An open-loop parameter regulation method of LLC resonant circuit

Abstract

The application discloses an open-loop parameter regulation method of an LLC resonant circuit, comprising the following steps: taking a resonant frequency calculated according to a resonant cavity nominal value as a working frequency; giving a command of setting a current value of a secondary side output of the LLC resonant circuit and sampling actual electrical parameters of the LLC resonant circuit; comparing the actually sampled electrical parameters with electrical parameters calculated according to nominal parameters of the LLC resonant circuit; if the deviation of the two exceeds a set threshold value, adjusting the current working frequency to an inherent resonant frequency corresponding to an actual value of the resonant cavity, otherwise maintaining the current working frequency, so that the LLC resonant circuit always works in a quasi-resonant state. The application has the beneficial effects that, compared with a traditional mode, the application can solve and reduce the system thermal failure problem and risk caused by parameter deviation in a high-power application scenario; by fine-tuning the working frequency, the system is closer to the quasi-resonant state, the switching loss and heat are reduced, and the system efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a method for controlling the open-loop parameters of an LLC resonant circuit. Background Technology

[0002] Currently, in high-power applications of LLC bidirectional energy storage, a single-tube solution is used on the high-voltage side. Due to the large power, conduction losses are significant, and conventional frequency-modulated LLC topologies exhibit extremely high switching losses. Therefore, the industry is considering controlling the LLC topology to operate in a fixed-frequency mode, particularly in a quasi-resonant state, to minimize switching losses. Simultaneously, to reduce resonant current, the magnetizing inductance is typically set much larger than the resonant inductance. Therefore, the conventional magnetic component design uses integrated leakage inductance for the resonant inductor, with the resonant inductance at the μH level and the magnetizing inductance at the mH level. However, due to the large inductance deviation of the integrated resonant inductor, and the component parameter deviation of the resonant capacitor, the combined effect of these two deviations negates the intended quasi-resonant state, potentially leading to significant switching or conduction losses.

[0003] To address the issue of resonant frequency shifts in resonant inductors and capacitors due to manufacturing deviations, potentially causing the system to operate in over-resonance (increased turn-off losses) or under-resonance (increased conduction losses) states, leading to thermal failure, existing technologies primarily offer two solutions: one involves rigorously controlling parameter deviations through extremely stringent manufacturing processes and methods; the other considers parameter deviations during the initial design phase to ensure the system operates in an under-resonance state, minimizing turn-off losses as much as possible.

[0004] For schemes that strictly control parameter deviations through extremely stringent process flows and methods, the main approach is to mitigate this risk by rigorously controlling the deviations of the resonant inductor and resonant capacitor. However, the effectiveness is very limited when inductors are manually wound, especially when generating resonant inductance through parasitic inductance. Schemes that consider parameter deviations in the initial design phase to ensure the system operates in an under-resonant state and minimize turn-off losses present challenges such as increased resonant current, increased component count, and increased cost. Summary of the Invention

[0005] One objective of this application is to provide an open-loop parameter control method for LLC resonant circuits that can solve at least one of the defects in the aforementioned background art.

[0006] To achieve at least one of the above objectives, the technical solution adopted in this application is as follows: an open-loop parameter control method for an LLC resonant circuit, comprising the following steps: using the resonant frequency calculated based on the nominal value of the resonant cavity as the operating frequency; giving the secondary side of the LLC resonant circuit an instruction to set a current value and sampling the actual electrical parameters of the LLC resonant circuit; comparing the actual sampled electrical parameters with the electrical parameters calculated based on the nominal parameters of the LLC resonant circuit; if the deviation between the two exceeds a set threshold, adjusting the current operating frequency to the inherent resonant frequency corresponding to the actual value of the resonant cavity; otherwise, maintaining the current operating frequency so that the LLC resonant circuit always operates in a quasi-resonant state.

[0007] Preferably, the non-quasi-resonant states of the LLC resonant circuit include an over-resonant state where the actual inherent resonant frequency of the resonant cavity is less than the operating frequency, and an under-resonant state where the actual inherent resonant frequency of the resonant cavity is greater than the operating frequency. When the LLC resonant circuit operates in the under-resonant state, the current operating frequency is increased; when the LLC resonant circuit operates in the over-resonant state, the current operating frequency is decreased.

[0008] Preferably, when the LLC resonant circuit operates in a non-quasi-resonant state, the current operating frequency is linearly adjusted according to a set ratio.

[0009] Preferably, the process of linearly adjusting the operating frequency is as follows: The resonant current and resonant frequency of the resonant cavity parameters at their nominal, minimum, and maximum values ​​are calculated, respectively denoted as quasi-resonant current and quasi-resonant frequency, under-resonant current and under-resonant frequency, and over-resonant current and over-resonant frequency; the ratio of the difference between the under-resonant frequency and the quasi-resonant frequency to the difference between the under-resonant current and the quasi-resonant current is used as a first ratio; the ratio of the difference between the over-resonant frequency and the quasi-resonant frequency to the difference between the over-resonant current and the quasi-resonant current is used as a second ratio; if the LLC resonant circuit operates in an under-resonant state, the difference between the current resonant current and the quasi-resonant current is multiplied by the first ratio as an increase in the operating frequency; if the LLC resonant circuit operates in an over-resonant state, the difference between the current resonant current and the quasi-resonant current is multiplied by the second ratio as a decrease in the operating frequency.

[0010] Preferably, during the non-operating phase of the LLC resonant circuit, the relationship between electrical parameters and resonant frequency under different resonant states is obtained by actual measurement using different design parameter offsets; when the LLC resonant circuit is operating in a non-quasi-resonant state, the corresponding resonant frequency is matched from the relationship table based on the actual sampled electrical parameters as the current operating frequency.

[0011] Preferably, when the LLC resonant circuit is working, the operating current of the LLC resonant circuit is sampled; the current operating state of the LLC resonant circuit is determined by comparing the actual value of the operating current with the nominal value of the operating current calculated based on the nominal parameters of the LLC resonant circuit.

[0012] Preferably, the operating current of the LLC resonant circuit is the primary current. When the difference between the effective value or the actual value of the maximum value of the primary current and the nominal value exceeds the set threshold, if the effective value or the actual value of the maximum value of the primary current is less than the nominal value, the LLC resonant circuit is determined to be operating in an over-resonance state; if the effective value or the actual value of the maximum value of the primary current is greater than the nominal value, the LLC resonant circuit is determined to be operating in an under-resonance state.

[0013] Preferably, the operating current of the LLC resonant circuit is the secondary current. When the difference between the effective value or the actual value of the maximum value of the secondary current and the nominal value exceeds a set threshold, if the effective value or the actual value of the maximum value of the secondary current is less than the nominal value, the LLC resonant circuit is determined to be operating in an over-resonance state; if the effective value or the actual value of the maximum value of the secondary current is greater than the nominal value, the LLC resonant circuit is determined to be operating in an under-resonance state.

[0014] Preferably, the operating current of the LLC resonant circuit is the primary-side turn-off current; if the difference between the actual value and the nominal value of the primary-side turn-off current exceeds a set threshold, and the current direction at turn-off is positive, the LLC resonant circuit is determined to be operating in an over-resonance state; if the difference between the actual value and the nominal value of the primary-side turn-off current exceeds a set threshold, and the current direction at turn-off is negative, the LLC resonant circuit is determined to be operating in an over-resonance state.

[0015] Preferably, when the LLC resonant circuit is operating, the zero-crossing point of the secondary diode of the LLC resonant circuit is sampled; if the actual position of the zero-crossing point of the secondary diode is earlier than the nominal position calculated according to the nominal parameters of the LLC resonant circuit, and the earlier time exceeds a set threshold, the LLC resonant circuit is determined to be operating in an over-resonance state; if the actual position of the zero-crossing point of the secondary diode is later than the nominal position calculated according to the nominal parameters of the LLC resonant circuit, and the later time exceeds a set threshold, the LLC resonant circuit is determined to be operating in an under-resonance state.

[0016] Compared with the prior art, the beneficial effects of this application are as follows:

[0017] Compared to the control method of traditional LLC topology, this application can solve and reduce the system thermal failure problem and risk caused by parameter deviation in high-power application scenarios; by fine-tuning the operating frequency, the system is brought closer to the quasi-resonant state, reducing switching losses and heat generation, and improving system efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the architecture of a traditional LLC resonant circuit.

[0019] Figure 2 A schematic diagram of the current waveform of the resonant inductor in a quasi-resonant state.

[0020] Figure 3 This is a schematic diagram of the current waveform of the resonant inductor in the underresonant state.

[0021] Figure 4 This is a schematic diagram of the current waveform of a resonant inductor in an over-resonant state.

[0022] Figure 5 This is a schematic diagram of the working process of this application.

[0023] Figure 6 This is a schematic diagram illustrating the specific workflow of this application based on primary-side current sampling. Detailed Implementation

[0024] The present application will now be further described in conjunction with specific embodiments. It should be noted that, in the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0025] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing 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, and should not be construed as limiting the specific protection scope of this application.

[0026] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0029] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0030] To facilitate understanding of the technical solution of this application, a simple description and analysis of the specific architecture of the LLC resonant circuit will be provided below.

[0031] like Figure 1 The diagram shows a typical LLC resonant circuit architecture, mainly including a switching circuit, a resonant cavity, a transformer, and a rectifier circuit. Both the switching and rectifier circuits employ a bridge structure. The switching circuit includes bridge-connected switching transistors Q1, Q2, Q3, and Q4, with Q1 to Q4 being field-effect transistors (FETs). The rectifier circuit includes bridge-connected switching transistors S1, S2, S3, and S4, with S1 to S4 being MOSFETs (Metal-Oxide-Semiconductor transistors). The resonant cavity includes a resonant inductance Lr and a resonant capacitor Cr connected in series with the primary winding of the transformer, and a primary inductance Lm connected in parallel with the primary winding of the transformer.

[0032] The operating states of an LLC resonant circuit mainly include quasi-resonance, over-resonance, and under-resonance states; among them, the over-resonance and under-resonance states can be referred to as non-quasi-resonance states. Specifically, when the operating frequency of the LLC resonant circuit is equal to or close to the actual inherent resonant frequency corresponding to the resonant inductor Lr and resonant capacitor Cr in the resonant cavity, the LLC resonant circuit operates in a quasi-resonance state; when the operating frequency of the LLC resonant circuit is greater than the actual inherent resonant frequency corresponding to the resonant inductor Lr and resonant capacitor Cr in the resonant cavity, the LLC resonant circuit operates in an over-resonance state; when the operating frequency of the LLC resonant circuit is less than the actual inherent resonant frequency corresponding to the resonant inductor Lr and resonant capacitor Cr in the resonant cavity, the LLC resonant circuit operates in an under-resonance state. When the LLC resonant circuit operates in different states, the current i in the resonant inductor Lr on the primary side... Lr The current in the secondary diode (the body diode in the MOSFET of the rectifier circuit) will have different waveforms.

[0033] Specifically, the current i of the resonant inductor Lr Lr For example, Figure 2 As shown, when the LLC resonant circuit operates in a quasi-resonant state, the current i in the resonant inductor Lr is... Lr It manifests as a sine wave, the frequency of which is the operating frequency, and also the actual inherent resonant frequency corresponding to the resonant inductor Lr and the resonant capacitor Cr. At this time, the relationship between the average current and the peak current of the LLC resonant circuit is:

[0034] ; .

[0035] Where Irms represents the current i in the resonant inductor Lr under quasi-resonant conditions. Lr The effective value of Iodc represents the average current required by the LLC resonant circuit, and Imax represents the current i in the resonant inductor Lr under quasi-resonant conditions. Lr The peak value.

[0036] like Figure 3 As shown, when the LLC resonant circuit operates in underresonance mode, the secondary diode will operate in discontinuous mode; for the same power requirement at the output port, i.e., requiring the same average current value Iodc, the current i of the resonant inductor Lr in the underresonance state will be... Lr A larger effective value results in a larger peak current; the specific relationship is as follows:

[0037] ; ;T z =1 / f z T q =1 / f q .

[0038] Among them, T z f represents the quasi-resonant period. z T represents the quasi-resonant frequency. q f represents the underresonant period. q The frequency i represents the underresonant frequency, and Irms_q represents the current i in the resonant inductor Lr under the underresonant state. Lr The effective value, Imax_q, represents the current i in the resonant inductor Lr under the underresonant state. Lr The peak value.

[0039] like Figure 4 As shown, when the LLC resonant circuit operates in the over-resonance state, the low-voltage side operates in the truncated sine wave state; for the same power requirement at the output port, i.e., requiring the same average current value Iodc, the current i of the resonant inductor Lr in the over-resonance state... Lr If the effective value is small, the peak value of the peak current will be smaller; the specific relationship is as follows:

[0040] ; ;T g =1 / f g .

[0041] Among them, T g f represents the resonant period. g The frequency is represented by Irms_g, and the current i in the resonant inductor Lr is represented by Irms_g at the resonant frequency. Lr The effective value, Imax_g, represents the current i in the resonant inductor Lr under resonant conditions. Lr The peak value.

[0042] Based on the above analysis, this application provides an open-loop parameter control method for an LLC resonant circuit, which can appropriately adjust the operating frequency by adjusting the offset of the resonant parameters in the open-loop condition; such as Figure 5 As shown, one preferred embodiment includes the following steps: using the resonant frequency calculated based on the nominal value of the resonant cavity as the operating frequency; giving the secondary side of the LLC resonant circuit a command to set the current value and sampling the actual electrical parameters of the LLC resonant circuit; comparing the actual sampled electrical parameters with the electrical parameters calculated based on the nominal parameters of the LLC resonant circuit; if the deviation between the two exceeds a set threshold, adjusting the current operating frequency to the inherent resonant frequency corresponding to the actual value of the resonant cavity; otherwise, maintaining the current operating frequency so that the LLC resonant circuit always operates in a quasi-resonant state.

[0043] Understandably, when preparing to start the system, i.e., when the LLC resonant circuit is about to start, the nominal values ​​of the resonant inductor Lr and resonant capacitor Cr are known. Therefore, the corresponding inherent resonant frequency can be calculated based on these values, and this inherent resonant frequency can be used as the operating frequency for starting the LLC resonant circuit. However, due to manufacturing errors and other reasons, the actual values ​​of the resonant inductor Lr and resonant capacitor Cr may deviate from their nominal values. This causes a mismatch between the operating frequency and the actual resonant frequency of the LLC resonant circuit, leading to increased switching losses and heat generation in the LLC resonant circuit. In the technical solution of this application, by analyzing the electrical parameters of the LLC resonant circuit after it has been operating, and based on the relationship between the actual inherent resonant frequency of the LLC resonant circuit and the electrical parameters, the current operating state of the LLC resonant circuit is confirmed. If the LLC resonant circuit is operating in a normal state, i.e., a quasi-resonant state, then it is only necessary to ensure that the LLC resonant circuit maintains its current operating frequency. If the LLC resonant circuit is operating in a non-quasi-resonant state, then the operating frequency of the LLC resonant circuit is adjusted to the corresponding actual inherent resonant frequency based on the relationship between the electrical parameters and the actual inherent resonant frequency, so that the LLC resonant circuit always operates in a quasi-resonant state. The entire process of adjusting the operating frequency does not require closed-loop control, which can effectively reduce switching losses and circuit heating, and significantly improve the operating efficiency of the LLC resonant circuit.

[0044] Specifically, as the analysis above shows, when the LLC resonant circuit operates in an overresonant state, the actual natural resonant frequency of the resonant cavity is lower than the operating frequency. Therefore, it is only necessary to reduce the operating frequency to the current actual natural resonant frequency of the resonant cavity. Similarly, when the LLC resonant circuit operates in an underresonant state, the actual natural resonant frequency of the resonant cavity is higher than the operating frequency. Therefore, it is only necessary to increase the operating frequency to the current actual natural resonant frequency of the resonant cavity.

[0045] Understandably, there are multiple ways to adjust the operating frequency of an LLC resonant circuit when it is operating in a non-quasi-resonant state. To facilitate understanding, two specific examples will be used to describe this in detail below.

[0046] Example 1: When the LLC resonant circuit operates in a non-quasi-resonant state, the current operating frequency is linearly adjusted according to a set ratio. That is, the resonant current of the LLC resonant circuit is linearly positively correlated with the resonant frequency. Therefore, when adjusting the operating frequency of the LLC resonant circuit, the adjustment value of the operating frequency can be obtained by proportional transformation based on the difference between the actual value and the nominal value of the resonant current of the LLC resonant circuit in the current state.

[0047] Specifically, the process of linearly adjusting the operating frequency is as follows: Calculate the resonant current and resonant frequency at the nominal, minimum, and maximum values ​​of the resonant cavity parameters, denoted as quasi-resonant current and quasi-resonant frequency, under-resonant current and under-resonant frequency, and over-resonant current and over-resonant frequency, respectively. The ratio of the difference between the under-resonant frequency and the quasi-resonant frequency to the difference between the under-resonant current and the quasi-resonant current is used as the first ratio. The ratio of the difference between the over-resonant frequency and the quasi-resonant frequency to the difference between the over-resonant current and the quasi-resonant current is used as the second ratio. If the LLC resonant circuit operates in an under-resonant state, multiply the difference between the current resonant current and the quasi-resonant current by the first ratio to obtain the increase in operating frequency. If the LLC resonant circuit operates in an over-resonant state, multiply the difference between the current resonant current and the quasi-resonant current by the second ratio to obtain the decrease in operating frequency.

[0048] To make it easier to understand, Example 1 will be described in detail below using specific parameters.

[0049] Assume the nominal value of the resonant inductor Lr in the LLC resonant circuit is 8uH, and the nominal value of the resonant capacitor Cr is 3.3uF; wherein the parameter deviation of the resonant inductor Lr is ±20%, and the parameter deviation of the resonant capacitor Cr is ±5%. Then the maximum value of the resonant inductor Lr is 9.6 uH, and the minimum value is 6.4 uH; the maximum value of the inductor and capacitor Cr is 3.465 uF, and the minimum value is 3.135 uF.

[0050] When the resonant inductance Lr and resonant capacitance Cr of the LLC resonant circuit are taken at their nominal values, the LLC resonant circuit operates in a quasi-resonant state. At this time, the natural resonant frequency of the resonant cavity at its nominal value is 30.97 kHz. Therefore, setting the operating frequency of the LLC resonant circuit to 30.97 kHz ensures that the LLC resonant circuit operates in a quasi-resonant state. When this LLC resonant circuit is applied to a 24kW, 100V energy storage system, the corresponding peak quasi-resonant current is 376.69 A. That is, 30.97 kHz is taken as the quasi-resonant frequency, and 376.69 A is taken as the quasi-resonant current.

[0051] When the resonant inductance Lr and resonant capacitance Cr of the LLC resonant circuit are both extremely small (6.4 uH, 3.135 uF), the natural resonant frequency of the resonant cavity is 35.53 kHz. Since the operating frequency of the LLC resonant circuit is 30.97 kHz, the LLC resonant circuit operates in an underresonant state; at this time, the peak value of the resonant current of the LLC resonant circuit is 432 A, and this current value is taken as the underresonant current, with an underresonant frequency of 35.53 kHz.

[0052] When the resonant inductance Lr and resonant capacitance Cr of the LLC resonant circuit are both extremely large (9.6uH, 3.465uF), the natural resonant frequency of the resonant cavity is 27.56kHz. Since the operating frequency of the LLC resonant circuit is 30.97kHz, the LLC resonant circuit is operating in an over-resonance state; at this time, the peak value of the resonant current of the LLC resonant circuit is 335.579A, which is taken as the over-resonance current, and the over-resonance frequency is 27.56kHz.

[0053] We can denote the first ratio as k1, then k1 = (35.53 - 30.97) / (432 - 376.69) ≈ 0.0824 kHz / A.

[0054] We can denote the second ratio as k2, then k2 = (27.59 - 30.97) / (335.579 - 376.69) ≈ 0.0822 kHz / A.

[0055] If the LLC resonant circuit is actually operating in an underresonant state, and the current underresonant current is 400A, then the increase in the operating frequency of the LLC resonant circuit can be calculated as (400-376.69)×0.0824≈1.921kHz. Therefore, simply increasing the operating frequency of the LLC resonant circuit from 30.97kHz to 32.891kHz will adjust the LLC resonant circuit from an underresonant state to a quasi-resonant state.

[0056] If the LLC resonant circuit is actually operating in an over-resonance state, and the current over-resonance current is 360A, then the decrease in the operating frequency of the LLC resonant circuit can be calculated to be approximately (360-376.69)×0.0822≈-1.372kHz. Therefore, simply reducing the operating frequency of the LLC resonant circuit from 30.97kHz to 29.598kHz will adjust the LLC resonant circuit from an over-resonance state to a quasi-resonance state.

[0057] Example 2: During the non-operational phase of the LLC resonant circuit, the relationship between electrical parameters and resonant frequency under different resonant states is obtained through actual measurements using different design parameter offsets. When the LLC resonant circuit operates in a non-quasi-resonant state, the corresponding resonant frequency is matched from the relationship table based on the actually sampled electrical parameters as the current operating frequency.

[0058] Understandably, taking the aforementioned specific parameters as an example, the resonant inductance Lr is known to range from 6.4 uH to 9.6 uH, and the resonant capacitor Cr is known to range from 3.135 uF to 3.465 uF. The ranges of the resonant inductance Lr and resonant capacitor Cr can be divided into 50 or 100 equal parts. The specific number of divisions can be chosen according to actual needs. For each divided value of the resonant inductance Lr and resonant capacitor Cr, the corresponding resonant current peak value and resonant frequency are calculated, and a relationship table is plotted. Therefore, during the operation of the LLC resonant circuit, the corresponding resonant frequency can be matched from the relationship table based on the actual sampled resonant current peak value. For example, if the resonant current peak value is 335.579A, the corresponding resonant frequency of the resonant cavity can be obtained from the relationship table as 27.56kHz. At this point, the operating frequency of the LLC resonant current can be adjusted to the resonant frequency of 27.56kHz.

[0059] It should be understood that both of the above examples can meet the actual needs of this application, and the appropriate example can be selected based on the actual needs of those skilled in the art. Considering that Example 1 involves less prior data calculation, this embodiment preferably adopts Example 1 for adjusting the operating frequency. As can be seen from the specific content of Example 1, the ratio of operating frequency adjustment in Example 1 is different in the over-resonance state and the under-resonance state. Therefore, before adjusting the operating frequency, it is necessary to determine the specific operating state of the LLC resonant circuit. There are various types of electrical parameters used to determine the specific operating state of the LLC resonant circuit, such as judging based on the operating current of the LLC resonant circuit, or judging based on the zero-crossing state of the secondary diode, etc. For ease of understanding, the determination of the specific operating state of the LLC resonant circuit will be described in detail below through specific embodiments.

[0060] I. For cases where the operating status is determined by the operating current of the LLC resonant circuit.

[0061] Specifically, when the LLC resonant circuit is working, the operating current of the LLC resonant circuit is sampled; the current operating state of the LLC resonant circuit is determined by comparing the actual value of the operating current with the nominal value of the operating current calculated based on the nominal parameters of the LLC resonant circuit.

[0062] It is understandable that the operating current types of LLC resonant circuits include primary current, secondary current, and primary turn-off current; primary current, secondary current, and primary turn-off current can all be used to determine the operating state of LLC resonant circuits. For ease of understanding, they will be described in detail below.

[0063] Specifically, when the operating current of the LLC resonant circuit is the primary current, the difference between the actual value and the nominal value of the primary current can be calculated, and the result is an absolute value. After calculating the difference between the actual and nominal values ​​of the primary current, the result can be compared with a set threshold. If the actual value of the primary current is less than the nominal value, since the resonant current is positively correlated with the resonant frequency, the inherent resonant frequency of the resonant cavity is less than the operating frequency, and the LLC resonant circuit can be determined to be operating in an over-resonance state. Conversely, if the actual value of the primary current is greater than the nominal value, the LLC resonant circuit can be determined to be operating in an under-resonance state.

[0064] It should be understood that the primary current is the resonant current corresponding to the resonant cavity, and it is an AC value. When determining the operating state of an LLC resonant circuit, the operating state can be determined by calculating the difference between the actual peak value of the primary current and the nominal peak value of the resonant current under the nominal parameters; alternatively, the operating state can be determined by calculating the difference between the effective value of the primary current and the nominal effective value of the resonant current under the nominal parameters. The specific choice between the peak value and the effective value of the primary current can be determined by those skilled in the art based on their actual needs.

[0065] It's also important to know that, to avoid continuous frequency adjustments in the LLC resonant circuit, the quasi-resonant state of the LLC resonant circuit can be limited within a certain range. For example, when the resonant current is within ±5% of the nominal value, the LLC resonant circuit is considered to be in a quasi-resonant state. The threshold corresponding to the difference between the actual and nominal values ​​of the primary current is then set to 5% of the nominal value. Only when the difference between the actual and nominal values ​​of the primary current is greater than 5% of the nominal value is the LLC resonant circuit considered to be operating in a non-quasi-resonant state. In this case, the specific operating state can be determined based on the actual relationship between the actual and nominal values ​​of the resonant current.

[0066] Similarly, when the operating current of an LLC resonant circuit is the secondary current, the difference between the actual and nominal values ​​of the secondary current can be calculated, and the result is an absolute value. After calculating the difference, the result can be compared with a set threshold. If the actual value of the secondary current is less than the nominal value, since the resonant current is positively correlated with the resonant frequency, the inherent resonant frequency of the resonant cavity is less than the operating frequency, and the LLC resonant circuit can be determined to be operating in an over-resonance state. Conversely, if the actual value of the secondary current is greater than the nominal value, the LLC resonant circuit can be determined to be operating in an under-resonance state.

[0067] Specifically, when the operating current of the LLC resonant circuit is the primary-side turn-off current; if the difference between the actual value and the nominal value of the primary-side turn-off current exceeds a set threshold, and the current direction during turn-off is positive, the LLC resonant circuit is determined to be operating in an over-resonance state. If the difference between the actual value and the nominal value of the primary-side turn-off current exceeds a set threshold, and the current direction during turn-off is negative, the LLC resonant circuit is determined to be operating in an over-resonance state.

[0068] It is understandable that when the LLC resonant circuit operates in a quasi-resonant state, the turn-off point of the primary-side switch should be located at the valley of the resonant current waveform, at which point the corresponding primary-side turn-off current is generally 0 or tends to be 0. However, when the LLC resonant circuit operates in an over-resonant state, such as Figure 4 As shown, the waveform of the resonant current is extracted and truncated, so that the current of the primary-side switch is still positive and greater than 0 when it is turned off, typically 0.3 to 0.5 times the nominal peak value of the resonant current. However, when the LLC resonant circuit operates in an underresonant state, as... Figure 3 As shown, the waveform period of the resonant current is lengthened, causing the current of the primary-side switch to tend towards the negative nominal peak value of the resonant current when it is turned off. Therefore, when judging the operating state of the LLC resonant circuit by the primary-side turn-off current, 0.1 or 0.2 times the nominal peak value of the resonant current can be selected as the set threshold. Then, the specific operating state is judged based on whether the difference between the actual value of the primary-side turn-off current of the LLC resonant circuit and the zero current exceeds the set threshold and the current direction.

[0069] II. The case of determining the operating status of the secondary diode of the LLC resonant circuit by means of the zero-crossing point.

[0070] Specifically, when the LLC resonant circuit is operating, the zero-crossing point of the secondary diode is sampled. If the actual position of the zero-crossing point of the secondary diode is earlier than the nominal position calculated based on the nominal parameters of the LLC resonant circuit, and the advance time exceeds a set threshold, the LLC resonant circuit is determined to be operating in an over-resonance state. If the actual position of the zero-crossing point of the secondary diode is later than the nominal position calculated based on the nominal parameters of the LLC resonant circuit, and the lag time exceeds a set threshold, the LLC resonant circuit is determined to be operating in an under-resonance state.

[0071] It is understandable that when the LLC resonant circuit operates in an underresonant state, such as Figure 3 As shown, the secondary current drops to zero earlier, causing the secondary diode to turn off earlier, resulting in a discontinuous secondary current waveform. When the LLC resonant circuit operates in an over-resonance state, as... Figure 4As shown, the secondary current will have a delayed zero-crossing, and the turn-off time of the secondary diode will be delayed. The specific time for advancing or delaying the turn-off time of the secondary diode can be calculated based on the specific parameter values ​​of the resonant cavity, and a corresponding threshold value can be selected based on the calculation results.

[0072] It is understood that the determination of the specific operating state of the LLC resonant circuit in the above two cases can meet the actual needs of this application. Considering that the resonant current needs to be sampled when adjusting the operating frequency, the primary current of the LLC resonant circuit can be preferred for determining the operating state. For ease of understanding, the specific process of determining the operating state of the LLC resonant circuit and adjusting the operating frequency using the primary current of the LLC resonant circuit will be described in detail below.

[0073] Specifically, such as Figure 6 As shown, when the LLC resonant circuit starts up, it can operate at the inherent resonant frequency corresponding to the nominal value of the resonant cavity. Then, a command to output a 200A current on the secondary side is given, and the maximum current value of the primary side resonant cavity is sampled. The sampled result is compared with the peak value of the quasi-resonant current in the quasi-resonant state. If the difference between the two does not exceed the set threshold, it is determined that the LLC resonant circuit is operating in the quasi-resonant state, and the LLC resonant circuit can be controlled to continue operating at the current operating frequency. Otherwise, the specific relationship between the sampled result and the peak value of the quasi-resonant current is judged. If the sampled result is greater than the peak value of the quasi-resonant current, it is determined that the LLC resonant circuit is operating in the under-resonant state, and the operating frequency can be increased according to the first ratio. If the sampled result is less than the peak value of the quasi-resonant current, it is determined that the LLC resonant circuit is operating in the over-resonant state, and the operating frequency can be decreased according to the second ratio.

[0074] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. An open-loop parameter regulation method of an LLC resonant circuit, characterized in that, The method comprises the following steps: calculating the resonant frequency according to the nominal value of the resonant cavity as the working frequency; setting the instruction of the current value of the secondary side output of the LLC resonant circuit and sampling the actual electrical parameters of the LLC resonant circuit; comparing the actually sampled electrical parameters with the electrical parameters calculated according to the nominal parameters of the LLC resonant circuit; if the deviation between the two exceeds the set threshold, adjusting the current working frequency to the inherent resonant frequency corresponding to the actual value of the resonant cavity, otherwise maintaining the current working frequency, so that the LLC resonant circuit always works in the quasi-resonant state; the non-quasi-resonant state of the LLC resonant circuit includes the over-resonant state in which the actual inherent resonant frequency of the resonant cavity is less than the working frequency, and the under-resonant state in which the actual inherent resonant frequency of the resonant cavity is greater than the working frequency; when the LLC resonant circuit works in the under-resonant state, increasing the current working frequency; when the LLC resonant circuit works in the over-resonant state, reducing the current working frequency; when the LLC resonant circuit works in the non-quasi-resonant state, linearly adjusting the current working frequency according to the set proportion; the linear adjustment process of the working frequency is as follows: respectively calculating the resonant current and the resonant frequency of the resonant cavity parameters under the nominal value, the minimum value and the maximum value, respectively recorded as the quasi-resonant current and the quasi-resonant frequency, the under-resonant current and the under-resonant frequency, and the over-resonant current and the over-resonant frequency; taking the ratio of the difference between the under-resonant frequency and the quasi-resonant frequency and the difference between the under-resonant current and the quasi-resonant current as the first proportion, and taking the ratio of the difference between the over-resonant frequency and the quasi-resonant frequency and the difference between the over-resonant current and the quasi-resonant current as the second proportion; if the LLC resonant circuit works in the under-resonant state, multiplying the difference between the current resonant current and the quasi-resonant current by the first proportion as the increase value of the working frequency; if the LLC resonant circuit works in the over-resonant state, multiplying the difference between the current resonant current and the quasi-resonant current by the second proportion as the decrease value of the working frequency.

2. The open-loop parameter tuning method of an LLC resonant circuit according to claim 1, wherein, when the LLC resonant circuit works, sampling the working current of the LLC resonant circuit; comparing the actual value of the working current with the nominal value of the working current calculated according to the nominal parameters of the LLC resonant circuit to determine the current working state of the LLC resonant circuit.

3. The open-loop parameter tuning method of an LLC resonant circuit according to claim 2, wherein, the working current of the LLC resonant circuit adopts the primary side current; when the difference between the actual value and the nominal value of the effective value or the maximum value of the primary side current exceeds the set threshold, if the actual value of the effective value or the maximum value of the primary side current is less than the nominal value, it is determined that the LLC resonant circuit works in the over-resonant state; if the actual value of the effective value or the maximum value of the primary side current is greater than the nominal value, it is determined that the LLC resonant circuit works in the under-resonant state.

4. The open-loop parameter tuning method of an LLC resonant circuit according to claim 2, wherein, the working current of the LLC resonant circuit adopts the secondary side current; when the difference between the actual value and the nominal value of the effective value or the maximum value of the secondary side current exceeds the set threshold, if the actual value of the effective value or the maximum value of the secondary side current is less than the nominal value, it is determined that the LLC resonant circuit works in the over-resonant state; if the actual value of the effective value or the maximum value of the secondary side current is greater than the nominal value, it is determined that the LLC resonant circuit works in the under-resonant state.

5. The open-loop parameter tuning method of an LLC resonant circuit according to claim 2, wherein, the working current of the LLC resonant circuit adopts the primary side off current; If the difference between the actual value and the nominal value of the primary side off current exceeds the set threshold value, and the current direction at the off time is positive, it is determined that the LLC resonant circuit works in the over resonant state; If the difference between the actual value and the nominal value of the primary side off current exceeds the set threshold value, and the current direction at the off time is negative, it is determined that the LLC resonant circuit works in the over resonant state.

6. The open-loop parameter tuning method of an LLC resonant circuit according to claim 1, wherein, When the LLC resonant circuit works, the zero-crossing point of the secondary side diode of the LLC resonant circuit is sampled; If the actual position of the zero-crossing point of the secondary side diode is advanced compared with the nominal position calculated according to the nominal parameters of the LLC resonant circuit, and the advanced time exceeds the set threshold value, it is determined that the LLC resonant circuit works in the over resonant state; If the actual position of the zero-crossing point of the secondary side diode is delayed compared with the nominal position calculated according to the nominal parameters of the LLC resonant circuit, and the delayed time exceeds the set threshold value, it is determined that the LLC resonant circuit works in the under resonant state.

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