On single-impulse and multi-impulse control

The question is phrased quite vaguely, so I’m not sure how to respond to the original poster. Impulse refers to the parameters involved in control; a single impulse means there is only one on-site input signal used for control, while three impulses mean there are three such input signals. For example, in a three-impulse boiler water level control system, the three impulses refer to the on-site water level signal L, the boiler’s steam output FT1, and the feedwater flow rate FT2 – all of which contribute to controlling the water level. As for the deaerator water level control or pressure control mentioned by the original poster, PI or PD control, or cascade control is generally used. The number of impulses chosen is either one or two.

The liquid level in the boiler drum is usually controlled using double or triple impulse control methods, in order to overcome the issues associated with false liquid level transitions. When the water supply to the drum suddenly decreases, and since the heat supplied to the drum by the boiler remains unchanged during this period, it causes a large amount of vaporization within the drum, thereby raising the liquid level. Similarly, an increase in the steam flow rate at the outlet also leads to an increase in the liquid level. Double impulse control ensures that when the steam flow rate increases, the water supply rate at the inlet increases as well, thus helping to maintain a stable liquid level. This control method involves adding steam feedforward control on top of single impulse control, and it is primarily used in small low-pressure boilers where the load changes rapidly. The disadvantage is that adjustments do not promptly reflect the disturbances in the feedwater measurement. Three-impulse control adds a signal for feedwater flow on top of the two-impulse control; it consists of water level, feedwater flow, and steam flow. In essence, it is a feedforward plus feedback system that is primarily used in large boilers. This post was last edited by wmhlaj on 2009-3-19 16:37]

1. Single impulse control: During the startup phase, when the steam flow is less than 30% of the rated value, single impulse control is used, with a PI calculation being performed on the set value and the measured water level. 2. Three impulse control: As the load continues to increase, relying solely on a single impulse regulator is no longer sufficient to ensure satisfactory control quality; therefore, when the load (steam flow) exceeds 30%, the three impulse control method is employed.