Patent Application
20240339836
The present application relates generally to electrical power systems, and in particular to prevention of reverse power flow from a grid-connected electrical circuit into an electrical utility grid.
Power flow control in systems that are connected to a utility grid and that include alternating current (AC) power sources typically involves grid-tie switches. These grid-tie switches are used to prevent power from flowing into the utility grid when the grid has failed or AC power is otherwise not available from the grid. This type of power flow prevention is also known as anti-islanding. Grid-tie switches prevent power from flowing from the AC sources into the grid and creating an “island” of the grid that is powered by the AC sources. This powered island of the utility grid is potentially dangerous to service personnel who expect the grid to be un-powered, for example.
Although grid-tie switches can provide some level of protection from AC sources powering a utility grid or parts of such a grid, improved approaches to reverse power flow prevention are desirable.
The present disclosure encompasses reverse power flow prevention that differs from grid-tie switch approaches in that reverse power flow can be prevented even if a utility grid has not failed and is still capable of supplying at least some power to connected electrical systems. Power can be prevented from flowing from a grid-connected electrical circuit, which includes one or more electrical power sources and one or more electrical loads, into a utility grid. Embodiments disclosed herein may allow the electrical load(s) to be powered from either or both of the utility grid and the local power source(s), without the risk of reverse power flow from the local power source(s) to the grid.
According to one aspect of the present disclosure, an apparatus includes a controllable switch and a power flow controller. The controllable switch is coupled between an electrical circuit connector for connection to an electrical circuit that includes an electrical load and an electrical power source to provide electrical power to the electrical load, and an electrical grid connector for connection to an electrical utility grid. The power flow controller is coupled to the controllable switch, to control a connection state between the electrical grid connector and the electrical circuit connector, by controlling the controllable switch based on respective voltages at the electrical circuit connector and at the electrical grid connector and a state of power flow between the electrical grid connector and the electrical circuit connector.
Another aspect of the present disclosure relates to a method that involves determining respective voltages at an electrical circuit connector for connection to an electrical circuit that includes an electrical load and an electrical power source to provide electrical power to the electrical load, and at an electrical grid connector for connection to an electrical utility grid; determining a state of power flow between the electrical grid connector and the electrical circuit connector; and controlling a connection state between the electrical grid connector and the electrical circuit connector based on the respective voltages at the electrical circuit connector and at the electrical grid connector and the state of power flow.
Other aspects and features of embodiments of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description.
Embodiments will be described, by way of example only, with reference to the accompanying drawings.
According to embodiments disclosed herein, reverse power flow prevention may be provided by a power flow control system connected between an electrical utility grid and an electrical circuit that includes one or more electrical power sources and one or more electrical loads. For ease of reference, an electrical utility grid may also be referred to herein as an electrical grid, a utility grid, or a grid. An electrical circuit may also be referred to herein as a local electrical circuit or a local circuit.
A power flow control system may include respective voltage sensors for sensing grid voltage, at an electrical grid connector for connection to an electrical utility grid for example, and local circuit or load voltage, at an electrical circuit connector for connection to a local electrical circuit for example, that is being supplied to one or more electrical loads in the local electrical circuit. As described in further detail at least below, the grid voltage and the local circuit voltage are used in determining whether a connection state between the utility grid and the local circuit, or equivalently between a grid connector and a local circuit connector for example, is to be maintained or changed. If a switch between the connectors is open, for an open connection state for example, and the grid voltage is greater than the voltage that is being applied to the load(s) by the power source(s) in the local circuit, then the switch may be controlled to close and connect the grid to the local circuit, thereby changing the connection state from an open connection to a closed connection.
Such a system may also include a current sensor for sensing current that is flowing from the utility grid. In some embodiments, the current and voltage sensing information is used to determine whether power that is flowing from the utility grid to the local electrical circuit is approaching zero. If power flowing from the utility grid approaches zero, a switch is controlled to open and disconnect the grid from the local circuit, thereby changing the connection state from a closed connection to an open connection.
With both voltage and current sensing, automatic control of switch opening and closing can be provided in such a way that power from local circuit power sources is prevented from flowing into a utility grid. The power source(s) in a local circuit will source power to supply the load(s) in the local circuit only when voltage is not applied from the grid and the switch is open in the open connection state between the grid and the local circuit, or when the switch is closed in the closed connection state between the grid and the local circuit and power flow is from the grid to the local electrical circuit. Put another way, with power flow control as disclosed herein to transition to the open connection state when power flow from the grid to the local circuit is approaching zero, the power source(s) in the local circuit will not source power to the grid.
These and other features are described in detail herein, at least below.
The power flow control system 108 include an electrical grid connector at the left in
An electrical circuit connector is also provided at the right of the power flow controller 108 in
For example, a connector may be or include any of various types of electrical connections, terminals, or devices for connection to a utility grid 104 or to a local electrical circuit. An electrical grid connector or an electrical circuit connector may be or include not only mating type connectors, but also or instead other types of elements or components that can be wired to or otherwise coupled to an electrical utility grid or to a local electrical circuit, such as terminals (as shown by way of example in
Power flow control as disclosed herein is not in any way restricted to particular types of electrical grid connectors at 102, 106 or electrical circuit connectors at 121, 123, or to embodiments in which an electrical grid connector and an electrical circuit connector are of the same type.
In the example shown, there are two voltage sensors 110, 118. These voltage sensors may be implemented in any of various ways, as will be apparent to those familiar with power electronics and power control. Some embodiments may include two voltage sensors as shown, and in other embodiments one voltage sensor is coupled across multiple pairs of terminals or nodes and is capable of measuring multiple voltages. The present disclosure is not limited to any particular type, or number, of voltage sensors.
The current sense element 114 may be implemented using, for example, a current shunt or a current transformer. The current sensor 112 is intended to represent a component by which a signal from current sense element 114 is processed in some way, as described by way of example at least below. For example, a current sense signal may be scaled and filtered by the current sensor 112, and these features may be implemented using power electronics for example. The exact form of the current sensor 112 is dependent upon the features that are to be supported. Embodiments disclosed herein are not in any way dependent upon particular types of current sense elements or current sensors.
Although the example shown in
The controllable switch 116, as also discussed in detail at least below, enables connection of the local electrical circuit to, and disconnection of the local electrical circuit from, the utility grid 104. Examples of switches that may be used to implement the controllable switch 116 include relays, solid state switches such as Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), and triacs. As noted for other components in
The power flow controller 126 may be implemented, entirely or partially, using hardware, firmware, processing devices that execute software, or some combination thereof. Microprocessors, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and Programmable Logic Devices (PLDs) are examples of processing devices that may be used to execute software stored in memory. Features of the power flow controller 126, which are described in detail at least below, may be provided or supported in other ways, and the present disclosure is not in any way limited to processing device-based implementation of a power flow controller such as 126.
Other components in a power flow control system, such as one or more voltage sensors or a current sensor, may also or instead be implemented using the same processing device or one or more separate processing devices.
Finally, in the local electrical circuit, the power source(s) 120 and electrical load(s) 124 may be or include any of various types of electrical power sources and loads. Power sources that may be connected to the utility grid 104 would be AC power sources, but may be implemented in any of various ways, to supply power to any of various types of loads. For example, a power source 120 may be or include a battery or other direct current (DC) power source with an inverter to convert to AC, or an AC power source that generates AC power without requiring conversion from DC. Although a power source 120 is provided to supply power to the load(s) 124, the power source may also consume power under certain conditions. For example, a power source 120 may be or include a rechargeable power storage device that is recharged from the utility grid 104. The load(s) 124 may include, for example, one or more typical household electrical loads.
It should be appreciated that the power control system 100 is an illustrative and non-limiting example. Other embodiments may include fewer, additional, and/or different elements, interconnected in a similar way or a different way than shown.
Turning now to operation, the first voltage sensor 110 determines the voltage from the utility grid 104 at the grid connector, represented by way of example in
Utility grid current, between the electrical grid connector and the local circuit connector, is sensed at the current sense element 114 in the example shown, but may be determined in other ways as described at least above. A current sense signal from the current sense element is processed, by scaling and/or filtering for example, the current sensor 112. The current sensor 112 is therefore an example of a component to determine the current between the electrical grid connector and the local circuit connector.
Although a current sense element 114 and a current sensor 112 are shown separately in
Electrical parameter sensing need not necessarily be distributed between multiple sensors as shown. Voltage sensing and current sensing may involve different techniques, but in some embodiments sense signals from multiple sensing elements may be received by a single sensor device or module for optional processing such as scaling and/or filtering, for example. In some embodiments, power sensing may be implemented, using a power sensor for example, that determines power flow and provides a power flow measurement to the power flow controller. The present disclosure is not in any way limited to any particular sensing architecture or implementation.
The power flow controller 126 controls a connection state between the electrical grid connector and the local circuit connector, by controlling the controllable switch 116 based on at least the respective voltages at the electrical circuit connector and at the electrical grid connector and a state of power flow between the electrical grid connector and the local circuit connector. Current and voltage sensing information is used by the power flow controller 126 in some embodiments to determine whether power is flowing from the utility grid 104 or is approaching zero, and the power flow controller 126 may then provide a control signal to control the controllable switch 116 and thus a connection state between the electrical grid connector and the local circuit connector based on, in this example, calculated power and the determination as to whether power is flowing or approaching zero.
As discussed in additional detail by way of example at least below, under a state of no power flow with the controllable switch 116 in an open position, the power flow controller 126 may control the switch based on the respective voltages at the electrical grid connector and the local circuit connector. The power flow controller 126 may determine that the controllable switch 116 is open and the state of power flow is no power flow between the electrical grid connector and the local circuit connector in any of various ways. For example, the controllable switch 116 may be configured to provide a state indication to the power flow controller 126, or the power flow controller may itself be configured to track whether it has most recently controlled the controllable switch to open or close.
In short, if the controllable switch 116 is open and the power flow state is no power flow between the electrical grid connector and the local circuit connector, then the power flow controller 126 may control the switch based on the respective voltages at the electrical grid connector and the local circuit connector. Some embodiments may involve determining current and power flow for the purpose of controlling the controllable switch 116, but it should be appreciated that current need not necessarily be used in all embodiments of switch control.
Another power flow state is a state of positive power flow from the electrical grid connector to the electrical circuit connector, with the controllable switch 116 in a closed position. Under this power flow condition, the power flow controller 126 controls the connection state by controlling the controllable switch 116 based on not only the respective voltages at the electrical grid connector and the local circuit connector, but further based on the current between the electrical grid connector and the electrical circuit connector with the switch in a closed position. In particular, according to embodiments disclosed herein, the power flow controller 126 controls the connection state by controlling the controllable switch 116 based on a calculation of power from the respective voltages at the connectors, and the current. The power flow controller 126 may itself be configured to calculate the power from the respective voltages and the current, or in other embodiments a power flow calculator may be coupled to the power flow controller, to calculate the power from the respective voltages and the current. Thus, the power flow controller 126 may perform a power calculation, or may include or be coupled to a power flow calculator. For example, power sensing using a power sensor is referenced at least above, and such a power flow sensor that senses power flow and provides and indication of power flow may be considered to be a form of power flow calculator. Power sensing or calculation may involve sensing voltage and current, and accordingly power flow sensing may also be considered to be based on current and the respective voltages at the electrical grid connector and the electrical circuit connector. This is further illustrative of how embodiments are not restricted to only an implementation as shown in
Embodiments may allow power to be supplied to the electrical load(s) 124 from the utility grid 104 and possibly also the power source(s) 120, when the controllable switch 116 is closed and the power flow state is a state of positive power flow from the electrical grid connector to the local circuit connector, or from the power source(s) 120 when the controllable switch 116 is open and the power flow state is a state of no power flow from the electrical grid connector to the local circuit connector. If power is flowing from the utility grid 104 but approaches zero, then the power flow controller 126 controls the controllable switch 116 to open, by signaling the switch to open for example. If the controllable switch 116 is open and one or more switch closing conditions are satisfied, then the power flow controller 126 controls the controllable switch 116 to close, by signaling the switch to close for example. Signaling the controllable switch 116 may also or instead be referred to as providing a control signal to the switch. In the case of controlling the controllable switch 116 to open, the control signal may be referred to as an “open” control signal. Similarly, in the case of controlling the controllable switch 116 to close, the control signal may be referred to as a “close” control signal.
Under a power flow state of no power flow, with the controllable switch 116 open, the power flow controller 126 uses voltage information related to the respective voltages at the grid connector and the local circuit connector, from the voltage sensors 110, 118 in the example shown in
Responsive to a switch closing condition being satisfied, such as when the grid voltage at the grid connector is greater than the local circuit voltage at the local circuit connector or when the respective voltages are substantially equal and have slopes that are of the same polarity in the above examples, the power flow controller 126 controls the controllable switch 116 to close. Otherwise, when the controllable switch 116 is in an open position and a switch closing condition is not satisfied, the switch is maintained in the open position. Maintaining the controllable switch 116 in an open position may involve providing a control signal to the switch to keep it open, or not providing a control signal to the switch so that it does not transition from open to closed position. In either case, it is the power flow controller 126 that controls the connection state between the grid connector and the local circuit connector, based on the respective voltages at the connectors in these examples.
These examples illustrate operation of the power flow controller 126 to control connection state between the connectors by maintaining the connection state of an open connection with the controllable switch 116 in an open position where the respective voltages at the connectors, and the state of power flow (which is no power flow with the switch open in these examples) do not satisfy a condition for the local circuit to be connected to the utility grid 104, or by changing the connection state of an open connection to a closed connection with the switch in a closed position where the respective voltages and the state of power flow (which again is no power flow with the switch open) satisfy a condition for the local circuit to be connected to the utility grid.
Turning now to the power flow state of positive power flow, with the controllable switch 116 in the closed position, the power flow controller 126 receives voltage information about the respective voltages at the connectors and current information related to current flow between the connectors, from the voltage sensors 110, 118 and the current sensor 112 in the example shown in
With the controllable switch 116 in the closed position, the respective voltages at the connectors is substantially the same, apart from a voltage drop across connection and switch impedance between the connectors. Thus, power may be determined in some embodiments based on a measurement of either of the respective voltages when the controllable switch 116 is closed. In this case, the voltage upon which a power determination is based may be the voltage at one connector but is also substantially the same as the voltage at the other connector, and in at least this sense the power determination and subsequent switch control may still be considered or characterized as being based on the respective voltages at the connectors.
Responsive to a switch opening condition being satisfied, such as when calculated power drops below a threshold, the power flow controller 126 controls the controllable switch 116 to open. Otherwise, when the controllable switch 116 is in a closed position and a switch opening condition is not satisfied, the switch is maintained in the closed position. Maintaining the controllable switch 116 in its present position, which is closed in the case of positive power flow, may involve providing a control signal to the switch to keep the switch closed or not providing a control signal to the switch so that it does not transition from closed to open position. Whether the controllable switch 116 is to be maintained in its present position, which is closed in this example, or transitioned to a different position, which is open in this example, it is the power flow controller 126 that controls the connection state between the grid connector and the local circuit connector, based on the respective voltages at the connectors, and further based on current flow between the connectors, in these examples.
These examples illustrate operation of the power flow controller 126 to control connection state between the connectors by maintaining the connection state of a closed connection with the controllable switch 116 in a closed position where the respective voltages and the positive state of power flow satisfy a condition for the local circuit to remain connected to the utility grid 104, or by changing the connection state to an open connection with the controllable switch in an open position where the respective voltages and the state of power flow do not satisfy a condition for the local circuit to remain connected to the utility grid.
Switch control and operation of the power flow controller 126 and the controllable switch 116 will be further described below with reference to
A first crossing point at 206 and a second crossing point 208 show two example points where the respective voltages at a grid connector and a local circuit connector are substantially equal and the slopes of both sine waves have the same polarity. This is an example of a switch closing condition described herein. Under a power flow state of no power flow, the power flow controller 126 in
This is shown by way of example in
The AC potentials from the utility grid at 302 and the local circuit power source(s) at 304 have crossing points 306, 308 where grid connector voltage and local circuit connector voltage are substantially equal and the slopes of both waveforms have the same polarity. At 310,
Other switch closing conditions may also or instead be used to determine when to change connection state from open to closed, and thereby connect a local circuit to a utility grid.
After the connection state transitions to closed at 310, by closing the controllable switch 116 in
Under a power flow state of positive power flow and a closed connection state, the power flow controller 126 in
At 402, power is flowing from utility grid 104 of
At 408,
Power flow control consistent with the present disclosure may involve any of various actions or operations, of which some may but not all need necessarily involve changing connection state or switch position. For example, power flow control may involve any one or more of the following:
A power flow control cycle may progress through multiple states, actions, or operations. When a power flow control system is first connected between a utility grid and a local electrical circuit, for example, its power switch will likely be in an open position. The connection state and power switch may be maintained open until one or more closing conditions are satisfied (or one or more conditions to maintain open are not satisfied), and then controlled to transition to closed responsive to the closing condition(s) being satisfied (or the condition(s) to maintain open no longer being satisfied). The connection state and power switch may then be maintained closed until one or more opening conditions are satisfied (or one or more conditions to maintain closed are not satisfied), and then controlled to transition to open responsive to the opening condition(s) being satisfied (or the condition(s) to maintain closed no longer being satisfied). This power flow control cycle may repeat during the service life of a power flow control system, as a utility grid is affected by outages and recovers from such outages for example.
Opening, closing, maintaining open, and maintaining closed condition(s) need not be the same or even related to each other. For example, in some embodiments a power switch may be controlled to open when only one condition (for example, power flow approaching zero) is satisfied, whereas the power switch is controlled to close only when all of multiple conditions (for example, connector voltages are substantially the same and have the same slope) are satisfied.
Default control actions are also contemplated. For example, in the case of an open switch, it may be preferable for safety to maintain a power switch open (and safe) than to close the switch if all switch closing conditions are not satisfied.
Embodiments are described above primarily in the context of power circuits or components thereof. Method embodiments are also possible.
The example method 500 involves, at 502, determining respective voltages at an electrical circuit connector and at an electrical grid connector. As described in detail elsewhere herein, with reference to
At 504,
Controlling the connection state between the electrical grid connector and the electrical circuit connector based on the respective voltages at the electrical circuit connector and at the electrical grid connector and the state of power flow is generally represented at 506.
Determining the voltages at 500 may involve, in some embodiments, sensing the respective voltages. The voltages may be sensed using one or more voltage sensors, as described at least above with reference to
Although not explicitly shown in
Controlling connection state at 506 may involve controlling the connection state based on a determination of power from the respective voltages and the current. A method may involve determining the power from the respective voltages and the current, or receiving an indication of power that was sensed or otherwise determined, by a power calculator such as a power sensor for example.
Controlling the connection state between the connectors may involve maintaining a present connection state as shown at 512 or changing the present connection state at shown at 514. At 510,
For example, controlling the connection state may involve maintaining the connection state of an open connection at 512 where it is determined at 510 the respective voltages and the state of power flow (which is no power flow for the case of an open connection) do not satisfy one or more conditions for the electrical circuit to be connected to the electrical utility grid, or changing the connection state of an open connection to a closed connection at 514 where it is determined at 510 that the respective voltages and the state of power flow (which again is no power flow with the switch open) satisfy one or more conditions for the electrical circuit to be connected to the electrical utility grid.
For a present connection state of a closed connection with a controllable switch such as the controllable switch 116 (
Various examples of conditions that may be assessed at 510 for maintaining a connection state at 512 or changing the connection state at 514 are provided at least above. These examples also apply to method embodiments.
As also described at least above, a power flow control cycle may progress through multiple states, actions, or operations, and the dashed return paths from 512, 514 to 502 in
The present disclosure shows, by way of example, how power can be supplied to local electrical circuits, which include one or more electrical loads and one or more power sources, from a utility grid while also preventing power from flowing from the power source(s) to the utility grid.
What has been described is merely illustrative of the application of principles of embodiments of the present disclosure. Other arrangements and methods can be implemented by those skilled in the art.
For example, other arrangements may refer to the use of various types of switches including semiconductors and the use of sensors for sensing power.
Embodiments need not include all elements or components that are shown in the drawings or described herein. Embodiments may include additional, fewer, and/or different components or elements.
It should also be appreciated that features disclosed herein in the context of a particular embodiment, such as an apparatus embodiment, are not limited only to that embodiment. Features may also or instead be implemented in other embodiments, such as a method embodiment. Similarly, method features may also or instead be implemented, supported, or otherwise provided in apparatus embodiments.
In addition, although described primarily in the context of methods and apparatus such as power circuits, other implementations are also contemplated, as instructions stored on a non-transitory computer-readable medium, for example.
