Harmonic suppression method and system based on feedforward control and virtual impedance

Abstract

The invention discloses a harmonic suppression method and system based on feedforward control and virtual impedance, and belongs to the field of electric energy quality control, and the method comprises the steps: constructing a harmonic extraction model based on the cascading of double third-order generalized integrators, and obtaining a voltage harmonic component based on the harmonic extraction model and real-time power grid data; based on a preset power outer loop control strategy, a preset voltage and current double closed loop control strategy, a preset harmonic voltage feed-forward control strategy and the voltage harmonic component, constructing a network construction type charging pile control model, and obtaining an initial output current; obtaining each virtual impedance based on the initial output current, the harmonic extraction model and the voltage harmonic component; and obtaining a harmonic suppression model based on each virtual impedance and the network construction type charging pile control model, so as to obtain a harmonic suppression output current based on the harmonic suppression model and the real-time power grid data. According to the harmonic suppression method and system based on feedforward control and virtual impedance provided by the invention, grid-connected output current harmonics controlled by a network-forming type charging pile are effectively suppressed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power quality control, and particularly relates to a harmonic suppression method and system based on feedforward control and virtual impedance. BACKGROUND

[0002] A virtual synchronous generator (VSG) is a common power electronic control technology, mainly applied to new energy power generation grid-connected (such as photovoltaic, wind power) and energy storage system inverters. Using VSG control for network-forming charging piles can simulate the operating characteristics and external behavior of traditional synchronous generators, thereby enhancing the stability of modern power grids dominated by new energy. Research on harmonic suppression strategies for network-forming charging piles has also attracted increasing interest from scholars. In the field of harmonic suppression research for network-forming charging piles, the coordinated application of feedforward control and virtual impedance has become a key technology direction for improving grid-connected power quality. Among them, a harmonic suppression method based on impedance remodeling VSG (VSG) of current negative feedforward is proposed, which extracts the harmonic component of the grid-side current through a band-pass filter and generates a harmonic voltage compensation, and combines a delay compensator to remodel the equivalent harmonic output impedance of the network-forming charging pile, significantly reducing the total harmonic distortion (THD) of the grid-connected current. From the perspective of impedance modeling, it is revealed that grid voltage feedforward control in network-forming charging piles can be equivalent to a parallel virtual impedance, which can correct the mid-high frequency phase characteristic from capacitive to inductive, effectively eliminating the risk of harmonic oscillation, and the harmonic linearization method verifies the role of this strategy in improving the stability of weak grids. For LCL-type grid-connected inverters, related research has found that virtual impedance can suppress resonance peaks through secondary differentiation feedback of grid-connected current, but it will amplify the negative impact of grid voltage harmonics on output current, so a complete voltage feedforward control is introduced, a second-order low-pass filter is connected in series with the second derivative term to equivalent replace the derivative link, which not only avoids high-frequency noise interference, but also reduces the THD to below 2.1%, while reducing the number of sensors. In addition, for the grid-side current harmonic problem of voltage-controlled network-forming charging piles, some research uses a second-order generalized integrator (SOGI) to extract the harmonic current component, which is fed forward to the modulation wave through a proportional-derivative (PD) regulator. Experiments show that this method can effectively suppress low-order harmonics.

[0003] Although the above-mentioned network-constructed charging pile harmonic suppression strategies have their own technical advantages, there are still obvious defects: first, there are deficiencies in the harmonic signal extraction method. The existing extraction methods using band-pass filters, SOGI, etc. need to be optimized in terms of response speed, extraction accuracy, or the ability to adapt to complex power grid conditions. Second, the feedforward control design is not perfect. Although some strategies solve specific problems (such as the resonance and noise problems of LCL-type inverters), they have limitations in control versatility and parameter robustness. Third, most studies do not involve virtual synchronous generator (VSG) control, which is a core technology for network-constructed charging piles to simulate the operating characteristics of traditional synchronous generators and enhance the stability of new energy power grids. The absence of this control dimension makes it difficult for existing strategies to fully adapt to the core functional requirements of network-constructed charging piles.

[0004] In summary, existing network-constructed charging pile harmonic suppression technologies have explored multiple dimensions around the coordinated application of feedforward control and virtual impedance. Each strategy has achieved certain results in reducing THD, suppressing resonance, or improving grid adaptability. However, due to the deficiencies in harmonic signal extraction methods, the defects in feedforward control design, and the absence of VSG control, existing technologies still cannot fully meet the actual needs of network-constructed charging piles for low-harmonic grid connection. Further optimization of technical solutions is needed to improve their performance and adaptability. SUMMARY

[0005] The present application provides a harmonic suppression method and system based on feedforward control and virtual impedance, which can solve the technical problem of grid-connected output current distortion caused by excessive harmonic components in existing technologies, effectively suppressing the harmonic of the grid-connected output current of network-constructed charging pile control and improving power quality.

[0006] The present application provides a harmonic suppression method based on feedforward control and virtual impedance, comprising:

[0007] A harmonic extraction model based on a double third-order generalized integrator cascade is constructed, and voltage harmonic components are obtained based on the harmonic extraction model and real-time grid data;

[0008] A network-constructed charging pile control model is constructed based on a preset power outer loop control strategy, a preset voltage and current double closed-loop control strategy, a preset harmonic voltage feedforward control strategy, and the voltage harmonic components, to obtain an initial output current based on the network-constructed charging pile control model and real-time grid data;

[0009] Each virtual impedance is obtained based on the initial output current, the harmonic extraction model, and the voltage harmonic components;

[0010] A harmonic suppression model is obtained based on the each virtual impedance and the network-constructed charging pile control model, to obtain a harmonic suppression output current based on the harmonic suppression model and real-time grid data, realizing harmonic suppression of the output current of the network-constructed charging pile.

[0011] The application provides a harmonic suppression method based on feedforward control and virtual impedance, constructs a harmonic extraction model based on double third-order generalized integrator cascades to accurately separate and extract harmonics, realizes faster dynamic response and accurate harmonic extraction, and reduces output signal distortion; an initial grid-connected charging pile control model is constructed by combining a voltage and current double closed-loop control strategy and a harmonic voltage feedforward control strategy, and a final harmonic suppression model is formed by combining virtual impedance, dynamic harmonic suppression is realized, grid-connected output current distortion caused by excessive harmonic components is effectively reduced, and power quality is improved.

[0012] Further, the harmonic extraction model based on double third-order generalized integrator cascades is constructed, the voltage harmonic component is obtained based on the harmonic extraction model and real-time grid data, and the harmonic extraction model based on double third-order generalized integrators is constructed based on two series-connected third-order generalized integrators; the voltage harmonic component is obtained based on the harmonic extraction model, real-time grid data and a preset angular frequency.

[0013] In the above scheme, two third-order generalized integrators are connected in series to construct the harmonic extraction model, the selective filtering capability for specific frequency harmonics is strengthened, the target harmonic and the non-target harmonic can be more accurately separated compared with a single integrator, the preset angular frequency is used to ensure that only the harmonic component of the corresponding frequency is extracted, the pertinence and accuracy of harmonic extraction are improved, faster dynamic response is realized, and the distortion rate of output current is reduced.

[0014] Further, the grid-connected charging pile control model is constructed based on the preset power outer loop control strategy, the preset voltage and current double closed-loop control strategy, the preset harmonic voltage feedforward control strategy and the voltage harmonic component, the initial output current is obtained based on the grid-connected charging pile control model and real-time grid data, and the active power reference data is obtained; the power outer loop control is performed based on the real-time grid data, the active power reference data and the preset power outer loop control strategy, and the electromotive force parameter is obtained; the voltage loop model and the current loop model are obtained, the voltage and current double closed-loop model is constructed based on the voltage loop model, the current loop model and the preset voltage and current double closed-loop control strategy; the grid-connected charging pile control model is obtained based on the electromotive force parameter, the voltage harmonic component, the voltage and current double closed-loop model and the preset harmonic voltage feedforward control strategy; and the initial output current is obtained based on the grid-connected charging pile control model and real-time grid data.

[0015] In the above scheme, first, the power outer loop control strategy is used to track the active power reference value, stabilize the electromotive force parameter, ensure the synchronous operation of the charging pile and the power grid, and then the voltage and current are controlled by the voltage and current double closed loop model to improve the dynamic response and anti-interference ability of the system, and the harmonic feedforward strategy is combined to use the voltage harmonic component to compensate the harmonic interference in advance, and to provide guarantee for the accuracy of the initial output current.

[0016] Further, the voltage loop model and the current loop model are obtained, the voltage and current double closed loop model is constructed based on the voltage loop model, the current loop model and the preset voltage and current double closed loop control strategy, and the voltage loop model is obtained based on the proportional-resonant controller and the preset power grid parameter; the current loop model is obtained based on the proportional controller; the voltage and current double closed loop model is constructed based on the voltage loop model, the current loop model and the preset voltage and current double closed loop control strategy; the fundamental wave current instruction is obtained based on the voltage loop model and the voltage harmonic component; and the voltage and current double closed loop control is performed based on the fundamental wave current instruction and the current loop model to construct the voltage and current double closed loop model.

[0017] In the above scheme, in the voltage loop model and the current loop model, the proportional-resonant controller is used to construct the voltage loop to realize the zero static error tracking of the fundamental wave voltage and ensure the stable fundamental wave current instruction output by the voltage loop; the proportional controller is used to construct the current loop to improve the current loop response speed, quickly track the fundamental wave current instruction and reduce the current fluctuation; the double closed loop collaborative control is realized to enhance the control precision, avoid the lag or overshoot problem of single loop control and improve the stability of the initial output current.

[0018] Further, the network type charging pile control model is obtained based on the electromotive force parameter, the voltage harmonic component, the voltage and current double closed loop model and the preset harmonic voltage feedforward control strategy, and the preset harmonic voltage feedforward control strategy includes that when the harmonic voltage feedforward control is performed based on the electromotive force parameter, the voltage harmonic component and the voltage and current double closed loop model, the feedforward point is set at the voltage loop model; the harmonic compensation instruction is obtained based on the electromotive force parameter and the voltage harmonic component; and the harmonic voltage feedforward control is performed based on the harmonic compensation instruction, the feedforward point and the voltage and current double closed loop model to obtain the network type charging pile control model.

[0019] In the above scheme, according to the preset harmonic voltage feedforward control strategy, the feedforward point is set at the voltage loop to make the harmonic compensation instruction directly act on the voltage control link, offset the harmonic interference on the voltage loop in advance and reduce the adjustment burden of the closed loop control; the compensation instruction is generated based on the electromotive force parameter and the voltage harmonic component to ensure that the compensation signal and the power grid harmonic are opposite in frequency and improve the timeliness and accuracy of the harmonic suppression.

[0020] Further, the obtaining the initial output current based on the grid-forming charging pile control model and the real-time power grid data comprises: performing harmonic extraction based on the grid-forming charging pile control model and the real-time power grid data to obtain a target harmonic component; obtaining a target direct current instruction based on the target harmonic component; performing power outer loop control based on the grid-forming charging pile control model and the real-time power grid data to obtain a target parameter setting; performing voltage-current double closed loop control based on the target parameter setting, the target harmonic component and the real-time power grid data to obtain a target fundamental wave voltage instruction; obtaining a target compensation instruction based on the target direct current instruction and inverse harmonic voltage feedforward control; and obtaining the initial output current based on the target compensation instruction and the target fundamental wave voltage instruction.

[0021] In the above scheme, when the initial output current is obtained based on the grid-forming charging pile control model and the real-time power grid data, the output current is regulated based on the preset power outer loop control strategy, the preset voltage-current double closed loop control strategy and the preset harmonic voltage feedforward control strategy, thereby laying a foundation for subsequent virtual impedance optimization.

[0022] Further, the obtaining the initial output current based on the target compensation instruction and the target fundamental wave voltage instruction comprises: obtaining an output driving signal based on the target compensation instruction and the target fundamental wave voltage instruction; and performing space vector pulse width modulation based on the output driving signal and a preset triangular carrier signal to obtain a pulse signal, and taking the pulse signal as the initial output current.

[0023] In the above scheme, the output driving signal is converted into an accurate driving pulse through space vector pulse width modulation, thereby reducing distortion in the signal conversion process.

[0024] Further, the obtaining the initial output current based on the initial output current, the harmonic extraction model and the voltage harmonic component comprises: obtaining a harmonic current component based on the initial output current, the harmonic extraction model and the voltage harmonic component; and obtaining each order virtual impedance based on the harmonic current component, the voltage harmonic component and a preset virtual impedance algorithm.

[0025] In the above scheme, the virtual impedance is designed for the harmonic current component in the initial output current, so that the impedance parameter is matched with the harmonic characteristics, thereby acting on the corresponding frequency harmonic and avoiding interference with the fundamental wave or other harmonics, and realizing frequency-accurate suppression.

[0026] Further, the harmonic suppression model is obtained based on the virtual impedances and the grid-connected charging pile control model, and the harmonic suppression output current is obtained based on the harmonic suppression model and real-time grid data, so that the harmonic suppression of the output current of the grid-connected charging pile is realized.

[0027] In the above scheme, the virtual impedance is introduced into the voltage-current double closed loop control and integrated into the harmonic suppression model, the virtual impedance cooperates with the original double closed loop and feedforward strategy to form a closed loop suppression mechanism, realizes dynamic suppression of harmonics, effectively improves the grid-connected power quality, and solves the current distortion problem caused by too high harmonic components.

[0028] The present application provides a kind of harmonic suppression method based on feedforward control and virtual impedance, first constructs the harmonic extraction model of double three-order generalized integrator cascade consisting of two three-order generalized integrators in series, and extracts voltage harmonic component from real-time grid data based on preset angular frequency, realizes accurate extraction of harmonic component;Then combine power outer loop control, voltage-current double closed loop control, harmonic voltage feedforward control and the above voltage harmonic component to construct grid-connected charging pile control model, wherein power outer loop control exports electromotive force parameter to realize synchronization with grid, voltage loop in voltage-current double closed loop control adopts proportional resonant controller to export fundamental current instruction, current loop adopts proportional controller to track the instruction, harmonic voltage feedforward control sets feedforward point at voltage loop and generates compensation instruction based on electromotive force parameter and voltage harmonic component, and then generates initial output current by space vector pulse width modulation;Then each harmonic current component is extracted from initial output current, combined with voltage harmonic component to design frequency virtual impedance, and each virtual impedance is introduced into voltage-current double closed loop control, integrated into harmonic suppression model with grid-connected charging pile control model, and finally accurate harmonic suppression is realized through the harmonic suppression model.

[0029] The present application also provides a kind of harmonic suppression system based on feedforward control and virtual impedance, for realizing the above-mentioned harmonic suppression method based on feedforward control and virtual impedance, comprising:

[0030] Double-cascade harmonic extraction module, for constructing harmonic extraction model based on double three-order generalized integrator cascade, and obtaining voltage harmonic component based on the harmonic extraction model and real-time grid data;

[0031] a double-loop harmonic control module, configured to construct a grid-connected charging pile control model based on a preset power outer loop control strategy, a preset voltage and current double-loop control strategy, a preset harmonic voltage feedforward control strategy, and the voltage harmonic component, to obtain an initial output current based on the grid-connected charging pile control model and real-time grid data;

[0032] a virtual impedance module, configured to obtain each-order virtual impedance based on the initial output current, a harmonic extraction model, and the voltage harmonic component;

[0033] a harmonic suppression module, configured to obtain a harmonic suppression model based on the each-order virtual impedance and the grid-connected charging pile control model, to obtain a harmonic suppression output current based on the harmonic suppression model and real-time grid data, and to realize harmonic suppression on the output current of the grid-connected charging pile.

[0034] The harmonic suppression system based on feedforward control and virtual impedance provided by the application realizes more rapid dynamic response and accurate harmonic extraction and reduces output signal distortion by constructing a harmonic extraction model based on double third-order generalized integrator cascades through a double-cascaded harmonic extraction module to accurately separate and extract harmonics. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the present application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0036] Figure 1 is a schematic diagram of a harmonic suppression method based on feedforward control and virtual impedance provided by the present embodiment;

[0037] Figure 2 is a schematic diagram of a double TOGI controller provided by the present embodiment;

[0038] Figure 3 is a schematic diagram of a grid-connected charging pile control model provided by the present embodiment;

[0039] Figure 4 is a schematic diagram of the overall process of a harmonic suppression method based on feedforward control and virtual impedance provided by the present embodiment. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0041] Unless otherwise defined, 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 application belongs; the terminology used in the specification herein is for describing the specific embodiments only and not intended to limit the application; the terms "comprise", "comprising", "include", "including", "have" and "having" and any variations thereof in the specification and claims and the above description of drawings are intended to cover non-exclusive inclusion.

[0042] In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0043] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0044] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present application generally represents an "or" relationship between the associated objects.

[0045] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0046] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through an intermediate medium, can be internal communication of two elements or interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0047] The embodiment provides a harmonic suppression method based on feedforward control and virtual impedance, which comprises the following steps: Figure 1

[0048] S1, constructing a harmonic extraction model based on double third-order generalized integrator cascade, and acquiring voltage harmonic components based on the harmonic extraction model and real-time grid data;

[0049] S2, constructing a grid-connected charging pile control model based on a preset power outer loop control strategy, a preset voltage and current double closed loop control strategy, a preset harmonic voltage feedforward control strategy and the voltage harmonic components, so as to acquire an initial output current based on the grid-connected charging pile control model and real-time grid data;

[0050] S3, acquiring each order virtual impedance based on the initial output current, the harmonic extraction model and the voltage harmonic components;

[0051] S4, acquiring a harmonic suppression model based on the each order virtual impedance and the grid-connected charging pile control model, so as to acquire a harmonic suppression output current based on the harmonic suppression model and real-time grid data, and realize harmonic suppression of the output current of the grid-connected charging pile.

[0052] The harmonic suppression method based on feedforward control and virtual impedance provided by the embodiment can construct a harmonic extraction model based on double third-order generalized integrator cascade to perform harmonic extraction, so as to accurately separate and extract harmonics, realize faster dynamic response and accurate harmonic extraction, and reduce distortion of an output signal. The initial grid-connected charging pile control model is constructed in combination with a voltage and current double closed loop control strategy and a harmonic voltage feedforward control strategy, and the final harmonic suppression model is formed in combination with virtual impedance, so as to realize dynamic harmonic suppression, effectively reduce grid output current distortion caused by too high harmonic components, and improve power quality.

[0053] Optionally, the harmonic extraction model based on double third-order generalized integrator cascade is constructed, and voltage harmonic components are acquired based on the harmonic extraction model and real-time grid data, which comprises the following steps: constructing the harmonic extraction model based on double third-order generalized integrator cascade based on two series-connected third-order generalized integrators; and acquiring the voltage harmonic components based on the harmonic extraction model, real-time grid data and a preset angular frequency.​

[0054] In the implementation process, in order to achieve faster dynamic response and reduce the output current, i.e. the distortion rate of the output waveform, a double TOGI controller is adopted by using two TOGIs (third-order generalized integrators) in series, a harmonic extraction model based on double third-order generalized integrator cascade is constructed, and by setting the angular frequency of the controller, the accurate extraction of each harmonic of the grid voltage when passing through the double TOGI control link can be realized. As shown in the double TOGI controller shown in Figure 2 The transfer function of a single TOGI is:

[0055]

[0056] The transfer function of the two TOGIs in cascade is:

[0057]

[0058] Wherein: v(s) represents the input signal, v d1 (s), v d2 (s), v d3 (s) represents the output signal of the TOGI, H d1 (s), H d2 (s), H d3 (s) respectively represent the closed-loop transfer functions of the three output signals. When the double TOGIs are cascaded, the value of h in the formula is set to the required harmonic component number, and ω is the preset angular frequency, so as to limit the components outside the set frequency bandwidth to flow through, and make the set frequency of the harmonic flow through the control link, thereby extracting the required harmonic voltage component. The two output signals v1(s) and v2(s) of the control link are the same frequency and amplitude as the input signal, v1(s) leads v2(s) by 90 degrees and is orthogonal to it, and neither of them is affected by the direct current component and noise of the input signal. In order to take into account better dynamic performance and filtering performance, the k value of the TOGI orthogonal signal generator needs to be compromised, and the double TOGI control link improves this problem, even if the value of k is larger, the harmonic suppression effect and dynamic performance are still very ideal.

[0059] Optionally, the preset power outer loop control strategy, the preset voltage and current double closed loop control strategy, the preset harmonic voltage feedforward control strategy and the voltage harmonic component are used to construct a grid-connected charging pile control model, and an initial output current is obtained based on the grid-connected charging pile control model and real-time grid data, including: obtaining active power reference data, performing power outer loop control based on the real-time grid data, the active power reference data and the preset power outer loop control strategy, and obtaining an electromotive force parameter; obtaining a voltage loop model and a current loop model, constructing a voltage and current double closed loop model based on the voltage loop model, the current loop model and the preset voltage and current double closed loop control strategy; obtaining a grid-connected charging pile control model based on the electromotive force parameter, the voltage harmonic component, the voltage and current double closed loop model and the preset harmonic voltage feedforward control strategy; and obtaining an initial output current based on the grid-connected charging pile control model and real-time grid data.

[0060] In the specific implementation process, when the real-time grid data, the active power reference data and the preset power outer loop control strategy are used to perform power outer loop control and obtain an electromotive force parameter, the preset power outer loop control strategy is implemented by using a rotor motion equation in the power outer loop of the grid-connected charging pile, the electromotive force parameter includes an electromotive force angle frequency and a phase of the grid-connected charging pile, and a calculation process satisfies the following formula:

[0061]

[0062] In the formula, J represents a virtual rotational inertia, ω θ and θ represent an electromotive force angle frequency and a phase of the grid-connected charging pile respectively, T m represents a mechanical torque, T e represents an electromagnetic torque, T d represents a damping torque, D represents a damping coefficient, ω N represents a rated angular frequency, P ref and P represent active power reference data and an active power actual value respectively.

[0063] Optionally, the voltage loop model and the current loop model are obtained, and the voltage and current double closed loop model is constructed based on the voltage loop model, the current loop model and the preset voltage and current double closed loop control strategy, including: obtaining the voltage loop model based on a proportional-resonant controller and preset grid parameters; obtaining the current loop model based on a proportional controller; constructing the voltage and current double closed loop model based on the voltage loop model, the current loop model and the preset voltage and current double closed loop control strategy: obtaining a fundamental current instruction based on the voltage loop model and the voltage harmonic component, performing voltage and current double closed loop control based on the fundamental current instruction and the current loop model, and constructing the voltage and current double closed loop model.

[0064] In practical implementation, based on the location of the harmonic voltage feedforward introduction, the control model can be simplified to a single-loop control form by combining voltage-current dual closed-loop control. From the equivalent transformation of the voltage-current dual closed-loop control model, it can be seen that the introduction of harmonic voltage does not change the gain within the grid-type charging pile system, and it can be regarded as a single-input / output system, facilitating independent control. When constructing the voltage loop model and current loop model, the preset voltage-current dual closed-loop control strategy includes: because the proportional resonant controller has good signal tracking ability and strong anti-interference ability, the voltage loop G... u (s) A proportional resonant controller is used, and the current loop G i (s) A proportional controller is used. The dual-loop control expression is as follows:

[0065]

[0066] Where: K up K represents the proportional gain of the voltage loop; ur Represents the resonance coefficient; ω i ω0 represents the fundamental resonant bandwidth; K represents the fundamental angular frequency of the power grid. ip This represents the proportionality coefficient of the current loop.

[0067] Optionally, the step of obtaining the grid-type charging pile control model based on the electromotive force parameters, voltage harmonic components, voltage-current dual closed-loop model, and preset harmonic voltage feedforward control strategy includes: the preset harmonic voltage feedforward control strategy includes: setting the feedforward point at the voltage loop model when performing harmonic voltage feedforward control based on the electromotive force parameters, voltage harmonic components, and voltage-current dual closed-loop model; obtaining harmonic compensation commands based on the electromotive force parameters and voltage harmonic components; and performing harmonic voltage feedforward control based on the harmonic compensation commands, feedforward point, and voltage-current dual closed-loop model to obtain the grid-type charging pile control model.

[0068] In the specific implementation process, in order to accurately extract each harmonic, separate the fundamental frequency, and facilitate the independent design of harmonic virtual impedance, a harmonic component extraction method based on dual TOGI cascade is adopted in the harmonic extraction module. The controller angular frequency is set to the fundamental frequency to accurately separate the fundamental and harmonic components from the grid voltage. Specifically, the h value in the transfer function of the dual TOGI link is set to the desired harmonic order for harmonic component extraction.

[0069] In the specific implementation process, the harmonic voltage feedforward control loop adopts a preset harmonic voltage feedforward control strategy and reverse control, including: feeding forward the harmonic components extracted by the dual TOGI controller to the voltage-current dual-loop control, thereby achieving harmonic compensation. The feedforward point of the harmonic voltage is set in the dual-loop controller. The feedforward control transfer function expression is as follows:

[0070]

[0071] Now, for the main 5th, 7th and 11th harmonic voltage components in the grid voltage, the value h in the transfer function is set to 5, 7 and 11 respectively, and the extracted harmonic voltage components are fed forward to the voltage outer loop of the double closed loop through the harmonic voltage feedforward link for control. The relationship between the input voltage U(s), the grid voltage Ug and the grid-connected output current of the grid-connected charging pile is as follows:

[0072]

[0073] In the formula: I o (s) represents the grid-connected output current of the grid-connected charging pile; Z(s) represents the output total impedance of the system.

[0074] Optionally, the initial output current is obtained based on the grid-connected charging pile control model and real-time grid data, including: performing harmonic extraction based on the grid-connected charging pile control model and real-time grid data to obtain target harmonic components; obtaining a target DC command based on the target harmonic components; performing power outer loop control based on the grid-connected charging pile control model and real-time grid data to obtain target parameter settings; performing voltage and current double closed loop control based on the target parameter settings, target harmonic components and real-time grid data to obtain a target fundamental voltage command; obtaining a target compensation command based on the target DC command and inverse harmonic voltage feedforward control; and obtaining the initial output current based on the target compensation command and the target fundamental voltage command.

[0075] Optionally, the initial output current is obtained based on the target compensation command and the target fundamental voltage command, including: obtaining an output drive signal based on the target compensation command and the target fundamental voltage command; performing space vector pulse width modulation based on the output drive signal and a preset triangular carrier signal to obtain a pulse signal, and taking the pulse signal as the initial output current.

[0076] In the specific implementation process, the target fundamental voltage command output by the voltage-current double closed loop is compensated and adjusted based on the target compensation command, so that the voltage-current double closed loop obtains an output drive signal, and the pulse signal obtained after comparing the output drive signal with a given preset triangular carrier signal is taken as the control signal of the IGBT of the grid-connected charging pile, i.e. the initial output current.

[0077] In the specific implementation process, according to the voltage harmonic components extracted in S1, a voltage-current double closed loop combined with harmonic voltage feedforward control is used to establish a virtual synchronous generator (grid-connected charging pile) control block diagram (corresponding to the grid-connected charging pile control model), as shown in Figure 3As shown, the basic links include: a voltage-current double closed loop control link based on a preset voltage-current double closed loop control strategy, a harmonic voltage feedforward control link based on a preset harmonic voltage feedforward control strategy, a power outer ring based on a preset power outer ring control strategy, a harmonic extraction module, and an SVPWM modulation module based on a space vector pulse width modulation. Wherein, U(s) represents an input voltage signal, that is, a control input voltage of the grid-connected charging pile.

[0078] Optionally, obtaining each order virtual impedance based on the initial output current, the harmonic extraction model and the voltage harmonic component comprises: obtaining each order harmonic current component based on the initial output current, the harmonic extraction model and the voltage harmonic component; and obtaining each order virtual impedance based on the each order harmonic current component, the voltage harmonic component and a preset virtual impedance algorithm.

[0079] In the specific implementation process, the embodiment constructs virtual impedance according to the grid-connected output harmonic current extracted by the double TOGI cascade controller. In order to facilitate independent design of the harmonic virtual impedance, the embodiment first adopts the double TOGI controller to accurately extract each order harmonic current that needs to be controlled, separates the fundamental and harmonic current components from the grid-connected output current, and thereby realizes independent design of the virtual impedance under different harmonic components. For the main 5th, 7th and 11th grid-connected output harmonic components, the h value in the double TOGI link transfer function is respectively set to 5, 7 and 11 harmonic component orders for harmonic component extraction, and each order harmonic current component is obtained, which respectively corresponds to design of the virtual impedance thereof.

[0080] Then, the harmonic impedance is designed according to the extracted each order grid-connected output harmonic current component of the grid-connected charging pile. For each order harmonic current component, the harmonic impedance value is respectively designed to improve the grid-connected output current quality of the grid-connected charging pile. The inductive virtual impedance and the resistive virtual impedance are expressed as follows:

[0081] Z Lv (s)=ωL v v dh (s)

[0082] Z Rv (s)=R v v qh (s)

[0083] In the formula, Z Lv (s) and Z Rv (s) are inductive impedance and resistive impedance respectively, L v is virtual inductance, R v is virtual resistance, v dh and v qh are two output signals of the double TOGI.

[0084] The above virtual impedance is introduced into the voltage-current double closed loop model through an additional loop, and the system total output impedance expression is as follows:

[0085] Z v (s)=Z Rv (s)+Z Lv (s)

[0086] Z ov (s)=G u (s)Z v (s)+Z o (s)

[0087] Wherein, Z o (s) is the original output impedance, Z v (s) is the sum of inductive impedance and resistive impedance, and Z ov (s) represents the system total output impedance.

[0088] The virtual impedance designed by the traditional second-order generalized integrator (SOGI) only has an impact on the impedance at the fundamental frequency, has almost no impact on the output impedance at the harmonic frequency, and has no suppression effect on the direct current component, and the expression of the total output impedance Z ov_SOGI (s) is as follows:

[0089]

[0090] And the final expression of the double TOGI total output impedance Z ov_D-TOGI is as follows:

[0091]

[0092] Since the direct current component in the input signal is suppressed by the quadrature signal generator when passing through the TOGI, the output impedance will have a certain attenuation; and only the impedance near the fundamental frequency is affected, and the output impedance at the harmonic frequency is not affected. Compared with the traditional SOGI method, the double TOGI method suppresses the direct current component and avoids the cross between the feedback networks, reducing the complexity of system control.

[0093] Optionally, the harmonic suppression model is obtained based on the virtual impedance and the network type charging pile control model, and the harmonic suppression output current is obtained based on the harmonic suppression model and real-time power grid data to realize harmonic suppression of the output current of the network type charging pile, including: introducing the virtual impedance into the network type charging pile control model based on the voltage-current double closed loop control to obtain a harmonic suppression model; and obtaining a harmonic suppression output current based on the harmonic suppression model and real-time power grid data to realize harmonic suppression of the output current of the network type charging pile.

[0094] In the implementation process, the virtual impedance is introduced into the voltage and current double closed loop control, integrated into the harmonic suppression model, and the harmonic suppression model of the grid-forming charging pile grid-connected output current is established based on the harmonic voltage feedforward control combined with the virtual impedance. By separately designing the harmonic virtual impedance corresponding to each harmonic component, the total output virtual impedance of the system is introduced into the voltage-current double closed loop control, which is consistent with the position of the aforementioned harmonic voltage feedforward, and the harmonic suppression model of the grid-forming charging pile grid-connected output current can be obtained after the combination of the harmonic voltage feedforward and the virtual impedance, and the open-loop transfer function G open (s) is:

[0095]

[0096] Wherein, G x (s) expression is:

[0097]

[0098] In the formula, K PWM represents the pulse modulation coefficient.

[0099] In summary, the overall flow of the harmonic suppression method based on feedforward control and virtual impedance provided by the embodiment is shown in Figure 4 The voltage loop, current loop double closed loop control is combined with the voltage harmonic feedforward H g (s), pulse modulation K PWM , harmonic extraction module H1(s) and virtual impedance Z ov_D-TOGI to suppress the harmonic of the input signal U(S) and obtain the output current after harmonic suppression. Wherein,

[0100] The embodiment provides a harmonic suppression method based on feedforward control and virtual impedance, first constructs a double third-order generalized integrator cascade harmonic extraction model composed of two third-order generalized integrators in series, and extracts voltage harmonic components from real-time power grid data based on a preset angular frequency, so that the voltage harmonic components are accurately extracted; then, a grid-connected charging pile control model is constructed in combination with power outer loop control, voltage and current double closed loop control, harmonic voltage feedforward control and the voltage harmonic components, wherein the power outer loop control outputs the electromotive force parameter to realize synchronization with the power grid, the voltage loop of the voltage and current double closed loop control adopts a proportional resonant controller to output a fundamental current instruction, the current loop adopts a proportional controller to track the instruction, the harmonic voltage feedforward control sets the feedforward point at the voltage loop and generates a compensation instruction based on the electromotive force parameter and the voltage harmonic component, and then generates an initial output current through space vector pulse width modulation; then, each harmonic current component is extracted from the initial output current, a frequency division virtual impedance is designed in combination with the voltage harmonic component, and each virtual impedance is introduced into the voltage and current double closed loop control to form a harmonic suppression model in combination with the grid-connected charging pile control model, and finally, accurate harmonic suppression is realized through the harmonic suppression model.

[0101] The embodiment provides a harmonic suppression strategy for a grid-connected charging pile based on feedforward control and virtual impedance, which is realized by using the harmonic suppression method, and includes the following steps: harmonic components in grid voltage are extracted by using a double third-order generalized integrator (TOGI) cascade mode; a grid-connected charging pile control block diagram is established by using voltage-current double closed loop control in combination with harmonic voltage feedforward control according to the extracted harmonic voltage; a virtual impedance is constructed according to the harmonic components of the grid-connected charging pile output current extracted by the double TOGI cascade control link; and a grid-connected charging pile output current harmonic suppression model is established based on the harmonic voltage feedforward control in combination with the virtual impedance.

[0102] Compared with the prior art, the embodiment has the following beneficial effects: the harmonic component extraction mode of the double TOGI cascade mode can effectively eliminate the direct current component in the system and improve the dynamic response speed of the harmonic component elimination; the harmonic voltage feedforward control of the voltage-current double closed loop and the virtual impedance can effectively reduce each harmonic component in the grid-connected output current of the grid-connected charging pile, effectively reduce the grid-connected output current distortion caused by the excessive harmonic component, and improve the power quality; the double TOGI harmonic component extraction mode sets the corresponding virtual impedance, so that the harmonic suppression effect is more ideal and has good dynamic performance, which is beneficial to better suppress the harmonic of the grid-connected output current of the grid-connected charging pile control and improve the power quality.

[0103] The embodiment also provides a harmonic suppression system based on feedforward control and virtual impedance, which is used to realize the harmonic suppression method, and includes the following components:

[0104] a double-cascaded harmonic extraction module, configured to construct a harmonic extraction model based on a double third-order generalized integrator cascade, and to obtain a voltage harmonic component based on the harmonic extraction model and real-time grid data;

[0105] a double-loop harmonic control module, configured to construct a grid-connected charging pile control model based on a preset power outer loop control strategy, a preset voltage and current double-loop control strategy, a preset harmonic voltage feedforward control strategy, and the voltage harmonic component, and to obtain an initial output current based on the grid-connected charging pile control model and real-time grid data;

[0106] a virtual impedance module, configured to obtain each-order virtual impedance based on the initial output current, the harmonic extraction model, and the voltage harmonic component;

[0107] a harmonic suppression module, configured to obtain a harmonic suppression model based on the each-order virtual impedance and the grid-connected charging pile control model, to obtain a harmonic suppression output current based on the harmonic suppression model and real-time grid data, and to realize harmonic suppression of the output current of the grid-connected charging pile.

[0108] The harmonic suppression system based on feedforward control and virtual impedance provided in the embodiment realizes harmonic extraction by constructing a harmonic extraction model based on a double third-order generalized integrator cascade through a double-cascaded harmonic extraction module, so as to accurately separate and extract harmonics, realize faster dynamic response and accurate harmonic extraction, and reduce output signal distortion; the harmonic suppression system realizes dynamic harmonic suppression by constructing an initial grid-connected charging pile control model through a double-loop harmonic control module in combination with a voltage and current double-loop control strategy and a harmonic voltage feedforward control strategy, and by forming a final harmonic suppression model through a virtual impedance module in combination with virtual impedance, effectively reduces grid output current distortion caused by excessively high harmonic components, and improves power quality.

[0109] The above describes preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements are also considered to be within the protection scope of the present application.

Claims

1. A harmonic suppression method based on feedforward control and virtual impedance, characterized in that, include: A harmonic extraction model based on a cascade of two third-order generalized integrators is constructed, and voltage harmonic components are obtained based on the harmonic extraction model and real-time power grid data. A grid-type charging pile control model is constructed based on a preset power outer loop control strategy, a preset voltage and current dual closed loop control strategy, a preset harmonic voltage feedforward control strategy, and the voltage harmonic components, so as to obtain the initial output current based on the grid-type charging pile control model and real-time grid data. The virtual impedances of each order are obtained based on the initial output current, harmonic extraction model, and voltage harmonic components. Based on the virtual impedance and the grid-type charging pile control model, a harmonic suppression model is obtained. Based on the harmonic suppression model and real-time grid data, the harmonic suppression output current is obtained, thereby realizing harmonic suppression of the output current of the grid-type charging pile.

2. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 1, characterized in that, The construction of a harmonic extraction model based on a cascaded dual third-order generalized integrator, and the acquisition of voltage harmonic components based on the harmonic extraction model and real-time power grid data, includes: A harmonic extraction model based on a cascade of two third-order generalized integrators is constructed. Voltage harmonic components are obtained based on the harmonic extraction model, real-time power grid data, and preset angular frequency.

3. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 1, characterized in that, The process involves constructing a grid-type charging pile control model based on a preset power outer loop control strategy, a preset voltage and current dual closed loop control strategy, a preset harmonic voltage feedforward control strategy, and the voltage harmonic components. The initial output current is then obtained based on this grid-type charging pile control model and real-time grid data. This includes: Obtain active power reference data, and perform power outer loop control based on the real-time grid data, active power reference data and preset power outer loop control strategy to obtain electromotive force parameters; Obtain the voltage loop model and the current loop model, and construct a voltage and current dual closed-loop model based on the voltage loop model, the current loop model and the preset voltage and current dual closed-loop control strategy; Based on the electromotive force parameters, voltage harmonic components, voltage and current dual closed-loop model and preset harmonic voltage feedforward control strategy, a grid-type charging pile control model is obtained. The initial output current is obtained based on the grid-type charging pile control model and real-time power grid data.

4. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 3, characterized in that, The process of acquiring the voltage loop model and current loop model, and constructing a voltage and current dual closed-loop model based on the voltage loop model, current loop model, and a preset voltage and current dual closed-loop control strategy, includes: Voltage loop model is obtained based on proportional resonant controller and preset grid parameters; Obtaining the current loop model based on a proportional controller; A voltage and current dual-closed-loop model is constructed based on the voltage loop model, the current loop model, and the preset voltage and current dual-closed-loop control strategy: the fundamental current command is obtained based on the voltage loop model and the voltage harmonic component, and the voltage and current dual-closed-loop control is performed based on the fundamental current command and the current loop model to construct the voltage and current dual-closed-loop model.

5. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 3, characterized in that, The process of obtaining the grid-type charging pile control model based on the electromotive force parameters, voltage harmonic components, voltage-current dual closed-loop model, and preset harmonic voltage feedforward control strategy includes: The preset harmonic voltage feedforward control strategy includes: when performing harmonic voltage feedforward control based on the electromotive force parameters, voltage harmonic components, and voltage-current dual closed-loop model, setting the feedforward point at the voltage loop model; Harmonic compensation commands are obtained based on the electromotive force parameters and voltage harmonic components. Harmonic voltage feedforward control is performed based on the harmonic compensation command, feedforward point, and voltage-current dual closed-loop model to obtain the grid-type charging pile control model.

6. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 3, characterized in that, The process of obtaining the initial output current based on the grid-type charging pile control model and real-time power grid data includes: Harmonic extraction is performed based on the aforementioned grid-type charging pile control model and real-time power grid data to obtain the target harmonic components; The target DC command is obtained based on the target harmonic components; Power outer loop control is performed based on the aforementioned grid-type charging pile control model and real-time grid data to obtain target parameter settings; Based on the target parameter settings, target harmonic components and real-time power grid data, voltage and current dual closed-loop control is performed to obtain the target fundamental voltage command; Harmonic voltage feedforward control is performed based on the target DC command to obtain the target compensation command; The initial output current is obtained based on the target compensation command and the target fundamental voltage command.

7. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 6, characterized in that, The step of obtaining the initial output current based on the target compensation command and the target fundamental voltage command includes: The output drive signal is obtained based on the target compensation command and the target fundamental voltage command; Space vector pulse width modulation is performed based on the output drive signal and the preset triangular carrier signal to obtain a pulse signal, and the pulse signal is used as the initial output current.

8. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 1, characterized in that, The process of obtaining virtual impedances for each order based on the initial output current, harmonic extraction model, and voltage harmonic components includes: Based on the initial output current, harmonic extraction model, and voltage harmonic components, the harmonic current components of each order are obtained. The virtual impedance is obtained based on the harmonic current component, voltage harmonic component, and preset virtual impedance algorithm.

9. The harmonic suppression method based on feedforward control and virtual impedance as described in claim 1, characterized in that, The process of obtaining a harmonic suppression model based on the virtual impedances and the grid-type charging pile control model, and obtaining a harmonic suppression output current based on the harmonic suppression model and real-time grid data to achieve harmonic suppression of the output current of the grid-type charging pile includes: The virtual impedances of each order are introduced into the grid-type charging pile control model based on the voltage and current dual closed-loop control to obtain the harmonic suppression model; Based on the harmonic suppression model and real-time power grid data, the harmonic suppression output current is obtained to achieve harmonic suppression of the output current of the grid-type charging pile.

10. A harmonic suppression system based on feedforward control and virtual impedance, characterized in that, A method for implementing a harmonic suppression method based on feedforward control and virtual impedance as described in any one of claims 1 to 9 includes: A dual-cascaded harmonic extraction module is used to construct a harmonic extraction model based on a cascade of two third-order generalized integrators, and to obtain voltage harmonic components based on the harmonic extraction model and real-time power grid data. The dual-closed-loop harmonic control module is used to construct a grid-type charging pile control model based on a preset power outer loop control strategy, a preset voltage and current dual-closed-loop control strategy, a preset harmonic voltage feedforward control strategy, and the voltage harmonic components, so as to obtain the initial output current based on the grid-type charging pile control model and real-time grid data. The virtual impedance module is used to obtain the virtual impedance of each order based on the initial output current, harmonic extraction model and voltage harmonic components. The harmonic suppression module is used to obtain a harmonic suppression model based on the virtual impedance and the grid-type charging pile control model, and to obtain the harmonic suppression output current based on the harmonic suppression model and real-time power grid data, so as to realize the harmonic suppression of the output current of the grid-type charging pile.

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