where K is a gain factor for each inverter, E, is the input voltage and 0 is the phase- shift between two inverters. Equation (3.1) indicates that the output voltage of a DC/AC inverter system, such as shown in Fig. 3(a), can be controlled by varying the phase-shift between the two inverters. This technique provides an excellent closed loop control of output voltage against any variation in input DC voltage (E,) and output load [4], Another advantage of this scheme is that the non-self-turn-off power semi-conductor devices such as Silicon Controlled Rectifiers (SCR) can be employed in the design of the inverter system. These devices have moderate of forward conduction losses (forward voltage drop approximately 1.5 V for a 600 V and 100 A device) and require negligible power to drive their gates. Therefore, the use of these devices simplifies the gate circuit and cooling requirements of the inverter system which can greatly be appreciated at high power levels. The main limitations of this scheme arise due to unequal current sharing between the two inverters. The unequal current sharing phenomenon is briefly explained in the following: Consider that the inverter system of Fig. 3 is supplying power to a resistive load and both the inverters are operating with a phase shift 0 to keep the output voltage constant. Figure 3(c) illustrates the current and voltage phasors of the inverter system under these operating conditions. Since the load is a resistance, the output current Zo is in phase with out voltage Vo. As
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