Dispatchable, distributed, and scalable solar power systems

Abstract

Exemplary embodiments of the present disclosure provide a current source converter comprising a transformer, a first circuit, and a second circuit. The transformer may comprise a first winding, a second winding, and a third winding. The first circuit may be electrically coupled to the first and second windings. The first circuit may comprise a battery port and a photovoltaic (PV) port. The battery port may be configured to interface with one or more batteries. The PV port may be configured to interface with one or more PV modules. The second circuit may be electrically coupled to the third winding. The second circuit may comprise an AC port configured to interface with an alternating current (AC) load.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 63 / 297,422, filed January 7, 2022, which is incorporated by reference in its entirety as if fully set forth below.

[0002] (Technical field) Various embodiments of the present disclosure relate generally to solar power systems, and more particularly to dispatchable, distributed, and scalable solar power systems. [Background technology]

[0003] As solar energy becomes more prevalent on the grid, it is important that grid-tied photovoltaic (PV) systems become easier to install and operate, and provide higher value through grid services and dispatchability. Current components are simple PV solar panels, typically rated at 300-500 watts, interconnected to achieve various DC voltage levels. Strings are connected in series on-site to achieve DC voltages up to 1500 volts. These PV strings are interconnected using combiner boxes to achieve higher current and power levels, and connected to the grid with DC / AC inverters. The entire system is custom designed, and the cost of the "peripheral equipment" including system design, civil engineering, labor, protection, isolation, and sensing is significantly higher than the cost of the power inverter (and sometimes the PV panels themselves). Additionally, PV inverters do not address dispatchable power. To achieve dispatchability, energy storage must be added along with further inverters (or isolated dc / dc converters), positioning and coordination of protectors and controls. Advanced grid services and coordination with grid operators imply additional complexities including communications, cybersecurity, and compliance with required protocols. Finally, the required sensing, analytics, and maintenance support are added. All these factors severely limit the scalability and rapid deployment of such large-scale systems. Nevertheless, the deployment of PV systems and systems with energy storage is exploding with electricity demand exceeding 100 GW per year, yet projects are delayed by as much as 3-4 years. Furthermore, existing solutions have difficulty providing advanced grid services such as inertial support, black start, and grid formation capabilities that may currently require detailed coordination with grid operators. This suggests that there is an opportunity for a different approach to realize a PV-based generation resource that is cost-effective, rapidly scalable to any level, and dispatchable and scalable.

[0004] The complexity and customization mentioned above are limiting the ability to rapidly deploy and scale. As mentioned above, this creates a huge pipeline of projects waiting for design and grid interconnection validation, with wait times measured in years. Considering the rapid learning rate of the technology itself, which is advancing at a very fast pace, usually in two-year cycles, it is clear that the complexity of system implementation will only increase as multiple technology generations need to be linked together in terms of unit-to-unit and grid-to-grid coordination. There is a need for plug-and-play solutions for dispatchable PV generating resources that are easy to install, commission, and safely maintain in many different operating environments, with guaranteed interoperability across multiple technology generations and years for a wide range of applications. Such capabilities are currently unavailable and are desirable to achieve the global goal of decarbonization.

[0005] Older generation inverters can generally be considered plug-and-play, raising the question of why they do not meet the requirements described here. Rooftop panels were connected to the grid using inverters, similar to large PV power plants. Because monetary compensation was based on delivered energy (watt-hours), early generation inverters typically operated to deliver maximum power to the grid under all operating conditions, sometimes using a maximum power point tracking (MPPT) control strategy. In such cases, each inverter operated independently of the others, simply pushing out power at the desired frequency and unity power factor using the grid as a "template". As inverters became more prevalent on the grid, inverters were expected to maintain connection to the grid even during transient and fault conditions, resulting in new requirements such as VAR support, low voltage ride-through (LVRT), unbalanced operation, and zero voltage ride-through (ZVRT). The majority of deployed inverters, including those deployed on rooftops, operate in such a "grid-following" mode, and therefore appear to operate "autonomously". However, its functionality is very limited and it can only operate and supply power to the grid when the grid is present and healthy.

[0006] As inverters became more prevalent in the grid, grid operators tried to use inverters to balance the grid and provide grid services such as VARs, frequency regulation, and inertial support. During times of congestion, grid operators tried to curtail PV power. Also, if additional power was needed beyond what the PV panels could provide at that moment, there was no way to achieve it. This required energy storage such as batteries or additional inverters. Galvanic isolation was also desired to ensure a safe ground and minimize degradation of the panels. It would be desirable for these inverters to be grid-forming capable to provide grid-forming and black-start capabilities, but these technologies are not widely prevalent or deployed. A PV power plant (of any size) to act as a grid resource would require PV, energy storage, an inverter to connect these DC devices to the AC grid, galvanic isolation to ensure safety and ability to manage failure mechanisms, communication with the grid operator, the ability to autonomously manage all transients and faults, and the ability to provide a set of grid services. Additionally, a future grid with abundant renewable energy would require large amounts of energy storage, so energy storage became a key piece of this puzzle. Figure 1 shows the layout of a possible 20 MW conventional PV power plant, including energy storage. This shows how complex it is to build a large-scale PV power plant.

[0007] Currently, batteries are commonly used for energy storage functions. Lithium-ion batteries have offered an acceptable alternative as their price has rapidly approached economically viable levels due to their rapid adoption in the EV sector. The batteries and packages developed needed to be lightweight and compact to meet on-board requirements, which required active cooling, mechanical bracing, and DC fast charging. The same battery architecture was also adapted for terrestrial applications. To achieve the storage levels required in bulk systems, over 100 megawatts of energy storage have been deployed in large PV power plants. This is widely done with systems costing $32 / MW-hour including PV and 4 hours of storage. The cost is well below the cost of typical fossil fuel-based generation. Energy storage systems are typically implemented in air-conditioned, temperature-controlled containers and store up to 1MW-hour of energy in a dense form factor. The batteries are connected in series at 600-1000V DC with an extensive battery management system that ensures that individual cell voltages do not exceed that and that individual cells do not overheat. A typical 1MW system may have 40,000 cells that need to be monitored, but in practice monitoring is difficult to do. Instead, monitoring is done at a sub-pack level, say 12 volts, with the assumption that the state of all cells is known. Due to the tight packaging and high power and energy density required, this can cause localized overheating. At best, this will throttle the battery capacity (if detected); at worst, it can cause thermal runaway, leading to a battery fire that is difficult to manage. There have been many battery fires that have caused safety hazards and received significant bad press, especially when deployed in crowded urban areas.

[0008] As a result, the overall system complexity and cost will be very high, causing significant problems and limiting scalability. Implementation requires significant technical expertise to design, build, commission, operate and maintain the facilities, which drives up overall costs. Many of these projects have economics based on a 20-year life cycle, which also creates hidden costs, i.e. the expertise to operate the system and the cost of maintaining obsolete parts and components to replace failed elements. It also requires the continuation of obsolete systems (power electronics, communications, controls) on a 2-year cycle. The steep learning rate calls into question the economic viability of the project as similar competing solutions become less costly, which can lead to stranded assets (e.g. "peak load" gas plants). This has a significant impact on the complexity and cost of implementation, and creates uncertainty as to whether the economic value will be fully realized. It is clear that a different approach is needed.

[0009] Therefore, to realize the benefits of scalability for virtually any level of PV solar system (from a few kilowatts to over 100 megawatts), modular plug-and-play building blocks are desired that can implement all grid services at any scale. This includes full dispatchability, ability to follow or form a grid, ability to connect or form a microgrid, and ability to support the grid during normal, transient, and fault conditions. The modules should be easy to deploy, highly available, and highly interoperable to accommodate rapid technology transitions. The modules should operate autonomously, meeting all real-time operating requirements in grid-tied or microgrid modes, and be able to adjust and optimize system-level performance through low-latency communications, where available. The modules should also be capable of detecting and protecting against faults and malfunctions, minimizing the impact of a failed module on the system, and allowing the system to be repaired and operational quickly without the need for highly trained technicians. Finally, the modules and systems should be inherently safe, free of dangerous voltage issues that maintenance and repair personnel may have access to, and free of thermal runaway and large-scale fire issues that have occurred in many high-power battery-based systems.

[0010] There have been several attempts to interconnect the various elements of a PV system. Microinverters, rated at around 200 watts, have been commercially available for years to be mounted on PV panels and fulfill the basic need of universal connectivity. Microinverters take the DC voltage available from the panels and convert it to AC voltage, which can be directly connected to the AC grid. While microinverters have only operated in grid-following mode up until now, recent microinverters claim grid-forming capabilities by utilizing the surplus power available at the PV panel level. The challenge of integrating energy storage at the PV panel level has not yet reached a solution that is considered commercially viable. As a result, currently available microinverters are unable to meet the above requirements. However, they are unable to interface with energy storage and therefore cannot provide advanced features that are key to true scalability and economics.

[0011] Moving away from the central plant level energy storage concept, the idea of ​​a more distributed 3-port configuration at the sub-plant level has also been proposed. Figure 2 shows the configuration of a PV hybrid power plant utilizing a medium voltage string inverter connecting to a 300kW DC 1000V PV string, with an energy storage module connected to the grid. Although simpler than the centralized concept of Figure 1, it still requires a significant level of customization and DC collection system, with replacement parts required to be available for the life of the plant. Furthermore, it cannot be easily scaled down to smaller systems. Therefore, the even simpler approach provided by the present disclosure is desirable. Summary of the Invention

[0012] An exemplary embodiment of the present disclosure provides a current source converter comprising a transformer, a first circuit, and a second circuit. The transformer may comprise a first winding, a second winding, and a third winding. The first circuit may be electrically coupled to the first winding and the second winding. The first circuit may comprise a battery port and a photovoltaic power port. The battery port may be configured to interface with one or more batteries. The PV port may be configured to interface with one or more PV modules. The second circuit may be electrically coupled to the third winding. The second circuit may comprise an alternating current (AC) port configured to interface with an AC load.

[0013] In any of the embodiments disclosed herein, the converter may be configured to operate in multiple modes to flow electrical energy between one or more of the battery port, the PV port, and the AC port and another of the battery port, the PV port, and the AC port.

[0014] In any of the embodiments disclosed herein, the multiple modes may include a first mode in which electrical energy is transferred from the PV port to the battery port.

[0015] In any of the embodiments disclosed herein, the multiple modes may include a second mode in which electrical energy is transferred from the PV port to the AC port.

[0016] In any of the embodiments disclosed herein, the multiple modes may include a third mode in which electrical energy is transferred from the battery port to the AC port.

[0017] In any of the embodiments disclosed herein, the multiple modes may include a fourth mode in which electrical energy is transferred from the AC port to the battery port.

[0018] In any of the embodiments disclosed herein, the battery port may be configured to operate at a voltage level of about 48V or less.

[0019] In any of the embodiments disclosed herein, the AC port may be a single phase AC port.

[0020] In any of the embodiments disclosed herein, the AC port may be a three-phase, three-wire AC port.

[0021] In any of the embodiments disclosed herein, the AC port may be a three-phase, four-wire AC port.

[0022] In any of the embodiments disclosed herein, the first circuit may further comprise a plurality of bidirectional switches.

[0023] In any of the embodiments disclosed herein, the bidirectional switch may be a silicon carbide switch, a silicon switch, a gallium nitride switch, or a combination thereof.

[0024] In any of the embodiments disclosed herein, the bidirectional switch may be configured to operate in a reverse blocking mode.

[0025] In any of the embodiments disclosed herein, the multiple bidirectional switches may include a second bidirectional switch connected in series with the first transformer winding and the battery port, and the converter may be configured to flow electrical energy from the battery port to the first winding during a switching cycle when the second bidirectional switch is in a closed position.

[0026] In any of the embodiments disclosed herein, the multiple bidirectional switches may include a first bidirectional switch connected in series with the second transformer winding and the battery port, and the converter may be configured to flow electrical energy from the second transformer winding to the battery port during a switching cycle when the first bidirectional switch is in a closed position.

[0027] In any of the embodiments disclosed herein, the multiple bidirectional switches may include a third bidirectional switch connected in series with the first transformer winding and the PV port, and the converter may be configured to flow electrical energy from the PV port to the first winding during a switching cycle when the third bidirectional switch is in a closed position.

[0028] In any of the embodiments disclosed herein, the first circuit may further include a clamp circuit configured to discharge leakage energy from the transformer.

[0029] In any of the embodiments disclosed herein, the first circuit may further include an energy recovery circuit shunt-connected to the clamp circuit.

[0030] In any of the embodiments disclosed herein, the first circuit may further include an energy recovery circuit configured to recover the discharged leakage energy to the battery port.

[0031] In any of the embodiments disclosed herein, the second circuit may further include a plurality of half-bridge branches, each of which may include a first reverse blocking switch and a second reverse blocking switch.

[0032] In any of the embodiments disclosed herein, the second circuit may further include an output capacitive / inductive ("CL") filter in parallel with the AC port, the output capacitive filter being configured to interface the AC port with an AC load.

[0033] In any of the embodiments disclosed herein, the transformer may have a ratio between the first winding, the second winding, and the third winding of N1:N1:N2.

[0034] Another embodiment of the present disclosure provides a method of operating a current source converter. The current source converter may include a transformer having a first winding, a second winding, and a third winding, a first circuit electrically coupled to the first winding and the second winding and including a battery port and a photovoltaic power port, and a second circuit electrically coupled to the third winding and including an AC port. The method may include transferring electrical energy from the battery port to the AC port, transferring electrical energy from the PV port to the AC port, and transferring electrical energy from the PV port to the battery port.

[0035] In any of the embodiments disclosed herein, the method may further include transferring electrical energy from the AC port to the battery port.

[0036] In any of the embodiments disclosed herein, the step of transferring electrical energy from the battery port to the AC port may include performing a switching cycle comprising closing a second bidirectional switch connected in series between the battery port and the first winding.

[0037] In any of the embodiments disclosed herein, the step of transferring electrical energy from the PV port to the AC port may include performing a switching cycle comprising closing a third bidirectional switch connected in series between the PV port and the first winding.

[0038] In any of the embodiments disclosed herein, transferring electrical energy from the PV port to the battery port may include performing a switching cycle comprising closing a third bidirectional switch connected in series between the PV port and the first winding and closing a first bidirectional switch connected in series between the battery port and the second winding.

[0039] In any of the embodiments disclosed herein, the method may further include discharging leakage energy from the transformer using a clamp circuit in the first circuit.

[0040] In any of the embodiments disclosed herein, the step of transferring leakage energy from the discharged transformer to the battery port may include implementing an energy recovery circuit.

[0041] These and other aspects of the present disclosure are described below in the Detailed Description of the Invention and in the accompanying drawings. Other aspects and features of the embodiments will become apparent to those skilled in the art upon review of the following description of certain exemplary embodiments in conjunction with the drawings. Although features of the present disclosure may be described in conjunction with certain embodiments and drawings, all embodiments of the present disclosure may include one or more of the features described herein. Furthermore, although one or more embodiments may be described as having certain advantageous features, one or more of such features may also be used with various embodiments described herein. Similarly, although exemplary embodiments may be described below as device, system, or method embodiments, it should be understood that such exemplary embodiments may be implemented in various devices, systems, and methods of the present disclosure.

[0042] The following detailed description of certain embodiments of the present disclosure will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the present disclosure, certain embodiments are shown in the drawings. It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings. [Brief description of the drawings]

[0043] [Figure 1] FIG. 1 is a schematic diagram illustrating a hybrid solar power plant according to one embodiment of the present disclosure.

[0044] [Diagram 2] FIG. 2 is a schematic diagram illustrating a hybrid solar power plant implementing a medium voltage multi-port string inverter in accordance with an embodiment of the present disclosure.

[0045] [Figure 3A] FIG. 3A is an illustration of an exemplary solar power device AC architecture according to one embodiment of the present disclosure. [Figure 3B] FIG. 3B is a diagram illustrating an exemplary solar power generation device three-port converter using a daisy chain according to the embodiment.

[0046] [Figure 4] FIG. 4 is a diagram illustrating a solar power generation device three-port converter according to an exemplary embodiment of the present disclosure.

[0047] [Figure 5A] FIG. 5A is a schematic diagram showing a conventional multi-converter implementation with dual active bridge HF links. [Figure 5B] FIG. 5B is a schematic diagram showing a conventional multi-converter implementation with dual active bridge HF links.

[0048] [Figure 6] FIG. 6 is a functional single line diagram of a three-port converter according to an exemplary embodiment of the present disclosure.

[0049] [Figure 7] FIG. 7 is a schematic diagram showing a conventional medium-voltage multi-port soft-switching semiconductor transformer with a PV port, a battery port, and an AC port configuration.

[0050] [Figure 8A] FIG. 8A is a schematic diagram illustrating a solar power device three-port converter with single phase output according to an exemplary embodiment of the present disclosure. [Figure 8B] FIG. 8B is a schematic diagram illustrating a solar power device three-port converter with three phase outputs according to an exemplary embodiment of the present disclosure.

[0051] [Figure 9] FIG. 9 illustrates a solar power device three-port converter control scheme according to an exemplary embodiment of the present disclosure.

[0052] [Figure 10A] FIG. 10A is a plot illustrating characteristic waveforms of an example solar power device three-port converter of the present disclosure. [Figure 10B] FIG. 10B is a plot illustrating simulated waveforms of an example solar power device three-port converter of the present disclosure.

[0053] [Figure 11] 11A and 11B are plots illustrating characteristic and simulated single-phase AC waveforms, respectively, of an example solar power device three-port converter of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] In order to facilitate the understanding of the principles and features of the present disclosure, various exemplary embodiments are described below. The components, steps, and materials described below as constituting various elements of the embodiments disclosed herein are intended to be illustrative and not limiting. Many suitable components, steps, and materials that will perform the same or similar functions as the components, steps, and materials described herein are intended to be encompassed within the scope of the present disclosure. Such other components, steps, and materials not described herein include, but are not limited to, similar components or steps developed after the development of the embodiments disclosed herein.

[0055] Disclosed is a dispatchable distributed solar power system (herein referred to as a "solar grid") with advanced grid support, grid formation, and microgrid capabilities. The solar grid can be built with multiple (from a few to thousands) "Solar Gen" devices, enabling systems rated from a few kilowatts to hundreds of megawatts. The "Solar Gen" devices are PV panel-level scalable building blocks that can interface with PV panels, grid-tied energy storage, three-port converters, communications, and control, enabling advanced functionality that enables technology-agnostic plug-and-play system designs that are highly scalable, rapidly deployable, and easily maintainable. The goal of the solar grid system is to eliminate / reduce the customization of electrical system design and construction at the plant level that is typically required to implement large-scale systems. The modular system, along with its architecture and interface specifications, provides a high degree of interoperability in the face of technology transitions, providing flexible building blocks to meet a wide variety of emerging needs for the renewable energy-rich grid of the future.

[0056] To achieve the desired solar grid functionality, a "photovoltaic device" can be used as a basic building block. Each photovoltaic device can include a PV panel and a single three-port converter box attached to or integrated with the PV panel (preferably behind the shaded panel), which can include communication, control, and protection elements as well as an energy storage battery to achieve the desired functionality and flexibility. The target power of these panels is expected to be on the order of 250-500 watts, but the disclosure is not so limited and those skilled in the art will appreciate that the system disclosed herein can be modified to many different power levels. The three-port converter, described in more detail below, can have at least two DC ports that are connected to the PV panel and the battery, and includes AC inverter functionality that can directly connect the third port to the AC grid at an available AC voltage (such as 240 volts single phase or 480 volts three phase). Additionally, the controller can be capable of autonomously and in real time controlling the bidirectional power flow between the PV panel, the battery, and the grid. The controller may also provide advanced control such as grid forming mode, power dispatch mode when grid connected, fault ride through, grid support, self-synchronization with the grid, providing various levels of inertial support as needed, and autonomous power frequency droop mode when operating as a grid independent microgrid. An exemplary rating for the AC panel is 350 watts, 277 volts AC single phase or 480 volts three phase, and 1.3 kW-hours of energy storage, although many other ratings are contemplated within the scope of the embodiments of the present disclosure. Each grid connected 3 port may be fully protected on the AC side as well as the DC side.

[0057] In a traditional PV plant, power is distributed from a high voltage substation using medium voltage lines to transformers (1-4MW for central inverters, 150kW for string inverters). A DC / AC inverter, typically optimized for efficiency, converts the 1000V to 1500V DC from the PV panels to 480 volts AC, which is then stepped up by a medium voltage transformer. The DC from the PV strings is custom laid out with DC collector buses, combiners, sensing, and protection. As mentioned above, this is all very customized and expensive. Examples are shown in Figure 1 and Figure 2.

[0058] A solar grid may follow a more traditional radial AC distribution grid architecture and may not involve custom elements. Medium voltage power may be distributed from a high voltage substation using poles and overhead lines (or buried cables). As with residential or commercial feeders, transformers on poles (or concrete pads) rated 50-150 kW may connect to the MV transmission line with fused disconnects and step down the voltage to standard AC voltages (240, 480, or 575 volts AC). This is a very scalable and cost-effective way to distribute large amounts of power to many points. An example of an arrangement for solar grid distribution is shown in Figure 3A.

[0059] In some embodiments, a solar grid system can be built with multiple photovoltaic device (see FIG. 4) units hung on mounting brackets (as shown in FIG. 3B) and connected in parallel to an AC power line by a daisy-chaining process with cost-effective weatherproof plug sockets or other arrangements known in the art. Another approach is to use tapped AC cables to power each photovoltaic device. An example is 30 amps at 480 volts three-phase AC for a maximum continuous output of 25 kW per PV string. Six such strings can generate 150 kW, forming a "scalable cell" of a PV plant. Assuming a 250 amp limit for a 13 kV feeder, the maximum power per line is over 5 MW, which can be doubled by doubling the number of conductors or increasing the ampacity. This "standard cell" can be replicated as needed, demonstrating the ease of scaling the system.

[0060] As mentioned above, the interconnection of energy storage elements at the panel level in some embodiments of photovoltaic devices is a major departure from many traditional centralized systems. Centralized battery storage systems can require complex monitoring, thermal management, and active cooling, all of which increase costs. The distributed form factor that photovoltaic devices can offer can eliminate the need to build high power, high voltage DC battery systems, eliminating concerns about protection, thermal runaway, and fire hazards. Energy return efficiency can also be improved, as the BMS process with high voltage battery strings typically loses as much as 20% of energy under fast charge and discharge conditions. To provide on-site safety, both the battery and the PV panel can operate at an intrinsically safe voltage, such as 48 volts DC, and be connected to the low voltage side. Since space is not as severely constrained as in centralized systems, the energy dissipation of the 48 volt 1.5 kW-hour cells that can be used in photovoltaic devices is minimal and can be passively managed. Local intelligence and a battery monitoring system (BMS) can manage the interconnected batteries and operate them within their design specifications. The lower battery voltage also makes it easier to equalize the thermal load on the batteries, simplifying the need for a BMS and dramatically reducing losses caused by traditional BMS when rapidly charging and discharging high-voltage battery packs, improving the energy handling capacity of the entire plant. The lower voltage of the batteries and PV panels also allows the modules to be designed so that batteries can be replaced in the field by less skilled technicians if necessary. The lower voltage of the PV panels also eliminates the need to be designed to withstand 1500V DC as in the past, eliminating a major degradation mechanism. This approach can also improve the reliability and lifespan of the batteries. Together, the batteries and PV panels can be combined with a three-port converter to provide a full range of functions for grid services, grid support, and grid formation.

[0061] To achieve the above functions, two different approaches can be considered. One is to use a microinverter for the power flow control function from PV to grid and add a second "box" containing a battery, a bidirectional DC / DC converter with high frequency isolation, and a DC / AC inverter for grid connection. An example is shown in Figure 5A and Figure 5B, where a dual active bridge (DAB) converter is used for HF isolation and a DC / AC inverter is used for grid connection. This approach can significantly increase the cost of the system by using another inverter for further HF isolation in addition to the PV inverter.

[0062] Therefore, a grid-tied three-port converter that can simultaneously manage the power flow between the PV panel, the battery, and the grid, and do so while meeting all the other operational requirements mentioned above, is an attractive solution. Conventional systems do not offer such a solution because conventional implementation methods are too expensive and infeasible.

[0063] Figure 6 is a single-line diagram showing an exemplary three-port converter that connects to a 48-volt PV panel and a 48-volt battery on the DC side, and to one or three-phase AC on the AC side. As mentioned above, this can be done with multiple converters, all of which include a DC / DC converter that interfaces with the battery and PV panel, another galvanically isolated DC / DC converter that converts the low voltage to a high DC voltage, and finally an inverter (typically a voltage-source inverter) that converts the DC to AC and connects to the grid. Filtering and EMI suppression are used, in addition to protection, synchronization, and fault ride-through. Stable operation of such a VSI continues to be a challenge that has not been fully solved in an unfamiliar and variable multi-converter environment.

[0064] Modern multi-port converters such as the S4T (including the AC-Cube implementation) (see Figure 7) offer a promising alternative, promising improved controllability over paralleled converters due to their interconnected three-port functionality and current source characteristics, but at the cost of a higher switch count and the need for two resonant switches and tanks that can be difficult to implement on the low-voltage side.

[0065] Various embodiments of the present disclosure provide a current source converter that addresses these shortcomings while still providing the desired three-port functionality. Exemplary converters are shown in Figures 8A and 8B. Figure 8A illustrates a current source converter with a single-phase AC output circuit, and Figure 8B illustrates a current source converter with a three-phase AC output circuit.

[0066] The current source converter may include a transformer 105, a first circuit 110, and a second circuit 115. The transformer 105 may be any of a number of transformers known in the art. The transformer 105 may include multiple windings. For example, as shown in FIG. 8A and FIG. 8B, the transformer may include a first winding 106, a second winding 107, and a third winding 108. The windings 106, 107, and 108 may have various winding ratios. In some embodiments, the transformer 105 may have a 1:1:N ratio between the first winding, the second winding, and the third winding.

[0067] The first circuit 110 (sometimes referred to as a DC circuit or input circuit) may be electrically coupled to the transformer 105. As shown in FIG. 8A and FIG. 8B, the first winding 106 and the second winding 107 may be electrically coupled to the first circuit 110. The first circuit 110 and the second circuit 115 may include one or more ports (i.e., electrical interface electrical devices / systems such as batteries, PV, generators, loads, networks, etc.). As shown in FIG. 8A and FIG. 8B, the first circuit 110 may include a battery port 120 and a PV port 125. The battery port 120 may be configured to interface with one or more batteries. The PV port 125 may be configured to interface with one or more PV modules.

[0068] The PV port 125 and the battery port 120 may be electrically coupled to the transformer 105 via one or more switches 111, 112, 113. The switches may be various switches known in the art. In some embodiments, the switches may be bidirectional switches. In some embodiments, the bidirectional switches may be configured to operate in a reverse blocking mode. The bidirectional switches may be implemented with silicon or wide bandgap semiconductors, including but not limited to silicon carbide and gallium nitride. Wide bandgap devices may minimize the possibility of reverse recovery currents that can lead to voltage spikes, excessive consumption, and reduced life. On the low voltage (LV) side, an exemplary silicon MOSFET device is rated at 100 volts, RD S is about 1 to 2 milliohms, and the loss is at the 0.1 watt level.

[0069] The second circuit 115 (sometimes referred to as an AC circuit or output circuit) may be electrically coupled to the third winding 108 of the transformer 105. The second circuit 115 may include an AC port 130 configured to interface with an alternating current (AC) load. As used herein, an "AC load" refers to any alternating current source, load, or network, such as an electric utility grid, a generator, a motor, or the like. In any of the embodiments disclosed herein, the AC port 130 may be a single-phase AC port, a three-phase three-wire AC port, a three-phase four-wire AC port, or other AC configurations. As shown in FIGS. 8A and 8B, the second circuit 115 may further include a plurality of half-bridge branches, each of which may include a first reverse blocking switch and a second reverse blocking switch. As shown in FIGS. 8A and 8B, the second circuit 115 may further include an output CL filter 140 in parallel with the AC port 130. The output CL filter 140 may be configured to interface the AC port 130 with an AC load.

[0070] In any of the embodiments disclosed herein, the converter may be configured to operate in multiple modes to flow electrical energy between one or more of the battery port, the PV port, and the AC port and another of the battery port, the PV port, and the AC port. For example, the multiple modes may include a first mode in which electrical energy is transferred from the PV port 125 to the battery port 120, a second mode in which electrical energy is transferred from the PV port 125 to the AC port 130, a third mode in which electrical energy is transferred from the battery port 120 to the AC port 130, and a fourth mode in which electrical energy is transferred from the AC port 130 to the battery port 120.

[0071] The controller may implement the various modes described above through switching cycles that control the on / off times and sequencing of the various switches in the converter. The converter may operate by "charging" the magnetizing inductor of the transformer 105 from the source that supplies power during one cycle and then "discharging" the inductor's energy to the source that receives power during that cycle. The switching sequence may be controlled to reduce switching losses and dv / dt and to manage energy trapped in the leakage inductance of the transformer. The principles of leakage energy management are well known to those skilled in the art.

[0072] For example, as shown in FIGS. 8A and 8B, the first circuit 110 may include a first bidirectional switch 111 connected in series between the battery port 120 and the second winding 107, a second bidirectional switch 112 connected in series between the battery port 120 and the first winding 106, and a third bidirectional switch 113 connected in series between the PV port 125 and the first winding 106. The converter may be configured to flow electrical energy from the battery port 120 to the first winding 106 during a switching cycle when the second bidirectional switch 112 is in a closed position. The converter may be configured to flow electrical energy from the second transformer winding 107 to the battery port 120 during a switching cycle when the first bidirectional switch 111 is in a closed position. The converter may be configured to flow electrical energy from the PV port 120 to the first winding 106 during a switching cycle when the third bidirectional switch 113 is in a closed position.

[0073] 8A and 8B, the first circuit may further comprise a clamp circuit 145 configured to discharge leakage energy from the transformer 105. This can be done, for example, by opening (i.e., turning off) the bidirectional switches 111, 112, 113 in the first circuit during the discharging process.

[0074] 8A and 8B, the first circuit may further comprise an energy recovery circuit 150 configured to recover leakage energy from the discharged transformer 105 with minimal losses to the battery port 125. An implementation of such a circuit may be realized in a flyback converter.

[0075] FIG. 9 shows an exemplary high-level basic control diagram of the solar photovoltaic device three-port converter shown in FIG. 8A and FIG. 8B. The controller can utilize AC voltage and active power as references in addition to local measurements to allocate charging time for each port. The gate signals for each switching device can then be determined by a dedicated state machine. FIG. 10A shows the magnetizing current (i ii ), battery current (i bat ), PV current (i p ), decoupling capacitor current (i dpl ), and the voltage of the high-frequency transformer winding (v L1 , v L2 , and v L3 10A and 10B show the characteristic waveforms of the converter and the simulated waveforms of the converter, respectively. Finally, Figs. 11A and 11B show the voltage-current characteristics and the simulated waveforms from the AC ports of the converter when a single-phase configuration is adopted.

[0076] Additionally, in some embodiments, the photovoltaic device panels can be connected via a secure RF or other communication link (such as with GAMMA) and can provide diagnostic and analytical information to the cloud, enabling system level optimization and providing maintenance information regarding battery and panel degradation due to environmental or wear and tear. Instructions from the grid operator can also be relayed to each 3-port converter, enabling dispatch, frequency regulation, VAR, inertia, etc. as grid services. At the interconnected PV plant level, this can unlock additional value streams by allowing the "plant" to participate in the overall energy market. The PV plant can also act as a peak load plant, providing operating reserve and negating the need to run a gas plant continuously to provide this function. Service calls can be notified and initiated based on the maintenance logs on the cloud. Battery replacement can be triggered from the panel itself, a simple process during a service call while the system is running.

[0077] In some embodiments, the protection of each 3-port converter can be tied within each converter. It can be, for example, a simple relay and / or an intelligent fuse that can be tripped when a converter-side fault is detected. The status of the 3-ports can be relayed to the cloud. The wires from each PV string can be directly connected to a medium voltage transformer, which is, for example, mounted on a utility pole (or a pad installed at the base of the utility pole) in the grid and connected to the medium voltage transmission line via a fused disconnector (current standard practice). The medium voltage transformer can also be monitored with a GAMMA type sensor, which can assess the health of the downstream wires and also serves as an RF relay point to the cloud. This allows visibility and control down to the individual panel, which was previously considered prohibitively expensive due to the need to continually drive down the cost of PV panels and inverters.

[0078] It is to be understood that the embodiments and claims disclosed herein are not limited in their application to the details of construction and arrangement of the components described herein and illustrated in the drawings. Rather, the specification and drawings provide examples of possible embodiments. The embodiments and claims disclosed herein are capable of further embodiments and can be implemented and carried out in various ways. It is also to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be construed as limiting the scope of the claims.

[0079] As such, those skilled in the art will appreciate that the conception underlying the present application and claims may be readily utilized as a basis for the designing of other structures, methods and systems for carrying out the purposes of the embodiments and claims presented herein, and it is important that the claims be regarded as including such equivalent constructions.

[0080] Furthermore, the purpose of the Abstract is to enable the U.S. Patent and Trademark Office and the general public, including those not familiar with patent and legal terminology and language, to quickly grasp the content and gist of the technical disclosure of the application upon a single reading. The Abstract does not define the scope of the claims of the application, nor does it limit the scope of the claims in any way.

Claims

1. A single-stage multi-port current source converter, comprising: a transformer having a first winding, a second winding, and a third winding; a first circuit electrically coupled to the first winding and the second winding, a battery port configured to interface with one or more batteries; a first circuit having a photovoltaic (PV) port configured to interface with one or more PV modules; a second circuit electrically coupled to the third winding and having an alternating current (AC) port configured to interface with an AC device; During a switching cycle, the current source converter is configured to flow electrical energy between a connected winding selected from the first winding, the second winding, and the third winding and a connected port selected from the battery port, the PV port, and the AC port; During an operating mode, the current source converter is further configured to cause electrical energy to flow between one or more of the battery port, the PV port, and the AC port and another of the battery port, the PV port, and the AC port.

2. The current source converter of claim 1 , wherein the AC device is selected from an AC load, an AC source, and an AC network.

3. In a first operating mode, electrical energy is transferred from the PV port to the battery port. In a second mode of operation, electrical energy is transferred from the PV port to the AC port. In a third mode of operation, electrical energy is transferred from the battery port to the AC port. In a fourth mode of operation, electrical energy is transferred from the AC port to the battery port; and In a fifth mode of operation, electrical energy is transferred from the PV port and the battery port to the AC port.

3. The current source converter of claim 2, wherein the current source converter is at least one of:

4. The current source converter of claim 1 , wherein the battery port is configured to operate at a voltage level of about 48V or less.

5. The current source converter of claim 1 , wherein the AC port is selected from a single-phase AC port, a three-phase three-wire AC port, and a three-phase four-wire AC port.

6. A current source converter, comprising: a transformer having a first winding, a second winding, and a third winding; a first circuit electrically coupled to the first winding and the second winding, a battery port configured to interface with one or more batteries; a photovoltaic (PV) port configured to interface with one or more PV modules; a first circuit having a bidirectional switch; a second circuit electrically coupled to the third winding, the second circuit having an alternating current (AC) port configured to interface with an AC device; the bidirectional switch is connected in series with the first winding and a battery port; The current source converter is configured to flow electrical energy from the battery port to the first winding during a switching cycle when the corresponding bidirectional switch is in a closed position.

7. The current source converter of claim 6 , wherein the bidirectional switch is selected from a silicon carbide switch, a silicon switch, and a gallium nitride switch.

8. 7. The current source converter of claim 6, wherein the second circuit further comprises one or more second circuit bidirectional switches, each configured to operate in a reverse blocking mode.

9. the first circuit has an additional bidirectional switch connected in series with a second winding and the battery port; 7. The current source converter of claim 6, wherein the current source converter is configured to flow electrical energy from the second winding to the battery port during the switching cycle when the additional bidirectional switch is in a closed position.

10. the first circuit further includes an additional bidirectional switch connected in series with the first winding and the PV port; 7. The current source converter of claim 6, wherein the current source converter is configured to flow electrical energy from the PV port to the first winding during the switching cycle when the additional bidirectional switch is in a closed position.

11. the one or more bidirectional switches include a third bidirectional switch connected in series with the first winding and the battery port; 7. The current source converter of claim 6, wherein the current source converter is configured to flow electrical energy from the battery port to the first winding during the switching cycle when the third bidirectional switch is in a closed position.

12. A transformer having a first winding, a second winding, and a third winding; a first circuit electrically coupled to the first winding and the second winding, a battery port configured to interface with one or more batteries; a photovoltaic (PV) port configured to interface with one or more PV modules; a clamp circuit configured to discharge leakage energy from the transformer; a second circuit electrically coupled to the third winding, the second circuit having an alternating current (AC) port configured to interface with an AC device selected from an AC load, an AC source, and an AC network; an energy recovery circuit shunt-connected to the clamp circuit; The energy recovery circuit is configured to recover leakage energy discharged from the transformer and provide the discharged leakage energy to the battery port.

13. 2. The current source converter of claim 1, wherein the second circuit further comprises a plurality of half-bridge branches, each half-bridge branch having a first reverse blocking switch and a second reverse blocking switch.

14. A current source converter as described in claim 12, wherein the second circuit further has a plurality of half-bridge branches, each of which has a first reverse blocking switch and a second reverse blocking switch.

15. the second circuit further comprising an output capacitive filter in parallel with the AC port; 2. The current source converter of claim 1, wherein the output capacitive filter is configured for the AC port to interface with the AC device.

16. 2. The current source converter of claim 1, wherein the transformer has a turns ratio of the first, second, and third windings of N1:N1:N2.

17. A process of transferring electrical energy from a battery port of a first circuit of a current source converter to an alternating current (AC) port of a second circuit of said current source converter by closing a corresponding first bidirectional switch connected in series between said battery port and a first winding of a transformer of said current source converter; transferring electrical energy from a PV port to the AC port of the first circuit by closing a corresponding second bidirectional switch connected in series between the PV port and the first winding; electrical energy from the PV port to the battery port; closing the corresponding second bidirectional switch; closing a corresponding third bidirectional switch connected in series between the battery port and a second winding of the transformer; and transmitting by

18. 18. The method of claim 17, further comprising transferring electrical energy from the AC port to the battery port.

19. 18. The method of claim 17, further comprising discharging leakage energy from the transformer using a clamp circuit in the first circuit.

20. The method of claim 19, further comprising recovering leakage energy discharged from the transformer using an energy recovery circuit and transmitting the discharged leakage energy to the battery port. (i) the first circuit further comprises a first bidirectional switch, a second bidirectional switch, and a third bidirectional switch; the second bidirectional switch is connected in series with the second winding and the battery port, and the current source converter is further configured to flow electrical energy from the second winding to the battery port during the switching cycle when the second bidirectional switch is in a closed position; the first bidirectional switch is connected in series with the first winding and the PV port, and the current source converter is further configured to flow electrical energy from the PV port to the first winding during the switching cycle when the first bidirectional switch is in a closed position; the third bidirectional switch is connected in series with the first winding and the battery port, and the current source converter is further configured to flow electrical energy from the battery port to the first winding during the switching cycle when the third bidirectional switch is in a closed position. (ii) the first circuit further comprises a clamp circuit configured to discharge leakage energy from the transformer; (iii) the second circuit further includes a plurality of half-bridge branches, each of the half-bridge branches including a first reverse blocking switch and a second reverse blocking switch; (iv) the second circuit further comprises an output capacitive filter in parallel with the AC port, the output capacitive filter configured to interface the AC port with the AC device; (v) the transformer has a turn ratio of the first, second, and third windings of N1:N1:N2; (vi) the current source converter further comprises an energy recovery circuit shunt-connected to the clamp circuit of the first circuit, the clamp circuit configured to discharge leakage energy from the transformer, the energy recovery circuit configured to recover leakage energy discharged from the transformer and supply the discharged leakage energy to the battery port; 2. The current source converter of claim 1, wherein the current source converter is at least one of:

22. The first circuit further includes a clamp circuit configured to discharge leakage energy from the transformer. the second circuit further includes a plurality of half-bridge branches, each of the half-bridge branches including a first reverse blocking switch and a second reverse blocking switch; the second circuit further comprising an output capacitive filter in parallel with the AC port, the output capacitive filter configured to interface the AC port with the AC device. The transformer has a turn ratio of N1:N1:N2 for the first, second, and third windings. the current source converter further comprises an energy recovery circuit shunt-connected to the clamp circuit of the first circuit, the clamp circuit configured to discharge leakage energy from the transformer, the energy recovery circuit configured to recover leakage energy discharged from the transformer and supply the discharged leakage energy to the battery port.

7. The current source converter of claim 6, wherein the current source converter is at least one of: (i) the first circuit further comprises a first bidirectional switch, a second bidirectional switch, and a third bidirectional switch; the second bidirectional switch is connected in series with the second winding and the battery port, and the current source converter is further configured to flow electrical energy from the second winding to the battery port during the switching cycle when the second bidirectional switch is in a closed position; the first bidirectional switch is connected in series with the first winding and the PV port, and the current source converter is further configured to flow electrical energy from the PV port to the first winding during the switching cycle when the first bidirectional switch is in a closed position; the third bidirectional switch is connected in series with the first winding and the battery port, and the current source converter is further configured to flow electrical energy from the battery port to the first winding during the switching cycle when the third bidirectional switch is in a closed position. (ii) the second circuit further includes a plurality of half-bridge branches, each of the half-bridge branches including a first reverse blocking switch and a second reverse blocking switch; (iii) the second circuit further comprises an output capacitive filter in parallel with the AC port, the output capacitive filter configured to interface the AC port with the AC device; (iv) the transformer has a turns ratio of the first, second, and third windings of N1:N1:N2; (v) the current source converter further includes an energy recovery circuit shunt-connected to the clamp circuit, the energy recovery circuit configured to recover leakage energy discharged from the transformer and supply the discharged leakage energy to the battery port; 17. The current source converter of claim 16, wherein:

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