The most likely "three modes of operation" are probably current source input (CSI), variable voltage input (VVI), and pulse width modulation (PWM).
There are also three different types of load characteristics, constant torque, variable torque, and constant power.
The control strategies could be divided into volts per hertz control, sensorless vector control, and vector control with shaft velocity and position feedback.
PS1
Upon further consideration, I think that the "speed, torque, position" is probably the appropriate answer to this question. However speed, torque and position control is generally provided by different types of drives rather than three modes of operating one type of drive. Variable speed drives are generally used mostly for speed control, occasionally for torque control, rarely for relative position control and very rarely if ever for absolute position control. Servo drives or motion control drives are used primarily for absolute position control.
The four quadrants of operating speed vs torque are an important aspect of drive operation, but don't seem to fit the question. Electric drives mostly operate in the first quadrant, positive speed and torque, forward motoring. The other quadrants (numbering optional) are negative speed and positive torque: reverse motoring, positive speed and negative torque: forward braking, and negative speed and torque: reverse braking. The motor is always acting as a generator when braking. The generated braking energy is either dissipated in resistors, dynamic braking or returned to the source, regenerative braking.
these are 4 modes of operation of electrical drives these are 1) Motoring 2) forward breaking 3) reverse blocking 4) generating mode
most of the electrical drives are works in two modes they are 1.motoring
1.a. forward motoring
b. reverse motoring
2.breaking
A. forward breaking
B.reverse breaking
3rd mode is depending up on the application (motor used in the drive )that is generator mode
( while breaking of the motor, the motor supplies power back to the system )
Position control, speed control, torque control. For some drives the control method may intentionally change during operation.
