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

Abstract

The present invention provides 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.　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 an overcurrent 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, Tt at at least 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 capacity Rth of the conductor 111; and a resistance estimation unit 105 that updates the estimated resistance R at the site X of unknown temperature on the basis of the updated temperature T.

Description

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

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

[0002] When an overcurrent occurs, the overcurrent is detected by an overcurrent detection device, and the semiconductor switching element of the semiconductor DC circuit breaker is controlled to cut off the current, or the semiconductor switching element used in the power conversion device is controlled to protect it.

[0003] A technology for measuring current is disclosed, for example, in Patent Document 1. In FIG. 5 and paragraph 0048 of Patent Document 1, a technology is described in which a voltage V1(T) that depends on temperature T and a voltage V2(I, T) that depends on current I and temperature T are measured, and the current I is calculated based on the measured voltages V1 and V2.

[0004] Japanese Patent Application Laid-Open No. 2007-187667

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

[0006] For example, when a large current flows instantaneously, a temperature may rise in a location different from the location where the temperature T can be accurately determined. Because the characteristics of current, voltage, and resistance are temperature-dependent, if there are locations where the temperature is unknown, an error will occur even if the current is calculated based on the measured voltage, resulting in a problem of reduced accuracy in overcurrent detection.

[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 where the 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.

[0008] In order to solve the above-mentioned problems, the overcurrent detection device / method of the present invention is characterized by comprising: an instantaneous current estimation unit / step that estimates an estimated instantaneous current I at a location X in the conductor whose temperature is unknown based on an instantaneous voltage V measured at a predetermined measurement location on the conductor and an estimated resistance R at the location X in 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 at the location X in the conductor whose temperature is unknown based on the power consumption P and a known temperature at at least one location on the conductor; and a resistance estimation unit / step that updates the estimated resistance R at the location X in the conductor whose temperature is unknown based on the temperature T updated by the temperature estimation unit / step.

[0009] Furthermore, the semiconductor DC circuit breaker of the present invention comprises the above-mentioned overcurrent detection device, a semiconductor switching element, and a control unit that controls the semiconductor switching element to cut off the 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 includes the above-mentioned overcurrent detection device, a power conversion circuit configured 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.

[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 where the temperature is unknown, for example, due to a large current flowing instantaneously, and a semiconductor DC circuit breaker and a power conversion device that use the same.

[0012] 1 is a functional block diagram of an overcurrent detection device according to a first embodiment. FIG. 2 is a top view illustrating an example of a conductor shape. FIG. 3 is a thermal equivalent circuit corresponding to FIG. 2 . FIG. 4 is a top view illustrating another example of a conductor shape. FIG. 5 is a thermal equivalent circuit corresponding to FIG. 4 . FIG. 6 is a diagram illustrating a thermal time constant. FIG. 7 is a diagram illustrating conditions for a simulation for illustrating the effects of the first embodiment. FIG. 8 is a diagram illustrating the results of a simulation for illustrating the effects of the first embodiment. FIG. 9 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a second embodiment. FIG. 10 is a perspective view of a semiconductor module according to a second embodiment. FIG. 11 is a perspective view of the interior of the semiconductor module according to the second embodiment. FIG. 12 is a top view of the interior of the semiconductor module according to the second embodiment. FIG. 13 is a top view of a first external terminal and a fuse of the semiconductor module according to the second embodiment. FIG. 14 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a third embodiment. FIG. 15 is a perspective view of the interior of the semiconductor module according to the third embodiment. FIG. 16 is a top view of the interior of the semiconductor module according to the third embodiment. 10 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to a seventh embodiment. FIG. 11 is a functional block diagram of a power conversion device according to an eighth embodiment.

[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 redundant explanations will be omitted.

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

[0015] The overcurrent detection device 11 of Example 1 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., substrate temperature Ta and terminal temperature Tt) at at least one point on the conductor 111. 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 known temperature, the device estimates an estimated instantaneous current I at a point X on the conductor 111 whose temperature is unknown, determines whether an overcurrent exists based on the estimated instantaneous current I, and outputs an overcurrent detection signal 107 if it determines that an overcurrent exists.

[0016] Specifically, the overcurrent detection device 11 of this embodiment has the following 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 the instantaneous current estimation step, the instantaneous current estimation unit 101 estimates an estimated instantaneous current I at the point X in the conductor 111 whose temperature is unknown, based on an instantaneous voltage V measured at a predetermined measurement point in 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 the overcurrent determination step, the overcurrent determination unit 102 determines whether an overcurrent exists based on the estimated instantaneous current I. The determination of whether an overcurrent exists can be made, for example, by using the equation "I≧ILIM" which determines whether the estimated instantaneous current I is equal to or greater than a threshold value ILIM. If this equation is satisfied, the overcurrent determination unit 102 determines that an overcurrent exists and outputs an 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 the formula "T = f(Tmodel, P, Ta, Tt)," for example. Details of the thermal equivalent circuit Tmodel and a method for estimating the temperature T will be described later.

[0022] In the 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, overcurrent determination step, power consumption calculation step, temperature estimation step, and resistance estimation step are repeatedly executed at predetermined intervals. The estimated resistance R updated in the resistance estimation step is used in the next instantaneous current estimation step.

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

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

[0026] 2, the conductor 111 to be measured includes a first portion 111A, a second portion 111B, and a portion X between the first portion 111A and the second portion 111B, the temperature of which is unknown. Here, we will assume 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. The temperature of the first portion 111A is assumed to be equal to the substrate temperature Ta. The substrate temperature Ta can be measured, for example, by a thermistor or a thermocouple provided on the substrate, and is assumed to be 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, for example, 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 unknown temperature portion X has a smaller width than the first portion 111A and the second portion 111B. Therefore, if a large current flows instantaneously, the temperature T of this portion is assumed to be higher than the known temperatures of the first portion 111A and the second portion 111B. Therefore, the heat dissipation direction 112 of the first portion 111A and the second portion 111B is the direction shown in FIG. 2 .

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

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

[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 capacitance Cth1 are connected in parallel in the first portion 111A, a thermal resistance Rth2 and a thermal capacitance 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 can be calculated as l / λA and the heat capacity Cth2 as cdAl. The thermal resistance Rth1 and the heat capacity Cth1 of the first portion 111A can be calculated in a similar manner.

[0034] In the thermal equivalent circuit Tmodel, power consumption P corresponds to current, temperature T corresponds to voltage, and loss, which is the integral of power consumption P, corresponds to charge, which is the integral of current. Therefore, for 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 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]

[0036]

[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 11, and a fourth portion 111B2 having a cross-sectional area A2 and a length 12, the thermal equivalent circuit Tmodel of the second portion 111B can be expressed using the thermal resistance Rth21 and the thermal capacitance Cth21 of the third portion 111B1 and the thermal resistance Rth22 and the thermal capacitance Cth22 of the fourth portion 111B2, as shown in Fig. 5. Here, the example is described in which the second portion 111B of the conductor 111 is divided into two stages, but the thermal equivalent circuit Tmodel can also be expressed in the case where it is divided into three or more stages by expanding the same concept.

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

[0040] 6 is a diagram illustrating the thermal time constant, in which the horizontal axis represents time t and the vertical axis represents 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 that the temperature changes from an initial temperature Tt0 to a steady-state temperature Tt', as shown in Figure 6. In this case, the thermal time constant τ is defined as the time required for a 63.2% change when the temperature rises 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 Figure 3, the thermal resistance Rth2 = Tt' / I'V' and the thermal capacitance Cth2 = τ / Rth2.

[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 unit 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, the explanation will be given assuming that the conductor 111 has the shape shown in Fig. 2 and that the thermal equivalent circuit Tmodel shown in Fig. 3 holds. In this case, the above-mentioned formulas (1) and (2) hold. The integral equation of formula (2) will be 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]

[0048] The history of temperature T, T(t), is calculated from this initial value, the history of power consumption 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]

[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]

[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]

[0055]

[0056] Since equation (1) is also valid for the updated value in this process, equation (1) can be rewritten so that the superscript becomes n+1, equation (7) is substituted, and rearranged to obtain the following equation (8).

[0057]

[0058] When equation (8) is solved for ΔT, the following equation (9) is obtained.

[0059]

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

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

[0062]

[0063] By performing the above-described 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 represents time t, the vertical axis in Fig. 7 represents current, and the vertical axis in Fig. 8 represents estimated instantaneous current I.

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

[0067] As shown in Fig. 8, the graph 121 without RC consideration in Comparative Example 1 is larger than the current shown in Fig. 7, resulting in an overestimation of the estimated instantaneous current I. Also, the graph 122 with RC consideration in Comparative Example 2 is smaller than the current shown in Fig. 7, resulting in an underestimation of the estimated instantaneous current I. On the other hand, the graph 123 with RC consideration in accordance with the method of this embodiment is closer to the current shown in Fig. 7, confirming that the accuracy of current estimation 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 overcurrent with high accuracy, even in cases where there are locations where the temperature is unknown due to, for example, a sudden flow of a large current.

[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 a power source 3 and a protected device 4, and cuts off the current when an overcurrent is detected. 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 with the semiconductor switching element 21, a voltage detection unit 14 that detects a voltage at a predetermined measurement point, a temperature detection unit 15 that detects a 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 in the first embodiment), and a temperature detected by the temperature detection unit 15 (corresponding to the substrate temperature Ta and terminal temperature Tt in 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 embodiment 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 fusing current of the fuse 25. Specifically, the semiconductor DC circuit breaker 1 has a fuse 25 connected in series with 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 fusing current of the fuse 25. The fusing 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 fails due to cosmic rays or the like, the current can be cut off by melting the fuse 25 connected in series. In other words, there is redundancy that allows the current to be cut off even if the semiconductor switching element 21 that is supposed to cut off the current when an overcurrent is detected fails.

[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 of 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 temperatures of at least one location of the conductor 111 include 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. Note that 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 21 a and the second switching element 21 b, but this is not limiting, 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 that incorporates a semiconductor switching element 21 .

[0080] Fig. 10 is a perspective view of a semiconductor module of Example 2, Fig. 11 is a perspective view of the interior of the semiconductor module of Example 2, Figs. 12 and 13 are top views of the interior 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 houses 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. In Fig. 9, an example is shown 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 blow 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 portion of the connection wiring 31a formed integrally with the first external terminal 31. This allows the fuse 25 to be provided 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 the fuse 25 may be formed, for example, by thinning a portion of the connection wiring 31a formed integrally with the first external terminal 31, or by making the portion of the connection wiring 31a from a material with a lower melting point than the other portions.

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

[0085] The interior 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, which improves the dielectric strength of the fuse 25 and allows it to be made smaller.

[0086] The fuse 25 also has parasitic resistance and parasitic inductance. The wiring of the semiconductor module 2 also has parasitic resistance and parasitic inductance. The parasitic resistance 23 shown in Figure 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 Example 2 also utilizes the parasitic resistance or parasitic inductance of the fuse 25, detects a voltage including the voltage generated across both ends of the parasitic resistance or parasitic inductance of the fuse 25, and detects an overcurrent using the overcurrent detection device 11 based on this voltage.

[0088] For this reason, the semiconductor module 2 is configured to have a measurement terminal, as an external terminal connected to the outside of the housing 38, capable of measuring a voltage including a voltage generated across the parasitic resistance or parasitic inductance of the fuse 25. 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 . However, the auxiliary terminal 37 for overcurrent measurement is not limited to this, and may be directly connected to the connection wiring 31 a 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 limited to 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 with a shape similar to that of the first external terminal 31. This allows the use of AC terminal components of semiconductor modules used in power conversion devices, etc. The first drain sense auxiliary terminal 35 is not limited to this, and may have 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. Wiring layers 48 are formed on the insulating substrates 47, some of which function as pads. The insulating substrates 47 and the wiring layers 48 are sometimes collectively referred to as a substrate.

[0092] 12, of the three upper insulating substrates 47, 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, of the three lower insulating substrates 47, two larger ones each have a plurality of second switching elements 21b mounted thereon, and the remaining one 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. However, this is not limited to this, and a three-parallel configuration or more may be used, or a single path may be used without dividing the elements into left and right. Furthermore, a configuration may be adopted in which the gate pad 43 and the 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. Furthermore, the first switching elements 21a and the second switching elements 21b may be mounted on a single insulating substrate 47 without dividing them into upper and lower substrates. In other words, 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 overcurrent measurement auxiliary terminal 37.

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

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

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

[0099] The auxiliary gate terminal 33 and the auxiliary source sense 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 auxiliary drain sense 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 auxiliary drain sense 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 Figure 9, in Example 2, fuses 25 are connected in series. The fuses 25 have a large inductance because they must be set to a high current density so that they will blow when a predetermined fusing current flows. If the inductance increases due to the series connection of fuses 25, the surge voltage increases when the semiconductor switching element 21 is turned off, so the semiconductor switching element 21 must have a high withstand voltage. However, increasing the withstand voltage of the semiconductor switching element 21 increases the on-resistance of the semiconductor switching element 21, which results in a problem of increased loss.

[0104] Therefore, in Example 2, a clamp circuit is provided to suppress the surge voltage. By providing a clamp circuit that includes semiconductor switching element 21 in its path but does not include fuse 25 in its path, the influence of the inductance of 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, a 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, a drain surge voltage is induced and a voltage exceeding the avalanche voltage is applied to the Zener diode 26. This causes the avalanche current to charge the gate G of the first switching element 21a, slowing down the switching speed and enabling the current to be cut off slowly. This makes it possible to limit the maximum voltage between the source S and drain D, allowing the use of 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 desirable to have a small parasitic inductance, a drain sense auxiliary terminal having a terminal smaller than the first drain sense auxiliary terminal 35 may be provided separately and connected thereto.

[0108] 9, a Zener diode 26 is also provided on the second switching element 21b side between the gate G and drain D of the second switching element 21b, thereby providing a clamp circuit that includes 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, the second drain sense auxiliary terminal 36 is more preferable because smaller parasitic inductance is more desirable.

[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 shown 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 above a certain level is applied, the varistor 13 avalanches, lowering its resistance and allowing current to bypass and flow to the varistor 13 side, making it possible to use a semiconductor switching element 21 with a low breakdown voltage. Furthermore, since the first clamp circuit imposes a thermal load on the semiconductor switching element 21 when it is operating, this second clamp circuit also has the effect of reducing this load.

[0111] One end of the varistor 13 may be connected to the first auxiliary drain sense terminal 35, and the other end may be connected to either the second auxiliary drain sense terminal 36 or the second external terminal 32. Since the second external terminal 32 has a larger current capacity than the second auxiliary drain sense terminal 36, it is preferable to connect it to the second external terminal 32. Similarly, it is preferable that the first auxiliary drain sense 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 such that there is no effect 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 configured to be provided outside the semiconductor module 2, but at least one of them may be built into the semiconductor module 2. Similarly, some or all of the voltage detection unit 14, temperature detection unit 15, overcurrent detection device 11, and control unit 12 may also be built into the semiconductor module 2.

[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 that allows current to be interrupted even if the semiconductor switching element 21 for interrupting current when an overcurrent is detected fails, and a semiconductor module 2 suitable for use therewith.

[0115] The third embodiment is a modification of the second embodiment. The third embodiment differs from the second embodiment in the method of realizing the fuse 25. Since the third embodiment is otherwise the same as the second embodiment, 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 according to a third embodiment, Fig. 16 is a perspective view of the inside of the semiconductor module according to the third embodiment, and Fig. 17 is a top view of the inside of the semiconductor module according to the third embodiment. 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 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 21 a, and the source S, which is the reference potential terminal of the second switching element 21 b. Even in this case, the fuse 25 and the semiconductor switching element 21 are considered to be connected in series because the current path is in series.

[0118] In the third embodiment, the built-in fuse 25 is formed from part of the wiring inside the housing 38, and is similar to the second embodiment in that it melts when a predetermined melting current flows. However, 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, thereby allowing the fuse 25 to function. Therefore, there is an advantage that it is easier to implement than 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 voltage is measured by voltage detection unit 14, and the parasitic resistance and parasitic inductance of fuse 25 are not included in parasitic resistance 23 and parasitic inductance 24, so the sensitivity for detecting overcurrent is higher in Example 2. 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, it differs from Example 2 in that the second clamp circuit is affected by an increase in inductance due to the series connection of fuse 25.

[0120] In relation to Example 1, as in Example 2, 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, because this terminal has a complex shape, there is a portion that becomes higher in temperature than the terminal temperature Tt that can be measured when a main current flows through it. Therefore, this high-temperature portion can be set as a location X in the conductor 111 whose temperature is unknown, and a thermal equivalent circuit Tmodel for this terminal can be constructed.

[0121] Example 4 is a modification of Example 3. Example 4 differs 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] 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.

[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 correspondence with the first embodiment, the conductor 111 corresponds to the fuse 25 formed of a portion 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 portion of the fuse 25, for example, the midpoint of the wiring constituting the fuse 25 that is the farthest from the substrate. Because no main current flows through the auxiliary source sense terminal 34, for the sake of simplifying calculations, the auxiliary source sense terminal 34 does not need to be included in the conductor 111. Furthermore, as the known temperature of at least one point on the conductor 111, the substrate temperature Ta may be used in place 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.

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

[0127] 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 is a diagram corresponding to FIG.

[0128] In the semiconductor DC circuit 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 of the third embodiment.

[0130] Example 6 is a modification of Example 5. Example 5 differs from Example 5 in the detection methods by the voltage detection unit 14 and the temperature detection unit 15. Other than this, Example 6 is the same as Example 5, so the differences will be mainly described and overlapping descriptions will be omitted.

[0131] 20 is a circuit diagram of a semiconductor DC circuit breaker and a semiconductor module according to Example 6. FIG. 20 is a diagram corresponding to FIG.

[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 correspondence with the first embodiment, fuse 25 corresponds to conductor 111. Location X of conductor 111 where the temperature is unknown is set to a part of fuse 25, for example, the location where the temperature is highest. Furthermore, the known temperature of at least one location of conductor 111 may be the temperature of fuse 25 or a location around it where the temperature can be measured, measured by temperature detection unit 15, and used.

[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 differences will be mainly described and overlapping descriptions will be omitted.

[0136] 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.

[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 of the fifth embodiment.

[0139] The eighth embodiment is an example 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 Example 8 includes the overcurrent detection device 11 of Example 1, 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, the terminal connected to the semiconductor switching element of the power conversion circuit 201 and through which the 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 orientation of the second switching element 21b is the same as that of the first switching element 21a in Fig. 21 of Example 7. In addition, an AC terminal is drawn as an external terminal from the connection node between the source S of the first switching element 21a and the drain 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 the semiconductor DC circuit breaker 1 and the power conversion device 200, and may be applied to other devices.

[0148] REFERENCE SIGNS LIST 1 semiconductor DC circuit breaker 2 semiconductor module 3 power supply 4 equipment to be protected 11 overcurrent detection device 12 control unit 13 varistor 14 voltage detection unit 15 temperature detection unit 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 first drain sense auxiliary terminal 36 second drain sense auxiliary terminal 37 overcurrent measurement auxiliary terminal 38 housing 39 base plate 41 first drain pad 42 second drain pad 43 gate pad 44 source sense pad 45 first drain sense pad 46 second drain sense pad 47 insulating substrate 48 Wiring layer 49 Bonding wire 101 Instantaneous current estimation unit 102 Overcurrent determination unit 103 Power consumption calculation unit 104 Temperature estimation unit 105 Resistance estimation unit 106 Thermal equivalent circuit storage unit 107 Overcurrent detection signal 111 Conductor 111A First part 111B Second part 111B1 Third part 111B2 Fourth part 112 Heat dissipation direction 121 No RC consideration 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 Part where temperature is 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 overcurrent detection device comprising: an instantaneous current estimation unit that estimates an estimated instantaneous current I at a location X in the conductor whose temperature is unknown based on an instantaneous voltage V measured at a specified measurement location on the conductor and an estimated resistance R at the location X in the conductor whose temperature is unknown; an overcurrent determination unit that determines whether there is an overcurrent based on the estimated instantaneous current I; a power consumption calculation unit that calculates 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 that estimates and updates a temperature T at the location X in the conductor whose temperature is unknown based on the power consumption P and a known temperature of at least one location on the conductor; and a resistance estimation unit that updates the estimated resistance R at the location X in the conductor whose temperature is unknown based on the temperature T updated by the temperature estimation unit.

2. An overcurrent detection device according to claim 1, 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. A semiconductor DC circuit breaker comprising: the overcurrent detection device according to claim 1; a semiconductor switching element; and a control unit which 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.

4. A semiconductor DC circuit breaker according to claim 3, further comprising a fuse connected in series with the semiconductor switching element, and 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 which is smaller than the melting current of the fuse.

5. A semiconductor DC circuit breaker according to claim 4, wherein the conductor is a terminal connected to the semiconductor switching element and through which the main current flows, the terminal has formed therein the fuse which melts when the fusing current flows, and location X of the conductor where the temperature is unknown is the location where the fuse is formed.

6. A semiconductor DC circuit breaker according to claim 5, characterized in that the known temperature of at least one location of the conductor includes the temperature of a substrate on which the semiconductor switching element is mounted and the temperature of a location of the terminal on the outer side of the fuse.

7. A semiconductor DC circuit breaker according to claim 4, wherein the conductor is the fuse, the fuse is formed from a portion of wiring connected to the semiconductor switching element, and the location X in the conductor whose temperature is unknown is a location that is a portion of the fuse.

8. A semiconductor DC circuit breaker according to claim 7, characterized in that the known temperature of at least one point of the conductor includes the temperature of a substrate on which the semiconductor switching element is mounted.

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

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

11. A power conversion device comprising: the overcurrent detection device according to claim 1; 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.

12. A power conversion device according to claim 11, 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 overcurrent detection method comprising: an instantaneous current estimation step of estimating an estimated instantaneous current I at a location X in the conductor whose temperature is unknown based on an instantaneous voltage V measured at a predetermined measurement location on the conductor and an estimated resistance R at the location X in the conductor whose temperature is unknown; an overcurrent determination step of determining whether or not there is an overcurrent based on the estimated instantaneous current I; a power consumption calculation step of calculating 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 at the location X in the conductor whose temperature is unknown based on a thermal equivalent circuit that takes into account at least the thermal resistance and heat capacity of the conductor, the power consumption P, and a known temperature of at least one location on the conductor; and a resistance estimation step of updating the estimated resistance R at the location X in the conductor whose temperature is unknown based on the temperature T updated in the temperature estimation step.

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

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