Parallel DC / DC converter for optimized photovoltaic applications

Abstract

A circuit arrangement (10) for converting a variable input DC voltage (UP) into an output DC voltage (UB) having a smaller fluctuation range comprises a control unit (11), a first DC voltage converter (12) and a second DC voltage converter (13). The first DC voltage converter (12) is configured to boost an input DC voltage (UP). The second DC voltage converter (13) is designed as a pure buck converter.

Description

Technical Field

[0001] The present invention relates to a circuit device for voltage conversion, in particular to a circuit device for converting a variable DC voltage into a DC voltage with a smaller fluctuation range. Background Art

[0002] US Pat. No. 8,400,123 B2 describes a voltage conversion circuit arrangement having a multiphase DC voltage converter, wherein a plurality of DC voltage converters are connected in parallel with one another and are regulated on the output side.

[0003] Voltage conversion circuit arrangements are used, for example, in solar technology, where the voltage provided by a solar panel depends on the instantaneous solar radiation and therefore fluctuates greatly.

[0004] In solar installations not connected to the grid, batteries are used to store the energy provided by solar panels. These can be low-voltage (LV) or high-voltage (HV) batteries. The voltage suitable for charging these batteries must lie within a relatively narrow voltage range.

[0005] Such off-grid solar systems can be installed in vehicles, for example. The solar panels can be mounted on the vehicle's roof or integrated into the vehicle. They can also be distributed throughout the vehicle, such as on the hood or tailgate, or in the cargo bed of a van or truck trailer.

[0006] Figure 2 A block diagram of a solar system is shown. Solar system 100 includes a solar panel 102, which provides a DC voltage UP whose magnitude varies with instantaneous solar radiation. Furthermore, solar system 100 includes a battery 103 for storing the electrical energy provided by solar panel 102. To convert the voltage UP provided by solar panel 102 into a voltage UB suitable for charging battery 103, solar system 100 also includes a circuit device 110.

[0007] Circuit device 110 receives a voltage UP provided by solar panel 102 at its input and outputs a converted voltage UB at its output. Circuit device 110 includes a control unit 111 for controlling the operation of circuit device 110 and two identical DC voltage converters 112 connected in parallel between input terminal IN and output terminal OUT, forming a two-phase DC voltage converter.

[0008] The DC voltage converter 112 converts the voltage UP provided by the solar panel 102 into a charging voltage UB suitable for charging the battery 103. Because the voltage UP provided by the solar panel 102 may be lower or higher than the allowable charging voltage range of the battery 103, the DC voltage converter 112 is configured as a buck-boost converter, which is configured to both step down (convert to a lower voltage) and step up (convert to a higher voltage) the voltage UP.

[0009] The power provided by the solar panel 102 is distributed to two DC voltage converters 112. For higher powers provided by the solar panel 102, more than two DC voltage converters 112 can be provided to distribute the power, thereby forming a multi-phase DC voltage converter. Such a circuit arrangement with a multi-phase DC voltage converter is described, for example, in US Pat. No. 8,400,123 B2.

[0010] Because a buck-boost converter must be configured for two different operating modes (buck and boost), it contains more components than a DC voltage converter dedicated to only one of these modes (buck or boost). Consequently, it costs more than such dedicated DC voltage converters and incurs higher losses during operation due to the additional components in the current path and additional switching losses in the transition region. Furthermore, multiphase DC voltage converters suffer from low efficiency at low power levels. Summary of the Invention

[0011] It is therefore an object of the present invention to provide a circuit arrangement for converting a variable DC voltage into a DC voltage with a smaller fluctuation range, which is less expensive than the prior art, has lower operating losses and is more efficient at low powers.

[0012] This object is achieved by the subject matter of the independent claims. Further developments of the invention are given in the dependent claims. The subject matter of the independent claims can also be developed by the features of the dependent claims of other independent claims.

[0013] A circuit device according to the present invention is used to convert a variable DC voltage into a DC voltage with a narrow fluctuation range. The circuit device includes a control unit, a first DC voltage converter, and a second DC voltage converter. The first DC voltage converter is configured to boost the input DC voltage. The second DC voltage converter is configured as a pure step-down converter.

[0014] By means of such a circuit arrangement, for example, the overall efficiency can be increased and the size and manufacturing costs of the entire circuit can be reduced.

[0015] In an advantageous embodiment, the first DC-DC converter is designed as a buck-boost converter.

[0016] This makes it possible, for example, to save components and make the overall circuit smaller and less expensive than providing a step-up converter and a step-down converter separately.

[0017] In an advantageous embodiment, the first DC-DC converter is designed as a pure step-up converter.

[0018] For example, the efficiency of the first DC converter can be increased as a result.

[0019] In an advantageous embodiment, the circuit arrangement includes two or more second DC-DC converters, all of which are designed as pure step-down converters. This makes it possible, for example, to adapt the circuit arrangement to a higher available power.

[0020] In an advantageous embodiment, the control unit includes a microcontroller.

[0021] As a result, for example, the circuit arrangement can be controlled in a simple and flexible manner.

[0022] In an advantageous embodiment, the control unit is configured to determine, based on input-side characteristic data, how many and which DC voltage converters are to be activated and to activate these DC voltage converters to convert the input DC voltage into the output DC voltage.

[0023] For example, the efficiency of the circuit arrangement can thereby be optimized.

[0024] A solar device according to the present invention includes: a solar panel for providing an input DC voltage that varies with solar radiation; a battery for storing the electrical energy provided by the solar panel; and a circuit arrangement according to the present invention for converting the input DC voltage into an output DC voltage suitable for charging the battery. This solar device, for example, can efficiently convert the voltage provided by the solar panel into a voltage suitable for charging the battery.

[0025] In an advantageous embodiment, the solar device is arranged on or in the vehicle, so that, for example, the vehicle battery can be efficiently charged using solar energy.

[0026] In an advantageous embodiment, the solar panels are mounted on the vehicle roof or integrated therein.

[0027] This makes it possible, for example, to achieve an optimum solar radiation for the solar panels and thus to obtain the highest possible usable electrical power.

[0028] The method according to the invention is used to operate a circuit arrangement or a solar system according to the invention. It comprises the steps of:

[0029] a) determining how many and which DC voltage converters are to be activated based on characteristic data on the input side; and

[0030] b) Activating the DC voltage converter determined in step a).

[0031] By means of such a method, for example, a variable input DC voltage can be converted flexibly and more efficiently into an output DC voltage with a smaller fluctuation range.

[0032] In an advantageous embodiment, the input-side characteristic data used in step a) are selected from the input DC voltage and data on the maximum power point tracking (MPPT) of the solar panels. This allows, for example, the number and type of DC converters to be activated to be determined depending on the available power.

[0033] In one advantageous embodiment, if it is determined based on the input-side characteristic data that one DC converter is sufficient to process the power provided by the solar panel, then in step a) only the first DC converter is activated. This allows, for example, voltage conversion to be performed by a single DC converter at low available power or input voltage.

[0034] In one advantageous embodiment, if it is determined based on the input-side characteristic data that two DC voltage converters are required to process the power provided by the solar panel, then in step a) activation of the first DC voltage converter and the second DC voltage converter is determined. Alternatively, if it is determined based on the input-side characteristic data that two DC voltage converters are required to process the power, in step a) activation of the first DC voltage converter and the two second DC voltage converters is determined.

[0035] For example, when the available power increases, it is thus possible to distribute the power between two DC converters operated in parallel.

[0036] In an advantageous embodiment, if it is determined based on the input-side characteristic data that a further DC-DC converter is required for processing the power provided by the solar panels, activation of a further second DC-DC converter is determined in step a).

[0037] As a result, for example, if the available power increases further, the power can be distributed to a larger number of DC converters operated in parallel.

[0038] Further features and expediency of the invention are apparent from the description of exemplary embodiments based on the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A circuit diagram of a solar device having a circuit arrangement according to one embodiment of the present invention is shown.

[0040] Figure 2 A circuit diagram of a conventional solar device is shown. DETAILED DESCRIPTION

[0041] Hereinafter, one embodiment of the present invention and various modifications thereof will be described with reference to the accompanying drawings.

[0042] Figure 1 The circuit diagram of solar system 1 is shown. Similar to solar system 100, it includes a solar panel 2 and a battery 3. Furthermore, it includes a circuit arrangement 10 for converting the voltage UP provided by solar panel 2 into a voltage UB suitable for charging battery 3, but its configuration differs from that of circuit arrangement 110. Solar system 1 is installed on or in a vehicle 20. Solar panel 2 is preferably mounted on the vehicle roof or integrated therein.

[0043] The circuit arrangement 10 comprises a control unit 11 for controlling the operation of the circuit arrangement 10. The control unit 11 may comprise a microcontroller, for example.

[0044] The circuit device 10 further includes a first DC voltage converter 12 and a second DC voltage converter 13 , which are connected in parallel between the input terminal IN and the output terminal OUT.

[0045] The first DC voltage converter 12 is configured to both step up and step down the input voltage, that is, it is configured as a buck-boost converter. The second DC voltage converter 13 is configured only to step down the input voltage, that is, it is configured as a pure buck converter.

[0046] Alternative Figure 1 In the illustrated structure, the circuit arrangement 10 may also include two or more second DC voltage converters 13, all of which are configured as pure buck converters. In addition, the first DC voltage converter 12 may also be configured only to boost the input voltage, that is, to be configured as a pure boost converter.

[0047] During operation, the solar panel 2 provides a voltage UP to the input IN of the circuit arrangement 10 , which voltage fluctuates with solar radiation (eg, in the range of 6 to 30 V). The solar panel 2 can provide a current of, for example, up to 30 A, depending on the total power.

[0048] The permissible range of the charging voltage UB of the battery 3 is, for example, 11 to 15 V. The charging current can be, for example, up to 30 A. Alternatively, the charging voltage can also be in the high voltage range.

[0049] The circuit device 10 converts the voltage UP applied to its input terminal into a voltage within the charge-permitting range of the battery 3 and outputs the converted voltage UB at its output terminal OUT.

[0050] To this end, control unit 11 first determines, based on input-side characteristic data, how many and which DC voltage converters are required for this voltage conversion. Typically, this involves detecting the U / I power value, which includes not only the voltage UP provided by the solar panel 2 but also the current IP it provides, to determine the optimal operating point (MPP = Maximum Power Point). Furthermore, control unit 11 can obtain further information via input terminal IN, such as data on the maximum power point tracking (MPPT) of the solar panel 2. Ambient temperature can also be factored into the decision.

[0051] Predefined thresholds or value ranges can be defined for the input-side characteristic data or the values ​​calculated therefrom by the control unit 11. If one (or more) input-side characteristic data is below a minimum threshold or within a minimum range, the control unit 11 determines that only a single DC voltage converter is required to process the power provided by the solar panel 2. Depending on which limit values ​​are exceeded or the ranges in which the input-side characteristic data / calculated values ​​are within, the control unit 11 determines that two or more DC voltage converters are required to process the power provided by the solar panel 2.

[0052] Under weak solar radiation, the voltage UP and current IP output by the solar panel 2 are relatively low, resulting in very low available power. Therefore, a single DC voltage converter is sufficient in this case. Since a voltage boost is required, the control unit 11 only activates the first DC voltage converter 12 in this case.

[0053] When available power increases due to increased solar radiation and needs to be distributed between the two DC converters, control unit 11 activates first DC converter 12 and second DC converter 13. At this point, the voltage UP provided by solar panels 2 is already high enough to require stepping down, so second DC converter 13 is sufficient as a pure step-down converter.

[0054] Alternatively, if two DC voltage converters are required, the control unit 11 does not activate the first DC voltage converter 12, but rather activates the two second DC voltage converters 13. This alternative is also selected if the first DC voltage converter 12 is designed as a pure step-up converter.

[0055] If the available power increases further, an additional second DC voltage converter 13 is activated for power distribution if necessary.

[0056] Compared to the circuit arrangement 110 consisting solely of a buck-boost converter, the circuit arrangement 10 achieves the following: Overall efficiency is improved, because a buck converter is more efficient than a buck-boost converter. However, the wide input voltage range of the buck-boost converter is retained, because the input voltage can still be stepped up or down.

[0057] By making the number of DC voltage converters to be activated dependent on the available power, efficiency can be further optimized: inefficient operation of the DC voltage converters at low power is avoided and fewer converters are activated instead.

[0058] The ripples of the output voltage and output current can be reduced.

[0059] The switching peaks that occur can also be reduced because the current is distributed and the switching is staggered.

[0060] A buck converter has fewer components than a buck-boost converter, which reduces overall circuit size and manufacturing cost.

[0061] Due to the reduced losses, smaller power components (MOSFETs, PCB copper thickness, inductors) can be used, which results in an improved thermal balance and a lower temperature level of the power components.

[0062] The smaller inductor enables the use of SMD packaging, allowing the entire manufacturing process to be carried out using SMD technology. This saves two additional steps (selective soldering) and optical inspection.

[0063] If the first DC voltage converter is configured as a buck-boost converter, a buck converter can be eliminated. This reduces components, making the overall circuit smaller and more cost-effective. If the first DC voltage converter is configured as a pure boost converter, its efficiency is superior to that of a buck-boost converter.

[0064] With the aid of a solar system equipped with the circuit arrangement 10 , a power range of approximately 100 watts to several kilowatts can be realized in vehicles such as passenger cars and trucks.

[0065] Reference Signs List

[0066] 1,100 solar equipment

[0067] 2,102 solar panels

[0068] 3,103 batteries

[0069] 10, 110 circuit devices

[0070] 11,111 control unit

[0071] 12, 13, 112 DC voltage converter

[0072] 20 vehicles

[0073] IN input terminal

[0074] IUP Current provided by solar panels

[0075] OUT output terminal

[0076] UB battery charging voltage

[0077] UP voltage provided by solar panels

Claims

1. A circuit arrangement (10) for converting a variable input DC voltage (UP) into an output DC voltage (UB) having a small fluctuation range, comprising: a control unit (11), a first DC voltage converter (12), and a second DC voltage converter (13), The first DC voltage converter (12) is configured to boost the input DC voltage (UP), and The second DC voltage converter (13) is configured as a pure step-down converter.

2. The circuit arrangement (10) according to claim 1, wherein The first DC voltage converter (12) is configured as a buck-boost converter.

3. The circuit arrangement (10) according to claim 1, wherein The first DC voltage converter (12) is configured as a pure boost converter.

4. The circuit arrangement (10) according to claim 1, comprising two or more second DC voltage converters (13), in, All second DC voltage converters (13) are configured as pure step-down converters.

5. The circuit arrangement (10) according to claim 1, wherein: The control unit (11) comprises a microcontroller.

6. The circuit arrangement (10) according to any one of claims 1 to 5, wherein: The control unit (11) is configured to determine how many and which DC voltage converters (12, 13) should be activated based on input-side characteristic data, and to activate the DC voltage converters to convert the input DC voltage (UP) into the output DC voltage (UB).

7. A solar device (1), comprising: A solar panel (2) for providing an input DC voltage (UP) that varies with solar radiation, a battery (3) for storing the electrical energy provided by the solar panel (2) and, The circuit arrangement (10) according to any one of claims 1 to 6, for converting the input DC voltage (UP) into an output DC voltage (UB) suitable for charging the battery (3).

8. The solar device (1) according to claim 7, which is installed in or on a vehicle (20).

9. The solar device (1) according to claim 7 or 8, wherein: The solar panel (2) is mounted on the roof of the vehicle or integrated into the roof of the vehicle.

10. A method for operating a circuit arrangement (10) according to any one of claims 1 to 6 or a solar system according to any one of claims 7 to 9, comprising: a) determining how many and which DC voltage converters (12, 13) should be activated based on input-side characteristic data, and b) Activating the DC voltage converter (12, 13) determined in step a).

11. The method according to claim 10, wherein: The characteristic data of the input side used in step a) are selected from: the input DC voltage (UP), the input DC current (IP), and data on maximum power point tracking of the solar panel (2).

12. The method according to claim 10 or 11, wherein: If it is determined based on the input-side characteristic data that one DC voltage converter is sufficient to process the power provided by the solar panel (2), in step a) it is determined that only the first DC voltage converter (12) is activated.

13. The method according to any one of claims 10 to 12, wherein If it is determined based on the input-side characteristic data that two DC voltage converters are required to process the power provided by the solar panel (2), activation of the first DC voltage converter (12) and the second DC voltage converter (13) is determined in step a).

14. The method according to any one of claims 10 to 12, wherein If it is determined based on the input-side characteristic data that two DC voltage converters are required to process the power provided by the solar panel (2), in step a) it is determined not to activate the first DC voltage converter (12) but to activate two second DC voltage converters (13).

15. The method according to any one of claims 10 to 14, wherein If it is determined based on the input-side characteristic data that a further DC voltage converter is required to process the power provided by the solar panel (2), activation of a further second DC voltage converter (13) is determined in step a).

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