Hybrid active damping method and device based on filter capacitor state variable compensation

Abstract

The invention discloses a hybrid active damping method and device based on filter capacitor state variable compensation. The method comprises the steps that basic parameters of a system are initialized; establishing a virtual impedance model equivalent to hybrid active damping, and obtaining a critical condition expression for evaluating the minimum phase characteristic of the system and an expression of an LCL filter transfer function damping ratio with respect to resonant frequency based on the model; establishing a plurality of constraint conditions about a system resonant frequency range, a minimum phase characteristic and an LCL filter transfer function damping ratio; the constraint condition is mapped to a three-dimensional parameter plane formed by the filter capacitor current feedback coefficient, the filter capacitor voltage feed-forward coefficient and the frequency to form a constraint region, and a feasible region is determined according to an effective intersection existing in the constraint region; and a group of optimal filter capacitor current feedback coefficients and filter capacitor voltage feed-forward coefficients are determined by taking minimization of the influence of power grid voltage disturbance on inverter current as an optimization target, so that the setting of the hybrid active damping coefficient is realized.

Description

Technical Field

[0001] This invention belongs to the field of power electronics, and particularly relates to a hybrid active damping method and device based on filter capacitor state variable compensation. Background Technology

[0002] As the global energy structure transitions towards low-carbon development, the penetration rate of new energy power generation is continuously increasing. The high proportion of new energy grid connection presents new challenges to the grid's inertial support and harmonic suppression. Grid-connected inverters, as core equipment connecting new energy power generation systems to the grid, have been widely installed. In current new energy power generation applications, LCL filters have become the mainstream choice for injecting high-quality current into the grid due to their better harmonic attenuation capability and smaller size compared to traditional L filters. However, since the transfer function of an LCL filter is a third-order system, its denominator polynomial contains a pair of conjugate poles. If the system is undamped, its transfer function gain approaches infinity at the resonant frequency, inevitably leading to system resonance. Furthermore, changes in grid strength and LCL filter parameters can cause the resonant frequency to drift, increasing the risk of system instability. To suppress the resonance introduced by the LCL filter in the system, numerous passive and active damping methods have been proposed. Generally, passive damping methods are implemented by physically connecting a resistor to the LCL filter. The method of paralleling a resistor with a filter capacitor effectively eliminates resonance peaks and does not affect the low-frequency and high-frequency performance of the system, but it is impractical due to excessive losses. Furthermore, virtual impedance is increasingly used to demonstrate the physical properties of active damping methods. Considering digital delay, the study of virtual impedance allows for a more specific and precise analysis of the impact of active damping on system performance. Fortunately, some active damping methods can introduce a virtual impedance in parallel with the filter capacitor into the system, such as capacitor voltage feedback, capacitor voltage feedforward, capacitor current feedback, and grid current feedback.

[0003] Currently, hybrid active damping technology is gradually becoming a research hotspot due to its advantages such as narrowing the frequency range of non-minimum phase characteristics, improving dynamic and steady-state performance, and enhancing the sensitivity of active damping coefficient adjustment. However, the inherent two-dimensional damping coefficient characteristics in hybrid active damping technology complicate the process. Establishing a robust damping method while balancing system dynamic response and stability is a key challenge for the effective application of this technology.

[0004] Since the hybrid active damping technology combining capacitor current feedback and capacitor voltage feedforward has not been fully studied, a reasonable and effective solution for tuning its damping coefficient is still lacking. It is worth noting that the damping effect of this technology on the circuit is equivalent to the physical structure of a parallel virtual impedance of a filter capacitor. Therefore, based on the analysis of the virtual impedance model, this application proposes a hybrid active damping method and device based on filter capacitor state variable compensation. Summary of the Invention

[0005] The purpose of this invention is to provide a hybrid active damping method and device based on filter capacitor state variable compensation. This addresses the problem that in the field of LCL resonance suppression, the hybrid active damping technology combining capacitor current feedback and capacitor voltage feedforward has not been fully studied, and a reasonable and effective solution for tuning its damping coefficient is still lacking. This invention not only avoids the trial-and-error process of two-dimensional damping, significantly shortening engineering debugging time, but the logic of this method can also be extended to other hybrid active damping technologies.

[0006] This application is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides a hybrid active damping method based on filter capacitor state variable compensation, wherein the filter capacitor state variable compensation includes current feedback and voltage feedforward, and the method includes: Initialize the system's basic parameters; A virtual impedance model equivalent to hybrid active damping is established, and based on this model, the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency are derived. Based on the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency, multiple constraints are established regarding the system's resonant frequency range, minimum phase characteristics, and the damping ratio of the LCL filter transfer function. The constraints are mapped onto a three-dimensional parameter plane consisting of the filter capacitor current feedback coefficient, the filter capacitor voltage feedforward coefficient, and the frequency to form a constraint region. The feasible region is determined based on the effective intersection of the constraint regions. Within the feasible region, with the optimization objective of minimizing the impact of grid voltage disturbances on inverter current, a set of optimal filter capacitor current feedback coefficients and filter capacitor voltage feedforward coefficients are determined, thereby achieving the tuning of the hybrid active damping coefficient.

[0008] In some embodiments, the basic parameters of the system include: sampling period, sampling frequency, switching frequency, base frequency, inverter-side filter inductor, grid-side filter inductor, and filter capacitor.

[0009] In some embodiments, the virtual impedance model equivalent to the hybrid active damping is established by equivalently connecting a virtual impedance in parallel across the filter capacitor, which includes a hybrid active damping element containing filter capacitor current feedback and filter capacitor voltage feedforward; the virtual impedance is composed of a virtual resistance and a virtual reactance connected in parallel.

[0010] In some embodiments, the virtual impedance model equivalent to the hybrid active damping is established by equivalently representing the hybrid active damping circuit, which includes filter capacitor current feedback and filter capacitor voltage feedforward, as a virtual impedance connected in parallel across the filter capacitor. Specifically, it includes the following steps: The control object of the three-phase grid-connected inverter system is clearly defined as the inverter current. A proportional resonant regulator is used as the controller, and grid synchronization phase information is obtained through a software phase-locked loop. A hybrid active damping strategy is adopted, and the filter capacitor current is connected to the output of the proportional resonant regulator through the feedback path and the filter capacitor voltage is connected through the feedforward path. The LCL filter transfer function from inverter voltage to grid current is derived considering digital delay. Based on the characteristic that hybrid active damping is equivalent to the parallel virtual impedance of a filter capacitor, the expressions for virtual impedance and the corresponding virtual resistance and virtual reactance are derived. Determine the critical frequency that distinguishes virtual resistor symbols and establish the conditions for the system to maintain minimum phase characteristics; Using the resonant frequency as an intermediate variable, we derive the expressions for the damping ratio and the grid inductance with respect to the resonant frequency, and obtain the quantitative relationship between the two. The tracking performance of the inverter current closed-loop control is evaluated by quantitatively analyzing the disturbance characteristics of grid voltage on inverter current.

[0011] In some embodiments, the critical condition expression for evaluating the minimum phase characteristic of the system is: , In the formula, The resonant frequency, To determine the distinction Critical frequency of the symbol It is positive.

[0012] In some embodiments, the expression for the damping ratio is: , In the formula, and These are the current feedback coefficient and voltage feedforward coefficient of the filter capacitor, respectively, where C is the filter capacitor. For system sampling time, It is the resonant frequency.

[0013] In some embodiments, the resonant frequency range is constrained to be between 10 times the fundamental frequency and 0.5 times the switching frequency.

[0014] In some embodiments, the constraint condition for minimum phase characteristics is: the maximum resonant frequency is less than the critical frequency, and the maximum resonant frequency is... The resonant frequency at that time.

[0015] In some embodiments, the constraint condition for the damping ratio of the LCL filter transfer function is: the damping ratio of the LCL filter transfer function must be greater than or equal to a set lower limit for the damping ratio of the LCL filter transfer function.

[0016] In some embodiments, the constraints further include constraints defined in the real number range.

[0017] In some embodiments, to ensure that the listed expressions are defined within the real number range, the following conditions must be met: , In the formula, and These are the current feedback coefficient and voltage feedforward coefficient of the filter capacitor, respectively, where C is the filter capacitor. For system sampling time, The resonant frequency, This is the inverter-side inductor.

[0018] In some embodiments, the constraint further includes setting an upper limit on the gain of the closed-loop transfer function from grid voltage to inverter current at the base frequency.

[0019] In some embodiments, the closed-loop gain A(ω) b )satisfy: , In the formula, This is the upper limit of the gain. This is the closed-loop transfer function from grid voltage to inverter current. The resonant frequency, It is the imaginary unit.

[0020] Secondly, the present invention provides a hybrid active damping device based on filter capacitor state variable compensation, wherein the filter capacitor state variable compensation includes current feedback and voltage feedforward, and the device includes: The initialization module is used to initialize the system's basic parameters. The virtual impedance model module is used to establish a virtual impedance model equivalent to hybrid active damping, and based on this model, to derive the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency. The constraint module is used to establish multiple constraints on the system's resonant frequency range, minimum phase characteristics, and LCL filter transfer function damping ratio based on the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency. The feasible region determination module is used to map the constraints onto a three-dimensional parameter plane consisting of the filter capacitor current feedback coefficient, the filter capacitor voltage feedforward coefficient, and the frequency to form a constraint region, and to determine the feasible region based on the effective intersection of the constraint regions. The optimal selection module is used to determine a set of optimal filter capacitor current feedback coefficients and filter capacitor voltage feedforward coefficients within the feasible region, with the optimization objective of minimizing the impact of grid voltage disturbances on inverter current, thereby achieving the tuning of the hybrid active damping coefficient.

[0021] Thirdly, the present invention provides an LCL-type T-type three-level inverter control system, including the above-mentioned hybrid active damping device based on filter capacitor state variable compensation.

[0022] Fourthly, the present invention provides an electronic device comprising: one or more processors; and a memory storing computer-executable instructions, which, when executed by the one or more processors, cause the one or more processors to perform the method described above.

[0023] Fifthly, the present invention provides a computer-readable storage medium storing instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform the method described above.

[0024] In a sixth aspect, the present invention provides a computer program product comprising instructions that, when executed by a processor, implement the above-described method.

[0025] The beneficial effects of this application are:

[0026] 1. This invention achieves rapid and robust tuning of the two-dimensional damping coefficient by establishing an accurate virtual impedance model and systematic constraints, providing a key solution for the effective application of hybrid active damping technology.

[0027] 2. This invention avoids the tedious trial-and-error process, is simple to operate, significantly shortens the engineering debugging time, and lowers the application threshold and implementation cost of hybrid active damping technology.

[0028] 3. The implementation of hybrid active damping only requires a voltage sensor to measure the voltage of the filter capacitor, while the current of the filter capacitor can be calculated using the voltage of the filter capacitor, eliminating the need for an additional current sensor.

[0029] 4. Compared with single-filter capacitor current feedback active damping, the proposed hybrid active damping, by adding capacitor voltage feedforward, can not only improve the dynamic response of the system, but also broaden the frequency range in which the system maintains minimum phase characteristics, thereby enhancing the robustness of the system. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain this application, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0031] Figure 1 A flowchart of a hybrid active damping method based on filter capacitor state variable compensation provided in an embodiment of this application;

[0032] Figure 2 This is a structural diagram of an LCL-type T-type three-level grid-connected inverter system provided in one embodiment of this application;

[0033] Figure 3 This is a diagram showing the constraint area provided in one embodiment of this application;

[0034] Figure 4 This is a feasible domain display diagram formed by common constraints provided in one embodiment of this application;

[0035] Figure 5 This is a simulated waveform of the grid current based on the proposed hybrid active damping strategy provided in one embodiment of this application.

[0036] It should be noted that these figures and descriptions are not intended to limit the scope of the concept of this application in any way, but rather to illustrate the concept of this application to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] This invention lays the theoretical foundation for two-dimensional damping by deriving expressions for the minimum phase characteristics, robustness, and tracking performance of the evaluation system.

[0039] Reference Figure 1As shown in one embodiment, a hybrid active damping method based on filter capacitor state variable compensation is provided. The method includes the following steps:

[0040] Step S100: Initialize the basic parameters of the system.

[0041] Furthermore, the basic parameters of the system include: sampling period, sampling frequency, switching frequency, base frequency, inverter-side filter inductor, grid-side filter inductor, and filter capacitor.

[0042] Step S200: Establish a virtual impedance model equivalent to hybrid active damping, and based on this model, derive the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency.

[0043] In this embodiment, the virtual impedance model equivalent to hybrid active damping is established by equating the hybrid active damping element, which includes filter capacitor current feedback and filter capacitor voltage feedforward, to a virtual impedance connected in parallel across the filter capacitor. The virtual impedance is composed of a virtual resistance and a virtual reactance connected in parallel.

[0044] The equivalent virtual impedance model of hybrid active damping is established by equating the hybrid active damping circuit, which includes filter capacitor current feedback and filter capacitor voltage feedforward, to a virtual impedance connected in parallel across the filter capacitor. Specifically, it includes the following steps:

[0045] Step S210: Define the control object of the three-phase grid-connected inverter system as the inverter current, use a proportional resonant regulator as the controller, and obtain grid synchronization phase information through a software phase-locked loop.

[0046] Specifically, for LCL-type three-phase grid-connected inverter systems, in single-current closed-loop control, the controlled object is clearly defined as the inverter current, and the controller adopts a proportional resonant (PR) regulator. To achieve unit power operation, precise grid synchronization phase information needs to be obtained through a software phase-locked loop (PLL).

[0047] The transfer function model of the PR regulator can be expressed as:

[0048] (1)

[0049] In the formula, and These are the proportional coefficient and the resonance coefficient, respectively. As the cutoff frequency, considering that the maximum allowable fluctuation range of the power grid frequency is ±0.2Hz, it can be... Set to 0.4π. It is the resonant frequency. It is the Laplace operator, and the theoretical gain of the PR regulator at this frequency is infinite, so it is usually set to the base frequency of the grid voltage.

[0050] Step S220: Using a hybrid active damping strategy, the filter capacitor current is connected to the output of the proportional resonant regulator through the feedback path and the filter capacitor voltage is connected through the feedforward path. The LCL filter transfer function from the inverter voltage to the grid current is derived considering digital delay.

[0051] Specifically, to effectively suppress LCL resonance, a hybrid active damping strategy is adopted. In the inverter current closed-loop control, this strategy is implemented as follows: the filter capacitor current is connected to the output of the PR regulator through a feedback path, while the filter capacitor voltage is connected to the output of the PR regulator through a feedforward path. To improve control accuracy, the impact of digital delay must be systematically considered when constructing the control block diagram.

[0052] In digital control systems, the delay element typically consists of a sample-and-hold delay and a pulse-width modulation (PWM) calculation delay, and its mathematical model is expressed as follows:

[0053] (2)

[0054] In the formula, For system sampling time, is the base of the natural logarithm. For the Laplace operator.

[0055] Based on the proposed inverter current closed-loop control block diagram using hybrid active damping, the transfer function of the LCL filter from inverter voltage to grid current can be derived, and its mathematical expression is as follows:

[0056] (3)

[0057] In the formula, For the inverter side inductor, For grid-side inductance With grid inductance The sum, where C is the filter capacitor. and These are the current feedback coefficient and the voltage feedforward coefficient of the filter capacitor, respectively. This is a delayed process.

[0058] Step S230: Based on the characteristic that the hybrid active damping is equivalent to the parallel virtual impedance of the filter capacitor, derive the expressions for the virtual impedance and the corresponding virtual resistance and virtual reactance.

[0059] Since the physical structure of the proposed hybrid active damping is equivalent to a virtual impedance connected in parallel with the filter capacitor, the hybrid active damping element in the original control block diagram can be removed, and an equivalent virtual impedance can be connected in parallel across the filter capacitor to obtain an inverter current closed-loop control block diagram based on virtual impedance.

[0060] Based on the inverter current closed-loop control block diagram based on virtual impedance, the LCL filter transfer function from the inverter output voltage to the grid current can be derived, and its expression is as follows:

[0061] (4)

[0062] In the formula, This represents the equivalent virtual impedance introduced into the circuit by the proposed hybrid active damping.

[0063] By comparing the transfer functions of the two LCL filters, formulas (3) and (4), the expression for the virtual impedance with respect to the damping coefficient can be derived as follows:

[0064] (5)

[0065] If virtual impedance From virtual resistance With virtual reactance component If the components are connected in parallel, then the above equation can be expanded using Euler's formula to derive:

[0066] (6)

[0067] In the formula, This refers to the system frequency.

[0068] Based on the above formula, the virtual resistance can be derived respectively. With virtual reactance The expression is:

[0069] (7)

[0070] (8)

[0071] Step S240: Determine the critical frequency for distinguishing virtual resistor symbols and establish the conditions for the system to maintain minimum phase characteristics.

[0072] Because when virtual resistance When the value is negative, it introduces an open-loop right-half-plane pole into the control system, causing the system to exhibit non-minimum phase characteristics; conversely, the virtual resistance... When positive, the minimum phase characteristic of the system can be ensured. Therefore, it is necessary to determine the distinguishing virtual resistance. Critical frequency of the symbol Let the above virtual resistor The denominator of the expression is zero, and both sides of the equation are divided by 0. C can then be used to derive the critical frequency. about The expression is:

[0073] (9)

[0074] In the formula, The physical meaning of can be considered as a coefficient of and The inverse capacitance of the ratio is expressed as:

[0075] (10)

[0076] Meanwhile, in order to construct a minimum-phase system, it is necessary to ensure that the system's resonant frequency is less than the critical frequency.

[0077] Furthermore, the critical condition expression for evaluating the minimum phase characteristic of the system is as follows:

[0078] (11)

[0079] Step S250: Using the resonant frequency as an intermediate variable, derive the expressions for the damping ratio and the grid inductance with respect to the resonant frequency, and obtain the quantitative relationship between the two.

[0080] Since it is impossible to directly establish an expression for the damping ratio with respect to the grid inductance, the resonant frequency can be used as an intermediate variable to establish expressions for both the damping ratio and the grid inductance with respect to the resonant frequency, thereby indirectly obtaining a quantitative relationship between the two. This method can be used to evaluate the robustness of a system.

[0081] Given virtual impedance From virtual resistance With virtual reactance component Parallel connection, and equivalent filter capacitor The filter capacitor C and the virtual reactance component Parallel connection. According to the circuit equivalence principle, the filter capacitor C is connected in parallel with a virtual impedance. The physical structure and equivalent filter capacitor Parallel virtual resistance The physical structures are completely equivalent.

[0082] Therefore, the LCL filter transfer function derived from formula (4) can be adjusted as follows:

[0083] (12)

[0084] According to the definition of damping ratio in classical control principles, the damping ratio ζ in the above formula can be expressed as:

[0085] (13)

[0086] resonant frequency The expression is represented as:

[0087] (14)

[0088] Due to the equivalent filter capacitor This represents the interaction between the filter capacitor C and the virtual reactance component. The equivalent capacitance formed by parallel connections is expressed as:

[0089] (15)

[0090] The virtual reactance derived from formula (8) Substituting the expression into the above equation, the equivalent filter capacitance is derived. The expression for the damping coefficient is:

[0091] (16)

[0092] The virtual resistance derived from formulas (16) and (7) Substituting the expression into formula (13) to derive the damping ratio ζ expression, we can derive the damping ratio ζ with respect to the resonant frequency. The expression.

[0093] Furthermore, the expression for the damping ratio is:

[0094] (17)

[0095] In the formula, and These are the current feedback coefficient and voltage feedforward coefficient of the filter capacitor, respectively, where C is the filter capacitor. For system sampling time, It is the resonant frequency.

[0096] Because of L s for and The sum of them, then It can be represented as:

[0097] (18)

[0098] The equivalent filter capacitor derived from formulas (18) and (16) The expression for the damping coefficient is substituted into formula (14) to establish the resonant frequency. After algebraic simplification, the expression is finally derived. Regarding the resonant frequency The expression is:

[0099] (19)

[0100] It should be noted that when deriving the expressions for the damping ratio and the grid inductance with respect to the resonant frequency, all original variables... All were replaced with resonant frequencies .

[0101] Step S260: Evaluate the tracking performance of the inverter current closed-loop control by quantitatively analyzing the disturbance characteristics of the grid voltage on the inverter current.

[0102] By quantitatively analyzing the disturbance characteristics of grid voltage on inverter current, the tracking performance of the inverter current closed-loop control can be evaluated. Based on the proposed hybrid active damping inverter current closed-loop control block diagram, the tracking performance of the inverter current closed-loop control can be derived from the grid voltage v. g The closed-loop transfer function to the inverter current i1 is expressed mathematically as follows:

[0103] (20)

[0104] Based on the analytical expressions for the amplitude-frequency response and phase-frequency response in classical control theory, the closed-loop transfer function can be calculated. At base frequency Amplitude gain at point for:

[0105] (twenty one)

[0106] Compared to amplitude requirements, phase requirements are secondary. Since the core objective of the system is to suppress grid voltage disturbances, when the amplitude gain... When fully suppressed, the effect of phase shift on overall performance is negligible.

[0107] Based on the above analysis, the following constraints are established for tuning the proposed hybrid active damping coefficient from the dimensions of resonant frequency range, minimum phase characteristics, validity of the real domain expression, robustness of the control system, and tracking performance.

[0108] Step S300: Based on the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency, establish multiple constraints on the system resonant frequency range, minimum phase characteristics, and damping ratio of the LCL filter transfer function.

[0109] Furthermore, to avoid low-frequency interference and suppress high-frequency harmonics, the resonant frequency range is constrained by the following condition: the resonant frequency range is often within 10 times the fundamental frequency. and 0.5 times the switching frequency between.

[0110] Therefore, resonant frequency The range can be represented as:

[0111] (twenty two)

[0112] When the system resonant frequency of formula (11) is... Less than the critical frequency When the condition is met, the system possesses minimum phase characteristics. The resonant frequency shown by formula (14) is... The total inductance L on the grid side in the expression and formula (18) s and grid inductance L g From the relationship, we can see that the grid inductance L g The increase will lead to the resonant frequency To ensure the system always maintains minimum phase characteristics, the maximum resonant frequency must be satisfied. Less than conditions.

[0113] Furthermore, the constraint condition for the minimum phase characteristic is that the maximum resonant frequency is less than the critical frequency.

[0114] Right now:

[0115] (twenty three)

[0116] When setting At that time, the system resonant frequency will reach its maximum value. At this point, the derivation of formula (19) is... Regarding the resonant frequency The expression can be simplified to:

[0117] (twenty four)

[0118] To visually represent the critical frequency The critical frequency derived from formula (9) is related to the damping coefficient. about The expression is adjusted to:

[0119] (25)

[0120] In an alternative embodiment, the constraints also include constraints that are defined within the real number range.

[0121] By analyzing the listed expressions, the following conditions must be met to ensure that they are defined within the real number range:

[0122] (26)

[0123] In the formula, and These are the current feedback coefficient and voltage feedforward coefficient of the filter capacitor, respectively, where C is the filter capacitor. For system sampling time, The resonant frequency, This is the inverter-side inductor.

[0124] In an alternative embodiment, the constraints further include setting an upper limit on the gain of the closed-loop transfer function from grid voltage to inverter current at the base frequency.

[0125] To ensure the ability to suppress LCL resonance and the robustness of the system, a lower limit for the damping ratio needs to be set. Therefore, the damping ratio ζ derived in step S250 with respect to the resonant frequency The expression can be modified as follows:

[0126] (27)

[0127] Due to the grid voltage v g The disturbance will directly affect the closed-loop control tracking performance of the inverter current i1, and the closed-loop function needs to be set. At base frequency Gain cap at [location] .

[0128] Furthermore, the closed-loop function shown by formula (21) At base frequency Gain at It should meet the following requirements:

[0129] (28)

[0130] Based on multiple constraints, a robust proposed hybrid active damping coefficient can be tuned.

[0131] To enhance understanding of the present invention, the specific embodiments of the technical solution are further described below. For example... Figure 2 As shown, the system adopts an LCL-type T-type three-level grid-connected inverter topology. Based on SVPWM (Space Vector Modulation) technology, switching control pulses are generated, which can first adjust the DC side voltage V... dcThe inverter converts the signal into a square wave, which is then filtered by an LCL filter to output a 50Hz sine wave. A PLL (software phase-locked loop) is used to accurately extract the grid voltage phase information, which is then used as a synchronization reference to achieve unit power operation of the grid-connected inverter. A single-closed-loop PR (proportional resonance) control strategy based on the inverter current i1 is adopted. To effectively suppress LCL resonance, the control loop includes a hybrid active damping term combining filter capacitor current feedback and filter capacitor voltage feedforward. Furthermore, For the inverter-side filter inductor, For grid-side filter inductance, C is the mains inductance, and C is the filter capacitor. i2 is the mains current, and i c V is the filter capacitor current. inv V is the inverter voltage. c V is the voltage across the filter capacitor. g This is the grid voltage.

[0132] For the two-dimensional implementation of the proposed hybrid active damping strategy, the specific steps are as follows:

[0133] System initialization parameters include sampling period Sampling frequency Switching frequency , baseband Inverter-side filter inductor , grid-side filter inductor And the filter capacitor C. Refer to Table 1 to find or calculate the values ​​of the above parameters.

[0134] Table 1 Basic parameters of grid-connected systems using LCL-type and T-type three-level inverters

[0135]

[0136] Therefore, the specific values ​​of the system initialization parameters are as follows:

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143]

[0144] To avoid low-frequency interference and suppress high-frequency harmonics, the resonant frequency Often at 10 times the base frequency and 0.5 times the switching frequency The values ​​are taken from between. Based on the parameter values ​​in step S1, the following can be calculated. The range that should be met is:

[0145]

[0146] To ensure the system always maintains minimum phase characteristics, the maximum resonant frequency must be satisfied. Less than the critical frequency conditions, namely:

[0147]

[0148] When setting At that time, the system resonant frequency will reach its maximum value. At this point, the damping coefficient has a maximum value with respect to the system's resonant frequency. The expression can be represented as:

[0149]

[0150] To illustrate visually The relationship with the damping coefficient will be derived in step four of the first aspect of the application. about The expression is adjusted to:

[0151]

[0152] To ensure that the listed expressions are defined within the real number range, the following conditions must be met:

[0153]

[0154] Based on the known system parameters and the constraints ensuring that the listed expressions are defined in the real number range, plot the damping coefficients. and Constraint region that varies with frequency.

[0155] To ensure the ability to suppress LCL resonance and the robustness of the system, a lower limit ζ of the damping ratio is set. min .

[0156] If ζ is here min If we set it to 0.2, then the derived ζ with respect to... The expression can be modified as follows:

[0157]

[0158] Based on the known system parameters and the damping ratio of the LCL filter transfer function, plot the damping coefficients. and Constraint region that varies with frequency.

[0159] Check if there is a valid intersection between the two determined constraint regions; this valid intersection is referred to as the feasible region. If it exists, continue to define the closed-loop function. At base frequency Gain cap at [location] x If it does not exist, adjust the lower limit of the damping ratio ζ. min After obtaining the value, continue with the subsequent steps.

[0160] Figure 3 The constraint regions are depicted for the two determined constraint regions. The solid-colored areas in the figure represent the feasible regions. If a feasible region exists, the execution of the defined closed-loop function continues. At base frequency Gain cap at [location] The steps.

[0161] Set the gain limit here. The value is -40dB.

[0162] Selecting the damping coefficient within the feasible region and After obtaining the value, based on the grid voltage v g Closed-loop transfer function to inverter current i1 Calculate the closed-loop function At base frequency Gain at .

[0163] Figure 4 This clearly demonstrates the feasible region formed by the common constraints. If we select from this feasible region... and Based on the system parameters listed in Table 1, the gain can be calculated. The result is:

[0164]

[0165] Determine the calculated gain Is it less than the set upper limit of gain? If so, then the output damping coefficient is... and The preferred value is determined; otherwise, the damping coefficient is reselected within the feasible region. and The value of .

[0166] Based on the judgment, the calculated gain Less than the set upper limit of gain Therefore, the output damping coefficient and The preferred values ​​are 14 and 0.6, respectively.

[0167] As a specific example of this invention, an LCL-type T-type three-level inverter grid-connected system was built in the Matlab simulation platform to verify the correctness of the example. The system parameters used in the simulation are consistent with those in Table 1. Among them, the grid inductance L... g The value is set to 1mH to simulate a weak power grid; the proportional gain k of the PR controller is used. p Take 15, resonance coefficient k r The value is set to 150; the hybrid active damping coefficient adopts the specific tuning result mentioned above, i.e., k. ic Take 14 and k vc Take 0.6.

[0168] To demonstrate the control performance of the proposed hybrid active damping, the simulation design was performed as follows: the total running time was set to 0.3 seconds. At the start of the simulation, the inverter current i1 was set to 40A; at 0.1 seconds, the inverter current i1 was reduced to 20A. At 0.2 seconds, the inverter current i1 was restored to 40A.

[0169] Table 2. THD analysis of grid current based on the proposed hybrid active strategy.

[0170]

[0171] Figure 5 The simulated waveforms of the grid current in the example are shown, and Table 2 shows the corresponding THD (Total Harmonic Distortion) results. Based on the simulation results and harmonic analysis, it can be seen that the proposed two-dimensional method for the hybrid active damping strategy can not only effectively suppress LCL filter resonance but also enable the grid current to exhibit good dynamic and steady-state performance.

[0172] The following is an embodiment of a hybrid active damping device based on filter capacitor state variable compensation according to the present invention, which can be used to execute an embodiment of a hybrid active damping method based on filter capacitor state variable compensation according to the present invention. For details not disclosed in the embodiment of the hybrid active damping device based on filter capacitor state variable compensation according to the present invention, please refer to the embodiment of the hybrid active damping method based on filter capacitor state variable compensation according to the present invention.

[0173] In one embodiment, a hybrid active damping device based on filter capacitor state variable compensation is proposed. The filter capacitor state variable compensation includes current feedback and voltage feedforward. The device includes:

[0174] The initialization module is used to initialize the system's basic parameters.

[0175] The virtual impedance model module is used to establish a virtual impedance model equivalent to hybrid active damping, and based on this model, to derive the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency.

[0176] The constraint module is used to establish multiple constraints on the system's resonant frequency range, minimum phase characteristics, and LCL filter transfer function damping ratio based on the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency.

[0177] The feasible region determination module is used to map the constraints onto a three-dimensional parameter plane consisting of the filter capacitor current feedback coefficient, the filter capacitor voltage feedforward coefficient, and the frequency to form a constraint region, and to determine the feasible region based on the effective intersection of the constraint regions.

[0178] The optimal selection module is used to determine a set of optimal filter capacitor current feedback coefficients and filter capacitor voltage feedforward coefficients within the feasible region, with the optimization objective of minimizing the impact of grid voltage disturbances on inverter current, thereby achieving the tuning of the hybrid active damping coefficient.

[0179] It should be noted that the above embodiments of the hybrid active damping device based on filter capacitor state variable compensation, when implementing a hybrid active damping method based on filter capacitor state variable compensation, are only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. Furthermore, the above embodiments of the hybrid active damping device based on filter capacitor state variable compensation and the hybrid active damping method based on filter capacitor state variable compensation belong to the same concept, and their implementation process is detailed in the embodiment of the hybrid active damping method based on filter capacitor state variable compensation, which will not be repeated here.

[0180] In one embodiment, an LCL-type T-type three-level inverter control system is proposed, which includes a hybrid active damping device based on filter capacitor state variable compensation.

[0181] For a description of the hybrid active damping device based on filter capacitor state variable compensation, please refer to the above embodiments, which will not be repeated here.

[0182] In one embodiment, an electronic device is proposed, comprising: one or more processors; and a memory storing computer-executable instructions that, when executed by the one or more processors, cause the one or more processors to perform a hybrid active damping method based on filter capacitor state variable compensation.

[0183] In one embodiment, a computer-readable storage medium stores instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform a hybrid active damping method based on filter capacitor state variable compensation.

[0184] In one embodiment, a computer program product includes instructions that, when executed by a processor, implement a hybrid active damping method based on filter capacitor state variable compensation.

[0185] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. This computer program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. The aforementioned storage medium can be a non-volatile storage medium such as a magnetic disk, optical disk, or read-only memory (ROM), or random access memory (RAM).

[0186] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0187] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A hybrid active damping method based on filter capacitor state variable compensation, characterized in that: The state variable compensation of the filter capacitor includes current feedback and voltage feedforward, and the method includes: Initialize the system's basic parameters; A virtual impedance model equivalent to hybrid active damping is established, and based on this model, the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency are derived. Based on the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency, multiple constraints are established regarding the system's resonant frequency range, minimum phase characteristics, and the damping ratio of the LCL filter transfer function. The constraints are mapped onto a three-dimensional parameter plane consisting of the filter capacitor current feedback coefficient, the filter capacitor voltage feedforward coefficient, and the frequency to form a constraint region. The feasible region is determined based on the effective intersection of the constraint regions. Within the feasible region, with the optimization objective of minimizing the impact of grid voltage disturbances on inverter current, a set of optimal filter capacitor current feedback coefficients and filter capacitor voltage feedforward coefficients are determined, thereby achieving the tuning of the hybrid active damping coefficient.

2. The hybrid active damping method based on filter capacitor state variable compensation according to claim 1, characterized in that: The basic parameters of the system include: sampling period, sampling frequency, switching frequency, base frequency, inverter-side filter inductor, grid-side filter inductor, and filter capacitor.

3. The hybrid active damping method based on filter capacitor state variable compensation according to claim 1, characterized in that: The virtual impedance model equivalent to the hybrid active damping is established by equating the hybrid active damping element, which includes filter capacitor current feedback and filter capacitor voltage feedforward, to a virtual impedance connected in parallel across the filter capacitor; the virtual impedance is composed of a virtual resistance and a virtual reactance connected in parallel.

4. The hybrid active damping method based on filter capacitor state variable compensation according to claim 3, characterized in that: The equivalent virtual impedance model of the hybrid active damping is established by equating the hybrid active damping element, which includes filter capacitor current feedback and filter capacitor voltage feedforward, to a virtual impedance connected in parallel across the filter capacitor. Specifically, it includes the following steps: The control object of the three-phase grid-connected inverter system is clearly defined as the inverter current. A proportional resonant regulator is used as the controller, and grid synchronization phase information is obtained through a software phase-locked loop. A hybrid active damping strategy is adopted, and the filter capacitor current is connected to the output of the proportional resonant regulator through the feedback path and the filter capacitor voltage is connected through the feedforward path. The LCL filter transfer function from inverter voltage to grid current is derived considering digital delay. Based on the characteristic that hybrid active damping is equivalent to the parallel virtual impedance of a filter capacitor, the expressions for virtual impedance and the corresponding virtual resistance and virtual reactance are derived. Determine the critical frequency that distinguishes virtual resistor symbols and establish the conditions for the system to maintain minimum phase characteristics; Using the resonant frequency as an intermediate variable, we derive the expressions for the damping ratio and the grid inductance with respect to the resonant frequency, and obtain the quantitative relationship between the two. The tracking performance of the inverter current closed-loop control is evaluated by quantitatively analyzing the disturbance characteristics of grid voltage on inverter current.

5. The hybrid active damping method based on filter capacitor state variable compensation according to claim 4, characterized in that: The critical condition expression for evaluating the minimum phase characteristic of the system is: ， In the formula, The resonant frequency, To determine the distinction Critical frequency of the symbol It is positive.

6. The hybrid active damping method based on filter capacitor state variable compensation according to claim 4, characterized in that: The expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency is: ， In the formula, and These are the current feedback coefficient and voltage feedforward coefficient of the filter capacitor, respectively, where C is the filter capacitor. For system sampling time, It is the resonant frequency.

7. The hybrid active damping method based on filter capacitor state variable compensation according to claim 4, characterized in that: The constraint on the resonant frequency range is that the resonant frequency range is set between 10 times the fundamental frequency and 0.5 times the switching frequency.

8. The hybrid active damping method based on filter capacitor state variable compensation according to claim 5, characterized in that: The constraint condition for minimum phase characteristics is: the maximum resonant frequency is less than the critical frequency, and the maximum resonant frequency is... The resonant frequency at that time.

9. The hybrid active damping method based on filter capacitor state variable compensation according to claim 6, characterized in that: The constraint condition for the damping ratio of the LCL filter transfer function is: the damping ratio of the LCL filter transfer function must be greater than or equal to the set lower limit of the damping ratio of the LCL filter transfer function.

10. The hybrid active damping method based on filter capacitor state variable compensation according to claim 1, characterized in that: The constraints also include constraints defined within the real number range.

11. The hybrid active damping method based on filter capacitor state variable compensation according to claim 10, characterized in that: To ensure that the listed expressions are defined within the real number range, the following conditions must be met: ， In the formula, and These are the current feedback coefficient and voltage feedforward coefficient of the filter capacitor, respectively, where C is the filter capacitor. For system sampling time, The resonant frequency, This is the inverter-side inductor.

12. The hybrid active damping method based on filter capacitor state variable compensation according to claim 1, characterized in that: The constraints also include setting an upper limit on the gain of the closed-loop transfer function from grid voltage to inverter current at the base frequency.

13. The hybrid active damping method based on filter capacitor state variable compensation according to claim 11, characterized in that: Closed-loop gain A(ω) b )satisfy: ， In the formula, This is the upper limit of the gain. This is the closed-loop transfer function from grid voltage to inverter current. The resonant frequency, It is the imaginary unit.

14. A hybrid active damping device based on filter capacitor state variable compensation, characterized in that: The filter capacitor state variable compensation includes current feedback and voltage feedforward, and the device includes: The initialization module is used to initialize the system's basic parameters. The virtual impedance model module is used to establish a virtual impedance model equivalent to hybrid active damping, and based on this model, to derive the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency. The constraint module is used to establish multiple constraints on the system's resonant frequency range, minimum phase characteristics, and LCL filter transfer function damping ratio based on the critical condition expression for evaluating the minimum phase characteristics of the system and the expression for the damping ratio of the LCL filter transfer function with respect to the resonant frequency. The feasible region determination module is used to map the constraints onto a three-dimensional parameter plane consisting of the filter capacitor current feedback coefficient, the filter capacitor voltage feedforward coefficient, and the frequency to form a constraint region, and to determine the feasible region based on the effective intersection of the constraint regions. The optimal selection module is used to determine a set of optimal filter capacitor current feedback coefficients and filter capacitor voltage feedforward coefficients within the feasible region, with the optimization objective of minimizing the impact of grid voltage disturbances on inverter current, thereby achieving the tuning of the hybrid active damping coefficient.

15. A control system for an LCL-type T-type three-level inverter, characterized in that: Includes the hybrid active damping device based on filter capacitor state variable compensation as described in claim 14.

16. An electronic device, characterized in that: include: One or more processors; And a memory storing computer-executable instructions, which, when executed by the one or more processors, cause the one or more processors to perform the method according to any one of claims 1 to 13.

17. A computer-readable storage medium, characterized in that: The device stores instructions that, when executed individually or jointly by one or more processors of the computing device, cause the computing device to perform the method of any one of claims 1 to 13.

18. A computer program product, characterized in that: The computer program product includes instructions that, when executed by a processor, implement the method according to any one of claims 1 to 13.

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