An efficiency-optimized modulation scheme and design method are developed for an existing hardware prototype of a bidirectional dual active bridge (DAB) dc/dc converter. The DAB being considered is used for an automotive application and is made up of a high-voltage port with port voltage V1, 240 V ≤ V1 ≤ 450 V, and a low-voltage port with port voltage V2, 11 V ≤ V2 ≤ 16 V; the rated output power is 2 kW. A much increased converter efficiency is achieved with the methods detailed in this paper: The average efficiency, calculated for different voltages V1 and V2, different power levels, and both directions of power transfer, rises from 89.6% (conventional phase shift modulation) to 93.5% (proposed modulation scheme). Measured efficiency values, obtained from the DAB hardware prototype, are used to verify the theoretical results.

Efficiency-Optimized High-Current Dual Active Bridge Converter for Automotive Applications

An accurate power loss model for a high-efficiency dual active bridge converter, which provides a bidirectional electrical interface between a 12-V battery and a high-voltage (HV) dc bus in a fuel cell car, is derived. The nominal power is 2 kW, the HV dc bus varies between 240 and 450 V, and the battery voltage range is between 11 and 16 V. Consequently, battery currents of up to 200 A occur at nominal power. In automotive applications, high converter efficiency and high power densities are required. Thus, it is necessary to accurately predict the dissipated power for each power component in order to identify and to properly design the heavily loaded parts of the converter. In combination with measured efficiency values, it is shown that conventional converter analysis predicts substantially inaccurate efficiencies for the given converter. This paper describes the main reasons why the conventional method fails and documents the different steps required to predict the power losses more accurately. With the presented converter prototype, an efficiency of more than 92% is achieved at an output power of 2 kW in a wide input/output voltage range.

Accurate Power Loss Model Derivation of a High-Current Dual Active Bridge Converter for an Automotive Application

The derivation of an accurate small-signal model for a galvanically isolated, bidirectional dc-dc converter and the implementation of a corresponding controller on a DSP as well as key methods and functions required for the digital implementation are detailed in this paper. The investigated dc-dc converter, an automotive dual active bridge (DAB) system, enables power transfer between a low-voltage port (ranging from 11 to 16 V) and an HV port (240 to 450 V). The nominal power rating is 2 kW. The developed small-signal model yields highly accurate results for the DAB system, but the proposed modeling procedure could also be applied to arbitrary resonant power converters with unidirectional or bidirectional power transfer.

Accurate Small-Signal Model for the Digital Control of an Automotive Bidirectional Dual Active Bridge

A comprehensive study on different types of faults and detection techniques for solar photovoltaic system

We present the analysis, design, and experimental validation of a model-based fault detection and identification (FDI) method for switching power converters using a model-based state estimator approach. The proposed FDI approach is general in that it can be used to detect and identify arbitrary faults in components and sensors in a broad class of switching power converters. The FDI approach is experimentally demonstrated on a nanogrid prototype with a 380-V dc distribution bus. The nanogrid consists of four different switching power converters, including a buck converter, an interleaved boost converter, a single-phase rectifier, and a three-phase inverter. We construct a library of fault signatures for possible component and sensor faults in all four converters. The FDI algorithm successfully achieves fault detection in under 400  $\mu$ s and fault identification in under 10 ms for faults in each converter. The proposed FDI approach enables a flexible and scalable solution for improving fault tolerance and awareness in power electronics systems.

Model-Based Fault Detection and Identification for Switching Power Converters

The dc-dc converter is a critical component in a hybrid electric vehicle since it supplies power to an electronic control unit, as well as chassis electric components such as power windows, wipers, etc. In this paper, a low-cost diagnostic method for MOSFET faults in a zero- voltage-switching dc-dc converter is proposed. The proposed method utilizes the dc-link current patterns as the signatures of faults of MOSFETs. A presignal processing circuit consists of a peak detector and an integrator circuit. The ratio of peak-to-integral values, which is similar to the crest factor, is useful for diagnosis.

Fault Diagnosis of a ZVS DC–DC Converter Based on DC-Link Current Pulse Shapes

In a stand alone system such as a hybrid electrical vehicle (HEV) and an electrical propulsion ship, an electric energy is transferred from a generator to a target motor via a converter-inverter set to control the motor torque or speed. In this case, whole power is handled by the converter-inverter system, and the power rating of the converter tends to be large. This work proposes a topology and a control scheme for a 4WD HEV system using a doubly fed induction motor (DFIM) which is driven by an internal combustion engine. The control aim is to produce a variable voltage variable frequency (VVVF) voltage from the stator terminal of the DFIM by injecting a slip frequency into the rotor winding through an inverter. In other words, the source voltage for target motor is not synthesized by an inverter after making a DC-link. Instead, the generator stator terminal directly provides a VVVF voltage to the motor. The inverter supplies current having slip frequency to the rotor via slip ring. Since the DFIG output voltage and frequency are controlled by the rotor current, the inverter power rating can be reduced significantly, when it is compared with the generated power. In this work, it is shown that with the proposed topology the power rating of a converter-inverter could be reduced to the 1/4 of the original converter-inverter system.

A new topology and control scheme for 4WD HEV using a DFIM with a reduced size converter-inverter

As the needs of motorization in vehicle system increase, studies on the motor driven power steering system (hereinafter referred to as MDPS (motor driven power steering) are actively in progress. Being combined with the current trend for the protection of environment and energy-saving, MDPS will be the main stream of future power steering systems and an intense target of technology innovation. This paper focuses on a computer simulations and experimental results using a real car to evaluate on-center characteristics on MDPS. A comparison between conventional hydraulic power steering system and MDPS for environmental vehicle that is hybrid electric vehicle is also addressed.

Ho-Gi Kim

Papers

Fault Diagnosis of a ZVS DC–DC Converter Based on DC-Link Current Pulse Shapes

A new topology and control scheme for 4WD HEV using a DFIM with a reduced size converter-inverter

On-center handling characteristics of MDPS system for environmental vehicle