Method for suppressing even harmonic generation of high-voltage power grid

Abstract

The invention discloses a suppression method for generation of even harmonics of a high-voltage power grid, and the method comprises the steps: deploying an intelligent sensor network at a key node, monitoring power parameters in real time in combination with a time-frequency analysis technology, and distinguishing current components flowing into the power grid through employing a conservation power theory, thereby achieving the precise recognition of the time and frequency characteristics of the even harmonics; meanwhile, by establishing a nonlinear characteristic mathematical model of the photovoltaic power generation system and evaluating the influence of the output power fluctuation and the access position of the photovoltaic power generation system on the harmonic level of the power grid, a phase-locked loop synchronization algorithm of a bisecond-order generalized integrator is adopted to ensure high-precision phase synchronization between the photovoltaic power generation system and the power grid; reactive power flow and transmission loss caused by phase errors are reduced; finally, by analyzing resonance conditions in the power grid, the proportional gain and the integral gain of the PLL are dynamically adjusted, a frequency compensation mechanism is introduced to cope with frequency fluctuation, and even harmonics are effectively suppressed.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit protection, and in particular to a method for suppressing generation of even-order harmonics in a high-voltage power grid. Background Art

[0002] Harmonics are non-sinusoidal periodic voltages or currents in power systems. Their frequencies are integer multiples of the fundamental wave. Harmonics can be divided into odd harmonics and even harmonics. "Even" means that the order of these harmonics is an even number, such as 2nd, 4th, 6th, etc.

[0003] The presence of even-order harmonics has multiple negative effects on high-voltage power grids: even-order harmonics cause additional current to flow, increasing energy loss during power transmission, causing wires and other electrical equipment to withstand higher temperatures, accelerating aging and shortening their service life; even-order harmonics can also disrupt the voltage and current waveforms of the power system, deteriorating the power quality and affecting the power experience of all users connected to the grid.

[0004] High-voltage power grids are usually three-phase power systems. Ideally, due to the symmetry and load balance of the three-phase power system, even harmonics tend to cancel each other out; however, in actual operation, when the system is asymmetric or there are nonlinear loads, even harmonics will appear.

[0005] However, in recent years, as new energy systems have been connected to high-voltage power grids, new problems have arisen regarding the generation of harmonics. New energy systems usually rely on conversion devices to convert renewable energy into alternating current suitable for use in the power grid. During operation, the conversion device will generate non-sinusoidal current or voltage, thereby introducing harmonic components. Semiconductor devices operate in a high-frequency switching manner, which will introduce a large number of even harmonics in the output waveform. The nonlinear characteristics of new energy access increase the nonlinear load in the high-voltage power grid, making it easy to have three-phase imbalance, which will destroy the symmetry of the power system and cause even harmonics to appear in the high-voltage power grid.

[0006] Therefore, it is necessary to improve the prior art method for suppressing even-order harmonics in high-voltage power grids to solve the above problems. Summary of the invention

[0007] The present invention overcomes the shortcomings of the prior art and provides a method for suppressing the generation of even-order harmonics in a high-voltage power grid, aiming to solve the problem of even-order harmonic amplification caused by nonlinear loads in the prior art.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a method for suppressing the generation of even-order harmonics in a high-voltage power grid, comprising:

[0009] S1. Obtain power parameters of the high-voltage power grid, perform real-time analysis on the power signal at the access point of the photovoltaic power generation system through time-frequency analysis, and obtain the time and frequency characteristics of even harmonics in the power signal at the access point of the photovoltaic power generation system;

[0010] S2. Analyze the nonlinear characteristics of the photovoltaic power generation system, and evaluate the impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid in combination with the output power and access point location of the photovoltaic power generation;

[0011] S3. Combined with the characteristics of the photovoltaic system, the power conservation theory is used to distinguish the current components flowing into the grid and perform real-time even harmonic detection;

[0012] S4, based on the real-time harmonic detection results, combined with the phase-locked loop synchronization algorithm of the double second-order generalized integrator, the phase between the photovoltaic power generation system and the power grid is synchronized;

[0013] S5. Analyze the resonance conditions in the high-voltage power grid and optimize the synchronization algorithm to suppress even-order harmonics.

[0014] In a preferred embodiment of the present invention, in step S1,

[0015] S11. Deploy smart sensor networks at key nodes of the high-voltage power grid, use the Internet of Things to build a distributed monitoring system, and analyze power parameters from sensors, including voltage and current;

[0016] S12, performing time-frequency analysis on power parameters based on short-time Fourier transform to obtain power spectrum density;

[0017] S13. Use heat maps to display power spectrum density, observe the changes in frequency components at different time points, and identify the time and frequency characteristics of even harmonics.

[0018] In a preferred embodiment of the present invention, time-frequency analysis of power parameters is performed based on short-time Fourier transform:

[0019] The input signal is the voltage or current signal at the access point of the photovoltaic power generation system. The input signal x(t) is divided into several overlapping small segments, and the window function x is applied to each segment. w (n) = x(n)·w(n), where n is a specific moment in the time series and the w(n) window function is used to limit the data fragment within the time window;

[0020] Apply discrete Fourier transform to the signal within each window to obtain the time-frequency representation Among them, τ is the time offset, representing different time periods, f is the frequency index, indicating the frequency component, and X(τ,f) is the complex value at a specific time and frequency, reflecting the frequency distribution at that moment.

[0021] In a preferred embodiment of the present invention, in step S2, a mathematical model of the nonlinear characteristics of the photovoltaic power generation system is established: Where V is voltage, I is current, and R s ,R p is the series resistance and parallel resistance, I ph is the photocurrent, I 0 is the reverse saturation current, V t is the thermal voltage, n is the diode quality factor, N s is the number of photovoltaic cells connected in series.

[0022] In a preferred embodiment of the present invention, in step S2, the impact of the photovoltaic power generation system on the harmonic level of the power grid near the access point is evaluated, and an evaluation model is established;

[0023] The output power of the photovoltaic power generation system is P = V*I, where V and I are the output voltage and current of the photovoltaic cell;

[0024] Evaluate the impact of access point location on harmonic levels: Where H(f) is the harmonic transfer function, which represents the efficiency of harmonic transfer from the photovoltaic power generation system to the grid, and Z grid (f) is the impedance of the grid at frequency f, Z PV (f) is the impedance of the photovoltaic power generation system at frequency f.

[0025] The nonlinear characteristics of the photovoltaic power generation system, output power fluctuations and the influence of the access point location are combined to evaluate the overall impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid:

[0026] THD grid is the total harmonic distortion rate of the power grid, f n is the frequency of the nth harmonic, I PV (f n ) is the photovoltaic power generation system at frequency f n Harmonic current at grid (f 1 ) is the grid at fundamental frequency f 1 The current at .

[0027] In a preferred embodiment of the present invention, in step S3, the power conservation theory is combined with the photovoltaic system characteristics obtained in S2 to distinguish the current components flowing into the grid, including active current, reactive current and harmonic current.

[0028] In a preferred embodiment of the present invention, in step S4, the steps of the phase-locked loop synchronization algorithm of the biquad generalized integrator include:

[0029] S41, using the collected voltage signal as the input of SOGI-PLL;

[0030] S42, SOGI module separates the fundamental component and generates an orthogonal component;

[0031] S43, constructing a PLL using the fundamental wave and quadrature signal provided by SOGI to detect the frequency and phase of the grid voltage;

[0032] S44. Calculate the phase difference between the actual output current and the expected value, and adjust the output of the inverter through a feedback mechanism to keep the two in phase.

[0033] In a preferred embodiment of the present invention, at each sampling time n, the phase error is e[n]=arctan2(v β [n],v α [n])-θ[n]; θ[n] is the angle of PLL output at the moment; v α [n] is the fundamental component, v β [n] is the orthogonal component;

[0034] According to the phase error, the amount and angle of the inverter output are adjusted to achieve phase synchronization between the photovoltaic power generation system and the power grid.

[0035] In a preferred embodiment of the present invention, in step S5, the resonant frequency is Calculate, where L is the inductance value and C is the capacitance value.

[0036] In a preferred embodiment of the present invention, a resonant frequency compensation mechanism is added to the PLL to further suppress even-order harmonics, and the proportional gain K p and integral gain K i After correction, K p (t) = K p0 +K pf (f(t)-f 0 ), K i (t) = K i0 +K if (f(t)-f 0 ), where K p0 , K i0 are the initial proportional and integral gains, K pf , K if is the frequency-dependent gain factor, f 0 is the standard grid frequency, and f(t) is the actual measured grid frequency.

[0037] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0038] (1) The present invention deploys intelligent sensor networks at key nodes, combines time-frequency analysis technology to monitor power parameters in real time, and uses the theory of power conservation to distinguish the current components flowing into the power grid, thereby achieving accurate identification of the time and frequency characteristics of even-order harmonics. At the same time, by establishing a mathematical model of the nonlinear characteristics of the photovoltaic power generation system, the impact of its output power fluctuation and access location on the harmonic level of the power grid is evaluated. Based on this, a phase-locked loop synchronization algorithm with a dual second-order generalized integrator is adopted to ensure high-precision phase synchronization between the photovoltaic power generation system and the power grid, reducing the reactive power flow and transmission loss caused by phase errors. Finally, by analyzing the resonant conditions in the power grid, the proportional gain and integral gain of the PLL are dynamically adjusted, and a frequency compensation mechanism is introduced to cope with frequency fluctuations, effectively suppressing even-order harmonics.

[0039] (2) The present invention combines the phase-locked loop synchronization algorithm of the dual second-order generalized integrator with the output of the photovoltaic power generation system to ensure the phase synchronization between the photovoltaic output current and the grid voltage, thereby reducing the reactive power flow caused by the phase error; further, the resonance conditions in the high-voltage power grid are analyzed and combined with the optimization of the synchronization algorithm to minimize the energy amplification phenomenon at a specific frequency, prevent the serious distortion of the voltage and current waveforms, reduce the transmission loss, and effectively prevent equipment damage; effectively suppress even harmonics, ensure that the ideal phase relationship between the photovoltaic current and the grid voltage is maintained, and further improve the stability of the power system and the power quality.

[0040] (3) The present invention combines the nonlinear characteristics of the photovoltaic power generation system and the influence of the access point location to establish an evaluation model to quantify the overall impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid; it not only considers the impact of the photovoltaic system on the power grid under static conditions, but also covers the rapid fluctuations caused by changes in light, so that it can more accurately predict and evaluate the even-order harmonic pollution risks that may be brought about by the photovoltaic power generation system. Through this comprehensive evaluation method, the even-order harmonic pollution risks that may be brought about by the photovoltaic power generation system can be more accurately predicted; compared with the existing technology, the predictability and controllability of the generation of even-order harmonics are further improved.

[0041] (4) The present invention realizes comprehensive and real-time monitoring of the power parameters of the high-voltage power grid by deploying an intelligent sensor network and using time-frequency analysis technology, and using the theory of conservation of power to distinguish the current components flowing into the power grid. Intelligent sensors are deployed at key nodes, and time-frequency analysis is performed through short-time Fourier transform to identify the time and frequency characteristics of even harmonics. It can not only capture the changes of even harmonics in a timely manner, but also accurately distinguish between active current, reactive current and harmonic current, especially even harmonic current. Compared with the prior art, it further achieves accurate identification of even harmonic sources and their influence range, providing a solid foundation for subsequent suppression measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 is a flow chart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0046] Application Overview:

[0047] With the popularization of renewable energy such as photovoltaic systems, a large number of distributed energy resources are connected to the high-voltage power grid. The new energy system relies on conversion devices to convert direct current into alternating current to meet the needs of the power grid. In this process, additional nonlinear and time-varying characteristics are introduced, resulting in more harmonic problems. Among them, even harmonics are particularly harmful to the power grid due to their amplification effect under specific conditions.

[0048] The existing methods for suppressing even harmonics in high-voltage power grids have the following defects: they focus on the design of physical filters while ignoring the possibility of software and algorithm optimization; traditional methods focus on suppressing odd harmonics. Taking photovoltaic systems as an example, when connected to the power grid, they have obvious intermittent and fluctuating characteristics due to their dependence on changes in sunlight intensity, and during the inversion process, the rapid opening and closing of semiconductor devices will cause distortion of current and voltage waveforms and produce non-sinusoidal waveforms. Faced with the presence of a large number of nonlinear loads, the existing technology performs poorly in processing even harmonics generated in complex power grid environments; lack of effective real-time monitoring means and technologies makes it difficult to accurately identify even harmonic sources and their impact range, which limits the effective control of even harmonics.

[0049] The present application proposes a method for suppressing the generation of even-order harmonics in a high-voltage power grid, thereby achieving effective monitoring and suppression of even-order harmonics in the high-voltage power grid.

[0050] Exemplary methods:

[0051] like Figure 1 As shown, a method for suppressing even-order harmonics generated in a high-voltage power grid comprises the following steps:

[0052] S1. Obtain power parameters of the high-voltage power grid, perform real-time analysis on the power signal at the access point of the photovoltaic power generation system through time-frequency analysis, and obtain the time and frequency characteristics of even harmonics in the power signal at the access point of the photovoltaic power generation system;

[0053] S2. Analyze the nonlinear characteristics of the photovoltaic power generation system, and evaluate the impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid in combination with the output power and access point location of the photovoltaic power generation;

[0054] S3. Combined with the characteristics of the photovoltaic system, the power conservation theory is used to distinguish the current components flowing into the grid and perform real-time even harmonic detection;

[0055] S4, based on the real-time harmonic detection results, combined with the phase-locked loop synchronization algorithm of the double second-order generalized integrator, the phase between the photovoltaic power generation system and the power grid is synchronized;

[0056] S5. Analyze the resonance conditions in the high-voltage power grid and optimize the synchronization algorithm to suppress even-order harmonics.

[0057] In step S1, a smart sensor network is deployed at key nodes of the high-voltage power grid, and a distributed monitoring system is constructed using the Internet of Things to analyze power parameters from sensors, including voltage and current;

[0058] Key nodes refer to locations in the high-voltage power grid that are sensitive to changes in power parameters and can reflect the power signal characteristics at the access point of the photovoltaic power generation system; including: the inverter output terminal, grid connection point, and near the main load or transformer inside the photovoltaic power station;

[0059] The inverter output end inside the photovoltaic power station is where direct current is converted into alternating current, and is one of the sources of harmonic generation. The grid connection point is where the photovoltaic power generation system is connected to the public high-voltage power grid, which directly reflects the impact of new energy access on the power grid. The propagation of harmonics caused by nonlinear loads can be obtained near the main load or transformer. By deploying smart sensors at the above-mentioned key nodes, power parameters such as voltage and current can be obtained in real time.

[0060] Time-frequency analysis is a signal processing technology that can provide detailed information about the signal in both time and frequency dimensions. Since the output power of the photovoltaic power generation system fluctuates with the change of sunlight intensity, this fluctuation is random and non-periodic. Traditional frequency domain analysis methods can only provide spectrum distribution in an average sense and cannot reflect these transient changes. However, time-frequency analysis can capture the changes in frequency components in the power signal in a short period of time, which is conducive to the identification and analysis of even harmonics.

[0061] Time-frequency analysis of power parameters based on short-time Fourier transform:

[0062] The input signal is the voltage or current signal at the access point of the photovoltaic power generation system. The input signal x(t) is divided into several overlapping small segments, and the window function x is applied to each segment. w (n) = x(n)·w(n), where n is a specific moment in the time series and the w(n) window function is used to limit the data fragment within the time window;

[0063] Apply discrete Fourier transform to the signal within each window to obtain the time-frequency representation Among them, τ is the time offset, representing different time periods, f is the frequency index, indicating the frequency component, N is the window size of the window function, and X(τ,f) is the complex value at a specific time and frequency, reflecting the frequency distribution at that moment;

[0064] Use heatmap to display the power spectral density |X(τ,f)| 2 Observe the changes in frequency components at different time points and identify the time and frequency characteristics of even harmonics.

[0065] Step S1 implements comprehensive and real-time monitoring of the power grid status through an intelligent sensor network to ensure that the time and frequency characteristics of even harmonics can be captured in a timely manner.

[0066] The nonlinear characteristics of the photovoltaic power generation system mainly come from the photovoltaic cells themselves and the grid-connected inverter. Especially under different light intensity and temperature conditions, its output power will change significantly. Considering that the photovoltaic inverter will inevitably generate harmonics when converting DC to AC, this step pays special attention to the impact of output power fluctuations and access location on the harmonic level of the entire power grid. By establishing a mathematical model to quantify this impact, the risk of even-order harmonic pollution that may be caused by the photovoltaic power generation system can be more accurately predicted and evaluated.

[0067] In step S2, a mathematical model of the nonlinear characteristics of the photovoltaic power generation system is established. When the light intensity or temperature changes, the maximum power point of the photovoltaic cell will also move accordingly. The basic working principle of the photovoltaic cell is represented by a single diode model: Where V is voltage, I is current, and R s ,Rp is the series resistance and parallel resistance, I ph is the photocurrent, I 0 is the reverse saturation current, V t is the thermal voltage, n is the diode quality factor, N s is the number of photovoltaic cells connected in series.

[0068] In step S2, in order to evaluate the impact of the photovoltaic power generation system on the harmonic level of the power grid near the access point, an evaluation model is established;

[0069] The output power of the photovoltaic power generation system will fluctuate with the changes in sunlight intensity and temperature. The output power is P = V*I, where V and I are the output voltage and current of the photovoltaic cell;

[0070] The location where the photovoltaic power generation system is connected to the high-voltage grid will affect the propagation and distribution of harmonics. It is necessary to consider the impedance of the access point and the topology of the grid to evaluate the impact of the access point location on the harmonic level: Where H(f) is the harmonic transfer function, which represents the efficiency of harmonic transfer from the photovoltaic power generation system to the grid, and Z grid (f) is the impedance of the grid at frequency f, Z PV (f) is the impedance of the photovoltaic power generation system at frequency f.

[0071] The nonlinear characteristics of the photovoltaic power generation system, output power fluctuations and the influence of the access point location are combined to evaluate the overall impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid: THD grid is the total harmonic distortion rate of the power grid, f n is the frequency of the nth harmonic, I PV (f n ) is the photovoltaic power generation system at frequency f n Harmonic current at grid (f 1 ) is the grid at fundamental frequency f 1 The current at .

[0072] Step S2 is based on the time-frequency analysis results of S1 and the nonlinear characteristics of photovoltaic power generation, combined with the actual access point location and output power factors of the photovoltaic power generation system, to evaluate how these factors affect the harmonic level in the high-voltage power grid, taking into account not only the impact under static conditions, but also the impact of rapid fluctuations caused by changes in light under dynamic conditions.

[0073] In step S3, the conservation of power theory is combined with the photovoltaic system characteristic information obtained in S2 to accurately distinguish the current components flowing into the power grid, including active current, reactive current and harmonic current. This application mainly focuses on the even harmonic current in the harmonic current. By distinguishing the current components, unnecessary reactive current can be identified and reduced, transmission losses can be reduced, and the overall efficiency of the system can be improved. The ability to detect and compensate for harmonic currents helps to reduce voltage distortion.

[0074] According to the acquired grid parameters, the time domain signal is converted into frequency domain representation through fast Fourier transform to separate the fundamental and harmonic components; for each frequency point, according to the instantaneous current formula Calculate the amplitude a corresponding to the fundamental and harmonic components n and b n , where n is the harmonic order and ω is the angular frequency;

[0075] Based on the fundamental current, through P = V rms I rms ·cos(φ) and Q=V rms I rms sin(φ), calculate the active power P and reactive power Q, and then get the functional overcurrent I P and reactive current I Q , where V rms ,I rms are the effective value voltage and effective value current, and φ is the phase difference.

[0076] The total current flowing into the grid is the vector sum of active current, reactive current and harmonic current;

[0077] Extract even harmonic current from harmonic current, Where N is the maximum harmonic number considered, I 2k The effective value of the 2kth harmonic current; square the effective values ​​of the harmonic currents corresponding to all even multiples of the fundamental frequency, add them together, and then take the square root to obtain the effective value of the total even-order harmonic current.

[0078] Step S3 identifies and separates the even harmonic components introduced by the photovoltaic power generation system, laying a solid foundation for the next step of synchronous compensation measures.

[0079] SOGI-PLL can accurately extract the fundamental component of the grid voltage and ensure good synchronization performance even in the presence of a large number of harmonics, helping to minimize the phase difference between the output current of the photovoltaic power generation system and the grid voltage, thereby reducing unnecessary reactive power flow and transmission losses.

[0080] In step S4, the steps of the phase-locked loop synchronization algorithm of the biquad generalized integrator include:

[0081] S41, using the collected voltage signal as the input of SOGI-PLL;

[0082] S42, SOGI module separates the fundamental component and generates an orthogonal component; the orthogonal component is a signal that is 90 degrees out of phase with the fundamental component;

[0083] S43, constructing a PLL using the fundamental wave and quadrature signal provided by SOGI to track the frequency and phase of the grid voltage;

[0084] S44. Calculate the phase difference between the actual output current and the expected value, and adjust the output of the inverter through a feedback mechanism to keep the two in phase.

[0085] For a discrete time system such as a photovoltaic power generation system, SOGI is described by the following difference equation: x[n] = a 1 x[n-1]+a 2 x[n-2]+b 0 u[n]+b 1 u[n-1]+b 2 u[n-2], where x[n] is the output sequence of SOGI, u[n] is the input voltage signal, and a i ,b i is the natural angular frequency ω n and the coefficient determined by the damping ratio;

[0086] SOGI has two outputs, including the fundamental component v α [n] and the orthogonal component v β [n];

[0087] PLL is a feedback control system that keeps the frequency and phase of the virtual or actual oscillation source used to generate a sinusoidal waveform with the same frequency and phase as the grid voltage in the photovoltaic power generation system consistent with the actual voltage signal of the grid; the formula for PLL is: Where θ(t) is the angle of the PLL output, ω(t) is the angular velocity of the PLL output, e(t) is the phase error, and K p , K i They are proportional gain and integral gain respectively;

[0088] At each sampling time n, the phase error is e[n]=arctan2(v β [n],v α [n])-θ[n]; θ[n] is the angle of the PLL output at the moment;

[0089] According to the phase error, the amount and angle of the inverter output are adjusted to achieve phase synchronization between the photovoltaic power generation system and the power grid.

[0090] Step S4 ensures that the output current of the photovoltaic power generation system is in phase synchronization with the grid voltage, reduces the reactive power flow caused by the phase error, and thus reduces the impact of even harmonics.

[0091] The resonance condition means that in the power system, when several components of the system are combined together, a natural oscillation frequency will be formed at a specific frequency. When this frequency matches the external input signal, such as the photovoltaic current of this application, resonance will occur, resulting in the amplification of energy at this frequency. In the power system, it will cause serious distortion of the voltage and current waveforms, increase transmission losses, and damage the equipment; since the energy is amplified, the adverse effects of even harmonics will also be amplified; resonance will cause distortion of the voltage waveform, thereby making the originally precise PLL synchronization mechanism inaccurate, causing the phase relationship between the photovoltaic current and the grid voltage to deviate from the ideal state.

[0092] In step S5, the resonant frequency is Calculate, where L is the inductance value and C is the capacitance value;

[0093] Add a resonant frequency compensation mechanism to the PLL to further suppress even-order harmonics, and the proportional gain K p and integral gain K i After correction, K p (t) = K p0 +K pf (f(t)-f 0 ), K i (t) = K i0 +K if (f(t)-f 0 ), where K p0 , K i0 are the initial proportional and integral gains, K pf , K if is the frequency-dependent gain factor, f 0 is the standard grid frequency, f(t) is the actual measured grid frequency, and the resonant frequency f r Use it as a reference point to consider whether additional protective measures are needed.

[0094] Step S5 analyzes the resonance conditions in the high-voltage power grid and optimizes the phase-locked loop synchronization algorithm based on the dual second-order generalized integrator to achieve effective suppression of even-order harmonics, minimize the energy amplification phenomenon at a specific frequency, prevent severe distortion of the voltage and current waveforms, and reduce transmission losses.

[0095] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for suppressing even-order harmonics in a high-voltage power grid, characterized in that: Includes steps: S1. Obtain power parameters of the high-voltage power grid, perform real-time analysis on the power signal at the access point of the photovoltaic power generation system through time-frequency analysis, and obtain the time and frequency characteristics of even harmonics in the power signal at the access point of the photovoltaic power generation system; S2. Analyze the nonlinear characteristics of the photovoltaic power generation system, and evaluate the impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid in combination with the output power and access point location of the photovoltaic power generation; S3. Combined with the characteristics of the photovoltaic system, the power conservation theory is used to distinguish the current components flowing into the grid and perform real-time even harmonic detection; S4, based on the real-time harmonic detection results, combined with the phase-locked loop synchronization algorithm of the double second-order generalized integrator, the phase between the photovoltaic power generation system and the power grid is synchronized; S5. Analyze the resonance conditions in the high-voltage power grid and optimize the synchronization algorithm to suppress even-order harmonics.

2. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 1, characterized in that: In step S1, S11. Deploy smart sensor networks at key nodes of the high-voltage power grid, use the Internet of Things to build a distributed monitoring system, and analyze power parameters from sensors, including voltage and current; S12, performing time-frequency analysis on power parameters based on short-time Fourier transform to obtain power spectrum density; S13. Use heat maps to display power spectrum density, observe the changes in frequency components at different time points, and identify the time and frequency characteristics of even harmonics.

3. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 2, characterized in that: Time-frequency analysis of power parameters based on short-time Fourier transform: The input signal is the voltage or current signal at the access point of the photovoltaic power generation system. The input signal x(t) is divided into several overlapping small segments, and the window function x is applied to each segment. w (n) = x(n)·w(n), where n is a specific moment in the time series and the w(n) window function is used to limit the data fragment within the time window; Apply discrete Fourier transform to the signal within each window to obtain the time-frequency representation Among them, τ is the time offset, representing different time periods, f is the frequency index, indicating the frequency component, and X(τ,f) is the complex value at a specific time and frequency, reflecting the frequency distribution at that moment.

4. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 1, characterized in that: In step S2, a mathematical model of the nonlinear characteristics of the photovoltaic power generation system is established: Where V is voltage, I is current, and R s ,R p is the series resistance and parallel resistance, I ph is the photocurrent, I0 is the reverse saturation current, Vt is the thermal voltage, n is the diode quality factor, N s is the number of photovoltaic cells connected in series.

5. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 4, characterized in that: In step S2, the impact of the photovoltaic power generation system on the harmonic level of the power grid near the access point is evaluated and an evaluation model is established; The output power of the photovoltaic power generation system is P = V*I, where V and I are the output voltage and current of the photovoltaic cell; Evaluate the impact of access point location on harmonic levels: Where H(f) is the harmonic transfer function, which represents the efficiency of harmonic transfer from the photovoltaic power generation system to the grid, and Z grid (f) is the impedance of the grid at frequency f, Z PV (f) is the impedance of the photovoltaic power generation system at frequency f. The nonlinear characteristics of the photovoltaic power generation system, output power fluctuations and the influence of the access point location are combined to evaluate the overall impact of the photovoltaic power generation system on the harmonic level of the high-voltage power grid: THD grid is the total harmonic distortion rate of the power grid, f n is the frequency of the nth harmonic, I PV (f n ) is the photovoltaic power generation system at frequency f n Harmonic current at grid (f1) is the current of the grid at the fundamental frequency f1.

6. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 1, characterized in that: In step S3, the power conservation theory is combined with the photovoltaic system characteristics obtained in step S2 to distinguish the current components flowing into the grid, including active current, reactive current and harmonic current.

7. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 1, characterized in that: In step S4, the steps of the phase-locked loop synchronization algorithm of the biquad generalized integrator include: S41, using the collected voltage signal as the input of SOGI-PLL; S42, SOGI module separates the fundamental component and generates an orthogonal component; S43, constructing a PLL using the fundamental wave and quadrature signal provided by SOGI to detect the frequency and phase of the grid voltage; S44. Calculate the phase difference between the actual output current and the expected value, and adjust the output of the inverter through a feedback mechanism to keep the two in phase.

8. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 7, characterized in that: At each sampling time n, the phase error is e[n]=arctan2(v β [n],v α [n])-θ[n]; θ[n] is the angle of PLL output at the moment; v α [n] is the fundamental component, v β [n] is the orthogonal component; According to the phase error, the amount and angle of the inverter output are adjusted to achieve phase synchronization between the photovoltaic power generation system and the power grid.

9. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 8, characterized in that: In step S5, the resonant frequency is Calculate, where L is the inductance value and C is the capacitance value.

10. A method for suppressing even-order harmonics in a high-voltage power grid according to claim 9, characterized in that: Add a resonant frequency compensation mechanism to the PLL to further suppress even-order harmonics, and the proportional gain K p and integral gain K i After correction, K p (t) = K p0 +K pf (f(t)-f0), K i (t) = K i0 +K if (f(t)-f0); where K p0 , K i0 are the initial proportional and integral gains, K pf , K if is the frequency-dependent gain coefficient, f0 is the standard grid frequency, and f(t) is the actual measured grid frequency.

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