AbstractIn AC electric railways, three‐phase voltage is changed into the single‐phase circuit of two circuits with the Scott‐connected transformer. If unbalancing of the load between single‐phase circuits becomes large, voltage fluctuation becomes large on the three‐phase side. Railway static power conditioner (RPC) was developed for the purpose of controlling voltage fluctuation on the three‐phase side. An RPC is comprised of a pair of self‐commutated PWM inverters. These inverters connect the main phase and teaser feeding buses, coupled with a DC side capacitor such as a back‐to‐back (BTB) converter. In this way, the two self‐commutated inverters can act as a static var compensator (SVC) to compensate for the reactive power and as an active power accommodator from one feeding bus to another. 20 MVA/60 kV RPCs started commercial operation in 2002 at each two substations on the newly extended Tohoku Shinkansen for compensating voltage fluctuation on the three‐phase side caused by traction loads, absorbing harmonic current. The results of operational testing indicate that an RPC can accommodate single‐phase loads such as those of PWM‐controlled Shinkansen and thyristor phase‐controlled Shinkansen, and handle the exciting rush current of transformers, as well as compensate for harmonics successfully. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 25–34, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20397