Installation of a diode rectifier to a transformerless Dynamic Voltage Restorer (DVR) provides an economical way for the DC-link to negotiate active power, but allows only unidirectional power flow. This configuration can extend the compensation capability for having in-phase, phase invariant and minimum energy injection schemes under voltage sag. During voltage swell, the in-phase and phase invariant algorithms will cause DVR power intake. Applying minimum energy injection scheme still cannot prevent power intake under unbalanced situation. The absorbed active power raises the DC-link voltage level, which endangers the storage capacitor and switching devices. In order to solve this unbalanced swell problem, a novel control algorithm including DVR compensation limit consideration is proposed. In this paper, the in-phase, phase invariant, minimum energy and the proposed control algorithms under voltage sag and swell conditions are compared and studied. Finally, the proposed control algorithm is verified by simulations compared with those three injection algorithms, which shows a superior compensation performance under unbalanced swell.