A wide-range LLC resonant converter single-loop operating point optimization control method

Abstract

This invention discloses a single-loop operating point optimization control method for a wide-range LLC resonant converter, belonging to the field of power electronic converter control technology. This invention employs a single-voltage-loop PI controller to adjust the output voltage, calculates the sensitivity index in real time, and compares it with preset dual thresholds: when the sensitivity index is below the low threshold, a phase shift angle is injected; when it is above the high threshold, the phase shift angle is withdrawn; and when it is between the two, the phase shift angle remains unchanged. The injected phase shift angle causes gain attenuation and voltage drop. The PI controller automatically reduces the switching frequency to compensate for the voltage, driving the operating point to move towards a lower frequency until the sensitivity recovers above the low threshold. This invention achieves automatic frequency clamping through a single-loop architecture, avoiding multi-loop switching oscillations. It does not rely on a precise physical model and features high parameter tolerance and fast dynamic response, making it suitable for wide-range output voltage scenarios such as electric vehicle charging, photovoltaic power generation, and data center power supplies.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, specifically to a method for optimizing the single-loop operating point control of a wide-range LLC resonant converter. Background Technology

[0002] LLC resonant converters are widely used in wide-voltage range applications such as electric vehicle charging, photovoltaic power generation, and data center power supplies due to their soft-switching characteristics and high efficiency across the entire load range. However, traditional pulse frequency modulation (PFM) faces serious challenges in wide-range input or output applications.

[0003] Under light load or low voltage gain requirements, the DC gain curve of the LLC resonant tank becomes extremely flat, causing the voltage regulation sensitivity to frequency changes to approach zero. This control dead zone phenomenon not only significantly reduces dynamic response capability but also leads to frequency runaway, resulting in severe electromagnetic interference and excessive magnetic component losses.

[0004] Existing technologies mostly employ hybrid control strategies that combine phase-shift modulation (PSM), but they are generally divided into two categories: one is a segmented switching strategy, where direct switching between different modes can easily cause sudden changes in loop gain and transient voltage oscillations; the other is a trajectory planning strategy based on time-domain analysis, which can achieve smooth switching, but it is highly dependent on an accurate physical model of the resonant tank and lacks sufficient adaptive capability and closed-loop robustness to disturbances such as magnetic component parameter drift and temperature changes.

[0005] In summary, existing hybrid control strategies either easily cause sudden changes in loop gain when switching directly between different modes, leading to transient oscillations in the output voltage; or they lack sufficient adaptability and closed-loop robustness when faced with drift in magnetic component parameters, temperature changes, or unpredictable load changes in practical engineering, easily resulting in degraded system dynamic performance or even stability problems. Therefore, there is an urgent need in this field for a control method that can avoid complex multi-loop switching architectures while effectively overcoming the dead zone problem in light-load control. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention proposes a single-loop operating point optimization control method for wide-range LLC resonant converters. More specifically, it is a sensitivity-oriented single-loop operating point optimization control method for wide-range LLC resonant converters, aiming to solve the problems of frequency instability and sensitivity degradation of wide-range LLC resonant converters under light loads without increasing the complexity of the control system.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows:

[0008] A method for optimizing the single-loop operating point control of a wide-range LLC resonant converter includes the following steps:

[0009] 1) A single-voltage-loop PI controller is used to perform closed-loop regulation of the output voltage of the LLC resonant converter. In each regulation cycle, the PI controller outputs a switching frequency command to the frequency conversion phase-shift modulator as the frequency input for generating the gate drive signal of the converter inverter circuit.

[0010] 2) In each adjustment cycle, the current switching frequency of the converter is sampled, and the sensitivity monitoring index at the current switching frequency is calculated in real time;

[0011] 3) Compare the sensitivity monitoring index with preset low and high thresholds, and update the phase shift angle of the gate drive signal of different bridge arms of the inverter circuit according to the comparison result:

[0012] If the sensitivity monitoring index is lower than the low threshold, it indicates that the converter is in a low sensitivity state. At this time, the first phase shift angle increment is actively injected based on the phase shift angle of the previous adjustment cycle.

[0013] If the sensitivity monitoring index is greater than the high threshold, it indicates that the current sensitivity of the converter is sufficient. At this time, the second phase shift angle increment is actively subtracted from the phase shift angle of the previous adjustment cycle.

[0014] If the sensitivity monitoring index is between the low threshold and the high threshold, then the phase shift angle remains unchanged;

[0015] The injection of phase shift angle causes the gain of LLC resonant converter to decrease, resulting in a drop in output voltage. After this voltage drop is detected by the single voltage loop PI controller, the PI controller automatically reduces the switching frequency to compensate for the gain, thereby implicitly driving the converter's operating point to shift from the operating region where the change in switching frequency has a weaker impact on voltage gain to the operating region where the change in switching frequency has a stronger impact on voltage gain.

[0016] In this invention, the phase shift angle is the phase difference in time between the switching drive waveforms of the two bridge arms on the inverter circuit of the converter. It reflects how much one bridge arm leads or lags behind the other (in degrees or radians).

[0017] In this invention, the phase-shift frequency converter is a circuit or algorithm that converts the switching frequency and phase shift angle into actual power device drive signals; it can be implemented on a control chip (MCU), but can also be implemented on other separate chips. The control chip drives the switching transistors through the phase-shift frequency converter.

[0018] In this invention, the sensitivity monitoring index is obtained by fitting the gain-frequency characteristics of the LLC resonant converter with a rational polynomial using the Pad approximation. The calculation formula is:

[0019] ;

[0020] in, To normalize the switching frequency, The attenuation coefficient is fitted based on the characteristics of the LLC resonant converter.

[0021] According to a preferred embodiment of the present invention, based on the target LLC resonant cavity parameters, a frequency sweep analysis is performed on the sensitivity index within the input voltage range, output voltage range, and load variation range to determine the boundary value at which the frequency adjustment capability begins to decrease significantly. Based on this, a low threshold is set before this boundary value to ensure that the auxiliary phase shift angle can be engaged in advance; and a high threshold is set to a value higher than the low threshold to form a hysteresis band and prevent repeated switching. The frequency sweep analysis of the sensitivity index involves calculating or measuring the sensitivity index point-by-point at different switching frequencies to observe its variation with frequency and determine the sensitivity boundary interval.

[0022] According to a preferred embodiment of the present invention, in the present invention, the first phase shift angle increment Greater than the second phase shift angle increment The reason is that when the sensitivity monitoring index is below the low threshold, it indicates that the converter has entered a low sensitivity state. At this time, it is necessary to increase the phase shift angle at a relatively fast speed in order to reduce the switching frequency in time and make the operating point leave the low sensitivity operating region. When the sensitivity monitoring index is above the high threshold, it indicates that the converter has recovered to the operating state that can be stably adjusted by a single voltage loop. At this time, reducing the phase shift angle with a smaller step size is beneficial to avoid over-adjustment, output fluctuation and frequent switching during the phase shift angle exit process, thereby taking into account both the operating point return speed and control stability.

[0023] First phase shift angle increment Second phase angle increment These are all engineering setting parameters used in the auxiliary phase shift angle adjustment process, and are not unique fixed values; among them, The input speed used to determine the auxiliary phase shift angle should ensure that the operating point can be pulled away from the low-sensitivity region in a timely manner. The exit speed used to determine the auxiliary phase shift angle should ensure that there is no excessive oscillation or frequent switching during the recovery of the operating point; those skilled in the art can determine its value through simulation or experimental tuning based on control objectives, system response and stability requirements.

[0024] The beneficial effects of this invention are:

[0025] This invention eliminates multi-loop competition and complex mode switching logic through a single-loop architecture, simplifying the implementation of the control algorithm. By utilizing a closed-loop mechanism of phase-shift injection to actively induce frequency back-off, it achieves automatic frequency clamping of the switching frequency across the entire load range, effectively avoiding frequency runaway. Meanwhile, the proposed sensitivity monitoring index based on Pad's approximation does not rely on a precise physical model or additional current sensors, exhibiting extremely high parameter tolerance and low computational burden, significantly improving the dynamic stability and engineering reliability of wide-range converters.

[0026] Furthermore, this invention avoids frequent injection and withdrawal of phase shift angle caused by fluctuations in the sensitivity index near the boundary by setting a low threshold and a high threshold to form a hysteresis comparison interval, thus eliminating the resulting system oscillation and additional losses of the switching transistor. A single-voltage loop architecture achieves a seamless transition between pure frequency modulation and phase-shift assisted modes, eliminating transient output voltage oscillations caused by sudden changes in loop gain in traditional segmented switching strategies. Under light load conditions, this invention can maintain stable output voltage without pushing the switching frequency to the extreme high frequency, effectively reducing switching losses, magnetic component losses, and electromagnetic interference levels, thus contributing to improved overall converter efficiency and power density. This invention has inherent robustness to parameter drift and operating temperature changes of components such as resonant capacitors, resonant inductors, and magnetizing inductors, maintaining consistent dynamic control performance in engineering mass production and long-term operation. Moreover, this invention achieves precise control under light loads without the need for an additional current sensor, reducing hardware costs and sampling circuit complexity, making it particularly suitable for cost- and size-sensitive applications such as on-board chargers and server power supplies. Attached Figure Description

[0027] Figure 1 This invention relates to a topology diagram of a full-bridge LLC resonant converter;

[0028] Figure 2 This is a schematic diagram of the gain characteristics and control dead zone of an LLC converter under different quality factors Q;

[0029] Figure 3 This is a block diagram of the sensitivity-guided single-loop control architecture proposed in this invention;

[0030] Figure 4 This is a control flowchart of the control method of the present invention;

[0031] Figure 5 This is a waveform diagram of the control method of the present invention operating under light load;

[0032] Figure 6 This is a schematic diagram of the key waveforms for dynamic response in this invention;

[0033] Figure 7 This is a schematic diagram illustrating the load regulation capability of the control method of the present invention. Detailed Implementation

[0034] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0035] This invention proposes a sensitivity-guided single-loop operating point optimization control method for wide-range LLC resonant converters. The wide-range LLC resonant converter targeted by this invention is a full-bridge LLC resonant converter, which typically includes an H-bridge inverter circuit composed of four power switching devices, a resonant network composed of resonant capacitors, resonant inductors, and transformer magnetizing inductors, a high-frequency transformer, and a rectifier and filter circuit.

[0036] The method of this invention does not strictly limit the specific circuit topology of the LLC resonant converter. As long as the LLC resonant converter has a primary-side inverter circuit that supports phase-shift modulation (such as a full-bridge or multi-level bridge structure), and can change the voltage gain of its resonant network by adjusting the switching frequency, and change the amplitude of the fundamental voltage input to the resonant network by adjusting the phase shift angle between the bridge arms, thereby having the hardware capability to coordinately regulate the output voltage, it is suitable for the method of this invention.

[0037] Here, the term 'wide range' mainly refers to the converter's need to meet a wide output / input voltage range (especially involving extremely low voltage gain requirements) and a wide load variation range (including from full load to extremely light load or no load) in practical applications. Under such wide-range operating conditions, traditional pure frequency modulation control is prone to getting stuck in the high-frequency control dead zone, while the method of this invention can effectively overcome this inherent defect.

[0038] See Figure 1 The diagram shows the circuit topology of an LLC resonant converter according to a preferred embodiment of the present invention. The LLC resonant converter specifically includes: a power device Q1, a power device Q2, a power device Q3, a power device Q4, a DC input source Vin, an input capacitor Cin, a resonant network section, a high-frequency transformer, a rectifier section, an output capacitor C0, and a load R0.

[0039] The input capacitor Cin is connected to the positive and negative terminals of the DC power supply Vin (i.e., the DC input source Vin). Power devices Q1, Q2, Q3, and Q4 together form an H-bridge inverter circuit connected in parallel across the positive and negative terminals of the DC power supply Vin. The gates of each power device Q1, Q2, Q3, and Q4 are connected to the corresponding drive output terminals of the external drive circuit. The external drive circuit receives logic level signals (such as PWM signals) from an external controller and converts them into gate drive signals that can reliably drive the power devices. The resonant network includes a resonant capacitor Cr, a resonant inductor Lr, and a magnetizing inductor Lm. One end of the resonant capacitor Cr is connected to the positive output terminal of the H-bridge inverter circuit (i.e., the connection point between power devices Q1 and Q2), and the other end is connected to one end of the magnetizing inductor Lm. One end of the resonant inductor Lr is connected to the negative output terminal of the H-bridge inverter circuit (i.e., the connection point between power devices Q3 and Q4), and the other end is connected to the other end of the magnetizing inductor Lm. The primary winding of the high-frequency transformer T1 is connected in parallel with the magnetizing inductor Lm. The rectifier section includes rectifier diodes D1 and D2. The specific circuit connection between the rectifier section and the high-frequency transformer T1 is as follows: the secondary winding of the high-frequency transformer T1 is divided into two half-windings of the same polarity, with a center tap directly connected to one end of the load resistor R0. The other ends of the two half-windings (i.e., the two outer ends of the secondary winding) are connected to the cathodes of rectifier diodes D1 and D2, respectively. The anodes of these two rectifier diodes are connected in parallel and then together connected to the other end of the load resistor R0. The output capacitor C0 is connected in parallel with the load resistor R0 to smooth and filter the rectified voltage and provide a stable DC power supply to the load. Finally, the primary winding of transformer T1 is connected in parallel with the transformer magnetizing inductor Lm.

[0040] See Figure 2 It shows Figure 1 The diagram shows the gain characteristics and control dead zone of an LLC resonant converter under different quality factors Q. The horizontal axis represents the normalized frequency fn, and the vertical axis represents the DC voltage gain M. The curves show that when the load is reduced (corresponding to a decrease in the quality factor Q) and the operating point enters the high-frequency region, the converter's voltage gain curve becomes extremely flat. At this point, the output voltage's response to changes in the switching frequency is extremely weak, resulting in a control dead zone. This makes traditional pulse frequency modulation (PFM) control highly susceptible to frequency runaway, revealing the physical essence of why traditional control methods fail under this condition. The occurrence of the aforementioned frequency runaway phenomenon is not limited to... Figure 1 The LLC resonant converter shown is prone to frequency runaway under traditional frequency conversion control methods.

[0041] Therefore, this invention provides a sensitivity-guided single-loop operating point optimization control method for wide-range LLC resonant converters. The LLC resonant converter is a full-bridge LLC resonant converter, comprising an H-bridge inverter circuit composed of four power switching devices, a resonant network composed of a resonant capacitor, a resonant inductor, and a transformer magnetizing inductance, and a rectifier and filter circuit. The method mainly includes the following steps:

[0042] 1) A single-voltage-loop PI controller is used to perform closed-loop regulation of the output voltage of the LLC resonant converter. In each regulation cycle, the PI controller outputs a switching frequency command to the frequency conversion phase-shift modulator as the frequency input for generating the gate drive signal of the converter inverter circuit.

[0043] In this embodiment, the single-voltage-loop PI controller uses the difference between the output voltage reference value and the actual output voltage of the LLC resonant converter as the error input and outputs a switching frequency command to form a single closed-loop negative feedback control architecture.

[0044] 2) In each adjustment cycle, the current switching frequency of the converter is sampled, and the sensitivity monitoring index at the current switching frequency is calculated in real time. The sensitivity monitoring index is obtained by fitting the gain-frequency characteristic of the LLC resonant converter with a rational polynomial using the Pad approximation. The calculation formula is:

[0045] ;

[0046] in, To normalize the switching frequency, This is the attenuation coefficient fitted based on the characteristics of the LLC resonant converter. For ease of description, the sensitivity monitoring index will be abbreviated as follows. .

[0047] 3) Compare the sensitivity monitoring index with the preset low threshold and high threshold, and update the phase shift angle of the gate drive signal of different bridge arms of the inverter circuit according to the comparison result: the step of performing saturation limiting processing on the updated phase shift angle, wherein the saturation limiting processing limits the phase shift angle to a physically permissible safe range to prevent the phase shift angle from having a negative value or exceeding the maximum value of the system's tolerance limit;

[0048] The low threshold is set to 1.1 to 1.5 times the sensitivity boundary value of single-voltage loop regulation failure, and is greater than 0 and less than 1. The sensitivity boundary value of single-voltage loop regulation failure is obtained by calculating the sensitivity monitoring index point by point within the preset switching frequency range. When adjusting the switching frequency by the single-voltage loop PI controller alone cannot make the actual output voltage track the output voltage reference value, the sensitivity monitoring index value corresponding to the switching frequency at that moment is taken as the boundary value for judging the single-voltage loop regulation capability. The high threshold is set to be greater than the low threshold and less than 1.

[0049] According to a preferred embodiment of the present invention, the high threshold is 1.3 to 2 times the low threshold.

[0050] In this invention, if the sensitivity monitoring index is lower than the low threshold, it indicates that the converter is in a low sensitivity state. At this time, based on the phase shift angle of the previous adjustment cycle, a first phase shift angle increment is actively injected. ;

[0051] If the sensitivity monitoring index is greater than the high threshold, it indicates that the current sensitivity of the converter is sufficient. At this time, the second phase shift angle increment is actively subtracted from the phase shift angle of the previous adjustment cycle. ;

[0052] If the sensitivity monitoring index is between the low threshold and the high threshold, then the phase shift angle remains unchanged;

[0053] The first phase shift angle increment of the present invention Greater than the second phase shift angle increment First phase shift angle increment The second phase shift angle increment is 1% to 10% of the maximum permissible phase shift angle. It is 0.5% to 5% of the maximum permissible phase shift angle.

[0054] This invention causes the gain of the LLC resonant converter to decrease by injecting a phase shift angle, resulting in a drop in output voltage. After this voltage drop is detected by the single-voltage-loop PI controller, the PI controller automatically reduces the switching frequency to compensate for the gain, thereby implicitly driving the converter's operating point to shift from the operating region where the switching frequency change has a weaker impact on the voltage gain to the operating region where the switching frequency change has a stronger impact on the voltage gain.

[0055] The core mechanism of the method proposed in this invention lies in utilizing the attenuation effect of phase-shifting operation on the fundamental voltage of the output voltage of the aforementioned H-bridge inverter circuit to actively induce a deflection in the closed-loop feedback trajectory of the system. Specifically, when a phase shift angle is introduced, the original gain balance is broken. To compensate for the power drop caused by the phase shift, the closed-loop control algorithm automatically reduces the current switching frequency, causing the operating point to fall back from the high-frequency smooth region to the resonant center frequency.

[0056] Although phase-shifting itself contributes negatively to gain in a single dimension, its combined effect in the multi-dimensional control space forces the system to relock to a lower frequency operating region with a steeper gain slope. Within this region, the gain contribution rate (sensitivity coefficient) of frequency changes is significantly improved due to the curvature of the gain curve. This frequency drop induced by phase shifting not only effectively solves the switching losses and electromagnetic interference problems caused by excessively high operating frequencies under light loads, but more importantly, it improves the system's control gain redundancy and dynamic convergence speed by optimizing the trajectory distribution on the gain plane, achieving synergistic optimization of high-precision voltage regulation and fast load response under light loads.

[0057] See Figure 3 The diagram illustrates the sensitivity-guided single-loop control architecture proposed in this invention. The diagram fully presents the control architecture of this invention: the control architecture begins at the summation point on the left. This stage calculates the difference between the output voltage reference value Vref and the actual output voltage Vout, generating a voltage error signal Error. This signal quantifies the deviation between the actual output and the target value, providing a core basis for subsequent control adjustments. Subsequently, the error signal Error is input to the PI voltage loop controller. This module, as the core of traditional PFM control, eliminates static errors through proportional and integral regulation and dynamically outputs a switching frequency command fs based on the magnitude of the deviation. Theoretically, the converter gain can be changed by adjusting the switching frequency to achieve output voltage stability.

[0058] To overcome the limitations of traditional PFM, this invention adds a sensitivity detection auxiliary closed loop based on the Pad approximation. The sensitivity detection module takes the switching frequency fs output by the PI loop as input and uses the Pad approximation to perform rational polynomial fitting on the gain-frequency characteristics of the LLC converter, calculating in real time the sensitivity index of the gain to frequency changes at the current frequency. The physical significance of this indicator lies in quantifying the effectiveness of frequency regulation: The smaller the value, the closer the current operating condition is to the control dead zone, and the weaker the impact of frequency adjustment on the gain. Based on this indicator, the phase shift injection module dynamically generates phase shift commands. ,when When <Th_Low, the system is determined to have entered the low sensitivity region, and the controller operates in steps. Actively accumulating injection phase shift angle ;when When Th_High, the system is determined to be in the high-sensitivity region, and the controller operates in steps. Gradually decrease the phase shift angle When Th_Low ≤ When ≤ Th_High, the controller neither increases nor decreases the phase shift angle.

[0059] As the core of the control strategy execution, the frequency converter phase shift modulator receives the switching frequency fs from the main control loop and the phase shift angle from the auxiliary loop. This generates a gate drive signal that combines frequency conversion and phase shifting characteristics. This drive signal is sent to the inverter circuit of the LLC resonant converter, driving the switching transistors to turn on and off according to a specified timing sequence. This causes the inverter circuit to convert DC power into AC power. Through energy transfer and rectification in the LLC resonant cavity, the final output is a DC voltage Vout. The actual output Vout of the converter is then fed back to the initial summation point and compared with Vref to generate a new error signal, thus completing the entire negative feedback control loop.

[0060] This hybrid control architecture enables adaptive control under all operating conditions: under normal operating conditions, it relies on efficient PFM control, and under light load and high frequency control dead zone conditions, it automatically activates phase shift compensation, effectively avoiding frequency runaway and ensuring the stable operation of the LLC converter across the entire load range.

[0061] See Figure 4 The diagram illustrates a control flow chart of a specific embodiment of the present invention. The entire control cycle is executed sequentially according to the following logical steps after it begins:

[0062] 1. Sampling switching frequency: The system first obtains the current actual operating state and samples the current switching frequency fs.

[0063] 2. Calculate the sensitivity index: Based on the sampled switching frequency fs, the algorithm internally calculates a sensitivity index to characterize the current system state. .

[0064] 3. Sensitivity threshold determination: The system will calculate the sensitivity index. The results are compared with preset sensitivity thresholds Th_Low and Th_High to determine... Relationship between Th_Low and Th_High:

[0065] if <Th_Low indicates that the system is currently in a low-sensitivity state (e.g., dead zone). In this case, phase shift injection is performed, i.e., at the current phase shift angle... Based on this, add a fixed step size. ,Right now

[0066]

[0067] if > Th_High indicates that the system's current sensitivity is sufficient. At this point, phase shift angle recovery is executed, meaning the phase shift angle is adjusted to the current position. Based on this, subtract a fixed step size. ,Right now

[0068]

[0069] If Th_Low ≤ If ≤ Th_High, it indicates that the system sensitivity is good and no phase shift angle adjustment is needed.

[0070] 4. Saturation limiting processing: Regardless of which branch the new phase angle is calculated from... All phase shift angles must pass through a saturation limiter. This limiter forces the phase shift angle to be restricted within a physically permissible safe range, i.e., 0 ≤ 0. ≤ This is to prevent the phase shift angle from becoming negative or exceeding the maximum value that the system can withstand.

[0071] 5. Modulator Update: Finally, the system will update the final phase shift angle after limiting. The update is then sent to the frequency converter phase shifter, which in turn drives the hardware circuitry to execute the latest switching action. At this point, the algorithm execution for one control cycle ends, and the next control cycle begins.

[0072] Figures 5 to 7 The key waveforms of the control method of the present invention under different operating conditions in one embodiment are shown to demonstrate the adjustment capability of the control method of the present invention for a wide range of outputs, thereby proving its effectiveness. First, Figure 5 The waveform diagram of the control method of the present invention under light load is shown. The reference voltage is set to 50V and the load is a 2Ω resistor. As can be seen from the figure, with the help of the injected phase shift angle, the switching frequency is clamped at 129KHz, the frequency is stable and there is no loss of control, and the actual output voltage is also stable at 50V, successfully tracking the reference voltage. Figure 6 The diagram illustrates key waveforms for dynamic response in this invention. The simulation test conditions involve fixing the output reference voltage at 50V and using a controlled current source to simulate a step change in the load. The output of this current source is shown below. Figure 6 As shown in (c), the output is 35A (representing heavy load) during the 0-20ms time period, 2A (representing light load) during the 20ms-40ms time period, and 35A (representing heavy load) during the 40ms-60ms time period. Figure 6 As can be seen in (a), at both time points of load change (20ms and 40ms), the output voltage exhibited slight fluctuations and recovered to the reference voltage within a short time; Figure 6 As can be seen from (b) in the figure, when the load changes from heavy load to light load (at 20ms), the switching frequency first increases to about 150KHz. At this time, the control system judges that the sensitivity index is less than the sensitivity threshold Th_Low, that is... <Th_Low, indicating the system has entered a control dead zone, therefore the first phase shift angle increment is... The phase shift angle gradually increases until the sensitivity index falls between Th_Low and Th_High, at which point the system reaches steady state. When the load changes from light to heavy (around 40ms), the switching frequency first decreases to about 100kHz. At this point, the control system determines that the sensitivity index is greater than the sensitivity threshold Th_High, i.e. > Th_High, assuming the system sensitivity is sufficient, a single PFM control can achieve the purpose of tracking the reference voltage. Therefore, the control system gradually reduces the phase shift angle until the sensitivity index falls between Th_Low and Th_High, at which point the system reaches steady state.

[0073] Figure 7 The load regulation capability of the control method of this invention was demonstrated. The test conditions involved linearly reducing the reference voltage from 55V to 10V within 5ms to 50ms, with the load being a 35A constant current source. Figure 7 As can be seen from (a) in the figure, the output voltage always perfectly tracks the reference voltage; from Figure 7 As can be seen from (b) and (c) in the figure, the phase shift angle gradually increases as the output power of the LLC resonant converter gradually decreases, which keeps the switching frequency below 150kHz. This proves that the present invention can achieve a wide range of output of the LLC resonant converter and avoid the loss of control of the switching frequency.

[0074] In summary, the present invention achieves this through... Figures 5 to 7 The control waveforms and experimental data analysis shown comprehensively verify the superiority of the proposed control strategy in terms of multi-dimensional performance indicators. The waveform evolution under light load demonstrates that this invention successfully avoids the frequency runaway problem of traditional PFM control under light load through the nonlinear mapping of phase shift angle and frequency. Furthermore, the comparison of dynamic response waveforms and load regulation characteristics further proves that the system can achieve rapid and lossless reconstruction of the output voltage with extremely high gain sensitivity when facing large load fluctuations. This control architecture, which integrates high-efficiency steady-state performance, wide load adaptability, and excellent transient suppression capability, not only effectively broadens the stable operating boundary of the converter but also provides practical technical support for the digital high-reliability operation of high-power-density resonant converters.

[0075] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for optimizing the single-loop operating point control of a wide-range LLC resonant converter, characterized in that, Includes the following steps: 1) A single-voltage-loop PI controller is used to perform closed-loop regulation of the output voltage of the LLC resonant converter. In each regulation cycle, the PI controller outputs a switching frequency command to the frequency conversion phase-shift modulator as the frequency input for generating the gate drive signal of the converter inverter circuit. 2) In each adjustment cycle, the current switching frequency of the converter is sampled, and the sensitivity monitoring index at the current switching frequency is calculated in real time; 3) Compare the sensitivity monitoring index with preset low and high thresholds, and update the phase shift angle of the gate drive signal of different bridge arms of the inverter circuit according to the comparison result: If the sensitivity monitoring index is lower than the low threshold, it indicates that the converter is in a low sensitivity state. At this time, the first phase shift angle increment is actively injected based on the phase shift angle of the previous adjustment cycle. If the sensitivity monitoring index is greater than the high threshold, it indicates that the current sensitivity of the converter is sufficient. At this time, the second phase shift angle increment is actively subtracted from the phase shift angle of the previous adjustment cycle. If the sensitivity monitoring index is between the low threshold and the high threshold, then the phase shift angle remains unchanged; The injection of phase shift angle causes the gain of LLC resonant converter to decrease, resulting in a drop in output voltage. After this voltage drop is detected by the single voltage loop PI controller, the PI controller automatically reduces the switching frequency to compensate for the gain, thereby implicitly driving the converter's operating point to shift from the operating region where the change in switching frequency has a weaker impact on voltage gain to the operating region where the change in switching frequency has a stronger impact on voltage gain.

2. The method according to claim 1, characterized in that, The sensitivity monitoring index is obtained by fitting the gain-frequency characteristics of the LLC resonant converter using the Pad approximation with a rational polynomial. The calculation formula is: ； in, To normalize the switching frequency, The attenuation coefficient is fitted based on the characteristics of the LLC resonant converter.

3. The method according to claim 1, characterized in that, Step 3) also includes a step of saturating and limiting the updated phase angle. The saturating and limiting process limits the phase angle to a physically permissible safe range to prevent the phase angle from becoming negative or exceeding the maximum value of the system's tolerance limit.

4. The method according to claim 1, characterized in that, The single-voltage-loop PI controller uses the difference between the output voltage reference value and the actual output voltage of the LLC resonant converter as the error input and outputs a switching frequency command, forming a single closed-loop negative feedback control architecture.

5. The method according to claim 1, characterized in that, The LLC resonant converter is a full-bridge LLC resonant converter, which includes an H-bridge inverter circuit composed of four power switching devices, a resonant network composed of a resonant capacitor, a resonant inductor and a transformer magnetizing inductor, and a rectifier and filter circuit.

6. The method according to claim 1, characterized in that, The low threshold is set to 1.1 to 1.5 times the sensitivity boundary value of single voltage loop regulation failure, and is greater than 0 and less than 1; the sensitivity boundary value of single voltage loop regulation failure is obtained by calculating the sensitivity monitoring index point by point within the preset switching frequency range. When adjusting the switching frequency by the single voltage loop PI controller alone cannot make the actual output voltage track the output voltage reference value, the sensitivity monitoring index value corresponding to the switching frequency at that moment is taken as the boundary value for judging the single voltage loop regulation capability. The high threshold is set to be greater than the low threshold and less than 1.

7. The method according to claim 6, characterized in that, The high threshold is 1.3 to 2 times the low threshold.

8. The method according to claim 1, characterized in that, First phase shift angle increment With the second phase angle increment They are not equal, and the first phase shift angle increment Greater than the second phase shift angle increment .

9. The method according to claim 1, characterized in that, First phase shift angle increment The second phase shift angle increment is 1% to 10% of the maximum permissible phase shift angle. It is 0.5% to 5% of the maximum permissible phase shift angle.

10. A control system for an LLC resonant converter, characterized in that: The control system employs the wide-range LLC resonant converter single-loop operating point optimization control method as described in any one of claims 1 to 9 to regulate the output voltage of the LLC resonant converter.

Images