JP5983217B2 - Inverter circuit - Google Patents

Description

  The present invention relates to an inverter circuit for driving an induction motor or the like.

  2. Description of the Related Art Conventionally, it is widely known to use an insulated gate bipolar transistor (IGBT) as a switching element of an inverter circuit for driving an induction motor or the like (see Patent Document 1).

  IGBTs are relatively slow in operating speed, but are relatively easy to increase withstand voltage and increase current capacity (current rating). It is suitable for an inverter circuit for driving. In particular, in this type of inverter circuit, it is necessary to supply a large current to the induction motor at the start of driving of the induction motor (at the time of overload driving), compared with that at the time of steady driving. An element is required.

Japanese Patent No. 331498

  In recent years, in an inverter circuit for driving an induction motor or the like, for the purpose of improving inverter efficiency, it is desired to increase a switching frequency during steady driving of the induction motor. In recent years, it has been realized that the withstand voltage of a relatively high speed MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is improved. Thus, the inventors of the present application have devised using a MOSFET as a switching element of this type of inverter circuit.

  However, in the high voltage MOSFET, it is difficult to increase the current capacity because the induction motor is overloaded. More specifically, in order to increase the current capacity, it is necessary to increase the transistor size. However, in the high voltage MOSFET, when the size is increased, the parasitic capacitance increases and the high-speed performance decreases. Thus, in an inverter circuit for driving an induction motor or the like, it is difficult to achieve both high speed during steady driving and large current capacity during overload driving.

  Therefore, an object of the present invention is to provide an inverter circuit capable of achieving both high speed and large current capacity.

  The inverter circuit of the present invention is an inverter circuit including a plurality of switching units, and each of the plurality of switching units includes a first MOSFET to which a control voltage is supplied and second and third MOSFETs connected in series. The series circuit of the second and third MOSFETs is connected in parallel to the first MOSFET, and the second MOSFET is supplied with a control voltage. A current sensor for detecting a current flowing through the first MOSFET, and when the current sensor detects that a current of a predetermined current value or more has flowed through the first MOSFET, the third MOSFET is turned on. It is characterized by becoming.

  According to this inverter circuit, for example, at the time of steady driving in which a current less than a predetermined current value is supplied to the induction motor, the current is supplied only by the first MOSFET, so that a transistor having high speed is applied to the first MOSFET. By doing so, the high-speed property at the time of steady drive of an inverter circuit can be improved.

  On the other hand, for example, at the start of driving to supply a current equal to or higher than a predetermined current value to the induction motor (at the time of overload driving), the third MOSFET is turned on, and the second MOSFET in addition to the first MOSFET is turned on. Since current supply is also performed, the current capacity at the start of driving the inverter circuit (during overload driving) can be increased.

  The current capacity of the second MOSFET may be greater than or equal to the current capacity of the first MOSFET, and the current capacity of the third MOSFET may be greater than or equal to the current capacity of the second MOSFET.

  According to this, it is suitable as an inverter circuit of an induction motor that needs to supply a current several times as much as that during steady driving at the start of driving to the induction motor.

  Further, the withstand voltage of the second MOSFET described above may be higher than the withstand voltage of the first MOSFET, and the withstand voltage of the third MOSFET described above may be lower than the withstand voltage of the first MOSFET.

  As described above, since the second MOSFET that performs switching control in cooperation with the first MOSFET has a high withstand voltage, the withstand voltage of the third MOSFET connected in series to the second MOSFET may be low.

  Further, the first to third MOSFETs described above may be formed of a wide band gap semiconductor.

  According to this, the breakdown voltage can be increased. In addition, the on-resistance can be reduced, and as a result, loss can be reduced and heat generation can be reduced. That is, the inverter circuit can operate at a relatively high temperature.

  According to the present invention, in an inverter circuit for driving an induction motor or the like, it is possible to achieve both high speed during steady driving and large current capacity during overload driving.

It is a circuit diagram showing an inverter circuit concerning an embodiment of the present invention. In FIG. 1, it is a figure which shows the inverter circuit which shows the 1st-6th switching part in detail. In FIG. 1, it is a figure which shows the equivalent circuit of an inverter circuit in the case of making the group of the 2nd and 3rd switching part into an ON state.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a circuit diagram showing an inverter circuit according to an embodiment of the present invention. The inverter circuit 1 converts DC power from a DC power source 2 into three-phase AC power and drives a three-phase induction motor 3. The inverter circuit 1 includes a capacitive element 4 connected between the high potential side terminal 2a and the low potential side terminal 2b of the DC power source 2, six switching units 10, 20, 30, 40, 50, 60, And a control unit 70.

  The first and second switching units 10 and 20 are connected in series between the high potential side terminal 2a and the low potential side terminal 2b of the DC power supply 2 in order. Specifically, one end of the first switching unit 10 is connected to the high potential side terminal 2 a of the DC power supply 2, and the other end of the first switching unit 10 is connected to one end of the second switching unit 20. ing. The other end of the second switching unit 20 is connected to the low potential side terminal 2 b of the DC power supply 2.

  The third and fourth switching units 30 and 40 are connected in series between the high potential side terminal 2a and the low potential side terminal 2b of the DC power supply 2 in order. Specifically, one end of the third switching unit 30 is connected to the high potential side terminal 2 a of the DC power supply 2, and the other end of the third switching unit 30 is connected to one end of the fourth switching unit 40. ing. The other end of the fourth switching unit 40 is connected to the low potential side terminal 2 b of the DC power supply 2.

  The fifth and sixth switching units 50 and 60 are connected in series between the high potential side terminal 2a and the low potential side terminal 2b of the DC power supply 2 in order. Specifically, one end of the fifth switching unit 50 is connected to the high potential side terminal 2 a of the DC power supply 2, and the other end of the fifth switching unit 50 is connected to one end of the sixth switching unit 60. ing. The other end of the sixth switching unit 60 is connected to the low potential side terminal 2 b of the DC power supply 2.

  The U-phase inductor of the three-phase induction motor 3 is connected between the intermediate node of the first and second switching units 10 and 20 and the intermediate node of the third and fourth switching units 30 and 40. The V-phase inductor of the three-phase induction motor 3 is connected between the intermediate node of the third and fourth switching units 30 and 40 and the intermediate node of the fifth and sixth switching units 50 and 60. A W-phase inductor of the three-phase induction motor 3 is connected between the intermediate node of the fifth and sixth switching units 50 and 60 and the intermediate node of the first and second switching units 10 and 20. . The control terminals of the first to sixth switching units 10 to 60 are connected to the control unit 70.

  The control unit 70 performs switching control of the first to sixth switching units 10 to 60. For example, the control unit 70 includes a set of the second and third switching units 20 and 30, a set of the fourth and fifth switching units 40 and 50, and a set of the sixth and first switching units 60 and 10. Are turned on by shifting them by 1/3 period, so that the DC power from the DC power source 2 is converted into three-phase AC power and supplied to the three-phase induction motor 3.

  Next, the 1st-6th switching parts 10-60 are demonstrated in detail. FIG. 2 is a diagram showing an inverter circuit showing details of the first to sixth switching units in FIG. The second switching unit 20 will be described as a representative, but the configuration of the first and third to sixth switching units 10, 30, 40, 50, 60 is the same as the configuration of the second switching unit 20. is there.

  That is, the first to third MOSFETs 11, 12, and 13, the first to third diodes 11d, 12d, and 13d, the current sensor 14, and the resistance elements 15a and 15b in the first switching unit 10 The same as the first to third MOSFETs 21, 22, 23, the first to third diodes 21 d, 22 d, 23 d, the current sensor 24, and the resistance elements 25 a, 25 b in the switching unit 20, and in the third switching unit 30 The first to third MOSFETs 31, 32, 33, the first to third diodes 31d, 32d, 33d, the current sensor 34, and the resistance elements 35a, 35b are respectively the first to third in the second switching unit 20. MOSFETs 21, 22 and 23, first to third diodes 21d, 22d and 23d, current sensor 24, resistor The first to third MOSFETs 41, 42, 43, the first to third diodes 41d, 42d, 43d, the current sensor 44, and the resistance elements 45a, 45b in the fourth switching unit 40 are the same as the elements 25a, 25b. Are the same as the first to third MOSFETs 21, 22, 23, the first to third diodes 21d, 22d, 23d, the current sensor 24, and the resistance elements 25a, 25b, respectively, in the second switching unit 20. The first to third MOSFETs 51, 52, and 53, the first to third diodes 51d, 52d, and 53d, the current sensor 54, and the resistance elements 55a and 55b in the fifth switching unit 50 are respectively the second switching unit. 20, first to third MOSFETs 21, 22, 23 and first to third diodes 21d, 22d, 23d. The current sensor 24 is the same as the resistance elements 25a and 25b, and the first to third MOSFETs 61, 62, and 63, the first to third diodes 61d, 62d, and 63d in the sixth switching unit 60, the current sensor 64, The resistive elements 65a and 65b are respectively the first to third MOSFETs 21, 22, and 23, the first to third diodes 21d, 22d, and 23d, the current sensor 24, and the resistive elements 25a and 25b in the second switching unit 20. Is the same.

  FIG. 3 is a diagram showing an equivalent circuit of the inverter circuit 1 when the set of the second and third switching units 20 and 30 in FIG. 1 is turned on. In FIG. 3, focusing on the second switching unit 20, the third switching unit 30 in the on state is shown as a short circuit state, and the first to third diodes 11 d in the first switching unit 10 in the off state are shown. , 12d, 13d are shown as one diode.

  2 and 3, the second switching unit 20 includes first to third MOSFETs 21, 22, 23, first to third diodes 21d, 22d, 23d, a current sensor 24, and a resistance element 25a. , 25b.

  The drain of the first MOSFET 21 is connected to one end of the switching unit 20 via the current sensor 24, and the source of the first MOSFET 21 is connected to the other end of the switching unit 20. A control voltage from the control unit 70 is supplied to the gate of the first MOSFET 21 through the resistance element 25a. A series circuit of second and third MOSFETs 22 and 23 is connected to the first MOSFET 21 in parallel.

  The drain of the second MOSFET 22 is connected to the source of the third MOSFET 23, and the source of the second MOSFET 22 is connected to the other end of the switching unit 20. The drain of the third MOSFET 23 is connected to one end of the switching unit 20. The control voltage from the control unit 70 is supplied to the gate of the second MOSFET 22 through the resistance element 25b. On the other hand, the gate of the third MOSFET 23 is connected to a terminal of the current sensor 24 opposite to the one end side of the switching unit 20.

  The anodes of the first to third diodes 21d, 22d, and 23d are connected to the sources of the first to third MOSFETs 21, 22, and 23, respectively, so that the first to third diodes 21d, 22d, and 23d are connected. Are connected to the drains of the first to third MOSFETs 21, 22 and 23, respectively.

  The current sensor 24 detects a current flowing through the first MOSFET 21. The current sensor 24 is, for example, a resistance element, and generates a voltage corresponding to the magnitude of the current flowing through the first MOSFET 21 as a voltage across the both ends. As a result, the third MOSFET 23 detects when the voltage across the current sensor 24 becomes equal to or higher than a predetermined value, that is, when the current sensor 24 detects that a current higher than the predetermined current value flows through the first MOSFET 21. Then, it will be in the on state.

  Here, the first MOSFET 21 has a high breakdown voltage. The first MOSFET 21 has a relatively small transistor size and high speed, but has a relatively small current capacity.

  On the other hand, the second MOSFET 22 has a high withstand voltage equal to or higher than that of the first MOSFET 11. Further, the second MOSFET 22 has a transistor size equal to or larger than that of the first MOSFET 21, and high speed is equal to or inferior to the first MOSFET 21, but the current capacity is equal to or larger than that of the first MOSFET 21.

  In addition, since the third MOSFET 23 is connected in series with the second MOSFET 22, the third MOSFET 23 may have a low withstand voltage and preferably has a current capacity equal to or higher than that of the second MOSFET 22. Further, the third MOSFET 23 only needs to have a low operation speed because the second MOSFET 22 only needs to be turned on during the switching operation.

  These first to third MOSFETs 21, 22, and 23 are preferably made of a wide band gap semiconductor such as SiC or GaN. According to this, the breakdown voltage can be increased. In addition, the on-resistance can be reduced, and as a result, loss can be reduced and heat generation can be reduced. That is, the inverter circuit can operate at a relatively high temperature.

  As described above, according to the inverter circuit 1 of the present embodiment, for example, during steady driving in which a current less than a predetermined current value is supplied to the induction motor 3, current is supplied only by the first MOSFET 21 having high speed. As a result, the high-speed performance during steady driving of the inverter circuit can be improved. As a result, according to this inverter circuit 1, the switching frequency can be increased, and the inverter efficiency during steady driving can be improved.

  On the other hand, for example, at the start of driving to supply a current of a predetermined current value or more to the induction motor 3 (at the time of overload driving), the third MOSFET 23 is turned on, and the second MOSFET 22 in addition to the first MOSFET 21 is turned on. Therefore, the current supply is also performed, so that the current capacity at the start of driving the inverter circuit (during overload driving) can be increased.

  Thus, according to the inverter circuit 1 of the present embodiment, it is possible to achieve both high speed during steady driving of the induction motor 3 and large current capacity during overload driving.

  According to the inverter circuit 1 of the present embodiment, the current capacity during overload driving can be increased without increasing the high speed during steady driving only by increasing the current capacity of the second MOSFET 22. Therefore, it is suitable as an inverter circuit for an induction motor that needs to supply a current several times as large as that during steady driving at the start of driving.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the present embodiment, an inverter circuit for driving an induction motor has been illustrated. However, the feature of the present invention is that not only the induction motor but also a relatively high pressure resistance is required, and further, a high speed during steady driving is required. And can be applied to all inverter circuits that require high current capacity at the time of overload driving.

  Moreover, in this embodiment, although the three-phase inverter circuit provided with six switching parts was illustrated, the feature of this invention is a full bridge type inverter circuit provided with four switching parts, or two switching parts. The present invention is also applicable to a half-bridge type inverter circuit provided.

  In the present embodiment, the first to third MOSFETs made of wide band gap semiconductors such as SiC and GaN are exemplified, but the semiconductor materials of the first to third MOSFETs are not limited to this.

  DESCRIPTION OF SYMBOLS 1 ... Inverter circuit, 2 ... DC power supply, 2a ... High potential side terminal, 2b ... Low potential side terminal, 3 ... Induction motor, 4 ... Capacitance element 10, 20, 30, 40, 50, 60 ... Switching part, 11 , 21, 31, 41, 51, 61 ... first MOSFET, 12, 22, 32, 42, 52, 62 ... second MOSFET, 13, 23, 33, 43, 53, 63 ... third MOSFET, 11d, 21d, 31d, 41d, 51d, 61d ... 1st diode, 12d, 22d, 32d, 42d, 52d, 62d ... 2nd diode, 13d, 23d, 33d, 43d, 53d, 63d ... 3rd diode 14, 24, 34, 44, 54, 64 ... current sensors, 15a, 15b, 25a, 25b, 35a, 35b, 45a, 45b, 55a, 55b, 65a, 65b ... Anti-element, 70 ... control unit.

Claims (4)

An inverter circuit that includes a plurality of switching units and converts DC power from a DC power source into AC power ,
Each of the plurality of switching units is
A first MOSFET to which a control voltage is supplied;
Second and third MOSFETs connected in series, wherein the series circuit of the second and third MOSFETs is connected in parallel to the first MOSFET, and the second MOSFET includes the control The second and third MOSFETs to which a voltage is supplied;
A current sensor for detecting a current flowing through the first MOSFET;
Have
The first to third MOSFETs are made of a wide band gap semiconductor,
The current sensor is disposed on the high potential side terminal side of the DC power supply with respect to the first MOSFET,
The third MOSFET is turned on when it is detected by the current sensor that a current greater than or equal to a predetermined current value flows in the first MOSFET.
Inverter circuit. The current capacity of the second MOSFET is greater than or equal to the current capacity of the first MOSFET;
The current capacity of the third MOSFET is equal to or greater than the current capacity of the second MOSFET.
The inverter circuit according to claim 1. The withstand voltage of the second MOSFET is not less than the withstand voltage of the first MOSFET,
The withstand voltage of the third MOSFET is lower than the withstand voltage of the first MOSFET.
The inverter circuit according to claim 1 or 2. The plurality of switching units include at least one pair of switching units connected in series between the high potential side terminal and the low potential side terminal of the DC power supply,
The inverter circuit as described in any one of Claims 1-3.

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