Feed-forward control method and feed-forward control device of grid-connected inverter and storage medium

Abstract

The invention discloses a feed-forward control method and a feed-forward control device of a grid-connected inverter and a storage medium. The feed-forward control method of the grid-connected inverter comprises the following steps: acquiring a common coupling point voltage of a common coupling point; performing low-pass filtering on the common coupling point voltage to obtain a first feed-forward voltage component; performing high-pass filtering on the common coupling point voltage to obtain a second feed-forward voltage component; adding the first feed-forward voltage component and the second feed-forward voltage component to obtain a feed-forward voltage; and controlling the grid-connected inverter by using the feed-forward voltage. The electric energy quality of the system can be improved under the condition that the dynamic characteristics of the system are not damaged, namely the stability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter grid-connected technology, and in particular to a feedforward control method, a feedforward control device and a storage medium of a grid-connected inverter. Background Art

[0002] At present, traditional fossil fuel power generation is facing the dual pressures of environmental impact and resource depletion, which makes renewable energy power generation the focus of global attention. In the field of renewable energy power generation, renewable energy such as solar energy and wind energy are widely distributed, and distributed power generation systems are increasingly becoming an important means to solve new energy problems.

[0003] For large-scale distributed power generation systems connected to the grid, the weak grid characteristics they exhibit pose challenges to the stable operation of grid-connected inverters. In a weak grid environment, negative resistance will appear in the inverter output impedance, affecting the stability of the system. Therefore, how to improve the stability of grid-connected inverters under weak grid conditions has become a key issue that needs to be solved urgently. To address this issue, corresponding control strategies need to be adopted to ensure the stable and efficient operation of grid-connected inverters.

[0004] In the related art, a feedforward control method can be used to improve the stability of the system. However, the feedforward control method in the related art will affect the dynamic characteristics of the system. Summary of the invention

[0005] The present invention provides a feedforward control method, a feedforward control device and a storage medium for a grid-connected inverter, so as to improve the power quality of the system without damaging the dynamic characteristics of the system, that is, to improve the stability of the system.

[0006] According to one aspect of the present invention, a feedforward control method for a grid-connected inverter is provided, comprising:

[0007] Obtaining a common coupling point voltage of a common coupling point;

[0008] Performing low-pass filtering on the common coupling point voltage to obtain a first feed-forward voltage component; performing high-pass filtering on the common coupling point voltage to obtain a second feed-forward voltage component;

[0009] Adding the first feed-forward voltage component and the second feed-forward voltage component to obtain a feed-forward voltage;

[0010] The grid-connected inverter is controlled by utilizing the feed-forward voltage.

[0011] Optionally, performing low-pass filtering on the common coupling point voltage to obtain a first feed-forward voltage component comprises:

[0012] The voltage at the point of common coupling is low-pass filtered using a low-pass filtering algorithm with a cut-off frequency less than or equal to 90% of the harmonic frequency of the point of common coupling.

[0013] The step of high-pass filtering the common coupling point voltage to obtain a second feed-forward voltage component comprises:

[0014] The common coupling point voltage is high-pass filtered using a high-pass filtering algorithm whose cut-off frequency is less than the resonant frequency of the LC filter corresponding to the grid-connected inverter.

[0015] Optionally, performing low-pass filtering on the common coupling point voltage to obtain a first feed-forward voltage component comprises:

[0016] Low-pass filtering the voltage at the common coupling point using a low-pass filtering algorithm with a cut-off frequency less than or equal to 90% of the harmonic frequency of the common coupling point;

[0017] The step of high-pass filtering the common coupling point voltage to obtain a second feed-forward voltage component comprises:

[0018] High-pass filtering is performed on the common coupling point voltage using a high-pass filtering algorithm whose cut-off frequency is less than the resonant frequency of the LC filter corresponding to the grid-connected inverter;

[0019] The cutoff frequency of the low-pass filtering algorithm and the cutoff frequency of the high-pass filtering algorithm are determined as follows:

[0020] In the feedforward control method, only the low-pass filtering algorithm is added, and the cutoff frequency of the low-pass filtering algorithm is determined; if the grid-connected inverter system is stable, the high-pass filtering algorithm is added, and the cutoff frequency of the high-pass filtering algorithm is determined.

[0021] Optionally, the cutoff frequency of the low-pass filtering algorithm is determined by:

[0022] Configuring an initial value of the cutoff frequency of the low-pass filtering algorithm;

[0023] Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the low-pass filtering algorithm. If it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continuously controlled to change in the first direction until the grid-connected inverter system is stable. If the instability of the grid-connected inverter system is increased by controlling the initial value to change in the first direction, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable. The first direction is opposite to the second direction.

[0024] Optionally, the cutoff frequency of the low-pass filtering algorithm is determined by:

[0025] Configuring an initial value of the cutoff frequency of the high-pass filtering algorithm;

[0026] Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the high-pass filtering algorithm. If it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continuously controlled to change in the first direction until the grid-connected inverter system is stable. If the instability of the grid-connected inverter system is increased by controlling the initial value to change in the first direction, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable. The first direction is opposite to the second direction.

[0027] Optionally, the feedforward control method of the grid-connected inverter further includes:

[0028] multiplying the common coupling point voltage by a weighting coefficient to obtain a weighted common coupling point voltage;

[0029] The step of low-pass filtering the common coupling point voltage to obtain a first feed-forward voltage component comprises:

[0030] Performing low-pass filtering on the weighted common coupling point voltage to obtain a first feedforward voltage component;

[0031] The step of high-pass filtering the common coupling point voltage to obtain a second feed-forward voltage component comprises:

[0032] High-pass filtering the weighted common coupling point voltage to obtain a second feedforward voltage component;

[0033] Among them, the weighting coefficient is K is the common coupling point voltage proportional feed-forward coefficient, and KPWM is the equivalent gain of the grid-connected inverter.

[0034] Optionally, the transfer function of the feed-forward voltage is:

[0035] Among them, G′ V is the feed-forward voltage, GLp is the transfer function of the low-pass filtering algorithm, and GHp is the transfer function of the high-pass filtering algorithm.

[0036] According to another aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program, and when the program is executed by a processor, the feedforward control method of the grid-connected inverter as described above is implemented.

[0037] According to another aspect of the present invention, there is provided a feedforward control device for a grid-connected inverter, comprising:

[0038] A common coupling point voltage acquisition module, used to acquire the common coupling point voltage of the common coupling point;

[0039] a low-pass filtering module, electrically connected to the common coupling point voltage acquisition module, and configured to perform low-pass filtering on the common coupling point voltage to obtain a first feedforward voltage component;

[0040] a high-pass filtering module, electrically connected to the common coupling point voltage acquisition module, and configured to perform high-pass filtering on the common coupling point voltage to obtain a second feedforward voltage component;

[0041] A first adding and subtracting module, configured to add the first feedforward voltage component and the second feedforward voltage component to obtain a feedforward voltage;

[0042] An output control unit is used to control the grid-connected inverter using the feed-forward voltage.

[0043] The technical solution of the embodiment of the present invention adopts a feedforward control method of a grid-connected inverter, which includes obtaining the common coupling point voltage of the common coupling point; performing low-pass filtering on the common coupling point voltage to obtain a first feedforward voltage component; performing high-pass filtering on the common coupling point voltage to obtain a second feedforward voltage component; adding the first feedforward voltage component and the second feedforward voltage component to obtain the feedforward voltage; and controlling the grid-connected inverter using the feedforward voltage. By adding low-pass filtering and high-pass filtering strategies to the feedforward control, the harmonics of the common coupling point are filtered out by low-pass filtering, thereby reducing the impact of the harmonics on the system. And by high-pass filtering, the high-frequency damping of the system can be improved. In other words, the solution of this embodiment can both filter out the harmonics of the common coupling point and improve the high-frequency damping of the system, thereby improving the stability of the system without affecting the dynamic characteristics of the system.

[0044] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0046] Figure 1A flow chart of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention;

[0047] Figure 2 A model diagram of a grid-connected inverter system provided by an embodiment of the present invention;

[0048] Figure 3 A control block diagram of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention;

[0049] Figure 4 A small signal model diagram of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention;

[0050] Figure 5 A generalized Nyquist curve before and after adding low-pass filtering to a feedforward control method of a grid-connected inverter system provided by an embodiment of the present invention;

[0051] Figure 6 A generalized Nyquist curve before and after adding high-pass filtering to a feedforward control method of a grid-connected inverter system provided by an embodiment of the present invention;

[0052] Figure 7 A simulation schematic diagram of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0054] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0055] Figure 1A flow chart of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention, Figure 2 A model diagram of a grid-connected inverter system provided by an embodiment of the present invention, Figure 3 A control block diagram of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention, Figure 4 A small signal model diagram of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention. Figures 1 to 4 The feedforward control method of the grid-connected inverter is applied to the grid-connected inverter system, which includes an LC topology structure 12 and a control loop 13. Figure 2 As shown, the output of the DC power supply 11 is connected to the grid after passing through the inverter. PCC is the grid access point, that is, the common coupling point; Zg is the line impedance between the grid access point and the grid, and Vg represents the grid voltage. It can be understood that the LC topology structure 12 of the grid-connected inverter includes multiple switch tubes (T1-T6), a topological inductor L1, a topological resistor R1 and a topological capacitor C. The control loop can perform dual closed-loop control of voltage and current according to the parameters of the grid access point to obtain the duty cycle of PWM modulation, and finally generate a PWM modulation signal through the SVPWM module, and use the PWM modulation signal to control the switch tube in the grid-connected inverter.

[0056] The feedforward control method of the grid-connected inverter includes:

[0057] Step S110, obtaining a common coupling point voltage of a common coupling point;

[0058] Specifically, the common coupling point voltage VPCCabc can be obtained by sampling the voltage of the common coupling point by the common coupling point voltage acquisition module, and the common coupling point voltage VPCCabc is a parameter in the abc coordinate system. The common coupling point voltage VPCCabc includes three voltages: VPCCa, VPCCb, and VPCCc. Of course, in the feedforward control method of the grid-connected inverter, sampling of the grid-connected current igabc can also be included, and the grid-connected current igabc includes three currents: iga, igb, and igc.

[0059] Step S120, performing low-pass filtering on the common coupling point voltage to obtain a first feed-forward voltage component;

[0060] Specifically, the common coupling point voltage may be low-pass filtered using a low-pass filtering algorithm to obtain the first feed-forward voltage component.

[0061] Step S130, high-pass filtering the common coupling point voltage to obtain a second feedforward voltage component;

[0062] Specifically, the common coupling point voltage can be high-pass filtered by a high-pass filtering algorithm to obtain the second feedforward voltage component. It should be noted that the execution order of step S120 and step S130 is not limited, and step S120 may be executed first and then step S130; step S130 may be executed first and then step S120; or step S120 and step S130 may be executed simultaneously.

[0063] Step S140, adding the first feed-forward voltage component and the second feed-forward voltage component to obtain a feed-forward voltage;

[0064] Step S150, controlling the grid-connected inverter using the feed-forward voltage;

[0065] Specifically, the first adder and subtractor can be used to add the first feedforward voltage and the second feedforward voltage to obtain the feedforward voltage. In the traditional voltage feedforward scheme, the voltage at the common coupling point is low-pass filtered or high-pass filtered to obtain the feedforward voltage, which will affect the dynamic characteristics of the system. In this embodiment, the feedforward control method is the superposition of low-pass filtering and high-pass filtering, that is, the transfer function of the high-pass filter and the transfer function of the low-pass filter are in an additive relationship, rather than a multiplicative relationship; or it can also be understood that the high-pass filter algorithm and the low-pass filter algorithm are in a parallel relationship, not a series relationship. By adding low-pass filtering to the feedforward control method, the harmonics at the common coupling point are filtered out, thereby reducing the impact of background harmonics on the system. And by high-pass filtering, the high-frequency damping of the system can be improved. In other words, the scheme of this embodiment can not only filter out the harmonics at the common coupling point, but also improve the high-frequency damping of the system, thereby improving the stability of the system without affecting the dynamic characteristics of the system.

[0066] The technical solution of this embodiment adopts a feedforward control method of a grid-connected inverter, which includes obtaining the common coupling point voltage of the common coupling point; performing low-pass filtering on the common coupling point voltage to obtain a first feedforward voltage component; performing high-pass filtering on the common coupling point voltage to obtain a second feedforward voltage component; adding the first feedforward voltage component and the second feedforward voltage component to obtain the feedforward voltage; and controlling the grid-connected inverter using the feedforward voltage. By adding low-pass filtering and high-pass filtering strategies to the feedforward control, the harmonics of the common coupling point are filtered out by low-pass filtering, thereby reducing the impact of the harmonics on the system. And by high-pass filtering, the high-frequency damping of the system can be improved. In other words, the solution of this embodiment can both filter out the harmonics of the common coupling point and improve the high-frequency damping of the system, thereby improving the stability of the system without affecting the dynamic characteristics of the system.

[0067] Optionally, for ease of description, the complete feedforward control scheme of the grid-connected inverter is first described below. The complete feedforward control scheme may include: collecting the grid-connected current and the common coupling point voltage;

[0068] Transform the grid-connected current and the voltage at the common coupling point into the dq coordinate system;

[0069] The voltage phase angle of the common coupling point voltage can be obtained through a phase-locked loop, and then the grid-connected current and the common coupling point voltage can be transformed into a dq coordinate system using the voltage phase angle and Park transformation.

[0070] The duty cycle of PWM modulation of grid-connected inverter is calculated by using voltage and current double closed-loop control method;

[0071] Specifically, the voltage-current dual closed-loop control method can be implemented by a voltage-current dual closed-loop control loop, that is, the control loop includes a voltage-current dual closed-loop control loop. In the voltage-current dual closed-loop control loop, the current loop serves as an inner loop, and current control is performed on the current command output by the voltage loop as an outer loop. In other words, the voltage-current dual closed-loop control method can be used to accurately control voltage and current, thereby optimizing system performance and improving system stability. Furthermore, adding feedforward control to the voltage-current dual closed-loop control method, that is, adding a feedforward control loop to the voltage-current dual closed-loop control loop, can effectively improve the anti-interference ability of the system and further improve the stability of the system. The feedforward control is the feedforward control described above that includes low-pass filtering and high-pass filtering.

[0072] Optionally, performing low-pass filtering on the common coupling point voltage to obtain the first feed-forward voltage component comprises: performing low-pass filtering on the common coupling point voltage using a low-pass filtering algorithm with a cut-off frequency less than or equal to 90% of the harmonic frequency of the common coupling point.

[0073] Specifically, the cutoff frequency of the low-pass filter is also the cutoff frequency of the low-pass filter algorithm. Background harmonics above the cutoff frequency cannot pass, while the normal working frequency of the power grid below the cutoff frequency can pass. The arrangement of this embodiment can ensure that the feedforward control method can effectively filter out harmonics. Exemplarily, the cutoff frequency of the low-pass filter can be 90%, 88%, 86%, 84%, 82%, 80%, 78%, 76%, 74%, 72% or 70% of the harmonics of the common coupling point. In the feedforward control loop, the low-pass filter algorithm can be an algorithm corresponding to an RC low-pass filter, an LC low-pass filter, or a Patello-Toon filter. The low-pass filter algorithm can be an algorithm corresponding to a passive low-pass filter or an active low-pass filter.

[0074] For example, reference Figure 5 , Figure 5 A feedforward control method for a grid-connected inverter system provided by an embodiment of the present invention is a generalized Nyquist curve before and after adding low-pass filtering. Figure 5It can be seen that the curve λ1 that only considers the parameters of the PCC voltage proportional feedforward coefficient and the inverter equivalent gain is compared with the curve λ1 that considers the PCC voltage proportional feedforward coefficient and the inverter equivalent gain and adds the feedforward with low-pass filtering. The curve after adding the low-pass filtering is located to the upper right of the point (-1, j0) and is farther away from the point (-1, j0), so the stability of the grid-connected inverter system is higher. In addition, the curve λ2 after adding the high-pass filtering and low-pass filtering shows that the system stability is also improved.

[0075] Optionally, performing high-pass filtering on the common coupling point voltage to obtain the second feed-forward voltage component includes:

[0076] The common coupling point voltage is high-pass filtered using a high-pass filtering algorithm whose cut-off frequency is less than the resonant frequency of the LC filter corresponding to the grid-connected inverter.

[0077] Specifically, the impedance of the grid-connected inverter is determined by the parameters of the LC filter corresponding to the grid-connected inverter. In this embodiment, the cutoff frequency of the high-pass filtering algorithm is less than the resonant frequency of the LC filter, which can greatly improve the high-frequency damping of the system without affecting the dynamic characteristics of the system. For example, Figure 6 A generalized Nyquist curve before and after adding high-pass filtering to a feedforward control method of a grid-connected inverter system provided by an embodiment of the present invention. Figure 6 It can be seen that, compared with the curve λ1 which only considers the parameters of the PCC voltage proportional feedforward coefficient and the inverter equivalent gain, and the curve λ1 which considers the PCC voltage proportional feedforward coefficient and the inverter equivalent gain and adds the feedforward of low-pass filtering and high-pass filtering, the curve after adding the low-pass filtering is located at the upper right of the point (-1, j0) and is farther away from the point (-1, j0), so the stability of the grid-connected inverter system is higher. In addition, the curve λ2 after adding the high-pass filtering and the low-pass filtering shows that the system stability is also improved. Exemplarily, the cutoff frequency of the high-pass filtering algorithm is, for example, 90%, 88%, 86%, 84%, 82%, 80%, 78%, 76%, 74%, 72% or 70% of the resonant frequency of the LC filter.

[0078] Optionally, the cutoff frequency of the low-pass filtering algorithm and the cutoff frequency of the high-pass filtering algorithm are determined as follows: only the low-pass filtering algorithm is added to the feedforward control method, and the cutoff frequency of the low-pass filtering algorithm is determined; if the grid-connected inverter system is unstable, the high-pass filtering algorithm is added, and the cutoff frequency of the high-pass filtering algorithm is determined.

[0079] Specifically, due to the inhibitory effect of low-pass filtering on harmonics, when designing the feedforward control loop, the parameters of the low-pass filtering algorithm are designed first, that is, the cutoff frequency of the low-pass filtering algorithm is designed first. After the cutoff frequency of the low-pass filtering algorithm is determined, the low-pass filtering algorithm and the high-pass filtering algorithm are added to the feedforward control loop. At this time, according to the Nyquist judgment basis, if the grid-connected inverter system is stable, the feedforward control loop design is completed. If the grid-connected inverter system is unstable, the grid-connected inverter system can be stabilized by adjusting other parameters of the high-pass filtering algorithm and / or the low-pass filtering algorithm except the cutoff frequency (such as center frequency, insertion loss or ripple, etc.).

[0080] Optionally, the cut-off frequency of the low-pass filter, that is, in the grid-connected inverter system design stage, the cut-off frequency of the low-pass filter algorithm is determined by the following method:

[0081] Configure the initial value of the cutoff frequency of a low-pass filtering algorithm;

[0082] Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the low-pass filtering algorithm. If it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continued to be controlled to change in the first direction until the grid-connected inverter system is stable. If the initial value is controlled to change in the first direction and the instability of the grid-connected inverter system is increased, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable. The first direction is opposite to the second direction.

[0083] Specifically, when designing a low-pass filtering algorithm in a feedforward control loop, an initial value can be first configured for the low-pass filtering algorithm based on the harmonic frequency of the power grid, such as configuring the initial value to be 85% of the harmonic frequency. Subsequently, the grid-connected inverter system will be determined to be stable based on the Nyquist judgment basis; if it is unstable, the initial value will be adjusted in the first direction, and the first direction can be a direction in which the value increases or a direction in which the value decreases. The second direction is opposite to the first direction, that is, if the first direction is a direction in which the value increases, the second direction is a direction in which the value decreases; if the first direction is a direction in which the value decreases, the second direction is a direction in which the value increases. For example, the initial value is adjusted to 84% of the harmonic frequency adjustment. If the instability of the grid-connected inverter system is reduced after the adjustment, that is, the generalized Nyquist curve is below the left of the point (-1, j0) and closer to the point (-1, j0), the initial value can be adjusted in the first direction until the system is stable. In addition, if the instability of the grid-connected inverter system increases after the initial value is adjusted to 84% of the harmonic frequency, it indicates that the cutoff frequency adjustment direction of the low-pass filtering algorithm is incorrect. In this case, the cutoff frequency value of the low-pass filtering algorithm is increased based on the initial value until the grid-connected inverter system is stable.

[0084] Optionally, the cutoff frequency of the high-pass filtering algorithm is determined as follows:

[0085] Configure the initial value of the cutoff frequency of a high-pass filter algorithm;

[0086] Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the high-pass filtering algorithm. If it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continued to be controlled to change in the first direction until the grid-connected inverter system is stable. If the initial value is controlled to change in the first direction and the instability of the grid-connected inverter system is increased, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable. The first direction is opposite to the second direction.

[0087] Specifically, similar to the parameter design of the low-pass filter algorithm, when designing the high-pass filter algorithm in the feedforward control loop, an initial value can be first configured for the high-pass filter algorithm based on the LC filter, such as configuring the initial value to be 85% of the harmonic frequency of the LC filter. Subsequently, the grid-connected inverter system will be determined to be stable based on the Nyquist judgment basis; if it is unstable, the initial value will be adjusted in the first direction, and the first direction can be the direction in which the value increases or the direction in which the value decreases. The second direction is opposite to the first direction, that is, if the first direction is the direction in which the value increases, the second direction is the direction in which the value decreases; if the first direction is the direction in which the value decreases, the second direction is the direction in which the value increases. For example, the initial value is adjusted to 84% of the harmonic frequency adjustment. If the instability of the grid-connected inverter system is reduced after the adjustment, that is, the generalized Nyquist curve is below the left of the point (-1, j0) and closer to the point (-1, j0), the initial value can be adjusted in the first direction until the system is stable. In addition, if the instability of the grid-connected inverter system increases after the initial value is adjusted to 84% of the harmonic frequency, it indicates that the cutoff frequency adjustment direction of the high-pass filtering algorithm is incorrect. In this case, the cutoff frequency value of the high-pass filtering algorithm is increased based on the initial value until the grid-connected inverter system is stable.

[0088] Optionally, the feedforward control method of the grid-connected inverter further includes: multiplying the common coupling point voltage by a weighting coefficient to obtain a weighted common coupling point voltage; performing low-pass filtering on the common coupling point voltage to obtain a first feedforward voltage component includes: performing low-pass filtering on the weighted common coupling point voltage to obtain a first feedforward voltage component; performing high-pass filtering on the common coupling point voltage to obtain a second feedforward voltage component includes: performing high-pass filtering on the weighted common coupling point voltage to obtain a second feedforward voltage component; wherein the weighting coefficient is K is the common coupling point voltage proportional feedforward coefficient, K PWM is the equivalent gain of the grid-connected inverter.

[0089] Specifically, refer to Figure 2 and Figure 3 , the transfer function of feedforward control is:

[0090]

[0091] Among them, G Lp is the low-pass filter algorithm transfer function, G Hp is the high-pass filter algorithm transfer function, K is the common coupling point voltage proportional feedforward coefficient, K PWM is the inverter equivalent gain. Among them, is the low-pass filter algorithm transfer function, is the high-pass filter algorithm transfer function, T is the time constant of the grid-connected inverter system, and s is the Laplace operator. For example, K≥1.2, at this time, the common coupling point voltage proportional feedforward coefficient is large, and the background harmonics introduced by the dead zone effect have a greater impact on the grid-connected inverter system. By adopting the feedforward control method described in this article, the impact of the harmonics introduced by the dead zone effect on the system can be reduced without damaging the dynamic characteristics of the grid-connected inverter system, thereby improving the power quality; so that the grid-connected inverter system can achieve a good compromise between power quality, dynamic performance and stability.

[0092] Alternatively, if Figure 2 and Figure 3 As shown, the voltage and current dual closed-loop control method includes a decoupling term, and the expression of the decoupling term is:

[0093]

[0094] Among them, Vdc is the DC bus voltage, L1 is the filter inductor, and ω is the phase-locked loop output frequency.

[0095] Specifically, adding a decoupling term to the voltage-current dual closed-loop control method can improve the dynamic performance and stability of the grid-connected inverter system, and can eliminate the coupling effect, thereby correcting the control signal and eliminating the coupling effect between the current loop and the voltage loop.

[0096] Optionally, in the above embodiment, if Figure 4 As shown in the figure, after considering the dynamics of the phase-locked loop, the dq coordinate system of the LC topology structure differs from the dq coordinate system of the control loop by one in, G PLL For the LC topology, the q-axis voltage perturbation is The transfer function of is the q-axis voltage disturbance of the LC topology. Furthermore,

[0097] in is the d-axis component of the voltage at the common coupling point under the dq coordinate axis of the LC topology;

[0098] where k pllp With k plli They are the proportional term and integral term of the PI controller in the phase-locked loop respectively.

[0099] Furthermore, in Figure 4 In the model shown, the closed-loop output impedance expression of the grid-connected inverter is:

[0100]

[0101] Among them, Z out is the system open-loop output impedance matrix, are disturbances caused by the dynamic phase-locked loop to the output current, PCC common coupling point voltage, and grid-connected inverter system duty cycle; G del is the dq impedance model PWM signal delay matrix of the grid-connected inverter, G dec is the dq impedance model dq current decoupling matrix of the grid-connected inverter, Gpi is the PI control matrix of the dq impedance model current of the grid-connected inverter, i1 is the grid-connected side dq current matrix of the grid-connected inverter; G il is the transfer function matrix from topology to output current. ref is the current reference value.

[0102] In addition, it should be noted that Y C is the admittance of the topological capacitor. The superscript “s” represents the variable of the system dq coordinate system; the superscript “c” represents the variable of the controller dq coordinate system; V d is the grid voltage on the d-axis, d c represents the controller duty cycle, d s Indicates the system duty cycle.

[0103] For example, reference Figure 7 , Figure 7 A simulation schematic diagram of a feedforward control method for a grid-connected inverter provided by an embodiment of the present invention. When the PCC voltage feedforward coefficient is large and the grid is weak, when only the PCC voltage proportional system feedforward strategy is used before time t1, the PCC voltage power quality is poor. When switching to the feedforward control method described in this embodiment at time t1, the system power quality is significantly improved. The experimental results prove the effectiveness of the feedforward control method.

[0104] The present invention also provides a feedforward control device for a grid-connected inverter, comprising: a common coupling point voltage acquisition module, used to acquire the common coupling point voltage of the common coupling point; a low-pass filtering module, electrically connected to the common coupling point voltage acquisition module, used to perform low-pass filtering on the common coupling point voltage to obtain a first feedforward voltage component; a high-pass filtering module, electrically connected to the common coupling point voltage acquisition module, used to perform high-pass filtering on the common coupling point voltage to obtain a second feedforward voltage component; a first addition and subtraction module, used to add the first feedforward voltage component and the second feedforward voltage component to obtain a feedforward voltage; and an output control unit, used to control the grid-connected inverter using the feedforward voltage.

[0105] Specifically, the common coupling point voltage acquisition module is, for example, a sampling module, which can sample the voltage of the common coupling point. Figure 2 and Figure 3 , the transfer function of the low-pass filtering algorithm is G LP , the transfer function of the high-pass filter module is G HP . The common coupling point voltage Vpcc is filtered by a low-pass filtering module to obtain a first feedforward voltage component, and is filtered by a high-pass filtering module to obtain a second feedforward voltage component; then the two feedforward voltage components are added together by a first addition and subtraction module to obtain a feedforward voltage. The first feedforward voltage is superimposed on the output control unit, so that the output control unit is used to control the grid-connected inverter. In this embodiment, by adding low-pass filtering and high-pass filtering strategies to the feedforward control, the harmonics at the common coupling point are filtered out by low-pass filtering, thereby reducing the impact of harmonics on the system. And by high-pass filtering, the high-frequency damping of the system can be improved. In other words, the scheme of this embodiment can both filter out the harmonics at the common coupling point and improve the high-frequency damping of the system, thereby improving the stability of the system without affecting the dynamic characteristics of the system.

[0106] Optionally, in the above embodiment, the output control unit includes a current loop, a decoupling controller and a second adder-subtractor, the current loop is used to generate a first signal based on the output current and a reference current of the grid-connected inverter, the decoupling controller is used to perform decoupling control on the output current of the grid-connected inverter to generate a second signal, and the second adder-subtractor is used to add the first signal, the second signal and the feed-forward voltage.

[0107] Specifically, Figure 2 and Figure 3 As shown, the transfer function of the current loop is represented by Gpi, that is, Gpi is the PI control matrix of the dq impedance model current of the grid-connected inverter. By adding decoupling control, the dynamic performance and stability of the grid-connected inverter system are improved, and the coupling effect can be eliminated, thereby correcting the control signal and eliminating the coupling effect between the current loop and the voltage loop. It can be understood that Figure 3 For Figure 2The control block diagram is obtained by adding a phase-locked loop on the basis of In this embodiment, the output control unit can control the SVPWM module to drive the grid-connected inverter.

[0108] Optionally, the cut-off frequency of the low-pass filtering algorithm is less than or equal to 90% of the harmonic frequency of the common coupling point; and / or,

[0109] The cut-off frequency of the high-pass filtering algorithm is less than the resonant frequency of the LC filter corresponding to the grid-connected inverter.

[0110] Optionally, the cutoff frequency of the low-pass filter is determined by the following method:

[0111] Configure the initial value of the cutoff frequency of a low-pass filter module;

[0112] Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the low-pass filter module; if it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continued to be controlled to change in the first direction until the grid-connected inverter system is stable; if the initial value is controlled to change in the first direction and the instability of the grid-connected inverter system is increased, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable; wherein the first direction is opposite to the second direction.

[0113] Optionally, the feedforward control device of the grid-connected inverter further includes a weighted controller, and the low-pass filter module and the high-pass filter module are both electrically connected to the common coupling point voltage acquisition module through the weighted controller; the weighted coefficient of the weighted controller is K is the common coupling point voltage proportional feedforward coefficient, K PWM is the equivalent gain of the grid-connected inverter.

[0114] Specifically, the specific processes of the above-mentioned embodiments can refer to the description of the feedforward control method of the present invention, which will not be repeated here.

[0115] The present invention also provides a computer-readable storage medium, wherein the computer-executable instructions are used to execute the feedforward control method of the grid-connected inverter provided by any embodiment of the present invention when executed by a computer processor.

[0116] Through the above description of the implementation methods, the technicians in the relevant field can clearly understand that the present invention can be implemented by means of software and necessary general hardware, and of course it can also be implemented by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory (FLASH), hard disk or optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, server, or network device, etc.) to execute the methods described in each embodiment of the present invention.

[0117] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0118] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A feedforward control method for a grid-connected inverter, characterized in that: include: Obtaining a common coupling point voltage of a common coupling point; Performing low-pass filtering on the common coupling point voltage to obtain a first feed-forward voltage component; Performing high-pass filtering on the common coupling point voltage to obtain a second feed-forward voltage component; Adding the first feed-forward voltage component and the second feed-forward voltage component to obtain a feed-forward voltage; The grid-connected inverter is controlled by utilizing the feed-forward voltage.

2. The feedforward control method of the grid-connected inverter according to claim 1, characterized in that: The step of low-pass filtering the common coupling point voltage to obtain a first feed-forward voltage component comprises: The voltage at the point of common coupling is low-pass filtered using a low-pass filtering algorithm with a cut-off frequency less than or equal to 90% of the harmonic frequency of the point of common coupling.

3. The feedforward control method of the grid-connected inverter according to claim 1, characterized in that: The step of high-pass filtering the common coupling point voltage to obtain a second feed-forward voltage component comprises: The common coupling point voltage is high-pass filtered using a high-pass filtering algorithm whose cut-off frequency is less than the resonant frequency of the LC filter corresponding to the grid-connected inverter.

4. The feedforward control method of the grid-connected inverter according to claim 1, characterized in that: The step of low-pass filtering the common coupling point voltage to obtain a first feed-forward voltage component comprises: Low-pass filtering the voltage at the common coupling point using a low-pass filtering algorithm with a cut-off frequency less than or equal to 90% of the harmonic frequency of the common coupling point; The step of high-pass filtering the common coupling point voltage to obtain a second feed-forward voltage component comprises: High-pass filtering is performed on the common coupling point voltage using a high-pass filtering algorithm whose cut-off frequency is less than the resonant frequency of the LC filter corresponding to the grid-connected inverter; The cutoff frequency of the low-pass filtering algorithm and the cutoff frequency of the high-pass filtering algorithm are determined as follows: In the feedforward control method, only the low-pass filtering algorithm is added, and the cutoff frequency of the low-pass filtering algorithm is determined; if the grid-connected inverter system is stable, the high-pass filtering algorithm is added, and the cutoff frequency of the high-pass filtering algorithm is determined.

5. The feedforward control method of the grid-connected inverter according to claim 4, characterized in that: The cut-off frequency of the low-pass filtering algorithm is determined as follows: Configuring an initial value of the cutoff frequency of the low-pass filtering algorithm; Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the low-pass filtering algorithm. If it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continuously controlled to change in the first direction until the grid-connected inverter system is stable. If the instability of the grid-connected inverter system is increased by controlling the initial value to change in the first direction, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable. The first direction is opposite to the second direction.

6. The feedforward control method of the grid-connected inverter according to claim 4, characterized in that: The cutoff frequency of the high-pass filtering algorithm is determined as follows: Configuring an initial value of the cutoff frequency of the high-pass filtering algorithm; Whether the grid-connected inverter system is stable is judged according to the generalized Nyquist curve. If it is stable, the initial value is determined to be the cutoff frequency of the high-pass filtering algorithm. If it is unstable, the initial value is controlled to change in a first direction. If the instability of the grid-connected inverter system is reduced, the initial value is continuously controlled to change in the first direction until the grid-connected inverter system is stable. If the instability of the grid-connected inverter system is increased by controlling the initial value to change in the first direction, the initial value is controlled to change in a second direction until the grid-connected inverter system is stable. The first direction is opposite to the second direction.

7. The feedforward control method of the grid-connected inverter according to claim 1, characterized in that: The feedforward control method of the grid-connected inverter also includes: multiplying the common coupling point voltage by a weighting coefficient to obtain a weighted common coupling point voltage; The step of low-pass filtering the common coupling point voltage to obtain a first feed-forward voltage component comprises: Performing low-pass filtering on the weighted common coupling point voltage to obtain a first feedforward voltage component; The step of high-pass filtering the common coupling point voltage to obtain a second feed-forward voltage component comprises: High-pass filtering the weighted common coupling point voltage to obtain a second feedforward voltage component; Among them, the weighting coefficient is K is the common coupling point voltage proportional feedforward coefficient, K PWM is the equivalent gain of the grid-connected inverter.

8. The feedforward control method of the grid-connected inverter according to claim 7, characterized in that: The transfer function of the feedforward voltage is: Among them, G v V is the feedforward voltage, G Lp is the transfer function of the low-pass filter, G Hp is the transfer function of the high-pass filter.

9. A computer-readable storage medium storing a computer program, characterized in that: When the program is executed by a processor, the feedforward control method of the grid-connected inverter as claimed in any one of claims 1 to 8 is implemented.

10. A feedforward control device for a grid-connected inverter, characterized in that: include: A common coupling point voltage acquisition module, used to acquire the common coupling point voltage of the common coupling point; a low-pass filtering module, electrically connected to the common coupling point voltage acquisition module, and configured to perform low-pass filtering on the common coupling point voltage to obtain a first feedforward voltage component; a high-pass filtering module, electrically connected to the common coupling point voltage acquisition module, and configured to perform high-pass filtering on the common coupling point voltage to obtain a second feedforward voltage component; A first adding and subtracting module, configured to add the first feedforward voltage component and the second feedforward voltage component to obtain a feedforward voltage; An output control unit is used to control the grid-connected inverter using the feed-forward voltage.

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