AU2022100152A4 - An inverter for an energy capture and storage system - Google Patents

Abstract

AUDIV ABSTRACT An inverter for use in an energy capture and storage system includes a DC power input configured to receive DC input power from at least one on-site power source. The inverter further includes a common internal DC-bus. At least one variable output inverter stage is coupled to the internal DC-bus, and having a variable AC output configured to supply an AC output power, at a time-averaged voltage that is variable between minimum and maximum levels. At least one grid-tie inverter stage is coupled to the internal DC-bus, and having a grid AC output configured to supply an AC output power to an AC grid. The inverter further includes one or more controllers configured to individually control the at least one variable output inverter stage and the at least one grid-tie inverter stage. 12 CNN N CL 00 Qo toc CD0 GO O 0 c Y-I C Ys-I i >O(D Y1/3

Description

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AN INVERTER FOR AN ENERGY CAPTURE AND STORAGE SYSTEM TECHNICAL FIELD

[0001] The present disclosure relates to an inverter for an energy capture and storage system, more

particularly a system utilising solar energy.

BACKGROUND

[0002] Solar energy is an important source of renewable, clean energy. Increasingly, solar energy systems

are being used to harness the sun's energy for everyday needs. The focus of these systems has

traditionally been for either direct use (e.g. heating domestic hot water), or storage in the form of

electrical charge within battery systems. However, inefficiencies exist within such use cases due to

available technology.

[0003] For example, a hot water cylinder connected to a solar photovoltaic ("PV") system traditionally

draws a power at a fixed rate from both the solar PV system and the mains electricity grid ("the grid")

until it is up to temperature, regardless of the power generated by the solar PV system at the time. By

way of example, a 3 kW rated cylinder will need to draw a total of 3 kW of power to heat the water. If the

solar PV system is not producing 3 kW, the balance of power required will be drawn from the grid. Because

the times of greatest demand on hot water use typically do not align with sunlight intensity, over a 24

hour period there may be a disproportionate amount of power generated by the solar PV system versus that utilized for heating water.

[0004] Australian Innovation Patent No. 2013100349 describes a system developed to address this issue,

having an inverter delivering a variable output voltage ("VOV"). This VOV output maximises the power

available from the solar PV system to be utilised by an electric element, such as that of a hot water

cylinder, where that amount of power would have been otherwise insufficient to power the element if

held at the nominal voltage relevant to that locality.

[0005] A consequence of this is that the VOV output from the inverter is unlikely to be equal to the

nominal voltage of the electricity network to which the premises connects to. As such, other appliances

connected to the network at those premises require another source of electricity of a more stable voltage

- i.e. other than the VOV output. Further, the power generating capabilities of the solar PV arrays are

effectively lost once the heating element reaches temperature. However, enabling the solar PV system to

service more than an electric heating element would require a second inverter, such as a standard grid

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tie inverter, which would be "switched" onto the solar PV array, and the VOV inverter "switched" out from

the solar PV array. This is cumbersome, requiring switches which are capable of switching solar PV arrays

strung at high DC voltages (e.g. in the order of 600-1000+ V). These switches are relatively expensive, at

the same time necessitating commensurate control systems to ensure correct operation (for example, to

ensure that they are not switched "on load" when switching the solar PV array between the VOV output inverter and the more generic grid-tied inverter).

[0006] Aspects of the technology of the present disclosure are directed to overcoming one or more of

the problems discussed above. It is an object of the present invention to address one or more of the

foregoing problems or at least to provide the public with a useful choice.

[0007] Further aspects and advantages of the present disclosure will become apparent from the ensuing

description which is given by way of example only.

SUMMARY

[0008] According to one aspect of the present technology there is provided an inverter for use

in an energy capture and storage system, the inverter comprising:

a DC power input configured to receive DC input power from at least one on-site power source;

a common internal DC-bus;

at least one variable output inverter stage coupled to the internal DC-bus, and having a variable AC output configured to supply an AC output power, at a time-averaged voltage that is variable between

minimum and maximum levels;

at least one grid-tie inverter stage coupled to the internal DC-bus, and having a grid AC output

configured to supply an AC output power to an AC grid;

one or more controllers configured to individually control the at least one variable output

inverter stage and the at least one grid-tie inverter stage.

[0009] According to one aspect of the present technology there is provided an energy capture and

storage system comprising:

at least one on-site power source; and

an inverter substantially as herein described, wherein the DC power input is electrically coupled

to the on-site power source.

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[0010] In examples the on-site power source may include one or more photovoltaic modules. However,

it is envisaged that the on-site power source may generate power using alternative energy sources, for

example one or more of: wind, hydro, geothermal, or biomass. In examples, the on-site power source may

include one or more energy storage devices - for example, batteries.

[0011] In examples, the energy capture and storage system includes one or more heating elements electrically coupled directly or indirectly to the variable AC output of the inverter. In examples the one or

more heating elements are used to heat a working medium stored in a vessel. In examples the one or

more heating elements are those of a hot water cylinder.

[0012] The common internal DC-bus provides an independently, or separately, regulated common

energy bus for behind the meter (BTM) energy transactions. Typically, Distributed Energy Resources (DER)

connect to the mains electricity grid, and are thereby subject to grid constraints. The common internal

DC-bus enables separate definition of grid connection limitations, independent of the DER capacities. This

is also envisaged as potentially reducing the fault level contribution to the grid, unlike traditional export

limiting methods.

[0013] It should be appreciated that reference to a time-averaged voltage that is variable between

minimum and maximum levels, as described herein, refers to a measure of the overall voltage level of the

AC signal, rather than the inherent regular wave-like fluctuations of AC. For example, the variable AC

voltage level may be measured by a time-averaged value such as root mean square or any other suitable measure. The amplitude of the AC voltage may also be varied, which will consequently vary the time

averaged value of the voltage. In examples, the outputted AC voltage level is variable to adjust the power

outputted by the inverter to the heating elements, so that it substantially matches the maximum amount

of power available from the photovoltaic modules. In embodiments of the present technology, varying

the outputted AC voltage level from the inverter allows the maximum power to be applied to heating

elements with fixed resistances.

[0014] In examples, the minimum level of AC root mean square voltage outputted by the inverter is 0

V. In examples the maximum level of AC root mean square voltage outputted by the inverter is the

nominal mains voltage, for example, 230 Vac. More preferably, where the heating elements have a higher

voltage rating than the nominal mains voltage, the maximum level of AC root mean square voltage

outputted by the inverter is able to match the higher voltage rating of the heating elements

[0015] In examples the variable AC output may be provided according to one or more modes in which

one or more other characteristics of the output may be varied. For example, the frequency and/or waveshape of the output may be varied according to a desired use case, such as to suit a specific appliance

or application (e.g. allowing for a boost power mode).

[0016] In examples, the inverter may include more than one variable output inverter stage. For

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example, the inverter may include a first variable output inverter stage having an output dedicated to

supplying power to a heating element, and a second variable output inverter stage having an output for

an alternative purpose.

[0017] Reference to an AC grid should be understood to mean a mains power grid operated by a power

utility company.

[0018] In examples, one or more of the inverter stages may provide a single phase output. In examples,

one or more of the inverter stages may provide a polyphase output.

[0019] In examples, at least two of the inverter stages may be the same phase. In examples, at least

two of the inverter stages may be phase separated - i.e. operate in a different phase. For example, one

inverter stage may have a 180 degree mode of conduction, and another inverter stage may have a 120

degree mode of conduction. It should be appreciated that these examples are not intended to be limiting.

In particular, it should be appreciated that the phase separation need not be dictated by constraints of

the mains grid. In examples, the at least one controller is configured to select which phase to connect,

and determine the phase angle. Traditional multiphase electricity networks have fixed phase angles

between phases, resulting in the limitation on how many phases are available to connections to the

networks. The inverter of the present technology is not limited by these constraints, being able to choose

multiple phases or poles depending on the number of stages configured within the inverter. The phase

angle between these multiple phases or poles is able to be set by the controller, which is not viable in traditional power system design. This allows a premises to have distribution within the premises which

not only has phases different to that on the networks, but potentially a different number of phases also.

[0020] In examples, the at least one grid-tie inverter stage may provide a split phase output configured

to connect to a split-phase grid. In an example, the split phase output may be configured to connect to a

Single Wire Earth Return (SWER) grid.

[0021] In examples, the inverter may include at least one separated internal site AC inverter stage

coupled to the internal DC-bus output, and having an internal site AC output configured to supply an AC

output power to an internal site AC grid. Reference to an internal site AC grid should be understood to

mean a user-side grid distributed independently from that connected to the mains electricity grid, with

designated loads determined by the user.

[0022] Reference to the one or more controllers being configured to individually control the at least

one variable output inverter stage and the at least one grid-tie inverter stage should be understood to

mean that one or more characteristics of each output may be controlled independently of the other(s). For completeness, this is not intended to exclude embodiments in which control of one stage is influenced

by one or more characteristics of the other. For example, two or more stages may be phase-locked

whether that be by a dynamically varying gain factor or an essentially fixed gain factor. It should be

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appreciated that the one or more controllers may be embodied in a single device controlling multiple

stages, dedicated devices for each stage, or multiple devices functioning in combination to control each

stage.

[0023] The above and other features will become apparent from the following description and the

attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further aspects of the present disclosure will become apparent from the following description

which is given by way of example only and with reference to the accompanying drawings in which:

[0025] FIG. 1 is a block schematic diagram of an exemplary architecture for an inverter for use in an

energy capture and storage system according to one aspect of the present technology.

[0026] FIG. 2 is a block schematic diagram of another exemplary architecture for an inverter for use in an

energy capture and storage system according to one aspect of the present technology.

[0027] FIG. 3 is a block schematic diagram of a further exemplary architecture for an inverter in use within

an energy capture and storage system according to one aspect of the present technology.

DETAILED DESCRIPTION

[0028] FIG. 1illustrates an exemplary architecture for an inverter 100 for use in an energy capture and storage system according to one aspect of the present technology. The inverter 100 includes a first DC

power input 102a configured to receive DC input power from at least one photovoltaic ("PV") modules

using incident solar radiation to generate electrical energy in the form of direct current (DC). Reference

to PV modules herein is intended to refer to any component or group of components able to produce

electrical energy from solar energy. Many conventional PV modules have a cellular structure and are

therefore known as PV cells. PV modules may be arranged in an array and have a panel-like form.

However, the invention is not limited to any particular type, structure or arrangement of photovoltaic

devices. In the example illustrated, a second DC power input 102b is also provided - for example for

connection to DC batteries.

[0029] The inverter includes an input stage 104 including voltage and current sensors 106, input filters

108, and conditioning devices 110 (including high frequency switching and micro storage devices),

controlled by one or more controllers 112.

[0030] The input stage 104 connects to a common internal DC-bus 114. It will be appreciated that the

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nominal DC-bus voltage may be selected based on the DC power input and/or intended output from the

inverter 100, but in an example the nominal DC-bus voltage may be in the order of 380 VDC.

[0031] A plurality of inverter output stages 116 are connected to the common internal DC-bus 114, and

controlled by the controller(s) 112. Each output stage 116 includes high frequency output filtering 118,

and waveform sensing providing feedback to the controller(s) 112. In this example, a first inverter output 122a provides a variable AC output configured to supply an AC output power, at a time-averaged voltage

that is variable between minimum and maximum levels. For example, the first inverter output 122a may

be configured to supply power to one or more heating elements of a hot water cylinder, as described in

Australian Innovation Patent No. 2013100349, the entire contents of which are herein incorporated by

reference.

[0032] In this example, a second inverter output 122b is configured to supply an AC output power to an

AC grid - i.e. a traditional 230 VAC output. In examples, the first inverter output 122a and the second

inverter output 122b may be the same phase. For example, the output stage 116 of the first inverter

output 122a may be phase locked to that of the second inverter output 122b by a dynamically varying

gain factor.

[0033] In this configuration, the "grid rating" (i.e. the utility recognised connection capacity and fault

level contribution) is effectively defined solely by the second inverter output 122b. As a result, the internal

DC-bus 114 is able to accommodate resources, for example, solar PV arrays, in excess of the limits placed on grid connected inverters. The limits placed on the grid connected inverters are a result of network

considerations and constraints. Where premises require more electricity than this limit, the premises is

forced to import electricity. The ability to have larger arrays beyond what can be seen by grid tie inverters

allows premises to implement more solar PV power, better aligned to its needs rather than the networks

considerations.

[0034] The inverter architecture of FIG. 1 demonstrates that in the present technology, the switching of

the power from the DC power source between outputs is carried out internally within the inverter 100.

The high input voltages, for example from a PV module, are controlled by a single piece of equipment

rated for these voltages, avoiding the need for multiple external DC arc-quenching switches and control

systems. This allows the power generated by the PV modules to be utilised wherever the controller

selects, ensuring fuller utilisation of the solar energy captured towards multiple uses.

[0035] FIG. 2 illustrates another exemplary architecture for an inverter 100 for use in an energy capture

and storage system according to one aspect of the present technology. In this example, the architecture is similar to that described above with reference to FIG. 1, but having a third inverter output stage 116

providing a third inverter output 122c. The third inverter output 122c may be configured to provide

another variable output voltage power source, or a fixed nominal voltage (e.g. a grid-separated internal

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consumer supply). In this example, all three outputs 122 are the same phase, with the output stage 116

of the third inverter output 122a phase locked to that of the second inverter output 122b - e.g. by a

dynamically varying gain factor for a variable output voltage, or an essentially fixed gain for a grid

separated output voltage. Again, the grid rating of the inverter is effectively defined solely by the second

inverter output 122b.

[0036] The inverter architecture of FIG. 2 demonstrates the ability of the multiple outputs of the present

technology to meet requirements within the premises to address a fixed resistance load in addition to

grid connected loads, and loads which require reliability beyond that provided by the grid. Such fixed

resistance loads would typically place loads on inverters requiring grid support to maintain.

[0037] FIG. 3 illustrates an energy capture and storage system 200 including an inverter 100 utilising a

similar architecture to that described above with reference to FIG. 1 and FIG. 2. The energy capture and

storage system 200 includes PV modules 202a and optionally batteries 202b providing DC input to the

inverter 100. In this example, the first inverter output stage 116a provides a variable AC output to a

heating element of a hot water system 204 of the energy capture and storage system 200, independent

from the grid.

[0038] In this example, the second inverter output stage 116b and third inverter output stage 116c are

configured to function as a grid connect to a split-phase grid, more particularly transformer 206 of a Single

Wire Earth Return (SWER) substation of a SWER grid. The inverter output stages 116a-c can be phase separated by up to 180 degrees, with the first output stage 116a operating phase independently of the

second inverter output stage 116b and third output stage 116c, with a dynamically varying voltage gain

factor.

[0039] For a firmware and/or software (also known as a computer program) implementation, the

techniques of the present disclosure may be implemented as instructions (for example, procedures,

functions, and so on) that perform the functions described. It should be appreciated that the present

disclosure is not described with reference to any particular programming languages, and that a variety of

programming languages could be used to implement the present invention. The firmware and/or

software codes may be stored in a memory, or embodied in any other processor readable medium, and

executed by a processor or processors. The memory may be implemented within the processor or

external to the processor. A general purpose processor may be a microprocessor, but in the alternative,

the processor may be any processor, controller, microcontroller, or state machine. A processor may also

be implemented as a combination of computing devices, for example, a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in

conjunction with a DSP core, or any other such configuration. The processors may function in conjunction

with servers, whether cloud based or dedicated, and network connections as known in the art.

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[0040] The steps of a method, process, or algorithm described in connection with the present disclosure

may be embodied directly in hardware, in a software module executed by one or more processors, or in

a combination of the two. The various steps or acts in a method or process may be performed in the order

shown, or may be performed in another order. Additionally, one or more process or method steps may

be omitted or one or more process or method steps may be added to the methods and processes. An additional step, block, or action may be added in the beginning, end, or intervening existing elements of

the methods and processes.

[0041] The illustrated embodiments of the disclosure will be best understood by reference to the figures.

The foregoing description is intended only by way of example and simply illustrates certain selected

exemplary embodiments of the disclosure. It should be noted that the flowchart and block diagrams in

the figures illustrate the architecture, functionality, and operation of possible implementations of

systems, apparatuses, methods and computer program products according to various embodiments of

the disclosure. In this regard, each block in the flowchart or block diagrams may represent a module,

segment, or portion of code, which includes at least one executable instruction for implementing the

specified logical function(s). It should also be noted that, in some alternative implementations, the

functions noted in the block may occur out of the order noted in the figures. For example, two blocks

shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes

be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block

diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems

that perform the specified functions or acts, or combinations of special purpose hardware and computer

instructions.

[0042] The entire disclosures of all applications, patents and publications cited above and below, if any,

are herein incorporated by reference. Reference to any prior art in this specification is not, and should

not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the

common general knowledge in the field of endeavour in any country in the world.

[0043] The invention(s) of the present disclosure may also be said broadly to consist in the parts,

elements and features referred to or indicated in the specification of the application, individually or

collectively, in any or all combinations of two or more of said parts, elements or features. Where in the

foregoing description reference has been made to integers or components having known equivalents

thereof, those integers are herein incorporated as if individually set forth.

[0044] Furthermore, the described features, structures, or characteristics may be combined in any

suitable manner in at least one embodiment. In the foregoing description, numerous specific details are

provided to give a thorough understanding of the exemplary embodiments. One skilled in the relevant art

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may well recognize, however, that embodiments of the disclosure can be practiced without at least one

of the specific details thereof, or can be practiced with other methods, components, materials, et cetera.

In other instances, well-known structures, materials, or operations are not shown or described in detail

to avoid obscuring aspects of the invention.

[0045] Throughout this specification, the word "comprise" or "include", or variations thereof such as "comprises", "includes", "comprising" or "including" will be understood to imply the inclusion of a stated

element, integer or step, or group of elements integers or steps, but not the exclusion of any other

element, integer or step, or group of elements, integers or steps, that is to say, in the sense of "including,

but not limited to".

[0046] Aspects of the present disclosure have been described by way of example only and it should be

appreciated that modifications and additions may be made thereto without departing from the scope

thereof.

Claims (5)

315358AUDIV CLAIMS

1. An inverter for use in an energy capture and storage system, the inverter including:

a DC power input configured to receive DC input power from at least one on-site power source;

a common internal DC-bus;

at least one variable output inverter stage coupled to the internal DC-bus, and having a variable AC output configured to supply an AC output power, at a time-averaged voltage that is variable between

minimum and maximum levels;

at least one grid-tie inverter stage coupled to the internal DC-bus, and having a grid AC output

configured to supply an AC output power to an AC grid; and

one or more controllers configured to individually control the at least one variable output

inverter stage and the at least one grid-tie inverter stage.

2. The inverter of claim 1, wherein at least one of the following is true:

the variable AC output is provided according to one or more modes in which one or more other

characteristics of the output is varied;

the inverter includes more than one variable output inverter stage;

one or more of the inverter stages is configured to provide a single phase output;

one or more of the inverter stages is configured to provide a polyphase output;

at least two of the inverter stages are in the same phase;

at least two of the inverter stages are phase separated;

the at least one grid-tie inverter stage provides a split phase output configured to connect to a

split-phase grid; and

the inverter includes at least one separated internal site AC inverter stage coupled to the internal DC-bus output, and having an internal site AC output configured to supply an AC output power to an

internal site AC grid.

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3. An energy capture and storage system including:

at least one on-site power source; and

an inverter as claimed in claim 1 or claim 2, wherein the DC power input is electrically coupled to

the on-site power source.

4. The energy capture and storage system of claim 3, wherein the on-site power source includes one

or more photovoltaic modules.

5. The energy capture and storage system of claim 3 or claim 4, including one or more heating

elements electrically coupled directly or indirectly to the variable AC output of the inverter, wherein the

one or more heating elements are used to heat a working medium.