TITLE A power conversion circuitry for multiple power sources

TECHNICAL FIELD

The invention relates to a power conversion circuitry for multiple power sources such as photovoltaic power sources and batteries, and which is able to transfer power between the multiple power sources in different modes such as a buck-, boost- and/or buck- boost-converter mode.

BACKGROUND

A power converter either converts electrical energy from one form to another such as between AC (Alternating Current) and DC (Direct Current) or changes the frequency and/or voltage. Different power conversion circuitries are known in the art for changing the voltage of a power source: a buck converter or step-down converter is a DC to DC converter and steps down the a higher input voltage of a power source into a lower output voltage; a boost converter or step-up converter is a DC to DC converter and steps up a lower input voltage of a power source into a higher output voltage; and a buck-boost converter combines a buck- and a boost-converter and i able to either step-down or step-up an input voltage of a power source into a lower or higher output voltage, respectively. SUMMARY OF INVENTION

It is an object of the present invention to propose a versatile power conversion circuitry, which is suitable for different power sources such as photovoltaic power sources and batteries, and which is able to transfer power between the multiple power sources. This object is achieved by the subject matter of the independent claims. Further embodiments are shown by the dependent claims.

The present invention is based on the idea to provide a power conversion circuitry, which has terminals for connecting to a photovoltaic power source, a battery and a DC link, and which can be operated in different modes such as a buck-, boost- and/or buck- boost-converter mode, thus allowing to charging the battery from a photovoltaic power source connected to the respective terminals or a power supply connected to the DC link terminals, to discharge the battery over the DC link terminals, and to power the DC link terminals directly from a photovoltaic power source connected to the respective terminals. The inventive power conversion circuitry is designed to be operated as a buck-, boost- or buck-boost-converter using only one inductor, which allows to adapt the power conversion circuitry for a large band of input voltages. Thus, photovoltaic panels with different voltage ranges can be used with the inventive power conversion circuitry to either charge a battery or directly supply a DC link. For example, the power conversion circuitry can be designed to be used with photovoltaic panels generating voltages up to 1000 Volts. The inventive power conversion circuitry can be integrated in an uninterruptible power supply (UPS) unit, or it can be designed a modular unit, which can be operated independently from the UPS unit.

An embodiment of the invention relates to a power conversion circuitry for multiple power sources comprising first positive and negative terminals for connecting to a photovoltaic power source, second positive and negative terminals for connecting to a battery, third positive and negative terminals for connecting to a DC line, wherein the third negative terminal is connected to the first negative terminal, a first series connection of a first switch, an inductor and a second switch, wherein the first series connection is connected between the first positive terminal and the third positive terminal and a first diode is connected between the terminals of the second switch with the cathode of the first diode being connected to the third positive terminal, a second series connection of a third switch and a second diode, wherein one terminal of the third switch is connected to the second positive terminal and the other terminal is connected with the cathode of the second diode and the anode of the second diode is connected to the connection of the inductor and the second switch, a fourth switch connected between the third negative terminal and the connection of the inductor and the second switch, a third diode, wherein the anode of the third diode is connected to the third negative terminal and the first negative terminal and the cathode of the third diode is connected to the connection of the inductor and the first switch, and a controllable semiconductor switch, wherein a first terminal of the controllable semiconductor switch is connected to the second positive terminal and a second terminal of the controllable semiconductor switch is connected to the connection of the inductor and the first switch

The circuitry can be operated in different modes by controlling the switches and the controllable semiconductor switch:

In a photovoltaic to battery boost mode the controllable semiconductor switch is operated in a non-conductive state and the first switch is closed and the second switch is open, and over the time the third switch and the fourth switch are alternatively closed and opened.

In a photovoltaic to battery buck mode the controllable semiconductor switch is operated in a non-conductive state and the third switch is closed and the second switch and the fourth switch are open, and over the time the first switch is alternatively closed and opened.

In a photovoltaic to DC link boost mode the controllable semiconductor switch is operated in a non-conductive state and the first switch is closed and the second switch and the third switch are open, and over the time the fourth switch is alternatively closed and opened.

In a photovoltaic to DC link buck mode the controllable semiconductor switch is operated in a non-conductive state and the second switch, the third switch and the fourth switch are open, and over the time the first switch is alternatively closed and opened.

In a battery to DC link boost mode the controllable semiconductor switch is operated in a conductive state and the first switch, the second switch and the third switch are open, and over the time the fourth switch is alternatively closed and opened.

The controllable semiconductor switch can be a thyristor, with the anode of the thyristor being the first terminal of the controllable semiconductor switch and the cathode of the thyristor being the second terminal of the controllable semiconductor switch.

A further embodiment of the invention relates to an UPS system comprising an UPS unit having terminals for connecting with a power supply from an electric grid, an electric load, a battery, and DC link terminals, a photovoltaic power source, a battery, a power conversion circuitry according to the invention and as described herein, wherein the photovoltaic power source is connected to the first positive and negative terminals of the power conversion circuitry, the battery is connected to the respective terminals of the UPS unit and the second positive and negative terminals of the power conversion circuitry, and the third positive and negative terminals of the power conversion circuitry are connected to the DC link terminals of the UPS unit.

In the UPS system, the power conversion circuitry can be operated in a photovoltaic to battery boost mode if the voltage of the photovoltaic power source is lower than the voltage of the battery, and in a photovoltaic to battery buck mode if the voltage of the photovoltaic power source is higher than the voltage of the battery.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. The invention will be described in more detail hereinafter with reference to exemplary embodiments. However, the invention is not limited to these exemplary embodiments.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 shows a schematic of an embodiment of a power conversion circuitry for multiple power sources according to the invention;

Fig. 2 shows the operation of the circuitry of Fig. 1 in a photovoltaic to battery boost mode;

Fig. 3 shows the operation of the circuitry of Fig. 1 in a photovoltaic to battery buck mode; Fig. 4 shows the operation of the circuitry of Fig. 1 in a photovoltaic to DC link boost mode;

Fig. 5 shows the operation of the circuitry of Fig. 1 in a photovoltaic to DC link buck mode;

Fig. 6 shows the operation of the circuitry of Fig. 1 in a battery to DC link boost mode; and

Fig. 7 shows a block diagram of an embodiment of an UPS system according to the invention.

DESCRIPTION OF EMBODIMENTS

In the following, functionally similar or identical elements may have the same reference numerals. Absolute values are shown below by way of example only and should not be construed as limiting the invention.

Fig. 1 shows a power conversion circuitry 10 for two power sources, namely a photovoltaic panel 12 and a battery 14). The circuitry 10 is provided to either charge the battery 14 from the photovoltaic panel 12 or to directly supply DC voltage from the photovoltaic panel 12 to a DC link. The circuitry 10 is further designed to be operated with different photovoltaic panels 12 generating voltages up to 1000 Volts. As shown in Fig. 1, the circuitry 10 comprises first positive and negative terminals PV+, PV- for connecting to the photovoltaic panel 12, second positive and negative terminals BAT+, BAT- for connecting to the battery 14, third positive and negative terminals DC+, DC- for connecting to a DC line (the above mentioned DC link).

The circuitry 10 uses enhancement mode MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) 16, 20, 22, 26 as electronic switches. Each MOSFETs comprises a diode 17, 21, 23, 27 being switched between the gate and drain of the respective MOSFET. Furthermore, the circuitry 10 comprises a thyristor 30, a first diode 21, a second diode 24, a third diode 28, a single inductor 18, and two capacitors 32, 34.

The third negative terminal DC- is connected to the first negative terminal PV-. A first series connection of a first MOSFET 16, the single inductor 18 and a second MOSFET 20 is connected between the first positive terminal PV+ and the third positive terminal DC+ and the first diode 21 is connected between the drain and source of the second MOSFET 20 with the cathode of the first diode 21 being connected to the third positive terminal DC+. The circuitry 10 comprises a second series connection of a third MOSFET 22 and the second diode 24. One terminal of the third MOSFET 22 is connected to the second positive terminal BAT+ and the other terminal is connected with the cathode of the second diode 24 and the anode of the second diode 24 is connected to the connection of the inductor 18 and the second MOSFET 20. A fourth MOSFET 26 is connected between the third negative terminal DC- and the connection of the inductor 18 and the second MOSFET 20. The anode of the third diode 28 is connected to the third negative terminal DC- and the first negative terminal PV- and the cathode of the third diode 28 is connected to the connection of the inductor 18 and the first switch 16.

The anode of the thyristor 30 is connected to the second positive terminal BAT+ and the cathode of the thyristor 30 is connected to the connection of the inductor 18 and the first MOSFET 16.

A series connection of the two capacitors 32, 34 is switched between the third positive and negative terminals DC+, DC- with the connection of the two capacitors 32, 34 is connected to a predefined reference potential such as ground.

Operation of the circuitry 10 will now be explained with reference to Figs. 2 to 6 showing different operating modes. The operating modes are configured by controlling the switches and the thyristor in order to switch electric paths for switching the circuitry in a buck-, boost- and/or buck-boost-mode. The switched electric paths are marked with thick lines in Figs. 2 to 6. In each of Figs. 2 to 6, the above schematic shows the circuitry in a first state of the selected operating mode, while the schematic below shows the circuitry in a second state of the selected operating mode:

Fig. 2 shows operation of the circuitry 10 in a photovoltaic to battery boost mode, in which the thyristor 30 is operated in a non-conductive state and the first MOSFET 16 is closed and the second MOSFET 20 is open, and over the time the third MOSFET 22 and the fourth MOSFET 26 are alternatively closed and opened. Thus, the battery 14 can be charged with a photovoltaic panel 12 generating a voltage, which would be too low for charging. By operating the circuitry 10 in the boost mode, the voltage generated by the panel 12 is stepped-up to the voltage required for charging.

Fig. 3 shows operation of the circuitry 10 in a photovoltaic to battery buck mode, in which the thyristor 30 is operated in a non-conductive state and the third MOSFET 22 is closed and the second MOSFET 20 and the fourth MOSFET 26 are open, and over the time the first MOSFET 16 is alternatively closed and opened. Thus, the battery 14 can be charged with a photovoltaic panel 12 generating a voltage, which would be too high for charging. By operating the circuitry 10 in the buck mode, the voltage generated by the panel 12 is stepped-down to the voltage required for charging.

Fig. 4 shows operation of the circuitry 10 in a photovoltaic to DC link boost mode, in which the thyristor 30 is operated in a non-conductive state and the first MOSFET 16 is closed and the second MOSFET 20 and the third MOSFET 22 are open, and over the time the fourth MOSFET 26 is alternatively closed and opened. Thus, the DC link connected with the third positive and negative terminals DC+, DC- 14 can be supplied with voltage generated by a photovoltaic panel 12, which is lower than the required DC link supply voltage. By operating the circuitry 10 in the boost mode, the voltage generated by the panel 12 is stepped-up to the voltage required for DC link supply voltage.

Fig. 5 shows operation of the circuitry 10 in a photovoltaic to DC link buck mode, in which the thyristor 30 is operated in a non-conductive state and the second MOSFET 20, the third MOSFET 22 and the fourth MOSFET 26 are open, and over the time the first MOSFET 16 is alternatively closed and opened. Thus, the DC link connected with the third positive and negative terminals DC+, DC- 14 can be supplied with voltage generated by a photovoltaic panel 12, which is higher than the required DC link supply voltage. By operating the circuitry 10 in the buck mode, the voltage generated by the panel 12 is stepped-down to the voltage required for DC link supply voltage.

Fig. 6 shows operation of the circuitry 10 in a battery to DC link boost mode, in which the thyristor 30 is operated in a conductive state and the first MOSFET 16, the second MOSFET 20 and the third MOSFET 22 are open, and over the time the fourth MOSFET 26 is alternatively closed and opened. Thus, the DC link connected with the third positive and negative terminals DC+, DC- 14 can be supplied with voltage from the battery 14, which is stepped-up to the voltage required for DC link supply voltage. Fig. 7 shows a block diagram of an UPS system 50 employing the power conversion circuitry 10. The system 50 comprises an UPS unit 52, the power conversion circuitry 10, and a photovoltaic panel 12 and a battery 14 both connected to the respective terminals of the circuitry 10. The terminals of the battery 14 are also connected to respective terminals of the UPS unit 52, and the third positive and negative terminals DC+, DC- of the circuitry 10 are connected to DC link terminals 58 of the UPS unit 52. The UPS unit 52 is also connected with respective terminals to a power supply from an electric grid 54 and to an electric load 56, for example an IT load. The circuitry 10 can be embodied as separate external module, which can be connected to the UPS unit 52, or it can be also integrated in the electronics of the UPS unit 52.

As shown in Fig. 7, the UPS unit 52 employs a first and a second AC-DC-converter 66, 68 and a DC-AC-converter 70. Over the first AC-DC-converter 66, the battery 14 connected to the respective terminals of the UPS unit 52 can be charged from the power supply from the electric grid 54. The second AC-DC-converter 68 converts the electric power from the electric grid 54 into an internal DC voltage of the UPS unit 52, for example 800 Volts. The DC-AC-converter 70 finally converts electric power from the electric grid 54, the battery 14, and from the photovoltaic panel 12 into an AC voltage required for the electric load 56. With the circuitry 10, the UPS system 50 can be operated in an online mode 60, a photovoltaic mode 62, and a battery mode 64.

In the online mode 60, the battery is charged with electric power from the electric grid 54 and the electric load 56 is supplied with electric power from the electric grid 54.

In the photovoltaic mode 62, the photovoltaic panel 12 supplies electric power for charging the battery 14 via the circuitry 10 and directly to the electric load 56 via the DC-AC converter 70, while the circuitry 10 is operated in a boost-, buck- or buck-boost- mode for adapting the voltage generated by the photovoltaic panel 12 to the requirements for charging the battery 14 and directly supplying the electric load 56.

In the battery mode 64, the battery 14 supplies electric power via the second AC-DC- converter 68 and the DC-AC-converter 70 and/or the circuitry 10 and the DC-AC - converter 70 to the electric load 56 depending on the available battery output voltage.