Indicates the The phase voltage of each subunit, Indicates the The common mode voltage of each subunit, represents the lumped impedance of the line and filter, Indicates the grid phase voltage.

[0069] For high-power conversion scenarios, the inductive reactance of filters and transmission lines is much greater than their resistive characteristics. Therefore, in the modeling process, their electrophysical characteristics can be replaced by inductive components. Therefore, the impact of a single converter on the total current at the public grid connection point can be expressed as:

[0070]

[0071] in, Indicates the The lumped voltage amplitude of each sub-unit is Indicates the The lumped voltage phase of each sub-unit, express Subharmonic The lumped impedance of the subunits, Indicates the phase number, Indicates the subunits, Represents any positive integer.

[0072] Therefore, the current at the public grid connection point can be expressed as:

[0073]

[0074] in, represents the total number of subunits, Indicates the The lumped voltage phase of each sub-unit, Indicates the harmonic order, is the converter coefficient, that is Therefore, the overall power quality optimization for the new energy station can be expressed as:

[0075]

[0076] in, Indicates the subunits Subharmonic current, Indicates the subunits Subharmonic voltage.

[0077] At the same time, in order to satisfy the fundamental volt-second characteristics and timing of the optimal pulse sequence, that is, to ensure that the resulting converter pulse width sequence has the desired fundamental amplitude and achievable timing constraints, the final optimization problem is subject to relevant restrictions (constraints), as shown below:

[0078]

[0079] in, represents the cost evaluation function, Indicates the upper limit of harmonics considered, Indicates the first DC bus voltage, Indicates the DC bus voltage, represents the expected fundamental modulation depth of the first subunit, Indicates the The expected fundamental modulation depth of each subunit, Indicates the The first subunit The switching moment, Indicates the The first subunit The switching moment.

[0080] S3: solving the optimization problem using an optimization solver to obtain an optimal switching pulse sequence of the converter cluster at an ideal operating point;

[0081] In this embodiment, the ideal operating point is solved: Based on the constructed optimization problem, an optimization solver, such as a commercial QP solver, is used to obtain the overall switching pulse sequence of the converter cluster at the ideal operating point. The ideal operating point refers to the ideal operating state of the system calculated based on the steady-state operating information data collected by the system. However, it is worth noting that the modulation index of the converter system is not fixed even under steady-state conditions. Therefore, the modulation index range corresponding to the pulse sequence needs to be expanded.

[0082] S4: Solve the optimization problem by using a gradient descent algorithm to obtain a pulse width modulation lookup table of a converter cluster in which an ideal operating point extends within a set modulation index range, and distribute the table to each converter.

[0083] In this embodiment, since the state of the system is dynamically stable, it is not possible to calculate only the optimal switch pulse switching sequence under the ideal working point, but it is necessary to extend it, the optimal pulse width extension and information distribution: further by changing the sub-unit expected fundamental modulation The final optimization problem is extended and solved using a gradient descent algorithm, enabling extended calculation of the switching pulse sequence for adjacent modulations around the ideal operating point of the converter cluster. Finally, through information exchange, the switching pulse data is distributed to each converter in the new energy station, replacing the original switching pulse sequence lookup table.

[0084] Specifically, by reconstructing the modulation index of each converter within a set modulation index range (preferably, within a range of ±0.3 modulation index), , taking the ideal operating point as the initial calculation point and solving it through the gradient descent method, we can obtain the pulse width modulation lookup table of the converter cluster under the working conditions near the ideal operating point. Finally, it is uniformly distributed to each converter through the central computing unit to update the lookup table.

[0085] S3 only calculated the optimal switching pulse sequence under a single operating condition. S4 further extends this calculation to include more operating conditions and calculates the optimal switching pulse sequence under other operating conditions. Based on the above method, this embodiment reduced the total harmonic distortion of the injected current by approximately 97% in the tested four-converter power unit compared to the traditional carrier solution.

[0086] Therefore, while traditional methods analyze the harmonic energy efficiency corresponding to switching pulses from the perspective of a single converter, the method proposed in this paper analyzes from the perspective of the entire station, comprehensively utilizing the selection of switching pulse combinations for each converter. This achieves harmonic cancellation within the cluster, improves power quality, and reduces overall harmonic injection. The additional degrees of freedom are the additional degrees of freedom of coordinated control brought about by cluster collaboration.

[0087] Example 2

[0088] This embodiment discloses a generalized synchronous optimal pulse width modulation system for new energy stations, including:

[0089] A data acquisition module is configured to: acquire steady-state operation information of a converter cluster in a new energy station;

[0090] a problem construction module configured to: construct a coordinated power quality optimization modulation equation based on the steady-state operation information, and add constraints to the coordinated power quality optimization modulation equation based on fundamental wave volt-second characteristics and time sequence to obtain an optimization problem;

[0091] A problem-solving module is configured to: solve the optimization problem by an optimization solver to obtain an optimal switch pulse switching sequence of the converter cluster at an ideal operating point;

[0092] The sequence extension module is configured to solve the optimization problem by a gradient descent algorithm, obtain a pulse width modulation lookup table of the converter cluster in which the ideal operating point is extended within a set modulation index range, and distribute the table to each converter.

[0093] Example 3

[0094] The purpose of this embodiment is to provide a computing device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method of embodiment 1 when executing the program.

[0095] Example 4

[0096] The purpose of this embodiment is to provide a computer-readable storage medium, a computer-readable storage medium having a computer program stored thereon, which performs the steps of the method of embodiment 1 when executed by a processor.

[0097] The steps involved in the apparatuses of Examples 3 and 4 above correspond to those of Method Example 1. For detailed implementation, please refer to the relevant description of Example 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and causing the processor to perform any of the methods of the present invention.

[0098] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0099] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

[0100] 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 solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A generalized synchronous optimal pulse width modulation method for new energy stations, characterized in that: include: Obtain steady-state operation information of converter clusters in new energy stations; Constructing a coordinated power quality optimization modulation equation based on the steady-state operation information, and adding constraints to the coordinated power quality optimization modulation equation based on the fundamental wave volt-second characteristic and time sequence to obtain an optimization problem; The collaborative power quality optimization modulation equation is expressed as: in, Represents the total harmonic distortion of the current, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the lumped harmonic current, represents the total number of subunits, Indicates the subunits Subharmonic current, represents the converter coefficient, Indicates the subunits Subharmonic voltage; The optimization problem is expressed as: in, represents the cost evaluation function, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the total number of subunits, represents the converter coefficient, Indicates the subunits Subharmonic voltage, Indicates the upper limit of harmonics considered, Indicates the first DC bus voltage, Indicates the DC bus voltage, represents the expected fundamental modulation depth of the first subunit, Indicates the The expected fundamental modulation depth of each subunit, Indicates the The first subunit The switching moment, Indicates the The first subunit Secondary switching moment; Solving the optimization problem by an optimization solver to obtain an optimal switching pulse sequence of the converter cluster at an ideal operating point; The optimization problem is solved by a gradient descent algorithm to obtain a pulse width modulation lookup table of a converter cluster in which an ideal operating point extends within a set modulation index range, and the table is distributed to each converter.

2. A generalized synchronous optimal pulse width modulation method for new energy stations according to claim 1, characterized in that: The steady-state operation information includes modulation index, phase, and circuit parameters.

3. The generalized synchronous optimal pulse width modulation method for new energy stations according to claim 1, characterized in that: Preferably, the optimization solver adopts a QP solver.

4. A generalized synchronous optimal pulse width modulation method for new energy stations according to claim 1, characterized in that: Solving the optimization problem by using the gradient descent algorithm specifically includes: changing the expected fundamental modulation degree of the sub-unit and using the gradient descent algorithm to extend and solve the optimization problem.

5. The generalized synchronous optimal pulse width modulation method for new energy stations according to claim 1, characterized in that: The pulse width modulation lookup table of the converter cluster is distributed to each converter through information interaction.

6. A generalized synchronous optimal pulse width modulation system for new energy stations, characterized by: include: A data acquisition module is configured to: acquire steady-state operation information of a converter cluster in a new energy station; a problem construction module configured to: construct a coordinated power quality optimization modulation equation based on the steady-state operation information, and add constraints to the coordinated power quality optimization modulation equation based on fundamental wave volt-second characteristics and time sequence to obtain an optimization problem; The collaborative power quality optimization modulation equation is expressed as: in, Represents the total harmonic distortion of the current, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the lumped harmonic current, represents the total number of subunits, Indicates the subunits Subharmonic current, represents the converter coefficient, Indicates the subunits Subharmonic voltage; The optimization problem is expressed as: in, represents the cost evaluation function, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the total number of subunits, represents the converter coefficient, Indicates the subunits Subharmonic voltage, Indicates the upper limit of harmonics considered, Indicates the first DC bus voltage, Indicates the DC bus voltage, represents the expected fundamental modulation depth of the first subunit, Indicates the The expected fundamental modulation depth of each subunit, Indicates the The first subunit The switching moment, Indicates the The first subunit Secondary switching moment; A problem-solving module is configured to: solve the optimization problem by an optimization solver to obtain an optimal switch pulse switching sequence of the converter cluster at an ideal operating point; The sequence extension module is configured to solve the optimization problem by a gradient descent algorithm, obtain a pulse width modulation lookup table of the converter cluster in which the ideal operating point is extended within a set modulation index range, and distribute the table to each converter.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of a generalized synchronous optimal pulse width modulation method for a new energy station as described in any one of claims 1 to 5 are implemented.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the generalized synchronous optimal pulse width modulation method for new energy stations according to any one of claims 1 to 5 are implemented.

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