AC drive system for a vehicle
An AC drive method and system enables a more efficient and robust energy transfer in vehicles. The system includes an engine and a gearbox driven by the engine, wherein the gearbox has two or more gear ratios, an AC alternator is driven by the gearbox at a variable speed to generate an AC electric current that varies in both frequency and voltage as the speed of the alternator varies, one or more AC traction motors is then powered directly by the AC electric current from the AC alternator.
1. An AC drive system for a vehicle, the AC drive system comprising:
an engine;
a gearbox driven by the engine, wherein the gearbox has two or more gear ratios;
an AC alternator driven by the gearbox at variable speeds to generate an AC electric output that varies in both frequency and voltage as the speed of the alternator varies; and
one or more AC traction motors powered directly by the AC electric output from the AC alternator.
2. The AC drive system of claim 1 , wherein the AC alternator generates a three-phase AC electric current.
3. The AC drive system of claim 2 , wherein the AC traction motors operate on the three-phase AC electric current.
4. The AC drive system of claim 2 , wherein the gearbox includes a reverse gear to effect a phase sequence change of the electric output from the alternator, thereby powering the AC traction motors in reverse.
5. The AC drive system of claim 2 , including a relay that is operable to interchange two of the three phases of the AC electric output, thereby powering the AC traction motors in reverse.
6. The AC drive system of claim 1 , wherein the gearbox is an automatic gearbox.
7. The AC drive system of claim 1 , wherein the AC alternator includes a field controller for controlling the voltage of the AC electric output.
8. The AC drive system of claim 1 , wherein the engine is a diesel or gas-fuelled reciprocating or turbine internal combustion engine.
9. The AC drive system of claim 1 , including a torque converter between the engine and the gearbox.
10. The AC drive system of claim 1 , including a resistor grid electrically connected to the terminals of the AC traction motors for dissipating energy from the AC traction motors during braking.
11. The AC drive system of claim 1 , including a regenerative braking module driven by electrical power from the AC traction motors acting as generators during braking.
12. The AC drive system as claimed in claim 11 , wherein the regenerative braking module includes a DC motor/generator connected to the gearbox.
13. The AC drive system as claimed in claim 12 , wherein the regenerative braking module includes a DC battery pack for storing electrical energy generated by the DC motor/generator during braking.
14. The AC drive system of claim 13 , wherein the DC battery pack is land based relative to the vehicle.
15. The AC drive system of claim 14 , wherein the AC drive system includes a catenary for electrically connecting the DC battery pack to the AC motor/generator or the DC motor/generator.
16. The AC drive system as claimed in claim 11 , wherein the regenerative braking module includes an AC motor/generator, an inverter, and a DC battery pack.
17. The AC drive system as claimed in claim 16 , wherein the DC battery pack is electrically connected to the AC motor/generator via the inverter.
18. A prime mover including the AC drive system of claim 1 .
19. The prime mover as claimed in claim 18 , wherein the prime mover is a locomotive.
20. The prime mover as claimed in claim 19 , wherein the AC traction motors are mechanically connected to one or more axles of a locomotive bogie to drive the axles.
21. The prime mover as claimed in claim 18 , wherein the prime mover is a heavy mining truck.
22. The prime mover of as claimed in claim 21 , wherein the AC traction motors are mechanically connected to wheels of the heavy mining truck.
23. The AC drive system of claim 1 , wherein the AC drive system includes a land-based battery off-board of the vehicle, wherein the land-based battery is electrically connected to components of the AC drive system on-board the vehicle.
24. The AC drive system of claim 23 , wherein the AC drive system further comprises a regenerative braking module to which the land-based battery electrically connects.
25. The AC drive system of claim 23 , wherein the AC drive system further comprises a catenary for electrical connection of the land-based battery with the components of the AC drive system on-board the vehicle.
26. A method of AC drive of vehicles such as trucks and locomotives, the method comprising:
driving an AC alternator at variable speed and variable torque via a multi-speed gearbox to produce an AC electric output that is variable in frequency and voltage as the speed of the alternator varies; and
powering AC traction motors with the AC electric output.
27. The method of claim 26 , further comprising operating an engine to drive an input shaft of the gearbox at required speed and torque so that an output shaft of the gearbox drives the alternator at required speed and torque.
28. The method of claim 26 , further comprising varying the field current of the AC alternator to vary the voltage of the AC electric output.