JP5807156B2 - Motor drive inverter control circuit and vacuum cleaner - Google Patents

Description

  The present invention relates to an inverter control circuit that converts direct current into alternating current in order to drive a load, for example, a motor.

  Conventionally, in this type of inverter control circuit, a power factor improving reactor is used as the input to a single-phase AC power supply, and the power converted into DC by a full-wave rectifier diode bridge is used as a large capacity electrolytic capacitor for smoothing. After the smoothing, the six switching elements and the diodes connected in parallel to them are controlled, and the direct current power that is the output is converted into the alternating current of the desired frequency to realize the driving of the motor.

  In order to clear the harmonic regulation with this circuit, a very large reactor is required, and therefore there are significant practical restrictions in terms of cost, weight, and size. When the reactor is small, the power supply current waveform becomes a sharp waveform and includes many harmonics.

  On the other hand, FIG. 4 is a diagram of a motor drive inverter control device described in Patent Document 1. In FIG. As shown in Patent Document 1, a motor drive inverter having an extremely small capacity reactor 11 and a very small capacity capacitor 12 between the DC buses of the inverter. In the PN voltage predicting means 19, the inverter actually outputs voltage. The DC voltage prediction value at the timing to be obtained is obtained from the time series data of the DC voltage detection value, so that the motor voltage is not applied more than necessary while the inverter DC voltage is rising, the appropriate current is supplied to the motor, and it is small and lightweight. A low-cost inverter control device for driving a motor has been proposed.

  In addition, the motor drive inverter control device described in Patent Document 2 is a single-phase AC power input to solve the problems in the cost, weight, and size of the conventional inverter control circuit. A diode full-wave rectifier circuit, a small-capacity smoothing capacitor about 1/100 of a smoothing capacitor for a conventional diode full-wave rectifier circuit connected to the diode, a control circuit composed of a control PWM inverter and a motor, A motor drive inverter control device has been devised that has improved the input power factor and waveform of the diode full-wave rectifier circuit. Thus, an inverter device having a high input power factor and high efficiency has been proposed with a small and simple circuit configuration.

Japanese Patent Laying-Open No. 2005-304248 JP 2002-51589 A

  However, in the conventional configuration, when the motor drive is controlled using a small-capacity reactor and a small-capacity smoothing capacitor, the output frequency of the inverter is close to the resonance frequency relative to the resonance frequency of the reactor and the smoothing capacitor. In this case, since the capacitor has a very small capacity, the voltage of the direct current portion greatly fluctuates. For this reason, the switching elements of the inverter are not normally controlled, and the motor cannot be driven or the efficiency of the circuit is reduced.

In addition, as a motor drive method, a rectangular wave drive method, a sine wave drive method, or the like is used. However, in particular, when a rectangular wave drive method with a small switching loss of the inverter circuit is used, voltage fluctuation appears significantly, and the rectangular wave drive method is used. When the driving method is used, the smoothing capacitor cannot be operated normally unless the capacity of the smoothing capacitor is increased, and there are problems such as a reduction in circuit efficiency and an increase in cost, shape, and weight.

  The present invention solves the above-described conventional problems, and by selecting a rectangular wave driving method and a sine wave driving method in accordance with the output frequency of the inverter without increasing the capacitance of the capacitor, the inverter can be downsized. An object is to provide a control circuit.

  In order to solve the above-described conventional problems, the inverter control circuit of the present invention has a full-wave rectifier circuit that receives an AC power supply and converts it into DC power, and a plurality of switching elements connected to the full-wave rectifier circuit. An inverter that converts electric power into AC power, a motor driven by the inverter, a small-capacity reactor connected to the AC input side of the full-wave rectifier circuit, and a small-capacity connected between the full-wave rectifier circuit and the inverter Smoothing capacitors, and drive the motor by switching between the rectangular wave drive method and the sine wave drive method so as to avoid resonance between the resonance frequency of the small-capacity reactor and the small-capacity smoothing capacitor and the output frequency of the inverter It was set as the structure made to do.

  This makes it possible to suppress fluctuations in DC voltage even when the output frequency of the inverter approaches the resonance frequency, such as during high-speed rotation, and control at high-speed rotation without using a large-capacity capacitor. Therefore, the circuit can be miniaturized.

  The inverter control circuit of the present invention is configured by a small and low-cost circuit, and can provide a highly efficient motor drive inverter control circuit.

The circuit block diagram of the inverter apparatus in this Embodiment 1. Driving signal timing chart of the rectangular wave driving method in the first embodiment The figure which showed the resonance area | region of LC resonance frequency in this Embodiment 1. Configuration diagram of another conventional inverter control circuit

  A first invention includes a full-wave rectifier circuit that receives AC power as input and converts it into DC power, an inverter that is connected to the full-wave rectifier circuit and has a plurality of switching elements, and that converts DC power into AC power, and an inverter And a small-capacity reactor connected between the full-wave rectifier circuit and the inverter, and a small-capacity smoothing capacitor connected between the full-wave rectifier circuit and the inverter. Further, the motor is driven by switching between the rectangular wave driving method and the sine wave driving method so as to avoid resonance between the resonance frequency of the smoothing capacitor having a small capacity and the output frequency of the inverter. As a result, the motor can be driven by the downsized inverter control circuit without increasing the capacity of the smoothing capacitor.

  The second invention compares the output frequency of the inverter with the resonance frequency of the small-capacity reactor and the small-capacity smoothing capacitor. When the difference between the output frequency of the inverter and the resonance frequency is within a predetermined value, the rectangular wave The motor is driven by switching from the driving method to the sine wave driving method. As a result, when the difference between the inverter output frequency and the resonance frequency is other than a predetermined value, the switching loss is reduced by performing rectangular wave driving with less switching of the switching element of the inverter, and the inverter output frequency and the resonance frequency are reduced. When the difference is within a predetermined value, the sine wave drive is performed, so that the voltage fluctuation of the DC part is suppressed and the motor can be driven without increasing the capacity of the smoothing capacitor.

  A third aspect of the invention is characterized in that the drive circuit of the fan motor of the vacuum cleaner is constituted by the inverter control circuit according to claim 1 or 2. Thereby, it becomes possible to provide a small and efficient electric vacuum cleaner.

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

(Embodiment 1)
FIG. 1 shows a main circuit configuration of the first embodiment, taking a motor drive inverter control circuit as an example, and shows a power conversion circuit and an inverter circuit. The AC power supplied from the AC power supply 21 is exchanged for DC through a diode bridge which is a full-wave rectifier circuit 23 through a reactor 22 for power factor improvement. A very small-capacity smoothing capacitor 24 is connected to both ends of the DC portion. The capacitance is, for example, about 20 μF, and a film capacitor can be used instead of an electrolytic capacitor that has a problem in life.
Further, the small capacity reduces the influence of the charging current of the capacitor on the current flowing from the AC power supply, so that the high frequency component is greatly reduced and so-called harmonic regulation can be cleared.

  Further, since the harmonic current of the reactor 22 is greatly reduced, the reactor 22 may be a small one of about 0.3 mH, and the size of the entire motor drive inverter control circuit can be made very small. This DC power has three phases of a series circuit composed of a switching circuit on the upper arm side constituted by switching elements 25a to 25f and a diode connected in parallel thereto, and a switching circuit on the lower arm side. The interconnection point between the upper arm and the lower arm is supplied to a circuit connected to the motor 26 as a load.

  The control means 27 controls the switching of the switching elements 25a to 25f so that the circuit outputs AC power that causes the motor 26 to rotate at a desired rotational speed. As a switching method, the output voltage is controlled by the time width of the drive pulse of the element, a rectangular pulse width modulation (PWM sine wave drive system), or a rectangular switching element with less switching loss than the PWM drive system. In the first embodiment, the driving signals of the switching elements 25a to 25f are two-phase among U phase winding, V phase winding, and W phase winding as shown in FIG. A rectangular wave drive system is used in which energization is sequentially applied to the windings and the energization is switched every 120 degrees. A magnetic pole detection position sensor 28 is provided, and a drive signal is generated from the control means 27 based on a signal from the position sensor 28.

  FIG. 3 shows the calculation of the LC resonance frequency f of the reactor 22 and the smoothing capacitor 24. The difference between the inverter output frequency and the LC resonance frequency f is set to ± 50%, and the resonance region is within the predetermined value. . In the first embodiment, a 0.3 mH reactor and a 20 μF capacitor are used, the LC resonance frequency is about 2 kH, and the resonance region is about 1 kHz to 3 kHz. When the output frequency of the inverter becomes 1 kHz when the motor 26 is driven and the rotational speed is increased, if the rectangular wave driving method is performed, the energization is switched every 120 degrees, and the voltage fluctuation of the DC section Becomes very large.

  Therefore, when the output frequency of the inverter enters the resonance region, the switching frequency of the switching elements 25a to 25f is switched at a high frequency such as 20 kHz by switching from the rectangular wave driving method to the sine wave driving method. It is possible to suppress voltage fluctuations.

As a result, when it does not enter the resonance region, it is possible to improve the efficiency of the circuit by performing a rectangular wave driving method with a small switching loss. By using a sine wave driving method that can be suppressed as compared with the wave driving method, the motor can be driven without increasing the capacitance of the capacitor, so that a miniaturized circuit can be realized.

  The inverter control circuit for driving a motor according to the present invention is used in an inverter control circuit that realizes a small and low-cost circuit while suppressing a power supply harmonic, in particular, an extremely small capacitor is provided in the direct current portion of the inverter control circuit. It is useful for inverter control circuits that require low cost, small size, and high efficiency features.

DESCRIPTION OF SYMBOLS 21 AC power source 22 Reactor 23 Full wave rectifier circuit 24 Smoothing capacitor 25 Inverter 25a-25f Switching element 26 Motor 27 Control means 28 Position sensor

Claims (3)

A full-wave rectifier circuit that receives AC power as input and converts it into DC power, an inverter that is connected to the full-wave rectifier circuit and has a plurality of switching elements and converts DC power into AC power, and is driven by the inverter A small-capacity reactor connected to the AC input side of the full-wave rectifier circuit; and a small-capacity smoothing capacitor connected between the full-wave rectifier circuit and the inverter, the small-capacity reactor And driving the motor by switching between a rectangular wave driving method and a sine wave driving method so as to avoid resonance between the resonance frequency of the smoothing capacitor having a small capacity and the output frequency of the inverter. Inverter control circuit. When the output frequency of the inverter is compared with the resonance frequency of the small-capacity reactor and the small-capacity smoothing capacitor, and the difference between the output frequency of the inverter and the resonance frequency is within a predetermined value, a rectangular wave The motor drive inverter control circuit according to claim 1, further comprising inverter control means for driving the motor by switching from a drive system to a sine wave drive system. A vacuum cleaner, wherein the control circuit for driving the fan motor comprises the inverter control circuit according to claim 1.