Analytical and Normalized Equations to Implement the Optimized Triple Phase-Shift Modulation Strategy for DAB Converters

Abstract

A fully normalized algorithm to implement the optimal triple-phase shift (TPS) modulation strategy of the dual active bridge converter is proposed in this paper. The algorithm evaluates three simple expressions that fit the optimal solutions obtained in recent works, which allows the algorithm to be implemented in real-time and valid for the whole operating range. As a result, the converter operates under zero voltage switching conditions and minimizes conduction losses. In addition, the algorithm considers the minimum current required to guarantee zero voltage switching condition that faces undesired deadband of switching devices effect. The proposal achieves soft transition between any operation region and fast closed-loop response with no stability concern, presenting robustness under leakage inductance deviation. Finally, the algorithm presented in this paper is verified with a 4 kW experimental prototype. Experimental results show that the algorithm proposed can be evaluated with less than 2.8 µs and allows soft transition between any operation region to be achieved. Besides, fast closed-loop changes of 750 µs through all the operating ranges, keeping minimum RMS current under zero voltage switching, are shown.Index Terms-Dual active bridge (DAB), normalizedmodulation, RMS current minimization, triple phase-shift (TPS), zero voltage switching (ZVS). I. INTRODUCTIONT HE dual active bridge (DAB) has an essential role in dc microgrids, which have high efficiency and fast dynamic response [1]. DAB topology presents outstanding characteristics that allow the bidirectional power flow between two dc voltage sources with galvanic isolation. It can operate under soft-switching mode, increasing the power density. The DAB converter offers modularity. It can work in series [2] or parallel as a current source converter [3]. Moreover, the current source behavior also enables step-up and step-down voltage as a function of control variables and load, allowing its use in applications as renewable energy integration where voltages of energy storage systems (ESSs) are widely variables [4].The DAB topology is shown in Fig. 1. It consists of two full bridges interconnected through a high-frequency transformer with no additional resonant passive elements needed.

An Improved AC-Link Voltage Matching Control for the Multiport Modular Multilevel DC Transformer in MVDC Applications

“…Such voltage fluctuations will cause mismatches between the AC-link voltage ratio of the M3DCT and the AC transformer voltage ratio, leading to degraded operational performance under conventional control [26][27][28]. Some enhanced phase-shift control methods, namely extended-phase-shift (EPS) [29], dual-phase-shift (DPS) [30], and triple-phase-shift (TPS) [31][32][33], have been developed to ameliorate AC-link circulating currents. Nonetheless, their effectiveness is compromised when the M3DCT operates at low power levels and experiences severe AC-link voltage mismatch ratios.…”

Current-sensorless model predictive control for DAB converter based on back-flow power optimization

“…To suppress the back-flow power of DAB converters, a Double-Phase-Shift (DPS) strategy is proposed, but it can only be achieved in the medium to low power range and is not optimal at full power [8] . A three-phase shift (TPS) strategy has been proposed for various operating conditions, but under this strategy, the DAB converter has three different degrees of freedom, multiple operating modes and a relatively complex model [9] . To reduce the power of the backflow, an Extended-Phase-Shift (EPS) control method is considered, which adds a degree of freedom in the primary bridge of the transformer for easy control [10] .…”

A Si IGBT/SiC MOSFET Hybrid Isolated Bidirectional DC–DC Converter for Reducing Losses and Costs of DC Solid State Transformer

“…To address the above problems, extensive research has been carried out on modulation and optimized strategies. By increasing the internal phase-shift angles within the primary or secondary H-bridges of DAB, the modulation strategies of extended phase shift (EPS) [6,7], dual phase shift (DPS) [8,9], and triple phase shift (TPS) [10][11][12][13][14] have been successively proposed, which reduce the conduction losses of the converter and expand the ZVS range with the suitable combination of phase-shift angles. On the other hand, Refs.…”

“…However, the modeling accuracy of the HCA method depends on the maximum order of the Fourier series, and the model is usually not accurate enough under non-unit voltage conversion ratio or asymmetric modulation. The optimized objective of DAB is usually chosen as current stress [8,14,15], rms value of current [7,12,13,18,19], or reactive power [9], and the constraints are usually chosen as ZVS constraints. The choice of optimized algorithm depends on the complexity of the model.…”

“…By comparing existing optimized modulation strategies, it is found that the optimized modulation strategies are mostly optimized for the operating characteristics such as current stress, rms value of current, and switching characteristics in the low-power and mediumpower regions, and still use SPS modulation in the high-power region [12][13][14][15]18,19]. Therefore, the turn-off current is high in the high-power region.…”