English:
[0002] LLC converters are most efficient when operating at their resonant frequency. Small deviations of the switching frequency of an LLC converter can have significant impacts on its efficiency. Consequently, maintaining operation of an LLC converter at, or close to, its resonant frequency is important in maintaining an efficient system. Current approaches to driving an LLC converter at its resonant frequency focus on monitoring the secondary side of the LLC converter to determine its resonant frequency. The information gathered at the secondary side is then provided to a driving mechanism for the LLC converter. The driving mechanism is on the primary side of the LLC converter. Consequently, monitoring an LLC converter from the secondary side introduces additional complexities (e.g., an increased number of components) and costs.
[0005] FIG. 1 depicts an example LLC converter 100 including a resonant frequency determination unit 1 10, according to some embodiments;
[0006] FIGS. 2 A and 2B are waveforms associated with an LLC converter, according to some embodiments;
[0007] FIG. 3 depicts the primary side of an example LLC converter including a current suppressor 312 and a detector 310, according to some embodiments;
[0008] FIG. 4 is a flow chart depicting example operations for determining a resonant frequency for an LLC converter by monitoring current on the primary side of the LLC converter, according to some embodiments.
[0009] As described hereinabove, maintaining operation of an LLC converter at its resonant frequency helps maximize the efficiency of the LLC converter. Current approaches rely on measurements taken on the secondary side of the LLC converter. Typically, these systems sense zero crossings of the current flowing through the secondary side of the rectifier. These approaches measure current on the secondary side because the current on the secondary side is isolated from the magnetizing current from the transformer. That is, the current can be monitored without having to account for the magnetizing current. While this allows for a direct measurement of current (i.e., the current is isolated from the magnetizing current), it introduces additional costs and complexities. One reason that measuring current on the secondary side of the LLC converter introduces additional costs and complexities is due to the fact that information must be transmitted back to the primary side of the LLC converter through an isolation barrier. The additional componentry necessary to facilitate this transmission increases the complexity of the circuit, and thus, the cost of the circuit.
[0010] Embodiments of the inventive subject matter allow an LLC converter to be driven at its resonant frequency without measuring current at the secondary side of the LLC converter. Put simply, embodiments of the inventive subject matter obviate the need for the additional componentry, and cost, associated with monitoring information on the secondary side of the LLC converter and transmitting that information to the primary side of the LLC converter. Instead of monitoring the secondary side of the LLC converter, embodiments of the inventive subject matter monitor current on the primary side of the LLC converter. However, as discussed above, the current on the primary side includes a magnetizing current produced by the transformer. Because the current on the primary side of the LLC converter includes both a sinusoidal portion and a magnetizing current, the sinusoidal portion of the current is isolated from the magnetizing current. In some embodiments, the sinusoidal portion of the current is isolated from the magnetizing current by performing mathematical calculations (e.g., calculating the second order derivative) on the current. Once the sinusoidal portion of the current is isolated, zero crossings of the sinusoidal portion of the current can be detected and the half bridge switches can be driven based on the zero crossings. In some embodiments, a resonant frequency determination unit is utilized to monitor current on the primary side of an LLC converter and determine a resonant frequency for the LLC converter. FIG. 1 provides an overview of an example LLC converter including a resonant frequency determination unit, while FIG. 3 provides additional information regarding an example resonant frequency determination unit.
[0011] FIG. 1 depicts an example LLC converter 100 including a resonant frequency determination unit 110, according to some embodiments. The LLC converter 100 has a primary side 102 and a secondary side 104. The resonant frequency determination unit 110 is located on the primary side 102. The resonant frequency determination unit 100 is able to determine the resonant frequency of the LLC converter 100 based on measurements taken at the primary side 102 of the LLC converter 100. More specifically, the resonant frequency determination unit 110 monitors the primary side current of the LLC converter 110 via a sensor 108. As previously discussed, the primary side current includes both a sinusoidal portion (i.e., the resonant current) and a ramp current (i.e., a magnetizing current caused by the transformer). The resonant frequency determination unit isolates the sinusoidal portion of the primary side current so that the resonant frequency can be detected. In one embodiment, the resonant frequency determination unit 110 isolates the sinusoidal portion of the primary side current by taking the second order derivative of the primary side current. The resonant frequency determination unit 110 analyzes the sinusoidal portion of the primary side current to determine the resonant frequency of the LLC converter 100. In some embodiments, the resonant frequency determination unit 110 determines the resonant frequency by detecting the point at which the sinusoidal portion crosses the magnetizing portion (i.e., the zero-crossing). The controller 106 receives resonant frequency information from the resonant frequency determination unit 110 and drives the LLC converter 100 at the resonant frequency.
[0012] While the discussion of FIG. 1 provides an overview of a circuit capable of determining a resonant frequency for an LLC converter via the primary side of the LLC converter, the discussion of FIGS. 2A - 2B provides additional information regarding the primary side current of an LLC converter.
[0013] FIG. 2A depicts a first waveform 202 and a second waveform 204. The first waveform 202 indicates the voltage across a first switch of an LLC converter, and the second waveform 204 indicates the voltage across a second switch of the LLC converter. As can be seen from FIG. 2A, the first switch is on during a first period 206 and the second switch is on during a second period 208. When an LLC converter is driven at its resonant frequency, switching from first period 202 to the second period 208 occurs at the point in time in which the sinusoidal portion of the primary side current crosses the magnetizing portion of the primary side current, as depicted in FIG. 2B.
[0014] FIG. 2B depicts a resonant current waveform 222 (i.e., the sinusoidal portion of the primary side current) and a magnetizing current wave form 224. The primary side current of an LLC converter is a composite of both the resonant current waveform 222 and the magnetizing current waveform 224. When operating at its resonant frequency, the LLC converter switches between the high side and low side switches on the primary side when the resonant current reaches the magnetizing current. This occurs when the resonant current waveform 222 and the magnetizing current waveform 224 intersect, as indicated by an intersection marking 226.
[0015] While the discussion of FIGS. 2A - 2B describes waveforms associated with an LLC converter, the discussion of FIG. 3 provides additional information regarding an example LLC converter including a resonant frequency determination unit.
[0016] FIG. 3 depicts the primary side 302 of an example LLC converter including a current suppressor 312 and a detector 310, according to some embodiments. The primary side 302 also includes half bridge switches 316 and a controller 306. The resonant frequency determination unit 314 monitors current on the primary side 302 (i.e., the primary side current) of the LLC converter and, based on the primary side current, determines the resonant frequency of the LLC converter.
[0017] The resonant frequency determination unit monitors the primary side current via a sensor 308. The current on the primary side 302 includes a sinusoidal portion (i.e., the resonant current) and a magnetizing portion caused by the transformer. To drive the LLC converter at its resonant frequency, the controller 306 should switch the half bridge switches 316 when the sinusoidal portion crosses the magnetizing portion of the primary side current. To find this crossing point, the resonant frequency determination unit 314 first isolates the sinusoidal portion from the magnetizing portion. In the example LLC converter, the resonant frequency determination unit 314 utilizes a current suppressor 312 to isolate the sinusoidal portion from the magnetizing portion. In one embodiment, the current suppressor 312 isolates the sinusoidal portion from the magnetizing portion by taking the second order derivative of the primary side current.
[0018] After isolating the sinusoidal portion of the primary side current, the resonant frequency determination unit 314 determines the crossing points of the sinusoidal portion and the magnetizing portion. In the example LLC converter, the resonant frequency determination unit 314 utilizes a detector 310 to determine the crossing points. In one embodiment, the detector 310 can be a comparator that compares the sinusoidal portion and the magnetizing portion to determine the crossing points. Based on the crossing points, the resonant frequency determination unit 314 determines the resonant frequency of the LLC converter.
[0019] In some embodiments, the resonant frequency determination unit 314 determines the resonant frequency of the LLC converter on a cycle-by-cycle basis. In such embodiments, the resonant frequency determination unit can adapt to changes in the LLC converter to ensure that the controller 306 continues driving the half bridge switches 316 at the resonant frequency.
[0020] While the discussion of FIG. 3 describes a specific example of a resonant frequency detection unit, the discussion of FIG. 4 provides example operations for determining the resonant frequency of an LLC converter via the primary side of the LLC converter.
[0021] FIG. 4 is a flow chart depicting example operations for determining a resonant frequency for an LLC converter by monitoring current on the primary side of the LLC converter, according to some embodiments. The flow begins at block 402.

中文:
[0002]LLC转换器在以其谐振频率操作时最为高效。LLC转换器的开关频率的小偏差对其效率可具有明显影响。因此,维持LLC转换器在其谐振频率下或在接近于其谐振频率的频率下的操作对于维持高效系统是至关重要的。在其谐振频率下驱动LLC转换器的当前途径聚焦于监测LLC转换器的次级侧以确定其谐振频率。接着将在次级侧处所收集的信息提供到LLC转换器的驱动机构。所述驱动机构在LLC转换器的初级侧上。因此,从次级侧监测LLC转换器引入额外复杂度(例如,增大数目的组件)和成本。
[0005]图1描绘根据一些实施例的包含谐振频率确定单元110的实例LLC转换器100;
[0006]图2A和2B为根据一些实施例的与LLC转换器相关联的波形;
[0007]图3描绘根据一些实施例的包含电流抑制器312和检测器310的实例LLC转换器的初级侧;
[0008]图4为描绘根据一些实施例的用于通过监测LLC转换器的初级侧上的电流而确定LLC转换器的谐振频率的实例操作的流程图。
[0009]如上文所描述,维持LLC转换器在其谐振频率下的操作有助于使所述LLC转换器的效率最大化。当前途径依赖于在所述LLC转换器的次级侧上进行的测量。通常,这些系统感测流动通过整流器的次级侧的电流的零交叉。由于次级侧上的电流与来自变压器的磁化电流隔离,因此这些途径测量次级侧上的电流。即,可监测所述电流而不必考虑磁化电流。尽管这实现对电流的直接测量(即,所述电流与磁化电流隔离),但这会引入额外成本和复杂度。测量LLC转换器的次级侧上的电流会引入额外成本和复杂度的一个原因是归因于以下事实:必须经由隔离势垒将信息发射回到LLC转换器的初级侧。促进此发射所必需的额外组件提高了电路的复杂度,且因此,增大了电路的成本。
[0010]本发明主题的实施例允许在不测量LLC转换器的次级侧处的电流的情况下在其谐振频率下驱动LLC转换器。简单地说,本发明主题的实施例排除对与监测LLC转换器的次级侧上的信息并将所述信息发射到LLC转换器的初级侧相关联的额外组件的需要,且排除与监测LLC转换器的次级侧上的信息并将所述信息发射到LLC转换器的初级侧相关联的成本。替代监测LLC转换器的次级侧,本发明主题的实施例监测LLC转换器的初级侧上的电流。然而,如上文所论述,初级侧上的电流包含通过变压器产生的磁化电流。由于LLC转换器的初级侧上的电流包含正弦部分和磁化电流两者,因此使电流的正弦部分与磁化电流隔离。在一些实施例中,通过对电流执行数学计算(例如,计算二阶导数)而使电流的正弦部分与磁化电流隔离。一旦电流的正弦部分经隔离,可检测到电流的正弦部分的零交叉且可基于所述零交叉驱动半桥式开关。在一些实施例中,利用谐振频率确定单元以监测LLC转换器的初级侧上的电流且确定LLC转换器的谐振频率。图1提供对包含谐振频率确定单元的实例LLC转换器的概述,同时图3提供关于实例谐振频率确定单元的额外信息。
[0011]图1描绘根据一些实施例的包含谐振频率确定单元110的实例LLC转换器100。LLC转换器100具有初级侧102和次级侧104。谐振频率确定单元110位于初级侧102上。谐振频率确定单元100能够基于在LLC转换器100的初级侧102处进行的测量确定LLC转换器100的谐振频率。更具体地说,谐振频率确定单元110经由传感器108监测LLC转换器110的初级侧电流。如先前论述,初级侧电流包含正弦部分(即,谐振电流)和斜坡电流(即,由变压器引起的磁化电流)两者。所述谐振频率确定单元隔离初级侧电流的正弦部分使得可检测到谐振频率。在一个实施例中,谐振频率确定单元110通过获得初级侧电流的二阶导数而隔离初级侧电流的正弦部分。谐振频率确定单元110分析初级侧电流的正弦部分以确定LLC转换器100的谐振频率。在一些实施例中,谐振频率确定单元110通过检测正弦部分与磁化部分交叉(即,零交叉)的点而确定谐振频率。控制器106从谐振频率确定单元110接收谐振频率信息且在所述谐振频率下驱动LLC转换器100。
[0012]在图1的论述提供对能够经由LLC转换器的初级侧确定LLC转换器的谐振频率的电路的概述的同时,图2A到2B的论述提供关于LLC转换器的初级侧电流的额外信息。
[0013]图2A描绘第一波形202和第二波形204。第一波形202指示跨越LLC转换器的第一开关的电压,且第二波形204指示跨越LLC转换器的第二开关的电压。如从图2A可见,所述第一开关在第一周期206期间接通且所述第二开关在第二周期208期间接通。当在LLC转换器的谐振频率下驱动LLC转换器时,在初级侧电流的正弦部分与初级侧电流的磁化部分交叉的时间点进行从第一周期202到第二周期208的切换,如图2B中所描绘。
[0014]图2B描绘谐振电流波形222(即,初级侧电流的正弦部分)和磁化电流波形224。LLC转换器的初级侧电流为谐振电流波形222和磁化电流波形224两者的组合。当在LLC转换器的谐振频率下操作时,LLC转换器在高侧与低侧之间切换,且当谐振电流达到磁化电流时,切换到初级侧。这发生在谐振电流波形222与磁化电流波形224相交时,如由相交标记226指示。
[0015]在图2A到2B的论述描述与LLC转换器相关联的波形的同时,图3的论述提供关于包含谐振频率确定单元的实例LLC转换器的额外信息。
[0016]图3描绘根据一些实施例的包含电流抑制器312和检测器310的实例LLC转换器的初级侧302。初级侧302还包含半桥式开关316和控制器306。谐振频率确定单元314监测LLC转换器的初级侧302上的电流(即,初级侧电流),并且基于所述初级侧电流确定LLC转换器的谐振频率。
[0017]谐振频率确定单元经由传感器308监测初级侧电流。初级侧302上的电流包含正弦部分(即,谐振电流)和由变压器引起的磁化部分。为了在LLC转换器的谐振频率下驱动LLC转换器,控制器306应在正弦部分与初级侧电流的磁化部分交叉时切换半桥式开关316。为了找到此交叉点,谐振频率确定单元314首先使正弦部分与磁化部分隔离。在实例LLC转换器中,谐振频率确定单元314利用电流抑制器312以使正弦部分与磁化部分隔离。在一个实施例中,电流抑制器312通过获得初级侧电流的二阶导数而使正弦部分与磁化部分隔离。
[0018]在隔离初级侧电流的正弦部分之后,谐振频率确定单元314确定正弦部分与磁化部分的交叉点。在实例LLC转换器中,谐振频率确定单元314利用检测器310以确定交叉点。在一个实施例中,检测器310可为比较器,其比较所述正弦部分与所述磁化部分以确定交叉点。基于所述交叉点,谐振频率确定单元314确定LLC转换器的谐振频率。
[0019]在一些实施例中,谐振频率确定单元314逐循环地确定LLC转换器的谐振频率。在这类实施例中,谐振频率确定单元可适应LLC转换器中的改变以确保控制器306继续在谐振频率下驱动半桥式开关316。
[0020]在图3的论述描述谐振频率检测单元的特定实例的同时,图4的论述提供用于经由LLC转换器的初级侧确定LLC转换器的谐振频率的实例操作。
[0021]图4为描绘根据一些实施例的用于通过监测LLC转换器的初级侧上的电流而确定LLC转换器的谐振频率的实例操作的流程图。流程开始于框402。