PROJECT TITLE :

Control of Parallel Three Phase PWMConverters under Generalized UnbalancedOperating Conditions - 2016

ABSTRACT:

This paper proposes a replacement management theme for parallel 3-phase pulse width modulation converters beneath generalized unbalanced operating conditions. An average model of the parallel system in positive-sequence synchronous reference frame comes to investigate the influence of generalized unbalanced operating conditions in ac side. It is seen that the unbalance factors in filter inductance can not solely provide rise to negative-sequence circulating current, but also contribute to generating zero-sequence circulating current (ZSCC). The negative-sequence circulating current will be inhibited by suppressing the negative-sequence components in ac output currents of parallel modules with a proportional integral resonant (PIR) controller. An improved feed-forward strategy and a PIR controller for ZSCC control are proposed for unbalanced operating conditions. The disturbances in ZSCC caused by unbalance factors in filter inductance will be rejected with feed-forward strategy. Because the disturbance in ZSCC is the fluctuation in grid frequency which can be suppressed by a resonance controller, therefore, a PIR controller is adopted in ZSCC controller. The proposed scheme can effectively suppress the circulating currents between the parallel modules and consequently, the distortions in output currents will be greatly reduced. Experimental results ensure the performance and effectiveness of the proposed methodology.