DC-DC conversion system and solar power generation system

Abstract

The DC-DC conversion system includes: a current detection mechanism that detects the current flowing from the solar cell panel to the power conversion device; and a DC-DC conversion device that is interposed between the battery device and the power conversion device and outputs the second DC power obtained by converting the first DC power output from the battery device to the power conversion device side. The DC-DC conversion device includes the following first operation mode: generating the second DC power in such a way that the output current and the output voltage simulate the current-voltage characteristics of the solar cell according to the current value detected by the current detection mechanism. The DC-DC conversion device may also include a boosting operation, i.e., a second operation mode, that increases the potential of the connection point, and a third operation mode that converts the voltage of the connection point to charge the battery device. The DC-DC conversion device may also be configured to selectively switch between the first operation mode, the second operation mode, and the third operation mode.

Description

Technical Field

[0001] The present application relates to a DC-DC conversion system that can be applied to a solar power generation system. Background Art

[0002] Conventionally, for example, as described in Japanese Patent No. 6475945, a solar power generation system configured as a DC link system has been known. As also described in paragraph 0024 of this patent document, the DC link system refers to a system in which electric power from a solar cell, a storage battery, etc. is connected in a state of DC power, and is converted into AC power by one inverter and supplied to a load.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 6475945 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] Conventionally, when providing the above-described existing DC link system, the solar cell, the power conversion device, and the DC / DC converter have been designed as a system from the beginning. On the other hand, the technology of additionally applying a DC / DC converter to a non-DC link type solar power generation system that was not originally designed as a DC link system is not common. The reason why such technology is not common is that there are problems such as complicated design changes required for both hardware and software. In such problems of design changes, as an example, it includes changes in control content for adding communication lines and sensors and cooperative control with an upper system.

[0008] The present application has been made to solve the above-described technical problems, and an object thereof is to provide a DC-DC conversion system that can be easily added to a solar power generation system and a solar power generation system including the DC-DC conversion system.

[0009] Means for Solving the Technical Problem

[0010] The DC-DC conversion system of the present application includes:

[0011] a current detection mechanism that detects the current flowing from the solar cell panel to the power conversion device; and

[0012] A DC-DC conversion device is clamped between a battery device and the power conversion device, and outputs second DC power obtained by converting first DC power output from the battery device to the power conversion device side. The DC-DC conversion device includes the following first operation mode: when it is sensed by the current value sensed by the current detection mechanism that the solar cell panel is not generating power, the second DC power is generated in such a way that the output current and the output voltage change according to a predetermined solar cell current-voltage simulation characteristic curve.

[0013] The solar power generation system of the present application includes:

[0014] A solar cell panel;

[0015] A reverse current blocking diode that receives DC power from the solar cell panel at its anode;

[0016] A power conversion device that receives the DC power from the cathode of the reverse current blocking diode;

[0017] A current detection mechanism that detects the current flowing from the solar cell panel to the power conversion device via the reverse current blocking diode;

[0018] A battery device; and

[0019] A DC-DC conversion device is connected to the connection point between the cathode of the reverse current blocking diode and the power conversion device, and outputs second DC power obtained by converting first DC power output from the battery device to the connection point. The DC-DC conversion device includes the following first operation mode: when it is sensed by the current value sensed by the current detection mechanism that the solar cell panel is not generating power, the second DC power is generated in such a way that the output current and the output voltage change according to a predetermined solar cell current-voltage simulation characteristic curve.

[0020] Advantages of the Invention

[0021] According to the present application, the DC-DC conversion device operates according to a predetermined solar cell current-voltage simulation characteristic curve to simulate the solar cell panel. Therefore, from the perspective of the power conversion device, the same operation as in the case of adding other solar cell panels can be performed. Thus, the addition of the DC-DC conversion system to the solar power generation system becomes easy. Description of the Drawings

[0022] Figure 1 It is a configuration diagram showing the DC-DC conversion system and the solar power generation system of the embodiment.

[0023] Figure 2It is a graph showing an example of the current-voltage characteristic curve simulated by the DC-DC conversion system of the embodiment.

[0024] Figure 3 It is a configuration diagram showing the DC-DC conversion system and the solar power generation system of the embodiment.

[0025] Figure 4 It is a configuration diagram showing the DC-DC conversion system and the solar power generation system of the embodiment. Detailed Embodiment

[0026] Figure 1 It is a configuration diagram showing the DC-DC conversion system 10 and the solar power generation system of the embodiment. Figure 1 The solar power generation system is a system connected to the power system 1.

[0027] Figure 1 The solar power generation system includes a solar cell array 2, a power conversion device 3, a reverse current blocking diode 4, a battery device 9, and a DC-DC conversion system 10. Figure 1 The arrow P0 shows the site combined power. The site combined power P0 is the sum of the output powers of the solar cell array 2 and the battery device 9 in the solar power generation system.

[0028] The solar cell array 2 is formed by arranging a plurality of solar cell panels in parallel. In Figure 1 , for the convenience of illustration, one solar cell array 2 is shown, but in an actual solar power generation system, a plurality of solar cell arrays 2 can also be provided and connected to each other in parallel or in series.

[0029] The power conversion device 3 converts the DC power generated by the solar cell array 2 into AC power. Specifically, the power conversion device 3 includes an inverter circuit and an inverter control circuit for controlling the inverter circuit. The inverter circuit is constructed by a plurality of switching elements such as IGBTs. The inverter control circuit generates a pulse width modulation signal as the gate drive signal of the switching element. The power conversion device 3 is also called a power conditioning system (PCS).

[0030] The power conversion device 3 is constructed to implement a well-known maximum power point tracking control (Maximum power point tracking: MPPT). The MPPT control is a control function for extracting the current with the maximum output voltage from the power of the solar cell array 2. Preferably, an output limiter function is also provided in the power conversion device 3.

[0031] The anode of the reverse current blocking diode 4 is connected to the solar cell array 2. The power conversion device 3 is connected to the cathode of the reverse current blocking diode 4. In addition, in the embodiment, asFigure 1 As shown, no other DC / DC converters are inserted in series in the series circuit between the solar cell array 2 and the power conversion device 3. This is one of the differences between the system of the embodiment and the systems described in Japanese Patent No. 6475945 Figure 1 and the like.

[0032] The battery device 9 includes a battery main body capable of charging and discharging, and a battery management system that manages the state of charge (SOC) and the like of the battery main body. Although the type of the battery main body of the battery device 9 is not limited, for example, it may be a single battery composed of a group including a fuel cell, a lithium ion battery, a lead storage battery, and a sodium sulfur battery. In addition, although the output characteristics of the battery main body are determined by its structure and materials, as an example, the current may be inversely proportional to the voltage, or, as another example, at least one of the output current and the output voltage may decrease according to the change in the SOC.

[0033] The DC-DC conversion system 10 includes a DC / DC converter 11 and a current sensor 12. The cathode of the reverse current blocking diode 4 is connected to the power conversion device 3 via a DC bus. The DC / DC converter 11 is connected to the connection point Px between the cathode of the reverse current blocking diode 4 and the power conversion device 3. The DC / DC converter 11 is interposed between the battery device 9 and the power conversion device 3. In addition, the power conversion device 3 and the DC / DC converter 11 may perform control separately without communicating with each other, so a communication line may not be provided between the power conversion device 3 and the DC / DC converter 11.

[0034] The DC / DC converter 11 is a DC-DC conversion device configured to step up and step down a DC voltage. The DC / DC converter 11 includes a converter circuit, a converter control device 11a, a first current-voltage sensor that measures the current and voltage input and output between the DC / DC converter 11 and the battery device 9, and a second current-voltage sensor that measures the current and voltage input and output between the DC / DC converter 11 and the connection point Px. The converter circuit, the first current-voltage sensor, and the second current-voltage sensor are omitted from the illustration. An example of the converter circuit may be a buck-boost converter circuit that combines a boost chopper circuit and a buck chopper circuit. The converter control device 11a gives drive signals (in other words, gate pulses) to the semiconductor switching elements of the boost chopper circuit and the buck chopper circuit based on the current and voltage measured by the first current-voltage sensor and the second current-voltage sensor, so as to achieve the output value indicated by the command value. The converter control device 11a has a known buck-boost control logic, and may include, for example, a constant current control based on a target current command value I out *, a constant voltage control based on a target voltage command value V outConstant voltage control of *, based on the target power command value P out Control of one or more of the constant power controls of *. The DC / DC converter 11 is configured to be able to selectively perform a discharging operation and a charging operation. The discharging operation is an operation of discharging the power stored in the battery device 9 to the connection point Px. The charging operation is an operation of taking in power from the connection point Px and charging the battery device 9.

[0035] The DC / DC converter 11 outputs the second DC power obtained by converting the first DC power output from the battery device 9 to one side of the power conversion device 3 according to the command value. In addition, the current sensor 12 detects the current flowing from the solar cell array 2 to the power conversion device 3 via the reverse current blocking diode 4.

[0036] The operation mode of the DC / DC converter 11 includes a "first operation mode". The first operation mode is a mode of outputting the second DC power in such a way that the output current and output voltage simulate the solar cell current-voltage characteristics. In the first operation mode, the DC / DC converter 11 operates in such a way as to simulate the power generation characteristics of the solar cell array 2 according to a "predetermined solar cell current-voltage simulation characteristic curve Sr1". As a result, when observed from the power conversion device 3, the same processing as in the case of simply adding other solar cell arrays in parallel can be performed. Therefore, the additional application of the DC-DC conversion system 10 becomes easy.

[0037] Explain in more detail the effects brought by the DC-DC conversion system 10 of the embodiment. According to the embodiment, it is possible to easily add the DC / DC converter 11 to a non-DC link type solar power generation system that was not originally designed as a DC link system.

[0038] If the DC link system is designed as a single system from the beginning, the system configuration (in other words, the solar cell array, battery device, DC / DC converter, and power conversion device) can be developed and designed simultaneously, so there are advantages that both hardware design and software design can be used flexibly.

[0039] In contrast, for a non-DC link type solar power generation system that was not originally designed as a DC link system, the technology of adding the DC / DC converter 11 is not common. The reason is that a large amount of design change work is required for both hardware design and software design. In the design change work, the following operations are included: the addition of communication lines and sensors is required, and design changes are required in the cooperative control with the upper system. Because of this situation, it is actually difficult to add and apply the DC / DC converter 11 in the case of a non-DC link system.

[0040] According to an embodiment, the DC / DC converter 11 can be easily applied to a solar power generation system including a solar cell array 2 and a power conversion device 3. The hardware configuration of the embodiment is that the DC / DC converter 11 is connected in parallel with a DC bus after a reverse current blocking diode 4 is inserted on the solar cell array 2 side. In the DC / DC converter 11, a current sensor 12 is also provided to grasp the power generation status of the solar cell array 2.

[0041] According to this configuration, the DC / DC converter 11 can be added without changing the hardware and software configurations on the side of the solar cell array 2 and the power conversion device 3. As a result, cost savings of the power conversion device 3 and reduction of preparation time can be achieved. In addition, since it does not depend on the hardware and software configurations on the side of the solar cell array 2 and the power conversion device 3, it can also be applied to a solar power generation system using a solar cell array 2 of other companies.

[0042] More specifically, the control content executed by the DC / DC converter 11 in the DC-DC conversion system 10 of the embodiment will be described. In the embodiment, a first operation mode, a second operation mode, and a third operation mode are provided.

[0043] (First operation mode)

[0044] The first operation mode is an operation mode during power generation stop of the solar cell array 2. In the first operation mode, discharge power is released in the direction of arrow P1, and the discharge power changes according to the current-voltage characteristic curve S1. That is, the first operation mode is a "PV simulation operation mode". Figure 1 is a graph showing an example of the current-voltage characteristic curve (IV curve) simulated by the DC-DC conversion system 10 of the embodiment. In the first operation mode, the DC / DC converter 11 performs discharge control to simulate the current-voltage characteristic curve S1 of the solar cell array 2.

[0045] Figure 2 also shows the power characteristic curve (PV curve) S2. Figure 2 also shows the solar cell current-voltage simulation characteristic curve Sr1 preset in the manner of simulating the current-voltage characteristic curve S1 and the solar cell power simulation characteristic curve Sr2 preset in the manner of simulating the power characteristic curve S2. Figure 2

[0046] Figure 2 ​​In the figure, the maximum power point Pmpp, the maximum output operating voltage Vmpp, the maximum output operating current Impp, the open circuit voltage Voc, and the short circuit current Isc are illustrated. The maximum power point Pmpp is the maximum point at which the power (product of the operating voltage and the operating current), i.e., the power characteristic curve S2, becomes maximum in the current-voltage characteristic curve S1. The maximum output operating voltage Vmpp is the operating voltage at the maximum power point ( Figure 2 MPP point) of the figure.

[0047] The maximum output operating current Impp is the operating current at the maximum power point. The open circuit voltage Voc is the voltage in a state where no load or the like is connected to the output terminals of the solar cell and the circuit is open. The short circuit current Isc is the current flowing when the output terminals of the solar cell are short-circuited.

[0048] In Figure 2 the figure, for convenience, the actual characteristic curves (S1, S2) and the simulated characteristic curves (Sr1, Sr2) are shown overlapped, but this is an example. In the "simulation" of the embodiment, the characteristic curves (S1, S2) to be used as a reference and the simulated characteristic curves (Sr1, Sr2) may have the same shape, or they may have substantially the same shape (in other words, an approximate shape).

[0049] Regarding the normal current-voltage characteristic curve S1, a substantially rectangular curve with a bent portion near the maximum power point MPP is depicted. Regarding the power characteristic curve S2, it rises linearly from a voltage of zero volts toward the maximum power point Pmpp and then drops sharply from the maximum power point Pmpp. Preferably, the DC / DC converter 11 performs DC-DC conversion control to simulate these normal characteristic curves as accurately as possible.

[0050] The first operation mode (PV simulation operation mode) is a mode in which the discharge output of the battery device 9 is controlled in such a way that the discharge amount changes in accordance with the simulated current-voltage characteristic curve Sr1 of the solar cell. The simulated current-voltage characteristic curve Sr1 of the solar cell simulates the current-voltage characteristic curve S1 of the solar cell array 2. In the embodiment, the "characteristic curve information" is stored in the converter control device 11a of the DC / DC converter 11. The characteristic curve information is electronic data representing the simulated current-voltage characteristic curve Sr1 of the solar cell. The converter control device 11a generates a command value based on the characteristic curve information, so that the output value of the DC / DC converter 11 can approximate the simulated current-voltage characteristic curve Sr1 of the solar cell. As an example, the characteristic curve information may be stored in the non-volatile memory of the converter control device 11a in the form of numerical data such as a table or in the form of mathematical formula data such as an approximate function.

[0051] As an example, the first operation mode can be implemented in the DC / DC converter 11 as described below. An instruction value setting logic for generating an instruction value based on the aforementioned characteristic curve information is executed on the converter control device 11a. The converter control device 11a also incorporates a discharge control logic for performing discharge control of the battery device 9 according to the instruction value. The instruction value setting logic and the discharge control logic can be implanted in the non-volatile memory of the converter control device 11a in the form of a software program, or can be implanted in a part of the converter control device 11a in hardware as a processing circuit.

[0052] Describe a specific example of the discharge control logic implemented in the Figure 1 solar power generation system in the first operation mode. In step S101, the DC / DC converter 11 performs DC-DC conversion control based on the instruction value and the measured values of the first current-voltage sensor and the second current-voltage sensor respectively. The instruction value is preset by assuming to obtain the same output power capacity as the solar cell array 2. The instruction value can be, for example, a power instruction value or a voltage instruction value. The DC / DC converter 11 performs switching control according to the instruction value based on the characteristic curve information as described above. As a result, the DC / DC converter 11 controls the output voltage and output current output to the connection point Px in such a way that the current-voltage characteristic at the connection point Px approximates the current-voltage characteristic curve of the solar cell array 2.

[0053] Next, in step S102, the power conversion device 3 performs MPPT control based on the current and voltage at the connection point Px. At this time, from the perspective of the power conversion device 3, the current-voltage at the connection point Px is the same as the current-voltage characteristic curve of the solar cell panel ( Figure 2 S1). Therefore, the power conversion device 3 can continue power conversion control without making changes or adjustments to MPPT control or sensor information acquisition, etc.

[0054] In addition, the solar cell current-voltage simulation characteristic curve Sr1, the solar cell power simulation characteristic curve Sr2, and their characteristic curve information of the embodiment can also be determined by considering the following aspects. There are various materials and structures in solar cells, including single-crystalline or polycrystalline silicon solar cells, amorphous silicon solar cells, and compound-based solar cells. In addition, the shape of the current-voltage characteristic curve of the solar cell sometimes varies according to the measurement state. The measurement state includes the temperature, spectral distribution, and irradiance of the solar cell.

[0055] As a specific embodiment, the aforementioned characteristic curve information can also be determined based on the measured values of the current-voltage characteristic curve, which are obtained by measuring a solar cell panel of the same type as the material and structure of the actual solar cell array 2 under a reference state determined according to a specific standard. As a specific standard, for example, the JIS standard is known, and the reference state of the JIS standard is determined as the temperature of the solar cell being 25 °C, the spectral distribution being reference sunlight, and the irradiance being 1000 W / m 2 in the state, so this condition can be applied.

[0056] Alternatively, as another specific embodiment, for example, characteristic curve information of multiple groups corresponding to multiple solar cell current-voltage simulation characteristic curves Sr1 can also be stored in the DC / DC converter 11. In this case, the converter control device 11a can also be configured to select a specific characteristic curve information from the multiple characteristic curve information according to a predetermined rule. In this case, it can be that the command value setting logic uses the selected characteristic curve information to calculate the command value and performs the first operation mode according to the command value.

[0057] Preferably, when the solar cell array 2 stops generating electricity, the DC / DC converter 11 performs discharge control in such a way that the discharge amount of the battery device 9 is consistent with the power generation amount at the peak power generation of the solar cell array 2. Preferably, in parallel with the first operation mode of the DC / DC converter 11, the power conversion device 3 performs MPPT control in such a way that the power generation amount is maximized.

[0058] Preferably, by controlling the DC voltage so that it is near the lower limit of the MPPT range, the efficiency can also be improved. According to the first operation mode, when viewed from the side of the solar cell array 2 and the power conversion device 3, it seems as if another solar cell array is added and generating electricity continuously, so the power conversion device 3 can perform MPPT control as usual.

[0059] (Second operation mode, third operation mode)

[0060] Figure 3 and Figure 4 are the configuration diagrams of the DC-DC conversion system 10 and the solar power generation system showing the embodiments. Use Figure 3 and Figure 4 , the second operation mode and the third operation mode of the embodiment are described. The second operation mode and the third operation mode are the operation modes when the solar cell array 2 and the battery device 9 operate in parallel. In Figure 3 and Figure 4 , the generated power Pg based on solar power generation is generated, which is the same asFigure 1 Different.

[0061] When both the solar cell array 2 and the battery device 9 are generating power, the DC / DC converter 11 operates in the second operation mode. In the second operation mode, power is released in the direction of arrow P2 to Figure 3 . In the implementation of the second operation mode, the solar cell array 2 and one side of the power conversion device 3 perform MPPT control as usual, and the DC / DC converter 11 compensates for the insufficient amount on the solar cell array 2 side through discharge control.

[0062] The second operation mode includes a discharge operation for increasing the potential of the connection point Px. Specifically, in the discharge operation mode, when the voltage at the connection point Px is below a predetermined specified voltage Vth, the DC / DC converter 11 performs a discharge operation to increase the potential of the connection point Px. The voltage of the MPPT control target is controlled by the inverter of the power conversion device 3, so that the battery device 9 can discharge a desired constant DC power.

[0063] The third operation mode is the mode when the solar cell array 2 is generating power and charging the battery device 9. In the third operation mode, power is obtained in the direction of arrow P3 to Figure 4 . Only the direction of the power between the battery device 9 and the DC / DC converter 11 is opposite to that in the second operation mode, and the control content is the same as that in the second operation mode. The third operation mode includes a mode for converting the voltage of the connection point Px in a manner that charges the battery main body of the battery device 9. That is, in the third operation mode, when the voltage of the connection point Px is higher than a predetermined specified voltage Vth, the voltage of the connection point Px is converted in a manner that charges the battery device 9.

[0064] According to the embodiment, when the DC / DC converter 11 detects that the solar cell array 2 is not generating power through the current value detected by the current sensor 12, it operates in the first operation mode (PV simulation operation mode). When the DC / DC converter 11 detects that the solar cell array 2 is generating power through the current value detected by the current sensor 12, it selectively switches between the second operation mode (discharge operation mode) and the third operation mode (charging operation mode) according to the magnitude relationship between the voltage of the connection point Px and the specified voltage Vth.

[0065] Thereby, in the stop of power generation of the solar cell array 2, the first operation mode for simulating the solar cell array 2 can be used. On the other hand, during the power generation of the solar cell array 2, it is also possible to distinguish and use the second operation mode for discharging to compensate for insufficient power generation and the third operation mode for charging the battery device 9 when the power generation is sufficient.

[0066] According to an embodiment, when the DC / DC converter 11 executes the first operation mode, the second operation mode, and the third operation mode, the power conversion device 3 implements the MPPT (Maximum Power Point Tracking) control. Since there is no situation where the MPPT control of the power conversion device 3 is hindered by the first operation mode to the third operation mode, the power conversion device 3 can implement the MPPT control seamlessly.

[0067] According to an embodiment, the first operation mode is configured to output the voltage and current at an operating point near the lower limit of the MPPT range in the MPPT control of the power conversion device 3. By controlling the DC voltage near the lower limit of the MPPT range, the efficiency can be improved.

[0068] As described above, according to an embodiment, the control mode of the DC / DC converter 11 can be switched according to the power generation status of the solar cell array 2 obtained from the current sensor 12. In the embodiment, there is an advantage that no cumbersome design changes are required for the hardware and software on the side of the solar cell array 2 and the power conversion device 3 including the upper-level system. Since the communication line between the power conversion device 3 and the DC / DC converter 11 can be omitted, and the design change of the control system of the power conversion device 3 can also be omitted, there is an advantage that the retrofit of the DC / DC converter 11 is easy.

[0069] In the DC-DC conversion system 10 of the embodiment, a modification example in which the first operation mode is omitted from the control content of the DC / DC converter 11 may be provided. In this case, it may also be configured that the DC / DC converter 11 as the first modification example is connected to the battery device 9 and is connected to the connection point Px between the cathode of the reverse current blocking diode and the power conversion device 3, and outputs the second DC power obtained by converting the first DC power output from the battery device 9 to the connection point Px. The DC / DC converter 11 includes the following discharge operation mode: when the voltage at the connection point Px is equal to or lower than a predetermined specified voltage, a discharge operation is performed to increase the potential of the connection point Px.

[0070] Alternatively, it may be configured that the DC / DC converter 11 as the second modification example is connected to the battery device 9 and is connected to the connection point Px between the cathode of the reverse current blocking diode and the power conversion device 3, and outputs the second DC power obtained by converting the first DC power output from the battery device 9 to the connection point Px. The DC / DC converter 11 of the second modification example includes the following charging operation mode: when the voltage at the connection point Px is higher than a predetermined specified voltage, the voltage of the connection point Px is converted to charge the battery device 9.

[0071] In addition, as Figure 2As shown, the current-voltage characteristic curve S1 depicts a graph of "roughly rectangular shape", so the solar cell current-voltage simulation characteristic curve Sr1 can also be set to the same roughly rectangular shape. This roughly rectangular shape can be roughly divided into three intervals as an example. The first interval is as shown in Figure 2 , which is the interval where, in the low voltage range starting from zero volts of voltage, Isc remains basically constant corresponding to the increase in voltage. The second interval is the interval where, when the voltage increases compared to the first interval, the current decreases represented by a gentle convex curve corresponding to the increase in voltage, and it can be determined as the specified interval near Figure 2 's V mpp . The third interval is the interval where the voltage further increases from the second interval to a certain voltage and then drops sharply. The command value setting logic of the converter control device 11a can be constructed to generate command values separately by at least dividing into these three intervals. For example, the command value setting logic can be composed of multiple setting logics that generate command values in a way that independently and separately simulate the first interval to the third interval of the current-voltage characteristic curve S1 of Figure 2 , and these multiple setting logics can also be switched.

[0072] As a modification example of the embodiment, the change in the approximate shape when the solar cell current-voltage simulation characteristic curve Sr1 is approximated to the current-voltage characteristic curve S1 will be described. As shown in Figure 2 , the current-voltage characteristic curve S1 is approximately constant in the low voltage region and drops sharply from Vmpp. The current-voltage characteristic curve S1, together with the current axis ( Figure 2 's vertical axis) and the voltage axis ( Figure 2 's horizontal axis), forms a roughly rectangular shape. Therefore, a modification example of the solar cell current-voltage simulation characteristic curve Sr1 can be, for example, one of a semi-trapezoidal graph, a first roughly trapezoidal graph, a second roughly trapezoidal graph, a first roughly rectangular graph, and a second roughly rectangular graph. In the semi-trapezoidal graph which is a broken line graph of a semi-trapezoid composed of one upper base and one leg, the corner formed by the upper base and the leg corresponds to the MPP point. The first roughly trapezoidal graph is obtained by chamfering the corner corresponding to the MPP point once or multiple times obliquely in the above semi-trapezoidal graph. The second roughly trapezoidal graph is obtained by rounding the corner corresponding to the MPP point in the above semi-trapezoidal graph. The first roughly rectangular graph is a right-angled broken line graph composed of one long side parallel to the voltage axis and one short side parallel to the current axis, and the corner corresponding to the MPP point is chamfered once or multiple times obliquely. The second roughly rectangular graph is obtained by rounding the corner corresponding to the MPP point in the above right-angled broken line graph.

[0073] On the other hand, if a modified example of the solar cell power simulation characteristic curve Sr2 is described, the power characteristic curve S2 is similar to a triangle (more specifically, an acute triangle) having the voltage axis ( Figure 2 the horizontal axis thereof) as the base and the vertex corresponding to Pmpp with respect to the base. Therefore, the modified example of the solar cell power simulation characteristic curve Sr2 can also be one of an acute triangle-shaped graph having Pmpp at the vertex, a first substantially triangle-shaped graph obtained by performing one or more diagonal chamfers or horizontal chamfers on the angle corresponding to Pmpp, and a second substantially triangle-shaped graph in which the angle corresponding to Pmpp is rounded.

[0074] In addition, as a modified example, the characteristic curve information stored in the converter control device 11a may include not only the solar cell current-voltage simulation characteristic curve Sr1 but also the solar cell power simulation characteristic curve Sr2 (see Figure 2 ). When the converter control device 11a performs control based on the power command value, the power command value may be generated according to the characteristic curve information to achieve the solar cell power simulation characteristic curve Sr2.

[0075] In addition, in the first operation mode, the output characteristics of the battery device 9 determine the input current and input voltage of the DC / DC converter 11. Therefore, the output characteristics of the battery main body included in the battery device 9 may also be taken into account in the setting of the command value. In addition, as a modified example, "one or more command value data generated according to the characteristic curve information" may be stored in the converter control device 11a instead of the characteristic curve information. In this modified example, a plurality of command value data determined in advance may be stored. In this case, the converter control device 11a may also be configured to select a specific one from the plurality of command value data according to a predetermined rule. Even if only the command value data is stored in the converter control device 11a as in this modified example, the output characteristics of the DC / DC converter 11 can be approximated to the output characteristics of the solar cell array 2 by generating the command value data based on the solar cell current-voltage simulation characteristic curve Sr1 or the solar cell power simulation characteristic curve Sr2.

[0076] Description of Reference Numerals

[0077] 1 Power system, 2 Solar cell array, 3 Power conversion device, 4 Reverse current blocking diode, 9 Battery device, 10 DC-DC conversion system, 11 DC / DC converter, 12 Current sensor, Px Connection point, S1 Current-voltage characteristic curve, S2 Power characteristic curve, Sr1 Solar cell current-voltage simulation characteristic curve, Sr2 Solar cell power simulation characteristic curve, P0 Site combined power, Pg Generated power.

Claims

1. A DC-DC conversion system, comprising: a current detection mechanism that detects the current flowing from a solar cell panel to a power conversion device; and a DC-DC conversion device interposed between a battery device and the power conversion device, and outputs second DC power obtained by converting first DC power output from the battery device to the power conversion device side. The DC-DC conversion device includes the following first operation mode: when it is sensed by the current value sensed by the current detection mechanism that the solar cell panel is not generating electricity, the second DC power is generated in such a manner that the output current and the output voltage change according to a predetermined solar cell current-voltage simulation characteristic curve. The battery device can be charged and discharged. The DC-DC conversion device includes a second operation mode and a third operation mode. In the second operation mode, the potential of the connection point between the power conversion device and the DC-DC conversion device is increased. In the third operation mode, the voltage of the connection point is converted in a manner to charge the battery device. The DC-DC conversion device is configured to selectively switch the mode between the second operation mode and the third operation mode according to the magnitude relationship between the voltage of the connection point and a specified voltage when it is sensed by the current value sensed by the current detection mechanism that the solar cell panel is generating electricity. The power conversion device and the DC-DC conversion device are configured to perform control actions separately without communicating with each other.

2. The DC-DC conversion system according to claim 1, The DC-DC conversion device is configured to operate in the second operation mode when the voltage of the connection point is equal to or lower than the specified voltage, operate in the third operation mode when the voltage of the connection point is higher than the specified voltage.

3. A solar power generation system, comprising: a solar cell panel; a reverse current blocking diode that receives DC power from the solar cell panel at its anode; a power conversion device that performs maximum power point tracking control and receives the DC power from the cathode of the reverse current blocking diode; the DC-DC conversion system according to claim 1 or 2; and a current detection mechanism that detects the current flowing from the solar cell panel to the power conversion device via the reverse current blocking diode.

4. The solar power generation system according to claim 3, when the DC-DC conversion device executes the first operation mode, the second operation mode, and the third operation mode, the power conversion device seamlessly implements MPPT maximum output point tracking control.

5. The solar power generation system according to claim 3, No other DC-DC conversion devices are provided for the series circuit between the solar cell panel and the power conversion device.

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