Abstract: A method of controlling a centrifugal compressor having a variable width diffuser section, the compressor being part of a chiller having a condenser and an evaporator, the method including the steps of defining the width of the diffuser which results in an optimum noise and performance level at given values of an operational parameter of the compressor, periodically sensing the operational parameter of the compressor, and periodically varying the diffuser width according to the sensed operational parameter to create a diffuser width that results in the optimum noise and performance levels at the sensed value of the operational parameter. The step of defining preferably defines the width based at least on the capacity at which the compressor is operating. The capacity is preferably determined by measuring the flow and temperature difference of the fluid passing through the evaporator. A control system for controlling the chiller system to minimize noise is also disclosed.

Abstract: Surge protection is provided for a d-c power supply, wherein rectified a-c line voltage is filtered in an LC filter having a shunt-connected filter capacitor, by inserting a limiting resistor in series with the filter capacitor during power-up to reduce the inrush current and the voltage overshoot to acceptable values. Once the power-up period is over and d-c power is fed to a load, the limiting resistor is bypassed.

Abstract: When a series string of similar circuit components, such as capacitors, are connected across a source of d-c voltage and those circuit components do not divide the applied voltage equally because of having different leakage resistances, and consequently different leakage currents, the voltage imbalance may become so great that the maximum allowable voltage or voltage rating of at least one of the circuit components may be exceeded, resulting in damage to or the destruction of that component. To limit the voltage imbalance, thereby to protect the circuit components, each of those components is shunted by a separate voltage limiting device, such as a zener diode. The threshold or breakdown voltage of each limiting device is less than the maximum acceptable voltage of the device's companion circuit component so the voltage across that component will be limited to and will never be greater than that maximum acceptable level regardless of the differences that exist in the leakage resistances.

Abstract: The control system of the invention regulates a centrifugal compressor having inlet guide vanes adjustable as one means for varying the compressor capacity. A variable speed motor is connected to drive the compressor, and provides another means for regulating the compressor capacity. The control system regulates the motor speed alone over one portion of the load variation curve, and regulates the motor speed jointly with the inlet guide vane opening over another portion of the load variation curve, to achieve the most energy-efficient operating condition while avoiding the surge condition. This optimum control path is realized by utilizing a signal which is a measure of the compressor head value. Compressor surge or instability is avoided by deriving a critical Mach number (speed indication) for any given operating condition, as a function of the compressor head and vane position, and preventing the motor speed from going below that Mach number under the specific operating conditions.

Abstract: The load currents, supplied by a three-phase AC power source to a three-phase load, are established and maintained at a preset desired level by sensing those currents and producing a feedback voltage which is compared with a reference potential. Anytime the load currents differ from the desired level the comparison produces a difference or error signal which causes an adjustment of the amplitudes of the three load currents such that they automatically return to the desired level, thereby regulating the current flow to the load. At start-up, the feedback arrangement is also effective in preventing instant current build-up to avoid sudden power surges. When the load is a three-phase motor, limiting the current flow facilitates a soft start with the motor gradually accelerating to full operating speed. Two overload protection circuits shut the system down in response to different overload or overcurrent conditions.