Inverter and method and device for avoiding broadband oscillation in parallel grid connection

Abstract

The present invention discloses an inverter and a method and device for avoiding broadband oscillation in parallel grid connection, which relates to the field of inverters and is used to quickly and efficiently solve or reduce the broadband oscillation phenomenon when multiple inverters are connected in parallel and grid connection in large-scale power generation sites. The present invention configures each inverter to randomly select a PWM operating frequency point within the first target frequency band when it is powered on; and randomly selects a feedback control frequency within the second target frequency band, or calculates a feedback control frequency through the PWM operating frequency point. The PWM operating frequency point controls the switching frequency of the PWM wave, and the feedback control bandwidth controls the duty cycle of the PWM wave. The present invention is simple and easy to implement, has high operating efficiency, and solves the problem of eliminating broadband oscillations in large-scale inverter parallel grid connection scenarios with low cost and high efficiency.

Description

Technical Field

[0001] The present invention relates to the field of inverters, in particular to an inverter, an inverter configuration method and device, and a method for avoiding broadband oscillation in parallel and grid-connected multi-inverters. Background Art

[0002] In large power generation sites such as centralized photovoltaic power stations, a large number of inverters are connected in parallel and run in grid connection. When a large number of inverters are connected in parallel and run in grid connection, broadband oscillation may occur due to the coupling between inverters and between inverters and grid or network. If this oscillation is serious, it will affect the safe operation of the grid. Therefore, in the scenario of multiple inverters connected in parallel and run in grid connection, it is necessary to consider the suppression of broadband oscillation.

[0003] A Chinese patent document with publication number CN114825441A proposes a control method for adaptive virtual impedance resonance suppression of a parallel inverter grid-connected system. According to the instructions of the upper system for the grid-connected inverter to output active and reactive power, the corresponding current command signal is obtained according to power calculation and coordinate transformation, and then added to the high-order harmonic components of the grid-connected current of the equivalent series virtual impedance on the inverter side as the input signal of the current controller to suppress the resonance caused by the coupling of the inverter output impedance and the grid line impedance.

[0004] Existing technologies similar to the above methods almost all calculate the operating parameters of the inverter by using grid parameters, and have good anti-oscillation effects. However, these methods require a series of collection and calculations for each inverter, have poor operating efficiency, cumbersome control strategies, and high control power consumption. They are only applicable to small power stations. For places with a large number of inverters, it is difficult to meet the timeliness requirements of inverter control. Summary of the invention

[0005] The object of the present invention is to provide an inverter and a method and device for avoiding broadband oscillation during parallel grid connection in order to quickly and efficiently solve or reduce the broadband oscillation phenomenon when multiple inverters are connected in parallel and grid-connected in large power generation sites in order to ...

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for avoiding wide-band oscillation in parallel grid-connected multi-inverters, wherein each inverter controls the switching frequency of a PWM wave when converting direct current into alternating current based on a corresponding PWM operating frequency point, and controls the duty cycle of the PWM wave when converting direct current into alternating current based on a corresponding feedback control frequency; the method comprises:

[0008] When each inverter is powered on, a PWM operating frequency point is randomly selected within the first target frequency band, and a feedback control frequency is randomly determined.

[0009] Furthermore, the feedback control frequency of each inverter is randomly selected within the second target frequency band.

[0010] Furthermore, the feedback control frequency of each inverter is calculated through its PWM operating frequency point.

[0011] Furthermore, the feedback control frequency of each inverter is calculated through a fixed proportional relationship with its PWM operating frequency.

[0012] Furthermore, the feedback control frequency of each inverter is calculated through a fixed difference relationship with its PWM operating frequency point.

[0013] The present invention also provides an inverter, which controls the switching frequency of the PWM wave when converting DC power into AC power based on the PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power into AC power based on the feedback control frequency; the inverter is configured as follows:

[0014] During power-on operation, a PWM operating frequency point is randomly selected within the first target frequency band; and a feedback control frequency is randomly determined.

[0015] The present invention also provides an inverter configuration method, wherein the inverter controls the switching frequency of the PWM wave when converting DC power to AC power based on the PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power to AC power based on the feedback control frequency; the method comprises:

[0016] configuring a first target frequency band range for the inverter; and,

[0017] configuring the inverter to randomly select a PWM operating frequency point within the first target frequency band when it is powered on; and,

[0018] Configure the inverter to randomly determine a feedback control frequency.

[0019] The present invention also provides an inverter configuration device, which includes a processor and a storage medium, wherein the storage medium stores a computer program, and the processor runs the computer program in the storage medium to execute the above-mentioned inverter configuration method.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] The method of the present invention is extremely simple and easy to implement. For large-scale inverter parallel grid-connected scenarios such as photovoltaic power stations, the uniform distribution characteristics of random sampling are utilized to allow each inverter to randomly select a PWM operating frequency point within the first target frequency band, and randomly confirm a feedback control frequency. The entire process does not require tedious sampling and calculation. The inverters are independent of each other and can work in parallel. In a low-cost manner, the broadband oscillation phenomenon in the parallel grid-connected large-scale inverters can be efficiently and significantly reduced or eliminated, which can reduce the preventive measures of the power station against broadband oscillation and reduce the investment in the power station. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0023] Figure 1 The flowchart of an embodiment of inverter operation in a scenario where multiple inverters are connected in parallel to the grid is provided.

[0024] Figure 2 It is a flow chart of another embodiment of inverter operation in a multi-inverter parallel grid-connected scenario. DETAILED DESCRIPTION

[0025] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0026] Any feature disclosed in this specification (including any additional claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0027] In order to solve the broadband oscillation problem that may be caused by the parallel grid-connected operation of multiple inverters in large-scale power stations, the existing technologies mostly sample the networking operation parameters for each inverter and then calculate a PWM operating frequency. Each inverter is calculated sequentially to avoid repetition. This method can almost completely eliminate the broadband oscillation phenomenon, but it is relatively cumbersome to operate. It is necessary to execute the parameter collection and PWM operating frequency calculation process for each inverter, and in order to avoid repetition, the working parameters of each inverter need to be calculated sequentially, which has a large amount of calculation, high computing power cost and time cost. For places with a large number of inverters such as large photovoltaic power stations, it is difficult to meet the actual use needs and the practicality is poor. For example, in a 100MW photovoltaic power station, there will be about 510 photovoltaic inverters connected in parallel to the grid. If the working parameters of each inverter are sampled and calculated one by one by the existing technology, the time cost, computing power cost and power consumption are all relatively large, which is difficult to meet the timeliness requirements for the grid-connected power generation of photovoltaic power stations.

[0028] To this end, an embodiment of the present application proposes a method for avoiding broadband oscillations in parallel grid-connected multi-inverters, aiming to efficiently reduce or eliminate possible broadband oscillations in parallel grid-connected scenarios of large-scale inverters (such as more than 10 inverters) in a low-cost manner.

[0029] In some embodiments, the method comprises:

[0030] When each inverter is powered on, a PWM operating frequency point is randomly selected within the first target frequency band, and a feedback control frequency is randomly determined.

[0031] Each inverter controls the switching frequency of the PWM wave when converting DC power into AC power based on the corresponding PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power into AC power based on the corresponding feedback control frequency.

[0032] In this way, the parallel inverters can select the PWM operating frequency and feedback control frequency independently and in parallel, with high operating efficiency. Each inverter only needs to be configured with the first target frequency band range, and can immediately select the PWM operating frequency and determine the feedback control frequency during operation, without the need for complicated data collection and calculation processes, and the system has low energy consumption and low hardware cost. With the help of the uniform distribution characteristics of random sampling, even if large-scale inverters are connected in parallel, the PWM operating frequency and feedback control frequency selected by each inverter tend to be evenly distributed, with less repetition, and even if repetition occurs between a very small number of inverters, the broadband oscillation caused by large-scale inverters is acceptable.

[0033] The randomly determined feedback control frequency in the above embodiment can be obtained by configuring the feedback control frequency of each inverter to be randomly selected within the second target frequency band, in some embodiments.

[0034] For example, the switching frequency of the PWM wave is usually between a few kilohertz and 100 kilohertz, and the feedback control frequency is also between a few kilohertz and 100 kilohertz. Generally, the feedback control frequency is less than or equal to the switching frequency of the PWM wave. As a feasible implementation method, Figure 1 As shown, a first target frequency range and a second target frequency range are configured for each inverter respectively, a PWM operating frequency point is randomly selected within the first target frequency range, and a feedback control frequency is randomly selected within the second target frequency range.

[0035] In other embodiments, Figure 2As shown in FIG. 1 , the feedback control frequency of each inverter is calculated by its PWM operating frequency. Since the PWM operating frequency of each inverter is already random, and each inverter calculates the corresponding feedback control frequency based on its PWM operating frequency, the result is also random as a whole and also satisfies the uniform distribution.

[0036] As a feasible implementation method, the feedback control frequency of each inverter is calculated by a fixed ratio relationship with its PWM operating frequency. That is, when configuring each inverter, a fixed ratio is configured for each inverter, and after the inverter randomly selects a PWM operating frequency, its feedback control frequency is obtained by multiplying the PWM operating frequency by the fixed ratio.

[0037] As another feasible implementation, the feedback control frequency of each inverter is calculated by a fixed difference relationship with its PWM operating frequency. That is, when configuring each inverter, a fixed difference is configured for each inverter, and after the inverter randomly selects a PWM operating frequency, its feedback control frequency is obtained by subtracting the PWM operating frequency from the fixed difference.

[0038] As a possible implementation, the first target frequency range configured by the inverter, and in some embodiments, the second target frequency range also configured, are specifically configured with some frequency points. These configured frequency points are configured in the inverter in the form of a frequency table for selection.

[0039] As a more complex but better way to eliminate broadband oscillations, in some embodiments, the PWM operating frequencies randomly selected by each inverter are different. This is based on the premise that the number of selectable frequencies in the configured first target frequency band is equal to or greater than the number of inverters in parallel. In addition, each inverter needs to first sample the PWM operating frequencies of other inverters in the network, and then select different PWM operating frequencies. Although the sampling process is increased, there is still no need for a complicated process of calculating the PWM operating frequency, and compared with the prior art, it still does not require high computing power and time costs. Correspondingly, in some embodiments, the feedback control frequencies of each inverter are also different.

[0040] The embodiment of the present application also proposes an inverter, which controls the switching frequency of the PWM wave when converting DC power to AC power based on the PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power to AC power based on the feedback control frequency. The inverter is configured as:

[0041] During power-on operation, a PWM operating frequency point is randomly selected within the first target frequency band; and a feedback control frequency is randomly determined.

[0042] In some embodiments, see Figure 1 , the inverter is configured to randomly select a feedback control frequency within a second target frequency band.

[0043] In other embodiments, see Figure 2 , the inverter is configured to calculate the feedback control frequency through its PWM operating frequency point.

[0044] As a possible implementation, the inverter is configured to calculate the feedback control frequency through a fixed proportional relationship with its PWM operating frequency.

[0045] As another possible implementation, the inverter is configured to calculate the feedback control frequency through a fixed difference relationship with its PWM operating frequency point.

[0046] According to the inventive concept of the present application, an embodiment of the present application further proposes an inverter configuration method, the method comprising:

[0047] configuring a first target frequency band range for the inverter; and,

[0048] configuring the inverter to randomly select a PWM operating frequency point within the first target frequency band when it is powered on; and,

[0049] Configure the inverter to randomly determine a feedback control frequency.

[0050] The inverter controls the switching frequency of the PWM wave when converting DC power into AC power based on the PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power into AC power based on the feedback control frequency.

[0051] In some embodiments, see Figure 1 , the feedback control frequency of the configured inverter is randomly selected within the second target frequency band.

[0052] In other embodiments, see Figure 2 , the feedback control frequency of the configured inverter is calculated through its PWM operating frequency.

[0053] As a feasible implementation method, the feedback control frequency of the inverter is calculated by a fixed proportional relationship with its PWM operating frequency.

[0054] As another feasible implementation manner, the feedback control frequency of the inverter is calculated by a fixed difference relationship with its PWM operating frequency point.

[0055] With reference to the above-mentioned embodiment of the method for avoiding broadband oscillation in parallel grid connection of multiple inverters, when configuring the inverter, it is also possible to consider selecting a PWM operating frequency different from other parallel inverters when configuring the inverter to select a PWM operating frequency. In addition, it is also possible to consider determining a feedback control frequency different from other parallel inverters when configuring the inverter to determine a feedback control frequency.

[0056] An embodiment of the present application further proposes an inverter configuration device, which includes a processor and a storage medium, wherein the storage medium stores a computer program, and the processor runs the computer program in the storage medium to execute the inverter configuration method as described in the above embodiment.

[0057] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for avoiding broadband oscillation in parallel grid connection of multiple inverters, wherein each inverter controls the switching frequency of the PWM wave when converting DC power into AC power based on the corresponding PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power into AC power based on the corresponding feedback control frequency; characterized in that: Methods include: When each inverter is powered on, a PWM operating frequency point is randomly selected within the first target frequency band, and a feedback control frequency is randomly determined.

2. The method for avoiding broadband oscillation in parallel connection of multiple inverters to a grid as claimed in claim 1, characterized in that: The feedback control frequency of each inverter is randomly selected within the second target frequency band.

3. The method for avoiding broadband oscillation in parallel connection of multiple inverters to a grid as claimed in claim 1, characterized in that: The feedback control frequency of each inverter is calculated through its PWM operating frequency point.

4. The method for avoiding broadband oscillation in parallel connection of multiple inverters to a grid as claimed in claim 3, characterized in that: The feedback control frequency of each inverter is calculated through a fixed proportional relationship with its PWM operating frequency.

5. The method for avoiding broadband oscillation in parallel connection of multiple inverters to a grid as claimed in claim 3, characterized in that: The feedback control frequency of each inverter is calculated through a fixed difference relationship with its PWM operating frequency point.

6. An inverter, which controls the switching frequency of the PWM wave when converting DC power into AC power based on the PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power into AC power based on the feedback control frequency; characterized in that: The inverter is configured as: During power-on operation, a PWM operating frequency point is randomly selected within the first target frequency band; and a feedback control frequency is randomly determined.

7. An inverter configuration method, wherein the inverter controls the switching frequency of the PWM wave when converting DC power into AC power based on the PWM operating frequency point, and controls the duty cycle of the PWM wave when converting DC power into AC power based on the feedback control frequency; characterized in that: method include: configuring a first target frequency band range for the inverter; and, configuring the inverter to randomly select a PWM operating frequency point within the first target frequency band when it is powered on; and, Configure the inverter to randomly determine a feedback control frequency.

8. An inverter configuration device, characterized in that: The invention comprises a processor and a storage medium, wherein the storage medium stores a computer program, and the processor runs the computer program in the storage medium to execute the inverter configuration method according to claim 7.

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