Multi-phase LLC resonant converter with shared auxiliary capacitor across-phase soft switching and control method thereof

Abstract

The application discloses a multi-phase LLC resonant converter with shared auxiliary capacitor cross-phase soft switching and a control method thereof. Each LLC power phase is input in parallel and output in parallel, and has a fixed resonant capacitor. Less than the number of phases of shared auxiliary capacitor is connected in parallel with the target fixed resonant capacitor through a bidirectional blocking phase selection switch. In cold start, when the excitation is not applied to the original side and the voltage difference between the shared auxiliary capacitor and the target fixed resonant capacitor is within the initial threshold value, the target phase selection switch is turned on first, and then the power conversion is started; when there is residual voltage and the initial voltage difference exceeds the threshold value, discharging, current limiting pre-charging or controlled voltage conditioning are performed. In operation, cross-phase transfer is completed according to low current disconnection, full off-state retention and voltage matching access, and multi-phase simultaneous access is prohibited through interlocking. The scheme can be used for multi-phase current sharing, parameter compensation and gain adjustment, and can reduce the charge equalization impact and inter-phase circulating current in the process of first access of the shared auxiliary capacitor and cross-phase transfer.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to a multiphase LLC resonant converter with shared auxiliary capacitor and phase-to-phase soft switching, and its control method. Background Technology

[0002] With the increasing demands for power density, conversion efficiency, and modularity in server power supplies, communication power supplies, energy storage systems, new energy vehicle charging power supplies, and industrial DC power supply systems, isolated DC-DC converters need to balance high efficiency, low switching losses, and low output ripple over a wide load range. For applications where a single power conversion module cannot meet high power or thermal design requirements, multiple LLC resonant power phases can be connected in parallel at both the input and output ends, allowing each power phase to share the output power and reducing output ripple through interleaved driving. This type of multiphase parallel system also facilitates modular expansion, light-load phase switching, and fault derating operation, but its stable operation depends on a reasonable current distribution among the power phases.

[0003] LLC resonant converters utilize resonant inductors, resonant capacitors, and transformer magnetizing inductance to form a resonant network. Within a suitable operating range, this enables zero-voltage switching on the primary side and reduces secondary-side rectification losses. To improve output power, modularity, and fault redundancy, the inputs and outputs of two or more LLC power phases are typically connected in parallel, and interleaved driving is used to reduce current ripple at the common output.

[0004] When there are manufacturing deviations in the resonant inductance, fixed resonant capacitor, magnetizing inductance, transformer turns ratio, switching delay, and parasitic parameters of each power phase, even if each power phase uses the same main switching frequency, there will be inconsistencies in resonant impedance, gain, and soft switching margin, resulting in uneven current distribution between phases, local overheating, and reduced device lifespan.

[0005] One existing technology involves setting up auxiliary capacitors and switches next to or within the resonant circuit of a fixed resonant capacitor in each power phase, forming a controllable auxiliary capacitor branch. By changing the connection state or connection range of the auxiliary branch switch, the resonant frequency and gain characteristics of the corresponding power phase can be altered, thereby compensating for parameter errors. However, when each phase is equipped with an independent auxiliary capacitor, bidirectional switch, and isolated drive, the number of components, detection channels, and cost increase with the number of phases.

[0006] If an adjustable capacitor is only installed on a fixed phase, this fixed adjustable phase may not always be the most advantageous adjustment target after changes in component deviation direction, load, or temperature, potentially requiring the pre-design of an asymmetric resonant cavity. Using a permanent common resonant capacitor would cause continuous coupling between different resonant networks, hindering phase cutoff, fault isolation, and independent control. Therefore, utilizing a shared auxiliary capacitor to select the service target based on the actual error direction has the potential to reduce the number of components and expand the compensation direction.

[0007] Switching between different power phases using a shared auxiliary capacitor introduces new engineering challenges. The body diode of a single power MOSFET cannot achieve bidirectional isolation during turn-off; even when using reverse-series power devices to form a bidirectional blocking switch, rapid charge redistribution and inrush current will still occur when the instantaneous voltages of the shared auxiliary capacitor and the target fixed resonant capacitor are not equal and are directly connected in parallel. If two phase-selective switches overlap in conduction, they will directly connect the resonant return nodes of different power phases, forming interphase differential-mode circulating current.

[0008] For a half-bridge LLC, the physical terminal voltage of the fixed resonant capacitor typically contains a DC bias close to half the DC bus voltage; it cannot be assumed that the fixed resonant capacitor necessarily passes through the initial voltage of the shared auxiliary capacitor every cycle. Without pre-charging or auxiliary conditioning, a natural voltage matching window for low-impact access may not be available for an extended period. Upon initial system power-up, both the shared auxiliary capacitor and the fixed resonant capacitor can be near zero voltage. Therefore, before applying excitation to the main bridge, the shared auxiliary capacitor can be connected in parallel with the pre-selected fixed resonant capacitor, and then the main bridge can be started, allowing both capacitors to jointly establish bias and AC voltage. If residual voltage exists during hot start or fault recovery, voltage detection and current limiting conditioning are still required.

[0009] Therefore, a new multiphase LLC resonant converter and control method are needed, which can selectively serve any power phase by a shared auxiliary capacitor according to the phase deviation direction, and can limit inrush current, prevent phase shoot-through, maintain current sharing function, and maintain the main LLC degradeable operation during startup and phase switching. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a multiphase LLC resonant converter with shared auxiliary capacitors and a control method thereof, which overcomes the shortcomings of the prior art and achieves multiphase selectable adjustment capability by using a shared auxiliary capacitor bank with fewer than the number of power phases.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a multiphase LLC resonant converter with shared auxiliary capacitor and cross-phase soft switching, comprising: At least two LLC power phases, the input terminals of each LLC power phase are connected in parallel to a DC input terminal, and the output terminals of each LLC power phase are rectified and then connected in parallel to a DC output terminal; The LLC power phase includes a primary-side power conversion unit for generating a periodic alternating excitation voltage, a resonant inductor, a fixed resonant capacitor, an isolation transformer with a magnetizing inductance, and a rectifier unit; one end of the fixed resonant capacitor is connected to a common reference point, and one end of the resonant inductor is connected between two series-connected switches in the primary-side power conversion unit; the other end of the resonant inductor and the other end of the fixed resonant capacitor are respectively connected to the two input terminals of the primary side of the isolation transformer, and the secondary side of the isolation transformer is connected to the rectifier unit; A shared auxiliary capacitor is connected at one end to the common reference point and at the other end to the connection point of two phase-selection semiconductor switch branches; one end of each of the two phase-selection semiconductor switch branches is connected between the corresponding LLC power phase resonant capacitor and the isolation transformer.

[0012] The phase-selection semiconductor switch branch includes two power MOSFETs connected in reverse series, with the body diodes of the two power MOSFETs having opposite directions.

[0013] The state-dependent series resonant frequency of the k-th LLC power phase Represented as: ;in, Let f be the state-dependent resonant capacitance of the k-th LLC power phase. , The fixed resonant capacitor for the k-th LLC power phase is... To share the auxiliary capacitor, Let be the resonant inductance of the k-th LLC power phase.

[0014] As an inventive concept, the present invention also provides a control method for the above-mentioned multiphase LLC resonant converter with shared auxiliary capacitor phase-to-phase soft switching, comprising: During the cold start phase, when the primary-side power conversion unit has not yet applied periodic alternating excitation, the initial voltage difference between the shared auxiliary capacitor and the fixed resonant capacitor of the pre-selected LLC power phase is detected. When the initial voltage difference is not greater than the initial access voltage threshold, the phase selection semiconductor switch corresponding to the pre-selected LLC power phase is first turned on. After the phase selection semiconductor switch is turned on, the primary-side power conversion unit of at least the pre-selected LLC power phase is started, so that the shared auxiliary capacitor and the fixed resonant capacitor of the pre-selected LLC power phase jointly establish DC bias and AC resonant voltage from the initial start-up state. When the system is in a state of hot restart, fault recovery, DC bus energized, reverse power supply on the output side, or residual charge, and the initial voltage difference between the shared auxiliary capacitor and the pre-selected LLC power phase fixed resonant capacitor is greater than the initial access voltage threshold, all phase selection semiconductor switches are kept off, and the voltage of the shared auxiliary capacitor is adjusted by waiting for natural discharge, controlled discharge, current-limited pre-charge, or controlled charge and discharge. After the initial voltage difference enters the allowable range, the phase selection semiconductor switches are pre-turned on and the primary-side power conversion unit is started.

[0015] The method of the present invention further includes: During normal operation, when it is determined that the shared auxiliary capacitor needs to be transferred from the source LLC power phase to the target power phase, the system first waits for the shared auxiliary capacitor branch current of the source LLC power phase to enter the preset shutdown current window and then turns off the phase selection semiconductor switch corresponding to the source LLC power phase. Subsequently, all phase selection semiconductor switches are kept off for at least one non-overlapping time to isolate the shared auxiliary capacitor from each LLC power phase. The terminal voltage of the shared auxiliary capacitor is detected or determined within the holding interval and is determined as the holding voltage. Then, the physical terminal voltage of the fixed resonant capacitor of the target LLC power phase is detected or predicted. When the difference between the holding voltage of the shared auxiliary capacitor and the voltage of the fixed resonant capacitor of the target LLC power phase enters the allowable access voltage window, the phase selection semiconductor switch corresponding to the target LLC power phase is turned on.

[0016] The formula for determining whether the shared auxiliary capacitor branch current of the source LLC power phase enters the preset shutdown current window is: ;in, To share the auxiliary capacitor branch current, The threshold for allowable shutdown current.

[0017] The method of the present invention further includes: when the holding voltage of the shared auxiliary capacitor is outside the voltage range that the fixed resonant capacitor of the target LLC power phase can reach within a preset prediction window, or when no voltage matching time that meets the requirements occurs within a preset waiting time, at least one of the following processes is performed: reselecting the disconnection time of the source LLC power phase, adjusting the voltage of the shared auxiliary capacitor, restoring the connection of the source LLC power phase, selecting other candidate LLC power phases, waiting for the change of operating state, or canceling the current cross-phase switching; after the shared auxiliary capacitor is connected to the target LLC power phase, it is maintained for multiple main switching cycles in the target LLC power phase, and the average current or average power of the target LLC power phase is adjusted by the whole cycle connection ratio, multi-cycle pulse density, or conduction interval within the cycle.

[0018] Compared with the prior art, the beneficial effects of this invention are as follows: This invention uses a shared auxiliary capacitor bank with fewer power phases to achieve multi-phase selectable regulation capability; the shared auxiliary capacitors can serve different power phases, thereby reducing the number of high-voltage auxiliary capacitors and simplifying the auxiliary modulation branch and its isolation power supply and protection circuits; the parallel connection before excitation during cold start can reduce or avoid the impact caused by the initial bias difference; the bidirectional blocking phase selection switch can isolate the shared auxiliary capacitors from each power phase within a preset holding range and keep the voltage of the shared auxiliary capacitors approximately constant; the low current disconnection of the source phase and the voltage matching connection of the target phase can reduce parasitic overvoltage and charge balance peak; when the auxiliary modulation network is turned off or its fault can be isolated and the fixed resonant branch of each power phase remains normal, the non-faulty power phases can still operate in normal LLC mode or derating mode. Attached Figure Description

[0019] Figure 1 A schematic diagram of a two-phase input parallel output parallel LLC and shared auxiliary capacitor topology; Figure 2 A schematic diagram of the fundamental equivalent circuit when a shared auxiliary capacitor is connected to the target phase; Figure 3 The connection state and operating mode of the shared auxiliary capacitor; Figure 4 A block diagram of the system control structure for sharing an auxiliary capacitor; Figure 5 Flowchart of the shared auxiliary capacitor control method; Figure 6 This is a schematic diagram of the cold start timing and residual voltage start-up criteria; Figure 7 This is a schematic diagram of the phase transition timing and natural matching window; Figure 8 This is a schematic diagram of a detection, decision-making, interlocking, and drive control system. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1As shown, this embodiment of the invention uses a two-phase parallel input and parallel output LLC resonant converter as an example. The converter includes a first LLC power phase, a second LLC power phase, a shared auxiliary capacitor, phase selection semiconductor switches corresponding to the two LLC power phases respectively, a detection unit, a controller, and a hardware interlock unit. The input terminals of the first LLC power phase and the second LLC power phase are connected in parallel to the DC input terminal, and their rectified output terminals are connected in parallel to the DC output terminal to jointly supply power to the load.

[0022] Each LLC power phase includes a primary-side power conversion unit, a resonant inductor, a fixed resonant capacitor, an isolation transformer with a magnetizing inductor, and a rectifier unit. The primary-side power conversion unit applies a periodic alternating excitation voltage to the corresponding resonant cavity. It can employ a half-bridge switching network, a full-bridge switching network, a three-level bridge switching network, or other power conversion structures capable of generating a periodic alternating excitation voltage. Preferably, each LLC power phase uses the same main switching frequency and is driven alternately according to a predetermined phase relationship, so that at least one major ripple component in the rectified output current of each phase is at least partially canceled out at the common output terminal.

[0023] In this embodiment, each power phase retains its own fixed resonant capacitor. When the shared auxiliary capacitor and its phase selection semiconductor switch are all turned off, each power phase still has a complete LLC resonant network and can therefore operate independently in the normal LLC operating mode. Thus, when the shared auxiliary capacitor modulation network is turned off or an isolated fault occurs, the non-faulty power phases can continue to operate, operate at reduced derating, or be disconnected according to a preset strategy.

[0024] For ease of explanation, the equipotential node connected to the first terminal of each fixed resonant capacitor is defined as the common reference node N, and the second terminal of the fixed resonant capacitor of the k-th power phase is defined as node x. k The first end of the shared auxiliary capacitor is connected to the common reference node N, and the second end of the shared auxiliary capacitor forms the shared selection node x. a The k-th phase selection semiconductor switch is connected to the shared selection node x. a and the corresponding node x k When the phase selection semiconductor switch of phase k is turned on, the shared auxiliary capacitor is connected in parallel with the fixed resonant capacitor of phase k; when the phase selection semiconductor switch is turned off, the shared auxiliary capacitor is isolated from the fixed resonant capacitor.

[0025] The common reference node N can be the negative terminal of the DC bus, the midpoint of the split bus, or other nodes that can maintain low impedance equipotential within the frequency range involved in the commutation of the shared auxiliary capacitor. In the half-bridge LLC implementation, the common reference node can be set as the negative terminal of the DC bus or a reference node connected to the common terminal of the fixed resonant capacitor. For the full-bridge or multi-level bridge implementation, the corresponding common reference node or equivalent selective connection network can be set according to the connection position of the fixed resonant capacitor in the resonant cavity, as long as the shared auxiliary capacitor can selectively form a parallel relationship with the fixed resonant capacitor of the target power phase.

[0026] The phase-selection semiconductor switch should have bidirectional blocking capability in the off state and bidirectional conduction capability in the on state. In one embodiment, each phase-selection semiconductor switch is composed of two power MOSFETs with opposite body diode orientations connected in reverse series. The two power MOSFETs can be connected in a common-source or common-drain configuration. In other embodiments, the phase-selection semiconductor switch can also use integrated power devices with bidirectional blocking capability. The power MOSFETs can be silicon MOSFETs, silicon carbide MOSFETs, gallium nitride MOSFETs, or other power semiconductor devices suitable for the corresponding switching frequency and voltage level.

[0027] The reverse series configuration prevents uncontrolled current paths from forming through the body diodes of the devices when the phase-selective semiconductor switches are turned off, ensuring bidirectional isolation of the shared auxiliary capacitor from each power phase during the off-state of all phase-selective semiconductor switches. Each power margin is determined without assuming that the two reverse-connected power devices must necessarily share the voltage equally.

[0028] like Figure 3 As shown, the shared auxiliary capacitor has at least an isolated state and multiple selective connection states. In the isolated state, all phase selection semiconductor switches are off, and the shared auxiliary capacitor is isolated from each power phase. In the first power phase connection state, only the phase selection semiconductor switch corresponding to the first power is on, and the shared auxiliary capacitor is connected in parallel with the fixed resonant capacitor of the first power phase. In the second power phase connection state, only the phase selection semiconductor switch corresponding to the second power is on, and the shared auxiliary capacitor is connected in parallel with the fixed resonant capacitor of the second power phase.

[0029] For an implementation including N LLC power phases, let s k s represents the connection state of the phase-selection semiconductor switch corresponding to the k-th power. k =1 indicates that the shared auxiliary capacitor is connected to the k-th power phase, s k =0 indicates that the shared auxiliary capacitor is not connected to the k-th power phase. The controller and hardware interlock unit jointly limit the connection of the same shared auxiliary capacitor to at most one LLC power phase at any given time, and its allowed state satisfies: (1) The aforementioned mutual exclusion condition is used to prevent the resonant nodes of two or more power phases from forming a low-impedance connection path through a shared auxiliary capacitor and phase-selection semiconductor switches. Since different power phases operating in an interleaved manner may have different instantaneous bridge arm voltages and resonant capacitor voltages, if two phase-selection semiconductor switches overlap in conduction, differential-mode circulating currents may form between different power phases. Therefore, the controller's software interlock, the driver-side logic interlock, and the independent hardware interlock jointly prohibit the simultaneous conduction of two phase-selection semiconductor switches, and establish a non-overlapping interval between different access states (break first, then turn on).

[0030] The duration of the non-overlapping interval is preferably not less than the sum of the drive propagation delay difference between the source power phase and the target power phase phase selection semiconductor switches, the power device turn-off delay, the gate voltage drop time, and a preset safety margin. During the non-overlapping interval, all phase selection semiconductor switches remain off. The hardware interlock unit can be implemented using mutually exclusive logic gates, programmable logic devices, drive enable latch circuits, or other circuits capable of independently blocking overlapping drive signals in the event of a controller malfunction.

[0031] When the shared auxiliary capacitor is continuously connected to the k-th power phase within an analysis interval, the capacitance of the k-th power phase participating in the main resonance is composed of the fixed resonant capacitor and the shared auxiliary capacitor. The state-dependent resonant capacitance of the k-th power phase is defined as: (2) In the formula, The fixed resonant capacitor for the k-th power phase is... For sharing auxiliary capacitors.

[0032] Under the approximation condition of neglecting the influence of the excitation branch on the series resonant frequency, the state-dependent series resonant frequency of the k-th power phase can be expressed as: (3) As can be seen from equations (2) and (3), after the shared auxiliary capacitor is continuously connected to the target power phase, the equivalent capacitance of the power phase participating in the resonance increases, and its series resonant frequency decreases relative to the unconnected state.

[0033] like Figure 2As shown, after the shared auxiliary capacitor is connected to the target power phase, the resonant current, transmission power, and rectified output current of that power phase are further altered by changing its resonant capacitance, resonant frequency, and input impedance. With the shared auxiliary capacitor connected to the target power phase, multiple main switching cycles can be maintained on that phase, and the average current or average power of the target power phase can be adjusted by the full-cycle connection ratio, multi-cycle pulse density, or conduction interval within a cycle. The direction of increase or decrease in phase current after connection is not fixed under all operating conditions, but depends on the position of the main switching frequency relative to the resonant frequency before and after connection, the load size, the ratio of excitation inductance to resonant inductance, the rectifier clamping state, and the direction of device parameter deviation. The controller can determine the adjustment direction and amount after connecting the shared auxiliary capacitor to each candidate power phase at different operating points through offline analysis, simulation calibration, prototype testing, table lookup, or online identification.

[0034] In one implementation, the shared auxiliary capacitor branch current is directly detected using a series sampling resistor, current transformer, Hall current sensor, or other current detection device. In another implementation, the shared auxiliary capacitor branch current can be estimated based on the resonant current of the corresponding power phase, the fixed resonant capacitor current, the phase-selection semiconductor switch state, and a pre-established current distribution model. Since the shared auxiliary capacitor and the fixed resonant capacitor may distribute branch currents according to their respective capacitances when connected in parallel, the phase-selection semiconductor switch of the source power phase preferably determines the turn-off time based on the detected or estimated value of the shared auxiliary capacitor branch current, rather than simply equating the zero-crossing of the main resonant current with the zero-crossing of the shared auxiliary capacitor branch current.

[0035] like Figure 5 and Figure 6 As shown, during the system cold start phase, the controller first determines the pre-selected power phase and detects the initial voltage difference between the shared auxiliary capacitor and the fixed resonant capacitor of the pre-selected power phase. The voltage of the fixed resonant capacitor and the voltage of the shared auxiliary capacitor can be obtained using an isolated differential sampling circuit, a voltage divider sampling circuit, or other voltage detection circuits that meet the insulation and bandwidth requirements.

[0036] When the primary power conversion unit has not yet been subjected to periodic alternating excitation, and the initial voltage difference between the shared auxiliary capacitor and the pre-selected power phase fixed resonant capacitor satisfies the following formula, parallel connection followed by excitation is permitted: (4) In the formula, The initial access voltage threshold, and These are the physical terminal voltages of the shared auxiliary capacitor and the pre-selected power phase fixed resonant capacitor, respectively.

[0037] When equation (4) is satisfied, the controller first turns on the phase selection semiconductor switch corresponding to the preselected power and waits for the isolation drive propagation, gate charging and channel establishment of the phase selection semiconductor switch to be completed. After a preset waiting time, the controller then causes the primary-side power conversion unit of at least the preselected power phase to start outputting periodic alternating excitation, so that the shared auxiliary capacitor and the fixed resonant capacitor of the preselected power phase jointly establish DC bias and AC resonant voltage from the initial startup state.

[0038] In a true cold start scenario, the shared auxiliary capacitor and each fixed resonant capacitor can be discharged before startup, causing their physical terminal voltages to approach zero. At this time, equation (4) can usually be satisfied naturally. Compared to connecting the zero-voltage shared auxiliary capacitor after the primary power conversion unit has been running and the fixed resonant capacitor has established a DC bias, connecting them in parallel before excitation can reduce the rapid charge redistribution caused by the different initial voltages of the two capacitors.

[0039] In a half-bridge LLC implementation where the common reference node is connected to the negative terminal of the DC bus, the steady-state physical terminal voltage of the fixed resonant capacitor typically contains both a DC bias component and a periodic AC component, with the DC bias possibly approaching half the DC bus voltage. For example, in a half-bridge implementation with a DC bus voltage of approximately 400V, the DC bias of the fixed resonant capacitor might be close to 200V. Whether the physical terminal voltage of the fixed resonant capacitor crosses zero depends on whether the amplitude of its AC component is sufficient to cross the DC bias; it cannot be assumed that it necessarily crosses zero in every cycle solely based on the AC coupling waveform or an ideal AC equivalent model.

[0040] For full-bridge or other bipolar excitation structures, the DC bias of the fixed resonant capacitor is determined by the primary-side excitation method, the resonant capacitor connection location, and the steady-state charge balance, and is not necessarily equal to half of the DC bus voltage. Therefore, the controller preferably directly detects the physical terminal voltages of the fixed resonant capacitor and the shared auxiliary capacitor, or uses a validated state estimation model to determine the actual voltage difference between them, rather than adopting a fixed bias assumption that is incompatible with the specific bridge structure.

[0041] The absence of a drive pulse from the primary-side power conversion unit does not equate to the shared auxiliary capacitor and fixed resonant capacitor being at zero voltage. When the system is in a hot restart, fault recovery, DC bus energized, reverse power supply on the output side, or residual charge remaining after the last shutdown, the controller should still detect the initial voltage difference described in equation (4). When the initial voltage difference exceeds the initial access voltage threshold, the controller keeps all phase selection semiconductor switches off and performs at least one of the following processes: waiting for natural discharge, controlled discharge, current-limited pre-charge, or controlled charge and discharge.

[0042] In one implementation of the voltage conditioning branch, the shared auxiliary capacitor is connected to a common reference node via a controlled switch and a current-limiting resistor. The controller controls the controlled switch to discharge the shared auxiliary capacitor with a limited current. In another implementation, the voltage conditioning branch includes a small commutator inductor and a bidirectional power switch for controlled charging or discharging of the shared auxiliary capacitor. A bidirectional buck-boost circuit or other voltage conditioning structures capable of limiting the conditioning current can also be used. The controller performs phase-selection semiconductor switch pre-conduction and primary-side power conversion unit startup only after confirming that the voltage difference between the shared auxiliary capacitor and the pre-selected fixed resonant capacitor has returned to the initial access voltage threshold.

[0043] The startup frequency trajectory of the primary-side power conversion unit is preferably determined based on the connection status of the shared auxiliary capacitor. When the shared auxiliary capacitor is already connected to the pre-selected power phase, startup can begin at a frequency higher than the resonant frequency corresponding to that connection status, and the main switching frequency or other modulation variables can be gradually adjusted to limit the startup current and maintain the required soft-switching conditions. In a two-phase implementation, the pre-selected power phase can be started first to establish output, followed by the startup of the other power phase; alternatively, both power phases can be started simultaneously, but current limiting and protection thresholds should be set separately for each phase based on the different resonant parameters that may exist during the startup phase.

[0044] After the system enters normal operation, the controller determines the degree of phase imbalance based on the output current, effective value of resonant current, input power, output power, or other physical quantities that characterize the phase-to-phase power distribution of each power phase, and determines the target power phase that the shared auxiliary capacitor should currently serve based on the pre-obtained adjustment direction. When the target power phase is different from the source power phase currently connected to the shared auxiliary capacitor, the controller proceeds according to... Figure 7 The phase transitions are performed in the order shown.

[0045] In the first stage of the phase transition, the controller waits for the current in the shared auxiliary capacitor branch of the source power phase to enter a preset low current window. When the current in the shared auxiliary capacitor branch satisfies the following equation, the controller issues a source phase selection semiconductor switch turn-off command: (5) In the formula, The allowable turn-off current threshold is determined based on the power device's turn-off capability, the commutation circuit's parasitic inductance, allowable overvoltage, allowable turn-off losses, and device temperature rise.

[0046] In one implementation, the maximum allowable voltage V after the phase-selective semiconductor switch is turned off is first determined based on the rated withstand voltage, permissible transient overvoltage, and design margin of the phase-selective semiconductor switch. a Let the voltage across the source-phase selection semiconductor switch before it is turned off be V. p The equivalent parasitic inductance of the commutation path is L.σ The equivalent capacitance that participates in absorbing turn-off energy is C. eq When the converter circuit is equipped with an absorption or clamping branch, the energy Ec that the absorption or clamping branch is allowed to absorb during a single turn-off process can be included in the turn-off energy margin. The allowable actual turn-off current can be determined according to the following formula: When there is no clamping or absorption branch, Ec can be set to 0. There are detection, calculation, isolation drive propagation, and device turn-off delays between the controller issuing the turn-off command and the phase-selection semiconductor switch actually turning off. Let the total delay be td, and the absolute value of the maximum rate of change of the current in the shared auxiliary capacitor branch during the delay period be S. max If the maximum error in current detection and estimation is ΔI, then the allowable turn-off current threshold preferably satisfies the following: Furthermore, the above calculation results are compared with the allowable turn-off current, safe operating area, and thermally permissible turn-off loss current specified in the phase-selection semiconductor switch datasheet. The smaller value is taken as the upper limit of the threshold design and multiplied by a safety factor K less than 1. I Therefore, we can conclude that: In the formula, I ov To determine the upper limit of current based on the allowable turn-off overvoltage, I SOA To determine the upper limit of current based on the safe operating area of ​​the phase-selective semiconductor switch, I oss This is the upper limit of the current determined based on allowable turn-off losses and temperature rise. The allowable turn-off current threshold can also be calibrated based on the above calculation results through circuit simulation or prototype testing to ensure that the peak voltage and turn-off losses after the source phase selection semiconductor switch is turned off are within the preset allowable range.

[0047] After the source phase selection semiconductor switch is turned off, the controller keeps all phase selection semiconductor switches off for at least a non-overlapping time, and a hardware interlock unit prevents the target phase selection semiconductor switch from turning on prematurely. This ensures bidirectional isolation between the shared auxiliary capacitor and each power phase within the isolation interval. The controller detects or determines the terminal voltage of the shared auxiliary capacitor before the target phase selection semiconductor switch turns on, and defines this terminal voltage as the holding voltage V. hold .

[0048] In the second stage of the phase transition, the controller detects or predicts the range of physical terminal voltages that the target power phase fixed resonant capacitor can reach within a preset prediction window. Let the minimum and maximum values ​​of this range be V0 and V1, respectively. min，target and V max，target The condition for the existence of a natural voltage matching window can be expressed as: (6) In the formula, V th The allowed access voltage difference threshold.

[0049] When equation (6) is satisfied, the controller continues to detect or predict the voltage of the fixed resonant capacitor of the target power phase within the prediction window, and issues a target phase selection semiconductor switch turn-on command when the following equation is satisfied: (7) Furthermore, the conduction of the target phase selection semiconductor switch can simultaneously satisfy the target power phase resonant current, the predicted auxiliary branch current, the main switch soft switching margin, and the device voltage and current stress within the allowable range.

[0050] The voltage matching time of the target power phase fixed resonant capacitor can be directly detected by a real-time comparator, or it can be predicted by a digital controller based on the sampled value of the previous cycle, the main switching frequency, phase, load state, and resonance model. In one embodiment, the controller synchronously samples the fixed resonant capacitor voltage in each main switching cycle and predicts the time when it will enter the allowable voltage window described in equation (7) next based on the sampling sequence. The advance or delay of the actual turn-on command can be compensated based on the sampling delay, calculation delay, isolation drive propagation delay, and power device turn-on delay.

[0051] When equation (6) is not satisfied, it indicates that the target power phase fixed resonant capacitor cannot naturally reach the holding voltage of the shared auxiliary capacitor within the current prediction window. In this case, even if the waiting time is extended, it may not be possible to obtain a low voltage difference access time. Instead of forcibly turning on the target phase selection semiconductor switch under a large voltage difference condition, the controller performs at least one of the following processes: reselecting the turn-off time of the source phase selection semiconductor switch to change the holding voltage; adjusting the voltage of the shared auxiliary capacitor through the voltage conditioning branch; reconnecting the source power phase; selecting other candidate target power phases; waiting for the system operating point to change and then re-judging; or canceling this cross-phase transfer.

[0052] When two capacitors with different initial voltages are connected in parallel, rapid charge exchange will occur. Let ΔV be the voltage difference between the shared auxiliary capacitor and the target power fixed resonant capacitor before connection. The series equivalent capacitance of the two capacitors during differential-mode commutation is: (8) When the equivalent inductance of the commutation circuit is L σ When the damping is relatively small, the peak value of the initial oscillation current can be approximated as: (9) Equation (9) shows that the current surge when the shared auxiliary capacitor is connected to the target power phase is directly related to the voltage difference before connection. Therefore, the bidirectional blocking phase selection semiconductor switch is mainly used for turn-off isolation and floating hold, and cannot eliminate the voltage mismatch surge at the moment of turn-on on on. The allowable connection voltage difference threshold V th The value can be determined based on the allowable peak current of the auxiliary branch, the capacitance of the two capacitors, the parasitic inductance of the commutation path, and the safety factor. In actual design, voltage sampling error, comparator error, control and drive propagation delay, parasitic parameter uncertainty, safe operating area of ​​power devices, and temperature rise margin should also be considered.

[0053] After the target phase selection semiconductor switch is turned on, the shared auxiliary capacitor preferably remains in the target power phase for at least a preset number of main switching cycles to avoid frequent phase switching due to instantaneous fluctuations in current sharing error. The controller can set the target phase entry threshold, exit threshold, minimum hold time, and switching hysteresis. When the phase imbalance exceeds the entry threshold, the target power phase can be redefined; when the phase imbalance is below the exit threshold, the current connection state is maintained or the shared auxiliary capacitor is isolated.

[0054] In one current sharing control implementation, the controller calculates the deviation between the output current of each power phase and the average output current of each phase, and selects the target power phase based on the expected current change direction of each candidate power phase after connecting the shared auxiliary capacitor. The selection of the target power phase can also comprehensively consider the branch loss of the shared auxiliary capacitor, the expected number of switching operations, the accessibility of the natural voltage matching window, the soft switching margin of the primary-side power switch, and the voltage and current stress of the resonant inductor, fixed resonant capacitor, shared auxiliary capacitor, and power devices.

[0055] When the single-cycle adjustment of the shared auxiliary capacitor on the target power phase is greater than the current-sharing adjustment required, a full-cycle proportional regulation can be used. Within a current-sharing control window that includes multiple main switching cycles, the shared auxiliary capacitor is connected to the target power phase during several complete main switching cycles, and remains isolated or in other preset states during the remaining cycles, thereby adjusting the average current or average power of the target power phase within the control window.

[0056] The full-cycle connection ratio describes the average effect of two or more discrete resonant states within the control time window, and does not mean that the shared auxiliary capacitor is linearly converted into a single physical capacitance according to the connection ratio. The controller can update the full-cycle connection ratio using proportional-integral control, lookup table control, model predictive control, adaptive control, or other closed-loop control methods, and limit the switching frequency of the auxiliary branch through the minimum continuous connection period and the minimum continuous disconnection period.

[0057] In another implementation, the shared auxiliary capacitor is connected to the target power phase according to a preset conduction interval within a single main switching cycle to form a switch-controlled capacitor modulation. The conduction interval within the cycle can be determined based on the target power phase resonant current, the fixed resonant capacitor voltage, and the required adjustment direction. Since the conduction mode within the cycle corresponds to a piecewise time-varying resonant network, its fundamental equivalent capacitance is usually related to the conduction interval, connection time, initial voltage, and load state. Therefore, the conduction ratio of the auxiliary switch is not simply equated to a linear combination of the fixed resonant capacitor and the shared auxiliary capacitor.

[0058] The shared auxiliary capacitor does not need to be transferred from one power phase to another in each main switching cycle. Preferably, the shared auxiliary capacitor remains on the same target power phase for multiple main switching cycles, and after the current sharing control window ends or the phase imbalance direction stabilizes, the phase transfer is performed in the order of source phase low current turn-off, full turn-off holding, and target phase voltage matching connection. This reduces the switching losses of the phase-selective semiconductor switch and reduces the control disturbances caused by frequent switching of the shared auxiliary capacitor between different power phases.

[0059] In one target phase prediction and selection implementation, the controller predicts the current deviation of each phase, auxiliary branch loss, main switch soft-switching margin, and device stress after the shared auxiliary capacitor is connected for each candidate power phase that meets the safe switching conditions, and selects the target power phase whose comprehensive performance meets the preset conditions. The prediction can be based on a fundamental equivalent model, a segmented state model, an offline calibration table, online parameter identification results, or a combination of the above methods. This invention does not limit the specific algorithms used for target phase selection and current sharing control.

[0060] like Figure 4 and Figure 8 As shown, the detection unit may include at least one of the following: input current detection unit for each power phase, resonant current detection unit, rectified output current detection unit, fixed resonant capacitor voltage detection unit, shared auxiliary capacitor voltage detection unit, shared auxiliary capacitor branch current detection unit, output voltage detection unit, and primary-side power switch status detection unit. Based on the detection results, the controller performs startup status identification, phase-to-phase imbalance calculation, target power phase selection, low-current turn-off time determination, voltage matching time determination, and fault handling.

[0061] The controller may be composed of a microcontroller, a digital signal processor, a field-programmable gate array, a programmable logic device, or a combination thereof. In one embodiment, the controller includes a processor and a memory connected to the processor. The memory stores a control program, which, when executed by the processor, performs initial voltage difference judgment, parallel connection before excitation, source phase low current turn-off, full turn-off maintenance, target phase voltage matching connection, current sharing control, and protection processing.

[0062] The phase selection semiconductor switch control signals output by the controller can undergo software interlocking and programmable logic interlocking before entering the isolation drive unit. The enable terminal of the isolation drive unit can also be controlled by independent hardware interlocking and fast overcurrent protection circuitry. When any two phase selection semiconductor switch control signals are simultaneously active, the hardware interlocking unit preferably shuts down all phase selection semiconductor switch drives and sends an interlock fault signal back to the controller.

[0063] When a shared auxiliary capacitor branch overcurrent occurs, a phase selection semiconductor switch drive malfunction occurs, a voltage matching wait timeout occurs, a shared auxiliary capacitor overvoltage occurs, a fixed resonant capacitor overvoltage occurs, the resonant current exceeds the allowable value, or any power phase fails, the controller turns off all phase selection semiconductor switches and isolates the shared auxiliary capacitor from each power phase. For auxiliary modulation network faults that can be isolated, each power phase continues to operate in normal LLC mode relying on its own fixed resonant capacitor; for a single power phase fault, the faulty power phase can be disconnected, and the remaining power phases can operate at a reduced derating.

[0064] This invention is not limited to Figure 1 The diagram shows two LLC power phases. For a system with N LLC power phases, one set of shared auxiliary capacitors can be used to serve all N power phases, or M sets of shared auxiliary capacitors can be used to serve predetermined subsets of power phases, where M is less than N. Each set of shared auxiliary capacitors can include one capacitor or multiple capacitors connected in series or parallel. Each set of shared auxiliary capacitors is equipped with a corresponding phase selection semiconductor switch and intra-set interlocking logic.

[0065] When multiple sets of shared auxiliary capacitors are set, each set should satisfy the selective connection constraint described in equation (1). Inter-set coordination interlocks can also be set between different sets of shared auxiliary capacitors to prevent two sets of shared auxiliary capacitors from being connected to the same power phase resonant node simultaneously under unacceptable circumstances, or forming unexpected current paths through different power phases. Different sets of shared auxiliary capacitors can have the same or different capacitances, and can be assigned service objects according to power phase grouping, adjustment range, or redundancy requirements.

[0066] The rectifier units for each power phase can employ diode full-bridge rectification, center-tapped rectification, synchronous rectification, or other rectifier structures suitable for LLC resonant converters. Each power phase can use the same transformer turns ratio and resonant parameters, or, within permissible limits, parameters with manufacturing deviations or design differences. This invention compensates for phase-to-phase current and power imbalances caused by manufacturing deviations, temperature variations, aging, or load changes by selecting the service targets of the shared auxiliary capacitor and their connection status.

[0067] Without changing the basic connection relationship where the shared auxiliary capacitor is connected in parallel with multiple power phase fixed resonant capacitors via a bidirectional blocking phase selection semiconductor switch, the device type, driving method, voltage and current detection method, voltage conditioning method, target power phase selection method, and access proportional modulation method of the phase selection semiconductor switch can all be adjusted according to the actual voltage level, power level, and control platform.

[0068] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0069] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A multiphase LLC resonant converter with shared auxiliary capacitor and phase-to-phase soft switching, characterized in that, include: At least two LLC power phases, the input terminals of each LLC power phase are connected in parallel to a DC input terminal, and the output terminals of each LLC power phase are rectified and then connected in parallel to a DC output terminal; The LLC power phase includes a primary-side power conversion unit for generating a periodic alternating excitation voltage, a resonant inductor, a fixed resonant capacitor, an isolation transformer with a magnetizing inductance, and a rectifier unit; one end of the fixed resonant capacitor is connected to a common reference point, and one end of the resonant inductor is connected between two series-connected switches in the primary-side power conversion unit; the other end of the resonant inductor and the other end of the fixed resonant capacitor are respectively connected to the two input terminals of the primary side of the isolation transformer, and the secondary side of the isolation transformer is connected to the rectifier unit; A shared auxiliary capacitor is connected at one end to the common reference point and at the other end to the connection point of two phase-selection semiconductor switch branches; one end of each of the two phase-selection semiconductor switch branches is connected between the corresponding LLC power phase resonant capacitor and the isolation transformer.

2. The multiphase LLC resonant converter with shared auxiliary capacitor phase-to-phase soft switching according to claim 1, characterized in that, The phase-selection semiconductor switch branch includes two power MOSFETs connected in reverse series, with the body diodes of the two power MOSFETs having opposite directions.

3. The multiphase LLC resonant converter with shared auxiliary capacitor phase-to-phase soft switching according to claim 1, characterized in that, The state-dependent series resonant frequency of the k-th LLC power phase Represented as: ;in, Let f be the state-dependent resonant capacitance of the k-th LLC power phase. , The fixed resonant capacitor for the k-th LLC power phase is... To share the auxiliary capacitor, Let be the resonant inductance of the k-th LLC power phase.

4. A control method for a multiphase LLC resonant converter with shared auxiliary capacitor phase-to-phase soft switching as described in claim 1 or 2, characterized in that, include: During the cold start phase, when the primary-side power conversion unit has not yet applied periodic alternating excitation, the initial voltage difference between the shared auxiliary capacitor and the fixed resonant capacitor of the pre-selected LLC power phase is detected. When the initial voltage difference is not greater than the initial access voltage threshold, the phase selection semiconductor switch corresponding to the pre-selected LLC power phase is first turned on. After the phase selection semiconductor switch is turned on, the primary-side power conversion unit of at least the pre-selected LLC power phase is started, so that the shared auxiliary capacitor and the fixed resonant capacitor of the pre-selected LLC power phase jointly establish DC bias and AC resonant voltage from the initial start-up state. When the system is in a state of hot restart, fault recovery, DC bus energized, reverse power supply on the output side, or residual charge, and the initial voltage difference between the shared auxiliary capacitor and the pre-selected LLC power phase fixed resonant capacitor is greater than the initial access voltage threshold, all phase selection semiconductor switches are kept off, and the voltage of the shared auxiliary capacitor is adjusted by waiting for natural discharge, controlled discharge, current-limited pre-charge, or controlled charge and discharge. After the initial voltage difference enters the allowable range, the phase selection semiconductor switches are pre-turned on and the primary-side power conversion unit is started.

5. The method according to claim 3, characterized in that, Also includes: During normal operation, when it is determined that the shared auxiliary capacitor needs to be transferred from the source LLC power phase to the target power phase, the system first waits for the shared auxiliary capacitor branch current of the source LLC power phase to enter the preset shutdown current window and then turns off the phase selection semiconductor switch corresponding to the source LLC power phase. Subsequently, all phase selection semiconductor switches are kept off for at least one non-overlapping time to isolate the shared auxiliary capacitor from each LLC power phase. The terminal voltage of the shared auxiliary capacitor is detected or determined within the holding interval and is determined as the holding voltage. Then, the physical terminal voltage of the fixed resonant capacitor of the target LLC power phase is determined. When the difference between the holding voltage of the shared auxiliary capacitor and the voltage of the fixed resonant capacitor of the target LLC power phase enters the allowable access voltage window, the phase selection semiconductor switch corresponding to the target LLC power phase is turned on.

6. The method according to claim 5, characterized in that, The formula for determining whether the shared auxiliary capacitor branch current of the source LLC power phase enters the preset shutdown current window is: ;in, To share the auxiliary capacitor branch current, The threshold for allowable shutdown current.

7. The method according to claim 3, characterized in that, Also includes: When the holding voltage of the shared auxiliary capacitor is outside the voltage range that the fixed resonant capacitor of the target LLC power phase can reach within the preset prediction window, or when no voltage matching moment that meets the requirements occurs within the preset waiting time, at least one of the following processes is performed: reselecting the disconnection time of the source LLC power phase, adjusting the voltage of the shared auxiliary capacitor, restoring the connection of the source LLC power phase, selecting other candidate LLC power phases, waiting for the change in operating state, or canceling this cross-phase switching. After the shared auxiliary capacitor is connected to the target LLC power phase, it is maintained for multiple main switching cycles in the target LLC power phase, and the average current or average power of the target LLC power phase is adjusted by the whole cycle connection ratio, multi-cycle pulse density, or conduction interval within the cycle.

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