Power conversion device and failure diagnosis method for switching element

Abstract

A power conversion device with a 3-level TNPP circuit of one form has: a voltage detection section that detects the voltage between a DC positive electrode and a DC neutral point, the voltage between the DC neutral point and a DC negative electrode, and the voltage between the DC positive electrode and the DC negative electrode; a test pulse output section that outputs a test pulse to an inner side switching element connected in forward direction from the DC neutral point toward an AC output terminal in the case where the voltage detected by the voltage detection section rises beyond a prescribed threshold value within a low voltage region, respectively; and a determination section that, in the case where the test pulse output section outputs a test pulse to the inner side switching element connected in forward direction from the DC neutral point toward the AC output terminal, determines that a short circuit failure has occurred in an outer side switching element connected to the DC negative electrode if the voltage between the DC neutral point and the DC negative electrode detected by the voltage detection section falls.

Description

Technical Field

[0001] This invention relates to a fault diagnosis method for power conversion devices and switching elements. Background Technology

[0002] A power conversion device that performs power conversion to supply DC power from a DC power supply device such as a solar power (PV) device to an AC power grid includes switching elements such as multiple IGBTs (Insulated Gate Bipolar Transistors).

[0003] Conventionally, fault diagnosis of switching elements is performed manually during inspections before power conversion devices are shipped from the factory. Furthermore, Patent Document 1 discloses an example of a power conversion device capable of fault diagnosis of switching elements.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6699253 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in the past, after the power conversion device was installed or stored for a long period of time, it was sometimes impossible to determine whether the switching elements were damaged when the power conversion device was first operated. For example, if the operator did not notice that the switching elements were damaged and operated the power conversion device, accidents or damage to components may occur.

[0009] The purpose of this invention is to provide a fault diagnosis method for power conversion devices and switching elements, which can diagnose the presence or absence of short-circuit faults in switching elements even when the device remains connected to a DC power supply.

[0010] Methods used to solve problems

[0011] One aspect of the present invention relates to a power conversion device equipped with a 3-level TNPP circuit, characterized by comprising: a voltage detection unit for detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit for outputting a test pulse to an inner switching element positively connected from the DC neutral point toward the AC output terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit for determining that a short circuit fault has occurred in an outer switching element connected to the DC negative terminal if the voltage detected by the voltage detection unit decreases when the test pulse output unit outputs a test pulse to the inner switching element positively connected from the DC neutral point toward the AC output terminal.

[0012] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level TNPP circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs a test pulse to an inner switching element connected in reverse from the DC neutral point toward the AC output terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs a test pulse to the inner switching element connected in reverse from the DC neutral point toward the AC output terminal, determines that a short circuit fault has occurred in the outer switching element connected to the DC positive terminal if the voltage detected by the voltage detection unit decreases when the voltage between the DC positive terminal and the DC neutral point drops.

[0013] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level TNPP circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs a test pulse to an outer switching element connected to the DC positive terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs a test pulse to the outer switching element connected to the DC positive terminal, determines that a short circuit fault has occurred in the inner switching element connected in reverse from the DC neutral point toward the AC output terminal if the voltage detected by the voltage detection unit decreases when the voltage between the DC positive terminal and the DC neutral point is lowered when the test pulse output unit outputs a test pulse to the outer switching element connected to the DC positive terminal.

[0014] Furthermore, one aspect of the present invention relates to a power conversion device equipped with a 3-level TNPP circuit, characterized by comprising: a voltage detection unit for detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit for outputting a test pulse to an external switching element connected to the DC positive terminal when the voltages detected by the voltage detection unit rise above a predetermined threshold; and a determination unit for determining that a short circuit fault has occurred in the external switching element connected to the DC negative terminal if the voltage detected by the voltage detection unit drops when the test pulse output unit outputs a test pulse to the external switching element connected to the DC positive terminal.

[0015] Furthermore, one aspect of the present invention relates to a power conversion device equipped with a 3-level TNPP circuit, characterized by comprising: a voltage detection unit for detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit for outputting a test pulse to an external switching element connected to the DC negative terminal when the voltages detected by the voltage detection unit rise above a predetermined threshold; and a determination unit for determining that a short circuit fault has occurred in the external switching element connected to the DC positive terminal if the voltage detected by the voltage detection unit drops when the test pulse output unit outputs a test pulse to the external switching element connected to the DC negative terminal.

[0016] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level TNPP circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs a test pulse to an outer switching element connected to the DC negative terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs a test pulse to the outer switching element connected to the DC negative terminal, determines that a short circuit fault has occurred in the inner switching element connected in the positive direction from the DC neutral point toward the AC output terminal if the voltage detected by the voltage detection unit decreases when the voltage between the DC neutral point and the DC negative terminal is lowered when the test pulse output unit outputs a test pulse to the outer switching element connected to the DC negative terminal.

[0017] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level NPP circuit, characterized by comprising: a voltage detection unit for detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit for outputting test pulses to an outer switching element connected to the DC positive terminal and an inner switching element on the DC positive terminal side when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit for determining that a short circuit fault has occurred in the inner switching element on the DC negative terminal side if the voltage detected by the voltage detection unit decreases when the test pulse output unit outputs test pulses to the outer switching element connected to the DC positive terminal and the inner switching element on the DC positive terminal side.

[0018] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level NPP circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs test pulses to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs test pulses to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side, determines that a short circuit fault has occurred in the outer switching element connected to the DC positive terminal if the voltage detected by the voltage detection unit between the DC positive terminal and the DC neutral point drops when the voltage between the DC positive terminal and the DC neutral point drops.

[0019] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level NPP circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs test pulses to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs test pulses to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side, determines that a short circuit fault has occurred in the outer switching element connected to the DC negative terminal if the voltage detected by the voltage detection unit between the DC neutral point and the DC negative terminal drops.

[0020] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a 3-level NPP circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs test pulses to the inner switching element on the DC negative terminal side and the outer switching element connected to the DC negative terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs test pulses to the inner switching element on the DC negative terminal side and the outer switching element connected to the DC negative terminal, determines that a short circuit fault has occurred in the inner switching element on the DC positive terminal side if the voltage detected by the voltage detection unit between the DC neutral point and the DC negative terminal drops.

[0021] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a two-level switching circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs a test pulse to a switching element connected to the DC positive terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs a test pulse to the switching element connected to the DC positive terminal, determines that a short circuit fault has occurred in the switching element connected to the DC negative terminal if the voltages detected by the voltage detection unit between the DC positive terminal and the DC neutral point and between the DC neutral point and the DC negative terminal decrease.

[0022] Furthermore, one aspect of the power conversion device according to the present invention is a power conversion device equipped with a two-level switching circuit, characterized by comprising: a voltage detection unit that detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output unit that outputs a test pulse to a switching element connected to the DC negative terminal when the voltages detected by the voltage detection unit rise and exceed a predetermined threshold; and a determination unit that, when the test pulse output unit outputs a test pulse to the switching element connected to the DC negative terminal, determines that a short circuit fault has occurred in the switching element connected to the DC positive terminal if the voltages detected by the voltage detection unit between the DC positive terminal and the DC neutral point and between the DC neutral point and the DC negative terminal decrease.

[0023] Furthermore, a fault diagnosis method for a switching element in a 3-level TNPP circuit according to one aspect of the present invention is characterized by comprising: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting a test pulse to an inner switching element positively connected from the DC neutral point toward the AC output terminal when the detected voltages rise above a predetermined threshold; and a determination step, determining that if the voltage between the DC neutral point and the DC negative terminal drops when a test pulse is output to the inner switching element positively connected from the DC neutral point toward the AC output terminal, a short circuit fault has occurred in the outer switching element connected to the DC negative terminal.

[0024] Furthermore, a fault diagnosis method for a switching element in a 3-level TNPP circuit according to one aspect of the present invention is characterized by comprising: a voltage detection step, which detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, which outputs a test pulse to an inner switching element that is reverse-connected from the DC neutral point toward the AC output terminal when the detected voltages rise above a predetermined threshold; and a determination step, which determines that a short-circuit fault has occurred in an outer switching element connected to the DC positive terminal if the voltage between the DC positive terminal and the DC neutral point drops when a test pulse has been output to the inner switching element that is reverse-connected from the DC neutral point toward the AC output terminal.

[0025] Furthermore, a fault diagnosis method for a switching element in a 3-level TNPP circuit according to one aspect of the present invention is characterized by comprising: a voltage detection step, which detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, which outputs a test pulse to the outer switching element connected to the DC positive terminal when the detected voltages rise above a predetermined threshold; and a determination step, which determines that a short circuit fault has occurred in the inner switching element connected in reverse from the DC neutral point toward the AC output terminal if the voltage between the DC positive terminal and the DC neutral point drops when a test pulse has been output to the outer switching element connected to the DC positive terminal.

[0026] Furthermore, a fault diagnosis method for a switching element in a 3-level TNPP circuit according to one aspect of the present invention is characterized by comprising: a voltage detection step, which detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, which outputs a test pulse to an external switching element connected to the DC positive terminal when the detected voltages rise above a predetermined threshold; and a determination step, which determines that a short circuit fault has occurred in the external switching element connected to the DC negative terminal if the voltage between the DC positive terminal and the DC negative terminal drops when a test pulse has been output to the external switching element connected to the DC positive terminal.

[0027] Furthermore, a fault diagnosis method for a switching element in a 3-level TNPP circuit according to one technical solution of the present invention is characterized by comprising: a voltage detection step, which detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, which outputs a test pulse to an external switching element connected to the DC negative terminal when the detected voltages rise above a predetermined threshold; and a determination step, which determines that a short circuit fault has occurred in the external switching element connected to the DC positive terminal if the voltage between the DC positive terminal and the DC negative terminal drops when a test pulse has been output to the external switching element connected to the DC negative terminal.

[0028] Furthermore, a fault diagnosis method for a switching element according to one aspect of the present invention is a fault diagnosis method for a switching element in a 3-level TNPP circuit, characterized by comprising: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting a test pulse to the outer switching element connected to the DC negative terminal when the detected voltages rise above a predetermined threshold; and a determination step, in which, when a test pulse is output to the outer switching element connected to the DC negative terminal, if the voltage between the DC neutral point and the DC negative terminal drops, it is determined that a short circuit fault has occurred in the inner switching element connected in the positive direction from the DC neutral point toward the AC output terminal.

[0029] Furthermore, a fault diagnosis method for a switching element according to one technical solution of the present invention is a fault diagnosis method for a switching element in a 3-level NPP circuit, characterized by comprising: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting test pulses to the outer switching element connected to the DC positive terminal and the inner switching element on the DC positive terminal side when the detected voltages rise and exceed a predetermined threshold; and a determination step, determining that if the voltage between the DC positive terminal and the DC neutral point drops when test pulses are output to the outer switching element connected to the DC positive terminal and the inner switching element on the DC positive terminal side, a short circuit fault has occurred in the inner switching element on the DC negative terminal side.

[0030] A fault diagnosis method for switching elements according to a technical solution of the present invention is a fault diagnosis method for switching elements in a 3-level NPP circuit, characterized by comprising: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting test pulses to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side when the detected voltages rise and exceed a predetermined threshold; and a determination step, determining that if the voltage between the DC positive terminal and the DC neutral point drops when test pulses are output to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side, a short circuit fault has occurred in the outer switching element connected to the DC positive terminal.

[0031] Furthermore, a fault diagnosis method for a switching element according to one technical solution of the present invention is a fault diagnosis method for a switching element in a 3-level NPP circuit, characterized by comprising: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting test pulses to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side when the detected voltages rise and exceed a predetermined threshold; and a determination step, determining that if the voltage between the DC neutral point and the DC negative terminal drops when test pulses are output to the inner switching element on the DC positive terminal side and the inner switching element on the DC negative terminal side, a short circuit fault has occurred in the outer switching element connected to the DC negative terminal.

[0032] Furthermore, a fault diagnosis method for a switching element according to a technical solution of the present invention is a fault diagnosis method for a switching element in a 3-level NPP circuit, characterized by comprising: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting test pulses to the inner switching element on the DC negative terminal side and the outer switching element connected to the DC negative terminal when the detected voltages rise and exceed a predetermined threshold; and a determination step, determining that if the voltage between the DC neutral point and the DC negative terminal drops when test pulses are output to the inner switching element on the DC negative terminal side and the outer switching element connected to the DC negative terminal, a short circuit fault has occurred in the inner switching element on the DC positive terminal side.

[0033] Furthermore, a fault diagnosis method for a switching element according to one technical solution of the present invention is a fault diagnosis method for a switching element provided in a 2-level switching circuit, characterized in that it includes: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting a test pulse to the switching element connected to the DC positive terminal when the detected voltages rise and exceed a predetermined threshold; and a determination step, in which, when a test pulse is output to the switching element connected to the DC positive terminal, if the voltage between the DC positive terminal and the DC neutral point and the voltage between the DC neutral point and the DC negative terminal decreases, it is determined that a short circuit fault has occurred in the switching element connected to the DC negative terminal.

[0034] Furthermore, a fault diagnosis method for a switching element according to one technical solution of the present invention is a fault diagnosis method for a switching element in a 2-level switching circuit, characterized in that it includes: a voltage detection step, detecting the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal; a test pulse output step, outputting a test pulse to the switching element connected to the DC negative terminal when the detected voltages rise and exceed a predetermined threshold; and a determination step, in which, when a test pulse is output to the switching element connected to the DC negative terminal, if the voltage between the DC positive terminal and the DC neutral point and the voltage between the DC neutral point and the DC negative terminal decrease, it is determined that a short circuit fault has occurred in the switching element connected to the DC positive terminal.

[0035] Invention Effects

[0036] According to the present invention, the presence or absence of a short-circuit fault in a switching element can be diagnosed even while maintaining the connection to a DC power supply device. Attached Figure Description

[0037] Figure 1 This is a diagram showing an example of the configuration of the power system of the power conversion device according to the first embodiment.

[0038] Figure 2 This is a diagram showing a TNPP circuit with one phase, representing a 3-level TNPP circuit.

[0039] Figure 3 This is a graph showing the relationship between the output target of the test pulse and the short-circuit faulty component in the fault diagnosis of the power conversion device.

[0040] Figure 4 This is a diagram illustrating an example of the configuration of a power system having the power conversion device according to the second embodiment.

[0041] Figure 5 This is a diagram showing a 3-level NPP circuit with a 1-phase NPP circuit.

[0042] Figure 6 This is a graph showing the relationship between the output target of the test pulse and the short-circuit faulty component in the fault diagnosis of the power conversion device.

[0043] Figure 7 This is a diagram illustrating an example of the configuration of a power system having the power conversion device according to the third embodiment.

[0044] Figure 8 This is a diagram showing a 2-level switching circuit with one phase.

[0045] Figure 9 This is a graph showing the relationship between the output target of the test pulse and the short-circuit faulty component in the fault diagnosis of the power conversion device. Detailed Implementation

[0046] Hereinafter, an embodiment of a power system having a power conversion device will be described using the accompanying drawings.

[0047] <First Implementation>

[0048] Figure 1 This is a diagram illustrating an example configuration of a power system 1 having the power conversion device according to the first embodiment. (See diagram below.) Figure 1 As shown, the power system 1 is configured such that the power conversion device 2 converts the DC power output from, for example, the solar power generation device 10 and supplies it to the AC power grid 12.

[0049] The power conversion device 2 has, for example, a three-phase three-level TNPP (Three Level T-Typed NeutralPoint Piloted) circuit 20, a filter 21, a circuit breaker 22, a circuit breaker 23, a voltmeter 24, a voltmeter 25, a voltage detection unit 26, an execution judgment unit 27, a test pulse output unit 28, and a judgment unit 29.

[0050] The 3-level TNPP circuit 20 is an inverter circuit that performs power conversion on the three phases (U, V, and W) in TNPP mode.

[0051] Filter 21, for example, is an LC filter that filters the three-phase power output from the 3-level TNPP circuit 20 and outputs it to the circuit breaker 23.

[0052] Circuit breaker 22 disconnects the DC power output from the solar power generation device 10. Circuit breaker 23 disconnects the power output from the filter 21.

[0053] The voltmeter 24 measures the voltage between the DC positive terminal (P) and the DC neutral point (C) of the 3-level TNPP circuit 20 and outputs it to the voltage detection unit 26.

[0054] The voltmeter 25 measures the voltage between the DC neutral point (C) and the DC negative terminal (N) of the 3-level TNPP circuit 20 and outputs it to the voltage detection unit 26.

[0055] The voltage detection unit 26 detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal based on the voltage measured by the voltmeter 24 and the voltage measured by the voltmeter 25, and outputs the detection results to the execution judgment unit 27 and the determination unit 29.

[0056] When the voltage detected by the voltage detection unit 26 rises and exceeds a predetermined threshold, the execution judgment unit 27 makes a judgment so that the power conversion device 2 performs a self-diagnosis of the fault of the switching element.

[0057] When the execution judgment unit 27 determines that self-diagnosis is to be performed, the test pulse output unit 28 outputs test pulses to each switching element of the 3-level TNPP circuit 20 as described later. The test pulse is, for example, a single pulse of a few milliseconds.

[0058] When the test pulse output unit 28 outputs a predetermined test pulse as described later, the determination unit 29 determines, based on at least one of the voltages detected by the voltage detection unit 26, whether a short circuit fault has occurred in each of the switching elements of the 3-level TNPP circuit 20.

[0059] Figure 2 This is a diagram showing a 3-level TNPP circuit 20 with one phase. The 3-level TNPP circuit 20 has three phases respectively. Figure 2 The TNPP circuit shown is illustrated below. The switching elements are described as follows.

[0060] Q1: External switching element connected to the DC positive terminal

[0061] Q2: The inner switching element connected in a positive direction from the DC neutral point toward the AC output terminal.

[0062] Q3: Inner switching element connected in reverse from DC neutral point to AC output terminal.

[0063] Q4: External switching element connected to the DC negative terminal

[0064] Figure 3 This is a diagram showing the relationship between the output target of the test pulse and the short-circuit fault element (switching element) in the fault diagnosis of the power conversion device 2.

[0065] like Figure 3 As shown, when the test pulse output unit 28 outputs a test pulse to the inner switching element that is positively connected from the DC neutral point to the AC output terminal, if the voltage detection unit 26 detects a drop in the voltage between the DC neutral point and the DC negative terminal, the determination unit 29 determines that a short circuit fault has occurred in the outer switching element connected to the DC negative terminal.

[0066] Furthermore, if the test pulse output unit 28 outputs a test pulse to the inner switching element that is connected in reverse from the DC neutral point to the AC output terminal, and the voltage detection unit 26 detects a drop in the voltage between the DC positive terminal and the DC neutral point, the determination unit 29 determines that a short circuit fault has occurred in the outer switching element connected to the DC positive terminal.

[0067] Furthermore, if the voltage detection unit 26 detects a drop in the voltage between the DC positive terminal and the DC neutral point when the test pulse output unit 28 outputs a test pulse to the outer switching element connected to the DC positive terminal, the determination unit 29 determines that a short circuit fault has occurred in the inner switching element that is connected in reverse from the DC neutral point toward the AC output terminal.

[0068] Furthermore, if the voltage detection unit 26 detects a drop in the voltage between the DC positive and DC negative terminals when the test pulse output unit 28 outputs a test pulse to the external switching element connected to the DC positive terminal, the determination unit 29 determines that a short circuit fault has occurred in the external switching element connected to the DC negative terminal.

[0069] Furthermore, if the voltage detection unit 26 detects a drop in the voltage between the DC positive and DC negative terminals when the test pulse output unit 28 outputs a test pulse to the external switching element connected to the DC negative terminal, the determination unit 29 determines that a short circuit fault has occurred in the external switching element connected to the DC positive terminal.

[0070] Furthermore, if the voltage detection unit 26 detects a drop in the voltage between the DC neutral point and the DC negative terminal when the test pulse output unit 28 outputs a test pulse to the outer switching element connected to the DC negative terminal, the determination unit 29 determines that a short circuit fault has occurred in the inner switching element that is connected in the positive direction from the DC neutral point toward the AC output terminal.

[0071] In addition, to avoid PN short circuit, the preferred diagnostic sequence for the power conversion device 2 is to diagnose Q1 and Q4 after diagnosing Q2 and Q3.

[0072] <Second Implementation Method>

[0073] Figure 4 This is a diagram illustrating an example configuration of a power system 1a having the power conversion device according to the second embodiment. (See diagram below.) Figure 4 As shown, the power system 1a is configured such that the power conversion device 2a converts the DC power output from, for example, the solar power generation device 10 and supplies it to the AC power grid 12. Hereinafter, unless otherwise described, configurations substantially the same as those described above will be given the same reference numerals.

[0074] The power conversion device 2a has, for example, a 3-phase 3-level NPP (Neutral Point Piloted) circuit 20a, a filter 21, a circuit breaker 22, a circuit breaker 23, a voltmeter 24, a voltmeter 25, a voltage detection unit 26, an execution judgment unit 27, a test pulse output unit 28, and a judgment unit 29.

[0075] The 3-level NPP circuit 20a is an inverter circuit that performs power conversion on the three phases (U-phase, V-phase, and W-phase) using NPP mode.

[0076] Figure 5 This is a diagram showing a 3-level NPP circuit 20a with one phase. The 3-level NPP circuit 20a has the following characteristics for each of the three phases: Figure 5 The NPP circuit shown is illustrated below. The switching elements are described as follows.

[0077] Q1: External switching element connected to the DC positive terminal

[0078] Q2: Inner switching element on the DC positive side

[0079] Q3: Inner switching element on the DC negative side

[0080] Q4: External switching element connected to the DC negative terminal

[0081] Figure 6 This is a diagram showing the relationship between the output target of the test pulse and the short-circuit fault element (switching element) in the fault diagnosis of the power conversion device 2a.

[0082] like Figure 6 As shown, when the test pulse output unit 28 outputs test pulses to the outer switching element connected to the DC positive terminal and the inner switching element on the DC positive terminal side, if the voltage detection unit 26 detects a drop in the voltage between the DC positive terminal and the DC neutral point, the determination unit 29 determines that a short circuit fault has occurred in the inner switching element on the DC negative terminal side.

[0083] Furthermore, if the test pulse output unit 28 outputs a test pulse to the inner switching element on the DC positive side and the inner switching element on the DC negative side, and the voltage detection unit 26 detects a voltage drop between the DC positive terminal and the DC neutral point, the determination unit 29 determines that a short circuit fault has occurred in the outer switching element connected to the DC positive terminal.

[0084] Furthermore, if the test pulse output unit 28 outputs a test pulse to the inner switching element on the DC positive side and the inner switching element on the DC negative side, and the voltage detection unit 26 detects a voltage drop between the DC neutral point and the DC negative point, the determination unit 29 determines that a short circuit fault has occurred in the outer switching element connected to the DC negative point.

[0085] Furthermore, if the test pulse output unit 28 outputs a test pulse to the inner switching element on the DC negative side and the outer switching element connected to the DC negative side, and the voltage detection unit 26 detects a voltage drop between the DC neutral point and the DC negative side, the determination unit 29 determines that a short circuit fault has occurred in the inner switching element on the DC positive side.

[0086] <Third Implementation Method>

[0087] Figure 7 This is a diagram illustrating an example configuration of a power system 1b having the power conversion device according to the third embodiment. (See diagram for example.) Figure 7 As shown, the power system 1b is configured such that the power conversion device 2b converts the DC power output from, for example, the solar power generation device 10 and supplies it to the AC power grid 12. Hereinafter, unless otherwise described, configurations substantially the same as those described above will be given the same reference numerals.

[0088] The power conversion device 2b includes, for example, a 3-phase 2-level switching circuit 20b, a filter 21, a circuit breaker 22, a circuit breaker 23, a voltmeter 24, a voltmeter 25, a voltage detection unit 26, an execution judgment unit 27, a test pulse output unit 28, and a judgment unit 29.

[0089] The 2-level switching circuit 20b is an inverter circuit that performs 2-level power conversion on the three phases of U, V and W respectively.

[0090] Figure 8 This diagram illustrates a 2-level switching circuit 20b with one phase. The 2-level switching circuit 20b has the following characteristics for each of the three phases: Figure 8 The circuit shown is a 2-level switch circuit. Here, the switching elements are described as follows.

[0091] Q1: Switching element connected to the DC positive terminal

[0092] Q4: Switching element connected to the DC negative terminal

[0093] Figure 9 This is a diagram showing the relationship between the output target of the test pulse and the short-circuit fault element (switching element) in the fault diagnosis of the power conversion device 2b.

[0094] like Figure 9 As shown, when the test pulse output unit 28 outputs a test pulse to the switching element connected to the DC positive terminal, if the voltage detection unit 26 detects a drop in the voltage between the DC positive terminal and the DC neutral point, and the voltage between the DC neutral point and the DC negative terminal, the determination unit 29 determines that a short circuit fault has occurred in the switching element connected to the DC negative terminal.

[0095] Furthermore, if the voltage between the DC positive terminal and the DC neutral point, and the voltage between the DC neutral point and the DC negative terminal, detected by the voltage detection unit 26, decrease when the test pulse output unit 28 outputs a test pulse to the switching element connected to the DC negative terminal, the determination unit 29 determines that a short circuit fault has occurred in the switching element connected to the DC positive terminal.

[0096] In this way, even if the DC power supply connected to the solar power generation device 10 remains unchanged, power conversion devices 2, 2a, and 2b can still diagnose the presence or absence of short-circuit faults in the switching elements.

[0097] For example, in the low-voltage region of the main circuit voltage charging such as sunrise, power conversion devices 2, 2a and 2b diagnose the presence or absence of short-circuit faults in the switching elements by sequentially outputting short-duration test pulses to all components based on the change in DC voltage (or the condition of DC current from the solar power generation device 10).

[0098] For example, power conversion devices 2, 2a, and 2b charge to a low voltage of around 50V and perform automatic diagnostics.

[0099] That is, power conversion devices 2, 2a and 2b can safely perform diagnostics by outputting test pulses in low voltage regions, and can prevent short circuit accidents and secondary damage to other components.

[0100] Label Explanation

[0101] 1, 1a, 1b… Power system; 2, 2a, 2b… Power conversion device; 10… Solar power generation device; 12… AC power grid; 20… 3-level TNPP circuit; 20a… 3-level NPP circuit; 20b… 2-level switching circuit; 21… Filter; 22… Circuit breaker; 23… Circuit breaker; 24… Voltmeter; 25… Voltmeter; 26… Voltage detection unit; 27… Execution judgment unit; 28… Test pulse output unit; 29… Judgment unit.

Claims

1. A power conversion device comprising a 3-level TNPP circuit, characterized in that, have: The voltage detection unit detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal. The test pulse output section outputs a test pulse to the inner switching element that is positively connected from the DC neutral point toward the AC output terminal when the voltage detected by the voltage detection section rises and exceeds a predetermined threshold in the low voltage region. as well as If the test pulse output unit outputs a test pulse to the inner switching element that is positively connected from the DC neutral point to the AC output terminal, and the voltage detection unit detects a voltage drop between the DC neutral point and the DC negative terminal, then it determines that a short circuit fault has occurred in the outer switching element connected to the DC negative terminal.

2. A power conversion device comprising a 3-level TNPP circuit, characterized in that, have: The voltage detection unit detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal. The test pulse output section outputs a test pulse to the inner switching element that is connected in reverse from the DC neutral point toward the AC output terminal when the voltage detected by the voltage detection section rises and exceeds a specified threshold in the low voltage region. as well as If the determination unit outputs a test pulse to the inner switching element that is connected in reverse from the DC neutral point to the AC output terminal when the test pulse output unit outputs a test pulse, and if the voltage detection unit detects a drop in the voltage between the DC positive terminal and the DC neutral point, then it determines that a short circuit fault has occurred in the outer switching element connected to the DC positive terminal.

3. A power conversion device comprising a 3-level TNPP circuit, characterized in that, have: The voltage detection unit detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal. The test pulse output unit outputs a test pulse to the external switching element connected to the DC positive terminal when the voltage detected by the voltage detection unit rises and exceeds a specified threshold in the low voltage region. as well as If the voltage detection unit detects a drop in the voltage between the DC positive terminal and the DC neutral point when the test pulse output unit outputs a test pulse to the outer switching element connected to the DC positive terminal, then the determination unit determines that a short circuit fault has occurred in the inner switching element that is connected in reverse from the DC neutral point toward the AC output terminal.

4. A power conversion device comprising a 3-level TNPP circuit, characterized in that, have: The voltage detection unit detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal. The test pulse output unit outputs a test pulse to the external switching element connected to the DC positive terminal when the voltage detected by the voltage detection unit rises and exceeds a specified threshold in the low voltage region. as well as If the voltage detection unit detects a voltage drop between the DC positive and DC negative terminals when the test pulse output unit outputs a test pulse to the external switching element connected to the DC positive terminal, then the determination unit determines that a short circuit fault has occurred in the external switching element connected to the DC negative terminal.

5. A power conversion device comprising a 3-level TNPP circuit, characterized in that, have: The voltage detection unit detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal. The test pulse output unit outputs a test pulse to the external switching element connected to the DC negative terminal when the voltage detected by the voltage detection unit rises and exceeds a specified threshold in the low voltage region. as well as If the voltage detection unit detects a voltage drop between the DC positive and DC negative terminals when the test pulse output unit outputs a test pulse to the external switching element connected to the DC negative terminal, then the determination unit determines that a short circuit fault has occurred in the external switching element connected to the DC positive terminal.

6. A power conversion device comprising a 3-level TNPP circuit, characterized in that, have: The voltage detection unit detects the voltage between the DC positive terminal and the DC neutral point, the voltage between the DC neutral point and the DC negative terminal, and the voltage between the DC positive terminal and the DC negative terminal. The test pulse output unit outputs a test pulse to the external switching element connected to the DC negative terminal when the voltage detected by the voltage detection unit rises and exceeds a specified threshold in the low voltage region. as well as If the test pulse output unit outputs a test pulse to the outer switching element connected to the DC negative terminal, and the voltage detection unit detects a voltage drop between the DC neutral point and the DC negative terminal, then the determination unit determines that a short circuit fault has occurred in the inner switching element that is connected in the positive direction from the DC neutral point toward the AC output terminal.

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