System structure of double-fed fan

Abstract

The invention provides a system structure of a double-fed fan, and relates to the technical field of generators. The structure comprises a mechanical system, an electrical system and a power grid, the mechanical system comprises a wind turbine and a gearbox, and the electrical system comprises a doubly-fed induction motor, a back-to-back converter and a transformer; the wind turbine captures wind energy and transmits mechanical energy to the doubly-fed induction motor through the gearbox; the doubly-fed induction motor converts mechanical energy into electric energy, a rotor of the doubly-fed induction motor is an excitation winding in spatial three-phase symmetry, and a stator voltage orientation mode is adopted; the back-to-back converter is used for controlling the operation of the doubly-fed induction motor; the transformer is used for adjusting voltage, connecting the motor with a power grid and providing insulation and protection; the power grid is used for supplying power to the electrical system and receiving or transmitting the generated electric energy to the outside. The system structure provided by the invention has the characteristics of high efficiency, stability and reliability, and a solution for sustainable development and application is provided for the wind power generation technology.

Description

Technical Field

[0001] This application relates to the field of generator technology, and more particularly to a system structure for a doubly fed wind turbine. Background Technology

[0002] With the rapid development of renewable energy and the increasing demand for clean energy, wind power generation systems have received widespread attention as an important renewable energy technology, and their proportion in the overall power system is also increasing. As is well known, wind power is generated by wind driving blades to rotate, which in turn drives a generator to convert wind energy into mechanical energy and thus generate electricity. However, wind speed is not constant, which causes instability in the blade rotation speed, leading to fluctuations in the voltage and frequency of the electricity generated by the generator. Therefore, how to ensure that wind turbines generate stable electrical energy has been a problem that has plagued people for many years. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art.

[0004] The first aspect of this application proposes a system structure for a doubly-fed induction generator (DFIG) wind turbine, comprising: a mechanical system, an electrical system, and a power grid. The mechanical system includes a wind turbine and a gearbox; the electrical system includes a DFIG induction motor, a back-to-back converter, and a transformer. The wind turbine captures wind energy and transmits mechanical energy to the DFIG induction motor via the gearbox. The DFIG induction motor converts mechanical energy into electrical energy. The rotor of the DFIG induction motor has a spatially three-phase symmetrical excitation winding and adopts a stator voltage orientation method. The back-to-back converter is used to control the operation of the DFIG induction motor. The transformer is used to adjust the voltage, connect the motor to the power grid, and provide insulation and protection. The power grid provides power to the electrical system and also receives or transmits generated electrical energy to external systems.

[0005] According to one embodiment of this application, if the synchronous speed of the rotor of the doubly fed induction motor is n0, when the back-to-back converter injects a three-phase AC voltage with a frequency of f2 into the rotor winding, a three-phase AC current with a frequency of f2 will be generated in the rotor winding, thereby generating a rotating magnetic field with a relative speed of n2 = 60f2 / p to the rotor, where p is the number of pole pairs and the rotor speed is n. Therefore, the rotational speed of the rotor magnetic field relative to the stator is n1 = n ± n2. When the wind speed changes, the back-to-back converter is controlled by pulse width modulation (PWM) to inject voltage into the rotor so that n1 = n0, which makes the power generation frequency equal to the grid frequency. Therefore, the doubly fed wind turbine can achieve variable speed constant frequency operation.

[0006] According to one embodiment of this application, when the doubly fed wind turbine is running, if n... 0＝When n + n2, that is, when n < n0, the doubly-fed induction generator (DFIG) operates in a sub-synchronous mode. At this time, the direction of the rotor rotating magnetic field is the same as the rotor rotation direction.

[0007] According to an embodiment of the present application, when the DFIG is operating, if n0 = n is satisfied, the DFIG operates in a synchronous mode. At this time, the rotor is DC-excited.

[0008] According to an embodiment of the present application, when the DFIG is operating, if n0 = n - n2, that is, when n > n0, the DFIG operates in a super-synchronous mode. At this time, the direction of the rotor rotating magnetic field is opposite to the rotor rotation direction.

[0009] According to an embodiment of the present application, the transformer connects the doubly-fed induction motor to the power grid. The transformer receives the electric energy transmitted from the power grid and transfers it to the back-to-back converter and the doubly-fed induction motor. At the same time, the transformer receives the electric energy generated by the motor and feeds it back to the power grid.

[0010] The present application at least achieves the following beneficial effects: The system structure of the DFIG proposed in the present application realizes the functions of capturing wind energy, converting mechanical energy into electric energy, and outputting or inputting electric energy through the power grid connection. This system structure is efficient, stable, and reliable, providing a solution for sustainable development and application of wind power generation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and / or additional aspects and advantages of the present application will become apparent and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0012] Figure 1 is a schematic diagram of a system structure of a DFIG shown in the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and intended to explain the present application and should not be construed as a limitation to the present application.

[0014] Figure 1 is a schematic diagram of a system structure of a DFIG shown in the present application, as Figure 1 shown. The system structure of the DFIG includes a mechanical system, an electrical system, and a power grid, where:

[0015] The mechanical system includes a wind turbine and gearbox, while the electrical system includes a double-fed induction generator (DFIG), a back-to-back converter, and a transformer.

[0016] Wind turbines capture wind energy and transfer mechanical energy to a doubly-fed induction motor via a gearbox.

[0017] A doubly-fed induction motor receives mechanical energy from a gearbox and converts it into electrical energy. The rotor of this doubly-fed induction motor employs a spatially three-phase symmetrical excitation winding and a stator voltage orientation method to achieve efficient conversion.

[0018] Back-to-back converters are used to control and regulate the operation of doubly-fed induction motors. By using back-to-back converters, the motor speed and output power can be effectively controlled, ensuring the stability and reliability of the system.

[0019] The transformer connects the doubly-fed induction motor to the power grid. It receives electrical energy from the grid and transmits it to the back-to-back converter and the doubly-fed induction motor. Simultaneously, the transformer receives electrical energy generated by the motor and feeds it back to the grid to adjust the voltage. It also provides insulation and protection functions, ensuring the safety and reliability of the electrical system.

[0020] The power grid provides power to the electrical system to meet its operational needs. Simultaneously, the grid receives or transmits electrical energy generated by the wind turbines. Thus, through connection to the grid, the doubly-fed induction generator (DFIG) wind turbine system can effectively deliver the generated electricity to where it is needed.

[0021] If the synchronous speed of the rotor of a doubly-fed induction generator (DFIG) is n0, when a three-phase AC voltage with frequency f2 is injected into the rotor windings by a back-to-back converter, a three-phase AC current with frequency f2 will be generated in the rotor windings. This generates a rotating magnetic field with a relative speed of n2 = 60f2 / p, where p is the number of pole pairs and the rotor's own speed is n. Therefore, the rotational speed of the rotor magnetic field relative to the stator is n1 = n ± n2. When the wind speed changes, the voltage injected into the rotor by the back-to-back converter is controlled by pulse width modulation (PWM) to make n1 = n0, thus making the power generation frequency equal to the grid frequency. Therefore, the DFIG wind turbine can achieve variable speed constant frequency operation. Through this variable speed constant frequency operation mode, the DFIG wind turbine can flexibly adjust its speed according to changes in wind speed while maintaining a stable power generation frequency to adapt to different operating conditions and grid requirements. This control method can improve the system's efficiency and stability, and reduce system costs and operational risks, bringing more advantages to the application of wind power generation technology.

[0022] In this application, the operation of the doubly fed wind turbine can be divided into three operating modes based on the relationship between the rotor's rotational speed relative to the stator and the synchronous speed:

[0023] When the doubly-fed wind turbine is operating, if it satisfies n 0＝ n + n2, that is, when n < n0, the doubly-fed wind turbine is in the sub-synchronous operation mode. At this time, the direction of the rotor rotating magnetic field is the same as the rotor rotation direction.

[0024] When the doubly-fed wind turbine is operating, if it satisfies n0 = n, the doubly-fed wind turbine is in the synchronous operation mode. At this time, the rotor is DC-excited.

[0025] When the doubly-fed wind turbine is operating, if it satisfies n0 = n - n2, that is, when n > n0, the doubly-fed wind turbine is in the super-synchronous operation mode. At this time, the direction of the rotor rotating magnetic field is opposite to the rotor rotation direction.

[0026] In this application, by flexibly controlling the voltage injected into the rotor by the back-to-back converter and selecting an appropriate operation mode according to the relationship between the rotational speed and the synchronous speed, the doubly-fed wind turbine can achieve efficient and stable power generation under different working conditions. The adjustment of this operation mode enables the doubly-fed wind turbine to have greater adaptability and reliability.

[0027] The system structure of the doubly-fed wind turbine proposed in this application realizes the functions of capturing wind energy, converting mechanical energy into electrical energy, and outputting or inputting electrical energy through grid connection. This system structure has the characteristics of high efficiency, stability and reliability, and provides a solution for the sustainable development and application of wind power generation technology.

[0028] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0029] Although the embodiments of this application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting this application. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A system structure for a doubly-fed wind turbine, characterized in that, This includes mechanical systems, electrical systems, and power grids, among which: The mechanical system includes a wind turbine and a gearbox, and the electrical system includes a doubly fed induction motor, a back-to-back converter, and a transformer. The wind turbine captures wind energy and transmits mechanical energy to the doubly-fed induction motor through the gearbox; The doubly fed induction motor converts mechanical energy into electrical energy. The rotor of the doubly fed induction motor is a spatially three-phase symmetrical excitation winding and adopts a stator voltage orientation method. The back-to-back converter is used to control the operation of the doubly fed induction motor; The transformer is used to adjust voltage, connect the motor to the power grid, and provide insulation and protection; The power grid is used to provide power to the electrical system, and also to receive or transmit generated electrical energy to the outside.

2. The system structure of the doubly-fed wind turbine according to claim 1, characterized in that, If the synchronous speed of the rotor of the doubly fed induction motor is n0, when the back-to-back converter injects a three-phase AC voltage with a frequency of f2 into the rotor winding, a three-phase AC current with a frequency of f2 will be generated in the rotor winding, thereby generating a rotating magnetic field with a relative speed of n2 = 60f2 / p, where p is the number of pole pairs and the rotor speed is n. Therefore, the rotational speed of the rotor magnetic field relative to the stator is n1 = n ± n2. When the wind speed changes, the back-to-back converter injects voltage into the rotor through pulse width modulation (PWM) control, so that n1 = n0, which makes the power generation frequency equal to the grid frequency. Therefore, the doubly fed wind turbine can achieve variable speed constant frequency operation.

3. The system structure of the doubly-fed wind turbine according to claim 2, characterized in that, When the doubly-fed wind turbine is operating, if it satisfies n 0＝ < n + n2, that is, when n < n0, the doubly-fed wind turbine is in the sub-synchronous operation mode. At this time, the direction of the rotor rotating magnetic field is the same as the rotor rotation direction.

4. The system structure of the doubly fed wind turbine according to claim 3, characterized in that, When the doubly fed fan is running, if n0 = n, the doubly fed fan is in synchronous operation mode, and the rotor is DC excitation.

5. The system structure of the doubly fed wind turbine according to claim 4, characterized in that, When the doubly fed fan is running, if n0 = n - n2, that is, n > n0, the doubly fed fan is in supersynchronous operation mode. At this time, the direction of the rotor rotating magnetic field is opposite to the rotor rotation direction.

6. The system structure of the doubly fed fan according to claim 5, characterized in that, The transformer connects the doubly-fed induction motor to the power grid. The transformer receives electrical energy transmitted from the power grid and transmits it to the back-to-back converter and the doubly-fed induction motor. At the same time, the transformer receives electrical energy generated by the motor and feeds it back to the power grid.

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