A positive and negative sequence separation method suitable for wind turbine generator set converter control

Abstract

The application discloses a positive and negative sequence separation method suitable for wind turbine generator set converter control and belongs to the field of wind power generation grid connection control. The method comprises the following steps: collecting three-phase voltage instantaneous signals of a power grid side and converting the three-phase voltage instantaneous signals to a stationary alpha-beta coordinate system; carrying out decoupling calculation on alpha-beta axis voltage signals, and respectively extracting positive sequence alpha-beta axis components and negative sequence alpha-beta axis components; and respectively using the extracted components in independent control loops of a converter to realize coordinated control under the condition of unbalanced power grid voltage. The decoupling calculation is realized by constructing a separation matrix comprising a positive sequence extraction operator and a negative sequence extraction operator, and carrying out matrix operation on the matrix by taking the alpha-beta axis voltage signals as an input vector. The application is based on the principle of one-fourth fundamental wave period delay decoupling, has fast response, high precision and simple calculation, and effectively improves the operation stability and fault ride-through capability of the converter under the condition of unbalanced power grid.

Description

Technical Field

[0001] This invention belongs to the field of wind power grid connection control technology, and relates to the control strategy of wind turbine generator converter operating under grid voltage imbalance conditions, specifically a positive and negative sequence separation method applicable to wind turbine generator converter control. Background Technology

[0002] Wind turbine generators are typically connected to the grid via full-power converters or doubly-fed induction generators. When the grid experiences three-phase voltage imbalance due to faults or load imbalances, the grid voltage contains not only positive-sequence components but also negative-sequence components. Traditional vector control strategies based on phase-locked loops and synchronous rotating coordinate systems usually treat the negative-sequence components as disturbances, leading to significant power pulsations at twice the fundamental frequency and current waveform distortion in the control loop. This can cause DC bus voltage fluctuations, converter overcurrent, and even trigger protection devices, resulting in grid disconnection. This severely impacts the fault ride-through capability of wind turbine generators and the stable operation of the grid.

[0003] To achieve high-performance control of wind turbine generators under grid imbalance conditions, the key lies in the ability to quickly and accurately separate the positive-sequence and negative-sequence components from the detected three-phase voltage (or current) signals in real time, so that the controller can adjust them independently. Existing methods for positive and negative sequence separation, such as those based on full-cycle delay cancellation and those based on complex filters, all have certain limitations: the former's dynamic response is constrained by inherent delays, and its separation accuracy decreases when the grid frequency deviates; the latter is more complex to design, and its parameter robustness needs to be improved.

[0004] Therefore, it is necessary to provide a positive and negative sequence separation method that is theoretically sound, has a rapid dynamic response, high separation accuracy, and is easy to implement digitally, so as to improve the control performance and operational stability of converters under complex power grid conditions. Summary of the Invention

[0005] To overcome the shortcomings of existing positive and negative sequence separation methods, such as slow dynamic response, accuracy affected by frequency offset, and complex implementation, this invention provides a positive and negative sequence separation method suitable for wind turbine generator converter control. By constructing a separation matrix based on quarter-fundamental period delay decoupling and performing matrix operations on the αβ axis voltage signals, fast and high-precision separation of positive and negative sequence components is achieved with minimal delay. The core algorithm is linear operation and fixed delay, resulting in a light computational burden.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A method for separating positive and negative sequence control applicable to wind turbine generator converters includes the following steps: S1. Collect the instantaneous three-phase voltage signal from the power grid side as the input signal; S2. Convert the instantaneous three-phase voltage signal to a two-phase stationary αβ coordinate system to obtain an αβ-axis voltage signal containing positive-sequence and negative-sequence components; S3. Decouple the αβ axis voltage signal to extract the positive-order αβ axis components and the negative-order αβ axis components respectively. The decoupling calculation is performed as follows: First, a separation matrix containing positive-order extraction operators and negative-order extraction operators is constructed; then, the αβ axis voltage signal is used as the input vector, and matrix operations are performed with the separation matrix to output the separated positive-order αβ axis components and negative-order αβ axis components. S4. The extracted positive-sequence αβ-axis components and negative-sequence αβ-axis components are used in the independent control loops of the wind turbine generator converter for coordinated control under grid voltage imbalance conditions.

[0007] Furthermore, the transformation expression in step S2 is constructed as follows: ; in: express Shaft voltage signal; express Shaft voltage signal; , , These represent the instantaneous three-phase voltage signals collected from the power grid side.

[0008] Furthermore, the separation matrix M mentioned in step S3 is represented as: ; in: It is a 2×2 identity matrix. .

[0009] Furthermore, step S3, which involves using the αβ axis voltage signal as an input vector and performing matrix operations with the separation matrix, specifically involves: Let the current time be The αβ axis voltage signal is Delay The αβ axis voltage signal is ,in The fundamental frequency period; Will , Performing matrix multiplication with the separation matrix M yields the separated positive-order αβ-axis components and negative-order αβ-axis components: ; in Indicates the current time orthogonal order Axial components; Indicates the current time orthogonal order Axial components; Indicates the current time negative order Axial components; Indicates the current time negative order Axial components; Indicates the current time of Shaft voltage signal; Indicates the current time of Shaft voltage signal; Indicates delay of Shaft voltage signal; Indicates delay of Shaft voltage signal.

[0010] Furthermore, the calculation process of the αβ axis voltage signal and the separation matrix includes one or more filtering steps.

[0011] Furthermore, the filtering stage involves introducing a low-pass filter for the input αβ axis voltage signal, or introducing a low-pass filter for the positive-sequence αβ axis component and the negative-sequence αβ axis component at the output.

[0012] Furthermore, the method is executed cyclically with a fixed sampling period, which is synchronized with the switching or control period of the converter.

[0013] This application also protects the application of the above-mentioned positive and negative sequence separation method for wind turbine generator converter control in the control of rotor-side converters of doubly fed wind turbine generators or grid-side converters of full-power wind turbine generators.

[0014] This application also protects a terminal device, the terminal device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when executed by the processor, implements the above-described positive and negative order separation method.

[0015] This application also protects a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described positive-negative order separation method.

[0016] The beneficial effects of this invention include: This method starts from the physical essence of three-phase unbalanced systems and constructs a separation matrix based on quarter-cycle fundamental period delay decoupling to perform matrix operations on αβ-axis voltage signals. The separation principle is clear, and the theoretical accuracy has no steady-state error (under ideal sine wave conditions and constant frequency). Compared with the traditional full-cycle delay method, this invention only requires a fixed delay of a quarter cycle, which significantly improves the dynamic response speed and can track grid fault changes faster. The core algorithm is linear operation and fixed delay, which has a light computational burden, does not require complex filter design and parameter tuning, has strong robustness, and is easy to implement on DSP or FPGA platforms. It provides high-precision positive and negative sequence component inputs for subsequent unbalanced control strategies, effectively improving the converter's operational stability, power quality, and fault ride-through capability during grid faults. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the positive and negative sequence vector relationship of three-phase voltages; Figure 2 This is a block diagram of a phase-locked loop structure based on cascaded DSC in the prior art; Figure 3 This is a schematic diagram of the dual-current inner loop control principle of the converter. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Example 1: A positive and negative sequence separation method suitable for wind turbine generator converter control, which is executed cyclically with a fixed sampling period synchronized with the converter's switching or control period. The steps include: Step 1: Three-phase signal acquisition and stationary coordinate transformation.

[0021] Real-time acquisition of instantaneous three-phase voltage signals from the power grid side , , As the input signal, the three-phase instantaneous voltage signal is transformed into a two-phase stationary αβ coordinate system using Clarke transform, resulting in an αβ-axis voltage signal containing positive and negative sequence components. The transformation formula is as follows: (1); in: express Shaft voltage signal; express Shaft voltage signal.

[0022] Step 2: Construct a decoupling and separation mathematical model.

[0023] Assume that under unbalanced conditions, the three-phase voltage can be decomposed into the sum of positive-sequence and negative-sequence components. In a coordinate system, any voltage signal It can be represented as: (2); In this context, the superscript '+' represents positive order and '-' represents negative order. Represents the positive-order components. Indicates negative-order components; express Positive sequence components of the axis; express Negative order components of the axis; express Positive sequence components of the axis; express Negative order component of axis.

[0024] Furthermore, the positive-order and negative-order components have specific transformation relationships in the complex plane or vector space. Define a rotation operator. Its matrix form is: (3); For the positive-order component, it is in In the coordinate system, angular velocity (The fundamental angular frequency of the power grid) rotates in the positive direction; for the negative sequence component, it rotates at an angular velocity... Reverse rotation. Therefore, a delay of one-quarter of the fundamental period ( The signal in question has a fixed phase relationship with the original signal. This embodiment utilizes this characteristic to construct a separation matrix. The mathematical derivation is as follows: Let the current time be The αβ axis voltage signal is Delay The αβ axis voltage signal is For angular frequency of orthogonal order Axis component, delay Equivalent to introducing Phase shift; for negative order Axial components are equivalent to introducing The phase shift. That is: (4); in, , .

[0025] By combining equations (2) and (4), we can decouple the following: The positive and negative order components at time points. The solution process is as follows: Extending equation (4) and combining it with equation (2), we obtain the following about... and The system of linear equations: (5); Write the system of equations (5) in matrix form: (6); in It is a 2×2 identity matrix. Inverting the coefficient matrix yields the separation matrix. : (7); The calculation yielded the following result: (8); After expansion, the final separation formula is obtained: (9); in Indicates the current time orthogonal order Axial components; Indicates the current time orthogonal order Axial components; Indicates the current time negative order Axial components; Indicates the current time negative order Axial components; Indicates the current time of Shaft voltage signal; Indicates the current time of Shaft voltage signal; Indicates delay of Shaft voltage signal; Indicates delay of Shaft voltage signal.

[0026] Step 3: Algorithm implementation and optimization.

[0027] In digital control systems, memory caching is used. The sampled data from before the time was used for real-time calculation according to formula (9). To suppress the influence of high-frequency noise and switching harmonics on the separation accuracy, a first-order low-pass filter with a cutoff frequency higher than the fundamental frequency of the power grid can be introduced for the input αβ axis voltage signal or for the positive sequence αβ axis component and the negative sequence αβ axis component at the output.

[0028] Step 4: Separate components are applied to control.

[0029] The positive sequence components obtained in real time and negative order components The signals are fed into the dual-loop control system of the converter. The positive-sequence component is used to maintain active power transmission and DC voltage stability; the negative-sequence component is used to generate compensation commands to suppress negative-sequence current or eliminate double-frequency power pulsation, thereby achieving high-performance, uninterrupted operation under grid voltage imbalance conditions.

[0030] Example 2: Taking a 1.5MW doubly fed wind turbine generator set as an example, its grid-side converter adopts the positive and negative sequence separation procedure described in this invention.

[0031] Step A: Hardware signal acquisition.

[0032] The power grid voltage transformer collects the three-phase voltage at point PCC. After signal conditioning, the controller's ADC module synchronously samples the voltage at a rate of 10kHz to obtain a discrete sequence. , , , This is the sampling point number.

[0033] Step B: Software algorithm execution.

[0034] Execute the following loop program in the converter master control DSP (such as TI TMS320F28335): 1. Coordinate transformation: Calculate the coordinates of the current sampling point according to formula (1). and .

[0035] 2. Delayed storage: Store the current... and Store in a circular buffer. Simultaneously, read from the buffer. Data before each point and ,in Sampling frequency, Since it is the rated power grid frequency, .

[0036] 3. Decoupled computation: As a digital implementation of formula (9), execute the following code: ``` u_alpha_plus = 0.5 * ; u_beta_plus = 0.5 * ; u_alpha_minus = 0.5 * ; u_beta_minus = 0.5 * ; ``` 4. Filtering optimization (optional): The calculated four variables, including u_alpha_plus, are passed through a first-order low-pass digital filter with a cutoff frequency of 150Hz to smooth out the small fluctuations caused by switching noise.

[0037] Step C: Control the application.

[0038] The filtered positive-sequence component is fed into a conventional power control loop based on a positive-sequence rotating coordinate system. Simultaneously, the negative-sequence component is fed into a separate negative-sequence current control loop, with its command value set to zero, to suppress negative-sequence current. The voltage commands output from the two loops are combined, modulated by PWM to generate a switching signal, which drives the IGBT.

[0039] Example 3: Effect verification.

[0040] Tests conducted using the RT-LAB hardware-in-the-loop simulation platform showed that when a single-phase voltage drop of 15% occurred in the power grid, the total harmonic distortion (THD) of the grid-side current reached 8.2% using the traditional method, and there was a significant imbalance. However, after adopting the separation procedure described in this invention, the current THD dropped to less than 3.1%, and the three-phase current remained basically balanced, significantly improving the power quality.

[0041] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for separating positive and negative sequence control applicable to wind turbine generator converters, characterized in that, Includes the following steps: S1. Collect the instantaneous three-phase voltage signal from the power grid side as the input signal; S2. Convert the instantaneous three-phase voltage signal to a two-phase stationary αβ coordinate system to obtain an αβ-axis voltage signal containing positive-sequence and negative-sequence components; S3. Decouple the αβ axis voltage signal to extract the positive-order αβ axis components and the negative-order αβ axis components respectively. The decoupling calculation is performed as follows: First, a separation matrix containing positive-order extraction operators and negative-order extraction operators is constructed; then, the αβ axis voltage signal is used as the input vector, and matrix operations are performed with the separation matrix to output the separated positive-order αβ axis components and negative-order αβ axis components. S4. The extracted positive-sequence αβ-axis components and negative-sequence αβ-axis components are used in the independent control loops of the wind turbine generator converter for coordinated control under grid voltage imbalance conditions.

2. The positive and negative sequence separation method for wind turbine generator converter control according to claim 1, characterized in that, The transformation expression for step S2 is constructed as follows: ； in: express Shaft voltage signal; express Shaft voltage signal; , , These represent the instantaneous three-phase voltage signals collected from the power grid side.

3. The positive and negative sequence separation method for wind turbine generator converter control according to claim 2, characterized in that, The separation matrix M mentioned in step S3 is represented as follows: ； in: It is a 2×2 identity matrix. .

4. The positive and negative sequence separation method for wind turbine generator converter control according to claim 3, characterized in that, Step S3 involves using the αβ axis voltage signal as an input vector and performing matrix operations with the separation matrix, specifically as follows: Let the current time be The αβ axis voltage signal is Delay The αβ axis voltage signal is ,in The fundamental frequency period; Will , Performing matrix multiplication with the separation matrix M yields the separated positive-order αβ-axis components and negative-order αβ-axis components: ； in Indicates the current time orthogonal order Axial components; Indicates the current time orthogonal order Axial components; Indicates the current time negative order Axial components; Indicates the current time negative order Axial components; Indicates the current time of Shaft voltage signal; Indicates the current time of Shaft voltage signal; Indicates delay of Shaft voltage signal; Indicates delay of Shaft voltage signal.

5. The positive and negative sequence separation method for wind turbine generator converter control according to claim 4, characterized in that, The calculation process of the αβ axis voltage signal and the separation matrix includes one or more filtering steps.

6. The positive and negative sequence separation method for wind turbine generator converter control according to claim 5, characterized in that, The filtering stage involves introducing a low-pass filter into the input αβ axis voltage signal, or introducing a low-pass filter into the positive-sequence αβ axis component and the negative-sequence αβ axis component at the output.

7. A positive and negative sequence separation method for wind turbine generator converter control according to any one of claims 1-6, characterized in that, The method is executed cyclically with a fixed sampling period, which is synchronized with the switching or control period of the converter.

8. The application of the positive and negative sequence separation method for wind turbine generator converter control as described in any one of claims 1-6 in the control of the rotor-side converter of a doubly fed wind turbine generator or the grid-side converter of a full-power wind turbine generator.

9. A terminal device, characterized in that, The terminal device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, it implements the positive and negative order separation method as described in any one of claims 1-6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the positive-negative order separation method as described in any one of claims 1-6.

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