GaN-based half-bridge LLC resonant converter hybrid modulation method suitable for wide input voltage scene

Abstract

The invention belongs to the technical field of power electronic conversion, and discloses a GaN-based half-bridge LLC resonant converter hybrid modulation method suitable for a wide input voltage scene. The method comprises the steps of constructing a half-bridge LLC resonant converter topology, designing a hybrid modulation control method, establishing a unified small signal model based on a fundamental wave analysis method, introducing an intermediate control quantity x, and establishing a mapping relation among a switching frequency fs, a duty ratio D and x to ensure efficient operation in a full-load range. The method comprises the following steps of: adaptively switching a modulation mode according to an input voltage by adopting an integral framework of mixed modulation of pulse frequency modulation and pulse width modulation and unified model control, building a half-bridge LLC resonant converter simulation model based on MATLAB / Simulink, and testing and verifying the half-bridge LLC resonant converter simulation model. The method has good stability and response speed for input voltage change, cross-mode control of a single variable x is realized through a unified model, and parameter setting steps are reduced.

Description

Technical Field

[0001] This invention belongs to the field of power electronic conversion technology and relates to a hybrid modulation method for GaN-based half-bridge LLC resonant converters suitable for wide input voltage scenarios, which can be applied to small and medium power isolated DC / DC conversion scenarios. Background Technology

[0002] GaN power devices, with their superior material properties, offer advantages such as low on-resistance, high switching frequency, and fast switching speed. These advantages effectively reduce switching losses while allowing for a reduction in the size of magnetic components. Doubling the switching frequency can reduce the size of magnetic components to one-quarter of their original size, making them a key component in resolving the contradiction between high power and small size in converters. LLC resonant converters, due to their soft-switching characteristics, low switching losses, and high power density, have become the core topology of isolated DC-DC converter systems. Among them, the half-bridge LLC topology, by reducing the number of switching transistors, lowers cost and size, and is widely used in low-to-medium power applications.

[0003] Generally, LLC converters employ PFM, but the limited operating frequency range of the converter restricts the realization of wide-range voltage regulation. Therefore, most traditional LLC topologies are used for DC converters with small input or output ranges. With the expansion of application areas, LLC converters with wide input or output ranges have become a new research area {J. Gao, J. Zhang, Q. Song, et al. An LLC resonant single-stage inverter with high-frequency link and soft-switching[J]}. To achieve a wide voltage output range for LLC converters within a limited operating frequency, various methods have been proposed from different aspects of circuit design. Optimizing drive signal modulation is an important method to increase the output voltage range. Typically, PWM, phase-shift modulation (PSM), and burst mode control can be added to PFM control {Y. Yue, Y. Liu, J. Zhang, et al. Hybrid Control Method of Full-Bridge LLC Resonant Converter Based on Electric Vehicle[J]}. Although these control methods have been widely used in other types of converters, some new problems arise when they are applied to LLC converters.

[0004] First, when LLC is applied to a wide input range, the frequency adjustment range is large, making the converter difficult to control and prone to problems such as increased secondary output current and increased conduction losses {Su Xi, Research on High-Frequency Automotive DC-DC Converter Based on Gallium Nitride Devices [D]}. Second, although the hybrid control method of PWM and PFM can achieve a lower voltage gain under low input voltage conditions, the soft-switching performance is not improved, resulting in limited output voltage and reduced output efficiency {H. Xun, H. Shen, W. Chen. Efficiency optimization strategy of LLC resonant converter based on hybrid PWM and PFM digital control mode [J]}. Third, there is a lack of modulation methods that can adapt to a wide input voltage range. Under low input voltage conditions, the efficiency is low, the mode switching impact is large, and the output gain of the main circuit will change {R. Moriyasu, H. Funaki, M. Shoyama, et al. Surge Current Analysis and Reduction in LLC Resonant Converter With a New Hybrid Control Strategy of Pulse-Frequency Modulation and Phase-Shift Modulation [J]}.

[0005] To effectively address the aforementioned issues with LLC controllers, this invention innovates on a unified model control method. By controlling the switching frequency and duty cycle with a single variable x, it simplifies controller design and improves dynamic response. For an input range of 200-400V, the mode switching logic is based on the input voltage threshold, preventing the switching frequency from deviating significantly from the resonant frequency, maintaining gain stability, and achieving wide input voltage adaptability. Through adaptive switching of PFM and PWM, it ensures ZVS / ZCS under high input voltage conditions and low circulating current under low input voltage conditions, achieving efficient operation over a wide input voltage range. At mode switching points, pre-adjustment and latch-up mechanisms reduce switching shocks, improve robustness, and smooth mode switching. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing half-bridge LLC resonant converters, such as poor modulation adaptability, low modeling accuracy, and large transient impact under wide input voltage range, and to provide a hybrid modulation method for gallium nitride-based half-bridge LLC resonant converters to achieve efficient and stable operation over a wide input voltage range.

[0007] The technical solution of the present invention:

[0008] A hybrid modulation method for GaN-based half-bridge LLC resonant converters suitable for wide input voltage scenarios includes the following steps:

[0009] Step 1: Construct a half-bridge LLC resonant converter topology;

[0010] The half-bridge LLC resonant converter topology includes input-side units, resonant cavity network units, isolation rectifier network units, and output-side units:

[0011] The input-side unit consists of an input voltage Vin, a voltage divider resistor Rin, a voltage divider capacitor Cin, half-bridge switches S1 and S2; the input voltage Vin and the voltage divider resistor Rin are connected in series and then in parallel with the voltage divider capacitor Cin; both half-bridge switches S1 and S2 are GaN MOSFETs, and fast recovery diodes and buffer capacitors C1 and C2 are connected in reverse parallel across their terminals respectively; the drain of half-bridge switch S1 is connected to the positive terminal of the voltage divider resistor Rin, the source of half-bridge switch S1 is connected to the drain of half-bridge switch S2, and the source of half-bridge switch S2 is connected to the negative terminal of the input voltage Vin;

[0012] The resonant cavity network unit consists of a resonant inductor Lr, a magnetizing inductor Lm, and a resonant capacitor Cr. One end of the resonant capacitor Cr is connected to the source of the half-bridge switch S1, and the other end is connected to the resonant inductor Lr. One end of the resonant inductor Lr is connected to the resonant capacitor Cr, and the other end is connected to the primary side of the high-frequency transformer T. The magnetizing inductor Lm is connected in parallel with the primary side of the high-frequency transformer T.

[0013] The isolated rectifier network unit includes a high-frequency transformer T with a turns ratio of 25:6, rectifier bridge diodes D1, D2, D3, and D4. The primary side of the high-frequency transformer T is connected to the resonant inductor Lr and the source of the half-bridge switch S2, respectively. The secondary side of the high-frequency transformer T is connected to the anodes of rectifier bridge diodes D2 and D3, respectively. The anode of rectifier bridge diode D2 is connected to the cathode of rectifier bridge diode D1, the anode of rectifier bridge diode D3 is connected to the cathode of rectifier bridge diode D4, the anodes of rectifier bridge diodes D1 and D4 are connected in parallel, and the cathodes of rectifier bridge diodes D2 and D3 are connected in parallel.

[0014] The output-side unit includes a filter capacitor Co and a load Ro. One end of the filter capacitor Co is connected to the output terminal of the parallel connection between the anode of rectifier bridge diode D1 and the anode of rectifier bridge diode D4, and the other end is connected to the output terminal of the parallel connection between the cathode of rectifier bridge diode D2 and the cathode of rectifier bridge diode D3. The load Ro is connected in parallel across the filter capacitor Co, and the voltage across the load Ro is the output voltage.

[0015] Step 2: Design a hybrid modulation control method, adopting a hybrid modulation and unified model control architecture of pulse frequency modulation (PFM) and pulse width modulation (PWM). The modulation mode can be adaptively switched according to the output voltage of the half-bridge LLC resonant converter topology to ensure efficient operation over a wide input voltage range.

[0016] Step 2.1: Establish the theoretical foundation:

[0017] Based on fundamental frequency analysis (FHA), the formula for pulse frequency modulation (PFM) is derived to obtain the transfer function of output voltage with respect to switching frequency. ,in It is a DC gain function. It is the output voltage. It is the input voltage; , where n is the turns ratio of the high-frequency transformer, R L The resistance value of the load Ro; Resonant frequency; normalized frequency Switching frequency Resonant frequency When the switching frequency equals the resonant frequency, the inductive reactance and capacitive reactance of the resonant cavity network unit are equal, and it exhibits purely resistive properties externally. As a complex variable, it is represented in the transfer function. The inductance ratio k = Lm / Lr is the ratio of the magnetizing inductance to the resonant inductance. Output filter capacitor The first-order poles introduced determine the output voltage response speed; is the second-order pole of the resonant cavity network unit, which is related to the inductance ratio k; The pole quality factor reflects the peak intensity in the resonant cavity network unit.

[0018] Based on the fundamental frequency analysis method (FHA), the formula for pulse width modulation (PWM) is derived to obtain the transfer function of output voltage with respect to duty cycle. ;

[0019] Step 2.2: Based on theoretical foundations, construct a unified model for hybrid modulation of Pulse Frequency Modulation (PFM) and Pulse Width Modulation (PWM), including a comparator, PI controller, PFM / PWM signal generator, and half-bridge LLC resonant converter topology:

[0020] The comparator inputs are the output voltage Vo and the reference voltage Vref of the half-bridge LLC resonant converter topology, and the output voltage error value e, which are then provided to the PI controller.

[0021] A PI controller is a type of feedback controller that regulates the system through proportional (P) and integral (I) actions. The proportional action quickly adjusts the output based on the deviation, while the integral action eliminates steady-state error by accumulating the deviation.

[0022] A PFM / PWM signal generator is used to introduce an intermediate control quantity x, which is the output of the PI controller, to establish the switching frequency f. s The mapping relationship between duty cycle D and intermediate control quantity x; The mode switching threshold is determined by the maximum gain. max With switching point gain shift Calculated , This represents the maximum output value of the PI controller; when x> When in pulse frequency modulation mode, the output switching frequency is... The inverse function of the switching frequency is solved using Newton's iteration method, where... When x≤ At this time, it is in pulse width modulation mode, and the output duty cycle is... , For maximum duty cycle; according to and It can generate drive signals;

[0023] In a half-bridge LLC resonant converter topology, the gate (g) of the half-bridge switch receives a drive signal, which in turn changes the output voltage, forming a closed-loop feedback control.

[0024] Step 3: Build a simulation model of a half-bridge LLC resonant converter based on MATLAB / Simulink: Set up the driving module according to the hybrid modulation method of the half-bridge LLC resonant converter topology built in Step 1 and the half-bridge LLC resonant converter topology built in Step 2. The driving module includes: setting the mode decision logic, designing the dual-loop feedback control, and setting the limiting protection strategy.

[0025] Step 3.1: Set the mode decision logic: Set the input voltage threshold V DC-th It is 200V, which is 50% of the rated input voltage of 400V, corresponding to the modulation mode switching boundary;

[0026] When the input voltage V DC >V DC-th At that time, PFM mode is used, by changing the switching frequency. Adjust the output voltage; the switching frequency range is 100kHz-150kHz, fluctuating around the resonant frequency of 100kHz; when the input voltage V... DC ≤V DC-th When switching to pulse width modulation (PWM) mode, the switching frequency is fixed. With a resonant frequency of 100kHz, the output voltage is adjusted by changing the duty cycle D, which ranges from 0.1 to 0.4. The performance of the half-bridge LLC resonant converter topology under various modulation modes and during modulation mode switching is tested by directly changing the input voltage or the load Ro.

[0027] Step 3.2: Design dual-loop feedback control: Dual-loop feedback control is a closed-loop control method that consists of an inner current feedback loop and an outer voltage feedback loop to form a dual closed-loop system. It can achieve more precise voltage and current control and compensate for the effects of time delay and disturbance.

[0028] The outer voltage loop uses a PI controller, with the input being the output voltage error e = V. o-ref - V o , where V o-ref For the output reference voltage, V o The output voltage is the intermediate control quantity x. Changing the input voltage or the load Ro will change the output voltage, thus affecting the output value of the intermediate control quantity x and changing the modulation mode. The inner current loop does not require an additional controller. It directly controls the drive signals of the half-bridge switches S1 and S2 through pulse frequency modulation (PFM) or pulse width modulation (PWM) to ensure the stability of the resonant inductor current.

[0029] Step 3.3: Set up a protection strategy to safeguard the topology and stabilize performance.

[0030] In the half-bridge LLC resonant converter topology, the half-bridge switching transistors use isolated driver chips with a 50ns dead time to prevent bridge arm shoot-through; simultaneously, overcurrent protection is integrated, detecting the resonant inductor current iLr and shutting off the drive when it exceeds 1.5 times the rated value; and overvoltage protection is integrated, detecting the output voltage V. o Protection is triggered when the voltage exceeds 50V, improving system reliability.

[0031] When the topology is powered on, a combination strategy of switching frequency ramp-up and duty cycle limitation is adopted: the initial switching frequency is set to 150kHz, which is higher than the resonant frequency, and then reduced to 100kHz at a rate of 5kHz / ms; at the same time, the initial duty cycle is limited to 0.1, and then increased to the target value at a rate of 0.05 / ms to avoid overshoot of the resonant cavity network unit current when powered on, that is, to control the peak value of the resonant cavity network unit current to be ≤ 1.2 times the rated value, and to protect the half-bridge switch, S1 half-bridge switch, S2 and the resonant cavity network unit;

[0032] When the modulation mode switches, the intermediate control quantity x is pre-adjusted through the outer voltage loop 10ms in advance to stabilize the gain at the switching point. shift The left and right fluctuations are controlled, and the integral element in the PI controller is locked for 5ms during the switching process to suppress transient voltage / current surges.

[0033] Step 4: Test and verify the simulation model of the half-bridge LLC resonant converter. Set up two modes: a high-voltage input of 400V and a low-voltage input of 200V, to verify the hybrid modulation effect. At high voltage, PFM mode is used: the switching frequency is stabilized around 100kHz, the GaN half-bridge switch triggers the drive signal after the voltage across it drops to zero (ZVS), and the rectifier bridge diodes turn off after the current drops to zero (ZCS). At low voltage, PWM mode is used: the switching frequency is fixed at 100kHz, and the duty cycle is 0.3. During mode switching, the resonant current fluctuation is ≤5A, the output voltage fluctuation is ≤0.5V, and there is no significant impact.

[0034] The beneficial effects of the present invention are: the present invention has good stability and response speed for wide input voltage changes, can operate efficiently in wide input voltage scenarios, with an overall efficiency of over 90%, and achieves cross-mode control of single variable x through a unified model, eliminating the need to design a separate PI controller for PFM and PWM, reducing parameter tuning steps by 50%. Attached Figure Description

[0035] Figure 1 This is a topology diagram of the half-bridge LLC resonant converter of the present invention;

[0036] Figure 2 This is a block diagram of the unified model hybrid modulation control of the present invention;

[0037] Figure 3 The diagram shows the input and output voltage and output power waveforms of the present invention, where (a) is the input AC voltage waveform of the present invention; (b) is the output voltage waveform of the present invention; and (c) is the output power waveform of the present invention.

[0038] Figure 4 The diagram shows the resonant cavity network unit results during mode switching of the control method of the present invention; wherein, (a) is the resonant cavity network unit current curve during mode switching of the control method of the present invention; (b) is a partial diagram of the resonant cavity network unit current curve before mode switching of the control method of the present invention; and (c) is a partial diagram of the resonant cavity network unit current curve after mode switching of the control method of the present invention.

[0039] Figure 5 This is the output efficiency waveform of the present invention. Detailed Implementation

[0040] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0041] In a specific application example, the parameter settings for each functional module and electronic component in the above-mentioned half-bridge LLC topology with control method are as follows:

[0042] DC input voltage: 400VDC;

[0043] Resonant inductance: 38.4uH;

[0044] Resonant capacitor: 66nF;

[0045] Magnetizing inductance: 192uH;

[0046] Two GaN switching transistors: enhancement type, 22A@25℃, 650V, switching frequency 100kHz;

[0047] Dead time: 50ns;

[0048] like Figure 1 The diagram shows the rectifier half-bridge LLC resonant topology of this invention, including an input-side unit, a resonant cavity network unit, an isolation rectifier network unit, and an output-side unit:

[0049] The input-side unit consists of an input voltage Vin, a voltage divider resistor Rin, a voltage divider capacitor Cin, half-bridge switches S1 and S2; the input voltage Vin and the voltage divider resistor Rin are connected in series and then in parallel with the voltage divider capacitor Cin; both half-bridge switches S1 and S2 are GaN MOSFETs, and fast recovery diodes and buffer capacitors C1 and C2 are connected in reverse parallel across their terminals respectively; the drain of half-bridge switch S1 is connected to the positive terminal of the voltage divider resistor Rin, the source of half-bridge switch S1 is connected to the drain of half-bridge switch S2, and the source of half-bridge switch S2 is connected to the negative terminal of the input voltage Vin;

[0050] The resonant cavity network unit consists of a resonant inductor Lr, a magnetizing inductor Lm, and a resonant capacitor Cr. One end of the resonant capacitor Cr is connected to the source of the half-bridge switch S1, and the other end is connected to the resonant inductor Lr. One end of the resonant inductor Lr is connected to the resonant capacitor Cr, and the other end is connected to the primary side of the high-frequency transformer T. The magnetizing inductor Lm is connected in parallel with the primary side of the high-frequency transformer T.

[0051] The isolated rectifier network unit includes a high-frequency transformer T with a turns ratio of 25:6, rectifier bridge diodes D1, D2, D3, and D4. The primary side of the high-frequency transformer T is connected to the resonant inductor Lr and the source of the half-bridge switch S2, respectively. The secondary side is connected to the anodes of rectifier bridge diodes D2 and D3, respectively. The anode of rectifier bridge diode D2 is connected to the cathode of rectifier bridge diode D1, the anode of rectifier bridge diode D3 is connected to the cathode of rectifier bridge diode D4, the anodes of rectifier bridge diodes D1 and D4 are connected in parallel, and the cathodes of rectifier bridge diodes D2 and D3 are connected in parallel.

[0052] The output-side unit includes a filter capacitor Co and a load Ro. One end of the filter capacitor Co is connected to the parallel output terminal of the anode of rectifier bridge diode D1 and the anode of rectifier bridge diode D4, and the other end is connected to the parallel output terminal of the cathode of rectifier bridge diode D2 and the cathode of rectifier bridge diode D3. The load Ro is connected in parallel across the two ends of the filter capacitor Co.

[0053] The design employs a hybrid modulation control method, combining pulse frequency modulation (PFM) and pulse width modulation (PWM) with a unified model control architecture. This allows for adaptive switching of the modulation mode based on the output voltage of the half-bridge LLC resonant converter topology, ensuring efficient operation over a wide input voltage range.

[0054] Theoretical Foundation: PFM mode adjusts the output voltage by changing the switching frequency. The core principle is establishing the relationship between the output voltage and the input voltage, i.e., the gain. Using fundamental frequency analysis (FHA), the square wave voltage output by the half-bridge is equivalent to the fundamental frequency component, whose effective value is: , Given the input voltage, the fundamental amplitude of the half-bridge square wave is half that of the full-bridge wave. The fundamental impedance of the resonant cavity network element is: The switching angular frequency , For switching frequency, The output-side load resistance Ro is reflected in the equivalent resistance of the resonant cavity network unit. Ignoring higher harmonics, the fundamental RMS value of the output voltage is... Combined with DC output voltage The DC gain transfer function of the PFM is then derived: ,in Where n is the turns ratio of the high-frequency transformer, and R is the load resistance. L The resistance of the load Ro. Normalized frequency. Switching frequency Resonant frequency When normalized frequency When the switching frequency is 1 (i.e., the resonant frequency), the gain is determined solely by the inductance ratio k = Lm / Lr, and is independent of the load; when... When the value is greater than 1, the switching frequency is higher than the resonant frequency, and the gain increases with frequency. Increase and decrease; when When the value is less than 1, the switching frequency is lower than the resonant frequency, and the gain increases with frequency. It decreases while increasing. Small-signal analysis requires linearizing the DC gain formula, introducing a disturbance such as the switching frequency disturbance. and output voltage disturbance ,right Find the partial derivative: , combined ,in Let this be the resonant frequency. Substitute it into the standard form of the small-signal model. ,in It is DC gain, which is essentially the ratio of the output DC voltage to the effective input DC voltage; The numerator polynomial contains zero-point information; This is the denominator polynomial containing pole information. Substituting it, we obtain the output voltage transfer function with respect to frequency: ,in As a complex variable, it is represented in the transfer function. ; Output filter capacitor The first-order poles introduced determine the output voltage response speed; is the second-order pole of the resonant cavity network unit, which is related to the inductance ratio k; The pole quality factor reflects the peak intensity in the resonant cavity network unit. The larger the value, the steeper the peak intensity waveform of the resonant cavity network unit.

[0055] In PWM mode, the switching frequency is fixed at the resonant frequency, and the output voltage is adjusted by changing the duty cycle D of the switching transistor. In this case, the fundamental RMS value of the half-bridge output square wave varies with the duty cycle: Substituting into the DC gain formula, we get At a fixed frequency, the gain is linearly related to the duty cycle D, avoiding efficiency degradation caused by a significant deviation of the switching frequency from the resonant frequency. At a fixed frequency, the resonant cavity network unit is purely resistive, and the transfer function of the output voltage with respect to the duty cycle simplifies to a first-order inertial element. .

[0056] Based on theoretical foundations, a unified model for hybrid modulation of PFM and PWM is constructed. The control block diagram of the unified model for hybrid modulation is as follows: Figure 2 As shown, the topology includes a comparator, a PI controller, a PFM / PWM signal generator, and a half-bridge LLC resonant converter.

[0057] The comparator inputs are the output voltage Vo and the reference voltage Vref of the half-bridge LLC resonant converter topology, and the output voltage error value e, which are then provided to the PI controller.

[0058] A PI controller is a type of feedback controller that regulates the system through proportional (P) and integral (I) actions. The proportional action quickly adjusts the output based on the deviation, while the integral action eliminates steady-state error by accumulating the deviation.

[0059] In the hybrid modulation unified model, a controller output x (i.e., the PI controller output) is introduced to establish a mapping between x and the switching frequency / duty cycle, ensuring linearity of the gains for both modes. In the model, the PFM mode is defined as x > x. sIt needs to meet the following requirements. PWM mode means x is less than x. s At that time, by When x= At that time, there was D max = To achieve seamless handover, the gains of the two modes must be equal at the handover point. Substituting into the gain formula, we obtain the normalized switching frequency. Duty cycle of switching point The correspondence is usually taken as .according to and It can generate drive signals;

[0060] In a half-bridge LLC resonant converter topology, the gate (g) of the half-bridge switch receives a drive signal, which in turn changes the output voltage, forming a closed-loop feedback control.

[0061] A simulation model of a half-bridge LLC resonant converter was built based on MATLAB / Simulink: the topology of the half-bridge LLC resonant converter and its hybrid modulation method, i.e., the driving module, is composed of: setting the mode decision logic, designing the dual-loop feedback control, and setting the limiting protection strategy.

[0062] In MATLAB / Simulink, the driver module consists of a PI controller function module and a PFM / PWM signal generator function module.

[0063] For the half-bridge LLC resonant converter topology, the mode decision logic is set as follows: The threshold voltage V of the input voltage is set. DC-th The voltage is 200V, which is 50% of the rated input voltage of 400V, corresponding to the modulation mode switching boundary; when the input voltage V DC >V DC-th At that time, PFM mode is used, by changing the switching frequency. Adjust the output voltage; the switching frequency range is 100kHz-150kHz, fluctuating around the resonant frequency of 100kHz; when the input voltage V... DC ≤V DC-th When switching to PWM mode, the switching frequency is fixed. With a resonant frequency of 100kHz, the output voltage is adjusted by changing the duty cycle D, which ranges from 0.1 to 0.4. The performance of the half-bridge LLC resonant converter topology under various modulation modes and during modulation mode switching is tested by directly changing the input voltage. This part of the function module is written into the PFM / PWM signal generator function module.

[0064] Design of a dual-loop feedback control: Dual-loop feedback control is a closed-loop control method consisting of an inner current feedback loop and an outer voltage feedback loop, forming a dual closed-loop system. This allows for more precise voltage and current control, compensating for time delays and disturbances. The outer voltage loop uses the sampled DC output voltage Vo, compared with the reference voltage Vref, and calculates the difference using a comparator to determine the DC output voltage error e, which is then provided to the PI controller. The PI controller reduces steady-state error and converts the output into an intermediate control quantity x. This difference calculation and control process is implemented using MATLAB function modules, and the generated intermediate control quantity x is provided to the PFM / PWM signal generator. The inner current loop requires no additional controller; it directly controls the GaN switching transistor drive signal via PFM or PWM to ensure the inductor current matches the reference current. This part of the function module is incorporated into the PI controller function module.

[0065] In the PFM / PWM signal generator function module, the modulation mode is selected based on the value of the intermediate control quantity x. PFM compares the frequency parameter converted from x with the resonant frequency; the resulting frequency difference is passed through a limiter to generate a sine wave with a varying frequency. This sine wave with a varying frequency is then compared with a set level to generate a square wave signal. PWM provides the duty cycle parameter converted from x to a comparator, which compares it with a reference triangular wave signal to obtain a square wave signal. This square wave signal is then fed to the gate (g) of the half-bridge switching transistors to drive them. By alternately switching the transistors, the current in the resonant cavity network unit changes, which in turn affects the output-side unit through the isolation rectifier network, changing the output voltage and forming a closed-loop feedback control.

[0066] In the PFM / PWM signal generator function module, set up limit protection design to protect the topology and stabilize performance:

[0067] In terms of topology, the GaN half-bridge switches use isolated driver chips, and a 50ns dead time is set in the function module to prevent bridge arm shoot-through; it also integrates overcurrent protection, detecting the resonant inductor current iLr, and shutting down the driver when it exceeds 1.5 times the rated value; and it integrates overvoltage protection, detecting the output voltage V. o Protection is triggered when the voltage exceeds 50V, improving system reliability.

[0068] When the topology is powered on, a combination strategy of switching frequency ramp-up and duty cycle limitation is adopted: the initial switching frequency is set to 150kHz, which is higher than the resonant frequency, and then reduced to 100kHz at a rate of 5kHz / ms; at the same time, the initial duty cycle is limited to 0.1, and then increased to the target value at a rate of 0.05 / ms to avoid overshoot of the resonant cavity network unit current when powered on, that is, to control the peak value of the resonant cavity network unit current to be ≤ 1.2 times the rated value, thus protecting the GaN switch S1, S2 and the resonant cavity network unit;

[0069] When the modulation mode switches, the intermediate control quantity x is pre-adjusted through the outer voltage loop 10ms in advance to stabilize the gain at the switching point. shift The left and right fluctuations are controlled, and the integral element in the PI controller is locked for 5ms during the switching process to suppress transient voltage / current surges.

[0070] The model was then tested and verified. Two modes were set up: a high-voltage input of 400V and a low-voltage input of 200V, to verify the hybrid modulation effect. In the high-voltage mode, PFM mode was used: the switching frequency was stabilized around 100kHz, the GaN half-bridge switch triggered the drive signal after the voltage across it dropped to zero (ZVS), and the rectifier bridge diodes turned off after the current dropped to zero (ZCS). In the low-voltage mode, PWM mode was used: the switching frequency was fixed at 100kHz, and the duty cycle was 0.3.

[0071] For the topology powered on with a high voltage of 400V DC input, sample the output voltage and other parameters, such as... Figure 3 The figures shown are performance test curves under steady-state operation or small disturbances, used to analyze the dynamic response and stability of current, voltage, and power, including... Figure 3 (a) Input AC voltage waveform, Figure 3 (b) Output voltage waveform, Figure 3 (c) Output power waveform. The AC voltage fluctuates slightly around 400V, remaining generally stable. The output voltage is maintained at around 46V with small fluctuations, indicating stable voltage output and reflecting the steady-state characteristics of the system in the voltage dimension. The output power is approximately 437.5W.

[0072] The waveforms of the resonant inductor current and magnetizing inductor current in the resonant cavity network unit are shown below, when the topology is powered on with a low voltage of 200V DC input and then boosted to a high voltage of 400V DC input after a period of time. Figure 4 As shown in (a). When the two current waveforms do not coincide, it is the resonance of two components, Lr and Cr; when the two current waveforms coincide, it is the resonance of three components, Lm, Cr, and Lr. Figure 4 (a) Obtained by local magnification Figure 4 (b) and Figure 4 (c) represents the conditions before and after interference, respectively. During input voltage transition, the resonant cavity network unit maintains its resonant state after a period of time. The current fluctuation of the resonant cavity network unit during mode switching is ≤5A, and the output voltage fluctuation is ≤0.5V, with no significant impact. The hybrid modulation method and model exhibit good robustness under interference. The final steady-state output efficiency can reach 94.84%, as shown in Figure 1. Figure 5 As shown.

Claims

1. A hybrid modulation method for GaN-based half-bridge LLC resonant converters suitable for wide input voltage scenarios, characterized in that, Includes the following steps: Step 1: Construct a half-bridge LLC resonant converter topology; The half-bridge LLC resonant converter topology includes input-side units, resonant cavity network units, isolation rectifier network units, and output-side units; Step 2: Design a hybrid modulation control method, adopting a hybrid modulation and unified model control architecture of pulse frequency modulation (PFM) and pulse width modulation (PWM). The modulation mode is adaptively switched according to the output voltage of the half-bridge LLC resonant converter topology to ensure efficient operation across the entire load range. Step 3: Build a simulation model of a half-bridge LLC resonant converter based on MATLAB / Simulink: Set up the driving module according to the hybrid modulation method of the half-bridge LLC resonant converter topology built in Step 1 and the half-bridge LLC resonant converter topology built in Step 2. The driving module includes: setting the mode decision logic, designing the dual-loop feedback control, and setting the limiting protection strategy. Step 4: Test and verify the simulation model of the half-bridge LLC resonant converter: Set two modes with high input voltage of 400V and low input voltage of 200V to verify the hybrid modulation effect.

2. The hybrid modulation method for GaN-based half-bridge LLC resonant converters suitable for wide input voltage scenarios according to claim 1, characterized in that, The specific structure of the half-bridge LLC resonant converter topology is as follows: The input-side unit consists of an input voltage Vin, a voltage divider resistor Rin, a voltage divider capacitor Cin, half-bridge switches S1 and S2; the input voltage Vin and the voltage divider resistor Rin are connected in series and then in parallel with the voltage divider capacitor Cin; both half-bridge switches S1 and S2 are GaN MOSFETs, and fast recovery diodes and buffer capacitors C1 and C2 are connected in reverse parallel across their terminals respectively; the drain of half-bridge switch S1 is connected to the positive terminal of the voltage divider resistor Rin, the source of half-bridge switch S1 is connected to the drain of half-bridge switch S2, and the source of half-bridge switch S2 is connected to the negative terminal of the input voltage Vin; The resonant cavity network unit consists of a resonant inductor Lr, a magnetizing inductor Lm, and a resonant capacitor Cr. One end of the resonant capacitor Cr is connected to the source of the half-bridge switch S1, and the other end is connected to the resonant inductor Lr. One end of the resonant inductor Lr is connected to the resonant capacitor Cr, and the other end is connected to the primary side of the high-frequency transformer T. The magnetizing inductor Lm is connected in parallel with the primary side of the high-frequency transformer T. The isolated rectifier network unit includes a high-frequency transformer T with a turns ratio of 25:6, rectifier bridge diodes D1, D2, D3, and D4. The primary side of the high-frequency transformer T is connected to the resonant inductor Lr and the source of the half-bridge switch S2, respectively. The secondary side of the high-frequency transformer T is connected to the anodes of rectifier bridge diodes D2 and D3, respectively. The anode of rectifier bridge diode D2 is connected to the cathode of rectifier bridge diode D1, the anode of rectifier bridge diode D3 is connected to the cathode of rectifier bridge diode D4, the anodes of rectifier bridge diodes D1 and D4 are connected in parallel, and the cathodes of rectifier bridge diodes D2 and D3 are connected in parallel. The output-side unit includes a filter capacitor Co and a load Ro. One end of the filter capacitor Co is connected to the output terminal of the parallel connection between the anode of rectifier bridge diode D1 and the anode of rectifier bridge diode D4, and the other end is connected to the output terminal of the parallel connection between the cathode of rectifier bridge diode D2 and the cathode of rectifier bridge diode D3. The load Ro is connected in parallel across the filter capacitor Co, and the voltage across the load Ro is the output voltage.

3. The hybrid modulation method for GaN-based half-bridge LLC resonant converters suitable for wide input voltage scenarios according to claim 2, characterized in that, The specific implementation process of step 2 is as follows: Step 2.1: Establish the theoretical foundation: Based on the fundamental frequency analysis method (FHA), the formula for pulse frequency modulation (PFM) is derived to obtain the transfer function of output voltage with respect to switching frequency. ,in It is a DC gain function. It is the output voltage. It is the input voltage; , where n is the turns ratio of the high-frequency transformer, R L The resistance value of the load Ro; Resonant frequency; normalized frequency Switching frequency Resonant frequency When the switching frequency equals the resonant frequency, the inductive reactance and capacitive reactance of the resonant cavity network unit are equal, and it exhibits purely resistive properties externally. As a complex variable, it is represented in the transfer function. The inductance ratio k = Lm / Lr is the ratio of the magnetizing inductance to the resonant inductance. Output filter capacitor The first-order poles introduced determine the output voltage response speed; is the second-order pole of the resonant cavity network unit, which is related to the inductance ratio k; The pole quality factor reflects the peak intensity in the resonant cavity network unit. Based on the fundamental frequency analysis method (FHA), the formula for pulse width modulation (PWM) is derived to obtain the transfer function of output voltage with respect to duty cycle. ; Step 2.2: Based on theoretical foundations, construct a unified model for hybrid modulation of Pulse Frequency Modulation (PFM) and Pulse Width Modulation (PWM), including a comparator, PI controller, PFM / PWM signal generator, and half-bridge LLC resonant converter topology: The comparator inputs are the output voltage Vo and the reference voltage Vref of the half-bridge LLC resonant converter topology, and the output voltage error value e, which are then provided to the PI controller. A PI controller is a type of feedback controller that regulates the system through proportional (P) and integral (I) actions. The proportional action quickly adjusts the output based on the deviation, while the integral action eliminates steady-state error by accumulating the deviation. A PFM / PWM signal generator is used to introduce an intermediate control quantity x, which is the output of the PI controller, to establish the switching frequency f. s The mapping relationship between duty cycle D and intermediate control quantity x; The mode switching threshold is determined by the maximum gain. max With switching point gain shift Calculated , This represents the maximum output value of the PI controller; when x> When in pulse frequency modulation mode, the output switching frequency is... The inverse function of the switching frequency is solved using Newton's iteration method, where... When x≤ At this time, it is in pulse width modulation mode, and the output duty cycle is... , For maximum duty cycle; according to and It can generate drive signals; In a half-bridge LLC resonant converter topology, the gate of the half-bridge switch receives a drive signal, which in turn changes the output voltage, forming a closed-loop feedback control.

4. The hybrid modulation method for GaN-based half-bridge LLC resonant converters suitable for wide input voltage scenarios according to claim 3, characterized in that, The specific implementation process of step 3 is as follows: Step 3.1: Set the mode decision logic: Set the input voltage threshold V DC-th It is 200V, which is 50% of the rated input voltage of 400V, corresponding to the modulation mode switching boundary; When the input voltage V DC >V DC-th At that time, PFM mode is used, by changing the switching frequency. Adjust the output voltage; the switching frequency range is 100kHz-150kHz, fluctuating around the resonant frequency of 100kHz; when the input voltage V... DC ≤V DC-th When switching to pulse width modulation (PWM) mode, the switching frequency is fixed. With a resonant frequency of 100kHz, the output voltage is adjusted by changing the duty cycle D, which ranges from 0.1 to 0.

4. The topology performance of the half-bridge LLC resonant converter under various modulation modes and during modulation mode switching is tested by directly changing the input voltage or the load Ro. Step 3.2: Design a dual-loop feedback control: The outer voltage loop uses a PI controller, with the input being the output voltage error e = V. o-ref - V o , where V o-ref For the output reference voltage, V o The output voltage is the intermediate control quantity x. When the input voltage or the load Ro is changed, the output voltage will also change, thus affecting the output value of the intermediate control quantity x and changing the modulation mode. The inner current loop does not require an additional controller. It directly controls the drive signals of the half-bridge switching transistors S1 and S2 through pulse frequency modulation (PFM) or pulse width modulation (PWM) to ensure the stability of the resonant inductor current. Step 3.3: Set up a restriction protection policy: In the half-bridge LLC resonant converter topology, the half-bridge switching transistors use isolated driver chips with a 50ns dead time to prevent bridge arm shoot-through; simultaneously, overcurrent protection is integrated, detecting the resonant inductor current iLr and shutting off the drive when it exceeds 1.5 times the rated value; and overvoltage protection is integrated, detecting the output voltage V. o Protection is triggered when the voltage exceeds 50V, improving system reliability; When the topology is powered on, a combination strategy of switching frequency ramp-up and duty cycle limitation is adopted: the initial switching frequency is set to 150kHz, which is higher than the resonant frequency, and then reduced to 100kHz at a rate of 5kHz / ms; at the same time, the initial duty cycle is limited to 0.1, and then increased to the target value at a rate of 0.05 / ms to avoid overshoot of the resonant cavity network unit current when powered on, that is, to control the peak value of the resonant cavity network unit current to be ≤ 1.2 times the rated value, and to protect the half-bridge switch, S1 half-bridge switch, S2 and the resonant cavity network unit; When the modulation mode switches, the intermediate control quantity x is pre-adjusted through the outer voltage loop 10ms in advance to stabilize the gain at the switching point. shift The system fluctuates left and right, and during the switching process, the integral element in the PI controller is locked for 5ms to suppress transient voltage / current surges.

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