Patent Application
20160343838
The present invention relates to power conversion apparatuses, and in particular relates to a semiconductor element drive apparatus that is suitable for being widely used in various devices from small power devices such as air conditioners and microwave ovens to large power devices such as inverters used in railroads and in iron foundries, and to a power conversion apparatus using the semiconductor element drive apparatus.
As a related technology that reduces the conductivity loss and recovery loss of a flywheel diode, a fabric in which a MOS gate is fabricated at an anode side or a fabric in which a MOS gate is fabricated at a cathode side has been proposed (Refer to Patent Literature 1 and Patent Literature 2, for example).
In addition, as a related technology about a fabric in which a MOS gate is fabricated at the collector side of an IGBT, a technology in which attention is focused on the reduction of a switching loss has been proposed (Refer to Patent Literature 3, Patent Literature 4, and Patent Literature 5, for example).
Furthermore, a mechanism that a vibration occurs owing to the reduction of charge at a cathode side has been also known conventionally (Refer to Nonpatent Literature 1 and Nonpatent Literature 2).
Various inverters and converters have been used for power conversion apparatuses for energy saving and renewable energy usage in recent years, and in order to realize a low-carbon society, it becomes indispensable for those to be more widely spread.
A flywheel diode 600 is connected to the IGBT 700 in antiparallel. The flywheel diode 600 turns a current flowing the upper arm IGBT 700 to a flywheel diode 600 connected to an IGBT 700 whose emitter is connected to a negative electric power supply terminal 901 (the IGBT is referred to as the lower arm IGBT hereinafter) when the upper arm IGBT is turned off, for example, and releases charge accumulated in the coil of the motor 950. When the upper arm IGBT 700 is turned on again, the lower arm flywheel diode 600 goes into a nonconductive state, and electric power is supplied to the motor 950 through the upper arm IGBT 700. Because the IGBT 700 and the flywheel diode 600 generate conductive losses when they are in conductive states, and switching losses when they are in switching states, it is necessary to reduce the conductivity losses and switching losses generated by the IGBT 700 and the flywheel diode 600 in order to downsize and streamline the IGBT 700 and the flywheel diode 600.
As mentioned above, technologies for reducing the conductivity loss and recovery loss of a flywheel diode are reported in Patent Literature 1 and Patent Literature 2. Although Patent Literature 1 discloses a fabric in which a MOS gate is fabricated at an anode side (Refer to FIG. 1 to FIG. 5 of Patent Literature 1) and a fabric in which a MOS gate is fabricated at a cathode side (Refer to FIG. 6 and FIG. 7 of Patent Literature 1), the present invention relates to a fabric in which a MOS gate is fabricated at a cathode side. Patent Literature 1 states that a trade-off between a forward voltage and a recovery loss can be improved because electron injection from a cathode can be controlled using a buried insulating gate.
However, the inventors of this application and others found that there was the following problem in the abovementioned Patent Literature 1 and Patent Literature 2. For example, in an invention disclosed in Patent Literature 1 as an embodiment (Refer to FIG. 6 and FIG. 7 of Patent Literature 1), a forward voltage is reduced by applying a positive voltage to a gate to form an electron storage layer during the time of conduction. On the other hand, at the time of recovery, a recovery loss is reduced by setting the gate voltage zero for suppressing electron injection from a cathode.
According to an experiment made by the inventor of this application and others, it has been found that, if an anode current is small (for example, one tenth of the rated current), the anode current and an anode voltage vibrate at the time of recovery. According to the analysis of the cause of the vibration, it has been found that, because the amount of the electron injection from the cathode is reduced if the gate voltage is set zero, electrons remaining at the cathode side are abruptly reduced during the period of the tail current of the recovery, which leads to the vibrations of the voltage and current. Here, a mechanism in which the occurrence of a vibration owing to the reduction of the amount of electrons at the cathode side is described in detail in Nonpatent Literature 1 and Nonpatent Literature 2.
In order to solve the above problem, it is set as an object of the present invention to suppress the vibration of the current and the vibration of the voltage of a diode (equivalent to noises) without increasing the losses of the diode.
In order to solve the above problem, a semiconductor element drive apparatus according to the present invention is fabricated, for example, as a semiconductor element drive apparatus for driving a semiconductor element that includes: a first conductivity type first semiconductor layer (n− type drift layer); a second conductivity type second semiconductor layer (p type anode layer) that is adjacent to the first semiconductor layer and is exposed on one main surface (anode side); a first conductivity type third semiconductor layer (n type cathode layer) adjacent to the first semiconductor layer, the third semiconductor layer being exposed on the other main surface (cathode side) and having an impurity concentration higher than that of the first semiconductor layer (n− type drift layer); and an insulating gate on the other main surface (cathode side). In addition, the semiconductor element drive apparatus is characterized in that it switches the insulating gate at a positive voltage to at a negative voltage just before recovery when an anode current is large, and holds the insulating gate at the positive voltage when the anode current is small.
Furthermore, a power conversion apparatus according to the present invention is, for example, a power conversion apparatus that includes: a pair of DC terminals; AC terminals the number of which is the same as that of the phases of an AC current; compositions each of which includes two parallel circuits that are serial-connected between the pair of DC terminals, each of the two parallel circuits including a switching element and a reversely-connected diode; and power conversion units the number of which is the same as the number of phases of an AC current in which the interconnection points of the parallel circuits are connected to different AC terminals respectively. Apparatuses for driving the diodes are the abovementioned semiconductor element drive apparatuses.
According to the present invention, because a diode with a low loss and a low noise can be provided, the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus can be realized.
In the present invention, using a MOS-controlled diode in which an insulating gate is fabricated at a cathode side, the drive sequence of the insulating gate voltage is switched in accordance with the magnitude of an anode current.
Hereinafter, some examples including concrete compositions and drive methods according to the present invention will be explained in detail with reference to the accompanying drawings as several embodiments.
Hereinafter, a first embodiment of the present invention (a typical cross-section structure of the present invention and a drive method) will be explained.
The behavior of this embodiment will be briefly explained. When the semiconductor element is in a conductive state, an n type storage layer is formed at the interface between the gate electrode 8 and the n type cathode layer 6 by applying a higher voltage to the gate electrode 8 than to the cathode electrode 11, and it is suppressed that holes injected from the p type anode layer 3 is discharged into the cathode electrode 11, with the result that the forward voltage (Vf) is lowered (it means that the conductivity loss is reduced).
On the other hand, when the semiconductor element is in a recovering state, a p type inversion layer is formed at the interface between the gate electrode 8 and the n type cathode layer 6 by applying a lower voltage to the gate electrode 8 than to the cathode electrode 11, and holes injected from the p type anode layer 3 is acceleratedly discharged into the cathode electrode 11, with the result that the recovery loss is reduced.
Next, the details of the behavior of this embodiment will be explained.
In the above description, although a term “p type inversion layer” is used, it is not indispensable that the absolute value of the negative gate voltage is larger than the “threshold (absolute value)” of the n type cathode layer 6, and even if the absolute value of the negative gate voltage is smaller than the “threshold (absolute value)”, because the potential of the relevant channel relative to the holes is lowered, the holes flow into the cathode electrode 11 via the channel route whose potential is lowered, therefore the discharge of the holes from the cathode is accelerated.
In other words, in this embodiment, it becomes possible to reduce the conductivity loss and the switching loss respectively by switching between a diode whose forward voltage (Vf) is small (that is, a diode with its recovery loss large) and a diode whose forward voltage (Vf) is large (that is, a diode with its recovery loss small) in accordance with the time axis using the gate electrode 8.
Next, advantageous effects brought about by the present invention will be explained.
As mentioned above, in examples of public knowledges (Patent Literature 1 and Patent Literature 2), the trade-off between the forward voltage (Vf) and the recovery loss is improved, and a large amount of loss reduction can be realized. However, the inventors of this application and others found that, when they examined the recovery characteristic of each of the examples of public knowledges under the condition that an anode current was small, there was a problem in that the voltage and the current vibrated. The vibrations of the voltage and the current became more remarkable at a room temperature than at a high temperature. In each of the examples of the public knowledges, because a hole density at a cathode side is reduced just before recovery in order to reduce the recovery loss, a depletion layer at the cathode side has a tendency to increase in length. Therefore, the depletion layer, which increases in length during the period of a tail current, discharges charges remaining at the cathode side, which brings about the vibrations of the voltage and the current. The details of a mechanism, in which, if the depletion layer at the cathode side has a tendency to increase in length, the vibrations of the voltage and the current occur, are described in detail in the abovementioned Nonpatent Literature 1.
In this embodiment, in order to solve this problem, the drive sequence for the gate voltage of a MOS-controlled diode is switched just before recovery in accordance with the magnitude of the anode current of the diode.
In the present invention, although the recovery loss in the case of the anode current being small increases in comparison with the low charge-injection mode because the recovery operation is performed in the high charge-injection mode, the increase of the recovery loss in the case of the anode current being small can be neglected because it is smaller than the recovery loss in the case of the anode current being large. In other words, the merit (the vibration suppression) according to the present invention gains an advantage over the demerit (increase of the loss).
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Although in this embodiment, the description have been made about a “longitudinal element”, in which the cathode electrode is fabricated on the rear surface of the substrate, so far, the same advantageous effects can be also obtained in the case of a “lateral element” in which the cathode electrode is installed on the front surface of the substrate together with an anode electrode.
Hereinafter, a second embodiment of the present invention (the cross-section structure of a semiconductor element having no p type layer at the cathode side) will be explained.
Also in this embodiment, the vibrations of an anode voltage and an anode current can be suppressed by controlling the gate voltage of a MOS-controlled diode in accordance with the anode current in a similar way as shown in
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Hereinafter, a third embodiment of the present invention (the cross-section structure of a semiconductor element having no p type layer at a cathode side and a gate electrode stretching to a cathode electrode side) will be explained.
Also in this embodiment, the vibrations of an anode voltage and an anode current can be suppressed by controlling the gate voltage of a MOS-controlled diode in accordance with the anode current in a similar way as shown in
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Hereinafter, a fourth embodiment of the present invention (the cross-section structure of a planar gate type semiconductor) will be explained.
Also in this embodiment, the vibrations of an anode voltage and an anode current can be suppressed by controlling the gate voltage of a MOS-controlled diode in accordance with the anode current in a similar way as shown in
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Hereinafter, a fifth embodiment of the present invention (the cross-section structure of a planar gate type semiconductor element having no p type layer at a cathode side) will be explained.
Also in this embodiment, the vibrations of an anode voltage and an anode current can be suppressed by controlling the gate voltage of a MOS-controlled diode in accordance with the anode current in a similar way as shown in
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Hereinafter, a sixth embodiment of the present invention (the cross-section structure of an IGBT semiconductor element) will be explained.
The suppression of the vibrations of a current and a voltage regarding a diode in the case of a small current recovery regarding a diode has been discussed so far. The concept that the vibrations are suppressed by controlling a charge density in an n− type drift layer 1 using a MOS gate can be applied not only to a diode but also to an IGBT. In order to suppress the vibrations of the collector voltage and collector current of an IGBT, it is necessary to fabricate a MOS gate at a collector side (rear surface) in a direction to which a depletion layer increases in length. As related technical literatures disclosing a structure in which a MOS gate is fabricated at the collector side of an IGBT, the abovementioned Patent Literature 3, Patent Literature 4, and Patent Literature 5 can be cited. However, in these literatures, attention is focused on the reduction of a switching loss, but there is no description about the reduction of a vibration. In other words, in these literatures, the MOS gate is controlled while attention is focused only on the reduction of a turnoff loss.
The behavior of this embodiment will be briefly explained. During the time of conduction (when a positive voltage is applied to the gate electrode 43 on the front surface), a p type inversion layer is formed at the interface between the gate electrode 8 and the n type collector layer 6 by applying a negative voltage to the gate electrode 8 with respect the collector electrode 41, and holes from the p+ type cathode layer 13 are acceleratedly injected, with the result that an on-voltage (Vce) is lowered (it means that a conductivity loss is reduced).
On the other hand, an n type storage layer is formed at the interface between the gate electrode 8 and the n type cathode layer 6 by applying a positive voltage to the gate electrode 8 with respect the collector electrode 41 just before the turnoff of the IGBT (that is, just before switching the voltage of the gate electrode 43 from a positive voltage to a zero volt or to a negative voltage), and the injection of holes from a p+ type cathode layer 13 is suppressed, with the result that a turnoff loss is reduced.
Next, the details of the behavior of this embodiment will be explained.
When a positive voltage (Vg=+15 V in the drawing) is applied to the gate electrode, the hole density at the collector side becomes lower than when 0 V voltage (Vg=0 V in the drawing) is applied. This is because the n type inversion layer is formed at the interface between the gate electrode 8 and the n type collector layer 6, and the injection of the holes from the p+ type cathode layer 13 is suppressed.
In the above description, although a term “p type inversion layer” is used, it is not indispensable that the absolute value of the negative gate voltage is larger than the “threshold (absolute value)” of the n type cathode layer 6, and even if the absolute value of the negative gate voltage is smaller than the “threshold (absolute value)”, because the potential of the relevant channel relative to holes is lowered, the holes are injected into the n− type drift layer 1 from the p+ type cathode layer 13 via the channel route whose potential is lowered.
In other words, in this embodiment, it becomes possible to reduce the conductivity loss and the turnoff loss respectively by switching between an IGBT whose on-voltage is small (that is, the IGBT with its turnoff loss large) and an IGBT whose on-voltage is large (that is, the IGBT with its turnoff loss small) in accordance with the time axis using the gate electrode 8.
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Hereinafter, a seventh embodiment of the present invention (the cross-section structure of a rear surface planar gate type IGBT semiconductor element) will be explained.
Also in this embodiment, the vibrations of a collector voltage and a collector current can be suppressed by controlling the gate voltage at the collector side (rear surface) in accordance with the collector current in a similar way as shown in
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced, therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Next, an eighth embodiment of the present invention (diode drive circuit) will be explained.
This embodiment is an embodiment of a circuit for driving a semiconductor element (MOS-controlled diode) used in any of the above-described first to fifth embodiments.
This embodiment includes: a control circuit 20; IGBT drive circuits 21; drive circuits 22 for driving semiconductor apparatuses according to the first to fifth embodiments; an upper arm IGBT 23; a lower arm IGBT 24; a semiconductor apparatus 25 that is described in any of the above-described first to fifth embodiments and applied to the upper arm; a semiconductor apparatus 26 that is described in any of the above-described first to fifth embodiments and applied to the lower arm; and a current detector 30. Circuit signs used for the semiconductor apparatuses 25 and 26 respectively represent the resistor values of diodes each of which is controlled by the relevant gate electrode, and these circuit signs are devised by the inventors and others for the purpose of convenience, and they are not common signs.
In the present invention, it has been required so far for the gate voltage to be changed just before recovery. However, because the recovery is a phenomenon brought about along with the turnon of the relevant IGBT, the diode itself cannot know when it starts to recover. In other words, if attention is focused only on the diode, it is difficult to change the gate voltage of the diode just before the recovery of the diode.
Therefore, it was considered whether a positive voltage could be applied to the gate electrode just before the recovery of the diode by sensing the timing of the recovery of the diode from the behavior of the inverter. The recovery of the diode occurs when the IGBT of the counterpart arm (the counterpart arm is the upper arm for the lower arm and the lower arm for the upper arm) turns on. Therefore, if the gate of the IGBT and a diode of the counterpart arm according to the first embodiment are controlled using the same control circuit 20, it becomes possible to change the gate voltage of the diode of the counterpart arm from the control circuit just before the IGBT turns on (that is, just before the diode recovers).
Although the current detector 30 is a detector for detecting a current flowing through a diode, it is also possible to indirectly detect the current flowing through the diode by detecting the relevant IGBT current. Furthermore, it is also possible to estimate the diode current by detecting the motor current. Which of the gate drive sequence in the case of the rated current and the gate drive sequence in the case of a small current should be selected is determined in accordance with the collector current detected by the current detector 30 by the control circuit 20.
As described above, according to this embodiment, the losses and the vibrations (equivalent to noises) can be reduced by detecting a diode current, and therefore the streamlining, downsizing, and cost reduction of a semiconductor apparatus and a power conversion apparatus using the same can be realized.
Hereinafter, a ninth embodiment of the present invention (a power conversion apparatus to which diodes according to the present invention are applied) will be explained.
The feature of this embodiment is the fact that diodes explained in the first to the fifth embodiments are applied to flywheel diodes 600. By applying diodes explained in the first to the fifth embodiments to diodes used in the inverter apparatus shown in
Hereinafter, a tenth embodiment of the present invention (a power conversion apparatus to which IGBTs according to the present invention are applied) will be explained.
The feature of this embodiment is the fact that IGBTs explained in the sixth and the seventh embodiments are applied to the IGBTs 700. By applying the IGBTs explained in the sixth and the seventh embodiments to the IGBTs used in the inverter apparatus shown in
Here, the configuration of the inverter apparatus shown in
In addition, in the above embodiments, the descriptions have been made about inverters that convert a DC current to an AC current, but the present invention is not limited to inverters, and it will be obvious that converters that convert an AC current to a DC current can obtain similar advantageous effects.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/052196 | 1/31/2014 | WO | 00 |
