JP5568954B2 - Inverter - Google Patents

Description

  The present invention relates to a power conditioner, and more particularly to a power conditioner that links a power generation unit and a commercial power supply system (system) in a power generation system including a power generation unit such as a fuel cell or a solar cell.

  In a power generation system including a power generation unit such as a fuel cell or a solar cell, a power conditioner is provided to link the power generation unit and a commercial power supply system (system). As shown in FIG. 4 (a), this type of power conditioner is configured to convert DC power generated by the power generation unit into AC power that can be supplied to the system. Converter section b, and inverter section c that converts the DC voltage boosted by converter section b into an AC voltage synchronized with system d (see, for example, Patent Document 1). In addition, in FIG. 4, e has shown the DC link capacitor (DC link part) of the inverter part c.

  FIG. 4B shows an example of a schematic configuration of the converter unit b. The converter section b shown in this figure is composed of an H bridge circuit f and a series-parallel circuit g. The H-bridge circuit f includes a resonant switching type switching element and two step-up transformers (both not shown), and two DC voltage outputs boosted in accordance with the turn ratio of the respective step-up transformers. The series-parallel circuit g is configured to be boosted and output within a range of 1 to 2 times by switching between series and parallel circuits. That is, the converter unit b is configured to boost the input voltage from the power generation unit a by the transformer turns ratio and the circuit switching of the series-parallel circuit.

  By the way, in the power conditioner configured as described above, in order to supply power from the power conditioner to the system, the voltage of the DC link unit e (DC link voltage) must be higher than the system voltage. Thus, the voltage value is set by adding a certain margin α to the peak value of the system voltage (system maximum voltage).

  For example, when the system is a three-phase AC 200V, the minimum required voltage as the DC link voltage is 200V × √2≈280V, but the target value of the DC link voltage is the system overvoltage determination value determined by the system. Assuming 120V, for example, 120V × 2 × √2≈340V, which is the maximum value, is the system maximum voltage, and a value obtained by adding a margin α to this voltage (where the margin α = 50V, the target value of the DC link voltage) Is set to 340V + 50V = 390V).

  FIG. 5 shows the relationship between the input voltage of the converter unit b (output voltage of the power generation unit a), the DC link voltage, and the system voltage. As shown in FIG. 5A, when the DC link voltage is higher than the system voltage, power having a normal voltage waveform can be supplied from the power conditioner to the system. However, when the DC link voltage becomes lower than the system voltage, the voltage waveform generated by the power conditioner is as shown in FIG. 5B, and the current waveform output to the system is distorted. Note that such a distorted current waveform is not allowed by the interconnection regulations.

  Here, in the conventional power conditioner described above, since the resonant switching method is used for the H-bridge circuit f in order to increase the efficiency of the converter section b, the output voltage cannot be controlled by switching that causes a decrease in efficiency. The control of the output voltage of the converter unit b is basically controlled by the transformer turns ratio.

  Therefore, in the conventional power conditioner, when the converter unit b is not in a state capable of outputting a voltage corresponding to the target value of the DC link voltage based on the input voltage to the converter unit b (the output voltage of the power generation unit a). The converter unit b (power conditioner) is prevented from starting. In other words, the converter unit b cannot be operated unless the input voltage of the converter unit b becomes a predetermined value or more.

JP 2009-48972 A

  However, such conventional power conditioners have the following problems, and improvements are desired.

  That is, for example, in the case of using a power generation unit a (for example, a fuel cell) of 100V to 160V as an output voltage range in a power conditioner having a transformer turns ratio of 2.2 times the converter unit b, If the converter unit b is started on condition that the output voltage becomes 100 V or more, the converter unit b can always output the target value of the DC link voltage (for example, 390 V described above).

  However, if this power conditioner is to be used for the power generation unit a having an output voltage range of 70V to 180V, when the output voltage of the power generation unit a is 70V, the boosting by the transformer of the converter unit b is 70V × 2.2. Since only 154V can be obtained, even if the series-parallel circuit g is switched in series (twice), only 308V can be output and the DC link voltage target value (390V) cannot be reached. On the other hand, when the input voltage of the converter unit b is 180 V, the voltage boosted by the transformer of the converter unit b becomes 180 V × 2.2 = 396 V. However, when the control is performed to the target value of DC link voltage 390 V, the H bridge A switching loss of the circuit f occurs, resulting in a decrease in efficiency. That is, in the conventional power conditioner, the range of the operation input voltage of the converter unit b (power conditioner) is limited, and the power generation unit a having a wide output voltage range may not be supported.

  Therefore, for example, when a fuel cell is used as the power generation unit a, the output voltage of the fuel cell is reduced due to a decrease in the operating temperature of the fuel cell due to aged deterioration of the fuel cell or a decrease in ambient temperature (for example, a decrease in temperature in winter, etc.) When the battery voltage temporarily decreases continuously or continuously, the converter unit b (power conditioner) is stopped, and there is a problem that power cannot be supplied to the system from the fuel cell. That is, even when the fuel cell is in a state where power can be generated to some extent, there may occur a state where the power generated by the fuel cell cannot be supplied to the system (cannot be used effectively). Even when the power generation unit a is a solar cell, the same problem occurs when the output voltage decreases due to deterioration over time or the shading of sunlight.

  In addition, in the conventional power conditioner, even if the target value of the DC link voltage can be output by the converter unit b, the input voltage of the converter unit b is the maximum voltage that can output the target value of the DC link voltage or When the voltage is close to the minimum voltage, the series-parallel circuit g is fixed in series or in parallel, so that there is a problem that the input ripple current cannot be suppressed and the DC link voltage is not stable. Such a state also has an adverse effect on the fuel cell stack.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a power conditioner having a wider operating input voltage range than the conventional one while preventing a reduction in efficiency of the converter unit. There is. As a result, it is possible to provide a power generation system that can supply power generated by the power generation unit to the system even when the output voltage of the power generation unit is lower than normal.

In order to achieve the above object, a power conditioner according to claim 1 of the present invention includes a converter unit that converts a DC voltage output from a power generation unit into a predetermined voltage, and a DC voltage output from the converter unit as an AC voltage. In a power conditioner including an inverter unit that converts the power to the system and supplies it to the system, the operation start input voltage of the power conditioner is set within the output voltage range of the power generation unit, and the control unit obtains the system voltage obtained by measurement. And setting the minimum target voltage value of the DC link unit of the inverter unit based on the allowable voltage value set based on the withstand voltage value of the DC link unit as the maximum target voltage value of the DC link unit, When the input voltage of the converter unit becomes equal to or higher than the operation start input voltage, the target voltage of the DC link unit is set in advance. The inverter is started using the initial value, and after that, even if the input voltage of the converter section becomes less than the operation start input voltage, an input voltage higher than the voltage value necessary for obtaining the minimum target voltage is obtained. If so, the target voltage value of the DC link unit is set in accordance with the input voltage value of the converter unit within the range of the minimum target voltage value to the maximum target voltage value.

  In the power conditioner according to this aspect, the target voltage value of the DC link unit (DC link capacitor) provided between the converter unit and the inverter unit is not fixed, and the input voltage value of the converter unit (that is, the power generation unit) It fluctuates according to the output voltage value. Therefore, when the input voltage of the converter unit is low, the target voltage value of the DC link unit can be lowered. For example, when the output voltage of the power generation unit is increasing at the beginning of power generation, the converter unit (power Conditioner) can be activated. Further, even when the input voltage of the converter unit is reduced while the converter unit (power conditioner) is operating, the operation of the converter unit can be continued while the target voltage value of the DC link unit is lowered. Therefore, according to the power conditioner of the first aspect, it is possible to provide a power conditioner having a wide operating input voltage range as compared with the conventional power conditioner in which the target value of the DC link voltage is fixed. .

  Further, since the target voltage value of the DC link unit can be lowered according to the input voltage of the converter unit, so that the target voltage of the DC link unit can be output even when the resonant switching method is adopted for the converter unit. Become.

  In addition, in setting the target voltage value of the DC link unit, the power conditioner according to claim 1 sets the lower limit value of the target voltage based on the system voltage obtained by measurement. The value does not fall below the system voltage, and power with a normal voltage waveform can always be supplied to the system. Moreover, since the upper limit value of the target voltage is set based on the withstand voltage value of the DC link unit, the DC link unit is not damaged even when the target voltage is increased.

  In a power conditioner according to a second aspect of the present invention, in the power conditioner according to the first aspect, the target voltage value of the DC link unit is set in proportion to the input voltage value of the converter unit. Features.

  In the power conditioner according to the second aspect, for example, even when the input voltage value of the converter unit temporarily decreases, the target voltage value of the DC link unit follows the decrease of the input voltage value. Therefore, the target voltage of the DC link unit can be output, and an efficient state can always be maintained.

  A power conditioner according to a third aspect of the present invention is the power conditioner according to the second aspect, wherein the amount of change per hour of the target voltage value of the DC link unit is limited to a predetermined value or less. And

  In the power conditioner according to the third aspect, since the amount of change per hour of the target voltage value of the DC link unit is limited to a predetermined value or less, the target voltage value of the DC link unit does not change rapidly. A sudden current change is not caused in the power generation unit. Therefore, it is possible to provide a power conditioner that is excellent in application to a power generation unit that dislikes rapid current fluctuation such as a solid oxide fuel cell (SOFC).

  A power conditioner according to a fourth aspect of the present invention is the power conditioner according to any one of the first to third aspects, wherein the minimum target voltage value is greater than a maximum value of a voltage allowed to be supplied to the system. It is allowed to be lowered.

  That is, in the conventional power conditioner, the voltage based on the system overvoltage determination value is set as the maximum value of the voltage allowed to be supplied to the system, but the system voltage actually used in the system is Often below the maximum. In the power conditioner according to claim 4, since it is allowed to set a value lower than the maximum value of the voltage allowed to be supplied to this system as the minimum target voltage value of the target voltage of the DC link voltage, The input voltage of the converter unit (output voltage of the power generation unit) can be effectively used up to a low region.

A power conditioner according to a fifth aspect of the present invention is the power conditioner according to any one of the first to fourth aspects, wherein the initial value preset as the target voltage of the DC link unit is a system overvoltage determination value. It is a value obtained by adding a predetermined margin to the maximum value.

  According to the present invention, the target voltage value of the DC link unit can be lowered when the input voltage value of the converter unit is low without fixing the target voltage value of the DC link unit to a constant value. A power conditioner having a wide operating input voltage range can be provided as compared with a conventional power conditioner having a fixed target voltage.

  Further, by lowering the target voltage value of the DC link unit according to the input voltage of the converter unit, the target voltage of the DC link unit is output even in a power conditioner having a converter unit employing a resonant switching method. be able to.

  In addition, since the lower limit value of the target voltage of the DC link unit is set based on the system voltage obtained by measurement, even if the target voltage of the DC link unit is set low, it does not fall below the system voltage. Therefore, power with a normal voltage waveform can always be supplied to the system.

  In addition, by setting the target voltage value of the DC link unit in proportion to the input voltage value of the converter unit, the target voltage value of the DC link unit also decreases as the input voltage value of the converter unit decreases. An efficient state can be maintained.

  In addition, since the target voltage of the DC link voltage is allowed to be lower than the maximum value of the voltage allowed to be supplied to the system, the output voltage of the power generation unit should be used effectively even in a low voltage region. Can do.

It is a circuit diagram which shows an example of schematic structure of the electric power generation system using the power conditioner which concerns on this invention. It is explanatory drawing which shows the voltage range which can be set as a target voltage of a DC link part in the same power conditioner. It is explanatory drawing which showed an example of the relationship between the input voltage of the converter part in the same power conditioner, and the target voltage of a DC link part. 4A and 4B are explanatory diagrams showing a conventional power conditioner, in which FIG. 4A is a circuit diagram showing a schematic configuration of the power conditioner, and FIG. 4B is a schematic configuration of a converter unit in the power conditioner. FIG. It is explanatory drawing which shows the relationship between the input voltage of the converter part in a power conditioner, the voltage of a DC link part, and a system voltage, Fig.5 (a) is supplying the electric power of a normal voltage waveform to a system. FIG. 5B shows a voltage waveform supplied to the system when the voltage of the DC link section is insufficient.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1

  FIG. 1 shows a schematic configuration of a power generation system to which a power conditioner according to the present invention is applied. As shown in FIG. 1, the power generation system includes a fuel cell 1 serving as a power generation unit, a power conditioner 3 for connecting the fuel cell 1 to a commercial power supply system (system) 2, and auxiliary units of the power generation unit. An auxiliary machine power supply unit (electric power supply means for the auxiliary machine 6) 4 that supplies electric power to the electric machine 6 is provided as a main part.

  The fuel cell 1 is a power generation device that generates power by supplying a fuel gas containing hydrogen such as natural gas and an oxidant gas containing oxygen such as air and causing a chemical reaction between hydrogen and oxygen. Is output as a DC voltage. The fuel cell 1 is classified into several types depending on differences in the electrolyte used, the operating temperature (stack temperature), and the like. In this embodiment, the solid oxide fuel cell (SOFC) using ion conductive ceramics as the electrolyte is used. Is used. Since the structure of the fuel cell 1 is well known, a detailed description thereof will be omitted, and the following description will focus on the configuration of the power conditioner.

  In FIG. 1, 5 indicates a power generation unit (stack) of the fuel cell 1. Since the operating temperature of SOFC is as high as several hundred degrees (for example, about 800 to 1000 ° C.), this fuel cell 1 requires one hour or more to prepare for startup from the start of startup to the start of power generation. When the power generation operation (steady operation) is started, the power generation unit 5 is configured to output a DC voltage of 70 to 180 V, for example. That is, in this embodiment, the fuel cell 1 having an output voltage range of 70 to 180 V is used.

  The auxiliary machine 6 is a peripheral device for operating the fuel cell 1, and includes an electrical load (not shown) such as a blower or a pump that operates during preparation for starting the fuel cell 1 or during a power generation operation. For example, a motor driven by a DC voltage (for example, DC 24V) is used. In addition, since the blower and pump which comprise the auxiliary machine 6 repeat on / off during starting of the fuel cell 1 and preparation for starting, the fluctuation | variation of the operating current during the operation | movement is very severe.

  The FC control unit 7 is a control device including a microcomputer as a control center, and is obtained from various sensors (not shown) that monitor the output voltage and output current of the power generation unit 5 and the state of the auxiliary machine 6. And the operation | movement of each part (including the auxiliary machine 6) of the fuel cell 1 is controlled based on the information obtained by communication with the PC control part 15 mentioned later.

  The commercial power supply system 2 includes a power supply line and a distribution board (none of which are shown) for supplying AC power supplied from a commercial power supply 8 (for example, three-phase AC200V) to an electrical load in the home. And connected to the fuel cell 1 via the power conditioner 3.

  The power conditioner 3 is a device for connecting the fuel cell 1 to the commercial power supply system 2, and as shown in FIG. 1, a converter unit 10, an inverter unit 11, a DC link unit 12, an AC bridge, and the like. The circuit part 13, the switch circuit part 14, and the PC control part 15 are provided as main parts.

  The converter unit 10 includes a DC / DC converter that converts a DC voltage output from the fuel cell 1 into a predetermined DC voltage, and converts the DC power output from the power generation unit 5 of the fuel cell 1 into an inverter unit. 11, the voltage is boosted to a state where electric power (for example, AC 200 V) that can be supplied to the commercial power supply system 2 can be generated, and supplied to the DC link unit 12.

  Specifically, the converter unit 10 has a hardware configuration similar to the converter unit in the above-described conventional power conditioner, that is, includes an H bridge circuit and a series-parallel circuit (FIG. 4B). The H-bridge circuit includes a resonant switching type switching element and two step-up transformers, and two DC voltage outputs boosted according to the turns ratio of these transformers are connected in series / parallel in a series-parallel circuit. By switching the circuit, the voltage is boosted in the range of 1 to 2 times that of one DC voltage output. In other words, the converter unit 10 converts the input voltage from the power generation unit 5 into a transformer turns ratio (2.2 times in the present embodiment) and a circuit switching between series-parallel circuits (parallel is 1 time and series is 2 times). Therefore, it can be controlled within a range of 1 to 2 times). The converter unit 10 is an insulating DC / DC converter having a transformer, and the fuel cell 1 and the commercial power supply system 2 are separated by the converter unit 10.

  The inverter unit 11 is a grid interconnection inverter connected to the converter unit 10 via the DC link unit 12, and the DC voltage output from the converter unit 10 is changed to a predetermined AC voltage (for example, AC 200V). A DC / AC inverter capable of performing a forward operation that is converted and supplied to the commercial power supply system 2 and a reverse operation that converts the AC voltage supplied from the commercial power supply system 2 into a predetermined DC voltage and outputs the DC voltage to the DC link unit 12 It consists of

  A switch circuit unit 14 is provided on the commercial power system side of the inverter unit 11, and the inverter unit 11 is connected to the contact A side of the switch circuit unit 14, and is connected to the commercial power system 2 via the switch circuit unit 14. It is configured to be interconnected (details will be described later). Further, a large-capacity DC link capacitor 12a is connected in parallel with the converter unit 10 on the converter unit side of the inverter unit 11 (that is, the DC link of the inverter), thereby forming the DC link unit 12. Yes.

  The AC bridge circuit unit 13 is a rectifier circuit for converting an AC voltage supplied from the commercial power supply system 2 (commercial power supply 8) into a predetermined DC voltage (for example, DC 280 V) and supplying the DC voltage to the DC link unit 12. As shown in FIG. 1, the input side is connected to the contact B side of the switch circuit unit 14, and the output side is connected to the DC link unit 12. The AC bridge circuit 13 may be provided with a smoothing circuit.

  The switch circuit unit 14 is configured by a changeover switch that is interposed in a connection portion between the commercial power supply system 2 and the power conditioner 3 and selects which of the inverter unit 11 or the AC bridge circuit unit 13 is connected to the commercial power supply system 2. Is done. The contact of the switch circuit unit 14 can be controlled by a PC control unit 15 described later, and the commercial power supply system 2 and the inverter unit 11 are connected by connecting the switch contact to the A side. Further, the commercial power supply system 2 and the AC bridge circuit unit 13 are connected by connecting the switch contact to the B side.

  In the present embodiment, the switch circuit unit 14 functions as a grid connection switch that links the power generation system of the fuel cell 1 and the commercial power supply system 2 and is not connected to the grid (when the system is disconnected). ) Is configured to connect the switch contact to the contact B side. The relay constituting the contact of the switch circuit unit 14 is configured to connect the contact to the B side when the relay drive circuit (not shown) is not energized, and the contact is made to the A side by energizing the relay circuit. It is configured to be connected to.

  In the present embodiment, the switch circuit unit 14 is used as a system interconnection switch. However, the system connection switch can be provided separately from the switch circuit unit 14. That is, it is also possible to provide a switch circuit (system connection relay) capable of disconnecting the system connection separately from the switch circuit unit 14 in series.

  The PC control unit 15 is a control device including a microcomputer as a control center, and includes various sensors (not shown) that monitor the input voltage, input current, stack temperature, and the like from the fuel cell 1 (power generation unit 5). While controlling the operation of each part of the power conditioner 3 based on information obtained, information obtained from the FC control unit 7 of the fuel cell 1, and information obtained from a remote control (operation unit) of the power generation system (not shown) The power generation system as a whole is also controlled.

  Specifically, the PC control unit 15 performs control of operation or stop of the converter unit 10 and the inverter unit 11, switching control of switch contacts of the switch circuit unit 14, and the like, and FC control of the fuel cell 1. Various commands (for example, commands for starting or stopping the fuel cell 1) are issued to the unit 7. The PC control unit 15 is supplied with driving power from the DC link unit 12 so that it can be operated even when the fuel cell 1 is not generating power, as in the auxiliary machine 6 described later.

  The auxiliary machine power supply unit 4 is a power supply device that generates a DC voltage (for example, DC 24V) to be supplied to the auxiliary machine 6 of the fuel cell 1. In this embodiment, the auxiliary machine power supply unit 4 is the converter unit 10. An isolated DC / DC converter configured separately is used. Specifically, the auxiliary power supply unit 4 is configured such that its input side is connected to the DC link unit 12 and receives DC power from the DC link unit 12, and its output side is connected to the auxiliary unit 6. Has been. In addition, since the auxiliary power supply unit 4 uses an insulated DC / DC converter as described above, the auxiliary power supply unit 4 separates the auxiliary machine 6 (fuel cell 1) and the commercial power supply system 2 from each other. Has been.

  In the present embodiment, as the DC link capacitor 12a, a 540 μF capacitor having an element withstand voltage of 450V is used. A capacitor (not shown) on the input side of the auxiliary power supply unit 4 has a 150 μF capacitor, and a power supply for the PC control unit (not shown) interposed between the DC link unit 12 and the PC control unit 15. A 15 μF capacitor is used as the input side capacitor.

  Next, the operation of the power generation system configured as described above will be described (specifically, focusing on the operation of the power conditioner 3).

  In the power conditioner 3, the chemical reaction of the power generation unit 5 of the fuel cell 1 is stabilized, and the output voltage from the power generation unit 5 (the input voltage Vcon in of the converter unit 10) is equal to or higher than the preset operation start input voltage V1. The program of the PC control unit 15 is set so as to start on the condition that it has become. Whether or not the chemical reaction of the power generation unit 5 is stable and whether or not the output voltage of the power generation unit 5 is equal to or higher than the operation start input voltage are determined by communication with the FC control unit 7 of the fuel cell 1. 15 does.

  Here, the operation start input voltage V <b> 1 of the power conditioner is set based on the output voltage range of the fuel cell 1. In the present embodiment, since the output voltage range of the power generation unit 5 (the output range during steady operation of the power generation unit) is 70 to 180V, the operation start input voltage V1 is set within this range. Specifically, the operation start input voltage V1 is set to a value close to the lower limit value of the output voltage range of the fuel cell 1 (in this embodiment, the operation start input voltage V1 is set to 100V). Thus, by setting the operation start input voltage V1 of the power conditioner to be close to the lower limit value of the output voltage range of the fuel cell 1, an early stage after the fuel cell 1 starts preparation for power generation operation (steady operation). The inverter can be started with. The fuel cell 1 is configured to start the power generation operation start-up by operating the auxiliary machine 6 on condition that the FC control unit 7 of the fuel cell 1 is given a power generation operation start command signal. Yes.

  Then, when the input voltage Vcon in of the converter unit 10 becomes equal to or higher than the operation start input voltage V1, the PC control unit 15 next sets the target voltage value V2 of the DC link unit 12. As the target voltage value V2, an initial value set in advance at the beginning of starting the converter unit 10 is used. This initial value is determined, for example, by a method similar to the determination of the target value of the DC link voltage in the conventional power conditioner. That is, when the three-phase AC200V is used as the commercial power supply system 2 as in the present embodiment, the initial value of the target voltage value V2 of the DC link unit 12 is, for example, the system maximum voltage that is the maximum value of the system overvoltage determination value. A value (390 V) obtained by adding a margin α (for example, 50 V) to (240√2 V≈340 V) is set.

  As described above, the power conditioner of the present embodiment uses an initial value set in advance as the target voltage value V2 of the DC link unit 12 at the beginning of the start-up of the converter unit 10, but after the start-up of the power conditioner (operation start) After), the PC control unit 15 sets the target voltage value V2 of the DC link unit 12 according to the value of the input voltage Vcon in of the converter unit 10. That is, the target voltage value V2 of the DC link unit 12 is made variable according to the value of the input voltage Vcon in of the converter unit 10.

  Specifically, the target voltage V2 of the DC link unit 12 is configured to vary within a voltage range set based on the system voltage obtained by measurement and the component withstand voltage value of the DC link unit 12. FIG. 2 is an explanatory diagram showing an example of this voltage range. 2 indicates the output voltage Vcon out of the converter unit 10 (input voltage of the DC link unit 12), and the horizontal axis indicates the input voltage Vcon in of the converter unit 10.

  As shown in FIG. 2, the lower limit (minimum target voltage value V2min) of the voltage range that can be set as the target voltage V2 of the DC link unit 12 is that the voltage of the DC link unit 12 is insufficient for supplying power to the system. In this case, the margin α is added to the system voltage obtained by the measurement. That is, the minimum target voltage value V2min is not set based on an assumed numerical value such as the maximum system voltage, but the system voltage actually used in the system is measured, and the margin α is added to the measured value. Thus, the target voltage V2 of the DC link unit 12 is set higher than the system voltage. That is, in the power conditioner of the present embodiment, the target voltage of the DC link unit 12 is set lower than the voltage necessary for outputting the voltage value of the system maximum voltage that is the maximum value of the voltage allowed to be supplied to the system. It is allowed to set.

  Here, as the measured value of the system voltage used for determining the minimum target voltage value V2min, any of the effective value, average value, or peak voltage value of the system voltage may be used. The peak voltage value of the system voltage can be obtained as the effective value of the system voltage × √2 or the average value of the system voltage × π / 2. Further, as a method of adding the margin α, there are a method of multiplying a measured value by a certain constant and a method of adding a certain numerical value to the measured value.

  On the other hand, the maximum value (maximum target voltage value V2max) of the target voltage value V2 of the DC link unit 12 is the component breakdown voltage value of the DC link unit 12 (specifically, the breakdown voltage value of the DC link capacitor 12a). In the form, the value does not exceed 450V). That is, if the target voltage V2 of the DC link unit 12 is set exceeding the withstand voltage value of the DC link capacitor 12a, the DC link unit 12 is damaged.

  By the way, in this embodiment, the converter unit 10 is configured to boost the input voltage Vcon in by switching the transformer turns ratio and switching the series-parallel circuit (switching between series (twice) and parallel (twice)). Therefore, the voltage that can be set as the target voltage V2 of the DC link unit 12 is also limited by the relationship with the input voltage Vcon in of the converter unit 10. That is, as shown in FIG. 2, a large value exceeding “input voltage Vcon in × transformer turns ratio × 2” cannot be set, and “input voltage Vcon in × transformer turns ratio × 1”. It is not possible to set a small value exceeding. As a result, the voltage range that can be set as the target voltage V2 of the DC link unit 12 is a range Z that is hatched in FIG.

  The power conditioner of the present embodiment sets the target voltage value V2 of the DC link unit 12 in accordance with the input voltage value Vcon in the converter unit 10 within the voltage range Z after the converter unit 10 is started. However, the setting is set so that the target voltage value V2 of the DC link unit 12 increases in proportion to the input voltage value Vcon in of the converter unit 10, for example, as shown in FIG.

  Specifically, in this control, when the input voltage Vcon in of the converter unit 10 is equal to or higher than the operation start input voltage V1 (100V), the initial value (390V) is set as the target voltage V2 of the DC link unit 12. maintain. On the other hand, when the input voltage Vcon in becomes less than the operation start input voltage V1, the conventional power conditioner stops the operation of the power conditioner at that time (disconnected from the system). In this power conditioner, even if the input voltage Vcon in is less than the operation start input voltage V1, if the input voltage Vcon in is higher than the voltage value necessary for obtaining the minimum target voltage value V2min, the input voltage Vcon in is input. The voltage value proportional to the voltage Vcon in is set as the target voltage V2 of the DC link unit 12, and the converter unit 10 is caused to boost the input voltage Vcon in. The target voltage V2 at that time is set as V2 = A × Vcon in + B (A and B are constants), for example.

  That is, in the power conditioner of the present embodiment, after the start of the converter unit 10, even if the input voltage Vcon in of the converter unit 10 decreases, as long as it does not become less than the minimum target voltage value V2min, The PC control unit 15 is configured to continue the operation of the power conditioner while lowering the target voltage V2 of the DC link unit 12 according to the input voltage Vcon in, and to continue supplying power to the commercial power supply system 2. Has been.

  Therefore, according to the power conditioner of this embodiment, compared with the conventional power conditioner in which the target voltage of the DC link unit 12 is fixed, the operating input voltage range (the converter unit 10 capable of operating the power conditioner) A power conditioner with a wide input voltage range can be provided. When the input voltage Vcon in of the converter unit 10 is lowered, the target voltage value V2 of the DC link unit 12 is lowered accordingly, so that the converter unit 10 employs a resonant switching type H-bridge circuit. Even if it exists, the target voltage V2 can be supplied to the DC link unit 12. In addition, since the target voltage of the DC link unit 12 does not fall below the actual system voltage, the commercial power system 2 can always be supplied with power having a normal current waveform.

  The setting method (control method) of the target voltage V2 of the DC link unit 12 can be appropriately changed as long as it is within the voltage range Z shown in FIG. For example, the target voltage V2 of the DC link unit 12 is configured to be set (reset) at a constant cycle (for example, at an interval of 10 milliseconds), or the amount of change per hour of the value of the target voltage V2 is limited to a predetermined value or less. can do. Specifically, when the target voltage V2 of the DC link unit 12 is set at intervals of 10 milliseconds, the difference between the currently set target voltage and the newly set target voltage is a predetermined value X (for example, 3V, specifically Is set so as not to exceed an allowable value in accordance with a current change allowed in the fuel cell 1, so that a sudden current change does not occur in the power generation unit 5 of the fuel cell 1. be able to.

  Further, in FIG. 3 described above, the target voltage V2 of the DC link unit 12 is shown as having an upper limit of 390V, but the upper limit can be appropriately changed as long as it is within the maximum target voltage value V2max.

  In the above-described embodiment, the case where the target voltage V2 is controlled by setting the minimum target voltage value V2min when setting the target voltage V2 of the DC link unit 12 has been shown. However, the setting of the minimum target voltage value V2min is as follows. , Set when the input voltage Vcon in of the converter unit 10 is equal to or lower than the voltage required to output the maximum voltage (system maximum voltage) allowed to be supplied to the commercial power supply system 2 in the power conditioner. It can also be configured to. That is, when the power conditioner can output the system maximum voltage, the target voltage V2 set based on other than the system voltage is used for setting the target voltage V2 of the DC link unit 12 until the system maximum voltage cannot be output. Alternatively, the target voltage V2 may be set based on the system voltage when the input voltage Vcon in of the converter unit 10 decreases. For example, when the power conditioner can output the maximum voltage (system maximum voltage) allowed to be supplied to the commercial power supply system 2 based on the input voltage Vcon in of the converter unit 10, the DC link unit 12 It is also possible to use a fixed value as the target voltage V2 and set the target voltage V2 based on the system voltage only when the maximum system voltage cannot be output. If the input voltage Vcon in of the converter unit 10 is equal to or lower than the voltage required to output the maximum voltage (system maximum voltage) allowed to be supplied to the commercial power supply system 2 in the power conditioner, The target voltage V2 of the DC link unit 12 is set based on the detected system voltage. In this case, the inverter unit 11 generates a voltage equal to or higher than the system voltage detected at that time as the target voltage V2 of the DC link unit 12. As long as it is equal to or higher than the voltage necessary for this, it is not always necessary to make it proportional to the input voltage Vcon in of the converter unit 10.

  In this power conditioner, power is supplied to the auxiliary machine 6 of the fuel cell 1 as follows.

  That is, when the fuel cell 1 is not performing power generation operation (steady operation) (when the fuel cell 1 is stopped or ready for starting), the auxiliary machine 6 is supplied with power from the commercial power system 2 side. It is configured. In this case, the PC control unit 15 connects the contact of the switch circuit unit 14 to the B side so that AC power from the commercial power supply 8 is supplied to the DC link unit 12 via the AC bridge circuit unit 13. Power is supplied to the power supply unit 4 via the DC link unit 12.

  On the other hand, when the fuel cell 1 is in a power generation operation (steady operation) state, the auxiliary machine 6 is supplied with power output from the converter unit 10, that is, power generated by the power generation unit 5. It is configured as follows. In other words, in this case, the PC control unit 15 connects the contact of the switch circuit unit 14 to the A side, and brings the inverter unit 11 and the commercial power supply system 2 into a connected state. In this state, the electric power output from the converter unit 10 is supplied to the auxiliary power supply unit 4 via the power supply line connected to the DC link unit 12. That is, in this case, the power supply line connecting the DC link unit 12 and the auxiliary machine power supply unit 4 functions as power supply means for supplying power to the auxiliary machine 6.

Embodiment 2
Next, another embodiment of the power conditioner will be described. This embodiment modifies the control of power supply to the auxiliary machine 6 in the power conditioner of the first embodiment described above.

  That is, in this embodiment, when the value of the input voltage Vcon in of the converter unit 10 is equal to or greater than a predetermined value, power is supplied from the DC link unit 12 to the inverter unit 11 and the power supply means, and the input of the converter unit 10 When the value of the voltage Vcon in is less than the predetermined value, power is supplied only from the DC link unit 12 to the auxiliary power supply unit 4 (the power supply unit).

  Specifically, in the power conditioner shown in this embodiment, the voltage of the DC link unit 12 is necessary to generate a voltage value obtained by adding the margin α to the system voltage when the converter unit 10 is operating. The voltage value of the input voltage Vcon in is stored in the PC control unit 15 as the predetermined value Y. When the value of the input voltage Vcon in is greater than or equal to the predetermined value Y, the PC control unit 15 The contact of the unit 14 is maintained on the A side so that power is supplied from the DC link unit 12 to the inverter unit 11 and the auxiliary power supply unit 4. On the other hand, when the value of the input voltage Vcon in of the converter unit 10 is less than the predetermined value Y, the inverter unit 11 is stopped and the contact of the switch circuit unit 14 is switched to the B side while continuing the operation of the converter unit 10. To disconnect the grid. That is, the output power of the converter unit 10 is supplied only to the auxiliary power supply unit 4.

  As described above, in the present embodiment, when the output power of the converter unit 10 is supplied only to the auxiliary power source unit 4, the target voltage V2 of the DC link unit 12 is further lowered than in the first embodiment, and the power condition is reduced. Therefore, the input voltage Vcon in to the converter unit 10 can be effectively used up to a low region. Further, at that time, since the inverter unit 11 is stopped, there is no power consumption by the inverter unit 11, and the power conditioner can be operated with power saving.

  The above-described embodiments show preferred embodiments of the present invention, and the present invention is not limited to these, and various design changes can be made within the scope of the invention.

  For example, in the above-described embodiment, the same value as the operation start input voltage in the conventional power conditioner is used as the operation start input voltage V1 of the power conditioner. However, the value of the operation start input voltage is set low, and the power conditioner It is also possible to accelerate the rise of na.

  Moreover, although the case where the solid oxide fuel cell (SOFC) was used as the fuel cell 1 was shown in the above-described embodiment, the fuel cell 1 has another type of fuel cell, for example, a solid polymer fuel cell. (PEFC) or the like can also be used. Moreover, it is applicable also to electric power generation parts (for example, a solar cell etc.) other than a fuel cell.

  Further, in the above-described embodiment, the configuration of the power generation system alone has been described. However, this power generation system recovers exhaust heat generated in the fuel cell 1 by exhaust heat recovery means (for example, a heat exchanger) and generates hot water. It can also be applied as a component of a cogeneration system, such as being used as a heat source.

  In the above-described embodiment, the case where the PC control unit 15 monitors the output voltage and the stack temperature of the fuel cell 1 has been shown. However, the control that the PC control unit 15 and the FC control unit 7 are responsible for ) Can be changed as appropriate. In other words, for example, the PC control unit 15 can perform all monitoring related to the stack.

1 Fuel Cell 2 Commercial Power Supply System 3 Power Conditioner 4 Auxiliary Power Supply Unit (Power Supply Means)
5 Power generation section (fuel cell stack)
6 Auxiliary machine 7 FC control unit 8 Commercial power supply 10 Converter unit 11 Inverter unit 12 DC link unit 13 AC bridge circuit unit 14 Switch circuit unit 15 PC control unit V2 Target voltage value V2min of DC link unit Minimum target voltage value V2max Maximum target voltage value

Claims (5)

A converter unit for converting a DC voltage output from the power generation unit into a predetermined voltage;
In a power conditioner including an inverter unit that converts a DC voltage output from the converter unit into an AC voltage and supplies the AC voltage to the system,
The operation start input voltage of the inverter is set within the output voltage range of the power generation unit,
The control unit sets a minimum target voltage value of the DC link unit of the inverter unit based on a system voltage obtained by measurement, and sets an allowable voltage value set based on a withstand voltage value of the DC link unit to the DC link. Set as the maximum target voltage value of the
When the input voltage of the converter unit becomes equal to or higher than the operation start input voltage, the power conditioner is started using an initial value set in advance as a target voltage of the DC link unit, and thereafter, the input voltage of the converter unit is If an input voltage equal to or higher than a voltage value necessary for obtaining a minimum target voltage is obtained even if the input voltage is less than the operation start input voltage , the converter unit within the range of the minimum target voltage value to the maximum target voltage value The target voltage value of the DC link unit is set according to the input voltage value of the power conditioner.   The power conditioner according to claim 1, wherein a target voltage value of the DC link unit is set in proportion to an input voltage value of the converter unit.   The power conditioner according to claim 2, wherein the amount of change per hour of the target voltage value of the DC link unit is limited to a predetermined value or less.   The power conditioner according to any one of claims 1 to 3, wherein the minimum target voltage value is allowed to be lower than a maximum value of a voltage allowed to be supplied to the system. 5. The initial value preset as the target voltage of the DC link unit is a value obtained by adding a predetermined margin to the maximum value of the system overvoltage determination value. 6. Power conditioner.

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