Dual-Input Isolated DC-DC Converter with Ultra-High Step-Up Ability Based on Sheppard Taylor Circuit

Abstract

A dual-input high step-up isolated converter (DHSIC) is proposed in this paper, which incorporates Sheppard Taylor circuit into power stage design so as to step up voltage gain. In addition, the main circuit adopts boosting capacitors and switched capacitors, based on which the converter voltage gain can further be improved significantly. Since the proposed converter possesses an inherently ultra-high step-up feature, it is capable of processing low input voltages. The DHSIC also has the important features of leakage energy recycling, switch voltage clamping, and continuous input-current obtaining. These characteristics advantage converter efficiency and benefit the DHSIC for high power applications. The structure of the proposed converter is concise. That is, it can lower cost and simplifies control approach. The operation principle and theoretical derivation of the proposed converter are discussed thoroughly in this paper. Simulations and hardware implementation are carried out to verify the correctness of theoretical analysis and to validate feasibility of the converter as well.

1. Introduction

Nowadays, electricity is mostly generated by fossil fuels and nuclear fuel. Although nuclear power plants can generate considerable power by utilizing a little amount of nuclear fuel, nuclear waste influencing the environment is inevitable. Fossil fuels have been overused and become in shortage. Therefore, human beings attempt to discover more alternatives for maintaining global economic development and environment protection. To alleviate the problems of global temperature rising and serious greenhouse gas emission, many kinds of clean-energy power generation, such as photovoltaic (PV) panel, wind turbine, and fuel-cell stack, are developed imperatively [1,2].

In general, renewable power systems need a DC-bus voltage in the range of 380 V–400 V for grid-tied connection or in high power applications. Unfortunately, the output voltage of a PV module, battery or fuel cell is much lower than the dc-bus voltage and thus conventional DC/DC converters cannot be utilized directly to serve as an energy interface for dealing with power control. In addition, if the power supplied from two input ports has to be processed simultaneously, dual-input converter with high voltage gain is essentially anticipated. Figure 1 illustrates a hybrid generation system that includes two sources, a high step-up converter, and an inverter for AC application, which reveals that a dual-input converter with high step-up voltage gain is urgent in such system.

Theoretically, conventional step-up converters, like Boost and Flyback [3,4,5,6], can achieve a high voltage gain under the operating with extremely high duty ratio or the design of a much higher turns ratio. However, extreme high duty cycle or turns ratio will dramatically degrade the conversion efficiency due to large conduction loss and copper loss of windings. In order to improve conversion efficiency and voltage gain, many transformerless high step-up converters are proposed [7,8,9,10]. Although these converters are designed to achieve high step-up characteristics with reasonable duty ratio, here still exits some problems, for instance, large transient current and limited voltage gain, confining converter flexibility. To mitigate the mentioned drawbacks, converters incorporating coupled inductor and/or switched capacitor are proposed [11,12,13,14], however, which are only able to process single-input source. In order to deal with two different kinds of inputs, dual-input converters (DIC) are proposed. In comparison with single input, a dual generation system is capable of providing higher reliability, durability and power rating. The structure of DICs can be simply classified as series type and parallel one. The conventional series-type DICs construct string connection at input ports [15,16]. Such a DIC will malfunction in case that either of the two inputs fails. The parallel-type DICs collocate different sources in parallel so that even if one of the inputs is out of commitment, it still can accomplish voltage stepping to meet DC-bus level [17,18,19,20,21,22,23]. Some of them are controlled with time-sharing scheme. That is, only one DC source is permitted to delivery its energy to the load at a time. Compared with series-type DICs, parallel ones possess much better features from the aspects of reliability and controllability. Nevertheless, limitation on voltage gain is unavoidable, which confines converter applications in the field of high DC-bus voltage requirement.

In order to convert a lower DC voltage to a much higher level and to provide consecutive power even under the situation that one input source shuts down, this paper proposes a DHSIC, which is developed by means of boosting capacitor, switched capacitor and Sheppard Taylor circuit. The proposed dual-input converter can achieve the following important features: ultra-high step-up ability, continuous input current, and galvanic isolation. Furthermore, the proposed converter possesses the competence of inherent voltage clamping without any additional devices and recycling leakage energy stored in transformers. Therefore, the voltage spike on the power switch can be suppressed and converter efficiency is also improved.

The structure of this paper is organized as follows. Following the introduction, the operation principle of the proposed dual-input high step-up isolated converter is described in Section 2. The steady-state analysis is discussed in Section 3, which covers voltage gain of the converter, voltage and current stresses of the semiconductor device, and magnetizing inductance design in continuous conduction mode (CCM). To verify the correctness of proposed converter, experimental results from a 200-W prototype are illustrated in Section 4. Finally, Section 5 summarizes the conclusions of this paper.

2. Operation Principle of Proposed Dual-Input Converter

The equivalent of the proposed DHSIC is shown in Figure 2. Parameters in Figure 2 are represented in the following. V_in1 and V_in2 are input voltages, while i_in1 and i_in2 denote input currents. The practical model of coupled inductor includes magnetizing inductance, leakage inductance, and an ideal transformer. The L_m1 and L_m2 are the magnetizing inductances of T₁ and T₂, respectively, meanwhile, leakage inductances are expressed as L_k1 and L_k2. The S₁–S₄ represent the four main power switches. The C₁ and C₂ function as boosting capacitors, and C₃ and C₄ serve as switched capacitors. These capacitors can elevate converter voltage gain effectively. The D₁–D₆ are rectifier diodes. In addition, D_o and C_o are the output diode and filter capacitor, respectively. Output voltage and current of DHSIC are in turn described as V_o and I_o. Finally, the output equivalent resistance is presented as R_o. Even though the proposed DHSIC works normally in dual input operation (DIO), it still possesses the ability to be in single-input operation (SIO) while either input source fails. In Section 2, DIO will be first discussed followed by SIO.

2.1. Dual-Input Operation

The switches S₁ and S₂ are turned on/off simultaneously, so do the switches S₃ and S₄. Assume that the turn-on period of S₁ and S₂ is D₁T_s and D₂T_s is for S₃ and S₄. In addition, the magnitude of V_in2 is twice that of V_in1. While the proposed DHSIC operates at DIO and in continuous conduction mode (CCM), converter operation over one switching cycle can be divided into six states. Converter operation will be described state by state as the following proceeds with. In addition, the equivalent of each state and conceptual waveforms are depicted in Figure 3 and Figure 4, respectively.

• State 1 [t₀~t₁]: Converter operation begins at this state, in which all switches S₁–S₄ are turned on at t = t₀. All diodes are reverse except the output diode D_o. The currents of leakage inductances, i_Lk1 and i_Lk2, increase linearly and steeply. Meanwhile, the energy stored in magnetizing inductances L_m1 and L_m2 is released to the output via transformers and diode D_o. When leakage inductance current rises to be equal to magnetizing current, the diode current flowing through D_o will drop to zero and then this state ends. The diode D_o turns OFF under zero current transition. That is, the reverse-recovery problem at D_o can be therefore overcome.
• State 2 [t₁~t₂]: In State 2, the switches S₁–S₄ remain ON. The diodes D₁–D₄ and D_o are reversely biased, but diodes D₅ and D₆ are forwarded. In this time interval, leakage inductance and magnetizing inductance of the coupled inductor T₁ absorb energy from V_in1 and C₁, similarly, L_k2 and L_m2 of T₂ from V_in1 and C₁. The voltage across T_r1 is V_in1 + V_C1 and T_r2 is V_in2 + V_C2. At the secondary of the DHSIC, switched capacitors C₃ and C₄ are charged by the energy from coupled inductors T_r1 and T_r2, respectively. This state lasts for a time interval much longer than that of State 2 and is a major state in the converter operation.
• State 3 [t₂~t₃]: During the period from t₂ to t₃, switches S₁ and S₂ continue conducting. On the contrary, S₃ and S₄ are turned off at t₂. The diodes D₁–D₄ and D_o are reversely biased, but D₅ and D₆ are in a forward state. The parasitic capacitances of S₃ and S₄ are charged and current i_Lk2 decreases dramatically. As the increasing voltages blocked by S₃ and S₄ reach V_C2, diodes D₃ and D₄ become forwarded and then the operation state enters State 4.
• State 4 [t₃~t₄]: All active switches remain the same on-off conditions as in State 3. That is, S₁ and S₂ are closed but S₃ and S₄ open. The voltage V_in1 + V_C1 will supply T_r1 and forwards the energy to charge switched capacitor C₃. Meanwhile, the capacitor C₂ absorbs energy from V_in2 and T_r2. Leakage energy of L_k2 is recycled to C₂. The voltage stress of S₃ and S₄ will be clamped to V_C2. This operation state ends at the time both switches S₁ and S₂ are turned off.
• State 5 [t₄~t₅]: After S₁ and S₂ are turned off, the voltage across both switches increases. At the same time, their parasitic capacitances are charging toward the value of V_C1. With respect to the other switches, S₃ and S₄ are still in the OFF state. Once parasitic capacitance-voltage approaches to V_C1, State 5 ends and blocking voltage of S₁ and S₂ will be clamped at V_C1. The switched capacitor C₃ is still charging. During the time interval of State 5, the current flowing through L_k1 drops steeply. The diodes D₁ and D₂ will be forwarded at t = t₅ and then this state ends.
• State 6 [t₅~t₆]: From t₅ to t₆, all switches remain OFF. The L_m1 pumps its stored energy to charge C₁ and to the output as well. With respect to L_m2, it is also in energy-releasing but charges toward C₂, meanwhile, part of its energy will be transformed to the secondary of T_r2 to power the output. The leakage energy stored in T_r1 and T_r2 will be recycled to capacitors C₁ and C₂, respectively. During State 6, the series voltage of T_r1, C₃, T_r2, and C₄ is connected to the output. That is, the output can accordingly obtain a high voltage level. Like State 2 and 4, State 6 also plays a major role in the converter operation. While switches S₁–S₄ are turned on again at t = t₆, this state ends and converter operation over one switching cycle is completed.

2.2. Single-Input Operation

Once one of the inputs fails to supply power, the proposed converter still can function as a high step-up feature. Suppose that only V_in1 powers the DHSIC and in CCM condition. The converter will have four operation states over switching cycle. The corresponding key waveforms and equivalent circuits are illustrated in Figure 5 and Figure 6 in turn.

• State 1 [t₀~t₁]: If only V_in1 supplies the converter, power processing is controlled by switches S₁ and S₂. Both switches are turned on at t = t₀ and converter operation begins. As shown in Figure 6a, the voltage across T_r1 will be equal to the series voltage of C₁ and V_in1. Magnetizing inductance L_m1 pumps its stored energy to the secondary of T_r1. Therefore, the current flowing through L_m1 decreases. The current i_Lk1 increases quickly. When i_Lk1 is equal to i_Lm1, this state ends. At this time, the current flowing through the diodes D_o and D₆ also drops to zero. That is, the reverse-recovery problem of both diodes is therefore resolved.
• State 2 [t₁~t₂]: The equivalent of State 2 is illustrated in Figure 6b, in which the switches S₁ and S₂ remain closed. The L_m1 absorbs energy form V_in1 and C₁ and thus i_Lm1 increases linearly. At the secondary of T_r1, the switched capacitor C₃ is charging continuously over this stage. State 2 is a major state in the converter operation at SIO. At time t = t₂, the switches S₁ and S₂ are turned off and then the converter operation enters the next stage.
• State 3 [t₂~t₃]: In State 2, all diodes are in reverse bias except D₅. The parasitic capacitance of power switches S₁ and S₂ are charged and the current i_Lm1 decreases. The blocking voltage of S₁ and S₂ is therefore increasing. The associated equivalent is shown in Figure 6c. When the voltage across S₁ and S₂ approaches to V_C1, diodes D₁ and D₂ become forwarded. Then, State 4 starts.
• State 4 [t₃~t₄]: The equivalent circuit refers to Figure 6d, in which the magnetizing inductance forwards its stored energy to charge capacitor C₁ and to the output via the ideal transformer. Meanwhile, the leakage energy of L_k1 is recycled to C₁, which also suppresses the voltage spike on the active switches. Over the time interval from t₃ to t₄, switches S₁ and S₂ are open. With respect to diode, the D₅ is in reverse state but D₁, D₂, D₆ and D_o are forward biased. State 4 is also a major state similar to State 2, dominating the converter operation. Both switches S₁ and S₂ will be turned on again at t = t₄ and then this state ends. Converter operation over one switching cycle is completed.

3. Steady-State Analysis of Proposed Converter

The voltage ratio of output to input, voltage stress and current stress of the semiconductor device, and magnetizing inductance design will be covered in this section. To simplify the steady-state analysis, the following assumptions are made.

• The values of the boosting capacitors C₁ and C₂ are large enough so as to keep their across voltages invariant.
• All diodes are regarded to be ideal. That is, forward drop voltage and ON-state resistance are neglected.
• The magnetizing inductance of the coupled inductor is much more than leakage inductance so that influence of the leakage inductance can be ignored.
• The turns ratios of the coupled inductors, N_1s/N_1p and N_2s/N_2p, are defined as n₁ and n₂, respectively.
• The DHSIC is at CCM operation.

The driving pattern relating to the four switches is the same as that discussed in the previous section. The S₁ and S₂ are closed for D₁T and S₃ and S₄ for D₂T. In addition, the duty ratio of D₁ is greater than D₂. Based on the assumptions made at the beginning of this section, states 2, 4 and 6 in Figure 4 will dominate the converter operation.

3.1. Voltage Conversion Ratio

The proposed DHSIC can be regarded as a combination of two step-up converters which are symmetrical to common ground at the input side and in series connection at the output port. Furthermore, the two step-up converters are capable of operating individually. Therefore, the obtaining of voltage conversion ratio of the DHSIC can simply be derived from a single input situation and then to augment to dual-input situation. Suppose that only the V_in1 powers the DIC and both switches S₁ and S₂ are closed for D₁T and open for (1 − D₁)T over one switching period. The equivalents of switch ON and OFF are depicted in Figure 7. Applying voltage second balance criterion to L_m1 can yield

$$V_{Lm1,on}·D_{1}T+V_{Lm2,off}·(1-D_1)T=0$$

(1)

From Figure 7b, the V_Lm1,on and V_Lm1,off can be obtained as follows:

$$V_{Lm1,on}=V_{in1}+V_{C1}$$

(2)

and

$$V_{Lm1,off}=V_{in1}-V_{C1}.$$

(3)

Substituting Equations (2) and (3) into Equation (1) can find the expression of V_C1:

$$V_{C1}=\frac{1}{1-2D_1}{V}_{in}{}_1.$$

(4)

From Figure 7a, the voltage across capacitor C₃, V_C3, is found by the multiplication of turns ratio n₁ and V_Lm1,on, and then, from Equations (2) and (4) the V_C3 can be written as

$$V_{C3}=\frac{2n_1(1-D_1)}{1-2D_1}{V}_{in}{}_1.$$

(5)

According to Figure 7b, the following relationship holds:

$$n_1{V}_{Lm1,off}=V_{C3}-V_o.$$

(6)

Based on Equations (3)–(6), the output voltage of the converter at SIO can be given by

$$V_o=\frac{2n_1}{1-2D_1}{V}_{in}{}_1.$$

(7)

According to Equation (7), the switch duty ratio has to be less than 0.5, which is the converter limitation. Figure 8 depicts the relationship of voltage gain and duty ratio under different turns ratio.

With respect to the DIO situation, the DHSIC has the same control scheme shown in Figure 3. The S₁ and S₂ are closed for D₁T and open for (1 − D₁)T, while S₃ and S₄ are closed for D₂T and open for (1−D₂)T over one switching period. Equations (4) and (5) can be applied to the finding for the voltages of C₂ and C₄. That is, V_C2 and V_C4 are calculated by

$$V_{C2}=\frac{1}{1-2D_2}{V}_{in}{}_2$$

(8)

and

$$V_{C4}=\frac{2n_2(1-D_2)}{1-2D_2}{V}_{in}{}_2,$$

(9)

respectively. Being similar to Equation (6), the following relationship will hold under a dual-input situation.

$$n_1{V}_{Lm1,off}+n_2{V}_{Lm2,off}=V_{C3}+V_{C4}-V_o.$$

(10)

Thus, the corresponding output voltage at DIO of the converter can be described as

$$V_o=\frac{2n_1}{1-2D_1}{V}_{in1}+\frac{2n_2}{1-2D_2}{V}_{in2}.$$

(11)

Assume that V_in2 = 2V_in1, D₁ = D₂ = D, and n₁ = n₂ = n, according to Equation (11), Figure 9 represents the relationship of voltage gain versus turns ratio, while under DIO situation.

3.2. Voltage Stress of Semiconductor Device

According to the structure of the DHSIC, the semiconductor devices, S₁, S₂, D_1, and D₂, will have the same voltage stress. In addition, the power stage has inherently symmetrical configuration and is able to operate independently and individually at primary side. Therefore, the voltage stress of S₁, S₂, D_1, and D₂ can be determined from Figure 7, accordingly all of which will be equal to V_C1. From Equation (4), this voltage stress is expressed as

$$V_{S1,stress}=V_{S2,stress}=V_{D1,stress}=V_{D2,stress}=V_{C1}={\frac{1}{1-2D}}_1{V}_{in}{}_1.$$

(12)

Similarly, voltage stress of S₃, S₄, D_3, and D₄ can be determined by

$$V_{S3,stress}=V_{S4,stress}=V_{D3,stress}=V_{D4,stress}=V_{C2}={\frac{1}{1-2D}}_2{V}_{in}{}_2.$$

(13)

With attention to the semiconductor devices at the output port (the secondary side of the DHSIC), an associated determination is discussed in the following. While all active switches are in OFF-state, the blocking voltages of diodes D₅ and D₆ are obtained by

$$V_{D5,stress}=V_{C3}+n_1(V_{C1}-V_{in1})$$

(14)

and

$$V_{D6,stress}=V_{C4}+n_2(V_{C2}-V_{in2}),$$

(15)

respectively. The V_C1 and V_C3 can be founded by Equations (4) and (5) in turn, and V_C2 and V_C4 by Equations (8) and (9). As a result, the above Equations (14) and (15) can be rewritten as

$$V_{D5,stress}=\frac{2n_1}{1-2D_1}{V}_{in1}$$

(16)

and

$$V_{D6,stress}=\frac{2n_2}{1-2D_2}{V}_{in2},$$

(17)

respectively. Voltage stress of the output diode D_O is estimated at the state that all active switches are closed and thus it will be

$$V_{Do,stress}=V_{C3}+n_1(V_{C1}-V_{in1})+V_{C4}+n_2(V_{C2}-V_{in2}).$$

(18)

Based on Equations (4), (5), (8) and (9), the expression of Equation (18) is rewritten as

$$V_{Do,stress}=\frac{2n_1}{1-2D_1}{V}_{in1}+\frac{2n_2}{1-2D_2}{V}_{in2}.$$

(19)

3.3. Magnetizing Inductance Design

The minimum currents of active switches S₁ and S₂, i_Lm1,min and i_Lm2,min, can be expressed as

$$i_{Lm1,\min }=I_{Lm1}-\frac{\Delta i_{Lm1}}{2},$$

(20)

and

$$i_{Lm2,\min }=I_{Lm2}-\frac{\Delta i_{Lm2}}{2},$$

(21)

respectively. The Δi_Lm1 and Δi_Lm2 stand for the current change on L_m1 and L_m2 in turn, while I_Lm1 and I_Lm2 are the average currents of L_m1 and L_m2. Assume that the converter is lossless. Then, The I_Lm1 and I_Lm2 can be determined as follows:

$$I_{Lm1}=\frac{2n_1}{(1-2D_1)}{I}_o,$$

(22)

and

$$I_{Lm2}=\frac{2n_2}{(1-2D_2)}{I}_o,$$

(23)

in which the I_o denotes output current. In addition, Δi_Lm1 and Δi_Lm2 can be calculated by

$$\Delta i_{Lm1}=\frac{V_{Lm1,on}}{L_{m1}}{D}_1{T}_s$$

(24)

and

$$\Delta i_{Lm2}=\frac{V_{Lm2,on}}{L_{m2}}{D}_2{T}_s.$$

(25)

At the boundary, Δi_Lm1 and Δi_Lm2 are equal to zero, that is,

$$\frac{2n_1{V}_o}{(1-2D_1)R_o}=\frac{V_{Lm1.on}}{2L_{m1}}{D}_1{T}_s$$

(26)

and

$$\frac{2n_2{V}_o}{(1-2D_2)R_o}=\frac{V_{Lm2,on}}{2L_{m2}}{D}_2{T}_s.$$

(27)

From Equations (26) and (27), the minimum magnetizing inductances for CCM operation have to meet the following inequality:

$$L_{m1}>\frac{(1-D_1)D_1{R}_o{V}_{in1}}{2n_1{f}_s(\frac{2n_1}{1-2D_1}{V}_{in1}+\frac{2n_2}{1-2D_2}{V}_{in2})}$$

(28)

and

$$L_{m2}>\frac{(1-D_2)D_2{R}_o{V}_{in2}}{2n_2{f}_s(\frac{2n_1}{1-2D_1}{V}_{in1}+\frac{2n_2}{1-2D_2}{V}_{in2})}.$$

(29)

Suppose that the turns ratio n₁ = n₂ = n, V_in2 = 2V_in1 = 24 V, switching frequency f_s = 40 kHz, and both switches have the same duty ratio denoted as D. In addition, the converter operates at boundary condition mode (BCM) at 25 W. Figure 10 illustrates the relationship between magnetizing inductance and duty ratio for L_m1 and L_m2.

The comparison with other similar converters is summarized in

Table 1. Performance Comparison among the Proposed and Other Multi-Input Converters.

Converter	Number of Switches	Number of Magnetic Components	Number of Capacitors	Input Current Ripple	Voltage Stress	Switch Voltage Camping	Galvanic Isolation	Output Voltage (Vo)
[15]	2	2	5	low	medium	no	no	$\frac{3}{1-D_{}}{V}_{in}{}_1=\frac{3}{1-D_{}}{V}_{in}{}_2$
[16]	4	2	2	high	low	yes	yes	$n_1{D}_1{V}_{in1}+n_2{D}_2{V}_{in2}$
[19]	3	1	5	high	medium	no	no	$\frac{3[D_1{V}_{in}{}_1+(D_1-D_2)V_{in}{}_2]}{(1-D_3)}$
[24]	6	2	2	low	high	no	no	$\frac{V_{in}{}_1}{(1-D_1)}=\frac{V_{in}{}_2}{(1-D_2)}$
DHSIC	4	2	5	medium	low	yes	yes	$\frac{2n_1}{(1-2D_1)}{V}_{in1}+\frac{2n_2}{(1-2D_2)}{V}_{in2}$

. It can be found that even though the DHSIC needs more power components, it achieves excellent voltage gain over other DICs in addition to that the features of galvanic isolation, continuous input current and switch voltage clamping still can be possessed.

4. Experimental Results

To verify the proposed DIC, a 200-W prototype is built, simulated and measured. Converter parameters and components adopted are summarized in

Table 2. Parameters of the DHSIC for Simulations and Practical Measurements.

Parameter	Value
Vin1 (PV arrays)	12–16 V
Vin2 (fuel-cells stack)	24–30 V
fs (switching frequency)	40 kHz
Vo (output voltage)	400 V
Power rating	200 W
Lm1 and Lm2 (magnetizing inductors)	176 μH and 302 μH
LLk1 and LLk2 (leakage inductors)	1.9 μH and 2.4 μH
S1–S4 (power MOSFET)	IRFP4668
D1, D2, D3, and D4	DSSK60-02AR
D5,D6 and Do	BYR29-600
C1	68 μF
C2	33 μF
C3 and C4	22 μF
Co	82 μF
n1 and n2 (transformer turns ratio)	3 and 2.5

. The control block diagram of the prototype is depicted in Figure 11. Power of input port 1 is calculated according to the detected input voltage and current, that is, V_in1,fb, and I_in1,fb, and then it is compared to a reference P_ref1. The control signals for S₁ and S₂ are determined by the PI power controller and the carrier. Accordingly, the input power at port 1 can be readily controlled. With respect to the other part of the control block diagram, the output voltage is regulated by controlling the switches S₃ and S₄. With such voltage regulation, the input port 2 can accommodate the supplement to output power and thus power dispatch at both input ports is accomplished. The proposed converter adopts MCU dsPIC30F4011 to serve as system controller. Figure 12 shows the control signals and the corresponding input currents at full load under DIO situation. In Figure 12 the duty ratios of S₁ and S₂ are 0.32 and 0.23, respectively, which is consistent with Equation (11) for a 400-V output. Meanwhile, the switch voltages, v_ds1 and v_ds2, are measured and shown in Figure 13, from which it can be observed that there is no voltage spike on active switches. That is, the boosting capacitors C₁ and C₂ are able to recycle leakage energy and can effectively clamp switch voltage. Additionally, withstood voltages on the switches at port 1 and port 2 are 34 V and 45 V, respectively, which verifies the theoretical analysis results of Equations (12) and (13). Figure 14 is the measurement of the voltages of boosting capacitors. This figure reveals that voltages of C₁ and C₂ are in turn 34 V and 45 V, both voltage magnitudes of which meet the theoretical results of Equations (4) and (8). While step change takes place from half load to full load and then drops back, Figure 15 shows the related output voltage and current. Figure 15 illustrates that constant 400-V output still can be kept with even under step change. The overshoots at step-up and step-down transitions are only 1 V and 0.7 V, respectively. With respect to SIO situation, once power failure occurs at input 1, Figure 16 shows the measured control signal, output voltage, and input current. Similarly, if at input 2, Figure 17 is the related measurement. Both figures demonstrate the operation ability of the converter at SIO situation. The measured waveform of output current is presented in Figure 18, from which it can be observed that the output current of the converter is near to be ripple-free. The efficiency of the proposed converter is measured and then shown in Figure 19, in which the peak value is about 91.4%. In the experiment, a very low level of voltage, V_in1 = 12 V, is considered, therefore, which yields that higher current has to be demanded at a specific power, resulting in large conduction loss. This is the major reason why the converter efficiency is not as high as satisfied in the measurement. However, if input voltage is raised, the converter efficiency will be advanced. At single-input situation, if only the 24 V of V_in2 suppled the DHSIC, measured converter efficiency is shown in Figure 20. This figure reveals that a higher voltage input can yield a better efficiency even under the operation of single input. A photo of the built-up DHSIC is shown in Figure 21.

5. Conclusions

In this paper, a dual-input converter is proposed, which possesses the characteristics of ultra-high voltage gain, continuous input currents, galvanic isolation, inherent voltage-clamp feature, and recycling the energy stored in leakage inductance. This converter is capable of controlling the dual inputs independently and individually. Moreover, it still can accomplish all the mentioned features even under the case that either input encounters power failure. That is, the converter has operation flexibility to operate at dual-input situation or single-input situation for accommodating input conditions. A maximum of measured efficient is about 91.4% at dual-input operation.