JP2014155268A - Driving device for reciprocal compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, when a compressor load torque variation is small, optimal torque control cannot be performed since a motor rotating position corresponding to a piston of a compressor cannot be identified.SOLUTION: A driving device comprises: a reciprocal compressor 105 including a reciprocation-type compression element 104; a synchronous motor 103 including a permanent magnet for driving the compression element 104 in its rotor; and an inverter 102 which causes an alternating current to flow to the synchronous motor 103 and varies a rotation speed to vary a refrigeration capability of the compressor. In the case where a reference rotation position of the synchronous motor 103 during one rotation cannot be determined, a rotation speed of the synchronous motor 103 is shifted down and load torque variations are intentionally increased. Thus, the reference rotation position can be surely detected and torque control can be stably operated.

Description

  The present invention relates to an inverter-driven reciprocating compressor mainly used for a refrigerator-freezer, and more particularly to a driving device for a reciprocating compressor having a compression element by a reciprocating motion in which a load torque greatly varies during one rotation. It is.

  Brushless motors have high efficiency, and in recent years, they have come to be used in many compressors used in refrigeration systems. In addition, it is well known that a brushless motor can be simplified by changing the voltage applied to the motor by pulse width modulation control (hereinafter referred to as PWM control).

For this reason, in the refrigerator-freezer, when the temperature is stable, the rotational speed is reduced, the efficiency of the entire refrigeration system including the compressor is increased, and energy saving is realized.
However, in a reciprocating compressor often used in a refrigerator-freezer, half of one rotation is a refrigerant suction process, and the other half rotation is a compression / discharge process. Therefore, a load torque is almost unnecessary in the suction process, but a large load torque is required in the compression / discharge process.

  On the other hand, the motor torque of the brushless motor is a substantially constant torque during one rotation. Therefore, the rotation speed (ie, angular velocity) fluctuates during one rotation due to the relationship between the load torque and the motor torque. This fluctuation in the rotational speed becomes a factor of vibration generation, which has been a major obstacle to lowering the rotational speed for further energy saving.

  Also, at high speeds, the energy due to the moment of inertia of the compressor's rotation system (rotor, shaft, piston, etc.) becomes sufficiently large and the load torque fluctuations can be sufficiently canceled out. This vibration is not a problem. Become a thing. In response to these phenomena, conventionally, efforts have been made to suppress the vibration of the compressor by generating a motor torque corresponding to the load torque at a low rotation and suppressing a fluctuation in the rotation speed during one rotation. (For example, refer to Patent Document 1).

A conventional compressor driving device will be described below with reference to the drawings.
FIG. 4 is a longitudinal sectional view of a general reciprocating compressor. Fits in the rotor 22 with a brushless motor 2 comprising a stator 21 having a three-phase winding in a hermetic container 1 and a rotor 22 having a permanent magnet, a cylinder 5, a piston 6 and the like arranged on the bearing body 4. And a compression mechanism portion including a rotation shaft 3 and the like for converting the rotational motion into the reciprocating motion of the piston 6 by the eccentric portion 31.

  In general, an internal vibration isolation structure is used in a reciprocating compressor, that is, discharged from a support spring 8 that supports a structure composed of the brushless motor 2 and the compression mechanism, or from the compression mechanism. A method of attenuating the vibration of the structure due to torque fluctuation generated according to the load by the loop pipe 9 or the like for guiding the generated gas and controlling the vibration or noise is employed.

  In the reciprocating compressor, the rotor 22 and the rotating shaft 3 should have an appropriate moment of inertia, together with a structure that attenuates the vibration of the structure by the support spring 8 and the loop pipe 9. Therefore, it is devised so that vibration is not transmitted to the outside of the sealed container 1.

  However, when this reciprocating compressor is controlled to change the rotation speed using inverter control, vibration suppression by the moment of inertia reaches its limit, especially in the low rotation speed area, and structurally suppressing vibration It becomes extremely difficult. In response to these phenomena, conventionally, efforts have been made to suppress the vibration of the compressor by generating a motor torque corresponding to the load torque at a low speed rotation and suppressing a fluctuation in the rotation speed during one rotation ( For example, see Patent Document 1).

  FIG. 5 is a timing chart showing the relationship between load torque and motor torque of a conventional compressor.

  In FIG. 5, the motor torque is controlled by dividing one rotation of the synchronous motor into 1/3 rotation section A (mainly compression / discharge process) and other section B (mainly suction process). By increasing the PWM control duty width in section A so that the motor current in section A flows more than the motor current in section B, it is a very simple system and input power for reciprocating compressor load torque fluctuations. The vibration was reduced without greatly increasing the vibration.

JP 2006-2732 A

  However, in the conventional control method, since the duty width of the PWM control is switched according to the load torque fluctuation caused by the reciprocating motion of the compressor piston, the rotational position of the rotor 22 corresponding to the suction / discharge process of the compressor is specified. Although it is necessary, there is no description regarding the specification of the rotational position of the rotor 22 corresponding to the suction / discharge process position of the compressor, and detailed control is unknown.

  The present invention solves the above-described conventional problems, and is a reciprocating compressor drive device capable of reliably detecting a reference rotational position and stably starting torque control even when a load torque fluctuation amount is small. The purpose is to provide.

  In order to solve the above conventional problems, the reciprocating compressor drive device according to the present invention intentionally increases the load torque fluctuation amount by shifting down the compressor rotational speed when the reference rotational position cannot be detected. And a control device that reliably detects the reference rotational position.

  As a result, even when the load torque fluctuation is low and the speed fluctuation within one rotation of the motor is small, it is possible to reliably detect the reference rotation position and apply the torque control to reduce the compressor vibration.

  The reciprocating compressor drive device according to the present invention is capable of reliably detecting the reference rotational position and performing optimum torque control even when the load torque fluctuation is low and the speed fluctuation within one rotation of the motor is small. In addition, the compressor can be driven to a low rotation range and energy saving can be improved.

The block diagram of the drive device of the compressor in Embodiment 1 of this invention (A) Flow chart of control in Embodiment 1 of the present invention (b) Flow chart of reference rotation position detection mode in the same embodiment (A) Timing diagram when the reference rotational position of the control in the first embodiment of the present invention is determined (b) Timing when the reference rotational position of the control in the same embodiment is not fixed and the downshift is performed to the minimum rotational speed Figure Vertical section of a general reciprocating compressor Timing chart of conventional invention control

  The reciprocating compressor drive device according to claim 1 includes a reciprocating compressor having a reciprocating compression element, a synchronous motor having a permanent magnet for driving the compression element in a rotor, and the synchronous motor. In the case where the reference rotational position during one rotation of the synchronous motor and the inverter for making the refrigerating capacity of the compressor variable by flowing an alternating current and changing the rotational speed at a variable speed cannot be determined, the rotational speed of the synchronous motor A control device that has a reference rotational position detection mode for detecting the reference rotational position by intentionally increasing the load torque fluctuation by shifting down the engine and operates the torque control based on the reference rotational position. Thus, the reference rotational position can be reliably detected, and the torque control can be stably operated.

  The drive unit for the reciprocating compressor according to claim 2 determines that the load torque fluctuation is small when the reference rotational position cannot be detected even when the synchronous motor is shifted down to the minimum rotational speed in the reference rotational position detection mode. By not applying torque control, it is possible to avoid an increase in input power due to the torque control operation.

  In the invention of the driving device for the reciprocating compressor according to claim 3, the reference rotational position detection mode is a method in which the rotational speed of the synchronous motor is shifted down when the reference rotational position cannot be detected. Correspondingly, the time required to detect the reference rotational position can be shortened by switching the number of downshift stages of the motor rotational speed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram of a reciprocating compressor driving apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, electric power necessary for driving is supplied from a commercial power source 100. For example, in the case of Japan, it is an AC power supply, and is a power supply of 100 V 50 Hz or 60 Hz.

  The rectifier circuit 101 converts the commercial power supply 100 into direct current. Here, the rectifier circuit 101 is shown as a full-wave rectifier circuit. A full-wave rectifier circuit is generally composed of four diodes and a smoothing capacitor connected in a bridge. With this circuit, a DC voltage of 140 V is obtained from the AC 100 V of the commercial power supply 100.

  The inverter 102 converts the DC voltage of the rectifier circuit 101 into three-phase AC again. The inverter 102 generally includes six switching elements connected in a three-phase bridge and six diodes connected in reverse to the switching elements in parallel. By controlling these six switching elements, a three-phase alternating current having an arbitrary voltage and an arbitrary frequency can be obtained.

Synchronous motor 103 is driven by the three-phase AC output of inverter 102. It consists of a stator (not shown) provided with a three-phase winding and a rotor (not shown) having a permanent magnet. For example, the stator is a 9-slot tooth wound directly through insulating paper, and a 3-phase 6-pole winding is star-connected. The rotor has 6 permanent magnets on the surface side with N and S poles And embedded magnet type rotors arranged alternately.

  The output from the inverter 102 can be set to an arbitrary voltage / arbitrary frequency, and the synchronous motor 103 has 6 poles. Therefore, the synchronous motor 103 is driven at a frequency (rotational speed) that is one third of the output frequency of the inverter 102. The

  For example, when the output frequency of the inverter 102 is 60 Hz, the rotational speed of the synchronous motor 103 can be driven at 20 r / s, and when the output frequency of the inverter 102 is 240 Hz, the rotational speed of the synchronous motor 103 can be driven at 80 r / s.

  The compression element 104 is driven by a synchronous motor 103 and performs compression work. Here, the compression element 104 is a reciprocating compression element whose load torque fluctuates during one rotation. In the case of a reciprocating type compression element, compression is performed by reciprocating movement of the piston. During one rotation, half is divided into the suction process, and half is completely divided from the compression process. These two processes are necessary. Since a large load torque is concentrated on the compression process side, the load torque varies greatly.

  The compressor 105 stores the synchronous motor 103 and the compression element 104 in a sealed container. Any refrigerant gas may be used, and it goes without saying that any refrigerant gas such as an alternative refrigerant (R-134a, etc.) or a natural refrigerant (R-600a, CO2, etc.) may be used.

  The compressor 105 includes a discharge pipe that discharges the compressed refrigerant and a suction pipe that sucks the refrigerant. A condenser 106, a decompressor 107, an evaporator 108, and the like are connected in series to the discharge pipe, and finally the refrigerant gas returns from the suction pipe to the compressor 105.

  By assembling such a refrigerating and air-conditioning system, a heat dissipation action occurs on the condenser 106 side and a heat absorption action occurs on the evaporator 108 side, so that heating or cooling can be performed. In addition, by attaching a fan motor to the condenser 106 or the evaporator 108 and sending air, the efficiency of heat exchange is increased, so that these heats can be effectively used to efficiently heat or cool.

  The control device 109 drives the inverter 102. The output drives the six switching elements of the inverter 102 via the drive means 110.

  In general, when driving a synchronous motor 103 having a permanent magnet as a rotor, the six switching elements of the inverter 102 are commutated at optimum positions while detecting the rotational position of the rotor, thereby synchronizing the rotor. The motor 103 is moved optimally.

  In general, a motor using this method is sometimes referred to as a brushless DC motor or a brushless motor.

  Further, the contents of the control device 109 will be described in detail.

  The position detector 111 detects the rotational position of the rotor of the synchronous motor 103. In general, a method for detecting the counter electromotive voltage generated in the stator winding of the synchronous motor 103 is well known, but recently, a method for estimating the rotational position from the motor current or the current of the DC section is also often used. It has been broken.

  Of course, there is a method of directly detecting the position using a magnetic sensor such as a Hall element. However, since it is difficult to attach such a sensor to a compressor, the former method (position sensorless method) is often taken. ing.

  In such a position sensorless system, since position detection is impossible at the time of start-up, a predetermined phase (for example, between U and W) of the synchronous motor 103 called positioning is forcibly energized before start-up so that the rotor is predetermined. A control circuit such as a method of rotating to a position or a forcible drive system for forcibly applying an AC waveform of a predetermined frequency and a predetermined voltage to drive the rotor is also necessary, but is omitted here.

  The commutation means 112 determines the timing for energizing the six switching elements of the inverter 102 based on the output of the position detection means 111. In general, the timing is determined so that the phase of the counter electromotive voltage coincides with the phase. However, in the case of a magnet-embedded motor (generally called an IPM motor), the reluctance torque is also taken into consideration and the motor current is slightly increased. There are also cases in which the operation is advanced with respect to the phase of the counter electromotive voltage. Although this phase advance varies depending on the type of motor (especially the amount of reluctance component used), it is common to have an advance angle of about 0 to 10 degrees.

  The rotational position determination means 113 detects the rotational position of the rotor of the synchronous motor 103 from the output of the position detection means 111, and specifies the mechanical rotational position of the rotor. Since the synchronous motor 103 operates completely in synchronization with the output from the inverter 102, the mechanical rotational position of the rotor of the synchronous motor 103 can be determined by analyzing this signal. More specifically, the rotational position signal output from the position detector 111 is output at every predetermined angle (for example, a mechanical angle of 20 °). When the behavior of the rotational position signal for each mechanical angle of 20 ° is viewed at one rotation of the rotor (mechanical angle 360 °), the load torque increases in the compression process, so the time required to rotate the mechanical angle by 20 ° is long ( The longest time at the top dead center), and the load torque decreases in the inhalation process, so the time required only to rotate the mechanical angle 20 ° is short (the shortest at the bottom dead center). As a result, by analyzing the speed fluctuation obtained from the rotation signal, the rotational position of the rotor corresponding to the top dead center / bottom dead center of the piston reciprocating motion can be specified, and PWM control (torque control) corresponding to the piston reciprocating motion can be performed. . Conversely, if this top dead center / bottom dead center cannot be detected properly, torque control will be applied at a timing deviated from the actual compressor piston motion, which will worsen the vibration. It will be.

  The rotation speed switching means 114 receives the signal indicating whether or not the reference rotation position can be detected from the rotation position determination means 113 and switches the rotation speed of the synchronous motor 103. If the reference rotation position can be detected, a predetermined rotation speed set in advance is set. If the reference rotation position cannot be detected, the rotation speed obtained by shifting down the rotation speed of the synchronous motor 103 is set, and the first PWM in the subsequent stage is set. Output to generating means.

  The first PWM generating means 115 indicates the duty of PWM (pulse width modulation) control (the ratio of the ON width in the carrier cycle) in order to operate at the rotational speed of the synchronous motor 103 output from the rotational speed switching means in the previous stage. ) Is output.

  The second PWM generator 116 generates a duty (for example, 10%) obtained by adding a predetermined amount of duty to the duty determined by the first PWM generator 115. Here, the duty to be added is a fixed value, but may be changed depending on the rotational speed and the load condition.

  The selection means 117 always selects the PWM signal of the first PWM generation means 115 when the rotation speed is high. When the rotational speed is low, the rotational position signal of the rotational position determining means 113 is received and a predetermined section A and section B are determined. In the case of the section A, the PWM signal of the second PWM generating means 116 is selected. In the case of section B, the PWM signal of the first PWM generating means 115 is selected.

  The commutation output of the commutation means 112 and the PWM signal of the selection means 117 are synthesized by the synthesis means 118 and output to the drive means 110 to control the inverter 102.

  The operation of the reciprocating compressor driving apparatus configured as described above will be described in more detail with reference to FIGS. FIG. 2A is a flowchart of the control in the first embodiment of the present invention, and FIG. 2B is a flowchart of the reference rotational position detection mode in the same embodiment.

  In step 1, the rotational speed is detected. Since the motor used in the present invention is a synchronous motor, the electrical frequency output from the inverter 102 and the rotational operation of the synchronous motor 103 coincide with each other. Can be detected. Although the number of rotations is used here, it may be the same as the number of rotations, for example, a rotation cycle or an angular velocity.

  Next, in STEP2, it is determined whether the rotational speed is equal to or less than a predetermined value. The predetermined value here is set to a low rotational speed, and is set to a rotational speed (for example, 20 r / s) at which vibration of the reciprocating compressor due to torque fluctuation of the load torque becomes large.

  Since the inertial force due to the inertia is sufficiently large at a rotational speed higher than the predetermined rotational speed, the influence of the torque fluctuation of the load torque is small, and the vibration resulting therefrom is also small. Therefore, the control according to the present invention is unnecessary and normal operation may be performed. Therefore, in STEP 3, the output of the first PWM generation means 115 is selected by the selection means 117, and the operation is performed at the first PWM.

  This predetermined value is determined by the configuration of the refrigeration air conditioning system, the type of compressor, the inertia of the rotor of the motor, etc., and sets the number of rotations at which vibrations due to load torque fluctuations occurring at low speeds of the compressor are to be suppressed. . Of course, a predetermined value that varies depending on the surrounding environment state (temperature, etc.) and the driving state may be determined.

  On the other hand, if it is equal to or lower than the predetermined rotation speed, the process proceeds to STEP 4 to determine whether or not the operation is stable. The determination of the stable operation may be made from the temperature condition of each part in the refrigeration air-conditioning system control device (not shown) or the elapsed time. When it is determined that the operation is not stable, that is, during the transition period, it is important that the operation is stable. Therefore, the process proceeds to STEP 3 and the operation is performed at the first PWM.

  If it is determined in STEP4 that the operation is stable, the process proceeds to STEP5. Subsequent STEP5 to STEP7 are executed by the rotational position determination means 113.

  In STEP 5, the top dead center of a piston (not shown) of the compression element 104 is detected, and the rotational position of the rotor of the synchronous motor 103 corresponding to the top dead center (hereinafter referred to as a reference rotational position) is determined. The rotational position determination means 113 switches the first PWM and the second PWM by the selection means 117 according to the load torque fluctuation with the reference rotational position as a reference.

  As detailed processing in STEP5, the rotor position of the synchronous motor 103 corresponding to the piston top dead center is specified as the detection of the reference rotational position in STEP51. First, the speed within one rotation is measured for every predetermined angle (for example, every mechanical angle of 20 °), and the place with the slowest speed is specified. In the piston reciprocating motion, the load torque becomes maximum at the top dead center and the speed is decelerated most. Therefore, the lowest speed portion is set as the reference rotational position.

If the reference rotation position is confirmed in STEP 52, the process proceeds to the next STEP 6 and STEP 7. On the other hand, when the speed fluctuation peak of the synchronous motor 103 is gently detected due to the influence of the refrigerant state in the cooling system (106 to 107), the compressor characteristics, the noise of the rotation position detection circuit (not shown), The location of the top dead center may not be identified. In that case, go to STEP53.

  In STEP 53, it is determined whether the currently operating rotational speed is the minimum rotational speed set in advance. If the currently operating rotational speed is the minimum rotational speed, the load torque fluctuation is small even at the minimum rotational speed at which the vibration is maximum, so it is determined that torque control is unnecessary, the reference position is not yet determined, and the process proceeds to the next step 6. It always operates at 1PWM. On the other hand, if the currently operating rotational speed is greater than the minimum rotational speed, the process proceeds to STEP54.

  In STEP 54, in order to increase the detection accuracy of the top dead center, the rotational speed is shifted down to intentionally increase the torque fluctuation, and the reference position is detected again in STEP 51. Thereafter, the process is repeated until the reference position detection is confirmed or the minimum rotational speed is reached. Further, with respect to the rotational speed shift down amount here, the processing time is shortened by switching the shift down amount according to the detection variation degree in the reference rotational position detection processing of STEP 51. For example, if there are two top dead center candidates in the reference rotational position detection process of STEP 51, the soft down is 1 r / s, but if there are five top dead center candidates, the top dead center is detected unless the number of revolutions is significantly reduced. If it is not possible, the processing time until the reference rotational position is determined can be shortened by shifting down by 4 r / s.

  STEP 7 is performed by the rotational position determination unit 113 and determines whether the rotational position is the section A or the section B. The rotational position determining means 113 can previously determine the mechanical rotational angle, and the top dead center of the piston (not shown) of the compression element 104 is used as a reference. Before that, the section with a mechanical angle of 120 degrees is defined as section A. If it is determined in STEP 7 that the rotational position is not the section A (that is, the section B), the process proceeds to STEP 3 to operate at the first PWM. If it is determined in STEP 7 that the rotational position is the section A, the process proceeds to STEP 8.

  In STEP 8, the output of the second PWM generation means 116 is selected by the selection means 117, and the operation is performed at the second PWM.

  By operating as described above, when the stable operation is performed at the low rotation speed operation, the operation is performed in the second PWM in the section A and in the first PWM in the section B. Since the duty of the second PWM is set to be larger than the duty of the first PWM, the current in the section A is higher than the current in the section B. Therefore, a large torque is generated in the section A. Since the section A is set before the top dead center of the compression element, the torque is increased during compression, and a reduction in the rotational speed can be prevented.

  Next, the actual operation will be described with reference to FIG. FIG. 3 is a control timing chart according to the first embodiment of the present invention. FIG. 3A is a timing chart when the reference rotation position is determined, and FIG. 3B is the minimum rotation without determining the reference rotation position. The timing diagram in the case of downshifting to a number is shown.

  In FIG. 3, the horizontal axis indicates the elapsed time from the reference rotational position determination process to the start of torque control, and the vertical axis indicates the rotational speed of the synchronous motor 103.

  In FIG. 3A, first, the reference rotational position is detected in order to start the PWM control according to the load torque fluctuation. At this time, if the load torque fluctuation is small and the top dead center at the reference rotational position cannot be detected (section A1), the rotational speed is shifted down to intentionally increase the load torque fluctuation, and the reference rotational position is detected again. The shift down and detection process are repeated until the reference rotation position can be detected (section B1 to section C1). When the reference rotation position can be determined, the torque control is operated by switching between the first PWM and the second PMW according to the load torque fluctuation (section D1).

  In FIG. 3B, similarly to FIG. 3A, the rotational speed shift down is repeated until the reference rotational position is determined (section A2 to section B2). If the reference rotational position cannot be detected even when the rotational speed is shifted down to the minimum rotational speed (section C2), it is determined that torque control is unnecessary, and thereafter the predetermined rotational speed is operated only by the first PWM generating means.

  As described above, the reciprocating compressor driving device according to the first embodiment includes a reciprocating compressor having a reciprocating compression element, and a synchronous motor having a permanent magnet in the rotor for driving the compression element. When an AC current is supplied to the synchronous motor and the refrigerating capacity of the compressor is made variable by changing the rotational speed and the reference rotational position during one rotation of the synchronous motor cannot be determined, By shifting down the rotation speed of the synchronous motor and intentionally increasing the load torque fluctuation, it is possible to reliably detect the reference rotation position, operate the torque control stably, reduce compressor vibration, and reduce the rotation speed. The compressor can be driven up to an area and energy savings can be improved.

  If the reference rotational position cannot be detected even after shifting down to the minimum rotational speed of the synchronous motor, it is determined that the load torque fluctuation is small and the torque control is not applied, so that unnecessary input power due to the torque control operation is eliminated. Can be avoided.

  If the reference rotational position cannot be detected, the time required for detecting the reference rotational position can be shortened by switching the number of shift down stages of the synchronous motor rotational speed according to the degree of variation in the detection result.

  As described above, the drive unit for the reciprocating compressor according to the present invention does not require a new sensor and can be realized with a processor with low processing capacity, so it is a simple system that can be realized with a very small size and low cost. In addition, since vibration can be suppressed without greatly increasing the input power, it can be applied to applications such as an air compressor in addition to a compressor for refrigeration purposes.

102 Inverter 103 Synchronous motor 104 Compression element 105 Compressor 109 Control device

Claims (3)

A reciprocating compressor having a reciprocating compression element, a synchronous motor having a permanent magnet for driving the compression element in a rotor, an alternating current flowing through the synchronous motor and a variable number of rotations, and the compressor When the reference rotational position during one rotation of the synchronous motor and the inverter for making the refrigerating capacity of the synchronous motor cannot be determined, the rotational speed of the synchronous motor is shifted down to intentionally increase the load torque fluctuation A reciprocating compressor drive device comprising a control device that has a reference rotation position detection mode for detecting a reference rotation position and operates torque control based on the reference rotation position. 2. The torque control is not applied if it is determined that the load torque fluctuation is small if the reference rotational position cannot be detected even if the synchronous motor is shifted down to the minimum rotational speed in the reference rotational position detection mode. Drive unit for reciprocating compressors. The reference rotational position detection mode is a method in which the rotational speed of the synchronous motor is shifted down step by step when the reference rotational position cannot be detected, and the number of downshift stages of the motor rotational speed is switched according to the detection result. The driving device for a reciprocating compressor according to claim 1 or 2.