An optimal modulation scheme that enables minimum conduction and copper losses is presented for a bidirectional dual active bridge (DAB) dc-dc converter. The considered converter system is employed for an automotive application and comprises of a high voltage (HV) port with port voltage V1, 240V ≤ V1 ≤ 450 V, and a low voltage (LV) port with port voltage V2, 11 V ≤ V2 ≤ 16 V; the rated output power is 2 kW. The closed-form expressions for the optimal control parameters are derived and implementation details are presented in order to facilitate the direct application to a given DAB converter. The paper further details the properties of the presented modulation scheme with respect to switching losses. Experimental results confirm a considerable increase of the converter efficiency achieved with the proposed optimal modulation scheme, compared to the efficiency obtained with conventional phase shift modulation. The efficiency increase is most distinct at V1=450V and V2 = 11V with an increase from 78.6% to 90.6% at 1 kW output power and from 85.9% to 90.7% at rated output power as compared to conventional phase shift modulation.

Closed Form Solution for Minimum Conduction Loss Modulation of DAB Converters

The nonresonant single-phase dual-active-bridge (NSDAB) dc–dc converter has been increasingly adopted for isolated dc–dc power conversion systems. Over the past few years, significant research has been carried out to address the technical challenges associated with modulations and controls of the NSDAB dc–dc converter. The aim of this paper is to review and compare these recent state-of-the-art modulation and control strategies. First, the modulation strategies for the NSDAB dc–dc converter are analyzed. All possible phase-shift patterns are demonstrated, and the correlation analysis of the typical phases-shift modulation methods for the NSDAB dc–dc converter is presented. Then, an overview of steady-state efficiency-optimization strategies is discussed for the NSDAB dc–dc converter. Moreover, a review of optimized techniques for dynamic responses is also provided. For both the efficiency and dynamic optimizations, thorough comparisons and recommendations are provided in this paper. Finally, to improve both steady-state and transient performances, a combination approach to optimize both the efficiency and dynamics for an NSDAB dc–dc converter based on the reviewed methods is presented in this paper.

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Overview and Comparison of Modulation and Control Strategies for a Nonresonant Single-Phase Dual-Active-Bridge DC–DC Converter

An essential requirement for a high-performance dual active bridge (DAB) dc-dc converter is to rapidly and accurately maintain its DC output voltage under all operating conditions This paper uses a novel harmonic modeling strategy to create a linearized dynamic model of a DAB that accurately identifies its transient response to both a reference voltage change and an output load-current change Using this model, a feedforward compensation strategy is presented that significantly improves the DAB's transient response to an output load change The transient performance is then further enhanced by analytically compensating for the nonlinear dead-time distortion that is caused by the converter switching processes The resultant control system achieves rapid and precise output voltage regulation for both reference voltage and output load changes The theoretical analysis is confirmed by both matching simulation and experimental investigations

Enhanced Load Step Response for a Bidirectional DC–DC Converter

In this paper, a bidirectional battery charger is proposed for grid-to-vehicle, vehicle-to-grid, and vehicle-to-home operations of electric vehicles. The proposed charger adopts sinusoidal charging to eliminate the use of electrolytic capacitors. A nonregulating series resonant converter is employed for isolation, thereby minimizing the ratings of the components and achieving zero-current switching turn on and off of switches. Meanwhile, an ac–dc converter is employed to control each mode and their mode changes, making the whole control scheme simple and the mode changes seamless. A 3.3-kW prototype was built in the laboratory to validate the proposed concept. Our experimental results demonstrate that the proposed charger has high efficiency and can seamlessly switch between the three operation modes.

An Electrolytic Capacitorless Bidirectional EV Charger for V2G and V2H Applications

Dual active bridge (DAB) converters offer an unmatched capability to transfer energy in either direction between two dc sources, while also providing galvanic isolation and high conversion efficiency However, to operate at higher efficiencies, the bridges must operate with zero voltage switching (ZVS) over as wide an operating range as possible The conventional approach to determine ZVS operation uses time domain analysis with ideal ac coupling inductances, which only approximately identifies the ZVS boundaries This paper proposes a new approach using harmonic decomposition of the bridge switching patterns, which gives an explicit theoretical solution under all operating conditions, while also accommodating more complex ac coupling structures, practical impedance nonidealities, and the switching impact of dead-time and device capacitance The methodology is confirmed by matching analytical predictions with experimental results for selected DAB systems

ZVS Soft Switching Boundaries for Dual Active Bridge DC-DC Converters Using Frequency Domain Analysis

It is important for a bi-directional dual active bridge DC-DC converter to maintain a stable output voltage under input voltage and output load changes, as well as providing a fast transient step response. However, designing a voltage regulator that achieves this performance is challenging, and requires a precise analytical converter model. This paper develops such a model, firstly by analysing the response of the converter to the individual harmonics of the phase shifted square waves that modulate the bridges, and then by combining these responses into a small signal model that accurately describes the dynamic performance of the converter. From this model, an adaptive voltage regulator is then proposed that adjusts its proportional and integral gains as the steady state operating conditions vary, to achieve the design target of a slightly underdamped response at all times. The theoretical analysis is confirmed by matching simulation and experimental results.

Adaptive dynamic control of a bi-directional DC-DC converter

Power electronic energy conversion systems for applications such as PHEV typically require single phase AC-DC bi-directional energy transfer with galvanic isolation. A common topology is an AC-DC single phase voltage source inverter, followed by a galvanically isolated high frequency DC-DC bi-directional dual active bridge. A major challenge for this topology is to minimize the intermediate DC bus capacitance, preferably down to a value where electrolytic capacitors are not required. For a single phase system, this is particularly challenging because of the need to match the oscillating power flow from the AC side, to a steady state power flow on the DC side of the system. This paper identifies the fundamental limiting issues for the DC bus capacitance in this application, and presents an optimized converter control strategy that minimizes its value. The analysis is confirmed by matching simulation and experimental results.

High-performance bi-directional AC-DC converters for PHEV with minimised DC bus capacitance

An essential requirement for a high performance dual active bridge (DAB) DC-DC converter is to rapidly and accurately maintain its DC output voltage under all operating conditions. This paper uses a harmonic modeling strategy to create a linearised dynamic model of a DAB that accurately identifies its transient response to both a reference voltage change and an output load current change. Using this model, a feedforward compensation strategy is presented that significantly improves the DAB's transient response to an output load change. The transient performance is then further enhanced by analytically compensating for the non-linear deadtime distortion that is caused by the converter switching processes. The resultant control system achieves rapid and precise output voltage regulation for both reference voltage and output load changes. The theoretical analysis is confirmed by both matching simulation and experimental investigations.

Enhanced load step response for a Bi-directional DC-DC Converter

Grid connected PWM inverters/rectifiers inevitably produce a high frequency switched common mode voltage on their DC bus, which can cause substantial EMI problems. The mitigation strategy proposed in this paper is to couple the Y point of the LCL filter capacitors to the DC bus mid-point to connect a virtual neutral to the DC bus, which significantly reduces the high frequency common mode voltages on the bus. However, additional common mode inductances and capacitances are required for this filter, to limit high frequency circulating currents and define the EMI filter breakpoint. Also, the converter current regulator must be split into differential and common mode sections, to eliminate phase coupling between the phase leg active damping current regulators, and to support damping of the common mode EMI filter resonance. The concept is verified by simulations and experimental results.

D. Segaran

Papers

Adaptive dynamic control of a bi-directional DC-DC converter

High-performance bi-directional AC-DC converters for PHEV with minimised DC bus capacitance

Enhanced load step response for a Bi-directional DC-DC Converter

DC bus voltage EMI mitigation in three-phase active rectifiers using a virtual neutral filter