The occurrence of bifurcation due to nonlinear nature of a dc series motor makes its speed control always challenging. This study therefore proposes a novel method for controlling the bifurcation of nominal period one speed response in a single-phase PWM controlled semi-converter fed dc series motor drive when the system is subjected to variable load torque condition. The basic idea for avoiding bifurcation of period one speed response includes investigation for the attributes of a periodic signal that should be incorporated in feedback circuit of the motor drive. This external periodic signal is necessary for manipulating the state transition matrix that represents the nominal period one behavior of the system to make all Eigen values inside unit circle. The proposed method can operate the motor drive with desired period-1 speed response for the entire or maximum possible range of variation in load torque. Numerical simulations and experimental results on a 1 2 hp dc series motor confirm the proposed technique for avoiding the occurrence of bifurcation.