# An Interleaved DC/DC Converter with Soft-switching Characteristic and high Step-up Ratio
## 1 Introduction  
Recently, renewable energies have been increasingly used to meet growing energy demands and mitigate climate change caused by the greenhouse effect due to the burning of large amounts of fossil fuels. Batteries are often used in energy storage systems to compensate the power fluctuation between renewable power generation systems and consumption [1; 2; 3]. Since battery voltage is usually small and has a wide range of variation, a high step-up dc/dc converter is indispensable on application where high dc voltage is required [4; 5; 6]. The boost converter has been widely adopted for step-up application because it has the advantages of simple circuit architecture and easy control [7; 8]. Theoretically, the voltage gain of a boost converter is tremendous high when its duty ratio is close to 1. Under ideal conditions, the value of the voltage gain at the 0.9 duty cycle is equal to 10. Nevertheless, it is impractical to operate a boost converter at such a high duty cycle, because when the resistance of the inductor and the semiconductor device is considered in the actual circuit, both the circuit efficiency and the voltage gain will be greatly reduced [9]. On the other hand, the voltage gain of a boost converter operating at discontinuous-conduction mode (DCM) is higher than that of a boost converter operating at continuous-conduction mode (CCM). A DCM operated boost converter could provide a reasonable solution for achieving high voltage gain. Nevertheless, a smaller inductor is used at DCM operationand the current ripples at both the input and the output sides are high. It requires a large capacitor to filter out the current ripple to obtain a smooth output voltage. The circuit efficiency is another important issue for direct current-to-direct current (DC/DC) converters. However, the traditional pulse-width modulation (PWM) converters operate at hard switching, leading to high switching losses and high voltage and/or current stresses. In order to solve the drawbacks of hard switching, researchers have proposed many soft-switching technologies to enable the semiconductor devices operate at either ZVS or ZCS. Synchronous rectification (SR) technique is popularly applied to reduce the conduction loss, especially when the output is low voltage and high current. SR technique use a synchronous switch to replace the freewheel diode. If the synchronous switch remains on until the inductor current decreases from positive to negative, the active switch can achieve ZVS operation by flowing the negative current of the inductor to release to charge stored in its parasitic capacitor [10; 11; 12]. However, the SR technique is more complicated since it requires a current sensor and corresponding control to precisely turn off the synchronous switch. The active clamping circuits or snubber circuits are often used to achieve soft-switching operation [13; 14; 15; 16]. However, these techniques need to use additional auxiliary active switches, diodes, and/or passive components to operate the main active switch at ZVS. The control circuit is more complicated and circuit cost is higher. Besides, the current loops in the active clamping or snubber circuits would cause conduction losses and even more switching losses. In addition to increasing power capacity and reducing current ripple, some interleaved dc/dc converters also have the advantages of ZVS operation [17; 18; 19; 20]. In these interleaved converters, the active switches are arranged to be turned on and off alternately and an additional inductor is added. The principle of ZVS operation is similar to that of SR technology. The additional inductor is operated at CCM. As soon as one active switch is turned off, the current of the additional inductor will flow through the parasitic capacitor of the other active switch to release its stored energy. When the parasitic capacitor is fully discharged, the diode connected in parallel with the active switch conducts to clamp the active switch at near zero volts. Then, it can be turned on at zero voltage.