Development of High-Power-Density DC-DC Converter Using Coupled Inductors for Clarity Plug-In Hybrid

Honda has developed an electric powertrain for a 2017 plug-in hybrid vehicle using its second-generation SPORT HYBRID i-MMD powertrain system as a base. The application of the newly developed powertrain system realizes a long all-electric range (AER), allowing operation as an EV for almost all everyday driving scenarios, with dynamic performance making it possible for the vehicle to operate as an EV across the entire speed range, up to a maximum speed of 100 mph. The amount of assist provided by power from the batteries during acceleration has been increased, helping to downsize the engine while also balancing powerful acceleration with quietness achieved by controlling racing of the engine. In order to realize this EV performance with the second-generation SPORT HYBRID i-MMD system as the base, it was necessary to increase the power output of the DC-DC converter, taking restrictions on space into consideration. An interleaved circuit design using coupled inductors was employed as the method of increasing the power density of the DC-DC converter. This circuit design reduced magnetic flux generated in the inductor cores by direct current, making it possible to reduce the size of the inductors. However, it was not possible to position electric devices such as current sensors close to the coupled inductors due to magnetic flux leakage to the exterior, making it challenging to increase the integration density of the components. In order to address this issue, a configuration of coupled inductors that reduces magnetic flux leakage was developed, making it possible to increase the integration density of the peripheral layout of the DC-DC converter. The application of the proposed coupled inductors has increased the continuous power density of the DC-DC converter approximately 2-fold in comparison with the conventional unit employed in previous Honda hybrids.