Stability and Power Quality Enhancement Strategy for DFIG System Connected to Harmonic Grid With Parallel Compensation

Distributed grid and microgrid are becoming increasingly important in power system nowadays. In these grids, reactive compensations and harmonic current suppression are commonly employed to improve power quality. For the doubly fed induction generator (DFIG), high frequency resonance (HFR) will occur when it is connected to parallel compensation grids. When DFIG system is connected to the harmonic grid with parallel compensation, frequency ranges of HFR and harmonics may have intersections. In this paper, some cases for DFIG system with the HFR damping and harmonics suppressor are given to reveal that the coupling between HFR damping control and harmonics suppression control may lead DFIG system into the unstable situation. Furthermore, a frequency detection is necessary for the existed HFR damping control when compensation capacitor changes, which will deteriorate the HFR damping performance due to the additional detection time on HFR frequency. This paper proposes an impedance reshaping control strategy based on a variable frequency resistance and chebyshev filter, the HFR damping control and harmonic current suppression can be achieved simultaneously to improve power quality for DFIG system connected to the harmonic grid with parallel compensation. Theoretical analysis, simulations, and experiments verify availability of the proposed control strategy.