Apparatus and method for limiting output fluctuation of PID controller

The invention relates to an apparatus and method for limiting output fluctuation of a PID controller, wherein the apparatus and the method are used for controlling a frequency converter of an induced draft fan of a reformer in an SMR hydrogen generating device. The apparatus comprises a subtraction module, an absolute value module, a comparison module, a first selection module, and a second selection module. The subtraction module is used for obtaining output values of a PID controller at two continuous sampling times and outputting a difference value; the absolute value module is used for receiving the difference value outputted by the subtraction module, taking an absolute value and then outputting the absolute value; the comparison module is used for comparing the absolute value outputted by the absolute value module with a set fluctuation amplitude value and outputting a comparison result; the first selection module is used for using the output values of the PID controller at two continuous sampling times