Stroke control apparatus of reciprocating compressor and method thereof

1. A stroke control apparatus of a reciprocating compressor, comprising:

a reciprocating compressor;

a current detecting unit for detecting a current applied to a motor of the reciprocating compressor;

a stroke detecting unit for detecting a piston stroke by using the current applied to the motor of the reciprocating compressor;

a phase difference detecting unit for detecting a phase difference between the piston stroke from the stroke detecting unit and the current from the current detecting unit;

an operational frequency determining unit for determining an operational frequency corresponding to an operation region according to the detected phase difference;

a frequency/stroke storing unit for storing a piston stroke value based on the determined operational frequency;

a reference stroke value determining unit for determining a reference stroke value corresponding to the determined operational frequency by using the stroke value pre-stored in the frequency/stroke storing unit;

a control unit for comparing the reference stroke value with a present piston stroke value after a certain time point and outputting a stroke control signal according to the comparison result; and

an inverter for varying an operational frequency and a voltage applied to the motor of the reciprocating compressor according to the stroke control signal of the control unit.

2. The apparatus of claim 1 , wherein the operational frequency determining unit includes:

an operation region storing unit for storing the detected phase difference between the current and the piston stroke within a high efficiency operation region;

a comparator for comparing the phase difference detected in the phase difference detecting unit with a phase difference within the operation region; and

an operational frequency determiner for adding/subtracting the operational frequency when the phase difference gets out of the operation region due to a load variation and outputting it.

3. The apparatus of claim 2 , wherein the operational frequency determiner determines the operational frequency at a certain time point as an operational frequency when the operational frequency at the certain time point places within the operation region by adding/subtracting a reference operational frequency in an early operation of the reciprocating compressor by a certain frequency units.

4. The apparatus of claim 2 , wherein the operational frequency determiner increases the operational frequency when the phase difference is greater than an upper limit of the operation region.

5. The apparatus of claim 2 , wherein the operational frequency determiner decreases the operational frequency when a the phase difference between the current and the piston stroke is smaller than a lower limit of the operation region.

6. The apparatus of claim 1 , wherein the inverter can vary a motor input voltage and a frequency.

7. The apparatus of claim 1 , wherein the inverter is a single-phase inverter varying a DC voltage into a single-phase AC voltage.

8. A stroke control method of a reciprocating compressor, comprising:

detecting a load variation while a reciprocating compressor operates with a reference operational frequency;

detecting an operational frequency in an operation region by varying an operational frequency when the load variation is detected;

storing a stroke value corresponding to each operational frequency; and

performing a stroke control according to a reference stroke value after determining the reference stroke value corresponding to the operational frequency in a high efficiency operation region.

9. A stroke control method of a reciprocating compressor, comprising:

detecting a load variation while a reciprocating compressor operates with a reference operational frequency;

detecting an operational frequency in an operation region by increasing or decreasing an operational frequency when the load variation is detected; and

performing a stroke control according to a reference stroke value after determining the reference stroke value corresponding to the operational frequency in a high efficiency operation region; and

detecting a phase difference placed in a high efficiency operation region and storing it.

10. A stroke control method of a reciprocating compressor, comprising:

detecting a load variation while a reciprocating compressor operates with a reference operational frequency;

detecting an operational frequency in an operation region by increasing or decreasing an operational frequency when the load variation is detected; and

performing a stroke control according to a reference stroke value after determining the reference stroke value corresponding to the operational frequency in a high efficiency operation region; wherein the load variation is detected by checking whether a phase difference between a motor current and a stroke is placed within the high efficiency operation region.

11. A stroke control method of a reciprocating compressor, comprising:

detecting a load variation while a reciprocating compressor operates with a reference operational frequency;

detecting an operational frequency in an operation region by increasing or decreasing an operational frequency when the load variation is detected; wherein the operational frequency detecting step includes the sub-steps of:

increasing the operational frequency when a phase difference between the current and the stroke is greater than an upper limit of the operation region;

decreasing the operational frequency when a phase difference between the current and the stroke is smaller than a lower limit of the operation region; and

determining an operational frequency by judging whether the increased/decreased operational frequency places within the operation region; and

performing a stroke control according to a reference stroke value after determining the reference stroke value corresponding to the operational frequency in a high efficiency operation region.

12. A stroke control method of a reciprocating compressor, comprising:

detecting an inflection point of a phase difference between a piston stroke and a motor current by increasing or decreasing a reference stroke value;

detecting a load variation after setting a piston stroke at the inflection point of the phase difference between the piston stroke and the motor current as a reference stroke value;

increasing or decreasing the reference operational frequency and decreasing the reference stroke value as a certain value when the load variation is detected and returning to the inflection point detecting step; and

controlling a stroke of the piston according to the set reference stroke value when the load variation is not detected.

13. The method of claim 12 , wherein the certain value is set through experiments so as to detect an inflection point of the phase difference between the piston stroke and the current easily.

14. The method of claim 12 , wherein the returning step includes the sub-steps of:

increasing the operational frequency when an inflection point of the phase difference between the piston stroke and the current is greater than an upper limit of a high efficiency operation region; and

decreasing the operational frequency when a phase difference between the current and the stroke is smaller than a lower limit of the operation region.

15. The method of claim 12 , wherein the load variation is detected by using a phase difference between the motor stroke and the motor current.

16. A stroke control method of a reciprocating compressor, comprising:

determining a phase variation placed in a high efficiency operation region and storing phase difference value;

decreasing an input of a compressor when there is no phase variation due to a load variation and an early piston stroke is greater than a reference stroke value after a certain point in time; and

increasing the input of the compressor when there is no phase variation due to the load variation and the early piston stroke is smaller than the reference stroke value after the certain point in time.

17. The method of claim 16 , wherein the load variation is detected by using the phase difference value between a motor stroke and a motor current.