Abstract: Chiller operating efficiency is optimized by controlling the system to maintain the condenser liquid refrigerant level at a value which will minimize or prevent gas bypass to the evaporator. This is accomplished by sensing the level of liquid refrigerant in the condensor and incorporating fuzzy logic to properly position a multi-position valve which can variably restrict the flow of this liquid into the evaporator, according to this sensed parameter. The fuzzy logic utilizes as inputs both the level error from a set point level and the rate of change of the sensed level. Each of these inputs are combined by fuzzy logic techniques to provide the required output signal to control the opening and closing of the valve.

Abstract: When a-c power line voltage is rectified by a phase-controlled SCR rectifier bridge to develop an adjustable d-c bus voltage which is then converted by an inverter back to a-c for driving a load, such as a motor, line voltage disturbances, resulting from momentary power outages or major power reductions, will have a deleterious effect on the operation of the inverter system. Such disturbances will cause improper firing of the SCR's and the d-c bus voltage may increase considerably, disrupting the normal operation of the inverter system and possibly destroying the switching devices in the inverter. Immunization against the effects of the line voltage disturbances is obtained by shutting down or disabling the phase-controlled SCR rectifier bridge anytime such a disturbance occurs.