Power supply system

Abstract

Provided is a power supply system capable of continuously suppressing parallel arc discharge. A power supply system 1 comprises: a power supply device 10 that supplies DC power; a power conversion device 20 that converts the DC power into AC power; transmission lines 15 that connect the power supply device 10 and the power conversion device 20; a detector 30 that detects parallel arc discharge occurring between the transmission lines 15; a circuit breaker 50 that suppresses parallel arc discharge by short-circuiting the transmission lines 15; a control power supply 35 that generates a control voltage for the circuit breaker 50 from the DC power; and a voltage generator 60 that generates a DC voltage. The circuit breaker 50 and the voltage generator 60 are connected in series between the transmission lines 15, and the circuit breaker 50 is of a normally open type and adopts a closed state when supplied with a control voltage upon detection of parallel arc discharge. The output voltage of the voltage generator is lower than a voltage at which parallel arc discharge can be generated or can continue, and is equal to or higher than a lower limit value of the input voltage of the control power supply 35.

Description

Power Supply System

[0001] The present invention relates to a power supply system.

[0002] A photovoltaic power generation system (hereinafter also referred to as a power supply system) including a PV (Photovoltaic) array and a PCS (Power Conditioning System), or a power supply system including a storage battery and a PCS is known.

[0003] For example, fires caused by construction work of photovoltaic power generation systems have been reported. For example, if the transmission line between the PV array and the PCS is damaged during construction, arc discharge occurs at the damaged portion of the transmission line, and in particular, parallel arc discharge occurs between the positive electrode line and the negative electrode line, which is considered to cause ignition at the damaged portion of the transmission line. Arc discharge generates large energy and high temperature. Furthermore, arc discharge tends to continue easily in DC power transmission lines.

[0004] In recent years, standards such as UL1699B and IEC63027 have been issued as standards that define techniques for detecting the occurrence of such arc discharge and interrupting the arc current of such arc discharge. However, these standards are standards for series arc discharge, and do not mention parallel arc discharge, which is considered one of the causes of fire based on verification of accident cases as described above.

[0005] In addition, Patent Documents 1 and 2 disclose a technique for photovoltaic power generation systems that detects the occurrence of series arc discharge in a transmission line between a PV array and a PCS, interrupts the arc current of the series arc discharge, and suppresses the series arc discharge.

[0006] In addition, Patent Document 3 discloses a technique for photovoltaic power generation systems that detects the occurrence of parallel arc discharge between a pair of transmission lines between a PV array and a PCS, and short-circuits the pair of transmission lines with a circuit breaker to suppress the parallel arc discharge.

[0007] International Publication No. 2019 / 208027, Japanese Unexamined Patent Application Publication No. 2016-151514, Japanese Unexamined Patent Application Publication No. 2018-121434

[0008] Paul G. Slade, “Electrical Contacts : Principles and Applications, Second Edition”, p590, CRC Press, December 17, 2013

[0009] However, in the parallel arc discharge suppression technique disclosed in Patent Document 3, the pair of transmission lines are short-circuited with a circuit breaker, causing the voltage at this short-circuit point to disappear. In practice, this makes it impossible to generate the control voltage necessary to close the circuit breaker, and thus impossible to maintain the circuit breaker in the closed state. Therefore, it is considered that it becomes impossible to continuously suppress parallel arc discharge by continuously short-circuiting the pair of transmission lines with a circuit breaker.

[0010] The present invention aims to provide a power supply system capable of continuously suppressing parallel arc discharge.

[0011] The power supply system according to the present invention comprises a power supply device that supplies DC power, a power conversion device that converts the DC power into desired AC power, a pair of transmission lines connecting the power supply device and the power conversion device, a detector that detects parallel arc discharge occurring between the pair of transmission lines, a circuit breaker that short-circuits the pair of transmission lines to suppress the parallel arc discharge, a control power supply that generates a control voltage for the circuit breaker from the DC power, and a voltage generator that generates a DC voltage. The circuit breaker and the voltage generator are connected in series between the pair of transmission lines, the circuit breaker is normally open, and closes when the parallel arc discharge is detected by the detector and the control voltage is supplied. The output voltage of the voltage generator is less than the voltage at which the parallel arc discharge occurs, or less than the voltage at which the parallel arc discharge can continue, and is greater than or equal to the lower limit of the input voltage of the control power supply.

[0012] According to the present invention, it is possible to continuously suppress parallel arc discharge in a power supply system.

[0013] This figure shows an example of the configuration of the power supply system according to this embodiment. This figure shows an example of a voltage generator in the power supply system shown in Figure 1. This figure shows an example of a voltage generator in the power supply system shown in Figure 1. This figure shows an example of a voltage generator in the power supply system shown in Figure 1. This figure shows an example of the voltage between a pair of transmission lines.

[0014] An example of an embodiment of the present invention will be described below with reference to the attached drawings. The same or corresponding parts will be denoted by the same reference numerals in each drawing. For convenience, hatching and component reference numerals may be omitted; in such cases, refer to other drawings.

[0015] Figure 1 shows an example of the configuration of a power supply system according to this embodiment. As shown in Figure 1, the power supply system 1 comprises a power supply device 10, a pair of transmission lines 15, a power converter 20, an arc discharge detector 30, a control power supply 35, a series arc circuit breaker 40, a parallel arc circuit breaker 50, and a voltage generator 60. When the power supply device 10 is a PV (Photovoltaic) array, the power supply system 1 is also called a solar power generation system.

[0016] The power supply device 10 is a device that supplies DC power. The power supply device 10 is, for example, a PV array or a storage battery.

[0017] The power converter 20 is a device that converts DC power into desired AC power. The power converter 20 is, for example, a PCS (Power Conditioning System).

[0018] The power supply device 10 and the power converter 20 are connected by a pair of transmission lines 15. The pair of transmission lines 15 are, for example, metal cables covered with an insulating material.

[0019] The arc discharge detector 30 detects series arc discharges occurring in the transmission line 15, or parallel arc discharges occurring between a pair of transmission lines 15. The arc discharge detector 30 can be any known detector. For example, the arc discharge detector 30 detects series or parallel arc discharges by detecting the high-frequency component of the arc current generated during an arc discharge.

[0020] Normally, the arc discharge detector 30 supplies a control voltage to the series arc circuit breaker 40, keeping it normally closed. When a series arc discharge is detected, the arc discharge detector 30 stops supplying the control voltage to the series arc circuit breaker 40, opening the series arc circuit breaker 40.

[0021] Furthermore, the arc discharge detector 30 normally does not supply a control voltage to the parallel arc circuit breaker 50, keeping the parallel arc circuit breaker 50 normally open. When a parallel arc discharge is detected, the arc discharge detector 30 supplies a control voltage to the parallel arc circuit breaker 50, closing the parallel arc circuit breaker 50.

[0022] As a more specific example, when the arc discharge detector 30 detects a high-frequency component of the arc current, it first opens the series arc circuit breaker 40. If the arc discharge is suppressed, it detects the generated arc discharge as a series arc discharge and continues to keep the series arc circuit breaker 40 open. On the other hand, if the arc discharge is not suppressed even with the series arc circuit breaker 40 open, the arc discharge detector 30 detects the generated arc discharge as a parallel arc discharge and closes the parallel arc circuit breaker 50. The arc discharge detector 30 then returns the series arc circuit breaker 40 to the closed state.

[0023] Alternatively, as another specific example, when the arc discharge detector 30 detects a high-frequency component of the arc current, it also monitors the voltage across the transmission line 15. If there is no voltage drop, it detects the generated arc discharge as a series arc discharge and opens the series arc circuit breaker 40. On the other hand, if there is a voltage drop, it detects the generated arc discharge as a parallel arc discharge and closes the parallel arc circuit breaker 50.

[0024] The operating voltage of the arc discharge detector 30 and the control voltages supplied to the series arc circuit breaker 40 and the parallel arc circuit breaker 50 are supplied from the control power supply 35. The control power supply 35 generates the operating voltage of the arc discharge detector 30 and the control voltages supplied to the series arc circuit breaker 40 and the parallel arc circuit breaker 50 from the DC power supplied from the power supply device 10. The control power supply 35 can be any known power supply. For example, the control power supply 35 is a power converter with a wide input voltage range.

[0025] The series arc circuit breaker 40 interrupts the arc current of a series arc discharge occurring in the transmission line 15. For example, the series arc circuit breaker 40 is connected in series with the transmission line 15 and is a normally closed type circuit breaker. The series arc circuit breaker 40 is normally closed in accordance with the control voltage supplied from the arc discharge detector 30. On the other hand, when a series arc discharge is detected by the arc discharge detector 30 and the supply of the control voltage is stopped, the series arc circuit breaker 40 becomes open. As a result, the arc current of the series arc discharge is interrupted and the series arc discharge is suppressed.

[0026] The parallel arc circuit breaker 50 short-circuits a pair of transmission lines 15 to reduce the arc voltage of a parallel arc discharge occurring between the pair of transmission lines 15. For example, the parallel arc circuit breaker 50 is inserted between a pair of transmission lines 15 and is a normally open type circuit breaker. Normally, the parallel arc circuit breaker 50 is normally open as no control voltage is supplied from the arc discharge detector 30. On the other hand, when a parallel arc discharge is detected by the arc discharge detector 30 and a control voltage is supplied, the parallel arc circuit breaker 50 closes. As a result, the pair of transmission lines 15 are short-circuited, the arc voltage of the parallel arc discharge is suppressed, and the parallel arc discharge is suppressed.

[0027] The parallel arc circuit breaker 50 and the voltage generator 60 are connected in series between a pair of transmission lines 15. The voltage generator 60 is a device that generates a DC voltage. More specifically, the voltage generator 60 is a device that generates a DC voltage by utilizing the short-circuit current generated by the parallel arc circuit breaker 50. Figures 2A to 2C show an example of a voltage generator in the power supply system shown in Figure 1.

[0028] As shown in Figure 2A, the voltage generator 60 may be composed of Zener diodes. In this case, the output voltage V of the voltage generator 60 is the Zener voltage Vz. Alternatively, as shown in Figure 2B, the voltage generator 60 may be composed of n diodes connected in series. In this case, the output voltage V of the voltage generator 60 is n times the forward voltage Vf (where n is an integer of 1 or more).

[0029] Alternatively, as shown in Figure 2C, the voltage generator 60 may consist of a Zener diode and m diodes connected in series. In this case, the output voltage V of the voltage generator 60 is Vz + Vf × m (where m is an integer greater than or equal to 1). Here, the Zener diode has a negative temperature characteristic, and as the temperature increases, the Zener voltage decreases. On the other hand, the diode has a positive temperature characteristic, and as the temperature increases, the forward voltage Vf increases. Therefore, by using a combination of a Zener diode and diodes, the temperature variation of the output voltage of the voltage generator 60 can be reduced.

[0030] Returning to Figure 1, the output voltage of the voltage generator 60 is: - below the voltage at which parallel arc discharge occurs, or below the voltage at which parallel arc discharge can be sustained, AND - above the lower limit of the input voltage of the control power supply 35.

[0031] For example, Non-Patent Document 1, mentioned above, discloses an example of the characteristics of arc discharge current-arc discharge voltage for each discharge gap. By referring to such characteristics, it is possible to design the voltage at which parallel arc discharge occurs, or the voltage at which parallel arc discharge can be sustained, according to the design target of how much of the gap to suppress parallel arc discharge.

[0032] As described above, according to the power supply system 1 of this embodiment, - The circuit breaker 50 and the voltage generator 60 are connected in series between a pair of transmission lines 15, - The circuit breaker 50 closes when a parallel arc discharge is detected and a control voltage is supplied, and - The output voltage of the voltage generator 60 is less than the voltage at which a parallel arc discharge occurs, or less than the voltage at which a parallel arc discharge can continue, and is above the lower limit of the input voltage of the control power supply 35.

[0033] As a result, as shown in Figure 3, the voltage between the pair of transmission lines 15 can be set to a voltage below the voltage at which parallel arc discharge occurs, or below the voltage at which parallel arc discharge can be sustained, thereby reducing the arc voltage required for parallel arc discharge. Therefore, it is possible to prevent parallel arc discharge from continuing and to suppress parallel arc discharge.

[0034] Furthermore, the voltage between the pair of transmission lines 15 can be set to be above the lower limit of the input voltage of the control power supply 35, and the control power supply 35 can continuously generate the control voltage necessary to close the circuit breaker 50. Therefore, the suppression of parallel arc discharge can be continued.

[0035] Incidentally, such a power supply system is connected to the commercial grid. In this case, the power supply system is required to continue supplying power even if the grid power goes out. In this respect as well, according to the power supply system 1 of this embodiment, even if the parallel arc circuit breaker 50 is closed to suppress parallel arc discharge, the voltage generator 60 generates voltage on the pair of transmission lines 15, so the PCS 20 can continue supplying power to the commercial grid.

[0036] Furthermore, as described in the aforementioned Patent Document 3, even if a voltage generator 60 is not provided and the parallel arc circuit breaker 50 simply short-circuits the pair of transmission lines 15 when a parallel arc discharge occurs, it is possible to continue supplying power to the commercial grid by using a secondary battery or the like as a backup battery. However, in a solar power generation system that is required to operate continuously for more than 10 years without replacing components, for example, using a secondary battery or the like as a backup battery is not practical in terms of battery life and battery cost. In this respect as well, the power supply system 1 of this embodiment can continue to supply power to the commercial grid while continuing to suppress parallel arc discharge without using a secondary battery or the like as a backup battery.

[0037] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible.

[0038] 1 Power supply system 10 Power supply device 15 Pair of transmission lines 20 Power converter 30 Arc discharge detector 35 Control power supply 40 Series arc circuit breaker 50 Parallel arc circuit breaker 60 Voltage generator

Claims

1. A power supply system comprising: a power supply device that supplies DC power; a power conversion device that converts the DC power into desired AC power; a pair of transmission lines connecting the power supply device and the power conversion device; a detector that detects parallel arc discharge occurring between the pair of transmission lines; a circuit breaker that short-circuits the pair of transmission lines to suppress the parallel arc discharge; a control power supply that generates a control voltage for the circuit breaker from the DC power; and a voltage generator that generates a DC voltage, wherein the circuit breaker and the voltage generator are connected in series between the pair of transmission lines; the circuit breaker is normally open and closes when the parallel arc discharge is detected by the detector and the control voltage is supplied; and the output voltage of the voltage generator is less than the voltage at which the parallel arc discharge occurs, or less than the voltage at which the parallel arc discharge can continue, and is greater than or equal to the lower limit of the input voltage of the control power supply.

2. The power supply system according to claim 1, wherein the voltage generator comprises a diode, a Zener diode, or a series-connected diode and Zener diode, and generates the DC voltage using the short-circuit current generated by the circuit breaker.

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