Abstract
A hold-up time extension circuit (HTEC) is used to charge and discharge an auxiliary capacitor. This capacitor stores the energy required to extend the operation time of critical loads experiencing short duration failures (SDF) at the DC bus to which they are connected. This paper presents complete modeling and a control-wise approach to a parallel HTEC based on the bidirectional buck-boost converter, which operates in Boundary Conduction Mode (BCM) with a variable switching frequency. The circuit permanently regulates the voltage of the auxiliary capacitor as well as the voltage of the DC bus during SDF, which is uncommon in industrial versions of HTEC. Enforcing the operation in BCM allows a reduction in the size of the inductor in the converter without requiring additional control circuitry. The entire behavior of the proposed HTEC, in all its operation modes, was analyzed theoretically and validated using simulation and experimental results, showing the potential of the circuit to be used in real applications.
Highlights
The occurrence of temporary interruptions and other short duration failures (SDF) in the input source of critical DC loads affects the reliability of many electrical systems considerably
When the continuous operation of a load is critical, the hold-up time has been extended by means of external additional devices—so-called hold-up time extension circuits (HTEC) [7,8,9]
An improved-control approach for the parallel HTEC, based on the bidirectional buck-boost converter (BBBC) operating in Boundary Conduction Mode (BCM), 5
Summary
The occurrence of temporary interruptions and other short duration failures (SDF) in the input source of critical DC loads affects the reliability of many electrical systems considerably. Most of the existing HTEC use an auxiliary capacitor for energy storage This element is charged during normal operation of the DC bus and discharged during SFD. The parallel on-line architectures of HTEC have a converter to charge and discharge the auxiliary capacitor to a higher voltage level, allowing more energy to be stored with the same capacitance [13]. Because of the intended intermittent operation, criteria such as simplicity and a reduced number of components become more relevant, as in Reference [16], where the authors employed a conventional synchronous boost converter In this case, as in some applications for microgrids, the symmetry of the circuit configuration for the charging and discharging mode of the conventional bidirectional buck-boost converter (BBBC) is a relevant criterion since it leads to simpler control [17].
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