WO2019023996A1 - 一种llc谐振直流变换器及其控制方法和系统 - Google Patents

一种llc谐振直流变换器及其控制方法和系统 Download PDF

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Publication number
WO2019023996A1
WO2019023996A1 PCT/CN2017/095647 CN2017095647W WO2019023996A1 WO 2019023996 A1 WO2019023996 A1 WO 2019023996A1 CN 2017095647 W CN2017095647 W CN 2017095647W WO 2019023996 A1 WO2019023996 A1 WO 2019023996A1
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Prior art keywords
llc resonant
dead time
current value
current
switch
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PCT/CN2017/095647
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English (en)
French (fr)
Inventor
戴国峰
程中原
郭冬寿
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深圳驿普乐氏科技有限公司
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Priority to PCT/CN2017/095647 priority Critical patent/WO2019023996A1/zh
Publication of WO2019023996A1 publication Critical patent/WO2019023996A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present invention relates to the field of DC converters, and in particular to an LLC resonant DC converter and a control method and system therefor.
  • the 10KW-20KW DC charging module has begun to spread.
  • DC/ The DC adopts three-level LLC.
  • the three-level LLC DC converter can reduce the voltage stress of the switch tube to half of the input DC bus (DC700V-850V).
  • the low-voltage device Under the high-voltage input, the low-voltage device is selected, and the LLC three-level resonance
  • the converter can realize ZVS (zero voltage switching) of the switching tube and ZCS (zero current switching) of the rectifier diode, improve conversion efficiency and reduce electromagnetic interference, but when the output voltage range is lower than the designed resonance point voltage, There is a relatively large loss when the switch is turned off, because the switch tube is hard-switched when turned off.
  • the invention mainly provides an LLC resonant DC converter and a control method and system thereof for reducing the switching loss of the bridge arm switch.
  • an embodiment of the present invention provides a method for controlling an LLC resonant DC converter, comprising the following steps:
  • the adjusting step increases or decreases the dead time according to the current of the LLC resonant cavity to reduce the switching loss of the bridge switch.
  • an embodiment of the present invention provides a control system for an LLC resonant DC converter, comprising:
  • a current sampling module for sampling the current of the LLC resonant cavity when the bridge arm switch is turned off
  • the control module is configured to increase or decrease the dead time according to the current of the LLC resonant cavity to reduce the switching loss of the bridge switch.
  • an embodiment of the present invention provides an LLC resonant DC converter comprising:
  • a current sampling module for sampling the current of the LLC resonant cavity when the bridge arm switch is turned off
  • the control module is configured to increase or decrease the dead time according to the current of the LLC resonant cavity to reduce the switching loss of the bridge switch.
  • the invention provides an LLC resonant DC converter and a control method and system thereof, wherein the method detects the current of the LLC resonant cavity when the bridge arm switch is turned off; and further increases or decreases according to the current of the LLC resonant cavity. Small dead time to reduce the switching loss of the bridge switch. By adjusting the dead time, the switching loss of the bridge arm switch is reduced, and the overall efficiency of the LLC resonant DC converter is improved.
  • FIG. 1 is a circuit diagram of an LLC resonant DC converter provided by the present invention
  • FIG. 2 is a circuit diagram of a DC output circuit, a switching bridge arm, and an LLC resonant cavity in an LLC resonant DC converter provided by the present invention
  • FIG. 3 is a waveform diagram of respective bridge arm switches, LLC resonator currents, and field currents in a conventional LLC resonant DC converter;
  • FIG. 4 is a waveform diagram of respective bridge arm switches, LLC resonant cavity currents and field currents in an embodiment of an LLC resonant DC converter according to the present invention
  • FIG. 5 is a waveform diagram of each bridge arm switch, LLC resonant cavity current and field current in another embodiment of the LLC resonant DC converter provided by the present invention
  • FIG. 6 is a flowchart of a method for controlling an LLC resonant DC converter provided by the present invention
  • FIG. 7 is a specific flowchart of an embodiment of a method for controlling an LLC resonant DC converter according to the present invention.
  • the present invention provides an LLC resonant DC converter comprising: a DC output circuit 10, a switching bridge arm 20, an LLC resonant network and power conversion circuit 30, a rectifier circuit 40, and a control system (circuit) 50.
  • the output end of the DC output circuit 10 is connected to the LLC resonant network and the power conversion circuit 30 through the switch bridge arm 20.
  • the output of the LLC resonant network and the power conversion circuit 30 is connected to the input end of the rectifier circuit 40; the control system (circuit) 50 is connected. LLC resonant network and power conversion circuit 30.
  • the DC output circuit 10 is configured to receive external DC power, and after filtering, output to the switch bridge arm 20 to provide power for the total conversion circuit.
  • the DC output circuit 10 includes a first capacitor C1' and a second capacitor C2'. One end of the first capacitor C1' is connected to the positive pole of the direct current, and the other end of the first capacitor C1' is connected to the negative pole of the direct current through the second capacitor C2', and the negative pole of the direct current is grounded.
  • the switch bridge arm 20 includes a plurality of bridge arm switches.
  • Each of the bridge arm switches may be composed of a single or a plurality of MOS tubes, a single or a plurality of IGBTs (Insulated Gate Bipolar Transistors), or a combination of MOS tubes and IGBTs.
  • the switch bridge arm 20 functions as a high frequency square wave generator for generating a high frequency square wave to change the direct current voltage into a high frequency square wave voltage.
  • the LLC resonant network and power conversion circuit 30 includes an LLC resonant cavity (LLC resonant circuit) and a power transformer.
  • LLC resonant circuit LLC resonant circuit
  • the switch bridge arm 20 is connected to the primary winding of the power transformer through an LLC resonant cavity, and the secondary winding of the power transformer is connected to the input end of the rectifier circuit 40.
  • the LLC resonant cavity includes a first inductor Lr, a second inductor Lm and a capacitor Cr, that is, a first inductor Lr, and the second inductor Lm and the capacitor Cr are connected in series to form a resonant circuit, and the resonant frequency thereof is
  • the LLC resonant cavity causes the current in the LLC resonant cavity to change in a sinusoidal manner when the power supply is a DC power supply. Since the current or voltage changes according to a sinusoidal law, there is a zero crossing. If the switching device (bridge arm switch) is turned on or off at this time, the loss generated is zero and the circuit is energized.
  • the second inductance Lm is the excitation inductance of the primary winding of the transformer, Ir is the resonant current in the circuit, Im is the excitation current, and the resistance Re is the equivalent load of the circuit.
  • the rectifying circuit 40 is configured to rectify the alternating current outputted from the secondary winding of the power transformer; and is composed of a common full bridge, full wave, half wave or other rectifying method and a filtering circuit.
  • the control system 50 is a master control of the input and output states of the entire DC converter, and controls the entire power transmission by controlling the respective bridge arm switches.
  • control system 50 includes a current sampling module 510 (specifically, a current sampling circuit) and a control module.
  • the current sampling circuit 510 is configured to sample the current of the LLC resonant cavity when the bridge arm switch is turned off.
  • the control module is configured to increase or decrease the dead time according to the current of the LLC resonant cavity to reduce the switching loss of the bridge switch.
  • the input end of the current sampling circuit 510 is connected to the LLC resonant cavity, the output end of the current sampling circuit 510 is connected to the input end of the control module, and the output end of the control module is connected to the switch bridge arm 20.
  • the invention reduces the switching loss of the bridge arm switch by adjusting the dead time, and improves the overall efficiency of the LLC resonant DC converter.
  • the LLC resonant DC converter is a three-level LLC resonant DC converter.
  • the switch bridge arm 20 includes a first diode D1', a second diode D2', a first bridge arm switch Q1, a second bridge arm switch Q2, a third bridge arm switch Q3, and a fourth bridge arm switch.
  • Q4; the first bridge arm switch Q1 and the second bridge arm switch Q2 are upper bridge switches.
  • the second bridge arm switch Q2 is turned off later than the first bridge arm switch Q1; the third bridge arm switch Q3 And the fourth bridge arm switch Q4 is a lower arm switch, and the third bridge arm switch Q3 is turned off later than the fourth bridge arm switch Q4 in one duty cycle.
  • the first pole of the first bridge arm switch Q1 is connected to the anode of the direct current, and the second pole of the first bridge switch Q1 is connected to the first pole of the second bridge switch Q2 and the cathode of the first diode D1'.
  • the control pole (gate) of the first bridge arm switch Q1 is connected to the first output end of the control module; the anode of the first diode D1' is connected to the cathode of the second diode D2'; the second bridge arm switch
  • the second pole of Q2 is connected to one end of the first inductor Lr and the first pole of the third bridge arm switch Q3; the other end of the first inductor Lr is connected to one end of the capacitor Cr through the primary winding of the transformer, and the other end of the capacitor Cr is connected to the first end
  • the first bridge arm switch Q1, the second bridge arm switch Q2, the third bridge arm switch Q3, and the fourth bridge arm switch are four identical power MOS tubes.
  • D1, D2, D3, and D4 are equivalent body diodes of respective corresponding power MOS tubes
  • C1, C2, C3, and C4 are equivalent output capacitors corresponding to the respective power MOS tubes.
  • the first diode D1' and the second diode D2' are three-level clamping diodes.
  • FIG. 3 is a waveform diagram of four bridge arm switches, a resonant current Ir, and an exciting current Im of a conventional three-level LLC resonant DC converter.
  • the working state of the resonance is that the resonant frequency fr is smaller than the switching frequency fo
  • the currents Ir and Im of the resonant cavity are increased, when at time t1, Q1 is turned off.
  • Q1 is turned off and Q2 is still on.
  • the current of Ir starts to drop, and the current of Im still rises.
  • the shutdown current at this time is ir, you can see The shutdown current at this time is still very large, and the time zone of t1-t2 is also called dead zone time 1; in t2-t3, Ir is equal to Im, and because of the turn-off of Q2 at time t2, the Im commutation is caused.
  • the time interval of t2-t3 is also called dead time 2; at time t3, Q3, Q4 is turned on, and then enters the lower half cycle, and its work is similar to the first half cycle.
  • the resonant current charges C1 and discharges to C4.
  • the resonant current simultaneously charges C1, C2, C3, C4, so that at the beginning of t3, the voltage of Q3, Q4MOS tube is zero, and then the MOS transistor ZVS (zero voltage switch) is turned on, and the resonant current starts. by.
  • the shutdown current is relatively large when Q1 is turned off, and the current ir flowing when Q2 is turned off. Both MOS transistors are turned off and hard-switched off, which increases the loss of the LLC resonant cavity. .
  • the shutdown current also determines whether the ZVS turn-on of the MOS transistor can be realized.
  • the simulated waveform of Figure 3 the operating frequency is 150Khz, the output is 500V 20A, and the current is about 15A when Q2 is turned off.
  • the control system provided by the invention can detect the real-time current of the LLC resonant cavity, and can realize the shutdown of the power bridge arm switch ZVS current, and reduce the loss when the current is relatively small, thereby reducing the loss and improving the efficiency. Simultaneously detecting the resonant current in real time, the state of the DC converter can be monitored in real time, thereby achieving more protection and improving system reliability.
  • the current sampling circuit The 510 is specifically configured to: detect a current of the LLC resonant cavity when the second bridge arm switch is turned off after a working cycle starts; and/or detect a current of the LLC resonant cavity when the third bridge arm switch is turned off.
  • the second bridge arm switch Q2 is the upper arm switch that is turned off after the two upper arm switches
  • the third bridge arm switch Q3 is the one of the two lower arm switches that is turned off later Bridge arm switch.
  • the current of the LLC resonant cavity when the second bridge arm switch is turned off is detected, and the current of the LLC resonant cavity when the third bridge arm switch is turned off is detected.
  • the control module includes a controller 520 and a driving circuit 530.
  • the input end of the controller 520 is an input end of the control module, and is connected to the output end of the current sampling circuit 510; the output end of the controller 520 is connected to the input end of the driving circuit 530; the output end of the driving circuit 530 is the output end of the control module, and is connected.
  • the control terminals of the individual bridge switches (Q1-Q4).
  • the driving circuit 530 is configured to drive on and off of the respective bridge arm switches (Q1-Q4).
  • the controller 520 is configured to compare a current value of the LLC resonant cavity with a preset current value; and when the current value of the LLC resonant cavity is greater than a preset current value, driving the corresponding bridge arm through the driving circuit 530 Turning on and/or off of the switch to increase the first dead time and/or increasing the third dead time; when the current value of the LLC resonant cavity is less than the preset current value, driving the corresponding circuit
  • the bridge arm is turned “on” and/or "off” to reduce the first dead time and/or reduce the third dead time.
  • each of the bridge arm switches in the switch bridge arm 20 operates periodically, so that the first dead time and the third dead time are increased or decreased, and the next time can be increased or decreased.
  • the first dead time and the third dead time may also increase or decrease the first dead time and the third dead time in one or more subsequent work cycles.
  • the preset current value is not lower than a minimum current value capable of realizing the zero voltage switch of the second bridge arm switch Q2 or the third bridge arm switch Q3, thereby ensuring the ZVS of the bridge arm switch while reducing the switching loss.
  • the first dead time is the first dead time in one working cycle, in other words, the first dead time is from the first bridge switch off to the second bridge switch off time.
  • the third dead time is the third dead time in one working cycle. In other words, the third dead time is from the fourth bridge switch to the third bridge in one working cycle. The time the arm switch is turned off.
  • FIG. 4 is a waveform diagram of four bridge arm switches, a resonant current Ir, and an exciting current Im of an LLC resonant DC converter employing the control system provided by the present invention.
  • the duty cycle is the work of the switch bridge arm 20 Cycle T.
  • the controller 520 controls the Q1 and Q2 to be simultaneously turned on by the driving circuit 530 during the time period t0-t1, the current Ir of the resonant cavity, Im increases, and at time t1, Q1 turns off.
  • Q1 is turned off, Q2 is still on, at this time, the current of Ir begins to decrease, and the current of Im still rises.
  • current sampling circuit 510 samples the LLC resonance when Q2 is turned off.
  • the current of the cavity when the current value of the LLC resonant cavity is greater than the preset current value, increases the first dead time (time interval of t1-t2) in the next working cycle, and the current value in the LLC resonant cavity is less than or equal to the pre-
  • the first dead time is reduced at the next duty cycle.
  • Ir is equal to Im, and at the same time, because of the turn-off of Q2 at time t2, the Im commutation is started, and the reverse reduction is started.
  • the time interval of this t2-t3 is also called the second dead time.
  • Q3 and Q4 are controlled to conduct, and then enter the second half cycle, and the operation is similar to the first half cycle.
  • Q4 is turned off, and the time interval of t4-t5 is the third dead time.
  • current sampling circuit 510 samples the current of LLC resonant cavity when Q3 is turned off, and increases the third dead time time in the next duty cycle when the current value of the LLC resonant cavity is greater than the preset current value ( The time interval of t4-t5), when the current value of the LLC resonator is less than or equal to the preset current value, the third dead time is decreased at the next duty cycle.
  • the time interval between t5 and the time t0 of the next duty cycle is the fourth dead time. Since the upper and lower arms are symmetrical, it is also possible to sample only the current of the LLC resonant cavity when Q2 or Q3 is turned off in one working cycle, and increase the first dead zone time and the third dead zone time in the next duty cycle. In this embodiment, the first dead zone time and the third dead zone time are increased, and the second dead zone time and the fourth dead zone time remain unchanged.
  • the time during which the first dead time and the third dead time increase is 50 ns.
  • the controller 520 employs a DSP controller with a built-in timer that samples the current when Q2 and/or Q3 are turned off by an interrupt of the timer. As shown in Fig. 4, the operating frequency is 150Khz, the output is 500V 20A, and the current 5A when Q2 is turned off is greatly reduced compared with the current in Fig. 3 of the prior art, which greatly reduces the turn-off loss.
  • the present invention detects the current of the resonant cavity in real time, adjusts the current value when the Q2 and Q3 are turned off according to the actual situation, optimizes the shutdown performance of the three-level LLC converter, greatly reduces the switching loss of the switching tube, and at the same time optimizes the A dead time period ensures that the second dead time is constant, and the ZVS function of the switch tube is also ensured, further improving the efficiency of the converter, and reducing the du/dt of the switch tube to cut off, which is beneficial to reducing electromagnetic interference; Real-time monitoring of resonant operating current changes, and therefore can also be used for converter overcurrent and overpower protection, etc., to improve system reliability.
  • the controller 520 has a large current value in the LLC resonant cavity.
  • the second dead time or the fourth dead time is also reduced by the driving circuit 530, or the operating frequency is slightly reduced (ie, the duty cycle is slightly increased); the second dead time is from The second bridge arm switch is turned off until the third bridge arm switch is turned on; the fourth dead time is a time from when the third bridge arm switch is turned off to when the second bridge arm switch is turned on in the next work cycle;
  • the corresponding waveform diagram is shown in Figure 5.
  • the present invention also provides a control method of the LLC resonant DC converter. As shown in FIG. 6, the method includes the following steps:
  • the detecting step the current sampling circuit detects a current of the LLC resonant cavity when the bridge arm switch is turned off.
  • the detecting step specifically includes:
  • the second bridge switch After a start of a duty cycle, detecting a current of the LLC resonant cavity when the second bridge arm is turned off; and/or detecting a current of the LLC resonant cavity when the third bridge switch is turned off; wherein the second bridge switch
  • the upper arm switch that is turned off later in the two upper arm switches, the third bridge switch is the lower arm switch that is turned off after the two lower arm switches.
  • the adjusting step the control module increases or decreases the dead time according to the current of the LLC resonant cavity to reduce the switching loss of the bridge switch.
  • the adjusting step specifically includes:
  • the preset current value is not lower than a minimum current value capable of achieving zero voltage switching of the bridge arm; the first dead time is the first dead time in a working cycle, and the third dead zone Time is the third dead time in a work cycle.
  • the LLC resonant DC converter is a three-level LLC resonant DC converter. Referring to FIG. 7, the specific process of the control method is as follows:
  • the current sampling circuit detects the current of the LLC resonant cavity in real time.
  • the controller timed the on and off times of the respective bridge arm switches in the working cycle by using a timer.
  • the controller obtains the current of the LLC resonant cavity when the second bridge arm is turned off according to the interrupt of the timer.
  • the controller compares and determines a current value of the LLC resonant cavity and a preset current value. Specifically, determining whether the current value of the LLC resonant cavity is greater than a preset current value; when the current value of the LLC resonant cavity is greater than a preset current value, proceeding to step S220; the current value in the LLC resonant cavity is less than or When it is equal to the preset current value, the process proceeds to step S230.
  • S220 Increase the first dead time in the next work cycle. It is preferably increased by 50 ns.
  • the controller compares and determines the current value of the LLC resonant cavity and the magnitude of the preset current value. Specifically, determining whether the current value of the LLC resonant cavity is greater than a preset current value; current in the LLC resonant cavity When the value is greater than the preset current value, the process proceeds to step S260; when the current value of the LLC resonant cavity is less than or equal to the preset current value, the process proceeds to step S270.
  • S260 Increase the third dead time in the next work cycle. It is preferably increased by 50 ns.

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Abstract

一种LLC谐振直流变换器及其控制方法和控制系统（50），其中，所述控制系统（50）包括电流采样电路（510）和控制模块。通过电流采样电路（510）采样桥臂开关关断时LLC谐振腔的电流。控制模块则根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。通过调节死区时间的大小，降低了桥臂开关的开关损耗，提高了LLC谐振直流变换器的整体效率。

Description

一种LLC谐振直流变换器及其控制方法和系统 技术领域
本发明涉及直流变换器领域，具体涉及一种LLC谐振直流变换器及其控制方法和系统。
背景技术
随着新能源产业的发展，充电桩行业的需求日益增加，同时对充电桩功率等级要求日益提高，10KW-20KW直流充电模块已经开始普及开来，在现在的AC/DC直流模块中，DC/DC多采用三电平LLC，三电平LLC直流变换器能够将开关管电压应力降为输入测直流母线(DC700V-850V)的一半，在高压输入情况下选取低压器件，同时LLC三电平谐振变换器既能实现开关管的ZVS(零电压开关),又能实现整流二极管的ZCS(零电流开关),提高变换效率，降低电磁干扰，但当输出电压范围低于设计的谐振点电压时，在开关管的关断时存在比较大的损耗，因为关断时开关管实现是硬开关。
因此，现有技术还有待改进和提高。
发明内容
本发明主要提供一种LLC谐振直流变换器及其控制方法和系统，以降低桥臂开关的开关损耗。
根据本发明第一方面，一种实施例中提供一种LLC谐振直流变换器的控制方法，包括如下步骤：
检测步骤，检测桥臂开关关断时LLC谐振腔的电流；
调整步骤，根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
根据本发明第二方面，一种实施例中提供一种LLC谐振直流变换器的控制系统，包括：
电流采样模块，用于采样桥臂开关关断时LLC谐振腔的电流；
控制模块，用于根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
根据本发明第三方面，一种实施例中提供一种LLC谐振直流变换器，包括：
电流采样模块，用于采样桥臂开关关断时LLC谐振腔的电流；
控制模块，用于根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
本发明提供的LLC谐振直流变换器及其控制方法和系统，其中，所述方法通过检测桥臂开关关断时LLC谐振腔的电流；进而根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。通过调节死区时间的大小，降低了桥臂开关的开关损耗，提高了LLC谐振直流变换器的整体效率。
附图说明
图1为本发明提供的LLC谐振直流变换器的电路图；
图2为本发明提供的LLC谐振直流变换器中，直流输出电路、开关桥臂和LLC谐振腔的电路图；
图3为现有的LLC谐振直流变换器中，各个桥臂开关、LLC谐振腔电流和励磁电流的波形图；
图4为本发明提供的LLC谐振直流变换器一实施例中，各个桥臂开关、LLC谐振腔电流和励磁电流的波形图；
图5为本发明提供的LLC谐振直流变换器另一实施例中，各个桥臂开关、LLC谐振腔电流和励磁电流的波形图；
图6为本发明提供的LLC谐振直流变换器的控制方法的流程图；
图7为本发明提供的LLC谐振直流变换器的控制方法中，一实施例的具体流程图。
具体实施方式
下面通过具体实施方式结合附图对本发明作进一步详细说明。其中不同实施方式中类似元件采用了相关联的类似的元件标号。在以下的实施方式中，很多细节描述是为了使得本申请能被更好的理解。然而，本领域技术人员可以毫不费力的认识到，其中部分特征在不同情况下是可以省略的，或者可以由其他元件、材料、方法所替代。在某些情况下，本申请相关的一些操作并 没有在说明书中显示或者描述，这是为了避免本申请的核心部分被过多的描述所淹没，而对于本领域技术人员而言，详细描述这些相关操作并不是必要的，他们根据说明书中的描述以及本领域的一般技术知识即可完整了解相关操作。
另外，说明书中所描述的特点、操作或者特征可以以任意适当的方式结合形成各种实施方式。同时，方法描述中的各步骤或者动作也可以按照本领域技术人员所能显而易见的方式进行顺序调换或调整。因此，说明书和附图中的各种顺序只是为了清楚描述某一个实施例，并不意味着是必须的顺序，除非另有说明其中某个顺序是必须遵循的。
本文中为部件所编序号本身，例如“第一”、“第二”等，仅用于区分所描述的对象，不具有任何顺序或技术含义。而本申请所说“连接”、“联接”，如无特别说明，均包括直接和间接连接(联接)。
请参阅图1，本发明提供一种LLC谐振直流变换器，包括：直流输出电路10，开关桥臂20，LLC谐振网络及功率转化电路30，整流电路40以及控制系统(电路)50。所述直流输出电路10的输出端通过开关桥臂20连接LLC谐振网络及功率转化电路30，LLC谐振网络及功率转化电路30的输出端连接整流电路40的输入端；控制系统(电路)50连接LLC谐振网络及功率转化电路30。
所述直流输出电路10，用于接收外部的直流电，经过滤波后输出给开关桥臂20，为总变换电路提供电源。所述直流输出电路10包括第一电容C1’和第二电容C2’。所述第一电容C1’的一端连接直流电的正极，第一电容C1’的另一端通过第二电容C2’连接直流电的负极，所述直流电的负极接地。
所述开关桥臂20，包括多个桥臂开关。各个桥臂开关可以由单个或多个MOS管，单个或多个IGBT(绝缘栅双极型晶体管)，或者MOS管与IGBT的组合构成。所述开关桥臂20起到高频方波发生器的作用，即用于产生高频方波，使直流电压变成高频方波电压。
所述LLC谐振网络及功率转化电路30，包括LLC谐振腔(LLC谐振电路)和功率变压器。所述开关桥臂20通过LLC谐振腔连接功率变压器的初级绕组，功率变压器的次级绕组连接整流电路40的输入端。
请参阅图2，所述LLC谐振腔包括第一电感Lr，第二电感Lm和电容Cr，即第一电感Lr，第二电感Lm和电容Cr串联构成谐振电路，其谐振频率为
Figure PCTCN2017095647-appb-000001
所述LLC谐振腔使得在电源为直流电源时，LLC谐振腔中的电流按照正弦规律变化。由于电流或电压按正弦规律变化，存在过零点，如果此时开关器件(桥臂开关)开通或关断，产生的损耗就为零，同时为电路提供能量。第二电感Lm为变压器初级绕组的励磁电感，电路中Ir为谐振电流，Im为励磁电流，电阻Re为电路的等效负载。
所述整流电路40，用于对功率变压器次级绕组输出的交流电进行整流；其由常用的全桥，全波，半波或其他整流方式及滤波电路构成。
所述控制系统50，为整个直流变换器的输入输出状态的总控，通过控制各个桥臂开关，进而控制整个功率传递。
进一步的，所述控制系统50包括电流采样模块510(具体为电流采样电路)和控制模块。
所述电流采样电路510，用于采样桥臂开关关断时LLC谐振腔的电流。
所述控制模块，用于根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
电流采样电路510的输入端与LLC谐振腔连接，电流采样电路510的输出端连接控制模块的输入端，控制模块的输出端连接开关桥臂20。
本发明通过调节死区时间的大小，降低了桥臂开关的开关损耗，提高了LLC谐振直流变换器的整体效率。
本实施例中，所述LLC谐振直流变换器为三电平LLC谐振直流变换器。
所述开关桥臂20，包括第一二极管D1'、第二二极管D2'、第一桥臂开关Q1、第二桥臂开关Q2、第三桥臂开关Q3和第四桥臂开关Q4；第一桥臂开关Q1和第二桥臂开关Q2为上桥臂开关，在一个工作周期中，第二桥臂开关Q2比第一桥臂开关Q1晚关断；第三桥臂开关Q3和第四桥臂开关Q4为下桥臂开关，在一个工作周期中，第三桥臂开关Q3比第四桥臂开关Q4晚关断。所述第一桥臂开关Q1的第一极连接直流电的正极，所述第一桥臂开关Q1的第二极连接第二桥臂开关Q2的第一极和第一二极管D1'的负极，所述第一桥臂开关Q1的控制极(栅极)连接控制模块的第一输出端；第一二极管D1'的正极连接第二二极管D2'的负极；第二桥臂开关Q2的第二极连接第一电感Lr的一端和第三桥臂开关Q3的第一极；第一电感Lr的另一端通过变压器的初级绕组连接电容Cr的一端，电容Cr的另一端连接第一电容C1'的另一端、 第一二极管D1'的正极和第二二极管D2'的负极；第二桥臂开关Q2的控制极(栅极)连接控制模块的第二输出端；第三桥臂开关Q3的第二极连接第二二极管D2'的正极和第四桥臂开关Q4的第一极，第三桥臂开关Q3的控制极(栅极)连接控制模块的第三输出端；第四桥臂开关Q4的第二极接地，第四桥臂开关Q4的控制极(栅极)连接控制模块的第四输出端。
本实施例中，第一桥臂开关Q1、第二桥臂开关Q2、第三桥臂开关Q3和第四桥臂开关为四个相同的功率MOS管。D1，D2,D3,D4为各个对应功率MOS管的等效体二极管，C1，C2,C3，C4为各个功率MOS管对应的等效输出电容。第一二极管D1'和第二二极管D2'为三电平钳位二极管。
图3为传统的三电平LLC谐振直流变换器的四个桥臂开关、谐振电流Ir和励磁电流Im的波形图。当谐振的工作状态为谐振频率fr小于开关频率fo时，在这种状态下，当t0-t1时间段内Q1,Q2同时打开，谐振腔的电流Ir，Im均增大，当在t1时刻，Q1关断。在t1-t2时间段内，Q1关断，Q2仍然开通，此时Ir的电流开始下降，而Im的电流仍然上升，当在t2时刻Q2关断，此时的关断电流为ir，可以看出此时的关断电流仍然很大，t1-t2的时间区也称作死区时间1；在t2-t3中，Ir与Im相等，同时因为t2时刻Q2的关断，导致Im换向，开始反向减少，此t2-t3的时间区间也称作死区时间2；在t3时刻Q3,Q4导通，进而进入下半周期，其工作与上半周期类似。同时在死区时间1里，谐振电流对C1充电，对C4放电。在死区时间2里谐振电流同时对C1,C2充电，C3,C4放电，使得在t3开始时，Q3,Q4MOS管的电压为零，进而实现MOS管ZVS(零电压开关)开通，谐振电流开始通过。由此可以看出，Q1关断时关断电流相对比较大，而Q2关断时流过的电流ir，这两个MOS管关断均为硬开关关断，增大了LLC谐振腔的损耗。同时此时的关断电流也决定了能否实现MOS管的ZVS开通。如果电流过低，Ir无法提供对上桥臂充电，下桥臂放电所需的能量，实现不了ZVS，使得整个系统的损耗大大的增加。图3的仿真波形：工作频率150Khz，输出500V 20A,Q2关断时电流大概为15A。
而本发明提供的控制系统，可以通过检测LLC谐振腔的实时电流，满足能够实现功率桥臂开关ZVS电流前提下，在比较小的电流时进行关断，进而减小损耗，提高效率。同时实时检测谐振电流，可以实时监控直流变换器的状态，进而做到更多的保护，提高系统可靠性。具体的，所述电流采样电路 510具体用于：在一个工作周期开始后，检测第二桥臂开关关断时LLC谐振腔的电流；和/或，检测第三桥臂开关关断时LLC谐振腔的电流。其中，所述第二桥臂开关Q2为两个上桥臂开关中后关断的那个上桥臂开关，所述第三桥臂开关Q3为两个下桥臂开关中后关断的那个下桥臂开关。本实施例中，即检测第二桥臂开关关断时LLC谐振腔的电流，又检测第三桥臂开关关断时LLC谐振腔的电流。
所述控制模块包括：控制器520和驱动电路530。控制器520的输入端为控制模块的输入端，连接电流采样电路510的输出端；控制器520的输出端连接驱动电路530的输入端；驱动电路530的输出端为控制模块的输出端，连接各个桥臂开关(Q1-Q4)的控制端。
所述驱动电路530，用于驱动各个桥臂开关(Q1-Q4)的导通和关断。
所述控制器520，用于比较所述LLC谐振腔的电流值与预设电流值的大小；在所述LLC谐振腔的电流值大于预设电流值时，通过驱动电路530驱动对应的桥臂开关的导通和/或关断以增大第一死区时间和/或增大第三死区时间；在所述LLC谐振腔的电流值小于预设电流值时，通过驱动电路驱动对应的桥臂开关的导通和/或关断以减小第一死区时间和/或减小第三死区时间。增大或减小第一死区时间，具体可通过调节Q1和/或Q2的PWM占空比实现；同样的，增大或减小第三死区时间，具体可通过调节Q3和/或Q4的PWM占空比实现。另外，LLC谐振直流变换器中，开关桥臂20中的各个桥臂开关为周期性工作，故增大或减小第一死区时间、第三死区时间，可以增大或减小下一次出现的第一死区时间、第三死区时间，也可以增大或减小后续一个或多个工作周期中的第一死区时间、第三死区时间。
其中，所述预设电流值不低于能实现第二桥臂开关Q2或第三桥臂开关Q3零电压开关的最小电流值，从而在降低开关损耗的同时也能保障桥臂开关的ZVS。所述第一死区时间为一个工作周期中第一次出现的死区时间，换而言之，所述第一死区时间为从第一桥臂开关关断到第二桥臂开关关断的时间。所述第三死区时间为一个工作周期中第三次出现的死区时间，换而言之，所述第三死区时间为一个工作周期中从第四桥臂开关关断到第三桥臂开关关断的时间。
图4为采用本发明提供的控制系统的LLC谐振直流变换器的四个桥臂开关、谐振电流Ir和励磁电流Im的波形图。所述工作周期为开关桥臂20的工 作周期T。当谐振的工作状态为谐振频率fr小于开关频率fo时，在这种状态下，所述控制器520通过驱动电路530控制Q1和Q2在t0-t1时间段内同时打开，谐振腔的电流Ir，Im均增大，当在t1时刻，Q1关断。在t1-t2时间段内，Q1关断，Q2仍然开通，此时Ir的电流开始下降，而Im的电流仍然上升，当在t2时刻Q2关断，电流采样电路510采样Q2关断时LLC谐振腔的电流，在LLC谐振腔的电流值大于预设电流值时，在下一工作周期时增大第一死区时间(t1-t2的时间区间)，在LLC谐振腔的电流值小于或等于预设电流值时，在下一工作周期时减小第一死区时间。在t2-t3中，Ir与Im相等，同时因为t2时刻Q2的关断，导致Im换向，开始反向减少，此t2-t3的时间区间也称作第二死区时间。在t3时刻控制Q3和Q4导通，进而进入下半周期，其工作与上半周期类似。在t4时刻控制Q4关断，t4-t5的时间区间为第三死区时间。在t5时刻控制Q3关断，电流采样电路510采样Q3关断时LLC谐振腔的电流，在LLC谐振腔的电流值大于预设电流值时，在下一工作周期时增大第三死区时间(t4-t5的时间区间)，在LLC谐振腔的电流值小于或等于预设电流值时，在下一工作周期时减小第三死区时间。t5到下一工作周期的t0时刻之间的时间区间为第四死区时间。由于上下桥臂对称，故一个工作周期内也可以只采样Q2或Q3关断时LLC谐振腔的电流，在下一个工作周期时对第一死区时间和第三死区时间进行增大。本实施例中，第一死区时间和第三死区时间增大，第二死区时间和第四死区时间保持不变。
优选的，第一死区时间和第三死区时间增大的时间为50ns。所述控制器520采用DSP控制器，其内置有定时器，通过定时器的中断采样Q2和/或Q3关断时的电流。如图4所示，工作频率150Khz，输出500V 20A，Q2关断时的电流5A,相比采用现有技术的图3中的电流，大为降低，大大降低了关断损耗。
可见，本发明通过实时检测谐振腔电流，根据实际情况调节Q2和Q3关断时电流值，优化的三电平LLC变换器的关断性能，大大降低了开关管的开关损耗，同时通过优化第一死区时间，保证第二死区时间不变，也保证了开关管的ZVS功能实现，进一步提升变换器的效率，减小的开关管关断的du/dt，有利于减少电磁干扰；同时实时监测谐振工作电流变化，因此也能用于的变换器过流及过功率等保护作用，提高系统的可靠性。
当然，在其他实施例中，所述控制器520在所述LLC谐振腔的电流值大 于预设电流值时，还通过驱动电路530减小第二死区时间或第四死区时间，或者略微减小工作频率(即略微增大工作周期)；所述第二死区时间为从第二桥臂开关关断到第三桥臂开关导通的时间；所述第四死区时间为从第三桥臂开关关断到下一工作周期中第二桥臂开关导通的时间；其对应的波形图如图5所示。
基于上述实施例提供的LLC谐振直流变换器及其控制系统，本发明还提供一种LLC谐振直流变换器的控制方法。如图6所示，所述方法包括如下步骤：
S10、检测步骤，所述电流采样电路检测桥臂开关关断时LLC谐振腔的电流。所述检测步骤具体包括：
在一个工作周期开始后，检测第二桥臂开关关断时LLC谐振腔的电流；和/或，检测第三桥臂开关关断时LLC谐振腔的电流；其中，所述第二桥臂开关为两个上桥臂开关中后关断的那个上桥臂开关，所述第三桥臂开关为两个下桥臂开关中后关断的那个下桥臂开关。
S20、调整步骤，所述控制模块根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。所述调整步骤具体包括：
比较所述LLC谐振腔的电流值与预设电流值的大小；
在所述LLC谐振腔的电流值大于预设电流值时，增大第一死区时间和/或第三死区时间；在所述LLC谐振腔的电流值小于预设电流值时，减小第一死区时间和/或第三死区时间。
其中，所述预设电流值不低于能实现桥臂零电压开关的最小电流值；所述第一死区时间为一个工作周期中第一次出现的死区时间，所述第三死区时间为一个工作周期中第三次出现的死区时间。
本实施例中，所述LLC谐振直流变换器为三电平LLC谐振直流变换器。请参阅图7，所述控制方法的具体流程如下：
S110、电流采样电路实时检测LLC谐振腔的电流。
S120、控制器通过定时器对工作周期中各个桥臂开关的导通和关断时间进行定时。
S130、控制器在当前工作周期开始后，根据定时器的中断得到第二桥臂开关关断时LLC谐振腔的电流。
S210、控制器比较并判断所述LLC谐振腔的电流值与预设电流值的大小, 具体的，判断所述LLC谐振腔的电流值是否大于预设电流值；在所述LLC谐振腔的电流值大于预设电流值时，进入步骤S220；在所述LLC谐振腔的电流值小于或等于预设电流值时，进入步骤S230。
S220、在下一个工作周期中增大第一死区时间。优选增大50ns。
S230、在下一个工作周期中减小第一死区时间。优选减小50ns。
S240、更新第一桥臂开关和/或第二桥臂开关的PWM比较值，以便于在下一工作周期中相应的增大或减小第一死区时间。
S140、根据定时器的中断得到第三桥臂开关关断时LLC谐振腔的电流。
S250、控制器比较并判断所述LLC谐振腔的电流值与预设电流值的大小,具体的，判断所述LLC谐振腔的电流值是否大于预设电流值；在所述LLC谐振腔的电流值大于预设电流值时，进入步骤S260；在所述LLC谐振腔的电流值小于或等于预设电流值时，进入步骤S270。
S260、在下一个工作周期中增大第三死区时间。优选增大50ns。
S270、在下一个工作周期中减小第三死区时间。优选减小50ns。
S280、更新第三桥臂开关和/或第四桥臂开关的PWM比较值，以便于在下一工作周期中相应的增大或减小第三死区时间。之后，返回步骤S130。
由于所述方法的原理和特点在上述系统实施例中已详细阐述，在此不再赘述。
以上应用了具体个例对本发明进行阐述，只是用于帮助理解本发明，并不用以限制本发明。对于本领域的一般技术人员，依据本发明的思想，可以对上述具体实施方式进行变化。

Claims (10)

  1. 一种LLC谐振直流变换器的控制方法，其特征在于，包括如下步骤：
    检测步骤，检测桥臂开关关断时LLC谐振腔的电流；
    调整步骤，根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
  2. 如权利要求1所述的LLC谐振直流变换器的控制方法，其特征在于，所述调整步骤具体包括：
    比较所述LLC谐振腔的电流值与预设电流值的大小；
    在所述LLC谐振腔的电流值大于预设电流值时，增大第一死区时间和/或第三死区时间；在所述LLC谐振腔的电流值小于预设电流值时，减小第一死区时间和/或第三死区时间；
    其中，所述预设电流值不低于能实现桥臂零电压开关的最小电流值；所述第一死区时间为一个工作周期中第一次出现的死区时间，所述第三死区时间为一个工作周期中第三次出现的死区时间。
  3. 如权利要求2所述的LLC谐振直流变换器的控制方法，其特征在于，所述LLC谐振直流变换器为三电平LLC谐振直流变换器。
  4. 如权利要求3所述的LLC谐振直流变换器的控制方法，其特征在于，所述检测步骤具体包括：
    在一个工作周期开始后，检测第二桥臂开关关断时LLC谐振腔的电流；和/或，检测第三桥臂开关关断时LLC谐振腔的电流；其中，所述第二桥臂开关为两个上桥臂开关中后关断的那个上桥臂开关，所述第三桥臂开关为两个下桥臂开关中后关断的那个下桥臂开关。
  5. 一种LLC谐振直流变换器的控制系统，其特征在于,包括：
    电流采样模块，用于采样桥臂开关关断时LLC谐振腔的电流；
    控制模块，用于根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
  6. 如权利要求5所述的LLC谐振直流变换器的控制系统，其特征在于,所述控制模块具体用于：
    比较所述LLC谐振腔的电流值与预设电流值的大小；
    在所述LLC谐振腔的电流值大于预设电流值时，增大第一死区时间和/或第三死区时间；在所述LLC谐振腔的电流值小于预设电流值时，减小第一 死区时间和/或第三死区时间；
    其中，所述预设电流值不低于能实现桥臂零电压开关的最小电流值；所述第一死区时间为一个工作周期中第一次出现的死区时间，所述第三死区时间为一个工作周期中第三次出现的死区时间。
  7. 如权利要求6所述的LLC谐振直流变换器的控制系统，其特征在于，所述LLC谐振直流变换器为三电平LLC谐振直流变换器。
  8. 如权利要求7所述的LLC谐振直流变换器的控制系统，其特征在于，所述电流采样模块具体用于：在一个工作周期开始后，检测第二桥臂开关关断时LLC谐振腔的电流；和/或，检测第三桥臂开关关断时LLC谐振腔的电流；其中，所述第二桥臂开关为两个上桥臂开关中后关断的那个上桥臂开关，所述第三桥臂开关为两个下桥臂开关中后关断的那个下桥臂开关。
  9. 一种LLC谐振直流变换器，其特征在于，包括：
    电流采样模块，用于采样桥臂开关关断时LLC谐振腔的电流；
    控制模块，用于根据所述LLC谐振腔的电流大小，增大或减小死区时间，以降低桥臂开关的开关损耗。
  10. 如权利要求9所述的LLC谐振直流变换器，其特征在于，所述控制模块包括：
    驱动单元，用于驱动桥臂开关的导通和关断；
    控制器，用于比较所述LLC谐振腔的电流值与预设电流值的大小；在所述LLC谐振腔的电流值大于预设电流值时，通过驱动单元增大第一死区时间和/或第三死区时间；在所述LLC谐振腔的电流值小于预设电流值时，通过驱动单元减小第一死区时间和/或第三死区时间；
    其中，所述预设电流值不低于能实现桥臂零电压开关的最小电流值；所述第一死区时间为一个工作周期中第一次出现的死区时间，所述第三死区时间为一个工作周期中第三次出现的死区时间。
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