Mppt charging current backflow prevention control method based on buck-boost circuit

Abstract

The application discloses a control method for preventing current backflow of MPPT charging based on a buck-boost circuit, and relates to the technical field of switching power supplies.The method comprises the following steps: collecting photovoltaic input voltage, battery output voltage and inductance current flowing through the inductor; calculating current input power based on the photovoltaic input voltage and the inductance current; dynamically adjusting a reference voltage through an MPPT loop algorithm; performing PI voltage loop operation on the output voltage and the adjusted reference voltage to generate an expected charging current; performing PI current loop operation on the expected charging current and the inductance current sample value adjusted by a proportional coefficient to output a PWM duty cycle control signal for adjusting the driving state of four switching tubes; and shielding the driving signal of the fourth switching tube when the determination circuit is in the discontinuous conduction mode and the critical condition is met, so that only a diode is used to realize a current passage and prevent current backflow in the reverse direction.The application effectively prevents battery current backflow, and improves system safety and energy utilization efficiency.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to a control method for preventing backflow during MPPT charging based on a Buck-Boost circuit. Background Technology

[0002] Currently, in solar photovoltaic (PV) power generation systems, maximum power point tracking (MPPT) technology is widely used to improve the energy conversion efficiency of PV panels. Because the PV input voltage varies significantly with light intensity and temperature, while the battery terminal voltage is relatively stable, a DC-DC converter topology capable of both boost and buck modes is often employed. Among these, the four-switch Buck-Boost circuit, due to its high efficiency, wide input range, and bidirectional energy regulation capability, has become an ideal choice for MPPT charge controllers.

[0003] However, in practical applications, when the solar photovoltaic power generation system operates under light load, when the battery is nearly fully charged, or when the photovoltaic input energy is insufficient, the circuit is prone to entering discontinuous conduction mode (DCM). In this state, traditional control strategies typically maintain continuous drive of all switching transistors.

[0004] Existing conventional four-switch Buck-Boost circuits, such as Figure 1 As shown, it can achieve both boost and buck conversion. However, when connected to a battery, with conventional buck or boost control in DCM mode, battery current flows through switching transistor Q24D, inductor L1, and switching transistor Q24B, back-feeding into the MPPT board. Figure 1 (PVin in the circuit), or grounded through switching transistor Q24D, inductor L1, and switching transistor Q24A. This causes reverse current, which not only results in additional losses but also increases safety hazards.

[0005] Especially in application scenarios where solar input fluctuates and the load is a variable battery system, some existing technologies only focus on backflow prevention control during the soft-start phase, and do not propose a continuous and effective protection mechanism for the DCM condition that frequently occurs during the MPPT dynamic adjustment process, so the current backflow prevention effect is still unsatisfactory.

[0006] Therefore, there is an urgent need for an MPPT charging control method suitable for four-switch Buck-Boost topologies to effectively prevent battery current backflow and improve system safety and energy utilization efficiency. Summary of the Invention

[0007] To provide an MPPT charging control method suitable for a four-switch Buck-Boost topology, effectively preventing battery current backflow and improving system safety and energy utilization efficiency, this application provides an MPPT charging anti-current backflow control method based on a Buck-Boost circuit.

[0008] Firstly, the objective of this invention is achieved through the following technical solution:

[0009] A control method for preventing reverse current flow during MPPT charging based on a Buck-Boost circuit is provided. The Buck-Boost circuit includes a first switch, a second switch, a third switch, and a fourth switch connected between the photovoltaic input terminal and the battery output terminal, and an inductor connected between the switching nodes. The first and second switches form an input-side half-bridge, and the third and fourth switches form an output-side half-bridge. The inductor is connected between the two half-bridges. The method includes:

[0010] The photovoltaic input voltage, battery output voltage, and inductor current flowing through the inductor are collected.

[0011] The current input power is calculated based on the photovoltaic input voltage and inductor current, and the reference voltage is dynamically adjusted using the MPPT loop algorithm.

[0012] The output voltage is compared with the reference voltage adjusted by the proportional coefficient to perform a PI voltage loop operation to generate the desired charging current.

[0013] The desired charging current is used to perform PI current loop operation with the sampled inductor current value adjusted by the proportional coefficient, and the PWM duty cycle control signal is output to adjust the driving state of the first switch, the second switch, the third switch and the fourth switch.

[0014] When the circuit is in intermittent conduction mode and the critical condition is met, the drive signal of the fourth switch is shielded to maintain the off state. The current path is achieved only by the body diode of the fourth switch to prevent the energy from the battery terminal from flowing back into the inductor and causing current backflow.

[0015] By adopting the above technical solution, this application provides an MPPT charging control method for a four-switch Buck-Boost topology, particularly suitable for application scenarios with fluctuating solar input and variable battery loads. This method effectively prevents battery current backflow and improves system safety and energy utilization efficiency without increasing hardware costs. Specifically, this application actively shields the drive signal of the fourth switch Q24D when the system is in deep discontinuous conduction mode (DCM), completely turning it off and relying solely on its body diode for forward conduction. This fundamentally blocks the path of battery energy flowing backward through Q24D and inductor L1 into the photovoltaic input terminal, achieving reliable suppression of backflow current and effectively eliminating the risk of battery current backflow. By reusing the MOSFET's own body diode as a unidirectional conduction element, without adding a dedicated anti-backflow diode or complex reverse current detection circuit (without increasing hardware costs), it ensures the smooth flow of the normal charging path while achieving reverse blocking functionality, significantly reducing system cost and complexity. This system continuously monitors and determines whether Q24D shielding is required throughout the entire MPPT operating cycle. It is particularly suitable for applications with large fluctuations in solar input and dynamic changes in battery load. It solves the problem that traditional technologies only prevent backflow during the soft-start phase and cannot handle light-load backflow during operation. It is applicable to the full-condition MPPT operation monitoring needs, not just the startup phase. By utilizing the MOSFET body diode in DCM mode, additional conduction losses are avoided. Therefore, this application achieves high-efficiency, low-cost, and intelligent backflow prevention control while ensuring the system safety of the solar photovoltaic power generation system. It is particularly suitable for applications with high reliability and energy efficiency requirements, such as photovoltaic MPPT charging.

[0016] In a preferred embodiment, this application determines that the circuit is in an intermittent conduction mode, including:

[0017] When operating in Buck mode, the inductor current is sampled multiple times during the switching cycle of the second switch. If the sampling results are all zero for M consecutive times, it is preliminarily determined that the intermittent conduction mode has been entered, where M is greater than or equal to 3.

[0018] When operating in Boost mode, the inductor current is sampled multiple times during the switching cycle of the third switch. If the results of M consecutive samplings are all zero, it is preliminarily determined that the intermittent conduction mode has been entered. The inductor current is detected by a Hall sensor and output to the main controller as a feedback signal.

[0019] By adopting the above technical solution, a preliminary criterion based on continuous sampling of inductor current is used to identify the DCM state of discontinuous conduction mode (DCM). Since the inductor current will completely return to zero and remain so for a period of time within one switching cycle under ideal DCM conditions, multiple consecutive sampling results of zero are direct evidence of entering DCM. This application effectively filters out noise interference, avoids misjudgment, and can quickly identify the DCM state by performing high-frequency sampling within the switching cycle of the second switch (Buck mode) or the third switch (Boost mode) and setting a threshold condition of "M consecutive zeros" (M≥3).

[0020] In a preferred embodiment of this application: after initially determining that it is in an intermittent conduction mode, a critical mode determination is further performed to decide whether to block the drive signal of the fourth switch, including:

[0021] If currently operating in Buck mode, calculate the critical duty cycle in Buck mode. The formula is:

[0022] in, The charging current is calculated by sampling the inductor current at its center point and dividing it by 2 for each switching cycle; L represents the inductance. For the switching cycle, Photovoltaic input voltage; This refers to the battery output voltage.

[0023] If currently operating in Boost mode, calculate the critical duty cycle in Boost mode. The formula is:

[0024] When the actual duty cycle is less than the corresponding critical duty cycle, it is confirmed that the deep DCM mode has been entered and the fourth switch driver is shielded.

[0025] By adopting the above technical solution, the critical duty cycle is calculated based on circuit parameter modeling to further determine whether drive shielding can be performed; the critical duty cycle in Buck mode reflects the minimum conduction ratio required to maintain continuous inductor current; the critical duty cycle expression in Boost mode is also derived based on energy conservation and is used to determine whether a deep light load state has been entered; when the actual duty cycle is less than the corresponding critical duty cycle, it is confirmed that a deep DCM mode has been entered. At this time, even if the fourth switch is turned off, it will not affect the normal energy transfer, but can instead eliminate the reverse conduction path; compared with a single sampling criterion, this method combines circuit topology parameters (L, ), running status ( , , Dynamic calculations are performed, which enhances the adaptability of the criterion to different loads and input conditions, and avoids false alarms and missed detections caused by fixed thresholds.

[0026] In a preferred embodiment of this application: the MPPT loop algorithm is a perturbation-observation method, comprising:

[0027] Each MPPT control cycle collects the current photovoltaic input voltage and input current, and calculates the current input power;

[0028] Compare the current input power with the input power of the previous cycle;

[0029] If the current power is greater than that of the previous cycle, the original disturbance direction will be maintained, and the reference voltage-inductor current will be adjusted. Increase the step size ΔV;

[0030] If the current power is less than that of the previous cycle, a reverse perturbation is performed to reduce the reference voltage by one step ΔV.

[0031] The reference voltage The initial value is set to 2.5V to adjust the target setting of the PI voltage loop to track the maximum power point.

[0032] By adopting the above technical solution and using the perturbation-observation method as the core algorithm of the MPPT loop, dynamic tracking of the photovoltaic maximum power point is achieved. This is achieved by periodically perturbing the reference voltage. And compare the power changes before and after, generating As the setting value of the PI voltage loop, it directly affects the expected charging current, achieving a seamless connection between the MPPT target and the battery charging requirements.

[0033] In a preferred embodiment of this application, the output of the PI voltage loop is the desired charging current. The calculation formula is:

[0034] in, The gain is proportional, and K is the period index. This is the error value. =Reference voltage -Currently acquired output voltage ×First proportional coefficient Calculated for the previous period The value, For integral gain, This represents the PWM period value.

[0035] By adopting the above technical solution, the PI voltage loop, as the outer loop, is responsible for stabilizing the output voltage and setting the charging current target. This application uses the PI voltage loop to convert the deviation between the reference voltage and the actual output voltage into the desired charging current. This facilitates precise energy management during the charging process of the solar panels. Proportional gain Provides fast response and integral gain Eliminate steady-state error and ensure Accurate tracking change.

[0036] In a preferred embodiment of this application: the input of the PI current loop is the desired charging current. The difference between the sampled inductor current and the output is the duty cycle control value N required for PWM modulation. The calculation formula is as follows:

[0037] Where N is a constant, and after being limited, N is mapped to the duty cycle command of the PWM generator; The proportional gain of the current loop. This is the integral gain of the current loop. = -Inductor current sample value × second proportional coefficient Calculated for the previous period The value of .

[0038] By adopting the above technical solution, the desired charging current is generated through a PI current loop. The deviation from the actual inductor current is converted into a PWM duty cycle control quantity, enabling precise driving of the power switch. As the inner loop, the PI current loop has high bandwidth characteristics, enabling rapid response to load disturbances and input fluctuations, thus improving the system's dynamic performance. The inductor current sample value is normalized by a second proportional coefficient to eliminate errors caused by sensor gain drift or temperature effects; N is limited and mapped to the duty cycle command of the PWM generator, directly driving the switching transistor.

[0039] In a preferred embodiment of this application: after shielding the drive signal of the fourth switch, the corresponding body diode is allowed to conduct during forward conduction to maintain a normal charging path; during reverse recovery, the reverse current is prevented from flowing from the battery terminal through the inductor and the fourth switch to the photovoltaic input terminal because the fourth switch is not actively turned on; and when the system transitions from intermittent conduction mode to continuous conduction mode, the drive shielding state of the fourth switch is dynamically released according to the duty cycle change trend.

[0040] By employing the above technical solution, after shielding the drive signal of the fourth switch, its body diode is cleverly utilized to achieve forward conduction and reverse blocking. Simultaneously, a dynamic release mechanism is designed to ensure a smooth transition between different conduction modes. Specifically, after shielding the fourth switch, its channel is turned off, but during the forward freewheeling phase, its body diode naturally conducts, maintaining the normal charging path. When the inductor current returns to zero and attempts to reverse, the body diode is reverse-biased and cut off, and without a gate drive signal, the channel cannot open, completely blocking the reverse charging path from battery to inductor to photovoltaic. When the system transitions from DCM (discontinuous conduction mode) to CCM (continuous conduction mode), the main controller dynamically releases the shield based on the increasing duty cycle trend, restoring the PWM drive of the fourth switch.

[0041] In a preferred example, this application: after calculating the critical duty cycle... and Then, a safety margin factor An is introduced, and the critical duty cycle actually used for comparison is set to... ×An, or, set as ×An; The safety margin factor An is adaptively adjusted based on the reverse recovery time of the body diode of the fourth switch, the junction temperature characteristics, and the system operating power level.

[0042] By adopting the above technical solution, a safety margin factor An is introduced into the critical duty cycle criterion, and the actual reliability of the criterion is improved by compensating for the characteristics of non-ideal devices through an adaptive adjustment mechanism. Specifically, the adaptive adjustment mechanism includes dynamic adjustment of An based on the reverse recovery time of the body diode, junction temperature, and system power level: at high temperature or high power, An takes a smaller value to enhance protection; at low temperature or light load, An is close to 1 to avoid excessive conservatism.

[0043] Secondly, the objective of this invention is achieved through the following technical solution:

[0044] The control system for preventing reverse current flow during MPPT charging based on Buck-Boost circuit includes: photovoltaic input terminal, battery output terminal, four-switch Buck-Boost power conversion circuit, Hall current sensor, digital controller and drive circuit.

[0045] The four-switch Buck-Boost circuit includes a first switch, a second switch, a third switch, a fourth switch, and an inductor. The first switch and the second switch form an input-side half-bridge, the third switch and the fourth switch form an output-side half-bridge, and the inductor is connected between the two half-bridges.

[0046] The Hall current sensor is used to detect the current flowing through the inductor in real time and input the sampling signal to the digital controller;

[0047] The digital controller executes the mppt charging anti-current backflow control method based on the Buck-Boost circuit as described above, specifically configured as follows:

[0048] MPPT tracking is achieved based on input voltage and inductor current;

[0049] PWM control signals are generated through PI voltage loop and PI current loop;

[0050] In Buck mode or Boost mode, based on the inductor current sampling results and the critical duty cycle criterion, it is dynamically determined whether to enter the deep DCM mode that requires the fourth switch to be shielded.

[0051] When the deep DCM mode is determined, a shielding signal is output to the drive circuit of the fourth switch to keep the fourth switch off and only use the corresponding body diode for forward conduction to prevent battery energy from flowing back in.

[0052] When transitioning from deep DCM mode to CCM mode, the shield is removed, and the normal PWM drive of the fourth switch is restored.

[0053] In summary, this application includes at least one of the following beneficial technical effects:

[0054] 1. Unlike existing technologies that only focus on backflow prevention during the soft-start phase and do not propose a continuous and effective protection mechanism for the DCM condition that frequently occurs during MPPT dynamic adjustment, this application addresses the issue of inconsistent solar input and variable battery loads. In particular, existing technologies lack a comprehensive control strategy that can actively identify the DCM state and intelligently shut down key switches (such as Q24D) throughout the entire operating cycle. Therefore, this application introduces a fourth switch drive shielding mechanism based on discontinuous conduction mode (DCM) identification in a four-switch Buck-Boost topology, fundamentally suppressing reverse energy flow from the battery. When the circuit operates under light load or insufficient input energy, the inductor current tends to zero and may reverse. If the fourth switch is still driven normally, its channel can conduct under reverse voltage, forming a backflow loop from the battery through the output half-bridge and inductor to the input side. Therefore, this application actively shields the fourth switch drive signal after determining that it is in DCM and meets the critical conditions, forcing it into a shutdown state and relying solely on the body diode for unidirectional conduction.

[0055] 2. Since the MOSFET body diode has unidirectional conductivity, it allows current to pass through during the forward charging phase, but cannot open the channel during the reverse recovery phase due to the lack of gate drive, thereby effectively blocking the reverse energy flow. This application realizes the active anti-reverse current function by utilizing the parasitic structure of the existing MOSFET without adding additional power devices. Attached Figure Description

[0056] Figure 1 This is a current four-switch Buck-Boost circuit diagram;

[0057] Figure 2 This is a flowchart of a control method for preventing reverse current flow during MPPT charging based on a Buck-Boost circuit in one embodiment of this application;

[0058] Figure 3 This is a circuit diagram of the Buck-Boost circuit in the control method for preventing backflow during MPPT charging based on the Buck-Boost circuit in one embodiment of this application. Detailed Implementation

[0059] The present application will be further described in detail below with reference to the accompanying drawings.

[0060] In one embodiment, such as Figure 2 and Figure 3 As shown, this application discloses a control method for preventing reverse current flow during MPPT charging based on a Buck-Boost circuit. The Buck-Boost circuit includes a first switch, a second switch, a third switch, and a fourth switch connected between the photovoltaic input terminal and the battery output terminal, and an inductor connected between the switching nodes. The inductor is an energy storage inductor. The first switch and the second switch form an input-side half-bridge, and the third switch and the fourth switch form an output-side half-bridge. The inductor is connected between the two half-bridges.

[0061] Furthermore, the buck mode and boost mode of the four-switch Buck-Boost circuit are described: For example... Figure 3 As shown, with Figure 3 Taking the circuit diagram shown as an example, the first switching transistor is... Figure 1 The transistors are: Q24A (second switch), Q24B (third switch), Q24C (fourth switch), and Q24D (fourth switch). The inductor is L1. ISEN1, connected in series with inductor L1, is a Hall sensor. Figure 3 In this context, PVin refers to the voltage input of the solar panel, and BAT refers to the battery.

[0062] When operating in Buck mode, BUCK mode operating state 1 is: inductor energy storage, Q24D normally on, Q24C normally off. Within one PWM cycle, Q24B is on, Q24A is off, inductor L1 stores energy, and the inductor current increases.

[0063] In BUCK mode, operating state 2 is as follows: inductor discharge, Q24D normally on, Q24C normally off. Within one PWM cycle, Q24B is off, Q24A is on, inductor L1 discharges, and the inductor current decreases.

[0064] BUCK mode operating state 3: When the load is small, the battery is fully charged, or the input PVin energy is insufficient, the inductor current decreases from state 2 to 0. Because Q24D is normally on and Q24C is normally off, within one PWM cycle, the drive maintains state 2, Q24B is off, Q24A is on, and the inductor current rises in the reverse direction. At this time, it enters discontinuous conduction mode (DCM), which requires charging current anti-reverse current control. See steps S1 to S5 below for specific control methods. This application utilizes the Q24D body diode. When in DCM mode, Q24D is not on, and BAT energy cannot flow in reverse through Q24D (because the body diode is reverse biased and Q24D is not driven). However, in DCM mode, the body diode can flow in the forward direction, which does not prevent charging of BAT in DCM mode.

[0065] When operating in Boost mode, the first operating state of Boost mode is: inductor energy storage, Q24B normally on, Q24A normally off. Within one PWM cycle, Q24C is on, Q24D is off, inductor L1 stores energy, and the inductor current increases.

[0066] In Boost mode, state 2 is as follows: inductor stores energy, Q24B is normally on, and Q24A is normally off. Within one PWM cycle, Q24C is off, Q24D is on, the inductor releases the stored energy, and the inductor current decreases.

[0067] The Boost mode operating state 3 is as follows: (when the load is small, the battery is fully charged, or the input PVin energy is insufficient), because Q24B is normally on and Q24A is normally off. (At this time, the control switches in state 2 are still maintained.) Within one PWM cycle, Q24C is off and Q24D is on. After the inductor current drops to 0, it causes a reverse current from the output Cout to the input Pvin. At this time, it enters the discontinuous conduction mode (DCM), which requires charging current reverse current control. For specific control methods, please refer to steps S1 to S5 below.

[0068] The control method for preventing backflow during MPPT charging based on Buck-Boost circuits includes the following steps:

[0069] S1: Collects photovoltaic input voltage, battery output voltage, and inductor current flowing through the inductor.

[0070] In this embodiment, in each PWM control cycle (switching frequency is 100kHz, i.e., switching cycle) (For 10 μs), at the beginning, the following sampling is performed:

[0071] The photovoltaic input voltage is acquired at the photovoltaic input terminal via ADC channel 1. ;

[0072] The battery output voltage is acquired through ADC channel 2 at the battery output terminal. ;

[0073] Inductor current is acquired via ADC channel 3. The sampling frequency is 800kHz, meaning that the current is sampled 8 times in each switching cycle to capture the current zero-crossing point.

[0074] S2: Calculate the current input power based on the photovoltaic input voltage and inductor current, and dynamically adjust the reference voltage through the MPPT loop algorithm.

[0075] In this embodiment, the perturbation-observation method is used for maximum power point tracking (MPPT), with a control period of 100ms.

[0076] Specifically, the MPPT loop algorithm is a perturbation-observation method, including:

[0077] Each MPPT control cycle collects the current photovoltaic input voltage and input current, calculates the current input power, compares the current input power with the input power of the previous cycle, and if the current power is greater than that of the previous cycle, maintains the original disturbance direction and increases the reference voltage-inductor current by a step size ΔV.

[0078] If the current power is less than that of the previous cycle, a reverse perturbation is applied, reducing the reference voltage by a step size ΔV. The step size ΔV is, for example, 0.1V.

[0079] In this embodiment, the initial value of the reference voltage can be set to 2.5V, with a variation range of 0 to 5V, to adjust the target setting of the PI voltage loop in order to track the maximum power point.

[0080] Further, calculate the current input power. : (Approximately the input current), the current power Compared with the power of the previous cycle Compare:

[0081] like > Then the reference voltage ;like < Then the reference voltage Reference voltage As the setting value for the PI voltage loop.

[0082] S3: Perform a PI voltage loop operation on the output voltage and the reference voltage adjusted by the proportional coefficient to generate the desired charging current.

[0083] In this embodiment, the main controller is a microcontroller such as the STM32F407, which has a built-in 12-bit ADC, PWM generator and floating-point arithmetic unit.

[0084] Specifically, the output of the PI voltage loop is the desired charging current. The calculation formula is:

[0085] in, The gain is proportional, and K is the period index. This is the error value. =Reference voltage -Currently acquired output voltage ×First proportional coefficient Calculated for the previous period The value, For integral gain, This represents the PWM period value. The period is the PWM control period. The first proportional coefficient is set to a value such as 0.01. Values ​​such as 2.0, Values ​​such as 0.5.

[0086] S4: Perform PI current loop operation on the desired charging current and the sampled inductor current value adjusted by the proportional coefficient, and output PWM duty cycle control signal to adjust the drive state of the first switch, the second switch, the third switch and the fourth switch.

[0087] Specifically, the input to the PI current loop is the desired charging current. The difference between the sampled inductor current and the output is the duty cycle control value N required for PWM modulation. The calculation formula is as follows:

[0088] Where N is a constant, and after being limited, N is mapped to the duty cycle command of the PWM generator; The proportional gain of the current loop. This is the integral gain of the current loop. = -Inductor current sample value × second proportional coefficient Calculated for the previous period The value of N. For example, the value of N ranges from 0 to 10. The second proportional coefficient is the current sampling gain coefficient, which is set according to the sensitivity of the Hall sensor. For example, if the sensitivity of the Hall sensor of model ACS712 is 66mV / A, then the second proportional coefficient = 1 / 0.066 ≈ 15.15. In this embodiment, the Hall sensor is used to sample the inductor current in real time during each PWM control cycle.

[0089] S5: When the circuit is in discontinuous conduction mode and the critical condition is met, the drive signal of the fourth switch is shielded to keep it off. The current path is achieved only by the body diode of the fourth switch to prevent the energy from the battery terminal from flowing back into the inductor and causing current backflow.

[0090] In this embodiment, the following backflow prevention logic is executed within each control cycle:

[0091] (1) Preliminary judgment of intermittent conduction mode (DCM):

[0092] If the system is working in Buck mode ( > Then, during the switching cycle of the second switching transistor, the inductor current... Perform 8 samplings;

[0093] If the system is working in Boost mode ( < If the value is 0, then 8 samples are taken during the switching cycle of the third switch. If the value is 0 for 3 consecutive samples, it is preliminarily determined that it is an intermittent conduction mode.

[0094] Specifically, determining whether a circuit is in intermittent conduction mode includes:

[0095] When operating in Buck mode, the inductor current is sampled multiple times during the switching cycle of the second switch. If the results of M consecutive samplings are all zero, it is preliminarily determined that the system has entered discontinuous conduction mode, where M is greater than or equal to 3. When operating in Boost mode, the inductor current is sampled multiple times during the switching cycle of the third switch. If the results of M consecutive samplings are all zero (or below the 5mA threshold), it is preliminarily determined that the system has entered discontinuous conduction mode. The inductor current is detected by a Hall sensor and output to the main controller as a feedback signal. The main controller is an STM32F407 microcontroller. The driving circuit for the fourth switch can use an isolated gate driver chip (such as UCC21520) to convert the PWM signal output by the controller into high-current drive pulses, which control the on / off states of the first, second, third, and fourth switches, respectively.

[0096] 1. Further perform critical mode determination:

[0097] After initially determining that it is in intermittent conduction mode, a critical mode determination is further performed to decide whether to block the drive signal of the fourth switch, including:

[0098] If currently operating in Buck mode, calculate the critical duty cycle in Buck mode. The formula is:

[0099] in, The charging current is calculated by sampling the inductor current at its center point and dividing it by 2 for each switching cycle; L represents the inductance. For the switching cycle, Photovoltaic input voltage; This refers to the battery output voltage.

[0100] If currently operating in Boost mode, calculate the critical duty cycle in Boost mode. The formula is:

[0101] When the actual duty cycle is less than the corresponding critical duty cycle, the system confirms entry into deep DCM mode and executes the fourth switch drive shielding. The main controller sends a "fourth switch shielding" command to the drive circuit, forcibly shutting down the PWM drive signal of the fourth switch and keeping it completely off; at this time, the body diode of the fourth switch can still conduct in the forward direction.

[0102] Furthermore, after shielding the drive signal of the fourth switch, the corresponding body diode is allowed to conduct during forward conduction to maintain the normal charging path; during reverse recovery, the reverse current is prevented from flowing from the battery terminal through the inductor and the fourth switch to the photovoltaic input terminal because the fourth switch is not actively turned on; and when the system transitions from discontinuous conduction mode to continuous conduction mode, the drive shielding state of the fourth switch is dynamically released according to the duty cycle change trend.

[0103] In practical applications, due to the enhanced light from the charging solar panels or the demand for battery charging, the entire solar photovoltaic power generation system will transition from discontinuous conduction mode (DCM) to continuous conduction mode (CCM). At this time, the reference voltage rises, causing the duty cycle D to gradually increase. When the duty cycle D is detected to be greater than the critical duty cycle and continues for several cycles, the main controller releases the shielding state of the fourth switch and restores its normal PWM drive, thus achieving a smooth transition of mode switching.

[0104] In one embodiment, a safety margin factor An is introduced to compensate for the reverse recovery time and temperature drift of the Q4 body diode. An is set to a value of 0.9 under high temperature and high power conditions. If currently operating in Buck mode, the critical duty cycle actually used for comparison is set to... ×An. If currently operating in Boost mode, the critical duty cycle actually used for comparison is set to... ×An; The safety margin factor An is adaptively adjusted based on the reverse recovery time of the body diode of the fourth switch, the junction temperature characteristics, and the system operating power level.

[0105] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0106] In one embodiment, a control system for preventing backflow of current during MPPT charging based on a Buck-Boost circuit is provided, which corresponds to the control method for preventing backflow of current during MPPT charging based on a Buck-Boost circuit in the above embodiment.

[0107] The control system for preventing reverse current flow during MPPT charging based on Buck-Boost circuits includes a photovoltaic input terminal, a battery output terminal, a four-switch Buck-Boost power conversion circuit, a Hall current sensor, a digital controller, and a drive circuit. Detailed descriptions of each functional module are as follows:

[0108] The four-switch Buck-Boost circuit includes a first switch, a second switch, a third switch, a fourth switch, and an inductor. The first switch and the second switch form the input half-bridge, the third switch and the fourth switch form the output half-bridge, and the inductor is connected between the two half-bridges.

[0109] Hall current sensors are used to detect the current flowing through an inductor in real time and input the sampled signal to a digital controller;

[0110] The digital controller implements a control method for preventing reverse current flow during MPPT charging, such as a Buck-Boost circuit-based control method, specifically configured as follows:

[0111] MPPT tracking is achieved based on input voltage and inductor current;

[0112] PWM control signals are generated through PI voltage loop and PI current loop;

[0113] In Buck mode or Boost mode, based on the inductor current sampling results and the critical duty cycle criterion, it is dynamically determined whether to enter the deep DCM mode that requires the fourth switch to be shielded.

[0114] When the deep DCM mode is determined, a shielding signal is output to the drive circuit of the fourth switch to keep the fourth switch off and only use the corresponding body diode for forward conduction to prevent battery energy from flowing back in.

[0115] When transitioning from deep DCM mode to CCM mode, the shield is removed, and the normal PWM drive of the fourth switch is restored.

[0116] For specific limitations regarding the control system for preventing backflow during MPPT charging based on Buck-Boost circuits, please refer to the limitations of the control method for preventing backflow during MPPT charging based on Buck-Boost circuits mentioned above, which will not be repeated here. Each module in the aforementioned control system for preventing backflow during MPPT charging based on Buck-Boost circuits can be implemented entirely or partially through software, hardware, or a combination thereof. Each module can be embedded in the processor of the computer device in hardware form or independent of it, or it can be stored in the memory of the computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0117] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0118] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A control method for preventing reverse current flow during MPPT charging based on Buck-Boost circuit, characterized in that, The Buck-Boost circuit includes a first switch, a second switch, a third switch, and a fourth switch connected between the photovoltaic input terminal and the battery output terminal, and an inductor connected between the switching nodes. The first and second switches form an input-side half-bridge, the third and fourth switches form an output-side half-bridge, and the inductor is connected between the two half-bridges. The method includes: The photovoltaic input voltage, battery output voltage, and inductor current flowing through the inductor are collected. The current input power is calculated based on the photovoltaic input voltage and inductor current, and the reference voltage is dynamically adjusted using the MPPT loop algorithm. The output voltage is compared with the reference voltage adjusted by the proportional coefficient to perform a PI voltage loop operation to generate the desired charging current. The desired charging current is used to perform PI current loop operation with the sampled inductor current value adjusted by the proportional coefficient, and the PWM duty cycle control signal is output to adjust the driving state of the first switch, the second switch, the third switch and the fourth switch. When the circuit is in the intermittent conduction mode and the critical condition is met, the drive signal of the fourth switch is shielded to keep it off. The current path is achieved only by the body diode of the fourth switch to prevent the energy from the battery terminal from flowing back into the inductor and causing current backflow. Determining whether the circuit is in intermittent conduction mode includes: When operating in Buck mode, the inductor current is sampled multiple times during the switching cycle of the second switch. If the sampling results are all zero for M consecutive times, it is preliminarily determined that the intermittent conduction mode has been entered, where M is greater than or equal to 3. When operating in Boost mode, the inductor current is sampled multiple times during the switching cycle of the third switch. If the results of M consecutive samplings are all zero, it is preliminarily determined that the intermittent conduction mode has been entered. The inductor current is detected by a Hall sensor and output to the main controller as a feedback signal. After initially determining that it is in an intermittent conduction mode, a critical mode determination is further performed to decide whether to block the drive signal of the fourth switch, including: If currently operating in Buck mode, calculate the critical duty cycle in Buck mode. The formula is: in, The charging current is calculated by sampling the inductor current at its center point and dividing it by 2 for each switching cycle; L represents the inductance. For the switching cycle, Photovoltaic input voltage; This refers to the battery output voltage. If currently operating in Boost mode, calculate the critical duty cycle in Boost mode. The formula is: When the actual duty cycle is less than the corresponding critical duty cycle, confirm entry into deep DCM mode and execute the fourth switch driver shielding. The critical duty cycle is calculated. and Then, a safety margin factor An is introduced, and the critical duty cycle actually used for comparison is set to... ×An, or, set as ×An; The safety margin factor An is adaptively adjusted based on the reverse recovery time of the body diode of the fourth switch, the junction temperature characteristics, and the system operating power level.

2. The control method for preventing backflow during MPPT charging based on Buck-Boost circuit according to claim 1, characterized in that, The MPPT loop algorithm is a perturbation-observation method, including: Each MPPT control cycle collects the current photovoltaic input voltage and input current, and calculates the current input power; Compare the current input power with the input power of the previous cycle; If the current power is greater than that of the previous cycle, the original disturbance direction is maintained and the reference voltage is increased by a step size ΔV. If the current power is less than that of the previous cycle, a reverse perturbation is performed, reducing the reference voltage by one step ΔV. The reference voltage The initial value is set to 2.5V to adjust the target setting of the PI voltage loop to track the maximum power point.

3. The control method for preventing backflow during MPPT charging based on Buck-Boost circuit according to claim 1, characterized in that, The output of the PI voltage loop is the desired charging current. The calculation formula is: in, The gain is proportional, and K is the period index. This is the error value. =Reference voltage -Currently acquired output voltage ×First proportional coefficient Calculated for the previous period The value, For integral gain, This represents the PWM period value.

4. The control method for preventing backflow during MPPT charging based on Buck-Boost circuit according to claim 1, characterized in that, The input to the PI current loop is the desired charging current. The difference between the sampled inductor current and the output is the duty cycle control value N required for PWM modulation. The calculation formula is as follows: Where N is a constant, and after being limited, N is mapped to the duty cycle command of the PWM generator; The proportional gain of the current loop. This is the integral gain of the current loop. = -Inductor current sample value × second proportional coefficient Calculated for the previous period The value of .

5. The control method for preventing backflow during MPPT charging based on Buck-Boost circuit according to claim 1, characterized in that, include: After shielding the drive signal of the fourth switch, the corresponding body diode is allowed to conduct during forward conduction to maintain the normal charging path; During reverse recovery, the reverse current is prevented from flowing from the battery terminal through the inductor and the fourth switch to the photovoltaic input terminal because the fourth switch is not actively turned on; and when the system transitions from intermittent conduction mode to continuous conduction mode, the driving shielding state of the fourth switch is dynamically released according to the duty cycle change trend.

6. A control system for preventing reverse current flow during MPPT charging based on Buck-Boost circuit, characterized in that, include: Photovoltaic input terminal, battery output terminal, four-switch Buck-Boost power conversion circuit, Hall current sensor, digital controller and drive circuit; The four-switch Buck-Boost circuit includes a first switch, a second switch, a third switch, a fourth switch, and an inductor. The first switch and the second switch form an input-side half-bridge, the third switch and the fourth switch form an output-side half-bridge, and the inductor is connected between the two half-bridges. The Hall current sensor is used to detect the current flowing through the inductor in real time and input the sampling signal to the digital controller; The digital controller executes the control method for preventing reverse current flow during MPPT charging based on a Buck-Boost circuit as described in any one of claims 1 to 5, specifically configured as follows: MPPT tracking is achieved based on input voltage and inductor current; PWM control signals are generated through PI voltage loop and PI current loop; In Buck mode or Boost mode, based on the inductor current sampling results and the critical duty cycle criterion, it is dynamically determined whether to enter the deep DCM mode that requires the fourth switch to be shielded. When the deep DCM mode is determined, a shielding signal is output to the drive circuit of the fourth switch to keep the fourth switch off and only use the corresponding body diode for forward conduction to prevent battery energy from flowing back in. When transitioning from deep DCM mode to CCM mode, the shield is removed, and the normal PWM drive of the fourth switch is restored.

Images