Safety low-voltage self-power supply method and device for photovoltaic tracking support

Abstract

This invention discloses a safe low-voltage self-powered method for photovoltaic (PV) tracking brackets. The method draws power from one or more PV modules within a PV module string on the PV tracking bracket, with the power source connected to the same input terminal of a PV power optimizer. The invention also discloses a safe low-voltage self-powered device for PV tracking brackets, comprising a PV power generation unit, a PV power optimizer, a power supply DC-DC converter, and a battery. This invention eliminates the need for a separate power supply or drawing power from a high-voltage PV string, providing a safe low-voltage supply. When applied to PV tracking systems, it offers the advantages of providing a safe, low-voltage DC power supply for the PV tracking bracket's drive system in a cost-effective, highly reliable, and efficient manner.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and in particular to a method and device for safe low-voltage self-powered photovoltaic tracking brackets. Background Technology

[0002] Photovoltaic tracking brackets are widely used in large and medium-sized ground-mounted solar photovoltaic power generation. Their function is to adjust the working angle of the tracking bracket so that the photovoltaic modules installed on the bracket can track the spatial position of the sun, thereby maximizing the reception of solar radiation energy.

[0003] To track the sun's position, a motor-driven mechanical mechanism is typically used to power the photovoltaic tracking bracket. Therefore, all solar tracking brackets require a power supply system with sufficient output power to drive the motor. The motor-driven photovoltaic tracking bracket operates in two ways: continuous and intermittent. Continuous operation refers to the continuous movement of the tracking bracket under abnormal conditions such as strong winds, where the motor drives it to quickly reset. In this case, the angular velocity of the tracking bracket is much greater than the angular velocity of the sun's position change; the maximum operating speed is typically tens of times the sun's speed, and the continuous operation time from the maximum position to the reset position usually does not exceed 4 minutes. Intermittent operation refers to the intermittent operation of the tracking bracket during normal sun tracking, within a set angular error tolerance range. Taking a north-south axis single-axis photovoltaic tracking bracket as an example, the tracking bracket's operating speed is 15 degrees per minute, the sun's average speed is 0.25 degrees per minute, and the allowable error is ±0.5 degrees. Therefore, the tracking bracket's operation pattern is: an average of once every 4 minutes, with each action lasting 4 seconds. In the case of intermittent operation, depending on the accuracy and range of the tracking angle of the bracket, the number of intermittent operation adjustments of a single-axis photovoltaic tracking bracket is usually less than 200 per day.

[0004] To achieve solar tracking, a mechanical mechanism driven by an electric motor is typically used to power the solar tracking bracket. Therefore, solar tracking brackets usually require a power supply system with sufficient output power to drive the motor. Currently, there are three common power supply methods for photovoltaic (PV) tracking brackets: centralized low-voltage AC power supply for plant use, local power supply from independent external PV modules, and high-voltage self-power supply from PV strings. Each of these methods has its own problems. The centralized low-voltage AC power supply method requires converting the low-voltage 220VAC AC to 24VDC before supplying power to the motor. This necessitates laying numerous power cables within the PV power plant, resulting in long transmission distances, high costs, complex construction, and difficulties in later operation and maintenance. It also suffers from low power conversion efficiency and energy waste. The local power supply method uses small, independently installed PV modules near the tracking bracket controller, whose power output powers the motor. While this power supply method eliminates the risk of high voltage and offers high safety, the electricity generated by independent photovoltaic modules is somewhat unstable. It requires large-capacity batteries to ensure the tracking system has sufficient power to rotate and reset the tracking bracket to its generating position for the next day when solar irradiance is insufficient and the small photovoltaic modules are generating power inadequately, or to rotate the tracking bracket to its reset position in extreme weather conditions when power generation is impossible. Because it requires large-capacity energy storage devices and external independent photovoltaic module generating units, this method increases the cost of the power supply system and wastes photovoltaic modules and their installation space. The high-voltage self-powered photovoltaic string method directly draws power from the high voltage of the photovoltaic strings, eliminating the need for external independent photovoltaic modules. Patent CN 212379765 U proposes a self-powered single-axis tracking bracket controller. This controller uses an ultra-high voltage isolated switching power supply to convert the DC voltage of the photovoltaic string, which can reach 500V or even 1500V, into a 24V motor power supply voltage. This power supply method requires a very high step-down ratio power conversion, resulting in low efficiency. It also carries the risk of introducing high DC voltages above 500V into the 24V motor drive circuit. This places higher demands on the ultra-high voltage isolated switching power supply device, as well as the construction, installation, and operation and maintenance of the project. The overall cost of this power supply method remains high, and there is also a safety hazard of high-voltage electric shock. Furthermore, directly drawing power from the photovoltaic string can affect the MPPT tracking accuracy of the photovoltaic inverter, further reducing the overall efficiency of the system.

[0005] Patent CN 215646180 U proposes a self-powered photovoltaic tracking bracket system. It suggests that the driving power supply draws power directly from one or more photovoltaic module sub-units coupled to the system. The photovoltaic string (36 500W photovoltaic modules, 1500V string voltage) is divided into three sub-units, each containing 12 modules. The sub-unit string voltage reaches as high as 500V, which still poses the aforementioned high-voltage risk. If a sub-unit only has 1-2 photovoltaic modules, the voltage drawn is only about 80V. While this eliminates the safety risk of high-voltage power draw, the driving power supply may still draw power up to 15W. At 0W, the power taken from the two photovoltaic modules may account for 15% of the total power of 1000W. This percentage will be even higher under low to medium solar irradiance. Since the two modules being powered are connected in series with the other 34 photovoltaic modules, the high power percentage of the two modules being powered will trigger the "weakest link" effect, causing mismatch power generation losses in the entire photovoltaic string, including the other 34 photovoltaic modules. The power generation efficiency loss of the photovoltaic string may be as high as 15% or more. Therefore, if the power source is directly powered from 1-2 modules in the coupled photovoltaic string, it will be economically infeasible. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art, the present invention provides a safe low-voltage self-powered method and device for photovoltaic tracking brackets. It does not require the installation of a separate power supply or drawing power from high-voltage photovoltaic strings. It provides safe low-voltage power and, when applied to photovoltaic tracking systems, can provide safe low-voltage DC power to the drive of photovoltaic tracking brackets in a low-cost, highly reliable, and highly efficient manner.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: On the one hand, a safe low-voltage self-powered method for photovoltaic tracking brackets is provided. The safe low-voltage self-powered method for photovoltaic tracking brackets is that the photovoltaic power generation unit draws power from one or more photovoltaic modules in the photovoltaic module string on the photovoltaic tracking bracket. The output terminal of the photovoltaic power optimizer of the photovoltaic power generation unit is connected in series with the output terminals of other photovoltaic modules on the photovoltaic tracking bracket, either directly or after being connected to the output terminal of the photovoltaic power optimizer, to form a photovoltaic module string. The connection method is that one or more photovoltaic modules in the photovoltaic string that draw power are connected to the input terminal of the same photovoltaic power optimizer.

[0008] Furthermore, the power supply voltage is a low voltage not exceeding 60V, and the upper limit of the power supply current is 5% of the maximum power operating current of the photovoltaic module under STC conditions. STC is an abbreviation for Standard Test Condition.

[0009] Furthermore, based on the intermittent short-term operation characteristics of the photovoltaic tracking bracket, the limited current output of the photovoltaic module is used to charge the battery. During the intermittent short-term operation, the battery discharges for a short period of 3s-6s, and after the battery discharges to a shallow depth, a small current with a limited current is used to charge the battery during the intermittent period, and the battery is fully charged within 200s-250s. Under the intermittent operation of the photovoltaic tracking bracket every day, the battery operates in a shallow charge and shallow discharge state.

[0010] On the other hand, a safe low-voltage self-powered device for a photovoltaic tracking bracket based on the above-mentioned safe low-voltage self-powered method is provided. The safe low-voltage self-powered device for the photovoltaic tracking bracket includes a photovoltaic power generation unit, a photovoltaic power optimizer, a power supply DC-DC converter, and a battery. The photovoltaic power generation unit is one or more photovoltaic modules in the photovoltaic module string on the photovoltaic tracking bracket. The output terminal of the photovoltaic power generation unit is connected to the input terminal of the photovoltaic power optimizer and the input terminal of the power supply DC-DC converter. That is, the input terminal of the photovoltaic power optimizer and the input terminal of the power supply DC-DC converter are connected in parallel. The output terminal of the photovoltaic power optimizer of the photovoltaic power generation unit is connected in series with the output terminals of other photovoltaic modules on the photovoltaic tracking bracket, either directly or after being connected to the output terminal of the photovoltaic power optimizer, to form the photovoltaic module string. The input port of the power supply DC-DC converter is connected to the output port of the photovoltaic power generation unit, and the positive and negative terminals of the input port of the power supply DC-DC converter correspond to the positive and negative terminals of the output port of the photovoltaic power generation unit, respectively. The output port of the power supply DC-DC converter is connected to the battery, and the positive and negative terminals of the output port of the power supply DC-DC converter correspond to the positive and negative terminals of the battery, respectively. The battery is directly connected to the power supply DC-DC converter, or the battery is connected to the power supply DC-DC converter after passing through the energy manager of the photovoltaic tracking bracket.

[0011] Furthermore, the photovoltaic power optimizer includes a maximum power point tracking (MPPT) circuit, which comprises a voltage and current detection unit, a multiplier, and a MPPT processing unit. The voltage and current detection unit is used to collect the output voltage and output current of the photovoltaic power optimizer. The multiplier is used to multiply the output voltage of the photovoltaic power generation unit through the photovoltaic power optimizer by the output current of the photovoltaic power generation unit to obtain the output power of the photovoltaic power optimizer. The output power of the photovoltaic power generation unit is the sum of the output power of the photovoltaic power optimizer and the input power of the power supply DC-DC converter. Under the power-limited output operation conditions of the power supply DC-DC converter in constant current and constant voltage operating modes, the maximum input power is limited to 5% of the maximum power of the photovoltaic module under STC conditions when operating in constant current mode.

[0012] Furthermore, the power supply DC-DC converter includes a DC-DC conversion circuit and a control module. The DC-DC conversion circuit is used to couple between the photovoltaic power generation unit and the battery, and the control module is provided in the DC-DC conversion circuit. When the photovoltaic tracking bracket is normally tracking the sun, the photovoltaic tracking bracket operates intermittently according to the angle allowable error set range, and the power supply DC-DC converter charges the battery intermittently. The control module is used to monitor the input voltage parameter of the DC-DC conversion circuit. When the voltage fluctuation of the input terminal voltage of the power supply DC-DC converter before and after charging is detected to exceed 10%, the control module of the power supply DC-DC converter controls the power supply DC-DC converter to stop charging the battery. The control module is also used to detect the output voltage parameter of the DC-DC conversion circuit and a threshold is preset for the output voltage parameter. The power supply DC-DC converter has two power supply modes: constant current and constant voltage. In constant current mode, the control module controls the DC-DC converter to maintain a fixed output current value, which is lower than 5% of the maximum power point operating current of the photovoltaic module under STC conditions. In constant voltage mode, the control module controls the output voltage of the DC-DC converter to maintain at the aforementioned output voltage threshold. When the control module detects that the output voltage of the DC-DC converter is lower than the preset voltage threshold, the control module controls the DC-DC converter to operate in constant current mode. If the control module detects that the output voltage of the DC-DC converter is equal to the preset voltage threshold, the control module controls the DC-DC converter to operate in constant voltage mode. If the control module detects that the output voltage of the DC-DC converter is higher than the preset voltage threshold, the control module controls the DC-DC converter to stop supplying power.

[0013] Furthermore, the photovoltaic power optimizer is also used to track the maximum power of the photovoltaic power generation unit and control the output current of the photovoltaic power optimizer to be consistent with the string current of the photovoltaic string; under the power-limited output operation condition of the power supply DC-DC converter in constant current and constant voltage working mode, the photovoltaic power optimizer tracks the maximum power of the photovoltaic module and determines the output voltage of the photovoltaic module at the maximum power; the power-limited output limit value of the power supply DC-DC converter under the constant current and constant voltage working mode is 5% of the maximum power of the photovoltaic module under STC condition.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention can draw power from one or more photovoltaic modules within a photovoltaic module string on a photovoltaic tracking bracket at a low voltage, without the need for a separate power supply or to draw power from a high-voltage photovoltaic string.

[0015] Compared with the high-voltage self-powered photovoltaic string, the power supply of the tracking bracket controller of this invention is drawn from one or more photovoltaic modules in the photovoltaic module string on the tracking bracket. The power draw voltage is a safe low voltage of no more than 60V. There is no need to configure an expensive ultra-high voltage isolation switching power supply of 500V-1500V or above. There is no risk of introducing the high voltage of 500V or above of the photovoltaic string into the power supply of the bracket controller. The power supply efficiency is high, the cost is low and the safety is high. This invention differs from the local power supply method of independent photovoltaic modules. Instead, it allows photovoltaic modules within a tracking photovoltaic system to generate their own power, eliminating the waste of independent photovoltaic modules and space. Furthermore, since the photovoltaic modules used in tracking photovoltaic systems are typically 540W or even 600W or higher, this power supply method is more reliable and stable than the typical 40-60W independent photovoltaic modules. It also reduces the requirement for battery capacity, further lowering the cost of the power supply system.

[0016] The power supply device of this invention adopts a front-end access method of photovoltaic module optimization device, which avoids the impact of power extraction on the maximum power output of the module string. Since the photovoltaic optimization device isolates the 1-2 photovoltaic modules whose power is extracted from the photovoltaic string, it will not cause the "weakest link" effect in the photovoltaic string and thus avoid the power generation mismatch loss of the photovoltaic string. At the same time, the device adopts a constant current and voltage limiting method for power supply, which can set 5% of the maximum power operating current of the photovoltaic module under STC conditions as the upper limit value of the current extracted by the power supply device, further avoiding the impact of power extraction on the MPPT tracking accuracy of the optimization device of the photovoltaic module connected to the power supply.

[0017] Based on the intermittent short-term operation characteristics of the tracking bracket, this invention uses the limited current output of the photovoltaic module to charge the battery. During the intermittent short-term operation, a large current output is used for a short period of 3s-6s to drive the motor and discharge the battery. After the battery discharges to a shallow depth, a limited current is used to charge the battery during the intermittent period. The battery is fully charged within 200s-250s. Under the intermittent operation of this tracking bracket every day, the battery operates under shallow charging and discharging conditions, thus effectively extending the battery life and reducing the equipment's operation and maintenance costs. Attached Figure Description

[0018] Figure 1 This is a block diagram (I) illustrating the principle of the safe low-voltage self-powered device for the photovoltaic tracking bracket of the present invention. Figure 2 This is a block diagram (II) illustrating the principle of the safe low-voltage self-powered device for the photovoltaic tracking bracket of the present invention. Figure 3 This is a schematic diagram of the current and voltage of the photovoltaic power generation unit that draws power from the DC-DC converter under high solar irradiance conditions in this invention. Figure 4 This is a schematic diagram of the current and voltage of the photovoltaic power generation unit that draws power from the DC-DC converter under low solar irradiance conditions according to the present invention. Figure 5 This is a schematic diagram of the output current and voltage of the DC-DC converter that powers the tracking bracket during intermittent operation of the present invention. Detailed Implementation

[0019] The following explanation, in conjunction with the accompanying drawings, provides further details.

[0020] The safe low-voltage self-powered method for photovoltaic tracking brackets in this embodiment draws power from the photovoltaic modules within the photovoltaic module string on the photovoltaic tracking bracket. The power draw voltage is a low voltage not exceeding 60V. The connection method involves one or more photovoltaic modules within the photovoltaic string being connected to the input terminal of the same photovoltaic power optimizer. 5% of the maximum operating current of the photovoltaic module under STC conditions is used as the upper limit of the power draw current during power supply. Based on the intermittent short-time operation characteristics of the photovoltaic tracking bracket, the limited current output of the photovoltaic module is used to charge the battery. During intermittent short-time operation, the battery discharges for a short period of 3s-6s, reaching a shallow discharge depth. During the interval, a limited current is used to charge the battery, completing a full charge within 200s-250s. Under the daily intermittent operation of the photovoltaic tracking bracket, the battery operates in a shallow charge and discharge state.

[0021] like Figure 1 , Figure 2 This invention relates to a safe low-voltage self-powered photovoltaic tracking bracket based on the aforementioned safe low-voltage self-powered method. The self-powered device comprises a photovoltaic power generation unit, a photovoltaic power optimizer, a power supply DC-DC converter, and a battery. The photovoltaic tracking bracket includes a tracking bracket controller, a motor driver, a motor, and a tracking bracket rotation mechanism connected to the motor. Figure 1 , Figure 2 Medium power optimizer DC-DC (mppt) is a photovoltaic power optimizer.

[0022] Furthermore, such as Figure 1As shown, the safe low-voltage self-powered device for photovoltaic tracking brackets also includes a Battery Management System (BMS), commonly known as a battery nanny or battery manager. Its main purpose is to intelligently manage and maintain each battery cell, preventing overcharging and over-discharging, extending battery life, and monitoring battery status. The BMS unit includes a BMS, a control module, a display module, a wireless communication module, electrical equipment, a battery for powering the electrical equipment, and a data acquisition module for collecting battery information. The BMS is connected to the wireless communication module and the display module via communication interfaces. The output of the data acquisition module is connected to the input of the BMS, and the output of the BMS is connected to the input of the control module. The control module is connected to both the battery and the electrical equipment. Figure 2 The BMS management in this context refers to the BMS battery management system.

[0023] In this embodiment, the photovoltaic power generation unit is one or more photovoltaic modules in the photovoltaic module string on the photovoltaic tracking bracket; the output terminal of the photovoltaic power generation unit is connected to the input terminal of the photovoltaic power optimizer and the power supply DC-DC converter, the input terminal of the photovoltaic power optimizer and the power supply DC-DC converter are connected in parallel, and the output terminal of the photovoltaic power optimizer is connected in series with the output terminals of other photovoltaic power optimizers or photovoltaic modules in the photovoltaic module string to form a photovoltaic module string.

[0024] The power supply DC-DC converter includes at least two ports. Its input port is connected to the output of the aforementioned photovoltaic power generation unit, with the positive and negative terminals of the input port corresponding to the positive and negative outputs of the photovoltaic module, respectively. Its output port is connected to the storage battery, with the positive and negative terminals of the output port corresponding to the positive and negative terminals of the storage battery, respectively. The storage battery is connected directly or via the energy manager of the photovoltaic tracking bracket to the power supply DC-DC converter. The tracking bracket controller is connected to the power supply DC-DC converter, the storage battery, and the motor driver, respectively.

[0025] The power supply DC-DC converter also includes a DC-DC conversion circuit and a control module. The DC-DC conversion circuit is used to couple between the photovoltaic power generation unit and the battery. The control module is connected to the DC-DC conversion circuit. The control module is used to detect the output voltage parameter of the DC-DC conversion circuit and has a preset threshold for the output voltage parameter. The power supply mode of the power supply DC-DC converter includes two operating modes: constant current and constant voltage. In the constant current mode of the power supply DC-DC converter, the control module controls the output current of the DC-DC conversion circuit to maintain a fixed output current setpoint. This fixed output current setpoint is lower than 5% of the maximum power point operating current of the photovoltaic module under STC conditions, so as to ensure that the power supply of the power supply DC-DC converter will not affect the tracking accuracy of the photovoltaic power generation unit during maximum power point tracking.

[0026] In the constant voltage mode of the power supply DC-DC converter, the control module controls the output voltage of the DC-DC conversion circuit to maintain at the aforementioned output voltage threshold. When the control module detects that the output voltage of the power supply DC-DC converter is lower than the preset voltage threshold, the control module controls the power supply DC-DC converter to operate in constant current mode; if the control module detects that the output voltage of the power supply DC-DC converter is equal to the preset voltage threshold, the control module controls the power supply DC-DC converter to operate in constant voltage mode; if the control module detects that the output voltage of the power supply DC-DC converter is higher than the preset voltage threshold, the control module controls the power supply DC-DC converter to stop supplying power.

[0027] The tracking bracket controller draws power from the self-powered device; the bracket controller is based on a microcontroller and controls the motor driver to rotate the motor to rotate the tracking bracket to the target angle, thereby achieving real-time automatic tracking.

[0028] Based on the characteristics of intermittent short-term operation of the tracking bracket, this invention uses the limited current output of the photovoltaic power generation unit to charge the battery. During the intermittent short-term operation, a large current output is used for a short period of 3s-6s to drive the motor and discharge the battery. After the battery discharges to a shallow depth, a limited current is used to charge the battery during the intermittent period. The battery is fully charged within 200s-250s. Under normal sunlight conditions, the tracking bracket performs repeated intermittent operations every day, and the battery operates under shallow charging and discharging conditions. Therefore, the battery life is effectively extended and the operation and maintenance costs of the equipment are reduced.

[0029] The output power of the photovoltaic power generation unit is the sum of the output power of the photovoltaic power optimizer and the input power of the power supply DC-DC converter. Under the condition of power supply DC-DC converter operating in constant current and constant voltage mode with limited power output, the maximum input power is operating in constant current mode, and the maximum input power is limited to 5% of the maximum power of the photovoltaic module under STC condition. Therefore, at this time, the photovoltaic power optimizer is used to track the maximum power of the photovoltaic power generation unit and control the output current of the photovoltaic power optimizer to be consistent with the string current of the photovoltaic string. Since the power supply DC-DC converter includes a DC-DC conversion circuit and a control module, the DC-DC conversion circuit is used to couple between the photovoltaic power generation unit and the battery. The control module is connected to the DC-DC conversion circuit and is used to monitor the input voltage parameters of the DC-DC conversion circuit. Thus, under normal solar irradiance conditions such as sunny and cloudy days, when the photovoltaic tracking bracket is tracking the sun normally, it operates intermittently according to the angle tolerance set range. Therefore, the power supply DC-DC converter also charges the battery intermittently. At this time, the voltage fluctuation at the input terminal of the power supply DC-DC converter before and after charging is very small, usually not exceeding 3%. However, on cloudy days or in the early morning or late evening when solar irradiance is low, and the photovoltaic tracking bracket still needs to track the sun, the power supply DC-DC converter operates in constant current mode, and its input power can... At this time, the photovoltaic power generation unit can account for a relatively high proportion of the photovoltaic power generated. Since the control module of the photovoltaic power optimizer needs to control its output current to be consistent with the string current of the photovoltaic string, it needs to perform a step-down and step-up power conversion. Under the condition that the input power of the power supply DC-DC converter is at a high proportion, its output voltage may be too low and stop power conversion. This causes the photovoltaic power optimizer to stop performing maximum power point tracking and the output voltage of the photovoltaic power generation unit to fluctuate greatly and generate large harmonic output. Therefore, the control module of the power supply DC-DC converter is also used to monitor the input voltage parameters of the DC-DC converter circuit. When the voltage fluctuation of the input terminal of the power supply DC-DC converter before and after charging exceeds 10%, the control module of the power supply DC-DC converter controls the power supply DC-DC converter to stop charging the battery.

[0030] The output terminal of the photovoltaic power generation unit connected to the safe low-voltage self-powered device of the photovoltaic tracking bracket is connected in series with the output terminal of other photovoltaic modules on the photovoltaic tracking bracket, either directly or after being connected to the output terminal of the photovoltaic power optimizer, to form the photovoltaic module string.

[0031] Figure 3 This is a schematic diagram of the current and voltage of a photovoltaic power generation unit that draws power from a DC-DC converter under high solar irradiance conditions. When the power supply DC-DC converter draws power, it operates under constant current and constant voltage mode with limited output power. The maximum input power of the power supply DC-DC converter is limited to 5% of the maximum power of the photovoltaic module under STC conditions during constant current operation. The output power of the photovoltaic power generation unit is the sum of the output power of the photovoltaic power optimizer and the input power of the power supply DC-DC converter. Figure 3 It can be seen that under high solar irradiance conditions, the power extraction operation of the DC-DC converter with 5% of the maximum power under the limited STC condition has little impact on the output power of the photovoltaic power optimizer. The DC-DC power conversion function of the photovoltaic power optimizer ensures the consistency of the string current of the photovoltaic string and the maximum power tracking of the photovoltaic power generation unit, and avoids the problems of difficulty in maximum power tracking of the photovoltaic string caused by directly extracting power from one photovoltaic module of the photovoltaic string, as well as the power generation loss caused by mismatch within the string when extracting power.

[0032] Figure 4 This is a schematic diagram of the current and voltage of a photovoltaic power generation unit powered by a DC-DC converter under low solar irradiance conditions. When the DC-DC converter draws power, it operates under power-limited output conditions in constant current and constant voltage modes. The maximum input power of the DC-DC converter is limited to 5% of the maximum power of the photovoltaic module under STC conditions during constant current operation. The output power of the photovoltaic power generation unit is the sum of the output power of the photovoltaic power optimizer and the input power of the DC-DC converter. Figure 3 It can be seen that under low solar irradiance conditions, the power extraction operation of the power supply DC-DC converter has a significant impact on the output power of the photovoltaic power optimizer. However, by limiting the maximum power of the power supply DC-DC converter to 5% under STC conditions, the DC-DC power conversion function of the photovoltaic power optimizer can still ensure the consistency of the string current of the photovoltaic string and the maximum power tracking of the photovoltaic power generation unit. This avoids the problems of difficulty in maximum power tracking of the photovoltaic string caused by directly extracting power from one photovoltaic module of the photovoltaic string, and the power generation loss caused by mismatch within the string during power extraction.

[0033] Figure 5 This is a schematic diagram of the output current and voltage of the self-powered DC-DC converter during the intermittent operation of the tracking bracket.

[0034] like Figure 5As shown, the photovoltaic tracking bracket features intermittent short-term operation. It uses the limited current output of the photovoltaic modules to charge the battery. During intermittent short-term operation, the battery discharges for a short period of 3-6 seconds, achieving a shallow discharge depth. Then, during the intermittent period, a limited current is used to charge the battery, completing a full charge within 200-250 seconds. Under the daily intermittent operation of the photovoltaic tracking bracket, the battery operates in a shallow charge and discharge state. The power supply DC-DC converter operates under limited power output conditions in constant current and constant voltage modes. The maximum input power of the power supply DC-DC converter, when operating in constant current mode, is limited to 5% of the maximum power of the photovoltaic modules under STC conditions. Therefore... Figure 5 During the rotation and subsequent periods after the photovoltaic tracking bracket stops, the output current of the self-powered DC-DC converter remains constant while the output voltage gradually increases until the battery is fully charged. After the input power of the self-powered DC-DC converter enters constant voltage operation mode, the output current of the self-powered DC-DC converter gradually decreases while the output voltage remains constant. When the photovoltaic tracking bracket rotates again, the output voltage of the self-powered DC-DC converter drops rapidly due to battery discharge. Using this self-powered method, the battery operates in a shallow charge-discharge state during the intermittent daily operation of the photovoltaic tracking bracket, extending battery life.

[0035] It should be stated that the above specific embodiments are only preferred embodiments of the present invention and the technical principles used. Within the scope of the technology disclosed in the present invention, any changes or substitutions that can be easily conceived by those skilled in the art should be covered within the protection scope of the present invention.

Claims

1. A safety low voltage self-powered device for a photovoltaic tracking support, characterized in that: The installation of the photovoltaic tracking bracket The all-low voltage self-powered device includes a photovoltaic power generation unit, a photovoltaic power optimizer, a power supply DC-DC converter, and a battery; The photovoltaic power generation unit is one or more photovoltaic modules in a photovoltaic module string on the photovoltaic tracking bracket. The output terminal of the photovoltaic power generation unit is connected to the input terminal of the photovoltaic power optimizer and the input terminal of the power supply DC-DC converter. That is, the input terminal of the photovoltaic power optimizer and the input terminal of the power supply DC-DC converter are connected in parallel. The output terminal of the photovoltaic power optimizer of the photovoltaic power generation unit is connected in series with the output terminals of other photovoltaic modules on the photovoltaic tracking bracket, either directly or after being connected to the output terminal of the photovoltaic power optimizer, to form a photovoltaic module string. The input port of the power supply DC-DC converter is connected to the output port of the photovoltaic power generation unit, and the positive and negative terminals of the input port of the power supply DC-DC converter correspond to the positive and negative terminals of the output port of the photovoltaic power generation unit, respectively. The output port of the power supply DC-DC converter is connected to the battery, and the positive and negative terminals of the output port of the power supply DC-DC converter correspond to the positive and negative terminals of the battery, respectively. The battery is directly connected to the power supply DC-DC converter, or the battery is connected to the power supply DC-DC converter after passing through the energy manager of the photovoltaic tracking bracket.

2. The safe low-voltage self-powered device for photovoltaic tracking brackets according to claim 1, characterized in that: The photovoltaic power optimizer includes a maximum power point tracking (MPPT) circuit, which comprises a voltage and current detection unit, a multiplier, and a MPPT processing unit. The voltage and current detection unit is used to acquire the output voltage and output current of the photovoltaic power optimizer. The multiplier is used to multiply the output voltage of the photovoltaic power generation unit after passing through the photovoltaic power optimizer by the output current of the photovoltaic power generation unit to obtain the output power of the photovoltaic power optimizer. The output power of the photovoltaic power generation unit is the sum of the output power of the photovoltaic power optimizer and the input power of the power supply DC-DC converter. Under the condition that the input power of the power supply DC-DC converter is limited to the power output value in constant current and constant voltage operating modes, the maximum input power is limited to 5% of the maximum power of the photovoltaic module under STC conditions.

3. The safe low-voltage self-powered device for photovoltaic tracking brackets according to claim 1, characterized in that: The power supply DC-DC converter includes a DC-DC conversion circuit and a control module. The DC-DC conversion circuit is used to couple between the photovoltaic power generation unit and the battery. The DC-DC conversion circuit is equipped with the control module. When the photovoltaic tracking bracket is normally tracking the sun, the photovoltaic tracking bracket operates intermittently according to the angle allowable error set range, and the power supply DC-DC converter charges the battery intermittently. The control module is used to monitor the input voltage parameters of the DC-DC converter circuit. When the input voltage is detected to fluctuate by more than 10% before and after charging of the power supply DC-DC converter, the control module of the power supply DC-DC converter controls the power supply DC-DC converter to stop charging the battery. The control module is also used to detect the output voltage parameters of the DC-DC converter circuit and a threshold is preset for the output voltage parameters. The power supply mode of the DC-DC converter includes two modes: constant current and constant voltage. In the constant current mode, the control module controls the output current of the DC-DC converter to maintain a fixed output current value, and this fixed output current setting value is lower than 5% of the maximum power point operating current of the photovoltaic module under STC conditions. In the constant voltage mode, the control module controls the output voltage of the DC-DC converter to maintain the output voltage at the above-mentioned output voltage threshold. When the control module of the power supply DC-DC converter detects that the output voltage of the power supply DC-DC converter is lower than the preset voltage threshold, the control module controls the power supply DC-DC converter to operate in constant current mode; if the control module detects that the output voltage of the power supply DC-DC converter is equal to the preset voltage threshold, the control module controls the power supply DC-DC converter to operate in constant voltage mode; if the control module detects that the output voltage of the power supply DC-DC converter is higher than the preset voltage threshold, the control module controls the power supply DC-DC converter to stop supplying power.

4. The safe low-voltage self-powered device for photovoltaic tracking brackets according to claim 1, characterized in that: The photovoltaic power optimizer is also used to track the maximum power of the photovoltaic power generation unit and control the output current of the photovoltaic power optimizer to be consistent with the string current of the photovoltaic string; under the power-limited output condition of the power supply DC-DC converter in constant current and constant voltage operating mode, the photovoltaic power optimizer tracks the maximum power of the photovoltaic module and determines the output voltage of the photovoltaic module at the maximum power; the power-limited output limit value of the power supply DC-DC converter under the constant current and constant voltage operating mode is 5% of the maximum power of the photovoltaic module under STC condition.

Images