An improved orthogonal signal generator and a new strong anti-interference phase-locked loop structure

Abstract

The present invention discloses an improved orthogonal signal generator and a novel strong anti-interference phase-locked loop structure. The improved orthogonal signal generator is improved on the basis of a second-order generalized integrator and is designed with a high-pass filter and a band-pass filter in parallel. It overcomes the defect that the quadrature-axis component of the traditional second-order generalized integrator can be regarded as a low-pass filter and cannot filter out the influence of the DC component and subharmonic components. The novel strong anti-interference phase-locked loop structure combines the improved orthogonal signal generator with the traditional phase-locked loop, which can not only suppress the influence of harmonics on phase synchronization, but also accurately achieve adaptive synchronization of the output signal to the input signal when the phase of the system suddenly changes. The novel strong anti-interference phase-locked loop structure has a strong attenuation effect on DC and interharmonic components, and is suitable for environments with high DC offset and interharmonic interference in power grids.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics technology, and specifically relates to an improved orthogonal signal generator and a novel strong interference-resistant phase-locked loop structure. The novel strong interference-resistant phase-locked loop structure is suitable for power grid environments containing relatively high DC and interharmonic components, and can improve the synchronization stability of the grid-connected system. Background Art

[0002] In power systems, the characteristics of AC power grids require that all power sources in the system operate at the same frequency. Therefore, when the system is in steady-state operation, the frequency of each power source converges to a constant frequency, and the phase difference between each power source remains fixed, thus enabling power transmission. Consequently, scholars have proposed a variety of phase synchronization techniques in recent years, including methods based on zero-crossing detection, Kalman filters, weighted least squares estimation, and recursive discrete Fourier transforms. Among these, phase-locked loops (PLLs) have been widely used in power systems due to their simple structure and ease of implementation.

[0003] In ideal three-phase grid-connected systems, the most commonly used phase-locked loop (PLL) technology is based on a synchronous rotating coordinate system. This technology utilizes rotating coordinate system transformations to perform the phase detector function, offering fast dynamic response and simple software implementation. However, in single-phase grid-connected systems, since there is only one voltage phasor, direct coordinate system transformation is not possible, making synchronous rotating coordinate system implementation more difficult. To address this issue, a common approach is to use an orthogonal signal generator to generate a voltage phasor of equal amplitude and orthogonal to the input voltage, thereby completing the rotating coordinate system transformation. The second-order generalized integrator has attracted considerable attention in recent years due to its simple structure, low computational complexity, frequency adaptability, and excellent filtering capabilities, making it an ideal choice for single-phase PLLs.

[0004] Second-order generalized integrator-based phase-locked loops (SOGI_PLLs) can solve phase synchronization issues during grid connection and are widely used. However, transient grid faults, grid voltage measurement and sampling, and A / D signal processing introduce DC components. Large voltage fluctuations and impactful nonlinear loads also introduce interharmonic components. Traditional SOGI_PLLs are ineffective at filtering out DC and interharmonic components. Therefore, in grid environments with high DC and interharmonic components, the phase-locked loop performance is significantly degraded, resulting in steady-state errors in the phase estimation and even synchronization instability during the grid connection process. Therefore, in order to ensure that grid-connected converters reliably synchronize with the grid in such grid environments, research is needed on higher-performance second-order generalized integrator phase-locked loops to meet practical requirements. Summary of the Invention

[0005] The purpose of the present invention is to address the problem that when the grid voltage contains high DC components and interharmonic components, the traditional second-order generalized integrator phase-locked loop system does not adequately attenuate the DC components and interharmonic components, resulting in large fluctuations in the detected grid synchronization signal and even system phase-lock failure. The present invention proposes an improved orthogonal signal generator and a new strong anti-interference phase-locked loop structure to achieve greater attenuation of the DC components and subharmonic components. Through simulation experiments, it is verified that the new strong anti-interference phase-locked loop structure designed by the present invention further improves the filtering performance of the DC components and interharmonic components, further optimizes the phase synchronization effect, and has a very significant effect on improving the synchronization stability of the grid-connected system. It is particularly suitable for application scenarios where weak grids have many downsampling and signal processing links, large voltage fluctuations, and grid frequency and phase are prone to sudden changes.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: designing an improved orthogonal signal generator, characterized by comprising a first negative feedback circuit, a first proportional link, a second negative feedback circuit, a first resonant link, a first integral link, a second resonant link, a second integral link, a third negative feedback circuit, a second proportional link, a fourth negative feedback circuit, a third resonant link, a third integral link, a fourth resonant link, and a fourth integral link;

[0007] An input voltage v is input from the positive input terminal of a comparison point of a first negative feedback circuit; an output terminal of the comparison point of the first negative feedback circuit is input to a first proportional link; an output terminal of the comparison point of the second negative feedback circuit is input to the positive input terminal of a comparison point of a second negative feedback circuit; an output terminal of the comparison point of the second negative feedback circuit is input to the positive input terminal of a comparison point of a third negative feedback circuit on the one hand, and to the first resonant link on the other hand; an output terminal of the first resonant link is input to a first integral link; an output terminal of the first integral link is input to the first negative feedback circuit on the one hand, and to the second integral link on the other hand; an estimated value ω' of the grid voltage frequency is input to the first resonant link and the second resonant link respectively; an output terminal of the second integral link is input to the second resonant link; and an output terminal of the second resonant link is input to the negative input terminal of a comparison point of a second negative feedback circuit;

[0008] The output of the output terminal of the comparison point of the third negative feedback circuit is input into the second proportional link, the output of the second proportional link is input into the positive input terminal of the comparison point of the fourth negative feedback circuit, the output of the output terminal of the comparison point of the fourth negative feedback circuit is input into the third resonant link, the output of the third resonant link is input into the third integral link, and the output of the third integral link is input into the third negative feedback circuit and the fourth integral link respectively; at the same time, the grid voltage frequency estimated value ω' is input into the third resonant link and the fourth resonant link respectively, the output of the fourth integral link is input into the fourth resonant link, and the output of the fourth resonant link is input into the negative input terminal of the comparison point of the fourth negative feedback circuit;

[0009] The output of the first integration link is the first orthogonal signal v α The output of the third integration link is the second orthogonal signal v' β , the phase difference between the first orthogonal signal and the second orthogonal signal is 90°;

[0010] The first orthogonal signal transfer function D(s) and the second orthogonal signal transfer function Q'(s) are respectively:

[0011]

[0012]

[0013] Where, v is the input voltage, v α is the first orthogonal signal, v' β is the second orthogonal signal, k1 and k2 are proportional coefficients, ω' is the estimated value of the grid voltage frequency, and s is the Laplace operator.

[0014] Furthermore, the present invention designs a novel strong anti-interference phase-locked loop structure, characterized in that the structure includes the improved orthogonal signal generator as described above and also includes a phase-locked loop; the first orthogonal signal and the second orthogonal signal output by the improved orthogonal signal generator are processed through a Park transform link, wherein the expression of the Park transform is:

[0015]

[0016] The q-axis component v at the output of the Park transformation link q The frequency output by the phase-locked loop is used as the grid voltage frequency estimation value ω' and is input into the four resonant links of the improved orthogonal signal generator respectively; the phase θ' output by the phase-locked loop is used as the grid voltage phase estimation value and is input into the Park transformation link.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the improved orthogonal signal generator designed by the present invention is improved on the basis of the second-order generalized integrator, and is designed with a structure in which a high-pass filter and a band-pass filter are in parallel, which overcomes the defect that the quadrature-axis component of the traditional second-order generalized integrator can be regarded as a low-pass filter and cannot filter out the influence of the DC component and subharmonic components. The new strong anti-interference phase-locked loop structure designed by the present invention combines the improved orthogonal signal generator with the traditional phase-locked loop, which can not only suppress the influence of harmonics on phase synchronization, but also accurately achieve adaptive synchronization of the output signal to the input signal when the phase of the system suddenly changes. The new strong anti-interference phase-locked loop structure has a strong attenuation effect on DC and interharmonic components, and is suitable for environments with high DC offset and interharmonic interference in power grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure shows the structure and principle of an improved orthogonal signal generator according to an embodiment of the present invention.

[0019] Figure 2 This is a structural and principle diagram of an embodiment of a novel strong anti-interference phase-locked loop structure of the present invention.

[0020] Figure 3 The structure and principle diagram of a phase-locked loop of an embodiment of a novel strong anti-interference phase-locked loop structure of the present invention (in the figure, k p Represents the proportional coefficient of the PI regulator, which is 8.88; T i represents the integral time constant of the PI regulator, which is 0.225; s is the Laplace operator; ω c Represents the fundamental frequency of the power grid, and its value is 100π).

[0021] Figure 4 The logarithmic amplitude-phase characteristic curve of the high-pass filter channel from the signal input terminal v to v' of an embodiment of an improved orthogonal signal generator of the present invention.

[0022] Figure 5 The logarithmic amplitude-phase characteristic curves of the direct-axis component transfer function D(s) and the quadrature-axis component transfer function Q'(s) of an improved orthogonal signal generator according to an embodiment of the present invention are shown.

[0023] Figure 6 This figure shows the filtering effects of the novel strong anti-interference phase-locked loop structure (SOGI^2_PLL) and the second-order generalized integrator phase-locked loop structure (SOGI_PLL) under the same conditions.

[0024] Figure 7 This is a phase synchronization diagram of the new strong anti-interference phase-locked loop structure (new phase-locked loop) of the present invention and the second-order generalized integrator phase-locked loop structure (traditional phase-locked loop) under the same conditions. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0026] The present invention provides an improved orthogonal signal generator (see Figure 1 ), based on a second-order generalized integrator, including a first negative feedback circuit, a first proportional link, a second negative feedback circuit, a first resonant link, a first integral link, a second resonant link, a second integral link, a third negative feedback circuit, a second proportional link, a fourth negative feedback circuit, a third resonant link, a third integral link, a fourth resonant link, and a fourth integral link.

[0027] An input voltage v is input from the positive input terminal of a comparison point of a first negative feedback circuit; an output terminal of the comparison point of the first negative feedback circuit is input to a first proportional link; an output terminal of the comparison point of the second negative feedback circuit is input to the positive input terminal of a comparison point of a second negative feedback circuit; an output terminal of the comparison point of the second negative feedback circuit is input to the positive input terminal of a comparison point of a third negative feedback circuit on the one hand, and to the first resonant link on the other hand; an output terminal of the first resonant link is input to a first integral link; an output terminal of the first integral link is input to the first negative feedback circuit on the one hand, and to the second integral link on the other hand; an estimated value ω' of the grid voltage frequency is input to the first resonant link and the second resonant link respectively; an output terminal of the second integral link is input to the second resonant link; and an output terminal of the second resonant link is input to the negative input terminal of a comparison point of a second negative feedback circuit;

[0028] The output of the output terminal of the comparison point of the third negative feedback circuit is input into the second proportional link, the output of the second proportional link is input into the positive input terminal of the comparison point of the fourth negative feedback circuit, the output of the output terminal of the comparison point of the fourth negative feedback circuit is input into the third resonant link, the output of the third resonant link is input into the third integral link, and the output of the third integral link is input into the third negative feedback circuit and the fourth integral link respectively; at the same time, the grid voltage frequency estimated value ω' is input into the third resonant link and the fourth resonant link respectively, the output of the fourth integral link is input into the fourth resonant link, and the output of the fourth resonant link is input into the negative input terminal of the comparison point of the fourth negative feedback circuit;

[0029] The output of the first integration link is the first orthogonal signal v α The output of the third integration link is the second orthogonal signal v' β , the phase difference between the first orthogonal signal and the second orthogonal signal is 90°.

[0030] The improved quadrature signal generator is similar to two second-order generalized integrators connected in series, but the difference is that the series connection point is between the input end of the first resonant link and the output end of the second proportional link.

[0031] The transfer functions of the direct-axis component (first orthogonal signal) and the quadrature-axis component (second orthogonal signal) are:

[0032]

[0033]

[0034] Where, v is the input voltage, v α is the first orthogonal signal, v' β is the second orthogonal signal, k1 and k2 are proportional coefficients, ω' is the estimated value of the grid voltage frequency, and s is the Laplace operator.

[0035] Specifically, compared with traditional orthogonal signal generators based on second-order generalized integrators, the quadrature-axis component's transfer function, Q'(s), consists of two parts: a high-pass filter transfer function from the input signal to the input of the first resonant link, and a band-pass filter transfer function from the input of the second proportional link to the output of the third integral link. The gain of Q'(s) is significantly attenuated in the low-frequency band. In other words, the quadrature-axis component's attenuation effect on the DC component and interharmonic components goes from zero to significant, and can even eliminate the influence of DC bias and harmonic components.

[0036] Furthermore, the present invention provides a novel strong anti-interference phase-locked loop structure (see Figure 2 ), the structure includes the above-mentioned improved orthogonal signal generator (the figure is marked as a new SOGI structure), and also includes a phase-locked loop; the first orthogonal signal and the second orthogonal signal output by the improved orthogonal signal generator are processed by the Park transform (Park transform) link and then input into the phase-locked loop, wherein the second orthogonal signal is connected to Alpha, the first orthogonal signal is connected to Beta, the first orthogonal signal and the second orthogonal signal serve as the input ends of the Park transform link, and the q-axis component v at the output end of the Park transform link q The frequency output by the phase-locked loop is used as the grid voltage frequency estimation value ω' and is input to the four resonant links of the improved orthogonal signal generator respectively; the phase θ' output by the phase-locked loop is used as the grid voltage phase estimation value and is input to the Park transformation link. The expression of Park transformation is:

[0037]

[0038] The phase-locked loop is a conventional structure, which is a prior art. Its structure and principle diagram are as follows: Figure 3 In the Park transformation link, the initial value of the phase θ' defaults to 0, because the initial moment is t = 0.

[0039] like Figure 1 As shown, the improved orthogonal signal generator designed by the present invention, v to v α The closed-loop transfer function is shown in formula (1). It can be seen that this is a bandpass filter, and its logarithmic amplitude-phase characteristic curve is as follows: Figure 4 In order to ensure the filtering performance of this bandpass filter, k1 takes the value At this time, the relationship between the settling time and the dynamic response overshoot is optimal. A high-pass filter channel from the signal input terminal v to v' is derived from the structure, and its closed-loop transfer function is shown in formula (4). At this time, the logarithmic amplitude-phase characteristic curve of the high-pass filter channel is as follows: Figure 4 By analyzing its Bode plot, it is found that before the fundamental frequency, the logarithmic amplitude-frequency characteristic curve is approximately a straight line with a slope of 40dB / dec, which can effectively suppress DC offset and interharmonic components.

[0040] The quadrature axis component is actually the result of the input signal passing through a high-pass filter and a band-pass filter connected in series. The transfer functions of the high-pass filter and the band-pass filter are:

[0041]

[0042]

[0043] Where v' is the output signal of the high-pass filter.

[0044] A second-order generalized integrator structure is connected in series at the output of the derived high-pass filter channel, from v' to v' β The closed-loop transfer function is shown in Equation (5). It can be seen that this is a bandpass filter with ω' as the central angular frequency, and the value of k2 is At this time, the relationship between the setting time and the dynamic response overshoot is optimal, from v to v' β The closed-loop transfer function of the series structure is shown in formula (2), and its logarithmic amplitude-phase characteristic curve is shown in Figure 5 By analyzing its Bode plot, it is found that before the fundamental frequency, the logarithmic amplitude-phase characteristic curve of Q'(s) is approximately a straight line with a slope of 60dB / dec, which can effectively filter out the DC component and interharmonic components in the input signal.

[0045] Through analysis Figure 5 , it can be found that: the direct axis component D(s) and the quadrature axis component Q'(s) are both bandpass filters. At the center angular frequency, that is, when ω' is equal to the input voltage angular frequency ω, v α and v' β It is still a pair of equal-amplitude and orthogonal voltage signals.

[0046] In order to achieve the output signal v' g For the input signal v g In order to achieve phase synchronization, it is necessary to connect the improved orthogonal signal generator to the phase-locked loop. Its structure is as follows: Figure 2 As shown. Among them, due to the v' in the output signal of the improved orthogonal signal generator β Phase angle ratio v α The phase angle of the Alpha input signal at the Park transform input terminal generally leads the phase angle of the Beta input signal by 90°. Therefore, v' β Connect with Alpha, v αIt is connected to Beta as the input of Park transformation. In addition, in order to realize the adaptive effect of the phase of the new strong anti-interference phase-locked loop structure, taking the monitoring of the grid voltage signal as an example, the phase-locked loop end ω' is used as the central angular frequency of the improved orthogonal signal generator to select the frequency of the input signal, and finally the new strong anti-interference phase-locked loop structure is constructed.

[0047] The new strong anti-interference phase-locked loop structure designed by this invention is used to set the phase-locked loop terminal ω according to the fundamental frequency of the known system. ref The frequency of the baseband signal ω can be filtered out. ref At the same time, when the phase of the system changes, the output signal v' g Synchronous following of the phase of the fundamental frequency signal v.

[0048] The following uses Matlab / Simulink simulation to simulate the grid environment with high DC and interharmonic components under weak power grid. The input signal sampling point of the second-order generalized integrator phase-locked loop is mainly the common point PCC end of the grid-connected system. Taking the grid-connected system with nonlinear loads and prone to voltage sampling and A / D conversion links as an example, the fundamental frequency voltage signal, harmonic voltage signal, DC bias and interharmonic voltage signal are injected into the input end of the new strong anti-interference phase-locked loop structure designed by the present invention. The accurate tracking of the fundamental frequency signal by the output signal of the phase-locked loop is verified through Simulink simulation, and the filtering effect of the new phase-locked loop on harmonics is verified; by changing the phase of the input voltage signal v at a certain moment, the output voltage signal v' is verified when the phase suddenly changes. g The specific steps for tracking the phase of the input voltage signal are as follows:

[0049] The first step is to create a simulation interface in Simulink. Figure 2 The new strong anti-interference phase-locked loop structure shown is named SOGI^2_PLL structure; at the same time, Figure 2 The improved orthogonal signal generator in the proposed method is replaced with a second-order generalized integrator connected to a phase-locked loop, named SOGI_PLL structure.

[0050] In the second step, a fundamental voltage signal with an amplitude of 311V and a frequency of 50Hz was injected into the input voltage signal v of the SOGI^2_PLL phase-locked loop structure and the SOGI_PLL phase-locked loop structure respectively. At 0.2s, a 3% DC bias, a 3% 1 / 10 interharmonic component, and 2% of the 5th, 7th, and 11th harmonic components were injected into the fundamental voltage signal. The output voltage signal v' after filtering of the two structures was observed. g The waveform that follows the input fundamental frequency voltage signal.

[0051] The third step is to analyze the waveform. Figure 6As shown in the figure, after injecting DC, interharmonic, and other harmonic components, the SOGI_PLL phase-locked loop waveform exhibits a certain offset and fails to follow the fundamental voltage signal after several cycles. However, after approximately one to two cycles, the SOGI^2_PLL phase-locked loop waveform outputs a voltage signal that essentially matches the fundamental voltage signal. This analysis demonstrates that the improved phase-locked loop structure further enhances both filtering performance and dynamic response.

[0052] In the fourth step, a fundamental voltage signal with an amplitude of 311V and a frequency of 50Hz, a 3% DC bias, a 3% 1 / 10th interharmonic component, and 2% each of the 5th, 7th, and 11th harmonic components were injected into the input voltage signal v. Simultaneously, a step transition was added before the fundamental voltage signal, adjusting the fundamental voltage signal from 50Hz to 49Hz in 0.35s. The phase synchronization effect of the two phase-locked loop output voltage signals on the input voltage signal was observed.

[0053] The fifth step is to analyze the waveform. Figure 7 As shown in the figure, after the phase of the input voltage baseband signal changes at 0.35s, the output signal tends to a steady state after about 0.2s; the output signal phase of the SOGI^2_PLL phase-locked loop structure stably follows the phase of the input baseband signal, while the output signal phase of the SOGI_PLL phase-locked loop structure is always in an oscillating state.

[0054] This simulation test was designed based on a requirement that the harmonic content in the power grid does not exceed 5%. Considering the high DC bias and interharmonic content in extreme environments, the harmonic content injected in the simulation was slightly modified. However, the simulation results show that the SOGI^2_PLL phase-locked loop structure designed in this invention still has high stability.

[0055] Any matters not described in the present invention are applicable to the prior art.

Claims

1. An improved orthogonal signal generator, characterized in that: It includes a first negative feedback circuit, a first proportional link, a second negative feedback circuit, a first resonance link, a first integral link, a second resonance link, a second integral link, a third negative feedback circuit, a second proportional link, a fourth negative feedback circuit, a third resonance link, a third integral link, a fourth resonance link, and a fourth integral link; The input voltage v is input from the positive input terminal of the comparison point of the first negative feedback circuit, the output of the output terminal of the comparison point of the first negative feedback circuit is input to the first proportional link, the output of the first proportional link is input to the positive input terminal of the comparison point of the second negative feedback circuit, the output of the output terminal of the comparison point of the second negative feedback circuit is input to the positive input terminal of the comparison point of the third negative feedback circuit on the one hand, and is input to the first resonant link on the other hand; The output of the first resonant link is input to the first integral link, and the output of the first integral link is input to the first negative feedback circuit on the one hand, and input to the second integral link on the other hand; The grid voltage frequency estimation value ω' is input to the first resonant link and the second resonant link respectively, the output of the second integral link is input to the second resonant link, and the output of the second resonant link is input to the negative input terminal of the comparison point of the second negative feedback circuit; The output of the output terminal of the comparison point of the third negative feedback circuit is input to the second proportional link, the output of the second proportional link is input to the positive input terminal of the comparison point of the fourth negative feedback circuit, the output of the output terminal of the comparison point of the fourth negative feedback circuit is input to the third resonant link, the output of the third resonant link is input to the third integral link, and the output of the third integral link is input to the third negative feedback circuit and the fourth integral link respectively; At the same time, the grid voltage frequency estimation value ω' is input to the third resonant link and the fourth resonant link respectively, the output of the fourth integral link is input to the fourth resonant link, and the output of the fourth resonant link is input to the negative input terminal of the comparison point of the fourth negative feedback circuit; The output of the first integration link is the first orthogonal signal v α The output of the third integration link is the second orthogonal signal v' β , the phase difference between the first orthogonal signal and the second orthogonal signal is 90°; The first orthogonal signal transfer function D(s) and the second orthogonal signal transfer function Q' (s) They are: Where, v is the input voltage, v α is the first orthogonal signal, v' β is the second orthogonal signal, k1 and k2 are proportional coefficients, ω' is the estimated value of the grid voltage frequency, and s is the Laplace operator.

2. The improved orthogonal signal generator according to claim 1, characterized in that: The value of k1 is The value of k2 is 3. A new strong anti-interference phase-locked loop structure, characterized in that: The structure includes the improved orthogonal signal generator according to any one of claims 1 or 2, and further includes a phase-locked loop; the first orthogonal signal and the second orthogonal signal output by the improved orthogonal signal generator are processed through a Park transform link, wherein the expression of the Park transform is: The q-axis component v at the output of the Park transformation link q The frequency output by the phase-locked loop is used as the grid voltage frequency estimation value ω' and is input into the four resonant links of the improved orthogonal signal generator respectively; the phase θ' output by the phase-locked loop is used as the grid voltage phase estimation value and is input into the Park transformation link.

Images