Non-isolated low-voltage flexible interconnection device low-frequency leakage current control method and system

Abstract

The present application relates to the technical field of power electronics and low-voltage distribution network flexible interconnection, and provides a low-frequency leakage current control method and system for a non-isolated low-voltage flexible interconnection device, which comprises establishing a third-order low-frequency leakage current physical model containing the coupling effect of filter inductance, grid-side inductance and ground parasitic capacitance, equivalent of the unmeasurable zero sequence voltage difference to an external disturbance source, and making clear the driving relationship of the leakage current loop; separating the fundamental frequency and third harmonic components from the total leakage current signal in real time, and constructing a passive control law containing a reference intrinsic term cancellation, active damping injection and a high-order shaping term; on the basis of meeting the passive stability constraint, introducing a selective damping link for the fundamental frequency and third harmonic, and establishing an analytical design relationship between the damping gain and the target suppression ratio, so that the control parameters are directly calculated and determined according to the engineering limit, to realize the low-frequency leakage current amplitude suppression without relying on communication.

Description

Technical Field

[0001] This invention relates to the field of power electronics and flexible interconnection technology of low-voltage distribution networks, and in particular to a low-frequency leakage current control method and system for a non-isolated low-voltage flexible interconnection device. 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] To achieve interconnection and flexible power flow control between distribution transformer areas, the application demand for non-isolated low-voltage flexible interconnection devices (FIDs) based on power electronics technology in distribution networks is constantly increasing. These devices are typically used for bidirectional energy regulation, power decoupling, and power quality support between two AC buses. Structurally, they often adopt a back-to-back converter or multi-converter configuration with a common DC bus, consisting of rectifier and inverter power units, filter inductors and capacitors, DC bus capacitors, and grounding protection networks. In low-voltage engineering applications, the devices need to balance power density, efficiency, and cost, while also meeting safety regulations and electromagnetic compatibility requirements. Low-frequency leakage current can directly cause problems such as malfunction of leakage current circuit breakers, heating of grounding conductors, accumulation of insulation stress, and long-term reliability degradation, which are key challenges that must be addressed for the safe and stable operation of non-isolated low-voltage FID systems.

[0004] Current methods for suppressing leakage current or ground loop current mainly include structural isolation, passive device suppression, and modulation and control improvements. Introducing an isolation transformer can structurally cut off the common-mode loop, resulting in a clear suppression effect, but it significantly increases size and cost, and introduces additional losses, which is detrimental to the high power density and high efficiency requirements of low-voltage scenarios. Furthermore, the coupling of passive networks with grid impedance and ground impedance may alter the system's low-frequency characteristics, leading to the risk of circulating current amplification or oscillation under specific operating conditions. From a modulation perspective, reducing the common-mode voltage level by improving space vector pulse width modulation, zero-sequence voltage injection, or limiting common-mode voltage jumps can improve leakage current under certain conditions. However, since it is difficult to keep the common-mode voltage difference between the two sides consistent within the same fundamental period and at every switching moment, even if the same modulation principle is used on both sides, due to unavoidable factors such as differences in operating modes, modulation states, dead-zone effects, device parameters, and power grid conditions, there will still be a slight deviation in the instantaneous common-mode voltage waveform between the two sides and ground. This slight deviation will be converted into a large current response through a low-impedance path in the low-frequency common-mode circuit, manifesting as significant low-frequency leakage current or ground loop current. Moreover, it has obvious sensitivity and uncertainty with changes in operating conditions, which brings difficulties to protection coordination and long-term reliable operation.

[0005] At the control level, proportional-integral control, resonant control, and model predictive control can be used for circulating current suppression or power quality optimization, but the engineering conditions of FID make it more difficult to implement: on the one hand, the equivalent inductance and grounding impedance of the power grid change significantly with the connection location, line and parallel system state, and the parameters are highly uncertain; on the other hand, under conditions of no communication or weak communication, it is difficult for the converters on both sides to share complete modulation state and common-mode information to ground, and the equivalent model often contains unmeasurable bias terms or disturbance terms, making it difficult to maintain the goal of zero error across the entire frequency band in the long term. Summary of the Invention

[0006] To address the technical problems of non-isolated low-voltage flexible interconnect devices, such as complex low-frequency leakage current mechanisms, low grounding loop impedance leading to extreme sensitivity to common-mode voltage differences, and poor robustness of traditional control methods under conditions of no communication and parameter uncertainty, this invention provides a low-frequency leakage current control method and system for non-isolated low-voltage flexible interconnect devices. This method can reshape the system impedance characteristics at the fundamental frequency and specific subharmonic frequencies through energy shaping, thereby achieving efficient suppression of low-frequency leakage current while ensuring the global passive stability of the system.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a method for controlling low-frequency leakage current in a non-isolated low-voltage flexible interconnect device.

[0008] In one or more embodiments, a method for controlling low-frequency leakage current in a non-isolated low-voltage flexible interconnect device is provided, comprising: Based on the non-isolated low-voltage flexible interconnect device, a common-mode equivalent circuit is constructed, and a third-order low-frequency leakage current physical model including the coupling effect of filter inductance, grid-side inductance and ground parasitic capacitance is established. The unmeasurable zero-sequence voltage difference is equivalent to an external disturbance source, and its driving relationship on the leakage current circuit is clarified. The fundamental frequency and third harmonic components are separated from the total leakage current signal in real time. Selective tracking error for the fundamental frequency and third harmonic is defined. A passive control law containing reference intrinsic term cancellation, active damping injection and higher-order shaping term is constructed so that the disturbed object is reshaped into a stable third-order error system with a clear dissipation structure and the control action is concentrated on the target low-frequency component. Based on the passive stability constraint, a selective damping element for the fundamental frequency and the third harmonic is introduced, and an analytical design relationship between the damping gain and the target suppression ratio is established, so that the control parameters can be directly calculated and determined according to the engineering limit, so as to achieve low-frequency leakage current amplitude suppression without relying on communication.

[0009] As one implementation method, the fundamental frequency and third harmonic components are separated from the total leakage current signal in real time based on phase-locked loop synchronous detection and low-pass filtering.

[0010] As one implementation method, the process of separating the fundamental frequency and third harmonic components from the total leakage current signal in real time based on phase-locked loop synchronous detection and low-pass filtering is as follows: The measured low-frequency leakage current is used to obtain the fundamental frequency synchronization angle and the third harmonic synchronization angle through a phase-locked loop. The low-frequency leakage current is multiplied by the orthogonal basis function to obtain four synchronous detection signals. The four synchronous detection signals are processed by first-order low-pass filters respectively; By using the output state and synchronization angle of a first-order low-pass filter, the fundamental frequency and third harmonic component of the low-frequency leakage current are reconstructed.

[0011] As one implementation method, the process of determining passive stability constraints is as follows: An augmented storage function is constructed that simultaneously contains the error system energy and the filter state energy. The strict passivity of the closed-loop system with respect to the generalized ports is obtained through energy flow analysis. It is further proven that under the condition of zero input and zero output at the port, the system state can only tend to zero, thus satisfying the zero-state measurability condition and ensuring the stability and boundedness of the closed loop under bounded disturbances.

[0012] As one implementation method, the selective damping element for the fundamental frequency and the third harmonic is a first-order leading element, which is used to compensate for the errors of the fundamental frequency and the third harmonic respectively.

[0013] As one implementation method, in order to suppress low-frequency leakage current, the obtained passive control law is injected into the original modulation wave using a zero-sequence injection method.

[0014] As one implementation method, without changing the basic framework of the main power control of the non-isolated low-voltage flexible interconnect device, the impedance characteristics of the common-mode circuit can be independently adjusted to achieve precise suppression of low-frequency leakage current.

[0015] A second aspect of the present invention provides a low-frequency leakage current control system for a non-isolated low-voltage flexible interconnect device.

[0016] In one or more embodiments, a low-frequency leakage current control system for a non-isolated low-voltage flexible interconnect device includes: The physical model construction module is used to construct a common-mode equivalent circuit based on a non-isolated low-voltage flexible interconnect device, and to establish a third-order low-frequency leakage current physical model that includes the coupling effect of filter inductance, grid-side inductance and ground parasitic capacitance. The unmeasurable zero-sequence voltage difference is equivalent to an external disturbance source, and its driving relationship on the leakage current circuit is clarified. The passive control law construction module is used to separate the fundamental frequency and third harmonic components from the total leakage current signal in real time, define the selective tracking error for the fundamental frequency and third harmonic, construct a passive control law including reference intrinsic term cancellation, active damping injection and higher-order shaping term, so that the disturbed object is reshaped into a stable third-order error system with a clear dissipation structure, and the control action is concentrated on the target low-frequency component. The low-frequency leakage current amplitude suppression module is used to introduce a selective damping element for the fundamental frequency and the third harmonic while meeting the passive stability constraints. It also establishes an analytical design relationship between the damping gain and the target suppression ratio, so that the control parameters can be directly calculated and determined based on the engineering limits, thereby achieving low-frequency leakage current amplitude suppression without relying on communication.

[0017] A third aspect of the present invention provides a computer-readable storage medium.

[0018] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the low-frequency leakage current control method for a non-isolated low-voltage flexible interconnect device as described above.

[0019] A fourth aspect of the present invention provides an electronic device.

[0020] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the low-frequency leakage current control method for a non-isolated low-voltage flexible interconnect device as described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are: This invention first establishes a third-order physical model of low-frequency leakage current, incorporating the coupling effects of filter inductors, grid-side inductors, and parasitic capacitance to ground, revealing the driving mechanism of the system by the unmeasurable zero-sequence voltage difference as an external port energy source. Based on this, it abandons the traditional control objective of constructing a full-band error system and instead constructs a passive control framework based on energy dissipation. This method extracts the fundamental frequency and third harmonic components from the total leakage current in real time through synchronous detection and low-pass filtering. Subsequently, through damping injection and error shaping, the closed-loop system is reshaped into a strictly passive system, ensuring the global asymptotic stability of the system from an energy perspective. Finally, for the energy-concentrated fundamental and third harmonic frequencies, a high-gain selective damping control law is injected, achieving precise suppression of low-frequency leakage current without relying on communication between the two sides. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a schematic diagram of the system structure and low-frequency leakage current loop of the non-isolated low-voltage FID according to an embodiment of the present invention; Figure 2 This is the common-mode equivalent circuit diagram of a non-isolated low-voltage FID according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the low-frequency leakage current suppression and augmentation system structure including the frequency extraction filter dynamics according to an embodiment of the present invention; Figure 4 This is a selective inhibition control block diagram according to an embodiment of the present invention; Figure 5 This is the operating condition where the voltage phases of the power grids on both sides are the same according to an embodiment of the present invention; Figure 6 This is the output current waveform of the left inverter under the condition that the voltage phases of the two grids are the same in an embodiment of the present invention; Figure 7 This is a simulation result of low-frequency leakage current under the condition that the voltage phases of the two power grids are the same in an embodiment of the present invention. Figure 8 This is the operating condition in which the voltage amplitudes of the two power grids on both sides are the same (phase difference of 30°) according to an embodiment of the present invention; Figure 9 This is the output current waveform of the left inverter under the condition that the voltage amplitudes of the two grids are the same (phase difference of 30°) in an embodiment of the present invention; Figure 10 This is a simulation result of low-frequency leakage current under the condition that the voltage amplitudes of the two power grids on both sides are the same (phase difference of 30°) according to an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] 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 herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] 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.

[0027] Because non-isolated low-voltage flexible interconnect devices (FIDs) have a non-isolated topology, the switching and modulation processes of power devices inevitably generate bridge arm-to-ground potential fluctuations, i.e., common-mode voltage. This common-mode voltage couples to the ground through paths such as the power device heatsink and chassis-to-ground capacitance, the filter network-to-ground coupling capacitance, and cable parasitic capacitance, thus forming leakage current or ground loop current in the path of "converter—parasitic capacitance—ground—grid or the other converter." For FIDs, the common-mode voltages to ground of the two converters are not independent; the voltage difference between the two converters is equivalent to a driving source in the grounding loop. This difference often includes the fundamental frequency and specific subharmonic components, causing low-frequency leakage current to persist over a longer timescale and exhibit significant amplitude fluctuations with changing operating conditions. Compared to high-frequency leakage current, low-frequency leakage current is more likely to trigger protection thresholds and is difficult to effectively suppress without significantly increasing size and losses using conventional electromagnetic interference filtering devices.

[0028] Passive control theory, constrained by energy and dissipation, enhances the system's stability margin against parameter drift and disturbances through damping injection. It features a clear structure, strong robustness, and ease of parallel implementation with main power control. Based on this approach, selective passive control that focuses on low-frequency critical components can improve the suppression of low-frequency leakage current caused by common-mode voltage differences without significantly increasing computational burden.

[0029] To address the low-frequency leakage current suppression requirements of non-isolated low-voltage FID systems operating in distribution network grounding scenarios, this embodiment proposes a selective suppression method based on passive theory. This method treats the zero-sequence effect at the other end under no-communication conditions as an equivalent external disturbance input, uses the measurable low-frequency leakage current as the feedback input, and combines dominant component extraction and damping injection to achieve directional suppression of the leakage current. Its control structure is as follows: Figure 4 As shown, a low-frequency leakage current control method for non-isolated low-voltage flexible interconnect devices includes: Step 1: Construct a common-mode equivalent circuit based on a non-isolated low-voltage flexible interconnect device, and establish a third-order low-frequency leakage current physical model that includes the coupling effect of filter inductance, grid-side inductance and parasitic capacitance to ground. Treat the unmeasurable zero-sequence voltage difference as an external disturbance source and clarify its driving relationship on the leakage current circuit.

[0030] The topology of non-isolated FID is as follows Figure 1 As shown, its core consists of two back-to-back three-level T-type three-phase four-bridge converters, which perform rectification and inversion functions respectively. To suppress switching harmonics, the A, B, C, and N phases of both converters are equipped with grid-side filter inductors L with identical parameters. g and filter capacitor C fTo further suppress high-frequency leakage current in the circuit, this topology directly connects the common point of the filter capacitors on both sides to the midpoint of the DC-side capacitor, thus providing a low-impedance path for high-frequency common-mode current. First, we analyze the mathematical model of the non-isolated FID that connects the common point of the filter capacitors and the midpoint of the DC-side capacitor.

[0031] Step 1 specifically includes the following steps: S1-1: According to Kirchhoff's voltage law Figure 1 The equivalent mathematical model of the converter on the left can be expressed as follows: (1) (2) in, L For the converter-side filter inductor, u x1 (x=a,b,c,n) represents the converter output voltage. i X1 , i x1 and i Cx1 The current is distributed as converter-side current, grid-side current, and filter capacitor current. u gx1 This is the grid voltage. u nN The voltage across the parasitic capacitance can be expressed as (3) in, C pv Parasitic capacitance, i Ccm1 The common-mode current of the filter capacitor, i.e., the high-frequency leakage current, satisfies... (4) Adding the equations in equations (1) and (2) respectively, we can obtain the equivalent model of the common-mode loop as follows: (5) in, u cm1 As a common mode excitation source, i cm1 This refers to the common-mode current on the converter side. i cmg For low-frequency leakage current, satisfy (6) By connecting the common point of the filter capacitors on both sides of the converter to the midpoint of the DC-side capacitor, a common-mode loop is added to the system, i.e. (7) in, udcm1 This is the DC side midpoint voltage. Adding the terms in the above equation yields... (8) Combining equations (1) to (8), the common-mode equivalent circuit of a non-isolated FID connecting the common point of the filter capacitor and the midpoint of the DC-side capacitor can be obtained as follows: Figure 2 Figure (a) shows an equivalent circuit containing four excitation sources: common-mode excitation sources. u cm1 and u cm2 DC excitation source 4 u dcm1 and 4 u dcm2 .

[0032] S1-2: The generation mechanism of low-frequency leakage current is relatively complex, influenced by the operating status of the converters on both sides, the grid conditions, and two... C f The combined effect of the capacitor branches allows us to utilize the series and parallel relationships of capacitors to first treat the capacitors on both sides as equivalent to a new capacitor. C b The equivalent model is as follows Figure 2 As shown in Figure (b) of the document.

[0033] (9) The KVL equations for the inductor voltage in the circuit are: (10) (11) (12) in v a For node a, the voltage across the bottom loop is... v b Let be the voltage of node b relative to the bottom loop.

[0034] For two branching nodes a and b, the KCL equations are: (13) (14) in i b1 For the left branch current, i b2 This refers to the current in the right branch. remember: (15) Eliminating variables from the above equation, we obtain the equation containing only... i cmgThe overall differential equation, first, in equations (13) and (14) i b1 , i b2 Substituting, we get: (16) (17) Differentiating equations (16) and (17) yields: (18) (19) From equations (10)(18), (12)(19), we can obtain: (20) (twenty one) Add equations (20) and (21) together: (twenty two) Taking the second derivative of equation (11) gives: (twenty three) From equations (11)(22)(23), we can obtain: (twenty four) Where a=2 LL g C b b=2( L + L g ).

[0035] S1-3: Under no communication conditions, the common mode from the other side on the right side is uncompensable and can be used as a disturbance bias. u r (t); (25) make (26) Then equation (24) is updated to (27) A third-order physical model of low-frequency leakage current is established based on the common-mode equivalent circuit. The model structure is consistent with the inductor-capacitor branch of the device, which can be used to clearly explain the generation mechanism and main influencing factors of low-frequency leakage current, and facilitate parameter tuning and engineering implementation.

[0036] For non-isolated flexible interconnect devices, existing research indicates that low-frequency leakage current mainly contains fundamental and third harmonic components. If the full-frequency error is taken according to conventional control and tracking methods...e (t) =γ (t) γ (t), then the error system will be subjected to an unmeasurable input Δ u Direct drive of 0(t). Due to the lack of communication, Δ u 0 is difficult to compensate for and usually cannot be guaranteed. e = = ë =0 corresponds to the true equilibrium point of the error system, thus distorting the equilibrium point and convergence conclusion under engineering conditions. Selective control is introduced, meaning that full-frequency tracking of the error system is no longer required; instead, the control objective is changed to suppressing the dominant fundamental frequency harmonic components of the low-frequency leakage current. and triple frequency Two spectral lines, whose amplitudes satisfy the constraints.

[0037] Step 2: Separate the fundamental frequency and third harmonic components from the total leakage current signal in real time, define the selective tracking error for the fundamental frequency and third harmonic, construct a passive control law that includes reference intrinsic term cancellation, active damping injection and higher-order shaping terms, so that the disturbed object is reshaped into a stable third-order error system with a clear dissipative structure, and the control action is concentrated on the target low-frequency component.

[0038] This invention proposes a selective suppression approach, limiting the control target to the fundamental and third harmonic dominant components of the low-frequency leakage current. This reduces the injection diffusion and modulation occupancy caused by strong constraints across the entire frequency band, making the suppression action more focused and the control side effects easier to constrain.

[0039] In step 2, the fundamental frequency and third harmonic components are separated from the total leakage current signal in real time based on the phase-locked loop synchronous detection and low-pass filtering method.

[0040] The process of separating the fundamental frequency and third harmonic components from the total leakage current signal in real time based on phase-locked loop synchronous detection and low-pass filtering is as follows: The measured low-frequency leakage current γ (t), the base frequency synchronization angle is obtained through a phase-locked loop. θ (t) and the third harmonic synchronization angle 3 θ (t), will γ (t) multiplied by orthogonal basis functions yields four synchronous detection signals. u 1c , u 1s , u 3c , u 3s for: (28) (29) The four synchronous detection signals are each passed through a first-order low-pass filter with a cutoff angular frequency of . The filter output state is defined as z 1c , z 1s , z 3c , z 3s Its continuous-time state equation is: (30) (31) By utilizing the low-pass output state and synchronization angle, the fundamental frequency and third harmonic component of the low-frequency leakage current are reconstructed. : (32) Write the extracted results in vector form. (33) The filter state and the synchronous detector input can be expressed in vector form as follows: (34) Combining equation (34), equations (30) and (31) can be combined into (35) In step 2, the reference component and the error vector are defined as follows: (36) in e 1, e 3 corresponds to the selective tracking error of the fundamental frequency and third harmonic channels, respectively.

[0041] Low-frequency leakage current γ (t) is described using the same third-order structure on the fundamental and third harmonic components. (37) (38) Where Δ u 0,13 Indicates the unmeasurable zero-sequence voltage difference at and The equivalent perturbation amount on the two spectral lines, u m The equivalent injection volume to be designed.

[0042] Depend on The error dynamic equation of the system is as follows: (39) Pick u m =0, the right-hand side still contains an unmeasurable disturbance Δ u 0,13 and reference inherent terms ,therefore e = = ë =0 is not the equilibrium point of the system (39), and the reference intrinsic terms need to be compensated and dissipated.

[0043] make (40) in , representing the proportional shaping, damping dissipation, and third-order structural shaping coefficients of the error system, respectively.

[0044] Substituting equation (40) into equation (39) yields (41) It can be seen that when Δ u 0,13 When =0, e = = ë =0 is the equilibrium point of system equation (41).

[0045] Step 3: Based on the passive stability constraint, a selective damping element for the fundamental frequency and the third harmonic is introduced, and an analytical design relationship between the damping gain and the target suppression ratio is established, so that the control parameters can be directly calculated and determined according to the engineering limit, so as to achieve low-frequency leakage current amplitude suppression without relying on communication.

[0046] The process of determining passive stability constraints is as follows: An augmented storage function is constructed that simultaneously contains the error system energy and the filter state energy. The strict passivity of the closed-loop system with respect to the generalized ports is obtained through energy flow analysis. It is further proven that under the condition of zero input and zero output at the port, the system state can only tend to zero, thus satisfying the zero-state measurability condition and ensuring the stability and boundedness of the closed loop under bounded disturbances.

[0047] Specifically, the state variables and output variables of the third-order error system are defined. (42) (43) Then there is (44) Construct generalized port variables, dynamically incorporate the extractor into the passive inequality, and select augmented port states, inputs, and outputs as... (45) Construct an augmented storage function that simultaneously contains the error system energy and the filter state energy. H(X) ,Pick (46) in (47) (48) Along equation (44) H x( x Differentiate and apply equation (25) to... H f ( z Differentiating and adding them together, we get (49) Right now (50) As can be seen from the definition of system passivity, a system with an extractor augments the relationship between input and output ports. u A , y A () is strictly passive, and the strict term is... and The schematic diagram of the augmented system structure is as follows: Figure 3 As shown.

[0048] According to the definition of Zero-State Measurability (ZSD), when the system's input and output ports are zero, the system's state gradually tends towards zero over time. Let... u A =0 and y A =0, then Δ u 0,13 =0、 , y =0、 z =0, by y = x 3=0 = x 3 = 0, therefore x 2 is a constant; at the same time, from equation (44) in Δ u 0,13 =0 (51) like x 2≠0 = x 2 make x 1. As time changes, equation (51) cannot hold true in the long term; therefore, only 1 / 2 can be true. x 2=0, and from equation (51) we getx 1 = 0. (Combined) x 3=0 and z =0, thus obtaining the complete state of this augmented system. X =0, which satisfies the definition of Zero State Measurable (ZSD).

[0049] The above proof shows that the constructed augmented system is passive, has no direct input path, and is zero-state measurable, due to the unmeasurable perturbation Δ. u 0,13 If this problem persists, constant gain output negative feedback needs to be introduced. u =- ky Amplitude controllable suppression is achieved by directly increasing the dissipation at the target frequency.

[0050] Because synchronous detection and low-pass filtering introduce phase lag, the negative feedback of the injected constant-gain output at the target frequency is weakened by the phase shift. Therefore, the selective damping element for the fundamental frequency and the third harmonic is a first-order leading element, which is used to compensate for the errors of the fundamental frequency and the third harmonic respectively.

[0051] (52) (53) Where s is the Laplace operator. T 1,i , T 2,i Let be the zero and pole time constants of the first-order lead compensation element of the i-th harmonic channel, respectively. This is the error vector after advance compensation.

[0052] Take constant gain output negative feedback as (54) in k 1, k 3 corresponds to the damping gain of the fundamental frequency and third harmonic channels, respectively.

[0053] At the target single frequency point At that frequency point, the equivalent frequency domain relation of equation (27) can be written as follows: (55) Where Γ( jω The low-frequency leakage current error system is at the specified frequency. The equivalent frequency domain response at Δ U 0( jω () represents the equivalent disturbance component at this frequency point when no control is applied. U ( jω ) represents the feedback control component injected by the controller at this frequency.

[0054] The injected feedback signal at this frequency is equivalent to (56) Define the suppression ratio (57) Where Γ0( jω To control the error system before injection at the target single frequency point The equivalent frequency domain response at that point.

[0055] Solving equation (57) yields (58) make For fundamental frequency and angular frequency, = and given the target suppression ratio r 1= r ( ), r 3= r ( ),but (59) Combining equations (40) and (54), the final injection control law can be obtained. u ( t ) (60) Expand as (61) in For error shaping parameters, K This is the selective damping gain matrix.

[0056] To suppress low-frequency leakage current, the obtained control law needs to be... u ( t The original modulated wave was injected using a zero-sequence injection method. U a , U b , U c In the middle, equation (24) is updated to (62) It is not difficult to see that when Δ u 0,13 When =0, e = = ë =0 is the equilibrium point of the system equation (62).

[0057] From (47), we can see that the storage function H(X) It is positive definite, and its derivative is: (63) Right now It is negative definite. Also... It is radially unbounded, therefore for system (62), according to the Lyapunov stability criterion, the equilibrium point is... e = = ë =0 is globally asymptotically stable, and both the filter state and the error state are bounded and converge, thus ensuring the stability and repeatability of the low-frequency leakage current component suppression process.

[0058] Without changing the basic framework of main power control for non-isolated low-voltage flexible interconnect devices, the impedance characteristics of the common-mode circuit can be independently adjusted to achieve precise suppression of low-frequency leakage current.

[0059] The overall control block diagram of the system is as follows: Figure 4 As shown, the overall system control architecture includes a main power control layer and a low-frequency leakage current suppression additional layer. The modulation strategy of both converters on the FID device adopts the three-dimensional space vector modulation (3D-SVM) algorithm. This modulation method improves the DC voltage utilization while being equivalent to sinusoidal pulse width modulation (SPWM) based on third harmonic injection.

[0060] Main power control layer: The right-side converter operates in rectification mode, the outer loop uses a PI controller to maintain DC bus voltage stability, and the inner loop... dq The grid current is decoupled and controlled in a rotating coordinate system to achieve command tracking of active and reactive power. The left-side converter operates in inverter mode, with grid-connected active and reactive power as the control targets. The main power control layer primarily adjusts the differential-mode voltage vector to determine the power flow direction and power quality of the device.

[0061] Low-frequency leakage current suppression additional layer: To address the zero-sequence path unique to non-isolated topologies, a passive selective suppression module of this invention is introduced into the modulation stage of the left-side converter. This module first samples the actual value of the low-frequency leakage current flowing through the grounding loop. i cmg The phase angle of the left-side grid-connected AC voltage obtained by combining the phase-locked loop (PLL) θ The frequency is fed into the frequency extraction unit to separate the fundamental frequency and third harmonic components; then, the extracted and reconstructed state variables are sent to the passive shaping controller, and the common-mode voltage correction, which includes the energy shaping term and the selective damping injection term, is calculated according to the control law designed by equation (61). u ( t Finally, this correction is superimposed onto the original modulation wave of the sinusoidal pulse width modulation (SPWM). This structure independently adjusts the impedance characteristics of the common-mode circuit without changing the dynamic characteristics of the main power control, thereby achieving precise suppression of low-frequency leakage current.

[0062] This embodiment proposes a method for selectively suppressing and controlling low-frequency leakage current in non-isolated low-voltage flexible interconnect devices. Figures 5-7 The figure shows the simulation results of the output current waveform and low-frequency leakage current of the left inverter under the condition that the voltage phases of the two grids are the same. After applying the proposed method, the low-frequency leakage current is... The current converges to around 0 A with only a small ripple, indicating that the low-frequency leakage current is effectively suppressed under the same phase condition without affecting the quality of the current waveform. Figures 8-10 The figure shows the simulation results of the output current waveform and low-frequency leakage current of the left inverter under the condition that the voltage amplitudes of the two grids are the same (phase difference of 30°). The three-phase current of the left inverter remains symmetrical and sinusoidal. After adopting the proposed method, The current is still suppressed to around 0.4A, with slight periodic fluctuations but a small overall value, demonstrating that this selective passive control still has good suppression effect and a certain degree of robustness under phase deviation conditions. This strategy does not rely on communication between the two sides and can achieve control injection through the common-mode channel without communication, without changing the basic framework of the main power control. The algorithm structure is clear, the computational load is small, and it is easy to integrate into existing digital control platforms. It can be used to suppress low-frequency leakage current and improve the operational reliability of flexible interconnection devices in low-voltage distribution networks under multiple operating conditions.

[0063] The embodiments of the present invention treat the common mode influence from the other side under no communication conditions as an equivalent disturbance bias term for processing. The control law design does not rely on the real-time acquisition and accurate compensation of unmeasurable terms in the model, and is suitable for FID application scenarios with no or weak communication.

[0064] Under a strictly passive framework, the closed-loop implementation of this invention provides an analytical approach that ensures energy dissipation and bounded states. It constrains the internal and error states of the filter from an energy perspective, reducing the risk of potential instability introduced by filter phase lag and dynamic coupling.

[0065] The embodiments of the present invention provide a method based on the suppression ratio Methods for determining the gain of the index, establishing the damping gain Compared to target suppression ratio The analytical relationship between them allows for direct calculation of the control gain based on leakage current limit requirements, reducing empirical trial and error and improving the certainty and portability of parameter tuning.

[0066] In this embodiment of the invention, the controlled injection amount is superimposed on the modulated common-mode component as a common-mode voltage correction amount, without changing the control channel of the differential-mode voltage, which facilitates parallel integration with the main power control.

[0067] The control method of this invention is adapted to a controller with a small amount of online computation. The control law consists of synchronous detection and a small amount of algebraic operations. It does not rely on iterative optimization and complex matrix operations, and is easy to execute in real time within a fixed sampling period.

[0068] The controller adapted to the control method of this invention has strong robustness. The control action is based on energy shaping and damping injection. It is less dependent on uncertainties such as grid equivalent parameters, grounding impedance and device discreteness. It can still maintain a stable suppression effect under disturbance and slow parameter change conditions.

[0069] The controller adapted to the control method of this invention has a fast response speed, and the damping dissipation term can directly suppress the amplitude change of low frequency components. It does not need to establish the control quantity through integral accumulation, and can converge faster and reduce envelope fluctuation when the operating conditions change.

[0070] In one or more embodiments, a low-frequency leakage current control system for a non-isolated low-voltage flexible interconnect device provided in this invention is also provided, which can be implemented in software. The low-frequency leakage current control system for a non-isolated low-voltage flexible interconnect device includes the following software modules: The physical model construction module is used to construct a common-mode equivalent circuit based on a non-isolated low-voltage flexible interconnect device, and to establish a third-order low-frequency leakage current physical model that includes the coupling effect of filter inductance, grid-side inductance and ground parasitic capacitance. The unmeasurable zero-sequence voltage difference is equivalent to an external disturbance source, and its driving relationship on the leakage current circuit is clarified. The passive control law construction module is used to separate the fundamental frequency and third harmonic components from the total leakage current signal in real time, define the selective tracking error for the fundamental frequency and third harmonic, construct a passive control law including reference intrinsic term cancellation, active damping injection and higher-order shaping term, so that the disturbed object is reshaped into a stable third-order error system with a clear dissipation structure, and the control action is concentrated on the target low-frequency component. The low-frequency leakage current amplitude suppression module is used to introduce a selective damping element for the fundamental frequency and the third harmonic while meeting the passive stability constraints. It also establishes an analytical design relationship between the damping gain and the target suppression ratio, so that the control parameters can be directly calculated and determined based on the engineering limits, thereby achieving low-frequency leakage current amplitude suppression without relying on communication.

[0071] It should be noted that each module in the low-frequency leakage current control system of the non-isolated low-voltage flexible interconnect device in this embodiment corresponds one-to-one with each step in the low-frequency leakage current control method of the non-isolated low-voltage flexible interconnect device in the above embodiment, and their specific implementation processes are the same, so they will not be repeated here.

[0072] In one or more embodiments, an electronic device is also provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the low-frequency leakage current control method for non-isolated low-voltage flexible interconnect devices as described above.

[0073] Specifically, according to embodiments of this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing a low-frequency leakage current control method for a non-isolated low-voltage flexible interconnect device. In such embodiments, the computer program can be downloaded and installed from a network via a communication component, and / or installed from a removable medium. When the computer program is executed by a central processing unit, it performs various functions defined in the apparatus of this application.

[0074] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling low-frequency leakage current in a non-isolated low-voltage flexible interconnect device, characterized in that, include: Based on the non-isolated low-voltage flexible interconnect device, a common-mode equivalent circuit is constructed, and a third-order low-frequency leakage current physical model including the coupling effect of filter inductance, grid-side inductance and ground parasitic capacitance is established. The unmeasurable zero-sequence voltage difference is equivalent to an external disturbance source, and its driving relationship on the leakage current circuit is clarified. The fundamental frequency and third harmonic components are separated from the total leakage current signal in real time. Selective tracking error for the fundamental frequency and third harmonic is defined. A passive control law containing reference intrinsic term cancellation, active damping injection and higher-order shaping term is constructed so that the disturbed object is reshaped into a stable third-order error system with a clear dissipation structure and the control action is concentrated on the target low-frequency component. Based on the passive stability constraint, a selective damping element for the fundamental frequency and the third harmonic is introduced, and an analytical design relationship between the damping gain and the target suppression ratio is established, so that the control parameters can be directly calculated and determined according to the engineering limit, so as to achieve low-frequency leakage current amplitude suppression without relying on communication.

2. The low-frequency leakage current control method for non-isolated low-voltage flexible interconnection devices as described in claim 1, characterized in that, Based on phase-locked loop synchronous detection and low-pass filtering, the fundamental frequency and third harmonic components are separated from the total leakage current signal in real time.

3. The low-frequency leakage current control method for non-isolated low-voltage flexible interconnection devices as described in claim 2, characterized in that, The process of separating the fundamental frequency and third harmonic components from the total leakage current signal in real time based on phase-locked loop synchronous detection and low-pass filtering is as follows: The measured low-frequency leakage current is used to obtain the fundamental frequency synchronization angle and the third harmonic synchronization angle through a phase-locked loop. The low-frequency leakage current is multiplied by the orthogonal basis function to obtain four synchronous detection signals. The four synchronous detection signals are processed by first-order low-pass filters respectively; By using the output state and synchronization angle of a first-order low-pass filter, the fundamental frequency and third harmonic component of the low-frequency leakage current are reconstructed.

4. The low-frequency leakage current control method for non-isolated low-voltage flexible interconnection devices as described in claim 1, characterized in that, The process of determining passive stability constraints is as follows: An augmented storage function is constructed that simultaneously contains the error system energy and the filter state energy. The strict passivity of the closed-loop system with respect to the generalized ports is obtained through energy flow analysis. It is further proven that under the condition of zero input and zero output at the port, the system state can only tend to zero, thus satisfying the zero-state measurability condition and ensuring the stability and boundedness of the closed loop under bounded disturbances.

5. The low-frequency leakage current control method for non-isolated low-voltage flexible interconnection devices as described in claim 1, characterized in that, The selective damping element for the fundamental frequency and the third harmonic is a first-order leading element, which is used to compensate for the errors of the fundamental frequency and the third harmonic respectively.

6. The low-frequency leakage current control method for non-isolated low-voltage flexible interconnection devices as described in claim 1, characterized in that, To suppress low-frequency leakage current, the obtained passive control law is injected into the original modulation wave using a zero-sequence injection method.

7. The low-frequency leakage current control method for non-isolated low-voltage flexible interconnection devices as described in claim 1, characterized in that, Without changing the basic framework of main power control for non-isolated low-voltage flexible interconnect devices, the impedance characteristics of the common-mode circuit can be independently adjusted to achieve precise suppression of low-frequency leakage current.

8. A low-frequency leakage current control system for a non-isolated low-voltage flexible interconnection device, characterized in that, The low-frequency leakage current control method for non-isolated low-voltage flexible interconnect devices according to any one of claims 1-7 includes: The physical model construction module is used to construct a common-mode equivalent circuit based on a non-isolated low-voltage flexible interconnect device, and to establish a third-order low-frequency leakage current physical model that includes the coupling effect of filter inductance, grid-side inductance and ground parasitic capacitance. The unmeasurable zero-sequence voltage difference is equivalent to an external disturbance source, and its driving relationship on the leakage current circuit is clarified. The passive control law construction module is used to separate the fundamental frequency and third harmonic components from the total leakage current signal in real time, define the selective tracking error for the fundamental frequency and third harmonic, construct a passive control law including reference intrinsic term cancellation, active damping injection and higher-order shaping term, so that the disturbed object is reshaped into a stable third-order error system with a clear dissipation structure, and the control action is concentrated on the target low-frequency component. The low-frequency leakage current amplitude suppression module is used to introduce a selective damping element for the fundamental frequency and the third harmonic while meeting the passive stability constraints. It also establishes an analytical design relationship between the damping gain and the target suppression ratio, so that the control parameters can be directly calculated and determined based on the engineering limits, thereby achieving low-frequency leakage current amplitude suppression without relying on communication.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the low-frequency leakage current control method for non-isolated low-voltage flexible interconnect devices as described in any one of claims 1-7.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the low-frequency leakage current control method for non-isolated low-voltage flexible interconnect devices as described in any one of claims 1-7.

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