Multi-dimensional performance improvement method and system for grid-connected inverter based on variable gain feedback phase-locked loop

Abstract

This invention provides a method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops (PLLs), comprising: Step S1: Setting a variable gain module in the feedback loop of the inverter's PLL to construct a novel PLL model based on variable gain feedback; wherein, the variable gain module includes a high-pass filter and a band-stop filter; the high-pass filter is used to extract harmonic components from the angular frequency information output by the PLL; the band-stop filter is used to reduce the gain on both sides of the fundamental frequency, increase the mid-frequency gain, and reduce the high-frequency gain, thereby improving the characteristics of the PLL, achieving lower gain at both the fundamental and high frequencies, demonstrating better harmonic suppression, and providing ample bandwidth in the absence of harmonic amplification. Step S2: Based on the constructed novel PLL model based on variable gain feedback, the harmonics on both sides of the fundamental frequency are weakened, high-frequency harmonics are suppressed, the harmonic suppression capability is improved, the mid-frequency bandwidth is maintained, and the dynamic characteristics are improved.

Description

Technical Field

[0001] This invention relates to the field of AC power generation, transmission, distribution and consumption, and more specifically, to a method and system for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops. Background Technology

[0002] The grid connection penetration rate of distributed energy sources such as wind, solar, and biomass energy is experiencing explosive growth. This trend, while optimizing the primary energy structure of the power system and reducing the pressure on carbon emission reduction on the generation side, has also made power electronics technology a research hotspot. In new power systems, renewable energy needs to be connected to the grid via power conversion equipment such as inverters. As the core interface for energy exchange, the stable operation capability of the inverter directly affects the utilization efficiency of renewable energy and the actual safety boundary of grid operation.

[0003] As the hub of power conversion, the inverter comprises a main power circuit and a complex control system, with the vector current loop and phase-locked loop (PLL) forming its control core. The vector current loop aims to precisely regulate the inverter's output power, while the PLL is responsible for capturing the phase and frequency of the grid voltage in real time, ensuring high-precision synchronization between the output current and the grid voltage. In existing technologies, the Synchronous Reference Frame Phase-locked Loop (SRF-PLL) is widely adopted due to its clear principle and ease of engineering implementation. The SRF-PLL relies on a phase detector to extract the phase deviation of the input signal, which is then filtered by a proportional-integral (PI) controller to remove high-frequency noise, ultimately driving a voltage-controlled oscillator to achieve frequency compensation and phase tracking.

[0004] However, the dynamic response and steady-state accuracy of SRF-PLL are highly dependent on the parameter design of the PI controller. Due to the complex and variable grid-connected operating conditions, a PI controller with fixed parameters struggles to maintain optimal performance across all operating conditions. Traditional phase-locked loops (PLLs) exhibit a harmonic amplification phenomenon near the fundamental frequency, meaning their harmonic suppression capability is poor. Adding external filters to enhance harmonic suppression reduces system bandwidth, leading to lag in the synchronization process. Conversely, blindly increasing bandwidth in pursuit of rapid synchronization can easily trigger resonance risks in the sub- / super-synchronous frequency range, jeopardizing grid stability. Therefore, the inherent deficiencies of SRF-PLLs in harmonic suppression, stability, and speed necessitate extensive theoretical calculations and experimental verification in PI parameter tuning. This results in cumbersome procedures that struggle to address multi-dimensional control objectives, becoming a bottleneck restricting the high-performance operation of inverters.

[0005] In summary, the traditional SRF-PLL phase-locked loop (PLL) faces challenges in balancing harmonic suppression, stability, and dynamic characteristics, leading to difficulties in designing the system's PI parameters. To address this, this invention reshapes the PLL's characteristics by modifying its internal structure, achieving: suppressed harmonics near the fundamental frequency, maintained bandwidth, and guaranteed stability. This overcomes the inherent limitations of traditional PLLs in balancing multiple performance aspects, thus improving the stability of renewable energy grid-connected systems.

[0006] Patent document CN117578517A (application number: 202311631310.9) discloses a method and system for suppressing near-power frequency oscillations in a new energy flexible direct transmission system. The method includes: adding a near-power frequency oscillation suppression stage to the phase-locked loop (PLL) of the grid-connected inverter controller of the new energy unit; inputting the synchronous angular frequency signal output from the PLL of the grid-connected inverter of the new energy unit into the near-power frequency oscillation suppression stage to obtain an oscillation voltage component; and subtracting the oscillation voltage component from the input of the PLL of the grid-connected inverter of the new energy unit, i.e., the q-axis voltage at the grid connection point, to suppress near-power frequency oscillations. This document also proposes adding a feedback channel inside the PLL, but its feedback loop only includes a high-pass filter and a fixed gain, therefore the gain is the same for different frequency harmonics, without differentiation. Figure 5 As shown, this makes it difficult for the system to simultaneously achieve both a "harmonic-free amplification region" and "sufficient system bandwidth." If the goal is to improve harmonic suppression, a smaller bandwidth is required, while a larger bandwidth results in poor filtering of harmonics near the fundamental frequency and at higher frequencies. This invention, by adding a band-stop filter structure to the feedback channel and flexibly setting the low-gain region, allows for arbitrary shaping of the phase-locked loop characteristics. The characteristic shape can be arbitrarily changed according to the requirements of the actual application scenario to improve system performance and achieve a balance of multiple characteristics (harmonic suppression, stability, and dynamic characteristics). Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops.

[0008] A method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops, provided by the present invention, includes: Step S1: Set up a variable gain module in the inverter phase-locked loop feedback loop to construct a new phase-locked loop model based on variable gain feedback; Step S2: Based on the constructed novel phase-locked loop model with variable gain feedback, the harmonics on both sides of the fundamental frequency are weakened, high-frequency harmonics are suppressed, the harmonic suppression capability is improved, the mid-frequency bandwidth is maintained, and the dynamic characteristics are improved.

[0009] Preferably, the inverter phase-locked loop feedback loop includes: The expression for the phase-locked loop input signal in the abc coordinate system is:

[0010] in, u a , u b and u c The three-phase voltage of the power grid U 1 represents the phase voltage amplitude. θ Voltage phase; Through Clark transformation, the grid voltage remains stationary in both phases. αβ The coordinates are represented as:

[0011] in, u α , u β For the grid voltage at α、β Voltage components on the axis; Further performing the Park transformation yields the voltage expression in the dq coordinate system:

[0012] in, u d , u q for dq Voltage components of the coordinate axes, θ PLL This is the phase angle value output by the phase-locked loop.

[0013] Preferably, the variable gain module in step S1 includes a high-pass filter and a band-stop filter; The high-pass filter is used to extract harmonic components from the angular frequency information output by the phase-locked loop. The band-stop filter is used to reduce the gain on both sides of the fundamental frequency, increase the gain in the mid-frequency band, and reduce the gain in the high-frequency band, thereby improving the characteristics of the phase-locked loop. It has lower gain at both the fundamental and high frequencies, exhibits better harmonic suppression, and has ample bandwidth in the absence of harmonic amplification.

[0014] Preferably, the high-pass filter comprises:

[0015] in, T h It is the time constant of the high-pass filter; For frequency domain Laplace; The transfer function of the high-pass filter added in the feedback loop; The band-stop filter includes:

[0016] in, For frequency domain Laplace, ω 0 represents the center frequency of the filter. Q 1, Q 2 is the quality factor; to achieve the band resistance effect, it is necessary to... Q 1> Q 2. To ensure the center frequency gain is less than 0dB; Let be the transfer function of the band-stop filter added to the feedback loop.

[0017] Preferably, the novel phase-locked loop model based on variable gain feedback includes:

[0018] in, The proportional gain of the phase-locked loop PI controller. For the integral coefficients of the phase-locked loop PI controller, This is the module gain value.

[0019] A multi-dimensional performance enhancement system for grid-connected inverters based on a variable gain feedback phase-locked loop, according to the present invention, includes: Module M1: A variable gain module is set in the inverter phase-locked loop feedback loop to construct a new phase-locked loop model based on variable gain feedback; Module M2: Based on the constructed novel phase-locked loop model with variable gain feedback, it weakens harmonics on both sides of the fundamental frequency, suppresses high-frequency harmonics, improves harmonic suppression capability, maintains mid-frequency bandwidth, and enhances dynamic characteristics.

[0020] Preferably, the inverter phase-locked loop feedback loop includes: The expression for the phase-locked loop input signal in the abc coordinate system is:

[0021] in, u a , u b and u c The three-phase voltage of the power grid U 1 represents the phase voltage amplitude. θ Voltage phase; Through Clark transformation, the grid voltage remains stationary in both phases. αβ The coordinates are represented as:

[0022] in, u α ,u β For the grid voltage at α、β Voltage components on the axis; Further performing the Park transformation yields the voltage expression in the dq coordinate system:

[0023] in, u d , u q for dq Voltage components of the coordinate axes, θ PLL This is the phase angle value output by the phase-locked loop.

[0024] Preferably, the variable gain module in module M1 includes a high-pass filter and a band-stop filter; The high-pass filter is used to extract harmonic components from the angular frequency information output by the phase-locked loop. The band-stop filter is used to reduce the gain on both sides of the fundamental frequency, increase the gain in the mid-frequency band, and reduce the gain in the high-frequency band, thereby improving the characteristics of the phase-locked loop. It has lower gain at both the fundamental and high frequencies, exhibits better harmonic suppression, and has ample bandwidth in the absence of harmonic amplification.

[0025] Preferably, the high-pass filter comprises:

[0026] in, T h It is the time constant of the high-pass filter; For frequency domain Laplace; The transfer function of the high-pass filter added in the feedback loop; The band-stop filter includes:

[0027] in, For frequency domain Laplace, ω 0 represents the center frequency of the filter. Q 1, Q 2 is the quality factor; to achieve the band resistance effect, it is necessary to... Q 1> Q 2. To ensure the center frequency gain is less than 0dB; Let be the transfer function of the band-stop filter added to the feedback loop.

[0028] Preferably, the novel phase-locked loop model based on variable gain feedback includes:

[0029] in, The proportional gain of the phase-locked loop PI controller. For the integral coefficients of the phase-locked loop PI controller, This is the module gain value.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention, through a variable gain feedback structure, can greatly improve the harmonic suppression capability, without amplifying harmonics near the fundamental frequency, and also improves the suppression capability of high-frequency harmonics. 2. By increasing the mid-frequency gain (but not exceeding 0dB), the phase-locked loop can maintain sufficient bandwidth without amplifying harmonics, thus ensuring the dynamic characteristics of the grid-connected inverter system. 3. This invention can simultaneously take into account the system's stability and dynamic speed requirements in different power grid scenarios, solving the problem of incompatibility between transient and steady-state characteristics in existing methods. Attached Figure Description

[0031] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the phase-locked loop control structure for a grid-connected inverter based on variable gain feedback.

[0032] Figure 2 This is a schematic diagram comparing the characteristics of a phase-locked loop (PLL) for a grid-connected inverter based on variable gain feedback with those of a traditional PLL.

[0033] Figures 3a to 3b This is a schematic diagram comparing the dynamic characteristics under sudden current changes.

[0034] Figure 4 A schematic diagram comparing the output phase angle error under harmonic injection (65Hz).

[0035] Figure 5 This is a comparative diagram of the Bode plot of a traditional phase-locked loop, existing literature, and the phase-locked loop of this invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0037] Example 1 According to the present invention, a method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops (PLLs) includes: setting a variable gain module in the feedback loop of the inverter's PLL to construct a novel PLL model based on variable gain feedback; and implementing refined modification of the characteristics of PLLs in different frequency bands based on the constructed novel PLL model based on variable gain feedback. In this embodiment, the harmonic amplification region is completely eliminated and the gain is significantly reduced on both sides of the fundamental frequency. The amplitude-frequency gain of the PLL is kept slightly less than 0dB near 20 and 80Hz, and the gain is significantly attenuated in the region above 80Hz. This achieves the purpose of weakening harmonics on both sides of the fundamental frequency, maintaining bandwidth in the mid-frequency band, and suppressing harmonics in the high-frequency band, effectively improving the characteristics of the PLL and enhancing the system's stability, harmonic suppression capability, and dynamic response.

[0038] In this embodiment, the analysis of the inverter phase-locked loop feedback loop and output phase angle characteristics includes: The expression for the phase-locked loop input signal (common coupling point voltage) in the abc coordinate system is: (1) in, u a , u b and u c The three-phase voltage of the power grid U 1 represents the phase voltage amplitude. θ This refers to the voltage phase.

[0039] Through Clark transformation, the grid voltage remains stationary in both phases. αβ Coordinates can be represented as: (2) in, u α , u β For the grid voltage at α、β Voltage components on the axis.

[0040] Further performing the Park transformation yields the voltage expression in the dq coordinate system: (3) in, u d , u q for dq Voltage components of the coordinate axes, θ PLL This is the phase angle value output by the phase-locked loop.

[0041] The novel phase-locked loop model based on variable gain feedback includes: When a disturbance is present on the input side of the phase-locked loop (PLL), the disturbance will pass through the PLL and affect the output phase angle value. The control structure block diagram of this invention is as follows: Figure 1 As shown, this structure first extracts the angular frequency information of the phase-locked loop output on the output side, and then extracts the harmonic components through a high-pass filter. The transfer function of the high-pass filter is as follows.

[0042] (4) in, T h It is the time constant of the high-pass filter; For frequency domain Laplace; The transfer function of the high-pass filter added in the feedback loop; After passing through this filter, the harmonic components are then input into a band-stop filter (variable gain feedback structure), whose transfer function is: (5) in, ω 0 represents the center frequency of the filter. Q 1, Q 2 is the quality factor; to achieve the band resistance effect, it is necessary to... Q 1> Q 2. To ensure that the center frequency gain is less than 0dB; The transfer function of the band-stop filter added in the feedback loop; Finally, the harmonics are amplitude-adjusted through the gain Ks and returned to the input to cancel them out. The open-loop transfer function of this structure is: (6) in, Let be the overall transfer function of the phase-locked loop. The proportional gain of the phase-locked loop PI controller. For the integral coefficients of the phase-locked loop PI controller, This is the module gain value; A comparison of the Bode plots of the closed-loop transfer functions of a traditional phase-locked loop (PLL) and the PLL proposed in this invention is shown below. Figure 2 As shown. Overall, the phase-locked loop (PLL) of this invention has three gain peaks symmetrical about the fundamental frequency, none of which exceed 0dB, exhibiting new characteristics in amplitude-frequency characteristics compared to traditional PLL structures. By reducing the gain on both sides of the fundamental frequency (30-70Hz), increasing the mid-frequency gain (20-30Hz; 70-80Hz), and reducing the high-frequency gain (>80Hz) through a band-stop filter, the characteristics of the PLL are improved. It has lower gain at both the fundamental and high frequencies, demonstrating better harmonic suppression, and can provide ample bandwidth in the region without harmonic amplification (the region with amplitude >0dB).

[0043] Ensuring that all system parameters except the phase-locked loop (PLL) are identical, a dynamic characteristic comparison is made between a traditional PLL and the PLL proposed in this invention. For example... Figures 3a to 3b As shown, when the system's d-axis current command value abruptly changes from 300A to 500A, the traditional phase-locked loop completely loses stability after a brief transient process. The phase-locked loop proposed in this invention, however, can regain system stability after a shorter transient process, demonstrating the multiple advantages of this new structure in terms of dynamic characteristics and system stability.

[0044] like Figure 4 As shown, a per-unit disturbance voltage of 0.1 pu (65 Hz) was added to the input voltage of the phase-locked loop (PLL), and the phase angle errors of the conventional PLL and the PLL of this invention were compared. Clearly, the conventional PLL and the PLL of this invention amplified and reduced the input harmonics, respectively. Therefore, the novel PLL proposed in this invention demonstrates a significant advantage in harmonic suppression.

[0045] The present invention also provides a multi-dimensional performance enhancement system for grid-connected inverters based on variable gain feedback phase-locked loops (VPLs). This system can be implemented by executing the steps of the method for multi-dimensional performance enhancement of grid-connected inverters based on VPLs. In other words, those skilled in the art can understand the method for multi-dimensional performance enhancement of grid-connected inverters based on VPLs as a preferred embodiment of the system for multi-dimensional performance enhancement of grid-connected inverters based on VPLs.

[0046] This embodiment establishes a phase-locked loop (PLL) system model and modifies the internal feedback loop of the PLL to achieve refined management of harmonics at different frequencies. It effectively suppresses high-frequency harmonics near the fundamental frequency while ensuring overall system performance. This invention provides a novel design and application approach for PLL systems in grid-connected inverters, offering the following advantages: This invention adds a feedback path to the phase-locked loop (PLL) for finely managed harmonics. It allows for adjustments to the actual feedback gain value based on harmonics in different frequency bands, thereby reshaping the PLL's amplitude-frequency characteristics. This significantly reduces the PLL gain on both sides of the fundamental frequency, and also lowers the high-frequency amplitude, eliminating the harmonic amplification region and enabling the inverter grid-connected system to exhibit excellent broadband harmonic suppression characteristics. While maintaining the PLL bandwidth and dynamic speed without reduction, it significantly enhances the system's harmonic suppression capability and stability, achieving a simultaneous improvement in the multi-dimensional performance of the inverter grid-connected system.

[0047] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0048] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for improving multi-dimensional performance of a grid-connected inverter based on variable gain feedback phase-locked loop, characterized in that, include: Step S1: Set up a variable gain module in the inverter phase-locked loop feedback loop to construct a new phase-locked loop model based on variable gain feedback; Step S2: Based on the constructed novel phase-locked loop model with variable gain feedback, the harmonics on both sides of the fundamental frequency are weakened, high-frequency harmonics are suppressed, the harmonic suppression capability is improved, the mid-frequency bandwidth is maintained, and the dynamic characteristics are improved.

2. The method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops according to claim 1, characterized in that, The inverter phase-locked loop feedback circuit includes: The expression for the phase-locked loop input signal in the abc coordinate system is: in, u a , u b and u c The three-phase voltage of the power grid. U 1 represents the phase voltage amplitude. θ Voltage phase; Through Clark transformation, the grid voltage remains stationary in both phases. αβ The coordinates are represented as: in, u α , u β For the grid voltage at α、β Voltage components on the axis; Further performing the Park transformation yields the voltage expression in the dq coordinate system: in, u d , u q for dq Voltage components of the coordinate axes, θ PLL This is the phase angle value output by the phase-locked loop.

3. The method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops according to claim 1, characterized in that, The variable gain module in step S1 includes a high-pass filter and a band-stop filter; The high-pass filter is used to extract harmonic components from the angular frequency information output by the phase-locked loop. The band-stop filter is used to reduce the gain on both sides of the fundamental frequency, increase the gain in the mid-frequency band, and reduce the gain in the high-frequency band, thereby improving the characteristics of the phase-locked loop. It has lower gain at both the fundamental and high frequencies, exhibits better harmonic suppression, and has ample bandwidth in the absence of harmonic amplification.

4. The method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops according to claim 3, characterized in that, The high-pass filter includes: in, T h It is the time constant of the high-pass filter; For frequency domain Laplace; Let be the transfer function of the high-pass filter added in the feedback loop; The band-stop filter includes: in, For frequency domain Laplace, ω 0 represents the center frequency of the filter. Q 1, Q 2 is the quality factor; to achieve the band resistance effect, it is necessary to... Q 1> Q 2. To ensure that the center frequency gain is less than 0dB; Let be the transfer function of the band-stop filter added to the feedback loop.

5. The method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops according to claim 4, characterized in that, The novel phase-locked loop model based on variable gain feedback includes: in, The proportional gain of the phase-locked loop PI controller. For the integral coefficients of the phase-locked loop PI controller, This is the module gain value.

6. A multi-dimensional performance enhancement system for grid-connected inverters based on a variable gain feedback phase-locked loop, characterized in that, include: Module M1: A variable gain module is set in the inverter phase-locked loop feedback loop to construct a new phase-locked loop model based on variable gain feedback; Module M2: Based on the constructed novel phase-locked loop model with variable gain feedback, it weakens harmonics on both sides of the fundamental frequency, suppresses high-frequency harmonics, improves harmonic suppression capability, maintains mid-frequency bandwidth, and enhances dynamic characteristics.

7. The multi-dimensional performance enhancement system for grid-connected inverters based on variable gain feedback phase-locked loops according to claim 6, characterized in that, The inverter phase-locked loop feedback circuit includes: The expression for the phase-locked loop input signal in the abc coordinate system is: in, u a , u b and u c The three-phase voltage of the power grid. U 1 represents the phase voltage amplitude. θ Voltage phase; Through Clark transformation, the grid voltage remains stationary in both phases. αβ The coordinates are represented as: in, u α , u β For the grid voltage at α、β Voltage components on the axis; Further performing the Park transformation yields the voltage expression in the dq coordinate system: in, u d , u q for dq Voltage components of the coordinate axes, θ PLL This is the phase angle value output by the phase-locked loop.

8. The method for multi-dimensional performance improvement of grid-connected inverters based on variable gain feedback phase-locked loops according to claim 6, characterized in that, The variable gain module in module M1 includes a high-pass filter and a band-stop filter; The high-pass filter is used to extract harmonic components from the angular frequency information output by the phase-locked loop. The band-stop filter is used to reduce the gain on both sides of the fundamental frequency, increase the gain in the mid-frequency band, and reduce the gain in the high-frequency band, thereby improving the characteristics of the phase-locked loop. It has lower gain at both the fundamental and high frequencies, exhibits better harmonic suppression, and has ample bandwidth in the absence of harmonic amplification.

9. The multi-dimensional performance enhancement system for grid-connected inverters based on variable gain feedback phase-locked loops according to claim 8, characterized in that, The high-pass filter includes: in, T h It is the time constant of the high-pass filter; For frequency domain Laplace; Let be the transfer function of the high-pass filter added in the feedback loop; The band-stop filter includes: in, For frequency domain Laplace, ω 0 represents the center frequency of the filter. Q 1, Q 2 is the quality factor; to achieve the band resistance effect, it is necessary to... Q 1> Q 2. To ensure that the center frequency gain is less than 0dB; Let be the transfer function of the band-stop filter added to the feedback loop.

10. The multi-dimensional performance enhancement system for grid-connected inverters based on a variable gain feedback phase-locked loop according to claim 9, characterized in that, The novel phase-locked loop model based on variable gain feedback includes: in, The proportional gain of the phase-locked loop PI controller. For the integral coefficients of the phase-locked loop PI controller, This is the module gain value.

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