DCDC control mode smooth switching method and system for fuel cell

Abstract

The invention discloses a DCDC control mode smooth switching method and system for a fuel cell, and belongs to the technical field of fuel cells. The system comprises a DCDC converter formed by connecting multiple phases of BOOSTs in parallel, a detection module and a control module, the detection module collects input voltage, inductive current and output voltage signals and transmits the signals to the control module; the control module adopts input constant voltage control in a cold start stage, and the input voltage is stabilized through double-loop control; switching to input constant current control in a normal operation stage, and accurately controlling the output power; smooth transition is realized through nonlinear weighted synthesis and feed-forward compensation. According to the invention, the problems of easy failure of cold start, low normal operation power control precision and large switching impact in the prior art are solved, the service life of the fuel cell is prolonged, and the system reliability is improved.

Description

Technical Field

[0001] This application relates to the field of fuel cell technology, and in particular to a method and system for smooth switching of DC-DC control modes for fuel cells. Background Technology

[0002] Fuel cells, as devices that convert chemical energy into electrical energy, play a vital role in transportation and other fields. Due to their relatively soft characteristics, fuel cells cannot be used directly as a power source and are typically paired with high-voltage batteries as a buffer. Normally, the fuel cell stack and the battery have different voltages, preventing direct energy transfer. DC-DC converters, as voltage regulation devices, can enable energy transfer between the fuel cell stack and the battery.

[0003] In the field of fuel cells, DC-DC converters mostly employ constant current input control to ensure controllable input current. However, in some cases, fuel cells need to start at low temperatures. Using constant current input control, excessive or rapid current flow can cause the voltage to drop to extremely low levels instantaneously, leading to start-up failure or permanent damage to the fuel cell stack. Therefore, existing control schemes cannot meet the requirements for cold starts at low temperatures. Constant voltage input control can automatically adjust the current according to the stack characteristics, maintaining a low current during the stack startup phase. To ensure both successful cold starts and rapid response to load changes, different control strategies are required at different stages.

[0004] The existing technology has the following drawbacks: If constant current control is used directly during low-temperature startup: when the stack voltage is still low and unstable, excessive or rapid current may cause the voltage to drop to an extremely low level instantly, which can easily lead to the collapse of the stack output voltage, resulting in "cold start failure" and seriously affecting the stack life.

[0005] If constant voltage control is maintained after startup: the output current changes according to the state of the fuel cell, which cannot meet the requirements for precise control of the load power.

[0006] When switching between constant voltage input control and constant current input control methods, a direct switch will cause a step jump in the controller output, which will impact the power circuit.

[0007] Therefore, there is an urgent need for a smooth switching strategy for DC-DC operating modes, which uses constant input voltage control to provide stable operating conditions for the fuel cell stack during the cold start phase, and switches to constant input current control after startup to optimize operating efficiency and lifespan. Summary of the Invention

[0008] This invention aims to address the problems of existing technologies in fuel cell DC-DC converters during control mode switching, including: low-temperature cold starts using constant current control leading to stack voltage collapse and start-up failure; inability to meet precise load power control requirements during normal operation while maintaining constant voltage control; and step-like voltage jumps during direct switching between two control modes causing impacts on the power circuit. The technical solution is as follows: On the one hand, a smooth switching system for DC-DC control mode of fuel cell is provided, including a DC-DC converter composed of multi-phase BOOST in parallel, a detection module and a control module; The DC-DC converter includes an inductor L, an output capacitor Cn, a diode Dn, and a switching transistor Qn. The switching transistor Qn, the diode Dn, the inductor L, and the output capacitor Cn are connected in sequence to realize energy transfer between the fuel cell stack and the battery. The detection module includes an input voltage detection module Vi, an inductor current detection module An, and an output voltage detection module Vo, which are used to collect input voltage data. Inductor current and output voltage The collected signals are then transmitted to the control module. The control module is used to switch control modes. During the cold start phase, it adopts the constant voltage input control mode. After the start-up is completed, it switches to the constant current input control mode. During the switching process, a smooth transition is achieved through weighted synthesis and feedforward compensation.

[0009] Optionally, the number of multiphase BOOST parallel channels of the DC-DC converter can be adjusted according to actual usage requirements, with a minimum of 3 channels.

[0010] Optionally, in the constant voltage input control mode, the voltage outer loop PI regulation output... As the control reference for the inner current loop, the inner current loop stabilizes the input voltage by adjusting the duty cycle of the switching transistor Qn.

[0011] Optionally, in the input constant current control mode, the control module adopts a dual-loop control of an outer output voltage loop and an inner current loop. The outer output voltage loop is used to stabilize the output voltage, and the inner current loop achieves constant current control.

[0012] Optionally, the detection module collects the input voltage. Inductor current and output voltage The data is transmitted in real time to the control module to provide data support for control mode switching and duty cycle adjustment.

[0013] On the other hand, a method for smooth switching of DC-DC control modes for fuel cells is provided, applicable to the aforementioned smooth switching system for DC-DC control modes for fuel cells, comprising: Step 1: The system operates in constant input voltage control mode. The control module adopts a dual-loop control with an outer voltage loop and an inner current loop. The outer voltage loop compares the input voltage collected by the input voltage detection module Vi. With input target voltage The output current loop reference after PI regulation Current inner loop tracking ,in , This is the proportionality coefficient. For the error term, The integral coefficient is... This is the voltage loop integral term; Step 2: When the fuel cell current reaches near its normal value, the system prepares to switch to the input constant current control mode. The constant current control outer loop of the control module is based on the target output voltage. and the output voltage detection module Vo collects Real-time calculation of target current ,in , This is the proportionality coefficient. For the error term, The integral coefficient is... This is the voltage loop integral term; the current setpoint in constant current mode is... , This serves as the final reference for the inner current loop in constant current control. For a given current reference; Step 3: Switch the reference command for the inner current loop within the transition range. The outer loop output is weighted and synthesized from the input constant voltage mode and the input constant current mode, i.e. ,in Here, k represents the weighting coefficient, and k is the number of control cycles completed during the transition process. Step 4, the weighting coefficients A non-linear transition method is adopted to meet the requirements. N is the number of control cycles for the duration of the transition process; Step 5: Add feedforward compensation during the switching process; feedforward compensation amount , For feedforward compensation gain and <1, during the switching process, the current inner loop reference is... .

[0014] Optionally, N is the number of control cycles that can be adjusted according to actual needs.

[0015] Optionally, the judgment criterion for "the stack current reaching near the normal value" in step 2 can be set automatically based on the stack performance and status.

[0016] Optionally, the duty cycle of the DC-DC converter and the output voltage satisfy the following conditions: , For output voltage, Input voltage, To control the duty cycle.

[0017] Optionally, the feedforward compensation amount Through weighting coefficients Adjustments are made to ensure that feedforward compensation and the switching process are synchronized and coordinated.

[0018] Compared with the prior art, the present invention has the following significant advantages.

[0019] This invention discloses a smooth switching system and method for DC-DC control modes in fuel cells, belonging to the field of dedicated switching power supply control for fuel cells. The system includes a DC-DC converter composed of multi-phase boosters in parallel, a detection module, and a control module. The detection module collects input voltage, inductor current, and output voltage signals and transmits them to the control module. During the cold start phase, the control module employs constant input voltage control, stabilizing the input voltage through dual-loop control. During normal operation, it switches to constant input current control to precisely control the output power. Smooth transition is achieved through nonlinear weighted synthesis and feedforward compensation. This invention solves the problems of easy cold start failure, low power control accuracy during normal operation, and large switching shocks in existing technologies, extending fuel cell life and improving system reliability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the Boost circuit and its control method; Figure 2 Provide a constant voltage control block diagram for Boost input; Figure 3 Block diagram for constant current control of Boost input; Figure 4 Here is a flowchart of the loop switching process; Figure 5 This is a schematic diagram of nonlinear weighting coefficients. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0022] In this article, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] To address the aforementioned technical problems, this invention provides a smooth switching system and method for DC-DC control modes in fuel cells, as detailed below. Figure 1-5 The technical solution and specific implementation details are explained in detail.

[0024] Example 1 On the one hand, a smooth switching system for DC-DC control mode of fuel cell is provided. The system includes a DC-DC converter composed of multi-phase BOOST in parallel, a detection module and a control module. The structural composition, connection relationship and implementation parameters of each component are as follows.

[0025] The DC-DC converter includes an inductor L, an output capacitor Cn, a diode Dn, and a switching transistor Qn. The switching transistor Qn, the diode Dn, the inductor L, and the output capacitor Cn are connected in sequence to realize energy transfer between the fuel cell stack and the battery.

[0026] The number of multi-phase booster parallel circuits in the DC-DC converter can be adjusted according to actual usage requirements, but is at least 3. The embodiment uses a 3-channel booster parallel architecture (this can be adjusted to 2, 4, etc., depending on power requirements). The selection and connection relationships of the core components of each booster circuit are as follows: Figure 1 The structure shown.

[0027] In one example, the inductor L is selected as CDRH127-220M (inductance value 22μH), one end of which is fixedly connected to the positive output terminal of the fuel cell stack, and the other end is electrically connected to the drain of the switching transistor Qn by soldering. In one example, the switching transistor Qn is a MOSFET IRF3205 with its source grounded and its gate connected to the PWM output port of the control module (such as the PA8 pin of the STM32F407) via a DuPont wire to receive the duty cycle control signal. In one example, the diode Dn is a Schottky diode SS34, with its anode soldered to the drain of the switching transistor Qn, and its cathode connected to the positive terminal of the output capacitor Cn via a copper busbar. In one example, the output capacitor Cn is a 100μF / 450V electrolytic capacitor with its negative terminal grounded and its positive terminal connected to the positive terminal of the high-voltage battery as the system output terminal. Through a multi-phase parallel architecture, the system peak power reaches 15kW, which meets the power requirements of the fuel cell.

[0028] When the circuit is working, it uses the formula To achieve voltage regulation, among which This represents the actual output voltage across the output capacitor Cn. D is the input voltage of the fuel cell stack, and D is the control duty cycle of the switching transistor Qn (in this embodiment, the adjustment range of D is 0.2-0.8).

[0029] The detection module includes an input voltage detection module Vi, an inductor current detection module An, and an output voltage detection module Vo, which are used to collect input voltage data. Inductor current and output voltage The acquired signal is then transmitted to the control module. The detection module acquires the input voltage. Inductor current and output voltage The data is transmitted in real time to the control module to provide data support for control mode switching and duty cycle adjustment.

[0030] Referring to the diagram, the deployment location of the detection module is... Figure 1 The annotations for Vi, An, and Vo correspond one-to-one, and the specific implementation is as follows.

[0031] In one example, the input voltage detection module Vi uses a voltage sensor LV28-P. Its two input terminals are connected in parallel to the positive and negative terminals of the fuel cell stack, respectively, and its output terminal is connected to the PA0 pin of the control module through an ADC signal line to acquire the input voltage in real time. (Sampling accuracy ±0.1V); In one example, the inductor current detection module An uses an ACS712 current sensor, connected in series in the wire between the inductor L and the switching transistor Qn. It is secured with a snap-fit ​​mechanism to prevent open circuits. Its output is connected to the PA1 pin of the control module to collect the inductor current. (Measurement range 0-100A, response time ≤5μs); In one example, the output voltage detection module Vo uses a voltage sensor LV28-P, connected in parallel across the positive and negative terminals of the output capacitor Cn. Its output is connected to the PA2 pin of the control module to acquire the output voltage. (Sampling frequency 1kHz); All signals from the detection module are transmitted through shielded wires to avoid electromagnetic interference and ensure the accuracy of the collected data.

[0032] The control module is used to switch control modes. During the cold start phase, it adopts the constant voltage input control mode. After the start-up is completed, it switches to the constant current input control mode. During the switching process, a smooth transition is achieved through weighted synthesis and feedforward compensation.

[0033] In one possible implementation, an STM32F407 microcontroller is selected as the core controller, which is soldered and fixed inside the system housing via a PCB board. Its power supply terminal is connected to a 12V auxiliary power supply, and its ground terminal shares a common ground with the system. The control module communicates with the detection module via an SPI interface and outputs control signals to the DC-DC converter via a PWM interface to achieve… Figure 1 The "detection-control-execution" closed-loop logic is shown.

[0034] Example 2 Further explanation of the implementation of the constant input pressure control mode and the constant input current control mode, namely, a method for smooth switching of DC-DC control mode for fuel cells is provided, which is applicable to the aforementioned smooth switching system for DC-DC control mode for fuel cells.

[0035] Step 1: The system operates in constant input voltage control mode. The control module adopts a dual-loop control with an outer voltage loop and an inner current loop. The outer voltage loop compares the input voltage collected by the input voltage detection module Vi. With input target voltage The output current loop reference after PI regulation Current inner loop tracking ,in , This is the proportionality coefficient. For the error term, The integral coefficient is... This is the voltage loop integral term.

[0036] The constant pressure input control mode is used for the low-temperature cold start stage (e.g., stack temperature < -10℃), and the control logic is as follows: Figure 2 The implementation details of the double-ring structure are as follows.

[0037] First, set the control parameters, such as the target input voltage. =20V (can be adjusted to 18V, 22V, etc. depending on the fuel cell model), such as the voltage loop proportional coefficient. =0.5, integral coefficient =0.1, the current inner loop response bandwidth is set to 1kHz.

[0038] In one example, after the system powers on, the control module automatically enters the constant input voltage mode, according to... Figure 2 The process shown initiates dual-loop control: the input voltage detection module Vi acquires data. (e.g., initial value 12V) and transmit it to the control module; the control module calculates the error term. = - =8V, according to the formula Calculate the current loop reference value, where For the voltage loop integral term (initial value 0, integration time constant 0.1s), the initial... =0.5*8+0.1*0=4A; Next, the inductor current detection module An collects the actual inductor current. (Initial value 0.5A), and After comparison and PI regulation via the current loop, the output duty cycle D=0.4, controlling the switching transistor Qn to turn on / off at a frequency of 10kHz; After continuous adjustment, in this example, The voltage is kept stable within the range of 20V±0.5V, and the input current is maintained at 3-5A to avoid voltage collapse of the fuel cell stack and ensure successful cold start.

[0039] Step 2: When the fuel cell current reaches near its normal value, the system prepares to switch to the input constant current control mode. The constant current control outer loop of the control module is based on the target output voltage. and the output voltage detection module Vo collects Real-time calculation of target current ,in , This is the proportionality coefficient. For the error term, This refers to the integral coefficient (note that although the names are the same, this is the integral coefficient in constant current mode, which is represented differently from the integral coefficient in constant voltage mode in step 1). This is the voltage loop integral term; the current setpoint in constant current mode is... , This serves as the final reference for the inner current loop in constant current control. For a given current reference; This step is implemented in constant current control mode, corresponding to... Figure 3 The Boost input constant current control block diagram is shown. This mode is used during the normal operation phase of the fuel cell stack (e.g., temperature ≥ 5℃). The judgment criterion for "fuel cell stack current reaching near normal value" in step 2 is set automatically based on the fuel cell stack performance and status. Implementation details are as follows.

[0040] First, the control parameter settings will be explained in detail with examples and data. Example target output voltage. =300V, given current reference =50A, current loop proportionality factor =0.3, integral coefficient =0.05, the voltage outer loop response bandwidth is set to 200Hz.

[0041] In one example, the implementation process is given. When the control module detects that the stack temperature has reached 5°C via a temperature sensor (such as an NTC thermistor), and the inductor current detection module An collects the current... After maintaining a stable A value of 45A (near the preset normal value) for 5 seconds, the system triggers a switching preparation and enters... Figure 3 The constant current control logic shown; The output voltage detection module Vo collects the voltage across the output capacitor Cn. (e.g., initial 280V), calculate the error term. = - =20V, according to the formula = * + * Calculate the target current, where For the current loop integral term (initial value 0), the initial value is... =0.3*20+0.05*0=6A; According to the formula Given the current setting, since 6A < 50A, therefore =6A; Therefore, in this example, the inner current loop will and By adjusting the duty cycle of the switching transistor Qn to 0.7, the output voltage is stabilized at 300V±2V, and the input current is maintained at 50A±1A, which meets the requirements for precise control of load power.

[0042] In summary, based on steps 1 and 2, in the constant voltage control mode, the voltage outer loop PI regulation output... As the control reference for the inner current loop, the inner current loop stabilizes the input voltage by adjusting the duty cycle of the switching transistor Qn. In the constant current control mode, the control module adopts a dual-loop control of the outer output voltage loop and the inner current loop. The outer output voltage loop is used to stabilize the output voltage, and the inner current loop achieves constant current control.

[0043] Step 3: Switch the reference command for the inner current loop within the transition range. The outer loop output is weighted and synthesized from the input constant voltage mode and the input constant current mode, i.e. ,in Here, k represents the weighting coefficient, and k is the number of control cycles completed during the transition process. Step 4, the weighting coefficients A non-linear transition method is adopted to meet the requirements. N is the number of control cycles for the duration of the transition process; Step 5: Add feedforward compensation during the switching process; feedforward compensation amount , For feedforward compensation gain and <1, during the switching process, the current inner loop reference is... .

[0044] Among them, feedforward compensation amount Through weighting coefficients Adjustments are made to ensure that feedforward compensation and the switching process are synchronized and coordinated.

[0045] The above steps 3 to 5 correspond to the implementation of the smooth handover process. Figure 4 Loop switching process Figure 5 Schematic diagram of nonlinear weighting coefficients. (Switching process reference) Figure 4 The process steps, and the adjustment of weighting coefficients and Figure 5 The curve characteristics are consistent, and the implementation details are as follows.

[0046] First, switch the triggering conditions. For example, if the fuel cell stack temperature is ≥5℃ and... When the current is ≥45A (for 3 consecutive control cycles), the control module triggers a switching command to enter the transition range.

[0047] Secondly, the transition parameters are set. For example, the number of control cycles for the transition process is N=100 (control cycle is 100μs, total transition time is 10ms), and the feedforward compensation gain is set. =0.8 (adjustable range 0.5-0.9).

[0048] Implementation steps correspond Figure 4 Steps 1-5.

[0049] Before the switch, the system maintains constant input voltage mode with current inner loop tracking. (In the example at this time) =4.5A); After switching to startup, the control module performs real-time calculations. (e.g., initial value 6A), and according to Figure 5 The nonlinear curve shown calculates the weighting coefficients. k increases sequentially from 0 to 100. When k=0, =(1+cos(0)) / 2=1; when k=50, =(1+cos(π*50 / 100)) / 2=0.5; when k=100, =(1+cos(π)) / 2=0, which satisfies the condition. Figure 5 The characteristics of "gradual changes at both ends and rapid changes in the middle" are present.

[0050] According to the formula Calculate the inner loop reference command for the current calculation. When k=0, =1*4.5+(1-1)*6=4.5A; when k=50, =0.5*4.5+0.5*6=5.25A; when k=100, =0*4.5+1*6=6A, achieving a smooth current transition.

[0051] Next, we come to the implementation of feedforward compensation. According to the formula... =0.8*(6-4.5)=1.2A to calculate the compensation amount, and then use the formula... Correct current reference. When k=50, =5.25 + 0.5 * 0.5 * 1.2 = 5.55A, accelerating dynamic response; Control module according to The duty cycle is adjusted in real time, the current fluctuation amplitude during the switching process is ≤3%, there is no step jump, and the impact voltage on the power circuit is ≤5V, which meets the requirements for smooth switching.

[0052] In addition, alternative solutions are provided for special cases. If the system power requirement is 10kW, the DC-DC converter can be adjusted to have two boosters in parallel (corresponding to...). Figure 1 (Topological modifications), such as selecting CDRH127-330M (33μH) for inductor L, selecting IRF4905 for switching transistor Qn, and replacing the control module with DSP chip TMS320F28335; Furthermore, for example, the transition parameter is adjusted to N=150 (total transition time 15ms), and the feedforward compensation is increased. =0.6, the weighting coefficients still follow the formula =(1+cos(π*k / N)) / 2, the current fluctuation during the switching process is ≤4%, thus achieving smooth switching; The control logic, module connection relationship and alternative embodiment Figure 1-5 The diagrams are consistent, only the component selection and parameter adaptation are different.

[0053] In summary, compared with the prior art, the present invention has the following significant beneficial effects.

[0054] To ensure successful cold start and fuel cell stack safety, through Figure 2 The constant voltage control dual-loop structure and parameter settings shown ensure that the input voltage is stabilized at 20V±0.5V and the current ≤5A during the cold start phase, completely preventing stack voltage collapse. Actual testing at low temperature (-20℃) showed a 100% start-up success rate. This optimizes fuel cell lifespan and efficiency: during normal operation... Figure 3 The constant current control mode stabilizes the fuel cell stack operating current at 50A±1A, increasing operating efficiency to 92% and extending the stack cycle life by 30% compared to existing technologies; it also achieves smooth energy flow management under all operating conditions, relying on... Figure 4 Switching process and Figure 5 The nonlinear weighting strategy ensures a smooth switching process and improves system operation. In vehicle operating condition testing, the voltage ripple is ≤2V, meeting the reliability requirements of fuel cell power systems.

[0055] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0056] Those skilled in the art will understand that all or part of the steps of the above embodiments can be implemented by hardware, or by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk. The above descriptions are merely optional embodiments of this application and are not intended to limit the application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A DC-DC control mode smooth switching system for fuel cells, characterized in that, It includes a DC-DC converter consisting of multi-phase BOOST parallel connection, a detection module, and a control module; The DC-DC converter includes an inductor L, an output capacitor Cn, a diode Dn, and a switching transistor Qn. The switching transistor Qn, the diode Dn, the inductor L, and the output capacitor Cn are connected in sequence to realize energy transfer between the fuel cell stack and the battery. The detection module includes an input voltage detection module Vi, an inductor current detection module An, and an output voltage detection module Vo, which are used to collect input voltage data. Inductor current and output voltage The collected signals are then transmitted to the control module. The control module is used to switch control modes. During the cold start phase, it adopts the constant voltage input control mode. After the start-up is completed, it switches to the constant current input control mode. During the switching process, a smooth transition is achieved through weighted synthesis and feedforward compensation.

2. The smooth switching system for DC-DC control mode of fuel cells according to claim 1, characterized in that, The number of multiphase BOOST parallel channels of the DC-DC converter can be adjusted according to actual usage requirements, with a minimum of 3 channels.

3. The smooth switching system for DC-DC control mode of fuel cells according to claim 1, characterized in that, In the input constant voltage control mode, the voltage outer loop PI regulation output As the control reference for the inner current loop, the inner current loop stabilizes the input voltage by adjusting the duty cycle of the switching transistor Qn.

4. The smooth switching system for DC-DC control mode of fuel cells according to claim 1, characterized in that, In the input constant current control mode, the control module adopts a dual-loop control of output voltage outer loop and current inner loop. The output voltage outer loop is used to stabilize the output voltage, and the current inner loop realizes constant current control.

5. The smooth switching system for DC-DC control mode of fuel cells according to claim 1, characterized in that, The detection module collects the input voltage Inductor current and output voltage The data is transmitted in real time to the control module to provide data support for control mode switching and duty cycle adjustment.

6. A method for smooth switching of DC-DC control modes for fuel cells, applicable to the smooth switching system for DC-DC control modes for fuel cells as described in any one of claims 1 to 5, characterized in that, include: Step 1: The system operates in constant input voltage control mode. The control module adopts a dual-loop control with an outer voltage loop and an inner current loop. The outer voltage loop compares the input voltage collected by the input voltage detection module Vi. With input target voltage The output current loop reference after PI regulation Current inner loop tracking ,in , This is the proportionality coefficient. For error terms, The integral coefficient is... This is the voltage loop integral term; Step 2: When the fuel cell current reaches near its normal value, the system prepares to switch to the input constant current control mode. The constant current control outer loop of the control module is based on the target output voltage. and the output voltage detection module Vo collects Real-time calculation of target current ,in , This is the proportionality coefficient. For error terms, The integral coefficient is... This is the voltage loop integral term; the current setpoint in constant current mode is... , This serves as the final reference for the inner current loop in constant current control. For a given current reference; Step 3: Switch the reference command for the inner current loop within the transition range. The outer loop output is weighted and synthesized from the input constant voltage mode and the input constant current mode, i.e. ,in Here, k represents the weighting coefficient, and k is the number of control cycles completed during the transition process. Step 4, the weighting coefficients A non-linear transition method is adopted to meet the requirements. N is the number of control cycles for the duration of the transition process; Step 5: Add feedforward compensation during the switching process; feedforward compensation amount , For feedforward compensation gain and <1, during the switching process, the inner current loop reference is... .

7. The method for smooth switching of DCDC control modes for fuel cells according to claim 6, characterized in that, N is the number of control cycles that can be adjusted according to actual needs.

8. The method for smooth switching of DCDC control modes for fuel cells according to claim 6, characterized in that, The judgment criterion for "the current of the fuel cell stack reaching near the normal value" in step 2 is set automatically based on the performance and status of the fuel cell stack.

9. The method for smooth switching of DCDC control modes for fuel cells according to claim 6, characterized in that, The duty cycle and output voltage of the DC-DC converter satisfy the following conditions: , For output voltage, Input voltage, To control the duty cycle.

10. The method for smooth switching of DCDC control modes for fuel cells according to claim 6, characterized in that, The feedforward compensation amount Through weighting coefficients Adjustments are made to ensure that feedforward compensation and the switching process are synchronized and coordinated.

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