The disturbances of the drum water level in thermal power units become larger under ultra-low load conditions and the control quality become worse under variable load conditions. To solve these problems

this study puts forward a design scheme combining linear multi-scale filtering and nonlinear dead zone filtering. This filter can selectively filter according to the amplitude of high frequency component in original signals. And the inertia filtering time increases under ultra-low load conditions and stable load conditions while it becomes smaller under high load conditions and variable load conditions. The experiment results of drum water level filter in a 600 MW unit show that this filter can effectively filter the disturbances of the drum water level under ultra-low load conditions. Moreover

this filter can change the drum water level from PI control to PID control to meet the needs of the unit deep and rapid peaking operation.