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4 Air Compressor Control
The AirSmart G2 Controller has been successfully implemented in a wide variety of compressor types
within the Gardener Denver product line from large variable speed, multi-stage, rotary screw
compressors to small fixed speed models. Each type of machine requires a certain amount of complexity
for control and the AirSmart Controller can employ everything from PID control loops with specialized I/O
down to simple binary (on/off) control. The following paragraphs present a brief description of how the
AirSmart G2 Controller regulates pressure depending on machine type.
4.1 Variable Speed Compressors
A variable speed compressor employs a Variable Frequency Drive (VFD) to regulate the airflow by
speeding up or slowing down the main motor which is directly connected to the airend. The Gardner
Denver VS and VST line of compressors are variable speed machines. The
Target Pressure
setting is
used to generate a difference value (error value) when compared to the package discharge or
Plant
Pressure
signal. The
Target Pressure
setting is compared to the air storage receiver or
System
Pressure
signal on units that are being run in Sequence mode of operation. The error value is fed into
a PID (Proportional, Integral and Derivative) algorithm in the AirSmart G2 Controller which produces an
appropriate command for the VFD to change the speed of the main motor thereby increasing or
decreasing the pressure so that the
Plant Pressure
value will match the
Target Pressure
value. In a
two-stage, variable speed compressor, a second PID algorithm is used to match the power output from
the second stage VFD to that of the first stage VFD. PID control algorithms require tuning in order to
function correctly without losing control of the machine. The PID algorithms in the AirSmart G2
Controller were carefully tuned for each compressor model during the product development process
and do not require any further adjustment by the end user.
During normal operation, as the demand for air increases, the speed of the compressor will also
increase to meet the demand. When the speed of the compressor reaches the set maximum value for
the given
Target Pressure
setting, it will not increase any further. As the demand for air decreases, the
speed of the compressor will decrease down to the set minimum value for the given
Target Pressure
setting. If the demand for air continues to decrease, the
Plant Pressure
value will increase until it
reaches the
Unload Pressure
value programmed into the AirSmart G2 Controller, at this time the
compressor will unload and the main motor will stop. The compressor will start again when
Plant
Pressure
falls below the
Load Pressure
setting. The minimum and maximum motor speeds are fixed
in the controller for each compressor model to ensure that the motor and VFD current limits are not
exceeded at any given
Target Pressure
setting.
Содержание AIRSMART
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