JP2012249488A - Inverter control circuit and vacuum cleaner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter control circuit for driving a motor with a simple cooling structure.SOLUTION: An inverter control circuit includes control means 25 that causes an inverter circuit 18 having plural upper/lower arms 18a and 18b to perform switching operation to drive a brushless DC motor 26 (referred to as motor 26). Switching elements 24 are capable of switching operation at a speed higher than switching elements 23. The control means 25 causes the switching elements 23 to turn ON at every 2π/3 in order in each phase voltage of 3-phase voltage applied to the motor 26 and causes the switching elements 24 to turn OFF to cyclically fix each phase voltage to drive the motor 26. Even when the switching elements 24 with higher switching speed are used for the lower arms 18b, since the switching loss at the upper arms 18a is controlled to be smaller than that at the lower arms 18b, uneven loss (heat generation) on each switching element is reduced resulting in a simple cooling structure.

Description

  The present invention relates to an inverter control circuit for converting a direct current into an alternating current in order to drive a load, for example, a motor, and a vacuum cleaner using the inverter control circuit.

  Conventionally, in this type of inverter control circuit, a switching circuit for driving a DC motor such as a compressor is composed of a total of 6 phases and 6 elements for upper and lower arms, and IGBTs and MOSFETs are often used as switching elements. Yes. In some cases, the switching elements are used in combination (see, for example, Patent Document 1).

  FIG. 3 is a circuit diagram of a conventional inverter control circuit for driving a DC motor described in Patent Document 1.

  In FIG. 3, in the conventional inverter control circuit, the switching element of the upper arm 4 is configured by IGBT or MOSFET, and the switching element of the lower arm 5 is configured by bipolar transistor, thereby generating noise and significantly increasing the cost. It is an inverter control circuit without accompanying.

JP-A-7-31182

  However, in the configuration of the conventional inverter control circuit as described in Patent Document 1, a switching element having different characteristics is used for each of the upper arm and the lower arm, so that the loss generated during switching is reduced between the upper arm and the lower arm. In contrast, the heat generation of the switching element is different between the upper and lower sides, and there is a problem that the cooling configuration is complicated.

  The present invention solves the above-mentioned conventional problems, and even when elements having different switching characteristics are used for the upper and lower arms, the variation in loss (heat generation) for each switching element is reduced by the upper and lower elements, and the cooling configuration is simplified. An object of the present invention is to provide an inverter control circuit and a vacuum cleaner using the inverter control circuit.

  In order to solve the conventional problems, an inverter control circuit according to the present invention includes an inverter circuit including a plurality of upper and lower arms, and a control unit that performs a switching operation of the inverter circuit to drive a motor, The switching element of the lower arm of the circuit is configured by a switching element capable of switching at a higher speed than the switching element of the upper arm, and the control means is 2π / 3 in each phase voltage of the three-phase voltage applied to the motor. The upper arm switching element is turned on in turn and the lower arm switching element is turned off to fix each phase voltage periodically to drive the motor. The lower arm is switched from the upper arm. Even when switching elements with high speed are used, the switching loss of the upper arm is less than that of the lower arm. By controlling such that, it is possible to simplify the cooling structure by reducing the variation in the loss (heat generation) of each switching element.

The vacuum cleaner of the present invention includes a fan and a motor that rotationally drives the fan, and includes a fan motor that generates suction force, and the inverter control circuit according to claim 1, wherein the motor is It is driven by an inverter control circuit, and it is possible to provide an energy saving and efficient vacuum cleaner.

  The inverter control circuit according to the present invention is an inverter in which a cooling structure is simplified by reducing variation in loss (heat generation) for each switching element in the lower element even when elements having different switching characteristics are used for the upper arm and the lower arm, respectively. An apparatus can be provided. Moreover, the vacuum cleaner of this invention is energy-saving and efficient.

Circuit diagram of inverter control circuit according to Embodiment 1 of the present invention The figure which shows the waveform of each phase voltage of each inverter control circuit, and each modulation signal Circuit diagram of conventional inverter control circuit

  According to a first aspect of the present invention, the inverter circuit includes a plurality of upper and lower arms, and a control unit that drives the motor by switching the inverter circuit. The switching element of the lower arm of the inverter circuit is connected to the upper arm. The control means turns on the upper arm switching element in turn every 2π / 3 in each phase voltage of the three phase voltage applied to the motor. The lower arm switching element is turned off to fix each phase voltage periodically, and the motor is driven. Even when a switching element having a higher switching speed than the upper arm is used for the lower arm, By controlling so that the switching loss of the arm is less than that of the lower arm, It is possible to simplify the cooling arrangement to reduce the variation in the loss (heat generation).

  In the second invention, in particular, the switching element of the lower arm of the first invention is a wide gap semiconductor such as diamond, GaN, SiC, etc., and switching loss at the time of switching or the switching element is conductive. Continuity loss can be reduced, and energy saving of the inverter control circuit can be achieved.

  A vacuum cleaner according to a third aspect of the present invention includes a fan and a motor that rotationally drives the fan, the fan motor that generates a suction force, and the inverter control circuit according to claim 1, wherein the motor It is driven by the inverter control circuit, and it is possible to provide an energy saving and efficient 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 is a circuit configuration diagram of an inverter control circuit according to Embodiment 1 of the present invention, and FIG. 2 is a diagram illustrating waveforms of interphase voltages and modulation signals of the inverter control circuit.

  The inverter control circuit in the present embodiment is turned on / off at a predetermined timing from a 100 V commercial power supply 20 via a converter circuit with a filter circuit unit 21 including a rectifier circuit, a power factor correction circuit, etc. An inverter circuit 18 for generating high-frequency power of a predetermined frequency by the switching elements 23 and 24, a control means 25 including a drive circuit for supplying a drive signal for driving the switching elements 23 and 24, a brushless DC motor 26, The fan 27 is attached to the brushless DC motor 26.

  In the present embodiment, the brushless DC motor 26 and the fan 27 constitute a fan motor 19 that generates a suction force.

  In the present embodiment, the switching element 23 of the upper arm 18a is formed of an IGBT, and the switching element 24 of the lower arm 18b is switched using gallium nitride (GaN) as an element capable of switching at a higher speed than the switching element 23. It consists of elements.

  At present, semiconductor devices using silicon as a semiconductor material are the mainstream as switching elements. These semiconductor devices are appropriately selected and used according to the application. For example, MOSFET (metal / oxide film / semiconductor field effect transistor), IGBT (insulated gate bipolar transistor), thyristor, etc. are mainly used. In recent years, however, wide gap semiconductor materials such as diamond, silicon carbide (SiC), and gallium nitride (GaN) are semiconductors that can realize superior power semiconductor devices such as high withstand voltage, low loss, high output and high frequency operation than silicon. It has attracted attention as a material, and some have reached a practical level.

  In terms of switching speed, high-speed switching that is three times or more that of silicon-based power semiconductors is also possible. The brushless DC motor 26 includes a stator (not shown) having three phase windings connected around a neutral point, and a rotor (not shown) having permanent magnets. The rotor is rotated by the interaction between the magnetic field generated by the current flowing through the magnetic field and the magnetic field generated by the permanent magnet.

  The control unit 25 generates a plurality of modulation signals having different phase angles as a main function, and generates a drive signal for driving the switching elements 23 and 24 by comparing each modulation signal with a triangular wave signal having a constant frequency. Let

  The operation and action of the inverter control circuit according to the present embodiment configured as described above will be described below.

  The power input from the AC power supply 20 is rectified by the filter circuit unit 21 and then turned on / off at a predetermined timing by the control means 25 as DC power smoothed through the smoothing circuit 22. Thus, the brushless DC motor 26 that is converted into a desired alternating current and uses the fan 27 as a load is driven to rotate.

  Next, FIG. 2 shows each part voltage waveform in the two-phase modulation method in which the switching element 23 of the upper arm 18a is controlled by being fixed by 2π / 3.

  Eu, Ev, and Ew are three-phase sine wave voltages whose phase angles are shifted from each other by 2π / 3, which can be calculated from the rotational speed of the brushless DC motor 26 and the like, but here a detailed description of the calculation method Is omitted. The three-phase sine wave voltages Eu, Ev, Ew change in frequency in proportion to the rotational speed of the brushless DC motor 26.

Then, by shaping the three-phase sine wave voltage waveforms Eu, Ev, and Ew, a period corresponding to 1/3 of the period of the three-phase sine wave voltages Eu, Ev, and Ew is negative as a switching pause period. A plurality of modulation signals Eu ₂ , Ev ₂ , Ew ₂ having a voltage waveform fixed at a constant level and having a phase angle shifted by 2π / 3 from each other are generated. By driving voltage comparison between the modulation signals Eu ₂ , Ev ₂ , Ew ₂ and a triangular wave signal (shown here only for Eu ₂ ), a drive signal (pulse width modulation signal) for driving the switching elements 23, 24 is generated. The This
It is possible to control the lower arm 18b so that the switching frequency of the upper arm 18a is reduced and the switching loss of the upper arm 18a is smaller than that of the lower arm 18b.

  Thus, even when elements having different switching characteristics are used for the upper arm 18a and the lower arm 18b, variation in loss (heat generation) for each switching element can be reduced, and the cooling configuration is changed for each of the upper arm 18a and the lower arm 18b. The cooling design can be easily performed.

  The switching element using diamond or gallium nitride (GaN) or the switching element using silicon carbide (SiC) used in the lower arm 18b of the first embodiment has excellent characteristics regarding switching and resistance. However, since it is very expensive compared to a silicon-based power semiconductor, the cost can be reduced by using it only for the lower arm 18b.

  The inverter control circuit described in the above embodiment and the fan motor 19 are mounted on a vacuum cleaner (not shown), and the brushless DC motor 26 of the fan motor 19 is driven and controlled by the inverter control circuit. If it makes it, it becomes possible to provide an energy-saving and efficient vacuum cleaner.

  As described above, the inverter control circuit according to the present invention can be used for applications that are driven by an inverter circuit, and is useful for inverter control circuits and vacuum cleaners that require low cost and high efficiency features. .

DESCRIPTION OF SYMBOLS 18 Inverter circuit 18a Upper arm 18b Lower arm 19 Fan motor 23, 24 Switching element 25 Control means 26 Brushless DC motor (motor)
27 fans

Claims (3)

An inverter circuit composed of a plurality of upper and lower arms, and a control means for driving the motor by switching the inverter circuit, and the switching element of the lower arm of the inverter circuit is faster than the switching element of the upper arm The switching means is configured by switching elements, and the control means turns on the switching elements of the upper arm in turn every 2π / 3 in each phase voltage of the three-phase voltage applied to the motor, An inverter control circuit, wherein the switching element is turned off to fix each phase voltage periodically to drive the motor. 2. The inverter control circuit according to claim 1, wherein the switching element of the lower arm is a wide gap semiconductor such as diamond, GaN, or SiC. A fan motor comprising a fan and a motor that rotationally drives the fan motor that generates suction force, and the inverter control circuit according to claim 1, wherein the motor is driven by the inverter control circuit. Electric vacuum cleaner.