An Improved Rotor Speed Observer for Standalone Brushless Doubly-Fed Induction Generator Under Unbalanced and Nonlinear Loads

Abstract

The conventional control methods for brushless doubly-fed induction generator (BDFIG) normally employ mechanical sensors to acquire the information of rotor speed, which brings many disadvantages in the cost, complexity, reliability, and so on. This paper presents an improved rotor speed observer (RSO) for the sensorless operation of standalone BDFIGs, which is based on the power winding (PW) voltage and control winding (CW) current. In order to eliminate the impact of unbalanced and nonlinear loads on the RSO, second-order generalized integrators (SOGIs) and low-pass filters (LPFs) are introduced to pre-filter the PW voltage and CW current, respectively. Through comprehensive parameter design, the response speed of the improved RSO will be not lower than that of the basic RSO with ensuring the filtering effect of these additional filters. In addition, the proposed RSO is independent to machine parameters except the pole pairs. Comprehensive experiments are conducted and results verify the proposed improved RSO applied to the standalone BDFIG. Also, the applicability of the proposed RSO on another dual-electrical-port machine, DFIG, is confirmed by simulation results. 1

Bidirectional Harmonic Current Control of Brushless Doubly Fed Motor Drive System Based on a Fractional Unidirectional Converter Under a Weak Grid

“…The two control target settings in this paper are shown in (14) and (20). According to (7), the negative sequence 5th-order and positive sequence 7th-order components in i p and u p are shown as 6th-order harmonics in the fundamental synchronous rotating coordinate system, which will not be changed by the system operating state.…”

“…Control methods for DFIM generation systems working under distorted grids were widely studied in [10]- [13]. A sensorless control method for the standalone BDFM generator with unbalanced and nonlinear loads was applied in [14]. In [10] - [12], as a part of the grid, the capacity of doubly-fed generator is far less than the distorted grid.…”

“…To improve the generator operation is the major control objectives, such as elimination of the stator harmonic currents [10], [11], reduction of the active and reactive power oscillation [12]. In the power grids introduced in [13] and [14], the DFIM and BDFM are the unique independent power supply for the system. Due to the existence of unbalanced and non-linear loads, the voltage at the point of common coupling (PCC) is distorted.…”

“…The limitations of power system maximum distortion were outlined in [15]. However, the harmonics distribution characteristics in this system and the control targets are different with the power generation system in [10]- [14]. The harmonic distortion of the grid voltage is not constant.…”

Recent Advances of Control Technologies for Brushless Doubly-Fed Generators

“… Machine-Parameter-Free Speed Observers All the closed-loop estimation approaches mentioned above are severely dependent on the machine parameters, which would degrade the system robustness against the machine parameter mismatch. In order to address this issue, some typical machine-parameter-free speed observers have been developed for standalone BDFIG [103]- [105].…”