Nonlinear PID (Proportion Integration Differentiation) control method and system of photovoltaic power generation three-phase grid-connected inverter

Abstract

The invention relates to the technical field of grid-connected control, in particular to a nonlinear PID control method and system for a photovoltaic power generation three-phase grid-connected inverter, and the method comprises the steps: reducing an error signal e (t) through proportional, integral and differential links according to a PID control theory; in combination with a nonlinear control strategy, dynamically adjusted nonlinear gain k (e) is added in PID control; and a Popov stability criterion is introduced, so that the stability performance of the control system is ensured. The method has the beneficial effects that the electric energy quality of the three-phase grid-connected photovoltaic power generation system is ensured by adopting a method of combining the nonlinear gain based on the Popov stability criterion and the traditional PID controller design. And by taking a two-stage three-phase grid-connected inverter photovoltaic power generation system as an example, after a traditional PID controller and a nonlinear PID controller are analyzed, the nonlinear PID controller is improved on the basis of a Popov stability criterion, so that the stability performance of the control system is improved, and the stability of the control system is improved. Meanwhile, a design method for improving nonlinear gain parameters in the nonlinear PID controller is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected control, and in particular to a nonlinear PID control method and system for a photovoltaic power generation three-phase grid-connected inverter. Background Art

[0002] With the growth of global energy demand, solar energy, as a clean, abundant and easily accessible green energy, is gradually becoming the mainstream trend of new energy generation due to its pollution-free and easily accessible resources. However, the performance of photovoltaic power generation systems is significantly affected by meteorological conditions, showing nonlinearity, periodicity and volatility, which poses challenges to efficient control design. Although single-stage single-phase grid-connected technology is favored in residential low-voltage applications due to its cost-effectiveness and reliability, it is not suitable for mainstream power systems. In addition, although the dq0 conversion method can theoretically reduce current ripple and maintain unity power factor through adaptive nonlinear control, its complexity and lack of experimental verification limit its feasibility in practical applications. Therefore, in order to improve the power transmission efficiency of three-phase photovoltaic power generation systems, reduce the reactive power transmission of the power grid, and improve the overall efficiency of the power grid, it is necessary to further study and develop the control technology of three-phase photovoltaic power generation systems. Summary of the invention

[0003] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a nonlinear PID control method and system for a three-phase grid-connected photovoltaic power generation inverter, which can solve the problems mentioned in the background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter, comprising reducing an error signal e(t) through proportional, integral and differential links according to PID control theory;

[0008] Combined with nonlinear control strategy, dynamically adjusted nonlinear gain k(e) is added to PID control;

[0009] The Popov stability criterion is introduced to ensure the stability of the control system.

[0010] As a preferred solution of the nonlinear PID control method of the photovoltaic power generation three-phase grid-connected inverter of the present invention, the error signal e(t) is the difference between the reference signal r(t) and the output signal c(t).

[0011] As a preferred solution of the nonlinear PID control method of the photovoltaic power generation three-phase grid-connected inverter of the present invention, the nonlinear gain k(e) is designed using the ultra-stability criterion.

[0012] As a preferred solution of the nonlinear PID control method of the photovoltaic power generation three-phase grid-connected inverter of the present invention, the nonlinear gain k(e) is nonlinearly related to the error signal e(t) and is proportional to the exponential basis function a.

[0013] As a preferred solution of the nonlinear PID control method of the photovoltaic power generation three-phase grid-connected inverter of the present invention, wherein: the Bove stability criterion is used to ensure that the state vector of the control system remains bounded in a subset of all possible input sets.

[0014] As a preferred solution of the nonlinear PID control method of the photovoltaic power generation three-phase grid-connected inverter of the present invention, the control system includes a front-stage system control and a rear-stage system control.

[0015] As a preferred solution of the nonlinear PID control method of the photovoltaic power generation three-phase grid-connected inverter of the present invention, the latter system control includes voltage outer loop control and current inner loop control.

[0016] In a second aspect, the present invention provides a nonlinear PID control system for a photovoltaic power generation three-phase grid-connected inverter, comprising: a theoretical module for reducing an error signal e(t) through proportional, integral and differential links according to PID control theory;

[0017] Strategy module, used to combine nonlinear control strategy and add dynamically adjusted nonlinear gain k(e) in PID control;

[0018] The judgment module is used to introduce the Popov stability criterion to ensure the stability of the control system.

[0019] In a third aspect, the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0020] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above method when the computer program is executed by a processor.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: a method combining nonlinear gain based on Popov stability criterion with traditional PID controller design is adopted to ensure the power quality of the three-phase grid-connected photovoltaic power generation system. And taking a two-stage three-phase grid-connected inverter photovoltaic power generation system as an example, after analyzing the traditional PID controller and the nonlinear PID controller, the nonlinear PID controller is improved on the basis of the Popov stability criterion to improve the stability performance of the control system, and a detailed design method for the nonlinear gain parameter in the improved nonlinear PID controller is given. Furthermore, the method proposed by the present invention has the advantages of fast convergence and small oscillation, which reduces the reactive power transmission of the power grid and improves the efficiency of the power grid compared to the traditional PID control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0023] Figure 1 This is the traditional PID control transfer function diagram.

[0024] Figure 2 This is the traditional nonlinear PID control transfer function diagram.

[0025] Figure 3 This is the transfer function diagram of ultra-stable nonlinear PID control.

[0026] Figure 4 It is the overall control block diagram of nonlinear PID control for a two-stage photovoltaic power generation system.

[0027] Figure 5 This is the control structure diagram of the previous system.

[0028] Figure 6 A schematic diagram of the internal structure of a computer device. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] Example 1

[0033] Reference Figure 1 to Figure 5 , which is the first embodiment of the present invention, and which provides a nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter, comprising:

[0034] S1. According to PID control theory, the error signal e(t) is reduced through proportional, integral and differential links.

[0035] Furthermore, the error signal e(t) is the difference between the reference signal r(t) and the output signal c(t).

[0036] It should be noted that the action of the traditional linear PID controller is initiated by the input of the error signal e(t). When the error signal e(t) is input, the PID controller reduces the error through its control design of proportional, integral and differential links to achieve the required target output signal V c (t), the error signal expression e(t) is:

[0037] e(t)=r(t)-c(t) (1)

[0038] Target output signal V c (t) is linearly related to the error signal e(t), that is, V c (t)∝e(t), the relationship between the two is:

[0039]

[0040] S2. Combined with the nonlinear control strategy, a dynamically adjusted nonlinear gain k(e) is added to the PID control.

[0041] It should be noted that since traditional PID control design completely relies on gain adjustment, it is difficult to maintain the accuracy of the design. Therefore, it is necessary to reduce the complexity of gain adjustment through a nonlinear controller.

[0042] Furthermore, the nonlinear gain k(e) is designed using the ultrastability criterion.

[0043] S3. Introduce the Popov stability criterion to ensure the stability of the control system.

[0044] It should be noted that, considering the continuous time linear steady-state system, its equation can be expressed as:

[0045]

[0046] Among them, the input is u, the output is y, and the state variable is x.

[0047] Furthermore, the Bove stability criterion is used to ensure that the state vector of the control system remains bounded for a subset of all possible input sets.

[0048] It should be noted that the Popov stability criterion adopted in the present technical solution describes a characteristic of the system, which requires that when the input of the control system is limited to a subset of all possible input sets, the state vector of the system should remain bounded, then for all time quantities T, it should satisfy:

[0049]

[0050] Here, δ(||x(0)||) represents a positive constant that depends on the initial state x(0).

[0051] In order to keep the state vector bounded, for any input that satisfies the above restrictions, there exists a normal book K such that the state vector satisfies the following equation:

[0052] ||x(t)||≤K(||x(t)||+δ) (5)

[0053] Further analysis of the nonlinear PID control method based on Popov's stability criterion, the output signal V c The relationship between (t) and the error signal e(t) is:

[0054]

[0055] Let ψ(e) = e(t)k(e), equation (6) can be rewritten as:

[0056]

[0057] In the formula, k p , k i and k d They represent the proportional, integral and differential control gains of the traditional linear PID controller respectively, y(e) represents the nonlinear function of the error, and k(e) represents the nonlinear gain.

[0058] The equivalent transfer function diagram of nonlinear PID control based on Popov stability criterion is as follows Figure 3 As shown, it is used to design the nonlinear gain parameter k(e). In summary, the upper transfer function expression of the system transfer function is:

[0059]

[0060] To ensure the asymptotic stability of the system, the lower transfer function m is set at a certain continuous time [t 0 , t p ] Domestic demand meets the following formula:

[0061]

[0062] in, Represents a positive definite number

[0063] Substituting ψ(e)=e(t)k(e) into equation (10), we can obtain:

[0064]

[0065] It should be further explained that the nonlinear gain parameter k(e) used in this scheme should be designed to meet the conditions given in equation (10), and its form can be any function of the error signal e(t). Furthermore, the nonlinear gain k(e) provides a larger gain for rapid convergence during system transient response, and reduces the gain to reduce the error during steady state.

[0066] Furthermore, the nonlinear gain k(e) is nonlinearly related to the error signal e(t) and is proportional to the exponential basis function a, that is, k(e)∝α e , the expression of nonlinear gain k(e) is:

[0067] k(e)=k n α e k n ,α≥0 (11)

[0068] The error expression when the range of a is wide is:

[0069]

[0070] Emax can be selected according to the system. Substituting equation (12) into equation (10), we can get:

[0071]

[0072] From formula (14), we can get:

[0073] k(e)=K n exp(elnα)K n ,α≥0 (15)

[0074] Substituting a=ln(a) into equation (15), we can obtain:

[0075] k(e)=K n exp(ae)K n ,α≥0 (16)

[0076] In the formula, K n and a are positive constants.

[0077] It should be noted that, through the derivation of the above theoretical formula, it can be known that the effective control of the system depends on the control of the error signal e(t). Therefore, when the error signal e(t) is too small, the nonlinear gain k(e) needs to be as small as possible to reduce the error. In order to further improve the efficiency of the nonlinear PID controller, it is given by a hyperbolic cosine function, as shown in the following formula:

[0078]

[0079] Here, a is a negative number, and a=-ln(a).

[0080] Furthermore, the control system includes a front-stage system control and a rear-stage system control.

[0081] It should be noted that the Figure 4 The two-stage three-phase grid-connected inverter control structure adopted in this scheme mainly includes photovoltaic array, Boost converter, three-phase inverter, LCL filter, grid voltage, front-stage system control and back-stage system control parts.

[0082] It should be further explained that Figure 5 This is the control structure diagram of the front-stage system: According to the photovoltaic voltage u output by the photovoltaic array pv and photovoltaic current i pv , after passing through the MPPT module, the photovoltaic voltage reference value u′ is obtained pv , and then compared with the actual photovoltaic voltage value u pv The error is input into the nonlinear PID control method based on Popov stability criterion proposed in this scheme. The output signal is modulated by PWM wave to obtain the switching signal of the power device of the Boost converter. At this point, the front-end system forms a complete closed-loop control.

[0083] Furthermore, the post-stage system control includes voltage outer loop control and current inner loop control.

[0084] It should be noted that the control of the subsequent system is similar. After the rotating coordinate system conversion, the nonlinear PID control method based on the Popov stability criterion proposed in this scheme is also used, and the control method is applied to the voltage outer loop and the current inner loop to finally obtain the PWM modulation wave required by the inverter.

[0085] In summary, the beneficial effect of the nonlinear PID control method of a three-phase grid-connected inverter for photovoltaic power generation of the present invention is that a method combining the nonlinear gain based on the Popov stability criterion with the traditional PID controller design is adopted to ensure the power quality of the three-phase grid-connected photovoltaic power generation system. And taking a two-stage three-phase grid-connected inverter photovoltaic power generation system as an example, after analyzing the traditional PID controller and the nonlinear PID controller, the nonlinear PID controller is improved on the basis of the Popov stability criterion to improve the stability performance of the control system, and a detailed design method of the nonlinear gain parameter in the improved nonlinear PID controller is given. Furthermore, the method proposed in the present invention has the advantages of fast convergence and small oscillation. Compared with the traditional PID control method, it reduces the reactive power transmission of the power grid and improves the efficiency of the power grid.

[0086] Example 2

[0087] This embodiment provides a nonlinear PID control system for a photovoltaic power generation three-phase grid-connected inverter, which includes a theoretical module for reducing an error signal e(t) through proportional, integral and differential links according to PID control theory;

[0088] Strategy module, used to combine nonlinear control strategy and add dynamically adjusted nonlinear gain k(e) in PID control;

[0089] The judgment module is used to introduce the Popov stability criterion to ensure the stability of the control system.

[0090] The above-mentioned unit modules may be embedded in or independent of a processor in a computer device in the form of hardware, or may be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above-mentioned modules.

[0091] Example 3

[0092] This embodiment provides a computer device, which may be a terminal, and its internal structure diagram may be as follows: Figure 6As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a nonlinear PID control method for a three-phase grid-connected inverter of photovoltaic power generation is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a key, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse.

[0093] This embodiment also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the following is achieved: according to the PID control theory, the error signal e(t) is reduced through proportional, integral and differential links; in combination with the nonlinear control strategy, a dynamically adjusted nonlinear gain k(e) is added to the PID control; and the Popov stability criterion is introduced to ensure the stability performance of the control system.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A nonlinear PID control method for a three-phase photovoltaic power generation grid-connected inverter, characterized in that: include, According to PID control theory, the error signal e(t) is reduced through proportional, integral and differential links; Combined with nonlinear control strategy, dynamically adjusted nonlinear gain k(e) is added to PID control; The Popov stability criterion is introduced to ensure the stability of the control system.

2. The nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter according to claim 1, characterized in that: The error signal e(t) is the difference between the reference signal r(t) and the output signal c(t).

3. The nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter according to claim 2, characterized in that: The nonlinear gain k(e) is designed using an ultrastability criterion.

4. The nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter according to claim 3, characterized in that: The nonlinear gain k(e) has a nonlinear relationship with the error signal e(t) and is proportional to the exponential basis function a.

5. The nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter according to claim 4, characterized in that: The Bove stability criterion is used to ensure that the state vector of the control system remains bounded over a subset of all possible input sets.

6. The nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter according to any one of claims 1 to 5, characterized in that: The control system includes a front-stage system control and a rear-stage system control.

7. The nonlinear PID control method for a photovoltaic power generation three-phase grid-connected inverter according to claim 6, characterized in that: The post-stage system control includes voltage outer loop control and current inner loop control.

8. A nonlinear PID control system for a three-phase photovoltaic power generation grid-connected inverter, characterized in that: include: Theoretical module, used to reduce the error signal e(t) through proportional, integral and differential links according to PID control theory; Strategy module, used to combine nonlinear control strategy and add dynamically adjusted nonlinear gain k(e) in PID control; The judgment module is used to introduce the Popov stability criterion to ensure the stability of the control system.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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