Photovoltaic network construction control method and device based on voltage amplitude self-adaptive regulation and control

Abstract

The invention discloses a photovoltaic network construction control method and device based on voltage amplitude self-adaptive regulation and control. The method comprises the following steps: acquiring an intermediate-stage direct-current voltage in a working process of a photovoltaic panel; the DC / DC module operates in an MPPT tracking mode when the intermediate-stage DC voltage is lower than a set threshold value, and is switched to a constant-voltage mode when the intermediate-stage DC voltage is lower than the set threshold value to limit photovoltaic output; and the DC / AC module adopts a modification droop control method based on voltage amplitude self-adaptive regulation and control, an amplitude control item is introduced in amplitude control, and the output amplitude of the DC / AC module is adjusted in real time according to the intermediate-stage DC voltage deviation, so that the photovoltaic converter can adaptively adjust the output voltage amplitude. According to the invention, when the photovoltaic output of the photovoltaic converter is sufficient, the AC voltage is independently constructed, and the network construction control is realized; and when the photovoltaic output is insufficient and cannot meet the load demand, the photovoltaic converter adaptively adjusts the amplitude of the output voltage and stabilizes the frequency of the output voltage at the same time.

Description

Technical Field

[0001] The present invention relates to a photovoltaic grid control method and device based on voltage amplitude adaptive regulation, and belongs to grid control technology in the field of new energy. Background Art

[0002] In recent years, photovoltaic power generation has become the form of renewable energy with the lowest cost per kilowatt-hour. Therefore, photovoltaic power generation has been widely used in microgrid systems and will occupy an even more important position in the field of microgrids. However, both the current grid-connected photovoltaic microgrid and the independent photovoltaic microgrid generally adopt a grid-following control strategy (which requires the external grid to provide clear voltage and frequency reference values). Both need to be connected to the main grid, which limits the application scenarios of photovoltaic microgrids. In other words, a strong grid is required as its support. In isolated grid conditions (such as islands, offshore platforms, and isolated grid power supply in remote areas), a starting power source such as a diesel generator or energy storage is required, and the starting power source is idle when the microgrid system is operating normally.

[0003] Grid-forming inverters, with their inertia characteristics similar to synchronous generators, can achieve self-synchronization by simulating their generation characteristics and synchronization mechanisms, without a phase-locked loop (PLL). They also output a given voltage amplitude and phase, providing stable frequency support for the system and enabling stable operation even without synchronous generators. These inverters have garnered significant industry attention in recent years. However, the randomness of photovoltaic output and the dynamic matching of loads remain core challenges in the implementation of grid-forming control technology. Currently, multi-timescale coordinated control requires integration with energy storage systems. Therefore, how to comprehensively consider physical constraints such as maximum photovoltaic output, operating range, and load size to achieve grid-forming control of photovoltaic inverters in isolated, off-grid conditions remains a hot topic in the field of renewable energy power generation control.

[0004] In response to the above-mentioned difficulties, the present invention designs a control strategy for photovoltaic power generation systems in low-voltage systems: First, for AC / DC converters, an improved grid-type droop control adaptive power cooperative control strategy based on DC voltage is designed, and a DC voltage control link is added to the control loop to achieve dynamic power balance between photovoltaic power generation and load absorption, and avoid voltage collapse caused by system power imbalance. Second, for DC / DC converters, an adaptive power cooperative control strategy based on intermediate-level DC voltage is designed to achieve dynamic power balance between photovoltaics and loads, and avoid voltage collapse caused by system power imbalance. The proposed method can solve the problems of stable system grid construction and dynamic power balance in low-voltage systems, such as in isolated microgrids, when photovoltaic output and load change, and provides a technical framework for stable operation of photovoltaic systems in low-voltage systems and cost reduction and efficiency improvement. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the existing technology and propose a photovoltaic grid control method and device based on voltage amplitude adaptive regulation. The photovoltaic power generation unit is connected to the island microgrid load through a DC / DC module and a DC / AC module. The adaptive voltage and frequency construction is achieved through a modified droop control method based on voltage amplitude adaptive regulation. When the photovoltaic power generation is insufficient, the output voltage amplitude can be adaptively adjusted.

[0006] The main technical solutions of the present invention include the following aspects: a photovoltaic grid control method based on voltage amplitude adaptive regulation, the method comprising:

[0007] (1) Obtaining the intermediate DC voltage during the operation of the photovoltaic panel;

[0008] (2) The DC / DC module of the photovoltaic grid operates in the MPPT tracking mode when the intermediate DC voltage is lower than the set threshold, and switches to the constant voltage mode when the intermediate DC voltage is lower than the set threshold to limit the photovoltaic output;

[0009] (3) The DC / AC module on the load side of the photovoltaic grid adopts a modified droop control method based on voltage amplitude adaptive regulation, specifically:

[0010] Frequency control equation: f=f*+m(QQ * )

[0011] Voltage control equation:

[0012] Among them, m is the frequency droop coefficient, n is the voltage droop coefficient, a is the amplitude compensation coefficient, P * , Q * are the active power reference value and reactive power reference value of the photovoltaic converter, P and Q represent the active power and reactive power output by the photovoltaic converter, V represents the output voltage amplitude of the photovoltaic converter, f represents the output voltage frequency of the photovoltaic converter, V * 、f * are the output voltage reference value and output frequency reference value of the photovoltaic converter respectively. dc is the DC voltage, V dc * is the DC voltage reference value.

[0013] Furthermore, the control logic of the DC / DC module is:

[0014] (1) The DC / DC module on the photovoltaic side When the maximum power tracking mode is running, It automatically switches to constant voltage mode to limit photovoltaic output; Indicates the intermediate DC voltage V dc The set threshold value;

[0015] (2) When the load power is lower than the maximum output power of the photovoltaic side When the load power exceeds the maximum output power of the photovoltaic side, the photovoltaic inverter can independently build the AC voltage to achieve grid control; when ... When the photovoltaic power generation fails to meet the load demand, the photovoltaic converter can adaptively adjust the output voltage amplitude while keeping the output voltage frequency stable and keeping the photovoltaic side in the maximum power output state.

[0016] Further, when When the reference power value is adjusted according to the linear relationship To limit the photovoltaic power output, k is the adaptive photovoltaic power limitation coefficient based on DC voltage.

[0017] Furthermore, the load of the photovoltaic grid is set as a pure resistive load.

[0018] Furthermore, in the modified droop control method based on adaptive regulation of voltage amplitude, the frequency is linearly related to reactive power, and the voltage amplitude is linearly related to active power; and in amplitude control, by introducing an amplitude control term, the output amplitude of the DC / AC module is adjusted in real time according to the intermediate-stage DC voltage deviation, so that the photovoltaic converter can adaptively adjust the output voltage amplitude.

[0019] Furthermore, the output voltage of the AC / DC converter is regulated according to the intermediate DC voltage during the operation of the photovoltaic panel. When the photovoltaic output fluctuates with the irradiance, the power balance between the photovoltaic side and the load is maintained to achieve grid-type control.

[0020] In the second aspect, the present invention also provides a photovoltaic grid control device based on adaptive regulation of voltage amplitude, comprising a memory and one or more processors, wherein the memory stores executable code, and when the processor executes the executable code, it implements the photovoltaic grid control method based on adaptive regulation of voltage amplitude.

[0021] In a third aspect, the present invention further provides a computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the photovoltaic grid control method based on adaptive voltage amplitude regulation.

[0022] In a fourth aspect, the present invention further provides a computer program product, comprising a computer program, which, when executed by a processor, implements the photovoltaic grid control method based on adaptive voltage amplitude regulation.

[0023] Beneficial effects of the present invention

[0024] 1. Traditional droop control is highly applicable in medium- and high-voltage power grids dominated by inductive impedance. However, in low-voltage systems with high line impedance, such as island microgrids, traditional droop control (Pf, QV) can be significantly less effective or even ineffective. Unlike traditional droop control, this invention incorporates DC voltage control into an improved droop control suitable for low-voltage systems. This allows low-voltage systems to achieve grid control without the need for energy storage, reducing configuration costs.

[0025] 2. The present invention realizes the dynamic power balance between photovoltaic output and load, and can quickly respond by adjusting frequency and voltage when photovoltaic output suddenly increases or decreases or load increases or decreases, ensuring the stable operation of the entire system. The designed photovoltaic grid control method based on voltage amplitude adaptive regulation can actively construct AC voltage, and realize grid operation without relying on external power grid or energy storage under light conditions, ensuring system voltage stability. When the photovoltaic output is insufficient to meet the load demand, the amplitude deviation is coupled with the intermediate-level DC voltage deviation, and the photovoltaic converter adaptively adjusts the output voltage amplitude, stabilizes the output voltage frequency, and maintains the maximum photovoltaic power output, ensuring the power balance between photovoltaic output and load. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the topology diagram of the photovoltaic grid control system based on adaptive voltage amplitude regulation.

[0027] Figure 2 Control strategy for DC / DC module and AC / DC module.

[0028] Figure 3 When the load increases, the DC voltage, AC voltage and frequency will change.

[0029] Figure 4 Changes in DC voltage, AC voltage and frequency are caused by changes in light amplitude.

[0030] Figure 5 This is a structural diagram of a photovoltaic grid control device based on voltage amplitude adaptive regulation provided by the present invention. DETAILED DESCRIPTION

[0031] To provide a more comprehensive and understandable understanding of the present invention, the following detailed description of the photovoltaic grid-connected control system based on adaptive voltage amplitude regulation is provided with reference to the accompanying figures. The core of this invention lies in the integration of an improved droop control strategy with an amplitude coordination mechanism based on intermediate DC voltage deviations to dynamically adjust the system amplitude and ensure stable operation under dynamic power fluctuations.

[0032] Figure 1This is the topology diagram of the photovoltaic grid control system under the low-voltage system. The system mainly consists of photovoltaic panels, DC / DC modules (integrated MPPT algorithm and voltage threshold control) and DC / AC modules. The DC / AC module uses LCL filter for progressive filtering, and the corresponding inductors and capacitors are L 2,3 and C, whose inductive capacitor voltage is V 01 .

[0033] Figure 2 The control strategy for the DC / DC module and DC / AC module includes the following steps:

[0034] DC / DC module control: The DC / DC module operates in MPPT tracking mode when the intermediate DC voltage is lower than the set threshold. When the intermediate DC voltage reaches or exceeds the set threshold, it automatically switches to constant voltage mode to limit the photovoltaic output. dc The reference value of photovoltaic output power is obtained by threshold limiting In MPPT mode, the output reference value is After real-time detection V PV and photovoltaic output power P PV , dynamically adjust PWM S1 The duty cycle of the photovoltaic panel always works at the intermediate DC voltage V dc A new maximum power point (MPP) within the threshold, maximizing energy capture efficiency.

[0035] The specific control logic is:

[0036] when When the MPPT algorithm is run, the photovoltaic output power is maximized;

[0037] when When the reference power value is adjusted, the switch is switched to the constant voltage mode. To limit the PV output power and prevent DC overvoltage, thus ensuring DC voltage stability. Where k is the adaptive PV power limit coefficient based on DC voltage.

[0038] DC / AC module control: The DC / AC module adopts a modified droop control method based on voltage amplitude adaptive regulation. The improved droop control is used in voltage control. Since the low-voltage system is resistive, the voltage amplitude is no longer linearly related to reactive power as in traditional droop control, but is linearly related to active power. On this basis, the DC side voltage deviation is introduced to dynamically adjust the system amplitude, ensuring the power balance between photovoltaic output and load. The details are as follows:

[0039] Taking the voltage at the common point with the load as the reference voltage E, the output voltage vector of the photovoltaic converter is V∠θ, and the impedance of the output line is expressed as Z=R+jX, where R is the line resistance, X is the line reactance, and the impedance angle is The output power of the photovoltaic converter is obtained as:

[0040]

[0041] Different from the situation in high-voltage transmission system where the output end is equivalent to a large inductor, that is, the resistance-to-inductance ratio R / X is very small, in low-voltage system, the line resistance is relatively large relative to the line inductance, that is, the resistance-to-inductance ratio R / X is very large. At this time, conventional droop control can no longer meet the control requirements of the low-voltage system. In order to simulate the situation where the resistance-to-inductance ratio is very large in the low-voltage system, the output line impedance is assumed to be purely resistive, that is, the output line impedance angle The output power of the photovoltaic inverter is simplified to the following power transmission equivalent model:

[0042]

[0043] When operating in steady state, the phase difference between the converter output voltage and the common point voltage is very small, that is:

[0044]

[0045] The output power of the photovoltaic inverter can be further simplified as:

[0046]

[0047] Where P and Q represent the active power and reactive power output by the converter, respectively; V is the voltage amplitude output by the converter; and θ is the voltage phase angle output by the converter.

[0048] In frequency control, frequency and reactive power are linearly related; in dual closed-loop control, the inner current loop realizes fast current tracking, and the outer voltage loop stabilizes the intermediate DC voltage V dc .

[0049] The specific control equation is:

[0050] Frequency control equation: f = f * +m(QQ * ), where m is the frequency droop coefficient;

[0051] Voltage control equation: Where n is the voltage droop coefficient, a is the voltage compensation coefficient;

[0052] Where, P * , Q *are the active power reference value and reactive power reference value of the photovoltaic converter, P and Q represent the active power and reactive power output by the photovoltaic converter, V represents the output voltage amplitude of the photovoltaic converter, f represents the output voltage frequency of the photovoltaic converter, V * 、f * are the output voltage reference value and output frequency reference value of the photovoltaic converter respectively. dc is the DC voltage, V dc * is the DC voltage reference value.

[0053] The above formula couples the amplitude deviation with the intermediate DC voltage deviation to dynamically adjust the system amplitude and ensure power balance between photovoltaic output and load.

[0054] Figure 3 Under the condition of constant photovoltaic irradiance, the increase of load causes the changes of DC voltage, AC voltage and frequency. Figure 3 (a) DC voltage V dc changes; Figure 3 (b) is the change of AC voltage V; Figure 3 (c) in the figure is the change of AC frequency f.

[0055] In the experiment, the load was set to increase in steps at 0.5s and 0.75s. At the beginning of the experiment (0.3-0.5s), the load was small and the maximum PV output was greater than the power required by the load. The PV side was in constant voltage mode, limiting the PV output to prevent DC overvoltage. The DC voltage, AC voltage, and AC frequency remained stable. At 0.5s, the load increased, causing the load to exceed the maximum PV output. At this time, the PV could not provide the power required by the load. The PV operated in MPPT tracking mode. Because the load exceeded the maximum PV output, it was unable to establish sufficient AC voltage and was in a step-down operation state. The AC and DC voltages remained stable after decreasing, and the AC frequency decreased after increasing and then stabilized. At 0.75s, the load increased again. At this time, the PV still could not provide the power required by the load. The AC and DC voltages remained stable after decreasing, and the AC frequency decreased after increasing and then stabilized.

[0056] Figure 4 Under the condition that the load size remains unchanged, the change of light amplitude causes the change of DC voltage, AC voltage and frequency. Figure 4 (a) DC voltage V dc changes; Figure 4 (b) is the change of AC voltage V; Figure 4 (c) in the figure is the change of AC frequency f.

[0057] In the experiment, the illumination amplitude was set to vary at intervals of 0.5s and 0.75s. At the beginning of the experiment (0.3-0.5s), the illumination intensity was sufficient, and the maximum PV output exceeded the load power requirement. The PV side operated in constant voltage mode, limiting PV output to prevent DC overvoltage. The DC voltage, AC voltage, and AC frequency remained stable. At 0.5s, the illumination amplitude decreased, causing the maximum PV output to fall below the load power requirement. At this point, the PV could no longer provide the required power, and the PV operated in MPPT tracking mode. Because the load exceeded the PV maximum output, it could not establish sufficient AC voltage and entered step-down operation. The AC and DC voltages remained stable after decreasing, while the AC frequency increased and then decreased before stabilizing. At 0.75s, the illumination amplitude returned to its initial state, meaning that the maximum PV output exceeded the load power requirement. The PV side resumed constant voltage mode, limiting PV output to prevent DC overvoltage. At this point, the AC and DC voltages returned to normal, and the AC frequency increased and then decreased before stabilizing.

[0058] In this embodiment, the PV load system can adaptively achieve power matching in the absence of energy storage in an isolated low-voltage system. When the maximum PV output exceeds the load, it can operate in constant voltage mode, limiting PV output and maintaining DC voltage. When the load exceeds the maximum PV output, it can automatically switch to MPPT tracking mode and adaptively switch to step-down operation. This system does not rely on communication and ensures real-time power balance between the PV and load.

[0059] Corresponding to the aforementioned embodiment of a photovoltaic grid-building control method based on voltage amplitude adaptive regulation, the present invention also provides an embodiment of a photovoltaic grid-building control device based on voltage amplitude adaptive regulation.

[0060] See also Figure 5 A photovoltaic grid control device based on adaptive regulation of voltage amplitude provided by an embodiment of the present invention includes a memory and one or more processors. The memory stores executable code. When the processor executes the executable code, it is used to implement a photovoltaic grid control method based on adaptive regulation of voltage amplitude in the above embodiment.

[0061] The embodiment of a photovoltaic grid control device based on adaptive voltage amplitude regulation provided by the present invention can be applied to any device with data processing capabilities, and the device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented through software, or through hardware or a combination of software and hardware. Taking software implementation as an example, as a device in a logical sense, it is formed by the processor of any device with data processing capabilities in which it is located reading the corresponding computer program instructions in the non-volatile memory into the memory for execution. From the hardware level, if Figure 5As shown in the figure, it is a hardware structure diagram of any device with data processing capability where a photovoltaic grid control device based on voltage amplitude adaptive regulation provided by the present invention is located. Figure 5 In addition to the processor, memory, network interface, and non-volatile memory shown, any device with data processing capabilities in which the apparatus in the embodiment is located may also include other hardware, generally based on the actual functions of the device with data processing capabilities, which will not be described in detail.

[0062] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0063] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present invention. A person of ordinary skill in the art can understand and implement the present invention without inventive work.

[0064] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, the photovoltaic grid control method based on voltage amplitude adaptive regulation in the above embodiment is implemented.

[0065] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the aforementioned embodiments, such as a hard disk or memory. The computer-readable storage medium may also be an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capabilities. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store data that has been output or is to be output.

[0066] The present invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the photovoltaic grid control method based on voltage amplitude adaptive regulation.

[0067] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A photovoltaic grid control method based on voltage amplitude adaptive regulation, characterized in that: The method includes: (1) Obtaining the intermediate DC voltage during the operation of the photovoltaic panel; (2) The DC / DC module of the photovoltaic grid operates in the MPPT tracking mode when the intermediate DC voltage is lower than the set threshold, and switches to the constant voltage mode when the intermediate DC voltage is lower than the set threshold to limit the photovoltaic output; (3) The DC / AC module on the load side of the photovoltaic grid adopts a modified droop control method based on voltage amplitude adaptive regulation, specifically: Frequency control equation: f = f * +m(QQ * ) Voltage control equation: Among them, m is the frequency droop coefficient, n is the voltage droop coefficient, a is the amplitude compensation coefficient, P * , Q * are the active power reference value and reactive power reference value of the photovoltaic converter, P and Q represent the active power and reactive power output by the photovoltaic converter, V represents the output voltage amplitude of the photovoltaic converter, f represents the output voltage frequency of the photovoltaic converter, V * 、f * are the output voltage reference value and output frequency reference value of the photovoltaic converter respectively. dc is the DC voltage, V dc * is the DC voltage reference value.

2. A photovoltaic grid control method based on voltage amplitude adaptive regulation according to claim 1, characterized in that: The control logic of the DC / DC module is: (1) The DC / DC module on the photovoltaic side When the maximum power tracking mode is running, It automatically switches to constant voltage mode to limit photovoltaic output; Indicates the intermediate DC voltage V dc The set threshold value; (2) When the load power is lower than the maximum output power of the photovoltaic side When the load power exceeds the maximum output power of the photovoltaic side, the photovoltaic inverter can independently build the AC voltage to achieve grid control; when ... When the photovoltaic power generation fails to meet the load demand, the photovoltaic converter can adaptively adjust the output voltage amplitude while keeping the output voltage frequency stable and keeping the photovoltaic side in the maximum power output state.

3. A photovoltaic grid control method based on voltage amplitude adaptive regulation according to claim 2, characterized in that: when When the reference power value is adjusted according to the linear relationship To limit the photovoltaic power output, k is the adaptive photovoltaic power limitation coefficient based on DC voltage.

4. A photovoltaic grid control method based on voltage amplitude adaptive regulation according to claim 1, characterized in that: The load of the photovoltaic grid is set as a pure resistive load.

5. The photovoltaic grid control method based on voltage amplitude adaptive regulation according to claim 1 is characterized in that: In the modified droop control method based on adaptive voltage amplitude regulation, the frequency is linearly related to reactive power, and the voltage amplitude is linearly related to active power. In amplitude control, an amplitude control term is introduced to adjust the output amplitude of the DC / AC module in real time according to the intermediate DC voltage deviation, so that the photovoltaic converter can adaptively adjust the output voltage amplitude.

6. The photovoltaic grid control method based on voltage amplitude adaptive regulation according to claim 1 is characterized in that: The output voltage of the AC / DC converter is regulated according to the intermediate DC voltage during the operation of the photovoltaic panel. When the photovoltaic output fluctuates with the irradiance, the power balance between the photovoltaic side and the load is maintained to achieve grid-type control.

7. A photovoltaic grid control device based on voltage amplitude adaptive regulation, comprising a memory and one or more processors, wherein the memory stores executable code, characterized in that: When the processor executes the executable code, a photovoltaic grid control method based on voltage amplitude adaptive regulation according to any one of claims 1 to 6 is implemented.

8. A computer-readable storage medium having a program stored thereon, characterized in that: When the program is executed by a processor, a photovoltaic grid control method based on voltage amplitude adaptive regulation according to any one of claims 1 to 6 is implemented.

9. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the photovoltaic grid control method based on voltage amplitude adaptive regulation according to any one of claims 1 to 6 is implemented.

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