Active power decoupling achieving optimum capacitance requirement with minimal compromise in efficiency

In single-phase AC/DC converters that achieve unity power factor (UPF) at the AC-side, the power waveform contains a large component at the double-line-frequency (DLF), in addition to the average power. This DLF ripple power can have serious undesirable effects on the load in different applications. In order to prevent it from flowing into the load, the DLF ripple power can be mitigated by connecting a capacitor to the DC-link. However, this method, called passive power decoupling, requires large values of capacitance to be used. For 400(VDC)/kW-level applications, it can be only realized using electrolytic capacitors, resulting in low power-density and low reliability. For applications in which power-density and reliability are more critical, an alternative solution is active power decoupling (APD). In active power decoupling, the storage capacitor has a higher utilization factor because the voltage across it is allowed to have larger variations. This situation can be made possible by separating the capacitor from the DC-link by means of a power electronic converter. The DC/DC buck is the simplest converter that can be used for this purpose. The problem with the buck APD is that it cannot use the theoretically minimum required value of capacitance; although many alternatives have been proposed in the literature, they all bring their own sets of disadvantages. In this work, a superior solution is introduced as an improvement to the buck topology which allows utilization of the theoretically minimum required capacitance with minimal compromise in efficiency. The design details and benefits assessment of this solution are elaborated and its operation is verified using both computer simulation and experiment.