Download Document

Modeling, Digital Control, and
Implementation of a Three-Phase Four-Wire
Power Converter Used as A Power
Redistribution Device
Abstract:
This paper presents a power electronic converter used to redistribute the power
among the phases in unbalanced power systems, which is supposed to be designed
based on the involved degree of unbalance. A bidirectional converter is chosen
for this purpose, whose modeling is presented in the dq0 system. This solution can
be considered as part of a unified control system, where conventional active power
filters (APFs) may be solely responsible for compensating harmonics and/or the
tuning of passive filters becomes easier, with consequent reduction of involved
costs in a decentralized approach. The adopted control strategy is implemented in
DSP (digital signal processor) TMS320F2812, while experimental results obtained
from an experimental prototype rated at 17.86 kVA are properly discussed
considering that the converter is placed at the secondary side of a transformer
supplying three distinct singlephase loads. It is effectively shown that the converter
is able to balance the currents in the transformer phases, thus leading to the
suppression of the neutral current.
Existing system:
 Distribution power systems are intrinsically dynamical considering that the
demand is not constant over time and the phase loading is typically
asymmetrical. Such important issues make the expansion planning essential
for the accurate operation of systems in face of continuous changes in
demand and also equipment utilization factor.
 The operation under balanced conditions is better recommended so that the
utilization factor of transformers and feeders can be improved. Thus it is
possible to minimize the risk of overload associated to several phenomena
such as the fluctuation of line voltage.
 It is also important to mention that load balancing can be achieved through
the reconfiguration of distribution networks by using switches or rearranging
the load among the system phases.
Proposed system:
 The design and implementation of a digitally-controlled four-wire converter
to balance the power among the phases of a distribution transformer have
been presented in this paper.
 A prototype rated at 17.86 kVA has been implemented, which processes
11.73 kVA to redistribute the complex powers that involve three distinct
loads. It can be seen that the converter is able to provide the balance of
phase currents and mitigation of neutral current in the transformer.
 The power redistribution concept has been defined as a simple strategy that
allows estimating the required amount of power for the design of the
converter that must be used.
 In order to rearrange the complex power among the system phases using the
proposed PRD, the rms phase currents must be nearly the same, as the
utilization factor of equipment such as cables and feeders is consequently
improved.
Circuit diagram:
Advantages:
Some distinct advantages of the proposal are the postponing of investments in the
distribution system
 Reduction of losses due to elimination of neutral currents and voltage drops
across the secondary windings of transformers.
 Increase of utilization factor of related equipment.
 And improvement of reliability and power quality indices.
Reference:
[1] M. Angulo, D. A. Ruiz-Caballero, J. Lago, M. L. Heldwein, and S. A.
Mussa, “Active power filter control strategy with implicit closed-loop
current control and resonant controller,” IEEE Trans. Ind. Electron., vol.
60, no. 7, pp. 2721–2730, Jul. 2013.
[2] G. Buticchi, L. Consolini, and E. Lorenzani, “Active filter for the
removal of the dc current component for single-phase power lines,”
IEEE Trans. Ind. Electron., vol. 60, no. 10, pp. 4403–4414, Oct. 2013.
[3] V. F. Corasaniti, M. B. Barbieri, and P. L. Arnera, “Compensation with
hybrid active power filter in an industrial plant,” IEEE Latin America
Transactions (Revista IEEE America Latina), vol. 11, no. 1, pp. 447–
452, Feb. 2013.
[4] T.-H. Chen, and Jeng-Tyan Cherng, “Optimal phase arrangement of
distribution transformers connected to a primary feeder for system
unbalance improvement and loss reduction using a genetic algorithm,”
IEEE Trans. Power Systems, vol. 15, no. 3, pp. 994–1000, Aug. 2000.