Analysis of a Soft Switching High Voltage Gain DC/DC Boost Converter for PV Systems

INTERNATIONAL JOURNAL of ENGINEERING TECHNOLOGIES-IJET Sarah Al-Hajm et al., Vol.4, No.2, 2018 Analysis of a Soft Switching High Voltage Gain DC/DC Boost Converter for PV Systems Sarah Al-Hajm*, Mehmet Ucar**‡ * Department of Electrical and Electronics Engineering, Graduate School of Natural and Applied Sciences, Duzce University, 81620, Duzce, Turkey ** Department of Electrical and Electronics Engineering, Faculty of Engineering, Duzce University, 81620, Duzce, Turkey (, ) ‡ Corresponding Author; Mehmet Ucar, Department of Electrical and Electronics Engineering, Faculty of Engineering, Duzce University, 81620, Duzce, Turkey, Tel: +90 380 542 10 36, Fax: +90 380 542 10 37, Received: 29.04.2018 Accepted: 26.05.2018 Abstract- This paper presents an analysis of a non-isolated soft switching high voltage gain DC/DC boost converter by using a coupled inductor, voltage quadrupler and active clamp circuit for Photovoltaic (PV) systems. The main advantage of this converter, coupled inductor with voltage quadrupler circuit is used to decrease voltage stress in semiconductor switches and providing high voltage gain. Therefore, low voltage valued and low on-resistance 𝑅𝐷𝑆(𝑂𝑁) MOSFETs can be used to decrease on-state losses. The reverse recovery and high frequency turn off losses is reduced for achieving Zero-Current Switching (ZCS) in all diodes. Voltage spike caused by leakage inductance of the coupled inductor is minimized by means of the active clamp circuit. Thus, Zero-Voltage Switching (ZVS) turn on of all MOSFET switches are achieved. The Perturb and Observe (P&O) method is utilized in this study to obtain maximum power from the PV system. In order to show the effectiveness of the converter, PSIM simulations are realized under various irradiance cases. The conversion efficiency is obtained about 95.97% at full load from the simulation results. Keywords DC/DC converter, high voltage gain, coupled inductor, voltage quadrupler, ZCS, ZVS, PV system. 1. Introduction In the past few decades, distributed generation with renewable energy sources have rapidly developed [1]. Much research has been carried out on renewable energy to get maximum power with high efficiency among renewable energy resources like wind, Photovoltaic (PV), etc. The output PV panel voltage is very low between (25-50 V) due to safety factors and for various applications is required boosting large voltage [2]. Maximum Power Point Tracking (MPPT) methods are commonly used with PV systems to maximize power extraction [3]. The Perturb and Observe (P&O) [4], [5] and the incremental conductance [6] MPPT algorithms are frequently used in the PV systems. These algorithms depend on the voltage-power characteristic, 𝑑𝑃 if ( < 0) right of the maximum power point MPP, while 𝑑𝑉 the left of the MPP when ( 𝑑𝑃 𝑑𝑉 > 0) [7]. In conventional boost converters, high losses are found on input side due to large peak current which adverse effects on the magnetic components. Because the large voltage across the switch, the switch conduction losses are increased (𝑅𝐷𝑆(𝑂𝑁) ∝ 𝑉𝐷𝑆 2 ). The inductor and capacitor resistances increase the losses due to large duty cycle. In addition, diode reverse recovery problem is a disadvantage [8]. For these reasons, the conventional boost converters are not appropriate to use for high voltage gain application. To get a high voltage gain without a high duty cycle, there are several proposed topologies. Among them, the coupled inductor is commonly used [9]. Although achieving high voltage gain with large turns ratio, its leakage inductance cause power losses and high voltage stress on the MOSFETs [10]. Therefore, passive or active clamp techniques are used to recycle leakage energy from the coupled inductor. Passive clamp circuits reform voltage gain, but cause high voltage stress on output diode. Utilizing active clamp circuit, Zero118 INTERNATIONAL JOURNAL of ENGINEERING TECHNOLOGIES-IJET Sarah Al-Hajm et al., Vol.4, No.2, 2018 Voltage Switching (ZVS) turn on with power switches are obtained [11]. In this paper, coupled inductor based high voltage gain soft switching DC-DC boost converter is analyzed and controlled for PV systems. This converter [11] has main advantages; firstly, the voltage quadrupler circuit is combined with secondary of the coupled inductor to produce high voltage gain. Secondly, at turn on for a MOSFET, coupled inductor transfers the energy to the voltage multiplier circuit. Thus, smaller magnetic component can be used with this converter. Thirdly, all diodes turned off at Zero-Current Switching (ZCS) and therefore reverse recovery losses, high frequency turn off losses are reduced and high voltage spike is eliminated. 2. Proposed System Overview and charge 𝐶𝑟2 of MOSFET 𝑆2 . Second, the dead time (∆𝑇) is enough for charge and discharge the MOSFET parasitic capacitor. For getting ZVS of MOSFETs, magnetizing inductance (𝐿𝑚𝑚𝑎𝑥 ) is obtained from equation (2). 𝐿𝑚𝑚𝑎𝑥 < 𝑉𝑖𝑛 𝐷max (1−𝐷max ) (2) 2(1+2𝑁)𝐼𝑜 𝑓𝑠 In this study, the magnetizing inductance (𝐿𝑚 ) is selected as 9µH, and dead time (∆𝑇) is determined from equation (3). ∆𝑇 ≥ √𝐿𝑚 (𝐶𝑟1 + 𝐶𝑟2 ) (3) ii) The ZCS turn off of diodes 𝐷1 , 𝐷2 , 𝐷𝑜1 and 𝐷𝑜2 is achieved if the minimum time to turn on MOSFET 𝑆1 is greater than the one-half of resonant period. Therefore, the capacitors 𝐶1 and 𝐶2 are obtained as equation (4). 𝐷2 𝑇 2 (1−𝐷𝑚𝑎𝑥 )2 𝑇𝑠2 𝑠 𝐶1 , 𝐶2 < ( 𝑚𝑖𝑛 , 2 𝜋 𝐿𝑘𝑠 The proposed system, including soft switching, high voltage gain converter is illustrated in Fig. 1. It involves of an input voltage (𝑉𝑃𝑉 ) and current (𝐼𝑃𝑉 ) from PV panel, input capacitor (𝐶𝑃𝑉 ), a coupled inductor primary side denotes (𝐿𝑚 and 𝐿𝑘𝑝 ) and secondary side denotes (𝐿𝑘𝑠 ), a clamp circuit (auxiliary switch 𝑆2 and out capacitor 𝐶𝑜3 ), a resonant voltage quadrupler circuit (consist of the diodes 𝐷1 , 𝐷2 , 𝐷𝑜1 , and 𝐷𝑜2 along with capacitors 𝐶1 , 𝐶2 , 𝐶𝑜1 , and 𝐶𝑜2 ), parasitic capacitors of MOSFETs (𝐶𝑟1 and 𝐶𝑟2 ) and output DC load (𝑅𝑜 ). The converter key waveforms as indicated in Fig. 2 and the nine operation interval are briefly described in [11]. 𝜋2 𝐿𝑘𝑠 ) (4) Do1 N1:N2 Lkp IPV Lks C1 D1 C2 D2 Co1 Lm Vi Co2 Cpv PV VPV S2 S1 VGS1 Cr1 Ro Do2 Cr2 Co3 VGS2 Fig. 2. The converter key waveforms. In the paper, high voltage gain is obtained without using high duty cycle or large magnetic components, which are main advantages over the conventional converter as indicated in Table 3. MPPT&Dead Time Generation Fig. 1. The proposed system block diagram. The conversion ratio (𝑀) of the converter is calculated from equation (1). The turn ratio of coupled inductor can be increased without increase MOSFET’s voltage stress. 𝑀= 𝑉𝑜 𝑉𝑖𝑛 = 1+2𝑁 1−𝐷 Table 3. Comparison of conventional and analyzed boost converter. Parameter (1) Soft switching operation of the converter is achieved as the following: i) For achieving ZVS turn on of MOSFET 𝑆1 there are two conditions: First, the stored magnetizing inductance energy is greater enou (...truncated)