JP2012161220A - Control unit for compressor - Google Patents

Abstract

[PROBLEMS] A conventional control method has a function of detecting only a motor back electromotive force voltage, so that the operation becomes unstable in an operation state where a spike voltage generation time is long such as at a high load, and the operation is normally performed. There was a problem that even when it was erroneously detected, it stopped.
By providing a rotor state detection circuit 5, it is possible to detect an unstable state of a motor behavior even when a back electromotive voltage does not appear during operation according to the position of a rotor 4a. Thus, it is possible to exhibit the effects of improving the stability of the system and, in turn, suppressing the step-out stop.
[Selection] Figure 2

Description

  More particularly, the present invention relates to a brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding. More particularly, the present invention relates to a method and apparatus for driving a brushless DC motor that is optimal for driving a compressor such as a refrigerator or an air conditioner.

  In recent years, most large refrigerators of 350L or more have become mainstay refrigerators, and most of these refrigerators are inverter-controlled refrigerators that variably drive the rotation speed of a highly efficient compressor. These refrigerator compressors generally employ a brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding for high efficiency. In addition, since the brushless DC motor is installed in an environment of high temperature, high pressure, refrigerant atmosphere, and oil atmosphere in the compressor, a position detection sensor such as a hall element normally used in a brushless DC motor cannot be used. Therefore, generally, a method of detecting the rotational position of the rotor from the counter electromotive voltage or direct current of the motor is often used.

  A conventional technique is disclosed in Patent Document 1, for example. The prior art will be described with reference to the drawings. FIG. 4 is a block diagram of a conventional driving apparatus for driving a brushless DC motor.

  In FIG. 4, a commercial power source 101 is an AC power source having a frequency of 50 Hz or 60 Hz and a voltage of 100 V in Japan.

  The rectifier circuit 102 converts the AC voltage of the commercial power supply 101 into a DC voltage. The rectifier circuit 102 includes bridge-connected rectifier diodes 102a to 102d and smoothing electrolytic capacitors 102e and 102f. In the circuit shown in FIG. 4, the voltage rectifier circuit is a voltage doubler rectifier circuit. Can be obtained.

  The inverter circuit 103 has a three-phase bridge configuration including six switch elements 103a, 103b, 103c, 103d, 103e, and 103f. Each switch element includes a diode for return current in the reverse direction of each switch element, but this is omitted in the figure.

  The brushless DC motor 104 includes a rotor 104a having a permanent magnet and a stator 104b having a three-phase winding. When the three-phase alternating current generated by the inverter 103 flows through the three-phase winding of the stator 104b, the rotor 104a can be rotated. The rotational movement of the rotor 104a is changed to a reciprocating movement by a crankshaft (not shown), and a piston (not shown) reciprocates in a cylinder (not shown) to compress the refrigerant. Drive.

  The counter electromotive voltage detection circuit 105 detects the rotational relative position of the rotor 104a from the counter electromotive voltage generated by the rotation of the rotor 104a having the permanent magnet of the brushless DC motor 104.

  The commutation circuit 106 performs logical signal conversion based on the output signal of the back electromotive voltage detection circuit 105, and generates a signal to be driven by sequentially switching the switch elements 103a, 103b, 103c, 103d, 103e, and 103f of the inverter 103.

  The synchronous drive circuit 107 forcibly outputs an output of a predetermined frequency from the inverter 103 and drives the brushless DC motor 104, and forcibly outputs a signal having the same shape as the logical signal generated by the commutation circuit 106. It is generated at a predetermined frequency.

  The load state determination circuit 108 determines a load state in which the compressor 104 is operated.

  The switching circuit 109 switches whether the brushless DC motor of the compressor 104 is driven by the commutation circuit 106 or the synchronous driving circuit 107 according to the output of the load state determination circuit 108.

  The drive circuit 110 drives the switch elements 103a, 103b, 103c, 103d, 103e, and 103f of the inverter 103 by the output signal from the switching circuit 109.

  Next, the operation of the above configuration will be described.

  When the load detected by the load state determination circuit 108 is a normal load, driving by the commutation circuit 106 is performed.

  The back electromotive voltage detection circuit 105 detects the relative position of the rotor 104 a of the brushless DC motor 104. Next, the commutation circuit 106 creates a commutation pattern that drives the inverter 103 in accordance with the relative position of the rotor 104a.

  This commutation pattern is supplied to the drive circuit 110 through the switching circuit 109, and drives the switch elements 103a, 103b, 103c, 103d, 103e, and 103f of the inverter 103.

  By this operation, the brushless DC motor 104 is driven in accordance with its rotational position.

  Next, the operation when the load increases will be described.

  When the load of the brushless DC motor increases, the rotational speed decreases due to the characteristics of the brushless DC motor. This state is determined by the load state determination circuit 108 to be a high load state, and the output of the switching circuit 109 is switched to the signal from the synchronous drive circuit 107. By driving in this way, it is possible to suppress a decrease in the rotational speed at the time of high load.

JP-A-9-88837

  However, the conventional configuration has the following problems.

From the output signal of the counter electromotive voltage detection circuit 105, the relative position of the rotor 104a can be detected in a load state in which the counter electromotive voltage generated by the brushless DC motor 104 appears. However, when the switching circuit 109 is driven at a high speed by the commutation circuit 106, the motor current flowing through the stator 104b is large, and accordingly, the time during which the motor current is fed back to the return current diode increases. However, the generation time of noise (also referred to as spike voltage) that hinders the appearance of the counter electromotive voltage becomes long. As a result, the relative position of the rotor 104a could not be detected, and control became impossible, resulting in fluctuations in the rotational speed, and eventually the state of step-out stop and protection stop.

  Further, when the brushless DC motor 104 has the IPM structure, the inductance tends to be larger than that of the SPM structure, and the energy stored in the stator 104b increases, so that the time for returning the motor current to the return current diode is further increased. Therefore, the counter electromotive voltage is further prevented from appearing. In addition, even when the stator 104b is an iron loss reduction type stator having a relatively large amount of winding, the inductance is increased and the spike voltage width is increased, which further prevents the counter electromotive voltage from appearing.

  The present invention solves the above-described conventional problems, and by making a configuration capable of detecting the zero cross point of the motor current, erroneous detection caused by the influence of the noise (ringing noise) generated when the power transistor is turned on. An object of the present invention is to provide a control device for a compressor that can be prevented.

  The compressor control device of the present invention includes a brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding, an inverter for supplying power to the three-phase winding, a three-phase winding, A rotor state detection circuit for detecting a position of the connected rotor of the motor, and a drive unit for driving a switch element of the inverter by an output signal from the switching circuit, and the rotor from a zero cross of the motor current The position is estimated.

  The compressor control device of the present invention can prevent false detection caused by noise.

The top view which shows the refrigerator concerning embodiment of this invention from the front 1 is a block diagram of a brushless DC motor driving device related to driving by a waveform generator in Embodiment 1 of the present invention. The schematic diagram which showed operation | movement of the noise determination part and signal determination part at the time of the drive by the waveform generation part in Embodiment 1 of this invention A block diagram of a driving device related to driving a conventional brushless DC motor

  The invention according to claim 1 is connected to a brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding, an inverter for supplying power to the three-phase winding, and a three-phase winding. A rotor state detection circuit for detecting a position of the rotor of the motor; and a drive unit for driving a switch element of the inverter by an output signal from the switching circuit, wherein the rotor position is detected from a zero cross of the motor current. Therefore, it is possible to prevent erroneous detection of the signal output from the rotor state detection circuit due to the influence of noise.

  According to a second aspect of the present invention, in addition to the first aspect of the present invention, a phase difference acquisition unit that acquires time information based on information of the rotor state detection circuit, and a phase difference during operation in which the duty is not low are provided. And a low-duty operation position estimator that estimates the induced voltage zero-cross point from the current zero-cross point at low duty.

  According to a third aspect of the present invention, in the second aspect of the present invention, a stable operation state is detected from the duty and the rotational speed, and the phase difference acquisition unit starts acquisition.

  Hereinafter, embodiments of a refrigerator according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments.

(Embodiment 1)
Hereinafter, an embodiment of a refrigerator according to the present invention will be described with reference to the drawings.

  FIG. 1 is a plan view showing a refrigerator according to an embodiment of the present invention from the front.

  As shown in the figure, a refrigerator 100 according to the present embodiment includes a main box 101 that opens to the front. Further, the main box body 101 includes a plurality of sub-box bodies that are formed by dividing the inside.

  Here, the main box 101 is a box having an opening on the front surface, and is provided with a heat insulating performance that blocks heat from entering and exiting the inside and outside of the refrigerator 100.

  The sub-box provided in the refrigerator 100 includes a refrigerating room 102, an ice making room 105, a switching room 106, a vegetable room 104, and a freezing room 103, which are provided in the ice making room 105 and can change the temperature in the refrigerator, depending on the function (cooling temperature). Each is formed.

  At the front opening of the refrigerator compartment 102, a rotary heat insulating door 107 filled with foam heat insulating material such as urethane is provided.

  In addition, drawers are provided in front opening portions of the ice making chamber 105, the switching chamber 106, the vegetable chamber 104, and the freezing chamber 103, respectively. Each of the ice making room 105, the switching room 106, the vegetable room 104, and the freezing room 103 is hermetically sealed by a front plate 108 having heat insulation performance so as not to leak cold air.

  In addition, an inverter compressor (not shown) is disposed behind the top surface of the refrigerator compartment 102 of the refrigerator 100.

  FIG. 2 is a block diagram of a brushless DC motor driving apparatus related to driving by the waveform generator in the first embodiment of the present invention.

  In FIG. 2, the commercial power source 1 is an AC power source having a frequency of 50 Hz or 60 Hz and a voltage of 100 V in Japan.

  The rectifier circuit 2 converts the AC voltage of the commercial power source 1 into a DC voltage. The rectifier circuit 2 comprises bridge-connected rectifier diodes 2a to 2d, smoothing electrolytic capacitors 2e and 2f, and a voltage regulator circuit 2g. In the case of a voltage doubler rectifier circuit as shown in FIG. Therefore, a DC voltage of about 280V can be obtained. Although voltage doubler rectification is used here, the voltage adjustment circuit 2g corresponds to a DC voltage variable chopper circuit or voltage doubler rectification / full wave rectification switching type circuit.

  The inverter circuit 3 has a three-phase bridge configuration including six switch elements 3a, 3b, 3c, 3d, 3e, and 3f. Each switch element includes a diode for return current in the reverse direction of each switch element, but this is omitted in the figure.

The brushless DC motor 4 includes a rotor 4a having a permanent magnet and a stator 4b having a three-phase winding. When the three-phase alternating current generated by the inverter 3 flows in the three-phase winding of the stator 4b, the rotor 4a can be rotated. The rotary motion of the rotor 4a is changed to a reciprocating motion by a crankshaft (not shown), and a piston (not shown) reciprocates in a cylinder (not shown) to compress the refrigerant. Drive. The three-phase winding portion connected to the switch element 3a (3b) is a U-phase winding, the three-phase winding portion connected to the switch element 3c (3d) is a V-phase winding, and the switch element 3e (3f). The three-phase winding portion connected to is called a W-phase winding.

  Further, U, V, and W in the figure, which are connection points between the three-phase winding, the switch element, and the terminal voltage detection circuit, are referred to as a U terminal, a V terminal, and a W terminal.

  The rotor state detection circuit 5 can compare each voltage of the U terminal, the V terminal, and the W terminal with a preset reference voltage and output information on the voltage change. Note that the operating state of the brushless DC motor 4 can be detected from the output information. Specifically, the rotational relative position of the rotor 4a can be detected from the counter electromotive voltage generated when the rotor 4a having the permanent magnet of the brushless DC motor 4 rotates. It is also possible to detect a disturbance in the motor current and a change in the load state by detecting an increase / decrease in the time during which the current flows through the return current diode.

  In addition, although it was set as the structure which detects the driving | running state of the brushless DC motor 4 from the voltage which generate | occur | produces in three terminals of U, V, and W, if it is a means which can detect the position of the rotor 4a, a motor current state, etc. For example, a configuration using other means such as current detection may be used.

  Based on the signal output from the rotor state detection circuit 5, the noise determination unit 6 detects the noise that inhibits the signal related to the relative position of the rotor 4a and the generation time thereof, and determines the end of the noise. For example, when the rotor state detection circuit 5 is configured to output a signal from the comparison between the terminal voltage of each phase of the three-phase winding and an arbitrary reference voltage as described above, the switch elements 3a to 3f of the inverter 3 Is detected, and the spike voltage generation time and information that the spike voltage is completed are output to the signal determination unit 7 at the end of the spike voltage.

  The signal determination unit 7 distinguishes and determines the signal output from the rotor state detection circuit 5 based on the noise end information from the noise determination unit 6. Specifically, after receiving the noise end information, the output signal of the rotor state detection circuit 5 detects a change and recognizes it as a position signal of the rotor 4a.

  The waveform generation unit 8 performs logical signal conversion based on the noise end information output from the signal determination unit 7 and the position information of the rotor 4a, and switches the switch elements 3a, 3b, 3c, 3d, and 3e of the inverter 3. 3f is generated. However, if the noise does not end even after a certain period of time, the waveform generator 8 has a function of forcibly outputting a waveform based on the target frequency and the actual frequency at that time, without depending on the position information. ing. Further, during operation according to the position information, duty control of PWM control and energization angle control are also performed in order to keep the rotation speed constant. According to the rotational position, the actual rotational speed of the brushless DC motor 4 can be detected and compared with the target rotational speed, and can be operated with an optimum duty, so that the most efficient operation is possible. The detection of the actual rotational speed can be realized by counting a certain time or measuring the period from the output timing of the position signal by the signal determination unit 7.

  The drive unit 9 drives the switch elements 3 a, 3 b, 3 c, 3 d, 3 e, 3 f of the inverter 3 by the output signal from the waveform generation unit 8. By this driving, an optimal AC output can be applied from the inverter 3 to the brushless DC motor 4, so that the rotor 4a can be rotated.

The microcomputer 10 realizes the aforementioned functions. These functions can be realized by a microcomputer program.

  The reference potential G is a reference point of the potential in this block diagram and corresponds to a connection point between the rectifier diode 2d and the electrolytic capacitor 2f. When the voltage supplied from the commercial power source 1 is AC100V, a DC voltage of about 280V can be obtained between the reference potential G and the connection point between the electrolytic capacitor 2e and the rectifier diode 2c and supplied to the inverter 3. Become.

  Next, the operation in FIG. 2 will be described with reference to FIGS.

  FIG. 3 is a schematic diagram illustrating operations of the noise determination unit and the signal determination unit during driving by the waveform generation unit according to the first embodiment.

  FIG. 2 shows a signal waveform output from the drive unit 9 to the two switch elements 3a and 3b related to the U phase of the three-phase winding in the operation by the waveform generation unit 8, and between the U terminal and the reference potential G. The voltage waveform “U-phase voltage” in which the potential difference is observed and the signal waveform “U5” output from the rotor state detection circuit 5 based on the comparison result between the voltage and the reference voltage are distinguished from the operation states a) to c). Show. P shown at the left end of the voltage waveform “U-phase voltage” indicates a voltage (positive potential) supplied to the inverter 3 and corresponds to a DC voltage of about 280V when the commercial power source 1 is AC100V. N indicates a reference potential G (negative potential) of the voltage supplied to the inverter 3 and corresponds to 0V. From above, a) is a waveform when the rotor state detection circuit 5 is outputting a position signal, b) is a waveform when the rotor state detection circuit 5 is not outputting a position signal, and c). Respectively show waveforms when the rotor 4a is in a locked state. However, here, a description will be given based on a waveform when driving at an advance angle of 7.5 °, but it is supplemented that the present embodiment does not limit the advance angle. Further, the advance angle represents the degree of advance of the current flowing in the stator 4b with respect to the counter electromotive voltage generated by the rotation of the rotor 4a in electrical angle. Here, for simplicity of explanation, only the description of the U phase is given as a representative, but the same operation is performed for the other two-phase V-phase and W-phase. Here, only the case where the conduction angle is 150 ° will be described, and the same applies to other conduction angles of 150 ° or less.

First, these three waveforms will be described. First, the signal waveform output by the drive unit 10 will be described. Both the switch elements 3a and 3b repeat the operation of turning on for 150 ° and turning off for 210 ° in electrical angle. In this figure, the signal waveform is shown centering on the timing when the switch element 3a becomes 150 ° conductive and the switch element 3b becomes 210 ° nonconductive. A two-dot chain line vertically drawn in the vicinity of the center of the figure indicates the center position of the conduction period of the switch element 3a. In addition, this figure is a signal waveform at the time of 100% duty operation. Second, the U-phase voltage waveform “U-phase voltage” will be described. Here, it demonstrates using FIG. A) for convenience. There is a convex shade on the left and a concave shade on the right, which will be called a spike voltage. The spike voltage is generated immediately after the switching elements 3a and 3b are turned off, while the energy stored in the stator 4b (U-phase winding) is released through the return diode, and is applied to the U-phase winding immediately before turning off. The generation time varies depending on the flowing current and the inductance of the U-phase winding. Therefore, depending on the stored energy, the width of the spike voltage may increase or decrease, and may not be generated depending on circumstances. When the switch element 3b (negative side) is turned off, it has a convex shape to regenerate current through the free-wheeling diode to the electrolytic capacitor 2e side (positive side), and when the switch element 3a (positive side) is turned off, the electrolytic capacitor 2f side It becomes concave to regenerate current on the negative side. In addition, there is a thick broken line part on the left side that rises to the right and a right side that falls on the right side. This is because the back electromotive force generated by the rotation of the rotor 4a is on the U-phase voltage waveform. It is the part that appears. The counter electromotive voltage appears for each of the U-phase, V-phase, and W-phase of the three-phase winding, but appears only when the two switch elements connected to each phase are both off. That is, in the case of the U phase, when one of the switch elements 3a and 3b is turned ON, the voltage waveform sticks to the P side and the N side, and therefore appears only when both switch elements are OFF. A dotted line drawn horizontally near the center is a reference voltage necessary for the rotor state detection circuit 5 to output a signal from the voltage waveform of the three-phase winding. The circle on the dotted line indicating the reference voltage represents the intersection with the spike voltage, and the rice on the dotted line represents the intersection with the back electromotive voltage. Third, the signal “U5” output from the rotor state detection circuit 5 will be described. The rotor state detection circuit 5 compares the reference voltage and the U-phase voltage waveform, and outputs a low level signal (hereinafter referred to as L signal) when the U-phase voltage waveform is smaller, and vice versa. A high level signal (hereinafter referred to as H signal) is output. A circle on the waveform indicates an edge portion of the signal output at the end of the spike voltage. The asterisk indicates the edge portion of the signal output when the back electromotive voltage and the reference voltage are at the same level, and the edge of the asterisk portion represents the relative position of the rotor 4a.

  Next, operations of the noise determination unit 6, the signal determination unit 7, and the waveform generation unit 8 will be described in detail with reference to FIGS. A) and b) drawn for each operation state. Note that the locked state in FIG. C) will be described later with reference to other drawings, and is omitted here.

  In the figure, a) is a diagram showing a waveform in a normal operation state. As can be seen from the figure, when the spike voltage width is 7.5 ° (less than 22.5 °), the back electromotive voltage waveform appears before the ON operation of the switch elements 3a and 3b and crosses the reference voltage. Both the relative position (◯ mark) and the end point (* mark) of the spike voltage (noise) can be detected.

  When a stable operation is performed with a sufficiently low current during driving by the waveform generator 8, the waveform is as in the normal state a). First, the noise determination unit 6 is in a period in which both the switch elements 3a and 3b are turned off (from the time when the switch element 3b is turned off until 3a is turned on, or after the switch element 3a is turned off until 3b is turned on During this period, the signal from the rotor state detection circuit 5 is observed, and the change point of the signal level is detected to recognize the end point of the spike voltage (noise) (marked with a circle in the figure). Next, the signal determination unit 7 that has received the noise end signal from the noise determination unit 6 outputs information that the noise generation has ended to the waveform generation unit 8 while observing the signal output from the rotor state detection circuit 5. To do. Then, when the rotor state detection circuit 5 changes the signal level at the point where the back electromotive voltage and the reference voltage intersect, the signal determination unit 7 that has input the change determines that it is a position signal and determines the waveform generation unit. The information is output to 8. Thereafter, the waveform generation unit 8 outputs a waveform so that the advance angle is 7.5 ° based on the position signal. That is, the waveform generation unit 8 outputs a waveform to the drive unit 9 when an electrical angle of 7.5 ° elapses from the time when the position signal output by the signal determination unit 7 is received. Further, the waveform generation unit 8 also observes the period in which the position signal is output from the signal determination unit 7, adjusts the duty and the energization angle so as to match the target period, and outputs the waveform so that the rotational speed is It is controlled to be constant.

  In the figure, b) is a diagram showing a waveform when in an overload operation state. As can be seen from the figure, when the spike voltage width is 22.5 ° (22.5 ° or more), the back electromotive voltage waveform appears before the ON operation of the switch elements 3a and 3b, but does not cross the reference voltage. Neither the relative position nor the spike voltage end point can be detected.

When the load torque increases during driving by the waveform generator 8, the motor current increases, and the waveform is like an overload state b) in which the generation time of the spike voltage (noise) is expanded. First, the noise determination unit 6 is in a period in which both the switch elements 3a and 3b are turned off (from the time when the switch element 3b is turned off until 3a is turned on, or after the switch element 3a is turned off until 3b is turned on. During this period, the signal from the rotor state detection circuit 5 is observed. However, since the back electromotive voltage reaches the level of the reference voltage at the same time as the end of the noise, the signal level output from the rotor state detection circuit 5 does not change, and the noise determination unit 6 detects the end point of the noise all at once. I can't. In addition, since the noise end signal cannot be input from the noise determination unit 6, the signal determination unit 7 cannot start observing the signal output from the rotor state detection circuit 5 and cannot detect the position signal. Then, the waveform generator 8 that cannot input the position information and the noise end information from the signal determination unit 7 forcibly outputs a waveform after a predetermined time has elapsed since no information is input for an arbitrary time or longer. In this way, even if there is no position information, the operation is continued, and when the torque becomes low, the state changes to a normal state where the position can be detected as shown in the right waveform of b). For example, when the brushless DC motor 4 is a motor that drives a compressor, the load torque increases gradually from the compressor suction stroke to the discharge stroke, but conversely the load torque increases from the discharge stroke to the suction stroke. Torque is getting lower. In such a system with a load fluctuation, b) If the operation is continued by forcibly generating a waveform only at a high load where the noise width becomes large as shown on the left side, the noise width as shown on the right side will gradually increase. It changes to a small waveform. In other words, the waveform when operating a system such as a compressor is as shown in b).

  As described above, the brushless DC motor driving apparatus according to the present invention can exhibit the effect of reducing noise and vibration, and thus can be used in various applications equipped with a brushless DC motor regardless of whether it is for home use or industrial use. It can also be applied to.

3 Inverter 4 Brushless DC motor 4a Rotor 4b Stator 5 Rotor state detection circuit

Claims (3)

A brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding, an inverter for supplying power to the three-phase winding, and detecting the position of the rotor of the motor connected to the three-phase winding And a drive unit for driving the switching element of the inverter by an output signal from the switching circuit, and a controller for the compressor that estimates the rotor position from a zero cross of the motor current . A phase difference acquisition unit that acquires time information based on information from the rotor state detection circuit and a phase difference during operation where the duty is not low, and a low low that estimates the induced voltage zero cross point from the current zero cross point at low duty The compressor control device according to claim 1, further comprising a duty operation position estimation unit. The compressor control device according to claim 2, wherein the phase difference acquisition unit acquires time information for each section obtained by dividing the motor rotation period by three times the number of magnetic poles.