Enhanced compensation strategy of voltage harmonics for Doubly-Fed induction generator

Using the idle capacity to compensate voltage harmonics at the point of common coupling (PCC) is an important reflection of participating in power grid regulation for the doubly-fed induction generator (DFIG), which is very beneficial to improve the power supply quality in the regional power grid. Due to the pouring of power electronized devices, the uncharacteristic harmonics of which frequencies are unfixed appear in the power grid. The existing voltage harmonics compensation methods mainly focus on the traditional characteristic harmonics. The frequencies of these kinds of harmonics are fixed and pre-known (6n +/- 1 orders). This fact makes the existing methods only work at the specific and fixed frequency, and cannot deal with the harmonics of which frequencies are uncharacteristic or unfixed. Therefore, starting from the theoretical analysis of voltage harmonics at PCC, this paper investigates the mechanism that can simultaneously compensate for the characteristic and uncharacteristic harmonics of PCC voltage, and indicates that decreasing the impedance of DFIG in the frequency range of harmonics is the core of voltage harmonics compensation. Then, this paper proposed a wideband control structure and the matched controller, so that the impedance of DFIG can be effectively decreased in a wideband frequency range. The design procedure of the harmonics controller co-currently considers the compensation performance and system stability. Finally, this paper carries on the evaluation based on the hardware-in-the-loop platform and scale-down experimental platform to verify the correctness of the theoretical analysis and the effectiveness of the control strategy.