JP2020188603A - Power system - Google Patents

Abstract

To provide a power system suitable for adjusting power taken out from a fuel cell power generation system to a DC power conversion device.SOLUTION: By first feedback control and second feedback control, a characteristic conversion circuit 100 brings about output voltage-output power characteristics where the output voltage from the characteristic conversion circuit 100 becomes maximum when the output voltage has a value within a prescribed range, and output voltage-output current characteristics where the output current from the characteristic conversion circuit 100 becomes smaller as the output voltage from the characteristic conversion circuit 100 becomes larger in a region where the output voltage from the characteristic conversion circuit 100 straddles some value. First feedback control is executed when the sensor output is small, and second feedback control is executed when the sensor output is large so that the output voltage from the characteristic conversion circuit 100 is maximized by a switching current. The switching current depends on detection error of a current sensor 128, and changes when variable output from a variable output power supply 123 is changed.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a power system.

Various power generation systems have been proposed. An example of a power generation system is a photovoltaic power generation system that generates electricity using a photovoltaic power generation panel. Another example of a power generation system is a fuel cell power generation system that uses a fuel cell to generate power.

In power generation systems, power conversion may occur. Patent Document 1 describes that the output power of a photovoltaic power generation system and a fuel cell power generation system is changed to a predetermined voltage by power conversion.

Further, it is known that the electric power of the photovoltaic power generation system is taken out by the maximum power point tracking control. Maximum power point tracking control is also referred to as MPPT control. According to MPPT control, the power extracted from the PV system is maximized. Specifically, a DC power conversion device can be connected to the photovoltaic power generation system, and the DC power conversion device can execute MPPT control.

JP-A-2017-117673

When configuring a power system capable of executing MPPT control of a photovoltaic power generation system, a DC power converter is designed so that MPPT control of the photovoltaic power generation system can be executed. The present disclosure is suitable for extracting power from a fuel cell power generation system to a DC power converter by performing MPPT control using the DC power converter designed in this way, and further adjusting the extracted power. Providing a power system.

This disclosure is
A DC power converter designed to perform MPPT control for photovoltaic systems that maximize output power when the output voltage is within a predetermined range.
In the fuel cell power generation system, the DC power generated by the fuel cell power generation system is supplied to the DC power conversion device and the fuel cell power generation system.
It is a characteristic conversion circuit provided on a path connecting the fuel cell power generation system and the DC power conversion device, and includes a characteristic conversion circuit including a current sensor and a variable output power supply.
The current sensor detects the output current of the characteristic conversion circuit and outputs a sensor output representing the result of the detection.
The current sensor outputs the sensor output as the output current of the characteristic conversion circuit increases.
The variable output power supply outputs a variable output and
In the characteristic conversion circuit
The first circuit that executes the first feedback control that increases the output power of the characteristic conversion circuit as the sensor output increases, and the second feedback control that decreases the output power of the characteristic conversion circuit as the sensor output increases. A second circuit, which is executed in cooperation with the first circuit, is provided.
In the characteristic conversion circuit
(A) The output voltage-output power characteristic at which the output power of the characteristic conversion circuit is maximized when the output voltage of the characteristic conversion circuit is a certain value within the predetermined range, and the output voltage of the characteristic conversion circuit are the above. As the output voltage of the characteristic conversion circuit increases in a region straddling a certain value, the output current of the characteristic conversion circuit decreases, resulting in an output voltage-output current characteristic.
(B) When the output current of the characteristic conversion circuit when the first feedback control and the second feedback control are switched is defined as a switching current, the output current of the characteristic conversion circuit is the switching current. To provide the output current-output power characteristic that maximizes the output power of the characteristic conversion circuit.
The first feedback control is executed when the sensor output is relatively small, and the second feedback control is executed when the sensor output is relatively large.
The switching current provides a power system that depends on the detection error and changes as the variable output is changed.

The power system according to the present disclosure includes a DC power converter designed to perform MPPT control of a photovoltaic power generation system. The electric power system according to the present disclosure is suitable for extracting electric power from the fuel cell power generation system to the DC electric power converter by executing MPPT control using the DC electric power converter. Further, the power system according to the present disclosure is suitable for adjusting the extracted power.

Block diagram of power system at the time of grid connection Block diagram of the power system during a power outage The figure for demonstrating the VP characteristic obtained by the characteristic conversion circuit. The figure for demonstrating the VP characteristic of the comparative form. Diagram for explaining the output characteristics of the characteristic conversion circuit The figure which shows the 1st example of the characteristic conversion circuit Explanatory drawing of the first shunt regulator Explanatory drawing of current sensor Explanatory diagram of the effect of individual variation of the current sensor Explanatory drawing about adjustment of switching current by variable voltage The figure which shows the 1st specific example of the characteristic conversion circuit

(Findings underlying this disclosure)
Suppose you have a DC power converter designed to perform MPPT control of your PV system. Consider extracting power from the fuel cell power generation system to the DC power converter by executing MPPT control using the DC power converter. Such power extraction can be achieved by transforming the output characteristics of the fuel cell power generation system. According to the study of the present inventor, such conversion can be performed by a characteristic conversion circuit including a current sensor. Then, a power system in which power is supplied from the fuel cell power generation system to the DC power conversion device via the characteristic conversion circuit can be configured.

Further, when power is supplied from the fuel cell power generation system to the DC power conversion device as described above, the operating point in the output voltage-output power characteristic of the characteristic conversion circuit is adjusted by MPPT control. MPPT control is known as control that adjusts the operating point to the maximum power point. However, when the MPPT control is configured for the photovoltaic power generation system, the operating point in the output voltage-output power characteristic of the characteristic conversion circuit may be adjusted to a point deviated from the maximum power point in the MPPT control. This deviation reduces the power extracted from the fuel cell power generation system to the DC power converter. The technology that suppresses the decrease in the extracted power due to this deviation is worth adopting.

Further, it is not easy to completely eliminate the individual variation of the current sensor used in the above characteristic conversion circuit, and it is easy to completely avoid the error caused by the individual variation in the detection result of the current sensor. is not. Therefore, when the above-mentioned electric power system is mass-produced, the maximum value of the output power of the characteristic conversion circuit may vary depending on the electric power system. The variation in the maximum value of the output power means that when the power is extracted from the characteristic conversion circuit by MPPT control, the extracted power varies.

From another point of view, it would be convenient if the power that can be extracted from the fuel cell power generation system could be adjusted according to the situation.

Hereinafter, embodiments will be described in detail with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of already well-known matters or duplicate explanations for substantially the same configuration may be omitted.

It should be noted that the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

Further, in the embodiment, the ordinal numbers such as first, second, third ... May be used. If an element has an ordinal number, it is not essential that a younger element of the same type exists. You can change the number of the ordinal numbers as needed.

In the embodiment, the combination of the output current, the output voltage, and the output power of the characteristic conversion circuit may be referred to as an operating point of the characteristic conversion circuit. The operating point when the output power of the characteristic conversion circuit is maximized is sometimes referred to as the maximum power point. The output power at the maximum power point of the characteristic conversion circuit may be referred to as the maximum power of the characteristic conversion circuit.
(Embodiment)
1 and 2 are block diagrams of the electric power system 300 according to the present embodiment. Specifically, FIG. 1 shows an example of power flow during grid connection. FIG. 2 shows an example of power flow during a power failure. In these figures, solid lines represent that power is flowing through the electrical circuit. The dotted line indicates that power is not flowing through the electric circuit. Further, VAC1 and VAC2 represent AC voltage. The effective value of the AC voltage VAC1 is smaller than the effective value of the AC voltage VAC2. The effective value of the AC voltage VAC1 is, for example, 100V. The effective value of the AC voltage VAC2 is, for example, 200V. In this example, the electric circuit or path of the AC voltage VAC1 is realized by two single-phase two-wire electric wires. Further, the electric circuit or path of the AC voltage VAC2 is realized by two ungrounded lines out of three single-phase three-wire electric wires.

The power system 300 is interconnected with the system power supply 200. Power can be supplied to the power system 300 from the system power supply 200. Further, the power system 300 can reverse power flow to the system power supply 200. The electric power system 300 includes a power station 10, a fuel cell power generation system 40, a substrate 60, a solar power generation system 31 and 32, a power storage device 25, a power switching unit 28, a first distribution board 80, and a first power system 300. It has a two-distribution board 90, loads 251,252 and 253, and an outlet 260. Hereinafter, the first distribution board 80 may be referred to as a main distribution board 80. Further, the second distribution board 90 may be referred to as an independent distribution board 90.
[Power Station 10]
The power station 10 includes a DC power converter 20, a first DC bus 11, a fourth DCDC converter 12, and a first inverter 13.

The DC power converter 20 is designed to perform maximum power point tracking control for a photovoltaic power generation system in which the output power is maximized when the output voltage is within a predetermined range. A photovoltaic power generation system is a system that generates electricity using a photovoltaic power generation panel. Hereinafter, the maximum power point tracking control may be referred to as MPPT control.

DC power is input to the DC power converter 20 from the photovoltaic power generation systems 31 and 32 and the fuel cell power generation system 40. The DC power output from the DC power converter 20 is supplied to the first DC bus 11.

Specifically, the DC power converter 20 includes a first DCDC converter 21, a second DCDC converter 22, and a third DCDC converter 23. DC power is input to the first DCDC converter 21 from the fuel cell power generation system 40. DC power is input to the second DCDC converter 22 from the first photovoltaic power generation system 31. DC power is input to the third DCDC converter 23 from the second photovoltaic power generation system 32. The DC power output from these DCDC converters 21, 22, and 23 is supplied to the first DC bus 11.

The 4th DCDC converter 12 converts the DC power input from the 1st DC bus 11 into DC power having different voltages. The DC power converted by the 4th DCDC converter 12 is supplied to the power storage device 25. Further, the 4th DCDC converter 12 converts the electric power input from the power storage device 25 into DC electric power having a different voltage and supplies the electric power to the 1st DC bus 11. That is, the fourth DCDC converter 12 is a bidirectional DCDC converter. The fourth DCDC converter 12 operates so that the terminal voltage of the power storage device 25 is within the rated range.

The first inverter 13 converts DC power into AC power. Specifically, the first inverter 13 converts the DC power input from the first DC bus 11 into AC power having a voltage V _AC1 or a voltage V _AC2 . When AC power of voltage V _AC1 is obtained by the first inverter 13, the power is supplied to the power switching unit 28. When AC power of voltage V _AC2 is obtained by the first inverter 13, the power is supplied to the main distribution board 80.

The first inverter 13 can also convert the AC power of the voltage V _AC2 input from the system power supply 200 via the main distribution board 80 into DC power. The DC power thus obtained is supplied to the power storage device 25 via the first DC bus 11 and the fourth DCDC converter 12.
[Solar power generation systems 31 and 32]
In the present embodiment, the power system 300 includes at least one photovoltaic power generation system that maximizes the output power when the output voltage is within a predetermined range. The DC power generated by the at least one photovoltaic power generation system is supplied to the DC power converter 20.

Specifically, the photovoltaic power generation systems 31 and 32 correspond to photovoltaic power generation systems in which the output power is maximized when the output voltage is within a predetermined range. The first photovoltaic power generation system 31 has at least one photovoltaic power generation panel 36. The first photovoltaic power generation system 31 generates electricity using the at least one photovoltaic power generation panel 36. The second photovoltaic power generation system 32 has at least one photovoltaic power generation panel 37. The second photovoltaic power generation system 32 generates electricity using the at least one photovoltaic power generation panel 37. The DC power generated by the photovoltaic power generation systems 31 and 32 is supplied to the DC power converter 20.
[Fuel cell power generation system 40]
The fuel cell power generation system 40 is a system that generates power using the fuel cell 41. The DC power generated by the fuel cell power generation system 40 can be supplied to the DC power converter 20. The AC power generated by the fuel cell power generation system 40 can be supplied to the main distribution board 80.

The fuel cell power generation system 40 includes a fuel cell 41, a fifth DCDC converter 42, a second DC bus 43, a second inverter 44, a sixth DCDC converter 45, a heater 46, a hot water storage unit 47, a controller 51, and the like. It has a low-voltage power supply 52 and an auxiliary power supply 55. The auxiliary power supply 55 may be referred to as a D1 power supply 55.

The fuel cell 41 generates DC electric power. Specifically, the fuel cell 41 includes a stack. The stack then produces DC power from oxygen and hydrogen.

The fifth DCDC converter 42 converts the DC power generated by the fuel cell 41 into DC power having different voltages. In this example, the fifth DCDC converter 42 boosts the DC power generated by the fuel cell 41. The boosted DC power is supplied to the second DC bus 43.

The second inverter 44 converts the DC power input from the second DC bus 43 into AC power having a voltage V _AC2 . The AC power obtained by the second inverter 44 is supplied to the main distribution board 80.

The sixth DCDC converter 45 converts the DC power input from the second DC bus 43 into DC power having different voltages. In this example, the sixth DCDC converter 45 steps down the DC power input from the second DC bus 43.

The heater 46 uses the DC power converted by the 6th DCDC converter 45 to heat the water. The warmed water (hereinafter, may be referred to as hot water) is stored in the hot water storage unit 47.

It is assumed that when the generated power of the fuel cell 41 is larger than the required load of the output destination of the second inverter 44, the fuel cell power generation system 40 outputs all the generated power of the fuel cell 41 from the second inverter 44. In that case, of the electric power output from the second inverter 44, the portion exceeding the required load (hereinafter, may be referred to as surplus electric power) is reverse-fed to the system power supply 200. In order to avoid reverse power flow, in this example, when the power obtained by adding a predetermined margin to the surplus power is larger than zero, the power is supplied from the second DC bus 43 to the heater 46 via the sixth DCDC converter 45. That is, the sixth DCDC converter 45 is for surplus power. Further, the heater 46 warms the water and prevents reverse power flow.

The controller 51 controls the DCDC converters 42 and 45, the second inverter 44, and the protection relay 62 described later. In this embodiment, the controller 51 is a micro control unit (MCU). The low-voltage power supply 52 supplies power for control to the controller 51, the protection relay 62, and the characteristic conversion circuit 100 described later. The D1 power source 55 is used to operate auxiliary equipment of the fuel cell power generation system 40 such as a pump, a blower, and a valve.
[Board 60]
The substrate 60 is provided on a path connecting the fuel cell power generation system 40 and the power station 10. DC power is supplied to the substrate 60 from the fuel cell power generation system 40, specifically, from the second DC bus 43. The substrate 60 includes a characteristic conversion circuit 100, an LC filter 61, and a protection relay 62.

As is clear from the above description, the characteristic conversion circuit 100 is provided on the path connecting the fuel cell power generation system 40 and the DC power conversion device 20, specifically on the DC power path.

3A and 4 show the output characteristics of the characteristic conversion circuit 100. FIG. 5 shows a first example of the characteristic conversion circuit 100.

As shown in FIG. 5, the characteristic conversion circuit 100 includes a voltage-current control circuit 160, a current sensor 128, and a variable output power supply 123.

The voltage / current control circuit 160 is a DCDC converter. The voltage-current control circuit 160 is provided between the fuel cell power generation system 40 and the current sensor 128. Specifically, the voltage-current control circuit 160 is provided between the second DC bus 43 and the current sensor 128.

The current sensor 128 detects the output current of the characteristic conversion circuit 100. The current sensor 128 outputs a sensor output representing the result of the detection. The current sensor 128 outputs a larger sensor output as the output current of the characteristic conversion circuit 100 increases. That is, the sensor output increases as the output current of the characteristic conversion circuit 100 increases. In this embodiment, the sensor output is the first sensor voltage V1. The current sensor 128 includes a sensor output unit 128a that outputs the first sensor voltage V1.

The variable output power supply 123 outputs a variable output. In this embodiment, the variable output is a variable voltage V4. The variable output power supply 123 is, for example, a digital-analog port of the controller 51.

In the characteristic conversion circuit 100, a first circuit 110 and a second circuit 120 are provided. The first circuit 110 executes the first feedback control in which the output power of the characteristic conversion circuit 100 increases as the sensor output increases. The second circuit 120 executes the second feedback control in which the output power of the characteristic conversion circuit 100 decreases as the sensor output increases in cooperation with the first circuit 110. In the characteristic conversion circuit 100, a feedback current supply unit 130 is also provided.

Specifically, the first circuit 110 executes the first feedback control in cooperation with the voltage-current control circuit 160 and the current sensor 128. The second circuit 120 executes the second feedback control in cooperation with the first circuit 110 and the voltage / current control circuit 160.

Regarding the output voltage-output power characteristic of (a) of the characteristic conversion circuit 100, the output power of the characteristic conversion circuit 100 is the maximum when the output voltage of the characteristic conversion circuit 100 is within a predetermined range as shown in FIG. 3A. Output voltage-output power characteristic. Further, the output voltage-output current characteristic of (a) is characterized as the output voltage of the characteristic conversion circuit 100 increases in a region where the output voltage of the characteristic conversion circuit 100 straddles a certain value as shown in FIGS. 3A and 4. It is an output voltage-output current characteristic that reduces the output current of the circuit 100. Here, the region where the output voltage of the characteristic conversion circuit 100 straddles the above-mentioned certain value is the region from the first value where the output voltage of the characteristic conversion circuit 100 is smaller than the above-mentioned certain value to the second value larger than the above-mentioned certain value. is there.

As described above, the DC power converter 20 is designed to be able to perform MPPT control of the photovoltaic power generation system that maximizes the output power when the output voltage is within a predetermined range. In the present embodiment, the characteristic conversion circuit 100 has the output voltage-output power characteristic of (a) above, in which the output power is maximized when the output voltage is a value within the predetermined range. Further, in the present embodiment, the characteristic conversion circuit 100 has an output voltage-output current characteristic in which the output current of the characteristic conversion circuit 100 decreases as the output voltage of the characteristic conversion circuit 100 increases in a region where the output voltage straddles a certain value. .. The output voltage-output power characteristic of the fuel cell power generation system is not always suitable for extracting power by MPPT control. However, the characteristic conversion circuit 100 having the output voltage-output power characteristic and the output voltage-output current characteristic of the above (a) is a fuel cell power generation system 40 by executing MPPT control using the DC power conversion device 20. It is possible to take out power from the DC power converter 20 to the DC power converter 20.

Further, according to the characteristic conversion circuit 100, it is easy to take out a large amount of electric power from the fuel cell power generation system 40 to the DC power conversion device 20 based on the MPPT control. Hereinafter, this point will be described with reference to FIGS. 3A and 3B.

As described above, in the region where the output voltage of the characteristic conversion circuit 100 straddles the above-mentioned value, the output voltage of the characteristic conversion circuit 100 becomes smaller as the output voltage of the characteristic conversion circuit 100 increases, resulting in an output voltage-output current characteristic. Due to this output voltage-output current characteristic, as shown in FIG. 3A, the graph of the output voltage-output power characteristic of the characteristic conversion circuit 100 shows that the output power is convex upward with respect to the output voltage in the region straddling the above-mentioned value. It becomes a curved shape of.

Temporarily, the graph of the output voltage-output power characteristic of the characteristic conversion circuit 100 is. It is assumed that the output power is a linear shape that is convex upward with respect to the output voltage as shown in FIG. 3B. In this case, it is assumed that the MPPT control is executed, but the operating point is adjusted to a point deviated from the maximum power point. Specifically, it is assumed that the output voltage of the characteristic conversion circuit 100 is adjusted to a voltage Vreal deviated from the output voltage Vtarget of the maximum power point. In this case, the output power of the characteristic conversion circuit 100 is reduced as compared with the case where the operating point is adjusted to the maximum power point. In FIG. 3B, this decrease is referred to as δPB.

On the other hand, also in the example of FIG. 3A, when the output voltage of the characteristic conversion circuit 100 is adjusted to the voltage Vreal deviated from the output voltage Vtarget of the maximum power point, the output power of the characteristic conversion circuit 100 has the operating point at the maximum power point. It decreases compared to the case where it is adjusted to. In FIG. 3A, this decrease is described as δPA.

As described above, regardless of whether the graph of the output voltage-output power characteristic of the characteristic conversion circuit 100 is linear or curved, if the operating point deviates from the maximum power point, the output power of the characteristic conversion circuit 100 will be increased. Decrease. However, the amount of decrease is different. Specifically, the reduction width δPA in the case of FIG. 3A is smaller than the reduction width δPB in FIG. 3B. The fact that the graph of the output voltage-output power characteristic has an upwardly convex curve suppresses the decrease in output power due to the above deviation, and from the fuel cell power generation system 40 to the DC power converter 20. It is advantageous from the viewpoint of suppressing the decrease in the power taken out.

In the actual MPPT control, in addition to the mountain climbing method, there is also a method of controlling the extraction voltage to a predetermined voltage, and it is not always easy to match the operating point with the maximum power point with high accuracy in such control. .. Even with the hill climbing method, it may not be possible to stably extract the maximum power depending on the control resolution. Therefore, the fact that the graph of the output voltage-output power characteristic has an upwardly convex curve is actually advantageous in that the decrease in output power due to the MPPT control method and resolution can be suppressed. ..

It is also possible that the user purchases the characteristic conversion circuit 100 from one vendor and the DC power converter 20 that performs MPPT control from another vendor. In that case, the characteristic conversion circuit 100 is connected to the DC power conversion device 20 having a performance unknown to the designer of the characteristic conversion circuit 100. In this case, the operating point may be adjusted to a point deviated from the maximum power point due to the fact that the characteristic conversion control and the MPPT control are not completely matched. From this, it can be said that the fact that the graph of the output voltage-output power characteristic has a convex curved shape is actually advantageous. Further, it can be said that the fact that the graph of the output voltage-output power characteristic has a convex curved shape enhances the compatibility of the characteristic conversion circuit 100 and reduces the restrictions of the DC power conversion device 20 that can be adopted.

Further, regarding the output current-output power characteristic of (b), the output power of the characteristic conversion circuit 100 becomes maximum when the output current of the characteristic conversion circuit 100 is the switching current isw as shown in FIGS. 3A and 4. Output voltage-output power characteristic. Here, the switching current isw is the output current of the characteristic conversion circuit 100 when the first feedback control and the second feedback control are switched.

The switching current isw depends on the error of detecting the output current of the characteristic conversion circuit 100 by the current sensor, and changes when the variable output is changed.

If there are individual variations in the current sensor 128, an error may occur in the detection of the current sensor 128. That is, an error may occur in the sensor output. If the sensor output having an error is used for control in the characteristic conversion circuit 100, the switching current isw may deviate from the target value (hereinafter, may be referred to as a target current). If the switching current isw deviates, the maximum power point shown in FIGS. 3A and 4 may deviate from the target point. If the maximum power point deviates, the maximum power of the characteristic conversion circuit 100 may deviate from the target value (hereinafter, may be referred to as a target power).

In this regard, according to the present embodiment, the switching current isw can be adjusted by changing the variable output. As a result, the deviation of the switching current isw from the target current can be reduced, the deviation of the maximum power point from the target point can be reduced, and the deviation of the maximum power from the target power can be reduced. Further, by adjusting the variable output and adjusting the switching current isw, it is possible to adjust the maximum power of the characteristic conversion circuit 100 according to the situation. For example, when the generated power of the photovoltaic power generation system connected to the DC power converter 20 is small, the maximum power may be increased, and when the generated power of the photovoltaic power generation system is large, the maximum power may be decreased. it can. Further, the maximum output power of the fuel cell power generation system 40 may decrease due to, for example, aged deterioration of the stack of the fuel cell 41. In such a case, by lowering the maximum power output from the characteristic conversion circuit 100, the maximum power can be kept within a range that can be supplied by the fuel cell power generation system 40.

By reducing the deviation of the maximum power from the target power, it is possible to reduce the deviation of the extracted power from the target power when the power is taken out from the characteristic conversion circuit 100 by MPPT control. By adjusting the maximum power of the characteristic conversion circuit 100 according to the situation, when the power is taken out from the characteristic conversion circuit 100 by MPPT control, the electric power taken out can be adjusted to a value according to the situation. For example, when the generated power of the photovoltaic power generation system connected to the DC power converter 20 is small, the extracted power is increased, and when the generated power of the photovoltaic power generation system is large, the extracted power is decreased. Can be done. Further, when the maximum output power of the fuel cell power generation system 40 is lowered, the power taken out can be reduced.

Typically, the characteristic conversion circuit 100 output voltage-output power characteristic is a characteristic in which the output power has a single peak with respect to the output voltage. The output voltage-output power characteristic and the output voltage-output current characteristic in (a) above show such characteristics.

The output characteristics of the characteristic conversion circuit 100 will be further described.

In FIG. 3A, the solid line represents the relationship between the output voltage of the characteristic conversion circuit 100 and the output power of the characteristic conversion circuit 100, that is, the output voltage-output power characteristic. The broken line represents the relationship between the output voltage of the characteristic conversion circuit 100 and the output current of the characteristic conversion circuit 100, that is, the output voltage-output current characteristic.

As can be seen from FIG. 3A, in the present embodiment, due to the first feedback control and the second feedback control, the characteristic conversion circuit 100 has the output voltage of the characteristic conversion circuit 100 larger than the above-mentioned value and smaller than the open circuit voltage. In the region, as the output voltage of the characteristic conversion circuit 100 increases, the output current of the characteristic conversion circuit 100 decreases, resulting in an output voltage-output current characteristic. Further, in a region where the output voltage of the characteristic conversion circuit 100 is larger than 0 and smaller than a certain value, the output voltage-output current characteristic of the characteristic conversion circuit 100 becomes smaller as the output voltage of the characteristic conversion circuit 100 increases. Bring. Here, the open circuit voltage is the output voltage of the characteristic conversion circuit 100 when the output current of the characteristic conversion circuit 100 is zero.

Combined with these feedback controls, the output voltage-output current characteristics of the characteristic conversion circuit 100 are shown by the broken lines in FIGS. 3A and 4. As a result, the output voltage-output power characteristic of the characteristic conversion circuit 100 has a single peak and is convex as shown by the solid line in FIG. 3A.

As described above, the output voltage-output power characteristic that is convex above the characteristic conversion circuit 100 enables MPPT control by the DC power conversion device 20. The MPPT control of the characteristic conversion circuit 100 can be executed by the DC power conversion device 20.

In the power conversion device 20 of this example, the first DCDC converter 21 changes the output voltage of the characteristic conversion circuit 100 by MPPT control. The second DCDC converter 22 changes the output voltage of the first photovoltaic power generation system 31 by MPPT control. The third DCDC converter 23 changes the output voltage of the second photovoltaic power generation system 32 by MPPT control. As described above, in this example, the multi-string type DC power conversion device 20 that individually MPPT controls the photovoltaic power generation systems 31 and 32 and the characteristic conversion circuit 100 is realized. However, the DC power conversion device may be a centralized type that collectively controls MPPT.

The configuration of the characteristic conversion circuit 100 will be further described.

As shown in FIG. 5, the first circuit 110 includes a first resistor 121, a second resistor 122, a sixth resistor 400, a current sensor 128, and a first shunt regulator 125. The second circuit 120 includes a current sensor 128, a sixth resistor 400, a sensor voltage adjusting circuit 120a, and a voltage-current conversion circuit 120b. The current sensor 128 and the sixth resistor 400 are shared by the first circuit 110 and the second circuit 120. The feedback current supply unit 130 includes a current supply power supply 131 and a third resistor 132. In this embodiment, the current supply power supply 131 is a constant voltage source.

In the voltage-current control circuit 160, the smaller the current flowing out from the current supply power supply 131, the larger the ratio of the output voltage to the input voltage of the voltage-current control circuit 160. In this way, the characteristic conversion circuit 100 is adapted so that the ratio is adjusted according to the current flowing out from the current supply power supply 131.

The first sensor voltage V1 output by the current sensor 128 of the first circuit 110 will be further described using a mathematical formula.

FIG. 7 shows the current sensor 128 of this embodiment. The current sensor 128 includes a shunt resistor 128r and a current sense amplifier 128s. The resistance value of the shunt resistor 128r is Rsence. When the current Iload flows through the shunt resistor 128r, the voltage Rsence * Iload is applied to the shunt resistor 128r. The current sense amplifier 128s outputs the total voltage of the voltage Rsence * Iload multiplied by the gain G and the bias voltage Vbias as the first sensor voltage V1.

That is, the first sensor voltage V1 generated by the current sensor 128 of the present embodiment is given by (Equation 1). However, another current sensor such as a Hall element type current sensor may be used as the current sensor 128, and the output of the current sensor may be used as the first sensor voltage V1. The current Iload corresponds to the output current of the characteristic conversion circuit 100. "*" Is a symbol representing multiplication.

図６を参照して、本実施形態の第１シャントレギュレータ１２５についてさらに説明する。第１シャントレギュレータ１２５は、第１参照電圧端子１２５ａと、第１カソード１２５Ｋと、第１アノード１２５Ａと、第１基準電圧源１２５ｓと、第１オペアンプ１２５оと、第１トランジスタ１２５ｔと、を含む。第１オペアンプ１２５оは、非反転増幅端子１２５оａと、反転増幅端子１２５оｂと、出力端子１２５оｃと、を含む。第１トランジスタ１２５ｔは、カソード側端子１２５ｔａと、アノード側端子１２５ｔｂと、制御端子１２５ｔｃと、を含む。非反転増幅端子１２５оａには、第１参照電圧端子１２５ａに入力された電圧が供給される。反転増幅端子１２５оｂの電圧は、第１基準電圧源１２５ｓによって、第１アノード１２５Ａの電圧よりも第１基準電圧Ｖs1だけ高い電圧に設定されている。第１参照電圧端子１２５ａに第１基準電圧Ｖs1よりも大きい電圧が入力されることによって非反転増幅端子１２５оａの電圧が反転増幅端子１２５оｂよりも電圧が大きくなると、出力端子１２５оｃから制御端子１２５ｔｃに電流が流れ、第１カソード１２５Ｋからカソード側端子１２５ｔａおよびアノード側端子１２５ｔｂをこの順に介して第１アノード１２５Ａへと第１電流ｉ１が流れる。図６の例では、第１トランジスタ１２５ｔは、バイポーラトランジスタであり、具体的にはＮＰＮトランジスタである。カソード側端子１２５ｔａは、コレクタである。アノード側端子１２５ｔｂは、エミッタである。制御端子１２５ｔｃは、ベースである。なお、この説明では、出力端子１２５оｃと制御端子１２５ｔｃの間で流れる電流、具体的にはベース電流、は十分に小さいものとして無視している。

The first shunt regulator 125 of the present embodiment will be further described with reference to FIG. The first shunt regulator 125 includes a first reference voltage terminal 125a, a first cathode 125K, a first anode 125A, a first reference voltage source 125s, a first operational amplifier 125о, and a first transistor 125t. The first operational amplifier 125о includes a non-inverting amplification terminal 125оa, an inverting amplification terminal 125оb, and an output terminal 125оc. The first transistor 125t includes a cathode side terminal 125ta, an anode side terminal 125tb, and a control terminal 125tc. The voltage input to the first reference voltage terminal 125a is supplied to the non-inverting amplification terminal 125оa. The voltage of the inverting amplification terminal 125оb is set by the first reference voltage source 125s to a voltage higher than the voltage of the first anode 125A by the first reference voltage Vs1. When a voltage larger than the first reference voltage Vs1 is input to the first reference voltage terminal 125a and the voltage of the non-inverting amplification terminal 125оa becomes larger than that of the inverting amplification terminal 125оb, a current is applied from the output terminal 125оc to the control terminal 125 tk. The first current i1 flows from the first cathode 125K through the cathode side terminal 125ta and the anode side terminal 125tb to the first anode 125A in this order. In the example of FIG. 6, the first transistor 125t is a bipolar transistor, specifically an NPN transistor. The cathode side terminal 125ta is a collector. The anode side terminal 125tb is an emitter. The control terminal 125tc is a base. In this description, the current flowing between the output terminal 125оc and the control terminal 125 tk, specifically, the base current, is ignored as being sufficiently small.

From the above description with reference to FIG. 6, the first reference voltage Vref1 follows a constant first reference voltage Vs1 by the first shunt regulator 125.

Further, the voltage appearing at the first connection point p1 may be referred to as a first reference voltage Vref1. The first reference voltage Vref1 is input to the first reference voltage terminal 125a of the first shunt regulator 125. The larger the first reference voltage Vref1 input to the first reference voltage terminal 125a, the larger the current i1 flowing through the current supply power supply 131, the third resistor 132, the first shunt regulator 125, and the reference potential in this order. In FIG. 6, the current i1 is a current flowing downward in the drawing through the first shunt regulator 125. Hereinafter, the current i1 may be referred to as a first current i1.

In the first circuit 110 shown in FIG. 5, the output voltage Vout of the characteristic conversion circuit 100 is given by the following (Equation 2). Here, R121 is the resistance value of the first resistor 121, R122 is the resistance value of the second resistor 122, and R400 is the resistance value of the sixth resistor 400.

（数２）から理解されるように、特性変換回路１００の出力電流が大きくなり第１センサ電圧Ｖ１が大きくなると、出力電圧Ｖoutは小さくなる。このように、第１センサ電圧Ｖ１は、出力電圧Ｖoutを調整するように作用する。

As can be understood from (Equation 2), when the output current of the characteristic conversion circuit 100 increases and the first sensor voltage V1 increases, the output voltage Vout decreases. In this way, the first sensor voltage V1 acts to adjust the output voltage Vout.

That is, in the first feedback control by the first circuit 110, when the first sensor voltage V1 becomes large, the current flowing from the current sensor 128 to the first connection point p1 via the sixth resistor 400 and the connection point ps in this order becomes large. .. The first reference voltage Vref1 follows a constant first reference voltage Vs1 by the first shunt regulator 125. In order to realize this tracking, a constant current flows through the second resistor 122. This means that as the current flowing through the sixth resistor 400 toward the first connection point p1 increases, the current flowing through the first resistor 121 toward the first connection point p1 decreases. When this current becomes small, it means that the voltage generated by the first resistor 121 becomes small.

Based on the description with reference to FIG. 5, the operation of the first circuit 110 can be described as follows. When the output current of the characteristic conversion circuit 100 increases, the voltage generated by the first resistor 121 decreases while the voltage at the first connection point p1 follows the first reference voltage Vref1. As a result, the output voltage Vout of the characteristic conversion circuit 100 becomes small. In this way, the first feedback control can obtain the output voltage-output current characteristic as shown in FIGS. 3A and 4 in which the output current of the characteristic conversion circuit 100 decreases as the output voltage of the characteristic conversion circuit 100 increases. ..

Further, the open circuit voltage of the characteristic conversion circuit 100 is controlled by the first feedback control. Here, the open circuit voltage is the output of the characteristic conversion circuit 100 when the output current of the characteristic conversion circuit 100 is zero. Since the output current of the characteristic conversion circuit 100 is zero, Iload becomes zero in (Equation 1), and V1 becomes equal to the bias voltage Vbias. Therefore, it is set to the open circuit voltage specified in (Equation 2). As described above, in the present embodiment, the first current i1 is set to a voltage determined by (Equation 2) so that the output voltage Vout of the voltage / current control circuit 160 becomes a voltage determined by the functions of the first shunt regulator 125 and the voltage / current control circuit 160. By being controlled, the open circuit voltage is set to a specified value.

Returning to FIG. 5, the sensor voltage adjusting circuit 120a of the second circuit 120 includes a variable output power supply 123, an input resistor R1, a feedback resistor R2, and a sensor voltage adjusting operational amplifier 124.

As described above, the current sensor 128 outputs the first sensor voltage V1. The variable output power supply 123 outputs a variable voltage V4. The sensor voltage adjusting circuit 120a generates a second sensor voltage V2 that changes according to the first sensor voltage V1 and the variable voltage V4.

If there are individual variations in the current sensor 128, an error may occur in the first sensor voltage V1. When the first sensor voltage V1 having an error is used for control in the characteristic conversion circuit 100, the switching current isw deviates from the target current, the maximum power point deviates from the target point, and the maximum power of the characteristic conversion circuit 100 deviates from the target power. There is a risk. In this respect, according to the present embodiment, the second sensor voltage V2 reflecting the first sensor voltage V1 and the variable voltage V4 can be generated. By using the second sensor voltage V2, which reflects the appropriately set variable voltage V4, for control in the characteristic conversion circuit 100, the deviation of the switching current isw from the target current is reduced, and the deviation from the target point of the maximum power point is reduced. The deviation can be reduced and the deviation of the maximum power from the target power can be reduced. Further, by adjusting the variable voltage V4 and adjusting the switching current isw, it is possible to adjust the maximum power of the characteristic conversion circuit 100 according to the situation.

Specifically, the sensor voltage adjusting operational amplifier 124 includes a sensor input terminal 124a, a variable voltage input terminal 124b, and a second sensor voltage output terminal 124c. The sensor input terminal 124a is connected to the sensor output unit 128a via the input resistor R1. A variable voltage V4 is input to the variable voltage input terminal 124b. The second sensor voltage output terminal 124c is connected to the sensor input terminal 124a via the feedback resistor R2. The sensor voltage adjusting operational capacitor 124 generates the second sensor voltage V2 based on the voltage difference between the sensor input terminal 124a and the variable voltage input terminal 124b, and outputs the second sensor voltage V2 from the second sensor voltage output terminal 124c.

Specifically, the sensor input terminal 124a is an inverting amplification terminal. The variable voltage input terminal 124b is a non-inverting amplification terminal.

The voltage-current conversion circuit 120b of the second circuit 120 includes a voltage supply power supply 129, an intervening resistor R3, a transistor drive operational amplifier 126, and a regulated current output transistor 127. The voltage supply power supply 129 outputs the threshold voltage V3. In this embodiment, the voltage supply power supply 129 is a constant voltage source.

In the voltage-current conversion circuit 120b, the adjustment current i3 starts to flow when the second sensor voltage V2 changes across the threshold voltage V3 due to the increase in the first sensor voltage V1. When the adjustment current i3 starts to flow, the first feedback control is switched to the second feedback control. The characteristic conversion circuit 100 whose control is switched at the timing when the current starts to flow is easy to design.

Specifically, the transistor drive operational amplifier 126 includes a power input terminal 126a, a second sensor voltage input terminal 126b, and a control voltage output terminal 126c. The power input terminal 126a is connected to the voltage supply power supply 129 via an intervening resistor R3. The second sensor voltage V2 is input to the second sensor voltage input terminal 126b. The transistor drive operational amplifier 126 generates a control voltage Vc based on the voltage difference between the power input terminal 126a and the second sensor voltage input terminal 126b, and outputs the control voltage Vc from the control voltage output terminal 126c.

Specifically, the power input terminal 126a is an inverting amplification terminal. The second sensor voltage input terminal 126b is a non-inverting amplification terminal.

The adjusting current output transistor 127 includes a control terminal 127c, a first terminal 127a, and a second terminal 127b. The control voltage Vc is input to the control terminal 127c. The first terminal 127a is connected to the voltage supply power supply 129 via the intervening resistor R3. The second terminal 127b outputs the adjustment current i3.

In the example of FIG. 5, the adjusted current output transistor 127 is a bipolar transistor, specifically a PNP transistor. The control terminal 127c is a base. The first terminal 127a is an emitter. The second terminal 127b is a collector.

The first sensor voltage V1, the second sensor voltage V2, the adjustment current i3, and the output voltage Vout of the second circuit 120 will be further described using mathematical formulas.

In the sensor voltage adjusting circuit 120a, the second sensor voltage V2 is generated by the differential amplification using the sensor voltage adjusting operational amplifier 124. The second sensor voltage V2 is given by the following (Equation 3). Here, R1 is the resistance value of the input resistor R1. R2 is the resistance value of the feedback resistor R2.

電圧電流変換回路１２０ｂでは、トランジスタ駆動オペアンプ１２６は、Ｖ２＜Ｖ３のときには、バーチャルショートにより電源入力端子１２６ａの電圧が第２センサ電圧入力端子１２６ｂの電圧に追従するように、調整電流出力トランジスタ１２７を駆動させる。具体的には、トランジスタ駆動オペアンプ１２６は、Ｖ２＜Ｖ３のときには、電源入力端子１２６ａの電圧が第２センサ電圧Ｖ２となり、閾値電圧Ｖ３と第２センサ電圧Ｖ２との電圧差Ｖ３−Ｖ２が介在抵抗Ｒ３にかかり、かつ、介在抵抗Ｒ３から第１端子１２７ａへと電流（Ｖ３−Ｖ２）／Ｒ３が流れるように、制御端子１２７ｃを駆動する。より具体的には、この駆動時に、制御電圧出力端子１２６ｃと制御端子１２７ｃの間で電流が流れる。ここで、Ｒ３は、介在抵抗Ｒ３の抵抗値である。Ｖ２＜Ｖ３のときには、調整電流ｉ３は、以下の（数４）で与えられる。Ｖ２≧Ｖ３のときには、調整電流ｉ３は、以下の（数５）で与えられる。なお、（数４）では、制御電圧出力端子１２６ｃと制御端子１２７ｃの間で流れる電流、図５の例ではベース電流、は十分に小さいものとして無視している。

In the voltage-current conversion circuit 120b, the transistor-driven operational amplifier 126 adjusts the current output transistor 127 so that the voltage of the power input terminal 126a follows the voltage of the second sensor voltage input terminal 126b due to a virtual short circuit when V2 <V3. Drive. Specifically, in the transistor drive operational amplifier 126, when V2 <V3, the voltage of the power input terminal 126a becomes the second sensor voltage V2, and the voltage difference V3-V2 between the threshold voltage V3 and the second sensor voltage V2 is an intervening resistor. The control terminal 127c is driven so as to be applied to R3 and the current (V3-V2) / R3 flows from the intervening resistor R3 to the first terminal 127a. More specifically, during this drive, a current flows between the control voltage output terminal 126c and the control terminal 127c. Here, R3 is the resistance value of the intervening resistor R3. When V2 <V3, the adjustment current i3 is given by the following (Equation 4). When V2 ≧ V3, the adjustment current i3 is given by the following (Equation 5). In (Equation 4), the current flowing between the control voltage output terminal 126c and the control terminal 127c, and the base current in the example of FIG. 5, are ignored as being sufficiently small.

図５の例では、トランジスタ駆動オペアンプ１２６は、調整電流出力トランジスタ１２７の端子１２７ｃ−１２７ａ間電圧の温度による変化により調整電流ｉ３が変化することを抑制している。具体的には、仮に、トランジスタ１２７の制御端子１２７ｃに第２センサ電圧Ｖ２が直接供給されると、第１端子１２７ａの電圧は、第２センサ電圧Ｖ２に端子１２７ｃ−１２７ａ間電圧を足し合わせた値となるため、端子１２７ｃ−１２７ａ間電圧の影響を受けることになる。これに対し、本実施形態では、オペアンプ１２６の端子１２６ａおよび１２６ｂがバーチャルショートしているため、第１端子１２７ａの電圧と第２センサ電圧Ｖ２とは実質的に同一となり、調整電流ｉ３は端子１２７ｃ−１２７ａ間電圧の影響を実質的に受けなくなる。先に述べた通り、具体的には、制御端子１２７ｃは、ベースである。第１端子１２７ａは、エミッタである。第２端子１２７ｂは、コレクタである。端子１２７ｃ−１２７ａ間電圧は、ベース−エミッタ間電圧である。

In the example of FIG. 5, the transistor drive operational amplifier 126 suppresses the change of the adjustment current i3 due to the change of the voltage between the terminals 127c-127a of the adjustment current output transistor 127 due to the temperature. Specifically, if the second sensor voltage V2 is directly supplied to the control terminal 127c of the transistor 127, the voltage of the first terminal 127a is the sum of the second sensor voltage V2 and the voltage between the terminals 127c-127a. Since it is a value, it is affected by the voltage between the terminals 127c-127a. On the other hand, in the present embodiment, since the terminals 126a and 126b of the operational amplifier 126 are virtually short-circuited, the voltage of the first terminal 127a and the second sensor voltage V2 are substantially the same, and the adjustment current i3 is the terminal 127c. It is virtually unaffected by the voltage between -127a. Specifically, as described above, the control terminal 127c is a base. The first terminal 127a is an emitter. The second terminal 127b is a collector. The voltage between terminals 127c-127a is the voltage between the base and the emitter.

As can be seen from the above description with reference to FIG. 6, the first shunt regulator 125 causes the first reference voltage Vref1 to follow a constant first reference voltage Vs1. The output voltage Vout is given by the following (Equation 6). Here, as in (Equation 2), R121 is the resistance value of the first resistor 121. R122 is the resistance value of the second resistor 122, and R400 is the resistance value of the sixth resistor 400. (Equation 6) indicates that the output voltage Vout of the characteristic conversion circuit 100 decreases as the sensor output (first sensor voltage V1) from the current sensor 128 increases and the adjustment current i3 increases.

（数６）、および、図４から理解されるように、調整電流ｉ３が流れると、出力電圧Ｖoutは小さくなる。このように、調整電流ｉ３は、出力電圧Ｖoutを調整するように作用する。調整電流ｉ３を、出力電圧調整電流ｉ３と称することができる。また、第２回路１２０を、調整回路と称することができる。

As can be seen from (Equation 6) and FIG. 4, the output voltage Vout becomes smaller when the adjustment current i3 flows. In this way, the adjustment current i3 acts to adjust the output voltage Vout. The adjustment current i3 can be referred to as an output voltage adjustment current i3. Further, the second circuit 120 can be referred to as an adjustment circuit.

In the present embodiment, the output characteristics of the fuel cell power generation system 40 are converted by using the first circuit 110 and the second circuit 120. It is often advantageous to play a role that software can play in a circuit from the viewpoint of simplification of control configuration, cost, and the like. In addition, this makes it possible to avoid software design and avoid the risk of software bugs.

Further, the method of performing characteristic conversion using a circuit is compatible with the fuel cell power generation system. Specifically, the output voltage and output power of the fuel cell power generation system are easy to maintain constant, unlike the wind power generation system and the like. In one embodiment, the output voltage and output power of the fuel cell power generation system are kept constant in the rated power generation. Therefore, when the power generation system connected to the characteristic conversion circuit is a fuel cell power generation system, it is less necessary to change the characteristics of the characteristic conversion according to the output voltage and / or output power of the power generation system, and the circuit is used. It is easy to adopt a method of character conversion.
[Individual variation of current sensor 128 and its suppression]
As described above, the current sensor 128 may have individual variations. The effects of individual variation will be described in detail with reference to FIGS. 8 and 9.

In this embodiment, the current sensor 128 has the configuration shown in FIG. The resistance value Rsence of the current sensor 128 is ideally a reference value. However, the resistance value Rsence may have an error in the range of tolerances. In the present embodiment, when the resistance value of the shunt resistor 128r is larger than the reference value, the current sensor 128 outputs a first sensor voltage V1 which is larger than when the resistance value of the shunt resistor 128r is the reference value. It is configured.

In FIG. 8, the horizontal axis represents the output current of the characteristic conversion circuit 100. The “output voltage (0) of the characteristic conversion circuit” indicates the output voltage of the characteristic conversion circuit 100 when the resistance value Rsence of the shunt resistor 128r is at the reference value. The “output voltage (+) of the characteristic conversion circuit” indicates the same output voltage when the resistance value Rsence is larger than the reference value. The “output voltage (−) of the characteristic conversion circuit” indicates the same output voltage when the resistance value Rsence is smaller than the reference value. “Adjustment current i3 (0)” indicates the adjustment current i3 when the resistance value Rsence of the shunt resistor 128r is at the reference value. “Adjustment current i3 (+)” indicates the adjustment current i3 when the resistance value Rsence is larger than the reference value. “Adjustment current i3 (−)” indicates the adjustment current i3 when the resistance value Rsence is smaller than the reference value. “Output power (0) of the characteristic conversion circuit” indicates the output power of the characteristic conversion circuit 100 when the resistance value Rsence is at the reference value. The “output power (+) of the characteristic conversion circuit” indicates the same output power when the resistance value Rsence is larger than the reference value. The “output power (−) of the characteristic conversion circuit” indicates the same output power when the resistance value Rsence is smaller than the reference value. “Switching current isw (0)” indicates the switching current isw when the resistance value Rsence is at the reference value. “Switching current isw (+)” indicates the switching current isw when the resistance value Rsence is larger than the reference value. “Switching current isw (−)” indicates the switching current isw when the resistance value Rsence is smaller than the reference value. As described above, the switching current isw is the output current of the characteristic conversion circuit 100 when the first feedback control and the second feedback control are switched.

When the resistance value Rsence is the reference value, the maximum power point is at the target point. This situation is as shown in FIGS. 3A and 4.

When the resistance value Rsence is at the reference value, the switching current isw matches the target current. The "switching current isw (0)" corresponds to the target current. When the resistance value Rsence is larger than the reference value, the switching current isw is smaller than when the resistance value Rsence is at the reference value. On the contrary, when the resistance value Rsence is smaller than the reference value, the switching current isw is larger than when the resistance value Rsence is at the reference value.

When the resistance value Rsence is at the reference value, the maximum power of the characteristic conversion circuit 100 matches the target power. The "output power (0) of the characteristic conversion circuit" when the output current of the characteristic conversion circuit 100 is the "switching current isw (0)" corresponds to the target power. When the resistance value Rsence is larger than the reference value, the maximum power is smaller than when the resistance value Rsence is at the reference value. On the contrary, when the resistance value Rsence is smaller than the reference value, the maximum power is larger than when the resistance value Rsence is at the reference value.
[Example of how to adjust variable voltage V4]
As shown in FIG. 7, individual variation of the resistance value Rsence of the shunt resistor 128r causes variation of the maximum power point of the characteristic conversion circuit 100. The variation of the maximum power point causes the variation of the switching current isw and the maximum power.

In this respect, in the present embodiment, the switching current isw of the characteristic conversion circuit 100 can be adjusted and the maximum power can be adjusted by adjusting the variable voltage V4.

For example, when the resistance value Rsence is smaller than the reference value, the maximum power is brought closer to the target power by adjusting the switching current isw by making the variable voltage V4 smaller than when the resistance value Rsence is at the reference value. be able to.

On the contrary, when the resistance value Rsence is larger than the reference value, the maximum power is set to the target power by adjusting the switching current isw by increasing the variable voltage V4 as compared with the case where the resistance value Rsence is at the reference value. You can get closer.

Here, as understood from (Equation 3), when the variable voltage V4 is increased, the second sensor voltage V2 is increased. On the contrary, when the variable voltage V4 is reduced, the second sensor voltage V2 becomes smaller.

When the second sensor voltage V2 is increased, the adjustment current i3 starts to flow when the output current of the characteristic conversion circuit 100 is larger. On the contrary, when the second sensor voltage V2 is reduced, the adjustment current i3 starts to flow when the output current of the characteristic conversion circuit 100 is smaller. It is shown that the switching current isw can be adjusted by adjusting the variable voltage V4 and adjusting the second sensor voltage V2. This adjustment adjusts the maximum power.

Next, it will be further described with reference to FIG. 9 that the adjustment of the variable voltage V4 can change the adjustment current i3 and the maximum power.

In adjusting the variable voltage V4, as an example, a wattmeter for measuring the output power and an electronic load device as a load are connected to the output of the characteristic conversion circuit 100.

As shown in FIG. 9A, the characteristic conversion circuit 100 is operated, the output current from the characteristic conversion circuit 100 is gradually increased by the power load device, and the output of the characteristic conversion circuit 100 is the target value (maximum power point). Adjust so that Next, the output voltage of the characteristic conversion circuit 100 is adjusted to the maximum power point (target value) by gradually lowering the variable voltage V4 and reducing the switching current isw.

FIG. 9B shows the adjusting current i3a and the switching current iswa. The current i3a is the adjusted current i3 after adjusting the variable voltage V4 and the second sensor voltage V2. The current iswa is the switching current isw at this time.

By adjusting the switching current isw by adjusting the variable voltage V4, the maximum power point can be brought closer to the value when the resistance value Rsence is at the reference value.

Further, from (Equation 1), (Equation 3), and (Equation 4), the relationship between the resistance value Rsence and the adjustment current i3 is given by (Equation 7).

（数７）より、図８に示したように、抵抗値Ｒsenceが大きいと調整電流ｉ３の傾きが大きくなり、反対に抵抗値Ｒsenceが小さいと調整電流ｉ３の傾きが小さくなる。

From (Equation 7), as shown in FIG. 8, when the resistance value Rsence is large, the slope of the adjustment current i3 becomes large, and conversely, when the resistance value Rsence is small, the slope of the adjustment current i3 becomes small.

Further, when the current sensor 128 has the configuration shown in FIG. 7, individual variation of the bias voltage Vbias can also cause variation of the maximum power point of the characteristic conversion circuit 100. Even when the current sensor 128 is another sensor such as a Hall element type current sensor, an error due to individual variation of the current sensor 128 may cause variation in the maximum power point of the characteristic conversion circuit 100. However, in these cases as well, as in the case where the resistance value Rsence of the shunt resistor 128r varies, the maximum power point of the characteristic conversion circuit 100 is brought closer to the target point by adjusting the variable voltage V4, and the switching current isw and the maximum power are adjusted. It can approach the target current and target power.
[Adjustment of maximum power of characteristic conversion circuit 100 according to the situation]
By adjusting the variable output, it is also possible to adjust the maximum power of the characteristic conversion circuit 100 according to the situation. In one example, the variable output is adjusted according to the power generation status of the photovoltaic power generation system connected to the DC power converter 20. Hereinafter, such an example will be described.

The electric power system 300 of the present embodiment includes a controller 51. In this embodiment, specifically, the fuel cell power generation system 40 includes a controller 51. However, the controller 51 may not be included in the fuel cell power generation system 40.

In one specific example, the controller 51 changes the variable output according to the power output of at least one photovoltaic power generation system. In this way, the output power of the characteristic conversion circuit 100 can be adjusted according to the power generation output of the photovoltaic power generation system.

The power generation output is, for example, a power generation voltage, a power generation power, a power generation current, or the like. The power output of at least one photovoltaic power generation system may be the power generation output of one photovoltaic power generation system included in at least one photovoltaic power generation system, and a plurality of photovoltaic power generation systems included in at least one photovoltaic power generation system. It may be a value determined by the power generation output of the photovoltaic power generation system of the above, or may be a value determined by the power generation output of all the photovoltaic power generation systems included in at least one photovoltaic power generation system. The value determined by the power output of multiple or all PV systems can be the sum or average. Specifically, the power generation output of at least one photovoltaic power generation system may be one of the photovoltaic power generation systems 31 and 32, and the total value or the average of the power generation outputs of the photovoltaic power generation systems 31 and 32. It may be a value.

In one embodiment, the power output is the voltage generated by at least one photovoltaic system. The controller 51 (a) changes the variable output so that the switching current isw becomes smaller when the generated voltage increases across the threshold power generation voltage, or (b) the larger the generated voltage, the more the switching current Change the variable output so that isw becomes smaller. Typically, when the generated voltage of the photovoltaic power generation system is large, the generated power of the photovoltaic power generation system is large. In this specific example, in such a case, the variable output is changed so that the switching current isw becomes small. By doing so, the maximum power of the characteristic conversion circuit 100 becomes small. By doing so, the power extracted from the characteristic conversion circuit 100 to the DC power conversion device 20 by the MPPT control becomes small. For the above reasons, according to this specific example, just enough electric power can be supplied to the DC power converter 20.

In one specific example, the controller 51 changes the variable output by using a control signal representing the power generation output. In this way, the variable output can be easily adjusted according to the power generation output. The control signal is generated by, for example, the DC power converter 20. Alternatively, the power system 300 may include an output sensor that generates a control signal that represents the power generation output.

Returning to FIGS. 1 and 2, the output power of the characteristic conversion circuit 100 is supplied to the DC power conversion device 20, specifically to the first DCDC converter 21, via the LC filter 61 and the protection relay 62.
[Power storage device 25]
As described above, power is supplied to the power storage device 25 from the 4th DCDC converter 12. Further, the power storage device 25 supplies electric power to the 4th DCDC converter 12.

The power storage device 25 is, for example, a lithium battery. However, a battery other than the lithium battery may be used as the power storage device 25. A capacitor may be used as the power storage device 25.
[Main distribution board 80]
The main distribution board 80 includes an interconnection breaker 81, a main breaker 82, a secondary interconnection breaker 83, and a first branch portion 85. The first branch portion 85 includes a plurality of branch breakers. In this example, the first branch 85 includes branch breakers 85a, 85b and 85c.

The main breaker 82 is connected to the system power supply 200 by the upstream electric circuit 88. The upstream electric circuit 88 is connected to the downstream electric circuit 89 via the main breaker 82.

A secondary interconnection breaker 83 is connected to the downstream electric circuit 89. The secondary interconnection breaker 83 is provided on a path connecting the main breaker 82 and the second inverter 44. The secondary interconnection breaker 83 is electrically connected to the first branch portion 85.

The first branch portion 85 is also connected to the downstream electric circuit 89. The branch breaker 85a of the first branch portion 85 is provided on a path connecting the main breaker 82 and the system power input unit 28a of the power switching unit 28. The branch breaker 85b is provided on a path connecting the main breaker 82 and the second load 252. The branch breaker 85c is provided on a path connecting the main breaker 82 and the third load 253.

The upstream electric circuit 88 has a second connection point p2. The interconnection breaker 81 is provided on a path connecting the second connection point p2 and the first inverter 13.

In this example, AC power of voltage VAC2 can be supplied from the system power supply 200 to the main breaker 82 via the second connection point p2. AC power of voltage VAC2 can be supplied from the system power supply 200 to the first inverter 13 via the second connection point p2 and the interconnection breaker 81 in this order. AC power of voltage VAC2 can be reverse-flowed from the first inverter 13 to the system power supply 200 via the interconnection breaker 81 and the second connection point p2 in this order. AC power of voltage VAC2 can be supplied from the first inverter 13 to the main breaker 82 via the interconnection breaker 81 and the second connection point p2 in this order. AC power of voltage VAC2 can be supplied to the secondary interconnection breaker 83 from the second inverter 44. AC power of voltage VAC1 can be supplied from the branch breaker 85a to the power switching unit 28. AC power of voltage VAC1 can be supplied from the branch breaker 85b to the second load 252. AC power of voltage VAC2 can be supplied from the branch breaker 85c to the third load 253.
[Power switching unit 28]
The power switching unit 28 has a plurality of input units and a power output unit 28c. The plurality of input units include a grid power input unit 28a and an independent power input unit 28b. The power switching unit 28 switches which of the plurality of input units is connected to the power output unit 28c. In this example, the power switching unit 28 switches which of the system power input unit 28a and the self-sustaining power input unit 28b is connected to the power output unit 28c. In this example, the power switching unit 28 thus selectively connects either the first inverter 13 or the branch breaker 85a to the self-sustaining distribution board 90, specifically to the main breaker 92.
[Independent distribution board 90]
The self-supporting distribution board 90 has a main breaker 92 and a second branch portion 95. The second branch portion 95 includes a plurality of branch breakers. In this example, the second branch 95 includes branch breakers 95a, 95b and 95c.

The main breaker 92 is connected to the power switching unit 28 by the upstream electric circuit 98. The upstream electric circuit 98 is connected to the downstream electric circuit 99 via the main breaker 92.

A second branch 95 is connected to the downstream electric circuit 99. The branch breaker 95a of the second branch portion 95 is provided on a path connecting the main breaker 92 and the D1 power supply 55. The branch breaker 95b is provided on a path connecting the main breaker 92 and the hot water storage unit 47. The branch breaker 95c is provided on a path connecting the main breaker 92 and the first load 251.

In this example, AC power of voltage VAC1 can be supplied from the power switching unit 28 to the downstream electric circuit 99 via the main breaker 92. AC power of voltage VAC1 can be supplied from the branch breaker 95a to the D1 power supply 55. AC power of voltage VAC1 can be supplied from the branch breaker 95b to the hot water storage unit 47. AC power of voltage VAC1 can be supplied from the branch breaker 95c to the first load 251 via the outlet 260.
[Operation of power system 300 during grid connection]
As shown in FIG. 1, at the time of grid connection, the protection relay 62 is in the open state based on the disconnection command from the controller 51. Here, the open state refers to a state in which current is prohibited from flowing through itself. Further, in the power switching unit 28, the system power input unit 28a and the power output unit 28c are connected. In this way, the power switching unit 28 connects the branch breaker 85a and the self-supporting distribution board 90.

The electric power generated by the fuel cell 41 is supplied to the second DC bus 43 via the fifth DCDC converter 42. Part or all of the electric power supplied to the second DC bus 43 is supplied to the secondary interconnection breaker 83 via the second inverter 44.

A part of the electric power supplied to the secondary interconnection breaker 83 is supplied to the main breaker 92 via the branch breaker 85a and the electric power switching unit 28 in this order. A part of the electric power supplied to the main breaker 92 is supplied to the D1 power supply 55 via the branch breaker 95a. Another part of the electric power supplied to the main breaker 92 is supplied to the hot water storage unit 47 via the branch breaker 95b. Yet another part of the electric power supplied to the main breaker 92 is supplied to the first load 251 via the branch breaker 95c and the outlet 260 in this order.

Another part of the electric power supplied to the secondary interconnection breaker 83 is supplied to the second load 252 via the branch breaker 85b. Yet another portion of the power supplied to the secondary interconnect breaker 83 is supplied to the third load 253 via the branch breaker 85c.

When the power obtained by adding the predetermined margin to the surplus power is larger than zero, the power is supplied from the second DC bus 43 to the heater 46 via the sixth DCDC converter 45.

Specifically, the DC power converter 20 takes out power from the first photovoltaic power generation system 31 by MPPT control, and supplies the taken out power to the first DC bus 11. Specifically, the DC power converter 20 takes out power from the second photovoltaic power generation system 32 by MPPT control, and supplies the taken out power to the first DC bus 11.

When the power storage device 25 is not in the fully charged state, a part of the electric power supplied to the first DC bus 11 is supplied to the power storage device 25, and the rest of the electric power is supplied to the first inverter 13. When the power storage device 25 is in a fully charged state, all of the electric power supplied to the first DC bus 11 is supplied to the first inverter 13. The electric power supplied to the first inverter 13 is supplied to the interconnection breaker 81.

As can be understood from the above description, in the power system 300 of this example, the power supplied from the second inverter 44 to the secondary interconnection breaker 83 is the load 251 to 253, D1 by at least the above margin. It is configured to be insufficient for the total required load of the power supply 55 and the hot water storage unit 47. The electric power corresponding to this shortage is supplied from the interconnection breaker 81 to the downstream electric circuit 89 via the main breaker 82, and together with the electric power supplied from the second inverter 44 to the secondary interconnection breaker 83, the first It is supplied to one branch 85. The balance of the electric power supplied to the interconnection breaker 81 is reverse-flowed to the grid power supply 200.

When the power generation by the photovoltaic power generation systems 31 and 32 is insufficient, the above-mentioned insufficient power is supplied from the system power supply 200 to the downstream electric circuit 89 via the main breaker 82, and the second inverter 44 to the second. Together with the electric power supplied to the next interconnection breaker 83, it is supplied to the first branch portion 85. If the power storage device 25 is not fully charged and the power generated by the photovoltaic power generation systems 31 and 32 is insufficient to charge the power storage device 25, the system power supply 200, the first inverter 13, and the first DC bus 11 Power is supplied to the power storage device 25 via the fourth DCDC converter 12.
[Operation of power system 300 during power failure]
As shown in FIG. 2, at the time of a power failure, the protection relay 62 is in the closed state based on the parallel command from the controller 51. Here, the closed state refers to a state in which an electric current is allowed to flow through itself. Further, the power switching unit 28 connects the first inverter 13 and the self-supporting distribution board 90.

The electric power generated by the fuel cell 41 is supplied to the second DC bus 43 via the DCDC converter 42. Part or all of the DC power supplied to the second DC bus 43 is supplied to the characteristic conversion circuit 100. Specifically, the DC power converter 20 takes out power from the characteristic conversion circuit 100 (strictly speaking, via the LC filter 61) by MPPT control, and supplies the taken out power to the first DC bus 11. To do.

Further, the DC power conversion device 20 extracts electric power from the photovoltaic power generation systems 31 and 32 and supplies the extracted electric power to the first DC bus 11 as in the case of grid connection.

When the total power extracted from the photovoltaic power generation systems 31 and 32 and the characteristic conversion circuit 100 by the DC power converter 20 is smaller than the required loads of the first load 251 and the D1 power supply 55 and the hot water storage unit 47, it corresponds to the shortage. Electric power is further supplied from the power storage device 25 to the first DC bus 11 via the fourth DCDC converter 12. If the extracted power is larger than the required load, the excess power is charged to the power storage device 25 via the 4th DCDC converter 12, and if the excess power remains even after this charging, the second DC bus 43 A part of the electric power of the above is supplied to the heater 46 via the sixth DCDC converter 45.

In this way, the electric power that is made to follow or is brought close to the required load is supplied from the first DC bus 11 to the main breaker 92 via the first inverter 13 and the electric power switching unit 28. The electric power supplied to the main breaker 92 is supplied to the D1 power supply 55, the hot water storage unit 47, and the first load 251 as in the case of grid connection.
[Advantages of connecting devices in the power system 300]
In this example, the power system 300 includes a power storage device 25. The photovoltaic power generation systems 31 and 32, the DC power conversion device 20, and the power storage device 25 are connected in this order. Further, the fuel cell power generation system 40, the characteristic conversion circuit 100, the DC power conversion device 20, and the power storage device 25 are connected in this order. Therefore, the power storage device 25 can be charged not only from the photovoltaic power generation systems 31 and 32 but also from the fuel cell power generation system 40.

In this example, the power system 300 includes a power storage device 25, an inverter 13 that converts DC power into AC power, and an outlet 260. The photovoltaic power generation systems 31 and 32, the DC power converter 20, the inverter 13, and the outlet 260 are connected in this order. The fuel cell power generation system 40, the characteristic conversion circuit 100, the DC power conversion device 20, the inverter 13, and the outlet 260 are connected in this order. The power storage device 25, the inverter 13, and the outlet 260 are connected in this order. Therefore, in this example, the fuel cell power generation system 40 can also supply power to the outlet 260 to which power is supplied from the photovoltaic power generation systems 31 and 32 and the power storage device 25. This is convenient during a power outage for the following reasons: That is, the photovoltaic power generation systems 31 and 32 cannot generate electricity at night or in the rain. Assuming that power cannot be supplied to the outlet 260 from the fuel cell power generation system 40, the period during which power can be taken out from the outlet 260 is limited based only on the power storage device 25 when a power outage continues at night or in the rain. Become. On the other hand, in this example, since the power can be supplied to the outlet 260 from the fuel cell power generation system 40, the above period can be extended. When a power outage continues at night or in the rain, it is convenient for the user to be able to take out power from one outlet for a long time without replacing it with another outlet.

Further, in this example, the same connection as the above connection to the outlet 260 is also made to the hot water storage unit 47. Therefore, when a power failure continues at night or in the rain, the electric power required for its operation can be supplied to the hot water storage unit 47 for a long time.

In this example, the power system 300 is configured to be able to supply power (specifically, to the D1 power source 55) from the power storage device 25 to the fuel cell power generation system 40. Specifically, the same connection as the above connection to the outlet 260 is also made to the D1 power supply 55. In this way, the dedicated power source for starting the fuel cell power generation system 40 in the event of a power failure can be omitted. The dedicated power source is typically a power source for supplying electric power to the auxiliary equipment of the fuel cell power generation system 40.
[Specific example of characteristic conversion circuit]
Hereinafter, the characteristic conversion circuit 100X, which is a specific example of the characteristic conversion circuit 100, will be described with reference to FIG. In the following, the elements already described with reference to FIG. 5 may be designated by the same reference numerals and the description thereof may be omitted.

The characteristic conversion circuit 100X constitutes an LLC converter. The LLC converter is configured so that the higher the current flowing out from the current supply power supply 131, the higher the oscillation frequency is defined, and the higher the oscillation frequency, the smaller the ratio of the output voltage to the input voltage of the characteristic conversion circuit 100X.

Specifically, the characteristic conversion circuit 100X includes a first circuit 110, a second circuit 120, a feedback current supply unit 130X, a current resonance control unit 140, and a voltage / current control circuit 160X.

The feedback current supply unit 130X has a first light emitting diode 135 in addition to the current supply power supply 131 and the third resistor 132. The current flowing out from the current supply power supply 131 flows through the first light emitting diode 135.

The current resonance control unit 140 includes a fourth resistor 141, a first capacitor 142, a fifth resistor 143, a first phototransistor 145, and a control IC 146. The combination of the fourth resistor 141, the first capacitor 142, the fifth resistor 143, and the first phototransistor 145 are connected in parallel with each other. The first phototransistor 145 cooperates with the first light emitting diode 135 to form the first photocoupler 150. The control IC 146 has a constant current source 147, a feedback terminal 148, a high-side driver output terminal 149a, and a low-side driver output terminal 149b.

In the current resonance control unit 140, a period during which the first capacitor 142 is charged with an electric charge (hereinafter, may be referred to as a charging period) and a period during which the electric charge is discharged from the first capacitor 142 (hereinafter, referred to as a discharging period). There is) and visit alternately. The discharge period and the charge period are switched based on the voltage of the feedback terminal 148.

Specifically, during the charging period, the first capacitor 142 is charged with electric charge from the constant current source 147 via the feedback terminal 148. As the charging progresses, the voltage of the feedback terminal 148 rises. When the voltage of the feedback terminal 148 reaches the first voltage, the discharge period is switched. During the discharge period, charging of the electric charge from the constant current source 147 to the first capacitor 142 is stopped. During the discharge period, the electric charge charged in the first capacitor 142 is discharged via the fourth resistor 141. During the discharge period, the charge is further discharged via the fifth resistor 143 and the first phototransistor 145. As the discharge progresses, the voltage of the feedback terminal 148 decreases. When the voltage of the feedback terminal 148 reaches the second voltage, the charging period is switched.

The larger the current flowing through the first light emitting diode 135, the larger the current flows through the first phototransistor 145, and the faster the electric charge is discharged through the fifth resistor 143 and the first phototransistor 145 during the discharge period, and the shorter the discharge period is. Therefore, the charge / discharge frequency becomes high. The charge / discharge frequency corresponds to the above oscillation frequency.

In a certain discharge period, a drive signal is output from the high-side driver output terminal 149a. In the next discharge period, a drive signal is output from the low-side driver output terminal 149b. In the next discharge period, a drive signal is output from the high-side driver output terminal 149a. In the next discharge period, a drive signal is output from the low-side driver output terminal 149b. This is repeated, and drive pulse signals having opposite phases are output from the driver output terminals 149a and 149b. The frequency of these drive pulse signals becomes higher as the charge / discharge frequency is higher. The charging period is a dead time in which no drive signal is output from either of the driver output terminals 149a and 149b.

The voltage / current control circuit 160X includes a second capacitor 161, a first switching element 162a, a second switching element 162b, a third capacitor 163a, a fourth capacitor 163b, a fifth capacitor 164, a transformer 165, and a third capacitor. It has a 1 diode 166a, a 2nd diode 166b, and a 6th capacitor 167.

The switching elements 162a and 162b are connected in series to form a series circuit. A second capacitor 161 is connected in parallel to this series circuit. A third capacitor 163a is connected in parallel to the first switching element 162a. A fourth capacitor 163b is connected in parallel to the second switching element 162b.

In this example, the switching elements 162a and 162b are MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Further, the fifth capacitor 164 is a resonance capacitor.

The transformer 165 has a first winding 165a, which is a primary winding, and a second winding 165b and a third winding 165c, which are secondary windings.

A current outflow terminal of the first switching element 162a and a current inflow terminal of the second switching element 162b are connected to one end of the first winding 165a. A fifth capacitor 164 is connected between the other end of the first winding 165a and the current outflow terminal of the second switching element 162b. In this example, the current outflow terminal is the source terminal. The current inflow terminal is a drain terminal.

The anode of the first diode 166a is connected to one end of the second winding 165b. One end of the sixth capacitor 167 and the cathode of the second diode 166b are connected to the cathode of the first diode 166a. The other end of the sixth capacitor 167 and the reference potential are connected to the other end of the second winding 165b.

The other end of the sixth capacitor 167 and the reference potential are connected to one end of the third winding 165c. The anode of the second diode 166b is connected to the other end of the third winding 165c.

A drive pulse signal is supplied from the high-side driver output terminal 149a to the control terminal of the first switching element 162a. A drive pulse signal is supplied from the low-side driver output terminal 149b to the control terminal of the second switching element 162b. As a result, the switching elements 162a and 162b are alternately turned on and off by supplying drive pulse signals having opposite phases to each other. In this example, the control terminal is a gate terminal.

The higher the frequency of the drive pulse signal supplied to the switching elements 162a and 162b, the smaller the ratio of the output voltage to the input voltage of the voltage-current control circuit 160X based on the LLC resonance.

The specific example of the characteristic conversion circuit 100 of FIG. 5 is not limited to the characteristic conversion circuit 100X of FIG. For example, the larger the current flowing out from the current supply power supply 131, the smaller the duty ratio is defined, and a DCDC converter that operates based on the duty ratio can be configured in the characteristic conversion circuit.

Various other modifications may also be applied to this disclosure. For example, the number of photovoltaic power generation systems in the electric power system may be one or three or more. The power system does not have to have a photovoltaic system. The DC power converter, the first inverter, and the like do not have to be incorporated in the power station. The electric power system may not have some of the illustrated elements such as a power storage device and a hot water storage unit. Further, the connection path between the power generation unit and the load is not limited to the one shown in the figure. For example, it is possible to omit the outlet 260 and supply electric power to the first load 251.
[effect]
As described above, the power system according to the first aspect of the present disclosure will be described.
A DC power converter designed to perform MPPT control for photovoltaic systems that maximize output power when the output voltage is within a predetermined range.
In the fuel cell power generation system, the DC power generated by the fuel cell power generation system is supplied to the DC power conversion device and the fuel cell power generation system.
It is a characteristic conversion circuit provided on a path connecting the fuel cell power generation system and the DC power conversion device, and includes a characteristic conversion circuit including a current sensor and a variable output power supply.
The current sensor detects the output current of the characteristic conversion circuit and outputs a sensor output representing the result of the detection.
The current sensor outputs the sensor output as the output current of the characteristic conversion circuit increases.
The variable output power supply outputs a variable output and
In the characteristic conversion circuit
The first circuit that executes the first feedback control that increases the output power of the characteristic conversion circuit as the sensor output increases, and the second feedback control that decreases the output power of the characteristic conversion circuit as the sensor output increases. A second circuit, which is executed in cooperation with the first circuit, is provided.
In the characteristic conversion circuit
(A) The output voltage-output power characteristic at which the output power of the characteristic conversion circuit is maximized when the output voltage of the characteristic conversion circuit is a certain value within the predetermined range, and the output voltage of the characteristic conversion circuit are the above. As the output voltage of the characteristic conversion circuit increases in a region straddling a certain value, the output current of the characteristic conversion circuit decreases, resulting in an output voltage-output current characteristic.
(B) When the output current of the characteristic conversion circuit when the first feedback control and the second feedback control are switched is defined as a switching current, the output current of the characteristic conversion circuit is the switching current. To provide the output current-output power characteristic that maximizes the output power of the characteristic conversion circuit.
The first feedback control is executed when the sensor output is relatively small, and the second feedback control is executed when the sensor output is relatively large.
The switching current depends on the detection error and changes when the variable output is changed.

The power system according to the first aspect includes a DC power conversion device designed to perform MPPT control of a photovoltaic power generation system. The electric power system according to the first aspect is suitable for extracting electric power from the fuel cell power generation system to the DC electric power converter by executing MPPT control using the DC electric power converter. Further, the power system according to the first aspect is suitable for adjusting the extracted power.

In the second aspect of the present disclosure, for example, in the power system according to the first aspect,
When the output voltage of the characteristic conversion circuit when the output current of the characteristic conversion circuit is zero is defined as an open circuit voltage, the open circuit voltage may be controlled by the first feedback control.

The second aspect is suitable for preventing the DC power converter from being supplied with a voltage exceeding the withstand voltage.

In the third aspect of the present disclosure, for example, in the power system according to the first or second aspect.
The sensor output may be the first sensor voltage.
The variable output may be a variable voltage.
The second circuit may include a sensor voltage adjusting circuit that generates a second sensor voltage that changes according to the first sensor voltage and the variable voltage.

According to the third aspect, the variable voltage can be reflected in the second sensor voltage. By using the second sensor voltage reflecting the variable voltage for control in the characteristic conversion circuit, the deviation of the switching current from the target value can be reduced, and the deviation of the maximum output power value from the target value can be reduced. .. Further, by adjusting the variable voltage and adjusting the switching current, it is possible to adjust the maximum value of the output power of the characteristic conversion circuit according to the situation.

In the fourth aspect of the present disclosure, for example, in the power system according to the third aspect,
The current sensor may include a sensor output unit that outputs the first sensor voltage.
The sensor voltage adjustment circuit
Input resistance and
Return resistance and
A sensor input terminal connected to the sensor output unit via the input resistor, a variable voltage input terminal to which the variable voltage is input, and a second sensor voltage connected to the sensor input terminal via the feedback resistor. A sensor voltage adjusting operational capacitor including an output terminal, which is a sensor that generates the second sensor voltage based on the voltage difference between the sensor input terminal and the variable voltage input terminal and outputs the second sensor voltage from the second sensor voltage output terminal. It may include a voltage regulating operational amplifier.

The configuration of the sensor voltage adjusting circuit of the fourth aspect is a specific example of a configuration for generating a second sensor voltage reflecting the first sensor voltage and the variable voltage.

In the fifth aspect of the present disclosure, for example, in the power system according to the third or fourth aspect.
The second circuit may include a voltage-current conversion circuit in which an adjustment current starts to flow when the second sensor voltage changes across a threshold voltage due to an increase in the first sensor voltage.
When the adjustment current starts to flow, the first feedback control may be switched to the second feedback control.

In the fifth aspect, the first feedback control is switched to the second feedback control at the timing when the adjustment current starts to flow. It is easy to design a characteristic conversion circuit whose control is switched when the current starts to flow.

In the sixth aspect of the present disclosure, for example, in the electric power system according to the fifth aspect,
The voltage-current conversion circuit
A voltage supply power supply that outputs the threshold voltage and
Intervening resistance and
A transistor-driven operational amplifier including a power supply input terminal connected to the voltage supply power supply via the intervening resistor, a second sensor voltage input terminal into which the second sensor voltage is input, and a control voltage output terminal. A transistor-driven operational amplifier that generates a control voltage based on the voltage difference between the power supply input terminal and the second sensor voltage input terminal and outputs the control voltage from the control voltage output terminal.
A regulated current output transistor including a control terminal into which the control voltage is input, a first terminal connected to the voltage supply power supply via the intervening resistor, and a second terminal for outputting the regulated current. It may be included.

The configuration of the voltage-current conversion circuit of the sixth aspect is a specific example of the configuration for generating the adjustment current.

In the seventh aspect of the present disclosure, for example, the electric power system according to any one of the first to sixth aspects is
It may further include at least one photovoltaic system that maximizes output power when the output voltage is within the predetermined range.
The DC power generated by the at least one photovoltaic power generation system may be supplied to the DC power conversion device.

According to the seventh aspect, the DC power generated by the photovoltaic power generation system can be supplied to the DC power converter.

In the eighth aspect of the present disclosure, for example, the electric power system according to the seventh aspect is
It may have more controls,
The controller may change the variable output according to the power generation output of the at least one photovoltaic power generation system.

According to the eighth aspect, the output power of the characteristic conversion circuit can be adjusted according to the power generation output of at least one photovoltaic power generation system.

In the ninth aspect of the present disclosure, for example, the electric power system according to the eighth aspect is
The power generation output may be a power generation voltage.
The controller
(A) When the generated voltage increases across the threshold generated voltage, the variable output may be changed so that the switching current becomes smaller, or
(B) The variable output may be changed so that the larger the generated voltage, the smaller the switching current.

The ninth aspect is suitable for supplying just enough electric power to the DC power converter.

In the tenth aspect of the present disclosure, for example, in the power system according to the eighth or ninth aspect.
The controller may change the variable output by using a control signal representing the power generation output.

According to the control signal of the tenth aspect, adjustment of the variable output according to the power generation output can be easily executed.

In the eleventh aspect of the present disclosure, for example, in the electric power system according to any one of the seventh to tenth aspects,
The at least one photovoltaic power generation system may include a first photovoltaic power generation system.
The DC power converter may include a first DCDC converter and a second DCDC converter.
The first DCDC converter may change the output power of the characteristic conversion circuit by MPPT control.
The second DCDC converter may change the output power of the first photovoltaic power generation system by MPPT control.

According to the eleventh aspect, it is possible to realize a multi-string type DC power conversion device that individually MPPT controls the photovoltaic power generation system and the characteristic conversion circuit.

In the twelfth aspect of the present disclosure, for example, in the power system according to any one of the seventh to eleventh aspects,
It may be further equipped with a power storage device,
The at least one photovoltaic power generation system, the DC power conversion device, and the power storage device may be connected in this order.
The fuel cell power generation system, the characteristic conversion circuit, the DC power conversion device, and the power storage device may be connected in this order.

According to the twelfth aspect, the power storage device can be charged not only from the photovoltaic power generation system but also from the fuel cell power generation system.

In the thirteenth aspect of the present disclosure, for example, the electric power system according to any one of the seventh to twelfth aspects is
Power storage device and
Inverters that convert DC power to AC power,
May be equipped with an outlet,
The at least one photovoltaic power generation system, the DC power conversion device, the inverter, and the outlet may be connected in this order.
The fuel cell power generation system, the characteristic conversion circuit, the DC power conversion device, the inverter, and the outlet may be connected in this order.
The power storage device, the inverter, and the outlet may be connected in this order.

According to the thirteenth aspect, power can also be supplied from the fuel cell power generation system to the outlet to which power is supplied from the photovoltaic power generation system and the power storage device.

In the 14th aspect of the present disclosure, for example, the electric power system according to the 12th or 13th aspect is
It may be configured so that electric power can be supplied from the power storage device to the fuel cell power generation system.

According to the fourteenth aspect, the fuel cell power generation system can be started by the electric power of the power storage device at the time of a power failure. According to the fourteenth aspect, the dedicated power source for starting the fuel cell power generation system in the event of a power failure can be omitted.

The technology according to the present disclosure can be used, for example, in a power system having a DC power conversion device designed for a photovoltaic power generation system and a fuel cell power generation system.

10 Power station 11,43 DC bus 12,21,22,23,42,45 DCDC converter 13,44 Inverter 20 DC power converter 25 Power storage device 28 Power switching unit 28a System power input unit 28b Independent power input unit 28c Power output Part 31, 32 Solar power generation system 36, 37 Solar power generation panel 40 Fuel cell power generation system 41 Fuel cell 46 Heater 47 Hot water storage unit 51 Controller 52 Low voltage power supply 55 D1 power supply 60 Board 61 LC filter 62 Protection relay 80, 90 Distribution Board 81, 82, 83, 85a, 85b, 85c, 92, 95a, 95b, 95c Breaker 85, 95 Branch 88, 89, 98, 99 Electric current 100, 100X Characteristic conversion circuit 110, 120 Circuit 121, 122, 132, 141,143,400, R1, R2, R3 Resistance 125 1st shunt regulator 125A 1st anode 125K 1st cathode 125a 1st reference Voltage terminal 124, 125о, 126 Operate 125t, 127 Transistor 120a Sensor voltage adjustment circuit 120b Voltage-current conversion Circuit 123 Variable output power supply 128 Current sensor 128a Sensor output unit 128r Shunt resistance 128s Current sense amplifier 129, 131 Power supply 130, 130X Feedback current supply unit 135 Light emitting diode 140 Current resonance control unit 142, 161, 163a, 163b, 164,167 Condenser 145 Phototransistor 146 Control IC
147 Constant current source 148, 149a, 149b Terminal 150 Photocoupler 160, 160X Voltage / current control circuit 162a, 162b Switching element 165 Transformer 165a, 165b, 165c Winding 166a, 166b Diode 200 System power supply 251,252,253 Load 260 Outlet 300 Power system p1, p2 connection point

Claims (14)

A DC power converter designed to perform MPPT control for photovoltaic systems that maximize output power when the output voltage is within a predetermined range.
In the fuel cell power generation system, the DC power generated by the fuel cell power generation system is supplied to the DC power conversion device and the fuel cell power generation system.
It is a characteristic conversion circuit provided on a path connecting the fuel cell power generation system and the DC power conversion device, and includes a characteristic conversion circuit including a current sensor and a variable output power supply.
The current sensor detects the output current of the characteristic conversion circuit and outputs a sensor output representing the result of the detection.
The current sensor outputs the sensor output as the output current of the characteristic conversion circuit increases.
The variable output power supply outputs a variable output and
In the characteristic conversion circuit
The first circuit that executes the first feedback control that increases the output power of the characteristic conversion circuit as the sensor output increases, and the second feedback control that decreases the output power of the characteristic conversion circuit as the sensor output increases. A second circuit, which is executed in cooperation with the first circuit, is provided.
In the characteristic conversion circuit
(A) The output voltage-output power characteristic at which the output power of the characteristic conversion circuit is maximized when the output voltage of the characteristic conversion circuit is a certain value within the predetermined range, and the output voltage of the characteristic conversion circuit are the above. As the output voltage of the characteristic conversion circuit increases in a region straddling a certain value, the output current of the characteristic conversion circuit decreases, resulting in an output voltage-output current characteristic.
(B) When the output current of the characteristic conversion circuit when the first feedback control and the second feedback control are switched is defined as a switching current, the output current of the characteristic conversion circuit is the switching current. To provide the output current-output power characteristic that maximizes the output power of the characteristic conversion circuit.
The first feedback control is executed when the sensor output is relatively small, and the second feedback control is executed when the sensor output is relatively large.
A power system in which the switching current depends on the detection error and changes when the variable output is changed. The power according to claim 1, wherein when the output voltage of the characteristic conversion circuit when the output current of the characteristic conversion circuit is zero is defined as an open circuit voltage, the open circuit voltage is controlled by the first feedback control. system. The sensor output is the first sensor voltage.
The variable output is a variable voltage.
The power system according to claim 1 or 2, wherein the second circuit includes a sensor voltage adjusting circuit that generates a second sensor voltage that changes according to the first sensor voltage and the variable voltage. The current sensor includes a sensor output unit that outputs the first sensor voltage.
The sensor voltage adjustment circuit
Input resistance and
Return resistance and
A sensor input terminal connected to the sensor output unit via the input resistor, a variable voltage input terminal to which the variable voltage is input, and a second sensor voltage connected to the sensor input terminal via the feedback resistor. A sensor voltage adjusting operating unit including an output terminal, which is a sensor that generates the second sensor voltage based on the voltage difference between the sensor input terminal and the variable voltage input terminal and outputs the second sensor voltage from the second sensor voltage output terminal. The power system according to claim 3, further comprising a voltage regulating operational amplifier. The second circuit includes a voltage-current conversion circuit in which an adjustment current starts to flow when the second sensor voltage changes across a threshold voltage due to an increase in the first sensor voltage.
The power system according to claim 3 or 4, wherein when the adjusted current starts to flow, the first feedback control is switched to the second feedback control. The voltage-current conversion circuit
A voltage supply power supply that outputs the threshold voltage and
Intervening resistance and
A transistor-driven operational amplifier including a power supply input terminal connected to the voltage supply power supply via the intervening resistor, a second sensor voltage input terminal into which the second sensor voltage is input, and a control voltage output terminal. A transistor-driven operational amplifier that generates a control voltage based on the voltage difference between the power supply input terminal and the second sensor voltage input terminal and outputs the control voltage from the control voltage output terminal.
A regulated current output transistor including a control terminal into which the control voltage is input, a first terminal connected to the voltage supply power supply via the intervening resistor, and a second terminal for outputting the regulated current. The power system according to claim 5, which includes. Further equipped with at least one photovoltaic power generation system that maximizes the output power when the output voltage is within the predetermined range.
The power system according to any one of claims 1 to 6, wherein the DC power generated by the at least one photovoltaic power generation system is supplied to the DC power conversion device. With more controls
The power system according to claim 7, wherein the controller changes the variable output according to the power generation output of the at least one photovoltaic power generation system. The power generation output is a power generation voltage.
The controller
(A) When the generated voltage increases across the threshold generated voltage, the variable output is changed or the variable output is changed so that the switching current becomes smaller.
(B) The power system according to claim 8, wherein the variable output is changed so that the larger the generated voltage, the smaller the switching current. The power system according to claim 8 or 9, wherein the controller changes the variable output by using a control signal representing the power generation output. The at least one photovoltaic power generation system includes a first photovoltaic power generation system.
The DC power converter includes a first DCDC converter and a second DCDC converter.
The first DCDC converter changes the output power of the characteristic conversion circuit by MPPT control.
The power system according to any one of claims 9 to 10, wherein the second DCDC converter changes the output power of the first photovoltaic power generation system by MPPT control. Equipped with a power storage device
The at least one photovoltaic power generation system, the DC power conversion device, and the power storage device are connected in this order.
The power system according to any one of claims 7 to 11, wherein the fuel cell power generation system, the characteristic conversion circuit, the DC power conversion device, and the power storage device are connected in this order. Power storage device and
Inverters that convert DC power to AC power,
Equipped with an outlet,
The at least one photovoltaic power generation system, the DC power conversion device, the inverter, and the outlet are connected in this order.
The fuel cell power generation system, the characteristic conversion circuit, the DC power conversion device, the inverter, and the outlet are connected in this order.
The power system according to any one of claims 7 to 12, wherein the power storage device, the inverter, and the outlet are connected in this order. The power system according to claim 12 or 13, which is configured to be able to supply power from the power storage device to the fuel cell power generation system.

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