Improved Interleaved Boost Converter with Soft-Switching: Analysis and Experimental Validation

This paper proposes a novel interleaved boost converter for renewable energy applications. The two-phase interleaved boost converter was improved with lossless passive snubber cells to ensure the Zero Voltage Switching (ZVS) condition. The ZVS condition is contributed by a resonant inductor, a resonant capacitor, and two diodes. The proposed converter was operated in continuous current mode on its primary side. The significant merits of this converter are reduced switching losses, better efficiency, and reduced input current ripples without auxiliary switches. The soft-switching ability of this converter is maintained under both light-and heavy-load conditions. This paper also presents the operating principles and design analysis of the proposed converter. Furthermore, a 50-320V prototype was operated at 250 W to validate the soft-switching operation and theoretical analysis, and the experimental results are presented.


INTRODUCTION
In contemporary power conversion systems, boost and Interleaved Boost Converters (IBCs) have gained widespread usage to elevate low-voltage inputs to desired output levels, commonly drawing energy from sources such as wind generator systems [1], DC microgrids [2], and batteries [3].The tristate interleaved converter design [4] employs auxiliary switches alongside primary switches to alleviate the challenges associated with input current fluctuations and output voltage ripple.However, this converter relies on excessive auxiliary switches and is primarily suited for low-voltage applications.
In response to these limitations, a dual-Coupled Inductor (CI)-based IBC that incorporates a clamping capacitor was proposed in [5].This innovation serves to reduce voltage stresses and improve overall efficiency.However, it is primarily recommended for low-power applications.Moreover, voltage multiplier cells have been integrated into high-gain converters [6][7] and IBCs [7][8] to achieve improved voltage conversion ratios.In a buck converter, switches are replaced with a resonant switch [9] and IBCs are assisted by a single auxiliary circuit without [10] and with CI [11][12][13], facilitating soft-switching operation at low power levels.The Zero Voltage Transition (ZVT) condition is achieved when the auxiliary switch operates at twice the converter's switching frequency.Similarly, CIs increase switched capacitor cells, and auxiliary circuits in IBC aim to achieve increased voltage gain and softswitching operation [14].However, the auxiliary switches experience elevated current stresses as a result of their higher switching frequency.Similarly, in [15], a large inductor and snubber capacitors were integrated into a conventional IBC to achieve soft-switching, i.e.ZVT condition.Continuing this approach, in [16], an auxiliary switch was used to achieve the ZVT condition.However, these systems typically operate at low voltage and low power levels.
In [17], a different strategy was proposed to achieve softswitching conditions, involving an IBC with an auxiliary circuit and voltage multiplier cells, which improved overall gain and achieved the ZVT condition.However, this converter primarily functions at very low output power levels.To further improve overall gain, it is necessary to increase the number of windings in current transformers (CIs).Efforts to efficiently recycle leakage energy and operate at high output power levels have led to the utilization of supplementary passive lossless clamp circuits [18] and active clamp circuits [19].In [20], an increased turns ratio of CIs was implemented to improve voltage gain, coupled with the achievement of Zero Current Switching (ZCS) through a Passive Lossless Clamp Circuit (PLCC) in IBC.This particular converter yielded reduced turnoff losses and an increased overall gain.Similarly, another PLCC-based IBC [21][22][23][24][25] attains ZVS during turn-off in addition to the aforementioned advantages.However, it should be noted that previous IBC designs have exhibited certain disadvantages, including a higher count of active devices, electromagnetic interference (EMI) resulting from increased CIs, complexity in the control circuitry, and operation primarily at low output power levels.To address these limitations comprehensively, this study introduces the novel Soft-Switched Interleaved Boost Converter (SSIBC) equipped with passive auxiliary components: a resonant inductor, a resonant capacitor, and a diode.The proposed converter exhibits several advantages in comparison to the existing IBCs, such as:  Fewer active and passive devices  Operates at high power  Reduces switching losses  Reduces the voltage stresses in the switching devices.
These advantages make the proposed converter a significant technology with the potential to revolutionize various industries where efficient and high-power conversion is of paramount importance.Figure 1 shows the generalized organization of Renewable Energy Sources (RESs) with IBC, along with loads such as DC microgrids and Electric Vehicles (EVs).Although the source RESs voltage ranges from 12 V to 48 V, the IBC provides a desirable range of 200-500 V for the load. Inductors L 1 and L 2 possess significant inductance and exhibit steady currents.
Figure 4 shows the key waveforms, illustrating the operating intervals from t 0 to t 8 .Figure 5 shows the equivalent current flow schematics for each interval.The operation of the converter is divided into 8 intervals.The steady-state operation of the proposed converter is demonstrated for each interval.
 Interval (t 0 -t 1 ): At t 0 , IGBT S 1 is conducting, S 2 is turned off, and hence, output current flows through L 2 -D 2 .At t 1 , the voltage across IGBT S 2 is increased to 2/3 of V o .The equations of L 1 , L 2 and S 2 are:  Interval (t 1 -t 2 ): At t 1 , IGBT S 1 is still conducting and the voltage across IGBT S 2 starts reducing smoothly to reach zero at t 2 .
 Interval (t 2 -t 3 ): This is a short interval.At the beginning of the interval, the body diode of S 2 starts conducting and stops at t 3 .Hence, the ZVS condition is achieved for S 2 .The current expression of IGBT S 2 is as follows:  Interval (t 3 -t 4 ): At t 4 , the voltage across IGBT S 2 increases to V in and reaches zero at t 4 .The load current continues to flow via L 2 -D 2 .
 Interval (t 4 -t 5 ): At the instant t 4 , IGBT S 2 is turned on with ZVS condition and S 1 is still conducting.Throughout this interval, the energy is accumulated in inductors L 1 and  Interval (t 5 -t 6 ): At t 5 , S 1 is turned-off, therefore the output current flows through where t 5 < t < t 6  Interval (t 6 -t 7 ): Throughout this interval, the voltage across S 1 starts decreasing and reaches zero at t 7 .

III. DESIGN ANALYSIS
The IBC operation was divided into two distinct states to determine the input current ripples of the proposed converter.The first state occurs when S 1 is turned on, while the next is when both S 1 and S 2 are on.
 State 2: In this region, the switching devices S 1 and S 2 are both turned on and energy is accumulated in both the inductors L 1 and L 2 .The input current is expressed as follows: The average value of the output voltage V o is expressed as follows: By substituting ( 19) in ( 17) and ( 18), the input current can be expressed as: Input current ripple is defined by ( 23) for two operating regions; The first is when only one IGBT is turned on (0 5 2 5 ) and the second is when both the IGBTs are conducting ( 5 2 5 1).
The input current ripple is expressed as: The overall voltage gain of the converter is defined The input and output currents of the converter are expressed as: where A = Figure 6 shows the voltage and current waveforms of the S 1 and S 2 IGBTs.According to the waveforms obtained, the voltages of the IGBTs reach zero smoothly, therefore, the ZVS condition is achieved without any additional voltage and current stresses.A 250 W prototype was built to validate the theoretical analysis.Table I shows the design parameters.The developed prototype was tested with a voltage of 50 V as input to get a 320 V output.The duty ratio was 0.85 and 0.6 for S 1 and S 2 , respectively.The overall gain of the converter, while operating    Figure 9 shows the collector-emitter voltage and collector currents of the S 1 and S 2 IGBTs.The proposed converter operates at a 50 V input voltage to produce a 320 V output voltage at a 400 Ω load resistance.The voltage stresses of the IGBTs are observed to be near 230 V, which is lower than the output voltage.The waveforms obtained validate the theoretical analysis, and the S 1 and S 2 IGBTs are turned on with the ZVS condition.When the converter operated at 30 V input voltage, it obtained 260 V output with the same duty ratios.Figure 10 shows the collector-emitter voltage and collector currents of the S 1 and S 2 IGBTs.The obtained waveforms demonstrate the ZVS condition.Figure 11 shows the voltage waveforms across the C a and C b resonant capacitors.It can be seen that the capacitors are charged up to the output voltage of 240 V and discharge smoothly.Figure 12 depicts the current flowing through the L a and L b inductors.The maximum current flowing through the inductors is 0.8 A, which is the output current.Figure 13 shows the turn-on transients of the main IGBTs, S 1 and S2.Without or voltage stresses and lower dv/dt rates, the softswitching condition, ZVS turn on, is achieved, when the converter is operated at 100 W output power.
All IGBTs achieve ZVS turn-on conditions without any additional current or voltage stresses.The converter has an overall gain higher than that of existing converters.The aforementioned qualities are more advantageous than those of the prior IBCs.Table II shows the comparison between the proposed soft-switched and existing IBCs.The proposed converter uses fewer auxiliary devices, experiences fewer turnon losses, and achieves 97% efficiency at 250 W output power.Figure 14 shows the efficiency curves.The efficiency measured at the output power of 100 W was 94.5%, at 150 W was 94.8%, at 200 W was 96.3%, and at 250 was 97%.When the converter operated at 250 W output power, the proposed IBC's maximum efficiency was 97%.

V. CONCLUSIONS
This study presented a novel two-phase IBC with passive lossless snubber cells, describing its design and operating concepts.There are no additional losses involved in achieving the ZVS condition.Using a 300 W laboratory prototype and a 50 V input voltage, the experimental investigations yielded a maximum output voltage of 320 V.The soft-switching ability of the proposed converter was tested up to the 250 W output power level.A passive lossless snubber provides ZVS turn-on of the IGBTs and plays an important role in achieving 97% efficiency.Compared to existing converters, the number of devices, including auxiliary switches, is reduced, thus reducing the overall cost.This proposed converter is suitable for medium-and high-power applications.

Fig. 1 .
Fig. 1.Generalized organization of RESs with an interleaved boost converter.II.PROPOSED INTERLEAVED DC-DC CONVERTERThe conventional IBC shown in Figure2comprises two inductors (L 1 , L 2 ), two IGBTs (S 1 , S 2 ), and two diodes (D 1 , D 2 ).Figure3shows the proposed soft-switching IBC, extended with two passive lossless snubber cells.The passive lossless snubber comprises inductors L a and L b , capacitors C a and C b , and diodes D a , D b , D c , and D d .The proposed converter obtains ZVC conditions in their main IGBTs with the help of a passive snubber cell.The following assumptions were considered to describe the steady-state analysis of the proposed converter.

Figure 3
shows the proposed soft-switching IBC, extended with two passive lossless snubber cells.The passive lossless snubber comprises inductors L a and L b , capacitors C a and C b , and diodes D a , D b , D c , and D d .The proposed converter obtains ZVC conditions in their main IGBTs with the help of a passive snubber cell.The following assumptions were considered to describe the steady-state analysis of the proposed converter. All IGBTs and passive elements are ideal. Parasite circuit components are ignored. The size of the output capacitor is large enough to ignore any fluctuations in output voltage.

 State 1 :
In this state, energy gets accumulated in the input inductor L 1 when only S 1 is turned on and the input current gets delivered to output through L 2 since S 2 is turned off.The input current is expressed as follows: 12385 www.etasr.comPopuri et al.: Improved Interleaved Boost Converter with Soft-Switching: Analysis and Experimental …

5 . ,- 1 I
resonant elements a , C a , L b , and C b are selected by taking the Q factor equal to 3 and characteristic impedance Z o .The input inductance values of 1 and L 2 are chosen by the following condition: H JK L M (30) The output filter capacitance o is taken from: of the voltage stress of the IGBT and the current stress of input inductors are determined by the following expressions: ANALYSIS AND EXPERIMENTAL RESULTS The PLECS software tool was used to design and simulate the proposed soft-switched IBC.The following values used as simulation parameters: input voltage: 50 V, switching frequency: 40 kHz, output voltage: 320 V, inductors L 1 , L 2 = 100 µH, resonant inductors L , L b = 1.5 µH, resonant capacitors, C a , C b = 2 nF, and output capacitor C o = 470 µF.

Figure 7 shows
Figure 7 shows V Ca and V Cb .The waveforms obtained from the C a and C b resonant capacitors confirm that they are charged to the output voltage of 2/3 of V o and discharge completely.Figure 8 shows the current through the resonant inductors L a and L b .

Figure 8
Figure 7 shows V Ca and V Cb .The waveforms obtained from the C a and C b resonant capacitors confirm that they are charged to the output voltage of 2/3 of V o and discharge completely.Figure 8 shows the current through the resonant inductors L a and L b .
12386 www.etasr.comPopuri et al.: Improved Interleaved Boost Converter with Soft-Switching: Analysis and Experimental … at 50 V input voltage and obtaining an output voltage of 320 V, was approximately 6.The PWM signals were generated with the help of a Texas Instruments TMSF28335 module.The proposed converter operated at a switching frequency of 40 kHz.Infineon IHW25N120 IGBTs S 1 and S 2 were used, having 25 A maximum rated current with 1200 V maximum rated voltage.Two FKP2O11150 capacitors were connected in parallel to obtain a capacitance of 2 nF.

TABLE I .
LABORATORY PROTOTYPE PARAMETERS

TABLE II
: number of switches, ND: number of diodes: NL: number of inductors: NC: number of capacitors: NRL: number of resonant inductors : NRC: number of resonant capacitors: NS*Coupled inductor, TDC: Total device count Vin: Input voltage, Vo: Output voltage