Frequency estimation system and method based on composite second-order generalized integrator-frequency-locked loop

Abstract

The invention belongs to the technical field of power systems, and provides a frequency estimation system and method based on a composite second-order generalized integrator-frequency-locked loop. The frequency estimation system based on the composite second-order generalized integrator-frequency-locked loop comprises an i-phase two-stage series second-order generalized integrator-orthogonal signal generator, the input signal of which is an i-phase voltage signal vi and an estimation frequency fed back by the frequency-locked loop, and is configured to convert vi into a signal vi'with the same frequency and the same phase as vi, simultaneously obtaining a signal qvi'and a voltage estimation error epsilon vi, wherein the frequency of the signal qvi 'is the same as that of the vi', and the phase lag is 90 degrees; the frequency-locked loop gain normalization module is configured to normalize the output signal; multiplying the voltage estimation error epsilon vi by the signal qvi'and the adaptive gain to obtain a frequency error variable of a corresponding phase; the phase-locked loop is configured to add the frequency error variables of the alpha phase and the beta phase, then multiply the frequency error variables of the alpha phase and the beta phase with the gain constant coefficient-gamma and the normalized gain coefficient A, and then perform integration to obtain the estimated frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and particularly relates to a frequency estimation system and method based on a composite second-order generalized integrator-frequency locked loop. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] With the increasing proportion of renewable energy such as photovoltaic and wind power being connected to the grid, quickly and accurately estimating the grid frequency is an important basis for ensuring the stability of the power system. Traditional frequency measurement methods mainly include zero-crossing detection method, discrete Fourier transform method, error minimization, frequency locked loop, and second-order generalized integrator, etc. Among them, the zero-crossing detection method is affected by harmonics, noise, and non-periodic components and is not accurate enough; the discrete Fourier transform method has a long sampling period, which will cause a deviation between the calculated frequency value and the frequency value at the current moment, and there are also problems such as large computational complexity; error minimization includes the least squares method and Newton iteration algorithm, etc., which are computationally complex and are easily affected by algorithm parameter settings and initial values. The frequency locked loop includes various methods, either difficult to cope with the problem of sudden changes in grid voltage, or computationally complex and with a large amount of calculation. It is difficult to be applied to the real-time changing grid frequency estimation.

[0004] The second-order generalized integrator-frequency locked loop can quickly and accurately extract the frequency, amplitude, and phase of the fundamental wave signal of the grid voltage, and performs well in terms of dynamic response and steady-state error. The gain of the frequency locked loop can be used to adjust its performance and is directly related to the bandwidth of the frequency locked loop. A fast response of frequency estimation requires a large bandwidth. However, this increases the coupling level between the input signal amplitude and the estimated frequency. When the input signal contains low-order harmonics or the amplitude changes suddenly, it will cause the information extracted by the second-order generalized integrator-frequency locked loop to be distorted. Summary of the Invention

[0005] In order to solve the technical problems existing in the above background technique, the present invention provides a frequency estimation system and method based on a composite second-order generalized integrator-frequency locked loop, which can quickly and smoothly track the grid frequency, enhance the ability to suppress harmonics and noise, and improve the accuracy of frequency estimation.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a frequency estimation system based on a composite second-order generalized integrator-frequency locked loop.

[0008] A frequency estimation system based on a composite second-order generalized integrator - phase-locked loop, comprising: a two-stage series-connected second-order generalized integrator - quadrature signal generator for the i-phase, a phase-locked loop gain normalization module, and a phase-locked loop; i = α, β; the damping coefficient of each stage of the second-order generalized integrator - quadrature signal generator is equal to k;

[0009] The input signal of the two-stage series-connected second-order generalized integrator - quadrature signal generator for the i-phase is the i-phase voltage signal v i and the estimated frequency fed back by the phase-locked loop, and is configured to: convert v i into a signal v i ' with the same frequency and the same phase as it, and at the same time obtain a signal qv i ' with the same frequency as v i ' and a phase lag of 90° and a voltage estimation error ε vi ;

[0010] The phase-locked loop gain normalization module is configured to: calculate the sum of the squares of the signals v i ' of the two phases and the signals qv i ', normalize the two sums of squares respectively using the weight coefficient 0.5 to obtain the normalized output signals of the corresponding phases; and multiply the voltage estimation error ε vi by the signal qv i ' and the adaptive gain to obtain the frequency error variable of the corresponding phase; the adaptive gain is adaptively adjusted according to the estimation error of the corresponding phase voltage signal;

[0011] The phase-locked loop is configured to: after adding the frequency error variables of the α and β phases, multiply by the gain constant coefficient -Γ and the normalized gain coefficient A and then integrate to obtain the estimated frequency; wherein, the normalized gain coefficient A is obtained by dividing the product of the estimated frequency fed back by the phase-locked loop and the damping coefficient k by the sum of the normalized output signals of the α and β phases.

[0012] The second aspect of the present invention provides a frequency estimation method based on a composite second-order generalized integrator - phase-locked loop.

[0013] A frequency estimation method based on a composite second-order generalized integrator - phase-locked loop, comprising:

[0014] The i-phase voltage signal v i is converted by a two-stage series-connected second-order generalized integrator - quadrature signal generator into a signal v i ' with the same frequency and the same phase, a signal qv i ' with the same frequency as v i ' and a phase lag of 90° and a voltage estimation error ε vi ; wherein, i = α, β; the damping coefficient of each stage of the second-order generalized integrator - quadrature signal generator is equal to k;

[0015] Calculate the signals v of the two phases i ′ and the signal qv i ′ of the sum of squares, and use the weight coefficient 0.5 to normalize the two sums of squares respectively to obtain the normalized output signals of the corresponding phases; the voltage estimation error ε vi and the signal qv i ′ are multiplied by the adaptive gain to obtain the frequency error variables of the corresponding phases; the adaptive gain is adaptively adjusted according to the estimation error of the corresponding phase voltage signal;

[0016] After adding the frequency error variables of the α and β phases, multiplying by the gain constant coefficient -Γ and the normalized gain coefficient A and then integrating to obtain the estimated frequency and feedback it to the input end of the first-stage second-order generalized integrator-orthogonal signal generator of the i-phase; among them, the normalized gain coefficient A is obtained by dividing the product of the estimated frequency and the damping coefficient k fed back by the phase-locked loop by the sum of the normalized output signals of the α and β phases.

[0017] The beneficial effects of the present invention are as follows:

[0018] The present invention uses a two-stage cascaded second-order generalized integrator-orthogonal signal generator to convert the α and β phase voltage signals corresponding to the input voltage signal into α and β phase voltage estimation errors, uses a phase-locked loop gain normalization module to normalize the output signals of the two-stage cascaded second-order generalized integrator-orthogonal signal generator, and calculates the frequency error variables of the corresponding phases according to the adaptive gain, and uses the adaptive gain to adjust according to the amplitude deviation level, which can alleviate the frequency estimation error caused by the coupling effect of amplitude and frequency during instantaneous amplitude changes and quickly and smoothly track the power grid frequency.

[0019] The advantages of the additional aspects of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0020] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0021] Figure 1 is a schematic structural diagram of a frequency estimation system based on a composite second-order generalized integrator-phase-locked loop according to an embodiment of the present invention;

[0022] Figure 2 is a flowchart of a frequency estimation method based on a composite second-order generalized integrator-phase-locked loop according to an embodiment of the present invention;

[0023] Figure 3 is the estimated frequency of three algorithms when the amplitude step changes suddenly. Detailed implementation manners

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise clearly specified in the context, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] The frequency estimation method of the present invention is based on an adaptive composite second-order generalized integrator-frequency-locked loop. By means of the adaptive gain μ, the gain of the frequency-locked loop has self-adaptability and can be adjusted according to the amplitude deviation level, quickly and smoothly tracking the power grid frequency. The adaptive mechanism adjusts the gain of the frequency-locked loop to alleviate the frequency estimation error caused by the coupling effect of amplitude and frequency when the amplitude changes instantaneously.

[0028] As Figure 1 shown, a frequency estimation system based on a composite second-order generalized integrator-frequency-locked loop according to an embodiment of the present invention is characterized by including: a two-stage series second-order generalized integrator-quadrature signal generator for the i phase, a frequency-locked loop gain normalization module, and a frequency-locked loop (FLL); i = α, β; the damping coefficients of each stage of the second-order generalized integrator-quadrature signal generator are all equal to k. Among them, the two-stage series second-order generalized integrator-quadrature signal generators of the two phases form Figure 1 the CSOGI-QSG in

[0029] The input signal of the two-stage series second-order generalized integrator-quadrature signal generator for the i phase is the i-phase voltage signal v i and the estimated frequency fed back by the frequency-locked loop, and is configured to: convert v i into a signal v i ′ with the same frequency and the same phase as it, and at the same time obtain a signal qv i ′ with the same frequency as v i ′ and a phase lag of 90° and a voltage estimation error εv i ;

[0030] The frequency-locked loop gain normalization module is configured to: calculate the signals v i ′ of the two phases and the signal qvi The sum of squares of ′, and the two sums of squares are normalized respectively using the weight coefficient 0.5 to obtain the normalized output signals of the corresponding phases; and the voltage estimation error εv i and the signal qv i ′ are multiplied by the adaptive gain to obtain the frequency error variables of the corresponding phases; the adaptive gain is adaptively adjusted according to the estimation error of the corresponding phase voltage signal;

[0031] The phase-locked loop is configured to: after adding the frequency error variables of the α and β phases, multiply by the gain constant coefficient and the normalized gain coefficient A and then integrate to obtain the estimated frequency; wherein, the normalized gain coefficient A is obtained by dividing the product of the estimated frequency fed back by the frequency-locked loop and the damping coefficient k by the sum of the normalized output signals of the α and β phases.

[0032] Specifically, the input signal of the two-stage cascaded second-order generalized integrator - quadrature signal generator of the α phase is the α-phase voltage signal v α , and is configured to: convert vα into a signal v′ with the same frequency and the same phase as it α , and at the same time obtain a signal qν′ with the same frequency as v′ α and a phase lag of 90° α and the α-phase voltage estimation error εv α .

[0033] The input signal of the two-stage cascaded second-order generalized integrator - quadrature signal generator of the β phase is the β-phase voltage signal v β , and is configured to: convert v β into a signal v′ with the same frequency and the same phase as it β , and at the same time obtain a signal qv′ with the same frequency as v′ β and a phase lag of 90° β and the β-phase voltage estimation error ε vβ .

[0034] The transfer functions of the two-stage cascaded second-order generalized integrator - quadrature signal generators of the α and β phases are:

[0035]

[0036] wherein, G εα (s), G εβ (s) are the transfer functions of the two-stage cascaded second-order generalized integrator - quadrature signal generators of the α and β phases respectively. k1 and k2 are the damping coefficients of the two-stage cascaded second-order generalized integrator - quadrature signal generator in the α phase; k3 and k4 are the damping coefficients of the two-stage cascaded second-order generalized integrator - quadrature signal generator in the β phase; k1 = k2 = k3 = k4 = k; ω′ is the estimated frequency.

[0037] It should be noted here that the working principle of each stage of the second-order generalized integrator-orthogonal signal generator is the same. When the input signal of the first-stage second-order generalized integrator-orthogonal signal generator is v = Vsin(ωt), the two output signals of the first-stage second-order generalized integrator-orthogonal signal generator are respectively:

[0038]

[0039] V is the amplitude of the input voltage signal; λ is a constant coefficient and is greater than zero; ω is the frequency of the input signal.

[0040] The magnitude of the constant coefficient λ is determined by the damping coefficient k of the second-order generalized integrator-orthogonal signal generator, and its calculation formula is: k < 2, and the general value is

[0041] In the frequency-locked loop gain normalization module, when the estimation error of the α and β phase voltage signals is above 0.1, the adaptive gain decreases from 1; when the estimation error of the α and β phase voltage signals approaches zero, the adaptive gain approaches 1.

[0042] In the frequency-locked loop gain normalization module, the calculation formula for the frequency error variable is:

[0043]

[0044] and ε fβ are the frequency error variables of the α and β phases respectively;

[0045] The adaptive gain is:

[0046]

[0047] where μ i is the adaptive gain of the i phase; i = α, β; V is the amplitude of the input voltage signal; λ is a constant coefficient and is greater than zero.

[0048] In the frequency-locked loop, the normalized gain coefficient A is:

[0049]

[0050] The gain constant coefficient is set as Γ, and it can be determined by the following formula:

[0051]

[0052] where t s is the adjustment time.

[0053] In one embodiment of the present invention, a simulation is designed where the amplitude steps from 1V to 2V at 5s. Based on the method proposed by the present invention, the estimation results are as follows Figure 3 shown. Compared with the traditional DSOGI-FLL (Double Second-Order Generalized Integrator Frequency Locked Loop) and CSOGI-FLL (Cascaded Second-Order Generalized Integrator Frequency Locked Loop), the frequency estimation system of the embodiment of the present invention has significantly better frequency accuracy, and its frequency estimation error is less affected by amplitude disturbances, enhancing the anti-amplitude disturbance ability. This is because the structure of the cascaded second-order generalized integrator - orthogonal signal generator is equivalent to adding a pre-stage filter on the basis of DSOGI-FLL, so its anti-disturbance ability will be better. However, at the same time, the present invention introduces more integrators by using the cascaded second-order generalized integrator - orthogonal signal generator, and its frequency dynamic response speed will also slow down accordingly.

[0054] In one or more embodiments, a frequency estimation method based on a composite second-order generalized integrator - frequency locked loop is further provided, including:

[0055] Step 1: The i-phase voltage signal v i is converted into a signal v i ′ with the same frequency and the same phase through two cascaded second-order generalized integrator - orthogonal signal generators, and a signal qv i ′ with the same frequency as v i ′ and a phase lag of 90°, and a voltage estimation error ε vi ; where i = α, β; the damping coefficients of each stage of the second-order generalized integrator - orthogonal signal generator are all equal to k;

[0056] Step 2: Calculate the sum of squares of the signals v i ′ of the two phases and the signals qv i ′, normalize the two sums of squares respectively using the weight coefficient 0.5 to obtain the normalized output signals of the corresponding phases; multiply the voltage estimation error ε vi with the signal qv i ′ and the adaptive gain to obtain the frequency error variable of the corresponding phase; the adaptive gain is adaptively adjusted according to the estimation error of the corresponding phase voltage signal;

[0057] Step 3: After adding the frequency error variables of the α and β phases, multiply the sum by the gain constant coefficient -Γ and the normalized gain coefficient A and then integrate to obtain the estimated frequency and feedback it to the input end of the first-stage second-order generalized integrator - orthogonal signal generator of the i-phase; where the normalized gain coefficient A is obtained by dividing the product of the estimated frequency fed back by the frequency locked loop and the damping coefficient k by the sum of the normalized output signals of the α and β phases.

[0058] In step 2, when the estimation error of the α and β phase voltage signals is above 0.1, the adaptive gain decreases from 1. When the estimation error of the α and β phase voltage signals approaches zero, the adaptive gain approaches 1.

[0059] The adaptive gain is as follows:

[0060]

[0061] where μ i is the adaptive gain of the i-th phase; V is the amplitude of the input voltage signal; λ is a constant coefficient and is greater than zero.

[0062] The magnitude of the constant coefficient λ is determined by the damping coefficient k of the second-order generalized integrator - quadrature signal generator, and its calculation formula is:

[0063] The present invention overcomes the problem that when the input signal contains low-order harmonics or the amplitude changes suddenly, the information extracted by the second-order generalized integrator - frequency-locked loop will be distorted. This method can quickly and smoothly track the power grid frequency, enhance the ability to suppress harmonics and noise, and improve the accuracy of frequency estimation.

[0064] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A frequency estimation system based on a composite second-order generalized integrator - phase-locked loop, characterized in that Including: The second-order generalized integrator-orthogonal signal generator in series of two stages in the i-phase, the frequency-locked loop gain normalization module, and the frequency-locked loop; i = α, β; the damping coefficients of each stage of the second-order generalized integrator-orthogonal signal generator are equal and are k; The input signal of the two-stage cascaded second-order generalized integrator-quadrature signal generator of the i-phase is the i-phase voltage signal v i and the estimated frequency fed back by the frequency-locked loop, and is configured to: convert v i into a signal v i ′ with the same frequency and the same phase as it, and at the same time obtain a signal qv i ′ with the same frequency as v i ′ and a phase lag of 90° and a voltage estimation error ε vi ; The frequency-locked loop gain normalization module is configured to: calculate the sum of squares of the signals v i ′ of two phases and the signal qv i ′, normalize the two sums of squares respectively using the weight coefficient 0.5 to obtain the normalized output signals of the corresponding phases; and multiply the voltage estimation error ε vi by the signal qv i ′ and the adaptive gain to obtain the frequency error variables of the corresponding phases; the adaptive gain is adaptively adjusted according to the estimation error of the corresponding phase voltage signal; The phase-locked loop is configured to: after adding the frequency error variables of the α and β phases, multiply the result by the gain constant coefficient -Γ and the normalization gain coefficient A, and then perform integration to obtain the estimated frequency; wherein, the normalization gain coefficient A is obtained by dividing the product of the estimated frequency fed back by the frequency-locked loop and the damping coefficient k by the sum of the normalized output signals of the α and β phases.

2. The frequency estimation system based on a composite second-order generalized integrator-frequency locked loop according to claim 1, wherein In the frequency-locked loop gain normalization module, when the estimated error of the voltage signals of the α and β phases is 0.1 or more, the adaptive gain decreases from 1.

3. The frequency estimation system based on a composite second-order generalized integrator-frequency locked loop according to claim 1, characterized in that, In the frequency-locked loop gain normalization module, when the estimated error of the voltage signals of the α and β phases approaches zero, the adaptive gain approaches 1.

4. The frequency estimation system based on a composite second-order generalized integrator-frequency locked loop according to claim 1, wherein, In the frequency-locked loop gain normalization module, the adaptive gain is: where μ i is the adaptive gain of the i-th phase; V is the amplitude of the input voltage signal; λ is a constant coefficient and is greater than zero.

5. The frequency estimation system based on the composite second-order generalized integrator-frequency locked loop according to claim 4, characterized in that, The magnitude of the constant coefficient λ is determined by the damping coefficient k of the second-order generalized integrator-orthogonal signal generator, and its calculation formula is:

6. A frequency estimation method based on a composite second-order generalized integrator-frequency locked loop, characterized in that, Including: The phase-i voltage signal v i is converted into signals v i ′ with the same frequency and in-phase through two cascaded second-order generalized integrator - quadrature signal generators i ′, the signal qv i ′ with the same frequency as v vi ′ and a phase lag of 90°, and the voltage estimation error ε; where i = α, β; the damping coefficients of each second-order generalized integrator - quadrature signal generator are equal and are k; Calculate the signals v of the two phases i ′ and the signal qv i ′ of the sum of squares, and use the weight coefficient 0.5 to normalize the two sums of squares respectively to obtain the normalized output signals of the corresponding phases; the voltage estimation error ε vi and the signal qv i ′ are multiplied by the adaptive gain to obtain the frequency error variables of the corresponding phases; the adaptive gain is adaptively adjusted according to the estimation error of the corresponding phase voltage signal; After adding the frequency error variables of the α and β phases, multiply the result by the gain constant coefficient -Γ and the normalization gain coefficient A, and then perform integration to obtain the estimated frequency and feed it back to the input end of the first-stage second-order generalized integrator-orthogonal signal generator in the i-phase; wherein, the normalization gain coefficient A is obtained by dividing the product of the estimated frequency fed back by the frequency-locked loop and the damping coefficient k by the sum of the normalized output signals of the α and β phases.

7. The frequency estimation method based on a composite second-order generalized integrator-frequency locked loop according to claim 6, characterized in that When the estimated error of the voltage signals of the α and β phases is 0.1 or more, the adaptive gain decreases from 1.

8. The frequency estimation method based on a composite second-order generalized integrator - phase-locked loop according to claim 6, characterized in that When the estimated error of the voltage signals of the α and β phases approaches zero, the adaptive gain approaches 1.

9. The frequency estimation method based on a composite second-order generalized integrator-frequency locked loop according to claim 6, characterized in that The adaptive gain is: where, μ i is the adaptive gain of the i-th phase; V is the amplitude of the input voltage signal; λ is a constant coefficient and is greater than zero.

10. The frequency estimation method based on a composite second-order generalized integrator-frequency locked loop according to claim 9, characterized in that, The magnitude of the constant coefficient λ is determined by the damping coefficient k of the second-order generalized integrator-orthogonal signal generator, and its calculation formula is:

Images