A novel quadratic Boost converter with low current and voltage stress on power switch for fuel-cell system applications

doi:10.1016/j.renene.2017.08.032

Renewable Energy

Volume 115, January 2018, Pages 836-845

https://doi.org/10.1016/j.renene.2017.08.032 Get rights and content

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PQBC’s good features: no abruptly changing on capacitors’ voltage and inductors’ current, non-pulsating input current.
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Result from comparison show PQBC has lowest voltage and current stress on MOSFET Q₂ and possesses the highest efficiency.
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Theoretical analysis, simulations and experiments show that PQBC is a good candidate for fuel-cell system applications.

Abstract

This paper presents a novel quadratic Boost converter with good features: no abruptly changing on capacitors' voltage and inductors' current in the whole switching cycle which can assure no instantaneous overcurrent or overvoltage on storage elements, non-pulsating input current that can make the input filter design easier, low current and voltage stress on power switch. The basic operating principles and the mathematical model of this novel quadratic Boost converter are presented. The steady state and the small signal dynamical behaviors are analyzed and the comparisons among other quadratic Boost converters are described and concluded. Finally, the Pspice simulations and the corresponding circuit experiments are presented for confirmation.

Introduction

As well known, the availability of fossil fuel is limited. With the society developing, the energy demand is increasing seriously and the fossil fuel is diminishing quickly, the renewable energy, including photovoltaic (PV) [1], fuel-cell [2] and wind energy [3], attracts more and more power industries and researchers' attention to study for relieving this condition. For the fuel-cell system [4], it typically consists of fuel-cell stacks, back-up batteries, DC-DC high step-up converter, and DC-AC inverter connected with the loads or grid. As general, the output voltage of the fuel-cell stacks is rated as 22─48 V and the input voltage of the DC-AC inverter is rated as (200-V) [4]. In other words, the input and output voltage of the DC-DC high step-up converter are (22–48 V) and (200-V), respectively. Without loss of generality, the input and output voltage of the DC-DC high step-up converter are chosen as 24 V and 200 V, respectively, which means that its voltage conversion ratio should be equal to 8.3333. When the traditional Boost converter is applied to realize this application, it is found that its duty cycle must be equal to 0.88 which is a little difficult to obtain in practical situation for the limitation of semiconductors. Moreover, even if this situation is satisfied, the high switching voltage stress with reverse recovery issues and the low efficiency of the traditional Boost converter limit its application [5]. Of course, the traditional Sepic converter can also be used to boost the low input voltage to the high output voltage. However, its duty cycle being 0.8928 must be used for this fuel-cell system application [6]. Hence, these two traditional DC-DC converters have the same drawbacks.

In order to overcome the drawback of the traditional Boost converter and other step-up converter with high voltage conversion ratio by using large duty cycle, a lot of DC-DC step-up converters with high voltage conversion ratio by using the suitable duty cycle have been proposed. As general, these converters can be classified into two types: isolated step-up converter and non-isolated step-up converter. For the DC-DC isolated step-up converter, the inevitable transformer is inserted into the converter for obtaining the high voltage conversion ratio [7]. However, the transformer causes switch voltage overshoot and EMI problems that lead to low efficiency and huge volume [8]. For the DC-DC non-isolated step-up converter, it only consists of the power switches, diodes, capacitors and inductors. In recent decades, many DC-DC non-isolated step-up converters with high voltage conversion ratio have been proposed [9], [10], [11], [12], [13]. For example, for obtaining the voltage conversion ratio being 2/(1 − D) where D is the steady state of duty cycle, the voltage-boosting converters with hybrid energy pumping was proposed by Hwu and Tu [9], and the sixth-order step-up converter integrated the traditional Boost converter with self-lift Sepic converter was proposed by Al-Saffar et al. [10]. By using the bootstrap capacitors and Boost inductors, Hwu and Tu also proposed the non-isolated step-up converters with the voltage conversion ratio being (3 + D)/(1 − D) and (3 − D)/(1 − D) [11]. Chien et al. proposed the interleaved step-up converter with the voltage conversion ratio being 3/(1 − D) [12]. By using the voltage-lift technique, Luo and Ye proposed the non-isolated step-up converter with the voltage conversion ratio being ((2 − D)/(1 − D))^N [13]. However, the abruptly changing on the voltage across the capacitor of all the above DC-DC non-isolated step-up converters results them in limiting in practical application to some extent.

Also, the switched capacitor or the switched inductor has been inserted into the existed DC-DC converter to obtain the high voltage conversion ratio, such as hybrid boost converter with the voltage conversion ratio being (1 + D)/(1 − D) in Ref. [14], the switched-capacitor-based active network converter with the voltage conversion ratio being (3 + D)/(1 − D) in Ref. [15], the PWM Z-source DC-DC converter with the voltage conversion ratio being (1 − D)/(1 − 2D) in Ref. [16]. However, the output voltages of these converters are floating. In Ref. [17], the quadratic Boost converter with low buffer capacitor stress and the voltage conversion ratio being 1/(1 − D)² was proposed by Ye and Cheng. Unfortunately, the input current of this quadratic Boost converter is pulsating so that it is necessary and difficult to design the input filter for filtering its harmonics. Hence, to overcome the above drawback, a novel quadratic Boost converter is proposed in this paper. The proposed quadratic Boost converter has some good advantages including no abruptly changing on capacitors' voltage and inductors' current in the whole switching period which can assure no instantaneous overcurrent or overvoltage on storage elements, non-pulsating input current that can make the input filter design easier, and low current and voltage stress on power switch.

This paper is organized as follows. In section 2, the basic operation principle of the proposed quadratic Boost converter in continuous conduction mode (CCM) is described. The steady state and small signal dynamical behaviors is analyzed in section 3. In section 4, the design procedure for the proposed quadratic Boost converter is presented, and some Pspice simulations are given for confirmation preliminary. In section 5, the comparisons among the traditional quadratic Boost converter [18], the modified quadratic Boost converter [17] and the proposed quadratic Boost converter are presented for describing the good features of the proposed quadratic Boost converter. The hardware circuit is designed and some experimental results are presented for validation in section 6. Finally, some concluding remarks and comments are given in section 7.

Section snippets

Proposed converter’ structure and its operating principles

The proposed quadratic Boost converter is shown in Fig. 1. This converter contains two power switches (Q₁ and Q₂), one energy-transferring capacitor C₁, one output capacitor C₂, two inductors (L₁ and L₂), two power diodes (D₁ and D₂), and one resistive load R. Note that, here, the currents through the inductor L₁ and L₂ are denoted by i_L1 and i_L2, respectively. The voltage across the capacitors C₁ and C₂ are defined as v_C1 and v₀, respectively. Two power switches (Q₁ and Q₂) are controlled

Analysis of the proposed converter

In order to carry out theoretical analysis conveniently, the components in the proposed quadratic Boost converter are assumed as ideal and some symbols are defined. 〈x〉 is the averaged value of x which is the circuit variable such as i_L1, i_L2, v_C1, v₀, v_in and d. X and $\hat{x}$ are defined as its DC and small ac values, respectively. Also, the following equation is assumed $〈 x 〉 = X + \hat{x} with \hat{x} < < X$

From the averaging method [19], the averaged model for the proposed quadratic Boost converter in CCM operation

Design procedure and Pspice simulations

In this section, the design procedure for the proposed quadratic Boost converter is presented and some Pspice simulations are given for verification preliminary.

Comparisons among quadratic boost converters

Up to now, there are two quadratic Boost converters in the open literature: the traditional quadratic Boost converter (TQBC) in Ref. [18] and the modified quadratic Boost converter (MQBC) in Ref. [17]. Their respective circuit diagrams are shown in Fig. 6(a) and (b).

From Figs. 1 and 6, one can see that the input current of TQBC and the proposed quadratic Boost converter (PQBC) are non-pulsating since their input current equals their respective inductor current i_L1 while MQBC's input current is

Circuit experiments

Based on the selected components in section 4, the hardware circuit for the average current mode controlled the proposed quadratic Boost converter is constructed. Note that, in the experiment, the drive circuit is realized by the photocoupler TLP250H. The inductor current i_L1 is transformed into the voltage with the same value by using the current transducer LA55-P. The digital oscilloscope GDS 3254 is applied to capture the measured time-domain waveforms. Under the given circuit parameters in

Conclusions

For fuel cell applications, as well known, it needs the high step-up converter with high voltage conversion ratio and high efficiency. In this study, the novel quadratic Boost converter with its voltage conversion ratio being 1/(1 − D)² is proposed. The steady state and small signal model are derived and analyzed. Compared with the traditional quadratic Boost converter and the modified quadratic Boost converter, the proposed quadratic Boost converter has lowest voltage and current stress on the

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant nos. 51377124 and 51521065), a Foundation for the Author of National Excellent Doctoral Dissertation of PR China (Grant no. 201337), the New Star of Youth Science and Technology of Shaanxi Province (Grant no. 2016KJXX-40).

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View full text

A novel quadratic Boost converter with low current and voltage stress on power switch for fuel-cell system applications

Abstract

Introduction

Section snippets

Proposed converter’ structure and its operating principles

Analysis of the proposed converter

Design procedure and Pspice simulations

Comparisons among quadratic boost converters

Circuit experiments

Conclusions

Acknowledgements

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IEEE Trans. Power Electron.

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