Advanced PET Control for Voltage Sags Unbalanced Conditions Using Phase-Independent VSC-Rectification

The power electronic transformer (PET) is an emerging technology that is quickly becoming a key component of the next-to-come power distribution networks (PDNs), due to its versatility on energy management, as well as, the improvement on the quality of the energy. PDNs are characterized by their unbalanced conditions, causing that PETs driven by conventional dq0 controls introduce current distortions on the primary winding of the transformer. Such distortion is evidenced in the 2ω oscillations of Vd and Vq acting as harmonic sources. 

In this sense, this paper proposes a novel control approach for PETs. The key idea behind of this proposal consists of operating each phase independently, which is achieved through the enclosed rectification and the mitigation of the 2ω oscillations in a Dual Active Bridge (DAB) topology. The attained advantages by this control scheme are: (a) balancing of the primary winding currents; (b) unitary power factor; (c) negligible harmonic distortion; and (d) 2ω oscillation mitigation on the DC bus.

Index Terms—AC-DC-AC, power conversion, power electronic transformer, dual active bridge, VSC, unbalanced control, voltage sags, unbalanced input voltages.