PEDS2009
EMI Performance Comparison of Switched-Capacitor Bidirectional Converter with and without QR ZCS Yuang-Shung Lee
Shiao-Chen Chu
Dept. of Electronic Engineering & ASE Institute Fu Jen Catholic University Taipei, Taiwan
[email protected]
Dept. of Electronic Engineering Fu Jen Catholic University Taipei, Taiwan
[email protected]
Abstract—The EMI performance of a non-isolated bidirectional switched-capacitor (SC) converter with quasi-resonant (QR) zero current switching (ZCS) converter is proposed in this paper. The quasi-resonant switched-capacitor converter presents low conducted EMI noise due to the sinusoidal resonant current advantages. Theoretical analysis and EMI measurement for the proposed bi-directional power conversion scheme is performed using a detailed equivalent circuit model and field test, respectively. The conducted common-mode (CM) and differential-mode (DM) noises could be separated using a power combiner from the converter circuit noises. Experimental verification is carried out to verify and compare the proposed QR ZCS SC bi-directional converter EMI performance with the conventional hard-switching device. Peak level EMI emissions in the measured frequency spectrums show the proposed device can significantly reduce from 1.5-14.3 dBμV compared with that measured in the converter without QR ZCS for the forward and reverse power flow control schemes at a specified frequency range. The radiated emissions are improved as well. It can also be observed from the CM/DM separated measurement experimental results that the DM noises are dominant. This may present better EMI suppression when designing the power line filter.
converter to overcome the aforementioned problems, This nonisolated converter provides voltage conversion ratios from 3 versus 13 to n versus 1/n by adding a different number of switched-capacitors and power MOSFET switches with a small series-connected resonant inductor for forward and reverse power flow control schemes [2-4]. The 3-mode / 13 mode QR ZCS SC bidirectional converter is proposed and designed in [3]. The conventional SC bidirectional converter is designed without the resonant inductor. The bidirectional dcdc power conversion scheme has received great interest in systems fed by dc power including battery powered electrical vehicles, fuel-cell systems and aerospace systems [2, 5]. The zero current switching operating principle, the EMI modeling and CM/DM emission separated method [7-12] for the quasiresonant switched-capacitor triple-/trisection-modes bidirectional dc-dc converter is elucidated in this paper. Analysis and experimental results are used to verify and validate the predicted EMI performance under the proposed quasi-resonant zero current switching switched-capacitor bidirectional converters.
Keywords-component; bidirectional converter.
I.
soft-switching,
EMI,
DM,
II.
CM,
CONVERTER TOPOLOGIES
Figure 1(a) shows the non-isolation type conventional switched-capacitor bi-directional converter. To reduce switching losses in the MOSFET switches, Fig. 1(b) shows an added small resonant inductor Lr to obtain the zero current soft switching effects. Figure 1(b) shows the circuit configuration of the proposed non-isolation and non-inverting type 3-mode / 13 -mode (triple-mode/ trisection-mode) zero current switching switched-capacitor bi-directional converter developed based on the ZCS SC QR converter. Each of these circuits uses 2n MOSFET switches (n = 3) and only a very small inductor series connected with the switched-capacitors is needed to construct the resonant tanks in the converter. A resonant inductor Lr is connected in series with a set of the switching-capacitors, comprised of C1b and C2b, to achieve a resonant characteristic when each of the switches QNS (contains QN1, QN2 and QN3) or QPS (contains QP1, QP2 and QP3) are switched on during the operating interval. These switches can be designed to switch on and off in the zerocurrent state while the Lr –Cr resonant current is rising or
INTRODUCTION
The modern power supply requires high-speed switching devices to achieve high performance in dynamic response, efficiency, acoustic noise, size and weight. However, these fast switching devices generate high voltage slew rate (dv/dt) and current slew rate (di/dt) that will cause electromagnetic interference (EMI) emission issues [1]-[6]. The switched-capacitor dc to dc converter is a nonmagnetic converter that only requires capacitor and MOSFET switches in the power stage. This converter has the following features: light weight, smaller size and fabrication on a semiconductor integrated circuit chip. Quasi- resonant converters that are able to operate at constant switching frequency with zero-current or zero- voltage switching (ZCS or ZVS) have been used to reduce the current stress in the
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PEDS2009 falling to zero to achieve zero current switching for reduced MOSFET switch power losses. Switches QN1 or QP1 can control the forward power flow from source V1 to the output source V3 as a triple-mode converter (i.e. V3 = 3V1) shown in Fig.2. Figures 2(a)-2(d) show the equivalent circuit for the proposed ZCS SC QR bidirectional DC/DC converter during various operation intervals under the forward power flow control scheme. Switches QN2, QN3, or QP2, QP3, can control the reverse power flow from the source V3 to the other source V1 as a trisectionmode converter (i.e. V1 = 13 V3) shown in Fig. 3. Figures 3(a)– 3(d) show the equivalent circuit for the proposed bidirectional converter during various operation intervals under the reverse power flow control scheme. When the resonant current increases to a peak value and decreases to zero current, it cannot reverse into negative current because there is a diode in the converter circuit loop which ceases current reversing. The working principle and theoretical analysis of the conventional switched-capacitor bi-directional converter, shown in Fig. 1(a), are same as that described in Fig. 1(b) but without the resonant inductor. The detailed circuit analysis and a demonstration of the non-inverting type 3-mode / 13 mode (triple-mode/ trisection-mode) ZCS SC bi-directional resonant converter is illustrated in the following sections [3].
III.
EMI TEST INSTALLATION
To validate the EMI performance of the proposed ZCS SC bi-directional dc/dc converter, experiments were carried out for the proposed triple-mode / trisection-mode non-inverting ZCS SC dc/dc converters. Figure 2(a) shows the conducted emission measured system installation and the DM/CM separated scheme. The line impedance stabilization network (LISN) is used to smooth the input impedance seen from the converter input and assess the conducted noise, which is measured using a spectrum analyzer (SA). This noise can be separated into CM- and DM-noises using the power combiner from the Line and Neutral output terminal of LISN [7-9]. Figure 2(b) shows the schematic configuration of the radiated emission measurement of DUT. Figures 3(a) and 3(b) show the corresponding The venin’s equivalent circuit model for CM- and DM- noises of the converter measured system, respectively [6,8].
(a)
(a)
(b) Fig.2 EMI test installation for (a) conducted emission and the DM/CM noises separated scheme, (b) radiated emission
From the equivalent circuit for the DM and CM EMI noises in the measurement system, the CM and DM noise current can be expressed as (1) and (2): (b) Fig. 1 Switched-capacitor bidirectional converter for (a) without QR ZCS, (b) with QR ZCS
inoise CM =
inoise 1 + inoise 2 2
(1)
inoise DM =
inoise 1 − inoise 2 2
(2)
According to the equivalent circuits, the CM and DM noise voltage can be separated as shown in (3) and (4), respectively.
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vnoise CM = ( Z supply CM + Z DUT CM ).inoise CM
(3)
vnoise DM = ( Z supply DM + Z DUT DM ).inoise DM
(4)
the QR ZCS, respectively. The test point measured comparison results corresponding to Figs. 8 and 9 are tabled in Tables III and IV, respectively.
Where Zsupply CM and ZDUT CM are noted the common-mode impedances of the supply source and device under test, respectively. Zsupply DM and ZDUT DM represent the differentialmode impedances of the supply source and device under test. All of the studied cases were implemented and experimentally investigated. The conducted emission spectrums were compared and analyzed.
From Figs. 5-9 and Tables I-IV, several observations for the EMI performance comparison of the SC bidirectional converters with/without the QR ZCS can be summarized as follows: The EMI noise suppression effect on the proposed QR ZCS bidirectional converter is better than without ZCS because it has turned on and turned off in the zero current state. The maximal EMI noise level for the converter can be significantly reduced compared with the conventional SC bidirectional converter over 14dBµV. The EMI noise in the forward power flow control is lower than it in the reverse control scheme due to fewer switch components in the reverse scheme. The dominant component of the EMI emission is differential-mode for the QR ZCS SC bi-directional converters. Therefore, there is higher noise level existing in the SC converters that will be significantly considered in the EMI filter design.
(a)
(b)
(a)
Fig. 3 Equivalent circuit for (a) common-mode, (b) differential-mode noises
IV.
EXPERIMENTAL RESULTS
Figures 4 and 5 show the measured results for the conducted converter EMI noise with and without QR ZCS under forward and reverse power flow control schemes, respectively. Tables I and II show a comparison of the test point measured results for the proposed converter with and without QR ZCS, respectively. The conducted EMI noise for the converter with QR ZCS is lower than that measured in the converter without it. The maximal noise level reductions are 14.29 dBµV and 12.48 dBµV at 0.62 MHz for the converter under forward and reverse power flow control schemes, respectively. Figures 6 and 7 show the EMI noise for the converter with and without the QR ZCS under forward and reverse power flow control for the common-mode and differential-mode noises, respectively. Figures 8 and 9 show the horizontal and vertical radiated EMI noises under the forward power flow control for the converter with and without
(b) Fig. 4 Measured line conducted EMI noise of the converter under forward power flow control for (a) with QR ZCS (b) without QR ZCS
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Test point
TABLE I. MEASURED RESULTS OF FIG. 4 Measured results (dB µV) Frequency converter without converter with ZCS (MHz) ZCS
1 2 3 4 5 6
0.15 0.31 0.46 0.62 0.93 1.24
82.31 82.32 82.09 82.06 81.99 82.82
80.30 81.22 81.07 67.77 79.36 79.02
(a)
(b)
(a)
Fig. 6 EMI noise for the converter with QR ZCS under forward power flow control for (a) common-mode (b) differential-mode noise
(a)
(b) Fig. 5 Measured line conducted EMI noise for the converter under reverse power flow control for (a) with QR ZCS (b) without QR ZCS
Test point
TABLE II. MEASURED RESULTS OF FIG. 5 Measured results (dB µV) Frequency (MHz) converter without converter with ZCS ZCS
1 2 3 4 5 6
0.15 0.31 0.46 0.62 0.93 1.24
82.26 82.16 82.07 82.06 82.01 81.27
80.90 81.06 69.47 69.58 76.44 80.86
(b) Fig. 7 EMI noise for the converter with QR ZCS under reverse power flow control for (a) common-mode noise (b) differential-mode
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(a)
(a)
(b) (b)
Fig. 8 Horizontal radiated EMI noise for the converter (a) with QR ZCS (b) without QR ZCS under the forward power flow control
Fig. 9 Vertical radiated EMI noise for converter under forward scheme for (a) with QR ZCS (b) without QR ZCS
TABLE III. COMPARED RESULTS OF HORIZONTAL RADIATED EMI NOISES Converter Improvement Test Frequency Converter (dB μV) with QR point (MHz) with QR ZCS ZCS (dB μV) (dB μV) 1 34.86 67.97 75.79 -7.82 2
52.14
59.55
71.69
-15.14
3
63.21
54.19
64.51
-10.32
4
95.61
43.10
151.5
47.37
52.23
-4.86
176.61
46.19
47.27
-1.08
5 6
TABLE IV. COMPARED RESULTS OF VERTICAL RADIATED EMI NOISES Improvement Converter Test Frequency Converter (dB μV) point (MHz) with QR ZCS without QR ZCS (dB μV) (dB μV) 1 37.02 63.85 80.61 -16.76 2
49.98
65.38
80.43
-15.05
3
63.21
53.69
65.99
-12.3
4
103.17
46.12
56.76
-10.64
143.94
50.02
5 6
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154.74
52.74
54.52
-1.78
240.06
51.92
52.65
-0.73
PEDS2009 VI.
CONCLUSIONS
[4]
An EMI performance comparison based on the predicted model and measurement results from the switched capacitor bidirectional converter with and without the quasi-resonant zero-current switching was presented. The measured results show that the conducted emission level in the proposed QR ZCS SC bidirectional converter has been effectively reduced by about 1.5-14.3 dBμV compared with the conventional SC converter at widely measured frequency ranges. Moreover, the radiated emission has also been improved. It can also be observed from the CM/DM separated measurement experimental results that the DM noise is dominant. This will be a significant issue for EMI filter design for the proposed converters. VI.
[5]
[6]
[7]
[8]
ACKNOWLEDGMENTS
This research work was supported by NSC 97-2221-E030-010.
[9]
REFERENCES [10]
[1]
K. W. E. Cheng, “Zero-Current-Switching Switched-Capacitor Converters,” IEE Proceedings Electric Power Application, Vol. 148, Sep 2001, pp. 403-409. [2] Y. S. Lee, Y. Y. Chiu, and M. W. Cheng, “ ZCS Switched-Capacitor Bidirectional Quasi-Resonant Converter,” IEEE Power Electronics And Drive System, Kuala Lumpur, Malaysia, Nov 28-Dec 01 2005, pp. 867871. [3] Y. S. Lee, Y. P. Ko, and C. A. Chi, “A Novel QR ZCS SwitchedCapacitor Bidirectional Converter,” IEEE Power Electronics And Drive System, Nov 27-30 2007, pp. 151-156.
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