This work introduces a set of PWM SEPIC dc-dc converters specially designed for high voltage-gain conversion, the voltage gain in the proposed converters can be adjusted by PWM and by adding diodes and capacitors in a diode-capacitor multiplier structure. They main features are: (i) high-voltage gain, without extreme duty cycles and transformer-less which allow high switching frequency and without cascaded connection, (ii) low voltage stress in switching devices, along with modular structures, and more output levels can be added without modifying the main circuit, which is highly desirable in some applications such as renewable energy generation systems (iii) it posses only one switch and two inductors, the voltage gain can increases by adding only diodes and capacitors. In addition, an average dynamic model is proposed for this converter. A detailed theoretical analysis is given. Both simulation and experimental results are provided to verify the principle of operation.