Closed-loop soft start control system and method suitable for LLC topology

Abstract

The invention relates to a closed-loop soft start control system and method suitable for LLC topology. According to the system and the method, the output voltage soft start Ref signal is calculated based on the maximum charging energy and the input voltage sampling value when the LLC topology is started, closed-loop soft start control of the LLC topology is realized, and the working reliability and stability of the LLC topology are improved. The closed-loop soft start Ref signal only needs to be calculated once before starting, the requirement for a digital controller is low, implementation is easy, and the component cost is reduced. Besides, compared with a control mode of a current-limiting start strategy, the closed-loop soft start control method disclosed by the invention realizes closed-loop controllability of LLC topology soft start time. According to the invention, the closed-loop control of the starting time of the power supply converter based on the LLC topology is realized, the starting time sequence control among the power supply converters in the power supply system is simplified, and the working stability and compatibility of the converter are improved.

Description

Technical Field

[0001] This invention relates to the field of LLC topology closed-loop soft-start control technology, and specifically to a closed-loop soft-start control system and method suitable for LLC topology. Background Technology

[0002] With the development of the national economy and the upgrading of industrial equipment, the output voltage of primary power supplies is becoming increasingly higher, leading to the emergence of high-voltage DC bus power supply architectures. While high-voltage DC bus power supply architectures offer advantages such as high energy efficiency and simple structure, their high output voltage poses challenges to the design of secondary power supply converters. Therefore, high-efficiency converters suitable for high-voltage DC buses have attracted widespread attention. Among them, a fixed-ratio converter based on LLC topology has gained favor among researchers due to its high efficiency, small size, and low noise.

[0003] Fixed-ratio converters based on LLC topology can reduce the high-voltage DC bus to a traditional low-voltage DC bus by a designed fixed ratio K, simplifying secondary power supply design, reducing R&D costs, and improving design flexibility. In this application, the LLC topology operates with a fixed switching frequency, fixed pulse width, and open-loop control, making steady-state control relatively simple. However, the resonant inductance of the LLC topology in this application is very small, making startup difficult to control. The core optimization direction for researchers both domestically and internationally is the startup time control and startup current control of the LLC topology during startup.

[0004] Existing soft-start control strategies for LLC topologies can be broadly categorized into open-loop soft-start control strategies (including frequency modulation start-up and duty cycle modulation start-up) and closed-loop soft-start control strategies (including current-limiting modulation start-up). Frequency modulation start-up strategies have high starting switching frequencies, large starting currents, and a non-closed-loop controllable startup process; duty cycle modulation start-up strategies have high losses and a non-closed-loop controllable startup process; current-limiting modulation start-up strategies have low starting currents, low losses, and a closed-loop controllable startup process, making them more suitable for soft-start control of LLC topologies, but their control algorithms are complex and the startup time is not fixed.

[0005] by Figure 1 Taking the half-bridge LLC topology as an example, this paper introduces the LLC topology in the existing technology. Figure 1 The half-bridge LLC topology in the diagram includes primary-side power transistors Q1 and Q2, and a resonant inductor L. r Magnetizing inductance L m Resonant capacitor C r The resonant cavity, transformer T, and output filter capacitor C are all components of this system. f and load resistance R L Among them, V in For the input voltage, i p V is the resonant cavity current. Lm V is the primary voltage of the transformer. CrV is the voltage across the resonant capacitor, n:1 is the transformer turns ratio, and V o This is the output voltage. In fixed-ratio converter applications with a high-voltage DC bus power supply architecture, the above topology maintains power transistors Q1 and Q2 operating with complementary 50% duty cycles and a fixed switching frequency. During steady-state operation, the resonant capacitor C... r DC bias voltage V Cr 0.5V in Transformer primary voltage V Lm 0.5V in This topology will convert the primary voltage V of the transformer. Lm Converted to output voltage using a fixed turns ratio n:1, i.e., output voltage V o For V in / 2n. Therefore, the resonant inductance L during steady-state operation r The voltage across the terminals is V in -V Cr -n·V o This is the ripple voltage across the resonant capacitor. Therefore, during steady-state operation, the resonant cavity current changes relatively little. However, during the initial startup process of the circuit, the resonant capacitor voltage V... Cr and output voltage V o All of these need to be established gradually, including the resonant inductor L. r The voltage across the terminals is relatively high, and the resonant current i p It is very large. Therefore, at the resonant capacitor voltage V Cr and output voltage V o During the gradual establishment process, the resonant cavity current i needs to be adjusted. p Control measures must be implemented, otherwise the circuit components will be burned out. LLC resonant topologies, including half-bridge LLC and full-bridge LLC topologies, all suffer from this problem during startup.

[0006] Currently, the more commonly used soft-start control strategies for LLC topologies include the following: (1) Frequency modulation start LLC frequency modulation start-up strategy, such as Figure 2 As shown, the startup switching frequency begins at a low-gain, high-frequency point and gradually decreases to the steady-state switching frequency. This control strategy requires increasing the initial switching frequency to several MHz during startup, which is difficult to achieve due to limitations in the switching speed of the MOSFET and the driving capability of the driver. This problem is particularly prominent in high-voltage DC bus scenarios. Furthermore, this control strategy is not a closed-loop control method, which is detrimental to the stable and reliable startup process of the LLC topology.

[0007] (2) Start by adjusting the duty cycle LLC duty cycle adjustment start-up strategy, such as Figure 3As shown, during startup, the duty cycle of the primary side is adjusted from zero and increased gradually, thereby controlling the startup gain to gradually increase from a small value to the steady-state operating point. This strategy causes the primary-side power transistor to lose its soft-switching characteristics during startup. In the LLC topology, the primary-side MOSFET will generate a turn-off voltage spike oscillation, resulting in high switching losses, high stress, and a high risk of power transistor burnout. Furthermore, this control strategy is not a closed-loop control method, which is detrimental to the stable and reliable startup process of the LLC topology.

[0008] (3) Flow limiting start LLC rate limiting startup strategy, such as Figure 4 As shown, the driving PWM wave of the primary-side power transistor is adjusted in a closed loop by sampling the resonant cavity current value at startup. Figure 4 +I MAX -I represents the upper limit of the resonant cavity current during startup. MAX This is the lower limit of the resonant cavity current during startup. This control strategy is essentially a frequency modulation + duty cycle adjustment startup strategy. It requires sampling the resonant cavity current value in each switching cycle and comparing it with the resonant cavity current limit to calculate the duty cycle and frequency of the power transistor's PWM wave signal for the next cycle. Calculating the PWM wave frequency and duty cycle of the power transistor for the next switching cycle based on the sampled resonant cavity current value and the resonant cavity current limit in each switching cycle requires the digital controller to have extremely high digital signal processing capabilities. Since the switching frequency of current fixed-ratio converters using LLC topologies is generally around 1MHz, it is extremely difficult for the digital controller to achieve a control closed loop within approximately 1 microsecond. Furthermore, this current-limiting startup control strategy adjusts the PWM waveform based on the limited resonant cavity current value, resulting in inconsistent startup times under different load conditions, which is detrimental to system stability and compatibility between power supply equipment. This control strategy achieves soft-start of the LLC topology based on the limited resonant cavity current value. The soft-start time of the LLC topology is long when the load is heavy and short when the load is light, which is also detrimental to power supply stability and compatibility between power supply equipment.

[0009] Therefore, in order to overcome the shortcomings of the existing technology, there is an urgent need to realize a closed-loop soft-start control system and method suitable for LLC topology. Summary of the Invention

[0010] The purpose of this invention is to provide a closed-loop soft-start control system and method suitable for LLC topologies. This control system and method can overcome the shortcomings of the prior art. Based on the maximum charging energy value and input voltage sampling value required during the soft-start process, a soft-start Ref reference signal is designed. Based on the soft-start Ref reference signal, closed-loop soft-start of LLC topologies is realized, achieving closed-loop controllability of the startup process, improving circuit compatibility and stability, and reducing the complexity of circuit control.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect of the invention, a closed-loop soft-start control system suitable for LLC topologies is disclosed. The control system includes a closed-loop feedback control unit; the closed-loop feedback control unit includes a Ref signal generation module, an error feedback signal generation module, and a soft-start control module.

[0012] The Ref signal generation module is used to calculate the maximum charging energy required for the LLC topology startup process based on the load characteristics and resonant capacitor characteristics in the LLC topology, and generate a soft-start Ref reference signal by combining the input voltage sampling value and the set average charging current of the resonant cavity.

[0013] The error feedback signal generation module is used to acquire the output voltage of the LLC topology in real time and compare it with the soft-start Ref reference signal to calculate the deviation value and generate an error feedback signal.

[0014] The soft-start control module is used to transmit the error feedback signal to the LLC topology and control the resonant cavity current by adjusting the resonant cavity impedance to achieve closed-loop soft-start control of the LLC topology.

[0015] As a further improvement to the above scheme, the control system also includes: a primary-side power circuit, a resonant cavity, a transformer T, and an output filter capacitor C. f and load resistance R L .

[0016] The input terminal of the primary power circuit is connected to the DC input voltage V. in The output terminal is connected to the input terminal of the resonant cavity; the output terminal of the resonant cavity is connected to the primary side of the transformer T; the secondary side of the transformer T is connected to a rectifier circuit, and the output terminal of the rectifier circuit is connected to the output filter capacitor C. f One end of the load resistor R L One end is connected to the output filter capacitor C. f The other end is connected to the load resistor R L The other end is connected.

[0017] As a further improvement to the above scheme, the control system also includes an auxiliary source circuit unit and a drive unit.

[0018] The input terminal of the auxiliary source circuit unit is connected to the output terminal of the soft-start control module, the output terminal of the auxiliary source circuit unit is connected to the input terminal of the drive unit, and the output terminal of the drive unit is connected to the primary-side power circuit.

[0019] The auxiliary source circuit unit is used to receive the error feedback signal output by the soft-start control module and adjust the power supply voltage output to the drive unit according to the error feedback signal.

[0020] The driving unit is used to adjust the amplitude of the driving signal output to the primary power circuit according to the power supply voltage.

[0021] The primary-side power circuit is used to adjust the channel resistance of its power transistor according to the amplitude of the driving signal, so as to change the impedance of the resonant cavity and realize closed-loop control of the resonant cavity current.

[0022] As a further improvement to the above scheme, the resonant cavity includes: a resonant inductor L r Magnetizing inductance L m and resonant capacitor C r The resonant inductor L r With the excitation inductor L m Then connected in series with the resonant capacitor C r The resonant cavity is connected in series with the primary side of the transformer T.

[0023] In a second aspect of the invention, a closed-loop soft-start control method suitable for LLC topologies is disclosed, the method comprising the following steps: S1, based on the full-load resistance R of the LLC topology Lmax Resonant capacitor C r The capacity and output filter capacitor C f Calculate the maximum charging energy E during the LLC topology startup process based on its capacity. max And combined with the input voltage V in The sampled value and the set average charging current i of the resonant cavity pmax Determine the soft-start time t of the LLC topology. start Generate a soft-start Ref reference signal.

[0024] S2, Real-time acquisition of output voltage V o The error feedback signal is generated by comparing it with the soft-start Ref reference signal.

[0025] S3. Based on the error feedback signal, adjust the power supply voltage of the drive unit output to the LCC topology, and adjust the amplitude of the drive signal output to the primary-side power circuit in the LLC topology based on the power supply voltage.

[0026] S4. The primary-side power circuit adjusts the channel resistance of the power transistor according to the amplitude of the drive signal, thereby changing the impedance of the resonant cavity and controlling the resonant cavity current i. p This makes the output voltage V o Establish the soft start reference signal based on the soft start Ref signal to complete the soft start.

[0027] As a further improvement to the above scheme, the maximum charging energy The calculation formula is: ; in, This represents the maximum charging energy during the LLC topology startup process; Indicates the resonant capacitance; Represents resonant capacitor The voltage across the two ends; Indicates the output filter capacitor; Indicates the input voltage; This indicates the input-output transmission ratio of a fixed-ratio converter; This represents the full-load resistance of the LLC topology; This indicates the soft-start time of the LLC topology.

[0028] As a further improvement to the above solution, the soft start time The calculation formula is: ; in, Indicates the soft-start time of the LLC topology; This indicates the input-output transmission ratio of a fixed-ratio converter; This represents the full-load resistance of the LLC topology; Indicates the resonant capacitance; Represents resonant capacitor The voltage across the two ends; Indicates the output filter capacitor; Indicates the input voltage; This represents the maximum charging energy during the LLC topology startup process; Indicates the excitation inductance L m The voltage across the two ends; This represents the set average charging current of the resonant cavity.

[0029] Compared with the prior art, the advantages of the present invention are: (1) The closed-loop soft-start control system and method of the present invention calculates the soft-start signal of the output voltage based on the maximum charging energy and the input voltage sampling value during startup, thereby realizing the closed-loop soft-start control of the LLC topology. Compared with the two open-loop soft-start strategies of frequency modulation startup and duty cycle modulation startup, the present invention improves the reliability and stability of the LLC topology. At the same time, compared with the closed-loop soft-start control method of sampling and calculating the resonant cavity current cycle by cycle in the current limiting startup strategy, the present invention only needs to calculate the closed-loop soft-start signal once before startup. Therefore, the present invention has low requirements for the digital controller in terms of the implementation of the control method and is easy to implement; in practical applications, a lower-cost digital controller can be selected, reducing the component cost. In addition, the closed-loop soft-start control method of the present invention, compared with the closed-loop soft-start control method of the current limiting startup strategy, realizes the closed-loop controllability of the soft-start time of the LLC topology. The converter with constant soft-start time is more convenient to cooperate with other power supply converters in the power supply system to complete the power supply timing control for equipment startup, improving the stability and compatibility of the converter operation.

[0030] (2) This invention achieves closed-loop controllability of the resonant cavity current during the soft-start process of the LLC topology, effectively avoiding the problem of excessive starting current causing component damage and ensuring circuit safety during the startup phase. This control method only requires calculating the closed-loop soft-start Ref reference signal once before startup, without needing to sample and calculate cycle by cycle during startup. This significantly reduces the signal processing capability requirements of the digital controller, making it easier to implement in engineering applications and allowing the selection of lower-cost controllers, thus greatly reducing component costs. Through precise Ref signal design, this control method can ensure that the LLC topology maintains a constant closed-loop soft-start time under different load conditions, without needing to adjust startup parameters due to load changes. This significantly improves the timing compatibility of the converter based on this topology with other devices in the power supply system, while also enhancing overall power supply stability. This invention supports adjusting the average charging current i of the resonant cavity according to the needs of the actual application scenario. pmax This allows for flexible setting and adjustment of the soft-start time in LLC topology configuration. This improves the flexibility of LLC topology operation, enabling better application to various complex scenarios. Attached Figure Description

[0031] Figure 1 This is a diagram of the existing half-bridge LLC topology; Figure 2 This is a diagram of the LLC frequency modulation startup strategy in the existing technology; Figure 3 This is a diagram of the LLC duty cycle adjustment startup strategy in existing technology; Figure 4 This is a diagram of the LLC rate-limiting startup strategy in existing technology; Figure 5This is a block diagram of the closed-loop soft-start control method applicable to LLC topology in this invention; Figure 6 This is the waveform diagram of the closed-loop feedback Ref signal; Figure 7 This is a waveform diagram of the closed-loop feedback Ref signal in a specific embodiment; Figure 8 This is a waveform diagram verifying the closed-loop soft-start control method. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings: Example 1 In existing technologies, LLC topologies require resonant cavity current control during startup; improper control can lead to startup failure due to excessive resonant cavity current. To address this issue, this invention discloses a method such as... Figure 5 The diagram shows a closed-loop soft-start control system suitable for LLC topology. The system includes: a primary-side power circuit, a resonant cavity, a transformer T, a rectifier circuit, and an output filter capacitor C. f Load resistance R L It consists of a closed-loop feedback control unit, an auxiliary source circuit unit, and a drive unit.

[0033] As a further improvement to the above scheme, the closed-loop feedback control unit includes a Ref signal generation module, an error feedback signal generation module, and a soft-start control module. The Ref signal generation module is used to calculate the maximum charging energy required for the LLC topology startup process based on the load characteristics and resonant capacitor characteristics in the LLC topology, and generate a soft-start Ref reference signal by combining the input voltage sampling value with the set average resonant cavity charging current. The error feedback signal generation module is used to collect the output voltage of the LLC topology in real time and compare it with the soft-start Ref reference signal to calculate the deviation value and generate an error feedback signal. The soft-start control module is used to transmit the error feedback signal to the LLC topology and control the resonant cavity current by adjusting the resonant cavity impedance to achieve closed-loop soft-start control of the LLC topology. The closed-loop feedback control unit is the core unit in the closed-loop soft-start control system of the present invention. This unit is used to calculate the maximum charging energy during the LLC topology startup process and, based on the average resonant cavity charging current i... pmax The soft-start time of the LLC topology is calculated, and the Ref signal is then calculated.

[0034] The core logic of this invention is based on the maximum charging energy required during the LLC topology startup process. Combined with the input voltage sampling value, a soft-start reference signal for the output voltage (Ref) is calculated and generated. During actual startup, the output voltage of the LLC topology gradually builds up according to the designed Ref signal, ultimately achieving closed-loop soft-start control of the LLC topology. It should be noted that the average charging current value i of the resonant cavity needs to be introduced during the calculation of the soft-start Ref signal. pmax This is a key parameter, and its value can be flexibly adjusted according to actual application scenarios and needs to adapt to diverse startup control requirements.

[0035] During the soft-start process of the LLC topology, the resonant capacitor C needs to be adjusted. r Output capacitor C f Load resistance R L If the charging process is not controlled, excessive charging current can easily be generated, thus hindering the normal startup of the LLC topology. To solve this problem, this invention uses a closed-loop feedback control unit to calculate the resonant capacitor C required to complete the soft-start process. r Output capacitor C f Load resistance R L The maximum charging energy required for charging. Since this charging energy needs to be transferred and injected through the resonant cavity current, this invention sets the average charging current i of the resonant cavity. pmax The three components are charged using this average charging current to achieve resonant cavity current control. After determining the maximum charging energy and the average charging current of the resonant cavity, the charging time, i.e., the constant soft-start time described in this invention, can be determined.

[0036] As is well known, determining the reference signal requires not only the X-axis time value but also the Y-axis amplitude value. In this invention, the LLC topology operates in an open-loop state during steady-state operation, and its output voltage follows the input voltage change, maintaining a fixed proportional relationship between the two. Based on this characteristic, the output voltage value needs to be calculated by sampling the input voltage value, and then the target value of the output voltage is calculated by combining it with a preset fixed transmission ratio. Finally, the amplitude value of the Ref signal on the Y-axis is calculated based on this. In a specific embodiment, the final amplitude value of the Ref signal is increased by several volts to bring the closed-loop feedback unit into a saturated operating state. This ensures that the auxiliary source output voltage is saturated to maximize the auxiliary voltage output, and also minimizes the channel resistance of the primary-side power MOSFET, thereby effectively reducing power loss during stable operation of the LLC topology after soft-start and optimizing overall energy efficiency.

[0037] The purpose of the above calculations is to generate a suitable Ref signal, which guides the LLC topology to ensure that, during startup, it can achieve the preset average resonant cavity charging current i. pmaxThe LLC topology is started with a fixed value and a fixed soft-start time, thus achieving closed-loop soft-start control. As long as the LLC topology strictly follows the designed Ref signal to gradually build up the output voltage during the startup phase, two key control indicators can be achieved simultaneously: precise control of the resonant cavity current and constant control of the soft-start time.

[0038] As a further improvement to the above scheme, the Ref signal generation module includes a digital controller with sampling function, which is used to generate the Ref reference signal. The digital controller first acquires the real-time input voltage data of the LLC topology; then, it combines this data with the fixed resonant capacitor C of the LLC topology. r Value, output capacitor C f Value, full load resistance R L value R Lmax And the average charging current i of the resonant cavity set according to actual needs. pmax The value is used to calculate the reference Ref signal waveform that meets the requirements of soft-start control.

[0039] The core of the error feedback signal generation module lies in generating an error feedback signal by sampling the output voltage of the LLC topology, without limiting the specific circuit structure. In practical applications, the hardware circuit can be flexibly designed according to requirements. The output voltage of the LLC topology can be directly connected to the feedback port of the operational amplifier, or the output voltage can be divided by resistors before being connected to the feedback port of the operational amplifier.

[0040] The error feedback signal generation module is a typical negative feedback circuit composed of operational amplifiers. This negative feedback circuit is a type II compensation circuit commonly used in feedback control systems. A set of resistor-capacitor components is connected in series between the negative feedback port and the output port of the operational amplifier, followed by a capacitor in parallel. It should be noted that common negative feedback circuits in feedback control systems also include type I compensation and type III compensation circuit structures, all of which can be applied to the error feedback signal generation module of this invention and can meet the control requirements of LLC topology closed-loop soft start. Therefore, this invention does not provide a detailed description of the specific circuit form of this module, but focuses on clarifying its core functional logic of acquiring the output voltage and generating the error feedback signal.

[0041] The working principle of the aforementioned three modules—Ref signal generation module, error feedback signal generation module, and soft-start control module—is as follows: The Ref signal generated by the Ref signal generation module serves to achieve constant soft-start time for the LLC topology and closed-loop control of the resonant cavity current, which is the core inventive point of this invention. Based on this Ref signal and combined with the real-time sampled LLC topology output voltage, closed-loop control logic is constructed to achieve closed-loop soft-start of the LLC topology. The LLC topology output voltage only needs to follow the calculated Ref signal to achieve constant resonant cavity current control and start-up time. Subsequent auxiliary source circuit units and drive units all serve this Ref signal, adjusting the supply voltage and drive signal amplitude by receiving the closed-loop feedback control signal, ultimately ensuring that the LLC topology output voltage can stably follow the Ref signal to complete the soft-start process.

[0042] As a further improvement to the above scheme, the input terminal of the primary-side power circuit is connected to the DC input voltage V. in The output terminal is connected to the input terminal of the resonant cavity; the output terminal of the resonant cavity is connected to the primary side of the transformer T; the secondary side of the transformer T is connected to a rectifier circuit, and the output terminal of the rectifier circuit is connected to the output filter capacitor C. f One end of the load resistor R L One end is connected to the output filter capacitor C. f The other end is connected to the load resistor R L The other end is connected. It should be noted that the above consists of the primary power circuit, resonant cavity, transformer T, rectifier circuit, and output filter capacitor C. f and load resistance R L The resulting circuit structure is known as an LLC topology circuit.

[0043] As a further improvement to the above scheme, the input terminal of the auxiliary source circuit unit is connected to the output terminal of the soft-start control module, the output terminal of the auxiliary source circuit unit is connected to the input terminal of the drive unit, and the output terminal of the drive unit is connected to the primary-side power circuit. The auxiliary source circuit unit is used to receive the error feedback signal output by the soft-start control module and adjust the supply voltage output to the drive unit according to the error feedback signal. The drive unit is used to adjust the amplitude of the drive signal output to the primary-side power circuit according to the supply voltage. The primary-side power circuit is used to adjust the channel resistance of its power transistor according to the amplitude of the drive signal to change the impedance of the resonant cavity and achieve closed-loop control of the resonant cavity current.

[0044] To enable the LLC topology to soft-start following the design's Ref signal, this invention adjusts the channel resistance of the MOSFET by regulating the voltage amplitude of the drive signal, thereby controlling the resonant cavity impedance and ultimately the resonant cavity current. By controlling the resonant cavity current, the LLC topology can avoid starting with an extremely large resonant cavity current within a few µs. Since the voltage amplitude of the drive signal originates from the supply voltage of the auxiliary source, this invention uses the output error signal of the closed-loop feedback unit as a reference for the auxiliary source circuit unit to regulate the supply voltage of the auxiliary source.

[0045] As a further improvement to the above scheme, the resonant cavity includes: a resonant inductor L r Magnetizing inductance L m and resonant capacitor C r The resonant inductor L r With the excitation inductor L m Then connected in series with the resonant capacitor C r The resonant cavity is connected in series, with its output terminal connected to the primary side of the transformer T. Figure 5 In the middle, V in For the input voltage, i p V is the resonant cavity current. Lm V is the primary voltage of transformer T. Cr For the resonant capacitor C r Voltage across terminals, n:1 is the turns ratio of transformer T, V o This is the output voltage.

[0046] like Figure 5 As shown, the resonant inductor L r The first terminal is connected to the first terminal of the primary power circuit, and the resonant inductor L r The second terminal is connected to the magnetizing inductor L m The first end is connected; the excitation inductor L m The second end is connected to the resonant capacitor C r The first end is connected, and the resonant capacitor C is connected. r The second terminal is connected to the second terminal of the primary power circuit. The magnetizing inductor L m The first terminal is connected to the corresponding terminal of the primary side of transformer T, and the magnetizing inductor L m The second terminal is connected to the opposite terminal of the primary winding of transformer T. Transformer T is used to transfer energy and transform voltage. The secondary winding of transformer T is connected to a rectifier circuit, which is typically a rectifier bridge structure composed of diodes. The output after rectification by the rectifier circuit passes through a filter capacitor C. f Filtering, supplying the load resistor R L Power supply, and simultaneously sample the output voltage V o Used for closed-loop feedback. Input voltage V inThe circuit is connected to the primary-side power circuit, and the output of the primary-side power circuit is connected to the input of the resonant cavity. The current i generated in the resonant cavity... p Participating in subsequent energy transfer processes. Figure 5 In the LLC topology circuit shown, the primary-side power circuit is mainly used to convert the DC input voltage V in The transformation is performed to drive the resonant cavity and provide the basis for energy transfer and conversion throughout the circuit.

[0047] Furthermore, the primary-side power circuit is composed of power switching transistors. Figure 5 The diagram illustrates a pair of switching transistors with anti-parallel diodes. Power switches in the primary-side power circuit typically use MOSFETs or similar switching devices. In a half-bridge LLC topology, two power switches are usually included; the input DC voltage is modulated by controlling the on / off state of these two switches. The drive signal output from the drive unit controls the on / off state of the switches in the primary-side power circuit. When one switch in the primary-side power circuit is on, the DC input voltage V... in The current is applied to a portion of the resonant cavity circuit. When another switch in the primary power circuit is turned on, the current flow direction changes. By periodically controlling the switching on and off of the switch, the DC input voltage is converted into a high-frequency AC square wave voltage, which in turn drives the resonant inductor L in the resonant cavity. r Magnetizing inductance L m and resonant capacitor C r Resonance is generated. During the conduction period of the switching transistor, energy is transferred from the DC power supply to the resonant cavity through the primary-side power circuit, and then to the secondary side through the transformer T. During the turn-off period of the switching transistor, energy storage components such as inductors and capacitors in the circuit store and convert energy to maintain the continuous operation of the circuit. In the closed-loop soft-start control method proposed in this invention, the primary-side power circuit operates in an appropriate manner in the initial stage of startup based on the output error signal of the closed-loop feedback unit, limiting the current in the resonant cavity and avoiding excessive startup current. As the soft-start process progresses, the primary-side power circuit gradually adjusts its operating state according to the control requirements of the closed-loop feedback, ultimately achieving a smooth startup and entering a stable energy conversion operating mode.

[0048] Example 2 This invention also includes a closed-loop soft-start control method suitable for LLC topologies, the method comprising the following steps: S1, based on the full-load resistance R of the LLC topology Lmax Resonant capacitor C r The capacity and output filter capacitor C f Calculate the maximum charging energy E during the LLC topology startup process based on its capacity. max And combined with the input voltage V inThe sampled value and the set average charging current i of the resonant cavity pmax Determine the soft-start time t of the LLC topology. start Generate a soft-start Ref reference signal.

[0049] S2, Real-time acquisition of output voltage V o The error feedback signal is generated by comparing it with the soft-start Ref reference signal.

[0050] S3. Based on the error feedback signal, adjust the power supply voltage of the drive unit output to the LCC topology, and adjust the amplitude of the drive signal output to the primary-side power circuit in the LLC topology based on the power supply voltage.

[0051] S4. The primary-side power circuit adjusts the channel resistance of the power transistor according to the amplitude of the drive signal, thereby changing the impedance of the resonant cavity and controlling the resonant cavity current i. p This makes the output voltage V o Establish the soft start reference signal based on the soft start Ref signal to complete the soft start.

[0052] As a further improvement to the above scheme, the maximum charging energy The calculation formula is: ; in, This represents the maximum charging energy during the LLC topology startup process; Indicates the resonant capacitance; Represents resonant capacitor The voltage across the two ends; Indicates the output filter capacitor; Indicates the input voltage; This indicates the input-output transmission ratio of a fixed-ratio converter; This represents the full-load resistance of the LLC topology; This indicates the soft-start time of the LLC topology.

[0053] As a further improvement to the above solution, the soft start time The calculation formula is: ; in, Indicates the soft-start time of the LLC topology; This indicates the input-output transmission ratio of a fixed-ratio converter; This represents the full-load resistance of the LLC topology; Indicates the resonant capacitance; Represents resonant capacitor The voltage across the two ends; Indicates the output filter capacitor; Indicates the input voltage; This represents the maximum charging energy during the LLC topology startup process; Indicates the excitation inductance L m The voltage across the two ends; This represents the set average charging current of the resonant cavity.

[0054] As can be seen from the above, this invention first calculates the maximum charging energy E of the LLC topology during the startup process based on the load characteristics and resonant capacitor characteristics of the fixed-ratio converter. max Combined with input voltage V in The sampled values ​​are used to calculate the soft-start Ref signal output by the LLC topology. The closed-loop feedback unit generates an error feedback signal based on this soft-start Ref signal and sends it to the auxiliary source circuit unit. The auxiliary source circuit unit uses this error feedback signal as a reference signal to adjust the supply voltage to the drive unit. The drive unit outputs drive signals with different voltage amplitudes to the primary-side power circuit due to different supply voltages. The primary-side power circuit unit adjusts the channel resistance of the primary-side power transistor based on the drive voltage amplitude from the closed-loop feedback. Since the primary-side power transistor is connected in series in the resonant cavity circuit, adjusting the channel resistance of the primary-side power transistor is equivalent to adjusting the resonant cavity impedance. Based on the principle that a large resonant cavity impedance results in a small resonant cavity current, and a small resonant cavity impedance results in a large resonant current, closed-loop control of the resonant cavity current is achieved.

[0055] In summary, this invention requires calculating the closed-loop feedback Ref signal based on the maximum charging energy and the input voltage sampling value before startup to control the startup current and startup time of the soft-start process. The maximum charging energy, based on the load characteristics and resonant capacitor characteristics of the fixed-ratio converter, needs to be configured in advance. The main charging unit in the LLC topology startup process includes the resonant capacitor C. r Output capacitor C f Load resistance R L Therefore, the maximum charging energy E during the startup process is calculated using the following formula. max : (1); In the formula, V o (t) represents the output voltage V during LLC startup. o A function that changes with time t, t start For the soft start time of the LLC topology, R Lmax The load resistor is the load resistor under full-load startup conditions for the LLC topology.

[0056] Assume the input voltage sampling value is V in If the input-output transfer ratio of a fixed-ratio converter is K, then the steady-state value of the output voltage V can be determined. o for: (2); Taking the commonly used output ramp start-up method as an example, the function of output voltage with time during LLC topology startup is: (3); The maximum charging energy during startup can be determined using the following formula. : (4); The above formula can be simplified to: (5); Assume the average charging current of the resonant cavity at startup is set to i. pmax Ignoring the impact of dead time, the energy supplied by the primary side during the LLC topology startup process needs to match the maximum charging energy, approximately as follows: (6); The soft-start time of the LLC topology can be derived from the above formula. for: (7).

[0057] The above soft start time t start Although the calculation is relatively complex, it only needs to be performed once before each startup, thus requiring low computational power from the digital control chip and is easy to implement. The aforementioned soft-start time t... start Based on the maximum charging energy during the LLC topology startup process, the resonant cavity current is smaller when the LLC topology is not fully loaded during startup, ensuring the safety and reliability of the LLC topology startup.

[0058] In summary, the closed-loop feedback Ref signal obtained by the soft-start control method described in this invention is as follows: Figure 6 As shown. To ensure minimal impedance of the resonant cavity and high steady-state operating efficiency after soft-start of the LLC topology, the closed-loop feedback Ref signal waveform is designed to continue increasing to V after soft-start. in / K+mV. This invention uses the closed-loop feedback Ref signal as the soft-start signal for the LLC topology output voltage, controlling the LLC topology resonant cavity current in a closed loop and realizing the LLC topology output voltage at t start Time-based soft boot to V in / K.

[0059] Depend on Figure 6 As can be seen from the closed-loop feedback Ref signal waveform, the closed-loop control method described in this invention controls the resonant cavity current by adjusting the reference value of the output voltage during the LLC topology startup process. During the LLC topology startup process, the closed-loop control method initially limits the resonant cavity current with a very small output voltage reference value and a large resonant cavity impedance. Then, it gradually increases the output voltage reference value and decreases the resonant cavity impedance to ultimately achieve a soft start for the LLC topology.

[0060] The LLC topology closed-loop soft-start control method described in this invention calculates the closed-loop feedback Ref signal based on the maximum charging energy and the sampled input voltage value to control the starting current and starting time during the soft-start process. Figure 1 Taking the half-bridge LLC topology as an example, the closed-loop soft-start control method of the present invention is verified, and the implementation parameters are shown in Table 1.

[0061] Table 1 Implementation Parameters

[0062] Based on the parameters in Table 1, calculate the steady-state value V of the output voltage. o for: ; Calculate LLC soft start time t start for: .

[0063] The waveform of the closed-loop feedback Ref signal is designed as follows: Figure 7 As shown, based on the implementation parameters in Table 1 and Figure 7 The closed-loop feedback Ref signal in the middle is verified by the waveform diagram shown below. Figure 8 As shown. From Figure 8 As can be seen from the waveforms, based on the designed closed-loop feedback Ref signal, the LLC topology completes the soft-start of the output voltage at approximately the designed value of 168.26µs. Simultaneously, based on the designed closed-loop feedback Ref signal, during the soft-start process, the LLC topology adjusts the amplitude of the auxiliary source output voltage and the drive waveform voltage in real time to control the resonant cavity impedance, achieving closed-loop controllable resonant cavity current. The experimental results are basically consistent with the content of the scheme described in this invention.

[0064] In summary, this invention designs a closed-loop feedback Ref signal based on the calculated maximum charging energy and the sampled input voltage. The calculation of the closed-loop feedback Ref signal only needs to be performed once at the beginning of the LLC topology soft start, simplifying control, reducing the requirements for the digital signal processing capabilities of the digital controller, facilitating digital controller selection, and lowering digital controller costs. The LLC topology output voltage soft start process, based on the closed-loop feedback Ref signal, ensures a constant soft start time, facilitating compatibility and coordination between the fixed-ratio converter power supply and other power supplies in the power supply equipment, thus improving the converter's power supply compatibility. At the beginning of the LLC topology soft start, the closed-loop feedback Ref signal voltage is very low. The auxiliary source voltage increases the resonant cavity impedance based on this low voltage, thereby controlling the resonant cavity current. Subsequently, this invention gradually increases the Ref voltage and decreases the resonant cavity impedance, achieving controllable resonant cavity current during the LLC start-up process. The closed-loop feedback Ref signal designed using the method described in this invention continues to increase until the Ref amplitude reaches V after the LLC topology soft start is achieved. in / K+mV, to achieve the lowest resonant cavity impedance and optimal efficiency of the LLC topology after soft-start. The soft-start time of the closed-loop feedback Ref signal designed using the method described in this invention is related to the set average resonant cavity charging current i. pmax Relatedly, in practical applications, within the acceptable range of average resonant cavity charging current, this invention allows for flexible adjustment of the set soft-start time according to the application scenario, improving the flexibility of LLC topology operation.

[0065] The core innovation of this invention lies in addressing the fundamental charging energy requirements during the LLC topology startup process. It breaks away from the conventional approach of relying on current limitations or frequency / duty cycle adjustments. This not only enables flexible and controllable resonant cavity current during the LLC topology soft-start process but also ensures a constant soft-start time under different load conditions, solving the core pain point of unstable startup timing caused by load variations in traditional solutions. This invention is simple to implement, yields significant results, and features a unique implementation approach, achieving this through unconventional techniques. From a technical implementation perspective, the closed-loop soft-start control system and method described in this invention accurately calculates the output voltage soft-start Ref signal by using the maximum charging energy calculated before startup and the input voltage sampling value, thus realizing closed-loop soft-start control of the LLC topology. This control system and method is not a combination of conventional techniques but an innovative design based on the startup characteristics of the LLC topology. This invention establishes the correlation logic between energy, current, and time through rigorous circuit theory reasoning and provides detailed calculation methods for key parameters such as maximum charging energy and soft-start time. The circuit's feasibility has been thoroughly verified.

[0066] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A closed-loop soft-start control system suitable for LLC topology, characterized in that, The control system includes: a closed-loop feedback control unit; the closed-loop feedback control unit includes a Ref signal generation module, an error feedback signal generation module, and a soft-start control module; The Ref signal generation module is used to calculate the maximum charging energy required for the LLC topology startup process based on the load characteristics and resonant capacitor characteristics in the LLC topology, and generate a soft-start Ref reference signal by combining the input voltage sampling value and the set average charging current of the resonant cavity. The error feedback signal generation module is used to acquire the output voltage of the LLC topology in real time and compare it with the soft-start Ref reference signal to calculate the deviation value and generate an error feedback signal. The soft-start control module is used to transmit the error feedback signal to the LLC topology and control the resonant cavity current by adjusting the resonant cavity impedance to achieve closed-loop soft-start control of the LLC topology.

2. The closed-loop soft-start control system suitable for LLC topology according to claim 1, characterized in that, The control system also includes: primary power circuit, resonant cavity, transformer T, and output filter capacitor C. f and load resistance R L ; The input terminal of the primary power circuit is connected to the DC input voltage V. in The output terminal is connected to the input terminal of the resonant cavity; the output terminal of the resonant cavity is connected to the primary side of the transformer T; the secondary side of the transformer T is connected to a rectifier circuit, and the output terminal of the rectifier circuit is connected to the output filter capacitor C. f One end of the load resistor R L One end is connected to the output filter capacitor C. f The other end is connected to the load resistor R L The other end is connected.

3. The closed-loop soft-start control system suitable for LLC topology according to claim 2, characterized in that, The control system also includes: an auxiliary source circuit unit and a drive unit; The input terminal of the auxiliary source circuit unit is connected to the output terminal of the soft-start control module, the output terminal of the auxiliary source circuit unit is connected to the input terminal of the drive unit, and the output terminal of the drive unit is connected to the primary-side power circuit. The auxiliary source circuit unit is used to receive the error feedback signal output by the soft-start control module and adjust the power supply voltage output to the drive unit according to the error feedback signal. The driving unit is used to adjust the amplitude of the driving signal output to the primary-side power circuit according to the power supply voltage. The primary-side power circuit is used to adjust the channel resistance of its power transistor according to the amplitude of the driving signal, so as to change the impedance of the resonant cavity and realize closed-loop control of the resonant cavity current.

4. The closed-loop soft-start control system suitable for LLC topology according to claim 2, characterized in that, The resonant cavity includes: a resonant inductor L r Magnetizing inductance L m and resonant capacitor C r The resonant inductor L r With the excitation inductor L m Then connected in series with the resonant capacitor C r The resonant cavity is connected in series with the primary side of the transformer T.

5. A closed-loop soft-start control method suitable for LLC topologies, characterized in that, The method includes the following steps: S1, based on the full-load resistance R of the LLC topology Lmax Resonant capacitor C r The capacity and output filter capacitor C f Calculate the maximum charging energy E during the LLC topology startup process based on its capacity. max And combined with the input voltage V in The sampled value and the set average charging current i of the resonant cavity pmax Determine the soft-start time t of the LLC topology. start Generate the soft-start Ref reference signal; S2, Real-time acquisition of output voltage V o The error feedback signal is generated by comparing it with the soft-start Ref reference signal. S3. Based on the error feedback signal, adjust the power supply voltage of the drive unit output to the LCC topology, and adjust the amplitude of the drive signal output to the primary-side power circuit in the LLC topology based on the power supply voltage. S4. The primary-side power circuit adjusts the channel resistance of the power transistor according to the amplitude of the drive signal, thereby changing the impedance of the resonant cavity and controlling the resonant cavity current i. p Make the output voltage V o Establish the soft start reference signal based on the soft start Ref signal to complete the soft start.

6. The closed-loop soft-start control method for LLC topologies according to claim 5, characterized in that, The maximum charging energy The calculation formula is: ； in, This represents the maximum charging energy during the LLC topology startup process; Indicates the resonant capacitance; Represents resonant capacitor The voltage across the two ends; Indicates the output filter capacitor; Indicates the input voltage; This indicates the input-output transmission ratio of a fixed-ratio converter; This represents the full-load resistance of the LLC topology; This indicates the soft-start time of the LLC topology.

7. The closed-loop soft-start control method for LLC topologies according to claim 6, characterized in that, The soft start time The calculation formula is: ； in, Indicates the soft-start time of the LLC topology; This indicates the input-output transmission ratio of a fixed-ratio converter; This represents the full-load resistance of the LLC topology; Indicates the resonant capacitance; Represents resonant capacitor The voltage across the two ends; Indicates the output filter capacitor; Indicates the input voltage; This represents the maximum charging energy during the LLC topology startup process; Indicates the excitation inductance L m The voltage across the two ends; This represents the set average charging current of the resonant cavity.

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