Dcdc converter, switchable dual stack fuel cell system and control method

Abstract

The application relates to a DCDC converter, a switchable double-fuel-cell stack system and a control method, which comprises the following steps: collecting the output currents of a first fuel cell stack and a second fuel cell stack, a load bus voltage, and the output currents of each boost circuit in a first boost power unit and a second boost power unit; taking the larger value from the output currents of the first fuel cell stack and the second fuel cell stack, comparing the larger value with a preset switching current threshold to determine the connection mode and the PWM phase angle of each switch tube in the first boost power unit and the second boost power unit; calculating an output current reference value according to the difference between a target output voltage and the load bus voltage, distributing the output current reference value to the distribution currents of each boost circuit; sending the difference between the distribution current and the output current of the corresponding boost circuit into a controller respectively to determine the PWM duty ratio and the phase angle of each switch tube; and driving the DCDC converter based on the determined duty ratio and phase angle of each switch tube.

Description

Technical Field

[0001] This application relates to the field of automotive parts technology, specifically to a DC-DC converter, a switchable dual-stack fuel cell system, and a control method. Background Technology

[0002] A fuel cell is a power generation device that directly converts the internal energy of fuel and oxidant into electrical energy through an electrochemical reaction, exhibiting high energy conversion efficiency. The output voltage of a single fuel cell is typically between 0.65 and 0.85V, requiring a certain number of fuel cell cells to be connected in series to increase the output voltage. To actively control the output power of the fuel cell and maintain the bus voltage at the power device end, a DC-DC converter is usually used to connect the fuel cell to the power bus. As the power of downstream power devices increases and higher efficiency is pursued, the bus voltage gradually increases to reduce current loss. To prevent excessive fuel cell current from increasing DC-DC costs and to maintain an appropriate DC-DC boost ratio to ensure transformer efficiency, the voltage of the fuel cell stack also needs to increase. In other words, at a given power, fuel cells tend to evolve towards higher voltage and lower current. There are two main ways to increase the voltage of the fuel cell stack: 1) increasing the voltage of individual fuel cell cells; 2) increasing the number of fuel cell cells connected in series. Considering fuel cell lifespan, there is an upper limit to the voltage of a single cell, often not exceeding 0.85V, which means that in actual matching processes, it is necessary to increase the number of cells connected in series. A fuel cell stack is made up of individual cells connected in series and sealed under a certain pressure. There is a clear upper limit to the number of cells connected in series within a single stack. Therefore, when the power and voltage requirements of the fuel cell stack are high, a dual-stack scheme can be adopted to avoid having too many cells in a single stack.

[0003] In the existing technology, each fuel cell stack is first connected to a DC-DC converter, and then the load is powered by the parallel connection. Alternatively, two fuel cell stacks are first connected in series with copper busbars, and then connected to a DC-DC converter to power the load. The above methods make it difficult to control the system size and weight, and the system cost is high. Summary of the Invention

[0004] This application provides a DC-DC converter, a switchable dual-stack fuel cell system, and a control method to solve the problem that the system volume and weight of the dual-stack fuel cell system are difficult to control in the prior art, resulting in high system cost.

[0005] In a first aspect, this application provides a DC-DC converter for switching the connection mode of a dual-stack fuel cell, characterized in that the DC-DC converter includes: a first boost power unit, a second boost power unit, and a switching unit; The input terminal of the first boost power unit is connected to the positive electrode of the first fuel cell stack in the dual-stack fuel cell, and the output terminal of the first boost power unit is connected to the load bus; the input terminal of the second boost power unit is electrically connected to the positive electrode of the second fuel cell stack in the dual-stack fuel cell, and the output terminal of the second boost power unit is connected to the load bus. The switching unit is connected to the negative electrode of the first fuel cell stack, the negative electrode of the second fuel cell stack, the input terminal of the first boost power unit, the input terminal of the second boost power unit, and the system common ground, respectively. The switching unit is used to configure the first fuel cell stack and the second fuel cell stack into parallel mode or series mode according to the control signal. In the parallel mode, the first boost power unit is used to boost the electrical energy output by the first fuel cell stack and transmit it to the load bus, and the second boost power unit is used to boost the electrical energy output by the second fuel cell stack and transmit it to the load bus; in the series mode, the first boost power unit and the second boost power unit jointly boost the electrical energy output by the first fuel cell stack and the second fuel cell stack and transmit it to the load bus.

[0006] Optionally, in the parallel mode, the switching unit connects the negative electrode of the first fuel cell stack to the system common ground and disconnects the connection between the negative electrode of the first fuel cell stack and the positive electrode of the second fuel cell stack, while isolating the input terminals of the first boost power unit and the second boost power unit from each other; in the series mode, the switching unit connects the negative electrode of the first fuel cell stack to the positive electrode of the second fuel cell stack, connects the input terminals of the first boost power unit and the second boost power unit to each other, and disconnects the connection between the negative electrode of the first fuel cell stack and the system common ground; wherein, the negative electrode of the second fuel cell stack is connected to the system common ground.

[0007] Optionally, the first boost power unit includes a first inductor, a second inductor, a first switching transistor, a second switching transistor, a first diode, a second diode, and a first output capacitor; wherein, one end of the first inductor and the second inductor are connected to the positive electrode of the first fuel cell stack, the other ends of the first inductor and the second inductor are respectively connected to the drain of the first switching transistor and the second switching transistor, and the anode of the first diode and the second diode, the source of the first switching transistor and the second switching transistor are connected to the system common ground, the cathode of the first diode and the second diode are connected to the output bus, and the first output capacitor is connected in parallel between the output bus and the system common ground.

[0008] Optionally, the second boost power unit includes a third inductor, a fourth inductor, a third switching transistor, a fourth switching transistor, a third diode, a fourth diode, and a second output capacitor; wherein, one end of the third inductor and the fourth inductor are connected to the positive electrode of the second fuel cell stack, the other ends of the third inductor and the fourth inductor are respectively connected to the drain of the third switching transistor and the fourth switching transistor and the anode of the third diode and the fourth diode, the source of the third switching transistor and the fourth switching transistor are connected to the system common ground, the cathode of the third diode and the fourth diode are connected to the output bus, and the second output capacitor is connected in parallel between the output bus and the system common ground.

[0009] Optionally, the switching unit includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch; wherein the source of the fifth switch is connected to the negative terminal of the first fuel cell stack, and the drain of the fifth switch is connected to the system common ground; the source of the sixth switch is connected to the positive terminal of the second fuel cell stack, and the drain of the sixth switch is connected to the input terminal of the second boost power unit; the source of the seventh switch is connected to the positive terminal of the second fuel cell stack, and the drain of the seventh switch is connected to the negative terminal of the first fuel cell stack; the source of the eighth switch is connected to the input terminal of the first boost power unit, and the drain of the eighth switch is connected to the input terminal of the second boost power unit.

[0010] Optionally, in the parallel mode, the fifth and sixth switches are turned on, and the seventh and eighth switches are turned off; in the series mode, the seventh and eighth switches are turned on, and the fifth and sixth switches are turned off.

[0011] In a second aspect, this application provides a switchable dual-stack fuel cell system, including the DC-DC converter, dual-stack fuel cell, and controller described in the first aspect; the dual-stack fuel cell includes a first fuel cell stack and a second fuel cell stack. The signal input terminal of the controller is connected to sensors for detecting the output current of the first fuel cell stack, the output current of the second fuel cell stack, the output current of each boost circuit in the first boost power unit, the output current of each boost circuit in the second boost power unit, and the load bus voltage, respectively. The output terminal of the controller is connected to the control terminals of the first boost power unit, the second boost power unit, and the switching unit, respectively. The controller generates a control signal based on a comparison between the larger of the output currents of the first fuel cell stack and the second fuel cell stack and a preset switching current threshold, and configures the first fuel cell stack and the second fuel cell stack into parallel mode or series mode according to the control signal; and adjusts the phase difference of the PWM drive signals of the internal switching transistors of the first boost power unit and the second boost power unit according to the parallel mode or series mode.

[0012] Optionally, in the parallel mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, the PWM phase difference between the two switches inside the second boost power unit is 180°, and the PWM phase angles of the corresponding two switches in the first boost power unit and the second boost power unit are synchronized; in the series mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, the PWM phase difference between the two switches inside the second boost power unit is 180°, and the PWM phase difference between the corresponding two switches in the first boost power unit and the second boost power unit is 90°.

[0013] Optionally, the switching current threshold is set to half of the rated current of the first fuel cell stack or the second fuel cell stack.

[0014] Thirdly, this application provides a DC-DC converter control method based on the system described in the second aspect, comprising: The output current of the first fuel cell stack, the output current of the second fuel cell stack, the load bus voltage, the output current of each boost circuit in the first boost power unit, and the output current of each boost circuit in the second boost power unit are collected. The larger value is taken from the output current of the first fuel cell stack and the output current of the second fuel cell stack, and the larger value is compared with a preset switching current threshold. The connection mode of the first fuel cell stack and the second fuel cell stack is determined based on the comparison result. The controller calculates the reference value of the output current based on the difference between the target output voltage and the load bus voltage. Based on the current connection mode, the output current reference value is allocated to each boost circuit to obtain the allocated current of each boost circuit; the difference between the allocated current of each boost circuit and the corresponding output current of the boost circuit is sent to the controller to determine the PWM duty cycle of each switching transistor.

[0015] The DC-DC converter is driven based on the current connection mode and the determined PWM duty cycle of each switch.

[0016] Optionally, determining the connection mode of the first fuel cell stack and the second fuel cell stack based on the comparison result includes: if the larger value is less than or equal to the switching current threshold, determining the connection mode of the first fuel cell stack and the second fuel cell stack as a parallel mode; if the larger value is greater than the switching current threshold, determining the connection mode of the first fuel cell stack and the second fuel cell stack as a series mode.

[0017] Optionally, in the parallel mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, the PWM phase difference between the two switches inside the second boost power unit is 180°, and the PWM phase angles of the corresponding two switches in the first boost power unit and the second boost power unit are synchronized; in the series mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, the PWM phase difference between the two switches inside the second boost power unit is 180°, and the PWM phase difference between the corresponding two switches in the first boost power unit and the second boost power unit is 90°.

[0018] The beneficial effects of this application are: 1) Independent or series control of dual battery stacks can be achieved using only one DC-DC converter (containing two boost power units), avoiding the doubling of the number of components caused by configuring an independent DC-DC converter for each battery stack, thereby reducing costs.

[0019] 2) By switching the unit, the fuel cells are connected in parallel when the power is low (high input voltage, small boost ratio) and in series when the power is high (high input voltage, small current), so that the DC-DC converter always operates in the high efficiency range.

[0020] 3) In parallel mode, two sets of 2-phase interleaved (phase difference 180°) are used, and in series mode, one set of 4-phase interleaved (phase difference 90°) is used. This increases the input current ripple frequency and reduces the amplitude, thereby effectively extending the life of the fuel cell. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the DC-DC converter structure provided in the embodiments of this application; Figure 2 This is a schematic diagram of the connection of components in a DC-DC converter provided in an embodiment of this application; Figure 3 A schematic diagram of the switchable dual-stack fuel cell system provided in an embodiment of this application; Figure 4 A flowchart illustrating the control method for a DC-DC converter provided in this application embodiment; Figure 5A schematic diagram comparing the DC-DC input voltage and current ranges under different connection modes of the dual-stack fuel cell provided in this application embodiment; Figure 6 This application provides a flowchart of dual-stack fuel cell switching and DC-DC control. Figure 7 This is a schematic diagram illustrating the output current change of the fuel cell stack during the switching process of the DC-DC converter, as provided in an embodiment of this application. Detailed Implementation

[0022] The embodiments of this application will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be understood that the preferred embodiments are only for illustrating this application and are not intended to limit the scope of protection of this application.

[0023] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0024] For ease of description, spatial relative terms may be used in the text to describe the relative position or movement of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "front," "back," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure undergoes a positional flip, orientation change, or change of motion, these directional indications will change accordingly. For instance, an element described as "below other elements or features" or "below other elements or features" will subsequently be oriented "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0025] To address the problem in existing dual-stack fuel cell systems where each stack has its own DC-DC converter, leading to difficulties in controlling system size and weight and resulting in high system costs, this application provides a DC-DC converter for switching the connection mode of dual-stack fuel cells, such as... Figure 1 As shown, the DC-DC converter 10 includes: a first boost power unit 101, a second boost power unit 102, and a switching unit 103; The input terminal of the first boost power unit 101 is connected to the positive terminal of the first fuel cell stack FC1 in the dual stack fuel cell, and the output terminal of the first boost power unit 101 is connected to the load bus. Therefore, the first boost power unit 101 can receive DC power from the first fuel cell stack FC1 and send the boosted power to the common load bus. The load bus is used to connect the common DC bus of downstream electrical equipment (such as motor drivers, DC / AC inverters, power batteries, etc.), and usually has a high and stable voltage.

[0026] Furthermore, in this embodiment, the system common ground refers to the reference zero point (0V potential point) for all voltage measurements in the circuit, and is the common path for all current return. Specifically, in this DC-DC converter, the source of the switching transistor, the negative terminal of the output capacitor, etc., are all connected to the system common ground.

[0027] The input terminal of the second boost power unit 102 is electrically connected to the positive electrode of the second fuel cell stack FC2 in the dual-stack fuel cell, and the output terminal of the second boost power unit 102 is connected to the load bus. The switching unit 103 is connected to the negative electrode of the first fuel cell stack FC1, the negative electrode of the second fuel cell stack FC2, the input terminal of the first boost power unit 101, the input terminal of the second boost power unit 102, and the system common ground, respectively. The switching unit 103 is used to configure the first fuel cell stack FC1 and the second fuel cell stack FC2 into parallel mode or series mode according to the control signal.

[0028] It should be noted that in parallel operation, each boost power unit is used to boost the electrical energy output from the corresponding fuel cell stack and transmit it to the load bus, because the power supply of the two stacks is independent; however, in series operation, the boost power units work together, changing from two-phase to four-phase. Therefore, in parallel mode, the first boost power unit 101 is used to boost the electrical energy output from the first fuel cell stack FC1 and transmit it to the load bus, and the second boost power unit 102 is used to boost the electrical energy output from the second fuel cell stack FC2 and transmit it to the load bus; in series mode, the first boost power unit 101 and the second boost power unit 102 jointly boost the electrical energy output from the first fuel cell stack FC1 and the second fuel cell stack FC2 and transmit it to the load bus.

[0029] As can be seen, in this embodiment, the DC-DC converter can connect two fuel cell stacks simultaneously using only one converter body, eliminating the need for a separate DC-DC converter for each stack, thereby significantly reducing system cost, size, and weight. Simultaneously, the switching unit enables rapid switching between two operating modes (parallel and series modes), allowing the DC-DC input voltage and current to adapt to different power demands, ensuring the converter always operates in boost mode and avoiding the use of complex buck-boost circuits.

[0030] Furthermore, in parallel mode, switching unit 103 connects the negative terminal of the first fuel cell stack FC1 to the system common ground and disconnects the connection between the negative terminal of the first fuel cell stack FC1 and the positive terminal of the second fuel cell stack FC2, while isolating the input terminals of the first boost power unit 101 and the second boost power unit 102 from each other; in series mode, switching unit 103 connects the negative terminal of the first fuel cell stack FC1 to the positive terminal of the second fuel cell stack FC2, connects the input terminals of the first boost power unit 101 and the second boost power unit 102 to each other, while disconnecting the connection between the negative terminal of the first fuel cell stack FC1 and the system common ground; wherein, the negative terminal of the second fuel cell stack FC2 is connected to the system common ground.

[0031] Therefore, in parallel mode, the positive terminals of the two fuel cells are connected together, and the negative terminals are both grounded. The output voltage is equal to the voltage of a single fuel cell, and the output current is the sum of the voltages of the two fuel cells. This mode is suitable for low-power, low-voltage operating conditions. In series mode, the positive and negative terminals of the two fuel cells are connected in series, and the total voltage is the sum of the voltages of the two fuel cells. The output current is equal to the current of a single fuel cell. This mode is suitable for high-power, high-voltage operating conditions. In other words, in the embodiments of this application, only one DC-DC converter (containing two boost power units) is needed to achieve independent or series control of dual fuel cells, which saves cost and reduces size compared to using two independent DC-DC converters. Moreover, in parallel mode (low power), the input voltage is high and the boost ratio is small; in series mode (high power), the input voltage is even higher (close to the bus voltage) and the boost ratio is close to 1. In both modes, the DC-DC converter operates in the high-efficiency range, improving operating efficiency.

[0032] In the embodiments of this application, such as Figure 2 As shown, the first boost power unit 101 includes a first inductor L1, a second inductor L2, a first switch Q1, a second switch Q2, a first diode D1, a second diode D2, and a first output capacitor C. out1 ; In this configuration, one end of the first inductor L1 and the second inductor L2 are connected to the positive terminal of the first fuel cell stack. The other ends of the first inductor L1 and the second inductor L2 are connected to the drain of the first switch Q1 and the second switch Q2, and the anode of the first diode D1 and the second diode D2, respectively. The source of the first switch Q1 and the second switch Q2 is connected to the system common ground. The cathodes of the first diode D1 and the second diode D2 are connected to the output bus. The first output capacitor C_out1 is connected in parallel between the output bus and the system common ground.

[0033] In the embodiments of this application, such as Figure 2 As shown, the second boost power unit 102 includes a third inductor L3, a fourth inductor L4, a third switch Q3, a fourth switch Q4, a third diode D3, a fourth diode D4, and a second output capacitor C. out2 ; In this configuration, one end of the third inductor L3 and the fourth inductor L4 are connected to the positive terminal of the second fuel cell stack. The other ends of the third inductor L3 and the fourth inductor L4 are connected to the drains of the third switch Q3 and the fourth switch Q4, and the anodes of the third diode D3 and the fourth diode D4, respectively. The sources of the third switch Q3 and the fourth switch Q4 are connected to the system common ground. The cathodes of the third diode D3 and the fourth diode D4 are connected together and then connected to the output bus. The second output capacitor C... out2 It is connected in parallel between the output bus and the system common ground.

[0034] In the embodiments of this application, the switching transistor can be a MOSFET, IGBT, GaN HEMT, or SiC MOSFET. The inductor can be a ferrite core, an iron-silicon-aluminum core, or an air-core inductor. The diode can be a fast recovery diode, a Schottky diode, or a synchronous rectifier MOSFET (alternative diode).

[0035] As can be seen, in this embodiment, the two boost power units are independent of each other in circuit structure, but their output terminals are connected to the same load bus (through their respective diode cathode common junctions). Furthermore, the input sides of the two boost power units can be connected or isolated from each other through a switching unit, thereby realizing parallel or series connection of the dual power stacks. Further, the switching transistors (Q1~Q4) of the two boost power units can be controlled independently, but in series mode, they need to be configured as four-phase interleaved (90° phase difference) to achieve lower ripple.

[0036] In the embodiments of this application, such as Figure 2 As shown, the switching unit 103 includes a fifth switch Q5, a sixth switch Q6, a seventh switch Q7, and an eighth switch Q8; In this configuration, the source of the fifth switch Q5 is connected to the negative terminal of the first fuel cell stack FC1, and the drain of the fifth switch Q5 is connected to the system common ground; the source of the sixth switch Q6 is connected to the positive terminal of the second fuel cell stack FC2, and the drain of the sixth switch Q6 is connected to the input terminal of the second boost power unit 102; the source of the seventh switch Q7 is connected to the positive terminal of the second fuel cell stack FC2, and the drain of the seventh switch Q7 is connected to the negative terminal of the first fuel cell stack FC1; the source of the eighth switch Q8 is connected to the input terminal of the first boost power unit 101, and the drain of the eighth switch Q8 is connected to the input terminal of the second boost power unit 102.

[0037] Furthermore, in parallel mode, the fifth switch Q5 and the sixth switch Q6 are turned on, while the seventh switch Q7 and the eighth switch Q8 are turned off; in series mode, the seventh switch Q7 and the eighth switch Q8 are turned on, while the fifth switch Q5 and the sixth switch Q6 are turned off.

[0038] As can be seen, the fifth switch Q5 controls whether the negative terminal of FC1 is connected to the system common ground. When it is on, the negative terminal of FC1 is connected to the system common ground; when it is off, the negative terminal of FC1 floats (in series mode, it is connected to the positive terminal of FC2 via Q7). The sixth switch Q6 controls the connection between the positive terminal of FC2 and the input terminal of the second boost power unit. In parallel mode, it is on, allowing the second boost power unit to obtain the voltage of FC2. In series mode, it is off, isolating the positive terminal of FC2 from the input terminal of the second boost power unit to avoid short circuit. The seventh switch Q7 is on in series mode, shorting the negative terminal of FC1 and the positive terminal of FC2 to achieve series connection of the fuel cell stacks. In parallel mode, it is off, keeping the two fuel cell stacks independent. The eighth switch Q8 controls the connection between the input terminals of the two boost power units. In series mode, it is on, switching node B (the input terminal of the second boost power unit) to node A (FC1+), allowing the two boost power units to share the total series voltage. In parallel mode, it is off, keeping the two input terminals independent.

[0039] As can be seen, in this embodiment, by making the connection between FC2+ and node B controlled through Q6, the short-circuit risk in the series mode is completely avoided. Moreover, the switching process is completed in microseconds, ensuring uninterrupted power supply to the fuel cell and a seamless system transition. In addition, dual-stack control can be achieved using only one DC-DC converter (containing two boost power units). Compared to the existing technology where each stack is equipped with an independent DC-DC converter, not only is the number of switching transistors reduced, but the number of inductors and capacitors is also reduced accordingly.

[0040] In the above Figure 1 and Figure 2 Based on this, this application also provides a switchable dual-stack fuel cell system, such as Figure 3 As shown, the system includes the above-mentioned Figure 1 The DC-DC converter 10, the dual-stack fuel cell 20, and the controller 30 are included; the dual-stack fuel cell 20 includes a first fuel cell stack FC1 and a second fuel cell stack FC2. The signal input terminals of the controller 30 are respectively connected to sensors used to detect the output current of the first fuel cell stack FC1, the output current of the second fuel cell stack FC2, the output current of each boost circuit in the first boost power unit 101, the output current of each boost circuit in the second boost power unit 102, and the load bus voltage. The output terminals of the controller 30 are respectively connected to the control terminals of the first boost power unit 101, the second boost power unit 102, and the switching unit 103. In this embodiment, the control terminal refers to the gate (or base) of the switching transistor, which is the access point for the controller to output control signals. Furthermore, the boost circuit in this embodiment is a single-path boost channel composed of a single inductor, a single switching transistor, and a single diode. That is, the first boost power unit has two boost circuits: one composed of L1, Q1, and D1, and the other composed of L2, Q2, and D2. The boost circuit in the second boost power unit is similar to that in the first boost power unit.

[0041] The controller 30 generates a control signal based on the comparison result of the larger value of the output current of the first fuel cell stack FC1 and the second fuel cell stack FC2 with a preset switching current threshold, and configures the first fuel cell stack FC1 and the second fuel cell stack FC2 into parallel mode or series mode according to the control signal; and adjusts the phase difference of the PWM drive signal of the internal switching transistors of the first boost power unit 101 and the second boost power unit 102 according to the parallel mode or series mode.

[0042] As can be seen, the controller in this embodiment has multiple input terminals and multiple output terminals. The multiple input terminals are respectively connected to the current sensor and the voltage sensor, and the multiple output terminals are respectively connected to the switching transistors Q1 and Q2 of the first boost power unit, the switching transistors Q3 and Q4 of the second boost power unit, and the switching transistors Q5 to Q8 of the switching unit.

[0043] In this embodiment, the switching current threshold is set to half of the rated current of the first fuel cell stack or the second fuel cell stack. In other application scenarios, the switching current threshold can also be determined based on the highest conversion efficiency point of the DC-DC converter.

[0044] Based on this, in parallel mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, and the PWM phase difference between the two switches inside the second boost power unit is also 180°. Furthermore, the PWM phase angles of the corresponding two switches in the first and second boost power units are synchronized, as detailed below. Figure 2 In the series configuration, Q1~Q4 have phase angles of 0°, 180°, 0°, and 180°, respectively. In series mode, the PWM phase difference between the two switches in the first boost power unit is 180°, and the PWM phase difference between the two switches in the second boost power unit is also 180°. Furthermore, the PWM phase difference between the corresponding two switches in the first and second boost power units is 90°. Specifically... Figure 2In the circuit, Q1~Q4 have phase angles of 0°, 180°, 90°, and 270°. It should be noted that the above phase angle values ​​for Q1~Q4 are illustrative examples; other values ​​that meet the above rules are also feasible. Therefore, in parallel mode, each fuel cell stack independently performs two-phase interleaved control, and the 180° phase difference maximally cancels out its individual input current ripple. In series mode, the four switches together form a four-phase interleaved parallel booster, with phases differing by 90° sequentially, further reducing overall input current ripple and output voltage ripple, while simultaneously increasing the equivalent switching frequency and reducing the size of passive components.

[0045] Based on the above Figures 1 to 3 This application also provides a DC-DC converter control method, such as... Figure 4 As shown, the steps of this method include: Step 401: Collect the output current I of the first fuel cell stack. in1 The output current I of the second fuel cell stack in2 Load bus voltage V out The output current (I) of each boost circuit in the first boost power unit out1 and I out2 The output current (I) of each boost circuit in the second boost power unit out3 and I out4 ); In this context, the output current of the first fuel cell stack refers to the total output current of the first fuel cell stack, and the output current of the second fuel cell stack refers to the total output current of the second fuel cell stack. The load bus voltage refers to the actual voltage at the output terminal of the DC-DC converter, serving as feedback for the voltage closed loop. The output current of each boost circuit in the first boost power unit refers to the output current of each inductor-switch-diode branch, used for current closed-loop current sharing control. The output current of each boost circuit in the second boost power unit is similar.

[0046] Step 402: Take the larger value between the output current of the first fuel cell stack and the output current of the second fuel cell stack, compare the larger value with a preset switching current threshold, and determine the connection mode of the first fuel cell stack and the second fuel cell stack, as well as the PWM phase angle of the switching transistors in the first boost power unit and the second boost power unit based on the comparison result. Step 403, based on the target output voltage V out_ref The difference between the voltage of the load bus and the voltage of the load bus is used by the controller to calculate the reference value I of the output current. out_ref ; The target output voltage is the preset desired bus voltage.

[0047] Step 404: Based on the current connection mode, the output current reference value is allocated to each boost circuit to obtain the allocated current of each boost circuit; the difference between the allocated current of each boost circuit and the output current of the corresponding boost circuit is sent to the controller to determine the PWM duty cycle of each switching transistor. In specific examples, if the current connection mode is series mode, allocating the output current reference value to each boost circuit means dividing the output current reference value equally, and then sending the difference between the evenly distributed current and the corresponding boost circuit output current to the controller. If the current connection mode is parallel mode, since the two fuel cells work independently in parallel mode, each fuel cell corresponds to one boost power unit, and since the voltages of FC1 and FC2 may differ slightly due to performance, temperature, and aging, the input voltages of the two units may be different. Therefore, the way to allocate the output current reference value to each boost circuit can be: 1) first allocate the total current of the unit according to the voltage ratio, and then divide it equally within the unit; 2) the two units divide the total current equally, and then divide it equally within the unit (similar to the series mode). That is to say, the difference in the embodiments of this application actually refers to the error of the boost circuit output current, and then the switching time ratio (between 0 and 1) calculated based on the current error (difference) is used to control the energy transfer of each boost circuit.

[0048] Step 405: Based on the connection mode, and combined with the determined PWM duty cycle and PWM phase angle of each switch, drive the DC-DC converter.

[0049] Among them, the driver of the DC-DC converter is to output the turn-on / turn-off signal to the switching unit (Q5~Q8) and output the PWM signal corresponding to the duty cycle and phase difference to the boost power unit (Q1~Q4).

[0050] The method of determining the connection mode of the first fuel cell stack and the second fuel cell stack based on the comparison results in step 402 above includes: 1) when the larger value is less than or equal to the switching current threshold, the connection mode of the first fuel cell stack and the second fuel cell stack is determined to be a parallel mode; 2) when the larger value is greater than the switching current threshold, the connection mode of the first fuel cell stack and the second fuel cell stack is determined to be a series mode.

[0051] Referring to the above figures and steps 401 to 404, in a specific example, taking two fuel cell stacks with a rated voltage of 300V and a rated current of 400A as an example, the target voltage of the load bus is set to 800V, and the switching current threshold is taken as 200A (half of the rated current).

[0052] Light load condition (36kW): Each fuel cell stack outputs 50A, less than the threshold. The system operates in parallel mode, with the fifth and sixth switches on and the seventh and eighth switches off. Both fuel cell stacks are grounded at their negative terminals. The first and second boost power units receive a 360V input. A two-phase interleaved design (180° phase difference) is used, with each boost circuit outputting approximately 111.5A. The input current ripple frequency is twice the switching frequency (e.g., 200kHz), and the peak-to-peak ripple is approximately 30% of the single-circuit current. The boost ratio is 2.22, and the DC-DC efficiency is approximately 95%.

[0053] Heavy-load operation (240kW): Each fuel cell stack outputs 400A, exceeding the threshold. The system switches to series mode, with the fifth and sixth switches off and the seventh and eighth switches on. The negative terminal of FC1 is shorted to the positive terminal of FC2, resulting in a total voltage equal to the sum of the voltages of FC1 and FC2 (approximately 600V). The eighth switch switches the input of the second boost power unit to the positive terminal of FC1, allowing both boost power units to share a common input of 600V. The four switches are configured in a four-phase interleaved configuration (phases of 0°, 180°, 90°, and 270° respectively), with each boost circuit outputting approximately 75A. The input current ripple frequency is four times the switching frequency (400kHz), and the peak-to-peak ripple is reduced to approximately 10%. Due to the input voltage being close to the bus voltage of 800V, the boost ratio is only about 1.33, and the output current of each boost circuit is extremely small, resulting in a DC-DC efficiency exceeding 98%.

[0054] Hot switching process: When the output current gradually increases from 50A to 400A, the controller monitors the current in real time and immediately executes the switching: simultaneously turning off Q5 and Q6, and simultaneously turning on Q7 and Q8. The switching time is less than 10 microseconds. During this period, the PWM duty cycle is automatically adjusted by the current inner loop PI controller. With the buffering effect of the input capacitor, the fuel cell stack output current transitions smoothly without impact or interruption. The measured bus voltage fluctuation is less than 5V, and the downstream equipment operates normally.

[0055] The following is in conjunction with the above. Figures 1 to 4 The present application will be explained and illustrated by the specific implementation of the embodiments of this application. The specific implementation provides a DC-DC converter topology system for dual-stack multiphase interleaved parallel boost of fuel cells, wherein the system includes a dual-stack fuel cell input unit, an interleaved boost power unit, and a switching unit.

[0056] The dual-stack fuel cell input unit includes fuel cell stack FC1 and fuel cell stack FC2, wherein, as Figure 2As shown, the positive terminal of fuel cell stack FC1 is connected to the input terminals of boost inductors L1 and L2 on the input side, and the negative terminal is connected to Q7 of the switching unit, and then connected to the system common ground via Q5. The positive terminal of fuel cell stack FC2 is connected to the input terminals of boost inductors L3 and L4 on the input side and Q7 of the switching unit, and the negative terminal is connected to the system common ground. Input capacitor C... in1 With C in2 They are connected in parallel to the output terminals of FC1 and FC2 respectively to smooth the current and ripple of the fuel cell and slow down the degradation of the fuel cell.

[0057] The interleaved boost power unit includes an upper power unit (first boost power unit) and a lower power unit (second boost power unit). As can be seen, the interleaved boost power unit adopts a two-way, two-phase interleaved parallel Boost topology, with each path corresponding to the power conversion of one fuel cell stack when operating independently. The upper power unit consists of inductors L1 and L2, power transistors Q1 and Q2, diodes D1 and D2, and an output capacitor Cout1. One end of L1 and L2 is connected to the positive terminal of FC1, and the other end is connected to the drain of Q1 and Q2 and the anode of D1 and D2, respectively. The sources of Q1 and Q2 are connected to the system common ground, and their gates receive PWM drive signals to achieve inductor energy storage and energy transfer. The cathodes of D1 and D2 are shorted and connected to the output bus, serving as boost output rectifier diodes to prevent reverse voltage flow. Cout1 is connected in parallel between the output bus and the system common ground to smooth the output voltage ripple of the upper unit. The lower power unit has the same structure as the upper unit, consisting of inductors L3 and L4, power transistors Q3 and Q4, diodes D3 and D4, and output capacitor C. out2 The composition and connection method are consistent with the upper unit. One end of L3 and L4 is connected to the positive terminal of FC2, and the other end is connected to the drain of Q3 and Q4 and the anode of D3 and D4 respectively. The source of Q3 and Q4 is connected to the system common ground, and the gate receives the PWM drive signal. The cathodes of D3 and D4 are connected to the output bus. The boost power unit uses phase-interleaved PWM control, which can reduce input and output current ripple and improve power quality. out1 I out2 I out3 with I out4 These represent the output currents of each boost circuit as measured by current sensors, used for power control. in1 with I in2 This provides the output current for the fuel cell stack.

[0058] Switching unit such as Figure 2As shown, the system consists of four high-current, low-on-resistance power semiconductor devices, Q5, Q6, Q7, and Q8, capable of switching between independent and series operation modes of the dual-stacking power units within microseconds. The source of Q5 is connected to the negative terminal of FC1, and its drain is connected to the system ground. The source of Q6 is connected to the positive terminal of FC2 and the drain of Q7. Q7 is connected to the negative terminal of FC1 and the positive terminal of FC2. Q8 is connected to four inductors to control the number of power phases. When Q5 and Q6 are on, and Q7 and Q8 are off, FC1 and FC2 are independent parallel inputs, supplying power to their respective boost power units, each with two phases out of phase. When Q7 and Q8 are on, and Q5 and Q6 are off, the negative terminal of FC1 is shorted to the positive terminal of FC2, resulting in a series input of the dual-stacking power units. The total input voltage is the sum of the voltages of the two stacks, and the boost power unit becomes a four-phase system.

[0059] It should be noted that the total output capacitor Cout is connected in parallel between the output bus and the system common ground to further smooth the output voltage and suppress high-frequency ripple; the load resistor R load This represents a typical load at the back end of the converter, such as a motor drive system, server or other electrical equipment, or other energy storage devices, with an output voltage V. out It provides a stable high-voltage DC output after step-up conversion for dual-reactor series or independent input, meeting the power supply requirements of downstream equipment.

[0060] Based on this, such as Figure 5 The diagram shows a comparison of the DC-DC input voltage and current when using a switchable multiphase interleaved parallel boost DC-DC topology with both series and independent parallel modes. In series mode, the maximum input current of the DC-DC is the rated current of the fuel cell stack. However, because the two fuel cells are connected in series, the voltage increases, exceeding the bus voltage in the low-current range. This necessitates the use of a buck converter to convert the fuel cell stack power in this range. When the two fuel cells are independently connected in parallel, although the DC-DC input voltage is only the voltage of one fuel cell stack (far lower than the bus voltage), allowing for the use of a boost circuit alone, the current multiplies after parallel connection, resulting in a significant increase in the specifications or number of power transistors.

[0061] When switching between the two connection topologies, the fuel cell maintains its output and performs thermal switching. The specific control logic is as follows: Figure 6 As shown, the controller collects the fuel cell stack output current I in real time. in1 with I in2 The output current I of each boost circuit out1 I out2 I out3 with I out4 and the real-time output voltage V of the DC-DC backend out Based on the target output voltage V out_ref With actual voltage V out The difference is used to calculate the reference value I of the output current of the outer voltage loop through the PI controller. out_PIand the allowable output current limit I out_ref1 Compare the values ​​and take the smaller value I. out_ref To ensure that electrical components are not damaged. Based on the obtained reference current I out_ref With the real-time measured output current I out1 I out2 I out3 with I out4 The duty cycle of each circuit is calculated using inner-loop current PI control. Then, the input currents of the two fuel cells are compared, and the larger value is taken and used in conjunction with the switching current I. td By comparison, when the switching current is less than or equal to the switching current, switching transistors Q5 and Q6 are turned on, while Q7 and Q8 are turned off, and the two fuel cells are independently connected in parallel for output. At this time, the phase difference of the PWM wave is 0°, 180° and 0°, 180°. When the switching current is greater than the switching current, switching transistors Q7 and Q8 are turned on, while Q5 and Q6 are turned off, and the two fuel cells are connected in series for output. At this time, the phase difference of the PWM wave is 0°, 180°, 90° and 270°, that is, the two fuel cells become four-phase staggered.

[0062] In this embodiment of the application, the current I during the switching between the two modes td There are two ways to determine the switching current: 1) It can be simply determined as half of the rated current of the fuel cell stack. In this way, when the two stacks are independently input, the current carrying capacity of the power transistor can be fully utilized, while the stack voltage after series connection can be appropriately reduced to ensure the minimum boost ratio; 2) The basis for determining the switching current is the best efficiency. Under the premise that the current is not higher than half of the rated current and the voltage after series connection is not higher than the bus voltage, the switching current point with the highest conversion efficiency is found.

[0063] Although the current carrying capacity of the power transistor remains the same before and after the switch, the increased input voltage reduces the boost ratio, resulting in a lower output current for the fuel cell under the same load, thus improving system efficiency. Figure 7 As shown. Furthermore, the pulse amplitude of the fuel cell current and the current ripple before and after the switch are controllable during the thermal switching process, preventing damage to the fuel cell.

[0064] This system also features fault redundancy. When the controller detects an abnormal output current (such as overcurrent, open circuit, or short circuit) in a boost circuit (e.g., a circuit consisting of L1, Q1, and D1), it immediately shuts down the corresponding switch Q1 and marks the circuit as faulty. In parallel mode, the remaining circuit (L2, Q2, D2) of the first boost power unit can continue to operate, but the current command within the unit needs to be adjusted to the sum of the original two circuits; that is, this unit operates only in single-circuit mode. If both circuits fail, the controller shuts down Q5, isolating the entire first fuel cell stack, and the system continues to operate in derating mode (only the second fuel cell stack operates). In series mode, failure of any circuit will cause the four-phase interleaving to degenerate into three-phase interleaving. The controller automatically adjusts the phase difference (0°, 120°, 240°) and redistributes the current command, maintaining system output, but reducing the total power. This redundancy design significantly improves system reliability, preventing vehicle breakdowns due to single-point failures.

[0065] The device embodiments described above are merely illustrative. 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 modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0066] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented using software plus a general-purpose hardware platform, or of course, using hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the related technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0067] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0068] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A DC-DC converter for switching the connection mode of a dual-stack fuel cell, characterized in that, The DC-DC converter includes: a first boost power unit, a second boost power unit, and a switching unit; The input terminal of the first boost power unit is connected to the positive electrode of the first fuel cell stack in the dual-stack fuel cell, and the output terminal of the first boost power unit is connected to the load bus. The input terminal of the second boost power unit is electrically connected to the positive electrode of the second fuel cell stack in the dual-stack fuel cell, and the output terminal of the second boost power unit is connected to the load bus. The switching unit is connected to the negative electrode of the first fuel cell stack, the negative electrode of the second fuel cell stack, the input terminal of the first boost power unit, the input terminal of the second boost power unit, and the system common ground, respectively. The switching unit is used to control the on / off combination of the four switching tubes in the switching unit according to the control signal to configure the first fuel cell stack and the second fuel cell stack into parallel mode or series mode. In the parallel mode, the first boost power unit is used to boost the electrical energy output by the first fuel cell stack and transmit it to the load bus, and the second boost power unit is used to boost the electrical energy output by the second fuel cell stack and transmit it to the load bus; in the series mode, the first boost power unit and the second boost power unit jointly boost the electrical energy output by the first fuel cell stack and the second fuel cell stack and transmit it to the load bus.

2. The DC-DC converter according to claim 1, characterized in that, In the parallel mode, the switching unit connects the negative electrode of the first fuel cell stack to the system common ground and disconnects the connection between the negative electrode of the first fuel cell stack and the positive electrode of the second fuel cell stack, while isolating the input terminals of the first boost power unit and the second boost power unit from each other. In the series mode, the switching unit connects the negative electrode of the first fuel cell stack to the positive electrode of the second fuel cell stack, connects the input terminal of the first boost power unit to the input terminal of the second boost power unit, and disconnects the connection between the negative electrode of the first fuel cell stack and the system common ground. The negative electrode of the second fuel cell stack is connected to the system common ground.

3. The DC-DC converter according to claim 1, characterized in that, The first boost power unit includes a first inductor, a second inductor, a first switching transistor, a second switching transistor, a first diode, a second diode, and a first output capacitor; In this configuration, one end of the first inductor and the second inductor are connected to the positive electrode of the first fuel cell stack, and the other ends of the first inductor and the second inductor are connected to the drains of the first switch and the second switch, and the anodes of the first diode and the second diode, respectively. The sources of the first switch and the second switch are connected to the system common ground, and the cathodes of the first diode and the second diode are connected to the output bus. The first output capacitor is connected in parallel between the output bus and the system common ground.

4. The DC-DC converter according to claim 1, characterized in that, The second boost power unit includes a third inductor, a fourth inductor, a third switching transistor, a fourth switching transistor, a third diode, a fourth diode, and a second output capacitor; In this configuration, one end of the third inductor and the fourth inductor are connected to the positive electrode of the second fuel cell stack, and the other ends of the third inductor and the fourth inductor are connected to the drain of the third switch and the fourth switch, and the anode of the third diode and the fourth diode, respectively. The source of the third switch and the fourth switch is connected to the system common ground, and the cathode of the third diode and the fourth diode is connected to the output bus. The second output capacitor is connected in parallel between the output bus and the system common ground.

5. The DC-DC converter according to claim 1, characterized in that, The switching unit includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch; In this configuration, the source of the fifth switch is connected to the negative terminal of the first fuel cell stack, and the drain of the fifth switch is connected to the system common ground; the source of the sixth switch is connected to the positive terminal of the second fuel cell stack, and the drain of the sixth switch is connected to the input terminal of the second boost power unit; the source of the seventh switch is connected to the positive terminal of the second fuel cell stack, and the drain of the seventh switch is connected to the negative terminal of the first fuel cell stack; the source of the eighth switch is connected to the input terminal of the first boost power unit, and the drain of the eighth switch is connected to the input terminal of the second boost power unit.

6. The DC-DC converter according to claim 5, characterized in that, In the parallel mode, the fifth and sixth switches are turned on, while the seventh and eighth switches are turned off. In the series mode, the seventh and eighth switches are turned on, while the fifth and sixth switches are turned off.

7. A switchable dual-stack fuel cell system, characterized in that, Includes the DC-DC converter, dual-stack fuel cell, and controller as described in any one of claims 1 to 6; the dual-stack fuel cell includes a first fuel cell stack and a second fuel cell stack; The signal input terminal of the controller is connected to sensors for detecting the output current of the first fuel cell stack, the output current of the second fuel cell stack, the output current of each boost circuit in the first boost power unit, the output current of each boost circuit in the second boost power unit, and the load bus voltage, respectively. The output terminal of the controller is connected to the control terminals of the first boost power unit, the second boost power unit, and the switching unit, respectively. The controller generates a control signal based on a comparison between the larger of the output currents of the first fuel cell stack and the second fuel cell stack and a preset switching current threshold, and configures the first fuel cell stack and the second fuel cell stack into parallel mode or series mode according to the control signal; and adjusts the phase difference of the PWM drive signals of the internal switching transistors of the first boost power unit and the second boost power unit according to the parallel mode or series mode.

8. The system according to claim 7, characterized in that, In the parallel mode, the PWM phase difference between the two switching transistors inside the first boost power unit is 180°, the PWM phase difference between the two switching transistors inside the second boost power unit is 180°, and the PWM phase angles of the corresponding two switching transistors in the first boost power unit and the second boost power unit are synchronized. In the series mode, the PWM phase difference between the two switching transistors inside the first boost power unit is 180°, the PWM phase difference between the two switching transistors inside the second boost power unit is 180°, and the PWM phase difference between the corresponding two switching transistors in the first boost power unit and the second boost power unit is 90°.

9. The system according to claim 7, characterized in that, The switching current threshold is set to half of the rated current of the first fuel cell stack or the second fuel cell stack.

10. A DC-DC converter control method based on the system according to any one of claims 7 to 9, characterized in that, include: The output current of the first fuel cell stack, the output current of the second fuel cell stack, the load bus voltage, the output current of each boost circuit in the first boost power unit, and the output current of each boost circuit in the second boost power unit are collected. The larger value is taken from the output current of the first fuel cell stack and the output current of the second fuel cell stack, and the larger value is compared with a preset switching current threshold. Based on the comparison result, the connection mode of the first fuel cell stack and the second fuel cell stack, as well as the PWM phase angle of each switching transistor in the first boost power unit and the second boost power unit, are determined. The controller calculates the reference value of the output current based on the difference between the target output voltage and the load bus voltage. Based on the current connection mode, the output current reference value is allocated to each boost circuit to obtain the allocated current of each boost circuit; the difference between the allocated current of each boost circuit and the corresponding output current of the boost circuit is sent to the controller to determine the PWM duty cycle of each switching transistor. Based on the current connection mode, and combined with the determined PWM duty cycle and PWM phase angle of each switch, the DC-DC converter is driven.

11. The method according to claim 10, characterized in that, The connection mode of the first fuel cell stack and the second fuel cell stack is determined based on the comparison results, including: If the larger value is less than or equal to the switching current threshold, the connection mode of the first fuel cell stack and the second fuel cell stack is determined to be a parallel mode; If the larger value is greater than the switching current threshold, the connection mode of the first fuel cell stack and the second fuel cell stack is determined to be a series mode.

12. The method according to claim 11, characterized in that, In the parallel mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, the PWM phase difference between the two switches inside the second boost power unit is 180°, and the PWM phase angles of the corresponding two switches in the first boost power unit and the second boost power unit are synchronized; in the series mode, the PWM phase difference between the two switches inside the first boost power unit is 180°, the PWM phase difference between the two switches inside the second boost power unit is 180°, and the PWM phase difference between the corresponding two switches in the first boost power unit and the second boost power unit is 90°.

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