How many module the auxiliary power unit is composed from?

It has the mechanical module (a gas turbines ) and the electrical module ( the generator ), and the control module. The mechanical module comprises a turbine engine complete with starter, compressor, combustion chambers, exhaust, inlet and auxiliary systems (lube oil, cooling air, seal air, air filters, fuel sytem and igniters),

The electrical module comprises a generator with all cabling, generator protection module, cabling, bus bars, etc

The control module comprises all a cabinet with cards for controlling the mode (iso or droop) of the turbine, has a provision for monitoring the combustion and exhaust temperatures, has a watchdog for acquiring and pinpointing "out of trend" data, has a provision for controlling turbine overspeed, and can create alarms for the following systems: lube oil, combustion temperature, power generation, cooling and sealing air, fuel and air flow thru the turbine.