Self-stabilising speed regulating differential mechanism for continuously variable speed wind power generation system

The speed regulating differential mechanism (SRDM) enables grid-connected wind turbines (WTs) to generate constant-frequency electric power without fully- or partially-rated converters. In this study, the authors present a self-stabilising SRDM (SS-SRDM) consisting of a planetary gear train (PGT), a differential mechanism, and a constant speed motor for WTs to dislodge the high-cost speed sensors, servo motor and the complicated control system from the electrical controlled SRDM. The kinematic principles and the four-axis dynamic characteristics of SS-SRDM are studied. An effective parameter configuration method for tuning the speed ratios of five key connection units is also proposed and used to obtain a PGT with optimal structural parameters. The detailed simulation model of a 3 MW WT with SS-SRDM is established and then validated through physical experiments. Results show the satisfactory accuracy of the built model (maximum steady-state errors in output shaft and speed regulating shaft are, respectively, 0.76 and 1.95%). Finally, case studies and verification work of the proposed methods are carried out, in which the rotational speed, power, speed error, and power ratio among wind rotor, SRM, and synchronous generator are obtained. Case studies well-illustrate the availability of parameter design and the effectiveness of speed-regulations of the proposed SS-SRDM method. © The Institution of Engineering and Technology 2020.