Control method for single-phase grid-connected inverter and computer storage medium

Abstract

The invention discloses a control method for a single-phase grid-connected inverter. The control method comprises an asymmetric Park conversion and wave trap control combined link, an oscillation suppression link and a sine pulse width modulation link, and the asymmetric Park conversion and wave trap control combined link comprises the following steps: performing first Park conversion and wave trap processing on a grid-connected current instruction signal to obtain a grid-connected current instruction dq component; carrying out second Park conversion on the grid-connected current signal and carrying out trap filter processing to obtain a grid-connected current dq component; and performing differencing operation on the grid-connected current instruction dq component and the grid-connected current dq component, and performing PI controller processing, decoupling processing and inverse Park transformation. According to the control method, an output current dq component control loop is constructed through a method of combining asymmetric Park conversion with wave trap control, and suppression of the harmonic peak of the LCL filter is realized through an oscillation suppression link, so that the control precision of the grid-connected current of the grid-connected inverter and the stability of the system are improved.

Description

Technical Field

[0001] The present invention generally relates to the fields of renewable energy 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] The single-phase grid-connected inverter is an important component of the renewable energy generation and energy storage system in the microgrid system. It converts DC power into high-quality AC power and feeds it into the grid. As the energy conversion interface between energy storage and AC grid, the grid-connected inverter plays a vital role in the stable and reliable operation of the microgrid system. At present, the single-phase grid-connected inverter is mainly used in microgrid systems with smaller capacity, and generally adopts a pulse width modulation (PWM) strategy, which leads to a large number of switching frequency harmonics in the inverter output PWM voltage, which affects the quality of the grid-connected current. Therefore, in order to effectively suppress the switching harmonics of the grid-connected current, the output end of the grid-connected inverter generally adopts an LCL filter. Despite this, there are still some problems in the operation of the single-phase grid-connected inverter, which are mainly manifested in the following two aspects.

[0003] First, since there is a resonance peak in the frequency response of the LCL filter, its phase jumps by -180° at the resonance frequency. Therefore, if the resonance peak is not effectively suppressed, it may cause the output current of the grid-connected inverter to oscillate and even eventually lead to system instability. Secondly, for the grid-connected current control system using a single-phase grid-connected inverter, technical personnel in this field often use 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 tracking of the AC signal; on the other hand, the proportional resonance controller has the disadvantages of difficult parameter adjustment and poor control system stability margin.

[0004] Although some improvement measures have been proposed in the prior art to solve the above problems, there are still some defects, which make it difficult to widely use only PI controller or proportional resonant controller. For example, in order to solve the stability problem caused by the resonance peak of LCL filter, those skilled in the art have proposed a passive damping method of connecting a resistor in series or in parallel with the inductor L1, L2 or the capacitor C (see Appendix Figure 3 301 in ). However, this method will increase the size of the equipment on the one hand, and increase the loss of the inverter on the other hand, so it has not been widely used. In addition, in order not to affect the working efficiency of the inverter, technicians have proposed an active damping method based on state variable feedback. Although this method can effectively suppress the resonance peak, it requires the addition of a current transformer, thereby increasing the cost of the system. Summary of the invention

[0005] To solve one or more problems in the above background technology, the present invention provides a control method for a single-phase grid-connected inverter. Therefore, the control method of the present invention proposes an asymmetric Park transformation combined with a notch filter control technology. In this technology, the grid-connected current of the single-phase grid-connected inverter is respectively subjected to an asymmetric Park transformation and a notch filter H. n (s) filtering process, thereby constructing the output current dq component i d and i q , and use the PI controller to construct i d and i q Control loop. This technology improves the quality and power factor of the grid-connected current and ultimately improves the stability of the control system by constructing the dq component of the single-phase grid-connected current in direct current form and using a traditional PI controller to achieve zero-static-error control of the dq component of the grid-connected current. To this end, 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 the notch filter control includes the following steps: performing a first Park transformation on a 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 a grid-connected current command dq component; 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 a grid-connected current dq component; performing a difference operation on the grid-connected current command dq component and the grid-connected current dq component 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.

[0007] In one embodiment, the oscillation suppression link includes the following steps: in response to the inverse Park transform, performing the first weighted delay, the second weighted delay and the third weighted delay operations on its output signal respectively to obtain the first weighted delay signal, the second weighted delay signal and the third weighted delay signal respectively; and summing 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 damped oscillation angular frequency of the LCL filter, k is the coefficient of variation of the inductance value of the inductor element under different operating powers of the grid-connected inverter; the delay angle of the second weighted delay is Its delay time is ψ2 / ω d .

[0009] In yet another embodiment, setting 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 coefficients ρ and m are set to ρ∈[1.5, 2.5], m∈[1.1, 1.4].

[0010] In one embodiment, A2 is set to a negative value, and according to constraint equation (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] in, ζ is the damping coefficient of the LCL filter.

[0013] On the other hand, the present invention further 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, the above-mentioned control method is implemented.

[0014] It can be seen from the schemes described in the above multiple embodiments that the present invention cleverly 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 cleverly combines multiple Park transformations and inverse Park transformations, proportional integral operations, decoupling operations, notch filtering and delay processes, so that the technical solution of the present invention not only perfectly solves the impact of various harmonics on the single-phase grid-connected inverter, but also enhances the robustness of the single-phase grid-connected inverter for parameter improvement of 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 ensure the safe and stable operation of the microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] By reading the detailed description below with reference to the accompanying drawings, the above-mentioned features and advantages of the present invention can be better understood, and its many purposes, features and advantages are obvious to those skilled in the art. The drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work, among which:

[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 flow chart showing an asymmetric Park transform combined with a notch filter control method according to an embodiment of the present invention;

[0018] Figure 3 is a circuit schematic 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 flow chart showing an oscillation suppression link according to an embodiment of the present invention; and

[0020] Figure 5 2 is a schematic diagram showing a principle of an oscillation suppression link according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below 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, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within 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] like Figure 1 As 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 flow of the control method 100 starts at step S101. At this step, an asymmetric Park transformation combined with a notch filter control process is performed to construct an output current dq component i d and i q , and use the PI controller to construct i d and i qControl loop, and the decoupling process is realized in this process. Then, the control method 100 executes step S102. At this step, the signal output from step S101 enters the oscillation suppression link. During the operation of this link, multiple delay operations are performed to suppress the resonance peak of the LCL filter, 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 from step S102 is subjected to sinusoidal pulse width modulation (SPWM), and finally a drive signal for controlling four IGBT devices is output, thereby realizing the control of the output power of the single-phase grid-connected inverter.

[0024] Figure 2 FIG. 2 is a flow chart showing an asymmetric Park transform combined with a notch filter control method 200 according to an embodiment of the present invention. Figure 3 3 is a schematic diagram of a circuit 300 for a 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 flow chart of the asymmetric Park transform combined with notch filter control method 200 corresponds to Figure 1 The overall block diagram of the control method 100 is step S101. Figure 3 The schematic diagram of the circuit 300 is Figure 1 and Figure 2 Specific implementation method, wherein 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 A single-phase grid-connected inverter is also shown in FIG. In this scenario, the single-phase grid-connected inverter may include a single-phase full bridge and an LCL filter, wherein 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 capacitance, u ab is the inverter output voltage, v g is the grid voltage. Figure 2 and Figure 3 , the asymmetric Park transform combined with the notch filter control principle of the present invention is described in detail.

[0025] like Figure 2 and Figure 3 As shown, the asymmetric Park transformation combined with notch filter control method 200 of the present invention starts at step S201. In this step, the grid-connected current command signal is subjected to the first Park transformation. Specifically, the grid-connected current command signal is first The rotation frequency is sent to the Park transformation unit with the fundamental angular frequency ω, and its α component is taken as The β component is set to 0. Then, the method executes step S202. In this step, in response to the first Park transformation, the output signal is subjected to a first filtering process through a notch filter to obtain the grid-connected current command dq component. Specifically, the d component and q component output by the first Park transformation are respectively filtered through the notch filter H n (s) processing, thereby obtaining the grid-connected current command d component respectively and q component

[0026] On the other hand, at the same time as step S201, the control method 200 process executes step S203. At this step, the grid-connected current command signal is subjected to a second Park transformation. Specifically, the grid-connected current i0 is sent to a Park transformation unit whose rotation frequency is 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, its output signal is subjected to a second filtering process through a notch filter to obtain the grid-connected current dq component. Specifically, the d component and q component output by the second Park transformation are respectively passed through the notch filter H n (s) is processed to obtain the grid-connected current d component i d and q component i q In particular, in order to filter out the AC signal with twice the fundamental frequency output by the Park transform unit, the transfer function of the notch filter can be taken as The central angular frequency ω0=2ω.

[0027] Next, the process of the control method 200 of the present invention proceeds to step S205. In this step, the grid-connected current command dq component and the grid-connected current dq component are subjected to a difference operation to obtain an error signal. Specifically, and i d The error signal e is obtained by subtracting d ; At the same time and i q The error signal e is obtained by subtracting q Then, the control method 200 executes step S206. In this step, the error signal is processed by a PI controller and decoupled. Specifically, the error signal e d Through PI controller H d (s) is processed to output signal v d1 Similarly, the error signal e q Through PI controller H q (s) is processed to output signal v q1 Furthermore, in order to achieve decoupling, vd1 With the error signal e q and ωL to obtain the signal v d ; At the same time, v q1 With the error signal e d and ωL to obtain the signal v q , thereby achieving decoupling of the dq current control loop, where L=L1+L2.

[0028] Finally, the process of the control method 200 of the present invention ends at step S207. In this step, in response to the decoupling process, the output signal after the decoupling process is subjected to an inverse Park transform. Specifically, the signal v d and v q The inverse Park transform with a rotation frequency of ω is input to output the signal v α and v β . Further, v α The signal is sent to the oscillation suppression link to output the modulation signal v. Subsequently, the signal v is processed by the sinusoidal pulse width modulation (SPWM) link to output a driving 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 flow chart showing an oscillation suppression link 400 according to an embodiment of the present invention; Figure 5 500 is a diagram showing the principle of an oscillation suppression link according to an embodiment of the present invention. It can be understood that, Figure 5 The oscillation suppression principle diagram is Figure 4 The specific implementation method of the sway suppression link 400 flow chart. Figure 4 and Figure 5 The oscillation suppression process of the present invention is described in detail.

[0030] like Figure 4 and Figure 5 As shown, the oscillation suppression link 400 process of the present invention may include steps S401-S404. First, the oscillation suppression link 400 process starts at step S401. At this step, in response to the inverse Park transform, the output signal thereof is subjected to a first weighted delay operation to obtain a first weighted delay signal. Specifically, the inverse Park transform output signal v α After being processed by the weighted delay 1 module, the signal v1 is obtained, where the weighted delay 1 module processes the input signal v α After weighted processing and delay time t1, the 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, at the same time as step S401, in step S402, in response to the inverse Park transform, the output signal thereof is subjected to a second weighted delay operation to obtain a second weighted delay signal. Specifically, the inverse Park transform output signal v α After being processed by the weighted delay 2 module, the signal v2 is obtained, where the weighted delay 2 module processes the input signal v α After weighted processing, the delay time is t2, and the output signal can be expressed as Where A2 is the weighting coefficient of the second weighted delay signal. Similarly, at the same time as steps S401 and S402, at step S403, in response to the inverse Park transform, the output signal thereof is subjected to a third weighted delay operation to obtain a third weighted delay signal. Specifically, the inverse Park transform output signal v α After being processed by the weighted delay 3 module, the signal v3 is obtained, wherein the weighted delay 3 module processes the input signal v α After weighted processing and a delay time of t3, the output signal can be expressed as Wherein A3 is the weighting coefficient of the third weighted delay signal.

[0031] Finally, the process of the oscillation suppression link 400 ends at step S404. In this step, the first weighted delay signal, the second weighted delay signal and the third weighted delay signal are summed. Specifically, the signals v1, v2 and v3 are summed to output a 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 Damping factor of LCL filter Where r is the equivalent resistance of the filter inductors L1 and L2.

[0032] Furthermore, in order to achieve rapid suppression of the LCL filter resonance peak of the single-phase grid-connected inverter, the present invention sets the parameters of the above-mentioned 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 coefficient of variation of the inductance of the inductor under different operating powers of the grid-connected inverter. Assume that the delay angle of the weighted delay 2 module is ψ2, which can be obtained by the formula Calculated, the 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, thereby affecting the natural angular frequency ω n In order to improve ω n The accuracy can be 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 range of the two coefficients ρ and m can be set to ρ∈[1.5, 2.5], m∈[1.1, 1.4].

[0034] In another embodiment, the method for solving the delay weighting coefficient is as follows: In order 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 relationship formula (1).

[0035]

[0036] After calculation, we can get: in

[0037] Based on the above description, it can be understood that the present invention only describes a brief step of a control method for a single-phase grid-connected inverter for the purpose of example and simplicity, but according to different application scenarios, the control method of the single-phase grid-connected inverter can also additionally include other steps. In addition, based on the above description, those skilled in the art can understand that the above-mentioned control method for a single-phase grid-connected inverter of the present invention can also be assisted by hardware or software instructions. Therefore, on the one hand, when the control method for a single-phase grid-connected inverter is completed by hardware, the present invention also discloses a new type of single-phase grid-connected inverter, which can 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 and a sinusoidal pulse width modulation link module. In the process of operation of this new single-phase grid-connected inverter, the present invention uses the aforementioned control method to control each of the above modules and units respectively, so as to realize that the new inverter outputs high-quality electric energy. On the other hand, when the control method of the single-phase grid-connected inverter is completed 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 implements the aforementioned control method for the single-phase grid-connected inverter of the present invention.

[0038] It should be understood that when the terms "first", "second", "third" and "fourth" etc. are used in the claims, description and drawings of the present invention, they are only used to distinguish different objects, rather than to describe a specific order. The terms "include" and "comprise" used in the description 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 collections.

[0039] It should also be understood that the terms used in this 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 of the present invention and the claims, the singular forms of "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should also be further understood that the term "and / or" used in the specification of the present invention and the claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

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

[0041] Although the embodiments of the present invention are as described above, the contents are only examples used to facilitate understanding of the present invention, and are not intended to limit the scope and application scenarios of the present invention. Any technician in the technical field of the present invention can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed by the present invention, but the scope of patent protection of the present invention shall still be based on the scope defined by the attached claims.

Claims

1. A control method for a single-phase grid-connected inverter, wherein the single-phase grid-connected inverter comprises 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 sinusoidal pulse width modulation link, wherein the asymmetric Park transformation combined with a notch filter control includes: Performing a first Park transformation on the grid-connected current command signal; In response to the first Park transformation, the output signal thereof is subjected to a first filtering process through a notch filter to obtain a grid-connected current command dq component; Performing a second Park transformation on the grid-connected current signal; In response to the second Park transformation, performing a second filtering process on the output signal thereof through a notch filter to obtain a dq component of the grid-connected current; Performing a difference operation on the grid-connected current command dq component and the grid-connected current dq component to obtain an error signal; Processing the error signal through a PI controller and performing decoupling processing; and In response to the decoupling process, an inverse Park transform is performed on the output signal after the decoupling process.

2. The control method according to claim 1, characterized in that: The oscillation suppression link includes: In response to the inverse Park transform, performing first, second and third weighted delay operations on the output signal thereof to obtain first, second and third weighted delay signals, respectively; and The first weighted delayed signal, the second weighted delayed signal and the third weighted delayed signal are summed.

3. The control method according to claim 2, characterized in that: 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, k is the coefficient of variation of the inductance value of the inductor component 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 .

4. The control method according to claim 3, characterized in that: set up 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 coefficients ρ and m are set to ρ∈[1.5, 2.5], m∈[1.1, 1.4].

5. The control method according to claim 3, characterized in that: Set A2 to a negative value, and solve 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 constraint equation (1). in, ζ is the damping coefficient of the LCL filter.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores program instructions for controlling a single-phase grid-connected inverter. When the program instructions are executed by a processor, the control method according to any one of claims 1 to 5 is implemented.

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