ABSTRACT:
This paper presents a transformerless
solution for front-end rectification, which is particularly suitable for
traction applications, requiring high voltages to be stepped down to appropriate
dc voltage. The proposed topology is based on pulse width modulation buck
rectifier (current source inverter topology) and is capable of rectification
and stepping down of single-phase ac supply, in a single stage. A new control
scheme is proposed to achieve constant dc output voltage and sinusoidal source
current, irrespective of large ripples in the dc inductor current. The proposed
scheme is configured in single-loop voltage control mode. The relevant
small-signal model is derived from the large-signal model using multi order
decomposition. An elaborate procedure of dc filter design is discussed, for
circuit operation with minimum energy storage. All analytical results are
validated by numerical simulation for sinusoidal and distorted source voltage.
Experimental verification is achieved through a 1.2-kW grid-connected
laboratory prototype.
KEYWORDS:
1.
Buck
rectifier (BR)
2.
Single-loop
control
3.
Single
phase
4.
Traction
5.
Transformerless
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
In this paper, a single-loop control
scheme for single-phase BR has been presented. A nonlinear modulation scheme is
proposed, and its effect is analyzed using a multi order system decomposition.
The effectiveness of the proposed scheme is proved by simulation and experimental
results. From experimental results, it is clear that the proposed control
scheme is capable of maintaining sinusoidal source current and near-UPF
operation with optimum filter volume, even under distorted grid conditions.
Generalized design of the dc inductor, which is the most critical element, is
presented in detail. Since source current wave shape is maintained despite
ripples in dc current, requirement of an inner current loop is rendered
superfluous. Apart from justifying the single-loop control scheme, this also
entails greatly simplified controller design and realization.
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