英文文献.pdf

Abstract A single rolling piston compressor SPRC is commonly applied to the low power room air conditioning system because of the low cost The SRPC has only one compression and discharge process per each mechanical rotation During compression process of the refrigerants the load torque is quite high On the other hand during discharge process of the refrigerant from the compressor room the load torque is low This load torque variation makes speed ripple and induce severe vibration which causes fatigue failures of pipes and compressor parts at low speed To relieve the vibration the compressor usually operates in the high speed range where the rotor and piston inertia reduce the vibration phenomenon Or a predefined feed forward load torque compensator is used at low speed to minimize the speed ripple and vibration However since the load torque variation varies depending on the temperature pressure and speed the predefined load torque table based on one operating condition is not appropriate to all In this paper an on line load torque observer for SRPC is proposed The proposed method utilizes the speed ripple as load torque ripple factor The speed ripple is transformed into frequency domain and compensates each frequency harmonic term in a feed forward way independently Experimental results are presented to verify the proposed method Index Terms load torque compensation PMSM motor rolling piston compressor I INTRODUCTION The use of inverter in appliance application has been increased dramatically The inverter increases the appliance efficiency by adjustable speed motor drive 1 4 Especially the air conditioning system is the one of the major inverter appliance application since the air conditioning system consumes much power of all power at home 3 Fig 1 shows the overall air conditioning cycle Every air conditioning system consists of compressor condenser expansion valve evaporator and two fans The compressor increases the refrigerant s pressure and temperature with electric motor support The pressed refrigerant flows from the compressor to the condenser The condenser changes the high pressure refrigerant vapor to a liquid by losing the temperature energy with fan support The liquid refrigerant flows from the condenser to the expansion valve and evaporator which removes the pressure from them so that they expand and become low temperature refrigerant vapor At the evaporator the cool air can be obtained with blower fan support 8 10 The rolling piston structure has been commonly utilized for a compressor of room air conditioning system for a long time 1 The rolling piston compressor can be classified according to the piston number The SRPC has one piston for compression process and twin has two Since the SRPC is cheaper than the twin it is commonly used for the low power room air conditioning system One of the rolling piston structure problems is the vibration The major vibration sources in the rolling piston compressor are load torque and radial force variation due to the gas compression discharge process bending vibration by unbalanced inertial of shafts and motion of internal elements such as discharge valves and vanes 1 These vibration sources are severe on the mechanical parts reliability Since the twin rolling piston compressor arranges pistons in the opposite position to countervail each other vibration effect the vibration problems are much reduced However the SRPC has severe vibration problems Except the mechanical sources the vibration effect due to the gas compression discharge process is related to the load torque variation and speed variation Hence it can be minimized by the load torque compensation technique reacting to the load torque variation Considering the compression and discharge process with rolling piston the motor s load torque has a large variation depending on the Online Load Torque Compensator for Single Rolling Piston Compressor Bon Gwan Gu1 Jun Hyuk Choi1 and In Soung Jung1 Senior Member IEEE 1 Korea electronics technology institute 203 101 Bucheon TP B D 192 Yakdae Dong Bucheon Si Gyeonggi Do R O Korea Evaporator Compressor Fan Fan Cold air Warm air Expansion Valve Refrigerant flow Cold vapor Hot vapor Condenser Refrigerant flow Warm Liquid Fig 1 Compressor cycle 8th International Conference on Power Electronics ECCE Asia May 30 June 3 2011 The Shilla Jeju Korea 978 1 61284 957 7 11 26 00 2011 IEEE WeP1 053 process When the piston compresses the refrigerants the piston room has high pressure Therefore the electrical motor load is quite high On the other hand after the discharge of the refrigerants the piston room has low pressure the electrical motor load is low This compression and discharge process makes an eccentricity load to the electric motor eventually causes vibration problem especially in low speed Fig 2 shows the load torque pattern of rolling piston compressor depending on the compression and discharge process To overcome the vibration problem of SRPC the compressor operates in high speed range where the rotor and piston inertia relieve the vibration phenomenon But this high speed operation decreases the overall system efficiency since it has to be ON OFF control to reach the demanded room temperature 2 Otherwise the predefined load torque compensator is used to minimize the speed ripple and vibration at low speed However the predefined load torque compensator is only for one operation condition which is determined by temperature pressure and speed If the operation conditions change the predefined compensator does not work well Another possible method is conventional load torque observer However since the compressor operates without position sensor the sensorless algorithms are normally has to be used The load torque observer diverges with the sensorless algorithm which has originally speed ripple and position error varying on electrical noise and the parameter variation by the saturation and measurement error In this paper we propose an online load torque compensator for SRPC with sensorless algorithm The proposed method separates each speed ripple harmonics order and compensates each term independently with injecting each harmonics compensation torque values Experimental results are presented to verify the proposed method II DESCRIPTION OF THE SPEED RIPPLE AND VIBRATION Fig 3 shows the overall system configuration r r and r denote estimated rotor speed rotor position and speed command respectively c T l T and m T are speed controller output load torque compensator output and torque command Morimoto s sensorless algorithm is used to drive the compressor PMSM 7 And the PI controller is used for the speed controller By the sensorless algorithm rotor position r and rotor speed r which are representing the load torque variation are obtained As explained in the previous section the eccentricity load which comes from compression and discharge process generates vibration and speed ripple also If the motor induce the counter torque against load torque variation the speed ripple and the vibration are reduced In the proposed method the speed ripple is used as an index of the load torque variation Since the motor speed is periodic at a steady state it is composed of constant speed and speed harmonics such that 210nthndstr 1 where 1 0 0 0 0 T tjn rnth dte T 0 T denotes the period time of spped 0 Assuming that rrt t 0 where r denotes rotor position 1 can Motor load t Exhaust valve open CompressionDischarge Exhaust port Intake port Refrigerant Rolling piston Blade Exhaust valve Fig 2 Load torque pattern of single rolling piston compressor Q1 Q2 Q3 Q4 Q5 Q6 PMSM SRPC Vdcia ib ic Sensorless Algo r r PI Torque current controller Tc PWM r r Vdc ia ib PWMVdc ia ib m Load Torque Compensator l r Fig 3 System configuration be represented in discrete equation as follow 2 0 0 r r jn r s nth e T T 2 where S T denotes one PWM period III PROPOSED LOAD TORQUE COMPENSATION METHOD Fig 4 shows the proposed online load torque compensator The proposed method regulates speed harmonics to suppress the compressor vibration With 2 the speed harmonics terms are calculated and the load torque is compensated separately The proposed method uses an on line search technique by manipulation of feed forward torque command l T 13 14 Assume that initially the feedback loop becomes active in the constant speed with initial 1 ln kT The controller increments 1 ln kT with n D as follow n DkTkT 1 lnln 3 With ln kT the new speed harmonics is compares with the old one 1 kk nthnth 4 If the speed difference is negative the incrementing is continued in the same direction until optimum ln T corresponding to the minimum nth The search will be abandoned in that direction when turns positive If initial operation starts in the constant speed operation ln T is incremented to reach the optimum point In steady state operate oscillates at the margin of n D Fig 4 shows the flowchart of the propose method IV EXPERIMENTAL RESULT Fig 5 shows the experimental setup SNW091AAW LG electronics is used as the air conditioning system To measure the vibration the compressor is installed out of the air conditioning system Fig 6 a shows a vibration measurement result of SRPC at 25Hz speed 1500rpm without any load torque compensator The measured vibration magnitude is 10 1 2 sm And the magnitude of the first order harmonics is 10 2 sm and the second order harmonics 3 2 sm Comparing with other order harmonics the first and second order harmonics are the most influential factors If the first and second vibration harmonics are reduced the overall vibration magnitude will be extremely reduced The proposed method is implanted in the same system and environment Since the 1st and 2nd order vibration harmonics magnitudes are dominant only two harmonics load torque compensators are implemented in the proposed method Fig 6 b shows the vibration measurement result of SRPC at speed 25Hz with the proposed method The measured vibration magnitude is 2 64 2 sm Comparing with Fig 3 a the overall vibration magnitude is extremely reduced Especially 1st and 2nd order harmonics are reduced more than any other order harmonics Fig 7 shows the test results a without and b with the proposed method In Fig 7 a the compressor speed and q axis current has ripple relating to the load torque variation In Fig 7 b the proposed method generates compensation torque By the compensation torque the q axis current has large ripple but the compressor speed ripple are reduced Fig 8 shows the vibration test results at speed 15 20 25 30 and 35Hz With the proposed method the vibration magnitudes are much reduced When the experiments are performed without the proposed method the vibration can be easily observed with bare eye and affects badly the compressor pipes With the proposed method the vibration cannot be observed and the noise also much is reduced Hence it can be operates at low speed without any bad influence to the pipe and compressor Fig 4 Proposed load torque compensator Fig 5 Experimental setup V CONCLUSION In this paper the online load torque compensator was proposed The proposed method utilizes the speed harmonics and compensated them independently With the proposed method the compressor can operate at low speed without pipe fatigue failure or noise problem Experimental results have shown to verify the proposed method REFERENCES 1 C M Young C C Liu and C H Liu Vibration analysis of rolling piston type compressors driven by single phase induction motor in Proc IECON2003 vol 2 pp918 923 2 T W Ching An investigation on electrical performance of variable frequency drives for air conditioning applications in Proc EPEC2008 3 H Murakami Y Honda and H Kiriyama The performance comparison of SPMSM IPMSM and SynRM in use as air conditioning compressor in Proc IAS Annual Meeting vol 2 pp 840 845 Oct 1999 a b Fig 6 Vibration test results when the compressor operates at 25Hz a without proposed load torque compensator method total vibration 10 1 b with proposed load torque compensation method total vibration 2 64 Fig 7 Plots of speed q axis current and load compensation current when the compressor operates at 25Hz a without proposed load torque compensator method b with proposed load torque compensation method Fig 8 Vibration test results when the compressor operates at 25Hz total vibration 10 1 2 sm 4 J Donlon J Achhammer H Iwamoto and M Iwasaki Power modules for appliance motor control IEEE Ind Appl Mag vol 8 no 4 pp 24 34 Jul Aug 2002 5 S Lim J Y Lim and T Park Load torque compensation for low vibration low speed contro