In recent years, attention is being given to 42V power supply technology for solving the problem of increased power demand in vehicles. Since 2001, Toyota Motor Corporation has been marketing a mild hybrid system (THS-M) in order to further improve fuel economy and reduce emissions; this system requires both 42V and 14V power sources.
The THS-M system consists of a 42V motor generator (M/G) connected to the engine crankshaft with a belt; an inverter; a 36V battery; a DC/DC converter for stepping down the 42V power supply to a conventional 12V battery; and high-power related electrical components. These components require additional costs, which must be reduced in order to increase the sales volume of THS-M vehicles.
We have devised a method to eliminate the conventional DC/DC converter from the THS-M, and as a result we have developed a new, revolutionary power conversion system (multi-function inverter). Instead of using a DC/DC converter, we derived a 14V power line from the neutral point of the motor generator, and added a reactor (a type of smoothing inductor) in this line for reducing 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, which are taken from the motor-generator drive, and connected to the 12V and 36V batteries, respectively.
The paper reports on the principle of operation and the test results, including torque and efficiency characteristics of the multi-function inverter.