Advanced PET Control for Voltage Sags Unbalanced Conditions Using Phase-Independent VSC-Rectification Power Electronics, Power Systems Projects


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 2! 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 2! 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) 2! oscillation mitigation on the DC bus.


  1. AC-DC-AC
  2. Power conversion
  3. Power electronic transformer
  4. Dual active bridge
  5. VSC
  6. Unbalanced control
  7.  Voltage sags
  8. Unbalanced input voltages.



Fig. 1. Three-phase VSC rectifier with an unbalanced control


Fig. 2. Simulation for an unbalanced voltage sag during V a g = 1\0_; V b g = 0:5\ 􀀀 120_; V c g = 0:5\120__


Fig. 3. Simulation for an unbalanced voltage sag during V a g = 1\0_; V b g = 1\ 􀀀 120_; V c g = 0:1\120__


Fig.4. Simulation for an unbalanced voltage sag during V a g = 0:8\0_; V b

g = 0:6\ 􀀀 133:9_; V c g = 0:6\133:9__


Fig. 5. Simulation for an unbalanced voltage sag with dq0 control during V a g = 1\0_; V b g = 1\ 􀀀 120_; V c g = 0:1\120__



The main contribution of this work consists in a new control structure, which employ a phasorial approach with a single PI control, for PETs working on distribution systems where the operation with unbalanced input voltages is frequently. The capacity of this control of independently generate the modulation variables mabc i with different magnitudes and angles, reach a better performance than other control structures; dq0, for example, to mitigate the problems caused by unbalanced input voltages conditions. Under these input conditions in a PET, the advantages achieve by the proposed control are: (i) balanced AC input currents, (ii) sinusoidal AC input current, and (iii) PF = 1. Furthermore, the control structure is an easy-to-implement and requires no additional components. Finally, in this work, all the advantages mentioned above were validated by using simulation and a lab prototype.


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