IEEE PEDS 2015, Sydney, Australia 9 – 12 June 2015 DOI: 10.1109/PEDS.2015.7203534 978-1-4799-4402-6/15/$31.00 ©2015 IEEE ZCS Interleaved Boost Converter with Saturable Inductors for Reverse-Recovery Reduction Wilmar Martinez, Jun Imaoka and Masayoshi Yamamoto Shimane University yamamoto@ecs.shimane-uc.jp Abstract-Conventional DC-DC step-up converters present problems of low efficiency and low power density because of: 1. High power losses caused by hard-switching and reverse-recovery phenomenon. 2. High conduction losses produced by large peak currents when the converter has to operate at a high duty cycle. 3. Bulky and heavy cooling systems needed to dissipate the semiconductors losses. And, 4. Big and heavy capacitors and inductors required for smoothing and decoupling. Therefore, a novel Zero-Current-Switching two-phase interleaved boost converter with saturable inductors for reverse-recovery reduction is proposed. This converter can reduce the switching losses in the semiconductors due to the effect of the saturable inductors. Moreover, downsizing of the inductors and the output capacitor can be achieved due to the interleaving technique and the use of saturable inductors. In addition, high step-up operation can be achieved due to the presence of tapped-inductors. In this paper, the circuit configuration and the operation principle of the proposed converter and the reverse-recovery reduction behavior are presented. Finally, the effectiveness of the proposed converter is experimentally validated with a 600W prototype where a recovery-reduction of 58% was achieved. I. INTRODUCTION Step-up DC-DC converters are used in application where the voltage required by the load is higher than the supply voltage, e.g. Renewable Energy and Electric Vehicles applications [1]- [3]. In these applications, conventional boost converters have been widely used because of its high power capability and high power factor [4]-[5]. However, these conventional converters have some issues related to: 1. Switches and diodes are operated under hard switching, which produce EMI/RFI noises and high switching losses due to the recovery phenomenon. 2. High conduction losses in the windings and in the power devices because of the large peak current generated when the voltage of the storage unit is quite lower than the output voltage. This behavior is presented due to the high duty cycle produced to obtain the required voltage gain. 3. Cooling system oversizing produced by the switching losses. And, 4. Bulky and heavy inductors and capacitors [6]-[9]. Consequently, tapped-inductor DC-DC converter was proposed as a solution for increasing the voltage gain and reducing the voltage stress on the switch. This topology uses one magnetic component which reduces the volume and the complexity of the converter [10]. Therefore, it is possible to achieve high power density, high efficiency and high voltage gain using the well-known magnetic coupling technique. Fig. 1 shows the conventional tapped-inductor boost converter. The tapped inductors of this converter have two windings n1and n2 magnetically coupled due to the fact of these windings are wound in only one magnetic core. This characteristic offers the advantage of a high voltage gain dependent on the ratio of the number of turns between the windings [11]. Fig. 1. Tapped-inductor boost converter. However, the conventional tapped-inductor topology presents some drawbacks: 1. Leakage inductances of the tapped-inductor, especially on winding n2, produce high voltage spikes on the switch when it is turned OFF. Additionally, high losses are induced. 2. EMI/RFI noise is generated by the large slope of voltage and current waveforms. And, 3. This topology operates under hard switching operation that produces high switching losses [12]. As a consequence, the Zero Current Switching (ZCS) converter, proposed in [13]- [14] and shown in Fig. 2, offers attractive features of increasing the efficiency, ZCS behavior and EMI/RFI reduction. Fig. 2. Conventional interleaved ZCS converter. This converter is a two-phase interleaved boost converter composed of a tapped inductor made of two windings L1a and L1b, two main diodes D1,3 two bypass diodes D2,4, two switching transistors S1,2, a smoothing capacitor Co and two particular auxiliary inductors Laux1 and Laux1 [15]-[16]. However, at large current operation, the commutation time when the current flows from the bypass diode D2,4 to the main diode D1,3 is longer and recovery phenomenon might occur in the diode D2,4 due to the stored charge in the bypass diode. Additionally, the reverse-recovery phenomenon is presented in the main diode.