Patent Publication Number: US-2022216725-A1

Title: Method of identifying when to initiate control sequences

Description:
BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Various applications require a nearly constant supply of reliable electrical power to operate effectively. For example, hospitals may require a constant and reliable supply of electricity to ensure medical equipment in operating rooms and the like function when needed. Further, food retailers such as supermarkets and grocery stores may require a constant and reliable supply of electricity to properly operate refrigeration systems associated with display cases and freezers to prevent food spoilage. 
     While utility companies generally provide electrical power consistently and reliably, such power is sometimes interrupted due to inclement weather, unforeseen accidents, or maintenance. Electrical power consumers seeking to mitigate or avoid even minor interruptions in their power supply often rely on generators and other backup systems to supply electrical power during periods when electrical service from a utility company is interrupted. Transfer switches enable these consumers to switch between a primary electrical source (e.g., from a utility company) and a secondary electrical source (e.g., a generator or other backup system) when one source becomes unreliable or requires maintenance. 
     SUMMARY 
     According to aspects of the disclosure, a method and system are provided for transferring a load between a primary power source and a secondary power source. In accordance with the disclosure, a controller senses, via a sensor, an electrical signal providing power from the primary power source to the load. The controller detects a non-conforming power condition or event. For example, such a non-conforming condition or event may be related to an under or over voltage event, an under or over current event, an harmonic content related event, a power (kW) related event, a voltage or current balance related event, a k factor related event, a crest related event and/or other similar power related parameters. 
     In one preferred arrangement, the controller detects the non-conforming power event by determining that a parameter of the electrical signal is less than or greater than a first threshold value and, responsive to the detection of the non-conforming power event, the controller determines a quantity of non-conforming power events that occur during a first time interval. The controller further compares the determined quantity of non-conforming power events to a second threshold value. Responsive to the determined quantity of non-conforming power events being greater than the second threshold value, the controller may generate a general control signal. As just one example, such a control signal may initiate a control sequence to transfer the load from the primary power source to a secondary power source. Alternatively, the controller may initiate a control sequence to transfer the load from a secondary power source to a primary power source. 
     The foregoing and additional aspects and implementations of the present disclosure will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments and/or aspects, which is made with reference to the drawings, a brief description of which is provided next. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an automatic transfer switch according to an example of the disclosure. 
         FIG. 2  is a graph depicting a detection of an instability condition according to an example of the disclosure. 
         FIG. 3  is a graph depicting a detection of a non-conforming power event or condition according to another example of the disclosure. 
         FIG. 4  is a flow chart depicting example operations in accordance with the disclosure. 
         FIG. 5  is another flow chart depicting example operations in accordance with the disclosure. 
     
    
    
     While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure. 
     DETAILED DESCRIPTION 
     I. Overview 
     Conventional transfer switches may detect a power outage condition for a primary power source and then responsively transfer a load from the primary power source to a secondary power source. Such conventional transfer switches may not be able to detect other types of conditions, which indicate that the primary power source is currently or may imminently experience an outage or other problem. The automatic transfer switches of the present disclosure can advantageously detect and/or predict instability in the power provided by the primary power source and then responsively transfer the load from the primary power source to the secondary power source. This may, among other things, beneficially facilitate automatically switching to a secondary power source before the primary power source experiences an outage. 
     II. Example System 
     Referring now to  FIG. 1 , a block diagram of an automatic transfer switch  100  is depicted. The transfer switch  100  selectively couples a load  110  to either a primary power source  112  or a secondary power source  114 . In an example, the primary power source  112  can be provided by a power utility (e.g., via the electric grid) and the secondary power source  114  can be provided by a backup generator. In other examples, the primary power source  112  and/or the secondary power source  114  can be other types of power supplies (e.g., a battery). For instance, in an alternative example, the primary power source  112  can be a renewable energy power generation system (e.g., a wind power system, a hydro-electric power generation system, a solar power generation system, etc.), which is onsite at the load  110 , and the secondary power source  114  can be a power utility. 
     As shown in  FIG. 1 , the primary power source  112  is coupled to the transfer switch system  100  via a primary conductor  116 A, the secondary power source  114  is coupled to the transfer switch system  100  via a secondary conductor  116 B, and the transfer switch system  100  is coupled to the load  110  via an output conductor  116 C. In general, the primary power source  112  and the secondary power source  114  can provide electric power in the form of an electric signal. In particular, for example, the electric signal can be an alternating current (AC) voltage signal. 
     While the power sources  112 ,  114 , the conductors  116 A- 116 C, and the load  110  are shown as a single-phase system in  FIG. 1 , other configurations can be utilized in other examples. For instance, the power sources  112 ,  114 , the conductors  116 A- 116 C, and/or the load  110  can be configured as a three-phase or another poly-phase system in other examples. In a single-phase system, the conductors  116 A- 116 C carry a single electric signal. In a three-phase system, three conductors  116 A- 116 C may each include multiple conductors to facilitate carrying three separate electric signals of the same frequency at different phases. 
     As also shown in  FIG. 1 , the transfer switch system  100  includes a switch  118 , which selectively connects the primary source  112  or the secondary power source  114  to the load  110 . The switch  118  may thus include one or more electrical devices. For example, such additional electrical devices may comprise one or more electromechanical contactors, solid state devices, circuit breaker devices, and/or other suitable devices for electric power transfer. In one example, the switch  118  includes a solenoid that activates an electrical contact to move between a connection to the primary conductor  116 A and a connection to the secondary conductor  116 B. Other examples are also possible. For examples, such electrical devices may be internal or external to the transfer switch system  100 . 
     In practice, the switch  118  can be operably switched between multiple states. In a first state, the switch  118  can connect the primary power source  112  to the load  110 . In a second state, the switch  118  can connect the secondary power source  114  to the load  110 . 
     The switch  118  is selectively switched between the first state and the second state under control of a controller  120 . The controller  120  may thus provide control signals to the switch  118 , which selectively control the state of the switch  118  to connect either the primary power source  112  or the secondary power source  114  to the load  110 . The controller  120  controls the switch  118  based on an analysis of the electric signal transmitted on the primary conductor  116 A from the primary power source  112  to the load  110 . In particular, the controller  120  monitors the electric signal on the primary conductor  116 A for certain conditions, which indicate that it may be beneficial to switch the load  110  from the primary power source  112  to the secondary power source  114  (e.g., an outage of the primary source  112  has or is likely to occur). 
     To monitor the electric signal on the primary conductor  116 A, the controller  120  is coupled to the primary conductor  116 A via a first sensor  122 . The first sensor  122  may be internal (i.e., integral) or external to the controller  120 . The sensor  122  senses the electric signal transmitted on the primary conductor  116 A and provides an indication of one or more parameters of the electric signal (e.g., a magnitude of current, voltage, power, etc.) to the controller  120 . Similarly, to monitor the electric signal in the secondary conductor  116 B, the controller  120  may be coupled to the secondary conductor  116 B via a second sensor. The second sensor may be similar in construction and/or function to the first sensor  122 . For example, the second sensor may be internal (i.e., integral) or external to the controller  120 . Various different types of sensors may be utilized. In one example, the first sensor  122  can include a current transformer coupled to the primary conductor  116 A. In such an example, as current flows through the primary conductor  116 A, the current transformer induces a current in the sensor  122  that is proportional to the current flowing through the primary conductor  116 A. The sensor  122  and/or the controller  120  may then determine from the induced current a voltage or current of the electric signal transmitted on the primary conductor  116 A from the primary power source  112  to the load  110 . Other examples are also possible. 
     The controller  120  can be, for example, a microcontroller, a microprocessor, an application specific integrated circuit (ASIC) device, field programmable gate array (FPGA), programmable logic controller (PLC) or the like. In  FIG. 1 , the controller  120  is further coupled to a memory  124 . The memory  124  can store any data required by the controller  120  for detecting conditions of the primary power source  112 , initiating a power transfer, or executing any other functionality. For example, the memory  124  can store one or more threshold values  126 ,  130 , one or more time intervals  128 ,  132 , application code (e.g., main functionality firmware), initialization parameters, boot code, code for executing algorithms, code for determining a non-conforming power and/or instability condition, code for setting user defined thresholds for algorithms, check sums to determine whether code is corrupted, lock codes, and/or other data. This data can be stored in the memory  124  at the factory, manually entered via an input/output device (not shown), or remotely downloaded via the input/output device. The memory  124  can be integrated with the controller  120 , or the memory  124  can be external and remotely coupled to the controller  120 . The memory  124  can be, for example, random access memory (RAM), read only memory (ROM), electronic erasable programmable read only memory (EEPROM), flash memory, or other volatile or non-volatile memory (i.e., non-transitory computer readable media). 
     III. Example Operations 
     In line with the discussion above, the controller  120  monitors the electric signal on the primary conductor  116 A for certain conditions, which indicate that it may be beneficial to switch the load  110  from the primary power source  112  to the secondary power source  114 . The controller  120  is configured or programmed to detect such conditions using the electric signal sensed by the sensor  122  and perhaps data stored in the memory  124  as inputs. For simplicity, operation of the controller  120  is described below in the context of the sensor  122  sensing a voltage of the electric signal (i.e., a voltage signal) on the primary conductor  116 A; however, the sensor  122  can additionally or alternatively sense a current or another parameter of the electric signal on the primary conductor  122  as an input for condition detection. 
     In one aspect, the controller  120  monitors the voltage signal on the primary conductor  116 A to detect an instability condition and/or a non-conforming power event. For example, in one exemplary arrangement, the instability condition may be characterized by relatively rapid fluctuations in the voltage signal and may indicate that the primary power source  112  may imminently experience a power outage. The controller  120  may detect the instability condition by detecting when more than a threshold number of fluctuations occur within a predetermined time interval. 
     In one example, the controller  120  monitors the voltage signal to detect non-conforming power events as previously described herein. As just one example, such non-conforming power condition or event may be a momentary power outage or power dip in which the voltage signal drops below a first threshold value  126  (which may be stored in the memory  124 ). In some implementations, the controller  120  may detect a non-conforming power event by detecting each time the voltage drops below the first threshold value  126 . In other implementations, the controller  120  may detect a non-conforming power event by detecting each time the voltage drops below and then returns above the first threshold value  126 . 
     When the controller  120  detects a non-conforming power event, the controller  120  initiates a timer. The timer begins to count a period of time equal to a first time interval  128  (which also may be stored in the memory  124 ). While the timer counts to the first time interval  128 , the controller  120  continues to monitor the voltage signal and count each time another non-conforming power event occurs. The controller  120  compares the quantity of non-conforming power events detected to a second threshold value  130  to determine whether a threshold number of non-conforming power events have occurred during the first time interval  128 . 
     If, at any time during the first time interval  128 , the controller  120  determines that the quantity of non-conforming power events detected is greater than the second threshold value  130 , the controller  120  (i) determines that an instability condition exists and (ii) initiates a control sequence to switch the load  110  from the primary power source  112  to the secondary power source  114 . The control sequence can involve the controller  120  providing a control signal to the switch  118  to cause the switch  118  to change from the first state to the second state. Additionally or alternatively, the control sequence can involve the controller  120  providing a control signal to the secondary power source  114  to cause the secondary power source  114  to prepare for providing power to the load  110 . For instance, responsive to the control signal from the controller  120 , the secondary power source  114  can power on, startup, and/or switch from an idle mode to an active mode, among other possibilities. 
     Whereas, if the controller  120  determines that the quantity of non-conforming power events is less than the second threshold value  130  at the end of the first time interval  128 , then the controller  120  can (i) determine that no instability condition exists, (ii) reset the timer, and/or (iii) maintain the switch  118  in the first state. 
       FIG. 2  is a graph illustrating a voltage signal  134  exhibiting an instability condition, which can be detected by the controller  120  as described above. As shown in  FIG. 2 , the voltage signal  134  initially drops below the first threshold value  126  at a time t 1 . Responsive to the controller  120  detecting this initial voltage signal  134  drop below the first threshold value  126  at time t 1 , the controller  120  initiates a timer that then counts up to the first time interval  128 . In the example shown in  FIG. 2 , the timer reaches the first time interval  128  at a time t 3 . 
     Also, responsive to the controller  120  detecting the initial voltage signal drop below the first threshold value  126  at time t 1 , the controller  120  initiates a counter for counting non-conforming power events via timer  136  (e.g., by setting the counter to an initial value such as 1). Timer  136  comprises another timer that may be used to determine the duration of what should be considered a monitored non-conforming power event. For example, if timer  136  is set to 1.0 seconds, then a voltage drop below the threshold for 0.5 seconds would not be categorized as a monitored event. However, if the voltage were to drop below the threshold for a duration of 1.5 seconds, such a duration would then be categorized as a monitored event. As such, the timer  136  may be used as a filter to avoid nuisance trips and used to count only events of a predetermined significant enough magnitude. Again, such filter parameters can be tailored to the specific transfer switch application. 
     Preferably, the timer  128  comprises a rolling timer. For example, such a rolling timer may be able to identify a grouping of events (i.e., a quantity defined by a threshold) that fall within the first time interval  128 . Although in certain situations an application may not meet the threshold value  130  number of events that are required within the time interval  128 =t 3 −t 1  as shown in  FIG. 2 , and the control process may still be initiated. As just one example, referring to  FIG. 2 , assume that a large gap were to be present between the first event  136  and the third event  136  to fall outside the first time interval  128 . In such a situation, if a fourth event were to occur in close proximity to the third event  136 , then the second, the third and the fourth event would fall within a timer period equal to or less than the time set in the first time interval  128  which would still initiate a control sequence. 
     While the timer progresses to the first time interval  128 , the controller  120  continues to monitor the voltage signal  134  to detect and count the occurrence of additional non-conforming power events  136  (e.g., a number of times the voltage signal  134  returns above the first threshold value  126  and then drops below the first threshold value  126  again). Each time the controller  120  detects a non-conforming power event  136 , the controller  120  increments the counter. The controller  120  continues in this manner until either the controller  120  determines that the number of non-conforming power events  136  indicated by the counter exceeds the second threshold value  130  or the timer reaches the first time interval  128  (e.g., at time t 3 ). 
     In this example, the second threshold value  130  is two non-conforming power events. Accordingly, as indicated in  FIG. 2 , the controller  120  determines that an instability condition exists at a time t 2  based on a determination that three non-conforming power events  136  have occurred within the first time interval  128  at time t 2 . Accordingly, at time t 2 , the controller  120  initiates a control sequence to switch the load  110  from the primary power source  112  to the secondary power source  114  as described above. 
     In another aspect, the controller  120  monitors the voltage signal on the primary conductor  116 A to detect a non-conforming power condition. The non-conforming power condition may be characterized by the primary power source  112  providing threshold low (or possibly zero) voltage on the primary conductor  116 A for at least a predetermined amount of time. This may, for example, help to mitigate power continuity issues when a power outage has occurred on the primary power source  112 . 
     In one example, to detect a non-conforming power condition, the controller  120  monitors the voltage signal to detect when the voltage signal drops below the first threshold value  126  (stored in the memory  124 ). Thus, in this example, the threshold value used to detect the non-conforming power condition is the same as the threshold value used to detect an instability condition as described above; however, in alternative examples, the threshold value used to detect the non-conforming power condition can be different than the threshold value used to detect the instability condition. 
     When the controller  120  detects that the voltage signal drops below the first threshold value  126 , the controller  120  then determines whether the voltage signal remains below the first threshold value  126  for a second time interval  132  (which may be stored in memory  124 ). For example, responsive to the controller  120  detecting that the voltage signal dropped below the first threshold value  126 , the controller  120  may initiate a timer. The timer begins to count a period of time equal to a second time interval  132 . If the controller  120  determines that the voltage signal returns to a level above the first threshold level  126  before the timer reaches the second time interval  132 , the controller  120  (i) determines that no non-conforming power condition exists, (ii) resets the timer, and (iii) maintains the switch  118  in the first state. As a result, the load  110  continues to receive power from the primary power source  112 . 
     Whereas, if the controller  120  determines that the voltage signal remains below the first threshold  126  for the entire second time interval  132 , then the controller  120  determines that a non-conforming power condition exists. Responsive to determining that a non-conforming power condition exists, the controller  120  initiates the control sequence to switch the load  110  from the primary power source  112  to the secondary power source  114 . As described above, the control sequence can involve the controller  120  providing control signals to the switch  118  and/or the secondary power source  114 . 
       FIG. 3  is a graph illustrating a voltage signal  134  exhibiting a non-conforming power condition, which can be detected by the controller  120  as described above. As shown in  FIG. 3 , the voltage signal  134  drops below the first threshold value  126  at a time t 1 . Responsive to the controller  120  detecting this voltage signal drop below the first threshold value  126  at time t 1 , the controller  120  initiates a timer that then counts up to the second time interval  132 . In the example shown in  FIG. 3 , the timer reaches the second time interval  132  at a time t 2 . 
     While the timer counts to the second time interval  132 , the controller  120  continues to monitor the voltage signal  134  to determine whether the voltage signal  134  returns to a level above the first threshold value  126 . At time t 2 , the controller  120  determines that the voltage signal  134  has remained below the first threshold value  126  for the entire second time interval  132 . Accordingly, at time t 2 , the controller  120  determines that a low power condition exists and responsively initiates a control sequence to switch the load  110  from the primary power source  112  to the secondary power source  114  as described above. Preferably, if at any time during this time interval, the voltage signal  134  rises above the threshold  126 , the timer will reset since the voltage signal  134  must remain below the threshold  126  for the entire time interval  132 . 
     According to aspects of the present disclosure, the automatic transfer switch can be operable to detect an instability condition, a non-conforming power condition, or both instability and non-conforming power conditions. Detecting both instability conditions and non-conforming power conditions may provide for more robust protection against power interruptions (or non-conforming power) at the load  110 . Notably, the methods for detecting non-conforming power conditions described above generally cannot detect an instability condition as the fluctuations characteristic of the instability condition are generally too brief to be considered a non-conforming power condition (e.g., in which an outage has occurred). However, the methods for detecting instability conditions may beneficially facilitate the controller  120  predicting that a non-conforming power condition is about to occur (or other non-conforming power condition) and thereby allow the automatic transfer switch  100  to take precautionary measures (potentially prior to a loss of primary power actually occurring). 
       FIG. 4  is next a flow chart depicting an example set of operations that can be carried out in an implementation of a process in accordance with aspects of the present disclosure. As shown in block  50 , the method begins with a controller sensing, via a sensor, an electrical signal providing power from the primary power source to the load. At block  52 , the controller detects a non-conforming power event (i.e., designated as a power event) by determining that a parameter of the electrical signal is less than a first threshold value. At block  54 , responsive to the detection of the non-conforming power event, the controller determines a quantity of non-conforming power events that occur during a first predetermined time interval. At block  56 , the controller compares the determined quantity of non-conforming power events to a second threshold value. At block  58 , responsive to the determined quantity of non-conforming power events being greater than the second threshold value, the controller initiates a control sequence to transfer the load from the primary power source to a secondary power source. 
       FIG. 5  is a flow chart depicting another example set of operations that can be carried out in an implementation of a process in accordance with aspects of the present disclosure. As shown in block  70 , the method begins with a controller sensing, via a sensor, an electrical signal providing power from the primary power source to the load. At block  72 , the controller detects a non-conforming power event (i.e., designated as a power event) by determining that a parameter of the electrical signal is less than a first threshold value. At block  74 , responsive to the detection of the non-conforming power event, the controller determines a quantity of non-conforming power events that occur during a first predetermined time interval. At block  76 , the controller compares the determined quantity of non-conforming power events to a second threshold value. At block  78 , responsive to the determined quantity of non-conforming power events being greater than the second threshold value, the controller initiates a control sequence to transfer the load from the primary power source to a secondary power source. 
     At block  80 , responsive to detecting the non-conforming power event, the controller waits a second predetermined time interval. At block  82 , after waiting the second predetermined time interval, the controller determines that the parameter of the electrical signal is less than the first threshold value. At block  84 , responsive to determining that the parameter of the electrical signal is less than the first threshold value after waiting the second predetermined time interval, the controller transfers the load from the primary power source to the secondary power source. 
     IV. Example Variations 
     As described above, the controller  120  can detect an instability condition exists when a threshold number of fluctuations relative to the first threshold value occur within the first time interval. In some implementations, the instability condition can indicate that the primary power source is currently unstable. Additionally or alternatively, the instability condition can indicate that the primary source is likely to become unstable (i.e., the instability condition can be predictive of the primary power source becoming unstable). 
     As described above, the instability condition and the non-conforming power condition may be detected by determining when a parameter of the electric signal drops below the first threshold value. In additional or alternative implementations, the first threshold value can be a range of values such that the instability condition and the non-conforming power condition are detected based on a determination of when the parameter of the electric signals is outside the range of values (e.g., drops below a lower boundary or rises above an upper boundary). 
     According to aspects of the present disclosure, the switch  118  can be configured as an open transfer switch, a delayed transfer switch, a closed transfer switch, an electromechanical transfer switch, a solid state transfer switch, a soft start transfer switch, and/or a static transfer switch. Additionally, although the switch  118  is describe above as having a first state in which the switch  118  connects the primary power source  112  to the load  110  and a second state in which the switch  118  connects the secondary power source  114  to the load  110 , the switch  118  may have a third state in which neither the primary power source  112  nor the secondary power source  114  are connected to the load  110  in additional or alternative implementations. 
     According to further aspects of the present disclosure, the threshold values and/or the time intervals can be predetermined values stored in memory at the time of manufacture and/or based on user input after manufacture. In general, however, the threshold values and the time intervals may be predetermined in the sense that they are set prior to the controller analyzing the electrical signal on the primary conductor. Alternatively, or in addition to such predetermined values, intelligent or automatic self programming of such settings may also be utilized. For example, the controller may be configured to monitor the signal for a predetermined period of time. Based on the quality and/or stability of its power during this monitored period of time, the controller may be configured to use a programmed algorithm to adjust the duration, timers, and/or thresholds of its own settings to adjust higher or lower sensitivities. One advantage of such a smart or intelligent controller is that it would allow the controller to self configure to optimal settings that might be unique to the specific transfer switch application (e.g., such as a hospital, a supermarket, a data center, etc.) and therefore reduce nuisance trips or missing certain events. 
     While particular implementations and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.