This example shows an aircraft electrical power generation and distribution system. The AC power frequency is variable and depends of the engine speed
Olivier Tremblay, Louis-A. Dessaint (Ecole de technologie superieure, Montreal)
The system is composed of six main sections.
The first section represents the generator mechanical drive and is modeled by a simple signal builder, which provides the mechanical speed of the engine shaft.
The second section represents the power AC generator. It is composed of a modified version of the simplified synchronous machine. The mechanical input of the modified machine of 50 kW is the engine speed. The Generator Control Unit regulates the voltage of the generator to 200 volts line to line.
The third section represents the Primary Distribution system. It is composed of three current and voltage sensors. There is also a 3-phase contactor controlled by the Generator Control Unit. Finally, a parasitic resistive load is required to avoid numerical oscillations.
The fourth section represents the secondary Power Distribution system. It is represented by 4 circuit breakers with adjustable current trip.
The fifth section represents the AC loads. There is a 4 kW Transformer And Rectifier Unit (which supplies 28 Vdc), a 12 kW induction machine (motor driving a pump), a 1 kW resistive load (lamps) and a 3 hp simplified (using an average value inverter) brushless DC drive (motor driving a ballscrew actuator).
Finally, the last section represents the DC loads. There are two resistive loads (heater and lamp) and a 300 W DC brush motor (motor driving a fuel pump).
Start the simulation. You can observe the AC and the DC measurements at the top level of the schematic. There are also scopes inside the AC Power Generation, the Induction motor, the Brushless DC motor and the DC brush motor.
At time t = 0 s, the engine accelerates from 0 rpm to 12000 rpm in 0.4 second.
At time t = 0.3 s, the speed reaches the threshold of 9000 rpm. The Generator Control Unit activates the primary contactor, which enables the AC power on the aircraft. All the resistive loads are now online. The DC bus voltage increases to 28 Vdc. The induction machine and the DC brush motor accelerate to nominal speed (the two mechanical loads are proportional to the speed of the motors).
At time t = 1.4 s, the Brushless DC motor starts accelerating to the set point of 500 rpm. Observe that the speed follows precisely the acceleration ramp.
At time t = 1.9 s, the speed set point of the Brushless drive is changed to -500 rpm. You can see that the main current decreases, because the motor acts as a generator. The current flows from the motor to the breaking chopper inside the drive. Open the drive scope to observe the increasing of the DC bus voltage to the breaking chopper activation voltage (290 Vdc).
At time t = 2 s, the engine speed decelerates from 12 000 rpm to 10 000 rpm in 1 second. Observe the speed of the induction machine, which decelerates according to the reduction of the generator frequency.
At time t = 3 s, the engine speed accelerates from 10 000 rpm to 18 000 rpm in 1.5 second.
At time t = 3.5 s, there is a manual breaker trip on the Transformer And Rectifier Unit. This cause a reduction of the main current. Observe the voltage and the current on the DC monitoring scope.
At time t = 4.5 s, the engine speed decelerates from 18 000 rpm to 0 rpm in 1.5 second.
At time t = 5.26 s, the speed reaches the threshold of 8900 rpm. So the GCU de-activates the primary contactor.
Finally, note how well the AC voltage is regulated during the whole simulation period.