JP2010246333A - Motor drive device and refrigerator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive device capable of carrying out optimum drive depending on a load status. <P>SOLUTION: In low-speed operation, a position signal from a brushless DC motor 4 is acquired by a position detecting unit 5, and PWM feedback control by a first waveform generating unit 6 is carried out to achieve higher efficiency. In high-speed operation, synchronous drive with a fixed frequency is carried out based on a waveform from a second waveform generating unit 9. In drive based on the second waveform generating unit 9, a load status is detected from the phase relationship between an induced voltage phase of the brushless DC motor 4 and an applied voltage phase generated by the second waveform generating unit 9, and either of drive based on the first waveform generating unit 6 and drive based on the second waveform generating unit 9 is selected depending on the load status, and the brushless DC motor 4 is driven according to the selection. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a device for driving a brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding by means of an inverter that supplies power to the three-phase winding. The present invention relates to a brushless DC motor driving apparatus that is optimal for driving a compressor such as an air conditioner.

  Conventionally, this type of motor driving apparatus realizes optimum driving according to the load by switching the waveform generation method according to the state of the driving load (see, for example, Patent Document 1).

  In FIG. 8, the AC power source 1 is a general commercial power source, and is AC 100 V, 50 or 60 Hz in Japan. The rectifying / smoothing circuit 2 includes a rectifying circuit in which four diodes are bridge-connected and two smoothing electrolytic capacitors, and is a voltage doubler rectifying circuit that inputs an AC 100V voltage and outputs a DC 280V.

  The inverter 3 has six switching elements connected in a three-phase bridge, converts the output of the rectifying / smoothing circuit 2 into three-phase AC power, and supplies it to the brushless DC motor 4.

  The brushless DC motor 4 includes a rotor 4a having a permanent magnet and a stator 4b having a three-phase winding, and a three-phase alternating current generated by the inverter 3 flows through the three-phase winding of the stator. Thus, the rotor can be rotated.

  The position detector 205 detects the relative rotational position of the rotor by detecting the induced voltage generated in the three-phase winding urged by the stator as the rotor of the brushless DC motor 4 rotates. It is.

  The first waveform generator 206 generates a signal for driving the switch element of the inverter 3 based on the position detection signal of the position detector 5. This driving signal is based on rectangular wave energization, and produces a rectangular wave with an energization angle of 120 degrees to 150 degrees. In addition to the rectangular wave, a trapezoidal wave having a slight inclination in rising / falling may be used as a waveform conforming thereto. The first waveform generator 206 also performs PWM control duty control in order to keep the rotational speed constant, and operates at the optimum duty according to the rotational position, so that the most efficient operation is possible.

  The rotation speed detection unit 207 detects the rotation speed of the brushless DC motor 4 from the output signal of the position detection unit 205. The rotation number can be detected by counting the output signal of the position detection unit 205 for a certain period of time or measuring the period.

  The frequency setting unit 208 changes only the output frequency while keeping the output duty constant.

  The second waveform generation unit 209 generates a signal for driving the switch element of the inverter 3 based on the output signal of the frequency setting unit 208. This driving signal creates a rectangular wave with a conduction angle of 130 degrees or more and less than 180 degrees. In addition to the rectangular wave, a waveform conforming thereto such as a sine wave or a distorted wave may be used. Further, here, the operation is performed at the maximum duty, and the operation is performed at a constant duty of 90 to 100%.

  The switching determination unit 210 determines the low speed / high speed based on the rotation speed detected by the rotation speed detection unit 207 and switches the waveform for operating the inverter 3 between the first waveform generation unit 206 and the second waveform generation unit 209. is there. Specifically, when the rotational speed is low, the signal from the first waveform generator 206 is selected, and when the rotational speed is high, the signal from the second waveform generator 9 is selected to operate the inverter 3.

  Here, the determination as to whether the rotational speed is low or high is based on the actual rotational speed from the rotational speed detection unit 207, but the set rotational speed and duty may be determined. Since the duty is the maximum duty (generally 100%) and the rotation speed by the PWM duty control in the position detection is maximized, the signal can be switched under this condition.

  The drive unit 211 drives the switch element of the inverter 3 by the output signal from the switching circuit 210. By this driving, an optimum AC output is applied from the inverter 3 to the brushless DC motor 4, so that the rotor can be rotated.

  The operation of the motor driving apparatus configured as described above will be described below.

  First, at a relatively low load and low speed, each switch element of the inverter 3 is driven by the first waveform generator 206 that operates based on the output timing of the position detector 205. At this time, the rotation speed of the brushless DC motor 4 is detected from the output signal of the position detection unit 205, and the first waveform generation unit 206 performs PWM duty control so that the driving speed approaches the target speed. The brushless DC motor 4 is efficiently driven by sensorless PWM control.

  In the load state in which the drive speed of the brushless DC motor 4 does not reach the target speed even though the PWM duty is maximized (for example, 100%) in the driving by the first waveform generation unit 206, the switching determination unit 210 The second waveform generation unit 209 operated by the frequency setting unit 208 is selected to drive the inverter 3. The drive signal of each phase of the inverter 3 is commutated so as to output a predetermined frequency according to the output of the frequency setting unit 208. At this time, the duty phase is constant and the commutation frequency is increased stepwise by synchronous driving regardless of the rotor position, so that the current phase is advanced with respect to the induced voltage phase of the brushless DC motor 4, so-called “weakening magnetic flux control”. The state becomes the same as that of the first waveform generation unit 206, and the driving can be performed at a significantly higher speed than the driving by the first waveform generation unit 206.

With the configuration as described above, the conventional motor driving device can improve the high-load high-speed performance of the brushless DC motor 4 as compared with the general PWM feedback control based on the induced voltage detection in the first waveform generation unit 206. Also, when using a motor with a large amount of stator winding and reduced torque (number of rotations), the first waveform generator 206 performs high-efficiency driving at low speed, and the high-speed driving performance is the second waveform generator 209. It can be ensured by driving at
JP 2004-282911 A

  However, the above-described conventional configuration can increase the efficiency of the brushless DC motor and expand the drivable speed and load range. However, even when the load is reduced from the high speed and high load driving state by the second waveform generating means, Since the two-waveform generating means performs synchronous driving with a constant duty, the applied voltage is high with respect to the load, and the motor current phase is delayed with respect to the induced voltage, so that the motor efficiency may be significantly deteriorated. Had the problem of being.

The present invention solves the above-described conventional problems, and by enabling detection of the load state of the brushless DC motor in driving by the second waveform generator, the waveform generator can be selected according to the load. An object of the present invention is to further improve the practicality of the conventional motor driving device by enabling the brushless DC motor to be optimally driven.

  In order to solve the above-described conventional problems, in the motor driving device of the present invention, when the brushless DC motor is driven by the second waveform generation unit, the waveform correction unit is generated by the second waveform generation unit at a predetermined timing. By driving the inverter through the drive unit with a waveform obtained by intermittently activating part or all of the generated waveform, it is possible to detect the induced voltage phase during synchronous driving, and the detected induced voltage phase and the second waveform generating unit From the phase relationship, the load state monitoring unit can determine whether or not the load state can be driven by the first waveform generation unit.

  As a result, it is possible to detect that the load has decreased and the low-load state that can be driven by the first waveform generating unit is detected while the second waveform generating unit is being driven, and the process proceeds to driving by the first waveform generating unit. The timing to do can be obtained accurately.

  The motor drive device of the present invention can drive the brushless motor with high efficiency and can expand the driveable load and speed range, so that the practicality can be enhanced.

  Moreover, since the refrigerator using the motor drive device of the present invention can drive the compressor in an optimum state according to the load state in the warehouse, it is driven by high efficiency at low load when the interior is in a stable cooling state. Power consumption can be reduced, and when the internal temperature is high, rapid internal cooling operation by high-speed and high-load driving is possible, and the food preservation performance can be improved.

  The invention according to claim 1 is a brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding, an inverter for supplying electric power to the three-phase winding, and a drive for driving the inverter A position detection unit that detects a relative rotational position of the rotor based on an induced voltage generated in a three-phase winding of the stator of the brushless DC motor and outputs a position signal; and the position detection unit A first waveform generator for outputting a rectangular wave or a sine wave or a waveform conforming thereto while performing duty control based on an output signal from the output, a frequency setting unit for changing only a predetermined frequency with a constant duty, and a rectangular wave Or a second waveform generating unit that outputs a sine wave or a waveform conforming thereto at a predetermined frequency determined by the frequency setting unit, and the brush detected by the position detecting unit A phase difference detector for detecting a phase difference between the relative position of the rotor of the DC motor and the phase of the waveform generated by the second waveform generator; and a load of the brushless DC motor from the phase difference obtained by the phase difference detector A load state monitoring unit for monitoring the state, and selecting whether to drive the inverter by the first waveform generation unit from the load state or to drive the inverter by the second waveform generation unit from the load state A switching determination unit that switches the waveform generation unit, and a waveform correction unit that corrects the waveform so that a part or all of the waveform generated in the second waveform generation unit is intermittent at a predetermined timing. Since the load state of the brushless DC motor is monitored at the time of driving by the second waveform generation unit, and it is detected that the load is a low load state that can be driven by the first waveform generation unit, the first waveform Can be obtained accurately when to transition to the driving of the raw part, it is possible to switch the waveform generating section at an optimum timing.

According to a second aspect of the present invention, in the motor driving apparatus according to the first aspect, the load state monitoring unit generates a first waveform when the load state of the brushless DC motor is driven by the second waveform generation unit. When it is detected that the driving by the unit is possible, the switching determination unit switches the brushless DC motor to the driving by the first waveform generation unit. As a result, when the brushless DC motor can be driven by the first waveform generation unit, the drive from the second waveform generation unit shifts to the drive by the first waveform generation unit. Can prevent the step-out caused by the transition in the load state that cannot be driven and can realize stable driving, and the first waveform generator enables high-efficiency driving by PWM feedback control based on position detection, and motor driving The reliability and practicality of the device can be increased.

  According to a third aspect of the present invention, in the first and second aspects of the invention, the driving of the brushless DC motor is shifted from driving at the second waveform generating unit to driving to the first waveform generating unit. The conduction angle before and after is set to 150 degrees or less. As a result, the position detection by detecting the induced voltage of the brushless DC motor can be surely performed immediately after the shift to the drive at the first waveform generation section, and there is no occurrence of an overcurrent or the like when switching the waveform generation section, and a smooth transition is achieved. In addition to being possible, stable driving is possible immediately after the transition, and the reliability and practicality of the motor driving device can be improved.

  According to a fourth aspect of the present invention, when the brushless DC motor is shifted from driving by the second waveform generating unit to driving by the first waveform generating unit in the first to third aspects of the invention, In the case of driving at an energization angle exceeding 150 degrees by driving at the two waveform generation section, the driving angle is lowered to 150 degrees or less and then the drive at the first waveform generation section is started. As a result, the energization angle of the waveform generated by the second waveform generator can be increased to a maximum of 180 degrees, the brushless DC motor can be driven at higher speed and higher torque, and immediately before the transition to the first waveform generator. Since reliable position detection is possible, a stable and smooth transition to the drive to the first waveform generator can be realized, and the reliability and practicality of the motor drive device can be improved.

  According to a fifth aspect of the present invention, the motor driving device according to the first to fourth aspects drives the compressor. Since the compressor is a load having a relatively large inertia due to its configuration, a very stable driving performance can be ensured even by the synchronous driving by the second waveform generator, and a part of the motor applied voltage or the Even when the brushless DC motor is driven in an intermittent pattern, there is almost no influence on fluctuations in driving speed, which is one of the applications that are very suitable for the motor driving device of the present invention.

  According to a sixth aspect of the present invention, the compressor according to the fifth aspect is a reciprocating type. Since the reciprocating compressor has a configuration in which the brushless DC motor 4 is suspended by a spring or the like inside the compressor, vibration and noise due to the driving of the brushless DC motor 4 are hardly leaked to the outside. Therefore, in the motor driving device of the present invention, even if a part of or all of the motor applied voltage is intermittently generated and a slight speed fluctuation occurs in the driving speed of the brushless DC motor 4, vibrations and noises accompanying the fluctuation are generated in the compressor 4. Therefore, noise and vibration performance equivalent to those in the prior art can be obtained without greatly increasing vibration and noise.

In a seventh aspect of the invention, the motor driving device according to the fifth or sixth aspect is used for driving a compressor of a refrigerator. High-load and high-efficiency drive is performed in high-load conditions such as the refrigerator's internal temperature being relatively high and the interior needs to be cooled rapidly, and then the low-speed when the interior is in a stable cooling state and the load is low Since the operation can be switched to the high-efficiency driving in accordance with the load state, the power consumption of the refrigerator can be reduced by the optimum driving, and the food freshening performance can be improved by suppressing the temperature fluctuation in the refrigerator.
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the same reference numerals are given to the same configurations as those of the conventional examples or the embodiments described above, and detailed description thereof will be omitted. The present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention.

  In FIG. 1, an input voltage from an AC power source 1 is converted into DC by a rectifying and smoothing circuit 2 and input to an inverter 3. The inverter 3 converts the direct current input into three-phase alternating current power and supplies it to the brushless DC motor 4.

  The position detector 5 detects the relative rotational position of the rotor by detecting the induced voltage generated in the three-phase winding urged by the stator as the rotor of the brushless DC motor 4 rotates. It is.

  The first waveform generator 6 generates a signal for driving the switch element of the inverter 3 based on the position detection signal of the position detector 5. This driving signal is based on rectangular wave energization, and produces a rectangular wave with an energization angle of 120 degrees to 150 degrees. In addition to the rectangular wave, a trapezoidal wave having a slight inclination in rising / falling may be used as a waveform conforming thereto. The first waveform generator 6 also performs PWM duty control in order to keep the rotational speed constant, and operates with the optimum duty according to the rotational position, so that the most efficient operation is possible.

  The rotation speed detector 7 detects the rotation speed of the brushless DC motor 4 from the output signal of the position detector 5. This rotation speed can be detected by counting the output signal of the position detector 5 for a certain period of time or measuring the period.

  The frequency setting unit 8 changes only the output frequency while keeping the output duty constant.

  The second waveform generation unit 9 generates a signal for driving the switch element of the inverter 3 based on the output signal of the frequency setting unit 8. This drive signal produces a rectangular wave with a conduction angle of 130 degrees or more and less than 180 degrees. In addition to the rectangular wave, a waveform conforming thereto such as a sine wave or a distorted wave may be used. Further, the PWM duty is operated at the maximum, and is constant at 90 to 100%.

  The switching determination unit 10 determines the low speed / high speed based on the rotation speed detected by the rotation speed detection unit 7, and sets the waveform for operating the inverter 3 from the load state of the brushless DC motor from the load state monitoring unit 15. The waveform generator 6 or the second waveform generator 9 is selected and switched. Specifically, when the rotational speed is low, the signal from the first waveform generator 6 is selected, and when the rotational speed is high, the signal from the second waveform generator 9 is selected to operate the inverter 3, Further, when the second waveform generator 9 is driven, when the load is reduced to a state where the first waveform generator can be driven, the first waveform generator is selected to drive the inverter 3.

  Here, the determination of whether the rotational speed is low or high is based on the actual rotational speed from the rotational speed detection unit 7, but the set rotational speed and duty may be determined. Since the duty is the maximum duty (generally 100%) and the rotational speed by the PWM duty control in the position detection is maximized, the signal can be switched under this condition.

  The drive unit 11 drives the switch element of the inverter 3 by the output signal from the switching circuit 10. By this driving, an optimum AC output is applied from the inverter 3 to the brushless DC motor 4, so that the rotor can be rotated.

The waveform correction unit 12 outputs the waveform generated by the second waveform generation unit 9 to the switching determination unit 10, but outputs a waveform in which a part or all of the waveform is intermittent for a certain period at a predetermined timing. The position signal determination unit 13 determines whether or not the signal input from the position detection unit 5 is credible as the position detection signal when driven by the second waveform generation unit 9, and the accurate brushless D
Only a signal including position information of the C motor 4 is extracted.

  The phase difference detection unit 14 detects a phase difference between the phase of the waveform generated by the second waveform generation unit 9 and the induced voltage phase of the brushless DC motor 4. Specifically, it can be detected from the time difference between the position signal output from the position signal determination unit 13 and the output timing of the waveform generated by the second waveform generation unit 9.

  The load state monitoring unit 15 determines whether the load is predetermined based on the phase difference between the induced voltage phase of the motor 4 detected by the phase difference detection unit 14 and the applied voltage generated by the second waveform generation unit in the driving by the second waveform generation unit. It is to monitor whether it is smaller or larger than the state.

  The compression element 16 is connected to the shaft of the rotor 4a of the brushless DC motor 4, and sucks, compresses and discharges the refrigerant gas. The brushless DC motor 4 and the compression element 16 are accommodated in the same hermetic container to constitute the compressor 17. The discharge gas compressed by the compressor 17 constitutes a refrigeration air conditioning system that returns to the suction of the compressor 17 through the condenser 18, the decompressor 19, and the evaporator 20. Then, since endotherm is performed, cooling and heating can be performed. In addition, a heat exchanger may be further accelerated | stimulated using a fan etc. for the condenser 18 or the evaporator 20 as needed. Further, in the present embodiment, the refrigeration system is configured to cool the interior 22 of the refrigerator 21 by the evaporator 20.

  FIG. 2 shows a cross-sectional view of the compressor 17 according to the first embodiment. In FIG. 2, the oil 24 is stored in the sealed container 23 of the compressor 17 and the refrigerant 25 of R600a is sealed, and the brushless DC motor 4 including the stator 4b and the rotor 4a and the compression element 16 driven by the brushless DC motor 4 are provided. It is elastically supported by a spring or the like, and is configured such that vibration due to rotation of the brushless DC motor 4 is difficult to leak out of the compressor.

  The compression element 16 supports a main shaft portion 26 of a crankshaft 28 composed of a main shaft portion 26 to which the rotor 4 a is fixed and an eccentric shaft portion 27, and has a compression chamber 29 and a cylinder 30. A reciprocating compression mechanism is provided by including a reciprocating piston 31 and connecting means 32 for connecting the eccentric shaft portion 27 and the piston 31. Therefore, in the present embodiment, when the second waveform generator 9 is driven, even if the brushless DC motor 4 is driven with a waveform in which a part or all of the waveform for a certain period is intermittent, the compressor 17 having a large inertia is used. In addition to having almost no influence (for example, speed change) on the rotational speed, vibration and noise due to speed fluctuations are less likely to occur due to the characteristics and sealing structure of the reciprocating compressor, and noise is less likely to leak outside the compressor 17. It has a configuration.

  FIG. 3 is a timing chart showing a driving state at a low speed in the first embodiment, and shows a signal of the drive unit 11 and an output terminal voltage state of the inverter 3. This timing chart is a rectangular wave with a conduction angle of 150 degrees, and shows driving in an advanced angle state of 15 degrees.

As shown in FIG. 3, in this state, when both the upper and lower switches of each UVW phase are in the OFF state, a dielectric voltage appears in the output terminal voltage. For example, as shown in the figure, for the U phase, when the output pattern is 11 and 5, both the U phase upper and lower switches are off and an induced voltage appears in the terminal voltage. In order to detect the zero cross point of the induced voltage from the terminal voltage as a position signal, the position detecting unit 5 determines a point where the magnitude relationship between the terminal voltage and 1/2 of the inverter input voltage is inverted (that is, the zero cross point of the induced voltage). Monitor. The detected zero cross point is set as a reference as the relative rotation position of the brushless DC motor rotor, and the next commutation timing is determined from this reference position. In the first embodiment, 150 degrees energization advance angle is 15 degrees, so the next commutation is zero seconds after position detection (that is, at the same time), and commutation (output pattern from 11 to 0 or 5 to 6).
Although FIG. 3 shows the position detection timing based on the U-phase terminal voltage and the U-phase, since the position detection is performed twice for each phase per electrical angle cycle, it is eventually 6 times in one electrical angle cycle. A position detection signal is generated, and each time the position signal is detected, an output voltage is sequentially switched to generate an alternating voltage of an arbitrary frequency and applied to the brushless DC motor 4 for driving.

  The rotation speed detector 7 detects the speed of the brushless DC motor 4 based on the position detection signal. When the detected speed is slower than the target speed, the first waveform generator 6 applies the voltage applied to the brushless DC motor 4. When the speed is higher than the target speed, the PWM duty width is controlled so as to decrease the voltage applied to the brushless DC motor 4 to realize stable driving at the target speed.

  Here, even if the load of the brushless DC motor 4 is large and the PWM duty is 100%, no further voltage can be applied in a state where the driving speed does not reach the target speed, so further high speed driving is impossible. It is. Therefore, at this time, the switching determination unit 10 performs switching so that the brushless DC motor 4 is driven by the second waveform generation unit 9.

  The driving by the second waveform generation unit 9 performs synchronous driving at a frequency set by the frequency setting unit 8 with a waveform having a maximum duty (ie, 100%) and a conduction angle of 130 degrees or more and less than 180 degrees. At the time of switching, the commutation cycle (that is, the driving speed) immediately before switching is the same as the energization angle, and the commutation is repeated at a predetermined timing regardless of the position signal. It can be easily realized without causing any problems.

  FIG. 4 is a timing chart showing a driving state at a high speed in the first embodiment of the present invention. FIG. 4 shows a driving state by the second waveform generation unit, and shows the state of the signal of the driving unit 11 and the W-phase terminal voltage. This timing chart shows driving with a rectangular wave having a conduction angle of 150 degrees.

  In the driving by the second waveform generation unit 9, synchronous driving is performed at an arbitrary frequency set by the frequency setting unit 8 regardless of the rotor position of the brushless DC motor 4, and the phase of the motor induced voltage and the terminal voltage is Equilibrium / stable with appropriate relationship according to driving speed and load condition. At this time, the rotor usually follows the commutation with a delay, that is, the terminal voltage advances with respect to the induced voltage. Therefore, the current phase of the brushless DC motor 4 advances, and the driving state with a so-called weak magnetic flux occurs. Thus, high-speed and high-load driving is possible, and high-speed and high-load performance can be extended compared to sensorless operation by the first waveform generator. On the other hand, in synchronous driving with a constant duty, when the applied voltage is too large with respect to the load and the driving speed, a driving state is applied while braking the rotation of the rotor, and finally the applied voltage and phase are compared with the motor induced voltage phase. There is a possibility that the current becomes a lagging phase, and the motor drive device greatly decreases in efficiency due to an increase in the motor current, or the step-out stop due to unstable driving occurs.

  Therefore, in the present invention, the phase relationship between the motor-induced voltage and the terminal voltage changes depending on the speed and load state during synchronous driving (the lead angle increases as the load increases, and a delay phase occurs when the load is small relative to the applied voltage). Therefore, the load state is detected from the phase difference between the induced voltage and the applied voltage, and the waveform generator is switched depending on the load state, so that optimum driving can be performed.

In FIG. 4, since the conduction angle is 150 degrees, the advance angle when the zero cross detection of the induced voltage coincides with the commutation timing (that is, the commutation is performed immediately after the zero cross detection) is 15 degrees. It turns out that the commutation occurs before the detection of the zero cross of the induced voltage, and the advance angle is 15 degrees or more. In FIG. 4, when both the upper and lower switching elements of the W phase are off, an induced voltage of the brushless DC motor 4 is generated in the terminal voltage. However, since the commutation occurs before the zero cross timing of the induced voltage, an inverter near the zero cross is generated. The terminal voltage is stuck to the input potential (when the upper switching element is on). Therefore, in such a driving state, it is difficult to accurately detect the reference point of the induced voltage phase, such as the zero cross of the induced voltage, and naturally it is difficult to detect the load state from the phase relationship between the induced voltage and the applied voltage.

  FIG. 5 is a timing chart showing position detection at the time of synchronous driving in the first embodiment of the present invention, and shows a signal of the drive unit 11 and an output terminal voltage state of the inverter 3. FIG. 5 shows a state in which synchronous driving is performed at 150 ° energization, and when the terminal voltage states of the V phase and the W phase are seen, since commutation is performed before the zero cross point of the induced voltage, it is 15 ° or more. It turns out that it is an advance angle state. Further, the induced voltage zero cross point is buried in the input voltage or the GND level of the inverter 3 due to the energization of the switch element, and is in an undetectable state.

  Therefore, in the first embodiment, the second waveform is forcibly turned off during a certain period during which the waveform correcting means 12 is expected to generate a zero cross point of the induced voltage in the energized section on the upper side of the U phase. The waveform of the generator 9 is corrected. As a result, the conduction angle at the time of correction is set to 150 degrees or less so that the zero cross of the induced voltage can be reliably detected (in the first embodiment, in the output pattern 0, the switching element on the upper side of the U phase is turned on, It is forcibly turned off and 150 degrees energization is 120 degrees). As a result, as shown in the U-phase terminal voltage waveform of FIG. 5, before the U-phase upper side commutates (that is, before switching to the output pattern 1), an induced voltage zero cross appears and can be detected. Accordingly, during this period, the rotor relative position of the brushless DC motor 4 can be accurately detected even by synchronous driving by the second waveform generator, and the phase difference between the motor-induced voltage phase and the applied voltage phase generated by the second waveform generator. Can be accurately detected.

  Here, the operation of the position signal determination unit 13 will be described. In the first embodiment, the relative position of the rotor of the brushless DC motor 4 is detected as position information at the time when the magnitude relation is inverted by comparing the magnitude of the inverter input voltage with 1/2 of the inverter output terminal voltage. In the V-phase and W-phase terminal voltages of 5, the point at which the magnitude relationship between the inverter terminal voltage and 1/2 of the inverter input voltage is reversed is clearly deviated from the induced voltage zero cross point (in the U-phase terminal voltage, the inverter terminal voltage This also applies to the point where becomes smaller than the inverter input voltage 1/2). Therefore, in order to reliably detect the rotor relative position of the brushless DC motor 4, it is necessary to take out only the signal including the rotor position information from the output signal of the position detector.

  Therefore, in the first embodiment, the position signal determination unit 13 selects the output signal of the position detection unit 5 and extracts only the signal including the position information of the brushless DC motor 4. Specifically, only the signal obtained at the time when the switching element is forcibly stopped to acquire the induced voltage and the output pattern before that time (in the case of the output patterns 11 and 0 in this embodiment) is extracted, This is realized by recognizing it as a signal.

  Next, the phase relationship between the zero cross point of the induced voltage obtained as described above and the applied voltage waveform generated by the second waveform generator 9 will be described.

  FIG. 6 is a timing chart showing changes in position detection timing depending on the load state in the first embodiment of the present invention.

  In FIG. 6, (A) and (B) show a high load (A) and a low load (B) when driving at the same speed. In this timing chart, the energization angle is 150 degrees as in FIG. 5, and the waveform correction unit 12 forcibly turns off the U-phase upper switching element of the waveform in the second waveform generation unit 9 in the output pattern 0. It is corrected as follows.

  In the high load state in FIG. 6A, the drive is stable in a large advance state, and therefore the position detection timing is delayed from the timing at which the output pattern 11 is switched to 0 (ie, commutation timing). When energization is 150 degrees and the advance angle is 15 degrees, the commutation is performed simultaneously with the position detection (that is, the induced voltage zero cross timing), so that it is understood that the drive is performed with the advance angle of 15 degrees or more. In addition, when the induced voltage zero cross point is used as a position signal, the maximum advance angle at 150 degrees energization is 15 degrees. Therefore, in the state shown in FIG. 6A, the first waveform generator 6 cannot be driven. . Accordingly, in such a load state, the switching determination unit 10 selects driving by the second waveform generation unit 9 and continues high load / high speed driving. As described above, the synchronous driving by the second waveform generator 9 balances in an appropriate advance angle state depending on the driving speed and the load state, so that the advance angle (timing delay from commutation to position detection) increases with the load. Will increase.

  On the other hand, in the low load state of FIG. 6B, position detection occurs at the same time when the output pattern is switched from 11 to 0 (that is, commutation timing). That is, since this state is a state where the lead angle of 15 degrees energization is 15 degrees, it is a load state in which the first waveform generator 6 can be driven. Although not shown, when the load is further reduced from the load state of FIG. 6B, the position detection signal is generated earlier than the timing at which the output pattern switches from 11 to 0, and the advance angle is less than 15 degrees. .

  In this way, during the synchronous driving by the second waveform generator 9, the advance angle changes depending on the speed and load state (the advance angle increases as the load increases), so the phase relationship between the applied voltage and the induced voltage is also in the load state. (The phase of the applied voltage advances with respect to the induced voltage as the load increases), so that the load state can be known by detecting the phase relationship between the applied voltage phase and the induced voltage phase.

  The phase difference detection unit 14 detects the relative difference between the applied voltage (phase current) phase and the motor induced voltage phase from the difference between the commutation timing and the position detection signal acquisition timing when driven by the second waveform generation unit 9. However, when this timing difference is larger than a predetermined difference, the load is large and the first waveform generator cannot be driven, so that it is output to the switch determiner 10, and the switch determiner 10 receives the second waveform generator. Select 9 to continue driving. When the difference is smaller than the predetermined timing difference, the driving by the first waveform generator 6 is possible, and the switching determination unit 10 selects the driving by the first waveform generator 6, switches the waveform generator, and outputs the position signal. High-efficiency drive by PWM feedback control based on this is performed.

  Note that the transition from the driving at the second waveform generator 9 to the driving at the first waveform generator 6 is based on the position signal detected in the driving at the second waveform generator 9. By detecting the commutation timing immediately after the section transition, a smooth transition can be realized without causing an overcurrent stop or a step-out stop due to a commutation timing shift or the like.

FIG. 7 is a flowchart showing selection of the waveform generation unit during synchronous driving in the first embodiment of the present invention. In FIG. 7, first, a signal input from the position detection unit 5 is acquired in STEP 101, and the process proceeds to STEP 102. In STEP102, the position signal determination unit 13 monitors whether or not the timing is such that the position signal can be accurately detected (that is, whether the output pattern in FIG. 5 is 11 or 0 in the embodiment of the present invention). When the signal cannot be detected, the process proceeds to STEP 111, discarding data on the assumption that the signal acquired in STEP 101 is not a signal including accurate position information, and the switching determination unit 10 selects and drives the second waveform generation unit 9. Continue. In the case where the position signal can be accurately detected in STEP 102, the process proceeds to STEP 103, where the phase difference detection unit 14 detects the timing difference between the applied voltage generated in the second waveform generation unit 9 and the position signal acquired in STEP 101. Proceed to In this embodiment, in order to easily detect the phase relationship between the motor induced voltage and the applied voltage generated by the second waveform generator 9, the position detection signal and the commutation (commutation from the output pattern 11 to 0). ) The timing difference is detected.

  In STEP 104, in order to determine the load state, the load state monitoring unit 15 determines the magnitude relationship between the timing difference obtained in STEP 103 and a predetermined value (in this embodiment, with respect to the commutation timing from the output pattern 11 to 0). Since it is determined whether the position detection signal is generated first or later, it is determined whether or not the timing difference is greater than 0). If it is greater than the predetermined value in STEP 104, it is determined that the load is large, and the process proceeds to STEP 121. The switching determination unit 10 selects the second waveform generation unit 9 and continues high speed and high load driving. move on.

  In STEP 105, it is determined whether or not the current energization angle is greater than 150 degrees. If the energization angle is less than 150 degrees, the process proceeds to STEP 106, the first waveform generator 6 is selected, and PWM feedback control based on position detection is performed. To do.

  When the energization angle is larger than 150 degrees in STEP 105, the process proceeds to STEP 131, where the switching determination unit 10 selects the second waveform generation unit 9 and decreases the energization angle by a predetermined angle (for example, 1 degree) in STEP 132.

  Even in such a light load state, when the energization angle is larger than 150 degrees, the second waveform generation unit 9 is selected without selecting the first waveform generation unit 6, and then the energization angle is reduced. Since the position can be reliably detected immediately after the shift to the drive at the first waveform generator 6, the shift to the drive at the first waveform generator 6 can be performed smoothly and the driving stability can be ensured.

  Further, when the drive by the first waveform generation unit 6 is shifted, the conduction angle in the drive by the second waveform generation unit 9 can be increased to a maximum of 180 degrees by reducing the conduction angle to 150 degrees or less. As a result, further high-speed and high-load drive performance can be extended, and the current rating of the switching element of the inverter 3 can be lowered because the phase current peak at high load can be suppressed by extending the conduction angle. Contributes to cost reduction and miniaturization.

  As described above, in the embodiment of the present invention, the brushless DC motor 4 including the rotor having the permanent magnet and the stator having the three-phase winding, the inverter 3 for supplying power to the three-phase winding, A drive unit 11 that drives the inverter 3 and a position detection unit 5 that detects a relative rotational position of the rotor based on an induced voltage generated in the three-phase winding of the stator of the brushless DC motor 4 and outputs a position signal. A first waveform generator 6 that outputs a rectangular wave, a sine wave, or a waveform equivalent thereto while performing duty control based on an output signal from the position detector, and a frequency that changes only a predetermined frequency with a constant duty A setting unit 8, a second waveform generation unit 9 that outputs a rectangular wave, a sine wave, or a waveform conforming to them at a predetermined frequency determined by the frequency setting unit 8, and a position detection unit 5 detect it. A phase difference detector 14 for detecting a phase difference between the rotor relative position of the brushless DC motor 4 and the phase of the waveform generated by the second waveform generator 9, and the brushless DC motor from the phase difference obtained by the phase difference detector 14 4, the load state monitoring unit 15 that monitors the load state, and the drive speed of the brushless DC motor 4 is driven by the first waveform generation unit 6 according to the load state, or the inverter is operated by the second waveform generation unit 9. A switching determination unit 10 that selects whether to drive and switches the waveform generation unit, and a waveform correction unit that corrects the waveform so that part or all of the waveform generated in the second waveform generation unit at a predetermined timing is intermittent. The load state monitoring unit monitors the load state of the brushless DC motor at the time of driving by the second waveform generating unit, and detects that it is in a low load state that can be driven by the first waveform generating unit. Runode, the timing of transition to the driving of the first waveform generator can be obtained accurately, it is possible to switch the waveform generating section at an optimum timing.

  When the load state monitoring unit 15 detects that the load state of the brushless DC motor 4 can be driven by the first waveform generation unit 6 during driving by the second waveform generation unit 9, the switching determination unit 10 The brushless DC motor 4 is switched to drive by the first waveform generator 6. Thus, when the first waveform generator 6 is in a load state where the brushless DC motor 4 can be driven, the drive from the second waveform generator 9 is shifted to the drive by the first waveform generator 6. Step-out due to transition in a load state where driving at 6 is impossible is prevented, stable driving can be realized, and high efficiency is achieved by PWM feedback control based on position detection by the first waveform generator 6 The motor can be driven, and the reliability and practicality of the motor drive device can be improved.

  In addition, the drive angle of the first waveform generator is set to 150 degrees or less before and after the drive of the brushless DC motor is shifted from the drive of the second waveform generator to the drive of the first waveform generator. The position detection by detecting the induced voltage of the brushless DC motor can be surely performed immediately after the transition to, and there is no occurrence of overcurrent or the like when switching the waveform generator, and a smooth transition is possible immediately after the transition. It can be driven, and the reliability and practicality of the motor drive device can be improved.

  Further, when the brushless DC motor is driven from the drive at the second waveform generation unit to the drive at the first waveform generation unit, when driven at an energization angle exceeding 150 degrees by the drive at the second waveform generation unit, Since the energization angle is reduced to 150 degrees or less and then the drive is performed by the first waveform generation unit, the energization angle of the waveform generated by the second waveform generation unit can be increased to a maximum of 180 degrees. The DC motor can be driven at a higher speed and higher torque, and the position can be detected reliably immediately before the transition to the first waveform generator 6, so that the drive to the first waveform generator can be performed stably and smoothly. And the reliability and practicality of the motor drive device can be improved.

  In addition, when the compressor is driven by the motor drive device of the present embodiment, the compressor is a load having a relatively large inertia due to its configuration, so a very stable driving performance is ensured even by synchronous driving by the second waveform generator. it can. In addition, even when the brushless DC motor is driven in a pattern in which a part or all of the motor applied voltage is intermittent to detect the induced voltage, there is almost no influence on the driving speed fluctuation, and therefore the compressor for the motor driving device of the present invention. Is one of the most suitable applications.

  In the present embodiment, the reciprocating compressor is configured so that the brushless DC motor 4 is suspended by a spring or the like inside the compressor because of its configuration. It is hard to leak. Therefore, even if a slight speed fluctuation occurs in the driving speed of the brushless DC motor 4 by intermittently applying a part or all of the motor applied voltage, the vibration and noise associated therewith can be absorbed inside the compressor 4. In addition, noise and vibration performance comparable to conventional compressors can be ensured without a significant increase in noise.

  In the present embodiment, the motor driving device of the present invention is used for driving the compressor of the refrigerator, so that the high-load high-efficiency driving is performed in a high-load state such as the need to rapidly cool the interior of the refrigerator. When the inside of the cabinet is in a stable cooling state and the load is low, the operation can be accurately switched to a high-efficiency drive at low speed depending on the load state, so it is possible to reduce the power consumption of the refrigerator by optimal compressor driving At the same time, the food preservation performance can be improved by suppressing the temperature fluctuation in the refrigerator.

The brushless DC motor driving device of the present invention realizes high-efficiency and low-noise operation at low speeds, and also enables high-load high-speed driving with a weak magnetic flux by current advance according to the load at high speeds. It is particularly suitable for use in driving compressors such as refrigerators and air conditioners, and fans and vacuum cleaners such as fans with a wide speed range and load range.

1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. Sectional drawing of the compressor of this Embodiment 1. Timing chart showing drive state at low speed in the first embodiment Timing chart showing driving state at high speed in the first embodiment Timing chart showing position detection during synchronous driving in the first embodiment Timing chart showing change in position detection timing according to load state in the first embodiment The flowchart which shows the waveform generation part selection at the time of the synchronous drive in Embodiment 1 of this invention Block diagram of a conventional motor drive device

DESCRIPTION OF SYMBOLS 3 Inverter 4 Brushless DC motor 5 Position detection part 7 1st waveform generation part 8 Frequency setting part 9 2nd waveform generation part 10 Switching determination part 11 Drive part 12 Waveform correction part 14 Phase difference detection part 15 Load condition monitoring part 16 Compressor 21 Refrigerator

Claims (7)

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, a drive unit for driving the inverter, and the brushless DC motor A position detector that detects the relative rotational position of the rotor based on the induced voltage generated in the three-phase winding of the stator and outputs a position signal, and a duty control based on the output signal from the position detector A first waveform generator that outputs a rectangular wave or a sine wave or a waveform conforming thereto, a frequency setting unit that changes only a predetermined frequency with a constant duty, and a rectangular wave or a sine wave or a waveform conforming thereto. A second waveform generator for outputting at a predetermined frequency determined by the frequency setting unit; and a rotor phase of the brushless DC motor detected by the position detector. A phase difference detection unit that detects a phase difference between a position and a phase of a waveform generated by the second waveform generation unit; and a load state monitor that monitors a load state of the brushless DC motor from the phase difference obtained by the phase difference detection unit And switching the waveform generation unit by selecting whether to drive the inverter by the first waveform generation unit or to drive the inverter by the second waveform generation unit from the driving rotational speed and load state of the brushless DC motor A switching determination unit, and a waveform correction unit that corrects the waveform so that part or all of the waveform generated in the second waveform generation unit at a predetermined timing is intermittent, and the load state monitoring unit is the second waveform generation unit A motor drive device that monitors the load state of the brushless DC motor during driving at the motor and detects that the load state can be driven by the first waveform generator. When the load state monitoring unit detects that the load state of the brushless DC motor can be driven by the first waveform generation unit, the switching determination unit switches the brushless DC motor to drive by the first waveform generation unit. The motor drive device according to claim 1 to be switched. 3. The motor according to claim 1, wherein the energization angle before and after the drive of the brushless DC motor shifts from driving by the second waveform generation unit to driving to the first waveform generation unit is 150 degrees or less. Drive device. When the brushless DC motor is driven from the drive at the second waveform generator to the drive at the first waveform generator, if the drive at the second waveform generator is driven at an energization angle exceeding 150 degrees, The motor motor drive device according to any one of claims 1 to 3, wherein the motor shifts to drive by the first waveform generation unit after the angle is lowered to 150 degrees or less. The motor driving apparatus according to any one of claims 1 to 4, wherein the brushless motor drives a compressor. The motor driving device according to claim 5, wherein the compressor has a reciprocating configuration. A refrigerator using the motor driving device according to claim 5 for driving a compressor.