A method and system for oscillation suppression of a meshing and meshing inverter hybrid system

Abstract

The application discloses an oscillation suppression method and system of a grid-following and grid-forming inverter hybrid system, and comprises the following steps: establishing a grid-following inverter decomposition model, and separating out a negative damping component causing instability of the grid-following inverter; designing a compensation term based on the negative damping component, injecting the compensation term into a grid-forming inverter, and reshaping output impedance of the grid-forming inverter to offset the influence of the negative damping component of the grid-following inverter on system stability. The negative damping component is injected into the grid-forming inverter after being taken in reverse, and a compensation term of the output impedance of the grid-forming inverter can be calculated, so that the influence of the negative damping component of the grid-following inverter on system stability is offset.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to an oscillation suppression method and system for a hybrid grid-connected and grid-connected inverter system. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, the penetration rate of renewable energy has gradually increased, and the traditional power system dominated by synchronous generators is transforming into a new type of power system dominated by power electronic devices. Currently, most grid-connected inverters use grid-following control methods; grid-following inverters achieve synchronization with the grid by tracking the grid voltage and frequency through phase-locked loops (PLLs). However, with the increase in new energy sources and power electronic devices, the grid strength weakens, and the performance of PLLs deteriorates, leading to system oscillations.

[0004] To address these issues, grid-connected inverters have attracted widespread attention due to their unique voltage source characteristics. Grid-connected inverters can provide support for the voltage and frequency at the grid connection point and exhibit strong adaptability to weak grids. Therefore, grid-connected inverters have been introduced into grid-connected systems to support weak grids and improve stability.

[0005] However, grid-connected inverters also have some drawbacks. For example, when the system is subjected to severe disturbances, the transient stability control of grid-connected inverters is more difficult. At the same time, because grid-connected inverters simulate the operating mechanism and characteristics of synchronous generators, grid-connected inverter parallel systems may experience active power oscillations similar to those of synchronous generators.

[0006] Hybrid systems, consisting of grid-connected inverters and grid-connected inverters, can leverage the advantages of both and have seen rapid development. However, in hybrid systems, the interaction between grid-connected inverters and grid-connected inverters makes the system stability mechanism more complex, and the impact of grid-connected inverters and grid-connected inverters with different output powers on system stability remains unclear.

[0007] Existing impedance stability analyses mainly target single grid-connected inverter systems or grid-connected inverter systems, or simplify inverter impedance, without considering the impact of specific control methods or parameters on hybrid systems, thus failing to accurately describe the oscillation characteristics of hybrid systems.

[0008] Most of the oscillation suppression methods disclosed in the prior art require a complex parameter design process, are sensitive to changes in operating conditions, and mainly focus on solving the oscillation problem of a single control method for grid-connected inverters or grid-connected inverters. They are not effective in suppressing oscillations in hybrid systems. Summary of the Invention

[0009] To address the aforementioned issues, this invention proposes an oscillation suppression method and system for a hybrid grid-connected and grid-connected inverter system. By calculating the negative damping component that causes instability in the grid-connected inverter, the impedance of the grid-connected inverter is reshaped to counteract the influence of the negative damping component of the grid-connected inverter in the hybrid system. This ensures stable operation of the hybrid system even when the output power and grid impedance vary widely.

[0010] In some implementations, the following technical solutions are adopted:

[0011] An oscillation suppression method for a hybrid grid-connected and grid-connected inverter system includes:

[0012] Establish a decomposition model of the grid-connected inverter and separate the negative damping component that causes instability of the grid-connected inverter;

[0013] Based on the negative damping component, a compensation term is designed and injected into the grid inverter to reshape the output impedance of the grid inverter, thereby offsetting the impact of the negative damping component of the grid inverter on the stability of the hybrid system.

[0014] As a further solution, the grid-connected inverter decomposition model specifically includes:

[0015] The positive sequence impedance of the grid-connected inverter, without considering the effect of the phase-locked loop;

[0016] When considering the effects of phase-locked loops:

[0017] Due to phase perturbation Δθ pll First-order perturbation modulated wave generated by PARK transform Δm x1 The generated first-order disturbance impedance, which is further decomposed into impedances Z GFL2a and impedance Z GFL2b Series;

[0018] And, due to phase perturbation Δθ pll First-order perturbation modulated wave generated by inverse Park transform Δm x2 The resulting first-order disturbance impedance;

[0019] Among them, impedance Z GFL2a The overall performance is negative damping, which is the main negative damping component causing instability of grid-connected inverters.

[0020] As a further solution, impedance Z GFL2a Specifically:

[0021] ;

[0022] in, V 1 represents the amplitude of the fundamental voltage of the grid-connected inverter; I 1 represents the amplitude of the fundamental current of the grid-connected inverter; The initial phase angle of the fundamental current; T PLL (s- jω 0) is the closed-loop transfer function of the phase-locked loop after complex frequency shift.

[0023] As a further solution, the negative damping component Z GFL2a Invert the impedance and inject it into the grid inverter to obtain the improved grid inverter impedance, specifically:

[0024] ;

[0025] in, and These represent the negative damping of grid-connected inverters with opposite signs in parallel connection. Z GFL2a The subsequent grid-connected inverter impedance model and the parallel grid-connected inverter with opposite signs of negative damping. Z GFL2a Previous grid inverter impedance model, A GFM (s) and B GFM (s) are respectively Z GFM The numerator and denominator of (s) C GFM (s) is the coupling quantity that is related to both the grid-connected inverter and the grid-connected inverter.

[0026] As a further solution, the coupling amount related to both grid-connected inverters and grid-connected inverters... C GFM (s) is divided into C GFM1 (s) and C GFM2 (s) Two parts:

[0027] ;

[0028] ;

[0029] in, V 1 represents the amplitude of the fundamental voltage of the grid-connected inverter; I 1 represents the amplitude of the fundamental current of the grid-connected inverter; The initial phase angle of the fundamental current is denoted as . ω 0 is the rated angular frequency. ωset This is the angular frequency reference value for the grid-connected inverter. E set This serves as a reference value for the voltage amplitude of the grid-connected inverter. The virtual phase angle for virtual synchronous machine control; V * represents the base frequency voltage of the grid-connected inverter; H p (s- jω 0) is the transfer function of the power loop of the grid inverter after complex frequency shift; H v (s- jω 0) is the transfer function of the voltage loop of the grid inverter after complex frequency shift; H i (s- jω 0) represents the proportional integral term after complex frequency shift. T PLL (s- jω 0) is the closed-loop transfer function of the phase-locked loop after complex frequency shift; L f2 It is the filter inductor of the grid inverter.

[0030] As a further option, C GFM2 (s) is used as a compensation term to compensate the modulation wave of the grid inverter, thereby realizing the parallel connection of a virtual impedance on the grid inverter side to offset the influence of the negative impedance of the grid inverter.

[0031] As a further solution, compensation items C GFM2 All parameters involved in (s) are set according to the filter parameters of the grid-connected inverter system and the control parameters of the grid-connected inverter and the actual operating values.

[0032] In other embodiments, the following technical solutions are adopted:

[0033] An oscillation suppression system for a hybrid grid-connected and grid-connected inverter system includes:

[0034] The model building module is used to build a decomposition model of the grid-connected inverter and separate the negative damping component that causes instability of the grid-connected inverter.

[0035] The impedance compensation module is used to design a compensation term based on the negative damping component and inject it into the grid inverter to reshape the output impedance of the grid inverter, so as to offset the impact of the negative damping component of the grid inverter on the system stability.

[0036] In other embodiments, the following technical solutions are adopted:

[0037] A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded and executed by the processor for the oscillation suppression method of the above-described grid-connected and grid-connected inverter hybrid system.

[0038] In other embodiments, the following technical solutions are adopted:

[0039] A computer-readable storage medium storing a plurality of instructions adapted for loading and execution by a processor of a terminal device of the above-described oscillation suppression method for a hybrid grid-connected and grid-connected inverter system.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] (1) This invention effectively separates the positive and negative damping components in the impedance of the grid-connected inverter, revealing the reason for the instability of the grid-connected inverter under weak grid conditions; by inverting the negative damping component and injecting it into the grid-connected inverter, the compensation term of the output impedance of the grid-connected inverter can be calculated, thereby offsetting the influence of the negative damping component of the grid-connected inverter on the system stability.

[0042] (2) When the overall system impedance has negative damping, this embodiment extracts the output current of the grid-connected inverter, designs a compensation function based on the negative damping component that affects the instability of the grid-connected inverter, cancels the negative damping, reshapes the output impedance of the grid-connected inverter, thereby changing the impedance characteristics of the hybrid system and eliminating the non-passive region; so that the phase angle of the inverter system is always between -90° and 90°, thereby suppressing the oscillation of the system.

[0043] (3) Impedance analysis of grid-connected inverters and grid-connected inverters shows that the risk of interactive oscillation between the grid-connected inverter and the grid impedance gradually increases with the increase of power, while the impedance characteristics of grid-connected inverters are less correlated with power; the present invention compensates for this. C GFM2 In (s), the influence of the grid-connected inverter output power is considered, which effectively improves the stable operating range of the hybrid system at different inverter output powers.

[0044] This invention eliminates the passive region of the system under different inverter output power and grid impedance. That is, the phase angle of the system impedance is always between -90° and 90°. Therefore, no matter how the grid impedance changes or how the amplitude-frequency response intersection of the grid impedance and the inverter system impedance changes, there will never be a situation where the phase angle difference at the intersection point is greater than 180°. In other words, it can effectively suppress the oscillation of the hybrid system of grid-connected and grid-connected inverters, so that the system can operate stably.

[0045] (4) This invention is not only applicable to two-level inverters, but also to different converter topologies such as three-level T-type, midpoint clamping type, and multi-level. It is highly practical and has a wide range of applications.

[0046] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0047] Figure 1 This is a structural diagram of a hybrid grid-connected and grid-connected inverter system in an embodiment of the present invention;

[0048] Figure 2 This is a typical block diagram of a network control method;

[0049] Figure 3 For grid-connected inverter small-signal model;

[0050] Figure 4 This is the equivalent circuit diagram of the decomposed impedance of the grid inverter in this embodiment of the invention;

[0051] Figure 5(a) shows the Bode plot of the overall impedance of the grid-connected inverter under different output powers;

[0052] Figure 5(b) shows the output power at different levels. Z GFL3 (s) Bode plot of impedance characteristics;

[0053] Figure 6 This is a typical block diagram of a network control method;

[0054] Figure 7 for C GFM (s), C GFM1 (s), C GFM2 Bode plot of (s);

[0055] Figure 8 This is a control flowchart of the method proposed in the embodiments of the present invention;

[0056] Figure 9 The output impedance characteristics of the mixed system before and after applying the oscillation suppression method proposed in this embodiment of the invention;

[0057] Figure 10 This refers to the phase margin of different systems when the output power of the grid-connected inverter changes in the embodiments of the present invention. Detailed Implementation

[0058] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0060] Example 1

[0061] Grid-connected inverters are used in weak grids to improve power quality and suppress system oscillations in hybrid systems because they can support the voltage and frequency at the grid connection point. However, the oscillation suppression capability of grid-connected inverters is limited, and the suppression effect is affected by the output power of the grid-connected inverter.

[0062] Based on this, in one or more embodiments, an oscillation suppression method for a hybrid grid-connected and grid-connected inverter system is disclosed, specifically including the following process:

[0063] S101: Connect the grid-connected inverter, which adopts virtual synchronous machine control, to the grid-connected inverter system to support grid voltage and frequency and suppress system oscillation; establish a decomposition model of the grid-connected inverter and separate the negative damping component that causes the grid-connected inverter to become unstable.

[0064] S102: Based on the negative damping component, design a compensation term and inject it into the grid inverter to reshape the output impedance of the grid inverter, so as to offset the influence of the negative damping component of the grid inverter on the system stability.

[0065] Specifically, Figure 1 This is a structural diagram of a hybrid system consisting of one grid-connected inverter and one grid-connected inverter connected in parallel. Figure 1 middle, L fx ( x =1,2) are the filter inductors of the grid-connected and grid-connected inverters; C fx ( x =1,2) are the filter capacitors of the grid-connected and grid-connected inverters; R cx ( x =1,2) are the damping resistors of the grid-connected and grid-connected inverters; L g It is the inductance of the power grid; U g It is the grid voltage;u pcc It is the voltage at the three-phase grid connection point; i pcc It is the three-phase grid-connected current of the grid-connected inverter; V dc It is DC voltage; C dc It is a DC-side capacitor; e x1 and i x1 ( x =a,b,c) are the three-phase output voltage and output current of the grid-connected inverter, respectively; e x2 and i x2 ( x =a,b,c) are the three-phase output voltage and output current of the grid inverter, respectively.

[0066] Figure 2 This is a typical block diagram of a network control method. Among them, i ref , u ref , u qref These are the current reference, output voltage reference, and q-axis voltage reference in the phase-locked loop (PLL), respectively. i dq The output current of the grid inverter in the dq coordinate system; u d , u q These are the grid connection point voltages on the d-axis and q-axis, respectively; ω 0 ω pll These are the rated angular frequency and the angular frequency calculated by the phase-locked loop, respectively. θ pll It is the phase obtained by the phase-locked loop tracking the voltage at the grid connection point; K m This is the modulation gain.

[0067] according to Figure 1 The relationship between the grid connection point voltage, the grid-connected inverter output current, and the output voltage can be obtained:

[0068] (1)

[0069] According to equation (1) and Figure 1 We can obtain:

[0070] (2)

[0071] in, Lf1 It is the filter inductor of the grid inverter; u pcc It is the voltage at the three-phase grid connection point; i pcc It is the three-phase grid-connected current; e x1 and i x1 These are the three-phase output voltage and output current of the grid-connected inverter. x =a,b,c; C f1 It is the filter capacitor of the grid-connected inverter; R c1 It is the damping resistor of the grid inverter; v a , v b , v c These are the grid connection point voltages for phases a, b, and c, respectively. m a , m b , m c These are phase modulation signals a, b, and c, respectively; V dc It is DC voltage; K m This is the modulation gain.

[0072] When the effect of the phase-locked loop (PLL) is not considered, the positive sequence impedance of the grid-connected inverter According to Figure 2 Combining equations (1) and (2), we get:

[0073] (3)

[0074] in, H i (s -jω 0)= k p + k i / (s -jω 0) is the current loop control transfer function after complex frequency shift; V p and I p These are the positive-sequence disturbance voltage and the positive-sequence disturbance current, respectively.

[0075] When considering the influence of the phase-locked loop (PLL), the steady-state quantity θ pll A disturbance caused by the grid connection point voltage was added to the middle. Δu pcc The generated phase perturbation Δθ pll Subsequently, new perturbations will also be generated during the coordinate transformation (all perturbations are expressed in terms of...). Δ (indicated by prefix), such as Figure 3 As shown. In this case, the system simultaneously contains steady-state quantities, first-order disturbance quantities, and second-order disturbance quantities (as shown). Δ 2 m x3 In the disturbance components, the first-order disturbances originate from the steady-state component and... Δθ pll The interaction between the Park transform and the inverse Park transform. This is to quantitatively evaluate the phase perturbation generated by the phase-locked loop. Δθ pll The impact on grid-connected system stability was assessed by calculating the first-order disturbance impedance generated by the Park transform and inverse Park transform, respectively. Since the effect of second-order disturbances on impedance is negligible, this embodiment ignores second-order disturbances. Δ 2 m x3 The impact.

[0076] First, according to Figure 2 and Figure 3 Phase perturbation can be obtained Δθ pll The d-axis and q-axis current disturbances generated after the Park transformation are as follows:

[0077] (4)

[0078] (5)

[0079] in, V 1 represents the amplitude of the fundamental voltage of the grid-connected inverter; I 1 represents the amplitude of the fundamental current of the grid-connected inverter; f 1 and f p These are the fundamental frequency and the disturbance frequency, respectively. The initial phase angle of the fundamental current; Δi d and Δi q These are the d-axis and q-axis current disturbances, respectively. T PLL (s) and H PLL (s) represent the closed-loop transfer function and the open-loop transfer function of the phase-locked loop, respectively; k pPLL and k iPLL These are the control parameters for the phase-locked loop.

[0080] go through Figure 2 After the current loop and inverse PARK transformation, the modulation wave generated by the current disturbance in equation (4) can be expressed as:

[0081] (6)

[0082] Combining equations (1) and (6), the first-order perturbation modulated wave Δm x1 The resulting first-order disturbance impedance is:

[0083] (7)

[0084] Similarly, the first-order perturbation modulated wave generated by the inverse Park transform considering phase perturbation Δm x2 for:

[0085] (8)

[0086] in, f 1 is the rated frequency. Combining equations (1) and (8), the first-order perturbation modulated wave Δm x2 The resulting first-order disturbance impedance is:

[0087] (9)

[0088] First-order disturbance impedance Z GFL2 and Z GFL3 middle, Z GFL2 It can be further decomposed into two impedances in series, namely:

[0089] (10)

[0090] (11)

[0091] Therefore, the impedance of a grid-connected inverter can be decomposed into steady-state impedance. Z GFL1 and first-order perturbation impedance Z GFL2a , Z GFL2b , Z GFL3 They are connected in parallel with the filter capacitor and damping resistor. The equivalent circuit of the decomposed impedance model is as follows: Figure 4 As shown.

[0092] Combining equations (1), (3), (9), (10), and (11), the total impedance of the grid-connected inverter is:

[0093] (12)

[0094] in, K m Modulation gain; V dc It is DC voltage; H i (s -jω 0)= k p + k i / (s -jω 0) is the current loop control transfer function after complex frequency shift; L f1 It is the filter inductor of the grid inverter; I 1 represents the amplitude of the fundamental current of the grid-connected inverter; The initial phase angle of the fundamental current; T PLL (s -jω 0) is the closed-loop transfer function of the PLL after complex frequency shift; V 1 represents the amplitude of the fundamental voltage of the grid-connected inverter; f 1 represents the fundamental frequency; ω 0 is the rated angular frequency.

[0095] The influence of the decomposed impedance on the overall passive region of the inverter is analyzed, and the changes in the impedance characteristics of the grid-connected inverter as the output power changes are presented. Figures 5(a) and 5(b) show the overall impedance of the grid-connected inverter and... Z GFL3 (s) Impedance characteristics change with output power. As shown in Figure 5(a), with the increase of output power, the amplitude-frequency response of the grid inverter impedance changes significantly, while the phase-frequency response remains relatively stable. According to passive theory, if the frequency of the intersection of the inverter impedance and the grid impedance in the amplitude-frequency response ( f int If the phase margin (PM) at point ) is less than 0, then f int The frequency is within the non-passive region. In this case, the system is at risk of oscillation. The non-passive region is defined as the area where the phase-frequency response of the system impedance differs from that of the grid inductance by more than 180°. As shown in Figure 5(a), with the increase of output power, the intersection frequency in the amplitude-frequency response... f int Gradually shifting to lower frequencies. With the intersection frequency... f int As the power decreases, the system's phase margin gradually decreases, leading to a more serious instability risk. As shown in Figure 5(b), with the increase of the grid-connected inverter's output power, ZGFL3 The passive region of (s) decreases, thereby reducing the risk of instability. This trend is opposite to the overall stability trend of the grid-connected inverter shown in Figure 5(a). Furthermore, Z GFL3 The impedance value of (s) is relatively large, making it difficult for it to intersect with the grid impedance in the amplitude-frequency response. Therefore, Z GFL3 (s) is not the main reason for the instability of the grid-connected inverter.

[0096] for Z GFL2a (s), due to the inclusion of - T PLL (s- jω 0), its overall behavior exhibits negative damping. Meanwhile, with I The change of 1 Z GFL2a (s) The amplitude decreases across all frequency bands, which will lead to Z GFL2a The phase margin at the intersection of the amplitude-frequency response (s) and the grid impedance decreases. Therefore, the system stability decreases. Z GFL2b In (s), s L f1 A 90° phase lead is introduced into the impedance. When - T PLL (s- jω 0) and s L f1 When multiplying, - T PLL (s- jω The non-passive region of 0) will be moved to the passive region. Meanwhile, the proportional integral term... H i (s- jω 0) and the constant term will not affect Z GFL2b The phase characteristics of (s). Therefore, Z GFL2b (s) essentially exhibits positive damping characteristics. In this case, I An increase of 1 only affects Z. GFL2b The amplitude-frequency characteristic of (s) is preserved without altering its phase-frequency characteristic, which does not affect the stability of the system. Therefore, Z GFL2a (s) is the main cause of grid-connected inverter instability.

[0097] As a further implementation method, an impedance model for the grid-connected inverter is established. Figure 6 This is a typical control block diagram for network control – virtual synchronizer control. (The diagram is from...) Figure 6The impedance model of the grid inverter can be obtained. Z GFM (s) is:

[0098] (13)

[0099] In the formula, ω set This is the reference value for the angular frequency of the grid-connected inverter; E set This serves as a reference value for the voltage amplitude of the grid-connected inverter. , θ vir These are the virtual phase angle and virtual phase, respectively, for virtual synchronous machine control;

[0100] H p (s -jω 0) = 1 / [ J (s -jω 0) 2 + D p (s -jω [0)] is the transfer function of the power loop after complex frequency shift;

[0101] H v (s -jω 0) = 1 / [ R vir + (s -jω 0) L vir [ ] is the transfer function of the voltage loop after complex frequency shift; J This is a virtual moment of inertia; D p This is the active damping coefficient; R vir and L vir Virtual resistors and virtual inductors for virtual synchronous machine control; V *and I *These represent the amplitudes of the base frequency voltage and current of the grid-connected inverter; L f2 It is the filter inductor of the grid inverter.

[0102] Figure 6 middle, P ref and Q ref These are the active power reference and reactive power reference for the grid-connected inverter, respectively. Q The instantaneous reactive power output of the grid-connected inverter; k q andk f These are the reactive power droop system and the active power droop coefficient, respectively. ω vir This refers to the actual angular frequency of the grid-connected inverter.

[0103] This leads to the impedance model of the hybrid system of grid-connected and grid-connected inverters:

[0104] (14)

[0105] As can be seen from the foregoing explanation, Z GFL2a As the main negative damping component causing instability in the grid-connected inverter system, a virtual impedance is connected in parallel with the grid-connected inverter side. This virtual impedance value is set to - Z GFL2a To offset the negative impedance component in the grid-connected inverter, the impedance of the grid-connected inverter after parallel connection is reduced. Z GFMp for:

[0106] (15)

[0107] in, Z GFMp (s) represents the negative damping of the grid-connected inverter with opposite signs in parallel. Z GFL2a Subsequent grid-connected inverter impedance model; A GFM (s) and B GFM (s) are the numerator and denominator of equation (13), respectively; C GFM (s) is the coupling quantity that is related to both the grid-connected inverter and the grid-connected inverter.

[0108]

[0109] Comparing equations (13) and (15), we can obtain that after paralleling this virtual impedance, the component added to the impedance of the grid inverter is: C GFM (s), divide it into C GFM1 (s) and C GFM2 (s) addition:

[0110] (16)

[0111] (17)

[0112] It can be seen from equation (16) that, CGFM1 The numerator of (s) contains a proportional integral term. H i (s- jω 0). C GFM1 The gain of (s) is maximum at the fundamental frequency, while the gain is negligible at other frequencies. Furthermore, this applies to the passive frequency band of the hybrid system. C GFM2 (s) and C GFM (s) are more similar, C GFM1 (s) Only in the low frequency band C GFM (s) has a significant impact. For example, Figure 7 As shown. Therefore, the final choice is... C GFM2 (s) is used as a compensation item.

[0113] The control block diagram of the oscillation suppression method proposed in this embodiment is as follows: Figure 8 As shown, Figure 8 Mainly includes Figure 6 The contents of the medium voltage and current double loop, H p (s) refers to the transfer function of the synchronization loop; combined with Figure 6 and Figure 8 The grid-connected voltage and three-phase output current of the grid-connected inverter are collected to calculate the instantaneous output reactive power. Q and instantaneous output active power P e The virtual phase is obtained from the active power loop and the synchronization loop. θ vir The virtual voltage is obtained from the reactive power loop. E vir Combined with virtual phase θ vir and virtual voltage E vir The three-phase voltage reference of the grid inverter is obtained. E ref The collected grid connection point voltage and E ref Controller of differential input voltage loop H v (s), combining the output of the voltage loop controller with... i x2 Differential input current loop controller H i (s), followed by the injection of compensation items C GFM2 (s), to obtain the output voltage reference u refAfter modulation, it is used to control the switching on and off of the switching transistors of the grid inverter.

[0114] This embodiment addresses the compensation item. C GFM2 The values ​​of all parameters involved in (s) are determined by setting them according to the filter parameters of the grid inverter system and the control parameters of the grid inverter and the actual operating values.

[0115] Figure 9 A comparison of the impedance characteristics of a hybrid system using and without the oscillation suppression method proposed in this embodiment is presented; Figure 9 middle Z h (s) and Z h_pro (s) represent the impedances of the hybrid system without the method of the present invention and with the method of the present invention, respectively, wherein Z h_pro (s)= Z GFL (s) / / Z GFMp (s). By Figure 9 It can be seen that when the grid-connected inverter output power P GFL At 40 kW and 60 kW, Z h The system contains a non-passive region, posing a risk of oscillation. However, by employing the method of this invention, Z h_pro The non-passive region in the system is eliminated. To further verify the effectiveness of the proposed method in improving the system stability margin at different output power levels, Figure 10 The output power of different grid-connected inverters was plotted. f int The variation trend of PM is shown. It can be seen that, compared to the hybrid system without the proposed method, the PM remains consistently between 80° and 100° after adopting the proposed method. The hybrid system remains stable under different power level conditions. Therefore, when using the method of this invention, the system can remain stable with a wide range of grid impedance and inverter output power variations, without the risk of oscillation.

[0116] When the overall system impedance has negative damping, this embodiment extracts the output current of the grid-connected inverter, designs a compensation function based on the negative damping component that affects the instability of the grid-connected inverter, cancels out the negative damping, and reshapes the output impedance of the grid-connected inverter, thereby changing the impedance characteristics of the hybrid system and eliminating the non-passive region; so that the phase angle of the inverter system is always between -90° and 90°, which can realize the oscillation suppression of the hybrid system under different output power and grid impedance, and improve the stable operating range of the hybrid system.

[0117] Example 2

[0118] In one or more embodiments, an oscillation suppression system for a hybrid grid-connected and grid-connected inverter system is disclosed, comprising:

[0119] The model building module is used to build a decomposition model of the grid-connected inverter and separate the negative damping component that causes instability of the grid-connected inverter.

[0120] The impedance compensation module is used to design a compensation term based on the negative damping component and inject it into the grid inverter to reshape the output impedance of the grid inverter, so as to offset the influence of the negative damping component of the grid inverter on the stability of the hybrid system.

[0121] It should be noted that the specific implementation methods of the above modules are exactly the same as those in Example 1, and will not be described in detail again.

[0122] Example 3

[0123] In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions adapted to be loaded by the processor and executed by the processor to perform the oscillation suppression method for the hybrid grid-connected and grid-connected inverter system described in Embodiment 1.

[0124] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0125] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0126] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0127] Example 4

[0128] In one or more embodiments, a computer-readable storage medium is disclosed, wherein a plurality of instructions are stored, the instructions being adapted to be loaded by a processor of a terminal device and executed by the oscillation suppression method for a hybrid grid-connected and grid-connected inverter system described in Embodiment 1.

[0129] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for oscillation suppression in a hybrid grid-connected and grid-connected inverter system, characterized in that, include: Establish a decomposition model of the grid-connected inverter and separate the negative damping component that causes instability of the grid-connected inverter; The grid-connected inverter decomposition model specifically includes: Without considering the effect of the phase-locked loop, the positive sequence impedance of the grid-connected inverter is: in, H i (s -jω 0)= k p + k i / (s -jω 0) is the current loop control transfer function after complex frequency shift; ω 0 is the rated angular frequency; K m Modulation gain; V dc It is DC voltage; L f1 It is the filter inductor of the grid inverter; V p and I p These are the positive-sequence disturbance voltage and the positive-sequence disturbance current, respectively. When considering the effects of phase-locked loops: Due to phase perturbation Δθ pll First-order perturbation modulated wave generated by PARK transform Δm x1 The generated first-order disturbance impedance, which is further decomposed into impedances Z GFL2a and impedance Z GFL2b Series; And, due to phase perturbation Δθ pll First-order perturbation modulated wave generated by inverse Park transform Δm x2 The resulting first-order disturbance impedance; Among them, impedance Z GFL2a The overall performance is negative damping, which is the negative damping component that causes instability in grid-connected inverters; Based on the negative damping component, a compensation term is designed and injected into the grid inverter to reshape the output impedance of the grid inverter, thereby offsetting the impact of the negative damping component of the grid inverter on the stability of the hybrid system.

2. The oscillation suppression method for a hybrid grid-connected and grid-connected inverter system as described in claim 1, characterized in that, impedance Z GFL2a Specifically: ； in, V 1 represents the amplitude of the fundamental voltage of the grid-connected inverter; I 1 represents the amplitude of the fundamental current of the grid-connected inverter; The initial phase angle of the fundamental current; T PLL (s- jω 0) is the closed-loop transfer function of the phase-locked loop after complex frequency shift.

3. The oscillation suppression method for a hybrid grid-connected and grid-connected inverter system as described in claim 1, characterized in that, negative damping component Z GFL2a Invert the impedance and inject it into the grid inverter to obtain the improved grid inverter impedance, specifically: ； in, Z GFMp (s) and Z GFM (s) represent the negative damping of the grid-connected inverters with opposite signs in parallel connection. Z GFL2a The subsequent grid-connected inverter impedance model and the parallel grid-connected inverter with opposite signs of negative damping. Z GFL2a Previous grid inverter impedance model, A GFM (s) and B GFM (s) are respectively Z GFM The numerator and denominator of (s) C GFM (s) is the coupling quantity that is related to both the grid-connected inverter and the grid-connected inverter.

4. The oscillation suppression method for a hybrid grid-connected and grid-connected inverter system as described in claim 3, characterized in that, Coupling quantity related to both grid-connected inverters and grid-connected inverters C GFM (s) is divided into C GFM1 (s) and C GFM2 (s) Two parts: ； ； in, V 1 represents the amplitude of the fundamental voltage of the grid-connected inverter; I 1 represents the amplitude of the fundamental current of the grid-connected inverter; The initial phase angle of the fundamental current is denoted as . ω 0 is the rated angular frequency. ω set This is the angular frequency reference value for the grid-connected inverter. E set This serves as a reference value for the voltage amplitude of the grid-connected inverter. The virtual phase angle for virtual synchronous machine control; V The base frequency voltage of the grid inverter; H p (s- jω 0) is the transfer function of the power loop of the grid inverter after complex frequency shift; H v (s- jω 0) is the transfer function of the voltage loop of the grid inverter after complex frequency shift; H i (s- jω 0) represents the proportional integral term after complex frequency shift. T PLL (s- jω 0) is the closed-loop transfer function of the phase-locked loop after complex frequency shift; L f2 It is the filter inductor of the grid inverter.

5. The oscillation suppression method for a hybrid grid-connected and grid-connected inverter system as described in claim 4, characterized in that, Will C GFM2 (s) is used as a compensation term to compensate the modulation wave of the grid inverter, thereby realizing the parallel connection of a virtual impedance on the grid inverter side to offset the influence of the negative impedance of the grid inverter.

6. The oscillation suppression method for a hybrid grid-connected and grid-connected inverter system as described in claim 4, characterized in that, Compensation C GFM2 All parameters involved in (s) are set according to the filter parameters of the grid-connected inverter system and the control parameters of the grid-connected inverter and the actual operating values.

7. An oscillation suppression system for a hybrid grid-connected and grid-connected inverter system, characterized in that, include: The model building module is used to build a decomposition model of the grid-connected inverter and separate the negative damping component that causes instability of the grid-connected inverter. The grid-connected inverter decomposition model specifically includes: Without considering the effect of the phase-locked loop, the positive sequence impedance of the grid-connected inverter is: in, H i (s -jω 0)= k p + k i / (s -jω 0) is the current loop control transfer function after complex frequency shift; ω 0 is the rated angular frequency; K m Modulation gain; V dc It is DC voltage; L f1 It is the filter inductor of the grid inverter; V p and I p These are the positive-sequence disturbance voltage and the positive-sequence disturbance current, respectively. When considering the effects of phase-locked loops: Due to phase perturbation Δθ pll First-order perturbation modulated wave generated by PARK transform Δm x1 The generated first-order disturbance impedance, which is further decomposed into impedances Z GFL2a and impedance Z GFL2b Series; And, due to phase perturbation Δθ pll First-order perturbation modulated wave generated by inverse Park transform Δm x2 The resulting first-order disturbance impedance; Among them, impedance Z GFL2a The overall performance is negative damping, which is the negative damping component that causes instability in grid-connected inverters; The impedance compensation module is used to design a compensation term based on the negative damping component and inject it into the grid inverter to reshape the output impedance of the grid inverter, so as to offset the influence of the negative damping component of the grid inverter on the stability of the hybrid system.

8. A terminal device comprising a processor and a memory, the processor for implementing instructions; the memory for storing multiple instructions, characterized in that, The instructions are adapted to be loaded by a processor and executed by the oscillation suppression method for a hybrid grid-connected and grid-connected inverter system according to any one of claims 1-6.

9. A computer-readable storage medium storing a plurality of instructions, characterized in that, The instructions are adapted to be loaded by the processor of the terminal device and executed by the oscillation suppression method of the hybrid grid-connected and grid-connected inverter system according to any one of claims 1-6.

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