Abstract
Unbalanced grid voltage sags are the severe challenge for wind power generation system which connected to the grid successfully. The dc bus voltage and output power will fluctuate under unbalanced grid voltage. Moreover, the voltage sags will lead to the increase of peak current, which will bring potential safety hazards to the operation of wind power system. This paper proposes a simple current limiting control scheme without auxiliary equipment, which based on the detailed analysis of the excessive peak current. In this scheme, the machine side converter (MSC) controller adjusts the electromagnetic power according to the power transmitted to the grid by the grid side converter (GSC). Meanwhile, it converts the unbalanced power on the dc-link into the rotor kinetic energy, avoiding the dc-link overvoltage. The GSC controller can not only ensure that the three-phase inverter currents are in the maximum safe range that the converters can bear, but also provide reactive power support for the grid. Furthermore, the fluctuations on dc bus voltage and output power can be eliminated effectively by using the GSC controller. The feasibility of the proposed scheme and the superiority over the traditional control schemes have been verified by simulations under different types of unbalanced voltage.
Highlights
With the increasingly serious environmental problems and energy crisis, many countries around the world have launched strategic deployment in the field of new energy
According to the structure of wind power system based on permanent magnet synchronous generator (PMSG), PMSG is directly connected to power grid through back-to-back (BTB) converters, and the stable operation of converters is vulnerable to unbalanced grid voltage sags
The performance of proposed modified method is compared with other two control strategies (I) Conventional control strategy. (Ï) DC-link voltage is controlled by machine side converter (MSC) and maximum power point tracking (MPPT) is enhanced by grid side converter (GSC) during grid voltage sags
Summary
With the increasingly serious environmental problems and energy crisis, many countries around the world have launched strategic deployment in the field of new energy. MSC is not sensitive to grid voltage sags and generates electric power continuously, resulting in the output power of MSC is not equal to the grid-connected power This leads to some practical problems, such as dc-link overvoltage or overcurrent of three-phase inverter currents [11]. The positive and negative sequence separation of voltage and current are inevitable and the degree of voltage imbalance needs to be fully considered in the realization of the control method Another control strategy is shown in [19], which determines the current reference value by looking up the table, so as to limit the excessive peak current. This paper proposes a modified power and current limiting control scheme for enhanced operation of wind power system during unbalanced grid voltage conditions.
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