Overcurrent detection device, overcurrent detection method, semiconductor DC breaker, and power conversion device

Abstract

To provide an overcurrent detection device that detects an overcurrent with high accuracy even when there is a site where the temperature is unknown due to an instantaneous large current.SOLUTION: An overcurrent detection device 11 comprises: an instantaneous current estimation unit 101 that estimates an estimated instantaneous current I at a site X of unknown temperature on the basis of a measured instantaneous voltage V of a conductor 111 and an estimated resistance R at the site X of unknown temperature in the conductor 111; an overcurrent determination unit 102 that determines whether an overcurrent is present on the basis of the estimated instantaneous current I; a power consumption calculation unit 103 that calculates power consumption P on the basis of the instantaneous voltage V and the estimated instantaneous current I; a temperature estimation unit 104 that estimates and updates a temperature T at the site X of unknown temperature on the basis of known temperatures Ta and Tt at least at one site of the conductor 111, the power consumption P, and a thermal equivalent circuit Tmodel designed in consideration of at least a thermal resistance Rth and a thermal capacitance Cth of the conductor 111; and a resistance estimation unit 105 that updates an estimated resistance R at the site X of unknown temperature on the basis of the updated temperature T.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an overcurrent detection device, an overcurrent detection method, a semiconductor DC circuit breaker, and a power conversion device. [Background technology]

[0002] When an overcurrent occurs, an overcurrent detection device detects the overcurrent and controls the semiconductor switching element of a solid-state DC circuit breaker to cut off the current, or controls the semiconductor switching element used in a power conversion device to protect it.

[0003] An example of a technology for measuring current is Patent Document 1. FIG. 5 and paragraph 0048 of Patent Document 1 describe a technology for measuring a voltage V1(T) that depends on temperature T and a voltage V2(I, T) that depends on current I and temperature T, and calculating current I based on the measured voltages V1 and V2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-187667 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technique disclosed in Patent Document 1 is based on the premise that the temperature T when the voltage V2 is measured can be accurately determined.

[0006] For example, when a large current flows instantaneously, the temperature may become high in some places other than the places where the temperature T can be accurately determined. Because the characteristics of current, voltage, and resistance are temperature dependent, if there are places where the temperature is unknown, an error will occur when calculating the current based on the measured voltage, resulting in a problem of low accuracy in detecting overcurrent.

[0007] The problem that the present invention aims to solve is to provide an overcurrent detection device and an overcurrent detection method that can detect overcurrents with high accuracy, even when there are locations whose temperatures are unknown due to, for example, a sudden flow of a large current, and a semiconductor DC circuit breaker and power conversion device that use the same. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the overcurrent detection device / method of the present invention is characterized by having an instantaneous current estimation unit / step that estimates an estimated instantaneous current I of a location X of a conductor whose temperature is unknown based on an instantaneous voltage V measured at a predetermined measurement location of the conductor and an estimated resistance R of the location X of the conductor whose temperature is unknown; an overcurrent determination unit / step that determines whether there is an overcurrent based on the estimated instantaneous current I; a power consumption calculation unit / step that calculates a power consumption P based on the instantaneous voltage V and the estimated instantaneous current I; a thermal equivalent circuit that takes into account at least the thermal resistance and heat capacity of the conductor; a temperature estimation unit / step that estimates and updates a temperature T of the location X of the conductor whose temperature is unknown based on the power consumption P and a known temperature of at least one location of the conductor; and a resistance estimation unit / step that updates the estimated resistance R of the location X of the conductor whose temperature is unknown based on the temperature T updated by the temperature estimation unit / step.

[0009] In addition, the semiconductor DC circuit breaker of the present invention has the above-mentioned overcurrent detection device, a semiconductor switching element, and a control unit that controls the semiconductor switching element to cut off a main current flowing through the semiconductor switching element when the overcurrent determination unit determines that an overcurrent exists.

[0010] In addition, the power conversion device of the present invention has the above-mentioned overcurrent detection device, a power conversion circuit constructed using a semiconductor switching element, and a protection circuit that controls to protect the semiconductor switching element when the overcurrent determination unit determines that an overcurrent exists. Effect of the Invention

[0011] According to the present invention, it is possible to realize an overcurrent detection device and an overcurrent detection method that can detect overcurrents with high accuracy, even when there are locations whose temperature is unknown due to, for example, a sudden flow of a large current, and a semiconductor DC circuit breaker and power conversion device that use the same. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a functional block diagram of the overcurrent detection device according to the first embodiment. [Diagram 2] FIG. 13 is a top view illustrating an example of a shape of a conductor. [Diagram 3] The thermal equivalent circuit corresponding to Fig. 2. [Figure 4] 13A and 13B are top views illustrating other examples of the shape of the conductor. [Diagram 5] The thermal equivalent circuit corresponding to Figure 4. [Figure 6] FIG. 4 is a diagram for explaining a thermal time constant. [Figure 7] FIG. 11 is a diagram showing the conditions of a simulation for explaining the effects of the first embodiment. [Figure 8] FIG. 11 is a diagram showing the results of a simulation for explaining the effects of the first embodiment. [Figure 9] FIG. 11 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a second embodiment. [Figure 10] FIG. 11 is a perspective view of a semiconductor module according to a second embodiment. [Figure 11] FIG. 11 is a perspective view of the inside of a semiconductor module according to a second embodiment. [Figure 12] FIG. 11 is a top view of the inside of a semiconductor module according to a second embodiment. [Figure 13] FIG. 11 is a top view of the inside of a semiconductor module according to a second embodiment. [Figure 14] FIG. 11 is a top view of a first external terminal and a fuse of a semiconductor module according to a second embodiment. [Figure 15] FIG. 11 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a third embodiment. [Figure 16] FIG. 11 is a perspective view of the inside of a semiconductor module according to a third embodiment. [Figure 17] FIG. 11 is a top view of the inside of a semiconductor module according to a third embodiment. [Figure 18] FIG. 11 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a fourth embodiment. [Figure 19] FIG. 13 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a fifth embodiment. [Figure 20] FIG. 13 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a sixth embodiment of the present invention. [Figure 21] FIG. 13 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a seventh embodiment. [Figure 22] FIG. 13 is a functional block diagram of a power conversion device according to an eighth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing and each embodiment, the same or similar components are designated by the same reference numerals, and duplicated explanations will be omitted. EXAMPLES

[0014] Fig. 1 is a functional block diagram of an overcurrent detection device according to a first embodiment of the present invention. Fig. 2 is a top view illustrating an example of a shape of a conductor. Fig. 3 is a thermal equivalent circuit corresponding to Fig. 2.

[0015] The overcurrent detection device 11 of the first embodiment receives as input an instantaneous voltage V measured at a predetermined measurement point on the conductor 111 to be measured and a known temperature (e.g., the substrate temperature Ta and the terminal temperature Tt) at at least one point on the conductor 111, and estimates an estimated instantaneous current I at a point X on the conductor 111 whose temperature is unknown based on a thermal equivalent circuit Tmodel that takes into account at least the thermal resistance Rth and heat capacity Cth of the conductor 111, and the input instantaneous voltage V and the known temperature, determines whether there is an overcurrent based on the estimated instantaneous current I, and outputs an overcurrent detection signal 107 if it determines that there is an overcurrent.

[0016] Specifically, the overcurrent detection device 11 of this embodiment has, as functional blocks, an instantaneous current estimation unit 101, an overcurrent determination unit 102, a power consumption calculation unit 103, a temperature estimation unit 104, a resistance estimation unit 105, and a thermal equivalent circuit storage unit 106. Each functional block can be realized by executing a program on a computer system such as a microcomputer.

[0017] Next, details of each functional block of the overcurrent detection device 11 of this embodiment and an overcurrent detection method will be described.

[0018] In an instantaneous current estimation step, the instantaneous current estimation unit 101 estimates an estimated instantaneous current I at a point X in the conductor 111 whose temperature is unknown, based on an instantaneous voltage V measured at a predetermined measurement point on the conductor 111 and an estimated resistance R at the point X in the conductor 111 whose temperature is unknown. The estimated instantaneous current I can be calculated, for example, by the formula "I=V / R".

[0019] In an overcurrent determination step, overcurrent determination unit 102 determines whether an overcurrent exists based on estimated instantaneous current I. The determination of whether an overcurrent exists can be made, for example, by the equation "I≧ILIM" which determines whether estimated instantaneous current I is equal to or greater than threshold value ILIM. If this equation is satisfied, overcurrent determination unit 102 determines that an overcurrent exists and outputs overcurrent detection signal 107.

[0020] In the power consumption calculation step, the power consumption calculation unit 103 calculates the power consumption P based on the instantaneous voltage V and the estimated instantaneous current I. The power consumption P can be calculated, for example, by the formula "P=IV". The power consumption P corresponds to the power consumption at a location X whose temperature is unknown.

[0021] In the temperature estimation step, the temperature estimation unit 104 estimates and updates the temperature T of a location X in the conductor 111 whose temperature is unknown, based on a thermal equivalent circuit Tmodel that takes into account at least the thermal resistance Rth and heat capacity Cth of the conductor 111, the power consumption P, and a known temperature of at least one location in the conductor 111 (e.g., the substrate temperature Ta and the terminal temperature Tt). The temperature T can be expressed by, for example, the formula "T=f(Tmodel, P, Ta, Tt)". Details of the thermal equivalent circuit Tmodel and a method for estimating the temperature T will be described later.

[0022] In a resistance estimation step, the resistance estimation unit 105 updates the estimated resistance R of the location X in the conductor 111 whose temperature is unknown, based on the temperature T updated by the temperature estimation unit 104. Since the estimated resistance R depends on the temperature T, it can be calculated using coefficients a and b, for example, by the formula "R=aT+b".

[0023] The instantaneous current estimation step, the overcurrent determination step, the power consumption calculation step, the temperature estimation step, and the resistance estimation step are repeatedly executed at a predetermined cycle. The estimated resistance R updated in the resistance estimation step is used in the next instantaneous current estimation step.

[0024] The thermal equivalent circuit storage unit 106 stores a thermal equivalent circuit Tmodel in advance.

[0025] Next, the thermal equivalent circuit Tmodel will be described in detail with reference to FIG. 2 and FIG.

[0026] 2, the conductor 111 to be measured is configured to include a first portion 111A, a second portion 111B, and a portion X with an unknown temperature that exists between the first portion 111A and the second portion 111B. Here, a description will be given assuming that a terminal through which a main current of a semiconductor module flows is used as an example of the conductor 111. This terminal is connected to a semiconductor switching element provided inside the semiconductor module.

[0027] The first portion 111A is connected to the substrate side on which the semiconductor switching elements are provided. It is assumed that the temperature of the first portion 111A is equal to the substrate temperature Ta. It is assumed that the substrate temperature Ta can be measured by, for example, a thermistor or a thermocouple provided on the substrate and is known.

[0028] The second portion 111B is the side of the terminal that is connected to the outside. It is assumed that the temperature of the second portion 111B is equal to the terminal temperature Tt. It is assumed that the terminal temperature Tt can be measured by a thermistor provided on a bus bar or the like and is known. It is also assumed that the instantaneous voltage V is measured at the second portion 111B.

[0029] The area X where the temperature is unknown has a smaller width than the first portion 111A and the second portion 111B. Therefore, for example, when a large current flows instantaneously, it is assumed that the temperature T of this area will be higher than the first portion 111A and the second portion 111B where the temperatures are known. Therefore, the heat dissipation direction 112 of the first portion 111A and the second portion 111B is the direction shown in FIG.

[0030] Here, since the characteristics of current, voltage, and resistance are temperature dependent, if there is a location X in the conductor 111 whose temperature is unknown, an error will occur if the current is calculated based on the measured instantaneous voltage V without taking into account the temperature T of the location X whose temperature is unknown, resulting in a problem of low accuracy in detecting overcurrent.

[0031] Therefore, in this embodiment, a thermal equivalent circuit Tmodel that takes into account at least the thermal resistance Rth and heat capacity Cth of the conductor 111 is used to estimate the temperature T of the location X in the conductor 111 whose temperature is unknown.

[0032] As shown in FIG. 3, the thermal equivalent circuit Tmodel corresponding to FIG. 2 has a structure in which a thermal resistance Rth1 and a thermal capacity Cth1 are connected in parallel in the first portion 111A, a thermal resistance Rth2 and a thermal capacity Cth2 are connected in parallel in the second portion 111B, and these are connected in series at a point X where the temperature is unknown.

[0033] For example, when the thermal conductivity of the second portion 111B is λ, the specific heat capacity is c, the density is d, the cross-sectional area is A, and the length is l, the thermal resistance Rth2=l / λA and the thermal capacity Cth2=cdAl can be calculated in a similar manner for the thermal resistance Rth1 and the thermal capacity Cth1 of the first portion 111A.

[0034] In the thermal equivalent circuit Tmodel, the power consumption P corresponds to current, the temperature T corresponds to voltage, and the loss, which is the integral of the power consumption P, corresponds to the charge, which is the integral of the current. Therefore, for the power consumption P generated at location X, whose temperature is unknown, power consumption P flows from temperature T to substrate temperature Ta via thermal resistance Rth1 as power consumption P1R and via thermal capacitance Cth1 as power consumption P1C, and also flows from temperature T to terminal temperature Tt as power consumption P2R and via thermal resistance Rth2 and via thermal capacitance Cth2 as power consumption P2C. Therefore, for the thermal equivalent circuit Tmodel, the following equations (1) and (2) hold at time t.

[0035]

number

[0036]

number

[0037] Fig. 4 is a top view illustrating another example of the shape of the conductor, and Fig. 5 is a thermal equivalent circuit corresponding to Fig. 4.

[0038] As shown in Fig. 4, when the second portion 111B of the conductor 111 is composed of a third portion 111B1 having a cross-sectional area A1 and a length l1, and a fourth portion 111B2 having a cross-sectional area A2 and a length l2, the thermal equivalent circuit Tmodel of the second portion 111B can be expressed using the thermal resistance Rth21 and the thermal capacity Cth21 of the third portion 111B1, and the thermal resistance Rth22 and the thermal capacity Cth22 of the fourth portion 111B2, as shown in Fig. 5. Here, the configuration in which the second portion 111B of the conductor 111 is divided into two stages is described as an example, but the thermal equivalent circuit Tmodel can be expressed by expanding the same concept when it is divided into three or more stages.

[0039] Furthermore, when the shape of the conductor 111 is complex, the temperature rise of the conductor 111 may be found by simulation, and the parameters of the thermal equivalent circuit Tmodel may be estimated.

[0040] Fig. 6 is a diagram for explaining the thermal time constant, in which the horizontal axis represents time t and the vertical axis represents the terminal temperature Tt, both of which are shown on a logarithmic scale.

[0041] For example, assume that a voltage V' is applied to the second portion 111B of the conductor 111, causing a current I' to flow, and the temperature changes from an initial temperature Tt0 to a steady-state temperature Tt' as shown in Fig. 6. In this case, the thermal time constant τ is defined as the time required for a 63.2% change in temperature from the initial temperature Tt0 to the steady-state temperature Tt'. If the thermal equivalent circuit Tmodel of the second portion 111B is defined as shown in Fig. 3, the thermal resistance Rth2=Tt' / I'V' and the thermal capacity Cth2=τ / Rth2 can be obtained.

[0042] If the simulation results cannot be accurately expressed using only one element of thermal resistance Rth and thermal capacity Cth, as shown in FIG. 3, the accuracy can be improved by increasing the number of elements of thermal resistance Rth and thermal capacity Cth, as shown in FIG. 5.

[0043] Next, a method for estimating the temperature T in the temperature estimating section 104 will be described.

[0044] The temperature estimation unit 104 estimates the temperature T by assuming that the initial value of the temperature T is equal to the initial value of a known temperature at least at one point of the conductor 111 (for example, the substrate temperature Ta and the terminal temperature Tt).

[0045] Here, it is assumed that the conductor 111 has the shape shown in Fig. 2 and the thermal equivalent circuit Tmodel in Fig. 3 holds. In this case, the above-mentioned formulas (1) and (2) hold. The integral equation of formula (2) is solved by a numerical method.

[0046] Assuming that the power consumption P is 0 as an initial value, and that the temperature T, the substrate temperature Ta, and the terminal temperature Tt are equal, the following equation (3) holds.

[0047]

number

[0048] The temperature history T(t) is calculated from this initial value, the power consumption history P (P(t) = I(t) V(t)), and the known temperature histories Ta(t) and Tt(t).

[0049] Differentiating equation (2) with respect to t gives the following equation (4).

[0050]

number

[0051] Assuming that the instantaneous voltage V, substrate temperature Ta, and terminal temperature Tt are measured at a predetermined sampling interval Δt, the derivative can be replaced by dividing the difference in the measured values ​​by the difference at time t (=Δt). Therefore, equation (4) becomes equation (5). Note that the superscripts n+1 and n indicate the value after the update in the current process and the value before the update in the current process, respectively.

[0052]

number

[0053] In equation (5), by substituting the difference ΔT in temperature T, the difference Δt in time t, the difference ΔTa in substrate temperature Ta, and the difference ΔTt in terminal temperature Tt as in the following equation (6), and rearranging the equation, we obtain the following equation (7).

[0054]

number

[0055]

number

[0056] Since equation (1) is still true for the updated values ​​in this process, we rewrite equation (1) so that the superscript becomes n+1, substitute equation (7), and rearrange to obtain the following equation (8).

[0057]

number

[0058] Solving equation (8) for ΔT gives the following equation (9).

[0059]

number

[0060] In formula (9), the updated value of the power consumption P (superscript n+1) can be the power consumption P calculated by the power consumption calculation unit 103. The values ​​of P1R and P2R before the update (superscript n) can be those obtained by formula (7) in the previous process. For ΔTa and ΔTt, the difference between the current measurement value and the previous measurement value can be used. For Δt, a predetermined sampling interval Δt can be used. For Rth1, Rth2, Cth1, and Cth2, the values ​​used in the thermal equivalent circuit Tmodel can be used. Therefore, ΔT can be obtained by formula (9). After ΔT is obtained, the updated values ​​of P1R and P2R (superscript n+1) are obtained by using formula (7) for the next process.

[0061] By determining the difference ΔT in temperature T, the updated value of temperature T in the current process (superscript n+1) can be determined by the following equation (10).

[0062]

number

[0063] By performing the above-mentioned processing, the temperature estimation unit 104 can estimate the temperature T.

[0064] Next, the results of verifying the accuracy of current estimation by the method of this embodiment through a simulation simulating an instantaneous large current will be described.

[0065] Fig. 7 is a diagram showing the conditions of a simulation for explaining the effect of Example 1. Fig. 8 is a diagram showing the results of a simulation for explaining the effect of Example 1. In Fig. 7 and Fig. 8, the horizontal axis is time t, the vertical axis in Fig. 7 is current, and the vertical axis in Fig. 8 is estimated instantaneous current I.

[0066] Here, the cross-sectional area is 12 mm 2 It is assumed that a maximum instantaneous large current of 5000 A occurs in 1000 us after a steady current of 500 A is passed through a conductor 111 having a length of 40 mm as shown in Fig. 7. Simulations were performed to obtain an estimated instantaneous current I using three types of thermal equivalent circuits Tmodel: Comparative Example 1 which does not consider thermal resistance Rth and thermal capacity Cth, Comparative Example 2 which considers only thermal resistance Rth, and the method of this embodiment which considers thermal resistance Rth and thermal capacity Cth.

[0067] As shown in Fig. 8, the graph of Comparative Example 1 without RC consideration 121 is larger than the current shown in Fig. 7, and the estimated instantaneous current I is overestimated. Also, the graph of Comparative Example 2 with R consideration 122 is smaller than the current shown in Fig. 7, and the estimated instantaneous current I is underestimated. On the other hand, the graph of Comparative Example 2 with RC consideration 123 by the method of this embodiment is close to the current shown in Fig. 7, and it was confirmed that the current estimation accuracy is high.

[0068] As described above, according to this embodiment, it is possible to realize an overcurrent detection device and an overcurrent detection method that can detect overcurrents with high accuracy, even in cases where there are locations whose temperatures are unknown due to, for example, an instantaneous large current flow. EXAMPLES

[0069] The second embodiment is an embodiment of a semiconductor DC circuit breaker 1 using the overcurrent detection device 11 of the first embodiment.

[0070] FIG. 9 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a second embodiment.

[0071] The semiconductor DC circuit breaker 1 of the second embodiment is connected between the power source 3 and the protected device 4, and cuts off the current when an overcurrent is detected. Here, the semiconductor DC circuit breaker 1 includes a semiconductor switching element 21 that cuts off the main current when an overcurrent is detected, a fuse 25 connected in series to the semiconductor switching element 21, a voltage detection unit 14 that detects the voltage at a predetermined measurement point, a temperature detection unit 15 that detects the temperature at a predetermined point, an overcurrent detection device 11 of the first embodiment that detects an overcurrent based on a thermal equivalent circuit Tmodel, a voltage detected by the voltage detection unit 14 (corresponding to the instantaneous voltage V of the first embodiment), and a temperature detected by the temperature detection unit 15 (corresponding to the substrate temperature Ta and terminal temperature Tt of the first embodiment), and a control unit 12 that turns off the semiconductor switching element 21 when an overcurrent is detected by the overcurrent detection device 11.

[0072] In other words, the semiconductor DC circuit breaker 1 of this embodiment has the overcurrent detection device 11 of Example 1, a semiconductor switching element 21, and a control unit 12 that controls the semiconductor switching element 21 to cut off the main current flowing through the semiconductor switching element 21 when the overcurrent determination unit 102 of the overcurrent detection device 11 determines that an overcurrent exists.

[0073] The magnitude of the overcurrent that turns off the semiconductor switching element 21 is set to be smaller than the melting current of the fuse 25. That is, in a specific configuration, the semiconductor DC circuit breaker 1 has a fuse 25 connected in series to the semiconductor switching element 21, and the overcurrent determination unit 102 of the overcurrent detection device 11 is configured to determine that an overcurrent has occurred when the estimated instantaneous current I is equal to or greater than a predetermined threshold value ILIM that is smaller than the melting current of the fuse 25. The melting current of the fuse 25 is set to be equal to or smaller than the allowable current of the protected device 4.

[0074] With this configuration, when an overcurrent flows, it is possible to detect the overcurrent and cut off the current by turning off the semiconductor switching element 21 before the fuse 25 melts, so that the semiconductor DC circuit breaker 1 can be reused, and even if the semiconductor switching element 21 breaks down due to cosmic rays or the like, the fuse 25 connected in series melts down to cut off the current. In other words, there is redundancy that allows the current to be cut off even if the semiconductor switching element 21 that cuts off the current when an overcurrent is detected breaks down.

[0075] Furthermore, the semiconductor DC circuit breaker 1 of this embodiment uses a terminal (first external terminal 31 in FIG. 14 described later) connected to the semiconductor switching element 21 and through which the main current flows as the conductor 111 of the first embodiment, and a fuse 25 that melts when a fusing current flows is formed in a part of this terminal, and a location X in the conductor 111 whose temperature is unknown is the location where the fuse 25 is formed. The voltage detection unit 14 measures the instantaneous voltage V of this terminal. Furthermore, the known temperature of at least one location of the conductor 111 includes a substrate temperature Ta, which is the temperature of the substrate on which the semiconductor switching element 21 is mounted, and a terminal temperature Tt, which is the temperature of a location on the outer side of the fuse 25 of this terminal.

[0076] The semiconductor switching element 21 is configured as a bidirectional switch in which the reference potential terminal of the first switching element 21a is connected to the reference potential terminal of the second switching element 21b. This allows current to be cut off in either direction. If there is no need to cut off current in both directions, a unidirectional semiconductor switching element 21 may be used.

[0077] FIG. 9 shows an example in which MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the first switching element 21a and the second switching element 21b, but this is not limited thereto, and other semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors) may also be used.

[0078] When the semiconductor switching element 21 is a MOSFET, the reference potential terminal through which the main current flows is the source S, which is one of the main terminals. A diode 22, which is a body diode built into the MOSFET, is connected in anti-parallel between the source S and the drain D, which is the other main terminal through which the main current flows. A control signal from the control unit 12 is input to the gate G to control on / off. In the case of an IGBT, the source may be read as the emitter, the drain as the collector, and an external diode may be used for the diode 22.

[0079] The semiconductor DC circuit breaker 1 has a semiconductor module 2 in which a semiconductor switching element 21 is built-in.

[0080] Fig. 10 is a perspective view of a semiconductor module of Example 2, Fig. 11 is a perspective view of the inside of the semiconductor module of Example 2, Figs. 12 and 13 are top views of the inside of the semiconductor module of Example 2, and Fig. 14 is a top view of a first external terminal and a fuse of the semiconductor module of Example 2. Note that Fig. 13 illustrates the external terminals and auxiliary terminals, and the connection wiring formed integrally therewith, but these are omitted in Fig. 12.

[0081] The semiconductor module 2 has a semiconductor switching element 21, a housing 38 that incorporates the semiconductor switching element 21, a first external terminal 31, and a second external terminal 32. The first external terminal 31 is connected to a first main terminal of the semiconductor switching element 21, and the second external terminal 32 is connected to a second main terminal of the semiconductor switching element 21. Fig. 9 shows an example in which the first main terminal is the drain D of the first switching element 21a, and the second main terminal is the drain D of the second switching element 21b.

[0082] Furthermore, in the second embodiment, the fuse 25 connected in series with the semiconductor switching element 21 is also built into the housing 38 of the semiconductor module 2. The built-in fuse 25 is formed from a part of the wiring inside the housing 38, and is designed to melt when a predetermined fusing current flows.

[0083] In the second embodiment, as an example of the built-in fuse 25, as shown in Fig. 14, the fuse 25 is formed by thinning a part of the connection wiring 31a formed integrally with the first external terminal 31. This makes it possible to provide the fuse 25 between the semiconductor switching element 21 and the protected device 4 as shown in Fig. 9. Note that the method of forming the fuse 25 is not limited to this, and for example, the fuse 25 may be formed by thinning a part of the connection wiring 31a formed integrally with the first external terminal 31 or by making the part of the connection wiring 31a from a material having a lower melting point than the other parts.

[0084] 2 of the first embodiment, the first external terminal 31, the connection wiring 31a formed integrally therewith, and the auxiliary terminal for overcurrent measurement 37 (see FIG. 11, etc.) directly connected to the first external terminal 31 are collectively considered as one terminal, and this terminal corresponds to the conductor 111. The location where the fuse 25 is formed corresponds to the location X of the conductor 111 whose temperature is unknown. In FIG. 14, the connection wiring 31a above the fuse 25 corresponds to the first portion 111A, and is connected to the substrate on which the semiconductor switching element 21 is mounted. The temperature of this substrate corresponds to the substrate temperature Ta. In FIG. 14, the connection wiring 31a below the fuse 25, the first external terminal 31, and the auxiliary terminal for overcurrent measurement 37 correspond to the second portion 111B. The temperature of the connection wiring 31a, the first external terminal 31, or the auxiliary terminal for overcurrent measurement 37 below the fuse 25 in FIG. 14, which is the location on the outer side of the fuse 25 of this terminal, corresponds to the terminal temperature Tt. A thermal equivalent circuit Tmodel of this terminal is obtained in advance and stored in thermal equivalent circuit storage unit 106. Since first drain sense auxiliary terminal 35 (see FIG. 11 etc.), which will be described later, is also used for measuring the voltage by voltage detection unit 14, first drain sense auxiliary terminal 35 may also be included in conductor 111 to construct thermal equivalent circuit Tmodel; however, since no main current flows through first drain sense auxiliary terminal 35 and it is not significantly affected by temperature rise, the thermal equivalent circuit Tmodel may be constructed without including first drain sense auxiliary terminal 35 in conductor 111 to simplify calculations.

[0085] The inside of the housing 38 of the semiconductor module 2 is sealed with a gel such as silicone gel (not shown), and the fuse 25 is also sealed with the gel. This improves the dielectric strength of the fuse 25 and allows for a smaller size.

[0086] In addition, the fuse 25 has a parasitic resistance and a parasitic inductance. The wiring of the semiconductor module 2 also has a parasitic resistance and a parasitic inductance. The parasitic resistance 23 shown in FIG. 9 includes the parasitic resistance of the wiring and the parasitic resistance of the fuse 25, and the parasitic inductance 24 includes the parasitic inductance of the wiring and the parasitic inductance of the fuse 25.

[0087] Therefore, the voltage detection unit 14 of the second embodiment is configured to also utilize the parasitic resistance or parasitic inductance of the fuse 25, detect a voltage including the voltage generated across both ends of the parasitic resistance or parasitic inductance of the fuse 25, and detect an overcurrent by the overcurrent detection device 11 based on this voltage.

[0088] For this purpose, the semiconductor module 2 is configured to have a measurement terminal capable of measuring a voltage including a voltage generated across the parasitic resistance or parasitic inductance of the fuse 25, as an external terminal connected to the outside of the housing 38. In the second embodiment, the overcurrent measurement auxiliary terminal 37 and the first drain sense auxiliary terminal 35 shown in FIG. 11 can be used as the measurement terminal.

[0089] The auxiliary terminal 37 for overcurrent measurement is a terminal connected to the right side of the voltage detection unit 14 in FIG. 9, and is directly connected to the first external terminal 31 in FIG. 11. The auxiliary terminal 37 for overcurrent measurement is not limited to this, and may be directly connected to the connection wiring 31a as long as it is closer to the first external terminal 31 than the fuse 25. Although the second embodiment shows an example in which the auxiliary terminal 37 for overcurrent measurement is provided on only one of the two first external terminals 31, it may be provided on the other first external terminal 31, or on both first external terminals 31. Also, the number of first external terminals 31 may be only one.

[0090] The first drain sense auxiliary terminal 35 is a terminal connected to the left side of the voltage detection unit 14 in FIG. 9, and is connected to the first drain sense pad 45 in FIG. 13. This makes it possible to measure the potential of the drain D of the first switching element 21a. Although two first drain sense auxiliary terminals 35 are provided in the second embodiment, only one may be provided. The first drain sense auxiliary terminal 35 is larger than the other auxiliary terminals and is an external terminal having a shape similar to that of the first external terminal 31. This allows the use of parts of the AC terminal of a semiconductor module used in a power conversion device or the like. The first drain sense auxiliary terminal 35 is not limited to this, and may be a small shape similar to that of the other auxiliary terminals.

[0091] 11 to 13, the semiconductor module 2 of the second embodiment has six insulating substrates 47 on a base plate 39. A wiring layer 48 is formed on the insulating substrates 47, and a part of the wiring layer 48 functions as a pad. The insulating substrates 47 and the wiring layer 48 may be collectively called a substrate.

[0092] 12, of the three upper insulating substrates 47, the two larger ones each have a plurality of first switching elements 21a mounted thereon and are connected by a bonding material such as solder or by bonding wires 49. The remaining one is an auxiliary substrate having a gate pad 43 connected to the gate G of the first switching element 21a and a source sense pad 44 connected to the source sense of the first switching element 21a.

[0093] Similarly, two of the three lower insulating substrates 47 have a plurality of second switching elements 21b mounted thereon, and the remaining substrate is an auxiliary substrate having a gate pad 43 connected to the gate G of the second switching element 21b and a source sense pad 44 connected to the source sense of the second switching element 21b.

[0094] Here, a plurality of first switching elements 21a and second switching elements 21b are used to ensure current capacity, and a two-parallel configuration is used with a left insulating substrate 47 and a right insulating substrate 47, but the present invention is not limited to this, and a three-parallel configuration or more may be used, or one path may be used without dividing the left and right sides. Also, a configuration may be used in which a gate pad 43 and a source sense pad 44 are provided on the insulating substrate 47 on which the first switching elements 21a and the second switching elements 21b are mounted without using an auxiliary substrate. Also, the first switching elements 21a and the second switching elements 21b may be mounted on one insulating substrate 47 without dividing the insulating substrate 47 into upper and lower sides. That is, the number of insulating substrates 47 is arbitrary.

[0095] As shown in Figures 11 and 13, the semiconductor module 2 has, as external terminals, a first external terminal 31, a second external terminal 32, a gate auxiliary terminal 33, a source sense auxiliary terminal 34, a first drain sense auxiliary terminal 35, a second drain sense auxiliary terminal 36, and an auxiliary terminal 37 for overcurrent measurement.

[0096] The first external terminal 31 is connected to the first drain pad 41 and to the drain D of the first switching element 21a, through which the main current flows. The second external terminal 32 is connected to the second drain pad 42 and to the drain D of the second switching element 21b, through which the main current flows.

[0097] The right gate auxiliary terminal 33 is connected to the upper gate pad 43 and is connected to the gate G of the first switching element 21a. The left gate auxiliary terminal 33 is connected to the lower gate pad 43 and is connected to the gate G of the second switching element 21b.

[0098] The right-side source sense auxiliary terminal 34 is connected to the upper source sense pad 44 and is connected to the source sense of the first switching element 21a. The left-side source sense auxiliary terminal 34 is connected to the lower source sense pad 44 and is connected to the source sense of the second switching element 21b.

[0099] The gate auxiliary terminal 33 and the source sense auxiliary terminal 34 are connected to the control unit 12, and the semiconductor switching element 21 is driven by a control signal from the control unit 12.

[0100] The first drain sense auxiliary terminal 35 and the overcurrent measurement auxiliary terminal 37 have already been described, and therefore a description thereof will be omitted.

[0101] The second drain sense auxiliary terminal 36 is connected to the second drain sense pad 46. This makes it possible to measure the potential of the drain D of the second switching element 21b. Although only one second drain sense auxiliary terminal 36 is provided in the second embodiment, two or more may be provided.

[0102] Next, a clamp circuit according to a second embodiment will be described.

[0103] As shown in Fig. 9, in the second embodiment, the fuses 25 are connected in series. The fuses 25 have a large inductance because the current density needs to be set high so that the fuses 25 will melt when a predetermined fusing current flows. If the inductance increases due to the series connection of the fuses 25, the surge voltage will increase when the semiconductor switching element 21 is turned off, and therefore a high-voltage element is required as the semiconductor switching element 21. However, increasing the voltage resistance of the semiconductor switching element 21 increases the on-resistance of the semiconductor switching element 21, which causes a problem of increased loss.

[0104] Therefore, in the second embodiment, a clamp circuit is provided to suppress the surge voltage. By providing a clamp circuit that includes the semiconductor switching element 21 in its path but does not include the fuse 25 in its path, the influence of the inductance of the fuse 25 can be suppressed.

[0105] In the second embodiment, an example having two types of clamp circuits is shown.

[0106] The first clamp circuit is a clamp circuit configured with a path including the first switching element 21a, the Zener diode 26 connected between the gate G and drain D of the first switching element 21a, and the control unit 12. When an overcurrent is detected and the control unit 12 removes charge from the gate of the first switching element 21a to cut off the current flowing through the first switching element 21a, if a drain surge voltage is induced and a voltage exceeding the avalanche voltage is applied to the Zener diode 26, the avalanche current is charged to the gate G of the first switching element 21a, so that the switching speed is slowed down to cut off the current slowly. This makes it possible to limit the maximum voltage between the source S and drain D, and to use a semiconductor switching element 21 with a low breakdown voltage.

[0107] The Zener diode 26 connected to the first switching element 21a may be connected between the gate auxiliary terminal 33 of the first switching element 21a and the first drain sense auxiliary terminal 35. Since it is preferable that the parasitic inductance is small, a drain sense auxiliary terminal made up of a terminal smaller than the first drain sense auxiliary terminal 35 may be provided separately and the Zener diode 26 may be connected thereto.

[0108] 9, a Zener diode 26 is also provided between the gate G and drain D of the second switching element 21b on the second switching element 21b side, thereby providing a clamp circuit including the second switching element 21b in its path. The Zener diode 26 connected to the second switching element 21b may be connected between the gate auxiliary terminal 33 and the second drain sense auxiliary terminal 36 of the second switching element 21b. Although it is possible to connect the Zener diode 26 to the second external terminal 32 instead of the second drain sense auxiliary terminal 36, it is preferable to use the second drain sense auxiliary terminal 36 since it is desirable to have a smaller parasitic inductance.

[0109] Since the fuse 25 is not included in the path of the first clamp circuit, the configuration is such that there is no effect even if the inductance increases due to the series connection of the fuse 25.

[0110] The second clamp circuit is a clamp circuit configured with a path including a semiconductor switching element 21 and a varistor 13 connected to both ends of the semiconductor switching element 21. The inductance illustrated next to the varistor 13 in FIG. 9 is the parasitic inductance of this clamp circuit. For example, a metal oxide varistor (MOV) can be used for the varistor 13. When a voltage equal to or higher than a predetermined level is applied to the varistor 13, the varistor 13 undergoes an avalanche and the resistance decreases, and the current bypasses and flows to the varistor 13 side, making it possible to use a semiconductor switching element 21 with a low breakdown voltage. In addition, the first clamp circuit applies a thermal load to the semiconductor switching element 21 when the first clamp circuit is operating, so the second clamp circuit has the effect of reducing this load.

[0111] One end of the varistor 13 may be connected to the first drain sense auxiliary terminal 35, and the other end may be connected to the second drain sense auxiliary terminal 36 or the second external terminal 32. Since the second external terminal 32 has a larger current capacity than the second drain sense auxiliary terminal 36, it is preferable to connect to the second external terminal 32. Similarly, it is preferable that the first drain sense auxiliary terminal 35 has a larger current capacity than the other auxiliary terminals.

[0112] Since the fuse 25 is not included in the path of this second clamp circuit, the configuration is not affected even if the inductance increases due to the series connection of the fuse 25.

[0113] 9, the Zener diode 26 and the varistor 13 are provided outside the semiconductor module 2, but at least one of them may be built into the semiconductor module 2. Similarly, the voltage detection unit 14, the temperature detection unit 15, the overcurrent detection device 11, and the control unit 12 may be built into the semiconductor module 2 in part or in whole.

[0114] As described above, according to the second embodiment, in addition to the effects of the first embodiment, it is possible to realize a semiconductor DC circuit breaker 1 having redundancy capable of cutting off current even if the semiconductor switching element 21 for cutting off current when an overcurrent is detected fails, and a semiconductor module 2 suitable for use therewith. EXAMPLES

[0115] Example 3 is a modification of Example 2. Example 3 differs from Example 2 in the method of realizing fuse 25. Other than this, Example 3 is the same as Example 2, so the following description will focus on the differences and omit redundant description.

[0116] Fig. 15 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module of Example 3, Fig. 16 is a perspective view of the inside of the semiconductor module of Example 3, and Fig. 17 is a top view of the inside of the semiconductor module of Example 3. Fig. 15 corresponds to Fig. 9, Fig. 16 corresponds to Fig. 11, and Fig. 17 corresponds to Fig. 12.

[0117] In the semiconductor DC circuit breaker 1 and the semiconductor module 2 of the third embodiment, the fuse 25 is formed between the source S which is the reference potential terminal of the first switching element 21a and the source S which is the reference potential terminal of the second switching element 21b. Even in this case, the current path is in series, so the fuse 25 and the semiconductor switching element 21 are considered to be connected in series.

[0118] In the third embodiment, the built-in fuse 25 is formed of a part of the wiring inside the housing 38, and is the same as in the second embodiment in that it melts when a predetermined melting current flows, but as shown in Fig. 17, the number of bonding wires 49 connecting the insulating substrate 47 on which the first switching element 21a is mounted and the insulating substrate 47 on which the second switching element 21b is mounted is reduced compared to Fig. 12, and this allows it to function as the fuse 25. Therefore, there is an advantage that it is easier to realize than in the second embodiment. The fuse 25 in the third embodiment can also be sealed with gel.

[0119] However, in Example 3, in a location where fuse 25 is not formed, a terminal connected to semiconductor switching element 21 and through which the main current of semiconductor switching element 21 flows is made to correspond to conductor 111 in Example 1, and the voltage is measured by voltage detection unit 14, and the parasitic resistance and parasitic inductance 24 do not include the parasitic resistance and parasitic inductance of fuse 25, so that Example 2 has a higher sensitivity for detecting overcurrent. Also, Example 3 is the same as Example 2 in that fuse 25 is not included in the path of the first clamp circuit, and therefore the same effect can be obtained, but since fuse 25 is included in the path of the second clamp circuit, Example 3 differs from Example 2 in that the second clamp circuit is affected by the increased inductance caused by connecting fuse 25 in series.

[0120] As for the correspondence with the first embodiment, as in the second embodiment, the first external terminal 31, the connection wiring 31a formed integrally therewith, and the auxiliary terminal for overcurrent measurement 37 (see FIG. 16) directly connected to the first external terminal 31 are collectively considered as one terminal, and this terminal corresponds to the conductor 111. However, the fuse 25 is not formed in this terminal. However, since this terminal has a complicated shape, there is a part that becomes hotter than the terminal temperature Tt that can be measured by the main current flowing therethrough. Therefore, this hot part can be set as a part X in the conductor 111 whose temperature is unknown, and a thermal equivalent circuit Tmodel of this terminal can be constructed. EXAMPLES

[0121] Example 4 is a modified example of Example 3. Example 4 is different from Example 3 in the position where the voltage is measured by the voltage detection unit 14 and the position where the temperature is measured by the temperature detection unit 15. Other than this, Example 4 is the same as Example 3, so the differences will be mainly described and overlapping descriptions will be omitted.

[0122] Fig. 18 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to Example 4. Fig. 18 is a diagram corresponding to Fig. 15.

[0123] In the semiconductor DC circuit breaker 1 of this embodiment, the voltage at the location where the fuse 25 is formed, i.e., the voltage between the source S of the first switching element 21a and the source S of the second switching element 21b, is measured by the voltage detection unit 14 using two source sense auxiliary terminals 34.

[0124] In terms of correspondence with the first embodiment, the conductor 111 corresponds to the fuse 25 formed of a part of the wiring connected to the semiconductor switching element 21. The point X in the conductor 111 where the temperature is unknown may be set to a part of the fuse 25, for example, the midpoint that is the farthest point from the substrate of the wiring constituting the fuse 25. Since no main current flows through the source sense auxiliary terminal 34, in order to simplify calculations, the source sense auxiliary terminal 34 does not need to be included in the conductor 111. Moreover, as the known temperature of at least one point of the conductor 111, the substrate temperature Ta may be used for both of them instead of the terminal temperature Tt in FIG. 2.

[0125] According to this embodiment, the current flowing through the fuse 25 can be estimated more accurately than in the third embodiment. EXAMPLES

[0126] Example 5 is a modification of Example 2 and Example 3. Example 5 differs from Examples 2 and 3 in that fuse 25 is provided outside semiconductor module 2. Other than this, Example 5 is the same as Example 2 and Example 3, so the following description will focus on the differences and omit redundant description.

[0127] Fig. 19 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a fifth embodiment of the present invention. Fig. 19 corresponds to Fig. 9 .

[0128] In the semiconductor DC breaker 1 and the semiconductor module 2 of the fifth embodiment, the fuse 25 is provided outside the semiconductor module 2. Therefore, a general fuse 25 can be used.

[0129] The correspondence with the first embodiment is the same as that with the third embodiment. EXAMPLES

[0130] Example 6 is a modified example of Example 5. Example 5 is different from Example 5 in the detection method by the voltage detection unit 14 and the temperature detection unit 15. Since the rest is the same as Example 5, the following description will focus on the differences and omit redundant description.

[0131] Fig. 20 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a sixth embodiment of the present invention. Fig. 20 corresponds to Fig. 19 .

[0132] In the semiconductor DC circuit breaker 1 and the semiconductor module 2 of the sixth embodiment, the fuse 25 is provided outside the semiconductor module 2, similarly to the fifth embodiment. Therefore, a general fuse 25 can be used.

[0133] Then, the voltage detection unit 14 detects a voltage including the voltage generated across the parasitic resistance or parasitic inductance of the fuse 25, and the overcurrent detection device 11 detects an overcurrent based on this voltage.

[0134] In terms of correspondence with the first embodiment, fuse 25 corresponds to conductor 111. A part of fuse 25, for example a part where the temperature is highest, is set as part X of conductor 111 where the temperature is unknown. In addition, as the known temperature of at least one part of conductor 111, the temperature of fuse 25 or a part around it where the temperature can be measured may be measured by temperature detection unit 15 and used. EXAMPLES

[0135] Example 7 is a modification of Example 5. Example 7 differs from Example 5 in that it does not include the fuse 25. Other than this, Example 7 is the same as Example 5, so the following description will focus on the differences and omit redundant description.

[0136] Fig. 21 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to Example 7. Fig. 21 is a diagram corresponding to Fig. 19.

[0137] In this embodiment, the overcurrent detection device 11 of the first embodiment is applied to a general semiconductor DC circuit breaker 1 in which the fuse 25 is not provided.

[0138] The correspondence with the first embodiment is the same as that with the fifth embodiment. EXAMPLES

[0139] The eighth embodiment is an embodiment of a power conversion device 200 using the overcurrent detection device 11 of the first embodiment.

[0140] FIG. 22 is a functional block diagram of a power conversion device according to an eighth embodiment.

[0141] The power conversion device 200 of the eighth embodiment includes the overcurrent detection device 11 of the first embodiment, a power conversion circuit 201 configured using a semiconductor switching element, and a protection circuit 202 that controls to protect the semiconductor switching element when the overcurrent determination unit 102 of the overcurrent detection device 11 determines that an overcurrent exists.

[0142] In order to correspond to the first embodiment, a terminal connected to a semiconductor switching element of the power conversion circuit 201 and through which a main current of this semiconductor switching element flows may be made to correspond to the conductor 111 .

[0143] The power conversion circuit 201 and the protection circuit 202 may have a generally known configuration.

[0144] The semiconductor module used in the power conversion circuit 201 corresponds to that in which the second switching element 21b and the first switching element 21a are oriented in the same direction as in Fig. 21 of the seventh embodiment. Also, an AC terminal is drawn out as an external terminal from a connection node between the source S of the first switching element 21a and the train D of the second switching element 21b.

[0145] The detection methods by the voltage detection unit 14 and the temperature detection unit 15 are the same as those in the seventh embodiment.

[0146] Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible within the scope of the technical concept of the present invention. In addition, some or all of the configurations described in each embodiment may be combined and applied.

[0147] Moreover, the overcurrent detection device 11 and the overcurrent detection method of the first embodiment are not limited to being applied to the semiconductor DC circuit breaker 1 and the power conversion device 200, but may be applied to other devices. [Explanation of symbols]

[0148] 1. Semiconductor DC circuit breaker 2. Semiconductor Module 3 Power supply 4. Protected Equipment 11. Overcurrent detection device 12 Control section 13. Barista 14 Voltage detection section 15 Temperature detection section 21 Semiconductor switching element 21a First switching element 21b Second switching element 22 Diode 23 Parasitic resistance 24 Parasitic inductance 25. Fuse 26 Zener Diode 31 First external terminal 31a Connection wiring 32 Second external terminal 33 Gate auxiliary terminal 34 Source sense auxiliary terminal 35 1st drain sense auxiliary terminal 36 Second drain sense auxiliary terminal 37 Auxiliary terminal for overcurrent measurement 38 Case 39 Base Plate 41 First drain pad 42 Second drain pad 43 Gate Pad 44 Source Sense Pad 45 1st Drain Sense Pad 46 2nd Drain Sense Pad 47 Insulating Substrate 48 wiring layer 49 Bonding Wire 101 Instantaneous current estimation section 102 Overcurrent judgment section 103 Power consumption calculation section 104 Temperature estimation section 105 Resistance estimation section 106 Thermal equivalent circuit storage section 107 Overcurrent detection signal 111 Conductor 111A Part 1 111B 2nd part 111B1 3rd part 111B2 Part 4 112 Heat radiation direction 121 RC not considered 122 R consideration 123 RC consideration 200 Power conversion device 201 Power Conversion Circuit 202 Protection circuit G Gate S Source D Drain V Instantaneous voltage X: Temperature unknown R Estimated resistance I Estimated instantaneous current P Power consumption Tmodel thermal equivalent circuit Rth thermal resistance Cth heat capacity T temperature Ta Substrate temperature Tt terminal temperature ILIM Threshold τ Thermal time constant t time

Claims

1. an instantaneous current estimating unit that estimates an estimated instantaneous current I at a point X in the conductor whose temperature is unknown, based on an instantaneous voltage V measured at a predetermined measurement point on the conductor and an estimated resistance R at the point X in the conductor whose temperature is unknown; an overcurrent determination unit that determines whether an overcurrent occurs based on the estimated instantaneous current I; a power consumption calculation unit that calculates a power consumption P based on the instantaneous voltage V and the estimated instantaneous current I; a temperature estimating unit that estimates and updates a temperature T of a location X of the conductor, the location X being an unknown temperature, based on a thermal equivalent circuit that takes into account at least a thermal resistance and a thermal capacity of the conductor, the power consumption P, and a known temperature of at least one location of the conductor; and a resistance estimating unit that updates the estimated resistance R of a location X in the conductor whose temperature is unknown, based on the temperature T updated by the temperature estimating unit.

2. In claim 1, The overcurrent detection device, wherein the temperature estimation unit estimates the temperature T by assuming that an initial value of the temperature T is equal to an initial value of a known temperature of at least one point of the conductor.

3. The overcurrent detection device according to claim 1 , A semiconductor switching element; a control unit that controls the semiconductor switching element to cut off a main current flowing through the semiconductor switching element when the overcurrent determination unit determines that an overcurrent has occurred.

4. In claim 3, a fuse connected in series to the semiconductor switching element; The semiconductor DC circuit breaker, wherein the overcurrent determination unit determines that an overcurrent has occurred when the estimated instantaneous current I is equal to or greater than a predetermined threshold value that is smaller than a melting current of the fuse.

5. In claim 4, the conductor is a terminal connected to the semiconductor switching element and through which the main current flows; The terminal has a fuse formed in a part thereof, the fuse being melted when the fusing current flows, The semiconductor DC circuit breaker is characterized in that the location X of the conductor whose temperature is unknown is a location where the fuse is formed.

6. In claim 5, The semiconductor DC circuit breaker, wherein the known temperature of at least one point of the conductor includes a temperature of a substrate on which the semiconductor switching element is mounted and a temperature of a point of the terminal that is external to the fuse.

7. In claim 4, the conductor is the fuse; the fuse is formed of a part of a wiring connected to the semiconductor switching element, A semiconductor DC circuit breaker, wherein the location X of the conductor whose temperature is unknown is a part of the fuse.

8. In claim 7, 13. A semiconductor DC circuit breaker, wherein the known temperature of at least one point of the conductor includes a temperature of a substrate on which the semiconductor switching element is mounted.

9. In claim 4, The semiconductor DC circuit breaker is characterized in that the conductor is a terminal connected to the semiconductor switching element and through which the main current flows.

10. In claim 3, The semiconductor DC circuit breaker is characterized in that the conductor is a terminal connected to the semiconductor switching element and through which the main current flows.

11. The overcurrent detection device according to claim 1 , A power conversion circuit configured using semiconductor switching elements; a protection circuit that performs control to protect the semiconductor switching element when the overcurrent determination unit determines that an overcurrent occurs.

12. In claim 11, The power conversion device according to claim 1, wherein the conductor is a terminal connected to the semiconductor switching element and through which a main current of the semiconductor switching element flows.

13. an instantaneous current estimating step of estimating an estimated instantaneous current I at a point X in the conductor whose temperature is unknown, based on an instantaneous voltage V measured at a predetermined measurement point of the conductor and an estimated resistance R at the point X in the conductor whose temperature is unknown; an overcurrent determination step of determining whether an overcurrent exists based on the estimated instantaneous current I; a power consumption calculation step of calculating a power consumption P based on the instantaneous voltage V and the estimated instantaneous current I; a temperature estimation step of estimating and updating a temperature T of a point X of the conductor, the temperature of which is unknown, based on a thermal equivalent circuit that takes into account at least a thermal resistance and a heat capacity of the conductor, the power consumption P, and a known temperature of at least one point of the conductor; and a resistance estimation step of updating the estimated resistance R of a point X in the conductor whose temperature is unknown, based on the temperature T updated in the temperature estimation step.

14. In claim 13, The overcurrent detection method, wherein the temperature estimation step estimates the temperature T by assuming that an initial value of the temperature T is equal to an initial value of a known temperature at least at one point of the conductor.

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