Volume 2013, Issue 1 834510

Research Article

Open Access

Performances of an Interleaved High Step-Up Converter with Different Soft-Switching Snubbers for PV Energy Conversion Applications

Corresponding Author

Sheng-Yu Tseng

[email protected]

Department of Electrical Engineering, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-shan, Taoyuan 33302, Taiwan cgu.edu.tw

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Hung-Yuan Wang,

Hung-Yuan Wang

Department of Electrical Engineering, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-shan, Taoyuan 33302, Taiwan cgu.edu.tw

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Chih-Yang Hsu,

Chih-Yang Hsu

Department of Electrical Engineering, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-shan, Taoyuan 33302, Taiwan cgu.edu.tw

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Sheng-Yu Tseng,

Corresponding Author

Sheng-Yu Tseng

[email protected]

Department of Electrical Engineering, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-shan, Taoyuan 33302, Taiwan cgu.edu.tw

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Hung-Yuan Wang,

Hung-Yuan Wang

Department of Electrical Engineering, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-shan, Taoyuan 33302, Taiwan cgu.edu.tw

Search for more papers by this author

Chih-Yang Hsu,

Chih-Yang Hsu

Department of Electrical Engineering, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-shan, Taoyuan 33302, Taiwan cgu.edu.tw

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First published: 22 December 2013

https://doi.org/10.1155/2013/834510

Citations: 1

Academic Editor: Wayne A. Anderson

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Abstract

This paper proposes an interleaved high step-up converter with different soft-switching snubbers for PV energy conversion applications. For the high step-up converter, interleaved and coupled-inductor technologies are used to reduce output ripple current and increase output power level. Simultaneously, two types of snubbers, a single-capacitor snubber and boost type snubber, are introduced separately into the discussed converters for comparing their performances of conversion efficiency and switching losses. For drawing maximum power from the PV arrays, a perturbation-and-observation method realized with the microcontroller is adopted to achieve maximum power point tracking (MPPT) algorithm and power regulating scheme. Finally, two prototypes of the interleaved coupled-inductor boost converter with a single-capacitor snubber and with boost type snubber are implemented, respectively. The experimental results obtained are used to verify and compare the performances and feasibilities of the discussed converters with different snubbers in PV conversion applications. The experimental results show that the proposed system is suitable for PV energy conversion applications when the duty ratios of switches of the converter are less than 0.5.

1. Introduction

In recent years, in order to offer enough energy to maintain the economic development of the world, one of the solutions is the solar energy which is a totally inexhaustible and completely clear energy source. However, due to the instability and intermittent characteristics of solar energy, photovoltaic (PV) power conversion systems with power converter and maximum power tracking algorithms are needed to convert solar energy into electrical energy and provide stable power output. With the rapid growth of power electronics techniques, the conversion efficiency of PV power conversion system has been increased obviously [1, 2]. Recently, PV power conversion systems are well recognized and widely used in electric power conversion system, such as PV power generation for grid connection, PV vehicle constriction, battery charger, water pumping, and satellite power conversion system.

To extract power from PV arrays, power converter is used in PV power conversion systems. In order to obtain the maximum power from PV arrays and thus increase utility rate of PV arrays, switching-mode converter must be operated at the maximum power point (MPP) of PV arrays, resulting in its output voltage without keeping in the desired dc constant voltage. Therefore, a switching-mode one with battery source in parallel is used for keeping the output voltage in the desired dc constant voltage, as shown in Figure 1(a). In Figure 1(a), dc voltages provided by the proposed PV power conversion system can be supplied to dc loads of dc/ac inverters for grid-connected power conversion system [3–8] and dc/dc converter for dc load [9–13]. In grid-connected power conversion system applications, control of power converters has to be taken into consideration. In [4], three different control topologies have been proposed according to the number of power processing stages. Since the multistage topology, as shown in Figure 1(b), possesses a better control performance of each DC/DC converter, it is adopted in the proposed PV power conversion system. Therefore, the PV power conversion system consists of a switching-mode converter for maximum power point tracking (MPPT) of PV arrays and a switching-mode converter for voltage regulation of dc load under the control of multistage topology.

Details are in the caption following the image — **Figure 1 (a)**
Open in figure viewer PowerPoint

Block diagram of PV power conversion system for (a) DC load applications and (b) grid connection.

In the MPPT algorithm research, several MPPT algorithms have been proposed [14–23]. Some of the popular MPPT algorithms are constant voltage method [14, 15], system oscillation method [16, 17], ripple correlation method [18], β method [19], incremental conductance method [20], and perturbation-and-observation method [21–23]. Under the consideration of simplicity and easy implementation, the perturbation-and-observation method is adopted and used in the proposed PV power conversion system.

For PV arrays, since output voltage V_PV of the PV arrays is in a low voltage level, the DC/DC converter with a higher step-up voltage ratio is needed [24–28]. In [24], the voltage-fed converters are not the optimal candidates for high step-up applications because they usually have a buck type configuration and (or) LC filter in the secondary rectification circuits. With this circuit structure, it results in a large transformer turns ratio, which makes the transformer design complex and leads to a large leakage inductance. Compared with the voltage-fed converters, the current-fed converters [25–27] and the coupled-inductor converters [28] are preferable choices for high voltage conversion ratio applications. Although the current-fed converters are adopted in the PV power system, they are also used as a voltage doubler or multiplier to increase the step-up voltage ratio. When the converters adopt the voltage doubler or multiplier, capacitors of the voltage doubler must be special capacitors with a low equivalent series resistance (ESR), high current ripple rating (CRR), and high operational bandwidth. Therefore, it is only suitable for using in the low power level applications. In [28], a high step-up converter achieved by a coupled inductor is presented. Compared with converters using an isolation transformer to obtain the high step-up voltage ratio, the one using the coupled inductor has a more simple winding structure and higher coupling coefficient. It not only reduces inductor currents to ensure a lower conduction loss but also decreases leakage inductance to attain a lower switching loss. Therefore, the boost converter with the coupled inductor is used in the proposed system.

For further increasing the power capability of the converter, the boost converter used in the proposed system is constructed in an interleaved manner [29–33]. Moreover, PWM ICs with two gate signals are used to drive switches of the interleaved converter. Since the voltage fed type of input sources are used in the converters and it is difficult to obtain a special PWM IC with duty ratio greater than 0.5 (≥0.5), PWM ICs with duty ratio within 0.5 are used to control the switches in the discussed boost converters. Therefore, the operation of the proposed converter is constrained under duty ratio of 0.5.

When a coupled inductor boost converter is used in the PV power conversion system, the energy trapped in the leakage inductor of coupled inductor not only increases voltage stresses but also induces switching lossless of switches in the converter, significantly. In order to solve these problems, several methods have been proposed [34–36]. In [34], a resistor-capacitor-diode (R-C-D) snubber is used to alleviate voltage stresses of switches by dissipating the energy trapped in the leakage inductor through the resistor, reducing the conversion efficiency of the converter. Therefore, a passive lossless circuit proposed in [35] is adopted to reduce voltage spike across switches. Its schematic diagram with the interleaved manner is shown in Figure 2. Although converters with a passive lossless circuit can improve conversion efficiency, active switches are still operated in hard switching at turn-on transition. In [36], an active clamp circuit is introduced to achieve zero-voltage switching (ZVS) and increased its conversion efficiency. However, the disadvantage of the active clamp circuit is that it is difficult to implement soft-switching features at light load for the boost converter. In order to solve this problem, a boost type snubber is inserted into the active clamp boost converter with coupled inductor, as shown in Figure 3. It can improve conversion efficiency of the boost converter at light load, significantly. Due to the complexity of circuit structures shown in Figures 2 and 3, they are, respectively, simplified by [37] and [38] and are shown in Figures 4(a) and 4(b). In this paper, performance comparisons between the discussed converters with the single-capacitor snubber and with boost type snubber are proposed.

2. Control Algorithm of the Proposed Converter

When a switching-mode dc/dc converter is adopted as their power processor for extracting power from PV arrays and converting the power into dc voltage supplied to dc loads, a proper power management system for managing the power is needed in the PV power conversion system. In the following, the circuit topology of the proposed converter power conversion system, MPPT algorithm, and power management are described.

2.1. Circuit Topology of the Proposed Converter

The proposed PV power conversion system uses PV arrays as one of its power sources. For increasing the utility rate of the PV arrays, the PV arrays have to be operated on their maximum power. Therefore, as shown in Figure 5, a PV power conversion system constructed of a switching-mode converter with PV array sources, a switching-mode converter with battery source, and a controller is proposed. In the proposed PV power system, the two dc/dc converters are realized by an interleaved coupled-inductor boost converter with single-capacitor snubber shown in Figure 4(a). The one with PV arrays source uses MPPT control algorithm for extracting the maximum power from PV arrays. The other with battery source uses voltage regulation control method to regulate powers between PV arrays and loads and to generate a constant output voltage supplied to dc loads. As shown in Figure 5, controller constructed by MPPT unit, power management unit, and PWM IC unit is used to control the dc/dc converter with PV array source for determining the MPP of PV arrays by the perturbation-and-observation method described in [21–23]. There are two signals generated by the power management, control signals M₁ and S_P. Control signal M₁ is used to regulate output powers of switching-mode converter with MPPT control algorithm. Control signal S_P is generated according to the relationships between the maximum power P_PV(max ) of PV arrays and power of load P_L. Based on the control signal S_P and the output V_O, PWM IC unit generates control signal M₂ with voltage regulation control method for obtaining constant output voltage. Protections are considered and implemented by microcontroller. The protections include over-current, over-voltage, and over-temperature protections of the two converters and undercharge of battery. Therefore, the proposed PV power conversion system can be used to achieve the optimal utility rate of PV arrays.

2.2. Power Management

The power of PV arrays is supplied to the load through the proposed interleaved boost converter. The power management of the proposed power conversion system is implemented by a microcontroller and is used to regulate the power of PV arrays and output power. According to relationships among the powers of P_PV, P_VB, and P_L, operational modes of power management can be divided into 8 modes and are illustrated in Table 1. Power P_PV is output power of switching-mode converter with PV arrays as its power source, P_VB is that of switching-mode converter with battery as its power source, and P_L is power of load. Moreover, “1” represents that the power is generated by switching-mode converter or is required by load, while “0” represents that the power is not generated by switching-mode converter or is not required by load. According to the operational modes illustrated in Table 1, PV power conversion system is shut down in operational modes of I, II, III, V, and VII. Therefore, operational modes IV, VI, and VIII are described as follows.

Table 1. Operational conditions of PV arrays for the proposed converter.

Operational modes	Power states			Operational conditions of PV power conversion system
Operational modes	P_PV	P_VB	P_L	Operational conditions of PV power conversion system
I	0	0	0	Shutdown
II	0	0	1	Shutdown
III	0	1	0	Shutdown
IV	0	1	1	Working
V	1	0	0	Shutdown
VI	1	0	1	Working
VII	1	1	0	Shutdown
VIII	1	1	1	Working

2.2.1. Operational Mode IV

In mode IV, the switching-mode converter with battery is used to supply power to the load. Once the condition of P_L > P_VB(max ) is reached or energy stored in battery is completely discharged, the proposed converter is shut down.

2.2.2. Operational Mode VI

In mode VI, the switching-mode converter with PV arrays as its power source is used to supply power to load. When power of P_PV(max ) is equal to or greater than that of P_L, power curve of PV arrays follows that of load. Once P_PV(max ) < P_L, the proposed converter is shut down.

2.2.3. Operational VIII

When PV power conversion system is operated in mode VIII, the interleaved boost converter supplies power to load, as shown in Figure 6. During this operational mode, (P_PV(max ) + P_B(max )) must be equal to or greater than P_L. If (P_PV(max ) + P_B(max )) < P_L, the proposed PV power conversion system is shut down. When (P_PV(max ) + P_B(max )) ≥ P_L, the operational condition can be further divided into two cases: P_PV(max ) ≥ P_L and P_PV(max ) < P_L. In the following, the two cases are briefly described.

(1) P_PV(max ) ≥ P_L and P_B(max ) < P_L. When P_PV(max ) ≥ P_L and P_B(max ) < P_L, the switching-mode converter with battery source is shut down, causing the output power P_PV of PV arrays to be equal to P_L, as shown in Figure 6(a). Hence, the switching-mode converter with PV arrays source is operated in voltage regulation mode to supply the desired dc voltage to load.

(2) P_PV(max ) < P_L and P_B(max ) < P_L. When P_PV(max ) < P_L and P_B(max ) < P_L, the switching-mode converter with PV array source is operated at the MPP of PV arrays to extract the maximum power from the PV arrays. On the other hand, the one with battery source is used to sustain the desired dc voltage. Power curve for operational mode VIII under P_PV(max ) < P_L and P_B(max ) < P_L is shown in Figure 6(b). From Figure 6(b), it can be seen that P_L is the sum of P_PV and P_B.

3. Control Design of the Proposed PV Power Conversion System

As shown in Figure 7, controller of the proposed power conversion system consists of two major units, the microcontroller and the PWM IC units. The microcontroller is further divided into the MPPT unit and the power management unit. In the following, functions of each block will be described briefly.

3.1. The MPPT Unit

The MPPT unit uses the perturbation-and-observation method to track MPPT of PV arrays and to decide the maximum power P_PV(max ) of PV array, resulting in the output power of P_P for further power management.

3.2. The Power Management Unit

In the power management unit, the maximum discharging current I_B(max ) of battery is set for obtaining the maximum battery discharging power P_B(max ) of V_BI_B(max ). Based on the output power of MPPT unit P_P, the maximum battery discharging power, and the load power P_L of V_OI_O, comparator number 1 determines the relationships between (P_PV + P_B(max )) and P_L. There are two relationships to be discussed.

3.2.1. Case I: (P_PV + P_B(max)) ≥ P_L

When (P_PV + P_B(max )) ≥ P_L, control signal S_P1 of comparator number 1 is in the low level, causing further comparison of P_P and P_L in comparator number 2. If P_P ≥ P_L, the low level output signal S₁ of comparator number 2 makes the power selector to set the power P_set to be equal to P_L. Once P_P < P_L, output signal S₁ of comparator number 2 becomes a high level and causes the power selector to set the power P_set to be equal to P_P. Then, in the reference current block, the power P_set and the reference voltage V_ref are used to calculate the reference current I_C for obtaining the current error value ΔI_C (=I_C − I_OP) with output current of the proposed converter with PV array source, I_OP, in the current error amplifier.

In the PWM generator of PV array, control signals G_1A and G_2A are obtained by comparing current error value ΔI_C with triangular wave generated by the PWM generator of PV arrays. The control signals G_1A and G_2A are used to drive switches M_1A and M_2A of the proposed converter with PV array source for controlling power flowed from PV arrays to load.

3.2.2. Case II: (P_PV + P_B(max)) < P_L

When (P_PV + P_B(max )) < P_L, control signal S_P1 of comparator #1 is in the high level, causing both of PWM generators of PV array and battery to be shut down. The power management unit also includes functions of protection, which are over-voltage, over-current, under-voltage, and undercharge protections. As shown in Figure 7, there are six input signals to the protection controller, V_O(max ), V_O(min ), I_O(max ), V_B(max ), I_O, V_O, and V_B, where V_O(max ) and V_O(min ) are maximum and minimum values of output voltage, I_O(max ) is maximum value of output current, V_B(min ) is minimum value of battery voltage, I_O is output current, V_O is output voltage, and V_B is voltage of battery. When V_O ≥ V_O(max ), the proposed converter is operated in over-voltage condition, causing the output signal S_P2 to be in a high level and shut down both of the PWM generators. Moreover, conditions of I_O ≥ I_O(max ) (over-current condition), V_O ≤ V_O(min ) (under-voltage condition), or V_B ≤ V_B(min ) (undercharge condition) also make signal S_P2 to be in a high level to shut down both of the PWM generators.

3.3. The PWM IC Unit

The proposed boost converter with battery source uses lead-acid battery as its power source. In order to implement power balance among PV arrays, battery, and load and sustain a constant output voltage, a PWM IC unit is adopted. This control unit includes voltage error amplifier and PWM generator of battery. Based on the output voltage V_O and reference voltage V_ref, the voltage error amplifier determines the voltage error value ΔV_C of (V_ref − V_O). The voltage error value ΔV_C is then sent to PWM generator of battery to be compared with triangle wave generated by PWM IC for obtaining PWM signals G_1B and G_2B. Signals G_1B and G_2B are used to control switches M_1B and M_2B for regulating powers between PV arrays and load. Similarly, the PWM generator of battery can be shut down either by signals S_P1 or S_P2.

4. Experimental Results

To verify performances of the proposed PV power conversion system, dc/dc converters realized by the interleaved coupled-inductor boost converter with single-capacitor snubber and boost type snubber for generating dc voltage of 400 V for dc load applications were implemented with the following specifications.

(A)
The proposed boost converter with PV arrays is as follows.
- (i)
  Input voltage V_PV: 34~42 V (PV arrays).
- (ii)
  Output voltage V_O: 400 V_dc.
- (iii)
  Output maximum current I_OP(max ): 3 A.
- (iv)
  Output maximum power P_PV(max ): 1.2 kW.
(B)
The proposed boost converter with battery is as follows.
- (i)
  Input voltage V_B: 44~54 V_dc (4 sets of 12 V battery connected in series).
- (ii)
  Output voltage V_O: 400 V_dc.
- (iii)
  Output maximum current I_OB(max ): 3 A.
- (iv)
  Output maximum power P_B(max ): 1.2 kW.

According to designs and specifications of the proposed boost converters with the single-capacitor snubber, components of power stages in the proposed one are determined as follows.

(i)
Switches M_1A, M_2A, M_1B, and M_2B: IRFP260N.
(ii)
Diodes D_1A, D_2A, D_1B, and D_2B: HFA08TB120 × 2 (connected in series).
(iii)
Coupled inductors L_m11, L_m21: 30 μH.
(iv)
Leakage inductors of coupled inductors (L_m11, L_m12) and (L_m21, L_m22): 1.1 μH.
(v)
Cores of coupled inductors (L_m11, L_m12) and (L_m21, L_m22): EE-55.
(vi)
Turns ratio N: 20.

Similarly, components of power stages in the proposed boost converters with boost type snubber are determined as follows.

(i)
Switches M_1A ~ M_SA: IRFP260N.
(ii)
Switches M_1B ~ M_SB: IRFP260N.
(iii)
Diodes D_1A, D_2A, D_1B, and D_2B: HFA08TB120 × 2 (connected in series).
(iv)
Diodes D_B1A, D_B2A, D_B1B, D_B2B, and D_s: HFA08TB120 × 2 (connected in series).
(v)
Coupled inductors L_m11, L_m21: 30 μH.
(vi)
Leakage inductors of coupled inductors (L_m11, L_m12) and (L_m21, L_m22): 1.1 μH.
(vii)
Cores of coupled inductor (L_m11, L_m12) and (L_m21, L_m22): EE-55.
(viii)
Turns ratio N: 20.
(ix)
Inductors L_1s, L_2s: 3 μH.
(x)
Cores of inductors L_1s, L_2s: DR28X12.
(xi)
Capacitors C_1A, C_2A, C_1B, C_2B: 15 μF.

To verify performances of the high step-up converter applied to the PV power system, some of important comparisons have been made and listed in Table 2. It can be seen from Table 2 that the proposed boost converter with the single-capacitor snubber has less component counts, lower cost, and easier control circuit, while the proposed one with boost type snubber has more component counts, higher cost, more complexity control circuit, and high conversion efficiency. They are suitable for middle or high power level applications. In addition, although the high step-up converters proposed in [25, 27] have higher conversion efficiency, they are only applied to low or middle power level applications.

Table 2. Preliminary comparisons among the different high step-up converters for the PV power system.

Items for comparison	The proposed boost converter with single-capacitor snubber	The proposed boost converter with boost type snubber	The boost converter proposed in [25]	The high step-up converter proposed in [27]
Key component counts
Active switch	2	5	4	4
Passive switch	2	5	4	2
Magnetic core	2	6	4	3
Resonant/output capacitor	2	3	6	3
Seft-switching features
Main switches	Turn on hard switching turn off ZVT	Turn on ZVS turn off hard switching	Turn on ZVS turn off hard switching	Turn on ZVS turn off hard switching
Auxiliary switches		Turn on ZVS turn off hard switching	Turn on ZVS turn off hard switching	Turn on ZVS turn off hard switching
Cost	Lower	High	Middle	Low
Duty ratio limitation	D < 0.5	D < 0.5	D > 0.5	D > 0.5
Turns ratio of transformer	20	20	2.5	2.125
Control complexity	Middle (86%)	High (90%)	Higher (94.4%)	Highest (96%)
Conversion efficiency under full load condition	Simplicity	Complexity	Complexity	Complexity
Power level application	Middle power level	High power level	Lower power level	Low power level

Moreover, hardware dimension of each DC/DC converter is about 210 × 297 mm. In order to verify the feasibility of the proposed boost converter with battery source, measured voltage V_DS and current I_DS waveforms of switches are shown in Figures 8 and 9. Figure 8 shows those waveforms of switches M_1B and M_2B under 50% of full-load condition when the proposed one adopts the single-capacitor snubber, while Figure 9 shows those waveforms of switches M_1B and M_3B under 20% of full load condition when the proposed one uses boost type snubber. Experimental results reveal that when the discussed boost converter with the single-capacitor snubber is adopted, switches can be operated with zero-switching transition (ZVT) at turn-off transition. Switches of the discussed one with boost type snubber are operated with ZVS at turn-on transition.

To make a fair comparison, the components of the boost converter with hard-switching circuit, the single-capacitor snubber, and boost type snubber are kept the same as possible. Figure 10 shows measured output voltage V_O and current I_O waveforms of the boost converter with three different snubbers under step-load changes between 0% and 100% of full load with repetitive rate of 0.5 Hz and a duty ratio of 50%. From Figure 10, it can be observed that voltage regulations of output voltage V_O of boost converter with the single-capacitor snubber and boost type snubber are approximately the same as the one with hard-switching circuit. It reveals that the boost converter with the single-capacitor snubber and boost type snubber can yield a good dynamic performance.

According to the operational principles of the proposed converters with the single-capacitor snubber and the boost type snubber, switches of the proposed one with the single-capacitor snubber have ZVT features at turn-off transition, while those switches with the boost type snubber have ZVS features at turn-on transition. Their conceptual waveforms are illustrated in Figures 11(b) and 11(c), respectively. Figures 12(a) and 12(b) show the current waveforms of switches and inductors in the interleaved coupled-inductor boost converter with hard-switching circuit and the single-capacitor snubber, respectively. From Figure 12(b), it can be seen that when switch of one boost converter in the interleaved boost converter is turned on, the diode current I_DC of the other boost converter in the interleaved one flows through the switch by the capacitor snubber. Therefore, the boost converter with the single-capacitor snubber will induce an extra turn-on switching loss. The key parameter values of the proposed interleaved boost converters with the single-capacitor snubber and with the boost type snubber under full-load condition are listed in Tables 3 and 4, respectively. It can be found from Tables 3 and 4 that switching losses of the proposed converter with the single-capacitor snubber, compared with those of the proposed one with the boost type sunbber, increase by 20~30 W. Comparison of efficiencies among the discussed interleaved boost converters with different types of snubbers is illustrated in Figure 13. It shows that the boost converter with boost type snubber can yield the highest conversion efficiency than that with single-capacitor snubber from light load to heavy load. Conversion efficiencies of boost converters under full-load condition with boost type snubber and single-capacitor are 86% and 90%, respectively. Since duty ratios of switches in two discussed PV power conversion systems are less than 0.5, their turns ratios of coupled inductors have higher values. Therefore, a higher current flows through switches of the converter, resulting in a larger switching losses and conduction losses. Therefore, conversion efficiency of the converter in the two discussed PV power conversion systems can be further increased by reducing turns ratio of coupled inductor. Moreover, if the conducted resistances R_DS(on ) of switches in the converters are reduced, those in the two discussed PV power conversion systems will be increased. That is, a lower conducted resistance R_DS(on ) of switch can be chosen. In addition, two switches connected in parallel can be used for reducing the conducted resistance. By doing so, conversion efficiency of the proposed converter can be further increased by about 3~5%.

Table 3. Parameter values of the boost converter with single-capacitor snubber under full-load condition.

Parameters	Formulas	Calculation values	Practical values
I_DB		38.87 A	39.5 A
I_DP		54.47 A	56 A
I_DC		12 A	63 A
Switch stress V_DS(max )		53 V	55 V
Voltage across snubber capacitor V_CS	(V_O + NV_PV)	1120 V	1120 V
Output diode stress	(V_O + NV_PV)	1120 V	1500 V
Duty ratio D		0.325	0.34
Snubber capacitor C_S		1.16 nF	10 nF
T_CC		1.2 ns	9.9 ns
Switching loss of each switch at turn-on P_son		5.86 W	21.14 W
Switching loss of each switch at turn-off P_soff		0 W	0 W
Conduction loss of each switch P_SC		28.58 W	30.31 W
Conduction loss of diode P_SCD		7.2 W	7.5 W
Forward drop voltage V_DF of output diode		4.8 V (2.4 V × 2)	4.8 V (2.4 V × 2)
t_son		87 ns	150 ns
t_soff		103 ns (P_son calculation)	500 ns (C_S calculation)
V_PV		36 V	36 V
V_O		400 V	400 V
T_S		20 μs	20 μs
I_O		3 A	3 A
N		20	20
t_on	DT_S	6.5 μs	6.8 μs
R_ds		0.04 Ω	0.04 Ω

Table 4. Parameter values of the boost converter with boost type snubber under full-load condition.

Parameters	Formulas	Calculation values	Practical values
I_DB		38.87 A	39 A
I_DP		54.47 A	56 A
Switch stress V_DS(max )		53 V	55 V
Output diode stress	(V_O + NV_PV)	1120 V	1500 V
Duty ratio D		0.325	0.34
Switching loss of each switch at turn-on P_son		0 W	0 W
Switching loss of each switch at turn-off P_soff		7.43 W	9.24 W
Conduction loss of each switch P_SC		28.58 W	30.31 W
Conduction loss of diode P_SCD		7.2 W	7.5 W
Forward drop voltage V_DF of output diode		4.8 V (2.4 × 2)	4.8 V
t_son		87 ns	100 ns
t_soff		103 ns	120 ns
V_PV		36 V	36 V
V_O		400 V	400 V
T_S		20 μs	20 μs
I_O		3 A	3 A
N		20	20
t_on	DT_S	6.5 μs	6.8 μs
R_ds		0.04 Ω	0.04 Ω

Since the proposed boost converters with the single-capacitor and boost type snubbers use the same control method, the measured results for MPPT and power management should be the same. Therefore, only the measured results of the proposed one with the single-capacitor snubber are shown in this paper. From the measured waveforms of voltage V_PV, current I_PV, and power P_PV under P_PV(max ) = 750 W shown in Figure 14, the tracking time of MPPT realized by the proposed converter with PV arrays as its power source is about 80 ms from 0 to the maximum power of PV arrays. Figure 15 shows the measured waveforms of output voltage V_O and current I_OB and I_O under P_L = 350 W, as the power management of the proposed PV power conversion system is operated in mode IV and P_B(max ) ≥ P_L. From Figure 15, it can be seen that output voltages V_O are sustained at 400 V and current I_BO is equal to I_O. When the proposed PV power conversion system with the single-capacitor snubber is operated in mode VI and P_PV(max ) ≥ P_L, measured waveforms of output voltage V_O and currents I_OP and I_L under P_PV(max ) = 700 W and P_L = 600 W are shown in Figure 16, illustrating that their output voltage are clamped at 400 V and current I_OP is equal to I_O and P_PV = 600 W.

The operational conditions of the proposed PV power conversion systems in mode VIII of (P_PV(max ) + P_B(max )) ≥ P_L can be divided into two conditions: P_PV(max ) ≥ P_L and P_PV(max ) < P_L. The measured waveforms of output voltage V_O, currents I_OP, I_OB, and I_O under P_PV(max ) = 700 W and P_L = 500 W are shown in Figure 17. In this operational condition, current I_OP is equal to I_O and I_B is equal to 0. That is, the proposed boost converter with MPPT is used to supply power to load and PV arrays are not operated at MPP, while the proposed boost one with voltage regulation is shut down. When P_PV(max ) < P_L, the measured output voltage V_O and currents I_OP, I_OB, and I_O under P_PV(max ) = 400 W and P_L = 700 W are shown in Figure 18, illustrating that output voltage V_O is still clamped at 400 V and I_O = I_OP + I_OB. The experimental results show that both of the proposed PV power conversion systems with the single-capacitor snubber and with boost type snubber can implement power management.

5. Conclusion

In this paper, an interleaved coupled-inductor boost converter with different soft-switching snubbers is proposed for PV arrays applications. To compare the performances of the proposed converter with the single-capacitor snubber or with the boost type snubber, MPPT algorithm, power management, and control design of the proposed PV power conversion system have been firstly described in detail. In addition, a perturbation-and-observation method is used to implement the MPPT algorithm. For further evaluating the performances and feasibilities of the proposed PV power conversion system, prototypes of PV power conversion system with different soft-switching snubbers and with specifications of P_PV(max ) = 1.2 kW and P_VB(max ) = 1.2 kW have been built. Experimental results have shown that the proposed converter with boost type snubber can yield higher efficiency than the ones with the single-capacitor snubber and with hard-switching circuit, where the conversion efficiencies for converter with single-capacitor snubber and boost type snubber are 86% and 90% under full load, respectively. Therefore, the proposed interleaved coupled-inductor boost converter with the single-capacitor snubber is suitable for PV arrays applications with a lower cost, while the proposed one with boost type snubber is applied to PV arrays for a higher conversion efficiency power conversion system.

References

1 Duarte J. L., Wijntjens J. A. A., and Rozenboom J., Designing light sources for solar-powered systems, 8, Proceedings of the 5th European Conference on Power Electronics and Applications, September 1993, 78–82, 2-s2.0-0027807943.
Google Scholar
2 Germann U. and Langer H. G., Low cost DC to AC converter for photovoltaic power con-version in residential applications, Proceedings of the IEEE Power Electronics Specialist Conference (PESC ′93), 1993, 588–594.
Google Scholar
3 Yu Y., Zhang Q., Liang B., Liu X., and Cui S., Analysis of a single-phase Z-Source inverter for battery discharging in vehicle to grid applications, Energies. (2011) 4, no. 12, 2224–2235, 2-s2.0-84855392820, https://doi.org/10.3390/en4122224.
Web of Science® Google Scholar
4 Kjaer S. B., Pedersen J. K., and Blaabjerg F., A review of single-phase grid-connected inverters for photovoltaic modules, IEEE Transactions on Industry Applications. (2005) 41, no. 5, 1292–1306, 2-s2.0-26844560797, https://doi.org/10.1109/TIA.2005.853371.
Web of Science® Google Scholar
5 Pérez P. J., Almonacid G., Aguilera J., and de la Casa J., RMS current of a photovoltaic generator in grid-connected PV systems: definition and application, International Journal of Photoenergy. (2008) 2008, 7, 2-s2.0-43949091119, https://doi.org/10.1155/2008/356261, 356261.
10.1155/2008/356261
Google Scholar
6 Yoo J., Park B., An K., AI-Ammar E. A., Khan Y., Hur K., and Kim J. H., Look-ahead energy management of a grid-connected residential PV system with energy storage under time-based rate programs, Energies. (2012) 5, article 4, 1116–1134, https://doi.org/10.3390/en5041116.
Google Scholar
7 Gerlando A. D., Foglia G., Iacchetti M. F., and Perini R., Analysis and test of diode rectifier solutions in grid-connected wind energy conversion systems employing modular permanent-magnet synchronous generators, IEEE Transactions on Industrial Electronics. (2012) 59, no. 5, 2135–2146, 2-s2.0-84857010205, https://doi.org/10.1109/TIE.2011.2157295.
Google Scholar
8 Ramirezand F. A. and Arjona M. A., Development of a grid-connected wind generationsys-temwith a modified PLL structure, IEEE Transactions on Sustainable Energy. (2012) 3, no. 3, 474–481, https://doi.org/10.1109/TSTE.2012.2190770.
Google Scholar
9 van Breussegem T. M. and Steyaert M. S. J., Monolithic capacitive DC-DC converter with single boundary—multiphase control and voltage domain stacking in 90 nm CMOS, IEEE Journal of Solid-State Circuits. (2011) 46, no. 7, 1715–1727, 2-s2.0-79959718700, https://doi.org/10.1109/JSSC.2011.2144350.
Google Scholar
10 Galigekere V. P. and Kazimierczuk M. K., Analysis of PWM Z-source DC-DC converter in CCM for steady state, IEEE Transactions on Circuits and Systems I. (2012) 59, no. 4, 854–863, 2-s2.0-84859720797, https://doi.org/10.1109/TCSI.2011.2169742.
Google Scholar
11 Wang Z. and Li H., A soft switching three-phase current-fed bidirectional DC-DC converter with high efficiency over a wide input voltage range, IEEE Transactions on Power Electronics. (2012) 27, no. 2, 669–684, 2-s2.0-84855412435, https://doi.org/10.1109/TPEL.2011.2160284.
Google Scholar
12 Do H.-L., Improved ZVS DC-DC converter with a high voltage gain and a ripple-free input current, IEEE Transactions on Circuits and Systems I. (2012) 59, no. 4, 846–853, 2-s2.0-84859733667, https://doi.org/10.1109/TCSI.2011.2169741.
Google Scholar
13 Qian W., Cha H., Peng F. Z., and Tolbert L. M., 55-kW variable 3X DC-DC converter for plug-in hybrid electric vehicles, IEEE Transactions on Power Electronics. (2012) 27, no. 4, 1668–1678, 2-s2.0-84857415434, https://doi.org/10.1109/TPEL.2011.2165559.
Google Scholar
14 Brunton S. L., Rowley C. W., Kulkarni S. R., and Clarkson C., Maximum power point tracking for photovoltaic optimization using ripple-based extremum seeking control, IEEE Transactions on Power Electronics. (2010) 25, no. 10, 2531–2540, 2-s2.0-77957730666, https://doi.org/10.1109/TPEL.2010.2049747.
Google Scholar
15 Agarwal V., Aggarwal R. K., Patidar P., and Patki C., A novel scheme for rapid tracking of maximum power point in wind energy generation systems, IEEE Transactions on Energy Conversion. (2010) 25, no. 1, 228–236, 2-s2.0-77950690809, https://doi.org/10.1109/TEC.2009.2032613.
Google Scholar
16 Taherbaneh M., Rezaie A. H., Ghafoorifard H., Rahimi K., and Menhaj M. B., Maximizing output power of a solar panel via combination of sun tracking and maximum power point tracking by fuzzy controllers, International Journal of Photoenergy. (2010) 2010, 13, 2-s2.0-79955039583, https://doi.org/10.1155/2010/312580, 312580.
10.1155/2010/312580
Web of Science® Google Scholar
17 Weidong X. and Dunford W. G., A modified adaptive hill climbing MPPT method for photovoltaic power conversion systems, Proceedings of the 35th Annual IEEE Power Electrons Specialists Conference, 2004, 1957–1963.
Google Scholar
18 Kobayashi K., Matsuo H., and Sekine Y., An excellent operating point tracker of the solar-cell power supply system, IEEE Transactions on Industrial Electronics. (2006) 53, no. 2, 495–499, 2-s2.0-33645707855, https://doi.org/10.1109/TIE.2006.870669.
Google Scholar
19 Subiyanto S., Mohamed A., and Shareef H., Hopfield neural network optimized fuzzy logic controller for maximum power point tracking in a photovoltaic system, International Journal of Photoenergy. (2012) 2012, 13, 2-s2.0-84855170543, https://doi.org/10.1155/2012/798361, 798361.
10.1155/2012/798361
Web of Science® Google Scholar
20 Jain S. and Agarwal V., A new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems, IEEE Power Electronics Letters. (2004) 2, no. 1, 16–19, 2-s2.0-2942711829, https://doi.org/10.1109/LPEL.2004.828444.
Google Scholar
21 Chung H. S.-H., Tse K. K., Hui S. Y. R., Mok C. M., and Ho M. T., A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter, IEEE Transactions on Power Electronics. (2003) 18, no. 3, 717–724, 2-s2.0-0038630873, https://doi.org/10.1109/TPEL.2003.810841.
Google Scholar
22 Billy Ho M. T., Henry Chung S. H., and Hui S. Y. R., An integrated inverter with maximum power tracking for grid-connected PV systems, 3, Proceedings of the 9th Annual IEEE Applied Power Electronics Conference and Exposition (APEC ′04), 2004, 1559–1565.
Google Scholar
23 Casadei D., Grandi G., and Rossi C., Single-phase single-stage photovoltaic generation system based on a ripple correlation control maximum power point tracking, IEEE Transactions on Energy Conversion. (2006) 21, no. 2, 562–568, 2-s2.0-33744530398, https://doi.org/10.1109/TEC.2005.853784.
Google Scholar
24 Liang Z., Guo R., Li J., and Huang A. Q., A high-efficiency PV module-integrated DC/DC converter for PV energy harvest in FREEDM systems, IEEE Transactions on Power Electronics. (2011) 26, no. 3, 897–909, 2-s2.0-79957486576, https://doi.org/10.1109/TPEL.2011.2107581.
Google Scholar
25 Kim H., Yoon C., and Choi S., An improved current-fed ZVS isolated boost converter for fuel cell applications, IEEE Transactions on Power Electronics. (2010) 25, no. 9, 2357–2364, 2-s2.0-77956907568, https://doi.org/10.1109/TPEL.2010.2048044.
Google Scholar
26 Tseng K. C., Huang C. C., and Shin W. Y., A high step-up converter with a voltage multiplier module for a photovoltaic system, IEEE Transactions on Power Electronics. (2013) 28, no. 66, 3047–3057.
Google Scholar
27 Kwon J.-M. and Kwon B.-H., High step-up active-clamp converter with input-current doubler and output-voltage doubler for fuel cell power systems, IEEE Transactions on Power Electronics. (2009) 24, no. 1, 108–115, 2-s2.0-61649117741, https://doi.org/10.1109/TPEL.2008.2006268.
Google Scholar
28 Zhao Y., Li W., Deng Y., and He X., Analysis, design, and experimentation of an isolated ZVT boost converter with coupled inductors, IEEE Transactions on Power Electronics. (2011) 26, no. 2, 541–550, 2-s2.0-79951528817, https://doi.org/10.1109/TPEL.2010.2065815.
Google Scholar
29 Yang F., Ruan X., Yang Y., and Zhihong Y., Interleaved critical current mode boost PFC converter with coupled inductor, IEEE Transactions on Power Electronics. (2011) 26, no. 9, 2404–2413, 2-s2.0-80053271231, https://doi.org/10.1109/TPEL.2011.2106165.
Google Scholar
30 Dwari S. and Parsa L., An efficient high-step-up interleaved DC-DC converter with a common active clamp, IEEE Transactions on Power Electronics. (2011) 26, no. 1, 66–78, 2-s2.0-78650979937, https://doi.org/10.1109/TPEL.2010.2051816.
Google Scholar
31 Hegazy O., Mierloand J. V., and Lataire P., Analysis, modeling, and implementation of amulti-device interleaved DC/DC converter for fuelcell hybrid electric vehicles, IEEE Transactions on Power Electronics. (2012) 27, no. 11, 4445–5558, https://doi.org/10.1109/TPEL.2012.2183148.
Google Scholar
32 Li W., Zhao Y., Wu J., and He X., Interleaved high step-up converter with winding-cross-coupled inductors and voltage multiplier cells, IEEE Transactions on Power Electronics. (2012) 27, no. 1, 133–143, https://doi.org/10.1109/TPEL.2009.2028688.
Google Scholar
33 Weichen L., Xiang X., Wuhua L., and He X., Interleaved high step-up ZVT converter with built-in transformer voltage doubler cell for distributed PV generation system, IEEE Transactions on Power Electronics. (2013) 28, no. 1, 300–313.
Google Scholar
34 Peipei M., Henglin C., Zheng S., Xinke W., and Zhaoming Q., Optimal design for the damping resistor in RCD-R snubber to suppress common-mode noise, Proceedings of the 25th Annual IEEE Applied Power Electronics Conference and Exposition (APEC ′10), 2010, 691–695.
Google Scholar
35 Li R. T. H., Henry H. S.-H., Chung A. K. T., and Sung A .K. T., Passive lossless snubber for boost PFC with minimum voltage and current stress, IEEE Transactions on Power Electronics. (2010) 25, no. 3, 602–613, https://doi.org/10.1109/TPEL.2009.2035123.
Google Scholar
36 Kim B., Ju H.-J., Ko K.-C., and Hotta E., Active clamping circuit to suppress switching stress on a MOS-gate-structure-based power semiconductor for pulsed-power applications, IEEE Transactions on Plasma Science. (2011) 39, no. 8, 1736–1742, 2-s2.0-80051800693, https://doi.org/10.1109/TPS.2011.2159136.
Google Scholar
37 Tseng S. Y., Shiang J. Z., and Su Y. H., A single-capacitor turn-off snubber for interleaved boost converter with coupled inductor, Proceedings of the 7th International Conference on Power Electronics and Drive Systems (PEDS ′07), 2007, 202–208, https://doi.org/10.1109/PEDS.2007.4487701.
Google Scholar
38 Tseng S. Y., Ou C. L., Peng S. T., and Lee J. D., Interleaved coupled-inductor boost converter with boost type snubber for PV system, Proceedings of the IEEE Energy Conversion Congress and Exposition (ECCE ′09), 2009, 1860–1867, https://doi.org/10.1109/ECCE.2009.5316192.
Google Scholar

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Performances of an Interleaved High Step-Up Converter with Different Soft-Switching Snubbers for PV Energy Conversion Applications

Abstract

1. Introduction

2. Control Algorithm of the Proposed Converter