JP2008182836A5 - - Google Patents

Description

Grid-connected inverter system and power control method for grid-connected inverter system

  In the present invention, a plurality of system inverters are connected in parallel between a DC power source and a power system, and one system inverter is used as a master machine, and the remaining system inverters are used as slave machines. The present invention relates to a grid-connected inverter system that is connected so that data communication can be performed between them, and a power control method for the grid-connected inverter system.

  Conventionally, as shown in, for example, JP-A-5-53042 and JP-A-2000-305634, a plurality of system inverters are connected in parallel between a DC power source such as a solar battery and a power system, There is known a grid-connected inverter system that controls the output power to the power system by controlling the output power of each system inverter in accordance with the fluctuation of the output power of the solar cell due to the fluctuation of the amount.

  In the system inverter provided between the solar cell and the power system, the output power-output voltage characteristic of the solar cell varies depending on the amount of solar radiation, and particularly the output voltage with respect to the maximum power (this output voltage is referred to as “optimum operating voltage”). Therefore, it has a maximum power tracking control function for automatically adjusting the output voltage of the solar cell to the optimum operating voltage. As a method of configuring a grid-connected inverter system by connecting a plurality of such system inverters in parallel, in order to properly control the power output from the entire system to the power system, an arbitrary one is mastered. It is known that the remaining system inverter is a slave machine, the master machine controls the output power by maximum power tracking control, and the slave machine controls the output power based on the power command value from the master machine. .

  FIG. 9 is a block diagram showing an example of a conventional grid-connected inverter system, and FIG. 10 is a diagram showing the contents of data communication between a master machine and a slave machine.

  A grid-connected inverter system 100 shown in FIG. 9 has three inverters 103, 104, and 105 having the same configuration connected in parallel between a solar cell 101 and a power system 102. Of the three inverters 103, 104, 105, any one (inverter 103 in FIG. 9) is set as the master unit of the grid-connected inverter system 100, and the remaining (inverters 104, 105 in FIG. 9) is grid-connected. Is set as a slave machine of the inverter system 100.

  The inverter 103 of the master machine (hereinafter referred to as “master inverter 103”) includes a DC-AC conversion circuit 103b that converts DC power input from the solar battery 101 into AC power, and the DC-AC conversion circuit 103b. A control unit 103a that controls the power conversion operation is provided. The master inverter 103 has a maximum power tracking control function. Therefore, the control unit 103a of the master inverter 103 uses the direct current I detected by the current sensor Sc provided on the input side of the DC-AC conversion circuit 103b and the direct current voltage V detected by the voltage sensor Sv. Follow-up control is performed.

  The master inverter 103 is connected to each other by inverters 104 and 105 of slave units (hereinafter referred to as “slave inverters 104 and 105”) and a communication cable 106 so that data communication is possible. The master inverter 103 calculates the output power that each of the inverters 103 to 105 should share from the maximum power that the solar battery 101 can output (varies depending on the amount of solar radiation), and the output power is transferred to the slave inverters 104 and 105 by data communication. Command and control the output power of each slave inverter 104,105.

Specifically, as shown in FIG.
(Processing a) Calculation of power command value of own device and slave inverters 104 and 105 and transmission of power command value and power storage command to slave inverters 104 and 105 (Processing b) Individual data with slave inverters 104 and 105 The two types of communication processing of acquiring information such as output power and operating state saved in the processing a by communication are repeated at a predetermined cycle T, whereby the total power output to the power system 102 (outputs of the inverters 103 to 105) Control the total power).

  The master inverter 103 performs data communication with the slave inverters 104 and 105 according to the communication procedure shown in FIG. The flowchart shown in FIG. 11 is executed by the master inverter 103 when the grid interconnection inverter system 100 is activated, and is repeated until the grid interconnection inverter system 100 stops.

The master inverter 103, at the update timing of the power command value (see the timing of ta in FIG. 10) (S101), the slave inverter 104 in the output power value P ₁₀₃ and the previous data communication of its own that is stored in the previous data communication calculates the output power value Ps of the system interconnection inverter system 100 adds the output power value P _104, P ₁₀₅ obtained from 105, the following power command by calculating an average value of the output power value Ps A value Pc (= Ps / 3) is calculated (S102). In the first calculation at the time of startup, since the previous output power values P _{103 to} P ₁₀₅ do not exist, the default value of the power command value Pc is used.

Subsequently, the master inverter 103 simultaneously transmits the calculated power command value Pc and the output power value storage command to the slave inverters 104 and 105 (S103). On the other hand, when the master inverter 103 simultaneously transmits the power command value Pc to the slave inverters 104 and 105, the master inverter 103 changes the output power of its own device to the power command value Pc. On the other hand, the slave inverter 104 and 105 receives the power command value Pc from the master inverter 103, after saving the output power value P _104, P ₁₀₅ during the reception in the buffer memory, respectively, change the output power to a power command value Pc To do.

Subsequently, the master inverter 103 sets the count value i for counting the number n of slave machines (n = 2 in the configuration of FIG. 9) to “1” (S104), and the n-th slave from the first slave machine. Data communication is performed in order up to the machine, and the output power value P _i stored from each slave machine is acquired (loop from S105 to S107). In the example of FIG. 9, data communication is sequentially performed for the first slave inverter 104 and the second slave inverter 105 to obtain output power values P ₁₀₄ and P ₁₀₅ stored from the slave inverters 104 and ₁₀₅ .

When the master inverter 103 acquires the output power value P _i from all the slave devices (S106: YES), the master inverter 103 returns to step S101 and performs the update process of the power command value at the next update timing.

Therefore, in the conventional grid-connected inverter system 100, the output power of each of the inverters of the master inverter 103 and the slave inverters 104 and 105 is updated at a predetermined period T. Therefore, the output of the solar battery 101 is changed according to the change in the amount of solar radiation. Even when the power-output voltage characteristic changes, the output power of each inverter is appropriately controlled following the change.

  For example, when the maximum power of the solar cell 101 is 300 kW and the maximum output capacity of each of the master inverter 103 and the slave inverters 104 and 105 is 100 kW, the master inverter 103 assumes that the conversion efficiency of the inverter is 100%. The power command value Pc of the master inverter 103 and the slave inverters 104 and 105 is set to 100 kW, which is a value obtained by dividing 300 kW into three, and the power command value Pc is commanded to the slave inverters 104 and 105. As a result, the master inverter 103 and the slave inverters 104 and 105 control the output power to 100 kW, so that the power system 102 is supplied with 300 kW of power, which is a sum of these output powers. Since each output power of the master inverter 103 and the slave inverters 104 and 105 is within the maximum output capacity, the operation of the grid interconnection inverter system 100 is normally maintained.

Japanese Patent Laid-Open No. 5-53042 JP 2000-305634 A

By the way, in the conventional grid-connected inverter system 100, as shown in FIG. 10, the master inverter 103 is configured such that the master inverter 103 and the slave inverter 104 in the processing period A to processing period A to D in which the power command value is updated. Since the power command value Pc of 105 is changed, the output power of the master inverter 103 and the slave inverters 104 and 105 is changed at a substantially cycle T. That is, the power that will be output from the system interconnection inverter system 100 is changed by approximately period T. In FIG. 10, for convenience, the change timing of the output power of the grid interconnection inverter system 100 is illustrated as the end timing of the process a.

  Therefore, for example, when a sudden change in the amount of solar radiation occurs during the process b (information acquisition process including the output power of the slave inverters 104 and 105), and the maximum power Pmax of the solar battery 101 decreases rapidly, The change value of the output power of the master inverter 103 and the slave inverters 104 and 105 does not become an appropriate value corresponding to the maximum power Pmax.

  That is, in FIG. 10, when the maximum power Pmax of the solar cell 101 is 300 kW, for example, when the maximum output Pmax suddenly decreases to 100 kW at the time t1 in the process b of the period A, the slave inverters 104 and 105 at that time. Since the power command values are respectively changed to 100 kW, the output powers of the slave inverters 104 and 105 are each controlled to 100 kW. That is, the total output power of the slave inverters 104 and 105 is 200 kW, which exceeds the maximum power Pmax of the solar cell 101 = 100 kW.

  If the output power Psum obtained by adding the output powers of the slave inverters 104 and 105 does not exceed the maximum power Pmax of the solar battery 101, the master inverter 103 performs power conversion so as to compensate for the difference ΔP = (Pmax−Psum). For example, if the maximum power Pmax is 250 kW, power of ΔP = 50 kW is output. However, as described above, when the difference ΔP becomes negative such as −100 kW, the shortage (−100 kW) ) From the power system 102 to the solar cell 101 side by reverse conversion. Therefore, the output power of the master inverter 103 becomes −100 kW from the time t1, and the conversion operation of the master inverter 103 becomes abnormal.

  As shown in FIG. 10, in the process a of the period B, the slaves are output with the output power values (100 kW each) of the slave inverters 104 and 105 stored in the process a of the period A and the output power value (100 kW) of the master inverter 103. Since the power command value Pc of the inverters 104 and 105 is calculated and the calculated value becomes 100 kW, the output power of the slave inverters 104 and 105 is not substantially changed. However, since the output power value of the master inverter 103 is changed from 100 kW to -100 kW in the process a in the period B, the output power of the slave inverters 104 and 105 is changed reflecting this content. Eventually, it comes after processing a in period C.

  That is, in the process a of period C, the value (33.3 kW) obtained by dividing the total value of the output power value of the master inverter 103 (−100 kW) and the output power values of the slave inverters 104 and 105 (each 100 kW) into three equal parts (33.3 kW). The power command values Pc of the inverter 103 and the slave inverters 104 and 105 are set, and the output power of the master inverter 103 and the slave inverters 104 and 105 at the end timing t2 of the process a in the period C is the power command value (33. 3 kW).

  Therefore, as shown in FIG. 12, the master inverter 103 performs an abnormal conversion operation in which the output power becomes negative for a period of approximately t1 to t2. In FIG. 12, the left vertical axis indicates the DC voltage [V] detected by the voltage sensor Sv of each inverter 103 to 105, and the right vertical axis indicates the AC power [kW] output from each inverter 103 to 105. ] Is shown. I represents the waveform of the DC voltage, II represents the waveform of AC power output from the slave inverters 104 and 105, and III represents the waveform of AC power output from the master inverter 103. In the figure, a period from t1 to t3 is a transient response period in which the conversion operation of the master inverter 103 changes corresponding to a sudden change in the amount of solar radiation.

  As described above, in the conventional grid-connected inverter system 100, since the master inverter 103 repeats the data communication including the processing a and the processing b and updates the output power of the slave inverters 104 and 105, the power generated by the data communication If the amount of solar radiation suddenly decreases within the update period of the command value Pc and the maximum power Pmax of the solar battery 101 decreases rapidly, the conversion operation of the master inverter 103 may become abnormal for at least one period.

  In the above example, since there are three inverters constituting the grid-connected inverter system, the update period of the power command value Pc is relatively short, but several tens to hundreds of tens of inverters are connected in parallel. When the grid-connected inverter system is configured, the update period of the power command value Pc becomes longer and the abnormal operation period of the master inverter becomes longer, so the problem that the conversion operation of the master inverter becomes abnormal is important. is there.

  For example, if the grid interconnection inverter system is composed of 50 grid inverters and the data communication time between the master inverter and each slave inverter in process b is 20 ms, the master inverter is used to update the power command value Pc. Takes at least 20 ms × 49 = 980 ms to collect output power from all slave inverters. Therefore, in such a large-scale grid-connected inverter system, the power command value update cycle is a time on the order of seconds, and the master inverter may stop in some cases, and abnormalities in the conversion operation of the master inverter cannot be ignored. It becomes a problem.

  The present invention has been conceived under the circumstances described above, and is a grid-connected inverter system capable of preventing an abnormality in the conversion operation of the master inverter when the power that can be output from the DC power supply changes suddenly. And it aims at providing the power control method of the grid connection inverter system.

  In order to solve the above problems, the present invention takes the following technical means.

  The grid-connected inverter system provided by the first aspect of the present invention includes a master inverter and at least one slave inverter connected in parallel between a DC power source and a power system, and the master An inverter and the slave inverter are connected to each other so as to be able to perform data communication with each other, and the master inverter controls the total power of the master inverter and the slave inverter that are output to the power system. In the inverter system, the master inverter calculates the power command value of the slave inverter based on the output power value of the slave inverter and the output power value of the own device acquired at the previous data communication in a predetermined cycle. , The power conservation command that commands the storage of the power command value and output power value. A first process for simultaneously transmitting a command to the slave inverter, and a second process for obtaining an output power value stored in accordance with the power storage command by performing data communication with the slave inverter in order after the first process. Power control means for controlling the total power output to the power system by repeating processing, power fluctuation detection means for detecting fluctuations in power that can be output from the DC power supply, and power fluctuations by the power fluctuation detection means Is detected, the power command value of the slave inverter is recalculated based on the output power value of the own device at the time of detecting the power fluctuation and the output power value of the slave inverter that is earned at the time of detection, A power command value transmitting means for simultaneously transmitting a power command value to the slave inverter; and the power control means after the recalculated power command value is transmitted. In the first process performed by the first step, the power instruction value is calculated and prohibiting means for prohibiting simultaneous transmission of the power instruction value to the slave inverter, the slave inverter from the master inverter When receiving the power storage command by the first processing, the output power value of the own device at the time of reception is stored according to the power storage command, and when the power command value by the first processing is received from the master inverter, Output power value is changed to the power command value, and when the recalculated power command value is received from the master inverter, the output power value of the own device is changed to the recalculated power command value. And when there is a request for an output power value by the second process from the master inverter, the stored output power value of the own device is Output power transmitting means for transmitting to the inverter.

  A grid-connected inverter system provided by the second aspect of the present invention includes a master inverter connected in parallel between a DC power source and a power system, at least one slave inverter, and the master inverter. And a control device communicably connected to the slave inverter, and the control device controls a total power obtained by combining the output power of the master inverter and the slave inverter output to the power system. In the interconnected inverter system, the master inverter detects power fluctuations that can be output from the DC power supply, and when power fluctuations are detected by the power fluctuation detection means, Power fluctuation transmission means for transmitting to the control device together with the output power value of the own device at the time of fluctuation detection The control device calculates power command values of the master inverter and the slave inverter based on output power values of the master inverter and the slave inverter acquired at the previous data communication in a predetermined cycle, and A first process of simultaneously transmitting a power command value and a power storage command for commanding the storage of the output power value to the master inverter and the slave inverter; and sequentially after the first process, the master inverter and the slave inverter Power control means for controlling the total power output to the power system by repeatedly performing a data communication and acquiring an output power value stored by the power storage command, from the master inverter When power fluctuation detection information and output power value at the time of power fluctuation detection are received, A power command that recalculates the power command value based on the output power value and the output power value of the slave inverter that is obtained when detecting the power fluctuation, and transmits the power command value to the master inverter and the slave inverter at the same time In the first process performed by the power control means after the value transmission means and the recalculated power command value are transmitted, the calculation of the power command value and the master inverter of the power command value, Prohibiting means for prohibiting simultaneous transmission to the slave inverter, and when the slave inverter receives the power storage command by the first processing from the control device, the output of the own device at the time of reception according to the power storage command When the power value is stored and the power command value by the first process is received from the control device, the output of the own device Output power changing means for changing the power value to the power command value, and receiving the recalculated power command value from the control device; When there is a request for the output power value by the second process from the control device, the control device includes output power transmission means for transmitting the stored output power value of the own device to the control device.

  The predetermined period includes at least the time required for the first process including a time for the master inverter to perform data communication simultaneously with all the slave inverters, and the master inverter sequentially transmits data to all the slave inverters. This is the total time required for the second processing including the time for performing communication.

  The power fluctuation detecting means is preset with a voltage change rate detecting means for detecting a change rate of a DC voltage output from the DC power supply and a DC voltage change rate detected by the voltage change rate detecting means. A comparison means for comparing with a predetermined threshold value, and a detection means for detecting the presence of power fluctuation when the change rate of the DC voltage is equal to or higher than the predetermined threshold value by the comparison means.

  The power command value is an average value of total power values obtained by combining the output power value of the master inverter and the output power value of the slave inverter.

  Further, the master inverter controls the output power of its own device by maximum power tracking control.

  A power control method for a grid-connected inverter system provided by the third aspect of the present invention is a master inverter that is connected between a DC power source and a power system and has a function of detecting power fluctuations of the DC power source. Based on the output power value obtained at the time of the previous data communication from the at least one slave inverter connected in parallel to the master inverter and capable of data communication with each other, and the output power value of the own device, A first step of calculating a power command value of the slave inverter and simultaneously transmitting the power command value and a power storage command for commanding storage of the output power value to the slave inverter; When receiving the power storage command and the power command value from the own machine according to the power storage command A second step of saving the power value and changing the output power value of the own device to the power command value, and data communication with the master inverter in turn with the slave inverter after the first step. And a third step of acquiring the output power value stored in accordance with the power storage command in a predetermined cycle, thereby connecting the master inverter and at least one slave inverter in parallel. In the power control method for controlling the power output from the system to the power system, when a power fluctuation of the DC power source is detected by the master inverter during the processing of the third step, the power is supplied to the master inverter. Output power value of own device at the time of detection of fluctuation and output power of slave inverter which is earned at the time of detection And a fourth step of simultaneously transmitting the power command value of the slave inverter to the slave inverter, and the power command value recalculated by the fourth step. In the first step that is performed first after the power is transmitted, the calculation of the power command value and the simultaneous transmission of the power command value to the slave inverter are prohibited.

  The power control method for the grid-connected inverter system provided by the fourth aspect of the present invention is connected to the control device so that mutual data communication is possible with the control device, and between the DC power source and the power system. The master inverter and the slave inverter based on each output power value acquired at the time of the previous data communication from the master inverter having a function of detecting the power fluctuation of the DC power supply connected in parallel and at least one slave inverter A first step of causing the master inverter and the slave inverter to transmit simultaneously the power command value and a power storage command for commanding the storage of the output power value, and the master inverter and the slave inverter. And receiving the power storage command and the power command value from the control device. A second step of storing the output power value of the own device at the time of reception in accordance with the power storage command, and changing the output power value of the own device to the power command value, and the control device of the first step The master inverter and at least one of the master inverter and the slave inverter are subsequently repeated in a predetermined cycle by repeating data communication with the master inverter and the slave inverter in order to obtain an output power value stored by the power storage command. In a power control method for controlling power output to the power system from a grid-connected inverter system formed by connecting the slave inverters in parallel, when a power fluctuation of the DC power source is detected, the master inverter A fourth step of transmitting detection information to the control device together with the output power value of the own device at the time of detecting the power fluctuation; When the detection information of the power fluctuation and the output power value are received from the master inverter during the processing of the third step, the control device is provided with the output power value of the master inverter and the power fluctuation at the time of detecting the power fluctuation. A fifth step of recalculating the power command value of the slave inverter based on the output power value of the slave inverter and transmitting the power command value to the master inverter and the slave inverter at the same time, In the first step, which is performed first after the recalculated power command value is transmitted by the step, the calculation of the power command value and the simultaneous transmission of the power command value to the slave inverter are prohibited. It is characterized by.

  In the above-described grid-connected inverter system or the power control method for the grid-connected inverter system, the DC power source may be configured by a solar cell.

According to the present invention, the master inverter or the control device repeats the first process and the second process at a predetermined cycle to change the power command values of the master inverter and the slave inverter, and from the grid-connected inverter system to the power system. When power output that can be output from the DC power supply occurs while controlling the output power, the master inverter or control device has already acquired the output power of the master inverter at the time of the power fluctuation and the power fluctuation. The power command value is recalculated based on the output power of the slave inverter, and the output power of the master inverter and slave inverter is immediately changed to the recalculated power command value. even when reduced to a small power value than the total power that is outputted from the system inverter system, its The total power and shorten as much as possible the period of the abnormal state of conversion of the master inverter is reversed converting operation in order to compensate for the difference between the power value of the DC power source, a situation that operation is stopped by the abnormal state it can be avoided enabled.

  In particular, when a solar cell is used as a DC power source, the power that can be output from the solar cell changes suddenly when the amount of solar radiation changes suddenly, and the conversion of the master inverter during control that periodically changes the power command value of the slave inverter Although an abnormal state in which the operation is reverse conversion occurs and the master inverter may be stopped in some cases, according to the present invention, such a problem can be effectively avoided.

  As an example of a grid-connected inverter system according to the present invention, a configuration in which three identical inverters are connected in parallel between a solar cell and a power system will be described with reference to the drawings.

  FIG. 1 is a diagram showing an overall configuration of a grid interconnection inverter system 1 according to the present invention. In the grid-connected inverter system 1 shown in the figure, three inverters 4, 5 and 6 having the same basic configuration are connected in parallel between a solar cell 2 and a power system 3. The solar cell 2 has a large number of photoelectric conversion elements made of a semiconductor such as silicon, and each photoelectric conversion element converts light energy into electric energy for output. The power system 3 is a power system that supplies a commercial power source (50 Hz or 60 Hz AC power in Japan).

  As is well known, the solar cell 2 has an output power-output voltage characteristic (generally a mountain-shaped characteristic) shown in FIG. The output voltage Vm corresponding to the maximum output power Pmax is referred to as “optimum operating voltage”. In the solar cell 2, when the output voltage Vdc exceeds the optimum operating voltage Vm, the output current Idc decreases rapidly, and accordingly the output power Po. Drops sharply. On the other hand, when the output voltage Vdc is smaller than the optimum operating voltage Vm, the output power Po of the solar cell 2 decreases substantially in proportion to the output voltage Vdc.

  Therefore, the inverters 4, 5 and 6 search for the optimum operating voltage Vm and operate the DC voltage at the input terminal to the optimum operating voltage Vm (the output power of the solar cell 2 is set to the maximum power Pmax) when operating independently. It has a function to perform maximum power tracking control.

  Of the three inverters 4, 5, 6, the inverter 4 is set as a master machine of the grid interconnection inverter system 1, and the inverters 5, 6 are set as slave machines of the grid interconnection inverter system 1. An inverter (hereinafter referred to as “master inverter”) 4 that is a master machine is connected to inverters (hereinafter referred to as “slave inverters” if necessary) 5 and 6 via a communication line 7, respectively. Has been. The master inverter 4 performs data communication with the slave inverters 5 and 6 through the communication line 7 at a predetermined cycle.

  The master inverter 4 and the slave inverters 5 and 6 have the same basic configuration, although the internal configuration of the control unit 17 is different as will be described later. That is, the inverters 4, 5, 6 include three current sensors 8, 9, 10, two voltage sensors 11, 12, a DC-AC (DC-AC) conversion circuit 13, a filter circuit 14, a transformer as constituent elements. 15, the disconnection contactor 16 and the control unit 17 are included. Hereinafter, the basic configuration of the master inverter 4 will be described.

  The DC-AC conversion circuit 13, the filter circuit 14, the transformer 15, and the disconnecting contactor 16 are serially connected in this order between the input terminal of the master inverter 4 (terminal to which DC power is input from the solar battery 2) and the power system 3. Arranged and connected to each other. The DC-AC conversion circuit 13 is connected to the control unit 17 by a control line.

  The current sensor 8 is provided on a line between the input terminal of the master inverter 4 and the DC-AC conversion circuit 13, and the current sensor 9 is provided on a line between the DC-AC conversion circuit 13 and the filter circuit 14. The sensor 10 is provided in a line between the filter circuit 14 and the transformer 15. The current sensor 8, the current sensor 9, and the current sensor 10 are each connected to the control unit 17. On the other hand, the voltage sensor 11 is connected between the DC-AC conversion circuit 13 and the control unit 17, and the voltage sensor 12 is connected between the input end of the transformer 15 and the control unit 17.

The direct current I input to the DC-AC conversion circuit 13 is detected by the current sensor 8, the alternating current i ₁ output from the DC-AC conversion circuit 13 is detected by the current sensor 9, and the transformer 15 is detected by the current sensor 10. The input alternating current i ₂ is detected. As will be described later, since the DC-AC conversion circuit 13 converts a DC voltage into a three-phase (U-phase, V-phase, W-phase) AC voltage, the AC current i ₁ output from the current sensor 9 A U-phase AC current i _1U , a V-phase AC current i _1V, and a W-phase AC current i _1W are included. Similarly, the AC current i ₂ output from the current sensor 10 includes a U-phase AC current i _2U , a V-phase AC current i _2V, and a W-phase AC current i _2W . Detection currents I, i ₁ , i ₂ of the current sensor 8, the current sensor 9, and the current sensor 10 are input to the control unit 17.

Electrostatic DC voltage V applied to the input terminal of the DC-AC converter circuit 13 is detected by the pressure sensor 11, the AC voltage v applied to the input terminal of the transformer 15 is detected by the voltage sensor 12. The AC voltage v output from the voltage sensor 12 includes a U-phase AC voltage v _U , a V-phase AC voltage v _V, and a W-phase AC voltage v _W. Detection voltages V and v of the voltage sensor 11 and the voltage sensor 12 are input to the control unit 17.

  The DC-AC conversion circuit 13 is configured by a voltage-controlled inverter circuit including a three-phase bridge circuit including six switching elements such as a bipolar transistor, a field effect transistor, and a thyristor. The on / off operations of the six switching elements of the three-phase bridge circuit are controlled by the PWM signal output from the control unit 17. The control unit 17 controls the value of the AC voltage v output from the DC-AC conversion circuit 13 by controlling the pulse width of the PWM signal.

  The filter circuit 14 is composed of an LC low-pass filter. The filter circuit 14 removes switching noise included in the AC voltage v output from the DC-AC conversion circuit 13. The transformer 15 boosts or steps down the AC voltage (sine wave voltage) output from the filter circuit 14 to a level substantially equal to the system voltage. The disconnecting contactor 16 is for disconnecting the grid-connected inverter system 1 from the power system 3 when an abnormality occurs.

  FIG. 3 is a block diagram showing an internal configuration of the control unit 17 of the master inverter 4.

  The control unit 17 includes a DC power calculation unit 17a, a maximum power tracking control unit 17b, a voltage control unit 17c, a current control unit 17d, a command value calculation unit 17e, a PWM signal generation unit 17f, an AC power calculation unit 17g, and a power control unit 17h. , The solar radiation amount variation detecting unit 17i, the power command value calculating unit 17j, and the communication control unit 17k have functional blocks.

  The DC power calculation unit 17 a is a functional block that calculates DC power Pdc input to the DC-AC conversion circuit 13. The detected current I of the current sensor 8 and the detected voltage V of the voltage sensor 11 are input to the DC power calculation unit 17a. The DC power calculation unit 17a calculates the DC power Pdc (actual value) by multiplying the detected current I (actual value) and the detection voltage V (actual value). The DC power Pdc is input to the maximum power tracking control unit 17b.

  The maximum power follow-up control unit 17b is a functional block that controls the conversion operation of the DC-AC conversion circuit 13 so that the DC power Pdc input from the solar cell 2 to the DC-AC conversion circuit 13 is maximized. The maximum power tracking control unit 17b changes the DC voltage V output from the solar cell 2 by a so-called hill climbing method, and controls the DC power Pdc output from the solar cell 2 to the maximum output power Pmax.

  Specifically, the maximum power follow-up control unit 17b generates a DC voltage command value Vc at a predetermined cycle, and outputs the DC voltage command value Vc to the voltage control unit 17c. The DC voltage command value Vc is a control target value of the DC voltage V input to the DC-AC conversion circuit 13. The maximum power tracking control unit 17b updates and stores the DC power Pdc input from the DC power calculation unit 17a at a predetermined cycle. Each time the DC power Pdc is input from the DC power calculation unit 17a, the maximum power tracking control unit 17b compares the DC power Pdc with the DC power Pdc input last time, and determines the increase or decrease of the DC power Pdc.

  When the DC power Pdc is increased, it is determined that the DC voltage V input to the DC-AC conversion circuit 13 is in a region lower than the optimum operating voltage Vm in the output power-output voltage characteristics shown in FIG. Therefore, the maximum power follow-up control unit 17b increases the previously generated DC voltage command value Vc by a predetermined value to generate a new DC voltage command value Vc, and outputs this DC voltage command value Vc to the voltage control unit 17c. To do. On the other hand, when the DC power Pdc is decreasing, in the output power-output voltage characteristics shown in FIG. 2, the DC voltage V input to the DC-AC conversion circuit 13 is in a region higher than the optimum operating voltage Vm. Since the determination is made, the maximum power follow-up control unit 17b reduces the previously generated DC voltage command value Vc by a predetermined value to generate a new DC voltage command value Vc, and this DC voltage command value Vc is used as the voltage control unit 17c. Output to.

The voltage control unit 17c is output from the DC-AC conversion circuit 13 so that the DC voltage V input to the DC-AC conversion circuit 13 becomes the DC voltage command value Vc input from the maximum power tracking control unit 17b. This is a functional block that generates a current command value icq for the effective axis q (hereinafter referred to as “effective current command value icq”) among the alternating current command value ic for controlling the alternating current i ₁ .

The alternating current command value ic is a control target value of the alternating current i ₁ output from the DC-AC conversion circuit 13. The voltage control unit 17c receives the detection voltage V (measured value) of the voltage sensor 11 and the DC voltage command value Vc (target value) generated by the maximum power follow-up control unit 17b. The voltage control unit 17c performs an error amplification operation between the DC voltage command value Vc and the detected voltage V, and generates an active current command value icq based on the control value. The effective current command value icq is output to the current control unit 17d, and is used to calculate the control value Eiq of the effective axis q among the control values Ei to be output to the command value calculation unit 17e. The AC current command value i cd (hereinafter referred to as “reactive current command value i cd”) of the reactive axis d is generated by the power control unit 17h as will be described later, and is transferred from the power control unit 17h to the current control unit 17d. Entered.

The current control unit 17d is a functional block that generates a control value for controlling the alternating current i ₁ output from the DC-AC conversion circuit 13 to be the alternating current command value ic. More specifically, the current control unit 17d calculates a control value Ei for the command value calculation unit 17e. The control value Ei includes a control value Eiq for the effective axis q and a control value Eid for the invalid axis d. The current control unit 17d performs error amplification operation of the active current command value icq input from the voltage control unit 17c and the detection current i _1, generates as the control value Eiq effective axis q. The current control unit 17d performs error amplification operation of the reactive current command value icd inputted from the power control unit 17h and the detection current i _1, generates as the control value Eid invalid axis d. These control values Eiq and Eid are input to the command value calculation unit 17e.

Since the three-phase AC currents i _1U , i _1V , i _1W are input from the current sensor 9 to the current control unit 17d, the current control unit 17d receives the three-phase AC currents i _1U , i _1V , i _1W . The alternating current iq of the effective axis q and the alternating current id of the ineffective axis d are converted by a predetermined three-phase / dq axis coordinate conversion formula, and a control value Eiq and a control value Eid are generated for each of the alternating currents iq and id.

  The command value calculation unit 17e is a functional block that calculates a command value of an AC voltage waveform to be output to the DC-AC conversion circuit 13. The command value calculation unit 17e generates a command value for an AC voltage waveform based on the control value Eiq for the effective axis q and the control value Eid for the invalid axis d input from the current control unit 17d. This command value is output to the PWM signal generator 17f.

The PWM signal generation unit 17 f is a functional block that generates a PWM signal for controlling the six switching elements of the three-phase bridge circuit in the DC-AC conversion circuit 13. The PWM signal generation unit 17f generates an AC voltage signal based on the command value of the AC voltage waveform input from the command value calculation unit 17e , and compares the AC voltage signal with a predetermined triangular wave signal to generate a PWM signal. To do. Note that the three-phase bridge circuit in the DC-AC conversion circuit 13 has two pairs as a set, and three pairs of switching elements are controlled on / off operation by three types of PWM signals having different phases, so that the PWM signal generation is performed. The unit 17 f generates three types of PWM signals having different phases, and these PWM signals are input to the DC-AC conversion circuit 13.

The AC power calculation unit 17g is a functional block that calculates the AC power output from the filter circuit 14. A detection current i ₂ of the current sensor 10 and a detection voltage v of the voltage sensor 12 are input to the AC power calculation unit 17g. The AC power calculation unit 17g calculates AC power (effective value) using the detected current i ₂ (actual value) and the detected voltage v (actual value). More specifically, the AC power calculator 17g uses the detected current i ₂ (actual value) and the detected voltage v (actual value) of the U phase, V phase, and W phase to invalidate the effective power Pac (effective value). Electric power Qac (effective value) is calculated. The calculation result of the active power Pac is input to the power command value calculation unit 17j, and the calculation result of the reactive power Qac is input to the power control unit 17h.

The power control unit 17h is a functional block that generates a reactive current command value cd for making the reactive power Qac output from the AC power calculating unit 17g zero. The power control unit 17h performs an error amplification calculation between the reactive power Qac input from the AC power calculation unit 17g and the reactive power command value (zero), and generates a reactive current command value cdd based on the control value. This reactive current command value cdd is input to the current control unit 17d.

  The solar radiation amount fluctuation detection unit 17i is a functional block that detects a sudden change in the solar radiation amount (sudden change in the amount of sunlight irradiated to the solar cell 2). The detection voltage V of the voltage sensor 11 is input to the solar radiation amount fluctuation detection unit 17i. The solar radiation amount variation detection unit 17i has a comparison circuit that detects a change rate (time differential value) Rv of the detection voltage V and compares the voltage change rate Rv with a predetermined threshold value Rth. A signal indicating whether Rv is equal to or less than the threshold value Rth is output.

  For example, the comparison circuit outputs a low level signal when the voltage change rate Rv is equal to or less than the threshold value Rth, and outputs a high level signal when the voltage change rate Rv is higher than the threshold value Rth. When the output signal of the comparison circuit is low level, the output signal indicates “no sudden change in solar radiation amount”, and when the output signal of the comparison circuit is high level, the output signal indicates “there is sudden change in solar radiation amount”. Show. The detection result (output signal of the comparison circuit) of the solar radiation amount fluctuation detection unit 17i is input to the power command value calculation unit 17j.

  The power command value calculation unit 17j is a functional block that calculates the power command value Pc of each inverter of the slave inverters 5 and 6. The active power Pac is input from the AC power calculation unit 17g to the power command value calculation unit 17j, and a detection signal indicating whether there is a sudden change in the solar radiation amount is input from the solar radiation amount variation detection unit 17i. Also, the active power Pac acquired from the slave inverters 5 and 6 by communicating with the slave inverters 5 and 6 from the communication control unit 17k is input to the power command value calculation unit 17j.

  The power command value calculation unit 17j uses the active power Pac input from the AC power calculation unit 17g and the active power Pac of the slave inverters 5 and 6 input from the communication control unit 17k for each communication cycle of the communication control unit 17k. Then, the power command value Pc of each inverter of the slave inverters 5 and 6 is calculated. Specifically, assuming that the active power Pac of the master inverter 4 is Pmain and the active power Pac of the slave inverters 5 and 6 are Psub1 and Psub2, respectively, the power command value calculation unit 17j has an average value Pave = (Pmain + Psub1 + Psub2) / 3 is calculated as the power command value Pc of each inverter. This calculation result is input to the communication control unit 17k.

  The power command value calculation unit 17j also performs the above average value Pave calculation process when the detection result of “there is a sudden change in the solar radiation amount” is input from the solar radiation amount variation detection unit 17i, and the communication control is performed on the calculation result. To the unit 17k. In this case, in the next calculation cycle thereafter, the power command value calculation unit 17j does not perform the calculation process of the average value Pave.

The power command value calculation unit 17j sets the solar radiation amount sudden change detection flag F to “1” when the detection result of “there is a sudden change in solar radiation amount” is input from the solar radiation amount variation detection unit 17i. The power command value calculation unit 17j performs the calculation of the power command value Pc in the next calculation cycle after performing the calculation processing of the power command value Pc of each inverter based on the detection result of “there is a sudden change in the amount of solar radiation”. The sudden change detection flag F is reset to “0”.

  The solar radiation amount sudden change detection flag F is a flag indicating whether or not there is a sudden change in the solar radiation amount. The abrupt solar radiation amount change detection flag F = 1 indicates “there is a sudden change in the solar radiation amount”, and the rapid solar radiation amount change detection flag F = 0 indicates “there is no abrupt change in the solar radiation amount”. The set and reset values of the solar radiation amount sudden change detection flag F may be reversed. Information on the abrupt solar radiation amount change detection flag F is input to the communication control unit 17k.

  The communication control unit 17k is a functional block that controls data communication with the slave inverters 5 and 6. The communication control unit 17k performs data communication with each of the slave inverters 5 and 6 in a predetermined cycle (hereinafter referred to as “communication cycle”).

Specifically, the communication control unit 17k is set in each communication cycle.
(Process a) power command value command to save active power Pac current and electric power command value Pc inputted from the operation unit 17j is output (hereinafter, referred to as "power save command".) To the slave inverter 5,6 (Processing b) A communication process for acquiring the active power Pac stored in the process a by data communication with the slave inverters 5 and 6 is performed. This communication processing is performed when the solar radiation amount sudden change detection flag F = 1 described later. In addition, since the communication time between inverters is about 20 ms, for example, the communication cycle (the sum of the communication times of processes a and b) is about 60 ms.

Further, the communication control unit 17k recalculates the power command value Pc ′ by the power command value calculation unit 17j in accordance with the detection result of “there is a sudden change in the solar radiation amount” of the solar radiation amount variation detection unit 17i, and the power command value Pc When 'is entered,
(Process c) The power command value Pc ′ input from the power command value calculation unit 17j is simultaneously transmitted to the slave inverters 5 and 6.

The communication control unit 17k, when performing the process c, the subsequent in the process a in the next communication cycle, since the power command value Pc from the power command value calculating section 17j is not input, the power save command only slave inverter 5, 6 to send simultaneously. This communication process (hereinafter referred to as “process a ′”) is performed when the solar radiation amount sudden change detection flag F = 0.

  In the above configuration, the master inverter 4 controls the output power to the power system 3 as follows.

  That is, in the master inverter 4, a command value of an AC voltage waveform to be output to the DC-AC conversion circuit 13 is output from the command value calculation unit 17e to the PWM signal generation unit 17f. The power follow-up control unit 17b is controlled so that the DC voltage V input to the DC-AC conversion circuit 13 becomes the optimum operating voltage Vm. Further, the reactive component is controlled so that the reactive power Qac at the interconnection point becomes zero.

  Therefore, when the output power-output voltage characteristic of the solar cell 2 changes according to the change in the amount of solar radiation, the maximum power point changes, and the optimum operating voltage Vm differs for each output power-output voltage characteristic. When the direct-current voltage V input to the DC-AC conversion circuit 13 is relatively shifted from the optimum operating voltage Vm with the change of the output voltage characteristic, the maximum power follow-up control unit 17b automatically converts the DC-AC conversion circuit 13. The operation is corrected, and the DC voltage V input to the DC-AC conversion circuit 13 is held at the optimum operating voltage Vm.

  In the master inverter 4, the maximum power follow-up control described above is performed regardless of the change in the amount of solar radiation, and the output power may become negative when the amount of solar radiation drops sharply. Will completely shift and will not be a normal conversion operation.

  FIG. 4 is a block diagram showing an internal configuration of the control unit 17 ′ of the slave inverters 5 and 6.

The control unit 17 ', the maximum power follow-up control unit 17b to the control unit 17 of the master inverter 4, the voltage control unit 17c, the date the configuration excluding the functional block morphism amount variation detecting unit 17i and the power command value calculating section 17j Have. In the grid- connected inverter system, the slave inverters 5 and 6 do not perform the maximum power follow-up control, and control the output power according to the power command value commanded from the master inverter 4, so that the above functional blocks are not required. Because.

  Therefore, the control unit 17 ′ includes functional blocks of the DC power calculation unit 17a, the current control unit 17d, the command value calculation unit 17e, the PWM signal generation unit 17f, the AC power calculation unit 17g, the power control unit 17h, and the communication control unit 17k. Have.

  The DC power calculation unit 17a performs the same operation as the DC power calculation unit 17a of the master inverter 4 described above. That is, the DC power calculation unit 17a calculates the DC power Pdc (actual value) by multiplying the detection current I (actual value) and the detection voltage V (actual value). This calculated value is used for referring to the state of the output power of the solar cell 2.

The current control unit 17d performs the same operation as the current control unit 17d of the master inverter 4 described above, but differs from the master inverter 4 in the following points. That is, since the active current command value icq and the reactive current command value icd are input from the power control unit 17h to the current control unit 17d, the current control unit 17d detects the detected current i ₁ (actual value) of the current sensor 9 and the power. A control value Eiq for the effective axis q and a control value Eid for the invalid axis d are generated using the active current command value icq and the reactive current command value cdd input from the control unit 17h.

The command value calculator 17e performs the same operation as the command value calculator 17e of the master inverter 4 described above, and the PWM signal generator 17f performs the same operation as the PWM signal generator 17f of the master inverter 4 described above. That is, the command value calculation unit 17e generates an AC voltage waveform command value based on the control value Eiq of the effective axis q and the control value Eid of the invalid axis d input from the current control unit 17d, and generates a PWM signal generation unit. 17f generates an AC voltage signal based on the command value of the AC voltage waveform input from the command value calculator 17e , and compares the AC voltage signal with a predetermined triangular wave signal to generate a PWM signal.

The AC power calculation unit 17g performs the same operation as the AC power calculation unit 17g of the master inverter 4 described above. That is, the AC power calculation unit 17g calculates the active power Pac and the reactive power Qac using the detected current i ₂ (measured value) and the detected voltage v (actual value) of the U phase, V phase, and W phase, respectively.

  The power control unit 17h performs the same operation as the power control unit 17h of the master inverter 4 described above, but differs from the master inverter 4 in the following points. That is, the power control unit 17h of the master inverter 4 generates the reactive power command value icd, but the power control unit 17h of the slave inverters 5 and 6 also generates the active power command value icq.

That is, the power control unit 17h performs an error amplification calculation between the reactive power Qac input from the AC power calculation unit 17g and the reactive power command value (zero), and generates a reactive current command value cdd based on the control value. . The power control unit 17h performs error amplification operation of the power command value Pc from the master inverter 4 which is input from the AC power calculating unit active power Pac a communication control unit 17k inputted from 17g, a control value The active current command value icq is generated based on These active current command value icq and reactive current command value cdd are output to the current control unit 17d.

  The communication control unit 17 k is a functional block that controls data communication with the master inverter 4. The communication control unit 17k performs data communication in response to a communication request from the master inverter 4. Specifically, when receiving the power command value Pc from the master inverter 4 in the process c or the process a in each communication cycle, the communication control unit 17k inputs the power command value Pc to the power control unit 17h.

The communication controller 17k receives the power save command in processing a within each communication cycle, to save active power Pac currently operational in the AC power calculation unit 17 g. AC power calculating section 17g includes a memory for temporarily storing active power Pac, the power save command from the communication control unit 17k is input, for temporarily storing active power Pac in its memory.

  Furthermore, when the communication control unit 17k receives the power transmission command in the process b or process c in each communication cycle, the communication control unit 17k causes the AC power calculation unit 17g to read out the effective power Pac temporarily stored in the memory, and the effective power Pac is transmitted to the master inverter 4.

  In the above configuration, the slave inverters 5 and 6 control the output power to the power system 3 as follows.

  That is, in the slave inverters 5 and 6, the command value calculation unit 17e outputs the command value of the AC voltage waveform to be output to the DC-AC conversion circuit 13 to the PWM signal generation unit 17f. Is controlled so that the active power Pac at the interconnection point becomes the power command value Pc commanded from the master inverter 4. Further, the reactive component is controlled so that the reactive power Qac at the interconnection point becomes zero.

  Since the current command value Pc is input from the master inverter 4 every communication cycle, the command value of the AC voltage waveform is generated by the power control unit 17h, the current control unit 17d, and the command value calculation unit 17e every communication cycle. It is input to the PWM signal generator 17f. Therefore, the conversion operation of the DC-AC conversion circuit 13 is controlled by updating the target value of the output power in units of communication cycles (for example, in units of 60 ms).

FIG. 5 is a flowchart showing a control procedure of output power to the power system 3 of the grid interconnection inverter system 1 in the master inverter 4. FIG. 6 is a diagram showing the contents of data communication between the master inverter 4 and the slave inverters 5 and 6. In FIG. 6, the content of the upper data communication is the content when there is no sudden change in the amount of solar radiation, and the content of the lower data communication is the content when there is a sudden decrease in the amount of solar radiation at the timing tb. It is.

  In the following description, for convenience, the maximum output power Pmax of the solar cell 2 when the amount of solar radiation is sufficient is 300 kW, and the maximum output power of the master inverter 4 and the slave inverters 5 and 6 is 100 kW. Further, the conversion efficiency of the master inverter 4 and the slave inverters 5 and 6 is set to 100%.

  Master inverter 4 performs data communication with slave inverters 5 and 6 in accordance with the communication procedure shown in FIG. The flowchart shown in FIG. 5 is executed by the master inverter 4 when the grid interconnection inverter system 1 is activated, and is repeated until the grid interconnection inverter system 1 is stopped.

The master inverter 4 initializes various data and starts an output power control operation (S1). In this initialization, the counter value i and the solar radiation sudden change detection flag F that counts the number of slave inverter in the process of acquiring the output power from the slave inverter 5, 6 will be described later is initialized to "0".

Subsequently, when the master inverter 4 reaches the power command value update timing (see timings ta1, ta2,..., Ta4 in FIG. 6) (S2: YES), the solar radiation amount sudden change detection flag F is set to “1”. It is determined whether or not (S2). The update timing of the first power command value, since the amount of solar radiation sudden change detection flag F is reset to "0", the master inverter 4, the process proceeds to step S 4, the slave inverter 5 obtained in the previous data communication, A power command value Pc is calculated from each of the active powers Psub1, Psub2 output from 6 and the active power Pmain output from the own device stored at the previous data communication.

That is, the master inverter 4 calculates the respective active power Psub1, Psub2 adds to system interconnection inverter system 1 of the output power value Ps of the active power Pmain of its own and the slave inverter 5,6 (= Pmain + Psub1 + Psub2 ) The power command value Pc (= Ps / 3) is calculated by calculating the average of the output power value Ps. In the first calculation at the time of startup, since the previous active power Pmain, Psub1, Psub2 does not exist, the default value of the power command value Pc is used.

  Subsequently, the master inverter 4 simultaneously transmits the calculated power command value Pc and the power storage command to the slave inverters 5 and 6 (S5). The processes in steps S2 to S5 correspond to the process a described above.

  Subsequently, the master inverter 4 proceeds to step S8 and performs data communication corresponding to the process b. First, the master inverter 4 sets the count value i to “1” (S8), and then determines whether or not the amount of solar radiation has suddenly changed (S9). This determination is performed based on a detection signal from the solar radiation amount fluctuation detection unit 17i. That is, if a high level detection signal is output from the solar radiation amount fluctuation detection unit 17i, it is determined that there is a sudden change in solar radiation amount, and if a low level detection signal is output from the solar radiation amount fluctuation detection unit 17i, It is determined that there is no sudden change in solar radiation.

If it is determined that there is no sudden change in the amount of solar radiation (S9: NO), the master inverter 4 proceeds to step S13 to perform data communication with the i-th slave inverter, and in step S5, a power storage command is issued. The active power Psub1 acquired is processed. In this embodiment, since there are two slave inverters, if the first slave inverter is the slave inverter 5 and the second slave inverter is the slave inverter 6, the master inverter 4 communicates with the slave inverter 5 in data communication. To obtain the active power Psub1.

Subsequently, the master inverter 4 determines whether or not the count value i is equal to or greater than the total number n of slave inverters (S14). If n> i (S14: NO), the master inverter 4 proceeds to step S15, increments the counter value i by “1”, returns to step S9, and performs the same data communication process for the next slave inverter. Do. In the present embodiment, since the total number of slave inverters is two, when the master inverter 4 acquires the active power Psub1 from the first slave inverter 5, the process proceeds from step S15 to step S9, and the second slave inverter 6 The same data communication process is performed.

Then, when the master inverter 4 acquires the active powers Psub1 and Psub2 stored for all the slave inverters 5 and 6 (S14: YES), the master inverter 4 returns to Step 2. The process of step S8-step S15 mentioned above is corresponded to the process b when the sudden change of solar radiation amount does not arise. That is, in FIG. 6, for example, this corresponds to the process b in the communication cycle A from the power command value update timing ta1 to ta2.

In the update timing ta1 communication cycle A of FIG. 6, the master inverter 4, if active power Psub1, Psub2 each 100kW of the previous active power Pmain of its own equipment acquired by the communication cycle and the slave inverter 5,6, processing At a, 100 kW obtained by dividing the total value 300 kW into three equal parts is calculated as the power command value Pc of the slave inverters 5 and 6, and the power command value Pc = 100 kW is simultaneously transmitted to the slave inverters 5 and 6.

  As a result, the master inverter 4 operates at 100 kW by maximum power tracking control, and the slave inverters 5 and 6 control the output power to the power command value Pc (= 100 kW). 300 kW of electric power will be supplied. Since each output power of the master inverter 4 and the slave inverters 5 and 6 is within the output capacity, the operation of the grid interconnection inverter system 1 is normal in the communication cycle A.

5 returns to step S 9 if determination of the amount of solar radiation sudden change detected "with sudden change insolation" in (S9: YES), the master inverter 4, the process proceeds to step S10, the re-calculation of the power command value Pc Do. That is, the master inverter 4 acquires the active power Pmain ′ at the current time (when “there is a sudden change in solar radiation”) from the AC power calculator 17g, and the slave acquired in the previous communication cycle with this active power Pmain ′. The effective powers Psub1 and Psub2 of the inverters 5 and 6 are summed to calculate the current output power value Ps ′ of the grid-connected inverter system 1. Then, the master inverter 4 calculates a value obtained by dividing the output power value Ps ′ into three equal parts as the power command value Pc ′ (= Ps ′ / 3) of the slave inverters 5 and 6 (S10).

Subsequently, the master inverter 4 sets the solar radiation amount sudden change detection flag F to “1” (S11), and then simultaneously transmits the recalculated power command value Pc to the slave inverters 5 and 6 (S12). The process proceeds to S13. As a result, the output power of the slave inverters 5 and 6 is changed to the power command value Pc ′. That is, the output power of the slave inverter 5, 6 step S5 had been changed to the power command value Pc, and its output power in step S 12 will be further changed to the power command value Pc '. The processes in steps S9 to S12 correspond to the process c described above.

  Returning to step S2 from step S14, as an example of processing at the update timing of the next communication cycle, the case of update timing ta2 of communication cycle B in FIG. 6 will be described. In communication cycle A, steps S2 to S5 and steps S8 and S9 are described. , S13 to S15 are performed, and the solar radiation amount sudden change detection flag F is “0”. Therefore, the processing of steps S2 to S5 is also performed in the communication cycle B.

  Accordingly, at the end timing of the process a in the communication cycle B, the output power of the master inverter 4 and the slave inverters 5 and 6 is controlled to the power command value Pc (= 100 kW), similarly to the end timing of the process a in the communication cycle A. The power system 3 is supplied with 300 kW of power, which is a sum of these output powers.

Thereafter, in the process of acquiring the active powers Psub1 and Psub2 by data communication with the slave inverter 5 or the slave inverter 6, for example, if the solar radiation amount suddenly changes at the timing of tb in FIG. 6, the processes of steps S9 to S12 are performed. Executed.

  For example, when the maximum power Pmax of the solar cell 2 suddenly decreases to 100 kW at the timing of tb, the power command value Pc of the slave inverters 5 and 6 is changed to 100 kW at that timing, so the outputs of the slave inverters 5 and 6 Each power is controlled to 100 kW. That is, the total output power Psum of the slave inverters 5 and 6 is 200 kW, which exceeds the maximum power Pmax of the solar cell 2 = 100 kW.

  On the other hand, since the total value Psum of the output power of the slave inverters 5 and 6 exceeds the maximum power Pmax of the solar battery 2, the master inverter 4 uses the shortage ΔP (= Pmax−Psum) = − 100 kW for the power system 3 To reverse the power to the solar cell 2 side to operate. Accordingly, the output power of the master inverter 4 becomes −100 kW from the timing tb, and an abnormal conversion operation is performed.

  However, the process proceeds to step S10 from the timing tb, and the processing corresponding to the processing c is performed in steps S10 to S12. Therefore, at the timing tc when the processing c ends, the output power of the master inverter 4 and the slave inverters 5 and 6 is output. Are each changed to 33.3 kW.

That is, the master inverter 4 acquires the effective power Pmain ′ = − 100 kW at the timing tb, and the effective power Pmain ′ and the effective powers Psub1 and Psub2 of the slave inverters 5 and 6 acquired in the previous communication cycle A (100 kW each). Are summed to calculate the output power value Ps ′ (= 100 kW) of the grid interconnection inverter system 1 at the timing tb.

  Then, the master inverter 4 calculates 33.3 kW obtained by dividing the output power value Ps ′ into three equal parts as the power command value Pc ′ of the slave inverters 5 and 6, and outputs the power command value Pc ′ to the slave inverters 5 and 6. While transmitting at the same time, the own device operates with the power command value Pc ′ by the maximum power tracking control. Thereby, at the timing tc when the process c ends, the output powers of the master inverter 4 and the slave inverters 5 and 6 are respectively changed to 33.3 kW.

  Returning to FIG. 5, the process returns from step S14 to step S2 after the process of steps S9 to S12. In the process at the update timing of the next communication cycle, the solar radiation amount sudden change detection flag F is set to “1”. Instead of steps S4 and S5, steps S6 and S7 are performed.

  That is, since the master inverter 4 has already transmitted the power command value Pc ′ recalculated in the previous data communication process when the process proceeds to step S6, the master inverter 4 transmits only the power storage command to the slave inverters 5 and 6, The solar radiation amount sudden change detection flag F is reset to “0” (S7), and the process proceeds to step S8.

  The processing of steps S3 to S7 will be described by taking the case of the update timing ta3 of communication cycle C in FIG. 6 as an example. In communication cycle B, the loop processing of steps S2 to S5 and steps S9 to S15 is performed. Since the sudden quantity change detection flag F is “1”, the processes of steps S3, S6, and S7 are performed in the communication cycle C.

That is, in the communication cycle C, the master inverter 4 transmits the power storage command to the slave inverters 5 and 6, and then acquires the active power Psub1 and the active power Psub2 stored in order from the slave inverter 5 and the slave inverter 6. Only. Therefore, in the communication cycle C, the output power of the master inverter 4 and the slave inverters 5 and 6 is controlled to 33.3 kW, and 100 kW of AC power is output from the grid-connected inverter system 1 to the power system 3.

Then, the update timing ta4 communication cycle D, the master inverter 4, active power before the active power Pmain of its own stored in the duration of a communication cycle C (= 33.3kW) Gets the slave inverter 5, 6 Psub1 , Psub2 (33.3 kW each) to calculate a new power command value Pc and change the output power of the slave inverters 5 and 6 to the new power command value Pc.

  In the example of FIG. 6, the sudden decrease state of the amount of solar radiation generated at the timing tb continues in the communication cycles C and D. Therefore, each output power of the master inverter 4 and the slave inverters 5 and 6 is 33 from the timing tb. Therefore, 100 kW of power is output from the grid interconnection inverter system 1 to the power grid 3.

  FIG. 7 is a diagram illustrating the input voltage (DC voltage) and output power (AC power) of each inverter when the amount of solar radiation in the grid-connected inverter system is rapidly reduced.

  In the figure, the vertical axis on the left indicates the DC voltage [V] input to the DC-AC conversion circuit 13 of each inverter 4-6, and the vertical axis on the right indicates the AC power [output from each inverter 4-6 [ kW]. I indicates the waveform of the DC voltage detected by the current sensor 8 of the master inverter 4, II indicates the waveform of AC power output from the slave inverters 5 and 6, and III indicates the AC output from the master inverter 4. A power waveform is shown. Further, tb, tc, and ta3 correspond to the timings tb, tc, and ta3 in FIG. 6, and during the period from tb to tb ′, the conversion operation of the master inverter 4 changes corresponding to the sudden change in the amount of solar radiation. Is the period of transient response.

As shown in FIG. 7, according to the grid-connected inverter system 1 according to the present embodiment, when a phenomenon in which the solar radiation amount suddenly changes at the timing tb, the master inverter 4 is effective due to the sudden change in the solar radiation amount. When the power Pmain suddenly changes, its effective power Pmain master inverter 4 (-100kW) and active power Psub1 slave inverter 5, 6 are controlled by the master inverter 4, Psub2 (each 100 kW) immediately power command value Pc by ' (33.3 kW) is calculated.

The master inverter 4 transmits the power command value Pc ′ to the slave inverters 5 and 6 to change the active power Psub1 and Psub2 of the slave inverters 5 and 6 to the power command value Pc ′, Since the operation is performed at Pc ′ by the power follow-up control, the period during which the master inverter 4 may perform an abnormal conversion operation or may stop can be extremely shortened.

  For example, in this embodiment, the communication cycle of the power control of the master inverter 4 is about 60 ms, but the master inverter 4 and the master inverter 4 have a period during which there is a possibility that the master inverter 4 performs an abnormal conversion operation or eventually stops. The time required for communication time with one slave inverter (20 ms) can be suppressed.

  In addition, although this embodiment demonstrated the grid connection inverter system 1 which consists of one master inverter and two slave inverters, the number of slave inverters which comprise the grid connection inverter system 1 is three or more. It may be.

  In a large-scale grid-connected inverter system having several tens of slave inverters, the communication cycle becomes long (may be on the order of seconds), and therefore the master inverter may perform an abnormal conversion operation accordingly. However, if the present invention is applied, the period can be suppressed to a millisecond order period even in a large-scale grid-connected inverter system, and the effect can be effectively exhibited.

  Further, in the present embodiment, the function of recalculating the power command value at the time of periodic calculation of the power command value and the sudden change in the amount of solar radiation is provided in the control unit 17 of the master inverter 4, but as shown in FIG. You may make it provide in the control apparatus 18 provided outside the master inverter 4 and the slave inverters 5 and 6. FIG.

In the configuration of FIG. 8, the control device 18 is connected to the control units 17 , 17 ′, 17 ′ of the master inverter 4 and the slave inverters 5, 6 by the communication line 7. The control device 18 performs data communication with the master inverter 4 and the slave inverters 5 and 6 at a predetermined cycle T, receives the operation state of each inverter, transmits the operation command, calculates the power command value Pc, and outputs the power. The command value Pc and the power saving command are transmitted to the master inverter 4 and the slave inverters 5 and 6 simultaneously. Thereby, the output power of the master inverter 4 and the slave inverters 5 and 6 is controlled to the power command value Pc at a predetermined cycle T.

The master inverter 4 monitors fluctuations in the solar radiation amount of the solar cell 2. When a sudden change in the solar radiation amount is detected, the master inverter 4 interrupts the control device 18 to detect the detected information and the effective power Pmain at the time when the solar radiation amount suddenly changes. Is transmitted to the control device 18. As a result, the control device 18 immediately recalculates the power command value Pc ′, and transmits the power command value Pc ′ to the master inverter 4 and the slave inverters 5 and 6 simultaneously. Thereby, the output power of the master inverter 4 and the slave inverters 5 and 6 is changed to the power command value Pc ′ in a very short time after the sudden change of the solar radiation amount.

  In the above explanation, the solar radiation amount fluctuation monitoring function and the power command value Pc calculation function of the solar cell 2 are provided in the master inverter 4, and when the solar radiation amount suddenly changes, the control device 18 is interrupted. Although the processing for sudden change in the amount of solar radiation is performed, these functions may be provided in the control device 18 so that if there is a sudden change in the amount of solar radiation without interrupting the control device 18, it is possible to take immediate action. .

In this case, when the amount of solar radiation of the solar cell 2 sharply decreases and the maximum power Pmax decreases rapidly, the control device 18 detects this, and the active power acquired from the master inverter 4 and the slave inverters 5 and 6 at the time of detection. The power command value Pc ′ is recalculated from Pmain, Psub1, and Psub2 and is simultaneously transmitted to the master inverter 4 and the slave inverters 5 and 6.

Therefore, in the master inverter 4, the active power Pmain is immediately changed to the power command value Pc ′ transmitted from the control device 18 by the maximum power tracking control, and in the slave inverters 5 and 6, the active powers Psub1 and Psub2 are changed from the control device 18. The power command value Pc ′ to be transmitted is immediately changed.

  Moreover, although this embodiment demonstrated the example applied to the electric power generation system using a solar cell, this invention can be applied also to the distributed power supply system using the other direct-current power source from which direct-current power generation output fluctuates. it can.

In short, the present invention periodically calculates the next power command value Pc from the output power values of a number of slave inverters acquired in the previous data communication, and transmits the power command value Pc to the number of slave inverters. in the configuration for changing the output power value of the slave inverter to the power command value Pc, the power command value Pc calculated using their output power value for acquisition timing of the output power values of the master inverter and a number of slave inverter The present invention can be widely applied to a configuration in which a time lag of a certain period occurs in the change timing of the output power value of the master inverter and a large number of slave inverters.

It is a figure which shows the whole structure of the grid connection inverter system which concerns on this invention. It is a figure which shows the general output electric power-output voltage characteristic of a solar cell. It is a block diagram which shows the internal structure of the control part of a master inverter. It is a block diagram which shows the internal structure of the control part of a slave inverter. It is a flowchart which shows the control procedure of the output electric power to the electric power grid | system of the grid connection inverter system in a master inverter. It is a figure which shows the content of the data communication between a master inverter and two slave inverters. It is a figure which shows the input voltage (DC voltage) and output electric power (AC electric power) of each inverter when the amount of solar radiation in the grid connection inverter system which concerns on this invention falls rapidly. It is a figure which shows the modification of the grid connection inverter system which concerns on this invention. It is a block diagram which shows an example of the conventional grid connection inverter system. It is a figure which shows the content of the data communication between the slave machines in the conventional grid connection inverter system. It is a flowchart which shows the procedure of the data communication with the slave machine of the master machine in the conventional grid connection inverter system. It is a figure which shows the input voltage (DC voltage) and output electric power (AC electric power) of each inverter when the amount of solar radiation in the conventional grid connection inverter system reduces rapidly.

DESCRIPTION OF SYMBOLS 1,1 'System interconnection inverter system 2 Solar cell 3 Electric power system 4, 5, 6 Inverter 7 Communication line 8-10 Current sensor 11, 12 Voltage sensor 13 DC-AC conversion circuit 14 Filter circuit 15 Transformer 16 Disconnection contactor 17 Control unit 17a DC power calculation unit 17b Maximum power tracking control unit 17c Voltage control unit 17d Current control unit 17e Command value calculation unit 17f PWM signal generation unit 17g AC power calculation unit 17h Power control unit 17i Solar radiation amount variation detection unit 17j Power command value Arithmetic unit 17k Communication control unit 18 Control device