JP2012191824A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that has a wide input current range and an output current range, outputs maximum power in response to variations in input current over a wide range, and is compact and inexpensive.SOLUTION: A power conversion device 100 for converting the input power input as DC power to output the output power includes: an input current detection section 2 for detecting an input current that is a current of the input power; a plurality of power conversion circuit sections 4-6 for converting the input power, which have different input current ranges and overlap with adjacent input current ranges; and a power conversion control section 1 for selecting one of the plurality of power conversion circuit sections 4-6 which can produce the highest output power from the input current detected by the input current detection section 2. In selecting one power conversion circuit section, the power conversion control section 1 controls so as to match an output voltage of the power conversion circuit section just after switching with an output voltage of the power conversion circuit section just before switching.

Description

  The present invention relates to a power conversion device that performs power conversion and outputs input power input as DC power.

  In recent years, in order to cope with the depletion of fossil fuels, the spread of renewable natural energy is desired due to the need for environmental considerations. In particular, solar cells have little impact on the environment, and further development is expected in the future. The electric power generated by the solar battery is effectively used by being stored in a storage battery or sold to an electric power company. Since the output of a solar cell varies depending on the amount of solar radiation, the output depends on the weather and the like, so it is difficult to control the amount of power supplied. In the solar cell, it is preferable that the output is taken out with high conversion efficiency in the entire output fluctuation range.

  FIG. 16 is a graph showing an example of characteristics of a general solar cell. In FIG. 16, the horizontal axis indicates the output voltage of the solar cell, and the vertical axis indicates the output current of the solar cell. As shown in FIG. 16, the output characteristics of the solar cell vary greatly depending on the amount of solar radiation. Since the output current width fluctuates particularly greatly, it is preferable that the power conversion device connected to the solar cell and taking out the output thereof has high conversion efficiency in a wide input current region.

  In a power conversion circuit, in order to maintain high conversion efficiency over a wide input current region, high conversion efficiency is required even when the output current region is wide. When the output voltage is maintained at a constant value, it is possible to produce a power conversion circuit having high conversion efficiency in a predetermined range of output current, but power that maintains high conversion efficiency in a wide output current range. It is difficult to produce a conversion circuit. In the conventional power conversion circuit, when the output current is out of the predetermined range, the conversion efficiency of the power conversion circuit is lowered. In other words, when a large current is required as the output current, a power conversion circuit having high conversion efficiency may be used when the output current is a large current, but when a small current is output by the power conversion circuit, Conversion efficiency may be reduced.

  In order to achieve high conversion efficiency for both large output current and small output current with a single power conversion circuit, the frequency and control method (PWM · PFM) in power conversion according to the range of output current ) And other control conditions are changed. For example, the circuit is controlled as PWM control with a constant frequency when the output current is large, and as PFM control with a constant ON width when the output current is small.

  Patent Document 1 discloses a power supply device that has a plurality of power conversion circuits having the same configuration and increases or decreases the number of circuits to be used according to output current. In this power supply device, by combining a plurality of circuits, a power conversion circuit corresponding to the output current can be configured, and high conversion efficiency can be maintained in a wider output current region than when a single power conversion circuit is used. .

JP 2009-232587 A

  As described above, high conversion efficiency can be maintained in a certain range of output current region by changing the frequency, control method (PWM / PFM), etc. in a single power conversion circuit. However, there is a limit to the range of the output current region, and it cannot be said that the range is sufficient to efficiently extract the output of the solar cell.

  The power supply device of Patent Document 1 can widen the range of the output current region in which high conversion efficiency can be maintained by increasing the number of circuits to be combined, but the range is also limited, and the output of the solar cell is efficiently It's not enough to take it out. Since the power supply device of Patent Document 1 combines circuits having the same configuration, the number of required circuits is relatively large, and thus there is a problem that the power supply device is increased in size and cost. Further, in order to construct an optimum power conversion circuit in a wide output current range by combining circuits having the same configuration, there is a problem that the circuit design becomes complicated and the time required for the circuit design becomes long.

  The present invention is an invention made in view of the above-mentioned circumstances, and its purpose is to have a wide input current range and an output current range, and to output power efficiently in response to fluctuations in the input current in a wide range, And it is providing the power converter device which can be reduced in size and cost.

  The power conversion device of the present invention is a power conversion device that converts input power input as DC power and outputs output power, and an input current detection unit that detects an input current that is a current of the input power; The input power is converted, and the input current ranges are different from each other, and the adjacent input current ranges have a plurality of power conversion circuit units, and among the plurality of power conversion circuit units, One power conversion circuit unit that obtains the largest output power in the input current detected by the input current detection unit is selected, and the selected power conversion circuit unit is controlled under control conditions that obtain the largest output power. A power conversion control unit, and the power conversion control unit turns off when selecting the one power conversion circuit unit and switching the power conversion circuit unit by the selection. The output voltage of the power converter circuit of the immediately preceding example, and controls such that the output voltage of the power converter circuit section directly after switching coincide with each other.

  According to the power conversion device of the present invention, it has a wide input current range and an output current range, and can efficiently output power corresponding to fluctuations in the input current over a wide range, and can be reduced in size and cost. It is.

It is a block diagram which shows the structure of the solar energy power generation system using the power converter device which concerns on this embodiment. It is a block diagram which shows an example of a structure of the power converter device which concerns on this embodiment. It is explanatory drawing which made a part of example of a structure of the power converter device which concerns on this embodiment into the circuit diagram. It is a graph which shows the relationship between the input current and output power of each power inverter circuit unit of the power converter concerning this embodiment. It is a graph which shows the example of the relationship between the output current in a power converter circuit unit, and conversion efficiency. It is a figure which shows an example of the efficiency versus output current data regarding a 1st power converter circuit unit. It is a figure which shows an example of the efficiency versus output current data regarding the 2nd power inverter circuit unit. It is a figure which shows an example of the efficiency versus output current data regarding the 3rd power converter circuit unit. It is a figure which shows the relationship between the output voltage and time in an example in case output power continues when switching a power converter circuit unit. It is a figure for demonstrating the change of the output voltage at the time of switching of a power converter circuit part. It is a figure which shows the relationship between the output voltage and time in an example in the case of controlling an output voltage when switching a power converter circuit unit. It is a flowchart which shows an example of the switching process of a power converter circuit unit. It is a flowchart which shows an example of the selection process which selects one power converter circuit unit. It is a flowchart which shows an example of the process of # 12 of FIG. It is a figure which shows the relationship between the output voltage and time in another example in the case of controlling an output voltage when switching a power converter circuit unit. It is a graph which shows the example of the characteristic of a solar cell.

  FIG. 1 is a block diagram illustrating a configuration of a photovoltaic power generation system using the power conversion device according to the present embodiment. As shown in FIG. 1, a photovoltaic power generation system used in conjunction with a commercial power system can be realized using the power conversion device 100 and the solar battery PV according to this embodiment. This solar power generation system is commercialized by further transforming the solar cell PV, the power conversion device 100 connected to the solar cell PV, the output converted by the power conversion device 100, or performing DC-AC conversion or the like. An interconnection matching device 200 for matching with the power system is provided, and the interconnection matching device 200 is connected to the commercial power system.

  The solar cell PV generates electric power according to the amount of solar radiation and outputs electric power.

  The power conversion device 100 converts the input power with high conversion efficiency and outputs the converted power. Details of the power conversion apparatus 100 will be described later.

  The interconnection matching device 200 includes a DC-AC inverter circuit, for example, and converts the output from the power conversion device 100 into an AC voltage of about 100 V so that the output can be transmitted to the commercial power system.

  The power output from the solar cell PV generated by the incidence of sunlight is input to the power conversion device 100. In the power converter 100, the output from the solar cell PV is used as input, and the power is converted with high conversion efficiency regardless of the range of the input current value. The power converted by the power conversion device 100 is input to the interconnection matching device 200, appropriately converted so as to be transmitted through the commercial power system, and transmitted to the commercial power system. Thus, the output from the solar cell PV can be sold effectively.

  Moreover, in the state which connected the solar cell PV to the input side of the power converter device 100, the output side can be connected to a rechargeable battery, and the electric power generated by the solar cell PV can also be stored in a storage battery.

  By using the power conversion device 100 according to the present embodiment, a photovoltaic power generation system that can extract the output from the solar cell PV with high conversion efficiency can be configured. A power conversion apparatus 100 according to the present embodiment will be described with reference to the drawings.

  FIG. 2 is a block diagram illustrating an example of the configuration of the power conversion apparatus according to the present embodiment. FIG. 3 is an explanatory diagram in which a part of an example of the configuration of the power conversion device according to this embodiment is a circuit diagram, and a solar cell PV is connected to the power conversion device 100. As illustrated in FIG. 2, the power conversion apparatus 100 includes a power conversion control unit 1, an input current detection unit 2 that detects an input current Iin that is a current of the input power Pin, and an input voltage Vin that is a voltage of the input power Pin. An input voltage detection unit 3 that detects power, a first power conversion circuit unit 4 that performs power conversion, a second power conversion circuit unit 5 and a third power conversion circuit unit 6, and an output current Iout that is a current of the output power Pout. An output current detector 7 for detecting, an output voltage detector 8 for detecting an output voltage Vout which is a voltage of the output power Pout, and an alarm output unit 9 for outputting an alarm signal are provided.

  The first to third power conversion circuit units 4 to 6 are circuits each configured to convert and output input power, and these have different input current ranges. The power input to the power conversion device 100 is input to the first to third power conversion circuit units 4 to 6, and the input is controlled by the power conversion control unit 1.

  As shown in FIG. 3, the first to third power conversion circuit units 4 to 6 are switching elements FET1, FET2, and FET3, commutation diodes D1, D2, and D3, and inductors for storing energy during power conversion. A certain coil (reactor) L1, L2, L3 and capacitors C1, C2, C3 are provided.

  All the switching elements FET1 to FET3 may be MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). The commutation diodes D1 to D3 may be ordinary diodes or Zener diodes. The first to third power conversion circuit units 4 to 6 constitute a step-down DC / DC converter. The gates of the switching elements FET1 to FET3 are respectively connected to the power conversion control unit 1, and ON and OFF are controlled by drive signals S1 to S3 transmitted from the power conversion control unit 1. The power conversion control unit 1 can select which of the first to third power conversion circuit units 4 to 6 is used to convert the output of the solar cell PV. Each of the ~ 3 power conversion circuit units 4 to 6 is controlled.

  In the first to third power conversion circuit units 4 to 6, the inductances of the coils L <b> 1 to L <b> 3 have different values from each other, and the values of the output power with respect to the input current are different from each other.

  The relationship between the input current Iin and the output power Pout of the first to third power conversion circuit units 4 to 6 will be described with reference to FIG. FIG. 4 is a graph showing the relationship between the input current and the output power of each power conversion circuit unit of the power conversion apparatus according to this embodiment. As shown in FIG. 4, the first to third power conversion circuit units 4 to 6 have different characteristics of the output power Pout with respect to the input current Iin. The value of the input current when obtaining the peak output power in each of the first to third power conversion circuit units 4 to 6 is also different from each other in each power conversion circuit unit.

  The input current ranges of the first to third power conversion circuit units 4 to 6 are different from each other and have overlapping portions with adjacent input current ranges. That is, as shown in FIG. 4, the input current ranges of the first power conversion circuit unit 4 and the second power conversion circuit 5 are adjacent to each other, and these current ranges overlap (indicated by a broken line in FIG. 4). See the part shown). Similarly, the input current ranges of the second power conversion circuit unit 5 and the third power conversion circuit unit 6 are adjacent to each other, and these current ranges overlap (see the portion indicated by the broken line in FIG. 4).

  When power conversion is performed using any one of the first to third power conversion circuit units 4 to 6, the boundary of the input current Iin of each power conversion circuit unit that can obtain the largest output power Pout is The threshold value th1 or 2 that is located on the small current side is defined as the small current side threshold value th1, and the one located on the large current side is defined as the large current side threshold value th2.

  The conversion efficiency of the first to third power conversion circuit units 4 to 6 varies depending on the values of the input current Iin and the output current Iout. In particular, the level of conversion efficiency is determined by the inductance and DC resistance of the coils L1 to L3. FIG. 5 is a graph showing an example of the relationship between the output current and the conversion efficiency in the power conversion circuit unit. FIG. 5A is a graph related to a power conversion circuit unit that is preferable when the output current Iout is relatively large, and FIG. 5B is a graph related to a power conversion circuit unit that is preferable when the output current Iout is relatively small. The conversion efficiency η is the ratio of the output power Pout to the input power Pin, and it can be said that the conversion efficiency η is a power conversion unit capable of performing power conversion with higher efficiency as the conversion efficiency η increases.

  Each of the power conversion circuit units used in FIGS. 5A and 5B is a power conversion circuit unit having a circuit configuration similar to that of the first to third power conversion circuit units 4 to 6. The coils have different inductances.

  5A operates under the conditions of an input voltage of 120 V, an output voltage of 100 V, and an output current of about 0.2 A to 10 A, and can obtain the highest conversion efficiency η when the input current is around 10 A. Designed to be able to. A coil capable of outputting a large current is selected for the power conversion circuit unit. Generally, a large current type coil has a comparatively small L value of 0.1 μH to several μH, and PWM switching control at a high frequency of 300 KHz to 1 MHz can realize a conversion efficiency of 90% or more when the output current is around 10 A. . However, when the output current is 1 A or less, the self-circuit loss is large, and the conversion efficiency η is reduced to about 50%.

  The power conversion circuit unit in FIG. 5B operates under conditions of an input voltage of 120 V, an output voltage of 100 V, and an output current of about 0 to 1 A so that the highest conversion efficiency η can be obtained when the input current is around 1 A. Designed. A coil capable of outputting a small current is selected for the power conversion circuit unit. Generally, a small current type coil has an L value of several tens of μH to several hundred μH, and PWM switching control is performed at a relatively low frequency of 300 KHz or less, so that the conversion efficiency is 90% in a current range of about 0.01 A to 1 A. Front and back can be realized. However, when the output current exceeds 1 A, the output decreases and a large current cannot be output.

  The first to third power conversion circuit units 4 to 6 perform power conversion with high conversion efficiency in different input current ranges, and are scheduled to be input to the power conversion device 100 depending on the input current ranges. The input current range can be covered.

  The first to third power conversion circuit units 4 to 6 may be converters having different input current ranges, and are not limited to the circuit configuration shown in FIG. What is necessary is just to design according to the intended purpose of the power converter device 100, respectively. For example, a bipolar transistor may be used as the switching element instead of the MOSFET. Further, instead of the commutation diode, a power conversion circuit unit that operates in the same manner as the first to third power conversion circuit units 4 to 6 can be configured even when a synchronous rectification type is used by using a switching element such as a MOSFET or a bipolar transistor. Can do. Moreover, you may use the power converter circuit part of a structure different from the 1st-3rd power converter circuit parts 4-6, for example, a boost type may be sufficient. Further, the number of power conversion circuit units is not limited to three as long as it is plural. The circuit configuration and the number of the power conversion circuit units may be appropriately adjusted according to the input current range of the power conversion device 100 determined according to the output of the power source connected to the power conversion device 100 and the like.

  The input current detection unit 2 detects the value of the input current Iin as needed and transmits it to the power conversion control unit 1. The input current detection unit 2 is configured using, for example, a current detection resistor, has an A / D converter, converts an analog signal detection value into a digital signal, and transmits the digital signal to the power conversion control unit 1.

  The input voltage detection unit 3 detects the value of the input voltage Vin as needed and transmits it to the power conversion control unit 1. The input voltage detection unit 3 is configured using, for example, a voltage dividing resistor, has an A / D converter, converts an analog signal detection value into a digital signal, and transmits the digital signal to the power conversion control unit 1.

  The output current detection unit 7 detects the value of the output current Iout as needed and transmits it to the power conversion control unit 1. The output current detection unit 7 is configured using, for example, a resistor for current detection, has an A / D converter, converts the detected value of the analog signal into a digital signal, and transmits the digital signal to the power conversion control unit 1.

  The output voltage detection unit 8 detects the value of the output voltage Vout as needed and transmits it to the power conversion control unit 1. The output voltage detection unit 8 is configured using, for example, a voltage dividing resistor, and has an A / D converter. The output voltage detection unit 8 converts an analog signal detection value into a digital signal and transmits the digital signal to the power conversion control unit 1.

  In FIG. 2, the power conversion control unit 1 includes an efficiency versus output current data storage unit 11, an output power acquisition unit 12, a selection unit 13, and a switching voltage calculation unit 14. The power conversion control unit 1 can be configured using, for example, a CPU, a nonvolatile memory, or the like. The power conversion control unit 1 selects, from among the first to third power conversion circuit units 4 to 6, one power conversion circuit unit that can obtain the largest power based on the input current Iin detected by the input current detection unit 2. Then, the power conversion circuit unit is controlled under control conditions such that the selected power conversion circuit unit can obtain the largest output power Pout.

  The efficiency vs. output current data storage unit 11 is, for example, a non-volatile memory, and stores efficiency vs. output current data TD1 to TD1 as shown in FIGS. The efficiency versus output current data TD1 to TD3 is data obtained by measurement in advance for each of the first to third power conversion circuit units 4 to 6, and the conversion efficiency in each of the first to third power conversion circuit units 4 to 6 It is data which shows the relationship between (eta) and output current Iout. The efficiency vs. output current data TD1 to TD3 are expressed in a graph showing the relationship between the conversion efficiency η and the output current Iout in the form of a table having the input current Iin and the output voltage Vout as parameters as shown in FIGS. be able to. FIGS. 6-8 is a figure which shows an example of the efficiency versus output current data regarding the 1st-3rd power converter circuit unit, respectively.

  The efficiency vs. output current data TD1 to TD3 is data for each input current Iin and for each output voltage Vout in each power conversion circuit unit. For example, the input current Iin is selected in 5A increments of 2A in a range of 1 to 9A. The output voltage is 80 to 120V, and five points are selected in increments of 10V. As shown in FIGS. 6 to 8, the efficiency versus output current data TD1 to TD1-3 are data in a table format divided by the input current Iin and the output voltage Vout.

  The range of the input current Iin in the efficiency versus output current data TD1 to TD1-3 is the range of the input current Iin that is actually planned to be used in the power conversion device 100. The range of the output voltage Vout in the efficiency versus output current data TD1 to TD1 is the range of the output voltage Vout that is actually planned to be used in the power conversion device 100. In these ranges, it can be said that the more the plurality of graphs, the more accurate power conversion can be performed. When the efficiency vs. output current data TD1 to TD3 is obtained by measurement, the amount of the efficiency vs. output current data TD1 to TD3 increases by decreasing the degree of the step of the input current Iin and the degree of the step of the output voltage Vout. Therefore, more accurate power conversion is possible.

  The output power acquisition unit 12 uses the detected value of the input current Iin detected by the input current detection unit 2 and the input voltage Vin, and the first to third power conversion circuit units 4 stored in the efficiency versus output current data storage unit 11. The maximum output power (circuit maximum output power Ph) that each of the first to third power conversion circuit units 4 to 6 can output is obtained from the efficiency versus output current data TD1 to TD3 for each of -6. When the input voltage Vin is fixed, the value may be used without detection. When the input voltage Vin fluctuates, the input voltage Vin is detected by the input voltage detection unit 3, and the detected value is obtained. Use it.

  The selection unit 13 compares each circuit maximum output power Ph acquired by the output power acquisition unit 12 with each other and obtains the largest output power among the first to third power conversion circuit units 4 to 6. Select the conversion circuit.

  The switching voltage calculation unit 14 is a target value of the output voltage Vout before and after switching of the power conversion circuit unit, based on the detected value of the output voltage Vout detected by the output voltage detection unit 8 and the target value Vm of the output voltage. The switching voltage Vch is calculated. The target value Vm of the output voltage is the output voltage Vout when the largest output power Pout is obtained in the selected power conversion circuit unit. The target value Vm of the output voltage is obtained in the selection process.

  The switching voltage Vch is a value between the detected value of the output voltage Vout of the power conversion circuit unit before switching and the target value Vm of the output voltage of the power conversion circuit unit after switching, for example, an average value of these values and do it. The switching voltage Vch may be, for example, a detected value of the output voltage Vout of the power conversion circuit unit before switching, or a target value Vm of the output voltage of the power conversion circuit unit after switching.

  The alarm output unit 9 receives the signal from the power conversion control unit 1 and outputs an alarm signal to notify the operator that an abnormality has occurred in the operation of the power conversion device 100. The alarm output unit 9 is a buzzer for notifying the operator of an abnormality by sounding an alarm sound, an alarm lamp (lamp) for notifying the operator of an abnormality by lighting or flashing, and displaying characters or the like on the display screen indicating the abnormality. Thus, a display device or the like that informs the operator may be used.

  In the power conversion device 100, when the power conversion circuit unit is switched so that the output power Pout does not change at the time of switching, the high conversion efficiency η can be maintained, but the output voltage Vout may change greatly before and after switching. There is.

  FIG. 9 is a diagram illustrating the relationship between the output voltage and time in an example in which the output power continues when the power conversion circuit unit is switched. In FIG. 9, the horizontal axis represents time, the vertical axis represents the output voltage Vout, and the maximum output power Pout (conversion efficiency η) in each power conversion circuit unit before and after switching with the input current Iin being constant at the time of switching. The change of the output voltage Vout in the case of switching so as to obtain the above is shown. The output voltage Vf is the output voltage Vout at the time of switching in the voltage conversion circuit unit before switching, and the output voltage Va is the output voltage Vout at the time of switching in the voltage conversion circuit unit after switching. If the conversion efficiency η is maximized in the power conversion circuit unit before and after switching, the output voltage Vf and the output voltage Va may be different, and when the difference between the output voltage Vf and the output voltage Va is large, FIG. As shown, the output voltage Vout changes greatly at the time of switching. The reason why the difference between the output voltage Vf and the output voltage Va becomes large will be described below with reference to FIG.

  FIG. 10 is a diagram for explaining a change in the output voltage when the power conversion circuit unit is switched, and is a diagram illustrating a relationship between the output current Iout and the conversion efficiency η before and after the switching operation of the power conversion circuit unit. . In the power conversion device 100, the range of the output voltage Vout is limited, so that the range of the output current Iout is also limited as shown in FIG. Further, the conversion efficiency η that maximizes the power conversion circuit unit before switching can be obtained at the position of the point F that is the vertex of the curve CV1. Moreover, it is the position of the point A that is the vertex of the curve CV2 that the conversion efficiency η that maximizes the power conversion circuit unit after switching can be obtained. In each power conversion circuit unit, the output current Iout may fluctuate within a limited range due to fluctuations in the output from the solar cell PV, but control is performed so as to maintain the position of the point F and the position of the point A, respectively (for example, , Maximum power follow-up control), it is possible to obtain a conversion efficiency η that maximizes each power conversion circuit unit.

  The power conversion circuit unit before switching is in a state where the conversion efficiency η is maximum at the time of switching (a state in the vicinity of the point F). Further, the power conversion circuit unit after switching is also in a state where the conversion efficiency η is maximum at the time of switching (a state in the vicinity of the point A). In other words, the point is moved from the point F to the point A by switching the power conversion circuit unit. As shown in FIG. 10, since the difference in the output current Iout is large between the point F and the point A, it can be said that the output current Iout increases rapidly by switching. Therefore, the output voltage Vout rapidly decreases as shown in FIG.

  When the output voltage Vout changes abruptly, the input voltage changes abruptly in the interconnection matching device 200 connected to the output side of the power conversion device 100, which causes a malfunction in the interconnection matching device 200. It can happen.

  However, in this embodiment, when the power conversion circuit unit is switched, control is performed so that the output voltage Vout of the power conversion circuit unit immediately before switching and the output voltage Vout of the power conversion circuit unit immediately after switching match each other. . FIG. 11 is a diagram illustrating the relationship between the output voltage and time in an example in which the output voltage is controlled when switching the power conversion circuit unit, where the horizontal axis is time and the vertical axis is the output voltage Vout. In the present embodiment, the switching voltage Vch is set, the output voltage Vout of the power conversion circuit unit before switching is controlled to change from the detected value of the output voltage Vout to the switching voltage Vch, and the power conversion circuit unit after switching The power conversion circuit unit is switched while the output voltage Vout of the output voltage Vout is maintained at the switching voltage Vch. After the switching is finished, control (step control) is performed so that the output voltage Vout of the power conversion circuit unit after switching changes from the switching voltage Vch to the target value Vm of the output voltage. Thereby, since the change of the output voltage Vout is performed gently at the time of switching, malfunction of the device connected to the output side of the power conversion device 100 is less likely to occur.

  The step control may be performed in parallel with the control for obtaining the maximum output power in the power conversion apparatus 100, for example, the maximum power follow-up control, or the control for obtaining the maximum output power temporarily. Instead of this, it may be performed.

  Next, the operation of the power conversion apparatus 100 will be described. In the solar power generation system shown in FIG. 1, the power generated by the solar cell PV is input to the power conversion device 100. In the power conversion device 100, the power conversion control unit 1 has one power conversion circuit unit that can obtain the largest output power from the first to third power conversion circuit units 4 to 6 every time a predetermined time elapses. A process of selecting (selection process) is performed. The predetermined time can be, for example, 10 to 100 ms, 100 to 1000 ms, or 1 to 10 seconds.

  When the PWM (Pulse Width Modulation) switching control is performed on the selected power conversion circuit unit, the power conversion control unit 1 obtains a control condition that provides the largest output power, and the selected 1 is selected according to the control condition. Two power conversion circuit units are controlled. Control conditions include switching frequency, target value Vm of output voltage, duty ratio of ON-OFF, and the like.

  When the selected power conversion circuit unit is a power conversion circuit unit that is currently used, the power conversion control unit 1 continues to control the power conversion circuit unit so as to obtain the largest output power Pout. to continue. However, when the selected power conversion circuit unit is different from the power conversion circuit unit currently used, the power conversion control unit 1 switches the input power Pin to the selected power conversion circuit unit. Thus, the selected power conversion circuit unit is controlled.

  With reference to FIGS. 12-14, the operation | movement of the power converter device 100 is demonstrated concretely. FIG. 12 is a flowchart showing an example of the switching process of the power conversion circuit unit, FIG. 13 is a flowchart showing an example of the selection process for selecting one power conversion circuit unit, and FIG. It is a flowchart which shows an example of 12 processes.

  As shown in FIG. 12, the power conversion control unit 1 determines whether or not the power conversion circuit unit needs to be switched, for example, every predetermined time (about 1 to 10 seconds) (# 11). When the power conversion control unit 1 selects a power conversion circuit unit different from the power conversion circuit unit currently used based on the result of the selection process of the power conversion circuit unit described later, the power conversion circuit unit Switching is necessary (Yes in # 11).

  Switching of the power conversion circuit unit is performed by the drive signals S1 to S3 of the power conversion control unit 1. For example, assuming that the first power conversion circuit unit 4 is currently selected, the drive signal S2 and the drive signal S3 are OFF, and only the drive signal S1 is transmitted. The drive signal S1 is a signal for the first power conversion circuit unit 4 to perform PWM switching control, and is a signal that repeats ON and OFF at a constant cycle. Since the drive signal S2 and the drive signal S3 are OFF, the input power Pin is not input to the second power conversion circuit unit 5 and the third power conversion circuit unit 6. Input power Pin is input only to the first power conversion circuit unit 4, and output power Pout is output.

  If the second power conversion circuit unit 5 is selected in the selection process, the power conversion control unit 1 turns off the drive signal S1 and transmits only the drive signal S2. Since the drive signal S1 and the drive signal S3 are OFF, the input power Pin is not input to the first power conversion circuit unit 4 and the third power conversion circuit unit 6. Input power Pin is input only to the second power conversion circuit unit 5, and output power Pout is output. In this way, the power conversion circuit unit is switched.

  The power conversion control unit 1 sets the target value Vm of the output voltage in the second power conversion circuit unit 5 instead of the first power conversion circuit unit 4 (# 12). The setting of the output voltage target value Vm means that the second power conversion circuit unit 5 is controlled so that the output voltage target value Vm is obtained.

  Switching in which the power conversion control unit 1 can obtain the target value Vm of the output voltage in the PWM switching control when the input current Iin of the detected value is input to the second power conversion circuit unit 5 Calculate frequency and duty ratio. The power conversion control unit 1 transmits the drive signal S2, and controls the second power conversion circuit unit 5 according to the calculated control conditions (switching frequency and duty ratio). As a result, the second power conversion circuit unit 5 outputs the output voltage Vout around the target value Vm of the output voltage, and the largest output power Pout is obtained.

  The power conversion control unit 1 compares the detected value of the output voltage Vout detected by the output voltage detection unit 8 with the target value Vm of the output voltage (# 13). In the case of No in # 11, power conversion may be performed by the currently selected first power conversion circuit unit 4, and thus the process proceeds to # 13 without performing # 12. Based on the comparison result in # 13, the power conversion control unit 1 adjusts the duty ratio by feedback control so that the detected value of the detected output voltage Vout and the target value Vm of the output voltage are matched (# 14).

  After the duty ratio is adjusted, the power conversion control unit 1 determines whether or not the target value Vm of the output voltage needs to be reset (# 15). Specifically, the power conversion control unit 1 compares the detected value of the current input current Iin with the detected value of the input current Iin used when selecting the second power conversion circuit unit 5. When the detected value of the input current Iin at the time of the selection process is different from the detected value of the current input current Iin and the difference is equal to or larger than a predetermined value set in advance, the output voltage target value Vm is reset. It is determined that it is necessary (Yes in # 15). This is because it is considered that the target value Vm of the output voltage may have changed significantly compared to the value when the second power conversion circuit unit 5 is selected.

  The power conversion control unit 1 again acquires and resets the target value Vm of the output voltage based on the efficiency versus output current data TD2 of the second power conversion circuit unit 5 shown in FIG. 7 (# 16). That is, the switching frequency and the power conversion control unit 1 can obtain the target value Vm of the output voltage obtained again by the PWM switching control when the input current Iin flows to the second power conversion circuit unit 5. The duty ratio is calculated, and the second power conversion circuit unit 5 is controlled according to this control condition.

  When the resetting of the output voltage target value Vm is unnecessary (No in # 15) and after the resetting of the output voltage target value Vm (# 16), the process returns to # 11 and the above steps are repeated.

  In FIG. 12, the power conversion circuit unit is automatically controlled by feedback.

  With reference to FIG. 13, a selection process for selecting one power conversion circuit unit that can obtain the largest output power Pout will be described. The input current Iin is detected by the input current detector 2 (# 21). Based on the detected value of the input current Iin and the efficiency versus output current data TD1 to TD1 of the first to third power conversion circuit units 4 to 6 stored in the efficiency versus output current data storage unit 11, a predetermined time ( For example, every 1 to 10 seconds), the output power Pout when the input power Iin is assumed to flow through each of the first to third power conversion circuit units 4 to 6 by the output power acquisition unit 12 is the output voltage Vout. (# 22).

  The output power acquisition unit 12 allows the first to third power conversion circuit units 4 to 6 in the range that the output voltage Vout can take from the output power Pout for each output voltage Vout in the first to third power conversion circuit units 4 to 6. The circuit maximum output power Ph in each is acquired (# 23). The range that the output voltage Vout can take is a value determined according to the output of the power source connected to the power conversion device 100, and the range of the output voltage Vout in which the power conversion device 100 is used. The circuit maximum output power Ph is the maximum output power that can be output in each power conversion circuit unit.

  The selection unit 13 of the power conversion control unit 1 compares the circuit maximum output power Ph of each power conversion circuit unit with each other, and obtains one power conversion circuit unit that obtains the largest output power, that is, the largest circuit maximum output power Ph. The power conversion circuit unit is selected (# 24). The power conversion control unit 1 determines whether switching is necessary according to the selected power conversion circuit unit (# 11 in FIG. 12).

  The above-described selection process in FIG. 13 will be specifically described. For example, assume that the detected input current Iin is 5 A (# 21).

  The output power acquisition unit 12 acquires the efficiency versus output current data TD1 to TD3 corresponding to each of the first to third power conversion circuit units 4 to 6 shown in FIGS. The For example, if the possible range of the output voltage Vout is 80 to 120 V, in each of the five data of 80 V, 90 V, 100 V, 110 V, and 120 V in the 5A row in each efficiency versus output current data TD1 to TD3. The data that maximizes the conversion efficiency η in the range that the output current Iout can take is selected. The range that the output current Iout can take is a value determined according to the output of the power source connected to the power conversion device 100, and the range of the output current Iout used in the power conversion device 100.

  The output power acquisition unit 12 calculates the input power Pin by multiplying the input current Iin (5A) and each input voltage Vin (Iin × Vin = Pin). The output power Pout for each output voltage Vout is calculated by multiplying the calculated input power Pin by the selected maximum conversion efficiency η (Pin × η = Pout). In this way, the output power Pout for each output voltage Vout is acquired (# 22). If the input voltage Vin is fixed, the value may be used without detection. If the input voltage Vin varies, the value detected by the input voltage detector 3 may be used.

The output power acquisition unit 12 compares the output power Pout for each output voltage Vout with each other, and acquires the circuit maximum output power Ph for each power conversion circuit unit (# 23). It is assumed that the conversion efficiencies when the output power becomes maximum in each of the first to third power conversion circuit units 4 to 6 are η _MAX 1, η _MAX 2, and η _MAX 3, respectively. Since the value obtained by multiplying the detected input current Iin and the input voltage Vin is Pin, the circuit maximum output power Ph of the first power conversion circuit unit 4 is η _MAX 1 × Pin, and the circuit of the second power conversion circuit unit 5 The maximum output power Ph is η _MAX 2 × Pin, and the circuit maximum output power Ph of the third power conversion circuit unit 6 is η _MAX 3 × Pin.

Of these three, for example, if the circuit maximum output power Ph (η _MAX 2 × P) of the second power conversion circuit unit 5 is maximum, the selection unit 13 selects the second power conversion circuit unit 5 (# 24). ).

The output voltage Vout when the circuit maximum output power Ph (η _MAX 2 × Pin) of the second power conversion circuit unit 5 can be obtained becomes the target value Vm of the output voltage. The switching frequency and the duty ratio may be set to values that can obtain the target value Vm of the output voltage when the input current Iin flows through the second power conversion circuit unit 5.

  Although the selection process has been described, besides this method, threshold values th1 and th2 of input current Iin are defined from the relationship between input current Iin and output power Pout shown in FIG. A conversion circuit unit can also be selected. For example, by comparing the input current Iin detected by the input current detection unit 2 with the threshold values th1 and th2, one power conversion circuit unit that can obtain the largest output power may be selected.

  Moreover, if the output power Pout which becomes the maximum with respect to the input current Iin in the first to third power conversion circuit units 4 to 6 is obtained in advance by measurement, and these values are also stored, the selected power conversion circuit And the detected value of the input current Iin, the maximum output power Pout can be obtained, and the target value Vm of the output voltage can be obtained from the detected value of the output current Iout. The power conversion control unit 1 obtains a duty ratio, a switching frequency, and the like based on the detected value of the input current Iin and the target value Vm of the output voltage, and controls the selected power conversion circuit unit according to the control conditions. That's fine.

  The power conversion control unit 1 also stores the above-described efficiency versus output current data TD1 to TD1 for each of the first to third power conversion circuit units 4 to 6, and the efficiency versus output current of the selected power conversion circuit unit Based on the data, the output voltage Vout having the largest conversion efficiency η in the detected value of the input current Iin is obtained, the output voltage Vout is set as the output voltage target value Vm, the duty ratio, the switching frequency, etc. are obtained, The selected power conversion circuit unit may be controlled according to the control conditions.

  Next, the process of # 12 of FIG. 12 is demonstrated using FIG. FIG. 14 is a flowchart showing an example of the process of # 12 of FIG. Currently, the first power conversion circuit unit 4 is selected and operating, and then the second power conversion circuit unit 5 is selected, and the first power conversion circuit unit 4 to the second power conversion circuit unit 5 are selected. Assume that it is necessary to switch to (# 11).

  The switching voltage setting unit 14 calculates the switching voltage Vch (# 31). Specifically, the average value of the detected value of the output voltage Vout before switching and the target value Vm of the output voltage obtained in the selection process is calculated. This average value is the switching voltage Vch.

  The detected value of the output voltage Vout corresponds to the output voltage Vf at which the largest output power is obtained in the first power conversion circuit unit 4 (power conversion circuit unit before switching) immediately before switching. Further, the target value Vm of the output voltage corresponds to the output voltage Va at which the largest output power is obtained in the second power conversion circuit unit 5 (power conversion circuit unit after switching) immediately after switching.

  The switching voltage setting unit 14 sets the switching voltage Vch in the first power conversion circuit unit 4 (# 32). Specifically, the control condition is changed by the switching voltage setting unit 14 so that the first power conversion circuit unit 4 outputs the switching voltage Vch.

  After the control condition is changed, the switching voltage setting unit 14 compares the switching voltage Vch and the detected value of the output voltage Vout (# 33). If these values are different (No in # 33), these values are compared. Are adjusted so that they match (# 34), # 33 is performed again, and feedback control is performed.

  If the switching voltage Vch and the detected value of the output voltage Vout match (Yes in # 33), the switching voltage setting unit 14 causes the second power conversion circuit unit 4 to output the second voltage while the output voltage Vout remains the switching voltage Vch. Switching to the power conversion circuit unit 5 is performed (# 35). Specifically, the switching voltage setting unit 14 controls the second power conversion circuit unit 5 to output the switching voltage Vch.

  After switching, the switching voltage setting unit 14 compares the switching voltage Vch and the detected value of the output voltage Vout (# 36). If these values are different (No in # 36), these values match. Thus, the duty ratio is adjusted (# 37), # 36 is performed again, and feedback control is performed.

  If the switching voltage Vch and the detected value of the output voltage Vout match (Yes in # 36), the switching voltage setting unit 14 sets the target value Vm of the output voltage in the second power conversion circuit unit 5 (# 38). ). Specifically, the control condition is changed so that the output voltage Vout at which the switching voltage Vch is set becomes the output voltage target value Vm.

  Then, the process proceeds to # 13 in FIG.

  By controlling the output voltage Vout as described above when switching the power conversion circuit unit, the change in the output voltage Vout becomes gentle as shown in FIG. Note that the power conversion apparatus 100 can maintain the high conversion efficiency η in other cases, although the output power Pout may slightly decrease when the power conversion circuit unit is switched.

  The switching voltage Vch is an average value of the detected value of the output voltage Vout and the target value Vm of the output voltage, but is not limited to this. A value between may be used.

  Further, when the difference between the output voltage Vout and the target value Vm of the output voltage is not less than a predetermined value, the change of the output voltage Vout between these values may be performed step by step at the time of switching. FIG. 15 is a diagram illustrating the relationship between the output voltage and time in another example in which the output voltage is controlled when the power conversion circuit unit is switched. As shown in FIG. 15, in addition to the switching voltage Vch, a switching neighborhood voltage Vchm1 which is a value between the detected value of the output voltage Vout and the target value Vm of the output voltage and is larger than the switching voltage Vch, and the switching voltage Vch. A smaller switching vicinity Vchm2 may be set, and the output voltage Vout may be changed stepwise when the power conversion circuit unit is switched. Thereby, even when the difference between the detected value of the output voltage Vout and the target value Vm of the output voltage is relatively large, the output voltage Vout can be changed gently. In addition, an absolute value or a ratio value can be obtained as a predetermined value of the differential voltage serving as a reference for performing stepwise control. For example, as the predetermined value, a value of the output voltage Vout in the range of about 1 V to several V, or a value in the range of several% to 10% can be used.

  In the power conversion device 100, the PWM switching control is used for the control of the first to third power conversion circuit units 4 to 6, but it is sufficient that power conversion can be performed, and other control methods such as PFM control may be used. Good. Further, when the input voltage Vin is a fixed value, it is not necessary to provide the input voltage detection unit 3, but a more accurate value can be used by providing the input voltage detection unit 3 and detecting the input voltage Vin. Highly accurate control is possible.

  If the change in the input voltage Vin is large, there is a possibility that some abnormality has occurred. The power conversion control unit 1 calculates the fluctuation range per predetermined time of the input voltage Vin detected by the input voltage detection unit 3 and compares it with a predetermined set value stored in advance. A signal may be transmitted to the alarm output unit 9, and the alarm output unit 9 outputs an alarm signal to notify the operator. For example, the lamp may be turned on, an alarm sound may be generated, or a warning display may be displayed on the display screen.

  Further, the power conversion control unit 1 calculates the output power Pout as needed by multiplying the output current Iout detected by the output current detection unit 7 and the output voltage Vout detected by the output voltage detection unit 8. A signal may be transmitted to the alarm output unit 9 when the value of the output power Pout becomes smaller than a predetermined value set in advance.

  In the above description, in the selection process, the power conversion control unit 1 selects all of the power conversion circuit units after obtaining all the circuit maximum output powers Ph of the first to third power conversion circuit units 4 to 6. is doing. However, since the switching of the power conversion circuit unit is normally performed between the power conversion circuit units having adjacent input current ranges, the currently selected power conversion circuit unit and the input current of the power conversion circuit unit The circuit maximum output power Ph with the power conversion circuit unit having the input current range adjacent to the range may be acquired, and any one power conversion circuit unit may be selected from them. As a result, the number of selection processing steps is reduced, and the time is also shortened.

  That is, when the first power conversion circuit unit 4 is currently selected, the circuit maximum output power Ph is obtained for each of the first power conversion circuit unit 4 and the second power conversion circuit unit 5 and compared. In this case, the power conversion circuit unit may be selected. When the second power conversion circuit unit 5 is currently selected, the circuit maximum output power Ph is set for each of the first power conversion circuit unit 4, the second power conversion circuit unit 5, and the third power conversion circuit unit 6. What is necessary is just to select a power converter circuit part by calculating | requiring and comparing them. Further, when the third power conversion circuit unit 6 is currently selected, the circuit maximum output power Ph is obtained for each of the second power conversion circuit unit 5 and the third power conversion circuit unit 6 and compared. In this case, the power conversion circuit unit may be selected.

  In the description of the power conversion device 100 described above, the power conversion control unit 1 performs the selection process for selecting any one of the first to third power conversion circuit units 4 to 6 every predetermined time. This process may be executed at the timing. For example, the power conversion control unit 1 detects the input current Iin detected by the input current detection unit 2 when the selection process for selecting one new power conversion circuit unit was performed last time, and the input current Iin detected most recently. When the difference value exceeds a predetermined set value, a selection process for selecting one of the first to third power conversion circuit units 4 to 6 may be executed.

  The power conversion device 100 according to the present embodiment has power conversion circuit units having different input current-output power characteristics, and by switching them, high conversion efficiency can be maintained in a wide input current region. Therefore, the configuration is not complicated and can be simplified, and the circuit design is easy. In addition, compared to power converters that have multiple identical circuits and combine them to accommodate a wide input current range, the increase in the number of parts for configuring the circuit is suppressed and a wide input current range is achieved. On the other hand, an output can be obtained efficiently. Therefore, downsizing and cost reduction are possible. In addition, since the change in the output voltage Vout is unlikely to change rapidly, the interconnection matching device 200 connected to the output side is unlikely to malfunction. When a storage battery is connected to the output side, the storage battery is efficiently stored.

  In the embodiment described above, the structure, shape, dimensions, number, material, composition, and the like of the entire power conversion device 100 or each part can be appropriately changed in accordance with the spirit of the present invention.

  The power conversion device 100 according to the embodiment described above has a wide input current range and an output current range, and can output maximum power in the entire current range in response to fluctuations in a wide range of input current. Further, downsizing and cost reduction are possible. For example, the power generated by the solar cell can be taken out more effectively by connecting to the solar cell. Therefore, it can be suitably used as a component of a solar power generation system.

DESCRIPTION OF SYMBOLS 1 Power conversion control part 2 Input current detection part 3 Input voltage detection part 4 1st power conversion circuit part 5 2nd power conversion circuit part 6 3rd power conversion circuit part 7 Output current detection part 8 Output voltage detection part 9 Alarm output part DESCRIPTION OF SYMBOLS 11 Efficiency vs. output current data storage part 12 Output power acquisition part 13 Selection part 14 Switching voltage setting part 100 Power converter 200 Matching apparatus L1-3 Coil C1-3 Capacitor FET1-3 Switching element D1-3 Commutation diode PV solar cell TD1-3 Efficiency vs. output current data th1 Small current side threshold th2 Large current side threshold

Claims (4)

A power conversion device that converts input power input as DC power and outputs output power,
An input current detector that detects an input current that is a current of the input power;
A plurality of power conversion circuit units that convert the input power into power, have input current ranges that are different from each other and overlap with adjacent input current ranges;
Among the plurality of power conversion circuit units, one power conversion circuit unit that obtains the largest output power in the input current detected by the input current detection unit is selected, and is the largest with respect to the selected power conversion circuit unit A power conversion control unit that performs control under a control condition for obtaining output power, and
The power conversion control unit, when selecting the one power conversion circuit unit, when the power conversion circuit unit is switched by the selection, the output voltage of the power conversion circuit unit immediately before switching, and the power conversion circuit immediately after switching Control so that the output voltage of the part matches each other,
The power converter characterized by the above-mentioned. The power conversion control unit
When selecting the one power conversion circuit unit, the power conversion circuit unit is switched by the selection,
The difference between the output voltage when the maximum output power is obtained in the power conversion circuit unit before switching and the output voltage when the maximum output power is obtained in the power conversion circuit unit after switching is a predetermined value. If it is above,
Control so that the change of the output voltage before and after the switching of the power conversion circuit unit is performed in stages.
The power conversion device according to claim 1. The power conversion control unit
Among the plurality of power conversion circuit units, a power conversion circuit unit that is currently selected, and a power conversion circuit having an input current range adjacent to the input current range of the power conversion circuit unit, the input current detection unit One power conversion circuit unit is selected based on the detected input current.
The power conversion device according to claim 1 or 2. An input voltage detector that detects an input voltage that is a voltage of the input power;
An alarm output unit that outputs an alarm signal when a change in the input voltage detected by the input voltage detection unit is large;
The power converter according to any one of claims 1 to 3.

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