Dynamic economic dispatch (DED) is one of the important optimization problems in power system operation. This paper proposes Maclaurin series based Lagrangian method (MSL) to solve the DED problem for generating units with valve-point effect, considering the ramp-rate limits and spinning reserve constraint. Using Maclaurin series, the sine term used to model the valve-point effect is expanded and solved with Lagrangian method. The feasibility of the proposed method is validated with five unit test system for 24 h. Minute-by-minute dispatch for a large system with 40-units is also carried out in this work. Test results obtained with the proposed approach are compared with other techniques in the literature. The results obtained substantiate the applicability of the proposed method for solving dynamic economic dispatch problems with non-smooth cost functions. © 2010 Elsevier Ltd. All rights reserved.