JP2021072028A - Power conversion device, and power system - Google Patents

Abstract

To provide a technique that can maintain maximum output power of a solar battery as much as possible even when a load fluctuates suddenly in a solar battery system.SOLUTION: A power conversion device according to the present invention temporarily switches from battery voltage-based control to battery current-based control when a solar battery deviates from an optimum operation point due to sudden change in a load.SELECTED DRAWING: Figure 3

Description

The present invention relates to a power conversion device that converts the power output by a solar cell.

In recent years, photovoltaic power generation systems have rapidly become widespread. Regarding solar power generation for home use, FIT (Feed In Tariff: feed-in tariff) has been completed, and how to utilize it is being studied. A market where solar power can be consumed in-house is being developed toward the introduction of distributed power sources after the end of FIT. At the same time, due to the widespread use of EVs (electric vehicles) and storage batteries, the direct current charged and discharged by EVs and storage batteries can be directly connected to the worship hall system via the DC bus, reducing the conversion loss that occurs when converting direct current to alternating current. DC systems are attracting attention. Even in a system that raises or lowers the voltage of a DC bus, such as a DC system, it is required to establish the competitiveness of the DC system by extracting the maximum power from the solar cell and maximizing the efficiency.

Patent Document 1 describes a method of stabilizing a DC power supply system including a solar cell, a storage battery, and a DC / DC converter while varying the voltage of the DC bus. Patent Document 2 describes a method of controlling a DC bus so as not to become an overvoltage in a composite power storage system including a solar cell and a DC / DC converter (boost pressure chopper) connected to the solar cell. Patent Document 3 and Non-Patent Document 1 describe a method for extracting maximum power from a solar cell. Patent Document 4 and Non-Patent Document 2 describe a method for determining the position of a photovoltaic power generation system equipped with a solar cell in terms of IV characteristics.

Japanese Unexamined Patent Publication No. 2012-147508 Japanese Unexamined Patent Publication No. 2014-099986 JP-A-2017-051099 Patent No. 6075997

IEEE Transactions on Energy Conversion, Vol. 22, No. 2, June 2007, pp 439-449 “Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques” IEEE Journal of Photovoltaics, Vol. 9, No. 3, May 2019, pp 780-789 “Fault-Diagnosis Architecture for Large-Scale Photovoltaic Power Plants That Does Not Require Additional Sensors”

When an EV or storage battery is connected to a DC bus, a large amount of charging power flows toward the charging target via the DC bus. As EVs and storage batteries become widespread, it is thought that the frequency of such operations will increase. As the capacities of EVs and storage batteries increase in the future, it is conceivable that the DC bus voltage and the solar cell voltage may drop sharply at the same time in such a large-capacity quick charging operation.

In Patent Documents 1 and 2, the system is stabilized by making the voltage of the solar cell smaller than the voltage of the DC bus. However, when the DC bus voltage and the solar cell voltage suddenly drop at the same time as described above, if the solar cell voltage is further reduced, the amount of power generation cannot be stably obtained from the solar cell.

Patent Document 3 and Non-Patent Document 1 describe a method for extracting the maximum electric power from a solar cell, but the document mainly describes a method for dealing with changes in the amount of solar radiation and partial shade. It is assumed that the load is stable. Therefore, it is difficult to cope with a sudden load change such as when the EV is rapidly charged.

Patent Document 4 and Non-Patent Document 2 describe a method of confirming whether or not the DC / DC converter is operating at the maximum power point of the solar cell while calculating the amount of solar radiation and the temperature. However, this document only grasps the operating state, and it is not always clear how to use the grasped operating state in control.

The present invention has been made in view of the above problems, and is a technique capable of maintaining the maximum output power of a solar cell as much as possible even when a sudden load fluctuation occurs in the solar cell system. The purpose is to provide.

The power conversion device according to the present invention temporarily switches from control based on the battery voltage to control based on the battery current when the solar cell deviates from the maximum power operating point due to a sudden change in load.

According to the power conversion device according to the present invention, the operation of the solar cell can be quickly restored to the optimum operating point by temporarily switching to the current control when the load suddenly changes. As a result, the maximum power can be supplied from the solar cell even when the load suddenly changes.

This is a configuration example of the DC bus system according to the first embodiment. This is another configuration example of the DC bus system according to the first embodiment. This is another configuration example of the DC bus system according to the first embodiment. This is another configuration example of the DC bus system according to the first embodiment. This is another configuration example of the DC bus system according to the first embodiment. This is a configuration example of a general power supply system that is wired from the distribution system to each component via AC / DC conversion. It is a circuit diagram of the power conversion apparatus 100 which concerns on Embodiment 1. It is a graph which illustrates the IV characteristic of a solar cell 200. It is a graph which illustrates the PV characteristic of the solar cell 200. It is a graph which illustrates the PI characteristic of the solar cell 200. The change in the general operating point on the IV characteristic when the load suddenly changes due to the rapid charging of the EV is shown. The process of controlling the operating point of the solar cell toward the maximum power operating point as the EV is rapidly charged is shown. It is a flowchart explaining the procedure which the arithmetic unit 141 calculates a command value Vcmd. It is a flowchart explaining the continuation of S605. It is a figure explaining the determination condition of S610.

<Embodiment 1>
FIG. 1A is a configuration example of the DC bus system according to the first embodiment of the present invention. The system has a DC bus. A system inverter connected to the distribution system, a DC / DC converter for controlling PV (photovoltaic battery), and a DC / DC converter for charging / discharging the storage battery in the EV are connected to the DC bus. The host controller controls the voltage of the DC bus.

FIG. 1B is another configuration example of the DC bus system according to the first embodiment. Multiple EVs can be connected to the DC bus. The components forming the DC bus are arranged together on the DC board.

FIG. 1C is another configuration example of the DC bus system according to the first embodiment. A stationary storage battery can also be connected to the DC bus. However, due to legal restrictions, a container box may be required.

FIG. 1D is another configuration example of the DC bus system according to the first embodiment. In this figure, a DC / DC converter that controls charging / discharging of the storage battery in the EV is built in the EV, and the DC version is the lightest in FIGS. 1A to 2.

FIG. 1E is another configuration example of the DC bus system according to the first embodiment. In this figure, the DC bus is connected to the load in parallel with the distribution system. As shown in FIG. 1E, it is also possible to connect a load such as lighting or air conditioning to the DC bus via a self-supporting converter.

FIG. 2 is a configuration example of a general power supply system wired from the distribution system to each component via AC / DC conversion. Compared with the DC system as shown in FIGS. 1A to 1E, the loss when converting from alternating current to direct current becomes a problem. In addition, the distance from each component (Power Conditioning System, inverter) to the connection destination of the distribution system is often long, and it takes a lot of man-hours to install the wiring and the connection board. In addition, foundation work is required to arrange each component. Therefore, since the system shown in FIG. 2 requires man-hours for installation, the configuration shown in FIGS. 1A to 1E is desirable.

FIG. 3 is a circuit diagram of the power conversion device 100 according to the first embodiment. The power conversion device 100 can be configured as a DC / DC converter that controls PV in FIGS. 1A to 1E. The power conversion device 100 includes a voltage sensor 110, a current sensor 120, a step-up chopper 130, and a control unit 140.

The step-up chopper 130 is composed of an inductor L, an IGBT (Insulated Gate Bipolar Transistor), a rectifying diode, and a smoothing capacitor C. The step-up chopper 130 connects the solar cell 200 and the DC bus 300.

The voltage sensor 110 measures the output voltage Vin of the solar cell 200. The current sensor 120 measures the output current Iin of the solar cell 200. The control unit 140 controls the output voltage (that is, the voltage of the DC bus 300) Vout of the power conversion device 100. Specifically, the arithmetic unit 141 acquires the measurement results of Vin and Iin, and also acquires the commands from the host controller 400, and calculates the command value Vcmd for Vout based on these. When the comparator 144 compares the output of the triangular wave generator 143 with the command value Vcmd, the command value Vcmd is converted into a fluxion α. The conversion formula is represented by the following formula 1.

FIG. 4A is a graph illustrating the IV characteristics (current-voltage characteristics) of the solar cell 200. The power conversion device 100 calculates the command value Vcmd so that the solar cell 200 operates at the operating point (white circle in FIG. 4A) where the output power of the solar cell 200 is maximized. Vin at the maximum power operating point may be referred to as the maximum operating voltage, and Iin at the maximum power operating point may be referred to as the maximum operating current. The battery current when the output terminal of the solar cell 200 is short-circuited is called a short-circuit current. As shown in Non-Patent Document 2, the ratio of the short-circuit current to the maximum operating current can be regarded as constant as long as it exceeds a certain amount of solar radiation.

FIG. 4B is a graph illustrating the PV characteristics (power-voltage characteristics) of the solar cell 200. Three characteristic graphs corresponding to FIG. 4A are illustrated.

FIG. 4C is a graph illustrating the PI characteristics (power-current characteristics) of the solar cell 200. As shown in FIG. 4C, the PI characteristic of the solar cell 200 changes sharply with the maximum power operating point as a turning point, so that the battery power suddenly changes with respect to a slight change in the battery current, and the short-circuit current (battery). Battery current corresponding to voltage = 0) may be reached. When this state is reached, the arithmetic unit 141 cannot continue to calculate the command value Vcmd, so that it becomes necessary to reset the control unit 140 once. Therefore, the arithmetic unit 141 generally calculates the command value Vcmd according to the IV characteristic (or PV characteristic).

FIG. 5A shows a change in a general operating point on the IV characteristic when the load suddenly changes due to the rapid charging of the EV. The DC / DC converter of a solar cell in a DC system performs various controls such as not only maximum power point control but also suppression control for reducing power and control of Vin by Vcmd while responding to changes in Vout. Therefore, in the normal operation mode, the operating point moves widely on the IV characteristic. If an EV is connected to the DC bus 300 for quick charging, the load will change suddenly. As a result, the Vout is lowered and the Vin is further lowered, so that the operating point moves on FIG. 5A as shown by the operating points 1 and 2.

FIG. 5B shows a process of controlling the operating point of the solar cell so as to move toward the maximum power operating point as the EV is rapidly charged. When the control procedure for sequentially directing the battery voltage to the maximum power operating point as described in Non-Patent Document 1 is used, the operating points sequentially transition toward the maximum power operating point for each control step as shown in FIG. 5B. .. When such a control procedure is used, a plurality of control steps are required before the solar cell reaches the maximum power operating point. That is, it takes time to reach the maximum power operating point, so it is difficult to supply the maximum power from the solar cell.

In order to quickly restore the solar cell to the maximum power operating point when the load suddenly changes, the current difference between the current operating point and the maximum power operating point on the PI characteristic curve is calculated, and the command value Vcmd is calculated according to the current difference. It is considered that it should be calculated. However, on the other hand, the control based on the PI characteristic is unstable as described in FIG. 4C. Therefore, in the first embodiment, during normal operation, the command value Vcmd is calculated according to the difference between the target value and the current value of Vout, and the battery voltage is sequentially changed as shown in FIG. 5B to obtain the maximum power. Head to the operating point. When the load suddenly changes, the control is temporarily switched to the control using the PI characteristic, and the command value Vcmd is calculated according to the current difference between the current operating point and the maximum power operating point on the PI characteristic curve. A specific procedure will be described with reference to the following flowchart.

FIG. 6A is a flowchart illustrating a procedure in which the arithmetic unit 141 calculates the command value Vcmd. Here, as shown in FIG. 5B, the command value Vcmd is calculated so as to sequentially transition toward the maximum power operating point for each control step during normal operation. The arithmetic unit 141 can execute this flowchart for each control cycle, for example. For convenience of description, some steps will be explained in the following sentences without giving step numbers. Each step of FIG. 6A will be described below.

(FIG. 6A: steps S601 to S604)
The arithmetic unit 141 acquires Vin from the voltage sensor 110 and Iin from the current sensor 120 (S601). The arithmetic unit 141 stores the acquired Vin in the array Vin [1], replaces Vin [1] at the time of the previous execution of this flowchart with Vin [0], and differs between Vin [0] and Vin [1]. Calculate ΔV (S602). The arithmetic unit 141 sets Iin [0] and Iin [1] for Iin in the same manner, and calculates the difference ΔI (S603). The arithmetic unit 141 obtains the current battery power Pin [1] by the product of Vin [1] and Iin [1], and the battery at the time of the previous execution of this flowchart by the product of Vin [0] and Iin [0]. The electric power Pin [0] is obtained, and the difference ΔP between the Pin [0] and the Pin [1] is calculated (S604).

(FIG. 6A: Steps S601 to S604: Supplement)
In the array Vin [], the array Iin [], and the array Pin [], the 0th element stores the value when this flowchart is executed last time, and the 1st element stores the value when this flowchart is executed this time. It will be.

(FIG. 6A: step S605)
Let TYPE be an internal flag variable indicating that the load has suddenly changed due to the EV being connected to the DC bus 300 or the like. TYPE = 1 represents a sudden change in load. The sudden change in load corresponds to the operating point in the PI characteristics being the operating point 1 in FIG. 5A when this flowchart was last executed, and transitioning to the operating point 2 in FIG. 5A when this flowchart was implemented this time. The arithmetic unit 141 proceeds to the flowchart of FIG. 6B when the TYPE is 1, and proceeds to S606 otherwise.

(FIG. 6A: Step S606: Part 1)
The arithmetic unit 141 calculates Vcmd so that when ΔV is larger than 0 (Vin is increased), Vin is increased if ΔP is larger than 0, and Vin is decreased if ΔP is 0 or less. This is because in the PV characteristics, Vin is increased when the operating point transitions from the left side of the maximum power point toward the maximum power point, and Vin is decreased when the operating point transitions from the maximum power point or its right side to the right side. , Means to bring the maximum power operating point closer.

(FIG. 6A: Step S606: Part 2)
The arithmetic unit 141 calculates Vcmd so that when ΔV is 0 or less (Vin is decreased), Vin is decreased if ΔP is larger than 0, and Vin is increased if ΔP is 0 or less. This is because in the PV characteristics, Vin is decreased when the operating point transitions from the right side of the maximum power point toward the maximum power point, and Vin is increased when the operating point transitions from the maximum power point or its left side to the left side. , Means to bring the maximum power operating point closer.

(FIG. 6A: step S607)
When the Vin decreases and the Pin also decreases, the state of the solar cell 200 has changed from the left side of the maximum power operating point to the left side in the PV characteristic. In this case, there is a possibility that the load has changed suddenly due to EV quick charging or the like. Therefore, the arithmetic unit 141 holds that fact by setting 1 in TYPE. The next time this flowchart is executed, the TYPE flag will be determined in S605.

(FIG. 6A: Step S607: Supplement)
The TYPE flag is for detecting the transition from the operating point 1 to 2 in FIG. 5A, which typically appears when the load suddenly changes. Whether or not the load has changed truly suddenly will be determined again in S610 when this flowchart is executed again after TYPE = 1. The grounds for determining a sudden load change in S610 will be described later.

(FIG. 6A: Steps S608-S609)
The arithmetic unit 141 stores the value of Vin [0] in the temporary variable Vin_a (S608). This is because it is necessary to use the previous value of Vin [0] (Vin [0] at the time of the previous execution of this flowchart) in the calculation formula described later, so that it is not overwritten in S602 at the next execution for convenience. It is a measure of. The arithmetic unit 131 calculates the fluxion α according to Equation 1 and controls Vout using this (S609).

FIG. 6B is a flowchart illustrating the continuation of S605. Each step of FIG. 6B will be described below.

(FIG. 6B: step S610)
The arithmetic unit 141 determines whether ΔP / ΔV is equal to the current value of Iin (Iin [1]) or is a peripheral value that can be regarded as equivalent thereto. That is, it is determined whether or not ΔP / ΔV≈Iin [1]. If the conditions are met, the process proceeds to S611, and if the conditions are not met, the process returns to S606. The reason for setting the conditions for this step will be described later.

(FIG. 6B: steps S611-S613)
The arithmetic unit 141 estimates the temperature T of the solar cell 200 using the following equations 2 to 3 (S611). The arithmetic unit 141 calculates ΔVin according to the following equation 4, and calculates the command value Vcmd by Vcmd = Vin [1] + ΔVin (S612). The arithmetic unit 141 returns the TYPE to 0 (S613) and returns to S609. The derivation process of Equations 2 to 4 will be described later.

Isc: Short-circuit current at standard solar cell 200 amount p: Solar cell 200 solar cell Is: Reverse saturation current of solar cell 200 Ncell: Number of cells of solar cell 200 nf: Diode performance constant of solar cell 200 k: Boltzmann Constant T: Temperature of solar cell 200 j = (Iin of current operating point in current solar cell) / (Short-circuit current in current solar cell)

FIG. 7 is a diagram for explaining the determination conditions of S610. The upper part of FIG. 7 shows the PV characteristics, and the lower part of FIG. 7 shows the IV characteristics at that time. In FIG. 7, the increment of the power P when the operating point changes from the dotted line circle to the black circle is expressed by Equation 5. When returning to the maximum power operating point after the load suddenly changes, the slope of the current I with respect to the voltage V on the IV characteristics can be regarded as almost 0 (see the lower diagram of FIG. 7). By substituting this into Equation 5, Equation 6 can be derived.

Therefore, the arithmetic unit 141 can determine in S610 that the load has suddenly changed when ΔP / ΔV is substantially equal to Iin [1]. Instead of or in combination with this, when ΔI / ΔV is 0 (or within a predetermined range in the vicinity of 0), it can be determined that the load has suddenly changed. Here, the range within a predetermined range near 0 is within −0.004. The ∂I / ∂V components of the equation (5) are represented by the voltage derivative of the equation (8), and are (a) constant components represented by nf, q, and T, (b) reverse saturation current, and (c) exp. It can be expressed by subtracting the term (d) affected by the deterioration of the shunt resistance from the multiplication of the components. (A) The constant component is in the range of 0.002 to 0.003 in the usage range of the solar cell, (b) the reverse saturation current is about 0.00001, and (c) the exp component in the low voltage range is about 1. If the deterioration of the solar cell is 0.3Ω with a shunt resistance corresponding to about 80%, the affected item (d) is about 0.004. Therefore, ∂I / ∂V can be determined to be near 0 within −0.004.

When calculating the command value Vcmd using the current difference between the maximum power operating point and the current operating point on the PI characteristics, the Vcmd is actually calculated after converting the current difference into a voltage difference. become. When carrying out this conversion, it is necessary to use the battery temperature T in the mathematical formula expressing the characteristics of the solar cell. Equations 2 to 4 calculate the command value Vcmd after reflecting the battery temperature T. The derivation process of Equations 2 to 4 will be described below.

The amount of solar radiation p can be expressed as the ratio of the short-circuit current at the current amount of solar radiation to the short-circuit current Isc at the standard amount of solar radiation. When the current operating current in the current amount of solar radiation is expressed as Iin_a, the short-circuit current in the current amount of solar radiation can be defined as Iin_a / j from the definition of the above reference numerals. Therefore, the amount of solar radiation p is expressed by (short-circuit current in the current amount of solar radiation) / Isc, that is, Equation 7. Using Equation 7 is useful when there are circumstances in which the maximum power operating point in the current amount of solar radiation cannot be specified.

Iin is represented by Equation 8. Solving Equation 8 for Vin, Vin is represented by Equation 9.

Vin can be obtained by substituting Equation 7 and Iin for Equation 9. Vin [1] is represented by Equation 12 by substituting Iin [1]. Vin [0] is represented by Equation 11 by substituting Iin [0]. Vin_a is Vin [0] at the time when the flowchart of FIG. 6 was carried out last time, and was saved in S608. When Iin [0] in the previous implementation is expressed as Iin_a, Vin_a is expressed by Equation 10 by substituting Iin_a.

Equations 13 and 14 are derived from Equations 10 to 12. Eliminating the battery temperature T from equations 13 and 14 leads to equation 2. The arithmetic unit 141 obtains a numerical value of j that satisfies Equation 2. For example, this can be obtained by searching for the numerical value of j that satisfies Equation 2 by numerical analysis. Searching for j is equivalent to searching for the battery current Iin that satisfies Equation 2. In the following, it will be described as assuming that j that satisfies Equation 2 is obtained.

Equation 3 can be obtained by solving Equations 11 and 12 for T. Further, assuming that Vin at the maximum power operating point is Vmpp and Iin at the maximum power operating point is Impp, Equation 15 can be derived by substituting Equation 7 and Impp for Equation 9. However, in Equation 15, it is assumed that the ratio of the short-circuit current to the maximum operating current can be regarded as a constant value (0.935: a numerical value specified in advance).

The command value Vcmd can be calculated by adding the difference ΔVin between Vmpp and Vin [1] to Vin [1]. Vmpp is obtained from Equation 15 and Vin [1] is obtained from Equation 12. Therefore, ΔVin can be calculated by Equation 16. Since Equations 12 and 15 are calculated using the maximum operating current Impp and the current operating point current Iin [1], respectively, ΔVin is between the maximum power operating point and the current operating point on the PI characteristics. It is calculated using the difference. That is, it is calculated using the current difference between the maximum power operating point and the current operating point.

By the above procedure, the arithmetic unit 141 temporarily switches to the control using the PI characteristic when the load suddenly changes, and calculates the command value Vcmd according to the current difference between the current operating point and the maximum power operating point on the PI characteristic curve. can do. As a result, the solar cell 200 can be quickly restored to the maximum power operating point.

<Embodiment 1: Summary>
The power conversion device 100 according to the first embodiment has (a) when the slope ΔP / ΔV of the PV characteristic is substantially equal to Iin [1], or (b) when the slope ΔI / ΔV of the IV characteristic is substantially 0. , It is determined that a sudden change in load has occurred due to rapid charging of the EV. As a result, sudden changes in load in the DC bus system can be accurately detected.

The power conversion device 100 according to the first embodiment temporarily switches to the control using the PI characteristic when the load suddenly changes, and the command value Vcmd according to the current difference between the current operating point and the maximum power operating point in the PI characteristic curve. Is calculated. As a result, the solar cell 200 can be quickly restored to the maximum power operating point when the load suddenly changes.

The power conversion device 100 according to the first embodiment estimates the temperature T of the solar cell 200 when calculating the current difference between the current operating point and the maximum power operating point in the PI characteristic curve. As a result, the current difference is calculated after reflecting the battery temperature T, so that the command value Vcmd can be accurately obtained.

The power conversion device 100 according to the first embodiment calculates the command value Vcmd based on the current difference in S612, and then returns the TYPE to 0 in S613. As a result, the next time the flowchart of FIG. 6 is executed, the control will return to the control based on the voltage difference. That is, the control based on the current difference is performed only in one control cycle, and then the control based on the voltage difference is promptly returned. As a result, the solar cell 200 can be quickly returned to the maximum power operating point while avoiding unstable control based on the PI characteristics.

The power conversion device 100 according to the first embodiment uses the ratio (j) between the current operating current Iin_a in the current amount of solar radiation and the short-circuit current in the current amount of solar radiation, and the short-circuit current Isc in the standard amount of solar radiation. The temperature T is calculated by temporarily setting p by the equation 7 and further searching for j that satisfies the equation 2. Thereby, for example, even if the maximum power operating point cannot be specified due to the specifications of the solar cell 200, the temperature T can be estimated using the current operating current Iin.

In the formula 15, the power conversion device 100 according to the first embodiment formulates a command value Vcmd based on the PI characteristics, assuming that the ratio between the short-circuit current and the maximum operating current in the current amount of solar radiation is a constant value. Calculated according to 16. Thereby, for example, the command value Vcmd can be calculated based on the PI characteristics even when the maximum power operating point cannot be specified due to the specifications of the solar cell 200.

<Embodiment 2>
In the first embodiment, it has been described that the power conversion device 100 is a DC / DC converter. The circuit or the like used by the power conversion device 100 to convert DC power is not limited to that described in the first embodiment, and any configuration can be used. For example, instead of the IGBT, an element using a SiC device as a semiconductor switching element may be adopted. Other suitable semiconductor switching elements may be used.

100: Power converter 110: Voltage sensor 120: Current sensor 130: Boost chopper 140: Control unit 141: Arithmetic logic unit 200: Solar cell 300: DC bus

Claims (10)

It is a power conversion device that converts the power output by the solar cell.
It is provided with a control unit that calculates a command value for the converted voltage output by the power conversion device.
In the control unit, the inclination of the battery power output by the solar cell with respect to the battery voltage output by the solar cell is equal to the battery current output by the solar cell or falls within a predetermined range around the battery current. If so, the command value is calculated according to the current difference between the detected value of the battery current and the target value of the battery current.
When the inclination of the battery power output by the solar cell with respect to the battery voltage output by the solar cell is not within a predetermined range around the battery current, the control unit sets the target value of the converted voltage as the target value. A power conversion device characterized in that the command value is calculated according to a voltage difference between the detected value of the converted voltage and the detected value. The control unit calculates the command value for each control cycle and calculates the command value.
The control unit calculates the command value according to the current difference in one control cycle, and then calculates the command value according to the voltage difference in the next control cycle. The power conversion device according to claim 1. The control unit acquires the detected value of the battery voltage output by the solar cell and the detected value of the battery current.
The control unit calculates the battery temperature of the solar cell by using the detected value of the battery voltage and the detected value of the battery current.
The electric power according to claim 1, wherein when the control unit calculates the command value using the current difference, the control unit calculates the command value by using the battery temperature in addition to the current difference. Conversion device. The control unit calculates the command value for each control cycle and calculates the command value.
The control unit
The battery voltage in the first control cycle,
The battery current in the first control cycle,
The battery voltage in the second control cycle following the first control cycle,
The battery current in the second control cycle,
The battery voltage in the third control cycle following the second control cycle,
The battery current in the third control cycle,
By estimating the battery current that satisfies the relational expression between, the operating point on the voltage-current curve of the solar cell is estimated.
The power conversion device according to claim 3, wherein the control unit calculates the battery temperature using the estimated operating point. The control unit sets the battery current output by the solar cell at the maximum power operating point of the solar cell as the target value of the battery current.
The control unit replaces the current difference with a voltage difference between the battery voltage output by the solar cell at the maximum power operating point and the detected value of the battery voltage.
The power conversion device according to claim 1, wherein the control unit uses the replaced voltage difference as the command value. In the control unit, the ratio between the battery current at the maximum power operating point of the solar cell under the current solar cell amount and the short-circuit current of the solar cell under the current solar cell amount is a fixed value. By assuming that, the battery current at the maximum power operating point under the current solar radiation amount is calculated.
The power conversion device according to claim 5, wherein the control unit uses the battery current at the maximum power operating point under the current amount of solar radiation to replace the current difference with a voltage difference. The control unit acquires the detected value of the battery voltage output by the solar cell and the detected value of the battery current.
The control unit calculates the battery temperature of the solar cell by using the detected value of the battery voltage and the detected value of the battery current.
The power conversion device according to claim 5, wherein the control unit calculates the replaced difference using the battery temperature. The power conversion device according to claim 1, wherein the power conversion device is configured as a DC converter that converts the DC power output by the solar cell into another DC power. The power conversion device according to claim 8, wherein the DC converter is configured to convert DC power output by the solar cell into another DC power by using a semiconductor switching element. The power conversion device according to claim 1.
Terminals for connecting the charging terminals of electric vehicles,
A power system characterized by being equipped with.

Images