Three phase motors and single phase motors rated at the same power and speed will give the same torque and speed as each other. (Thus the same power)
Power is (Torque*Speed/9550) so if you reduce either speed or torque the power will reduce.
So if you have a 1KW motor rated at 3000 RPM and you reduce the speed to 1000 RPM, then the power will be 333W. (assuming the torque stays the same)
You can only control the speed of an AC induction motor by varying the frequency, and this is only with a three phase motor.
A three phase motor comes Star or Delta and motors under 7.5KW are normally 220V Delta and 380-415V Star; you can use a single phase inverter and connect the motor in delta to run it from a single phase supply.