Method for suppressing common-mode current in a multi-converter wind power generator and device therefor

Abstract

The embodiment of the present application provides a method and device for suppressing common-mode current of a multi-converter wind power generator. The wind power generator has multiple sets of windings, and each converter is connected to a corresponding set of windings. The method comprises: sampling to obtain multiple common-mode current values of multiple converters in a predetermined time interval; determining a time interval of PWM operation phase shift based on the PWM operation period of the converter, the predetermined time interval, the number of converters, and the multiple common-mode current values of the multiple converters; determining a corresponding PWM operation phase shift time for each converter to suppress common-mode current based on the time interval of PWM operation phase shift; and performing phase shift control on the PWM signal of each converter based on the corresponding PWM operation phase shift time of each converter. Thus, the common-mode current generated by the multiple converters can be effectively suppressed.

Description

Technical Field

[0001] This invention relates to the field of wind power generation technology, and in particular to a method and apparatus for suppressing common-mode current in a multi-converter wind turbine. Background Technology

[0002] With the gradual depletion of energy sources such as coal and oil, humanity is increasingly emphasizing the utilization of renewable energy. Wind energy, as a clean and renewable energy source, is receiving growing attention worldwide. Along with the continuous development of wind power technology, the application of wind turbine generators in power systems is increasing. Wind turbine generators are large-scale devices that convert wind energy into electrical energy, typically installed in areas rich in wind resources.

[0003] The converter is one of the core components of a wind turbine generator set. In recent years, with the increase in the power of wind turbine generator sets, especially offshore wind turbine generator sets, more and more high-power generators are adopting a design scheme with multiple windings and multiple converters. However, converters generate common-mode current during operation. A large common-mode current will increase the shaft current of the wind turbine generator, reduce the reliability of the motor bearings, and also worsen the electromagnetic compatibility performance of the entire system. In some cases, it may even cause arcing at poorly connected points, thus affecting the operational safety of the entire wind turbine generator set. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for suppressing common-mode current in multi-converter wind turbines, which can effectively suppress the common-mode current generated by multiple converters.

[0005] One aspect of this invention provides a method for suppressing common-mode current in a multi-converter wind turbine. The wind turbine has multiple sets of windings, with each converter connected to a corresponding set of windings. The method includes: sampling and obtaining multiple common-mode current values ​​of the multiple converters at a predetermined time interval; determining a PWM phase-shifting time interval based on the PWM operating cycle of the converters, the predetermined time interval, the number of converters, and the collected multiple common-mode current values ​​of the multiple converters; determining a corresponding PWM phase-shifting time for each converter to suppress common-mode current based on the PWM phase-shifting time interval; and performing phase-shifting control on the PWM signal of each converter based on the corresponding PWM phase-shifting time of each converter.

[0006] Another aspect of this invention provides a device for suppressing common-mode current in a multi-converter wind turbine. The device includes a wind turbine and multiple converters. The wind turbine has multiple sets of windings. Each converter is connected to a corresponding set of windings. Each converter includes a controller, and each converter controller collects multiple common-mode current values ​​at predetermined time intervals. One converter controller acts as a main controller, and the controllers of the other converters act as auxiliary controllers. The other auxiliary controllers transmit the collected common-mode current values ​​to the main controller. The main controller calculates the PWM phase-shift time interval based on the obtained common-mode current values ​​and transmits the PWM phase-shift time interval to the other auxiliary controllers. The main controller and the other auxiliary controllers set the PWM phase-shift time of their respective converters based on the PWM phase-shift time interval.

[0007] The method and apparatus for suppressing common-mode current in multi-converter wind turbines according to one or more embodiments of the present invention reduce the overall common-mode current of the converter by changing the control method, reduce the impact of shaft current on bearings, and improve the overall electromagnetic compatibility environment of the wind turbine generator set. Attached Figure Description

[0008] Figure 1 A flowchart illustrating a method for suppressing common-mode current in a multi-converter wind turbine according to an embodiment of the present invention;

[0009] Figure 2 The following are the specific steps for determining the PWM phase shift time interval based on the PWM operating cycle of the converter, a predetermined time interval, the number of converters, and multiple common-mode current values ​​collected from multiple converters, according to one embodiment of the present invention.

[0010] Figure 3 This is a schematic block diagram of a device for suppressing common-mode current in a multi-converter wind turbine according to an embodiment of the present invention. Detailed Implementation

[0011] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses consistent with some aspects of the invention as detailed in the appended claims.

[0012] The terminology used in this invention embodiment is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless otherwise defined, the technical or scientific terms used in this invention embodiment should be understood in their ordinary sense by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, "a" or "one," and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. "A plurality" or "several" indicates two or more. Unless otherwise stated, "front," "rear," "lower," and / or "upper," and similar terms are for ease of description only and are not limited to a location or spatial orientation. The terms "comprising" or "including," and similar terms mean that the element or object preceding "comprising" covers the element or object listed following "comprising" or "including" and its equivalents, and do not exclude other elements or objects. The terms "connected," "linked," and similar terms are not limited to physical or mechanical connections and can include electrical connections, whether direct or indirect. The singular forms “a,” “the,” and “the” used in this specification and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0013] This invention provides a method for suppressing common-mode current in a multi-converter wind turbine. The wind turbine has multiple sets of windings, with each converter connected to a corresponding set of windings. In some embodiments, each converter is designed and has the same capacity, and the windings connected to each converter are symmetrical.

[0014] Figure 1 A flowchart illustrating a method for suppressing common-mode current in a multi-converter wind turbine according to an embodiment of the present invention is provided. Figure 1 As shown, a method for suppressing common-mode current in a multi-converter wind turbine according to an embodiment of the present invention may include steps S1 to S4.

[0015] In step S1, multiple common-mode current values ​​of multiple converters are sampled and obtained over a predetermined time interval T.

[0016] Multiple converters, for example, include N converters, each labeled 1, 2, ..., N. The PWM operating cycle signals of the N converters are synchronized. S common-mode current values ​​are obtained at predetermined time intervals T during operation.

[0017] In step S2, the PWM phase shift time interval Td can be determined based on the PWM operating period P of the converter, the predetermined time interval T, the number of converters N, and the multiple common-mode current values ​​of the multiple converters collected in step S1.

[0018] Figure 2 This invention discloses the specific steps of determining the PWM phase shift time interval Td based on the PWM operating period P of the converter, a predetermined time interval T, the number of converters N, and multiple common-mode current values ​​of multiple converters collected in step S1. For example... Figure 2 As shown, in some embodiments, step S2 may further include steps S21 to S23.

[0019] Step S21: The multiple common-mode current values ​​of each converter collected are labeled in chronological order as follows:

[0020] X (i-1)·S+1 ,X (i-1)·S+2 ,X (i-1)·S+3 ,…,X (i-1)·S+S ,

[0021] Where i represents the current converter number.

[0022] Step S22: Calculate the average value G of the sum of squares of the common-mode currents of multiple converters, where the integer d ranges from 1 to P÷T÷N. d .

[0023] The average value G of the sum of squares of the common-mode currents of multiple converters (interleaved) d The calculation formula is shown in the following formula:

[0024]

[0025] Where P is the PWM operating cycle of the converter, T is the predetermined time interval, N is the number of converters, S is the number of common-mode current values ​​collected for each converter, and X with different subscripts represents the common-mode current value of the corresponding converter at the corresponding sampling time point.

[0026] Step S23: Based on the average value G of the sum of squares of the interleaved common-mode currents of the multiple converters calculated in step S22. d To determine the time interval Td for PWM phase shifting.

[0027] In some embodiments, step S23 may further include steps S231 and S232.

[0028] In step S231, the value dMin corresponding to the minimum value of the average value Gd of the sum of squares of the interleaved common-mode currents of the multiple converters calculated in step S22 is found.

[0029] In step S232, the PWM operating phase shift time interval Td is calculated based on the value dMin and the predetermined time interval T. In one embodiment, the PWM operating phase shift time interval Td is equal to the product of the value dMin and the predetermined time interval T, as shown in the following formula:

[0030] Td=dMin·T

[0031] Return to reference Figure 1 As shown, in step S3, the corresponding PWM phase shift time for suppressing common-mode current of each converter can be determined based on the PWM phase shift time interval Td determined in step S2.

[0032] In some embodiments, the PWM phase shift times of the N converters can be set to 0 and 1·T, respectively. d 2·T d ..., (N-1)·T d .

[0033] In step S4, the PWM signal of each converter can be phase-shifted based on the corresponding PWM operating phase-shift time of each converter determined in step S3.

[0034] The method for suppressing common-mode current in multi-converter wind turbines according to embodiments of the present invention reduces the overall common-mode current of the converter by changing the control method, reduces the impact of shaft current on bearings, and improves the overall electromagnetic compatibility environment of the wind turbine generator set.

[0035] Figure 3 A schematic block diagram of a device 100 for suppressing common-mode current in a multi-converter wind turbine according to an embodiment of the present invention is shown. Figure 3 As shown, an embodiment of the present invention provides a device 100 for suppressing common-mode current in a multi-converter wind turbine, comprising a wind turbine 110 and multiple converters 120. The wind turbine 110 has multiple sets of windings 111. Each of the multiple converters 120 is connected to a corresponding set of windings 111.

[0036] Each converter 120 includes a controller 121, and the controller 121 of each converter 120 collects multiple common-mode current values ​​at predetermined time intervals T. One converter 120 serves as the main converter 120, and its controller 121 serves as the main controller 121. The other converters 120 serve as auxiliary converters 120, and their controllers 121 serve as auxiliary controllers 121. The other auxiliary controllers 121 can transmit the collected common-mode current values ​​of their respective converters 120 to the main controller 121.

[0037] The main controller 121 can calculate the PWM phase shift time interval Td based on the common-mode current value of the converter 120 acquired by itself and obtained from other auxiliary controllers 121, and can transmit the calculated PWM phase shift time interval Td to other auxiliary controllers 121. The main controller 121 and other auxiliary controllers 121 can set the PWM phase shift time of their respective converters 120 based on the PWM phase shift time interval Td.

[0038] In one embodiment, the controller 121 of each converter 120 may include an FPGA (Field-Programmable Gate Array) and a DSP (Digital Signal Processor). The FPGA of each converter 120 can acquire the common-mode current value of its respective converter 120 and perform corresponding carrier phase-shift control. The DSP in the main converter 120 can calculate the PWM phase-shift time interval Td based on the common-mode current values ​​of the converter 120 it acquires and those obtained from other auxiliary controllers 121.

[0039] In some embodiments, the main controller 121 may be used to perform steps S21 to S23 as described above.

[0040] The device 100 for suppressing common-mode current in a multi-converter wind turbine according to the present invention has similar beneficial technical effects to the method for suppressing common-mode current in a multi-converter wind turbine described above, and therefore will not be repeated here.

[0041] To make the technical means, creative features, objectives and effects of the method and apparatus for suppressing common-mode current in multi-converter wind turbines of the present invention easy to understand, the present invention will be further illustrated below with a specific example.

[0042] In this example, three converters are used, each connected to one of the three windings of a wind turbine. Each winding of the wind turbine is three-phase. Each converter uses the same design, and they are controlled by carrier phase shifting via an FPGA. Simultaneously, the FPGA samples the three-phase current of the wind turbine, and the common-mode current value is obtained from the sum of the three-phase currents. The PWM duty cycle of each converter is 500μs. During initial operation, the PWM duty cycle signals of the three converters are synchronized. After all converters reach steady state, the FPGA samples 5000 common-mode current values ​​for each converter, with a time interval of 1.5μs between each common-mode current value. These common-mode current values ​​are labeled X1, X2, X3, ..., X... according to their time sequence and converter number. 5000 ;X 5001 ,X 5002 ,X 5003 ,…,X 10000 ;X 10001 ,X 10002 ,X 10003 ,…,X 15000 Calculate G within the range of integer d from 1 to 111. d value, In the calculation of G d The results showed that when d=20, G... d The value is the minimum, therefore, dMin = 20. Calculate T. d =20 × 1.5 μs = 30 μs. The above sampling data was obtained by sampling from three converters respectively, and the data was transmitted to one of the converters acting as the main converter, which then calculated T. d =30μs, and transmits it to the other two converters via communication. The three converters set their PWM operating phase shift times to 0μs, 30μs, and 60μs respectively based on the calculated values. The optimal phase shift time for suppressing the common-mode current of the three converters is found through the above method, and the PWM signal of each converter is phase-shifted accordingly. The common-mode current generated by each converter is superimposed and eliminated.

[0043] The method for suppressing common-mode current in multi-converter wind turbines using embodiments of the present invention can reduce the common-mode current of the converter by 30% compared to methods not using embodiments of the present invention.

[0044] The method and apparatus for suppressing common-mode current in a multi-converter wind turbine provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the method and apparatus for suppressing common-mode current in a multi-converter wind turbine according to the embodiments of the present invention. The descriptions of the above embodiments are only for helping to understand the core idea of ​​the present invention and are not intended to limit the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the spirit and principle of the present invention, and these improvements and modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for suppressing common-mode current in a multi-converter wind turbine, wherein the wind turbine has multiple sets of windings, and each converter is connected to a corresponding set of windings, characterized in that: It includes: Multiple common-mode current values ​​of the multiple converters are obtained by sampling at predetermined time intervals; The PWM phase shift time interval is determined based on the PWM duty cycle of the converter, the predetermined time interval, the number of converters, and multiple common-mode current values ​​collected from multiple converters, including: Step a: Identify the multiple common-mode current values ​​of each converter in chronological order as follows: X (i-1)•S+1 ,X (i-1)•S +2 ,X (i-1)•S +3 ,… , X (i-1)•S +S , where i represents the current converter number; Step b: Calculate the average value G of the sum of squares of the common-mode currents of multiple converters, within the range of integer d from 1 to P÷T÷N. d , Wherein, P is the PWM operating cycle of the converter, T is the predetermined time interval, N is the number of converters, S is the number of common-mode current values ​​collected for each converter, and X with different subscripts represents the common-mode current value of the corresponding converter at the corresponding sampling time point; Step c: Based on the average value G of the sum of squares of the interleaved common-mode currents of the multiple converters calculated in step b. d To determine the time interval for the PWM phase shift; The corresponding PWM phase shift time for suppressing common-mode current for each converter is determined based on the time interval of the PWM phase shift; and The PWM signal of each converter is phase-shifted based on the corresponding PWM operating phase-shift time of each converter.

2. The method as described in claim 1, characterized in that: Each of the converters is designed and has the same capacity, and the windings connected to each converter are symmetrical.

3. The method as described in claim 1, characterized in that: The PWM operating cycle signals of multiple converters are synchronized.

4. The method as described in claim 1, characterized in that: Step c includes: The average value G of the sum of squares of the interleaved common-mode currents of the multiple converters calculated in step b. d Find the average value G of the sum of squares of the interleaved common-mode currents of multiple converters. d The value corresponding to the minimum is dMin; and The time interval Td for the PWM phase shift is calculated based on the value dMin and the predetermined time interval.

5. The method as described in claim 4, characterized in that: The time interval Td for the PWM phase shift is equal to the product of the value dMin and the predetermined time interval T.

6. The method as described in claim 5, characterized in that: The determination of the corresponding PWM phase shift time for suppressing common-mode current for each converter based on the PWM phase shift time interval includes: The PWM phase shift times of the N converters are set to 0 and 1•T, respectively. d 2•T d ..., (N-1)•T d .

7. A device for suppressing common-mode current in a multi-converter wind turbine generator, characterized in that: It includes: Wind turbines have multiple sets of windings; and Multiple converters are provided, each connected to a corresponding set of windings. Each converter includes a controller, and the controller of each converter collects multiple common-mode current values ​​at predetermined time intervals. One of the converter controllers acts as the main controller, and the controllers of the other converters act as auxiliary controllers. The auxiliary controllers transmit the collected common-mode current values ​​to the main controller. The main controller calculates the PWM phase-shift time interval based on the obtained common-mode current values ​​and transmits the PWM phase-shift time interval to the other auxiliary controllers. The main controller and the other auxiliary controllers set the PWM phase-shift time of their respective converters based on the PWM phase-shift time interval. The main controller is used to execute: Step a: Identify the multiple common-mode current values ​​of each converter in chronological order as follows: X (i-1)•S+1 ,X (i-1)•S +2 ,X (i-1)•S +3 ,… , X (i-1)•S +S , where i represents the current converter number; Step b: Calculate the average value G of the sum of squares of the common-mode currents of multiple converters, within the range of integer d from 1 to P÷T÷N. d , Wherein, P is the PWM operating cycle of the converter, T is the predetermined time interval, N is the number of converters, S is the number of common-mode current values ​​collected for each converter, and X with different subscripts represents the common-mode current value of the corresponding converter at the corresponding sampling time point; Step c: Based on the average value G of the sum of squares of the interleaved common-mode currents of the multiple converters calculated in step b. d To determine the time interval for the PWM phase shift.

8. The apparatus as claimed in claim 7, characterized in that: The main controller is used for: In step b, find the value dMin corresponding to the minimum value of the average sum of squares of the interleaved common-mode currents of the multiple converters, Gd; and The time interval for PWM phase shift is calculated based on the product of the value dMin and the predetermined time interval.

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