Active and Reactive Power Formulations for Grid Code Requirements Verification

Wind power penetration has reached important levels in several European, American and other world countries. Wind electric energy production in some countries is comparable with that obtained through the nuclear and other conventional energies, thus System Operators in many nations have established wind farms grid codes in order to remain grid stability. Grid code requirements have been developed in response to the technical and regulatory necessities in each country; so there are a great variety of wind farms connection requirements. However, all grid codes have in common some quantities such as voltage, frequency and active and reactive powers and currents must be verified. In other hand, grid code requirements do not specify which active and reactive power and current formulations must be used. A lot of power approaches can be used. Several recently established approaches consider active and reactive phenomena must be analyzed by the fundamental-frequency, positive-sequence voltages and currents; this is because these last quantities determinate generators working and electromechanical stability. The IEEE Standard 1459-2010 explicitly holds one of these theories, due to A.E. Emanuel. The p-q-r theory, developed by Akagi and others, also establishes fundamental-frequency, positivesequence active and reactive powers. The Unified Theory described in this Chapter gives one more step in front of the two above mentioned theories and decomposes fundamentalfrequency, positive-sequence active and reactive powers and currents into two quantities: a) due to the active and reactive loads and b) caused by the unbalances. According to the Unified Theory unbalances can originate additional active and reactive powers and currents which can have the same or different sign of those due to active and reactive loads and, therefore, total active and reactive powers and currents can be increased or decreased. This active and reactive powers and currents decomposition can deliver important complementary information for verifying accomplishment of the grid code requirements and to regulate wind generators in order to win without disconnection transitory perturbations, such as voltage dips. In this Chapter, the two above indicated fundamental-frequency, positive-sequence active and reactive components of powers and currents are expressed and their properties are established. Formulations of these quantities are applied on actual wind farms to verify some European Grid Code requirements, focusing on the Spanish grid code, and their results are compared with those obtained from other power approaches.