Abstract
This paper firstly adopts a fault accommodation structure, a five-phase permanent magnet synchronous generator (PMSG) with trapezoidal back-electromagnetic forces, in order to enhance the fault tolerance of tidal current energy conversion systems. Meanwhile, a fault-tolerant control (FTC) method is proposed using multiple second-order generalized integrators (multiple SOGIs) to further improve the systematic fault tolerance. Then, additional harmonic disturbances from phase current or back-electromagnetic forces in original and Park’s frames are characterized under a single-phase open condition. Relying on a classical field-oriented vector control scheme, fault-tolerant composite controllers are then reconfigured using multiple SOGIs by compensating q-axis control commands. Finally, a real power-scale simulation setup with a gearless back-to-back tidal current energy conversion chain and a small power-scale laboratory prototype in machine side are established to comprehensively validate feasibility and fault tolerance of the proposed method. Simulation results show that the proposed method is able to suppress the main harmonic disturbances and maintain a satisfactory fault tolerance when third harmonic flux varies. Experimental results reveal that the proposed model-free fault-tolerant design is simple to implement, which contributes to better fault-tolerant behaviors, higher power quality and lower copper losses. The main advantage of the multiple SOGIs lies in convenient online implementation and efficient multi-harmonic extractions, without considering system’s model parameters. The proposed FTC design provides a model-free fault-tolerant solution to the energy harvested process of actual tidal current energy conversion systems under different working conditions.
Highlights
Compared with classical three-phase rotating generators, multiphase generators [1] have irreplaceable merits, such as better fault tolerance, lower fluctuations and more degrees of control freedom
A conveniently implemented model-free fault-tolerant control (FTC) strategy is proposed in this paper based on multiple SOGIs, applying to five-phase permanent magnet synchronous generator (PMSG)-based tidal current energy conversion systems
The dominant harmonic disturbances in different orders are accurately estimated using multiple SOGIs. These extracted harmonic disturbances are injected to the q-axis current control loops in order to constrain torque ripples and improve the fault tolerance of the entire system
Summary
Compared with classical three-phase rotating generators, multiphase generators [1] have irreplaceable merits, such as better fault tolerance, lower fluctuations and more degrees of control freedom. By a five-phase permanent magnet synchronous generator (PMSG) studied in this paper, tidal current energy conversion systems (TCECS) with a most-used back-to-back conversion chain via a horizontal-axis turbine can be configured as the following three designs in Figure 1 according to the convenience of submarine maintenance. The passive FTC algorithms are still worth being studied as they are inspired by classical robust control methods that concern only the sensitivity level of a fault instead of a fault’s size and location. Kiselev et al [16] proposed a robust fault tolerant method by model predictive control based on a finite control set This is similar to the passive FTC, as the fault detection is provided by the predicted variables.
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