Single-phase grid-connected inverter with double frequency ripple suppression and hybrid synchronization control method

Abstract

This invention discloses a hybrid synchronous control method for a single-phase grid-type converter with second-harmonic ripple suppression, belonging to the field of power electronics and energy storage control. The method obtains virtual α and β axis components from the voltage waveform, and then obtains d and q axis voltage components through Park transformation. It determines whether filtering of the q-axis voltage component is needed; if so, it performs filtering, and then calculates the PLL branch angular frequency. Combining the VSG active loop angular frequency with the grid rated angular frequency, a fused angular frequency is calculated. This fused angular frequency is used to calculate the corrected phase for active loop control, and the corrected phase is input to the voltage-current dual closed-loop module. This method can suppress second-harmonic ripple, improve transient overcurrent suppression capability, improve waveform distortion, and enhance system stability under grid intensity variations.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and energy storage control technology, specifically relating to a hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression. Background Technology

[0002] With the increasing penetration rate of renewable energy sources such as wind power and photovoltaics, the power system is accelerating its transformation towards a "dual-high" model of high renewable energy and high power electronic equipment. During this process, problems such as insufficient system inertia and decreased frequency and voltage support capabilities caused by the grid connection of new energy sources are becoming increasingly severe, placing higher demands on the synchronous control performance of grid-connected converters.

[0003] Currently, grid-connected converter synchronization control is mainly divided into two categories: grid-following control uses a phase-locked loop (PLL) to track the grid phase to achieve synchronization. It has a fast synchronization speed under large disturbances, but its stability is insufficient under weak grid conditions, and it cannot actively provide inertia and voltage support. Grid-building control is typically based on a virtual synchronous generator (VSG). It autonomously establishes voltage and frequency by simulating the rotor motion equation of a synchronous generator, and can provide inertia and damping support for the grid.

[0004] However, the fusion angular frequency of the active power loop in a traditional VSG is determined solely by the active power-frequency droop characteristic and rotor inertia, without incorporating the grid angular frequency measured by a phase-locked loop. Synchronization is maintained entirely by the active power loop's own regulation, lacking the rapid phase tracking capability required for grid-based control. Under complex disturbance conditions such as grid voltage dips and wide-range variations in grid strength, the transient stability of traditional VSGs becomes particularly problematic, with the power angle easily increasing. If faults are not cleared in time, the converter is prone to losing synchronization with the grid.

[0005] Furthermore, existing control methods are mostly designed for three-phase systems. When directly applied to single-phase grid-connected energy storage converters, they suffer from inherent technical bottlenecks: the inherent second-harmonic ripple of instantaneous power in a single-phase system, after coupling through the control loop, significantly increases the harmonics of the grid-connected current, deteriorating power quality. Conventional solutions use low-pass filters to suppress 100Hz ripple, but this requires setting the cutoff frequency to around 10Hz, which drastically reduces the dynamic response speed of the power loop, making it difficult to simultaneously meet the requirements of ripple suppression and rapid adjustment. Summary of the Invention

[0006] This invention proposes a hybrid synchronous control method for single-phase grid converters with second harmonic ripple suppression, which overcomes the problems of severe second harmonic ripple interference, insufficient transient overcurrent suppression capability leading to waveform distortion, and easy instability under changes in grid strength in existing single-phase grid converters.

[0007] A hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression includes the following steps:

[0008] S1: Obtain the single-phase output voltage waveform and rated angular frequency of the single-phase grid converter from time 0 to the current time t. Then, obtain the voltage waveform through a Laplace transform. The data is then input into SOGI, where it is processed to obtain virtual α and β axis components.

[0009] S2: Perform an inverse Laplace transform on the virtual α and β axis components to obtain the α axis components in the time domain. and β-axis components Using the reference phase of the virtual synchronous generator (VSG) as a reference, Park transformation is performed to obtain the d-axis component and the q-axis voltage component.

[0010] S3: The Step module of the power grid generates a gating signal based on the current transition disturbance to determine whether the q-axis voltage component needs to be adjusted. Filter; if necessary, proceed to step S4;

[0011] S4: For the q-axis voltage component A notch filter is used for filtering, and the angular frequency of the PLL branch output is calculated. ;

[0012] S5: Active power reference value and rated angular frequency of the power grid Calculate the angular frequency of the VSG active loop in the power grid based on the actual output active power. ;

[0013] S6: Combine the angular frequencies from S4 and S5 to obtain the combined angular frequency. And calculate the corrected phase. ;

[0014] S7: Through the corrected phase Update VSG reference phase It also participates in active power loop control; simultaneously, the corrected phase The input is fed into a voltage and current dual closed-loop module to provide a precise phase reference for the converter; the corrected q-axis voltage component is calculated. .

[0015] Furthermore, in step S1, the processing formula for SOGI is:

[0016]

[0017] Represents the virtual α-axis component; This represents the virtual β-axis component; k represents the control coefficient. This indicates the rated angular frequency of a single-phase grid converter; The frequency domain representation of the single-phase output voltage waveform of a single-phase grid converter after Laplace transform; s represents the Laplace operator.

[0018] Furthermore, in step S2, the formula for the Park transformation is:

[0019]

[0020] In the formula, and These represent the d-axis component and the q-axis voltage component, respectively. Indicates the VSG reference phase;

[0021] Further, in step S4, the center frequencies of the two notch filters are 100Hz and 200Hz, respectively, and their center angular frequencies are respectively... and The damping ratio is taken as 0.707.

[0022] The transfer function of a 100Hz notch filter is:

[0023]

[0024] In the formula, Represents the Laplace operator;

[0025] The transfer function of the 200Hz notch filter is:

[0026]

[0027] In the formula, Represents the Laplace operator;

[0028] q-axis voltage component Using the Laplace transform, we obtain The formula for calculating the angular frequency of the PLL branch output is:

[0029]

[0030]

[0031] In the formula, This indicates the angular frequency output by the PLL branch; This represents the transfer function of the two notch filters connected in series.

[0032] Furthermore, in step S5, the formula for calculating the angular frequency of the VSG active loop is:

[0033]

[0034] In the formula, Represents virtual inertia; Indicates the damping coefficient; This represents the virtual angular frequency generated by the VSG active power loop; This is a reference value for active power. This represents the actual active power value after the notch filter module filters out the second harmonic ripple; It is expressed as the rated angular frequency of the power grid.

[0035] Furthermore, the corrected formula for calculating the phase is as follows:

[0036] ;

[0037] In the formula, This indicates the corrected phase. This indicates the fused angular frequency.

[0038] Furthermore, the corrected q-axis voltage component The calculation formula is:

[0039] ;

[0040] In the formula, This represents the corrected q-axis voltage component; This represents the single-phase output voltage of a single-phase grid-type converter, obtained through acquisition. This indicates the phase of a single-phase grid converter, obtained through acquisition.

[0041] The beneficial effects that can be achieved by adopting the above technologies are:

[0042] 1. By introducing a notch filter, the attenuation of the notch filter at 100Hz is much greater than that of a low-pass filter, while the gain of both is close to 0dB at the 50Hz fundamental frequency, which does not affect the transmission of fundamental power. Therefore, the notch filter can more effectively filter out second harmonic ripple while ensuring dynamic performance. The notch filter scheme of this invention maintains the fast dynamic response of the active power loop while effectively filtering out second harmonic ripple.

[0043] 2. SOGI constructs virtual orthogonal components to achieve single-phase dq decoupling. Through precise transfer function design, SOGI constructs virtual orthogonal components with stable phase difference and good amplitude consistency, effectively avoiding phase deviation and amplitude attenuation problems inherent in traditional orthogonal component construction methods. Simultaneously, SOGI has a certain suppression effect on harmonics and noise interference in the grid voltage, ensuring the accuracy of subsequent PLL-assisted synchronization and phase compensation, and guaranteeing voltage phase stability during steady-state operation of the single-phase VSG.

[0044] 3. Traditional VSGs rely solely on rotor motion equations to adjust phase, resulting in large phase deviations and slow responses during grid disturbances, making them prone to power angle instability. This solution introduces a PLL-assisted phase tracking system to rapidly suppress frequency shifts during transients, significantly improving synchronization stability and preventing loss of synchronization with the grid.

[0045] 4. Under steady state, the phase deviation is approximately 0, the PLL does not function, and the system maintains the traditional VSG inertia support, damping characteristics and good steady-state accuracy; during disturbances, the PLL automatically engages to quickly correct the phase, taking into account both inertia support and fast synchronization capability, which is superior to single VSG or single PLL control. Attached Figure Description

[0046] Figure 1 This is a block diagram of hybrid synchronous control;

[0047] Figure 2 This is a simulation diagram of the virtual orthogonal components after Park transform and then passing through a notch filter module.

[0048] Figure 3 This is the Bode plot of a notch filter and a low-pass filter;

[0049] Figure 4 This is a simulation diagram of the PLL model;

[0050] Figure 5 This is a simulation diagram of the VSG active power loop.

[0051] Figure 6 This is a simulation setup diagram for a dual closed-loop voltage and current circuit.

[0052] Figure 7 This is a comparison waveform diagram of current limiting control; Figure 7 The left image shows the waveform of PI current limiting control in a rotating coordinate system. Figure 7 The right figure shows the dq-axis PI current limiting control waveform.

[0053] Figure 8 This is a waveform comparison diagram of voltage sag (VSG) and voltage sag (HSC); Figure 8 The left image in the diagram is a voltage sag (VSG) waveform. Figure 8 The right figure in the diagram is the voltage sag HSC waveform;

[0054] Figure 9 This is a waveform comparison diagram of VSG and HSC for changes in power grid intensity; Figure 9 The left figure in the image is a VSG waveform diagram showing the change in power grid intensity; Figure 9 The right figure in the diagram is the HSC waveform diagram of power grid intensity change. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] like Figure 1 As shown, a hybrid synchronous control method for a single-phase grid converter with second-harmonic ripple suppression includes the following steps:

[0057] S1: Construct the virtual orthogonal components of the single-phase grid converter through the second-order generalized integrator SOGI.

[0058] Specifically, this involves obtaining the single-phase output voltage waveform and rated angular frequency of the single-phase grid converter from time 0 to the current time t, and then performing a Laplace transform on the voltage waveform to obtain... The data is then input into SOGI, where it is processed to obtain the virtual α and β axis components. The SOGI processing formula is as follows:

[0059] (1)

[0060] In the formula, Represents the virtual α-axis component; This represents the virtual β-axis component; k represents the control coefficient, ranging from 0.5 to 1.5. This represents the rated angular frequency of a single-phase grid converter. ; The frequency domain representation of the single-phase output voltage waveform of a single-phase grid converter after Laplace transform; s represents the Laplace operator.

[0061] and Let be mutually orthogonal components, where and In phase, Lag The two coordinates are at 90°, forming a standard αβ orthogonal coordinate system, which provides the necessary prerequisite support for the subsequent Park transformation.

[0062] S2: Perform an inverse Laplace transform on the virtual α and β axis components to obtain the α axis components in the time domain. and β-axis components Park transformation is performed based on the reference phase of the virtual synchronous generator (VSG) (see simulation setup diagram for Park transformation). Figure 2 This yields the d-axis and q-axis voltage components; the formula is:

[0063]

[0064] In the formula, and These represent the d-axis component and the q-axis voltage component, respectively. Indicates the VSG reference phase;

[0065] S3: The Step module of the power grid generates a gating signal based on the current transition disturbance to determine whether the q-axis voltage component needs to be adjusted. Filtering.

[0066] The logic for judging the gating signal is as follows:

[0067] When jump time At that time, the q-axis voltage component is not considered. Filtering.

[0068] When jump time When this occurs, the notch filter stage in step S4 is triggered.

[0069] S4: Two second-order notch filters are used in series to filter out the second and fourth harmonics in the power grid.

[0070] In conventional VSG control strategies, to eliminate the impact of second-harmonic ripple, a low-pass filter (LPF) with a bandwidth of 1 / 10 of the second-harmonic ripple (i.e., 10Hz) is typically introduced into the power calculation. However, introducing an LPF reduces the bandwidth, making accurate tracking difficult when power changes rapidly during transient processes. To address this issue, this solution introduces a notch filter for filtering. A notch filter is incorporated into the PLL controller to... Perform filtering.

[0071] Two second-order notch filters connected in series can filter out the second and fourth harmonics in the power grid. The center frequencies of the two notch filters are 100Hz and 200Hz, respectively, and their center angular frequencies are respectively... and The damping ratio is taken as 0.707.

[0072] Therefore, the transfer function of the 100Hz notch filter is:

[0073] In the formula, Represents the Laplace operator; This indicates the damping ratio, set to 0.707; This indicates the center angular frequency of a 100Hz notch filter;

[0074] The transfer function of the 200Hz notch filter is:

[0075]

[0076] In the formula, Represents the Laplace operator; This indicates the damping ratio, set to 0.707; This indicates the center angular frequency of a 200Hz notch filter.

[0077] q-axis voltage component The q-axis voltage component in the frequency domain is obtained by using the Laplace transform. .Will The angular frequency of the PLL branch output is obtained by filtering through a series notch filter (see simulation diagram of the PLL model). Figure 4 The formula is:

[0078]

[0079]

[0080] In the formula, This indicates the angular frequency output by the PLL branch; This represents the transfer function of the two notch filters connected in series. Represents the q-axis voltage component in the frequency domain;

[0081] S5: Calculate the angular frequency of the VSG active power loop of the power grid using the grid's active power reference value, rated angular frequency, and actual output active power. See the VSG active power loop simulation diagram. Figure 5 .

[0082] The formula is:

[0083]

[0084] In the formula, This represents the virtual inertia, which is set to 0.02 in this embodiment. This represents the damping coefficient, which is set to 5 in this embodiment; This represents the virtual angular frequency generated by the VSG active power loop; For the active power reference value, 1kW is used in this embodiment. This indicates the actual value of active power after the notch filter module filters out the second harmonic ripple, which can prevent the second harmonic ripple in the original active power from introducing power loop oscillation; This is represented as the rated angular frequency of the power grid; in this embodiment, the value is taken as... .

[0085] S6: The angular frequency output from the aforementioned PLL branch. Performing the inverse Laplace transform yields Combined with the results obtained in step S5 and Calculate the fused angular frequency and then calculate the corrected phase based on the fused angular frequency.

[0086] The formula is:

[0087]

[0088] In the formula, Indicates the corrected phase; This indicates the fused angular frequency.

[0089] S7: Through the corrected phase Update VSG reference phase And participate in active power loop control; at the same time, the corrected The input voltage and current dual closed-loop module provides a precise phase reference for the converter.

[0090] Corrected q-axis voltage component The calculation formula is:

[0091]

[0092] In the formula, This represents the corrected q-axis voltage component; This represents the single-phase output voltage of a single-phase grid-type converter, obtained through acquisition. This indicates the phase of a single-phase grid converter, obtained through acquisition.

[0093] Effect comparison:

[0094] First and second harmonic ripple suppression effect;

[0095] like Figure 3 As shown, the frequency response Bode plots of the notch filter in this scheme are compared with those of a traditional low-pass filter. The notch filter exhibits significantly greater attenuation at 100Hz than the low-pass filter (which has almost no attenuation), thus effectively filtering out 100Hz signals. At the 50Hz fundamental frequency, the gain of both filters is close to 0dB, not affecting the transmission of fundamental power. Therefore, the notch filter can more effectively filter out second-harmonic ripple while maintaining dynamic performance.

[0096] II. Comparison of current limiting effects;

[0097] Current limiting control comparison waveforms are as follows Figure 7 As shown in the simulation, the grid voltage drops by 50% at 0.1s. The waveform shows that the control strategy before the improvement cannot meet the current limiting requirements, which will cause serious distortion of the output voltage and current. The improved control strategy can better limit the current and keep it synchronized with the grid.

[0098] Figure 7The left and right figures show the limiting waveform of a traditional rotating coordinate system PI control: when the current exceeds the limit value, only the output of the voltage inner loop is clamped, which leads to distortion of the current reference command, severe clipping distortion of the output current waveform, a significant increase in harmonic content, and system oscillation.

[0099] Figure 7 The right-middle figure shows the dq-axis PI control limiting waveform of the present invention: Independent PI control and limiting are performed on the d-axis current (active component) and q-axis current (reactive component) in the dq-axis rotating coordinate system. After limiting, the current waveform remains sinusoidal and without distortion, and the system operates smoothly.

[0100] III. Transient comparison of VSG and HSC under grid voltage dips;

[0101] like Figure 8 As shown in the simulation, the grid voltage drops by 50% at 1s and recovers at 2s. The waveform shows that the VSG cannot keep synchronized with the grid during the voltage drop, while the HSC can smoothly overcome the voltage drop process.

[0102] Figure 8 The left figure shows traditional VSG control: during voltage dips, active power oscillates violently, phase deviation continues to increase, it cannot track the grid phase, and eventually loses synchronization with the grid; even after the voltage recovers, it still cannot return to stability.

[0103] Figure 8 The right figure in the figure shows the hybrid synchronous control of the present invention: the transient detection unit quickly identifies disturbances, activates the PLL to assist phase compensation, the active power fluctuation is small during voltage drop, and the phase deviation converges quickly; after the voltage recovers, it smoothly transitions to steady state and always maintains synchronous and stable operation.

[0104] IV. Transient Comparison of VSG and HSC under Power Grid Intensity Variation

[0105] like Figure 9 As shown in the simulation, the short-circuit ratio (SCR) of the power grid suddenly drops from 5 (strong power grid) to 1 (weak power grid) at 1 second and recovers at 2 seconds. It can be seen from the waveform that the VSG cannot keep in sync with the power grid during the change of power grid strength, while the HSC can stably control the active and reactive power and smoothly transition through the process of power grid strength change.

[0106] Figure 9 The left figure shows traditional VSG control: during a sudden drop in grid strength, the power exhibits low-frequency oscillations; when the grid strength recovers, the system cannot keep up, the power angle becomes unstable, and eventually, synchronization is lost.

[0107] Figure 9The right figure in the figure shows the hybrid synchronization control of the present invention: during the entire process of grid strength change, active power and reactive power remain stable. The PLL auxiliary synchronization module automatically adjusts the compensation intensity according to the phase deviation. After the grid strength recovers, it quickly returns to steady state and always maintains synchronization stability.

[0108] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A single-phase network configuration type converter hybrid synchronization control method with a double-frequency ripple suppression function, characterized in that, Includes the following steps: S1: obtain the single-phase output voltage waveform of the single-phase network type converter from 0 time to the current t time and the rated angular frequency, and obtain the voltage waveform through Laplace transform and input into SOGI, processed by SOGI, and obtain the virtual alpha and beta axis components; S2: inverse Laplace transform of the virtual α and β axis components to obtain the time domain α axis component and β axis component Park transform based on the reference phase of the virtual synchronous generator VSG to obtain the d-axis component and the q-axis voltage component; S3: The Step module of the power grid generates a gating signal based on the current transition disturbance to determine whether the q-axis voltage component needs to be adjusted. Filter; if necessary, proceed to step S4; S4: For the q-axis voltage component A notch filter is used for filtering, and the angular frequency of the PLL branch output is calculated. ; S5: Active power reference value and rated angular frequency of the power grid Calculate the angular frequency of the VSG active loop in the power grid based on the actual output active power. ; S6: Combine the angular frequencies from S4 and S5 to obtain the combined angular frequency. And calculate the corrected phase. ; S7: Through the corrected phase Update VSG reference phase It also participates in active power loop control; simultaneously, the corrected phase The input is fed into a voltage and current dual closed-loop module to provide a precise phase reference for the converter; the corrected q-axis voltage component is calculated. .

2. The hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression function according to claim 1, characterized in that, In step S1, the SOGI processing formula is as follows: ； Represents the virtual α-axis component; This represents the virtual β-axis component; k represents the control coefficient. This indicates the rated angular frequency of a single-phase grid converter; The frequency domain representation of the single-phase output voltage waveform of a single-phase grid converter after Laplace transform; s represents the Laplace operator.

3. The hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression function according to claim 2, characterized in that, In step S2, the formula for the Park transformation is: ； In the formula, and These represent the d-axis component and the q-axis voltage component, respectively. This indicates the VSG reference phase.

4. The hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression function according to claim 1, characterized in that, In step S4, the center frequencies of the two notch filters are 100Hz and 200Hz, respectively, and their center angular frequencies are respectively... and The damping ratio is taken as 0.

707. The transfer function of a 100Hz notch filter is: ； In the formula, Represents the Laplace operator; The transfer function of the 200Hz notch filter is: ； In the formula, Represents the Laplace operator; q-axis voltage component Using the Laplace transform, we obtain The formula for calculating the angular frequency of the PLL branch output is: ； ； In the formula, This indicates the angular frequency output by the PLL branch; This represents the transfer function of the two notch filters connected in series.

5. The hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression function according to claim 4, characterized in that, In step S5, the formula for calculating the angular frequency of the VSG active loop is: ； In the formula, Represents virtual inertia; Indicates the damping coefficient; This represents the virtual angular frequency generated by the VSG active power loop; This is a reference value for active power. This represents the actual active power value after the notch filter module filters out the second harmonic ripple; It is expressed as the rated angular frequency of the power grid.

6. The hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression function according to claim 5, characterized in that, The corrected formula for calculating the phase is: ； In the formula, This indicates the corrected phase. This indicates the fused angular frequency.

7. The hybrid synchronous control method for a single-phase grid converter with second harmonic ripple suppression function according to claim 6, characterized in that, Corrected q-axis voltage component The calculation formula is: ； In the formula, This represents the corrected q-axis voltage component; This represents the single-phase output voltage of a single-phase grid-type converter, obtained through acquisition. This indicates the phase of a single-phase grid converter, obtained through acquisition.

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