Considerations for starting combustion engines with AC machines

To initiate its combustion cycles, internal combustion engines require a minimum rotational speed that can be given from several sources (muscular, electrical, pneumatic, among others). Advantages of initiating an ICE with an AC electrical machine is that it can integrate starter motor and generator in one device, provide a linear ramp of acceleration when starting, and assist the ICE in torque production. This article illustrates considerations for the design of a starting system with an AC electrical machine. Initially, criteria of torque, rotational speed and power requirements are analysed, considering resistances of compression, friction, and inertia of the slider-crank mechanism, as well as accessories, with a preliminary experimental validation. Also, types of three-phase AC electrical machines are put to comparison, as well as their associated electronic components needed for driving them in each case, concluding that AC induction machines require a complex 4-quadrant inverter. PM synchronous machines require a simpler inverter, but with highly specified power electronics components. The classical wound rotor machine requires the simplest inverter, with unidirectional power flow, less power transfer losses and less critical power electronics components. Finally, considerations for using of a battery assisted with supercapacitor as complementary DC power source are made.