Soft start control method and system of CLLC resonant converter and automobile

Abstract

The application discloses a soft start control method and system of a CLLC resonant converter and an automobile. The method comprises the following steps: generating a square wave signal during the start process of the CLLC resonant converter; wherein the duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter; controlling the first H-bridge circuit based on the square wave signal to charge the second filter capacitor, so that the voltage across the second filter capacitor gradually rises to a target voltage. The control method controls the soft start of the CLLC resonant converter based on the square wave signal with a fixed duty cycle and a fixed frequency, greatly simplifies the start control process of the CLLC resonant converter, and effectively limits the current on the primary side and the secondary side of the CLLC resonant converter during the soft start process due to the small duty cycle and frequency of the square wave signal, thereby avoiding the generation of a large impact current.

Description

Technical Field

[0001] This application relates to the field of resonant converter control technology, and in particular to a soft-start control method, system and automobile for a CLLC resonant converter. Background Technology

[0002] CLLC resonant converters fully utilize the resonant characteristics of the resonant cavity to achieve soft switching of the switching transistors, greatly improving the power density of the converter. They are widely used in distributed microgrids, electric vehicles, and energy storage components.

[0003] The CLLC circuit has a symmetrical structure, requiring no additional buffer circuitry. Power can flow bidirectionally, and its operating characteristics are equivalent to an LLC resonant converter in both forward and reverse operation. Furthermore, the resonant characteristics of the resonant cavity can be used to achieve ZVS and ZCS of the switching transistors. The converter employs a high-frequency transformer; as the frequency increases, it helps to reduce the converter's size. In practical applications, magnetic integration technology is often used, employing the transformer's leakage inductance as the primary resonant inductor, further increasing power density. Simultaneously, through the resonant network, the current flowing through the high-frequency transformer can be made sinusoidal, which helps reduce eddy current losses and converter transmission losses.

[0004] The output of a CLLC resonant converter is filtered by a capacitor, which in practice has a relatively large capacitance. During circuit startup, the output voltage is zero, and the entire bridge arm voltage is applied to the resonant cavity, resulting in a large inrush current. Therefore, a reliable soft-start control strategy is necessary to ensure safe startup of the converter. Traditional methods include series resistors or adding auxiliary windings, which increase component costs. Methods without adding components include frequency-adjusted duty cycle startup, where the switching frequency or duty cycle needs to be continuously changed during startup, making control complex. Summary of the Invention

[0005] In view of the above-mentioned problems existing in the prior art, this application provides a soft-start control method, system and vehicle for a CLLC resonant converter. The technical solution adopted in the embodiments of this application is as follows:

[0006] A soft-start control method for a CLLC resonant converter, the CLLC resonant converter including a first filter capacitor, a first H-bridge circuit, and a first resonant circuit located on the primary side, a second resonant circuit, a second H-bridge circuit, and a second filter capacitor located on the secondary side, and transformers connected to the primary side and the secondary side respectively, the method comprising:

[0007] During the startup process of the CLLC resonant converter, a square wave signal is generated; wherein, the duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter;

[0008] The first H-bridge circuit is controlled by the square wave signal to charge the second filter capacitor, so that the voltage across the second filter capacitor gradually increases to the target voltage.

[0009] In some embodiments, the first H-bridge circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to form a first branch, and the two ends of the first branch are respectively connected to the positive and negative terminals of the power supply. The third switch and the fourth switch are connected in series to form a second branch, and the second branch is connected in parallel with the first branch.

[0010] The control period of the CLLC resonant converter includes a positive half-cycle and a negative half-cycle;

[0011] The control of the first H-bridge circuit based on the square wave signal includes:

[0012] During the positive half-cycle, the square wave signal is sent to the first switch and the fourth switch, and during the negative half-cycle, the square wave signal is sent to the second switch and the third switch, so as to form four modes respectively during the positive half-cycle and the negative half-cycle;

[0013] The phases of the four modes in the positive half-cycle are opposite to the phases of the four modes in the negative half-cycle.

[0014] In some embodiments, the method further includes:

[0015] Obtain the attribute parameters of the electronic components of the CLLC resonant converter;

[0016] Based on the attribute parameters, the duty cycle of the square wave signal is determined.

[0017] In some embodiments, determining the duty cycle of the square wave signal based on the attribute parameters includes:

[0018] Based on the attribute parameters, construct the modal equations for the four modes of the positive half-cycle and / or the four modes of the negative half-cycle;

[0019] Based on the modal equations, and the first and second constraints, the duration of the first mode among the four modes is determined at least. The first constraint includes that the current on the primary side and the current on the secondary side are both less than the withstand current of the CLLC resonant converter, and that the voltage of the first resonant capacitor in the first resonant circuit and the voltage of the second resonant capacitor in the second resonant circuit are both less than the withstand voltage of the CLLC resonant converter. The second constraint includes maximizing the charging current of the second filter capacitor while satisfying the first constraint.

[0020] The duration of the first mode is used as the proportion of the control cycle to determine the duty cycle of the square wave signal.

[0021] In some embodiments, determining the duration of the first mode among at least four modes based on the modal equations, the first constraint, and the second constraint includes:

[0022] Based on the modal equations, the following set of equations is obtained, and based on the set of equations, the first constraint condition, and the second constraint condition, the duration of the first mode is determined;

[0023]

[0024] Among them, i p，A (0) represents the current on the primary side at the start of the first mode; i p，C (φ3) represents the current on the primary side at the end of the third mode; i s，A (0) represents the current on the secondary side at the start of the first mode; i s，D (φ4) represents the current on the secondary side at the end of the fourth mode; i p，A (φ1) represents the current on the primary side at the end of the first mode; i p，B (0) represents the current on the primary side at the start of the second mode; i s，A (φ1) represents the current on the secondary side at the end of the first mode; i s，B (0) represents the current on the secondary side at the start of the second mode; i p，B (φ2) represents the current on the primary side at the end of the second mode; i p，D (0) represents the current on the primary side at the start of the fourth mode; i s，B (φ2) represents the current on the secondary side at the end of the second mode; i s，C (0) represents the current on the secondary side at the start of the third mode; i s，C (φ3) represents the current on the secondary side at the end of the third mode; i s，D (0) represents the current on the secondary side at the start of the fourth mode; i p，C (0) represents the current on the primary side at the start of the third mode;

[0025] u cr1A (0) represents the voltage across the first resonant capacitor at the start of the first mode; u cr1，D (φ4) represents the voltage across the first resonant capacitor at the end of the fourth mode; u cr2，A (0) represents the voltage across the second resonant capacitor at the start of the first mode; ucr2，D (φ4) represents the voltage across the second resonant capacitor at the end of the fourth mode; u cr1，A (φ1) represents the voltage across the first resonant capacitor at the end of the first mode; u cr1，B (0) represents the voltage across the first resonant capacitor at the start of the second mode; u cr2，A (φ1) represents the voltage across the second resonant capacitor at the end of the first mode; u cr2，B (0) represents the voltage across the second resonant capacitor at the start of the second mode; u cr1，B (φ2) represents the voltage across the first resonant capacitor at the end of the second mode; u cr1，C (0) represents the voltage across the first resonant capacitor at the start of the third mode; u cr2，B (φ2) represents the voltage across the second resonant capacitor at the end of the second mode; u cr2，C (0) represents the voltage across the second resonant capacitor at the start of the third mode; u cr2，C (φ3) represents the voltage across the second resonant capacitor at the end of the third mode; u cr2D (0) represents the voltage across the second resonant capacitor at the start of the fourth mode;

[0026] φ1 represents the duration of the first mode; φ2 represents the duration of the second mode; φ3 represents the duration of the third mode; φ4 represents the duration of the fourth mode; T represents the control period.

[0027] Another embodiment of this application provides a soft-start control system for a CLLC resonant converter, including a CLLC resonant converter and a controller; the CLLC resonant converter includes a first filter capacitor, a first H-bridge circuit and a first resonant circuit located on the primary side, a second resonant circuit, a second H-bridge circuit and a second filter capacitor located on the secondary side, and a transformer connecting the primary side and the secondary side;

[0028] The controller is configured as follows:

[0029] During the startup process of the CLLC resonant converter, a square wave signal is generated; wherein, the duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter;

[0030] The first H-bridge circuit is controlled by the square wave signal to charge the second filter capacitor, so that the voltage across the second filter capacitor gradually increases to the target voltage.

[0031] In some embodiments, the first H-bridge circuit includes a first switch, a second switch, a third switch, and a fourth switch, and the first filter capacitor is connected in parallel with the first H-bridge circuit;

[0032] The first resonant circuit includes a first resonant inductor and a first resonant capacitor. The first resonant inductor, the first resonant capacitor and the primary coil of the transformer are connected in series, and the magnetizing inductance of the transformer is connected in parallel with the primary coil.

[0033] The second H-bridge circuit includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch, and the second filter capacitor is connected in parallel with the second H-bridge circuit;

[0034] The second resonant circuit includes a second resonant inductor and a second resonant capacitor, and the second resonant inductor, the second resonant capacitor and the secondary coil of the transformer are connected in series.

[0035] In some embodiments, the first H-bridge circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to form a first branch, and the two ends of the first branch are respectively connected to the positive and negative terminals of the power supply. The third switch and the fourth switch are connected in series to form a second branch, and the second branch is connected in parallel with the first branch.

[0036] The control period of the CLLC resonant converter includes a positive half-cycle and a negative half-cycle;

[0037] The controller is specifically configured as follows:

[0038] During the positive half-cycle, the square wave signal is sent to the first switch and the fourth switch, and during the negative half-cycle, the square wave signal is sent to the second switch and the third switch, so as to form four modes respectively during the positive half-cycle and the negative half-cycle;

[0039] The phases of the four modes in the positive half-cycle are opposite to the phases of the four modes in the negative half-cycle.

[0040] In some embodiments, the controller is further configured to:

[0041] Obtain the attribute parameters of the electronic components of the CLLC resonant converter;

[0042] Based on the attribute parameters, the duty cycle of the square wave signal is determined.

[0043] In some embodiments, the controller is specifically configured as follows:

[0044] Based on the attribute parameters, construct the modal equations for the four modes of the positive half-cycle and / or the four modes of the negative half-cycle;

[0045] Based on the modal equations, and the first and second constraints, the duration of the first mode among the four modes is determined at least. The first constraint includes that the current on the primary side and the current on the secondary side are both less than the withstand current of the CLLC resonant converter, and that the voltage of the first resonant capacitor in the first resonant circuit and the voltage of the second resonant capacitor in the second resonant circuit are both less than the withstand voltage of the CLLC resonant converter. The second constraint includes maximizing the charging current of the second filter capacitor while satisfying the first constraint.

[0046] The duration of the first mode is used as the proportion of the control cycle to determine the duty cycle of the square wave signal.

[0047] In another aspect, this application provides a vehicle including a soft-start control system for a CLLC resonant converter as described above.

[0048] The control method of this application embodiment controls the soft start of the CLLC resonant converter based on a square wave signal with a fixed duty cycle and a fixed frequency, which greatly simplifies the start-up control process of the CLLC resonant converter. Furthermore, since the duty cycle and frequency of the square wave signal are relatively small, it can effectively limit the current on the primary and secondary sides during the soft start-up process of the CLLC resonant converter, thus avoiding the generation of large inrush current. Attached Figure Description

[0049] Figure 1 This is a circuit schematic diagram of the CLLC resonant converter in the control system of this application embodiment;

[0050] Figure 2 This is a flowchart of the control method according to an embodiment of this application;

[0051] Figure 3 Modal waveform diagram for control period;

[0052] Figure 4 This is the circuit schematic for the first mode;

[0053] Figure 5 This is the circuit schematic for the second mode;

[0054] Figure 6 and Figure 7 The circuit schematics are for the two time ranges of the third mode, respectively.

[0055] Figure 8 This is the circuit schematic for the fourth mode;

[0056] Figure 9 The graph shows the input and output voltages during the soft-start process of the CLLC resonant converter.

[0057] Figure 10 This is a schematic diagram of the simulation results of the modal waveforms during the soft-start process of the CLLC resonant converter. Detailed Implementation

[0058] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0059] It should be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be considered as limiting, but merely as an example of embodiments. Other modifications within the scope and spirit of this application will be apparent to those skilled in the art.

[0060] The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.

[0061] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0062] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application.

[0063] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.

[0064] Specific embodiments of this application are described thereafter with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to avoid unnecessary or redundant details that could obscure the application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in a variety of substantially any suitable detailed structures.

[0065] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.

[0066] This application provides a soft-start control method for a CLLC resonant converter. See also... Figure 1As shown, the CLLC resonant converter may include a first filter capacitor C located on the primary side. in The first H-bridge circuit 10 and the first resonant circuit 20, the second resonant circuit 40, the second H-bridge circuit 50, and the second filter capacitor C located on the secondary side. out , and transformers 30 connected to the primary side and secondary side respectively.

[0067] First filter capacitor C in The two ends are connected to the positive and negative terminals of the power supply, respectively, and the first filter capacitor C in It is connected in parallel with the first H-bridge circuit 10.

[0068] The first H-bridge circuit 10 includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch are connected in series to form a first branch, and the two ends of the first branch are connected to the positive and negative terminals of the power supply, respectively. The third switch S3 and the fourth switch S4 are connected in series to form a second branch, and the second branch is connected in parallel with the first branch.

[0069] The first resonant circuit 20 includes a first resonant inductor L. r1 and the first resonant capacitor C r1 The first resonant inductor L r1 First resonant capacitor C r1 The primary coil of transformer 30 is connected in series to form a third branch. One end of the third branch is connected between the first switch S1 and the second switch S2, and the other end of the third branch is connected between the third switch S3 and the fourth switch S4. The magnetizing inductance Lm of transformer 30 is connected in parallel with the primary coil.

[0070] The second H-bridge circuit 50 includes a fifth switch S5, a sixth switch S6, a seventh switch S7, and an eighth switch S8. The fifth switch S5 and the sixth switch S6 are connected in series to form a fourth branch. The two ends of the fourth branch are respectively connected to the second filter capacitor C. out The two ends are connected, and the seventh switch S7 and the eighth switch S8 are connected in series to form the fifth branch, which is connected in parallel with the fourth branch. Moreover, each switch in the first H-bridge circuit 10 and the second H-bridge circuit 50 is equipped with a body diode.

[0071] The second resonant circuit 40 includes a second resonant inductor L. r2 Second resonant capacitor C r2 The second resonant inductor L r2 Second resonant capacitor C r2 The secondary coil of transformer 30 is connected in series to form the sixth branch. One end of the sixth branch is connected between the fifth switch S5 and the sixth switch S6, and the other end of the sixth branch is connected between the seventh switch S7 and the eighth switch S8.

[0072] It should be noted that the above-described CLLC resonant converter is merely an example, and CLLC resonant converters may also include other electronic components.

[0073] Figure 2 This is a flowchart of the soft-start control method for the CLLC resonant converter according to an embodiment of this application. See also... Figure 2 As shown, the control method in this application embodiment may specifically include the following steps:

[0074] S110 generates a square wave signal during the startup process of the CLLC resonant converter. The duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter.

[0075] The duty cycle and frequency of the square wave signal can be pre-configured preferred duty cycle and frequency, or they can be preferred duty cycle and frequency calculated in real time upon receiving a control command to indicate the start of the CLLC resonant converter. However, regardless of whether they are pre-set fixed values ​​or obtained through real-time calculation after receiving the control command, the duty cycle and frequency of the square wave signal do not change during the soft start process of the CLLC resonant converter.

[0076] Optionally, upon receiving a control command to instruct the CLLC resonant converter to start, the controller can generate the square wave signal based on a preset duty cycle and frequency, or based on a calculated duty cycle and frequency.

[0077] S120, based on the square wave signal, controls the first H-bridge circuit 10, and uses the second filter capacitor C as the second filter capacitor C. out Charging causes the second filter capacitor C to... out The voltage across the terminals gradually increases to the target voltage.

[0078] The square wave signal has high and low levels. Sending the square wave signal to the switching transistor in the first H-bridge circuit 10 can control the switching transistor's on / off state, thereby connecting or disconnecting the CLLC resonant converter from the power supply, and thus serving as the second filter capacitor C. out Charge.

[0079] The control cycle of the CLLC resonant converter includes a positive half-cycle and a negative half-cycle. During the positive half-cycle, square wave signals can be sent to the first switch S1 and the fourth switch S4. Taking the case where all switches in the first H-bridge circuit 10 are turned on when they receive a high-level signal as an example, the square wave signal can be configured to be high during the first time period of the positive half-cycle and low during the other time periods of the positive half-cycle.

[0080] During the first time interval of the positive half-cycle, the first switch S1 and the fourth switch S4 are turned on, while the second switch S2 and the third switch S3 are turned off. The input voltage on the primary side is the first resonant capacitor C. r1 Charging, such as Figure 4 As shown, the current on the primary side, the current on the secondary side, and the first resonant capacitor C r1 The voltage across the two ends and the second resonant capacitor C r2 The voltage at both ends gradually increases, thus forming the first mode, such as Figure 3 As shown in step A.

[0081] During the second time interval of the positive half-cycle, the square wave signal switches from high level to low level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all turned off, and the first resonant inductor L... r1 Under the freewheeling effect, the body diodes of the second switch S2 and the third switch S3 are turned on, which is equivalent to applying a voltage with the opposite phase to that in the first time period to the primary side, such as... Figure 5 As shown, the current on both the primary and secondary sides gradually decreases until it reaches the first resonant inductor L. r1 The freewheeling effect disappears, and the current on the original side gradually decreases to zero. The first resonant inductor L... r1 The voltage across the two ends and the second resonant inductor L r2 The voltage across the terminals continues to increase gradually, thus forming the second mode, such as Figure 3 As shown in step B.

[0082] During the third time interval of the positive half-cycle, the square wave signal is still at a low level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all off. The first resonant capacitor C... r1 Discharge begins, and the body diodes of the first switching transistor S1 and the second switching transistor S2 conduct, as... Figure 6 and Figure 7 As shown. The voltage applied to the primary side in this third time interval is in phase with the voltage applied to the primary side in the first time interval, but the current flow direction on the primary side in this third time interval is opposite to the current flow direction in the first time interval. The first resonant inductor L... r1 The voltage across the terminals gradually decreases. During the first time interval of the third time period, the current flow direction on the secondary side is the same as that in the second time period. The body diodes of the fifth switch S5 and the eighth switch S8 are turned on, acting as the second filter capacitor C. out Charging, as shown in Figure 6. The current on the secondary side gradually decreases to zero, and the second resonant inductor L... r2 The voltage across the terminals continues to rise gradually, as... Figure 3As shown in step C. During the second time range of the third time period, the current on the secondary side switches to the opposite direction to the first time range, and the body diodes of the sixth switch S6 and the seventh switch S7 are turned on to continue supplying power to the second filter capacitor C. out Charging, such as Figure 7 As shown. The second resonant inductor L r2 The voltage across the terminals gradually decreases, thus forming the third mode, such as Figure 3 As shown in step C.

[0083] During the fourth time interval of the positive half-cycle, the square wave signal is still at a low level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all off. The first resonant capacitor C... r1 After the discharge ends, the current on the primary side drops to near zero and oscillates, and the first resonant inductor L... r1 The voltage across the terminals also drops to near zero. The second resonant unit still participates in resonance, and the current flow direction on the secondary side is the same as the second time range of the third time period. The body diodes of the sixth switch S6 and the seventh switch S7 are turned on, as... Figure 8 As shown. The second resonant inductor L r2 The voltage across the terminals continues to gradually decrease until the positive half-cycle ends, forming the fourth mode, as shown below. Figure 3 As shown in step D.

[0084] During the negative half-cycle, sending square wave signals to the second switch S2 and the third switch S3 can also form four modes. However, the phases of the four modes in the negative half-cycle are exactly opposite to the phases of the four modes in the positive half-cycle. The specific process is similar to that in the positive half-cycle, and will not be repeated here.

[0085] The control method of this application embodiment controls the soft start of the CLLC resonant converter based on a square wave signal with a fixed duty cycle and a fixed frequency, which greatly simplifies the start-up control process of the CLLC resonant converter. Furthermore, since the duty cycle and frequency of the square wave signal are relatively small, it can effectively limit the current on the primary and secondary sides during the soft start-up process of the CLLC resonant converter, thus avoiding the generation of large inrush current.

[0086] In some embodiments, the method further includes:

[0087] S130: Obtain the property parameters of the electronic components of the CLLC resonant converter.

[0088] S140 determines the duty cycle of the square wave signal based on attribute parameters.

[0089] Optionally, the attribute parameters of the electronic components of the CLLC resonant converter may include the first resonant inductor L. r1 The inductance value L1 and the first resonant capacitor C r1The capacitance value C1 and the second resonant inductance L r2 The inductance value L2 and the second resonant capacitor C r2 The values ​​of C2, L3, and turns ratio of transformer 30, as well as the voltage withstand value and current withstand value of each electronic component, etc.

[0090] After obtaining the attribute parameters of the electronic components, the duty cycle of the square wave signal can be directly determined using optimization algorithms based on these parameters. Further processing of the attribute parameters is also possible; for example, the inductance ratio of a CLLC resonant converter can be calculated. And set the voltage output ratio That is, the output voltage U of the CLLC resonant converter out With input voltage U in The ratio of the two values ​​is then used. Subsequently, based on the processed data, an optimization algorithm is employed to determine the duty cycle of the square wave signal.

[0091] The optimization process can be executed after each soft start of the CLLC resonant converter, or it can be performed in advance by using the optimization process to determine the duty cycle of the square wave signal and configuring the duty cycle to the controller. When the soft start of the CLLC resonant converter is triggered, the controller generates a square wave signal based on the duty cycle.

[0092] In some embodiments, step S104, determining the duty cycle of the square wave signal based on attribute parameters, may include:

[0093] S141, based on the attribute parameters, construct the modal equations for the four modes of the positive half-cycle and / or the four modes of the negative half-cycle.

[0094] Since the four modes of the positive half-cycle correspond one-to-one with the four modes of the negative half-cycle, only with opposite phases, in practical implementation, it is sufficient to construct only the modal equations for the four modes of the positive half-cycle or the four modes of the negative half-cycle. Taking the positive half-cycle as an example, the modal equations for the four modes of the positive half-cycle are shown below.

[0095]

[0096] Among them, i p，A (φ) represents the current on the primary side in the first mode; φ represents the time variable; A1, A2, A3, and A4 are the mode coefficients of the first mode; i s，A (φ) represents the current on the secondary side in the first mode; u cr1,A (φ) represents the first resonant capacitance C in the first mode. r1 Voltage across the terminals; u cr2,A (φ) represents the voltage across the second resonant capacitor Cr2 in the first mode; k represents the inductance ratio of the CLLC resonant converter. M represents the voltage output ratio. U in U represents the input voltage of the CLLC resonant converter. ou t represents the output voltage of the CLLC resonant converter.

[0097]

[0098] Among them, i p,B (φ) represents the current on the primary side in the second mode; B1, B2, B3, and B4 are the mode coefficients of the second mode; i s,B (φ) represents the current on the secondary side in the second mode; u cr1,B (φ) represents the first resonant capacitance C in the second mode. r1 Voltage across the terminals; u cr2,B (φ) represents the second resonant capacitance C in the second mode. r2 The voltage at both ends.

[0099]

[0100] Among them, i p,C (φ) represents the current on the primary side in the third mode; C1, C2, C3, and C4 are the mode coefficients of the third mode; i s,C (φ) represents the current on the secondary side in the third mode; u cr1,C (φ) represents the first resonant capacitance C in the third mode. r1 Voltage across the terminals; u cr2,C (φ) represents the second resonant capacitance C in the third mode. r2 The voltage at both ends.

[0101]

[0102] Among them, i p，D (φ) represents the current on the primary side in the fourth mode; D1 and D2 are the mode coefficients of the fourth mode, respectively; i s，D (φ) represents the current on the secondary side in the fourth mode; u cr1,D (φ) represents the first resonant capacitance C in the fourth mode. r1 Voltage across the terminals; u cr2，D (φ) represents the second resonant capacitance C in the fourth mode. r2 The voltage at both ends.

[0103] S142, based on the modal equations and the first and second constraints, determine the duration of the first mode among at least four modes.

[0104] The first constraint includes that the current on the primary side and the current on the secondary side are both less than the withstand current of the CLLC resonant converter, and the first resonant capacitor C of the first resonant circuit 20. r1 The voltage of the second resonant circuit 40 and the second resonant capacitor C r2 The voltages of all components are less than the withstand voltage of the CLLC resonant converter. The withstand current of the CLLC resonant converter is the minimum withstand current of all electronic components in the CLLC resonant converter, and the withstand voltage of the CLLC resonant converter is the minimum withstand voltage of all electronic components in the CLLC resonant converter. The second constraint condition includes, on the basis of satisfying the first constraint condition, ensuring that the second filter capacitor C... out The charging current is maximized. That is, during soft-start, the current on both the primary and secondary sides must not exceed the withstand current of the CLLC resonant converter and the first resonant capacitor C. r1 The voltage and the second resonant capacitor C r2 Based on the premise that the voltages do not exceed the withstand voltage of the CLLC resonant converter, the modal equations are solved to determine the voltage that allows the second filter capacitor C to operate at its maximum capacity. out The duration of the first mode that maximizes the charging current.

[0105] Optionally, the following set of equations can be derived based on the modal equations, and the duration φ1 of the first mode can be determined based on the set of equations, the first constraint condition, and the second constraint condition.

[0106]

[0107] The meanings of the symbols in this system of equations are as follows.

[0108] Table 1

[0109]

[0110]

[0111] S143 uses the proportion of the duration of the first mode in the control cycle as the duty cycle of the square wave signal.

[0112] Optionally, the duty cycle of the square wave signal can be determined based on the following formula.

[0113] φ1=DT

[0114] Where D represents the duty cycle of the square wave signal.

[0115] The control method of this application embodiment will be described below with reference to a specific example.

[0116] The attribute parameters of the electronic components of the CLLC resonant converter are shown in Table 2.

[0117] Table 2

[0118] <![CDATA[First resonant inductor L r1 has an inductance value L1]]> 20.8uH <![CDATA[First resonant capacitor C r1 has a capacitance value C1]]> 54.12nF <![CDATA[Inductance value L3 of the magnetizing inductor Lm]]> 88.56uH <![CDATA[Second resonant inductor L r2 has an inductance value L2]]> 3.4uH <![CDATA[Second resonant capacitor C r2 capacitance value C2]]> 330.68nF Transformer 30 turns ratio § 17∶7

[0119] First, calculate the inductance ratio. The converter's rated input voltage is 750V, and its rated output voltage is 410V. The modal equations derived using the modal method are calculated under per-unit conditions. Therefore, the voltage and current withstand values ​​of the electronic components are per-unitized to obtain i. smax =0.6, and using this as the first constraint condition for solving the modal equation, the optimal control duty cycle of the square wave signal is obtained by substituting it into the duty cycle optimization algorithm, which is D = 0.117.

[0120] The PWM square wave signal generated based on the duty cycle is used to control the first H-bridge circuit 10 of the CLLC resonant converter, thereby realizing narrow pulse control soft start. Figure 9 The graph shows the input and output voltage curves during the soft-start process of a CLLC resonant converter. Figure 10 This is a schematic diagram of the simulation results of the modal waveforms during the soft-start process of the CLLC resonant converter. It can be seen that under the control of a PWM square wave signal with a duty cycle of 0.117, the CLLC resonant converter achieves the predetermined soft-start target. The current on the primary side and the second resonant capacitor C... r2 The voltage across the terminals gradually rises to a steady state within the tolerance value.

[0121] See Figure 1 As shown in the figure, this application embodiment also provides a soft-start control system for a CLLC resonant converter, which includes a CLLC resonant converter and a controller (not shown in the figure).

[0122] The CLLC resonant converter includes a first filter capacitor C located on the primary side. in The first H-bridge circuit 10 and the first resonant circuit 20, the second resonant circuit 40, the second H-bridge circuit 50, and the second filter capacitor C located on the secondary side. out , and transformer 30 connecting the primary side and the secondary side.

[0123] First filter capacitor C in The two ends are connected to the positive and negative terminals of the power supply, respectively, and the first filter capacitor C in It is connected in parallel with the first H-bridge circuit 10.

[0124] The first H-bridge circuit 10 includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch are connected in series to form a first branch, and the two ends of the first branch are connected to the positive and negative terminals of the power supply, respectively. The third switch S3 and the fourth switch S4 are connected in series to form a second branch, and the second branch is connected in parallel with the first branch.

[0125] The first resonant circuit 20 includes a first resonant inductor L. r1 and the first resonant capacitor C r1 The first resonant inductor L r1 First resonant capacitor C r1 The primary coil of transformer 30 is connected in series to form a third branch. One end of the third branch is connected between the first switch S1 and the second switch S2, and the other end of the third branch is connected between the third switch S3 and the fourth switch S4. The magnetizing inductance Lm of transformer 30 is connected in parallel with the primary coil.

[0126] The second H-bridge circuit 50 includes a fifth switch S5, a sixth switch S6, a seventh switch S7, and an eighth switch S8. The fifth switch S5 and the sixth switch S6 are connected in series to form a fourth branch. The two ends of the fourth branch are respectively connected to the second filter capacitor C. out The two ends are connected, and the seventh switch S7 and the eighth switch S8 are connected in series to form the fifth branch, which is connected in parallel with the fourth branch. Moreover, each switch in the first H-bridge circuit 10 and the second H-bridge circuit 50 is equipped with a body diode.

[0127] The second resonant circuit 40 includes a second resonant inductor L. r2 Second resonant capacitor C r2 The second resonant inductor L r2 Second resonant capacitor C r2 The secondary coil of transformer 30 is connected in series to form the sixth branch. One end of the sixth branch is connected between the fifth switch S5 and the sixth switch S6, and the other end of the sixth branch is connected between the seventh switch S7 and the eighth switch S8.

[0128] It should be noted that the above-described CLLC resonant converter is merely an example, and CLLC resonant converters may also include other electronic components.

[0129] The controller is configured to generate a square wave signal during the startup process of the CLLC resonant converter; wherein the duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter; and to control the first H-bridge circuit 10 based on the square wave signal, which is the second filter capacitor C. out Charge the second filter capacitor C. outThe voltage across the terminals gradually increases to the target voltage.

[0130] The duty cycle and frequency of the square wave signal can be pre-configured preferred duty cycle and frequency, or they can be preferred duty cycle and frequency calculated in real time upon receiving a control command to indicate the start of the CLLC resonant converter. However, regardless of whether they are pre-set fixed values ​​or obtained through real-time calculation after receiving the control command, the duty cycle and frequency of the square wave signal do not change during the soft start process of the CLLC resonant converter.

[0131] Optionally, when the controller receives a control command to instruct the CLLC resonant converter to start, it can generate the square wave signal based on a preset duty cycle and frequency, or based on a calculated duty cycle and frequency.

[0132] The square wave signal has high and low levels. The controller sends the square wave signal to the switching transistor in the first H-bridge circuit 10, which controls the switching transistor's on / off state, thereby connecting or disconnecting the CLLC resonant converter from the power supply, and thus serving as the second filter capacitor C. out Charge.

[0133] The control cycle of the CLLC resonant converter includes a positive half-cycle and a negative half-cycle. During the positive half-cycle, the controller can send square wave signals to the first switch S1 and the fourth switch S4. Taking the case where all switches in the first H-bridge circuit 10 are turned on when they receive a high-level signal as an example, the square wave signal can be configured to be high during the first time period of the positive half-cycle and low during the other time periods of the positive half-cycle.

[0134] During the first time interval of the positive half-cycle, the first switch S1 and the fourth switch S4 are turned on, while the second switch S2 and the third switch S3 are turned off. The input voltage on the primary side is the first resonant capacitor C. r1 Charging, such as Figure 4 As shown, the current on the primary side, the current on the secondary side, and the first resonant capacitor C r1 The voltage across the two ends and the second resonant capacitor C r2 The voltage at both ends gradually increases, thus forming the first mode, such as Figure 3 As shown in step A.

[0135] During the second time interval of the positive half-cycle, the square wave signal switches from high level to low level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all turned off, and the first resonant inductor L... r1 Under the freewheeling effect, the body diodes of the second switch S2 and the third switch S3 are turned on, which is equivalent to applying a voltage with the opposite phase to that in the first time period to the primary side, such as... Figure 5As shown, the current on both the primary and secondary sides gradually decreases until it reaches the first resonant inductor L. r1 The freewheeling effect disappears, and the current on the original side gradually decreases to zero. The first resonant inductor L... r1 The voltage across the two ends and the second resonant inductor L r2 The voltage across the terminals continues to increase gradually, thus forming the second mode, such as Figure 3 As shown in step B.

[0136] During the third time interval of the positive half-cycle, the square wave signal is still at a low level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all off. The first resonant capacitor C... r1 Discharge begins, and the body diodes of the first switching transistor S1 and the second switching transistor S2 conduct, as... Figure 6 and Figure 7 As shown. The voltage applied to the primary side in this third time interval is in phase with the voltage applied to the primary side in the first time interval, but the current flow direction on the primary side in this third time interval is opposite to the current flow direction in the first time interval. The first resonant inductor L... r1 The voltage across the terminals gradually decreases. During the first time interval of the third time period, the current flow direction on the secondary side is the same as that in the second time period. The body diodes of the fifth switch S5 and the eighth switch S8 are turned on, acting as the second filter capacitor C. out Charging, as shown in Figure 6. The current on the secondary side gradually decreases to zero, and the second resonant inductor L... r2 The voltage across the terminals continues to rise gradually, as... Figure 3 As shown in step C. During the second time range of the third time period, the current on the secondary side switches to the opposite direction to the first time range, and the body diodes of the sixth switch S6 and the seventh switch S7 are turned on to continue supplying power to the second filter capacitor C. out Charging, such as Figure 7 As shown. The second resonant inductor L r2 The voltage across the terminals gradually decreases, thus forming the third mode, such as Figure 3 As shown in step C.

[0137] During the fourth time interval of the positive half-cycle, the square wave signal is still at a low level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all off. The first resonant capacitor C... r1 After the discharge ends, the current on the primary side drops to near zero and oscillates, and the first resonant inductor L... r1 The voltage across the terminals also drops to near zero. The second resonant unit still participates in resonance, and the current flow direction on the secondary side is the same as the second time range of the third time period. The body diodes of the sixth switch S6 and the seventh switch S7 are turned on, as... Figure 8As shown. The second resonant inductor L r2 The voltage across the terminals continues to gradually decrease until the positive half-cycle ends, forming the fourth mode, as shown below. Figure 3 As shown in step D.

[0138] During the negative half-cycle, sending square wave signals to the second switch S2 and the third switch S3 can also form four modes. However, the phases of the four modes in the negative half-cycle are exactly opposite to the phases of the four modes in the positive half-cycle. The specific process is similar to that in the positive half-cycle, and will not be repeated here.

[0139] The control system of this application embodiment controls the soft start of the CLLC resonant converter based on a square wave signal with a fixed duty cycle and a fixed frequency, which greatly simplifies the start-up control process of the CLLC resonant converter. Furthermore, since the duty cycle and frequency of the square wave signal are relatively small, it can effectively limit the current on the primary and secondary sides during the soft start-up process of the CLLC resonant converter, thus avoiding the generation of large inrush current.

[0140] In some embodiments, the controller is further configured to:

[0141] Obtain the property parameters of the electronic components of the CLLC resonant converter;

[0142] The duty cycle of the square wave signal is determined based on the attribute parameters.

[0143] In some embodiments, the controller is specifically configured as follows:

[0144] Based on the attribute parameters, construct the modal equations for the four modes of the positive half-cycle and / or the four modes of the negative half-cycle;

[0145] Based on the modal equations, and the first and second constraints, the duration of the first mode among the four modes is determined at least. The first constraint includes that both the current on the primary side and the current on the secondary side are less than the withstand current of the CLLC resonant converter, and the first resonant capacitor C of the first resonant circuit 20... r1 The voltage of the second resonant circuit 40 and the second resonant capacitor C r2 The voltages are all less than the withstand voltage of the CLLC resonant converter; the second constraint condition includes, on the basis of satisfying the first constraint condition, ensuring that the second filter capacitor C out Maximize the charging current;

[0146] The duration of the first mode within the control cycle is used as the duty cycle of the square wave signal.

[0147] This application also provides a vehicle that includes a soft-start control system for a CLLC resonant converter as described in any of the preceding embodiments. Since the above control system can avoid inrush current during the soft-start process of the CLLC resonant converter and has a relatively simple control flow, the vehicle using this control system also has the aforementioned advantages.

[0148] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A soft-start control method for a CLLC resonant converter, characterized in that, The CLLC resonant converter includes a first filter capacitor, a first H-bridge circuit, and a first resonant circuit located on the primary side; a second resonant circuit, a second H-bridge circuit, and a second filter capacitor located on the secondary side; and transformers connected to the primary side and the secondary side respectively. The method includes: During the startup process of the CLLC resonant converter, a square wave signal is generated; wherein, the duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter. Based on the square wave signal, the first H-bridge circuit is controlled to charge the second filter capacitor so that the voltage across the second filter capacitor gradually increases to the target voltage. The first H-bridge circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to form a first branch, and the two ends of the first branch are connected to the positive and negative terminals of the power supply, respectively. The third switch and the fourth switch are connected in series to form a second branch, and the second branch is connected in parallel with the first branch. The control period of the CLLC resonant converter includes a positive half-cycle and a negative half-cycle; The control of the first H-bridge circuit based on the square wave signal includes: During the positive half-cycle, the square wave signal is sent to the first switch and the fourth switch, and during the negative half-cycle, the square wave signal is sent to the second switch and the third switch, so as to form four modes respectively during the positive half-cycle and the negative half-cycle; The phases of the four modes in the positive half-cycle are opposite to the phases of the four modes in the negative half-cycle. The method further includes: Obtain the attribute parameters of the electronic components of the CLLC resonant converter; Based on the attribute parameters, the duty cycle of the square wave signal is determined; Determining the duty cycle of the square wave signal based on the attribute parameters includes: Based on the attribute parameters, construct the modal equations for the four modes of the positive half-cycle and / or the four modes of the negative half-cycle; Based on the modal equations, and the first and second constraints, the duration of the first mode among the four modes is determined at least. The first constraint includes that the current on the primary side and the current on the secondary side are both less than the withstand current of the CLLC resonant converter, and that the voltage of the first resonant capacitor in the first resonant circuit and the voltage of the second resonant capacitor in the second resonant circuit are both less than the withstand voltage of the CLLC resonant converter. The second constraint includes maximizing the charging current of the second filter capacitor while satisfying the first constraint. The duration of the first mode is used as the proportion of the control cycle to determine the duty cycle of the square wave signal.

2. The method according to claim 1, characterized in that, The determination of the duration of the first mode among at least four modes based on the modal equations, the first constraint, and the second constraint includes: Based on the modal equations, the following set of equations is obtained, and based on the set of equations, the first constraint condition, and the second constraint condition, the duration of the first mode is determined; in, This represents the current on the primary side at the start of the first mode; This represents the current on the primary side at the end of the third mode; This represents the current on the secondary side at the start of the first mode; This represents the current on the secondary side at the end of the fourth mode; This represents the current on the primary side at the end of the first mode; This represents the current on the primary side at the start of the second mode; This represents the current on the secondary side at the end of the first mode; This represents the current on the secondary side at the start of the second mode; This represents the current on the primary side at the end of the second mode; This represents the current on the primary side at the start of the fourth mode; This represents the current on the secondary side at the end of the second mode; This represents the current on the secondary side at the start of the third mode; This represents the current on the secondary side at the end of the third mode; This represents the current on the secondary side at the start of the fourth mode; This represents the current on the primary side at the start of the third mode; This represents the voltage across the first resonant capacitor at the start of the first mode; This represents the voltage across the first resonant capacitor at the end of the fourth mode; This represents the voltage across the second resonant capacitor at the start of the first mode; This represents the voltage across the second resonant capacitor at the end of the fourth mode; This represents the voltage across the first resonant capacitor at the end of the first mode; This represents the voltage across the first resonant capacitor at the start of the second mode; This represents the voltage across the second resonant capacitor at the end of the first mode; This represents the voltage across the second resonant capacitor at the start of the second mode; This represents the voltage across the first resonant capacitor at the end of the second mode; This represents the voltage across the first resonant capacitor at the start of the third mode; This represents the voltage across the second resonant capacitor at the end of the second mode; This represents the voltage across the second resonant capacitor at the start of the third mode; This represents the voltage across the second resonant capacitor at the end of the third mode; This represents the voltage across the second resonant capacitor at the start of the fourth mode; Indicates the duration of the first mode; Indicates the duration of the second mode; Indicates the duration of the third mode; The duration of the fourth mode is represented by T; the control period is represented by T.

3. A soft-start control system for a CLLC resonant converter, characterized in that, The system includes a CLLC resonant converter and a controller; the CLLC resonant converter includes a first filter capacitor, a first H-bridge circuit and a first resonant circuit located on the primary side, a second resonant circuit, a second H-bridge circuit and a second filter capacitor located on the secondary side, and a transformer connecting the primary side and the secondary side; The controller is configured as follows: During the startup process of the CLLC resonant converter, a square wave signal is generated; wherein, the duty cycle of the square wave signal is fixed and less than 50%, and the frequency of the square wave signal is fixed and lower than the resonant frequency of the CLLC resonant converter. Based on the square wave signal, the first H-bridge circuit is controlled to charge the second filter capacitor so that the voltage across the second filter capacitor gradually increases to the target voltage. The first H-bridge circuit includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to form a first branch, and the two ends of the first branch are connected to the positive and negative terminals of the power supply, respectively. The third switch and the fourth switch are connected in series to form a second branch, and the second branch is connected in parallel with the first branch. The control period of the CLLC resonant converter includes a positive half-cycle and a negative half-cycle; The controller is specifically configured as follows: During the positive half-cycle, the square wave signal is sent to the first switch and the fourth switch, and during the negative half-cycle, the square wave signal is sent to the second switch and the third switch, so as to form four modes respectively during the positive half-cycle and the negative half-cycle; The phases of the four modes in the positive half-cycle are opposite to the phases of the four modes in the negative half-cycle. The controller is also configured to: Obtain the attribute parameters of the electronic components of the CLLC resonant converter; Based on the attribute parameters, the duty cycle of the square wave signal is determined; The controller is specifically configured as follows: Based on the attribute parameters, construct the modal equations for the four modes of the positive half-cycle and / or the four modes of the negative half-cycle; Based on the modal equations, and the first and second constraints, the duration of the first mode among the four modes is determined at least. The first constraint includes that the current on the primary side and the current on the secondary side are both less than the withstand current of the CLLC resonant converter, and that the voltage of the first resonant capacitor in the first resonant circuit and the voltage of the second resonant capacitor in the second resonant circuit are both less than the withstand voltage of the CLLC resonant converter. The second constraint includes maximizing the charging current of the second filter capacitor while satisfying the first constraint. The duration of the first mode is used as the proportion of the control cycle to determine the duty cycle of the square wave signal.

4. The system according to claim 3, characterized in that, The first H-bridge circuit includes a first switch, a second switch, a third switch, and a fourth switch, and the first filter capacitor is connected in parallel with the first H-bridge circuit; The first resonant circuit includes a first resonant inductor and a first resonant capacitor. The first resonant inductor, the first resonant capacitor and the primary coil of the transformer are connected in series, and the magnetizing inductance of the transformer is connected in parallel with the primary coil. The second H-bridge circuit includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch, and the second filter capacitor is connected in parallel with the second H-bridge circuit; The second resonant circuit includes a second resonant inductor and a second resonant capacitor, and the second resonant inductor, the second resonant capacitor and the secondary coil of the transformer are connected in series.

5. A car, characterized in that, Includes a soft-start control system for the CLLC resonant converter as described in claim 3 or 4.

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