Three-phase LLC device loop control method applied to data center high-voltage direct-current system and three-phase LLC device

Abstract

The invention provides a three-phase LLC device loop control method applied to a data center high-voltage direct-current system and a three-phase LLC device, the method is applied to the three-phase LLC device and used for conversion from three-phase alternating current to isolated high-voltage direct current in the data center high-voltage direct-current system, and the method comprises the following steps: collecting an output voltage signal and an output current signal of the three-phase LLC device; inputting the output voltage signal and the output current signal into a PID (Proportion Integration Differentiation) control unit, and calculating the current output gain Gv of the device by the PID control unit; the current output gain Gv is input into a Gv gain look-up table unit, and the Gv gain look-up table unit is matched with a corresponding control stage and outputs a corresponding control parameter; and the PWM generation unit generates a PWM driving signal according to the control parameters, and controls the switching tubes of the three groups of bridge arms to be switched on or switched off. By adopting the scheme, the adaptability of the three-phase LLC device to the dynamic change of the data center load can be improved, and the stability and the control precision of the output voltage are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric power, in particular to a three-phase LLC device loop control method applied to a data center high-voltage direct-current system and a three-phase LLC device. BACKGROUND

[0002] A data center high-voltage direct-current power supply system needs to convert three-phase alternating current on a power grid side into isolated high-voltage direct current to meet the demand of core devices such as servers for stable power. A three-phase LLC resonant converter has the characteristics of high conversion efficiency and high power density, and becomes the core device in the conversion process. The performance of the loop control technology thereof is directly related to the reliability of the power supply system.

[0003] In the loop control of an existing three-phase LLC device, the impedance characteristics of a resonant cavity are usually changed by continuously adjusting the operating frequency, and then the output gain of the device is adjusted to match the demand of a load for an output voltage. This control logic has been applied in some scenarios where the load fluctuation is small.

[0004] However, practice shows that this loop control technology based on single frequency regulation has obvious defects: poor load adaptability, and difficulty in adapting to the scenario of dynamic fluctuation of a data center load. The load of a server in a data center often changes with the demand for computing power, and the light load and full load states are frequently switched. However, the gain adjustment range of single frequency regulation is limited: when the load is light, the gain is excessive due to the excessively high frequency, which causes the output voltage to overshoot; when the load is full, the gain is insufficient due to the excessively low frequency, which cannot meet the requirement of the rated output voltage; and when the load is switched, the sharp adjustment of the frequency also easily causes the output voltage to fluctuate, which affects the stable operation of the backend server. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a three-phase LLC device loop control method applied to a data center high-voltage direct-current system and a three-phase LLC device, which effectively improves the adaptability of the three-phase LLC device to the dynamic change of the data center load, widens the gain adjustment range, improves the stability and control accuracy of the output voltage, and provides strong support for the reliable operation of the data center high-voltage direct-current power supply system.

[0006] In a first aspect, an embodiment of the present application provides a three-phase LLC device loop control method applied to a data center high-voltage direct-current system, which is applied to a three-phase LLC device; is used for the conversion of three-phase alternating current into isolated high-voltage direct current in a data center high-voltage direct-current system; and includes the following steps: S1: collecting an output voltage signal and an output current signal of the three-phase LLC device; S2: input the output voltage signal and the output current signal into the PID control unit, and calculate the current output gain Gv by the PID control unit; S3: input the current output gain Gv into the Gv gain lookup table unit, match the corresponding control stage by the Gv gain lookup table unit, and output the corresponding control parameter; S4: generate the PWM driving signal according to the control parameter by the PWM generation unit, and control the switch tubes of the three groups of bridge arms to be turned on or turned off.

[0007] Optionally, in step S2, the PID control unit calculates the output gain Gv in the following manner: The first adjustment amount is calculated by comparing the output voltage value of the acquisition device with the output voltage instruction value; The second adjustment amount is calculated by comparing the output current value of the acquisition device with the maximum allowed output current value; The smaller one of the first adjustment amount and the second adjustment amount is taken as the output gain Gv.

[0008] Optionally, when the Gv gain lookup table unit matches to the frequency modulation stage, the specific control process in step S4 includes: S411: the PWM generation unit generates the PWM driving signal for controlling the three groups of bridge arms to have a 120° out-of-phase angle according to the frequency signal; S412: the PWM driving signal controls the duty cycle of all the upper bridge arm switch tubes Q1, Q3, Q5 to be fixed at 50%, controls the duty cycle of all the lower bridge arm switch tubes Q2, Q4, Q6 to be fixed at 50%, and controls the lower bridge arm switch tubes and the upper bridge arm switch tubes to be complementarily turned on; S413: the Gv gain lookup table unit adjusts the frequency signal according to the change of the Gv value; S414: the PWM generation unit updates the driving signal according to the adjusted frequency signal.

[0009] Optionally, when the Gv gain lookup table unit matches to the phase shift stage, the specific control process in step S4 includes: S421: the PWM generation unit generates the PWM driving signal for controlling the LLC working frequency to be fixed and the upper and lower bridge arm switch tubes to have fixed dead zones according to the phase difference signal and the duty cycle adjustment signal; S422: the PWM driving signal controls the driving phase angle of the first bridge arm Q1 / Q2, the second bridge arm Q3 / Q4 and the third bridge arm Q5 / Q6, and adjusts the driving phase angle from 120° to 180° continuously and smoothly according to the fitting curve in the Gv gain lookup table unit; S423: the phase angle adjustment step is output by the Gv gain lookup table unit, and the duty cycle adjustment value of Q1, Q3, Q5 is output by the Gv gain lookup table unit according to the fitting curve, so as to synchronously reduce the duty cycle of Q1, Q3, Q5.

[0010] Optionally, when the Gv gain lookup unit matches to the modulation duty cycle stage, the specific control process in step S4 includes: S431: The PWM generation unit generates a PWM driving signal for controlling the LLC working frequency fixed, the phase angle of the three groups of bridge arms fixed according to the duty cycle signal; S432: The phase angle of the three groups of bridge arms satisfies that the first bridge arm and the second bridge arm are in the same phase, and the third bridge arm is 180° out of phase, and the dead zone of the upper and lower bridge arm switching tubes is fixed; S433: The PWM driving signal only adjusts the duty cycle of the upper bridge arm switching tubes Q1, Q3 and Q5.

[0011] Optionally, the fitting process of the control parameters in the Gv gain lookup unit includes: S51: In an open loop state, at least two different fixed load conditions are set to cover the low load, medium load and high load intervals, and tests are performed at different input voltage points; S52: The input voltage, output voltage and resonant cavity current data of the three groups of bridge arms under different conditions are collected; S53: According to the efficiency and current balance target, the optimal control parameters including frequency, phase difference and duty cycle are selected for each Gv value; S54: The selected parameter points are linearly or appropriately fitted to obtain the control curve under each fixed load condition; S55: The curves obtained under the at least two different fixed load conditions are integrated to form the actual use control curve covering the entire load range; or the control curve can also be directly obtained through theoretical calculation; S56: The final control curve is stored in the Gv gain lookup unit.

[0012] In a second aspect, the embodiments of the present application provide a three-phase LLC device applied to a data center high-voltage direct current system, for realizing the loop control method of the three-phase LLC device applied to the data center high-voltage direct current system in any of the optional embodiments of the first aspect, and converting three-phase alternating current of a power grid side into isolated high-voltage direct current output; The device includes a three-phase interleaved LLC resonant circuit and a control module; The three-phase interleaved LLC resonant circuit includes three groups of bridge arms, each group of bridge arms including an upper bridge arm switching tube, a lower bridge arm switching tube and a freewheeling diode connected in parallel with the upper bridge arm switching tube; specifically, the first bridge arm includes the upper bridge arm switching tube Q1, the lower bridge arm switching tube Q2 and the freewheeling diode D1, the second bridge arm includes the upper bridge arm switching tube Q3, the lower bridge arm switching tube Q4 and the freewheeling diode D3, and the third bridge arm includes the upper bridge arm switching tube Q5, the lower bridge arm switching tube Q6 and the freewheeling diode D5; The control module comprises a PID control unit, a Gv gain lookup table unit, a PWM generation unit and a current monitoring unit; The input end of the voltage monitoring unit is connected to the output end of the device, and the output end is connected to the input end of the PID control unit, for collecting the output voltage signal and transmitting it to the PID control unit; The output end of the PID control unit is connected to the input end of the Gv gain lookup table unit, configured to receive the output voltage signal and the output current signal, and calculate the output gain Gv only according to the two; The output end of the Gv gain lookup table unit is connected to the input end of the PWM generation unit, configured to match the corresponding control stage according to the Gv value output by the PID control unit, and output the corresponding control parameters; the control parameter curve in the Gv gain lookup table unit is established in the following way: in an open-loop state, at least two different fixed load conditions are set to cover the low load, medium load and high load intervals, the input voltage is changed and the output voltage and three groups of bridge arm currents are monitored, the optimal control parameters including frequency, phase difference and duty cycle are selected, and the curves under the at least two different fixed load conditions are fitted and integrated; or obtained through theoretical calculation; The output end of the PWM generation unit is connected to the control end of the three groups of bridge arm switching tubes, for generating PWM driving signals according to the control parameters of the Gv gain lookup table unit.

[0013] Optionally, when the Gv gain lookup table unit matches to the frequency modulation stage: The driving signals generated by the PWM generation unit control the three groups of bridge arms to be out of phase by 120°; The duty cycles of all upper bridge arm switching tubes Q1, Q3 and Q5 are fixed at 50%, the duty cycles of all lower bridge arm switching tubes Q2, Q4 and Q6 are fixed at 50%, and the lower bridge arm switching tubes and the upper bridge arm switching tubes are complementary to be turned on; The Gv gain lookup table unit adjusts the frequency signal to change the LLC working frequency according to the Gv value.

[0014] Optionally, when the Gv gain lookup table unit matches to the phase shift stage: The driving signals generated by the PWM generation unit control the LLC working frequency to be fixed; The dead zone of the upper and lower bridge arm switching tubes is controlled by the driving signals to be fixed; The adjustment step length of the phase angle from 120° to 180° is output by the Gv gain lookup table unit; The duty cycle adjustment value of the upper bridge arm switching tubes Q1 and Q3 is output by the Gv gain lookup table unit according to the fitting curve.

[0015] Optionally, when the Gv gain lookup table unit matches to the duty cycle modulation stage: The driving signal generated by the PWM generation unit controls the LLC operating frequency to be fixed, and the phase angles of the three groups of bridge arms to be fixed. The phase angles of the three groups of bridge arms satisfy that the first bridge arm and the second bridge arm are in the same phase, and the third bridge arm is out of phase by 180 degrees, and the dead zones of the upper and lower bridge arm switching tubes are fixed. The driving signal only adjusts the duty cycles of the upper bridge arm switching tubes Q1, Q3 and Q5.

[0016] The technical scheme provided in the application has the following beneficial effects: The output voltage signal and the output current signal of the three-phase LLC device are collected, the output voltage signal reflects the matching of the power supply capacity and the load voltage demand, and the output current signal reflects the load power consumption state, and the two are the core electrical quantities of the interaction between the device and the load. Directly collecting these two types of signals can avoid data deviation caused by relying on non-core intermediate signals, ensure that the original data is directly related to the load side demand, and provide reliable input basis for subsequent output gain calculation.

[0017] The output voltage signal and the output current signal are input into the PID control unit to calculate the output gain Gv, and the PID control unit can quantize the static deviation of the current output gain, eliminate the steady-state error, and predict the dynamic change trend of the gain. Compared with the traditional simple gain calculation method, this logic solves the problems of insufficient static precision and dynamic response lag, and ensures that the output gain Gv can reflect the matching degree of the device running state and the load demand in real time and accurately.

[0018] The output gain Gv is input into the Gv gain lookup table unit to match the control stage and output the control parameters, and the Gv gain lookup table unit pre-stores the corresponding relationship of "output gain Gv-control stage-control parameter" under all working conditions. After receiving the Gv value, the control stage (frequency adjustment, phase shift, duty cycle adjustment) that is suitable for matching can be quickly matched by looking up the table, and the optimal control parameters (frequency signal, phase difference signal, duty cycle adjustment signal and duty cycle signal) under the corresponding working condition are output, so that the efficiency of stage matching and parameter output is improved, and different working conditions such as light load, medium load and full load of the data center are adapted.

[0019] The PWM generation unit generates a driving signal according to the control parameters to control the switching tube to be turned on or turned off, and the PWM generation unit can convert the abstract control parameters (frequency, phase difference and duty cycle) into PWM driving signals executable by the switching tube, so that the switching tube action meets the control requirements. Combined with the characteristics of the three-phase LLC topology, the driving signal can offset the output ripple by cooperatively controlling the three groups of bridge arms, and achieve the adjustment target (wide range gain coverage in the frequency adjustment stage, consideration of efficiency and accuracy in the phase shift stage, fine adjustment in the duty cycle adjustment stage) in different control stages, so as to ensure that the device output stably matches the power supply requirements.

[0020] The control method solves the problems of large data deviation, inaccurate gain calculation, poor working condition adaptability and insufficient output stability in the traditional scheme through the cooperation of collecting core electrical quantity, calculating Gv, checking table adaptive control strategy and PWM driving execution, realizes the adaptation to the load change of the data center, widens the gain adjustment range, improves the output voltage stability and control precision, and provides support for reliable operation of the data center high-voltage DC power supply system.

[0021] In order to make the above-mentioned purpose, features and advantages of the present application more obvious and easy to understand, the following preferred embodiments are described in detail below, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0023] Figure 1 A flow chart of a three-phase LLC device loop control method applied to a data center high-voltage DC system provided by the embodiment one of the present application is shown; Figure 2 A phase matching relationship diagram of three-phase interleaved LLC gain lookup table provided by the embodiment one of the present application is shown; Figure 3 A waveform verification synthesis diagram of three-phase interleaved LLC gain lookup table provided by the embodiment one of the present application is shown; Figure 4 A signal diagram of three-phase interleaved LLC frequency modulation control and resonator current provided by the embodiment one of the present application is shown; Figure 5 A waveform diagram of resonator current under three-phase interleaved LLC frequency modulation control provided by the embodiment one of the present application is shown; Figure 6 A signal diagram of three-phase interleaved LLC phase shift control and resonator current provided by the embodiment one of the present application is shown; Figure 7 A waveform diagram of resonator current under three-phase interleaved LLC phase shift control provided by the embodiment one of the present application is shown; Figure 8 A signal diagram of three-phase interleaved LLC duty cycle control and resonator current provided by the embodiment one of the present application is shown; Figure 9A waveform diagram of resonator current under three-phase interleaved LLC duty ratio control provided by the embodiment one of the present application is shown. Figure 10 A structure schematic diagram of a three-phase LLC device provided by the embodiment two of the present application is shown. Figure 11 A structure schematic diagram of a second three-phase LLC device provided by the embodiment two of the present application is shown. Figure 12 A structure schematic diagram of a third three-phase LLC device provided by the embodiment two of the present application is shown. DETAILED DESCRIPTION

[0024] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0025] Embodiment one The present method is limited to be applied to a three-phase LLC device, because the three-phase LLC device has the characteristics of large output power and high efficiency, and is suitable for the demand of large power supply of the data center high voltage direct current power supply system. The core demand of the data center high voltage direct current power supply system is to convert three-phase alternating current on the power grid side into isolated high voltage direct current output, so as to meet the stable power supply requirements of servers and other equipment. The subsequent steps are set around this core demand, and are aimed at solving the problems of narrow working range, large difference between light load and full load loop characteristics, and high output ripple voltage of the existing three-phase LLC device through orderly control logic.

[0026] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application. Figure 1 The content described in the flowchart of a three-phase LLC device loop control method applied to a data center high voltage direct current system provided by the embodiment one of the present application is used to describe the embodiment one of the present application.

[0027] Referring to Figure 1 , Figure 1The application discloses a three-phase LLC device loop control method applied to a data center high-voltage direct-current system, which is applied to a three-phase LLC device and is used for conversion of three-phase alternating current into isolated high-voltage direct current in the data center high-voltage direct-current system. S1: output voltage signals and output current signals of the three-phase LLC device are collected.

[0028] Specifically, the current monitoring unit collects resonant cavity current signals of three bridge arms, and the signals provide data support for subsequent current balance control. Meanwhile, related signals (including input voltage, output voltage, resonant cavity voltage and other electrical signals associated with gain of the device) are collected, and an output gain Gv is calculated. The Gv is a key index for judging the matching degree of the output capacity of the device and the target demand, and the prior art is prone to control stage switching confusion due to inaccurate Gv calculation. The current signals and the related signals are collected synchronously in the step, so that the Gv calculation is accurate, and a foundation is laid for accurate matching in the subsequent control stage.

[0029] S2: the output voltage signals and the output current signals are input into a PID control unit, and the current output gain Gv of the device is calculated by the PID control unit.

[0030] Specifically, an output voltage instruction value is obtained through an instruction setting unit; a first adjustment amount is calculated by comparing an output voltage value of the device with the output voltage instruction value; a second adjustment amount is calculated by comparing an output current value of the device with a maximum allowable output current value; and the smaller one of the first adjustment amount and the second adjustment amount is taken as the output gain Gv. The instruction setting unit can provide an accurate output voltage instruction value for the PID control unit by receiving a voltage demand instruction of an external system or presetting a voltage parameter, so that the reference for gain calculation is accurate.

[0031] The current output gain Gv is input into a Gv gain lookup table unit, and the unit establishes a corresponding relationship between the gain Gv and a control stage, that is, the gain Gv from high to low corresponds to a frequency modulation stage, a phase shift stage and a duty ratio modulation stage in sequence, which is determined based on the gain characteristics of the three-phase LLC device, and specifically, Under a high gain condition, frequency modulation control can realize wide-range gain adjustment and has high efficiency; under a medium gain condition, phase shift control can accurately adjust the gain while ensuring the efficiency; and under a low gain condition, duty ratio modulation control can realize fine adjustment of the gain. The corresponding relationship can enable the device to select an optimal control mode under different gain conditions, thereby widening the working range and solving the problem of narrow working range in the prior art.

[0032] Referring to Figure 2 as shown, Figure 2A three-phase interleaved LLC gain lookup table phase matching relationship diagram provided by the embodiment one of the present application is shown, wherein the overall presents the matching relationship of gain Gv-control phase-core parameter, and provides the basis for the three-stage control strategy; wherein RR refers to the resonance period range (inversely proportional to the frequency, the smaller the period, the higher the frequency), Prd is the resonance period, PHASE refers to the phase, PHASE_delt refers to the phase difference (unit: period ratio), and Duty refers to the duty ratio. The left half part shows the corresponding logic of the control phase and the gain with the horizontal coordinate “CTRL” and the vertical coordinate “gain Gv”, from left to right, in turn, the duty ratio adjusting stage, the phase shifting stage, and the frequency adjusting stage, the rising broken line indicates that the gain Gv continuously increases with the control phase advancing, and the core parameter range is marked below each stage: the duty ratio adjusting stage is “RR=MinPrd, PHASE_delt=1 / 6, Duty=D1-D2”, the phase shifting stage is “RR=MinPrrd, PHASE_delt=0-1 / 6, Duty=D2-50%”, and the frequency adjusting stage is “RR=MinPrrd+MaxPrd, PHASE_delt=0, Duty=50%”, which clearly shows the core regulation parameters and values in each stage.

[0033] Referring to Figure 3 as shown, Figure 3 A three-phase interleaved LLC gain lookup table waveform verification comprehensive diagram provided by the embodiment one of the present application is shown, wherein in the four waveforms of Gv, PRD (waveform representation of the resonance period, reflecting the frequency change), PHASE_delt, and duty in the right half part, the Gv waveform continuously rises and echoes the gain trend in the left half part, the PRD waveform is stable in the early stage (the frequency is fixed in the duty ratio adjusting stage and the phase shifting stage), and rises in the later stage (the frequency is reduced in the frequency adjusting stage), reflecting the frequency regulation effect in the frequency adjusting stage, the PHASE_delt waveform maintains 1 / 6 in the early stage (the phase difference is 60° in the duty ratio adjusting stage), decreases to 0 in the middle stage (the phase difference is adjusted from 60° to 0° in the phase shifting stage), and remains 0 in the later stage (the phase difference is fixed at 0° in the frequency adjusting stage), embodying the phase regulation logic when the phase shifting stage transitions to the frequency adjusting stage, the duty waveform rises from D1 to D2 in the early stage (the duty ratio is adjustable in the duty ratio adjusting stage), rises from D2 to 50% in the middle stage (the duty ratio is continuously adjusted in the phase shifting stage), and remains 50% in the later stage (the duty ratio is fixed in the frequency adjusting stage), matching the duty ratio change requirements in each stage, and finally, through the combination of the schematic diagram and the waveform diagram, the cooperative matching relationship of the gain Gv and the three-stage control of the duty ratio adjusting, the phase shifting, and the frequency adjusting and the corresponding parameters (duty ratio, phase difference, resonance period / frequency) is completely verified.

[0034] S3: input the current output gain Gv into the Gv gain lookup table unit, match the corresponding control phase by the Gv gain lookup table unit, and output the corresponding control parameter.

[0035] Specifically, the gain lookup table unit outputs the corresponding control parameters according to the matched control stage, because the core regulation object is different in different control stages: The frequency modulation stage adjusts the gain by changing the LLC operating frequency, and thus outputs a frequency signal; the phase-shift modulation stage needs to adjust the bridge arm phase difference and duty cycle to cooperatively optimize the gain, and thus outputs a phase difference signal and a duty cycle adjustment signal to avoid overcurrent caused by single adjustment of the phase difference; the duty cycle modulation stage adjusts the duty cycle to achieve low-gain output, and thus outputs a duty cycle signal.

[0036] This parameter output logic can ensure that the PWM generation unit obtains control instructions adapted to the current control stage, avoid control failure caused by parameter mismatch, and ensure the rationality and accuracy of the parameters based on the curves fitted under open-loop conditions (the fitting process will be described in detail later), thereby providing a guarantee for stable operation of the device.

[0037] S4: The PWM generation unit generates a PWM driving signal according to the control parameters to control the switching tubes of the three bridge arms to be turned on or turned off.

[0038] Specifically, the PWM generation unit is an execution module of the control instructions, and the core function is to convert the frequency, phase difference, duty cycle, and other abstract control parameters output by the Gv gain lookup table unit into PWM driving signals recognizable by the switching tubes. The switching tube is a key execution element for electric energy conversion of the three-phase LLC device, and the timing and duration of its conduction or non-conduction directly determine the efficiency and output characteristics of electric energy conversion. By controlling the conduction or non-conduction of the switching tube through the PWM driving signal, the output voltage and current of the three-phase LLC device can be accurately regulated to meet the requirements of the data center high-voltage direct-current power supply system for output stability.

[0039] At the same time, transmitting the PWM driving signal to the control end of the switching tube of the three bridge arms is to utilize the characteristics of the three-phase interleaved structure, cooperatively control the switching actions of the three bridge arms, reduce the output ripple, and solve the problem of excessive output ripple in the prior art.

[0040] In an optional embodiment, in step S2, the PID control unit calculates the output gain Gv in the following manner: The first adjustment amount is calculated by comparing the output voltage value of the device with the output voltage instruction value; the second adjustment amount is calculated by comparing the output current value of the device with the maximum allowed output current value; and the smaller one of the first adjustment amount and the second adjustment amount is taken as the output gain Gv.

[0041] Specifically, the calculation method essentially realizes double-loop control of the voltage loop and the current loop, and priority judgment is performed through the minimum value logic. The first adjustment amount is calculated by the voltage loop PID controller according to the voltage deviation, representing the gain adjustment amount required to eliminate the voltage error; the second adjustment amount is calculated by the current loop PID controller or a simple limiter according to the current deviation, representing the maximum gain allowed to prevent the output current from exceeding the safety threshold. When the system is working normally and the current does not reach the limit, the voltage loop plays a leading role, and Gv is mainly determined by the first adjustment amount; when the load is too heavy or a fault occurs, causing the current to approach or exceed the maximum value, the second adjustment amount will automatically limit the increase of Gv, or even make it decrease, thereby clamping the current within a safe range and achieving overcurrent protection of the system. This method ensures that the system pursues voltage stability without sacrificing safety.

[0042] In an optional embodiment, when the Gv gain lookup table unit matches the frequency modulation stage, the specific control process in step S4 includes: S411: The PWM generation unit generates PWM driving signals for controlling the three sets of bridge arms with a phase difference of 120° according to the frequency signal.

[0043] Specifically, the PWM generation unit generates driving signals according to the frequency signal, because the core adjustment means of the frequency modulation stage is to change the LLC working frequency, and the frequency signal directly determines the period of the driving signal. Controlling the three sets of bridge arms with a phase difference of 120° is based on the phase characteristics of the three-phase circuit: the three-phase bridge arms with a phase difference of 120° can make the output current ripples cancel each other out, greatly reducing the output ripple voltage.

[0044] S412: The PWM driving signals control the duty cycles of all upper bridge arm switches Q1, Q3, Q5 to be fixed at 50%, and the duty cycles of all lower bridge arm switches Q2, Q4, Q6 to be fixed at 50%, and the lower bridge arm switches and the upper bridge arm switches are complementary on.

[0045] Specifically, the frequency modulation stage fixes the duty cycles of the upper bridge arm switches Q1, Q3, Q5 at 50%, because in the frequency modulation control logic, when the duty cycle is fixed at 50%, the gain adjustment of the LLC device is only related to the frequency, which can avoid the interference of the duty cycle change on the gain adjustment and simplify the control logic. At the same time, 50% duty cycle is the optimal duty cycle for the LLC device to realize soft switching, which can effectively reduce the switching loss of the switch and improve the efficiency of the device, meeting the demand for high efficiency and energy saving of the data center power supply system. In addition, fixing the duty cycles of the three sets of upper bridge arm switches uniformly can ensure that the working states of the three sets of bridge arms are consistent, laying a foundation for subsequent current balancing control.

[0046] S413: The Gv gain lookup table unit adjusts the frequency signal according to the change of the Gv value.

[0047] Specifically, although the frequency modulation stage optimizes the current distribution through the 120° phase shift and the fixed duty cycle, power grid voltage fluctuations and load changes may still cause the resonant cavity currents of the three bridge arms to deviate. The current monitoring unit monitors the current in real time, so as to timely capture the current deviation and avoid overcurrent damage to the switch tubes of a certain group of bridge arms due to current imbalance, and also to provide data support for subsequent current balancing adjustment. If the current is not monitored in real time, the current deviation may continue to expand, thereby causing problems such as output ripple exceeding the standard and device efficiency decreasing, which cannot meet the requirements of data centers on power supply stability.

[0048] S414: The PWM generation unit updates the driving signal according to the adjusted frequency signal.

[0049] Specifically, the setting of the preset threshold is based on the hardware parameters (such as the rated current of the switch tube and the resonant cavity element parameters) of the three-phase LLC device, and the purpose is to define a reasonable range for current balancing and avoid frequent triggering of adjustment due to minor deviations, so as to ensure system stability. When the current deviation exceeds the threshold, the PID control unit generates a correction signal, because the PID control has precise deviation adjustment capability and can generate an appropriate correction instruction according to the deviation size. The Gv gain lookup table unit adjusts the frequency signal according to the correction signal, because the gain adjustment in the frequency modulation stage depends on the frequency change, and the resonant cavity current can be indirectly adjusted by adjusting the frequency, for example, when the current of a certain group of bridge arms is too large, appropriately adjusting the frequency can change the impedance characteristics of the resonant cavity, thereby balancing the currents of each group and solving the current imbalance problem.

[0050] Referring to Figure 4 , it is shown that Figure 4 A signal diagram of the resonant cavity current under the three-phase interleaved LLC frequency modulation control provided by the embodiment one of the present application is shown, which shows the PWM driving signals of the first bridge arm Q1 / Q2, the second bridge arm Q3 / Q4 and the third bridge arm Q5 / Q6, the phase shift angle of the three groups of driving signals is 120°, and the duty cycle of the upper bridge arm switch tubes Q1, Q3 and Q5 is fixed.

[0051] Referring to Figure 5 , it is shown that Figure 5 A waveform diagram of the resonant cavity current under the three-phase interleaved LLC frequency modulation control provided by the embodiment one of the present application is shown, which presents the waveforms of the resonant cavity currents LIA, LIB and LIC. The three current waveforms are sinusoidal pulsation and phase-shifted by 120°, and the peak values are basically consistent, which intuitively reflects the effects of current balancing and ripple suppression under the frequency modulation stage driving with a 120° phase shift and a fixed duty cycle, and verifies the effectiveness of the control logic in the frequency modulation stage.

[0052] In an optional embodiment, when the Gv gain lookup table unit matches to the phase shift stage, the specific control process in step S4 includes: S421: The PWM generation unit generates a PWM driving signal for controlling the LLC working frequency and the fixed dead time of the upper and lower bridge arms according to the phase difference signal and the duty cycle adjustment signal.

[0053] Specifically, the phase-shift stage controls the LLC working frequency to be fixed because the core regulation means of this stage is the phase difference, and fixing the frequency can avoid the interference of frequency change on the phase difference regulation, ensuring the gain regulation accuracy. The upper and lower bridge arms are controlled to have fixed dead time because the dead time directly affects the soft switching of the switch tube: too large dead time is easy to cause gain reduction, and too small dead time is easy to cause the upper and lower bridge arms to be short-circuited, and fixing the dead time can ensure that the device maintains stable soft switching state in the phase-shift stage, reducing the switching loss. The PWM generation unit receives the phase difference signal and the duty cycle adjustment signal at the same time because the phase-shift stage needs to be controlled by both signals to avoid overcurrent of the Q5 / Q6 bridge arm caused by single adjustment of the phase difference, ensuring the safe operation of the device.

[0054] S422: The PWM driving signal controls the driving phase angle of the first bridge arm Q1 / Q2, the second bridge arm Q3 / Q4, and the third bridge arm Q5 / Q6, and adjusts it from 120° to 180° in a segmented and continuous smooth manner according to the fitting curve in the Gv gain lookup table unit.

[0055] Specifically, the driving phase angle is adjusted from 120° to 180°, and 120° phase angle corresponds to a higher mid-gain, and 180° phase angle corresponds to a lower mid-gain, and the adjustment in this range can realize continuous coverage of the mid-gain interval. According to the fitting curve in the Gv gain lookup table unit, because the fitting curve is generated based on the resonant cavity current data and efficiency data under open-loop state, it can ensure that the phase angle adjustment and gain change are linearly corresponding, solving the nonlinearity problem of the prior art gain. The segmented and continuous smooth adjustment can avoid current shock caused by sudden change of the phase angle, reduce output ripple, and at the same time ensure smooth transition of the device gain, meeting the requirement of data center for power supply voltage stability.

[0056] S423: The phase angle adjustment step is output by the Gv gain lookup table unit, and the duty cycle adjustment value of Q1, Q3, and Q5 is output by the Gv gain lookup table unit according to the fitting curve, and the duty cycle of Q1, Q3, and Q5 is reduced synchronously.

[0057] Specifically, the phase angle adjustment step is output by the Gv gain lookup table unit, because the step needs to match the current gain Gv: the step in the high gain interval can be appropriately increased to improve the adjustment speed, and the step in the low gain interval needs to be reduced to ensure the adjustment accuracy and avoid the adjustment error caused by the fixed step. The duty cycles of Q1, Q3 and Q5 are synchronously reduced, because when the phase angle increases in the phase shift stage, the current load of the Q5 / Q6 bridge arm is prone to increase, and reducing the duty cycles of the three switching tubes can balance the currents of the bridge arms, thereby avoiding the overcurrent problem. The adjustment value is output based on the fitting curve, which can ensure that the duty cycle adjustment is adapted to the phase angle adjustment, thereby ensuring the gain adjustment effect and considering the operation safety.

[0058] Referring to Figure 6 as shown, Figure 6 A signal diagram of the resonator current in the three-phase interleaved LLC phase shift control provided by the embodiment one of the present application is shown, wherein the PWM driving signals of the first bridge arm Q1 / Q2, the second bridge arm Q3 / Q4 and the third bridge arm Q5 / Q6 are displayed, the phase angle is gradually adjusted from 120° to 180°, and the duty cycles of Q1, Q3 and Q5 are synchronously reduced.

[0059] Referring to Figure 7 as shown, Figure 7 A waveform diagram of the resonator current in the three-phase interleaved LLC phase shift control provided by the embodiment one of the present application is shown, wherein the waveforms of the resonator currents LIA, LIB and LIC are presented, the current peak values of LIA and LIB gradually decrease with the adjustment of the phase angle, the current peak value of LIC is basically stable and does not exceed the overcurrent threshold, thereby verifying the effects of the current balance and overcurrent protection in the phase shift stage with the coordinated adjustment of the phase angle and the duty cycle, and embodying the rationality of the control logic in the phase shift stage.

[0060] In an optional embodiment, when the Gv gain lookup table unit matches to the duty cycle adjustment stage, the specific control process in step S4 includes: S431: The PWM generation unit generates the PWM driving signal for controlling the LLC working frequency fixedly and the phase angles of the three groups of bridge arms fixedly according to the duty cycle signal.

[0061] Specifically, the LLC working frequency and the phase angles of the three groups of bridge arms are fixed in the duty cycle adjustment stage, because the core adjustment means of this stage is the duty cycle, and the fixed frequency and phase angle can exclude the interference of the two on the gain adjustment, so that the gain change is only related to the duty cycle, thereby greatly improving the adjustment accuracy in the low gain interval and solving the problem of insufficient adjustment accuracy in the low gain working condition in the prior art.

[0062] The PWM generation unit generates the driving signal according to the duty cycle signal, which can ensure that the on duration of the switching tube is performed according to the preset duty cycle, thereby realizing the fine adjustment of the gain and adapting to the high requirement of the data center load on the stability of the supply voltage.

[0063] S432: The phase angles of the three groups of bridge arms satisfy that the first bridge arm and the second bridge arm are in phase, and the third bridge arm is out of phase by 180 degrees, and the dead zones of the upper and lower bridge arm switches are fixed.

[0064] Specifically, the first bridge arm and the second bridge arm are in phase and the third bridge arm is out of phase by 180 degrees, which is based on the current balance requirement in the low gain working condition: the phase angle setting can make the currents of the first and second bridge arms complement each other after superposition, reduce the output ripple, and avoid that the current of a group of bridge arms is too large.

[0065] The dead zones of the upper and lower bridge arm switches are fixed, because the duty cycle range is large in the duty cycle adjustment stage, and the fixed dead zone can ensure that the upper and lower bridge arms will not be short-circuited regardless of the adjustment of the duty cycle, avoid damage to the switch, maintain a stable soft switching state, and ensure that the device still has high efficiency in the low gain working condition.

[0066] S433: The PWM driving signal only adjusts the duty cycles of the upper bridge arm switches Q1, Q3 and Q5.

[0067] Specifically, only the duty cycles of the upper bridge arm switches Q1, Q3 and Q5 are adjusted, because the change of the duty cycle of the upper bridge arm switch has a more direct and higher linear effect on the gain, and can avoid the current fluctuation caused by adjusting the duty cycle of the lower bridge arm switch. At the same time, this adjustment method can simplify the control logic, without the need to adjust the duty cycles of the upper and lower bridge arms synchronously, reduce the operation load of the control module, and is suitable for the requirement of real-time control in industrial scenes.

[0068] In addition, adjusting only the duty cycle of the upper bridge arm can ensure that the conduction timing of the lower bridge arm switch is relatively stable, further reduce the output ripple, and meet the demand of low ripple power supply in data centers.

[0069] Referring to FIG. 4, Figure 8 as shown, Figure 8 a signal diagram of a three-phase interleaved LLC duty cycle adjustment control and resonator current is shown, wherein it is shown that the first bridge arm Q1 / Q2 and the second bridge arm Q3 / Q4 driving signals are in phase, the third bridge arm Q5 / Q6 driving signals are out of phase by 180 degrees, and only the duty cycles of the upper bridge arm switches Q1, Q3 and Q5 are adjustable.

[0070] Referring to FIG. 4, Figure 9 as shown, Figure 9A waveform diagram of resonator current under three-phase interleaved LLC duty ratio control provided by the embodiment one of the present application is shown, which presents the waveforms of resonator currents LIA, LIB and LIC, the current presents the segmented response characteristics of rising when Q1 / Q3 / Q5 or Q2 / Q4 / Q5 is turned on, the resonant cavity voltage is 0 and the current is reduced to excitation current when Q2 / Q4 / Q6 is turned on, and the peak value of LIC current is equal to the sum of the peak values of LIA and LIB currents, verifying the effect of the fixed phase of the duty ratio stage, only adjusting the duty ratio of the upper bridge arm, and the current balance and energy transfer, supporting the feasibility of the control logic of the duty ratio stage.

[0071] In an optional embodiment, the fitting process of the control parameters of each stage in the Gv gain lookup table unit includes: S51: In an open loop state, at least two different fixed load conditions are set to cover the low load, medium load and high load intervals, and tests are performed at different input voltage points.

[0072] Specifically, the open loop state refers to disconnecting the closed loop feedback link of the control module, and only obtaining output data through preset parameter input, which can avoid the interference of closed loop feedback on experimental data, and ensure that the collected data can truly reflect the corresponding relationship between parameters and output characteristics. Covering the input voltage range and the load rate range is to ensure that the fitted curve adapts to the full working condition of the device: the input voltage range should include the possible fluctuation range of the grid side (such as 380V±20%), and the load rate range should cover light load (such as 10% load) to full load (such as 100% load).

[0073] S52: Collect input voltage, output voltage and resonant cavity current data of three groups of bridge arms under different conditions.

[0074] Specifically, resonant cavity current data and efficiency data under different Gv are collected, because current data reflects the safety of operation, and efficiency data reflects the economy of operation, and the combination of the two can ensure that the fitted parameters consider both safety and efficiency.

[0075] S53: According to the efficiency and current balance target, select the optimal control parameters for each Gv value, including frequency, phase difference and duty ratio.

[0076] Specifically, this step is the core optimization link of parameter fitting. For the Gv value obtained at each test point, there may be multiple sets of different control parameters (combination of frequency, phase difference, and duty cycle) that can achieve the gain. At this time, a comprehensive evaluation function needs to be established, with maximum efficiency as the primary goal, and current balance as the constraint condition. For example, the parameter combination that minimizes the difference between the peak values of the three sets of bridge arm resonant cavity currents (i.e., the most balanced current) can be selected first, and then among these combinations, the set with the highest efficiency is selected as the optimal parameter corresponding to the Gv value. Alternatively, the current imbalance can be quantified as a penalty term and added to the efficiency evaluation function, and the optimal solution is determined by calculating the comprehensive score. This selection method ensures that the final fitted control curve not only accurately achieves the target gain, but also enables the device to operate in the most efficient and safest state under the working condition.

[0077] S54: Linear or appropriate fitting is performed on the selected parameter points to obtain the control curve under each fixed load condition.

[0078] Specifically, the Gv parameter can be intuitively related by fitting the curve with Gv as the horizontal coordinate and frequency, phase difference, and duty cycle as the vertical coordinate, which facilitates quick access by the Gv gain lookup table unit.

[0079] S55: The curves obtained under the at least two different fixed load conditions are integrated to form an actual control curve covering the entire load range; or the control curve can also be obtained directly through theoretical calculation.

[0080] Specifically, the integration process can adopt an interpolation method or a piecewise function form. For example, if three control curves are obtained at 25%, 50%, and 75% fixed load points, respectively, in actual application, when the system detects that the current load rate is 60%, the controller can automatically perform linear interpolation between the two curves corresponding to 50% and 75% load, thereby calculating the accurate control parameters required under the current load. This method avoids testing at all possible load points, greatly reducing the fitting workload, while still ensuring the smoothness and accuracy of control in the entire load range. Another way is to directly calculate the optimal control parameters under different Gv, input voltage, and load based on the steady-state model of the LLC resonant converter. This method has a large amount of calculation, but has high precision and does not depend on experimental data.

[0081] S56: The final control curve is stored in the Gv gain lookup table unit.

[0082] Specifically, the fitted curve is stored in the Gv gain lookup table unit, which can directly read the corresponding parameters according to the current Gv during control without real-time fitting, improving the control response speed and meeting the real-time requirements of industrial scenarios.

[0083] Embodiment two Embodiment two of the present application provides a three-phase LLC device applied to a high-voltage direct-current system of a data center, for realizing the loop control method of the three-phase LLC device applied to the high-voltage direct-current system of the data center shown in the above embodiment one, converting three-phase alternating current of a power grid into isolated high-voltage direct-current output; the device comprises a three-phase interleaved LLC resonant circuit and a control module.

[0084] The three-phase interleaved LLC resonant circuit comprises three groups of bridge arms, each group of bridge arms comprising an upper bridge arm switch tube, a lower bridge arm switch tube and a freewheeling diode connected in parallel with the upper bridge arm switch tube; specifically, the first bridge arm comprises an upper bridge arm switch tube Q1, a lower bridge arm switch tube Q2 and a freewheeling diode D1, the second bridge arm comprises an upper bridge arm switch tube Q3, a lower bridge arm switch tube Q4 and a freewheeling diode D3, and the third bridge arm comprises an upper bridge arm switch tube Q5, a lower bridge arm switch tube Q6 and a freewheeling diode D5.

[0085] Specifically, the three groups of bridge arms are the core components of the three-phase interleaved LLC resonant circuit, each group of upper bridge arm switch tube-lower bridge arm switch tube constitutes a half-bridge structure, which can realize rectification and inversion of alternating current and meet the power conversion requirements of the LLC resonant circuit; the freewheeling diodes (D1, D3, D5) connected in parallel with the upper bridge arm switch tubes provide a freewheeling path for the resonant cavity current when the switch tube is turned off, avoiding damage to the switch tube due to reverse voltage, while ensuring continuous current and helping to reduce output ripple; the multiple groups of LLC resonant circuits can further suppress ripple and improve power density through interleaved operation, adapting to the requirement of miniaturization of the power supply device of the data center.

[0086] The control module comprises an instruction setting unit, a PID control unit, a Gv gain lookup table unit, a PWM generation unit, a voltage monitoring unit and a current monitoring unit.

[0087] Specifically, the instruction setting unit is configured to receive an output voltage instruction value input from outside or set internally, and provide the output voltage instruction value to the PID control unit to provide a reference voltage parameter for gain calculation; the voltage monitoring unit collects an output voltage signal, and the current monitoring unit collects a resonant cavity current signal of the three bridge arms, both of which are input to the PID control unit together with the output of the instruction setting unit to ensure the accuracy of the output gain Gv calculation. The PID control unit is responsible for proportional, integral and differential processing of the signal collected by the current monitoring unit to eliminate noise and deviation and generate accurate correction instructions; the Gv gain lookup table unit is the core of stage decision, matches the duty cycle, phase shift and frequency modulation three control stages according to the output gain Gv, and fits the control parameters (frequency, phase difference, duty cycle, etc.) of each stage based on the resonant cavity current and efficiency data in the open loop state; the PWM generation unit converts the abstract control parameters output by the Gv gain lookup table unit into PWM drive signals recognizable by the switching tube; the current monitoring unit collects the resonant cavity current raw signal in real time to provide data support for deviation correction and stage decision, and the five units cooperatively form a complete control link to ensure stable operation of the device.

[0088] The input end of the voltage monitoring unit is connected to the output end of the device, and the output end is connected to the input end of the PID control unit, for collecting an output voltage signal and transmitting the output voltage signal to the PID control unit.

[0089] Specifically, the voltage monitoring unit is composed of a high-voltage sensor (such as a voltage dividing resistor network, a Hall voltage sensor or an isolation amplifier) and a signal conditioning circuit. It is responsible for converting a high-amplitude DC output voltage (such as 380V or 400V) into a low-level analog signal (such as 0-3.3V or 0-5V) that can be processed by a controller (such as an MCU or a DSP). The signal conditioning circuit will filter, amplify and isolate the collected signal to remove noise interference and ensure electrical isolation between the control unit, ensuring the safety of the control core. The processed clean signal is sent to the ADC (analog-to-digital converter) interface of the PID control unit to provide accurate feedback values for voltage loop calculation.

[0090] The output end of the PID control unit is connected to the input end of the Gv gain lookup table unit, which is configured to receive an output voltage signal, an output current signal and an output voltage instruction value from the instruction setting unit, and calculate an output gain Gv.

[0091] Specifically, the PID control unit contains at least two independent PID controllers: a voltage loop PID and a current loop PID. The voltage loop PID continuously compares the output voltage command value with the actual output voltage collected by the voltage monitoring unit, calculates the deviation between the two, and generates a gain adjustment requirement for eliminating the deviation, i.e., the first adjustment amount, through proportional (P), integral (I), and differential (D) operations. Meanwhile, the current loop PID or a current limiter compares the actual output current with the maximum allowed current and calculates the second adjustment amount. The core logic of the PID control unit lies in its decision mechanism: it compares the two adjustment amounts and selects the smaller one as the final output gain Gv, which is sent to the Gv gain lookup table unit. This process realizes the organic combination of voltage stabilization and overcurrent protection.

[0092] The output end of the Gv gain lookup table unit is connected to the input end of the PWM generation unit, which is configured to match the corresponding control stage according to the Gv value output by the PID control unit and output the corresponding control parameters; the control parameter curve in the Gv gain lookup table unit is established by the following method: in the open-loop state, at least two different fixed load conditions are set to cover the low load, medium load, and high load intervals, the input voltage is changed, and the output voltage and three groups of bridge arm currents are monitored, the optimal control parameters including frequency, phase difference, and duty cycle are selected, and the curves under the at least two different fixed load conditions are fitted and integrated; or obtained through theoretical calculation.

[0093] Specifically, the Gv gain lookup table unit stores the control curve or data table fitted and integrated in step S5 of embodiment one. After receiving the Gv value from the PID control unit, it first determines which control stage (frequency adjustment, phase shift, or duty cycle adjustment) it should be in according to the size of Gv. The judgment basis is the preset Gv threshold, which is determined based on the gain characteristic curve of the device. Once the stage is determined, the unit will query the control curve of the corresponding stage, and according to the current Gv value, quickly retrieve or calculate the corresponding optimal control parameters. For example, if it is in the phase shift stage, it will output the corresponding phase difference signal and duty cycle adjustment signal at the same time. These parameters are "pre-calculated", so the lookup table process is very fast, ensuring the real-time response performance of the system. This way simplifies the complex nonlinear control problem into efficient lookup table operation, which is the key to realizing the three-stage control strategy.

[0094] The output end of the PWM generation unit is connected to the control end of the three groups of bridge arm switching tubes, which is used to generate PWM drive signals according to the control parameters of the Gv gain lookup table unit.

[0095] Specifically, the current monitoring unit directly collects original signals from the resonance cavity current sampling points of the three bridge arms, and after the original signals are transmitted to the PID control unit, the PID control unit processes the signals, generates a correction signal and sends it to the Gv gain lookup table unit; the Gv gain lookup table unit determines the current control stage according to the correction signal and the output gain Gv, and outputs corresponding parameters (such as frequency signal in the frequency modulation stage, phase difference and duty cycle adjustment signal in the phase shift stage) to the PWM generation unit; the PWM generation unit generates a PWM drive signal accordingly, which is transmitted to the control end of the switch tube of the three bridge arms, so as to realize precise control of the switch tube conduction / cutoff; at the same time, the Gv gain lookup table unit adjusts through the open-loop fitting parameters without relying on the input voltage adjustment, thereby improving the control response speed and the adaptability of the full gain range.

[0096] Referring to Figure 10 as shown, Figure 10 A structure schematic diagram of a three-phase LLC device provided by the embodiment two of the application is shown, wherein the diagram contains: input side: input capacitor V i , power supply for three sets of half-bridge arms (switch tubes Q1 and Q2, Q3 and Q4, Q5 and Q6 respectively form a set of half-bridge arms); intermediate resonance part: the bridge arm output is connected to three sets of LLC resonance circuits (each set contains a capacitor, a resonance inductor and a transformer, and is provided with current monitoring marks LIA, LIB and LIC); output side: the resonance circuit output is connected to a rectification structure composed of rectifier diodes D1 and D2, D3 and D4, and D5 and D6, and after rectification, the output is filtered through an output capacitor V0 to output high-voltage direct current. The device adopts a topology form of three-phase interleaved LLC-half-bridge-output rectification, and supports three-stage control of frequency modulation, phase shift and duty cycle adjustment.

[0097] In an optional embodiment, when the Gv gain lookup table unit matches to the frequency modulation stage: the drive signal generated by the PWM generation unit controls the three bridge arms to be out of phase by 120°; the drive signal controls the duty cycle of all upper bridge arm switch tubes Q1, Q3 and Q5 to be fixed at 50%, and the duty cycle of all lower bridge arm switch tubes Q2, Q4 and Q6 to be fixed at 50%, and the lower bridge arm switch tube and the upper bridge arm switch tube are complementary to be turned on; the Gv gain lookup table unit adjusts the frequency signal according to the Gv value to change the LLC working frequency.

[0098] Specifically, the frequency modulation stage is the control mode of the high-gain working condition of the device, which meets the demand for stable high-voltage output in the light load scenario of the data center. The PWM generation unit controls the three groups of bridge arms to be out of phase by 120°, which is to utilize the phase characteristics of the three-phase circuit to make the output current ripples of the three groups of bridge arms offset each other, thereby greatly reducing the overall output ripple voltage. The duty cycle of the upper bridge arm switching tubes Q1, Q3 and Q5 is fixed at 50%, which can simplify the control logic. At this time, the gain adjustment of the LLC device is only related to the frequency, avoiding the interference of the duty cycle change on the gain. On the other hand, 50% duty cycle is a key condition for the LLC circuit to realize soft switching, which can effectively reduce the switching loss of the switching tube and improve the operating efficiency of the device. The Gv gain lookup table unit changes the LLC operating frequency by adjusting the frequency signal, because the frequency modulation control can realize wide-range gain adjustment, meeting the voltage adaptation demand in the high-gain working condition. The current monitoring unit collects the resonant cavity currents of the three groups of bridge arms, which is to monitor the current balance state in real time, avoiding the current deviation caused by the voltage fluctuation of the power grid or the load change, and ensuring the stable operation of the device in the frequency modulation stage.

[0099] In an optional embodiment when the Gv gain lookup table unit matches to the phase shift stage: The driving signal generated by the PWM generation unit controls the LLC operating frequency to be fixed; the dead time of the driving signal controlling the upper and lower bridge arm switching tubes is fixed; the adjustment step of the phase angle from 120° to 180° is output by the Gv gain lookup table unit; the duty cycle adjustment value of the upper bridge arm switching tubes Q1, Q3 and Q5 is output by the Gv gain lookup table unit according to the fitting curve.

[0100] Specifically, the phase shift stage is the control mode of the medium-gain working condition of the device, which adapts to the medium load scenario in the data center. The PWM generation unit fixes the LLC operating frequency, which is to exclude the interference of the frequency change on the phase difference adjustment, ensuring the gain adjustment accuracy; the dead time of the upper and lower bridge arm switching tubes is fixed, because the dead time directly affects the realization of soft switching, and too large dead time is easy to cause gain decrease, and too small dead time is easy to cause shoot-through damage of the upper and lower bridge arm, fixing the dead time can maintain the stable soft switching state of the device and reduce the switching loss; the phase angle is adjusted from 120° to 180°, because 120° phase angle corresponds to relatively high gain, and 180° phase angle corresponds to relatively low medium gain, and the adjustment of this range can realize continuous coverage of the medium gain interval, and the adjustment step is output by the Gv gain lookup table unit, which can match the current gain Gv to balance the adjustment speed and accuracy; the duty cycle adjustment value of the upper bridge arm switching tubes Q1, Q3 and Q5 is output based on the fitting curve, and the synchronous adjustment of the duty cycle is to avoid the overcurrent of the third bridge arm Q5 / Q6 caused by the single adjustment of the phase angle. When the phase angle increases in the phase shift stage, the current of Q5 / Q6 is easy to rise, and reducing the duty cycle of these three switching tubes can share the load of Q5 / Q6. The current monitoring unit focuses on collecting the resonant cavity currents of Q5 / Q6, because this bridge arm has the highest risk of overcurrent in the phase shift stage, and real-time collection can timely capture the overcurrent hidden danger, ensuring the safe operation of the device.

[0101] In an optional embodiment, when the Gv gain lookup table unit matches to the duty ratio adjustment stage: The driving signal generated by the PWM generation unit controls the LLC operating frequency to be fixed, and the phase angles of the three groups of bridge arms to be fixed; the phase angles of the three groups of bridge arms satisfy that the first bridge arm and the second bridge arm are in the same phase, and the third bridge arm is out of phase by 180°, and the dead zones of the upper and lower bridge arm switching tubes are fixed; the driving signal only adjusts the duty ratios of the upper bridge arm switching tubes Q1, Q3 and Q5.

[0102] Specifically, in the duty ratio adjustment stage, the driving signal generated by the PWM generation unit controls the LLC operating frequency to be fixed, and the phase angles of the three groups of bridge arms to be fixed; the phase angles of the three groups of bridge arms satisfy that the first bridge arm and the second bridge arm are in the same phase, and the third bridge arm is out of phase by 180°, and the dead zones of the upper and lower bridge arm switching tubes are fixed; the driving signal only adjusts the duty ratios of the upper bridge arm switching tubes Q1, Q3 and Q5. Under this control mode, the fixed frequency and phase angle can exclude the interference of the gain, so that the gain change is only adjusted by the duty ratio, and the adjustment accuracy in the low gain range is improved; the phase setting of the first and second bridge arms in the same phase and the third bridge arm out of phase by 180° can make the current of the former two superimposed and complementary to the current of the third bridge arm, thereby reducing the output ripple; only adjusting the duty ratio of the upper bridge arm can ensure the directness and linearity of the gain adjustment, simplify the control logic, avoid the current fluctuation caused by the adjustment of the duty ratio of the lower bridge arm, maintain the stability of the conduction timing of the lower bridge arm, and further reduce the ripple.

[0103] Referring to Figure 11 , it is shown that Figure 11 a structure schematic diagram of a second three-phase LLC device provided by the second embodiment of the present application is shown, wherein the input side in the figure is provided with an input capacitor V i , which supplies power to the left three groups of half-bridge arms composed of switching tubes Q7 and Q8, Q9 and Q10, and Q11 and Q12, respectively. The middle resonant part is that the bridge arm output is connected to three groups of LLC resonant circuits (each group contains a capacitor, a resonant inductor, and a transformer). The output side is that the resonant circuit output is connected to the right three groups of half-bridge arms (composed of switching tubes Q7 and Q8, Q9 and Q10, and Q11 and Q12, respectively), and finally outputs high-voltage direct current through an output capacitor V o filter. The device adopts the topology form of three-phase interleaved LLC cooperating with input and output side half-bridge, and can realize the conversion of electric energy from input to output through the control of multiple groups of switching tubes (Q7-Q12), thereby providing hardware support for three-stage control (frequency adjustment, phase shift, and duty ratio adjustment).

[0104] Referring to Figure 12 , it is shown that Figure 12 a structure schematic diagram of a third three-phase LLC device provided by the second embodiment of the present application is shown, wherein the input side in the figure is provided with an input capacitor V iThe left three groups of half-bridge arms are powered; the left half-bridge arms are respectively composed of switch tubes Q13 and Q14, Q15 and Q16, and Q17 and Q18. The middle resonance part: the bridge arm output is connected with three groups of LLC resonance circuits (each group contains a capacitor, a resonance inductor, and a transformer), and is provided with current monitoring marks LIA, LIB, and LIC for collecting the resonance cavity current signals of the corresponding branches. The output side: the resonance circuit output is connected with a rectification structure composed of rectifier diodes D13 and D14, D15 and D16, and D17 and D18, and the rectified output is output through an output capacitor V o The device adopts a topology form of three-phase interleaved LLC-half-bridge-output rectification, can realize the conversion from three-phase alternating current to isolated high-voltage direct current through the control of switch tubes (Q13-Q18) and the rectification of rectifier diodes (D13-D18), and simultaneously provides data support for current balance control, supports three-stage control of frequency modulation, phase shift, and duty ratio adjustment.

[0105] The three-stage control of duty ratio adjustment, phase shift, and frequency modulation disclosed in Embodiment One of the present application also has a current balance closed-loop feedback (current monitoring is performed first, then PID correction is performed, then parameters are adjusted through Gv table lookup, and finally PWM driving is updated), and a gain parameter fitting method, which is not only suitable for three-phase LLC devices Figure 10 , but also suitable for three-phase LLC devices Figure 11 and Figure 12 . The gain parameter fitting method is to collect data in the range of input voltage 380V±20% and load rate 10% to 100% under an open-loop state, and then fit out the frequency curve in the frequency modulation stage, the phase difference-duty ratio curve in the phase shift stage, and the duty ratio curve in the duty ratio adjustment stage. Although the switch tube labels and some details of these circuits are different, the core topologies are all three-phase interleaved LLC resonance circuits plus half-bridge arms, have a hardware basis for realizing three-stage control, and can complete electric energy conversion and gain adjustment through the cooperative work of control modules.

[0106] It should be noted that: similar labels and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings, and in addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0107] Finally, it should be noted that the above-described embodiments are merely specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit the present application, and the protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some technical features therein, within the technical scope disclosed by the present application, and these modifications, changes or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application. All should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A loop control method for a three-phase LLC device applied to a high-voltage DC system in a data center, characterized in that, Applied to three-phase LLC devices; used for the conversion of three-phase AC power to isolated high-voltage DC power in data center high-voltage DC systems; the method includes the following steps: S1: Acquire the output voltage and output current signals of the three-phase LLC device; S2: Input the output voltage signal and output current signal into the PID control unit, and the PID control unit calculates the current output gain Gv of the device; S3: Input the current output gain Gv into the Gv gain lookup table unit, which will match the corresponding control stage and output the corresponding control parameters. S4: The PWM generation unit generates PWM drive signals according to the control parameters to control the switching transistors of the three bridge arms to turn on or off.

2. The loop control method for a three-phase LLC device applied to a data center high-voltage DC system according to claim 1, characterized in that, In step S2, the PID control unit calculates the output gain Gv in the following way: The first adjustment amount is calculated by comparing the output voltage value of the acquisition device with the output voltage command value. The second adjustment value is calculated by comparing the output current value of the acquisition device with the maximum allowable output current value. The smaller of the first and second adjustment values ​​is taken as the output gain Gv.

3. The loop control method for a three-phase LLC device applied to a data center high-voltage DC system according to claim 1, characterized in that, When the Gv gain lookup table unit matches to the frequency modulation stage, the specific control process in step S4 includes: S411: The PWM generation unit generates PWM drive signals to control the three bridge arms with a phase misalignment angle of 120° based on the frequency signal; S412: The PWM drive signal controls the duty cycle of all upper bridge arm switches Q1, Q3, and Q5 to be fixed at 50%, and the duty cycle of all lower bridge arm switches Q2, Q4, and Q6 to be fixed at 50%, and the lower bridge arm switches and the upper bridge arm switches are complementary in conduction. S413: The Gv gain lookup table unit adjusts the frequency signal according to the change in the Gv value; S414: The PWM generation unit updates the drive signal based on the adjusted frequency signal.

4. The loop control method for a three-phase LLC device applied to a data center high-voltage DC system according to claim 1, characterized in that, When the Gv gain lookup table unit matches to the phase shift stage, the specific control process in step S4 includes: S421: The PWM generation unit generates a PWM drive signal that controls the LLC to operate at a fixed frequency and the dead time of the upper and lower bridge arm switches based on the phase difference signal and the duty cycle adjustment signal. S422: The PWM drive signal controls the drive phase angle of the first bridge arm Q1 / Q2, the second bridge arm Q3 / Q4 and the third bridge arm Q5 / Q6. The phase angle is continuously and smoothly adjusted in segments according to the fitting curve in the Gv gain lookup table unit, gradually adjusting from 120° to 180°. S423: The phase angle adjustment step size is output by the Gv gain lookup table unit, and at the same time, the duty cycle adjustment values ​​of Q1, Q3, and Q5 are output by the Gv gain lookup table unit according to the fitted curve, and the duty cycle of Q1, Q3, and Q5 is reduced synchronously.

5. The loop control method for a three-phase LLC device applied to a data center high-voltage DC system according to claim 1, characterized in that, When the Gv gain lookup table unit matches to the duty cycle adjustment stage, the specific control process in step S4 includes: S431: The PWM generation unit generates a PWM drive signal that controls the LLC to operate at a fixed frequency and has fixed phase angles for the three bridge arms, based on the duty cycle signal. S432: The phase angles of the three bridge arms satisfy that the first and second bridge arms are in phase and are 180° out of phase with the third bridge arm, and the dead zone of the upper and lower bridge arm switches is fixed. S433: The PWM drive signal only adjusts the duty cycle of the upper bridge arm switching transistors Q1, Q3, and Q5.

6. The loop control method for a three-phase LLC device applied to a data center high-voltage DC system according to claim 1, characterized in that, The fitting process of the control parameters in each stage within the Gv gain lookup table unit includes: S51: In open-loop mode, set at least two different fixed load conditions to cover low load, medium load and high load ranges, and test at different input voltage points; S52: Collects input voltage, output voltage, and resonant cavity current data of the three bridge arms under different operating conditions; S53: Select the optimal control parameters for each Gv value based on efficiency and current balance objectives, including frequency, phase difference, and duty cycle; S54: Perform linear or appropriate fitting on the selected parameter points to obtain the control curves under various fixed load conditions; S55: Integrate the curves obtained under the at least two different fixed load conditions to form a control curve that covers the entire load range and is actually used; or, the control curve can also be obtained directly through theoretical calculation. S56: Store the final control curve in the Gv gain lookup table unit.

7. A three-phase LLC device for use in a data center high-voltage DC system, characterized in that, The loop control method for a three-phase LLC device applied to a data center high-voltage DC system according to any one of claims 1 to 6 converts the three-phase AC power from the grid side into an isolated high-voltage DC output. The device includes a three-phase interleaved LLC resonant circuit and a control module; The three-phase interleaved LLC resonant circuit includes three bridge arms. Each bridge arm includes an upper bridge arm switch, a lower bridge arm switch, and a freewheeling diode connected in parallel with the upper bridge arm switch. Specifically, the first bridge arm includes an upper bridge arm switch Q1, a lower bridge arm switch Q2, and a freewheeling diode D1; the second bridge arm includes an upper bridge arm switch Q3, a lower bridge arm switch Q4, and a freewheeling diode D3; and the third bridge arm includes an upper bridge arm switch Q5, a lower bridge arm switch Q6, and a freewheeling diode D5. The control module includes a PID control unit, a Gv gain lookup table unit, a PWM generation unit, a voltage monitoring unit, and a current monitoring unit. The input terminal of the voltage monitoring unit is connected to the output terminal of the device, and the output terminal is connected to the input terminal of the PID control unit, which is used to collect the output voltage signal and transmit it to the PID control unit. The output terminal of the PID control unit is connected to the input terminal of the Gv gain lookup table unit, and is configured to receive the output voltage signal and the output current signal, and calculate the output gain Gv based only on the two signals. The output of the Gv gain lookup table unit is connected to the input of the PWM generation unit. It is configured to match the corresponding control stage based on the Gv value output by the PID control unit and output the corresponding control parameters. The control parameter curves in the Gv gain lookup table unit are established in the following way: In the open-loop state, at least two different fixed load conditions are set to cover low load, medium load, and high load ranges. By changing the input voltage and monitoring the output voltage and three sets of bridge arm currents, the optimal control parameters, including frequency, phase difference, and duty cycle, are selected and fitted. The curves under the at least two different fixed load conditions are then integrated to obtain the curves; or they can be obtained through theoretical calculations. The output of the PWM generation unit is connected to the control terminals of the three bridge arm switches, and is used to generate PWM drive signals according to the control parameters of the Gv gain lookup table unit.

8. The three-phase LLC device for use in a data center high-voltage DC system according to claim 7, characterized in that, When the Gv gain lookup table unit matches to the frequency modulation stage: The drive signal generated by the PWM generation unit controls the three bridge arms to be out of phase by 120°. The drive signal controls the duty cycle of all upper bridge arm switches Q1, Q3, and Q5 to be fixed at 50%, and the duty cycle of all lower bridge arm switches Q2, Q4, and Q6 to be fixed at 50%, with the lower bridge arm switches and upper bridge arm switches conducting in a complementary manner. The Gv gain lookup table unit adjusts the frequency signal based on the Gv value to change the LLC operating frequency.

9. The three-phase LLC device for use in a data center high-voltage DC system according to claim 7, characterized in that, When the Gv gain lookup table unit matches to the phase-shifting stage: The drive signal generated by the PWM generation unit controls the LLC operating frequency to be fixed. The dead zone of the upper and lower bridge arm switching transistors is fixed by the drive signal control. The phase angle adjustment step size from 120° to 180° is output by the Gv gain lookup table unit; The duty cycle adjustment values ​​of the upper bridge arm switches Q1 and Q3 are output by the Gv gain lookup table unit based on the fitted curve.

10. The three-phase LLC device for use in a data center high-voltage DC system according to claim 7, characterized in that, When the Gv gain lookup table unit matches to the duty cycle adjustment stage: The drive signal generated by the PWM generation unit controls the LLC to have a fixed operating frequency and the phase angles of the three bridge arms to be fixed. The phase angles of the three bridge arms satisfy that the first and second bridge arms are in phase and 180° out of phase with the third bridge arm, and the dead zone of the upper and lower bridge arm switching transistors is fixed. The drive signal only adjusts the duty cycle of the upper bridge arm switching transistors Q1, Q3, and Q5.

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