In land vehicles with high-power electrical loads, other than the low-voltage DC bus (14V, 28V, or 42V) for the low-power conventional loads, a high-voltage bus, e.g., 200V DC, is required for high-power loads such as hotel loads and electrically-assisted propulsion systems. In addition, some advanced electrical loads including luxury loads and AC power point require 120V, 60Hz AC voltage. These land vehicles include heavy duty, fire fighting, and military vehicles. There are two traditional approaches in obtaining a dual DC voltage bus system. The first one is to obtain the low-voltage DC from the alternator and boost it to the high-voltage DC. The second method is to obtain the high-voltage DC directly from the alternator and reduce it to the low-voltage. Both approaches require additional step-up or step-down power conversion stages, which inherently result in a reduced efficiency. In this paper, a new approach with a 28V/200V dual voltage alternator is considered. This system avoids the additional power conversion stage and, as a result, increases the efficiency of the system.
The primary objective of this paper is to demonstrate the design and operation of a high power density, 2.5 kW, single-phase, DC/AC pulse width modulated (PWM) inverter. The IGBT-based inverter operates from the 200V DC voltage output of the dual voltage alternator and consists of a low-pass LC filter at its output. The RMS value of the AC output voltage attained from the mobile power supply is 120V at a frequency of 60Hz. The sinusoidal pulse width modulation (SPWM) method is used as the control technique for the purpose of inverter switching. These PWM control signals are generated using a digital signal processor (DSP) and are eventually used to drive the gates of the IGBT switches of the proposed inverter. Due to the simplified power stage and the usage of an efficient DSP-based modulation technique, the total harmonic distortion (THD) of the output voltage is fairly low (less than 2%) and a relatively small overall inverter size is achieved. A detailed description of the system along with simulation and experimental results are presented in this paper.