Dc / dc converter, voltage boosting method, and fuel cell system

Abstract

The application relates to the field of new energy vehicles, and specifically discloses a DC / DC converter, a boosting method and a fuel cell system. The converter comprises a Boost circuit, a PWM circuit and a control circuit. The control circuit obtains a duty cycle control signal according to an input current and a reference current of the Boost circuit. The control circuit determines a target frequency according to an input voltage of the Boost circuit and a segmented frequency modulation mode, and obtains a frequency control signal based on the target frequency. The PWM circuit outputs a PWM wave according to the duty cycle control signal and the frequency control signal. The duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency. The Boost circuit boosts the input voltage of the Boost circuit according to the PWM wave, so that the Boost circuit outputs a preset voltage. According to the scheme, the Boost circuit can output a higher voltage when the input voltage of the Boost circuit is relatively low.

Description

Technical Field

[0001] This application relates to the field of new energy electric vehicles, and in particular to a DC / DC converter, a boost method, and a fuel cell system. Background Technology

[0002] In the global wave of new energy vehicles, electrification has become an unstoppable trend in automotive development. Among numerous renewable energy sources, hydrogen fuel cells have become a strategically important area for automotive power development due to their advantages of zero pollution, renewability, and high efficiency. Because of their relatively soft output characteristics, they typically require a DC / DC converter to achieve controllable output. Figure 1 As shown, the voltage output by the fuel cell is transmitted to the load via a DC / DC converter to enable the load to operate.

[0003] A fuel cell stack, as a power generation device, is composed of multiple cells stacked in series. The electrochemical characteristics of each cell determine that when starting at a low temperature (around 0°C), the fuel cell's reaction performance significantly decreases, resulting in the stack producing only a low output voltage. When the topology, switching frequency, and minimum turn-off time of the DC / DC converter connected to the stack are fixed, the maximum boost ratio of this DC / DC converter determines that it cannot operate normally across the entire voltage range of the fuel cell stack. Summary of the Invention

[0004] This application provides a DC / DC converter, a boost method, and a fuel cell system. The solutions proposed in this application can solve the aforementioned technical problems.

[0005] In a first aspect, embodiments of this application provide a DC / DC converter, including: a Boost circuit, a pulse width modulation (PWM) circuit, and a control circuit, wherein the input terminal of the control circuit is connected to the first input terminal of the Boost circuit, the output terminal of the control circuit is connected to the control terminal of the PWM circuit, and the output terminal of the PWM circuit is connected to the control terminal of the Boost circuit.

[0006] The control circuit is used to obtain the duty cycle control signal based on the input current and reference current of the Boost circuit; and to determine the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and to obtain the frequency control signal based on the target frequency.

[0007] A PWM circuit is used to output a PWM wave based on a duty cycle control signal and a frequency control signal. The duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency.

[0008] The Boost circuit is used to boost the input voltage of the Boost circuit according to the PWM wave so that the Boost circuit outputs a preset voltage, which is much larger than the input voltage of the Boost circuit.

[0009] By adjusting the duty cycle and frequency of the PWM wave, the Boost circuit can achieve higher boost capability, freeing it from the limitations of the switching devices within the Boost circuit. Furthermore, by determining the PWM wave frequency through segmented frequency modulation, fluctuations in the Boost circuit's input voltage can be prevented from affecting the PWM wave frequency and thus causing output voltage instability.

[0010] In one feasible embodiment, the control circuit includes a current control circuit and a frequency control circuit;

[0011] The control circuit includes a first input terminal and a second input terminal of the current control circuit, and an input terminal of the frequency control circuit. The control circuit also includes an output terminal of the current control circuit and an output terminal of the frequency control circuit. The PWM circuit includes a first control terminal and a second control terminal. The first input terminal of the current control circuit and the input terminal of the frequency control circuit are both connected to the first input terminal of the Boost circuit. The output terminals of the current control circuit and the frequency control circuit are respectively connected to the first control terminal and the second control terminal of the PWM circuit.

[0012] The current control circuit is used to obtain the duty cycle control signal based on the input current of the Boost circuit and the reference current input from the second input port of the current control circuit.

[0013] The frequency control circuit is used to determine the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and to obtain the frequency control signal based on the target frequency; wherein, the smaller the input voltage, the smaller the target frequency.

[0014] In one feasible embodiment, the segmented frequency modulation method includes:

[0015] During the input voltage rise phase of the Boost circuit, if the input voltage of the Boost circuit is higher than the first preset threshold, the target frequency is determined according to the first preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is higher than the second preset threshold, the target frequency is determined according to the second preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold.

[0016] During the input voltage drop phase of the Boost circuit, if the input voltage of the Boost circuit is lower than the third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is lower than the fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

[0017] The relationship between the input voltage and the frequency of the PWM wave is determined by a function relating the input voltage and the frequency of the PWM wave. This function can be expressed as:

[0018]

[0019] Among them, V out For the aforementioned preset voltage, T off V is the turn-off time of the PWM wave. in f is the input voltage, and f is the frequency of the PWM wave.

[0020] In one feasible embodiment, the segmented frequency modulation method includes:

[0021] Determine the voltage range to which the input voltage of the Boost circuit belongs; obtain the median of the voltage range; determine the frequency corresponding to the median based on the functional relationship between the input voltage and the frequency of the PWM wave, and the frequency corresponding to the median is the target frequency.

[0022] In one feasible embodiment, the current control circuit includes an adder and a proportional-integral (PI) regulator;

[0023] The first and second input terminals of the adder are respectively the first and second input terminals of the current control circuit. The output terminal of the adder is connected to the input terminal of the PI regulator, and the output terminal of the PI regulator is the output terminal of the current control circuit.

[0024] The adder is used to process the input current and reference current of the Boost circuit to obtain the processed current;

[0025] A PI controller is used to obtain a duty cycle control signal based on the processed current.

[0026] Secondly, embodiments of this application provide a boost method applied to a DC-DC converter, the DC-DC converter including a boost circuit, a PWM circuit, and a control circuit, the method including:

[0027] The control circuit obtains the duty cycle control signal based on the input current and reference current of the Boost circuit; it determines the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains the frequency control signal based on the target frequency.

[0028] The PWM circuit outputs a PWM wave based on the duty cycle control signal and the frequency control signal. The duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency.

[0029] The Boost circuit boosts the input voltage of the Boost circuit according to the PWM wave so that the Boost circuit outputs a preset voltage, which is much larger than the input voltage of the Boost circuit.

[0030] In one feasible embodiment, the control circuit includes a current control circuit and a frequency control circuit; the control circuit obtains a duty cycle control signal based on the input current and reference current of the Boost circuit; and obtains a frequency control signal based on the input voltage of the Boost circuit, including:

[0031] The current control circuit obtains the duty cycle control signal based on the input current of the Boost circuit and the reference current input from the second input port of the current control circuit.

[0032] The frequency control circuit determines the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains the frequency control signal based on the target frequency; wherein, the smaller the input voltage, the smaller the target frequency.

[0033] In one feasible embodiment, the segmented frequency modulation method includes:

[0034] During the input voltage rise phase of the Boost circuit, if the input voltage of the Boost circuit is higher than the first preset threshold, the target frequency is determined according to the first preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is higher than the second preset threshold, the target frequency is determined according to the second preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold.

[0035] During the input voltage drop phase of the Boost circuit, if the input voltage of the Boost circuit is lower than the third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is lower than the fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

[0036] The relationship between the input voltage and the frequency of the PWM wave is determined based on the functional relationship between them; this functional relationship can be expressed as:

[0037]

[0038] Among them, V out For the aforementioned preset voltage, T off V is the turn-off time of the PWM wave. in f is the input voltage, and f is the frequency of the PWM wave.

[0039] In one feasible embodiment, the segmented frequency modulation method includes:

[0040] Determine the voltage range to which the input voltage of the Boost circuit belongs; obtain the median of the voltage range; determine the frequency corresponding to the median based on the functional relationship between the input voltage and the frequency of the PWM wave, and the frequency corresponding to the median is the target frequency.

[0041] Thirdly, embodiments of this application also provide a fuel cell system, including a fuel cell, a load, and a DC / DC converter as described in the first aspect.

[0042] It can be seen that by adjusting the duty cycle and frequency of the PWM wave input to the Boost circuit, a high output voltage can be ensured even when the input voltage of the Boost circuit is low, while also eliminating the risk of the switching transistor in the Boost circuit failing. Furthermore, by determining the frequency of the PWM wave through segmented frequency modulation, fluctuations in the PWM frequency caused by fluctuations in the input voltage of the Boost circuit can be avoided, thus preventing unstable output voltage.

[0043] These or other aspects of this application will become more apparent in the following description of the embodiments. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the structure of a fuel cell system provided in an embodiment of this application;

[0046] Figure 2 A schematic diagram of a DC / DC converter provided in an embodiment of this application;

[0047] Figure 3 A schematic diagram of another DC / DC converter provided in this application embodiment;

[0048] Figure 4 A schematic diagram of another DC / DC converter provided in this application embodiment;

[0049] Figure 5 A schematic diagram illustrating the functional relationship between the frequency of a PWM wave and the input voltage, provided in an embodiment of this application;

[0050] Figure 6 A schematic diagram illustrating the functional relationship between the frequency of another PWM wave and the input voltage, provided for an embodiment of this application;

[0051] Figure 7a This is a schematic diagram showing the change in the gate voltage of the MOSFET when a PWM wave is input.

[0052] Figure 7b This is a schematic diagram showing how the frequency of a PWM wave changes with its duty cycle.

[0053] Figure 8 This is a schematic flowchart of a boost method based on a DC / DC converter provided in an embodiment of this application. Detailed Implementation

[0054] The following sections will provide detailed explanations.

[0055] The terms "first," "second," "third," and "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0056] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0057] "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.

[0058] The embodiments of this application will now be described with reference to the accompanying drawings.

[0059] See Figure 2 , Figure 2 This is a schematic diagram of a DC / DC converter provided in an embodiment of this application. Figure 2 As shown, the DC / DC converter 200 includes a Boost circuit 201, a PWM circuit 202, and a control circuit 203;

[0060] The input terminal of the control circuit 203 is connected to the first input terminal of the Boost circuit 201, the output terminal of the control circuit 203 is connected to the control terminal of the PWM circuit 202, and the output terminal of the PWM circuit 202 is connected to the control terminal of the Boost circuit 201.

[0061] The control circuit 203 is used to obtain a duty cycle control signal based on the input current and reference current of the Boost circuit 201; and to determine the target frequency based on the input voltage and segmented frequency modulation method of the Boost circuit 201, and to obtain a frequency control signal based on the target frequency.

[0062] The PWM circuit 202 is used to output a PWM wave according to the duty cycle control signal and the frequency control signal. The duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency.

[0063] The Boost circuit 201 is used to boost the input voltage of the Boost circuit 201 according to the PWM wave so that the Boost circuit 201 outputs a preset voltage, which is much larger than the input voltage of the Boost circuit 201.

[0064] The PWM circuit 202 determines the target duty cycle based on the duty cycle control signal and the target frequency based on the frequency control signal. Then, the PWM circuit 202 outputs a PWM wave with the target duty cycle and the target frequency.

[0065] It should be noted that the duty cycle control signal can be a digital signal used to indicate the target duty cycle.

[0066] Optionally, the preset voltage can be 200V, 210V, 220V, 230V, 240V, 250V, 700V, 710V, 720V, 730V, 740V, 750V, etc.

[0067] Specifically, the preset voltage being much greater than the input power supply of the Boost circuit 201 means that the boost ratio of the Boost circuit 201 is greater than the preset ratio; optionally, the preset ratio can be 10, 20, 50, 80, 100 or other values.

[0068] It can be seen that by adjusting the duty cycle and frequency of the PWM wave, the Boost circuit can achieve a higher boost capability, free from the limitations of the switching devices within the Boost circuit. Furthermore, by determining the frequency of the PWM wave through segmented frequency modulation, the fluctuation of the PWM wave frequency due to the input voltage of the Boost circuit can be avoided, thus preventing the output voltage from becoming unstable.

[0069] In a specific example, such as Figure 3 As shown, the control circuit 203 includes a current control circuit 204 and a frequency control circuit 205;

[0070] The control circuit 203 includes a first input terminal and a second input terminal of the current control circuit 204, and an input terminal of the frequency control circuit 205. The output terminal of the control circuit 203 includes the output terminal of the current control circuit 204 and the output terminal of the frequency control circuit. The control terminal of the PWM circuit 202 includes a first control terminal and a second control terminal. The first input terminal of the current control circuit 204 and the input terminal of the frequency control circuit 205 are both connected to the first input terminal of the Boost circuit 201. The output terminal of the current control circuit 204 and the output terminal of the frequency control circuit 205 are respectively connected to the first control terminal and the second control terminal of the PWM circuit 202.

[0071] The current control circuit 204 is used to obtain a duty cycle control signal based on the input current of the Boost circuit 201 and the reference current input from the second input port of the current control circuit 204.

[0072] The frequency control circuit 205 is used to determine the target frequency based on the input voltage of the Boost circuit 201 and the segmented frequency modulation method, and to obtain a frequency control signal based on the target frequency; wherein, the smaller the input voltage, the smaller the target frequency.

[0073] Furthermore, such as Figure 4 As shown, the current control circuit 204 includes an adder 207 and a proportional-integral (PI) regulator 206.

[0074] The first and second input terminals of adder 207 are respectively the first and second input terminals of current control circuit 204. The output terminal of adder 207 is connected to the input terminal of PI regulator 206, and the output terminal of PI regulator 206 is the output terminal of current control circuit 204.

[0075] Adder 207 is used to process the input current and reference current of Boost circuit 201 to obtain the processed current;

[0076] The PI regulator 206 is used to obtain the duty cycle control signal based on the processed current; specifically, the PI regulator 206 obtains the duty cycle control signal by linearly combining the proportional and integral values ​​of the processed current.

[0077] In a specific example, such as Figure 4 As shown, the Boost circuit 201 includes an inductor L, a transistor M, a diode D, and a capacitor C. The first end of the inductor L is the first input terminal of the Boost circuit 201, and the second end of the inductor L is connected to the source of the transistor M and the positive terminal of the diode D. The gate of the transistor M is connected to the output terminal of the PWM circuit 202, and the negative terminal of the diode D is connected to the first end of the capacitor C. The drain of the transistor M and the second end of the capacitor C constitute the second input terminal and the second output terminal of the Boost circuit 201. The negative terminal of the diode D and the first end of the capacitor C constitute the first input terminal of the Boost circuit 201. The input voltage is input through the first and second input terminals of the Boost circuit 201, and the preset voltage is output through the first and second output terminals of the Boost circuit 201.

[0078] It should be noted that the input current at the first input terminal of the above Boost circuit is the current flowing through the inductor L.

[0079] By adjusting the duty cycle and frequency of the PWM wave output by the PWM circuit 202, the closing and opening times of the source and drain of the transistor M are controlled, thereby adjusting the boost ratio of the Boost circuit 201.

[0080] Optionally, the transistor M mentioned above can be replaced with a bipolar transistor.

[0081] In one feasible embodiment, the segmented frequency modulation method includes:

[0082] During the input voltage rise phase of the Boost circuit, if the input voltage of the Boost circuit 201 is higher than the first preset threshold, the target frequency is determined according to the first preset threshold and the correspondence between the input voltage and the frequency of the PWM; if the input voltage of the Boost circuit 201 is higher than the second preset threshold, the target frequency is determined according to the second preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold.

[0083] During the input voltage drop phase of the Boost circuit, if the input voltage of the Boost circuit 201 is lower than the third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit 201 is lower than the fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

[0084] The correspondence between the input voltage and the frequency of the PWM wave is determined based on the functional relationship between the input voltage and the frequency of the PWM wave.

[0085] Specifically, the input voltage V in Output voltage V out The period T of the PWM wave, the duty cycle D, and the off-time T of transistor M. off The relationship is as follows:

[0086]

[0087] Based on the frequency of the PWM wave f = 1 / T, simplifying the above equation yields the functional relationship between the input voltage and the frequency of the PWM wave:

[0088]

[0089] When V out It is 750V, and T off Minimum shutdown time T offmin At that time, the functional relationship between the input voltage and the frequency of the PWM wave is as follows:

[0090]

[0091] The minimum turn-off time is 1 millisecond, and the preset voltage is 750V. The functional relationship between the input voltage and the frequency of the PWM wave is as follows: Figure 5 As shown.

[0092] Following the above method, the functional relationship between the input voltage and the frequency of the PWM wave can be determined. To avoid instability in the PWM wave frequency due to unstable input voltage, this application proposes a segmented frequency modulation method, specifically including: during the input voltage rise phase of the Boost circuit 201, if the input voltage of the Boost circuit 201 is lower than a first preset threshold, a target frequency is determined based on the first preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit 201 is lower than a second preset threshold, a target frequency is determined based on the second preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold.

[0093] During the input voltage drop phase of the Boost circuit 201, if the input voltage of the Boost circuit 201 is higher than the third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is higher than the fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

[0094] For example, such as Figure 6 As shown, for Figure 5 The graph shown has five frequency points, corresponding to inputs of 20V, 30V, 40V, 50V, and 60V, with frequencies of 26.67kHz, 40kHz, 53.33kHz, 66.66kHz, and 80kHz respectively. During the input voltage rise phase of the Boost circuit 201, if the input voltage of the Boost circuit 201 is higher than 20V, the PWM wave frequency is 26.67kHz; if the input voltage of the Boost circuit 201 is higher than 30V, the PWM wave frequency is 40kHz; if the input voltage of the Boost circuit 201 is higher than 40V, the PWM wave frequency is 53.33kHz; and if the input voltage of the Boost circuit 201 is higher than 50V, the PWM wave frequency is 66.66kHz. During the input voltage drop phase of the Boost circuit 201, the hysteresis voltage is 5V. If the input voltage of the Boost circuit 201 is lower than 55V, the frequency of the PWM wave is 66.66kHz; if the input voltage of the Boost circuit 201 is lower than 45V, the frequency of the PWM wave is 53.33kHz; if the input voltage of the Boost circuit 201 is lower than 35V, the frequency of the PWM wave is 40kHz; if the input voltage of the Boost circuit 201 is lower than 25V, the frequency of the PWM wave is 26.67kHz.

[0095] In one feasible embodiment, if the input voltage of the Boost circuit is within a first voltage range, the target frequency is determined based on the first voltage range and the correspondence between the voltage range and the frequency of the PWM wave; if the input voltage of the Boost circuit is within a second voltage range, the target frequency is determined based on the second voltage range and the correspondence between the voltage range and the frequency of the PWM wave; wherein the difference between the maximum value of the first voltage range and the minimum value of the second voltage range is less than a preset threshold; if the input voltage of the Boost circuit is within a third voltage range, the target frequency is determined based on the third voltage range and the correspondence between the voltage range and the frequency of the PWM wave; wherein the difference between the maximum value of the second voltage range and the minimum value of the third voltage range is less than a preset threshold.

[0096] For example, suppose there are four voltage ranges: [20V, 29.5V], [30V, 39.5V], [40V, 49.5V], and [50V, 60V]. These four voltage ranges correspond to frequencies of 26.67kHz, 40kHz, 53.33kHz, and 66.66kHz, respectively. If the input voltage of the Boost circuit is 24V, the target frequency is 26.67kHz; if the input voltage of the Boost circuit is 37V, the target frequency is 40kHz; if the input voltage of the Boost circuit is 42V, the target frequency is 53.33kHz; and if the input voltage of the Boost circuit is 56V, the target frequency is 66.66kHz.

[0097] After determining the target frequency in the above manner, the corresponding frequency control signal is then determined based on the target frequency. The PWM circuit can output a PWM wave with the target frequency according to the frequency control signal.

[0098] It can be seen that when the output voltage of the fuel cell is low, that is, when the input voltage of the Boost circuit 201 is low, such as 20V, the Boost circuit 201 can output a voltage of up to 750V in the above manner, and there is no risk of the transistor in the Boost circuit 201 bursting.

[0099] Since the output voltage of the fuel cell changes continuously, the voltage output by the Boost circuit 201 also changes continuously according to the above method. Therefore, in order to obtain a stable output voltage, in a feasible embodiment, the preset rules include:

[0100] Determine the voltage range to which the input voltage of the Boost circuit 201 belongs; and obtain the median of the voltage range; determine the frequency corresponding to the median based on the functional relationship between the input voltage and the frequency of the PWM wave, and the frequency corresponding to the median is the target frequency.

[0101] Specifically, multiple non-overlapping voltage ranges are set, and in any two adjacent voltage ranges, the maximum value of the preceding voltage range is the same as the minimum value of the following voltage range. After obtaining the input voltage of the Boost circuit 201, the voltage range to which the input voltage of the Boost circuit 201 belongs is determined. Based on this voltage range, a voltage value is determined, which can be the median, maximum, or minimum value of the voltage range. Then, the frequency corresponding to this voltage value is determined according to the functional relationship between the input voltage and the frequency of the PWM wave. The frequency corresponding to the input voltage of the Boost circuit makes the output voltage of the Boost circuit a preset voltage. The frequency control signal is determined based on the frequency corresponding to the input voltage of the Boost circuit.

[0102] For example, suppose there are four voltage ranges: [20V, 30V), [30V, 40V), [40V, 50V), and [50V, 60V). If the input voltage is 52V, which falls within the voltage range [50V, 60V), then based on the functional relationship between the input voltage and the frequency of the PWM wave, the minimum value of the voltage range [50V, 60V], 50V, corresponds to a frequency of 66.66kHz.

[0103] Since the input voltage of the Boost circuit may vary around the boundary point of the two adjacent voltage ranges, there is a certain overlap between adjacent voltage ranges when setting multiple voltage ranges. When the input voltage of the Boost circuit belongs to the intersection of two voltage ranges, if the input voltage of the Boost circuit is in the boost stage, the target frequency is determined according to the maximum, minimum, or median value of the voltage range with the larger minimum value. If the input voltage of the Boost circuit is in the buck stage, the target frequency is determined according to the maximum, minimum, or median value of the voltage range with the smaller maximum value.

[0104] Assume there are four voltage ranges: [20V, 31V), (29V, 41V), (39V, 51V), and (49V, 60V). If the input voltage is 40V, 40V falls within the voltage ranges (29V, 41V) and (39V, 51V). If the input voltage of the Boost circuit is in the boost phase, the frequency corresponding to the median value of 46V in the voltage range (39V, 51V) is determined as the target frequency. If the input voltage of the Boost circuit is in the buck phase, the frequency corresponding to the median value of 36V in the voltage range (29V, 41V) is determined as the target frequency.

[0105] In one feasible embodiment, since the output voltage of the Boost circuit is related to the input voltage of the Boost circuit, the duty cycle of the PWM wave, and its frequency, when the input voltage is stable and the output voltage of the Boost circuit is determined, the control circuit 203 determines the frequency of the PWM wave based on its duty cycle, so that the Boost circuit outputs a preset voltage. The relationship between the duty cycle of the PWM wave and its frequency can be determined according to the following formula:

[0106]

[0107] like Figure 7b As shown, assuming the duty cycle of the PWM wave is 0.96, the frequency of the PWM wave is 26.67kHz; if the duty cycle of the PWM wave is 0.90, the frequency of the PWM wave is 80kHz.

[0108] At low temperatures (0°C), the electrochemical properties of the fuel cell stack dictate a low output voltage of only 20V. This represents a relatively low input voltage for the DC / DC converter. For converters requiring outputs up to 750V, the performance will decrease along with the output capability of the preceding stage due to limitations in the Boost circuit topology, transistor engineering parameters, and switching frequency. This will cause numerous inconveniences in engineering applications. When a MOSFET receives PWM wave control from its gate, there is a certain delay in the transition between high and low levels. The fundamental reason for this is: Figure 7a As shown, the dashed line represents the actual change in the gate voltage of the MOSFET, and the solid line represents the PWM wave input to the gate. When the gate voltage changes from 0 to Vm, the MOSFET first enters the amplification region, and the switch will be in a semi-conducting state at this time. The MOSFET will only fully enter saturation conduction when the gate voltage equals Vm. The "gradual" rise and fall time of the curve in the figure can be called the minimum turn-off time T. offmin The physical characteristics of MOSFETs directly dictate that a minimum turn-off time margin must be provided for them in practical engineering control strategies; otherwise, there is a risk of MOSFET failure during normal operation. In actual DC test data, the minimum turn-off time of a MOSFET is approximately 1µs, and the frequency of the MOSFET used in engineering is 80kHz, at which point the maximum duty cycle is 92%. However, under extreme conditions of low temperature and a 20V to 750V boost voltage requirement, the PWM wave duty cycle needs to reach 97.3%, which clearly exceeds the maximum duty cycle limited by the minimum turn-off time of the MOSFET. This directly restricts the output capability of the DC / DC converter, failing to meet engineering requirements. By employing the method described in this application, simultaneously adjusting the PWM wave duty cycle and frequency, the Boost circuit can output a higher voltage (e.g., 750V) when the input voltage of the Boost circuit is low (e.g., 20V), while also avoiding the risk of MOSFET failure in the Boost circuit.

[0109] See Figure 8 , Figure 8 This is a flowchart illustrating a boost method based on a DC / DC converter, provided as an embodiment of this application. The method is applied to a DC / DC converter, which includes a boost circuit, a PWM circuit, and a control circuit. The method includes:

[0110] S801: The control circuit obtains the duty cycle control signal based on the input current and reference current of the Boost circuit; determines the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains the frequency control signal based on the target frequency.

[0111] In one feasible embodiment, the control circuit includes a current control circuit and a frequency control circuit; the control circuit obtains a duty cycle control signal based on the input current and reference current of the Boost circuit; determines the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains a frequency control signal based on the target frequency, including:

[0112] The current control circuit obtains the duty cycle control signal based on the input current of the Boost circuit and the reference current input from the second input port of the current control circuit.

[0113] The frequency control circuit determines the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains the frequency control signal based on the target frequency; wherein, the smaller the input voltage, the smaller the target frequency.

[0114] In one feasible embodiment, the segmented frequency modulation method includes:

[0115] During the input voltage rise phase of the Boost circuit, if the input voltage of the Boost circuit is higher than the first preset threshold, the target frequency is determined according to the first preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is higher than the second preset threshold, the target frequency is determined according to the second preset threshold and the function between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold.

[0116] During the input voltage drop phase of the Boost circuit, if the input voltage of the Boost circuit is lower than the third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the function between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is lower than the fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the function between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

[0117] The relationship between the input voltage and the frequency of the PWM wave is determined by a function relating the input voltage and the frequency of the PWM wave; this function can be expressed as:

[0118]

[0119] Among them, V out For the aforementioned preset voltage, T off V is the turn-off time of the PWM wave. in f is the input voltage, and f is the frequency of the PWM wave.

[0120] In one feasible embodiment, the segmented frequency modulation method includes:

[0121] Determine the voltage range to which the input voltage of the Boost circuit belongs; and obtain the median of the voltage range; determine the frequency corresponding to the median based on the functional relationship between the input voltage and the frequency of the PWM wave; the frequency corresponding to the median is the target frequency.

[0122] The S802 PWM circuit outputs a PWM wave based on the duty cycle control signal and the frequency control signal. The duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency.

[0123] The S803 Boost circuit boosts the input voltage of the Boost circuit based on the PWM wave, so that the Boost circuit outputs a preset voltage, which is much larger than the input voltage of the Boost circuit.

[0124] It should be noted that the specific implementation process of S801-S803 can be found in [reference needed]. Figures 2-6 The relevant descriptions of the embodiments shown will not be repeated here.

[0125] It can be seen that by adjusting the duty cycle and frequency of the PWM wave input to the Boost circuit, a high output voltage can be ensured even when the input voltage of the Boost circuit is low, and there is no risk of the switching transistor in the Boost circuit bursting.

[0126] This application also provides a fuel cell system, including a fuel cell, a load, and a DC / DC converter disclosed in this application.

[0127] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A DC / DC converter, characterized in that, include: The system includes a Boost circuit, a Pulse Width Modulation (PWM) circuit, and a control circuit, wherein the input terminal of the control circuit is connected to the first input terminal of the Boost circuit, the output terminal of the control circuit is connected to the control terminal of the PWM circuit, and the output terminal of the PWM circuit is connected to the control terminal of the Boost circuit. The control circuit is used to obtain a duty cycle control signal based on the input current and reference current of the Boost circuit; and to determine a target frequency based on the input voltage and segmented frequency modulation method of the Boost circuit, and to obtain a frequency control signal based on the target frequency. The PWM circuit is used to output a PWM wave according to the duty cycle control signal and the frequency control signal, wherein the duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency. The Boost circuit is used to boost the input voltage of the Boost circuit according to the PWM wave so that the Boost circuit outputs a preset voltage, which is much larger than the input voltage of the Boost circuit. The control circuit includes a current control circuit and a frequency control circuit; The control circuit includes a first input terminal and a second input terminal of the current control circuit, and an input terminal of the frequency control circuit. The control circuit also includes the output terminals of the current control circuit and the frequency control circuit. The PWM circuit includes a first control terminal and a second control terminal. Both the first input terminal of the current control circuit and the input terminal of the frequency control circuit are connected to the first input terminal of the Boost circuit. The output terminals of the current control circuit and the frequency control circuit are respectively connected to the first control terminal and the second control terminal of the PWM circuit. The current control circuit is used to obtain the duty cycle control signal based on the input current of the Boost circuit and the reference current input from the second input port of the current control circuit. The frequency control circuit is used to determine the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and to obtain the frequency control signal based on the target frequency; wherein, the smaller the input voltage, the smaller the signal based on the target frequency.

2. The converter according to claim 1, characterized in that, The segmented frequency modulation method includes: During the input voltage rise phase of the Boost circuit, if the input voltage of the Boost circuit is higher than a first preset threshold, the target frequency is determined according to the first preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is higher than a second preset threshold, the target frequency is determined according to the second preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold. During the input voltage drop phase of the Boost circuit, if the input voltage of the Boost circuit is lower than a third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is lower than a fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

3. The converter according to claim 1, characterized in that, The segmented frequency modulation method includes: Determine the voltage range to which the input voltage of the Boost circuit belongs, and obtain the median value of the voltage range; The frequency corresponding to the median value is determined based on the functional relationship between the input voltage and the frequency of the PWM wave; the frequency corresponding to the median value is the target frequency.

4. The converter according to claim 1, characterized in that, The current control circuit includes an adder and a proportional-integral (PI) regulator. Wherein, the first input terminal and the second input terminal of the adder are respectively the first input terminal and the second input terminal of the current control circuit, the output terminal of the adder is connected to the input terminal of the PI regulator, and the output terminal of the PI regulator is the output terminal of the current control circuit; The adder is used to process the input current and reference current of the Boost circuit to obtain the processed current. The PI regulator is used to obtain the duty cycle control signal based on the processed current.

5. A boost method based on a DC / DC converter, applied to a DC-DC converter, wherein the DC-DC converter includes a boost circuit, a pulse width modulation (PWM) circuit, and a control circuit, characterized in that, The method includes: The control circuit obtains a duty cycle control signal based on the input current and reference current of the Boost circuit; determines a target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains a frequency control signal based on the target frequency; wherein, the control circuit includes a current control circuit and a frequency control circuit; the current control circuit obtains the duty cycle control signal based on the input current of the Boost circuit and the reference current; the frequency control circuit determines the target frequency based on the input voltage of the Boost circuit and the segmented frequency modulation method, and obtains the frequency control signal based on the target frequency; wherein, the smaller the input voltage, the smaller the target frequency; The PWM circuit outputs a PWM wave according to the duty cycle control signal and the frequency control signal. The duty cycle of the PWM wave is determined based on the duty cycle control signal, and the frequency of the PWM wave is the target frequency. The Boost circuit boosts the input voltage of the Boost circuit according to the PWM wave so that the Boost circuit outputs a preset voltage, which is much larger than the input voltage of the Boost circuit.

6. The method according to claim 5, characterized in that, The segmented frequency modulation method includes: During the input voltage rise phase of the Boost circuit, if the input voltage of the Boost circuit is higher than a first preset threshold, the target frequency is determined according to the first preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is higher than a second preset threshold, the target frequency is determined according to the second preset threshold and the correspondence between the input voltage and the frequency of the PWM wave; the first preset threshold is less than the second preset threshold. During the input voltage drop phase of the Boost circuit, if the input voltage of the Boost circuit is lower than a third preset threshold, the target frequency is determined based on the third preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; if the input voltage of the Boost circuit is lower than a fourth preset threshold, the target frequency is determined based on the fourth preset threshold, the hysteresis voltage, and the correspondence between the input voltage and the frequency of the PWM wave; the third preset threshold is greater than the fourth preset threshold.

7. The method according to claim 5, characterized in that, The segmented frequency modulation method includes: Determine the voltage range to which the input voltage of the Boost circuit belongs, and obtain the median value of the voltage range; The frequency corresponding to the median value is determined based on the functional relationship between the input voltage and the frequency of the PWM wave; the frequency corresponding to the median value is the target frequency.

8. A fuel cell system, characterized in that, The fuel cell system includes a fuel cell, a load, and a DC / DC converter as described in any one of claims 1-4.

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