Generalized synchronous optimal pulse width modulation method and system for new energy station

Abstract

The invention discloses a generalized synchronous optimal pulse width modulation method and system for a new energy station. The method comprises the following steps: acquiring steady-state operation information of a converter cluster in the new energy station; constructing a cooperative power quality optimization modulation equation based on the steady-state operation information, and adding constraints in the cooperative power quality optimization modulation equation based on the fundamental wave volt-second characteristics and the time sequence to obtain an optimization problem; solving the optimization problem through an optimization solver to obtain an optimal switching pulse switching sequence of the converter cluster under the ideal working point; and solving an optimization problem through a gradient descent algorithm to obtain a converter cluster pulse width modulation lookup table with an ideal working point extending in a set modulation degree range, and distributing the converter cluster pulse width modulation lookup table to each converter. For the harmonic pollution problem of the high-power new energy station under the low switching frequency, the extra control freedom degree brought by a current transformer cluster in the new energy station is fully utilized, and the harmonic distortion of the injection current of the public grid-connected point of the new energy station is greatly reduced.

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 vigorous development of renewable energy, large-scale power conversion systems such as high-power photovoltaic power stations and offshore wind farms are increasingly used in the energy field. In these systems, power converters are the core equipment for efficient conversion of electric energy. In order to reduce losses and meet heat dissipation requirements, high-power power converters usually operate at low switching frequencies, which can cause serious harmonic distortion in the output current and voltage, pollute the power grid, increase filtering costs, and reduce the overall performance of the system.

[0004] High-power grid-connected converter systems are limited by switching losses and system thermal limits, and generally operate at low switching frequencies in industrial products. This results in significant system switching nonlinearity and severe harmonic distortion. Therefore, large passive filtering equipment is generally required, resulting in large system volumes and high hardware costs.

[0005] Pulse width modulation (PWM) technology is a key part of power converters. Existing PWM technologies such as carrier modulation and space vector modulation are prone to generate low-order harmonics at low switching frequencies. Although programmed modulation can manage harmonics, existing research focuses on the optimization of a single converter, ignoring the advantages of converter cluster coordination. In actual large-scale power conversion systems, multiple power converters are often connected to the grid through a common coupling point (PCC), and the coordinated control of converter clusters is crucial to system performance. Therefore, it is urgent to develop a modulation technology that can fully utilize the advantages of converter clusters and reduce harmonic distortion.

[0006] Programming modulation technology is an effective way 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 situation where the converter systems within new energy stations are clustered, the degree of optimization of this method is limited, and there is an insurmountable bottleneck in improving the overall performance of the system. Summary of the invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a generalized synchronous optimal pulse width modulation method and system for new energy stations, which aims at the harmonic pollution problem under low switching frequency 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-connected 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: In a first aspect, the present invention provides a generalized synchronous optimal pulse width modulation method for a new energy station, comprising: 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 fundamental wave volt-second characteristics and time sequence to obtain an optimization problem; Solving the optimization problem by using an optimization solver to obtain an optimal switch pulse switching sequence of the converter cluster at an ideal working point; The optimization problem is solved by a gradient descent algorithm, and a pulse width modulation lookup table of a converter cluster extending an ideal working point within a set modulation range is obtained and distributed to each converter.

[0009] According to a further technical solution, the steady-state operation information includes modulation index, phase, and circuit parameters.

[0010] Further technical solution, the collaborative power quality optimization modulation equation is expressed as:

[0011] in, Represents the total harmonic distortion of the current, Indicates the inductive reactance of the line and filter, represents the harmonic order, represents the total harmonic current, represents the total number of subunits, Indicates subunit Subharmonic current, represents the converter factor, Indicates subunit Subharmonic voltage.

[0012] Further technical solution, the optimization problem is expressed as:

[0013] 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 factor, Indicates subunit Subharmonic voltage, Indicates the upper limit of harmonics taken into account, represents the first DC bus voltage, Indicates The DC bus voltage, represents the expected fundamental modulation of the first subunit, Indicates The expected fundamental modulation of each subunit, Indicates The subunit The switching time of the second switch, Indicates The subunit The time of the second switch switching.

[0014] As a further technical solution, preferably, the optimization solver adopts a QP solver.

[0015] 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 by using a gradient descent algorithm.

[0016] A further technical solution is to distribute the converter cluster pulse width modulation lookup table to each converter through information interaction.

[0017] In a second aspect, the present invention provides a generalized synchronous optimal pulse width modulation system for new energy stations, comprising: 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 is 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; 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 working point; The sequence extension module is configured to solve the optimization problem by a gradient descent algorithm, obtain a converter cluster pulse width modulation lookup table in which the ideal working point is extended within a set modulation range, and distribute the table to each converter.

[0018] 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.

[0019] 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, wherein 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.

[0020] One or more of the above technical solutions have the following beneficial effects: The present invention makes full use of the extra degrees of freedom brought by the converter cluster, establishes a global optimization problem for power quality by analyzing the pulse harmonic coupling mechanism inside the station, and thus obtains the optimal switching pulse sequence that can minimize the harmonic pollution at the grid-connected access point of the new energy station. The proposed method can significantly reduce the harmonic impact of the new energy station on the power grid.

[0021] The present invention can further improve the friendliness of new energy stations and grid connections, 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.

[0022] Compared with traditional methods, this invention makes full use of the extra degrees of freedom brought by the converter cluster in the new energy station, and achieves less harmonic injection / pollution at the grid connection point (compared with traditional carrier modulation technology, at an extremely low switching frequency of 250HZ, the total harmonic distortion of the four-converter unit can be reduced by 97%). The deployment of the solution can further improve the grid connection friendliness of new energy stations, reduce the size and capacity of filters, promote the cost reduction and efficiency improvement of new energy conversion equipment, and promote the development of related industrial chains. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, 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.

[0024] Figure 1 is an implementation flow chart of the generalized synchronous optimal pulse width modulation method according to an embodiment of the present invention; Figure 2 This is a simplified frequency domain model of the power converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0027] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0028] Embodiment 1 This embodiment discloses a generalized synchronous optimal pulse width modulation method for a new energy station, the method comprising the following steps: S1: Obtain the steady-state operation information of the converter cluster in the new energy station; In this embodiment, a unified central control unit collects steady-state operation information of each converter in the new energy station, including modulation index, phase, and circuit parameters, and these data will be used to construct the optimization equation.

[0029] New energy stations such as Figure 1 As shown, the renewable energy power plant includes multiple power units (power converters), each of which 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.

[0030] 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; In this embodiment, (1) analysis of the converter harmonic pulse coupling mechanism 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:

[0031] in, is the fundamental frequency period, represents the harmonic order of decomposition, represents the total harmonic order, , are the Fourier coefficients, Indicates the time, represents the switching pulse function. Therefore, if Figure 1 For the pulse sequence shown, its harmonic composition can be determined, namely:

[0032] in, Indicates the fundamental angular frequency.

[0033] Since the quarter-symmetrical waveform has inherent DC component, even-order component, and cosine elimination capability, the present invention adopts this symmetrical solution. That is, the coupling relationship between the harmonic voltage and the switching pulse can be converted into:

[0034] in, is the order of switching moments, is the number of switching times within a quarter cycle, Indicates the DC bus voltage, Indicates the switching pulse angle. According to the formula provided above, the relationship between the pulse sequence and the voltage harmonics can be accurately established, providing a theoretical basis for subsequent harmonic optimization.

[0035] 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 incentive Sub-current harmonics, The inverter generates Sub-voltage harmonics, represents the circuit equivalent parasitic resistance, Indicated in 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:

[0036] in, represents the total 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.

[0037] The total harmonic distortion of the system current is defined as:

[0038] in, Represents the total harmonic distortion of the current, represents the total harmonic current, Indicates the fundamental current.

[0039] 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: .

[0040] However, the above optimization is limited to a single converter system, and has limited effect on improving the setting performance of new energy stations. In order to make full use of the additional degrees of freedom brought by the converter cluster in the station, the harmonic coupling relationship within the converter cluster is further derived.

[0041] (2) Constructing the coordinated power quality optimization modulation equation The effect of a single converter on the current injection of the common point can be deduced by Kirchhoff's law, namely:

[0042] in, Indicates The phase current of each sub-unit, Indicates The phase voltage of each subunit, Indicates The common mode voltage of each sub-unit, represents the lumped impedance of the line and filter, Indicates the grid phase voltage.

[0043] For high-power conversion scenarios, the inductive characteristics of filters and transmission lines are 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:

[0044] in, Indicates The lumped voltage amplitude of each sub-unit is Indicates The lumped voltage phase of each sub-unit is express Subharmonic The lumped impedance of the sub-units, Indicates the phase number, Indicates subunits, Represents any positive integer.

[0045] Therefore, the public grid connection point current can be expressed as:

[0046] in, represents the total number of subunits, Indicates The lumped voltage phase of each sub-unit is 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:

[0047] in, Indicates subunit Subharmonic current, Indicates subunit Subharmonic voltage.

[0048] At the same time, in order to satisfy the basic fundamental volt-second characteristics and timing of the optimal pulse sequence, that is, in order to make the resulting converter pulse width sequence have the desired fundamental amplitude and achievable timing constraints, the final optimization problem is added with relevant restrictions (constraints), as shown below:

[0049] in, represents the cost evaluation function, Indicates the upper limit of harmonics taken into account, represents the first DC bus voltage, Indicates The DC bus voltage, represents the expected fundamental modulation of the first subunit, Indicates The expected fundamental modulation of each subunit, Indicates The subunit The switching time of the second switch, Indicates The subunit The time of the second switch switching.

[0050] S3: solving the optimization problem by using an optimization solver to obtain an optimal switch pulse switching sequence of the converter cluster at an ideal working point; In this embodiment, the ideal operating point is solved: according to the constructed optimization problem, the overall switch pulse switching sequence of the converter cluster under the ideal operating point can be obtained through an optimization solver, such as a commercial QP solver. The ideal operating point refers to the state of the system in the ideal working state calculated based on the steady-state operation information data collected by the system. However, it is worth noting that the modulation degree of the converter system is not fixed even under steady-state conditions. Therefore, it is necessary to extend the modulation degree range corresponding to the pulse sequence to be solved.

[0051] S4: Solve the optimization problem by using a gradient descent algorithm to obtain a pulse width modulation lookup table of a converter cluster extending an ideal working point within a set modulation range, and distribute the table to each converter.

[0052] In this embodiment, since the state of the system is dynamically stable, it is not possible to only calculate 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 gradient descent algorithm is used to extend the solution of the final optimization problem, so as to realize the extended calculation of the switch pulse switching sequence of the adjacent modulation around the ideal working point of the converter cluster. And finally, the switch pulse data is distributed to each converter of the new energy station through information interaction to replace the original switch pulse sequence lookup table.

[0053] Specifically, by reconstructing the modulation index of each converter within a set modulation index range (preferably, within a range of plus or minus 0.3 modulation index), , taking the ideal working point as the initial point of calculation and solving it through the gradient descent method, the pulse width modulation lookup table of the converter cluster under the working conditions near the ideal working point can be obtained, and finally it is uniformly distributed to each converter through the central computing unit to update the lookup table.

[0054] S3 only calculates the optimal switch pulse switching sequence under a single working condition, and S4 further extends to more working conditions to calculate the optimal switch pulse switching sequence under other working conditions. According to the above method, in the tested four-converter power unit of this embodiment, the total harmonic distortion of the injected current is reduced by about 97% compared with the traditional carrier solution.

[0055] Therefore, the traditional method analyzes the harmonic energy efficiency corresponding to the switching pulse from the perspective of a single converter, while the method proposed in the present invention analyzes from the perspective of the entire station, comprehensively utilizing the selection of each converter switching pulse combination, thereby achieving the cancellation of harmonics within the cluster, improving the power quality, and reducing the overall harmonic injection. Additional degrees of freedom are the additional collaborative control degrees of freedom brought by cluster collaboration.

[0056] Embodiment 2 This embodiment discloses a generalized synchronous optimal pulse width modulation system for new energy stations, including: 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 is 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; 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 working point; The sequence extension module is configured to solve the optimization problem by a gradient descent algorithm, obtain a converter cluster pulse width modulation lookup table in which the ideal working point is extended within a set modulation range, and distribute the table to each converter.

[0057] Embodiment 3 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.

[0058] Embodiment 4 The purpose of this embodiment is to provide a computer-readable storage medium, a computer-readable storage medium having a computer program stored thereon, and when the program is executed by a processor, the steps of the method of embodiment 1 are performed.

[0059] The steps involved in the apparatus of the above embodiments 3 and 4 correspond to the method embodiment 1, and the specific implementation method can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0060] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0062] Although the above describes the specific implementation mode 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 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 fundamental wave volt-second characteristics and time sequence to obtain an optimization problem; Solving the optimization problem by using an optimization solver to obtain an optimal switch pulse switching sequence of the converter cluster at an ideal working point; The optimization problem is solved by a gradient descent algorithm, and a pulse width modulation lookup table of a converter cluster extending an ideal working point within a set modulation range is obtained and distributed to each converter.

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

3. A generalized synchronous optimal pulse width modulation method for new energy stations as claimed in claim 1, characterized in that: The coordinated 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 total harmonic current, represents the total number of subunits, Indicates subunit Subharmonic current, represents the converter factor, Indicates subunit Subharmonic voltage.

4. A generalized synchronous optimal pulse width modulation method for new energy stations as claimed in claim 3, characterized in that: 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 factor, Indicates subunit Subharmonic voltage, Indicates the upper limit of harmonics taken into account, represents the first DC bus voltage, Indicates The DC bus voltage, represents the expected fundamental modulation of the first subunit, Indicates The expected fundamental modulation of each subunit, Indicates The subunit The switching time of the second switch, Indicates The subunit The switching moment.

5. A generalized synchronous optimal pulse width modulation method for new energy stations as claimed in claim 1, characterized in that: Preferably, the optimization solver adopts a QP solver.

6. A generalized synchronous optimal pulse width modulation method for new energy stations as claimed in claim 1, characterized in that: Solving the optimization problem by using the gradient descent algorithm is specifically as follows: by changing the expected fundamental modulation degree of the subunit, the optimization problem is extended and solved by using the gradient descent algorithm.

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

8. A generalized synchronous optimal pulse width modulation system for new energy stations, characterized in that: include: A data acquisition module, which is configured to: acquire steady-state operation information of a converter cluster in a new energy station; A problem construction module is 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; 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 working point; The sequence extension module is configured to solve the optimization problem by a gradient descent algorithm, obtain a converter cluster pulse width modulation lookup table in which the ideal working point is extended within a set modulation range, and distribute the table to each converter.

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

10. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps in the generalized synchronous optimal pulse width modulation method for new energy stations as described in any one of claims 1-7 are implemented.

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