A method and apparatus for estimating the voltage frequency and phase of a wind turbine based on phase correction.

Abstract

This invention discloses a method for estimating the voltage frequency and phase of a wind turbine based on phase correction. The method comprises the following steps: Step 1, acquiring the output voltage of the wind turbine and constructing an orthogonal signal estimator to obtain the transformed signal; Step 2, based on the transformed signal, constructing a voltage frequency estimator to calculate the grid estimated frequency; Step 3, based on the grid estimated frequency, constructing a voltage phase estimator and initially calculating the grid phase; Step 4, based on the grid estimated frequency and grid phase, performing phase correction to refine the estimated phase. This invention eliminates steady-state errors caused by continuous frequency changes while maintaining good dynamic performance; furthermore, the method is simple in structure and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of voltage detection technology, specifically relating to a method and device for estimating the voltage frequency and phase of a wind turbine based on phase correction. Background Technology

[0002] With the rapid development of new energy power generation technologies, renewable energy sources such as wind power have been widely applied and rapidly promoted. Accurate estimation of the frequency and phase of the output voltage is crucial in wind turbine fault detection and AC power rectification. However, the power generation characteristics of wind turbines are highly dependent on wind speed; as wind speed increases or decreases, the frequency of the output voltage also rises or falls accordingly, posing a significant challenge to estimating the frequency and phase of the wind turbine output voltage.

[0003] Traditional voltage detection methods are mostly designed for fixed-frequency operating conditions, such as second-order phase-locked loops (PLLs). (See S. Golestan, M. Monfared, F.D. Reijedo, and J.M. Guerrero, "Advantages and Challenges of a Type-3 PLL," in IEEE Transactions on Power Electronics, vol. 28, no. 11, pp. 4985-4997, Nov. 2013). These methods are prone to phase estimation errors under continuously changing frequency operating conditions, potentially leading to erroneous estimation results and affecting the accuracy of wind turbine fault detection and the stable operation of the wind power rectifier system. To suppress steady-state estimation errors caused by continuous frequency changes, some studies have introduced third-order PLL structures. Third-order PLLs, by adding a second-order loop filter, can effectively eliminate estimation biases caused by linear frequency changes. However, the additional second-order filtering also reduces the system's dynamic response speed, causing a decline in estimation performance when frequency and phase fluctuate rapidly.

[0004] In summary, existing methods for estimating the frequency and phase of wind turbine output voltage have two main shortcomings: First, conventional second-order phase-locked loops have a fast dynamic response, but they suffer from steady-state estimation errors under time-varying frequency conditions; second, while third-order phase-locked loops can eliminate steady-state errors, they suffer from poor dynamic performance. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a method and device for estimating the voltage frequency and phase of wind turbine generators based on phase correction. On the one hand, the method eliminates the steady-state error caused by continuous frequency changes and maintains good dynamic performance; on the other hand, the method has a simple structure and is easy to implement.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for estimating the voltage frequency and phase of a wind turbine based on phase correction is disclosed. The specific process includes acquiring three-phase grid voltage signals and constructing an orthogonal signal estimator, then constructing a voltage frequency estimator, constructing a voltage phase estimator, and finally obtaining the final estimated frequency and phase through phase correction.

[0007] Specifically, it includes the following steps; Step 1: Collect the output voltage of the wind turbine generator and construct an orthogonal signal estimator to obtain the transformed estimated signal; Step 2: Based on the transformed estimated signal, construct a voltage frequency estimator and calculate the estimated frequency of the power grid; Step 3: Based on the estimated frequency of the power grid, construct a voltage phase estimator to obtain the preliminary calculated power grid phase; Step 4: Based on the estimated frequency and phase of the power grid, perform phase correction to adjust the estimated phase.

[0008] Step one specifically involves: Step 1.1 Use an analog-to-digital converter (ADC) to sample the single-phase voltage signal of the power grid; obtain the power grid voltage signal of the wind power system. Specifically; 1. Ensure that the sampling frequency satisfies the Nyquist sampling theorem, that is, the sampling frequency is at least twice the highest frequency of the signal; 2. Sampling process: Within a specified time interval, the instantaneous values ​​of single-phase voltage are continuously collected, and the analog values ​​of the three-phase power grid are converted into digital values. The analog values ​​refer to the continuous digital values ​​obtained after multiple instantaneous samplings. The expression for the sampled three-phase grid voltage is: In the formula , , Let k be the grid voltage signal of the wind power system at time k. Let k be the phase of the wind power system grid at time k. Let k be the grid frequency of the wind power system at time k. This is the initial phase of the power grid. The sampling period; Step 1.2 involves performing a coordinate transformation, or Clarke transformation, on the wind power system grid voltage signal sampled in Step 1.1. This transforms the signal from a three-phase stationary coordinate system to a two-phase stationary coordinate system, providing data for the subsequent second coordinate transformation. The Clarke transformation formula is as follows: In the formula, , The signal at time k is the two-phase stationary coordinate system. Step 1.3: Construct an orthogonal signal estimator from the signals obtained in the two-phase stationary coordinate system in Step 1.2. Its expression is as follows: In the formula, It is the k-th time pair The estimated signal, It is the k-th time pair The estimated orthogonal signals, At time k-1, The estimated signal, It is the (k-1)th time pair The estimated orthogonal signals, It is the estimated frequency at time k-1, derived from the output of step two at the previous time. This is the estimator parameter; it can be 0.707 or 1. The above formula is for the signal The constructed orthogonal signal estimator, for the signal The same expression can be used to construct an orthogonal signal estimator.

[0009] Step two specifically involves: Step 2.1: Based on the estimated signal obtained in Step 1.3, calculate the error signal required by the voltage frequency estimator, the expression of which is as follows: In the formula, , Let be the error signal at time k; Step 2.2: Based on the error signal obtained in Step 2.1, construct a voltage-frequency estimation device. The estimator expression is as follows: In the formula, As an intermediate variable for the frequency estimator, This is an estimate of the voltage frequency at time k. The control parameter is the estimated value of the rate of change of voltage frequency at time k. , These are voltage and frequency normalization coefficients, used to eliminate the influence of frequency and voltage amplitude on the estimator control loop. Their expression is: .

[0010] Step three specifically involves: Step 3.1: Based on the estimated signal obtained in Step 1, calculate the error signal of the phase estimator, whose expression is as follows: In the formula, The error signal of the phase estimator at time k is calculated. The estimated value of the phase estimator at time k-1 is derived from the estimated value in step 3.2 at the previous time. Step 3.2: Based on the error signal, construct a voltage phase estimator, the expression of which is as follows: In the formula, As an intermediate variable for the phase estimator, The estimated phase for the phase estimator, , The control parameters are 92 and 4232, respectively. These parameters are commonly used for estimating power grid frequency and phase.

[0011] Step four specifically involves: The final estimated phase expression obtained based on phase correction is: That is, the estimated phase at time k obtained by final calculation, where a / k i This is the calculated compensation value used to compensate for steady-state errors.

[0012] A wind turbine voltage frequency and phase estimation device based on phase correction includes a voltage signal acquisition unit, a coordinate transformer, an orthogonal signal estimator, a voltage frequency estimator, a voltage phase estimator, and a phase corrector. The voltage signal is collected by a voltage signal acquisition device, and the acquired signal is passed through a coordinate transformer. The voltage signal after coordinate transformation is then passed through an orthogonal signal estimator. The output signal of the orthogonal signal estimator is sent to a voltage frequency estimator, which calculates the voltage frequency and the rate of change of frequency. The voltage phase estimator calculates the voltage phase, and finally, the phase corrector calculates the voltage phase without steady-state error based on the estimated rate of change of frequency.

[0013] The beneficial effects of this invention are: On the one hand, conventional second-order phase-locked loops have a fast dynamic response, but they have steady-state estimation errors under time-varying frequency conditions; on the other hand, although third-order phase-locked loops can eliminate steady-state errors, they have poor dynamic performance.

[0014] This invention, through modeling and analysis of a conventional second-order phase-locked loop (PLL), reveals that the PLL generates a steady-state error (a / ki) when faced with a frequency ramp signal. Based on this, the invention utilizes a proposed frequency estimator to accurately estimate the frequency change rate, and then uses this estimate to compensate for the impact of continuous frequency changes on phase estimation, effectively eliminating phase estimation bias.

[0015] The power grid frequency estimator and phase estimator used in this invention are designed in parallel, and their operation does not interfere with each other. The output of the phase estimator is compensated only by the output signal of the frequency estimator. In addition, since the proposed frequency estimator converges faster than the phase estimator, the final output after compensation can also remain stable after the output of the phase estimator reaches a steady state, thereby ensuring the dynamic response speed of the system.

[0016] The compensation method adopted in this invention can not only effectively eliminate phase estimation errors, but also ensure that the system maintains good dynamic performance. Moreover, the method has a simple structure, is easy to implement in engineering, and has strong practicality. Attached Figure Description

[0017] Figure 1 This is a flowchart of the wind turbine voltage frequency and phase estimation method implemented and provided by the present invention.

[0018] Figure 2 This is a schematic diagram of the device for estimating the voltage, frequency, and phase of a wind turbine generator set, as implemented and provided by this invention.

[0019] Figure 3 This is a simulation diagram of the phase estimation error under phase jump conditions provided by the present invention.

[0020] Figure 4 This is a simulation diagram of frequency estimation error under phase transition provided by the present invention.

[0021] Figure 5 This is a simulation diagram of the phase estimation error under frequency jumps provided by the present invention.

[0022] Figure 6 This is a simulation diagram of frequency estimation error under frequency jumps, provided by the present invention.

[0023] Figure 7 This is a simulation diagram of the phase estimation error under continuous frequency variation, which is provided by the present invention.

[0024] Figure 8 This is a simulation diagram of frequency estimation error under continuous frequency variation, provided by the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings.

[0026] like Figure 1 As shown, a method for estimating the voltage frequency and phase of a wind turbine based on phase correction includes the following steps; Step 1: Collect the output voltage of the wind turbine and construct an orthogonal signal estimator; Step 1.1 Use an analog-to-digital converter (ADC) to sample the single-phase voltage signal of the power grid. The function of the ADC is to convert the continuous analog voltage signal into a digital signal for subsequent digital signal processing.

[0027] Specifically, this step needs to ensure that: 1. Ensure that the sampling frequency satisfies the Nyquist sampling theorem, that is, the sampling frequency is at least twice the highest frequency of the signal, in order to avoid aliasing and ensure that the sampled digital signal can accurately reflect the original analog signal.

[0028] 2. Sampling Process: Instantaneous values ​​of single-phase voltages are continuously acquired within specified time intervals, and these analog values ​​are converted into digital values ​​to provide a data foundation for subsequent signal processing and analysis. During this process, an appropriate ADC resolution needs to be selected to ensure sufficient sampling accuracy. The expression for the sampled three-phase grid voltage is as follows: In the formula , , Let k be the grid voltage signal of the wind power system at time k. , Let the phase and frequency of the wind power system grid be at time k. This is the initial phase of the power grid. The sampling period.

[0029] Step 1.2 involves performing a coordinate transformation, or Clarke transformation, on the wind power system grid voltage signal sampled in Step 1.1. The purpose of this transformation is to convert the signal from a three-phase stationary coordinate system to a two-phase stationary coordinate system, providing data for the subsequent second coordinate transformation. The Clarke transformation formula is as follows: In the formula, , Let be the signal in the two-phase stationary coordinate system at time k.

[0030] Step 1.3: Construct an orthogonal signal estimator from the signals obtained in Step 1.2, the expression of which is as follows: In the formula, It is the k-th time pair The estimated signal, It is the k-th time pair The estimated orthogonal signals, At time k-1, The estimated signal, It is the (k-1)th time pair The estimated orthogonal signals, It is the estimated frequency at time k-1, derived from the output of step two at the previous time. Here are the estimator parameters; they can be 0.707 or 1. The above formula is for the signal... The constructed orthogonal signal estimator, for the signal The same expression can be used to construct an orthogonal signal estimator.

[0031] The purpose of the steps in Step 1 is to perform preliminary processing on the obtained wind turbine voltage signal. The orthogonal signal estimator filters the original signal and obtains an estimated orthogonal signal. This step is a routine operation for voltage frequency and phase estimation.

[0032] Step 2: Construct a voltage frequency estimator; Step 2.1: Based on the estimated signal obtained in Step 1.3, calculate the error signal required by the voltage frequency estimator, the expression of which is as follows: In the formula, , The error signal at time k Step 2.2: Based on the error signal obtained in Step 2.1, construct a voltage-frequency estimation device. The estimator expression is as follows: In the formula, As an intermediate variable for the frequency estimator, This is an estimate of the voltage frequency at time k. The control parameter is the estimated value of the rate of change of voltage frequency at time k. , These are the voltage and frequency normalization coefficients, used to eliminate the influence of frequency and voltage amplitude on the estimator control loop. Their expression is: .

[0033] The purpose of step two is to estimate the voltage frequency and the rate of frequency change. The estimated rate of frequency change can be used to calculate the final estimated phase in step four. This step constructs a frequency estimator by calculating the error signal in step 2.1. The error is negative when the estimated frequency is less than the actual frequency, and positive otherwise. This relationship is used to calculate the frequency and the rate of frequency change. Compared to similar methods, it can estimate the rate of frequency change simultaneously with the estimated frequency.

[0034] Step 3: Construct a voltage phase estimator; Step 3.1: Based on the estimated signal obtained in Step 2, calculate the error signal of the phase estimator, whose expression is as follows: In the formula, The error signal of the phase estimator at time k is calculated. The estimated value of the phase estimator at time k-1 is obtained from step 3.2; Step 3.2: Based on the error signal, construct a voltage phase estimator, the expression of which is as follows: In the formula, As an intermediate variable for the phase estimator, The estimated phase for the phase estimator, , The control parameters are 92 and 4232, respectively.

[0035] Step 4: Correct the estimated phase based on phase correction.

[0036] The final estimated phase expression obtained based on phase correction is: .

[0037] This is the estimated phase at time k, which is the final calculated phase. The purpose of this step is to compensate for the phase error generated by the conventional second-order phase-locked loop algorithm when encountering a frequency ramp signal when estimating the grid phase. The phase error a / ki is obtained by establishing the transfer function of the phase estimation algorithm and using the final value theorem.

[0038] Firstly, while conventional second-order phase-locked loops (PLLs) have a fast dynamic response, they suffer from steady-state estimation errors under time-varying frequency conditions. Secondly, although third-order PLLs can eliminate steady-state errors, they suffer from poor dynamic performance. This invention addresses this issue by using a proposed frequency estimator to estimate the frequency change rate (a / ki) of a second-order PLL when facing a frequency ramp signal. This estimated value is then used to eliminate the impact of continuous frequency changes on phase estimation. This method maintains good dynamic performance while eliminating phase estimation errors, and it is simple and easy to implement.

[0039] like Figure 2 As shown, a wind turbine voltage frequency and phase estimation device based on phase correction includes a voltage signal acquisition unit, a coordinate transformer, an orthogonal signal estimator, a voltage frequency estimator, a voltage phase estimator, and a phase corrector. The voltage signal is collected by a voltage signal acquisition device, and the acquired signal is passed through a coordinate transformer. The voltage signal after coordinate transformation is then passed through an orthogonal signal estimator. The output signal of the orthogonal signal estimator is sent to a voltage frequency estimator, which calculates the voltage frequency and the rate of change of frequency. The voltage phase estimator calculates the voltage phase, and finally, the phase corrector calculates the voltage phase without steady-state error based on the estimated rate of change of frequency.

[0040] The effects of this invention are illustrated below with simulation results. The unit of the phase estimation error graph in the simulation results is degrees, and the unit of the frequency estimation error graph is Hz.

[0041] Figure 3 and Figure 4 The phase estimation error diagram for a 30-degree phase jump is given. Figure 3 ) and frequency estimation error plot ( Figure 4 As can be seen from the figure, compared with the conventional method (third-order phase-locked loop), the convergence process of the present invention is faster and the fluctuation is smaller, so the present invention has better dynamic performance.

[0042] Figure 5 and Figure 6 The phase estimation error diagram for the 5Hz frequency jump is given. Figure 5 ) and frequency estimation error plot ( Figure 6 As can be seen from the figure, compared with the conventional method (third-order phase-locked loop), the convergence process of the present invention is faster and the fluctuation is smaller, which also proves that the present invention has better dynamic performance.

[0043] Figure 7 and Figure 8 A phase estimation error diagram for a continuously varying frequency of 20 Hz / s is given. Figure 7 ) and frequency estimation error plot ( Figure 8 As can be seen from the figure, the present invention has no steady-state error even when the frequency changes continuously, and its convergence process has smaller fluctuations. Therefore, the method proposed in this invention can effectively cope with the situation of continuous frequency changes and its performance is better.

Claims

1. A method for estimating the voltage frequency and phase of a wind turbine based on phase correction, characterized in that, Includes the following steps; Step 1: Collect the output voltage of the wind turbine generator and construct an orthogonal signal estimator to obtain the transformed estimated signal; Step 2: Based on the transformed estimated signal, construct a voltage frequency estimator and calculate the estimated frequency of the power grid; Step 3: Based on the estimated frequency of the power grid, construct a voltage phase estimator to obtain the preliminary calculated power grid phase; Step 4: Based on the estimated frequency and phase of the power grid, perform phase correction to adjust the estimated phase.

2. The method for estimating the voltage frequency and phase of a wind turbine based on phase correction according to claim 1, characterized in that, Step one specifically involves: Step 1.1: Use an analog-to-digital converter (ADC) to sample the single-phase voltage signal of the power grid; obtain the power grid voltage signal of the wind power system. Step 1.2: Perform a coordinate transformation, namely Clarke transformation, on the wind power system grid voltage signal obtained in Step 1.1; convert the signal in the three-phase stationary coordinate system into the signal in the two-phase stationary coordinate system. Step 1.3: Construct an orthogonal signal estimator from the signals in the two-phase stationary coordinate system obtained in Step 1.

2.

3. The method for estimating the voltage frequency and phase of a wind turbine based on phase correction according to claim 2, characterized in that, Step 1.1 specifically includes:

1. Ensure that the sampling frequency satisfies the Nyquist sampling theorem, that is, the sampling frequency is at least twice the highest frequency of the signal; 2. Within a specified time interval, continuously collect the instantaneous values ​​of single-phase voltage and convert the analog values ​​of the three-phase power grid into digital values. The analog values ​​refer to the continuous digital values ​​obtained after multiple instantaneous samplings. The expression for the sampled three-phase grid voltage is: In the formula , , Let k be the grid voltage signal of the wind power system at time k. Let k be the phase of the wind power system grid at time k. Let k be the grid frequency of the wind power system at time k. This is the initial phase of the power grid. The sampling period.

4. In the wind turbine voltage frequency and phase estimation method based on phase correction according to claim 3, in step 1.2, the Clarke variation is as follows: In the formula, , Let be the signal in the two-phase stationary coordinate system at time k.

5. In the method for estimating the voltage frequency and phase of a wind turbine based on phase correction according to claim 4, the expression for constructing the orthogonal signal estimator in step 1.3 is as follows: In the formula, It is the k-th time pair The estimated signal, It is the k-th time pair The estimated orthogonal signals, At time k-1, The estimated signal, It is the (k-1)th time pair The estimated orthogonal signals, It is the estimated frequency at time k-1, derived from the output of step two at the previous time. These are the estimator parameters.

6. The method for estimating the voltage frequency and phase of a wind turbine based on phase correction according to claim 5, characterized in that, Step two specifically involves: Step 2.1: Based on the estimated signal obtained in Step 1.3, calculate the error signal required by the voltage frequency estimator, the expression of which is as follows: In the formula, , Let be the error signal at time k; Step 2.2: Based on the error signal obtained in Step 2.1, construct a voltage-frequency estimation device. The estimator expression is as follows: In the formula, As an intermediate variable for the frequency estimator, This is the estimated value of the voltage frequency at time k. This is an estimate of the rate of change of voltage frequency at time k. The voltage and frequency normalization coefficients are expressed as follows: 。 7. The method for estimating the voltage frequency and phase of a wind turbine based on phase correction according to claim 6, characterized in that, Step three specifically involves: Step 3.1: Based on the estimated signal obtained in Step 1, calculate the error signal of the phase estimator, the expression of which is as follows: In the formula, The error signal of the phase estimator at time k is calculated. The estimated value of the phase estimator at time k-1 is derived from the estimated value in step 3.2 at the previous time. Step 3.2: Based on the error signal, construct a voltage phase estimator, the expression of which is as follows: In the formula, As an intermediate variable for the phase estimator, The estimated phase for the phase estimator, , These are control parameters.

8. The method for estimating the voltage frequency and phase of a wind turbine based on phase correction according to claim 1, characterized in that, Step four specifically involves: The final estimated phase expression obtained based on phase correction is: That is, the estimated phase at time k obtained by final calculation, where a / k i This is the calculated compensation value used to compensate for steady-state errors.

9. A wind turbine voltage-frequency and phase estimation device based on phase correction for implementing the method according to any one of claims 1-8, characterized in that, It includes a voltage signal acquisition unit, a coordinate transformer, an orthogonal signal estimator, a voltage frequency estimator, a voltage phase estimator, and a phase corrector; The voltage signal is collected by a voltage signal acquisition device, and the acquired signal is passed through a coordinate transformer. The voltage signal after coordinate transformation is then passed through an orthogonal signal estimator. The output signal of the orthogonal signal estimator is sent to a voltage frequency estimator, which calculates the voltage frequency and the rate of change of frequency. The voltage phase estimator calculates the voltage phase, and finally, the phase corrector calculates the voltage phase without steady-state error based on the estimated rate of change of frequency.

Images