Reverse pre-charging control method of vehicle-mounted DC / DC converter

Abstract

The invention provides a reverse pre-charging control method of a vehicle-mounted DC / DC converter, and relates to the field of power supply control. The vehicle-mounted DC / DC converter comprises a primary side circuit, a transformer and a secondary side circuit which are in cascade connection, the primary side circuit is connected with a high-voltage side capacitor in parallel, the secondary side circuit is connected with a low-voltage side capacitor in parallel, and the secondary side circuit comprises a low-voltage side inductor, at least one switch tube and a stress absorption circuit connected with the switch tube in parallel. Wherein the stress absorption circuit comprises an absorption capacitor, a bleeder resistor and a bleeder switching tube which are connected in series, when the duty ratio of the switching tube in the secondary circuit is smaller than or equal to 50%, the initial voltage of the absorption capacitor is reduced, and the stress of the switching tube in the secondary circuit is inhibited by reducing the single-cycle energy storage of the low-voltage side inductor.

Description

Technical Field

[0001] The invention relates to the field of power supply control, and in particular to a reverse pre-charging control method for a vehicle-mounted DC / DC converter. Background Art

[0002] As the advantages of new energy vehicles become increasingly apparent and the penetration rate of new energy vehicles in the market continues to rise, the market's requirements for the performance of on-board power supplies are also gradually increasing.

[0003] The vehicle power supply includes a vehicle DC / DC converter, which is used to convert high-voltage DC (such as 400V) into low-voltage DC (such as 12V) to charge the low-voltage battery or power the load. The high-voltage side is generally designed with a large capacitor, which needs to be connected in parallel with the high-voltage battery during normal operation and disconnected in other states. During normal operation, if the large capacitor is directly connected to the high-voltage battery, a large inrush current will be generated.

[0004] To solve this problem, the mainstream approach of general car companies is to add a pre-charging branch, which can be seen in Figure 1 The schematic diagram of the pre-charging circuit of the prior art is shown. It includes a pre-charging resistor R and a pre-charging relay Relay. When the relay Relay is closed, the high-voltage side capacitor HV Cap is pre-charged first, and the voltage of the high-voltage side capacitor HV Cap and the high-voltage battery HV BAT is detected in real time. When the two are close, the high-voltage battery HV BAT is cut in to avoid the problem of impact current. However, this measure not only makes the control process cumbersome, but also brings additional hardware costs, space occupation and other issues. In the context of current car companies reducing costs and increasing efficiency, it is contrary to the search for a low-cost, high-efficiency pre-charging solution.

[0005] With the development of vehicle power supply technology, vehicle DC / DC converters can usually also operate in a reverse working mode, that is, converting low-voltage direct current (such as 12V) into high-voltage direct current (such as 400V).

[0006] In order to solve the problem of precharging the high-voltage side capacitor HV Cap mentioned above, some current practices are to reuse the existing switching devices in the vehicle-mounted DC / DC converter and realize the reverse precharging function through the reverse operation of the vehicle-mounted DC / DC converter. However, this type of solution has the problem of switching device voltage stress and inductor current overshoot during the precharging process, which has become a new challenge.

[0007] Existing solutions include using a backfeed circuit (Oring circuit) for soft start, adding current limiting resistors, increasing absorption capacitors, etc., but all of these add additional components to varying degrees, resulting in increased costs and volume, and even affecting the forward working control strategy of the on-board DC / DC converter. In addition, the Oring circuit soft start solution itself also has the risk of voltage stress on the switch tube in the Oring circuit, which requires additional optimization measures.

[0008] Therefore, how to achieve reverse pre-charging while reducing costs and size is a technical problem that the industry urgently needs to solve. Summary of the invention

[0009] The present application proposes a reverse pre-charge control method for a vehicle-mounted DC / DC converter, wherein the vehicle-mounted DC / DC converter comprises a primary circuit, a transformer and a secondary circuit connected in cascade, wherein the primary circuit is connected in parallel with a high-voltage side capacitor, wherein the secondary circuit is connected in parallel with a low-voltage side capacitor, wherein the secondary circuit comprises a low-voltage side inductor, at least one switch tube and a stress absorption circuit connected in parallel with the switch tube, wherein the stress absorption circuit comprises an absorption capacitor, a discharge resistor and a discharge switch tube connected in series, and when the duty cycle of the switch tube in the secondary circuit is less than or equal to 50%, the control method comprises:

[0010] S1: Turn on the machine;

[0011] S2: Controlling the vehicle-mounted DC / DC converter to operate in a current loop soft start mode, and gradually increasing the current reference value of the current loop until the current reference value is equal to the current reference set value;

[0012] S3: Control the vehicle-mounted DC / DC converter to operate in a current loop and a voltage loop dual-loop competition mode, compare the duty cycle of the switch tube in the secondary circuit obtained by the current loop and the voltage loop, and use the smaller one as the duty cycle of the switch control signal for controlling the switch tube in the secondary circuit until the voltage on the high-voltage side capacitor reaches a voltage setting value, wherein

[0013] During step S2 and step S3, the discharge switch tube in the stress absorption circuit is turned on after the switch tube in the secondary circuit connected in parallel therewith is turned on and is turned off before being turned on again, so that the conduction time of the discharge switch tube is maximized.

[0014] Furthermore, step S2 includes:

[0015] S21: Setting the current reference value of the current loop to 0;

[0016] S22: the current reference value Iref increases with a fixed step size or a variable step size;

[0017] S23: Determine whether the current reference value reaches the current reference setting value. If so, exit the current loop soft start mode, go to step S3; if not, go to step S22.

[0018] Furthermore, in step S2, the current loop soft-start mode is an open-loop control mode or a closed-loop control mode.

[0019] Furthermore, the current reference setting value is issued by the entire vehicle.

[0020] Furthermore, in step S2, the vehicle-mounted DC / DC converter operates in a small pulse startup stage.

[0021] Furthermore, step S3 includes:

[0022] S31: obtaining a first duty cycle of controlling the switch tube in the secondary circuit according to the current loop, and obtaining a second duty cycle of controlling the switch tube in the secondary circuit according to the voltage loop;

[0023] S32: comparing whether the first duty cycle is smaller than the second duty cycle, if so, using the switch control signal with the first duty cycle as the duty cycle to control the switch tube in the secondary circuit, otherwise, using the switch control signal with the second duty cycle as the duty cycle to control the switch tube in the secondary circuit;

[0024] S33: Determine whether the voltage on the high-voltage side capacitor reaches the voltage setting value. If yes, the process ends; otherwise, the process proceeds to step S31.

[0025] Furthermore, after determining the switch control signal of the switch tube in the secondary circuit according to step S2 and step S3, the turn-on time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time of the switch control signal of the switch tube, and the turn-off time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time again of the switch control signal of the switch tube, and the turn-on time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is maximized.

[0026] Furthermore, the discharge switch tube is controlled to be turned on after a delay of t11 time after the switch tube is turned on, and the discharge switch tube is controlled to be turned off before a time t22 time when the switch tube is turned on again.

[0027] Furthermore, the primary circuit is a full-bridge switch unit or a half-bridge switch unit.

[0028] Furthermore, the secondary circuit is a synchronous rectification circuit, a full-bridge rectification circuit, a full-wave rectification circuit or a current doubler rectification circuit.

[0029] Furthermore, the stress absorption circuit further includes a first diode and a fifth capacitor, and the first diode and the fifth capacitor are connected in parallel at both ends of the discharge resistor and the discharge switch tube.

[0030] The above is a fairly broad overview of the features and technical advantages of the present application, so that the following detailed description of the present application can be better understood. The additional features and advantages of the present application will be described below, and they form the subject matter of the claims of the present application. It will be appreciated by those skilled in the art that the disclosed concepts and specific embodiments can be easily utilized as the basis for modifying or designing other structures or processes for realizing the same purpose of the present application. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present application as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more fully understand the present application and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0032] Figure 1 A schematic diagram of a pre-charging circuit in the prior art is shown;

[0033] Figure 2 A schematic diagram of an existing vehicle-mounted DC / DC converter is shown;

[0034] Figure 3 Shows Figure 2 A schematic diagram of a first working state of the vehicle-mounted DC / DC converter;

[0035] Figure 4 Shows Figure 2 A schematic diagram of a second working state of the vehicle-mounted DC / DC converter;

[0036] Figure 5 A flow chart of a reverse pre-charging control method for a vehicle-mounted DC / DC converter according to an embodiment of the present application is shown;

[0037] Figure 6 A schematic diagram showing the change of the voltage V on the high-voltage side capacitor and the low-voltage side inductor current IL over time during the reverse pre-charging process of the vehicle-mounted DC / DC converter according to an embodiment of the present application is shown;

[0038] Figure 7 A schematic diagram of control signals of a secondary switch tube and a discharge switch tube connected in parallel therewith in a secondary circuit of an embodiment of the present application is shown;

[0039] Figure 8 A schematic diagram of a vehicle-mounted DC / DC converter according to an embodiment of the present application is shown.

[0040] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0041] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0042] An embodiment of the present application proposes a reverse pre-charge control method for an on-vehicle DC / DC converter, wherein the on-vehicle DC / DC converter includes a primary circuit, a transformer, and a secondary circuit connected in cascade, the primary circuit is connected in parallel with a high-voltage side capacitor, the secondary circuit is connected in parallel with a low-voltage side capacitor, the secondary circuit includes a low-voltage side inductor, at least one switch tube, and a stress absorption circuit connected in parallel with the switch tube, wherein the stress absorption circuit includes an absorption capacitor, a discharge resistor, and a discharge switch tube connected in series, when the duty cycle of the switch tube in the secondary circuit is less than or equal to 50%, the control method includes: S1: power on; S2: control the on-vehicle DC / DC converter to operate in a current loop soft start mode, step by step Step S2: increasing the current reference value of the current loop until the current reference value is equal to the current reference setting value; S3: controlling the on-board DC / DC converter to operate in a current loop and a voltage loop dual-loop competition mode, comparing the duty cycles of the switch tube in the secondary circuit obtained by the current loop and the voltage loop, and taking the smaller one as the duty cycle of the switch control signal for controlling the switch tube in the secondary circuit until the voltage on the high-voltage side capacitor reaches the voltage setting value, wherein during steps S2 and S3, the discharge switch tube in the stress absorption circuit is turned on after the switch tube in the secondary circuit connected in parallel therewith is turned on and is turned off before being turned on again, and the on-time of the discharge switch tube is maximized.

[0043] Furthermore, step S2 includes: S21: setting the current reference value of the current loop to 0; S22: increasing the current reference value Iref with a fixed step size or a variable step size; S23: determining whether the current reference value reaches the current reference setting value, if so, exiting the current loop soft start mode, entering step S3, if not, entering step S22.

[0044] Furthermore, in step S2, the current loop soft-start mode is an open-loop control mode or a closed-loop control mode.

[0045] Furthermore, the current reference setting value is issued by the entire vehicle.

[0046] Furthermore, in step S2, the vehicle-mounted DC / DC converter operates in a small pulse startup stage.

[0047] Furthermore, step S3 includes: S31: obtaining a first duty cycle for controlling the switch tube in the secondary circuit according to the current loop, and obtaining a second duty cycle for controlling the switch tube in the secondary circuit according to the voltage loop; S32: comparing whether the first duty cycle is smaller than the second duty cycle, if so, controlling the switch tube in the secondary circuit with a switch control signal having the first duty cycle as the duty cycle, otherwise controlling the switch tube in the secondary circuit with a switch control signal having the second duty cycle as the duty cycle; S33: determining whether the voltage on the high-voltage side capacitor reaches the voltage setting value, if so, ending, otherwise entering step S31.

[0048] Furthermore, after determining the switch control signal of the switch tube in the secondary circuit according to step S2 and step S3, the turn-on time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time of the switch control signal of the switch tube, and the turn-off time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time again of the switch control signal of the switch tube, and the turn-on time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is maximized.

[0049] Furthermore, the discharge switch tube is controlled to be turned on after a delay of t11 time after the switch tube is turned on, and the discharge switch tube is controlled to be turned off before a time t22 time when the switch tube is turned on again.

[0050] Furthermore, the primary circuit is a full-bridge switch unit or a half-bridge switch unit.

[0051] Furthermore, the secondary circuit is a synchronous rectification circuit, a full-bridge rectification circuit, a full-wave rectification circuit or a current doubler rectification circuit.

[0052] Furthermore, the stress absorption circuit further includes a first diode and a fifth capacitor, and the first diode and the fifth capacitor are connected in parallel between the discharge resistor and the discharge switch tube.

[0053] See also Figure 2 A schematic diagram of an existing vehicle-mounted DC / DC converter is shown. It includes a primary circuit 110, a transformer T1 and a secondary circuit 120 connected in cascade. Among them, the primary circuit 110 is a full-bridge switch unit formed by the fifth switch tube S5 to the eighth switch tube S8, and the high-voltage side capacitor HV Cap is connected in parallel with the primary circuit 110. The transformer T1 is a center-tapped transformer. The secondary circuit 120 is a synchronous rectification circuit formed by the first switch tube S1, the second switch tube S2 and the low-voltage side inductor L1, and the low-voltage side capacitor C1 is connected in parallel with the secondary circuit 120.

[0054] In order to reduce the voltage stress on the first switch tube S1 and the second switch tube S2 during the operation of the vehicle-mounted DC / DC converter, a stress absorption circuit is usually connected in parallel on both sides of the first switch tube S1 and the second switch tube S2. Figure 2 As shown, a first stress absorption circuit 121 is connected in parallel at both ends of the first switch tube S1, and the first stress absorption circuit 121 includes an absorption capacitor C3, a discharge resistor R1 and a first discharge switch tube S3 connected in series. More specifically, as Figure 2 As shown, it may also include a first diode D1 and a fifth capacitor C5, wherein the discharge resistor R1 and the first discharge switch tube S3 are connected in series and then connected in parallel with the first diode D1 and the fifth capacitor C5 to form a first parallel branch, and the first parallel branch is connected in series with the absorption capacitor C3 to form a first stress absorption circuit 121. Similarly, the second switch tube S2 is also connected in parallel with a second stress absorption circuit 122 formed by an absorption capacitor C4, a discharge resistor R2, a second discharge switch tube S4, a second diode D2 and a sixth capacitor C6, and its connection relationship is the same as the first stress absorption circuit 121, which will not be repeated here.

[0055] The absorption capacitor C3 is used to absorb the energy after the first switch tube S1 is turned off, and the first discharge switch tube S3 is used to control the energy discharge of the absorption capacitor C3. The absorption capacitor C4 is used to absorb the energy after the second switch tube S2 is turned off, and the second discharge switch tube S4 is used to control the energy discharge of the absorption capacitor C4.

[0056] Figure 2 The vehicle-mounted DC / DC converter shown can realize both forward operation and reverse operation. Forward operation is to convert the high-voltage side DC power into the low-voltage side DC power, and reverse operation is to convert the low-voltage side DC power into the high-voltage side DC power.

[0057] In order to solve the problem of precharging the high-voltage side capacitor HV Cap, it is usually used Figure 2 The reverse working process of the vehicle-mounted DC / DC converter shown realizes reverse pre-charging, that is, energy is transferred from the low-voltage side capacitor C1 to the high-voltage side capacitor HV Cap.

[0058] See also Figure 3 shown Figure 2 The first working state schematic diagram of the vehicle-mounted DC / DC converter in FIG. 1 shows a schematic diagram of the freewheeling path when the duty ratio of the first switch tube S1 and the second switch tube S2 is greater than 50%. Figure 3As shown, when the first switch tube S1 and the second switch tube S2 are both turned off, the current of the low-voltage side inductor L1 is freewheeling through the first stress absorption circuit 121 and the second stress absorption circuit 122 respectively. Since the current of the low-voltage side inductor L1 has a good freewheeling path, the voltage stress on the first switch tube S1 and the second switch tube S2 is low. Therefore, when the duty ratio Duty of the first switch tube S1 and the second switch tube S2 is greater than 50%, there is no need to consider the stress problem of the first switch tube S1 and the second switch tube S2.

[0059] See also Figure 4 shown Figure 2 The second working state schematic diagram of the vehicle-mounted DC / DC converter in FIG. 1 shows a schematic diagram of the freewheeling path when the duty ratio of the first switch tube S1 and the second switch tube S2 is ≤50%. Figure 4 As shown, when the duty cycle Duty of the first switch tube S1 and the second switch tube S2 is ≤50%, after the first switch tube S1 or the second switch tube S2 is turned off, the low-voltage side lacks an effective freewheeling path for the current of the low-voltage side inductor L1. Since the energy stored in the low-voltage side inductor L1 cannot be released, the voltage stress of the first switch tube S1 and the second switch tube S2 will be high, and the greater the current of the low-voltage side inductor L1, the higher the stress will be. Therefore, in the process of reverse pre-charging, in order to reduce the voltage stress of the first switch tube S1 and the second switch tube S2, it is necessary to limit the current of the low-voltage side inductor L1 when the duty cycle Duty of the first switch tube S1 and the second switch tube S2 is ≤50%.

[0060] Specifically, in the reverse pre-charging process, the related factors of the voltage stress on the first switch tube S1 and the second switch tube S2 when their duty ratio Duty≤50% can be obtained by approximate calculation. Specifically, taking the first switch tube S1 as an example:

[0061] Single cycle current change of low voltage side inductor L1: Where T on is the conduction time of the first switch tube S1 and the second switch tube S2, V in is the low voltage side DC input voltage, V T is the transformer secondary winding voltage;

[0062] The initial current of the low-voltage side inductor L1 is represented by I0, and the peak current is represented by I1, then I0 = I1-ΔIL1;

[0063] Single cycle energy storage of low voltage side inductor L1:

[0064] Total energy of absorption capacitor C3: Among them U C3 is the initial voltage of the absorption capacitor C3;

[0065] The voltage at the end of the absorption capacitor C3:

[0066] It can be obtained that the voltage stress of the first switch tube S1 in a single cycle is:

[0067]

[0068] According to formula (1), the voltage stress of the first switch tube S1 and the initial voltage U of the absorption capacitor C3 are C3 , the capacitance of the absorption capacitor C3 and the single-cycle energy storage ΔQ of the low-voltage side inductor L1 L1 Then we can increase the capacitance of the absorption capacitor C3 and reduce the initial voltage U of the absorption capacitor C3. C3 , reduce the single cycle energy storage ΔQ of the low voltage side inductor L1 L1 To reduce the voltage stress on the first switch tube S1 during the pre-charging process.

[0069] Regarding increasing the capacitance C3 of the absorption capacitor, based on the current market background that vehicle power supplies generally pursue higher power density, there are certain restrictions on the space and volume inside the power supply, which will limit the increase in the number of components and the increase in volume, so this strategy is not recommended.

[0070] Then the initial voltage U of the absorption capacitor C3 can be reduced C3 , or by reducing the single-cycle energy storage ΔQ of the low-voltage side inductor L1 L1 Optimize in two aspects.

[0071] Based on this, in one embodiment of the present application, a control method for a vehicle-mounted DC / DC converter is provided. The vehicle-mounted DC / DC converter can refer to Figure 2 The vehicle-mounted DC / DC converter shown in the figure. For details, please refer to Figure 5 The flowchart of the reverse pre-charging control method of the vehicle-mounted DC / DC converter according to one embodiment of the present application is shown, which includes:

[0072] S1: Turn on the machine;

[0073] S2: Control the vehicle-mounted DC / DC converter to work in the current loop soft start mode, and gradually increase the current reference value Iref of the current loop until the current reference value Iref is equal to the current reference set value Iset;

[0074] S3: Control the vehicle-mounted DC / DC converter to work in the current loop and voltage loop dual-loop competition mode, compare the duty cycle of the switch tube in the secondary circuit 120 obtained by the current loop and the voltage loop, and use the smaller one as the duty cycle of the switch control signal for controlling the switch tube in the secondary circuit 120, until the voltage on the high-voltage side capacitor HV Cap reaches the voltage setting value Vset, where

[0075] During step S2 and step S3, the discharge switch tube in the stress absorption circuit is turned on after the secondary switch tube in the secondary circuit connected in parallel therewith is turned on and is turned off before being turned on again, so that the conduction time of the discharge switch tube is maximized.

[0076] In a specific embodiment, step S2 includes: S21: setting the current reference value Iref of the current loop to 0; S22: increasing the current reference value Iref of the current loop with a fixed step size or a variable step size; S23: determining whether the current reference value Iref of the current loop reaches the current reference setting value Iset, if so, exiting the current loop soft start mode, entering step S3, if not, entering step S22.

[0077] In actual implementation, the current loop control mode of step S2 can be open loop control or closed loop control.

[0078] In actual implementation, the current reference set value Iset is issued by the vehicle.

[0079] After starting up, the on-board DC / DC converter is first controlled to work in the current loop soft start mode, which can limit the low-voltage side inductor current, thereby limiting the single-cycle energy storage ΔQ of the low-voltage side inductor L1. L1 , that is, the stress of the switch tube in the secondary circuit 120 is suppressed.

[0080] See also Figure 6 The schematic diagram of the voltage V on the high-voltage side capacitor and the low-voltage side inductor current IL changing with time during the reverse pre-charging process of the vehicle-mounted DC / DC converter is shown in FIG. Figure 6 As shown, before time t1, the on-board DC / DC converter operates in the current loop soft start mode, and the voltage V on the high-voltage side capacitor HV Cap and the current I on the low-voltage side inductor L1 both gradually increase from 0 until the low-voltage side inductor current IL reaches the current reference set value Iset at time t1.

[0081] In actual implementation, the current loop soft start mode control in step S2 enables the vehicle-mounted DC / DC converter to operate in a small pulse start-up phase, for example, the initial pulse width may be set to about 20ns for startup.

[0082] In a specific embodiment, step S3 includes: S31: obtaining a first duty cycle for controlling the switch tube in the secondary circuit according to the current loop, and obtaining a second duty cycle for controlling the switch tube in the secondary circuit according to the voltage loop; S32: comparing whether the first duty cycle is less than or equal to the second duty cycle, if so, controlling the switch tube in the secondary circuit with a switch control signal with the first duty cycle as the duty cycle, otherwise controlling the switch tube in the secondary circuit with a switch control signal with the second duty cycle as the duty cycle; S33: judging whether the voltage on the high-voltage side capacitor reaches the voltage setting value Vset, if so, ending, otherwise entering step S31.

[0083] Among them, the voltage setting value Vset is issued by the whole vehicle.

[0084] If the soft start ends and the current loop and voltage loop dual-loop control are directly entered, it will cause the inductor current to overshoot. This application adopts the current loop and voltage loop dual-loop competition mode after the soft start ends to avoid the overshoot of the inductor current, thereby limiting the single-cycle energy storage ΔQ of the low-voltage side inductor L1. L1 , which means that the stress of the switching tube in the secondary circuit is suppressed.

[0085] See also Figure 6 In one embodiment, after the current loop soft start ends, the voltage loop control mode is entered through the current loop and voltage loop dual-loop competition mode, that is, the constant current region of the voltage loop control is entered at time t1. During this period, the low-voltage side inductor current IL remains unchanged and is suppressed to a small value. The voltage on the high-voltage side capacitor HV Cap gradually increases. At time t2, the voltage on the high-voltage side capacitor HVCap reaches the voltage setting value Vset, and the constant current region ends (such as Figure 6 As shown, there is a short current drop phase before time t2, and the current loop control mode is entered through the current loop and voltage loop dual-loop competition mode. During this period, the low-voltage side inductor current IL gradually decreases, and the voltage V on the high-voltage side capacitor HV Cap is maintained at a voltage setting value Vset that is basically constant.

[0086] The vehicle-mounted DC / DC converter of the present application can maintain the voltage for a period of time after reaching the set value, that is, it has a constant voltage control area to achieve the effect of pre-charging the high-voltage side capacitor by the vehicle power supply, and at the same time has a constant current control area to limit the inductor current during the charging process. In this way, the reverse pre-charging control method of the vehicle-mounted DC / DC converter of the present application satisfies the effect of pre-charging the high-voltage side capacitor by the vehicle power supply, and limits the inductor current during the charging process, thereby limiting the single-cycle energy storage ΔQ of the low-voltage side inductor L1 L1 , which means that the stress of the switching tube in the secondary circuit is suppressed.

[0087] The applicant has found that if the current loop and voltage loop dual-loop competition mode is entered at startup, there will be loop competition and oscillation problems due to the uncertainty of the initial value of the voltage on the high-voltage side capacitor at the beginning of pre-charging. The present application forces the current loop to enter the stage at the beginning of pre-charging, and soft-starts the current loop. After stabilizing the current closed-loop control, the dual-loop competition control mode is switched on. Figure 6 It can be seen that the low-voltage side inductor current IL has been suppressed to a smaller value, achieving the purpose of suppressing the stress of the switch tube in the secondary circuit, and the dual closed-loop competition control can solve the steady-state problem during the charging process.

[0088] During step S2 and step S3, the discharge switch tube in the stress absorption circuit is turned on after the secondary switch tube in the secondary circuit connected in parallel with it is turned on and turned off before it is turned on again, so that the conduction time of the discharge switch tube is maximized. Specifically:

[0089] After determining the switch control signal for controlling the secondary switch tube in the secondary circuit according to step S2 and step S3, the turn-on time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time of the switch control signal of the secondary switch tube in the secondary circuit, and the turn-off time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time again of the switch control signal of the secondary switch tube, and the turn-on time of the discharge switch tube is maximized.

[0090] See also Figure 7 Schematic diagram of control signals of a secondary switch tube and a discharge switch tube connected in parallel in a secondary circuit of an embodiment of the present application, as shown in FIG. Figure 7 As shown, after the secondary switch tube S1 is turned on, the discharge switch tube is controlled to be turned on after a delay of t11, and the discharge switch tube is controlled to be turned off t22 in advance when the secondary switch tube S1 is turned on again (i.e., in the next switching cycle). That is, the discharge switch tube connected in parallel with the secondary switch tube S1 is determined according to the switch control signal of the secondary switch tube S1, and the time of t11 and t22 is made as short as possible to increase the turn-on time of the discharge switch tube as much as possible. In each switching cycle, the absorption capacitor is discharged for as long as possible, which can reduce the initial voltage of the absorption capacitor and suppress the stress of the switch tube in the secondary circuit.

[0091] As described above, the current loop soft start mode in step S2 and the current loop and voltage loop dual loop competition mode in step S3 only need to obtain the switch control signal of the switch tube in the secondary circuit, and the switch tube in the primary circuit has no action. Specifically, the reverse pre-charge is achieved through the body diode of the switch tube in the primary circuit. Therefore, the type of the primary circuit 110 is not limited, such as Figure 2 The full bridge shown is applicable, and the half bridge is also applicable.

[0092] In practical applications, this application does not limit the type of secondary circuit, such as Figure 2 The synchronous rectification circuit shown is applicable, and full-bridge rectification, full-wave rectification, current doubler rectification, etc. are all applicable. Figure 2 This is just an example, please refer to Figure 8 The schematic diagram of the vehicle-mounted DC / DC converter according to an embodiment of the present application is shown. In fact, the primary circuit 110 can be any applicable switch unit, and the secondary circuit 120 can also be any applicable switch unit.

[0093] From the above description, it can be seen that the control method of the present invention can reuse the original hardware circuit of the vehicle-mounted DC / DC converter to the greatest extent to reduce the stress of the switching tube in the secondary circuit, thereby reducing the hardware cost of the pre-charging solution and improving the stability of the pre-charging function.

[0094] Although the embodiments of the present application and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

[0095] In addition, the scope of the present application is not limited to the specific embodiments of the processes, machines, manufactures, material compositions, modes, methods, and steps described in this specification. Those skilled in the art will readily understand from the disclosure of the present application that, according to the present application, currently existing or later to be developed processes, machines, manufactures, material compositions, modes, methods, or steps that perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein may be utilized. Therefore, it is intended that the appended claims include such processes, machines, manufactures, material compositions, modes, methods, or steps within their scope.

Claims

1. A reverse pre-charge control method for a vehicle-mounted DC / DC converter, wherein the vehicle-mounted DC / DC converter comprises a primary circuit, a transformer and a secondary circuit connected in cascade, wherein the primary circuit is connected in parallel with a high-voltage side capacitor, wherein the secondary circuit is connected in parallel with a low-voltage side capacitor, wherein the secondary circuit comprises a low-voltage side inductor, at least one switch tube and a stress absorption circuit connected in parallel with the switch tube, wherein the stress absorption circuit comprises an absorption capacitor, a discharge resistor and a discharge switch tube connected in series, wherein: When the duty cycle of the switch tube in the secondary circuit is less than or equal to 50%, the control method includes: S1: Turn on the machine; S2: Controlling the vehicle-mounted DC / DC converter to operate in a current loop soft start mode, and gradually increasing the current reference value of the current loop until the current reference value is equal to the current reference set value; S3: Control the vehicle-mounted DC / DC converter to operate in a current loop and a voltage loop dual-loop competition mode, compare the duty cycles of the switch tube in the secondary circuit obtained by the current loop and the voltage loop, and use the smaller one as the duty cycle of the switch control signal for controlling the switch tube in the secondary circuit until the voltage on the high-voltage side capacitor reaches a voltage setting value, wherein During step S2 and step S3, the discharge switch tube in the stress absorption circuit is turned on after the switch tube in the secondary circuit connected in parallel therewith is turned on and is turned off before being turned on again, so that the conduction time of the discharge switch tube is maximized.

2. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 1, characterized in that: Step S2 includes: S21: Setting the current reference value of the current loop to 0; S22: the current reference value Iref increases with a fixed step size or a variable step size; S23: Determine whether the current reference value reaches the current reference setting value. If so, exit the current loop soft start mode, go to step S3; if not, go to step S22.

3. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 2 is characterized in that: In step S2, the current loop soft-start mode is an open-loop control mode or a closed-loop control mode.

4. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 2, characterized in that: The current reference setting value is issued by the vehicle.

5. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 4 is characterized in that: In step S2, the vehicle-mounted DC / DC converter operates in a small pulse startup stage.

6. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 1, characterized in that: Step S3 includes: S31: obtaining a first duty cycle of controlling the switch tube in the secondary circuit according to the current loop, and obtaining a second duty cycle of controlling the switch tube in the secondary circuit according to the voltage loop; S32: comparing whether the first duty cycle is smaller than the second duty cycle, if so, using the switch control signal with the first duty cycle as the duty cycle to control the switch tube in the secondary circuit, otherwise, using the switch control signal with the second duty cycle as the duty cycle to control the switch tube in the secondary circuit; S33: Determine whether the voltage on the high-voltage side capacitor reaches the voltage setting value. If yes, the process ends; otherwise, the process proceeds to step S31.

7. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 1, characterized in that: After determining the switch control signal for controlling the switch tube in the secondary circuit according to step S2 and step S3, the turn-on time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time of the switch control signal of the switch tube, and the turn-off time of the discharge switch tube in the stress absorption circuit connected in parallel therewith is determined according to the turn-on time again of the switch control signal of the switch tube, and the turn-on time of the discharge switch tube is maximized.

8. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 7, characterized in that: The discharge switch tube is controlled to be turned on after a delay of t11 after the switch tube is turned on, and the discharge switch tube is controlled to be turned off before a time t22 before the switch tube is turned on again.

9. The reverse pre-charging control method of the vehicle-mounted DC / DC converter according to claim 1, characterized in that: The primary circuit is a full-bridge switch unit or a half-bridge switch unit.

10. The reverse pre-charging control method of a vehicle-mounted DC / DC converter according to claim 1 or 9, characterized in that: The secondary circuit is a synchronous rectification circuit, a full-bridge rectification circuit, a full-wave rectification circuit or a current doubler rectification circuit.

11. The reverse pre-charging control method of a vehicle-mounted DC / DC converter according to claim 1, characterized in that: The stress absorption circuit further includes a first diode and a fifth capacitor, and the first diode and the fifth capacitor are connected in parallel at both ends of the discharge resistor and the discharge switch tube.

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