Multi-motor-driven loads can be found in a wide range of
applications in industry such as conveyor belts for
transportation of raw material, mill motors used in iron and
pulp and paper industries, mining drills, etc. The term “load
sharing” is commonly used when describing such systems
wherein typically a number of mechanically-coupled
induction motors (IMs) are fed by corresponding variable
frequency drives (VFDs) as shown in Figs. 1(a) and (b) [1].
These VFDs range from the more advanced and expensive
vector-controlled schemes, wherein the torque control may
be achieved practically instantaneously, to the conventional
Volts-per-Hertz (V/F) control which relies on steady-state
analysis and is often used along with a closed-loop speed
regulator as shown in Fig. 1(c). The former is advantageous
because it is capable of both speed and torque control and
can implement load sharing schemes such as torque follower
or trim control [1]. Nevertheless, the latter is
widely used in many industrial applications mainly because
of simplicity and low cost.
The properties of a load sharing system also depend on
the type of coupling used between the motors [2].The focus
in this paper is on the cases that the load sharing is carried