Flow battery power supply system and control method thereof

Abstract

The invention provides a flow battery power supply system and a control method thereof, and the flow battery power supply system comprises an off-grid inverter which is provided with a first input end and a first output end, and the first input end is connected to a DC end of a flow battery; the change-over switch is provided with a second input end, a third input end and a second output end, the second input end is connected to the first output end, and the third input end is connected to the power supply grid; the frequency converter is provided with a fourth input end and a third output end, the frequency converter comprises a rectifier module, a capacitive component and an inverter module which are electrically connected in sequence, the fourth input end is connected to the second output end, and the third output end is connected to an electrolyte circulating pump in the flow battery; and the control unit at least has the following configuration: monitoring the states of the power supply grid, the change-over switch, the off-grid inverter and the capacitive component, and sending a switching instruction to the change-over switch. According to the invention, off-network operation of the flow battery and charge state balance in the flow battery are realized.

Description

Technical Field

[0001] This invention relates primarily to the field of flow battery technology, and more particularly to a flow battery power supply system and its control method. Background Technology

[0002] A flow battery (such as a vanadium redox flow battery, VFB) is an energy storage device that converts electrical energy into chemical energy through electrochemical reactions of ions with different valence states in the electrolyte at the positive and negative electrodes. It is also commonly referred to as a flow battery system. Taking a vanadium redox flow battery as an example, it mainly consists of power units (stack modules), capacity units (electrolyte and storage tanks), electrolyte delivery units (pipelines, valves, pumps, heat exchangers, etc.), and a battery management system (BMS). The main electrical equipment within the battery system includes pumps and valves for delivering the electrolyte, and the battery management system responsible for overall control. Pumps are typically controlled by frequency converters to start, stop, and adjust the operating frequency, thereby changing the electrolyte flow rate. The battery management system, as the control center of the entire battery system, undertakes functions such as data acquisition, processing, analysis, and command execution. It is a critical load necessary for the stable operation of the battery system and requires a continuous and reliable power supply.

[0003] However, in existing flow battery power systems, fluctuations in the power supply or unstable power quality can directly affect the normal operation of the various electrical devices within the system. A power outage can even cause these devices to shut down, impacting the functionality of the entire battery system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a flow battery power supply system and its control method, so as to realize the offline operation of the flow battery and the state of charge balance within the flow battery.

[0005] To address the aforementioned technical problems, in a first aspect, the present invention provides a flow battery power supply system, comprising: an off-grid inverter having a first input terminal and a first output terminal, the first input terminal being connected to the DC terminal of the flow battery; a switching switch having a second input terminal, a third input terminal, and a second output terminal, the second input terminal being connected to the first output terminal, and the third input terminal being connected to the power grid; a frequency converter having a fourth input terminal and a third output terminal, and extending from the fourth input terminal to the third output terminal, the frequency converter comprising a rectifier module, a capacitive component, and an inverter module electrically connected in sequence; the fourth input terminal being connected to the second output terminal, and the third output terminal being connected to an electrolyte circulation pump in the flow battery; and a control unit having at least the following configurations: monitoring the status of the power grid, the switching switch, the off-grid inverter, and the capacitive component; and sending a switching command to the switching switch, the switching command instructing the switching switch to be electrically connected to the off-grid inverter or the power grid.

[0006] Optionally, the DC terminal of the flow battery includes one of the following: stack power supply, liquid circuit power supply, battery module power supply, and battery system power supply, wherein a battery system includes a plurality of battery modules, a battery module includes a plurality of liquid circuits, and a liquid circuit includes a plurality of stacks.

[0007] Optionally, the switching switch is an automatic transfer switch or a static transfer switch.

[0008] Optionally, the capacitive component includes a string-connected supercapacitor bank.

[0009] Optionally, the capacitive component includes a supercapacitor bank or a parallel circuit of the supercapacitor bank and a DC-DC circuit.

[0010] Optionally, the rated current of the switching switch is determined based on the maximum operating current of the control unit, wherein the maximum operating current of the control unit is determined by the following formula:

[0011] In the formula, I This indicates the maximum operating current of the control unit. P load This indicates the power of all electrical devices controlled by the control unit. U Indicates AC line voltage. Cos Indicates the power factor. η Indicates efficiency.

[0012] Optionally, the rated power of the off-grid inverter is not less than 1.5 times the total power of all electrical devices.

[0013] Optionally, the rated voltage of the capacitive component is not less than the highest voltage of the DC bus capacitor in the frequency converter and / or the capacitance of the capacitive component is determined by the following formula:

[0014] In the formula, C required This indicates the capacitance of the capacitive component. t Indicates the duration of the stabilizing support level. P This indicates the rated power of the electrolyte circulation pump. V max This represents the initial voltage of the DC bus capacitor in the inverter. V min This indicates the cutoff voltage of the DC bus capacitor in the inverter.

[0015] Optionally, the off-grid inverter is further configured with a DC-DC transformer module for changing the input voltage of the off-grid inverter, and / or an isolation module for isolation protection of the off-grid inverter.

[0016] Optionally, the frequency converter has a speed reduction energy regeneration backup function.

[0017] Secondly, the present invention provides a control method applied to a flow battery power supply system as described in the first aspect, comprising: during the operation of the flow battery, determining whether the flow battery power supply system has switching capability, wherein having the switching capability includes at least: the phase-locked loop of the off-grid inverter follows the frequency of the power grid, and the DC voltage at the first input terminal of the off-grid inverter is greater than a first voltage, wherein the first voltage is a preset minimum operating voltage; if the switching capability is present, determining whether the flow battery power supply system meets a first switching condition, wherein meeting the first switching condition includes at least: the off-grid inverter is operating normally, the power grid quality is unstable, or the flow battery meets an balancing condition, wherein the balancing condition includes at least: the state-of-charge difference ratio of the energy storage units in the flow battery is less than a set threshold; if the first switching condition is met, sending a first switching command to the switching switch, wherein the first switching command instructs the switching switch to be electrically connected to the off-grid inverter.

[0018] Optionally, the control method further includes an initialization process: powering on the control unit and sending a second switching command to the switching switch, the second switching command instructing the switching switch to be electrically connected to the power grid; determining whether the voltage of the capacitive component is greater than a second voltage, the second voltage being a preset lower limit of the operating voltage of the capacitive component; if the voltage of the capacitive component is greater than the second voltage, sending a parallel connection command to the capacitive component, the parallel connection command instructing the capacitive component to be connected in parallel to the DC bus circuit.

[0019] Optionally, the control method further includes: if the voltage of the capacitive component is less than the second voltage, sending a charging command to the capacitive component, the charging command being used to start the charging process of the capacitive component; and when the voltage of the capacitive component after charging is greater than the second voltage, sending a parallel connection command to the capacitive component or connecting it in parallel to the DC bus circuit during charging.

[0020] Optionally, the control method further includes: after the control unit is powered on, monitoring whether the components that enable the flow battery to operate are normal; if the components that enable the flow battery to operate are normal, sending a start command, the start command instructing the flow battery to start, including starting the electrolyte circulation pump in the flow battery.

[0021] Optionally, the control method further includes: when the DC voltage at the first input terminal of the off-grid inverter is less than the first voltage, replenishing the DC terminal of the flow battery with power until the DC voltage at the first input terminal of the off-grid inverter is greater than the first voltage.

[0022] Optionally, the control method further includes: determining whether the flow battery power supply system meets the second switching conditions, wherein meeting the second switching conditions includes at least the stable quality of the power grid, the abnormal operation of the off-grid inverter, or the flow battery not meeting the balancing conditions; if the second switching conditions are met, sending a second switching command to the switching switch, wherein the second switching command instructs the switching switch to be electrically connected to the power grid.

[0023] Compared with existing technologies, this invention has the following advantages: First, the flow battery has two power inputs, one from the power grid and the other from the flow battery itself. This means it can utilize the flow battery's own energy storage. When the power grid experiences instability or power outages, a switch will connect it to the flow battery's own power supply mode, providing seamless, high-quality backup power for the flow battery's critical loads, thus achieving off-grid / uninterrupted operation. Second, the state of charge (SOC) of each energy storage unit (such as the liquid circuit unit) in the flow battery can become inconsistent during use. To address this, energy storage units with low SOC are switched to the power grid to reduce their energy consumption, while those with high SOC are switched to their own power supply, thereby reducing the difference in SOC between the energy storage units. Connecting different energy storage units to the off-grid inverter produces different balancing effects; for example, connecting to the liquid circuit results in liquid circuit-level balancing, while connecting to the tank level results in tank-level balancing. This balancing is achieved by the flow battery itself, eliminating the need for additional external equipment and saving on equipment investment costs. Attached Figure Description

[0024] The accompanying drawings are included to provide a further understanding of this application; they are incorporated into and constitute a part of this application. The drawings illustrate embodiments of this application and, together with this specification, serve to explain the principles of this application. In the drawings: Figure 1 It is a traditional flow battery power supply method; Figure 2 It is another traditional method of powering a flow battery; Figure 3 This is a schematic diagram of the flow battery power supply system in this embodiment; Figure 4 This is a schematic diagram of the communication and control of the control unit in this embodiment; Figure 5 This is a schematic diagram of the composition of a flow battery; Figure 6 This is a flowchart illustrating a control method for a flow battery power supply system according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the initialization process in one embodiment of the present invention; Figure 8 This is a schematic diagram of the switching process in one embodiment of the present invention; Figure 9 This is a schematic diagram illustrating the switching process in one embodiment of the present invention; Figure 10 This is a schematic diagram illustrating the effect of applying the present invention in one operating state; Figure 11 This is a schematic diagram illustrating the effect of applying the present invention in another operating state. Detailed Implementation

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0026] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0027] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0028] It should be understood that when a component is referred to as "on another component," "connected to another component," "coupled to another component," or "in contact with another component," it can be directly on, connected to, coupled to, or in contact with that other component, or there may be an intervening component. In contrast, when a component is referred to as "directly on another component," "directly connected to," "directly coupled to," or "directly in contact with" another component, there is no intervening component. Similarly, when a first component is referred to as "electrically contacting" or "electrically coupled to" a second component, there is an electrical path between the first and second components that allows current to flow. This electrical path may include capacitors, coupled inductors, and / or other components that allow current to flow, even if there is no direct contact between the conductive components.

[0029] Flowcharts are used in this application to illustrate the operations performed according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, various steps can be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from them.

[0030] Figure 1 This is a traditional flow battery power supply method, see reference. Figure 1 As shown, the power grid enters the BMS distribution cabinet to distribute power to the equipment connected to the BMS, such as the electrolyte circulation pump in the flow battery and other various equipment / loads. In this mode, when the power grid experiences unstable power supply, such as voltage drops, frequency oscillations, or significant harmonics, it will affect the various equipment connected to the BMS. Especially when the power grid fails, the equipment will cease to operate. Therefore, this flow battery power supply method cannot operate off-grid or disconnected from the grid.

[0031] Figure 2 This is another traditional flow battery power supply method, see reference. Figure 2As shown, this power supply method involves adding a high-capacity, high-power UPS device downstream of the power grid to ensure power quality and off-grid switching. However, this method also has some drawbacks. The main drawbacks are the high cost and large size of the high-capacity, high-power UPS equipment. For conventional grid-connected flow batteries to achieve off-grid operation, a 50kW, 25kWh UPS is required. Furthermore, the UPS battery itself is a lead-acid battery, which has a short energy storage life and requires frequent replacement, needing to be replaced every 2-3 years. Moreover, at low temperatures, the performance of lead-acid batteries degrades significantly, and their capacity decreases substantially. Finally, the UPS's power electronics are also voltage-sensitive; large voltage fluctuations will trigger the UPS's protection mechanisms, resulting in reports of AC overvoltage or undervoltage, which cannot completely guarantee a stable and reliable power supply from the flow battery. Furthermore, for flow batteries, the response speed of cold and hot standby is crucial in power plant applications. In many cases, flow batteries operate in a long-term hot standby state, with the electrolyte circulation pump running continuously. This results in high and prolonged self-power consumption within the flow battery, leading to low conversion efficiency over its entire lifespan. Simultaneously, flow batteries exhibit significant self-discharge during prolonged idling, with electrical energy continuously being converted into heat and wasted.

[0032] refer to Figure 3 As shown, this embodiment provides a flow battery power supply system, including an off-grid inverter (OGI), a switching switch, a frequency converter (VFD), and a control unit (not shown in the figure). The off-grid inverter has a first input terminal and a first output terminal. The first input terminal is connected to the DC terminal of the flow battery, as shown by LQV in the figure. The off-grid inverter is an inverter that operates off-grid and can be used to monitor the operating frequency of the power grid. When a problem occurs in the power grid, it directly follows the frequency of the power grid. The switching switch has a second input terminal, a third input terminal, and a second output terminal. The second input terminal is connected to the first output terminal, and the third input terminal is connected to the power grid. The frequency converter has a fourth input terminal and a third output terminal. From the fourth input terminal to the third output terminal, the frequency converter includes a rectifier module (REC), a capacitive component (C3), and an inverter module (INV) connected in sequence. The fourth input terminal is connected to the second output terminal, and the third output terminal is connected to the electrolyte circulation pump in the flow battery. The control unit must have at least the following configurations: monitor the status of the power grid, switching switch, off-grid inverter, and capacitive components; send switching commands to the switching switch; and instruct the switching switch to electrically connect to the off-grid inverter or the power grid. The control unit (Battery Management Unit, BMS) can monitor the electrical and thermal parameters of the flow battery and has corresponding control, protection, and communication functions.

[0033] In this embodiment, based on the original functions of the BMS, the BMS also has the following new functions, including sampling and detecting the power grid, monitoring and controlling the status of switching switches, monitoring the status of off-grid inverters and capacitive components, etc. (See reference...) Figure 4 As shown, the left side of the BMS displays newly added BMS peripheral devices and data transmission and control, while the right side displays conventional BMS peripheral devices and data transmission and control. For example, power grid sampling and detection: This detects the power quality and frequency of the power grid. The BMS uses the sampled values ​​to make judgments and thus switch the power supply. Power supply switch: This selects the power source based on the BMS's internal algorithm and judgment. Off-grid inverter: The BMS controls the output power of the inverter circuit and synchronizes it with the power grid frequency to ensure reliable operation of downstream equipment after power supply switching, and also monitors the parameters of the off-grid inverter during operation. Capacitive components: The BMS monitors the overall capacitor voltage and operating status of the capacitive components, and provides protection and early warning to ensure the long-term stable operation of the capacitive components.

[0034] In this embodiment, the switching switch has two power supply sources: one from the power grid and the other from the flow battery itself, thus utilizing the energy stored in the flow battery. The DC side port (first input terminal) of the off-grid inverter is powered by the flow battery itself; the liquid circuit voltage can be selected as the power input for the DC port. Powered by the flow battery itself, the self-discharge energy loss during hot standby can be converted into power to maintain the operation of the BMS equipment, eliminating the need for an external power grid and disconnecting from the external grid. This utilizes the self-discharge of the flow battery during long-term idling, reducing energy waste caused by the conversion of electricity into heat. Each inverter individually controls an electrolyte circulation pump. The rated power of the inverter is generally one level higher than the rated power of the electrolyte circulation pump; for example, if the power of the electrolyte circulation pump is 5.5 kW, the power of the inverter can be 7.5 kW. Capacitive components ( Figure 3 C3 (highlighted by the dashed line) is connected in parallel to the DC bus between the rectifier and inverter modules of the frequency converter. Each frequency converter incorporates one capacitive component in parallel. By adding an additional capacitive component, especially an F-class supercapacitor, to the DC bus of the frequency converter, the electrolyte circulation pump can continue to operate at a flow rate higher than the minimum required flow rate during dual-power switching, without directly shutting down due to momentary power loss. This ensures that even if the flow battery is in a dual-power switching state during charging and discharging, the charging and discharging state of the flow battery energy storage system will not be affected. It should be noted that... Figure 3This is a simplified circuit diagram of the power supply system in this embodiment. Some conventional components or functions are not shown. While simplifying the representation, it does not affect the understanding of the essential content shown in this embodiment. For example, the off-grid inverter has a phase-locked loop, enabling it to follow the frequency of the power grid. The capacitive component C3 does not represent a single capacitor, but rather a combination of components that can achieve capacitive energy storage. The frequency converter also has a pre-charge circuit (…). Figure 3 (C1+C2 are the DC bus capacitors of the frequency converter), etc., which will not be elaborated here.

[0035] The flow battery power supply system based on the above circuit can utilize the energy stored in the flow battery itself. When the power grid experiences unstable power supply or power outage, it can switch to the flow battery's own power supply mode through a switching switch, thereby providing seamless and high-quality backup power for the flow battery's critical loads and realizing the flow battery's offline / uninterrupted operation.

[0036] This embodiment's power supply system can also achieve state of charge (SOC) balancing of the flow battery, with a SOC range of 0%-100%, used to understand the state of the stored energy in the flow battery. There may be an imbalance in the SOC among the energy storage units within the flow battery. Switching energy storage units with low SOC to the mains power supply reduces their energy consumption, while switching energy storage units with high SOC to their own power supply reduces the difference in SOC between the energy storage units. This balancing is achieved by the flow battery itself and does not require additional external equipment. In one implementation, the DC terminal of the flow battery includes one of the following: stack power supply, liquid circuit power supply, battery module power supply, and battery system power supply. A battery system includes several battery modules, a battery module includes several liquid circuits, and a liquid circuit includes several stacks. (See reference...) Figure 5As shown in the diagram. The stack voltage (CSV) is the voltage between the positive and negative terminals of a single stack in a flow battery, typically operating within a range of 52V to 80.6V. The liquid level voltage (LQV) is the voltage formed by the series and parallel connection of stacks within the same liquid level (a pair of positive and negative electrode tanks), typically operating within a range of 156V to 242V. The battery module voltage (MDV) is the voltage between the positive and negative terminals of a single power box in a flow battery, typically operating within a range of 312V to 484V. The flow battery system voltage (BATV), i.e., the total battery voltage, operates within a range determined by the number of battery modules connected in series (Num), typically ranging from 312V × Num to 484V × Num. It is evident that the minimum voltage range of the off-grid inverter varies depending on the input voltage source. For example, with an input voltage of LQV, the minimum operating voltage is calculated as: (Number of stacks connected in series in the current liquid level × Number of stack cells × Minimum operating voltage) = 3 × 52 × 1 = 156V. Therefore, off-grid inverters can achieve different balancing effects by sampling different input voltages. For example, an off-grid inverter with an input voltage from an LQV can achieve liquid-level balancing, while an off-grid inverter with an input voltage from an MDV can achieve tank-level balancing, and so on.

[0037] In one example, the switching device is either an automatic transfer switch (ATS) or a static transfer switch (STS). For an ATS, it uses a mechanical switching structure with a relatively long switching interval, typically 100ms to 1 second. For a STS, under normal operating conditions, when the main power supply is within its normal voltage range, the load automatically switches back to the main power supply after the main power supply returns to normal. The STS switch uses a break-before-make switching method, providing dual-bus power supply for single-power loads. It uses an SCR (Silicon Controlled Rectifier) ​​electronic switch for switching, with a switching interval of 10ms to 100ms.

[0038] In one example, the capacitive component includes a string-connected supercapacitor bank. A supercapacitor bank (SCB) is a combination of a series of small-voltage, high-capacity capacitors and external protection circuitry. The external protection circuitry may include voltage equalization, a pre-charge circuit, and reverse-current protection circuitry. Depending on the capacitor capacity, it can store different amounts of charge. The capacitor string voltage can be directly matched to the DC bus voltage. Combined with the pre-charge circuit, it protects the inverter's rectifier bridge, preventing excessive pull-down of the DC bus voltage during capacitor charging, while ensuring the stored energy meets the power support capacity.

[0039] In one example, the capacitive component includes a supercapacitor bank or a supercapacitor bank connected in parallel with a DC-DC circuit, which may be a bidirectional BUCK-BOOST circuit. In this embodiment, the capacitor bank string voltage does not need to perfectly match the DC bus voltage; it only needs to ensure that the stored energy multiplied by the conversion efficiency meets the power support capacity.

[0040] In one example, the rated current of the switching switch is determined based on the maximum operating current of the control unit, where the maximum operating current of the control unit is determined by the following formula:

[0041] In the formula, I This indicates the maximum operating current (A) of the control unit. P load This indicates the total power (kW) of all electrical devices controlled by the control unit. U It represents the AC line voltage (V). Cos Indicates the power factor. η Indicates efficiency.

[0042] In this embodiment, the rated switching current of the switching switch can be reasonably calculated based on the power of the BMS cabinet. For example, if the total load of all electrical equipment (loads) in the BMS cabinet is approximately 12kW, the operating current in the BMS cabinet can be calculated using the above formula. I ≈24A, but since the current values ​​for each range are fixed in the product specifications, and a certain level of safety performance must be maintained, the calculation... I Based on approximately 24A, the rated switching current of the switching switch STS can be selected as 32A.

[0043] In one example, the rated power of the off-grid inverter is not less than 1.5 times the total power of all electrical devices. For instance, if the total power of all electrical devices in the BMS cabinet is 12kW, then 12 × 1.5 = 18kW is calculated. Based on product specifications and safety considerations, a 20kW rated power off-grid inverter can be selected.

[0044] In one example, the rated voltage of the capacitive component is not less than the highest voltage of the DC bus capacitor in the frequency converter, and / or the capacitance of the capacitive component is determined by the following formula:

[0045] In the formula, C required This indicates the capacitance of a capacitive component. t Indicates the duration of the stabilizing support level. P This indicates the rated power of the electrolyte circulation pump. V maxThis represents the initial voltage of the DC bus capacitor in the frequency converter. V min This indicates the cutoff voltage of the DC bus capacitor in the frequency converter.

[0046] For example, the highest voltage of the DC bus capacitor in the frequency converter is about 540V. Therefore, the rated voltage of the capacitive component is ≥540V. A conventional supercapacitor is nominally 3.0V, 3.75Wh, and has a capacity of 16.7F. If the required capacity of the capacitive component is 3000F, then 180 individual supercapacitors can be configured in series. The overall parameters of this supercapacitor group are: withstand voltage 540V, capacity 3000F.

[0047] In one example, the off-grid inverter is also equipped with a DC-DC transformer module to change the input voltage of the off-grid inverter, and / or an isolation module for isolation protection of the off-grid inverter. For example, taking the boost function of the DC-DC transformer module as an example, if the input voltage range of the off-grid inverter is 156V-242V, the DC-DC transformer module needs to boost the DC voltage to above 565V, and then convert it to AC voltage to 400V. The isolation module filters the AC output of the off-grid inverter, isolating the DC component of the AC port of the off-grid inverter and suppressing common-mode interference and surges. It can be seen that the off-grid inverter can form a DC-DC + AC-DC + isolation structure, performing DC boost + inversion + AC boost on the input voltage, finally achieving the required voltage output.

[0048] In one example, the frequency converter has a deceleration energy backup function. Deceleration energy backup (DEB / dEb) is a motor deceleration and stopping function in the event of a momentary power outage. When a momentary power outage occurs in an application, this function can be used to decelerate the motor to zero speed. If the power supply is restored at this time, the motor can be restarted after the restoration time. In this embodiment, the frequency converter can be an integrated rectifier and inverter or a single rectifier with multiple inverters.

[0049] Another embodiment of the present invention provides a control method that can be applied to the aforementioned flow battery power supply system, but is not limited thereto. See reference... Figure 6As shown, method 600 mainly includes: S610, during the operation of the flow battery, determining whether the flow battery power supply system has switching capability; having the switching capability includes at least: the phase-locked loop of the off-grid inverter follows the frequency of the power grid, the DC voltage of the first input terminal of the off-grid inverter is greater than a first voltage, the first voltage being a preset minimum operating voltage; S620, if the switching capability is present, determining whether the flow battery power supply system meets a first switching condition; meeting the first switching condition includes at least: the off-grid inverter is operating normally, the power grid quality is unstable, or the flow battery meets the balancing condition, the balancing condition including at least: the state of charge difference ratio of the energy storage units in the flow battery is less than a set threshold; S630, if the first switching condition is met, sending a first switching command to the switching switch, the first switching command instructing the switching switch to be electrically connected to the off-grid inverter.

[0050] One of the main applications of the control method in this embodiment is that when the external power grid is unstable, it can switch to power supply from the flow battery itself, thereby enabling the flow battery to operate offline / uninterruptedly. Therefore, the basic requirement is that the current power supply system has the ability to switch between different power sources. In this embodiment, at least the following capability judgments are required: First, whether the phase-locked loop of the off-grid inverter follows the frequency of the power grid. If frequency following is satisfied, the flow battery can smoothly transition after the switching switch switches the input power to flow battery power, avoiding voltage instability caused by frequency differences. Second, whether the DC voltage at the first input terminal of the off-grid inverter is greater than a first voltage, which is a preset minimum operating voltage. If the input voltage of the off-grid inverter is too low, the necessary conditions for continuous operation of the flow battery will not be met. Other switching capabilities required by the flow battery power supply system can be determined based on the operating conditions of the flow battery and the requirements for the flow battery in actual applications; this embodiment does not impose specific limitations on them. Then, the control unit needs to determine whether the power supply system needs to switch power sources in the current state. For switching from the power grid to the voltage output of the flow battery itself, i.e., when the switching switch is electrically connected to the off-grid inverter, this embodiment has the following judgment methods: first, the off-grid inverter is operating normally and the power grid quality is unstable; second, the off-grid inverter is operating normally and the flow battery meets the balancing conditions.

[0051] In one example, the control method may further include an initialization process, specifically including: powering on the control unit and sending a second switching command to the switching switch, the second switching command instructing the switching switch to be electrically connected to the power grid; determining whether the voltage of the capacitive component is greater than a second voltage, the second voltage being a preset lower limit of the capacitive component's operating voltage; if the voltage of the capacitive component is greater than the second voltage, sending a parallel connection command to the capacitive component, the parallel connection command instructing the capacitive component to be connected in parallel to the DC bus circuit. Further, the control method may also include sending a charging command to the capacitive component if the voltage of the capacitive component is less than the second voltage, the charging command being used to initiate the charging process of the capacitive component; and sending a parallel connection command to the capacitive component or connecting it in parallel to the DC bus circuit during charging when the voltage of the charged capacitive component is greater than the second voltage.

[0052] It should be noted that the lower limit of the operating voltage of the capacitive component in this embodiment may vary depending on the composition of the capacitive component. Figure 7 This is a schematic diagram of the initialization process in one embodiment of the present invention, see reference. Figure 7 As shown, for the BMS, it is first powered on. In the initial state, the switching switch should be electrically connected to the power grid to enable the flow battery to start. Therefore, initially, the BMS needs to send a second switching command to the switching switch to connect it to the power grid. After the switching switch is connected to the power grid, the inverter's rectifier bridge and pre-charge circuit can charge the DC bus capacitor in the inverter. Then, it is determined whether the voltage of the capacitive component is greater than the second voltage. If the voltage of the capacitive component is greater than the second voltage, it indicates that the current capacitive component meets the power requirements, and the capacitive component can be directly connected in parallel to the DC bus circuit to respond to the flow battery start command at any time. If the voltage of the capacitive component is less than the second voltage, it indicates that the current capacitive component does not meet the power requirements, and the capacitive component needs to be charged to meet the power requirements before being connected in parallel to the DC bus circuit. Of course, if there is a fault in the capacitive component or the inverter, corresponding alarm prompts can be set to facilitate the reporting or inspection of related equipment. After completing the above process, the entire initialization process ends, ready to respond to the boot command.

[0053] In one example, after the control unit is powered on, it monitors whether the components that enable the flow battery to operate are functioning properly; if the components that enable the flow battery to operate are functioning properly, a start command is sent to instruct the flow battery to start, including starting the electrolyte circulation pump in the flow battery.

[0054] For reference Figure 8As shown, after receiving the start command, the BMS performs a test on the entire flow battery system, including components in the operating and power supply systems, to ensure that the flow battery can start normally. For example, it tests components such as valves, contactors, and fuses. If they are normal, the inverter starts, which in turn drives the electrolyte circulation pump to work, allowing the flow battery to complete its initial charging state.

[0055] In one example, the control method may further include replenishing the DC terminal of the flow battery with electricity when the DC voltage at the first input terminal of the off-grid inverter is less than a first voltage, until the DC voltage at the first input terminal of the off-grid inverter is greater than the first voltage. (Continue to refer to...) Figure 8 As shown, and combined with the foregoing, the flow battery power supply system needs to have switching capability. This switching capability includes at least the phase-locked loop of the off-grid inverter following the frequency of the power grid, and the DC voltage at the first input terminal of the off-grid inverter being greater than a first voltage. If the DC voltage at the first input terminal of the off-grid inverter is less than the first voltage, it indicates that the energy storage unit of the currently connected flow battery is insufficient to support the flow battery's off-grid operation, therefore, the flow battery needs to be recharged.

[0056] In one example, the control method may further include: determining whether the flow battery power supply system meets the second switching conditions, wherein meeting the second switching conditions includes at least stable power grid quality, abnormal operation of the off-grid inverter, or the flow battery not meeting the balancing conditions; if the second switching conditions are met, sending a second switching command to the switching switch, the second switching command instructing the switching switch to be electrically connected to the power grid. (See also...) Figure 9 As shown, when the first switching condition is met, the switching switch is switched from being connected to the power grid to being connected to the off-grid inverter, realizing the off-grid operation or state-of-charge balancing of the flow battery. When the power grid quality is stable, the off-grid inverter is malfunctioning, or the flow battery does not meet the balancing condition, the control unit sends a second switching command to the switching switch, causing the switching switch to perform a switching action to connect to the power grid.

[0057] Figure 9 This is a schematic diagram illustrating the switching process in one embodiment of the present invention, see reference. Figure 9As shown, during the switching process indicated by the BMS, if the AC voltage is unstable and affects the DC bus voltage of the inverter, the inverter will take the following actions: Firstly, if the DC bus voltage is lower than the DEB operating level, the inverter's DEB function will activate, causing the inverter to decelerate and generate reverse power to maintain the DC bus voltage. Simultaneously, capacitive components will be engaged to maintain the DC bus voltage. Then, the inverter will automatically decelerate, wait for the DC bus voltage to recover, and determine if the recovered DC bus voltage exceeds the DEB recovery level. If the recovered DC bus voltage exceeds the DEB recovery level, a 3-second DEB recovery time will be waited before the inverter frequency linearly accelerates until it returns to the set frequency, thus completing the switching process. If the DC bus voltage recovers but is lower than the DEB recovery level, then the DC bus voltage is currently below the inverter's DC undervoltage lower limit. Wait another 30 seconds for the DC bus voltage to recover, and then again check if the recovered DC bus voltage is greater than the DEB recovery level. If the recovered DC bus voltage is greater than the DEB recovery level, wait 3 seconds for the DEB recovery time, and the inverter frequency will linearly accelerate until it returns to the set frequency, thus completing the switching. Otherwise, it indicates a BMS indication fault or a related equipment malfunction.

[0058] Figure 10 This is a schematic diagram illustrating the effect of applying the present invention in one operating state. (Refer to...) Figure 10 As shown, the dEb function in the frequency converter operates on an automatic acceleration / deceleration basis, with the frequency recovering after power restoration. The power supply status at this time is as follows: a momentary power outage in the power grid or an unstable / sudden heavy load causing a power drop. When the input voltage is restored, during the frequency converter's deceleration process (including 0Hz operation), if the AC input voltage is higher than the dEb recovery level, the frequency converter maintains the current frequency for 3 seconds before accelerating back to the target frequency. Therefore, when the frequency converter's DC bus voltage is unstable and lower than the dEb operating level but not lower than the frequency converter's low voltage Lv level, the frequency converter will decelerate from the set frequency, the motor will transform into a generator, and reverse power generation will maintain the DC bus voltage. Once the DC bus voltage recovers to above the dEb recovery level, there is a delay to wait for the DC bus voltage to stabilize before linearly accelerating to the target frequency.

[0059] Figure 11 This is a schematic diagram illustrating the effect of applying the present invention in another operating state. (Refer to...) Figure 11As shown, the dEb function in the frequency converter operates on an automatic acceleration / deceleration basis, with the frequency recovering after power restoration. The power supply status at this time is as follows: prolonged power grid instability / excessive switching time of the transfer switch / insufficient capacity of the capacitive components. The AC input voltage recovers after the DC bus voltage falls below the Lv level. The frequency converter decelerates to 0Hz, and the DC bus voltage continues to decrease until it falls below the Lv level, at which point the frequency converter disconnects the Softstart relay (i.e., dEb is not triggered). Once the AC input voltage recovers and the DC bus voltage rises above the Lv recovery level, the dEb function is retried. When the DC bus voltage rises above the dEb recovery level, the frequency converter maintains the frequency for 3 seconds before resuming linear acceleration. Therefore, when the frequency converter's DC bus voltage is unstable and the voltage value is below the dEb operating level and below the frequency converter's low-voltage Lv recovery level, the frequency converter will decelerate from the set frequency, the motor will switch to a generator, and reverse power generation will maintain the DC bus voltage until the frequency reaches 0 and remains there. Even if the DC bus voltage is below the Lv level, no fault is reported. Once the DC bus voltage recovers to above the dEb recovery level, there is a delay to wait for the DC bus voltage to stabilize before linearly accelerating the frequency to the target frequency. However, if the DC bus voltage drops below the Lv level for 30 seconds, the BMS determines that the DC bus capacitor in the inverter has failed to maintain its position, triggering a BMS fault signal.

[0060] The basic concepts have been described above. Obviously, for those skilled in the art, the above disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore remain within the spirit and scope of the exemplary embodiments of this application.

[0061] Some aspects of this application can be executed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The aforementioned hardware or software may be referred to as a "data block," "module," "engine," "unit," "component," or "system." The processor may be one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. Furthermore, aspects of this application may manifest as computer products residing in one or more computer-readable media, including computer-readable program code. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, magnetic tapes, etc.), optical discs (e.g., compressed CDs, digital multifunction DVDs, etc.), smart cards, and flash memory devices (e.g., cards, sticks, key drives, etc.).

[0062] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of scope in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

[0063] Although this application has been described with reference to specific embodiments, those skilled in the art should recognize that the above embodiments are only used to illustrate this application, and various equivalent changes or substitutions can be made without departing from the spirit of this application. Therefore, any changes or modifications to the above embodiments within the essential spirit of this application will fall within the scope of the claims of this application.

Claims

1. A liquid flow battery power supply system, characterized by, The off-grid inverter has a first input end and a first output end, the first input end is connected to a direct current end of a flow battery; The switching switch has a second input end, a third input end and a second output end, the second input end is connected to the first output end, the third input end is connected to a power supply grid; The frequency converter has a fourth input end and a third output end, and from the fourth input end to the third output end, the frequency converter includes a rectifier module, a capacitive component and an inverter module connected in sequence; the fourth input end is connected to the second output end, and the third output end is connected to an electrolyte circulating pump in the flow battery; The control unit at least has the following configurations: monitoring the state of the power supply grid, the switching switch, the off-grid inverter and the capacitive component; sending a switching instruction to the switching switch, the switching instruction instructs the switching switch to be electrically connected to the off-grid inverter or the power supply grid. The direct current end of the flow battery includes one of the following: a stack power supply, a liquid path power supply, a battery module power supply and a battery system power supply, wherein a battery system contains a plurality of battery modules, a battery module contains a plurality of liquid paths, and a liquid path contains a plurality of stacks.

2. The liquid flow battery power system of claim 1, wherein, The switching switch is an automatic transfer switch or a static switching switch.

3. The liquid flow battery power system of claim 1, wherein, The capacitive component includes a group string directly connected super capacitor group.

4. The liquid flow battery power system of claim 1, wherein, The capacitive component includes a super capacitor group or a parallel circuit of the super capacitor group and a DC-DC circuit.

5. The liquid flow battery power system of claim 1, wherein, The rated current of the switching switch is determined according to the maximum operating current of the control unit, wherein the maximum operating current of the control unit is determined by the following formula:

6. The liquid flow battery power system of claim 1, wherein, Cos wherein I represents the maximum operating current of the control unit, P load represents the power of all electrical devices controlled by the control unit, U represents the AC line voltage, η represents the power factor, The rated power of the off-grid inverter is not less than 1.5 times the total power of all electrical equipment. represents the efficiency.

7. The liquid flow battery power system of claim 1, wherein, The rated voltage of the capacitive component is not less than the highest voltage of the direct current bus capacitor in the frequency converter, and / or the capacitance capacity of the capacitive component is determined by the following formula:

8. The liquid flow battery power system of claim 1, wherein, The off-grid inverter is further provided with a DC-DC voltage conversion module for changing the input voltage of the off-grid inverter, and / or an isolation module for isolation protection of the off-grid inverter. wherein C required represents the capacitance of the capacitive component, t represents the voltage support time, P represents the rated power of the electrolyte circulation pump, V max represents the initial voltage of the DC bus capacitor in the frequency converter, V min represents the cut-off voltage of the DC bus capacitor in the frequency converter.

9. The liquid flow battery power system of claim 1, wherein, The frequency converter has a deceleration energy regeneration backup function.

10. The liquid flow battery power system of claim 1, wherein, The off-grid inverter has a first input end and a first output end, the first input end is connected to a direct current end of a flow battery; 11. A control method applied to the liquid flow battery powered system according to any one of claims 1-10, characterized in that, The switching switch has a second input end, a third input end and a second output end, the second input end is connected to the first output end, the third input end is connected to a power supply grid; The frequency converter has a fourth input end and a third output end, and from the fourth input end to the third output end, the frequency converter includes a rectifier module, a capacitive component and an inverter module connected in sequence; the fourth input end is connected to the second output end, and the third output end is connected to an electrolyte circulating pump in the flow battery; The control unit at least has the following configurations: monitoring the state of the power supply grid, the switching switch, the off-grid inverter and the capacitive component; sending a switching instruction to the switching switch, the switching instruction instructs the switching switch to be electrically connected to the off-grid inverter or the power supply grid. The direct current end of the flow battery includes one of the following: a stack power supply, a liquid path power supply, a battery module power supply and a battery system power supply, wherein a battery system contains a plurality of battery modules, a battery module contains a plurality of liquid paths, and a liquid path contains a plurality of stacks. The switching switch is an automatic transfer switch or a static switching switch.

12. The control method according to claim 11, characterized by, The capacitive component includes a group string directly connected super capacitor group. The capacitive component includes a super capacitor group or a parallel circuit of the super capacitor group and a DC-DC circuit. The rated current of the switching switch is determined according to the maximum operating current of the control unit, wherein the maximum operating current of the control unit is determined by the following formula: Cos η The rated power of the off-grid inverter is not less than 1.5 times the total power of all electrical equipment. The rated voltage of the capacitive component is not less than the highest voltage of the direct current bus capacitor in the frequency converter, and / or the capacitance capacity of the capacitive component is determined by the following formula: The off-grid inverter is further provided with a DC-DC voltage conversion module for changing the input voltage of the off-grid inverter, and / or an isolation module for isolation protection of the off-grid inverter. The frequency converter has a deceleration energy regeneration backup function. The off-grid inverter has a first input end and a first output end, the first input end is connected to a direct current end of a flow battery; The switching switch has a second input end, a third input end and a second output end, the second input end is connected to the first output end, the third input end is connected to a power supply grid; The frequency converter has a fourth input end and a third output end, and from the fourth input end to the third output end, the frequency converter includes a rectifier module, a capacitive component and an inverter module connected in sequence; the fourth input end is connected to the second output end, and the third output end is connected to an electrolyte circulating pump in the flow battery; The control unit at least has the following configurations: monitoring the state of the power supply grid, the switching switch, the off-grid inverter and the capacitive component; sending a switching instruction to the switching switch, the switching instruction instructs the switching switch to be electrically connected to the off-grid inverter or the power supply grid. The direct current end of the flow battery includes one of the following: a stack power supply, a liquid path power supply, a battery module power supply and a battery system power supply, wherein a battery system contains a plurality of battery modules, a battery module contains a plurality of liquid paths, and a liquid path contains a plurality of stacks. The switching switch is an automatic transfer switch or a static switching switch. The capacitive component includes a group string directly connected super capacitor group. The capacitive component includes a super capacitor group or a parallel circuit of the super capacitor group and a DC-DC circuit. The rated current of the switching switch is determined according to the maximum operating current of the control unit, wherein the maximum operating current of the control unit is determined by the following formula: Cos η The rated power of the off-grid inverter is not less than 1.5 times the total power of all electrical equipment. The rated voltage of the capacitive component is not less than the highest voltage of the direct current bus capacitor in the frequency converter, and / or the capacitance capacity of the capacitive component is determined by the following formula: The off-grid inverter is further provided with a DC-DC voltage conversion module for changing the input voltage of the off-grid inverter, and / or an isolation module for isolation protection of the off-grid inverter. The frequency converter has a deceleration energy regeneration backup function. The control unit is powered on, and a second switching command is sent to the switching switch, the second switching command instructing the switching switch to be electrically connected to the power grid. Determine whether the voltage of the capacitive component is greater than a second voltage, where the second voltage is a preset lower limit of the operating voltage of the capacitive component; If the voltage of the capacitive component is greater than the second voltage, a parallel connection command is sent to the capacitive component, which instructs the capacitive component to be connected in parallel to the DC bus circuit.

13. The control method according to claim 12, characterized by Also includes: If the voltage of the capacitive component is less than the second voltage, a charging command is sent to the capacitive component, and the charging command is used to start the charging process of the capacitive component. When the voltage of the capacitive component after charging is greater than the second voltage, a parallel connection command is sent to the capacitive component or it is connected in parallel to the DC bus circuit during charging.

14. The control method according to claim 12, characterized by, Also includes: After the control unit is powered on, monitor whether the components that enable the flow battery to operate are functioning properly; When all components of the flow battery are functioning normally, a start command is sent, which instructs the flow battery to start, including starting the electrolyte circulation pump in the flow battery.

15. The control method according to claim 11, characterized by, Also includes: If the DC voltage at the first input terminal of the off-grid inverter is less than the first voltage, the DC terminal of the flow battery is charged until the DC voltage at the first input terminal of the off-grid inverter is greater than the first voltage.

16. The control method according to claim 11, characterized by Also includes: Determine whether the flow battery power supply system meets the second switching condition. Meeting the second switching condition includes at least the stable quality of the power grid, the abnormal operation of the off-grid inverter, or the flow battery not meeting the balancing condition. If the second switching condition is met, a second switching command is sent to the switching switch, the second switching command instructing the switching switch to be electrically connected to the power grid.

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