This paper presents a feasibility study into the application of a 100V, 50kHz high frequency alternating current (HFAC) network for powering automotive electrical auxiliaries. The study is focused on motoractuated loads, and is divided into two sections. First, the investigation indicates the benefits of replacing low-torque DC motors with lighter and more efficient 400Hz AC machines for applications such as electric fans, fuel pumps or blower motors. A comparative examination of commercially available machines indicates space and weight reduction of more than 60%, and efficiency savings between 25% and 100% are possible. Second, the inquiry evaluates the viability of replacing existing DC/AC inverters with HFAC/AC converters for high-torque AC machines as employed for example in the electric power assisted steering (EPAS) or the heating, ventilation and air conditioning (HVAC) systems. Based on experimental and simulation results for a column-assist EPAS application, employing a three-phase permanent magnet synchronous motor, this study shows that a HFAC drive is expected to reduce the voltage harmonic content below 50kHz by at least 10% compared to the DC/AC inverter. However, the disadvantages of the former drive make it less attractive than the existing DC/AC circuit. Specifically, the EPAS motor torque ripple is expected to be approximately 2% higher compared to the DC counterpart drive. Further drawbacks of the HFAC/AC drive include high MOSFET conduction losses, higher voltage harmonics above 50kHz and complex control requirements of the inverter. Conclusively, significant HFAC advantages for motor loads can be attributed only to machines with a nominal torque capability that is limited to 2Nm. However, given the number of such devices within a typical vehicle, this translates into a possible vehicle mass saving of 30kg and a potential reduction in fuel consumption by 0.8L/100km.

Abstract-In this work, the classical linear model of a permanent magnet synchronous motor (PMSM) is modified by adding d and q-axes harmonic inductances so that the modified model can consider non-linearities present in an interior permanent magnet (IPM) motor. Further, a method has been presented to assess the effect of saturation and cross-saturation on constant torque curves of PMSM. Two IPM motors with two different rotor topologies and different specifications are designed to evaluate the effect of saturation on synchronous and harmonic inductances, and on operating points of the machines.

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