You appear to have two questions.
Can 3-phase FOC control be done without current measurement?
No; The point of field orientated control is to ... control the field in the electrical machine. This relies on knowing what the field is
Can a FOC control scheme be done using a rotary encoder to measure the
position, speed and acceleration directly, or is measuring current
necessary?
Well, Field orientated control relies on knowing where the rotor is so that correctly phase aligned currents can be synthesised.
A rotary encoder (resolver, analogue hall effect sensing etc...) can be used to measure the instantaneous position & thus derive speed and acceleration. The existence of position sensing is to complement current sensing.
Sensorless control would remove the need for a rotary encoder, although the workable schemes end up using voltage sensing so "sensorless" is a bit misleading.
Torque control of the generator works by changing the electrical load felt by the generator. The grid-side converter is adjusted to supply whatever power to the grid will result in the desired generator driving torque. The generator driving torque is determined by measuring current, voltage, frequency and phase angle of the power transferred from the generator to the machine-side converter. Using a mathematical model of the PMSG, the generator torque and speed can be calculated from the measured operating data.
The desired torque, the torque required for the maximum power that can be produced at a given wind speed, is calculated from the wind turbine characteristics and the wind speed. In one of the papers cited, the turbine pitch angle is also set by the machine control system.
The system could not control the counter torque down to zero, because the turbine must produce enough power to supply the losses in the system before there is any power available to transfer to the grid. However, the system can probably control the system quite well over the torque range that is useful for turbine operation.
Torque Control for Machines other than Wind Turbines
Similar control systems could be used for torque control of generators driven by machines other than wind turbines. An absorbing dynamometer might require torque control to torque and speed operating points approaching zero. The operating range of both torque and speed might be very wide. For best performance, it would be desirable to implement field oriented control with shaft torque meter and shaft speed / position encoder feedback. Such a system could hold torque against a driving force at zero speed. In that case, the losses of the absorbing machine would be supplied by the grid-side converter. Direct torque control without shaft transducers has been used to approach the performance of a systems with such transducers, but the performance has not been adequate for the most demanding applications. The PMSG may or may not be the best machine for the most demanding torque control applications.
Best Answer
Generally FOC consists of the following components,
In a direct torque control the first five components are replaced by two hysteresis comparators and a selection table.The direct torque control is different from vector control in such a way, that it does not control the flux through the current control, but it directly controls the flux itself. The direct torque control is also different from vector control in the sense that the reference frame here is stator flux instead of rotor flux used in vector control.The input to the direct toque controller are the torque error, error in magnitude of the stator flux space vector, and the angle of the stator flux space vector, from which the states of the power switches are determined. Based on this information, a certain voltage vector or combination of voltage vectors is directly applied to the inverter with a certain average timing. This gives the induction motor drives a very fast response.
the DTC scheme has the following features.
1.There are no current loops; hence the current is not regulated directly. 2. Coordinate transformation is not required. 3. Stator flux vector and torque estimation is required.
for more information you can refer to the book "High Performance AC Drives Modelling Analysis and Control by Mukhtar Ahmad"