Abstract
In single-phase ac/dc applications where reliability and/or power-density are critical, active power decoupling (APD) circuits can be employed to reduce the required capacitance on the dc-link. Various APD circuits have been proposed so far, all with their advantages and disadvantages. However, many confusions still exist in the literature on this topic which is mainly attributed to a lack of unified and comprehensive assessment criteria. In this paper, first the decisive criteria for a modern APD circuit are established, and the buck APD is identified as the current state-of-the-art, based on them. Then the buck-plus-unfolder topology with triangular current mode (TCM) modulation is proposed as an improvement, and a simple, yet solid foundation is introduced to choose the superior decoupling solution at different specifications. The operation equations for the APD with TCM modulation are derived next, and the operation of the proposed solution is demonstrated using a hardware prototype.
Highlights
It is well known that in single-phase ac/dc converters that achieve unity power factor at the ac-side, the power waveform contains a large component pulsating at the doubleline-frequency (DLF)
In order to prevent it from flowing into the load, the DLF ripple power can be mitigated by directly connecting bulk capacitors to the dc-link
There is always a large amount of redundant energy stored in the capacitor, and only a small portion of its energy storage capability is utilized to deal with the DLF ripple
Summary
It is well known that in single-phase ac/dc converters that achieve unity power factor at the ac-side, the power waveform contains a large component pulsating at the doubleline-frequency (DLF). If the voltage across the buffer capacitor is expected to regularly exceed Vdc = 400 V , these superior GaN switches [21] cannot be used anymore, and the choice will be limited to other types of switching devices such as Si and SiC MOSFETs or IGBTs. among the solutions that satisfy both of the above-mentioned requirements, it is preferred to use the minimum possible value of buffer capacitance, and preferably achieve the optimum capacitance requirement. There are three qualities that are important in APrD converters used in 400 Vdc/kW-level applications: Requirement (I): Be controlled independently from the r main converter Requirement (II): The maximum voltage in the APD be r less than the dc-link voltage Preference (III): Among the solutions that satisfy requirements (I) and (II), it is preferred to achieve the minimum possible required buffer capacitance
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