JP2007135256A - Interconnected inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a system power from being cut off and an interconnected inverter from charging it reversely and also to suppress the influence on the system power at the time of unnecessary detection, in a interconnected inverter which is utilized for solar light generating system. <P>SOLUTION: The interconnect inverter 1 is equipped with a received power metering means 3 for metering the power received from the system power 2, and a detected sensitivity improving means 5 for raising the detection sensitivity of single operation, by controlling it so that the power difference between generated power and a home load may be unbalanced, in case that the power difference between the generated power and the home load is under a specified quantity from the metered received power and that a means 4 for detecting the single operation of the interconnected inverter 1 judges that it might be in a single operation state. Accordingly, even if the generated power and the load power are balanced, it controls them into an unbalanced state thereby improving the detection sensitivity of single operation, thus the effect of making it a safer system can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an isolated operation detection method for a grid-connected inverter used for photovoltaic power generation using inverter technology.

  In recent years, fossil fuel depletion and global warming have occurred due to an increase in the load on ordinary households. Use of clean energy and energy-saving devices such as solar power generation systems, power-saving devices, and system voltage stabilization devices have been developed. It has been demanded.

  Conventionally, a grid interconnection inverter in this type of photovoltaic power generation system is known to output a disturbance signal to the system in an active manner and detect it by divergence of the disturbance signal (for example, Patent Document 1 or Patent Document). 2).

  Hereinafter, the detection of the isolated operation in Patent Document 1 will be described with reference to FIG.

  As shown in the figure, a power supply device 101 that outputs DC power, such as a solar cell, an inverter circuit 102 that converts DC power output from the power supply device 101 into AC power, and a load 103 that is linked to the inverter circuit 102. Based on the voltage at the connection point detected by the voltage detection means 105, the voltage detection means 105 for detecting the voltage at the connection point between the inverter circuit 102 and the commercial power system 104 , The commercial power system 104 is stopped, the single operation determination unit 106 that determines that the commercial power system 104 is in the single operation state, the active fluctuation creation unit 107 that varies the output current of the inverter circuit 102, and the commercial power system 104 stop. When the single operation determination unit 106 determines that it is in the single operation state, the inverter circuit 102 and the commercial power system 104 are disconnected. The grid interconnection protection device 108 includes a random fluctuation output unit 109 when the output current of the inverter circuit 102 varies, so that a random value can be selected from a certain range of numerical values. The active variation signal is output at a random value variation amount at predetermined time intervals. By giving a random value variation, it is possible to detect an isolated operation even when a power generation facility that employs an active method is connected to the same wiring.

  Next, detection of isolated operation in Patent Document 2 will be described with reference to FIG.

  FIG. 10 shows the configuration of the inverter device 115. The inverter device 115 converts the DC power input from the DC power supply 116 into AC power and supplies it to the load 117, a voltage detector 119 for detecting the load supply voltage Vo supplied to the load 117, Zero cross detection circuit 120 for generating output synchronization signal Vs based on load supply voltage Vo, current detector 121 for detecting output current Io of inverter main circuit 118, and A / D for A / D conversion of output current Io Converter 122, digital signal processor 123 for PWM control of inverter main circuit 118 based on output current Io and output synchronization signal Vs, and voltage abnormality for detecting voltage abnormality of load supply voltage Vo supplied to load 117 Based on the PWM data output from the detection circuit 124 and the digital signal processor 123, the gate pulse signal is transmitted. A timer counter circuit 125 to produce a Gp, and a gate drive circuit 126 for controlling switching of switching elements of the inverter main circuit 118 based on the gate pulse signal Gp.

In this inverter device 115, when the AC power system 127 becomes a single operation state due to a power failure or the like, when the active power from the inverter device 115, the reactive power, the active power of the load 117, and the reactive power are unbalanced, When an abnormality in the load supply voltage Vo or the frequency of the load supply voltage is detected and the single operation state is entered, the switching control of the inverter main circuit 118 is stopped, whereby the inverter main circuit 118 stops the inverter output. Next, when the inverter device 115 enters the single operation state in a state where the active power and reactive power supplied by the inverter device 115 substantially match the active power and reactive power requested by the load 117, the load supply voltage Vo And since the frequency hardly fluctuates, by adding distortion to the inverter output, regardless of the power factor of the load impedance, the frequency of the load supply voltage Vo in the single operation state is changed and the single operation state is reliably detected. is doing.
Japanese Patent No. 3402159 (FIG. 1) JP-A-9-342255 (FIG. 1)

  In such a conventional grid-connected inverter, isolated operation detection outputs a disturbance signal to the grid in an active manner, but when multiple grid-connected inverters are connected in parallel, the detection sensitivity due to mutual interference May be reduced, or unnecessary operations may occur due to mutual disturbance signals, or the sensitivity may be lowered to reduce unnecessary operations, and safety may be impaired. It is necessary to detect the isolated operation that is difficult to generate, and to stabilize the system power supply.

  In addition, when the islanding operation detection function operates unnecessary, the power output from the grid-connected inverter is gate-blocked, so there is a problem that sudden fluctuations in the load occur when viewed from the grid power supply. There is also a need for stability that does not cause the adverse effect of sudden changes in the load on the system power supply due to unnecessary operations.

  The present invention solves such a conventional problem, and does not reduce the detection sensitivity, and can detect an isolated operation at a higher speed, and can minimize the load fluctuation as seen from the system power supply side when an unnecessary operation occurs. The purpose is to provide a grid-connected inverter.

  In order to achieve the above object, the grid-connected inverter of the present invention has a power receiving measuring means for measuring the received current or received power from the system power supply, and the difference between the generated power and the household load from the measured received current or received power. Controls the difference between the generated power and the household load to be in an unbalanced state when the amount falls below the predetermined amount and it is determined that there is a possibility of a single operation state by the single operation detection means of the grid interconnection inverter. And it is set as the structure provided with the detection sensitivity improvement means which raises the detection sensitivity of an independent driving | operation.

  By this means, even when the system has a power generation output and is in a state balanced with the load power, the generated power and the load power are unbalanced to improve the detection sensitivity of the isolated operation, making it safer. System.

  Further, the detection sensitivity improving means is configured to suppress the generated power.

  By this means, improvement in detection sensitivity can be realized by a circuit for controlling the generated power that is normally used, that is, by a simpler and less expensive system.

  Further, the detection sensitivity improving means is configured to adjust the load power.

  By this means, it is possible to realize without suppressing the generated power, and it is possible to further increase the system efficiency and detect the power failure of the system reliably.

  The detection sensitivity improving means is configured to adjust the load power by controlling the voltage supplied to the load.

  By this means, the influence on the system and the load can be reduced during an unnecessary operation when the system power supply is healthy.

  Furthermore, the detection sensitivity improving means is configured to control so that the load power exceeds at least the generated power.

  By this means, it is possible to improve the detection sensitivity without excessively increasing the voltage on the load side, and it is possible to improve the detection sensitivity of the single operation without adversely affecting the load.

  The detection sensitivity improving means is configured to control so as to decrease the voltage supplied to the load.

  By this means, it is possible to improve the detection sensitivity without excessively increasing the voltage on the load side, and it is possible to improve the detection sensitivity of the single operation without adversely affecting the load.

  Further, the detection sensitivity improving means is configured to control so as to increase the voltage supplied to the load.

  By this means, it is possible to improve the detection sensitivity without excessively reducing the voltage on the load side, and it is possible to improve the detection sensitivity of the single operation without causing a load stop or the like.

  Further, the control of the supply voltage to the load is configured to be within a predetermined voltage range.

  By this means, the detection sensitivity of the isolated operation can be improved without stopping the load or applying an excessive voltage to the load.

  Further, the generated power is suppressed in a predetermined power range.

  By this means, the detection sensitivity of the isolated operation can be improved without causing a sudden change in the load viewed from the system side during an unnecessary isolated operation.

  In addition, the suppression of the generated power suppresses the output of the inverter unit of the grid interconnection inverter, and the DC- which controls the generated power according to the voltage rise of the capacitor arranged on the input side of the inverter unit due to the suppression of the inverter unit. The output power of the DC converter unit is suppressed.

  By this means, the output to the system power supply side can be quickly suppressed, and the detection sensitivity of the isolated operation can be improved and at the same time the detection can be performed at high speed.

  Further, the generated power is suppressed by suppressing the output power of the DC-DC converter unit of the grid-connected inverter and suppressing the output of the inverter unit according to the voltage drop of the capacitor arranged on the output side of the DC-DC converter unit. It is set as the structure which carries out.

  By this means, it is possible to improve the detection sensitivity of the single operation and at the same time improve the reliability and extend the life without excessively increasing the voltage of the capacitor.

  Further, the DC-DC converter unit and the inverter unit are configured so that the control voltage of the capacitor is different from each other.

  By this means, it is possible to eliminate the need for correcting variations in the control time constant of the DC-DC converter section and the control time constant of the inverter section for each device.

  According to the present invention, the power receiving measuring means for measuring the received current or the received power from the system power supply, the case where the power difference between the generated power and the household load is less than a predetermined amount from the measured received current or the received power, and the system Detection that increases the detection sensitivity of isolated operation by controlling the difference between the generated power and the household load to be in an unbalanced state when the isolated operation detection means of the interconnection inverter determines that there is a possibility of isolated operation Even if the system has a power generation output and is in a state of being balanced with the load power, it is possible to detect the isolated operation with the generated power and the load power in an unbalanced state. It is possible to provide a grid-connected inverter having an effect of improving sensitivity and making a safer system.

  In addition, the detection sensitivity improving means is configured to suppress the generated power, so that the detection sensitivity can be improved by a circuit for controlling the generated power that is normally used, that is, by a simpler and cheaper system. It is possible to provide a grid-connected inverter that has the effect of being able to.

  In addition, the detection sensitivity improvement means can be realized without suppressing the generated power by adjusting the load power, so that the system efficiency can be further improved and the power failure of the system can be detected reliably. It is possible to provide a grid-connected inverter that has the effect of being able to.

  In addition, the detection sensitivity improving means is configured to adjust the load power by controlling the voltage supplied to the load, thereby reducing the influence on the system and the load during an unnecessary operation when the system power supply is healthy. It is possible to provide a grid-connected inverter that has the effect of being able to.

  Furthermore, the detection sensitivity improvement means is configured to control the load power so that it at least exceeds the generated power, so that the detection sensitivity can be improved without excessively increasing the voltage on the load side, which adversely affects the load. Therefore, it is possible to provide a grid-connected inverter having an effect of improving the detection sensitivity of the single operation without exerting any influence.

  In addition, the detection sensitivity improvement means is configured to control so as to decrease the voltage supplied to the load, so that the detection sensitivity can be improved without excessively increasing the voltage on the load side, and the load is adversely affected. Therefore, it is possible to provide a grid-connected inverter having an effect of improving the detection sensitivity of the single operation without exerting any influence.

  Furthermore, the detection sensitivity improving means is configured to control so as to increase the voltage supplied to the load, so that the detection sensitivity can be improved without excessively reducing the voltage on the load side, and the load is stopped. Thus, it is possible to provide a grid-connected inverter that has an effect of improving the detection sensitivity of the single operation without causing the above.

  In addition, the control of the supply voltage to the load is configured to have a predetermined voltage range, so that the detection sensitivity of the single operation can be improved without stopping the load or applying an excessive voltage to the load. It is possible to provide a grid-connected inverter that is effective.

  Furthermore, by suppressing the generated power to a predetermined power range, it is possible to improve the detection sensitivity of isolated operation without abruptly changing the load seen from the system side during unnecessary isolated operation. It is possible to provide a grid-connected inverter that has the effect of being able to.

  In addition, the suppression of the generated power suppresses the output of the inverter unit of the grid interconnection inverter, and the DC- which controls the generated power according to the voltage rise of the capacitor arranged on the input side of the inverter unit due to the suppression of the inverter unit. By adopting a configuration that suppresses the output power of the DC converter unit, it is possible to quickly suppress the output to the system power supply side, and there is an effect that the detection sensitivity of the isolated operation can be improved and at the same time the detection can be performed at high speed. A grid interconnection inverter can be provided.

  Further, the generated power is suppressed by suppressing the output power of the DC-DC converter unit of the grid-connected inverter and suppressing the output of the inverter unit according to the voltage drop of the capacitor arranged on the output side of the DC-DC converter unit. This configuration improves the detection sensitivity of isolated operation, and at the same time improves the reliability and extends the life without excessively increasing the capacitor voltage. Can provide.

  In addition, the DC-DC converter unit and the inverter unit are configured so that the capacitor control voltage is different from each other, so that the control time constant of the DC-DC converter unit and the control time constant of the inverter unit vary from device to device. Therefore, it is possible to provide a grid-connected inverter that has the effect of eliminating the need for correction.

  According to the first aspect of the present invention, the power reception measuring means for measuring the received current or the received power from the system power supply, and the power difference between the generated power and the household load from the measured received current or the received power is less than a predetermined amount. In this case, when it is determined that there is a possibility of an isolated operation by the isolated operation detection means of the grid interconnection inverter, the power difference between the generated power and the household load is controlled to be in an unbalanced state. Even if the system has a power generation output and balances with the load power, the generated power and the load power are unbalanced. As a state, the detection sensitivity of the single operation is improved, and a safer system can be obtained.

  The detection sensitivity improvement means is configured to suppress the generated power, and the detection sensitivity improvement is realized by a circuit that controls the generated power that is normally used, that is, realized by a simpler and less expensive system. Has the effect of being able to

  Furthermore, the detection sensitivity improving means is configured to adjust the load power, and can be realized without suppressing the generated power, further improving the system efficiency and reliably detecting the power failure of the system. Has the effect of being able to

  Also, the detection sensitivity improvement means is configured to adjust the load power by controlling the voltage supplied to the load, and to reduce the influence on the system and load during unnecessary operation when the system power supply is healthy. Has the effect of being able to

  Further, the detection sensitivity improving means is configured to control the load power so that it at least exceeds the generated power, and can improve the detection sensitivity without excessively increasing the voltage on the load side. It has the effect that the detection sensitivity of the isolated operation can be improved without adverse effects.

  Further, the detection sensitivity improving means is configured to control so as to decrease the voltage supplied to the load, and the detection sensitivity can be improved without excessively increasing the voltage on the load side. It has the effect that the detection sensitivity of the isolated operation can be improved without adverse effects.

  Further, the detection sensitivity improving means is configured to control so as to increase the voltage supplied to the load, and the detection sensitivity can be improved without excessively reducing the voltage on the load side. It has the effect that the detection sensitivity of the isolated operation can be improved without causing a stop or the like.

  In addition, the control of the supply voltage to the load is configured to have a predetermined voltage range, and the detection sensitivity of the isolated operation can be improved without stopping the load or applying an excessive voltage to the load. Has the effect of being able to.

  Furthermore, the generated power is suppressed within a predetermined power range, and the detection sensitivity of isolated operation is improved without abruptly changing the load viewed from the system side during unnecessary isolated operation. It has the effect of being able to.

  In addition, the suppression of the generated power suppresses the output of the inverter unit of the grid interconnection inverter, and the DC- which controls the generated power according to the voltage rise of the capacitor arranged on the input side of the inverter unit due to the suppression of the inverter unit. It has a configuration that suppresses the output power of the DC converter, and can quickly suppress the output to the system power supply side, improving the detection sensitivity of isolated operation and simultaneously detecting at high speed. Have.

  Further, the generated power is suppressed by suppressing the output power of the DC-DC converter unit of the grid-connected inverter and suppressing the output of the inverter unit according to the voltage drop of the capacitor arranged on the output side of the DC-DC converter unit. This has the effect of improving the detection sensitivity of the single operation and at the same time improving the reliability and extending the life without excessively increasing the voltage of the capacitor.

  Also, the DC-DC converter unit and the inverter unit are configured so that the control voltage of the capacitor is different from each other, and the control time constant of the DC-DC converter unit and the control time constant of the inverter unit are set for each device. This has the effect that correction of variation can be made unnecessary.

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

(Embodiment 1)
FIG. 1 shows a configuration diagram of a grid-connected inverter in the first embodiment.

  As shown in the figure, the grid interconnection inverter 1 includes a current sensor 3a, a voltage sensor 3b, and an instantaneous value of the current sensor 3a and a voltage sensor 3b. The power calculation unit 3c that calculates power from the instantaneous value of the power, and the power difference between the generated power and the household load from the measured received power is a predetermined amount (for example, when the power generation means is a solar cell, the fluctuation of the maximum power tracking control is taken into account) When the power difference is less than 50 W), and when it is determined by the isolated operation detection means 4 of the grid-connected inverter 1 that there is a possibility of an isolated operation, the difference between the generated power and the household load is unbalanced. The detection sensitivity improving means 5 is provided to increase the detection sensitivity of the single operation. Here, by controlling the generated power and the home load to be in an unbalanced state, when there is no power supply from the system power source 2, that is, when the single operation state is occurring, Cannot be supplied, and the voltage of the output part of the grid interconnection inverter 1 is lowered. The isolated operation can be easily detected by the voltage drop of the output section. Moreover, as an example of the control for setting the unbalanced state, when the power generation means is a solar cell, the power of the 150 W household load is increased as the power difference considering the fluctuation of the maximum power tracking control.

  Next, a control flowchart of the detection sensitivity improving means 5 is shown in FIG.

  As shown in FIG. 2, the detection sensitivity improvement means 5 inputs the presence / absence of the possibility of an isolated operation state by the isolated operation detection means 4. When it is determined that there is a possibility of isolated operation, the output command of the inverter unit 1a of the grid interconnection inverter 1 is commanded to be lowered. The power command value for decreasing the output command at this time is set to a power lower than the load power. Since the voltage of the capacitor 1b increases by lowering the output command inside the grid interconnection inverter 1, the DC-DC converter 1c that controls the power generation unit (for example, a solar cell) When the voltage of the capacitor 1b exceeds a specified value Vc1 (for example, 350V), the maximum power follow-up control is canceled and the voltage of the capacitor 1b is switched to the constant voltage control so as to be Vc1. If the follow-up control is performed so as to be lower than the load power during the specified time t, and the power supply voltage of the system power supply 2 is not decreased or the frequency is not changed even after the specified time has elapsed, the unnecessary operation of the independent operation detecting means 4 The DC-DC converter 1c switches from the constant voltage control of the capacitor 1b to the maximum power tracking control. In this case, since the voltage of the capacitor 1b rises again, the inverter unit 1a switches from the tracking control below the load power to the constant voltage control of the capacitor 1b. The control of the inverter unit 1a is switched when the voltage of the capacitor 1b exceeds Vc2 (for example, 360V). The target voltage of the capacitor 1b controlled by the inverter unit 1a at this time is Vc3 (eg, 340V). Further, if the power supply voltage of the system power supply 2 drops below the specified value or changes in frequency exceeding the specified value during the specified time t, it is determined that the operation is independent, and the inverter unit 1a is gate-blocked. Then, the inverter output is stopped, the MC unit 1d is further turned off, and the system power supply 2 is disconnected.

  The isolated operation detection means 4 includes a frequency shift method for changing the frequency and a reactive power fluctuation method for changing the reactive power. However, since it is a known technique, detailed description thereof is omitted.

  As described above, according to the first embodiment, the received power from the grid power source 2 is measured, and the difference between the received power, the generated power, and the household load is less than a predetermined amount, and the grid-connected inverter When the single operation detection means 4 determines that there is a possibility of a single operation state, the voltage of the system power supply 2 is controlled during power failure by controlling the power difference between the generated power and the household load to be in an unbalanced state. It is possible to increase the fluctuation range of the power supply, or increase the fluctuation range of the frequency or the reactive power, and increase the detection sensitivity of the isolated operation.

(Embodiment 2)
FIG. 3 shows a configuration diagram of the grid interconnection inverter in the second embodiment.

  As shown in the figure, the grid interconnection inverter 1 includes a current sensor 3a and a voltage sensor 3b as power reception measuring means for measuring a power reception current and voltage from the system power supply 2, and an instantaneous value of the current sensor 3a and the voltage sensor 3b. The power calculation unit 3c that calculates power from the instantaneous value, and the power difference between the generated power and the household load from the measured received power is a predetermined amount (for example, when the power generation means is a solar cell, the power considering the fluctuation of the maximum power tracking control) When the difference is less than 50 W) and when it is determined by the isolated operation detecting means 4 of the grid-connected inverter 1 that there is a possibility of an isolated operation state, the power supply voltage of the system power supply 2 is reduced to reduce the household load. Detection sensitivity improving means 5b is provided for controlling the electric power to be lowered and increasing the detection sensitivity of the single operation.

  Next, FIG. 4 shows a control flowchart of the detection sensitivity improving means 5b.

  As shown in FIG. 4, the detection sensitivity improving means 5 b inputs the presence / absence of the possibility of the isolated operation state by the isolated operation detecting means 4. When it is determined that there is a possibility of isolated operation, the output command of the inverter unit 1a of the grid interconnection inverter 1 lowers the power supply voltage of the grid power supply 2, that is, injects reactive power and advances the phase. Command. The injection amount of reactive power at this time has an upper limit of the injection amount when the power factor is 0.85 or the power supply voltage of the system power supply 2 falls below a predetermined voltage range (for example, 95 V as the lower limit value). If the phase advance reactive power control is performed during the specified time t, and the power supply voltage of the system power supply 2 does not decrease by a specified amount or change in frequency even after the specified time has elapsed, the isolated operation detecting means 4 is regarded as an unnecessary operation. Determine and switch to power factor 1 control. Also, if the power supply voltage of the system power supply 2 drops below the specified value or changes in frequency exceeding the specified value during the specified time t, it is determined that the operation is independent, and the inverter unit 1a is gate-blocked. The inverter output is stopped, and the MC unit 1d is turned off to disconnect from the system power source 2.

  The isolated operation detection means 4 includes a frequency shift method for changing the frequency and a reactive power fluctuation method for changing the reactive power. However, since it is a known technique, detailed description thereof is omitted.

  As described above, according to the second embodiment, the power received from the grid power source 2 is measured, and the grid-connected inverter is used when the power difference between the received power, the generated power, and the household load falls below a predetermined amount. When the single operation detection means 4 determines that there is a possibility of the single operation state, the voltage fluctuation or frequency of the system power supply 2 is adjusted by adjusting the power of the household load by lowering the power factor by the phase advance reactive power control. Fluctuations are generated and the detection sensitivity of the isolated operation is improved.

(Embodiment 3)
FIG. 5 shows a configuration diagram of the grid interconnection inverter according to the third embodiment.

  As shown in the figure, the grid interconnection inverter 1 includes a current sensor 3a and a voltage sensor 3b as power reception measuring means for measuring a power reception current and voltage from the system power supply 2, and an instantaneous value of the current sensor 3a and the voltage sensor 3b. The power calculation unit 3c that calculates power from the instantaneous value, and the power difference between the generated power and the household load from the measured received power is a predetermined amount (for example, when the power generation means is a solar cell, the power considering the fluctuation of the maximum power tracking control) If the difference is less than 50 W) and if it is determined by the isolated operation detection means 4 of the grid-connected inverter 1 that there is a possibility of an isolated operation state, the power supply voltage of the system power supply 2 is increased to increase the household load. Detection sensitivity improving means 5b is provided for controlling the electric power to increase and increasing the detection sensitivity of the single operation.

  Next, a control flowchart of the detection sensitivity improving means 5c is shown in FIG.

  As shown in FIG. 6, the detection sensitivity improving unit 5 c inputs the presence / absence of the possibility of the single operation state by the single operation detection unit 4. When it is determined that there is a possibility of isolated operation, the output command of the inverter unit 1a of the grid-connected inverter 1 is a command to increase the power supply voltage of the system power supply 2, that is, inject reactive power and delay the phase. To do. The injection amount of reactive power at this time has an upper limit of the injection amount when the power factor 0.85 or the power supply voltage of the system power supply 2 exceeds a predetermined voltage range (for example, 107 V as an upper limit value). If the slow reactive power control is performed for the specified time t and the power supply voltage of the system power supply 2 does not decrease by a specified amount or change in frequency even after the specified time has elapsed, the isolated operation detecting means 4 is regarded as an unnecessary operation. Determine and switch to power factor 1 control. Also, if the power supply voltage of the system power supply 2 drops below the specified value or changes in frequency exceeding the specified value during the specified time t, it is determined that the operation is independent, and the inverter unit 1a is gate-blocked. The inverter output is stopped, and the MC unit 1d is turned off to disconnect from the system power source 2.

  The isolated operation detection means 4 includes a frequency shift method for changing the frequency and a reactive power fluctuation method for changing the reactive power. However, since it is a known technique, detailed description thereof is omitted.

  As described above, according to the second embodiment, the power received from the grid power source 2 is measured, and the grid-connected inverter is used when the power difference between the received power, the generated power, and the household load falls below a predetermined amount. When the single operation detection means 4 determines that there is a possibility of the single operation state, the voltage fluctuation or frequency of the system power supply 2 is adjusted by adjusting the power of the household load by reducing the power factor by the slow reactive power control. Fluctuations are generated and the detection sensitivity of the isolated operation is improved.

(Embodiment 4)
FIG. 7 shows a configuration diagram of the grid interconnection inverter in the third embodiment.

  As shown in the figure, the grid interconnection inverter 1 includes a current sensor 3a, a voltage sensor 3b, and an instantaneous value of the current sensor 3a and a voltage sensor 3b. The power calculation unit 3c that calculates power from the instantaneous value of the power, and the power difference between the generated power and the household load from the measured received power is a predetermined amount (for example, when the power generation means is a solar cell, the fluctuation of the maximum power tracking control is taken into account) When the power difference is less than 50 W), and when it is determined by the isolated operation detection means 4 of the grid-connected inverter 1 that there is a possibility of an isolated operation, the difference between the generated power and the household load is unbalanced. The detection sensitivity improving means 5 is provided to increase the detection sensitivity of the single operation. Here, by controlling the generated power and the home load to be in an unbalanced state, when there is no power supply from the system power source 2, that is, when the single operation state is occurring, Cannot be supplied, and the voltage of the output part of the grid interconnection inverter 1 is lowered. The isolated operation can be easily detected by the voltage drop of the output section. Moreover, as an example of an unbalanced state, when a power generation means is a solar cell, it shows that the electric power of 150W household load becomes large as an electric power difference which considered the fluctuation | variation of maximum electric power tracking control.

  Next, a control flowchart of the detection sensitivity improving means 5d is shown in FIG.

  As shown in FIG. 8, the detection sensitivity improving unit 5 d inputs the presence / absence of the possibility of the single operation state by the single operation detection unit 4. When it is determined that there is a possibility of isolated operation, the output command of the DC-DC converter 1c of the grid interconnection inverter 1 is commanded to be lowered. The power command value for decreasing the output command at this time is set in a range in which the capacitor 1b does not fall below a specified voltage Vc4 (for example, 330V). In the grid-connected inverter 1, the voltage of the capacitor 1b is reduced by lowering the output command of the DC-DC converter 1c, and the inverter 1a has a voltage of the capacitor 1b equal to a specified voltage Vc5 (eg, 340V). Since the constant voltage control is performed as described above, the output power to the system power supply 2 is reduced. If the follow-up control is performed so as to be lower than the load power during the specified time t, and the power supply voltage of the system power supply 2 is not decreased or the frequency is not changed even after the specified time has elapsed, the unnecessary operation of the independent operation detecting means 4 The DC-DC converter 1c switches from the constant voltage control of the capacitor 1b to the maximum power tracking control. In this case, since the voltage of the capacitor 1b rises, the inverter unit 1a performs constant voltage control so that the voltage of the capacitor 1b becomes the specified voltage Vc5. Therefore, the output power to the system power supply 2 is It increases and returns to the normal state. If the power supply voltage of the system power supply 2 drops below the specified value or changes in frequency exceeding the specified value during the specified time t, it is determined that the system is operating independently, and the inverter unit 1a gate-blocks the inverter. The output is stopped, the MC unit 1d is further turned off, and the system power supply 2 is disconnected.

  The isolated operation detection means 4 includes a frequency shift method for changing the frequency and a reactive power fluctuation method for changing the reactive power. However, since it is a known technique, detailed description thereof is omitted.

  As described above, according to the third embodiment, the received power from the grid power source 2 is measured, and the difference between the received power, the generated power, and the household load is less than a predetermined amount, and the grid-connected inverter When the single operation detection means 4 determines that there is a possibility of a single operation state, the voltage of the system power supply 2 is controlled during power failure by controlling the power difference between the generated power and the household load to be in an unbalanced state. It is possible to increase the fluctuation range of the power supply, or increase the fluctuation range of the frequency or the reactive power, and increase the detection sensitivity of the isolated operation.

  Since the detection method of the independent operation of the grid-connected inverter that outputs the power generated using the solar battery or the fuel cell to the grid power supply and the adverse effect on the grid power supply can be suppressed, the grid-connected inverter is especially connected to the grid power supply. In addition to preventing mutual interference when connected in parallel, the present invention can also be applied to a centralized interconnection application that requires high-speed detection.

Configuration diagram of the grid interconnection inverter of Embodiment 1 of the present invention Control flow chart of the detection sensitivity improving means 5 Configuration diagram of system interconnection inverter according to embodiment 2 of the present invention Control flow chart of the detection sensitivity improving means 5b The block diagram of the grid connection inverter of Embodiment 3 of this invention Control flow chart of the detection sensitivity improving means 5c The block diagram of the grid connection inverter of Embodiment 4 of this invention Control flow chart of the detection sensitivity improving means 5d The block diagram of the grid connection inverter in the conventional patent document 1 The block diagram of the inverter apparatus in the conventional patent document 2

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 System connection inverter 1a Inverter part 1b Capacitor 1c DC-DC converter 1d MC part 2 System power supply 3 Power receiving measurement means 3a Current sensor 3b Voltage sensor 3c Power calculation part 4 Independent operation detection means 5 Detection sensitivity improvement means 5b Detection sensitivity improvement means 5c Detection sensitivity improvement means 5d Detection sensitivity improvement means

Claims (12)

A grid-connected inverter that outputs the generated power from the power generation means to the system power supply, the power receiving measurement means for measuring the received current or the received power from the system power supply, the generated power and the household load from the measured received current or the received power The power difference between the generated power and the household load is set to an unbalanced state when the power difference is less than a predetermined amount and when it is determined that there is a possibility of a single operation state by the single operation detection means of the grid interconnection inverter. The grid interconnection inverter provided with the detection sensitivity improvement means which controls so that it may become and raises the detection sensitivity of a single operation. The grid-connected inverter according to claim 1, wherein the detection sensitivity improving means suppresses generated power. The grid-connected inverter according to claim 1, wherein the detection sensitivity improving means adjusts load power. 4. The grid interconnection inverter according to claim 3, wherein the detection sensitivity improving means adjusts the load power by controlling a voltage supplied to the load. 4. The grid interconnection inverter according to claim 3, wherein the detection sensitivity improving means controls the load power to at least exceed the generated power. 5. The grid interconnection inverter according to claim 4, wherein the detection sensitivity improving means controls the voltage supplied to the load to be lowered. 5. The grid interconnection inverter according to claim 4, wherein the detection sensitivity improving means controls so as to increase a voltage supplied to the load. 5. The grid-connected inverter according to claim 4, wherein the supply voltage to the load is controlled within a predetermined voltage range. The grid-connected inverter according to claim 2, wherein the generated power is suppressed within a predetermined power range. Suppression of generated power is a DC-DC converter that suppresses the output of the inverter unit of the grid-connected inverter and controls the generated power according to the voltage rise of the capacitor arranged on the input side of the inverter unit due to the suppression of the inverter unit The grid-connected inverter according to claim 2, wherein output power of the unit is suppressed. Suppression of generated power suppresses the output power of the DC-DC converter unit of the grid-connected inverter, and suppresses the output of the inverter unit according to the voltage drop of the capacitor arranged on the output side of the DC-DC converter unit. The grid interconnection inverter according to claim 2. The grid-connected inverter according to claim 10 or 11, wherein the DC-DC converter unit and the inverter unit have different capacitor control voltages.

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