JP2009189188A - Power generation system and method for controlling power generation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power generation system for converting an output current of a transformer into a sine wave without hindering reduction in cost and size of the device. <P>SOLUTION: This power generation system 100 includes: an inverter 2; a switch 105; an output instruction part 9 for determining an output current command value before correction of the inverter 2; a current detection part 3 provided between the inverter 2 and the transformer; a current waveform storage part 110 for storing an excitation current value of the transformer 4 based on a current value detected by the current detection part 3 when the switch 105 is opened for no-load operation of the inverter 2; and a current control part 8 for controlling an output current of the inverter 2 based on an inverter output current command value after correction obtained by adding the excitation current value of the transformer 4 stored in the current waveform storing part 110 to the inverter output current command value before correction from the output instruction part 9 when the switch 105 is closed to interconnect the inverter 2 with a power system 6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power generation system that converts an output of a direct current power source such as a fuel cell or a solar cell into alternating current by an inverter and outputs the alternating current to an electric power system, and a control method for the power generation system.

  In a power generation system using a DC power source such as a fuel cell or a solar cell, an interconnected operation with an AC power system is performed using an inverter in order to measure stable power supply.

  FIG. 5 is a diagram showing a configuration of a conventional power generation system (see, for example, Patent Document 1). As shown in FIG. 5, a conventional power generation system 10 includes, for example, a DC power source 1 made of a fuel cell, a solar cell, etc., an inverter 2 that converts DC power from the DC power source 1 into AC power, and an output of the inverter 2 A system comprising a transformer 4 for transforming the voltage to a required voltage of the power system 6, a current detector 3 provided between the inverter 2 and the transformer 4, and an AC power system 6 downstream of the transformer 4. The switch 5 that cuts off the linkage, the output command unit 9 that commands the output current of the inverter 2, the inverter power current command from the output command unit 9 and the input current signal from the current detector 3 are received by the pulse signal to the inverter 2 It is comprised with the current control part 8 which outputs a certain PWM (Pulse Width Modulation) control command. The current detector 3 detects the input current of the transformer 4 output from the inverter 2 and outputs an input current signal to the current control unit 8. The output command unit 9 outputs an inverter output current command to the current control unit 8 so as to be synchronized with the output of the power system 6. The current control unit 8 compares the input current signal from the current detector 3 with the inverter output current command sent from the output command unit 9 and outputs a PWM control command to the inverter 2 in consideration of the error. . The inverter 2 converts the DC power from the DC power source 1 into AC power based on the PWM control command from the current control unit 8.

  As another conventional technique, a power generation system as shown in FIG. 6 has been proposed (see, for example, Patent Document 1). FIG. 6 is a diagram illustrating a configuration of another power generation system. As shown in FIG. 6, in the power generation system 20, in addition to the configuration of the power generation system shown in FIG. 5, a current detector 21 that is provided between the transformer 4 and the switch 5 and detects the output current of the transformer 4, A fundamental wave blocking filter 22 that removes the fundamental wave from the current waveform from the current detector 21 is provided. The current detector 21 detects the output current of the transformer 4 and outputs an output current signal to the fundamental wave blocking filter 22. The fundamental wave rejection filter 22 removes the fundamental wave from the current waveform from the output current signal and extracts a harmonic component. The extracted waveform of the harmonic component is amplified as a harmonic extraction signal and sent to the current control unit 8.

The output command unit 9 sends a pre-correction inverter output current command to the current control unit 8 so that a desired output current is generated by the transformer 4. The current control unit 8 subtracts the harmonic extraction signal from the pre-correction inverter output current command, and receives a post-correction inverter output current command from the transformer 4 so that no harmonic component is generated. The current detector 3 detects the input current of the transformer 4 and sends an input current signal to the current control unit 8. The current control unit 8 receives the input current signal from the current detector 3, compares it with the corrected inverter output current command transmitted from the output command unit 9, and performs PWM control on the inverter 2 in consideration of the error. Send a command. The inverter 2 converts the DC power from the DC power source 1 into AC power based on the PWM control command received from the current control unit 8. Thereby, PWM control of an inverter can be performed so that a harmonic component is not generated, and a sine wave can be obtained from the output current of the transformer 4.
Japanese Patent Laid-Open No. 7-15878

  However, in the power generation system 10 shown in FIG. 5, an excitation current is required for the operation of the transformer 4, and this excitation current includes a harmonic component. Therefore, when the inverter 2 is controlled so that the input current of the transformer 4 becomes a sine wave, the excitation current is supplied from the output side of the transformer 4, so that the harmonic current corresponding to the excitation current is added to the output current of the transformer 4. Are superimposed, and as a result, the output current of the transformer 4 is distorted. In addition, there is a method of predicting the excitation current of the transformer 4 in advance and adding it to the inverter output current command before correction of the inverter 2, but cannot follow when the transformer 4 is changed. In addition, since the exciting current differs somewhat depending on the characteristics of each transformer, for example, when producing a large number of power generation systems, it is necessary to individually grasp the exciting current, which may complicate the work.

  Further, in the power generation system 20 shown in FIG. 6, a current detector and an arithmetic circuit are required on both the input side and the output side of the transformer 4, which becomes a factor that hinders cost reduction and downsizing of the device.

  Therefore, the present invention has been made in view of the above problems, and there is provided a power generation system and a power generation system capable of making the output current of a transformer into a sine wave without hindering cost reduction and downsizing of the device. An object is to provide a control method.

  In order to solve the above problems, a power generation system according to the present invention includes an inverter that converts input power into AC power and outputs the power, a transformer that transforms an output voltage of the inverter and outputs the voltage to an electric power system, and the transformer A switch for opening and closing between the power system, an output command unit for determining a pre-correction output current command value of the inverter, a current detection unit provided between the inverter and the transformer, and opening the switch During operation of the inverter, a current storage unit that stores an excitation current value of the transformer based on a current value detected by the current detection unit, and an operation that connects the inverter to the power system by closing the switch Based on the corrected inverter output current command value obtained by adding the excitation current value of the transformer stored in the current storage unit to the inverter output current command value before correction from the output command unit, And a control unit for controlling the output current of the serial inverter.

  According to the present invention, when the switch is opened and the inverter is operated, only the transformer in an unloaded state is connected to the inverter. The exciting current of the transformer is equal to the no-load current of the transformer, so that the output current of the inverter at this time is the same as the exciting current of the transformer. Therefore, the exciting current value of the transformer is stored in the current storage unit. Next, in an operation state in which the switch is closed and the inverter is connected to the power system, the output current value of the inverter is output from, for example, a sine wave current waveform based on the output command value from the output command unit and the current storage unit The waveform is obtained by adding the excitation current value of the transformer. The transformer consumes an exciting current, and as a result, a sine wave current is output to the power system side on the output side of the transformer. Moreover, since it is sufficient to provide a current detector or the like only on the input side of the transformer, the cost and size of the device can be reduced.

  In the power generation system of the present invention, the output destination of the current value detected by the current detection unit is set to the current storage unit when the switch is opened and the inverter is operated, and the inverter is connected to the power system when the switch is closed. And a switching unit that selectively switches to the control unit during operation linked to the control unit. According to the present invention, since the feedback control and the excitation current waveform can be stored by one current detection unit, the cost and size of the apparatus can be reduced.

  Further, in the above configuration, the switch is opened when the inverter is started to put the inverter in a no-load operation state, and the switching unit detects the current value detected by the current detection unit every time the inverter is not loaded. It outputs to the said current memory | storage part, It is characterized by the above-mentioned.

  According to the present invention, the excitation current is measured using the no-load operation state that is inevitably required in the starting process when the inverter reaches the rated operation from the stop, and is used for the subsequent control of the inverter. Therefore, even when the transformer is replaced due to a transformer failure or specification change, and the aspect of the excitation current changes, the excitation current is grasped every time the inverter is started. Can be kept sinusoidal.

  Moreover, the said structure WHEREIN: The said current saving part memorize | stores the exciting current value of the said transformer for at least 1 period for every control calculation period of the said inverter. According to the present invention, the output current of the transformer can be made a sine wave with a small storage capacity.

  Further, the present invention provides a method for controlling a power generation system, comprising: an inverter that converts input power into AC power and outputs the power; and a transformer that transforms the output voltage of the inverter and outputs the power to the power system. When the inverter is operated by opening a switch that opens and closes between the power systems, the excitation current value of the transformer is stored as a current based on the current value detected by the current detection unit provided between the inverter and the transformer And storing the current storage unit in the pre-correction inverter output current command value from the output command unit for determining the pre-correction output current command value of the inverter during the operation in which the inverter is connected to the power system. And a control step for controlling the output current of the inverter based on the corrected inverter output current command value obtained by adding the excitation current value of the transformer stored in . According to the present invention, the output current of the transformer can be made a sine wave without increasing the number of current detectors and arithmetic circuits.

  The power generation system control method according to the present invention includes the step of opening the switch to place the inverter in a no-load operation state when the inverter is started, and the current detection unit detecting each time the inverter is in no-load operation. And a step of outputting the measured current value to the current storage unit. According to the present invention, even when the transformer is replaced due to a failure of the transformer or a change in the specification and the aspect of the excitation current is changed, the excitation current is grasped every time the inverter is started. It is possible to keep the output current of the device sinusoidal.

  According to the present invention, it is possible to provide a power generation system and a method for controlling the power generation system that can make the output current of the transformer into a sine wave without hindering cost reduction and downsizing of the device.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a configuration of a power generation system according to an embodiment of the present invention. As shown in FIG. 1, a power generation system 100 according to an embodiment of the present invention includes a DC power source 1, an inverter 2, a current detector 3, a transformer 4, a switch 105, an output command unit 9, a current control unit 8, and a changeover switch. 107, a current waveform storage unit 110 is provided. The current detector 3 corresponds to a current detection unit, the current control unit 8 corresponds to a control unit, and the current waveform storage unit 110 corresponds to a current storage unit.

  The DC power source 1 is composed of, for example, a fuel cell or a solar cell. The inverter 2 converts DC power from the DC power source 1 into AC power. The current detector 3 is provided between the inverter 2 and the transformer 4 and detects the output current of the inverter 2, that is, the input current of the transformer 4. The transformer 4 transforms the output voltage of the inverter 2 to a required voltage of the power system 6. The switch 105 is provided on the downstream side of the transformer 4 and cuts off the system linkage with the power system 6.

  The changeover switch 107 selectively switches the output destination of the current value detected by the current detector 3. Specifically, the changeover switch 107 has a terminal 7a connected at the time of no-load operation and a terminal 7b connected at the time of linked operation, and the output destination of the current value detected by the current detector 3 is switched to When the inverter 105 is opened and the inverter 2 is in a no-load operation, the terminal is switched to the terminal 7a on the current waveform storage unit 110 side, and when the switch 105 is closed and the inverter 2 is connected to the electric power system 6, the current control unit 8 side Switch. The changeover switch 107 may be a mechanical switch or a software switch in the system linkage inverter control unit.

  The current waveform recording unit 110 has an area for storing the excitation current waveform of the transformer 4 based on the current value detected by the current detector 3 during no-load operation of the inverter 2. For example, a RAM (Random Access Memory) It is comprised with temporary storage media like.

  The output command unit 9 determines a pre-correction output current command value for the inverter 2. Specifically, the output command unit 9 calculates a current waveform having an amplitude and a phase according to output power (for example, 100 kW) set by an operator or the like using a sine wave synchronized with the system voltage as a basic waveform. Then, it is sent to the current control unit 8 as a pre-correction inverter output current command.

  The current control unit 8 receives the pre-correction inverter output current command from the output command unit 9 and sends a pulse signal to the inverter 2 to perform PWM control. Specifically, the current control unit 8 stores the pre-correction inverter output current command value from the output command unit 9 in the current waveform storage unit 110 during operation in which the switch 105 is closed and the inverter 2 is connected to the power system 6. The output current of the inverter 2 is controlled based on the corrected inverter output current command value to which the excitation current waveform value of the transformer 4 is added.

  FIG. 2 is an explanatory diagram of an outline of operation during each operation of the power generation system according to the embodiment of the present invention. The figure (a) is a figure for demonstrating operation | movement of the electric power generation system when the inverter 2 is a no-load operation, The figure (b) is the operation | movement of the electric power generation system when the inverter 2 is connected to the electric power grid 6. It is a figure for demonstrating.

  As shown in FIG. 2A, when the switch 105 is opened and the inverter 2 is in a no-load operation, the changeover switch 107 connects the contact to the terminal 7a connected to the current waveform storage unit 110. Thereby, the waveform of the input current of the transformer 4 detected by the current detector 3 is sent to the current waveform storage unit 110.

  At this time, when the inverter 2 is operated at a constant voltage, only the no-load transformer 4 is connected to the inverter 2, so the no-load current of the transformer 4 that can be detected by the current detector 3 is It becomes substantially equal to the excitation current of the device 4. For this reason, the exciting current of the transformer 4 can be measured by the current detector 3. The exciting current of the transformer 4 detected by the current detector 3 is sent to the current waveform storage unit 110 as an input current signal. The current waveform storage unit 110 stores the input current signal from the current detector 3 as an excitation current value of the transformer.

  On the other hand, as shown in FIG. 2B, during the operation in which the switch 105 is closed and the inverter 2 is connected to the power system 6, the changeover switch 107 switches the contact to the terminal 7 b that is connected to the current control unit 8. As a result, the current value detected by the current detector 3 is sent to the current control unit 8. From the current waveform storage unit 110, the excitation current value of the transformer 4 stored in the no-load state is sent. The output command unit 9 calculates a current waveform having an amplitude or phase corresponding to the output power set by the operator or the like, and sends the current waveform to the current control unit 8 as an inverter output current command before correction.

  The current control unit 8 receives the corrected inverter output current command value obtained by adding the transformer excitation current value stored in the current waveform storage unit 110 to the pre-correction inverter output current command value from the output command unit 9. The current control unit 8 compares the input current value from the current detection unit 3 with the corrected inverter output current command value, and sends a PWM control command to the inverter 2 in consideration of the error. The inverter 2 converts the DC power from the DC power source 1 into AC power based on the PWM control command sent from the current control unit 8. Thereby, the PWM control of the inverter 2 can be performed so that the harmonic component is not generated in the output current of the transformer 4.

  FIG. 3 is a graph showing a current waveform used in the power generation system according to the embodiment of the present invention.

  FIG. 3A is a graph showing a waveform of the pre-correction inverter output current command sent from the output command unit 9 to the current control unit 8 in FIG. The vertical axis represents current and the horizontal axis represents time. The output command unit 9 calculates a current waveform having an amplitude and phase according to the output power set by the operator or the like using a sine wave synchronized with the system voltage as a basic waveform, and controls the current as an inverter output current command before correction. Send to part 8.

  FIG. 3B is a graph showing an excitation current waveform sent from the current waveform storage unit 110 to the current control unit 8. As shown in FIG. 3B, the current waveform storage unit 110 preferably stores at least one period of the excitation current waveform of the transformer 4 for each control calculation period (sampling period) of the inverter 2.

  The corrected inverter output current command input to the current control unit 8 is obtained by adding the pre-correction inverter output current command shown in FIG. 3 (a) and the excitation current waveform of the transformer 4 shown in FIG. 3 (b). The signal becomes an output current waveform. The current control unit 8 compares the corrected inverter output current command with the inverter output current detected by the current detector 3, and controls the inverter 2 so that the inverter output current matches the corrected inverter output current command. As a result, the inverter output current, that is, the input current of the transformer 4 is supplied with the excitation current in addition to the sine wave current, and the excitation current is consumed in the transformer 4, and as a result, the transformer output current is the excitation current. A sinusoidal current not included.

  The changeover switch 107 opens the switch 5 and outputs the output current waveform detected by the current detector 3 to the current waveform storage unit 110 every time the inverter 2 is in a no-load operation. Thereby, the waveform of the exciting current unique to the transformer can be stored in the current waveform storage unit 110. For this reason, even if the transformer 4 is replaced, a new excitation current waveform can be stored in the current waveform storage unit 110 by performing constant voltage operation of the inverter once during no-load operation of the DC power supply. As a result, it is not necessary to set the inverter output current command before correction from the output command unit 9 individually for each transformer, and even before the correction from the output command unit 9 individually when the grid-connected inverter is mass-produced. Since there is no need to set an inverter output current command, the number of man-hours can be greatly reduced.

  Next, the operation of the power generation system 100 will be described. FIG. 4 is an operation follow chart of the power generation system according to the embodiment of the present invention.

  In step S <b> 10, the power generation system 100 starts the inverter 2. In this process, the power generation system 100 confirms that the inverter 2 is in a no-load operation state and activates the inverter 2. When this process is completed, the process proceeds to step S20.

  In step S <b> 20, the power generation system 100 executes the constant voltage operation of the inverter 2. In this process, since the inverter 2 is in the no-load operation state, the transformer 4 connected to the inverter 2 is in the no-load state. When the inverter 2 is operated so as to have a rated voltage, the input current of the transformer 4 is substantially equal to the excitation current of the transformer 4, and the excitation current of the transformer 4 is detected by the current detector 3 that detects the input current of the transformer 4. And the measured excitation current value of the transformer 4 is sent to the current waveform storage unit 110 switched by the changeover switch 107. The current waveform storage unit 110 stores the excitation current value of the transformer 4 and proceeds to step S30.

  In step S30, the power generation system 100 determines whether or not there is an interconnection operation command. In this process, the power generation system 100 determines whether there is a command to turn on the switch 105 that connects the inverter 2 to the power system 6. If it is determined that there is an interconnection operation command, the process proceeds to step S40. If it is not determined that there is an interconnection operation command, the process returns to step S20.

  In step S40, the power generation system 100 executes a synchronous control process. In step S50, the power generation system 100 determines whether or not the synchronous control is completed. When it is determined that the synchronization control is completed, the process proceeds to step S60. If it is not determined that the synchronization control has been completed, the process returns to step S40.

  In step S <b> 60, the power generation system 100 executes a process of closing and connecting the interconnection switch 105. When the switch 105 is connected, the AC power generated by the DC power source 1 and converted into AC power by the inverter 2 can be supplied to the power system 6 side with AC power controlled in synchronism with the power system 6 by the control described above. Become. When this process is completed, the process proceeds to step S70.

  In step S70, the power generation system 100 executes an output increase process. In this process, the current control unit 8 has the corrected inverter output current obtained by adding the excitation current waveform of the transformer 4 shown in FIG. 3B to the pre-correction inverter output current command shown in FIG. A command is input. The current control unit 8 compares the corrected inverter output current command with the inverter output current detected by the current detector 3, and controls the inverter 2 so that the inverter output current matches the corrected inverter output current command. The power generation system 100 increases the output of the DC power supply 1 and supplies more power to the power system 6 side. When this process is completed, this routine ends.

  In this way, in the starting process when the inverter 2 goes from the stop to the rated output operation, the inductive no-load operation state is used to measure the excitation current of the transformer 4, and the measurement waveform is stored. Thus, the excitation current waveform is used for the subsequent inverter control, and the output current of the transformer 4 can be a sine wave. For this reason, the output current of the transformer 4 can be made into a sine wave without using a new detector and a complicated arithmetic circuit, and without affecting the starting process.

  As described above, according to the present embodiment, when the switch 105 is opened and the inverter 2 is in a no-load operation, the exciting current value of the transformer 4 is stored based on the current value detected by the current detector 3, and the inverter 2 is turned on. During operation connected to the grid 6, based on the corrected inverter output current command value obtained by adding the excitation current value of the transformer 4 stored in the current waveform storage unit 110 to the inverter output current command value before correction from the output command unit 9. By controlling the output current of the inverter 2, the transformer 4 consumes the exciting current, and as a result, a sine wave current is output to the power system 6 side on the output side of the transformer 4. Moreover, since it is sufficient to provide a current detector or the like only on the input side of the transformer 4, the cost and size of the device can be reduced.

  In addition, the current waveform storage unit 110 stores only one period as a waveform among the current values detected by the current detector 3, and further performs a current for each unit calculation time which is a unit of the smallest time for controlling the inverter 2. A value is recorded and stored as a waveform for one period. As a result, the current waveform storage unit 110 does not always need to store, and a waveform for one period is recorded in a unit calculation time (for example, 1 ms), and other current values are erased. The capacity of 110 can be reduced.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the gist of the present invention described in the claims. It can be changed. For example, in the present embodiment, an excitation current waveform sent from the current waveform storage unit 110 is added to the pre-correction inverter output current command sent from the output command unit 9 to obtain a corrected inverter output current command that is sent to the current control unit 8. However, it is not particularly limited to this. For example, the excitation current waveform sent from the current waveform storage unit 110 is transmitted to the output command unit 9, and the inverter output current command before correction and the excitation current waveform are added in the output command unit 9 to become a corrected inverter output current command. It may be sent to part 8. Further, the excitation current waveform sent from the current waveform storage unit 110 is transmitted to the current control unit 8, and the inverter output current command before correction and the excitation current waveform are added in the current control unit 8 to become a corrected inverter output current command. A PWM control command in consideration of the current signal may be sent to the inverter 2.

  Moreover, in this embodiment, although the current waveform memory | storage part 110 has memorize | stored only the waveform of the electric current of the current detector 3 at the time of the constant voltage driving | operation of the inverter 2, it does not specifically limit to this. For example, the current waveform of the current detector 3 is stored at a predetermined time during the continuous operation, and the current waveform during the daily continuous operation is monitored, so that defects or malfunctions of the inverter 2 can be detected in advance. It becomes possible to discover.

It is the figure which showed the structure of the electric power generation system which concerns on embodiment of this invention. (A) is a figure for demonstrating operation | movement of the electric power generation system at the time of an inverter no load operation, (b) is a figure for demonstrating operation | movement of the electric power generation system at the time of an inverter connected to an electric power grid | system. It is the graph which showed the electric current waveform used with the electric power generation system which concerns on embodiment of this invention. It is an operation | movement follow chart of the electric power generation system which concerns on embodiment of this invention. It is the block diagram which showed the structure of the conventional electric power generation system. It is the block diagram which showed the structure of the other conventional electric power generation system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Power generation system 1 DC power supply 2 Inverter 3 Current detector 4 Transformer 6 Power system 8 Current control part 9 Output command part 105 Switch 107 Changeover switch 110 Current waveform memory | storage part

Claims (6)

An inverter that converts input power into AC power and outputs the power;
A transformer for transforming the output voltage of the inverter and outputting it to the power system;
A switch for opening and closing between the transformer and the power system;
An output command unit for determining a pre-correction output current command value of the inverter;
A current detector provided between the inverter and the transformer;
When the inverter is operated by opening the switch, a current storage unit that stores an excitation current value of the transformer based on a current value detected by the current detection unit;
After the operation in which the switch is closed and the inverter is connected to the electric power system, the transformer excitation current value stored in the current storage unit is added to the inverter output current command value before the correction from the output command unit. And a control unit that controls an output current of the inverter based on an inverter output current command value. The output destination of the current value detected by the current detection unit is the current storage unit when the switch is opened and the inverter is operated, and the control unit is closed when the switch is closed and the inverter is connected to the power system. The power generation system according to claim 1, further comprising a switching unit that selectively switches to the power generation unit. The switch is opened when the inverter is started to place the inverter in a no-load operation state,
The power generation system according to claim 2, wherein the switching unit outputs the current value detected by the current detection unit to the current storage unit every time the inverter is in a no-load operation. 4. The power generation according to claim 1, wherein the current storage unit stores at least one period of the excitation current value of the transformer for each control calculation period of the inverter. 5. system. In a control method of a power generation system having an inverter that converts input power into AC power and outputs the power, and a transformer that transforms an output voltage of the inverter and outputs the power to the power system.
When the inverter is operated by opening a switch that opens and closes between the transformer and the power system, the excitation current of the transformer is based on a current value detected by a current detection unit provided between the inverter and the transformer. A storage step of storing the value in the current storage unit;
During operation in which the inverter is connected to the power system, the excitation current of the transformer stored in the current storage unit in the inverter output current command value before correction from the output command unit that determines the output current command value before correction of the inverter And a control step for controlling the output current of the inverter based on the corrected inverter output current command value to which the value has been added. When starting the inverter, opening the switch to place the inverter in a no-load operation state; and
The method for controlling a power generation system according to claim 5, further comprising a step of outputting the current value detected by the current detection unit to the current storage unit every time the inverter is in a no-load operation state.

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