An improved SOGI structure and phase-locked loop structure

Abstract

This invention discloses an improved SOGI structure and a phase-locked loop (PLL) structure. The improved SOGI structure includes a proportional element, a first integral element, and a second integral element. Voltage is input from the input of the proportional element, passes through the first integral element to output a first-order voltage hysteresis signal, and passes through the second integral element to output a second-order voltage hysteresis signal. The phase difference between the first-order and second-order voltage hysteresis signals is 90°. A notch filter is connected in parallel at the output of the second-order voltage hysteresis signal. The improved SOGI structure provided by this invention connects a notch filter in parallel at the output of the second-order voltage hysteresis signal in the traditional SOGI structure, making the actual second-order voltage hysteresis signal the difference between the output of the second-order voltage hysteresis signal in the traditional SOGI structure and the output of its corresponding notch filter. This enhances the filtering capability in both low and high frequency bands and effectively filters out DC offset in the input signal. This invention also discloses an improved PLL structure using the aforementioned improved SOGI structure.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation technology, and in particular to an improved SOGI structure and phase-locked loop structure. Background Technology

[0002] Traditional energy sources, primarily oil, coal, and natural gas, not only pollute the environment but also face depletion. Therefore, new energy power generation has become a global focus. Due to the widespread distribution of new energy sources such as solar and wind power, unified collection and utilization are difficult. Distributed generation systems have become one of the most effective solutions to this problem. To ensure the quality of grid-connected current, it needs to be accurately synchronized with the grid voltage. Phase-locked loops (PLLs) are a key technology for achieving grid-connected synchronization control. However, background harmonics and grid faults can affect the normal operation of PLLs and impact the quality of grid-connected current. Second-order generalized integrators (SOGIs) have a good suppression effect on higher harmonics.

[0003] The prior art, such as the second-order generalized integrator circuit and phase-locked loop disclosed in Chinese Patent Publication No. CN206149242U, includes a proportional element, a first integral element, a second integral element, and a subtraction circuit. The input terminal of the proportional element receives a voltage signal. The proportional element, the first integral element, and the second integral element are connected in series. The subtraction circuit is connected between the output terminals of the proportional element and the second integral element, and a low-pass filter is provided on the subtraction circuit. The output terminal of the first integral element outputs a first-order voltage hysteresis signal, and the output terminal of the second integral element outputs a second-order voltage hysteresis signal. The phase difference between the first-order voltage hysteresis signal and the voltage signal, and the phase difference between the second-order voltage hysteresis signal and the first-order voltage hysteresis signal, are both 90°. The circuit also includes a first resonant element and a second resonant element. The first resonant element is connected in series between the proportional element and the first integral element, and the second resonant element is connected in series between the first integral element and the second integral element. A first negative feedback loop is also included, with one end located between the first integral element and the second resonant element, and the other end connected to the input terminal of the proportional element.

[0004] However, the second-order generalized integrator circuit disclosed in the above patent has a weak ability to suppress low-order harmonics, especially when the input signal contains a DC component, SOGI-PLL cannot accurately extract its positive-sequence component.

[0005] In the existing technology, some scholars have proposed using multi-stage cascaded modules to eliminate the influence of total harmonic components on the output of the phase-locked loop, but the increased system delay due to the multi-stage system slows down the response speed; other scholars have proposed adding a difference node in SOGI, which can eliminate the influence of DC components, but reduces its filtering capability for higher harmonics. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides an improved SOGI structure and phase-locked loop structure.

[0007] An improved SOGI structure includes a proportional element, a first integral element, and a second integral element connected in series. The voltage is input from the input terminal of the proportional element, and after passing through the first integral element, a first-order voltage hysteresis signal is output. After passing through the second integral element, a second-order voltage hysteresis signal is output. The phase difference between the first-order voltage hysteresis signal and the second-order voltage hysteresis signal is 90°. A notch filter is connected in parallel at the output of the second-order voltage hysteresis signal.

[0008] Preferably, the notch frequency of the notch filter is the fundamental AC frequency.

[0009] Preferably, it also includes a first resonant element connected in series between the proportional element and the first integral element, and a second resonant element connected in series between the first integral element and the second integral element.

[0010] Preferably, it further includes a first feedback circuit, the two ends of which are respectively connected to the input terminal of the proportional element and the input terminal of the second resonant element.

[0011] Preferably, it further includes a second feedback circuit, the two ends of which are respectively connected to the input terminal of the first resonant element and the output terminal of the second integrator element.

[0012] Preferably, it also includes a third feedback circuit, the two ends of which are respectively connected to the input terminal of the first resonant element and the input terminal of the notch filter.

[0013] Preferably, the direct-axis transfer function and the quadrature-axis transfer function of the improved SOGI structure are respectively:

[0014]

[0015]

[0016] Where v is the input voltage, v' is the first-order voltage hysteresis signal, k is the damping factor, ω is the grid voltage estimate, s is the Laplace operator, qv' is the second-order voltage hysteresis signal, and G... NF (s) is the transfer function of the notch filter.

[0017] Specifically, compared with the traditional SOGI structure, the gain of the cross-axis component transfer function G(s) is significantly reduced in the low-frequency band. In other words, the improved SOGI structure enhances its filtering capability in the low-frequency band and can effectively filter out the DC offset in the input signal.

[0018] An improved phase-locked loop structure, employing the improved SOGI structure as described in any of the preceding claims, further includes a Clark transform unit. The two output axes of the Clark transform unit are respectively connected to the improved SOGI structure. The expression for the order output signal of the improved SOGI structure connected to the two output axes tracking the positive-sequence component of the fundamental signal is as follows:

[0019]

[0020]

[0021] Where α and β represent the two output axes of the Clark transform unit, the α-axis and the β-axis, respectively, and v α + With v β + These are the output voltages after eliminating negative sequence components on the α and β axes, respectively.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] A notch filter circuit is connected in parallel at the second-order voltage hysteresis signal output of the traditional SOGI structure, so that the actual second-order voltage hysteresis signal is the difference between the second-order voltage hysteresis signal output of the traditional SOGI structure and the output of its corresponding notch filter circuit. By adding an additional notch filter circuit, the filtering capability of the SOGI structure in the low-frequency band is enhanced, which can effectively filter out the DC offset in the input signal and further enhance its filtering capability for high-frequency harmonics. Attached Figure Description

[0024] Figure 1 A schematic diagram of the improved SOGI structure provided by this invention;

[0025] Figure 2 A schematic diagram of the improved phase-locked loop topology provided by this invention;

[0026] Figure 3 Comparison of Bode plots before and after the improvement of the cross-axis component transfer function G(s) provided by this invention;

[0027] Figure 4 A comparison diagram of the output of the improved SOGI structure provided by this invention and the traditional SOGI structure when the input is asymmetrical;

[0028] Figure 5The output comparison diagram of the phase-locked loop based on the improved SOGI structure and the phase-locked loop based on the traditional SOGI structure provided by this invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, the improved SOGI structure includes a proportional element 10, a first integral element 21, and a second integral element 22 connected in series. The voltage is input from the input terminal of the proportional element 10, and after passing through the first integral element 21, a first-order voltage hysteresis signal is output. After passing through the second integral element 22, a second-order voltage hysteresis signal is output. The phase difference between the first-order voltage hysteresis signal and the second-order voltage hysteresis signal is 90°. A notch filter 30 is connected in parallel at the output of the second-order voltage hysteresis signal. The notch filter 30 has a notch frequency that is the fundamental AC frequency.

[0031] It also includes: a first resonant circuit 41 connected in series between the proportional circuit 10 and the first integral circuit 21, and a second resonant circuit 42 connected in series between the first integral circuit 21 and the second integral circuit 22; a first feedback circuit 51, the two ends of which are respectively connected to the input terminal of the proportional circuit 10 and the input terminal of the second resonant circuit 42; a second feedback circuit 52, the two ends of which are respectively connected to the input terminal of the first resonant circuit 41 and the output terminal of the second integral circuit 22; and a third feedback circuit 53, the two ends of which are respectively connected to the input terminal of the first resonant circuit 41 and the input terminal of the notch filter 30.

[0032] The direct-axis and quadrature-axis transfer functions of the improved SOGI structure are as follows:

[0033]

[0034]

[0035] Where v is the input voltage, v' is the first-order voltage hysteresis signal, k is the damping factor, ω is the grid voltage estimate, s is the Laplace operator, qv' is the second-order voltage hysteresis signal, and G... NF (s) is the transfer function of the notch filter.

[0036] Specifically, compared with the traditional SOGI structure, the gain of the cross-axis component transfer function G(s) is significantly reduced in the low-frequency band. In other words, the improved SOGI structure enhances its filtering capability in the low-frequency band and can effectively filter out the DC offset in the input signal.

[0037] like Figure 2As shown, the improved phase-locked loop structure, employing the improved SOGI structure described in any of the preceding embodiments, also includes a Clark transform unit. The two output axes of the Clark transform unit are respectively connected to the improved SOGI structure. The expression for the order output signal of the improved SOGI structure connected to the two output axes tracking the positive-sequence component of the fundamental signal is as follows:

[0038]

[0039]

[0040] Where α and β represent the two output axes of the Clark transform unit, the α-axis and the β-axis, respectively, and v α + With v β + These are the output voltages after eliminating negative sequence components on the α and β axes, respectively.

[0041] like Figure 3 As shown, after adding an additional notch filter 30 loop, the amplitude of the low-frequency band of the quadrature-axis component transfer function G(s) drops significantly, which means that the improved phase-locked loop can effectively suppress low-frequency harmonics and DC components in the input signal. In addition, the amplitude of the high-frequency band of the improved quadrature-axis component transfer function G(s) also decreases to a certain extent, which means that its filtering capability for high-frequency harmonics is further enhanced.

[0042] like Figure 4 As shown, when the input is asymmetrical, the peak values ​​of the output voltages on the α-axis and β-axis of the traditional SOGI structure after eliminating the negative sequence components are significantly different. However, the peak values ​​of the output voltages on the α-axis and β-axis of the improved SOGI structure after eliminating the negative sequence components are almost the same, which means that the improved SOGI structure has a stronger filtering capability when the input is asymmetrical compared to the traditional SOGI structure.

[0043] like Figure 5 As shown, a DC offset is added to the input signal at 0.15s. At this time, the phase-locked loop based on the traditional SOGI cannot track the phase of the input voltage well, and the output fluctuates. The phase-locked loop based on the improved SOGI structure can track the phase of the input voltage quickly and stably.

Claims

1. An improved SOGI structure, characterized in that, It includes a proportional element, a first integral element, and a second integral element connected in series. The voltage is input from the input terminal of the proportional element. After passing through the first integral element, a first-order voltage hysteresis signal is output. After passing through the second integral element, a second-order voltage hysteresis signal is output. The phase difference between the first-order voltage hysteresis signal and the second-order voltage hysteresis signal is 90°. A notch filter is connected in parallel at the output of the second-order voltage hysteresis signal. The notch filter frequency is the AC fundamental frequency. The direct-axis and quadrature-axis transfer functions of the improved SOGI structure are as follows: ； ； in, Input voltage, It is a first-order voltage hysteresis signal. The damping factor, This is an estimated value for the grid voltage. For the Laplace operator, It is a second-order voltage hysteresis signal. This is the transfer function of the notch filter.

2. The improved SOGI structure according to claim 1, characterized in that, It also includes a first resonant element connected in series between the proportional element and the first integral element, and a second resonant element connected in series between the first integral element and the second integral element.

3. The improved SOGI structure according to claim 2, characterized in that, It also includes a first feedback circuit, the two ends of which are connected to the input of the proportional element and the input of the second resonant element, respectively.

4. The improved SOGI structure according to claim 3, characterized in that, It also includes a second feedback circuit, the two ends of which are connected to the input of the first resonant element and the output of the second integrator element, respectively.

5. The improved SOGI structure according to claim 4, characterized in that, It also includes a third feedback circuit, the two ends of which are connected to the input of the first resonant element and the input of the notch filter, respectively.

6. An improved phase-locked loop structure, characterized in that, The improved SOGI structure according to any one of claims 1-5 further includes a Clark transform unit, wherein the two output axes of the Clark transform unit are respectively connected to the improved SOGI structure, and the expression for the order output signal of the improved SOGI structure connected to the two output axes to track the positive sequence component of the fundamental signal is: ; ;in, , These represent the two output axes of the Clark transform unit. axis, axis, and They are respectively shaft and The output voltage after eliminating the negative sequence component.

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