A dual mode operated boost inverter and its control strategy for ripple current reduction in single-phase uninterruptible power supplies

In single-phase uninterruptible power supply (UPS) applications, it is well known that the AC side instantaneous power is not constant by nature. The resulting input current from the DC source side will inevitably contain low frequency ripple components that may largely deteriorate the system performance in terms of efficiency and reliability. In order to solve this issue, this paper presents a dual-mode operated boost inverter, which can simultaneously work in both Differential Mode (DM) and Common Mode (CM) operations. Its DM operation ensures regulated sinusoidal AC output voltage as well as active power conversion, while its CM operation is controlled in such a way that the low frequency ripple current on the DC side can be maintained in a minimum level. The proposed ripple current reduction method may not only work with linear loads, but also nonlinear loads, where more sophisticated controller design are required. Since the presented inverter essentially consists of two DC/DC boost converters, an interleaved Pulse-Width Modulation (PWM) can be adopted to further reduce the high frequency switching ripple current on the DC side. Both Simulation and experimental results are presented to demonstrate the effectiveness of input ripple current reduction.