JP6973336B2 - Power element diagnostic device - Google Patents

Description

The present invention relates to a diagnostic device for a gate threshold voltage of a power element composed of a SiC MOSFET provided in a power conversion circuit.

FIG. 12 is a configuration diagram showing a power conversion device in Patent Document 1. Patent Document 1 discloses a method of suppressing a short-circuit accident of a DC power supply. Specifically, when the self-extinguishing semiconductor element (GTO) starts executing turn-off, the control means measures the time required for the voltage between the gate electrode and the cathode electrode of the GTO to exceed the threshold value, and from that time. Estimate the breaking current of the GTO.

FIG. 13 is a configuration diagram showing a power conversion device in Patent Document 2. Patent Document 2 discloses a power conversion device including an arm configured by connecting one or a plurality of unit converters in series. If the DC capacitor voltage fluctuates due to system disturbance or the like, there is a risk that communication abnormalities between the control device and the unit converter, such as gate control failure, will occur. In Patent Document 2, by monitoring the threshold voltage (DC capacitor voltage), protection of each unit converter is realized even when the above-mentioned communication abnormality occurs.

Patent No. 3636615 WO2016 / 203516A1

Aivars J. Lelis, Ron Green, Daniel B. Habersat, Mooro El, “Basic Mechanisms of Threshold-Voltage Instability and Implications for Reliability Testing of SiC MOSFETs” IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL62, NO. 2, pp316-323, FEBRUARY2015 .. Akio Nakagawa, Yusuke Kawaguchi, "Technological Trends in Power Devices for Power Supply," IEJJournal, VOL125, No. 12, pp758-761,2005

However, although Patent Document 1 discloses a method for suppressing a short circuit accident such as a multi-level power conversion device, it does not detect an increase in the gate threshold voltage of the power element.

Further, Patent Document 2 discloses a protection method for each unit converter such as a multi-level power converter, but the threshold voltage is a DC capacitor voltage. Therefore, an increase in the gate threshold voltage of the power element is not detected.

Further, Patent Documents 1 and 2 require a separate estimation circuit, sensor, etc. other than the power conversion circuit to realize the device, and are not suitable for miniaturization.

From the above, it is a problem to diagnose the gate threshold voltage of the power element in the power element diagnostic device without adding a new measuring instrument or a measuring circuit.

The present invention has been devised in view of the above-mentioned conventional problems, and one aspect thereof is an on-time acquisition unit for acquiring an integrated value of on-time of a power element composed of a SiC MOSFET provided in a power conversion circuit. An off-time acquisition unit that acquires the integrated value of the off-time of the power element, a threshold voltage fluctuation table that stores the fluctuation value of the gate threshold voltage corresponding to the integrated value of the on-time and the integrated value of the off-time, and the on An abnormality is found in the power element by comparing the fluctuation value and the fluctuation threshold of the gate threshold voltage corresponding to the integrated value of the on-time acquired by the time acquisition unit and the integrated value of the off-time acquired by the off-time acquisition unit. It is characterized by including an abnormality diagnosis unit for diagnosing whether or not it has occurred, and a result notification unit for notifying the diagnosis result of the abnormality diagnosis unit.

Further, as one aspect thereof, the power conversion circuit is a multi-level power conversion circuit having three or more levels, and the abnormality diagnosis unit has a difference in the integrated value of the on-time between the power elements and each power element. When the difference between the integrated values of the off-time is larger than the time difference threshold value, it is determined that an abnormality has occurred in the power element.

Further, as one aspect thereof, it is characterized in that the fluctuation value of the gate threshold voltage is multiplied by a coefficient k of 0 <k <1.

According to the present invention, in the power element diagnostic apparatus, it is possible to diagnose the gate threshold voltage of the power element without adding a new measuring instrument or measuring circuit.

The graph which shows the gate threshold voltage fluctuation when a positive gate voltage is applied to a SiC MOSFET. The graph which shows the gate threshold voltage fluctuation when a negative gate voltage is applied to a SiC MOSFET. The control block diagram of Embodiment 1. The flowchart which shows the operation of Embodiment 1. The flowchart (on-time) which shows the operation of the abnormality diagnosis part in Embodiment 1. FIG. The flowchart (off time) which shows the operation of the abnormality diagnosis part in Embodiment 1. FIG. The figure which shows the circuit example (1 phase part) of a 3 level inverter. Graph showing voltage command value and carrier wave. The figure which shows the switching pattern example (one phase part) of a three-level inverter. The flowchart (on-time) which shows the operation of the abnormality diagnosis part in Embodiment 2. The flowchart (off time) which shows the operation of the abnormality diagnosis part in Embodiment 2. The schematic diagram which shows the power conversion apparatus in Patent Document 1. FIG. The schematic diagram which shows the power conversion apparatus in Patent Document 2.

Hereinafter, embodiments 1 to 3 of the power element diagnostic apparatus according to the present invention will be described in detail with reference to FIGS. 1 to 11.

[Embodiment 1]
The first embodiment is supposed to be applied to a power conversion circuit having two or more levels.

The SiC MOSFET currently on the market has a problem that the gate threshold voltage fluctuates when a voltage is applied between the gate and the source. As shown in FIGS. 1 and 2, in general, the fluctuation amount of the gate threshold voltage fluctuation ΔVth depends on the applied voltage value and the applied time. It is also known that when a positive gate-source voltage is applied, the gate threshold voltage fluctuates in an increasing direction, and when a negative gate-source voltage is applied, the gate threshold voltage fluctuates in a decreasing direction (non-patented). See Document 1).

SiC MOSFETs are considered to be used for the purpose of increasing the power density of equipment. In that case, adding a new measuring circuit or measuring device leads to an increase in the size of the device.

FIG. 3 shows the power element diagnostic device according to the first embodiment. As shown in FIG. 3, the gate signal output from the gate drive control unit 1 is input to the power element (SiC MOSFET) in the power conversion circuit 2. The power conversion circuit 2 converts DC power into AC power by switching the power element, and outputs the DC power to the load 3.

The power element diagnostic device 4 includes an off time acquisition unit 5, an on time acquisition unit 6, a threshold voltage fluctuation table 7, an abnormality diagnosis unit 8, and a result notification unit 9.

The off time acquisition unit 5 acquires and integrates the off time of the power element. The on-time acquisition unit 6 acquires and integrates the on-time of the power element. The threshold voltage fluctuation table 7 stores the fluctuation value α of the gate threshold voltage for each integrated value of the on-time and each integrated value of the off-time acquired in advance. The abnormality diagnosis unit 8 uses the integrated value of the on time acquired by the on time acquisition unit 6, the integrated value of the off time acquired by the off time acquisition unit 5, and the information obtained from the threshold voltage fluctuation table 7 to obtain the power element. Diagnose. The result notification unit 9 notifies the diagnosis result.

FIG. 4 shows a flowchart showing the operation of the power element diagnostic device 4 in the first embodiment. In S1, the power conversion circuit 2 is driven. Next, in S2, at the same time as driving the power conversion circuit 2 of S1, the on-time acquisition unit 6 and the off-time acquisition unit 5 acquire the on-time and the off-time at an arbitrary cycle and integrate them. In S3, the threshold voltage fluctuation table 7 is referred to based on the integrated value of the on-time acquired by the on-time acquisition unit 6 and the integrated value of the off-time acquired by the off-time acquisition unit 5.

In S4, the abnormality diagnosis unit 8 has a fluctuation value α of the gate threshold voltage Vth corresponding to the integrated value of the on time and a fluctuation value of the gate threshold voltage Vth corresponding to the integrated value of the off time from the threshold voltage fluctuation table 7 prepared in advance. Estimate α and determine if an abnormality has occurred in the power element. If no abnormality has occurred in the power element, the process proceeds to S5, the power conversion circuit 2 continues to be driven, and the process returns to S1. If an abnormality has occurred in the power element, the process proceeds to S6 and the result is displayed by the result notification unit 9, so that the user of the circuit confirms the display of the result notification unit 9 and detects the abnormality of the power element. You can check.

The on-time can be obtained, for example, by measuring the on-time from the timing when the gate signal is switched from off to on in the gate drive control unit 1 to the timing when the gate signal is switched from on to off.

The off time can be obtained, for example, by measuring the off time from the timing at which the gate signal is switched from on to off to the timing at which the gate signal is switched from off to on in the gate drive control unit 1.

Further, the threshold voltage fluctuation table to be acquired in advance is created by, for example, the following method. First, the DC positive gate-source voltage of the value used for the power element is continuously applied for a certain period of time, and a plot of the fluctuation of the gate threshold voltage for each time is prepared. From the extrapolation of these plots, it is possible to obtain a threshold voltage fluctuation table (positive threshold voltage fluctuation table) when the DC positive gate-source voltage is continuously applied until the design lifetime of the power conversion circuit.

Similarly, first, the DC negative gate-source voltage of the value used for the power element is continuously applied for a certain period of time, and a plot of the fluctuation of the gate threshold voltage for each time is prepared. From the extrapolation of these plots, it is possible to obtain a threshold voltage fluctuation table (negative threshold voltage fluctuation table) when the DC negative gate-source voltage is continuously applied until the design lifetime of the power conversion circuit. In this way, the threshold voltage fluctuation table up to the design life time of the power conversion circuit can be created.

Next, the abnormality diagnosis unit 8 (S4) will be described with reference to FIG. In S11, the acquired integrated value of the on-time and the integrated value of the off-time are input to the abnormality diagnosis unit 8. In S12, the fluctuation value α of the positive gate threshold voltage corresponding to the integrated value of the on-time acquired by the on-time acquisition unit 6 is acquired from the positive threshold voltage fluctuation table.

In S13, the abnormality diagnosis unit 8 compares the fluctuation value α of the positive gate threshold voltage with the fluctuation threshold βon on the positive side for notifying the abnormality, and the fluctuation value α of the positive gate threshold voltage is smaller than the fluctuation threshold βon on the positive side. In that case, the process proceeds to S19 and the driving of the power conversion circuit is continued. When the fluctuation value α of the positive gate threshold voltage is equal to or greater than the fluctuation threshold βon on the positive side, it is determined that an abnormality has occurred in the power element in S14, and the result notification unit 9 is notified of the abnormality in the power element in S15. When an abnormality is notified, the user of the power conversion circuit inspects and maintains the device.

Since the on-resistance of the power element depends on the gate threshold voltage, for example, when the gate threshold voltage of one power element fluctuates in the increasing direction, the on-resistance may increase. Therefore, the loss increases, and the power element may generate abnormal heat. Therefore, the fluctuation threshold value βon on the positive side is set based on the value at which the power element generates abnormal heat. Further, a value set by the manufacturer may be used for the fluctuation threshold value βon on the positive side.

Next, a method of comparing the fluctuation value α of the negative gate threshold voltage and the fluctuation threshold βoff on the negative side will be described with reference to FIG.

As for the variation of the gate threshold voltage fluctuation, for example, when the gate threshold voltage of one power element fluctuates in the decreasing direction, the element tends to erroneously ignite and may be short-circuited (Non-Patent Document 2).

FIG. 6 operates with the same configuration as that of FIG. 5, and differs only in the algorithms of the estimation of the fluctuation value α of the negative gate threshold voltage α (S23) and the operation of the abnormality diagnosis unit 8 (S23).

In S22, the fluctuation value α of the negative gate threshold voltage corresponding to the integrated value of the off time acquired by the off time acquisition unit 5 is acquired from the negative threshold voltage fluctuation table.

In S23, the abnormality diagnosis unit 8 compares the fluctuation value α of the negative gate threshold voltage with the fluctuation threshold βoff on the negative side, and when the fluctuation value α of the negative gate threshold voltage is equal to or greater than the fluctuation threshold βoff on the negative side, the power element It is judged that an abnormality has occurred in.

The fluctuation threshold βoff on the negative side is set to a value that does not cause an erroneous roll call or short circuit of the power element according to each circuit configuration.

According to the configuration of the first embodiment, a device for diagnosing the gate threshold voltage of a power element and a power conversion circuit provided with the diagnostic device are provided without adding a new measuring instrument or measuring circuit to the power conversion circuit. It becomes possible.

Further, according to the first embodiment, the on-resistance of the power element is increased, it is possible to suppress abnormal heat generation of the power element, and it is possible to suppress erroneous call and short circuit of the power element.

[Embodiment 2]
The second embodiment is supposed to be applied to a three-level power conversion circuit. In a multi-level power conversion circuit having three or more levels, the switching pattern of each power element differs depending on the operating state of the load (for example, a motor), and the on time and off time differ for each power element.

FIG. 7 is a schematic diagram showing a circuit example (one phase component) of a three-level inverter. As shown in FIG. 7, the first and second DC power supplies DC1 and DC2 are connected in series. The first and fourth power elements Q1 and Q4 are connected in series between the positive electrode of the first DC power supply DC1 and the negative electrode of the second DC power supply DC2. The second and third power elements Q2 and Q3 are connected in reverse series between the connection points of the first and second DC power supplies DC1 and DC2 and the connection points of the first and fourth power elements Q1 and Q4. The connection points of the first and fourth power elements Q1 and Q4 are AC terminals AC.

As shown in FIG. 8, the voltage command value is compared with the carrier waves of the first and second power elements Q1 and Q2 and the carrier waves of the third and fourth power elements Q3 and Q4. The on / off of the fourth power elements Q1 to Q4 is determined.

As described above, in the multi-level power conversion circuit having three or more levels, the on-time and the off-time of each power element differ depending on the operating conditions, so that the fluctuation of the gate threshold voltage may vary greatly.

Therefore, in the second embodiment, not only the fluctuation value α of the positive gate threshold voltage and the fluctuation threshold βon on the positive side, and the fluctuation value α of the negative gate threshold voltage and the fluctuation threshold βoff on the negative side are compared, but also each power. Calculate the difference between the integrated values of the on-time and the difference of the integrated value of the off-time between the elements. If the difference between the integrated values of the on-time and the integrated value of the off-time of each power element is large, the control may be unstable, the output waveform may be distorted, or the difference may exceed the dead time, resulting in a short circuit. Therefore, in the second embodiment, if the difference between the integrated values of the on-time and the integrated value of the off-time of each power element is equal to or greater than the time difference threshold value, it is determined that an abnormality may have occurred.

The processing in the second embodiment is shown in FIGS. 10 and 11. FIG. 10 shows the addition of S16 to S18 to the first embodiment, and since S11 to S15 and S19 are the same as those of the first embodiment, the description thereof will be omitted.

When the fluctuation value α of the positive gate threshold voltage is not equal to or greater than the fluctuation threshold βon on the positive side, in S16, the difference in the integrated value of the on-time between the power elements (hereinafter referred to as the on-time difference) γon is calculated. In S17, the positive time difference threshold δon and the on-time difference γon are compared. When the on-time difference γon is equal to or greater than the positive time difference threshold value δon, it is determined in S14 that an abnormality has occurred in the power element, and the result is displayed in the result notification unit in S15. You can check the display of the power element to confirm the abnormality. When the on-time difference γon is not equal to or more than the positive time difference threshold value δon, it is determined in S18 that no abnormality has occurred in the power element, and in S19, the driving in the power conversion circuit 2 is continued.

Further, as shown in FIG. 11, when the fluctuation value α of the negative gate threshold voltage is not equal to or more than the fluctuation threshold βoff on the negative side, the difference in the integrated value of the off time between the power elements in S26 (hereinafter referred to as the off time difference). (Referred to as) γoff is calculated, and in S27, the negative time difference threshold δoff and the off time difference γoff are compared. When the off time difference γoff is equal to or greater than the negative time difference threshold value δoff, it is determined in S14 that an abnormality has occurred in the power element, and in S15, the result is displayed by the result notification unit 9, so that the power conversion circuit 2 is used. The person can confirm the abnormality of the power element by confirming the display of the result notification unit 9. When the off time difference γoff is not equal to or more than the negative time difference threshold value δoff, it is determined in S18 that no abnormality has occurred in the power element, and the power conversion circuit is continued to be driven in S19.

The time difference threshold δon on the positive side and the time difference threshold δoff on the negative side cause problems such as unstable control due to fluctuations in the gate threshold voltage, distortion of the output waveform, and short circuit, depending on the circuit configuration and the like. It shall be decided in advance.

As shown above, according to the second embodiment, in addition to the operation and effect of the first embodiment, the control becomes unstable due to the difference in the integrated value of the on time and the difference in the integrated value of the off time of each power element. It is possible to suppress problems such as distortion of the output waveform and short circuit.

[Embodiment 3]
The fluctuation ΔVth of the gate threshold voltage shown in FIGS. 1 and 2 is a chart when a positive voltage is continuously applied and a negative voltage is continuously applied. However, in actual operation, the positive voltage and the negative voltage are not continuously applied, and the positive voltage is applied or the negative voltage is applied.

Therefore, the actual fluctuation of the gate threshold voltage is smaller than that shown in FIGS. 1 and 2. That is, FIGS. 1 and 2 assume the worst case and are different from the actual ones. Therefore, in the third embodiment, the coefficient k is multiplied by the fluctuation value α of the positive gate threshold voltage and the fluctuation value α of the negative gate threshold voltage. Here, the coefficient k is 0 <k <1.

This makes it possible to make the fluctuation value α of the gate threshold voltage closer to the actual value.

Although the above description has been made in detail only for the specific examples described in the present invention, it is obvious to those skilled in the art that various modifications and modifications are possible within the scope of the technical idea of the present invention. It goes without saying that such modifications and modifications fall within the scope of the claims.

1 ... Gate drive control unit 2 ... Power conversion circuit 3 ... Load 4 ... Power element diagnostic device 5 ... Off time acquisition unit 6 ... On time acquisition unit 7 ... Threshold voltage fluctuation table 8 ... Abnormality diagnosis unit 9 ... Result notification unit

Claims (3)

An on-time acquisition unit that acquires the integrated value of the on-time of a power element consisting of a SiC MOSFET provided in the power conversion circuit, and an on-time acquisition unit.
An off-time acquisition unit that acquires an integrated value of the off-time of the power element,
A threshold voltage fluctuation table that stores the fluctuation values of the gate threshold voltage corresponding to the integrated value of the on time and the integrated value of the off time, and
The power element is subjected to comparison between the fluctuation value of the gate threshold voltage corresponding to the integrated value of the on-time acquired by the on-time acquisition unit and the integrated value of the off-time acquired by the off-time acquisition unit. An abnormality diagnosis unit that diagnoses whether or not an abnormality has occurred, and
A result notification unit for notifying the diagnosis result of the abnormality diagnosis unit,
A power element diagnostic device characterized by being equipped with. The power conversion circuit is a multi-level power conversion circuit having three or more levels.
The abnormality diagnosis unit
When the difference in the integrated value of the on-time between the power elements and the difference in the integrated value of the off-time between the power elements are larger than the time difference threshold, it is determined that an abnormality has occurred in the power element. The power element diagnostic apparatus according to claim 1. The power element diagnostic apparatus according to claim 1 or 2, wherein the fluctuation value of the gate threshold voltage is multiplied by a coefficient k of 0 <k <1.

Images