Shuntaro Inoue

Loss estimation of an isolated three-port DC-DC converter for automotive applications

A three-port DC/DC converter (TPC) having DC48V and DC12V ports, and an isolated DC port is designed and analyzed. The newly designed TPC integrates a non-isolated bi-directional DC-DC (NBC) converter and an isolated dual-active-bridge (DAB) converter using a coupling inductor technique, and DC power can be delivered multi-directionally among three DC ports. In the present study, a loss estimation method for the TPC is developed in order to analyze losses in all load conditions. A 750 W, 125 kHz prototype using a Si MOSFET is constructed in order to confirm the accuracy of the newly developed estimation method. The measured efficiency is over 90% for a wide range of load conditions, and the calculated efficiency curves correspond well with the measured efficiencies. In addition, the improvement in efficiency provided by using a GaN FET is also discussed. The efficiency is expected to increase 2% by replacing the Si MOSFET with a GaN FET. Finally, a prototype using a GaN FET is constructed in order to verify the above estimation.

Novel SPICE model for common mode choke including complex permeability

A highly accurate filter simulation requires a high precision SPICE model for the common mode choke. Conventional SPICE models for chokes consist of parallel RLC circuits and show a substantial difference between the measured and simulated impedance characteristics due to the lack of frequency-dependent complex permeability considerations. Here, we propose a novel SPICE model for a common mode choke that includes the frequency-dependent complex permeability. This model uses a transfer function in the s-domain to describe frequency-dependent elements. Moreover, two model parameter estimation methods are proposed; a measurement based method and a datasheet based method. High accuracy is achieved with the measurement based model by extracting the model parameter using the measured impedance characteristics of the actual coil. In the datasheet based method, the model parameter is estimated from the datasheet and the shape of the coil without the actual coil. Finally, we show that not only the impedance characteristics of a choke can be expressed, but also the insertion loss of a T-type filter can be predicted much more accurately than presently possible using a conventional model. This SPICE model is the first to express the frequency-dependent inductance and resistance of the choke with high accuracy; therefore, it is expected to be useful for filter design.

28 W/cm 3 high power density three-port DC/DC converter cell for dual-voltage 12-V/48-V HEV subsystem

Realizing both of compact and low energy consumption is technical issue on development of electricity-rich automotive subsystems. In the present work, a 12-V/48-V dual-voltage subsystem using three-port DC/DC converter cells is proposed, and the high power density cell design is studied to achieve ultra-compact subsystem in hybrid-electric-vehicle. A 500 W, 400 kHz prototype is developed with GaN FETs, and its efficiencies are evaluated. The prototype achieves power density of 28 W/cm at rated power, and its efficiency is measured more than 91% over a wide output power range, with a maximum efficiency of 93.7%.

An isolated three-port DC-DC converter with high power density in 10 cm × 5 cm × 0.8 cm card size for flexible automotive systems

A credit-card sized three-port dc-dc converter (TPC) has been designed and constructed. The TPC has three DC ports in one circuit, and DC power can be transferred without interference mutually. A dual active bridge converter (DAB) and a non-isolated bi-directional dc-dc converter (NBC) are integrated in the TPC by using a technique known as magnetic coupling inductor. Both thermal and soft-switching analysis are conducted to realize a high energy density of prototype, where a 750 W, 375 kHz, 18 W/cc is achieved. The efficiency and total losses have been measured in order to verify the validity of the proposed converter, and efficiency over 90% in wide range of output power is achieved by using Si MOSFETs.

Design and modulation method of Multi-port DC/DC converter for next generation HV sub system

A multi-port DC/DC converter having DC48V and DC12V ports is proposed for next generation HV sub system. The converter integrates an isolated DC/DC converter and a non-isolated DC/DC converter in one circuit. A low voltage side full-bridge and an inductor are shared by two topologies, and the number of switches and magnetic components can be saved. In the present study, a duty modulation method is proposed to reduce losses in light load condition. Moreover, to achieve compatibility of high efficiency and high power density, the switching frequency is increased and 600 V cascode type GaN FET is used for high voltage side switches. A 175 kHz, 1.0 kW prototype is constructed, and power density of 55 W/in3 is achieved. The loss reduction in light load condition using the proposed duty modulation is verified. The measured efficiency is over 90% for a wide output range, and the maximum value achieves 93.9% for DC12V, and 95.3% for DC48V, respectively.