JP2015015789A - Power conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conditioner capable of determining whether a rise in a charging voltage of an input capacitor is caused by failures or electric power system disturbance, and of controlling so as to disconnect itself from the electric power system and protect the power conditioner itself in the former case and so as not to disconnect the power conditioner itself in the latter case.SOLUTION: A power conditioner comprises: phase control means controlling a control signal of an inverter so that an output voltage phase of the inverter follows voltage phase change of an AC electric power system; gate block means, when detecting that an input capacitor voltage of the inverter is a certain voltage or more, performing gate block for blocking the input of the control signal to a control terminal of the inverter, and then, cancelling the gate block after a lapse of a first time period; and protection means disconnecting a power conditioner main unit from the electric power system when the input capacitor voltage is not reduced less than the certain voltage within a second time period during the gate block.

Description

  The present invention relates to a power conditioner provided in a distributed power supply facility such as a solar power generation system linked to an electric power system, and more particularly to a power conditioner that automatically disconnects from the system when an abnormality occurs.

  In recent years, distributed power sources such as photovoltaic power generation systems have been interconnected in a wide area and in large quantities with the power system. When power is supplied to the power system (reverse power flow), A power conditioner is provided for ensuring a certain level of power quality so as not to adversely affect consumers.

  The power conditioner has a DC-AC conversion function, which stabilizes the output voltage and frequency, and in the event of a system disturbance, the system is not disconnected from the system immediately, but is continuously operated under certain conditions. Is required. This is because if a large number of distributed power supplies are disconnected at the same time when the system is disturbed, a significant disturbance will be given to the system. Such an operation continuation request for a distributed power source such as a solar power generation system is provided as a guideline by the Agency for Natural Resources and Energy (Non-Patent Document 1).

  The above operation continuation request is specifically defined as an operation continuation performance requirement (FRT: Fault Ride Through). For example, in the FRT requirement of a photovoltaic power generation system, the system voltage is rated in the case of a single-phase fault in the system. The operation of the power conditioner is continued until the state reduced to 20% continues for 1 second, and a voltage drop tolerance is required to prevent disconnection. Further, in the case of a three-phase accident, a voltage drop tolerance is required so that the operation of the power conditioner is continued until the state where the system voltage is reduced to the rated value of 20% continues for 0.3 seconds so as not to be disconnected. In the case of other two-phase short-circuits, conditions for voltage drop and phase change that allow disconnection are defined.

“Guidelines for grid interconnection technical requirements for ensuring power quality” (May 2013) “URL: http://www.enecho.meti.go.jp/denkihp/genjo/rule/keito_index.html”

  In the above guidelines, the power conditioner can be disconnected depending on the degree of disturbance when the phase is greatly changed due to disturbance in the system more than required to continue the operation of the power conditioner. Originally, since there is a phase adjustment function, it can be considered that it is not necessary to reach a disconnection if the adjustment time can be secured.

  On the other hand, in the case of an abnormality in the distributed power supply equipment including the power conditioner, it is necessary to disconnect this from the system in order to protect the power conditioner. As an abnormality detection method, the capacitor voltage on the input side from the solar cell panel to the inverter in the power conditioner is detected, and if the capacitor charging voltage rises above a certain voltage, it may be determined that the device is abnormal. It is done. This is because, in a power conditioner, an increase in input voltage is an event that requires the greatest care for protection. When the power conditioner is operating normally, when the phase of the grid is shifted by more than 90 ° due to disturbance, the inverter in the power conditioner is in a forward power flow state where power is supplied from the grid. It acts to charge the capacitor on the input side. Then, the capacitor is charged by both the solar battery panel and the inverter, and a phenomenon that the capacitor voltage increases occurs. In this case, although the device is not abnormal, it is determined that the device is abnormal due to the rise of the capacitor voltage as described above, and the power conditioner is disconnected. In this way, although it is only necessary to control the phase of the power conditioner and the system to coincide with each other, the power conditioner does not operate until the power conditioner is manually restored, and power generation cannot be performed during that time. Since power cannot be sold, resources are wasted.

It is an object of the present invention to determine whether an increase in the charging voltage of the input capacitor is due to a failure or a system disturbance. In the former case, the power conditioner is protected by disconnecting, and not in the latter case. An object of the present invention is to provide a power conditioner to be controlled.

  The present invention is provided in a distributed power supply facility such as a solar power generation system.

  The power conditioner of the present invention includes an inverter that orthogonally transforms DC input power obtained from a photovoltaic power generation system or the like and outputs it to an AC power system, an input capacitor connected in parallel to the input side of the inverter, and an output of the inverter A grid connection relay switch connected in series on the side, and a control circuit for controlling the inverter.

  The input capacitor stabilizes the input voltage of the inverter, and a chopper is provided in the preceding stage to maintain the intermediate voltage of the input capacitor constant.

Capacitor voltage detection means for detecting the voltage of the input capacitor;
Phase control means for controlling the control signal of the inverter so that the output voltage phase of the inverter follows the voltage phase change of the AC power system;
When detecting that the capacitor voltage detected by the capacitor voltage detection means is equal to or higher than a certain voltage, gate block means for performing a gate block for blocking control signal input to the control terminal of the inverter;
When the voltage of the input capacitor does not drop below the constant voltage after a lapse of a first time from the start of the gate block, a disconnection process for disconnecting the power conditioner body from the AC power system; and Release processing for releasing the gate block when the voltage of the input capacitor drops below the certain voltage after the lapse of one time and the reduction continues until the second time passes from the start of the gate block And a protection means for performing

  In the power conditioner of the present invention, the cause of the voltage increase of the input capacitor is that the disturbance of the AC power system (hereinafter referred to as the system) is significantly larger than expected in the FRT requirement, and the phase shift is more than 90 °. If the cause is large, the system is not disconnected from the system, and if the cause of the voltage increase of the input capacitor is due to a failure, the system is disconnected from the system.

  (1) When the input capacitor voltage rises due to system disturbance.

  Due to the disturbance of the system, a forward flow in which current flows into the inverter from the system side occurs, and the capacitor voltage rises above a certain voltage. Then, the gate block is performed to stop the inverter output, and at the same time, the first time is awaited. At this time, since the phase control means continues to operate, the output voltage phase of the inverter follows the voltage phase change of the AC power system immediately after the gate block starts.

  During the gate block, the stored power of the input capacitor is consumed in the circuit, so that the voltage gradually decreases. If the voltage of the input capacitor drops below the certain voltage after the first time elapses and the reduction continues until the second time elapses from the start of the gate block, the cause of the rise in the capacitor voltage is It is determined that there is no device abnormality, the gate block is released after the elapse of the second time from the start of the gate block, and the inverter is restarted.

  In this way, even if a large disturbance in the system beyond what is assumed in the FRT requirement occurs, the output of the second time inverter is interrupted, and the power conditioner body is disconnected from the system without disconnecting from the system. Conditioner operation continues.

  (2) When the condition of the voltage rise of the input capacitor is a power conditioner failure.

  For example, if a control circuit (such as a boost chopper) for input power from a solar cell system or the like fails, or if some circuit failure occurs and the time during which charging is dominant over discharging from the capacitor continues, the capacitor voltage becomes a constant voltage. It rises above. Then, as in the case of the disturbance of the system, the gate is blocked only for the second time.

  However, if the input capacitor voltage exceeds a certain voltage even after the first time has elapsed since the start of the gate block, it is determined that the device is abnormal, and the protection circuit turns off the grid connection relay switch. Disconnect the conditioner body from the grid.

  In this invention, when the cause of the voltage increase of the input capacitor is a disturbance of the system, the system is not disconnected from the system, and when the cause of the voltage increase of the input capacitor is due to a failure, the system is disconnected from the system. Even if a disturbance due to a phase short-circuit accident occurs, a large number of distributed power sources can be prevented from being disconnected at the same time when the system is disturbed. On the other hand, if the device is abnormal, it is surely disconnected from the system.

The schematic block diagram of the solar energy power generation system which is embodiment of this invention is shown. A waveform diagram during reverse power flow is shown. A waveform diagram during forward flow is shown. The flowchart which shows control operation is shown. The waveform diagram when the capacitor voltage Vpn (intermediate voltage) rises due to a failure is shown. The waveform diagram when the capacitor voltage Vpn (intermediate voltage) rises due to system disturbance is shown.

  FIG. 1 is a schematic configuration diagram of a photovoltaic power generation system according to an embodiment of the present invention.

  The solar cell system 1 is connected to a boost chopper 2, and the boost chopper 2 is connected to a power conditioner body 3. The boost chopper 2 and the power conditioner main body 3 constitute a power conditioner. The solar cell output V1 is charged to a predetermined intermediate voltage V2 by the boost chopper 2. The power conditioner body 3 is connected to an AC power system (hereinafter, system) 4.

  The power conditioner body 3 is connected in series to a single-phase DC / AC inverter (hereinafter referred to as an inverter) 30, an input capacitor (hereinafter referred to as a capacitor) 31 connected in parallel to the input side of the inverter 30, and the output side of the inverter 30. A grid connection relay switch (hereinafter referred to as a relay switch) 32 and a control circuit 33 for controlling the inverter 30 are provided. The rated (charging) voltage of the capacitor 31 is 310 V in this embodiment.

  The control circuit 33 includes a capacitor voltage detector 330 that detects the voltage (hereinafter referred to as capacitor voltage) Vpn of the capacitor 31, a system voltage detector 331 that detects the u-w phase system voltage Vuw, and the inverter output current Iinv. And a current detection circuit 332 for detecting the magnitude.

  The control circuit 33 further includes a phase control circuit 333 that controls the control signal of the inverter 30 so that the output current phase of the inverter 30 follows the voltage phase change of the system 4. This operation of the phase control circuit 333 is referred to as a phase synchronization operation. The phase control circuit 333 includes a phase comparison unit 333a and a voltage control oscillation unit 333b, and outputs a frequency signal S1 that matches the phase of the system voltage Vuw. The frequency of the frequency signal S1 decreases when the phase of the system voltage Vuw is delayed, and increases when the phase of the system voltage Vuw advances.

  A voltage difference between the capacitor voltage Vpn detected by the capacitor voltage detector 330 and the rated voltage 310V of the capacitor 31 is detected by the voltage comparator 334, and an amplitude signal S2 is obtained. The amplitude signal S2 increases in amplitude when the capacitor voltage Vpn is equal to or higher than the rated voltage 310V, and decreases in amplitude when the capacitor voltage Vpn is equal to or lower than the rated voltage 310V.

  The multiplier 335 multiplies the frequency signal S1 and the amplitude signal S2 to generate a frequency / amplitude signal S3. The frequency / amplitude signal S3 corresponds to the phase and magnitude of the current to be output from the inverter 30.

  The subtractor 336 detects a difference between the frequency / amplitude signal S3 and the inverter output current Iinv, and generates a signal S4. This signal S4 corresponds to the error between the current to be output by the inverter 30 and the actual current.

  The signal S4 is input to a control signal generation unit 337 for supplying a PWM signal to the inverter 30. The control signal S5 generated by the control signal generation unit 337 is input to the gate 338, and the signal from the gate 338 is input to the control terminal of the inverter 30.

  With the above configuration, the control signal S5 composed of the PWM signal is input to the control terminal of the switching element of the inverter. The pulse width of the control signal S5 is the same as the phase of the inverter output current Iinv and the phase of the system voltage Vuw. Further, the magnitude of the output current obtained by the calculation by the subtractor 336 is determined to be the inverter output current Iinv so that the voltage Vpn becomes the rated voltage 310V.

  The protection circuit 339 includes a gate block circuit 339a and a disconnection control circuit 339b.

  The disconnection control circuit 339b includes a first timer of 3 seconds (first time) and a second timer of 5 seconds (second time) (not shown), and 3 seconds (first time) at the same time as the gate block starts. 1), the capacitor voltage Vpn is determined to have dropped below a constant voltage of 425V, and the reduction continues until 5 seconds (second time) has elapsed since the start of the gate block. Is determined to be normal, the gate block is released, and the inverter is restarted. If the capacitor voltage Vpn does not drop below the constant voltage 425 V after 3 seconds (first time), it is determined that the device is abnormal, the control signal RY of the relay switch 32 is set to L, and the RY is always on (RY is H) The relay switch 32 is turned off. By turning off the relay switch 32, the inverter 30 is stopped and the power conditioner body 3 is disconnected from the system 4. When the capacitor voltage Vpn drops below the constant voltage 425 V after 3 seconds (first time), the control signal RY is maintained at H, so that the power conditioner body 3 can be prevented from being disconnected from the system. . Note that two times can be measured with one timer. In this example, the relay switch 32 is used to disconnect the power conditioner main body 3 and the system 4, but other switches such as a magnet contactor may be used.

  In this example, the first time is set to 3 seconds, but this may be any time as long as the phase is matched by the phase control circuit 333 and the capacitor voltage drops below a certain voltage. In addition, the second time is set to 5 seconds, but this may be any time that can reliably complete the determination of the capacitor voltage, and may be the same as the first time, but the determination time of the capacitor voltage, that is, the first time This is slightly better than the time.

  Here, since the boost chopper maintains the capacitor voltage at a constant intermediate voltage (310 V in this example), the boost chopper is stopped when the protection circuit operates and the capacitor voltage is 425 V or more.

  Next, the operation will be described.

(1) When the device is not broken Normally, the inverter 30 supplies power to the grid 4, but in a normal state, the inverter output current Iinv is in phase with the grid voltage Vuw (reverse power flow). . In reverse power flow, output power is output to the 100% grid side. FIG. 2 shows the state of reverse power flow. When the phase of the system voltage Vuw changes due to a slight disturbance in the system in the reverse power flow state, the phase of the inverter output current Iinv becomes in phase with the phase of the system voltage Vuw by the phase synchronization operation by the phase control circuit 333. Thus, inverter control is performed. Even if the capacitor voltage Vpn moves up and down or the inverter output current Iinv moves up and down, the pulse width of the control signal S5 of the inverter 30 is adjusted by the operation of the feedback system of the control circuit 33, and the output power is always output. Is controlled to a reverse power flow state that is output to the 100% system side.

  On the other hand, when the phase of the system voltage Vuw changes greatly and the phase lag (advance) is greater than 90 °, such as when the system disturbance is large, power flows from the system to the inverter side (in order). Tidal current). The forward flow is not preferable because electric power flows from the system to the inverter side. FIG. 3 shows a forward power flow state in which the phase of the inverter output current Iinv is 180 degrees different from the system voltage Vuw.

(2) When the device has failed When the capacitor voltage Vpn increases due to a failure, it is necessary to disconnect the inverter from the system 4 and repair it.

  Therefore, when the capacitor voltage Vpn increases due to a failure, the relay switch 32 is turned off by the disconnection control circuit 339b in the protection circuit 339 and the inverter 30 is disconnected from the system 4.

(3) Failure determination and protection circuit operation The cause of the increase in the capacitor voltage Vpn may be a failure or a large-scale disturbance of the system and a phase change of the system voltage Vuw larger than 90 °.

  In order to make these determinations, the following operation is performed.

  First, the gate block circuit 339a of the protection circuit 339 sets the gate block signal S6 to L and blocks the gate when the capacitor voltage Vpn becomes equal to or higher than the constant voltage 425V. Thereby, the operation of the inverter 30 is stopped. However, although the inverter operation is stopped, the operation of the feedback system including the phase control circuit 333 in the control circuit 33 is continued. The gate block lasts 5 seconds (second time).

  Then, after 3 seconds (first time) from the start of the gate block, it is monitored whether or not the capacitor voltage Vpn has dropped below a constant voltage of 425V. If the capacitor voltage Vpn decreases to a constant voltage of less than 425 V after 3 seconds and the decrease continues until 5 seconds (second time) has elapsed from the start of the gate block, the increase in the capacitor voltage Vpn is not due to a device failure. Judge that there is no. If the capacitor voltage Vpn does not drop below the constant voltage 425 V after 3 seconds, it is determined that the increase in the capacitor voltage Vpn is based on a failure of the device.

  That is, if the device is not malfunctioning, the capacitor voltage Vpn is consumed in the circuit and gradually decreases. Therefore, when the capacitor voltage Vpn drops below a constant voltage of 425 V after 3 seconds, and the drop continues until 5 seconds (second time) has elapsed from the start of the gate block, the rise in the capacitor voltage Vpn is a malfunction of the device. It is determined that it is not based on. On the other hand, for example, when the boost chopper 2 fails, the charging current to the capacitor increases more than the capacitor voltage Vpn is consumed in the circuit, and when the inverter 30 fails, the capacitor voltage is considered to be maintained at a high value. It is done. Therefore, when the capacitor voltage Vpn does not drop below the constant voltage 425V within 3 seconds, it is determined that the increase in the capacitor voltage Vpn is based on a failure of the device.

  If the capacitor voltage Vpn does not drop below the constant voltage 425 after 3 seconds from the start of the gate block, it is determined that the device has failed, the control signal RY of the relay switch 32 is set to L, and the RY is always on (RY is H) The relay switch 32 is turned off. On the other hand, if the device has not failed, the state of the relay does not change. That is, the control signal RY remains H.

  In this way, it is determined that the capacitor voltage Vpn has decreased 3 seconds after the start of the gate block and the device is normal, and further, the decrease in the capacitor voltage Vpn continues until 5 seconds have elapsed from the start of the gate block. It is determined with certainty that the device is normal. At this time, the gate block signal S6 is switched to H to release the gate block, and the output of the inverter 30 is restarted. Therefore, if the device is not broken down, the inverter output is interrupted for a short time, and the reverse power flow from the power conditioner body 3 to the system side, that is, the power sale can be resumed. Therefore, even if the voltage of the capacitor 31 becomes the same as that of the device abnormality due to a factor that is not the device abnormality of the power conditioner main body 3, the power conditioner main body 3 is not disconnected from the system. Power generation can be continued without wasting resources. Moreover, in the case of an apparatus abnormality actually, the power conditioner main body 3 can be reliably disconnected from the system, and the apparatus can be protected. Thus, when the second time is longer than the first time and it is determined that the device is abnormal, the power conditioner body 3 is immediately disconnected from the system to prevent the device from being damaged, and the device is normal. If it is determined, the determination is made reliably, and the gate block is released after the inverter 30 is restarted sufficiently, and the reverse power flow from the power conditioner body 30 to the system is resumed. ing.

  FIG. 4 is a flowchart showing the operation of the control circuit 33.

  In step S1, if the inverter 30 is connected to the system 4 and is in linked operation, it is determined in S2 whether the capacitor voltage Vpn (intermediate voltage) is 425 V or more. If it is 425 V or more, the gate block is started in S3. To do. The gate block is continued for 5 seconds in S5 and S6.

  At the same time as starting the gate block in S3, it is monitored whether 3 seconds have passed in S4. If yes, it is determined in S5 whether the capacitor voltage is 425 V or more. If yes, the power conditioner body 3 is checked in S7. Disconnect from system 4.

  In S5, it is determined whether the capacitor voltage is 425 V or more. If NO, it is monitored in S6 whether 5 seconds have elapsed since the start of the gate block. After the elapse of 5 seconds, when the gate block is released in S8, the inverter 30 is in the reverse power flow mode in phase with the system, so that the normal operation is restored. If the capacitor voltage becomes 425 V or higher in the loop of S5 to S6, the disconnection process is performed in S7.

  Thus, when the capacitor voltage Vpn rises to 425 V or more during the operation of the inverter 30, the capacitor block Vpn is monitored by waiting for 3 seconds at the same time as starting the gate block and monitoring the capacitor voltage Vpn after 3 seconds. It is possible to determine whether the cause of the increase is due to a failure or a large disturbance in the system. In the former case, the relay switch 32 is turned off and the inverter 30 is disconnected. In the latter case, the capacitor voltage Vpn is further monitored for 2 seconds to confirm that there is no increase in the voltage. Continue system operation.

  FIG. 5 shows a waveform diagram when the capacitor voltage Vpn (intermediate voltage) rises due to a failure. In the figure, 1) to 4) indicate the contents and order of actions or behaviors. That is, 1) When the capacitor voltage Vpn (intermediate voltage) rises, 2) The gate block is suspected of system disturbance, but 3) The capacitor voltage Vpn (intermediate voltage) is high after 3 seconds. It is judged and it cancels.

  FIG. 6 shows a waveform diagram when the capacitor voltage Vpn (intermediate voltage) rises due to system disturbance. That is, 1) When a phase jump exceeding ± 90 degrees occurs due to system disturbance, 2) the output current is absorbed (forward power flow), 3) the capacitor voltage Vpn (intermediate voltage) rises, and 4) the gate block. 5) The output current is turned off by the gate block, 6) the increase of the capacitor voltage Vpn (intermediate voltage) is stopped, and 7) it gradually decreases thereafter. 8) The gate block is released after 5 seconds from the start of the gate block. At this time, since the phase of the output current is in phase with the system voltage, 9) the output current becomes a reverse flow and returns to the original state.

  Here, due to an abnormality of the inverter 30 or the like, there may be a device abnormality in which the capacitor voltage decreases when the output of the inverter 30 is stopped. In that case, the capacitor voltage may drop to less than 425V 3 seconds after the start of the gate block, as in the case of the disturbance of 90 ° or more of the system. In this case, if the inverter is restarted after 5 seconds from the start of the gate block, the capacitor voltage will rise to 425 V or more again. Therefore, when the capacitor voltage abnormality in S2 and the cycle of restarting the inverter 30 in S8 (S2 → S8) are repeated a predetermined number of times, for example, three times, within a predetermined time, for example, within one minute, the power conditioner body 3 Can be controlled to be disconnected from the grid.

1-solar cell system 2-boost chopper 3-power conditioner body 4-power system 30-inverter 33-control circuit 333-phase control circuit 339c-protection circuit

Claims (4)

An inverter that orthogonally transforms DC input power and outputs it to an AC power system, an input capacitor connected in parallel to the input side of the inverter, a grid connection relay switch connected in series to the output side of the inverter, In a power conditioner including a control circuit for controlling an inverter,
The control circuit includes:
Capacitor voltage detection means for detecting the voltage of the input capacitor;
Phase control means for controlling the control signal of the inverter so that the output voltage phase of the inverter follows the voltage phase change of the AC power system;
When detecting that the capacitor voltage detected by the capacitor voltage detection means is equal to or higher than a certain voltage, gate block means for performing a gate block for blocking control signal input to the control terminal of the inverter;
When the voltage of the input capacitor does not drop below the constant voltage after the first time has elapsed from the start of the gate block, the disconnection processing for disconnecting the power conditioner body from the AC power system, and from the start of the gate block Release that releases the gate block when the voltage of the input capacitor drops below the constant voltage after the first time elapses and the reduction continues until the second time elapses from the start of the gate block. Safeguards for processing,
Power conditioner characterized by having The power conditioner according to claim 1, wherein the second time is longer than the first time. 3. The power conditioner according to claim 1, wherein the first time is a time in which the output voltage phase of the inverter can follow the voltage phase change of the AC power system in the phase control unit. The protective means is
When the release process is repeated a predetermined number of times within a predetermined time,
The power conditioner according to claim 1 or 2, wherein the power conditioner body is disconnected from the AC power system.

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