View at Google Scholar K. The control system operates with regard to functionality and integration of the turbine, taking into consideration the characteristics of each component and its reaction to external effects as well as adjustment efforts. It is a resistance in parallel with an inductance that is connected between the rotor windings terminals and the rotor side converter RSC terminals to protect the rotor windings against harmful effects from the RSC which include bearing currents, capacitive leakage currents, and degradation of insulation due to polarization effect by the resultant capacitive displacement current from sudden rise in voltage. Subscribe to Table of Contents Alerts. SMC is superior to PI controllers used in VOC in that it [ 53 , 54 , 56 , 57 ] i improves performance of the system against unmodeled dynamics, ii reduces overshoot and transient time, iii is robust to external disturbances and machine parameter changes due to generator temperature rise, magnetic saturation, and skin effect, among others; this is because the control signals only depend on the selected switching variables states, iv has simple implementation as it does not require the decomposition of the voltage and current sequences in the VSC or use of a phase locked loop PLL to obtain the grid voltage positive sequence; this avoids time consuming computations as well as the challenges of the PLL losing synchronism with system frequency following a fault [ 40 , 58 , 59 ], v has better reference tracking. However, the generator response must go beyond just securing machine operation during the fault.
Controls for the RSC and GSC under both normal conditions and grid disturbance conditions must ensure that predetermined set-points are met. Once sufficient wind is available, the turbine starts rotating and the machine starts generating power. The amplitude is the remaining voltage value during the sag. This subsystem includes the turbine rotors, the hub, the low speed shaft, the gearbox, and the high speed shaft that is connected to the generator rotor. This limits its accuracy in modelling rotor current transient behaviour; however, the reduced complexity makes it best suited for large-scale wind farm simulations.
Some approaches utilize combinations of the solutions outlined above in a bid to cover the effects of severe faults. Curves for low-voltage ride-through requirements for different countries [ 7 ].
Journal of Engineering
The main topology, the natural clamped converter, consists of two two-level back-to-back VSCs with a circuit to provide resonance in between them. It does not strictly require a mathematical model of the plant.
A matrix converter, also called a cycloconverter, transfers AC supply directly into an AC load of a different frequency. It also has a wound rotor which is brought out through slip rings and carbon brushes for connection to a power electronic converter PEC and then either directly or through a transformer, to the stator terminals.
Many works have been done on various aspects of the DFIG WECS, such as the aerodynamic energy conversion, the electromechanical energy conversion, control underbalanced and imbalanced grid voltages, power electronic converters and their modulation schemes, and power evacuation to the grid. This is made more difficult by the intermittent and uncertain nature of the prime mover, the wind [ 34 ].
View at Google Scholar A. This allows optimal rotor speed reference tracking [ 60 ]. It also reduces time delays and errors [ 97 ]. Monitoring equipment must also be set up to verify actual behaviour during faults.
Correspondence should be addressed to Julius Mwaniki ; moc. The control system operation is aimed at regulating the turbine power in high winds and optimizing it in low yhesis winds.
It acts as a backup system when the main control system fails or when activated by an operator-controlled emergency stop button.
The control and supervision of a thedis turbine are automated so as to realize benefits such as reduced cost of operation, increased staff safety, and increased energy yield. To receive news and publication updates for Journal of Engineering, enter your email address in the box below. For cost effectiveness, the DFIG WECS must operate at full efficiency during both steady and transient states while producing as much power as possible under psxad prevailing wind and grid conditions.
Slip power is also sent to the DC-link. Section 7 covers possible faults and proposed solutions while simulation is handled in Section 8. These include frequency fluctuations, voltage sags, and voltage swells. The latter leads to generator speed increase and increase in DC-link voltage. Two-level back-to-back VSC in parallel connection [ 8 ].
Petersson, Analysis, modeling and control of doubly-fed induction generators for wind turbines [Ph. It has the rfig of redundancy and hence increases reliability of the converter.
This paper is divided into ten sections. Among the reviewed proposed control systems, the SMC strategy, especially in simhlation with FLC as proposed in [ 56 ], seems the most attractive choice as it best meets the qualities given above. Common grid connection requirements include [ 2192730 — 34 ] the following. While individual machine performance is of interest, grid operators are more interested in the overall simulstion of the wind farm and make this a prerequisite for connection.
A Condensed Introduction to the Doubly Fed Induction Generator Wind Energy Conversion Systems
Various combinations of the four control strategies above are also utilized with the aim of taking advantage of the strong points of each of the control strategies in the combination while minimizing their shortcomings. This paper seeks to bridge these works for a complete picture into this multifaceted system.
Conceptual diagram for DFIG wind turbine ;scad partial scale power converter showing control strategy levels [ 14 ]. The variable switching frequency makes design of appropriate filters difficult.
The DFIG WECS is presented from its construction, operation, advantages and shortcomings, modelling, control solutions, response to faults, and, finally, simulation.
This is as shown in Figure 4. In addition, the speed increases to 1.