JP2005176437A - Method and device for driving brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a conventional system wherein changeover timing of the switching of an inverter is switchable by a switch by direction of a load state judging part, but it can not switch carrier frequency even if a Duty ratio is small and ripple of a current increases since it does not have a carrier frequency switching means, therefore, it can not reduce noise and vibration. <P>SOLUTION: The invention enables the carrier frequency to be switched into two kinds or more according to the state of waveform outputted to a motor, or the number of revolutions. This suppresss the noise and vibration by switching the carrier frequency, according to the input voltage (the voltage of a commercial power source), the supply voltage (DC voltage) to the inverter 103, the load state(Duty ratio), and the number of revolutions of a rotor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

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

  A conventional technique is disclosed in Patent Document 1, for example. The prior art will be described with reference to the drawings. FIG. 10 is a block diagram of a conventional brushless DC motor driving apparatus.

  In FIG. 10, a commercial power source 101 is an AC power source having a frequency of 50 Hz or 60 Hz and a voltage of 100 V in Japan. The rectifier circuit 102 is a circuit that converts the AC voltage of the commercial power supply 101 into a DC voltage, and includes rectifier diodes 102a to 102d and smoothing electrolytic capacitors 102e and 102f that are bridge-connected. In the circuit shown in FIG. It becomes a rectifier circuit, and a DC voltage of 280 V can be obtained from the AC 100 V input of the commercial power source 101.

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

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

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

  The commutation unit 106 performs logical signal conversion based on the output signal of the back electromotive voltage detection circuit 105, and generates signals for driving the switch elements 103a, 103b, 103c, 103d, 103e, and 103f of the inverter 103.

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

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

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

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

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

  When the load detected by the load state determination unit 108 is a normal load, driving by the commutation unit 106 is performed. The back electromotive voltage detection circuit 105 detects the relative position of the rotor 104 a of the brushless DC motor 104. Next, the commutation unit 106 creates a commutation pattern for driving the inverter 103 from the relative position of the rotor 104a. This commutation pattern is supplied to the drive circuit 110 through the switching unit 109, and drives the switch elements 103a, 103b, 103c, 103d, 103e, and 103f of the inverter 103.

  By this operation, the brushless DC motor 104 performs driving in accordance with the rotational position, which is an efficient driving method.

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

The load on the brushless DC motor 104 increases, and the rotational speed decreases due to the characteristics of the brushless DC motor 104. The load state determination unit 108 determines that this state is a high load state, and switches the output of the switching unit 109 to a signal from the synchronous drive unit 107. By driving in this way, it is intended to suppress a decrease in the rotational speed at the time of high load. In other words, the driving method emphasizes higher power than efficiency.
JP-A-9-88837

  However, the conventional configuration has the following problems.

  Although switching to the commutation unit 106 at low load realizes efficiency reduction suppression, since it does not have a carrier frequency switching means, the carrier frequency at low rotation is increased, current ripple is suppressed, There was a problem that more efficient, quiet and stable operation could not be realized.

  The present invention solves the conventional problems, and a brushless DC capable of sufficiently suppressing noise and vibration even when the operation state is a small duty ratio depending on the supply voltage to the inverter, the state of the load, and the rotational speed. It is an object of the present invention to provide a motor driving method and apparatus.

  In order to solve the above problems, the present invention enables switching of two or more types of carrier frequencies depending on the state of the waveform output to the motor. The input voltage (commercial power supply voltage) and the supply voltage to the inverter are provided. Noise and vibration can be suppressed by switching the carrier frequency according to (DC voltage), load state (Duty ratio), and the number of rotations of the rotor.

  In addition, by having a voltage detection unit that detects the power supply voltage supplied to the inverter and a carrier frequency switching unit that switches the carrier frequency in accordance with the voltage detected by the voltage detection unit, instantaneous voltage drop, power failure, and steep Noise and vibration generated when the power supply voltage rises or the supply voltage to the inverter changes, such as when used under different commercial power supply voltage environments, can be quickly reduced.

  A voltage adjustment unit that adjusts a power supply voltage supplied to the inverter; a voltage control unit that controls a voltage adjustment signal output to the voltage adjustment unit; and a carrier frequency switching unit that switches a carrier frequency according to the voltage adjustment signal; Thus, the optimum power supply voltage can be supplied to the inverter according to the number of rotations of the motor and the like, and the occurrence of noise and vibration due to the change in the power supply voltage can be quickly reduced. Further, since the carrier frequency is switched by the change of the voltage adjustment signal, noise and vibration can be reduced more quickly than the means for switching by the change of the supply voltage to the inverter.

  Also, noise generated when the load state changes by having a duty ratio control unit that adjusts the duty ratio and a carrier frequency switching unit that switches the carrier frequency according to the duty ratio adjusted by the duty ratio control unit And vibration can be reduced quickly. In addition, since the carrier frequency is switched by changing the duty ratio, the input voltage (commercial power supply voltage), the inverter supply voltage (DC voltage), and the voltage adjustment signal do not change as in the case of load fluctuation. In this case, noise and vibration can be reduced.

  In addition, by having a carrier frequency switching unit that switches the carrier frequency according to the rotational speed of the rotor determined by the synchronous rotational speed setting unit, noise and vibration generated when the rotational speed of the rotor is accelerated and decelerated can be quickly obtained. Can be reduced. Further, since the carrier frequency is switched by changing the rotation speed, noise and vibration can be reduced even when the rotation speed is accelerated and decelerated while keeping the duty ratio and voltage constant.

  The present invention makes it possible to switch between two or more types of carrier frequencies depending on the state of the waveform output to the motor. The input voltage (commercial power supply voltage), the supply voltage to the inverter (DC voltage), and the load state Noise and vibration can be suppressed by switching the carrier frequency according to (Duty ratio).

  In addition, by having a voltage detection unit that detects the power supply voltage supplied to the inverter and a carrier frequency switching unit that switches the carrier frequency in accordance with the voltage detected by the voltage detection unit, instantaneous voltage drop, power failure, and steep Noise and vibration generated when the power supply voltage rises or the supply voltage to the inverter changes, such as when used under different commercial power supply voltage environments, can be quickly reduced.

  A voltage adjustment unit that adjusts a power supply voltage supplied to the inverter; a voltage control unit that controls a voltage adjustment signal output to the voltage adjustment unit; and a carrier frequency switching unit that switches a carrier frequency according to the voltage adjustment signal; Thus, the optimum power supply voltage can be supplied to the inverter according to the number of rotations of the motor and the like, and the occurrence of noise and vibration due to the change in the power supply voltage can be quickly reduced. Further, since the carrier frequency is switched by the change of the voltage adjustment signal, there is an effect that noise and vibration can be reduced more quickly than the means for switching by the change of the supply voltage to the inverter.

  In addition, by having a duty ratio control unit that adjusts the duty ratio and a carrier frequency switching unit that switches the carrier frequency in accordance with the duty ratio adjusted by the duty ratio control unit, the duty ratio and voltage are kept constant. It is possible to quickly reduce the noise and vibration generated when it changes. In addition, since the carrier frequency is switched by changing the duty ratio, the input voltage (commercial power supply voltage), the inverter supply voltage (DC voltage), and the voltage adjustment signal do not change as in the case of load fluctuation. In this case, there is an effect that noise and vibration can be avoided.

  Moreover, it occurs when the rotation speed changes by having a synchronous rotation speed setting section that determines the rotation speed and a carrier frequency switching section that switches the carrier frequency according to the rotation speed determined by the synchronous rotation speed setting section. Noise and vibration can be quickly reduced. In addition, since the carrier frequency is switched according to the change in the rotational speed, even if the state of the waveform output to the motor does not change, such as when the rotational speed is changed while maintaining the duty ratio and voltage, noise and vibration There is also an effect that can be avoided.

  According to the first aspect of the present invention, two or more types of carrier frequencies can be switched depending on the state of the waveform output to the motor, and the input voltage (commercial power supply voltage) or the supply voltage to the inverter (DC) The noise and vibration can be suppressed by switching the carrier frequency according to the voltage), the load state (Duty ratio), and the rotation speed of the rotor.

  The invention according to claim 2 includes a voltage detection unit that detects a power supply voltage supplied to the inverter, and a carrier frequency switching unit that switches the carrier frequency according to the voltage detected by the voltage detection unit. Noise and vibration generated when the supply voltage to the inverter changes due to voltage drop, power outage, steep rise in power supply voltage, or use under different commercial power supply voltage environments can be reduced quickly.

  According to a third aspect of the present invention, there is provided a voltage adjustment unit for adjusting a power supply voltage supplied to the inverter, a voltage control unit for controlling a voltage adjustment signal output to the voltage adjustment unit, and a carrier frequency according to the voltage adjustment signal. By providing the carrier frequency switching unit for switching between them, an optimal power supply voltage can be supplied to the inverter according to the number of rotations of the motor and the like, and the occurrence of noise and vibration due to changes in the power supply voltage can be quickly reduced. Further, since the carrier frequency is switched by the change of the voltage adjustment signal, noise and vibration can be reduced more quickly than the means for switching by the change of the supply voltage to the inverter.

  The invention according to claim 4 includes a duty ratio control unit that adjusts the duty ratio, and a carrier frequency switching unit that switches the carrier frequency in accordance with the duty ratio adjusted by the duty ratio control unit. It is possible to quickly reduce noise and vibration generated when the change occurs. In addition, since the carrier frequency is switched by changing the duty ratio, the input voltage (commercial power supply voltage), the inverter supply voltage (DC voltage), and the voltage adjustment signal do not change as in the case of load fluctuation. In this case, noise and vibration can be reduced.

  In the case of accelerating or decelerating the rotational speed of the rotor by having a carrier frequency switching section that switches the carrier frequency according to the rotational speed of the rotor determined by the synchronous rotational speed setting section. Generated noise and vibration can be quickly reduced. Further, since the carrier frequency is switched by changing the rotation speed, noise and vibration can be reduced even when the rotation speed is accelerated and decelerated while keeping the duty ratio and voltage constant.

  According to a sixth aspect of the present invention, in the second to fifth aspects of the present invention, a rotor position detecting unit that detects the position of the rotor, and a load state determining unit that determines a load state of the brushless DC motor. Then, the timing for sequentially switching a plurality of switching elements connected to the three-phase winding is determined based on the position information detected by the rotor position detection unit, or determined by the synchronous rotation number setting unit A switching timing selection unit that selects whether to determine based on the number of rotations performed by the load state determination unit, has a feature that can be operated efficiently under low load conditions that do not require power, By realizing the switching of the carrier frequency, not only noise and vibration can be suppressed, but also the ripple current can be reduced, and the effect is further improved in high efficiency.

  A seventh aspect of the present invention is the rotor according to any one of the second to sixth aspects, wherein the brushless DC motor is a rotor in which a permanent magnet is embedded in the iron core of the rotor and has a saliency. Such a rotor has a saliency, and a reluctance torque due to the saliency acts in addition to the magnet torque of the permanent magnet. Since the ripple increases, it has a characteristic that noise and vibration are likely to occur.

  The invention described in claim 8 is the invention according to any one of claims 2 to 7, wherein the brushless DC motor drives the compressor, and is one of the extremely important applications that can realize low noise in the compressor. is there.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, about the same structure as the past, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted. Further, 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, a commercial power source 1 is an AC power source having a frequency of 50 Hz or 60 Hz and a voltage of 100 V in Japan.

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

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

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

  The rotation speed command circuit 5 is a circuit that commands a desired rotation speed. For example, a refrigerator, an air conditioner or the like is composed of a temperature sensor or the like, and a general-purpose brushless DC motor 4 drive device is a portion composed of a SW or the like for operation by a user, and a necessary number of rotations is set. This is a command circuit.

  The synchronous rotation speed setting unit 6 performs logical signal conversion according to the command rotation speed of the rotation speed command circuit 5, and determines the timing for sequentially switching the switch elements 3a, 3b, 3c, 3d, 3e, and 3f of the inverter 3. The synchronous rotation speed setting unit 6 can convert the signal to a logical signal pattern that causes the brushless DC motor 4 to be driven synchronously, and can forcibly generate a signal pattern at a predetermined frequency.

  The voltage detector 7 detects the output voltage (DC voltage) of the rectifier circuit 2.

  The duty ratio control unit 8 receives the outputs of the synchronous rotation speed setting unit 6 and the voltage detection unit 7 and adjusts the duty ratio so that the output waveform of the inverter 3 is optimized. Here, the duty ratio indicates a ratio between the on-time and the carrier period. The larger the duty ratio, the higher the output voltage.

  The PWM carrier frequency switching unit 9 is a motor that generates a PWM carrier frequency in PWM control, an output signal from the voltage detection unit 7, a voltage adjustment signal from the voltage adjustment unit 13, a duty ratio determined by the duty ratio control unit 8, and the like. 4 has a function of switching the carrier frequency by judging the state of the waveform output to 4, and a function of switching the carrier frequency from the number of rotations determined by the synchronous rotation number setting unit 6. Here, PWM means pulse width modulation, and a carrier frequency that is sufficiently large with respect to the drive frequency (rotation speed) of the motor is selected. Generally, a carrier frequency of about 2 kHz to 20 kHz is used.

  Based on the cycle determined by the synchronous rotation speed setting unit 6 and the duty ratio adjusted by the duty ratio control unit 8, the switch element switching unit 10 switches the switch elements 3a, 3b, 3c, 3d, 3e, A signal for driving 3f is output. The drive circuit 11 drives the switch elements 3 a, 3 b, 3 c, 3 d, 3 e, 3 f of the inverter 3 by the drive signal output from the switch element switching unit 10. The microcomputer 12 realizes the aforementioned functions. These functions can be realized by a microcomputer program. The voltage control unit 13 outputs a voltage adjustment signal to the voltage adjustment circuit 2g, and realizes a function of controlling the voltage supplied to the inverter 3.

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

  FIG. 2 is a diagram illustrating an example of a carrier frequency control pattern representing the present embodiment. In the figure, the horizontal axis represents the supply voltage detected by the voltage detector 7, and the vertical axis represents the carrier frequency. From the figure, the carrier frequency is reduced in the low voltage region, and the carrier frequency is set higher as the voltage increases. In this example, three types of carrier frequencies are switched according to the voltage.

  Therefore, in the relatively high voltage region, the current ratio increases because the duty ratio becomes small. However, since the carrier frequency is increased, the energization OFF time in one cycle is shortened, and the current decrease can be reduced. Vibration and noise due to ripples can be suppressed.

  The reduction in current drop will be described with reference to FIGS.

  FIG. 3 is a diagram showing a switching pattern and a current waveform of each phase in 120-degree rectangular wave energization. In the figure, the horizontal axis represents the electrical angle. The electrical angle represents one rotation at 360 degrees when the rotor 4a has two poles, one rotation at 720 degrees when the rotor 4a has four poles, and one rotation at 1080 degrees when the rotor 4a has six poles. The vertical axis indicates the signal for driving each switch element of the inverter 3 output from the switch element switching unit 10 to the driver unit 12 and the current waveform flowing through each of the three-phase windings in the stator 4b. Symbols in order from the top are the drive signal U of the switch element 3a, the drive signal X of the switch element 3b, the drive signal V of the switch element 3c, the drive signal Y of the switch element 3d, the drive signal W of the switch element 3e, and the switch element 3f. The driving signal Z, the U-phase winding current Iu in the stator 4b, the V-phase winding current Iv in the stator 4b, and the W-phase winding current Iw in the stator 4b.

  An outline of the operation of FIG. 3 will be described. According to the rotational speed determined by the synchronous rotational speed setting unit 6, switching (commutation) of the switch elements constituting the inverter 3 is sequentially performed in 120 degree intervals. The upper arm drive signals U, V, W perform duty control by PWM control. In this figure, the case where the PWM carrier frequency is 3 kHz is illustrated.

  FIG. 4 is a diagram showing a switching pattern and a current waveform of each phase in 120-degree rectangular wave energization when the carrier frequency is doubled with respect to FIG. The symbols and operations in FIG. 4 are the same as those in FIG.

  As is clear from the comparison of the winding currents Iu, Iv, and Iw in FIGS. 3 and 4, the current drop due to energization OFF can be reduced by doubling the carrier frequency. It turns out that the current ripple accompanying ON / OFF can be reduced significantly.

  The reduction of the current ripple works more effectively in a region where the duty ratio is small, that is, a region where the supply voltage to the inverter 3 is large. On the contrary, in the region where the supply voltage is small, it is necessary to increase the average voltage by PWM control. Therefore, the duty ratio is increased to shorten the OFF time with respect to the carrier ON time, and inevitably suppress the current ripple. can do.

  Since the conventional driving apparatus as shown in FIG. 10 does not have a carrier frequency switching unit, the carrier frequency cannot be switched even if the voltage increases. Further, when the voltage changes, the power supplied to the motor 4 increases, the current waveform is disturbed, and the duty ratio control unit 8 needs to reduce the duty ratio so that a desired current waveform is obtained. If the present embodiment includes means for detecting the relative position of the brushless DC motor 4, an appropriate current waveform can be realized by adjusting the duty ratio. However, since the motor 4 generally has an inertial force (a force that works so as to maintain the rotation speed of the motor), it takes time to detect an abnormality in the relative position after the voltage increases. Therefore, if the carrier frequency is switched according to the supply voltage detected by the voltage detection unit 7 instead of switching the carrier frequency according to the duty ratio adjusted by the duty ratio control unit 8, before the duty ratio decreases. The carrier frequency can be switched, and the carrier frequency can be switched before the ripple current increases. As a result, the means for detecting the state of the waveform output to the motor 4 due to the change in the supply voltage is more effective in reducing noise and vibration than the means for detecting the state of the waveform output to the motor 4 due to the change in the duty ratio. Will be big.

  FIG. 5 is a timing chart illustrating an example of a carrier frequency control pattern representing the present embodiment. In the figure, the horizontal axis represents time. The vertical axis represents, in order from the top, the carrier frequency switched by the PWM carrier frequency switching unit 9, the supply voltage (DC voltage) to the inverter 3, and the voltage adjustment signal output from the voltage control unit 13 to the voltage adjustment circuit 2g. The numbers 1 to 3 drawn in the voltage adjustment signal in the figure indicate the contents of the voltage adjustment signal, and the voltage adjustment circuit 2g supplies a larger voltage to the inverter 3 as the number increases. Is shown. From the figure, the carrier frequency is decreased when the voltage control unit 13 is outputting a voltage adjustment signal that makes the voltage relatively low, and the carrier is more output when the voltage adjustment signal that makes the voltage higher is outputted. The frequency is set large. In the case of this example, an example in which three types of carrier frequencies are switched according to the voltage adjustment signal is shown.

  Therefore, since the carrier frequency is increased in a relatively high voltage region, the energization OFF time in one cycle can be shortened, current drop can be reduced, and vibration and noise due to current ripple can be reduced. Since reduction of current drop has already been described with reference to FIGS. 3 and 4, description thereof is omitted here.

  Since the conventional driving apparatus as shown in FIG. 10 does not have a carrier frequency switching unit, the carrier frequency cannot be switched. Further, when the voltage is changed by the voltage control unit 13, a time constant delay occurs due to the electrolytic capacitors 2e and 2f for smoothing, and a voltage adjustment signal for the voltage control unit 13 to supply a larger voltage to the inverter 3 is provided. It takes time until the value of the voltage detected by the voltage detector 7 actually increases after the output. In general, the voltage detection unit 7 includes a noise reduction capacitor, so it is estimated that further delay occurs. Therefore, if the carrier frequency is switched every time the supply voltage adjustment signal output from the voltage control unit 13 is switched instead of switching the carrier frequency according to the supply voltage detected by the voltage detection unit 7, the carrier frequency is supplied to the inverter 3. The carrier frequency can be switched before the voltage to be boosted is increased, and the carrier frequency can be switched more quickly in response to an increase in ripple current. As a result, the means for detecting the state of the waveform output to the motor 4 by the change of the voltage adjustment signal is less in the noise and vibration than the means for detecting the state of the waveform output to the motor 4 by the change of the supply voltage. The effect is significant.

  FIG. 6 is a diagram showing an example of a carrier frequency control pattern representing the present embodiment. In the figure, the horizontal axis represents the duty ratio adjusted by the duty ratio control unit 8, and the vertical axis represents the carrier frequency. From the figure, the carrier frequency is increased in the region with a small duty ratio, and the carrier frequency is set smaller as the duty ratio increases. In this example, three types of carrier frequencies are switched according to the duty ratio.

  Therefore, since the carrier frequency is increased in the region of a relatively low duty ratio, the energization OFF time in one cycle is shortened, and the current drop can be reduced, and vibration and noise due to current ripple can be reduced. Since reduction of current drop has already been described with reference to FIGS. 3 and 4, description thereof is omitted here.

  In the conventional driving apparatus as shown in FIG. 10, when the load state changes, the load state determination circuit 108 is provided but the carrier frequency switching unit is not included, and therefore the carrier frequency cannot be switched. Further, when the load torque becomes small, there is no change point in the supply voltage detected by the voltage detection unit 7 or in the voltage adjustment signal output from the voltage control unit 13, so that FIGS. Even if such a driving method is used, the carrier frequency cannot be switched. Therefore, when the carrier frequency is switched according to the duty ratio adjusted by the duty ratio control unit 8, the carrier frequency is switched when the load torque becomes small and the duty ratio adjusted by the duty ratio control unit 8 becomes small. The carrier frequency can be quickly switched with respect to the ripple current increase. As a result, the noise / vibration reduction effect of the means for detecting the state of the waveform output to the motor 4 due to the change in the duty ratio is less than the other means for detecting the state of the waveform output to the motor 4. It will be big.

  FIG. 7 is a diagram illustrating an example of a carrier frequency control pattern representing the present embodiment. In the figure, the horizontal axis represents the rotor rotational speed determined by the synchronous rotational speed setting unit 6, and the vertical axis represents the carrier frequency. In the case of this example, an example in which three types of carrier frequencies are switched according to the number of rotations is shown. Here, the carrier frequency is reduced in the low rotation speed region, the carrier frequency is maximized at the medium rotation speed, and the carrier frequency is set relatively low when the rotation speed is high.

  FIG. 7 will be described in a little more detail. In the present embodiment, when the voltage control unit 13 is provided, the DC voltage input to the inverter 3 is lowered by the voltage adjustment circuit 2g as the rotational speed is lowered, and the reduction in the duty ratio can be suppressed. . In this case, as described in the description of FIG. 3 and FIG. 4, current ripple can be inevitably suppressed, and the effect of switching the carrier frequency is reduced. However, when the voltage adjustment circuit 2g is a voltage doubler rectification / full wave rectification switching type circuit, the DC voltage can be changed only in two stages, and therefore the DC voltage is adjusted so that the duty ratio is always increased. It becomes impossible. Therefore, it can be said that the medium rotational speed region is the region with the lowest duty, and is easily affected by vibration of current ripple and noise. Therefore, switching is performed so that the carrier frequency in this region is maximized. In the high rotation region, since the current increases, the temperature of the switch elements 3a, 3b, 3c, 3d, 3e, and 3f increases. Further, since increasing the carrier frequency also leads to a temperature rise, the carrier frequency is switched to a relatively low carrier frequency. Since it is necessary to increase the average voltage by PWM control in the high rotation range, the duty ratio is increased, the OFF time is shortened with respect to the carrier ON time, and current ripple can be suppressed inevitably. There is no problem with a relatively small carrier frequency.

  Therefore, since the carrier frequency is increased in the middle rotation speed region, the energization OFF time in one cycle can be shortened, current drop can be reduced, and vibration and noise due to current ripple can be reduced. Since reduction of current drop has already been described with reference to FIGS. 3 and 4, description thereof is omitted here.

  In the conventional driving apparatus as shown in FIG. 10, the carrier frequency cannot be switched because the carrier frequency switching unit is not provided when the rotation speed changes. In addition, when the rotation speed determined by the synchronous rotation speed setting unit 6 changes from a high rotation speed to an intermediate rotation speed, the voltage output from the voltage control section 13 also in the supply voltage detected by the voltage detection section 7 Since there is no change point in the adjustment signal, the carrier frequency cannot be switched even using the driving method as shown in FIGS. In addition, when high rotation is realized while keeping the duty ratio constant during operation with 120-degree rectangular wave energization, high rotation may be realized by energizing the energization period longer than the electrical angle of 120 degrees. In this case, the current flowing through the motor increases, leading to a temperature rise, but the duty ratio does not change, so that the carrier frequency cannot be switched even using the driving method described with reference to FIG. Therefore, if the carrier frequency is switched according to the rotational speed determined by the synchronous rotational speed setting unit 6, the carrier frequency can be switched without detecting the state of the waveform output to the brushless DC motor 4. The carrier frequency can be switched quickly in response to an increase in current. As a result, the noise / vibration reduction effect is greater in the means for switching the carrier frequency by changing the rotation speed than in the means for switching the carrier frequency by detecting the state of the waveform output to the motor 4.

  Next, the structure of the brushless DC motor 4 will be described. FIG. 8 is a structural diagram of the rotor of the brushless DC motor according to the first embodiment of the present invention. The rotor core 20 is formed by stacking punched thin steel sheets of about 0.35 mm to 0.5 mm. The four magnets 21 a, 21 b, 21 c, 21 d are embedded in the rotor core 20 in a reverse arc shape with respect to the drive shaft 22. This magnet is usually a ferrite type, but if a rare earth magnet such as neodymium is used, a plate structure may be used.

  In the rotor having the structure as shown in FIG. 8, assuming that the axis from the rotor center to the magnet center is the d axis and the axis from the rotor center to the magnet is the q axis, the inductance Ld in each axial direction , Lq have opposite saliency and are different.

  In addition to the magnetic flux generated by the current flowing in the armature winding and the torque (magnet torque) following the Fleming's left-hand rule generated by the action of the magnetic flux generated by the permanent magnet, the magnetic flux generated by the current flowing in the armature winding is embedded. As a result, the force (reluctance torque) that attracts the iron part of the rotor surface acts by changing the shape of the iron part of the part where the magnet is embedded and the part where it is not embedded (reverse saliency). Since the torque ripple is increased compared to the type rotor, the control of the present embodiment can be used to significantly reduce the rotor shaft resonance associated with the torque ripple in a low load, high voltage region, and to suppress noise. be able to.

  As described above, the driving method of the brushless DC motor according to the first embodiment is connected to the brushless DC motor 4 including the rotor 4a having a permanent magnet and the stator 4b having a three-phase winding, and the three-phase winding. Inverter 3 for supplying power by a plurality of drive switching elements 3a to 3f, a carrier frequency generation unit 9 for generating a switching frequency of the switching element groups 3a to 3f, and the carrier frequency generation unit 9 A duty ratio control unit 8 that adjusts a duty ratio that is a ratio of an on-time within a carrier cycle, a rotational speed setting unit 6 that determines a rotational speed based on an instruction from the rotational speed command circuit 5, and the switching element. A switch element switching unit 10 for sequentially switching the groups 3a to 3f, and depending on the state of the waveform output from the inverter 3, the carrier frequency Since it is possible to switch two or more types, the carrier frequency can be switched according to the input voltage (commercial power supply voltage), the supply voltage to the inverter (DC voltage), and the load state (Duty ratio). Noise and vibration can be suppressed.

  Since the means for switching the carrier frequency according to the state of the output waveform of the inverter is provided, the current ripple generated during driving of the motor with a small duty ratio can be reduced, and the effect of suppressing noise and vibration is improved by this embodiment.

  By having a voltage detection unit 7 that detects the power supply voltage supplied to the inverter 3 and a carrier frequency switching unit 9 that switches the carrier frequency according to the voltage detected by the voltage detection unit 7, an instantaneous voltage drop / power failure In addition, noise and vibration generated when the supply voltage to the inverter is changed, such as when the power supply voltage is suddenly increased or when the supply voltage to the inverter is changed, such as when used in different commercial power supply voltage environments, can be quickly reduced.

  Since the means for switching the carrier frequency according to the supply voltage to the inverter is provided, the current ripple can be reduced when the input voltage fluctuates, and the effect of suppressing noise and vibration is improved by this embodiment.

  A voltage adjustment unit 2g for adjusting a power supply voltage supplied to the inverter 3, a voltage control unit 13 for controlling a voltage adjustment signal output to the voltage adjustment unit 2g, and a carrier frequency for switching a carrier frequency in accordance with the voltage adjustment signal By including the switching unit 9, it is possible to supply an optimal power supply voltage to the inverter according to the number of rotations of the motor and the like, and it is possible to quickly reduce the occurrence of noise and vibration due to changes in the power supply voltage. Further, since the carrier frequency is switched by the change of the voltage adjustment signal, there is an effect that noise and vibration can be suppressed more quickly than the means for switching by the change of the supply voltage to the inverter.

  Since there is means for switching the carrier frequency by a signal for controlling the supply voltage to the inverter, the current ripple generated when the voltage to the inverter is changed can be reduced by the present embodiment. As a vibration suppression effect.

  Noise generated when the load state changes by including the duty ratio control unit 8 that adjusts the duty ratio and the carrier frequency switching unit 9 that switches the carrier frequency according to the duty ratio adjusted by the duty ratio control unit. And vibration can be reduced quickly. In addition, since the carrier frequency is switched by changing the duty ratio, the input voltage (commercial power supply voltage), the inverter supply voltage (DC voltage), and the voltage adjustment signal do not change as in the case of load fluctuation. In this case, there is an effect that noise and vibration can be reduced.

  It occurs when the load drops because it has means to switch the carrier frequency according to the duty ratio adjusted according to the load fluctuation, instead of switching the means for converting the signal to output to the inverter by detecting the load fluctuation. The current ripple can be reduced, and the effect of suppressing noise and vibration is improved by the present embodiment.

  Further, the brushless DC motor 4 is a rotor 4a in which permanent magnets 21a to 21d are embedded in the iron core of the rotor 4a, and has a rotor 4a having saliency. In addition, reluctance torque due to saliency acts and torque ripple increases as compared with a magnet surface-arranged rotor, so that noise and vibration are easily generated.

  The brushless DC motor 4 drives the compressor, and is one of extremely important applications that can realize low noise in the compressor. In particular, a refrigerator, which is one of products using a compressor, is used in various countries, in other words, used under various input voltage environments. Since the carrier frequency is switched by the voltage supplied to the inverter, the effect of the present embodiment is more effective in an environment where the input voltage is likely to increase current ripple and is high.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 9 is a block diagram of a brushless DC motor driving apparatus according to Embodiment 2 of the present invention.

  In FIG. 9, the same components as those described in FIG.

  The reverse voltage detection circuit 30 detects the rotational relative position of the rotor 4a from the back electromotive voltage generated when the rotor 4a having the permanent magnet of the brushless DC motor 4 rotates. Although the voltage detection circuit is used here, any other detection means such as current detection may be used as long as it is a means for detecting the position of the rotor 4a.

  The rotor position detection unit 31 performs logical signal conversion based on the output signal of the back electromotive voltage detection circuit 30, and determines the timing for sequentially switching the switch elements 3a, 3b, 3c, 3d, 3e, and 3f of the inverter 3. The rotor position detection unit 31 can generate a logical signal converted so that the brushless DC motor 4 is aligned with the rotational relative position of the rotor 4a.

  The load state determination unit 32 determines the load state of the brushless DC motor 4, and sets the timing (timing) for sequentially switching the switching elements 3 a, 3 b, 3 c, 3 d, 3 e, and 3 f of the inverter 3 to the synchronous rotation speed setting unit 6. Whether to be based or based on the rotor position detector 31 is determined.

  The switching timing selector 33 adjusts the timing of switching the switching elements 3a, 3b, 3c, 3d, 3e, and 3f of the inverter 3 to the rotational speed determined by the synchronous rotational speed setting section 6 or detects the rotor position. Whether to match the rotational relative position detected by the unit 31 is selected based on the determination of the load state determination unit 32.

  The switch element switching unit 34 outputs a signal for driving the switch elements 3a, 3b, 3c, 3d, 3e, and 3f of the inverter 3 based on the logical signal pattern selected by the switching timing selection unit 33. .

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

  The load state determination unit 32 determines the load state of the brushless DC motor 4 and switches the inverter 3 based on the position information obtained from the position detection unit 31 when it is necessary to perform a high rotation operation under a high load state. If the elements 3a, 3b, 3c, 3d, 3e, and 3f are sequentially switched, it is determined that high-speed operation cannot be realized, and the rotor 4a is operated synchronously according to the rotational speed determined by the synchronous rotational speed setting unit 6. To the switching time selector 33. At this time, it becomes possible to forcibly generate a signal pattern at a predetermined frequency, and the motor 4 operates as a synchronous motor. On the contrary, under a relatively low load state, it is determined that a certain number of rotations can be realized even by sequentially switching based on the position information, and the switching elements 3a, 3b are determined according to the position information of the position detection unit 31. 3c, 3d, 3e, and 3f are transmitted to the switching timing selector 33 so as to be sequentially switched. This operation can be rephrased as changing the switching timing of the switching element between a high-speed operation requiring higher power than the efficiency and a low-speed operation focusing on efficiency.

  Furthermore, as described in the first embodiment, the carrier frequency switching unit 9 that can switch the carrier frequency according to the state of the waveform output to the motor 4 and the rotation number determined by the synchronous rotation number setting unit 6. Therefore, it is possible to suppress an increase in current ripple caused by a decrease in the duty ratio, and a more efficient operation can be realized.

  If this operation is replaced with a refrigerator, the effect becomes more specific. In the refrigerator, when operating for the first time, it is necessary to cool at a stretch from room temperature to several tens of degrees Celsius below freezing point. However, once the interior is cooled (especially at night when the doors are open and closed), the interior does not heat up easily, so it is a relatively low load and cooling capacity is not required so low speed operation is sufficient. is there. Since most of the normal operating states are in a low load state in time for such a low rotation operation, the influence of the operation efficiency in the low load state on the power consumption is large, and an operation emphasizing efficiency is required. Thus, this embodiment is very effective as a device for driving a compressor such as a refrigerator.

  As described above, the brushless DC motor driving apparatus according to the second embodiment includes the rotor position detection unit 31 that detects the position of the rotor 4a, the load state determination unit 32 that determines the load state of the brushless DC motor 4, and the like. The timing for sequentially switching the plurality of switching elements connected to the three-phase winding 4b is determined based on the position information detected by the rotor position detector 31 or the synchronous rotation speed setting unit 6 The switching time selection unit 33 that selects whether to determine based on the number of revolutions determined in accordance with the instruction of the load state determination unit 32, the efficiency-oriented driving means and the high power-oriented driving means are provided. Since the current ripple can be reduced by having the carrier frequency switching unit 9 in combination, a greater effect can be exhibited in high efficiency.

  By switching the signal pattern output to the inverter according to the change in the load state, it is possible not only to select a more efficient signal pattern in a low load state, but also to adjust the duty adjusted according to the change in the load state Since the means for switching the carrier frequency based on the ratio is provided, the effect according to the present embodiment, which can reduce the current ripple generated during operation with a small duty ratio, is better as an effect for higher efficiency.

  As described above, the present invention suppresses noise and vibration by switching the carrier frequency according to the input voltage (commercial power supply voltage), the supply voltage (DC voltage) to the inverter, and the load state (Duty ratio). Therefore, it can be widely used as a brushless DC motor drive method and drive device, and can be effectively applied to achieve energy saving, low noise, and low vibration of products adopting the brushless DC motor.

1 is a block diagram of a brushless DC motor driving apparatus according to Embodiment 1 of the present invention. The figure showing an example of the control pattern of the carrier frequency at the time of taking supply voltage on the horizontal axis in Embodiment 1 of this invention The figure which showed the carrier waveform 3kHz switching pattern and the current waveform of each phase in 120 degree | times rectangular wave energization in Embodiment 1 of this invention The figure which showed the switching pattern of the carrier frequency of 6 kHz in 120 degree | times rectangular wave energization in Embodiment 1 of this invention, and the current waveform of each phase Timing chart showing an example of a carrier frequency control pattern in Embodiment 1 of the present invention The figure showing an example of the control pattern of the carrier frequency at the time of taking Duty ratio on the horizontal axis in Embodiment 1 of this invention The figure showing an example of the control pattern of the carrier frequency at the time of taking rotor rotation speed on the horizontal axis in Embodiment 1 of this invention Structure diagram of rotor of brushless DC motor according to embodiment 1 of the present invention Block diagram of a brushless DC motor driving apparatus according to Embodiment 2 of the present invention. Block diagram of a conventional brushless DC motor drive device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Rectifier circuit 3 Inverter 3a-3f Switching element 4 Brushless DC motor 6 Synchronous rotation speed setting part 8 Duty ratio control part 9 Carrier frequency generation part 10 Switching element switching part

Claims (8)

A brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding; an inverter for supplying power by a plurality of driving switching elements connected to the three-phase winding; and the switching element group A carrier frequency generation unit that generates a switching frequency of the following, a synchronous rotation number setting unit that determines a rotation number for operating the brushless DC motor as a synchronous motor, and a switching element switching unit that sequentially switches the switching element group, A method of driving a brushless DC motor, wherein two or more types of carrier frequencies can be switched depending on the state of a waveform output from the inverter. A brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding; an inverter for supplying power by a plurality of driving switching elements connected to the three-phase winding; and the switching element group A carrier frequency generating unit for generating a switching frequency of the motor, a synchronous rotational speed setting unit for determining a rotational speed for operating the brushless DC motor as a synchronous motor, a switching element switching unit for sequentially switching the switching element group, and the inverter A brushless DC motor drive device comprising: a voltage detection unit that detects a power supply voltage supplied to the carrier; and a carrier frequency switching unit that switches the carrier frequency in accordance with the voltage detected by the voltage detection unit. A brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding; an inverter for supplying power by a plurality of driving switching elements connected to the three-phase winding; and the switching element group A carrier frequency generation unit that generates a switching frequency of the motor, a synchronous rotation number setting unit that determines a rotation number for operating the brushless DC motor as a synchronous motor, a switching element switching unit that sequentially switches the switching element group, and the inverter A voltage adjustment unit for adjusting a power supply voltage supplied to the voltage adjustment unit, a voltage control unit for controlling a voltage adjustment signal output to the voltage adjustment unit, and the carrier frequency according to the voltage adjustment signal output to the voltage adjustment unit A brushless DC motor drive device having a carrier frequency switching unit for switching between the two. A brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding; an inverter for supplying power by a plurality of driving switching elements connected to the three-phase winding; and the switching element group A carrier frequency generation unit that generates a switching frequency of the output, a duty ratio control unit that adjusts a duty ratio that is a ratio of an on-time within a carrier period determined by the carrier frequency generation unit, and the brushless DC motor as a synchronous motor A carrier speed switching unit that switches the carrier frequency in accordance with a duty ratio adjusted by the duty ratio control unit; a switching element switching unit that sequentially switches the switching element group; And a brushless DC motor driving device. A brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding; an inverter for supplying power by a plurality of driving switching elements connected to the three-phase winding; and the switching element group A carrier frequency generation unit that generates a switching frequency of the switching element, a synchronous rotation number setting unit that determines a rotation number for operating the brushless DC motor as a synchronous motor, a switching element switching unit that sequentially switches the switching element group, and the synchronization A brushless DC motor driving device comprising: a carrier frequency switching unit that switches the carrier frequency according to the number of rotations determined by a rotation number setting unit. A rotor position detector that detects the position of the rotor, a load state determination unit that determines the load state of the brushless DC motor, and a timing for sequentially switching a plurality of switching elements connected to the three-phase winding. Switching timing for selecting by the load state determination unit whether to determine based on the position information detected by the rotor position detection unit or based on the rotation number determined by the synchronous rotation number setting unit The brushless DC motor drive device according to any one of claims 2 to 5, further comprising a selection unit. The brushless DC motor according to any one of claims 2 to 6, wherein the brushless DC motor is a rotor in which a permanent magnet is embedded in an iron core of the rotor and has a rotor having saliency. Drive device. The brushless DC motor driving device according to any one of claims 2 to 7, wherein the brushless DC motor drives the compressor.

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