Device and method for providing a power interface

Abstract

The present application relates to an apparatus and method for providing a power interface. The aspects and embodiments described herein are directed to a power interface device, which includes a first power interface configured to be coupled to an electric utility and a second power interface configured to be coupled to a microgrid including one or more power sources and one or more loads, wherein the one or more power sources include a generator. The power interface device also includes a power conversion circuit coupled to the first power interface and the second power interface and a controller coupled to the power conversion circuit. The controller is configured to allow connection between an electric utility operating at a first frequency and voltage and a microgrid operating at a second frequency and voltage by at least the following operations: detecting an operating frequency of the generator and controlling the power flow between the electric utility and the microgrid based on the operating frequency of the generator.

Description

[0001] This application is a divisional application of an application with an application date of August 21, 2013, application number 201380079725.8, and invention name “Device and method for providing a power interface”. Technical Field

[0002] At least one embodiment of the invention generally relates to the control of a power interface device.

[0003] Related technical discussions

[0004] A microgrid can be a small local power grid that can include one or more different power sources. For example, a microgrid can include wind turbines, solar generators, diesel generators, and other power generators. A microgrid can also include loads. For example, a microgrid can include a building, a data center, a port, an industrial site, a campus, or even a small town. A microgrid can also be connected to a larger grid (e.g., an electric utility). An electric utility can provide power to a microgrid (e.g., to provide additional power to the load and / or to improve reliability).

[0005] SUMMARY OF THE DISCLOSURE

[0006] This disclosure provides the following:

[0007] 1. A device comprising:

[0008] a first power interface configured to couple to an electric utility;

[0009] a second power interface configured to couple to a microgrid including one or more power sources and one or more loads, the one or more power sources including a generator;

[0010] a power conversion circuit coupled to the first power interface and the second power interface, and

[0011] A controller coupled to the power conversion circuit, the controller configured to enable interfacing between the electric utility operating at a first frequency and voltage and the microgrid operating at a second frequency and voltage by at least:

[0012] detecting an operating frequency of the generator; and

[0013] Power flow between the electric utility and the microgrid is controlled based on the operating frequency of the generator.

[0014] 2. The power interface device of claim 1, wherein the controller is configured to provide power from the power utility to the microgrid.

[0015] 3. The power interface device of claim 2, wherein the controller is configured to provide power from the power utility to the microgrid in response to an amount of power required by the one or more loads exceeding an amount of power generated by the one or more power sources.

[0016] 4. The power interface device of claim 1, wherein the controller is configured to provide power from the microgrid to the electric utility.

[0017] 5. The power interface device of claim 4, wherein the controller is configured to provide power from the microgrid to the electric utility in response to an amount of power generated by the one or more power sources and not used by the one or more loads.

[0018] 6. The power interface device of claim 1, wherein the controller is further configured to determine a reactive current reference to compensate for reactive power generated by the one or more loads.

[0019] 7. The power interface device of claim 1, wherein the controller is configured to control the power flow between the electric utility and the microgrid independently of instructions from other controllers.

[0020] 8. The power interface device according to item 1, wherein the power interface device is an uninterruptible power supply.

[0021] 9. The power interface device according to 8, further comprising a battery, and wherein the controller is further configured to control a second power flow between the battery and the microgrid.

[0022] 10. A method for distributing power using a power interface device, the power interface device comprising a first power interface configured to be coupled to a power utility, a second power interface configured to be coupled to a microgrid, and a power conversion circuit, the method comprising:

[0023] detecting the operating frequency of the generator; and

[0024] Power flow between the electric utility and the microgrid is controlled based on the operating frequency of the generator.

[0025] 11. The method of claim 10, wherein controlling the power flow comprises providing power from the electric utility to the microgrid.

[0026] 12. The method of claim 11, wherein controlling the power flow comprises providing power from the electric utility to the microgrid in response to an amount of power required by the one or more loads exceeding an amount of power generated by the one or more power sources.

[0027] 13. The method of claim 10, wherein controlling the power flow comprises providing power from the microgrid to the electric utility.

[0028] 14. The method of claim 13, wherein controlling the power flow comprises providing power from the microgrid to the electric utility in response to an amount of power generated by the one or more power sources and not used by the one or more loads.

[0029] 15. The method of claim 10, further comprising determining a reactive current reference to compensate for reactive power generated by the one or more loads.

[0030] 16. The method of claim 10, comprising controlling the power flow between the electric utility and the microgrid independently of instructions from other controllers.

[0031] 17. The method according to 10, wherein the power interface device is an uninterruptible power supply.

[0032] 18. The method of claim 17, wherein the uninterruptible power supply further comprises a battery, and wherein the method further comprises controlling a second power flow between the battery and the microgrid.

[0033] 19. A power interface device, comprising:

[0034] a first power interface configured to couple to an electric utility;

[0035] a second power interface configured to couple to a microgrid including one or more power sources and one or more loads, the one or more power sources including a generator;

[0036] a power conversion circuit coupled to the first power interface and the second power interface; and

[0037] means for detecting an operating frequency of the generator; and

[0038] Power flow between the electric utility and the microgrid is controlled based on the operating frequency of the generator.

[0039] Aspects and embodiments described herein are directed to a power interface device that includes a first power interface configured to couple to a power utility and a second power interface configured to couple to a microgrid that includes one or more power sources and one or more loads, the one or more power sources including a generator. The power interface device also includes a power conversion circuit coupled to the first power interface and the second power interface and a controller coupled to the power conversion circuit. The controller is configured to allow a connection between a power utility operating at a first frequency and voltage and a microgrid operating at a second frequency and voltage by at least detecting an operating frequency of the generator and controlling a power flow between the power utility and the microgrid based on the operating frequency of the generator.

[0040] In some embodiments, the controller is configured to provide power from an electric utility to the microgrid. In some embodiments, the controller is configured to provide power from an electric utility to the microgrid in response to an amount of power required by one or more loads exceeding an amount of power generated by one or more power sources.

[0041] In some embodiments, the controller is configured to provide power from the microgrid to the electric utility. In some embodiments, the controller is configured to provide power from the microgrid to the electric utility in response to an amount of power generated by one or more power sources and not used by one or more loads.

[0042] In some embodiments, the controller is further configured to determine a reactive current reference to compensate for reactive power generated by one or more loads.

[0043] In some embodiments, the controller is configured to control power flow between the electric utility and the microgrid independently of instructions from other controllers.

[0044] In some embodiments, the power interface device is an uninterruptible power supply. In some embodiments, the power interface device further comprises a battery, and the controller is further configured to control a second power flow between the battery and the microgrid.

[0045] The aspect also relates to a method for distributing power using a power interface device, the power interface device comprising a first power interface configured to be coupled to a power utility, a second power interface configured to be coupled to a microgrid, and a power conversion circuit, the method comprising detecting an operating frequency of a generator and controlling power flow between the power utility and the microgrid based on the operating frequency of the generator.

[0046] In some implementations, controlling the power flow includes providing power from the electric utility to the microgrid.

[0047] In some embodiments, controlling the power flow includes providing power from the electric utility to the microgrid in response to an amount of power required by the one or more loads exceeding an amount of power produced by the one or more power sources.

[0048] In some implementations, controlling the power flow includes providing power from the microgrid to the electric utility.

[0049] In some implementations, controlling the power flow includes providing power from the microgrid to the electric utility in response to an amount of power generated by the one or more power sources and not used by the one or more loads.

[0050] In some implementations, the method further includes determining a reactive current reference to compensate for reactive power generated by the one or more loads.

[0051] In some embodiments, the method includes controlling the power flow between the electric utility and the microgrid independently of instructions from other controllers.

[0052] In some embodiments, the power interface device is an uninterruptible power supply.

[0053] In some embodiments, the uninterruptible power supply further includes a battery, and wherein the method further includes controlling a second power flow between the battery and the microgrid.

[0054] Aspects are also directed to a power interface device, which includes a first power interface configured to couple to an electric utility, a second power interface configured to couple to a microgrid including one or more power sources including a generator and one or more loads, a power conversion circuit coupled to the first power interface and the second power interface, and a device for detecting an operating frequency of the generator and controlling power flow between the electric utility and the microgrid based on the operating frequency of the generator.

[0055] These and other aspects and embodiments are discussed in detail below. The above information and the following detailed description include illustrative examples of various aspects and embodiments, and provide an overview or framework for understanding the nature and characteristics of the claimed aspects and embodiments. The accompanying drawings provide further understanding of the various aspects and embodiments, and are incorporated into and constitute a part of this specification. The accompanying drawings, together with the remainder of the specification, are used to describe and explain the claimed aspects and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component illustrated in various figures is represented by a like numeral. For clarity, not every component may be labeled in every drawing. In the drawings:

[0057] Figure 1 is a schematic block diagram depicting an example microgrid according to the prior art;

[0058] Figure 2 is a schematic block diagram depicting an example microgrid according to the prior art;

[0059] Figure 3 is a schematic block diagram depicting an example microgrid and an example power interface device according to an embodiment;

[0060] Figure 4 is a functional block diagram depicting an example power interface device according to an embodiment;

[0061] Figure 5 is a simplified block diagram depicting an example microgrid and an example power interface device according to an embodiment;

[0062] Figure 6 is a graph depicting frequency droop of a portion of a microgrid according to an embodiment;

[0063] Figure 7 is a block diagram depicting an example control algorithm according to an embodiment;

[0064] Figure 8 is a graph depicting generator power of a portion of a microgrid according to an embodiment;

[0065] Fig. 9 is a graph depicting voltage droop of a portion of a microgrid according to an embodiment; and

[0066] Fig.10 is a block diagram depicting an example control algorithm according to an implementation. DETAILED DESCRIPTION

[0067] The microgrid may include power sources (e.g., renewable energy sources) and other power sources. Renewable energy sources may include power sources (e.g., solar generators, wind turbines, and other renewable energy sources). The microgrid may also include a generator (e.g., a diesel generator). The microgrid may be coupled to a larger power grid (e.g., a power utility). A power interface device may provide an interface between the microgrid and the larger power grid. The power interface device may allow the microgrid to operate at a frequency and voltage independent of the power utility. The power interface device may also adjust the voltage and frequency to provide higher quality power from the power utility. The power interface device may also compensate for the reactive power of the microgrid. In some embodiments, the power interface device may be an uninterruptible power supply (UPS) configured to provide a power interface between the microgrid and the larger power grid.

[0068] The systems and methods described herein are not limited in their application to the details of the construction and arrangement of the components set forth in the description or shown in the accompanying drawings. The present invention can be practiced or implemented in other embodiments and in various ways. In addition, the wording and terminology used herein are for descriptive purposes and should not be considered restrictive. The use of "including", "comprising", "having", "containing", "involving" and variations thereof herein is intended to include the items listed thereafter, their equivalents and additional items, and optional embodiments consisting of the items specifically listed thereafter.

[0069] Various aspects and embodiments are directed to an uninterruptible power supply. In one example, an uninterruptible power supply (UPS) may include an inverter, a controller, and a bypass switch. The controller operates the inverter during online operation to regulate the inverter output voltage and provide the output voltage from the inverter at the UPS output. The controller may also operate the inverter during bypass and other operating modes to provide, among other things, power factor correction, harmonic current distortion control, and active power to charge a backup power supply. The controller may time the operation of a switch in the inverter to provide an output voltage.

[0070] Figure 1An example prior art microgrid 100 is shown. The microgrid 100 includes multiple power sources. The power sources may include renewable energy sources, such as a solar generator 102 and a wind turbine 108. The solar generator 102 may include a solar panel 104 coupled to a solar inverter 106. The power source may also include a gas generator 110. The microgrid 100 may also include one or more loads 112. Additionally or alternatively, the microgrid 100 may include a power source and one or more loads may be coupled to the microgrid 100 to receive power from the microgrid 100. The microgrid 100 is connected to a larger power grid (including an electric utility 140). The microgrid 100 may be connected to the utility 140 via an interconnect 150. The interconnect 150 may be a circuit breaker or other switch.

[0071] The microgrid 100 can receive power from the facility 140 (e.g., when the power demand from one or more loads 112 exceeds the power provided by the power sources 102, 108, 110). For example, the power provided by the renewable energy sources (e.g., the solar generator 102 and the wind turbine 108) may fluctuate depending on factors (e.g., the environment). The solar generator 102 may be able to provide more energy on sunny days (relative to cloudy days or at night). The wind turbine 108 may rely on the strength of the wind to provide electricity. In such an example, power can be obtained from the facility 140 to meet the requirements of the load 112, such as when the renewable energy source provides less power.

[0072] Additionally, because there may be fewer loads 112 on the microgrid 100, the amount of power required by the loads 112 may vary more widely than a larger grid, as a larger grid with more loads may take advantage of an averaging effect among a larger number of loads. As the total load varies more widely, the regulation of multiple power sources 102, 108, 110 operating in parallel may become complicated.

[0073] Typically, if the microgrid 100 is connected to the facility 140 through a direct connection (e.g., interconnect 150), the microgrid 100 operates at the same voltage and frequency as the electric utility 140. When connected to the facility, the microgrid 100 may also be susceptible to disturbances in the facility. The interconnect 150 can be opened to disconnect the microgrid 100 from the larger grid and the facility 140. For example, when the facility 140 is shut down or provides low-quality power, the microgrid 100 can be disconnected from the larger grid.

[0074] refer to Figure 2, an example prior art microgrid 200 includes a solar generator 202, a wind turbine 208, and a generator 210. The generator 210 may be, for example, a diesel generator. The microgrid 200 includes one or more loads 212 and is connected to a larger grid including a facility 240 via an interconnect 250. The microgrid 200 also includes a grid controller 260 coupled to each of the power sources 202, 208, 210 and the wires that interconnect the elements of the microgrid 200. The grid controller 260 may monitor the power sources 202, 208, 210, the loads 212, and the facilities 240 to control the power sources 202, 208, 210 and ensure that the loads 212 are receiving sufficient power. The grid controller 260 may also determine when the interconnect 250 should be opened and closed.

[0075] The grid controller 260 may also be configured to reduce the power generated by the generator 210, preferring renewable energy sources (e.g., solar generators 202 and wind turbines 208) as the preferred energy source. The grid controller 260 may also be configured to avoid receiving power from the facility 140 unless the generator 210 is at full capacity, as the load 212 may then be powered by the power sources 202, 208, 210 of the microgrid 200. The grid controller 260 may also be configured to open the interconnect 250 (if there is a power outage at the facility 240 or if the power quality from the facility 240 is below a threshold level).

[0076] In general, if the power generated by the microgrid 200 exceeds the power required by the load 212, the microgrid 200 can also be configured to provide power to the larger grid. For example, when the microgrid 200 generates excess power, the facility 240 can purchase power from the microgrid 200. In some embodiments, the power received by the facility 240 from the microgrid 200 is limited to power generated by renewable energy sources. The grid controller 260 can be configured to avoid providing power from the generator 210 to the facility 240.

[0077] The grid controller 260 can be configured to control the microgrid 200 by measuring the current of the load 212 and the voltage of the microgrid 200 and the facility 240. The grid controller 260 can be coupled to the wires to each load 212 to measure the load current. The grid controller 260 can also be coupled to the output line of the facility 240 between the facility 240 and the interconnect 250 and the input line of the microgrid 200 between the interconnect 250 and the microgrid 200 to measure the voltage of the facility 240 and the voltage of the microgrid 200, respectively. The grid controller 260 can also be coupled to the interconnect 250 to provide commands for opening and closing to the interconnect 250. The grid controller 260 can also be coupled to each of the power sources 202, 208, 210 to receive the measurement results and provide commands such as output power references.

[0078] In some embodiments of the present disclosure, the interconnects 150 and 250 described above may be replaced by a power interface device. Figure 3 A microgrid 300 is shown that includes renewable energy sources such as a solar generator 302 and a wind turbine 308. The microgrid 300 also includes a main generator 310. The main generator 310 can be, for example, a diesel generator. The microgrid 300 also includes one or more loads 312. The microgrid 300 is connected to a larger power grid (including facility 340) via a power interface device 350. In some embodiments, the power interface device 350 can be an uninterruptible power supply UPS (e.g., a reversible UPS).

[0079] In some embodiments, the power interface device 350 allows the microgrid 300 to operate at a frequency and voltage different from the facility 340. The power interface device 350 can also adjust the voltage and frequency to improve the quality of power received by the microgrid 300 from the facility 340. The power interface device 350 can also compensate for reactive power of the loads 312 of the microgrid 300. In some embodiments, the power interface device 350 can also include a battery and / or other energy storage device. The power interface device 350 can also provide low harmonic current and low reactive power for power factor correction on the facility side.

[0080] The power interface device 350 includes a controller 352. In some embodiments, the main generator 310 operates the output frequency and output voltage amplitude in a droop mode. Other power sources (e.g., renewable energy sources 302, 308) can operate as current sources. The power interface device 350 can measure the frequency and voltage of the microgrid 300 and calculate the active power to be exchanged between the larger grid and the microgrid 300. The power interface device 350 can also calculate the reactive power to be provided to the microgrid 300.

[0081] For example, Figure 4 A power interface device 350 is shown connected to the microgrid 300 and a larger grid including the facility 340. The power interface device 350 includes a controller 352, a power factor correction circuit 358, a current inverter 354, a DC / DC converter 356, and a battery 360. In some embodiments, the power interface device 350 is a double conversion UPS. The power factor correction circuit 358 is coupled to a grid terminal, which is connected to the larger grid. In some embodiments, the power factor correction circuit 358 is an AC / DC power converter. The power factor correction circuit 358 is coupled to the current inverter 354, which is coupled to the microgrid terminal, which is connected to the microgrid 300. In some embodiments, the current inverter 354 outputs a sinusoidal current with an active component and a reactive component following a reference provided by a control algorithm implemented by the controller 358.

[0082] In some embodiments, the control algorithm calculates the active power reference and the reactive power reference based on various rules. For example, the rules may include the main generator (e.g., Figure 3 The rule may also include that the main generator 310 of the microgrid 300 generates an output power that does not exceed the rated output power. The rule may also include that the main generator generates a non-negative output power. The rule may also include generating substantially maximum output power from renewable energy sources. The rule may also include generating a main generator output power factor close to 1. Other such rules may be considered by the control algorithm.

[0083] For example, refer again to Figure 3 , the power provided by the power sources 302, 308, 310 and drawn by the load 312 can be related according to Equation 1

[0084] P 主 +∑P 再生 +P 接口 -∑P 负载 =0 (1)

[0085] The system can also be represented (considering an equivalent load and an equivalent renewable energy source) as in Figure 5 As shown in FIG. 1 , the system includes a microgrid 500 including a main generator 510, an equivalent renewable energy source 502, and an equivalent load 512 connected to a larger grid including a facility 340 via a power interface device 350 including a controller 352. In addition, considering only active power, the equation can be simplified to

[0086] Pa 主 =Pa 负载 -Pa 再生 -Pa 接口 (2)

[0087] In some embodiments, the renewable energy source is operated to provide maximum capacity. Depending on environmental factors, the maximum capacity may be variable. If the maximum capacity exceeds the requirements from the load, the surplus may be provided to the larger grid. If the maximum capacity does not meet the requirements from the load, the main generator and the facility may supplement the power provided by the renewable energy source as needed. The power requirements of the load may also vary. Therefore, [Pa 负载 -Pa 再生 ] can change as each or both components change.

[0088] If [Pa 负载 -Pa 再生] is greater than the maximum rated output power of the main generator 510, the main generator will operate at an overload. The power interface device 350 can be configured to automatically provide a power difference from the facility 340 so that the main generator 510 can operate at or near maximum capacity without exceeding the maximum rated capacity. In some embodiments, the power interface device 350 can be configured to maintain other thresholds for the main generator 510 (e.g., 50% of maximum capacity or allowing the maximum rated capacity to be exceeded).

[0089] If [Pa 负载 -Pa 再生 ] is less than zero, the renewable energy source 502 is generating more power than the load 512 requires. The power interface device 350 can be configured to provide excess power to a larger grid or to a battery or other energy storage device to prevent the main generator 510 from operating under reverse power or stopping due to a reverse power fault.

[0090] In some embodiments, the power interface device 350 can monitor the frequency of the microgrid 300 and use the frequency to monitor the load of the main generator 510. When the main generator 510 is operating in a droop mode, the output frequency can provide information about the output active power of the main generator 510. For example, Figure 6 A graph 600 shows an example correlation 602 between an output frequency 604 and an output active power 606 of a main generator 510 operating in a droop mode. The monitored output frequency 604 may range between values ​​F0 and F1 as the output active power 606 varies from 0 to a value Pn. The output active power 606 may correspond to the requirements of the load and the supply of renewable energy. For example, the output active power 606 may be [Pa 负载 -Pa 再生 ]. The maximum rated power of the main generator 510 may correspond to the frequency Fmin. 负载 -Pa 再生 ] is too high, the frequency may drop below Fmin, and the control algorithm may determine that the power interface device 350 should deliver positive active power until the frequency exceeds Fmin. The frequency Fmax may correspond to a threshold value, [Pa 负载 -Pa 再生 ] is too low (e.g., zero) below which the threshold is too low. For example, when the load on the main generator 510 is zero or less, because the power supplied by the renewable energy source meets or exceeds the required power, the control algorithm can deliver negative active power until the frequency drops below Fmax.

[0091] Figure 7 can be, for example, Figure 5700 is a block diagram of an example control algorithm 700 implemented by a controller 352 of a power interface device 350 of FIG. The control algorithm 700 may be composed of two control loops 750, 760 and a selector 722. The first control loop 750 may receive the frequency of the microgrid F load 702. The first control loop 750 may also receive F max 704 and subtract F max 704 from F load 702. If F load 702 is greater than F max 704, then subtracting F max 704 from F load 702 will result in a positive number. The result may be provided to a negation block 706 that negates the received value. The result from the negation block 706 may be provided to a proportional integral controller 708, followed by a saturation block 710. The saturation block 710 may output 0 or the negative maximum allowed active current value of the power interface device -Ia_max or any value in between. Therefore, if the selector 722 is switched to the first control loop 750, the first control loop 750 may output a negative reference current 724 as the active current reference 730 output by the power interface device. Once the load of the main generator returns to a value within the rated operating range of the main generator, the saturation block 710 may allow the output negative reference current 724 to be set to zero.

[0092] The second control loop 760 may be similar to the first control loop 750. 负载 702 is less than Fmin 714 and provides a positive reference current 726. The second control loop 760 can also receive F 负载 702 and F minimum 714, from F 负载 702 minus Fmin 714. The result may be provided to negation block 716, followed by proportional-integral controller 708, followed by saturation block 720. Saturation block 720 may output either 0 or the positive maximum allowed active current Ia of the power interface device. _ Therefore, if the selector 722 is switched to the second control loop 760, the second control loop 760 can output the positive reference current 726 as the active current reference 730 of the power interface device. The selector 722 can be based on an algorithm (e.g., in F 负载 702, F 最大 704 and F 最小 714) to determine the position. For example, when F 负载 When F 702 approaches F max 704, selector 722 may be switched to first control loop 750. For example, if F 负载 702 is greater than Fmax 704-10% or some other buffer, the selector 722 can switch to the first control loop 750. Similarly, when F 负载 702 is close to F minimum 714, for example if it is less than F 最小714+10%, then the selector 722 may be switched to the second control loop 750. If no condition is true, then the selector 722 may be set to a null reference setting.

[0093] Figure 8 is based on, for example, [Pa 负载 -Pa 再生 ]810 The load of the main generator 510 measured shows the output power P from the power interface device 350 接口 820 and the corresponding output power P of the main generator 510 发电机 802 is a graph 800 of an example function. When [Pa 负载 -Pa 再生 ]810 changes from 0 to P 最小 812:00, P 接口 820 provides negative active power so that P 发电机 802 does not drop to the threshold value P 最小 806 or less. When [Pa 负载 -Pa 再生 ]810 in P 最小 812 and P 最大 814 (which may correspond to [Pa 负载 -Pa 再生 ] value), the load of the main generator 510 can be within the rated operating range. The main generator 510 can then provide the electrical energy required to support the load 512 (in addition to the electrical energy received from the renewable energy source 502). 接口 820 can be 0 in this range. When [Pa 负载 -Pa 再生 ]810 is greater than P 最大 At 814, P 接口 820 can provide positive active power so that P 发电机 802 does not exceed the threshold P 最大 804. P 最大 804 may be configured so that the main generator 510 remains below the maximum rated output and does not operate overloaded.

[0094] In some embodiments, the power interface device 350 can also compensate for reactive power of the microgrid and / or the main generator. Fig. 9 Graph 900 showing an example correlation between the output voltage 902 of the main generator 510 and the reactive power 904 of the main generator 510. When the main generator 510 is operated in a droop mode, the output voltage 902 may vary with the reactive power 904. 0905, the main generator 510 operates without reactive power. When the reactive power 904 increases, the output voltage 902 of the main generator 510 also increases until it reaches a value corresponding to the maximum lagging Q 最大 Maximum voltage of 910 V 最大 906. As reactive power 904 decreases, output voltage 902 also decreases until it reaches a value corresponding to the maximum leading –Q 最大 The minimum voltage V of 912 最小 908. The control algorithm can operate to sufficiently maintain the output voltage 902 at V 0 905.

[0095] For example, Fig.10 1 is a block diagram of an example algorithm 1000 for calculating a reactive current reference for the power interface device 350. The controller 352 may receive a voltage of the microgrid at an output terminal of the power interface device 350, which corresponds to the output voltage V of the main generator 510. 输出 902 and subtracting a prescribed voltage V corresponding to operation of the main generator 510 without reactive power 0 905. The result may be provided to a proportional-integral controller 1006 followed by a saturation block 1008. The saturation block 1008 may limit the output to a positive or negative reference current (e.g., + / - Ir _ Maximum), + / -Ir _ The maximum may be the maximum allowed reactive current at the power interface output. The output reference current from the saturation block 1008 may be provided as the output reactive current reference 1010 to maintain the voltage of the microgrid at V 0 905 and maintain the main generator 510 operating without reactive power. In this manner, the power interface device 350 can compensate for the reactive power of the load 512 on the microgrid 500.

[0096] In some embodiments, the above algorithm allows power interface device 350 to operate without communicating with a controller of microgrid 500 .

[0097] In some embodiments, the power interface device 350 may include and / or be coupled to a load current sensor. The load current sensor may detect harmonics generated by components on the microgrid 500. The power interface device 350 may include an algorithm to filter and compensate for the detected harmonics to reduce the detected harmonics.

[0098] In some embodiments, the power interface device 350 can shut down, stop, or put components of the power interface device 350 into a standby mode. For example, if the active current reference is 0 and the power interface device 350 does not need to provide active power, the power interface device 350 can stop the inverter 354 and the power factor correction circuit 358 of the power interface device 350. The power interface device 350 can also stop compensating for reactive power.

[0099] Having now described some illustrative embodiments, it is apparent that the foregoing is illustrative rather than restrictive, and has been presented by way of example. In particular, although many of the examples presented herein relate to specific combinations of method behaviors or system elements, it will be understood that those behaviors and those elements can be combined in other ways to accomplish the same purpose. The behaviors, elements, and features discussed only with respect to one embodiment are not intended to be excluded from similar effects in other embodiments.

[0100] Notice Figures 1 to 10 , the enumerated items are shown as separate elements. However, in actual implementations of the systems and methods described herein, they may be integral components of other electronic devices (e.g., digital computers). Therefore, the above-described behaviors may be implemented at least in part in software, which may be embodied in an article of manufacture including a program storage medium. The program storage medium includes non-transitory and other data signals embodied in one or more of a carrier wave, a computer disk (magnetic, or optical (e.g., CD or DVD, or both)), a nonvolatile memory, a magnetic tape, a system memory, and a computer hard drive.

[0101] Any references to front and back, left and right, top and bottom, or upper and lower, etc. are intended for descriptive convenience and are not intended to limit the present systems and methods or their components to any one position or spatial orientation.

[0102] Any reference to an embodiment or element or behavior of a system and method cited herein in the singular may also include an embodiment including multiple elements of these elements, and any reference to any embodiment or element or behavior herein in the plural may also include an embodiment including only a single element. References in singular or plural form are not intended to limit the currently disclosed systems or methods, their components, behaviors, or elements to singular or plural configurations. References to any behavior or element based on any information, behavior, or element may include an embodiment in which the behavior or element is based at least in part on any information, behavior, or element.

[0103] Any embodiment disclosed herein may be combined with any other embodiment, and references to "an embodiment," "some embodiments," "optional embodiments," "various embodiments," "one embodiment," etc. are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described with respect to the embodiment may be included in at least one embodiment. Such terms as used herein do not necessarily all refer to the same embodiment. Any embodiment may be combined with any other embodiment in any manner consistent with the aspects and embodiments disclosed herein.

[0104] References to "or" may be interpreted as including such that any term described using "or" may indicate any of the single, more than one, and all described terms. Intervening implementations, behaviors, or elements are not required unless so listed. Any solution to a problem or any element or behavior presented herein in an alternative (e.g., using the word "or") is neither ambiguous nor indirect because it can be presented in an alternative. Any such alternative implementation, solution, element, or behavior is directly derivable and unambiguous because at least one implementation is independent of any other alternative solution, element, or behavior.

[0105] Where technical features in the drawings, detailed description or any claims are followed by reference signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the drawings, detailed description and claims. Therefore, neither the reference signs nor their absence shall have any limiting effect on the scope of any claim element.

[0106] Those skilled in the art will recognize that the systems and methods described herein can be embodied in other specific forms without departing from their characteristics. For example, the uninterruptible power supply can be a single-phase or three-phase uninterruptible power supply. In addition, the coupling between the uninterruptible power supply components includes direct coupling and indirect coupling in which the intervening elements can exist. The controller can include a combination of hardware, software and firmware and a dedicated integrated circuit, a programmable logic device and a processor. The input power supply can be provided by an AC power supply, or any second or backup power supply and a combination thereof. The embodiment described with the input power supply from any one of these power supplies can include a variation in which the power supply is provided at least partially from another of these power supplies. The inverter can have different topologies and can include a secondary or tertiary inverter and other topologies or a multi-level topology including a four-level topology. The foregoing embodiments are illustrative, rather than limiting the systems and methods described. The scope of the systems and methods described herein is therefore represented by the appended claims rather than by the foregoing description, and changes within the equivalent meaning and scope of the claims are included therein.

Claims

1. A power interface device, comprising: a first power interface configured to couple to an electric utility; a second power interface configured to couple to a microgrid including one or more power sources and one or more loads, the one or more power sources including a generator; a power conversion circuit coupled to the first power interface and the second power interface; as well as A controller coupled to the power conversion circuit, the controller configured to enable interfacing between the electric utility operating at a first frequency and voltage and the microgrid operating at a second frequency and voltage by at least: detecting an operating frequency of the generator; as well as controlling power flow between the electric utility and the microgrid based on the operating frequency of the generator, wherein the power interface device monitors the frequency of the microgrid and uses the frequency to monitor the load of the generator, and, wherein, when the generator is operated in droop mode, the output frequency provides information about the output active power of the generator, Wherein controlling the power flow comprises at least one of the following: When the operating frequency is lower than a minimum frequency, receiving a first power at the first frequency and voltage at the first power interface, regulating the first power to a second power at the second frequency and voltage, and providing the second power to the microgrid at the second power interface until the operating frequency rises above the minimum frequency; and When the operating frequency is higher than the maximum frequency, a third power at the second frequency and voltage is received at the second power interface, the third power is adjusted to a fourth power at the first frequency and voltage, and the fourth power is provided to the power utility at the first power interface until the operating frequency drops below the maximum frequency. 2 . The power interface device of claim 1 , wherein the controller is configured to provide power from the power utility to the microgrid.

3. The power interface device of claim 2, wherein the controller is configured to provide power from the power utility to the microgrid in response to an amount of power required by the one or more loads exceeding an amount of power generated by the one or more power sources. 4 . The power interface device of claim 1 , wherein the controller is configured to provide power from the microgrid to the electric utility.

5. The power interface device of claim 4, wherein the controller is configured to provide power from the microgrid to the electric utility in response to an amount of power generated by the one or more power sources and not used by the one or more loads. 6 . The power interface device of claim 1 , wherein the controller is further configured to determine a reactive current reference to compensate for reactive power generated by the one or more loads. 7 . The power interface device of claim 1 , wherein the controller is configured to control the power flow between the electric utility and the microgrid independently of instructions from other controllers.

8. The power interface device of claim 1, wherein the power interface device is an uninterruptible power supply.

9. The power interface device of claim 8, further comprising a battery, and wherein the controller is further configured to control a second power flow between the battery and the microgrid.

10. A method for distributing power using a power interface device, the power interface device comprising a first power interface configured to be coupled to a power utility, a second power interface configured to be coupled to a microgrid including one or more power sources and one or more loads, and a power conversion circuit, the method comprising: Detecting the operating frequency of the generator; and controlling power flow between the electric utility and the microgrid based on the operating frequency of the generator, wherein the power interface device monitors the frequency of the microgrid and uses the frequency to monitor the load of the generator, and, wherein, when the generator is operated in droop mode, the output frequency provides information about the output active power of the generator, Wherein controlling the power flow comprises at least one of the following: When the operating frequency is lower than a minimum frequency, receiving a first power at a first frequency and voltage at the first power interface, regulating the first power to a second power at a second frequency and voltage, and providing the second power to the microgrid at the second power interface until the operating frequency rises above the minimum frequency; and When the operating frequency is higher than the maximum frequency, a third power at the second frequency and voltage is received at the second power interface, the third power is adjusted to a fourth power at the first frequency and voltage, and the fourth power is provided to the power utility at the first power interface until the operating frequency drops below the maximum frequency. 11 . The method of claim 10 , wherein controlling the power flow comprises providing power from the electric utility to the microgrid.

12. The method of claim 11, wherein controlling the power flow comprises providing power from the electric utility to the microgrid in response to an amount of power required by the one or more loads exceeding an amount of power generated by the one or more power sources.

13. The method of claim 10, wherein controlling the power flow comprises providing power from the microgrid to the electric utility.

14. The method of claim 13, wherein controlling the power flow comprises providing power from the microgrid to the electric utility in response to an amount of power generated by the one or more power sources and not used by the one or more loads.

15. The method of claim 10, further comprising determining a reactive current reference to compensate for reactive power generated by the one or more loads.

16. The method of claim 10, comprising controlling the power flow between the electric utility and the microgrid independent of instructions from other controllers.

17. The method of claim 10, wherein the power interface device is an uninterruptible power supply.

18. The method of claim 17, wherein the uninterruptible power supply further comprises a battery, and wherein the method further comprises controlling a second power flow between the battery and the microgrid.

19. A power interface device, comprising: a first power interface configured to couple to an electric utility; a second power interface configured to couple to a microgrid including one or more power sources and one or more loads, the one or more power sources including a generator; a power conversion circuit coupled to the first power interface and the second power interface; as well as means for detecting the operating frequency of said generator; as well as controlling power flow between the electric utility and the microgrid based on the operating frequency of the generator, wherein the power interface device monitors the frequency of the microgrid and uses the frequency to monitor the load of the generator, and, wherein, when the generator is operated in droop mode, the output frequency provides information about the output active power of the generator, Wherein controlling the power flow comprises at least one of the following: When the operating frequency is lower than a minimum frequency, receiving a first power at a first frequency and voltage at the first power interface, regulating the first power to a second power at a second frequency and voltage, and providing the second power to the microgrid at the second power interface until the operating frequency rises above the minimum frequency; and When the operating frequency is higher than the maximum frequency, a third power at the second frequency and voltage is received at the second power interface, the third power is adjusted to a fourth power at the first frequency and voltage, and the fourth power is provided to the power utility at the first power interface until the operating frequency drops below the maximum frequency.

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