Method and apparatus for detecting surge in centrifugal compressors driven by electric motors

A surge detection apparatus for use in a refrigeration system having a centrifugal compressor driven by an electric motor comprising:

• means for sensing a condenser pressure;
• means for sensing an evaporator pressure;
• a first bandpass digital filter responsive to said condenser pressure and said evaporator pressure for generating a first signal representative of the rate of change of the pressure developed across the compressor;
• means for sensing a current in the electric motor driving the compressor;
• a second bandpass digital filter responsive to said motor current for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor;
• means for generating a third signal representative of a differential pressure threshold;
• means for generating a fourth signal representative of a first motor current threshold and a second motor current threshold;
• and
• computing means responsive to said first through fourth signals for indicating when a valid surge is occurring in the compressor.

A method for detecting surge in a refrigeration system having a centrifugal compressor driven by an electric motor comprising the steps of:

• sensing a condenser pressure;
• sensing an evaporator pressure;
• generating a first signal representative of the rate of change of the pressure developed across the compressor in response to the condenser pressure and the evaporator pressure;
• sensing a current in the electric motor driving the compressor;
• generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor in response to the motor current;
• generating a third signal representative of a differential pressure threshold;
• generating a fourth signal representative of a first motor current threshold and a second motor current threshold;
• and
• indicating when a valid surge is occurring in the compressor in response to the first through fourth signals.

A surge detection apparatus for detecting surge in a compressor of a compressor-driven system comprising:

• means for generating a first signal representative of the rate of change of the pressure developed across the compressor;
• means for sensing a current in an electric motor driving the compressor;
• means responsive to said motor current for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor;
• means for generating a third signal representative of a differential pressure threshold;
• means for generating a fourth signal representative of a first motor current threshold and a second motor current threshold;
• and
• means responsive to said first through fourth signals for indicating when a valid surge is occurring in the compressor.