Output current ripple reduction method applied to PFC and LLC two-stage charging device

Abstract

The invention discloses an output current ripple reduction method applied to a PFC and LLC two-stage charging device, and relates to the technical field of power electronic conversion. According to the method, effective suppression of 100Hz power frequency ripples in output current is realized by configuring ripple compensation logic and a DCBus dynamic adjustment module. The ripple compensation logic comprises a 100Hz quasi-resonance controller and a PI controller, the 100Hz quasi-resonance controller extracts and amplifies 100Hz ripple information from an original error signal of an output current feedback signal and a reference signal, the 100Hz ripple information and the original error signal are synthesized into an optimized error signal, and the optimized error signal is processed by the PI controller to generate a PFM signal to control an LLC module power tube; and the DCBus dynamic adjustment module outputs a voltage reference adjustment amount to the PFC module by collecting the operation frequency of the LLC module so as to adjust the voltage reference value of the DCBus, so that the LLC module always works near the resonant frequency so as to obtain a stable 100Hz power frequency ripple suppression effect. The method does not need an additional current sensor, reduces the hardware cost and performance requirements, is stable in ripple suppression effect, and is suitable for charging scenes of electric vehicles, energy storage batteries and the like.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion, specifically to a method for reducing output current ripple in a two-stage charging device using PFC and LLC. Background Technology

[0002] In the field of charging devices, the PFC+LLC two-stage topology is widely used in various battery charging scenarios due to its advantages such as high power factor, high conversion efficiency, and wide output voltage adjustment range. In this topology, the PFC module converts the AC grid voltage into a stable DC bus voltage, and the LLC module uses this DC bus voltage to achieve constant current or constant voltage charging control of the battery. However, since the grid voltage is a 50Hz sine wave, both the grid voltage and current on the input side of the PFC module exhibit a 50Hz periodic change, resulting in a fluctuation of twice the power frequency (100Hz) in the instantaneous power output of the PFC module. According to the principle of power conservation, as the downstream stage of energy transfer, the LLC module inevitably introduces this 100Hz power frequency ripple into its output charging current. This ripple not only affects the stability of the charging process but may also exacerbate the internal polarization effect of the battery and shorten its lifespan. Therefore, effective measures must be taken to suppress the 100Hz ripple in the output current.

[0003] In existing technologies, two main solutions are used to address the aforementioned ripple problem. One is based on a conventional single PI control loop, which increases the interrupt operation frequency and open-loop crossover frequency of the control loop to achieve higher gain at 100Hz to suppress ripple. However, this solution has significant limitations: firstly, it requires a high-performance DSP chip to support high-frequency interrupt operations, increasing hardware costs, and it is difficult to integrate the control logic of PFC and LLC into the same chip; secondly, a high crossover frequency can easily lead to insufficient loop phase margin, imposing stringent requirements on PI parameter design, and the operating frequency of the LLC module at different charging powers can cause fluctuations in the open-loop gain curve, resulting in unstable ripple suppression performance.

[0004] Another approach involves adding a current sensor to the rectifier side of the LLC module transformer to sample the ripple signal and feed it back to the control loop for compensation. However, this approach requires an additional current sensor, increasing hardware costs. Furthermore, the 100Hz ripple signal amplitude is relatively small and easily overwhelmed by circuit noise, resulting in insufficient sampling accuracy and affecting ripple suppression.

[0005] Therefore, in order to solve the problems mentioned above and existing technologies, this invention proposes a method for reducing output current ripple in two-stage charging devices of PFC and LLC. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for reducing output current ripple in two-stage charging devices such as PFC and LLC.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for reducing output current ripple in a two-stage charging device using PFC and LLC includes the following steps: The PFC module outputs a DCBus voltage to the LLC module, which charges the battery based on this DCBus voltage. A ripple compensation logic and a DCBus dynamic adjustment module are configured. The ripple compensation logic includes a 100Hz quasi-resonant controller and a PI controller. The 100Hz quasi-resonant controller receives the original error signals from the output current feedback signal and the reference signal, extracts and amplifies the 100Hz ripple information, and then synthesizes it with the original error signal to form an optimized error signal. The optimized error signal is processed by the PI controller to generate a PFM signal to control the power transistors of the LLC module. The DCBus dynamic adjustment module acquires the operating frequency of the LLC module and outputs a voltage reference adjustment amount to the PFC module to adjust the DCBus voltage reference value. The ripple compensation logic does not require an additional current sensor.

[0008] As a further improvement of the present invention, the execution steps of the ripple compensation logic include: acquiring the output current feedback signal of the LLC module, performing a difference calculation between the output current feedback signal and a preset output current reference signal to obtain the original error signal; processing the original error signal by a 100Hz quasi-resonant controller, separating out the 100Hz ripple component and amplifying it to generate a compensation ripple signal; superimposing the compensation ripple signal with the original error signal to form an optimized error signal; and outputting a control signal after the optimized error signal is processed by a PI controller, which is then converted into a PFM signal to adjust the switching frequency of the power transistor in the LLC module.

[0009] As a further improvement of the present invention, the DCBus dynamic adjustment module includes a start-up condition judgment unit, which presets a start-up threshold current. The start-up condition judgment unit collects the output charging current of the LLC module in real time. When the output charging current is greater than the start-up threshold current, the DCBus dynamic adjustment module starts and performs subsequent adjustment operations. When the output charging current is less than or equal to the start-up threshold current, the DCBus dynamic adjustment module is in an inactive state, and the DCBus voltage reference value of the PFC module remains at the initial setting value.

[0010] As a further improvement of the present invention, the DCBus dynamic adjustment module includes a frequency monitoring unit, which is configured with a frequency recording window. The length of the frequency recording window satisfies that the window time length is not less than 1 / 100Hz. The frequency monitoring unit continuously records the operating frequency data of the PFC module within a set time period through the frequency recording window, and after statistically analyzing the operating frequency data, outputs the current voltage reference value of the PFC module.

[0011] As a further improvement of the present invention, the DCBus dynamic adjustment module includes a voltage reference adjustment unit. This voltage reference adjustment unit presets frequency thresholds corresponding to the resonant frequency of the LLC module, one of which is less than the resonant frequency and the other is greater than the resonant frequency. When the actual operating frequency output by the frequency monitoring unit is lower than the smaller frequency threshold, the voltage reference adjustment unit outputs a voltage reference adjustment amount to reduce the DCBus voltage reference value of the PFC module. When the actual operating frequency is higher than the larger frequency threshold, the voltage reference adjustment unit outputs a voltage reference adjustment amount to increase the DCBus voltage reference value of the PFC module. When the actual operating frequency is between the two frequency thresholds, the voltage reference adjustment unit does not output a voltage reference adjustment amount, and the DCBus voltage reference value of the PFC module remains at the current setting.

[0012] As a further improvement of the present invention, the resonant frequency of the 100Hz quasi-resonant controller is set to 100Hz, which is used to specifically extract the ripple information corresponding to twice the power grid frequency in the original error signal. Its gain at the 100Hz frequency point is higher than the gain at other frequency points.

[0013] As a further improvement of the present invention, the PI controller receives the optimization error signal and performs proportional-integral adjustment. The output control signal is used to adjust the frequency of the PFM signal so that the output current of the LLC module tracks the reference signal. The interrupt frequency and open-loop crossover frequency of the control loop are conventional set values.

[0014] As a further improvement of the present invention, the PFC module is an adjustable voltage PFC form, which supports unidirectional or bidirectional energy flow; the LLC module outputs charging current through the secondary rectifier circuit of the transformer, and the output current feedback signal is taken from the output terminal of the rectifier circuit.

[0015] The beneficial effects of this invention are: (1) Reduced hardware performance requirements and enhanced compatibility: This invention provides high gain at 100Hz frequency through a quasi-resonant controller, eliminating the need to increase the interrupt frequency and open-loop crossover frequency of the control loop to achieve ripple suppression. This reduces the requirements for the DSP chip's computing performance, allowing the control logic of the PFC module and LLC module to be combined and run on the same conventional performance chip, reducing hardware resource consumption and improving system compatibility. Furthermore, this invention directly extracts 100Hz ripple information from the output current feedback signal through a 100Hz quasi-resonant controller, eliminating the need to add a current sensor on the secondary rectifier side of the transformer. This avoids additional hardware procurement and installation costs, while also reducing noise interference introduced by the sensor, thus solving the defects of "high cost and low sampling accuracy" in existing sensor-adding solutions.

[0016] (2) Improved ripple suppression effect: The loop gain curve of the present invention has high gain only at the 100Hz frequency point, and the gain at other frequency points is consistent with the conventional single PI control, which avoids the problem of insufficient phase margin caused by high crossover frequency and reduces the difficulty of PI parameter design; In addition, the DCBus dynamic adjustment module monitors the LLC operating frequency in real time and dynamically adjusts the DC bus voltage, so that the LLC module always works near the resonant frequency, ensuring the stability of the open-loop gain curve under different charging power, and solving the problem that the ripple suppression effect fluctuates with power change in the prior art. Attached Figure Description

[0017] Figure 1 This is a block diagram of the LLC charging control logic of the conventional control method of this invention; Figure 2 This is a block diagram of the LLC charging control logic for resonant cavity sampling in this invention; Figure 3 This is a block diagram of the LLC charging control logic proposed in this invention; Figure 4 This is the loop gain curve at the LLC resonant frequency of this invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Identical components are denoted by the same reference numerals. It should be noted that the terms "front," "rear," "left," "right," "upper," and "lower" used in the following description refer to directions in the accompanying drawings, and the terms "bottom surface," "top surface," "inner," and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0019] This invention proposes a method for reducing output current ripple in a two-stage charging device using PFC and LLC, such as... Figures 1 to 4 As shown, it includes: The PFC module outputs a DCBus voltage to the LLC module, which charges the battery based on this DCBus voltage. A ripple compensation logic and a DCBus dynamic adjustment module are configured. The ripple compensation logic includes a 100Hz quasi-resonant controller and a PI controller. The 100Hz quasi-resonant controller receives the original error signals from the output current feedback signal and the reference signal, extracts and amplifies the 100Hz ripple information, and then synthesizes it with the original error signal to form an optimized error signal. The optimized error signal is processed by the PI controller to generate a PFM signal to control the power transistors of the LLC module. The DCBus dynamic adjustment module acquires the operating frequency of the LLC module and outputs a voltage reference adjustment amount to the PFC module to adjust the DCBus voltage reference value. The ripple compensation logic does not require an additional current sensor.

[0020] The PFC module, or Power Factor Correction module, primarily functions to convert the AC grid input voltage into a stable DC bus voltage, improving the power factor on the grid side and reducing harmonic pollution. This DC bus voltage is then supplied to the LLC module, which acts as a resonant converter, achieving efficient energy conversion based on this DC bus voltage to provide a stable charging current for the battery.

[0021] To reduce the 100Hz power frequency ripple in the output current, this method incorporates ripple compensation logic and a DC bus dynamic adjustment module. The ripple compensation logic, the core control component for ripple suppression, comprises a 100Hz quasi-resonant controller and a PI controller. The quasi-resonant controller is a control unit with specific frequency selectivity; its core characteristic is extremely high gain at a preset resonant frequency, while gain is lower at other frequencies. Here, by setting its resonant frequency to 100Hz, it can accurately identify and extract the 100Hz ripple component from the signal.

[0022] During the operation of the ripple compensation logic, the actual charging current output by the LLC module is first acquired as the output current feedback signal, reflecting the current charging state. This feedback signal is compared with a preset output current reference signal; the difference between the two is the original error signal, which contains the deviation of the output current from the target value and the ripple component. After receiving the original error signal, the 100Hz quasi-resonant controller separates the 100Hz ripple information using its frequency selection characteristics and amplifies this ripple information to form a targeted compensation ripple signal. Subsequently, this compensation ripple signal is superimposed and synthesized with the original error signal to obtain the optimized error signal. The optimized error signal retains the original deviation information while enhancing the suppression capability of the 100Hz ripple.

[0023] The optimization error signal is input to the PI controller, which processes the signal using a proportional-integral (PI) control algorithm and outputs a control signal that reflects the adjustment requirements. This control signal is further converted into a PFM (Pulse Frequency Modulation) signal, which controls the switching state of the power transistor in the LLC module by adjusting the pulse frequency. As the core switching device in the LLC module, the power transistor's switching frequency alters the module's energy transfer efficiency and output characteristics, ultimately achieving dynamic adjustment of the output current and suppressing 100Hz ripple. It is noteworthy that the entire ripple compensation logic does not require an additional current sensor to acquire ripple information; ripple extraction and compensation are achieved solely through signal processing.

[0024] The DC bus dynamic adjustment module ensures the stability of ripple suppression. Its core function is to maintain the stable operation of the LLC module by adjusting the DC bus voltage. This module acquires the operating frequency of the LLC module in real time. The operating frequency is a key parameter reflecting the operating state of the LLC module and is directly related to its resonant characteristics. When the operating frequency of the LLC module deviates from its inherent resonant frequency, it will cause changes in its open-loop gain curve, thus affecting the stability of the ripple suppression effect. Based on the acquired operating frequency, the DC bus dynamic adjustment module generates a voltage reference adjustment amount and sends this adjustment amount to the PFC module to adjust the DC bus voltage reference value output by the PFC module. Through this dynamic adjustment, the operating frequency of the LLC module can be kept stable near the resonant frequency, ensuring that its gain characteristics remain unchanged, thereby guaranteeing the consistency of the 100Hz ripple suppression effect.

[0025] Specifically, such as Figures 1 to 4 As shown, the execution steps of the ripple compensation logic include: acquiring the output current feedback signal of the LLC module, performing a difference calculation between the output current feedback signal and a preset output current reference signal to obtain the original error signal; processing the original error signal with a 100Hz quasi-resonant controller, separating out the 100Hz ripple component and amplifying it to generate a compensation ripple signal; superimposing the compensation ripple signal with the original error signal to form an optimized error signal; and outputting a control signal after the optimized error signal is processed by a PI controller, which is then converted into a PFM signal to adjust the switching frequency of the power transistor in the LLC module.

[0026] Specifically, the output current feedback signal of the LLC module is acquired. This signal is obtained through a current sensing element located at the output of the LLC module and can reflect the magnitude and change status of the charging current output to the battery in real time. The output current feedback signal is then compared with a preset output current reference signal, which is a target current value preset according to the battery charging requirements. The difference between the two is the original error signal, which contains the deviation between the actual output current and the target value, and also carries the 100Hz ripple component that needs to be suppressed.

[0027] The 100Hz quasi-resonant controller processes the original error signal, incorporating frequency selection and amplification functions. The frequency selection function precisely separates the 100Hz ripple component from the original error signal. This separation is based on the resonant characteristics of the quasi-resonant controller, which produces a significant response only to the 100Hz frequency component, while the response to other frequency components is weak. The separated 100Hz ripple component is amplified to form a compensation ripple signal with sufficient adjustment capability. This signal has the opposite phase to the original ripple component and can be used to cancel out the ripple component in the original error signal.

[0028] The compensated ripple signal is superimposed on the original error signal to form an optimized error signal. The superposition process is achieved through a signal synthesis circuit, which enables the compensated ripple signal to effectively cancel the 100Hz ripple component in the original error signal, while retaining the DC deviation information in the original error signal, ensuring that the subsequent control circuit can accurately adjust the average value of the output current.

[0029] The optimized error signal is processed by the PI controller, which outputs a control signal. The PI controller processes the optimized error signal through proportional and integral components. The proportional component responds quickly to changes in error, while the integral component eliminates static errors, ensuring the output current stably tracks the reference signal. The control signal output by the PI controller reflects the adjustment requirements for the LLC module's output current. This control signal is then converted into a PFM signal. The PFM signal adjusts the switching frequency of the power transistors in the LLC module by changing the pulse frequency. Changes in the power transistor switching frequency alter the energy transfer efficiency of the LLC resonant cavity, thereby adjusting the output current and ultimately achieving suppression of 100Hz ripple and precise control of the output current.

[0030] Specifically, such as Figures 1 to 4As shown, the DCBus dynamic adjustment module includes a start-up condition judgment unit, which presets a start-up threshold current. The start-up condition judgment unit collects the output charging current of the LLC module in real time. When the output charging current is greater than the start-up threshold current, the DCBus dynamic adjustment module starts and performs subsequent adjustment operations. When the output charging current is less than or equal to the start-up threshold current, the DCBus dynamic adjustment module is in an inactive state, and the DCBus voltage reference value of the PFC module remains at the initial setting value.

[0031] Specifically, the DC bus dynamic adjustment module includes a start-up condition judgment unit, which is the core of the module's trigger control. Internally, it presets a start-up threshold current to determine the start-up timing. The start-up threshold current is set based on the actual operating characteristics of the charging device, primarily considering that the system's sensitivity to ripple is low in low-power charging scenarios, and stability requirements can be met without dynamic adjustment.

[0032] The startup condition judgment unit is connected to the current detection loop at the output of the LLC module to collect the charging current output by the LLC module in real time. After signal conditioning, the collected charging current signal is compared with the preset startup threshold current. When the monitored output charging current is greater than the startup threshold current, it indicates that the charging power is high. The operating frequency of the LLC module is prone to shift with power changes, which may lead to fluctuations in ripple suppression effect. Therefore, the DC bus dynamic adjustment module is activated and performs subsequent frequency monitoring and voltage adjustment operations.

[0033] When the output charging current is less than or equal to the start-up threshold current, it means the system is in a low-power charging state. At this time, the LLC module operates relatively stably with a small frequency offset, and its impact on ripple suppression is negligible. To avoid unnecessary adjustments introducing new system disturbances, the DC bus dynamic adjustment module is inactive, and the DC bus voltage reference value of the PFC module remains unchanged from its initial setting, ensuring charging stability in low-power scenarios. This on-demand start-up control logic ensures the stability of ripple suppression in high-power scenarios while reducing the system's computational burden in low-power scenarios.

[0034] Specifically, such as Figures 1 to 4 As shown, the DCBus dynamic adjustment module includes a frequency monitoring unit, which is equipped with a frequency recording window. The length of the frequency recording window is such that the window time length is not less than 1 / 100Hz. The frequency monitoring unit continuously records the operating frequency data of the LLC module within a set time period through the frequency recording window. After statistically analyzing the operating frequency data, it outputs the current actual operating frequency value of the LLC module.

[0035] Specifically, the DC bus dynamic adjustment module includes a frequency monitoring unit, which is the core component for realizing the operating status perception of the LLC module. This unit is mainly used to capture the operating frequency characteristics of the LLC module in real time. The frequency monitoring unit is internally configured with a frequency recording window, which is a continuous time interval used to centrally collect and store the operating frequency data of the LLC module within that interval.

[0036] To ensure complete capture of the frequency variation characteristics related to the 100Hz power frequency ripple, the length of the frequency recording window must be no less than 10 milliseconds. This time length corresponds to a complete cycle of the 100Hz signal, which can cover the basic periodic characteristics of the ripple signal and avoid frequency data distortion caused by insufficient sampling time.

[0037] The frequency monitoring unit connects to the signal interface of the LLC module's control loop to continuously acquire the LLC module's operating frequency data. This data is stored in real-time in chronological order into a frequency recording window, forming a continuous sequence of frequency changes. During data recording, the frequency monitoring unit performs statistical analysis on the operating frequency data within the window, filtering out transient interference signals and extracting frequency characteristic values ​​reflecting the stable operating state of the LLC module through average value calculation or trend analysis. After processing, the frequency monitoring unit outputs the current actual operating frequency value of the LLC module, providing an accurate status basis for subsequent voltage reference adjustments and ensuring that DC bus voltage adjustments precisely match the actual operating state of the LLC module. This window-based frequency monitoring method ensures both the continuity and integrity of frequency data and enhances the anti-interference capability of frequency detection through statistical analysis.

[0038] Specifically, such as Figures 1 to 4 As shown, the DCBus dynamic adjustment module includes a voltage reference adjustment unit. This voltage reference adjustment unit presets frequency thresholds corresponding to the resonant frequency of the LLC module, with one frequency threshold being less than the resonant frequency and the other frequency threshold being greater than the resonant frequency. When the actual operating frequency output by the frequency monitoring unit is lower than the smaller frequency threshold, the voltage reference adjustment unit outputs a voltage reference adjustment amount to reduce the DCBus voltage reference value of the PFC module. When the actual operating frequency is higher than the larger frequency threshold, the voltage reference adjustment unit outputs a voltage reference adjustment amount to increase the DCBus voltage reference value of the PFC module. When the actual operating frequency is between the two frequency thresholds, the voltage reference adjustment unit does not output a voltage reference adjustment amount, and the DCBus voltage reference value of the PFC module remains at its current setting.

[0039] Specifically, the DC bus dynamic adjustment module includes a voltage reference adjustment unit, which is the core execution component for achieving precise control of the DC bus voltage. It is mainly used to output targeted voltage adjustment commands based on the operating status of the LLC module.

[0040] The voltage reference adjustment unit has two preset frequency thresholds, which are set around the resonant frequency of the LLC module. The resonant frequency is the inherent operating frequency determined during the design of the LLC module. At this frequency, the module's energy conversion efficiency is the highest, the resonant cavity characteristics are the most stable, and the open-loop gain curve is also the most ideal. One set of frequency thresholds is lower than the resonant frequency, and the other set is higher than the resonant frequency. Together, the two sets of thresholds constitute a frequency range used to define whether the LLC module is in a stable operating state.

[0041] When the actual operating frequency output by the frequency monitoring unit is lower than a small frequency threshold, it indicates that the current operating frequency of the LLC module deviates too low from the resonant frequency, which may lead to a decrease in energy transfer efficiency or fluctuations in gain characteristics. At this time, the voltage reference adjustment unit outputs a voltage reference adjustment amount, which acts on the voltage control loop of the PFC module, lowering the DC bus voltage reference value of the PFC module. After the DC bus voltage decreases, the input voltage of the LLC module adjusts accordingly, and its operating frequency rises back towards the resonant frequency, thereby improving its operating condition.

[0042] When the actual operating frequency exceeds a significant frequency threshold, it indicates that the LLC module's current operating frequency deviates too much from the resonant frequency, which will also affect the stability of the resonant characteristics. The voltage reference adjustment unit then outputs a corresponding voltage reference adjustment amount, increasing the DC bus voltage reference value through the PFC module's control loop. As the DC bus voltage increases, the LLC module's operating frequency will fall back towards the resonant frequency, restoring stable operating characteristics.

[0043] When the actual operating frequency falls between the two sets of frequency thresholds, it indicates that the LLC module is currently operating close to its resonant frequency, its resonant characteristics are stable, and the open-loop gain curve shows no significant fluctuations. At this time, the voltage reference adjustment unit does not output a voltage reference adjustment value, and the DC bus voltage reference value of the PFC module remains unchanged, avoiding unnecessary adjustments that could interfere with system stability. This dynamic adjustment logic based on frequency range ensures that the LLC module always operates within the frequency range of optimal resonant characteristics, guaranteeing the stability of ripple suppression.

[0044] Specifically, such as Figures 1 to 4 As shown, the resonant frequency of the 100Hz quasi-resonant controller is set to 100Hz, which is used to specifically extract the ripple information corresponding to twice the power grid frequency in the original error signal. Its gain at the 100Hz frequency point is higher than the gain at other frequency points.

[0045] Specifically, the resonant frequency of the 100Hz quasi-resonant controller is set to 100Hz. A quasi-resonant controller is a frequency-selective control component whose core characteristic is extremely high gain at a specific resonant frequency, while the gain decreases significantly at other frequencies. This frequency selectivity stems from its internal resonant network design, which can strongly respond to signals at the target frequency while effectively suppressing signals at non-target frequencies.

[0046] The power grid frequency is 50Hz. Since both the grid voltage and current are sinusoidal, the instantaneous power product of the two will produce a fluctuation twice the power frequency, i.e., a power fluctuation of 100Hz. This fluctuation will form a corresponding 100Hz ripple in the output current through energy transfer, and this ripple corresponds to twice the harmonic of the power grid frequency. The design of the 100Hz quasi-resonant controller is specifically aimed at this characteristic. By precisely setting the resonant frequency to 100Hz, it can selectively extract this ripple information from the original error signal.

[0047] During signal processing, the original error signal contains multiple frequency components, including the 100Hz ripple that needs to be suppressed, as well as interference signals and DC deviation components at other frequencies. The 100Hz quasi-resonant controller, leveraging its frequency selectivity, amplifies only the signal at the 100Hz frequency, making its gain at that frequency significantly higher than at other frequencies. This high-gain characteristic enhances the compensation capability for the 100Hz ripple, ensuring sufficient adjustment in the control loop to counteract its effects, while avoiding over-adjustment of other frequency components. This achieves precise suppression of the target ripple without affecting the overall system stability. This targeted frequency response design is key to effectively suppressing the 100Hz ripple without increasing the control loop interruption frequency and open-loop crossover frequency.

[0048] Specifically, such as Figures 1 to 4 As shown, the PI controller receives the optimization error signal and performs proportional-integral adjustment. The output control signal is used to adjust the frequency of the PFM signal so that the output current of the LLC module tracks the reference signal. The interrupt frequency and open-loop crossover frequency of the control loop are set to conventional values.

[0049] Specifically, the PI controller receives the optimized error signal and performs proportional-integral regulation. The PI controller is a classic closed-loop control component that achieves precise processing of the error signal through the synergistic effect of proportional and integral regulation. Proportional regulation responds to the instantaneous magnitude of the error signal; the larger the error, the stronger the regulation, quickly reducing the deviation. Integral regulation, on the other hand, accumulates the historical changes of the error signal, gradually eliminating static deviations and ensuring that the system's final output stably tracks the reference value. This combination guarantees both regulation speed and zero steady-state error control.

[0050] After the optimization error signal undergoes proportional-integral (PI) calculations by the PI controller, the output control signal carries the specific adjustment requirements for the LLC module's output current. This control signal is then sent to the pulse frequency modulation unit to adjust the frequency of the PFM signal. The PFM signal is a signal form that transmits control commands by changing the pulse frequency; its frequency change directly corresponds to the adjustment of the switching frequency of the LLC module's power transistors. When the PFM signal frequency changes, the energy transfer characteristics of the LLC module's resonant cavity change accordingly, and the output current is adjusted accordingly, thereby enabling the LLC module's output current to accurately track the preset reference signal and achieve stable charging control.

[0051] In this design, the interrupt frequency of the control loop refers to the periodic frequency at which the control chip samples and processes the feedback signal, while the open-loop crossover frequency is the frequency corresponding to the intersection of the open-loop gain curve and the 0 dB line, reflecting the loop's response speed to signal changes. In this method, both frequencies use conventional setpoints and do not need to be deliberately increased to suppress 100Hz ripple. This is because the 100Hz quasi-resonant controller has already specifically enhanced its ability to suppress 100Hz ripple; there is no need to increase the processing speed by increasing the interrupt frequency, nor is there a need to increase the high-frequency gain by increasing the open-loop crossover frequency. This avoids the potential for insufficient phase margin and system stability risks that may result from high-frequency settings. This design simplifies the difficulty of adjusting control parameters and reduces the performance requirements of the control chip.

[0052] Specifically, such as Figures 1 to 4 As shown, the PFC module is an adjustable voltage PFC type, which supports unidirectional or bidirectional energy flow; the LLC module outputs charging current through the transformer secondary rectifier circuit, and the output current feedback signal is taken from the output terminal of the rectifier circuit.

[0053] Specifically, the PFC module is an adjustable voltage PFC module. A PFC module, or power factor correction module, has the core function of converting AC grid input into DC power and using control strategies to ensure that the grid-side current waveform matches the voltage waveform, thereby improving the power factor. The adjustable voltage PFC form means that the module can dynamically adjust the output DC bus voltage according to the downstream load demand, rather than outputting a fixed voltage value. This adjustable characteristic provides a foundation for achieving stable operation in conjunction with the LLC module.

[0054] This PFC module supports unidirectional or bidirectional energy flow. Unidirectional energy flow means that electrical energy can only be transferred from the AC grid side to the DC bus side, meeting the energy requirements of conventional charging scenarios; bidirectional energy flow allows electrical energy to be transferred in both directions between the AC grid side and the DC bus side, which is suitable for scenarios requiring energy feedback and improves the applicability and flexibility of the device.

[0055] The LLC module outputs charging current through the transformer secondary rectifier circuit. As a resonant converter, the LLC module consists of a primary-side switching circuit, a high-frequency transformer, and a resonant network, enabling efficient power conversion and isolation. The transformer secondary rectifier circuit is a key component of the LLC module's output, converting the high-frequency AC power output from the transformer secondary into DC power suitable for battery charging. The rectifier circuit typically consists of diodes or synchronous rectifier tubes, achieving AC-DC conversion through unidirectional conductivity.

[0056] The output current feedback signal is taken from the output terminal of the rectifier circuit, which is directly connected to the battery load. The current signal at this location most accurately reflects the actual charging state of the battery. Acquiring the feedback signal from this point ensures that the acquired current information includes complete ripple characteristics and load changes, providing accurate raw signal input for subsequent ripple compensation logic and guaranteeing the adjustment accuracy of the entire control loop. This signal acquisition method eliminates the need for additional detection points, simplifying the circuit structure while improving signal accuracy.

[0057] The foregoing has illustrated and described the basic features, principles, and advantages of the present invention. It should be noted that the present invention is not limited to the above embodiments, but only to some embodiments. Any improvements and additions made without departing from the spirit and scope of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A method for reducing output current ripple in a two-stage charging device (PFC and LLC), characterized in that, The steps include: The PFC module outputs a DCBus voltage to the LLC module, which charges the battery based on this DCBus voltage. A ripple compensation logic and a DCBus dynamic adjustment module are configured. The ripple compensation logic includes a 100Hz quasi-resonant controller and a PI controller. The 100Hz quasi-resonant controller receives the original error signals from the output current feedback signal and the reference signal, extracts and amplifies the 100Hz ripple information, and then synthesizes it with the original error signal to form an optimized error signal. The optimized error signal is processed by the PI controller to generate a PFM signal to control the power transistors of the LLC module. The DCBus dynamic adjustment module acquires the operating frequency of the LLC module and outputs a voltage reference adjustment amount to the PFC module to adjust the DCBus voltage reference value. The ripple compensation logic does not require an additional current sensor.

2. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, The execution steps of the ripple compensation logic include: acquiring the output current feedback signal of the LLC module, performing a difference calculation between the output current feedback signal and a preset output current reference signal to obtain the original error signal; processing the original error signal with a 100Hz quasi-resonant controller, separating out the 100Hz ripple component and amplifying it to generate a compensation ripple signal; superimposing the compensation ripple signal with the original error signal to form an optimized error signal; and outputting a control signal after the optimized error signal is processed by a PI controller, which is then converted into a PFM signal to adjust the switching frequency of the power transistor in the LLC module.

3. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, The DCBus dynamic adjustment module includes a start-up condition judgment unit, which presets a start-up threshold current. The start-up condition judgment unit collects the output charging current of the LLC module in real time. When the output charging current is greater than the start-up threshold current, the DCBus dynamic adjustment module starts and performs subsequent adjustment operations. When the output charging current is less than or equal to the start-up threshold current, the DCBus dynamic adjustment module is in an inactive state, and the DCBus voltage reference value of the PFC module remains at the initial setting value.

4. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, The DCBus dynamic adjustment module includes a frequency monitoring unit, which is equipped with a frequency recording window. The length of the frequency recording window is such that the window time length is not less than 1 / 100Hz. The frequency monitoring unit continuously records the operating frequency data of the PFC module within a set time period through the frequency recording window. After statistical analysis of the operating frequency data, it outputs the current voltage reference value of the PFC module.

5. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, The DCBus dynamic adjustment module includes a voltage reference adjustment unit. This voltage reference adjustment unit presets a frequency threshold corresponding to the resonant frequency of the LLC module. One frequency threshold is less than the resonant frequency, and the other frequency threshold is greater than the resonant frequency. When the actual operating frequency output by the frequency monitoring unit is lower than the smaller frequency threshold, the voltage reference adjustment unit outputs a voltage reference adjustment amount to reduce the DCBus voltage reference value of the PFC module. When the actual operating frequency is higher than a larger frequency threshold, the voltage reference adjustment unit outputs a voltage reference adjustment amount to increase the DCBus voltage reference value of the PFC module. When the actual operating frequency is between two frequency thresholds, the voltage reference adjustment unit does not output a voltage reference adjustment amount, and the DCBus voltage reference value of the PFC module remains at the current setting.

6. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, The resonant frequency of the 100Hz quasi-resonant controller is set to 100Hz, which is used to specifically extract the ripple information corresponding to twice the power grid frequency in the original error signal. Its gain at the 100Hz frequency point is higher than the gain at other frequency points.

7. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, After receiving the optimization error signal, the PI controller performs proportional-integral adjustment, and the output control signal is used to adjust the frequency of the PFM signal so that the output current of the LLC module tracks the reference signal. The interrupt frequency and open-loop crossover frequency of the control loop are set to conventional values.

8. The method for reducing output current ripple in a two-stage charging device (PFC and LLC) according to claim 1, characterized in that, The PFC module is an adjustable voltage PFC type, which supports unidirectional or bidirectional energy flow; the LLC module outputs charging current through the transformer secondary rectifier circuit, and the output current feedback signal is taken from the output terminal of the rectifier circuit.

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