Super-capacitor-lithium battery hybrid energy storage dynamic voltage recovery control method, system and device

Abstract

This application relates to the field of hybrid energy storage control technology, and in particular to a dynamic voltage recovery control method, system, and device based on supercapacitor-lithium battery hybrid energy storage. The method acquires a sampled value of the grid-side voltage, compares the sampled value with a reference voltage, and determines whether the grid-side voltage fluctuates. When the grid-side voltage fluctuates, it acquires the voltage sag depth and voltage change rate, determines the fluctuation level, selects a power allocation mode, outputs a first power setpoint for the supercapacitor energy storage branch and a second power setpoint for the lithium battery energy storage branch, and controls the two energy storage branches to coordinate the output of compensation power. This system and device are used to execute the above control process. Through the above technical solution, the voltage fluctuation response speed, continuous support capability, and power switching smoothness can be improved, while reducing the risks of high-frequency impacts on lithium batteries and deep discharge of supercapacitors.

Description

Technical Field

[0001] The embodiments of this application relate to the field of hybrid energy storage control technology; in particular, to a method, system, and device for dynamic voltage recovery control of supercapacitor-lithium battery hybrid energy storage. Background Technology

[0002] Dynamic voltage restorers (DVRs) are typically installed between the power grid and critical loads to quickly establish compensating voltage to the load side when voltage dips, fluctuations, or short-term interruptions occur on the grid side. This maintains the continuous operation of production equipment, information equipment, or other sensitive loads. In industrial and commercial energy storage, uninterruptible power supply, and high-reliability power distribution scenarios, DVRs need to meet millisecond-level takeover requirements while providing sufficient energy support when voltage anomalies persist.

[0003] In existing technologies, DC-side energy storage typically employs a single supercapacitor or a single lithium battery. When using a supercapacitor, the system can quickly establish high-power transient support after a voltage drop, making it suitable for handling short-duration fluctuations. However, supercapacitors have low energy density; designing them to independently cover operating conditions lasting from several seconds to tens of seconds significantly increases the required capacity, cost, and difficulty in voltage equalization management. When using a lithium battery, the system has good continuous power supply capability, suitable for handling medium- to long-term anomalies. However, lithium batteries and their converters exhibit a relatively slow output setup under high-power rapid takeover scenarios, which can easily lead to insufficient compensation response under heavy load and millisecond-level voltage drops.

[0004] Hybrid energy storage solutions that simultaneously connect supercapacitors and lithium batteries to the DC side also exist in this field. Although such solutions can utilize the different characteristics of the two types of energy storage units at the same time, if the control logic only adopts a fixed ratio allocation, fixed delay switching, or only controls based on a single voltage threshold, problems such as inaccurate mode selection, unsmooth switching transition, lithium batteries being subjected to unnecessary high-frequency shocks, and supercapacitors entering excessively deep discharge regions can easily occur when the depth, rate of change, and duration of voltage anomalies change.

[0005] Therefore, existing solutions still lack a processing mechanism that balances rapid response, continuous support, lifespan protection, and control stability within the typical medium-duration fluctuation range of five to sixty seconds. Summary of the Invention

[0006] The purpose of this application is to provide a dynamic voltage recovery control method, system, and device for supercapacitor-lithium battery hybrid energy storage, in order to solve the problems in the prior art where a single energy storage scheme cannot simultaneously achieve millisecond-level fast response and medium-duration continuous support, as well as the problems of power mismatch, increased device stress, and unstable branch switching caused by the mismatch between control logic and operating conditions in hybrid energy storage schemes.

[0007] The first aspect of this application provides a dynamic voltage recovery control method for supercapacitor-lithium battery hybrid energy storage, comprising: acquiring a grid-side voltage sampling value; comparing the grid-side voltage sampling value with a reference voltage to determine whether the grid-side voltage fluctuates; when the grid-side voltage fluctuates, acquiring a voltage sag depth and a voltage change rate based on the grid-side voltage sampling value; determining a fluctuation level based on the voltage sag depth and the voltage change rate; selecting a power allocation mode based on the fluctuation level; outputting a first power setpoint for the supercapacitor energy storage branch and a second power setpoint for the lithium battery energy storage branch based on the power allocation mode; controlling the supercapacitor energy storage branch to output compensation power according to the first power setpoint, and controlling the lithium battery energy storage branch to output compensation power according to the second power setpoint when a preset intervention condition is met.

[0008] Using the above method, a closed-loop processing chain can be established around the grid-side voltage sampling value, from fluctuation judgment, level determination, mode selection to power setting and branch intervention control. This allows the supercapacitor energy storage branch to be used for rapid initial compensation, and the lithium battery energy storage branch to be used for medium-duration continuous compensation, thereby improving the adaptability of the dynamic voltage recovery device to voltage fluctuations of different durations and severity.

[0009] In some implementations, determining the fluctuation level based on the voltage sag depth and the voltage change rate, and selecting a power allocation mode based on the fluctuation level, includes: when the voltage sag depth is greater than a third threshold and the absolute value of the voltage change rate is greater than a change rate threshold, determining the fluctuation level as Level 1 and selecting an overcapacitor independent mode; when the voltage sag depth is between a second threshold and a third threshold, determining the fluctuation level as Level 2 and selecting a coordinated transition mode; when the voltage sag depth is between a first threshold and a second threshold, determining the fluctuation level as Level 3 and selecting a lithium battery-dominated mode. By using both the voltage sag depth and the voltage change rate for classification, misclassification caused by relying on only a single threshold can be avoided, thereby improving the targeting of mode selection.

[0010] In some implementations, in the coordinated transition mode, controlling the initial compensation power to be provided by the supercapacitor energy storage branch and controlling the lithium battery energy storage branch to take over the output when the preset intervention condition is met includes: setting the preset intervention condition to at least one of the following: the supercapacitor energy storage branch has been discharged for a preset switching time threshold; the energy storage terminal voltage corresponding to the supercapacitor energy storage branch drops to a predetermined proportion of a preset lower limit voltage; the estimated duration of the grid-side voltage fluctuation exceeds the remaining time that the supercapacitor energy storage branch can independently support; when the preset intervention condition is met, increasing the second power setpoint and decreasing the first power setpoint. Using the above multi-condition intervention logic can prevent the lithium battery energy storage branch from being prematurely activated during short-term fluctuations, and can also prevent the supercapacitor energy storage branch from independently undertaking the compensation task after entering an excessively deep discharge zone during long-term fluctuations.

[0011] In some implementations, increasing the second power setpoint and decreasing the first power setpoint when the preset intervention condition is met includes: decreasing the first power setpoint from its current value to zero within a preset ramp time; increasing the second power setpoint from zero to the load-side compensation power demand value within the preset ramp time; and maintaining the sum of the first power setpoint and the second power setpoint equal to the load-side compensation power demand value within the preset ramp time. This method can reduce power jumps and bus disturbances during branch switching.

[0012] In some implementations, maintaining the sum of the first power setpoint and the second power setpoint equal to the load-side compensation power demand value within a preset ramp time includes: detecting the sum of the actual output power of the supercapacitor energy storage branch and the lithium battery energy storage branch; calculating the deviation between the sum of the actual output power and the load-side compensation power demand value; and correcting the first power setpoint and the second power setpoint based on the deviation. This closed-loop verification method can further improve the smoothness of the coordinated switching process.

[0013] The second aspect of this application provides a dynamic voltage recovery control system for supercapacitor-lithium battery hybrid energy storage, comprising: a voltage sampling module, a fluctuation judgment module, a parameter extraction module, a classification judgment module, a mode selection module, a power setting module, and an intervention control module. Each module establishes control logic sequentially around grid-side voltage sampling, fluctuation judgment, classification determination, mode selection, and power setting. Through this system, the core innovation of the dynamic voltage recovery device can be focused on the data flow and control division of labor between functional modules.

[0014] In some implementations, the system further includes a power coordination module and a health status assessment module. The power coordination module, when preset intervention conditions are met, reduces the first power setpoint and increases the second power setpoint within a preset ramp time, while maintaining their sum equal to the load-side compensation power demand. The health status assessment module determines the health status based on the operating data of the supercapacitor energy storage branch and the lithium battery energy storage branch, and adjusts the power upper limit, discharge threshold, and branch participation parameters based on the health status. By introducing the power coordination module and the health status assessment module, power gaps, bus fluctuations, and inverter output disturbances during branch switching can be reduced, and control parameters can be adjusted promptly when the performance of the energy storage unit deteriorates.

[0015] A third aspect of this application provides a supercapacitor-lithium battery hybrid energy storage dynamic voltage recovery device, comprising a grid input line and a load line; a static switch module disposed between the grid input line and the load line; an inverter module connected to the load line on the AC side and to the DC bus on the DC side; a supercapacitor energy storage branch connected to the DC bus via a first bidirectional DC / DC converter; a lithium battery energy storage branch connected to the DC bus via a second bidirectional DC / DC converter; and a dynamic voltage recovery control system connected to the static switch module, the inverter module, the first bidirectional DC / DC converter, and the second bidirectional DC / DC converter. Through the above device, a complete closed loop of detection, decision-making, execution, and feedback can be formed between the control system and the external grid, the load, and the dual energy storage branches. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the dynamic voltage recovery control method in the embodiments of this application; Figure 2 This is a functional module logic diagram of the dynamic voltage recovery control system in the embodiments of this application; Figure 3 This is a diagram showing the connection relationship between the dynamic voltage recovery device and the external circuit in the embodiments of this application. Detailed Implementation

[0017] The embodiments of this application will be further described below with reference to the accompanying drawings. The following embodiments are used to explain the technical solution of this application, and not to limit the scope of protection. The grid-side voltage referred to herein may be the effective value of the three-phase line voltage, the effective value of the phase voltage, or the equivalent voltage calculated according to control requirements; the reference voltage referred to herein may be the rated voltage, the center value of the rated operating window, or the reference voltage after per-unit processing. The various first power setpoints and second power setpoints referred to below are respectively used to drive the supercapacitor energy storage branch and the lithium battery energy storage branch to establish the target output power; in different implementation methods, the setpoint can represent the active power command, the current reference value conversion result, or the power outer loop output. Parameter examples are given below after the principle description. These parameter examples are only used to illustrate the engineering implementation method and parameter coordination relationship, and do not constitute a limitation on the scope of protection.

[0018] The first embodiment of this application provides a dynamic voltage recovery control method for supercapacitor-lithium battery hybrid energy storage. This embodiment corresponds to the technical solution defined in claim 1. The control method first addresses how to determine the compensation strategy based on grid-side voltage sampling information, and further outputs the corresponding control quantities for the supercapacitor energy storage branch and the lithium battery energy storage branch.

[0019] For ease of explanation, this embodiment refers to the main body executing the method as the controller and its associated functional circuit modules. The controller and associated functional circuit modules are used to acquire grid-side voltage sampling information, and to compare, judge, classify, and make control decisions based on this grid-side voltage sampling information, so as to output corresponding power setpoints and control signals. The controller can be implemented using a digital signal processor, microcontroller, programmable logic device, industrial control computer, or other hardware with data processing and control output capabilities, or it can be implemented by a processor calling program instructions from memory. It should be understood that the specific hardware form of the controller does not constitute a limitation on the control method of this application. As long as it can perform the voltage sampling processing, fluctuation judgment, fluctuation classification, mode selection, intervention control, and power coordination functions described in this application, it can be used as a specific implementation of the controller.

[0020] For dynamic voltage recovery, whether the load side can maintain stable power supply after a grid-side voltage anomaly depends on whether fluctuation detection, severity assessment, and branch-level adjustment can be completed within a very short time. If only a binary judgment is made based on whether the voltage exceeds the limit, only the conclusion of whether compensation is triggered can be obtained, which cannot simultaneously reflect the scale of the voltage deficit, the speed of the anomaly, and the subsequent support requirements. Therefore, it is difficult to provide sufficient criteria for power allocation mode selection and lithium battery intervention timing. Based on this, this embodiment establishes control logic around the processing chain of "voltage sampling - fluctuation judgment - parameter extraction - level determination - mode selection - power setting - branch intervention control".

[0021] like Figure 1 As shown, the control method of the first embodiment includes: S1. Obtain the sampled voltage value on the grid side; S2. Compare the sampled grid-side voltage value with the reference voltage to determine whether the grid-side voltage has fluctuated; S3. When the grid-side voltage fluctuates, the voltage sag depth and voltage change rate are obtained based on the grid-side voltage sampling value; S4. Determine the fluctuation level based on the voltage sag depth and the voltage change rate; S5. Select the power distribution mode according to the fluctuation level; S6. Output the first power setpoint of the supercapacitor energy storage branch and the second power setpoint of the lithium battery energy storage branch according to the power distribution mode; S7. Control the supercapacitor energy storage branch to output compensation power according to the first power setpoint, and control the lithium battery energy storage branch to output compensation power according to the second power setpoint when the preset intervention condition is met.

[0022] First, step S1 acquires the grid-side voltage sample value, typically through a voltage sensor and an analog-to-digital converter circuit. The sampled value can be the effective value of the three-phase line voltage, or the positive-sequence voltage, phase voltage, or equivalent voltage calculated by the controller according to a set period.

[0023] Under normal operating conditions, step S2 compares the current sampled value with a preset reference voltage. This comparison can be made using either absolute deviation or per-unit deviation. For critical load scenarios, to avoid misinterpreting normal minor disturbances as anomalies requiring DVR intervention, a detection threshold and hold time can be set. When the deviation exceeds the threshold and continues to meet the set criteria, the controller determines that the grid-side voltage is fluctuating and transitions to subsequent tiered control.

[0024] If the controller determines that the grid-side voltage has not fluctuated, it keeps the supercapacitor energy storage branch and the lithium battery energy storage branch in standby or preset operating state. The controller continues to cyclically sample and compare the grid-side voltage without entering the fluctuation classification, mode selection and compensation power output control, until it determines that the grid-side voltage has fluctuated, and then performs subsequent processing.

[0025] Upon detecting a voltage fluctuation on the grid side, step S3 is performed to further obtain the voltage sag depth and voltage rate of change based on the grid side voltage sampling values. The voltage sag depth represents the percentage shortfall of the current voltage relative to the normal operating value, while the voltage rate of change represents the speed at which the voltage enters an abnormal state. The voltage sag depth primarily affects the required compensation amplitude on the load side, while the voltage rate of change primarily affects the controller's requirements for power build-up speed. Using both together in subsequent judgments allows the controller to simultaneously grasp amplitude and dynamic information in the early stages of a fluctuation, thereby improving the accuracy of power allocation mode selection.

[0026] The voltage sag depth can be calculated using the following formula: in, Indicates the reference voltage. This represents the grid-side voltage during the current sampling period.

[0027] The calculation of the voltage change rate on the grid side can be based on the following formula: in, This represents the grid-side voltage during the current sampling period. This represents the grid-side voltage in the previous sampling period. Indicates the sampling interval.

[0028] After obtaining the voltage sag depth and voltage change rate, step S4 determines the fluctuation level based on these two quantities, and in step S5, selects the overcapacitance independent mode, coordinated transition mode, or lithium battery-dominated mode according to the fluctuation level. There are also methods in this field that use only a single voltage threshold for grading or directly fix the switching mode. These solutions are simple to implement, but when voltage deficit, entry speed, and continuous demand change simultaneously, the controller struggles to balance rapid takeover and continuous support.

[0029] Specifically, in this embodiment, severe and rapidly entering operating conditions are classified as Level 1, where the supercapacitor energy storage branch undertakes all compensation power; operating conditions with a transitional relationship between duration and power demand are classified as Level 2, where the supercapacitor energy storage branch outputs first, followed by the lithium battery energy storage branch; operating conditions with relatively small voltage deficits but potentially long durations are classified as Level 3, where the lithium battery energy storage branch establishes continuous output earlier, while the supercapacitor energy storage branch mainly undertakes voltage build-up and short-term support tasks. After completing the level determination, a power allocation mode is selected according to the fluctuation level, and in step S6, the first power setpoint value for the supercapacitor energy storage branch and the second power setpoint value for the lithium battery energy storage branch are output according to the selected mode.

[0030] Because the two types of energy storage units differ in power density, energy density, and transient response capability, the first power setpoint and the second power setpoint are not in a fixed proportional relationship, but should be dynamically adjusted according to the mode, branch status, and duration prediction. Therefore, after the power allocation mode is determined, step S7 first instructs the supercapacitor energy storage branch to establish compensation power according to the first power setpoint, and then controls the lithium battery energy storage branch to output compensation power according to the second power setpoint when the preset intervention conditions are met, so that the supercapacitor undertakes the task of rapid support and the lithium battery undertakes the task of continuous support.

[0031] The following is a set of parameterized examples corresponding to the aforementioned principles, illustrating how the control logic is actually implemented in engineering. Taking a three-phase 380V, 50Hz industrial and commercial low-voltage system as an example, the rated active power of the important load can be 100kW, the power factor can be 0.95, corresponding to an apparent power of approximately 105kVA; the target DC bus voltage can be set to 760V. The fluctuation detection threshold can be set to 8% of the reference voltage, i.e., a fluctuation is determined to have occurred when the grid-side voltage is below 349.6V. The first, second, and third sag depth thresholds can be set to 0.10, 0.35, and 0.70, respectively, and the rate of change threshold can be set to 60V / ms.

[0032] In one optional energy storage configuration, the supercapacitor bank can consist of 96 individual cells rated at 2.7V and 3000F connected in series, with a series rated voltage of 259.2V and an equivalent capacitance of approximately 31.25F; the first bidirectional DC / DC converter can have a continuous power rating of 120kW and a five-second overload power rating of 180kW. The lithium battery bank can consist of 180 lithium iron phosphate cells rated at 3.2V and 50Ah connected in series, with a nominal voltage of approximately 576V and a nominal energy of approximately 28.8kWh; the second bidirectional DC / DC converter can have a continuous power rating of 120kW and a ten-second overload power rating of 150kW. Based on the supercapacitor bank discharging from 260V to 120V, it can release approximately 0.23kWh of energy. Under the conditions of a DC-side efficiency of 0.94 and an output power of 100kW, the supercapacitor energy storage branch can independently support the operation for about 7.8 seconds. Even if the lithium battery bank is calculated based on 80% of its usable energy, it is sufficient to cover continuous support conditions for more than tens of seconds.

[0033] In a Level 1 operating condition, the grid-side voltage drops from 380V to 100V within 1.5ms and remains there for 0.6s. At this point, the voltage sag depth is approximately 0.737, and the voltage change rate is approximately 186.7V / ms. The controller determines the fluctuation level as Level 1 and selects the overcapacitance independent mode. The controller can issue a cutoff command within 0.8ms after detecting the fluctuation and increase the first power setpoint to nearly 100kW within approximately 1ms, while maintaining the second power setpoint at 0. Due to the short duration and less than the stabilization time required for lithium battery intervention, the lithium battery energy storage branch does not intervene.

[0034] In a set of Level 2 operating conditions, the grid-side voltage drops from 380V to 210V within 6ms and remains there for 12s. At this point, the voltage sag depth is approximately 0.447, and the voltage change rate is approximately 28.3V / ms. The controller determines the fluctuation level to be Level 2 and selects a coordinated transition mode. For the initial 20ms, the first power setpoint is maintained at 100kW, and the second power setpoint is 0, to ensure rapid voltage build-up on the load side. Subsequently, the controller comprehensively judges the intervention conditions based on the discharge time, supercapacitor terminal voltage, and duration prediction. Once the intervention conditions are met, the second power setpoint is increased, and the first power setpoint is decreased, allowing the lithium battery energy storage branch to gradually assume the main continuous compensation task.

[0035] In a Level 3 operating condition, the grid-side voltage drops from 380V to 300V within 15ms and remains there for 20s. At this point, the voltage sag depth is approximately 0.211, and the voltage change rate is approximately 5.3V / ms. The controller determines the fluctuation level as Level 3 and selects the lithium-ion battery-dominated mode. The controller first outputs approximately 40kW from the supercapacitor energy storage branch for about 100ms to suppress transient fluctuations on the bus, then increases the second power setpoint to approximately 80kW and maintains continuous output. Under this condition, the supercapacitor energy storage branch primarily handles voltage build-up and short-term support, while the lithium-ion battery energy storage branch provides the main energy supply.

[0036] The second embodiment of this application further illustrates a highly inventive multi-condition intervention control scheme based on the first embodiment.

[0037] For the coordinated transition mode, the timing of the lithium battery energy storage branch's intervention is determined after jointly assessing the current support status of the supercapacitor energy storage branch and the subsequent support requirements for grid-side voltage fluctuations. Because grid-side voltage fluctuations have significant uncertainties in duration, sag depth, and recovery process, switching based solely on a fixed delay is insufficient to simultaneously address the rapid compensation needs under short-term large disturbance scenarios and the continuous energy supply needs under medium-term fluctuation scenarios. If the fixed delay is set too short, for voltage fluctuations with short duration but large transient impacts, the lithium battery energy storage branch will intervene prematurely while the supercapacitor energy storage branch still has sufficient support capacity. This causes the lithium battery to participate in high-frequency, high-rate charging and discharging processes in scenarios where compensation could be completed independently by the supercapacitor, increasing the transient current impact and cyclic load on the lithium battery. If the fixed delay is set too long, when the duration of voltage fluctuation on the grid side exceeds the current remaining support time of the supercapacitor, the supercapacitor energy storage branch will continue to operate in a lower voltage range. Its output regulation margin and continued support capability will decrease, and a compensation power gap may occur before the lithium battery energy storage branch has completed output establishment, resulting in increased DC bus voltage fluctuations, which in turn affects the inverter output stability.

[0038] Based on the above problems, in this embodiment, the intervention condition for the lithium battery energy storage branch in the coordinated transition mode is set to at least one of the following: the discharge time of the supercapacitor energy storage branch reaches a preset switching time threshold; the voltage at the energy storage terminal corresponding to the supercapacitor energy storage branch drops to a predetermined proportion of a preset lower limit voltage; the estimated duration of the grid-side voltage fluctuation exceeds the remaining time that the supercapacitor energy storage branch can independently support. One of the above three intervention conditions can be judged individually, or two or three can be combined for judgment. In this way, the intervention of the lithium battery energy storage branch is jointly determined by multiple state variables representing the remaining support capacity of the supercapacitor and the subsequent demand for the current fluctuation.

[0039] The discharge time reflects the duration for which the supercapacitor energy storage branch has been providing compensation output since the voltage fluctuation occurred. As the discharge time increases, the energy stored inside the supercapacitor is gradually consumed. Even if its terminal voltage has not yet dropped to the minimum allowable value, the time it can maintain rated or near-rated compensation output will continue to shorten. Therefore, using the discharge time as one of the intervention conditions allows for direct constraint on the cumulative supported load of the supercapacitor energy storage branch without relying on complex prediction models, preventing it from independently undertaking compensation tasks for a long period during medium-duration fluctuations. Especially under conditions where the load power change is not significant but the grid-side voltage recovery time is uncertain, this time criterion can trigger the lithium battery energy storage branch to prepare for operation earlier, thereby reducing the risk of deep discharge caused by the supercapacitor maintaining a large output power for a long time.

[0040] The terminal voltage of the supercapacitor energy storage branch reflects the remaining level of energy that can be released. Since the energy storage capacity of a supercapacitor is directly related to its terminal voltage state, a continuous decrease in its terminal voltage during power compensation means a reduction in the effective energy that can be released. This also means a gradual increase in the boost ratio and current stress required by the DC / DC converter to maintain the same output power. When the terminal voltage approaches a preset lower limit, requiring the supercapacitor to solely bear the main compensation power would not only cause it to enter a deeper discharge region but also increase the device stress and control difficulty of the power converter. Therefore, setting a predetermined proportion of the terminal voltage dropping to the preset lower limit as one of the intervention conditions for the lithium battery energy storage branch allows the lithium battery energy storage branch to bear part or all of the subsequent compensation power before the supercapacitor's output capacity begins to decline significantly.

[0041] The comparison between the estimated duration of grid-side voltage fluctuations and the remaining time that the supercapacitor energy storage branch can independently support is used to establish the correspondence between external disturbance demands and internal energy storage margins. Discharge time and energy storage terminal voltage both reflect the current state of the supercapacitor, while the estimated duration indicates the length of time the voltage fluctuation may continue, and the remaining time indicates the length of time the supercapacitor can still independently support the current power output level. When the estimated duration exceeds the remaining time, it indicates that even if the supercapacitor can still output compensation power, the time it can maintain this compensation state is insufficient to cover the subsequent demands of the fluctuation. In this case, delaying the intervention of the lithium battery energy storage branch will cause the supercapacitor to lose its independent support capability prematurely in the later stages. Therefore, by comparing the estimated duration and the remaining time, the controller can link future support demands with the current energy storage margin, so that the intervention timing of the lithium battery energy storage branch no longer depends solely on the current state and can take into account subsequent energy supply demands.

[0042] In some implementations, the initial estimated duration of grid-side voltage fluctuations can be estimated based on the voltage sag depth and voltage change rate, and dynamically corrected according to the voltage recovery trend in subsequent sampling periods. One possible initial estimation method is as follows: in, Indicates the estimated duration. This represents the empirical correction factor. This indicates a current voltage deficit. This represents the rate of voltage change. This formula does not require precise predictions for all operating conditions; its purpose is to establish an initial timescale that can be used for intervention decisions in the early stages of fluctuations. As the sampling window updates, the controller can adjust the estimated duration upwards or downwards based on the voltage recovery slope and the magnitude of the sustained deviation.

[0043] The remaining time that the supercapacitor energy storage branch can independently sustain can be calculated by dividing the remaining available energy by the current reference output power. One possible formula is as follows: in, This represents the combined efficiency of the supercapacitor energy storage branch and the first bidirectional DC / DC converter. This represents the equivalent capacitance of the supercapacitor bank. This indicates the current terminal voltage of the supercapacitor bank. Indicates the minimum allowable discharge voltage. This represents the current output power reference value of the supercapacitor energy storage branch. The corrected estimated duration is compared with the remaining support time. If the estimated duration is longer than the remaining time, the second power setpoint can be increased in advance, while the first power setpoint is decreased simultaneously.

[0044] In the aforementioned example of secondary operating condition parameters, the intervention conditions are comprehensively judged based on the discharge time, supercapacitor terminal voltage, and duration prediction. When the supercapacitor terminal voltage drops to approximately 205V, and the estimated duration is revised from the initial approximately 6.7s to approximately 11.5s, which is greater than the revised approximately 4.8s, the controller increases the second power setpoint and decreases the first power setpoint during the subsequent coordination phase, thereby allowing the lithium battery energy storage branch to gradually assume the main continuous compensation power. Through the above multi-condition intervention control, the intervention timing can be more in line with actual operating conditions, and both rapid support and continuous power supply can be taken into account in medium-duration fluctuation scenarios.

[0045] The third embodiment of this application further explains power coordination, reverse charging prevention, and total power closed-loop verification based on the first and second embodiments.

[0046] For Level 2 operating conditions, a hard switching method involving sudden withdrawal of the supercapacitor and sudden takeover of the lithium battery is generally not feasible. If a hard switch is adopted, the first and second power setpoints will experience significant jumps at the moment of switching, disrupting the DC bus power balance and making the inverter output prone to momentary drops or overshoots. To avoid this, within a preset ramp time, the first power setpoint is decreased from its current value to zero, and the second power setpoint is increased from zero to the load-side compensation power requirement, maintaining their sum equal to the load-side compensation power requirement within the ramp interval. In this embodiment, the preset ramp time refers to the time interval used for continuous adjustment of the first and second power setpoints during the transfer of compensation power from the supercapacitor energy storage branch to the lithium battery energy storage branch; within this time interval, the first power setpoint is gradually decreased, and the second power setpoint is gradually increased, maintaining their sum to meet the load-side compensation power requirement.

[0047] The control objective of the aforementioned power coordination process is to redistribute the workload of the two energy storage branches while keeping the total compensation power constant. By continuously adjusting the first and second power setpoints, the supercapacitor energy storage branch is gradually phased out, while the lithium battery energy storage branch is gradually established.

[0048] As an optional implementation, a closed-loop verification can be performed on the sum of the actual output power of the two branches. When a deviation is detected between the sum of the actual output power and the load-side compensation power requirement, the deviation is fed back to the correction loop of the first power setpoint and the second power setpoint to reduce the impact of sampling delay, drive delay and current loop establishment time on switching smoothness.

[0049] After coordinating the switch to the tail end, the safety of the supercapacitor energy storage branch's exit also needs to be considered. If the lithium battery energy storage branch has already established a high output, and the supercapacitor energy storage branch is not turned off in time, a reverse current may flow from the DC bus to the supercapacitor energy storage branch. This reverse current will cause the supercapacitor to undergo unexpected recharging during the exit phase, which will not only interfere with the power switching logic but also increase device stress. Therefore, this embodiment specifies that: when the first power setpoint decreases to a preset minimum power threshold, a first shutdown signal is output; when a reverse current flowing from the DC bus to the supercapacitor energy storage branch is detected, the first shutdown signal is maintained to prevent the lithium battery energy storage branch from recharging the supercapacitor energy storage branch in reverse.

[0050] Among a set of selectable parameters, the preset ramp time can be 50ms, and the preset minimum power threshold can be 5kW. Under secondary operating conditions, the controller reduces the first power setpoint from 100kW to 0 within the 50ms ramp time and increases the second power setpoint from 0 to 100kW, while maintaining the sum of the two values ​​approximately equal to 100kW. When the output power of the supercapacitor energy storage branch drops below 5kW, the controller outputs a first shutdown signal. If a reverse current flowing from the DC bus to the supercapacitor energy storage branch is subsequently detected, the first shutdown signal is maintained, keeping the supercapacitor energy storage branch in an off-state. By employing ramp coordination, total power closed-loop verification, and reverse charging prevention control, the power transfer process in the coordinated transition mode can be made smoother and more reliable.

[0051] The fourth embodiment of this application, based on the first three embodiments, describes the control system for implementing the above control method and the connection method of the control system in the dynamic voltage recovery device.

[0052] like Figure 2 As shown, Figure 2 The logical relationships of functional modules in a dynamic voltage recovery control system are illustrated. The control system includes a voltage sampling module 101, a fluctuation judgment module 102, a parameter extraction module 103, a grading judgment module 104, a mode selection module 105, a power setting module 106, and an intervention control module 107. In some implementations, the control system further includes a power coordination module 108 and a health status assessment module 109.

[0053] The voltage sampling module 101 is used to acquire the grid-side voltage sampling value and can provide updated voltage measurement information to other modules according to a set sampling period. The fluctuation judgment module 102 is used to compare the grid-side voltage sampling value with the reference voltage and determine whether the grid-side voltage has fluctuated; when it is determined that no fluctuation has occurred, the system keeps the supercapacitor energy storage branch and the lithium battery energy storage branch in standby or preset operating state and continues to perform sampling and comparison; when it is determined that a fluctuation has occurred, it provides the parameter extraction module 103, the hierarchical judgment module 104 and the mode selection module 105 with the judgment information required to start the subsequent control process.

[0054] The parameter extraction module 103 is used to obtain the voltage sag depth and voltage change rate based on the grid-side voltage sampling value after a voltage fluctuation occurs. The classification judgment module 104 is used to determine the fluctuation level based on the voltage sag depth and voltage change rate. The mode selection module 105 is used to select the power distribution mode based on the fluctuation level. In some implementations, when the classification judgment module 104 determines the fluctuation level to be a Level 1 operating condition, the mode selection module 105 selects the overcapacitance independent mode; when the classification judgment module 104 determines the fluctuation level to be a Level 2 operating condition, the mode selection module 105 selects the coordinated transition mode; and when the classification judgment module 104 determines the fluctuation level to be a Level 3 operating condition, the mode selection module 105 selects the lithium battery dominant mode.

[0055] The power setting module 106 outputs a first power setting value for the supercapacitor energy storage branch and a second power setting value for the lithium battery energy storage branch according to the power distribution mode. The intervention control module 107 controls the activation and deactivation of the two energy storage branches according to preset intervention conditions. The power coordination module 108 continuously adjusts the first and second power setting values ​​after the preset intervention conditions are met and the system enters the coordination transition mode. The health status assessment module 109 determines the health status based on the operating data of the supercapacitor energy storage branch and the lithium battery energy storage branch, and sends the health status information to the mode selection module 105, the power setting module 106, the intervention control module 107, and the power coordination module 108 to correct the maximum allowable output power, minimum allowable discharge threshold of the supercapacitor energy storage branch, the maximum allowable output power of the lithium battery energy storage branch, the intervention criteria, and the coordination parameters.

[0056] In a set of optional implementations, combined Figure 2 and Figure 3As shown, the grid input line 7 is connected to the load line 8 via the static switch module 2. The AC side of the inverter module 3 is connected to the load line 8, and the DC side is connected to the DC bus 4. The supercapacitor energy storage branch 5 is connected to the DC bus 4 via a first bidirectional DC / DC converter, and the lithium battery energy storage branch 6 is connected to the DC bus 4 via a second bidirectional DC / DC converter. The dynamic voltage recovery control system is connected to the static switch module 2, the inverter module 3, the supercapacitor energy storage branch 5, and the lithium battery energy storage branch 6, respectively. The supercapacitor energy storage branch 5 includes a first bidirectional DC / DC converter and a supercapacitor bank, and the lithium battery energy storage branch 6 includes a second bidirectional DC / DC converter and a lithium battery bank, thereby translating control decisions into execution control of external circuits.

[0057] Specifically, regarding measurement information input, the control system is connected to the grid-side voltage sampling circuit to acquire grid-side voltage sampling values; connected to the DC bus voltage sampling circuit to acquire the DC bus voltage; connected to the voltage, current, and temperature sampling circuits of the supercapacitor energy storage branch 5 to acquire the supercapacitor bank terminal voltage, branch current, and operating temperature; and connected to the voltage, current, and temperature sampling circuits of the lithium battery energy storage branch 6 to acquire the lithium battery bank terminal voltage, branch current, and operating temperature. In some implementations, the control system can also acquire the output voltage, output current, load-side power demand information of the inverter module 3, and the reverse current detection signal flowing from the DC bus 4 to the supercapacitor energy storage branch 5.

[0058] Regarding control information output, the control system is connected to the static switch module 2 to output a cut-off control signal when voltage fluctuations occur in the grid input line 7, and to output a recovery control signal after the grid stabilizes; it is connected to the inverter module 3 to output an inverter modulation control signal or an AC compensation control signal, enabling the inverter module 3 to establish an output according to the compensation requirements of the load line 8; it is connected to the first bidirectional DC / DC converter to output a first power setpoint, a start / stop control signal, and a turn-off control signal to control the output state of the supercapacitor energy storage branch 5; and it is connected to the second bidirectional DC / DC converter to output a second power setpoint and a start / stop control signal to control the output state of the lithium battery energy storage branch 6.

[0059] Under normal operating conditions, the static switch module 2 remains on, the grid input line 7 supplies power to the load line 8, and the control system continuously acquires the grid-side voltage and the operating status of each branch, keeping the supercapacitor energy storage branch 5 and the lithium battery energy storage branch 6 in standby or preset operating states. When the control system detects a voltage fluctuation in the grid input line 7, it outputs a cut-off control signal to the static switch module 2, and determines the voltage sag depth, voltage change rate, and fluctuation level based on the grid-side voltage sampling value. It then further selects the power distribution mode and outputs the first and second power setpoints. Subsequently, the control system controls the supercapacitor energy storage branch 5 to prioritize establishing compensation power, and controls the inverter module 3 to utilize the compensation power on the DC bus 4 to establish AC compensation voltage on the load line 8.

[0060] When the control system determines that the intervention conditions of the lithium battery energy storage branch 6 are met, it outputs a second power setpoint to the second bidirectional DC / DC converter and continuously adjusts the first and second power setpoints through the power coordination module 108. This gradually reduces the output power of the supercapacitor energy storage branch 5 and gradually increases the output power of the lithium battery energy storage branch 6, while maintaining the sum of the output power of the two energy storage branches to meet the load-side compensation power requirements. During this process, the DC bus 4 serves as the energy collection node between the two energy storage branches and the inverter module 3. The control system continuously monitors the DC bus voltage and branch current to correct the power distribution during the coordinated switching process.

[0061] Overall, in the control process, the mode selection module determines the power allocation mode based on the fluctuation level; the power setting module outputs a first power setting value and a second power setting value based on the selected power allocation mode; when the selected power allocation mode is a coordinated transition mode, the power coordination module continuously adjusts the first power setting value and the second power setting value; the intervention control module outputs control signals to the first bidirectional DC / DC converter corresponding to the supercapacitor energy storage branch and the second bidirectional DC / DC converter corresponding to the lithium battery energy storage branch based on the preset intervention conditions and the adjusted first power setting value and second power setting value.

[0062] Once the grid input line 7 returns to normal and remains stable within a set time window, the control system gradually exits the compensation state of the inverter module 3 and resumes conduction of the static switch module 2. In some implementations, the control system also performs subsequent recharge management based on the status information of the supercapacitor energy storage branch 5 and the lithium battery energy storage branch 6. Through the above access and control relationships, the control system can form a complete closed loop of sampling, judgment, decision-making, execution, and feedback around the external grid, load, and energy storage branch.

[0063] In some implementations, the operational data acquired by the health status assessment module 109 includes at least one of the following: terminal voltage, current, temperature, estimated internal resistance, estimated capacity, historical charge / discharge data, and operating time for both the supercapacitor energy storage branch and the lithium battery energy storage branch. For the supercapacitor energy storage branch, the health status assessment module 109 can estimate the equivalent series resistance and available capacitance retention rate based on the terminal voltage response characteristics, current variation characteristics, and temperature rise. For the lithium battery energy storage branch, the health status assessment module 109 can estimate the available capacity, internal resistance, and allowable discharge rate based on open-circuit voltage, terminal voltage, current, temperature rise, and cumulative capacity information. The health status information output by the health status assessment module 109 can be used to correct the maximum allowable output power and minimum allowable discharge threshold of the supercapacitor energy storage branch, as well as the maximum allowable output power of the lithium battery energy storage branch; it can also be used to correct the intervention criteria, ramp time, and power coordination parameters in the coordinated transition mode. Through these corrections, the control system can ensure that the mode selection, power setting, intervention control, and power coordination are consistent with the current actual capabilities of the energy storage branch.

[0064] In a set of parameter examples, the first and second thresholds for the supercapacitor's health status can be set to 80% and 60%, respectively, and the first and second thresholds for the lithium battery's health status can also be set to 80% and 60%, respectively. When the supercapacitor's health status drops from 100% to 75%, the controller can adjust the maximum allowable output power of the supercapacitor energy storage branch from 120kW to 96kW and increase the minimum allowable discharge voltage from 420V to 450V. When the lithium battery's health status drops from 100% to 78%, the controller can adjust the maximum allowable continuous output power of the lithium battery energy storage branch from 120kW to 100kW and advance the lithium battery intervention time in the coordinated transition mode. Through these adjustments, the power setting and intervention control can be made closer to the device's current capabilities.

[0065] In some implementations, when the health status assessment result falls below a preset threshold, the control system can enter a derating operation state and output maintenance alarm information. For supercapacitor energy storage branches, the minimum allowable discharge threshold can be appropriately increased and the upper limit of the first power setpoint can be decreased; for lithium battery energy storage branches, the upper limit of continuous output power can be decreased and the intervention constraint can be increased. Through derating operation and alarm management, system availability can be maintained when device performance degrades, and overcurrent, deep discharge, or excessive thermal stress can be avoided.

[0066] Regarding recharge management, after the power grid returns to normal, the control system first confirms that the grid-side voltage remains stable within the normal range within a set time window before executing recharge control. Prioritizing the recharge of the supercapacitor bank allows the system to recover the rapid response capability required for the next transient fluctuation more quickly; subsequently, the lithium battery bank is recharged to reduce additional power fluctuations during the initial recovery phase on the AC side. The charging power and cutoff threshold can also be limited using parameters corrected for the health status during the recharge phase. The time calculation logic, alarm logic, and recharge logic are all described in text in this application, and their criteria, adjustment methods, and control objectives are clear without relying on additional diagrams.

[0067] It should be noted that the fluctuation detection threshold in the above embodiments should not be set too low to avoid false triggering by normal minor disturbances; nor should it be set too high to avoid the system failing to take over when the load has entered the sensitive power failure window. The sag depth threshold should be determined comprehensively based on the load tolerance, the rated power of the supercapacitor, the rated power of the lithium battery, and the system's allowable switching frequency; the rate of change threshold should consider the sampling frequency and measurement noise to avoid level fluctuations caused by measurement jitter. The preset switching time threshold, preset minimum power threshold, and preset ramp time should be determined comprehensively based on the current loop response speed of the two energy storage branches, the thermal design boundary, and the allowable voltage fluctuation range of the load. The empirical correction coefficient K can be obtained by adjusting statistical data from typical operating conditions, simulation results, or field trial operation data.

[0068] The above embodiments are only used to illustrate the technical solution and working principle of this application, and are not intended to limit the scope of protection. Without departing from the core inventive concept of this application, those skilled in the art can make equivalent substitutions or modifications to the voltage sampling form, the graded threshold setting method, the duration estimation model, the energy storage unit type, the power converter topology, the alarm strategy, and the recharge management strategy. All such substitutions or modifications fall within the scope of this application; the final scope of protection is determined by the technical solution defined in the claims.

Claims

1. A dynamic voltage recovery control method based on supercapacitive-lithium battery hybrid energy storage, characterized in that, include: Obtain the voltage sampling value on the grid side; The grid-side voltage sample value is compared with the reference voltage to determine whether the grid-side voltage has fluctuated. When the grid-side voltage fluctuates, the voltage sag depth and voltage change rate are obtained based on the grid-side voltage sampling value. The fluctuation level is determined based on the voltage sag depth and the voltage change rate; Select the power allocation mode based on the fluctuation level; The first power setpoint of the supercapacitor energy storage branch and the second power setpoint of the lithium battery energy storage branch are output according to the power distribution mode. The supercapacitor energy storage branch is controlled to output compensation power according to the first power setpoint, and the lithium battery energy storage branch is controlled to output compensation power according to the second power setpoint when the preset intervention conditions are met.

2. The dynamic voltage recovery control method for supercapacitive-lithium battery hybrid energy storage as described in claim 1, characterized in that, The step of determining the fluctuation level based on the voltage sag depth and the voltage change rate, and selecting the power allocation mode based on the fluctuation level, includes: When the voltage sag depth is greater than the third threshold and the absolute value of the voltage change rate is greater than the change rate threshold, the fluctuation level is determined to be a first-level operating condition, and the overcapacitance independent mode is selected. When the voltage sag depth is between the second threshold and the third threshold, the fluctuation level is determined to be a level two operating condition, and a coordinated transition mode is selected. When the voltage sag depth is between the first threshold and the second threshold, the fluctuation level is determined to be a level three operating condition, and the lithium battery-dominated mode is selected. In the supercapacitor independent mode, all compensation power is provided by the supercapacitor energy storage branch. In the coordinated transition mode, the initial compensation power is provided by the supercapacitor energy storage branch, and the lithium battery energy storage branch takes over the output when the preset intervention conditions are met. In the lithium battery-dominated mode, the initial compensation power is provided by the supercapacitor energy storage branch, and the subsequent continuous compensation power is undertaken by the lithium battery energy storage branch.

3. The dynamic voltage recovery control method for supercapacitive-lithium battery hybrid energy storage as described in claim 2, characterized in that, In the coordinated transition mode, the initial compensation power is provided by the supercapacitor energy storage branch, and the lithium battery energy storage branch takes over the output when the preset intervention condition is met. Set the preset intervention condition to at least one of the following: The supercapacitor energy storage branch has reached the preset switching time threshold after discharging for a certain period of time. The voltage at the energy storage terminal of the supercapacitor energy storage branch drops to a predetermined percentage of the preset lower limit voltage. The estimated duration of grid-side voltage fluctuations exceeds the remaining time that the supercapacitor energy storage branch can independently support. When the preset intervention conditions are met, the second power setpoint is increased and the first power setpoint is decreased.

4. The dynamic voltage recovery control method for supercapacitive-lithium battery hybrid energy storage as described in claim 3, characterized in that, The step of increasing the second power setpoint and decreasing the first power setpoint when the preset intervention condition is met includes: Within a preset ramp time, the first power setpoint is reduced from its current value to zero; During the preset ramp time, the second power setpoint is incremented from zero to the load-side compensation power demand value; And within the preset ramp time, the sum of the first power setpoint and the second power setpoint is kept equal to the load-side compensation power demand value.

5. The dynamic voltage recovery control method for supercapacitive-lithium battery hybrid energy storage as described in claim 4, characterized in that, The step of decreasing the first power setpoint from its current value to zero within a preset ramp time includes: When the first power setpoint decreases to the preset minimum power threshold, a first shutdown signal is output; When a reverse current is detected flowing from the DC bus to the supercapacitor energy storage branch, the first shutdown signal is maintained to prevent the lithium battery energy storage branch from reversing to the supercapacitor energy storage branch.

6. The dynamic voltage recovery control method for supercapacitive-lithium battery hybrid energy storage as described in claim 4, characterized in that, Maintaining the sum of the first power setpoint and the second power setpoint equal to the load-side compensation power demand value within the preset ramp time includes: The sum of the actual output power of the supercapacitor energy storage branch and the lithium battery energy storage branch is measured. Calculate the deviation between the sum of the actual output power and the load-side compensation power requirement; The first power setpoint and the second power setpoint are corrected based on the deviation.

7. The dynamic voltage recovery control method for supercapacitive-lithium battery hybrid energy storage as described in claim 3, characterized in that, The estimated duration of the grid-side voltage fluctuations exceeding the remaining time that the supercapacitor energy storage branch can independently support includes: The initial estimated duration of voltage fluctuations on the grid side is determined based on the voltage sag depth and the rate of change of voltage. The initial estimated duration is dynamically corrected based on the voltage recovery trend in subsequent sampling periods; The revised estimated duration is compared with the remaining time that the supercapacitor energy storage branch can independently support.

8. A dynamic voltage recovery control system based on supercapacitive-lithium battery hybrid energy storage, characterized in that, include: The voltage sampling module acquires voltage sampling values ​​from the grid side. The fluctuation detection module compares the sampled voltage value of the grid side with the reference voltage and determines whether the grid side voltage has fluctuated. The parameter extraction module obtains the voltage sag depth and voltage change rate based on the grid-side voltage sampling value when the grid-side voltage fluctuates. The classification judgment module determines the fluctuation level based on the voltage sag depth and the voltage change rate; The mode selection module selects the power distribution mode according to the fluctuation level; The power setting module outputs a first power setting value for the supercapacitor energy storage branch and a second power setting value for the lithium battery energy storage branch according to the power distribution mode. The intervention control module controls the supercapacitor energy storage branch to output compensation power according to the first power setpoint, and controls the lithium battery energy storage branch to output compensation power according to the second power setpoint when the preset intervention conditions are met.

9. The supercapacitive-lithium battery hybrid energy storage dynamic voltage recovery control system as described in claim 8, characterized in that, Also includes: The power coordination module is used to reduce the first power setpoint and increase the second power setpoint within a preset ramp time when the preset intervention conditions are met, and to maintain the sum of the first power setpoint and the second power setpoint equal to the load-side compensation power demand value within the preset ramp time. The health status assessment module is used to determine the health status based on the operating data of the supercapacitor energy storage branch and the lithium battery energy storage branch, and to correct the maximum allowable output power, minimum allowable discharge threshold and maximum allowable output power of the supercapacitor energy storage branch and the lithium battery energy storage branch based on the health status.

10. A dynamic voltage recovery device based on supercapacitive-lithium battery hybrid energy storage, characterized in that, include: Power grid input lines and load lines; A static switch module is disposed between the power grid input line and the load line; The inverter module has its AC side connected to the load line and its DC side connected to the DC bus. The supercapacitor energy storage branch is connected to the DC bus via a first bidirectional DC / DC converter. The lithium battery energy storage branch is connected to the DC bus via a second bidirectional DC / DC converter. And the dynamic voltage recovery control system based on supercapacitive-lithium battery hybrid energy storage as described in claim 8, wherein the dynamic voltage recovery control system is connected to the static switching module, the inverter module, the first bidirectional DC / DC converter and the second bidirectional DC / DC converter respectively.

Images