A control method and computer storage medium for a single-phase grid-connected inverter

Abstract

The present invention discloses a control method for a single-phase grid-connected inverter. The control method includes an asymmetric Park transformation combined with a notch filter control, an oscillation suppression link, and a sine pulse width modulation link. The asymmetric Park transformation combined with the notch filter control includes: performing a first Park transformation on the grid-connected current command signal and performing a notch filter process to obtain the dq components of the grid-connected current command; performing a second Park transformation on the grid-connected current signal and performing a notch filter process to obtain the dq components of the grid-connected current; performing a difference operation on the dq components of the grid-connected current command and the dq components of the grid-connected current, and performing a PI controller process, a decoupling process, and an inverse Park transformation. The control method of the present invention constructs an output current dq component control loop through the method of asymmetric Park transformation combined with a notch filter control, and realizes the suppression of the resonance peak of the LCL filter through the oscillation suppression link, thereby improving the control accuracy of the grid-connected current of the grid-connected inverter and the stability of the system.

Description

Technical Field

[0001] The present invention generally relates to the fields of new energy power generation, microgrids and smart grids. More specifically, the present invention relates to a control method for a single-phase grid-connected inverter and a computer-readable storage medium. Background Art

[0002] A single-phase grid-connected inverter is an important component of a new energy power generation and energy storage system in a microgrid system. It converts DC electrical energy into high-quality AC electrical energy and feeds it into the grid. As an energy conversion interface between energy storage and the AC grid, the grid-connected inverter plays a crucial role in the stable and reliable operation of the microgrid system. Currently, single-phase grid-connected inverters are mainly used in microgrid systems with relatively small capacities and generally adopt a pulse width modulation (PWM) strategy. This strategy results in a large number of switching frequency harmonics in the PWM voltage output by the inverter, which affects the quality of the grid-connected current. Therefore, in order to effectively suppress the switching harmonics of the grid-connected current, an LCL-type filter is generally adopted at the output end of the grid-connected inverter. Nevertheless, there are still some problems during the operation of the single-phase grid-connected inverter, mainly manifested in the following two aspects.

[0003] Firstly, due to the frequency response of the LCL-type filter having a resonance peak and its phase undergoing a -180° jump at the resonance frequency, if this resonance peak cannot be effectively suppressed, it may cause the output current of the grid-connected inverter to oscillate and even ultimately lead to system instability. Secondly, for the grid-connected current control system using a single-phase grid-connected inverter, those skilled in the art often adopt methods such as PI control or proportional resonance control to improve the signal quality, but both have their limitations. On the one hand, the PI controller cannot achieve zero-static-error tracking of AC signals; on the other hand, the proportional resonance controller has disadvantages such as difficult parameter tuning and poor stability margin of the control system.

[0004] In response to the above problems, although some improvement measures have been proposed in the prior art, there are still some defects, such that only using a PI controller or a proportional resonance controller cannot be widely applied. For example, in response to the stability problem caused by the resonance peak of the LCL filter, those skilled in the art have proposed a method of passive damping by connecting a resistor in series or in parallel at the inductor L1, L2 or capacitor C (refer to 301 in the appendix Figure 3 . However, this method will increase the volume of the equipment on the one hand and also increase the loss of the inverter on the other hand, and thus has not been widely applied. In addition, in order not to affect the working efficiency of the inverter, those skilled in the art have proposed an active damping method based on state variable feedback. Although this method can effectively suppress the resonance peak, it requires adding a current transformer, thus increasing the cost of the system. Summary of the Invention

[0005] To solve one or more of the problems in the above background art, the present invention provides a control method for a single-phase grid-connected inverter. Thus, the control method of the present invention proposes an asymmetric Park transformation combined with a notch filter control technique. In this technique, the grid-connected current of the single-phase grid-connected inverter is respectively processed by asymmetric Park transformation and notch filter H n (s) filtering, so as to construct the dq components i d and i q of the output current, and a PI controller is used to construct the i d and i q control loops. This technique constructs the dq components of the single-phase grid-connected current in a DC form and uses a traditional PI controller to achieve the static error-free control of the dq components of the grid-connected current, thereby improving the quality of the grid-connected current and the power factor, and ultimately improving the stability of the control system. For this reason, the present invention provides solutions through the following multiple embodiments.

[0006] Specifically, on the one hand, the present invention discloses a control method for a single-phase grid-connected inverter, wherein the single-phase grid-connected inverter includes a single-phase full bridge and an LCL filter. The control method includes an asymmetric Park transformation combined with a notch filter control, an oscillation suppression link, and a sinusoidal pulse width modulation link, wherein the asymmetric Park transformation combined with a notch filter control includes the following steps: performing a first Park transformation on the grid-connected current command signal; in response to the first Park transformation, performing a first filtering process on its output signal through a notch filter to obtain the dq components of the grid-connected current command; performing a second Park transformation on the grid-connected current signal; in response to the second Park transformation, performing a second filtering process on its output signal through a notch filter to obtain the dq components of the grid-connected current; performing a difference operation on the dq components of the grid-connected current command and the dq components of the grid-connected current to obtain an error signal; processing the error signal through a PI controller and performing decoupling processing; and in response to the decoupling processing, performing an inverse Park transformation on the output signal after the decoupling processing.

[0007] In one embodiment, the oscillation suppression link includes the following steps: in response to the inverse Park transformation, performing first weighted delay, second weighted delay, and third weighted delay operations on its output signal respectively to obtain a first weighted delay signal, a second weighted delay signal, and a third weighted delay signal; and performing a summation operation on the first weighted delay signal, the second weighted delay signal, and the third weighted delay signal.

[0008] In another embodiment, the delay time of the first weighted delay is 0; the delay angle of the third weighted delay is ψ3, and its delay time is kψ3 / ω d where ω dis the damping oscillation angular frequency of the LCL filter, and k is the variation coefficient considering the inductance value change of the inductance element under different operating powers of the grid-connected inverter; the delay angle of the second weighted delay whose delay time is ψ2 / ω d .

[0009] In another embodiment, it is set that where P N is the rated power of the single-phase grid-connected inverter, P is the actual output power of the single-phase grid-connected inverter, and the value ranges of the coefficients ρ and m are set as ρ ∈ [1.5, 2.5] and m ∈ [1.1, 1.4].

[0010] In one embodiment, A2 is set to a negative value, and according to the constraint relation (1), the weighting coefficient A1 of the first weighted delay, the weighting coefficient A2 of the second weighted delay, and the weighting coefficient A3 of the third weighted delay are solved

[0011]

[0012] wherein ζ is the damping coefficient of the LCL filter.

[0013] On the other hand, the present invention also discloses a computer-readable storage medium, on which program instructions for controlling a single-phase grid-connected inverter are stored. When the program instructions are executed by a processor, it enables the implementation of the above control method.

[0014] As can be seen from the solutions described in the above multiple embodiments, the present invention ingeniously designs the construction method of the dq components of the grid-connected current and carefully sets multiple parameters of multiple delay units. In these control processes, the present invention ingeniously combines multiple Park transformations and inverse Park transformations, proportional-integral operations, decoupling operations, notch filtering, and delays, etc., so that the technical solution of the present invention not only perfectly solves the influence of each harmonic on the single-phase grid-connected inverter, but also enhances the robustness of the single-phase grid-connected inverter to parameter improvements in grid-connected current quality and power factor changes, so that the system including the single-phase grid-connected inverter can output high-quality electric energy, and finally ensures the safe and stable operation of the microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] By reading the following detailed description with reference to the accompanying drawings, the above features and advantages of the present invention can be better understood, and its numerous objects, features, and advantages are obvious to those skilled in the art. The accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts, where

[0016] Figure 1 is an overall block diagram showing a control method for a single-phase grid-connected inverter according to an embodiment of the present invention;

[0017] Figure 2 is a flowchart showing an asymmetric Park transformation combined with a notch filter control method according to an embodiment of the present invention;

[0018] Figure 3 is a schematic circuit diagram showing a control method for a single-phase grid-connected inverter according to an embodiment of the present invention;

[0019] Figure 4 is a flowchart showing an oscillation suppression link according to an embodiment of the present invention; and

[0020] Figure 5 is a schematic diagram showing an oscillation suppression link according to an embodiment of the present invention. Detailed implementation manners

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0022] Figure 1 is an overall block diagram showing a control method 100 for a single-phase grid-connected inverter according to an embodiment of the present invention.

[0023] As Figure 1 shown, the control method 100 for a single-phase grid-connected inverter of the present invention may include steps S101, S102, and S103. First, the process of the control method 100 starts from step S101. At this step, an asymmetric Park transformation combined with a notch filter control process is performed to construct the dq components i d and i q , and a PI controller is used to construct i d and i qThe control loop simultaneously implements the decoupling process during this process. Then, the control method 100 executes step S102. At this step, the signal output by step S101 enters the oscillation suppression link. During the operation of this link, through multiple delay operations, the resonance peak of the LCL filter is suppressed, thereby improving the control accuracy of the grid-connected current of the grid-connected inverter and the stability of the system. Finally, the control method 100 terminates at step S103. At this step, the signal output by step S102 is subjected to sinusoidal pulse width modulation (SPWM), and finally the drive signal for controlling 4 IGBT devices is output, thereby realizing the control of the electrical energy output by the single-phase grid-connected inverter.

[0024] Figure 2 is a flowchart showing the asymmetric Park transformation combined with notch filter control method 200 according to an embodiment of the present invention. Figure 3 is a schematic diagram of circuit 300 of the control method for a single-phase grid-connected inverter according to an embodiment of the present invention. It can be understood that Figure 2 The flowchart of the asymmetric Park transformation combined with notch filter control method 200 corresponds to Figure 1 Step S101 of the overall block diagram of control method 100. Figure 3 The schematic diagram of circuit 300 is Figure 1 and Figure 2 The specific implementation manners, where 302 corresponds to S101 and 200; 303 corresponds to S102; 304 corresponds to S103. Further, in order to better understand the technical solution of the present invention, Figure 3 also shows a single-phase grid-connected inverter. In this scenario, the single-phase grid-connected inverter may include a single-phase full bridge and an LCL filter. Among them, the single-phase full bridge may include a DC-side filter capacitor C dc and 4 IGBT devices; the LCL filter may include a filter capacitor C and inductors L1 and L2, where L1 and L2 are the inverter-side and grid-side inductors respectively, C is the filter capacitor, i0 is the grid-side inductor current, U dc is the DC-side voltage, C dc is the DC-side capacitor, u ab is the inverter output voltage, v g is the grid voltage. The following combines Figure 2 and Figure 3 to describe in detail the asymmetric Park transformation combined with notch filter control principle of the present invention.

[0025] As Figure 2 and Figure 3 shown, the process of the asymmetric Park transformation combined with notch filter control method 200 of the present invention starts at step S201. At this step, the grid-connected current command signal is subjected to the first Park transformation. Specifically, first, the grid-connected current command signal Feed it into a Park transformation unit with a rotational frequency of the fundamental angular frequency ω, and take its α component as Take its β component as 0. Then, the method executes step S202. At this step, in response to the first Park transformation, the output signal thereof is subjected to first filtering processing through a notch filter to obtain the grid-connected current command dq components. Specifically, the d component and the q component output by the first Park transformation are respectively processed by the notch filter H n (s) to respectively obtain the grid-connected current command d component and the q component

[0026] On the other hand, simultaneously with step S201, the control method 200 process executes step S203. At this step, a second Park transformation is performed on the grid-connected current command signal. Specifically, the grid-connected current i0 is fed into a Park transformation unit with a rotational frequency of the fundamental angular frequency ω, and its α component is taken as i0, and its β component is taken as 0. Then, the control method 200 executes step S204. At this step, in response to the second Park transformation, the output signal thereof is subjected to second filtering processing through a notch filter to obtain the grid-connected current dq components. Specifically, the d component and the q component output by the second Park transformation are respectively processed by the notch filter H n (s) to respectively obtain the grid-connected current d component i d and the q component i q . In particular, in order to filter out the AC signal with a double fundamental frequency output by the Park transformation unit, the transfer function of the notch filter can be taken as whose central angular frequency ω0 = 2ω.

[0027] Next, the process of the control method 200 of the present invention proceeds to step S205. At this step, a subtraction operation is performed on the grid-connected current command dq components and the grid-connected current dq components to obtain an error signal. Specifically, and i d are subtracted to obtain the error signal e d ; at the same time, and i q are subtracted to obtain the error signal e q . Subsequently, the control method 200 executes step S206. At this step, the error signal is processed through a PI controller and decoupled. Specifically, the error signal e d is processed by the PI controller H d (s) to output the signal v d1 . Similarly, the error signal e q is processed by the PI controller H q (s) to output the signal v q1 . Further, in order to achieve decoupling, vd1 Subtract the product of the error signal e q and ωL to obtain the signal v d ; meanwhile, add v q1 to the product of the error signal e d and ωL to obtain the signal v q , thereby realizing the decoupling of the dq current control loop, where L = L1 + L2.

[0028] Finally, the process of the control method 200 of the present invention terminates at step S207. At this step, in response to the decoupling process, the output signal after the decoupling process is subjected to an inverse Park transformation. Specifically, the signals v d and v q are fed into an inverse Park transformation with a rotation frequency of ω to output the signals v α and v β . Further, v α is fed into an oscillation suppression link to output a modulation signal v. Subsequently, the signal v is further processed by a sinusoidal pulse width modulation (SPWM) link to output a drive signal for controlling the IGBT device of the single-phase grid-connected inverter, thereby controlling the operation of the single-phase grid-connected inverter.

[0029] Figure 4 is a flowchart showing the oscillation suppression link 400 according to an embodiment of the present invention; Figure 5 is a diagram showing the principle 500 of the oscillation suppression link according to an embodiment of the present invention. It can be understood that Figure 5 the diagram of the principle 500 of the oscillation suppression link is Figure 4 a specific implementation manner of the flowchart of the oscillation suppression link 400. The oscillation suppression process of the present invention will be described in detail below with reference to Figure 4 and Figure 5 .

[0030] As Figure 4 and Figure 5 shown, the process of the oscillation suppression link 400 of the present invention may include steps S401 - S404. First, the process of the oscillation suppression link 400 starts at step S401. At this step, in response to the inverse Park transformation, a first weighted delay operation is performed on its output signal to obtain a first weighted delay signal. Specifically, the output signal v α of the inverse Park transformation is processed by a weighted delay 1 module to obtain the signal v1, where the weighted delay 1 module performs a weighted process on the input signal v α , and the delay time is t1, and its output signal can be expressed as Where A1 is the weighting coefficient of the first weighted delay signal, and δ(t) is the impulse function. Similarly, simultaneously with step S401, at step S402, in response to the inverse Park transformation, the output signal thereof is subjected to a second weighted delay operation to obtain a second weighted delay signal. Specifically, the output signal v of the inverse Park transformation α is processed by the weighted delay 2 module to obtain the signal v2, where the weighted delay 2 module performs a weighting process on the input signal v α with a delay time of t2, and its output signal can be expressed as Where A2 is the weighting coefficient of the second weighted delay signal. Similarly, simultaneously with steps S401 and S402, at step S403, in response to the inverse Park transformation, the output signal thereof is subjected to a third weighted delay operation to obtain a third weighted delay signal. Specifically, the output signal v of the inverse Park transformation α is processed by the weighted delay 3 module to obtain the signal v3, where the weighted delay 3 module performs a weighting process on the input signal v α with a delay time of t3, and its output signal can be expressed as Where A3 is the weighting coefficient of the third weighted delay signal.

[0031] Finally, the process of the oscillation suppression link 400 terminates at step S404. At this step, the first weighted delay signal, the second weighted delay signal, and the third weighted delay signal are subjected to a summation operation. Specifically, the signals v1, v2, and v3 are subjected to a summation operation to output the signal v. Based on the above principle, the transfer function corresponding to the oscillation suppression link can be obtained as: Where s is a complex variable, ω n is the natural oscillation angular frequency of the LCL filter, and the damping coefficient of the LCL filter Where r is the equivalent resistance of the filter inductors L1 and L2.

[0032] Furthermore, in order to achieve fast suppression of the resonance peak of the LCL filter of the single-phase grid-connected inverter, the present invention sets the parameters of the above delay weighting link. Specifically, first, the delay time of the weighted delay 1 module is set to 0, that is, t1 = 0. Secondly, the delay angle of the weighted delay 3 module is set to ψ3, and its corresponding delay time t3 = kψ3 / ω d , where ω d is the damped oscillation angular frequency of the LCL filter, and k is the change coefficient considering the inductance value change of the inductor element under different operating powers of the grid-connected inverter. Let the delay angle of the weighted delay 2 module be ψ2, which can be calculated by the formula and its corresponding delay time t2 = ψ2 / ω d .

[0033] In one embodiment, the method for determining the k value is as follows: Generally, as the power increases, the inductance value shows a downward trend, thus affecting the calculation of the natural angular frequency ω. n To improve the accuracy of ω n it is possible to set where P N is the rated power of the grid-connected inverter, P is the output power of the grid-connected inverter, and the value ranges of the two coefficients ρ and m can be set as ρ ∈ [1.5, 2.5] and m ∈ [1.1, 1.4].

[0034] In another embodiment, the method for solving the delay weighting coefficient is as follows: To improve the rapidity of the control system, A2 can be set to a negative value. Further, the weighting coefficient can be solved according to the following constraint relation formula (1).

[0035]

[0036] Through calculation, it can be obtained that: where

[0037] Based on the above description, it can be understood that the present invention only describes the brief steps of a control method for a single-phase grid-connected inverter for the purpose of example and conciseness. However, according to different application scenarios, the control method for the single-phase grid-connected inverter may additionally include other steps. Additionally, based on the above description, those skilled in the art can understand that the above control method for the single-phase grid-connected inverter of the present invention can also be assisted by hardware or software instructions. Thus, on the one hand, when the control method for the single-phase grid-connected inverter is implemented by hardware, the present invention also discloses a new type of single-phase grid-connected inverter, which may include a single-phase full bridge, an LCL filter, an asymmetric Park transformation combined with a notch filter control module, an oscillation suppression link module, a sine pulse width modulation link module, etc. During the operation of this new type of single-phase grid-connected inverter, the present invention uses the aforementioned control method to control the above-mentioned various modules and units respectively, so as to achieve the output of high-quality electric energy by this new type of inverter. On the other hand, when the control method for the single-phase grid-connected inverter is implemented by software, the present invention also discloses a computer-readable storage medium, on which program instructions for controlling the single-phase grid-connected inverter are stored. When the program instructions are executed by a processor, it enables the implementation of the aforementioned control method for the single-phase grid-connected inverter of the present invention.

[0038] It should be understood that when terms such as "first", "second", "third", and "fourth" are used in the claims, the specification, and the drawings of the present invention, they are only used to distinguish different objects and not to describe a specific order. The terms "comprising" and "including" used in the specification and claims of the present invention indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0039] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification and claims of the present invention, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms. It should be further understood that the term "and / or" used in the specification and claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0040] As used in this specification and the claims, the term "if" can be interpreted as "when", "once", "in response to determining", or "in response to detecting" depending on the context. Similarly, the phrase "if determined" or "if [the described condition or event] is detected" can be interpreted as meaning "once determined", "in response to determining", "once [the described condition or event] is detected", or "in response to detecting [the described condition or event]" depending on the context.

[0041] Although the embodiments of the present invention are as described above, the above content is only an example used for facilitating the understanding of the present invention and is not intended to limit the scope and application scenarios of the present invention. Any person skilled in the art within the technical field of the present invention can make any modifications and changes in the form of implementation and details without departing from the spirit and scope disclosed by the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A control method for a single-phase grid-connected inverter, wherein the single-phase grid-connected inverter includes a single-phase full-bridge and an LCL filter, characterized in that, The control method includes an asymmetric Park transformation combined with a notch filter control, an oscillation suppression link, and a sine pulse width modulation link, wherein the asymmetric Park transformation combined with the notch filter control includes: Performing a first Park transformation on the grid-connected current command signal; In response to the first Park transformation, subjecting the output signal thereof to a first filtering process through a notch filter to obtain the dq components of the grid-connected current command; Performing a second Park transformation on the grid-connected current signal; In response to the second Park transformation, subjecting the output signal thereof to a second filtering process through a notch filter to obtain the dq components of the grid-connected current; Performing a difference operation on the dq components of the grid-connected current command and the dq components of the grid-connected current to obtain an error signal; Processing the error signal through a PI controller and performing a decoupling process; and In response to the decoupling process, performing an inverse Park transformation on the output signal after the decoupling process; Wherein, the oscillation suppression link includes: In response to the inverse Park transformation, respectively performing first weighted delay, second weighted delay, and third weighted delay operations on the output signal thereof to respectively obtain a first weighted delay signal, a second weighted delay signal, and a third weighted delay signal; and Performing a summation operation on the first weighted delay signal, the second weighted delay signal, and the third weighted delay signal; The delay time of the first weighted delay is 0; The delay angle of the third weighted delay is ψ3, and its delay time is kψ3 / ω d , where ω d is the damped oscillation angular frequency of the LCL filter, and k is the change coefficient considering the inductance value change of the inductance element under different operating powers of the grid-connected inverter; and The delay angle of the second weighted delay Its delay time is ψ2 / ω d ; Setting where P N is the rated power of the single-phase grid-connected inverter, P is the output power of the single-phase grid-connected inverter, and the value ranges of the coefficients ρ and m are set as ρ ∈ [1.5, 2.5], m ∈ [1.1, 1.4]; Setting A2 to a negative value, and solving the weighting coefficient A1 of the first weighted delay, the weighting coefficient A2 of the second weighted delay, and the weighting coefficient A3 of the third weighted delay according to the constraint relation formula (1); Among them, ζ is the damping coefficient of the LCL filter.

2. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores program instructions for controlling a single-phase grid-connected inverter, and when the program instructions are executed by a processor, the control method of claim 1 is implemented.

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