Andress Kernick

Static inverter with neutralization of harmonics

LARGER THAN 1-KVA static inverters are beginning to receive widespread application as converters of direct current to precision 3-phase alternating current. This paper pertains to same, and Appendix I presents a specification typical of aero-space requirements.1

Controlled Current Feedback in a Static Inverter with Neutralization of Harmonics

Controlled Current Feedback Transformers (CCFT) are used to achieve optimum efficiency in a transistorized static inverter for the Apollo Command Module. Base-drive is established instantaneously as a predetermined function of collector current and of minimum beta. Techniques for steering the CCFT are incorporated in a circuit which synthesizes in one power transformer a 3-phase, stepped-voltage output of low harmonic content before filtering. A buck-boost voltage regulator is used to accomplish high performance with fewer power transistors.

The Central Inverter in a Spacecraft Power System

The central static inverter used to establish a 1250 VA, 115/200 volt, 3-phase, 400 c/s ac power distribution system for the Apollo Spacecraft Command and Service Module is one of the loads operating in parallel from the dc power distribution system. Some of the other dc loads cause transient and steady-state ripple voltages on the dc system bus of 10 c/s to 1000 c/s frequency that is critical because passive filter networks of reasonable size and weight cannot provide adequate attenuation. A static inverter is susceptible to dc input voltage ripple, and a demodulator network is required when ac output voltage modulation must be less than 1/2 percent. The various static inverter circuits which can provide the demodulation function are discussed. Particular emphasis is given to the non-dissipative approach afforded by the voltage buck-boost regulator5 type of dc link static inverter in which available and reliable components have been incorporated. A circuit model is analyzed in order to substantiate the demodulation approach and the data taken from an actual hardware inverter.

Magnetic output amplifiers for digital control

WITH THE ADVENT of power-frequency magnetic-amplifier devices for logic systems, a need has developed for 10 to 1,000 volt-ampere output magnetic amplifiers conrolled by 0.1 to 1 volt-ampere logic signals. Digital output requirements are particularly stringent because the amplifier is adapted to complete, existing lines of transducer devices (e.g., solenoid valves, power contactors, small motors, etc.) intended to operate from a power line directly or through a step-down transformer where flat (0 to 5%) voltage regulation is demanded of the amplifier, although instantaneous load variation may be as great as 20 to 1 between transient and steady-state conditions.