Abstract
When wind power is transmitted via high-voltage direct current (HVDC), the problem of high-voltage ride-through (HVRT), caused by direct-current (DC) blocking must be seriously taken into account. All the wind turbines in a wind farm are usually equivalent to a single turbine in the existing research on HVRT, which ignores the generator terminal voltage distribution in a wind farm. In view of the fact that the severity of fault voltage felt by each wind turbine in the field is different, an improved HVRT strategy considering voltage distribution is proposed in this article. First, this article analyzes the mechanism of voltage swell failure caused by DC blocking, and the characteristics of the generator terminal voltage distribution in wind farms. Second, the reactive power characteristic equations of the synchronous condenser and the doubly-fed induction generator (DFIG) are derived. Third, based on the extraction of the key node voltage, this article takes the key node voltage as the compensation target, and put forwards a HVRT strategy combining the synchronous condenser and wind turbine. Finally, the simulation is carried out to demonstrate the effectiveness of the proposed strategy in improving the HVRT capability of all wind turbines.
Highlights
With the massive consumption of primary energy, energy shortage has become a worldwide problem
In the case of a voltage swell fault caused by DC blocking, even if the voltage of the grid-connection point is stabilized within the normal operating range through the reactive power compensation, the generator terminal voltage of the wind turbine at the end of the collection line is very likely to exceed the normal operating range, which will cause trip-off accidents
While the generator terminal voltage of a few wind turbines is higher than 1.1 p.u. and Ukp is lower than 1.1 p.u., only the downstream doubly-fed induction generators (DFIG) participate in additional reactive power compensation
Summary
With the massive consumption of primary energy, energy shortage has become a worldwide problem. Reference [15] analyzed the generator terminal voltage distribution inside a wind farm, and put forward a corresponding voltage coordinated control strategy, but the influence of DC blocking fault scenarios and the application of synchronous condensers were not considered in the paper. The installation of a synchronous condenser in wind farms can effectively improve the high and low voltage ride-through capabilities of the wind turbine by considering the voltage and reactive power distribution inside the wind farm. Reference [17] showed that the reactive power compensation capability of the synchronous condenser is better than STATCOM when facing the transient overvoltage problem caused by a DC blocking fault at the sending-end grid. By means of controlling the voltage of the extracted node, the proposed strategy coordinates the reactive power output of the synchronous condenser and DFIGs, effectively avoiding trip-off accidents during the voltage swell period.
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