<p>This paper aims to extend an existing result on parallel operation of electric motors collectively driving a common rotational load. The objectives of parallel operation are to achieve output regulation and torque consensus. Recently, a consensus based control law has been proposed to achieve such objectives. In the existing result, it has been assumed that communication graphs for consensus are undirected, and the connectivity of the graphs has been shown to be a necessary condition for achieving torque consensus. This paper shows that the existing consensus-based law also works under directed communication graphs and the existence of a spanning tree in the graphs is necessary for achieving torque consensus. Simulation results are provided to show the performance of the consensus based parallel operation under directed communication graphs.</p>