ZVS Resonant DC-link Inverter using Soft Switching Boost Converter Young-Ho Kim School of Information and Communication Engineering. Sungkyunkwan University, Suwon, South Korea. e-mail:
[email protected] u
Gil-Ro Cha School of Information and Communication Engineering. Sungkyunkwan University, Suwon, South Korea. e-mail:
[email protected] u
Young-Hyok Ji School of Information and Communication Engineering. Sungkyunkwan University, Suwon, South Korea. e-mail:
[email protected] u
Abstract—In this paper, ZVS resonant DC-link inverter using soft switching boost converter is proposed. In the resonant inverter consisted of converter stage and inverter stage, converter stage switches S1, S2 are turned on and off with zerovoltage-switching (ZVS) and zero-current-switching (ZCS), and inverter stage switches S3, S4, S5, S6 and S7, are turned on and off with ZVS. As a result, the proposed circuit can reduce the switching loss. Operational principles and detailed analysis are presented. Simulation results indicate that the switches of the proposed resonant inverter are operated under the ZVS condition
I.
INTRODUCTION
Today, the power electronics are in need of the development of smaller, lighter more efficient, less expensive and more reliable systems. The increase of the switching frequency reduces the size of the magnetic components but increases the switching losses [1], [2]. To solve these problems, many ZVS or ZCS circuits present. In order to achieve better performance, higher efficiency, and higher power density, soft-switching techniques have recently been applied in the design of inverters [3], [4]. Therefore, this paper proposes the two stage resonant inverter using soft switching boost converter. In first stage, a soft switching boost converter performs ZVS and ZCS to improve the efficiency of a boost. Under the condition of zero-voltage and zero-current by inductor and capacitor resonance, soft switching can reduce the voltage stress and switch loss produced at the switch [5]-[8]. In second stage, resonant inverter switches are performed ZVS by the switch in DClink. The resonant switch in DC-link is turned on and off when the resonant capacitor value in the first stage is zerovoltage. Because of ZVS and ZCS, the inverter can decrease the switching stress and loss. In this paper, we have analyzed the operational principle of the proposed resonant DC-link inverter. Simulation results will be presented to confirm the theoretical analysis.
Jae-Hyung Kim School of Information and Communication Engineering. Sungkyunkwan University, Suwon, South Korea. e-mail:
[email protected]. ac.kr
Yong-Chae Jung Department of Electronic Engineering. Namseoul University, Cheonan, South Korea e-mail:
[email protected] r
†
Chung-Yuen Won School of Information and Communication Engineering. Sungkyunkwan University, Suwon, South Korea. e-mail:
[email protected]. ac.kr
II. PROPOSED SOFT SWITCHING H-BRIDGE INVERTER A. Proposed inverter circuit Fig. 1 shows a conventional H-bridge inverter using softswitching boost converter. Additionally, the soft-switching boost converter has a switch, inductor, capacitor and two diodes circuit against the conventional boost converter. So, the converter state switches are turned on and off with ZVS and ZCS. But the inverter stage switches of the conventional inverter are turned on and off with hard switching. Therefore conventional inverter switches generate the switching loss and stress. Fig. 2 shows the ZVS resonant DC-link inverter using softswitching boost converter. The converter stage equals the conventional soft-switching boost converter, but the second stage differs from the conventional H-bridge inverter stage. Fig. 2 inverter stage includes one switch in DC-link. The additional switch in DC-link is turned on and off with ZVS because of the anti-parallel diode and resonant capacitor Cr. Using the switch in DC-link, the switch 4, 5, 6 and 7 of inverter stage are turned on and off with ZVS. Therefore, all of the switches operate soft-switching when the each switch is turned on and off and the switching loss and voltage stress are reduced.
Fig. 1 The conventional H-bridge inverter using soft-switching boost converter
Fig. 2 The proposed ZVS resonant DC-link inverter using soft-switching boost converter
B. Operation mode analysis To analyze the operational modes of the proposed circuit, it is explained in divided seven modes with the current paths as shown in Fig. 3. (This mode analysis represents H-bridge inverter as current source) L
L S1
D2
D1
Lr S2
V in
S3
Cr C
C
S2
D1
Mode 2
L
M1 M2 M3 M4 M5 M6 M 7
L
D2
S1
S3 Cr
Lr
D2
S1
V in
S3 C
S2
D1
Fig. 4 The operational waveforms of the proposed resonant inverter
Cr
Lr
C
S2
D1
Mode 4
Mode 3
L
L
D2
S1
V in
S3
Cr
Lr
Mode 1
V in
D2
S1
V in
D1
S3 Cr
Lr
C
S2
V in
D2
S1 D1
S2
D2
S1
ωr =
Lr Cr 1
Lr Cr iL ≅ imax
S3
(5)
(6) (7)
Cr
Lr D1
(4)
C
L V in
vLr ( t1 ) = Vdc
Z=
Mode 6
Mode 5
(3)
S3 Cr
Lr
vLr ( t0 ) = 0
C
S2 Mode 7
Fig. 3 Operation mode diagram of a ZVS resonant DC-link inverter using soft-switching boost converter
Mode 1 (M1) In this mode, the switch S1 and S2 are turned off with ZVS. The resonance between resonant inductor Lr and resonant capacitor Cr is started. The resonant capacitor Cr is charged to output voltage by the main inductor current iL and resonant inductor current iLr. The energy stored in the main inductor L is the maximum. The corresponding equations are given by (1)-(7). The resonant capacitor voltage vCr equals the output voltage at the end of Mode 1 iLr ( t ) = ( I min − I o ) − ( I max − I Lr max ) cos ωr t
(1)
vCr ( t ) = ( I max − I Lr max ) Z r sin ωr t
(2)
Mode 2 (M2) This mode occurs when the resonant capacitor voltage is charged from main inductor and resonant. The energy stored in the main inductor L is decreased linearly. The DC-link capacitor is charged because the main inductor L and resonant inductor Lr energy are transferred to DC-link capacitor C through anti-parallel diode of S3. The corresponding equations are given by (8)-(10). The diode D1 and D2 is turned off with the zero-voltage at the end of Mode 2.
Vdc t + iLr ( t1 ) Lr V − Vdc iL ( t ) = i t + imax L vLr ( t ) = Vdc
iLr ( t ) = −
(8) (9) (10)
Mode 3 (M3) The switch S3 is turned on with ZVS. The DC-link capacitor C is charged by main inductor L. The energy stored in the main inductor L is decreased linearly. The corresponding equations are given by (11)-(13). The DC-link capacitor is completely charged at the end of Mode 3. Vi − Vdc t + iL ( t2 ) L iLr ( t ) = 0
iL ( t ) =
VCr ( t ) = Vdc
iLr ( t6 ) = iLr max
(23)
vLr ( t5 ) = Vdc
(24)
vLr ( t6 ) = 0
(25)
Zr =
ωr =
(11)
Lr Cr
(26)
1
(27)
Lr Cr iL ≅ I min
(12)
(28)
(13)
Mode 4 (M4) In this mode, the DC-link capacitor C begins to discharge the stored energy. The energy stored in the main inductor L is decreased linearly. The corresponding equations are given by (14)-(16). The switch S1, S2 is turned on with ZCS at the end of Mode 4.
Mode 7 (M7) In this mode, the switch S1 and S2 keep up the turn on state and the freewheeling diodes of D1 and D2 are turned on. Therefore the resonant inductor current flows through the two freewheeling paths. The energy stored in the main inductor L is increased linearly. The corresponding equations are given by (29)-(31). The energy stored in the resonant capacitor Cr is completely discharged at the end of Mode 7
iLr ( t ) = 0
(14)
i Lr ( t ) = I 2
(29)
vCr ( t ) = Vdc
(15)
v Cr ( t ) = 0
(30)
Vi − Vdc t + iL ( t3 ) L
iL ( t ) =
(16)
Mode 5 (M5) This mode occurs when the switch S1 and S2 are turned on with ZCS. The energy stored in the resonant inductor Lr is increased linearly. The energy stored in the main inductor L is decreased linearly. The corresponding equations are given by (17)-(20). The switch S3 is turned off with ZVS at the end of Mode 5. Vi − Vdc t + iL ( i4 ) L iLr ( t4 ) = 0
i L (t ) =
Vdc t Lr VLr ( t ) = Vdc
iLr ( t ) =
iLr ( t ) = ( I min − I o ) +
Vo sin ωr t Zr
Vi t + I min L
(31)
III. SIMULATION RESULTS This proposed ZVS resonant DC-link inverter using softswitching boost converter is simulated to demonstrate the features and theoretical analysis. A 3kW prototype resonant inverter is built and simulated using the PSIM tool. The parameters used for simulations areas follow TABLE I. Fig. 5 shows Principle operation waveforms of the proposed resonant inverter. Fig. 6 shows Key waveforms of the proposed resonant inverter.
(17) (18) (19) (20)
Mode 6 (M6) The resonant capacitor Cr and the resonant inductor Lr start a resonance. The DC-link switch S3 is turned off with ZVS. The energy stored in the main inductor L is the minimum. The corresponding equations are given by (21)-(28). The energy stored in the resonant capacitor Cr is completely discharged at the end of Mode 6. vCr ( t ) = Vo cos ωr t
iL ( t ) =
(21)
(22)
TABLE I THE SIMULATION PARAMETER Parameter
Value
Rated Power
3 [kW ]
Input Voltage
200 [Vdc ]
DC-link Voltage
400 [Vdc ]
Main inductor
500 [µ H ]
DC-link capacitor
680 [ µ F ]
Resonant inductor
10 [ µ H ]
Resonant capacitor
30 [ nF ]
Switching Freq. ( Converter ) Switching Freq. ( Inverter )
30 [kHz ] 15 [kHz ]
Fig. 5 Principle operation waveforms of the proposed resonant inverter (1)Switch 1, 2 gate signal waveform (2)Switch 3 gate signal waveform (3)Main inductor currnet waveform (4)Resonant inductor current waveform (5)Resonant capacitor voltage waveform
Fig. 6 Key waveforms of the proposed resonant inverter (1)Switch 1, 2 votage (2)Switch 1, 2 currnet waveform (3)Diode 1, 2 currnet waveform (4)Switch 3 voltage waveform (5)Switch 3 current waveform
Fig. 8 The waveforms of the voltage and the current of the switch S1, S2 at turn-off with ZVS
Fig. 8 shows the switch S1 and S2 are turned off with ZVS. After the switch 1, 2 currents change 26[A] to the zerozero current, the switch 1, 2 voltage waveforms slowly are rising because the resonant capacitor Cr is linearly charged.
Fig. 9 The waveforms of the voltage and the current of the switch S3 at turnon with ZCS
Fig. 9 shows the switch S3 is turned on with ZVS. After the switch 3 voltage change 383[V]] to 0[V], the switch 3 current waveform slowly is rising -20[A] 20[A] to 3[A].
Fig. 7 The waveforms of the voltage and the current of the switch S1, S2 at turn-on with ZCS
Fig. 7 shows the switch S1 and S2 are turned on with ZCS. ZCS After the switch 1, 2 voltages change 200[V] to the zerozero voltage, the he switch 1, 2 current waveforms slowly are rising because the resonant inductor Lr is linearly charged. charged
Fig. 10 The waveforms of the voltage and the current of the switch S3 at turnoff with ZVS
Fig. 10 shows the switch S3 is turned off with ZVS. After the switch 3 current changes 3[A] to the zero-current, zero the switch 3 voltage waveform slowly is rising because switch 3 anti-parallel diode has been turned on.
the proposed resonant inverter are operated in the softswitching state when the switches are turned on and off. Softswitching can reduce the switching switchin stress and loss. The proposed inverter is analyzed, and its validity is proven pr through simulations. ACKNOWLEDGMENT This work is outcome of the fostering project of the Specialized Graduate School supported financially financia by the Ministry of Knowledge Economy(MKE). Economy(MKE REFERENCES
Fig. 11 The waveforms of the voltage and the current of the inverter switch S4 and S7 at turn-on and off with the ZVS
Fig. 12 The waveforms of the voltage and the current of the inverter switch S5, S6 at turn-on and off with the ZVS
Fig. 11, 12 show a schematic diagram of the waveforms of the switch 4, 5, 6 and 7 voltage and current. The inverter switches are turned on and off with ZVS. Therefore, all the switching devices are operated in the softsoft switching state when the switches are turned on and off. IV. CONCLUSION soft A ZVS resonant DC-link inverter using soft-switching boost converter has been proposed and analyzed in this paper. This inverter has the two stages. The first stage is a softswitching boost converter circuit constituted by adding an auxiliary switch, inductor, capacitor and diodes compared with the conventional boost converter rter circuit. The second stage is a resonant DC-link link inverter included the DC-link DC switch. In addition, in order to design and control inverter switches, the resonant DC-link switch S3 is needed. needed The DClink resonant switch S3 is controlled in the second stage. s The resonant DC-link inverter performs a ZVS when the switch S3 is turned on and off. Therefore, all the switching devices device on
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