LLC resonant converter soft start control method and system

Abstract

The application discloses a soft-start control method and system of an LLC resonant converter, and realizes soft-start of the LLC resonant converter. The method comprises the following steps: when a start command is received, a driving signal for controlling the LLC resonant converter is generated by using a pulse density modulation mode in an output quantity closed-loop control system of the LLC resonant converter; when the pulse density of the driving signal reaches a set value, the driving signal is generated by switching to using a pulse width plus frequency modulation mode, and until the closed-loop control system reaches a steady state, the soft-start of the LLC resonant converter is completed; wherein the pulse width plus frequency modulation mode refers to a modulation mode in which a pulse width modulation mode and a pulse frequency modulation mode act simultaneously.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a soft-start control method and system for an LLC resonant converter. Background Technology

[0002] LLC resonant converters have become a popular DC / DC topology due to their high efficiency and high power density. However, during the startup process of an LLC resonant converter, if a soft start (where the gain of the LLC resonant converter gradually increases from 0 to the target gain) cannot be achieved, a large resonant current and voltage will appear in the resonant network of the LLC resonant converter, which may cause the resonant inductor or resonant capacitor in the resonant network to burn out. Summary of the Invention

[0003] In view of this, the present invention provides a soft-start control method and system for LLC resonant converters to achieve soft-start of LLC resonant converters.

[0004] A soft-start control method for an LLC resonant converter includes:

[0005] When a start command is received, the LLC resonant converter output closed-loop control system generates a drive signal to control the LLC resonant converter using pulse density modulation.

[0006] When the pulse density of the drive signal reaches the set value, the drive signal is generated by pulse width and frequency modulation until the closed-loop control system reaches a steady state, at which point the soft start of the LLC resonant converter ends.

[0007] The pulse width-plus-frequency modulation method refers to a modulation method in which pulse width modulation and pulse frequency modulation are applied simultaneously.

[0008] Optionally, the pulse width plus frequency modulation method is adjusted with f1 and D1 as initial values;

[0009] Wherein, f1 and D1 are the frequency and duty cycle of the driving signal when the pulse density of the driving signal reaches the set value.

[0010] Optionally, the switching to generate the driving signal using pulse width modulation and frequency modulation includes:

[0011] The modulation is performed in n stages. In the i-th stage, f i and D i As an initial value, the frequency and duty cycle of the driving signal are adjusted to f using pulse width modulation and frequency modulation. i+1 and D i+1 i = 1, 2, ..., n, where n is an integer greater than or equal to 2;

[0012] Among them, f i D i f i+1 and D i+1 All are preset values; the frequency and duty cycle of the drive signal are adjusted to f j and D j The corresponding gain is M j j = 1, 2, ..., n+1; coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n From coordinates (M1, t) to coordinates (M1, t) and (M2, t) n+1 The distances of the straight line segments determined by (t) do not exceed the preset distance, where t represents time.

[0013] Optional, n=2, M2=M3 / 2.

[0014] Optionally, the closed-loop control system is a single-loop voltage system, a single-loop current system, or a dual-loop system consisting of an inner current loop and an outer voltage loop.

[0015] Optionally, the closed-loop control system employs proportional-integral-derivative (PID), proportional-integral (PI), proportional-derivative (PD), two-pole two-zero (2P2Z), two-pole single-zero (2P1Z), three-pole two-zero (3P2Z), three-pole three-zero (3P3Z), or four-pole four-zero (4P4Z) control algorithms for closed-loop control.

[0016] A closed-loop control system for the output of an LLC resonant converter includes: a sampling circuit and a control unit; the control unit includes a closed-loop controller and a modulator.

[0017] The sampling circuit is used to sample the output of the LLC resonant converter and feed it back to the input of the closed-loop controller;

[0018] The closed-loop controller is used to calculate the output based on the deviation between the feedback value and the reference value;

[0019] The modulator is used to generate a drive signal for controlling the LLC resonant converter by taking the output signal of the closed-loop controller as input and using pulse density modulation. When the pulse density of the drive signal reaches a set value, it switches to pulse width and frequency modulation to generate the drive signal until the deviation does not exceed the preset deviation value, at which point the soft start of the LLC resonant converter ends.

[0020] The pulse width-plus-frequency modulation method refers to a modulation method in which pulse width modulation and pulse frequency modulation are applied simultaneously.

[0021] Optionally, the pulse width plus frequency modulation method used by the modulator is adjusted with f1 and D1 as initial values;

[0022] Wherein, f1 and D1 are the frequency and duty cycle of the driving signal when the pulse density of the driving signal reaches the set value.

[0023] Optionally, after the modulator switches to pulse width plus frequency modulation, modulation is performed in n stages. In the i-th stage, f i and D i As an initial value, the frequency and duty cycle of the drive signal are adjusted to f. i+1 and D i+1 i = 1, 2, ..., n, where n is an integer greater than or equal to 2;

[0024] Among them, f i D i f i+1 and D i+1 All are preset values; the frequency and duty cycle of the drive signal are adjusted to f j and D j The corresponding gain is M j j = 1, 2, ..., n+1; coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n From coordinates (M1, t) to coordinates (M1, t) and (M2, t) n+1 The distances of the straight line segments determined by (t) do not exceed the preset distance, where t represents time.

[0025] Optionally, in the above-mentioned LLC resonant converter output closed-loop control system, n = 2, M2 = M3 / 2.

[0026] As can be seen from the above technical solution, when the present invention receives the start command, it first uses pulse density modulation to drive the LLC resonant converter, so that the gain gradually increases from 0; when the pulse density under pulse density modulation reaches the set value, it switches to pulse width and frequency modulation to generate the drive signal, so that the gain continues to gradually increase; when the closed-loop control system reaches steady state, the gain also increases to the target gain, and the LLC resonant converter switches from soft start to normal operation. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of a soft-start control method for an LLC resonant converter disclosed in an embodiment of the present invention;

[0029] Figure 2 Gain M - Duty Cycle D / Normal Operating Duty Cycle D under different quality factors Q n Schematic diagram of the curve;

[0030] Figure 3 Gain M-frequency ω / resonant frequency ω under different quality factors Q n Schematic diagram of the curve;

[0031] Figure 4 This is a schematic diagram of a driving signal;

[0032] Figure 5 This is a schematic diagram of a closed-loop control system for the output of an LLC resonant converter, as disclosed in an embodiment of the present invention. Detailed Implementation

[0033] For the sake of clarity and reference, the technical terms, abbreviations, or acronyms used below are summarized as follows:

[0034] PDM: Pulse Density Modulation;

[0035] PWM: Pulse Width Modulation;

[0036] PFM: Pulse Frequency Modulation;

[0037] PID stands for Proportional-Integral-Differential.

[0038] PI: Proportional-Integral;

[0039] PD: Proportional-Differential;

[0040] 2P2Z: Two poles and two zeros;

[0041] 2P1Z: Two poles and one zero;

[0042] 3P2Z: Three poles and two zeros;

[0043] 3P3Z: Three poles and three zeros;

[0044] 4P4Z: Four poles and four zeros.

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] See Figure 1 This invention discloses a soft-start control method for an LLC resonant converter, comprising:

[0047] Step S01: When the start command is received, in the LLC resonant converter output closed-loop control system, the drive signal for controlling the LLC resonant converter is generated using PDM modulation.

[0048] Step S02: When the pulse density of the driving signal reaches the set value, the driving signal is generated by switching to pulse width modulation and frequency modulation until the closed-loop control system reaches a steady state, at which point the soft start of the LLC resonant converter ends; wherein, the pulse width modulation and frequency modulation refers to a modulation method in which pulse width modulation and pulse frequency modulation are used simultaneously.

[0049] Specifically, the LLC resonant converter output closed-loop control system feeds back the output of the LLC resonant converter to the input of the closed-loop control system, and then dynamically adjusts the output of the LLC resonant converter according to the deviation between the feedback value and the reference value, so as to reduce or eliminate the deviation.

[0050] The closed-loop control system can be a single voltage loop, a single current loop, or a dual closed-loop system with an inner current loop and an outer voltage loop; it is not limited to any particular type. The types of feedback and reference values ​​in this closed-loop control system depend on its overall type. Specifically: when the closed-loop control system is a single voltage loop or a dual closed-loop system with an inner current loop and an outer voltage loop, the feedback value is the output voltage of the LLC resonant converter, and the reference value is the set output voltage reference. When the closed-loop control system is a single current loop, the feedback value is the output current of the LLC resonant converter, and the reference value is the set output current reference.

[0051] The closed-loop controller and modulator are the key components in this closed-loop control system. The closed-loop controller calculates the output based on the deviation between the feedback value and the reference value of the LLC resonant converter. The output signal of the closed-loop controller is sent to the modulator, which calculates and outputs a drive signal to the LLC resonant converter, thereby realizing the closed-loop control of the output of the LLC resonant converter.

[0052] The control algorithm inside the closed-loop controller can be PID, PI, PD, 2P2Z, 2P1Z, 3P2Z, 3P3Z or 4P4Z, and is not limited to any particular type.

[0053] The design of the modulation scheme within the modulator is crucial for achieving soft-start in an LLC resonant converter. PWM, PFM, and PDM are all well-known modulation schemes. PWM modulation adjusts the duty cycle D of the drive signal, PFM modulation adjusts the frequency ω of the drive signal, and PDM modulation adjusts the pulse density of the drive signal.

[0054] Corresponding to PWM modulation method, Figure 2 The diagram shows the gain M-duty cycle D / normal operating duty cycle D under different quality factors Q (Q = 0.05, Q = 0.1, Q = 0.5, Q = 1, Q = 5, the value of Q is related to the load size). n A schematic diagram of the curve, from Figure 2 It can be seen that the gain M increases with the increase of the duty cycle D, and the rate of change of the gain M decreases with the increase of the duty cycle D; when the duty cycle D is small, the gain M changes very quickly, which is not conducive to precise control.

[0055] Corresponding PFM modulation method Figure 3 The gain M-frequency ω / resonant frequency ω is shown for different quality factors Q (Q = 0.05, Q = 0.1, Q = 0.5, Q = 1, Q = 5, the value of Q is related to the load size). n The curve diagram shows that the upper and lower limits of the frequency ω of the drive signal of the LLC resonant converter are both to the right of the gain peak. Figure 3 It can be seen that within the allowable frequency adjustment range, the gain M increases as the frequency ω decreases, and the rate of change of the gain M increases as the frequency ω decreases. When PFM modulation is used alone, even if the frequency ω at the start of the LLC resonant converter is set to an extremely high value, the LLC resonant converter still has a large gain at the moment of start-up. However, an excessively high frequency ω also places high demands on the device and is difficult to implement.

[0056] PDM modulation allows for gradual gain adjustment from 0 by regulating pulse density, but it cannot achieve wide-range gain adjustment because: the drive signals of the upper and lower switches in the inverter bridge of an LLC resonant converter are out of phase by 180°. Therefore, the duty cycle of the drive signal for either switch cannot exceed 50%, otherwise it will cause the upper and lower switches to shoot through. Thus, the pulse density in PDM modulation has an upper limit; the time interval s between two pulses cannot be less than one pulse duration. Figure 4 As shown, when the pulse density reaches the upper limit, the gain may not have reached the target gain.

[0057] The ideal gain curve of an LLC resonant converter over time is as follows: the gain changes uniformly (i.e., linearly) starting from 0 and gradually increases to the target gain. Using any one of the modulation methods—PDM, PWM, or PFM—alone cannot make the gain curve of the LLC resonant converter over time approach this ideal curve. Therefore, this embodiment of the invention combines the advantages and disadvantages of PDM, PWM, and PFM. It first uses PDM modulation, and then switches to simultaneous PWM and PFM modulation (i.e., pulse width plus frequency modulation) when the pulse density of the drive signal reaches the set value, so that the gain curve of the LLC resonant converter over time approaches the ideal curve.

[0058] In PDM modulation, as the pulse density and frequency gradually increase, the gain gradually increases from 0. When the pulse density in PDM modulation reaches a set value (the set value is less than or equal to the upper limit of the pulse density), it switches to pulse width plus frequency modulation. To ensure a smooth switch, that is, to ensure a smooth change in gain at the moment of switch, the pulse width plus frequency modulation can be set to be adjusted with f1 and D1 as initial values, where f1 and D1 are the frequency and duty cycle of the driving signal when the pulse density of the driving signal reaches the set value.

[0059] In pulse width modulation (PWM) and frequency modulation (PFM), the frequency and duty cycle change simultaneously (frequency changes from large to small, and duty cycle changes from small to large), and the gain changes accordingly. However, since the rate of gain change gradually decreases in PWM modulation and gradually increases in PFM modulation, the combined effect of the two results in a more fixed rate of gain change in PWM, meaning the gain-time curve is more linear.

[0060] As described above, when the embodiment of the present invention receives a start command, it first uses pulse density modulation to drive the LLC resonant converter, so that the gain gradually increases from 0; when the pulse density under pulse density modulation reaches the set value, it switches to pulse width and frequency modulation to generate the drive signal, so that the gain continues to gradually increase; when the closed-loop control system reaches a steady state, the gain also increases to the target gain, and the LLC resonant converter switches from soft start to normal operation.

[0061] Optionally, to further improve the linearity of the gain-time curve, modulation can be performed in n segments using pulse width-plus-frequency modulation (PWM). This involves setting several points on or near the gain-time curve and tracking each point for PWM, thereby making the gain-time curve more linear. The specific implementation scheme is as follows:

[0062] The modulation is performed in n stages. In the i-th stage, f i and D iAs an initial value, the frequency and duty cycle of the driving signal are adjusted to f using pulse width modulation and frequency modulation. i+1 and D i+1 i = 1, 2, ..., n, where n is an integer greater than or equal to 2;

[0063] f i D i f i+1 and D i+1 All are preset values; the frequency and duty cycle of the drive signal are adjusted to f j and D j The corresponding gain is M j j = 1, 2, ..., n+1; coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n From coordinates (M1, t) to coordinates (M1, t) and (M2, t) n+1 The distances of the straight line segments determined by t) do not exceed the preset distances, where t represents time and M is the mean. n+1 For target gain. The smaller this preset distance, and the better the coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n The more uniform the distribution of (t), the closer the gain curve is to a straight line.

[0064] In one embodiment, n = 2 and M2 = M3 / 2 can be set.

[0065] Corresponding to the above method embodiments, this invention also discloses a closed-loop control system for the output of an LLC resonant converter, such as... Figure 5 As shown, it includes: a sampling circuit and a control unit; the control unit includes a closed-loop controller and a modulator;

[0066] The sampling circuit is used to sample the output of the LLC resonant converter and feed it back to the input of the closed-loop controller;

[0067] The closed-loop controller is used to calculate the output based on the deviation between feedback value 1 and reference value 2;

[0068] The modulator is used to generate a drive signal 3 for controlling the LLC resonant converter by taking the output signal of the closed-loop controller as input and using pulse density modulation. When the pulse density of the drive signal 3 reaches a set value, it switches to using pulse width and frequency modulation to generate the drive signal 3 until the deviation does not exceed the preset deviation value, at which point the soft start of the LLC resonant converter ends.

[0069] The pulse width-plus-frequency modulation method refers to a modulation method in which pulse width modulation and pulse frequency modulation are applied simultaneously.

[0070] Optionally, the modulator uses a pulse width plus frequency modulation method that is adjusted with f1 and D1 as initial values, where f1 and D1 are the frequency and duty cycle of the driving signal when the pulse density of the driving signal reaches a set value.

[0071] Optionally, after the modulator switches to pulse width plus frequency modulation, modulation is performed in n stages. In the i-th stage, f i and D i As an initial value, the frequency and duty cycle of the drive signal are adjusted to f. i+1 and D i+1 i = 1, 2, ..., n, where n is an integer greater than or equal to 2;

[0072] f i D i f i+1 and D i+1 All are preset values; the frequency and duty cycle of the drive signal are adjusted to f j and D j The corresponding gain is M j j = 1, 2, ..., n+1; coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n From coordinates (M1, t) to coordinates (M1, t) and (M2, t) n+1 The distances of the straight line segments determined by (t) do not exceed the preset distance, where t represents time.

[0073] Optional, n=2, M2=M3 / 2.

[0074] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0075] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar but different objects and are not necessarily used to describe a specific order or sequence. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0076] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0077] The system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0078] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0079] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the embodiments of the invention. Therefore, the embodiments of the invention are not to be limited to the embodiments shown herein, but are to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A soft-start control method for an LLC resonant converter, characterized in that, include: When a start command is received, the LLC resonant converter output closed-loop control system generates a drive signal to control the LLC resonant converter using pulse density modulation. When the pulse density of the drive signal reaches the set value, the drive signal is generated by pulse width and frequency modulation until the closed-loop control system reaches a steady state, at which point the soft start of the LLC resonant converter ends. The pulse width modulation plus frequency modulation method refers to a modulation method in which pulse width modulation and pulse frequency modulation are used simultaneously. The pulse width modulation plus frequency modulation method is adjusted with f1 and D1 as initial values. f1 and D1 are the frequency and duty cycle of the driving signal when the pulse density of the driving signal reaches the set value. The switching to generate the drive signal using pulse width modulation and frequency modulation includes: The modulation is performed in n stages. In the i-th stage, f i and D i As an initial value, the frequency and duty cycle of the driving signal are adjusted to f using pulse width modulation and frequency modulation. i+1 and D i+1 i = 1, 2, ..., n, where n is an integer greater than or equal to 2; Among them, f i D i f i+1 and D i+1 All are preset values; the frequency and duty cycle of the drive signal are adjusted to f j and D j The corresponding gain is M j j = 1, 2, ..., n+1; coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n From coordinates (M1, t) to coordinates (M1, t) and (M2, t) n+1 The distances of the straight line segments determined by (t) do not exceed the preset distance, where t represents time.

2. The soft-start control method for an LLC resonant converter according to claim 1, characterized in that, n=2, M2= M3 / 2.

3. The soft-start control method for an LLC resonant converter according to any one of claims 1 to 2, characterized in that, The closed-loop control system is a single-loop voltage system, a single-loop current system, or a dual-loop system consisting of an inner current loop and an outer voltage loop.

4. The soft-start control method for an LLC resonant converter according to any one of claims 1 to 2, characterized in that, The closed-loop control system employs proportional-integral-derivative (PID), proportional-integral (PI), proportional-derivative (PD), two-pole two-zero (2P2Z), two-pole single-zero (2P1Z), three-pole two-zero (3P2Z), three-pole three-zero (3P3Z), or four-pole four-zero (4P4Z) control algorithms for closed-loop control.

5. A closed-loop control system for the output of an LLC resonant converter, characterized in that, include: A sampling circuit and a control unit; the control unit includes a closed-loop controller and a modulator; The sampling circuit is used to sample the output of the LLC resonant converter and feed it back to the input of the closed-loop controller; The closed-loop controller is used to calculate the output based on the deviation between the feedback value and the reference value; The modulator is used to generate a drive signal for controlling the LLC resonant converter by taking the output signal of the closed-loop controller as input and using pulse density modulation. When the pulse density of the drive signal reaches a set value, it switches to pulse width and frequency modulation to generate the drive signal until the deviation does not exceed the preset deviation value, at which point the soft start of the LLC resonant converter ends. The pulse width plus frequency modulation method refers to a modulation method in which pulse width modulation and pulse frequency modulation are used simultaneously. The pulse width plus frequency modulation method used by the modulator is adjusted with f1 and D1 as initial values. f1 and D1 are the frequency and duty cycle of the driving signal when the pulse density of the driving signal reaches the set value. After the modulator switches to pulse width plus frequency modulation, it performs modulation in n stages. In the i-th stage, f i and D i As an initial value, the frequency and duty cycle of the drive signal are adjusted to f. i+1 and D i+1 i = 1, 2, ..., n, where n is an integer greater than or equal to 2; Among them, f i D i f i+1 and D i+1 All are preset values; the frequency and duty cycle of the drive signal are adjusted to f j and D j The corresponding gain is M j j = 1, 2, ..., n+1; coordinates (M2, t), coordinates (M3, t), ..., coordinates (M n From coordinates (M1, t) to coordinates (M1, t) and (M2, t) n+1 The distances of the straight line segments determined by (t) do not exceed the preset distance, where t represents time.

6. The LLC resonant converter output closed-loop control system according to claim 5, characterized in that, n=2, M2=M3 / 2.

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