An Automatic Power Decoupling Control Method on Three Level DC-AC Converter to Suppress the Double-Line-Frequency Ripple

In single phase DC-AC converter, power decoupling is always required due to the inherent double line frequency ripple caused by the instantaneous power unbalance between DC and AC side. The existing solutions include passive power decoupling and active power decoupling. Passive power decoupling scheme would apply a large electrolytic capacitor and consequently increase passive component requirement. Active power decoupling is to introduce a low power converter to compensate the ripple which inevitably increase the system cost and control complexity. To overcome these drawbacks, [1] proposed a novel double-line-frequency ripple suppression method based on three-level topology which redistributes the unbalanced power between two series connected capacitors and makes the capacitor voltage ripple complementary to each other. Thus the dc-link voltage ripple could be reduced to a large extent. However it is an open loop system, this paper proposed an automatic power decoupling control algorithm that can avoid the direct control of double line frequency ripple which reduces the amount of calculation. At the same time, it could achieve satisfied dynamic response and robust circuit operation. Theory analysis and experiment results will be explained in the following sections.