Two-Stage Bi-Directional Single-Phase Converter with DC-Link Capacitor Reduction
It is well-known that single-phase ac-dc conversion requires a bulky dc-link capacitor for filtering the ripple power from the grid, thus leading a overall bulky converter size. Also, in order to interface a dc renewable energy system to a single-phase utility grid, bi-directional power flow control and dc-bus voltage regulation are major concerns. Many methods have been proposed to reduce the dc-link capacitor value, such as adding extra phase-leg to absorb the ripple power into inductor or capacitors. However, all methods cannot well maintain the dc-bus voltage ripple very well when reduce the dc-link capacitor size. Also, none of the existing methods or topologies are verified under bi-directional power regulation case. The proposed two-stage grid-interfaced single-phase PWM converter topology uses full-bridge in series with a bidirectional SR dc-dc converter which much reduces the dc-link capacitor value. The proposed topology and control system can easily achieve the bi-directional power flow regulation, bi-directional current interrupt protection capability, and the predictable dc-bus terminal characteristics. It is very suitable for dc-based distribution renewable energy system at residential power level, such as dc nano-grid applications. Instead of the traditional electrolytic capacitors, the film capacitors thus can be used as the dc-link capacitor since the value is reduced. The film capacitor life-time will be much longer. Moreover, the commercial three-phase IGBT module can be directly used as the power stage, which reduces the overall converter cost.
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