JP7613125B2 - Power Conversion Equipment - Google Patents

Description

The present invention relates to a power conversion device equipped with a short circuit fault detection device.

In a power conversion device that drives a load such as a motor, an excessive current may flow through the semiconductor switching elements that make up the power conversion device. If such an excessive current flows for a long period of time, there is a risk that the semiconductor switching elements will be destroyed. Therefore, a short circuit fault detection device is provided in the power conversion device to detect the excessive current flowing through the semiconductor switching elements and stop the power conversion device.

In this type of short circuit fault detection device, a shunt resistor, a current transformer (CT), a Rogowski coil, or the like is used to detect the current flowing through the semiconductor switching element. Among these, the Rogowski coil has the advantage that it is possible to make the short circuit fault detection device compact because it does not have a core, and that it is also possible to measure large currents.

Patent Document 1 discloses a technology for detecting a short circuit fault in an arm using a Rogowski coil in a power conversion device that drives a load via an arm including a semiconductor switching element. FIG. 9 is a circuit diagram showing the configuration of the device disclosed in Patent Document 1. In FIG. 9, a gate drive circuit 96 supplies a gate voltage to a semiconductor switching element 91 via a gate resistor 95 to drive the semiconductor switching element 91. A Rogowski coil 97 outputs a terminal voltage proportional to the time gradient di/dt of the current flowing through the semiconductor switching element 91. A short circuit detector 98 determines that an arm short circuit has occurred by detecting that the terminal voltage of the Rogowski coil 97 has continued to have a large value for a certain period of time or more, and stops driving the semiconductor switching element 91 by the gate drive circuit 96.

However, in addition to the arm short circuit described above, short circuit faults that can occur in power conversion equipment include load short circuit, in which a load connected to the output side of the power conversion equipment is short-circuited. Therefore, Patent Document 2 discloses a technology for detecting arm short circuit current using an air-core coil and detecting load short circuit current using a CT (Current Transformer).

JP 2001-169533 A

International Publication No. 2018/073909

The technology disclosed in the above-mentioned Patent Document 1 is effective in detecting arm short circuits, but has the problem that it is difficult to detect load short circuits. This problem will be explained below.

Figure 10 is a circuit diagram illustrating a current path RT1 of a short-circuit current when an arm short circuit occurs in a power conversion device. Also, Figure 11 is a circuit diagram illustrating a current path RT2 of a short-circuit current when a load short circuit occurs in the same power conversion device.

10 and 11, an arm consisting of an anti-parallel connected semiconductor switching element SW1 and a flywheel diode D1, and an arm consisting of an anti-parallel connected semiconductor switching element SW2 and a flywheel diode D2 are connected in series between the terminals of a capacitor storing a DC voltage E. In addition, an arm consisting of an anti-parallel connected semiconductor switching element SW3 and a flywheel diode D3, and an arm consisting of an anti-parallel connected semiconductor switching element SW4 and a flywheel diode D4 are connected in series between the terminals of the capacitor. A load Z such as a motor winding is connected between the common connection node of the semiconductor switching elements SW1 and SW2 and the common connection node of the semiconductor switching elements SW3 and SW4. In addition, in FIG. 10 and FIG. 11, L1 is a self-inductance that is interposed in the current path of the short-circuit current when the arm is short-circuited. Furthermore, L2 is a self-inductance present in the current path from the common connection node of the semiconductor switching elements SW1 and SW2 through the load Z to the common connection node of the semiconductor switching elements SW3 and SW4.

10, when the semiconductor switching element SW1 is OFF and the semiconductor switching element SW2 is ON, a short-circuit failure occurs in the semiconductor switching element SW1, and an arm short-circuit current ia flows through a current path RT1 from the capacitor that outputs the DC voltage E to the semiconductor switching element SW1 to the semiconductor switching element SW2 to the capacitor. In this case, the following equation is established for the arm short-circuit current ia.
E=L1×dia/dt...(1)

11, when the semiconductor switching elements SW1 and SW4 are ON and the semiconductor switching elements SW2 and SW3 are OFF, a short-circuit fault occurs in the load Z, and a load short-circuit current ir flows through a current path RT2 from the capacitor that outputs the DC voltage E to the semiconductor switching element SW1 to the load Z to the semiconductor switching element SW4 to the capacitor. In this case, the following equation is established for the load short-circuit current ir.
E=(L1+L2)×dir/dt...(2)

Here, the self-inductances L1 and L2 have the relationship L1<<L2. Therefore, it can be seen from the above equations (1) and (2) that the following equation holds:
dir/dt≪dia/dt...(3)

12 is a diagram illustrating the current waveforms of the arm short circuit current ia and the load short circuit current ir. In FIG. 12, the horizontal axis is time t, and the vertical axis is current value i. The self-inductance L1 intervening in the current path RT1 of the arm short circuit current ia is small. Therefore, if the semiconductor switching element SW2 is turned on at t=0, the arm short circuit current ia rises to a large current value in a short time, and the charge stored in the capacitor that outputs the DC voltage E is discharged in a short time. Therefore, the arm short circuit current ia is generated in a short time after the semiconductor switching element SW2 is turned on. On the other hand, the self-inductance L2 intervening in the current path RT2 of the load short circuit current ir is very large compared to the self-inductance L1. Therefore, the load short circuit current ir increases with a very gentle time gradient after the semiconductor switching elements SW1 and SW4 are turned on. And, when focusing on the frequency domain, the upper limit frequency of the frequency band of the arm short circuit current is an order of magnitude higher than the upper limit frequency of the frequency band of the load short circuit current.

To detect a load short circuit current ir with a small time gradient, it is necessary to increase the number of turns of the Rogowski coil, for example, to increase the sensitivity of the Rogowski coil. Therefore, if an attempt is made to detect a load short circuit current using a Rogowski coil, the Rogowski coil becomes larger, which leads to a problem of the power conversion device becoming larger and more complicated.

In addition, when the number of turns of the Rogowski coil is increased, the self-inductance of the Rogowski coil increases. However, in order to accurately detect the terminal voltage of the Rogowski coil both when the arm is short-circuited and when the load is short-circuited, it is necessary to reduce the self-inductance of the Rogowski coil and to sufficiently increase the resonant frequency of the LC resonant circuit consisting of the self-inductance and parasitic capacitance of the Rogowski coil. Specifically, the resonant frequency must be higher than the upper limit frequency of the frequency band of the terminal voltage of the Rogowski coil when the arm is short-circuited. If this resonant frequency is within the frequency band, the terminal voltage waveform of the Rogowski coil is distorted due to the effect of resonance, making it difficult to detect the arm short-circuit. Therefore, in order to avoid the effect of resonance, it is necessary to reduce the self-inductance of the Rogowski coil and increase the resonant frequency. However, in order to reduce the self-inductance of the Rogowski coil, the sensitivity of the Rogowski coil must be reduced. In this case, since the time gradient dia/dt of the load short-circuit current ia is extremely small, the terminal voltage of the Rogowski coil is buried in noise, making it extremely difficult to detect the load short-circuit.

In the technology disclosed in Patent Document 2, the arm short-circuit current is detected by an air-core coil, and the load short-circuit current is detected by a CT. However, the use of a CT increases costs and increases the number of discrete components, making the power conversion device more complex.

This invention has been made in consideration of the problems described above, and its first object is to provide a power conversion device equipped with a short circuit fault detection device capable of detecting a load short circuit using a Rogowski coil without complicating the device. Also, the second object of the invention is to provide a power conversion device equipped with a short circuit fault detection device capable of detecting both a load short circuit and an arm short circuit using a Rogowski coil without complicating the device.

The first aspect of the power conversion device of the present invention is a power conversion device that supplies power to a load through two or more arms including semiconductor switching elements, and is characterized in that a short circuit fault detection device is provided in some of the two or more arms, and the short circuit fault detection device has a first Rogowski coil that outputs a first detection signal corresponding to a current flowing in the arm in which the short circuit fault detection device is provided due to a short circuit in the load, and detects a short circuit fault based on the first detection signal.

A second aspect of the power conversion device of the present invention is a power conversion device that supplies power to a load through an arm including a semiconductor switching element, and is characterized in that it comprises a first Rogowski coil that outputs a first detection signal corresponding to a current flowing through the arm due to a short-circuit fault in the load, and a second Rogowski coil that outputs a second detection signal corresponding to a current flowing through the arm due to a short-circuit fault in a diode connected in series to the arm, and includes a short-circuit fault detection device that detects a short-circuit fault based on the first detection signal or the second detection signal.

In a first aspect of the present invention, a short circuit fault detection device provided in one arm of a power conversion device detects a load short circuit current using a first Rogowski coil. In this aspect, since it is only necessary to provide the first Rogowski coil in one arm, it is possible to detect a load short circuit current without increasing the size and complexity of the power conversion device. In a second aspect of the present invention, a short circuit fault in the load can be detected using a first Rogowski coil suitable for such detection, and a short circuit fault in a diode connected in series to an arm can be detected using a second Rogowski coil suitable for such detection.

1 is a circuit diagram showing a configuration of a power conversion device according to an embodiment of the present invention. 2 is a circuit diagram showing a configuration of a short-circuit fault detection device in the embodiment. FIG. FIG. 4 is a waveform diagram showing the operation of the embodiment. FIG. 4 is a waveform diagram showing the operation of the embodiment. FIG. 4 is a waveform diagram showing the operation of the embodiment. FIG. 4 is a circuit diagram showing a first operation example of the embodiment. FIG. 11 is a circuit diagram showing a second operation example of the embodiment. FIG. 11 is a circuit diagram showing a third operation example of the embodiment. FIG. 2 is a diagram showing a specific example of the embodiment. FIG. 11 is a circuit diagram showing an example of application of the short-circuit fault detection device to another power conversion device. FIG. FIG. 1 is a circuit diagram showing a configuration of a conventional short-circuit fault detection device. 1 is a circuit diagram showing a current path of an arm short-circuit current in a power conversion device. 2 is a circuit diagram showing a current path of a load short-circuit current in the power conversion device. FIG. FIG. 4 is a diagram showing current waveforms of an arm short-circuit current and a load short-circuit current.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a power conversion device 1 according to an embodiment of the present invention. In this power conversion device 1, a capacitor 30 is charged by a DC power supply 40 and outputs a DC voltage. Arms 10_1 and 10_2 are connected in series between both terminals of the capacitor 30, arms 10_3 and 10_4 are connected in series between the terminals, and arms 10_5 and 10_6 are connected in series between the terminals. A load Z such as a motor winding is connected to a common connection node between the arms 10_1 and 10_2, a common connection node between the arms 10_3 and 10_4, and a common connection node between the arms 10_5 and 10_6. Each of the arms 10_1 to 10_6 includes a semiconductor switching element. The gate drive circuits 20_1 to 20_6 drive each of the semiconductor switching elements of the arms 10_1 to 10_6 by generating gate signals to be applied to the respective semiconductor switching elements of the arms 10_1 to 10_6. Thus, the power conversion device 1 has two or more arms 10_1 to 10_6 each including a semiconductor switching element, and supplies power from the DC power supply 40 to the load Z via these arms.

In the power conversion device 1, if one arm (for example, arm 10_2) is focused on, an arm short-circuit current flows through this arm 10_2 when a short-circuit fault occurs in the arm 10_2 or when a short-circuit fault occurs in another arm 10_1. In addition, in the power conversion device 1, if a short-circuit fault occurs in the load Z, a load short-circuit current may flow through the arm 10_2.

If such an arm short-circuit current or load short-circuit current flows through arm 10_2 for a long period of time, the semiconductor switching element of arm 10_2 may be destroyed. Therefore, a short-circuit fault detection device 100_2 is provided for arm 10_2, which detects the occurrence of an arm short-circuit or load short-circuit based on the current flowing through arm 10_2 and stops the driving of the semiconductor switching element by gate drive circuit 10_2. There is a possibility that similar arm short-circuit currents and load short-circuit currents may flow through the other arms 10_1, 10_3 to 10_6. Therefore, in this embodiment, short-circuit fault detection devices 100_2, 100_4, and 100_6 are provided for some of the two or more arms 10_1 to 10_6, specifically, arms 10_2, 10_4, and 10_6, which are half of the total arms.

In the following, when there is no need to distinguish between them, arms 10_1 to 10_6 are collectively referred to as arms 10, gate drive circuits 20_1 to 20_6 are collectively referred to as gate drive circuits 20, and short-circuit fault detection devices 100_2, 100_4, and 1 to 100_6 are collectively referred to as short-circuit fault detection device 100.

In this embodiment, the reasons for providing short circuit fault detection devices 100_2, 100_4, and 100_6 for arms 10_2, 10_4, and 10_6 are as follows.

There are three current paths through which the arm short-circuit current passes:
Current path R12 passing through arms 10_1 and 10_2: When a short-circuit fault occurs in one of arms 10_1 or 10_2, an arm short-circuit current flows through this current path R12.
Current path R34 passing through arms 10_3 and 10_4: When a short-circuit fault occurs in one of the arms 10_3 or 10_4, an arm short-circuit current flows through this current path R34.
Current path R56 passing through arms 10_5 and 10_6: When a short-circuit fault occurs in one of the arms 10_5 or 10_6, an arm short-circuit current flows through this current path R56.

To detect arm short-circuit currents in all current paths, it is necessary to provide a short-circuit fault detection device 100 in either arm 10_1 or 10_2, either arm 10_3 or 10_4, and either arm 10_5 or 10_6. This is condition 1.

In addition, there are six current paths through which the load short-circuit current passes:
Current path R14 passing through arms 10_1 and 10_4: When a short-circuit fault occurs in the section of load Z sandwiched between arms 10_1 and 10_4, a load short-circuit current flows through this current path R14.
Current path R32 passing through arms 10_3 and 10_2: When a short-circuit fault occurs in the section of load Z sandwiched between arms 10_3 and 10_2, a load short-circuit current flows through this current path R32.
Current path R36 passing through arms 10_3 and 10_6: When a short-circuit fault occurs in the section of load Z sandwiched between arms 10_3 and 10_6, a load short-circuit current flows through this current path R36.
Current path R54 passing through arms 10_5 and 10_4: When a short-circuit fault occurs in the section of load Z sandwiched between arms 10_5 and 10_4, a load short-circuit current flows through this current path R54.
Current path R52 passing through arms 10_5 and 10_2: When a short-circuit fault occurs in the section of load Z sandwiched between arms 10_5 and 10_2, a load short-circuit current flows through this current path R52.
Current path R16 passing through arms 10_1 and 10_6: When a short-circuit fault occurs in the section of load Z sandwiched between arms 10_1 and 10_6, a load short-circuit current flows through this current path R16.

To detect the load short-circuit current of all current paths, it is necessary to provide a short-circuit fault detection device 100 in one of arms 10_1 or 10_4, one of arms 10_3 or 10_2, one of arms 10_3 or 10_6, one of arms 10_5 or 10_4, one of arms 10_5 or 10_2, and one of arms 10_1 or 10_6. This is condition 2.

There are two possible means for satisfying both conditions 1 and 2. The first means is to provide a short-circuit fault detection device 100 in arms 10_1, 10_3, and 10_5. The second means is to provide a short-circuit fault detection device 100 in arms 10_2, 10_4, and 10_6. In this embodiment, the second means is used to detect arm short-circuit currents in all current paths and load short-circuit currents in all current paths.

Figure 2 is a circuit diagram showing an example of the configuration of the short-circuit fault detection device 100 in this embodiment. In addition, in Figure 2, the arm 10 and the gate drive circuit 20 are shown together with the short-circuit fault detection device 100 to facilitate understanding of the short-circuit fault detection device 100.

In FIG. 2, the arm 10 includes a semiconductor switching element 11 and a flywheel diode 12 connected in inverse parallel to the semiconductor switching element 11. In this example, the semiconductor switching element 11 is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The drain of the semiconductor switching element 11 is connected to the capacitor 30 or another arm via a conductor 51, and the source of the semiconductor switching element 11 is connected to the capacitor 30 or another arm via a conductor 52. The gate drive circuit 20 drives the semiconductor switching element 11 to turn it on and off by supplying a gate signal to the semiconductor switching element 11.

In the example shown in FIG. 2, a conductor 52 is inserted into the first Rogowski coil 101 and the second Rogowski coil 102. Here, the first Rogowski coil 101 is provided for the purpose of detecting a load short-circuit current, and the second Rogowski coil 102 is provided for the purpose of detecting an arm short-circuit current. When a current flows through the conductor 52, a magnetic field is generated that rotates in a circular shape around the current, and a voltage corresponding to the time change in the strength of this magnetic field is induced in the first Rogowski coil 101 and the second Rogowski coil 102. As a result, a first detection signal S1 and a second detection signal S2 having a voltage waveform proportional to the time gradient di/dt of the current flowing through the conductor 52 are output from the first Rogowski coil 101 and the second Rogowski coil 102, respectively.

In this embodiment, the first Rogowski coil 101 is a coil optimized for detecting load short-circuit current, and the second Rogowski coil 102 is a coil optimized for detecting arm short-circuit current. Focusing on the sensitivity to the time gradient di/dt of the current to be detected, that is, the ratio of the output voltage of the Rogowski coil to the time gradient di/dt of the current, the sensitivity of the second Rogowski coil 102 is lower than that of the first Rogowski coil 101. Specifically, for example, the number of turns of the second Rogowski coil 102 is smaller than the number of turns of the first Rogowski coil 101. The reason why the sensitivity of the second Rogowski coil 102 is lower than that of the first Rogowski coil 101 is to increase the resonant frequency of the LC resonant circuit consisting of the self-inductance and parasitic capacitance of the second Rogowski coil 102 by lowering the self-inductance of the second Rogowski coil 102, and to place this resonant frequency outside the frequency band of the arm short-circuit current. In addition, the sensitivity of the first Rogowski coil 101 is made higher than that of the second Rogowski coil 102 in order to accurately detect load short-circuit currents with small time gradients.

The arm short-circuit determination circuit 112 is a circuit that determines that an arm short-circuit has occurred in the power conversion device 1 based on the second detection signal S2. Specifically, the arm short-circuit determination circuit 112 determines that an arm short-circuit has occurred when the second detection signal S2 maintains a level higher than the second reference level Vref2 beyond the second reference time Tref2. When the arm short-circuit determination circuit 112 determines that an arm short-circuit has occurred, it changes the short-circuit determination signal E2 from the inactive level "0" to the active level "1."

The load short-circuit determination circuit 111 is a circuit that determines that a load short-circuit has occurred in the power conversion device 1 based on the first detection signal S1. Specifically, the load short-circuit determination circuit 111 determines that a load short-circuit has occurred when the first detection signal S1 maintains a level higher than the first reference level Vref1 beyond the first reference time Tref1. When the load short-circuit determination circuit 111 determines that a load short-circuit has occurred, it changes the short-circuit determination signal E1 from the inactive level "0" to the active level "1."

The shutoff control circuit 120 detects that some kind of short-circuit fault has occurred in the power conversion device 1 based on the short-circuit discrimination signal E2 output by the arm short-circuit discrimination circuit 112 and the short-circuit discrimination signal E1 output by the load short-circuit discrimination circuit 111, and generates a short-circuit detection signal E. In this example, the shutoff control circuit 120 includes an OR circuit that generates the short-circuit detection signal E as the logical sum of the short-circuit discrimination signal E1 and the short-circuit discrimination signal E2.

In addition, when the short circuit detection signal E is generated, the shutoff control circuit 120 performs control to shut off the arm short circuit current or the load short circuit current. More specifically, when the short circuit determination signal E2 is generated, the shutoff control circuit 120 outputs a shutoff signal C to stop driving the semiconductor switch 11 of the arm 10 in which the short circuit failure detection device 100 is provided and the semiconductor switch 11 of the other arm 10 in which the short circuit failure detection device 100 is not provided. Specifically, when the short circuit determination signal E2 is generated in the short circuit failure detection device 100_2 in FIG. 1, the shutoff control circuit 120 of this short circuit failure detection device 100_2 outputs shutoff signals C2 and C1 to the gate drive circuits 20_2 and 20_1 of the arm 10_2 in which the arm short circuit current is detected and the other arm 10_1. In addition, when the short circuit determination signal E1 is generated, the shutoff control circuit 120 outputs a shutoff signal C to the gate drive circuit 20 of the arm in which the load short circuit current is detected to stop driving the semiconductor switch 11 of the arm.

In addition, when a short circuit detection signal E is generated, the shutoff control circuit 120 outputs a fault signal F to the control device 1000. Upon receiving this fault signal F, the control device 1000 starts control to stop the power conversion device 1.

3A, 3B, and 3C are waveform diagrams showing an example of the operation of this embodiment. FIG. 3A shows the waveform of the current i flowing through the conductor 52, the waveform of the second detection signal S2, the waveform of the level judgment signal D2 generated in the arm short-circuit judgment circuit 112, and the waveform of the short-circuit judgment signal E2 output by the arm short-circuit judgment circuit 112, for each of the normal state, the arm short-circuit state, and the load short-circuit state. FIG. 3B shows the waveform of the current i flowing through the conductor 52, the waveform of the first detection signal S1, the waveform of the level judgment signal D1 generated in the load short-circuit judgment circuit 111, and the waveform of the short-circuit judgment signal E1 output by the load short-circuit judgment circuit 111, for each of the normal state, the arm short-circuit state, and the load short-circuit state. 3C also shows the waveform of the current i flowing through the conductor 52, the waveform of the short circuit determination signal E2 output by the arm short circuit determination circuit 112, the waveform of the short circuit determination signal E1 output by the load short circuit determination circuit 111, and the waveform of the short circuit detection signal E output by the shutdown control circuit 120, for each of the normal state, the arm short circuit, and the load short circuit. In these figures, the horizontal axis is time t, and the vertical axis is the voltage value, the current value, or the truth value.

First, the operation of the arm short-circuit determination circuit 112 will be described with reference to FIG. 3A. In the arm short-circuit determination circuit 112, the second detection signal S2 output from the second Rogowski coil 102 is compared with the second reference level Vref2, and when the second detection signal S2 exceeds the second reference level Vref2, the level determination signal D2 is set to the active level "1". When the arm is short-circuited, a current i with a large time gradient di/dt flows through the conductor 52. Therefore, the arm short-circuit determination circuit 112 is required to detect such a large time gradient di/dt. For this reason, the second reference level Vref2 is set to a sufficiently large voltage value suitable for comparison with the second detection signal S2 when an arm short-circuit occurs. In addition, in the arm short-circuit determination circuit 112, when the level determination signal D2 exceeds the second reference time Tref2 and maintains the active level "1", the arm short-circuit determination signal E2 is set to the active level "1". When the arm is short-circuited, the current i with a large time gradient di/dt that flows through the conductor 52 reaches a current value that instantly damages the semiconductor switching element 11. Therefore, when the arm is short-circuited, the time that current can flow through the semiconductor switching element 11 is short. For this reason, the second reference time Tref2 is set to a time that is sufficiently short to enable detection of an arm short-circuit, for example, several tens to several hundreds of ns.

Under normal circumstances, when the semiconductor switching element 11 is turned on, the current i flowing through the conductor 52 rises, and during the rising period of this current i, the second detection signal S2 indicating the time gradient di/dt of the current i exceeds the second reference level Vref2, and the level determination signal D2 becomes active level "1". However, the rising period of the current i is short, and the period during which the level determination signal D2 becomes active level "1" is shorter than the second reference time Tref2. Therefore, the short circuit determination signal E2 does not become active level "1".

When the load is short-circuited, the semiconductor switching element 11 is turned on, causing the current i flowing through the conductor 52 to rise, and then the current i increases with a time gradient determined by the self-inductance present in the current path of the load short-circuit current. In this case, during the rise period of the current i, the second detection signal S2 indicating the time gradient di/dt of the current i exceeds the second reference level Vref2. However, as in normal times, the rise period of the current i is short, and the period during which the level determination signal D2 is at the active level "1" is shorter than the second reference time Tref2. Therefore, the short-circuit determination signal E2 never becomes active level "1".

The operation when an arm is short-circuited is as follows. When the semiconductor switching element 11 of an arm 10 is turned on, if a short-circuit fault occurs in another arm 10 connected in series with the semiconductor switching element 11, the current i flowing through the conductor 52 rises with a time gradient determined by the self-inductance present in the current path of the current i. As a result, the second detection signal S2 indicating the time gradient di/dt of the current i exceeds the second reference level Vref2, and the level determination signal D2 becomes active level "1". The rise period of the current i in this case is longer than the rise period of the current i in normal operation, and the level determination signal D2 maintains the active level "1" beyond the second reference time Tref2. Therefore, the short-circuit determination signal E2 becomes active level "1".

In this example, the second Rogowski coil 102 detects with high accuracy the time gradient di/dt of the current when the second detection signal S2 is in region A2p or region A2n. The second reference level Vref2 is in region A2p. Therefore, the arm short-circuit determination circuit 112 can detect an arm short-circuit with high accuracy.

Next, referring to FIG. 3B, the operation of the load short-circuit determination circuit 111 will be described. In the load short-circuit determination circuit 111, the first detection signal S1 output from the first Rogowski coil 101 is compared with the first reference level Vref1, and when the first detection signal S1 exceeds the first reference level Vref1, the level determination signal D1 is set to the active level "1". When the load is short-circuited, a small current i with a time gradient di/dt flows through the conductor 52. Therefore, the load short-circuit determination circuit 111 is required to detect such a small time gradient di/dt. For this reason, the first reference level Vref1 is set to a sufficiently small voltage value suitable for comparison with the first detection signal S1 when a load short-circuit occurs. In addition, in the load short-circuit determination circuit 111, when the level determination signal D1 exceeds the first reference time Tref1 and maintains the active level "1", the short-circuit determination signal E1 is set to the active level "1". When the load is short-circuited, the time during which the time gradient di/dt of the current i flowing through the conductor 52 becomes large is longer than in normal operation and when the arm is short-circuited. For this reason, the first reference time Tref1 is set to a sufficiently long time so that normal operation or an arm short-circuit is not mistaken for a load short-circuit, for example, a value that is several tens to several hundreds of times longer than the reference time Tref2.

Under normal circumstances, when the semiconductor switching element 11 is turned on, the current i flowing through the conductor 52 rises, and during the rising period of this current i, the first detection signal S1 indicating the time gradient di/dt of the current i exceeds the first reference level Vref1, and the level determination signal D1 becomes active level "1". However, the period during which the level determination signal D1 becomes active level "1" is shorter than the first reference time Tref1. Therefore, the short circuit determination signal E1 does not become active level "1".

When the semiconductor switching element 11 connected in series with the semiconductor switching element 11 is short-circuited, and the semiconductor switching element 11 is turned on, an arm short circuit occurs. At this time, the current i flowing through the conductor 52 rises with a time gradient determined by the self-inductance present in the current path of the arm short-circuit current. As a result, the first detection signal S1 indicating the time gradient di/dt of the current i exceeds the first reference level Vref1, and the level determination signal D1 becomes active level "1". However, when the arm is short-circuited, the second detection signal S2 also exceeds the second reference level Vref2, and the level determination signal D2 becomes active level "1". Since the respective short-circuit detection times are Tref2<<Tref1, when an arm short circuit occurs, the short-circuit determination signal E2 becomes active level "1" before the short-circuit determination signal E1. For this reason, the occurrence of an arm short circuit does not cause a load short circuit to be detected.

When the load is short-circuited, the semiconductor switching element 11 is turned on, causing the current i flowing through the conductor 52 to rise, and then the current i increases with a time gradient determined by the self-inductance present in the current path of the load short-circuit current. While the current i rises in this way and then increases with a constant time gradient, the first detection signal S1 indicating the time gradient di/dt of the current i exceeds the first reference level Vref1, and the level determination signal D1 becomes active level "1". When the load is short-circuited, this level determination signal D1 exceeds the first reference time Tref1 and maintains the active level "1". Therefore, the short-circuit determination signal E1 becomes active level "1".

In this example, the first Rogowski coil 101 detects with high accuracy the time gradient di/dt of the current at which the first detection signal S1 is a signal within region A1. The first reference level Vref1 is within region A1. Therefore, the first detection signal S1 generated by a load short circuit can be detected with high accuracy.

Next, the operation of the shutoff control circuit 120 will be described with reference to FIG. 3C. As shown in FIG. 3C, the shutoff control circuit 120 outputs the logical sum of the short circuit discrimination signal E1 and the short circuit discrimination signal E2 as the short circuit detection signal E. Therefore, when an arm short circuit or load short circuit occurs, the short circuit detection signal E is output to the gate drive circuit 20, and the drive of the semiconductor switching element 11 by the gate drive circuit 20 is stopped.

Next, an overall operation example of this embodiment will be described. FIG. 4 is a circuit diagram showing a first operation example of this embodiment. In this first operation example, a short circuit fault occurs in arm 10_1. This short circuit fault may be a fault in the semiconductor switching element 11 of arm 10_1, or may be an event in which the semiconductor switching element 11 is erroneously turned ON due to noise, for example. In the first operation example, an arm short circuit current caused by the short circuit fault in arm 10_1 flows through arm 10_2, which is in the ON state.

In the short-circuit fault detection device 100_2 provided in the arm 10_2, the arm short-circuit determination circuit 112 generates a short-circuit determination signal E2, and the shutoff control circuit 120 outputs a shutoff signal C2 to the gate drive circuit 20_2 of the arm 10_2 and a shutoff signal C1 to the gate drive circuit 20_1 of the arm 10_1. This shuts off the arm short-circuit current that uses the arms 10_1 and 10_2 as a current path. Also, in the short-circuit fault detection device 100_2, the shutoff control circuit 120 outputs a fault signal F2 to the control device 1000. This causes the control device 1000 to start control to stop the power conversion device 1.

Figure 5 is a circuit diagram showing a second operation example of this embodiment. In this second operation example, when arm 10_1 is in the ON state, a short circuit fault occurs in arm 10_2 connected to arm 10_1, and an arm short circuit current flows to arm 10_2 via arm 10_1.

In this case, too, in the short circuit fault detection device 100_2 provided in the arm 10_2, the arm short circuit determination circuit 112 generates a short circuit determination signal E2, and the shutoff control circuit 120 outputs a shutoff signal C2 to the gate drive circuit 20_2 of the arm 10_2 and a shutoff signal C1 to the gate drive circuit 20_1 of the arm 10_1. As a result, the arm 10_1, which was in the ON state, becomes in the OFF state, and the arm short circuit current with the arms 10_1 and 10_2 as the current path is shut off. Also in this case, in the short circuit fault detection device 100_2, the shutoff control circuit 120 outputs a fault signal F2 to the control device 1000.

Figure 6 is a circuit diagram showing a third operation example of this embodiment. In this third operation example, a short circuit occurs in the section between arms 10_1 and 10_4 in load Z, and when arms 10_1 and 10_4 are in the ON state, a load short-circuit current flows through arms 10_1 and 10_4.

In the short circuit fault detection device 100_4 provided in the arm 10_4, the load short circuit determination circuit 111 generates a short circuit determination signal E1, and the shutoff control circuit 120 outputs a shutoff signal C4 to the gate drive circuit 20_4 of the arm 10_4. This shuts off the load short circuit current that has arms 10_1 and 10_4 as a current path. In the short circuit fault detection device 100_4, the shutoff control circuit 120 also outputs a fault signal F2 to the control device 1000.

As described above, according to this embodiment, by using a Rogowski coil, it is possible to accurately detect both arm short circuits and load short circuits that occur in the power conversion device 1. Furthermore, according to this embodiment, since discrete components such as CTs are not used to detect short circuit currents, it is possible to reduce costs and avoid an increase in size of the short circuit fault detection device.

In addition, in this embodiment, a short-circuit fault detection device is provided in only some of the arms that constitute the power conversion device 1. When the short-circuit fault detection device detects a short-circuit fault, it stops driving the semiconductor switching elements of the other arms that do not have the short-circuit fault detection device. Therefore, it is possible to achieve a smaller size and lower cost of the power conversion device 1 while protecting the semiconductor switching elements of the power conversion device 1 from short-circuit faults.

In this embodiment, a first Rogowski coil 101 capable of generating a first detection signal S1 of an appropriate magnitude when the load is short-circuited, and a second Rogowski coil 102 capable of generating a second detection signal S2 of an appropriate magnitude when the arm is short-circuited are required. Specific examples of such a first Rogowski coil 101 and second Rogowski coil 102 are given below.

In the first specific example, the number of turns n2 of the second Rogowski coil 102 for detecting an arm short circuit is different from the number of turns n1 of the first Rogowski coil 101 for detecting a load short circuit.

The voltage v induced in the Rogowski coil is given by:
v=-μ・(SQ・n/LG)・(di/dt)……(4)
Here, μ is the magnetic permeability of air (same as the magnetic permeability of a vacuum), SQ is the magnetic path cross-sectional area of the Rogowski coil, n is the number of turns of the Rogowski coil, LG is the magnetic path length of the Rogowski coil, and di/dt is the time gradient of the current i that is the object of detection by the Rogowski coil. The magnetic path cross-sectional area SQ is the cross-sectional area of the space surrounded by the Rogowski coil. The magnetic path length is the length of the space surrounded by the Rogowski coil.

By solving the above equation (5) for the number of turns n, the following equation is obtained.
n=-(LG・v)/(μ・SQ・(di/dt))...(5)
This equation (5) shows that when the time gradient di/dt of the current is small, in order to obtain a sufficient voltage v from the Rogowski coil, the number of turns n needs to be increased.

In the second specific example, the magnetic path cross-sectional area SQ1 of the first Rogowski coil 101 for detecting a load short circuit and the magnetic path cross-sectional area SQ2 of the second Rogowski coil 102 for detecting an arm short circuit are different. Specifically, there is a relationship of SQ1>SQ2 between the magnetic path cross-sectional areas SQ1 and SQ2.

By solving the above equation (5) for the magnetic path cross-sectional area SQ, the following equation is obtained.
SQ=-(LG・v)/(μ・n・(di/dt))...(7)
This equation (7) shows that when the time gradient di/dt of the current is small, in order to obtain a sufficient voltage v from the Rogowski coil, the magnetic path cross-sectional area SQ needs to be increased.

In the third specific example, the magnetic path length LG1 of the first Rogowski coil 101 for detecting a load short circuit is different from the magnetic path length LG2 of the second Rogowski coil 102 for detecting an arm short circuit. Specifically, there is a relationship of LG1<LG2 between the magnetic path lengths LG1 and LG2.

When the above equation (5) is solved for the magnetic path length LG, the following equation is obtained.
LG=-(μ・SQ・n・(di/dt))/v……(8)
Therefore, in the third specific example, in equation (8), the time gradient di/dt of the current when the arm is short-circuited is set to, for example, about 10 times the time gradient di/dt of the current when the load is short-circuited, to calculate the required magnetic path lengths LG1 and LG2, and Rogowski coils 101 and 102 are provided with the calculated magnetic path lengths LG1 and LG2. In this way, both the arm short-circuit and the load short-circuit can be detected with high accuracy.

The fourth specific example is a specific example regarding the implementation of the first Rogowski coil 101 and the second Rogowski coil 102. Figures 7A and 7B are diagrams showing the fourth specific example. Here, Figure 7A is a diagram showing the first Rogowski coil 101 and the second Rogowski coil 102 as viewed from the semiconductor switching element 11 side of Figure 7B. Also, Figure 7B is a cross-sectional view along line A-A' in Figure 7A.

In FIG. 7B, a multilayer wiring board consisting of a first layer wiring board 61, a second layer wiring board 62, and a third layer wiring board 63 is sandwiched between the semiconductor switching element 11 and the main wiring board 70. Here, the first layer wiring board 61 is separated from the main wiring board 70, the second layer wiring board 62 is separated from the first layer wiring board 61, the third layer wiring board 63 is separated from the second layer wiring board 62, and the semiconductor switching element 11 is separated from the third layer wiring board 63.

The conductors 51 and 52 correspond to the conductors 51 and 52 in FIG. 1 above, and are connected to the source and drain of the semiconductor switching element 11, respectively. These conductors 51 and 52 extend from the semiconductor switching element 11, pass through the third layer wiring board 63, the second layer wiring board 62, and the first layer wiring board 61, and are connected to the main wiring board 70. The semiconductor switching element 11 is connected to other semiconductor switching elements or power lines in the power conversion device 1 via the conductors 51 or 52 and the main wiring board 70.

The second Rogowski coil 102 for detecting arm short circuits is arranged on the first layer wiring board 61, the second layer wiring board 62, and the third layer wiring board 63 so as to surround the conductor 51. The first Rogowski coil 101 for detecting load short circuits is arranged on the first layer wiring board 61, the second layer wiring board 62, and the third layer wiring board 63 so as to surround the conductor 52.

More specifically, the second Rogowski coil 102 is composed of an outgoing path 41 wound in a toroidal coil shape, and a return path 42 that connects the start and end of the toroidal coil and rewinds it. The return path 42 is formed on the second layer wiring board 62. The outgoing path 41 is also composed of wiring on the first layer wiring board 61, wiring from the first layer wiring board 61 to the third layer wiring board 63 via a through hole formed in the second layer wiring board 62, and wiring on the third layer wiring board 63. The first Rogowski coil 101 is also composed of an outgoing path 43 and a return path 44 similar to the outgoing path 41 and the return path 42 of the second Rogowski coil 102.

In this fourth specific example, both arm short circuit and load short circuit can be detected with high accuracy. Moreover, in the fourth specific example, unlike the configuration of FIG. 1, the second Rogowski coil 102 and the first Rogowski coil 101 are arranged separately on the source side and the drain side of the semiconductor switching element 11. That is, in the fourth specific example, the second Rogowski coil 102 and the first Rogowski coil 101 are arranged at each position on one side (e.g., conductor 51) and the other side (e.g., conductor 52) of the arm in the current path passing through the arm. Therefore, the fourth specific example has the advantage that the wiring length between the semiconductor switching element 11 and the capacitor 30 (see FIG. 1) can be shortened.

In the fifth concrete example, a second Rogowski coil 102 for detecting arm short circuits and a first Rogowski coil 101 for detecting load short circuits are arranged to cover the current path to be measured, such as a bus bar. In the fifth concrete example, a shield plate made of metal or the like is arranged between the first Rogowski coil 101 and the second Rogowski coil 102. According to this fifth concrete example, it is possible to prevent the current flowing through the first Rogowski coil 101 and the current flowing through the second Rogowski coil 102 from interfering with each other.

Figure 8 is a circuit diagram showing an example of application of the short circuit fault detection device 100 in this embodiment to another power conversion device. Figure 8 shows a step-down chopper 1a as an example of application. Note that in Figure 8, parts corresponding to those shown in Figures 1 and 2 described above are given the same reference numerals.

8, the arm 10 includes a semiconductor switching element 11 and a flywheel diode 12 connected in inverse parallel to the semiconductor switching element 11. In this example, the semiconductor switching element 11 is also a MOSFET. The drain of the semiconductor switching element 11 is connected to the positive electrode of the DC power supply 40 and one electrode of the capacitor 30 via a conductor 51, and the source of the semiconductor switching element 11 is connected to the cathode of the diode 302 via a conductor 52. The anode of the diode 302 is connected to the negative electrode of the DC power supply 40 and the other electrode of the capacitor 30. That is, the diode 302 is connected in series to the arm 10. The diode 302 is connected in parallel to the series circuit of the reactor 301 and the load Za. The gate drive circuit 20 drives the semiconductor switching element 11 ON/OFF by supplying a gate signal to the semiconductor switching element 11.

While the semiconductor switching element 11 is ON, a current flows from the capacitor 30 through the conductor 51, the semiconductor switching element 11, the conductor 52, and the reactor 301 to the load Za. When the semiconductor switching element 11 is turned OFF, the electrical energy stored in the reactor 301 while the semiconductor switching element 11 is ON is released, and a current flows through the loop consisting of the reactor 301, the load Za, and the diode 302. In this way, the step-down chopper 1a, which is a power conversion device, supplies power to the load Za through the arm 10 including the semiconductor switching element 11.

In the configuration shown in FIG. 8, the conductor 52 between the semiconductor switching element 11 and the diode 302 is inserted through the first Rogowski coil 101 and the second Rogowski coil 102. The first Rogowski coil 101 is a coil optimized for detecting a load short-circuit current, and the second Rogowski coil 102 is a coil optimized for detecting a short-circuit current flowing through the arm 10 due to a short-circuit failure of the diode 302.

The arm short-circuit determination circuit 112 is a circuit that determines that a short-circuit failure has occurred in the diode 302 in the step-down chopper 1a based on the second detection signal S2 obtained from the second Rogowski coil 102. Specifically, when the second detection signal S2 maintains a level higher than the second reference level Vref2 beyond the second reference time Tref2, the arm short-circuit determination circuit 112 determines that a short circuit has occurred in the diode 302, and changes the short-circuit determination signal E2 from the inactive level "0" to the active level "1."

The load short-circuit determination circuit 111 is a circuit that determines that a load short-circuit has occurred in the step-down chopper 1a based on the first detection signal S1 obtained from the first Rogowski coil 101. Specifically, when the first detection signal S1 maintains a level higher than the first reference level Vref1 beyond the first reference time Tref1, the load short-circuit determination circuit 111 determines that a load short-circuit has occurred and changes the short-circuit determination signal E1 from the inactive level "0" to the active level "1."

The shutoff control circuit 120 detects that some kind of short circuit fault has occurred in the step-down chopper 1a based on the short circuit discrimination signals E1 and E2, and outputs a shutoff signal C that stops the drive of the semiconductor switching element 11, and also outputs a fault signal F to the control device 1000 (see Figure 1).

This step-down chopper 1a also provides the same effects as the power conversion device 1 shown in Figure 1 above.

<Other embodiments>
Although one embodiment of the present invention has been described above, other embodiments of the present invention are also possible. For example, the following embodiments are possible.

(1) This invention may be applied to other types of power conversion devices, such as inverters other than three-phase and DC/DC converters other than step-down choppers.

(2) In the above embodiment, a MOSFET is given as an example of a semiconductor switching element, but the semiconductor switching element is not limited to this and may be another semiconductor switching element such as an IGBT (Insulated Gate Bipolar Transistor).

(3) In the above embodiment, the arm short-circuit determination circuit 111, the load short-circuit determination circuit 112, and the shutoff control circuit 120 are provided separately, but these circuits may be implemented as a single circuit.

(4) In the configuration of FIG. 1, the short-circuit fault detection device 100 is provided in half of the two or more arms of the power conversion device, but the short-circuit fault detection device 100 may be provided in some of the two or more arms, or at least half of the two or more arms. In this way, the redundancy of the power conversion device is increased, and safety can be improved.

(5) In the configuration of Figure 1, the above-mentioned conditions 1 and 2 are satisfied by providing the short-circuit fault detection devices 100_2, 100_4, and 100_6, each having both the first Rogowski coil 101 and the second Rogowski coil 102, in the arms 10_2, 100_4, and 100_6, which are all lower arms. However, the above-mentioned conditions 1 and 2 may be satisfied by providing a short-circuit fault detection device having only the first Rogowski coil 101 and a short-circuit fault detection device having only the second Rogowski coil 102 in different arms. For example, a short circuit fault detection device having a first Rogowski coil 101 capable of detecting a load short circuit fault may be provided on each of the upper arms 10_1, 10_3, and 10_5 provided between the high potential power supply and the load Z, and a short circuit fault detection device having a second Rogowski coil 102 capable of detecting an arm short circuit fault may be provided on each of the lower arms 10_2, 10_4, and 10_6 provided between the low potential power supply and the load Z. In this embodiment as well, the above-mentioned conditions 1 and 2 are satisfied.

1...power conversion device, 1a...step-down chopper, 30...capacitor, 40...DC power supply, 10_1 to 10_6, 10...arm, 20_1 to 20_6, 20...gate drive circuit, 100_2, 100_4, 100_6, 100...short circuit fault detection device, 11, 11D...semiconductor switching element, 12...flywheel diode, 302...diode, 51, 52...conductor, 101...first Rogowski coil, 102...second Rogowski coil, 41, 43...forward path, 42, 44...return path, 70...main wiring board, 61...first layer wiring board, 62...second layer wiring board, 63...third layer wiring board, 112...arm short circuit determination circuit, 111...load short circuit determination circuit, 120...shutdown control circuit, Z, Za...load.

Claims (7)

1. A power conversion device that supplies power to a load through two or more arms including semiconductor switching elements,
A short circuit fault detection device is provided in a part of the two or more arms,
A short circuit fault detection device provided in the part of the arms ,
a first Rogowski coil that outputs a first detection signal corresponding to a current flowing through an arm in which the short circuit fault detection device is provided due to a short circuit in the load, and a circuit that detects a short circuit fault based on the first detection signal;
a second Rogowski coil that outputs a second detection signal corresponding to a current flowing through the arm when a short circuit occurs in the arm provided with the short circuit fault detection device or in another arm, and a circuit that detects a short circuit fault based on the second detection signal;
A power conversion device, characterized in that the sensitivity of a detection signal to a time gradient of the detection current of the second Rogowski coil is lower than the sensitivity of the detection signal to a time gradient of the detection current of the first Rogowski coil . The power conversion device according to claim 1 , wherein a short-circuit fault detection device including both the first Rogowski coil and the second Rogowski coil is provided in one of the arms. The power conversion device according to claim 1 , wherein a short-circuit fault detection device having only the first Rogowski coil and a short-circuit fault detection device having only the second Rogowski coil are provided in different arms among the some of the arms. 3. The power conversion device according to claim 2, wherein the short-circuit fault detection device is provided in at least half of the two or more arms. 5. The power conversion device according to claim 2, wherein the first Rogowski coil and the second Rogowski coil are arranged at positions on one side and the other side of the arm in a current path passing through the arm. The power conversion device according to any one of claims 1 to 4, characterized in that the short-circuit fault detection device includes a shutoff control circuit that, when a short-circuit fault is detected, stops driving of a semiconductor switching element of an arm in which the short-circuit fault detection device is provided and a semiconductor switching element of another arm in which the short-circuit fault detection device is not provided. 1. A power conversion device that supplies power to a load through an arm including a semiconductor switching element,
a first Rogowski coil that outputs a first detection signal corresponding to a current flowing through the arm due to a short-circuit fault in the load;
a second Rogowski coil that outputs a second detection signal corresponding to a current flowing through the arm due to a short-circuit failure of a diode connected in series to the arm;
Equipped with
A power conversion device comprising: a short-circuit fault detection device that detects a short-circuit fault based on the first detection signal or the second detection signal.

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