MPPT (Maximum Power Point Tracking) multi-mode control method and MPPT controller of photovoltaic energy storage system

Abstract

The embodiment of the invention provides an MPPT (Maximum Power Point Tracking) multi-mode control method of a photovoltaic energy storage system and an MPPT controller. The method is used for an MPPT controller, and the MPPT controller is used for controlling H4 bridge arm topology and collecting inductive current of an energy storage inductor, photovoltaic voltage of a photovoltaic input end and battery voltage of a battery output end in real time. Comparing the photovoltaic voltage with the battery voltage, judging whether the H4 bridge arm topology currently works in a buck state or a boost state according to a comparison result, and obtaining a buck-boost judgment result; based on the buck-boost judgment result and the real-time comparison between the inductive current and a preset current threshold value, adaptive switching is carried out between a non-synchronous rectification mode and a synchronous rectification mode in a corresponding working state; the asynchronous rectification mode comprises a Buck circuit mode and a Boost circuit mode, and the synchronous rectification mode comprises a Buck synchronous rectification mode and a Boost synchronous rectification mode. According to the technical scheme provided by the embodiment of the invention, the problem of current backflow is solved, the follow current loss is reduced, and the MPPT efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and in particular to an MPPT multi-mode control method and MPPT controller for a photovoltaic energy storage system. Background Technology

[0002] As a core device for achieving efficient utilization of distributed energy, the performance of home energy storage systems directly affects the collection and storage efficiency of photovoltaic (PV) power. Among them, the maximum power point tracking (MPPT) module is a key component of home energy storage systems. It is responsible for tracking the maximum power point of the PV panels in real time and converting the unstable output voltage of the PV panels into a stable voltage suitable for battery storage. The topology and operating mode of the MPPT module are the core factors that determine its efficiency, losses, and reliability.

[0003] The topology of an MPPT module is typically a Buck+Boost two-switch, two-diode topology, containing two power switching transistors and two freewheeling diodes. Switching between buck and boost operating modes is achieved by controlling the on / off state of the switching transistors. Since the freewheeling circuit relies on diodes, and the forward voltage drop of ordinary silicon-based diodes is typically 0.7-1.2V, the conduction loss of the diodes increases sharply under low-voltage, high-current conditions. If the system operates for a long time, this will not only lead to a decrease in the overall efficiency of the MPPT module but also cause the module temperature to rise due to diode heating, resulting in lower safety of the MPPT module. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a multi-mode MPPT control method and an MPPT controller for a photovoltaic energy storage system, in order to solve the current backflow problem, reduce follow current loss, and improve MPPT efficiency.

[0005] On one hand, embodiments of the present invention provide an MPPT multi-mode control method for a photovoltaic energy storage system, used for an MPPT controller. The MPPT controller is used to control an H4 bridge arm topology, which includes a photovoltaic input terminal, a battery output terminal, a first switch, a second switch, a third switch, a fourth switch, and an energy storage inductor. The method includes: The inductor current of the energy storage inductor, the photovoltaic voltage at the photovoltaic input terminal, and the battery voltage at the battery output terminal are collected in real time. The photovoltaic voltage is compared with the battery voltage, and based on the comparison result, it is determined whether the H4 bridge arm topology should currently be operating in buck or boost mode, and the buck / boost determination result is obtained. Based on the buck-boost determination result and the real-time comparison of the inductor current with the preset current threshold, adaptive switching is performed between asynchronous rectification mode and synchronous rectification mode under the corresponding working state. The asynchronous rectification modes include Buck circuit mode and Boost circuit mode, and the synchronous rectification modes include Buck synchronous rectification mode and Boost synchronous rectification mode.

[0006] Optionally, the photovoltaic voltage is compared with the battery voltage, and based on the comparison result, it is determined whether the H4 bridge arm topology should currently operate in buck or boost mode, and a buck / boost determination result is obtained, including: When the photovoltaic voltage is greater than or equal to the sum of the battery voltage and the buck mode trigger threshold, it is determined that the H4 bridge arm topology should currently operate in buck mode, and the switching occurs between the Buck circuit mode and the Buck synchronous rectification mode; or... When the photovoltaic voltage is less than or equal to the difference between the battery voltage and the boost mode trigger threshold, it is determined that the H4 bridge arm topology should currently operate in boost mode, and the system switches between the Boost synchronous rectification mode and the Boost circuit mode; or... When the photovoltaic voltage is greater than the difference between the battery voltage and the boost mode trigger threshold and less than the sum of the battery voltage and the buck mode trigger threshold, the current control mode is maintained.

[0007] Optionally, based on the buck-boost determination result and the real-time comparison of the inductor current with a preset current threshold, adaptive switching is performed between asynchronous rectification mode and synchronous rectification mode under the corresponding operating state, including: Under buck operation, when the inductor current is greater than a preset current threshold, the system switches from the Buck circuit mode to the Buck synchronous rectification mode; or, when the inductor current is less than the difference between the preset current threshold and the current hysteresis threshold, the system switches from the Buck synchronous rectification mode to the Buck circuit mode. Under boost operation, when the inductor current is greater than a preset current threshold, the system switches from the Boost circuit mode to the Boost synchronous rectification mode; or, when the inductor current is less than the difference between the preset current threshold and the current hysteresis threshold, the system switches from the Boost synchronous rectification mode to the Boost circuit mode.

[0008] Optionally, in the Buck circuit mode, the second switch, the third switch, and the fourth switch remain in the off state, and the first switch is periodically turned on and off according to the pulse width modulation signal; When the first switch is turned on, the input voltage forms a circuit with the energy storage inductor through the first switch, the energy storage inductor stores energy, and the inductor current increases linearly. When the first switch is turned off, the energy storage inductor releases energy and charges the battery through the battery voltage, the back electromotive force of the energy storage inductor itself, and the circuit parasitic parameters, and the inductor current decreases linearly.

[0009] Optionally, in the Buck synchronous rectification mode, when the first switch is turned on, the second switch is turned off, the third switch is turned on, and the fourth switch is turned off, the input voltage forms a loop through the first switch, the energy storage inductor, and the third switch, the energy storage inductor stores energy, and the inductor current rises; When the first switch is turned off, the second switch is turned on, the third switch is turned off, and the fourth switch is turned on, the energy storage inductor releases energy, forming a freewheeling circuit through the second switch, the battery output terminal, and the fourth switch to charge the battery at the battery output terminal, and the inductor current decreases.

[0010] Optionally, in the Boost synchronous rectification mode, when the second switch is turned on, the first switch is turned off, the fourth switch is turned on, and the third switch is turned off, the input voltage forms a loop through the second switch, the energy storage inductor, and the fourth switch, the energy storage inductor stores energy, and the inductor current rises; When the second switch is turned off, the first switch is turned on, the fourth switch is turned off, and the third switch is turned on, the energy released by the energy storage inductor is superimposed on the input voltage, and forms a circuit through the first switch, the third switch, and the battery output terminal to perform boost charging, and the inductor current decreases.

[0011] Optionally, in the Boost circuit mode, the first switch remains normally open, the second switch and the third switch remain normally closed, and when the fourth switch is turned on, the input voltage forms a loop through the first switch, the energy storage inductor and the fourth switch, the energy storage inductor stores energy and the inductor current increases; When the fourth switch is turned off, the energy storage inductor releases energy, which forms a circuit through the first switch and the battery output terminal to perform boost charging, and the inductor current decreases.

[0012] Optionally, it also includes: The pulse width modulation signals of the complementary switching transistors among the first, second, third, and fourth switching transistors are configured with a set dead time. After adaptive switching between asynchronous rectification mode and synchronous rectification mode, the duty cycle of the pulse width modulation signal is adjusted in a stepwise manner. During the switching process between asynchronous rectification mode and synchronous rectification mode, if the inductor current is greater than a set ratio of the rated current, the first switch, the second switch, the third switch and the fourth switch are turned off and restarted after a set time.

[0013] On the other hand, embodiments of the present invention provide a storage medium including a stored program, wherein, when the program is running, it controls the device where the storage medium is located to execute the MPPT multi-mode control method of the photovoltaic energy storage system described above.

[0014] On the other hand, embodiments of the present invention provide an MPPT controller, including a memory and a processor. The memory is used to store information including program instructions, and the processor is used to control the execution of the program instructions. When the program instructions are loaded and executed by the processor, the steps of the MPPT multi-mode control method of the photovoltaic energy storage system described above are implemented.

[0015] In the technical solution provided by this invention, the method is used in an MPPT controller. The MPPT controller controls the H4 bridge arm topology and collects in real time the inductor current of the energy storage inductor, the photovoltaic voltage at the photovoltaic input terminal, and the battery voltage at the battery output terminal. The photovoltaic voltage is compared with the battery voltage, and based on the comparison result, it is determined whether the H4 bridge arm topology should currently operate in buck or boost mode, obtaining a buck / boost determination result. Based on the buck / boost determination result and the real-time comparison of the inductor current with a preset current threshold, adaptive switching is performed between asynchronous rectification mode and synchronous rectification mode under the corresponding operating state. The asynchronous rectification mode includes Buck circuit mode and Boost circuit mode, and the synchronous rectification mode includes Buck synchronous rectification mode and Boost synchronous rectification mode. The technical solution provided by this invention solves the current backflow problem, reduces freewheeling loss, and improves MPPT efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the topology of an MPPT module provided in related technologies; Figure 2This is a schematic diagram of another MPPT module topology provided in related technologies; Figures 3A-3D This is a schematic diagram of an H4 bridge arm topology provided in an embodiment of the present invention; Figure 4 A flowchart of an MPPT multi-mode control method for a photovoltaic energy storage system provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of an MPPT controller provided in an embodiment of the present invention. Detailed Implementation

[0018] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0020] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0021] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0022] A topology for an MPPT module is provided in the related technology. Figure 1 This is a schematic diagram of the topology of an MPPT module provided in related technologies, such as... Figure 1As shown, this MPPT module uses a traditional Buck+Boost two-switch, two-diode topology, comprising two power switches Q11 and Q14 and two freewheeling diodes D12 and D13. The MPPT module includes a photovoltaic input terminal, a capacitor C11, switches Q11, freewheeling diodes D12 and D13, a switch Q14, an inductor L11, a capacitor C12, and a battery output terminal. The photovoltaic input terminal is connected in parallel with capacitor C11. Switch Q11 and freewheeling diode D12 are connected in series and in parallel with capacitor C11. Freewheeling diode D13 and switch Q14 are connected in series and in parallel with capacitor C12. The battery output terminal is connected in parallel with capacitor C12. Switch Q11, freewheeling diodes D12 and D13, and switch Q14 are each connected to inductor L11.

[0023] Figure 1 The solution switches between buck and boost modes by controlling the on / off state of the switching transistor. Specifically, when the photovoltaic input voltage Vpv is higher than the battery output voltage Vbat, it switches to Buck mode. The high-side switch (Q11) uses pulse width modulation (PWM) to step down the high voltage at the photovoltaic input to charge the battery. When the photovoltaic voltage Vpv is lower than the battery voltage Vbat, it switches to Boost mode. The low-side switch (Q14) uses PWM to step up the low voltage at the photovoltaic input to match the battery output voltage requirement. However, this solution has significant drawbacks in low-voltage home energy storage systems below 60V. Because the freewheeling circuit relies on diodes, and the forward voltage drop of ordinary silicon diodes is typically 0.7-1.2V, the conduction loss of the diodes increases dramatically under low-voltage, high-current conditions. If the system runs for a long time, it will not only lead to a decrease in the overall efficiency of the MPPT module (usually a 5%-8% reduction in efficiency), but also cause the module temperature to rise due to diode heating, affecting the lifespan of surrounding components, and even posing a risk of overheating protection triggering the system to shut down.

[0024] Another topology for the MPPT module is provided in related technologies. Figure 2 This is a schematic diagram of another MPPT module topology provided in related technologies, such as... Figure 2As shown, this MPPT module uses an H4 topology and consists of a bridge arm structure composed of four power switches (Q21, Q22, Q23, and Q24). The MPPT module includes: a photovoltaic input terminal, a capacitor C21, switches Q21, Q22, Q23, and Q24, an inductor L21, a capacitor C22, and a battery output terminal. The photovoltaic input terminal is connected in parallel with capacitor C21. Switches Q21 and Q22 are connected in series and in parallel with capacitor C21. Switches Q23 and Q24 are connected in series and in parallel with capacitor C22. The battery output terminal is connected in parallel with capacitor C22. Switches Q21, Q22, Q23, and Q24 are each connected to inductor L21.

[0025] Figure 2 Synchronous rectification is achieved by controlling the complementary conduction of the switching transistors. In synchronous rectification mode, the freewheeling circuit no longer relies on diodes, but instead achieves freewheeling through a low on-resistance switching transistor, significantly reducing freewheeling losses.

[0026] Because this scheme uses complementary conduction logic for the bridge arm switches in both Buck and Boost modes (i.e., Q21 and Q22 are complementary, and Q23 and Q24 are complementary), the path of the freewheeling circuit dynamically changes with the state of the switches. When the system is charging the battery in Boost mode, if an abnormal voltage rise occurs at the battery output (such as battery overcharging or sudden load disconnection), the battery voltage may be higher than the MPPT output voltage. In this case, the conduction timing of the switches in the freewheeling circuit cannot be adjusted in time, resulting in a reverse current flowing back from the battery output to the photovoltaic input through the freewheeling circuit. The withstand voltage of the photovoltaic input is usually low (e.g., the maximum withstand voltage of a single crystalline silicon PV panel is 100V, far exceeding its rated output voltage). The reverse current will cause the internal junction voltage of the photovoltaic input to rise, leading to overvoltage damage. In severe cases, it may cause the PV panel at the photovoltaic input to crack or burn out, resulting in economic losses for users and posing safety hazards.

[0027] To address the technical problems in related technologies, an embodiment of the present invention provides an H4 bridge arm topology. Figures 3A-3D This is a schematic diagram of an H4 bridge arm topology provided in an embodiment of the present invention, as shown below. Figures 3A-3DAs shown, the H4 bridge arm topology includes: a photovoltaic input terminal, a first capacitor C1, a first switch Q1, a second switch Q2, a third switch Q3, a fourth switch Q4, an energy storage inductor L1, a second capacitor C2, and a battery output terminal. The photovoltaic input terminal is connected in parallel with the first capacitor C1. The first switch Q1 and the second switch Q2 are connected in series and in parallel with the first capacitor C1. The third switch Q3 and the fourth switch Q4 are connected in series and in parallel with the second capacitor C2. The battery output terminal is connected in parallel with the second capacitor C2. The first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 are each connected to the energy storage inductor L1. The photovoltaic input terminal may include a PV panel, and the battery output terminal may include an energy storage system.

[0028] Based on the aforementioned H4 bridge arm topology, this topology can be configured with four control modes: Buck circuit mode, Buck synchronous rectification mode, Boost synchronous rectification mode, and Boost circuit mode. While retaining the low-loss advantages of synchronous rectification, it can completely solve the current backflow problem and is compatible with different photovoltaic voltages and battery voltages.

[0029] In this embodiment of the invention, Figures 3A-3D In the diagram, light gray switches represent normally off states, where no current flows and the device is not in operation; black switches represent MOSFETs (Metal-Oxide-Semiconductor Transistors) in normal operation, driven by PWM, used to control the flow of system energy; and dark gray switches represent switches in which the body diode is active and current flows.

[0030] like Figure 3A As shown, in the Buck circuit mode, the second switch Q2, the third switch Q3, and the fourth switch Q4 remain off, while the first switch Q1 is periodically turned on and off according to the pulse width modulation signal. When the first switch Q1 is on, the input voltage forms a loop through the first switch Q1 and the energy storage inductor L1, storing energy and causing the inductor current to rise linearly. When the first switch Q1 is off, the energy storage inductor L1 releases energy, charging the battery through the battery voltage and the freewheeling path (at this time, because the second switch Q2, the third switch Q3, and the fourth switch Q4 are off, the freewheeling current depends on the back electromotive force of the energy storage inductor and the circuit parasitic parameters, and is only stable under low current conditions), causing the inductor current to decrease linearly. In the Buck circuit mode, the step-down function is achieved only through the PWM signal control of the first switch Q1, making it suitable for scenarios with low inductor current.

[0031] like Figure 3BAs shown, in the Buck synchronous rectification mode, the first switch Q1 and the second switch Q2 adopt complementary PWM control (i.e., when the first switch Q1 is turned on, the second switch Q2 is turned off, and when the first switch Q1 is turned off, the second switch Q2 is turned on). The third switch Q3 and the fourth switch Q4 adopt complementary PWM control, and the turn-on timing of the third switch Q3 is consistent with that of the first switch Q1, and the turn-on timing of the fourth switch Q4 is consistent with that of the second switch Q2. The dead time of all switches (first switch, second switch, third switch and fourth switch) is set to 50-100ns, which can avoid bridge arm shoot-through.

[0032] When the first switch Q1 is on, the second switch Q2 is off, the third switch Q3 is on, and the fourth switch Q4 is off, the photovoltaic input terminal forms a circuit with the first switch Q1, the energy storage inductor L1, and the third switch Q3. The energy storage inductor L1 stores energy, and the inductor current increases. When the first switch Q1 is off, the second switch Q2 is on, the third switch Q3 is off, and the fourth switch Q4 is on, the energy storage inductor L1 releases energy, forming a freewheeling circuit through the second switch Q2, the battery output terminal, and the fourth switch Q4, charging the battery at the battery output terminal, and the inductor current decreases. Since the freewheeling process is achieved through the second switch Q2 and the fourth switch Q4 with low on-resistance, the conduction loss is reduced by more than 80% compared to traditional diode freewheeling, making it suitable for buck converter applications with high inductor current.

[0033] like Figure 3C As shown, in the Boost synchronous rectification mode, the first switch Q1 and the second switch Q2 adopt complementary PWM control (the second switch Q2 is off when the first switch Q1 is on, and the second switch Q2 is on when the first switch Q1 is off), and the third switch Q3 and the fourth switch Q4 adopt complementary PWM control (the fourth switch Q4 is off when the third switch Q3 is on, and the fourth switch Q4 is on when the third switch Q3 is off). The PWM duty cycle is adjusted to adapt to the boost requirement (duty cycle D=1-Vin / Vout, where Vin is the photovoltaic voltage at the photovoltaic input terminal and Vout is the battery voltage at the battery output terminal).

[0034] When the second switch Q2 is on, the first switch Q1 is off, the fourth switch Q4 is on, and the third switch Q3 is off, the input voltage forms a loop through the second switch Q2, the energy storage inductor L1, and the fourth switch Q4, storing energy and causing the inductor current to rise. When the second switch Q2 is off, the first switch Q1 is on, the fourth switch Q4 is off, and the third switch Q3 is on, the energy released by the energy storage inductor L1 is superimposed on the photovoltaic voltage, forming a loop through the first switch Q1, the third switch Q3, and the battery output terminal for boost charging, causing the inductor current to decrease. In this mode, the freewheeling circuit achieves synchronous rectification through the second switch Q2 and the fourth switch Q4, reducing losses and making it suitable for boost conditions with high inductor current.

[0035] like Figure 3D As shown, in the Boost circuit mode, the first switch Q1 remains normally open, while the second and third switches Q2 and Q3 remain normally closed. Only the fourth switch Q4 is controlled by the PWM signal, achieving periodic on and off switching. When the fourth switch Q4 is on, the input voltage forms a loop through the first switch Q1, the energy storage inductor L1, and the fourth switch Q4, storing energy and causing the inductor current to rise. When the fourth switch Q4 is off, the energy storage inductor L1 releases energy, forming a loop through the first switch Q1 and the battery output (the second and third switches Q2 and Q3 are off to prevent current backflow) for boost charging, causing the inductor current to decrease. In this mode, because the first switch Q1 is normally open and the second and third switches Q2 and Q3 are off, the reverse loop from the battery output to the photovoltaic input is effectively cut off, making it suitable for boost conditions where the inductor current is low and the photovoltaic voltage at the photovoltaic input is low.

[0036] based on Figures 3A-3D In an embodiment of the present invention, a multi-mode MPPT control method for a photovoltaic energy storage system is provided, based on the dual judgment logic of inductor current and voltage comparison. The MPPT controller collects inductor current, photovoltaic voltage at photovoltaic input and battery voltage at battery output in real time, and achieves adaptive switching through a preset algorithm. Figure 4 A flowchart of an MPPT multi-mode control method for a photovoltaic energy storage system provided in an embodiment of the present invention is shown below. Figure 4 As shown, the method includes: Step 102: Real-time acquisition of the inductor current of the energy storage inductor, the photovoltaic voltage at the photovoltaic input terminal, and the battery voltage at the battery output terminal.

[0037] In this embodiment of the invention, each step is executed by the MPPT controller for control. Figures 3A-3D The H4 bridge arm topology in the example.

[0038] In an embodiment of the present invention, the inductor current IL of the energy storage inductor, the photovoltaic voltage Vin at the photovoltaic input end, and the battery voltage Vout at the battery output end can be collected.

[0039] Step 104: Compare the photovoltaic voltage with the battery voltage, determine whether the H4-bridge arm topology should currently operate in the buck state or the boost state according to the comparison result, and obtain the buck-boost determination result.

[0040] In an embodiment of the present invention, the difference between the photovoltaic voltage Vin and the battery voltage Vout can be calculated in real time. When the photovoltaic voltage Vin is greater than or equal to the sum of the battery voltage Vout and the buck-mode trigger threshold ΔV1 (Vin≥Vout + ΔV1), it is determined that the H4-bridge arm topology should currently operate in the buck state and switch between the Buck circuit mode and the Buck synchronous rectification mode. Among them, the buck-mode trigger threshold ΔV1 can be set according to the actual situation. For example, the buck-mode trigger threshold ΔV1 is 1 - 3V, which can avoid frequent switching of the control mode.

[0041] When the photovoltaic voltage Vin is less than or equal to the difference between the battery voltage Vout and the boost-mode trigger threshold ΔV2 (Vin≤Vout - ΔV2), it is determined that the H4-bridge arm topology should currently operate in the boost state and switch between the Boost synchronous rectification mode and the Boost circuit mode. Among them, the boost-mode trigger threshold ΔV2 can be set according to the actual situation. For example, the boost-mode trigger threshold ΔV2 is 1 - 3V.

[0042] When the photovoltaic voltage Vin is greater than the difference between the battery voltage Vout and the boost-mode trigger threshold ΔV2 and less than the sum of the battery voltage Vout and the buck-mode trigger threshold ΔV1 (Vout - ΔV2 < Vin < Vout + ΔV1), the current control mode is maintained. Through the anti-jitter mechanism, it is possible to avoid frequent switching of the control mode caused by voltage fluctuations.

[0043] Step 106: Based on the buck-boost determination result and the real-time comparison between the inductor current and the preset current threshold, adaptively switch between the asynchronous rectification mode and the synchronous rectification mode in the corresponding working state. The asynchronous rectification mode includes the Buck circuit mode and the Boost circuit mode, and the synchronous rectification mode includes the Buck synchronous rectification mode and the Boost synchronous rectification mode.

[0044] In an embodiment of the present invention, the inductor current IL is collected in real time and compared with the preset current threshold IL_th. Among them, the preset current threshold IL_th can be set according to the rated current of the switching tube, the rated current of the inductor, and the system loss target. For example, the preset current threshold IL_th can be 3% - 5% of the rated current.

[0045] Under the step-down condition, when the inductor current \(I_L\) is greater than the preset current threshold \(I_{L\_th}\), it switches from the Buck circuit mode to the Buck synchronous rectification mode (using synchronous rectification to reduce losses at high currents). When the inductor current \(I_L\) is less than the difference between the preset current threshold \(I_{L\_th}\) and the current hysteresis threshold \(\Delta I_L\) (\(I_L < I_{L\_th}-\Delta I_L\)), it switches from the Buck synchronous rectification mode to the Buck circuit mode (at low currents, the control complexity of the non-synchronous rectification mode (Buck circuit mode) is lower and the loss difference is smaller). Among them, the current hysteresis threshold \(\Delta I_L\) can be set according to the actual situation. For example, the current hysteresis threshold \(\Delta I_L\) can be 1% - 2% of the preset current threshold \(I_{L\_th}\).

[0046] Under the step-up condition, when the inductor current \(I_L\) is greater than the preset current threshold \(I_{L\_th}\), it switches from the Boost circuit mode to the Boost synchronous rectification mode. When the inductor current \(I_L\) is less than the difference between the preset current threshold \(I_{L\_th}\) and the current hysteresis threshold \(\Delta I_L\), it switches from the Boost synchronous rectification mode to the Boost circuit mode.

[0047] In the embodiment of the present invention, to avoid the switch tubes being directly connected or current impact during the control mode switching, the following protection mechanism is set during the switching process: The pulse width modulation signals of the complementary switch tubes among the first switch tube \(Q1\), the second switch tube \(Q2\), the third switch tube \(Q3\), and the fourth switch tube \(Q4\) are set with a set dead time. For example, the set dead time is 50 - 100 ns to ensure that all switch tubes do not conduct simultaneously.

[0048] After the adaptive switching between the non-synchronous rectification mode and the synchronous rectification mode, the duty cycle of the pulse width modulation signal is adjusted in a stepwise manner (each adjustment is 0.5% - 1%) to avoid sudden rises and falls of the inductor current.

[0049] During the switching process between the non-synchronous rectification mode and the synchronous rectification mode, if the inductor current is greater than the set ratio of the rated current (for example, the set ratio is 150%), then the first switch tube \(Q1\), the second switch tube \(Q2\), the third switch tube \(Q3\), and the fourth switch tube \(Q4\) are turned off, and after a set time (for example, the set time is 10 ms), the control mode judgment is restarted to prevent component damage.

[0050] The above photovoltaic control method is described below with a specific embodiment.

[0051] Assume that in a typical balcony photovoltaic system, the Figures 3A-3D H4 bridge arm topology is adopted, and two PV panels with an open-circuit voltage of 30V are connected in series to the photovoltaic input end, and the battery voltage at the battery output end is 50V.

[0052] When the device is powered on but the PV board is not inserted, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 of the H4 bridge arm topology are in the off state, continuously monitoring the connection status of the PV board. At this time, the system is in standby mode with extremely low power consumption.

[0053] When the sun rises, the PV panel is connected to the system. At this time, the photovoltaic input terminal detects a photovoltaic voltage of 60V, which is greater than the battery voltage of 50V. The MPPT starts to work. At this time, the light is weak and the power generated is small, so the system enters the Buck circuit mode.

[0054] When the light intensity increases, the operating power of the PV board increases, the inductor current rises, and the system switches from Buck circuit mode to Buck synchronous rectification mode.

[0055] When a cloud passes by or covers a single PV panel, its voltage drops rapidly and its output power decreases simultaneously. At this time, the photovoltaic voltage at the photovoltaic input terminal of the system's MPPT drops to about 40V, which is lower than the battery voltage of 50V. Meanwhile, the uncovered PV panels continue to generate power at full capacity, and the system enters the Boost synchronous rectification mode.

[0056] When the light intensity decreases and shading is present, the power of the uncovered PV panel decreases, causing the inductor current to decrease. At this time, the system switches from Boost synchronous rectification mode to Boost mode.

[0057] As can be seen from the above implementation process, it can adapt to the changes in photovoltaic voltage of PV panels in practical applications, quickly enter a high-efficiency working state, and maintain a high energy conversion efficiency under different lighting conditions, while effectively controlling costs.

[0058] In the technical solution provided by this invention, the method is used in an MPPT controller. The MPPT controller controls the H4 bridge arm topology and collects in real time the inductor current of the energy storage inductor, the photovoltaic voltage at the photovoltaic input terminal, and the battery voltage at the battery output terminal. The photovoltaic voltage is compared with the battery voltage, and based on the comparison result, it is determined whether the H4 bridge arm topology should currently operate in buck or boost mode, obtaining a buck / boost determination result. Based on the buck / boost determination result and the real-time comparison of the inductor current with a preset current threshold, adaptive switching is performed between asynchronous rectification mode and synchronous rectification mode under the corresponding operating state. The asynchronous rectification mode includes Buck circuit mode and Boost circuit mode, and the synchronous rectification mode includes Buck synchronous rectification mode and Boost synchronous rectification mode. The technical solution provided by this invention solves the current backflow problem, reduces freewheeling loss, and improves MPPT efficiency.

[0059] The technical solution provided by the embodiments of the present invention significantly reduces the loss of low-voltage systems and improves MPPT efficiency. In view of the problem of high diode loss in the traditional Buck+Boost two-switch two-diode solution in low-voltage systems, the embodiments of the present invention adopt synchronous rectification mode under high inductor current conditions, and realize freewheeling by replacing diodes with MOSFETs with low on-resistance, which significantly improves the energy utilization efficiency of home energy storage systems.

[0060] The technical solution provided by this invention completely solves the current backflow problem and can protect the safety of the PV board. In response to the current backflow risk of the synchronous rectification scheme of the H4 bridge arm topology, this invention switches to the commonly used Buck mode and Boost mode when the inductor current is low to prevent current backflow to the PV board.

[0061] The technical solution provided in this invention utilizes a dual judgment logic based on voltage comparison and current threshold comparison. Without complex algorithm models, it only requires real-time acquisition of three key parameters (inductor current IL of the energy storage inductor, photovoltaic voltage Vin at the photovoltaic input terminal, and battery voltage Vout at the battery output terminal) by the MPPT controller to achieve adaptive switching. The control delay is less than 10μs, meeting the real-time tracking requirements of the MPPT module. Simultaneously, dead-zone control, current ramp-up, and overcurrent protection mechanisms during control mode switching avoid risks such as switch shoot-through and current surges, balancing high system efficiency and high reliability.

[0062] This invention provides a storage medium that includes a stored program. When the program runs, it controls the device where the storage medium is located to execute the steps of the embodiment of the MPPT multi-mode control method for the photovoltaic energy storage system described above. For a detailed description, please refer to the embodiment of the MPPT multi-mode control method for the photovoltaic energy storage system described above.

[0063] This invention provides an MPPT controller, including a memory and a processor. The memory stores information including program instructions, and the processor controls the execution of the program instructions. When the program instructions are loaded and executed by the processor, they implement the steps of the above-described embodiment of the MPPT multi-mode control method for photovoltaic energy storage system. For a detailed description, please refer to the above-described embodiment of the MPPT multi-mode control method for photovoltaic energy storage system.

[0064] Figure 5 This is a schematic diagram of an MPPT controller provided in an embodiment of the present invention. Figure 5As shown, the MPPT controller 20 of this embodiment includes a processor 21, a memory 22, and a computer program 23 stored in the memory 22 and executable on the processor 21. When the computer program 23 is executed by the processor 21, it implements the MPPT multi-mode control method applied to the photovoltaic energy storage system in this embodiment. To avoid repetition, it will not be described in detail here.

[0065] The MPPT controller 20 includes, but is not limited to, a processor 21 and a memory 22. Those skilled in the art will understand that... Figure 5 This is merely an example of MPPT controller 20 and does not constitute a limitation on MPPT controller 20. It may include more or fewer components than shown, or combine certain components, or different components. For example, MPPT controller may also include input / output devices, network access devices, buses, etc.

[0066] The processor 21 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0067] The memory 22 can be an internal storage unit of the MPPT controller 20, such as the hard disk or RAM of the MPPT controller 20. The memory 22 can also be an external storage device of the MPPT controller 20, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the MPPT controller 20. Furthermore, the memory 22 can include both internal storage units and external storage devices of the MPPT controller 20. The memory 22 is used to store computer programs and other programs and data required by the MPPT controller. The memory 22 can also be used to temporarily store data that has been output or will be output.

[0068] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0069] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0070] The units described as separate components may or may not be physically separate. 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 units can be selected to achieve the purpose of this embodiment according to actual needs.

[0071] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0072] The integrated units implemented as software functional units described above can be stored in a computer-readable storage medium. These software functional units, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute some steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-mode MPPT control method for a photovoltaic energy storage system, characterized in that, An MPPT controller is used to control an H4 bridge arm topology, the H4 bridge arm topology including a photovoltaic input terminal, a battery output terminal, a first switch, a second switch, a third switch, a fourth switch, and an energy storage inductor; the method includes: The inductor current of the energy storage inductor, the photovoltaic voltage at the photovoltaic input terminal, and the battery voltage at the battery output terminal are collected in real time. The photovoltaic voltage is compared with the battery voltage, and based on the comparison result, it is determined whether the H4 bridge arm topology should currently be operating in buck or boost mode, and the buck / boost determination result is obtained. Based on the buck-boost determination result and the real-time comparison of the inductor current with the preset current threshold, adaptive switching is performed between asynchronous rectification mode and synchronous rectification mode under the corresponding working state. The asynchronous rectification modes include Buck circuit mode and Boost circuit mode, and the synchronous rectification modes include Buck synchronous rectification mode and Boost synchronous rectification mode.

2. The method according to claim 1, characterized in that, The photovoltaic voltage is compared with the battery voltage. Based on the comparison result, it is determined whether the H4 bridge arm topology should currently operate in buck or boost mode, and the buck / boost determination result is obtained, including: When the photovoltaic voltage is greater than or equal to the sum of the battery voltage and the buck mode trigger threshold, it is determined that the H4 bridge arm topology should currently operate in buck mode, and the switching occurs between the Buck circuit mode and the Buck synchronous rectification mode; or... When the photovoltaic voltage is less than or equal to the difference between the battery voltage and the boost mode trigger threshold, it is determined that the H4 bridge arm topology should currently operate in boost mode, and the system switches between the Boost synchronous rectification mode and the Boost circuit mode; or... When the photovoltaic voltage is greater than the difference between the battery voltage and the boost mode trigger threshold and less than the sum of the battery voltage and the buck mode trigger threshold, the current control mode is maintained.

3. The method according to claim 2, characterized in that, Based on the buck-boost determination result and the real-time comparison of the inductor current with the preset current threshold, the adaptive switching between asynchronous rectification mode and synchronous rectification mode is performed under the corresponding operating state, including: Under buck operation, when the inductor current is greater than a preset current threshold, the system switches from the Buck circuit mode to the Buck synchronous rectification mode; or, when the inductor current is less than the difference between the preset current threshold and the current hysteresis threshold, the system switches from the Buck synchronous rectification mode to the Buck circuit mode. Under boost operation, when the inductor current is greater than a preset current threshold, the system switches from the Boost circuit mode to the Boost synchronous rectification mode; or, when the inductor current is less than the difference between the preset current threshold and the current hysteresis threshold, the system switches from the Boost synchronous rectification mode to the Boost circuit mode.

4. The method according to claim 1, characterized in that, In the Buck circuit mode, the second switch, the third switch, and the fourth switch remain in the off state, and the first switch is periodically turned on and off according to the pulse width modulation signal. When the first switch is turned on, the input voltage forms a circuit with the energy storage inductor through the first switch, the energy storage inductor stores energy, and the inductor current increases linearly. When the first switch is turned off, the energy storage inductor releases energy and charges the battery through the battery voltage, the back electromotive force of the energy storage inductor itself, and the circuit parasitic parameters, and the inductor current decreases linearly.

5. The method according to claim 1, characterized in that, In the Buck synchronous rectification mode, when the first switch is turned on, the second switch is turned off, the third switch is turned on, and the fourth switch is turned off, the input voltage forms a loop through the first switch, the energy storage inductor, and the third switch, the energy storage inductor stores energy, and the inductor current rises. When the first switch is turned off, the second switch is turned on, the third switch is turned off, and the fourth switch is turned on, the energy storage inductor releases energy, forming a freewheeling circuit through the second switch, the battery output terminal, and the fourth switch to charge the battery at the battery output terminal, and the inductor current decreases.

6. The method according to claim 1, characterized in that, In the Boost synchronous rectification mode, when the second switch is turned on, the first switch is turned off, the fourth switch is turned on, and the third switch is turned off, the input voltage forms a loop through the second switch, the energy storage inductor, and the fourth switch, the energy storage inductor stores energy, and the inductor current rises. When the second switch is turned off, the first switch is turned on, the fourth switch is turned off, and the third switch is turned on, the energy released by the energy storage inductor is superimposed on the input voltage, and forms a circuit through the first switch, the third switch, and the battery output terminal to perform boost charging, and the inductor current decreases.

7. The method according to claim 1, characterized in that, In the Boost circuit mode, the first switch is kept in the normally open state, and the second and third switches are kept in the normally closed state. When the fourth switch is turned on, the input voltage forms a loop through the first switch, the energy storage inductor, and the fourth switch. The energy storage inductor stores energy, and the inductor current increases. When the fourth switch is turned off, the energy storage inductor releases energy, which forms a circuit through the first switch and the battery output terminal to perform boost charging, and the inductor current decreases.

8. The method according to claim 1, characterized in that, Also includes: The pulse width modulation signals of the complementary switching transistors among the first, second, third, and fourth switching transistors are configured with a set dead time. After adaptive switching between asynchronous rectification mode and synchronous rectification mode, the duty cycle of the pulse width modulation signal is adjusted in a stepwise manner. During the switching process between asynchronous rectification mode and synchronous rectification mode, if the inductor current is greater than a set ratio of the rated current, the first switch, the second switch, the third switch and the fourth switch are turned off and restarted after a set time.

9. A storage medium, characterized in that, The storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the storage medium to perform the MPPT multi-mode control method of the photovoltaic energy storage system according to any one of claims 1 to 8.

10. An MPPT controller, comprising a memory and a processor, the memory for storing information including program instructions, the processor for controlling the execution of the program instructions, characterized in that, When the program instructions are loaded and executed by the processor, they implement the steps of the MPPT multi-mode control method for the photovoltaic energy storage system according to any one of claims 1 to 8.

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