Drive device for semiconductor element, semiconductor device, and power conversion device

Abstract

The semiconductor device (D) has a power switch element (1) and a driving device (100) for driving the power switch element (1). The driving device (100) includes: a voltage source (3); a switch element (15); a capacitor (4) connected in parallel with the voltage source (3) via the switch element (15); switch elements (5, 6) provided between the capacitor (4) and the gate terminal of the power switch element (1); a first comparator (U1) that outputs a comparison result between the voltage of the capacitor (4) and a reference value (VQR); a second comparator (U2) that outputs a comparison result between the gate voltage of the power switch element (1) and a reference value (VR); and a short-circuit determiner (14) that determines a short circuit of the power switch element (1) using the output signal of the first comparator (U1) and the output signal of the second comparator (U2).

Description

Technical Field

[0001] The present invention relates to a driving device for a semiconductor element, a semiconductor device having the semiconductor element and the driving device, and a power conversion device. Background Art

[0002] As a power semiconductor element constituting a power converter, an IGBT (Insulated Gate Bipolar Transistor) made of Si (silicon) is often used. Recently, however, in order to further miniaturize and enhance the efficiency of the power converter, the application of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) made of SiC (silicon carbide) has become popular.

[0003] In a power converter, if the power semiconductor element is in a short-circuit state, a large current flows in a state where the DC link voltage of the power converter is applied to the power semiconductor element, and extremely large losses (heat) may be generated. Therefore, in order to ensure the reliability of the power converter, it is preferable to provide a circuit for detecting the short-circuit state of the power semiconductor element.

[0004] As a method for quickly detecting the short-circuit state of a power semiconductor element, among conventional driving devices for power semiconductor elements, there is a driving device having a device for detecting the gate charge supplied to the gate of the power semiconductor element and a device for detecting the gate voltage of the power semiconductor element (for example, Patent Document 1).

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-53749 Summary of the Invention

[0006] The driving device described in Japanese Unexamined Patent Application Publication No. 2015-53749 (Patent Document 1) needs a detection device for detecting the gate charge in order to detect the short-circuit state by utilizing the fact that the relationship between the gate charge and the gate voltage is different between short-circuit and normal times. This detection device detects the gate current by monitoring the output of a current sensor and the voltage across a gate resistor, and integrates the detected gate current to detect the gate charge. Therefore, an integrator is required, and there is a problem that the circuit scale becomes large.

[0007] The present invention has been made to solve the above problems, and an object thereof is to be able to perform short-circuit determination of a power semiconductor element by a simple circuit without using an integrator.

[0008] The driving device involved in the present invention is a driving device for a power semiconductor element having a gate terminal. Among them, the driving device of the semiconductor element has: a first voltage source; a switching element; a capacitor connected in parallel with the first voltage source via the switching element; a switching device provided between the capacitor and the gate terminal of the semiconductor element and configured to be able to switch the voltage applied to the gate terminal; a first comparison device that outputs a signal representing the comparison result between the voltage of the capacitor and a first reference value; a second comparison device that outputs a signal representing the comparison result between the voltage of the gate terminal or the voltage differential value and a second reference value; and

[0009] a determiner that determines whether the semiconductor element is in a short-circuit state by using the output signal of the first comparison device and the output signal of the second comparison device.

[0010] In the above driving device, the short-circuit determination of the semiconductor element is not performed based on the result obtained by directly detecting the gate charge amount, but by monitoring the voltage of the capacitor and the gate voltage of the switching element or its differential value. Therefore, the short-circuit determination of the semiconductor element can be performed by a simple circuit without using an integrator for detecting the gate charge amount.

[0011] Effects of the Invention

[0012] According to the present invention, the short-circuit determination of the power semiconductor element can be performed by a simple circuit without using an integrator. Description of the Drawings

[0013] Figure 1 It is a diagram (part 1) showing an example of a semiconductor device.

[0014] Figure 2 It is a diagram showing the relationship between the gate charge amount and the gate voltage and the relationship between the capacitor voltage and the gate voltage.

[0015] Figure 3 It is a flowchart showing an example of the processing flow of the short-circuit determiner.

[0016] Figure 4 It is a diagram (part 2) showing an example of a semiconductor device.

[0017] Figure 5 It is a diagram (part 3) showing an example of a semiconductor device.

[0018] Figure 6 It is a diagram showing an example of the relationship between the gate charge amount and the gate current.

[0019] Figure 7 It is a diagram (part 4) showing an example of a semiconductor device.

[0020] Figure 8 This is a diagram (Diagram 5) showing an example of a semiconductor device.

[0021] Figure 9 This is a diagram (Diagram 1) showing an example of the relationship between gate charge and gate voltage.

[0022] Figure 10 This is a diagram (Diagram 6) showing an example of a semiconductor device.

[0023] Figure 11 This is a diagram (Diagram 2) showing an example of the relationship between gate charge and gate voltage.

[0024] Figure 12 This is a block diagram showing the structure of a power conversion system. Detailed Implementation Modes

[0025] Hereinafter, while referring to the accompanying drawings, the implementation modes of the present invention will be described in detail. In addition, the same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

[0026] Implementation Mode 1

[0027] Figure 1 This is a diagram showing an example of a semiconductor device D having a drive device 100 according to the present Implementation Mode 1. The semiconductor device D has a switching element 1 as a power semiconductor element and a drive device 100 for driving the switching element 1.

[0028] In the present Implementation Mode 1, the case where the switching element 1 is a MOSFET will be described. Generally, a MOSFET is configured to be in an off state (cut-off state) where no drain current (current flowing between the source and the drain) is generated when the gate voltage (voltage between the gate and the source) is less than the threshold voltage, and in an on state (conductive state) where a drain current is generated when the gate voltage is greater than or equal to the threshold voltage.

[0029] Regarding the switching elements 5, 6, 15, and 50 described below, the case where the switching element is a MOSFET will be described in the same manner as the switching element 1. In addition, the switching element 1 and the switching elements 5, 6, 15, and 50 are not limited to MOSFETs, and may be, for example, voltage-driven semiconductor elements such as IGBTs. Further, the IGBT may be a reverse-conducting IGBT (RC-IGBT).

[0030] In addition, the switching elements 1, 5, 6, and 15 can be applied to devices made of any one of Si (silicon), SiC (silicon carbide), GaN (gallium nitride), and Ga2O3 (gallium oxide).

[0031] The driving device 100 includes an instruction unit 2, voltage sources 3, 7, 9, a capacitor 4, switching elements 5, 6, 15, a diode 8, a pair of output terminals 17, 18, a first comparator U1, a second comparator U2, a short-circuit determiner 14, and a gate resistor 16. The first comparator U1 has a comparison unit 10 and a voltage source 11. The second comparator U2 has a comparison unit 12 and a voltage source 13.

[0032] The output terminals 17, 18 are respectively connected to the gate and source of the switching element 1.

[0033] The voltage source 3 is connected to the capacitor 4 via the switching element 15. Specifically, the positive electrode of the voltage source 3 is connected to one end of the capacitor 4 via the switching element 15, and the negative electrode of the voltage source 3 is connected to the other end of the capacitor 4.

[0034] The voltage source 9 is connected in series with the voltage source 3. The positive electrode of the voltage source 9 is connected to the negative electrode of the voltage source 3 and the output terminal 18, and the negative electrode of the voltage source 9 is connected to the drain terminal of the switching element 6.

[0035] The capacitor 4 is connected in parallel with the voltage source 3 via the switching element 15.

[0036] The voltage source 7 is connected to one end of the capacitor 4 via the diode 8 to supply the driving voltage Von to one end of the capacitor 4. The voltage in the steady on-state of the switching element 1 is stabilized at the driving voltage Von by the voltage source 7 and the diode 8.

[0037] The switching element 5 is an N-type MOSFET. The source terminal of the switching element 5 is connected to the output terminal 17 of the driving device 100 via the gate resistor 16. The gate resistor 16 is a resistor for adjusting the on / off speed of the switching element 5. The drain terminal of the switching element 5 is connected to one end of the capacitor 4 and is also connected to the positive electrode of the voltage source 3 via the switching element 15.

[0038] The gate terminal of the switching element 5 is connected to the instruction unit 2 to receive the gate voltage from the instruction unit 2. If the gate voltage from the instruction unit 2 is applied to the gate terminal of the switching element 5, the switching element 5 becomes in the on state, and one end of the capacitor 4 is connected to the output terminal 17. Thus, the output voltage of the driving device 100 becomes the voltage of the capacitor 4 (the voltage between the terminals of the capacitor 4, hereinafter also simply referred to as "capacitor voltage").

[0039] The switching element 6 is an N-type MOSFET in the same way as the switching element 5. The drain terminal of the switching element 6 is connected to the output terminal 17 of the driving device 100 via the gate resistor 16. The source terminal of the switching element 6 is connected to the negative electrode of the voltage source 9.

[0040] The gate terminal of the switch element 6 is connected to the command unit 2, and receives the gate voltage from the command unit 2. When the gate voltage from the command unit 2 is applied to the gate terminal of the switch element 6, the switch element 6 becomes on, and the negative electrode of the voltage source 9 is connected to the output terminal 17. As a result, the output voltage becomes the negative bias potential Voff provided by the voltage source 9.

[0041] The switch elements 5 and 6 are controlled by the command unit 2 so as to act complementarily to each other. That is, when the switch element 5 is in the on state, the switch element 6 is in the off state, and when the switch element 5 is in the off state, the switch element 6 is in the on state. Thus, the drive voltage Von can be applied to the gate terminal of the switch element 1 when the switch element 1 is steadily on, and the negative bias potential Voff can be applied to the gate terminal of the switch element 1 when the switch element 1 is steadily off.

[0042] The command unit 2 controls the on and off of the switching elements 5, 6, and 15 by applying gate voltages to the switching elements 5, 6, and 15 at a predetermined timing based on a gate signal input from the outside. The command unit 2 is configured to be able to control the on and off of the switching element 5, the on and off of the switching element 6, and the on and off of the switching element 15 separately.

[0043] The switch element 1 switches between an on state and an off state based on a signal from the command unit 2 .

[0044] When the switch element 1 is turned off, the command unit 2 outputs an off command to the switch elements 5, 6, and 15 to turn on the switch element 15, turn off the switch element 5, and turn on the switch element 6. By turning on the switch element 15, the capacitor 4 is charged by the voltage source 3, and the capacitor voltage becomes the output voltage of the voltage source 3. Thus, the amount of charge required for turning on and off the switch element 1 is accumulated in the capacitor 4. In addition, by turning off the switch element 5 and turning on the switch element 6, the negative bias potential Voff from the voltage source 9 is applied to the gate terminal of the switch element 1.

[0045] When changing the switch element 1 from the off state to the on state, the command unit 2 first changes the switch element 15 from the on state to the off state to disconnect the capacitor 4 from the voltage source 3 .

[0046] Then, the instruction unit 2 switches the switching element 5 to the on state and the switching element 6 to the off state respectively. Thus, the gate terminal of the switching element 1 is connected to the capacitor 4 via the gate resistor 16. The charge stored in the capacitor 4 flows into the gate of the switching element 1. As the gate voltage of the switching element 1 rises, the voltage of the capacitor 4 drops. At this time, by setting the initial value of the capacitor voltage (the output voltage of the voltage source 3) to a voltage higher than the driving voltage Von (the output voltage of the voltage source 7), the switching element 1 can be switched on and off at a higher speed compared with the case of constant voltage driving with the driving voltage Von.

[0047] If the capacitor voltage drops from the initial value to the driving voltage Von, the diode 8 conducts, and the output voltage is constant at the driving voltage Von. At this time, the amount of charge flowing into the gate of the switching element 1 from the driving device 100 (hereinafter also referred to as "gate charge amount") is equal to the amount of charge released by the capacitor 4. Therefore, when the gate charge amount is denoted as "Qg", the capacitance of the capacitor 4 is denoted as "Cb", and the decrease amount of the capacitor voltage is denoted as "ΔV", the following relational expression (1) holds among them.

[0048] ΔV×Cb = Qg…(1)

[0049] In the above relational expression (1), the capacitance Cb of the capacitor 4 is a pre-determined value. Therefore, by detecting the capacitor voltage to obtain the decrease amount ΔV of the capacitor voltage, the gate charge amount Qg can be detected. Therefore, when detecting the gate charge amount Qg, an arithmetic circuit such as an integration circuit is not required, and the gate charge amount Qg can be directly detected based on the capacitor voltage. Therefore, the circuit scale can be reduced.

[0050] The first comparison device U1 detects the gate charge amount Qg based on the capacitor voltage by using the above relational expression (1). Specifically, as described above, the first comparison device U1 has a comparison unit 10 and a voltage source 11. The voltage source 11 outputs the voltage of the reference value VQR to the comparison unit 10.

[0051] The comparison unit 10 compares the capacitor voltage with the voltage of the reference value VQR output by the voltage source 11 to detect that the capacitor voltage has dropped to the reference value VQR, thereby detecting that the gate charge amount Qg has reached the reference value QR.

[0052] The comparison unit 10 outputs an output signal S1 representing the comparison result between the capacitor voltage and the reference value VQR to the short-circuit determination device 14. The comparison unit 10 sets the output signal S1 to the low potential state when the capacitor voltage is less than or equal to the reference value VQR, and sets the output signal S1 to the high potential state when the capacitor voltage is greater than the reference value VQR.

[0053] In addition, as described above, the second comparison device U2 includes a comparison unit 12 and a voltage source 13. The voltage source 13 outputs the voltage of the reference value VR to the comparison unit 12. The comparison unit 12 compares the gate voltage of the switching element 1 (the voltage applied from the driving device 100 to the gate terminal of the switching element 1) with the voltage of the reference value VR output by the voltage source 13, thereby detecting that the gate voltage of the switching element 1 has reached the reference value VR.

[0054] The comparison unit 12 outputs an output signal S2 representing the comparison result between the gate voltage of the switching element 1 and the reference value VR to the short-circuit determination unit 14. The comparison unit 12 sets the output signal S2 to a low potential state when the gate voltage of the switching element 1 is less than or equal to the reference value VR, and sets the output signal S2 to a high potential state when the gate voltage of the switching element 1 is greater than the reference value VR.

[0055] The short-circuit determination unit 14 detects the short-circuit state of the switching element 1 using the output signal S1 of the first comparison device U1 and the output signal S2 of the second comparison device U2.

[0056] [Short-circuit determination of switching element 1]

[0057] Figure 2 is a diagram showing the relationship (left side) between the gate charge amount and the gate voltage of the switching element 1 during the on-operation of the switching element 1 and the relationship (right side) between the capacitor voltage and the gate voltage of the switching element 1. In the left diagram showing the relationship between the gate charge amount and the gate voltage, the normal (non-short-circuit) relationship of the switching element 1 is represented by a dotted line L1, and the relationship when the switching element 1 has a bridge short circuit is represented by a solid line L2. In addition, in the right diagram showing the relationship between the capacitor voltage and the gate voltage, the normal relationship of the switching element 1 is represented by a dotted line L3, and the relationship when the switching element 1 has a bridge short circuit is represented by a solid line L4.

[0058] In addition, in Figure 2 the relationship in the case where the switching element 1 is a MOSFET made of SiC (silicon carbide) (hereinafter also referred to as "SiC-MOSFET") is illustrated.

[0059] In the normal state of the switching element 1, when the gate voltage rises, the gate charge amount increases and the capacitor voltage decreases. When the gate voltage rises to the voltage Vm, the rising rate of the gate voltage drops significantly. When the gate voltage reaches the voltage Vm, the gate charge amount is the charge amount Q0, and the capacitor voltage is the voltage VQ0 (VQ0 = Q0 / Cb). In addition, "Cb" is the capacitance of the capacitor 4 as described above.

[0060] Then, if the gate charge reaches a charge Q1 (Q1 > Q0), the capacitor voltage becomes a voltage VQ1 (VQ1 = Q1 / Cb). During the period when the gate charge reaches from the charge Q0 to the charge Q1, the rise of the gate voltage becomes very slow, and the gate voltage is maintained approximately at the voltage Vm. The period from when the gate charge reaches from the charge Q0 to the charge Q1 is called the "Miller period".

[0061] Then, if the gate charge exceeds the charge Q1, the gate voltage rises again to reach the gate drive power supply voltage Vd. Thereby, the switching element 1 becomes in an on state.

[0062] In the relationship between the gate charge and the gate voltage in the SiC-MOSFET such as the switching element 1, the presence of the feedback capacitance plays a great role. The feedback capacitance in the SiC-MOSFET is equivalent to the drain-gate capacitance and has a large voltage dependence.

[0063] During the normal conduction operation of the switching element 1, based on an instruction from the instruction unit 2, the gate voltage rises and the gate-source is charged. If the gate voltage exceeds the threshold voltage, a drain current (the current flowing between the source and the drain) starts to flow, and the drain-source voltage drops. The gate current supplied from the drive device 100 to the switching element 1 flows from the gate terminal of the switching element 1 to the drain terminal via the feedback capacitance. Thereby, a Miller period in which the rise of the gate voltage is very slow appears. Since the feedback capacitance has a large voltage dependence, if the drain-source voltage drops to the on voltage of the switching element 1, the value of the feedback capacitance becomes a value that is one to two orders of magnitude larger. As a result, after the end of the Miller period, the gate voltage slowly rises to the gate drive power supply voltage Vd.

[0064] However, when a short circuit occurs in the bridge arm of the switching element 1, such a Miller period does not appear, and the gate voltage of the switching element 1 immediately rises to the gate drive power supply voltage Vd.

[0065] The short-circuit determiner 14 according to the present embodiment determines the presence or absence of a short circuit in the bridge arm of the switching element 1 by using Figure 2 the relationship shown below. Hereinafter, a method for determining a short circuit in the bridge arm of the switching element 1 will be described.

[0066] In the present embodiment, in the relationship between the gate charge and the gate voltage shown on the left side of Figure 2 , the reference value QR of the gate charge and the reference value VR of the gate voltage are set such that the reference value QR of the gate charge and the reference value VR of the gate voltage are included in the region A1 surrounded by the normal dotted line L1, the solid line L2 at the time of bridge arm short circuit, and the gate drive power supply voltage Vd. When converting it to Figure 2In the case of the relationship between the capacitor voltage and the gate voltage shown on the right side, the reference value VQR of the capacitor voltage (the capacitor voltage when the gate charge is the reference value QR) and the reference value VR of the gate voltage are included in the region A2 surrounded by the dotted line L3 in the normal state, the solid line L4 when the arm is short-circuited, and the gate drive power supply voltage Vd.

[0067] When the switching element 1 is turned on and off, if the gate charge flowing out of the capacitor 4 reaches the reference value QR, the capacitor voltage drops to the reference value VQR, and the output signal S1 of the first comparison device U1 changes from the high-potential state to the low-potential state.

[0068] When the output signal S1 of the first comparison device U1 is in the high-potential state and the output signal S2 of the second comparison device U2 changes from the low-potential state to the high-potential state (that is, when the gate voltage reaches the reference value VQR when the capacitor voltage is greater than the reference value VQR), it is considered that the relationship between the capacitor voltage and the gate voltage is shown by the operating point P4 on the solid line L4 during short-circuit without the Miller period (if replaced by the relationship between the gate charge and the gate voltage, it is shown by the operating point P2 on the solid line L2 during short-circuit without the Miller period). Therefore, the short-circuit determiner 14 determines that the switching element 1 is in the short-circuit state and outputs a high-potential signal indicating that the switching element 1 is in the short-circuit state to the instruction unit 2.

[0069] On the other hand, when the output signal S2 of the second comparison device U2 is in the low-potential state and the output signal S1 of the first comparison device U1 changes from the high-potential state to the low-potential state (that is, when the gate voltage is less than or equal to the reference value VR and the capacitor voltage drops from a value greater than the reference value VQR to the reference value VQR), it is considered that the relationship between the capacitor voltage and the gate voltage is shown by the operating point P3 on the dotted line L3 in the normal state with the Miller period (if replaced by the relationship between the gate charge and the gate voltage, it is shown by the operating point P1 on the solid line L1 in the normal state with the Miller period). Therefore, the short-circuit determiner 14 determines that the switching element 1 is in the normal state (not in the short-circuit state) and outputs a low-potential signal indicating that the switching element 1 is in the normal state to the instruction unit 2.

[0070] Figure 3 It is a flowchart showing an example of the processing flow executed by the short-circuit determiner 14 when performing the short-circuit determination of the switching element 1. This flowchart is repeatedly executed every time a predetermined condition is satisfied (for example, in units of a predetermined period) during the conduction operation of the switching element 1. In addition, the processing of the short-circuit determiner 14 can be implemented by software processing or by the processing of dedicated hardware (electronic circuit).

[0071] When the output signal S1 of the first comparator U1 is at a high potential state, the short-circuit detector 14 determines whether the output signal S2 of the second comparator U2 has changed from a low potential state to a high potential state (step S10).

[0072] When the output signal S2 changes from a low potential state to a high potential state while the output signal S1 is at a high potential state (YES in step S10), that is, when the gate voltage reaches the reference value VQR while the capacitor voltage is greater than the reference value VQR, the short-circuit detector 14 determines that the switching element 1 is in a short-circuit state and outputs a high potential signal to the instruction unit 2 (step S12).

[0073] On the other hand, when it is determined as NO in step S10, the short-circuit detector 14 determines whether the output signal S1 of the first comparator U1 has changed from a high potential state to a low potential state while the output signal S2 of the second comparator U2 is at a low potential state (step S14).

[0074] When the output signal S1 changes from a high potential state to a low potential state while the output signal S2 is at a low potential state (YES in step S14), that is, when the capacitor voltage drops from a value greater than the reference value VQR to the reference value VQR while the gate voltage is less than or equal to the reference value VR, the short-circuit detector 14 determines that the switching element 1 is in a normal state and has entered the Miller period, and outputs a low potential signal to the instruction unit 2 (step S16).

[0075] In addition, when the instruction unit 2 receives a high potential signal (a signal indicating that the switching element 1 is in a short-circuit state) from the short-circuit detector 14, it outputs the above disconnection instruction (an instruction for setting the switching element 15 to the on state, setting the switching element 5 to the off state, and setting the switching element 6 to the on state) to each of the switching elements 5, 6, and 15. Thereby, the short-circuit state of the switching element 1 can be released.

[0076] Moreover, in the driving device 100 according to the present embodiment, the capacitance Cb of the capacitor 4 is designed to satisfy the following relational expression (2).

[0077] |Voff - Von|×Ci ≥ |Vc - Von|×Cb…(2)

[0078] In the above relational expression (2), "Ci" represents the input capacitance of the switching element 1 (the overall capacitance obtained by summing the gate-source capacitance and the gate-drain capacitance), and "Vc" represents the capacitor charging voltage (the initial value of the capacitor voltage). In addition, the negative bias potential Voff, the driving voltage Von, and the capacitance Cb of the capacitor 4 are as described above.

[0079] The left side of Equation (2) is equivalent to the electric charge required for the gate voltage of the switching element 1 to rise from the negative bias potential Voff to the drive voltage Von.

[0080] The right side of Equation (2) is equivalent to the electric charge released by the capacitor 4 until the capacitor voltage drops from the initial value Vc to the drive voltage Von.

[0081] When the above Equation (2) is not satisfied, the gate voltage becomes higher than the drive voltage Von. Therefore, it may cause a decrease in the life of the oxide film in the switching element 1.

[0082] In contrast, in the present embodiment, the above Equation (2) is satisfied. Thus, during the on / off operation of the switching element 1, the capacitor voltage drops to the drive voltage Von, and the diode 8 becomes conductive. Therefore, the gate voltage in the steady on-state of the switching element 1 can be stabilized at the drive voltage Von (the output voltage of the voltage source 7). As a result, a decrease in the life of the oxide film in the switching element 1 can be suppressed.

[0083] As described above, the drive device 100 according to the first embodiment includes: a voltage source 3 (first voltage source); a switching element 15; a capacitor 4 that is connected in parallel with the voltage source 3 via the switching element 15; switching elements 5 and 6 (switching device) that are provided between the capacitor 4 and the gate terminal of the power switching element 1; a first comparison device U1 that outputs a signal S1 representing the comparison result between the voltage of the capacitor 4 and a reference value VQR; a second comparison device U2 that outputs a signal S2 representing the comparison result between the gate voltage of the switching element 1 and a reference value VR; and a short-circuit determiner 14 that determines whether the switching element 1 is in a short-circuit state using the output signal S1 of the first comparison device U1 and the output signal S2 of the second comparison device U2.

[0084] According to this configuration, the short-circuit state of the switching element 1 is determined using the comparison result between the voltage of the capacitor 4 and the reference value VQR (the output signal S1 of the first comparison device U1) and the comparison result between the gate voltage of the switching element 1 and the reference value VR (the output signal S2 of the second comparison device U2). Therefore, an integrator is not required, and the circuit can be simplified.

[0085] Embodiment 2

[0086] Figure 4 FIG. is an example showing a semiconductor device DA having a drive device 100A according to the second embodiment. Figure 4 The drive device 100A shown is relative to the above Figure 1The drive device 100 shown deletes the voltage source 9 that outputs the negative bias potential Voff and replaces the switching element 6 with the disconnecting resistor 20. The other structure of the drive device 100A is the same as that of the above drive device 100, and thus, the detailed description here is not repeated.

[0087] In this drive device 100A, when the switching element 1 is in the off state, the instruction unit 2 sets the switching element 5 to the off state. As a result, the voltage between the output terminals 17 and 18 of the drive device 100A drops to 0V through the gate resistor 16 and the disconnecting resistor 20. Therefore, the gate voltage of the switching element 1 is lower than the threshold voltage, and the switching element 1 becomes the off state.

[0088] In this way, it is also possible to adopt the drive device 100A in which the structure of the drive device 100 is simplified.

[0089] Embodiment 3

[0090] In the above Embodiment 1, an example of determining the short circuit of the switching element 1 using the relationship between the gate charge amount and the gate voltage of the switching element 1 (see Figure 2 ) was described.

[0091] In contrast, in this Embodiment 3, the short circuit of the switching element 1 is determined using the relationship between the gate charge amount and the gate current of the switching element 1.

[0092] Figure 5 FIG. is an example of a semiconductor device DB having a drive device 100B according to this Embodiment 3. Figure 5 The drive device 100B shown is a drive device in which the first comparison device U1 and the second comparison device U2 are respectively replaced with the first comparison device U1B and the second comparison device U2B with respect to the drive device 100 shown above. Figure 1 The other structure of the drive device 100B is the same as that of the above drive device 100, and thus the detailed description here is not repeated.

[0093] The first comparison device U1B includes a comparison unit 10a and a voltage source 11a, a comparison unit 10b and a voltage source 11b, and a logic circuit 60. The voltage source 11a outputs a voltage corresponding to a reference value Vrq1 to the comparison unit 10a. The comparison unit 10a outputs the comparison result between the capacitor voltage and the voltage output from the voltage source 11a to the logic circuit 60. The voltage source 11b outputs a voltage corresponding to a reference value Vrq2 to the comparison unit 10b. The comparison unit 10b outputs the comparison result between the capacitor voltage and the voltage output from the voltage source 11b to the logic circuit 60. The logic circuit 60 can detect that the gate charge falls within the range from the reference value Vrq1 to the reference value Vrq2 by obtaining the logical product of the outputs of the comparison units 10a and 10b. The logic circuit 60 outputs the detection result to the short-circuit determiner 14.

[0094] The second comparison device U2B includes a differentiator 30, a comparison unit 31, and a voltage source 32. The differentiator 30 is provided between the capacitor 4 and the comparison unit 31 and outputs the value obtained by differentiating the capacitor voltage to the comparison unit 31. In addition, the output of the differentiator 30 (the differential value of the capacitor voltage) corresponds to the gate current of the switching element 1 (the current flowing from the driving device 100B to the gate of the switching element 1). The voltage source 32 outputs a voltage corresponding to a reference value Vri to the comparison unit 31. The comparison unit 31 can detect that the gate current is less than the reference value Vri by comparing the output of the differentiator 30 (the value corresponding to the gate current) with the voltage output from the voltage source 32. The comparison unit 31 outputs the comparison result to the short-circuit determiner 14.

[0095] In Figure 5 the driving device 100B shown, it is also possible to implement short-circuit detection of the switching element 1 without using an integrator, improving the design freedom.

[0096] Figure 6 is a diagram showing an example of the relationship between the gate charge and the gate current during the turn-on operation of the switching element 1. In Figure 6 it, the normal relationship of the switching element 1 is represented by a dashed line L5, and the relationship when the arm of the switching element 1 is short-circuited is represented by a solid line L6.

[0097] Normally, due to the existence of the above-mentioned Miller period, as shown by the dashed line L5, there is a period during which the change rate of the gate current is very slow (the period during which the gate current is approximately constant at the current value Im). On the other hand, when the arm is short-circuited, since there is no Miller period, as shown by the solid line L6, the gate current simply decreases monotonically.

[0098] In order to determine the difference between the dotted line L5 and the solid line L6, the range surrounded by the reference value Vri of the gate current and the reference values ​​Vrq1 and Vrq2 of the gate charge amount is defined as Figure 6 In the shaded area shown, the output voltages of the voltage sources 11 a , 11 b , and 32 are set so that the short-circuit determination of the switching element 1 can be performed.

[0099] As mentioned above, in Figure 5 In the driving device 100B shown, the gate current value can be obtained by differentiating the capacitor voltage, and the gate current can be used to determine whether the switching element 1 is short-circuited. Therefore, in the driving device 100B, it is also possible to determine whether the switching element 1 is short-circuited without using an integrator.

[0100] Implementation 4

[0101] Figure 7 1 is a diagram showing an example of a semiconductor device DC including a driving device 100C according to the fourth embodiment. Figure 7 The driving device 100C shown is relative to the above Figure 1 The driving device 100 shown in the figure is a driving device in which filters 40 and 41 are added to the input parts of the comparison units 10 and 12, respectively. The other structures of the driving device 100C are the same as those of the driving device 100 described above, and therefore, detailed description thereof will not be repeated here.

[0102] Comparing units 10 and 12 may malfunction due to noise such as radiation noise from outside the circuit. Therefore, by inserting filters 40 and 41 into the input parts of the comparing units 10 and 12, respectively, a configuration that malfunction is unlikely to occur can be adopted.

[0103] In addition, Figure 7 The Figure 1 Although the driving device 100 shown in the figure is a modified example, the same effect can be obtained by inserting a filter into the input part of the comparison part or the differentiator in other driving devices 100A and 100B.

[0104] Implementation method 5

[0105] In the above-mentioned first to fourth embodiments, in any of the embodiments, the short-circuited state of the switching element 1 is detected by determining the presence or absence of the Miller period.

[0106] In contrast, in the fifth embodiment, when the Miller period is detected, the output voltage of the drive device 100 is reduced to prevent the switching speed of the switching element 1 from being excessively increased, thereby reducing the time rate of change of the drain voltage.

[0107] Figure 8This is a diagram showing an example of a semiconductor device DD having a driving device 100D according to Embodiment 5. Figure 8 The shown driving device 100D is relative to the above Figure 1 The shown driving device 100 is a driving device that adds a switching element 50 and a control unit 51 and inputs the output of the short - circuit determiner 14 to the control unit 51. The other structures of the driving device 100D are the same as those of the above - mentioned driving device 100, so the detailed description here will not be repeated.

[0108] The capacitor 4 is connected to the switching element 5 via a MOSFET, i.e., the switching element 50. When the control unit 51 receives a low - potential signal from the short - circuit determiner 14 (i.e., when it detects the entry into the Miller period), it sets the switching element 50 to the off state to cut off the supply of charge from the capacitor 4 to the switching element 5. Thus, when it detects the entry into the Miller period, the output voltage of the driving device 100D is switched to the driving voltage Von output from the voltage source 7. Therefore, the on - off speed of the subsequent switching element 1 can be suppressed, and the change speed (the amount of change per unit time) of the main voltage that causes noise can be suppressed.

[0109] Figure 9 This is a diagram showing an example of the relationship between the gate charge amount and the gate voltage of the switching element 1 during the on - operation of the switching element 1. In Figure 9 it, the relationship when the current value of the Miller voltage higher than the reference value VR is turned on and off is shown by the solid line L7, and the relationship when the current value of the Miller voltage lower than the reference value VR is turned on and off is shown by the dashed line L8.

[0110] When the current value of the Miller voltage higher than the reference value VR is turned on and off, as shown by the solid line L7, there is no region where the gate voltage is lower than the reference value VR and the gate charge amount is higher than the reference value QR. Therefore, the on - off speed does not decrease, and the conduction loss does not increase.

[0111] On the other hand, when the current value of the Miller voltage lower than the reference value VR is turned on and off, as shown by the dashed line L8, there is a region where the gate voltage is lower than the reference value VR and the gate charge amount is higher than the reference value QR. When this region is detected, the short - circuit determiner 14 determines that the Miller period has entered and outputs a low - potential signal to the control unit 51. If the control unit 51 receives a low - potential signal from the short - circuit determiner 14, it turns off the switching element 50. As a result, the output voltage of the driving device 100D drops from the voltage across the capacitor 4 to the driving voltage Von of the voltage source 7. Therefore, the change speed (the amount of change per unit time) of the main voltage of the switching element 1 can be suppressed.

[0112] Embodiment 6

[0113] Figure 10 FIG. 2 is an example of a semiconductor device DE having a driving device 100E according to Embodiment 6. Figure 10 The driving device 100E shown is the driving device obtained by adding a third comparator U3 and a fourth comparator U4 to the driving device 100D shown above and changing the short-circuit determiner 14 to a short-circuit determiner 14E. Since other structures of the driving device 100E are the same as those of the driving device 100D above, detailed description thereof will not be repeated here. Figure 8

[0114] In Embodiment 5 above, during the on / off of the Miller current that becomes lower than the reference value VR, after the end of the Miller period, the short-circuit determiner 14 outputs a high-potential signal, and there may be a condition where the suppression of the rate of change of the main voltage of the switching element 1 is insufficient.

[0115] Figure 11 FIG. 3 is an example showing the relationship between the gate charge and the gate voltage of the switching element 1 during the conduction operation of the switching element 1. In Figure 11 FIG. 3, the relationship in the case where the current value of the Miller voltage that becomes lower than the reference value VR and higher than the reference value VR2 is turned on and off is shown by a solid line L9, and the relationship in the case where the current value of the Miller voltage that becomes lower than the reference values VR and VR2 is turned on and off is shown by a dashed line L10.

[0116] Figure 11 In the example shown in FIG. 3, when the Miller period is determined by the reference value QR of the gate charge and the reference value VR of the gate voltage, in the waveform of the dashed line L10 with a small current, the timing at which the gate voltage becomes lower than the reference value VR and the gate charge becomes higher than the reference value QR (i.e., the detection timing of the Miller period) is after the end of the Miller period.

[0117] Therefore, in Embodiment 6, in addition to the first comparator U1 and the second comparator U2, a third comparator U3 and a fourth comparator U4 are further provided.

[0118] The third comparator U3 includes a comparison unit 10e and a voltage source 11e. The voltage source 11e outputs a reference value different from the reference value VQR (the value of the gate voltage when the gate charge becomes a value QR2 lower than the reference value QR) to the comparison unit 10e. The comparison unit 10e outputs a signal S3 representing the comparison result between the capacitor voltage and the voltage output from the voltage source 11 to the short-circuit determiner 14E.

[0119] ​The fourth comparison device U4 includes a comparison unit 12e and a voltage source 13e. The voltage source 13e outputs a voltage of a reference value VR2 that is lower than the reference value VR to the comparison unit 12e. The comparison unit 12e outputs a signal S4 representing the comparison result between the gate voltage of the switching element 1 and the voltage output by the voltage source 13e to the short-circuit determiner 14E.

[0120] The short-circuit determiner 14E detects the Miller period of the switching element 1 using the output signal S1 of the first comparison device U1, the output signal S2 of the second comparison device U2, the output signal S3 of the third comparison device U3, and the output signal S4 of the fourth comparison device U4.

[0121] When the short-circuit determiner 14E detects the Miller period of the switching element 1, the control unit 51 turns off the switching element 50.

[0122] Thus, in Embodiment 6, by additionally providing the third comparison device U3 and the fourth comparison device U4, it is possible to appropriately detect the Miller period even under conditions where the magnitude of the current is different, and to reduce the output voltage of the drive device 100D. Therefore, even under conditions where the magnitude of the current is different, it is possible to appropriately suppress the change rate (change amount per unit time) of the main voltage of the switching element 1.

[0123] Embodiment 7

[0124] In this Embodiment 7, any one of the semiconductor devices D to DE according to the above Embodiments 1 to 6 is applied to a power conversion device. Hereinafter, as Embodiment 7, the case where the present invention is applied to a three-phase inverter will be described.

[0125] Figure 12 is a block diagram showing the configuration of a power conversion system to which the power conversion device according to this Embodiment 7 is applied.

[0126] Figure 12 The power conversion system shown has a power source 1000, a power conversion device 2000, and a load 3000. The power source 1000 is a DC power source that supplies DC power to the power conversion device 2000. The power source 1000 can be composed of various power sources. For example, it can be composed of a DC system, a solar cell, a storage battery, or can also be composed of a rectifier circuit and an AC / DC converter connected to an AC system. In addition, the power source 1000 can also be composed of a DC / DC converter that converts the DC power output from the DC system into power that can be used by the load 3000.

[0127] The power conversion device 2000 is a three-phase inverter connected between a power source 1000 and a load 3000, which converts the DC power supplied from the power source 1000 into AC power and supplies the AC power to the load 3000. As shown in Figure 12 it has: a main conversion circuit 2010 that converts DC power into AC power and outputs it; and a control circuit 2030 that outputs a control signal for controlling the main conversion circuit 2010 to the main conversion circuit 2010.

[0128] The load 3000 is a three-phase motor driven by the AC power supplied from the power conversion device 2000. In addition, the load 3000 is a motor mounted on various electrical devices. For example, it is used as a motor for hybrid vehicles, electric vehicles, rail vehicles, elevators, or air conditioning equipment.

[0129] Hereinafter, the details of the power conversion device 2000 will be described. The main conversion circuit 2010 has switching elements (not shown). By turning the switching elements on and off, the DC power supplied from the power source 1000 is converted into AC power and supplied to the load 3000. The specific circuit structure of the main conversion circuit 2010 is various, but the main conversion circuit 2010 according to this embodiment is a two-level three-phase full-bridge circuit and can be composed of 6 switching elements and 6 freewheeling diodes reversely connected in parallel with each switching element. The main conversion circuit 2010 has a semiconductor device 2020, and the semiconductor device 2020 has each switching element and a driving device for driving each switching element. Each switching element and each driving device of the semiconductor device 2020 are the switching element 1 and the driving device of any one of the semiconductor devices D to DE according to the above embodiments 1 to 6. The 6 switching elements are connected in series two by two to form upper and lower bridge arms, and each upper and lower bridge arm forms each phase (U phase, V phase, W phase) of the full-bridge circuit. And the 3 output terminals of the main conversion circuit 2010, which are the output terminals of each upper and lower bridge arm, are connected to the load 3000.

[0130] The control circuit 2030 controls the switching elements of the main conversion circuit 2010 to supply desired power to the load 3000. Specifically, based on the power to be supplied to the load 3000, the time (on-time) during which each switching element of the main conversion circuit 2010 should be in the on state is calculated. For example, the main conversion circuit 2010 can be controlled by PWM control that modulates the on-time of the switching elements corresponding to the voltage to be output. Further, a control instruction (control signal) is output to the drive circuit included in the main conversion circuit 2010 to output an on signal to the switching elements that should be in the on state and an off signal to the switching elements that should be in the off state at each time point. The drive circuit outputs the on signal or the off signal as a drive signal to the control electrodes of the respective switching elements in accordance with this control signal.

[0131] In the power conversion device according to the seventh embodiment, the semiconductor device 2020 constituting the main conversion circuit 2010 is any of the semiconductor devices according to the first to sixth embodiments. Thus, as in the first to sixth embodiments, the short-circuit state of the power switching elements can be detected by a simple circuit without using an integrator.

[0132] In the seventh embodiment, an example in which the present invention is applied to a two-level three-phase inverter has been described, but the present invention is not limited thereto, and can be applied to various power conversion devices. In the seventh embodiment, a two-level power conversion device is assumed, but it may also be a three-level or multi-level power conversion device. When power is supplied to a single-phase load, the present invention can also be applied to a single-phase inverter. Further, when power is supplied to a DC load or the like, the present invention can also be applied to a DC / DC converter or an AC / DC converter.

[0133] In addition, the power conversion device to which the present invention is applied is not limited to the case where the load is a motor as described above. For example, it can also be used as a power supply device for an electric discharge machine, a laser processing machine, an induction heating cooker, or a non-contact power supply system, and can also be used as a power conditioner for a solar power generation system, a power storage system, or the like.

[0134] It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0135] Description of reference numerals

[0136] 1, 5, 6, 15, 50 switching elements, 2 instruction units, 3, 7, 9, 11, 11a, 11b, 11e, 13, 13e, 32 voltage sources, 4 capacitors, 8 diodes, 10, 10a, 10b, 10e, 12, 12e, 31 comparison units, 14, 14E short-circuit detectors, 16 gate resistors, 17, 18 output terminals, 20 disconnection resistors, 30 differentiators, 40, 41 filters, 51 control units, 60 logic circuits, 100, 100A, 100B, 100C, 100D, 100E drive devices, 1000 power supplies, 2000 power conversion devices, 2010 main conversion circuits, 2020, D, DA, DB, DC, DD, DE semiconductor devices, 2030 control circuits, 3000 loads, U1, U1B first comparison devices, U2, U2B second comparison devices, U3 third comparison devices, U4 fourth comparison devices.

Claims

1. A driving device for a semiconductor element, which is a driving device for a power semiconductor element having a gate terminal, Among them, The driving device for the semiconductor element has: A first voltage source; A switching element; A capacitor, which is connected in parallel with the first voltage source via the switching element; A switching device, which is provided between the capacitor and the gate terminal of the semiconductor element and is configured to be able to switch the voltage applied to the gate terminal; A first comparison device, which outputs a signal representing the comparison result between the voltage of the capacitor and a first reference value; A second comparison device, which outputs a signal representing the comparison result between the voltage of the gate terminal or the value obtained by differentiating the voltage of the capacitor and a second reference value; And A determiner, which uses the output signal of the first comparison device and the output signal of the second comparison device to determine whether the semiconductor element is in a short-circuit state.

2. The driving device for the semiconductor element according to claim 1, wherein The first comparison device outputs a signal representing a low-potential state when the voltage of the capacitor is less than or equal to the first reference value, The first comparison device outputs a signal representing a high-potential state when the voltage of the capacitor is greater than the first reference value, The second comparison device outputs a signal representing a low-potential state when the voltage of the gate terminal or the value obtained by differentiating the voltage of the capacitor is less than or equal to the second reference value, The second comparison device outputs a signal representing a high-potential state when the voltage of the gate terminal or the value obtained by differentiating the voltage of the capacitor is greater than the second reference value, When the output signal of the second comparison device has changed from the low-potential state to the high-potential state when the output signal of the first comparison device is in the high-potential state, the determiner determines that the semiconductor element is in a short-circuit state, When the output signal of the first comparison device has changed from the high-potential state to the low-potential state when the output signal of the second comparison device is in the low-potential state, the determiner determines that the semiconductor element is not in a short-circuit state.

3. The driving device for the semiconductor element according to claim 1, wherein It further has a second voltage source connected in series with the first voltage source, The switching device is configured to be connected in parallel with the first voltage source and the second voltage source and is able to switch the voltage applied to the gate terminal between the positive voltage from the first voltage source or the capacitor and the negative voltage from the second voltage source.

4. The driving device for the semiconductor element according to claim 2, wherein It further has a second voltage source connected in series with the first voltage source, The switching device is configured to be connected in parallel with the first voltage source and the second voltage source and is able to switch the voltage applied to the gate terminal between the positive voltage from the first voltage source or the capacitor and the negative voltage from the second voltage source.

5. The driving device for a semiconductor element according to any one of claims 1 to 4, wherein, It further has: An output terminal that can be connected to the semiconductor element; A separating device, which is disposed between the capacitor and the output terminal and operates in such a manner as to separate the capacitor from the output terminal according to the output of the determiner; and A voltage source for stabilization, which is connected in parallel with the capacitor via the separating device and a diode, and is connected to the output terminal via the diode, and outputs a voltage lower than the voltage of the capacitor.

6. The driving device for a semiconductor element according to claim 5, wherein, It further has: A third comparison device, which outputs a signal representing the comparison result between the voltage of the capacitor and a reference value different from the first reference value; and A fourth comparison device, which outputs a signal representing the comparison result between the voltage of the gate terminal or the value obtained by differentiating the voltage of the capacitor and a reference value different from the second reference value, The determiner uses the output signals of the first comparison device, the second comparison device, the third comparison device, and the fourth comparison device to detect the Miller period of the semiconductor element, The separating device operates in such a manner as to separate the capacitor from the output terminal according to the detection of the Miller period by the determiner.

7. The driving device for a semiconductor element according to any one of claims 1 to 4, wherein The second comparison device has: A differentiator, which outputs the differential value of the voltage of the capacitor; and A comparator, which compares the output of the differentiator with the second reference value.

8. The driving device for a semiconductor element according to any one of claims 1 to 4, wherein When the voltage of the gate terminal when the semiconductor element is set to the on state is denoted as Von, the voltage of the gate terminal when the semiconductor element is set to the off state is denoted as Voff, the input capacitance of the semiconductor element is denoted as Ci, the charging voltage of the capacitor is denoted as Vc, and the capacitance of the capacitor is denoted as Cb, The capacitance Cb of the capacitor satisfies The relational expression of Cb≤{|Voff - Von| / |Vc - Von|×Ci}.

9. The driving device for a semiconductor element according to any one of claims 1 to 4, wherein The semiconductor element is an element made of any one of silicon, silicon carbide, gallium nitride, and gallium oxide.

10. A semiconductor device, which has the driving device and the semiconductor element according to any one of claims 1 to 9.

11. A power conversion device, which has: A main conversion circuit, which has the driving device and the semiconductor element according to any one of claims 1 to 9, and converts the input power and outputs it; and A control circuit, which outputs a control signal for controlling the main conversion circuit to the main conversion circuit.

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