Direct-current grid-connected intermediate-frequency doubly-fed wind power generation system

Abstract

The invention relates to the technical field of electric power, and particularly discloses a direct-current grid-connected intermediate-frequency doubly-fed wind power generation system which is characterized in that the intermediate-frequency doubly-fed wind power generation system works in an interval of 100 Hz to 300 Hz; when the doubly-fed wind generator is started, the bidirectional direct current-direct current converter provides direct current bus voltage for the rotor side converter, stator voltage of the doubly-fed wind generator is established by controlling the rotor side converter, and self-starting of the system is completed. After grid connection is started, in a subsynchronous operation state, a direct current power grid provides energy for a rotor side converter through a bidirectional direct current-direct current converter; in a super-synchronous operation state, rotor side energy of the doubly-fed wind generator flows to a direct current power grid through the bidirectional direct current-direct current converter; the voltage sensor is used for detecting stator-side voltage, rotor-side voltage and direct-current power grid voltage of the doubly-fed wind generator.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a DC grid-connected medium-frequency double-fed wind power generation system. Background Art

[0002] With global attention to environmental issues continuing to rise and the need for energy transformation becoming increasingly urgent, the development of renewable energy has become a key path for countries to achieve sustainable development. In this process, wind power generation plays an increasingly important role.

[0003] While conventional wind power grid-connected technology has made some progress, it still presents numerous challenges in complex energy application scenarios. Traditional AC grid-connected wind power systems, due to the inherent intermittent and fluctuating nature of wind power, are prone to power quality issues such as voltage fluctuations and harmonic pollution when integrating large-scale wind power into the AC grid. This poses numerous challenges to the stable and reliable operation of the grid. Furthermore, the multi-stage converters required to achieve AC grid connection are not only expensive but also generate significant energy losses during the multiple AC conversion processes, making it difficult to fully realize the economic benefits of wind power. Summary of the Invention

[0004] To address these issues, the present invention provides a DC grid-connected medium-frequency doubly-fed wind turbine generation system. In DC grid-connected mode, the system can adjust the stator frequency and increase the stator operating frequency to the medium frequency range. By optimizing the high-frequency flux design and achieving a lightweight structure, this system effectively addresses the bulky and costly issues of traditional power-frequency motors, thereby improving system efficiency, reducing material consumption, and enhancing the ease of transportation, installation, and maintenance.

[0005] The present invention provides a DC grid-connected medium-frequency doubly-fed wind power generation system, comprising: a doubly-fed wind turbine generator, a rotor-side converter, a bidirectional DC-DC converter, an AC transformer, a rectifier unit, a control unit, a current sensor, a voltage sensor, and a speed sensor; the medium-frequency doubly-fed wind power generation system operates in the range of 100 Hz to 300 Hz;

[0006] The stator side of the doubly-fed wind turbine generator is connected to the input end of the AC transformer, the output end of the AC transformer is connected to the rectifier unit, and the rotor side of the doubly-fed wind turbine generator is connected to the bidirectional DC-DC converter via the rotor-side converter; the control unit is connected to the current sensor, the voltage sensor, the speed sensor and the rotor-side converter;

[0007] When the doubly-fed wind turbine generator is started, the bidirectional DC-DC converter provides a DC bus voltage to the rotor-side converter, and establishes the stator voltage of the doubly-fed wind turbine generator by controlling the rotor-side converter, thereby completing system self-starting;

[0008] After starting and connecting to the grid, in a subsynchronous operation state, the DC grid provides energy to the rotor-side converter through the bidirectional DC-DC converter;

[0009] In the supersynchronous operation state, the rotor-side energy of the doubly-fed wind turbine flows to the DC grid through the bidirectional DC-DC converter;

[0010] The voltage sensor is used to detect the stator side voltage, rotor side voltage and DC grid voltage of the doubly-fed wind turbine generator;

[0011] The power sensor is used to detect the stator side current and the rotor side current of the doubly fed wind turbine generator;

[0012] The speed sensor is used to detect the rotor speed of the doubly-fed wind turbine generator;

[0013] The control unit determines a rotor voltage reference value of the doubly-fed wind turbine generator according to the stator-side voltage, the rotor-side voltage, the DC grid voltage, the stator-side current, the rotor-side current, and the rotor speed, and adjusts the operating state of the rotor-side converter according to the rotor voltage reference value.

[0014] In a possible implementation, the stator frequency of the doubly-fed wind turbine generator is determined according to the following formula:

[0015]

[0016] Among them, f is the stator frequency, p is the number of motor pole pairs, N is the gearbox ratio, n blade is the blade speed.

[0017] In a possible implementation, the number of pole pairs of the doubly-fed wind turbine is 2-8 pairs, the gearbox transmission ratio is 50-150, and the blade rotation speed is 10-15 rpm.

[0018] In a possible implementation, the medium frequency doubly-fed wind turbine generator has a rotational speed operating range of 750 rpm to 2250 rpm.

[0019] In a possible implementation, the AC transformer operates in a range of 100 Hz to 300 Hz.

[0020] In a possible implementation, the rectifier unit adopts a six-pulse topology structure or a twelve-pulse topology structure.

[0021] In a possible implementation, the six-pulse topology includes six-pulse uncontrolled rectification and six-pulse thyristor rectification.

[0022] In a possible implementation, the twelve-pulse topology structure includes twelve-pulse uncontrolled rectification and twelve-pulse thyristor rectification.

[0023] In a possible implementation, the bidirectional DC-DC converter adopts voltage closed-loop control;

[0024] The bidirectional DC-DC converter obtains a voltage error by subtracting a preset target DC voltage from an actual DC voltage;

[0025] The PI controller of the bidirectional DC-DC converter performs phase correction on the initial control signal of the control unit according to the voltage error and the phase shift control algorithm to obtain a corrected control signal; the initial control signal is generated by the control unit;

[0026] The control unit controls the bidirectional DC-DC converter according to the modified control signal to achieve closed-loop control of the output DC voltage.

[0027] In a possible implementation, the rotor voltage reference value includes a d-axis rotor voltage reference value and a q-axis rotor voltage reference value;

[0028] The rotor-side converter adopts dual closed-loop vector control; the rotor-side converter includes a d-axis and a q-axis; the d-axis is composed of a cascade of a d-axis outer-loop PI controller and a d-axis inner-loop PI controller; the q-axis is composed of a cascade of a q-axis outer-loop PI controller and a q-axis inner-loop PI controller;

[0029] The d-axis outer loop PI controller outputs a d-axis current reference value according to the difference between the preset stator frequency and the actual stator frequency, which is used for closed-loop regulation of the stator frequency; the d-axis inner loop PI controller outputs a d-axis rotor voltage reference value according to the difference between the d-axis current reference value and the actual d-axis current;

[0030] The q-axis outer loop PI controller outputs a q-axis current reference value according to the difference between the preset stator active power and the actual stator active power, which is used for closed-loop regulation of the stator active power; the q-axis inner loop PI controller outputs a q-axis rotor voltage reference value according to the difference between the q-axis current reference value and the actual q-axis current, so as to track the rotor side current;

[0031] The actual d-axis current and the actual q-axis current are obtained through the current sensor; and the actual stator frequency and the actual stator active power are obtained through the voltage sensor.

[0032] The DC grid-connected medium-frequency doubly-fed wind power generation system provided by the present invention has an operating frequency between 100Hz and 300Hz. The stator side of the doubly-fed wind turbine generator is connected to an AC transformer and then connected to the medium-voltage DC grid through a rectifier unit. The rotor side is connected to a bidirectional DC-DC converter via a rotor-side converter. The bidirectional DC-DC converter provides the rotor-side converter with an initial DC bus voltage when the system starts, and adjusts the bidirectional energy flow according to the operating status after grid connection. The wind turbine adopts vector control technology and can flexibly adjust the operating frequency within the medium frequency range according to wind speed changes, thereby quickly adapting to changes in wind speed. The increase in system frequency reduces the number of turns or magnetic flux of the motor at the same voltage level, which can significantly reduce the size and weight of the motor, reduce material consumption, and improve the economy and transportation and installation convenience of system-related equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A circuit diagram of a medium-frequency doubly-fed wind power generation system provided by an embodiment of the present invention;

[0034] Figure 2 A control principle diagram of a medium-frequency doubly-fed wind power generation system provided by an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of a grid-connected medium-frequency doubly-fed wind power generation system according to an embodiment of the present invention;

[0036] Among them, 1-doubly fed wind turbine generator, 2-rotor side converter, 3-bidirectional DC-DC converter, 4-AC transformer, 5-rectifier unit, 6-control unit. DETAILED DESCRIPTION

[0037] The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are intended to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention. That is, the present invention is not limited to the preferred embodiments described, and the scope of the present invention is defined by the claims.

[0038] In the description of the present invention, it should be noted that, unless otherwise specified, “plurality” means two or more; the terms “first”, “second”, etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0039] The DC grid-connected medium frequency doubly-fed wind power generation system operating at medium frequency has unique advantages. The DC grid-connected medium frequency doubly-fed wind power generation system of the present invention operates in the medium frequency range of 100Hz to 300Hz, can quickly track changes in wind speed, and adjust the power generation power in a timely and flexible manner, thereby quickly adapting to changes in wind speed and outputting relatively stable electric energy. In addition, the medium frequency motor itself has significant structural advantages. Compared with traditional industrial frequency motors, when operating at medium frequency, the volume of its winding can be reduced, and the size of the iron core can be finely optimized, thereby achieving a double reduction in volume and weight. This not only reduces the consumption of raw materials in the motor production process and cuts manufacturing costs, but also brings great convenience to the transportation, installation and subsequent maintenance of wind turbines, thereby improving the implementation efficiency of the entire wind power project.

[0040] In addition, the DC grid-connected medium-frequency double-fed wind power generation system of the present invention adopts a unique grid-connected method. Although the motor as a whole is still AC operation, the stator of the single machine is connected to the rectifier device, which can directly convert AC power into DC power and integrate it into the DC grid. In this way, the cumbersome and energy-consuming links in the traditional AC grid connection are abandoned, and the power quality problems of the wind turbine AC grid connection are effectively avoided. The rectified DC power is accurately and smoothly integrated into the DC grid, which perfectly meets the current explosive power demand of DC loads such as new energy vehicle fast charging stations and large data centers, and also helps to build distributed and intelligent DC microgrids.

[0041] Figure 1 The circuit schematic diagram of the medium frequency double-fed wind power generation system provided by the embodiment of the present invention is as follows: Figure 1 As shown, the present invention provides a DC grid-connected medium-frequency doubly-fed wind power generation system, comprising: a doubly-fed wind turbine generator 1, a rotor-side converter 2, a bidirectional DC-DC converter 3, an AC transformer 4, a rectifier unit 5, a control unit 6, a current sensor, a voltage sensor, and a speed sensor;

[0042] The stator side of the doubly-fed wind turbine generator 1 is connected to the input end of the AC transformer 4, the output end of the AC transformer 4 is connected to the rectifier unit 5, and the rotor side of the doubly-fed wind turbine generator 1 is connected to the bidirectional DC-DC converter 3 via the rotor-side converter 2; the control unit 6 is connected to the current sensor, voltage sensor, speed sensor and rotor-side converter 2.

[0043] The medium frequency doubly fed wind power generation system of the present invention converts medium frequency alternating current into direct current and incorporates it into the DC grid. The stator frequency can be adjusted under DC grid connection, and the regulation of the stator side output frequency is the key part to achieve medium frequency operation.

[0044] In one possible implementation, when the doubly-fed wind turbine generator 1 is started, the bidirectional DC-DC converter 3 provides a DC bus voltage to the rotor-side converter 2, and establishes the stator voltage of the doubly-fed wind turbine generator 1 by controlling the rotor-side converter 2, completing the system self-start; after starting and connecting to the grid, in the subsynchronous operation state, the DC grid provides energy to the rotor-side converter 2 through the bidirectional DC-DC converter 3; in the supersynchronous operation state, the rotor-side energy of the doubly-fed wind turbine generator 1 flows to the DC grid through the bidirectional DC-DC converter 3. In one possible implementation, the voltage sensor is used to detect the stator-side voltage u of the doubly-fed wind turbine generator 1. sa 、u sb 、u sc , rotor side voltage u ra 、u rb 、u rc , DC grid voltage u dc ; The power sensor is used to detect the stator side current i of the doubly fed wind turbine 1 sa 、i sb 、i sc , and the rotor side current i ra 、i rb 、i rc ; The speed sensor is used to detect the rotor speed n of the doubly fed wind turbine 1 r .

[0045] Figure 2 The control principle diagram of the medium frequency double-fed wind power generation system provided by the embodiment of the present invention is as follows: Figure 2 As shown, θ s represents the stator position angle, θ r represents the rotor position angle, θ sl represents the slip angle, ω r represents the rotor angular velocity.

[0046] According to the current stator voltage frequency reference value, the control unit 6 obtains the rotor voltage reference value of the doubly-fed wind turbine 1. Based on the rotor voltage reference value, the control unit 6 outputs a PMW signal to control the rotor-side converter 2.

[0047] In one possible implementation, a bidirectional DC-DC converter employs voltage closed-loop control. The bidirectional DC-DC converter obtains a voltage error by subtracting a preset target DC voltage from an actual DC voltage. A PI controller of the bidirectional DC-DC converter performs phase correction on an initial control signal of a control unit based on the voltage error and a phase-shift control algorithm to obtain a corrected control signal. The initial control signal is generated by the control unit.

[0048] The control unit controls the bidirectional DC-DC converter according to the corrected control signal to achieve closed-loop control of the output DC voltage.

[0049] In a possible implementation, the rotor voltage reference value includes a d-axis rotor voltage reference value and a q-axis rotor voltage reference value;

[0050] The rotor-side converter adopts dual closed-loop vector control; the rotor-side converter includes a d-axis and a q-axis; the d-axis is composed of a cascade of a d-axis outer-loop PI controller and a d-axis inner-loop PI controller; the q-axis is composed of a cascade of a q-axis outer-loop PI controller and a q-axis inner-loop PI controller;

[0051] The d-axis outer loop PI controller outputs the d-axis current reference value i according to the difference between the preset stator frequency and the actual stator frequency. rd * , used for closed-loop regulation of stator frequency; the d-axis inner loop PI controller is based on the d-axis current reference value i rd * The difference between the actual d-axis current and the actual d-axis current is used to output the d-axis rotor voltage reference value u rd * ;

[0052] The q-axis outer loop PI controller outputs the q-axis current reference value i according to the difference between the preset stator active power and the actual stator active power. rq * , used for closed-loop regulation of stator active power; the q-axis inner loop PI controller is based on the q-axis current reference value i rq * The difference between the actual q-axis current and the q-axis rotor voltage reference value u is output. rq * , to track the rotor side current;

[0053] The actual d-axis current and the actual q-axis current are obtained through current sensors; the actual stator frequency and the actual stator active power are obtained through voltage sensors.

[0054] The rotor d-axis rotor voltage reference value u rd * , q-axis rotor voltage reference value u rq * After coordinate transformation, the rotor voltage reference value u is obtained ra * 、u rb * 、u rc * Based on the rotor voltage reference value, the control unit 6 outputs a PMW signal to control the rotor-side converter 2.

[0055] In a possible implementation, the rectifier unit 5 uses a six-pulse topology or a twelve-pulse topology. Under the DC grid-connected condition, the stator operating frequency is adjusted to the medium frequency range. Among them, the six-pulse topology includes six-pulse uncontrolled rectification and six-pulse thyristor rectification, respectively. Figure 3 (a) and Figure 3 (b) As shown; the twelve-pulse topology includes twelve-pulse uncontrolled rectification and twelve-pulse thyristor rectification, respectively. Figure 3 (c) and Figure 3 (d) shown.

[0056] In one possible implementation, in order to increase the stator frequency, collaborative optimization is performed from two dimensions: increasing the synchronous speed and increasing the number of pole pairs. The number of pole pairs of the doubly fed wind turbine 1 is 2-8 pairs, the gearbox transmission ratio is 50-150, and the blade speed is 10-15 rpm to achieve medium frequency operation.

[0057] In a possible implementation, the generator operating frequency is determined to be 100-300 Hz based on the above constraints, controlled within the range of 0.8-1.2Wb, and the core cross-sectional area is reduced to 40-60% of that of the power frequency motor.

[0058] In one possible implementation, a medium-frequency double-fed wind power generation system with DC grid connection can reduce the volume and weight of the equipment by reducing the core flux and optimizing the winding design, thereby reducing the total weight of the motor by 30%-50%.

[0059] In one possible implementation, bidirectional DC-DC converter 3 uses closed-loop voltage control to adjust the control signal from the control unit based on the difference between the input target DC voltage and the actual DC voltage and a phase-shift control algorithm. Bidirectional DC-DC converter 3 operates during system startup to stabilize the DC bus voltage near U* and enables bidirectional energy flow after grid connection.

[0060] In one possible implementation, the doubly-fed wind turbine generator 1 operates in a medium frequency range of 100 Hz to 300 Hz. The speed range of the medium frequency doubly-fed wind turbine generator is 750 rpm to 2250 rpm. The AC transformer operates in a range of 100 Hz to 300 Hz.

[0061] Determine the stator frequency according to the following formula:

[0062]

[0063] Among them, f is the stator frequency, p is the number of motor pole pairs, N is the gearbox ratio, n blade is the blade speed.

[0064] To achieve the medium frequency target, it is necessary to coordinate optimization from two dimensions: increasing the speed and increasing the number of pole pairs. Increasing the speed mainly depends on the gearbox ratio. High-power offshore wind turbines (>4MW) are adapted to low wind speed scenarios. By using high-efficiency gear materials and optimizing the design, the transmission ratio can be increased to N = 1:160. However, when N = 1:150 is exceeded, the gear contact stress and bearing load increase significantly. Therefore, the maximum transmission ratio is limited to N = 1:150. The blade speed is constrained by the tip speed ratio. According to Betz theory, the optimal tip speed ratio is 6 to 8, and the corresponding blade speed upper limit is: n blade ≤λv60 / 2πR The blade speed can be stabilized in the range of 10 to 15rpm.

[0065] By f s ∝p shows that at the same speed, the frequency increases by Δf when the number of pole pairs increases by 1. s =n rotor / 60, the increase in the number of pole pairs will lead to the matching problem between the number of stator slots Qs and the number of rotor slots Qr. The use of fractional slot winding (such as Qs = 54, p = 6) can reduce the cogging torque and suppress vibration noise.

[0066] Combined with the previous analysis of various variables, the constraints of the frequency formula are as follows:

[0067]

[0068] According to the above constraints, the relationship between frequency, pole pair number and gearbox ratio is plotted. It provides an intuitive reference for achieving operation in the medium frequency range of 100Hz to 300Hz, and provides a theoretical basis for the realization of medium frequency doubly fed system.

[0069] Through the coordinated design of a high transmission ratio gearbox (N≤150) and a multi-pole logarithmic motor (p≤8), and combined with the optimization of aerodynamics, mechanics and motors, the doubly-fed wind turbine 1 can stably operate in the medium frequency range of 100Hz to 300Hz.

[0070] The DC grid-connected medium-frequency double-fed wind power generation system provided by the present invention has the following beneficial effects:

[0071] The innovative design significantly improves the compactness and economy of the equipment. Specifically, the system reduces the core flux amplitude (33%-50% of the power frequency system) and combines formula A core =A base Ψ base / Ψ new, reducing the core cross-sectional area to 40%-60% of that of a power-frequency motor, thereby reducing both core volume and weight (total weight is reduced by 30%-50%). Simultaneously optimized fractional-slot winding designs (such as a 54-slot / 6-pole configuration) further reduce winding volume, copper loss, and material consumption. This lightweight design not only lowers raw material costs but also significantly simplifies wind turbine transportation, installation, and maintenance.

[0072] In a medium frequency operating environment (100Hz-300Hz), the AC step-up transformer connected to the stator side decreases sharply in size due to the increase in frequency. According to the inverse square relationship between transformer volume and frequency, V∝1 / f 2 When the frequency increases from 50Hz to 100Hz, the transformer volume is reduced to 59.5%. At 175Hz, the volume is further reduced to 39.1% of the power frequency, directly reducing raw material usage and equipment investment costs by over 30%. Furthermore, medium-frequency operation significantly optimizes reactive power compensation design: while the reactance remains constant, increasing the frequency simultaneously reduces the required inductance (L = X / (2πf)) and capacitance (C = 1 / (2πfX), reducing the volume of reactive power compensation components by 50%-60%.

[0073] The system's stator side uses a rectifier for rectification, and the rectified DC power is precisely connected to the DC grid, making it perfectly suitable for high-power DC load scenarios such as new energy vehicle fast charging stations and large data centers.

[0074] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A DC grid-connected medium-frequency double-fed wind power generation system, characterized in that: include: Doubly-fed wind turbine generator, rotor-side converter, bidirectional DC-DC converter, AC transformer, rectifier unit, control unit, current sensor, voltage sensor and speed sensor; the medium-frequency doubly-fed wind turbine generator system operates in the range of 100 Hz to 300 Hz; The stator side of the doubly-fed wind turbine generator is connected to the input end of the AC transformer, the output end of the AC transformer is connected to the rectifier unit, and the rotor side of the doubly-fed wind turbine generator is connected to the bidirectional DC-DC converter via the rotor-side converter; the control unit is connected to the current sensor, the voltage sensor, the speed sensor and the rotor-side converter; When the doubly-fed wind turbine generator is started, the bidirectional DC-DC converter provides a DC bus voltage to the rotor-side converter, and establishes the stator voltage of the doubly-fed wind turbine generator by controlling the rotor-side converter, thereby completing system self-starting; After starting and connecting to the grid, in a subsynchronous operation state, the DC grid provides energy to the rotor-side converter through the bidirectional DC-DC converter; In the supersynchronous operation state, the rotor-side energy of the doubly-fed wind turbine flows to the DC grid through the bidirectional DC-DC converter; the voltage sensor is used to detect the stator-side voltage, rotor-side voltage and DC grid voltage of the doubly-fed wind turbine; The power sensor is used to detect the stator side current and the rotor side current of the doubly fed wind turbine generator; The speed sensor is used to detect the rotor speed of the doubly-fed wind turbine generator; The control unit determines a rotor voltage reference value of the doubly-fed wind turbine generator according to the stator-side voltage, the rotor-side voltage, the DC grid voltage, the stator-side current, the rotor-side current, and the rotor speed, and adjusts the operating state of the rotor-side converter according to the rotor voltage reference value.

2. The DC grid-connected medium-frequency double-fed wind power generation system according to claim 1, characterized in that: The stator frequency of the doubly-fed wind turbine generator is determined according to the following formula: Among them, f is the stator frequency, p is the number of motor pole pairs, N is the gearbox ratio, n blade is the blade speed.

3. The DC grid-connected medium-frequency double-fed wind power generation system according to claim 1, characterized in that: The number of pole pairs of the doubly-fed wind turbine is 2-8 pairs, the gearbox transmission ratio is 50-150, and the blade rotation speed is 10-15 rpm.

4. The DC grid-connected medium-frequency double-fed wind power generation system according to claim 1, characterized in that: The speed operating range of the medium frequency doubly fed wind turbine is 750 rpm-2250 rpm.

5. The DC grid-connected medium frequency doubly-fed wind power generation system according to claim 1, characterized in that: The AC transformer operates in the range of 100 Hz to 300 Hz.

6. The DC grid-connected medium frequency doubly-fed wind power generation system according to claim 1, characterized in that: The rectifier unit adopts a six-pulse topology structure or a twelve-pulse topology structure.

7. The DC grid-connected medium frequency doubly-fed wind power generation system according to claim 6, characterized in that: The six-pulse topology structure includes six-pulse uncontrolled rectification and six-pulse thyristor rectification.

8. The DC grid-connected medium-frequency double-fed wind power generation system according to claim 6, characterized in that: The twelve-pulse topology structure includes twelve-pulse uncontrolled rectification and twelve-pulse thyristor rectification.

9. The DC grid-connected medium-frequency doubly-fed wind power generation system according to claim 1, characterized in that: The bidirectional DC-DC converter adopts voltage closed-loop control; The bidirectional DC-DC converter obtains a voltage error by subtracting a preset target DC voltage from an actual DC voltage; The PI controller of the bidirectional DC-DC converter performs phase correction on the initial control signal of the control unit according to the voltage error and the phase shift control algorithm to obtain a corrected control signal; the initial control signal is generated by the control unit; The control unit controls the bidirectional DC-DC converter according to the modified control signal to achieve closed-loop control of the output DC voltage.

10. The DC grid-connected medium frequency doubly-fed wind power generation system according to claim 1, characterized in that: The rotor voltage reference value includes a d-axis rotor voltage reference value and a q-axis rotor voltage reference value; The rotor-side converter adopts dual closed-loop vector control; the rotor-side converter includes a d-axis and a q-axis; the d-axis is composed of a cascade of a d-axis outer-loop PI controller and a d-axis inner-loop PI controller; the q-axis is composed of a cascade of a q-axis outer-loop PI controller and a q-axis inner-loop PI controller; The d-axis outer loop PI controller outputs a d-axis current reference value according to the difference between the preset stator frequency and the actual stator frequency, which is used for closed-loop regulation of the stator frequency; the d-axis inner loop PI controller outputs a d-axis rotor voltage reference value according to the difference between the d-axis current reference value and the actual d-axis current; The q-axis outer loop PI controller outputs a q-axis current reference value according to the difference between the preset stator active power and the actual stator active power, which is used for closed-loop regulation of the stator active power; The q-axis inner loop PI controller outputs a q-axis rotor voltage reference value according to the difference between the q-axis current reference value and the actual q-axis current to track the rotor side current; wherein the actual d-axis current and the actual q-axis current are obtained by the current sensor; The actual stator frequency and the actual stator active power are obtained through the voltage sensor.

Images