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Recently, the parallel speed control of two induction motors, which uses only one inverter, has been proposed by the vector control method. However, the conventional control method does not consider both the efficiency of the motor control and the condition of different load torque to each induction motor (IM). This paper proposes a new high efficient parallel speed control method of two induction motors on condition of different load torque, which is based on non-linear programming method. The non-linear programming method requires the information on load torque and speed reference. Each load torque is estimated by disturbance observer and current simulator. The IM drive system requests only speed sensor such as rotary encoder. Hence, it has no current sensor and no voltage sensor. Moreover, this paper discusses the condition of low-resolution rotary encoder, such as 60pulse/rev. The numerical simulation results point out that both induction motors keep the nearly same speed control performance with high efficiency in steady state and the transient state on condition of different load torque.