AC power monitoring and parameter determination

Devices and methods for monitoring and determining alternating current (AC) power system parameters are provided. In some implementations, the device can include a processor; and at least one non-transitory computer-readable medium storing computer-executable instructions for implementing a number of components. The components include a monitor configured to: sense an AC line voltage signal and an AC current voltage signal; filter the AC line voltage signal; calculate average AC line voltage and current values based, at least, on a DC voltage and current values corresponding to the AC line voltage and current signals, respectively; determine fundamental AC line voltage and current signals based, at least, on zero crossings of the respective average AC line voltage value and the average AC line current value; and determine one or more AC power system parameters based, at least, on the fundamental AC line voltage signal and the fundamental AC line current signal.

BACKGROUND

The following description relates to alternating current (AC) power systems, in general, and to monitoring and determining AC power system parameters, in particular.

Data centers are responsible for reliably storing and providing data worldwide. Data centers perform such functions via servers, computers and other electrical devices communicatively coupled to one another. As such, monitoring the electrical power utilized or allocated within a data center is of vital importance. Data center-level or circuit level decision-making can be performed as a result of the monitoring, and policy decisions can be formed that are then propagated down to power supplies for the data center. However, in existing AC power monitoring systems, complex Fast Fourier Transforms (FFTs) are employed by processors to facilitate monitoring and determination of AC power system parameters. Unfortunately, these processors are expensive and FFT processing results in significant delay with regard to parameter calculation. Accordingly, devices, circuitry and methods for monitoring and determining AC power system parameters while foregoing the use of FFTs, are desirable.

SUMMARY

In one or more implementations, the disclosed subject matter relates to a device that includes a processor; and at least one non-transitory computer-readable medium. The computer-readable medium can be communicatively coupled to the processor, and store computer-executable instructions for implementing at least one of a number of components. The components include an AC power system monitor configured to: sense an AC line voltage signal and an AC line current signal; filter the AC line voltage signal and remove one or more harmonic frequencies of the AC line voltage signal; calculate a direct current (DC) voltage value based, at least, on the filtered AC line voltage signal; calculate a DC current value based, at least, on the AC line current signal; calculate an average filtered AC line voltage value and an AC line current value based, at least, on the DC voltage value and the DC current value; determine a fundamental AC line voltage signal and a fundamental AC line current signal based, at least, on one or more zero crossings of the respective average filtered AC line voltage value and the average AC line current value; and determine one or more AC power system parameters based, at least, on the fundamental AC line voltage signal and the fundamental AC line current signal.

In another implementation, the disclosed subject matter also relates to a method. The method can include employing at least one processor executing computer-executable instructions embodied on at least one non-transitory computer-readable medium. The computer-executable instructions can be embodied on the computer-readable medium to perform operations including: filtering an AC line voltage signal and removing one or more harmonic frequencies of the AC line voltage signal; calculating a DC voltage value based, at least, on the filtered AC line voltage signal; calculating a DC current value based, at least, on an AC line current signal; calculating an average filtered AC line voltage value and an AC line current value based, at least, on the DC voltage value and the DC current value; determining a fundamental AC line voltage signal and a fundamental AC line current signal based, at least, on one or more zero crossings of the respective average filtered AC line voltage value and the average AC line current value; and determining one or more AC power system parameters based, at least, on the fundamental AC line voltage signal and the fundamental AC line current signal.

In another implementation, the disclosed subject matter relates to another method. The method can include employing at least one processor executing computer-executable instructions embodied on at least one non-transitory computer-readable medium. The computer-executable instructions can be embodied on the computer-readable medium to perform operations including: determining a total harmonic distortion (THD) of the AC system based, at least, on a fundamental AC line voltage signal and a fundamental AC line current signal; and re-computing the total harmonic distortion at approximately every half AC cycle.

Toward the accomplishment of the foregoing and related ends, the one or more implementations include the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth herein detail certain illustrative aspects of the one or more implementations. These aspects are indicative, however, of but a few of the various ways in which the principles of various implementations can be employed, and the described implementations are intended to include all such aspects and their equivalents.

DETAILED DESCRIPTION

Various implementations are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more implementations. It can be evident, however, that such implementations can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more implementations.

FIG. 1is an illustration of a block diagram of an exemplary non-limiting device configured to facilitate AC power system monitoring and parameter determination according to implementations described herein. The device102can include resistors108,110and a microcontroller109. The microcontroller109can include a calculation component112, a filtering component116, and an averaging component114. The resistors108,110and microcontroller109(and/or components thereof) can be electrically and/or communicatively coupled to one another to perform one or more functions of device102. Device102can be communicatively coupled to AC power supply106. As such, the device102can perform monitoring and parameter determination for an AC power system for which electrical power is provided by the AC power supply106.

As shown inFIG. 1, AC line voltage, vs, and AC line current, is, can be sensed by microcontroller109. The AC line voltage, vs, can contain harmonic frequencies and, as such, vs, can be filtered with filtering component116. The filtering component can be a low pass filter (LPF) in some implementations. In other implementations, any filter configured to filter out harmonic frequencies can be employed.

The filtering component116can substantially remove the harmonic frequencies by low pass filtering the AC line voltage signal such that only the signal with fundamental frequency remains and the signals with harmonic frequencies are substantially removed. The filtered AC line voltage, vs,filteredcan be output from the filtering component116as shown inFIG. 1.

One or more functions of the microcontroller109and the filtering component116can be illustrated with reference toFIG. 2.FIG. 2is an illustration of a graph depicting AC line voltage waveforms for facilitating AC power system monitoring and parameter determination according to implementations described herein.

The AC line voltage signal vs, corresponds to reference numeral206, the filtered AC line voltage signal, vs,filtered, corresponds to208, and the fundamental AC line voltage signal, vs1, corresponds to210. The zero crossings correspond to reference numerals202,204.

As shown inFIG. 2, the AC line voltage vs,206can be sensed, and the filtered AC line voltage, vs,filtered,208can be output. The filtered AC line voltage, vs,filtered,208can cross the zero axis at zero crossings202,204, as shown. The fundamental frequency, f, can be determined based on the zero crossings. Additionally, the angular position, θv=2πf·t of the filtered AC line voltage can be determined and updated every zero crossing of vs,filtered. In various implementations, the device102can update AC data every half AC line cycle (e.g., every 8 to 10 milliseconds (msecs)). In the United States, the fundamental frequency can be at 60 Hertz (Hz), and in Europe, the fundamental frequency can be at 50 Hz.

Once the zero crossing times are determined, the filtered AC line voltage signal can be obtained that corresponds to the zero crossing location. The filtering component116can output an AC line voltage signal that includes the fundamental frequency, i.e., the fundamental voltage, vs1. The fundamental voltage can be substantially without delay. Based, at least, on the fundamental voltage, vs1, the average voltage and/or the average current can be calculated by providing the fundamental voltage and/or the fundamental current to the averaging component114. Now, in lieu of performing signal processing using an FFT, averaging can be employed to enable determination of the AC power system parameters as shown in the Equations below.

FIG. 3is an illustration of an exemplary block diagram configured to calculate the fundamental voltage for facilitating AC power system monitoring and parameter determination according to implementations described herein. As shown inFIG. 3, the fundamental voltage can be calculated as follows. The parameters vMand vPcan be transformed from the AC voltage signals into substantially equivalent DC voltage values. In some embodiments, the parameters can be obtained in the block diagram inFIG. 3according to the equations shown in Equations 1 and 2 below.
vM=√{square root over (2)}vssin θv(1)
vP=√{square root over (2)}vscos θv(2)

While not shown inFIG. 3, in some embodiments, prior to computing the average values, as noted above, the AC line voltage signals can be transformed into substantially equivalent DC values. Such values can then be averaged in the AVE302,304. The averages of vMand vPcan be calculated at AVE302,304as shown in Equations 3 and 4. In some embodiments, the average values can be DC values that are updated, for example, at one or more zero crossings. In some embodiments, one or more of the average values can be updated at every zero crossing. The value, vM, can represent the portion of voltage associated with the active power, and the value, vP, can represent the portion of voltage associated with the power factor angle between the voltage and the current. In applications in which the load is a 3-phase AC motor, M can represent torque component and P can represent flux component.

The average valuesvMandvPcan be calculated and updated approximately every half AC line cycle according to the equations shown in Equations 3 and 4, where, n is the number of samples in a single AC cycle.

The averages can be added to calculate the fundamental voltage, vs1.

As shown, the fundamental AC line voltage can be calculated from the averages. The angle, α, between the filtered AC line voltage and the fundamental AC line voltage, vs1can be calculated as shown in Equation 5.

The angular position θi=2πf·t of the fundamental AC line voltage can be obtained from α and can be used as a reference angular position for the AC line current.

The root mean square (RMS) fundamental AC line voltage can then be calculated as shown below with the RMS fundamental AC line voltage being calculated according to that shown in Equations 6 and 7.
vs,1=√{square root over (vM2+vP2)}  (6)

FIG. 4is an illustration of a graph depicting AC line current waveforms for facilitating AC power system monitoring and parameter determination according to implementations described herein. The AC line current signal, is, corresponds to402, the AC filtered voltage, vs,filtered, corresponds to404, and the AC fundamental current is1corresponds to406. The AC line fundamental current406needs to be determined.

FIG. 5is an illustration of an exemplary block diagram configured to calculate the fundamental AC line current for facilitating AC power system monitoring and parameter determination according to implementations described herein. As shown inFIG. 5, the fundamental current can be calculated as follows. The parameters iMand iPcan be transformed from the AC current signals into substantially equivalent DC current values. In some embodiments, the parameters can be obtained in the block diagram inFIG. 5according to the equations shown in Equations 8 and 9 below, where sin θiis synchronized with the fundamental AC line voltage. While not shown inFIG. 5, in some embodiments, prior to computing the average values, as noted above, the AC line current signals can be transformed into substantially equivalent DC values. Such values can then be averaged as shown at502,504ofFIG. 5.

Specifically, the value, iM, can represent the portion of current associated with the active power, and the value, iP, can represent the portion of current associated with the power factor angle between the voltage and the current.
iM=√{square root over (2)}issin θi,  (8)
iP=√{square root over (2)}iscos θi,  (9)

The AVE valuesiMandiPare updated every half AC line cycle and can be calculated as shown in Equations 10 and 11.

In some embodiments, the average values are DC values. These values can be updated at one or more zero crossings. In some embodiments, the values are updated at every zero crossing. The power factor angle φ between the fundamental AC line voltage and fundamental AC line current can be calculated as shown at Equation 12.

The RMS fundamental AC line current can be calculated as shown at Equation 13 and the RMS AC line current can be calculated as shown at Equation 14. The fundamental AC line current can be obtained without any delay.
Is,1=√{square root over (iM2+iP2)}.  (13)

The THD can be calculated as the ratio of the harmonic RMS value, Uh, and the fundamental value, U1, of both voltage and current as shown in Equation 15, where Us1is either a power level of the fundamental AC line voltage or a power level of the fundamental AC line current, and Usis either a power level of the AC line voltage or a power level of the AC line current. The THD can be expressed as a percentage.

Accordingly, as shown above, the need to perform an FFT to determine the U value is avoided and the U can be determined using an inexpensive microcontroller (that does not include FFT circuitry or software). The microcontroller can determine the fundamental AC line voltage and the fundamental AC line current, and correspondingly, the THD.

The PF and displacement PF (DPF) can be calculated according to the following Equations 16 and 17, where φ is the angle between the fundamental AC line voltage and the fundamental AC line current.
DPF=cos φ  (16)

Therefore, the fundamental AC line voltage, the fundamental AC line current and the THD. In various implementations, the DPF and the PF parameters can be calculated as well. The THD, DPF and/or the PF can be calculated as described herein (without resort to use of an FFT).

FIGS. 6 and 7are illustrations of exemplary flow diagrams of methods that can facilitate AC power system monitoring and parameter determination according to implementations described herein. The methods600and700can include employing at least one processor executing computer-executable instructions. The computer-executable instructions can be embodied on at least one non-transitory computer-readable medium to perform the operations described for methods600and700.

Turning first toFIG. 6, at602, method600can include filtering an AC line voltage signal and removing one or more harmonic frequencies of the AC line voltage signal. The filtering can be performed by a LPF in some implementations.

At604, method600can include calculating a DC voltage value based, at least, on a filtered AC line voltage signal. At606, method600can include calculating a DC current value based, at least, on an AC line current signal.

At608, method600can include calculating an average filtered AC line voltage value and an AC line current value based, at least, on the DC voltage value and the DC current value.

At610, method600can include determining a fundamental AC line voltage signal and a fundamental AC line current signal. The determination can be performed at times corresponding to one or more zero crossings of the respective average filtered AC line voltage value and the average AC line current value. In some implementations, although not shown inFIG. 6, method600can also include re-calculating the average AC line voltage value and the AC line current value approximately every half AC cycle. As noted above, the average values can be DC values. These average values can be updated at every zero crossing in some embodiments, and at one or more zero crossings in other embodiments.

At612, method600can include determining one or more AC power system parameters. The AC power system parameters can be based, at least, on the fundamental AC line voltage signal and the fundamental AC line current signal.

In some embodiments, although not shown, power control policy decisions can be made based on the AC power system parameters. In some embodiments, power can be provided to servers of a data center based on the AC power system parameters.

Turning now toFIG. 7, at702, method700can include determining a total harmonic distortion of an AC power system based, at least, on a fundamental AC line voltage signal and a fundamental AC line current signal. At704, method700can include re-computing the total harmonic distortion at approximately every half AC cycle. In some implementations, although not shown, method700can also include determining a power factor of the AC power system. The power factor can be based on the angle between the fundamental AC line voltage signal and the fundamental AC line current signal.

In some embodiments, although not shown, policy decisions can be made and/or power can be provided to one or more servers, based on the total harmonic distortion and/or the power factor.

In various implementations, parameters for three phase AC power systems can be determined based on the monitoring and calculation methodologies and devices provided herein. In these implementations, the devices and methodologies provided above can be provided for two or more phases of a three phase AC power system. For example, the devices and methodologies provided above can be provided for each of the three phases of a three phase AC power system. In some implementations, for each phase of the three phases, AC line voltage signals can be filtered and corresponding values can be averaged, the AC line current value can also be averaged. The fundamental AC line voltage can be obtained and the fundamental AC line current can be obtained. The THD, DPF and/or the PF can be calculated as described herein (without resort to use of an FFT).

Implementations described herein can be designed as centralized or distributed computing environments. For example, the microcontroller109, calculation component112, averaging component114and/or the filtering component116can be included in or be designed as either a centralized computing environment or a distributed computing environment. With regard to distributed computing environments, there are a variety of systems, components, and network configurations that support distributed computing environments. For example, computing systems can be connected together by wired or wireless systems, by local networks or widely distributed networks. Currently, many networks are coupled to the Internet, which provides an infrastructure for widely distributed computing and encompasses many different networks, though any network infrastructure can be used for exemplary communications made incident to the systems as described in various implementations.

Computing devices performing one or more functions described herein (the averaging or filtering functions and/or the detection of zero crossings, for example). These computing devices can typically include a variety of computer readable media, or computer storage media. The computer storage media can be in the form of volatile and/or nonvolatile memory such as read only memory (ROM) and/or random access memory (RAM). By way of example, and not limitation, memory can also include an operating system, application programs, other program modules, and program data. Computing devices typically include a variety of media, which can include computer-readable storage media and/or communications media, in which these two terms are used herein differently from one another as follows. Computer-readable storage media can be any available storage media that can be accessed by the computer, is typically of a non-transitory nature, and can include both volatile and nonvolatile media, removable and non-removable media. By way of example, and not limitation, computer-readable storage media can be implemented in connection with any method or technology for storage of information such as computer-readable instructions, program modules, structured data, or unstructured data. Computer-readable storage media can include, but are not limited to, RAM, ROM, electrically erasable programmable read only memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital versatile disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or other tangible and/or non-transitory media which can be used to store desired information. Computer-readable storage media can be accessed by one or more local or remote computing devices, e.g., via access requests, queries or other data retrieval protocols, for a variety of operations with respect to the information stored by the medium.

It is to be understood that the techniques described herein can be implemented in hardware, software, firmware, middleware, microcode, or any combination thereof. For example, the calculation component112and/or the averaging component114can be implemented by software, hardware or firmware. As another example, the techniques described with reference toFIGS. 6 and 7can be implemented by software, hardware or firmware. For a hardware implementation, the processing units can be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers (e.g., microcontroller109), microprocessors and/or other electronic units designed to perform the functions described herein, or a combination thereof.

What has been described above includes examples of one or more implementations. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned implementations, but one of ordinary skill in the art can recognize that many further combinations and permutations of various implementations are possible. Accordingly, the described implementations are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.

The aforementioned systems have been described with respect to interaction between several components. For example, the averaging component114, the calculation component112and/or the filtering component116. It can be appreciated that such systems and components can include those components or specified sub-components, and/or additional components, and according to various permutations and combinations of the foregoing. Sub-components can also be implemented as components communicatively coupled to other components rather than included within parent components (hierarchical). Additionally, it is to be noted that one or more components can be combined into a single component providing aggregate functionality or divided into several separate sub-components. For example, the microcontroller109can be composed of the averaging component114, the filtering component116and the calculation component112. Additionally, any components described herein can also interact with one or more other components not specifically described herein but generally known by those of skill in the art.

In view of the exemplary systems described above methodologies that can be implemented in accordance with the described subject matter will be better appreciated with reference to the flowcharts of the various figures. While for purposes of simplicity of explanation, the methodologies ofFIGS. 6 and 7are shown and described as a series of blocks, it is to be understood and appreciated that such subject matter is not limited by the order of the blocks, as some blocks can occur in different orders and/or concurrently with other blocks from what is depicted and described herein.