Engine Speed Speed Control Generator Torque Control Torque - - + + Speed Reference Engine Observer (Subsystem Model) Generator Observer Torque Reference Speed Reference G.T. Observer Torque Engine Shaft Torque Reference Generator Figure 6. A MATlAB/Simulink model of two motor drives with a mechanical coupler. to emulate the steady-state and dynamic characteristics of the gas turbine engine model in Figure 4. This can be implemented by inserting the engine observer block between the torque reference from the generator and the speed reference into the motor. In such a setup, the ac motor gets its speed reference from the model of the gas turbine engine, given the load torque from the brushless dc motor. The whole system model is tested in simulation, and the results have shown that the controlled ac motor and drive with speed closed-loop control is able to operate in accordance with the IEEE Electrific ation Magazine / d ec em be r 2 0 1 4 29