Power conversion device and power conditioner

Abstract

To provide a power conversion device capable of detecting contact abnormality in a grid-connected relay without outputting an inverter output.SOLUTION: A power conversion device includes an inverter, a relay system connection end connected to a system power source side, an electric line between the inverter and the relay system connection end, a grid-connected relay interposed in the electric line, and a relay abnormality detection circuit provided per grid-connected relay. The relay abnormality detection circuit includes a detection power source that makes a detection current flow toward a detection unit, a first open / close unit between the detection power source and one end of the grid-connected relay and a second open / close unit connected to the other end of the grid-connected relay. The detection unit is connected to the second open / close unit and outputs a detection signal when the detection current is detected, and the relay abnormality detection circuit closes the first open / close unit and the second open / close unit by receiving the output stop of AC power and open of a relay portion and detects the abnormality of the grid-connected relay by the detection signal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a power conversion device and a power conditioner that control DC power sources such as photovoltaic cells, wind power generation, and fuel cells, and to detection of abnormalities such as contact abnormality and welding in an interconnection relay used for system interconnection in the device. [Background technology]

[0002] A power conversion device such as a power conditioner can control power from a DC power source, link with a (commercial) grid power source, and supply power directly and indirectly to an AC load such as a household load. The power conversion device supplies power through the contacts of a relay, but in the event of an abnormality or shutdown, the power conversion device must be isolated from the grid power source and the load. In such a power conversion device, the contacts of each relay must be kept in a closed state, i.e., closed state, while the device is connected to the grid power source or while power is being supplied to the load. On the other hand, while the device is stopped, the contacts of the relay must be in an open state, i.e., open. In addition, for example, when a ground fault or short circuit occurs in a distribution line in which the power conversion device is operating in a grid-connected state, or when the transmission of power from a substation to the distribution line is stopped due to a planned blackout or the like (i.e., when an isolated operation state is reached), in order to prevent an influence on the operation and to ensure safety during maintenance work on the distribution line, etc., a grid-connection relay (also called a grid-connection relay) is opened, and the power conversion device is disconnected from the grid power source. However, due to contact abnormality or welding of the contact piece of the relay unit, the relay unit may be in a closed state even though the interconnection relay should be in an open state.

[0003] In order to detect such contact abnormalities, welding, etc., a method is known as a conventional technique in which an auxiliary contact piece is provided to detect welding, etc. (Patent Document 1). However, in this case, the power supplied to the exciting coil for operating the relay unit becomes large, and a solution to this problem has arisen. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2014 / 020671 Summary of the Invention [Problem to be solved by the invention]

[0005] Meanwhile, as another conventional method for detecting contact abnormality, welding, etc. in a system-connected relay, there is a method for electrically detecting the contact abnormality by outputting an AC inverter output from an inverter in a power conversion device to the system side. However, in this method, in the event of a power outage on the system side, a reverse current occurs from the low voltage side to the high voltage side in a transformer (pole transformer) that converts high voltage to low voltage, so that an excessive voltage occurs on the high voltage side. Therefore, there is a demand for an electrical contact abnormality detection method that does not output this inverter output. However, although the above-mentioned Patent Document 1 detects contact abnormality, welding, etc., and discloses a technology for solving the problem of an increase in the power supplied to an exciting coil for operating a relay unit, it does not disclose or suggest any solution to the problem of the reverse current occurrence in the method for electrically detecting contact abnormality by outputting the inverter output.

[0006] In view of the above, an object of the present invention is to provide a power conversion device and a power conditioner that can detect a contact abnormality in a grid interconnection relay without outputting an inverter output, and that can also contribute to energy saving. [Means for solving the problem]

[0007] As a result of various investigations, the present inventors have found that the above object can be achieved by the present invention described below.

[0008] That is, the power conversion device according to the present invention is A power conversion device including an inverter that receives output power from a DC power source or power obtained by voltage-converting the output power from the DC power source and converts it into AC power, and a relay system connection terminal that is connected to a system power source side, Further, the power supply system includes at least one electric line between the inverter and the relay system connection end, an interconnection relay interposed in at least one of the at least one electric line, and a relay abnormality detection circuit provided for each of the interconnection relays, the relay abnormality detection circuit has a detection power supply that flows a detection current toward a detection unit, a first opening / closing unit between the detection power supply and one end of the interconnection relay, and a second opening / closing unit connected to the other end of the interconnection relay, the detection unit is connected to the second opening / closing unit, and outputs a detection signal when the detection current is detected, The inverter stops output of the AC power in response to a command from an inverter output stop command unit, and the interconnection relay opens a relay unit in response to a command from a relay open command unit, The relay abnormality detection circuit closes the first opening / closing unit and the second opening / closing unit after a command to stop the output of the AC power is output from the inverter output stop command unit and a command to open the relay unit is output from the relay open command unit, and detects an abnormality in the interconnection relay based on the detection signal from the detection unit. The relay abnormality detection circuit may detect a contact abnormality or a welding in the interconnection relay. Also, the detection power supply may be an insulated power supply.

[0009] As can be seen from the above configuration, the power conversion device according to the present invention does not perform electrical detection by outputting an AC inverter output from the inverter to the grid side as in the conventional case, because the inverter output stop command unit outputs a command to stop the output of the AC power, and the first and second switching units are closed after the relay open command unit outputs a command to open the relay unit, so that in the event of an abnormality in the grid relay such as a contact abnormality or welding, a detection current flows through the relay unit even though the relay unit is open, and therefore the abnormality in the grid relay is detected by the detection signal from the detection unit. Thus, the power conversion device according to the present invention can detect a contact abnormality in the grid-connection relay without outputting an inverter output as in the conventional case.

[0010] Here, the detection power supply is provided uniquely for each relay abnormality detection circuit. The detection power supply does not use the power output via the inverter, but uses, for example, power branched from the power itself input to the power conversion device. As described above, the detection power supply does not pass a current directed to consumption by the grid or household loads like the inverter output, but passes the detection current toward the detection unit, so it can be seen that the detection power supply is provided uniquely for each relay abnormality detection circuit exclusively for detecting an abnormality in the grid relay. Therefore, the relay abnormality detection circuit should be distinguished from a technology that detects an abnormality in the grid relay by using a voltage from the inverter or the like to compare with a comparator or the like. As described above, since the detection power supply does not pass a current directed to consumption by the grid or household loads like the inverter output, it can also contribute to energy saving.

[0011] The power conversion device according to the present invention may include two-phase electric lines between the inverter and the relay system connection end, the interconnection relays interposed in all of the two-phase electric lines, and the relay abnormality detection circuit provided for each of the interconnection relays. As a result, in a specific configuration in which the interconnection relays are interposed in the two-phase electric lines, so-called U-phase and W-phase, the above-mentioned effects can be achieved.

[0012] The power conditioner according to the present invention comprises: The power conversion device includes: It controls the solar power generation device, which is the DC power source. Therefore, the power conditioner according to the present invention can achieve the same effects as those of the above-mentioned power conversion device. Effect of the Invention

[0013] The power conversion device and power conditioner according to the present invention can detect a contact abnormality in a grid-connection relay without outputting an inverter output, and can also contribute to energy conservation. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an example of a conventional connection including a connection between an inverter and a power grid side and an interconnection relay interposed therebetween. [Diagram 2] FIG. 2 is a diagram showing an example of a connection configuration according to the present embodiment, including a connection between an inverter and a system power supply side, an interconnection relay interposed between them, and a relay abnormality detection circuit provided for each of the interconnection relays. [Diagram 3] FIG. 4 is a diagram showing an example of a detection power supply of the relay abnormality detection circuit in the connection configuration according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same reference numerals indicate the same or corresponding parts, and the description thereof will be omitted as appropriate unless otherwise specified.

[0016] FIG. 1 shows an example of a connection between a conventional power conversion device and a system power supply side. The power conversion device 1 is, for example, a power conditioner (hereinafter also simply referred to as a power conditioner) 1, and is connected to a solar power generation device 200, which is a DC power source, via a DC / DC converter 300 that converts the voltage of the output power of the DC power source, and controls the solar power generation device 200, such as MPPT control (maximum power point tracking control). The power conversion device 1 also includes an inverter 120 to which the DC / DC converter 300 is connected, and the inverter 120 outputs single-phase three-wire [U phase, O phase, W phase] or three-phase [u phase, v phase, w phase] AC power to a switching box 400 that supplies power to a household load L such as a so-called home appliance, but in this embodiment, it outputs single-phase three-wire [U phase, O phase, W phase] AC power. The switching box 400 performs a switching operation so that two of the inverter 120, the system power source G, and the household load L are connected.

[0017] In the power conditioner 1, the inverter 120 and the relay system connection end 110 connected to the system power source G side are connected via the grid relay 130. At least one-phase electric line and the grid relay 130 interposed in at least one of the at least one-phase electric lines are provided between the inverter 120 and the relay system connection end 110. Typically, two-phase [U-phase, W-phase] electric lines Lu, Lw and each of the grid relays 135 (130), 136 (130) interposed in all of the two-phase electric lines are provided between the inverter 120 outputting the single-phase three-wire [U-phase, O-phase, W-phase] AC power and the relay system connection end 110.

[0018] The interconnection relays 135, 136 are provided in the inverter unit 1 for protection in the event of an abnormality in the inverter 1 or an abnormality on the system side (such as a power outage when there is no voltage on the system power supply G side). If the inverter 1 operates with a contact abnormality, such as welding, between the contacts CPu, CPw of the relay parts (relays) Su, Sw included in the interconnection relays 135, 136, this may lead to a breakdown or accident, and therefore it is necessary to detect contact abnormalities, such as welding, in the relays.

[0019] When there is no voltage on the system power supply G side, the ON (closed state of the contacts and the switches) / OFF (open state of the contacts and the switches) combination of the relay unit Su and the relay unit Sw is set to one of three combinations: (Su: ON, Sw: OFF), (Su: OFF, Sw: ON), and (Su: OFF, Sw: OFF). After that, the inverter output of AC power is output from the inverter 120 toward the system side, and a voltage Esd is generated. At this time, the inter-phase voltage Euw between the U phase and the W phase on the system power supply G side is measured, and the voltage |Esd-Euw| is calculated. If the calculation result is equal to or greater than a predetermined threshold, it is detected that a contact abnormality such as welding of the relay unit (hereinafter, welding is taken as an example) has occurred.

[0020] If the relay unit is welded, the inverter output (AC voltage Esd) is output toward the grid, resulting in an unsafe state. That is, until now, it was thought that safety was ensured because the voltage Esd is a low voltage. However, it has been found that in a transformer (pole transformer) that converts high voltage to low voltage, a reverse flow occurs from the low voltage side to the high voltage side, and an excessive voltage is generated on the high voltage side. That is, it has been found that the voltage Esd becomes high voltage through the pole transformer, resulting in an unsafe state on the grid side. In order to address this, a power conversion device according to one embodiment of the present invention will be described below.

[0021] FIG. 2 shows an example of a connection between a power conversion device according to an embodiment of the present invention and a system power supply side. In this embodiment, a relay abnormality detection circuit is provided for each interconnection relay 130 between the inverter 120 and the relay system connection end 110 in comparison with FIG. 1. Specifically, relay abnormality detection circuits 170 and 180 are provided for each interconnection relay 135 and 136. In this embodiment, the relay abnormality detection circuits 170 and 180 detect contact abnormality or welding in the interconnection relays 135 and 136 in the corresponding phases, respectively. Note that the relay abnormality detection circuits that detect the interconnection relay to be determined may be provided on one or both sides of the two phases, but in this embodiment, they are provided on both sides as described above.

[0022] 2 controls the DC / DC converter 300, the inverter 120, the grid-connection relays 135 and 136, the changing unit 400, etc. The control circuit 500 of this embodiment includes an inverter output stop command unit 510 that outputs an inverter output command to stop (and / or start) the output of AC power from the inverter 120, and a relay open command unit 530 that outputs a relay command to open (and / or close) the relay units Su and Sw in the grid-connection relays 135 and 136.

[0023] The relay abnormality detection circuit 170 (180) has a detection power supply V1SR (V2SR) that flows a detection current Iu (Iw) toward a detection unit 179 (189), a first switching unit 173 (183) between the detection power supply V1SR (V2SR) and one end Tu1 (Tw1) of the interconnection relay, and a second switching unit 177 (187) connected to the other end Tu2 (Tw2) of the interconnection relay. The detection units 179 and 189 are connected to the second switching units 177 and 187, respectively, and in this embodiment, are connected between the second switching units 177 and 187 and grounds (earths) V1_GND and V2_GND corresponding to the power supply V1SR (V2SR), and output a detection signal Su_chk (Sw_chk) when the detection current Iu (Iw) is detected.

[0024] The detection power supply V1SR (V2SR) in this embodiment is provided uniquely for each relay abnormality detection circuit, and does not use the power output via the inverter 120, but uses, for example, power branched from the power itself input to the power conversion device 1. As described above, the detection power supply V1SR (V2SR) flows the detection current Iu (Iw) toward the detection unit 179 (189), so it can be seen that the detection power supply V1SR (V2SR) does not flow a current directed to consumption of the grid or household loads like the inverter output, and is provided uniquely for each relay abnormality detection circuit exclusively for detecting an abnormality in the grid relay. Therefore, the relay abnormality detection circuit 130 should be distinguished from a technology that detects an abnormality in the grid relay by using a voltage from the inverter 120 or the like and comparing it with a comparator or the like. As described above, the detection power supply V1SR (V2SR) does not flow a current directed to consumption of the grid or household loads like the inverter output, and can also contribute to energy saving. Here, the detection power supplies V1SR and V2SR serve as power supplies for driving, i.e., opening and / or closing, the relay units Su and Sw in the grid-connection relays 135 and 136. The supply source of the detection power supplies V1SR and V2SR is obtained, for example, from the output of the photovoltaic power generation device 200 or the output of the DC / DC converter 300 via an insulating transformer (not shown). Note that, in the case where a storage battery (not shown) is provided, the supply source of the detection power supplies V1SR and V2SR may be obtained from the output of the storage battery via an insulating transformer (not shown).

[0025] In this embodiment, welding detection is performed separately for the U phase and the W phase. In the conventional technology, when welding detection is performed, the inverter output (AC voltage Esd) is output toward the grid side as described above, and the inverter 120 is operated, but in this embodiment, the inverter 120 is not operated. That is, the AC voltage Esd output toward the grid side is zero. Therefore, in this embodiment, since it is possible to detect a contact abnormality in the grid-connected relay without outputting the inverter output, it is possible to avoid a conventional unsafe state on the grid side caused by a reverse flow from the low voltage side to the high voltage side in a transformer (pole transformer) that converts high voltage to low voltage, which generates an excessive voltage on the high voltage side.

[0026] A method for detecting a contact abnormality (such as welding) in this embodiment will be described by taking as an example a method for detecting welding of the grid-connection relay 135 on the U-phase side. First, the inverter 120 stops the output of the AC power upon receiving an inverter output command from the inverter output stop command unit 510, and the grid-connection relay 135 opens the relay unit Su in response to a relay command from the relay open command unit 530 (relay unit Su is OFF). The relay abnormality detection circuit 170 closes the first opening / closing unit 173 and the second opening / closing unit 177 after the inverter output command is output from the inverter output stop command unit 510 and the relay command is output from the relay open command unit 530. The relay abnormality detection circuit 170 detects whether an abnormality has occurred in the grid-connection relay 135 based on a detection signal Su_chk from the detection unit 179. That is, in the detection unit 179, if no contact abnormality such as welding occurs in the relay unit Su, no detection current flows through the relay unit Su. However, if a contact abnormality such as welding occurs in the relay unit Su, a detection current flows through the relay unit Su, and the detection current Iu (Iw) is detected. When the detection current is detected, a detection signal for a contact abnormality such as welding is output. The relay abnormality detection circuit 170 detects that an abnormality has occurred in the interconnection relay 135 based on the output of the detection signal.

[0027] Specifically, when the first switching unit 173 and the second switching unit 177 are turned ON (the relay unit Su is OFF), if the relay unit Su is welded or the like, a current flows from the power source V1SR(+) to the first switching unit 173 to the relay unit Su to the second switching unit 177 to the detection unit 179 to the ground V1_GND, as shown in the figure. If no welding or the like has occurred, no current flows through the above-mentioned path. Therefore, by detecting this current (which may be in the form of a voltage) with the detection unit 179, the presence or absence of a contact abnormality such as welding in the interconnection relay 135 is detected. If welding or the like has occurred, the detection unit 179 outputs the detection signal Su_Chk. The same method is used to detect welding of the interconnection relay 136 on the W-phase side.

[0028] FIG. 3 shows a specific example of the detection power supply of the relay abnormality detection circuit in FIG. 2, taking the U phase as an example. The detection power supply V1SR in FIG. 3 is connected to the ground V1_GND, and is realized by an insulated power supply using a transformer or the like. Note that the red arrow in FIG. 3 shows that when the first switching unit 173 and the second switching unit 177 are turned ON (indicated by solid lines in FIG. 3), since the relay unit Su is OFF (indicated by broken lines in FIG. 3) but is welded (indicated by solid lines in FIG. 3), a current flows through the insulated power supply V1SR(+) ⇒ first switching unit 173 ⇒ relay unit Su ⇒ second switching unit 177 ⇒ detection unit 179 ⇒ ground V1_GND, and the detection signal Su_Chk is output from the detection unit 179. Note that the specific example of the detection power supply on the W phase side is similar.

[0029] The present invention is not limited to the above-described embodiment, and various additions, modifications, and deletions are possible without departing from the scope of the present invention. Therefore, such modifications are also included in the scope of the present invention. [Explanation of symbols]

[0030] 1 Power conversion device, power conditioner 110 Relay system connection end 120 Inverter 135, 136 Interconnection relay 170, 180 Relay abnormality detection circuit 173, 183 First opening and closing section 177, 187 Second opening and closing section 179, 189 Detector 200 Solar power generation equipment (DC power supply) 510 Inverter output stop command unit 530 Relay Opening Command Center Lu, Lw Electric line V1SR, V2SR detection power supply

Claims

1. A power conversion device including an inverter that receives output power from a DC power source or power obtained by voltage-converting the output power from the DC power source and converts it into AC power, and a relay system connection terminal that is connected to a system power source side, Further, the power supply system includes at least one electric line between the inverter and the relay system connection end, an interconnection relay interposed in at least one of the at least one electric line, and a relay abnormality detection circuit provided for each of the interconnection relays, the relay abnormality detection circuit has a detection power supply that flows a detection current toward a detection unit, a first opening / closing unit between the detection power supply and one end of the interconnection relay, and a second opening / closing unit connected to the other end of the interconnection relay, the detection unit is connected to the second opening / closing unit, and outputs a detection signal when the detection current is detected; The inverter stops output of the AC power in response to a command from an inverter output stop command unit, and the interconnection relay opens a relay unit in response to a command from a relay open command unit, the relay abnormality detection circuit closes a first opening / closing unit and a second opening / closing unit after a command to stop the output of the AC power is output from the inverter output stop command unit and a command to open the relay unit is output from the relay open command unit, and detects an abnormality in the interconnection relay based on the detection signal from the detection unit. Power conversion equipment.

2. The power conversion device according to claim 1, The relay abnormality detection circuit detects a contact abnormality or a welding in the interconnection relay. Power conversion equipment.

3. The power conversion device according to claim 1, The detection power supply is an isolated power supply. Power conversion equipment.

4. The power conversion device according to claim 1, The system includes two-phase electric lines between the inverter and the relay system connection terminal, the interconnection relays interposed in all of the two-phase electric lines, and the relay abnormality detection circuit provided for each of the interconnection relays. Power conversion equipment.

5. The power conversion device according to claim 4, Controlling a solar power generation device which is the DC power source. Power conditioner.

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