Abstract: A control system for automatically controlling the coefficient of excitation of a DC machine comprises, in general, generator means for generating a pulse signal having a predetermined frequency and pulse width. Demand signal means are utilized for producing an electrical demand signal corresponding to the demand on the DC machine. Armature current sensing means are coupled to the armature winding for producing an electrical drive signal corresponding to the armature current in the DC machine. Control circuit means are coupled to the generator means and are responsive to the demand signal and the drive signal for adjusting the pulse width of the pulse signal.

Abstract: A DC-to-AC inverter is disclosed utilizing a clock oscillator and an amplifying circuit for delivering AC power at a relatively high output level. A protection circuit is provided to sense potentially damaging transient signals, isolate them from the amplifier circuitry, and return most of the power of the transient signals to the DC supply to both conserve power and protect the solid state circuitry. The output transistors are biased such that, as the collector current approaches a predetermined maximum current level, the base-emitter bias voltage of the transistor approaches the maximum amplitude of the applied base drive signal, to limit the collector current which in turn limits the AC output current of the inverter under short circuit conditions. An amplitude sensing circuit measures the output level of the inverter and disables the inverter whenever the AC output or the DC supply voltage goes below a predetermined level.