Power Conversion Device

Abstract

To provide an electric power conversion system capable of utilizing weak power of a power generator by charging the electric power into a capacitor without using a switching element.SOLUTION: An electric power conversion system 1, converting generated power of a power generator 2 into electric power adapted to a load 3, includes: a diode 11 for preventing a counterflow into the power generator 2; a converter 13 for converting generated power of the power generator 2 into electric power adapted to the load 3; and a capacitor 12 connected with wiring X for connecting the diode 11 with the converter 13. The converter 13 operates with voltage control of the capacitor 12 so that voltage of the capacitor 12 becomes a preset voltage command value VC and when the voltage of the capacitor 12 is under an operation stop voltage VL lower than the voltage command value VC, stops the operation, and when the voltage of the capacitor 12 is over an operation start voltage VH higher than an operation stop voltage VL, starts the operation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device that converts the power generated by a power generation device into power that matches a load. [Background technology]

[0002] Solar cells have become widespread in recent years, but the power generated by solar cells is affected by environmental conditions such as the season and weather, and only weak power can be generated under adverse conditions. Furthermore, the weak generated power is lost in power conditioners, DC-DC converters, etc., and therefore cannot be used. Therefore, a technology has been proposed that efficiently recovers the weak generated current using a capacitor, thereby efficiently utilizing the power generated by solar cells (see, for example, Patent Document 1).

[0003] In Patent Document 1, a capacitor connected to a solar cell is provided, and when the amount of power generated by the solar cell exceeds a predetermined value, power from the solar cell is supplied to a load, and when the amount of power generated by the solar cell is below the predetermined value, power from the solar cell is charged into the capacitor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-129980 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional technology, charging of the capacitor is controlled by turning on and off a switch element according to the amount of power generated by the solar cell. Therefore, the cumbersome task of setting an appropriate threshold for turning on and off the switch element is required. The on / off operation of the switch element causes periods when the power conditioner and DC-DC converter are stopped, resulting in a loss of generated power that cannot be sent to the load.

[0006] An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a power conversion device that can utilize the weak power of a power generation device by charging a capacitor without using a switching element. [Means for solving the problem]

[0007] The power conversion device of the present invention is a power conversion device that converts power generated by a power generation device into power that matches a load, and includes a diode that prevents backflow to the power generation device, a converter that converts the power generated by the power generation device into power that matches the load, and a capacitor connected to wiring that connects the diode and the converter, wherein the converter operates by controlling the voltage of the capacitor so that the voltage of the capacitor becomes a predetermined voltage command value, stops operation when the voltage of the capacitor falls below a predetermined operation stop voltage that is lower than the voltage command value, and starts operation when the voltage of the capacitor exceeds a predetermined operation start voltage that is higher than the operation stop voltage. , the operation start voltage is set to a value lower than the voltage command value. It is characterized by: [Effects of the Invention]

[0008] According to the present invention, by simply setting the stop voltage at which the converter stops operating and the start voltage at which the converter starts operating, it is possible to charge the weak power of the power generation device into a capacitor and utilize it without using a switch element. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram showing a configuration of an embodiment of a power conversion device according to the present invention; [Figure 2] 2 is a diagram showing the relationship between the generated power of the power generating device shown in FIG. 1 and the voltage of a capacitor. [Figure 3] 2 is a diagram illustrating an application example of the power conversion device shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, components having similar functions will be denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0011] Referring to FIG. 1, a power conversion device 1 of this embodiment is a device that converts power generated by a power generation device 2 into power suitable for a load 3, and includes a diode 11, a capacitor 12, and a converter 13.

[0012] The power generation device 2 that is the target of conversion by the power conversion device 1 is a type of power generation facility in which the generated power fluctuates depending on environmental conditions, such as a solar cell or plant power generation that generates power from natural energy.

[0013] The diode 11 is a backflow prevention diode with its anode connected to the output terminal of the power generation device and its cathode connected to the input terminal of the converter 13 , and prevents the charge in the capacitor 12 from flowing back to the power generation device 2 .

[0014] Capacitor 12 is connected to wiring X that connects the cathode of diode 11 and converter 13. Capacitor 12 exhibits a charging curve in which the voltage gradually increases from 0 V as it is charged, and is directly charged with the power generated by power generation device 2 via diode 11. Capacitor 12 functions as a buffer that supports the voltage required for the operation of converter 13 during normal times when power generation device 2 is generating sufficient power. The lower limit of the capacity of capacitor 12 is determined by the loss of converter 13, and the upper limit of the capacity of capacitor 12 is determined by the charging time (amount of power) that is desired to be secured when power generation device 2 is low (when light is weak in the case of a solar cell).

[0015] A nano-hybrid capacitor (NHC) or a super-redox capacitor (SRC) can be used as the capacitor 12. When a nano-hybrid capacitor is used as the capacitor 12, the capacitor 12 can function as a filter for low-frequency voltage ripples, thereby reducing the burden on the electrolytic capacitor in the converter 13 and enabling the converter 13 to be made smaller and have a longer lifespan.

[0016] Converter 13 is a converter that converts the power generated by power generation device 2 into power suitable for load 3. If load 3 is an AC system or self-consumption, etc., and the suitable power is AC power, a DC-AC converter is used as converter 13. If load 3 is a storage battery, etc., and the suitable power is DC power, a DC-DC converter is used as converter 13.

[0017] The converter 13 operates by controlling the voltage of the capacitor 12, that is, the voltage value of the wiring X to which the capacitor 12 is connected is set to a predetermined voltage command value V C For example, if the power generation device 2 is a solar cell, the voltage of the capacitor 12 is controlled to match the voltage command value V C , and the power generated by the power generation device 2 and the output power of the converter 13 become equal.

[0018] The converter 13 also has a shutdown voltage V L is set in advance, and the voltage value of wire X is the operation stop voltage V L When the voltage drops below 1 V, the converter 13 stops converting. When the converter 13 stops operating, the power generated by the power generation device 2 is charged into the capacitor 12, and the voltage of the capacitor 12 (wire X) rises.

[0019] Furthermore, the converter 13 is provided with an operation start voltage V H is set in advance, and the voltage value of wire X is the operation start voltage V H When the voltage exceeds the threshold, conversion starts. H is the voltage command value V used in the voltage control of the capacitor 12. C However, the operation start voltage V H is the voltage command value V C By setting the value lower than , the voltage of capacitor 12 can be maintained at a low voltage, and weak power from power generation device 2 can be charged into capacitor 12 more efficiently.

[0020] Next, the relationship between the power generated by the power generation device 2 and the voltage of the capacitor 12 (wire X) will be described in detail with reference to Fig. 2. In Fig. 2, (a) shows the time transition of the power generated by the power generation device 2, and (b) shows the time transition of the voltage of the capacitor 12 (wire X).

[0021] During normal operation when the power generation device 2 is generating sufficient power, the voltage of the capacitor 12 is controlled by the voltage control of the converter 13 to a voltage command value V C , and capacitor 12 functions as a buffer to support the voltage required for the operation of converter 13. Then, converter 13 outputs to load 3 power equal to the power generated by power generation device 2.

[0022] At time T1, the power generated by the power generator 2 reaches the minimum operating power setting value P L When the minimum operating power setting value P L is the operating power of converter 13, below which the efficiency of converter 13 is low and most of the power generated by power generation device 2 is lost in converter 13, and is not a value set externally but a value set according to the characteristics of converter 13.

[0023] Then, at time T2, the voltage of the capacitor 12 reaches the operation stop voltage V L , converter 13 stops the conversion operation. In the state where converter 13 stops the conversion operation, the power generated by power generator 2 is charged into capacitor 12, and the voltage of capacitor 12 rises as shown in the time period from time T2 to time T3. In other words, when the power generated by power generator 2 falls below the minimum operating power setting value P L The capacitor 12 is charged with a weak power that is below the power consumption and is lost in the converter 13.

[0024] At time T3, the voltage of capacitor 12 reaches the operation start voltage V H When the voltage of the capacitor 12 exceeds the voltage V , the converter 13 starts the conversion operation. As a result, the voltage of the capacitor 12 decreases, and at time T4, the voltage of the capacitor 12 reaches the operation stop voltage V LWhen the voltage drops below this value, converter 13 stops the conversion operation. As a result, the weak power generated by power generation device 2 from time T2 to time T3 is charged into capacitor 12, and then supplied to load 3 by converter 13 from time T3 to time T4.

[0025] Then, the voltage of the capacitor 12 becomes the operation start voltage V H At time T5 when the converter 13 starts the conversion operation, the power generated by the power generator 2 exceeds the minimum operating power setting value P L , the voltage of the capacitor 12 is equal to the voltage command value V C The state will be fixed at

[0026] As shown in Fig. 3, the power conversion device 1 may be connected in parallel to a power conditioner 4 that performs maximum power point tracking control (MTTP control). In this case, the power conditioner 4 operates when the power generated by the power generation device 2 is equal to or greater than a preset power threshold, and stops operating when the power is below the power threshold. As a result, when the power generated by the power generation device 2 is equal to or greater than the power threshold, the generated power can be used efficiently by the maximum power point tracking control of the power conditioner 4, and when the power generated by the power generation device 2 is below the power threshold, the generated power (weak power) can be used without waste by the power conversion device 1.

[0027] As described above, according to this embodiment, the power conversion device 1 converts the power generated by the power generation device 2 into power suitable for the load 3, and includes the diode 11 that prevents backflow to the power generation device 2, the converter 13 that converts the power generated by the power generation device 2 into power suitable for the load 3, and the capacitor 12 connected to the wiring X that connects the diode 11 and the converter 13, and the converter 13 controls the voltage of the capacitor 12 to be equal to the preset voltage command value V C The voltage of the capacitor 12 is controlled so that the voltage of the capacitor 12 is equal to the voltage command value V C Lower shutdown voltage V L When the voltage of the capacitor 12 falls below the operation stop voltage V L Higher than the operating start voltage V H When it exceeds this value, it starts to operate. This configuration allows the converter 13 to stop operating at a stop voltage V L and the start voltage V at which the converter 13 starts operating. H By simply setting the above, the weak power of the power generation device 2 can be charged into the capacitor 12 and utilized without using a switch element.

[0028] Furthermore, according to this embodiment, the operation start voltage V H is set to a value lower than the voltage command value. With this configuration, the voltage of capacitor 12 can be maintained at a low voltage, and the weak power of power generation device 2 can be charged into capacitor 12 more efficiently.

[0029] Furthermore, according to this embodiment, the power generator 2 is connected in parallel to a power conditioner 4 that performs maximum power point tracking control, operates when the power generated by the power generator 2 is equal to or greater than a power threshold, and stops operating when the power is below the power threshold. With this configuration, when the power generated by the power generation device 2 is equal to or greater than the power threshold, the generated power can be efficiently utilized by the maximum power point tracking control of the power conditioner 4, and when the power generated by the power generation device 2 is less than the power threshold, the generated power (weak power) can be utilized without waste by the power conversion device 1.

[0030] Although the present invention has been described above with reference to specific embodiments, it goes without saying that the above embodiments are merely examples and can be modified and implemented without departing from the spirit of the present invention. [Explanation of symbols]

[0031] 1 Power conversion device 2. Power generating equipment 3. Load 4 Power Conditioner 11 Diode 12 Capacitors 13 Converter P L Minimum operating power setting V C Voltage command value V H Start Voltage V L Shutdown Voltage X wiring

Claims

1. A power conversion device that converts generated power from a power generation device into power suitable for a load, a diode for preventing backflow to the power generating device; a converter that converts the generated power of the power generation device into power suitable for the load; a capacitor connected to a wiring connecting the diode and the converter; the converter operates by controlling the voltage of the capacitor so that the voltage of the capacitor becomes a predetermined voltage command value, stops operation when the voltage of the capacitor falls below a predetermined operation stop voltage that is lower than the voltage command value, and starts operation when the voltage of the capacitor exceeds a predetermined operation start voltage that is higher than the operation stop voltage, the operation start voltage being set to a value lower than the voltage command value.

2. 2. The power conversion device according to claim 1, wherein the power conversion device is connected in parallel with a power conditioner that performs maximum power point tracking control, operates when the power generated by the power generation device is equal to or greater than a predetermined power threshold, and stops operating when the power generated by the power generation device is less than the power threshold.

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