Mechanistic analysis and suppression of the positive feedback of active power for grid-connected converters under a weak grid

• Based on the small-signal analysis of the whole GCC system, a small-signal model representing the complex relationship between the active power control and the voltage amplitude control is derived. • According to the derived model, it is revealed that the mechanism of instability of GCC under a weak grid can be attributed to the positive feedback in the active power control loop, which is caused by the coupling relationship between the d -axis current reference and the q -axis current response. • To enhance the stability of the GCC system under a weak grid, a damping controller is proposed, which is implemented on the q -axis voltage feedforward. This damping controller offers satisfactory control performance and is convenient for practical implementation. The grid-connected converter (GCC) synchronized through a phase-locked loop (PLL) suffers from stability problems under a weak grid, which is essentially attributed to fluctuations in the voltage at the point of common coupling due to the active power transmission. To investigate the mechanism of this destabilization, firstly, a small-signal model describing the active power control and voltage amplitude control is derived in this paper. Then, based on the derived model, the analysis of the destabilization mechanism is conducted from the perspective of active power. It is identified that destabilization of the GCC system can be attributed to the positive feedback of the active power, which is introduced by the coupling relationship between the d -axis current reference and the q -axis current response. To restrain the influence of this positive feedback, a damping controller based on q -axis voltage feedforward is proposed to attenuate active power fluctuations induced by this positive feedback. Thus, the stability of the GCC system is enhanced. Finally, the effectiveness of the analysis and the damping controller proposed in this paper is verified by experimental results.