Modeling and control of a doubly fed induction generator with a disturbance observer: a stator voltage oriented approach

Abstract

The popularity of renewable energy conversion systems, and especially of wind energy, has been growing in recent years. Doubly fed induction generator (DFIG)-based wind energy systems are extensively used due to their wide range of active and reactive power controllability. Conventional DFIG control structures consist of decoupled PI rotor current controllers with stator flux orientation and machine parameter-dependent compensating terms. The accuracy of stator flux calculations is dependent on how accurately the stator resistance is known. Integration problems also exist and additional low-pass filters are implemented to accurately calculate the stator flux. In the current study, machine-dependent compensating terms are estimated with a first-order low-pass filter disturbance observer. Therefore, a single proportional (P) controller is sufficient to control decoupled rotor currents. The proposed controller structure is implemented on a MATLAB/Simulink platform with the parameters of 500 kW DFIG used in the MİLRES (Turkish National Wind Energy) project. The proposed controller is also experimentally validated in an experimental setup.

Experimental behaviour analysis for optimally controlled standalone DFIG system

“…DFIGs have been widely used for large-scale wind generation systems. Their control and operation have been subjects of intense research during the past few years [2][3][4]. The conventional DFIG control structures consist of the decoupled proportional-integral (PI) rotor current controllers with stator flux orientation and machine parameter-dependent compensating terms.…”

Electrical design and testing of a 500 kW doubly fed induction generator for wind power applications

“…In the design of the DFIG, the standard construction capabilities of the machine manufacturers are especially taken into consideration and unsuitable/special design parameter values are avoided intentionally. In this way, it is aimed that the designed DFIG can easily and cost-effectively be manufactured by local machine manufacturers, which is the main objective of the MILRES Project [22][23][24]. Therefore, determined values of initial design parameters are discussed with national machine manufacturers and the corresponding parameters are modified by considering standard construction capabilities of the manufacturers such as the interior diameter and length of the maximum motor frame (810 mm and 1453 mm), the maximum shaft diameter (164 mm) and its torsional stress strength, magnetic specifications of the lamination material (M400-50A), the maximum conductor diameter (1.32 mm), the maximum slot filling factor (45%), etc.…”

“…This generator is developed in the context of the MILRES (Turkish National Wind Energy Systems) Project [22][23][24]. The MILRES wind turbine system is shown in Figure 1.…”

Control Strategy for a Grid-Connected Inverter under Unbalanced Network Conditions—A Disturbance Observer-Based Decoupled Current Approach

“…DOb-based current controllers are applied to DFIGs and GCIs in [39,40] by considering robustness against parameter variations under balanced voltage sets. However, this method must be carefully tuned to suppress double-frequency oscillations.…”