JP2007129848A - Inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter in which a reverse current flowing through a circulation diode can be suppressed sufficiently, and efficiency can be enhanced significantly by significantly reducing power loss. <P>SOLUTION: When circulation currents flow, respectively, through the circulation diodes Du-, Dv- and Dw- on the MOSFETs 4u, 4v and 4w side, reverse voltages are applied from reverse voltage application circuits 5u, 5v and 5w to the circulation diodes Du-, Dv- and Dw-, respectively, before the switching elements of IGBTs 3u, 3v and 3w are turned on. In particular, a voltage V2(=5V) of level lower than the drive voltage V1(=15V) of the IGBT and MOSFET is employed as the operating voltage of the reverse voltage application circuits 5u, 5v and 5w. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter device that outputs driving power to an inductive load such as a motor.

  An inverter device that outputs driving power for a load including an inductive component, for example, a brushless DC motor, has a plurality of series circuits of two switching elements that are upstream and downstream along the voltage application direction. Each switching element has a free-wheeling diode connected in antiparallel, and an interconnection point of each switching element is connected to each phase winding of the brushless DC motor.

  Recently, many IGBTs and MOSFETs have been adopted as switching elements.

  When the IGBT is used, the voltage between both ends when the IGBT is turned on is constant, so that the loss at the time of high voltage and high current output is small, and the driving circuit is simpler than the case where a transistor is used.

  When a MOSFET is used, there is a merit that high-frequency switching is possible because the on / off speed of the MOSFET is fast, and a motor with a small output such as a fan motor is driven because loss at low voltage and low current output is small. Often used in cases.

  However, when the switching element is a MOSFET, a reflux (parasitic) diode having a bad reverse recovery characteristic is formed on the element in the process of manufacturing the element. Further, in the case of a super-junction MOSFET having a low on-resistance and improved characteristics of a switching element developed in recent years, the reverse recovery characteristic of a freewheeling diode formed on the element is even worse. For this reason, when the forward current due to the energy stored in the inductive load flows to the freewheeling diode, a large reverse current flows to the freewheeling diode as the other switching element is turned on, resulting in a large power loss. It has been difficult to adopt in air conditioner compressor drive inverters that require a larger current than fan motors.

Therefore, conventionally, a reverse voltage application circuit for applying a reverse voltage to the freewheeling diode prior to turning on the other switching element is provided, and this reverse voltage prevents the reverse current flowing in the freewheeling diode when the other switching element is on. However, there is one that reduces power loss (for example, Patent Document 1). According to this document, the power source that is the source of the reverse voltage applied to the freewheeling diode and the gate drive power source of the MOSFET are composed of the same power source, and the applied voltages are the same.
Japanese Patent Laid-Open No. 10-327585

  When the reverse current flowing through the freewheeling diode is suppressed by the reverse voltage application circuit, further improvement of the suppression effect is desired.

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an inverter device that can further reduce power loss when suppressing a reverse current flowing in a freewheeling diode and improve efficiency.

  The inverter device according to the first aspect of the present invention includes a series circuit in which at least one of the two switching elements is upstream and downstream along the voltage application direction, and at least one of which is a MOSFET. A switching circuit having free-wheeling diodes connected in reverse parallel to the switching elements, the interconnection point of each switching element being connected to an inductive load, a controller for alternately turning on and off the switching elements, and Prior to turning on the switching element paired with the MOSFET, a reverse voltage applying circuit for applying a reverse voltage to the free wheel diode of the MOSFET, and a reverse voltage applied to the free wheel diode of the MOSFET is lower than the driving voltage for the MOSFET. And a power supply circuit for supplying a low voltage to the reverse voltage application circuit. .

  According to the inverter device of the present invention, when the reverse current flowing through the freewheeling diode is suppressed, the power loss is reduced and the efficiency can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, M is a brushless DC motor (load) used as a compressor motor of an air conditioner, and has a stator having three phase windings Lu, Lv, and Lw that are star-connected around a neutral point C. , And a rotor having permanent magnets. The rotor rotates due to the interaction between the magnetic field generated by the current flowing through the phase windings Lu, Lv, and Lw and the magnetic field created by the permanent magnet. The brushless DC motor M is connected with the inverter device 1 of the present invention.

  Inverter device 1 receives input terminals P and N to which DC voltage Vd (= 280 V) is applied, receives DC voltage Vd between input terminals P and N, and supplies current to and from the phase windings Lu, Lv, and Lw. The switching circuit 2 that performs switching, the control unit 10 that drives and controls the switching circuit 2, the rectifier circuit 31 that rectifies the AC voltage of the commercial AC power supply 30, and the output voltage (DC voltage) of the rectifier circuit 31 that is smoothed A smoothing capacitor 32 applied between the terminals P and N and a power supply circuit 11 are provided. The power supply circuit 11 generates a DC voltage V1 (= 15V) for driving the switching circuit 2 from an AC voltage of the commercial AC power supply 30, and a DC voltage V2 for operating the control unit 10 and the switching circuit 2. (= 5V) is generated and output.

  The switching circuit 2 includes a series circuit of a switching element on the upstream side, for example, an IGBT (Insulated Gate Bipolar Transistor), and a switching element on the downstream side, for example, a low-loss power MOSFET, along the application direction of the DC voltage Vd. The IGBT 3u is provided upstream of the U phase, the MOSFET 4u is provided downstream, the IGBT 3v is provided upstream of the V phase, the MOSFET 4v is provided downstream, the IGBT 3w is upstream of the W phase, and the MOSFET 4w is downstream. It has. The free-wheeling diodes Du +, Dv +, and Dw + are connected in reverse parallel to the IGBTs 3u, 3v, and 3w, respectively. The free-wheeling diodes Du−, Dv−, and Dw− are connected in reverse parallel to the MOSFETs 4u, 4v, and 4w, respectively.

  The interconnection point between the IGBT 3u and the MOSFET 4u becomes the output terminal Qu, the interconnection point between the IGBT 3v and the MOSFET 4v becomes the output terminal Qv, and the interconnection point between the IGBT 3w and the MOSFET 4w becomes the output terminal Qw. Then, the non-connection end of the phase winding Lu is connected to the output terminal Qu, the non-connection end of the phase winding Lv is connected to the output terminal Qv, and the non-connection end of the phase winding Lw is connected to the output terminal Qw. It is connected.

  Further, the switching circuit 2 is connected to the upstream when a forward current (return current) flows through the free-wheeling diodes Du−, Dv−, and Dw− by the energy stored in the phase windings Lu, Lv, and Lw that are inductive loads. In order to suppress the reverse current flowing through the free-wheeling diodes Du-, Dv-, Dw- when the IGBTs 3u, 3v, 3w on the side are turned on, the free-wheeling diodes Du-, Dv- are turned on prior to turning on the IGBTs 3u, 3v, 3w, respectively. , Dw− are provided with reverse voltage application circuits 5u, 5v, 5w for applying a reverse voltage.

An example of the current path in the switching circuit 2 is shown in FIG.
When both IGBT 3u and MOSFET 4v are on, current flows through the path of input terminal P, IGBT 3u, phase windings Lu and Lv, MOSFET 4v, and input terminal N as shown by the solid line in FIG. Thereafter, when the IGBT 3u is turned off and the MOSFET 4u is turned on, the current based on the energy stored in the phase windings Lu and Lv passes from the phase windings Lu and Lv through the MOSFET 4v to the MOSFET 4u side as shown by the broken lines in FIG. It flows through the freewheeling diode Du− in the forward direction. Thus, when the upstream IGBT 3u is turned on in a state in which a forward current (return current) flows through the freewheeling diode Du−, a voltage (= 280 V) between the terminals P and N is applied to the freewheeling diode Du− through the IGBT 3u. At this time, a large reverse current Irr such as a short-circuit current flows through the freewheeling diode Du−. Since the reverse current Irr flows through the IGBT 3u, a large power loss is caused in the IGBT 3u at this time. In order to suppress this loss, a reverse voltage application circuit 5u is provided.

  The configuration of the reverse voltage application circuit 5u and its peripheral part is shown in FIG. The power supply circuit 11 shown in FIG. 1 is configured to be able to output two different DC voltages, a high voltage V1 (for example, 15V) and a voltage V2 (for example, 5V) lower than that voltage.

  A DC voltage V1 output from the power supply circuit 11 is applied between the terminals A and N. The base of the IGBT 3 u is connected to the terminal A via the diode 41 and the semiconductor switch element 51. Further, a capacitor 42 is connected from the connection point between the diode 41 and the semiconductor switch element 51 to the emitter of the IGBT 3u. Further, the gate of the MOSFET 4 u is connected to the terminal A via the semiconductor switch element 52. The semiconductor switch elements 51 and 52 are ON / OFF controlled by the control unit 10.

  A DC voltage V2 output from the power supply circuit 11 is applied between the terminals B and N. The DC voltage V2 is also used as a power source for the control unit 10 formed of an electronic circuit such as a microcomputer. A reverse voltage application capacitor 60 is connected between the terminals B and N via a backflow prevention diode 61. The voltage stored in the reverse voltage application capacitor 60 is applied as a reverse voltage to the freewheeling diode Du− via the resistor 62, the drain-source of the reverse voltage application MOSFET 63, and the reverse current prevention diode 64. A free-wheeling diode Dx is connected in reverse parallel to the reverse voltage application MOSFET 63. The gate of the MOSFET 63 is connected to the terminal A via the diode 65 and the semiconductor switch element 53, and a capacitor 66 is connected from the connection point between the diode 65 and the semiconductor switch element 53 to the source of the MOSFET 63. Although not shown, the semiconductor switch element 53 is ON / OFF controlled by a reverse voltage application signal output from the control unit 10.

  These diode 61, reverse voltage application capacitor 60, resistor 62, reverse voltage application MOSFET 63, diode 64, diode 65, semiconductor switch element 53, and capacitor 66 constitute a reverse voltage application circuit 5u.

  When the semiconductor switch element 53 is turned on, the reverse voltage application MOSFET 63 is turned on, and the voltage stored in the reverse voltage application capacitor 60 is applied as a reverse voltage to the freewheeling diode Du−.

  The other reverse voltage application circuits 5v and 5w and their peripheral parts are also the same as those shown in FIG. Therefore, the description is omitted.

Next, the operation will be described.
As shown in FIG. 4, the control unit 10 compares the pseudo sine wave voltage Eu with the triangular wave signal Eo in order to generate a PWM waveform. Note that the frequency of the sine wave Eu changes in proportion to the speed of the brushless DC motor M. By this voltage comparison, an upper element driving signal for driving on / off of the IGBT 3u and a lower element driving signal for driving on / off of the MOSFET 4u which is substantially inverted from the IGBT 3u are generated. The upper element drive signal is supplied to the semiconductor switch element 51, and the lower element drive signal is supplied to the semiconductor switch element 52.

  Multi-phase energization in which the IGBT of at least one series circuit in the switching circuit 2 is turned on and off and the MOSFET of at least one other series circuit is turned on by the upper element drive signal and the lower element drive signal thus created Are switched sequentially. As a result of the switching of the plurality of phases, three interphase voltages are generated between the output terminals Qu, Qv, and Qw, and the interphase voltages are applied to the phase windings Lu, Lv, and Lw of the brushless DC motor M. Thereby, a sinusoidal current flows through Lu, Lv, and Lw, and the brushless DC motor M operates.

  A dead time td is ensured between the timing when the MOSFET 4u is turned off and the timing when the IGBT 3u is turned on. The dead time td is also ensured between the timing when the IGBT 3u is turned off and the timing when the MOSFET 4u is turned on. By securing the dead time td, a short circuit of the series circuit due to simultaneous turn-on of the IGBT 3u and the MOSFET 4u is prevented. Similarly in other series circuits, dead time is secured.

  As described with reference to FIG. 2, when the IGBT 3u is turned off (the MOSFET 4v continues to be turned on), the current based on the energy stored in the phase windings Lu and Lv passes through the MOSFET 4v from the phase windings Lu and Lv. Flows in the forward direction through the freewheeling diode Du-. This so-called return current flows as Ia only to the return diode Du− while the MOSFET 4u is turned off, and flows as Ia and Ib to the return diode Du− and the MOSFET 4u when the MOSFET 4u is turned on. Thus, in a state where the return current is flowing, prior to turning on the upstream IGBT 3u, an operation instruction from the control unit 10 to the reverse voltage application circuit 5u, that is, an on command for turning on the semiconductor switch element 53 is output. The MOSFET 4u is naturally turned off in advance. Thereby, the semiconductor switch element 53 is turned on, the reverse voltage application MOSFET 63 of the reverse voltage application circuit 5u is turned on, and the voltage stored in the reverse voltage application capacitor 60, that is, the output voltage V2 (about 5V) of the power supply circuit. Is applied to the free-wheeling diode Du− as a reverse voltage. The reverse voltage application period from the reverse voltage application circuit 5u to the free-wheeling diode Du− is a predetermined period that starts after the MOSFET 4u off timing, that is, during the dead time period td, and includes the on timing of the IGBT 3u. The control unit 10 turns on the semiconductor switch element 53 for that time. The timing for starting the application of the reverse voltage from the reverse voltage application circuit 5u to the free-wheeling diode Du− is set based on, for example, the OFF timing (falling timing of the lower element drive signal) of the MOSFET 4u.

  When a reverse voltage is applied from the reverse voltage application circuit 5u to the freewheeling diode Du−, a reverse current Irr flows through the freewheeling diode Du−.

  At this time, since the reverse current Irr is low in voltage applied from the reverse voltage application circuit 5u to the freewheeling diode Du-, the level of the reverse current Irr can be extremely small.

  That is, FIG. 5 shows the reverse voltage Va applied to the freewheeling diode Du−, the source voltage Vb of the reverse voltage application MOSFET 63 in the reverse voltage application circuit 5u, the drain voltage Vc of the reverse voltage application MOSFET 63, and the reverse voltage application MOSFET 63. The relationship of on-timing T1 is shown. Since the voltage V2 (about 5V) is applied between the terminals B and N of the reverse voltage application circuit 5u, the reverse voltage Va, the source voltage Vb, and the drain voltage Vc are lowered.

  If a voltage having the same level as the drive voltage V1 (about 15 V) of the IGBT 3u and the MOSFET 4u is applied between the terminals B and N of the reverse voltage application circuit 5u, the reverse voltage Va, the source voltage Vb, and the drain voltage Vc Becomes higher as shown in FIG.

  When the voltage V2 (about 5V) is applied between the terminals B and N of the reverse voltage application circuit 5u, the value of the reverse current Irr flowing through the freewheeling diode Du− is between the terminals B and N of the reverse voltage application circuit 5u. Driving voltage V1 is as small as about 1/3 when the same voltage is applied. However, the reverse current Irr period is about three times longer when the voltage V2 is applied than when the same voltage as the driving voltage V1 is applied. For this reason, when applying a low voltage as a reverse voltage, it is necessary to set the reverse voltage application time longer than when applying a higher voltage.

  FIG. 7 shows the difference between the value and the period (also referred to as a reverse recovery period) of the reverse current Irr when the applied voltage is V2 and V1. Further, FIG. 8 shows the difference between the electric power in the freewheeling diode Du− and the integrated electric power that is an integrated value thereof according to the difference in the value and the period of the reverse current Irr.

  The integrated power is the product of power consumption and time, and represents the power loss due to this circuit operation. It can be seen that if the value of the reverse current Irr is reduced to about 1/3, the integrated power, that is, the power loss is significantly reduced even if the period of the reverse current Irr is increased to about three times.

As described above, by applying reverse voltages from the reverse voltage application circuits 5u, 5v, and 5w to the free-wheeling diodes Du-, Dv-, and Dw-, respectively, before turning on the switching elements of the IGBTs 3u, 3v, and 3w, the free-wheeling diodes. The reverse current flowing in Du−, Dv−, and Dw− can be suppressed.
In particular, by using a voltage V2 at a level lower than the driving voltage V1 of the IGBT and MOSFET as the operating voltage of the reverse voltage application circuits 5u, 5v, and 5w, the reverse current flowing through the freewheeling diodes Du−, Dv−, and Dw−. Directional current can be suppressed with low power consumption. As a result, power loss can be greatly reduced and efficiency can be improved.

  In the above embodiment, the case where each upstream switching element in the switching circuit 2 is an IGBT has been described as an example. However, the case where each upstream switching element in the switching circuit 2 is the same MOSFET as the downstream switching element is also described. Can be implemented as well. In this case, a reverse voltage application circuit having the same configuration is added to the MOSFET as each upstream switching element.

  In addition, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

The figure which shows the structure of one Embodiment of this invention, and the structure of a refrigerating cycle. The figure which shows an example of the current pathway in the switching circuit of one Embodiment. The block diagram which shows the structure of the reverse voltage application circuit and its peripheral part in one Embodiment. The time chart which shows the signal waveform of each part in one Embodiment. The figure which shows the relationship between the reverse voltage Va, source voltage Vb, and drain voltage Vc in one Embodiment. The figure which shows the relationship between the reverse voltage Va, the source voltage Vb, and the drain voltage Vc when the voltage of the same level as the drive voltage V1 in one Embodiment is applied to the reverse voltage application circuit. The figure which shows the difference of the value and period of the reverse direction current Irr in the case where the applied voltage in one Embodiment is V2 and V1. The figure which shows the difference of the power consumption accompanying the difference of the value and period of the reverse direction current Irr in one Embodiment, and its integrated value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inverter apparatus, 2 ... Switching circuit, 3u, 3v, 3w ... IGBT, 4u, 4v, 4w ... MOSFET, 5u, 5v, 5w ... Reverse voltage application circuit, Du, Dv, Dw ... Freewheeling diode, P, N ... Input terminal, Qu, Qv, Qw ... output terminal, 10 ... control unit, 11 ... power supply circuit, M ... brushless DC motor, Lu, Lv, Lw ... phase winding

Claims (2)

A free-wheeling diode having two switching elements upstream and downstream along the voltage application direction, at least one of which has a series circuit composed of MOSFETs, and connected in reverse parallel to each switching element of the series circuit A switching circuit in which an interconnection point of each switching element is connected to an inductive load;
A controller for alternately turning on and off each of the switching elements;
Prior to turning on the switching element paired with the MOSFET, a reverse voltage application circuit for applying a reverse voltage to the freewheeling diode of the MOSFET;
A power supply circuit for supplying a low voltage to the reverse voltage application circuit so that a reverse voltage applied to the free-wheeling diode of the MOSFET is lower than a driving voltage for the MOSFET;
An inverter device comprising:   2. The inverter device according to claim 1, wherein the power supply circuit supplies a driving voltage to the MOSFET and supplies a voltage lower than the driving voltage to the control unit and the reverse voltage application circuit.

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