Cross-references to Related Applications:

[0001] This application claims priority under 35 U.S.C. § 119 to the United States Provisional Patent Application No. 62/664,092, filed April 28, 2018, the disclosures of which is incorporated herein by reference in their entirety.

[0002] This application is also related to United States Patent No. 9,819,185; United States Patent No. 9,148,058; United States Patent No. 9,819,279; United States Patent No. 9,979,312; United States Patent No. 9,712,048; and United States Patent Application No. 14/979,475; the disclosures of which are incorporated herein by reference in their entirety.

Field of the Invention:

[0003] The present disclosure relates generally to electrical power distribution grid systems and more specifically relates to systems for enabling distributed energy generation (DEG) devices.

Background:

[0004] The present legacy electrical system and power quality being delivered to users is being degraded by several disruptive technological and legislative impacts. What came with the deregulation legislation was the rapidly increasing myriad of privately owned and operated domestic and commercial DEG devices connected at any point across a low voltage (LV) distribution network, which has the capacity of connecting small power generators from renewable energy sources such as photovoltaic (PV) solar panels, solar thermal power generators, and wind turbines which generates power to the HV transmission grids.

[0005] These small privately owned and operated domestic and commercial DEG device installations accelerated with the introduction of, then later updated and modified, Feed in Tariff (FIT) policies in the past few years. The FIT policies mandate transmission operators to pay owners of DEG devices minimum prices for excess power being generated and exported, or added back into the electrical power distribution grid. The myriad of privately owned and operated domestic and commercial DEG devices, connected in increasing numbers to the local LV distribution networks, creates a large impact on power quality not only for the end consumers, but for the stability of the electrical power distribution grid as a whole. There is a greatly increased chance of a transmission grid trip due to the reduction of spinning reserves with the offloading of the large central utilities due to additional power being generated by the growing number of commercial and especially domestic DEG device installation. The resultant voltage, current, and frequency aberrations from these privately owned and operated domestic and commercial DEG devices that are superimposed onto the distribution networks and transmission grids increase the possibility of setting off the system trip protective switch gears, which are normally adjusted to the tight tolerance and long-established legacy electrical power specifications.

[0006] When a voltage on a distribution network is over the regulated voltage limits, the DEG device interface control electronics disables the DEG device interface. This is generally referred to in the industry as overvoltage lockout (OVLO), and also undervoltage lockout (UVLO) when the voltage falls below the statutory lower voltage limit. An OVLO is typically implemented with an electromechanical relay for safety reasons to guarantee a full and complete electrical disconnection from the distribution network grid, and especially for anti-islanding. UVLO is implemented in the same manner. During an OVLO or UVLO, the distribution network not only shuts off any DEG energy recovery from the DEG devices and stops batteries from charging, it also eliminates any FIT recovery for the end consumers. Hence, the more exporting DEG interfaces connected to a local electrical power distribution network, for example a neighborhood of domestic PV installations or exporting battery systems, as the distribution network voltages increase due to the amount of excess energy being exported or delivered onto the distribution network by the DEG installations, the greater the number of these DEG interfaces are disabled as the OVLO relays are activated by the DEG interface control electronics. This inhibits energy recovery and FIT for the end consumers. This also possibly stops batteries from charging as the OVLO relays of the grid-tied battery systems are also activated.

[0007] Further, there is the potential of the DEG devices, including battery systems, being degraded or even destroyed by the OVLO relay oscillation or‘chattering’ (the repeated connecting and disconnecting at the statutory disconnection intervals). Due to the sub-standard or older legacy installations of the customer mains or sub- mains wiring from the point of use (POU) switchboard to the point of common connection (PCC), when a DEG device is exporting energy on to the grid, the exporting current of the DEG device is driven along the high resistance (sometimes > 1 Ohm) of the customer mains or sub-mains wiring, the voltage at the POU may increase above the PCC voltage. When voltage at the POU as sensed by the DEG interface is over the regulated voltage limit, the DEG interface control electronics triggers the OVLO relay and shuts off the DEG energy recovery from the DEG device for the statutory disconnection time, which is typically two or three minutes. When the POU voltage drops with no exporting current, the DEG device is reconnected again. The cycle repeats and hence the OVLO relay is oscillating or ‘chattering’ continuously locally at the POU, independent of the grid.

[0008] FIG. 1 illustrates a‘chattering’ phenomenon using waveforms of the DEG inverter’s current and the voltage on the energy consumer’s premises (i.e. a residential house), wherein the inverter that uses a mechanical relay for isolation from the grid. As shown in FIG. 1, the voltage on the consumer’s premises rises when the inverter connects the DEG device to the grid and exports current. The rising voltage then triggers the OVLO relay causing the inverter to disconnect from the grid for the statutory disconnection time. Such cycle repeats itself and results in relay ‘chattering’ that potentially shortens the life of the relay.

[0009] Therefore, there is a need for a method or apparatus for depressing, if not completely eliminating the‘chattering’ phenomenon from the increasing numbers of connections of DEG devices while meeting the requirements of tightly regulated and legislated legacy electrical standards imposed on HV transmission operators.

Summary of the Invention:

[0010] These and other needs are addressed by various embodiments of the present invention, wherein an approach is provided for a system for enabling distributed energy generation (DEG) device having an energy processing unit that interacts with the electrical power distribution grid and loads to eliminate the ‘chattering’ phenomenon.

[0011] In accordance with various embodiments of the present invention, a system for interacting with an electrical power distribution grid and the loads connected to it is provided. The system comprises a plurality of DEG devices and a plurality of EPUs. Each of the DEG devices has a first OVLO relay. The EPU is installed at a POU of the electrical power distribution grid. Each EPU is associated with the one or more DEG devices and comprises an input connection and an output connection. The input connector of the EPU connects to the electrical power distribution grid. The output connector of the EPU connects to the one or more loads and the OVLO relay of the corresponding DEG device.

[0012] In accordance to one aspect of the present invention, the EPU selectively disconnects or turns off the DEG device or the first OVLO relay when‘chattering’ phenomenon is detected.

[0013] In one embodiment of the present invention, the EPU further comprises a first current sensing unit coupled between the output connector of the EPU and the first OVLO relay.

[0014] In another embodiment, the system further comprises a battery module and a second OVLO relay. The second OVLO relay is coupled between the output connector of the EPU and the battery module.

[0015] In accordance to another aspect of the present invention, the EPU is configured for selectively disconnecting the second OVLO relay when‘chattering’ phenomenon is detected.

[0016] In one embodiment, the EPU further comprises a first current sensing unit coupled between the output connector of the EPU and the first OVLO relay.

[0017] In another embodiment, the EPU further comprises a second current sensing unit coupled between the output connector of the EPU and the second OVLO relay.

[0018] The first and second current sensing unit may be a current transformer.

[0019] In an embodiment, the EPU further comprises a communicating interface configured to communicate with the DEG device.

[0020] Accordingly, the EPU installed between the DEG device and the electrical power distribution grid protects and isolates the relay of the DEG device from customer mains wiring. As such, the chattering phenomenon can be depressed and eliminated.

Brief Description of Drawings:

[0021] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which:

[0022] FIG. 1 illustrates a chatter phenomenon using waveforms of the inverter’ s current and the voltage on an energy consumer’s premises;

[0023] FIG. 2 depicts a schematic diagram of an exemplary implementation of a system for DEG devices connected to an external electrical power distribution grid and corresponding loads in accordance with one embodiment of the present invention;

[0024] FIG. 3 depicts a schematic diagram of an exemplary implementation of an EPU coupled between the DEG device and the electrical power distribution grid in accordance with one embodiment of the present invention;

[0025] FIG. 4 depicts a schematic diagram of an exemplary implementation of the EPU in accordance with another embodiment of the present invention;

[0026] FIG. 5 depicts an illustration of the system for DEG devices connected to an external electrical power distribution grid and corresponding loads in accordance with one embodiment of the present invention;

[0027] FIG. 6 depicts a more detailed illustration of the system for DEG devices as shown in FIG. 5; and

[0028] FIG. 7 depicts an illustration of the cause of the‘chattering’ phenomenon.

Detailed Description:

[0029] In the following description, methods and systems of electrical power generation and distribution and the like are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

[0030] FIG. 2 depicts a schematic diagram of an exemplary implementation of a system for DEG devices connected to an external electrical power distribution grid and corresponding loads in accordance with one embodiment of the present invention. In FIG. 2, the system comprises a plurality of DEG devices 10, and a plurality of EPUs 12 installed at a POU of the electrical power distribution gird 14. Each EPU 12 comprises an input connector and an output connector. The input connector of the EPU 12 connects the electrical power distribution grid 14, and the output connector of the EPU 12 is connected to the corresponding load 16 and the DEG device 10. In this embodiment, each EPU 12 is connected to its corresponding DEG devices 10. However, a person skilled in art should realize that a single EPU 12 is allowed to connect to more than one DEG devices.

[0031] The POU may be a single or a number of circuits connected between the PCC 18 of the local low voltage (LV) grid 20 and the energy consumer’s premises (e.g. a residential house). As shown in FIG. 2, the switchboard 22 of the house is coupled to the LV grid 20 through a customer mains wiring 24 (i.e., sub mains wiring), and the EPU 12 is electrically coupled between the switchboard 22 with an optional meter 26 and the loads 16 of the house. The EPU 12 can be installed at each connection at the end of the POU, such as, but not limited to, the switchboard 22, electrical power connection service point, switch room, remotely at a single circuit connection to a single consumer premises, an adjacent location inside or outside of the energy consumer’s premises, or on an electric pole. The loads 16 of the energy consumer’s premise may be a house wiring, electronic appliances or illuminants.

[0032] FIG. 3 depicts a schematic diagram of an exemplary implementation of an EPU connected between the DEG device and the electrical power distribution grid in accordance with one embodiment of the present invention. The DEG device 10 comprises a power generation module 30, an inverter 32 and an overvoltage lockout (OVLO) relay 34. In this embodiment, the power generation module 30 may be a PV solar panel that converts energy from sunlight received into direct current (DC) electricity. The inverter 32 then converts the DC electricity into an alternating current (AC) electricity. Instead of being situated between the power generation module 30 and the inverter 32, the OVLO relay 34 is coupled between the inverter 32 and the output connector 122 of the EPU 12. The OVLO relay 34 is configured to selectively turn ON and OFF for protecting the inverter 32 and allowing electrical energy to be exported onto the electrical power distribution grid.

[0033] Since the power generation module 30 cannot store the electrical energy it generates, the energy generated must either be dispersed to an energy storage system such as a battery or consumed by a load 16. In this case, the DEG device 10 may further comprises an optional battery module 36. The DEG device 10 is connected to the output connector 122 of the EPU 12 that allows the EPU 12 to provide a regulated voltage to the load 16 and/or charge the battery module 36. The EPU 12 also exports any excess energy via its input connector 121 onto the electrical power distribution grid 14.

[0034] Once the DEG device 10 is connected to the output connector 122 of the EPU 12, the OVLO relay 34 is no longer isolating the inverter 32 from the electrical power distribution grid 14, and as such the DEG device 10 sees and senses only the nominal output (i.e. regulated voltage) of the EPU 12 instead of the voltage at the POU end of the customer mains wiring, which could increases as energy generated from the DEG device 10 is exported onto the power distribution grid 14. This way, energy generated by the DEG device 10 is passed back through the bidirectional EPU 12 onto the electrical power distribution grid 14 without triggering the OVLO relay 34, and at the same time eliminates the‘chattering’ phenomenon at the OVLO relay 34 of the DEG device 10.

[0035] In providing the regulated voltage and to ensure the power quality (e.g. commanding the DEG devices to turn off DEG energy export) in the electrical power distribution grid 14, the EPU 12 is configured to monitor monitored parameters including at least the input voltage and output voltage of the EPU 12, the POU current, DEG device 10 current, and export/import condition of the DEG device 10 current. From the monitored parameters, the EPU 12 determines the relevant parameters of the operating environment of the EPU 12 and the DEG device 10; these determined operational parameters include at least the voltage at the PCC 18, the customer mains wiring resistance from the switchboard 22 to the PCC 18, and compensation for the voltage increase or drop along the customer mains wiring from the EPU 12 to the PCC 18.

[0036] Various methods may be employed in the computation of the customer mains wiring resistance including, but not limited to, conditional statements, fuzzy logic, neural network, decision tree learning, or any machine learning as examples; alternatively, a method based on the Ohm’s law with two power quality data sets may be taken at the EPU 12 or the DEG device 10. The Ohm’s law-based method comprises sensing and recording the change in the EPU 12 input voltage ( W _»« 4 divided by the change in the EPU 12 current (/ _sense ) sampled over a period of time, and calculating the customer mains wiring resistance (R _w ) by:

[0037] In one embodiment, the battery module 36 includes an OVLO relay 38 coupled between the EPU 12 and the battery module 36. Similarly, by connecting the OVLO replay 38 to the output connector 122 of the EPU 12, the battery module 36 sees only the nominal output of the EPU 12 instead of the voltage at the POU end of the mains wiring. This in turn depresses, if not eliminates entirely, the ‘chattering’ phenomenon at the OVLO relay 38 of the battery module 36.

[0038] FIG. 4 depicts a schematic diagram of an exemplary implementation of the EPU in accordance with another embodiment of the present invention. In this embodiment, the EPU 12 further comprises a first current sensing unit CS1 and a second current sensing unit CS2. The first current sensing unit CS1 is coupled between the output connector 122 of the EPU 12 and OVLO relay 34 of the inverter 32. The second current sensing unit CS2 is coupled between the output connector 122 of the EPU 12 and OVLO relay 38 of the battery module 36. The first and the second current sensing units CS1 and CS2 respectively are configured for EPU 12 to sense the current of the corresponding OVLO 34, 36 respectively. In one embodiment, each of the first and the second current sensing units CS1 and CS2 respectively is a current transformer.

[0039] In this embodiment, the EPU 12 monitors the current to and from the DEG device 10 and the current to and from the battery module 36 via the first and the second current sensing units CS1 and CS2 respectively for waveform pattern of repeated turning on and off of DEG energy export, which ensures that the‘chattering’ phenomenon does not occur. If OVLO relay 34, 36 of the DEG device does chatter, EPU 12 then is able to disconnect or turn off the DEG device 10 through a data communicating interface 40.

[0040] In accordance to one embodiment, the EPU is configured to monitor and transmit information data on one or more monitored parameters including, but not limited to, the input voltage and output voltage of the EPU, the POU current, DEG device current, export/import condition of the DEG device current, frequency, temperature, and status of the EPU with respect to temperature, overvoltage protection (OVP), undervoltage protection (UVP), and bypass; in the case of a battery system, in addition, charged state, export/import condition of the battery current, and battery temperature.

[0041] FIG. 5 is used to further illustrate the working principle of the present invention. FIG. 5 depicts a schematic illustration of an exemplary residential house with a customer mains wiring from the grid PCC to the house switchboard. A series connected EPU is installed in this premises. The output of the EPU is connected to the house wiring, generally through the switchboard and relevant breakers (not shown in the figure) and to the shunt DEG device. The EPU comprises the following functional features:

[0042] 1. The EPU tolerates wide ranges of AC input voltages and generate a tightly regulated output voltage delivered directly at the POU and the DEG devices with programmable OVP and UVP that either one activates the EPU bypass relay.

[0043] 2. The EPU serves also as either a step down, a step up, or a full automatic voltage regulator (AVR) depending upon the application. In one embodiment, the EPU includes a high frequency series AC voltage regulator as disclosed in United States Patent No. 9,148,058, United States Patent No. 9,819,279, or United States Patent No. 9,979,312.

[0044] 3. The EPU is configurable and controllable remotely via a data communication interface.

[0045] 4. The EPU monitors one or more monitored parameters including, but not limited to, the input voltage and output voltage of the EPU, the POU current, DEG device current, export/import condition of the DEG device current, frequency, temperature, and status of the EPU with respect to temperature, OVP, UVP, and bypass; in the case of a battery system, in addition, charged state, export/import condition of the battery current, and battery temperature.

[0046] 5. The EPU determines from the monitored parameters relevant parameters of the operating environment of the EPU and the DEG devices installed there within; these determined operational parameters include, but not limited to, voltage at the grid PCC, the customer mains wiring resistance from the POU main switchboard to the grid PCC, compensation for the voltage increase or drop along the customer mains wiring from the EPU to the grid PCC, derivations in the monitored parameters from the international grid tie statutory standards and DEG device specifications;

[0047] 6. The EPU further comprises a data communication interface for sending to a remote computing device or server the monitored parameters and/or determined operational parameters; the data communication interface also allows SCADA control, configuration, and software/firmware updates to the EPU.

[0048] 7. The EPU is further configured to report and/or generate alarms any malfunction of the DEG devices including, but not limited to, the detection of OVLO relay‘chattering’.

[0049] In one embodiment, the EPU computes the grid PCC voltage based on the sensed voltage at the EPU installed at the POU main switchboard and the current flowing through it. Through data communication with the energy-exporting DEG devices, the EPU may command the DEG devices to reduce export current when the EPU recognized a local voltage rise in the computed grid PCC voltage. This is particularly important in maintaining the grid power quality, especially for local electrical power distribution areas (microgrids) that have high concentration of DEG device installations. In extreme cases of overabundance of DEG devices in small local electrical power distribution areas, the EPU may further comprise a controllable disconnect relay, internal or external to the EPU, to totally disengage and isolate any DEG device and maintain the voltage quality or voltage limits of the grid at the PCC. Also, by controlling the amount of DEG energy export or completely disconnecting the DEG device, operating life of the OVLO disconnect electro-mechanical relay is prolonged.

[0050] In one embodiment, the EPU is configured to sense and determine the polarity and the value of DEG current flowing in the current import or export direction. In cases where the grid voltage is going over statutory or quality limits, the EPU can increase the voltage across its output to cause the DEG device in sensing a higher voltage. This may reduce the DEG device power generation and increase the system consumption through the inverse of conservative voltage reduction (CVR), thereby reducing the export current or increasing the import current to allow the usage of over-supplied renewable energy.

[0051] In another embodiment, the EPU is configured to detect electrical system malfunction and/or installation errors, particularly by computing the local impedance, the EPU can determine whether the local impedance is above the allowable limit and inform the installer or the utility company as such. This prevents both voltage drop in the case of DEG current import and voltage rise in the case of DEG current export, and in turn prevents power quality issues like flickering, appliance degradation, or any other nuisance. In addition, the EPU can be used in testing DEG device statutory compliance. By deliberately allowing the EPU output voltage to rise under controlled conditions, the EPU can detect whether the DEG OVLO is functioning normally. For testing the proper functioning of DEG UVLO, the EPU reduces its output voltage under controlled conditions and that no load is consuming energy.

[0052] In yet another embodiment, the EPU is configured to provide real-time power quality data and allow cloud-based, ad-hoc, or mesh-based grid management by balancing the energy demand and supply for an electrical network by utilizing the EPU functions as described above. Balanced energy management allows legacy standby energy sources to reduce operations and improve efficiency of the electrical power generation and distribution network.

[0053] In another embodiment of the present invention, portions or all functions and/or software/firmware provided and incorporated in the EPU are incorporated and implemented in the DEG device and/or any electrical power generation device that export electrical energy onto the grid or local grid (microgrid). As such, any DEG device or electrical power generation device that incorporates the same or similar portions or all features of the EPU as described herein falls within the scope of this invention.

[0054] The embodiments disclosed herein may be implemented using computing devices, computer processors, microcontrollers, or electronic circuitries including but not limited to digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), and other programmable logic devices configured or programmed according to the teachings of the present disclosure. Computer instructions or software codes running in the computing devices, computer processors, or programmable logic devices can readily be prepared by practitioners skilled in the software or electronic art based on the teachings of the present disclosure.

[0055] The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

[0056] The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.