Reactive Power Influence on the Thermal Cycling of Multi-MW Wind Power Inverter

TLDR: In this article, the reactive power influence on the thermal cycling of power devices in grid-connected inverter for 10MW wind turbines is investigated, and a new concept is then proposed to stabilize the thermal fluctuation of the power devices during wind gusts.

Abstract: In this paper, the reactive power influence on the thermal cycling of power devices in grid-connected inverter for 10-MW wind turbines is investigated. Restrained by the grid codes, the allowable reactive power ranges in relation to amplitude and phase angle of the load current for a single converter system are first presented at different wind speeds. Furthermore, the interaction between paralleled converter systems in a wind park is also considered and analyzed. By controlling the reactive power circulated among paralleled converters, a new concept is then proposed to stabilize the thermal fluctuation of the power devices during wind gusts. It is concluded that the reactive power may change the thermal distribution of power devices. By properly controlling the reactive power, it is possible to achieve a more stable junction temperature in the power devices during the fluctuation of wind speed and thereby could provide a new way to improve the reliability of the wind power conversion system.

Figures

Fig. 11. Reactive power circulated in paralleled wind power converters.

Fig. 12. Operation range of reactive power when complying with grid codes (dot line represents underexcited Q-, real line represents overexcited Q+).

Fig. 10. Loss distribution of 3L-NPC inverter with different extreme reactive powers (Complying with grid codes).

Fig. 1. The phasor diagram from the power grid point of view by introducing reactive power in grid converter (Uc represents the converter output voltage, Ug grid voltage, UL voltage drop on filter inductor, Ig load current, IP active current, IQ reactive current, cosθ power factor, α the phase angle).

Fig. 14. Current distribution of 3L-NPC inverter under different reactive powers (Considering interaction of inverters, 10 m/s wind speed).

Fig. 13. Output waveforms of 3L-NPC inverter under different reactive power (Considering interaction of inverters, 10 m/s wind speed), output voltage pulses (Green), grid voltage (blue), phase current (red).