JP2014011834A - Power conditioner and fuel cell power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to undertake abnormality diagnosis on the basis of a detection signal related to a purchase power quantity at the time by proactively causing variations enough to perform abnormality determination in the purchase power quantity without requiring a dummy load with large power consumption in a power conditioner that outputs generated power to premises in system interconnection with a commercial power system and is performed load follow-up control so that the output power will not reversely flow to the commercial power system.SOLUTION: A power conditioner comprises a control unit which inputs a detection signal of current flowing from a commercial power system to premises and undertakes abnormality diagnosis of the signal at prescribed timing. The control unit reduces the output power when the current quantity indicated by the signal is less than a prescribed value and based on variations of the signal at the time, it undertakes abnormality diagnosis.

Description

  The present invention relates to a power conditioner for a private power generation system such as a fuel cell and a fuel cell power generation system.

  Conventionally, in fuel cell power generation systems and gas engine power generation systems where reverse power flow to the commercial power system is not permitted, output control of the power conditioner is performed so that reverse power flow does not occur, sensor malfunctions, etc. Even when there is an abnormality, it is required to determine the abnormality and stop the output of the power conditioner.

  For example, in the power conditioner described in Patent Document 1 below, when the power conditioner is not operating, power consumption is reduced by repeatedly energizing and de-energizing a load device different from the home load (premises load). It is diagnosed whether or not it fluctuates based on the detected value of the current sensor (current transformer) or voltage sensor for measuring purchased power, and if the measured value is smaller than the rated power consumption of the load device, the sensor malfunctions Therefore, the power conditioner is configured not to operate.

  Further, in Patent Document 2 below, the power output value S and the current output value I are used for power detection as signals relating to the purchased power amount from the commercial power system based on the current detection value by the current transformer and the voltage detection value by the voltage sensor. The calculation is performed in the IC, and the power output value S has a predetermined abnormal mode (for example, the generation period of singular points such as maximum value, minimum value, and zero value does not become a predetermined period, or the generation of singular points is irregular In such a case, there is disclosed a technique for reliably avoiding a reverse power flow by starting full use control of generated power in a case where a situation occurs.

JP 2010-283944 A JP 2006-280097 A

  However, in the technique described in Patent Document 1, abnormality diagnosis is performed by temporarily stopping the operation of the power conditioner and performing energization control to a load device different from the home load. In order to perform an abnormality diagnosis, it is necessary to connect another load device with a certain amount of power consumption (for example, about 1000 W) to the system as a dummy load to the system, and this dummy load is connected to the commercial power system. Since the operation is performed with the purchased power, if such abnormality diagnosis is performed every day, the monthly accumulated power consumption also increases to some extent, causing an extra burden of about several hundred yen per month to the user.

  Further, in the technique described in Patent Document 2, the complete use control of generated power is not started unless an abnormality occurs in the current detection value by the current transformer, but the normal load following control of the output of the power conditioner is well adapted to the domestic load. If this is done, the detected value of the current transformer for measuring the purchased electric energy is stabilized near zero, so there is a problem that it cannot be diagnosed whether the current transformer cannot detect current due to an abnormality.

  Therefore, the present invention can actively vary the amount of purchased power while eliminating the need for a dummy load with large power consumption, and can perform abnormality diagnosis based on a detection signal relating to the amount of purchased power at that time. The purpose is to provide a power conditioner that can be used.

  In order to achieve the above object, the present invention takes the following technical means.

  That is, the present invention provides a power conditioner in which the output power is controlled so that the output power is connected to a commercial power system and the generated power is output to a local electrical load and the output power does not flow backward to the commercial power system. A control unit is provided that inputs a signal related to the detected current amount flowing from the power system to the premises electrical load and performs an abnormality diagnosis of the signal at a predetermined timing, and the control unit has a current amount indicated by the signal of less than a predetermined value. The output power is reduced at a certain time, and the abnormality diagnosis is performed based on the fluctuation of the signal at that time (Claim 1). According to the present invention, the output power is subjected to load follow-up control following the on-site electrical load (including the home load) connected to the commercial power system, thereby detecting the amount of current flowing in the premise. When the detection signal (signal related to the detected current amount) of the current transformer is near zero, the output power is reduced by the output suppression control of the power conditioner, and the detection indicated by the signal according to this output reduction amount By monitoring whether or not the amount of current increases, it is possible to perform an abnormality diagnosis as to whether or not sensors for detecting the purchased power amount such as a current transformer are operating normally. Generally, the rated maximum output power of a power conditioner in a household power generation system is about 600 to 1000 W, and at least a few tens of W depending on the power consumption of a refrigerator that is always operating by load following control and the standby power of various electric devices. Since a certain amount of power is output to the grid, the amount of current that actually flows from the commercial power grid to the premises electrical load can be increased from near zero to about 1 A by the output suppression control of the power conditioner, and the detected current amount For example, it can be determined reliably and easily even if detection error due to power fluctuation or the like is taken into consideration. Furthermore, since a large dummy load of several hundred watts is unnecessary, even if abnormality diagnosis is performed once a day according to the present invention, there is no extra power consumption for operating the dummy load, and the power consumption is suppressed as much as possible. Can do.

  The power conditioner of the present invention includes an inverter driven by a gate drive signal and a gate block circuit that gate-blocks the inverter during operation, and the output power of the inverter becomes the output power to the premises electrical load. can do. In this case, the control unit operates the gate block circuit to gate block the inverter when the abnormality determination based on the fluctuation of the signal is not made even if the output power of the inverter is reduced to a predetermined power or less. It is preferable that the abnormality diagnosis is performed. According to this, the output power to the system can be made substantially zero without stopping the power generation by the power generation unit such as the fuel cell, and the increase in the purchased power amount can be reduced only by the control of the power conditioner. The power output from the power conditioner to the system after diagnosis of abnormality can be restarted only by stopping the gate block circuit and without having to stop or restart the fuel cell. is there.

  In addition, the control unit can be configured to operate the first electric load that consumes the surplus of the generated power due to the decrease in the output power at the time of the abnormality diagnosis. Preferably, the first electric load is composed of a DC power device such as an auxiliary heater of the hot water storage tank, and can be connected to the power generation unit in parallel with the power conditioner. A relay that switches between energization and de-energization of the power supply, a distributor that distributes the generated power output from the power generation unit to the power conditioner and the first electric load in a controllable distribution ratio, and the like. By controlling the controller, it is possible to cause the first electric load to consume the surplus of the generated power due to the decrease in the output power. According to this, when the output power of the power conditioner is reduced or when the inverter is gate-blocked, the surplus generated power is consumed by the first electric load to maintain the generated power of the power generation unit. This is particularly useful in the case of a fuel cell power generation system that cannot perform increase / decrease control of power generation output in a short time.

  The controller can be configured to forcibly operate the second electric load connected to the commercial power system during the abnormality diagnosis. The second electric load can be a 100V AC power load such as a freeze prevention heater for a cogeneration system provided with a fuel cell, and the power consumption is preferably about 100 W in total. According to this, for example, when the power consumption of the household load at the time of abnormality diagnosis is extremely low, when the abnormality determination cannot be made only by the output power reduction by the power conditioner output suppression or output stop, the second By operating the electric load, the on-site power consumption can be increased as much as possible, and the abnormality diagnosis can be performed more reliably. In addition, by making the second electric load have a relatively low power consumption, the purchased electric energy can be kept as low as possible even when the second electric load is operated at the time of abnormality diagnosis, and the power conditioner When abnormality diagnosis is performed by reducing the output power, it is not necessary to operate the second electrical load, and the overall power consumption can be suppressed as low as possible.

  Further, the present invention can be suitably realized as a fuel cell power generation system mainly composed of the power conditioner and a fuel cell for supplying generated power to the power conditioner (Claim 5), more preferably from a fuel cell. This can be suitably implemented as a cogeneration system that stores hot water in a hot water storage tank using the exhaust heat of the water. According to this, it is possible to perform abnormality diagnosis of a sensor such as a current transformer for detecting purchased power by controlling the output suppression of the power conditioner without suppressing the generated power of the fuel cell. It becomes possible to improve.

  According to the power conditioner of the first aspect of the present invention, the output power is subjected to load following control following the on-premise electric load (including the home load), thereby detecting the amount of current flowing in the premise. When the detection signal (signal related to the detected current amount) of the current transformer is near zero, the output power is reduced by the output suppression control of the power conditioner, and the detection indicated by the signal according to this output reduction amount By monitoring whether or not the amount of current increases, it is possible to perform an abnormality diagnosis as to whether or not sensors for detecting the purchased power amount such as a current transformer are operating normally. Generally, the rated maximum output power of a power conditioner in a household power generation system is about 600 to 1000 W, and at least a few tens of W depending on the power consumption of a refrigerator that is always operating by load following control and the standby power of various electric devices. Since about the amount of power is output to the system, the current amount actually flowing from the commercial power system to the premises can be increased from near zero to about 1 A by the output suppression control of the power conditioner. The determination as to whether or not the current has risen from near zero of less than 0.05 A to about 1 A can be reliably and easily performed even if detection errors due to power fluctuations are taken into account. Furthermore, since a large dummy load of several hundred watts is unnecessary, even if abnormality diagnosis is performed once a day according to the present invention, there is no extra power consumption for operating the dummy load, and the power consumption is suppressed as much as possible. Can do.

  Further, according to the power conditioner of claim 2 of the present invention, the output power to the system can be made substantially zero without stopping the power generation by the power generation unit such as the fuel cell, and the control of the power conditioner As a result, it is possible to increase the amount of purchased power as much as possible, and restarting power output from the power conditioner to the system after abnormality diagnosis only stops the gate block circuit, and stops or restarts the fuel cell. It is unnecessary and can be done quickly.

  According to the power conditioner of claim 3 of the present invention, when the output power of the power conditioner is reduced or when the inverter is gate-blocked, the surplus generated power is consumed by the first electric load. This is particularly useful in the case of a fuel cell power generation system in which the power generated by the power generation unit can be maintained and increase / decrease control of the power generation output cannot be performed in a short time.

  Further, according to the power conditioner of claim 4 of the present invention, when the power consumption of the household load at the time of abnormality diagnosis is extremely low, an abnormality is caused only by a decrease in the output power due to output suppression or output stop of the power conditioner. When the determination cannot be made, the on-site power consumption is increased by operating the second electric load as much as possible, so that the abnormality diagnosis can be performed more reliably. In addition, by making the second electric load have a relatively low power consumption, the purchased electric energy can be kept as low as possible even when the second electric load is operated at the time of abnormality diagnosis, and the power conditioner When abnormality diagnosis is performed by reducing the output power, it is not necessary to operate the second electrical load, and the overall power consumption can be suppressed as low as possible.

  Moreover, according to the fuel cell power generation system of claim 5 of the present invention, an abnormality of a sensor such as a current transformer for detecting purchased power by output suppression control of the power conditioner without suppressing power generated by the fuel cell. Diagnosis can be performed and the COP of the system can be further improved.

It is a premise wiring schematic diagram of a fuel cell power generation system provided with a power conditioner concerning one embodiment of the present invention. It is a flowchart of CT check task which performs abnormality diagnosis in the control part of the power conditioner. It is a flowchart of the abnormality monitoring task which performs abnormality diagnosis in the control part of the power conditioner.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 schematically shows wiring between a fuel cell power generation system 10 according to an embodiment of the present invention and a commercial power system. A single-layer three-wire lead-in line 1 of the commercial power system includes an ampere breaker 2 and It is connected to a single-layer three-wire premises wiring 4 via a main circuit breaker 3 (earth leakage breaker), and a household load 5 (premises electrical load) is connected to the premises wiring 4 so that a commercial power system is connected to the household load 5. Commercial power is supplied from Normally, a branch breaker (safety breaker) is further provided for each installation location of the outlet, but the illustration is omitted. The ampere breaker 2, the main breaker 3, and the safety breaker are generally provided on the switchboard, and are wired to the connection terminals of the breakers using lead wires.

  The lead-in line 1 between the ampere breaker 2 and the main breaker 3 is provided with a current transformer 6 (current sensor) for detecting the amount of current flowing from the commercial power system to the home load 5. The detection signal 6 is output to the power conditioner 11 described later via the wiring box 7. In the illustrated example, the current transformer 6 is provided for each of the U phase and the V phase. In the case of reverse power flow from the premises to the commercial power system, the detection value of the current transformer 6 is output as a negative value.

  More specifically, the current transformer 6 (CT) is often attached to the lead wire in the vicinity of the connection terminal of the main breaker 3, so that the current can be detected correctly for installation and installation in a narrow switchboard. In some cases, the current transformer 6 is not attached from the beginning of construction, and when the lid of the switchboard is closed, the current transformer 6 is pushed into the lid and the current cannot be detected correctly. In addition, the current transformer 6 may break down due to lightning strikes and other causes. Thus, if current detection by the current transformer 6 is not performed normally, the output power control of the power generation system 10 cannot be performed normally, and a reverse power flow from the premises to the commercial power system occurs. In the power generation system 10, the power conditioner 11 has a current transformer abnormality diagnosis function for confirming the normal operation of the current transformer 6 at a predetermined timing such as every 24 hours.

  The power generation system 10 of the present embodiment converts a fuel cell 12 and direct-current power generated by the fuel cell 12 into alternating-current power connected to a commercial power system, via a fuel cell breaker 13 and a premises wiring 4. And a power conditioner 11 for outputting to the home load 5. Furthermore, in this embodiment, it is comprised as a cogeneration system provided with the hot water storage tank 14 which stores hot water by utilizing the exhaust heat of the fuel cell 12, and this system is the heater 15 for auxiliary heating of the hot water storage tank 14 (first). 1) and a 100V AC power load 16 (second electric load) comprising a freeze prevention heater (power consumption of about 50 W) of hot water piping (not shown) connected to the hot water storage tank 14 and the like. ing. The load 16 is provided between U-N and V-N, and the power consumption of each of the U-phase and the V-phase is increased by the operation of each load 16.

  An appropriate type of fuel cell 12 such as SOFC or PEFC can be used, and the operation is controlled by the fuel cell control unit 12a so as to stabilize the generated power and increase the power generation efficiency. The fuel cell control unit 12a is also configured to control the operation of the AC power load 16, and the load 16 is normally operated according to the operation state of the cogeneration system. When a load increase command signal sent from the controller 11a is input, the load 16 is forcibly activated regardless of the operating state of the cogeneration system.

  The generated power output from the fuel cell 12 is supplied to the power conditioner 11 and also supplied to the auxiliary heater 15 via the relay 17, and each relay 17 is controlled by the controller 11 a of the power conditioner 11 to generate power. The surplus power is consumed in the auxiliary heater 15 when the relay 17 is energized.

  The power conditioner 11 (inverter in a broad sense) includes a control unit 11a mainly composed of a high-function microcomputer capable of multitask control, and a DC / DC converter 11b that rectifies and boosts the generated power supplied from the fuel cell 12 and outputs it. An inverter 11c (inverter in a narrow sense) that converts the output of the converter 11b into AC power that is grid-connected to the commercial power system, and a circuit breaker 11d (relay) for disconnecting the power conditioner 11 from the system The converter 11b, the inverter 11c, and the circuit breaker 11d are controlled by the control unit 11a.

  Since the basic configuration of the power conditioner 11 is conventionally known, a detailed description thereof will be omitted. However, when the functions necessary for understanding the present invention are described, the control unit 11a controls the output of the converter 11b. An output suppression control function for suppressing the active power of the AC power output from the inverter 11c, a reactive power control function for controlling the power factor of the AC power output from the inverter 11c by controlling the inverter 11c, and a predetermined A disconnection control function for disconnecting the power conditioner 11 from the system by operating the circuit breaker 11d when the disconnection condition is satisfied is provided, and the power conditioner 11 is provided by the output suppression control function and the reactive power control function. Increase or decrease the output power of the home following the power consumption of the household load 5 It is adapted to perform a load-following control.

  Moreover, the inverter 11c uses what is mainly comprised by several IGBT, and is driven by the gate drive signal from the gate driver 18 of the control part 11a, and when predetermined conditions are satisfied in the control part 11a An operating gate block circuit 19 is further provided that gates the inverter 11c to null the output power by disabling the gate drive signal when activated.

  The current transformer abnormality diagnosis function by the controller 11a of the power conditioner 11 is realized by a CT confirmation task activated in the microcomputer, and its control flow is shown in FIG. This CT confirmation task is started by the main control task when one day has passed since the end of the previous task, and first, detection of generated power supplied from the fuel cell 12 is performed to determine whether or not the fuel cell 12 is generating power. Determination is made by appropriate means such as a value and an operation state signal from the control unit 12a of the fuel cell 12, and if power generation is not in progress, the system waits (step S1). In addition, when not generating electricity, you may comprise so that a CT confirmation task may be once complete | finished. Further, instead of determining whether or not power generation is in progress, it is determined whether or not the output power of the power conditioner 11 is equal to or higher than a predetermined power, for example, 100 W or higher. You may make it do. This is because if the output power of the power conditioner 11 is not large to some extent, the detected value of the current transformer 6 does not increase sufficiently even if the output decreases, and reliable abnormality determination cannot be performed.

  Next, the purchased power amount obtained by calculation based on the detection signal of the current transformer 6 (signal relating to the detected current amount flowing from the commercial power system to the on-site electrical load) and the detection signal of the system voltage is a predetermined value, for example, an absolute value. Is less than 5W, and if it is not less than the predetermined value, it waits (step S2).

  If it is confirmed that the purchased power amount is less than the predetermined value, the monitoring task shown in FIG. 3 is newly activated (step S3). Thereafter, until the monitoring task is terminated, the CT confirmation task and the monitoring task are executed in parallel by multitask control. This monitoring task determines whether the current transformer 6 is normal by determining whether or not the current value indicated by the detection signal of the current transformer 6 increases from near zero and exceeds a predetermined threshold (for example, 500 mA). If it is determined that the current transformer 6 is normal, the monitoring task is also terminated after performing the forced termination processing of the CT confirmation task as the parent task. Accordingly, if a normal determination is made during the subsequent sequence by the CT confirmation task, the CT confirmation task is also forcibly terminated at that time.

  Next, in the CT confirmation task, control for reducing the output power of the power conditioner 11 is performed by temporarily invalidating the above-described normal load follow-up control or prioritizing the load follow-up control (step S4). Such a reduction in output power may be reduced step by step by a predetermined amount every predetermined time, or may be gradually reduced with time. If normality is determined by the monitoring task in the process, termination processing is performed as described above. Note that the output power of the power conditioner 11 may already be reduced to the limit at the start of the CT confirmation task by the load following control described above.

  If the normal determination is not made even if the output power of the power conditioner 11 falls below a predetermined controllable limit value (step S5), the gate block circuit 19 is operated to activate the inverter 11c as a gate block. As a state, the output of the inverter 11c is stopped (step S6), thereby reducing the output power of the power conditioner 11 to substantially zero. If normality is determined by the monitoring task at this point, the end processing is performed as described above. If normality is not yet determined, the process proceeds to the next step. The circuit breaker 11d may be actuated to disconnect the power conditioner 11, but the response speed required for restarting the output of the power conditioner 11 is faster when the gate block is turned on and off, and normality is determined. It is preferable because normal control can be quickly restored.

  Next, by outputting a load increase command signal to the fuel cell control unit 12a, the control unit 11a forcibly operates the 100V AC power load 16 via the fuel cell control unit 12a, and the power consumption in the premises Is increased by about 100 W (step S7), and in that state, a predetermined abnormality determination grace time, for example, 30 seconds is waited (step S8). If an increase in the detection value of the current transformer 6 cannot be confirmed even after this grace period has elapsed, it is clear that the current transformer 6 is abnormal, and therefore the monitoring task is terminated (step S9). A failure determination process of the transformer 6 is performed, and when such a failure determination is made, the power conditioner 11 is disconnected, the power generation operation of the fuel cell 12 is stopped, a warning process for the user, and the like are performed.

  According to the power conditioner 11 according to the present embodiment described above, output power from the power conditioner 11 is substantially zeroed by the gate block of the inverter 11c at the time of CT confirmation so that only purchased power from the commercial power system is on the premises. Since the power is not supplied, even when the power consumption of the 100V AC power load 16 of the cogeneration system is small, it is possible to cause a sufficient amount of power fluctuation for abnormality determination, thereby reducing erroneous determination of abnormality of the current transformer 6. However, power generation can be continued for a long time.

  The present invention is not limited to the above-described embodiment. For example, a gas engine power generation device can be used as a power generation unit instead of a fuel cell. In addition to the detection signal itself of the current transformer 6 described above, the signal related to the detected current flowing from the commercial power system to the premises electrical load is an appropriate analog or digital signal obtained by converting the detection signal of the current transformer 6. It may also be a signal indicating the purchased electric energy obtained by calculation based on the detection signal of the current transformer 6. In the above embodiment, it is indirectly determined that the amount of current indicated by the detection signal of the current transformer 6 is less than the predetermined value by determining that the purchased power is less than the predetermined value as the monitoring task activation condition. Based on the detection signal of the current transformer 6, it may be directly determined that the amount of current flowing through the premises is less than a predetermined value. In the above embodiment, the controller 11a of the power conditioner 11 forcibly operates the 100V AC power load 16 via the fuel cell controller 12a during abnormality diagnosis. A control unit for controlling the operation of the 100V AC power load 16 (including a microcomputer control circuit and a simple relay circuit) is provided separately from the fuel cell control unit 12a, and a load increase command signal to this control unit is provided. The 100V AC power load 16 can also be configured to be forcibly operated.

5 Domestic load (on-site electrical load)
6 Current transformer 10 Fuel cell power generation system 11 Power conditioner 11a Control unit 11c Inverter 12 Fuel cell (power generation unit)
DESCRIPTION OF SYMBOLS 15 1st electric load 16 2nd electric load 18 Gate driver 19 Gate block circuit

Claims (5)

  In a power conditioner in which the output power is controlled so that the generated power is connected to the commercial power system and the generated power is output to the on-site electrical load and the output power does not flow backward to the commercial power system. A control unit that inputs a signal related to the detected current amount flowing into the device and performs abnormality diagnosis of the signal at a predetermined timing, and the control unit outputs the output power when the current amount indicated by the signal is less than a predetermined value. The power conditioner is configured to perform the abnormality diagnosis based on a change in the signal at that time.   The power conditioner according to claim 1, comprising: an inverter driven by a gate drive signal; and a gate block circuit that gate-blocks the inverter during operation, wherein the output power of the inverter is output power to a local electrical load. In the power conditioner, the control unit operates the gate block circuit when the abnormality determination based on the fluctuation of the signal is not made even if the output power of the inverter is reduced to a predetermined power or less, and the inverter is operated. A power conditioner characterized in that the abnormality diagnosis is performed using a gate block.   3. The power conditioner according to claim 1, wherein the control unit is configured to operate a first electric load that consumes a surplus of generated power due to a decrease in the output power during the abnormality diagnosis. A power conditioner characterized by   4. The power conditioner according to claim 1, wherein the control unit forcibly operates a second electric load connected to a commercial power system during the abnormality diagnosis. 5. .   A fuel cell power generation system mainly composed of the power conditioner according to any one of claims 1 to 4 and a fuel cell for supplying generated power to the power conditioner.

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