JP2008005639A - Method and device for driving brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a position cannot be detected when DC voltage is low, efficiency is deteriorated, and a motor stops in the worst case when capacity of a smoothing capacitor is made small in conventional sensor-less driving. <P>SOLUTION: In the driving method of the brushless DC motor, the position by a position detecting means 20 is estimated and an inverter is operated when the position cannot be detected. A system is synchronized with position detection at every rotation period in addition to position detection at every switching period. Thus, a stable operation where vibration is reduced becomes possible. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a driving method and apparatus for a brushless DC motor mounted on a compressor or the like used in a refrigerating and air conditioning system such as a refrigerator or an air conditioner, and more particularly to a smoothing capacitor in a rectifier circuit for miniaturization. The present invention relates to position detection control that does not use a position sensor in a case where the capacity is greatly reduced.

  In general, a driving device for a brushless DC motor mounted on a compressor or the like in a conventional refrigeration and air-conditioning system generally includes a rectifier circuit having a sufficiently large smoothing capacitor, an inverter, and an induced voltage or motor current by eliminating a position detection sensor. It was driven by detecting the position. This is because it is extremely difficult to attach the position sensor in a high-temperature atmosphere such as a compressor, a refrigerant atmosphere, or an oil atmosphere.

  In recent years, in order to reduce the size of this drive device, efforts have been made to significantly reduce the capacity of the smoothing capacitor of the rectifier circuit (see, for example, Patent Document 1).

  The conventional brushless DC motor driving apparatus will be described with reference to the drawings.

  FIG. 6 is a block diagram of a conventional brushless DC motor driving apparatus.

  In FIG. 6, reference numeral 1 denotes a single-phase AC power source. Reference numeral 2 denotes a diode full-wave rectifier circuit, the input of which is connected to a single-phase AC power source 1 and the output of which is connected to a smoothing capacitor 3. The smoothing capacitor 3 has a sufficiently small capacity, and is a conventional capacitor having a capacity of about 1/100.

  Reference numeral 4 denotes a PWM (pulse width modulation) inverter, in which six switching elements (including diodes in the reverse direction) are connected in a three-phase bridge. The input is connected to both ends of the smoothing capacitor 3.

  Reference numeral 5 denotes a motor provided with a three-phase winding, which is connected to the output of the PWM inverter 4 and is driven thereby.

Reference numeral 6 denotes a control circuit which is optimally inputted with information such as the voltage v of the single-phase AC power source 1, the DC current idc, the output currents ia, ib, ic of the PWM inverter 4, and the position information θ from the position detection sensor 7. The gate of the PWM inverter 4 is driven so that proper driving is possible.
JP 2002-51589 A

  However, in the above-described conventional configuration, the position detection sensor can be attached like a compressor, although the position detection can be performed even if the DC voltage is lowered if the encoder or the hall element which is a position detection sensor is attached. It cannot be used for purposes that cannot.

  In general, methods for driving a brushless DC motor without using a position detection sensor include a method for detecting an induced voltage of the motor and a method for detecting a rotational position from a motor current.

  However, this position detection is possible when the smoothing capacitor is sufficiently large and the ripple voltage is small. At this time, the induced voltage and the motor current are stable, so that a sufficiently stable position can be detected.However, if the smoothing capacitor is greatly reduced as in this conventional example, the ripple voltage will increase significantly, When the voltage is low, the induced voltage cannot be detected, and since the voltage is low, the motor current necessary for position detection cannot flow.

  As a result, the position cannot be detected when the DC voltage is low, the commutation is greatly shifted in timing, the efficiency is reduced, and in the worst case, a large current flows and the motor stops. Had problems.

  The present invention solves the above-described conventional problem, and even when there is a large ripple voltage with a significantly reduced smoothing capacitor, the efficiency is not reduced without using a position detection sensor, and the current is also stabilized. An object of the present invention is to provide a brushless DC motor driving method and apparatus that can reduce vibrations without stopping the motor and can be driven stably.

  In order to solve the above problems, the present invention provides an AC power supply, a rectifier circuit having a small-capacitance capacitor with the AC power supply as an input, an inverter connected to the rectifier circuit, a brushless DC motor driven by the inverter, , A position detecting means A for detecting the rotational position of the rotor in the brushless DC motor for each switching period from the induced voltage or motor current of the brushless DC motor, and operating the inverter; and one of the rotors in the brushless DC motor. Position detection means B that detects the rotational position for each rotation period and operates the inverter, and estimates the position when position detection by means of the position detection means A and position detection means B is impossible. The inverter is operated.

  As a result, in addition to position detection for each switching cycle by the position detection means A, synchronization with position detection for each rotation period by the position detection means B enables stable operation with reduced vibration.

  The motor driving device of the present invention includes position detecting means A that detects the rotational position of the rotor of the brushless DC motor from the induced voltage or motor current of the brushless DC motor and operates the inverter, and each rotation period of the rotor. A position detecting means B for detecting the rotational position of the inverter and operating the inverter, and when the position detecting means A cannot detect the position, the position is estimated and the inverter is operated. Thus, even when position detection is impossible, the position can be estimated and commutation according to position detection can be performed, and by adding a correction value obtained from the difference from the position detection means B, vibration can be obtained. Can be suppressed, stable operation is possible, and its application can be greatly expanded.

  The invention according to claim 1 is an AC power supply, a rectifier circuit having a small-capacitance capacitor with the AC power supply as an input, an inverter connected to the rectifier circuit, a brushless DC motor driven by the inverter, Position detecting means A for detecting the rotational position of the rotor in the brushless DC motor at each switching period from the induced voltage or motor current of the brushless DC motor, and operating the inverter, and one rotational period of the rotor in the brushless DC motor Position detecting means B for detecting the rotational position of each and operating the inverter, and when the position detecting means A and position detecting means B cannot detect the position, the position is estimated and the inverter Is to operate.

  Thus, when the position detection by the position detection means A is impossible, the position is estimated and the inverter is operated. Therefore, in addition to the position detection for each switching period, the position detection is synchronized with the position detection for each rotation period. By doing so, stable operation with reduced vibration becomes possible.

  According to a second aspect of the present invention, the position is corrected from the difference between the result of multiplying the switching period of the position detection means A by the number of switching and one rotation period of the position detection means B. .

  As a result, a correction value is added to the position detection for each switching cycle, the difference from the position detection for each rotation cycle is corrected, and stable operation with reduced vibration is possible.

  According to the third aspect of the present invention, the predetermined time is determined based on the detection time when the position can be detected, and the position is switched every predetermined time when the position cannot be detected. Estimate.

  As a result, in a state where position detection is not possible, a motor such as a compressor operates with inertia (moment of inertia), so that stable operation can be realized and motor stop can be prevented.

  According to a fourth aspect of the present invention, when the output voltage of the rectifier circuit is equal to or lower than a predetermined voltage, it is determined that position detection is impossible.

  As a result, it is possible to accurately determine a portion where position detection is not possible, and thus more stable operation can be performed.

  The invention according to claim 5 is a three-phase bridge connection of an AC power source, a rectifier circuit that receives the AC power source, a small-capacitance capacitor connected to the output side of the rectifier circuit, and six switch elements. A position at which a rotation position of the brushless DC motor for each switching period is detected from an induced voltage or a motor current of the brushless DC motor, and the inverter is operated. A position detecting means A and a position detecting means B for detecting the rotational position of each rotation period of the rotor in the brushless DC motor to operate the inverter, and the position by the position detecting means A and the position detecting means B. Position estimation means for estimating the position when it is impossible to detect, position detection means A, position detection Switching between said position estimating means and stage B is obtained by having a control means so as to operate the inverter.

  By adopting such a configuration, in addition to position detection for each switching period, synchronization with position detection for each rotation period enables stable operation with reduced vibration.

  According to a sixth aspect of the present invention, there is provided correction means for correcting the position based on a difference between a result obtained by multiplying the switching period of the position detection means A by the number of switching and one rotation period of the position detection means B. It is.

  By adopting such a configuration, it is possible to perform stable operation with reduced vibration by correcting the difference with the position detection for each rotation cycle in addition to the position detection for each switching cycle.

  According to a seventh aspect of the present invention, the position estimating means determines a predetermined time based on a detection time when position detection is possible, and an estimated position when position detection is impossible is determined by timer means. It is determined using.

  By adopting such a configuration, in a system having a proper inertia (moment of inertia) such as a compressor, stable operation can be realized with a simple and easy configuration.

  According to an eighth aspect of the present invention, when the voltage across the capacitor is detected and the voltage is equal to or lower than a predetermined voltage, the inverter is operated by the output from the position estimating means.

  By adopting such a configuration, it is possible to accurately determine a state in which the DC voltage decreases and position detection cannot be performed, and appropriate switching can be performed, so that more stable operation can be realized.

  According to the ninth aspect of the present invention, the brushless DC motor drives a compressor, a condenser, a decompressor, an evaporator, and the like constituting a refrigeration air conditioning system.

  By adopting such a configuration, it is possible to realize a small-capacitance capacitor in an application in which a position detection sensor cannot be provided, so that it is possible to realize a significant downsizing of the device that could not be considered so far.

  In a tenth aspect of the present invention, a blower that sends wind is driven by the brushless DC motor.

  By adopting such a configuration, especially in applications where the moment of inertia (inertia) is large, such as a blower, a large ripple due to a small-capacitance capacitor can rotate the motor without significantly affecting its rotational speed. Thus, it is possible to realize a significant downsizing of the device that could not be considered so far.

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

(Embodiment 1)
FIG. 1 is a block diagram of a brushless DC motor driving apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, an AC power supply 10 is a general commercial AC power supply of 100 V 50 Hz or 60 Hz in the case of Japan. The rectifier circuit 11 is configured by bridge-connecting four diodes as is well known. A small-capacitance smoothing capacitor 12 provided at the subsequent stage of the rectifier circuit 11 is a chip capacitor of 4 μF or less.

  In recent years, a capacitor having a high withstand voltage and a large capacity can be realized on a chip.

  Therefore, conventionally, an electrolytic capacitor having a large capacity (several hundred μF in the case of 200 W output) has been mainly used for this capacitor. However, in the first embodiment, the capacitor is very small due to the above-described miniaturization. The driving device can be realized.

  A circuit in which the rectifier circuit 11 and the capacitor 12 are combined becomes a waveform rectifier.

  Conventionally, this smoothing capacitor generally includes an output capacity ([W] or [VA]) of the inverter 13, an input capacity ([W] or [VA]) of the entire driving device, and a ripple of a DC voltage. The capacitance of the capacitor was determined from the characteristics of the ripple resistance of the smoothing capacitor depending on the amount and ripple current.

  In consideration of these conditions, a capacity of about 2 to 4 μF / W is generally secured. That is, in the case of an output capacity of 200 W, an electrolytic capacitor of about 400 to 800 μF was used.

  On the other hand, in the first embodiment, a capacitor having a capacitance of 0.1 μF / W or less is used as the capacitor 12. That is, in the case of an output capacity of 200 W, a capacitor of 20 μF or less is used.

  The inverter 13 is configured by three-phase bridge connection of six circuits in which a diode connected in the opposite direction to the switching element IGBT is set.

  The brushless DC motor 14 is driven by the three-phase output of the inverter 13. The stator of the brushless DC motor 14 is provided with a three-phase star-connected winding. This winding method may be concentrated winding or distributed winding. A permanent magnet is disposed on the rotor. The arrangement method may be a surface magnet type (SPM) or a magnet embedded type (IPM), and the permanent magnet may be a ferrite or a rare earth.

  The compression element 15 connected to the rotor shaft of the brushless DC motor 14 has a known configuration, and sucks, compresses and discharges the refrigerant gas. The brushless DC motor 14 and the compression element 15 are connected to each other. The compressor 16 is configured by being housed in the same sealed container.

  The compressor 16 is used in a well-known refrigeration cycle configuration, and the discharge gas compressed by the compressor 16 returns to the suction of the compressor through the condenser 17, the decompressor 18, and the evaporator 19. Is configured.

  As is well known, according to the refrigeration and air conditioning system, the condenser 17 radiates heat and the evaporator 19 absorbs heat, so that cooling and heating can be performed. If necessary, blowers F1, F2, etc. may be added to the condenser 17 and the evaporator 19 to further promote heat exchange.

  The position detection means A20 multiplies the rotational position of the rotor in the brushless DC motor 14 for each switching period CF from the induced voltage or motor current of the brushless DC motor 14, the switching period CF, and the switching number SA, thereby rotating one rotation period TA. Detection is performed.

  In the first embodiment, a method for detecting the rotational position of the rotor from the induced voltage will be described.

  Further, the inverter 13 is a 120-degree energization type rectangular wave drive that can produce a phase that is not energized at all times. The inverter 13 detects the zero-cross point of the induced voltage that occurs in the non-energized phase and detects the rotational position. .

  The position estimation means 21 includes a timer means (not shown), and when the position detection means A20 is normally detecting the position, it measures the time of the detection timing. Based on this timing time, position estimation is performed to output a drive output.

  The voltage detection means 22 detects the voltage across the capacitor 12, determines whether the voltage value is larger or smaller than a predetermined value set in advance, and outputs a signal.

  The switching means 23 receives the output of the voltage detection means 22 as an input, selects either the position detection means A20 or the position estimation means 21 and outputs it.

  The commutation means 24 receives the output of the switching means 23 and controls ON / OFF of the six IGBTs of the inverter 13.

  The position detection means B25 detects the rotational position of the rotor of the brushless DC motor 14 for each rotation period TB from the induced voltage or motor current of the brushless DC motor 14.

  In the first embodiment, description will be made assuming that the position detection of the rotor is detected from the induced voltage.

  That is, the inverter 13 is a 120-degree energization type rectangular wave drive, and a phase that is not always energized is generated. The rotation position is detected by detecting the zero-cross point of the induced voltage generated in this non-energized phase, and the difference between one rotation period TA and one rotation period TB obtained by multiplying the switching period SA and the switching number CF is corrected. By doing so, stable rotation with less vibration becomes possible.

  Next, the operation of the brushless DC motor driving apparatus configured as described above will be described.

  The AC power supply 10 is full-wave rectified by the rectifier circuit 11, but the capacitor 12 has a much smaller capacity than the conventional one, so that its output voltage (voltage across the capacitor 12) is not smoothed as will be described later. , With a big ripple.

  Further, since the position detecting means A20 detects the rotational position of the rotor of the brushless DC motor 14 from the induced voltage, when the output voltage of the rectifier circuit 11 is low, a desired voltage (current) cannot be secured sufficiently. Therefore, the position cannot be detected.

  Furthermore, since only the position detection means A20 performs detection for each switching cycle SA, the accuracy is poor when the single rotation cycle TA is calculated by multiplication with the switching number CF, and in driving the brushless motor 14, The vibration was getting bigger.

  On the other hand, the position estimation means 21 always detects the position detection timing of the position detection means 20, and outputs a position estimation signal at the same timing as the previous timing when no position detection signal is input.

  Further, if the voltage across the capacitor 12 detected by the voltage detecting means 22 is higher than a preset value (50 V in the first embodiment), the switching means 23 selects the signal of the position detecting means 20. -Switch and output to commutation means 24. On the contrary, if it is lower than the predetermined value, the switching means 23 selects / switches the signal of the position estimation means 21 and outputs it to the commutation means 24.

  The position detection means B25 is a means for directly detecting one rotation period TB from the motor current of the brushless DC motor 14 irrespective of the switching period, and this detection signal is a reference timing at which stable rotation can be performed.

  Although not shown here, the drive control of the brushless DC motor 14 is performed by detecting that the voltage across the capacitor 12 is changed by the voltage detection means 22 and performing feedforward control to the duty of the output PWM control. The output voltage or current of the inverter 13 is controlled to be constant.

  That is, with respect to the base (basic) duty obtained by speed control, the voltage or current of the output is adjusted by decreasing the duty when the voltage across the capacitor 12 is high, and conversely when the voltage is low, the duty is increased. The brushless DC motor 14 is driven smoothly.

  Next, voltage waveforms at both ends of the capacitor 12 will be described with reference to FIGS.

  FIG. 2 is a timing chart showing the voltage waveform of the capacitor in the first embodiment of the present invention.

  In FIG. 2, the vertical axis represents voltage and the horizontal axis represents time. The AC power supply 10 is a 100 V 50 Hz AC power supply.

  In the same figure, a waveform A is a waveform when the load current is very small (almost no current flows), and the charge of the capacitor 12 is hardly used and the voltage is hardly lowered. However, the load current here is the output current of the rectifier circuit 11, that is, the input current to the inverter 13. In waveform A, the average voltage is 141 V, the ripple voltage is 0 V, and the ripple content is 0%. In addition, a ripple voltage and a ripple content rate are defined as follows.

  Next, as the load current is increased, the charge stored in the capacitor 12 is used, and as shown in the waveform B, the voltage decreases instantaneously. However, the instantaneous maximum voltage determined from the power supply voltage is 141 V and does not change.

  In the case of waveform B, since the instantaneous minimum voltage is 40V, the average voltage is about 112V, the ripple voltage is 101V, and the ripple content is 90%.

  When the load current is further increased, almost no charge is stored in the capacitor 1, and the instantaneous minimum voltage decreases to almost 0V as shown in the waveform C. However, the instantaneous maximum voltage determined from the power supply voltage is 141 V and does not change. In the case of waveform C, since the instantaneous minimum voltage is 0V, the average voltage is about 100V, the ripple voltage is 141V, and the ripple content is 141%.

  Thus, when the capacitor 12 has a small capacity, when the load current is taken out, the input AC power supply 10 is not fully smoothed but has a waveform obtained by full-wave rectification.

  Next, the relationship between the load current, the instantaneous minimum voltage, and the ripple content will be described in more detail with reference to FIG.

  FIG. 3 is a characteristic diagram showing the load current and the instantaneous minimum voltage / ripple content in Embodiment 1 of the present invention.

  In FIG. 3, the horizontal axis indicates the load current, and the vertical axis indicates the instantaneous minimum voltage and the ripple content. Further, the solid line indicates the instantaneous minimum voltage characteristic, and the broken line indicates the ripple content ratio characteristic.

  The current waveform shown in the waveform A described in FIG. 2 is a case where the load current is 0 A, the instantaneous minimum voltage is 141 V, and the ripple content is 0%. The current waveform shown in waveform B is a case where the load current is 0.25 A, the instantaneous minimum voltage is 40 V, and the ripple content is 90%. The current waveform shown in the waveform C is a case where the load current is 0.35 A, the instantaneous minimum voltage is 0 V, and the ripple content is 141%. And at a current of 0.35 A or more, neither the instantaneous minimum voltage nor the ripple content ratio changes.

  In the brushless DC motor driving apparatus according to the first embodiment, the actual use range is assumed to be a load current of 0.25 A or more and 1.3 A or less. Further, in the actual use range, a small-capacitance capacitor 12 whose ripple content is always 90% or more is selected.

  In the first embodiment, as described above, the position cannot be detected at 50 V or less, and as a result, a portion where the position cannot be detected in any actual use range is included.

  Next, the operation in FIG. 1 will be described in more detail with reference to FIG.

  FIG. 4 is a flowchart showing the contents of the control operation in Embodiment 1 of the present invention.

  First, in STEP 1, the voltage detection means 22 detects the DC voltage Vdc. The DC voltage Vdc here is the voltage across the capacitor 12.

  Next, in STEP 2, the position detecting means A20 detects the switching period SA and the switching number CF.

  In STEP 3, the single rotation period TA of the brushless motor 14 is obtained by multiplying the switching period SA by the switching number CF.

  In STEP 4, the position detection means B25 directly detects one rotation period TB from the motor current of the brushless DC motor 14 regardless of the switching period.

  In STEP5, if the TA calculated from the position detecting means A20 is equal to and smaller than the TB detected from the position detecting means B25, the position estimated value is corrected by + S, and the process proceeds to STEP6. Conversely, if the TA calculated from the position detection means A20 is larger than the TB detected from the position detection means B25, the estimated position value is corrected by -S, and the process proceeds to STEP7.

  Next, in STEP 8, the voltage is compared with a predetermined value 50V at which position detection cannot be performed.

  In STEP9, the switching means 23 switches so as to select the position estimating means 21 based on the result of STEP8.

  As a result, as shown in STEP 10, the position estimation unit 21 determines whether or not the position detection signal has passed a predetermined time from the previous change. This fixed time is a time determined in advance by position detection, and the time varies depending on the rotational speed. Further, correction values + S and −S determined in any one of STEPs 6 and 7 are added to absorb the calculation error for a certain time.

  Here, if the fixed time has not passed, it passes and completes as it is, and if the fixed time has passed, the process proceeds to STEP 11 and the switching element of the inverter 13 is converted into the commutation means on the assumption that commutation, that is, position detection is performed. The operation of switching at 24 is performed.

  Further, in STEP8, the voltage is compared with a predetermined voltage 50V at which position detection is impossible. If it is 50V or more, the process proceeds to STEP12.

  In STEP 12, the switching means 23 is switched so as to select the position detecting means 20.

  As a result, the position detecting means 20 determines whether or not the position detection signal has changed from the previous change, as shown in STEP 13.

  If the state has not changed in STEP 13, it passes and completes as it is, and if the state has changed, the process proceeds to STEP 14, and it is assumed that commutation, that is, position detection has been performed. Perform switching operation. Further, correction values + S and −S determined in any one of STEPs 6 and 7 are added to absorb the calculation error for a certain time.

  By repeating the above operation within a predetermined time, the voltage detection means 22 can always detect the state of the DC voltage, and the signal between the position detection means 20 and the position estimation means 21 can be switched by the switching means 23 according to the state. The commutation operation can be performed even in a state where the position detection with a low DC voltage cannot be performed, and the operation can be continued.

  A waveform when the above-described operation is performed will be further described with reference to FIG.

  FIG. 5 is a timing diagram showing waveforms at various parts in the first embodiment of the present invention.

  In FIG. 5, (A) is a DC voltage, which is a voltage waveform across the capacitor 12. (B) is voltage detection and is an output waveform of the voltage detection means 22. The voltage detection means 22 outputs a result obtained by comparing the direct current voltage of (A) with a predetermined voltage (50 V in the first embodiment). If the voltage detection means 22 is 50 V or higher, the high level is set. If it is less than 50 V, the low level is set. Output a signal. FIG. 5 shows a case where the DC voltage is 50 V or less at times T6 and T7.

  (C) is position detection, and shows an output waveform of the position detection means A20. (D) shows the output waveform of the position detecting means B25. Further, (C + D) is position estimation, and shows an output waveform of the position estimation means 21.

  Therefore, as shown by the waveforms (C) and (D), position detection is possible when the DC voltage is 50 V or more, and position detection is performed in a normal state during the time T1 to T5 and time T8 to T12. It can be carried out.

  On the other hand, at times T6 and T7 in FIG. 5, since the DC voltage is less than 50V, the position detection signal from the position detection means 20 is not output, or even if it is output, a malfunction that does not match the timing at all. It is likely to be a triggering signal.

  Therefore, at time T6 and T7, the signal of the position estimation means 21 is used for commutation.

  That is, the position estimation means 21 measures the time from the previous commutation timing T5, and performs commutation at the timing of time T6 when a predetermined time has elapsed. Similarly, at time T7, commutation is performed after a predetermined time has elapsed from time T6.

  The predetermined time here is a time during which position detection is normally performed, for example, a time period between time T4 and T5, and one rotation period TA calculated by the position detection means A20 and one time detected by the position detection means B. A predetermined time is obtained by adding a correction value calculated from the rotation period TB. The timing is shown in the waveform of (C + D) position estimation in FIG.

  As described above, at time T1 to T5 and time T8 to T12, the switching unit 23 selects and outputs the output of the position detection unit A20. At times T6 and T7, the switching means 23 selects and outputs the output of the position estimating means 21.

  The output of the switching means 23 is input to the commutation means 24, and the commutation means 24 turns on the six switching elements of the inverter 13 as shown in the waveforms (E) to (J) of FIG. / OFF operation. In FIG. 5, the High level indicates an ON operation and the Low level indicates an OFF operation. Therefore, the hatched range is in the ON operation state.

  As an example of the output voltage waveform of the inverter 13, the U-phase voltage waveform is shown in the waveform (K) of FIG.

  As shown in the figure, the maximum output voltage is regulated by the DC voltage, and the envelope of the U-phase voltage (shown by a broken line) matches the DC voltage of (A).

  Similar waveforms are formed with respect to the U phase for the other V and W phases.

  As described above, since the duty of PWM control is changed according to the voltage level of the DC voltage, as shown in the waveform (K) of FIG. 5, the duty is increased at a low voltage (for example, between time T5 and T6). The duty is lowered at a high voltage (for example, between times T11 and T12). This prevents current instability due to voltage fluctuations.

  In the first embodiment, the position of the rotor in the brushless DC motor 14 is detected by the voltage detection means 22 that directly detects the voltage level. However, the timing such as zero crossing is detected, and the voltage level according to the time is detected. It does not matter if it is estimated.

  Further, the position detecting means A20 and the position estimating means 21 are switched by the DC voltage. However, it is also possible to automatically switch to the position estimating means 21 when no position detection signal is output.

  Furthermore, in the first embodiment, the driving load of the brushless DC motor 14 has been described by taking the compressor 16 as an example. However, as in the fans F1 and F2 shown in FIG. 1, the inertia moment (inertia) is large. Even when applied to the use of motor equipment, the motor can be rotated without being greatly affected by large ripples due to the small-capacitance capacitors. Miniaturization can be realized.

  In the first embodiment, the position detection of the rotor, such as the position detection means A20 that detects the position in real time, and the position detection means B25 that detects each rotation period are used. By doing so, it is possible to suppress vibrations generated from uneven rotation and to perform stable rotation driving.

  As described above, according to the first embodiment, when position detection by the position detection means A20 is impossible, the position is estimated and the inverter 13 is operated. In addition to position detection for each switching period, By synchronizing with position detection for each rotation cycle, stable operation with reduced vibration becomes possible.

  Further, when position detection by the position detection means A20 is impossible, the position is estimated and the inverter 13 is operated. Therefore, a correction value is added to position detection for each switching period, and position detection for each rotation period is performed. By correcting the difference, the operation with low vibration and stable rotation can be performed.

  Further, since it is estimated that the position is switched every predetermined time when the position of the rotor cannot be detected, the compression operating with inertia (moment of inertia) in a state where the position cannot be detected. Equipment such as the machine 16 can achieve stable operation and prevent motor stoppage.

  Further, since it is determined that position detection is impossible when the output voltage of the rectifier circuit 11 is equal to or lower than a predetermined voltage, it is possible to accurately determine a portion where position detection is not possible, and more stable. You can drive.

  Furthermore, in order to estimate the position and operate the inverter 13 when position detection by the position detection means A20 is impossible, in addition to position detection for each switching period, synchronization with position detection for each rotation period Thus, stable operation with reduced vibration becomes possible.

  Further, when position detection by the position detection means A20 is impossible, in addition to position detection for each switching cycle by the position detection means A20, a difference from position detection for each rotation period by the position detection means B25 is corrected. Thus, stable operation with reduced vibration becomes possible.

  Furthermore, since the estimated position is determined using the timer means when the position of the rotor cannot be detected, it is simple and easy in a system having an appropriate inertia (moment of inertia) such as a compressor. A stable operation can be realized with a simple configuration.

  Further, when the voltage across the capacitor 12 is detected and the voltage is equal to or lower than a predetermined voltage, the inverter 13 is operated by the output from the position estimating means 21, so that the DC voltage decreases and the position cannot be detected. Since it can be determined accurately and appropriate switching can be performed, more stable operation can be realized.

  Furthermore, by using the brushless DC motor 14 as a drive source of a device to which a position detection sensor cannot be attached, such as the compressor 16 constituting the refrigeration air conditioning system, a small-capacitance capacitor can be realized in the motor drive device. It is possible to realize a significant downsizing of the device that could not be considered before.

  Further, by using the brushless DC motor 14 as a drive source of a device having a large moment of inertia (inertia) like the fans F1 and F2, the rotation speed is not greatly affected by a large ripple caused by a small-capacitance capacitor. The device can be rotated stably, and a significant downsizing of the device that could not be considered before can be realized.

  As described above, the brushless DC motor driving method and apparatus according to the present invention estimate the position when the position cannot be detected by the position detecting means A, and operate the inverter. In addition to position detection, by synchronizing with position detection for each rotation cycle, stable operation with reduced vibration is possible, and it can be widely applied to refrigeration and air-conditioning equipment using a brushless DC motor as a drive source, washing machines, etc. is there.

1 is a block diagram of a brushless DC motor driving apparatus according to Embodiment 1 of the present invention. Timing chart showing voltage waveform of capacitor in the same embodiment Characteristic diagram showing load current and instantaneous minimum voltage / ripple content in the same embodiment Flow chart showing the contents of the control operation in the same embodiment Timing chart showing waveforms of respective parts in the same embodiment Block diagram of a conventional brushless DC motor drive device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 AC power supply 11 Rectifier circuit 12 Capacitor 13 Inverter 14 Brushless DC motor 16 Compressor 17 Condenser 18 Decompressor 19 Evaporator 20 Position detection means A
21 position estimation means 22 voltage detection means 23 switching means 25 position detection means B
F1, F2 blower

Claims (10)

  AC power source, a rectifier circuit having a small-capacitance capacitor with the AC power source as an input, an inverter connected to the rectifier circuit, a brushless DC motor driven by the inverter, an induced voltage or a motor current of the brushless DC motor To detect the rotational position of the rotor in the brushless DC motor for each switching period and detect the rotational position of the rotor in the brushless DC motor for each rotational period by detecting the rotational position of the rotor in the brushless DC motor. A brushless DC motor having position detecting means B for operating an inverter, and estimating the position and operating the inverter when position detection by the position detecting means A and position detecting means B is impossible Driving method.   2. The method of driving a brushless DC motor according to claim 1, wherein position correction is performed based on a difference between a result obtained by multiplying a switching period of the position detection unit A by a switching number and one rotation cycle of the position detection unit B. 3.   The estimation is performed on the assumption that the predetermined time is determined based on the detection time when the position can be detected, and the position is switched at every predetermined time when the position cannot be detected. The driving method of the brushless DC motor according to 2.   The brushless DC motor according to any one of claims 1 to 3, wherein when the output voltage of the rectifier circuit is equal to or lower than a predetermined voltage, it is determined that position detection is impossible. Driving method.   An AC power supply, a rectifier circuit using the AC power supply as input, a small-capacitance capacitor connected to the output side of the rectifier circuit, an inverter in which six switch elements are connected in a three-phase bridge, and driven by the inverter Brushless DC motor, position detection means A for detecting the rotational position of the brushless DC motor for each switching period from the induced voltage or motor current of the brushless DC motor, and operating the inverter, and the brushless DC motor And a position detecting means B for operating the inverter by detecting a rotational position for each rotation period of the rotor, and when position detection by the position detecting means A and the position detecting means B is impossible Position estimating means for estimating position, position detecting means A, position detecting means B and position estimating means Brushless DC motor driving device provided with the control means so as to operate the inverter by switching.   6. The brushless DC motor according to claim 5, further comprising correction means for correcting a position from a difference between a result obtained by multiplying a switching cycle of the position detection means A by a switching number and a rotation cycle of the position detection means B. Drive device.   6. The position estimating means determines a predetermined time based on a detection time when position detection is possible, and determines an estimated position when position detection is impossible using timer means. The brushless DC motor driving device according to claim 6.   8. The inverter according to claim 5, wherein the inverter is operated by an output from the position estimation unit when a voltage across the capacitor is detected and is equal to or lower than a predetermined voltage. Brushless DC motor drive device.   The drive of the brushless DC motor according to any one of claims 5 to 8, wherein the brushless DC motor drives a compressor, a condenser, a decompressor, an evaporator, and the like that constitute a refrigeration and air conditioning system. apparatus.   The brushless DC motor drive device according to any one of claims 5 to 8, wherein the brushless DC motor drives a blower that sends wind.

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