Control Of Dual Active Bridge Research Articles

Output voltage control of DAB converters based on uncertainty and disturbance estimation.

The dual active bridge (DAB) converter is a power electronic device commonly used for DC voltage regulation and stabilization. However, during its control process, external disturbances, load variations, input voltage variations, switching tube voltage drops, dead time, etc. lead to errors in the control output, thus reducing the control accuracy of the system. Therefore, this article propose a robust control scheme for the output voltage based on uncertainty and disturbance estimator. In this article, an average small-signal model of the dual active bridge converter was established in terms of the basic principles and operation mechanisms, simplifying the controller's design. Then, the basic principles of the uncertainty and disturbance estimator (UDE) are introduced. The small-signal model of the dual active bridge (DAB) converter is applied to the UDE to minimize output voltage error by enabling the controller to directly regulate the shift ratio. Finally, this article discusses the application and effectiveness of the uncertainty and disturbance estimator (UDE) in the simulation and control of dual active bridge (DAB) converters. A series of experimental comparative studies are conducted, demonstrating that this scheme offers significant advantages in suppressing system uncertainties and disturbances.

Phase shift control of dual active bridge DC‐DC converter based on feedforward compensation and transient optimization strategy

SummaryIn the context of the dual active bridge (DAB) bidirectional DC‐DC converter using the traditional dual‐phase‐shift (DPS) control method, a transient DC bias occurs during power co‐direction and commutation conversion. This bias negatively impacts the converter's transient performance and can lead to harsh effects, such as hard switching problems, resulting in power loss and excessive current stress. In a closed‐loop control system, poor transient response may destroy the stability of the converter. In this paper, the transient‐optimized‐dual‐phase‐shift (TODPS) control strategy is proposed to eliminate the transient DC bias and to maintain soft switching during transient states. It reduces power loss, eliminates excessive current stress, and allows for smooth transitions between single‐phase‐shift (SPS) and DPS control strategies without introducing DC bias. A closed‐loop control system based on TODPS control is established with feed‐forward compensation to adjust the primary‐side current and modify transmission power. This adjustment enhances the transient performance of the DAB converter. The proposed strategy is versatile and applicable to various power conversion scenarios involving DAB converters. It enables quick switching of the magnitude and direction of the primary‐side current during transient states, resulting in a smooth transient effect without noticeable overshoot or oscillation. The experiment results verify the effectiveness of the proposed transient optimization strategy.

Model predictive control for DAB under extended‐phase‐shift considering components uncertainty

AbstractFor the dual active bridge (DAB) DC‐DC converters, parameter uncertainty (circuit parameters, input and/or load perturbations) affect their performance, such as the dynamic performance and backflow power. Here, to deal with the uncertainties, a robust model predictive control (RMPC) for the DAB DC‐DC converter under extended‐phase‐shift (EPS) control is proposed to improve dynamic performance and reduce the backflow power of the DAB for the first time. First, a cost function consisting of backflow power and the output voltage is established. Second, considering the uncertainty of the circuit parameters, a robust term is added to the prediction model to increase the robustness. Finally, the effectiveness and superiority of the proposed method are verified by experiments and comparisons with existing methods. The proposed RMPC method shows superior performance in the sense of improved dynamic performance and reduced backflow power.

A Load Adaptive Hybrid DPS Control for DAB to Secure Minimum Current Stress and Full ZVS Operation Over Wide Load and Voltage Conversion Ratio

Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange's multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.

Dual-Mode Control Scheme to Improve Light Load Efficiency for Dual Active Bridge DC-DC Converters Using Single-Phase-Shift Control

In vehicle-to-grid (V2G) applications, dual active bridge (DAB) converters are commonly used as the power interface because they offer high efficiency, galvanic isolation, and bidirectional power flow. For the DAB control strategy, phase-shift control is the mainstream, especially the single-phase-shift (SPS) method because of its ease of implementation. However, due to the phase shift, a DAB converter operated under this control method has relatively high backflow power, resulting in poor efficiency. The SPS control method has the drawback of high backflow power, especially at light loads. Thus, this paper proposes a new dual-mode control scheme to improve the light load efficiency of DAB converters by taking advantage of the pulse-width modulation (PWM) strategy in combination with the conventional SPS strategy for DAB converters based on load conditions. In other words, when the DAB converter operates under light load conditions, the PWM control strategy is used to avoid considerable backflow power. A prototype DAB converter with a power rating of 1 kW under a switching frequency of 100 kHz interfacing a DC bus (400 V) and a battery pack (50 V) is designed and implemented to verify the feasibility of this control strategy. A detailed analysis of the working principle and design parameters of the proposed converter is provided in this paper. Experimental results show that the highest efficiency of the proposed converter at light loads (10–200 W) was 96.2% for the forward power conversion and 97.3% for the backward power conversion.

Open-Circuit Switching Fault Analysis and Tolerant Strategy for Dual-Active-Bridge DC–DC Converter Considering Parasitic Parameters

The dual-active-bridge (DAB) is a typical topology of dc–dc converter for bus connection, voltage conversion, power transmission, and electrical isolation in dc power grids. The open-circuit switching fault (OCSF) may threaten the safe operation of DAB and should be eliminated in time. However, the researches on parasitic parameters mainly focus on traditional dc–dc converters, and there are still few discussions on parasitic parameters in the high-frequency dc–dc converter such as DAB. The power components are usually considered without parasitic parameters in OCSF analysis and tolerant control, leading to deviations in modality analysis and practical control for DAB. To solve this issue, the modality analysis considering parasitic parameters during OCSF in DAB is investigated, and the sneak circuits and electrical characteristics with parasitic parameters are discussed in this article. Besides, to realize fault tolerance for DAB during OCSF considering parasitic parameters, a new fault tolerance control strategy including modeling, topology transformation principle, and practical control architecture are also proposed. Compared with conventional fault tolerance strategy, the proposed strategy will be more efficient, rapid and feasible for DAB during OCSF process. The experimental results in DAB prototype verify correctness and effectiveness of analysis and proposed strategy.

Overall Efficiency Improvement of a Dual Active Bridge Converter Based on Triple Phase-Shift Control

This paper proposes a control scheme based on an optimal triple phase-shift (TPS) control for dual active bridge (DAB) DC–DC converters to achieve maximum efficiency. This is performed by analyzing, quantifying, and minimizing the total power losses, including the high-frequency transformer (HFT) and primary and secondary power modules of the DAB converter. To analyze the converter, three operating zones were defined according to low, medium, and rated power. To obtain the optimal TPS variables, two optimization techniques were utilized. In local optimization (LO), the offline particle swarm optimization (PSO) method was used, resulting in numerical optimums. This method was used for the low and medium power regions. The Lagrange multiplier (LM) was used for global optimization (GO), resulting in closed-form expressions for rated power. Detailed analyses and experimental results are given to verify the effectiveness of the proposed method. Additionally, obtained results are compared with the traditional single phase-shift (SPS) method, the optimized dual phase-shift (DPS) method, and TPS method with RMS current minimization to better highlight the performance of the proposed approach.

Bidirectional Power Sharing of Modular DABs to Improve Voltage Stability in DC Microgrids

The dual active bridge (DAB) converters have the capability of handling high power in compact form and it is one of the key elements for interconnecting different dc microgrid clusters. A DAB also offers bidirectional power transfer with galvanic isolation between two power buses of similar or different voltage levels, i.e., low voltage and high voltage buses. In microgrid applications, bus voltage regulation is necessary for an uninterrupted power flow and reliable operation of dc microgrids. Due to the galvanic isolation and modularity nature of a DAB, the output can be easily interconnected for efficient and reliable power sharing. In this article, taking the advantage of modularity property of the DAB, an efficient and improved power sharing scheme is developed to stabilize the bus voltage in microgrid applications. A robust bidirectional power sharing control strategy is developed between DABs from different high voltage buses to low voltage buses that improves the voltage stability. An advanced supervisory controller is designed by considering the nonlinearity and uncertainty that ensures stable dc bus voltage and reliable power sharing among DABs under different operating conditions. The controller is validated theoretically and a small-scale laboratory prototype is developed. The concept is verified experimentally at different possible scenarios. From theoretical and experimental results, it is found that the proposed DAB control provides excellent performance in terms of power sharing, dc-bus voltage regulation and power quality.

Self-Healing Predictive Control of Battery System in Naval Power System With Pulsed Power Loads

This article presents a model predictive self-healing control (MPSC) scheme for battery system interfaced dual active bridge (DAB) converter in navy ship power system (NSPS) with pulsed power loads (PPLs). The voltage and frequency of NSPS are vulnerable to PPLs energization. A properly controlled battery system with fast dynamic response can mitigate this vulnerability. Model predictive control (MPC) is a potential solution for the battery system interfaced DAB converter to achieve fast dynamic response and mitigate disturbances imposed to the NSPS by PPLs. However, conventional MPC framework suffers from current prediction error due to the pulsating AC-link inductor's voltage profile in DAB converter. This article proposes a self-healing control loop that utilizes the feasible range of power transfer in conjunction with the AC-link inductor's voltage profile. The proposed method can validate and autonomously correct the predicted current and phase shift in DAB converter interfaced a battery system. The proposed control scheme on DAB converter prevents voltage and frequency collapse in a hybrid AC/DC NSPS particularly during the PPL energization. The system stability is studied based on Lyapunov stability analysis. The theoretical concepts are validated by several case studies implemented on a hardware-in-the-loop (HIL) testbed of a NSPS. The case studies demonstrate voltage and frequency regulation of the NSPS with fast dynamic response during PPLs energization. The proposed MPSC performance is compared with proportional-integral (PI) based control for DAB in NSPS with PPLs.

Model Predictive Control for Dual Active Bridge in Naval DC Microgrids Supplying Pulsed Power Loads Featuring Fast Transition and Online Transformer Current Minimization

Pulsed power loads (PPLs) are commonly incorporated in medium voltage dc microgrids on naval vessels. To mitigate their detrimental effects, dedicated energy storage systems can be installed and their converters need to have excellent disturbance rejection capability. To facilitate this objective, a moving-discretized-control-set model-predictive-control (MDCS-MPC) is proposed in this letter and applied on a dual-active-bridge converter. Fixed switching frequency is maintained, enabling easy passive components design. The proposed MDCS-MPC has a small number of calculating points in each switching period, which enables the implementation in standard commercial control platforms. The operating principle of the MDCS-MPC is introduced in development of a cost function that, on one hand, provides stiff voltage regulation; on the other hand, minimizes transformer current stress online. Theoretical claims are verified on a 20 kHz 1 kW dual active bridge.

Frequency‐domain‐based complete loss model for 10 kV/1 MW solid‐state transformer

This study proposes a frequency-domain-based loss model for dual active bridge (DAB) inside modular multi-level cascaded solid-state transformer (SST). Previously, the loss model is mainly derived in the time domain and requires enormous modelling effort. This study establishes the frequency-domain model of DAB. Based upon that, the switching loss, conduction loss and ferrite loss are derived. The loss model is then used to determine the control scheme for SST. The effect of a PR controller and notch filter on DAB is compared, and the detailed loss analysis is also presented. For the DAB control with a notch filter, it obtains higher efficiency and is implemented in the SST system. The experiment results in both DAB and SST systems verify the effectiveness of the proposed methods.

Improved Fault-Tolerant Method and Control Strategy Based on Reverse Charging for the Power Electronic Traction Transformer

Power electronic traction transformer (PETT) is a new topology for a traction drive system, which can realize the high voltage and power conversion through multilevel converters and high-/medium-frequency transformer link. Reliability becomes a key issue for PETT adopting the module-cascaded structure. In this paper, an improved fault-tolerant method based on reverse-charging control of dual active bridge is proposed, which is suitable for PETT and other two-stage structure converters. The control strategy and operating process of an improved fault-tolerant method are introduced. Comparisons among improved and traditional fault-tolerant methods are also presented. Simulation and experimental results are provided to show the correctness and effectiveness of the improved fault-tolerant method.

Minimize Reactive Power Losses of Dual Active Bridge Converters using Unified Dual Phase Shift Control

This paper proposed an unified dual-phase-shift (UDPS) control for dual active bridge (DAB) converters in order to improve efficiency for a wide output power range. Different operating modes of UDPS are characterized with respect to the reactive current distribution. The proposed UDPS has the same output power capability with conventional phase-shift (CPS) method. Furthermore, its implementation is simple since only the change of the leading phase-shift direction is required for different operating power range. The proposed UDPS control can minimize both the inductor rms current and the circulating reactive current for various voltage conversion ratios and load conditions. The optimal phase-shift pairs for two bridges of DAB converter are derived with respect to the comprehensive reactive power loss model, including the reactive components delivered from the load and back to the source. Simulation and experimental results are illustrated and explained with details. The effectiveness of the proposed method is verified in terms of reactive power losses minimization and efficiency improvement.

Optimal SOC Reference Based Active Cell Balancing on a Common Energy Bus of Battery

This paper presents a study on the state-of-charge (SOC) reference based active cell balancing in real-time. The optimal references of SOC are determined by using the proposed active cell balancing system with the bidirectional DC/DC converters via the dual active bridge (DAB) type. Then, the energies between cells can be balanced by the power flow control of DAB based bidirectional DC/DC converters. That is, it provides the effective management of battery by transferring energy from the strong cell to the weak one until the cell voltages are equalized to the same level and therefore improving the additional charging capacity of battery. In particular, the cell aging of battery and power loss caused from energy transfer are considered. The performances of proposed active cell balancing system are evaluated by an electromagnetic transient program (EMTP) simulation. Then, the experimental prototype is implemented in hardware to verify the usefulness of proposed system.

Pwm control of dual active bridge: Comprehensive analysis and experimental verification

The dual-active-bridge (DAB) topology is ideally suited for high-power dc-dc conversion, especially when bidirectional power transfer is required. However, it has the drawback of high circulating currents and hard switching at light loads, if wide variation in input and output is expected. To address these issues, this paper presents a comprehensive analysis and experimental results with pulsewidth-modulation (PWM) control of the DAB. The PWM control is in addition to phase-shift modulation between the two H-bridges. The analysis addresses PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low-load operation. Finally, a composite scheme combining single and dual PWM is proposed that extends the soft-switching range down to zero-load condition, reduces rms and peak currents, and results in significant size reduction of the transformer. Experimental results are presented with a 10-kW prototype.