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谐振变换器同步整流技术
资料介绍
谐振变换器同步整流技术 对比了传统的同步整流，提出了一种大信号检测的同步整流
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| LLC_Synchronous_Rectification_Using_Resonant_Capacitor_Voltage.pdf | 6M |
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（完整内容请下载后查看）10970
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 34, NO. 11, NOVEMBER 2019
LLC Synchronous Rectification Using Resonant
Capacitor Voltage
Jhih-Da Hsu , Student Member, IEEE, Martin Ordonez , Member, IEEE, Wilson Eberle , Member, IEEE,
Marian Craciun, Member, IEEE, and Chris Botting , Member, IEEE
Abstract—Synchronous rectification (SR) for LLC resonant con-
verters has been developed to enhance the power conversion effi-
ciency and achieve high-power-density design. Conventional SR
driving strategies can be categorized as current-driven methods,
vDS-ON sensing methods, and alternative approaches. T
drey t rt se
thrtahR rvs. The CTs
are lossy and bulky, which is unfavorable to high-power-density
design. Tedcuny
see tte,
yeteilafd
tive e fom imsMost alternative
approaches avoid sensing noise-sensitive signals; however, the op-
erating range is narrow due to the limited information from the
converter. This paper proposes an SR driving strategy based on
the resonant capacitor voltage (RCV) to address those issues. The
Rdednrre. T
sensed RCV is insensitive to the parasitic effects. In addition,
the RCV strategy controls the SR ON-time effectively over a wide
range of operating frequency and loading conditions. Simulation
and experimental results of a 650-W/24-V LLC converter are pre-
sented to validate the effectiveness of the proposed RCV strat-
egy. Compared with the conventional vDS-ON sensing method, the
ON-time error caused by the parasitic effect is greatly reduced,
which improves the power conversion efficiency and reduces the SR
MOSFET temperature.
because of the ability to achieve wide output regulation range
and perform soft switching even at no-load conditions [4]–[6].
Alt siit
tiskhoton
hidny nt tio
out lnwnoulb
ao owerte lae tes f e ut retfir. To further
boost the power conversion efficiency, synchronous rectifiers
(SRs) are favorable choices to reduce the conduction losses in
the rectifier stage. In particular, for high-power and high-current
applications such as server power supplies [7]–[9] and electric
vehicle battery chargers [10]–[13], there is a need for employing
an SR to achieve high efficiency and better thermal performance.
In recent years, vast amounts of research have been conducted in
the field of SRs for LLC converters. Based on the SR control sig-
nal sensing strategies, these SR techniques can be categorized as
follows: current-driven methods, sensing methods, and
alternatives.
Regarding the first category, the current-driven methods, cur-
rent transformers (CTs) are widely applied as the current sensor.
The CT monitors the rectifier current and generates SR driving
signals, as the CT1 illustrated in Fig. 1. Mounting the CT on the
secondary side in series with the SR switches facilitates the gate
driving, for the SR driving signal is naturally synchronous with
t[14]. Yet, the CT introduces extra conduc-
tion losses due to the high rectifier current. In the research [15],
an energy recovery current-driven SR is proposed. st o
egng tlg
thcrreeieey aece mreefficecf
thCTHowever, each SR requires one CT for gate driving; two
CTs for center-tapped full-wave rectification are needed. For
full-bridge rectification, the transformer structure is even more
complicated. The high volume occupied by the CT is unfavor-
able for high-power-density design. Guo et al. [16] propose a
current-driven SR for center-tapped full-wave rectifiers that re-
quires only one CT. The CTs are integrated into one, and the
utilization of the CT is improved. However, each SR needs one
set of winding to detect the current, and hence, the conduction
losses are similar. In [17]–[19], the application targets toward
the voltage-doubler and full-bridge rectifier topology, and the
current sensor count for each topology is reduced to one as well.
Another idea to reduce the space occupied by the CTs is to in-
tegrate them with the main transformer, as investigated in the
literature [20]. Intrinsically, placing the CT in series with the
power loop introduces power losses. The peak rectifier current
Index Terms—Current sensorless, LLC resonant converter,
resonant capacitor voltage (RCV), synchronous rectification (SR).
I. INTRODUCTION
ESONANT converters are advantageous for high-
switching-frequency design for their capability of reduc-
R
ing the switching losses of active components by performing soft
switching [1]–[3]. Among those various topologies of resonant
converters, the LLC resonant converter is attractive primarily
Manuscript received April 10, 2018; revised September 6, 2018 and Decem-
ber 23, 2018; accepted February 5, 2019. Date of publication February 20,
2019; date of current version August 29, 2019. This work was supported by
the Natural Sciences and Engineering Research Council of Canada (NSERC).
Recommended for publication by Associate Editor T. Qian. (Corresponding
author: Martin Ordonez.)
J. Hsu, M. Ordonez, and W. Eberle are with the Department of Electrical
and Computer Engineering, The University of British Columbia, Vancouver,
BC V6T 1Z4, Canada (e-mail:,
M. Craciun and C. Botting are with Delta-Q Technologies Corpora-
tion, Burnaby, BC V5G 3H3, Canada (e-mail:,
Color versions of one or more of the figures in this paper are available online
Digital Object Identifier 10.1109/TPEL.2019.2900459
0885-8993 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
HSU et al.: LLC SYNCHRONOUS RECTIFICATION USING RESONANT CAPACITOR VOLTAGE
10971
Fig. 1. Conventional LLC SR control methods: current-driven method with the CT mounted on the secondary side ➊ for sensing the rectifier current, current-driven
method with the CT located on the primary side ➊ for sensing the resonant current, and the vDS-ON sensing method ➊.
of LLC converters is high, and the CT in series with the power sacrifices the power conversion efficiency and increases the de-
loop has to be well designed to prevent saturation.
vice temperature.
For avoiding high current sensing, the other group of the
The second group of the vDS-ON sensing method is to add an
current-driven method places the CT in series with the reso- RC compensation network in parallel with the MOSFET to com-
nant tank on the primary side [21]–[24], as the CT2 illustrated pensate for the inductive voltage offset and further reduces the
in Fig. 1. The current stress of this kind is less than that of SR ON-time error. In the literature [29], Fu et al. propose a re-
secondary-side CTs for most applications using LLC convert- settable RC circuit to compensate for the voltage offset caused
ers. Only one CT is needed for sensing the resonant current. by the stray inductance. In order to achieve good performance,
However, the zero-current crossing of the resonant current () the time constant of the RC circuit must be carefully selected
is different from that of the rectifier current () due to the to match the impedance ratio of the stray inductance and the
component of magnetizing current (), as illustrated in Fig. 1. MOSFET ON-state resistance. However, the stray inductance
Therefore, additional circuits for canceling im are needed. Since varies with the MOSFET package and is usually not a confined
the slope of im is proportional to the output voltage (Vout) when specification in datasheets. Besides, the MOSFET ON-state re-
the transformer is coupled, the output voltage is sensed and con- sistance drifts with temperature. Therefore, it is challenging to
verted to cancel im . As a result, as long as the portion of im match the impedance ratio. Later, Wang et al. introduce an-
is completely subtracted from ir , the rest portion is in-phase other RC compensation circuit to tackle the inductive voltage
and proportional to the rectifier current and can be applied to offset issue [30], [31]. Compared with the prior research, the
generate the SR gate driving signal.
compensation circuit is simplified, and yet, accurate impedance
The second category of the SR techniques for LLC converters matching is still required.
is the vDS-ON sensing method. The primary benefit compared
Since the inductive voltage caused by the stray inductance is
with the current-driven methods is the removal of the current difficult to be compensated externally, other research using the
sensors, which eliminates the power losses and reduces the lay- vDS-ON sensing method focuses on adaptive SR ON-time, which
out space. The first group of this category, which is also widely are sorted as the third group in this category. The characteris-
adopted in the industry, is to sense the voltage across the SR tic of the adaptive SR ON-time technique is that the controller
MOSFETs during the turn-ON phase (vDS-ON) [25]–[27]. Due to attempts to increase or decrease a time step for the present SR
the small turn-ON resistance of the SR MOSFETs, the sensed switching cycle based on the amount of ON-time error from
voltage is minimal. As a result, high accuracy, small offset, and the previous cycle, in order to compensate for the uncertain
fast response comparator design is needed. Besides, the small amount of ON-time error caused by the inductive voltage. The
vDS-ON is easily affected by the voltage drops on the parasitic adaptive control method for adjusting the SR turn-OFF instant
components. As illustrated in Fig. 1, the sensed voltage sig- is introduced in [32] and [33]; the concept is applied to the SR
nal contains the voltage across the stray inductance (Lstray ). turn-ON delay reduction in the follow-up research [34], [35].
The inductive voltage offsets the sensed vDS-ON, which causes The adaptive SR controllers compare the SR ON-time with the
premature turn-OFF of the SR. The stray inductance exists in falling and the rising edge of the drain–source voltage of the SR
both the signal sensing loop and the MOSFET package, so even MOSFET. When a sizable ON-time error is detected, the controller
if the signal sensing trace can be minimized, the stray induc- increases the SR ON-time gradually in the following switching
tance in the MOSFET package is still significant [28]. Premature cycles; when the ON-time error is small, the controller shrinks
turn-OFF of the SR leads to ON-time error; more portion of the the ON-time until the large ON-time error is detected again.
rectifier current is conducted by the MOSFET body diode, which As the ON-time shrinks, a certain amount of safe operation
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