JP2017051099A - Power conditioner and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably continue an operation even at occurrence of momentary voltage drop of a commercial power system, and to quickly restore output before the occurrence of the momentary voltage drop when the commercial power system is restored.SOLUTION: A power conditioner 1 includes: a DC/DC converter 11 for converting voltage of a DC power to be close to constant voltage; and a control section 14 for controlling the DC/DC converter 11. At occurrence of momentary voltage drop of a commercial power system 15, the control section 14 sets an input current target value of the DC/DC converter 11 on the basis of degree of drop of the voltage of the commercial power system 15 and magnitude of input power before the occurrence of the momentary voltage drop of the DC/DC converter 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conditioner and a control method thereof.

  Conventionally, power conditioners are required to take measures against an instantaneous voltage drop (hereinafter also referred to as “instantaneous drop”) of a commercial power system (hereinafter also referred to as “system”). Specifically, in order to prevent unnecessary disconnection of the power conditioner connected to the system, if the voltage drop time of the instantaneous drop is within a certain time, the power conditioner is not disconnected and the operation is continued. Or it is calculated | required to set it as the system which can reset automatically (for example, refer nonpatent literature 1).

  With reference to FIG. 8, the operation when a sag occurs during operation in the conventional power conditioner 2 will be described. In general, it is known that a power conditioner for photovoltaic power generation performs maximum power point tracking (MPPT) control in the control unit 24 in order to extract the input power from the solar cell to the maximum. (For example, see Patent Document 1 and Patent Document 2).

  The control unit 24 adjusts the input voltage of the solar cell by controlling the DC / DC converter 21. By performing MPPT control with the DC / DC converter 21, the maximum power is always obtained from the solar cell 20 regardless of the state of the system 25, and this is supplied to the system 25 by the inverter 23 using the system voltage value and output current value. There is a reverse current. Therefore, when an instantaneous drop in the system 25 occurs, the output current increases rapidly in proportion to the degree of decrease in the system voltage.

  As an example, let us consider a situation where an instantaneous drop occurs for 200 seconds from 40V to t1 seconds when a reverse power flow occurs at a system voltage of 200V and an output current of 20A. Due to the MPPT control of the DC / DC converter 21, the inverter 23 tries to output 20A to the system 25 even after the occurrence of a sag. In this case, the output power P1 before the voltage drop is P1 = 20A × v1 = 20A × 200V = 4000W. Due to the action of the MPPT control, the power P1 is continuously output even after the instantaneous drop. Therefore, the output power P2 after the voltage drop is I2 = 100A from P2 = 4000W = I2 × 40V, and the power conditioner 2 tries to output 100A when the voltage drop occurs.

  As described above, when a voltage sag occurs, the output current of the power conditioner 2 increases. However, since the upper limit of the actual output current is regulated by the rated current of the hardware, the operation is usually stopped as an output overcurrent. In addition, by regulating the output current, energy of the input power that cannot be output is accumulated in the smoothing capacitor 22, and the voltage between the terminals of the smoothing capacitor 22 (internal DC voltage) increases rapidly. In this case, in order to protect the overvoltage of the smoothing capacitor 22, the operation is also stopped as an overvoltage abnormality.

  In recent years, with the spread of solar power generation, power conditioners are becoming widespread. As further spreads in the future, the influence of power conditioners introduced in large quantities on the system will increase. In particular, there is a risk that the system will become unstable if the power conditioner is shut down all at once when a system sag occurs, or if the system does not resume operation for a while after recovery from the sag. . For this reason, power conditioners that will be developed in the future are newly required to be able to operate stably even during a sag and to quickly return to the output before the sag when the sag recovers (for example, Non-Patent Document 2).

  As an operation stabilization method that quickly restores the output when the voltage drop recovers, output control is performed so that the output current during the voltage drop becomes the value before the voltage drop occurs, and the internal DC voltage (voltage across the terminals of the smoothing capacitor) There is known an automatic control method in which the DC input current is changed so as to be a preset target voltage (see, for example, Patent Document 3). In this method, it is possible to continue the operation by suppressing both the output overcurrent and the overvoltage of the smoothing capacitor due to the system voltage drop.

  Further, a method of limiting the upper limit value of the input current is known in order to reduce the output power in accordance with the voltage drop degree of the system voltage (see, for example, Patent Document 4).

Japanese Patent No. 3426947 JP-A-2005-73321 JP 2012-55036 A JP 2008-228494 A

"System interconnection regulations JEAC 9701-2006", NEC Corporation "Individual testing methods for grid interconnection protection devices for multi-unit photovoltaic power generation systems, etc. JETGR0003-4-1.0 (2011)", Institute for Electrical Safety and Environment

  Since the smoothing capacitor mounted on the power conditioner is desired to have a relatively large capacity in consideration of capacity loss due to secular change, the control delay time becomes large. In this case, in order to appropriately control the internal DC voltage from the input current, automatic control performance is required. As the first performance of automatic control, it is necessary to increase the control gain to obtain the required tracking performance. In particular, in a transient state such as a system sudden change, gain selection different from the steady state may be performed. When the delay time is large, the proportional gain and integral gain are generally increased, but on the other hand, increasing the gain increases the risk of oscillation of the control loop. It becomes difficult.

  Further, as the second performance of the automatic control, it is necessary to obtain a response performance by increasing the control loop cycle. For this purpose, a program is operated at high speed by a control means having a somewhat high specification (here, a CPU to which a storage device is connected). For this reason, use of an expensive CPU increases the product price. For example, it is difficult to realize the control disclosed in Patent Document 3 with an inexpensive power conditioner using inexpensive control means (CPU).

  Here, home power conditioners for photovoltaic power generation are roughly classified into two types when focusing on the connection method with the solar battery. First, a plurality of solar cell modules connected in series to increase the output voltage (hereinafter referred to as “solar cell string”) are connected in parallel in a connection box or the like, and collected in one system. In this manner, the direct current is increased and input to the power conditioner.

  The second is a form in which a plurality of solar cell strings are directly input to the power conditioner. A power conditioner having a plurality of DC power input units and a plurality of DC / DC converters is generally referred to as a multi-string input power conditioner. In recent years, multi-string input power conditioners with flexible solar panel installation have become widespread.

  The methods disclosed in Patent Document 3 and Patent Document 4 can be applied when the DC power is only one input to the power conditioner, but is applicable to a multistring input power conditioner in which the DC power is a plurality of inputs. There is a problem that you can not.

  An object of the present invention made in view of such circumstances is that in a power conditioner, the operation can be stably continued even when an instantaneous voltage drop of the commercial power system occurs without increasing the cost by a simple control method, and the commercial power An object of the present invention is to provide a power conditioner that can quickly return to the output before the instantaneous voltage drop when the system is restored.

A power conditioner according to an embodiment of the present invention is:
A power conditioner having a DC power input,
A DC / DC converter for converting the voltage of the DC power so as to approach a constant voltage;
A controller for controlling the DC / DC converter,
When the instantaneous voltage drop of the commercial power system occurs, the control unit uses the degree of reduction of the voltage of the commercial power system and the magnitude of the input power before the occurrence of the instantaneous voltage drop of the DC / DC converter. Set the input current target value.

Furthermore, in the power conditioner according to an embodiment of the present invention,
An inverter that converts the DC voltage converted by the DC / DC converter into AC;
The control unit performs control to lower the output current target upper limit value from the inverter when the instantaneous voltage drops in the commercial power system, thereby reducing the output current target value from the value before the occurrence of the instantaneous voltage drop. I do.

Furthermore, in the power conditioner according to an embodiment of the present invention,
A smoothing capacitor for smoothing the DC voltage converted by the DC / DC converter and outputting the same to the inverter;
The controller monitors the voltage between the terminals of the smoothing capacitor when the instantaneous voltage of the commercial power system drops, and reduces the input current target value when the voltage between the terminals exceeds a predetermined threshold. .

Moreover, the control method of the power conditioner which concerns on one Embodiment of this invention is the following.
A control method for a power conditioner comprising a DC / DC converter for converting a voltage of DC power so as to approach a constant voltage,
When an instantaneous voltage drop of the commercial power system occurs, the input current target value of the DC / DC converter is calculated using the degree of voltage drop of the commercial power system and the magnitude of the input power before the occurrence of the instantaneous voltage drop of the DC / DC converter. Including setting.

  According to the present invention, in the power conditioner, without increasing the cost by a simple control method, it is possible to continue stably even when the instantaneous voltage drop of the commercial power system, and at the time of recovery of the commercial power system, The output before the instantaneous voltage drop can be quickly restored.

It is a block diagram which shows the structural example of the power conditioner which concerns on one Embodiment of this invention. It is a functional block diagram of the control part of the power conditioner which concerns on one Embodiment of this invention. It is a flowchart which shows the control action of the control part of the power conditioner which concerns on one Embodiment of this invention. It is a schematic diagram which shows the control at the time of normal operation of the control part of the power conditioner which concerns on one Embodiment of this invention. It is a figure which shows IV curve of the solar cell which carried out the linear approximation. It is a schematic diagram which shows the control immediately after generation | occurrence | production of the instantaneous drop of the control part of the power conditioner which concerns on one Embodiment of this invention. It is a schematic diagram which shows the control in the time of generation | occurrence | production of the instantaneous drop of the control part of the power conditioner which concerns on one Embodiment of this invention. It is a block diagram which shows the structural example of the conventional power conditioner. It is a figure which shows the example of the instantaneous drop generation | occurrence | production of a commercial power system.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration example of a power conditioner according to an embodiment of the present invention. In the multi-string input type power conditioner 1 of the present embodiment, the number of input solar cell strings 10 is three (10-1, 10-2, 10-3). Is not limited to three. The power conditioner 1 includes a DC / DC converter 11, a smoothing capacitor 12, an inverter 13, and a control unit 14.

  The DC / DC converter 11 (11-1, 11-2, 11-3) boosts the voltage input from the solar cell string 10 to make it constant.

  The smoothing capacitor 12 smoothes the DC voltage boosted by the DC / DC converter 11.

  The inverter 13 converts the direct current voltage smoothed by the smoothing capacitor 12 into alternating current, and is connected to the commercial power system 15. The AC voltage in the commercial power system 15 is a voltage having an effective value of single phase 100 V and a frequency of 50 Hz or 60 Hz in Japan.

  The control unit 14 controls the operation of the DC / DC converter 11 and the inverter 13. When a sag is detected, control is performed so as to switch from a normal operation to an operation for a sag (hereinafter referred to as “middle sag operation”).

  FIG. 2 is a diagram illustrating functional blocks of the control unit 14. As shown in FIG. 2, the control unit 14 includes an MPPT control unit 141, an inverter control unit 142, a voltage sag detection unit 143, a voltage sag converter control unit 144, and a voltage sag inverter control unit 145. . The control unit 14 performs normal operation by the MPPT control unit 141 and the inverter control unit 142 when the voltage drop is not detected by the voltage drop detection unit 143, and when the voltage drop is detected by the voltage drop detection unit 143. The operation during the sag is performed by the sag converter control unit 144 and the sag inverter control unit 145. The control unit 14 may be configured by hardware, or a function may be realized by causing a CPU to execute a program.

  FIG. 3 is a flowchart showing the control operation of the control unit 14. Hereinafter, the control operation of the control unit 14 will be described with reference to FIG.

(Control during normal operation)
The control unit 14 controls each DC / DC converter 11 so as to extract the input power from each solar cell string 10 to the maximum by the MPPT control unit 141 during normal operation (when no instantaneous drop occurs). (Step S11).

  FIG. 4 is a schematic diagram illustrating control of the MPPT control unit 141 during normal operation of the control unit 14. As shown in FIG. 4, the input power is calculated from the input current Ipv and the input voltage Vpv of the solar cell string 10, the input current target value Ipvtgt is determined so that the input power becomes maximum, and the input current Ipv is the input current target. A gate signal for controlling the DC / DC converter 11 is generated so as to approach the value Ipvtgt. The MPPT control has a voltage type and a current type. In the present embodiment, the current type is used, and therefore the target current command is used.

  During normal operation, the control unit 14 determines the output current target value Iactgt from the difference between the inter-terminal voltage (internal DC voltage) Vdc of the smoothing capacitor 12 and the internal DC voltage target value Vdctgt by the inverter control unit 142, A gate signal for controlling the inverter 13 is generated so that Iac approaches the output current target value Iactgt (step S12).

  The control unit 14 continuously monitors the voltage of the commercial power system 15 (hereinafter also referred to as “system voltage”) by the voltage sag detection unit 143, and determines whether or not a voltage sag has occurred (step S20). In addition, since it is used for control during a sag, sensor value information and a control state immediately before the sag are temporarily recorded. The method for detecting the instantaneous drop is not particularly limited, but it is desirable to detect the voltage as soon as possible, for example, by monitoring the system voltage in a half cycle or less. If the detection of the instantaneous drop is delayed, the output power is reduced in a state where the input power is not reduced, so that the risk of the operation being stopped due to the overvoltage of the smoothing capacitor 12 is increased. When a sag is detected in step S20, the control unit 14 stops the normal operation and switches the control to the operation during the sag.

(Control immediately after the instantaneous drop occurs)
In starting the operation during the sag, the control unit 14 first performs a procedure immediately after the occurrence of the sag. In order to suppress the output overcurrent, the control unit 14 reduces the output current target upper limit value Iactgt_max from the inverter 13 by the inverter control unit 145 at the time of a sag, thereby reducing the output current target value Iactgt to a value before the occurrence of the sag. (Step S33). The output current target upper limit value Iactgt_max is a rated current that is limited by hardware components during normal operation, but during an instantaneous drop, this output current target upper limit value Iactgt_max is reduced to limit the output current, thereby reducing the output overcurrent. To prevent. Then, the control unit 14 drives the gate of the inverter 13 so that the output current Iac becomes an output current command by the inverter control unit 145 at the time of a sag.

  For example, in the case of a 4 kW power conditioner, if the output current target upper limit value Iactgt_max during normal operation is 20 A and the output current target immediately before the occurrence of the sag is 10 A, the output current target upper limit value Iactgt_max is The output current target immediately before the occurrence of the instantaneous drop is limited to 10A. Here, the output current target value Iactgt during the voltage sag is not fixed to 10A, but the output current target upper limit value Iactgt_max is limited, so that the normal operation can be smoothly restored to the recovery from the voltage sag.

  Next, regarding the control of the DC / DC converter 11, the control unit 14 first stops the MPPT control by the MPPT control unit 141 (step S31). Then, the input current Ipv is quickly reduced according to the instantaneous drop level. The output current Iac has already been limited to the output current target upper limit value Iactgt_max. By reducing the input power to the smoothing capacitor 12 and balancing the input / output balance of the power conditioner 1, the smoothing capacitor 12 The purpose is to avoid excessive voltage rise. Therefore, the controller 14 drives the gate signal of the DC / DC converter 11 and moves the input operating point so that the input current Ipv becomes the input current command by the instantaneous voltage drop converter control unit 144.

  Here, in the method disclosed in Patent Document 3, a control loop for adjusting the input current Ipv is operated in order to control the internal DC voltage to a preset target value simultaneously with the occurrence of a sag. In this configuration, the internal DC voltage control loop and the input current control loop constitute feedback control, respectively, and the determination of the input current target value Ipvtgt immediately after the instantaneous drop depends on the performance of the control loop. As described above, there is a problem in rapidly reducing the input current Ipv by feedback control as in the method disclosed in Patent Document 3. Therefore, the control unit 14 of the present invention uses the converter control unit 144 at the time of a sag to calculate the input current target value Ipvtgt immediately after the occurrence of the sag, not the calculation by feedback control, but the voltage before and after the sag and the input power just before the sag. The input current command to the DC / DC converter 11 is immediately determined immediately after the instantaneous drop (step S32).

  Specifically, the input current target value Ipvtgt during the sag is determined for a plurality of DC / DC converters 11 as follows. When the system voltage drops to 1 / N times due to the instantaneous drop, the output current Iac of the power conditioner 1 becomes N times as described above. In the present invention, since the output current target upper limit value Iactgt_max during the voltage sag is set to the output current value before the voltage sag, the output current Iac is decreased before the voltage sag when the system voltage decreases to 1 / N times due to the voltage sag. If the value is maintained, the output power of the power conditioner 1 is reduced to 1 / N times. Therefore, in order to prevent the voltage of the smoothing capacitor 12 from rising excessively, the input power is reduced to 1 / N times as the output power is reduced to 1 / N times. Strictly speaking, considering loss such as deterioration in conversion efficiency due to a decrease in output, it is not 1 / N times, but high-speed processing is possible by simplifying the calculation.

  In order to accurately reduce the input power to 1 / N times, it is necessary to recognize the IV curve of the solar cell. However, the IV curve is constantly changing due to solar radiation and temperature, and when the solar cell is shaded, irregularities are formed on the IV curve, so it is difficult to grasp the IV curve during operation in real time. Since the present invention aims to be realized even with an inexpensive low-spec CPU, the solar cell characteristics are simplified to provide a linear approximation.

  FIG. 5 is a diagram showing an IV curve of a solar cell approximated by a straight line. Immediately before the voltage sag, the input operating point is normally at the optimum operating point (MPP) by the action of MPPT control. I want to reduce the input power to 1 / N times when an instantaneous drop occurs in this state. Here, considering the IV characteristics of the solar cell by linear approximation as shown in FIG. 5, in order to make the input power 1 / N times, the input voltage Vpv remains constant and the input current Ipv is 1 / N times. It may be reduced to. From this, the input current command during the instantaneous drop is determined. As a premise, it is assumed that there is no change in solar radiation or temperature in a short time during the sag, and the value of the commercial power system 15 is used by temporarily recording the input current Ipv of each solar cell string 10 before the sag. Calculate the total input current target value based on the degree of voltage drop. Then, the total input current target value is distributed according to the magnitude of the input power immediately before the occurrence of the instantaneous drop, and the current distribution value Ipvtgt0 is obtained by the following equation.

Ipvtgt0 = (1 / N) × Ipv
Ipvtgt0-n = (Ppv-n / Ppv-all) × Ipvtgt0
Here, Ipv is the total input current immediately before the momentary drop, and is usually the maximum input current due to the MPPT operation. Ipvtgt0 is the total input current target value during the instantaneous drop. Ipvtgt0-n is the current distribution value of the solar cell string 10-n, Ppv-n is the input power of the solar cell string 10-n immediately before the voltage drop, and Ppv-all is the entire input immediately before the voltage drop. Ipv-n is an input current immediately before the instantaneous drop of the solar cell string 10-n.

  In the case of the three-string input as in the present embodiment, the current distribution value Ipvtgt0-1 of the solar cell string 10-1, the current distribution value Ipvtgt0-2 of the solar cell string 10-2, and the instantaneous drop of the solar cell string 10-3 The current distribution value Ipvtgt0-3 is obtained, and is set as the input current target value Ipvtgt of each solar cell string 10. In the sag converter control unit 144, the input current Ipv of each solar cell string 10 is reduced according to the current distribution value Ipvtgt0 which is the input current target value Ipvtgt, so that the input power of the power conditioner 1 as a whole becomes 1 / It can be quickly reduced to N times.

  FIG. 6 is a schematic diagram showing the control of the converter controller 144 at the time of a sag immediately after the occurrence of a sag by the controller 14. As shown in FIG. 6, a current distribution value as an input current target value Ipvtgt is obtained from the system voltage value before and after the occurrence of the sag and the input current Ipv and input voltage Vpv (input power) of the solar cell string 10 immediately before the occurrence of the sag. Ipvtgt0 is determined, and a gate signal for controlling each DC / DC converter 11 is generated so that the input current Ipv approaches the input current target value Ipvtgt.

(Control of operation during low voltage)
For the control of the inverter 13, the control unit 14 continues the output current target upper limit value Iactgt_max determined in step S33 by the instantaneous voltage drop inverter control unit 145 (step S42).

  In the control immediately after the occurrence of the voltage sag, the output current Iac is limited to be equal to or less than the value immediately before the voltage sag, and the input current Ipv is reduced to the input target value Ipvtgt0 determined by calculation in order to balance the power with it. As a result, it is possible to avoid the operation stop due to the output overcurrent and the overvoltage of the smoothing capacitor 12. Ideally, during the sag, the output current and the input power are balanced with the input current target, and the voltage of the smoothing capacitor 12 is maintained at a constant level. However, the input current target value Ipvtgt0 is a simplified approximation calculation. As a result, the power is not always balanced on the actual IV curve. When the input current Ipv is larger than the output current Iac, the internal DC voltage Vdc of the smoothing capacitor 12 gradually increases, and eventually the operation is stopped at an overvoltage. On the other hand, when the input current Ipv is small with respect to the output current Iac, the internal DC voltage Vdc gradually decreases and becomes lower than the voltage required for generating the AC waveform (for example, if the system voltage is 200V, it is at least 282V). If the voltage is insufficient, the operation will be stopped.

  For example, when a smoothing capacitor 12 having a withstand voltage of 400 V is used and the internal DC voltage target value Vdctgt is controlled to 330 V during normal operation and the overvoltage level is set to 390 V, the internal DC voltage is set to 330 V of the internal DC voltage target value Vdctgt. When Vdc is 300 V or less, it is determined that the control is abnormal because the voltage is insufficient.

  Therefore, during the sag, the control unit 14 causes the sag converter control unit 144 to decrease the input current target value Ipvtgt when the internal DC voltage Vdc becomes equal to or higher than the internal DC voltage threshold Vth (eg, 360 V). (Step S41). For example, when the internal DC voltage Vdc is less than the internal DC voltage threshold Vth, the correction input current target value Ipvtgt1 is set to the maximum input current value (for example, 10A) allowed by the solar cell string 10, and the internal DC voltage Vdc is internal. When the direct current voltage threshold value Vth is exceeded, the current value is automatically controlled so as to gradually decrease from the maximum input current value toward 0 A. Then, the sag converter control unit 144 compares the correction input current target value Ipvtgt1 with the current distribution value Ipvtgt0 obtained by calculation immediately after the sag and sets the smaller one as the input current target value Ipvtgt.

  When the correction input current target value Ipvtgt1 is smaller than the current distribution value Ipvtgt0, the input power is less than the output power, and the internal DC voltage Vdc gradually decreases. If the internal DC voltage Vdc decreases to less than 360 V, the correction input current target value Ipvtgt1 increases stepwise up to the maximum input current value, and this time, the current distribution value Ipvtgt0 becomes smaller. Then, the instantaneous voltage drop converter control unit 144 selects the current distribution value Ipvtgt0 as the input current target value Ipvtgt again.

  This voltage control loop is an auxiliary position for correcting the input current target value Ipvtgt, and the current distribution value Ipvtgt0 obtained by calculation immediately after the voltage drop is used as the input current target value Ipvtgt during the voltage drop. Therefore, the control loop does not require high responsiveness and can be easily realized even with a low-spec CPU.

  On the other hand, there is no need to particularly consider the voltage shortage of the internal DC voltage Vdc in the present embodiment. If it takes half a period of time when a voltage drop occurs during monitoring of the system voltage and the program determines that the voltage drop is instantaneous, the input power is accumulated in the smoothing capacitor 12 because the input power is greater than the output power during that half period. The internal DC voltage Vdc increases. Since the internal DC voltage Vdc has already risen from several volts to several tens of volts before the start of the voltage sag operation, the internal DC voltage Vdc is not expected to drop significantly during the very short time of the voltage sag. It is omitted in the form. When taking measures against voltage shortage, a control loop for increasing the input current target value may be incorporated when the internal DC voltage Vdc decreases.

  FIG. 7 is a schematic diagram showing the control of the converter controller 144 at the time of a sag during the occurrence of a sag by the controller 14. As shown in FIG. 7, the converter controller 144 at the time of sag comparison compares the input current target value Ipvtgt1 obtained from the internal DC voltage Vdc and the internal DC voltage threshold Vth with the input current target value Ipvtgt0 determined immediately after the occurrence of the sag. Thus, a gate signal is generated for the DC / DC converter 11 so that the input current Ipv approaches the smaller value.

(Control during instantaneous low recovery)
The control unit 14 uses the voltage sag detector 143 to monitor the system voltage during the voltage sag and detect recovery from the voltage sag (step S50). Then, the control part 14 complete | finishes operation during a sag and switches to normal operation. The detection method of the instantaneous drop recovery is not particularly limited, but detection as early as possible is desirable, such as monitoring the system voltage in half a cycle or less. If detection of this instantaneous drop recovery is delayed, the output current remains limited to the value before the occurrence of the instantaneous drop, and the high-speed recovery performance required in the future cannot be satisfied.

  When returning to the normal operation, the control unit 14 ends the voltage limiting control of the internal DC voltage Vdc by the instantaneously low converter control unit 144. At the same time, the control unit 14 restarts the MPPT control by the MPPT control unit 141 (step S61). Further, the control unit 14 returns the output current target upper limit value Iactgt_max to the value at the time of the normal operation by the instantaneous voltage drop inverter control unit 145 (step S62).

  As described above, the control unit 14 of the power conditioner 1 according to the present invention calculates the overall input current target value based on the voltage decrease degree of the commercial power system 15 when the commercial power system 15 has an instantaneous voltage decrease. The distribution value that is distributed according to the magnitude of the input power before the occurrence of the instantaneous voltage drop of each DC / DC converter is defined as the input current target value Ipvtgt0 of each DC / DC converter. Therefore, according to the present invention, in the power conditioner, the operation can be continued by an inexpensive method without stopping the operation when the instantaneous voltage drops. In addition, since the input current Ipv of only one of the plurality of solar cell strings is not decreased when the instantaneous voltage is decreased, the input current Ipv of each solar cell string can be decreased according to the input power. When the power system 15 is restored, the time required for the respective DC / DC converters to return to the optimum operating point before the instantaneous drop can be made uniform, and as a result, the output before the instantaneous voltage drop can be quickly returned.

  Further, the control unit 14 reduces the output current target value Iactgt from a value before the occurrence of the instantaneous voltage drop by reducing the output current target upper limit value Iactgt_max from the inverter 13 when the commercial power system 15 has an instantaneous voltage drop. Let As a result, output overcurrent can be prevented, and normal operation can be smoothly restored upon recovery from a sag.

  In addition, the power conditioner 1 includes a smoothing capacitor 12 that smoothes the DC voltage converted by the DC / DC converter 11 and outputs the smoothed voltage to the inverter 13. The inter-terminal voltage (internal DC voltage) Vdc is monitored, and when the internal DC voltage Vdc exceeds a predetermined threshold, the input current target value is decreased. For example, when the internal DC voltage Vdc is less than a predetermined threshold Vth, the maximum input current value of the DC power generated by the solar cell string 10 is used, and when the internal DC voltage Vdc is equal to or higher than the predetermined threshold Vth. The correction input current target value Ipvtgt1, which is a value stepwise reduced from the maximum input current value, is compared with the input current target value Ipvtgt0, and the smaller one is set as the final input current target value. As a result, it is possible to prevent the smoothing capacitor 12 from being stopped due to overvoltage and voltage shortage.

  Although the power conditioner and the control method thereof according to the above-described embodiments have been described as typical examples, it is obvious to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Power conditioner 10 Solar cell string 11 DC / DC converter 12 Smoothing capacitor 13 Inverter 14 Control part 15 Commercial power system 141 MPPT control part 142 Inverter control part 143 Instantaneous voltage drop detection part 144 Instantaneous voltage converter control part 145 Instantaneous voltage drop inverter Control unit

Claims (4)

A power conditioner having a DC power input,
A DC / DC converter for converting the voltage of the DC power so as to approach a constant voltage;
A controller for controlling the DC / DC converter,
When the instantaneous voltage drop of the commercial power system occurs, the control unit uses the degree of reduction of the voltage of the commercial power system and the magnitude of the input power before the occurrence of the instantaneous voltage drop of the DC / DC converter. A power conditioner that sets an input current target value. An inverter that converts the DC voltage converted by the DC / DC converter into AC;
The control unit performs control to lower the output current target upper limit value from the inverter when the instantaneous voltage drops in the commercial power system, thereby reducing the output current target value from the value before the occurrence of the instantaneous voltage drop. The power conditioner according to claim 1, wherein: A smoothing capacitor for smoothing the DC voltage converted by the DC / DC converter and outputting the same to the inverter;
The controller monitors the voltage between the terminals of the smoothing capacitor when the instantaneous voltage of the commercial power system drops, and reduces the input current target value when the voltage between the terminals exceeds a predetermined threshold. The power conditioner of Claim 1 or 2 characterized by the above-mentioned. A control method for a power conditioner comprising a DC / DC converter for converting a voltage of DC power so as to approach a constant voltage,
When an instantaneous voltage drop of the commercial power system occurs, the input current target value of the DC / DC converter is calculated using the degree of voltage drop of the commercial power system and the magnitude of the input power before the occurrence of the instantaneous voltage drop of the DC / DC converter. A method for controlling an inverter, comprising a setting step.

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