Current loop control method and system suitable for photovoltaic inverter grid connection

Abstract

The invention discloses a current loop control method and system suitable for grid connection of a photovoltaic inverter, and relates to the technical field of photovoltaic control, and the method comprises the steps: obtaining a three-phase current at a grid connection point, inputting the three-phase current into a pre-constructed Clark coordinate converter, and carrying out the coordinate conversion, and obtaining an alpha-axis current component and a beta-axis current component; the method comprises the following steps: acquiring a grid-connected point voltage, inputting the grid-connected point voltage into a pre-constructed voltage outer loop PI controller, enabling the grid-connected point voltage to enter a phase-locked loop through coordinate transformation to obtain a voltage deviation value, and obtaining reference current components of an alpha axis and a beta axis through PI control of the voltage deviation value; the current components of the alpha axis and the beta axis and the reference current components of the alpha axis and the beta axis are input into a pre-constructed nF-DPCI controller, a PWM modulation signal is output, the PWM modulation signal is input into a PWM generator to be modulated, a switching tube driving signal is obtained, and control over the current of the grid-connected inverter is achieved based on the switching tube driving signal.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic control technology, and in particular to a current loop control method and system suitable for photovoltaic inverter grid connection. Background Art

[0002] With the rapid expansion of solar photovoltaic (PV) power generation systems worldwide, PV system control has become a research focus. PV power generation systems are often connected to distribution networks via grid-connected inverters. Grid-connected inverters transmit power to the grid, while grid-connected current control is a key issue in the precise control of PV systems. Commonly used grid-connected current control methods include constant frequency hysteresis control, predictive control, repetitive control, single-cycle control, sliding mode control, feedback linearization control, deadbeat control, and proportional-integral control. Proportional-integral control, the most commonly used control method, is relatively simple in principle and design, and easy to implement.

[0003] The current inner loop, which uses proportional-integral current control, has infinite gain only for DC quantities. Positive-sequence AC signals appear as DC signals in the dq coordinate system. Therefore, a PI controller can accurately control positive-sequence AC signals. However, the coupling effect between the d-axis and q-axis currents in the dq coordinate system affects the dynamic characteristics of the current loop. Summary of the Invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the object of the present invention is to provide a current loop control method and system suitable for photovoltaic inverter grid connection.

[0005] In a first aspect, the purpose of the present invention can be achieved by the following technical solution: a current loop control method suitable for photovoltaic inverter grid connection, the method comprising the following steps:

[0006] Obtain the three-phase current at the grid connection point and input the three-phase current into the pre-built Clark coordinate converter for coordinate conversion to obtain the current components of the α-axis and β-axis;

[0007] Obtain the grid connection point voltage, input it into the pre-built voltage outer loop PI controller, and after coordinate transformation, enter the phase-locked loop to obtain the voltage deviation value. The voltage deviation value is used to obtain the reference current components of the α-axis and β-axis through PI control;

[0008] The current components of the α-axis and β-axis and the reference current components of the α-axis and β-axis are input into a pre-built nF-DPCI controller, which outputs a PWM modulation signal. The PWM modulation signal is input into a PWM generator for modulation to obtain a switch tube drive signal. Based on the switch tube drive signal, the current of the grid-connected inverter is controlled.

[0009] In combination with the first aspect, in certain implementations of the first aspect, the method further includes: the voltage outer loop PI controller is as follows:

[0010]

[0011] Where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain.

[0012] In combination with the first aspect, in certain implementations of the first aspect, the method further includes: the pre-constructed nF-DPCI controller is constructed based on the voltage outer loop PI controller by introducing a complex proportional integral link s-jω.

[0013] In combination with the first aspect, in certain implementations of the first aspect, the method further includes: the control transfer function of the nF-DPCI is:

[0014]

[0015] where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain, j is a complex unit, ω is the control frequency, and the grid frequency is f.

[0016] In combination with the first aspect, in some implementations of the first aspect, the method further includes: N =2πf,K p =k·L,K i =k·R L Where L represents the filter inductor, R L is the equivalent resistance, and k is the controller gain.

[0017] In combination with the first aspect, in certain implementations of the first aspect, the method further includes: a mathematical model of the grid-connected converter in a two-phase stationary α and β coordinate system:

[0018]

[0019] Where u α (t),u β (t) is the component of the converter output voltage on the α and β axes respectively; i α (t), i β (t) is the component of the converter output current on the α and β axes respectively.

[0020] In a second aspect, in order to achieve the above-mentioned object, the present invention discloses a current loop control system suitable for photovoltaic inverter grid connection, comprising:

[0021] The first conversion module is used to obtain the three-phase current at the grid connection point, input the three-phase current into a pre-built Clark coordinate converter for coordinate conversion, and obtain the current components of the α-axis and the β-axis;

[0022] The second conversion module is used to obtain the grid connection point voltage, input the grid connection point voltage into a pre-built voltage outer loop PI controller, enter the phase-locked loop after coordinate conversion to obtain the voltage deviation value, and obtain the reference current components of the α-axis and β-axis through the voltage deviation value through PI control;

[0023] The signal output module is used to input the current components of the α-axis and β-axis and the reference current components of the α-axis and β-axis into the pre-built nF-DPCI controller, output a PWM modulation signal, input the PWM modulation signal into the PWM generator for modulation, obtain the switch tube drive signal, and control the grid-connected inverter current based on the switch tube drive signal.

[0024] In conjunction with the second aspect, in certain implementations of the second aspect, the system further includes: a voltage outer loop PI controller of the second conversion module is as follows:

[0025]

[0026] Where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain;

[0027] The nF-DPCI controller pre-built in the signal output module is constructed based on the voltage outer loop PI controller by introducing the complex proportional integral link s-jω;

[0028] The control transfer function of nF-DPCI is:

[0029]

[0030] where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain, j is the complex unit, ω is the control frequency, and the grid frequency is f;

[0031] ω N =2πf,K p =k·L,K i =k·R L Where L represents the filter inductor, R L is the equivalent resistance, k is the controller gain;

[0032] The mathematical model of the converter connected to the grid by the first conversion module in the two-phase static α and β coordinate system is:

[0033]

[0034] Where u α (t),u β (t) is the component of the converter output voltage on the α and β axes respectively; i α (t), i β (t) is the component of the converter output current on the α and β axes respectively.

[0035] In another aspect of the present invention, in order to achieve the above-mentioned purpose, a terminal device is disclosed, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores a computer program capable of running on the processor, and when the processor loads and executes the computer program, it adopts the current loop control method suitable for photovoltaic inverter grid connection as described above.

[0036] In another aspect of the present invention, in order to achieve the above-mentioned purpose, a computer-readable storage medium is disclosed, in which a computer program is stored. When the computer program is loaded and executed by a processor, a current loop control method suitable for grid-connected photovoltaic inverters as described above is adopted.

[0037] This invention can directly process three-phase AC signals, avoiding the need to convert the signals to a dq coordinate system, and has excellent dynamic response and steady-state performance. Advantages include: eliminating the phase-locked loop (PLL), reducing errors caused by synchronization issues, avoiding loss of synchronization due to frequency or phase changes in microgrids, aviation applications, or remote networks, reducing control computational complexity, and being suitable for smaller, cost-sensitive systems (such as photovoltaic grid-connected converters). It also has better response to unbalanced grids and imperfect system inductance imbalances. Fractional-order control can estimate and compensate for disturbances online, significantly improving the system's transient response and tracking performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0039] Figure 1 It is a schematic flow chart of the method of the present invention;

[0040] Figure 2 This is a schematic diagram of the photovoltaic grid-connected inverter of the present invention;

[0041] Figure 3 Schematic diagram of the inverter control model based on current feedback decoupling of the present invention;

[0042] Figure 4 This is a schematic diagram of the nF-DPCI control principle of the present invention;

[0043] Figure 5 This is a schematic diagram of the three-phase grid-connected current of the present invention;

[0044] Figure 6 is the grid-connected phase current I a With phase voltage U a Schematic diagram;

[0045] Figure 7 Schematic diagram of the change of phase A current after disturbance in the present invention;

[0046] Figure 8 It is a schematic diagram of the system structure of the present invention. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0048] Example 1:

[0049] The following is an introduction to the relevant terms involved in the embodiments of this application:

[0050] Photovoltaic Inverter: A photovoltaic inverter (PV inverter or solar inverter) converts the variable DC voltage generated by photovoltaic (PV) solar panels into AC power at mains frequency, which can be fed back into the commercial transmission system or used in off-grid power grids. PV inverters are a key balance of system (BOS) component in PV array systems and can be used with conventional AC-powered equipment. Solar inverters have special features for PV arrays, such as maximum power point tracking and islanding protection.

[0051] like Figure 1 As shown, a current loop control method suitable for photovoltaic inverter grid connection includes the following steps:

[0052] S101: Obtain the three-phase current at the grid connection point, input the three-phase current into a pre-built Clark coordinate converter for coordinate conversion, and obtain the current components of the α-axis and β-axis;

[0053] Mathematical model of the grid-connected converter in the two-phase static α and β coordinate system:

[0054]

[0055] Where u α (t),u β (t) is the component of the converter output voltage on the α and β axes respectively; i α (t), i β (t) is the component of the converter output current on the α and β axes respectively.

[0056] Now define the complex vector f αβ =f α +jf β , so the voltage and current can be expressed in complex vector form:

[0057]

[0058] Will The formula is rewritten into vector form

[0059]

[0060] According to the transfer function of the converter in the two-phase coordinate system, it can be written as:

[0061]

[0062] The nF-DPCI current inner loop control transfer function is:

[0063]

[0064] After simplification, we can get:

[0065] The current loop closed-loop transfer function can be derived from the above formula:

[0066]

[0067] S102: Obtain the grid connection point voltage, input the grid connection point voltage into a pre-built voltage outer loop PI controller, enter the phase-locked loop after coordinate conversion to obtain a voltage deviation value, and obtain the reference current components of the α-axis and β-axis through the voltage deviation value through PI control;

[0068] The voltage outer loop PI controller is as follows:

[0069]

[0070] Where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, sλ is the fractional-order complex frequency domain.

[0071] S103: Input the current components of the α-axis and β-axis and the reference current components of the α-axis and β-axis into a pre-built nF-DPCI controller, output a PWM modulation signal, input the PWM modulation signal into a PWM generator for modulation, obtain a switch tube drive signal, and control the grid-connected inverter current based on the switch tube drive signal.

[0072] The pre-built nF-DPCI controller is constructed by introducing a complex proportional integral link s-jω into a voltage outer loop PI controller.

[0073] The control transfer function of the nF-DPCI is:

[0074]

[0075] where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain, j is a complex unit, ω is the control frequency, and the grid frequency is f.

[0076] The ω N =2πf,K p =k·L,K i =k·R L Where L represents the filter inductor, R L is the equivalent resistance, and k is the controller gain.

[0077] Specifically, the present invention will be further described below through examples:

[0078] according to Figure 4 Compared with the traditional controller, nF-DPCI control is a complex controller, which makes it difficult to implement the controller principle. However, the nF-DPCI control is based on the two-phase stationary coordinate system m α =jm β The relationship between , thus realizing the complex number j, that is, the amplitude remains unchanged and the phase rotates 90° in the positive direction.

[0079] according to Figure 5 、 Figure 6 The simulation results verify the dynamic performance of nF-DPCI. Figure 5 The three-phase grid-connected current waveform output by the photovoltaic grid-connected inverter shows that after the switch is closed at 0.02 seconds, the current reaches the steady-state value after about one cycle. Figure 6 The output current can quickly track the grid voltage phase by taking the phase A current and voltage in , thus achieving unity power factor grid-connected power generation. Figure 7In the figure, a disturbance of 0.1 second is applied at 0.6 second to simulate the power change of photovoltaic due to the change of external environment. It can be seen that after adopting the nF-DPCI current controller, the A phase current quickly recovers to the stable value, and the system has good dynamic stability and fast tracking performance.

[0080] Example 2: The second aspect, as Figure 8 As shown, in order to achieve the above-mentioned purpose, the present invention discloses a current loop control system suitable for photovoltaic inverter grid connection, comprising:

[0081] The first conversion module 11 is used to obtain the three-phase current at the grid connection point, input the three-phase current into a pre-built Clark coordinate converter for coordinate conversion, and obtain the current components of the α-axis and the β-axis;

[0082] The second conversion module 12 is used to obtain the grid connection point voltage, input the grid connection point voltage into a pre-built voltage outer loop PI controller, enter the phase-locked loop after coordinate conversion to obtain a voltage deviation value, and obtain the reference current components of the α-axis and β-axis through the voltage deviation value through PI control;

[0083] The signal output module 13 is used to input the current components of the α-axis and β-axis and the reference current components of the α-axis and β-axis into a pre-built nF-DPCI controller, output a PWM modulation signal, input the PWM modulation signal into the PWM generator for modulation, obtain a switch tube drive signal, and control the grid-connected inverter current based on the switch tube drive signal.

[0084] In conjunction with the second aspect, in certain implementations of the second aspect, the system further includes: the voltage outer loop PI controller of the second conversion module 12 is as follows:

[0085]

[0086] Where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain;

[0087] The nF-DPCI controller pre-built in the signal output module 13 is constructed based on the voltage outer loop PI controller by introducing a complex proportional integral link s-jω;

[0088] The control transfer function of nF-DPCI is:

[0089]

[0090] where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λis the fractional-order complex frequency domain, j is the complex unit, ω is the control frequency, and the grid frequency is f;

[0091] ω N =2πf,K p =k·L,K i =k·R L Where L represents the filter inductor, R L is the equivalent resistance, k is the controller gain;

[0092] The mathematical model of the grid-connected converter of the first conversion module 11 in the two-phase static α and β coordinate systems is:

[0093]

[0094] Where u α (t),u β (t) is the component of the converter output voltage on the α and β axes respectively; i α (t), i β (t) is the component of the converter output current on the α and β axes respectively.

[0095] Based on the same inventive concept, the present invention also provides a computer device, which includes: one or more processors and a memory for storing one or more computer programs; the program includes program instructions, and the processor is used to execute the program instructions stored in the memory. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is used to implement one or more instructions, specifically for loading and executing one or more instructions in a computer storage medium to implement the above method.

[0096] It should be further explained that, based on the same inventive concept, the present invention also provides a computer storage medium having a computer program stored thereon, which executes the above method when executed by a processor. The storage medium can be any combination of one or more computer-readable media. The computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electrical, magnetic, infrared, or semiconductor system, device or component, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In the present invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, device or component.

[0097] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0098] The above shows and describes the basic principles, main features and advantages of the present disclosure. Those skilled in the art should understand that the present disclosure is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present disclosure. Various changes and improvements may be made to the present disclosure without departing from the spirit and scope of the present disclosure, and such changes and improvements shall fall within the scope of the present disclosure.

Claims

1. A current loop control method suitable for photovoltaic inverter grid connection, characterized in that: The method comprises the following steps: Obtain the three-phase current at the grid connection point, input the three-phase current into the pre-built Clark coordinate converter for coordinate conversion, and obtain the current components of the α-axis and the β-axis; Obtain the grid connection point voltage, input the grid connection point voltage into the pre-built voltage outer loop PI controller, enter the phase-locked loop after coordinate conversion to obtain the voltage deviation value, and obtain the reference current components of the α-axis and β-axis through the voltage deviation value through PI control; The current components of the α-axis and β-axis and the reference current components of the α-axis and β-axis are input into a pre-built nF-DPCI controller to output a PWM modulation signal, which is input into a PWM generator for modulation to obtain a switch tube drive signal, and the current of the grid-connected inverter is controlled based on the switch tube drive signal.

2. A current loop control method suitable for photovoltaic inverter grid connection according to claim 1, characterized in that: The voltage outer loop PI controller is as follows: In the formula, K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain.

3. A current loop control method suitable for photovoltaic inverter grid connection according to claim 1, characterized in that: The pre-constructed nF-DPCI controller is constructed by introducing a complex proportional integral link s-jω into the voltage outer loop PI controller.

4. A current loop control method suitable for photovoltaic inverter grid connection according to claim 3, characterized in that: The control transfer function of the nF-DPCI is: Where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain, j is a complex unit, ω is the control frequency, and the grid frequency is f.

5. A current loop control method suitable for photovoltaic inverter grid connection according to claim 4, characterized in that: The ω N =2πf,K p = k·L,K i = k·R L Where L represents the filter inductor, R L is the equivalent resistance, and k is the controller gain.

6. A current loop control method suitable for photovoltaic inverter grid connection according to claim 1, characterized in that: The mathematical model of the grid-connected converter in the two-phase static α, β coordinate system is: Where u α (t),u β (t) is the component of the converter output voltage on the α and β axes respectively; i α (t), i β (t) are the components of the converter output current on the α and β axes respectively.

7. A current loop control system suitable for photovoltaic inverter grid connection, characterized in that: include: The first conversion module is used to obtain the three-phase current at the grid connection point, input the three-phase current into a pre-built Clark coordinate converter for coordinate conversion, and obtain the current components of the α-axis and the β-axis; The second conversion module is used to obtain the grid connection point voltage, input the grid connection point voltage into the pre-built voltage outer loop PI controller, enter the phase-locked loop after coordinate conversion to obtain the voltage deviation value, and obtain the reference current components of the α-axis and β-axis through the voltage deviation value through PI control; The signal output module is used to input the current components of the α-axis and β-axis and the reference current components of the α-axis and β-axis into a pre-built nF-DPCI controller, output a PWM modulation signal, input the PWM modulation signal into the PWM generator for modulation, obtain a switch tube drive signal, and control the current of the grid-connected inverter based on the switch tube drive signal.

8. A current loop control system suitable for photovoltaic inverter grid connection according to claim 7, characterized in that: The voltage outer loop PI controller of the second conversion module is as follows: In the formula, K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain; The nF-DPCI controller pre-built in the signal output module is constructed based on the voltage outer loop PI controller by introducing a complex proportional integral link s-jω; The control transfer function of nF-DPCI is: Where K p is the proportional coefficient of the controller, K i is the controller integral coefficient, s λ is the fractional-order complex frequency domain, j is a complex unit, ω is the control frequency, and the grid frequency is f; ω N =2πf,K p = k·L,K i = k·R L Where L represents the filter inductor, R L is the equivalent resistance, k is the controller gain; The mathematical model of the converter connected to the grid by the first conversion module in the two-phase static α, β coordinate system is: Where u α (t),u β (t) is the component of the converter output voltage on the α and β axes respectively; i α (t), i β (t) are the components of the converter output current on the α and β axes respectively.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: The memory stores a computer program that can be run on the processor. When the processor loads and executes the computer program, a current loop control method suitable for photovoltaic inverter grid connection according to any one of claims 1 to 6 is adopted.

10. A computer-readable storage medium having a computer program stored therein, characterized in that: When the computer program is loaded and executed by the processor, a current loop control method suitable for photovoltaic inverter grid connection according to any one of claims 1 to 6 is adopted.

Images