An optimum three-stage stator winding connections for wind-driven stand-alone self-excited induction generators for enhanced annual energy output

Abstract

A special three-phase stator winding consisting of a parallel combination of delta and star is proposed for wind-driven, self–excited induction generators (SEIGs), increasingly used for supplying isolated loads. This winding configuration enables the SEIG to be operated over a wide range of wind speeds, in three stages. The winding is set at parallel delta-star connection at higher wind speeds and then changed to conventional series delta and series star connections at medium and low wind speeds, respectively. An equivalent circuit has been developed for SEIG with this unconventional winding, and the expressions for the evaluation of its performance characteristics have been derived. A method of determining a suitable value of excitation capacitor bank has also been formulated using genetic algorithm. Taking an example of a 2.2 kW, three-phase SEIG, its predetermined characteristics and the corresponding experimental results have been presented. Taking the wind data from an actual wind farm, the annual energy output obtainable from this generator is also estimated. The proposed switching scheme is thus shown to be optimum for covering a wide range of wind speeds. A cluster of several such generators can lead to the establishment of battery charging stations and formation of micro-grids.

Appendix

1.1 Magnetisation characteristics of series delta, series star and parallel star connections

For series delta connection

$$\begin{aligned} E & = - 5.2422 \times 10^{ - 13} X_{{\text{m}}}^{6} + 8.9825 \times 10^{ - 10} X_{{\text{m}}}^{5} - 5.6677 \times 10^{ - 7} X_{{\text{m}}}^{4} \\ & \quad + 0.15694 \times 10^{ - 3} X_{{\text{m}}}^{3} + 0.018683X_{{\text{m}}}^{2} - 0.64815X_{{\text{m}}} + 568.54 \\ \end{aligned}$$

(18)

$${{R}}_{ 1} { = 15} . 2 1 {{\,\Omega , R}}_{ 2} { = 29} . 2 6 {{\,\Omega\,{\rm and}\,X}}_{ 1} {{ = X}}_{ 2} { = 14} . 2 5 {{\,\Omega }}.$$

For series star connection

$$\begin{aligned} E & = - 3.8593 \times 10^{ - 13} X_{{\text{m}}}^{6} + 4.6257 \times 10^{ - 10} X_{{\text{m}}}^{5} - 1.7192 \times 10^{ - 7} X_{{\text{m}}}^{4} \\ & \quad + 1.1902 \times 10^{ - 5} X_{{\text{m}}}^{3} + 0.00252X_{{\text{m}}}^{2} - 0.3855X_{{\text{m}}} + 570.51 \\ \end{aligned}$$

(19)

$${{R}}_{ 1} { = 15} . 2 1 {{\,\Omega , R}}_{ 2} { = 15} . 9 0 {{\,\Omega\,{\rm and}\,X}}_{ 1} {{ = X}}_{ 2} { = 20} . 1 7 {{\,\Omega }}.$$

For parallel star connection

$$\begin{aligned} E & = - 1.0886 \times 10^{ - 10} X_{{\text{m}}}^{6} + 1.9531 \times 10^{ - 8} X_{{\text{m}}}^{5} - 1.7937 \times 10^{ - 7} X_{{\text{m}}}^{4} \\ & \quad - 0.0002X_{{\text{m}}}^{3} + 0.0113X_{{\text{m}}}^{2} - 0.2982X_{{\text{m}}} + 260.36 \\ \end{aligned}$$

(20)

$${{R}}_{ 1} { = 3} . 8 1 {{\,\Omega , R}}_{ 2} { = 2} . 6 3 {{\,\Omega\,{\rm and}\,X}}_{ 1} {{ = X}}_{ 2} { = 4} . 7 5 {{\,\Omega }}.$$