Abstract
In Part I of this work, a static voltage security region was introduced to guarantee the safety of wind farm reactive power outputs under both base conditions and N-1 contingency. In this paper, a mathematical representation of the approximate N-1 security region has further studied to provide better coordination among wind farms and help prevent cascading tripping following a single wind farm trip. Besides, the influence of active power on the security region is studied. The proposed methods are demonstrated for N-1 contingency cases in a nine-bus system. The simulations verify that the N-1 security region is a small subset of the security region under base conditions. They also illustrate the fact that if the system is simply operated below the reactive power limits, without coordination among the wind farms, the static voltage is likely to exceed its limit. A two-step optimal adjustment strategy is introduced to shift insecure operating points into the security region under N-1 contingency. Through extensive numerical studies, the effectiveness of the proposed technique is confirmed.
Highlights
Centralized wind power integration in China has been beset by cascading tripping incidents involving wind farms
In the first part of work, the concept of voltage security region of wind farms could be expressed as a set of constraints limiting the reactive power of each wind farm to maintain its static nodal voltage in the secure range, given the active power generation of each wind farm, which was compared with a sampling-based approach and several different linear approximation techniques
Operating below the reactive power limits does not guarantee that voltages will remain within limits, and a voltage security region is a must
Summary
Centralized wind power integration in China has been beset by cascading tripping incidents involving wind farms. In order to guarantee that the voltage will remain within limits under both normal operating conditions and wind farm N-1 tripping conditions, N-1 security region is studied in detail in this work. It was pointed out in [1] that cascading trips tend to happen very quickly (usually in less than 2 s), rendering an effective response virtually impossible once an incident has begun. Numerical results for the optimal adjustment strategy are presented; these provide an intuitive prospective adjustable voltage range for the AVC with minimum adjustment of the wind farm reactive power outputs.
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