A power grid parameter identification method and device based on frequency and harmonic error compensation

Abstract

The application discloses a power grid parameter identification method and device based on frequency and harmonic error compensation, comprising the following steps: step one, collecting a power grid voltage signal, and constructing a delay signal generator to obtain a delay signal; step two, based on the voltage signal and the delay signal, performing a first coordinate transformation to obtain a signal after coordinate transformation; step three, based on the signal after coordinate transformation, constructing a power grid frequency estimator to obtain an initial estimated phase and frequency; and step four, based on the signal after coordinate transformation and the initial estimated phase and frequency, constructing a power grid phase estimator to obtain a final estimated phase and frequency. On one hand, the method can effectively suppress the error caused by harmonic disturbance, and on the other hand, the method can eliminate the steady-state error caused by frequency fluctuation.

Description

Technical Field

[0001] This invention belongs to the field of electrical variable measurement technology, specifically relating to a method and device for identifying power grid parameters based on frequency and harmonic error compensation. Background Technology

[0002] With the rapid development of new energy power generation technologies, renewable energy sources such as wind power are being rapidly connected to the grid on a large scale. However, due to the fluctuating and uncontrollable nature of wind power output, centralized grid connection can easily introduce a large number of high-order harmonics, thereby reducing power quality and interfering with the normal operation of protection and control devices. Therefore, when identifying grid parameters, it is necessary to suppress harmonic interference to improve identification accuracy.

[0003] Currently, the main method for single-phase power grid parameter identification is phase-locked loop (PLL). For example, YF Wang and Y.W. Li, "A Grid Fundamental and Harmonic Component Detection Method for Single-Phase Systems," in IEEE Transactions on Power Electronics, vol. 28, no. 5, pp. 2204-2213, May 2013, explain that unlike three-phase power grids, single-phase power grids only have a single voltage signal. Therefore, orthogonal signal generators are required to achieve parameter identification within the PLL. Among various orthogonal signal generators, methods based on delayed signals are widely used due to their simplicity.

[0004] However, when the grid frequency fluctuates, the delay-based quadrature signal generator will produce output deviations, which will affect the estimation accuracy of the phase-locked loop (PLL) and lead to steady-state errors in phase estimation. Furthermore, due to the superposition of frequency changes and harmonic interference, the performance of the delay-based single-phase PLL is further deteriorated, making it difficult to achieve satisfactory results.

[0005] In summary, existing grid parameter identification methods based on delayed single-phase phase-locked loops have two main shortcomings: first, the steady-state identification accuracy decreases when facing harmonic interference; and second, frequency fluctuations can cause steady-state errors in the output. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a method and device for identifying power grid parameters based on frequency and harmonic error compensation. On the one hand, the method can effectively suppress the error caused by harmonic disturbances, and on the other hand, the method can eliminate the steady-state error caused by frequency fluctuations.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for identifying power grid parameters based on frequency and harmonic error compensation includes the following steps: measuring the power grid voltage signal and performing two coordinate transformations; constructing a power grid parameter estimator from the transformed signal; and calculating the final estimated frequency and phase using the power grid parameter estimator. Specifically, it includes the following steps: Step 1: Acquire the grid voltage signal and build a delay signal generator to obtain the delayed signal of the grid voltage signal; Step 2: Based on the grid voltage signal and its delay signal, perform a coordinate transformation to obtain the transformed signal; Step 3: Calculate the error signal based on the signal after coordinate transformation, and construct a power grid frequency estimator to obtain the estimated value of the power grid frequency; Step four: Based on the coordinate transformed signal, the error signal, and the estimated power grid frequency, construct a power grid phase estimator to obtain the final estimated phase and frequency.

[0008] Step one specifically involves: Step 1.1: Sample the single-phase voltage signal of the power grid using an analog-to-digital converter (ADC); (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 analog instantaneous values ​​of single-phase voltage are continuously collected, and these analog instantaneous values ​​are converted into digital values. The analog instantaneous values ​​refer to the continuous digital values ​​obtained after multiple instantaneous samplings. Choose an appropriate ADC resolution (ADC refers to analog-to-digital converter, and its sampling frequency is generally required to be more than ten times the grid frequency) to ensure sufficient sampling accuracy; the expression for the sampled single-phase grid voltage is: In the formula Let k be the single-phase grid voltage signal at time k. Let k be the power grid phase at time k. Let k be the power grid frequency at time k. This is the initial phase of the power grid. The sampling period; Step 1.2: Construct a delay signal generator based on the single-phase grid voltage signal sampled in Step 1.1. The output expression of the delay signal generator is: In the formula, The output of the delay signal generator, Let be the grid voltage signal at time kn, where n is the delay parameter, and its calculation formula is: .

[0009] Ts is the sampling period.

[0010] The purpose of this parameter is to calculate the number of delay points required for sampling T / 4 cycles.

[0011] Step two specifically involves: Based on the voltage signal and the delayed signal obtained in step one, a coordinate transformation, namely the Park transformation, is performed. The expression for the Park transformation process is as follows: In the formula, , This is the signal in the two-phase rotating coordinate system at time k, used for calculation in step three. The rotation angle at time k-1 is obtained from step four; each step at each time has an output, and this step uses the output of step four from the previous time.

[0012] Step three specifically involves: Step 3.1: Construct an error signal based on the signal in the two-phase rotating coordinate system at time k to eliminate the influence of voltage amplitude changes on the power grid parameter estimator. The expression of the error signal is as follows; In the formula, This is the error signal at time k. The purpose of this step is to eliminate the influence of voltage amplitude. Step 3.2: Based on the error signal obtained in Step 3.1 at time k, a single-phase power grid frequency estimator is constructed. The calculation result of the single-phase power grid frequency estimator includes the estimated value w of the power grid frequency; its expression is as follows: In the formula, This is the estimated power grid frequency at time k. This is the estimated power grid frequency at time k-1. This is the estimated power grid frequency at time k-2. Let be the intermediate variable at time k. It is an intermediate variable at time k-1. These are system control parameters. The purpose of these system control parameters is to implement a second-order low-pass filter. The design requirement for these system control parameters is that the amplitude response of signals with frequencies greater than 50Hz should be close to 0.

[0013] The purpose of this step is to calculate intermediate variables. And use this to calculate the estimated frequency of the power grid. .

[0014] Step four specifically involves: Step 4.1: Based on the signal after coordinate transformation and the initial estimated phase and frequency, calculate the intermediate variables. The expressions for the intermediate variables are as follows: In the formula, , is an intermediate variable at time k, used for the rotation angle in the coordinate transformation in step two. In conventional algorithms, it is generally used as the final phase estimate. For system parameters; Step 4.2: Based on the intermediate variables obtained in Step 4.1 at time k, calculate the power grid phase, the expression of which is as follows: In the formula, This is the grid phase estimate at time k, which is the final output grid phase estimate. .

[0015] A power grid parameter identification device based on frequency and harmonic error compensation. It includes a grid voltage acquisition unit, a delay signal generator, a Parker converter, a grid frequency estimator, and a grid phase estimator; The grid voltage acquisition device samples the grid voltage to obtain a digital signal. The sampled signal is then passed through a delay signal generator to obtain a signal delayed by a quarter cycle. The sampled digital signal and the delayed signal are then passed through a Parker transformer to obtain the voltage signal in a two-phase rotating coordinate system. A grid frequency estimator is constructed based on the transformed voltage. Finally, the output of the grid frequency estimator is input to the grid phase estimator to calculate the accurate grid phase signal after compensating for the interference caused by the frequency transformation and harmonic interference.

[0016] The beneficial effects of this invention are: This invention provides a method and apparatus for identifying power grid parameters based on frequency and harmonic error compensation. On the one hand, this method can effectively suppress errors caused by harmonic disturbances, and on the other hand, it can eliminate steady-state errors caused by frequency fluctuations.

[0017] The frequency estimation method of this invention adopts different calculation methods, which can greatly suppress the frequency estimation disturbance caused by harmonic interference; the phase estimation is compensated, which greatly eliminates the steady-state error caused by frequency fluctuations, harmonic interference and other factors. Attached Figure Description

[0018] Figure 1 This is a flowchart of the power grid parameter identification method implemented and provided by the present invention.

[0019] Figure 2 This is a schematic diagram of the structure of the power grid parameter identification method and device provided by the present invention.

[0020] Figure 3 This is a schematic diagram of phase estimation error under harmonic conditions provided by the present invention.

[0021] Figure 4 This is a schematic diagram of frequency estimation error under harmonic conditions provided by the present invention.

[0022] Figure 5 This is a schematic diagram of the phase estimation error under frequency jump conditions provided by the present invention.

[0023] Figure 6 This is a schematic diagram of frequency estimation error under frequency jump conditions provided by the present invention.

[0024] Figure 7 This is a schematic diagram of the phase estimation error under the phase jump condition provided by the present invention.

[0025] Figure 8 This is a schematic diagram of frequency estimation error under phase jump conditions provided by the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings.

[0027] like Figure 1 As shown, a method for identifying power grid parameters based on frequency and harmonic error compensation includes the following steps; Step 1: Acquire the grid voltage signal and construct a delay signal generator; Step 1.1 Sample the single-phase voltage signal of the power grid using an analog-to-digital converter (ADC). The function of the ADC is to convert the continuous analog voltage signal into a digital signal for subsequent digital signal processing. Specifically, this step includes the following key points: (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 voltage are continuously acquired within a specified time interval, and these analog values ​​are converted into digital values ​​to provide a data basis for subsequent signal processing and analysis. During this process, a suitable ADC resolution needs to be selected to ensure sufficient sampling accuracy. The expression for the sampled single-phase grid voltage is: In the formula Let k be the single-phase grid voltage signal at time k. , Let the grid phase and frequency be at time k. This is the initial phase of the power grid. The sampling period.

[0029] Step 1.2: Construct a delay signal generator based on the single-phase grid voltage signal sampled in Step 1.1. The output expression of the delay signal generator is: In the formula, The output of the delay signal generator, Let be the grid voltage signal at time kn, where n is the delay parameter, and its calculation formula is: .

[0030] The delay parameters are calculated to obtain an orthogonal signal delayed by a quarter of a period.

[0031] Step 2: Based on the voltage signal and delay signal obtained in Step 1, perform a coordinate transformation; Based on the voltage and delayed signals obtained in step one, a coordinate transformation, namely the Park transformation, is performed. The purpose of this coordinate transformation is to convert the rotating signal into a DC signal, facilitating subsequent single-phase power grid frequency and phase estimation. The expression for the Park transformation process is as follows: In the formula, , It is the signal in the two-phase rotating coordinate system at time k. The rotation angle at time k-1 is obtained from step four.

[0032] Step 3: Based on the signal obtained in Step 2, construct a power grid frequency estimator; Step 3.1: Construct an error signal based on the signal obtained in Step 2 in the two-phase rotating coordinate system. The purpose of this step is to eliminate the influence of voltage amplitude changes on the power grid parameter estimator. The expression for the error signal is as follows.

[0033] In the formula, Let be the error signal at time k.

[0034] Step 3.2: Construct a single-phase power grid frequency estimator based on the error signal obtained in Step 3.1, the expression of which is as follows: In the formula, , , These are the estimated grid frequency values ​​at times k, k-1, and k-2. , It is an intermediate variable at time k and time (k-1). These are system control parameters. The purpose of these parameters is to implement a second-order low-pass filter, and the design requirement is that the amplitude response of signals with frequencies greater than 50Hz should be close to 0.

[0035] Step 4: Based on the signals obtained in Step 2 and Step 3, construct a power grid phase estimator.

[0036] Step 4.1: Based on the signals obtained in Steps 2 and 3, calculate the intermediate variables. The expressions for the intermediate variables are as follows: In the formula, This is an intermediate variable at time k, which can be used for coordinate transformation in step two as a rotation angle; These are system parameters.

[0037] Step 4.2: Based on the intermediate variables obtained in Step 4.1, calculate the power grid phase, the expression of which is as follows: In the formula, This is the estimated power grid phase value at time k. .

[0038] Steps three and four constitute the core innovation of this invention. Compared with traditional delay-based single-phase phase-locked loops, the proposed single-phase power grid parameter estimator based on frequency and harmonic error compensation has been structurally improved.

[0039] 1. The calculation method for frequency estimation has been modified, which improves the frequency estimation's ability to resist harmonic interference; 2. To address the errors caused by power grid frequency fluctuations and harmonic interference, this invention first utilizes the proportional relationship between high-frequency disturbances introduced by harmonic interference in phase estimation and intermediate variables. This allows for the extraction of high-frequency disturbance compensation for the intermediate variables in the phase estimation. Then, to compensate for the steady-state error in phase estimation caused by frequency changes, the error value is calculated and applied to the phase estimation. In summary, this invention can effectively eliminate frequency / phase estimation errors caused by harmonics and frequency fluctuations.

[0040] The first two steps of this invention are based on a delay-type phase-locked loop algorithm. The frequency estimation structure in step three differs from conventional power grid parameter identification methods, achieving better filtering results. In step four, this invention calculates the rotation angle... Compensation can yield a phase estimate with smaller fluctuations under harmonic disturbances.

[0041] like Figure 2 As shown, it includes a grid voltage acquisition unit, a delay signal generator, a Parker converter, a grid frequency estimator, and a grid phase estimator; The grid voltage acquisition device samples the grid voltage to obtain a digital signal. The sampled signal is then passed through a delay signal generator to obtain a signal delayed by a quarter-cycle. The sampled digital signal and the delayed signal are then passed through a Parker transformer to obtain the voltage signal in a two-phase rotating coordinate system. Based on the transformed voltage, a grid frequency estimator is constructed. Finally, the output of the grid frequency estimator is input to the grid phase estimator to calculate the accurate grid phase signal after compensating for interference caused by frequency transformation and harmonic interference. The effectiveness of this invention is explained below with simulation results. In the simulation figures, the unit of phase estimation is degrees, and the unit of frequency estimation is Hz.

[0042] Figure 3 and Figure 4 The phase estimation errors are given for the 5th harmonic at 10% fundamental frequency amplitude, the 7th harmonic at 6% fundamental frequency amplitude, the 11th harmonic at 2% fundamental frequency amplitude, and the 13th harmonic at 2% fundamental frequency amplitude. Figure 3 ) and frequency estimation error ( Figure 4 As can be seen from the figure, the frequency and phase estimation of the present invention is significantly better than that of conventional methods, and its error is smaller.

[0043] Figure 5 and Figure 6 The phase estimation error under a 0.5Hz frequency jump is given. Figure 5 ) and frequency estimation error ( Figure 6 As can be seen from the figure, the phase estimation of the present invention has no steady-state error because it eliminates the phase / frequency estimation error of delay-type algorithms caused by frequency changes.

[0044] Figure 7 and Figure 8 The phase estimation error under a 30-degree phase jump is given. Figure 7 ) and frequency estimation error ( Figure 8 As can be seen from the figure, the present invention exhibits similar dynamic performance to conventional methods, which demonstrates that the present invention is not a simple method that sacrifices dynamic performance for filtering effect.

Claims

1. A method for power grid parameter identification based on frequency and harmonic error compensation, characterized in that, Includes the following steps; Step 1: Acquire the grid voltage signal and build a delay signal generator to obtain the delayed signal of the grid voltage signal; Step 2: Based on the grid voltage signal and its delay signal, perform a coordinate transformation to obtain the transformed signal; Step 3: Calculate the error signal based on the signal after coordinate transformation, and construct a power grid frequency estimator to obtain the estimated value of the power grid frequency; Step four: Based on the coordinate transformed signal, the error signal, and the estimated power grid frequency, construct a power grid phase estimator to obtain the final estimated phase and frequency.

2. The method of claim 1, wherein, 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 to obtain the single-phase power grid voltage signal; Step 1.2: Construct a delay signal generator based on the single-phase grid voltage signal obtained from step 1.

1.

3. The method of claim 2, wherein, The output expression of the delay signal generator is: In the formula, is the output of the delay signal generator, i.e. the delay signal, is the grid voltage signal at the k-n time instant, where n is a delay parameter, the calculation formula of which is: Ts is the sampling period.

4. The method of claim 2, wherein, In step 1.1, (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 analog instantaneous value of single-phase voltage, and convert the analog instantaneous value into a digital value. The analog instantaneous value refers to the continuous digital value obtained after multiple instantaneous samplings.

5. The method of grid parameter estimation based on frequency and harmonic error compensation according to claim 4, characterized in that, Choose an appropriate ADC resolution; the expression for the sampled single-phase grid voltage is: In the formula Let k be the single-phase grid voltage signal at time k. Let k be the power grid phase at time k. Let k be the power grid frequency at time k. This is the initial phase of the power grid. The sampling period.

6. The method of claim 1, wherein, Step two specifically involves: The coordinate transformation is a Park transformation, and the expression for the Park transformation process is as follows: In the formula, , This is the signal in the two-phase rotating coordinate system at time k, used for calculation in step three. The rotation angle at time k-1 is obtained from step four; each step at each time has an output, and the step at that time uses the output of step four from the previous time.

7. The power grid parameter identification method based on frequency and harmonic error compensation according to claim 6, characterized in that, Step three specifically involves: Step 3.1: Construct an error signal based on the signal in the two-phase rotating coordinate system at time k to eliminate the influence of voltage amplitude changes on the power grid parameter estimator. The expression of the error signal is as follows; In the formula, is the error signal at the kth moment; Step 3.2: Based on the error signal obtained in Step 3.1 at time k, a single-phase power grid frequency estimator is constructed. The calculation result of the single-phase power grid frequency estimator includes the estimated value of the power grid frequency; its expression is as follows: In the formula, This is the estimated power grid frequency at time k. This is the estimated power grid frequency at time k-1. This is the estimated power grid frequency at time k-2. Let be the intermediate variable at time k. It is an intermediate variable at time k-1. These are system control parameters. The design requirement for system control parameters is that the amplitude response of signals with a frequency greater than 50Hz should be close to 0.

8. The method of grid parameter estimation based on frequency and harmonic error compensation according to claim 7, characterized in that, Step four specifically involves: Step 4.1: Based on the coordinate-transformed signal, the error signal, and the estimated power grid frequency, calculate the intermediate variables. The expressions for the intermediate variables are as follows: In the formula, is the intermediate variable at the kth moment, used for the rotation angle in the coordinate transformation in step two, as the final phase estimate; is a system parameter; Step 4.2: Based on the intermediate variables obtained in Step 4.1 at time k, calculate the power grid phase, the expression of which is as follows: In the formula, is the grid phase estimation value at the kth moment, that is, the final output grid estimation phase .

9. A power grid parameter identification device based on frequency and harmonic error compensation for implementing the method of any one of claims 1-8, comprising a power grid voltage collector, a delay signal generator, a Park converter, a power grid frequency estimator, and a power grid phase estimator. The grid voltage acquisition device samples the grid voltage to obtain a digital signal. The sampled signal is then passed through a delay signal generator to obtain a signal delayed by a quarter cycle. The sampled digital signal and the delayed signal are then passed through a Parker transformer to obtain the voltage signal in a two-phase rotating coordinate system. A grid frequency estimator is constructed based on the transformed voltage. Finally, the output of the grid frequency estimator is input to the grid phase estimator to calculate the accurate grid phase signal after compensating for the interference caused by the frequency transformation and harmonic interference.

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