System and method of operation of multiple screw compressors with continuously variable speed to provide noise cancellation

A system for attenuating noise in at least two positive displacement compressors proximately located from each other for use with at least one heating or cooling system comprising:

• at least two positive displacement compressors, the at least two compressors including a reference compressor, the at least two compressors having a selectably controllable rotational speed and a selectably controllable phase of operation;
• and
• a control circuit for controlling a rotational speed and a phase of operation of each of the at least two compressors, the control circuit including:
• a first phase-lock loop circuit associated with a reference compressor;
• a second phase-lock loop circuit associated with a second compressor;
• the second phase-lock loop circuit being interconnected with the first phase-lock loop circuit in a closed feedback loop;
• wherein the first phase-lock loop circuit is configured to detect a difference between a phase of a pressure pulse waveform generated by the reference compressor and a phase of a pressure pulse waveform generated by the second compressor, and to generate an error signal proportional to a detected difference in phase between the pressure pulse waveforms;
• and
• a controller configured to process the error signal for input to a speed controller connected to the second compressor, to control the rotational speed and phase of operation of the second compressor, to control the rotational speed of the second compressor at substantially the same rotational speed as the reference compressor, and to shift the phase of operation of the second compressor so that an outlet pressure pulse operatively produced by the second compressor is substantially evenly spaced between successive outlet pulses operatively produced by the reference compressor.

A circuit for controlling a rotational speed and a phase of operation of each of a plurality of positive displacement compressors, comprising:

• a first phase-lock loop circuit associated with a reference compressor, the first phase-lock loop circuit having a phase detector circuit, the phase detector circuit including a first input for connecting to a reference compressor discharge pressure sensor to receive a reference compressor pulsation signal, a reference input connected in a closed feedback loop, and an output;
• the first phase-lock loop circuit output connected to an oscillator through a filter, and a divider circuit connected to the oscillator, first phase-lock loop circuit configured to synchronize the first input with the reference input and to generate a timing signal;
• a delay circuit driven by the timing signal, the delay circuit being configured to generate at least one reference signal, each reference signal being phase-delayed in a predetermined increment based on the timing signal;
• at least one lagging phase-lock loop circuit, each lagging phase-lock loop circuit associated with a lag compressor that is mechanically interconnected with the reference compressor, each lagging phase-lock loop circuit including a first input connected to one of the phase-delayed reference signals, a second input connected to a lag compressor discharge pressure sensor to receive a pulsation signal of the associated lag compressor and an output filter circuit:
• wherein each lagging phase-lock loop circuit is configured to generate a speed control signal to the associated lag compressor to shift a phase of a pressure pulse of the lag compressor, to interleave the reference compressor and each lag compressor pressure pulsations, thereby increasing a frequency of an aggregate pressure pulsation of the mechanically interconnected reference and lag compressors.