A generalized firing angle controller using a phase-locked loop, for control of thyristors is described. Different types of firing angle variation characteristics are possible because of the generalized phase detector used in the circuit. The controller can operate over a wide range of supply frequencies and is immune to the transients and harmonic distortions in the supply voltage. Also changes in the supply voltage amplitude do not have any effect on the firing angle. The same circuit can be used to provide firing pulses for three- or six-element thyristor configurations. The scheme can be successfully used for thyristor converters and cycloconverters.

A method to stabilize a phase-locked loop (PLL) dc motor control system is described. Integral square error (ISE) criterion is used to find out the constants of the stabilizing circuit for giving an optimum response. Transient response of the system is calculated for a sudden loading condition and changes in reference frequency. Experimental oscillograms are also included.

A novel analog-type phase locked loop (PLL) control scheme for a separately excited dc motor is described. The steady-state analysis has been carried out to study the variation of phase angle difference between the reference and feedback signals, under no-load and load conditions. The effect of moment of inertia, amplifier gain, and differentiator time constant on stability of the system has been examined using the parameter plane method. Experimental results pertaining to a fabricated PLL controlled 5-hp dc motor are given.