JP2016059086A - Motor driving device and electronic equipment using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that some power source impedance may cause voltage increase due to PWM switching when the capacitance of a smoothing capacitor is reduced to miniaturize the smoothing capacitor.SOLUTION: The carrier frequency is set to be higher than the resonance frequency of a capacitor 103 and a reactor 104, whereby the resonance frequency of an inductance component containing a power source impedance and the capacitor 103 is set to be lower than the resonance frequency between the capacitor 103 and the reactor 104. Therefore, the resonance frequency of the inductance component and the capacitor 103 is not coincident with the carrier frequency, so that voltage increase caused by switching of an inverter 105 can be reduced.SELECTED DRAWING: Figure 1

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 type of brushless sensorless DC motor is generally driven by detecting the position from the induced voltage or motor current without the rectifier circuit having a sufficiently large smoothing capacitor, the inverter, and the position detection sensor. It was. 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. 5 shows a conventional motor driving apparatus described in Patent Document 1. As shown in FIG. 5, 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 conventional configuration, there is no problem in an environment equipped with a power source with a very small power source impedance such as a stabilized power source such as a laboratory, but when there is an inductance component in the power source impedance such as an area where power supply conditions are bad, There exists a state in which the resonance frequency of the inductance component of the small-capacitance capacitor and the power source impedance matches the carrier frequency of the PWM inverter. In the case of matching, since the capacitor capacity is small, the rise of the voltage between the DC buses is large, and there is a problem that it is necessary to use high-voltage parts with high withstand voltage in order to prevent withstand voltage breakdown.

  The present invention solves the above-described conventional problem, and even when the capacity of the smoothing capacitor is extremely small, the motor drive that can suppress the increase in the voltage between the DC buses due to switching of the inverter The purpose is to provide a device.

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 input 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 and having a value determined so that the maximum value of the voltage at both ends is at least twice the minimum value, and a carrier higher than the resonance frequency of the reactor and the capacitor A PWM type inverter that converts a direct current obtained from the capacitor at a frequency into an alternating current, and a motor that drives the load using the alternating current obtained from the inverter as an input.

  As a result, even when the power supply impedance is included, the inductance value of the entire circuit is increased, and the resonance frequency of the capacitor and the inductance component including the reactor and the power supply impedance is higher than the resonance frequency of the reactor and the capacitor. Therefore, the carrier frequency is always higher than the resonance frequency, and the resonance frequency and the carrier frequency do not coincide with each other.

  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 Simulation waveform diagram of DC bus voltage when carrier frequency and resonance frequency match Simulation waveform diagram of DC bus voltage when carrier frequency is 1.5 times the resonance frequency Block diagram showing the electrical circuit configuration of a 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 input 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 capacitor which is connected and has a value determined so that the maximum value of the voltage at both ends is at least twice the minimum value, and a direct current obtained from the capacitor is converted into an alternating current at a carrier frequency higher than the resonance frequency of the reactor and the capacitor. By having a PWM type inverter and a motor that drives the load using the alternating current obtained from the inverter as an input, the inductance value of the entire circuit becomes large even when the power supply impedance is included, and the LC resonance frequency is Since it is only lower than the LC resonance frequency of the capacitor, the capacitor and the reactor increase the resonance frequency. That and will be determined, the carrier frequency is always higher frequency than the LC resonance frequency. This eliminates the coincidence between the LC resonance frequency and the carrier frequency, so that an increase in the voltage between the DC buses due to switching of the inverter can be suppressed even if the capacitor has a 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.

  The third invention is an electric apparatus using the motor driving device of the first or second invention. 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 when the capacitor 103 has a small 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 control means 113 operates the switching element of the inverter 105 by PWM control that changes the ratio of the ON and OFF times of the pulses that are output for a certain period, and generates a smooth voltage that greatly pulsates based on the position information of the position detection means 112. The corresponding motor drive command 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.

  When a common mode filter that removes high frequency is configured, the inductance component of the common mode filter and the combined component of the reactor are considered.

  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 of the capacitor 103 has a small capacity, when the load current is extracted, the input AC power supply 101 is not smoothed and approaches the waveform obtained by full-wave rectification. Since the rate is improved, the current execution value output from the AC power supply 101 and the current peak are reduced, so that the efficiency can be improved and the temperature rise of the parts 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.

  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, the determination of the carrier frequency will be described. When viewed in one carrier cycle, the amount of current flowing from the reactor 104 to the capacitor 103 when the switching element is turned on at the timing when the peak of the current flowing into the capacitor 103 coincides with the switching OFF and the current flowing through the reactor becomes zero. The maximum rise in voltage between the DC buses is maximized.

  FIG. 3 shows a simulation waveform of the DC bus voltage when the voltage of the AC power supply 101 fluctuates to 120 [V] and the carrier frequency and the LC resonance frequency fLC coincide. In FIG. 3, the vertical axis represents voltage, and the horizontal axis represents time.

  The voltage peak of the AC power supply 101 is 170 [V], but when the carrier frequency and the LC resonance frequency fLC coincide with each other, the voltage peak value jumps greatly as shown in FIG. Further, even if the frequency obtained by dividing the LC resonance frequency fLC matches the carrier frequency, the voltage similarly increases.

  Since the cycle in which such a current change occurs is the resonance frequency of the capacitor 103 and the reactor 104, a condition in which the voltage rise is maximized can be avoided by setting the carrier cycle to the LC resonance frequency fLC or higher.

  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 capacitor is arranged between the DC buses.

  If only the coincidence between the LC resonance frequency fLC on the circuit and the carrier frequency is avoided, the carrier frequency can be set to a value lower than the LC resonance frequency fLC. However, such a condition that the carrier frequency is lower than the LC resonance frequency fLC is not a problem in a favorable condition between power sources such as a laboratory where a stabilized power source is used. In an environment having an inductance component, a voltage increase due to switching occurs. When the power supply has an inductance component, the resonance frequency needs to be calculated by adding the inductance component of the power supply. Therefore, 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 the capacitor 103. And the LC resonance frequency fLC which is the resonance frequency of the reactor 104. In addition, since the inductance component of the power source impedance is indefinite, the upper limit of the LC resonance frequency fLCZ is determined by the resonance frequency of the capacitor 103 and the reactor 104, but the lower limit is not determined, and all frequencies lower than the upper limit can be taken.

  That is, when a carrier frequency lower than the LC resonance frequency fLC is set, there is a possibility that the carrier frequency and the LC resonance frequency fLCZ coincide with each other, so that a voltage increase due to switching may occur. On the other hand, if the carrier frequency is higher than the LC resonance frequency fLC, there is no possibility of matching with the LC resonance frequency fLCZ. Therefore, in any power supply environment, the voltage rise due to switching can be suppressed. it can.

  Specifically, since the voltage rise is suppressed as the difference between the LC resonance frequency fLCZ and the carrier frequency increases, the carrier frequency is set in consideration of the breakdown voltage of the component to which the voltage between the DC buses is applied.

  For example, if the maximum variation of the AC power supply 101 is 120 [V], the maximum value after rectification is 170 [V]. When a component with a withstand voltage of 200 [V] is used, if the design target is to suppress the increase in the voltage between the DC buses to 190 [V] or less in view of the margin, the voltage increase due to the switching of the inverter 105 may occur. By raising the carrier so as to be 20 [V] or less, it becomes possible to use a component having a withstand voltage of 200 [V].

  FIG. 4 shows a simulation waveform of the voltage between the DC buses when the carrier frequency is 1.5 times the LC resonance frequency fLC. In FIG. 4, the vertical axis represents voltage, and the horizontal axis represents time. If the carrier frequency is 1.5 times the LC resonance frequency fLC, the voltage rise due to switching will be reduced to about 30% as can be seen from the comparison with FIG. The voltage rise can be greatly improved by setting the LC resonance frequency fLC to 1.5 times or more.

As described above, in the present embodiment, the AC power supply 101, the rectifier circuit that rectifies the alternating current output from the alternating current power supply 101 into direct current, the reactor 104 connected to the input side or the output side of the rectifier circuit, A capacitor 103 connected to the output side of the rectifier circuit 102 and having a value determined so that the maximum value of the voltage at both ends is at least twice the minimum value, the reactor 104 and the capacitor 10
3 having a PWM inverter 105 that converts a direct current obtained from the capacitor 103 into an alternating current at a carrier frequency higher than the resonance frequency 3 and a motor 106 that drives the load using the alternating current obtained from the inverter 105 as an input. Even when impedance is included, since the inductance value of the entire circuit is increased and the LC resonance frequency fLCZ is only lower than the LC resonance frequency fLC of the reactor and the capacitor, the carrier frequency is always higher than the LC resonance frequency fLCZ. Thus, since the LC resonance frequency fLCZ and the carrier frequency do not coincide with each other, an increase in the DC bus voltage due to switching of the inverter can be suppressed even if the capacitor has a small capacity.

  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.

  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. Since the reliability is improved by suppressing the voltage rise when the motor stops, not only in the claims, but also in AV equipment (particularly small equipment) that requires a small motor driving device, etc. Can also be widely used.

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 Control means

Claims (3)

  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 voltage of both ends connected to the output side of the rectifier circuit A capacitor whose value is determined such that the maximum value is twice or more the minimum value, a PWM inverter that converts direct current obtained from the capacitor into alternating current at a carrier frequency higher than the resonance frequency of the reactor and the capacitor, A motor driving device having a motor that receives an alternating current obtained from the inverter as an input and drives a load.   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.   The electric equipment provided with the brushless DC motor driven by the motor drive device of any one of Claim 1 or 2.