System of phase-free sensor for identifying one cylinder compression TDC (Top Dead Center) of three-cylinder engine

The invention discloses a system of a phase-free sensor for identifying one cylinder compression TDC (Top Dead Center) of a three-cylinder engine. The system comprises a crankshaft position sensor, a pulse disk, a storage battery voltage acquisition module and a cylinder judging module, wherein the storage battery voltage acquisition module is used for collecting and outputting voltage of a storage battery to the cylinder judging module; the cylinder judging module detects transient spike voltage generated by the crankshaft position sensor; if the transient spike voltage gets distortion, the storage battery voltage corresponding to an Eth transient spike voltage generating time before the transient spike voltage gets distortion is minus the storage battery voltage corresponding to an Fth transient spike voltage generating time before the transient spike voltage gets distortion to obtain a difference value; and according to the comparison of the difference value with a positive exhaust valve value and a negati