Multi-peak MPPT control method based on global scanning for micro inverters

Abstract

The present invention relates to a multi-peak MPPT control method based on global scanning for a micro-inverter, and belongs to the field of photovoltaic technology. The method of the invention first applies the perturbation observation method to find the first power peak point Pmpp1; then adopts the global scanning method to scan from Umpp1 to the direction of voltage reduction, find multiple power peak points Pmpp2 and Umpp2, determine the peak point Pmpp with the maximum power and the corresponding voltage value Umpp; finally, at the voltage value Umpp position, the curve is tracked by the small step perturbation observation method to obtain the global maximum power Pmax. Compared with the traditional single-peak MPPT algorithm, the method of the present invention can avoid falling into a local optimal solution, so that the MPPT efficiency of the micro-inverter reaches 99% or more. Compared with other multi-peak MPPT algorithms, the method of the present invention is simple in logic, and no additional hardware equipment needs to be installed to detect changes in photovoltaic components. Therefore, the application cost is low, the application method is simple, and the application range is wider.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, in particular to the field of inverter control method technology, and specifically refers to a multi-peak MPPT control method based on global scanning for a micro inverter. Background Art

[0002] Photovoltaic arrays are easily affected by the environment during use, such as clouds, buildings or trees, and dust on the surface of the panels, which results in a reduction in the output power of the photovoltaic array. In order to achieve the maximum output power, the photovoltaic inverter control in the prior art adopts MPPT (Maximum Power Tracking).

[0003] Common single-peak MPPT algorithms include perturbation observation method, conductance increment method, short-circuit pulse method, etc.

[0004] When a photovoltaic array composed of multiple photovoltaic cells connected in series is partially blocked, the PU curve of the photovoltaic array will have a local maximum power point. At this time, if the MPPT algorithm based on the photovoltaic array PU curve with a single peak shape is used, misjudgment may occur. Therefore, it is necessary to study the MPPT method suitable for the local maximum power point situation, that is, the multi-peak MPPT algorithm. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a multi-peak MPPT control method based on global scanning for a micro inverter that can effectively track multiple peak points.

[0006] In order to achieve the above-mentioned purpose, the multi-peak MPPT control method based on global scanning of the micro inverter of the present invention comprises the following steps:

[0007] (10) Use the perturbation observation method to find the first power peak point Pmpp1 of the micro inverter and record the voltage value Umpp1 here;

[0008] (20) Using a global scanning method, scanning from the voltage value Umpp1 in the direction of voltage reduction, finding multiple power peak points Pmpp2 and Umpp2, comparing the power peak point Pmpp2 with the first power peak point Pmpp1, and determining the peak point Pmpp with the maximum power and the corresponding voltage value Umpp;

[0009] (30) At the voltage value Umpp position, the curve is tracked by a perturbation observation method with a small step size, and the power peak around the Umpp position is obtained as the global maximum power Pmax.

[0010] In the multi-peak MPPT control method based on global scanning, the step (20) specifically includes:

[0011] (21) Scanning from the voltage value Umpp1 in the direction of voltage reduction, recording the power Pn and voltage Un at the location;

[0012] (22) Compare the power Pn with the voltage value Pmpp1. If Pn≥Pmpp1, record Pn at this moment as the power peak point Pmpp2, and the corresponding Un at this moment is Umpp2; if Pn<Pmpp1, discard this value;

[0013] (23) Scan until the short-circuit current position is reached, and determine the maximum power peak point Pmpp and the corresponding voltage value Umpp from the first power peak point Pmpp1 and each power peak point Pmpp2.

[0014] The multi-peak MPPT control method based on global scanning also includes: (40) when the power mutation is greater than the set value or a preset restart time has passed, returning to step (10) and restarting the method.

[0015] In the multi-peak MPPT control method based on global scanning, the power mutation greater than the set value is specifically:

[0016] The output power change value ΔP is greater than a preset value, where ΔP = |Pn-Pmax| / Pmax;

[0017] Among them, Pn is the current output power of the micro inverter, and Pmax is the global maximum power.

[0018] In the multi-peak MPPT control method based on global scanning, the preset value of the output power change value ΔP is 0.1.

[0019] The multi-peak MPPT control method based on global scanning of the micro-inverter of the invention is adopted. First, the perturbation observation method is applied to find the first power peak point Pmpp1 of the micro-inverter; then the global scanning method is adopted to scan from the voltage value Umpp1 of the first power peak point to the direction of voltage reduction, and multiple power peak points Pmpp2 and Umpp2 are found, and multiple power peak points are compared to determine the peak point Pmpp with the maximum power and the corresponding voltage value Umpp; finally, at the voltage value Umpp position, the curve is tracked by the perturbation observation method with a small step size to obtain the global maximum power Pmax. Compared with the traditional single-peak MPPT algorithm, the method of the present invention can avoid falling into the local optimal solution, so that the MPPT efficiency of the micro-inverter reaches 99% or more. Compared with other multi-peak MPPT algorithms, the method of the present invention has simple logic and does not need to install additional hardware equipment to detect changes in photovoltaic components. Therefore, the application cost is low, the application method is simple, and the application range is wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the multi-peak MPPT control method based on global scanning of the micro inverter of the present invention;

[0021] Figure 2 It is a flow chart of the multi-peak MPPT control method based on global scanning of the micro inverter of the present invention in practical application;

[0022] Figure 3 A schematic diagram of the test results of the first method of the present invention with two peak points;

[0023] Figure 4 A schematic diagram of the test results of the second method of the present invention with two peak points;

[0024] Figure 5 A schematic diagram of a third test result with two peak points using the method of the present invention;

[0025] Figure 6 A schematic diagram of the test results of the first method of the present invention with two peak points;

[0026] Figure 7 A schematic diagram of the second test result with 2 peak points using the method of the present invention. DETAILED DESCRIPTION

[0027] In order to more clearly understand the technical content of the present invention, the following embodiments are given in detail.

[0028] See also Figure 1 As shown, it is a flow chart of the multi-peak MPPT control method based on global scanning of the micro inverter of the present invention.

[0029] In one embodiment, the multi-peak MPPT control method based on global scanning of the micro inverter includes:

[0030] (10) Use the perturbation observation method to find the first power peak point Pmpp1 of the micro inverter and record the voltage value Umpp1 here;

[0031] (20) Using a global scanning method, scanning from the voltage value Umpp1 in the direction of voltage reduction, finding multiple power peak points Pmpp2 and Umpp2, comparing the power peak point Pmpp2 with the first power peak point Pmpp1, and determining the peak point Pmpp with the maximum power and the corresponding voltage value Umpp;

[0032] (30) At the voltage value Umpp position, the curve is tracked by a perturbation observation method with a small step size, and the power peak around the Umpp position is obtained as the global maximum power Pmax.

[0033] Wherein, the step (20) specifically includes:

[0034] (21) Scanning from the voltage value Umpp1 in the direction of voltage reduction, recording the power Pn and voltage Un at the location;

[0035] (22) Compare the power Pn with the voltage value Pmpp1. If Pn≥Pmpp1, record Pn at this moment as the power peak point Pmpp2, and the corresponding Un at this moment is Umpp2; if Pn<Pmpp1, discard this value;

[0036] (23) Scan until the short-circuit current position is reached, and determine the maximum power peak point Pmpp and the corresponding voltage value Umpp from the first power peak point Pmpp1 and each power peak point Pmpp2.

[0037] In a preferred embodiment, the multi-peak MPPT control method based on global scanning of the micro inverter of the present invention further includes the following steps:

[0038] (40) When the power mutation is greater than the set value or the preset restart time has passed, return to step (10) and restart the method.

[0039] The power mutation greater than the set value is specifically:

[0040] The output power change value ΔP is greater than a preset value, where ΔP = |Pn-Pmax| / Pmax;

[0041] Among them, Pn is the current output power of the micro inverter, and Pmax is the global maximum power.

[0042] Preferably, the preset value of the output power variation value ΔP is 0.1.

[0043] In practical applications, a flow chart of a multi-peak MPPT control method based on global scanning for a micro inverter of the present invention is provided.

[0044] Step 1: Use the perturbation observation method to find the first peak point

[0045] First, the first peak point Pmpp1 is detected using the conventional disturbance observation method, and the voltage value Umpp1 here is recorded.

[0046] Step 2: Global Scanning Method

[0047] At the Umpp1 voltage, scan in the direction of voltage reduction and record Pn and Un at this moment. Compare Pn and Pmpp1.

[0048] If Pn≥Pmpp1, then record Pn at this moment as Pmpp2 and Un as Umpp2.

[0049] If Pn<Pmpp1, discard this value and do not record it.

[0050] In this way, the scan is continued until the short-circuit current position is reached, which is the minimum voltage of the MPPT device, about 20V, so as to obtain larger Pmpp and Umpp.

[0051] Step 3: Apply the perturbation and observation method at the Umpp position

[0052] The system returns to the Umpp position and tracks the curve through the perturbation observation method with a small step size to obtain the peak value around the Umpp2 point, which is the final Pmax value, that is, the global maximum power point.

[0053] For photovoltaic modules on the market with an output power below 800W, the maximum number of bypass diodes is 3. When the cells of the photovoltaic module are partially blocked, there will be a maximum of 3 knee points on the UI characteristic curve of the entire photovoltaic array, and there may be 3 peak points on the corresponding PU characteristic curve.

[0054] Figures 3 to 5 The test results of 2 peak points can find the global maximum peak point.

[0055] Figure 3 The power difference between the two peak points is large, and the maximum peak point is at a smaller voltage, so it can be correctly tracked to MPP2.

[0056] Figure 4 The power difference between the two peak points is moderate, and the maximum peak point is at a larger voltage, so it can be correctly tracked to MPP1.

[0057] Figure 5 The power difference between the two peak points is small, and the maximum peak point is at a smaller voltage, so it can be correctly tracked to MPP2.

[0058] It can be obtained that no matter how much the power difference between the two peak points is, whether the maximum peak point is close to the open circuit voltage or far away from the open circuit voltage, it can be correctly tracked to the maximum peak point.

[0059] Figure 6 , Figure 7 The test results of 3 peak points can find the global maximum peak point.

[0060] Figure 6The maximum peak point of the three peak points is in the middle and can be correctly tracked to MPP2.

[0061] Figure 7 The maximum peak point of the three peak points is close to the open circuit voltage and can be correctly tracked to MPP2.

[0062] When external conditions change, the output PU curve will also change, and the position and power of the peak point will also change. It is necessary to re-track the global maximum peak point. Therefore, it is necessary to restart the global scanning algorithm. It mainly includes timed restart and power mutation restart.

[0063] 1. Scheduled restart

[0064] The light irradiance changes with time during the day, and the PU curve changes accordingly. Through the timed restart, the system timed restarts the global scanning algorithm. Using a photovoltaic simulator for testing, the restart interval is 5 minutes. The timed restart interval in the control method of this application can be set to 30 minutes.

[0065] 2. Power Sudden Restart

[0066] If the photovoltaic array is partially blocked by clouds, trees, etc., the power will change greatly, making the output power size ΔP,

[0067] ΔP=|Pn-Pmax| / Pmax;

[0068] Among them, Pn is the current output power of the micro inverter, and Pmax refers to the previously recorded global maximum peak point.

[0069] The criterion for power mutation is ΔP>0.1. When this criterion is met, the global scanning algorithm of the present invention is restarted.

[0070] Compared with the traditional single-peak MPPT algorithm, the multi-peak MPPT algorithm of the present invention can avoid falling into a local optimal solution, thereby making the MPPT efficiency of the micro-inversion reach 99% or more.

[0071] Compared with other multi-peak MPPT algorithms, the logic of the present invention is simple, and no additional hardware equipment is required to detect changes in photovoltaic modules. Although the scanning time of the global scanning algorithm is increased to about 3 to 5 seconds, the increased scanning time is negligible for a whole day's micro-inverter power generation.

[0072] The multi-peak MPPT control method based on global scanning of the micro-inverter of the invention is adopted. First, the perturbation observation method is applied to find the first power peak point Pmpp1 of the micro-inverter; then the global scanning method is adopted to scan from the voltage value Umpp1 of the first power peak point to the direction of voltage reduction, and multiple power peak points Pmpp2 and Umpp2 are found, and multiple power peak points are compared to determine the peak point Pmpp with the maximum power and the corresponding voltage value Umpp; finally, at the voltage value Umpp position, the curve is tracked by the perturbation observation method with a small step size to obtain the global maximum power Pmax. Compared with the traditional single-peak MPPT algorithm, the method of the present invention can avoid falling into the local optimal solution, so that the MPPT efficiency of the micro-inverter reaches 99% or more. Compared with other multi-peak MPPT algorithms, the method of the present invention has simple logic and does not need to install additional hardware equipment to detect changes in photovoltaic components. Therefore, the application cost is low, the application method is simple, and the application range is wider.

[0073] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it is apparent that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be regarded as illustrative rather than restrictive.

Claims

1. A multi-peak MPPT control method based on global scanning for a micro inverter, characterized in that: include: (10) Use the perturbation observation method to find the first power peak point Pmpp1 of the micro inverter and record the voltage value Umpp1 here; (20) Using a global scanning method, scanning from the voltage value Umpp1 in the direction of voltage reduction, finding multiple power peak points Pmpp2 and Umpp2, comparing the power peak point Pmpp2 with the first power peak point Pmpp1, and determining the peak point Pmpp with the maximum power and the corresponding voltage value Umpp; (30) At the voltage value Umpp position, the curve is tracked by a perturbation observation method with a small step size, and the power peak around the Umpp position is obtained as the global maximum power Pmax.

2. The multi-peak MPPT control method based on global scanning of the micro inverter according to claim 1 is characterized in that: The step (20) specifically includes: (21) Scanning from the voltage value Umpp1 in the direction of voltage reduction, recording the power Pn and voltage Un at the location; (22) Compare the power Pn with the voltage value Pmpp1. If Pn≥Pmpp1, record Pn at this moment as the power peak point Pmpp2, and the corresponding Un at this moment is Umpp2; if Pn<Pmpp1, discard this value; (23) Scan until the short-circuit current position is reached, and determine the maximum power peak point Pmpp and the corresponding voltage value Umpp from the first power peak point Pmpp1 and each power peak point Pmpp2.

3. The multi-peak MPPT control method based on global scanning of the micro inverter according to claim 1, characterized in that: The following steps are also included: (40) When the power mutation is greater than the set value or the preset restart time has passed, return to step (10) and restart the method.

4. The multi-peak MPPT control method based on global scanning of the micro inverter according to claim 3 is characterized in that: The power mutation greater than the set value is specifically: The output power change value ΔP is greater than a preset value, where ΔP = |Pn-Pmax| / Pmax; Among them, Pn is the current output power of the micro inverter, and Pmax is the global maximum power.

5. The multi-peak MPPT control method based on global scanning of a micro inverter according to claim 3, characterized in that: The preset value of the output power variation value ΔP is 0.1.

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