Single-phase thyristor full converter and semi been made in the present paper and all the possible modes of converter fed dc drives with phase angle control scheme have operation and the sub-cases therein have been identified and been analysed under all possible modes of operation of continuous the corresponding expressions for the various performance and discontinuous armature current conduction. For each case, factors derived for both thyristor full converter and semi expressions for the various performance quantities have been v presented comprehensively. All the cases have been simulated converter. using power system block set tool box in MATLAB and the III. MODES OF OPERATION simulation results are found to be same as those obtained from the derived expressions. Results obtained on a 220 V, 5 hp separatelyIn the analysis of these converters, we have duty interval(s) excited dc motor operating under all modes of operation, were in which the ac source is connected to the load through a set of also in agreement with simulated / calculated values. thyristors. Depending on the armature circuit inductance, armature current and speed setting there may be a zero current I. NOMENCLATURE interval also. In addition, in the semi converter there could be a free-wheeling interval in which load current flows only E motor back emf, V through the devices and the source current is zero. Based on io : instantaneous armature current ( load current ), A these, the various modes identified are classified in Table 1. is : instantaneous ac supply current, A fundamental component of rms ac supply current, A I : rms ac supply current, A In any mode of operation, considering one-half cycle i.e., Kb back emf constant, volts/rad/sec starting from the instant of firing of one set of devices to the La motor armature circuit inductance, H instant of firing of the other set of devices, the input and output Ra motor armature circuit resistance, Q voltage and current equations of the converter circuits are: Vm maximum value of the ac supply voltage, V VS : instantaneous ac supply voltage, V Duty interval (is = io) vO : instantaneous converter dc output voltage, V VO = vs = Vm Sin o)t (1) V0 average converter dc output voltage, V Raio +La(dio/dt)+E Vs (2) Z motor impedance, Q oc : firing angle, deg Free-wheeling interval (is = 0): P : extinction angle, deg vO= 0 (3) O instant at which the instantaneous supply voltage is Ra io + La (dio / dt) + E = 0 (4) equal to the motor back emf, deg X : angle at which conduction starts, deg Zero current interval (is = = 0) 0) :rotor speed in rad/sec vO = E (5)