A power conversion apparatus is for converting polyphase ac power directly to ac power. Each of the pressure holding valves in the front is a normally open valve, and each of the pressure holding valves in the rear is a normally closed valve. Each variable is defined in the specification. Thus, since the cell number of the active measurement set is smaller than that defined by the WCDMA system, the number of neighboring cells required to be measured is reduced, so as to reduce the power dissipation and increase the idle time on the user equipment.