Protective relay and power control device

Abstract

To provide a technique capable of increasing a power generation amount of a distributed power supply while using an existing distributed power supply system.SOLUTION: A protective relay includes a distributed power supply, a power conversion device, and a control device for controlling the conversion device to control power generation by the distributed power supply, and is used by a power system for controlling operation of the distributed power supply in cooperation with a commercial power system. The protective relay includes a power measurement part for measuring power at a power reception point from the commercial power system, a reverse power flow determination part for detecting reverse power flow to the commercial power system on the basis of a power value measured by the power measurement part, and transmitting a command signal to stop power generation to the control device in the case of detecting the reverse power flow, and a power generation suppression part for transmitting information for making the control device perform control for suppressing a power generation amount of the distributed power supply on the basis of the power value measured by the power measurement part until prescribed time passes after stop of power generation based on at least a command of the reverse power flow determination part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a protective relay and a power control device. [Background technology]

[0002] It has been known for some time that a self-consumption distributed power system, such as a solar power generation system, that is operated in connection with a commercial power grid should be provided with a reverse power relay (RPR) or a protective relay equipped with such a relay to prevent reverse power flow from the distributed power source to the grid. However, when a reverse power relay detects reverse power flow and stops power generation, the loss of power generation until power generation resumes is significant. Therefore, the output power (power generation amount) from a power conditioning system (PCS) is controlled to correspond to the load (load following control).

[0003] Specifically, as shown in Figure 7, in addition to a protective relay that combines an ammeter and an RPR, a power measurement unit is provided that measures the output power of the PCS in the system and the power consumption of the load and transmits the combined value to a controller that controls the PCS, and the controller controls the output of the PCS based on the combined value. In this configuration, since the protective relay including the RPR and the power measurement unit that inputs the combined value to the controller are different, especially when multiple PCSs are included in the system, it is necessary to control the output of the PCS with a large margin (the amount of power generation must be somewhat suppressed) to prevent power generation from being stopped due to the RPR, taking into account the time lag.

[0004] Meanwhile, as shown in Fig. 8, a configuration has been proposed in which an ammeter for detecting reverse power flow and a wattmeter for calculating a total value for load following control are combined into a common device, i.e., a configuration in which a device for measuring the total value is integrated into a protective relay (see, for example, Patent Document 1). The technology described in Patent Document 1 makes it possible to match the power measurement value for detecting reverse power flow with that used for load following control, making it possible to simply shut down the PCS (or significantly reduce output) before power generation is stopped by the RPR. Note that, hereinafter, this type of PCS control is also referred to as pseudo-shutdown.

[0005] However, even if such pseudo-shutdown control is performed and a shutdown by RPR (hereinafter referred to as a real shutdown) is avoided, as soon as normal power generation resumes from the pseudo-shutdown and output from the PCS increases, a pseudo-shutdown (or in some cases a real shutdown by RPR) will occur, and a cycle of shutdown - restart power generation - shutdown, etc. will be repeated (hereinafter this condition will be referred to as hunting).

[0006] To address this issue, as shown in Figure 10, by integrating the power meter, RPR determiner, and controller, it is possible to perform load following control at high speed and with high accuracy when power generation resumes, thereby preventing hunting. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-193865 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the configuration shown in Figure 10, a dedicated device is required in which the PCS controller is integrated with the power meter and RPR judger, making the system installation large-scale. For this reason, it cannot be added to an existing distributed power generation system, and the entire system would have to be replaced.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide technology that makes it possible to increase the amount of power generated by a distributed power source while using an existing distributed power source system. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention employs the following configuration as one aspect. A protective relay used in a power system that is interconnected with a commercial power system and controls operation of the distributed power source, the power system including: a distributed power source; a converter for converting power output from the distributed power source; and a controller that controls the converter to control power generation by the distributed power source, the protective relay comprising: a power measurement unit that measures power at a receiving point from the commercial power system; a reverse power flow determination unit that detects a reverse power flow to the commercial power grid based on the power value measured by the power measurement unit, and that transmits a command signal to the control device to stop the power generation when the reverse power flow is detected; a power generation suppression unit that transmits information to the control device to control the control device to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit at least during a period from when the power generation is stopped based on a command from the reverse power flow determination unit until a predetermined time has elapsed, It is a protective relay.

[0011] The term "power conversion device" here includes a so-called PCS. The "control device" may be integrated with the power conversion device. With this configuration, after RPR restarts power generation after a power generation stop, the amount of power generated is suppressed until a predetermined time has elapsed, preventing hunting and reducing loss of power generation opportunities. In other words, the amount of power generated by the distributed power source can be increased.

[0012] The power measurement unit, the reverse power flow determination unit, and the power generation suppression unit may be housed in a single housing. With this configuration, the system configuration is simplified and control to prevent reverse power flow can be performed with higher accuracy.

[0013] The power generation suppression unit may calculate a compensation value by compensating for the power value measured by the power measurement unit, and transmit the compensation value to the control device as the power value at the power receiving point. Note that the compensation value is a value obtained by compensating for an upward correction of the output power (or a downward correction of the power consumption) when viewed from the combined value of the output power (power generation amount) of the PCS and the power consumption of the load.

[0014] In this way, it is possible to increase the amount of power generated by the distributed power sources with a simple configuration (without performing complex calculations).

[0015] Furthermore, the compensation value transmitted by the power generation suppression unit to the control device may be set so that the compensated value gradually decreases to 0 during the period from when the power generation is stopped based on a command from the reverse flow determination unit until the predetermined time has elapsed.

[0016] In addition, the power generation suppression unit may transmit the compensation value to the control device if the power value measured by the power measurement unit deviates from a predetermined threshold value before the predetermined time has elapsed.

[0017] Furthermore, the reverse power flow determination unit detects a sign of reverse power flow before detecting the reverse power flow, and when the sign is detected, transmits to the control device a command signal to execute a pseudo-power generation stop process that sets a time period for which the power generation is suppressed to be shorter than when the power generation is stopped; The power generation suppression unit may transmit information to the control device to enable the control device to control the suppression of the power generation amount of the distributed power source based on the power value measured by the power measurement unit during a predetermined time period after the pseudo-power generation is stopped.

[0018] Here, "pseudo-shutdown" does not only mean "stopping" power generation, but also includes control to rapidly reduce the amount of power generated. With this configuration, pseudo-shutdown of power generation prior to the actual shutdown by RPR can shorten the time that power generation is suppressed, and control to suppress hunting can be performed even after power generation resumes after the pseudo-shutdown, thereby further increasing the amount of power generated by distributed power sources.

[0019] In addition, the power generation suppression unit may transmit an upper limit value of the power generation amount of the distributed power source to the control device, and the upper limit value may gradually increase from the time when the power generation is stopped based on an instruction from the reverse flow determination unit until the specified time has elapsed.

[0020] In addition, the power generation suppression unit may send a command signal to the control device to slow down the rate of increase in the power generation amount of the distributed power source during the period from when the power generation is stopped based on a command from the reverse flow determination unit until the specified time has elapsed.

[0021] With this configuration, hunting can be prevented when power generation is resumed after being stopped by RPR, regardless of the measured power value at the power receiving point, i.e., even if the power generation suppression unit is not configured integrally with the power measurement unit and the reverse flow determination unit.

[0022] The present invention can also be adopted as the following aspect: A power control device is used in a power system interconnected with a commercial power grid, the power control device including a distributed power source and a converter for converting power output from the distributed power source, the power control device controlling the converter to control power generation by the distributed power source, a control unit that transmits a command signal to the converter to control the output power of the converter; a power measurement unit that measures power at a receiving point from the commercial power system; a reverse power flow determination unit that detects a reverse power flow to the commercial power grid based on the power value measured by the power measurement unit, and that outputs a stop command signal to the control unit to stop the power generation when the reverse power flow is detected; and a power generation suppression unit that outputs information to the control unit to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit, at least during the period from when the power generation is stopped based on an instruction from the reverse flow determination unit until a predetermined time has elapsed.

[0023] That is, the protective relay and the control device can be configured as an integrated unit, and the control device can incorporate the functions of the protective relay. When the protective relay and the control device are integrated, there is a small time lag in transmitting power at the receiving point, and accurate load following control is possible, but hunting after power generation is stopped and then resumed cannot be completely prevented. For this reason, by implementing the functions of the power generation suppression unit according to the present invention, the occurrence of hunting can be more effectively suppressed.

[0024] In the power control device, the power generation suppression unit calculates a compensation value by compensating for the power value measured by the power measurement unit, and calculates the compensation value as a power value at the power receiving point. It may be output as a force value.

[0025] The compensation value may be set so that the compensated value gradually decreases to 0 during the predetermined time period from when the power generation is stopped based on a command from the reverse power flow determination unit.

[0026] Furthermore, the power generation suppression unit may output the compensation value when the power value measured by the power measurement unit deviates from a predetermined threshold value before the predetermined time has elapsed.

[0027] In addition, in the power control device, the reverse flow determination unit detects a sign of reverse flow before detecting the reverse flow, and when the sign is detected, outputs to the control unit a command signal to execute a pseudo-power generation stop process that sets a time period for which the power generation is suppressed to be shorter than when the power generation is stopped, The power generation suppression unit may output information to the control unit to enable the control unit to control the suppression of the power generation amount of the distributed power source based on the power value measured by the power measurement unit during a predetermined time period after the pseudo-power generation is stopped.

[0028] In addition, the power generation suppression unit may output an upper limit value of the power generation amount of the distributed power source to the control unit, and the upper limit value may gradually increase from the time when the power generation is stopped based on an instruction from the reverse flow determination unit until the specified time has elapsed.

[0029] In addition, the power generation suppression unit may output a command signal to the control unit to slow down the rate of increase in the power generation amount of the distributed power source during the period from when the power generation is stopped based on a command from the reverse flow determination unit until the specified time has elapsed.

[0030] The present invention can be achieved by combining the above-described configurations and processes as long as no technical contradiction occurs. [Effects of the Invention]

[0031] According to the present invention, it is possible to increase the amount of power generated by a distributed power source while using an existing distributed power source system. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a system diagram showing a schematic configuration of a power system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a time chart illustrating the contents of power generation control performed in the power system according to the first embodiment of the present invention. [Figure 3]FIG. 3 is a system diagram showing a schematic configuration of a power system according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a time chart illustrating the contents of power generation control performed in the power system according to the second embodiment of the present invention. [Figure 5] FIG. 5 is a system diagram showing a schematic configuration of a power system according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a time chart illustrating the contents of power generation control performed in the power system according to the third embodiment of the present invention. [Figure 7] FIG. 7 is a system diagram showing a schematic configuration of a first conventional example related to the present invention. [Figure 8] FIG. 8 is a system diagram showing a schematic configuration of a second conventional example related to the present invention. [Figure 9] FIG. 9 is a time chart for explaining the contents of power generation control performed in the first and second conventional examples related to the present invention. [Figure 10] FIG. 10 is a system diagram showing a schematic configuration of a third conventional example related to the present invention. [Figure 11] FIG. 11 is a system diagram showing a schematic configuration of a power system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] <Application example> (Overall configuration of the system related to the application example) The present invention can be applied to, for example, a power system 100 as shown in Fig. 1. The power system 100 includes loads 4a and 4b, is interconnected with a commercial power grid 5, and includes photovoltaic (PV) systems 1a and 1b as distributed power sources. For example, the load 4a can be a three-phase load and the load 4b can be a single-phase load, but is not limited to this.

[0034] The PV systems 1a and 1b are respectively subjected to direct current to alternating current power conversion and output (power generation amount) control by the PCSs 2a and 2b. Note that each of the PCSs 2a and 2b is comprehensively controlled by a controller 91, and therefore output control from each of the PV systems 1a and 1b (i.e., control of the power generation amount of the PV systems 1a and 1b) is essentially performed by the controller 91. The controller 91 can be, for example, a general-purpose computer equipped with any processor such as a CPU (Central Processing Unit), a main storage device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), an auxiliary storage device such as a flash memory, a communication IF (Interface), and the like. Note that the PV systems 1a and 1b and the PCSs 2a and 2b can employ any known technology, and therefore detailed description thereof will be omitted.

[0035] In the following, the PV systems 1a, 1b, PCSs 2a, 2b, and loads 4a, 4b will be described as being two each, but the number of these is not limited to two and may be one, or three or more. In the following, the PV systems 1a, 1b, PCSs 2a, 2b, and loads 4a, 4b may be simply referred to as the PV system 1, the PCS 2, the load 4, etc., unless it is necessary to distinguish between them in the description.

[0036] The present invention can be applied as a protective relay 10 that is used in such a power system 100 and that serves to prevent reverse power flow of power generated by the PV system 1 to the commercial power grid 5. Before describing the protective relay 10 according to this application example, an example of a configuration that has conventionally been adopted to prevent reverse power flow to the commercial power grid 5 will be described.

[0037] (Conventional Example 1) 7 is a system diagram showing a schematic configuration of a power system 400 according to a first conventional example. In the following examples, the same components as those already described are given the same reference numerals, and detailed description thereof will be omitted.

[0038] The power system 400 includes a PV system 1, a PCS 2, a controller 3, a load 4, a protective relay 40, and a power meter 45. The protective relay 40 includes an ammeter and has the functional units of a power measurement unit 41 and a determination unit 42. The power meter 45 also has the functional unit of a power measurement unit 46.

[0039] The power measurement unit 41 of the protective relay 40 measures the power value at the receiving point from the commercial power system 5 in the power system 400, and outputs the measured value to the determination unit 42. The determination unit 42 determines whether the reverse power relay The PCS 2 functions as a power supply (RPR) and is connected to the controller 3 via a communication line (not shown). When the power at the power receiving point deviates from a threshold value (for example, 0 W), the PCS 2 transmits a reverse power flow detection signal to the controller 3. When the controller 3 receives the reverse power flow detection signal, it performs control to stop the power output from the PCS 2 (power generation by the PV system 1). Note that, hereinafter, the stop of power output based on the reverse power flow detection signal is also referred to as "abnormal stop."

[0040] The power measurement unit 46 of the power meter 45 also measures the power at the power receiving point in the power system 400, and the measured value is transmitted to the controller 3 via a communication line (not shown). The value measured by the power measurement unit 46 is the sum of the output power of the PCSs 2a and 2b (i.e., the amount of power generated by the PVs 1a and 1b) and the power consumption of the loads 4a and 4b. The controller 3 uses this sum to control the output of the PCSs 2a and 2b so that the amount of power generated does not exceed the load power consumption, i.e., so that no reverse power flow to the commercial power grid 5 occurs (load following control).

[0041] However, in the above-described power system 400, the measurement values ​​used by the controller 3 for load following control differ from the measurement values ​​used by the determination unit 42 for reverse power flow detection, so if the controller 3 performs load following control with little margin, reverse power flow is likely to occur. For this reason, it is necessary to provide a large margin for the load following control and to somewhat suppress the amount of power generation.

[0042] (Conventional example 2) Next, a second conventional example will be described with reference to Fig. 8. Fig. 8 is a system diagram showing a schematic configuration of a power system 500 according to the second conventional example. The power system 500 has a configuration generally similar to that of the power system 400, but the controller 3 receives power measurement values ​​from a power measurement unit 51 included in a protective relay 50. That is, in the power system 500, the function of the power meter 45 (power measurement unit 46) in the power system 400 is integrated into the protective relay 50, and the measurement value used by the determination unit 52 to detect reverse power flow matches the measurement value used by the controller 3 for load following control.

[0043] With this configuration, the measurement value used by the controller 3 for load following control matches the measurement value used by the judgment unit 52 to detect reverse power flow, so a threshold can be set to detect signs of reverse power flow before the judgment unit 52 detects it, and if the threshold is exceeded, control can be performed to virtually stop the PCS2.

[0044] (Issues with Conventional Examples 1 and 2) Incidentally, in either the power system 400 or 500, an abnormal shutdown (pseudo shutdown) is unavoidable, and in such a case, power generation by the PV system 1 will be resumed after a certain period of time has elapsed. Fig. 9 shows a time chart illustrating the output control situation of the PCS 2 in such a conventional system configuration.

[0045] In FIG. 9, the "Load Consumption" column indicates the load power consumed by load 4a and load 4b, with values ​​increasing downward in the diagram. The "Power Generation Amount" column indicates the power output from PCS 2 (i.e., the power generated by PV system 1), with values ​​increasing upward in the diagram. The "Power at Power Receiving Point" column indicates the value obtained by subtracting the load power consumption from the power generation amount, and the dashed dotted line indicates the threshold for detecting reverse power flow. For example, if a power value that exceeds the threshold for a certain period of time (e.g., 0.5 seconds) is measured due to a sudden decrease in load consumption, the determination unit (42, 52) sends a reverse power flow detection signal to controller 3, which causes an abnormal shutdown.

[0046] When an abnormal stop occurs, power generation is resumed after a predetermined time (for example, 10 seconds or more) has elapsed or after manual recovery processing. After power generation is resumed, load following control is performed to rapidly increase the amount of power generation. However, if the load further decreases at this timing or if power generation If there is an increase or decrease in the load power consumption immediately after the transition to the stage of stabilizing the amount of power generated, the amount of power generated will not be able to accurately follow the load, and an abnormal shutdown will occur again, resulting in a phenomenon in which this control is repeated (hunting).

[0047] The reason why accurate load tracking is not possible is thought to be that the controller 3 and the protective relays (40, 50) are separate entities, which causes a communication time lag before the measured value of the power receiving point is provided to the controller 3.

[0048] (Conventional example 3) In this regard, in the power system 600 shown in FIG. 10, the protective relay 60 is configured to include a power measurement unit 61, a determination unit 62, and a controller 63, and there is no problem of a time lag in receiving the measurement value from the power measurement unit 61. Load following control can be performed quickly and accurately when power generation is resumed, and hunting can be suppressed.

[0049] (Problem with Conventional Example 3) However, with a configuration like power system 600, a dedicated device that integrates the PCS2 controller with the power meter and RPR is required, making the system installation large-scale. For this reason, it cannot be added to an existing distributed power generation system, and the technology can only be introduced by replacing the entire system.

[0050] (Features of application example) In order to solve the above-mentioned problems, the protective relay 10 according to this application example employs the following configuration. The protective relay 10 has functional units, namely, a power measurement unit 11, a determination unit 12, and a compensation unit 13. The power measurement unit 11 measures the power value at the receiving point from the commercial power system 5 in the power system 100, and outputs the measured value to the determination unit 12 and the compensation unit 13. The determination unit 12 functions as a reverse power relay (RPR), is connected to a controller 91 via a communication line (not shown), and transmits a reverse power flow detection signal to the controller 91 when the power at the receiving point deviates from a threshold value. When the controller 91 receives the reverse power flow detection signal, it performs control to stop power output from the PCS 2.

[0051] The compensator 13 calculates a compensation value by compensating for the measurement value measured by the power measuring unit 11 during a certain time period (for example, 30 seconds) after the determination unit 12 detects a reverse power flow and the power generation of the PV system 1 is stopped, and transmits this to the controller 91. Note that the compensation value is a value obtained by compensating for an upward correction of the output power (or a downward correction of the power consumption) when viewed from the combined value of the output (power generation amount) of the PCS 2 and the power consumption of the load.

[0052] The controller 91 controls the output of the PCS2 based on this compensation value for a certain period of time after power generation is resumed (i.e., the period during which load following control is likely to become unstable), and therefore performs output control that is restrained relative to the threshold value. This makes it possible to prevent the power at the receiving point from deviating from the threshold value for reverse power flow detection.

[0053] <Embodiment 1> Next, the embodiments of the present invention will be described in more detail with reference to the drawings, including those already described. The protective relay 10 of the power system 100 according to this embodiment shown in Fig. 1 has the same configuration as that described in the application example. The power system 100 is also the same as that described in the application example.

[0054] Although not shown, the protective relay 10 includes a hardware configuration including an ammeter, a processing unit, a main memory, an auxiliary memory, and a communication interface. The processing unit reads a program into the main memory, and the power measurement unit 11 and the determination unit 12, which are described in the application example, are then executed. 2. Each functional unit of the compensation unit 13 is realized. In this embodiment, the determination unit 12 corresponds to the reverse power flow determination unit in the present invention, and the compensation unit 13 corresponds to the power generation suppression unit in the present invention.

[0055] Power output control in the power system 100 according to this embodiment will be described with reference to Fig. 2. Like Fig. 9, Fig. 2 is a time chart showing the power consumption of the load 4, the output power of the PCS 2 (the amount of power generated by the PV system 1), and the power value at the power receiving point measured by the power measurement unit 11. In addition to these, Fig. 2 also shows a column for the compensation amount (value compensated for the power receiving point power) in the compensation value output by the compensation unit 13. The dashed dotted line in the power receiving point power column indicates a threshold value (for example, 0 W) for detecting reverse power flow.

[0056] As shown in Fig. 2, in the PCS2 according to this embodiment, when a power value that exceeds a threshold value for a certain period of time is measured due to a sudden decrease in load consumption or the like, the determination unit 12 sends a reverse power flow detection signal to the controller 92, which causes an abnormal shutdown of power generation. Power generation resumes a certain period of time after the abnormal shutdown, but until a predetermined period of time has passed since power generation was stopped, the compensator 13 outputs a compensation value to the controller 91, which is the power at the power receiving point compensated for by a value corresponding to the compensation amount. The controller 91 performs load following control based on this compensation value.

[0057] In Figure 2, the dotted lines shown in the power generation amount column and the power receiving point power column are predictions of the respective fluctuations if compensation for the compensation amount is not made. If compensation for the compensation amount is not made, there is a margin up to the reverse power flow detection threshold immediately after power generation resumes, so control is performed to rapidly increase the power generation amount. On the other hand, the compensation value after compensation for the compensation amount (the solid line part after abnormal shutdown) is close to the reverse power flow detection threshold, so the power generation amount increases gradually.

[0058] The compensator 13 calculates the compensation value by gradually reducing the value of compensation to be performed for the power receiving point power so that the value of compensation for the power receiving point power becomes 0 at a timing when a predetermined time has elapsed since power generation was stopped.

[0059] With the above configuration, even if there is a sudden change in load power consumption, a margin sufficient to absorb it is created, preventing deviation from the reverse power flow detection threshold and ultimately preventing hunting after power generation is resumed. As a result, the overall amount of power generation by PV1 can be increased.

[0060] Furthermore, the protective relay 10 is configured separately from the controller 91, and by replacing the reverse power relay of an existing power system 100, the present technology can be easily introduced into the existing system.

[0061] <Embodiment 2> Next, another embodiment of the present invention will be described with reference to Figures 3 and 4. Figure 3 is a schematic diagram showing the general configuration of a power system 200 according to this embodiment, and Figure 4 is a time chart of power output control in this embodiment.

[0062] 3, the power system 200 of this embodiment has almost the same configuration as the power system 100 of embodiment 1. The present embodiment differs from the embodiment in that the determination unit 22 of the protective relay 20 transmits a pseudo stop signal to the controller 92.

[0063] The pseudo stop signal is a signal that is transmitted to the controller 92 when a sign of reverse power flow is detected before the detection of the reverse power flow. Specifically, for example, if the condition for the determination unit 22 to detect reverse power flow is that the power at the power receiving point has deviated from the reverse power flow detection threshold for 0.5 seconds, the pseudo stop signal may be output when the power at the power receiving point has deviated from the reverse power flow detection threshold for 0.2 seconds.

[0064] Note that the "pseudo shutdown" referred to here does not necessarily mean actually stopping the output from PCS2, but may also include control that significantly reduces the output from PCS2. When a pseudo shutdown is performed, power generation can be easily resumed without the need for the complicated recovery procedures (such as stopping power generation for a long period of time or manually restarting power generation) that are required in the case of an abnormal shutdown. Furthermore, while an abnormal shutdown is a control that stops all PCS2, including PCS2a and PCS2b, a pseudo shutdown may stop only some of the PCS2.

[0065] The compensator 23 according to this embodiment transmits a compensation value to the controller 92 not only in the case of an abnormal shutdown but also in the case of a pseudo shutdown, for a predetermined time period after the shutdown. However, unlike the first embodiment, the compensator 23 does not continue to output a compensation value for a predetermined time period after power generation is stopped. The power output control according to this embodiment will be described with reference to FIG. 4.

[0066] 2, Fig. 4 shows columns for the power consumption of the load 4, the output power of the PCS 2 (the amount of power generated by the PV system 1), the power value at the power receiving point measured by the power measurement unit 11, and the compensation amount in the compensation value output by the compensation unit 23. As shown in Fig. 4, when the power at the power receiving point deviates from the threshold value due to a sudden load decrease or the like, in this embodiment, the determination unit 22 transmits a pseudo-stop signal to the controller 92, thereby performing a pseudo-stop.

[0067] Thereafter, power generation resumes earlier than in the case of an abnormal shutdown, but in this embodiment, the compensation unit 23 transmits a compensation value to the controller 92 if the power at the receiving point reaches a value close to the reverse flow detection threshold (for example, set as a threshold for outputting a compensation value) until a predetermined time (for example, 30 seconds) has elapsed after the pseudo-shutdown.

[0068] In Figure 4, the dotted lines shown in the power generation amount column and the power receiving point power column represent predicted fluctuations in the case where compensation for the compensation amount is not performed. If compensation for the compensation amount is not performed, the power generation amount will increase at the same rate as before, even when the load increases, and the power receiving point power will again be likely to deviate from the reverse power flow detection threshold. However, when the power receiving point power actually approaches the reverse power flow detection threshold, the compensator 23 transmits a compensation value obtained by compensating for the power receiving point power measured by the power measuring unit 11 to the controller 92, thereby suppressing the power generation amount and preventing the power receiving point power from deviating from the reverse power flow threshold.

[0069] This allows for a speedy restart of power generation through pseudo-shutdown, and also makes it possible to suppress hunting after power generation is restarted, thereby enabling the amount of power generated by the PV system 1 to be increased more than ever before.

[0070] <Embodiment 3> Next, still another embodiment of the present invention will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a schematic diagram showing the general configuration of a power system 300 according to this embodiment, and Fig. 6 is a time chart of power output control in this embodiment.

[0071] 5, a power system 300 in this embodiment differs from that in the first embodiment in that a protective relay 30 is composed of a first housing 30a including a power measurement unit 31 and a determination unit 32, and a suppression command unit 33. In this embodiment, the suppression command unit 33 corresponds to the power generation suppression unit in the present invention.

[0072] The suppression commander 33 receives the reverse power flow detection signal when the determination unit 32 outputs it, and transmits to the controller 93 a command signal (suppression operation signal) to suppress the increase in the amount of power generation within a predetermined period after the power generation is resumed. If the controller 93 is configured to be able to receive a command for the upper limit of the output of the PCS2 from outside, the signal may be a signal indicating the upper limit of the output. Alternatively, if the controller 93 has a suppressed operation mode or a soft start mode that gradually increases the output power of the PCS2, the signal may be a signal (flag) that turns on such a mode.

[0073] The power output control in this embodiment will be described with reference to Fig. 6. Similar to Fig. 2, Fig. 6 shows columns for the power consumption of the load 4, the output power of the PCS 2 (the amount of power generated by the PV system 1), and the power value at the power receiving point measured by the power measurement unit 11, as well as a column showing the ON / OFF state of the suppression operation signal (suppression flag) sent by the suppression commander 33 to the controller 93.

[0074] 6, when the power at the power receiving point deviates from the threshold due to a sudden load decrease or the like, the determination unit 32 transmits a reverse power flow detection signal to the controller 93, thereby causing an abnormal shutdown. The reverse power flow detection signal is also transmitted to the suppression command device 33, and upon receiving the reverse power flow detection signal, the suppression command device 33 transmits a signal to the controller 93 to suppress output from the PCS 2 for a predetermined period after power generation is resumed.

[0075] When the suppression command device 33 transmits an upper limit value for power generation, the output of the PCS2 is controlled so as not to exceed the upper limit value until a predetermined period has elapsed. Also, when the suppression command device 33 transmits a signal instructing the suppression operation mode to be ON, the controller 93 controls the increase in the output of the PCS2 so as to be gradual until the predetermined period has elapsed.

[0076] In this embodiment, the suppression command device 33 transmits a suppression operation signal to the controller 93 that is unrelated to the receiving point power measured by the power measurement unit 31, and therefore can be configured separately from the power measurement unit 31 and the judgment unit 32.

[0077] <Embodiment 4> In the above examples, the present invention has been described as being applied to a protective relay separate from a controller, but it is also possible to apply the present invention to a power control device incorporating the functions of the protective relays of the above examples. Such an embodiment will be described with reference to Fig. 11. Fig. 11 is a schematic diagram showing the general configuration of a power system 700 according to this embodiment.

[0078] 11 , the present embodiment differs from the power system 100 of the first embodiment in that, instead of the configuration of the protective relay 10 and the controller 91, the present embodiment has a controller 70 including a power measurement unit 71, a determination unit 72, a compensation unit 73, and a control unit 74. In the present embodiment, the power measurement unit 71, the determination unit 72, and the compensation unit 73 perform the same functions as those in the power system 100 of the first embodiment, and the control unit 74 performs the same function as the controller 91 in the power system of the first embodiment.

[0079] When the protective relay and the controller are integrated, there is a small time lag in transmitting power at the receiving point, enabling accurate load following control, but this does not mean that hunting can be completely prevented after power generation is resumed after being stopped. For this reason, by implementing the functions of the power generation suppression unit according to the present invention in a controller that has the functions of a protective relay as described above, the occurrence of hunting can be more effectively suppressed.

[0080] <Other> The above examples merely exemplify the present invention, and the present invention is not limited to the specific embodiments described above. The present invention can be modified in various ways within the scope of its technical concept. For example, the compensating unit 23 in the second embodiment can be configured in the same way as the compensating unit 13 in the first embodiment, and conversely, the compensating unit 13 in the first embodiment can be configured in the same way as the compensating unit 23 in the second embodiment. In other words, the timing and period for outputting the compensation value, the compensation value for the power receiving point power, and the like can be changed. The amount of compensation can be set appropriately.

[0081] The determination unit 32 in the third embodiment and the determination unit 72 in the fourth embodiment can also be configured to output a pseudo-power outage signal. In this case, the suppression command unit 33 and the compensation unit 73 may also be configured to output a suppression operation signal when recovering from a pseudo-stop.

[0082] Furthermore, in the above examples, the distributed power source has been described as a PV system, but it is not limited to this and may also be a power generation facility using other renewable energy sources, a fuel cell, or the like.

[0083] <Appendix 1> A protective relay (10, 20, 30) for use in a power system (100, 200, 300) interconnected with a commercial power system (5) and controlling operation of the distributed power sources, the power system (100, 200, 300) comprising: distributed power sources (1a, 1b); converters (2a, 2b) for converting power output from the distributed power sources; and a controller (91, 92, 93) for controlling the converters to control power generation by the distributed power sources, the protective relay comprising: a power measurement unit (11, 31) that measures power at a receiving point from the commercial power system; a reverse power flow determination unit (12, 22, 32) that detects a reverse power flow to the commercial power system based on the power value measured by the power measurement unit, and that transmits a command signal to the control device to stop the power generation when the reverse power flow is detected; a power generation suppression unit (13, 23, 33) that transmits information to the control device for the control device to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit at least during a period from when the power generation is stopped based on a command from the reverse power flow determination unit until a predetermined time has elapsed, Protective relay.

[0084] <Appendix 2> The power measurement unit, the reverse power flow determination unit, and the power generation suppression unit are accommodated in a single housing. 2. A protective relay according to claim 1,

[0085] <Appendix 3> the power generation suppression unit calculates a compensation value by compensating for the power value measured by the power measurement unit, and transmits the compensation value to the control device as the power value at the power receiving point. 3. A protective relay according to claim 1 or 2,

[0086] <Appendix 4> the compensation value transmitted by the power generation suppression unit to the control device is set so that the value of the compensated amount gradually decreases to 0 during the period from when the power generation is stopped based on the command of the reverse power flow determination unit until the predetermined time has elapsed. 4. A protective relay according to claim 3,

[0087] <Appendix 5> the power generation suppression unit transmits the compensation value to the control device when the power value measured by the power measurement unit deviates from a predetermined threshold value before the predetermined time has elapsed. 4. A protective relay according to claim 3,

[0088] <Appendix 6> The reverse power flow determination unit detects a sign of reverse power flow before detecting the reverse power flow, and When the sign is detected, a command signal is sent to the control device to execute a pseudo-power generation shutdown process, which sets the time for which the power generation is suppressed to be shorter than when the power generation is actually stopped; the power generation suppression unit transmits to the control device information for the control device to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit during a predetermined time period from the time when the pseudo power generation is stopped. 6. A protective relay according to any one of claims 1 to 5.

[0089] <Appendix 7> the power generation suppression unit transmits an upper limit value of the amount of power generation of the distributed power source to the control device, and the upper limit value gradually increases from the time when the power generation is stopped based on the command of the reverse flow determination unit until the predetermined time has elapsed. 2. A protective relay according to claim 1,

[0090] <Appendix 8> the power generation suppression unit transmits to the control device a command signal to slow down the rate of increase in the amount of power generated by the distributed power source, for a period from the time when the power generation is stopped based on the command of the reverse power flow determination unit until the predetermined time has elapsed; 2. A protective relay according to claim 1,

[0091] <Appendix 9> A power control device (70) for use in a power system (700) interconnected with a commercial power system (5), the power system (700) including distributed power sources (1a, 1b) and converters (2a, 2b) for converting power output from the distributed power sources, the power control device (70) controlling the converters to control power generation by the distributed power sources, a control unit (74) that transmits a command signal to the converter to control the output power of the converter; a power measurement unit (71) that measures power at a receiving point from the commercial power system; a reverse power flow determination unit (72) that detects a reverse power flow to the commercial power system based on the power value measured by the power measurement unit, and that outputs a stop command signal to the control unit to stop the power generation when the reverse power flow is detected; a power generation suppression unit (73) that outputs information to the control unit, based on the power value measured by the power measurement unit, for the control unit to perform control to suppress the amount of power generation of the distributed power source, at least during a period from when the power generation is stopped based on a command from the reverse power flow determination unit until a predetermined time has elapsed, Power control device.

[0092] <Appendix 10> the power generation suppression unit calculates a compensation value by compensating for the power value measured by the power measurement unit, and outputs the compensation value as the power value at the power receiving point. 10. The power control device according to claim 9,

[0093] <Appendix 11> the compensation value is set so that the value of the compensated amount gradually decreases to 0 during the period from when the power generation is stopped based on the command of the reverse power flow determination unit until the predetermined time has elapsed. 11. The power control device according to claim 10.

[0094] <Appendix 12> the power generation suppression unit outputs the compensation value when the power value measured by the power measurement unit deviates from a predetermined threshold value before the predetermined time has elapsed. 11. The power control device according to claim 10.

[0095] <Appendix 13> the reverse power flow determination unit detects a sign of reverse power flow before detecting the reverse power flow, and when the sign is detected, outputs to the control unit a command signal to execute a pseudo-power generation stop process that sets a time period for which the power generation is suppressed to be shorter than when the power generation is stopped; the power generation suppression unit outputs, to the control unit, information for the control unit to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit during a predetermined time period from the time when the pseudo power generation is stopped. 13. The power control device according to any one of appendices 9 to 12.

[0096] <Appendix 14> the power generation suppression unit outputs an upper limit value of the amount of power generation of the distributed power source to the control unit, and the upper limit value gradually increases from the time when the power generation is stopped based on the command of the reverse flow determination unit until the predetermined time has elapsed. 10. The power control device according to claim 9,

[0097] <Appendix 15> the power generation suppression unit outputs to the control unit a command signal to slow down the rate of increase in the amount of power generated by the distributed power source, for a period from the time when the power generation is stopped based on the command from the reverse power flow determination unit until the predetermined time has elapsed. 10. The power control device according to claim 9, [Explanation of symbols]

[0098] 1a, 1b... Solar power generation system 2a, 2b... Power conditioner 3, 63, 70, 91, 92, 93... Controller 4a, 4b...Load 5...Commercial power system 10, 20, 30, 40, 50, 60...protective relay 11, 31, 41, 51, 61...Power measurement section 12, 22, 32, 42, 52, 62...judgment section 30a···First housing 100, 200, 300, 400, 500, 600, 700... Power System

Claims

1. A protective relay used in a power system that is interconnected with a commercial power system and controls operation of the distributed power source, the power system including: a distributed power source; a converter for converting power output from the distributed power source; and a controller that controls the converter to control power generation by the distributed power source, the protective relay comprising: a power measurement unit that measures power at a receiving point from the commercial power system; a reverse power flow determination unit that detects a reverse power flow to the commercial power grid based on the power value measured by the power measurement unit, and that transmits a command signal to the control device to stop the power generation when the reverse power flow is detected; a power generation suppression unit that transmits information to the control device to control the control device to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit at least during a period from when the power generation is stopped based on a command from the reverse power flow determination unit until a predetermined time has elapsed, Protective relay.

2. The power measurement unit, the reverse power flow determination unit, and the power generation suppression unit are accommodated in a single housing.

2. The protective relay according to claim 1 .

3. the power generation suppression unit calculates a compensation value by compensating for the power value measured by the power measurement unit, and transmits the compensation value to the control device as the power value at the power receiving point.

2. The protective relay according to claim 1 .

4. the compensation value transmitted by the power generation suppression unit to the control device is set so that the value of the compensated amount gradually decreases to 0 during the predetermined time period from when the power generation is stopped based on the command of the reverse power flow determination unit.

4. A protective relay according to claim 3.

5. the power generation suppression unit transmits the compensation value to the control device when the power value measured by the power measurement unit deviates from a predetermined threshold value before the predetermined time has elapsed.

4. A protective relay according to claim 3.

6. the reverse power flow determination unit detects a sign of reverse power flow before detecting the reverse power flow, and when the sign is detected, transmits to the control device a command signal to execute a pseudo-power generation stop process that sets a time period for which the power generation is suppressed to be shorter than when the power generation is stopped; the power generation suppression unit transmits to the control device information for the control device to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit during a predetermined time period from the time when the pseudo power generation is stopped.

2. The protective relay according to claim 1 .

7. the power generation suppression unit transmits an upper limit value of the amount of power generation of the distributed power source to the control device, and the upper limit value gradually increases from the time when the power generation is stopped based on the command of the reverse flow determination unit until the predetermined time has elapsed.

2. The protective relay according to claim 1 .

8. the power generation suppression unit transmits to the control device a command signal to slow down the rate of increase in the amount of power generated by the distributed power source, for a period from the time when the power generation is stopped based on the command of the reverse power flow determination unit until the predetermined time has elapsed; 2. The protective relay according to claim 1 .

9. A power control device is used in a power system interconnected with a commercial power grid, the power control device including a distributed power source and a converter for converting power output from the distributed power source, the power control device controlling the converter to control power generation by the distributed power source, a control unit that transmits a command signal to the converter to control the output power of the converter; a power measurement unit that measures power at a receiving point from the commercial power system; a reverse power flow determination unit that detects a reverse power flow to the commercial power grid based on the power value measured by the power measurement unit, and that outputs a stop command signal to the control unit to stop the power generation when the reverse power flow is detected; a power generation suppression unit that outputs information to the control unit to enable the control unit to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit at least during a period from when the power generation is stopped based on a command from the reverse flow determination unit until a predetermined time has elapsed, Power control device.

10. the power generation suppression unit calculates a compensation value by compensating for the power value measured by the power measurement unit, and outputs the compensation value as the power value at the power receiving point.

10. The power control device according to claim 9.

11. the compensation value is set so that the value of the compensated amount gradually decreases to 0 during the period from when the power generation is stopped based on the command of the reverse power flow determination unit until the predetermined time has elapsed.

11. The power control device according to claim 10.

12. the power generation suppression unit outputs the compensation value when the power value measured by the power measurement unit deviates from a predetermined threshold value before the predetermined time has elapsed.

11. The power control device according to claim 10.

13. the reverse power flow determination unit detects a sign of reverse power flow before detecting the reverse power flow, and when the sign is detected, outputs to the control unit a command signal to execute a pseudo-power generation stop process that sets a time period for which the power generation is suppressed to be shorter than when the power generation is stopped; the power generation suppression unit outputs, to the control unit, information for the control unit to perform control to suppress the amount of power generation of the distributed power source based on the power value measured by the power measurement unit during a predetermined time period from the time when the pseudo power generation is stopped.

13. A power control device according to any one of claims 9 to 12.

14. the power generation suppression unit outputs an upper limit value of the amount of power generation of the distributed power source to the control unit, and the upper limit value gradually increases from the time when the power generation is stopped based on the command of the reverse flow determination unit until the predetermined time has elapsed.

10. The power control device according to claim 9.

15. the power generation suppression unit outputs to the control unit a command signal to slow down the rate of increase in the amount of power generated by the distributed power source, for a period from the time when the power generation is stopped based on the command from the reverse power flow determination unit until the predetermined time has elapsed.

10. The power control device according to claim 9.

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