Switching of small power grids using zero-crossing detection

Abstract

The technique enables switching of small power grids using zero-crossing detection. The flexible load management system includes a virtual critical load panel (vCLP) that utilizes breakers in cooperation with a companion module configured to sense power delivered to one or more loads to identify zero crossings. If a pre-configured number of consecutive missed zero crossings are detected, the companion module is alerted about a potential primary power loss and transitions to a virtual critical load (vCL) mode for load regulation before operating under local power. Upon detection of primary power loss, the companion module is configured for load activation (or deactivation) by the state of one or more vCL bits that configure each load to an ON or OFF state when operating under local power.

Description

[Technical Field]

[0001] The present disclosure relates generally to the field of power, and more particularly to systems and techniques for flexibly managing power consumption of loads on premises (buildings, stores). [Background technology]

[0002] Electric power system sources, such as generators and microgrids, are often deployed commercially locally by customers or users of facilities in various types and sizes. The total power capacity of a local power source, such as a generator or battery, may be less than the amount of power (energy) that a facility, such as a home or office, may consume. Therefore, during the switchover of power from utility power to a local power source (e.g., a microgrid), there is a need to prevent overload of the local power source while minimizing power outages during the switchover. However, existing load management solutions typically isolate the entire microgrid to allow power distribution adjustments in a fixed panel configuration to avoid overloads when ultimately switching to the local power source.

[0003] The above and further advantages of the embodiments herein may be better understood by reference to the following description in conjunction with the accompanying drawings, in which like reference numbers indicate identical or functionally similar elements. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 illustrates an exemplary deployment of a Flexible Load Management (FLM) system within a facility. [Figure 2] Block diagram of the companion module of the FLM system. DETAILED DESCRIPTION OF THE INVENTION

[0005] Overview

[0003] Embodiments described herein are directed to a small power grid switching technique using zero-crossing detection that prevents overloads upon eventual switchover to a secondary (local) power source while reducing power outages during the switchover, thereby eliminating the need for a separate controller or UPS to manage the small power grid. The flexible load management (FLM) system includes a virtual critical load panel (vCLP) utilizing breakers (circuit breakers) in cooperation with a companion module (i.e., an intelligent controller) for each branch circuit, configured to sense power delivered to one or more loads to identify zero crossings. If a preset number of consecutive missed zero crossings are detected, each companion module warns of a potential loss of primary power (e.g., unstable power from the utility grid) and subsequently transitions to virtual critical load (vCL) mode for load regulation before operating under local power. That is, a companion module controller configured to separately control power to each branch circuit detects the number of missed zero crossings indicating a loss of utility power and transitions to a virtual critical load mode where it immediately adjusts for reduced power to avoid overloading the local power source. Upon detection of a loss of primary power, the companion module is configured for load activation (or deactivation) according to the state of one or more vCL bits that configure each load to an on or off state when operating under local power.Advantageously, the vCL bit of the present technology eliminates the need for a Panel Bridge Controller (PBC) to command (e.g., by message exchange) a companion module to switch (turn on / off) the load in response to a main power loss, thereby eliminating the time (e.g., several seconds) spent exchanging messages that could result in load downtime (because the local power source is overloaded and trips its breaker). Furthermore, the time during which multiple missed zero crossings occur may coincide with the transition time of power supplied from the main power source to power supplied from the local power source, thereby significantly reducing downtime.

[0006] In one embodiment, vCLP is a preferential enumeration (i.e., prioritization) of loads within a facility, where the loads are deemed important enough to be protected by a local power source. According to this technique, the PBC first configures (sets) the state of the vCL bit and sends the configured vCL bit to the companion module. The vCLP is then dynamically configurable by the user in real time using the vCL bit. A loss of primary power can be detected by the companion module based on consecutive missed zero crossings. The default number of consecutive missed zero crossings can be configured as four, but any number of consecutive missed zero crossings can be pre-configured. For example, upon detection of four consecutive missed zero crossings, the companion module may transition to vCL mode and activate (maintain) or deactivate (reduce) power to each load before operating under local power, based on the state of the vCL bit associated with the load. Therefore, the local power may be overloaded tripping its breaker, thus requiring manual intervention to disconnect the excess load(s) (i.e., alleviate the overload condition) and to reset the local power breaker. Additionally, the PBC may reconfigure the vCL bit of any companion module that loses its state after a main power interruption.

[0007] explanation 1 illustrates an exemplary deployment of a flexible load management (FLM) system 100 within a facility, such as an office or residence. The FLM system 100 utilizes one or more virtual critical load panels (vCLPs), each of which prioritizes loads deemed important enough to warrant protection by the facility's secondary (local) power source 102 as a failover and / or to supplement power availability. As described herein, the FLM system 100 utilizes circuit breakers or breakers 122 in cooperation with a companion module 200 (i.e., an intelligent controller) to change the prioritization of loads within the facility by time of day, season, or even dynamically.

[0008] In one or more embodiments, the local power source 102 for the facility may be a generator or a battery inverter that converts direct current (DC) from a battery into high voltage alternating current (AC). However, in an exemplary embodiment: Bureau The local power source 102 may be, for example, a small-scale power grid (microgrid) configured to generate enough power in the range of 5 kilowatts (kW) to 30 kW, which is sufficient to power a large number of different types of loads.

[0009] The small-scale power grid controller 106 is configured to manage power consumption and / or other high-level control functions (e.g., determining which loads to activate) in the FLM 100. To that end, the small-scale power grid controller 106 may include a processor configured to execute software and manipulate data structures maintained in memory (e.g., persistent or volatile memory) having storage locations for storing the software and data structures. The data structures may include a state center that may utilize the state of components / devices in the FLM system 100 to describe their configuration and to maintain other types of information. The small-scale power grid controller 106 may also include interfaces that incorporate the mechanical, electrical, and signaling circuitry necessary to connect to and communicate with these components / devices. In one embodiment, the small-scale power grid controller 106 may be implemented based on a commercially available small-scale power grid controller from Savant Systems, LLC.

[0010] A panel bridge controller (PBC) 108 connects to the microgrid controller 106 via a local area network (LAN) 110, such as Ethernet. The PBC 108 is configured to convert commands received from the microgrid controller 106 via the LAN 110 into messages, which are provided to the load center via a wireless LAN (WLAN) 112 according to a wireless messaging protocol, such as Bluetooth. The commands received from the microgrid controller 106 via the LAN 110 and WLAN 112 are configured to control a companion module 200 in the load center 120. As described further herein, the companion module 200 monitors (senses) the voltage and current (power) of the load and wirelessly communicates (via Bluetooth) with the PBC 108 to enable remote control of the companion module from a mobile application (e.g., running on a user's mobile device).

[0011] The load center 120 may include one or more electrical panels that, during normal operation, receive, for example, 200 amperes (A) of power from a public power grid 140. In one embodiment, the load center 120 is configured to receive power from the power grid 140 via a feeder 136 via a main feeder 132 and an automatic transfer switch (ATS) 130 (which has a switching time for switching to power provided from a local power source) and distribute power (i.e., current) to facility branch circuits via breakers 122 housed within the electrical panel. Illustratively, the electrical panel is embodied as a vCLP 125 by including a companion module 200 hardwired (e.g., in series) with the breakers 122 to control activation / deactivation of the individual breakers. The companion module 200 and associated breakers 122 may be located in separate electrical boxes (e.g., a main electrical panel and a companion module panel) within the load center 120.

[0012] In one embodiment, the ATS 130 is an intelligent power switching device having a microprocessor-based controller configured to automatically disconnect from the main feeder 132 of the public power grid 140 and connect to the local feeder 134 of the local power source 102 when power from the public power grid 140 goes down (i.e., is lost or unavailable). Illustratively, the ATS 130 includes a low-voltage control 135 in communication with a microgrid controller configured to trigger the start of the local power source 102 in the absence of power from the public power grid 140. When power from the public power grid 140 goes down (terminates), the microgrid controller signals the ATS via the control 135 to start the local power source 102 during a transfer period (not shown). Power is then supplied to the load center 120 via the local feeder 134, through the ATS 130, and via the feeder 136.

[0013] The power grid voltage transformer (VT) 142 is configured to monitor the public power grid voltage (e.g., via a voltage monitoring branch circuit) to determine when the voltage drops sufficiently (e.g., near a zero crossing) to safely turn on (activate) the local power source 102. In one embodiment, the power grid VT 142 converts and isolates the utility line voltage (e.g., 240V) to a low voltage suitable for digital sampling. The panel VT 146 is a transformer configured to monitor the voltage supplied to the load center 120. In one embodiment, the FLM system 100 may also include one or more current transformers (CTs) configured to monitor the current from the public power grid 140 supplied to the load center 120.

[0014] A smart energy monitor (SEM) 144 is configured to monitor (measure) voltage and current from the transformer and from other loads (e.g., air conditioners) within the facility. Illustratively, the SEM 144 is embodied as an analog-to-digital (AD) converter that receives and samples the voltage / current from the VT / CT. The voltage and current are preferably sampled at a high data rate (e.g., 1 kHz) by the SEM 144, which performs operations (i.e., calculations) directed to, for example, power factor, apparent power / real power, etc., for power management calculations. According to embodiments described herein, the sampled data is then provided to the microgrid controller 106 via control and data lines 148 to determine the power capacity level of the FLM system.

[0015] 2 is a block diagram of a companion module 200. In one embodiment, the companion module operates to support (e.g., turn on (and off)) one or more relays (e.g., one 30A / 240VAC circuit or, illustratively, two 15A / 240VAC circuits). A power measurement digital signal processor (DSP) 202 is coupled to a breaker controller 204 having a processor with an on-board wireless (Bluetooth®) transceiver. The power measurement DSP 202 is also coupled to voltage sense lines 206 and current sense lines 208. As described further herein, the breaker controller 204 also includes memory 225 (e.g., RAM and / or flash) adapted to store a virtual critical load (vCL) bit configurable by the PBC 108.

[0016] A pair of relays 210 are respectively coupled between a pair of screw terminals 212 and a pair of current (e.g., Hall effect) sensors 214. The relays 210 are normally open (NO) to conduct power to the branch circuit and are coupled to a pair of screw terminals 212, which serve as connection points for conventional 15A / 120VAC breakers 122 (e.g., arc fault breakers) that can be manually activated. Alternatively, each relay 210 may be embodied as a mechanically actuated switch, which provides adequate safety while eliminating the need for a conventional breaker. A pair of screw terminals 216 each serve as connection points for a desired load (not shown). An AC-DC power supply 218 outputs +12VDC and +3.3VDC to power the companion module 200. As an alternative to using the power measurement DSP 202 to output a pulse when the detected voltage and current reach approximately zero, a zero-crossing detection circuit 220 can be used to generate a square wave output signal that is coupled to the breaker controller 204 via line 222.

[0017] In one embodiment, power measurement DSP 202 can calculate, among other values, a separate instantaneous power consumption for each load connected to screw terminals 216, as well as average and peak power consumption over a predetermined period of time. Power measurement DSP 202 can also be configured to output a pulse via line 205 to breaker controller 204 when the current and voltage reach approximately zero. By knowing when the current and voltage zero crossings are occurring, breaker controller 204 ensures that relay 210 is switched (i.e., opened or closed) only coincident with the occurrence of one or more zero crossings. This benefit tends to reduce arcing and increase the useful life of relay 210.

[0018] In operation, the companion module 200 is configured to turn on (and off) loads to ensure the appropriate amount of power for the facility's loads can be supported by the local power source 102 (e.g., microgrid) according to the load prioritization provided by the vCLP. In other words, the companion module 200 is computer-wired (instructed) to turn on and off (activate / deactivate) loads based on the prioritization. In particular, the companion module of the vCLP 125 can be configured by a user through a mobile application running on a mobile device (not shown). After installation by an electrician, the mobile application can be executed to configure a "bucket" of virtual critical loads (vCL) that can be supported by the local power source 102 until the limit of the supportable load is reached. To change (i.e., add) a load to a vCL bucket, the user must remove other loads from that bucket. This allows users to change the critical load through the mobile application, which is an improvement over the traditional critical load panel approach where the critical load is hardwired (hardwired loads cannot be easily changed).

[0019] However, conventional deployments of companion modules 200 include backup power provided by an uninterrupted power supply (UPS) to power the companion module when the public power grid fails. In the event of a power loss, power sharing regulation by the companion module can be performed through an immediate switchover to UPS power for the module. The present invention eliminates the need for a UPS unit, thereby reducing cost, improving reliability, and reducing the complexity of a UPS-powered controller to communicate to / configure the companion module upon loss of primary power (thus avoiding an overloaded local power source and downtime upon loss of primary power) by enabling load regulation to be performed while the ATS transitions to power provided from the local power source (e.g., during the transition period).

[0020] The embodiments described herein are directed to a technique for switching microgrids using zero-crossing detection to reduce power outages during the switchover while preventing overloads upon final switchover to a secondary (local) power source, thereby eliminating the need for a separate controller or UPS to manage the microgrid. Each companion module 200 senses the power delivered to the load to identify zero crossings. If a preset number of consecutive missed zero crossings are detected, the companion module warns of a potential primary power loss (e.g., unstable power from the public power grid 140) and, therefore, transitions to virtual critical load (vCL) mode for load regulation before operating under the local power source 102 (e.g., the microgrid). That is, the companion module's (breaker) controller 204, configured to separately control power to each branch circuit, detects the number of missed zero crossings indicating a loss of utility power and transitions to a virtual critical load mode, immediately adjusting for reduced power to avoid overloading the local power source. Upon detection of a loss of primary power, the companion module is configured for load activation (or deactivation) via the state of one or more vCL bits 250, which configure each load to an on or off state when operating under local power, for example. In accordance with this technique, the PBC 108 first configures (sets) the state of the vCL bits 250 before sending the configured vCL bits to the companion module 200. Thereafter, the vCLP 125 may be dynamically configurable by a user in real time using the vCL bits 250. Advantageously, the vCL bit of the present technology eliminates the need for the PBC 108 to instruct (e.g., by message exchange) the companion module 200 to switch (turn on / off) the load in response to a main power loss, thereby eliminating the time (e.g., several seconds) spent on message exchange that may result in load downtime.Furthermore, the time when many missed zero crossings occur may coincide with the transition time of power supplied from the mains to power supplied from the local power supply, thereby significantly reducing downtime.

[0021] The local power source (hereinafter, the micropower grid 102) is configured to quickly detect an out-of-bounds frequency or voltage level. Upon detection of the out-of-bounds level, a switching event (e.g., similar to an ATS operation) occurs, in which case the power “levels out” during a transition time (e.g., 70 milliseconds). This leveling event serves as a signal sent to the companion module 200, in which case the module may detect a primary power loss based on consecutive missed zero crossings. In one embodiment, the default number of consecutive missed zero crossings may be configured as four, but any number of consecutive missed zero crossings may be pre-configured (e.g., two to eight missed zero crossings) to allow adjustment for various ATS 130s. For example, upon detection of four consecutive missed zero crossings, the companion module 200 may transition to vCL mode and activate (maintain) or deactivate (reduce) power to each load before operating under local power based on the state of the vCL bit 250 associated with the load. In response, the companion module relays 210 are commanded to open / close their respective breakers 122 accordingly. If power is restored within 70 milliseconds, there is no overload on the microgrid 102.

[0022] Essentially, the transition time represents a "switching" time period (e.g., 70 milliseconds) during which the ATS typically switches. The techniques described herein ensure that each companion module 200 is powered (alive) and able to execute its switch before the expiration of the switch time period. Note that the companion module includes sufficient residual energy through one or more capacitors (not shown) to power the breaker controller 204 during the power transition so that the companion module can operate during that time period. To that end, the time required for the companion module 200 to execute its switch includes (1) the time to detect a loss of power (e.g., four consecutive missed zero crossings) and (2) the time to command the relays 210 to turn their breakers 122 on / off. In one embodiment, four consecutive missed zero crossings consume 2.0 cycles of 60 Hz, where (i) each zero crossing is half a cycle, (ii) one cycle is 16 ms, and (iii) each zero crossing is 8 ms. Thus, the time to detect a power loss is 32 ms, and the time to command the relay must require at most 70 ms - 32 ms = 38 ms.

[0023] If the switching time exceeds 70 milliseconds, the companion modules 200 lose power (i.e., the capacitor power drops below a sufficient voltage level) and their relays / circuits automatically open. Subsequently, during a restart / reset, the companion modules examine their vCL bits to learn the status of their individual loads. Specifically, assuming the companion modules 200 start up and are in critical (power) mode, the PBC 108 can obtain information about the utility grid's main power (e.g., through utility grid VT signaling) to inform the modules when they should assume normal mode operation (i.e., similar to the initial configuration mode during installation). For example, if a load is enabled within vCLP 125, the companion module 200 assumes that the load should be on. If the load's normal state is off, then the PBC 108 commands the module to turn off the load. It should be noted that there are two aspects to being in the on state: (i) the load is listed in vCLP125, and (ii) the user has turned on the load via the vCL bit.

[0024] When in critical mode, a load can only be turned on if it has an associated vCL bit 250. In one embodiment, a user can turn on the vCL bit from a mobile application as needed to activate the load. In accordance with the present technology, the vCL bit 250 is used to hide loads that are turned on during normal operation, essentially filtering out those loads that the user does not want turned on when operating on local power. Illustratively, the vCL bit 250 serves to hide (mask) the on / off state of the load.

[0025] In essence, the companion module 200 "self-determines" to quickly transition (enter) critical mode when battery power is exceeded to avoid tripping a breaker in the local power source (e.g., battery / generator). By quickly entering critical mode, the companion module may quickly shed excess load to avoid overloading the local power source 102. Notably, transitioning the companion module to critical mode should occur before switching over to the local power source. To that end, the companion module is configured to shed excess load before switching over to local power.

[0026] The above description is directed to particular embodiments of the present invention. However, as will become apparent, other variations and modifications can be made to the described embodiments, with the attainment of some or all of their advantages. For example, it is specifically contemplated that the teachings of the present invention may be embodied in software, hardware, firmware, or combinations thereof, including a computer-readable medium having program instructions executing on a computer. Accordingly, this description should be construed as merely exemplary, and not otherwise limiting the scope of the invention. Thus, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.

Claims

1. an automatic transfer switch (ATS) configured to disconnect primary power from the primary power source and provide secondary power from the secondary power source when the primary power fails; one or more companion modules installed within a load center and connected to the secondary power source via the ATS, each companion module controlling power to an individual branch circuit of the load center and including a zero-crossing detector for voltage on the individual branch circuit, each companion module including a processor and memory connected to the individual zero-crossing detector, the processor configured to set a state of power supply to the individual branch circuits based on information stored in the memory when the secondary power is supplied from the secondary power source in response to detecting a preset number of consecutive missed zero crossings from a failed main power source; The apparatus, wherein setting the state of power supply to the individual branch circuits occurs during a transition time from supplying the primary power from the primary power source to supplying the secondary power from the secondary power source.

2. 2. The apparatus of claim 1, wherein each companion module further includes a capacitor for powering its respective processor during a transition time from receiving the primary power from the primary power source to receiving the secondary power from the secondary power source.

3. The apparatus of claim 1 , wherein the preset number of consecutive missed zero crossings has a default value of four.

4. 4. The apparatus of claim 1, wherein the information stored in the memory for setting the state of power supply to the individual branch circuits comprises states for turning on or off power to the individual branch circuits according to a prioritization of the individual branch circuits.

5. 4. The apparatus of claim 1, wherein the information stored in the memory for setting the state of power supply to the individual branch circuits is used to mask a previous state of power supply to the individual branch circuits while the main power is being supplied from the main power source in order to filter out activation of loads when operating on the secondary power.

6. The device according to any one of claims 1 to 3, wherein the information stored in the memory for setting the state of the power supply to the individual branch circuits is configured using a critical load mobile application.

7. 4. The apparatus of claim 1, wherein the information stored in the memory for setting the state of power supply to the individual branch circuits includes a mask for filtering the state of power supply to the individual branch circuits, and a bit for setting the state of power supply to the individual branch circuits according to prioritization of the individual branch circuits when the secondary power is supplied from the secondary power source.

8. 4. The apparatus of claim 1, wherein the processor of each companion module is configured to turn on or off power to the individual branch circuits according to a prioritization of the individual branch circuits.

9. 10. The apparatus of claim 1, wherein the processor of each companion module remains powered during the transition time from receiving primary power from the primary power source to receiving secondary power from the secondary power source.

10. a non-transitory computer-readable medium having program instructions executable by a processor of a companion module located at a load center, the non-transitory computer-readable medium comprising: The companion module controls power to a branch circuit of the load center that is supplied in accordance with an automatic transfer switch for transferring primary power supplied from a primary power source to secondary power supplied from a secondary power source when the primary power fails, the companion module including a zero-crossing detector for voltage on the branch circuit, and the program instructions include: configured to set a state of power supply to the branch circuit based on information stored in a memory when the secondary power is supplied from the secondary power source in response to detecting a preset number of consecutive missed zero crossings; A non-transitory computer-readable medium, wherein setting the state of the power supply to the branch circuit occurs during a transition time from supplying the primary power from the primary power source to supplying the secondary power from the secondary power source.

11. The persistent computer-readable medium of claim 10, wherein the companion module remains powered during the transition time from receiving primary power from the main power source to receiving secondary power from the secondary power source.

12. The non-transitory computer-readable medium of claim 10 or 11, wherein the preset number of consecutive missed zero crossings has a default value of four.

13. 12. The non-transitory computer-readable medium of claim 10 or 11, wherein the information stored in the memory for setting the state of power supply to the branch circuits comprises states for turning on or turning off power to the branch circuits according to a prioritization of the branch circuits.

14. 12. The non-transitory computer-readable medium of claim 10 or 11, wherein the information stored in the memory for setting the state of power supply to the branch circuit is used to mask a prior state of power supply to the branch circuit while the primary power is being supplied from the main power source in order to filter out activation of a load when operating on the secondary power source.

15. 12. The non-transitory computer-readable medium of claim 10 or 11, wherein the information stored in the memory for setting the state of power supply to the branch circuits includes a mask for filtering the state of power supply to the branch circuits, and a bit for setting the state of power supply to the branch circuits according to a prioritization of the branch circuits when power is being supplied from the secondary power source.

16. 12. The non-transitory computer-readable medium of claim 10 or 11, wherein the program instructions are further configured to turn on or turn off power supplies to the branch circuits according to a prioritization of the branch circuits.

17. 1. A method of controlling power to branch circuits of a load panel, each branch circuit being controlled by a companion module mounted on the load panel during a transition from supplying primary power from a primary power source to supplying secondary power from a secondary power source during a primary power outage, comprising: and setting a state of power supply to each branch circuit based on information stored in a memory of each companion module when the secondary power is supplied from the secondary power source in response to detecting a predetermined number of consecutive missed zero crossings of AC voltage in each branch circuit; The method, wherein setting the state of power supply to each branch circuit occurs during a transition time from supplying primary power from the main power source to supplying secondary power from the secondary power source.

18. The method described in claim 17, wherein the companion module remains powered during the transition time from receiving main power from the main power source to receiving secondary power from the secondary power source.

19. Setting the state of power supply to each branch circuit includes:

19. The method of claim 17 or 18, further comprising applying information stored in the memory of each companion module as a mask to filter a prior state of power supply to each branch circuit while the main power is being supplied from the main power source.

20. A method as described in claim 17 or 18, further comprising turning on or off the power supply to each of the branch circuits according to the prioritization of each of the branch circuits.

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