Protontherapy accelerators use radiofrequency Klystron amplifiers for particle acceleration. This amplifier requires a high voltage power supply called modulator. The goal of the project is the design of a klystron modulator connected to the three phase distribution system with high power factor, low harmonic distortion and constant power consumption. On the capacitor side the main requirements are low ripple and high precision in the output voltage. The second goal of the project is the definition of construction criteria for High Voltage Pulse transformers.