Dual Active Bridge Operation Research Articles

Selected aspects of the operation of Dual Active Bridge DC/DC converters

This review paper discusses the concept of a bidirectional Dual Active Bridge (DAB) DC/DC converter. Practical applications and control methods are explored, and various types of DAB converters are introduced and characterized. Aspects of operation are discussed, enriched by the results of theoretical analyses, simulations, and experimental measurements of the original authors works.

A Full-Power-Range Optimization Scheme Under Double-Side Asymmetrical Phase-Shift Modulation in DAB-Based Distributed Energy Storage System

For distributed energy storage system, dual-active-bridge (DAB) is often employed as interface among photovoltaic port, storage system and load. Efficient DAB operation will be beneficial to energy conversion efficiency. Nevertheless, for conventional DAB modulation, many problems exist including that wider soft-switching range is always accompanied with high peak current. In order to overcome these problems, a double-side asymmetrical phase-shift modulation (DAPM) is proposed, which combines phase-shift modulation on the primary side and variable-duty modulation on the secondary side. Based on DAPM, a full-power-range optimization scheme is employed to reduce current stress and widen zero-voltage-switching (ZVS) range. Consequently, most of DAPM modes can realize all semiconductors ZVS. ZVS ranges are widened dramatically with lower peak current and lower root-mean-square (RMS) current. Within entire power range, compared with conventional DAB modulations, DAPM modes can achieve lowest RMS current, lowest peak current and widest ZVS ranges. Finally, a DAB-based prototype is established to verify effectiveness of proposed DAPM.

Constant Power Load Stabilization With Fast Transient Boundary Control for DAB-Converters-Based Electric Drive Systems

Due to the negative incremental impedance of constant power loads (CPLs), many undesirable issues such as the oscillations or even possible collapse of the main dc bus voltage may occur, which may significantly degrade the system stability of Electrical Vehicles (EVs). This paper presents a natural-switching-surface (NSS) fast-transient-boundary-control (FTBC) based stabilization solution for EVs with dual-active-bridge (DAB) converters as the main power interface. Based on the mathematical models of multiple natural switching surfaces (NSS) and characteristics of CPL, the proposed FTBC control can achieve stable operation of DAB converters feeding CPLs and fast dynamic response irrespective operating stages such as the startup, sudden voltage and power reference changing conditions. Compared with other strategies such as load shedding, the proposed FTBC has no additional requirements for hardware, which is cost-effective. The analytical derivation of the proposed algorithm under the CPL condition is presented together with simulation and experimental evaluations, which validate that the proposed FTBC is capable of achieving 2 times faster start-up process and at least 33% dynamic response improvement compared with proportional integrator (PI) closed-loop control while eliminating the dc-bias current and guaranteeing the CPL stability by regulating the dynamic trajectories of DAB converters in the geometric domain.

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.

A High-Precision Sensor Based on AC Flux Cancellation for DC Bias Detection in Dual Active Bridge Converters

DC bias in a transformer is a threat to the safe and efficient operation of dual active bridge (DAB) converters. Detecting a dc component in milliamperes mixed with a large ac current is difficult. This article proposes a current sensor based on ac magnetic flux (MF) cancellation. The proposed sensor utilizes a current transformer (CT) to extract the ac component in the measured current. Then, a power op-amp copies the CT signal to an additional winding to generate an ac MF opposite to that of the main ac current. Hence, the sensor range required to measure the dc is greatly reduced for a much smaller absolute measurement error. Using only a CT and a simple op-amp circuit, the proposed solution features low complexity and power consumption. The relative error in a range of 15-A ac current is 0.038%, showing a five-fold improvement compared to off-the-shelf sensors. The proposed sensor is verified on a 1-kW DAB prototype, where the dc bias is suppressed to nearly null owing to the proposed sensor.

Comparative analysis of dual active bridge dc–dc converter employing Si, SiC and GaN MOSFETs for G2V and V2G operation

Electric vehicles (EVs) are ideally suited for carbon footprint reduction and energy-efficient transportation. EV battery chargers comprise of cascade connection of ac–dc and dc–dc converters. With the bidirectional dc–dc converters, EV chargers can implement grid-to-vehicle (G2V) and vehicle-to-grid (V2G) functionality. Dual active bridge (DAB) converter is a bidirectional dc–dc converter that can support G2V and V2G operation. DAB converters are operated at high switching frequencies (fsw) leading to higher switching loss. This issue can be addressed by employing SiC and GaN-MOSFETs, which work with lesser switching losses and can operate at much higher fsw. This paper presents a detailed comparative analysis of DAB converter employing Si, SiC and GaN MOSFETs for G2V and V2G operation. The EV charging system with a DAB converter employing V2G and G2V operation is modeled in PSIM software. Single phase shift (SPS) modulation technique is employed for DAB converter. The system operation is analyzed for V2G and G2V operation with the fsw of 20 kHz, 50 kHz, 100 kHz and 200 kHz. The performance comparison reveals that DAB converter with GaN-MOSFETs has the highest operating efficiency. To validate the DAB operation with SPS modulation, experimental studies have been carried out with SPS modulation being implemented on TMS320F28335 DSP using SimCoder Module of PSIM. A step-by-step procedure to implement the modulation technique with SimCoder is also provided.

EMI Performance of Active Neutral Point Clamped Phase Leg for Dual Active Bridge DC–DC Converter

This article evaluates the electromagnetic interference (EMI) caused by active neutral point clamped (ANPC) phase leg undergoing zero voltage switching (ZVS). ZVS, together with a high fundamental frequency operation is encountered in dual active bridge (DAB) converters. This allows ANPC phase leg to be operated in a different manner than its inverter counterpart. A comprehensive evaluation of four switching schemes for NPC/ANPC-DAB with regard to their EMI performance, voltage overshoot, and losses have been done. Switching state redundancies have been used to reduce the EMI of the ANPC phase leg. To further help in reduction of high frequency EMI and voltage overshoot, a low inductance busbar design has been presented for through-hole discrete devices. Finite element simulation and measurement results show a busbar inductance of 7.7 nH for long commutation loops. Finally, EMI performance (conducted and radiated) together with the busbar design has been experimentally validated for two of the most useful switching schemes. The switching schemes and the busbar design can boost adoption of NPC/ANPC-DAB by ensuring EMI compliance and improved efficiency without affecting the normal DAB operation or using additional hardware.

Improved hybrid current modulation for bidirectional power flow of single-stage dual active bridge AC/DC converter

In this paper, an improved hybrid current modulation (iHCM) method for bidirectional power flow operation of dual active bridge (DAB) ac/dc converter is proposed. In this method, trapezoidal (TZM) and triangular (TRM) current modulations are performed together in a grid period to obtain distortionless grid current with forming minimum RMS current in the transformer of DAB. This study put forward a detailed analysis of the mode changing instants (between TRM and TZM), RMS and peak current values of the transformer and required magnetic core sizes. Furthermore, the iHCM is compared in analysis and simulations by the variable switching frequency dual phase shift modulation (VSF DPSM) method that have small RMS current advantage in the vicinity of nominal output power. According to the analysis, the iHCM, unlike the VSF DPSM, can operate over a wide range of transformer turn ratio (or over the wide range of ac peak voltage/reflected dc voltage, λ) without increasing the size of transformer, and can provide small RMS currents at light loads as it has no nonactive (circulating) current. The theoretical analysis is validated with a downsized 250 W experimental prototype.

Flux Balancing Control of Ungapped Nanocrystalline Core-Based Transformer in Dual Active Bridge Converters

Transformer flux dc bias is a critical issue, impacting the reliable operation of dual active bridge (DAB) converters especially when ungapped high permeability nanocrystalline core is used. Steady state current dc bias can easily saturate ungapped nanocrystalline transformers, and it is even more dangerous in transient conditions. A dc bias model is proposed to analyze steady state dc bias in different load conditions. The magnetizing current detection is necessary for closed-loop control of dc bias; conductors’ position is shown to impact sensor noise, and it is analyzed in detail. To deal with both steady state and transient dc bias, a unified flux balancing control (UFBC) is proposed introducing a predictive bias suppression (PBS) method with closed-loop flux balancing control (CFBC). With the proposed PBS, both primary/secondary current balance and flux balance can be achieved within one switching cycle using UFBC. Power characteristics and interaction between power control and flux balancing control of DAB converters are analyzed, and the CFBC needs to work in a low bandwidth due to sensor bandwidth limitation and interaction between power control and flux balancing control. The UFBC is verified on a 300-kW cascaded DAB converter prototype.

An Improved Generalized Average Model of DC–DC Dual Active Bridge Converters

Improvements are proposed for generalized average models of dual active bridge (DAB) converters. Generalized average modeling involves a tradeoff between accuracy and tractability. To maintain an acceptable level of complexity, existing DAB models are derived using a first harmonic approximation. These models provide accurate small-signal representations, but are limited as large-signal analysis tools due to persistent steady-state error. This study proposes a modeling framework that provides accurate large and small-signal models without significant increases in the overall complexity. The framework describes DAB operation with a triple phase shift modulation, and is easily simplified for single, dual, or extended phase shift modulation schemes. The special case of a single phase shift modulation, which experiences the most significant large-signal error, is given additional consideration. The framework is applied to open and closed-loop operation, and both large- and small-signal models are discussed. Models are validated in simulation and hardware experiments using a small scale DAB prototype.

Multifrequency approximation and average modelling of an isolated bidirectional dc–dc converter for dc microgrids

This study presents a generalised analysis of isolated bidirectional dual active bridge (DAB) dc–dc converter with triple-phase-shift (TPS) control. The multifrequency approximation is used to analyse performance characteristics of DAB, and a novel numerical solver is developed to determine the optimised modulation scheme based on TPS control. Specially, the proposed solver can be considered as a unified solver for determining the optimised operation of DAB with required transmission power and voltage conversion ratio. The multifrequency average model of DAB is then described in this study. A universal control-to-output-voltage transfer function is derived for DAB with any modulation scheme, and the closed-loop operation is discussed based on the proposed average model. Finally, a laboratory prototype is implemented and experimental results verify the theoretical analysis.

Analysis of quasi-square-wave operation of DAB DC–DC converter

This work makes a novel contribution to the analysis of quasi-square-wave operation of dual-active bridge (DAB) converter by deriving equations for root mean square (RMS) and average device currents and RMS and peak inductor/transformer currents – these equations are useful in predicting device and passive component losses. Quasi-square-wave operation of the DAB converter is verified through Saber simulations and experimentation, validating the mathematical analysis. It is observed that quasi-square-wave mode improves average power transfer and the converter efficiency besides enhancing its soft-switching region without introducing additional passive components. The effect of quasi-square-wave on RMS and peak currents of devices and transformer/inductor is also discussed.