Inrush current limiting circuit

Abstract

Inrush current limiting circuit (2, 3), comprising: a first connecting line (L1) that connects a positive terminal of a battery (B) and an electrical consumer; a second connecting cable (L2) that connects a negative terminal of the battery (B) and the electrical consumer; a switch (SW) which is provided in a first line of the first and second connection lines (L1,L2); a voltage sensor (13); and a current limiting circuit (10) provided in a second line of the first and second connecting lines (L1,L2); wherein the current limiting circuit (10) comprises: a current sensor (11) provided in the second line; and a switching element (Q) provided in the second line; wherein the voltage sensor (13) detects a voltage difference between the ends of the switching element (Q); an operational amplifier (OP) which receives a signal at an inverting input terminal in accordance with a detection value obtained by the current sensor (11) and receives a current command value at a non-inverting input terminal; wherein the switching element (Q) provided in the second line receives an output signal from the operational amplifier (OP) at a control terminal and performs a switching operation in accordance with the output signal; characterized by the fact that the inrush current limiting circuit (2, 3) further comprises: a capacitor (C) with a first electrode connected to the first terminal (L1) and a second electrode connected to the second terminal (L2); During a period from when the switch (SW) is turned on until the charging of the capacitor (C) is completed, the current command value is set to a value, which is smaller than a value corresponding to the smallest of the rated currents of components included in the inrush current limiting circuit (2, 3) and is set to a value that is smaller than a maximum current value in a safe operating range of the switching element (Q); the current command value is set to a value to put the switching element (Q) into a fully switched-on state when the charging of the capacitor (C) is complete after the switch (SW) is switched on and a period of occurrence of an inrush current has ended; a product of the value of a current flowing through the switching element (Q) and the voltage difference between the ends of the switching element (Q) is set to a constant value; and the inrush current limiting circuit (2, 3) further comprises: an operator (14) which, based on a signal from the voltage sensor (13) and a signal from the current sensor (11), calculates the current command value to make the product of the value of the current flowing through the switching element (Q) and the voltage difference between the ends of the switching element (Q) constant, and outputs the calculated current command value to the non-inverting input terminal of the operational amplifier (OP).

Description

[0001] The present invention relates to an inrush current limiting circuit.

[0002] In cases where a large-capacity smoothing capacitor is connected in parallel with an electrical load, an inrush current limiting circuit has typically been proposed to reduce the inrush current flowing into the smoothing capacitor from a battery when power is supplied from the battery to the electrical load. The inrush current limiting circuit comprises a first connecting lead for linking a positive terminal of the battery and the electrical load, a second connecting lead for linking a negative terminal of the battery and the electrical load, switches provided in both the first and second connecting leads, and a current limiting circuit connected in parallel with each of these switches.

[0003] The current-limiting circuit comprises a switching element, a pre-charge resistor, and a leakage current detection circuit. The switch and the switching element, located in the second connecting line, are activated first when the power supply to the electrical load is started. Consequently, the smoothing capacitor is slowly charged via the pre-charge resistor, thus suppressing inrush current (see patent reference 1). Further aspects of current-limiting circuits are known from patent references 2 to 5. List of oppositions patent literature Patent literature 1: JP 4 123 441 B2 Patent literature 2: EP 2 562 896 A2 Patent literature 3: EP 0 524 425 A1 Patent literature 4: JP 2010- 074 874 A Patent literature 5: DE 200 10 283 U1

[0004] However, in the inrush current limiting circuit described in patent literature 1, it is necessary to provide the switches in the first and second connecting lines respectively and to provide the switching element and the pre-charge resistor, which inevitably complicates the design.

[0005] The present invention was developed to solve this problem, wherein an object of the present invention is to provide an inrush current limiting circuit suitable for preventing damage to a component by an inrush current, while avoiding complexity in its design. This is achieved by independent claim 1.

[0006] In the inrush current limiting circuit, according to the invention, the current command value is set to a value smaller than the smallest of the rated currents of the components in the circuit during the period from when the switch is turned on until the capacitor is fully charged. Therefore, because of the operational amplifier's ability to adjust the values ​​at both terminals so that they are equal, the current sensor's sensing value is adjusted by the switching element to match the current command value, thus preventing damage to the components from an inrush current during the period until the capacitor is fully charged.Furthermore, there is no need to provide multiple switches because the current-limiting circuit is located in the second conductor, outside of the first and second connection conductors, with the switch itself only being present in one of these two conductors. Consequently, damage to components caused by inrush current is prevented, while also avoiding design complexity. Because the current command value is set to a value lower than the maximum current within the safe operating range of the switching element, no second breakdown event occurs in the switching element, allowing it to be used effectively.

[0007] Preferably, the switching element is a static induction transistor made of silicon carbide.

[0008] In the inrush current limiting circuit, it is even better to use a static induction transistor made of silicon carbide in an active area than a MOSFET with a gate oxide layer.

[0009] Because the operator is designed to calculate the current command value based on the signals from the voltage and current sensors, in order to keep the product of the current and voltage values ​​of the switching element constant and output the calculated current command value to the non-inverting input of the operational amplifier, a current command value can be calculated in the inrush current limiting circuit by actually monitoring a voltage difference of the switching element. This makes it possible, for example, to compensate for changes in the resistance values ​​of the respective components or similar factors depending on the temperature environment in which the inrush current limiting circuit is used, thus keeping the power applied to the switching element more consistently stable.

[0010] Furthermore, the inrush current limiting circuit of the present invention preferably also includes a decision segment which determines, based on the signal from the voltage sensor, whether the charging of the capacitor has been completed or not, and if the decision segment determines that the charging of the capacitor has been completed, the operator sets the switching element to a fully switched-on state by changing the current command value so that it is higher than in the period when the switch is turned on until the charging of the capacitor is completed.

[0011] In the inrush current limiting circuit, there is no need to determine the completion of the capacitor charging based on the elapsed time, because the decision segment determining the completion of the capacitor charging is provided, whereby the determination can be made based on an actual voltage difference of the switching element, so that the switching element can be set to a fully switched-on state with more precise timing control.

[0012] The present invention can provide an inrush current limiting circuit suitable for preventing damage to a component by an inrush current, while avoiding complexity in its design. [ Fig. 1] Fig. Figure 1 is a circuit diagram that represents an example of an inrush current limiting circuit according to an exemplary embodiment. [ Fig. 2] Fig. Figure 2 is a schematic representation illustrating the operation of the inrush current limiting circuit of the embodiment, in which the input of a current command value into a non-inverting input terminal of an operational amplifier is shown. [ Fig. 3] Fig. Figure 3 is a schematic representation that explains the operation of the inrush current limiting circuit of the embodiment, illustrating a current value, a voltage value and the like. [ Fig. 4] Fig. Figure 4 is a circuit diagram representing an inrush current limiting circuit according to an embodiment of the present invention. [ Fig. 5] Fig. 5A and Fig. Figure 5B are schematic representations illustrating a power output in the inrush current limiting circuit of the embodiment, wherein Fig. 5A illustrates a drain voltage and a drain current and Fig. 5B represents the performance. [ Fig. 6] Fig. 6A and Fig. Figure 6B are schematic representations illustrating a performance in the inrush current limiting circuit of the modification, where Fig. 6A a first example and Fig. 6B presents a second example. [ Fig. 7] Fig. Figure 7 is a diagram representing the current, voltage, and power of a switching element of the modification. [ Fig. 8] Fig. Figure 8 is a circuit diagram that represents an inrush current limiting circuit according to a second modification of the embodiment.

[0013] An exemplary embodiment will now be described on the basis of the accompanying drawings, it being noted that the present invention is not limited to the following embodiment. Fig. Figure 1 is a circuit diagram illustrating an example of an inrush current limiting circuit according to an exemplary embodiment.

[0014] The inrush current limiting circuit 1 of the present embodiment is one that is provided in a power supply system for supplying power to an electrical consumer (such as an inverter) of a hybrid vehicle or an electric vehicle and, as in Fig. 1 shows a first connecting line L1, a second connecting line L2, an inverter capacitor (capacitor) C, a relay switch (switch) SW and a current limiting circuit 10.

[0015] The first connecting cable L1 connects a positive terminal of battery B to the electrical load, and the second connecting cable L2 connects a negative terminal of battery B to the electrical load. The inverter capacitor C is located in a third connecting cable L3, which connects the first connecting cable L1 and the second connecting cable L2. The capacitor has one electrode connected to the first connecting cable L1 and the other electrode connected to the second connecting cable L2. Hereinafter, a connection point between the first connecting cable L1 and the third connecting cable L3 is referred to as a first node "a", and a connection point between the second connecting cable L2 and the third connecting cable L3 is referred to as a second node "b".

[0016] The relay switch SW is installed in the first connection line L1 in a section between battery B and the first node "a" to be switched on when power is supplied to the electrical load and switched off when the power supply is interrupted. The current limiting circuit 10 is installed in the second connection line L2 in a section between battery B and the second node "b" to limit an inrush current that occurs when the relay switch SW is switched on.

[0017] This current limiting circuit 10 comprises a current sensor 11, an operational amplifier OP, and a switching element Q. The current sensor 11 is connected to the second terminal L2 to output a voltage signal corresponding to a sensing value to a non-inverting input of the operational amplifier OP, using, for example, a shunt resistor. The operational amplifier OP receives the voltage signal corresponding to the sensing value of the current sensor 11 at an inverting input and receives a current command value at the non-inverting input.

[0018] The switching element Q is specifically a silicon carbide static induction transistor (SiC-SIT) whose control electrode (control terminal) is connected to the output of the operational amplifier OP to perform a switching operation according to an output signal from the operational amplifier OP that is input to the control electrode. This switching element Q has a drain electrode connected to the second node "b" and a source electrode connected to one side of the current sensor 11. Incidentally, the switching element Q is not limited to the silicon carbide static induction transistor, but could be a MOSFET, an IGBT, a bipolar transistor, or the like.

[0019] Furthermore, during the period when the relay switch SW is switched on until the charging of the inverter capacitor C is completed, the current command value input into the non-inverting input terminal of the operational amplifier OP is set in the present embodiment to a voltage value that is smaller than a voltage value corresponding to the smallest of the rated currents of the components contained in the inrush current limiting circuit 1 (such as the relay switch SW and the inverter capacitor C).

[0020] Because of the operational amplifier OP's ability to set values ​​at both terminals to be equivalent, the current sensor reading 11 is adjusted by the switching element Q to match the current command value. Therefore, during the period until the inverter capacitor C is fully charged, the current flowing through the second terminal L2 is balanced, thus preventing damage to the components from an inrush current.

[0021] Next, the operation of the inrush current limiting circuit 1 of the present embodiment will be described. Fig. Figure 2 is a schematic representation that explains the operation of the inrush current limiting circuit 1 of the present embodiment and shows the current command value that is input into the non-inverting input terminal of the operational amplifier OP.

[0022] First, when the relay switch SW is turned on at time t0, the current command value is set to V1. Then, at time t1, after a prescribed time has elapsed, the current command value is changed to V2 (> V1). Afterwards, the current command value is held at V2.

[0023] Here, as described above, the current command value V1 is set to a voltage value that is lower than the voltage value corresponding to the smallest of the rated currents of the components contained in the inrush current limiting circuit 1. More specifically, the current command value V1 is set to a value that is lower than a voltage value corresponding to the maximum current value in a safe operating area (SOA) of the switching element Q. Specifically, the current command value V1 is set to 0.1 V. Consequently, the switching element is controlled so that a current measured by the current sensor 11 as 0.1 V can flow.

[0024] Furthermore, the current command value V2 is set to a sufficiently large value compared to a value of the current flowing through the second connecting line L2 in a normal period (corresponding to a stage in which a desired power is supplied to the electrical consumer after the end of an inrush current limiting period) and is set to a value to fully switch on the switching element Q.

[0025] Furthermore, the prescribed time from time t0 to time t1 is set to a time that is necessary to eliminate the inrush current, or a time that is longer than this necessary time, and is specifically set to about 0.2 seconds.

[0026] Next, the operation of the inrush current limiting circuit 1 of the present embodiment will be described with reference to Fig. 3 described in more detail. Fig. Figure 3 is a schematic representation that explains the operation of the inrush current limiting circuit 1 of the present embodiment, in which a current value, a voltage value and the like are illustrated.

[0027] First, it is assumed that the relay switch SW is switched on at time 0 s. The current command value is set to V1 (0.1 V), and the switching element Q is controlled so that a current measured by the current sensor 11 as 0.1 V can flow. Consequently, immediately after the relay switch SW is switched on, a drain current of approximately 1.5 A flows, and a drain voltage of approximately 70 V is applied. Furthermore, the power, corresponding to the product of the drain current and the drain voltage, is immediately approximately 110 W. It should be noted that the control voltage at this point is approximately 6 V.

[0028] Next, at 0.05 s, the drain voltage is reduced to approximately 50 V. Therefore, the power is also reduced to approximately 75 W.

[0029] The drain voltage is then also reduced, reaching 0 V and thus 0 W before 0.2 s. At this point, the charging of the inverter capacitor C is complete, and one inrush current cycle has ended.

[0030] Afterwards, although not shown in the drawing, the current command value is changed to V2, and the switching element Q is set to a fully switched-on state.

[0031] In this way, the current command value in the inrush current limiting circuit 1 of the present embodiment is set to a value that is smaller than the value corresponding to the smallest of the rated currents of the components contained in the inrush current limiting circuit 1 during the period from when the relay switch SW is turned on until the charging of the inverter capacitor C is complete. Therefore, due to the property of the operational amplifier OP to compare values ​​at both terminals, the sensing value of the current sensor 11 is set by the switching element Q to correspond to the current command value, thus preventing damage to the components by an inrush current during the period until the charging of the inverter capacitor C is complete.Because the current limiting circuit 10 is provided in the second connection line L2, there is also no need to provide multiple relay switches SW, as only the relay switch SW is provided in the second connection line L2. Consequently, damage to the components caused by an inrush current can be prevented, while also avoiding the complexity of the design. Furthermore, no second breakdown event occurs in the switching element Q, since the current command value V1 is set to a value that is lower than the value corresponding to the maximum current value in the safe operating range of the switching element Q, so that the switching element Q can be used effectively.

[0032] Because the switching element Q is a silicon carbide static induction transistor, it is better to use a silicon carbide static induction transistor than a MOSFET with a gate oxide layer when using a silicon carbide static induction transistor in an active area.

[0033] The present invention has been described so far based on the embodiment described above; however, it should be noted that the present invention is not limited to the embodiment described above, but can be modified and changed without deviating from the scope of the present invention. Although, for example, in the present embodiment the relay switch SW is provided in the first connecting line L1 and the current limiting circuit 10 in the second connecting line L2, the present invention is not limited to this embodiment, but the relay switch SW can be provided in the second connecting line L2 with the current limiting circuit 10 provided in the first connecting line L1.

[0034] Furthermore, the inrush current limiting circuit 1 of the present embodiment can be designed as follows: First, in the inrush current limiting circuit 1 of the present embodiment, during the second half of the period when the relay switch SW is switched on until the charging of the inverter capacitor C is completed (in Fig. 3. Specifically, time 0.1 s to 0.2 s), the rated power of the switching element Q is an excess power. In other words, it is necessary to set the maximum power of the switching element Q in the SOA (safe operating range) to a value corresponding to the maximum power applied to the switching element Q at the beginning of the inrush current (that is, 110 W in Fig. 3) Therefore, it is necessary to include a switching element Q in the inrush current limiting circuit 1, which has the maximum rated power corresponding to the start of the inrush current, but in the second half of the period until the charging of the inverter capacitor C is completed, such a maximum power is not necessary in the SOA and is excess power.

[0035] If the maximum power of the switching element Q is reduced in the SOA, a problem arises because the time until the inverter capacitor C is fully charged becomes longer. Therefore, the following design can be used.

[0036] Fig. Figure 4 is a circuit diagram illustrating an inrush current limiting circuit 2 according to an embodiment of the present invention. As shown in Fig. As shown in Figure 4, the inrush current limiting circuit 2 contains a voltage sensor 13 and an operator 14.

[0037] The voltage sensor 13 outputs a signal to the operator 14 corresponding to the voltage difference between the two ends of the switching element Q. The operator 14 generates a current command value corresponding to the signal, which is the voltage difference between the two ends of the switching element Q detected by the voltage sensor 13, and outputs it to the non-inverting input of the operational amplifier OP. In other words, the operator 14 calculates a current command value based on a signal from the voltage sensor 13 and a signal from the current sensor 11, making the product of the current flowing through the switching element Q and the voltage difference between the two ends of the switching element Q constant, and outputs it to the non-inverting input of the operational amplifier OP.

[0038] This current command value, similar to the current command value described above, is set to a voltage value that is lower than a voltage value corresponding to a value that does not exceed the SOA of the switching element Q during the period from when the relay switch SW is turned on until the charging of the inverter capacitor C is complete. Furthermore, in this modification, the current command value is set to a value that makes the product of the current flowing through the switching element Q and the voltage difference between the two ends of the switching element Q, as described above, constant. Consequently, the power applied to the switching element Q is constant, and therefore, the power applied to the switching element Q can be made constant throughout the entire period from when the relay switch SW is turned on until the charging of the inverter capacitor C is complete. As a result, the following effect is observed.

[0039] Fig. 5A and Fig. Figures 5B are schematic representations illustrating the power in the inrush current limiting circuit 1 of the present embodiment, wherein Fig. 5A the drain voltage and the drain current and Fig. 5B illustrates the performance. As in Fig. As shown in the diagram (5A), the drain current is essentially constant throughout the period when the relay switch SW is turned on until the inverter capacitor C is fully charged. In contrast, the drain voltage is high in the initial stage and decreases as the inverter capacitor C is charged. As shown in Fig. As shown in Figure 5B, the power corresponding to the product of the drain voltage and the drain current has a large value W1 in the initial stage and becomes smaller when the inverter capacitor C is charged.

[0040] Fig. 6A and Fig. Figure 6B are schematic representations illustrating a power output in the inrush current limiting circuit 2 of the modification, where Fig. 6A a first example and Fig. 6B presents a second example. If a current command value is input into the operational amplifier OP to keep the product of the value of a current flowing through the switching element Q and the voltage difference between the two ends of the switching element Q constant, the power is, for example, as shown in Fig. Figure 6A is shown. Specifically, the power applied to the switching element Q remains essentially constant at a value W2 throughout the entire period from when the relay switch SW is energized until the inverter capacitor C is fully charged. However, this value is not high in the initial stage and does not decrease once the inverter capacitor C is fully charged. Therefore, a switching element Q with a maximum power output of W2 at the SOA (Switching Over Current) can be included in the inrush current limiting circuit 2, thus solving the excess power problem.

[0041] Alternatively, as in Fig. Figure 6B shows a current command value being input into the operational amplifier OP to keep the power of a value W1 essentially constant throughout the entire period. This solves the problem where the switching element Q has excess power in the second half of the period and also reduces the time required to charge the inverter capacitor C.

[0042] Fig. Figure 7 is a diagram illustrating the current, voltage, and power of the switching element Q of the modification. As shown in Fig. As shown in Figure 7, a current command value is input to the operational amplifier OP to maintain the power of the switching element Q at 1800 W. Specifically, a current command value is input to the operational amplifier OP to maintain a drain current of approximately 2.5 A and a drain voltage slightly higher than 700 V when the relay switch SW is in the on state. The power of the switching element Q at this point is approximately 1800 W.

[0043] Furthermore, at time 0.10 s (with the relay switch activated at time 0.01 s), the drain current becomes approximately 3.5 A and the drain voltage slightly higher than 500 V, while at time 0.15 s the drain current becomes slightly higher than 5 A and the drain voltage approximately 350 V. Subsequently, immediately before time 0.19 s (when charging is complete), the drain current becomes essentially 1 A and the drain voltage approximately 1800 V.

[0044] Operator 14 is designed to calculate current command value data to achieve this current, voltage, and power. Therefore, a situation such as the case where the current command value is a constant value can be avoided, where the power of the switching element Q is high in the first half of the period from when the relay switch SW is turned on until the charging of the inverter capacitor C is complete, and low in the second half, and the power can be made essentially constant over the entire period. Consequently, the (wasteful) excess power of the maximum power of the switching element Q during the SOA can be avoided, and it is possible to suppress the maximum power of the switching element Q during the SOA and / or to shorten the period required to complete the charging of the inverter capacitor C.

[0045] Because the operator 14 described above is provided, a current command value can also be calculated by actually monitoring a voltage difference of the switching element Q, and it is possible, for example, to cope with the change in the resistance values ​​of the respective components or the like depending on the temperature environment in which the inrush current limiting circuit 2 is used, and therefore the power applied to the switching element Q can be kept more constant.

[0046] Fig. Figure 8 is a circuit diagram illustrating an inrush current limiting circuit 3 according to a second modification of the present embodiment. The inrush current limiting circuit 3 of the in Fig. The second modification shown in Figure 8 includes a decision segment 15 in addition to the components of the modification described above.

[0047] Decision segment 15 determines, based on the signal supplied by voltage sensor 13, whether the charging of the inverter capacitor C has been completed or not. Furthermore, if it is determined that the charging of the inverter capacitor C has been completed, decision segment 15 transmits a corresponding signal to operator 14.

[0048] Furthermore, in a third modification, when the decision segment 15 determines that the charging of the inverter capacitor C has been completed, the operator 14 puts the switching element Q into a fully switched-on state by changing the current command value so that it is higher than during the period when the relay switch SW is switched on until the charging of the inverter capacitor C is completed.

[0049] In this way, there is no need to determine the completion of the charging of the inverter capacitor C based on the elapsed time (for example, slightly less than 0.2 s) as in the embodiment and modification described above, but a current voltage difference of the switching element Q can be used for determination, and therefore the switching element Q can be set to a fully switched-on state with more precise timing control.

[0050] Incidentally, the modification methods and the second modification can be incorporated into the inrush current limiting circuit 1 of the present embodiment, or part of the methods can be incorporated.

[0051] The characteristics of the embodiment of the inrush current limiting circuit of the present invention are now summarized below as shown in [1] to [5]. [1] An inrush current limiting circuit comprising: a first connecting line (L1) that connects a positive terminal of a battery (B) and an electrical consumer; a second connecting cable (L2) that connects a negative terminal of the battery and the electrical consumer; a capacitor (inverter capacitor C) with one electrode connected to the first terminal and another electrode connected to the second terminal; a switch (relay switch SW) that is provided in a first line outside the first and second connection lines; and a current limiting circuit (10) provided in a second line outside the first and second connecting lines, wherein the current limiting circuit comprises: a current sensor (11) provided in the second line; an operational amplifier (op) which receives at an inverting input terminal a signal in accordance with a sensing value obtained by the current sensor and receives at a non-inverting input terminal a current command value; and a switching element (Q) provided in the second line which receives at a control terminal an output signal from the operational amplifier and performs a switching operation in accordance with the output signal, and During a period from when the switch is turned on until the capacitor is fully charged, the current command value is set to a value less than a value corresponding to the smallest of the rated currents of any components included in the circuit, and to a value less than a maximum current value in a safe operating range of the switching element. [2] The inrush current limiting circuit according to [1] above, in which the switching element is a static induction transistor made of silicon carbide. [3] The inrush current limiting circuit according to [1] or [2] above, in which the product of the value of a current flowing through the switching element and a voltage difference between the ends of the switching element is set to a constant value. [4] The inrush current limiting circuit according to [3] above, further comprising: a voltage sensor (13) that detects the voltage difference between the ends of the switching element; and an operator (14) which, based on a signal from the voltage sensor and a signal from the current sensor, calculates the current command value in order to make the product of the value of the current flowing through the switching element and the voltage difference between the ends of the switching element constant and to output the calculated current command value to the non-inverting input terminal of the operational amplifier. [5] The inrush current limiting circuit according to [4] above further includes a decision segment (15) which determines, on the basis of the signal from the voltage sensor, whether the charging of the capacitor has been completed or not, In the case where, if the decision segment determines that the charging of the capacitor has been completed, the operator sets the switching element to a fully on state by changing the current command value so that it is higher than during the period when the switch is turned on until the charging of the capacitor is complete.

[0052] The present invention has been described in detail with reference to the specific embodiment, and it is obvious to a person skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

[0053] This application is based on the earlier Japanese patent application filed on August 27, 2013 (Japanese patent application no. 2013-175257) and the Japanese patent application filed on June 12, 2014 (Japanese patent application no. 2014-121496), the entire contents of which are incorporated herein by reference.

[0054] According to the present invention, damage to a component caused by an inrush current can be prevented, while avoiding a complex design. The present invention, which exhibits this effect, is suitable for an inrush current limiting circuit. 1 - 3 ... Inrush current limiting circuit 10 ... Current limiting circuit 11 ... current sensor 13 ... voltage sensor 14 ... Operator 15 ... Decision segment B ... Battery C ... inverter capacitor (capacitor) L1 ... first connection line L2 ... second connection line L3 ... third connection line OP ... Operational Amplifier Q ... switching element SW ... Relay switch (switch)

Claims

[1] Inrush current limiting circuit (2, 3), comprising: a first connecting line (L1) that connects a positive terminal of a battery (B) and an electrical consumer; a second connecting cable (L2) that connects a negative terminal of the battery (B) and the electrical consumer; a switch (SW) which is provided in a first line of the first and second connection lines (L1,L2); a voltage sensor (13); and a current limiting circuit (10) provided in a second line of the first and second connecting lines (L1,L2); wherein the current limiting circuit (10) comprises: a current sensor (11) provided in the second line; and a switching element (Q) provided in the second line; wherein the voltage sensor (13) detects a voltage difference between the ends of the switching element (Q); an operational amplifier (OP) which receives a signal at an inverting input terminal in accordance with a detection value obtained by the current sensor (11) and receives a current command value at a non-inverting input terminal; wherein the switching element (Q) provided in the second line receives an output signal from the operational amplifier (OP) at a control terminal and performs a switching operation in accordance with the output signal; characterized by the fact that the inrush current limiting circuit (2, 3) further comprises: a capacitor (C) with a first electrode connected to the first terminal (L1) and a second electrode connected to the second terminal (L2); During a period from when the switch (SW) is turned on until the charging of the capacitor (C) is completed, the current command value is set to a value, which is smaller than a value corresponding to the smallest of the rated currents of components included in the inrush current limiting circuit (2, 3) and is set to a value that is smaller than a maximum current value in a safe operating range of the switching element (Q); the current command value is set to a value to put the switching element (Q) into a fully switched-on state when the charging of the capacitor (C) is complete after the switch (SW) is switched on and a period of occurrence of an inrush current has ended; a product of the value of a current flowing through the switching element (Q) and the voltage difference between the ends of the switching element (Q) is set to a constant value; and the inrush current limiting circuit (2, 3) further comprises: an operator (14) which, based on a signal from the voltage sensor (13) and a signal from the current sensor (11), calculates the current command value to make the product of the value of the current flowing through the switching element (Q) and the voltage difference between the ends of the switching element (Q) constant, and outputs the calculated current command value to the non-inverting input terminal of the operational amplifier (OP). [2] Inrush current limiting circuit (2, 3) according to claim 1, wherein the switching element (Q) is a static induction transistor made of silicon carbide. [3] Inrush current limiting circuit (2, 3) according to claim 1 or claim 2, further comprising a decision segment (15) which determines, on the basis of the signal from the voltage sensor (13), whether the charging of the capacitor (C) has been completed or not; wherein, if the decision segment (15) determines that the charging of the capacitor (C) has been completed, the operator (14) sets the switching element (Q) to the fully switched-on state by changing the current command value so that it is higher than during the period when the switch (SW) is turned on until the charging of the capacitor (C) is completed.

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