A method for improving light load efficiency of a GaN-based LLC resonant converter

Abstract

The application provides a GaN-based LLC resonant converter light load efficiency improving method, wherein the LLC resonant converter primary side adopts a full-bridge structure, and the switching tube selects a GaN device with high frequency and low parasitic capacitance; the secondary side adopts full-bridge rectification, and the switching tube selects a GaN device with low conduction loss; the resonant inductance is generated by the transformer leakage inductance; the excitation inductance is generated by the transformer parasitic inductance; the resonant frequency is controlled at the MHz level; the LLC resonant converter has two working modes; when the load is large, the PFM frequency modulation mode is adopted; the load voltage and the reference voltage are compared; PI closed-loop control is carried out; the switching frequency is adjusted to realize stable output; when the load is small, the pulse dynamic removal mode is started; on the basis of the PFM frequency control, the pulse dynamic removal control strategy is increased; the primary side current is collected; the switching tube driving pulse dynamic removal position is determined through operation; and the pulse quantity is reduced to realize stable output.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a method for improving the light-load efficiency of GaN-based LLC resonant converters. Technical Background

[0002] LLC resonant converters are widely used in data centers, automotive, medical, marine, and aerospace fields. High efficiency and high power density have always been hot topics in LLC resonant converter research. LLC resonant converters can achieve soft switching within the load range, effectively reducing switching losses. With the rapid development of third-generation wide-bandgap semiconductor technology, GaN switches, due to their high electron mobility, can operate at high frequencies. Increasing the switching frequency can reduce the size of energy storage and magnetic components, thereby increasing power density. Pulse frequency modulation (PFM) is the most commonly used control method for controlling the voltage gain of LLC resonant converters. However, for wide load ranges with large frequency variations, PFM control is less efficient under light load conditions, making it difficult for the switches to achieve zero-voltage turn-on (ZVS). Drive losses, switching losses, and high-frequency magnetic losses also increase, and there is a risk of gain distortion under light loads. Therefore, it is necessary to optimize the light-load control strategy. Common methods for improving efficiency under light load include adding dummy loads, intermittent control, and frequency pulse width hybrid modulation (PFM+PWM). Adding dummy loads introduces additional losses and increases costs. Intermittent control significantly improves efficiency under light loads by intermittently locking the converter to operate at its highest efficiency point, but it is sensitive to voltage loop width design; an excessively large loop width leads to increased ripple. PFM+PWM modulation control has a simple structure and is easy to implement, but its efficiency improvement is not significant under extremely light load conditions. Summary of the Invention

[0003] The purpose of this invention is to provide a method for improving the light-load efficiency of GaN-based LLC resonant converters. This method enables operation across the entire load range within a limited frequency range. When the load is light, the average power is reduced by decreasing the number of pulses, thus maintaining stable output voltage. This approach balances output voltage ripple and light-load efficiency.

[0004] The technical solution to achieve the purpose of this invention is as follows:

[0005] A method for improving the light-load efficiency of a GaN-based LLC resonant converter reduces the average power by decreasing the number of pulses within a limited frequency range, while maintaining stable output voltage. This method balances ripple and light-load efficiency. The method includes:

[0006] Step 1: Collect the primary side current of the transformer and calculate the secondary side load current based on the primary side current;

[0007] Step 2: Monitor the load current in real time and compare the load current with the full load current. When the load current is greater than the threshold, only the PFM frequency modulation mode is used to achieve stable voltage output; otherwise, the pulse dynamic removal mode is started in the PFM frequency modulation mode, and step 3 is executed.

[0008] Step 3: Based on the given optimal efficiency load current, use linear interpolation to calculate the number and location of pulse dynamic removal.

[0009] Step 4: Calculate the driving pulse waveform based on the pulse generated at each removal position and the continuous pulse waveform output under PFM frequency modulation mode, and complete the dynamic removal of pulses to reduce the number of pulses and achieve stable voltage output.

[0010] Furthermore, the secondary-side load current calculated in step 1 is: ,in For load current, For transformer turns ratio, This is the primary side current.

[0011] Furthermore, the threshold in step 2 is , This is the full load current.

[0012] Furthermore, in step 2, a hysteresis width is introduced. ,Will As a lower limit threshold As an upper limit threshold, when the load current Reduce to When the pulse dynamic removal mode is activated, the load current... Increase to The pulse dynamic removal mode is turned off when the load current is greater than 1000 rpm. Less than At that time, maintain the mode of the previous moment.

[0013] Furthermore, the number and location of pulse dynamic removals in step 3 satisfy the following:

[0014]

[0015]

[0016] in, For optimal efficiency load current. This is the measured value of the load current; The number of pulses to be removed; This represents the total number of pulses within a single removal cycle. This represents the proportion of the total number of pulses removed within a single removal cycle. To remove the location of the pulse, round is a rounding function.

[0017] Furthermore, the total number of pulses within a single removal cycle The value is set to 10 times the optimal efficiency load current value.

[0018] Furthermore, the driving pulse waveform in step 4 is as follows:

[0019]

[0020] Where A is the continuous pulse waveform output in PFM frequency modulation mode, and B is the waveform of the pulse generated at the removal position. Invert B.

[0021] Furthermore, the pulse width generated at the removal position is set to 1.2 times the width of the continuous pulse wave output in PFM frequency modulation mode.

[0022] Furthermore, the primary side of the LLC resonant converter adopts a full-bridge structure with GaN devices as the switching transistors; the secondary side adopts a full-bridge rectification with GaN devices as the switching transistors.

[0023] In view of the above-described structure of the present invention, the present invention has the following advantages:

[0024] 1. This invention uses GaN as the switching transistor, which has a high switching frequency and low conduction loss, and can improve the conversion efficiency across the entire load range;

[0025] 2. This invention adopts a pulse dynamic removal control strategy to uniformly remove high-frequency pulses, achieving full load range operation within a narrow frequency range. ZVS can be achieved across the entire load range, resulting in significant efficiency improvement under light load and low output voltage ripple under light load.

[0026] 3. This invention uses a fixed pulse width method, which avoids the ZVS loss problem of PWM modulation under light load; the pulse width remains unchanged before and after load switching, and the frequency is finely adjusted to quickly reach a steady state;

[0027] 4. For LLC resonant converters with different design parameters, the pulse dynamic removal control strategy is universal and has a wide range of applications. Attached Figure Description

[0028] Figure 1 This is a topology diagram of an LLC resonant converter.

[0029] Figure 2 This is a flowchart of the pulse dynamic removal control.

[0030] Figure 3 This is a schematic diagram of the pulse dynamic removal mode switching.

[0031] Figure 4 This is a schematic diagram of the waveform generation process for the pulse dynamic removal mode.

[0032] Figure 5 This is a comparison chart of output voltage ripple.

[0033] Figure 6 This is a graph comparing efficiency. Detailed Implementation

[0034] The following is in conjunction with the appendix Figures 1-6 The specific embodiments of the present invention will be further described below:

[0035] The topology of the LLC resonant converter of this invention is as follows: Figure 1 As shown, this topology is a well-known structure. The primary side of the LLC resonant converter adopts a full-bridge structure, and the switching transistors are high-frequency, low-parasitic-capacitance GaN devices. The secondary side adopts a full-bridge rectification, and the switching transistors are low-conduction-loss GaN devices. Through reasonable design of the integrated transformer, the resonant inductance is generated by the transformer leakage inductance, and the magnetizing inductance is generated by the transformer parasitic inductance. The resonant frequency is controlled at the MHz level. The LLC resonant converter has two operating modes. When the load is large, the PFM frequency modulation mode is used, which collects the load voltage and compares it with the reference voltage, performs PI closed-loop control, and achieves stable output by adjusting the switching frequency. When the load is small, the pulse dynamic removal mode is activated. On the basis of PFM frequency control, a pulse dynamic removal control strategy is added. The primary side current is collected, and the position of the switching transistor driving pulse dynamic removal is determined by calculation. Stable output is achieved by reducing the number of pulses.

[0036] The control flow of the pulse dynamic removal control strategy is as follows: Figure 2 As shown, the specific execution steps are as follows:

[0037] 1. Collect the primary current of the transformer, and calculate the secondary current (load current) based on the primary current. ,in For load current, For transformer turns ratio, This is the primary side current;

[0038] 2. Real-time monitoring of load current And compare the load current. With full load current Relationship, when When the value is greater than a certain value, only the PFM frequency modulation mode is used; when When the value is less than a certain threshold, the pulse dynamic removal mode is activated, adding a pulse dynamic removal control strategy to the PFM frequency control. To avoid frequent switching in critical mode and affecting operational stability, a hysteresis width is introduced. The upper limit is The lower limit is ;when Reduce to When the pulse dynamic removal mode is activated, Increase to The pulse dynamic removal mode is turned off at this time. The mode switching timing is as follows: Figure 3 As shown;

[0039] 3. Based on the given optimal efficiency load current, the number and location of pulse dynamic removal are calculated using linear interpolation. The specific formula is as follows:

[0040]

[0041]

[0042] in, For optimal efficiency load current. This is the measured value of the load current; The number of pulses to be removed; This represents the total number of pulses within a single removal cycle. To ensure the accuracy of dynamic pulse removal... The value is set to 10 times the optimal efficiency load current value; This represents the proportion of the total number of pulses removed within a single removal cycle. To remove the location of the pulse, for example... This indicates that the total number of pulses in a single removal cycle is 20. The 7th, 13th, and 20th pulses need to be removed in a single removal cycle, for a total of 3 pulses.

[0043] 4. The specific generation process of the pulse dynamic removal waveform in the controller is as follows: In PFM frequency modulation mode, the output is a continuous pulse waveform A. When the pulse dynamic removal mode is enabled, waveform B is introduced. Waveform B is defined as generating a pulse at the removal position and keeping it low at other positions; the pulse width of waveform A is defined as... The pulse width of waveform B is To ensure complete removal of the pulse at the designated location, Slightly greater than The present invention takes The new control output is waveform C, which is defined as the result of operations performed between A and B. The specific implementation process is as follows: Figure 4 As shown.

[0044] For example, the parameters of a GaN-based LLC resonant converter are as follows:

[0045] Output voltage Maximum output power Optimal efficiency load current The commonly used typical load current is ;

[0046] When the load current is At that time, based on the above execution steps, the total number of pulses within a single removal cycle. Number of pulses removed ;

[0047] According to the formula The pulse removal positions can be obtained as follows: ;

[0048] Through calculation The load current is obtained as The driving waveform at the specified time is calculated using the same method as the driving waveform at other load currents.

[0049] The output voltage waveform of the aforementioned LLC resonant converter in pulse dynamic rejection mode is as follows: Figure 5 As shown, compared with the traditional intermittent mode, the output voltage ripple is smaller, with an average reduction of 62.5%; Figure 6 As shown, the LLC resonant converter with pulse dynamic removal mode exhibits a significant improvement in light-load efficiency; the smaller the load, the more pronounced the efficiency improvement, with a maximum increase of 7.7%. This invention has broad application prospects, significantly enhancing the energy efficiency of data center server power supplies, electric vehicle chargers, and other equipment during low-load operation, directly reducing system standby power consumption and operating costs. The economic benefits are significant, and it is expected to help related power supply products gain an advantage in energy efficiency standard certification, enhance market competitiveness, and create considerable economic value.

[0050] It should be noted that the LLC resonant converter topology and PFM frequency modulation mode control in this application are prior art and will not be described in detail here, nor are they the points of protection of this invention.

[0051] The above description is merely one example of the present invention. For LLC resonant converters with different parameters, the testing method is similar to this example. As long as their topology design and overall principle are consistent with those described in this invention, they should be considered within the scope of this invention. It should be noted that those skilled in the art can make several improvements without departing from the principles of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for improving the light-load efficiency of a GaN-based LLC resonant converter, characterized in that: include: Step 1: Collect the primary side current of the transformer and calculate the secondary side load current based on the primary side current; Step 2: Monitor the load current in real time and compare the load current with the full load current. When the load current is greater than the threshold, only the PFM frequency modulation mode is used to achieve stable voltage output; otherwise, the pulse dynamic removal mode is started in the PFM frequency modulation mode, and step 3 is executed. Step 3: Based on the given optimal efficiency load current, use linear interpolation to calculate the number and location of pulse dynamic removal. Step 4: Calculate the driving pulse waveform based on the pulse generated at each removal position and the continuous pulse waveform output under PFM frequency modulation mode, and complete the dynamic removal of pulses to reduce the number of pulses and achieve stable voltage output.

2. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 1, characterized in that: The secondary load current is calculated in step 1 as follows: ,in For load current, For transformer turns ratio, This is the primary side current.

3. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 1, characterized in that: The threshold in step 2 is , This is the full load current.

4. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 3, characterized in that: In step 2, the hysteresis width is introduced as follows: ,Will As a lower limit threshold As an upper limit threshold, when the load current Reduce to When the pulse dynamic removal mode is activated, the load current... Increase to The pulse dynamic removal mode is turned off when the load current is greater than 1000 rpm. Less than At that time, maintain the mode of the previous moment.

5. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 3, characterized in that: In step 3, the number and location of pulse dynamic removals satisfy the following: in, For optimal efficiency load current. This is the measured value of the load current; The number of pulses to be removed; This represents the total number of pulses within a single removal cycle. This represents the proportion of the total number of pulses removed within a single removal cycle. To remove the location of the pulse, round is a rounding function.

6. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 5, characterized in that: Total number of pulses in a single removal cycle The value is set to 10 times the optimal efficiency load current value.

7. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 1, characterized in that: The driving pulse waveform in step 4 is as follows: Where A is the continuous pulse waveform output in PFM frequency modulation mode, and B is the waveform of the pulse generated at the removal position. Invert B.

8. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 1, characterized in that: The pulse width generated at the removal position is set to 1.2 times the width of the continuous pulse wave output in PFM frequency modulation mode.

9. The method for improving the light-load efficiency of a GaN-based LLC resonant converter according to claim 1, characterized in that: The primary side of the LLC resonant converter adopts a full-bridge structure with GaN devices as the switching transistors; the secondary side adopts a full-bridge rectification with GaN devices as the switching transistors.

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