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An Improved Adaptive Synchronous Rectification Method With the Enhanced Capacity to Eliminate Reverse Current
一种改进的自适应同步整流方法,具有增强的消除反向电流的能力

Qinsong Qian , Qi Liu , Student Member, IEEE, Min Zheng, Ziyan Zhou, Shengyou Xu,
钱勤松 , 刘琦 , IEEE学生会员, 郑敏, 周子妍, 徐胜友,
and Weifeng Sun , Senior Member, IEEE
伟峰,IEEE资深会员

Abstract 抽象

Adaptive synchronous rectification (SR) is a good solution to solve duty cycle loss for resonant converter. Usually, whether the synchronous rectifier is turned OFF prematurely or late can be detected by whether the body diode is conducted on or not. However, when the switching frequency is below the resonant frequency, both SR turning-OFF prematurely and late may generate body diode conduction (BDC), which will cause logic errors in the conventional adaptive SR strategy. Then, a large reverse current from load to source will occur, which damages the efficiency. To solve the problem, the time-domain modeling of the SR drain-tosource voltage is established to analyze the mechanism of BDC caused by SR turning-off late. Moreover, an improved adaptive SR driving scheme is proposed, which can identify the two different types of BDC and tune SR to be turned OFF exactly. Finally, a prototype is built to verify the established model and the proposed SR method. The prototype proves that both the duty cycle loss and the reverse current are eliminated and efficiency improvement of is achieved.
自适应同步整流(SR)是解决 谐振变换器占空比损耗的良好解决方案。通常,同步整流器是否过早关闭或延迟关闭可以通过体二极管是否导通来检测。然而,当开关频率低于谐振频率时,SR过早关断和过晚关断都可能产生体二极管导通(BDC),这将导致传统自适应SR策略中的逻辑误差。然后,从负载到电源会产生较大的反向电流,从而损害效率。针对该问题,建立了SR漏源电压的时域建模,分析了SR晚关断导致BDC的机理。此外,该文还提出了一种改进的自适应SR驱动方案,该方案可以识别两种不同类型的BDC,并精确地调谐SR的关闭。最后,构建原型 对已建立的模型和所提出的SR方法进行验证。该原型证明了消除了占空比损耗和反向电流,并实现了效率的 提高。

Index Terms-Adaptive synchronous rectification, body diode conduction (BDC), efficiency optimization, high frequency, resonant converter, reverse current, ZCS.
索引术语-自适应同步整流、体二极管导通 (BDC)、效率优化、高频、 谐振转换器、反向电流、ZCS。

I. INTRODUCTION 一、引言

ECENTLY, the rapid development of information technology has increased the demand for high-power-density power supplies. Thus, the requirement for both the switching frequency and efficiency are becoming higher and higher. As shown in Fig. 1, LLC resonant converter with synchronous rectification is an excellent candidate for high-frequency and high-efficiency applications due to the features of achieving
实际上,信息技术的快速发展增加了对高功率密度电源的需求。因此,对开关频率和效率的要求越来越高。如图1所示,具有同步整流功能的LLC谐振转换器是高频和高效率应用的绝佳候选者,因为它具有以下特点:
Fig. 1. LLC resonant converter with synchronous rectification.
图 1.具有同步整流功能的LLC谐振转换器。
zero voltage switching (ZVS) for primary switches and zero current switching (ZCS) for secondary switches [1]-[4]. The performance of synchronous rectification is one of the keys to improving efficiency. However, as the switching frequency increases, the duty cycle loss caused by stray inductance is more and more serious [5]. The conventional sensing based scheme is no longer suitable for high-frequency applications. Research on high-frequency SR strategies is becoming more and more important.
初级开关为零电压开关(ZVS),次级开关为零电流开关(ZCS)[1]-[4]。同步整流的性能是提高效率的关键之一。然而,随着开关频率的增加,杂散电感引起的占空比损耗越来越严重[5]。传统的 基于传感的方案不再适用于高频应用。对高频SR策略的研究变得越来越重要。
Over the last few years, the synchronous rectification of resonant converter can be classified into: current sensing based method [6]-[11]; sensing based method [12]-[19]; primaryside voltage sensing-based method [20], [21]; and the adaptive driving method [5], [22]-[30].
近几年来,谐振变换器的同步整流 可分为:基于电流检测的方法[6]-[11]; 基于传感的方法[12]-[19];基于初级侧电压检测的方法[20],[21];以及自适应驾驶方法[5],[22]-[30]。

A. Current Sensing-Based Method
A. 基于电流检测的方法

Sampling the zero-crossing point of (the current through the synchronous rectifier) to generate the driving signals is the most direct SR solution [6]-[9]. However, sensing the secondary-side current will result in large sampling loss and volume, which is unacceptable. As shown in Fig. 2, the improved method is the indirect current sensing-based scheme. By sensing the resonant inductor current and magnetizing inductor current and comparing between two current signals, the driving signal for SR can be generated. In the literature [10], the resonant current is sampled by a current transformer, and the magnetizing current is obtained by the integration of the voltage across the transformer. In the literature [11], an external inductor is paralleled with the magnetizing inductance and
对过零点 (通过同步整流器的电流)进行采样以产生驱动信号是最直接的SR解决方案[6]-[9]。然而,检测次级侧电流将导致较大的采样损耗和体积,这是不可接受的。如图2所示,改进的方法是基于间接电流检测的方案。通过检测谐振电感电流和磁化电感电流,并比较两个电流信号,可以生成SR的驱动信号。在文献[10]中,谐振电流 由电流互感器采样,并通过对变压器两端的电压进行积分来获得磁化电流。在文献[11]中,外部电感器 与磁化电感 并联,并且
Fig. 2. Current sensing-based SR strategy.
图 2.基于电流检测的SR策略。
Fig. 3. Stray inductance leads to duty cycle loss.
图 3.杂散电感会导致占空比损耗。
is much smaller than . Thus, the magnetizing current flows through the external inductor, which can be sampled to drive SR. The drawbacks of these indirect strategies are that the sensing loss is still considerable; the current transformer introduces the additional volume; the isolation performance is degraded; and the parameter deviation will seriously affect the performance of synchronous rectification.
小得多。因此,磁化电流流过外部电感器,可以对外部电感器进行采样以驱动SR。这些间接策略的缺点是传感损失仍然相当大;电流互感器引入额外的体积;隔离性能下降;参数偏差会严重影响同步整流的性能。

B. VDS Sensing-Based Method
B. 基于VDS传感的方法

In the literature [12], is sampled and converted to the signal through a well-designed impedance network. The method owns the ultralow-cost but is sensitive to the switching frequency. sensing based method is widely applied in the smart driver integrated circuits(ICs) [13], [14] due to the feature of low sensing loss. While for the high-frequency resonant converter, di/dt of the secondary-side current increases drastically, which enlarges the duty cycle loss (see Fig. 3) caused by the stray inductance [15]. The compensation scheme [13], [15]-[19] is especially important for high-frequency applications.
在文献[12]中, 通过精心设计的阻抗网络进行采样并转换为 信号。该方法具有超低成本,但对开关频率敏感。 基于传感的方法由于具有低传感损耗的特点,在智能驱动集成电路(IC)中得到了广泛的应用[13],[14]。而对于高频 谐振转换器,次级侧电流的di/dt急剧增加,这扩大了由杂散电感引起的占空比损耗(见图3)[15]。补偿方案[13]、[15]-[19]对于高频应用尤为重要。
In the literature [15], an active RC compensation network is designed to sense the actual voltage on . In the literature [16], two switches are simplified in the compensation network with no change of performance. In the literature [13], [17], a well-designed inductor is in series at the source terminal to balance the phase leading generated by the equivalent series inductance(ESL). In the literature [18], the gate drive voltage is deliberately reduced before SR turning-OFF to increase . Then, the early turning-OFF problem caused by ESL can be relieved. In the literature [19], the same effect is achieved through different drive timings for parallel MOSFET to relieve duty cycle loss. These methods can compensate for the influence
在文献[15]中,有源RC补偿网络被设计用于检测上 的实际电压。在文献[16]中,在补偿网络中简化了两个开关,性能没有变化。在文献[13]、[17]中,在源端串联了一个设计良好的电感器,以平衡等效串联电感(ESL)产生的相位超前。在文献[18]中,在SR关断之前故意降低栅极驱动电压以增加 。然后,可以缓解 ESL 导致的早期关闭问题。在文献[19]中,通过不同的并联MOSFET驱动时序可以达到相同的效果,以减轻占空比损耗。这些方法可以补偿影响

Fig. 4. Adaptive SR strategy proposed in [5].
图 4.[5]中提出的自适应SR策略。
of stray inductance to reduce duty cycle loss at the cost of circuit complexity. However, the parameters such as the stray inductance and should be extracted and the performance of compensation depends sensitively on the accuracy of these extracted parameters. Moreover, it is difficult to design a compensator suitable for all working conditions, since varies at different temperatures.
的杂散电感,以降低占空比损耗,但代价是电路复杂性。然而, 杂散电感等参数和补偿性能敏感地取决于这些提取参数的精度。此外,由于 在不同温度下会有所不同,因此很难设计出适合所有工作条件的补偿器。

C. Primary-Side Voltage Sensing-Based Method
C. 基于初级侧电压检测的方法

Based on the operation principles of the resonant converter, SR only conducts during operation stage. Therefore, the SR driving signal can be generated by the recognition of operation stage [31], which can be obtained by sampling the primary-side voltage. In the literature [20], the polarities of the half-bridge midpoint voltage and the voltage of the transformer are sampled and compared to determine operation stage. In the literature [21], the sampled resonant capacitor voltage is integrated and compared with both input and output voltage to determine operation stage. The two methods can significantly reduce the sampling loss and immune to the high-frequency noise.
根据 谐振变换器的工作原理,SR仅在 工作阶段导通。因此,SR驱动信号可以通过 识别工作级[31]产生,该信号可以通过对初级侧电压进行采样来获得。在文献[20]中,对半桥中点电压和变压器电压的极性进行采样和比较,以确定 工作阶段。在文献[21]中,对采样谐振电容电压 进行积分,并与输入和输出电压进行比较,以确定 工作级。这两种方法都能显著降低采样损耗,不受高频噪声的影响。

D. Adaptive SR Driving Method
D. 自适应SR驱动方式

The adaptive SR driving scheme introduces the concept of closed-loop to thoroughly eliminate duty cycle loss. The gate driver signal of the current cycle is tuned by the sensed turning. OFF status of the previous cycle.
自适应SR驱动方案引入了闭环概念,彻底消除了占空比损耗。电流周期的栅极驱动器信号由感测的律速进行调谐。上一个周期的 OFF 状态。
The features of the body diode conduction (BDC) are used to identify whether SR is turned OFF prematurely or late. As shown in Fig. 4, a universal adaptive driving scheme is proposed in the literature [5], where the turning-OFF point lags when BDC is detected and leads when BDC does not occur. In the literature [22], the adaptive driving scheme is applied to the low-cost microcontroller through multi-cycle adjustment. In the
体二极管传导 (BDC) 的特征用于识别 SR 是过早关闭还是延迟关闭。如图4所示,文献[5]提出了一种通用的自适应驱动方案,其中当检测到BDC时,律断点滞后,当BDC不发生时,律断点领先。文献[22]中,自适应驱动方案通过多周期调整应用于低成本微控制器。在
Fig. 5. BDC caused by SR turning-OFF late.
图 5.SR 关闭延迟导致的 BDC。
literature [23], the body diode information is sensed to add delay to eliminate the duty cycle loss. In the literature [25], the regulation of turning-OFF point is achieved by the regulation of the turning-OFF voltage threshold and multilevel thresholds are set to ensure fast and accurate regulation. In the literature [26], an analytic-adaptive SR strategy is proposed for improving the transient-state performance. The dual verification strategy for SR turning-OFF is proposed in [27] to regulate the proper turning-OFF point of SR.
文献[23]中,体二极管信息被检测以增加延迟以消除占空比损耗。文献[25]中,通过调节关断电压阈值来实现关断点的调节,并设置多级阈值,确保快速准确的调节。文献[26]提出了一种分析自适应SR策略来改善瞬态性能。文献[27]提出了SR关断的双重验证策略,以规范SR的正确关断点。
With the development of these years, adaptive SR strategy has gradually been accepted by the industry. Several IC products [28]-[30] have adopted the concept to solve the duty cycle loss. Meanwhile, with the development of the performance of the lowcost microcontrollers, it will become more and more popular to use adaptive SR strategies to solve the high-frequency SR problems.
随着这些年的发展,自适应SR策略逐渐被业界所接受。一些IC产品[28]-[30]采用了这一概念来解决占空比损耗问题。同时,随着低成本微控制器性能的发展,使用自适应SR策略解决高频SR问题将越来越流行。
The similarity of these adaptive schemes is that sensing BDC to identify the turning-OFF information of the current cycle and BDC represents that SR turns OFF prematurely. As shown in Fig. 5, when the SR turns OFF late, the reverse current will charge the junction capacitance, and the subsequent resonance process will also cause BDC [24]. In other words, both turning-OFF prematurely and late will lead to the conduction of the body diode. If the detected BDC is caused by SR turning-OFF late, the control logic in [5] and [22] will be reversed, causing a large reverse current from the load to the source.
这些自适应方案的相似之处在于,感应 BDC 以识别当前周期的关断信息,而 BDC 表示 SR 过早关闭。如图5所示,当SR关断较晚时,反向电流将对结电容充电,随后的谐振过程也会引起BDC[24]。换言之,过早关断和过晚关断都会导致体二极管导通。如果检测到的BDC是由SR关断较晚引起的,则[5]和[22]中的控制逻辑将反转,从而导致从负载到电源的反向电流很大。
In this article, the issue of BDC caused by turning-OFF late is analyzed quantitatively through the model for sr during the dead-time. Moreover, an improved adaptive SR strategy is proposed to distinguish the two different types of BDC and to take the corresponding measures to regulate the turning-OFF point. The proposed method can solve the problems of the reverse current from load to the source caused by SR turning-OFF late. Meanwhile, the proposed method is fully compatible with the conventional adaptive SR strategy.
本文通过死区 期间sr模型定量分析了延迟关断导致的BDC问题。此外,提出了一种改进的自适应SR策略来区分两种不同类型的BDC,并采取相应的措施来调节关断点。该方法可以解决SR关断较晚导致负载到电源的反向电流问题。同时,所提方法与传统的自适应SR策略完全兼容。
This article is structured as follows. The time-domain model between the drain-source voltage sr of SR and the reverse current is established in Section II. Then, the generation mechanism and the condition of BDC caused by turning-OFF late are discussed quantitatively. In Section III, the sampling circuits and the control logic of the proposed adaptive SR strategy are described. The sampling circuits are simple and low-loss,
本文的结构如下。第二节建立了SR漏源电压 sr与反向电流 之间的时域模型。然后,定量讨论了延迟关断导致的BDC的产生机理和情况;在第III节中,描述了所提出的自适应SR策略的采样电路和控制逻辑。采样电路简单,损耗低,
Fig. 6. Definition of the symbol of the related voltage and current.
图 6.相关电压和电流符号的定义。
while the control logic is compatible with the conventional adaptive SR strategy. A comparison of different SR driving schemes is presented in Section IV. Finally, the experimental results and the conclusion are given in Sections V and VI, respectively
而控制逻辑与传统的自适应SR策略兼容。第四节介绍了不同SR驱动方案的比较。最后,实验结果和结论分别在第五节和第六节给出

II. ISSUE OF BDC CAUSED BY SR TURNING-OFF LATE
II. SR关闭延迟导致的BDC问题

In this section, the principle of the BDC after turning OFF late will be analyzed. Since this type of BDC only occurs at the condition of , the other two conditions are not discussed in this section, but will be covered in the following section. For the convenience of the effective presentation, the symbol of the related voltage and current are defined as follows.
在本节中,将分析延迟关闭后BDC的原理。由于这种类型的 BDC 仅在 的条件下发生,因此本节不讨论其他两个条件,但将在下一节中介绍。为了便于有效显示,相关电压和电流的符号定义如下。
  1. Resonant current .
    谐振电流
  2. Magnetic current .
    磁电流
  3. Midpoint voltage of the half bridge .
    半桥 的中点电压。
  4. Drain-source voltage of the synchronous rectifier .
    同步整流器 的漏源电压。
  5. Voltage across the transformer .
    变压器 两端的电压。
  6. Voltage across the resonant capacitor .
    谐振电容两端的电压
As shown in Fig. 6, the positive directions of and are from to and from to , respectively. The positive directions of , and pri are from to , from to , and from a to d.
如图 6 所示,和 的 正方向分别为 from to 和 from to 。和 pri 的 正方向是 from to 、from to 和 from a to d。
Fig. 7 shows the main voltage and current waveform during the dead-time when . There are three stages before the BDC. The equivalent circuits of these stages are shown in Fig. 8 .
图 7 显示了死区期间 的主要电压和电流波形。BDC 之前有三个阶段。这些级的等效电路如图8所示。
  1. Stage : At , the resonant current equals the magnetic current and the current through decreases to 0 . Since is still , keeps falling to the negative. The current is transferring from the load to the source. During this stage, .sr is slightly larger than 0 and is clamped to be . At , this stage ends when is turned OFF.
    阶段 :在 时,谐振电流 等于磁电流 ,通过 的电流减小到 0。由于 是静止 的, 所以一直下降到负数。电流从负载传递到电源。在此阶段, .sr 略大于 0,并被 钳制为 。在 时,此阶段在关闭时 结束。
  2. Stage : After is turned OFF, the reversed charges the junction capacitance of , causing .sr to rise. The amplitude of gradually decreases as increases. When returns reaches the peak value of this stage. At this time, equals to . This is a multiresonance process composed of the four energy storage devices , and . Then, 'sr will continue to decrease and may cause the at the lowest point (shown as the red dashed circle in Fig. 7). As shown in Fig.9, the simplified equivalent circuits of stage
    阶段 :关断后 ,反向 充电的结电容 ,导致 .sr上升。的 振幅随着 的增加而逐渐减小。当回报 达到此阶段的峰值时 。此时, 等于 .这是一个由四个储能装置 组成的多谐振过程 。然后,'sr 将继续减小, 并可能导致最低点( 如图 7 中的红色虚线圆圈所示)。如图9所示,简化后的平台等效电路
Fig. 7. Main waveforms during the dead-time when .
图 7.死区期间 的主要波形。
Fig. 8. Simplified equivalent circuits of stage 2.
图 8.简化了阶段 2 的等效电路。
2 can be obtained by converting the junction capacitance of the synchronous rectifier to the primary side.
2可以通过将同步整流器的结电容转换为初级侧来获得。
Based on Kirchhoff's law, the Time-Domain Equations of this stage can be obtained that
根据基尔霍夫定律,可以得到这个阶段的时域方程
where is the sum of the primary-side parasitic capacitance of the transformer and the equivalent junction capacitance converted from the synchronous rectifier. The voltage of can be represented by the voltage across .
其中 ,变压器的初级侧寄生电容与从同步整流器转换而来的等效结电容之和。的 电压可以用两端 的电压来表示。
Through Laplace transformation, (1) can be transformed into
通过拉普拉斯变换,(1)可以转化为
Then, can be represented that
那么, 可以表示为
where , and are the coefficients related to the initial values of the voltage and current and can be represented that
其中 , 和 是与电压和电流的初始值相关的系数,可以表示为
where and are the constant related to the resonant parameters and can be represented that
其中 是与谐振参数相关的常数,可以表示为
The time-domain equation of can be obtained by inverse Laplace transformation
时域方程可以通过逆拉普拉斯变换得到
where and are the angular frequency resonated by , , and