The invention discloses a co-phase power supply device and a
traction power supply system. The co-phase power supply device comprises a first MMC (modular multilevel converter) valve and a second MMC valve. One end of the first MMC valve is coupled to a first power supply arm of a
traction transformer, the other end of the first MMC valve is connected with a return wire, and the first MMC valve is used for converting AC (
alternating current)
voltage of the first power supply arm of the
traction transformer into DC (
direct current)
voltage; one end of the second MMC valve is coupled to a second power supply arm of the
traction transformer, the other end of the second MMC valve is connected with the return wire, and the second MMC valve is used for inverting
DC voltage transmitted by the first MMC valve into AC
voltage which is identical to the second power supply arm of the traction
transformer in amplitude and phase. By means of inter-transmission of active energy of the two power supply arms on sides of the traction
transformer, negative-phase sequence current can be eliminated, the capacity
utilization rate of the traction
transformer can be maximized and electric split-phase of a traction network can be eliminated; the MMC valves compensate idle power and
harmonic waves of the two power supply arms, and the increase of risk of overhigh
harmonic waves of devices such as capacitors, SVCs (
static var compensator) and SVGs (
static var generator) can be avoided, so that the co-phase power supply device can be applied to comprehensive treatment of
power quality of traction transformers.