Protecting system and method for preventing PLC from dead halt

The invention relates to the technical field of power electrical application, and discloses a protecting system and method for preventing a PLC from dead halt. The system comprises the PLC, a frequency relay, an ordinary relay 1, an ordinary relay 2, an ordinary relay 3, a set safety chain and a set off-grid and on-grid circuit. The method includes the following steps of firstly, designing a small program; secondly, dividing the program into three executing tasks according to control content; thirdly, judging faults. Compared with the prior art, the system and method have the advantages that a digital amount output point is set on an I/O module of the PLC, the small program is designed and used for controlling the frequency pulse output of the digital amount output point, the output frequency of the point can be determined according to the frequency of the selected frequency relay, the frequency relay is connected to the safety chain of a wind turbine set and connected to a grid and other hardware links in se