BACKGROUND OF THE INVENTION

1. Field of the Invention

The prevent disclosure relates to power conversion for a renewable energy site. More particularly, the present disclosure relates to a hybrid power converter system that is configured to provide connections of three different power buses together. The power buses may include a power bus for a DC power source, a power bus for an AC load, and a power bus for an energy storage unit. Embodiments of the disclosure may also include a renewable energy site comprising the hybrid power converter system and a method of energy conversion at a renewable energy site.

2. Description of Related Art

By way of background, the following patents and patent applications are each hereby incorporated by reference in their entireties: Chinese Patent Application Nos. CN 102769302 and CN 103296695; Japanese Patent Application No. JP 2012075224; Korean Patent Application Nos. KR 20110014027, KR 20120110478, and KR 20130138611; Taiwanese Patent Application No. TW 201328101; U.S. Patent Application Nos. US 20090189445, US 20110095606, US 20110137481, US 20120013190, US 20120013192, US 20120313436, US 20130051105, US 20130234521, and US 20130328397; U.S. Pat. No. 7,411,308, U.S. Pat. No. 8,344,550, and U.S. Pat. No. 8,482,155; and PCT Application Nos. WO 2013004067 and WO 2007018830.

Renewable energy sources like solar power plants are subject to unpredictable power output due to changes in the environment in their vicinity. Chief among these are the movement of clouds which can rapidly cause their power output to fluctuate. As the percentage of power from such plants supplied to the public power grid increases the severity of the problem also increases. Recently, power utilities are demanding that new solar power plants be designed with features to prevent their output from changing faster than a specified rate.

There are two methods to meet these new requirements. The first and most common approach is to include some type of energy storage or generation capability within the scope of the power plant. These include battery systems or diesel generators which can supplement the power produced by the plant when cloud events occur such that the power output remains within the required specifications. While technically straightforward this approach severely affects the economic viability of the project due to the high cost of the storage element or resistance to application of diesel generators. The second and less common approach is to forecast weather in such a way that the output of the plant can be gradually changed in advance of when cloud cover would appear. The above methods can be applied independently or in combination in varying degrees.

Previous approaches of the power storage method have required some form of power conversion. Power conversion allows power flow from power sources and loads which have much different characteristics. In particular, voltage and frequency often do not match between a power source and a power load. In addition, different loads may have different characteristics. In systems with three power buses, typically two power converters must be applied to connect the three buses- one converter to convert power between the renewable source and the AC grid and a second converter between the AC grid and the energy storage element, often a battery bank. One problem with this approach is that it requires two converters and the infrastructure to connect them to the AC grid. This effectively doubles the cost of the converter hardware. Thus, there is a need in the art for improved systems and methods for power conversion at renewable energy sites.

SUMMARY OF THE INVENTION

The present disclosure provides a hybrid power converter system that provides a practical means to allow power conversion among three power buses each of which have different characteristics. The topology of the system has the advantage of providing a single power converter capable of causing power to flow among the three different power buses. The present disclosure has particular application for renewable energy power plants where systems often incorporate energy storage elements.

Included in embodiments is a hybrid power converter for connecting at least three power buses, the hybrid power converter comprising:

a power bridge capable of producing AC power from a DC bus supplied by a renewable power source;

an energy storage element;

a switch for isolating the power bridge from an AC power bus;

a switch for isolating the power bridge from the energy storage element;

a controller for sequencing the switches according to the amount of power available from the renewable resource.

Such embodiments can also incorporate more than one power bridge operating in parallel.

Another embodiment of the present disclosure is a hybrid power converter system for connecting at least three different power buses, the system comprising a power converter or power bridge capable of producing AC power from a DC bus supplied by a renewable power source, an energy storage element, a switch for isolating the power converter from the AC power bus, a switch for isolating the power converter from the power storage element, and optionally a controller for sequencing the switches according to the amount of power available from the renewable resource. The power converter system may further comprise more than one power converter operating in parallel.

Another embodiment of the present disclosure is a hybrid power converter system for connecting at least three different power buses, comprising a first, second, and third power bus. The first power bus may be connected to a DC power source, the second power bus may be connected to an AC load, and the third power bus may be connected to an energy storage element. The hybrid power converter system may further comprise a first power converter connected to the first power bus and capable of connection with the second and third power buses and capable of producing AC power from the DC power supplied by the first power bus, a first switch capable of connecting or disconnecting the first power converter to or from the second power bus, a second switch capable of connecting or disconnecting the first power converter to or from the third power bus, and optionally a controller operable for sequencing the first and second switches according to the amount of power available from the DC power source.

Further, any embodiment of the system of this disclosure may comprise a plurality of power converters operating in parallel. One embodiment may comprise a second power converter connected to the first power bus in parallel with the first power converter, the second power converter having the same or different capabilities as the first power converter and being connected to a third switch capable of connecting or disconnecting the second power converter to or from the second power bus and a fourth switch capable of connecting or disconnecting the second power converter to or from the third power bus. Another embodiment may comprise a third power converter connected to the first power bus in parallel with the first and second power converter, the third power converter having the same or different capabilities as the first and/or second power converters and being connected to a fifth switch capable of connecting or disconnecting the third power converter to or from the second power bus and a sixth switch capable of connecting or disconnecting the third power converter to or from the third power bus. Another embodiment may comprise a fourth power converter connected to the first power bus in parallel with the first, second, and third power converters, the fourth power converter having the same or different capabilities as the first, second, and/or third power converters and being connected to a seventh switch capable of connecting or disconnecting the fourth power converter to or from the second power bus and an eighth switch capable of connecting or disconnecting the fourth power converter to or from the third power bus. Another embodiment may comprise one or more additional power converters connected to the first power bus in parallel with the first, second, third, and/or fourth power converters, each additional power converter capable of connection with the second and third power buses and capable of producing AC power from the DC power supplied by the first power bus, and each additional power converter being connected to an additional pair of switches capable of connecting or disconnecting the additional power converter with the second and third power buses. Generally, in embodiments, when one switch to a power converter is open the other switch is closed, such that power only flows through either the second or third power bus from that power converter. Further, in any of the embodiments provided by this disclosure, the controller may be operable to sequence one or more or all of the switches according to the amount of power available from the DC power source.

In any embodiment of this disclosure, the DC power source may comprise one or more photovoltaic modules at a solar energy site or one or more turbines at a wind or tidal energy site. Likewise, in any embodiment of this disclosure, one or more or each power converter may comprise an inverter.

An additional embodiment of this disclosure includes a renewable energy site comprising a hybrid power converter of this disclosure.

An additional embodiment of this disclosure includes a method of energy conversion at a renewable energy site, comprising sequencing the first and second switches of the hybrid power converter system of this disclosure according to the amount of power available from the DC power source such that when the power available from the DC power source is reduced, the first switch is activated to disconnect the first power converter from the second power bus and the second switch is activated to connect the first power converter to the third power bus, wherein the sequencing is performed by a computer processor.

In an embodiment, the hybrid power converter system further comprises one or more additional converters connected to the first power bus in parallel with the first converter wherein each additional converter has an additional pair of switches capable of connecting or disconnecting the additional converter with the second and third power buses, wherein the method further comprises sequencing the additional pair of switches according to the amount of power available from the DC power source.

Specific embodiments of this disclosure include Aspect 1, which is a hybrid power converter system comprising:

a DC power source, such as one or more photovoltaic (PV) module;

a DC bus;

a three phase power converter for converting DC power to AC power, wherein the power converter is operably connected with a first power bus comprising the DC power source and the DC bus;

wherein the power converter is operably connected by a first switch S1 with a second power bus comprising a transformer, and is operably connected by a second switch S2 with a third power bus comprising an energy storage device, provided that, during use, no more than one of switch S1 or S2 is open;

such that, during use, when switch S1 is open and switch S2 is closed, power is capable of being delivered from the DC power source to the transformer, and when switch S2 is open and switch S1 is closed, power is capable of being delivered from the DC power source to the energy storage device.

Aspect 2 comprises the system of Aspect 1, wherein the DC power source is a device for converting a renewable energy source into DC power.

Aspect 3 comprises the system of Aspect 1 or 2, wherein the device for converting a renewable energy source into DC power is one or more PV modules.

Aspect 4 comprises the system of any of Aspects 1-3, wherein the device for converting a renewable energy source into DC power is a photovoltaic (PV) array of photovoltaic modules.

Aspect 5 comprises the system of any of Aspects 1-4, wherein the PV array comprises PV modules connected in series and parallel relative to one another.

Aspect 6 is the system of any of aspects 1-5, further comprising a controller operably configured for sequencing switches S1 and S2 during use according to an amount of power available from the DC power source.

Aspect 7 is a hybrid power converter system comprising:

a first power bus comprising one or more photovoltaic modules operably connected with a DC bus;

a first and a second three phase power converter, each configured for converting DC power to AC power, and operably connected in parallel with the first power bus;

a second power bus with one or more transformer and operably connected to the first and second three phase power converters, each by a switch;

a third power bus with one or more energy storage device and operably connected to the first and second three phase power converters, each by a switch;

provided that, during use, no more than one switch between the first power converter and the second or third power bus is open, and no more than one switch between the second power converter and the second or third power bus is open;

such that, during use, when a switch between the second power bus and the first or second power converters is open, power can be delivered from the photovoltaic modules through the second power bus to an AC load, and when a switch between the third power bus and the first or second power converters is open, power is capable of being delivered from the energy storage device through the third power bus to an AC load to supplement or replace power from the photovoltaic modules.

Aspect 8 is the system of Aspect 7, wherein the one or more photovoltaic modules comprises a photovoltaic (PV) array comprising a plurality of PV modules connected in series and in parallel relative to one another.

Aspect 9 is the system of Aspect 7 or 8, further comprising a controller operably configured for sequencing the switches during use according to an amount of power available from the photovoltaic modules.

Aspect 10 is the system of any of Aspects 7-9, further comprising:

one or more additional power converters operably connected to the first power bus in parallel with the first and second power converters;

wherein each of the one or more additional power converters is operably connected to the second power bus by a switch and to the third power bus by a switch;

provided that, during use, no more than one (meaning only one or none) switch between the additional power converter and the second or third power bus is open, and no more than one (meaning only one or none) switch between the additional power converter and the second or third power bus is open;

wherein during use, power is capable of being delivered to an AC load:

from the photovoltaic modules through the second power bus and any one or more of the first, second, or additional power converters when a switch between the first, second, or additional power converter and the transformer is open; and/or

from the energy storage device through the third power bus and any one or more of the first, second, or additional power converters when a switch between the first, second, or additional power converter and the energy storage device is open.

Aspect 11 is the system of any of Aspects 7-10, further comprising a controller operably configured for sequencing the switches during use according to an amount of power available from the photovoltaic modules.

Aspect 12 is the system of any of Aspects 7-11 comprising:

a first and a second three phase power converter and two additional power converters for a total of four power converters;

wherein each of the four power converters is operably connected to the first power bus in parallel with one another;

wherein the power converters each have an identical rated power (PU);

such that, during use, the system is capable of a minimum AC output, a maximum AC output, and an energy storage power as follows:

a) with the switch of each power converter open to the second power bus and no switch open between any of the power converters and the third power bus, the system is capable of a minimum AC output of 0 PU, a maximum AC output of 4 PU, and an energy storage power of 0 PU;

b) with the switch of three power converters open to the second power bus and the switch of one power converter open to the third power bus, the system is capable of a minimum AC output of 1 PU, a maximum AC output of 3 PU, and an energy storage power of +/âˆ’1 PU;

c) with the switch of two power converters open to the second power bus and the switch of two power converters open to the third power bus, the system is capable of a minimum AC output of 2 PU, a maximum AC output of 2 PU, and an energy storage power of +/âˆ’2 PU;

d) with the switch of one power converter open to the second power bus and the switch of three power converters open to the third power bus, the system is capable of a minimum AC output of 1 PU, a maximum AC output of 1 PU, and an energy storage power of âˆ’3 PU to +1 PU;

e) with no switch open between any of the power converters and the second power bus and the switch of each power converter open to the third power bus, the system is capable of a minimum AC output of 0 PU, a maximum AC output of 0 PU, and an energy storage power of âˆ’4 PU to 0 PU.

Aspect 13 is the system of any of Aspects 7-12, further comprising a controller operably configured for sequencing the switches during use according to an amount of power available from the photovoltaic modules.

Aspect 14 is the system of any of Aspects 1-13, wherein the DC power source comprises one or more photovoltaic modules at a solar energy site, one or more turbines at a wind energy site, or one or more turbines at a tidal energy site.

Aspect 15 is a method of managing energy provided from a power source, such as a DC power source, to an AC load comprising:

monitoring an amount of power available from a DC power source connected with a first power bus to identify change or potential change in power output;

in response to identifying a reduced amount of power from the DC power source, closing a switch between a power converter, which power converter is connected with the first power bus, and a second power bus comprising a transformer; and opening a switch between that power converter and a third power bus comprising one or more energy storage devices; and

allowing power to flow to an AC load from the energy storage devices.

Aspect 16 is the method of Aspect 15, wherein the first power bus is part of a hybrid power converter system further comprising:

a DC power source;

a DC bus;

a three phase power converter for converting DC power to AC power;

wherein the power converter is operably connected with the first power bus which comprises the DC power source and the DC bus;

wherein the power converter is operably connected by a first switch S1 with a second power bus comprising a transformer, and is operably connected by a second switch S2 with a third power bus comprising an energy storage device, provided that, during use, no more than one of switch S1 or S2 is open;

such that, during use, when switch S1 is open and switch S2 is closed, power is capable of being delivered from the DC power source to the transformer, and when switch S2 is open and switch S1 is closed, power is capable of being delivered from the DC power source to the energy storage device.

Aspect 17 is the method of Aspect 15 or 16, wherein the first power bus comprises one or more photovoltaic modules operably connected with a DC bus, and wherein the first power bus is part of a hybrid power converter system further comprising:

a first and a second three phase power converter, each configured for converting DC power to AC power, and operably connected in parallel with the first power bus;

a second power bus comprising one or more transformer and operably connected to the first and second three phase power converters, each by a switch;

a third power bus with one or more energy storage device and operably connected to the first and second three phase power converters, each by a switch;

provided that, during use, no more than one switch between the first power converter and the second or third power bus is open, and no more than one switch between the second power converter and the second or third power bus is open;

such that, during use, when a switch between the second power bus and the first or second power converters is open, power is capable of being delivered from the photovoltaic modules through the second power bus to an AC load, and when a switch between the third power bus and the first or second power converters is open, power is capable of being delivered from the energy storage device through the third power bus to an AC load to supplement or replace power from the PVmodules.

Aspect 18 is the method of any of Aspects 15-17, wherein the hybrid power converter system further comprises: