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In traditional unit commitment models, the ramping process of coal-fired generators is often represented by either a static average ramping rate or a once-changing rate model. However, this approach fails to accurately capture the actual ramping process of the unit, resulting in scheduling biases, particularly in systems with renewable energy sources. To address this issue, we propose a dynamic piecewise linear ramping (DPWLR) model that allows arbitrary multi-changes of ramping rates within a single period. We shift our focus from slope changes to time changes. By using a series of location indicator variables that satisfy the type 2 special ordered set, we locate the forward and backward time change limits and then determine the up and down power output limits of the units at each hour. We tested the intraperiod multiple-changing DPWLR model, as part of the unit commitment model, on different systems, including a 3-unit system, a 10-unit system, the IEEE RTS-79, and a 100-unit system. Comparative analysis demonstrates the functionality and superior performance of our proposed model. • A dynamic ramping model to simulate the unit's ramping process is proposed. • The model allows multiple ramping rate changes in one period. • The model uses location indicator variables to identify the ramping limits. • Some reproducibility studies on previous papers are carried out. • Comparison studies between the proposed model and the existing model are conducted. [ABSTRACT FROM AUTHOR]