A power supply system for a hydrogen fuel cell and a control method

Abstract

The application discloses a power supply system and a control method of a hydrogen fuel cell, relates to the technical field of power supply of the hydrogen fuel cell, and discloses the power supply system, which comprises a fuel cell stack, a battery pack, a boost-buck DCDC converter, a reverse current blocking module, a USB output module, a power detection module, a constant current control module and a microcontroller MCU. The microcontroller MCU controls the working mode of the boost-buck DCDC converter according to the fuel cell stack state, the battery pack state and the load state collected by the power detection module, and adjusts the constant current control module through a digital-to-analog converter (DAC) output control signal. The application sets the boost-buck DCDC converter between the fuel cell and the battery pack, realizes automatic matching between the wide-range fuel cell output voltage and the battery voltage, enables the fuel cell to realize stable energy transmission when the output voltage is higher or lower than the battery voltage, and effectively prevents the battery from reverse filling the fuel cell in combination with the reverse current blocking circuit.

Description

Technical Field

[0001] This invention relates to the field of power supply technology for hydrogen fuel cells, specifically to a power supply system and control method for hydrogen fuel cells. Background Technology

[0002] With the rapid development of hydrogen energy technology and portable energy storage devices, hydrogen fuel cells are gradually being applied to outdoor power supplies, mobile charging devices, emergency power supplies and new energy vehicles due to their advantages such as high energy density, zero emissions and long driving time. However, the output voltage of fuel cells fluctuates greatly with changes in load, stack operating status and hydrogen pressure and temperature, and its output characteristics are relatively soft, making it difficult to directly meet the requirements of electronic devices for stable power supply. Therefore, it is usually necessary to form a hybrid power supply system with lithium batteries to achieve energy buffering and power compensation.

[0003] Existing fuel cell hybrid power systems typically use a shared bus for power supply to the fuel cell, battery pack, and load. When the fuel cell output voltage is higher than the battery voltage, it can charge the battery. However, when the fuel cell output voltage is lower than the battery voltage, the battery can easily supply power to the fuel cell in reverse. This not only reduces system efficiency but may also damage the fuel cell stack catalyst and affect the stack's lifespan.

[0004] In addition, the output voltage range of fuel cells is typically 9 to 18V, while the voltage range of lithium batteries is generally 9 to 12.6V. The voltage ranges of the two are mismatched, and existing solutions are unable to meet the needs of both battery charging and load power supply.

[0005] Furthermore, with the widespread application of fast charging protocols such as USBPD and QC, different terminal devices have different requirements for output voltage. The original output voltage of fuel cells or battery packs usually cannot directly meet the needs of multiple fast charging protocols, requiring the configuration of corresponding voltage conversion circuits and protocol control circuits. Existing power supply systems have poor compatibility.

[0006] Furthermore, when the system is under no-load or light-load conditions, the fuel cell continues to output power. Existing technologies typically lack a dynamic control mechanism for the output power of the fuel cell. All the energy output by the fuel cell is used to charge the battery. When the charging current exceeds the battery's allowable safe charging current, it can easily cause the battery to overcharge, overheat, or even cause a safety accident, seriously affecting the safety and reliability of the system.

[0007] Therefore, achieving wide voltage matching between the fuel cell and the battery, preventing reverse charging of the fuel cell from the battery, dynamically limiting the fuel cell output power according to the system load state, and ensuring compatibility with multiple USB fast charging protocols are technical problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0008] This invention provides a power supply system and control method for a hydrogen fuel cell, which can effectively solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a power supply system for a hydrogen fuel cell, comprising: a fuel cell stack and a battery pack; Also includes: A buck-boost DC-DC converter, whose input is connected to the fuel cell stack and whose output is connected to the bus and battery pack, is used to operate in boost mode or buck mode according to the relationship between the output voltage of the fuel cell stack and the voltage of the battery pack. The reverse current blocking module is located between the buck-boost DC-DC converter and the bus to prevent the battery pack from supplying reverse power to the fuel cell stack. The USB output module includes a boost converter, a buck converter, and a USB protocol chip connected in sequence. The USB protocol chip is used to identify the fast charging protocol of the load and output the output voltage required by the corresponding protocol. The power detection module is used to detect the output voltage, output current, battery pack voltage, battery charging current, and load status of the fuel cell stack. The constant current control module is located in the output circuit of the fuel cell stack and is used to regulate the output current of the fuel cell stack. The microcontroller (MCU) is connected to the power detection module, the constant current control module, and the buck-boost DC-DC converter, respectively. in, The microcontroller (MCU) controls the operating mode of the buck-boost DC-DC converter based on the fuel cell stack status, battery pack status, and load status collected by the power detection module, and adjusts the constant current control module by outputting control signals through the digital-to-analog converter (DAC).

[0010] According to the above technical solution, the buck-boost DC-DC converter adopts a four-switch Buck-Boost topology or SEPIC topology. When the output voltage of the fuel cell stack is higher than the battery pack voltage, it operates in buck mode, and when the output voltage of the fuel cell stack is lower than the bus voltage, it operates in boost mode.

[0011] According to the above technical solution, the reverse current blocking module includes a MOSFET and a reverse protection controller, and the reverse protection controller controls the MOSFET to turn on or off according to the current direction.

[0012] According to the above technical solution, the constant current control module includes a power MOSFET, an error amplifier, and a current sampling resistor; The error amplifier receives the reference voltage output by the DAC at its first input terminal, receives the current sampling signal at its second input terminal, and connects to the feedback control terminal of the buck-boost DC-DC converter. The output current of the fuel cell stack is adjusted by controlling the conduction state of the power MOSFET inside the buck-boost DC-DC converter.

[0013] According to the above technical solution, the microcontroller (MCU) calculates the target output power based on the fuel cell voltage, battery temperature, and load power, and generates the corresponding DAC output voltage based on the target output power.

[0014] According to the above technical solution, when the load current is detected to be lower than the preset threshold, the microcontroller (MCU) controls the DAC to reduce the reference voltage, so that the constant current control module limits the output current of the fuel cell stack to a preset safe value.

[0015] According to the above technical solution, in the USB output module, the boost converter is used to boost the bus voltage to the highest operating voltage supported by the USB protocol, and the USB protocol chip controls the buck converter to output 5V, 9V, 12V, 15V or 20V according to the identified USB fast charging protocol.

[0016] According to the above technical solution, the microcontroller (MCU) divides the charging process into a pre-charging stage, a constant current charging stage, and a constant voltage charging stage based on the battery charging state, and controls the DAC to output different reference voltages respectively, so as to realize staged charging control.

[0017] According to the above technical solution, a control method for a hydrogen fuel cell power supply system includes the following steps: Acquire fuel cell stack output voltage, stack output current, battery pack voltage, battery charging current, and load status; The buck-boost DC-DC converter is controlled to operate in either boost or buck mode based on the output voltage of the fuel cell stack and the voltage of the battery pack. The target output power of the fuel cell stack is determined and calculated based on the load status and battery status. The MCU generates the DAC control signal based on the target output power; The constant current control module is adjusted according to the DAC control signal to limit the output current of the fuel cell stack; The system detects the fast charging protocol of the USB load and controls the USB output module to output the corresponding output voltage required by the protocol.

[0018] According to the above technical solution, when the load is detected to be disconnected or the load power is lower than the first threshold, the MCU reduces the DAC output voltage to limit the output current of the fuel cell stack to the range of the battery's allowable charging current, or shuts down the charging circuit to put the fuel cell stack into a low-power operating state and protect the fuel cell stack.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves automatic matching between the fuel cell output voltage and the battery voltage over a wide range by setting a buck-boost DC-DC converter between the fuel cell and the battery pack. This enables the fuel cell to achieve stable energy transmission when the output voltage is higher or lower than the battery voltage. At the same time, combined with a reverse current blocking circuit, it effectively prevents the battery from reverse-feeding the fuel cell, improves the safety of system operation, and extends the service life of the fuel cell stack.

[0020] 2. This invention constructs a closed-loop power control system through MCU, DAC and constant current control module, which can collect the operating status of fuel cell, battery and load in real time, and dynamically adjust the output power of fuel cell according to system operating conditions. Under no-load or light-load conditions, it automatically limits the charging current or reduces the output power of fuel cell, effectively avoids battery overcharging and improves the safety and reliability of the system.

[0021] 3. This invention adopts a USB multi-protocol output structure that combines a boost converter and a buck converter. First, the bus voltage is boosted to the highest voltage supported by the USB protocol. Then, different levels of power supply voltage are output according to the identification result of the USB protocol chip, thereby being compatible with multiple fast charging protocols such as USBPD and QC, improving the applicability and charging efficiency of the system.

[0022] 4. This invention can dynamically adjust the charging current according to the battery voltage, temperature and charging stage, and realize adaptive control of different charging stages such as pre-charging, constant current charging and constant voltage charging. This not only improves charging efficiency, but also takes into account the charging safety and service life of different types of batteries. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0024] In the attached diagram: Figure 1 This is a diagram showing the system architecture and connection relationships of the present invention; Figure 2 This is a schematic diagram of the MCU control logic of the present invention; Figure 3 This is the control circuit diagram of the present invention; Figure 4 This is the logic circuit diagram of the present invention. Detailed Implementation

[0025] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] Example 1: like Figure 1 As shown, the present invention provides a technical solution: a power supply system for a hydrogen fuel cell, comprising: a fuel cell stack and a battery pack; Also includes: The buck-boost DC-DC converter has its input end connected to the fuel cell stack and its output end connected to the bus and battery pack. It is used to operate in boost mode or buck mode according to the relationship between the output voltage of the fuel cell stack and the voltage of the battery pack, so as to realize bidirectional energy conversion. The reverse current blocking module is located between the buck-boost DC-DC converter and the bus to prevent the battery pack from supplying reverse power to the fuel cell stack. The USB output module includes a boost converter, a buck converter, and a USB protocol chip connected in sequence. The USB protocol chip is used to identify the fast charging protocol of the load and output the output voltage required by the corresponding protocol. The power detection module is used to detect the output voltage, output current, battery pack voltage, battery charging current, and load status of the fuel cell stack. The constant current control module is located in the output circuit of the fuel cell stack and is used to regulate the output current of the fuel cell stack. The microcontroller (MCU) is connected to the power detection module, the constant current control module, and the buck-boost DC-DC converter, respectively. in, The microcontroller (MCU) controls the operating mode of the buck-boost DC-DC converter based on the fuel cell stack status, battery pack status, and load status collected by the power detection module. It also adjusts the constant current control module by outputting control signals through the digital-to-analog converter (DAC) to limit the output power of the fuel cell stack to the target power range.

[0027] According to the above technical solution, the buck-boost DC-DC converter adopts a four-switch Buck-Boost topology or SEPIC topology. When the output voltage of the fuel cell stack is higher than the battery pack voltage, it operates in buck mode, and when the output voltage of the fuel cell stack is lower than the bus voltage, it operates in boost mode.

[0028] According to the above technical solution, the reverse current blocking module includes a MOSFET and a reverse protection controller. The reverse protection controller controls the MOSFET to turn on or off according to the current direction to prevent the battery pack from generating reverse current to the fuel cell stack.

[0029] According to the above technical solution, the constant current control module includes a power MOSFET, an error amplifier, and a current sampling resistor; The error amplifier receives the reference voltage output by the DAC at its first input terminal, receives the current sampling signal at its second input terminal, and connects to the feedback control terminal of the buck-boost DC-DC converter. The output current of the fuel cell stack is adjusted by controlling the conduction state of the power MOSFET inside the buck-boost DC-DC converter.

[0030] According to the above technical solution, the microcontroller (MCU) calculates the target output power based on the fuel cell voltage, battery temperature and load power, and generates a corresponding DAC output voltage based on the target output power to control the output current of the fuel cell stack.

[0031] According to the above technical solution, when the load current is detected to be lower than the preset threshold, the microcontroller (MCU) controls the DAC to reduce the reference voltage, so that the constant current control module limits the output current of the fuel cell stack to a preset safe value, or shuts down the buck-boost DC-DC converter to avoid overcharging of the battery pack.

[0032] According to the above technical solution, in the USB output module, the boost converter is used to boost the bus voltage to the highest operating voltage supported by the USB protocol, and the USB protocol chip controls the buck converter to output 5V, 9V, 12V, 15V or 20V according to the identified USB fast charging protocol.

[0033] According to the above technical solution, the microcontroller (MCU) divides the charging process into a pre-charging stage, a constant current charging stage, and a constant voltage charging stage based on the battery charging state, and controls the DAC to output different reference voltages respectively, so as to realize staged charging control.

[0034] According to the above technical solution, a control method for a hydrogen fuel cell power supply system includes the following steps: Acquire fuel cell stack output voltage, stack output current, battery pack voltage, battery charging current, and load status; The buck-boost DC-DC converter is controlled to operate in either boost or buck mode based on the output voltage of the fuel cell stack and the voltage of the battery pack. The target output power of the fuel cell stack is determined and calculated based on the load status and battery status. The MCU generates the DAC control signal based on the target output power; The constant current control module is adjusted according to the DAC control signal to limit the output current of the fuel cell stack; The system detects the fast charging protocol of the USB load and controls the USB output module to output the corresponding output voltage required by the protocol.

[0035] According to the above technical solution, when the load is detected to be disconnected or the load power is lower than the first threshold, the MCU reduces the DAC output voltage to limit the output current of the fuel cell stack to the range of the battery's allowable charging current, or shuts down the charging circuit to put the fuel cell stack into a low-power operating state and protect the fuel cell stack.

[0036] Example 2: like Figure 1 As shown, Scenario 1: Normal power supply (fuel cell stack + battery simultaneously supplying the load) The fuel cell stack generates electricity with a voltage that fluctuates between 9V and 18V.

[0037] When the MCU detects that the battery power is low and the bus voltage is permissible, it controls the bidirectional buck-boost circuit to operate in "buck mode" to convert the battery stack voltage to a suitable charging voltage for the battery (e.g., 12.6V) and limits the current to no more than 0.3A (assuming 0.5C) through the DAC.

[0038] Meanwhile, the bus voltage is boosted to 16V by the boost circuit, and the output is adjusted by the USB-PD chip to identify the mobile phone's needs (such as 15V).

[0039] Example 3: like Figure 1 As shown, Scenario 2: No-load protection (preventing overcharging) The user disconnected all loads, and the system is now in an idle state.

[0040] The fuel cell stack is still generating electricity at this time, and if left unattended, the voltage will spike instantly.

[0041] When the MCU detects a load disconnection (or an abnormal rise in bus voltage), it immediately outputs a voltage control signal through the DAC to force the charging current of the bidirectional buck-boost circuit to be limited to a small value (such as within 0.5C), or directly shuts off the charging path, forcing the battery pack into standby or low-power operation, thereby protecting the downstream circuits (which may damage the battery pack).

[0042] Example 4: like Figure 1 As shown, Scenario 3: Battery reverse power supply (fuel cell stack not working) The fuel cell stack is shut down, and the battery provides power only.

[0043] The bidirectional buck-boost circuit operates in "boost mode," boosting the battery voltage (e.g., 11V) to the bus voltage (12V), and then outputting it through the boost circuit and protocol chip.

[0044] Example 5: like Figure 2 As shown, Bidirectional buck-boost circuit: A synchronous rectification Buck-Boost chip (such as LTC3780) can be used. At the same time, a reverse protection controller is added to the output terminal in combination with a MOSFET. The controller detects the current direction at both ends to control the conduction of the MOSFET, and the body diode characteristics or dead time control of the MOSFET are used to achieve electrical isolation and prevent reverse flow.

[0045] MCU Control Logic: The MCU's power detection block diagram for the entire system is shown below, with the red area indicating the power monitoring location: The core lies in the "feedback loop". The power detection module collects voltage and current information and feeds it back to the MCU in real time through on-board communication. The MCU judges the changes in the working condition and calculates the power that the fuel cell should output. The actual voltage signal is obtained after calculation and sent to the DAC through communication, thereby changing the reference voltage of the constant current source's feedback loop and realizing real-time control of the fuel cell power.

[0046] Feedback loop description: Output characteristics of the fuel cell stack: The larger the output current, the greater the voltage drop of the fuel cell stack. Therefore, the normal output voltage range of the fuel cell stack is Vfc = (0.5~1). N, where N is the number of individual fuel cells. Therefore, the current operating status of the fuel cell stack can be determined based on the stack's output voltage value, and whether it can meet the load power output requirements.

[0047] By connecting a DC-DC chip LTC3780 to the back of the fuel cell stack, the loop parameters of the chip can be controlled to enable the DC-DC to obtain the required power from the input side (the output of the fuel cell).

[0048] This control is implemented through an integrator circuit, which compares the DAC output with the real-time current (converted to voltage). When the DAC output is higher than the actual current value, the op-amp output goes low, the diode is cut off, and the 0.8V generated by voltage division stabilizes the output voltage of the DC-DC chip at the set value Vset. At this point, if the load power is high, the output current of the DC-DC chip will increase to meet the load power output. Conversely, if the DAC value is decreased, the negative input of the op-amp will be lower than the positive input (the negative input is the voltage value controlled by the DAC, and the positive input is the detected current value, Vdec = Idec). (Rdec) At this time, the op-amp will output a positive voltage, so the diode conducts, inputting the positive voltage to the Vosense pin of the DC-DC converter. The internal loop control of the chip will reduce the output current, achieving the purpose of constant voltage and current limiting. The calculation formula of the integrator circuit is as follows: The DAC output formula is shown below, where P is the target power and VDCDC is the current DC-DC output voltage: In practice, the battery is charged according to its current temperature and voltage. The greater the voltage difference and the higher the temperature, the lower the charging power will be from 3C to 1C.

[0049] Example 6: like Figure 3-4 As shown, The LTC3780's Vosense control logic decreases the output current and VITH when V>0.8V, and increases the output current when V<0.8V.

[0050] When V=0.8V, it will stabilize at the output voltage. This is equivalent to stabilizing the output voltage at 12.6V, but the output power will continue to increase.

[0051] The op-amp will only output a high voltage when V+ is higher than V-. By adding a diode at the output terminal and using the unidirectional conductivity of the diode to control the Vosense pin, the output can be limited.

[0052] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A power supply system for a hydrogen fuel cell, characterized in that: include: Fuel cell stacks and battery packs; Also includes: A buck-boost DC-DC converter, whose input is connected to the fuel cell stack and whose output is connected to the bus and battery pack, is used to operate in boost mode or buck mode according to the relationship between the output voltage of the fuel cell stack and the voltage of the battery pack. The reverse current blocking module is located between the buck-boost DC-DC converter and the bus to prevent the battery pack from supplying reverse power to the fuel cell stack. The USB output module includes a boost converter, a buck converter, and a USB protocol chip connected in sequence. The USB protocol chip is used to identify the fast charging protocol of the load and output the output voltage required by the corresponding protocol. The power detection module is used to detect the output voltage, output current, battery pack voltage, battery charging current, and load status of the fuel cell stack. The constant current control module is located in the output circuit of the fuel cell stack and is used to regulate the output current of the fuel cell stack. The microcontroller (MCU) is connected to the power detection module, the constant current control module, and the buck-boost DC-DC converter, respectively. in, The microcontroller (MCU) controls the operating mode of the buck-boost DC-DC converter based on the fuel cell stack status, battery pack status, and load status collected by the power detection module, and adjusts the constant current control module by outputting control signals through the digital-to-analog converter (DAC).

2. The power supply system for a hydrogen fuel cell according to claim 1, characterized in that, The buck-boost DC-DC converter adopts a four-switch Buck-Boost topology or SEPIC topology. When the output voltage of the fuel cell stack is higher than the battery pack voltage, it operates in buck mode, and when the output voltage of the fuel cell stack is lower than the bus voltage, it operates in boost mode.

3. The power supply system for a hydrogen fuel cell according to claim 1, characterized in that, The reverse current blocking module includes a MOSFET and a reverse protection controller. The reverse protection controller controls the MOSFET to turn on or off according to the current direction.

4. The power supply system for a hydrogen fuel cell according to claim 1, characterized in that, The constant current control module includes a power MOSFET, an error amplifier, and a current sampling resistor; The error amplifier receives the reference voltage output by the DAC at its first input terminal, receives the current sampling signal at its second input terminal, and connects to the feedback control terminal of the buck-boost DC-DC converter. The output current of the fuel cell stack is adjusted by controlling the conduction state of the power MOSFET inside the buck-boost DC-DC converter.

5. A power supply system for a hydrogen fuel cell according to claim 4, characterized in that, The microcontroller (MCU) calculates the target output power based on the fuel cell voltage, battery temperature, and load power, and generates the corresponding DAC output voltage based on the target output power.

6. The power supply system for a hydrogen fuel cell according to claim 1, characterized in that, When the load current is detected to be lower than a preset threshold, the microcontroller (MCU) controls the DAC to reduce the reference voltage, so that the constant current control module limits the output current of the fuel cell stack to a preset safe value.

7. A power supply system for a hydrogen fuel cell according to claim 1, characterized in that, In the USB output module, the boost converter is used to boost the bus voltage to the highest operating voltage supported by the USB protocol. The USB protocol chip controls the buck converter to output 5V, 9V, 12V, 15V or 20V according to the identified USB fast charging protocol.

8. A power supply system for a hydrogen fuel cell according to claim 1, characterized in that, The microcontroller (MCU) divides the charging process into a pre-charging stage, a constant current charging stage, and a constant voltage charging stage based on the battery charging state, and controls the DAC to output different reference voltages for each stage to achieve phased charging control.

9. A control method for a hydrogen fuel cell power supply system according to any one of claims 1-8, characterized in that, Includes the following steps: Acquire fuel cell stack output voltage, stack output current, battery pack voltage, battery charging current, and load status; The buck-boost DC-DC converter is controlled to operate in either boost or buck mode based on the output voltage of the fuel cell stack and the voltage of the battery pack. The target output power of the fuel cell stack is determined and calculated based on the load status and battery status. The MCU generates the DAC control signal based on the target output power; The constant current control module is adjusted according to the DAC control signal to limit the output current of the fuel cell stack; The system detects the fast charging protocol of the USB load and controls the USB output module to output the corresponding output voltage required by the protocol.

10. The control method for a power supply system of a hydrogen fuel cell according to claim 9, characterized in that, When the load is detected to be disconnected or the load power is lower than the first threshold, the MCU reduces the DAC output voltage to limit the fuel cell stack output current to within the range of the battery's allowable charging current, or shuts down the charging circuit to put the fuel cell stack into a low-power operating state and protect the fuel cell stack.

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