Abstract
An electric vehicle (EV) charger can operate in an autonomous mode to create its own grid by utilizing the EV batteries during grid blackouts. This requires three-phase four-wire inverters as the grid-side ac/dc port of the EV charger to supply unbalanced loads. Although silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) can be adopted to increase the power density of these inverters, the second-order ripples exhibited on the dc bus caused by unbalanced loads need to be mitigated by a large dc capacitance—increasing the size of inverters. In this article, an improved neutral leg for three-phase four-wire inverters is presented, which not only provides the neutral current for unbalanced loads, such as a conventional neutral leg, but also reduces the second-order ripples on the dc bus without the need for additional hardware components. Furthermore, it can reduce by 50% the dc capacitance compared to its conventional counterpart. A control strategy featuring power decoupling capability is included for the improved leg. It was built with SiC MOSFETs and experimentally assessed with a three-phase inverter, with results verifying its effectiveness. For completeness, the performance of the improved neutral leg is also evaluated through simulations in PLECS and compared to a conventional neutral leg.
Highlights
T HREE-phase inverters have been widely used as an interface between active distribution networks and distributed energy resources [1], such as solar photovoltaics, energy storage systems and electric vehicles (EVs)
This paper has presented an improved neutral leg, which provides the neutral current as its conventional counterpart, and reduces the second order ripples and dc capacitance on the dc bus
It is shown that due to the reduction of dc bus ripples, the improved neutral leg can decrease by 50% the dc capacitance value compared to the conventional one
Summary
T HREE-phase inverters have been widely used as an interface between active distribution networks and distributed energy resources [1], such as solar photovoltaics, energy storage systems and electric vehicles (EVs). Voltage balancing of the split capacitors can be maintained and the capacitance value reduced This topology allows an independent control of the neutral leg and avoids the electromagnetic interference problems exhibited by the four-leg inverter [17]. It consists of an isolated dc/dc converter and, the aforementioned third topology of three-phase fourwire inverters, which has an independently controlled neutral leg, and LC filters In this system, besides the need to supply neutral current, another challenge is the second order current and voltage ripples on the dc bus caused by unbalanced loads [19], which is not addressed in the aforementioned literature. An improved neutral leg for three-phase four-wire EV chargers including its operation principles is presented This topology provides neutral current and reduces second order ripples on the dc bus while simultaneously enables an adequate operation under unbalanced loads. 3) Due to the reduced second-order ripples, the improved neutral leg can reduce by 50% the dc capacitance value compared to a conventional neutral leg
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