Reverse pre-charging method and reverse pre-charging system of resonant converter

Abstract

The embodiment of the invention discloses a reverse pre-charging method and a reverse pre-charging system of a resonant converter, which are used for the technical field of power control. The method comprises the following steps: acquiring the start-up frequency of the resonant converter when the current of a low-voltage side switching tube of the resonant converter reaches the minimum value in the pre-charging start-up process; the resonant converter is controlled to perform pre-charging start-up at the start-up frequency, the low-voltage side switch tube is turned off when the current reaches the minimum value, the turn-off current of the low-voltage side switch tube is small, and hard turn-off of the low-voltage side switch tube is avoided; in a frequency raising process after the resonant converter is pre-charged and started, an inverter bridge output voltage at a high-voltage side of the resonant converter is controlled to perform external phase shift based on a preset phase lag value so as to lag the phase of a resonant capacitor voltage at the high-voltage side, and when a switch tube at a low-voltage side is turned off, the resonant capacitor continues to release energy to a resonant cavity current, so that the resonant converter is started. The reverse current turn-off of the low-voltage side switch tube is ensured, the soft turn-off range of the frequency raising process is improved, and the hard turn-off of the low-voltage side switch tube is avoided.

Description

Technical Field

[0001] This application relates to the field of power control technology, and in particular to a reverse pre-charging method and system for a resonant converter. Background Technology

[0002] Existing LLC resonant converters include a power battery side, a high-voltage side, and a low-voltage side. On the power battery side, a pre-charge relay is connected to the power battery, and on the low-voltage side, a storage battery is connected. When reverse pre-charging begins, the pre-charge relay is in the open state. By controlling the opening and closing of the low-voltage side switch, the energy of the storage battery is transferred to the high-voltage side to charge the bus capacitor on the high-voltage side. Until the voltage of the bus capacitor is close to the voltage of the power battery, the pre-charge relay is closed, completing the reverse pre-charging and realizing soft start.

[0003] During reverse pre-charge, LLC resonant converters need to control the voltage stress on the low-voltage side switching transistors to protect them. Existing methods often employ frequency-modulated resonant methods for reverse pre-charge. By adjusting the frequency, the reverse current from the high-voltage side is injected into the low-voltage side in a resonant manner, thereby achieving soft turn-off when the low-voltage side switching transistor is turned off, reducing the voltage stress on the low-voltage side switching transistor.

[0004] However, in reverse pre-charging using frequency-modulated resonant technology, the difference in resonant characteristics between different LLC resonant converters makes it difficult to determine a suitable start-up frequency during the pre-charging startup process. This can easily lead to a large turn-off current in the low-voltage side switch, resulting in hard turn-off. Furthermore, as the operating frequency of the LLC resonant converter increases, the conduction time of the switch continuously decreases, and the LLC resonant converter approaches a steady state. This results in a smaller reverse amplitude of the resonant cavity current and a smaller soft turn-off range for the low-voltage side switch. If the resonant capacitor voltage of the LLC resonant converter does not match the operating frequency, the low-voltage side switch can easily turn off with forward current, leading to hard turn-off. In other words, in reverse pre-charging using frequency-modulated resonant technology, hard turn-off of the low-voltage side switch can occur during both the pre-charging startup process and the frequency increase process, resulting in significant voltage stress on the low-voltage side switch. Summary of the Invention

[0005] This application provides a reverse precharge method and a reverse precharge system for a resonant converter, which can prevent hard turn-off of the low-voltage side switch during the precharge startup process and frequency ramping process, and effectively suppress the voltage stress of the low-voltage side switch.

[0006] This application provides a reverse precharge method for a resonant converter, including:

[0007] The startup frequency of the resonant converter is obtained when the current of the low-voltage side switch of the resonant converter reaches its minimum value during the pre-charge startup process.

[0008] The resonant converter is controlled to perform pre-charge startup at the startup frequency.

[0009] During the frequency ramp-up process after the resonant converter is precharged and started, the output voltage of the inverter bridge on the high-voltage side of the resonant converter is externally shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side.

[0010] Furthermore, obtaining the startup frequency of the resonant converter when the current of the low-voltage side switch of the resonant converter reaches its minimum value during the pre-charge startup process includes:

[0011] The conduction time of the low-voltage side switch tube when the current of the low-voltage side switch tube reaches the minimum value during the pre-charge start-up process is obtained.

[0012] The start-up frequency of the resonant converter is determined based on the conduction time of the low-voltage side switch.

[0013] Furthermore, the step of obtaining the conduction time of the low-voltage side switch when the current of the low-voltage side switch of the resonant converter reaches its minimum value during the pre-charge start-up process includes:

[0014] The resonant period of the resonant converter is obtained based on the resonant capacitor and resonant inductor on the high-voltage side.

[0015] Based on the position corresponding to the resonance period when the excitation current of the resonant converter increases to its maximum value in the positive direction during the pre-charge start-up process and the resonant cavity current of the resonant converter increases to its maximum value in the reverse direction, the conduction time of the low-voltage side switch is determined.

[0016] Furthermore, determining the start-up frequency of the resonant converter based on the conduction time of the low-voltage side switch includes:

[0017] The startup frequency of the resonant converter is determined based on the conduction time of the low-voltage side switch and the dead time of the resonant converter during the pre-charge startup process.

[0018] Furthermore, before controlling the resonant converter to perform pre-charge startup at the startup frequency, the method further includes:

[0019] The inductance ratio of the magnetizing inductance to the resonant inductance of the resonant converter is configured to be greater than a preset threshold, so that the resonant cavity current of the resonant converter is greater than the magnetizing current of the resonant converter.

[0020] Furthermore, the step of controlling the output voltage of the inverter bridge on the high-voltage side of the resonant converter to perform external phase shifting based on the phase lag value includes:

[0021] The inverter bridge drive signal on the high-voltage side is controlled to lag the drive signal of the low-voltage side switch by the phase lag value, so as to control the output voltage of the inverter bridge on the high-voltage side of the resonant converter to perform an external phase shift.

[0022] Furthermore, after controlling the output voltage of the inverter bridge on the high-voltage side of the resonant converter to perform an external phase shift based on a preset phase lag value, the method further includes:

[0023] Obtain the target voltage gain value for reverse pre-charge;

[0024] When the operating frequency of the resonant converter is increased to the highest operating frequency, if the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side does not reach the target voltage gain value, the output voltage of the inverter bridge is controlled to perform an internal phase shift so that the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side reaches the target voltage gain value.

[0025] Furthermore, obtaining the target voltage gain value for reverse pre-charge includes:

[0026] The voltage difference between the bus capacitor voltage value on the high-voltage side and the voltage reference value is input into the voltage loop to obtain the current reference value output by the voltage loop.

[0027] The input current value of the low-voltage side battery of the resonant converter and the current difference of the current reference value are input into the current loop to obtain the target voltage gain value output by the current loop.

[0028] This application provides a reverse precharge system, including: a resonant converter and a controller; the controller is connected to the high-voltage side inverter bridge of the resonant converter and the low-voltage side switching transistor of the resonant converter;

[0029] The controller is used to execute the reverse pre-charge method described above.

[0030] Furthermore, the reverse precharge system also includes a voltage sampler and a current sampler;

[0031] The voltage sampler is connected to the bus capacitor on the high-voltage side of the resonant converter, and samples the bus capacitor voltage on the high-voltage side to obtain the bus capacitor voltage value on the high-voltage side.

[0032] The current sampler is connected to the low-voltage side battery of the resonant converter and is used to sample the input current value of the low-voltage side battery of the resonant converter.

[0033] The controller is connected to the voltage sampler and the current sampler, and is used to execute the above-described reverse pre-charge method based on the bus capacitor voltage value on the high-voltage side and the input current value of the low-voltage battery of the resonant converter.

[0034] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0035] In this embodiment, the startup frequency of the resonant converter is obtained when the current of the low-voltage side switch reaches its minimum value during the pre-charge startup process. The resonant converter is controlled to perform pre-charge startup at the startup frequency. At this time, the low-voltage side switch is turned off when the current reaches its minimum value, and the turn-off current of the low-voltage side switch is small, avoiding hard turn-off of the low-voltage side switch. During the frequency ramp-up process after the resonant converter pre-charge startup, the output voltage of the inverter bridge on the high-voltage side of the resonant converter is externally phase-shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side. When the low-voltage side switch is turned off, the resonant capacitor continues to release energy to the resonant cavity current, ensuring that the low-voltage side switch is turned off with reverse current, improving the soft turn-off range of the frequency ramp-up process, and avoiding hard turn-off of the low-voltage side switch. That is, in this embodiment, hard turn-off of the low-voltage side switch can be avoided during the pre-charge startup process and the frequency ramp-up process, effectively suppressing the voltage stress of the low-voltage side switch. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0037] Figure 1 This is a flowchart of a reverse precharge method for a resonant converter disclosed in an embodiment of this application;

[0038] Figure 2 This is a flowchart of another resonant converter reverse precharge method disclosed in an embodiment of this application;

[0039] Figure 3 This is a flowchart of an internal phase shifting process disclosed in an embodiment of this application;

[0040] Figure 4 This is a circuit diagram of an LLC resonant converter disclosed in an embodiment of this application;

[0041] Figure 5 This is a waveform diagram of the reverse precharge up-band operation disclosed in an embodiment of this application;

[0042] Figure 6This is a waveform diagram of a reverse precharge precharge start-up process disclosed in an embodiment of this application;

[0043] Figure 7 This is a waveform diagram of a reverse precharged up-band frequency band after phase shift, as disclosed in an embodiment of this application.

[0044] Figure 8 This is a control block diagram of a reverse pre-charge disclosed in an embodiment of this application;

[0045] Figure 9 This is a logic block diagram of a reverse precharge driving wave generation disclosed in an embodiment of this application;

[0046] Figure 10 This is a schematic diagram illustrating the overall reverse pre-charging effect disclosed in an embodiment of this application.

[0047] Figure 11 This is a driving waveform diagram of a pre-charge process disclosed in an embodiment of this application;

[0048] Figure 12 This is a structural block diagram of a reverse pre-charge system disclosed in an embodiment of this application. Detailed Implementation

[0049] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0050] In the description of the embodiments of this application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0051] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0052] In this embodiment, the LLC resonant converter is as follows: Figure 4 As shown, the LLC resonant converter includes a power battery side, a high-voltage side, and a low-voltage side; the power battery side includes a power battery and a pre-charge relay, U Battery The voltage of the power battery; the high-voltage side includes: bus capacitor C HV Inverter bridge (switching transistors S1, S2, S3, and S4), resonant inductor L r Resonant capacitor C r Magnetizing inductance L m And the primary winding of the transformer, where N is the turns ratio of the transformer; U HV For bus capacitor C HV voltage, u AB i is the output voltage of the inverter bridge. Lr For the resonant cavity current (i.e., the resonant inductance L) r (current), i Lm For the excitation current, u cr For the resonant capacitor C r voltage, u tr This refers to the primary winding voltage of the transformer (the high-voltage side voltage); the low-voltage side includes: rectifier switches SR1 and SR2, leakage inductances L1 and L2, and the battery; where i L1 i is the current flowing through the switching transistor SR1. L2 V is the current flowing through the switching transistor SR2. ds1 V is the voltage across the switching transistor SR1. ds2 The voltage across the switching transistor SR2 is u. tr1 and u tr2 U is the voltage between the two secondary windings of the transformer. LV This is the output voltage of the battery.

[0053] When the reverse pre-charge begins, the LLC resonant converter's pre-charge relay is in the open state. By controlling the opening and closing of the low-voltage side switching transistor, the energy of the battery is transferred to the high-voltage side to charge the bus capacitor on the high-voltage side. Until the voltage of the bus capacitor is close to the voltage of the power battery, the pre-charge relay is closed to complete the reverse pre-charge and achieve soft start.

[0054] In existing LLC resonant converters using frequency-modulated resonant reverse pre-charge, the pre-charge startup process is challenging due to differences in the resonant characteristics of different LLC resonant converters. This makes it difficult to determine a suitable startup frequency, easily leading to a large turn-off current in the low-voltage side switch, resulting in hard turn-off and significant voltage stress. Specifically, the low-voltage side switch current i... L1 =(i Lm +iLr )×N, where the excitation current i Lm and the resonant cavity current i Lr This represents the signed current value (positive / negative indicates forward / reverse direction). When the startup frequency is too high, the resonant cavity current i Lr It cannot achieve complete resonance and remains in the positive direction of flow, while the excitation current i Lm At startup, the current increases unidirectionally from 0 and remains positive. At this time, the low-voltage side switching current i L1 =(|i Lm |+|i Lr |)×N,The turn-off current of the low-voltage side switch is at its maximum positive value, which can easily lead to extremely high turn-off voltage stress. When the start-up frequency is too low, the resonant cavity current i Lr When the resonance exceeds its limit, the resonant cavity current i Lr In reverse state, the low-voltage side switching current i L1 =(|i Lm |-|i Lr |)×N; However, at this time the resonant cavity current i Lr The absolute value of the excitation current |i has already decayed from its reverse maximum value. Lm | Much greater than the absolute value of the resonant cavity current|i Lr This means that the current of the low-voltage side switch is still relatively large, and a large turn-off voltage stress will also be generated when the low-voltage side switch is turned off.

[0055] Furthermore, to achieve the entire reverse pre-charge boosting process for the bus capacitor, in addition to the pre-charge start-up process, frequency boosting is also required to increase the voltage gain of the bus capacitor. However, during the frequency boosting process after pre-charge start-up, the conduction time of the LLC resonant converter's switching transistors continuously decreases, and the LLC resonant converter tends to a steady state. This results in a smaller reverse amplitude of the resonant cavity current and a smaller soft turn-off range for the low-voltage side switching transistors. If the resonant capacitor voltage of the LLC resonant converter does not match the operating frequency, even if the resonant cavity current can cross zero and reverse at resonance, it still cannot resonate to a large current value. After conversion with the excitation current, it cannot be reversed and transmitted to the low-voltage side, which easily leads to a decrease in the low-voltage side switching transistor current i. L1 =(|i Lm |-|i Lr |)×N>0, which can easily cause the low-voltage side switch to turn off with a positive current, resulting in a hard turn-off of the low-voltage side switch. When the low-voltage side switch is turned off, a large turn-off voltage stress will also be generated.

[0056] like Figure 5As shown, in this embodiment, PWM1A is the PWM signal for driving the inverter bridge switch S1, PWM2B is the PWM signal for driving the inverter bridge switch S4, PWM3A is the PWM signal for driving the low-voltage side switch SR1, and PWM3B is the PWM signal for driving the low-voltage side switch SR2. The reverse pre-charge frequency ramping process (capacitive low-frequency band) can be divided into four segments for analysis:

[0057] 1) 0-t1: Excitation current i Lm and the resonant cavity current i Lr This already exists and belongs to a non-zero state response process. At this time, the low-voltage side switch SR1 is turned on, and the high-voltage side magnetizing inductance L... m When a positive voltage is applied, the magnetizing inductor L m Under the influence of positive voltage, it gradually changes towards a positive zero crossing, but due to the resonant cavity current i Lr Smaller, low-voltage side switching current: i L1 =(i Lm +i Lr When N × N is negative, energy is fed back from the high-voltage side to the low-voltage side. Resonant capacitor C r When the voltage discharges to near 0, the energy reinjection on the high-voltage side ends, and the current i of the low-voltage side switching transistor increases. L1 The forward transmission begins, and the low-voltage side resumes providing energy to the high-voltage side until time t1 drives PWM3A to turn off. Since the low-voltage side switch SR1 is turned off with forward current at this time, a large turn-off voltage stress will be generated.

[0058] 2) t1-t2: At time t1, the current is hard-turned off, and the low-voltage side leakage inductance L1 instantaneously generates a large reverse voltage, which is different from the voltage V across the switching transistor SR1. ds1 Coupling leads to voltage u on the high-voltage side of the transformer. tr A reverse spike appears, which will cause the resonant cavity current i Lr The current continues to change in the negative direction, i.e., the resonant cavity current i Lr The excitation current increases instantaneously in the reverse direction. During the dead zone, the excitation current i Lm Greater than the resonant cavity current i Lr According to the low-voltage side switch current i L2 =(i Lm +i Lr )×N, we can calculate that at this time, the switching transistor SR2 will have a reverse current flowing through the anti-parallel diode, and the resonant cavity current i Lr The energy is fed back to the bus capacitor C on the high-voltage side. HV Resonant capacitor C r And charge the low-voltage side battery.

[0059] 3) t2-t3: At time t2, the switching transistor SR2 is turned on, due to the magnetizing inductance L on the high-voltage side. m The voltage is negative, and the excitation current i Lm Under the influence of negative voltage, the resonant cavity current i gradually changes towards zero in the negative direction, similar to the 0-t1 stage. Lr The value is relatively small, and the low-voltage side switching current i is calculated. L2 If the voltage is negative, energy continues to flow back from the high-voltage side to the low-voltage side until the resonant capacitor C... r After the discharge is complete, the low-voltage side begins to supply positive current to the high-voltage side. At time t3, the same as at time t1, the switching transistor SR2 is forcibly turned off with positive current, generating a large turn-off voltage stress.

[0060] 4) t3-t4: This stage is the same as t1-t2. Hard shutdown causes the high-voltage side voltage u of the transformer to be lowered. tr A reverse spike appears, causing the resonant cavity current i Lr The excitation current increases instantaneously in the reverse direction. After the reverse spike disappears, due to the excitation current i Lm If the voltage is too high, the switching transistor SR1 will have a reverse current flowing through the anti-parallel diode, resulting in energy backflow from the high-voltage side.

[0061] It can be seen that the hard shutdown during the frequency ramping process of reverse precharge is due to the resonant cavity current i Lr Less than the excitation current i Lm Energy backflow occurs from the high-voltage side to the low-voltage side. After the energy backflow ends, the current of the low-voltage side switch is transmitted in the forward direction. At the moment when the low-voltage side switch is turned off, a large voltage stress is generated due to the forward current during turn-off.

[0062] In summary, existing LLC resonant converters using frequency-modulated resonant reverse precharge suffer from hard turn-off of the low-voltage side switch during both precharge startup and frequency ramp-up, resulting in significant voltage stress on the low-voltage side switch. Therefore, this application provides a reverse precharge method for a resonant converter that avoids hard turn-off of the low-voltage side switch during precharge startup and frequency ramp-up, effectively suppressing voltage stress on the low-voltage side switch. Figure 1 As shown, the specific steps are as follows:

[0063] 101. Obtain the startup frequency of the resonant converter when the current of the low-voltage side switching transistor of the resonant converter reaches its minimum value during the pre-charge startup process.

[0064] In this embodiment, the startup frequency of the resonant converter when the current of the low-voltage side switch reaches its minimum value during the pre-charge startup process can be obtained. This pre-charge startup process is the first conduction cycle of the PWM signal corresponding to the low-voltage side switch. In this embodiment, a pre-charge startup experiment can be performed on the resonant converter beforehand. During the first conduction cycle of the PWM signal, the current of the low-voltage side switch of the resonant converter is detected to determine the position of the conduction cycle corresponding to the minimum current of the low-voltage side switch. That is, when the low-voltage side switch is turned off at the position of this conduction cycle, the turn-off current is at its minimum value. This position of the conduction cycle has a certain conduction time (i.e., conduction duration). Then, the derivative of this conduction time can be calculated to obtain the startup frequency of the resonant converter when the current of the low-voltage side switch reaches its minimum value.

[0065] 102. Control the resonant converter to precharge and start it up at the start-up frequency.

[0066] After obtaining the startup frequency of the resonant converter when the current of the low-voltage side switch reaches its minimum value during the pre-charge startup process, the resonant converter can be controlled to perform pre-charge startup at this startup frequency. It is understood that, in this embodiment, controlling the resonant converter to perform reverse pre-charge mainly involves sending PWM signals to the inverter bridge switch on the high-voltage side and the low-voltage side switch of the resonant converter, thereby driving the inverter bridge switch on the high-voltage side and the low-voltage side switch to achieve reverse pre-charge. Specifically, the process of controlling the resonant converter to perform pre-charge startup at the startup frequency involves sending PWM signals with the same startup frequency (i.e., PWM signals with the same period duration) to the inverter bridge switch on the high-voltage side and the low-voltage side switch to control the resonant converter to perform pre-charge startup.

[0067] 103. During the frequency ramp-up process after the resonant converter is precharged and started, the output voltage of the inverter bridge on the high-voltage side of the resonant converter is externally phase-shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side.

[0068] To improve the soft-shutdown range during the frequency ramp-up process, in this embodiment, during the frequency ramp-up process after the resonant converter's pre-charge start-up, the inverter bridge output voltage on the high-voltage side of the resonant converter is externally phase-shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side. The preset phase lag value can be any phase lag value from 0% to 17% (excluding 0%), and is not specifically limited here; in one embodiment, the preset phase lag value can be a 5% phase lag.

[0069] Specifically, the timing of the PWM signal of the high-voltage side inverter bridge can be adjusted by adding a fixed phase shift angle to the PWM signal, causing the phase of the output voltage of the high-voltage side inverter bridge to lag. This gives the high-voltage side inverter bridge output voltage a fixed phase delay, causing the phase of the resonant capacitor voltage on the high-voltage side to be synchronously delayed, thus extending the discharge phase of the resonant capacitor on the high-voltage side. When the low-voltage side switch is turned off, the resonant capacitor on the high-voltage side still releases energy to the resonant inductor, increasing the resonant cavity current so that it is greater than the excitation current. At this time, the low-voltage side switch is turned off with reverse current, improving the soft turn-off range during frequency ramping.

[0070] As can be seen, in this embodiment, the startup frequency of the resonant converter is obtained when the current of the low-voltage side switch reaches its minimum value during the pre-charge startup process; the resonant converter is controlled to perform pre-charge startup at the startup frequency. At this time, the low-voltage side switch is turned off when the current reaches its minimum value, and the turn-off current of the low-voltage side switch is small, avoiding hard turn-off of the low-voltage side switch; during the frequency ramp-up process after the resonant converter pre-charge startup, the output voltage of the inverter bridge on the high-voltage side of the resonant converter is externally phase-shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side. When the low-voltage side switch is turned off, the resonant capacitor continues to release energy to the resonant cavity current, ensuring that the low-voltage side switch is turned off with reverse current, improving the soft turn-off range of the frequency ramp-up process, and avoiding hard turn-off of the low-voltage side switch. That is, in this embodiment, hard turn-off of the low-voltage side switch can be avoided during the pre-charge startup process and the frequency ramp-up process, effectively suppressing the voltage stress of the low-voltage side switch.

[0071] Furthermore, the reverse pre-charging process of the resonant converter in the embodiments of this application will be described in detail below, such as... Figure 2 As shown, the specific steps include the following:

[0072] 201. Obtain the conduction time of the low-voltage side switch when the current of the low-voltage side switch reaches the minimum value during the pre-charge start-up process.

[0073] In this embodiment, the conduction time of the low-voltage side switch when the current of the low-voltage side switch reaches its minimum value during the pre-charge start-up process can be obtained. It is understood that when the current of the low-voltage side switch reaches its minimum value during the pre-charge start-up process, it is when the excitation current of the resonant converter increases to its maximum value in the forward direction, and the resonant cavity current of the resonant converter increases to its maximum value in the reverse direction. The moment when the current of the low-voltage side switch reaches its minimum value can be determined by analyzing the transient process of the pre-charge start-up. Figure 6 As shown, the pre-charge start-up can be analyzed in four stages:

[0074] 1) 0-t1: At this time, the low-voltage side switch SR1 is turned on, and the low-voltage side switch current i L1Starting from 0, the upper half of the circuit corresponding to the low-voltage side switch SR1 provides power to the high-voltage side. Based on the coupling relationship of the same terminals, the magnetizing inductance voltage u on the high-voltage side... tr =N×u tr1 i Lm and i Lr The current increases from 0 under forward voltage drop.

[0075] 2) t1-t2: Resonant capacitance C r With resonant inductor L r Resonance occurs when the resonant cavity current i Lr After reaching its maximum current, it will gradually decrease in a sinusoidal manner, but the excitation current i Lm Under the influence of the transformer's forward voltage drop, it will continue to increase in the positive direction. According to Kirchhoff's Current Law (KCL) formula: i L1 =(i Lm +i Lr )×N, resonant cavity current i Lr The slope decreases, starting small and then increasing, and the excitation current i Lm The slope of the voltage drop across the leakage inductance L1 will gradually decrease. At this time, the low-voltage side switching current i L1 It will increase first and then decrease.

[0076] 3) t2-t3: Resonant cavity current i at time t2 Lr The resonant inductance L is 0. r After discharge, the resonant capacitor C r At this point, energy is fed back to the resonant inductor L. r Therefore, the resonant cavity current i Lr It will cross zero and increase in the opposite direction until it reaches its maximum.

[0077] 4) t3-t4: Resonant capacitance C at time t3 r Discharge complete, resonant cavity current i Lr and excitation current i Lm Each reaches its maximum value i Lrmax and i Lmmax The difference between the two maximum values ​​also reaches its minimum, corresponding to the low-voltage side switching current i. L1 The current is at its minimum at point Q in the diagram. At this point, the resonant cavity current i... Lr It will feed energy back to the resonant capacitor C. r Above, the resonant cavity current i Lr The voltage begins to decrease due to the voltage drop caused by the leakage inductance L1 and the output voltage U of the low-voltage side battery. LV The effect of the drop, the excitation current i Lm It may remain unchanged, or even show a decreasing trend, but the resonant cavity current i Lr The reduction is greater than that of the excitation current i. LmMore intense, therefore manifested as low-voltage side switching current i L1 When the angle is upward, the turn-off current increases, and the turn-off stress is greater compared to point Q.

[0078] As can be seen, during the pre-charge startup process, the moment when the current of the low-voltage side switch reaches its minimum value is point Q. At this point, it is necessary to control the startup frequency to keep the turn-off point of the low-voltage side switch at point Q. If the startup frequency is set too low (i.e., the period corresponding to the PWM signal is too large), the low-voltage side switch will miss point Q when turning off, turning off at the point where the current of the low-voltage side switch rises, resulting in greater turn-off voltage stress. If the startup frequency is set too high (i.e., the period corresponding to the PWM signal is too small), the t2-t3 operating condition will be lost, and the resonant cavity current i Lr The inability to increase the voltage in reverse direction until the maximum value results in the low-voltage side switching transistor failing to reach the Q point, which also generates a large turn-off voltage stress.

[0079] It is understandable that during the pre-charge startup process of the resonant converter, the resonance process of the resonant capacitor and resonant inductor on the high-voltage side is involved. The resonant period of the resonant converter can be obtained based on the resonant capacitor and resonant inductor on the high-voltage side. Specifically, the inherent resonant frequency f can be calculated first. r :

[0080]

[0081] The corresponding resonant period is the resonant frequency f. r The reciprocal of.

[0082] Next, the conduction time of the low-voltage side switch can be determined based on the position of the resonant period when the excitation current of the resonant converter increases to its maximum value in the forward direction and the resonant cavity current of the resonant converter increases to its maximum value in the reverse direction during the pre-charge start-up process. This conduction time is the conduction time corresponding to the minimum turn-off current. It can be understood that the position of the resonant period when the excitation current of the resonant converter increases to its maximum value in the forward direction and the resonant cavity current of the resonant converter increases to its maximum value in the reverse direction during the pre-charge start-up process is the position of point Q corresponding to the resonant period. A total of 3 / 4 of the resonant periods are conducted. At this time, the conduction time of the low-voltage side switch is:

[0083]

[0084] 202. Determine the start-up frequency of the resonant converter based on the conduction time of the low-voltage side switch.

[0085] After obtaining the conduction time of the low-voltage side switch, the startup frequency of the resonant converter can be determined based on the conduction time of the low-voltage side switch. Alternatively, the startup frequency can be obtained by directly taking the reciprocal of the conduction time of the low-voltage side switch. By analyzing the changes in the startup transient process, the position corresponding to the minimum current of the low-voltage side switch during the resonant period can be determined, thus identifying the conduction time of the low-voltage side switch. Based on the conduction time of the low-voltage side switch, the startup frequency of the resonant converter can be accurately determined.

[0086] Preferably, the dead time T needs to be considered during the pre-charge start-up process of the resonant converter. dead Dead time refers to the time interval during which both upper and lower switches on the same arm of the inverter bridge are in the off state. In a resonant converter, the two switches on the same arm cannot be turned on simultaneously, otherwise a huge short-circuit current will be generated, damaging the switches. Therefore, in this embodiment, the start-up frequency of the resonant converter is determined based on the conduction time of the low-voltage side switch and the dead time of the resonant converter during pre-charge start-up, further ensuring the normal soft start of the resonant converter. Specifically, the corresponding start-up frequency f start The calculation formula is:

[0087]

[0088] Combining the formula above, we can obtain the startup frequency f. start The expression is:

[0089]

[0090] It can be seen that the startup frequency f start The corresponding parameters of the resonant converter are the resonant inductance L. r and resonant capacitor C r .

[0091] Furthermore, the traditional method for determining the start-up frequency involves calibrating different start-up frequencies and determining the best start-up frequency based on the test results. This requires a large number of experiments to determine the most suitable soft-shutdown frequency, which often leads to a huge amount of debugging work and may also result in serious consequences such as excessive stress during the testing process, causing the transistor to fail.

[0092] In this embodiment, the relationship between the resonant inductor current, the excitation current, the turn-off current of the low-voltage side switch, and the resonant period is determined. That is, the position corresponding to the resonant period when the excitation current increases to its maximum value in the forward direction and the resonant cavity current of the resonant converter increases to its maximum value in the reverse direction is the position corresponding to the minimum turn-off current of the low-voltage side switch. The start-up frequency expression corresponding to the minimum turn-off current conduction time can be calculated. This start-up frequency expression only includes the parameters of the resonant capacitor and the resonant inductor.

[0093] For different LLC resonant converters, the parameters of the corresponding resonant capacitor and resonant inductor can be input into the start-up frequency expression to redetermine the start-up frequency. This allows the obtained start-up frequency to be adapted to the resonant characteristics of different LLC resonant converters, accurately obtaining the start-up frequency of the resonant converter. This avoids determining the start-up frequency of the resonant converter through a large number of tests, reducing the tediousness of traditional start-up frequency calibration.

[0094] 203. Configure the ratio of the excitation inductance of the resonant converter to the resonant inductance of the resonant converter to be greater than a preset threshold, so that the resonant cavity current of the resonant converter is greater than the excitation current of the resonant converter.

[0095] Furthermore, although the Q point described above represents the minimum turn-off current of the low-voltage side switch, this minimum turn-off current is still positive, which will generate a certain turn-off voltage stress. To further achieve soft turn-off during startup, in this embodiment, before controlling the resonant converter to perform pre-charge startup at the startup frequency, the inductance ratio of the resonant converter's magnetizing inductance to its resonant inductance is configured to be greater than a preset threshold. This ensures that the resonant cavity current of the resonant converter is greater than its magnetizing current, further reducing the turn-off voltage stress during startup. That is, in the resonant converter, the inductance ratio... Greater than the preset threshold.

[0096] Specifically, in this embodiment, the magnetizing inductor and resonant inductor can be voltage-controlled inductors. The controller can output an adjustable voltage signal and apply it to the control terminal of the voltage-controlled inductor to change its internal equivalent permeability, thereby adjusting the inductance value. Alternatively, the magnetizing inductor and resonant inductor can be magnetically controlled inductors. The controller can control the coil current of the magnetically controlled inductor through an adjustable DC current, thereby controlling the permeability of the magnetic core of the magnetically controlled inductor to adjust the inductance value. The specific method of adjusting the inductance value is not limited here.

[0097] 204. Control the resonant converter to precharge and start it at the start-up frequency.

[0098] It is understandable that step 204 is similar to step 102 above, and the details will not be repeated here.

[0099] 205. Control the phase lag value of the inverter bridge drive signal on the high-voltage side relative to the drive signal of the low-voltage side switch tube, so as to control the output voltage of the inverter bridge on the high-voltage side of the resonant converter to perform external phase shift.

[0100] like Figure 7 The diagram shows the steady-state operation with a 5% hysteresis phase shift added during the frequency ramp-up process. The analysis focuses on the conduction portion of the drive signal PWM3A for the low-voltage side switch SR1, which can be divided into four segments:

[0101] 1) 0-t1: At time 0, switch SR1 is turned on, due to the excitation current |i Lm |Ratio of resonant cavity current|i Lr The current is small, requiring compensation for the remaining energy on the low-voltage side, and the current in the switching transistor SR1 starts flowing forward from 0. The resonant inductor voltage u is calculated according to Kirchhoff's Voltage Law (KVL). Lr = -u cr +u tr -u AB The resonant converter is still in the early capacitive low-frequency range (frequency upscaling process), and the high-voltage side has not yet established a high voltage level, so the inverter bridge output voltage u AB The value is small, and at this time the resonant converter is in a phase-shifted state, the resonant capacitor voltage u cr Compared to the state without phase shift, the phase lag is present, and the voltage value is also relatively small. Therefore, the calculated resonant inductor voltage u is... Lr It remains positive, and the resonant cavity current i Lr Continue to increase.

[0102] 2) t1-t2: At this time, the corresponding switches S1 and S4 of the high-voltage side inverter bridge are turned on, and the current in the inverter bridge switches from the diodes of the original switches to the MOS channels of the switches to continue flowing. As the resonant capacitor voltage u... cr The voltage u of the oscillating inductor continues to rise. Lr As the current gradually decreases and crosses zero to become negative, under the influence of resonance, the resonant cavity current i Lr It also begins to gradually decrease from its maximum value. This is because the phase shift increases the resonant cavity current i. Lr Amplitude, resonant cavity current i Lr When switching to negative current, the current amplitude will be greater than the excitation current |i Lm | Larger, at this time the low-voltage side switching current i L1 Reverse. At time t2, the low-voltage side switch will turn off with reverse current. The reverse current freewheels from the diode of the switch, achieving soft turn-off and avoiding the problem of low-voltage side switch (MOSFET) failure due to voltage stress caused by hard turn-off during frequency ramping.

[0103] 3) t2-t3: Switches S1 and S4 of the high-voltage side inverter bridge remain on, and the inverter bridge output voltage u AB Maintaining a positive voltage, the resonant capacitor voltage u cr Also because of u AB This causes phase lag, and it is also in a state of positive voltage energy release, which allows us to obtain the resonant inductor voltage u. Lr It is still negative, and the resonant cavity current i Lr The trend of continued negative growth continues.

[0104] 4) t3-t4: During this period, the high-voltage side inverter bridge switches S1 and S4 are turned off. The inverter bridge current freewheels through the anti-parallel diodes of switches S2 and S3, and the inverter bridge output voltage u... AB The resonant inductor voltage u instantly commutates to a negative value. Lr The resonant cavity current i suddenly becomes positive. Lr It begins to rise until the excitation current |i Lm |=|i Lr The energy injected back from the high-pressure side to the low-pressure side is 0.

[0105] It is evident that by controlling the output voltage of the inverter bridge on the high-voltage side to externally phase-shift and lag the phase of the inverter bridge output voltage, the resonant capacitor can be phase-lagged without changing the existing resonant converter circuit, allowing the resonant capacitor to continue releasing energy (continuous discharge) and increasing the resonant cavity current. This can achieve soft turn-off of the low-voltage side switching transistor even when the resonant capacitor voltage is mismatched with the operating frequency, thereby increasing the soft turn-off range during the frequency ramp-up process.

[0106] Furthermore, when it is necessary to raise the voltage of the high-voltage side bus capacitor to the voltage of the power battery, simply relying on the external phase shift corresponding to the phase lag value to gain the bus capacitor voltage is far from sufficient. Therefore, in this embodiment, when the operating frequency of the resonant converter is increased to the highest operating frequency, the output voltage of the high-voltage side inverter bridge can also be internally phase shifted to further gain the bus capacitor voltage, so as to ensure that the soft start of the resonant converter is carried out normally. Figure 3 As shown, the specific steps include the following:

[0107] 301. Obtain the target voltage gain value for reverse pre-charge.

[0108] In this embodiment, the target voltage gain value for reverse pre-charging can be obtained. Generally, the target voltage gain value is the difference between the voltage value of the power battery and the voltage value of the bus capacitor on the high-voltage side, so that the voltage of the bus capacitor on the high-voltage side is as close as possible to the voltage value of the power battery, thereby achieving soft start.

[0109] Furthermore, the target voltage gain value for reverse pre-charge can be obtained through the voltage loop and current loop, such as... Figure 8 As shown in the figure, 5% PhaseShift represents the phase lag value corresponding to the outward shift, and Startup frequency is the start-up frequency; voltage sampling can be performed on the high-voltage side bus capacitor, and the high-voltage side bus capacitor voltage value U... HV and voltage reference value U ref The voltage difference is input to the voltage loop (outer loop of high-voltage side voltage control) to obtain the current reference value output by the voltage loop. To avoid this current reference value being too large, it can be compared with the preset current reference value I.ref The values ​​are compared, and the minimum value is taken as the final current reference value i. ref The input current of the low-voltage side battery of the resonant converter is sampled, and the input current value i of the low-voltage side battery of the resonant converter is obtained. LV and current reference value i ref The input current loop (low-voltage side current control inner loop) yields the target voltage gain value Loop Out. This allows the high-voltage side voltage to be controlled at a selected voltage reference value U. ref And control the input current value i of the battery in real time. LV This is to prevent the low-voltage side battery from being damaged.

[0110] Next, the target voltage gain value (Loop Out), 5% hysteresis phase shift, and startup frequency can be input into the frequency upscaling and phase shifting algorithm. This frequency upscaling and phase shifting algorithm can execute step 102 above: controlling the resonant converter to perform pre-charge startup at the startup frequency; specifically, the frequency upscaling and phase shifting algorithm can output the corresponding frequency signal (frequency) to the PWM drive waveform generation module based on the startup frequency, controlling the PWM drive waveform generation module to send PWM signals with the same startup frequency to the inverter bridge switch on the high-voltage side and the switch on the low-voltage side, so as to control the resonant converter to perform pre-charge startup. The frequency upscaling and phase shifting algorithm can also execute the above step 103: during the frequency upscaling process after the resonant converter is precharged and started, the output voltage of the inverter bridge on the high-voltage side of the resonant converter is externally phase shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side; specifically, during the frequency upscaling process after the resonant converter is precharged and started, the frequency upscaling and phase shifting algorithm can output the corresponding phase shift signal PhaseShift to the PWM drive waveform generation module based on the 5% lag external phase shift (i.e., the preset phase lag value), and control the PWM drive waveform generation module to adjust the timing of the PWM signal sent to the high-voltage side inverter bridge to control the output voltage of the inverter bridge on the high-voltage side of the resonant converter to externally shift the phase and lag the phase of the resonant capacitor voltage on the high-voltage side.

[0111] Furthermore, this frequency upscaling and phase shifting algorithm can also control the inverter bridge output voltage to perform internal phase shifting based on the target voltage gain value, as shown in step 302 below.

[0112] 302. When the operating frequency of the resonant converter is increased to the highest operating frequency, if the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side does not reach the target voltage gain value, the inverter bridge output voltage is controlled to perform an internal phase shift so that the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side reaches the target voltage gain value.

[0113] In this embodiment, when the operating frequency of the resonant converter is increased to the highest operating frequency, if the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side does not reach the target voltage gain value, the inverter bridge output voltage is controlled to undergo an internal phase shift so that the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side reaches the target voltage gain value. Here, the highest operating frequency is the maximum operating frequency of the LLC resonant converter in steady-state operation. The internal phase shift is achieved by controlling the switching transistors of the high-voltage side inverter bridge to adjust the inverter bridge output voltage u... AB From two levels (+u) AB and -u AB ) becomes three-level (+u AB , 0, -u AB ), at the inverter bridge output voltage u AB Adding a zero level to the inverter bridge output voltage u AB It becomes a three-level modulation, and the newly added zero level can reduce the resonant capacitor voltage u. cr Delay, for the resonant inductor L r Continuous discharge increases the resonant cavity current i. Lr This improves the gain of the reverse precharge of the resonant converter.

[0114] The PWM drive signals for the high-voltage side inverter bridge switching transistors and the low-voltage side switching transistors corresponding to the frequency upscaling process and the subsequent internal phase shifting process are as follows: Figure 9 As shown; where PWM1A is the PWM signal driving the inverter bridge switch S1, PWM2A is the PWM signal driving the inverter bridge switch S2, PWM1B is the PWM signal driving the inverter bridge switch S3, PWM2B is the PWM signal driving the inverter bridge switch S4, PWM3A is the PWM signal driving the low-voltage side switch SR1, and PWM3B is the PWM signal driving the low-voltage side switch SR2. It can be seen that during the frequency ramp-up phase, the duty cycle of the PWM drive signal remains at 50%, and the frequency increases from the startup frequency to the maximum operating frequency. During the internal phase shift phase, the frequency remains at the maximum operating frequency, and the internal phase shift angle increases slowly until the voltage gain value corresponding to the high-voltage side bus capacitor voltage reaches the target voltage gain value.

[0115] The effect diagrams corresponding to the embodiments of this application are as follows: Figure 10 as well as Figure 11 As shown, Figure 10 This describes the overall pre-charge process of the resonant converter, where CH2 represents the voltage V across the low-voltage side switch SR1. ds1 CH3 is the high-voltage side bus capacitor C. HV The pre-charge current, CH4 is the high-voltage side bus capacitor C HV The pre-charged high voltage. Figure 11To illustrate the driving behavior during the pre-charge process, in the diagram, CH1 represents the drive signal PWM3A for the low-voltage side switch SR1, and CH2 represents the voltage V across the low-voltage side switch SR2. ds2 CH3 is the drive signal PWM2B for inverter bridge switch S4, and C4 is the drive signal PWM1A for inverter bridge switch S1. It can be seen that in this embodiment, the boost gain capability of reverse pre-charge is improved, and the turn-off voltage stress of the low-voltage side switch is effectively suppressed.

[0116] This application also provides a reverse pre-charge system, such as... Figure 12 As shown, it includes: a resonant converter 1201 and a controller 1202; the controller 1202 is connected to the high-voltage side inverter bridge of the resonant converter 1201 and the low-voltage side switching transistor of the resonant converter 1201; the controller 1202 is used to execute the reverse pre-charge method described above.

[0117] Furthermore, the reverse precharge system also includes a voltage sampler 1204 and a current sampler 1203;

[0118] The voltage sampler 1204 is connected to the bus capacitor on the high-voltage side of the resonant converter 1201, and samples the bus capacitor voltage on the high-voltage side to obtain the bus capacitor voltage value on the high-voltage side.

[0119] The current sampler 1203 and the low-voltage side battery of the resonant converter 1201 are used to sample the input current value of the low-voltage side battery of the resonant converter 1201.

[0120] The controller 1202 is connected to the voltage sampler 1204 and the current sampler 1203, and is used to execute the above-described reverse pre-charge method based on the bus capacitor voltage value on the high-voltage side and the input current value of the low-voltage side battery of the resonant converter 1201.

[0121] This application also provides a computer-readable storage medium including instructions that, when executed on a computer, cause the computer to perform the method described above.

[0122] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process of the system described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0123] In the several embodiments provided in this application, it should be understood that the disclosed reverse pre-charge method and reverse pre-charge system can be implemented in other ways. For example, the reverse pre-charge system embodiments described above are merely illustrative, and the division of the reverse pre-charge system is only a logical functional division. In actual implementation, there may be other division methods. For example, the voltage sampler and / or current sampler can be integrated into the controller. The specific implementation is not limited here.

Claims

1. A reverse pre-charge method for a resonant converter, characterized in that, include: The startup frequency of the resonant converter is obtained when the current of the low-voltage side switch of the resonant converter reaches its minimum value during the pre-charge startup process. The resonant converter is controlled to perform pre-charge startup at the startup frequency; During the frequency ramp-up process after the resonant converter is precharged and started, the output voltage of the inverter bridge on the high-voltage side of the resonant converter is externally shifted based on a preset phase lag value to lag the phase of the resonant capacitor voltage on the high-voltage side.

2. The reverse pre-charge method according to claim 1, characterized in that, The step of obtaining the startup frequency of the resonant converter when the current of the low-voltage side switch of the resonant converter reaches its minimum value during the pre-charge startup process includes: The conduction time of the low-voltage side switch tube when the current of the low-voltage side switch tube reaches the minimum value during the pre-charge start-up process is obtained. The start-up frequency of the resonant converter is determined based on the conduction time of the low-voltage side switch.

3. The reverse pre-charge method according to claim 2, characterized in that, The process of obtaining the conduction time of the low-voltage side switch when the current of the low-voltage side switch of the resonant converter reaches its minimum value during the pre-charge start-up includes: The resonant period of the resonant converter is obtained based on the resonant capacitor and resonant inductor on the high-voltage side. Based on the position corresponding to the resonant period when the excitation current of the resonant converter increases to its maximum value in the positive direction during the pre-charge start-up process and the resonant cavity current of the resonant converter increases to its maximum value in the reverse direction, the conduction time of the low-voltage side switch is determined.

4. The reverse pre-charge method according to claim 2, characterized in that... The determination of the start-up frequency of the resonant converter based on the conduction time of the low-voltage side switch includes: The startup frequency of the resonant converter is determined based on the conduction time of the low-voltage side switch and the dead time of the resonant converter during the pre-charge startup process.

5. The reverse pre-charge method according to claim 1, characterized in that, Before controlling the resonant converter to perform pre-charge startup at the startup frequency, the method further includes: The inductance ratio of the magnetizing inductance to the resonant inductance of the resonant converter is configured to be greater than a preset threshold, so that the resonant cavity current of the resonant converter is greater than the magnetizing current of the resonant converter.

6. The reverse pre-charge method according to claim 1, characterized in that, The method of controlling the output voltage of the inverter bridge on the high-voltage side of the resonant converter to perform external phase shifting based on the phase lag value includes: The inverter bridge drive signal on the high-voltage side is controlled to lag the drive signal of the low-voltage side switch by the phase lag value, so as to control the output voltage of the inverter bridge on the high-voltage side of the resonant converter to perform an external phase shift.

7. The reverse pre-charge method according to claim 1, characterized in that, After the inverter bridge output voltage on the high-voltage side of the resonant converter is externally phase-shifted based on a preset phase lag value, the method further includes: Obtain the target voltage gain value for reverse pre-charge; When the operating frequency of the resonant converter is increased to the highest operating frequency, if the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side does not reach the target voltage gain value, the output voltage of the inverter bridge is controlled to perform an internal phase shift so that the voltage gain value corresponding to the bus capacitor voltage on the high-voltage side reaches the target voltage gain value.

8. The reverse pre-charge method according to claim 7, characterized in that, The process of obtaining the target voltage gain value for reverse pre-charge includes: The voltage difference between the bus capacitor voltage value on the high-voltage side and the voltage reference value is input into the voltage loop to obtain the current reference value output by the voltage loop. The input current value of the low-voltage side battery of the resonant converter and the current difference of the current reference value are input into the current loop to obtain the target voltage gain value output by the current loop.

9. A reverse pre-charge system, characterized in that, include: A resonant converter and a controller; the controller is connected to the high-voltage side inverter bridge of the resonant converter and the low-voltage side switching transistor of the resonant converter; The controller is used to execute the reverse pre-charge method according to any one of claims 1 to 8.

10. The reverse pre-charge system according to claim 9, characterized in that, The reverse precharge system also includes: a voltage sampler and a current sampler; The voltage sampler is connected to the bus capacitor on the high-voltage side of the resonant converter, and samples the bus capacitor voltage on the high-voltage side to obtain the bus capacitor voltage value on the high-voltage side. The current sampler is connected to the low-voltage side battery of the resonant converter and is used to sample the input current value of the low-voltage side battery of the resonant converter. The controller is connected to the voltage sampler and the current sampler, and is used to execute the reverse pre-charge method described in claim 8 based on the bus capacitor voltage value on the high-voltage side and the input current value of the low-voltage side battery of the resonant converter.

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