Abstract:
The present invention provides a control method and a control apparatus of an inverter compressor in which when a trip occurs immediately after the inverter is started, retry can be performed in a short period of time with restart being performed in accordance with the detected conditions after the retry waiting times which are different from each other elapse. There are provided two or more kinds of retry waiting times, and the retry waiting time immediately after starting is made shorter than the others.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to retry control (restart control) when an inverter trip of an inverter compressor occurs. 
     As an example of an inverter compressor, there is an inverter oil-cooled screw compressor. The oil-cooled screw compressor supplies a lubricant to a screw unit of the compressor. However, when the compressor stops, some of the lubricant remains inside a main body of the compressor. Therefore, when the compressor is started at a low temperature lower than, for example, the lower limit of a predetermined temperature, the viscosity of the lubricant which remains inside the main body of the compressor is increased so as to generate an excessive torque caused by compression of the lubricant immediately after the starting, thereby generating overcurrent to cause a trip in the inverter in some cases. Further, even in an oil-free compressor, the viscosity of a lubricant which remains in a bearing unit is increased when a main body of the compressor is started, which possibly causes generation of an excessive torque and an overcurrent trip of the inverter at the time of starting. Especially, a high-efficiency synchronous motor as a driving motor shows this tendency due to a small starting torque. As a related art of such retry control when the inverter trip occurs, is represented by Japanese Patent No. 3255213, titled “CONTROL METHOD FOR PACKAGE TYPE SCREW COMPRESSOR AND CONTROL DEVICE”. 
     SUMMARY OF THE INVENTION 
     In the above-described related art, when the inverter trip occurs, retry control (restart control) is performed after an internal pressure (a pressure on the discharge side of the main body of the compressor) of a separator  6  is lowered to a pressure (a pressure where the staring torque becomes sufficiently small) where the main body of the compressor can be restarted. 
     Further, when the compressor stops due to occurrence of the trip in the oil-cooled screw compressor, the air mixed with the lubricant in the separator rises to an upper surface of the lubricant inside the separator while expanding along with lowering of the internal pressure of the separator to generate a bubbling phenomenon. When the bubbling phenomenon is excessively generated, there is a trouble such as lacking of the lubricant at the time of starting due to consumption of the lubricant caused by the bubbling phenomenon. Thus, it takes a long time, for example, about 10 to 30 seconds, to lower the internal pressure of the separator to almost the atmosphere pressure. Therefore, as a retry waiting time, the same time period is needed. In an example of the above-describe related art, the waiting time is set to 20 seconds. 
     In the meantime, in the case where the trip occurs immediately after the inverter is started, the pressure on the discharge side of the main body of the compressor hardly rises from the pressure where the compressor waits before starting, and it is not necessary to lower the pressure on the discharge side of the compressor. Thus, the compressor can be immediately restarted. However, since the retry waiting time is uniformly set to 10 to 30 seconds from the viewpoint of suppressing the bubbling inside the separator as described above, it is necessary to wait for a long time to retry even when the inverter trip immediately after the starting, and the pressure necessary in the compressor can not be promptly secured. 
     The present invention provides a control method of an inverter compressor and an inverter compressor in which when a trip occurs immediately after the inverter is started, retry can be performed in a short period of time. 
     In order to solve the above described problem, the present invention provides a control method of an inverter compressor in which when an inverter trip occurs, the compressor is restarted after a retry waiting time which is preliminarily set so as to lower a pressure on a discharge side of a main body of the compressor to a pressure where the main body of the compressor can be restarted elapses, wherein conditions when the inverter trip occurs are detected and restarting is performed in the retry waiting times which are different from each other in accordance with the detected conditions. 
     Further, as the above-described conditions, an operation elapsed time from the time the inverter is started to the time the trip occurs is detected, and the retry waiting time is determined in accordance with the detected operation elapsed time. 
     Further, as the above-described conditions, the rotation speed of a motor immediately before the inverter trip occurs is detected, and the retry waiting time is determined in accordance with the detected rotation speed of the motor. 
     Further, as the above-described conditions, the pressure on the discharge side of the main body of the compressor when the inverter trip occurs is detected, and the retry waiting time is determined in accordance with the detected pressure. 
     Further, at least two kinds of retry waiting times t 1  and t 2 , which are different from each other are set, and t 2 &lt;t 1  is set so that t 2  denotes the retry waiting time when the trip occurs immediately after the inverter is started and t 1  denotes the retry waiting time when the trip occurs in a normal operation of the inverter. 
     Further, the present invention provides an inverter compressor, which is restarted after a retry waiting time which is preliminarily set so as to lower a pressure on a discharge side of a main body of the compressor to a pressure, where the main body of the compressor can be restarted elapses when an inverter trip occurs, wherein there is provided a control unit that detects conditions when the inverter trip occurs and issues a restart instruction in the retry waiting times which are different from each other in accordance with the detected conditions. 
     Further, the control unit includes a detection unit that detects an operation elapsed time from the time the inverter is started to the time the trip occurs, with the retry waiting time is determined in accordance with the detected operation elapsed time. 
     Further, the control unit includes a detection unit that detects the rotation speed of a motor immediately before the inverter trip occurs, with the retry waiting time is determined in accordance with the detected rotation speed of the motor. 
     Further, the control unit includes a detection unit that detects the pressure on the discharge side of the main body of the compressor when the inverter trip occurs, with the retry waiting time is determined in accordance with the detected pressure. 
     Further, the control unit includes memories that store at least two kinds of retry waiting times t 1  and t 2 , which are different from each other, and t 2 &lt;t 1  is set where t 2  denotes the retry waiting time when the trip occurs immediately after the inverter is started and t 1  denotes the retry waiting time when the trip occurs in a normal operation of the inverter. 
     According to the present invention, a necessary retry waiting time is secured when an inverter trip occurs in a normal operation and the retry waiting time can be shortened when the inverter trip occurs immediately after the starting, so that restarting can be performed in a short time and a necessary pressure can be promptly secured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a retry control flow diagram according to a first embodiment of the present invention; 
         FIG. 2  is an operation flowchart according to the first embodiment of the present invention; 
         FIG. 3  is a time chart in the case where a trip occurs in a rated operation in the first embodiment of the present invention; and 
         FIG. 4  is a time chart in the case where the trip occurs immediately after starting the compressor in the first embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, a first embodiment of the present invention will be described. 
     First Embodiment 
       FIG. 1  is a diagram for showing a flow of an oil-cooled screw compressor. The reference numeral  1  denotes a main body of the oil-cooled screw compressor which is rotationally driven by, for example, a synchronous motor  2 . The main body  1  of the compressor which is rotationally driven sucks the air in the atmosphere through a filter  3  and a suction check valve  4  to compress the air into a predetermined pressure. Since the compressed air in the main body  1  of the compressor contains a lubricant, the compressed air is substantially separated from the lubricant by an oil separator  5 , and then is discharged to an external load of a package  8  through a check valve  6  and a compressed-air heat exchanger  7 . On the other hand, the lubricant which is separated from the compressed air by the oil separator  5  is fed to the main body  1  of the compressor again after the temperature of the lubricant is automatically adjusted through a lubricant temperature adjusting valve  9  and a lubricant heat exchanger  10 . 
     A control unit  12  issues an operation instruction to an inverter  13  so as to operate the motor  2 , and controls the rotation speed of the motor  2  in accordance with the pressure which is detected by a pressure detection unit  11  to be discharged to the external load. The reference numeral  14  denotes a discharge valve which is opened or closed by the control unit  12  and through which the pressure on the discharge side  15  of the compressor is discharged. The discharge valve  14  is opened at the same time when an inverter trip occurs, and is closed at the same time when an inverter retry waiting time elapses. 
     The control unit  12  includes a detection unit  12   a  which detects an operation elapsed time from the time the inverter  13  is started to the time the trip occurs, and memories  12   b  and  12   c  which stores t 1  and t 2  of the inverter retry waiting times, respectively. The both waiting times satisfy the relation of t 1 &gt;t 2 . In addition, an operation logic shown in  FIG. 2  is incorporated into the control unit  12 . In  FIG. 2 , tm denotes the operation elapsed time from the time the inverter  13  is started to the time the trip occurs, t 3  denotes a preliminarily-set standard elapsed time which corresponds to an elapsed time for example, about 1 second) from the time the inverter  13  is started to the time immediately after the inverter  13  is started, and tr denotes a retry waiting time. 
     Next, there will be described a retry control (restart control) operation after the inverter causes the trip. When the inverter being operated causes the trip, the detection unit  12   a  of the control unit  12  detects the operation elapsed time tm until the occurrence of the trip in S 101  of  FIG. 2 . The time tm is detected as an elapsed time from the time the inverter is started to the time the trip occurs. At the same time, the discharge valve  14  is opened with an instruction of the control unit  12 , and the pressure of the oil separator  5  begins to be lowered. 
     Next, the operation elapsed time tm and the standard elapsed time t 3  are compared to each other in S 102 . In the case where the comparison result shows tm≧t 3 , the time t 1  in the memory  12   b  is selected as the retry waiting time tr in S 103  to wait during the time t 1  in a state where the inverter is stopped after the occurrence of the trip. Then, after the time t 1  elapses, the discharge valve  14  is closed in S 105 , and the inverter is retried. The time tm at this Lime exceeds the time (standard elapsed time) immediately after the inverter  13  is started, and the compressor is in a rated operation or is operated at a level where the compressor is started up towards the rated operation, so that the internal pressure on the discharge side is increased. 
     The time t 1  is set to a time (for example, 10 to 30 seconds) during which the internal pressure of the oil separator  5  is discharged through the discharge valve  14  so that the internal pressure is lowered to a pressure where the inverter can restarted within the retry waiting time. Accordingly, if the inverter is retried after the time t 1  elapses, the motor is reliably started and the compressor is driven. 
     In the case where tm&lt;t 3  is satisfied in S 102 , the time t 2  in the memory  12   c  is selected as the retry waiting time tr in S 104  to wait during the time t 2  in a state where the inverter is stopped after the occurrence of the trip. Then, after the time t 2  elapses, the inverter is retried in S 105 . Since the time tin at this time corresponds to the time immediately after the inverter  13  is started, the compressor is hardly operated, and the pressure (the pressure of the oil separator  5 ) on the discharge side of the main body of the compressor hardly rises from the pressure before the starting. The time t 2  is set to a sufficiently short waiting time (for example, 5 seconds) because it is not necessary to lower the pressure of the oil separator  5 . Accordingly, if the inverter is retried in a short time after the occurrence of the trip, it is possible to reliably start the motor. 
       FIG. 3  is a time chart for showing a retry operation when an output current value is rapidly increased and the trip occurs in the state of tm≧t 3  during the operation of the inverter  13  in a normal state. Since the operation elapsed time tm from the time the inverter is started (the time the operation instruction is generated) to the time the trip occurs exceeds the standard elapsed time t 3 , t 1  is selected as the retry waiting time tr in accordance with S 102  and S 103  of the flowchart shown in  FIG. 2 . The pressure of the oil separator reaches a rated pressure PS at the time the trip occurs and a torque (load) at the time of restarting is too large due to the pressure PS in this state. Accordingly, if the inverter is retried, the motor can not be restarted. 
     After the trip occurs, the operation instruction from the inverter  13  is stopped, and the compressor waits during the time t 1  in a stopped state, so that the discharge valve  14  is opened. The discharge valve  14  is opened during the time t 1 , the pressure of the oil separator is lowered to a pressure where the synchronous motor  2  can be restarted, and the pressure becomes almost 0 in  FIG. 3 . In this state, the synchronous motor  2  is stopped in an in-phase state caused by pull-in operation of a magnetic. After the time t 1  elapses from the occurrence of the trip (after tm+t 1  elapses from the starting), the discharge valve  14  is closed and a control instruction of retry is issued by the control unit  12 , so that reoperation instruction is issued from the inverter  13 . The synchronous motor is restarted without failure to drive the motor, and along with this, the pressure of the oil separator  5  rises again. 
       FIG. 4  is a time chart for showing a retry operation when an output current value is rapidly increased immediately after the inverter  13  is started and an overcurrent trip occurs in the state of tm&lt;t 3 . Since the operation elapsed time tm from the time the inverter is started to the time the trip occurs does not exceed the standard elapsed time t 3 , t 2  is selected as the retry waiting time in accordance with S 102  and S 103  of the flowchart shown in  FIG. 2 . Since the time tm at this time corresponds to the time immediately after the inverter  13  is started, the pressure of the oil separator  5  hardly rises from the pressure where the inverter waits before the starting. Accordingly, a torque at the time of restarting is extremely small. After the trip occurs, a control instruction of retry is issued by the control unit  12  after the short retry waiting time t 2  selected elapses, and a reoperation instruction is issued from the inverter  13 . The motor  2  is restarted without failure to drive the compressor, and along with this, the pressure of the oil separator  5  rises again. 
     In the embodiment, the retry waiting time tr is set to two kinds (t 1  and t 2 ), and t 1  and t 2  are associated with two kinds of large and small operation elapsed times tm before and after the standard elapsed time t 3 . However, the setting values of the retry waiting time may be increased to more than two kinds. In this case, the kind of the standard elapsed time t 3  may be increased in accordance with the setting values of the retry waiting time. As described above, if the kinds of the setting values of the retry waiting time are increased, the retry control can be performed after the more-detailed retry waiting time elapses, so that the restarting can be performed in a shorter time after the trip which occurs at various timings. 
     Further, in the first embodiment, the retry waiting time tr is selected based on the operation elapsed time tm from the time the operation instruction is issued (the inverter is started) to the time the inverter trip occurs. However, since the operation elapsed time tm is in proportion to the rotation speed of the motor and the pressure in the oil separator  5  immediately before the occurrence of the trip, the retry waiting time tr may be selected based on the rotation speed (nm) and the pressure (pm) in the oil separator  5 . 
     Second Embodiment 
     In the case where the rotation speed nm of the motor is based as a second embodiment, a standard rotation speed n 3  corresponding to the standard elapsed time t 3  in the first embodiment is set. When the trip occurs after the motor is started, the rotation speed nm of the motor as well as the trip of the inverter is detected in S 101  of  FIG. 2 , and the detected rotation speed nm of the motor and the standard rotation speed n 3  are compared to each other in the next S 102 . In the case where the comparison result shows nm≧n 3 , t 1  is selected as the retry waiting time tr in S 103 . In the case where the comparison result shows nm&lt;n 3 , t 2  is selected as the retry waiting time tr in S 103 . The operation steps thereafter are the same as those in the first embodiment. 
     In the embodiment, the rotation speed nm of the motor is detected by the detection unit  12   a  while retrieving an instruction frequency issued from the inverter  13  to the motor  2  into the control unit  12 . Accordingly, it is not necessary to include a rotation sensor or the like in the motor. Further, in the embodiment, the rotation speed nm of the motor is based. However, the torque of the compressor and the rotation speed of the motor which are necessary to determine whether or not to restart are preliminarily recognized, so that the retry control can be executed only by setting the standard rotation speed n 3  without trying. 
     Third Embodiment 
     In the case where the pressure pm in the oil separator  5  is used for a base as a third embodiment, a standard pressure p 3  corresponding to the standard elapsed time t 3  in the first embodiment is set. When the trip occurs after the motor is started, the pressure pm in the oil separator  5  as well as the trip of the inverter is detected in S 101  of  FIG. 2 , and the detected pressure pm and the standard pressure p 3  are compared to each other in the next S 102 . In the case where the comparison result shows pm≧p 3 , t 1  is selected as the retry waiting time tr in S 103 . In the case where the comparison result shows pm&lt;p 3 , t 2  is selected as the retry waiting time tr in S 103 . The operation steps thereafter are the same as those in the first embodiment. 
     In the embodiment, the pressure pm in the oil separator  5  is output from a pressure sensor  5   a  installed therein and is detected by the detection unit  12   a  while being retrieved into the control unit  12 . Further, in the embodiment, the pressure pm in the oil separator  5  is used for a base. However, the pressure on the discharge side of the compressor which can be restarted is preliminarily recognized, so that the retry control can be executed only by setting the pressure as the standard pressure p 3  without trying. Furthermore, if the retry control is performed after waiting until the pressure in the oil separator  5  is lowered to a pressure where the compressor can be restarted without using the retry waiting time, the retry control in accordance with the actual condition can be performed, so that it is possible to control without an unnecessary waiting time.