High-voltage direct-current bus active discharge method, vehicle-mounted DC / DC conversion device, and electric vehicle

Abstract

The application provides a high-voltage DC bus active discharge method, a vehicle-mounted DC / DC conversion device and an electric vehicle. The method comprises the following steps: S1, receiving an active discharge instruction; S2, obtaining a high-voltage DC bus voltage value VC2 on the high-voltage DC bus through a detection circuit; S3, judging whether the high-voltage DC bus voltage value VC2 is greater than an active discharge voltage setting value; if yes, entering step S4; S4, controlling the high-voltage bidirectional DC / DC converter and the low-voltage DC / DC converter to work simultaneously, so as to discharge the electric energy on the high-voltage DC bus to the first capacitor or consume the electric energy on the high-voltage DC bus by the high-voltage bidirectional DC / DC converter, and discharge the electric energy on the high-voltage DC bus to the low-voltage battery or consume the electric energy on the high-voltage DC bus by the low-voltage DC / DC converter; entering step S5; S5, judging whether the high-voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value; if yes, the discharge is ended; if not, entering step S4.

Description

Technical Field

[0001] This application relates to the field of power supply, particularly to active discharge methods for high-voltage DC buses, on-board DC / DC converters, and electric vehicles. Background Technology

[0002] With the development of science and technology and society, and the deepening shift of electric vehicles from policy-driven to market-driven, electric vehicles have been widely used and are gradually becoming the mainstream trend in the automotive industry, accounting for an increasingly larger share.

[0003] Current electric vehicles typically include a high-voltage battery. The onboard power supply usually includes a power-saving (PFC) circuit and a high-voltage bidirectional DC / DC converter. This converter draws energy from the power grid and converts it into high-voltage direct current (DC) on the high-voltage DC bus. The high-voltage battery is connected in parallel with the DC bus, allowing energy to be stored within it, thus providing the electric power source for the electric vehicle. The onboard power supply also typically includes a low-voltage DC / DC converter, which converts the energy from the high-voltage battery into low-voltage DC and stores it in the low-voltage battery to power the loads within the electric vehicle.

[0004] After an electric vehicle stops operating, the high-voltage power battery is disconnected from the high-voltage DC bus. However, because a large amount of residual electrical energy remains on the high-voltage DC bus, failure to release this energy promptly could result in electric shock. Based on the high-voltage safety requirements of electric vehicles, the national standard GB / T18488.1-2015 stipulates that after the high-voltage power battery is disconnected from the high-voltage DC bus, the voltage in the high-voltage DC bus must be discharged to below 60V within 5 seconds.

[0005] Active discharge technology emerged to address the discharge problem of high-voltage electrical systems in electric vehicles, in order to meet safety requirements. However, current active discharge technologies still suffer from issues such as slow discharge speed, complex control, and large inrush current.

[0006] Furthermore, with technological advancements, there is a growing desire for high-voltage batteries in electric vehicles to provide even higher voltage levels. Currently, the traditional 400V high-voltage electricity is gradually moving towards higher voltage levels, such as 600V and 800V, to meet the demands of higher voltage levels. However, the continuous increase in the voltage level and energy of high-voltage electrical systems also brings new safety challenges. Summary of the Invention

[0007] According to one embodiment, this application provides an active discharge method for a high-voltage DC bus in an on-board DC / DC converter, wherein the on-board DC / DC converter includes a cascaded high-voltage bidirectional DC / DC converter and a low-voltage DC / DC converter. A first terminal of the high-voltage bidirectional DC / DC converter is connected to a first capacitor, and a second terminal is connected to the high-voltage DC bus. A first terminal of the low-voltage DC / DC converter is connected to the high-voltage DC bus, and a second terminal is connected to a low-voltage battery. The method includes:

[0008] S1: Received active discharge command;

[0009] S2: Obtain the high voltage DC bus voltage value VC2 on the high voltage DC bus through the detection circuit;

[0010] S3: Determine whether the high voltage DC bus voltage value VC2 is greater than the active discharge voltage setting value. If so, proceed to step S4.

[0011] S4: Control the high-voltage bidirectional DC / DC converter and the low-voltage DC / DC converter to work simultaneously, so as to discharge the electrical energy on the high-voltage DC bus to the first capacitor or consume it by the high-voltage bidirectional DC / DC converter, and discharge the electrical energy on the high-voltage DC bus to the low-voltage battery or consume it by the low-voltage DC / DC converter, and proceed to step S5;

[0012] S5: Determine whether the high voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value. If yes, the discharge ends; otherwise, proceed to step S4.

[0013] Furthermore, in step S3, if the determination is negative, proceed to S5.

[0014] Furthermore, after step S4, the method further includes: determining whether the decrease in the high-voltage DC bus voltage value VC2 within a predetermined time interval is less than a set value; if not, then continue with step S4; if yes, then output an active discharge failure signal.

[0015] Furthermore, the high-voltage bidirectional DC / DC converter includes:

[0016] A primary-side switching unit includes at least one switching transistor, with its first end connected to the first capacitor and its second end connected to the primary-side winding of the first transformer.

[0017] The secondary-side switching unit includes at least one switching transistor, with its first end connected to the secondary winding of the first transformer and its second end connected to the high-voltage DC bus voltage.

[0018] The low-voltage DC / DC converter includes:

[0019] A primary-side switching unit includes at least one switching transistor, with its first end connected to the voltage of the high-voltage DC bus and its second end connected to the primary winding of the second transformer.

[0020] The secondary-side switching unit includes at least one switching transistor, with its first end connected to the secondary winding of the second transformer and its second end connected to the low-voltage battery.

[0021] Furthermore, step S4, controlling the operation of the high-voltage bidirectional DC / DC converter, includes:

[0022] S411: Output a first switch control signal to the secondary side switch unit of the high-voltage bidirectional DC / DC converter, wherein the duty cycle of the first switch control signal is fixed and the frequency is the first switch frequency;

[0023] S412: Within a first set time period, reduce the frequency of the first switch control signal from the first switch frequency to the second switch frequency, while keeping the duty cycle constant, and proceed to step S5.

[0024] Furthermore, the first switching frequency is high frequency, and the second switching frequency is low frequency.

[0025] Furthermore, step S4, controlling the operation of the low-voltage DC / DC converter, includes:

[0026] S421: Obtain the low-voltage battery voltage value E on the low-voltage battery, and determine whether the high-voltage DC bus voltage value VC2 is greater than or equal to 4*N2*E*k, where N2 is the turns ratio of the second transformer and k is the margin coefficient. If yes, proceed to step S422; if no, proceed to step S423.

[0027] S422: Output a second switching control signal to the primary-side switching unit of the low-voltage DC / DC converter, wherein the duty cycle of the second switching control signal is... The frequency is the third switching frequency, and then proceeds to steps S421 and S5;

[0028] S423: Output a third switch control signal to the primary side switch unit of the low-voltage DC / DC converter, wherein the duty cycle of the third switch control signal is fixed and the frequency is the fourth switch frequency, wherein the third switch frequency is less than the fourth switch frequency, and proceed to step S5.

[0029] Furthermore, the third switching frequency is low frequency, and the fourth switching frequency is high frequency.

[0030] According to one embodiment, this application also provides an on-board DC / DC converter, comprising:

[0031] High-voltage bidirectional DC / DC converter, including:

[0032] A primary-side switching unit includes at least one switching transistor, with its first end connected to the first capacitor and its second end connected to the primary-side winding of the first transformer.

[0033] The secondary-side switching unit includes at least one switching transistor, with its first end connected to the secondary winding of the first transformer and its second end connected to the high-voltage DC bus voltage.

[0034] Low-voltage DC / DC converters, including:

[0035] A primary-side switching unit includes at least one switching transistor, with its first end connected to the voltage of the high-voltage DC bus and its second end connected to the primary winding of the second transformer.

[0036] The secondary-side switching unit includes at least one switching transistor, with its first end connected to the secondary winding of the second transformer and its second end connected to the low-voltage battery.

[0037] A high-voltage DC bus voltage detection circuit is used to detect the voltage on the high-voltage DC bus and output the high-voltage DC bus voltage value VC2.

[0038] A low-voltage battery voltage detection circuit is used to detect the voltage on the low-voltage battery and output the low-voltage battery voltage value E;

[0039] The control unit receives the high-voltage DC bus voltage value VC2 and the low-voltage battery voltage value E, and executes the following after receiving the active discharge command:

[0040] S3: Determine whether the high voltage DC bus voltage value VC2 is greater than the active discharge voltage setting value. If so, proceed to step S4.

[0041] S4: Control the high-voltage bidirectional DC / DC converter and the low-voltage DC / DC converter to work simultaneously, so as to discharge the electrical energy on the high-voltage DC bus to the first capacitor or consume it by the high-voltage bidirectional DC / DC converter, and discharge the electrical energy on the high-voltage DC bus to the low-voltage battery or consume it by the low-voltage DC / DC converter, and proceed to step S5;

[0042] S5: Determine whether the high voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value. If yes, the discharge ends; otherwise, proceed to step S4.

[0043] Furthermore, step S4, controlling the operation of the high-voltage bidirectional DC / DC converter, includes:

[0044] S411: Output a first switch control signal to the secondary side switch unit of the high-voltage bidirectional DC / DC converter, wherein the duty cycle of the first switch control signal is fixed and the frequency is the first switch frequency;

[0045] S412: Within a first set time period, reduce the frequency of the first switch control signal from the first switch frequency to the second switch frequency, while keeping the duty cycle constant, and proceed to step S5.

[0046] Furthermore, step S4, controlling the operation of the low-voltage DC / DC converter, includes:

[0047] S421: Obtain the low-voltage battery voltage value E on the low-voltage battery, and determine whether the high-voltage DC bus voltage value VC2 is greater than or equal to 4*N2*E*k, where N2 is the turns ratio of the second transformer and k is the margin coefficient. If yes, proceed to step S422; if no, proceed to step S423.

[0048] S422: Output a second switching control signal to the primary-side switching unit of the low-voltage DC / DC converter, wherein the duty cycle of the second switching control signal is... The frequency is the third switching frequency, and then proceeds to steps S421 and S5;

[0049] S423: Output a third switch control signal to the primary side switch unit of the low-voltage DC / DC converter, wherein the duty cycle of the third switch control signal is fixed and the frequency is the fourth switch frequency, wherein the third switch frequency is less than the fourth switch frequency, and proceed to step S5.

[0050] According to one embodiment, this application also provides an electric vehicle including the above-described on-board DC / DC converter.

[0051] The features and technical advantages of this disclosure have been outlined quite extensively above to facilitate a better understanding of the detailed description that follows. Additional features and advantages of this disclosure, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifying or designing other structures or processes to achieve the same purpose as this disclosure. Those skilled in the art will also recognize that such equivalent structures do not depart from the spirit and scope of this disclosure as set forth in the appended claims. Attached Figure Description

[0052] To gain a more complete understanding of this disclosure and its advantages, the following description is given in conjunction with the accompanying drawings, wherein:

[0053] Figure 1 A schematic diagram of a typical vehicle-mounted DC / DC converter is shown.

[0054] Figure 2 A flowchart of an active discharge method for a high-voltage DC bus in an on-board DC / DC converter according to an embodiment of this application is shown;

[0055] Figure 3 A flowchart of an active discharge method for a high-voltage DC bus in an on-board DC / DC converter according to another embodiment of this application is shown;

[0056] Figure 4 A flowchart illustrating an active discharge method for a high-voltage DC bus in an on-board DC / DC converter according to another embodiment of this application is shown.

[0057] Unless otherwise stated, corresponding numbers and symbols in the various figures generally refer to corresponding parts. These figures are drawn to clearly illustrate relevant aspects of the various embodiments and are not necessarily drawn to scale. Detailed Implementation

[0058] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0059] See also Figure 1 The schematic diagram of a typical on-board DC / DC converter shown includes a cascaded high-voltage bidirectional DC / DC converter 100 and a low-voltage DC / DC converter 200. The first terminal of the high-voltage bidirectional DC / DC converter 100 is connected to a first capacitor C1, and the second terminal is connected to a high-voltage DC bus C2. The first terminal of the low-voltage DC / DC converter 200 is connected to the high-voltage DC bus C2, and the second terminal is connected to a low-voltage battery BE. The high-voltage power battery is connected in parallel with the high-voltage DC bus C2, allowing energy to be stored in the high-voltage power battery, thus becoming the source of electrical energy within the electric vehicle.

[0060] Typically, the preceding stage of the high-voltage bidirectional DC / DC converter 100 also includes a PFC circuit (not shown in the figure). When charging the high-voltage power battery, the PFC circuit draws electrical energy from the power grid, and the high-voltage bidirectional DC / DC converter 100 operates to convert the energy into high-voltage DC power on the high-voltage DC bus C2 to charge the high-voltage power battery.

[0061] The low-voltage DC / DC converter 200 is used to convert electrical energy from the high-voltage power battery into low-voltage DC power and store it in the low-voltage battery BE to power the load in the electric vehicle.

[0062] In practical applications, both the high-voltage bidirectional DC / DC converter 100 and the low-voltage DC / DC converter 200 can be bidirectional DC / DC converters to meet the demand for more power conversion in electric vehicles.

[0063] Typically, the high-voltage bidirectional DC / DC converter 100 and the low-voltage DC / DC converter 200 are isolated converters. For example... Figure 1 As shown, the high-voltage bidirectional DC / DC converter 100 includes a cascaded primary-side switching unit 110, a first transformer T1, and a secondary-side switching unit 120. Specifically, the primary-side switching unit 110 is connected between the first capacitor C1 and the primary winding T1p of the first transformer T1, and is implemented as a full-bridge switching unit formed by the first switch Q1 to the fourth switch Q4. The secondary-side switching unit 120 is connected between the secondary winding T1s of the first transformer T1 and the high-voltage DC bus C2, and is implemented as a full-bridge switching unit formed by the fifth switch Q5 to the eighth switch Q8. That is, the high-voltage bidirectional DC / DC converter 100 is implemented as a full-bridge isolated bidirectional DC / DC converter.

[0064] Typically, the specific structure of the high-voltage bidirectional DC / DC converter 100 is not limited, as long as it can meet the power conversion requirements of electric vehicles. For example, the primary-side switching unit 110 and the secondary-side switching unit 120 can also be implemented as a half-bridge switching unit, a three-level switching unit, etc. Furthermore, such as... Figure 1 As shown, a resonant cavity 130 is also included between the primary side switching unit 110 and the first transformer T1, so that the high-voltage bidirectional DC / DC converter 100 forms an LLC resonant converter.

[0065] Please refer to the following: Figure 1 The low-voltage DC / DC converter 200 includes a cascaded primary-side switching unit 210, a second transformer T2, and a secondary-side switching unit 220. Specifically, the primary-side switching unit 210 is connected between the high-voltage DC bus C2 voltage and the primary winding T2p of the second transformer T2, and is implemented as a half-bridge switching unit formed by the ninth switch Q9, the tenth switch Q10, the third capacitor C3, and the fourth capacitor C4. The secondary-side switching unit 220 is connected between the secondary winding T2s of the second transformer T2 and the low-voltage battery BE, and is implemented as a current-multiplying rectifier unit formed by the eleventh switch Q11, the twelfth switch Q12, the first inductor L1, and the second inductor L2.

[0066] Typically, the specific structure of the low-voltage DC / DC converter 200 is not limited, as long as it can meet the power conversion requirements of electric vehicles. For example, the primary-side switching unit 210 can also be implemented as a full-bridge switching unit, a three-level switching unit, etc., and the secondary-side switching unit 220 can also be implemented as a full-wave rectifier unit, a full-bridge rectifier unit, etc.

[0067] In practical applications, it also includes detection circuits, such as... Figure 1 The system includes a high-voltage DC bus voltage detection circuit 310 and a low-voltage battery voltage detection circuit 320, and also includes a control unit 330. The detection circuit, control unit 330, and on-board DC / DC converter together constitute an on-board DC / DC converter. The detection circuit is used to detect the electrical parameters of the on-board DC / DC converter, such as voltage signals and current signals. The control unit 330 outputs switching control signals to control the operation of the high-voltage bidirectional DC / DC converter 100 and the low-voltage DC / DC converter 200 based on the detection signals, so as to meet the power conversion requirements of electric vehicles.

[0068] The following will use an on-board DC / DC converter as an example. Figure 1 Taking the example shown, the principle of the active discharge method of the high-voltage DC bus C2 in the vehicle DC / DC converter is explained.

[0069] One embodiment of this application provides an active discharge method for the high-voltage DC bus in an on-board DC / DC converter, which can be found in [reference needed]. Figure 2 The flowchart shown is a method for active discharge of the high-voltage DC bus in an on-board DC / DC converter according to an embodiment of this application. The method for active discharge of the high-voltage DC bus in an on-board DC / DC converter includes:

[0070] S1: Received active discharge command;

[0071] S2: Obtain the high voltage DC bus voltage value VC2 on the high voltage DC bus C2 through the detection circuit;

[0072] S3: Determine whether the high voltage DC bus voltage value VC2 is greater than the active discharge voltage setting value Vset. If so, proceed to step S4.

[0073] S4: Control the high-voltage bidirectional DC / DC converter 100 and the low-voltage DC / DC converter 200 to work simultaneously, so as to discharge the electrical energy on the high-voltage DC bus C2 to the first capacitor C1 or consume it by the high-voltage bidirectional DC / DC converter 100, and discharge the electrical energy on the high-voltage DC bus C2 to the low-voltage battery BE or consume it by the low-voltage DC / DC converter 200, and proceed to step S5;

[0074] S5: Determine whether the high-voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value Vset. If yes, the active discharge ends; otherwise, proceed to step S4.

[0075] Thus, when the high-voltage DC bus C2 needs to discharge, by controlling the high-voltage bidirectional DC / DC converter 100 and the low-voltage DC / DC converter 200 to work simultaneously to discharge or consume energy, the charge on the high-voltage DC bus C2 can be quickly discharged to a safe range, improving the discharge speed. Its control is simple and does not require any additional hardware circuitry.

[0076] More specifically, in step S3, if the determination is negative, proceed to S5 to determine whether the active discharge can be terminated or the discharge phase can be entered.

[0077] In one embodiment, see reference Figure 3 The flowchart of the active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to another embodiment of this application shows that, after step S4, the method further includes: determining whether the decrease in the high-voltage DC bus voltage value VC2 by ΔVC2 within a predetermined time interval is less than a set value ΔVset; if not, continuing to step S4; if yes, outputting an active discharge failure signal. If the decrease in the high-voltage DC bus voltage value VC2 is detected to be less than 10V within 5s, it indicates that the high-voltage DC bus C2 has not been successfully discharged, and an active discharge failure signal is output; otherwise, discharge continues.

[0078] In one embodiment, please refer to Figure 4 The flowchart shown below illustrates the active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to another embodiment of this application. Step S4, controlling the operation of the high-voltage bidirectional DC / DC converter, includes:

[0079] S411: Output the first switch control signal to the secondary side switch unit of the high-voltage bidirectional DC / DC converter 100, wherein the duty cycle of the first switch control signal is fixed and the frequency is the first switch frequency f1;

[0080] S412: Within a first set time period, reduce the frequency of the first switch control signal from the first switch frequency f1 to the second switch frequency f2, and keep the duty cycle fixed, then proceed to step S5.

[0081] Specifically, the first switching frequency f1 is high-frequency, such as 300kHz. The second switching frequency f2 is low-frequency, such as 80kHz. Of course, the specific values ​​of the first switching frequency f1 and the second switching frequency f2 are not limited. It's just that in step S412, the frequency of the first switching control signal is gradually changed from high-frequency to low-frequency.

[0082] In actual implementation, in step S412, the frequency of the first switch control signal is linearly reduced from the first switch frequency f1 to the second switch frequency f2, so as to reduce the impact on the operation of the high-voltage bidirectional DC / DC converter 100 during the change.

[0083] As described above, upon initiating active discharge, the high-voltage bidirectional DC / DC converter 100 initially operates at a high-frequency first switching frequency f1 with a fixed duty cycle. We know that for the high-voltage bidirectional DC / DC converter 100, with a fixed duty cycle, a higher switching frequency results in lower gain. Therefore, at the start of active discharge, step S411 initially discharges with a lower gain, reducing the inrush current and improving the reliability of the high-voltage bidirectional DC / DC converter 100. Then, step S412 reduces the switching frequency to a lower frequency to increase the gain of the high-voltage bidirectional DC / DC converter 100, thereby accelerating the discharge speed. This approach balances inrush current and discharge speed.

[0084] In practical implementation, the length of the first set time can be obtained through experiments or other methods depending on the product. In one embodiment, the first set time is selected as 200ms.

[0085] In one embodiment, the duty cycle of the first switch control signal is fixed at 0.5, that is, fixed at the maximum duty cycle, in order to improve the discharge speed. Of course, the duty cycle can also be fixed at other values.

[0086] for Figure 1 The secondary-side switching unit shown is a high-voltage bidirectional DC / DC converter 100 of a full-bridge switching unit. The first switching control signal causes the fifth switch Q5 and the eighth switch Q8 to work synchronously, the sixth switch Q6 and the seventh switch Q7 to work synchronously, the fifth switch Q5 and the sixth switch Q6 to work complementaryly, and the seventh switch Q7 and the eighth switch Q8 to work complementaryly, and the duty cycle of each is fixed at 0.5.

[0087] Specifically, only the first switching control signal for driving the secondary-side switching unit 120 of the high-voltage bidirectional DC / DC converter 100 needs to be provided, and its primary-side switching unit 110 can achieve the rectification function through the operation of its internal diode.

[0088] In practical operation, controlled by steps S411 and S412, when the high-voltage DC bus voltage VC2 is greater than the voltage on the first capacitor C1, the high-voltage bidirectional DC / DC converter 100 operates in reverse charging mode, discharging the energy on the high-voltage DC bus C2 to the first capacitor C1, thus discharging the high-voltage DC bus C2. When the high-voltage DC bus voltage VC2 is less than the voltage on the first capacitor C1, the switching unit within the secondary side switching unit 120 of the high-voltage bidirectional DC / DC converter 100 consumes the electrical energy on the high-voltage DC bus C2.

[0089] It can be seen that the process of the high-voltage bidirectional DC / DC converter 100 discharging is an open-loop control process.

[0090] In one embodiment, please refer again Figure 4 Step S4, controlling the low-voltage DC / DC converter, includes:

[0091] S421: Obtain the low-voltage battery voltage value E on the low-voltage battery BE, and determine whether the high-voltage DC bus voltage value VC2 is greater than or equal to 4*N2*E*k, where N2 is the turns ratio of the second transformer T2 and k is the margin coefficient. If yes, proceed to step S422; otherwise, proceed to step S423.

[0092] S422: Outputs a second switching control signal to the primary-side switching unit 210 of the low-voltage DC / DC converter 200, wherein the duty cycle of the second switching control signal is... The frequency is the third switching frequency f3, and then proceeds to steps S421 and S5;

[0093] S423: Output the third switch control signal to the primary side switch unit 210 of the low-voltage DC / DC converter 200, wherein the duty cycle of the third switch control signal is fixed and the frequency is the fourth switch frequency f4, wherein the third switch frequency f3 is less than the fourth switch frequency f4, and proceed to step S5.

[0094] In one embodiment, the margin factor k can be 1.1. However, this application does not limit its specific value. In practical applications, it can be set according to the discharge rate required by the actual product and the circuit parameters.

[0095] In practice, the third switching frequency f3 is a low frequency, such as 80kHz. The fourth switching frequency f4 is a high frequency, such as 300kHz. Of course, the specific values ​​of the third switching frequency f3 and the fourth switching frequency f4 are not limited.

[0096] As mentioned above, if the high-voltage DC bus voltage VC2 is greater than or equal to 4*N2*E*k, then based on the obtained high-voltage DC bus voltage VC2, low-voltage battery voltage E, and the turns ratio N2 of the second transformer T2, according to the formula... The duty cycle D of the second switch control signal is calculated in real time, that is, the duty cycle D of the second switch control signal is obtained in the closed-loop control mode. At the same time, the high voltage DC bus voltage value VC2 is monitored to see if it is greater than or equal to 4*N2*E*k and whether the conditions for exiting active discharge are met. If the conditions for exiting active discharge are not met, step S422 is performed until the high voltage DC bus voltage value VC2 is less than 4*N2*E*k. At this time, the frequency of the third switch control signal is pushed from the low frequency third switch frequency f3 to the high frequency fourth switch frequency f4, and the duty cycle is fixed. At this time, the energy is consumed by the primary side switch unit 210 of the low voltage DC / DC converter 200 to discharge the high voltage DC bus C2.

[0097] Specifically, in step S423, the duty cycle of the third switch control signal is fixed to the maximum value of the duty cycle of the third switch control signal in step S423. From the formula... As can be seen, with the discharge in step S422, the duty cycle D gradually increases. When exiting step S422, the duty cycle D reaches its maximum value Dmax. Therefore, when entering step S423, the duty cycle of the third switch control signal is fixed at this maximum value Dmax. Thus, from step S422 to step S423, the duty cycle of the third switch control signal does not undergo a step change, resulting in high reliability of the low-voltage DC / DC converter 200.

[0098] Furthermore, step S423 also includes gradually increasing the frequency of the third switching control signal from the third switching frequency f3 to the fourth switching frequency f4, such as linearly increasing it to the fourth switching frequency f4. This is to reduce the impact on the operation of the high-voltage bidirectional DC / DC converter 100 during the change.

[0099] Please refer to the following: Figure 1 This application also provides an on-board DC / DC converter, which includes:

[0100] High-voltage bidirectional DC / DC converter 100, including:

[0101] The primary-side switching unit 110 includes at least one switching transistor, with its first end connected to a first capacitor C1 and its second end connected to the primary-side winding T1p of a first transformer T1.

[0102] The secondary-side switching unit 120 includes at least one switching transistor, with its first end connected to the secondary winding T1s of the first transformer T1 and its second end connected to the voltage of the high-voltage DC bus C2.

[0103] Low-voltage DC / DC converter 200, including:

[0104] The primary side switching unit 210 includes at least one switching transistor, with its first end connected to the voltage of the high voltage DC bus C2 and its second end connected to the primary side winding T2p of the second transformer T2.

[0105] The secondary-side switching unit 220 includes at least one switching transistor, with its first end connected to the secondary-side winding T2s of the second transformer T2 and its second end connected to the low-voltage battery BE.

[0106] The high-voltage DC bus voltage detection circuit 310 is used to detect the voltage on the high-voltage DC bus C2 and output the high-voltage DC bus voltage value VC2.

[0107] The low-voltage battery voltage detection circuit 320 is used to detect the voltage on the low-voltage battery BE and output the low-voltage battery voltage value E.

[0108] Control unit 330 receives the high-voltage DC bus voltage value VC2 and the low-voltage battery voltage value E, and executes the following after receiving the active discharge command:

[0109] S3: Determine whether the high voltage DC bus voltage value VC2 is greater than the active discharge voltage setting value Vset. If so, proceed to step S4.

[0110] S4: Control the high-voltage bidirectional DC / DC converter 100 and the low-voltage DC / DC converter 200 to work simultaneously, so as to discharge the electrical energy on the high-voltage DC bus C2 to the first capacitor C1 or consume it by the high-voltage bidirectional DC / DC converter 100, and discharge the electrical energy on the high-voltage DC bus C2 to the low-voltage battery BE or consume it by the low-voltage DC / DC converter 200, and proceed to step S5;

[0111] S5: Determine whether the high-voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value Vset. If yes, the active discharge ends; otherwise, proceed to step S4.

[0112] In one embodiment, controlling the operation of the high-voltage bidirectional DC / DC converter in step S4 includes:

[0113] S411: Output the first switch control signal to the secondary side switch unit of the high-voltage bidirectional DC / DC converter 100, wherein the duty cycle of the first switch control signal is fixed and the frequency is the first switch frequency f1;

[0114] S412: Within a first set time period, reduce the frequency of the first switch control signal from the first switch frequency f1 to the second switch frequency f2, and keep the duty cycle fixed, then proceed to step S5.

[0115] In one embodiment, controlling the low-voltage DC / DC converter to operate in step S4 includes:

[0116] S421: Obtain the low-voltage battery voltage value E on the low-voltage battery BE, and determine whether the high-voltage DC bus voltage value VC2 is greater than or equal to 4*N2*E*k, where N2 is the turns ratio of the second transformer T2 and k is the margin coefficient. If yes, proceed to step S422; otherwise, proceed to step S423.

[0117] S422: Outputs a second switching control signal to the primary-side switching unit 210 of the low-voltage DC / DC converter 200, wherein the duty cycle of the second switching control signal is... The frequency is the third switching frequency f3, and then proceeds to steps S421 and S5;

[0118] S423: Output the third switch control signal to the primary side switch unit 210 of the low-voltage DC / DC converter 200, wherein the duty cycle of the third switch control signal is fixed and the frequency is the fourth switch frequency f4, wherein the third switch frequency f3 is less than the fourth switch frequency f4, and proceed to step S5.

[0119] In practical applications, the high-voltage DC bus voltage detection circuit 310, the low-voltage battery voltage detection circuit 320, and the control unit 330 are essential hardware circuits for the operation of the vehicle DC / DC converter. This application integrates the active discharge function into the inherent hardware circuit, so there is no need to change the hardware circuit of the vehicle DC / DC converter, no cost increase, and the design difficulty can be reduced.

[0120] The principle and advantages of active discharge in vehicle-mounted DC / DC converters are the same as those of the active discharge method for high-voltage DC buses in vehicle-mounted DC / DC converters, and will not be repeated here.

[0121] In one embodiment of this application, an electric vehicle is also provided, which includes the above-described on-board DC / DC converter.

[0122] In actual implementation, the control unit 330 can be implemented as a digital control unit such as a DSP or MCU.

[0123] Although embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the present disclosure as defined by the appended claims.

[0124] Furthermore, the scope of this application is not intended to be limited to the specific embodiments of the processes, machines, manufactures, compositions of matter, apparatuses, methods, and steps described in the specification. As will be readily understood by those skilled in the art from the disclosure of this publication, processes, machines, manufactures, compositions of matter, means, methods, or steps that perform substantially the same function, currently exist or will be developed or implemented thereafter, will yield substantially the same results as the corresponding embodiments described herein that are available according to this disclosure. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, apparatuses, methods, or steps within their scope.

Claims

1. An active discharge method for a high-voltage DC bus in an on-board DC / DC converter, wherein the on-board DC / DC converter includes a cascaded high-voltage bidirectional DC / DC converter and a low-voltage DC / DC converter, the high-voltage bidirectional DC / DC converter comprising: A primary-side switching unit includes at least one switching transistor, with its first end connected to a first capacitor and its second end connected to the primary winding of a first transformer. A secondary-side switching unit includes at least one switching transistor, with a first terminal connected to the secondary winding of the first transformer and a second terminal connected to the high-voltage DC bus voltage; the low-voltage DC / DC converter includes: a primary-side switching unit, including at least one switching transistor, with a first terminal connected to the high-voltage DC bus voltage and a second terminal connected to the primary winding of the second transformer; a secondary-side switching unit, including at least one switching transistor, with a first terminal connected to the secondary winding of the second transformer and a second terminal connected to a low-voltage battery, characterized in that it includes: S1: Received active discharge command; S2: Obtain the high voltage DC bus voltage value VC2 on the high voltage DC bus through the detection circuit; S3: Determine whether the high voltage DC bus voltage value VC2 is greater than the active discharge voltage setting value. If so, proceed to step S4. S4: Control the high-voltage bidirectional DC / DC converter and the low-voltage DC / DC converter to work simultaneously, so as to discharge the electrical energy on the high-voltage DC bus to the first capacitor or consume it by the high-voltage bidirectional DC / DC converter, and discharge the electrical energy on the high-voltage DC bus to the low-voltage battery or consume it by the low-voltage DC / DC converter, and proceed to step S5; S5: Determine whether the high-voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value. If yes, the discharge ends; otherwise, proceed to step S4. The step S4 of controlling the operation of the high-voltage bidirectional DC / DC converter includes: S411: outputting a first switch control signal to the secondary side switch unit of the high-voltage bidirectional DC / DC converter, wherein the duty cycle of the first switch control signal is fixed and the frequency is a first switch frequency; S412: reducing the frequency of the first switch control signal from the first switch frequency to a second switch frequency within a first set time, while keeping the duty cycle fixed, and proceeding to step S5.

2. The active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to claim 1, characterized in that, If the determination is negative in step S3, proceed to step S5.

3. The active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to claim 1, characterized in that, After step S4, the method further includes: determining whether the decrease in the high voltage DC bus voltage value VC2 within a predetermined time interval is less than a set value; if not, then continue with step S4; if yes, then output an active discharge failure signal.

4. The active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to claim 1, characterized in that, The first switching frequency is high frequency, and the second switching frequency is low frequency.

5. The active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to claim 1, characterized in that, Step S4, controlling the operation of the low-voltage DC / DC converter, includes: S421: Obtain the low-voltage battery voltage value E on the low-voltage battery, and determine whether the high-voltage DC bus voltage value VC2 is greater than or equal to 4*N2*E*k, where N2 is the turns ratio of the second transformer and k is the margin coefficient. If yes, proceed to step S422; if no, proceed to step S423. S422: Output a second switching control signal to the primary-side switching unit of the low-voltage DC / DC converter, wherein the duty cycle of the second switching control signal is... The frequency is the third switching frequency, and then proceed to steps S421 and S5; S423: Output a third switch control signal to the primary side switch unit of the low-voltage DC / DC converter, wherein the duty cycle of the third switch control signal is fixed and the frequency is the fourth switch frequency, wherein the third switch frequency is less than the fourth switch frequency, and proceed to step S5.

6. The active discharge method for the high-voltage DC bus in an on-board DC / DC converter according to claim 5, characterized in that, The third switching frequency is low frequency, and the fourth switching frequency is high frequency.

7. A vehicle-mounted DC / DC converter, characterized in that, include: High-voltage bidirectional DC / DC converter, including: A primary-side switching unit includes at least one switching transistor, with its first end connected to a first capacitor and its second end connected to the primary winding of a first transformer. The secondary-side switching unit includes at least one switching transistor, with its first end connected to the secondary winding of the first transformer and its second end connected to the high-voltage DC bus voltage. Low-voltage DC / DC converters, including: A primary-side switching unit includes at least one switching transistor, with its first end connected to the voltage of the high-voltage DC bus and its second end connected to the primary winding of the second transformer. The secondary-side switching unit includes at least one switching transistor, with its first end connected to the secondary winding of the second transformer and its second end connected to a low-voltage battery. A high-voltage DC bus voltage detection circuit is used to detect the voltage on the high-voltage DC bus and output the high-voltage DC bus voltage value VC2. A low-voltage battery voltage detection circuit is used to detect the voltage on the low-voltage battery and output the low-voltage battery voltage value E; The control unit receives the high-voltage DC bus voltage value VC2 and the low-voltage battery voltage value E, and executes the following after receiving the active discharge command: S3: Determine whether the high voltage DC bus voltage value VC2 is greater than the active discharge voltage setting value. If so, proceed to step S4. S4: Control the high-voltage bidirectional DC / DC converter and the low-voltage DC / DC converter to work simultaneously, so as to discharge the electrical energy on the high-voltage DC bus to the first capacitor or consume it by the high-voltage bidirectional DC / DC converter, and discharge the electrical energy on the high-voltage DC bus to the low-voltage battery or consume it by the low-voltage DC / DC converter, and proceed to step S5; S5: Determine whether the high-voltage DC bus voltage value VC2 is less than or equal to the active discharge voltage setting value. If yes, the discharge ends; otherwise, proceed to step S4. The step S4 of controlling the operation of the high-voltage bidirectional DC / DC converter includes: S411: outputting a first switch control signal to the secondary side switch unit of the high-voltage bidirectional DC / DC converter, wherein the duty cycle of the first switch control signal is fixed and the frequency is a first switch frequency; S412: reducing the frequency of the first switch control signal from the first switch frequency to a second switch frequency within a first set time, while keeping the duty cycle fixed, and proceeding to step S5.

8. The vehicle-mounted DC / DC converter according to claim 7, characterized in that, Step S4, controlling the operation of the low-voltage DC / DC converter, includes: S421: Obtain the low-voltage battery voltage value E on the low-voltage battery, and determine whether the high-voltage DC bus voltage value VC2 is greater than or equal to 4*N2*E*k, where N2 is the turns ratio of the second transformer and k is the margin coefficient. If yes, proceed to step S422; if no, proceed to step S423. S422: Output a second switching control signal to the primary-side switching unit of the low-voltage DC / DC converter, wherein the duty cycle of the second switching control signal is... The frequency is the third switching frequency, and then proceed to steps S421 and S5; S423: Output a third switch control signal to the primary side switch unit of the low-voltage DC / DC converter, wherein the duty cycle of the third switch control signal is fixed and the frequency is the fourth switch frequency, wherein the third switch frequency is less than the fourth switch frequency, and proceed to step S5.

9. An electric vehicle, characterized in that, include: The vehicle-mounted DC / DC converter as described in claim 7 or 8.

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