DC / DC converters for distributed storage and solar energy systems

Abstract

A multi-power distributed storage system includes: a first power source; a second power source electrically connected to a common bus together with the first power source; and a single-input port inverter electrically connected to the common bus. The system includes a controller configured to communicate with at least the second power source and the single-input port inverter. The second power source includes a plurality of battery packs, and a plurality of bidirectional DC / DC converters configured to charge and discharge the plurality of battery packs and provide DC to the single-input port inverter.

Description

Technical Field

[0001] The present invention relates to dual power systems and methods for distributed storage and solar energy systems. More particularly, the present invention relates to solar energy systems, and more particularly to solar tracking systems and control systems and algorithms for switching between solar energy and battery power to drive an energy grid. Background Art

[0002] Several solutions have been developed for power control in dual and multi-power power systems. In the solar tracker scenario, certain control systems have been developed. One of these control systems determines the power to be applied to a load such as a grid. While one source is the power generated by the solar array, the second source is typically a battery system.

[0003] Sometimes the energy produced by a solar power plant is not enough to supply the grid. This can happen when the sun is blocked by clouds or when demand is such that the solar power plant cannot produce enough electricity to supply the energy grid. In these types of examples, a DC storage power plant is employed to provide additional power. As will be appreciated, the ability to switch or combine energy from two power supply systems (i.e., a solar power plant and a DC storage power plant) is an important feature of any such system. Although systems have been developed that are capable of this conversion, there is always a need for improved and more efficient systems.

[0004] Figure 6 Depicting a prior art multi-port inverter solar tracker system 600. This architecture for DC coupled solar energy and storage utilizes a multi-port inverter 630. The multi-port inverter 630 manages the solar array 610 following a maximum power point tracking (MPPT) algorithm, and the battery 620 charges and discharges separately for distributed and large applications. The ratio of solar array 610 to battery 620 is determined by the specific circumstances of each installation. Typically, the multi-port inverter 630 will be oversized to meet large power requests from the grid and responses from either the solar array 610 or the battery 620. The correlation between the central multi-port inverter 630 and the battery charger 625 can be complex and communication delays also limit this configuration for fast response microgrid applications.

[0005] Therefore, in view of these shortcomings, improved solutions with greater efficiency and higher speed are desired. Summary of the invention

[0006] Embodiments of the present invention are described in detail with reference to the figures of the drawings, wherein like reference numerals identify similar or identical elements.

[0007] Aspects of the present invention provide a method for implementing a multi-power distributed power storage and generation system. The method includes: feeding the output voltage from a solar power plant and a DC storage power plant to a single-input port inverter via a common bus, the DC storage power plant including multiple bidirectional DC / DC converters configured to charge and discharge multiple battery packs; for a given load, using a power droop method to maintain the constant power output of the DC storage power plant in the MPPT region of the solar power plant; when the bus voltage is higher than the MPPT region, ramping down the output power of the DC / DC converter, when the bus voltage is higher than the MPPT region, ramping up the output power of the DC / DC converter, and maintaining the maximum power output of the solar power plant, wherein the ramping up and ramping down of the output power are achieved at least initially without active control of the DC / DC converter.

[0008] In one aspect, the method further includes: using a controller to monitor the power demand of the load; using the controller to monitor the DC charging state and battery health state of the DC storage power plant, using the controller to monitor the output power and voltage of the solar power plant, and when the load demand is stable, the controller determines which battery groups of the multiple battery groups will supply output power to the bus.

[0009] Another aspect of the present invention provides a multi-power distributed storage system, which includes: a first power source, a second power source, the second power source and the first power source are electrically connected to a common bus, a single-input port inverter, which is electrically connected to the common bus, and a controller configured to communicate with at least the second power source and the single-input port inverter. The second power source includes a DC storage power plant, which includes a plurality of battery packs and a plurality of bidirectional DC / DC converters, the plurality of bidirectional DC / DC converters are configured to charge and discharge the plurality of battery packs, and when a grid power reduction command is received at the single-input port inverter, the bus voltage rises, and both the first power source and the second power source reduce output power without active control, and wherein when the load increases, the bus voltage decreases, and both the first power source and the second power source increase output power without active control.

[0010] In a further aspect, the first power source comprises a solar power plant. In another aspect, the solar power plant utilizes MPPT to maintain maximum output power. In another aspect, the solar power plant comprises a plurality of solar modules.

[0011] In yet another aspect of the present invention, the DC storage power plant includes a controller, the controller including: at least one processor and a memory having instructions stored thereon, which, when executed by the at least one processor, communicates with the bidirectional DC / DC converter to adjust the battery packs supplying power to the bus. Still further aspects describe that each battery pack is managed individually.

[0012] In one aspect, the battery supplies power to the bus to maintain the shape of the PV power curve, thereby allowing the single input port inverter to operate at MPPT. In one aspect, the controller further maintains the operating state of charge of the DC storage power plant at or above a minimum charge level.

[0013] In another aspect of the present invention, a method for implementing a multi-power distributed power storage system is provided. The method includes: feeding the output voltage from the first power source and the second power source to a single-input port inverter, the second power source including a plurality of converters; for a given load, using a power droop method to maintain a constant power output of a DC storage power plant in the MPPT region of a solar power plant, when the bus voltage is higher than the MPPT region, ramping down the output power of the DC / DC converter, when the bus voltage is higher than the MPPT region, ramping up the output power of the DC / DC converter; and maintaining the maximum power output of the single-input port inverter. The ramping up and ramping down of the output power are achieved at least initially without active control of the DC / DC converter.

[0014] In yet another aspect, the first power source comprises a solar power plant. In a further aspect, the second power source comprises a DC storage power plant. In yet another aspect, the plurality of converters comprises bidirectional DC / DC converters. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Various aspects of the invention are described herein below with reference to the drawings, which are incorporated into and constitute a part of this specification, in which:

[0016] Figure 1 Depicting a dual-source power plant according to the present invention;

[0017] Figure 2 Depicting an MPPT diagram of a dual power plant according to the present invention;

[0018] Figure 3 A graph depicting a DC / DC converter output curve for a battery backup portion of a dual source power plant according to the present invention;

[0019] Figure 4 a graph depicting grid demand response of a dual-source power plant in accordance with the present invention;

[0020] Figure 5 Describes the logic flow for a control algorithm according to the present invention; and

[0021] Figure 6 A prior art multi-input port inverter system is described in conjunction with a dual-source power plant. DETAILED DESCRIPTION

[0022] The present invention relates to systems and methods for implementing multiple power sources and distributed power storage systems, whereby a single load can be driven by two separate power sources, both individually and together. Although generally described herein in the context of a solar tracking system that utilizes both a photovoltaic (solar) power plant and a DC storage power plant to provide energy to drive an energy grid, the systems, schematics, and algorithms described herein are applicable to any scenario where two power sources are present. In particular, the systems and algorithms of the present invention are useful in situations where there is one power source that is a preferred power source to be utilized, but the system should experience little to no lag in switching to another power source.

[0023] Typically, photovoltaic power plants are connected to a large power grid and may be associated with a large battery pack that can be used to provide power to the grid when solar panels cannot meet demand. Co-owned U.S. Patent Publication No. 2017 / 0288184, filed on March 31, 2017, entitled "Standard energy storage container platform," teaches a battery container, and U.S. Patent Application Serial No. 15 / 872,071, entitled "Direct Current Battery String Aggregator for Standard Energy Storage Enclosure Platform," teaches a controller and system for connecting batteries and photovoltaic systems to an energy grid. Both references are incorporated herein by reference. Other dual power energy systems that require monitoring and switching between energy supply systems are also contemplated to be within the scope of the present invention.

[0024] Figure 1A distributed solar energy and storage system 10 is depicted, which can be deployed as part of a larger array. It is expected that the present application can be used for solar tracker systems, fixed tilt solar energy systems, rooftop solar energy, and any type of solar array. Each distributed solar energy and storage system 10 includes a single input port inverter 40, which is fed with the output voltage of a first power source such as a solar power plant 20 and a second power source such as a DC storage power plant 30 through a common bus 50. Other types of power sources are expected, such as steam, nuclear power, geothermal, hydroelectric, wind power, etc. It is expected that more than two power sources can be utilized. The single input port inverter 40 can be sized for the AC output requirements of the power grid to which it is connected. The common bus 50 allows for a nearly instantaneous response to changes in system power requirements.

[0025] The DC storage power plant 30 typically includes a plurality of battery packs 31, a bidirectional DC / DC converter 32, and a controller 60. The controller 60 can supervise the charging and discharging rates. The bidirectional DC / DC converter 32 can be configured to charge the battery pack 31. The bidirectional DC / DC converter 32 can be sized to fit the battery output or input. Each battery pack 31 and DC / DC converter 32 are managed separately. The bidirectional DC / DC converter 32 adopts a power droop algorithm that maintains a constant power output in the normal MPPT region. When the voltage is above or below the MPPT region, the bidirectional DC / DC converter 32 can ramp up the power or ramp down the power output to the bus 50. The power droop algorithm enables local control of the power output from the DC power plant 30 based on the external load. In addition, the internal resistance of the bidirectional DC / DC converters 32 connected in parallel maintains relatively equal current sharing between the battery packs 31. The power droop algorithm in conjunction with the battery bank 31 and photovoltaic panel array 21 sharing a common bus 50 eliminates the need for additional communications and allows for fast response to microgrid applications (eg, load changes on the inverter 40 ).

[0026] The single-input port inverter 40 receives power from the common bus 50 and converts it to an AC voltage. The single-input port inverter 40 can be sized for the AC output requirements of the distributed solar energy and storage system 10. The single-input port inverter 40 maintains the output power at the maximum power point (MPP) by using, for example, a voltage tracking method. It is expected that other methods known in the art can be used. Maximum power point tracking (MPPT) runs at the input port of the single-input port inverter 40, and the maximum power point tracking is a process of finding a point where the load characteristics will be kept at the system optimized to give the highest power transfer. The output power from the solar power plant is sampled and the appropriate load characteristics (resistance) are applied to obtain the maximum power. When the grid reduction command arrives at the solar power plant 20 and the DC storage power plant 30, the single-input port inverter 40 experiences a rise in the system voltage at the bus 50, and both the solar power plant 20 and the DC storage power plant 30 reduce the power output without active control. Similarly, in a load increase scenario, the single input port inverter 40 experiences a drop in the system voltage at the bus 50, and both the solar power plant 20 and the DC storage power plant 30 increase power output without active control. These changes in voltage are nearly instantaneous at the single input port inverter 40.

[0027] like Figure 2 As can be seen in FIG. 4 , when the system voltage increases beyond the MPPT, the power and current outputs drop sharply as the voltage rises. In parallel with this drop in power and current, the controller 60 can communicate with individual bidirectional DC / DC converters to manage the output of each of the individual battery packs 31, thereby achieving the same power and current output in a more efficient manner and according to the health and charge state of each of the individual battery packs 31, as described in more detail below. It is contemplated that the battery packs 31 and the DC / DC converters 32 are managed separately. Therefore, the single input port inverter 40 is able to maintain the power output of the solar power plant 20 and the DC storage power plant 30 in the MPPT region.

[0028] Figure 2 A graph 200 is depicted depicting the MPPT region of a distributed solar energy and storage system 10 according to the present invention. MPPT can be implemented generally on a variable power source. Graph 200 depicts a series of V / I and P / V curves. To achieve maximum solar energy, the photovoltaic panel array 21 of the solar power plant 20 is equipped with a system for calculating and maintaining the MPPT. As demonstrated by graph 200, as the amount of sunlight changes, the load characteristics that provide the maximum power transfer efficiency also change. By varying the load and supply characteristics, power transfer can be maintained at a high efficiency point. Figure 1The distributed solar and storage system 10 depicted in FIG. 1 will operate such that a single input port inverter 40 can operate within the MPPT region and simply add or remove supplied power in response to demand.

[0029] Figure 3 A graph depicting a bidirectional DC / DC converter output curve 300 according to the present invention. The curve depicts output power versus voltage. The power droop algorithm employed by the bidirectional DC / DC converter 32 and the inverter 40 maintains the output at a relatively constant power. As shown in the graph 300, the constant power region 310 depicts the power output of the DC / DC converter 32 at a given voltage. Although relatively constant, the power is depicted to droop as the voltage increases. The constant power regions 310 of the graph 300 substantially overlap Figure 2 When the output voltage of the common bus 50 is higher than the MPPT region, the bidirectional DC / DC converter can automatically react and increase its output voltage to a value higher than the MPPT region. Figure 2 The MPPT area depicted in the figure is high, such as Figure 3 . When the output voltage of the common bus 50 is below the MPPT region, the bidirectional DC / DC converter can react automatically and the output power can be ramped up. This allows the bidirectional DC / DC converter 32 to automatically respond to changes in the load as a result of changes in the current drawn from the battery pack 31 to always maintain the inverter 40 at or near the MPPT.

[0030] As the voltage increases, and the power delivered from the battery packs 31 through the bidirectional DC / DC converter 32 decreases, the controller 60 is able to communicate with the bidirectional DC / DC converter to adjust how that reduced or increased power is delivered to the common bus 50, albeit lagging behind the nearly instantaneous response caused by the change in bus 50 voltage (caused by the load change). That is, the controller can adjust which battery packs 31 actually feed the common bus 50. In this way, the controller can remove battery packs 31 from the common bus 50 to both adjust the delivered power and reduce the bus voltage, thereby shifting the operating point of the inverter 40 into the inverter nominal operating region, and Figure 2 As will be appreciated, this also works in reverse when load is added to the inverter 40. As the load on the common bus 50 increases, the combined Figure 3 The voltage observed by the power droop curve of the controller will drop, and the bidirectional DC / DC converter will recognize that it is outside the constant power region and additional battery packs 31 will be connected to the common bus 50. While some number of battery packs 31 will be able to automatically connect to the common bus 50 based on their state of charge, other battery packs 31 may have received communications from the controller preventing them from further discharging until a certain charge level (e.g., 80% of maximum capacity) is achieved before being permitted to discharge.

[0031] Generally speaking, the response of the bidirectional DC / DC converter 32 to the load, which is connected to or separated from the common bus 50, is initially driven by the bus voltage. Secondly, it is driven by the controller 60 to more directly manage which battery packs 31 and bidirectional DC / DC converters 32 supply power to the common bus 50 and the inverter 40, or are charged by the solar power plant 20.

[0032] Figure 4 A graph depicting grid demand response 400 according to the present invention is shown. For example, in an embodiment, an 80 kW solar power plant and ten 10 kW batteries sharing a common bus 50 may cause all battery banks 31 to run fully discharged, as in the top trace in graph 400. As voltage increases, output power also increases because system 10 maintains output power at a level such as Figure 2 By shutting down all batteries 31, only the solar power plant 20 will continue to provide power to the grid, as in the middle trajectory 420. For example, if half of the battery banks 31 need to be charged, the curve will follow the lower trajectory 430. In all of the above situations, the distributed solar and storage system 10 will attempt to remain in the MPPT region as shown in the middle trajectory 420. Figure 2 4, so that the single input port inverter 40 will still be able to provide maximum power. If the single input port inverter 40 voltage rises through the MPPT region and enters the power reduction region of the graph 400 of any of the above traces 410, 420, 430, the solar power plant 20 and the DC storage power plant 30 will automatically respond by reducing power to the common bus 50 without the need for commands.

[0033] In another embodiment, when the AC load demand changes, it produces a change in frequency, which will translate into a change in bus voltage on the input side of the single input port inverter 40. When the grid frequency is low and frequency support is needed, the single input port inverter 40 will reduce the system voltage on the common bus 50 to search for system maximum power.

[0034] Figure 5Depicts the logic flow for a control algorithm according to the present invention. In one embodiment, at step 510, the system controller 60 may monitor the power demand of a particular load. At step 520, the controller 60 may monitor the DC charging state of the DC storage power plant 30, and at step 530, monitor the output power and voltage of the solar power plant 20. In another embodiment, based on the monitoring, the controller 60 may detect whether the load has increased 540, and after the load has stabilized, at step 550, the controller 60 may adjust the power available from the DC storage power plant 30 according to the power droop algorithm. In yet another embodiment, based on the monitoring steps 510, 520, and 530, at step 560, the controller 60 may detect or receive a communication indicating the presence of one or more bad batteries in the battery pack 31. In the DC storage power plant 30, a bad battery may cause the entire battery pack 31 to go bad and therefore be unavailable to safely meet the load demand. Therefore, in step 570, the controller may shut down the affected battery pack 31, thereby preventing it from being used to respond to the changed load demand, and ensuring that any battery pack 31 with a faulty battery is not permitted to connect to the bus 50 and feed power to the inverter. It is expected that the controller 60 maintains the charging operating state of the DC storage power plant 30 at or above the minimum charging level. In another embodiment, based on the monitoring steps 510, 520 and 530, at step 580, the controller 60 may detect whether the demand has dropped. In general, the response of the bidirectional DC / DC converter 32 to the load is initially driven by the bus voltage. However, when the load demand stabilizes, the controller 60 may adjust the amount of power supplied from the DC storage power plant 30. It is expected that any of the detection steps 540, 560 and 580 may occur in parallel with each other.

[0035] Although several embodiments of the present invention have been shown in the drawings, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad as the art will allow, and the specification is to be read as such. Any combination of the above embodiments is also conceivable and within the scope of the appended claims. Therefore, the above description should not be interpreted as limiting, but merely as an example of a particular embodiment, and a person skilled in the art will envision other modifications within the scope of the appended claims.

Claims

1. A method for implementing a multi-power distributed power storage and generation system, comprising: directly feeding the common bus with electricity generated by a plurality of solar arrays of a solar power plant; Discharging power from at least one of the plurality of battery packs directly to the common bus by a plurality of bidirectional DC / DC converters of the DC storage power plant; feeding the voltage on the common bus to a single input port inverter; The power demand of the external load is monitored by the system controller; maintaining a constant power output from the DC storage power plant in a maximum power point tracking (MPPT) region of the solar power plant using a power droop method, so that the power output from the DC storage power plant can be locally controlled based on the power demand of the external load; When the voltage on the common bus is higher than the MPPT region, ramping down the output power of the plurality of bidirectional DC / DC converters; When the voltage on the common bus is lower than the MPPT region, ramping up the output power of the plurality of bidirectional DC / DC converters; and Maintaining maximum power output of the solar power plant.

2. The method according to claim 1, further comprising: monitoring, by the system controller, a state of charge of the plurality of battery packs of the DC storage power plant; monitoring, by the system controller, the output power of the solar power plant; and Based on the monitoring of the state of charge and the output power of the solar power plant, it is determined by the system controller which battery packs of the plurality of battery packs supply output power to the single input port inverter via the common bus.

3. A multi-power distributed storage system, comprising: a first power source electrically and directly connected to the common bus; a second power source electrically and directly connected to the common bus; a single input port inverter electrically connected to the common bus; and a system controller configured to communicate with at least the second power source and the single input port inverter, The first power source comprises a solar power plant, and the solar power plant comprises a plurality of solar modules. wherein the second power source comprises a DC storage power plant including a plurality of battery packs and a plurality of bidirectional DC / DC converters configured to charge and discharge the plurality of battery packs, wherein when a grid power reduction command is received at the single input port inverter, a common bus voltage increases, and the second power supply reduces output power in response to the increase in the common bus voltage, When the load increases, the common bus voltage decreases, and the second power supply increases the output power, and When maintaining constant power, a power droop method is used to maintain constant power output from the DC storage power plant, so that the power output from the DC storage power plant can be locally controlled based on the power demand of the external load.

4. The system of claim 3, wherein the solar power plant utilizes maximum power point tracking (MPPT) to maintain maximum output power.

5. The system of claim 3, wherein the DC storage power plant further comprises a controller comprising at least one processor and a memory having instructions stored thereon, which, when executed by the at least one processor, cause the at least one processor to communicate with the bidirectional DC / DC converter to regulate the plurality of battery packs supplying power to the common bus.

6. The system of claim 5, wherein each battery pack is managed individually.

7. The system of claim 6, wherein a battery supplies power to the common bus to maintain the shape of a PV power curve, thereby allowing the single input port inverter to operate at MPPT.

8. The system of claim 5, wherein the system controller further maintains the charged operating state of the DC storage power plant at or above a minimum charge level.

9. A method for implementing a multi-power distributed power storage system, comprising: feeding a single input port inverter with output voltages from a first power source and a second power source, the second power source comprising a bidirectional DC / DC converter directly coupled to the first power source and the second power source via a common bus; Maintaining a constant power output of the DC storage power plant in the maximum power point tracking (MPPT) region of the first power source using a power droop method, so that the power output from the second power source can be locally controlled based on the power demand of the external load; When the voltage on the common bus is higher than the MPPT region, ramping down the output power of the bidirectional DC / DC converter; When the voltage on the common bus is lower than the MPPT region, ramping up the output power of the bidirectional DC / DC converter; and Maintaining the maximum power output of the single-input port inverter.

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