ABSTRACT
A Transient Response Improvement by Output
Power Feedforward Compensation for Single-
Phase Solid-State Transformer
Bang Jaehyeon
Department of Electrical Engineering
Graduate School of Konkuk University
This paper proposes a output power feedforward compensation method for
Dual Active Bridge(DAB) converter based 2-stage single-phase solid-state
transformer. Solid-State Transformer(SST) is a bidirectional power
converter which is capable of electrical isolation between input and output
stage. SST enables the connection of DC power sources such as PV panels,
Fuel Cells, and ESS much easier compared with conventional transformers by
forming DC bus.
Each stage of SST composes of AC-DC converter and isolated DCDC
converter. Especially, DAB converter, which has advantages of
galvanic isolation with high frequency(HF) transformer, facility of
bidirectional operation, and ease of realizing soft switching, is regarded
as one of the most fundamental elements in SST. In contrast to
conventional PWM converters, DAB converter controls output power by
adjusting the phase shift between output voltage of two H-bridges.
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For designing output voltage feedback controller, small signal model
of DAB converter derived from output power equation with phase
reference
DAB d is applied. Also, bandwidth limitation caused by 120Hz
power ripple in DC-link voltage controller, which induces unequal input
and output voltage ratio compared with turns ratio of HF transformer, is
described. For eliminating this voltage decoupling with current peak
rising of leakage inductor, output power-based feedforward
compensation method for DC-link voltage controller is proposed.
Furthermore, the effectiveness of feedforward term is identified by
confirming the reduction in output impedance of converter based on
small signal model. In comparison of experimental results, proposed
method verified the improvement in transient DC-link voltage decrease
by 24.8% and leakage inductor current peak increase by 27.7% during
load step input. It also yielded improvement in DC-link voltage increase
by 23% while unload transient.
Keyword : Solid-State Transformer(SST), Dual Active Bridge(DAB) converter
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