In recent years, switching power supplies are widely employed in industry. Thus improving the performance of DC-DC converters is highly considered by researchers. Generally switching converters are Since some renewable systems such as fuel cells and solar cells have low output voltage which varies with output load, thus converters with high voltage gain are required to increase the voltage level and provide regulation. The main advantage of the current source converters is higher voltage gain than the voltage source converters. Thus, it is possible to use transformers with lower conversion ratio. Another advantage of current source converters is the absence of output inductance in its structure. Therefore, these topologies are more cost effective, when several output voltages are required. Since most renewable systems cannot produce high peak currents, therefore current source converters are preferred. It is important to reduce the size and weight of switching power supplies. Therefore, power supplies at high switching frequencies are designed. But, higher switching frequencies would increase switching losses and reduces the circuit efficiency. Therefore soft switching techniques are inevitable to reduce losses and increase switching frequency. On the other hand, the use of soft switching techniques is suitable solution to reduce RFI and EMI noise and get a better performance from semiconductor devices. For high power applications, series and parallel structures are important to reduce current stress and ripple. In modern converters, interleaved structures are considered for high - current and high - power applications due to advantages such as power distribution, fast transient response, smaller size of passive elements and current ripple. In this thesis, two new interleaved PWM Zero Current Switching (ZCS) boost converter are proposed to create soft switching conditions for all main and auxiliary switches. The proposed converters use only one auxiliary switch to provide soft switching condition. In order to reduce switching losses and to obtain a high efficiency a non dissipative soft-switching cell is used. In the proposed interleaved converter, soft switching is obtained for all semiconductor devices. The main and auxiliary switches turn on and off under zero-current condition. Keywords: Current source converters, Voltage source converter, Interleaved boost converters, Soft switching, Zero current switching, Zero voltage switching