JP2015089142A - Motor driver and electrical apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-size motor driver using a smoothing capacitor with a small capacity capable of preventing the voltage on both ends of the capacitor from increasing depending on the driving speed.SOLUTION: The commutation frequency of the motor 106 is determined so that resonant frequencies of a capacitor 103 and a reactor 104 do not coincide with each other. With this, the timing the current supplied to an inverter 105 gets the smallest and the timing the current flowing from the reactor 104 to the capacitor 103 gets the maximum never coincide with each other; thus the voltage is prevented from increasing.

Description

  The present invention relates to a motor driving device that drives a brushless DC motor and an electric device using the same.

  Conventionally, this kind of brushless sensorless DC motor generally has a reactor for suppressing harmonics, a rectifier circuit having a sufficiently large smoothing capacitor, an inverter, a position detection sensor, and an induced voltage or a motor current. It was driven by detecting the position. The reason for eliminating the position detection sensor is that it is inexpensive and it is extremely difficult to attach the position sensor in a high-temperature atmosphere such as a compressor, a refrigerant atmosphere, or an oil atmosphere.

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

  FIG. 4 shows a conventional motor driving apparatus described in Patent Document 1. As shown in FIG. 4, a single-phase AC power source 1, a diode full-wave rectifier circuit 2 that rectifies the single-layer AC power source 1, a smoothing small capacity of about 1/100 of the conventional capacity for smoothing the output of the rectifier circuit Capacitor 3, PWM (pulse width modulation) inverter 4 connected to both ends of capacitor 3, and 6 switching elements (including reverse diodes) connected in a three-phase bridge, connected to the output of inverter 4 and three-phase winding The brushless DC motor 5 to which the wire is applied, the position detection sensor 6 that detects the position of the brushless DC motor 5, the voltage v of the single-phase AC power supply 1, the DC current idc, the output currents ia, ib, ic, and the position of the inverter 4 The control circuit 7 is configured to drive the gate of the PWM inverter 4 so that optimum driving can be performed using information such as position information θ from the detection sensor 6 as an input.

JP 2002-51589 A

  However, in the above-described conventional configuration, when the inverter driving method is a rectangular wave, the current supplied from the smoothing capacitor to the inverter for each commutation is almost zero. Therefore, the smoothing capacitor, the reactor, the circuit pattern, etc. When the resonance frequency of the inductance component and the commutation cycle match, the current supplied to the inverter is the smallest, and the timing at which the current flowing from the reactor into the capacitor is the maximum coincides. As a result, there is a problem that it is necessary to use a high-cost component with a high pressure resistance in order to prevent pressure breakdown.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and even when the smoothing capacitor has a very small capacity, a motor driving device capable of suppressing a rise in voltage across the capacitor due to commutation The purpose is to provide.

In order to solve the above-described conventional problems, a motor driving device according to the present invention includes an AC power source, a rectifier circuit that rectifies AC output from the AC power source into DC, and an input side or an output side of the rectifier circuit. A connected reactor, a capacitor connected to the output side of the rectifier circuit, a PWM inverter that converts a direct current obtained from the capacitor into an alternating current, and a motor that drives the load using the alternating current obtained from the inverter as an input And determining the value of the capacitor so that when the motor drives the load, the maximum value of the voltage at both ends is at least twice the minimum value, and the number of phases, poles and driving speed of the motor are determined. The driving speed of the motor is determined so that the product does not coincide with the resonance frequency of the reactor and the capacitor.

  As a result, the current supplied to the inverter becomes the smallest and the timing at which the current flowing from the reactor into the capacitor becomes maximum does not coincide with each other, so that the voltage rise can be suppressed.

  The motor drive device of the present invention can suppress an increase in the voltage between the DC buses due to switching of the inverter even if the capacity of the smoothing capacitor is extremely small.

The block diagram which shows the electric circuit structure of the drive device of the motor in Embodiment 1 of this invention. Timing chart showing voltage waveform between DC buses in the same embodiment Timing chart showing a waveform of a current flowing from capacitor 103 to inverter 105 in the same embodiment The block diagram which shows the electric circuit structure of the conventional motor drive device

  According to a first aspect of the present invention, there is provided an AC power source, a rectifier circuit that rectifies AC output from the AC power source into DC, a reactor connected to an input side or an output side of the rectifier circuit, and an output side of the rectifier circuit A connected capacitor, a PWM inverter that converts direct current obtained from the capacitor into alternating current, and a motor that drives the load using the alternating current obtained from the inverter as input, and when the motor drives the load The value of the capacitor is determined so that the maximum value of the voltage at both ends is at least twice the minimum value, and the product of the number of phases, the number of poles, and the driving speed of the motor does not match the resonant frequency of the reactor and the capacitor By determining the driving speed of the motor, the current supplied to the inverter becomes the smallest and the current flowing from the reactor into the capacitor is maximized. To become timing is not continuously match, it is possible to suppress the increase of the DC bus voltage capacitor caused by the commutation of the motor driving even small capacity.

  According to the second aspect of the invention, in particular, by determining the values of the reactor and the capacitor so that the resonance frequency of the reactor and the capacitor of the first aspect of the invention is higher than 40 times the frequency of the AC power supply. The distortion of the generated current is not subject to harmonic regulation, and an inexpensive motor drive device that does not require special harmonic countermeasures can be provided.

  According to a third aspect of the invention, there is provided voltage detecting means for detecting the voltage across the capacitor, particularly when the voltage value detected by the voltage detecting means exceeds a predetermined threshold value. By changing the speed, it is possible to operate without matching the inductance component including the power supply impedance that varies depending on the power supply situation and the period of the LC resonance frequency and the commutation period of the capacitor. Voltage rise can be suppressed even in a bad area.

The fourth invention is an electric apparatus using the motor driving device of the first to third inventions. Thereby, when used in a refrigerator as an electric device, the motor drive device can be reduced in size so that it can be stored in a small space of a refrigerator that is driven at a constant speed, and a more efficient refrigerator capable of changing the speed. It can be provided at low cost. Further, when the blower is used as an electric device, since the blower has a very large inertia, a small blower that is easy to carry can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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 AC power supply 101 is a general commercial AC power supply having a voltage of 100 [V] and a frequency of 50 [Hz] or 60 [Hz] in Japan. As is well known, the rectifier circuit 102 is a bridge connection of four diodes.

  The capacitor 103 is connected to the output side of the rectifier circuit 102. The capacitor 103 is a small-capacitance capacitor for miniaturization, and the output voltage pulsates greatly at a frequency that is approximately twice the AC power supply frequency. In this embodiment, the capacitance of the capacitor is 3 [μF].

  Further, a reactor 104 is connected between the capacitor 103 and the rectifier circuit 102 for reducing the peak value of the inrush charging / discharging current to the capacitor. By setting the resonance frequency fLC (LC resonance frequency) of the capacitor 103 and the reactor 104 to be 40 times or more of the AC power supply frequency, and setting the frequency of the current due to resonance outside the range of the power supply harmonic regulation, the harmonic current Can be reduced. In this embodiment, the inductance of the reactor is 0.5 [mH]. Further, the capacitance of the capacitor 103 becomes a current waveform close to the frequency of the AC power supply 101 by setting a value at which the maximum value of the voltage is twice or more the minimum value, and the harmonic current is improved.

  The capacitance of the capacitor 103 of the present embodiment is 3 [μF], and the minimum value of the voltage between the DC buses is reduced to almost 0 [V] under operating conditions with a large load, so the maximum value is at least twice the minimum value. The harmonic current is improved.

  In this embodiment, the reactor 104 is connected between the rectifier circuit 102 and the capacitor 103. However, the reactor 104 may be inserted between the AC power source 101 and the film capacitor constituting the capacitor 103. It doesn't matter.

  The inverter 105 is a PWM inverter configured by a plurality of semiconductor switching elements that convert an output voltage from the capacitor 103 into a desired voltage value and frequency for driving the motor 106.

  The motor 106 may be any motor that drives an inverter, such as an induction motor or a brushless DC motor. In this embodiment, a brushless DC motor is used. Since the brushless DC motor is more efficient, smaller, and has a wider speed variable range than the induction motor, it is very useful for reducing the size of the capacitor 103 and the motor driving device as a whole. The motor 106 includes a rotor having a permanent magnet and a stator having a three-phase winding. The motor 106 rotates the rotor of the motor 106 when the three-phase alternating current generated by the inverter 105 flows in the three-phase winding of the stator of the motor 106. The stator of the motor 106 is provided with a three-phase star-connected winding. This winding method may be concentrated winding or distributed winding. A permanent magnet is disposed on the rotor of the motor 106. The arrangement method may be a surface magnet type (SPM) or a magnet embedded type (IPM), and the permanent magnet may be a ferrite or a rare earth. In the case of IPM, reluctance torque can be used, and the voltage between the DC buses pulsates, so that the output torque can be reduced by increasing the angle even when the voltage value is reduced.

  A compression element 107 connected to the rotor shaft of the motor 106 draws in refrigerant gas, compresses it, and discharges it. The motor 106 and the compression element 107 are accommodated in the same hermetic container to constitute the compressor 108. That is, the load of the motor drive device of the present embodiment is a compression mechanism of the compressor 108. The compression method (mechanism form) of the compressor 108 may be anything such as a rotary or a scroll, but this time it is a reciprocating type. The reciprocating type has particularly large inertia and is difficult to reduce the rotational speed even when the voltage drops. The reciprocating type can be operated more smoothly with a small capacity capacitor.

  The refrigerant gas may be anything such as R134a, but R600a is adopted in the first embodiment. R600a has a lower refrigeration capacity than R134a, and increases the cylinder volume of the compression element 107 to compensate for a decrease in the refrigeration capacity. As a result, the compressor 108 has a large inertia. As a result, even when the voltage drops, the motor 106 rotates due to inertia, so the speed is unlikely to drop, and stable operation is possible even if the smoothing portion (capacitor) 103 has a small capacitor capacity. .

  The discharge gas compressed by the compressor 108 constitutes a refrigeration air conditioning system that returns to the suction of the compressor 108 through the condenser 109, the decompressor 110, and the evaporator 111. At this time, the condenser 109 radiates heat and the evaporator 111 absorbs heat, so that cooling and heating can be performed. If necessary, a fan or the like can be used for the condenser 109 and the evaporator 111 to further promote heat exchange.

  The position detector 112 detects the magnetic pole position of the rotor of the motor 106. As a means for detecting the position, since the motor 106 is included in the compressor 108, it is difficult to use a sensor. However, a method of detecting from the induced voltage appearing in the terminal voltage of the motor 106, There is a method of calculating from the flowing current. In the present embodiment, the position is detected from the induced voltage as the position detecting means.

  The voltage detection unit 113 detects the voltage of the capacitor 103.

  The control means 114 operates the switching element of the inverter 105 by PWM control that changes the ratio of ON and OFF times of pulses output at a constant period, and is a smooth voltage that greatly pulsates based on the position information of the position detection means 112. The motor drive command corresponding to is given.

  The PWM carrier frequency is set to be higher than the LC resonance frequency fLC. In the present embodiment, the carrier frequency is 8 [kHz], which is 1.5 times higher than the LC resonance frequency fLC. The driving waveform is a 120-degree conduction rectangular wave, the first half 60 degrees is switched, and the second half 60 degrees is 100% conduction. As a result, regeneration from the motor 106 to the capacitor 103 during commutation with 120-degree energization is reduced, and voltage increase due to regeneration of the capacitor 103 can be suppressed.

Further, when the detection result of the voltage detection means 113 exceeds a predetermined threshold value, the speed is changed. If the drive speed is sufficiently higher than the original speed, a high speed is output. If not, a low speed is output. If a common mode filter that removes high frequency is configured, the common mode filter is output. Consider the inductance component and the composite component of the reactor.

The operation and action of the motor driving apparatus configured as described above will be described below.
First, voltage waveforms at both ends of the capacitor 103 will be described with reference to FIGS.
FIG. 2 is a timing chart showing a voltage waveform between the DC buses in the first embodiment.

In FIG. 2, the vertical axis represents voltage, and the horizontal axis represents time.
Waveform A is a state when the load current is very small (almost no current flows), and the charge of the capacitor 103 is hardly used, and the voltage is hardly lowered. However, the load current here is the output current of the rectifier circuit 102, that is, the input current to the inverter 105. The maximum value of the voltage after rectification is 141 [V] and the minimum value is 141 [V], so the voltage difference is almost zero.

  Next, as the load current is increased, the charge stored in the capacitor 103 is used, and the minimum voltage decreases instantaneously as shown in the waveform B.

  When the load current is further increased, almost no charge is stored in the capacitor 103, and as shown in the waveform C, the instantaneous minimum voltage decreases to almost 0 [V].

  In this way, when the capacitor 103 has a small capacity, when the load current is taken out, the input AC power supply 101 is not almost smoothed and approaches the waveform obtained by full-wave rectification, and the harmonic component of the AC power supply current can be suppressed and the power factor is reduced. Since the current execution value and the current peak output from the AC power supply 101 are reduced due to the improvement, the efficiency can be improved and the rise in the component temperature can be reduced. As a result, it is possible to adopt cheaper parts with lower part ratings.

  Furthermore, in order to suppress the harmonic component of the AC power supply current and comply with the IEC standard, the LC resonance frequency fLC, which is the resonance frequency of the small-capacitance capacitor and the small-capacity reactor, becomes larger than 40 times the AC power supply frequency fs. Thus, the combination of a small capacitor and a small reactor is determined.

  Here, when the capacitance of the small-capacitance capacitor is C [F] and the inductance value of the small-capacity reactor is L [H], the LC resonance frequency fLC is expressed as Equation 1.

即ち、ｆＬＣ＞４０×ｆｓを満たすように小容量コンデンサと小容量リアクタの組み合わせを決定するものである。（ＩＥＣ規格では交流電源電流の高調波成分において第４０次高調波まで規定されているため）。

That is, the combination of the small capacitor and the small reactor is determined so as to satisfy fLC> 40 × fs. (Because the IEC standard specifies the 40th harmonic in the harmonic component of the AC power supply current).

  As described above, by determining the combination of the small-capacitance capacitor and the small-capacity reactor, it is possible to suppress the harmonic component of the AC power supply current and comply with the IEC standard.

  In this embodiment, since the capacitance of the capacitor 103 is 3 [μF] and the inductance value of the reactor is 0.5 [mH], the LC resonance frequency fLC is about 4109 [Hz], and the power source of the AC power source 101 is Even if the frequency is 60 [Hz], 40 times is 2400 [Hz], which is a sufficiently high resonance frequency.

  Next, speed determination will be described with reference to FIG. FIG. 3 is a timing chart showing a waveform of a current flowing from capacitor 103 to inverter 105 in the present embodiment. When viewed in one commutation cycle, when the peak of the current flowing from the reactor 104 to the capacitor 103 and the commutation coincide with each other, the amount of current flowing from the reactor 104 to the capacitor 103 is maximized. Become. As shown in FIG. 3, the current supplied from the capacitor 103 to the inverter 105 decreases once to near 0 after commutation, and then gradually increases. For this reason, immediately after commutation is a section where the current becomes the smallest, the energy stored in the reactor 104 flows most into the capacitor 103, and the voltage rises. As described above, the commutation frequency and the LC resonance frequency fLC coincide with each other, so that the voltage of the capacitor 103 greatly increases.

  That is, the condition in which the voltage rise is maximized can be avoided by not matching the commutation period with the LC resonance frequency fLC.

  Since the product of the number of phases and the number of poles of the motor 106 is the number of commutations per rotation, in the three-phase motor of the motor 106 of the present embodiment, if the number of poles is 4, the number of commutations 12 times per revolution. If there are 6 poles, there will be 18 commutations per revolution. Further, the product of the number of commutations per rotation and the speed is the commutation frequency. If the speed is 50 r / s, a commutation frequency of 900 Hz is obtained in a three-phase six-pole motor. In the following description, the number of poles is six.

  Since the LC resonance frequency fLC is about 4109 [Hz], even a 6-pole motor allows a speed command up to about 150 Hz from the viewpoint of voltage increase due to commutation. In addition, the final command speed is determined from a plurality of factors such as the refrigeration cycle resonance and compressor limitation.

  In addition, even in a combination of LCs having the same resonance frequency, the increase in voltage increases as the capacitance of the capacitor decreases and the inductance value increases, so that the maximum voltage between the DC buses is more than twice the minimum. This is particularly a problem in a circuit configuration in which a small-capacitance capacitor is arranged between the DC buses.

  In countries where power supply conditions are poor, the power supply impedance may have a large inductance component. In this case, for example, when the inductance component of the power supply impedance is 9.9 mH, the LC resonance frequency fLCZ of the capacitor 103 and the value obtained by adding the inductance component of the power supply impedance to the reactor is about 901 Hz, and the frequency is 50 r / s. Since they are almost the same, the voltage increases with each commutation.

  In order to prevent this, the voltage of the capacitor 103 is detected by the voltage detection means 113, and when the detected voltage exceeds a predetermined threshold value, the control means 114 changes the driving speed.

  For example, when the compressor 108 may output a speed up to 80 r / s, the speed that can be sufficiently output is higher than 50 r / s, so the speed is increased from 50 r / s to 1.5 times 75 r / s. . Since the commutation frequency is 1350 Hz and greatly deviates from the resonance frequency, the voltage rise can be suppressed low.

  When the commutation frequency and the LC resonance frequency fLCZ coincide with each other due to the influence of the power supply impedance and the power supply voltage exceeds the threshold, when the commutation frequency is set to 1.5 times the LC resonance frequency fLCZ or 1 / 1.5, The amplitude of voltage fluctuation due to commutation is reduced to about 30%. As a guide, the voltage rise can be greatly improved by determining a new driving speed so that the commutation frequency is 1.5 times or more of the commutation frequency when the threshold value is exceeded or 1 / 1.5 or less.

  As described above, in the present embodiment, the AC power supply 101, the rectifier circuit 102 that rectifies the alternating current output from the alternating current power supply 101 into direct current, and the reactor 104 that is connected to the input side or output side of the rectifier circuit 102 A capacitor 103 connected to the output side of the rectifier circuit 102, a PWM inverter 105 that converts a direct current obtained from the capacitor 103 into an alternating current, and a motor 106 that drives the load using the alternating current obtained from the inverter 105 as an input. Then, when the motor 106 drives the load, the value of the capacitor 103 is determined so that the maximum value of the voltage at both ends is twice or more the minimum value, and the product of the number of phases, the number of poles, and the driving speed of the motor 106 is the reactor. Since the drive speed of the motor 106 is determined so as not to coincide with the resonance frequency of the capacitor 104 and the capacitor 103, the inverter 10 The timing at which the current becomes equal to the maximum flow into the capacitor 103 from the reactor 104 current becomes smallest supplied is continuously matched voltage rises since no suppression, it is possible to use such a low inexpensive withstand voltage component to.

  Further, in the present embodiment, the values of the reactor 104 and the capacitor 103 are determined so that the resonance frequency of the reactor 104 and the capacitor 103 is higher than 40 times the frequency of the AC power supply 101. Since the power harmonic current of the order is suppressed, it becomes possible to comply with the IEC standard. Furthermore, since no special parts are used as a countermeasure against harmonics, an inexpensive motor drive device can be provided.

  Further, in the present embodiment, the voltage detection means 113 for detecting the voltage across the capacitor 103 is provided, and the speed is changed when the voltage value detected by the voltage detection means 113 exceeds a predetermined threshold value. As a result, even if there is an influence of the inductance component of the power source impedance, the voltage increase due to the coincidence of the commutation frequency, the power source impedance, the combined inductance of the reactor and the resonance frequency of the capacitor 103 is suppressed. A simple motor driving device can be provided.

  In addition, since it is an electric device using the motor drive device of the present embodiment, when used in a refrigerator as an electric device, the motor drive device can be miniaturized, so that there is less space in the refrigerator that is driven at a constant speed. It is possible to provide a more efficient refrigerator that can be housed in a lower speed and that can change speed.

  As described above, the motor drive device according to the present invention can provide a stable current supply while maintaining efficiency without using a position detection sensor even when there is a large ripple voltage with a smoothing capacitor greatly reduced in capacity. Further, since the reliability is improved by suppressing the voltage rise due to the coincidence of the commutation frequency of the motor and the LC resonance frequency of the reactor and the capacitor, not only the claims but also a small motor driving device can be realized. It can also be widely used for required AV equipment (particularly small equipment).

DESCRIPTION OF SYMBOLS 101 AC power supply 102 Rectifier circuit 103 Capacitor 104 Reactor 105 Inverter 106 Motor 107 Compression element 108 Compressor 109 Condenser 110 Decompressor 111 Evaporator 112 Position detection means 113 Voltage detection means 114 Control means

Claims (4)

  An AC power source, a rectifier circuit that rectifies AC output from the AC power source into DC, a reactor connected to an input side or an output side of the rectifier circuit, a capacitor connected to an output side of the rectifier circuit, A PWM type inverter that converts direct current obtained from the capacitor into alternating current, and a motor that drives the load using the alternating current obtained from the inverter as input, and the maximum voltage at both ends when the motor drives the load The value of the capacitor is determined so that the value is at least twice the minimum value, and the product of the number of phases, the number of poles, and the drive speed of the motor does not match the resonance frequency of the reactor and the capacitor. Determine the motor drive device.   The motor driving device according to claim 1, wherein the values of the reactor and the capacitor are determined so that a resonance frequency of the reactor and the capacitor is higher than 40 times a frequency of the AC power supply.   3. The motor according to claim 1, further comprising a voltage detection unit configured to detect a voltage across the capacitor, wherein the speed is changed when a voltage value detected by the voltage detection unit exceeds a predetermined threshold value. Drive device.   An electrical apparatus comprising a brushless DC motor driven by the motor drive device according to claim 1.

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