Comparative Analysis of Efficiency and Harmonic Generation in Multiport Converters: Study of Two Operating Conditions

This paper presents a comparative study between the traditional phase shift (also referred to as the Single-Phase Shift (SPS)) and the Dual-Phase Shift (DPS) controlled Triple Active Bridge (TAB) converter. Being a multi-port DC-DC converter with flexible power flow control and characterized by high power density, the TAB converter is applicable in almost any situation where a DC-DC converter is needed. With the availability of multiple control schemes, this work highlights the advantages and disadvantages of the most employed control scheme used on the TAB converter, in comparison with the DPS control scheme that has so far been applied only on Dual-Active Bridge (DAB) converters. As an example, for a TAB converter with a 14 kW maximum power capacity, the work sees the comparison of the backflow power, the maximum possible current, the processed power at the different ports of the converter, the transformer voltage and current waveforms, and the Total Harmonic Distortion (THD). Based on the results obtained, we found that the DPS-controlled TAB converter was more efficient when applied to the TAB converter compared to the traditional phase shift control algorithm.

An autonomous dc microgrid system has been developed that consists of triple active bridge (TAB) converters as power routing units. To achieve high-speed response of the system to power demand and short-circuit faults, high stability of voltages at all connecting points between TAB converters, and high operational stability of the entire system, a model of mutually connected TAB converters and a control system for the converters must be developed. In this paper, a linearized model of mutually connected TAB converters is proposed and used to analyze the operational stability of the control system. Next, an experiment using prototype TAB converters was conducted to validate the stability analysis. When the power flow pattern among ports of the TAB converters changed in step, the power value of each port converged to the desired power value. Therefore, we conclude that the TAB converters are stably operated by using the developed control system even when TAB converters are connected in series.

A hybrid AC/DC microgrid systems that uses a triple active bridge (TAB) converter as a power routing unit has been proposed. Since the demand and supply balance of power fluctuates in the microgrid system, the power handled by the TAB converter also varies with time. Therefore, a TAB converter with a small load-factor dependence of transmission efficiency is necessary to reduce the unit's overall loss and design highly efficient microgrid systems. We previously fabricated a prototype TAB converter rated at 400 V, 20 kHz, and 10 kW using SiC-MOSFETs and demonstrated that it can control transmission power. In this study, the load-factor dependence of the TAB converter's transmission efficiency was investigated based on experimental results. The results show that the transmission efficiency of the TAB converter decreased under low-load conditions such as a load factor of less than 20%. In addition, the loss components involved in this dependence was analyzed. The analysis results indicate that switching loss is the main component of transmission-efficiency degradation under low-load conditions.

In recent decade, the demand for power distribution system in data centers are significantly climbed, while the requirements for advanced power flow control for DC power distribution systems are in urge needed. This paper presents higher-reliability DC power distribution systems using a triple active bridge (TAB) converter that can be applied in a data center, and it will be shown a power flow control among the three DC power distribution systems. The TAB converter is composed of three DC/AC converters connected via a transformer, and has ability to transmit the power to arbitrary directions. This paper proposes DC power distribution systems for data center using the TAB converter for balancing the power from the voltage sources. The feature of this system has no batteries. Then, the power flow control with closed-loop feedback control and the load balancing control are explained for adjusting the unbalanced load condition in data centers. The simulation designed the operation of DC power distribution system using 380V TAB converter in data center, and the power flow control for the power distribution system. From these results, the performance of the power flow control is confirmed, while the functional behavior of proposed three DC power distribution systems using the TAB converter is proved.

A decentralized coordinated control scheme for the DC network with a multiport converter

Triple Active Bridge (TAB) converter is a popular topology used for interfacing multiple sources and loads. In this paper, we show that the large-signal and small-signal model of the TAB converter based on Fundamental Harmonic Analysis (FHA) presented in literature can be erroneous for a range of operating conditions. It could result in an error in the power flow calculation in addition to performance degradation of the closed-loop control systems. Further, we present a Generalised Harmonic Model (GHM) for the Triple Active Bridge (TAB) converter that offers superior accuracy. The small-signal transfer functions for the TAB converter are derived based on the proposed model and are verified using switching circuit simulations. A TAB converter hardware prototype has been developed and experimental results are provided to validate the proposed GHM.

Triple active bridge converters are an extension of dual active bridge converters and used to combine multiple energy sources. The advantages of using a triple active bridge converter are its high power density, providing isolation along with elimination of low frequency transformer and high efficiency power conversion. To address the intermittent nature of solar energy, it is always appropriate to include a energy storage device along with it. Triple active bridge converter acts a viable option in integrating these two energy sources in the most efficient manner. Further, this energy can be fed to the grid by using a voltage source converter cascaded with this triple active bridge converter. This paper discusses the cascaded converter with its control algorithms and different operating modes. A laboratory prototype of a triple active bridge converter integrated with the grid through a voltage source converter is developed and the different control and operating modes are verified, which are also included in this paper.

The isolated three port active-bridge-based DC-DC converter, referred to as Triple Active Bridge (TAB) converter is a popular multi-port converter topology. This paper proposes a simple and systematic design methodology for the TAB converter. The Fundamental Harmonic Approximation (FHA) technique is used to model the TAB converter for analyzing its operation. A systematic method is proposed for the selection of TAB converter parameters such as the multi-winding transformer turns-ratio and the series inductance at each AC port. Switching circuit simulations are performed to compare various TAB converter designs and to showcase the benefits of the proposed design. A 1 kW rated TAB converter hardware prototype is constructed in the laboratory and experimental results are provided to validate the effectiveness of the proposed design procedure.

This paper introduces a systematic methodology to develop a unified model for a multi-port Triple Active Bridge (TAB) converter. The proposed model accurately predicts the AC port currents in a TAB converter. The model can be used to compute performance metrices of the TAB converter such as the peak and RMS currents at the AC ports, and the average currents at the DC ports. One of the features of the proposed model is that it can predict the impact of transformer magnetizing inductance on the AC and DC port currents. The proposed model is valid for all operating modes and modulation strategies of the TAB converter. The accuracy of the model has been verified against extensive switching circuit simulations for a variety of operating conditions. Experimental results from a TAB converter laboratory prototype are also presented to showcase the impact of magnetizing inductance variation on TAB converter performance.

We propose an autonomous DC microgrid consisting of triple active bridge (TAB) converters. In microgrids, various renewable energies, batteries, and local consumer appliances could be integrated by using TAB converters with different operating DC voltages such as 400-V DC bus voltages, 110-V battery systems, and 48-V ICT equipment. We constructed a prototype TAB converter rated at 10 kW and developed a decoupling power flow control system with a voltage difference between each port of the TAB converter. The prototype rated at 400 V/400 V/48 V was implemented to demonstrate the feasibility of the control system. In addition, a linearized model of mutually connected TAB converters was investigated. An experiment using prototype TAB converters was conducted to validate the control system based on the model. When the power flow pattern among the ports of the converters changed in step, the power value of each port converged to the desired power value. Therefore, we conclude that TAB converters can be stably operated by using the developed control system even when TAB converters are connected in series.

This paper presents the computer simulations of a proposed system of integration of energy sources in which the TAB (Triple Active Bridge) converter serves as interface. The system has a load, a main voltage source and an auxiliary power source formed by a photovoltaic panel and a Sepic converter. The TAB converter is fed into voltage, and it applies a method of decoupling loops for control of the voltage. The proposed system can be applied in UPS and micro-grids.

A triple active bridge (TAB) converter consisting of three full-bridge inverters and a three-winding transformer has been researched to improve its power conversion performance as a bi-directional isolated multiport converter. Previous research established a current control method using a decoupling system to solve the complex power transmission structure of the TAB converter. However, it is challenging to integrate voltage factors into the decoupling system because DC-bus voltages of the TAB converter are assumed to be constant. Active bridge control against voltage variations has become essential to achieving high-performance DC/DC power conversion systems using high-frequency transformers such as a TAB converter. This paper proposes a TAB converter control method, which is an expansion of the conventional method, to integrate the DC-bus voltage variation into the control model. Model predictive control is used to achieve tracking control by incorporating voltage variation factors into the control method using an established model structure as a basis for predictive calculations. Simulations were conducted to verify that the proposed method improves the output responses compared to the conventional methods when the DC-bus voltages change. Also, experiments using a prototype converter show that the proposed control method can achieve current tracking control during the voltage variation.

The integration of energy storage elements to solar photovoltaic (PV) systems provide a wide range of operational flexibilities. Traditional approaches use separate converter for PV and energy storage element, i.e. battery which cause significant conversion losses. This paper presents an isolated high frequency link multi-port converter based on triple active bridge (TAB) topology for PV integrated battery systems in residential applications. The conventional dual active bridge (DAB) is extended to establish the proposed high frequency link TAB topology. Limited soft-switching capability and high circulating current are common problems in this style of converters when there is a mismatch in the dc-link voltages. This is pronounced at lower powers with the single phase shift (SPS) modulation technique. To overcome these problems, this paper proposes an improved modulation and control method based on a quintuple phase shift modulation (QPSM) strategy. The QPSM modulation method produces 3-level modulated square wave bridge voltages. A mathematical model of the proposed high frequency linked multi-port converter with QPSM modulation is developed based on a harmonic analysis approach. The simulation and experimental results show that the QPSM scheme applied to the proposed multi-port converter provides better operation and improves the efficiency compared to the traditional SPS modulation scheme.

The multiport active bridge (MAB) converter has been recently proposed aiming to increase the power density and the availability of electrical power distribution systems. However, the dynamic performance of proportional-integral (PI) controller for MAB voltage control is characterized by a relatively slow response and large overshoot. To address this issue, a power decoupling based configurable control (PDC-MPC) strategy inspired by the model predictive control (MPC) was developed. The proposed control strategy can achieve good transient performance and high control flexibility with good precision to comply to DC voltage regulations. In this paper, the PDC-MPC was investigated and implemented in a triple active bridge (TAB) converter with multi-winding high frequency transformers. The operating principle of the PDC-MPC is divided into two phases: prediction of the DC current through a binary search and decoupling of the desired power of each isolated virtual branch to its phase shift angles under the single phase shift (SPS) modulation strategy. Steady-state and dynamic performances of the proposed PDC-MPC for TAB converters were analysed using modified cost function and predictive models. Simulation and experiments were conducted to validate the theoretical analyses.

Due to significant issue of energy consumption and sharp power demand of information and computing systems in worldwide, the applications of DC micro-grid that can utilize renewable energy sources such as photovoltaic power and wind energy have been advanced. Consequently, a DC micro-grid should be upgraded to achieve high reliability in power distribution systems. For DC power distribution in a data center, power managements including power flow control and demand analysis are highly recommended. In this paper, a prototype of DC power distribution system is proposed using the triple active bridge (TAB) converter for data centers. Furthermore, the power management for distributed system uses the TAB converter for power flow control is introduced. Eventually, performance test of power management in high reliable system is verified by simulation, and the reliability analysis proofed the reliability of proposed system superior than the conventional power distribution systems.