Harmonic resonance suppression method, device and equipment based on phase margin compensation

Abstract

The invention discloses a harmonic resonance suppression method, device and equipment based on phase margin compensation, and relates to the field of harmonic resonance suppression, and the method comprises the steps: carrying out the equivalent modeling of a photovoltaic grid-connected system, and determining the equivalent impedance of a power grid; determining an open-loop transfer function of the photovoltaic grid-connected system; a quasi PR controller is determined; determining the open-loop cut-off frequency of the photovoltaic grid-connected system based on the quasi-PR controller and the open-loop transfer function; determining a phase margin index of the photovoltaic grid-connected system; determining a harmonic generation mechanism of the photovoltaic grid-connected system based on the phase margin index and the power grid equivalent impedance; judging whether the photovoltaic grid-connected system is stable or not; if not, constructing an advance link according to the maximum phase angle compensation amount; compensating the phase margin of the photovoltaic grid-connected system based on the lead link; constructing a proportion compensation link; adjusting the open-loop cut-off frequency of the photovoltaic grid-connected system based on the proportional compensation link; harmonic resonance possibly caused by the photovoltaic grid-connected inverter system can be effectively suppressed, and meanwhile, the low-frequency characteristic of the system is ensured.

Description

Technical Field

[0001] The present application relates to the field of harmonic resonance suppression, and in particular to a harmonic resonance suppression method, device and equipment based on phase margin compensation. Background Art

[0002] As photovoltaic (PV) penetration continues to increase, its grid-connected systems incorporate a large number of power electronic devices, generating significant harmonics. This poses significant challenges to grid security, stability, and power quality. Therefore, studying the harmonic resonance mechanisms of large-scale PV power plants and exploring solutions to these problems is crucial for their safe and stable operation.

[0003] Existing literature has investigated harmonic resonance in multi-inverter parallel systems caused by grid impedance. This primarily involves transforming the passive network model of a multi-inverter parallel system, finding that the grid impedance of a system with n parallel inverters is equivalent to amplifying it by a factor of n when applied to each inverter. Further consideration of the controller reveals that three types of resonance exist in multi-inverter parallel systems: internal resonance, parallel resonance, and series resonance. Other studies have analyzed the impact of the number and composition of parallel inverters and current controller parameters on the resonant characteristics of multi-inverter parallel systems in the presence of grid impedance. They have also analyzed the effects of inverter control and carrier asynchronous operation on the harmonic resonance characteristics of multi-inverter parallel systems. Using the root locus method and impedance analysis, the impact of grid impedance on the stability and harmonic content of the grid-connected current of multi-inverter parallel systems has been studied. However, further research is needed to investigate the impact of system stability margin variations on harmonic resonance. To address the harmonic resonance problem in multi-rectifier parallel systems, some scholars have proposed adding a resistive active damper at the common connection point of two parallel rectifier systems. This approach has some effect on resolving the system's harmonic resonance, but requires additional hardware, increasing system cost and reducing reliability. Solutions to the harmonic resonance problem in a single inverter include: improving the inverter's equivalent output impedance to eliminate the impact of grid impedance on the system. However, the grid-connected point voltage feedforward link in this approach is equivalent to introducing positive feedback into the current loop, reducing the system's stability in weak grid conditions; or reshaping the inverter's equivalent output impedance by connecting virtual impedances in series and parallel with the filter inductor and capacitor branches. This aims to suppress harmonic resonance by changing the inverter's output impedance. However, the virtual resistor connected in parallel with the capacitor branch is equivalent to the active damping link of the LCL, which is sensitive to changes in grid impedance.

[0004] Therefore, how to effectively suppress the harmonic resonance that may be caused by the photovoltaic grid-connected inverter system while ensuring the low-frequency characteristics of the system has become an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of this application is to provide a harmonic resonance suppression method, device and equipment based on phase margin compensation, which can effectively suppress the harmonic resonance that may be caused by the photovoltaic grid-connected inverter system while ensuring the low-frequency characteristics of the system.

[0006] To achieve the above objectives, this application provides the following solutions: In a first aspect, the present application provides a harmonic resonance suppression method based on phase margin compensation, comprising: Equivalent modeling of the photovoltaic grid-connected system to determine the equivalent impedance of the grid; Determine the open-loop transfer function of the photovoltaic grid-connected system; Determine the quasi-PR controller; Determining an open-loop cutoff frequency of a photovoltaic grid-connected system based on the quasi-PR controller and the open-loop transfer function; Determining a phase margin index of a photovoltaic grid-connected system based on the open-loop cut-off frequency; Determining a harmonic generation mechanism of a photovoltaic grid-connected system based on the phase margin index and the grid equivalent impedance; Determining whether the photovoltaic grid-connected system is stable based on the phase margin indicator; If it is unstable, then build an advance link based on the maximum phase angle compensation amount; Compensating the phase margin of the photovoltaic grid-connected system based on the leading link; Construct proportional compensation link; The open-loop cutoff frequency of the photovoltaic grid-connected system is adjusted based on the proportional compensation link.

[0007] Optionally, an equivalent model is constructed for the photovoltaic grid-connected system to determine the equivalent impedance of the grid. Specifically, the following formula is used: L eq = L 2+ nL g in, L g represents the equivalent impedance of the power grid, n Indicates the number of inverters, L eq Represents equivalent inductance ，L 2 Indicates grid-side inductance 。

[0008] Optionally, the open-loop transfer function of the photovoltaic grid-connected system is determined by using the following formula:

[0009] in, represents the open-loop transfer function of the photovoltaic grid-connected system, Indicates the output grid-connected current, represents the reference current, represents the equivalent gain of the PWM inverter, represents the transfer function of the quasi-PR controller, represents the differential operator, represents the inductance on the inverter side, represents the equivalent inductance, Represents the filter capacitor, Represents the active damping coefficient of capacitor current.

[0010] Alternatively, the expression of the quasi-PR controller is as follows:

[0011] in, represents the transfer function of the quasi-PR controller, represents the proportional gain coefficient, represents the resonant gain coefficient, represents the PR cutoff frequency, represents the differential operator.

[0012] Optionally, the open-loop cutoff frequency of the photovoltaic grid-connected system is determined based on the quasi-PR controller and the open-loop transfer function using the following formula:

[0013] in, Indicates the open-loop cutoff frequency of the photovoltaic grid-connected system, represents the proportional gain coefficient, represents the equivalent gain of the PWM inverter, represents the inductance on the inverter side, represents the equivalent inductance, represents the resonant gain coefficient, Indicates the PR cutoff frequency.

[0014] Optionally, the phase margin index of the photovoltaic grid-connected system is determined based on the open-loop cut-off frequency by using the following formula:

[0015] Among them, PM represents the phase margin index, Indicates the open-loop cutoff frequency of the quasi-PR controller in the photovoltaic grid-connected system The phase angle at It represents the open-loop cutoff frequency of the current open-loop transfer function in the photovoltaic grid-connected system when the quasi-PR controller is not considered. The phase angle, represents the inductance on the inverter side, represents the equivalent gain of the PWM inverter, represents the active damping coefficient of the capacitor current, represents the PR cutoff frequency, represents the resonant gain coefficient, represents the proportional gain coefficient, represents the resonant frequency, Indicates the resonant frequency when there is no PR controller. The calculation formula is as follows: ; in, Indicates filter capacitor.

[0016] Optionally, the mathematical model of the advance link is:

[0017] in, represents the lead link transfer function, represents the graduation coefficient, T represents the time constant, s represents the differential operator.

[0018] Optionally, the construction ratio compensation link specifically adopts the following formula:

[0019] in, represents the proportional compensation gain, Indicates the frequency corresponding to the phase peak, express The frequency corresponds to the lead link transfer function, express The frequency corresponds to the open-loop transfer function.

[0020] In a second aspect, the present application provides a harmonic resonance suppression device based on phase margin compensation, comprising: The grid equivalent impedance determination module is used to perform equivalent modeling of the photovoltaic grid-connected system and determine the grid equivalent impedance; An open-loop transfer function determination module is used to determine the open-loop transfer function of the photovoltaic grid-connected system; A quasi-PR controller determination module, used for determining a quasi-PR controller; An open-loop cutoff frequency determination module, configured to determine an open-loop cutoff frequency of a photovoltaic grid-connected system based on the quasi-PR controller and an open-loop transfer function; A phase margin index determination module, configured to determine a phase margin index of a photovoltaic grid-connected system based on the open-loop cut-off frequency; A photovoltaic grid-connected system harmonic generation mechanism determination module, configured to determine the photovoltaic grid-connected system harmonic generation mechanism based on the phase margin index and the grid equivalent impedance; A judgment module, configured to judge whether the photovoltaic grid-connected system is stable based on the phase margin indicator; An advance link construction module is used to construct an advance link according to a maximum phase angle compensation amount when the system is unstable; A phase margin compensation module, configured to compensate for the phase margin of the photovoltaic grid-connected system based on the leading link; A proportional compensation link building module is used to build a proportional compensation link; The open-loop cut-off frequency adjustment module is used to adjust the open-loop cut-off frequency of the photovoltaic grid-connected system based on the proportional compensation link.

[0021] In a third aspect, the present application provides a computer device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of any one of the above-mentioned methods for suppressing harmonic resonance based on phase margin compensation.

[0022] According to the specific embodiments provided in this application, this application discloses the following technical effects: The present application provides a harmonic resonance suppression method, device and equipment with phase margin compensation. The suppression strategy of the present application can always maintain sufficient stability margin for the system during the change of grid impedance, so that the cutoff frequency changes within a reasonable range, essentially avoiding the occurrence of system harmonic resonance; compared with other suppression methods for real-time adjustment of controller parameters, the suppression strategy proposed in the present application only needs to adjust the proportional compensation link in real time according to the measured grid impedance after the lead link is pre-set; compared with passive damping and traditional active damping methods, after adding the proposed suppression strategy, the system can always remain stable during the dynamic adjustment of the proportional coefficient, and the suppression strategy has good robustness to grid impedance measurement errors, making the choice of grid impedance measurement method more free. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 A flow chart of a harmonic resonance suppression method for phase margin compensation provided in one embodiment of the present application; Figure 2 This is a schematic diagram of the equivalent circuit structure of a large photovoltaic power station in one embodiment of the present application; Figure 3 Schematic diagram of a grid-connected inverter control strategy in a two-phase stationary coordinate system in one embodiment of the present application; Figure 4This is a block diagram of the system control structure in one embodiment of the present application; Figure 5 Schematic diagram of a harmonic resonance suppression strategy based on phase margin compensation in one embodiment of the present application; Figure 6 Schematic diagram of the open-loop phase curve of the original system under different grid impedances in one embodiment of the present application; Figure 7 Schematic diagram of a phase curve after leading link compensation under different grid impedances in one embodiment of the present application; Figure 8 This is a schematic diagram of a suppression strategy implementation scheme in an embodiment of the present application; Figure 9 Schematic diagram of a feedback parameter adjustment strategy for impedance parameter change in one embodiment of the present application; Figure 10 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0027] Figure 1 A flow chart of a harmonic resonance suppression method for phase margin compensation provided in one embodiment of the present application is shown as follows: Figure 1 As shown, the method in this application includes the following steps: Step 101: Build an equivalent model for the photovoltaic grid-connected system and determine the equivalent impedance of the grid.

[0028] Step 102: Determine the open-loop transfer function of the photovoltaic grid-connected system.

[0029] The detailed description of step 101 and step 102 is as follows: Large photovoltaic power stations are usually composed of multiple LCL inverters connected in parallel. The equivalent structure is as follows: Figure 2 As shown in the figure, L 1j 、 C fj 、 L 2j Inverter jThe inverter side inductor, filter capacitor and grid side inductor; i sjabc 、 u pabc Inverter j Three-phase grid-connected current and grid-connected point voltage; Z g is the grid impedance, which mainly includes the leakage inductance of the step-up transformer and the equivalent resistance and reactance of the high-voltage transmission line. Since the resistance of the high-voltage transmission line is much smaller than the reactance, this application only considers the inductive component and records Z g ( s )= sL g .

[0030] For large-scale photovoltaic systems, in order to improve efficiency and minimize energy loss during power conversion, the control structure is often a single-stage structure. In actual projects, photovoltaic power stations usually use inverters with the same circuit structure and parameters. The control structure in a two-phase stationary coordinate system is as follows: Figure 3 shown. Figure 3 middle, k c is the active damping coefficient of the capacitor current, MPPT is maximum power point tracking, and PLL is phase-locked loop. A quasi-PR (proportional resonant) controller that can achieve zero-error tracking for sinusoidal AC is used to control the grid current. Its mathematical model is shown in Equation (1): (1) For n A large photovoltaic power station composed of the same inverters, the equivalent grid impedance of each inverter is n Z g , when there is no grid voltage feedforward, the grid impedance can be considered to be L 2. Therefore, Figure 2 The equivalent control structure of the inverter system in the large photovoltaic power station in the s domain can be obtained, such as Figure 4 As shown (since the α and β axes are symmetrical, only the α axis is analyzed as an example). Figure 3 middle, L eq = L 2+ nL g , then the open-loop transfer function from the reference current to the output grid-connected current is shown in formula (2).

[0031] (2) Step 103: Determine a quasi-PR controller.

[0032] Step 104: Determine the open-loop cutoff frequency of the photovoltaic grid-connected system based on the quasi-PR controller and the open-loop transfer function.

[0033] Step 105: Determine a phase margin index of the photovoltaic grid-connected system based on the open-loop cut-off frequency.

[0034] Step 106: Determine the harmonic generation mechanism of the photovoltaic grid-connected system based on the phase margin index and the grid equivalent impedance.

[0035] Steps 103 to 106 are described in detail as follows: In order to suppress high-frequency harmonics, the open-loop cutoff frequency ω of the system c Generally set to be much smaller than the switching frequency ω s , and the filter capacitor has little effect on the low-frequency characteristics, so in ω c The influence of the filter capacitor can be ignored, and jω c Substituting into equation (2) we can obtain the amplitude of the open-loop transfer function at the cutoff frequency: (3) For the quasi-PR controller, although a large amplitude gain can be obtained at the pole frequency ω0, the phase-frequency curve of the system crosses the 0° line at this frequency, causing a -180° phase shift on the system phase. In order to reduce the impact of the controller on the system phase margin, ω is usually c It is designed to be much larger than ω0. c The quasi-PR controller can be simplified to: (4) Will G c (jω c ) into formula (4), and the amplitude of the open-loop transfer function at the cutoff frequency is 1, we can obtain: (5) According to the cutoff frequency ω c , we can get the system phase margin index PM and the grid-connected system harmonic generation mechanism, and we can get ω by solving equation (5) c , then jω c Substituting into equation (1), we can get the quasi-PR controller at ω c The phase angle at: (6) According to formula (2), the current open-loop transfer function without considering the quasi-PR controller is obtained at the cutoff frequency ω c The phase angle at: (7) Therefore, the phase margin of the system can be obtained: (8) According to the definition of phase boundary frequency and open-loop cutoff frequency, it can be seen that under normal circumstances, the phase boundary frequency ω g Greater than the open-loop cutoff frequency ω c , so in ω g Current controller G c (s) can also be simplified to formula (4), which is g The phase at is: (9) The open-loop transfer function without the current controller is obtained from equation (2) at ω g The phase angle at: (10) We can find ω g , jω g Substituting into formula (2), we can get the amplitude margin of the system: (11) The system's open-loop transfer function will not experience resonant spikes due to an increase in the equivalent grid impedance. That is, the system will not experience harmonic resonance due to active damping failure caused by changes in the equivalent grid impedance. The following analyzes the impact of reduced stability margin on system harmonic resonance from the perspective of closed-loop gain. The system current closed-loop transfer function can be simplified to: (12) Since the amplitude-frequency curve of the system open-loop transfer function is at the cutoff frequency ω c The phase-frequency curve crosses the 0dB line at the phase boundary frequency ω g If it crosses the -180° line, then jω c 、jω g Substituting them into formula (12) respectively, we can obtain the system's amplification factor for the harmonic current at the cutoff frequency and phase boundary frequency: (13) (14) In the formula, γ and σ are the phase margin and amplitude margin of the system respectively. As the phase margin and amplitude margin decrease, the system c 、ω g As the phase margin (amplitude margin) decreases, the peak of the amplitude-frequency characteristic curve at the corresponding frequency gradually increases, that is, the amplification effect on the corresponding frequency harmonics is enhanced, and the content of the corresponding frequency harmonics in the grid-connected current increases.

[0036] In summary, the phase margin index is related to the equivalent impedance of the grid and the control strategy of the photovoltaic grid-connected inverter. In engineering applications, the specific value needs to be determined based on debugging.

[0037] Step 107: Determine whether the photovoltaic grid-connected system is stable based on the phase margin indicator.

[0038] When the phase margin is greater than 0, the system is stable. When the phase margin is negative, the system enters an unstable operating state and needs to be regulated.

[0039] Step 108: If it is unstable, construct an advance link according to the maximum phase angle compensation amount.

[0040] Step 109: Compensating the phase margin of the photovoltaic grid-connected system based on the leading link.

[0041] From equations (13) and (14), we can see that as the phase margin and amplitude margin decrease, the system c 、ω g The amplitude of the current amplification factor at the two frequencies increases, and the amplification effect on the harmonic currents at these two frequencies is enhanced. As the phase margin (amplitude margin) decreases, the peak of the amplitude-frequency characteristic curve at the corresponding frequency gradually increases, that is, the amplification effect on the corresponding frequency harmonics is enhanced, and the content of the corresponding frequency harmonics in the grid-connected current increases. According to automatic control theory, when the phase margin is reduced to zero, the amplitude margin must also be zero, ω c With ω g Overlap, at this time ω c The amplitude of the harmonic current amplification factor at ω tends to infinity. c The amplification effect of the harmonics at this frequency is infinite, and the system will experience harmonic resonance at this frequency. At this time, a large amount of ω will appear in the grid-connected current. c The harmonics at the grid current waveform are seriously distorted.

[0042] Therefore, if the system can maintain sufficient phase margin during the change of the equivalent grid impedance, it can ensure that the system has sufficient stability margin, thereby avoiding the occurrence of system harmonic resonance. Accordingly, this application proposes a method for real-time compensation of the system phase margin to achieve the suppression of harmonic resonance.

[0043] The lead link can compensate for the phase at a specific frequency of the system and has little effect on the open-loop gain. This application uses the lead link to compensate for the phase at the open-loop cutoff frequency of the system. Its mathematical model is: (15) Where λ is the graduation coefficient and T is the time constant. m is the maximum phase angle compensation, as shown in formula (16); it is used to determine the frequency point corresponding to the maximum phase angle compensation, as shown in formula (17). The frequency range to be compensated is 1 / ( λT )~1 / T Select the phase margin you want to increase ψm , thus solving λ , select the frequency ω at the maximum phase m , and then solve it to get T , thus constructing the advanced link.

[0044] (16) (17) The system's harmonic resonance suppression strategy based on phase margin compensation is as follows: Figure 5 shown.

[0045] when L g When it approaches infinity, the phase limit of the open-loop transfer function of the original system is shown in formula (18): (18) It is known that L g When it is much larger than the filter inductance, the phase curve of the system tends to be constant, such as Figure 6 As shown, the original system is at the rated cutoff frequency ω c0 There is a maximum value for the phase angle change at (the open-loop cutoff frequency of the system when there is no grid impedance). The maximum phase angle change is shown in formula (19): (19) In the process of grid impedance change, in order to meet the requirements of system phase margin and cutoff frequency, it is necessary to pre-set the leading link: the frequency point ω corresponding to the maximum phase angle compensation amount m Set to the nominal cutoff frequency ω of the original system c0 The maximum phase angle of compensation is set to Δψ. The open-loop transfer function of the system after leading link compensation is: G opc (s), the phase limit when the grid impedance tends to infinity is shown in formula (20): (20) It can be seen that when the grid impedance is much larger than the filter inductance, the system phase tends to be constant, and its change with the equivalent grid impedance is as follows: Figure 7 shown.

[0046] Depend on Figure 7 It can be seen that the phase-frequency curve of the open-loop transfer function corresponding to each grid impedance value after compensation by the leading link is from 3 times the fundamental frequency to the phase boundary frequency ω g There is a peak value in the range. k e Make the open-loop cutoff frequency always at the frequency point ω corresponding to the above phase peak pIf the phase margin is obtained, the system will always have sufficient phase margin and will not cause harmonic resonance due to the reduction of the phase margin.

[0047] Step 110: Construct a proportional compensation link.

[0048] Step 111: adjusting the open-loop cutoff frequency of the photovoltaic grid-connected system based on the proportional compensation link.

[0049] While compensating for the phase, the lead network will also change the open-loop gain of the system, thereby changing the cutoff frequency, causing the frequency point corresponding to the maximum phase angle compensation to deviate from the cutoff frequency, and failing to achieve the purpose of compensating the phase margin. k e The method is to adjust the system open loop cut-off frequency. k e The design process is analyzed. The measured grid impedance L g Substitution G opc (s), according to formula (21), the frequency point ω corresponding to the phase curve of the open-loop transfer function of the system containing the lead compensation link crossing -180° can be obtained g : (twenty one) According to formula (22), the open-loop transfer function of the system including the lead compensation link can be obtained from 3 times the fundamental frequency to the phase boundary frequency ω g The frequency ω corresponding to the phase peak within the range p .

[0050] (twenty two) Set s=jω p Substituting the constraints on the open-loop gain at the cutoff frequency | k e G e (s) G op (s)|=1, we can get: (twenty three) In summary, the implementation scheme of harmonic resonance suppression strategy for large photovoltaic power stations based on phase margin compensation is as follows: Figure 8 As shown, the parameter design process of the compensation network is as follows Figure 9 As shown. It can be seen that after the advance link is pre-set, the system only needs to adjust the proportional link parameters according to the real-time measured grid impedance during operation. k eSince the suppression strategy is applied to each inverter in the PV power plant, and each inverter can adjust its own parameters according to the impedance measured at its output to maintain stability, this method is also applicable to PV power plants with different inverter parameters.

[0051] Based on the same inventive concept, embodiments of the present application also provide a phase margin compensation-based harmonic resonance suppression device for implementing the aforementioned phase margin compensation-based harmonic resonance suppression method. The solution provided by this device is similar to the solution described in the aforementioned method. Therefore, the specific limitations of one or more phase margin compensation-based harmonic resonance suppression device embodiments provided below can be found in the limitations of the phase margin compensation-based harmonic resonance suppression method described above and will not be further elaborated here.

[0052] In an exemplary embodiment, a harmonic resonance suppression device based on phase margin compensation is provided, comprising: The grid equivalent impedance determination module is used to perform equivalent modeling of the photovoltaic grid-connected system and determine the grid equivalent impedance; An open-loop transfer function determination module is used to determine the open-loop transfer function of the photovoltaic grid-connected system; A quasi-PR controller determination module, used for determining a quasi-PR controller; An open-loop cutoff frequency determination module, configured to determine an open-loop cutoff frequency of a photovoltaic grid-connected system based on the quasi-PR controller and an open-loop transfer function; A phase margin index determination module, configured to determine a phase margin index of a photovoltaic grid-connected system based on the open-loop cut-off frequency; A photovoltaic grid-connected system harmonic generation mechanism determination module, configured to determine the photovoltaic grid-connected system harmonic generation mechanism based on the phase margin index and the grid equivalent impedance; A judgment module, configured to judge whether the photovoltaic grid-connected system is stable based on the phase margin indicator; An advance link construction module is used to construct an advance link according to a maximum phase angle compensation amount when the system is unstable; A phase margin compensation module, configured to compensate for the phase margin of the photovoltaic grid-connected system based on the leading link; A proportional compensation link building module is used to build a proportional compensation link; The open-loop cut-off frequency adjustment module is used to adjust the open-loop cut-off frequency of the photovoltaic grid-connected system based on the proportional compensation link.

[0053] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Figure 10As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O) and a communication interface. The processor, memory and input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The database of the computer device is used to store harmonic resonance suppression data based on phase margin compensation. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a harmonic resonance suppression method based on phase margin compensation is implemented.

[0054] Those skilled in the art will understand that Figure 10 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0055] In an exemplary embodiment, a computer device is further provided, including a memory and a processor. The memory stores a computer program, and the processor implements the steps in the above method embodiments when executing the computer program.

[0056] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0057] In an exemplary embodiment, a computer program product is provided, including a computer program. When the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0058] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0059] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments. In particular, any reference to memory, database, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0060] The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processors involved in the various embodiments provided herein may include, but are not limited to, general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic units, data processing logic units based on quantum computing, and the like.

[0061] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A harmonic resonance suppression method based on phase margin compensation, characterized in that: The harmonic resonance suppression method based on phase margin compensation includes: Equivalent modeling of the photovoltaic grid-connected system to determine the equivalent impedance of the grid; Determine the open-loop transfer function of the photovoltaic grid-connected system; Determine the quasi-PR controller; Determining an open-loop cutoff frequency of a photovoltaic grid-connected system based on the quasi-PR controller and the open-loop transfer function; Determining a phase margin index of the photovoltaic grid-connected system based on the open-loop cutoff frequency; a calculation formula for the phase margin index includes a phase angle parameter of the quasi-PR controller and a phase angle parameter when there is no quasi-PR controller; Determining a harmonic generation mechanism of a photovoltaic grid-connected system based on the phase margin index and the grid equivalent impedance; Determining whether the photovoltaic grid-connected system is stable based on the phase margin indicator; If it is unstable, then build an advance link based on the maximum phase angle compensation amount; Compensating the phase margin of the photovoltaic grid-connected system based on the leading link; Construct proportional compensation link; The open-loop cutoff frequency of the photovoltaic grid-connected system is adjusted based on the proportional compensation link.

2. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: Equivalent modeling of the photovoltaic grid-connected system is performed to determine the equivalent impedance of the grid. The following formula is used: L eq = L 2+ nL g ； in, L g represents the equivalent impedance of the power grid, n Indicates the number of inverters, L eq represents the equivalent inductance, L 2 represents the grid-side inductance.

3. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: The open-loop transfer function of the photovoltaic grid-connected system is determined by the following formula: ； in, represents the open-loop transfer function of the photovoltaic grid-connected system, Indicates the output grid-connected current, represents the reference current, represents the equivalent gain of the PWM inverter, represents the transfer function of the quasi-PR controller, represents the differential operator, represents the inductance on the inverter side, represents the equivalent inductance, Represents the filter capacitor, Represents the active damping coefficient of capacitor current.

4. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: The expression of the quasi-PR controller is as follows: ； in, represents the transfer function of the quasi-PR controller, represents the proportional gain coefficient, represents the resonant gain coefficient, represents the PR cutoff frequency, represents the differential operator.

5. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: The open-loop cutoff frequency of the photovoltaic grid-connected system is determined based on the quasi-PR controller and the open-loop transfer function using the following formula: ； in, Indicates the open-loop cutoff frequency of the photovoltaic grid-connected system, represents the proportional gain coefficient, represents the equivalent gain of the PWM inverter, represents the inductance on the inverter side, represents the equivalent inductance, represents the resonant gain coefficient, Indicates the PR cutoff frequency.

6. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: The phase margin index of the photovoltaic grid-connected system is determined based on the open-loop cut-off frequency using the following formula: ； Among them, PM represents the phase margin index, Indicates the open-loop cutoff frequency of the quasi-PR controller in the photovoltaic grid-connected system The phase angle at It represents the open-loop cutoff frequency of the current open-loop transfer function in the photovoltaic grid-connected system when the quasi-PR controller is not considered. The phase angle, represents the inductance on the inverter side, represents the equivalent gain of the PWM inverter, represents the active damping coefficient of the capacitor current, represents the PR cutoff frequency, represents the resonant gain coefficient, represents the proportional gain coefficient, represents the resonant frequency, Indicates the resonant frequency when there is no PR controller. The calculation formula is as follows: ； in, Indicates filter capacitor.

7. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: The mathematical model of the advance link is: ； in, represents the lead link transfer function, represents the graduation coefficient, T represents the time constant, s represents the differential operator.

8. The harmonic resonance suppression method based on phase margin compensation according to claim 1, characterized in that: The construction ratio compensation link specifically adopts the following formula: ； in, represents the proportional compensation gain, Indicates the frequency corresponding to the phase peak, express The frequency corresponds to the lead link transfer function, express The frequency corresponds to the open-loop transfer function.

9. A harmonic resonance suppression device based on phase margin compensation, characterized in that: The harmonic resonance suppression device based on phase margin compensation includes: The grid equivalent impedance determination module is used to perform equivalent modeling of the photovoltaic grid-connected system and determine the grid equivalent impedance; An open-loop transfer function determination module is used to determine the open-loop transfer function of the photovoltaic grid-connected system; A quasi-PR controller determination module, used for determining a quasi-PR controller; An open-loop cutoff frequency determination module, configured to determine an open-loop cutoff frequency of a photovoltaic grid-connected system based on the quasi-PR controller and an open-loop transfer function; A phase margin index determination module, configured to determine a phase margin index of a photovoltaic grid-connected system based on the open-loop cut-off frequency; A photovoltaic grid-connected system harmonic generation mechanism determination module, configured to determine the photovoltaic grid-connected system harmonic generation mechanism based on the phase margin index and the grid equivalent impedance; A judgment module, configured to judge whether the photovoltaic grid-connected system is stable based on the phase margin indicator; An advance link construction module is used to construct an advance link according to a maximum phase angle compensation amount when the system is unstable; A phase margin compensation module, configured to compensate for the phase margin of the photovoltaic grid-connected system based on the leading link; A proportional compensation link building module is used to build a proportional compensation link; The open-loop cut-off frequency adjustment module is used to adjust the open-loop cut-off frequency of the photovoltaic grid-connected system based on the proportional compensation link.

10. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the harmonic resonance suppression method based on phase margin compensation according to any one of claims 1 to 8.

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