CN217282712U - DC/DC converter and conversion system - Google Patents

Abstract

The utility model discloses a DC/DC converter and a conversion system. The DC/DC converter comprises: a control unit and a plurality of parallel-connected power conversion circuits connected with the control unit; The main circuit connected to the positive pole of the input terminal of the DC converter and the power module connected to the main circuit, the positive input terminal of each power module is connected to the negative input terminal of the power module through a capacitor, and the main circuit is connected with the main relay; A charging branch circuit, a precharging relay and a precharging resistor are connected in series on the precharging branch, the precharging resistor is connected to the positive input terminal of each power module, and the positive input terminals of other power modules are connected to the precharging resistor through the second precharging relay connection; the DC/DC converter provided by the utility model solves the problem of increasing the overall volume and design cost of the DC/DC converter due to the large volume and high cost of the high-voltage and high-current relay through the shunt design.

Description

A DC/DC converter and conversion system

technical field

The present application relates to the field of circuit technology, and in particular, to a DC/DC converter and a conversion system.

Background technique

In recent years, fuel cell hybrid vehicles have been greatly developed. They generally use fuel cells and power batteries as dual power systems, which can be switched under different working conditions according to the set program. Fuel cell hybrid vehicles usually run on high-power vehicle electricity, and the vehicle voltage is as high as 750VDC or more. In practical applications, the output voltage of the fuel cell is generally within 400V, which is far from meeting the voltage demand of the fuel cell vehicle, and the DC/DC (direct current-direct current) converter can convert its voltage to the voltage required by the vehicle.

With the development of fuel cell technology, the power demand of the whole vehicle is increasing, and the current output by the stack also increases, reaching as high as 800A or even higher. In order to effectively protect the fuel cell, a main relay will be set at the input end of the DC/DC converter, but the high-voltage and high-current relays currently on the market are usually too bulky and expensive, and a DC/DC converter is virtually added Overall volume and design cost.

Utility model content

The utility model provides a DC/DC converter, which is used to solve the problem that due to the large input current of the DC/DC converter, the required high-voltage and high-current relay is too large in size, high in cost, and increases the DC/DC The overall volume and design cost of the converter.

An embodiment of the present utility model provides a DC/DC converter, comprising:

a control unit and a plurality of power conversion circuits connected to the control unit, wherein the plurality of power conversion circuits are connected in parallel;

Each of the power conversion circuits includes a main circuit and a power module. One end of the main circuit is connected to the positive terminal of the DC/DC converter input terminal, and the other terminal is connected to the positive input terminal of the power module. The negative input terminal of each power module is connected to the above-mentioned DC/DC converter. The negative electrode of the DC/DC converter is connected, and a capacitor is connected between the positive input terminal and the negative input terminal, and a main relay is connected on the main circuit;

A precharge branch in parallel with one of the main circuits, the precharge branch is connected in series with a first precharge relay and a precharge resistor, the precharge resistor is connected to the positive input end of the power module connected to the main circuit, and other power modules are connected in series. The positive input terminal is connected with the above-mentioned pre-charging resistor through the second pre-charging relay;

The above-mentioned control unit is used to determine that each main relay in the above-mentioned DC/DC converter is in an open state according to the voltage at both ends of each main relay, and control the pre-charging relay to close to perform pre-charging. According to the voltage at both ends of each main relay and the input current of the power module After it is determined that the above-mentioned DC/DC converter is pre-charged, the main relay is controlled to close, and the first pre-charge relay and the second pre-charge relay are disconnected.

As an optional implementation manner, the positive input terminals of the above-mentioned other power modules are connected to the positive input terminals of the adjacent power modules through the second pre-charging relay, and are indirectly connected to the above-mentioned pre-charging resistors.

As an optional implementation manner, the positive input terminals of the above-mentioned other power modules are directly connected to the above-mentioned pre-charging resistors through the second pre-charging relay.

As an optional implementation manner, a filter capacitor is connected between the positive pole and the negative pole of the output terminal of the DC/DC converter.

As an optional implementation manner, each power module includes at least one boost module.

As an optional implementation manner, each power module includes a plurality of boost booster modules, each boost booster module includes an inductor, a field effect transistor and a diode, and one end of the inductor is connected to the positive input end of the power module , the other end is connected with the anode of the diode and the drain of the FET, the sources of the FETs of the multiple boost modules are connected with the negative output terminal of the power module, and the cathodes of the diodes are connected together.

As an optional implementation manner, the above-mentioned DC/DC converter also includes:

The total negative relay is connected to the negative pole of the input terminal of the DC/DC converter, and the other end of the total negative relay is connected to the negative input terminal/negative output terminal of each power module.

As an optional implementation manner, the above-mentioned DC/DC converter also includes:

A current sampler, connected in series between the main circuit and the power module, is used to measure the input current of the power module.

As an optional implementation manner, the above-mentioned DC/DC converter also includes:

The first voltage sampler and the second voltage sampler are correspondingly connected at both ends of the main circuit connected in parallel with the precharge branch;

The third voltage sampler is correspondingly connected between the other power modules and the main relay.

The embodiment of the present invention also provides a DC/DC conversion system, comprising:

The fuel cell;

The above-mentioned DC/DC converter, the input end of which is connected to the above-mentioned fuel cell, and the output end is connected to the power battery;

The power battery is used to provide electricity for the whole vehicle.

Based on the above DC/DC converter, the following beneficial effects can be produced:

The above-mentioned DC/DC converter realizes the shunt design of the input current of the DC/DC converter through the parallel design of a plurality of power conversion circuits. Therefore, the use of high-voltage and high-current relays is avoided, which solves the problem that due to the large input current of the DC/DC converter, the required high-voltage and high-current relays are too large in size, high in cost, and increase the DC/DC conversion. The overall volume and design cost of the device are

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present utility model. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative labor.

FIG. 1 is a schematic structural diagram of a common system for a fuel cell hybrid electric vehicle provided by an embodiment of the present application;

FIG. 2 is a schematic structural diagram of a DC/DC converter according to an embodiment of the present application;

3 is a schematic diagram of a connection mode of a second precharge relay provided by an embodiment of the present application;

4 is a schematic diagram of another connection mode of a second precharge relay provided by an embodiment of the present application;

FIG. 5 is a schematic diagram of a connection mode of a boost boosting module provided by an embodiment of the present application;

FIG. 6 is a flowchart of a method for precharging a DC/DC converter according to an embodiment of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

In this application, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between the two elements, unless otherwise specified limit. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or an intervening element may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

In addition, if there are descriptions related to "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only for the purpose of description, and should not be construed as indicating or implying Its relative importance or implicitly indicates the number of technical features indicated. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the realization by those of ordinary skill in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that the combination of such technical solutions does not exist. , is not within the scope of protection claimed in this application.

FIG. 1 is a schematic structural diagram of a common system of a fuel cell hybrid electric vehicle provided by an embodiment of the application. Please refer to FIG. 1. Currently, with the continuous advancement of the “dual carbon” goal, fuel cell hybrid electric vehicles have been greatly developed. Battery hybrid vehicles generally use fuel cells and power batteries as dual power systems, which can be switched under different working conditions according to the set program. Because the fuel cell hybrid vehicle usually runs under the high-power vehicle power, the vehicle voltage is as high as 750V DC (direct current) or more, but in practical applications, the output voltage of the fuel cell is generally within 400V, which is far from satisfying the fuel cell’s overall voltage. Therefore, a direct current-direct current (DC/DC) converter needs to be used to convert the lower output voltage of the fuel cell into a high voltage commonly used by the vehicle.

With the development of fuel cell technology and the complexity of application scenarios, the power demand of the whole vehicle is increasing, and the current output by the fuel cell also increases, reaching 800A or even higher. In order to effectively protect the fuel cell, the main relay is usually set at the input end of the DC/DC converter. However, the existing high-voltage and high-current relays on the market usually have the problems of too large volume and high cost, which increases the DC/DC The overall volume and design cost of the DC converter.

In order to solve the above problems, the present application proposes a DC/DC converter, which realizes the shunt control of the input current of the DC/DC converter through the design of a plurality of power conversion circuits in parallel.

FIG. 2 is a schematic structural diagram of a DC/DC converter provided by an embodiment of the present application. The DC/DC converter is formed by two power conversion circuits in parallel. It should be noted that the DC/DC converter shown in FIG. 2 It is only one of the structures of the DC/DC converters provided by the embodiments of the present application for ease of understanding and description.

Among them, for the convenience of description, the power conversion circuit located on the upper side of the two parallel power conversion circuits in FIG. 2 is referred to as the first power conversion circuit, and the power conversion circuit located on the lower side is referred to as the first power conversion circuit. , the main relay K1 is called the first main relay, the main relay K2 is called the second main relay, the power module located in the first power conversion circuit is called the first power module, and the power module located in the second power conversion circuit is called the first power module. Called the second power module.

Referring to FIG. 2 , the embodiment of the present application takes the parallel connection of two power conversion circuits as an example to introduce the structure of the DC/DC converter provided by the embodiment of the present application. The DC/DC converter includes:

A control unit and a plurality of power conversion circuits connected to the control unit, and the plurality of power conversion circuits are connected in parallel, such as the first power conversion circuit and the second power conversion circuit in FIG. Control the closing and opening of each relay in the DC/DC converter to achieve the desired control effect.

Specifically, the control unit determines that each main relay in the DC/DC converter is in an open state according to the voltage at both ends of each main relay, controls the precharge relay to close for precharging, and determines according to the voltage at both ends of each main relay and the input current of the power module After the DC/DC converter is pre-charged, the main relay is controlled to close, and the first pre-charge relay and the second pre-charge relay are disconnected.

Each power conversion circuit includes a main circuit and a power module;

As shown in FIG. 2 , the first power conversion circuit includes a first main circuit composed of a first main relay K1 and a first power module, and the second power conversion circuit includes a second main circuit composed of a second main relay K2 road, and the second power module;

It should be noted that, in the embodiments of the present application, the power modules included in each power conversion circuit may be one or more. When the power conversion circuit includes multiple power modules, the multiple power modules are connected in parallel, wherein , the number of power modules included in each power conversion circuit can be set according to actual needs.

One end of the main circuit is connected to the positive input terminal of the DC/DC converter, the other end is connected to the positive input terminal of the power module, the negative input terminal of each power module is connected to the negative terminal of the DC/DC converter, and the positive input terminal and the negative input terminal are connected between A capacitor is connected, and a main relay is connected to the main circuit;

As shown in Figure 2, taking the first power conversion circuit as an example, one end of the first main circuit (the left side of the main relay K1) is connected to the positive terminal IN+ of the input terminal of the DC/DC converter, and the other end (the right side of the main relay K1) is connected to the input terminal IN+ of the DC/DC converter. The positive input terminal A+ of the first power module is connected; the negative input terminal A- of the first power module is connected to the negative terminal IN- of the DC/DC converter, and the positive input terminal A+ and the negative input terminal A- of the first power module are connected with a The capacitor C1 is connected to the main relay K1 on the first main circuit, and the specific structure of the second power conversion module is similar to that, which will not be repeated here.

The precharge branch is connected in parallel with one of the main circuits. The precharge branch is connected in series with a first precharge relay and a precharge resistor. The precharge resistor is connected to the positive input terminal of the power module connected to the main circuit. The input terminal is connected with the precharge resistor through the second precharge relay;

As shown in FIG. 2 , one of the above-mentioned main circuits is the first main circuit in FIG. 2 , and the pre-charging branch is connected in series with a first pre-charging relay K4 and a pre-charging resistor R1, and one end of the pre-charging resistor R1 is connected to the first pre-charging resistor R1. The charging relay is connected, the other end is connected to the positive input terminal A+ of the first power module, and the positive input terminal B+ of the second power module is connected to the precharging resistor K4 through the second precharging relay K5;

The above-mentioned pre-charging resistors are usually selected as power-type resistors, and the types and resistance values of the pre-charging resistors are not limited in the embodiments of the present application, and can be selected according to actual needs.

It should be noted that the embodiment of the present application does not limit the main circuit connected in parallel with the precharge branch. In implementation, the main circuit connected in parallel with the precharge branch may be the first main circuit in FIG. 2 , or may be Main circuit corresponding to other power modules.

Referring to FIG. 3 and FIG. 4 , when the DC/DC conversion circuit includes three or more parallel-connected power conversion circuits, the manner in which the positive input terminals of the above-mentioned other power modules are connected to the pre-charging resistors in the embodiments of the present application, that is, The specific layout position of the second precharge relay is introduced:

Mode 1: The positive input terminals of the above other power modules are connected to the positive input terminals of the adjacent power modules through the second precharging relay, and are indirectly connected to the precharging resistor;

Specifically, the positive input terminals of two adjacent power modules are connected through the second precharge relay. As shown in FIG. 3 , the positive input terminal of the power module 2 is connected to the positive input terminal of the power module 1 through the second precharge relay K5 , the positive input terminal of the power module 3 is connected to the positive input terminal of the power module 2 through the second pre-charging relay K6, and the positive input terminals of the adjacent power modules are directly connected through the corresponding second pre-charging relay, so as to realize the above-mentioned other power modules. The positive input terminal of 1 is directly connected to the pre-charge resistor R1.

Mode 2: The positive input terminals of the above other power modules are directly connected to the precharging resistor through the second precharging relay;

Specifically, the positive input terminals of other power modules are directly connected to the precharge resistor through the second precharge relay. As shown in FIG. 4 , the power module 2 is connected to the precharge resistor R1 through the second precharge relay K5 and is in phase with the power module 1 At the same time, the power module 3 is also connected to the end of the precharging resistor R1 connected to the power module 1 through the second precharging relay K6, so as to realize the direct connection between the positive input terminals of the other power modules and the precharging resistor R1.

It should be noted that the second precharge relay in the embodiment of the present application is not a specific relay, but a type of relay with the same function. Each power module except the first power module) has a corresponding second relay.

An optional implementation is that a filter capacitor is connected between the positive electrode and the negative electrode of the output end of the DC/DC converter, such as the filter capacitor C3 in FIG. 2 .

An optional implementation is that the above-mentioned DC/DC converter further includes: a total negative relay (relay K3 in FIG. 2 ) connected to the negative pole of the input end of the above-mentioned DC/DC converter, and the other end of the above-mentioned general negative relay is connected. Connect to the negative input terminal/negative output terminal of each power module.

An optional implementation manner is that each power module includes at least one Boost boosting module; the number of Boost boosting modules in each power module is not limited in this application, and different power modules may include different numbers of booster boosting modules. Boost boosting module, the boosting boosting module is used for boosting conversion. During implementation, the boosting degree of the DC/DC converter can be controlled by controlling the number of boosting boosting modules in the power module.

As shown in FIG. 5 , when the power module includes multiple boost modules, the multiple boost modules are connected in parallel, wherein each boost module includes an inductor, a field effect transistor and a diode, and the inductor One end is connected to the positive input end of the power module, the other end is connected to the anode of the diode and the drain of the FET, the sources of the FETs of the multiple boost modules are connected to the negative output end of the power module, and the negative electrode of the diode is connected together. connected.

The Boost boosting module further includes a current regulator for detecting the current flowing through the module, and the currents passing through each Boost boosting module are equal.

In some embodiments, the DC/DC converter includes two parallel power conversion circuits, the input current of the DC/DC converter is N*Im, the current that can pass Im in each boost module, the two power The modules are respectively configured with n boost boost modules and (N-n) boost boost modules. The input current can be easily divided into two parts, n*Im and (N-n)*Im, through the two-stage power conversion circuit to process the large current of N*Im, and pass through two relays respectively, which not only ensures the distribution of the current, but also can detect The fault between the two relays is eliminated, thereby reducing space and cost.

The DC/DC converters provided in the embodiments of the present application further include:

A current sampler, connected in series between the main circuit and the power module, for measuring the input current of the power module, such as A1 and A2 in Figure 2;

The first voltage sampler and the second voltage sampler are correspondingly connected at both ends of the main circuit connected in parallel with the precharge branch, and the third voltage sampler is correspondingly connected between the other power modules and the main relay; as shown in Figure 2 As shown, the first voltage sampler is V1, the second voltage sampler is V2, and the third voltage sampler is V3, wherein the first voltage sampler V1 is used to measure the input voltage of the DC/DC converter, the second voltage The sampler V2 is used to measure the input voltage of the first power module, and the third voltage sampler V3 is used to measure the input voltage of the second power module; The voltage difference between the two ends of the main relay can be determined by the first voltage sampler V1 and the third voltage sampler V3, and the voltage difference between the two ends of the second main relay can be determined.

Since the structure of a DC/DC converter composed of three or more parallel power conversion circuits is similar, the specific structure can refer to the above-mentioned DC/DC converter composed of two parallel power conversion circuits, so its structure is omitted here. Repeat.

The above-mentioned DC/DC converter realizes the shunt design of the input current of the DC/DC converter through the parallel design of multiple power conversion circuits. The conversion circuits are shared, and the current borne by each power conversion circuit is reduced. Therefore, the use of high-voltage and high-current relays is avoided, and the high-voltage and high-current required by the DC/DC converter due to its large input current is solved. The size of the relay is too large and the cost is too high, which increases the overall size and design cost of the DC/DC converter.

The embodiment of the present application also provides a DC/DC conversion system, including:

The fuel cell;

The above-mentioned DC/DC converter, the input end of which is connected to the above-mentioned fuel cell, and the output end is connected to the power battery;

The power battery is used to provide electricity for the whole vehicle.

FIG. 6 is a flowchart of a method for precharging a DC/DC converter provided by an embodiment of the present application. Please refer to FIG. 2 and FIG. 6 . The following describes the method for precharging using the DC/DC converter in the implementation of the present application in detail. Elaboration, it should be noted that the following precharging method is described by taking a DC/DC converter with two-stage power conversion circuits in parallel as an example, and the pre-charging method of a DC/DC converter with three-level and above power conversion circuits connected in parallel is the same as Similar to:

Step 1. Detect the voltages across the first main relay K1 and the second main relay K2 respectively.

Step 2. Determine whether the front-end voltage of the first main relay K1 is greater than the back-end voltage and greater than the first preset threshold, and whether the front-end voltage of the second main relay K2 is greater than the back-end voltage and greater than the second preset threshold; if the result is yes, Then go to step 3, otherwise go to step 4.

In implementation, the front-end voltage of the first main relay K1 and the front-end voltage of the second main relay K2 are determined by the first voltage sampler V1, the back-end voltage of the first main relay K1 is determined by the second voltage sampler V2, and the back-end voltage of the first main relay K1 is determined by the second voltage sampler V2. The voltage sampler V3 determines the back-end voltage of the second main relay K2;

Wherein, the above-mentioned first preset threshold and first preset threshold are set according to requirements.

Step 3: Make sure that each main relay in the DC/DC converter is in an off state, close the total negative relay K3 and the second precharge relay K5, and execute Step 5.

Step 4. Determine that the DC/DC converter is in an undervoltage state (each main relay is not in a disconnected state), report an undervoltage fault, and prohibit precharging.

Step 5. The first pre-charging relay K4 is closed to start charging the DC/DC internal capacitors C1 and C2.

Step 6: Determine whether the first precharge relay K4 and the second precharge relay K5 are successfully closed.

In the implementation, detect the input current through the first power module and the second power module respectively by the current sampler A1 and A2, judge whether the first precharge relay K4 and the second precharge relay K5 are closed successfully; If both the first precharge relay K4 and the second precharge relay K5 are closed successfully), step 7 is performed; otherwise, step 3 is returned.

In implementation, if the current sampler A1 detects the current and the current is greater than the third preset threshold, it is determined that the first precharge relay K4 is successfully closed; if the current sampler A2 detects the current and the current is greater than the fourth preset threshold, Then it is judged that the second pre-charging relay K5 is successfully closed.

Wherein, the above-mentioned third preset threshold and fourth preset threshold are set according to requirements.

Step 7, through the second voltage sampler V2 and the third voltage sampler V3, respectively detect whether the back-end voltage of the first main relay and the second main relay begins to rise; if the result is yes (the back-end voltage of the first main relay begins to rise; high, and the back-end voltage of the second main relay starts to increase), then go to step 9, otherwise, go to step 8.

Step 8. Determine the fault of the pre-charging circuit, report the short-circuit fault and stop the pre-charging.

Step 9. Detect whether the voltage difference between the front and rear of the first main relay and the second main relay is lower than the set threshold; if the result is yes (below the set threshold), go to step 10, otherwise, go to step 11.

In the implementation, the first voltage sampler V1, the second voltage sampler V2 and the third voltage sampler V3 are used to detect and calculate whether the voltage difference between the front and rear ends of the first main relay K1 and the second main relay K2 is respectively lower than the fifth setting. Threshold value and sixth preset threshold value, and detect whether the current in the first power module and the second power module is lower than the seventh preset threshold value and the eighth preset threshold value through the current samplers A1 and A2 respectively;

When the voltage difference between the front and rear ends of the first main relay K1 and the second main relay K2 is lower than the fifth set threshold and the sixth set threshold, respectively, and the input currents of the first power module and the second power module are respectively lower than the When the threshold is set seven and the threshold is set eighth, the determination result is yes.

Step 10, closing the first main relay K1 and the second main relay K2, disconnecting the second pre-charging relay K5, and then disconnecting the first pre-charging relay K4 to complete the pre-charging.

Step 11 , check whether the pre-charge has timed out (exceeds the preset duration); if it is determined to be yes, go to step 12 , otherwise, go back to step 6 .

Step 12: Determine that the pre-charge is overtime, report the pre-charge timeout fault and fail to pre-charge.

It should be noted that, when the DC/DC conversion circuit includes three or more parallel power conversion circuits, and the second precharge relay adopts the connection mode shown in FIG. 3, the second precharge relay in the above precharge method The closing method is to sequentially close the second pre-charging relay according to the distance from the pre-charging branch from far to near. When the circuit structure is shown in Figure 3, the second pre-charging relay K6, the second pre-charging relay The sequence of K5 is closed;

When the DC/DC conversion circuit includes three or more parallel power conversion circuits, and the second precharge relay adopts the connection method shown in FIG. 4 , the closing mode of the second precharge relay in the above precharge method is all The second precharge relays are closed at the same time. When the circuit structure is as shown in FIG. 4 , that is, the second precharge relay K6 and the second precharge relay K5 are closed at the same time.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present utility model fall within the scope of the claims of the present utility model and their equivalents, the present utility model is also intended to include these modifications and variations.

Claims (10)

1. a direct current-direct current DC/DC converter, is characterized in that, comprises: a control unit and a plurality of power conversion circuits connected to the control unit, the plurality of power conversion circuits are connected in parallel; Each of the power conversion circuits includes a main circuit and a power module. One end of the main circuit is connected to the positive terminal of the DC/DC converter input terminal, and the other terminal is connected to the positive input terminal of the power module. The negative input terminal is connected with the negative pole of the DC/DC converter, a capacitor is connected between the positive input terminal and the negative input terminal, and a main relay is connected on the main circuit; A precharge branch connected in parallel with one of the main circuits, the precharge branch is connected in series with a first precharge relay and a precharge resistor, the precharge resistor is connected to the positive input end of the power module connected to the main circuit, and the other The positive input end of the power module is connected to the precharging resistor through the second precharging relay; The control unit is used to determine that each main relay in the DC/DC converter is in the disconnected state according to the voltage at both ends of each main relay, control the precharge relay to close for precharge, and according to the voltage at both ends of each main relay and the power module After the input current determines that the DC/DC converter is pre-charged, the main relay is controlled to close, and the first pre-charge relay and the second pre-charge relay are disconnected. 2 . The DC/DC converter according to claim 1 , wherein the positive input terminals of the other power modules are connected to the positive input terminals of the adjacent power modules through the second precharge relay, and are indirectly connected to the positive input terminals of the power module. 3 . Precharge resistor connection. 3 . The DC/DC converter according to claim 1 , wherein the positive input terminals of the other power modules are directly connected to the precharging resistor through a second precharging relay. 4 . 4 . The DC/DC converter according to claim 1 , wherein a filter capacitor is connected between the positive pole and the negative pole of the output end of the DC/DC converter. 5 . 5 . The DC/DC converter according to claim 1 , wherein each power module includes at least one boosting module. 6 . 6 . The DC/DC converter according to claim 5 , wherein each power module includes a plurality of Boost boosting modules, and each Boost boosting module comprises an inductor, a field effect transistor and a diode. 6 . One end of the inductor is connected to the positive input end of the power module, and the other end is connected to the positive electrode of the diode and the drain of the FET. The sources of the FETs of the multiple boost modules are connected to the negative output end of the power module. The negative poles are connected together. 7. DC/DC converter according to claim 1, is characterized in that, also comprises: A total negative relay connected to the negative pole of the input terminal of the DC/DC converter, and the other end of the total negative relay is connected to the negative input terminal/negative output terminal of each power module. 8. DC/DC converter according to claim 1, is characterized in that, also comprises: A current sampler, connected in series between the main circuit and the power module, is used to measure the input current of the power module. 9. DC/DC converter according to claim 7, is characterized in that, also comprises: The first voltage sampler and the second voltage sampler are correspondingly connected at both ends of the main circuit connected in parallel with the precharge branch; The third voltage sampler is correspondingly connected between the other power modules and the main relay. 10. A DC/DC conversion system, characterized in that, comprising: The fuel cell; The DC/DC converter according to any one of claims 1 to 9, wherein an input end of the DC/DC converter is connected to the fuel cell, and an output end is connected to a power battery; The power battery is used to provide electricity for the whole vehicle.

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