Electric power conversion system (EPCS), which consists of a generator and power converter, is one of the most important subsystems in a direct-drive wind turbine (DD-WT). However, this component accounts for the most failures (approximately 60% of the total number) in the entire DD-WT system according to statistical data. To improve the reliability of EPCSs and reduce the operation and maintenance cost of DD-WTs, numerous researchers have studied condition monitoring (CM) and fault diagnostics (FD). Numerous CM and FD techniques, which have respective advantages and disadvantages, have emerged. This paper provides an overview of the CM, FD, and operation control of EPCSs in DD-WTs under faults. After introducing the functional principle and structure of EPCS, this survey discusses the common failures in wind generators and power converters; briefly reviewed CM and FD methods and operation control of these generators and power converters under faults; and discussed the grid voltage faults related to EPCSs in DD-WTs. These theories and their related technical concepts are systematically discussed. Finally, predicted development trends are presented. The paper provides a valuable reference for developing service quality evaluation methods and fault operation control systems to achieve high-performance and high-intelligence DD-WTs.
. [J]. Frontiers of Mechanical Engineering, 2017, 12(3): 281-302.
Shoudao HUANG, Xuan WU, Xiao LIU, Jian GAO, Yunze HE. Overview of condition monitoring and operation control of electric power conversion systems in direct-drive wind turbines under faults. Front. Mech. Eng., 2017, 12(3): 281-302.
Judgment is not accurate, and it is related to load and power supply reliability
Symmetrical component method
[15,16]
Monitoring of inter-turn short-circuit fault
Insulation is not monitored
Park vector analysis of stator current
[17,18]
Monitoring of inter-turn short-circuit fault
Relationship between the ellipticity of the trajectory of (id, iq) and the fault is unclear
Axial magnetic flux leakage
[19–21]
Monitoring of inter-turn short-circuit fault as well as phase-to-phase and phase-to-ground insulation deterioration
Installation of multiple probes with high concentricity is required
Vibration signal analysis
[22–24]
Monitoring of inter-turn short-circuit fault and winding insulation deterioration
Multiple vibration sensors should be installed
Temperature signal analysis
[25–30]
Monitoring of inter-turn short-circuit fault and phase-to-ground insulation deterioration
Temperature sensors, which are difficult to locate, should be installed
Partial discharge
[31–34]
Monitoring of inter-turn short-circuit fault and insulation deterioration
High cost
Tab.1
Fig.4
Methods for demagnetization detection
References
Features
Static prevention methods
[45]
Permanent-magnet materials were studied, and an expression for demagnetization in specific cases were derived by this method
[46]
The effect of the alternating magnetic field on the permanent-magnetic material was studied by this method
Off-line detection methods
[48]
The method of “D-the Module” flux observation was proposed. The method can respond to the changing flux linkage, but it can only observe fluctuations in the flux amplitude in a fixed direction
[49]
An improved back-EMF method was proposed. The method can be used to estimate the flux linkage, but it can only observe the fluctuations in the flux amplitude in a fixed direction
[51]
A reactive power feedback method to compensate for the torque ripple caused by flux linkage was proposed. However, the method can only consider the fluctuations in the flux linkage amplitude
On-line detection methods
[47]
An on-line flux linkage monitoring method based on the Kalman filter was proposed. The method can ensure the optimal operation of PMSGs under fluctuating magnetic field of the permanent magnet
Tab.2
Fig.5
Fig.6
Fig.7
Stator fault types
References
Number of faults
Diagnostic methods
Inter-turn short circuit
[73–88]
50
a. Model-based diagnostic methods b. Signal-based diagnostic methods c. Knowledge-based diagnostic methods
Insulation fault
[31,89]
45
TGA-B diagnostic instrument; O3 monitoring
Cracks and deformation in core and base
[90–92]
5
a. Finite-element diagnosis b. Electrical signal-based diagnosis
Tab.3
Demagnetization fault diagnosis methods
Methods presented in references
References
Features
Demagnetization fault diagnosis based on signal transformation
HHT
[100]
This method can detect demagnetization fault under steady-state dynamic situations
CWT
[101]
This method can rapidly diagnose faults
DWT
[101]
This method can acquire the spectrum of the stator current
FFT
[102]
This method is capable of detecting demagnetization, but it is not applicable under conditions of changing loads and variable speed
Demagnetization fault diagnosis based on an equivalent magnetic circuit
Semi-analyticalequivalent model
[103]
The accuracy of calculation is low, but the computational speed is fast
Tab.4
Fig.8
Fig.9
Fig.10
Fig.11
Fig.12
Fault types
Symptoms
Control
Symmetrical voltage drop
Conversion system energy accumulation and DC-bus voltage rapid increase
Energy balance control
Asymmetrical voltage drop
1) Conversion system energy accumulation and DC-bus voltage rapid increase 2) Double-frequency DC-bus voltage fluctuations affecting the generator stator current
Energy balance control and suppression of second-order frequency fluctuation
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