2003-01-0307 Novel Power Conversion System for Cost Reduction in Vehicles with 42V/14V Power Supply Yasushi Kusaka and Kimi toshi Tsuji Toyota Motor Corporation Copyright © 2003 SAE International ABSTRACT In recent years, attention is being given to 42V power supply technology for solving the problem of increasedpower demand in vehicles. Since 2001, Toyota MotorCorporation has been marketing a mild hybrid system(THS-M) in order to further improve fuel economy andreduce emissions; this system requires both 42V and14V power sources. The THS-M system consists of a 42V motor generator (M/G) connected to the engine crankshaft with a belt; aninverter; a 36V battery; a DC/DC converter for steppingdown the 42V power supply to a conventional 12Vbattery; and high-power related electrical components.These components require additional costs, which mustbe reduced in order to increase the sales volume ofTHS-M vehicles. We have devised a method to eliminate the conventional DC/DC converter from the THS-M, and asa result we have developed a new, revolutionary powerconversion system (multi-function inverter). Instead ofusing a DC/DC converter, we derived a 14V power linefrom the neutral point of the motor generator, and addeda reactor (a type of smoothing inductor) in this line forreducing ripple. In addition, we applied a new inverter switching system which allows us to simultaneously and independently control both the 14V and 42V system voltages, whichare taken from the motor-generator drive, andconnected to the 12V and 36V batteries, respectively. The paper reports on the principle of operation and the test results, including torque and efficiencycharacteristics of the multi-function inverter. INTRODUCTION Over the past several years, social demands for fueleconomy and low emissions have become more strict.To meet these requirements, Toyota has introduced thePrius, Estima Hybrid, Crown Mild Hybrid and otherhybrid vehicles which combine a highly efficient enginewith a motor-generator (M/G). The Toyota Mild HybridSystem (THS-M) used in the Crown Mild Hybrid uses a 42V system (36V battery), which is a sharply lowerpower supply than the higher voltage systems (typicallyover 200V) used on other hybrid vehicles, therebypromoting downsizing and simplification of the M/Gsystem components. Such 42V power systems cover not only the large power requirement characteristics of hybrid vehicles, but alsomeet the increased electrical load of existing vehicles.In this regard, international standardization is beingpromoted for 42V power supply to replace the existing14V power supply system (12V battery) as the nextgeneration vehicle power supply. However, since amajor investment is required to switch every existing14V system auxiliary load to the 42V system all at once,we believe the 42V/14V dual-power supply system willremain the mainstream for a period of time, beforeshifting to a single 42V power supply. Therefore, at present, it is imperative to have a power conversion system (DC/DC converter) to supply powerfrom 42V to 14V. DC/DC converters normally havemany components and high reliability is required, whichresults in higher costs of the converter and the M/Gsystem. In this research, we have developed a newpower conversion system and its control method (multi-function inverter) to realize the same functions as aDC/DC converter, by simply using a conventionalinverter and a modified M/G. Fig. 1 Toyota Mild Hybrid SystemDownloaded from SAE International by Univ of Nottingham - Kings Meadow Campus, Monday, September 10, 2018APPLICATION SYSTEM This section explains the M/G system of the conventional THS-M and application of the new multi-function inverter. Conventional THS-M System As shown in Fig. 2, the 42V M/G is installed in the same position as a conventional 14V alternator to improve fueleconomy while driving on urban roads. The engine isautom