A partition control method and system suitable for wide operating range LLC resonant converter

Abstract

This invention discloses a zoned control method and system applicable to LLC resonant converters with a wide operating range. The method determines the operating range of the converter by real-time acquisition and analysis of the converter's operating state parameters and adaptively selects a matching control strategy. The operating range includes a loss reduction control state, a steady-state regulation control state, and a voltage equalization enhancement control state. In the loss reduction control state, an intermittent resonant excitation mechanism is introduced to reduce the equivalent switching frequency; in the steady-state regulation control state, continuous modulation is used to achieve stable output voltage regulation; in the voltage equalization enhancement control state, voltage equalization control is superimposed on steady-state regulation. This invention can balance system efficiency, output stability, and operational reliability over a wide load range, and has good engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of frequency conversion control technology for isolated half-bridge three-level LLC converters, specifically relating to a partitioned control method and system suitable for LLC resonant converters with a wide operating range. Background Technology

[0002] Isolated half-bridge three-level converters are widely used in high-power, high-voltage industrial power supply systems due to their lower voltage stress on the switching transistors and good adaptability to high-voltage input conditions. With the increasing demands for energy efficiency, output stability, and long-term reliability in power electronic systems, these converters often need to operate continuously under different operating conditions in practical applications. The energy transfer characteristics and control objectives differ significantly under different operating conditions. Under low-current output conditions, the converter's primary goal is to reduce system losses. If continuous high-frequency modulation is still used, the switching and driving losses generated by the power switching devices and their drive circuits account for a significantly higher proportion of the total losses, leading to a decrease in overall system efficiency. Under high-current output conditions, the DC bus composed of upper and lower voltage divider capacitors in the half-bridge three-level structure is prone to voltage imbalance due to device parameter dispersion and load changes, thereby increasing the voltage stress on the power devices and reducing the safety and reliability of system operation. Existing control methods mostly use a single modulation method or a fixed control structure, making it difficult to adaptively adjust to the control requirements under different operating conditions and to balance multiple control objectives under different output conditions. Based on the above problems, it is necessary to propose a partitioned operation method for isolated half-bridge three-level converters. According to the changes in operating state, it can reasonably switch between loss reduction control mode, steady-state adjustment control mode and equalization enhancement control mode, thereby improving the overall performance of the converter over a wide operating range. Summary of the Invention

[0003] This invention provides a zoned control method applicable to wide-range LLC resonant converters, characterized by: acquiring the converter's operating status information, including output voltage, output current, and voltage divider capacitor voltage; determining the current operating range of the converter based on the operating status information, and selecting a corresponding control mode according to the determination result; the control modes include loss reduction control mode, steady-state regulation control mode, and equalization enhancement control mode; in loss reduction control mode, generating resonant excitation control quantity based on output voltage feedback, and introducing an intermittent excitation mechanism so that the resonant network is excited in part of the cycle and suppressed in the remaining cycle; in steady-state regulation control mode, exiting the intermittent excitation mechanism, and using continuous modulation to adjust the resonant excitation parameters to maintain output voltage stability; in equalization enhancement control mode, based on steady-state regulation control, introducing a voltage equalization regulation mechanism to correct the resonant excitation signal to suppress voltage imbalance between energy storage units.

[0004] Preferably, the determination of the operating range is based on the effective value of the output current, and is determined by comparing it with a preset low current threshold value I. L and high current threshold value I H The comparison is implemented where: when the effective value of the output current is less than or equal to the low current threshold value I L When the converter enters the loss reduction control mode, it is determined that the effective value of the output current is greater than the low current threshold value I. L And less than or equal to the high current threshold value I H When the converter enters steady-state regulation and control mode, it is determined that the effective value of the output current is greater than the high current threshold value I. H When this occurs, it is determined that the converter has entered the equalization enhancement control mode.

[0005] Preferably, for the low current threshold value I L and high current boundary value I H Upper and lower hysteresis thresholds are set separately to form a hysteresis-based operating range determination mechanism. Control mode switching is only triggered when the output current exceeds the corresponding hysteresis threshold range.

[0006] Preferably, when switching between different control modes, a smooth transition strategy of linear weighted fusion is adopted, in which the resonant excitation control quantity in the original control mode and the resonant excitation control quantity in the target control mode are weighted and fused cycle by cycle according to a preset number of transition cycles.

[0007] Preferably, in the initial stage of the transition, the controller adopts the resonant excitation control quantity corresponding to the original control mode; as the transition period progresses, the proportion of the resonant excitation control quantity corresponding to the target control mode in the fusion result is gradually increased, and the weight of the original control mode control quantity is reduced accordingly; at the end of the transition period, the fusion result is entirely composed of the resonant excitation control quantity of the target control mode.

[0008] Preferably, in the loss reduction control mode, the intermittent excitation mechanism sets a partition enable period parameter M, so that the resonant network is excited only in a portion of the M periods.

[0009] Preferably, in the steady-state regulation control mode, the resonant converter adopts a frequency conversion control method with a fixed duty cycle, and the output voltage is regulated by continuously adjusting the resonant excitation frequency.

[0010] Preferably, in the balanced enhancement control mode, a voltage equalization control strategy and a frequency micro-bias equalization strategy are introduced into the resonant excitation parameters of the upper and lower half cycles to achieve dynamic adjustment of the voltage deviation of the voltage divider capacitor.

[0011] A zone control system for an isolated half-bridge three-level LLC resonant converter with a wide operating range, used to implement the aforementioned zone control method, is characterized by comprising: an information acquisition module for acquiring the converter's operating status information; a zone determination module for determining the operating zone of the converter based on the operating status information; and a resonant control module for executing a corresponding control strategy according to the operating zone, wherein: in loss reduction control mode, intermittent resonant excitation control is introduced; in steady-state regulation control mode, continuous modulation control is adopted; and in equalization enhancement control mode, voltage equalization control is superimposed on steady-state regulation.

[0012] Compared with the prior art, the LLC resonant converter partition control method and system proposed in this invention, applicable to a wide operating range, has at least the following beneficial effects: By dividing the operating states into loss reduction control mode, steady-state regulation control mode, and equalization enhancement control mode, the LLC resonant converter can adaptively adjust the control strategy according to changes in power demand, emphasizing efficiency optimization, steady-state performance, and operational reliability in different operating ranges. Under low-power operating conditions, intermittent excitation significantly reduces system losses; under medium-power operating conditions, continuous modulation ensures output stability; and under high-power operating conditions, equalization enhancement control effectively suppresses voltage deviation. This method achieves smooth switching between multiple operating ranges by introducing a hysteresis load range determination mechanism, avoiding voltage fluctuations and system oscillations caused by mode switching, and has good engineering applicability and promotion value. Attached Figure Description

[0013] Figure 1 This is a flowchart of a partitioned control method for LLC resonant converters with a wide operating range, according to the present invention.

[0014] Figure 2 This is a circuit diagram of the half-bridge three-level isolated converter of the present invention.

[0015] Figure 3 This is a schematic diagram of the basic modulation unit control logic in an embodiment of the present invention.

[0016] Figure 4 This is a control block diagram of the loss reduction control state in an embodiment of the present invention.

[0017] Figure 5 This is a control block diagram of the steady-state adjustment and control state according to an embodiment of the present invention.

[0018] Figure 6 This is a control block diagram of the equalization enhancement control state in an embodiment of the present invention.

[0019] Figure 7 This is a schematic diagram of the simulated waveform with a reference voltage of 48V and an output current of 2A under the loss reduction control state of this embodiment of the invention.

[0020] Figure 8 This is a schematic diagram of the simulated waveform of a reference voltage of 48V and an output current of 10A under steady-state regulation control conditions according to an embodiment of the present invention.

[0021] Figure 9 This is a simulation diagram of the voltage divider capacitor of the converter without using a zone control method under full load operation, according to an embodiment of the present invention.

[0022] Figure 10 This is a simulation diagram of the voltage divider capacitor of the converter using the partition control method under full-load operation according to an embodiment of the present invention.

[0023] Figure 11 This is a schematic diagram of the simulated waveform when switching between different working intervals according to an embodiment of the present invention. Detailed Implementation

[0024] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the linguistic context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0025] Example 1: As Figure 1 The diagram shows a flowchart of a zoned control method for an isolated half-bridge three-level LLC resonant converter with a wide load range. The control method includes: real-time acquisition and analysis of the converter's output state parameters; determination of the converter's current operating state based on these parameters; and selection of a control strategy matching this operating state to achieve adaptive adjustment of the converter under different operating requirements. The operating states include at least a loss reduction control state, a steady-state adjustment control state, and a balance enhancement control state.

[0026] When the converter is in a loss reduction control state with the main goal of reducing system losses, the control system calculates the frequency control quantity for adjusting the output voltage based on the output voltage feedback signal using a PI control algorithm. On this basis, an intermittent modulation mechanism combining periodic enable and disable is introduced. By setting a predetermined intermittent control period parameter, an equivalent power modulation effect is formed.

[0027] When the converter operates in a steady-state regulation control state with the primary objective of output stability adjustment, the control system stops the intermittent modulation mode and switches to continuous modulation operation mode.

[0028] When the converter enters the balanced enhancement control state with the main goal of enhancing operational reliability, the control system further introduces a voltage balance regulation mechanism for the voltage divider capacitors based on the steady-state regulation control strategy.

[0029] Specifically, the control method may include the following steps.

[0030] Step S1: Acquire output status information. The control system obtains the converter's output status parameters, including output voltage, output current, and voltage divider capacitor voltage, through the information acquisition module for subsequent mode determination and control calculations.

[0031] Step S2: Determine the current operating mode. Based on the output status information collected in step S1, the control system determines the current load condition of the converter and selects the corresponding control mode accordingly. The control modes include: loss reduction control mode, steady-state adjustment control mode, and equalization enhancement control mode.

[0032] Step S3: Determine whether the output current exceeds the upper hysteresis threshold I of the low current threshold. Lhigh If yes, proceed to the next step; otherwise, determine whether the output current is lower than the lower hysteresis threshold I of the low current threshold. Llow If yes, then the current mode is determined to be loss reduction control mode; otherwise, a switch is triggered, and a linear weighted smooth frequency transition is adopted. In loss reduction control mode, the intermittent excitation mechanism reduces the equivalent switching frequency by setting the partition enable period parameter M, so that the resonant network is only excited in a portion of the M periods.

[0033] Step S4: Determine whether the output current exceeds the upper hysteresis threshold I of the high current threshold. Hhigh If yes, proceed to the next step; if no, determine whether the output current is lower than the lower hysteresis threshold I of the high current threshold. Hlow If yes, the current mode is determined to be steady-state regulation control; otherwise, a switching is triggered, and the frequency is continuously adjusted linearly. In steady-state regulation control mode, the resonant converter adopts a frequency conversion control method with a fixed duty cycle, and the output voltage is regulated by continuously adjusting the resonant excitation frequency.

[0034] Step S5: Determine that the current mode is equalization enhancement control mode. In equalization enhancement control mode, a small difference is introduced in the resonant excitation parameters of the upper and lower half cycles to achieve dynamic adjustment of the voltage deviation of the voltage divider capacitor.

[0035] When the converter is in loss reduction control mode, the control system aims to reduce losses under light-power operating conditions. Based on the deviation between the output voltage and the reference voltage, the controller calculates the frequency value used to maintain the target output voltage using a PI control algorithm and limits this control quantity to meet the safe operation requirements of the resonant converter. Furthermore, an intermittent excitation control strategy is introduced. By setting a partitioned enable period parameter M, the resonant network is excited only during certain periods, remaining suppressed during the remaining periods. This reduces the equivalent switching frequency and decreases switching and drive losses.

[0036] When the converter operates in steady-state regulation control mode, the control system exits the intermittent excitation mode and adopts a continuous modulation strategy to control the LLC resonant converter. The controller uses the output voltage feedback signal, the difference between the output voltage and the reference voltage, as the input value of the PI control algorithm, calculates the modulation control quantity in real time, and limits it within a preset range. By continuously adjusting the equivalent excitation parameters of the resonant network, smooth control of the resonant energy transfer process is achieved, thereby ensuring the steady-state accuracy and dynamic response performance of the output voltage under medium power operation conditions.

[0037] When the converter enters the equalization enhancement control mode, a voltage equalization regulation mechanism for the DC bus or key energy storage units is further introduced on the basis of steady-state regulation control. The control system acquires relevant voltage signals in real time, calculates the voltage difference between each energy storage unit, and generates corresponding equalization regulation quantities through a PI control algorithm. The equalization regulation quantities are superimposed with the original modulation control quantities to correct the resonant excitation signal, thereby achieving dynamic suppression of voltage deviation and improving the safety and reliability of the LLC resonant converter under high-power operating conditions.

[0038] This embodiment divides the operating state into a loss reduction control mode, a steady-state regulation control mode, and a balanced enhancement control mode, enabling the LLC resonant converter to adaptively adjust its control strategy according to changes in power demand. In different operating ranges, it emphasizes efficiency optimization, steady-state performance, and operational reliability respectively. Under low-power operating conditions, intermittent excitation significantly reduces system losses; under medium-power operating conditions, continuous modulation ensures output stability; and under high-power operating conditions, balanced enhancement control effectively suppresses voltage deviation. This method achieves smooth switching between multiple operating ranges by introducing a hysteresis load range determination mechanism, avoiding voltage fluctuations and system oscillations caused by mode switching, and has good engineering applicability and promotional value.

[0039] Example 2: This example should be understood as including at least all the features of any of the foregoing examples, and further improving upon them; To achieve smooth switching between different control modes, this embodiment introduces a load range determination mechanism with hysteresis in the zoned control method. Specifically, the control system collects the converter output current in real time and compares it with two preset current boundary values ​​I. L with I H A comparison is made. To avoid frequent mode switching caused by output current fluctuations near the threshold, upper and lower hysteresis ranges are set for each threshold: two upper and lower hysteresis thresholds I are set for the low current threshold. Llow with I Lhigh Two upper and lower hysteresis thresholds I are set for the high current threshold. Hlow with I HhighThe mode switch is triggered only when the output current exceeds the upper limit or falls below the lower limit, while the current mode continues to operate during the transition phase.

[0040] During mode switching, the controller employs a linear weighted fusion strategy to achieve a smooth transition of the modulation amount. That is, in N... trans Within each switching cycle, the control frequency or duty cycle f of the original mode will be... orig Control frequency or duty cycle f of the target mode target Continuous fusion as follows: Among them, f s (k) is the switching frequency of the kth transition cycle, N trans This represents the number of smooth switching cycles, and its value is determined based on the converter's resonant circuit bandwidth, output filtering capability, and allowable output transient deviation. If N trans If N is too small, the switching frequency changes too quickly during mode switching, and the resonant circuit and output filter respond insufficiently, which may lead to output voltage oscillation or resonant current fluctuation; if N trans If the value is too large, the mode switching response will be sluggish, and the advantages of multi-mode control cannot be fully utilized. Taking into account the resonant circuit time constant, output filtering characteristics, and controller sampling period, this embodiment selects N. trans =10 switching cycles, ensuring smooth and continuous mode switching while avoiding abrupt changes in output voltage and resonant current, thus improving the operational safety of power devices and system reliability. In each transition cycle, the controller, based on f trans (k) Update the drive signal of the power switch, and inherit or maintain the integral of the PI regulator and the voltage equalization calculation state of the capacitor, thereby ensuring continuous change of the modulation signal and avoiding step changes in the switching frequency. Through the smooth switching mechanism of hysteresis judgment and linear weighted fusion, the converter can achieve smooth switching between loss reduction control mode, steady-state regulation control mode and equalization enhancement control mode over a wide load range, effectively improving the output voltage stability, dynamic performance and overall system reliability, while avoiding transient output voltage impact and sudden increase in power switch stress caused by mode switching.

[0041] This embodiment uses the above-described cycle-by-cycle weight adjustment method to make the resonant excitation parameters change continuously during mode switching, thereby avoiding sudden changes in the resonant excitation frequency or modulation parameters and ensuring the stability and control continuity of the converter operation.

[0042] The upper hysteresis threshold I at low current threshold Lhigh The lower hysteresis threshold I at low current threshold Llow The upper hysteresis threshold I of the high current threshold Hhigh and the lower hysteresis threshold I of the high current threshold Hlow Determined based on rated output current.

[0043] Low current threshold I L To differentiate between loss reduction control mode and steady-state regulation control mode, its design should ensure that intermittent modulation control can effectively reduce switching losses and improve light-load efficiency under low-load conditions, while avoiding frequent switching within the normal low-power continuous operation range, thus guaranteeing output voltage stability. Taking into account output power level, device on-resistance, and output filtering capability, I... L The value is set to 10% to 15% of the rated output current; in this embodiment, I is taken as... L =3A, to balance efficiency and steady-state performance. Based on this, to achieve smooth mode switching, upper and lower hysteresis ranges are set for each threshold current: the upper and lower hysteresis thresholds for the low current threshold are I... Llow =0.9×I L I Lhigh =1.1×I L High current threshold value I H To distinguish between steady-state regulation control mode and equalization enhancement control mode, its design must consider the possibility of significant voltage imbalance in the voltage divider capacitor under high-power operation, ensuring that equalization control can intervene in a timely manner. If I H If the setting is too low, the control system may prematurely activate complex voltage equalization regulation under medium load, increasing the control load; if I H Setting it too high may delay the intervention of voltage equalization control, affecting the safety of power devices. H Set to 45% to 55% of the rated output current; in this embodiment, I is taken as... H =13A, ensuring the heavy-load control strategy can start promptly in the high-power range. The upper and lower hysteresis thresholds for the high current boundary are set to I. Hlow =0.9×I H I Hhigh =1.1×I H This embodiment, through the hysteresis interval design, can effectively suppress frequent jitter of the load near the threshold and achieve smooth switching of control modes.

[0044] Figure 2This is a circuit diagram of the half-bridge three-level isolated converter described in this invention. The converter includes a DC bus at the input end, with an upper voltage divider capacitor C1 and a lower voltage divider capacitor C2 connected in series at both ends of the bus to provide a three-level DC voltage and achieve capacitor voltage equalization. The power conversion unit consists of four power switching devices S1, S2, S3, and S4 arranged sequentially from top to bottom, where S1 and S2 form the upper bridge arm, and S3 and S4 form the lower bridge arm. The switching devices are connected to the DC bus voltage divider capacitors through a common node to achieve switching control of the three-level output between the upper and lower bridge arms. The output end of the power conversion unit is connected to the primary winding of a high-frequency isolation transformer and forms an LLC resonant converter through a series resonant network. Through the electromagnetic isolation of the transformer and the LLC resonant characteristics, the DC power at the input end is efficiently transferred to the secondary side. During the operation of the converter, the switching frequency can be adjusted to make the converter L m The transformer maintains zero-voltage or zero-current switching characteristics over a wide load range, thereby reducing switching losses. A rectifier diode bridge and filter capacitor are installed on the secondary side of the transformer to convert high-frequency AC power into a stable DC output for the load, while ensuring that the output voltage ripple and dynamic response meet system requirements. The power switching devices S1 to S4 can be power MOSFETs or IGBTs, selected according to the converter's rated power and operating frequency, and used in conjunction with the gate drive circuit to achieve fast switching and precise duty cycle control. Where V... s For DC power supply, P is the anode of DC power supply, N is the cathode of DC power supply, and u c1 The voltage across capacitor C1, u c2 The voltage across capacitor C2 is C. coss1 C is a capacitor connected in parallel with S1. coss2 For the capacitor connected in parallel with S2, C coss3 D is a capacitor connected in parallel with S3. s1 D s2 D s3 D s4 D1, D2, D3, and D4 are all diodes, and C r C f Both are capacitors, R o For resistance, i o For the output current, u o This is the output voltage.

[0045] Figure 3This is a schematic diagram of the control logic of the basic modulation unit described in this invention. The half-bridge three-level LLC converter uses the same basic modulation unit logic in all three operating modes. During each switching cycle, the upper bridge arm switches S1 and S2, and the lower bridge arm switches S3 and S4, conduct for half a switching cycle T / 2, forming an alternating three-level output. Specifically, switches S2 and S1 conduct complementaryly, and switches S4 and S3 conduct complementaryly, while the conduction of switch S3 lags behind S1 by half a cycle to ensure the symmetry of the output waveform. Under this control logic, the duty cycle D is fixed at 0.5, and the output voltage is adjusted by regulating the switching frequency to adapt to the voltage requirements of different load conditions. Simultaneously, this basic modulation unit can be used in conjunction with higher-level strategies such as intermittent control, continuous PWM control, or capacitor voltage equalization control to achieve precise control of loss reduction, steady-state regulation, and balanced enhancement modes, thereby optimizing system efficiency and dynamic performance while ensuring stable output voltage.

[0046] Figure 4 The control block diagram under loss reduction control is shown. Under low current conditions, this invention introduces an intermittent control strategy based on the basic modulation unit logic to significantly optimize the converter's light-load efficiency. The control system first adjusts the output voltage V... o Perform real-time sampling and compare with reference voltage V ref A voltage error signal is generated through comparison. This error signal is input to the PI controller, which calculates the operating frequency based on the error and adjusts the output voltage during the energy transfer phase of the converter using a fixed duty cycle. This stabilizes the output voltage near the reference value, ensuring steady-state control accuracy. The calculation expression for the PI controller under the above control process is as follows.

[0047] First, define the output voltage error as: The switching frequency command output by the PI controller is: Where f0 is the base operating frequency set in the loss reduction control mode, which is set to 40kHz in this embodiment, and k p1 k is the proportionality coefficient. i1 is the integral coefficient.

[0048] The intermittent control module periodically enables and disables the basic modulation unit according to a set number of cycles M. Within a continuous M switching cycle, only the first M cycles are enabled. on The basic modulation unit is enabled in one cycle, transferring energy to the load according to the dynamic duty cycle; in the remaining M... off =M−M onDuring each cycle, the drive signal output is disabled, keeping the power switch in a zero-level clamped state, thereby blocking energy transfer and reducing the equivalent switching frequency. Through this intermittent operating mode, the converter's equivalent switching frequency is significantly reduced, effectively lowering the switching and drive losses of the power devices.

[0049] Specifically, the number of intermittent control cycles M is dynamically adjusted according to the output current, and is related to the low current threshold I. L Correspondingly, when the output current is close to zero load, a larger value of M is chosen to minimize the equivalent switching frequency; as the output current gradually approaches I... L By gradually decreasing M, a balance is achieved between output voltage ripple and system stability, and a smooth transition from light load to medium load mode is facilitated. The maximum number of intermittent control cycles, M, is... max Due to constraints related to output voltage ripple, the reduction effect of the equivalent switching frequency, and system stability: if M is too large, the output capacitor discharge time will be prolonged during the disabled phase, potentially leading to increased voltage ripple and decreased voltage loop stability; if M is too small, the reduction effect of the equivalent switching frequency will be limited, and the energy-saving effect under light load will be insignificant. Based on simulation analysis of the converter's rated output current of 25A and filter parameters, this embodiment will adjust M... max The value was initially set between 20 and 30, but was ultimately set to 25. Minimum number of intermittent control cycles, M. min This is used to ensure effective differentiation between intermittent control and continuous PWM control, and to support a smooth transition from light load to medium load mode. A value that is too small will weaken the intermittent power supply characteristics and reduce control variability. In this embodiment, M... min The value was set in the range of 3 to 5, and finally set to 4, in order to improve the efficiency under light load while ensuring the stability of the output voltage.

[0050] Under loss reduction control, the number of intermittent cycles M and the output current I o The relationship can be represented as: Where I min The minimum effective output current near no-load is set to 0.5A to avoid numerical jitter. ⌊⌋ indicates rounding down to ensure that the number of intermittent cycles is an integer.

[0051] Figure 5 This is the control block diagram under steady-state regulation control. When the converter is in steady-state regulation mode, the control system exits the intermittent control mode under loss reduction control and switches to a continuous frequency modulation control mode with a fixed duty cycle. In this mode, the controller collects the output voltage V in real time. o and with reference voltage V refA comparison is made to generate a voltage error signal. This error signal is input to a PI controller, which analyzes the error amplitude and its trend to output a control quantity for frequency regulation, thereby maintaining the converter's output voltage stability under a fixed duty cycle. The calculation expression for the PI controller under the above control process is as follows.

[0052] First, define the output voltage error as: The switching frequency command output by the PI controller is: Where f1 is the initial switching frequency of the steady-state regulation mode, and k p2 k is the proportionality coefficient. i2 is the integral coefficient.

[0053] In terms of control logic, switches S1 and S4 are simultaneously turned on, while the lower bridge arm power switches S2 and S3 are turned on during another time period. The turn-on phase of S3 lags behind S1 by half a switching cycle, thus forming a symmetrical three-level high-frequency voltage waveform on the primary side of the transformer. By adjusting the switching frequency to control the effective voltage amplitude on the primary side, continuous regulation of the energy transfer of the isolation transformer is achieved, thereby ensuring the steady-state performance of the output voltage and the high efficiency of system operation under steady-state regulation control.

[0054] Figure 6 The control block diagram for the balanced enhancement control state is shown below. Under the premise of maintaining synchronous conduction of upper bridge arm switches S1 and S4, and synchronous conduction of lower bridge arm switches S2 and S3, with each switch conducting for half a cycle in each switching cycle, a voltage balancing control strategy is introduced to dynamically adjust the voltage balance of voltage divider capacitors C1 and C2. The control system acquires the voltage signals of C1 and C2 in real time and calculates the voltage deviation ΔV = V. c1 -V c2 Among them, V c1 V is the voltage across the voltage divider capacitor at the input terminal. c2 The voltage across the input voltage divider capacitor is used. This deviation signal is input to the PI controller to obtain the voltage equalization adjustment Δf, which is used to fine-tune the equivalent operating frequency of the switching in the first and second half-cycles. Under the above control process, the output error of the PI controller is: The switching frequency command output by the PI controller is: Where, k pd k is the proportionality coefficient. id Let be the integral coefficient, and t be the current time, a continuously advancing time variable. The integral calculates the error e from the beginning to the current time t. vThe sum of the history of (τ).

[0055] Specifically, when ΔV > 0, the controller slightly decreases the equivalent frequency of the half-cycle of switches S1 and S4 while increasing the equivalent frequency of the half-cycle of switches S2 and S3; when ΔV < 0, the controller slightly increases the equivalent frequency of the half-cycle of switches S1 and S4 while decreasing the equivalent frequency of the half-cycle of switches S2 and S3. This slight frequency shift between the upper and lower half-cycles allows the high-voltage capacitor to release some energy to the low-voltage capacitor, gradually eliminating the voltage imbalance. Simultaneously with this slight frequency shift, the controller also samples the output voltage V. o and with reference voltage V ref The difference is calculated and input to the PI controller. The PI controller then generates the output frequency control value to maintain the stability of the converter's output voltage. The output voltage error is first defined as: The formula for calculating the switching frequency output of the PI controller is: Where f2 is the initial switching frequency of the equalization enhancement control mode, and k p3 k is the proportionality coefficient. i3 is the integral coefficient.

[0056] The control frequency in this mode is f. s (t)±Δf. By continuously calculating ΔV in real time and updating the upper and lower half-cycle frequencies, the output voltage is stabilized while effectively suppressing the voltage deviation of the three-level DC bus voltage divider capacitors, improving the reliability and safety of the system under heavy load conditions. To avoid introducing high-frequency harmonics or interference through slight frequency deviation, the deviation Δf should be limited to a safe range. Based on the load size and dynamic characteristics of the output filter, the frequency deviation Δf is generally set to no more than ±1% to ±3% of the rated switching frequency. This control strategy, combined with basic fixed duty cycle logic, achieves high-precision stability of the output voltage and dynamic balancing of the voltage divider capacitors in the balanced enhancement mode.

[0057] Figure 7 The simulation waveforms are shown under the conditions of loss reduction control mode, reference voltage 48V, and output current 2A. Under loss reduction control, the drive signals of power switches S1 and S2 exhibit typical intermittent mode control characteristics. This strategy significantly reduces the average switching frequency by dynamically skipping some switching cycles and transferring energy only when necessary. Correspondingly, the output voltage V... o During the energy transfer phase, the current rises rapidly to the reference value, and then slowly decays during the holding phase, but its fluctuations are always limited within the preset ripple band. Output current I oThe output remained stable at 2A with minimal ripple, indicating that the intermittent control strategy effectively ensured output quality under light loads while achieving high efficiency and energy saving.

[0058] Figure 8 This presents simulation results for steady-state regulation control mode under a 48V reference voltage and a 10A output current. In this mode, the converter operates in conventional continuous PWM modulation, and all switches run continuously according to the basic control logic. Output voltage V o Its regulation characteristics are smooth, and it can closely follow the reference value. Output current I o It also presents as a continuous and smooth waveform, and its average value precisely matches the set load point, which fully demonstrates that the control mode has efficient and stable power transmission capability under steady-state regulation control conditions.

[0059] Figure 9 The capacitor voltage before adding voltage equalization control. Figure 10 The capacitor voltage after adding voltage equalization control. Figure 9 and Figure 10 Simulated waveforms of the balanced enhancement control mode under full load (48V / 25A) conditions are presented. While maintaining fixed duty cycle PWM modulation, the converter introduces active voltage equalization control targeting the DC bus capacitors. This mechanism dynamically fine-tunes the voltages of voltage divider capacitors C1 and C2 by injecting a slight asymmetry into the drive signals of the upper and lower bridge arms, thereby suppressing their natural deviation. Simulations show that the voltage ripple of the voltage divider capacitors is reduced. This verifies that the proposed voltage equalization strategy can effectively improve the reliability and robustness of the system during high-power operation.

[0060] Figure 11 The diagram shows the waveforms of the control circuit automatically switching between loss reduction control, steady-state regulation control, and equalization enhancement control states according to load changes. It is evident that, through the modal determination and smooth switching logic designed in this invention, the output voltage does not exhibit significant abrupt changes at the switching point, and the output current can also quickly track changes in its command value. This effectively solves the output oscillation or instability problems that may occur in traditional converters when operating conditions change abruptly.

[0061] This embodiment uses a low current boundary value I. L and high current boundary value I H Each was configured with a hysteresis interval (I) Llow / I Lhigh and I Hlow / I Hhigh The determination threshold is determined by combining the output current with I. L I HBased on the relative relationships, a load range determination mechanism with hysteresis was constructed. This design effectively suppresses the frequent switching of control modes caused by fluctuations in output current near the set threshold value. Mode switching is only triggered when the current continuously exceeds the corresponding hysteresis threshold range. Simultaneously, this method introduces a linearly weighted fusion smooth transition strategy during mode switching, enabling the resonant excitation frequency control quantity within the switching cycle to continuously and smoothly transition from the original mode value to the target mode value. The combination of these two mechanisms ensures smooth and disturbance-free switching between the three states of loss reduction control mode, steady-state regulation control mode, and balanced enhancement control mode across a wide load range. This fundamentally avoids output voltage surges, system oscillations, or sudden stress increases in power switching devices caused by abrupt mode changes, thereby significantly improving the system's operational stability, dynamic performance, and overall reliability.

[0062] Example 3: This example should be understood as including at least all the features of any of the foregoing examples, and further improving upon them; A zone control system for an isolated half-bridge three-level LLC resonant converter with a wide operating range is provided for implementing the aforementioned zone control method. The control system includes: an information acquisition module for acquiring the operating status information of the LLC resonant converter, including output voltage, output current, and voltage divider capacitor information; a zone determination module for determining the current operating range of the converter based on the operating status information, and accordingly determining whether the converter is in a loss reduction control mode, a steady-state regulation control mode, or a balanced enhancement control mode; and a resonant control module for executing the corresponding control strategy according to the zone determination result. Specifically: in the loss reduction control mode, intermittent resonant excitation control is introduced to reduce the equivalent switching frequency; in the steady-state regulation control mode, continuous modulation is used to regulate the resonant energy; and in the balanced enhancement control mode, voltage equalization control is superimposed on steady-state regulation to achieve stable control under high-power operation.

[0063] The control system acquires real-time operating status information of the isolated half-bridge three-level LLC converter, including output current, output voltage, and voltage divider capacitor voltage, reflecting the current energy transfer status and load changes. Based on this operating status information, the effective value of the output current is extracted and compared with a pre-set low current threshold value I. L and high current threshold value I H A comparison is made, where the low current threshold value characterizes the boundary between the low-power and medium-power operating ranges, and the high current threshold value characterizes the boundary between the medium-power and high-power operating ranges. Specifically, this includes: when the effective value of the output current is less than or equal to the low current threshold value I... LWhen the effective value of the output current is greater than the low current threshold value I, the converter is determined to enter the loss reduction control mode; L And not exceeding the high current threshold value I H When the effective value of the output current is greater than the high current threshold value I, the converter is determined to enter the steady-state regulation and control mode; H When this occurs, it is determined that the converter has entered the equalization enhancement control mode.

[0064] This embodiment describes a complete control system corresponding to the zone control method. Through the division of labor and cooperation between the information acquisition module, the zone determination module, and the resonant control module, this system can perceive the real-time operating status of the converter (output voltage, current, voltage divider capacitor voltage) and accurately determine the current operating zone accordingly (e.g., by comparing the effective value of the output current with a preset I). L I H (Threshold comparison). Based on the judgment result, the system can automatically and adaptively select and switch between three core control strategies: intermittent resonant excitation control, continuous modulation control, and enhanced control with superimposed voltage equalization. This hardware and software integrated system realizes closed-loop intelligent management of the half-bridge three-level LLC resonant converter over a wide operating range, enabling it to automatically adjust the control focus according to changes in actual power demand. This optimizes efficiency at low power, ensures steady-state performance at medium power, and enhances operational reliability at high power, ultimately achieving comprehensive optimization of efficiency, stability, and safety at the system level.

Claims

1. A partitioned control method applicable to wide-range LLC resonant converters, characterized in that: The converter's operating status information is collected, including output voltage, output current, and voltage divider capacitor voltage. Based on the operating status information, the current operating range of the converter is determined, and the corresponding control mode is selected according to the determination result. The control modes include loss reduction control mode, steady-state adjustment control mode and equalization enhancement control mode. In the loss reduction control mode, the resonant excitation control quantity is generated based on the output voltage feedback, and an intermittent excitation mechanism is introduced so that the resonant network is excited in part of the cycle and suppressed in the rest of the cycle. In steady-state regulation control mode, the intermittent excitation mechanism is exited, and continuous modulation is used to adjust the resonant excitation parameters to maintain stable output voltage; In the balanced enhancement control mode, a voltage equalization regulation mechanism is introduced on the basis of steady-state regulation control to correct the resonant excitation signal in order to suppress the voltage imbalance between energy storage units.

2. The partition control method according to claim 1, characterized in that: The determination of the operating range is based on the effective value of the output current, and is determined by comparing it with a preset low current threshold value I. L and high current threshold value I H The comparison is implemented where: when the effective value of the output current is less than or equal to the low current threshold value I L When the effective value of the output current is greater than the low current threshold value I, the converter is determined to enter the loss reduction control mode; when the effective value of the output current is greater than the low current threshold value I. L And less than or equal to the high current threshold value I H When the converter enters steady-state regulation and control mode, it is determined that the effective value of the output current is greater than the high current threshold value I. H When this occurs, it is determined that the converter has entered the equalization enhancement control mode.

3. The partition control method according to claim 2, characterized in that: Regarding the low current threshold value I L and high current boundary value I H Upper and lower hysteresis thresholds are set separately to form a hysteresis-based operating range determination mechanism. Control mode switching is only triggered when the output current exceeds the corresponding hysteresis threshold range.

4. The partition control method according to any one of claims 1 to 3, characterized in that: When switching between different control modes, a smooth transition strategy of linear weighted fusion is adopted, which weights and fuses the resonant excitation control quantity in the original control mode with the resonant excitation control quantity in the target control mode according to the preset number of transition cycles.

5. The partition control method according to claim 4, characterized in that: In the initial stage of the transition, the controller adopts the resonant excitation control quantity corresponding to the original control mode; as the transition period progresses, the proportion of the resonant excitation control quantity corresponding to the target control mode in the fusion result is gradually increased, and the weight of the original control mode control quantity is reduced accordingly; at the end of the transition period, the fusion result is entirely composed of the resonant excitation control quantity of the target control mode.

6. The partition control method according to claim 1, characterized in that: In the loss reduction control mode, the intermittent excitation mechanism sets a partition enable period parameter M, so that the resonant network is excited only in a portion of the M periods.

7. The partition control method according to claim 1, characterized in that: In the steady-state regulation control mode, the resonant converter adopts a frequency conversion control method with a fixed duty cycle, and the output voltage is regulated by continuously adjusting the resonant excitation frequency.

8. The partition control method according to claim 1, characterized in that: In the aforementioned balanced enhancement control mode, a voltage equalization control strategy and a frequency micro-bias equalization strategy are introduced into the resonant excitation parameters of the upper and lower half cycles to achieve dynamic adjustment of the voltage deviation of the voltage divider capacitor.

9. A partitioned control system suitable for a wide operating range isolated half-bridge three-level LLC resonant converter, used to implement the partitioned control method according to any one of claims 1 to 8, characterized in that, include: The information acquisition module is used to collect the converter's operating status information; The partition determination module is used to determine the operating interval of the converter based on the operating status information. The resonant control module is used to execute corresponding control strategies according to the operating range, wherein: in the loss reduction control mode, intermittent resonant excitation control is introduced; in the steady-state adjustment control mode, continuous modulation control is adopted; In the balanced enhancement control mode, voltage equalization control is superimposed on steady-state regulation.

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