Impedance Shaping of Isolated Two-Stage AC-DC-DC Converter for Stability Improvement

Abstract

The isolated two-stage ac-dc-dc converter containing an isolated dual-active-bridge (DAB) dc-dc converter and an ac-dc rectifier has been widely used for connecting the dc sources to the ac utility grid. However, the impedance interaction between the DAB converter and the ac-dc rectifier may cause the instability problem. To address this issue, this paper proposes two control methods to reshape the impedances of the isolated two-stage ac-dc-dc converter by building a virtual impedance connected in parallel or series with the input impedance of the DAB converter. The magnitude of the input impedance of the DAB converter is increased to satisfy the Middlebrook criterion without changing its negative resistance characteristics by the proposed control methods. Furthermore, the design requirements for the proposed controllers are also given to ensure the stable operation of the two-stage converter. The comparison of these two proposed methods is also discussed in terms of stabilizing ability, dynamic performance, and cost. The comprehensive experimental results are provided to validate the proposed methods. INDEX TERMS Impedance shaping, modeling, stability criterion, two-stage converter.

Full‐state discrete‐time model‐based stability analysis and parameter design of dual active bridge converter in energy storage system

“…Combining Equations ( 15) and ( 18), the discrete domain transfer function G v o 𝜑 (z ) from the phase shift angle to the output voltage can be obtained as shown in Equation (19), where [0 1] represents the conversion relationship between the output voltage and the state variables.…”

“…In this model, only the DC term and first order terms of the inductor current are considered, which may result in relatively large error especially when there are large harmonic distortions. There are also the reduced-order impedance models of the DAB converters in [19][20][21][22] which neglect the dynamics of the AC conversion stage. As a result, these models are suffering in low accuracy in high frequencies [11].…”

Impedance-Based Modeling and Common Bus Stability Enhancement Control Algorithm in DC Microgrid

“…The PR control can reduce the influence of harmonics by increasing the size of a specific frequency preferred by the designer without significantly changing the steady-state error and the system stability on the existing controller [34]. The PR controller applied in this paper is expressed as (25). The AC input and diode rectifier are used to simulate the AC power source simply.…”

“…In other words, distorted currents and voltages can adversely affect the common bus, resulting in a decrease in the entire system stability. [25] analyzes the interaction between converters when the input is AC and proposes an impedance shaping method for stable operation. However, the harmonic problem is not considered.…”

Duty-Cycle Dependent Phase Shift Modulation of Dual Three-Phase Active Bridge Four-Port AC–DC/DC–AC Converter Eliminating Low Frequency Power Pulsations

“…Most related publications describe the realization of a conventional ac-dc/dc converter structure, i.e., the series connection of a primary-side three-phase rectifier and a dc/dc converter with galvanic isolation, which can be immediately extended to an ac-dc/dc-ac structure. Documented examples include the series connection of a two-level six-switch rectifier and single-phase Dual Active Bridge (DAB) converter [7] or full-bridge dc/dc converter [8]; the combination of a threelevel T-type rectifier and full-bridge dc/dc converter [9] or of a three-level Neutral Point Clamped (NPC) rectifier and threephase DAB converter [10].…”