An Improved Automotive Power Distribution System Using Nonlinear Resonant Switch Converters

Insertion of a de-dc converter between the automobile battery and electrical loads is proposed. This would allow gradual conversion to higher battery voltage, regulation of de distribution voltage, and multiple distribution voltage levels. Switching loss arising from parasitic inductances is a serious problem in this application. The nonlinear resonant switch can remove this source of loss, achieving zero current switching without sacrificing conduction loss or MOSFET switch utilization. A lowvoltage high-current nonlinear resonant switch converter operating at 700kHz and producing 600W is described. I . Introduction Automotive electrical system power requirements for upoption GM vehicles have grown from 840 watts in 1975 to 1330 watts in 1989. By 1993, if growth continues at the historical rate and transient loads such as electrically heated windshields are not included, the load requirement could be 1540 watts (Fig. 1). The impact of this is considerable: charging systems are larger and heavier, battery discharge at idle can be significant, the horsepower used to drive the generator causes a measurable decrease in gas mileage and requires better belts, and the application of new electrically driven accessories can be inhibited. Until new means of generating electrical power on automobiles are developed, the automotive engineers must find ways to generate and use electrical power more efficiently. Furthermore, since these systems usually must operate in high ambient temperatures under the hood, heatsink size can be prohibitive unless efficiency is high. Today, most automobiles have Lundell-type alternators with diode bridge rectification. The alternator is sized to produce adequate load current and has electronic voltage regulation which provides proper voltage for 12 volt battery charging. These systems have two areas of inefficiency: (1) the generatorthe Lundell machine, due to brushes and slip rings, high leakage flux, and diode forward drop, has an efficiency of only 40 70 % depending on speed and load (Fig. 2), and (2) the loadsinefficiencies in the load side of the automotive electrical system occur primarily because the voltage is controlled to the battery rather than the load needs, with resulting wide voltage variations. This wok was sponsored in part by-qrant from the D~ICORemy Division of the General Motors Corporation Boulder Ronald A. Martin Technology Development