JP2010231456A - Power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain the output of a solar cell near the maximum power point while adopting configurations to intermittently instruct the operation of a power converter by communication. <P>SOLUTION: A DC power supply device 10 includes a power converter 13 for power-converting the output of a solar cell 11, and configured to supply a DC power to a main power supply device 30 which outputs a constant voltage and through a DC supply line Ld to load equipment 40. A power supply management part 20 intermittently acquires the output voltage and output currents of the solar cell 11 by communication, and intermittently applies a current command value to adjacent the output currents of the power converter 13 by communication. Furthermore, the power supply management part 20 includes: a main search part 25 for searching a voltage corresponding to the maximum output point of the solar cell 11 within a specific retrieval range; and a voltage maintaining part 26 for using the voltage searched by the main search part 25 for a target voltage, and for applying a current command value set to maintain the output voltage of the solar cell 11 to the target voltage to the DC power supply device 10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power supply system that supplies DC power to a load from a DC power supply device that includes a power converter that converts power output from a solar cell.

  In general, it is known that in a panel-like solar cell installed on a house roof or the like, current-voltage characteristics fluctuate mainly due to the amount of solar radiation (intensity of solar radiation) and the temperature of the solar cell (panel temperature). Therefore, when supplying the power generated by the solar cell to the load, power conversion is performed using a power converter such as an inverter or a DC / DC converter, and the output voltage and output frequency of the power converter are required specifications of the load. The operation of the power converter is controlled to meet the above. In addition, the power converter is provided with an MTTP (Maximum Power Point Tracking) function so that the maximum power can always be obtained according to the solar radiation intensity and the panel temperature of the solar cell. Many (see, for example, Patent Document 1).

  Patent Document 1 discloses a configuration in which the power of a solar cell is converted into DC power by a power converter, and this DC power is supplied to a load and a buffer secondary battery. A technique is described that pays attention to the fact that the slope of the tangent of the current-voltage characteristic becomes −45 degrees when the output power of the battery reaches the maximum value. That is, the output voltage and output current of the solar cell are detected, and the on-duty of the switching element provided in the power converter is set so that the slope of the tangent of the current-voltage characteristic becomes −45 degrees based on the detected voltage and the detected current. By determining the (time ratio), the MTTP function is realized.

  Furthermore, Patent Document 1 discloses a technique for controlling the operation of a power converter, an output of a power converter as a conventional technique for realizing an MTTP function that maximizes the product of the output current and output voltage of a solar cell. A technique for controlling the operation of the power converter so as to maximize the voltage or output current and a technique for controlling the operating point by measuring the panel temperature are described.

Japanese Patent No. 3394996

  By the way, when supplying the electric power of a solar cell to a load, a technique for converting to AC power using a device called a power controller or a power conditioner and performing system interconnection with an AC system such as a commercial power source has been conventionally known. Yes. When grid connection is performed, when surplus power is generated exceeding the power consumed by the solar battery, the surplus power is reversely flowed through the grid to sell power to the power company. In many cases.

  In other words, even if surplus power is generated while controlling the operation of the power converter (inverter) so that the output power of the solar cell is always maximized, it is possible to use surplus power without waste by selling electricity. It has become. However, if a power outage occurs on the grid side, the system is separated by opening the disconnect switch provided between the power converter and the grid, and the current generated by the solar cell when the grid side malfunctions This prevents it from flowing to the wiring on the side. Also, in the system separation state, it is difficult to balance the power generated by the solar cell with the power required by the load, and it is difficult to maximize the output power of the solar cell. In many cases, the supply to the load is stopped.

  On the other hand, when supplying DC power to the load as in the technique described in Patent Document 1 described above, a secondary battery is provided on the output side of the power converter (DC / DC converter), and surplus power is It is considered that the fluctuation of the output power of the power converter is buffered by storing in the secondary battery.

  When continuously controlling the operation of the power converter according to the output power of the solar cell, it is possible to add the MTTP function by the above-described technology. In the case of instructing from this device, it is difficult to maintain the maximum power point because the operation of the power converter can be given only intermittently due to restrictions on the traffic on the communication path.

  Further, in order to realize the MTTP function, a period for searching for the maximum power point is required. However, if a configuration in which an operation instruction to the power converter is intermittently performed by communication is employed, the maximum power point of the solar cell is searched. Since the process takes a relatively long time, the ratio of the time occupied by the search process for the maximum power point increases. Although the fluctuation of the maximum power point is considered to be small within a relatively short time, the output power of the solar cell is not the maximum power point for most of the period during the search process. If the processing is continued, the occupation ratio of the period that is not the maximum power point becomes very large, and the maximum power point is not maintained. In other words, if the MTTP function is to be realized in a configuration in which the power converter is intermittently controlled by communication, the maximum power point is maintained even if the same technology as that for continuously controlling the power converter is adopted. As a result, there arises a problem that the utilization efficiency of the power generated by the solar cell is lowered.

  The present invention has been made in view of the above-mentioned reasons, and its purpose is to maintain the output of the solar cell near the maximum power point while adopting a configuration in which the operation of the power converter is intermittently instructed by communication. An object of the present invention is to provide a power supply system adapted to the above.

  The invention according to claim 1 includes a main power supply device that outputs DC power of a constant voltage and supplies DC power to a load device via a DC supply line, and a power converter that converts the output of the solar cell to power. Together with the DC power supply that supplies DC power to the load equipment via the DC supply line, and the output voltage and output current of the solar cell are obtained intermittently by communication between the DC power supply and the output of the power converter A power management unit that intermittently applies a current command value for adjusting current to the DC power supply by communication, and the power management unit sets a voltage corresponding to the maximum output point of the solar cell within a specified search range. The main search unit to search, and the voltage maintenance that gives the DC power supply device a current command value set to maintain the output voltage of the solar cell acquired by communication with the voltage obtained by the main search unit as the target voltage Characterized in that it comprises and.

  In the invention of claim 2, in the invention of claim 1, a smoothing capacitor for smoothing the output voltage of the solar cell and inputting it to the power converter is added, and the output voltage of the solar cell is supplied to the power management unit. When the power converter is below the specified value, the power converter is stopped to increase the voltage across the smoothing capacitor, and a pre-search unit is added to find the voltage corresponding to the maximum power point while the output voltage of the solar cell rises. The main search unit sets a search range narrower than the voltage change in the pre-search unit based on the voltage at the maximum power point obtained by the pre-search unit.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the voltage maintaining unit is configured such that when the state where the same target voltage is used after the setting of the target voltage reaches a predetermined maintaining time, the main search unit To search for the maximum power point and update the target voltage.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the voltage maintaining unit exceeds a predetermined allowable range with respect to a power value at a maximum power point at which the output power of the solar cell is searched. And at least one of when the output voltage of the solar cell fluctuates beyond a predetermined allowable range with respect to the target voltage, the main search unit searches for the maximum power point and sets the target voltage. It is characterized by updating.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, when the output voltage of the solar cell is lower than the target voltage, the voltage maintaining unit is connected to the DC power supply device during the next communication. The current command value to be applied is made lower than the current current command value, and the load amount by the power converter for the solar cell is reduced to increase the output voltage of the solar cell.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, when the output voltage of the solar cell is higher than the target voltage, the voltage maintaining unit is connected to the DC power supply device during the next communication. The current command value to be applied is set higher than the current current command value, and the load amount by the power converter for the solar cell is increased to decrease the output voltage of the solar cell.

  According to a seventh aspect of the present invention, in any one of the first to fourth aspects of the present invention, when the output voltage of the solar cell is different from the target voltage, the voltage maintaining unit supplies the DC power supply device during the next communication. The current command value is changed by a certain step size, and the load amount by the power converter for the solar cell is increased or decreased to bring the output voltage of the solar cell closer to the target voltage.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to fourth aspects, when the output voltage of the solar cell is different from the target voltage, the voltage maintaining unit and the output power of the solar cell and the power converter A current command value to be given to the DC power supply device at the time of next communication is obtained based on the output voltage of the solar cell, and the load amount by the power converter for the solar cell is increased or decreased to bring the output voltage of the solar cell closer to the target voltage. And

  According to the configuration of the invention of claim 1, the output voltage and output current of the solar cell are obtained intermittently, and the current command value that determines the output current is intermittently supplied to the power converter that converts the output of the solar cell to power. In the power supply system of the given configuration, the voltage corresponding to the maximum output point of the solar cell is obtained and set as the target voltage, and the current command value is adjusted so as to maintain the target voltage. Even when the time interval for acquiring the output current and the time interval for giving the current command value to the power converter are relatively long, the solar cell can be operated near the maximum power point, and The battery can generate electricity.

  According to the configuration of the invention of claim 2, since the output voltage of the solar cell is smoothed by the smoothing capacitor, even if the output power of the solar cell fluctuates temporarily due to a shadow of a cloud or the like, Variations can be suppressed. Also, when the output voltage of the solar cell rises from 0V or a low voltage, such as when starting for the first time or in the morning, the voltage across the smoothing capacitor is rapidly increased with the power converter stopped. As a result, the maximum power point can be detected in a relatively short time.

  However, since communication is performed intermittently, the maximum power point cannot be accurately detected while the output voltage of the solar cell rises as the smoothing capacitor is charged. Therefore, a relatively narrow search range is set based on the maximum power point obtained as described above, and the maximum power point is accurately obtained in a relatively short time by obtaining the maximum power point in the narrowed search range. Is possible. That is, since the time occupied by the search process for the maximum power point can be shortened and the ratio of the time used for maintaining the maximum power point can be increased, the utilization efficiency of the power generated by the solar cell can be further increased. it can.

  According to the configuration of the invention of claim 3, when the maintenance time elapses without updating the target voltage, the maximum power point is re-searched and the target voltage is updated, so that sunlight due to changes in the altitude of the sun, etc. The target voltage can be changed in response to a gradual change in the amount and the panel temperature, and the followability to the change in the maximum power point can be improved.

  According to the configuration of the invention of claim 4, when a change exceeding the allowable range occurs in at least one of the output power and the output voltage of the solar cell, the target voltage is immediately updated to follow the rapid change in the maximum power point. It becomes possible to do.

  According to the configuration of the invention of claim 5, the current command value given to the power converter can be lowered to reduce the load amount of the solar cell, and as a result, the output voltage of the solar cell can be changed in the increasing direction.

  According to the configuration of the invention of claim 6, the current command value given to the power converter can be increased to increase the load amount of the solar cell, and as a result, the output voltage of the solar cell can be changed in the decreasing direction.

  According to the configuration of the invention of claim 7, when the output voltage of the solar cell is different from the target voltage, the load amount of the solar cell by the power converter is changed by changing the current command value with a constant step size for each communication. Since the output voltage of the solar cell is brought close to the target voltage by changing the load, even if the output voltage of the solar cell changes greatly temporarily, the change in the load amount becomes gradual, and overshoot and undershoot are less likely to occur There is.

  According to the configuration of the invention of claim 8, when the output voltage of the solar cell is different from the target voltage, the next current command value is determined based on the output power of the solar cell and the output voltage of the power converter. The change width of the current command value can be dynamically changed, and the output voltage of the solar cell can be brought close to the target voltage accurately and quickly.

It is a block diagram which shows embodiment. It is a figure which shows the operating characteristic of a solar cell. It is operation | movement explanatory drawing which shows the output characteristic of the power converter used for embodiment. It is a block diagram which shows one structural example of the power converter used for embodiment. It is operation | movement explanatory drawing which shows the outline | summary of the operation | movement in embodiment. It is a block diagram which shows the power management part used for the same as the above. FIG. 3 is an operation explanatory diagram illustrating the first embodiment. FIG. 10 is an operation explanatory diagram illustrating the second embodiment.

(Basic configuration)
In the following embodiment, the system configuration shown in FIG. 1 will be described as an example. In the illustrated example, the DC power supply device 10 is provided with a power converter 13 that outputs DC power using the output of the solar cell 11 installed on the roof of a building such as a house as an input power source. The DC power supply device 10 supplies power to the load device 40 through a DC supply line Ld wired in the building, and the load device 40 operates with DC power supplied through the DC supply line Ld. However, the configuration shown in the figure is used to explain the gist of the present invention, and is not intended to limit the scope of application of the present invention.

  In the DC power supply device 10, a smoothing capacitor 12 is connected in parallel between output terminals of the solar cell 11. That is, by providing the smoothing capacitor 12 on the input side of the power converter 13, the influence on the input of the power converter 13 due to fluctuations in the amount of power generated by the solar cell 11 due to changes in solar radiation intensity or panel temperature is reduced. .

  That is, when the power generation amount of the solar cell 11 exceeds the power required by the power converter 13, the increase in output power of the power converter 13 is suppressed by storing surplus power in the smoothing capacitor 12, and the solar cell 11. When the amount of power generated cannot satisfy the power required by the power converter 13, the charge stored in the smoothing capacitor 12 is discharged, thereby suppressing the decrease in the output power of the power converter 13. As the smoothing capacitor 12, an electric double layer capacitor (EDLC) is used.

  The DC power supply device 10 is provided with a current sensor 14 that detects the output current of the solar battery 11 and a voltage sensor 15 that detects the input voltage of the power converter 13 as the output voltage of the solar battery 11. As will be described later, the power converter 13 has a function of adjusting the output current based on a current command value given from the outside, and has a function of monitoring the output current and the output voltage.

  The output current and output voltage of the solar cell 11 detected by the current sensor 14 and the voltage sensor 15, the current command value to the power converter 13, and the output current and output voltage of the power converter 13 will be described later through the communication unit 16. Exchanged with the power management unit 20.

  The DC power output from the DC power supply device 10 is supplied to the DC supply line Ld. In the present embodiment, the DC power supply line Ld is supplied with DC power from an AC power supply AC such as a commercial power supply, in addition to the load device 40 having a load 41 that operates when DC power is supplied from the DC power supply line Ld. Are connected to a main power supply device 30 provided with a power converter 31 as an AC / DC converter that performs power conversion, and an auxiliary power supply device 50 provided with a secondary battery 51 stored by surplus power of the DC power supply device 10. The Although not shown, the DC supply line Ld may be connected to a DC power source that generates power using a wind power generator, a generator driven by an internal combustion engine, a fuel cell, or the like.

  The DC power supply device 10, the main power supply device 30, the load device 40, and the auxiliary power supply device 50 have a function of performing communication through the DC supply line Ld. Actually, the power supply management unit 20 provided in the main power supply device 30 performs wired communication with the DC power supply device 10, the load device 40, and the auxiliary power supply device 50 through the DC supply line Ld, whereby the DC power supply device. 10. Monitors the status of the main power supply device 30, the load device 40, and the auxiliary power supply device 50 and instructs the operation. Therefore, not only the DC power supply device 10 but also the load device 40 and the auxiliary power supply device 50 are provided with the communication units 42 and 52. Furthermore, the power management unit 20 is also provided with a communication unit 21 (see FIG. 6).

  The main operation of the power management unit 20 is to distribute the supply power so that the required power from the load device 40 is satisfied by the supply power from the DC power supply device 10, the main power supply device 30, and the auxiliary power supply device 50. In other words, the operations of the DC power supply device 10 and the auxiliary power supply device 50 are controlled so that the solar battery 11 always generates power at the maximum power point.

  That is, the power management unit 20 manages the charging / discharging of the secondary battery 51 so that the charging rate of the secondary battery 51 provided in the auxiliary power device 50 is maintained within a specified range. Specifically, when the power that can be supplied from the DC power supply device 10 is larger than the required power of the load device 40, the secondary battery 51 is charged with surplus power, and the power that can be supplied from the DC power supply device 10 is supplied to the load device 40. When the charging power of the secondary battery 51 is less than the lower limit of the specified range, the secondary battery 51 is discharged. In short, the auxiliary power supply device 50 has a function of buffering fluctuations in the output power of the DC power supply device 10.

  Furthermore, when the required power of the load device 40 cannot be satisfied by the output power of the DC power supply device 10 and the auxiliary power supply device 50, the shortage is satisfied by the power from the main power supply device 30. Since the main power supply device 30 includes a power converter 31 as a constant voltage power supply as will be described later, when the output power of the DC power supply device 10 and the auxiliary power supply device 50 is insufficient with respect to the required power of the load device 40. The main power supply 30 automatically supplies the insufficient power.

  In the signal transmission method used for communication between the power management unit 20 and the DC power supply device 10, the load device 40, and the auxiliary power supply device 50, a high-frequency transmission signal is superimposed on the DC voltage applied to the DC supply line Ld. The method is used. That is, DC power line carrier communication in which the DC supply line Ld is shared for power supply and signal transmission is used. In the present embodiment, since the DC power line carrier communication is used, there is an advantage that it is not necessary to provide a communication signal line separately from the DC supply line Ld for supplying DC power. However, the communication used in the present embodiment is relatively slow, and collision and congestion occur when the frequency of communication increases and traffic increases. Therefore, communication is intermittently performed at relatively long time intervals (for example, every 2 seconds). Done.

  By the way, it is known that the power voltage characteristic at the output of the solar cell 11 is a single peak type as shown in FIG. 2, and the position of the apex (maximum power point) is as shown in FIG. Varies depending on panel temperature. Specifically, as shown in FIG. 2A, when the solar radiation intensity is high (curve A), the power at the vertex (maximum power point) becomes larger than when the solar radiation intensity is low (curve B), and the vertex The output voltage corresponding to the position decreases. Further, as shown in FIG. 2B, when the panel temperature is high (curve c), the change in the magnitude of power at the low panel temperature (curve d) and the apex (maximum power point) is small (panel). As the temperature increases, the power tends to decrease), and the output voltage decreases. In FIG. 2, the voltage corresponding to the maximum power point is indicated by a vertical line passing through the apex position of the power voltage characteristic.

  By the way, as shown in FIG. 3, the DC power supply device 10 (actually, the power converter 13) used in this embodiment has a constant slope of the voltage-current characteristic when the current command value is constant. It is configured to have. Further, as shown in FIG. 3, when the current command values I1 and I2 are given to the power converter 13 from the outside and the voltage Vo is applied between the DC supply lines Ld, the voltage-current characteristics have the above-described slope. , And changes on a straight line passing through the intersection of the voltage Vo applied to the DC supply line Ld and the current command values I1 and I2. Control for giving the above-described characteristics to the power converter 13 is referred to as tilt control.

  In order to perform the inclination control described above, the power converter 13 of the present embodiment has the configuration of FIG. In the illustrated example, PWM control is performed to control the output by changing the on-duty of a switching element (not shown) provided in the step-down chopper circuit 61 that steps down the output voltage of the solar cell 11. Here, in the step-down chopper circuit 61, the output decreases as the on-duty of the switching element decreases.

  The power converter 13 includes a current detection unit 62 that detects the output current of the step-down chopper circuit 61 and a voltage detection unit 63 that detects a voltage between the output terminals of the power converter 13 (that is, between the DC supply lines Ld). With. The current detection unit 62 outputs a detection current obtained by smoothing the output current with an appropriate time constant so that instantaneous fluctuation of the output current of the step-down chopper circuit 61 does not affect the detection current.

  The current detected by the current detector 62 is compared with a current command value given from the outside by the error amplifier 64, and a voltage signal proportional to the difference between the two is given to the differential amplifier 65. A detection voltage from the voltage detector 63 is also input to the differential amplifier 65. The output of the differential amplifier 65 increases as the detection current for the current command value decreases, decreases as the detection current for the current command value increases, and decreases as the detection voltage increases.

  The output voltage of the differential amplifier 65 is input to the comparator 67 together with the triangular wave output from the triangular wave generator 66, and the comparator 67 compares the output voltage of the differential amplifier 65 with the triangular wave voltage. A binary rectangular wave signal is output, and on / off of the switching element of the step-down chopper circuit 61 is controlled by the rectangular wave signal.

  By using the power converter 13 having the above-described configuration, when the current detected by the current detection unit 62 increases beyond the current command value, the input voltage to the comparator 67 rises and the rectangular wave signal that turns on / off the switching element is turned on. The period is shortened and the output is reduced. Also, if the detected current decreases below the current command value, the input voltage to the comparator 67 decreases, the on period of the rectangular wave signal becomes longer, and the output increases. That is, feedback control is performed so that the current detected by the current detection unit 62 maintains the current command value.

  On the other hand, if the detection voltage by the voltage detection unit 63 increases, the input voltage of the comparator 67 decreases. Therefore, the ON period of the rectangular wave signal for turning on / off the switching element becomes longer, the output further increases, and the detection voltage decreases. For example, since the input voltage of the comparator 67 increases, the ON period of the rectangular wave signal is shortened and the output decreases.

  As described above, the change in increase / decrease in the output voltage and output current of the power converter 13 is a change opposite to the rectangular wave signal for turning on / off the switching element of the step-down chopper circuit 61 (the voltage increases or the current decreases). Then, the pulse width increases, and when the voltage decreases or the current increases, the pulse width decreases.

  By the way, the power converter 31 provided in the main power supply device 30 is an AC / DC converter using a switching power supply, and is configured to output a constant voltage. The main power supply 30 uses an AC power supply AC as a power supply, and has a capacity that does not substantially cause variation in output voltage. That is, the voltage applied between the DC supply lines Ld is regulated by the output voltage of the main power supply device 30. Therefore, the voltage detected by the voltage detector 63 varies instantaneously due to variations in the output of the step-down chopper circuit 61, but is maintained at a substantially constant voltage.

  Hereinafter, the operation of the power converter 13 will be described in more detail. First, the case where the output voltage of the solar cell 11 fluctuates will be described. When the output voltage of the solar cell 11 fluctuates instantaneously, it is relaxed by the smoothing capacitor 12 and does not affect the input voltage of the power converter 13. On the other hand, when the smoothing capacitor 12 cannot cope with fluctuations in the output voltage of the solar battery 11, the output voltage and output current of the power converter 13 change. Now, assuming that the input voltage of the power converter 13 fluctuates without changing the load on the power converter 13, the output voltage of the power converter 13 fluctuates.

  Since the voltage-current characteristic of the output of the power converter 13 is determined by the current command value, when the input voltage of the power converter 13 fluctuates and the output voltage fluctuates, the voltage is stepped down according to the voltage-current characteristic determined by the current command value. The on-duty of the rectangular wave signal that drives the chopper circuit 61 changes in a direction that matches the output current with the current command value. However, since the amount of power generated by the solar cell 11 is fluctuating, there is a possibility that the output current determined by the current command value will be insufficient or excessive.

  Such deficiencies and surpluses are dealt with by adjusting the amount of charge supplied from the main power supply device 20 and the auxiliary power supply device 50. By performing this correspondence, the output of the power converter 13 is kept substantially constant regardless of the load amount variation until the current command value is changed.

  Next, a case where the load amount on the power converter 13 varies will be described. Immediately after the load on the power converter 13 fluctuates, the voltage detected by the voltage detector 63 fluctuates, and the on-duty of the rectangular wave signal that drives the step-down chopper circuit 61 changes. Since the power converter 13 performs tilt control, the output current changes along a straight line determined according to the current command value, and the output current changes until the line voltage Vo of the DC supply line Ld is reached.

  The output current of the power converter 13 is a current value instructed by the current command value, and in this case as well, there is a possibility that a shortage or a surplus occurs with respect to the load amount required for the voltage detection unit 63. Such deficiencies and surpluses can be dealt with by using the same technique as when the input voltage to the power converter 13 fluctuates.

  In short, as shown in FIG. 1, in the configuration in which the DC power supply device 10 of the solar cell is connected to the DC supply line Ld and DC power is supplied to the DC device 40, the output fluctuation of the solar cell 11 and the load of the DC power supply device 10. When there is a shortage or surplus in the output of the power converter 13 due to fluctuations in the amount, a reverse power flow to the commercial power supply system cannot be performed. Here, the shortage can be dealt with only by the main power supply device 30 that outputs a constant voltage, but the surplus cannot be solved by the reverse power flow. Therefore, if there is a surplus, it is stored in the auxiliary power supply 50. The power supply management unit 20 gives instructions for operations for deficiencies and surpluses.

  Next, a case where the current command value is changed will be described. Assume that the current command value I1 shown in FIG. 3 is changed to a current command value I2 (<I1). Immediately after the change to the current command value I2, the current detected by the current detector 62 is larger than the current command value I2, so the on period of the square wave signal for driving the step-down chopper circuit 61 is shortened, and the step-down chopper circuit 61 Output decreases. Therefore, the detection voltage by the voltage detection part 63 falls.

  Here, since the current command value I2 is set in the power converter 13, the voltage-current characteristic of the power converter 13 is a straight line passing through the intersection of the line voltage Vo of the DC supply line Ld and the current command value I2. Therefore, the square wave signal that drives the step-down chopper circuit 61 changes so that the detected current changes along the straight line, and the detected current matches the current command value I2. That is, the output current of the power converter 13 becomes the current indicated by the current command value I2.

  As described above, the line-to-line voltage of the DC supply line Ld is kept substantially constant by the output voltage of the main power supply device 30. Therefore, by changing the current command value instructed to the DC power supply device 10, the DC power supply The output power can be changed by adjusting the output current while the output voltage of the device 10 is kept substantially constant. That is, by adjusting the output power of the DC power supply device 10, the power required by the power converter 13 for the input side (solar cell 11 and smoothing capacitor 12) changes, and the load on the solar cell 11 changes.

  Therefore, if the power required from the power converter 13 to the input side can be determined so as to maximize the output power of the solar cell 11, the MTTP function is realized. That is, by giving an appropriate current command value to the power converter 13, the output power of the solar cell 11 can be maintained at the maximum power point. In the following embodiments, a technique for giving a current command value for realizing the MTTP function from the power converter 31 will be described.

(Embodiment 1)
In the present embodiment, as information necessary for realizing the MTTP function, the output current of the solar cell 11 and the output voltage of the solar cell 11 are detected, and the output power of the solar cell 11 is calculated. Further, in the present embodiment, although not specifically described, the output power of the DC power supply device 10 is calculated from the output current and output voltage of the DC power supply device 10.

  The output current of the solar cell 11 is detected by a current sensor (for example, a direct current transformer) 14 provided between the solar cell 11 and the smoothing capacitor 12. Further, the output voltage of the solar cell 11 is detected by a voltage sensor (for example, voltage dividing resistor) 15 that detects the input voltage of the power converter 13. The input voltage of the power converter 13 is the voltage across the smoothing capacitor 12 and corresponds to the terminal voltage of the output terminal of the solar cell 11.

  As the output current and output voltage of the DC power supply device 10, the current detected and the voltage detected by the current detector 62 and the voltage detector 63 provided in the power converter 13 are used.

  Here, if the maximum power point is constantly monitored and the operation of the power converter 13 is controlled with respect to the change in the maximum power point due to the change in the solar radiation intensity or the panel temperature as shown in FIG. It becomes possible to follow without delay. However, in the configuration shown in FIG. 1, as described above, the DC power supply 10 adjusts the output current according to the current command value acquired by communication with the power management unit 20 provided in the main power supply 30. Since communication is performed intermittently, it is impossible to constantly monitor the maximum power point and follow fluctuations in the maximum power point without delay. That is, the load amount for the power converter 13 to maintain the maximum power point of the solar cell 11 can be adjusted only intermittently.

  By the way, as shown in FIG. 2, the power voltage characteristic of the solar cell 11 is a single peak type, and the maximum power point corresponds to the output voltage of the solar cell 11 on a one-to-one basis. It is considered that the output voltage of the solar cell 11 may be adjusted so that an output voltage corresponding to the maximum power point can be obtained.

  In addition, since it is considered that the fluctuation of the maximum power point is small in a relatively short time in a normal use state, communication is performed at a time interval that keeps the maximum power point substantially constant, and the power to the solar cell 11 is It is considered that the maximum output point of the solar cell 11 can be substantially followed by adjusting the load amount of the converter 13.

  In the present embodiment, based on such knowledge, first, an output voltage corresponding to the maximum power point of the solar cell 11 is obtained and the output voltage is set as a target voltage, and then the fluctuation of the maximum power point of the solar cell 11 is small. In the meantime, a configuration is adopted in which the current command value given to the power converter 13 is adjusted so that the output voltage of the solar cell 11 is maintained at the target voltage.

  That is, as shown in FIG. 5, first, a voltage corresponding to the maximum power point of the solar cell 11 (actually the input voltage of the power converter 13) is searched (FIGS. 5 (1) (2)), and the detected voltage Is used as the target voltage Vd, and the current command value applied to the power converter 13 is adjusted so that the target voltage Vd is maintained. Thereafter, when a condition such that the maximum power point exceeds the allowable range Vii−Vss is satisfied, the maximum power point is searched again to update the target voltage (FIG. 5 (3)), thereby following the maximum power point. MTTP function is realized.

  The MTTP function described above is performed when the power management unit 20 provided in the main power supply device 30 communicates with the DC power supply device 10. The power management unit 20 uses a microcomputer as a main component, and causes the microcomputer to realize the following functions by executing a program.

  That is, as shown in FIG. 6, the power management unit 20 transmits and receives data by communicating with the communication units 16, 42, and 52 in the DC power supply device 10, the load device 40, and the auxiliary power supply device 50. And a data input / output unit 22 that exchanges data with the DC power supply device 10, the load device 40, and the auxiliary power supply device 50 through the communication unit 21. A monitoring unit 28 is connected to the data input / output unit 22, and the monitoring unit 28 operates the DC power supply device 10 and the auxiliary power supply device 50 so as to satisfy the required power of the load device 40 as described as the basic configuration. To control.

  By the way, the data acquired by the data input / output unit 22 from the DC power supply device 10 via the communication unit 21 such as the output current of the solar cell 11 and the output voltage of the solar cell 11 is given to the determination unit 23. When the output voltage of solar cell 11 (that is, the input voltage of power converter 13) is a specified value (for example, 10 V) or less, determination unit 23 determines that the smoothing capacitor 12 is not charged and is in a stopped state. When the input voltage of the condenser 13 exceeds the specified value, it is determined that the operating state is stored in the smoothing capacitor 12.

  The stop state is not only at the time of initial startup of the solar cell 11 but also when the power generation of the solar cell 11 is stopped at night and the electric charge of the smoothing capacitor 12 is discharged and the power generation of the solar cell 11 is resumed the next morning. Also, it is determined that the solar cell is in a stopped state when it is restarted after power generation is stopped. Note that it is desirable to stop the operation of the power converter 13 when the power generation amount of the solar cell 11 decreases at night and the voltage across the smoothing capacitor 12 decreases below a specified value.

  When the determination unit 23 determines that it is in the stopped state, the pre-search unit 24 that searches for the maximum power point of the solar cell 11 for almost the entire range of the lower limit and the upper limit of the output voltage of the solar cell 11 is activated. Further, when the determination unit 23 determines that the operation state is in effect, the main search unit 25 that searches for the maximum power point of the solar cell 1 in a specific search range of the output voltage of the solar cell 11 is activated.

  The power management unit 20 also maintains a voltage that calculates the current command value of the DC power supply 10 so that the maximum power point is maintained when the pre-search unit 24 or the main search unit 25 detects the maximum power point. A portion 26 is provided. In the voltage maintaining unit 26, the output voltage of the solar cell 11 (input voltage of the power converter 13) corresponds to the maximum power point (for example, 17V) as the target voltage Vd (see FIG. 5), and the target voltage Vd is maintained. The current command value is determined as follows.

  The current command value determined by the voltage maintaining unit 26 is notified to the DC power supply device 10 through the data input / output unit 22 and the communication unit 21, and the DC power supply device 10 outputs an output current corresponding to the current command value. Thus, the amount of load on the solar cell 11 is adjusted, and as a result, feedback control is performed so as to maintain the output voltage of the solar cell 11 at the target voltage Vd.

  Hereinafter, operations of the determination unit 23, the pre-search unit 24, the main search unit 25, and the voltage maintaining unit 26 in the power management unit 20 will be described in more detail with reference to FIG. First, the determination unit 23 acquires the output voltage of the solar cell 11 and compares it with a specified value (S1). Here, when the output voltage of the solar cell 11 is equal to or lower than the specified value, it is determined that the vehicle is stopped (S1: no), and the pre-search unit 24 is activated. The pre-search unit 24 stops the operation of the power converter 13 (S2), thereby disconnecting the power converter 13 from the load of the solar cell 11 so that only the smoothing capacitor 12 is loaded. In this state, the voltage across the smoothing capacitor 12, that is, the output voltage of the solar cell 11, rises in a relatively short time with the passage of time.

  The pre-search unit 24 acquires and stores the output current of the solar cell 11 and the output voltage of the solar cell 11 until the input voltage of the power converter 13 reaches a specified voltage (for example, 20 V) (S4) (S3). ). In the pre-search unit 24, the output power of the solar cell 11 is obtained from the product of the output voltage of the solar cell 11 and the input voltage of the power converter 13, and the output voltage of the solar cell 11 when the maximum output power is obtained is obtained. The voltage corresponding to the maximum power point is set (S5).

  Here, the output power of the solar cell 11 can be obtained only for each time interval at which communication is performed between the main power supply device 30 and the DC power supply device 10, but the input voltage of the power converter 13 (both ends of the smoothing capacitor 12). The maximum power point can be detected by setting the communication time interval to be shorter than the time until the voltage reaches the upper limit voltage. The voltage corresponding to the maximum power point is stored in the power management unit 20.

  In order to obtain the maximum power point, for example, the output power of the solar battery 11 acquired for each communication is compared with the output power acquired in the previous communication, and if the output power acquired this time is larger, the stored output power , And if the output power acquired this time is smaller, a procedure is adopted in which the output power acquired this time is discarded. By this processing, the maximum power point can be obtained roughly (with low accuracy) when the upper limit voltage is reached.

  Note that the determination unit 23 does not determine the voltage while the pre-search unit 24 is activated. Further, the specified voltage for ending the process of the pre-search unit 24 is set lower than the open circuit voltage of the solar cell 11. When the operation of the pre-search unit 24 ends, the output voltage of the solar cell 11 is normally equal to or higher than a specified value, so that the determination unit 23 determines that the operation is in progress (S1: yes). That is, the main search unit 25 is activated.

  The main search unit 25 first sets a range for searching for the maximum power point (S6). The search range is set to a predetermined range (for example, a range of ± 30%) around the voltage corresponding to the maximum power point detected by the pre-search unit 24 with respect to the output voltage of the solar cell 11.

  Next, the operation of the power converter 13 is started (S7), and the input voltage of the power converter 13 is changed from the specified voltage used in the pre-search unit 24 toward the lower limit voltage of the search range set in the main search unit 25. Let That is, the input voltage of the power converter 13 is lowered by gradually increasing the current command value to be supplied to the power converter 13 (S8). However, since the current command value cannot be changed continuously, it is changed by a predetermined step size (for example, 0.1 A) for each communication.

  This step size is appropriately selected according to the accuracy for obtaining the voltage corresponding to the maximum power point and the time used for the search. In other words, if the step size is increased, the accuracy for obtaining the voltage is lowered, but the time required for the search can be shortened.If the step size is reduced, the time required for the search is increased, but the accuracy for obtaining the voltage is increased. Get higher.

  In the main search unit 25, the current command value given to the power converter 13 of the DC power supply device 10 until the input voltage of the power converter 13 acquired by communication reaches the lower limit voltage of the search range set in step S6 (S10). Increase gradually. Each time the current command value is increased, the output current and output voltage of the solar cell 11 are acquired (S9), the output power of the solar cell 11 is calculated by the product of the current and voltage, and the pre-search unit 24 The maximum power point is obtained in the same manner as in the above operation, and the voltage corresponding to the maximum power point is obtained.

  If the input voltage of the power converter 13 does not decrease with the increase of the current command value before reaching the lower limit voltage of the search range set in step S6 (S10, S11), the maximum power point is greatly increased. It is determined that the output has changed (the output voltage of the solar cell 11 has greatly decreased), and the pre-search unit 24 is restarted (S2).

  The main search unit 25 can obtain the voltage corresponding to the maximum power point with higher accuracy than the pre-search unit 24 by obtaining the maximum power point by the above-described operation. In the main search unit 25, since the change range of the input voltage of the power converter 13 is narrower than that of the pre-search unit 24, the maximum power can be obtained in a relatively short time even if the current command value is changed in small increments. It becomes possible to extract a voltage corresponding to a point.

  When the voltage corresponding to the maximum power point of the solar cell 11 is obtained by the main search unit 25 (S11: yes), this voltage is supplied to the voltage maintaining unit 26 provided in the power management unit 20 as the target voltage Vd (see FIG. 5). (S12). The voltage maintaining unit 26 generates a current command value so as to maintain the output voltage of the solar cell 11 at the target voltage Vd, and gives the voltage instruction value to the power converter 13 for each communication with the DC power supply device 10.

  That is, when the target voltage Vd is obtained by the main search unit 25, the voltage maintaining unit 26 is activated, and the voltage maintaining unit 26 acquires the output current and output current of the solar cell 11 for each communication with the DC power supply device 10. Then, the output voltage of the solar cell 11 (the input voltage of the power converter 13) is compared with the target voltage Vd (S14, S15).

  When the voltage acquired from the DC power supply device 10 is lower than the target voltage Vd (S15: low), the load on the solar cell 11 is reduced by reducing the current command value given to the power converter 13 by a predetermined step size (S16). The amount is decreased to increase the output voltage of the solar cell 11. On the contrary, when the voltage acquired from the DC power supply device 10 is higher than the target voltage Vd (S15: high), by raising the current command value given to the power converter 13 (S17), the load amount on the solar cell 11 is increased. Increase the output voltage of the solar cell 11 to decrease. The current command value is changed at a constant step size (for example, 0.1 A), similarly to the operation of the main search unit 25. Further, when the acquired voltage substantially matches the target voltage Vd (within a predetermined range), the current command value is not changed.

  In the voltage maintaining unit 26, if the variation in solar radiation intensity or panel temperature is not large, it is considered that the variation in output voltage is small even if the maximum power point of the solar cell 11 varies, and the output voltage of the solar cell 11 is set to the target voltage Vd. Although the feedback control is performed so as to maintain the target voltage Vd, if the variation of the solar radiation intensity or the panel temperature increases, the target voltage Vd searched for by the main search unit 25 is greatly deviated from the maximum power point.

  Therefore, the voltage maintaining unit 26 determines that the maximum power point has changed when at least one of the output power and the output voltage of the solar cell 11 acquired during communication is outside the allowable range (S14), and sets the search range. After that (S18), the process returns to step S8 and the main search unit 25 searches for the target voltage again.

  The allowable range is a range indicated by Vi−Vs in FIG. 5, and is set to, for example, ± 20% with respect to the power value of the searched maximum power point, or is set to, for example, ± 0.3 V with respect to the target voltage Vd. Or set. Whether the allowable range is set with a fixed width with respect to the reference value (the power value at the maximum power point or the target voltage Vd) or the ratio with respect to the reference value can be appropriately selected.

  The re-search condition can be determined using only one of the output power and the output voltage of the solar cell 11 (the operation in FIG. 7 uses only the output voltage), but the power at the maximum power point. Depending on the value, the case where the output power is used and the case where the output voltage is used may be properly used.

  For example, paying attention to the fact that the power voltage characteristic at the output of the solar cell 11 is bell-shaped and the power value at the maximum power point is larger, the characteristic becomes sharper. Whether the power value at the maximum power point is greater than or equal to a specified threshold value or less than the threshold value The re-search condition may be switched according to the above. That is, when the power value is greater than or equal to the threshold value, the rate of change of the output power with respect to the change of the output voltage is large, so that the output power is out of the allowable range as a re-search condition, Since the rate of change of the output power with respect to the change of the output voltage becomes small, the condition for the re-search may be that the output voltage is outside the allowable range.

  At the time of re-searching, the load amount of the solar cell 11 by the power converter 13 is reduced by setting the current command value lower by a specified ratio (for example, 30%) than the current current command value. Thus, the amount of charge stored in the smoothing capacitor 12 is increased. That is, the search range Vii-Vss (see FIG. 5) for re-search is set using the current current command value (S18), the output voltage of the solar cell 11 is once increased, and then the maximum power point is searched. .

  Here, as in the stop state, it is possible to increase the voltage across the smoothing capacitor 12 to the open voltage of the solar cell 11 by stopping the power converter 13, but when the power converter 13 is stopped, Since a sharp voltage drop in the supply current from the DC power supply apparatus 10 may cause a large voltage fluctuation in the line voltage of the DC supply line Ld and affect the operation of the load device 40, the power converter 13 is stopped. The control which reduces the load amount of the solar cell 11 is adopted.

  In the above-described operation, a case has been described in which the maximum power point is re-searched when the output voltage of the solar cell 11 changes more than a specified ratio with respect to the target voltage Vd. Even if the change in the voltage is less than a prescribed ratio with respect to the target voltage Vd, if the state using the same target voltage Vd reaches a prescribed maintenance time (for example, 15 minutes) (S19), the main search The target voltage Vd is searched again by the unit 25. By performing the process of step S19, it is possible to cope with changes in solar radiation intensity or panel temperature associated with changes in solar altitude, movement of clouds, changes in the position of shadows of buildings and trees, and the like.

  As described above, after the voltage corresponding to the maximum power point is detected by the main search unit 25, the voltage is set as the target voltage Vd, and the power conversion is performed if the variation of the maximum power point of the solar cell 11 is within the allowable range. By adjusting the current command value applied to the battery 11, feedback control is performed so that the target voltage Vd is maintained, and the output power of the solar cell 11 is maintained in the vicinity of the maximum power point. Further, when the variation of the maximum power point of the solar cell 11 exceeds the allowable range Vi−Vs, the main search unit 25 is activated and the voltage corresponding to the maximum power point is re-searched. When the power point changes greatly, the maximum power point can be changed following the change. That is, the MTTP function can be realized.

(Embodiment 2)
In the first embodiment, in order to maintain the target voltage in the voltage maintaining unit 26, the current command value given to the power converter 13 is changed at a constant step size, so that the current supplied to the DC supply line Ld is suddenly increased. Although it does not fluctuate, the rate of change of the input voltage of the power converter 13 is constant, and the communication between the main power supply device 30 and the DC power supply device 10 is performed intermittently. The problem arises that the time constant increases as the accuracy of the command value increases. That is, in the first embodiment, the voltage maintaining unit 26 cannot achieve both the accuracy of maintaining the target voltage corresponding to the maximum power point and the response speed.

In the present embodiment, the output power Pp of the solar cell 11 acquired during the previous communication and the output power Pe of the solar cell 11 acquired during the current communication are used and given to the power converter 13 during the next communication using the following equation. The current command value Ia is determined.
Ia = Ie−α (Ip−Ie)
However, Ie = ε (Pe ÷ Ve), Ip: previous current command value, Ve: output voltage of the power converter 13 acquired this time, α: constant indicating the speed to return to the target voltage, ε: power converter 13 Conversion efficiency (for example, 0.9). By giving the current command value Ia thus calculated to the power converter 13, the load amount of the power converter 13 with respect to the solar cell 11 is changed as in the first embodiment, and the output voltage of the solar cell 11 is changed to the target voltage. Can be close to. In addition, by adjusting the constant α, it is possible to adjust the speed of returning to the target voltage, so that both the accuracy of maintaining the output voltage of the solar cell 11 and the speed of response can be achieved.

  In the present embodiment, the current maintaining value obtained from the output power of the solar cell 11 (product of the output current of the solar cell 11 and the input voltage of the power converter 13) and the output voltage of the power converter 13 is used as the voltage maintaining unit. 26, the voltage maintaining unit 26 adopts a configuration in which the output voltage of the solar cell 11 matches the target voltage for each communication between the main power supply device 30 and the DC power supply device 10. It is possible to achieve both maintaining accuracy and response speed.

  Further, in the present embodiment, the current command value is calculated using the above equation regardless of the level of the output voltage and the target voltage of the solar cell 11, so that the case classification in step S15 shown in FIG. That is, the operation of this embodiment is summarized as shown in FIG. As can be seen by comparing FIG. 8 with FIG. 7, in this embodiment, instead of the determination process in step S <b> 15 of FIG. 7, a current command value is calculated, and the calculated current command value is instructed to the DC power supply device 10. (S15). Other configurations and operations are the same as those of the first embodiment.

  In the configuration of the first and second embodiments, the power management unit 20 can be provided separately from the main power supply device 30, and it is not essential to use the DC supply line Ld for the communication path. It is possible to use a provided wired communication path or wireless communication path. The main power supply device 30 employs a configuration that outputs DC power by converting an AC power source AC such as a commercial power source into DC power, and is a configuration that outputs DC power at a constant voltage, The configuration of the main power supply device 30 is not particularly limited as long as the power supply device has a capacity capable of stably supplying power with respect to the load fluctuation of the load device 40.

DESCRIPTION OF SYMBOLS 10 DC power supply device 11 Solar cell 12 Smoothing capacitor 13 Power converter 14 Current sensor 15 Voltage sensor 20 Power supply management part 21 Communication part 24 Presearch part 25 Main search part 26 Voltage maintenance part 30 Main power supply apparatus 31 Power converter 40 Load apparatus 41 Load 42 Communication Unit 50 Auxiliary Power Supply Device 51 Secondary Battery 52 Communication Unit
61 Step-down chopper circuit 62 Current detection unit 63 Voltage detection unit Ld DC supply line

Claims (8)

  A main power supply device that outputs DC power at a constant voltage and supplies DC power to a load device via a DC supply line, and a power converter that converts the output of the solar cell into power, together with the main power supply device via the DC supply line A DC power supply that supplies DC power to the load equipment, and a current command value that intermittently obtains the output voltage and output current of the solar cell through communication with the DC power supply and adjusts the output current of the power converter A power management unit that intermittently provides a direct current power supply device by communication, the power management unit, a main search unit that searches for a voltage corresponding to the maximum output point of the solar cell within a specified search range, A voltage maintaining unit that supplies the DC power supply device with a current command value set so as to maintain the output voltage of the solar cell acquired by communication using the voltage obtained by the main search unit as the target voltage. Power supply system and butterflies.   A smoothing capacitor for smoothing the output voltage of the solar cell and inputting it to the power converter is added, and the power management unit stops the power converter when the output voltage of the solar cell is below a specified value. This increases the voltage across the smoothing capacitor and adds a pre-search unit that calculates the voltage corresponding to the maximum power point while the output voltage of the solar cell increases. The main search unit is obtained by the pre-search unit. The power supply system according to claim 1, wherein a search range narrower than a voltage change in the pre-search unit is set based on a voltage at a maximum power point.   The voltage maintaining unit searches for a maximum power point by the main search unit and updates the target voltage when a state in which the same target voltage is used after setting the target voltage reaches a predetermined maintaining time. The power supply system according to claim 1 or 2.   The voltage maintaining unit is configured such that when the output power of the solar cell fluctuates beyond a predetermined allowable range with respect to the power value of the searched maximum power point, and the output voltage of the solar cell with respect to the target voltage 4. The target voltage is updated by searching for a maximum power point by the main search unit in at least one of cases where the fluctuation exceeds a predetermined allowable range. 5. Power system.   When the output voltage of the solar cell is lower than the target voltage, the voltage maintaining unit lowers the current command value to be given to the DC power supply device during the next communication than the current current command value, and The power supply system according to any one of claims 1 to 4, wherein an output voltage of the solar cell is increased by reducing a load amount by the power converter.   When the output voltage of the solar cell is higher than the target voltage, the voltage maintaining unit makes the current command value to be given to the DC power supply device at the time of next communication higher than the current current command value, and The power supply system according to any one of claims 1 to 5, wherein an output voltage of the solar cell is decreased by increasing a load amount by the power converter.   When the output voltage of the solar cell is different from the target voltage, the voltage maintaining unit changes a current command value to be given to the DC power supply device at the time of next communication by a certain increment, and the power converter for the solar cell The power supply system according to any one of claims 1 to 4, wherein an output voltage of the solar cell is brought close to a target voltage by increasing or decreasing a load amount due to.   The voltage maintaining unit, when the output voltage of the solar cell is different from the target voltage, a current command to be given to the DC power supply device during the next communication based on the output power of the solar cell and the output voltage of the power converter 5. The power supply system according to claim 1, wherein a value is obtained and an output voltage of the solar cell is made closer to a target voltage by increasing or decreasing a load amount of the power converter with respect to the solar cell.

Images