Gas compressor

A gas compressor, comprising:

• a compressor main body that compresses gas;
• a motor that drives and rotates the compressor main body;
• an inverter that changes a rotational speed of the motor;
• a check valve that is arranged downstream of the compressor main body;
• air release means that releases the compressed gas upstream of the check valve;
• pressure detection means that detects a load-side pressure downstream of the check valve;
• and
• a controller that controls an output frequency from the inverter according to the pressure detected by the pressure detection means, wherein
• the controller is configured to operate the motor with the air release means closed at a first inverter output frequency and a second, higher inverter output frequency by selecting one of the first and second inverter output frequencies in response a relationship between the load-side pressure and a target pressure,
• wherein the controller is configured to open the air release means and to operate the motor at a minimum inverter output frequency in response to the load-side pressure reaching an upper limit pressure,
• wherein if a resonant frequency is between the minimum inverter output frequency and a lower limit frequency, the controller is configured to operate the motor by switching between the minimum inverter output frequency and the lower limit frequency in response to the load-side pressure reaching an unloaded operation target pressure or an unloaded operation threshold pressure that is higher than the unloaded operation target pressure, and
• wherein if the resonant frequency is not between the minimum inverter output frequency and the lower limit frequency, the controller is configured to operate the motor by switching between the minimum inverter output frequency and the lower limit frequency in response to the load-side pressure reaching the unloaded operation target pressure.