# Patent

## Title
Systems and methods for edge of network voltage control of a power grid

## Abstract

Systems and methods for an edge of network voltage control of a power grid are described. In some embodiments, a system comprises a distribution power network, a plurality of loads, and a plurality of shunt-connected, switch-controlled VAR sources. The loads may be at or near an edge of the distribution power network. Each of the loads may receive power from the distribution power network. The plurality of shunt-connected, switch-controlled VAR sources may be located at the edge or near the edge of the distribution power network where they may each detect a proximate voltage. Further, each of the VAR sources may comprise a processor and a VAR compensation component. The processor may be configured to enable the VAR source to determine whether to enable the VAR compensation component based on the proximate voltage and to adjust network volt-ampere reactive by controlling a switch to enable the VAR compensation component.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of U.S. patent application Ser. 13/488,330, filed Jun. 4, 2012, entitled “Systems and Methods for Edge of Network Voltage Control of a Power Grid,” which in turn claims the benefit of U.S. Provisional Patent Application No. 61/535,892, filed Sep. 16, 2011, entitled “Systems and Methods of a Distributed Dynamic VAR (D-DVAR) Compensator,” U.S. Provisional Patent Application No. 61/567,580, filed Dec. 6, 2011, entitled “Systems and Methods for Dynamic VAR Optimization,” U.S. Provisional Patent Application No. 61/579,610, filed Dec. 22, 2011, and entitled “Systems and Methods for Managing Power,” U.S. Provisional Patent Application No. 61/635,799, filed Apr. 19, 2012, and entitled “Systems and Methods for Dynamic AC Line Voltage Regulation with Energy Saving Tracking,” and U.S. Provisional Patent Application No. 61/635,797, filed Apr. 19, 2012, and entitled “Systems and Methods for Fast VAR Source with Anti-Resonance Function,” all of which are incorporated by reference herein.


BACKGROUND
1. Field of the Invention(s)
The present invention(s) generally relate to power distribution grid network optimization strategies. More particularly, the invention(s) relate to systems and methods for edge of network voltage control of a power distribution grid.
2. Description of Related Art
The conventional approach to power distribution grid voltage control is based on techniques developed about 70 years ago. In recent years, highly complex and expensive systems have been required to implement improved effective voltage control and conservation voltage reduction (CVR) based demand reduction. Under present requirements, alternating current (AC) line voltage for connected users needs to fall within a narrow band specified by ANSI C84.1 under all conditions of loading and substation voltage. Typically, utilities operate in a narrow band of 116-124 volts, even though level ‘A’ service allows for a range of 114-126 volts. The difficulty in adhering to a tight regulation band arises from normal fluctuations in incoming line voltage at the substation, as well as load changes along the feeder. These changes cause the line voltage to vary, with utilities required to maintain voltage for consumers within specified bounds.
The prior art volt-ampere reactive regulation devices (VAR devices) for voltage control may be split into several categories including: 1) prior art VAR devices with slow responding capacitors and electro-mechanical switches; ii) prior art VAR devices with medium response capacitors and thyristor switched capacitors; and iii) prior art VAR devices with power converter based VAR control using Static VAR sources or static synchronous condensers (STATCOMs).
It should be noted that capacitors in the prior art VAR devices are mainly used for power factor control when used by customers and for voltage control when used by utilities. For power factor control, the downstream line current must be measured. Capacitors and/or inductors may be switched on or off based on the line current to realize a desired overall power factor (e.g., typically at a value of unity). In the second case of voltage control used by utilities, capacitors are controlled based on: 1) local voltage measurements; 2) other parameters such as temperature; and/or 3) dispatches communicatively received from a control center. The control center may dispatch decisions regarding capacitor control based on information received from multiple points in the network.
Most capacitors of prior art VAR devices are switched using electromechanical switches. The electromechanical switches are limited in switching speed and by life of the switches. Many electromechanical switches are limited to 3-4 switches per day. A response time of approximately fifteen minutes is often required to enable voltage control with prior art VAR devices. During this time, the following steps may be performed: 1) sensing voltages locally; 2) communicating the sensed voltages to a centralized control center; 3) power and/or voltage modeling of the system at the centralized control center; 4) determining to take action based on the model and perceived potential improvements; and 5) dispatching one or more commands from the centralized control center to the prior art VAR device to switch the capacitor. More advanced Volt-VAR Optimization or VVO systems are moving to such centralized implementations so they can try to optimize the profile of voltage along an entire distribution feeder and reduce infighting between prior art VAR devices.
SUMMARY
Systems and methods for an edge of network voltage control of a power grid are described. In some embodiments, a system comprises a distribution power network, a plurality of loads, and a plurality of shunt-connected, switch-controlled VAR sources. The loads may be at or near an edge of the distribution power network. Each of the loads may receive power from the distribution power network. The plurality of shunt-connected, switch-controlled VAR sources may be located at the edge or near the edge of the distribution power network where they may each detect a proximate voltage. Further, each of the VAR sources may comprise a processor and a VAR compensation component. The processor may be configured to enable the VAR source to determine, after a delay, whether to enable the VAR compensation component based on the proximate voltage and to adjust network volt-ampere reactive by controlling a switch to enable the VAR compensation component.
The delay of each of the plurality of shunt-connected, switch-controlled VAR sources may not be equal. The different delays of different members of the plurality of shunt-connected, switch-controlled VAR sources may prevent infighting between at least two of the different members. In various embodiments, the delay of at least two of the plurality of shunt-connected, switch-controlled VAR sources may be equal but the delay of a third of the plurality of shunt-connected, switch-controlled VAR sources may not be equal to the other two VAR sources.
The switch may comprise a semiconductor switch in series with an NTC or resistor. The semiconductor switch (in series with the NTC or resistor) may be in parallel with a relay. The semiconductor switch may be controlled by a first signal from the processor and the relay may be controlled by a second signal from the processor. The semiconductor switch may control enabling the VAR compensation component and relieves the relay of switching stress. The relay may conduct when the semiconductor switch is active thereby reducing semiconductor device conduction losses.
In various embodiments, at least two of the plurality of shunt-connected, switch-controlled VAR sources are on a low voltage side of a transformer of the power distribution network. The VAR compensation component may comprise capacitors or inductors.
In some embodiments, each of the plurality of shunt-connected, switch-controlled VAR sources includes at least one voltage set point. Each of the processors of the plurality of shunt-connected, switch-controlled VAR sources may be configured to determine whether to enable the VAR compensation component based on a comparison of the proximate voltage to the at least one voltage set point. Each of the plurality of shunt-connected, switch-controlled VAR sources may increase leading volt-ampere reactive if the at least one voltage set point is higher than the detected proximate voltage and decrease leading volt-ampere reactive if the at least one voltage set point is lower than the detected proximate voltage.
In some embodiments, each of the plurality of shunt-connected, switch-controlled VAR sources comprises a communication module configured to receive at least one voltage set point. The communication module of different shunt-connected, switch-controlled VAR sources may receive updates for the at least one voltage set point(s). The communication module may be configured to update the voltage set point and a rate of update of the voltage set point may be significantly slower than adjusting the network volt-ampere reactive by controlling the switch to enable the VAR compensation component based on the determination. In some embodiments, at least two of the plurality of shunt-connected, switch-controlled VAR sources receive different voltage set points.
In some embodiments, the processor is further configured to detect an overvoltage condition and disable the switch based on the detected overvoltage condition. In various embodiments, the system self-determines which VAR compensation components of the plurality of VAR sources are enabled and which VAR compensation components of the plurality of VAR sources are not enabled.
An exemplary method comprises detecting, by a first shunt-connected, switch-controlled VAR source at an edge or near the edge of a distribution power network proximate to a first load, a first proximate voltage, the first load configured whether to receive power from the distribution power network, the first shunt-connected, switch-controlled VAR source comprising a processor and a VAR compensation component, determining, after a first delay, by the processor of the first shunt-connected, switch-controlled VAR source, whether to enable the VAR compensation component based on the first proximate voltage, adjusting, by the VAR compensation component of the first shunt-connected, switch-controlled VAR source, a network volt ampere based on the determination.
The method may further comprise detecting, by a second shunt-connected, switch-controlled VAR source at the edge or near the edge of the distribution power network proximate to a second load, a second proximate voltage, the second shunt-connected, switch-controlled VAR source comprising a VAR compensation component and a processor, determining, after a second delay, by the processor of the second shunt-connected, switch-controlled VAR source, whether to enable the VAR compensation component based on the second proximate voltage after a second delay; adjusting, by the VAR compensation component of the second shunt-connected, switch-controlled VAR source, the network volt ampere based on the determination.
The first delay may not equal to the second delay. The different delays of different members of the plurality of shunt-connected, switch-controlled VAR sources may prevent infighting between at least two of the different members.
Another exemplary method may comprise coupling a first switch-controlled VAR source in shunt on a distribution power network, the first switch-controlled VAR source being proximate to a first load at or near an edge of the distribution power network, the first load being configured to receive power from the distribution power network, the first switch-controlled VAR source configured to detect a first proximate voltage at the edge or near the edge of the distribution power network, the first switch-controlled VAR source comprising a VAR compensation component and a processor, the processor configured to enable the first switch-controlled VAR source to determine, after a first delay, whether to enable the VAR compensation component based on the first proximate voltage and to adjust network volt-ampere reactive by controlling a switch to enable the VAR compensation component based on the determination.
The method may further comprise coupling a second switch-controlled VAR source in shunt on a distribution power network, the second switch-controlled VAR source being proximate to a second load at or near an edge of the distribution power network, the second load being configured to receive power from the distribution power network, the second switch-controlled VAR source configured to detect a second proximate voltage at the edge or near the edge of the distribution power network, the second switch-controlled VAR source comprising a VAR compensation component and a processor, the processor configured to enable the second switch-controlled VAR source to determine, after a second delay, whether to enable the VAR compensation component based on the second proximate voltage and to adjust network volt-ampere reactive by controlling a switch to enable the VAR compensation component based on the determination.
The first delay may not be equal to the second delay. The different delays of different members of the plurality of shunt-connected, switch-controlled VAR sources may prevent infighting between at least two of the different members.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a depicts a typical distribution feeder fed from a single substation in some embodiments.
FIG. 1b depicts a distribution feeder fed from a single substation and including a plurality of edge of network voltage optimization (ENVO) devices in some embodiments.
FIG. 1c depicts another distribution feeder fed from a single substation and including the plurality of ENVO devices in some embodiments.
FIG. 2 is a diagram depicting voltage drop along feeders due to loads without the implementation of capacitor banks in the prior art.
FIG. 3a is a diagram depicting a power distribution grid with shunt-connected, switch-controlled VAR sources at or near each load in some embodiments.
FIG. 3b is another diagram depicting a power distribution grid with shunt-connected, switch-controlled VAR sources at or near each load in some embodiments.
FIG. 4a is a circuit diagram of an exemplary switch-controlled VAR source which may be connected in shunt in some embodiments.
FIG. 4b is a graph that depicts activating the semiconductor switch relative to the relay to engage VAR compensation in some embodiments.
FIG. 4c is a graph that depicts deactivating the semiconductor switch relative to the relay to disengage VAR compensation in some embodiments.
FIGS. 5a and 5b are graphs that depict a desired voltage range in relation to set points in some embodiments.
FIG. 6 is a flow chart for voltage regulation by a switch-controlled VAR source in some embodiments.
FIG. 7 is a time sequence of events of network regulation with two switch-controlled VAR sources in some embodiments.
FIG. 8 is a graph that depicts a typical voltage profile at various nodes in the prior art.
FIG. 9 is a graph that depicts relatively flat voltage profile at various nodes in some embodiments realized with 240 switch controlled VAR sources operating to regulate the voltage along the edge of the distribution feeder.
FIG. 10 is a graph that depicts a dynamic response of the ENVO system to line voltage changes (which can be caused by solar PV plants), as well as to step changes in line loading in some embodiments.
FIG. 11a is another circuit diagram of a plurality of switch-controlled VAR sources that may be within or next to a pole top transformer or any grid asset in some embodiments.
FIG. 11b depicts a switch-controlled VAR source in some embodiments.
FIG. 11c depicts a plurality of switch-controlled VAR sources in some embodiments.
FIG. 11d depicts a controller in some embodiments.
FIG. 11d-1 is an exploded schematic view of the corresponding element of FIG. 11d. 
FIG. 11d-2 is an exploded schematic view of the corresponding element of FIG. 11d. 
FIG. 11d-3 is an exploded schematic view of the corresponding element of FIG. 11d. 
FIG. 11d-4 is an exploded schematic view of the corresponding element of FIG. 11d. 
FIG. 11e depicts power module comprising ADC circuitry and ZCD circuitry coupled to the controller in some embodiments.
FIG. 12 is a block diagram of an exemplary digital device.



DETAILED DESCRIPTION
New requirements for distribution dynamic voltage control are emerging, driven by distribution renewable energy penetration and the need to increase grid capacity without building new lines or infrastructure. Applications such as Conservation Voltage Reduction (CVR) and Volt VAR Optimization (VVO) promise 3-5% increase in system capacity, simply by lowering and flattening the voltage profile along a distribution grid. To achieve CVR and VVO in the prior art, improvements to the power grid are slow in operation, difficult to model due to increased complexity of the overall system, require considerable back end infrastructure (e.g., modeling, and a centralized, computation and communication facility), are expensive to install in sufficient numbers to improve performance, and difficult to maintain. Further, conventional VVO schemes realize poor voltage regulation due to few control elements and poor granular response.
In various embodiments discussed herein, line voltage may be regulated at or near every customer point (i.e., at the load along a distribution power grid). For example, a utility may install a shunt-connected, switch-controlled volt-ampere reactive (VAR) source at each customer location. Each shunt-connected, switch-controlled volt-ampere reactive (VAR) source may detect a voltage proximate to the device and make a determination to enable a VAR compensation component (e.g., capacitor(s) and/or inductor(s)) to regulate voltage on the network. The plurality of shunt-connected, switch-controlled volt-ampere reactive (VAR) sources, switching independently, may operate collectively to flatten the voltage curve (e.g., voltage impact along a medium voltage distribution feeder starting from a substation) along a power network. The plurality of VAR sources may be controlled to prevent fighting between sources, while allowing connected points to reach a desired voltage set point with much higher granularity and accuracy.
If distributed VAR compensation is implemented, the utility may realize several benefits. For example, a desired voltage profile may be maintained optimally along the line even as system configuration changes, system losses may decrease, and/or system stability and reliability may be improved. New cascading grid failure mechanisms, such as Fault Induced Delayed Voltage Recovery (FIDVR) may also be avoided through the availability of distributed dynamically controllable VARs.
In various embodiments, distributed fast voltage controllers and/or compensators at or near a power network edge provides a solution that is able to act autonomously on local information with little to no infighting. This approach may remove uncertainty about the voltage variations at a range of nodes, flatten the voltage profile along the edge of the network, and allow a Load Tap Changer (LTC) to drop the voltage to the lowest level possible.
FIG. 1a depicts a typical distribution feeder 106 fed from a single substation 102 in some embodiments. Standard design practice involves the use of load tap changing (LTC) transformers 104 at substations 102, with fixed and switchable medium voltage capacitors on the feeder. FIG. 1 depicts a series of houses (i.e., loads) 110, 112, 114, and 116 that receive power from various distribution feeders coupled to the primary feeder 106 (e.g., distribution feeders separated from the primary feeder by transformers 108a-d). In the prior art, as the distance from the substation 102 increases, utility voltage 118 along the primary feeder (e.g., medium voltage distribution feeder 106) decreases.
In the prior art, load tap changers, slow acting capacitor banks, and line voltage regulators may be sporadically placed along one or more primary feeders 106 to improve voltage range. Without Conservation Voltage Reduction or CVR, the first houses 110 have a required utility voltage of approximately 124.2 volts. Houses 112 have a significantly reduced utility voltage of approximate 120-121 volts. Houses 114 further have a required voltage between 115 and 116 while houses 116 has a required voltage between 114 and 115.
FIG. 1b depicts a distribution feeder 106 fed from a single substation 102 and including a plurality of edge of network voltage optimization (ENVO) devices 120a-d in some embodiments. In various embodiments, VAR compensators (e.g., or any VAR source), including, for example, ENVO devices 120a-d, may be placed at or near any number of the loads (e.g., houses 110, 112, 114, and 116). As a result, the overall voltage range may be flattened along the distance from the substation 102 thereby saving energy, increasing responsiveness, and improving overall control along longer distribution feeders. In order to avoid infighting between one or more VAR sources, the action of switching (e.g., the timing of switching or the point at which VAR compensation is engaged/disengaged) may be different between all or a portion of the VAR sources.
The VAR source may each act (e.g., activate or deactivate one or more VAR components such as a capacitor and/or inductor) quickly and independently, based at least on voltages proximate to the VAR sources, respectively, to improve voltage regulation and achieve Edge of Network Volt Optimization (ENVO) (see ENVO line 122). The ENVO line 122 depicts that the voltage required for houses 110 is approximately 120 volts. Houses 112, 114, and 116, may require a reasonably flat voltage range around approximately 120 volts as well. Those skilled in the art will appreciate that the ENVO line 122 achieves a desired flattening of the required voltage range while the line indicating utility voltage 118 without VAR compensation drops precipitously.
FIG. 1c depicts another distribution feeder 106 fed from a single substation 102 and including the plurality of ENVO devices 120a-d in some embodiments. In various embodiments, the ENVO devices 120a-d may further apply Conservation Voltage Reduction (CVR) to further reduce required voltage. Line 124 represents the voltage required for houses 110, 112, 114, and 116 with ENVO devices 132a-b applying CVR. For example, line 124 (like ENVO line 122) is relatively flat. Houses 110 and 112 may require approximately 115.2 volts while houses 114 may require approximately 115 volts. Further, houses 116 may require 115.4 volts in this example. The need to improve system capacity utilization is driving utilities to implement peak demand reduction and capacity expansion using techniques such as Conservation Voltage Reduction (CVR) and Volt VAR Optimization (VVO) on non-ENVO devices. Utility companies currently apply CVR by receiving information from multiple points in the power grid, modeling the performance, modeling proposed improvements, and potentially coordinating activities of capacitor banks along the primary feeder on the medium voltage side of the transformers.
Poor controllability of preexisting voltage regulation devices presents severe challenges to managing voltage variations for system planners and operators. In particular, poor controllability limits the length of a distribution feeder that can be managed. Poor controllability also limits the load variability that can be handled, while keeping all voltages at end-user locations within bounds.
Further, new trends are seeing an increased use of sectionalizers with breaker/reclosers to isolate faulted segments and to restore power to other non-faulted line segments, resulting in a significant change in the network, and voltage profiles. Increased use of network reconfiguration also makes the task of placing capacitor banks and LTCs at fixed locations more problematic, as the placement has to meet the needs of multiple configurations. Moreover, the increasing use of distributed generation resources, such as roof top photovoltaic (PV) arrays can result in a reversal of power flows locally, with higher line voltages farther away from the substation, and a breakdown of any voltage regulation algorithm that was implemented.
Those skilled in the art will appreciate that VAR sources at or near the edge of the power grid may individually react and correct for higher line voltages that may be a result of PV arrays (e.g., green energy improvement such as solar panels). These VAR sources may allow both the customer and the network to enjoy the benefits of green power without significantly redesigning or altering the grid to accommodate the change. Since the edge of the network is quickly and independently reactive to events or changes along the power grid, a centralized algorithm, containing a complete state of the grid including all variables that affect load and input, for slow voltage control and regulation may also become unnecessary.
FIG. 2 is a diagram depicting voltage drop along feeders due to loads without the implementation of capacitor banks in the prior art. As depicted in FIG. 2, the length of the feeder lines from the substation is limited by the voltage drop. In this example, there is a 10% variance in available voltage. In the prior art, the objective is to keep voltage within a broad band. As few control handles are available, only very course control is possible. Ideally, the voltage should be closely regulated to specifications all along the line, including in the presence of dynamic fluctuations. With few sensors, few correction points, slow communication, and a limited number of operations, prior art control is unable to meet the dynamic control requirements of the new and future distribution power grid.
By utilizing sporadically placed capacitor banks, voltage regulation may be implemented to flatten the available voltage range and reduce losses. The capacitor banks may operate based on temperature, for example, or based on commands from a centralized control facility. When based on temperature, for example, to avoid interactions and to maximize switch life of the capacitor banks, switching to activate or deactivate one or more capacitors is infrequent and slow. Capacitor banks that are operated under the control a centralized facility may be individually commanded to avoid interactions.
In spite of the attempts of controlling voltage through CVR, drops along the length of the feeder are only marginally effected the activation of the capacitor banks. In these examples, the capacitor bank may be switched three-to-four times per day. The process may be slow as well. In one example, it may take up to fifteen minutes to: 1) detect conditions; 2) provide the conditions to a centralized facility; 3) the centralized facility model conditions and make a determination to enable or disable a capacitor bank; 4) provide a command to one or more capacitor banks; and 5) receive the command and perform the switching. Even if one or more of these disadvantages were overcome, there may still be infighting between multiple devices attempting to control voltage. For example, multiple thyristor switched capacitors may fight with each other as each device attempts to compensate for a power state of the power network. As the thyristor switched capacitors work at cross purposes, they tend to overcompensate and undercompensate while constantly reacting to the corrections of other thyristor switched capacitors on the power network.
FIG. 3a is a diagram depicting a power distribution grid with shunt-connected, switch-controlled VAR sources at or near each load in some embodiments. Loads are depicted as houses or residences. In addition to houses or residences, those skilled in the art will appreciate that the loads can be any loads including, but not limited to, commercial or industrial establishments. A load is any component, circuit, device, piece of equipment or system on the power distribution network which consumes, dissipates, radiates or otherwise utilizes power. A power distribution grid is an electrical grid, such as an interconnected network, for delivering electricity from suppliers to consumers.
In this example, voltage may be regulated at or near the edge of the network thereby allowing edge of network volt optimization (ENVO). An edge of the network is the portion of a power distribution network that is proximate to the load that is to receive power. In one example, the load is a customer load. An edge of the network may be on the low-voltage side of a transformer. For example, the edge of the network may comprise one or more feeder lines configured to provide power to multiple customer loads (e.g., housing residences).
In FIG. 3, a substation provides power to residences (e.g., loads) over a series of regional distribution feeders. Each residence and shunt-connected, switch-controlled VAR source is coupled to the power distribution grid. In various embodiments, each shunt-connected, switch-controlled VAR source is configured to detect voltage and adjust network volt-ampere reactive (VARs) based on the detected voltage. In one example, the shunt-connected, switch-controlled VAR source enables a capacitor and/or an inductor to change (e.g., reduce or eliminate) the reactive power of the power distribution grid thereby regulating voltage of the network (i.e., network voltage). The change in reactive power may reduce the voltage drop along the distribution feeder.
As discussed regarding FIG. 1, shunt-connected, switch-controlled VAR sources may be placed at or near any number of the loads. As a result, the overall voltage range may be flattened along the distance from the substation thereby saving energy, increasing responsiveness, and improving overall control along longer distribution feeders. The VAR source may each act (e.g., activate or deactivate one or more VAR components such as a capacitor and/or inductor) quickly and independently, based at least on voltages proximate to the VAR sources, respectively, acting collectively to improve voltage regulation and achieve ENVO. FIG. 3 depicts that the voltage distribution drop is flatter, for example a +/−2% variance across the network depicted in FIG. 3 without the implementation of the capacitor banks.
FIG. 3b is another diagram depicting a power distribution grid with shunt-connected, switch-controlled VAR sources at or near each load in some embodiments. In FIG. 3b, a substation 302 with a load top changer (LTC) 304 feeds a distribution feeder 306 with line inductance throughout the distribution feeder 306. Loads 312, 314, 316, and 318 receive power from the distribution feeder 306 via transformers 310a-d respectively. Further, each subfeeder between a transformer and the loads may include on or more ENVO devices 310a-e that may be configured to act as one or more VAR compensators. In various embodiments, multiple ENVO devices (e.g., ENVO VAR units) may be deployed along the length of a typical distribution feeder to flatten the required voltage and respond to network conditions.
In various embodiments, an optional central controller 320 may communicate with one or more of the ENVO devices 310a-e to receive sensor information and/or behavior information regarding the actions of one or more ENVO devices 310a-e. In some embodiments, one or more of the ENVO devices 310 may include a communication interface configured to communicate with each other and/or the central controller 320. The central controller 320 may, in some embodiments, provide one or more set points (discussed herein) that may assist in controlling when one or more of the ENVO devices 310 become active (e.g., based on comparing one or more set points to voltage of a portion of the power distribution network. The central controller 320 is further discussed herein.
FIG. 4a is a circuit diagram of an exemplary switch-controlled VAR source 400 which may be connected in shunt in some embodiments. The switch-controlled VAR source 400 may be a part of a large number of switch-controlled VAR sources 400 at or near an edge of the power distribution grid (i.e., the power network).
At a high level, the switch-controlled VAR source 400 comprises a capacitor 412 (e.g., a VAR compensation component) that is controlled through a relay 414 in parallel with a semiconductor switch 416 (e.g., triac 420-NTC 418 is optional). A processor, such as controller 426, may control the relay 414 and semiconductor switch 416 based on voltage. For example, the controller 426 may detect voltage proximate to the switch-controlled VAR source 400 (e.g., through line 402). Based on the detected voltage, the controller 426 may enable or disable the capacitor by controlling the relay 414 and semiconductor switch 416. As discussed herein, the relay 414 and semiconductor switch 416 may work together to protect and prolong the life of various components of the switch-controlled VAR source 400 during switching operations.
The exemplary switch-controlled VAR source 400 comprises a lines 402 and 430, fuse 404, inductor 406, resistors 408, 410, 418, 422, and 424, capacitor 412, relay 414, a switch 416 comprising an optional NTC 418 and triac 420, controller 426, and power supply unit (PSU) 428. Lines 402 and 430 may be coupled to a feeder such as a feeder on the low voltage side of a transformer. In one example, lines 402 and 430 may be coupled to any line or feeder configured to provide power to one or more loads (e.g., on or at the edge of a network). In some embodiments, the switch-controlled VAR source 400 is proximate to a residential or commercial load. For example, the switch-controlled VAR source 400 may be within a smart meter, ordinary meter, or transformer within proximity to a load. Those skilled in the art will appreciate that the switch-controlled VAR source 400 may be within any grid asset.
The fuse 404 is configured to protect the switch-controlled VAR source 400 from voltage spikes, transients, excessive current, or the like. The fuse 404 may be any fuse and may be easily replaceable. In some embodiments, if the fuse 404 short circuits and the switch-controlled VAR source 400 are disconnected from the power distribution network, the power delivered to the residential and/or commercial loads may not be interrupted.
The inductor 406 and resistor 408 may act as an L-R snubber to control peak inrush currents (e.g., during startup conditions) and to manage resonance. In some embodiments, the inductor 406 and resistor 408 may prevent wear on the capacitor 412 and/or the other circuits of the switch-controlled VAR source 400 caused by changes in voltage or power received from the line 402 and/or activation or deactivation of the switch-controlled VAR source 400.
Those skilled in the art will appreciate that, in some embodiments, the inductor 406 and resistor 408 may reduce susceptibility of the capacitor 412 to harmonic resonance. In various embodiments, the switch-controlled VAR source 400 does not comprise the inductor 406 and/or the resistor 408.
The capacitor 412 may be any capacitor configured to compensate for reactive power (e.g., VARs). In various embodiments, the relay 414 and/or the semiconductor switch 416 may form a switch that completes the circuit thereby allowing the capacitor 412 to influence reactive power of the network. In one example, if the relay 414 is open and the triac 420 (of the semiconductor switch 416) is deactivated, the capacitor 412 may be a part of an open circuit may, therefore, have no effect on the power distribution gird or the load.
The resistor 410 is an optional bleed resistor. In some embodiments, when the capacitor is disabled or otherwise disconnected by the switch (e.g., via relay 414 and/or semiconductor switch 416), the resistor 410 may potentially receive energy from the capacitor 412 thereby allowing the energy state of the capacitor 412 to decrease.
The relay 414 may be used to reduce losses when the semiconductor switch 416 is active. The semiconductor switch 416 may be used to provide precise and fast response at turn on and turn off. Those skilled in the art will appreciate that any appropriately tested relay (e.g., a tested electromechanical relay) may be used.
The triac 420 of the semiconductor switch 416 is a gate-controlled thyristor in which current is able to flow in both directions. The relay 414 and/or the triac 420 may perform as one or more switches. For example, the controller 426 may open the relay 414 and deactivate the triac 420 to create an open circuit to disconnect the capacitor 412.
Those skilled in the art will appreciate that any switch may be used. For example, a switch S, such as an IGBT, thyristor pair, or thyristor/diode arrangement may also be used. In another example, a mosfet or IGBT may be used with a diode in parallel to control the capacitor 412.
Those skilled in the art will appreciate that the relay 414 and the triac 420 may work together to preserve the life of all or some of the components of the switch-controlled VAR source 400. The controller 426 may be configured to control the relay 414 and the triac 420 to switch off the circuit in a manner that avoids transients or other undesired power characteristics that may impact the lifespan of the circuit. For example, the controller 426 may ensure that the relay 414 is open (e.g., instruct the relay 414 to open if the relay 414 is closed) before instructing the triac 420 to deactivate (e.g., 1⁄2 cycle later). This process may prevent sparking or arcing across the relay 414 and, further, may preserve the life of the relay 414. In some embodiments, the triac 420 may be switched on and, after a sufficient delay, the relay 414 may be closed. The controller 426 may then instruct the relay 414 to open thereby protecting the one or more components of the circuit.
In various embodiments, the switch-controlled VAR source 400 comprises the relay 414 but not the semiconductor switch 416. In one example, the controller 426 may instruct the relay 414 to open or close thereby enabling or deactivating the capacitor 412. In other embodiments, the switch-controlled VAR source 400 comprises the semiconductor switch 416 but not the relay 414. The controller 426 may similarly control the triac 420 to enable or disable the capacitor 412.
The optional resistor 418 may be a negative temperature coefficient (NTC) resistor or thermistor. The NTC resistor 418 is a type of resistor whose resistance may vary with temperature. By controlling the NTC resistor 418, the triac 420 may be activated or deactivated without waiting for a zero voltage crossing of the AC power from the line 402 allowing insertion of the VAR source with minimal delay. For example, without the NTC resistor 418, the triac 420 may only be activated when AC voltage crosses zero volts. The NTC resistor 418 may be configured such that the triac 420 may be activated at any point with little or no undesirable effect (e.g., minimal or reduced inrush).
Resistors 422 and 424 may attenuate filter the signal from the line 402 to be received by the controller 426.
The controller 426 may be configured to determine a proximate voltage based on the voltage of line 402 and may enable or disable the capacitor 412. In various embodiments, the controller 426 is a processor such as a microprocessor and/or a Peripheral Interface Controller (PIC) microcontroller may detect voltage of the feeder 402.
In some embodiments, based on the voltage, the controller 426 may control the relay 414 and/or the triac 420 to open or close the circuit thereby enabling or disabling the capacitor 412. For example, if the voltage detected is not desirable, the controller 426 may enable the capacitor 412 by commanding the triac 420 to activate and/or the relay 414 to close. The capacitor 412 may then compensate for reactive power (e.g., regulate network voltage).
Those skilled in the art will appreciate that there may be a delay in the response of relay 414 (e.g., the relay 414 may be an electromechanical relay that is slow to react when compared to the triac 420). In this example, the command to open the relay 414 may be sent in advance of the command to deactivate the triac 420.
One of the most common failure mechanisms for capacitors on the grid is overvoltage. In some embodiments, the relay 414 and triac 420 may be deactivated when overvoltage is detected thereby protecting the capacitor(s).
The controller 426 may delay activation of the switch (e.g., relay 414 and semiconductor switch 416). In various embodiments, a multitude of switch-controlled VAR sources 400 which react to voltages within a power grid. In order to prevent infighting among the switch-controlled VAR sources 400, one or more of the devices may delay enabling or disabling the VAR compensation component (e.g., capacitor 412). In various embodiments, the controller of each switch-controlled VAR source 400 includes a different delay. As a result, each switch-controlled VAR source 400 may activate the switch to regulate voltage at a different time thereby giving each device time to detect voltage changes that may result from one or more switch-controlled VAR sources 400.
Those skilled in the art will appreciate that the delay may be set during manufacture of the switch-controlled VAR source 400 or may be uploaded from a centralized communication facility. The delay may be randomly set for each different switch-controlled VAR source 400.
The power supply unit (PSU) may adapt the power to be suitable to the controller 426. In some embodiments, the controller 426 is supplied from power supplied by the line 402, batteries, or any other power source. The PSU 428 may be any power supply.
Although FIG. 4a depicts the line coupled to the resistor 422 as being on the unprotected side of the fuse 404, those skilled in the art will appreciate that the fuse 404 may protect the controller 426 and PSU 428. For example, the resistor 422 may be coupled to the line 402 via the fuse 404.
In various embodiments, the switch-controlled VAR source 400 may operate both dynamically and autonomously to regulate voltage and/or compensate for grid faults. Those skilled in the art will appreciate that the switch-controlled VAR source 400 may adjust reactive power and thus the network voltage based on detected voltage without detecting or analyzing current. In some embodiments, load current information can be derived from an additional current sensor, or from the smart meter.
In some embodiments, the switch-controlled VAR source 400 may comprise an inductor which may be used to adjust voltage. For example, one or more inductors may be in place of capacitor 412. In another example, one or more inductors may be in parallel with the capacitor 412. The inductor(s) may be coupled to the fuse 404 (or a different fuse) and may be further coupled to a separate switch. For example, the inductor(s) may be coupled to a relay in parallel with a triac (or mosfet or IGBT) which may perform switching similar to the relay 414 and the semiconductor switch 416. The controller 426 may enable the inductor and disable the capacitor 412 by enabling one switch and creating an open circuit with the other. Similarly, the controller 426 may disable the inductor and enable the capacitor 412 or, alternately, disable both. Those skilled in the art will appreciate that the triac associated with the inductor may also be coupled to an NTC resistor to allow the triac to be deactivated at any time.
The switch-controlled VAR source 400 may be shunt-connected to the power distribution grid. In one example, the switch-controlled VAR source 400 is coupled in shunt via conductive lines 402 and 430 at or proximate to a residence or other commercial load. A shunt connection may be the connection of components within a circuit in a manner that there are multiple paths among which the current is divided, while all the components have the same applied voltage.
In one example, a feed line may extend from a transformer to one or more loads (e.g., residences). The feeder may also be coupled with a switch-controlled VAR source 400 in shunt. In some embodiments, if the switch-controlled VAR source 400 fails or was otherwise inoperative, the delivery of power by the power distribution grid is not interrupted because of the shunt connection (e.g., even if the connection to the switch-controlled VAR source 400 became an open circuit, there may be no interruption of power between the transformer and the one or more loads along the feed line).
In various embodiments, the switch-controlled VAR source 400 may be collocated inside or with a utility meter (e.g., smart meter), so that installation can be piggybacked, saving the utility in total installation and reading costs. The switch-controlled VAR source 400 may leverage a communication link inside a smart meter to communicate with the utility, take VAR dispatch or voltage set-point commands, and/or inform the utility of malfunction. Multiple switch-controlled VAR sources 400 may be collocated in a common housing and can be mounted on another grid asset, such as a pole-top or pad-mount transformer. This may allow lower cost VAR compensation, reduce the cost of a communication link, and allow additional value to be derived, such as assessing status and life expectancy of the asset.
In various embodiments, a plurality of switch-controlled VAR sources may each comprise a communication module. A communication module is any hardware configured to communicate wirelessly or by wire with one or more digital devices or other shunt-connected, switch-controlled VAR sources. The communication module may comprise a modem and/or an antenna.
One or more of the switch-controlled VAR sources may receive one or more set points with which to compare against voltage to assist in the determination to engage the VAR compensation component. A set point may be a predetermined value to improve voltage regulation. The processor of switch-controlled VAR source may determine whether to adjust voltage based on the comparison of the proximate voltage to the set points. Those skilled in the art will appreciate that the set points may be different for different switch-controlled VAR sources.
For example, the switch-controlled VAR source may compare detected voltage of a feeder (e.g., proximate voltage) to one or more set points to make the determination of whether to activate the capacitor based on the comparison. For example, if the detected voltage is higher than a previously received set point, the switch-controlled VAR source may enable the capacitor to reduce voltage. Alternately, if the voltage is lower than a previously received set point, the switch-controlled VAR source may disable an otherwise active capacitor in order to reduce voltage.
In some embodiments, a communication facility may dispatch and/or update one or more set points. The switch-controlled VAR sources may communicate via a cellular network, power line carrier network (e.g., via the power grid), wirelessly, via near-field communications technology, or the like. The communication facility may update set points of any number of switch-controlled VAR sources at any rate or speed. For example, the communication facility may update set points based on changes to the grid, power usage, or any other factors.
In some embodiments, one or more of the switch-controlled VAR sources may both receive and provide information. For example, one or more of the switch-controlled VAR sources may provide voltage information, current information, harmonic information, and/or any other information to one or more communications facilities (e.g., digital devices).
The information detected, received, or otherwise processed by one or more of the switch-controlled VAR sources may be tracked and assessed. For example, voltage and/or other power information may be tracked by the VAR source or a centralized facility to determine usage rates and identify inconsistent usage. A history of expected usage may be developed and compared to updated information to identify changes that may indicate theft, failure of one or more grid components, or deteriorating equipment. In some embodiments, one or more switch-controlled VAR sources may provide information to monitor aging equipment. When changes to voltage or other information indicates deterioration or degradation, changes, updates, or maintenance may be planned and executed in advance of failure.
Those skilled in the art will appreciate that the controller of the switch-controlled VAR source may enable or disable an inductor. In some embodiments, as discussed herein, the switch-controlled VAR source may comprise an inductor and a capacitor in parallel. In some examples, based on the comparison of the detected voltage to one or more received set points, the controller of the shunt-connected, switch-controlled VAR source may enable or disable the inductor and the capacitor independently.
FIG. 4b is a graph that depicts activating the semiconductor switch relative to the relay to engage VAR compensation in some embodiments. As discussed herein, when activating the switch-controlled VAR source 400, the controller 426 may be configured to activate the triac 420 prior to activating the relay 414. In some embodiments, the controller 426 may activate the relay 414 following a predetermined delay. The delay may be any delay. In one example, the controller 426 may receive a predetermined delay (e.g., as software or firmware) during calibration or installation either before or after manufacture of the switch-controlled VAR source 400.
As depicted in FIG. 4b, the triac 420 may be activated when the voltage is low and/or the capacitive current is approximately 0. After a delay which may be, for example, approximately a cycle, the relay 414 may be closed. Those skilled in the art will appreciate that, with the NTC resistor 418, the triac 420 may be activated at any time. Further, the relay 414 may be closed at any time after the triac 420 is active (i.e., the delay may be any length of time).
FIG. 4c is a graph that depicts deactivating the semiconductor switch relative to the relay 414 to disengage VAR compensation in some embodiments. As discussed herein, when deactivating the switch-controlled VAR source 400, the controller 426 may be configured to ensure that the relay 420 is closed prior to deactivating the triac 420. The controller 426 may subsequently deactivate (open) the relay 420. In some embodiments, the controller 426 may deactivate the relay triac 414 following a predetermined delay. The delay may be any delay which may be software or firmware received during calibration or installation.
As depicted in FIG. 4c, the relay 420 may be closed at any time. In some embodiments, the controller 426 confirms that the relay 420 is closed. If the relay 420 is open, the controller 426 may control the relay 420 to close. After a delay (e.g., after approximately a cycle or any time), the controller 426 may deactivate the triac 420. Those skilled in the art will appreciate that the triac 420 may be deactivated at any point. The controller 426 may control the relay 414 open after the triac 420 is deactivated. In some embodiments, the controller 426 controls the relay 414 to open after a predetermined delay. The delay may be equal or not equal to the delay between closing the relay and deactivating the triac 414.
FIGS. 5a and 5b are graphs 500 and 508 that depict a desired voltage range in relation to set points in some embodiments. In various embodiments, a switch-controlled VAR source may comprise a single set point 502 (e.g., 240 volts). The switch-controlled VAR source may be configured to adjust voltage (e.g., through controlling the VAR compensation component) by comparing the detected voltage to the set point 502. Threshold 504 and 506 may identify an allowed voltage range (e.g., +/−2 volts) before the switch-controlled VAR source may enable or disable the VAR compensation component.
Those skilled in the art will appreciate that the thresholds 504 and 506 may be equal or unequal. Further, the thresholds 504 and 506 may be change over time (e.g., through an algorithm that changes based on time of day, season, temperature, voltage, current, rate of change in detected voltage, or the like).
FIG. 5b is a graph depicting voltage over time and identifying set points 510 and 512 in some embodiments. Set points 510 and 512 bracket the desired “ideal” voltage (e.g., 240 volts). In various embodiments, a switch-controlled VAR source may detect a proximate voltage and compare the detected voltage to set points 510 and 512. If the voltage is higher than set point 510 or lower than set point 512, the switch-controlled VAR source may enable/disable a VAR compensation component or otherwise regulate the voltage to make corrections. Although the impact of one switch-controlled VAR source may not change the network voltage significantly, multiple VAR sources operating autonomously to change the network voltage may regulate the voltage over multiple points. As such, a limited change by many devices may create significant efficiencies and improvements in distribution with limited additional cost.
In various embodiments, one or more of the switch-controlled VAR sources do not have communication modules but rather may comprise set points previously configured at manufacture. In other embodiments, one or more of the switch-controlled VAR sources comprise communication modules and, as a result, set points may be altered or updated by other switch-controlled VAR sources or one or more communication facilities.
In some embodiments, one or more of the switch-controlled VAR source may comprise regulation profiles. A regulation profile may comprise a policy that changes one or more set points based on time, proximate conditions, or usage in order to improve conservation. If usage is likely to spike (e.g., based on heat of the day, business loads, residential loads, or proximity to electric car charging facilities), a regulation profile may adjust the set points accordingly. As a result, set points may be changed depending upon sensed usage, voltage changes, time of day, time of year, outside temperature, community needs, or any other criteria.
Those skilled in the art will appreciate that one or more of the switch-controlled VAR sources may receive regulation profiles at any time over the communications modules. In some embodiments, one or more of the switch-controlled VAR sources may not comprise a communication module but may still comprise one or more regulation profiles which may have been previously configured.
FIG. 6 is a flow chart for voltage regulation by a switch-controlled VAR source in some embodiments. In step 602, the switch-controlled VAR source may receive a first set point. In some embodiments, the switch-controlled VAR source comprises a communication module that may receive the set point from a digital device (e.g., wirelessly or through a communication module of a smart meter), from another shunt-connected, switch-controlled VAR source (e.g., through near field communication), power line carrier communication, or the like. The set point may activate the switch-controlled VAR source to enable VAR compensation or, in some embodiments, the set point may be a voltage set point which may be compared to a detected proximate voltage.
In some embodiments, the utility may include a VAR source server or other device configured to communicate with different VAR sources (e.g., via WiFi, cellular communication, near field communication, wired, or power line carrier). In various embodiments, the VAR source server may communicate with one or more other servers to communicate with the VAR sources. For example, the VAR source server may communicate through smart meters or servers that communicate with smart meters. One or more smart meter may comprise a VAR source or otherwise communicate with one or more VAR sources.
The first set point (e.g., a voltage set point) may be a part of a regulation profile. In one example, a plurality of regulation profiles may be received by the switch-controlled VAR source either during manufacture or through a communication module. Each regulation profile may comprise one or more different set points to improve power distribution and/or efficiency based on a variety of factors (e.g., time of day, history of usage, type of load, green energy production, and the like). In various embodiments, the processor of the switch-controlled VAR source may switch regulation profiles based on detected voltage, rate of change of voltage, communication with other switch-controlled VAR sources, communication with a VAR source server, temperature, time of day, changes to the grid or the like. Once implemented from the regulation profile, the processor of a switch-controlled VAR source will continue to detect proximate voltage and compare the voltage to the new set point(s) in order to determine whether a VAR compensation component should be enabled or disabled.
In step 604, the controller 426 (i.e., processor) detects proximate voltage at the edge of the network (e.g., near a load of the power grid). Proximate voltage is the voltage received from line 402 (e.g., the voltage at the point the line 402 is coupled to a feeder line or grid asset. The proximate voltage may be the voltage of where the shunt-connected, switch-controlled VAR source 400 is coupled in the power distribution grid at the time of voltage detection.
In some embodiments, the switch-controlled VAR source may detect voltage through another switch-controlled VAR source or a grid asset. In some embodiments, a smart meter, transformer, or other power device may detect voltage. The switch-controlled VAR source may receive the detected voltage from the other device or intercept the detected voltage at or during transmission.
In step 606, the controller 426 may compare the detected proximate voltage to any number of set points to determine if the VAR compensation component may be enabled or disabled. As discussed herein, the controller 426 may control a switch (e.g., relay and/or semiconductor switch) to enable or disable one or more capacitors and/or one or more inductors based on the comparison. Those skilled in the art will appreciate that the determination to enable or disable the VAR compensation component may be made by the processor of the switch-controlled VAR source as opposed to a centralized facility. The determination may be made autonomously and independent of other switch-controlled VAR sources.
Through the operation of any number of switch-controlled VAR sources operating to regulate voltage within the desired range, voltage regulation of the network may be achieved. Further, the voltage range may be flat and capable of dynamically responding to changes along one or more distribution lines and/or feeders.
In step 608, the controller 426 may delay switching the VAR compensation component for a predetermined time. As discussed herein, in order to avoid infighting between any number of switch-controlled VAR sources, one or more of the switch-controlled VAR sources may delay switching for a predetermined time. The time of delay may be different for different switch-controlled VAR source. For example, even if a first switch-controlled VAR source detects the need to regulate voltage, the first switch-controlled VAR source may wait until after a second switch-controlled VAR source has made a similar determination and enabled VAR compensation. The first switch-controlled VAR source may detect the change in the network and make another determination whether to further enable additional VAR compensation. As a result, multiple switch-controlled VAR source may not constantly correct and re-correct changes in network voltage caused by other switch-controlled VAR sources.
The delay time may be updated by the VAR source server, other switch-controlled VAR sources, or be a part of the regulation profile (e.g., which may comprise multiple different delay times depending on the need). In some embodiments, if detected voltage is changing at a substantial rate, the delay time may be accelerated. Those skilled in the art will appreciate that there may be many different ways to provide, update, and/or alter the delay time of a switch-controlled VAR source.
In step 610, after detecting and determining a need to change the network voltage and waiting the delay time, the switch-controlled VAR source may again detect any changes to the voltage and compare the change against one or more of the set points. If there remains a decision in step 612 that is consistent with the previous determination in step 606 (e.g., that the VAR compensation component should be enabled or disabled), then the switch-controlled VAR source may adjust the network voltage by engaging a switch to enable or disable the VAR compensation component.
In one example, if the proximate voltage is above a first set point, the controller 426 may control the relay 414 and the triac 420 to either form the connection to the line 402 or to confirm that the relay 414 is closed and/or the triac 420 is enabled. If the proximate voltage is below the second set point, the controller 426 may control the relay 414 and the triac 420 to either open the connection to the line 402 or to confirm that the relay 414 is open and/or the triac 420 is disabled.
In some embodiments, each of the plurality of shunt-connected, switch-controlled VAR sources may increase leading volt-ampere reactive if the set point is higher than the detected proximate voltage and decrease leading volt-ampere reactive if the set point is lower than the detected proximate voltage.
In some embodiments, the controller 426 may enable or disable an inductor based on the comparison of the detected proximate voltage to the set points. For example, based on the comparison, the controller 426 may disable the capacitor and enable an inductor (e.g., the controller 426 may control the relay 414 the triac 520 to create an open circuit to disable the capacitor while controlling another relay and another triac to enable the inductor to regulate voltage).
In various embodiments, voltage may be tracked over time. In some embodiments, the controller 426 may track the detected proximate voltage over time and provide the information to another switch-controlled VAR source and/or a digital device. For example, one switch-controlled VAR source may be in communication with any number of other switch-controlled VAR source (e.g., in a pole top enclosure). The one or more switch-controlled VAR sources may be a part of any grid asset such as a substation or transformer.
In some embodiments, the tracked detected voltage may be assessed and/or compared to a voltage history. The voltage history may be a history of past usage or may indicate an expected usage. In various embodiments, the controller 426 or a digital device may detect a failing grid asset based on the comparison. For example, the expected output and/or input of a grid asset may be determined and compared to the tracked detected proximate voltage. If the currently detected proximate voltage and/or tracked detected proximate voltage are not within the expected range, the tracked detected proximate voltage may be reviewed to determine if a grid asset has failed or is deteriorating. As a result, deteriorating equipment that may need to be replaced or receive maintenance may be identified and budgeted before performance significantly suffers thereby improving efficiency in both power delivery and upkeep of the distribution power grid.
Those skilled in the art will appreciate that potential theft may be identified. In various embodiments, each switch-controlled VAR source may detect and track voltage. The tracked voltage may be logged and/or provided to a VAR source server (e.g., via the communication module or antenna of another digital device such as a smart meter). The VAR source server may, for example, track voltage identified by all of the switch-controlled VAR sources along a feeder line and compare the voltage to consumption as tracked by the utility (e.g., via smart meters). Based on the comparison, theft may be detected. Further, based in part on the effect of any number of switch-controlled VAR sources, the theft may be localized for further investigation.
As suggested herein, massively distributed dynamically controllable VAR source strategy leverages other costs that a public utility is already bearing. For example, a switch-controlled VAR source may be located inside a smart meter or may be co-located with a smart meter so that the installation can proceed concurrently with meter installation or reading/servicing. These meters sense voltage and current to calculate the power consumption of the load, and have communications to relay the information to a central data repository. The cost of installing these is already built into the meter cost.
A simple communication mechanism with the meter may allow communication between the meter and the switch-controlled VAR source (e.g., for reporting to the utility on status, receiving set points, receiving delay times, and/or for taking commands to activate). In some embodiments, the load current measurement inside the smart meter may be communicated to the switch-controlled VAR source for use in the determination for voltage regulation.
In various embodiments, a meter switch-controlled VAR source may be very compact and ultra low-cost. In some embodiments, a typical rating may be 240 VARs at 240 volts, corresponding to 2 Amperes of capacitive current. This may be approximately the VAR drop across the leakage impedance of a 5% impedance transformer supplying 5 kW to a customer. Utility networks and asset loading calculations may be done on a statistical basis, assuming a load diversity factor. If all the meters (e.g., 10,000) on a distribution circuit have switch-controlled VAR sources, then there may be 2.5 MVARs of dynamically controllable VARs on that line, deployed on a per phase basis. Raising the compensation per switch-controlled VAR source to 500 VARs, for example, may only raise cost marginally, but may provide 5.0 MVARs of dynamic VAR compensation.
In various embodiments, the switch-controlled VAR source may be integrated into or be alongside any utility asset, such as a pole-mount transformer or lighting pole. As discussed herein, communication capability is not a requirement for switch-controlled VAR source operation, but may augment the ability to take dispatch instructions and to communicate status to the utility. A possible implementation would be to bundle multiple switch-controlled VAR sources into a common housing and locating the bundle within or proximate to a transformer supplying multiple residential or commercial loads. The bundle may be connected to the transformer on the low-voltage side thereby minimizing or reducing requirements for BIL management on the switch-controlled VAR sources.
Those skilled in the art will appreciate that the bundling may allow integration of a single communication module with multiple switch-controlled VAR sources, thereby allowing greater cost savings. This class of device may be measured in cost as a ratio of the dollars of cost of the actual device to the kiloVARs delivered ($/kVAR). This bundling may also allow the use of a single power supply and controller and provide reliable information on the switching behavior of the different switch-controlled VAR source.
In a bundled unit, it may be possible to minimize or reduce impact of harmonics on the grid. This implementation may maintain the basic features of the single user units, however, the bundle may provide more value to utility customers by integrating current and temperature measurement into the unit, using transformer loading and temperature excursions to calculate impact on transformer life, and/or communicating transformer status to the utilities. The bundled switch-controlled VAR source implementation, particularly when located in close proximity to pole-top or pad-mount transformers as conventionally used in the utility industry, may offer high value to the utility by performing dynamic volt-VAR optimization, and serving as an asset monitor for the millions of transformers located on the distribution network.
In various embodiments, in order to avoid multiple switch-controlled VAR sources from adjusting and readjusting the reactive power based on changes perceived by other switch-controlled VAR sources, one or more controllers may activate or deactivate different switch-controlled VAR source based on a different detected voltage.
The switch-controlled VAR source may perform reactive power compensation based on measured line voltage and not load or line current. As a result, the switch-controlled VAR source may not perform power factor correction. Power factor compensation may look at the line current and voltage to assess the level of correction required and may operate to bring customer load power factor to unity. Power factor correction may not manage reactive power for grid voltage regulation. Those skilled in the art will appreciate that power factor correction is often used to reduce penalties, and may reduce energy supplied by the utility to some extent (if loads have a significant lagging power factor). In other embodiments, the switch-controlled VAR source may detect current (e.g., via a meter, grid asset, or assessment by the controller 524) and perform power factor correction in addition to voltage regulation using a weighting algorithm.
FIG. 7 is a time sequence of events of network regulation with two switch-controlled VAR sources in some embodiments. In various embodiments, the first and second switch-controlled VAR sources may be proximate to each other (e.g., coupled to the same or related feeder line). Changes to voltage caused by one switch-controlled VAR source may be detected and reacted to by the other switch-controlled VAR source. As a result, to avoid infighting (e.g., constant correcting and re-correcting voltage in view of other switch-controlled VAR source actions), the switching process for one or more of the switch-controlled VAR sources may be delayed by a different delay time. As a result, even if the first switch-controlled VAR source originally determined to enable the VAR compensation component based on the detected voltage, the first switch-controlled VAR source may wait the delay time thereby giving the second switch-controlled VAR source an opportunity to correct voltage. If the action of the second switch-controlled VAR source was sufficient, then the first switch-controlled VAR source may detect the change and not perform any switching action.
In step 702, the first switch-controlled VAR source detects a first voltage proximate to a first edge of the network. In some embodiments, the first switch-controlled VAR source detects a voltage at a particular load on the low power side of a transformer. In step 704, the first switch-controlled VAR source may compare the first proximate voltage to a set point to determine if the VAR compensation component of the first switch-controlled VAR source should be enabled. In step 706, the switch-controlled VAR source may delay switching to engage the VAR compensation component for a first predetermined time (i.e., for a first delay).
In step 708, the second switch-controlled VAR source detects a second voltage proximate to a second edge of the network. In some embodiments, the second switch-controlled VAR source detects a voltage at a particular load on the low power side of a transformer. In one example, both the first and second switch-controlled VAR source may be coupled to the same feeder line and/or on the same side of the same transformer. In step 710, the second switch-controlled VAR source may compare the second proximate voltage to a set point to determine if the VAR compensation component of the second switch-controlled VAR source should be enabled. In step 712, the switch-controlled VAR source may delay switching to engage the VAR compensation component for a second predetermined time (i.e., for a second delay).
The first and second delay may be for different periods of time. As a result, each switch-controlled VAR source may delay acting on the comparison of the detected proximate voltage to one or more set points until other switch-controlled VAR sources have had an opportunity to correct voltage of the network. If, after the predetermined time, the initial determination is still necessary (e.g., the proximate voltage has remained unchanged or still outside of the set point(s) after expiration of the delay time), then a switch-controlled VAR source may control a switch to engage or disengage the VAR compensation component.
In various embodiments, delays may be used to avoid infighting between two or more switch-controlled VAR sources. The delays may be updated and/or communicated by another digital device (e.g., wirelessly, over power line carrier, or via a smart meter).
As discussed herein, the delay time may be altered based on conditions of the power network. For example, if the rate of change of voltage, current, or any power characteristic is significant, the delay time may be shortened or extended. In some embodiments, there are different delay times for different switch-controlled VAR sources, however, all of the delay times may be changed in the similar manner (e.g., shortened or extended) under similar conditions.
In step 714, the second switch-controlled VAR source detects proximate voltage after the second delay time (e.g., after the second predetermined delay). In various embodiments, the switch-controlled VAR sources detect proximate voltage at predetermined times or continuously. Once the delay is expired, the controller of the second switch-controlled VAR source may retrieve the last detected voltage or detect voltage of the line. In step 716, the second switch-controlled VAR source determines whether to enable VAR compensation based on comparison of the last detected proximate voltage to one or more set points.
In step 718, if, based on the comparison, the second switch-controlled VAR source determines to enable the VAR compensation component, the second switch-controlled VAR source may adjust the network voltage (e.g., by regulating VAR).
In various embodiments, the first switch-controlled VAR source may continue the delay before switching the related VAR compensation component. The first switch-controlled VAR source may detect a change in voltage caused by the action of the second switch-controlled VAR source. If, after the first delay, the newly detected proximate voltage is still outside a range established by one or more set points, the first switch-controlled VAR source may engage the VAR compensation component. If, however, after the delay, the action of the second switch-controlled VAR source improves network voltage (e.g., the newly detected voltage is within a range of the one or more set points), the first switch-controlled VAR source may not take further action.
In step 720, the first switch-controlled VAR source detects proximate voltage after the first delay time (e.g., after the first predetermined delay). In one example, once the delay is expired, the controller of the first switch-controlled VAR source may retrieve the last detected voltage or detect voltage of the line. In step 722, the first switch-controlled VAR source determines whether to enable VAR compensation based on comparison of the last detected proximate voltage to one or more set points.
In step 724, if, based on the comparison, the first switch-controlled VAR source determines to enable the VAR compensation component, the first switch-controlled VAR source may adjust the network voltage (e.g., by regulating VAR).
Those skilled in the art will appreciate that the voltage set points may be preconfigured. In some embodiments, one or both switch-controlled VAR sources may comprise communication module(s) configured to receive set point(s). In one example, a switch-controlled VAR source may receive new set points that may replace or supplement previously received and/or pre-existing set points.
Although only two switch-controlled VAR sources are discussed regarding FIG. 7, those skilled in the art will appreciate that there may be any number of switch-controlled VAR sources working to adjust the network volt ampere reactive (e.g., each may have different delays to prevent infighting).
FIG. 8 is a graph that depicts a typical voltage profile at various nodes in the prior art. Colored dots represent various times of the day. With the prior art's approaches, a VVO or CVR solution is limited by the highest and lowest voltage nodes.
FIG. 9 is a graph that depicts relatively flat voltage profile at various nodes in some embodiments realized with 240 switch controlled VAR sources operating to regulate the voltage along the edge of the distribution feeder. Edge of Network Voltage Optimization (ENVO) as discussed herein may be achieved through dynamic, autonomous actions of multiple switch-controlled, VAR sources at or near the edge of the network. The switch-controlled, VAR sources may react automatically and autonomously (e.g., independent switching to enable or disable a VAR compensation component) to varying levels of loading on the feeder, maintaining the edge of network voltage all along the feeder within a tight regulation band.
This regulation may be maintained automatically even as heavily loaded regions shift randomly and stochastically over the design range for the feeder. In some embodiments, what results is a remarkably flat voltage profile across all measured edge of network points which is unprecedented under current technology. The graph shows voltage with ENVO that is relatively flat, voltage without ENVO that drops significantly, and a relatively flat voltage utilizing ENVO in CVR mode. The voltage spread is seen to reduce from +1/−5% without compensation to +/−1% with ENVO when operated with the same feeder and the same load.
FIG. 10 is a graph that depicts a dynamic response of the ENVO system to line voltage changes (which can be caused by solar PV plants), as well as to step changes in line loading in some embodiments. In both cases, the voltage across the entire line is seen to quickly stabilize, demonstrating the high speed response. It may be noted that the initial changes to the lines beginning at time 0 and the changes to the lines after time 2.5 are a part of the set up and deactivation of a simulation.
FIG. 10 shows the ability to implement CVR with ENVO compensation, realizing a flat and reduced voltage profile along the length of the feeder. Coordinating with an LTC at the substation, it is seen that the edge of network voltage may be reduced by 3-6% (e.g., 4%) giving a reduction of 3.2% of energy consumed under a typical CVR factor of 0.8. This level of performance is simply not possible with conventional VVC or VVO solutions in the prior art.
The ENVO system operation may not be generally impacted by network configuration or by direction of power flows (e.g., from sporadic green energy generation), as are other VVO methods that rely on concentrated positions of devices that may work for one configuration but not another. As a result, network reconfiguration due to Fault Detection Isolation and Restoration (FDIR) schemes may not negatively impact the ENVO. Further, operation of tap changers may be simplified, as can the implementation of CVR functionality due to the increased control of the edge of network voltage profile. Moreover, the ENVO system sources may respond rapidly (e.g., within or much less than a cycle such as equal or less than 16.6 ms), to system faults helping to avert cascading failures such as Fault Induced Delayed Voltage Recovery or FIDVR events.
While no communication is required to achieve a flatter voltage profile along the entire length of the line, in various embodiments, inexpensive slow-speed variable-latency communications may allow advanced functions such as VVO and CVR (e.g., through set points), without the complexity of current VVO systems, at a cost that is substantially lower. Further, significant opportunities may exist to leverage existing investments in communications and other grid infrastructure to further reduce the total cost of ownership.
In mature markets, such as in the US, the ENVO system may implement a cost-effective distribution automation technology with a strong return on investment (ROI). In some embodiments, the ability to dynamically and/or automatically compensate for line-voltage drops all along the feeder allows building longer feeders, allows an increase in the capacity of existing feeders, particularly in rural areas, and significantly reduces the number of tap changing regulators needed as well as reduces the frequency of tap changes. It may also allow easier integration of distributed generation resources and may counteract the rapid voltage fluctuations caused by green energy generation (e.g., unpredictable clouds or wind change).
FIG. 11a is another circuit diagram of a plurality of switch-controlled VAR sources that may be within or next to a pole top transformer or any grid asset in some embodiments. FIGS. 1b-3 focus on different portions of the circuit diagram of FIG. 11a. In various embodiments, any transformer (e.g., pole top transformer), smart meter, meter, or grid asset may comprise one or more VAR sources. Each of a plurality of VAR sources may make determinations and adjust voltage autonomously from others in the pole top transformer. In some embodiments, a plurality of VAR sources may share any number of components, including, for example, a controller and/or a power supply unit.
In various embodiments, one or more controllers may control two or more of the VAR sources in a pole top transformer to coordinate voltage adjustment. For example, a single controller may detect proximate voltage, compare the voltage against one or more set points, determine a voltage adjustment, and determine which of the VAR sources should be enabled (or disabled) to achieve the desired effect and provide the appropriate commands.
In some embodiments, one or a subset of the VAR sources may comprise one or more inductors in parallel with one or more capacitors. Those skilled in the art will appreciate that the inductor may be enabled when necessary to adjust voltage. In other embodiments, there may any number of inductors and any number of capacitors in any number of the shunt-connected, switch-controlled VAR sources.
FIG. 11a depicts a switch-controlled VAR source 1102, a plurality of switch-controlled VAR sources 1104, a controller 1106, and a power module 1108. The switch-controlled VAR source 1102 may be any one of the plurality of switch-controlled VAR sources 1104. The switch-controlled VAR source 1102 may be similar to the switch-controlled VAR source 400. The plurality of switch-controlled VAR sources 1104 may comprise any number of switch-controlled VAR sources. The controller 1106 may be a microprocessor, PIC, or any processor. The power module 1108 may perform voltage detection and/or zero crossing threshold detection (ZCD).
Those skilled in the art will appreciate that the circuits depicted in FIG. 11 may be a part of any device or combination of devices and is not limited to pole top transformers. For example, there may be a plurality of switch-controlled VAR sources 1104, controllers 1106, and/or power modules 1108 associated with any grid asset or as a standalone unit (e.g., coupled to a feeder line in shunt).
FIG. 11b depicts a switch-controlled VAR source 1102 in some embodiments. The switch-controlled VAR source 1102 may comprise a fuse, capacitor, harmonic sensor, zero voltage detection for ADC circuitry, I sense detection for ADC circuitry, and a relay circuit. The switch-controlled VAR source 1102 may be coupled to a feeder in shunt, adjust reactive power, and provide information (e.g., harmonic information, ZVD, and/or I sense signals) to the controller 1106. The triac and relay circuit may be controlled by signals from the controller 1106.
In some embodiments, the harmonic sensor may detect harmonic resonance which may be subsequently reduced or eliminated. The I sense detection for ADC circuitry and zero voltage detection for ADC circuitry may be used to detect current, harmonics, and/or voltage which may allow the controller 1106 to better protect the circuit and make adjustments for voltage regulation. The relay circuitry may be a part of the switch to enable or disable the capacitor.
FIG. 11c depicts a plurality of switch-controlled VAR sources 1104 in some embodiments. Each switch-controlled VAR source of FIG. 11c may include similar or dissimilar components from the other switch-controlled VAR sources. For example, one or more of the switch-controlled VAR sources may comprise an inductor in parallel with a capacitor. A single controller may control one or more of the switch-controlled VAR sources.
FIG. 11d (and FIGS. 11d-1, 11d-2, 11d-3, and 11d-4 which are exploded views of the corresponding sections/elements illustrated in FIG. 11d) depicts a controller 1106 in some embodiments. The controller 1106 may control any number of switch-controlled VAR sources 1104. The controller may receive information (harmonic information, ZVD, and/or I sense signals) from one or more of the switch-controlled VAR sources and use the information to control triacs, relays, and/or reduce harmonic resonance. For example, the controller 1106 may receive and make adjustments based on voltage detection of only one of the plurality of switch-controlled VAR sources 1104. Although only one processor is depicted in FIGS. 11a and 11d, those skilled in the art will appreciate that there may be any number of processors coupled to any number of switch-controlled VAR sources.
FIG. 11e depicts power module 1108 comprising ADC circuitry and ZCD circuitry coupled to the controller 1106 in some embodiments. The ADC circuitry and ZCD circuitry may be coupled to the feeder and provide information and/or power to the controller 1106. The ADC circuitry and ZCD circuitry may provide the controller 1106 power and/or information regarding voltage. In some embodiments, the controller 1106 controls one or more of the triacs of the plurality of the switch-controlled VAR sources 1102 based on the zero crossing detection.
Those skilled in the art will appreciate that other circuit designs, components, and the like may perform similar functionality or perform similar results and still be within the invention(s) described herein.
FIG. 12 is a block diagram of an exemplary digital device 1200. In some embodiments, the digital device 1200 may provide set points and/or profiles to one or more switch-controlled VAR sources. The digital device 1200 may also receive voltage and/or power tracking information which may be used to track usage, identify potential theft, and/or maintain grid assets. Further, in various embodiments, the digital device 1200 may coordinate and/or control any number of switch-controlled VAR sources.
The digital device 1200 comprises a processor 1202, a memory system 1204, a storage system 1206, a communication network interface 1208, an optional I/O interface 1210, and an optional display interface 1212 communicatively coupled to a bus 1214. The processor 1202 is configured to execute executable instructions (e.g., programs). In some embodiments, the processor 1202 comprises circuitry or any processor capable of processing the executable instructions.
The memory system 1204 is any memory configured to store data. Some examples of the memory system 1204 are storage devices, such as RAM or ROM. The memory system 1204 can comprise the ram cache. In various embodiments, data is stored within the memory system 1204. The data within the memory system 1204 may be cleared or ultimately transferred to the storage system 1206.
The data storage system 1206 is any storage configured to retrieve and store data. Some examples of the data storage system 1206 are firmware memory, flash drives, hard drives, optical drives, and/or magnetic tape. In some embodiments, the digital device 1200 includes a memory system 1204 in the form of RAM and a data storage system 1206 in the form of flash data. Both the memory system 1204 and the data storage system 1206 comprise computer readable media which may store instructions or programs that are executable by a computer processor including the processor 1202.
The communication network interface (com. network interface) 1208 can be coupled to a network (e.g., communication network 164) via the link 1216. The communication network interface 1208 may support communication over an Ethernet connection, a serial connection, a parallel connection, or an ATA connection, for example. The communication network interface 1208 may also support wireless communication (e.g., 802.16 a/b/g/n, WiMax). It will be apparent to those skilled in the art that the communication network interface 1208 can support many wired and wireless standards.
The optional input/output (I/O) interface 1210 is any device that receives input from the user and output data. The optional display interface 1212 is any device that is configured to output graphics and data to a display. In one example, the display interface 1212 is a graphics adapter. It will be appreciated that not all digital devices 1200 comprise either the I/O interface 1210 or the display interface 1212.
It will be appreciated by those skilled in the art that the hardware elements of the digital device 1200 are not limited to those depicted in FIG. 12. A digital device 1200 may comprise more or less hardware elements than those depicted. Further, hardware elements may share functionality and still be within various embodiments described herein. In one example, encoding and/or decoding may be performed by the processor 1202 and/or a co-processor located on a GPU (i.e., NVidia).
The above-described functions and components can be comprised of instructions that are stored on a storage medium such as a computer readable medium. The instructions can be retrieved and executed by a processor. Some examples of instructions are software, program code, and firmware. Some examples of storage medium are memory devices, tape, disks, integrated circuits, and servers. The instructions are operational when executed by the processor to direct the processor to operate in accord with embodiments of the present invention. Those skilled in the art are familiar with instructions, processor(s), and storage medium.
Various embodiments are described herein as examples. It will be apparent to those skilled in the art that various modifications may be made and other embodiments can be used without departing from the broader scope of the present invention(s). Therefore, these and other variations upon the exemplary embodiments are intended to be covered by the present invention(s).

## Claims

1. A system comprising:
a distribution power network;
a plurality of loads at an edge of the distribution power network, each load configured to receive power from the distribution power network; and
a plurality of shunt-connected, switch-controlled Volt-Ampere Reactive (“VAR”) sources, wherein each VAR source is located at or near the edge of the distribution power network, is configured to non-continuously monitor and detect a proximate voltage at or near the edge of the distribution power network, and comprises a processor and a VAR compensation component, the processor configured to enable the VAR source to determine, after a delay, whether to enable the VAR compensation component based on the proximate voltage and adjust network volt-ampere reactive by controlling a switch to enable the VAR compensation component based on the determination;
wherein the delay associated with each VAR source extends for a predetermined length of time that is not equal to the delay associated with any other of the plurality of VAR sources.

2. The system of claim 1, wherein different delays of different members of the plurality of shunt-connected, switch-controlled VAR sources prevents infighting between at least two of the different members.

3. The system of claim 1, wherein the delay of at least two of the plurality of shunt-connected, switch-controlled VAR sources is equal but the delay of a third of the plurality of shunt-connected, switch-controlled VAR sources is not equal.

4. The system of claim 1, wherein the switch comprises a semiconductor switch in series with a Negative Temperature Coefficient (“NTC”) or resistor, and wherein the semiconductor switch in series with the NTC or resistor is in parallel with a relay.

5. The system of claim 4, wherein the semiconductor switch is controlled by a first signal from the processor and the relay is controlled by a second signal from the processor, wherein the semiconductor switch controls enabling the VAR compensation component and relieves the relay of switching stress.

6. The system of claim 5, wherein the relay conducts when the semiconductor switch is active thereby reducing semiconductor device conduction losses.

7. The system of claim 6, wherein the semiconductor switch is configured to deactivate when the relay conducts.

8. The system of claim 1, wherein at least two of the VAR sources are on a low voltage side of a transformer of the power distribution network.

9. The system of claim 1, wherein the VAR compensation component comprises capacitors or inductors.

10. The system of claim 1, wherein the determination to enable the corresponding VAR compensation component is based on a comparison of the proximate voltage point to a voltage set point.

11. The system of claim 10, wherein at least two VAR sources comprise communication modules configured to receive the respective voltage set point.

12. The system of claim 10, wherein each VAR source increases leading volt-ampere reactive if the voltage set point is higher than the detected proximate voltage and decreases leading volt-ampere reactive if the voltage set point is lower than the detected proximate voltage.

13. The system of claim 10, wherein the communication module is configured to update the voltage set point and wherein a rate of update of the voltage set point is significantly slower than adjusting the network volt-ampere reactive by controlling the switch to enable the VAR compensation component based on the determination.

14. The system of claim 11, wherein the at least two of the plurality of shunt-connected, switch-controlled VAR sources receive different voltage set points.

15. The system of claim 1, wherein the processor is further configured to detect an overvoltage condition and disable the switch based on the detected overvoltage condition.

16. The system of claim 1, wherein the system self-determines which VAR compensation components of the VAR source are enabled and which VAR compensation components of the VAR source are not enabled.