Power converter

Abstract

To provide a power converter capable of preventing power conversion efficiency from being lowered, by appropriately cooperating with a photovoltaic power-generating part.SOLUTION: A power converter 7 is arranged between a storage battery 4 and an AC / DC conversion circuit 5 for converting AC power supplied from a system power line 2 into DC power in addition to a DC / DC conversion circuit 6 for being supplied to a DC output terminal of the AC / DC conversion circuit 5 by converting a voltage of a DC power generated with solar light via a solar panel 3 thereinto to bi-directionally convert the voltage of the DC power thereinto. A control part 9 in the power converter 7 controls a power supply part 8 so as to change a bus voltage of the DC output terminal according to the power generated by the solar panel 3. Specifically, the bus voltage is made to be lower than conventional when the power generated by the solar panel 3 is lower than a threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power conversion device applied to a system including a photovoltaic power generation unit that generates electric power by sunlight.

Background Art

[0002] Recently, in the trend of promoting carbon neutrality, the interest in improving the efficiency of power supply devices has been increasing. In particular, attention has been focused on natural energy, and among them, the photovoltaic power generation system has been widely popularized for both commercial and household use. In a household photovoltaic power generation system, by connecting to the grid power supply, it is possible to purchase electricity and sell the generated electricity by sunlight according to the electricity usage situation in the household. However, in this system, in order to prevent electric shock when a power outage occurs in the grid power supply, it is necessary to stop the operation of the power controller and power converter arranged on the photovoltaic power generation side, and there is a problem that electricity cannot be used during a disaster.

[0003] Therefore, in order to supply power even during a disaster, a V2H (Vehicle to Home) system that uses a large-capacity battery mounted on a storage battery, an electric vehicle, or a hybrid electric vehicle has also been proposed and put on the market. In this system, as shown in FIG. 6, the charger of the battery mounted on the vehicle is provided with an independent discharge function that is used only during a power outage. And when a power outage occurs, the power supply from the grid power supply to electrical appliances in the distribution board is disconnected, and by connecting to the independent discharge line, AC power is supplied to the electrical appliances in the household.

[0004] The power converter on the photovoltaic power generation side detects the AC waveform of the independent discharge line even in an emergency, recognizes as if the grid power supply is normal, and supplies the generated power to the load in the same way as in normal times. In order to continue the above operation, the charger on the vehicle side must output a sine wave without distortion like the grid power supply. However, depending on the compatibility with the above power converter and the usage situation of electrical appliances, a distorted AC waveform may be output. Then, since the power converter stops operating, power cannot be supplied.

[0005] To solve these problems, as disclosed in Patent Document 1, there is a technology that integrates the power conditioner and the charger / discharger in order to coordinate with the power conditioner on the solar power generation side in the event of an emergency. In other words, the charger / discharger that was installed on the vehicle side is incorporated into a system located on the home side. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-193444 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the system configuration of Patent Document 1, the DC bus voltage needs to be matched to the power conditioner on the solar power generation side. Generally, the voltage of the power supplied by solar power generation often exceeds 400V, while the voltage of the battery installed on the vehicle side is often below 400V. Therefore, the amount of voltage reduction when charging the above battery becomes large, and the losses that occur during the step-down conversion become large, which reduces the power conversion efficiency of the system.

[0008] This invention has been made in view of the above circumstances, and its purpose is to provide a power conversion device that can prevent a decrease in power conversion efficiency by appropriately coordinating with the solar power generation unit. [Means for solving the problem]

[0009] According to the power conversion device described in claim 1, the isolation converter section is arranged between an AC / DC converter that converts AC power supplied from a grid power line into DC power, a DC / DC converter that converts the voltage of DC power generated by sunlight in a photovoltaic power generation section and supplies it to the DC output terminal of the AC / DC converter, and a power storage section that stores power, and converts the voltage of the DC power in both directions.

[0010] The control unit then controls the isolation converter unit to change the voltage at the DC output terminal according to the power generated by the solar power generation unit. With this configuration, even if the power generated by the solar power generation unit changes over time, the isolation converter unit can change the voltage at the DC output terminal of the AC-DC converter, thereby controlling the power conversion efficiency when charging the energy storage unit or discharging from the energy storage unit to be optimal.

[0011] in particular , regulation When the power generated by the solar power generation unit falls below a threshold, the unit lowers the voltage at the DC output terminal to a level lower than normal. This reduces the potential difference before and after conversion in the isolation converter unit, thereby minimizing the decrease in power conversion efficiency.

[0012] Claim 2 According to the power conversion device described, the control unit reduces the switching frequency of the isolation converter section to a lower level than normal when the power generated by the solar power generation section falls below a threshold. This reduces the switching losses that occur in the isolation converter section, thereby further improving efficiency.

[0013] Claim 3 According to the power conversion device described, the isolation converter section is a resonant converter, and the control unit compares the switching frequency of the isolation converter section corresponding to the voltage of the DC output terminal to be reduced with the resonant frequency of the isolation converter section, and selects the higher frequency to perform the switching operation. This avoids excessively reducing the switching frequency, which would shorten the lifespan of the circuit elements.

[0014] Claim 4 According to the power conversion device described, the isolation converter section is placed between an AC / DC converter that converts AC power supplied from the grid power line into DC power, a first DC / DC converter that converts the voltage of DC power generated by sunlight in the photovoltaic power generation section, and a power storage section that stores power, thereby converting the voltage of the DC power in both directions.

[0015] Also, arrange the second DC-DC converter between the first DC-DC converter and the isolation converter section, convert the voltage converted by the first DC-DC converter, and supply it to the DC output terminal of the AC-DC converter. Then, the control unit controls the second DC-DC converter so as to change the voltage of the DC output terminal according to the power generated by the solar power generation section. Thus, by the control unit controlling the second DC-DC converter instead of the isolation converter section of claim 1, the same effect as in claim 1 can be obtained. According to 5 the power conversion device described, the isolation converter section is a DAB converter.

Brief Description of the Drawings

[0016] [Figure 1] 2]The first embodiment, a diagram showing the configuration of a power conversion system [Figure 2] A flowchart showing the processing content by the control unit of the power conversion device [Figure 3] An example of a time chart showing the generated power amount, bus voltage, and switching frequency that change corresponding to the processing of FIG. 2 over time [Figure 4] A diagram showing an equivalent circuit including resonance circuits on both sides of a transformer [Figure 5] The second embodiment, a diagram showing the configuration of a power conversion system [Figure 6] A diagram showing the configuration of a general V2H system

Modes for Carrying Out the Invention

[0017] (First Embodiment) Hereinafter, the first embodiment will be described. FIG. 1 shows the configuration of a V2H system which is the power conversion system of the present embodiment. The V2H system 1 converts and transmits power among the utility power line 2, the solar panel 3 which is a solar power generation section, and the storage battery 4 which is a power storage section. Note that the storage battery 4 may be a battery that supplies driving power to a running drive motor mounted on an electric vehicle or a battery not mounted on an electric vehicle.

[0018] The V2H system 1 includes a power conversion device 7 disposed between an AC / DC conversion circuit 5 connected to the grid power line 2, a DC / DC conversion circuit 6 connected to the solar panel 3, and the battery 4. The power conversion device 7 consists of a power supply unit 8 and a control unit 9. The power supply unit 8 is a resonant isolation converter, which includes a transformer 11 as an insulation part. On both sides of the transformer 11, a full-bridge circuit 12V and a full-bridge circuit 12P, which are formed by H-bridge connecting switching elements, for example, N-channel MOSFETs _Q1 to _Q4, are respectively connected. That is, the power supply unit 8 is also a DAB (Double Active Bridge) converter. In the figure, the left side is the vehicle side, so it is called the V side, and the right side in the figure is the grid power line 2 side, so it may be called the P side. Also, when there is no need to particularly distinguish between the V side and the P side, it is omitted to attach "V, P" to the reference signs.

[0019] The common connection point of FETs _Q1 and _Q3 constituting the full-bridge circuit 12V is connected to one end of the V-side coil of the transformer 11 via the coil 13V. Also, the common connection point of FETs _Q2 and _Q4 is connected to the other end of the V-side coil via the capacitor 14V. The common connection point of FETs _Q1 and _Q3 constituting the full-bridge circuit 12P is connected to one end of the P-side coil of the transformer 11 via the capacitor 14P. Also, the common connection point of FETs _Q2 and _Q4 is connected to the other end of the P-side coil via the coil 13P.

[0020] A smoothing capacitor 15 is connected in parallel to the full-bridge circuit 12. A series circuit of FETs _Q5 and _Q6 is connected in parallel to the smoothing capacitor 15V. The common connection point of FETs _Q5 and _Q6 is connected to the positive terminal of the battery 4 via the inductor 16. FETs _Q5 and _Q6 and the inductor 16 constitute a buck-boost chopper 25. Also, when the transformer 11 and the full-bridge circuits 12V and 12P are regarded as a DAB converter 26, the power supply unit 8 is constituted by combining the buck-boost chopper 25 and the DAB converter 26.

[0021] The DC output terminal of the DC / DC conversion circuit 6 is connected to the DC output terminal of the AC / DC conversion circuit 5 and to the voltage measurement unit 18 via the ammeter 17 of the control unit 9. The measurement result of the ammeter 17 is acquired by the current measurement unit 19. The voltage measurement unit 18 measures the voltage at the DC output terminal, and the current measurement unit 19 measures the current flowing from the DC / DC conversion circuit 6 to the DC output terminal.

[0022] The output terminals of the voltage measurement unit 18 and the current measurement unit 19 are connected to the input terminals of the power calculation unit 20, respectively. The power calculation unit 20 calculates the power output from the DC / DC conversion circuit 6. The result of this calculation is input to the operation mode determination unit 21, which determines the operation mode of the power supply unit 8 based on the input power value. The result of this determination is input to the power supply control unit 22. The power supply control unit 22 controls the switching operation of each FETQ1 to Q6 of the power supply unit 8 according to the input operation mode. In the following, the voltage at the DC output terminal of the DC / DC conversion circuit 6 may be referred to as the "bus voltage".

[0023] Next, the operation of this embodiment will be described. As shown in Figure 2, the control unit 9 measures the power generated by the solar panel 3 in the power calculation unit 20 (S1), and then compares the generated power with a threshold value (S2). Note that PV in the figure means Photovoltaic; solar panel. The threshold value is set to, for example, about 10W.

[0024] Then, if the generated power exceeds the threshold (Yes), it is determined that the time of day is daytime, and the power supply unit 8 is operated in normal mode (S3). That is, the bus voltage and the switching frequency of the power supply unit 8 are set to normal values. For example, the voltage is set to 380V and the switching frequency to 200kHz.

[0025] On the other hand, if the generated power does not exceed the threshold (No), it is determined that the time of day is nighttime, and the power supply unit 8 is operated in high-efficiency mode (S4). That is, the bus voltage and the switching frequency of the power supply unit 8 are reduced from the values ​​of the normal mode. For example, the bus voltage is reduced to 340V and the switching frequency to 180kHz. Figure 3 shows an example of how the generated power, bus voltage, and switching frequency change over time in accordance with the processing shown in Figure 2.

[0026] Next, we will explain the constraints on the switching frequency to be reduced in high-efficiency mode. Figure 4 shows an equivalent circuit including the resonant circuits on both sides of the transformer 11. Let Lr1 be the inductance of coil 13V, Lm1 be the inductance of the V-side coil of transformer 11, and C1 be the capacitance of capacitor 14V. Let Lr2, Lm2, and C2 be the corresponding constants on the P-side, respectively.

[0027] If the switching frequency is f, the switching frequency f when discharging the battery 4 is normally controlled to be within the following range. 1 / {2π×(Lr1+Lm1)×C1} <f<1 / (2π×Lr1×C1) Then, if we let f'd be the switching frequency calculated based on the reduced bus voltage, we compare frequency f'd with frequency [1 / {2π×(Lr1+Lm1)×C1}] and select the higher value.

[0028] Furthermore, the switching frequency f when charging the battery 4 is normally controlled to be within the following range. 1 / {2π×(Lr²+Lm²)×C²} <f<1 / (2π×Lr2×C2) Then, if we let f'c be the switching frequency calculated based on the reduced bus voltage, we compare the frequency f'c with the frequency [1 / {2π×(Lr2+Lm2)×C2}] and select the higher value.

[0029] As described above, according to this embodiment, the power conversion device 7 is placed between the AC / DC conversion circuit 5, which converts AC power supplied from the grid power line 2 into DC power, the DC / DC conversion circuit 6, which converts the voltage of the DC power generated by the solar panel 3 using sunlight and supplies it to the DC output terminal of the AC / DC conversion circuit 5, and the storage battery 4, thereby converting the voltage of the DC power in both directions.

[0030] The control unit 9 of the power converter 7 controls the power supply unit 8 to change the bus voltage of the DC output terminal according to the power generated by the solar panel 3. Specifically, when the power generated by the solar panel 3 falls below a threshold, the control unit 9 lowers the bus voltage to a level lower than normal. This reduces the potential difference before and after conversion in the power supply unit 8, minimizing the decrease in power conversion efficiency and allowing for optimal power conversion efficiency when charging the battery 4 or discharging from the battery 4.

[0031] Furthermore, when the power generated by the solar panel 3 falls below a threshold, the control unit 9 lowers the switching frequency of the power supply unit 8 to a level lower than normal. This reduces the switching losses that occur in the power supply unit 8, thereby further improving efficiency.

[0032] Furthermore, using the power supply unit 8 as a resonant DAB converter, the control unit 9 compares the switching frequency f' of the power supply unit 8 corresponding to the reduced bus voltage with the resonant frequency f of the power supply unit 8, and selects the higher frequency to perform the switching operation. This avoids excessively reducing the switching frequency, which would shorten the lifespan of the circuit elements.

[0033] (Second Embodiment) In the following description, parts identical to those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted, while the differences are described. In the V2H system 31 of the second embodiment shown in Figure 5, the DC / DC conversion circuit 32 corresponds to the power converter 7 of the first embodiment, but does not perform the processing shown in Figure 2 and is always configured to operate in normal mode. Another DC / DC conversion circuit 33 is added between the AC / DC conversion circuit 5 and the DC / DC conversion circuit 6. The DC / DC conversion circuit 33 is configured to perform step-down operation with unidirectional conversion.

[0034] With this configuration, even if the operating mode of the DC / DC conversion circuit 32 is not switched as in the first embodiment, if it is determined to be nighttime, the DC / DC conversion circuit 33 will lower the bus voltage as in step S4, thereby preventing a decrease in conversion efficiency.

[0035] The present invention is not limited to the embodiments described above or shown in the drawings, and the following modifications or extensions are possible. The switching element is not limited to an N-channel MOSFET; a P-channel MOSFET or an IGBT may be used on the power supply side. The bus voltage, switching frequency, and threshold values ​​for switching operating modes should be set appropriately according to the specific design. [Explanation of Symbols]

[0036] In the diagram, 1 represents the V2H system, 2 represents the grid power line, 3 represents the solar panel, 4 represents the battery, 5 represents the AC / DC conversion circuit, 6 represents the DC / DC conversion circuit, 7 represents the power converter, 8 represents the power supply unit, 9 represents the control unit, 11 represents the transformer, 12 represents the full-bridge circuit, 25 represents the step-up / step-down chopper, and 26 represents the DAB converter.

Claims

1. An AC / DC converter that converts AC power supplied from the grid power line into DC power, a DC / DC converter that converts the voltage of DC power generated by sunlight from the solar power generation unit and supplies it to the DC output terminal of the AC / DC converter, and an isolation converter unit that is positioned between the power storage unit and the power storage unit and converts the voltage of the DC power in both directions, The system includes a control unit that controls the isolation converter unit to change the voltage of the DC output terminal in accordance with the power generated by the solar power generation unit, The control unit is a power conversion device that, when the power generated by the solar power generation unit falls below a threshold, lowers the voltage of the DC output terminal to a level lower than normal.

2. The power conversion device according to claim 1, wherein the control unit reduces the switching frequency of the isolation converter unit to a lower level than normal when the power generated by the solar power generation unit falls below a threshold.

3. The isolation converter section is a resonant type converter. The power conversion device according to claim 2, wherein the control unit compares the switching frequency of the isolation converter section corresponding to the voltage of the DC output terminal to be reduced with the resonant frequency of the isolation converter section, and selects the higher frequency to perform the switching operation.

4. An AC-DC converter that converts AC power supplied from the grid power line into DC power, a first DC-DC converter that converts the voltage of DC power generated by sunlight in the solar power generation unit, and an isolation converter unit positioned between the power storage unit and the power storage unit that stores power, which converts the voltage of DC power in both directions. A second DC converter is positioned between the first DC converter and the isolation converter section, and converts the voltage converted by the first DC converter and supplies it to the DC output terminal of the AC-DC converter. A power conversion device comprising: a control unit that controls the second DC converter to change the voltage of the DC output terminal in accordance with the power generated by the solar power generation unit.

5. The power conversion device according to any one of claims 1 to 4, wherein the isolation converter section is a DAB (Double Active Bridge) converter.

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