Patent ID: 12249837

DETAILED DESCRIPTION

Embodiments of the present disclosure comprise methods and apparatus which use a single phase microinverter comprising integrated neutral forming function. For example, a microinverter configured for use with an AC storage system comprises switching circuitry connected at an AC output of the microinverter. A three-line connector is connected at the AC output and comprises a neutral line connected between two lines configured to connect to at least one of a single phase grid system or a split phase grid system. The neutral line is connected to the microinverter at a point that maintains a mid-way voltage between the two lines voltage. The methods and apparatus described herein provide a required neutral forming transformer function for both North American and Japanese (e.g., 120/240 Vac) split-phase residential off-grid systems that are integrated into a battery storage microinverter. Additionally, the methods and apparatus described herein provide relatively low system/maintenance costs when compared to existing methods and apparatus that use smart grid connection relays.

FIG.1is a block diagram of a system100(e.g., power conversion system), in accordance with at least some embodiments of the present disclosure. The diagram ofFIG.1only portrays one variation of the myriad of possible system configurations. The present disclosure can function in a variety of environments and systems.

The system100comprises a structure102(e.g., a user's structure), such as a residential home or commercial building, having an associated DER118(distributed energy resource). The DER118is situated external to the structure102. For example, the DER118may be located on the roof of the structure102or can be part of a solar farm. The structure102comprises one or more loads and/or energy storage devices114(e.g., appliances, electric hot water heaters, thermostats/detectors, boilers, water pumps, and the like), which can be located within or outside the structure102, and a DER controller116, each coupled to a load center112. Although the energy storage devices114, the DER controller116, and the load center112are depicted as being located within the structure102, one or more of these may be located external to the structure102.

The load center112is coupled to the DER118by an AC bus104and is further coupled, via a meter152and a MID150(microgrid interconnect device), to a grid124(e.g., a commercial/utility power grid). The structure102, the energy storage devices114, DER controller116, DER118, load center112, generation meter154, meter152, and MID150are part of a microgrid180. It should be noted that one or more additional devices not shown inFIG.1may be part of the microgrid180. For example, a power meter or similar device may be coupled to the load center112.

The DER118comprises at least one renewable energy source (RES) coupled to power conditioners122(microinverters). For example, the DER118may comprise a plurality of RESs120coupled to a plurality of power conditioners122in a one-to-one correspondence (or two-to-one correspondence). In embodiments described herein, each RES of the plurality of RESs120is a photovoltaic module (PV), e.g., one or more photovoltaic modules, although in other embodiments the plurality of RESs120may be any type of system for generating DC power from a renewable form of energy, such as wind, hydro, and the like. The DER118may further comprise one or more batteries (or other types of energy storage/delivery devices) coupled to the power conditioners122in a one-to-one correspondence, where each pair of power conditioner122and a corresponding battery may be referred to as an AC battery130.

The power conditioners122invert the generated DC power from the plurality of RESs120and/or the battery141to AC power that is grid-compliant and couple the generated AC power to the grid124via the load center112. The generated AC power may be additionally or alternatively coupled via the load center112to the one or more loads (e.g., a solar pump) and/or the energy storage devices114. In addition, the power conditioners122that are coupled to the batteries141convert AC power from the AC bus104to DC power for charging the batteries141. A generation meter154is coupled at the output of the power conditioners122that are coupled to the plurality of RESs120in order to measure generated power.

In some alternative embodiments, the power conditioners122may be AC-AC converters that receive AC input and convert one type of AC power to another type of AC power. In other alternative embodiments, the power conditioners122may be DC-DC converters that convert one type of DC power to another type of DC power. In some of embodiments, the DC-DC converters may be coupled to a main DC-AC inverter for inverting the generated DC output to an AC output.

The power conditioners122may communicate with one another and with the DER controller116using power line communication (PLC), although additionally and/or alternatively other types of wired and/or wireless communication may be used. The DER controller116may provide operative control of the DER118and/or receive data or information from the DER118. For example, the DER controller116may be a gateway that receives data (e.g., alarms, messages, operating data, performance data, and the like) from the power conditioners122and communicates the data and/or other information via the communications network126to a cloud-based computing platform128, which can be configured to execute one or more application software, e.g., a grid connectivity control application, to a remote device or system such as a master controller (not shown), and the like. The DER controller116may also send control signals to the power conditioners122, such as control signals generated by the DER controller116or received from a remote device or the cloud-based computing platform128. The DER controller116may be communicably coupled to the communications network126via wired and/or wireless techniques. For example, the DER controller116may be wirelessly coupled to the communications network126via a commercially available router. In one or more embodiments, the DER controller116comprises an application-specific integrated circuit (ASIC) or microprocessor along with suitable software (e.g., a grid connectivity control application, switching control circuitry, etc.) for performing one or more of the functions described herein. For example, the DER controller116can include a memory (e.g., a non-transitory computer readable storage medium) having stored thereon instructions that when executed by a processor perform a method for grid connectivity control, as described in greater detail below.

The generation meter154(which may also be referred to as a production meter) may be any suitable energy meter that measures the energy generated by the DER118(e.g., by the power conditioners122coupled to the plurality of RESs120). The generation meter154measures real power flow (kWh) and, in some embodiments, reactive power flow (kVAR). The generation meter154may communicate the measured values to the DER controller116, for example using PLC, other types of wired communications, or wireless communication. Additionally, battery charge/discharge values are received through other networking protocols from the AC battery130itself.

The meter152may be any suitable energy meter that measures the energy consumed by the microgrid180, such as a net-metering meter, a bi-directional meter that measures energy imported from the grid124and well as energy exported to the grid124, a dual meter comprising two separate meters for measuring energy ingress and egress, and the like. In some embodiments, the meter152comprises the MID150or a portion thereof. The meter152measures one or more of real power flow (kWh), reactive power flow (kVAR), grid frequency, and grid voltage.

The MID150, which may also be referred to as an island interconnect device (IID), connects/disconnects the microgrid180to/from the grid124. The MID150comprises a disconnect component (e.g., a contactor or the like) for physically connecting/disconnecting the microgrid180to/from the grid124. For example, the DER controller116receives information regarding the present state of the system from the power conditioners122, and also receives the energy consumption values of the microgrid180from the meter152(for example via one or more of PLC, other types of wired communication, and wireless communication), and based on the received information (inputs), the DER controller116determines when to go on-grid or off-grid and instructs the MID150accordingly. In some alternative embodiments, the MID150comprises an ASIC or CPU, along with suitable software (e.g., an islanding module) for determining when to disconnect from/connect to the grid124. For example, the MID150may monitor the grid124and detect a grid fluctuation, disturbance or outage and, as a result, disconnect the microgrid180from the grid124. Once disconnected from the grid124, the microgrid180can continue to generate power as an intentional island without imposing safety risks, for example on any line workers that may be working on the grid124.

In some alternative embodiments, the MID150or a portion of the MID150is part of the DER controller116. For example, the DER controller116may comprise a CPU and an islanding module for monitoring the grid124, detecting grid failures and disturbances, determining when to disconnect from/connect to the grid124, and driving a disconnect component accordingly, where the disconnect component may be part of the DER controller116or, alternatively, separate from the DER controller116. In some embodiments, the MID150may communicate with the DER controller116(e.g., using wired techniques such as power line communications, or using wireless communication) for coordinating connection/disconnection to the grid124.

A user140can use one or more computing devices, such as a mobile device142(e.g., a smart phone, tablet, or the like) communicably coupled by wireless means to the communications network126. The mobile device142has a CPU, support circuits, and memory, and has one or more applications (an application146, which can be a grid connectivity control application) installed thereon for controlling the connectivity with the grid124as described herein. The application146may run on commercially available operating systems, such as IOS, ANDROID, and the like.

In order to control connectivity with the grid124, the user140interacts with an icon displayed on the mobile device142, for example a grid on-off toggle control or slide, which is referred to herein as a toggle button. The toggle button may be presented on one or more status screens pertaining to the microgrid180, such as a live status screen (not shown), for various validations, checks and alerts. The first time the user140interacts with the toggle button, the user140is taken to a consent page, such as a grid connectivity consent page, under setting and will be allowed to interact with toggle button only after he/she gives consent.

Once consent is received, the scenarios below, listed in order of priority, will be handled differently. Based on the desired action as entered by the user140, the corresponding instructions are communicated to the DER controller116via the communications network126using any suitable protocol, such as HTTP(S), MQTT(S), WebSockets, and the like. The DER controller116, which may store the received instructions as needed, instructs the MID150to connect to or disconnect from the grid124as appropriate.

FIG.2is a block diagram of a microinverter200(e.g., power conditioners122) configured for use with the system100ofFIG.1, in accordance with at least some embodiments of the present disclosure. As noted above, the DER controller116controls operation of the microinverter200. For example, in addition to comprising voltage and current sampling circuitry (not shown), control circuitry117can be communicatively coupled to a line-cycle monitoring module (not shown) for receiving data used to control a cycloconverter205which produces a three-phase AC output. The cycloconverter205comprises four (4) AC side MOSFETS204(a cycloconverter comprising switches and related components at the output side of the microinverter200). The control circuitry117coordinates timing of the AC side MOSFETS204based on measurements from the voltage and current sampling circuitry, e.g., using pulse width modulation (PWM).

The control circuitry117controls the AC side MOSFETS204to generate a single-phase AC output that is coupled to an AC output port210. The control circuitry117also controls the microinverter200to cycle power through (i.e., charge and discharge) a line-cycle energy storage capacitor (a DC side input capacitor216) to output power that is sinusoidal to AC output port210and/or to AC mains.

The control circuitry117drives four (4) DC side MOSFETS202(input side of microinverter) and the four (4) AC side MOSFETS204using power from a housekeeping power supply that derives power from a DC input206. For example, the housekeeping power supply is powered up from the DC voltage present across the DC side input capacitor216. A 100 kHz voltage generated across the DC side of the main isolation transformer212can be rectified by body-diodes214of the DC side MOSFETS202. The body-diodes214of the DC side MOSFETS202rectify the 100 kHz voltage and charge up a DC side input capacitor216. A main control ASIC (e.g., in the DER controller116) can be powered up and the main control ASIC generates valid gate drivers signals to drive both the DC side MOSFETS202and AC side MOSFETS204. Switching gate drivers of the AC side MOSFETS204are configured to drive a voltage into the AC side of a main isolation transformer212. An inductor Lr is connected in series with a secondary winding of the main isolation transformer212and a pair of capacitors Cr are connected in series with a corresponding pair of the AC side MOSFETS204to maintain a predetermined voltage at a drain of the corresponding pair of the AC side MOSFETS204.

The microinverter200is bi-directional from a power conversion perspective, i.e., DC→AC and AC→DC, which is central to the microinverter200being used in a battery energy storage microinverter. Additionally, the bi-directional functionality of the microinverter200allows for PV applications in that the microinverter is able to continue to run once the sun goes down. That is, if the power output from the PV module falls to zero (e.g., at nighttime) the microinverter200starts to operate in the AC→DC mode, thus allowing a housekeeping power supply to be powered from power that is derived from the AC side of the microinverter200. In this way the microinverter200is able to run indefinitely during the nighttime.

The microinverter200is configured, at the AC output port210, for connection to a 230 Vac/240 Vac single phase grid and/or a split phase grid. In at least some embodiments (e.g., North American residential applications) an AC output of the microinverter200is configured to connect to Line-1 (L1) and Line-2 (L2) connections of a residential 120/240 Vac split-phase system. In at least some embodiments (e.g., rest of world (RoW) applications) the AC output of the microinverter200is configured to connect to the L1 and L2 connections (e.g., live & neutral) of the 230 Vac single phase residential system.

The inventor has found that by adding an additional inductor (Ln) provides a third neutral connection (N) to the AC output port210of the microinverter200. The third neutral connection N provides an EMC/surge filter (e.g., a three input and three output connection filter), based on a high frequency switching of the AC side MOSFETS204(e.g., AC bridge MOSFETs). For example, under control of the control circuitry117, a first (top) node of the inductor Ln is alternately connected by the AC side MOSFETS204so that the inductor Ln is connected about 50% of the time to the L1 connection and connected about 50% of the time to the L2 connection. In at least some embodiments, the inductor Ln averages out the AC side MOSFETS204(AC bridge switching) such that a second (bottom) node of the inductor Ln is maintained at a predetermined voltage. In at least some embodiments, the predetermined voltage can be about mid-way between a potential of the L1 connection and the L2 connection (e.g., an average voltage between the two lines voltage). That is, the additional inductor Ln functions as a neutral forming transformer and, in at least some embodiments, can have the same inductance as the inductor Lr.

FIG.3is a schematic diagram of a microinverter300of a storage system configured for use with the energy management system ofFIG.1, in accordance with at least some embodiments of the present disclosure. The microinverter300is substantially identical to the microinverter200. Accordingly, only those features that are unique to the microinverter are described herein. For example, unlike the microinverter200, the microinverter300is a full-bridge microinverter. That is, the microinverter300comprises cycloconverter305comprising eight (8) AC side MOSFETS304, four (4) AC side MOSFETS304connected in series on each leg of the output side of the microinverter300300. Additionally, on each side of the secondary windings of the transformer212a pair of inductors Lr and Capacitors Cr are connected in series with each other. Moreover, instead of using an inductor Ln, the third neutral connection (N) is directly connected to a mid-point of the secondary windings of the transformer (e.g., center tap—neutral forming transformer). Furthermore, the control circuitry117controls the AC side MOSFETS304in a manner as described above, making the necessary adjustments to accommodate the four additional MOSFETS. The four additional MOSFETS are driven with the same gate signals but transposed left to right.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.