Prasad, Low voltage ride-through capability for matrix converters fed adjustable-speed induction machine drives for industrial and wind appliances [Ph. Its control rule is qualitatively expressed on the basis of logic-language variation [ 56 ]. Morneau, A comparative evaluation of low voltage ride through solutions in wind turbines using doubly fed induction generators [M. These include frequency fluctuations, voltage sags, and voltage swells. The error between calculated instantaneous active and reactive power and their estimated values is used to select, from a switching table, the converter switching state. This is caused by idealized modelling of the system, time delay of actual switching, and the discretization of digital control [ 55 ].

For external faults, voltage swells cause high temperatures in the generator windings. On occurrence of voltage sag, the WECS must remain connected for a given set time before disconnecting. On the other hand, IEC defines a voltage dip as a sudden voltage reduction at any point in the electrical system lasting from anywhere between half a cycle to a few seconds [ 35 ]. View at Google Scholar C. Iwanski, Doubly Fed Induction Machine: 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.

The second subsystem carries out the conversion of the ni power into electrical power. These consist of a two-level back-to-back current source converter CSCdesignated the primary converter, in parallel with a two-level back-to-back VSC, and designated the secondary converter.

A Condensed Introduction to the Doubly Fed Induction Generator Wind Energy Conversion Systems

It is seen that the machines are disconnected due to overcurrents which go up to 1. This however increases the control gain and reduces the inhibitory effect on chattering. The voltage across the inductor is given, in the reference frame, by where and are voltages at GSC output terminals while and are voltages at the grid.

View at Google Scholar S. The WECS must operate within typical grid frequency limits. To receive news and publication updates for Journal of Engineering, enter your email address in the box below. It is composed of a rectifier bridge utilizing insulated gate bipolar transistors IGBT and diodes. It has lower harmonics and lower switching losses. Schematic of GSC connection to grid [ 11 ]. SMC is superior to PI controllers used in VOC in that it [ 53545657 ] 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 [ 405859 ], v has better reference tracking.


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 the prevailing wind and grid conditions.

A matrix converter, also called a cycloconverter, transfers AC supply directly into an AC load of a different frequency. It however requires a high frequency sampling for satisfactory performance and has variable switching frequency. Components of a wind turbine [ 5 ]. Among the applied wind energy conversion systems WECS configurations, i four most common ones are designated types A to D.

These include the following [ 781423 ].

These currents in the rotor are induced by both the voltage induced by the rotating stator field and the voltage supplied by the RSC. The latter leads to generator speed increase and increase in DC-link voltage. The switching between the different functions is determined by plant states represented by a switching simulqtion and so can change at any time during system operation unlike in feedback control.


View at Google Scholar T. Indices and indicate direct and quadrature axis simukation, respectively, while and indicate stator and rotor quantities, respectively, and is grid electrical angular speed, is rotor electrical angular speed and slip speed, and is given by.

phd thesis dfig simulation in pscad

Beyond point D, power regulation is introduced to ensure output power does not exceed rated power as smulation speed continues rising. Sample simulation results have been presented underlining the need for FRT capability. It has the advantage of redundancy and hence increases reliability of the converter.

Figure 9 shows the waveform of a voltage swell. View at Google Scholar M. When voltage goes above its upper limit, usually at 1. The system should also not introduce other problems that will require suppression or elimination.

This is as shown in Figure 4.

Journal of Engineering

Since the DFIG is an asynchronous generator, its electromagnetic torque is developed when currents induced in the rotor windings set up a magnetic field which interacts with the stator field.

German and Danish grid code reactive current requirements during sags [ 10 ].

phd thesis dfig simulation in pscad

Single-line diagram showing SMES connection for reactive power compensation [ 15 ]. The direct and quadrature stator and rotor flux components are decoupled magnetically and are given by where andand are stator leakage and rotor self-inductances, and is mutual inductance H. Its control rule is qualitatively expressed on the basis of logic-language variation [ simulattion ].

Simuoation carries out tasks such as monitoring wind and other loading conditions, sending information to the control system, monitoring operation for safe conditions, monitoring grid conditions, actuating emergency systems, and switching between operating states that facilitate connection and disconnection to the grid.