Seamless maximum power point tracking control system for solar energy generation system

Abstract

The present invention has the effect of preventing discontinuous sections from occurring even when the MPPT mode is switched according to the reference voltage due to fluctuations in the solar cell voltage.

Description

Technology Field

[0001] The present invention relates to a non-interrupted maximum power point tracking control system for a photovoltaic power generation system. Background Technology

[0002] In general, due to the advantages of easy maintenance and long-term use, the installation of large-capacity solar power generation systems is increasing compared to other renewable energies, and accordingly, detailed research and development of the system are actively underway.

[0003] Among them, the output characteristics of the open-circuit voltage and short-circuit current of the solar panels in a photovoltaic power generation system change depending on changes in solar irradiance and temperature, and accordingly, the location of the maximum power output point where efficiency can be maximized also changes.

[0004] As the solar cell voltage fluctuates due to changes in the maximum power output point caused by changes in the external environment, the performance of the MPPT algorithm capable of operating at the maximum power output point is critical for photovoltaic power generation systems.

[0005] Therefore, high-efficiency operation can be achieved by selecting a standard for solar cell voltage based on changes in the external environment and using different MPPT modes and algorithms.

[0006] When MPPT mode switching is required while executing different MPPT algorithms according to the MPPT mode, discontinuities in solar cell voltage and current can have a significant impact on the photovoltaic power generation system. Therefore, there is a need for a seamless MPPT operation mode control technique that prevents fluctuations in solar cell voltage and current during switching. The problem to be solved

[0007] The purpose is to provide a seamless maximum power point tracking control system for a photovoltaic power generation system that prevents fluctuations in the voltage and current of the solar cell during switching, which has been devised to solve the problems described above. means of solving the problem

[0008] The objective of the present invention described above is to provide a non-interrupted maximum power point tracking control system for a photovoltaic power generation system, comprising: a solar cell array that produces power through solar energy; a first execution unit that performs MPPT (Maximum Power Point Tracking) in a first MPPT mode through duty control, and if the output voltage output from the solar cell array is greater than or equal to a reference voltage while operating in the first MPPT mode, switches to a second MPPT mode, sets the voltage at the time of switching to the second MPPT mode as the voltage command value of the DC connection unit, and performs an operation of fixing the duty to 0; and a second execution unit that performs MPPT in a second MPPT mode through voltage command value control of the DC connection unit, and if the output voltage output from the solar cell array is less than or equal to a reference voltage while operating in the second MPPT mode, switches to the first MPPT mode and performs an operation of increasing the voltage command value of the DC connection unit through a soft start. It includes a DC connection unit provided between the first performing unit and the second performing unit; wherein the first performing unit is a DC conversion unit that is any one of a single-phase boost converter, a multi-phase boost converter, and a 3-level boost converter, and the second performing unit is an AC conversion unit that is any one of a 2-level inverter, a 3-level inverter, a 3-phase inverter, a single-phase inverter, and a 3-phase 3-wire inverter.

[0009] In addition, the second execution unit is characterized by increasing the voltage command value of the DC connection unit linearly or non-linearly according to the characteristics of the output voltage output from the solar cell array for a certain period of time before switching to the first MPPT mode.

[0010] In addition, the second execution unit is characterized by increasing the duty cycle in proportion to the increase in the voltage command value of the DC connection unit to maintain the output voltage at the reference voltage. Effects of the invention

[0011] As described above, the present invention has the effect of preventing discontinuous sections from occurring even when the MPPT mode is switched according to the reference voltage due to fluctuations in the solar cell voltage.

[0012] In addition, by configuring a first execution unit and a second execution unit, there is an effect of efficiently preventing discontinuous sections from occurring even when the MPPT mode is switched according to the reference voltage. Brief explanation of the drawing

[0013] FIG. 1 is a configuration diagram showing a seamless maximum power point tracking control system according to one embodiment of the present invention. FIG. 2 is a graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system according to an embodiment of the present invention. FIG. 3 is another graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. FIG. 4 is another graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. FIG. 5 is another graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. FIG. 6 is a graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. FIG. 7 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. FIG. 8 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. FIG. 9 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system according to one embodiment of the present invention. Specific details for implementing the invention

[0014] Hereinafter, a non-interrupted maximum power point tracking control system for a photovoltaic power generation system according to an embodiment of the present invention will be described in detail with reference to the attached drawings.

[0015] FIG. 1 is a configuration diagram showing a seamless maximum power point tracking control system according to one embodiment of the present invention.

[0016] As illustrated in FIG. 1, a non-interrupted maximum power point tracking control system (simply put, non-interrupted maximum power point tracking control system) (100) for a photovoltaic power generation system according to one embodiment of the present invention may include a solar cell array (110), a first execution unit (130), a second execution unit (170), and a supply chain (190).

[0017] The non-interrupted maximum power point tracking control system (100) according to the present invention may include a two-stage power unit composed of a DC converter and an AC converter in order to expand the MPPT operating range of the solar cell array (110).

[0018] The present invention is a system (100) that eliminates discontinuous sections in voltage and current of a solar cell array (110) that appear during MPPT (Maximum Power Point Tracking) mode switching in a photovoltaic power generation system and switches without interruption.

[0019] The solar cell array (110) changes the output characteristics of the open-circuit voltage and short-circuit current of the solar cells according to changes in solar irradiance and temperature, and accordingly, the location of the maximum power output point that can maximize efficiency also changes.

[0020] In this way, the seamless maximum power point tracking control system (100) selects a reference voltage to distinguish MPPT modes for stable power supply because the solar cell voltage fluctuates due to changes in the maximum power output point depending on the external environment, and can eliminate discontinuous sections that appear during the switching process between each MPPT mode.

[0021] When the solar cell voltage increases above the reference voltage V2 in MPPT mode 1 (first MPPT mode), it switches to MPPT mode 2 (second MPPT mode), and when switching, the solar cell voltage at the moment of switching is set as the initial value of the DC link voltage controller.

[0022] When the solar cell voltage decreases to below the reference voltage V2 in MPPT mode 2, it switches to MPPT mode 1. When switching, the DC link voltage controller command increases from the reference voltage V2 to the reference voltage V1. Through a transition section in which the DC converter maintains the solar cell voltage at a constant reference voltage V2 through duty control, it is possible to enable seamless switching without discontinuity in the solar cell voltage and current.

[0023] Meanwhile, the above solar cell array (110) can produce energy through sunlight.

[0024] The above first execution unit (130) can receive power through solar energy and perform MPPT depending on whether the reference voltage is exceeded.

[0025] Here, the first performing unit (130) may be a DC converter.

[0026] The second execution unit (170) can receive energy through the solar cell array (110) and perform MPPT depending on whether the reference voltage is exceeded.

[0027] The above second execution unit (170) may be an AC converter.

[0028] Here, the second execution unit (170) can perform a second MPPT mode if the voltage supplied from the solar array (110) is greater than or equal to the reference voltage.

[0029] Meanwhile, a DC connection part (150) may be further provided between the first execution part (130) and the second execution part (170).

[0030] Here, the DC converter may be any one of a single-phase boost converter, a multi-phase boost converter, and a 3-level boost converter.

[0031] In addition, the above AC converter may be a 2-level inverter, a 3-level inverter, a 3-phase inverter, a single-phase inverter, or a 3-phase 3-wire inverter.

[0032] Meanwhile, FIG. 2 is a graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention, and FIG. 3 is another graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention.

[0033] In addition, FIG. 4 is another graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention, and FIG. 5 is another graph showing that a switching operation is performed when the solar cell voltage increases above a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention.

[0034] In addition, FIG. 6 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention, and FIG. 7 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention.

[0035] In addition, FIG. 8 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention, and FIG. 9 is another graph showing that a switching operation is performed when the solar cell voltage decreases to a reference voltage in a non-interrupted maximum power point tracking control system (100) according to one embodiment of the present invention.

[0036] As shown in FIGS. 2 to 9, when the solar cell voltage increases above the reference voltage V1, it exhibits a seamless switching operation in which it switches from MPPT mode 1 (first MPPT mode) to MPPT mode 2 (second MPPT mode).

[0037] In FIGS. 2 to 5, VDC, VPV, IPV, and Duty represent the voltage of the DC-Link section (DC connection section (150)) between the DC-DC power converter and the DC-AC power converter, the solar cell voltage, the solar cell current, and the duty command value of the DC-DC power converter, respectively.

[0038] In MPPT mode 1, the solar cell voltage increases due to the relationship between the input voltage and the output voltage as ΔDuty decreases, and when the reference voltage V1 or higher is reached, the MPPT mode is switched.

[0039] When switching modes, the solar cell voltage calculated in the existing MPPT mode 1 is set to the command value of the DC-Link voltage controller in MPPT mode 2, and the duty cycle is fixed at 0 to perform seamless switching operation, so that no discontinuous sections occur in the solar cell voltage and current.

[0040] In MPPT Mode 2, the maximum power output point is tracked by controlling the command value of the DC link voltage controller.

[0041] FIGS. 6 to 9 illustrate a seamless switching operation in which the solar cell voltage is switched from MPPT mode 2 to MPPT mode 1 when the solar cell voltage decreases to a reference voltage V2 or lower.

[0042] VDC, VPV, IPV, and Duty represent the voltage of the DC-Link section (DC connection section) between the DC-DC power converter and the DC-AC power converter, the solar cell voltage, the solar cell current, and the duty command value of the DC-DC power converter, respectively.

[0043] In order to track the lowered maximum power output point in MPPT mode 2, the solar cell voltage is reduced by ΔVpv, and when the reference voltage V2 or lower is reached, the system switches from MPPT mode 2 to MPPT mode 1.

[0044] When switching modes, the MPPT algorithm is not executed immediately in Mode 1, and the command value of the DC link voltage controller is increased from the current reference voltage V2 to the reference voltage V1 through a soft start. The soft start slope can be linear or non-linear depending on the solar cell characteristics.

[0045] The duty cycle is increased proportionally to the increase in the command value of the DC link voltage controller, based on the relationship between the solar cell input and output voltages, to maintain the solar cell voltage at the reference voltage V2.

[0046] Through this transition process, seamless switching is performed, and the maximum power output point is tracked without any discontinuities in solar cell voltage and current.

[0047] According to the present invention configured as described above, even if the MPPT mode is switched according to the reference voltage due to fluctuations in the solar cell voltage, no discontinuous section occurs.

[0048] In addition, the first execution unit (130) and the second execution unit (170) are configured so that even when the MPPT mode is switched according to the reference voltage, discontinuous sections do not occur efficiently.

[0049] Although a preferred embodiment of the present invention has been described above, it is clear that the present invention may use various variations, modifications, and equivalents, and that the above embodiment may be appropriately modified and applied in the same way. Therefore, the above description does not limit the scope of the present invention as defined by the limitations of the following claims. Explanation of the symbols

[0050] 100: System 110: Solar cell array 130: 1st Execution Unit 150: Connecting Unit 170: Second Execution Unit 190: Supply Chain

Claims

Claim 1 A non-interrupted maximum power point tracking control system for a photovoltaic power generation system comprises: a solar cell array that produces power through solar energy; a first execution unit that performs MPPT (Maximum Power Point Tracking) in a first MPPT mode through duty control, switches to a second MPPT mode if the output voltage output from the solar cell array is greater than or equal to a reference voltage while operating in the first MPPT mode, sets the voltage at the time of switching to the second MPPT mode as the voltage command value of the DC connection unit, and performs an operation of fixing the duty to 0; a second execution unit that performs MPPT in a second MPPT mode through voltage command value control of the DC connection unit, switches to the first MPPT mode if the output voltage output from the solar cell array is less than or equal to a reference voltage while operating in the second MPPT mode, and performs an operation of increasing the voltage command value of the DC connection unit through soft start; and a DC connection unit provided between the first execution unit and the second execution unit; wherein the first execution unit is a DC converter that is any one of a single-phase boost converter, a multi-phase boost converter, and a 3-level boost converter. A seamless maximum power point tracking control system characterized in that the second performing unit is an AC converter that is one of a 2-level inverter, a 3-level inverter, a 3-phase inverter, a single-phase inverter, or a 3-phase 3-wire inverter. Claim 2 A seamless maximum power point tracking control system according to claim 1, wherein the second performing unit increases the voltage command value of the DC connection unit linearly or non-linearly according to the characteristics of the output voltage output from the solar cell array for a certain period of time before switching to the first MPPT mode. Claim 3 A seamless maximum power point tracking control system according to claim 1, wherein the second performing unit increases the duty in proportion to the increase in the voltage command value of the DC connection unit to maintain the output voltage at the reference voltage.

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