Off-grid system equalization control method and system

Abstract

The application provides an off-grid system equalization control method and system, and relates to the technical field of power electronics and micro-grid control. The method comprises the following steps: obtaining the operation parameters of the batteries connected to each inverter and determining the current absolute residual power; combining the current maximum output power allowed to calculate the current supportable operation time of each inverter; determining the system target operation time reference according to the supportable operation time; calculating the target power corresponding to each inverter based on the absolute residual power and the time reference; adjusting the droop control parameters of each inverter according to the target power, so that each inverter outputs with different droop control parameters, and the actual supportable operation time is adjusted to be consistent. The application can realize the differentiated load distribution of each inverter in the off-grid system according to the energy state difference, avoid the early disconnection of the weak unit, and prolong the overall operation time of the system.

Description

Technical Field

[0001] This invention belongs to the field of energy storage system technology, specifically relating to an off-grid system equalization control method and system. Background Technology

[0002] In off-grid power supply systems, parallel operation of multiple inverters is a common technique for improving system capacity and reliability. These systems typically employ a classic droop control strategy to achieve power distribution and current sharing among the parallel units. The basic principle is to utilize the linear droop relationship between inverter output frequency and active power, and output voltage and reactive power. By setting a uniform droop coefficient, the system ensures that during steady-state operation, each inverter automatically shares the load power according to a preset ratio. In traditional implementations, the droop coefficient is often calculated and set uniformly based on the system's rated power to ensure that after parallel operation stabilizes, the output frequency and voltage of all inverters remain consistent, thereby achieving equal distribution of output power or distribution according to the rated capacity ratio. This control method has a mature architecture, requires no complex communication links, and can effectively maintain the stability of off-grid bus voltage and frequency, thus finding widespread application in scenarios such as energy storage microgrids and emergency power supply.

[0003] For example, in off-grid parallel systems, classic droop control is typically used:

[0004] Formula for drooping of the sensory system:

[0005]

[0006] in:

[0007] System output frequency; System output voltage; System rated frequency; System rated voltage; , Initially, there is / is no reactive power; , System frequency droop factor;

[0008] The transformation yields:

[0009]

[0010] In the traditional approach, , Usually based on rated power Unified calculation, for example:

[0011] Frequency droop range 0–0.5 Hz —>

[0012] Voltage droop range 0–10 V —>

[0013] In the same system , With the same values, each machine stabilizes after parallel operation. , Consistent, therefore the output power of each inverter is consistent. , The same.

[0014] However, in practical engineering applications, the battery packs connected to the inverters operating in parallel often exhibit significant differences. These differences are not only reflected in the nominal capacity and voltage level of the batteries, but also in variations in state of charge (SOC), state of health (SOH), and real-time temperature over time. Furthermore, the inverter's own heat dissipation conditions and the aging of its components can cause dynamic changes in its maximum permissible output power. Under existing conventional control modes, this can easily lead to situations where some low-energy or performance-limited devices are forced to bear loads incompatible with their current state, making them highly susceptible to triggering over-discharge, over-temperature, and other protection mechanisms, resulting in grid disconnection.

[0015] Once a single unit goes offline, the remaining equipment will experience a sudden surge in load, potentially triggering a chain reaction that could ultimately cause the entire off-grid power supply system to collapse, failing to achieve the expected continuous power supply target. These issues not only affect the system's power supply reliability but also increase maintenance costs due to frequent equipment protection shutdowns, shorten the lifespan of critical components, and reduce overall energy efficiency. Summary of the Invention

[0016] The purpose of this invention is to address the shortcomings of existing technologies by providing an off-grid system equalization control method and system. This method enables each inverter to bear load differently based on its own energy reserves and load-carrying capacity, thus solving the technical problem in traditional droop control where differences in battery voltage level, ampere-hour capacity, SOC, temperature, and lifespan among the connected batteries cause weaker units to prematurely over-discharge / over-temperature and disconnect from the grid after power equalization, leading to a chain reaction of system failures.

[0017] In a first aspect, the present invention provides an off-grid system balancing control method, applied to an off-grid power supply system consisting of multiple inverters connected in parallel, each inverter being connected to a battery, comprising the following steps:

[0018] The operating parameters of the batteries connected to each inverter are obtained, and the current absolute remaining capacity of the batteries connected to each inverter is determined based on the operating parameters. The operating parameters include at least the parameters used to characterize the current voltage, ampere-hour capacity and current state of charge of the batteries.

[0019] Calculate the current operating time that each inverter can support based on its current absolute remaining power and its current maximum allowable output power.

[0020] The system target operating time baseline is determined based on the current supported operating time of each inverter.

[0021] The target power of each inverter is calculated based on the current absolute remaining power of each inverter and the target operating time of the system.

[0022] Adjust the droop control parameters of each inverter according to the target power of each inverter, so that each inverter outputs with different droop control parameters in parallel operation, so as to adjust the actual supporting operating time of each inverter to be closer to the same.

[0023] In conjunction with the first aspect, in one possible implementation, the current absolute remaining power is the product of the current voltage, ampere-hour capacity, and current state of charge of the batteries connected to each inverter.

[0024] In conjunction with the first aspect, in one possible implementation, the maximum allowable output power of each inverter is determined by the limitations of the battery management system and / or the inverter's own temperature limitations.

[0025] In conjunction with the first aspect, in one possible implementation, the system target runtime benchmark includes at least one of minimum supportable runtime, maximum supportable runtime, and average supportable runtime.

[0026] In conjunction with the first aspect, in one possible implementation, calculating the target power corresponding to each inverter based on the current absolute remaining power of each inverter and the system target operating time reference includes:

[0027] Calculate the first target power for each inverter based on the current absolute remaining power of each inverter and the maximum supported operating time.

[0028] And / or, calculate the second target power corresponding to each inverter based on the current absolute remaining power of each inverter and the minimum supportable operating time;

[0029] And / or, calculate the third target power for each inverter based on the current absolute remaining power of each inverter and the average operating time that can be sustained.

[0030] In conjunction with the first aspect, in one possible implementation, the step of calculating the target power corresponding to each inverter based on the current absolute remaining power of each inverter and the system target operating time reference includes:

[0031] Obtain the current actual load power of the system, and determine the current load rate of the system based on the ratio of the actual load power to the sum of the third target power of each inverter;

[0032] The first target power and the second target power are weighted and summed according to the load rate to obtain the final target power of each inverter, so as to determine the droop control parameters of each inverter.

[0033] In conjunction with the first aspect, in one possible implementation, when the load rate tends to a minimum, the final target power of each inverter tends to the second target power; when the load rate tends to a maximum, the final target power of each inverter tends to the first target power.

[0034] In conjunction with the first aspect, in one possible implementation, the droop control parameter is a frequency droop coefficient or a voltage droop coefficient.

[0035] In conjunction with the first aspect, in one possible implementation, the steps of acquiring operating parameters, determining absolute remaining power, calculating the available operating time, determining the system target operating time reference, calculating the target power, and adjusting the droop control parameters are continuously iterated after the system enters the off-grid operation state until the actual available operating time of each inverter tends to be consistent.

[0036] Secondly, the present invention provides an off-grid system equalization control system for any of the above-described schemes, comprising:

[0037] The parameter acquisition unit is used to acquire the operating parameters of the batteries connected to each inverter. The operating parameters include at least the parameters characterizing the current voltage, ampere-hour capacity and current state of charge of the battery.

[0038] The power calculation unit is used to determine the current absolute remaining power of the batteries connected to each inverter based on the operating parameters.

[0039] The time calculation unit is used to calculate the current operating time that each inverter can support based on its current absolute remaining power and its current maximum allowable output power.

[0040] The time base determination unit is used to determine the target operating time base of the system based on the supportable operating time of each inverter;

[0041] The power calculation unit is used to calculate the target power of each inverter based on the current absolute remaining power of each inverter and the target operating time of the system.

[0042] The droop parameter adjustment unit is used to adjust the droop control parameters of each inverter according to the target power of each inverter, so that each inverter outputs with different droop control parameters in parallel operation, so as to adjust the actual support time of each inverter to be consistent.

[0043] In conjunction with the second aspect, one possible implementation also includes:

[0044] The off-network status detection unit is used to trigger the parameter acquisition unit to start working when the system is detected to have entered an off-network operation state.

[0045] Compared with the prior art, the beneficial effects achieved by at least one of the above-mentioned technical solutions adopted in this invention include: an innovative design of an off-grid system balancing control method and system that includes acquiring battery operating parameters, calculating absolute remaining power and supportable operating time, determining the system target operating time benchmark, and dynamically adjusting droop control parameters. By constructing a complete mapping chain from battery physical state to operating time to power distribution, each inverter can bear the load differently according to its own energy reserves and load-carrying capacity when operating in parallel, rather than mechanically sharing the power equally; effectively avoiding the overall system paralysis caused by premature shutdown of a single unit, significantly improving the operational stability, range consistency, and overall reliability of the off-grid power supply system under complex operating conditions, extending the overall system operating time, and significantly improving the robustness of the system. Attached Figure Description

[0046] Figure 1 This is a flowchart of the off-grid system balancing control method of this application.

[0047] Figure 2 This is a flowchart illustrating the process of determining the final target power based on load rate weighted summation in the off-grid system balancing control method of this application.

[0048] Figure 3 This is a structural block diagram of the off-grid system equalization control system of this application. Detailed Implementation

[0049] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0050] <Example 1>

[0051] like Figure 1 As shown, this embodiment provides an off-grid system balancing control method applied to an off-grid power supply system consisting of multiple inverters connected in parallel, each inverter being connected to a battery. This off-grid system balancing control method enables each inverter to handle loads differently based on its own energy reserves and load-carrying capacity. The method includes steps S1-S5. Specifically,

[0052] S1. Obtain the operating parameters of the batteries connected to each inverter, and determine the current absolute remaining capacity of the batteries connected to each inverter based on the operating parameters. The operating parameters include at least the parameters used to characterize the current voltage, ampere-hour capacity and current state of charge of the batteries.

[0053] Operating parameters are fundamental data for evaluating the battery's energy storage state and directly determine the inverter's maximum continuous power supply capacity. In this embodiment, operating parameters specifically include the battery's current voltage, ampere-hour capacity, and current state of charge (SOC). These parameters can be obtained, for example, through communication with the Battery Management System (BMS), using the Controller Area Network (CAN) bus or Modbus communication protocol to collect the terminal voltage, total ampere-hour capacity, and current SOC percentage of each battery pack in real time. Alternatively, the battery terminal voltage can be directly detected by the inverter's internal sampling circuit, and the current SOC can be estimated by combining a preset capacity lookup table method and an ampere-hour integration method.

[0054] The current absolute remaining capacity characterizes the total energy that a battery can actually release in its current state. Its calculation logic couples the current voltage, ampere-hour capacity, and current state of charge (SOC). Determining the current absolute remaining capacity can be achieved, for example, by multiplying the current battery voltage, ampere-hour capacity, and current SOC to obtain the absolute energy value in watt-hours (Wh) or kilowatt-hours (kWh). Alternatively, a temperature correction factor or discharge efficiency curve can be introduced into the product to perform nonlinear calibration on the theoretically calculated value. By calculating the current absolute remaining capacity, energy assessment biases caused by differences in battery voltage levels or capacities can be eliminated, providing a unified and accurate energy benchmark for subsequent power allocation.

[0055] In one specific implementation, the current absolute remaining power is calculated by multiplying the current voltage, ampere-hour capacity, and current state of charge of the batteries connected to each inverter. This can be expressed by the formula:

[0056]

[0057] Where i is the number of the i-th inverter (and its connected battery), It is the current absolute remaining capacity (in Wh) of the battery connected to the i-th inverter. It is the current voltage (in V) of the battery connected to the i-th inverter. It is the ampere-hour capacity (unit: Ah) of the battery connected to the i-th inverter. It is the current state of charge of the battery connected to the i-th inverter (value range: 0 to 1).

[0058] By multiplying the three parameters mentioned above, the calculated current absolute remaining energy is expressed in watt-hours (Wh), representing the total energy actually contained in the battery. This calculation process quantifies the remaining energy storage of batteries of different specifications (such as different voltage levels or different ampere-hour capacities) into an absolute energy value. Compared to using only the percentage of state of charge (SOC) as a reference, introducing the product of voltage and Wh capacity can correct for energy assessment biases caused by differences in battery specifications. This accurately reflects the true energy storage capacity of the batteries connected to each inverter, ensuring that the remaining energy of each battery is comparable in a physical dimension. This provides an accurate input data basis for calculating the target operating time benchmark of the system and the target power corresponding to each inverter.

[0059] S2. Calculate the current operating time that each inverter can support based on its current absolute remaining power and its current maximum allowable output power.

[0060] The current supported operating time refers to the theoretical duration for which the inverter can continuously output a specific power until the energy is depleted under the current battery energy state. The current maximum allowable output power serves as a boundary condition limiting the inverter's output capability, and its determination process comprehensively considers the safety constraints on both the battery side and the device side. For example, the upper limit of power can be obtained by reading the protection strategy of the battery management system, based on conditions such as the maximum battery discharge rate and voltage lower limit protection; alternatively, the maximum allowable output power can be dynamically calculated based on temperature constraints such as heat sink temperature and power transistor junction temperature, using the smaller of the two values ​​as the final limit.

[0061] In one specific implementation, the maximum allowable output power of each inverter is determined by the limitations of the battery management system and / or the inverter's own temperature limitations. The formula for calculating the current supported operating time is:

[0062]

[0063] Where i is the number of the i-th inverter (and its connected battery), The battery connected to the i-th inverter can currently support the operating time. It is the maximum allowable output power of the battery connected to the i-th inverter. It represents the current absolute remaining charge of the battery connected to the i-th inverter.

[0064] In addition, the limiting condition of the battery management system refers to the real-time protection threshold output by the battery management system connected to the inverter. Parameters reported by the battery management system are read in real time through the communication interface. These parameters characterize the instantaneous safety boundaries on the battery side, including the current battery temperature, state of charge, and the real-time health status of the battery. Based on these parameters, the battery management system dynamically calculates and outputs a maximum allowable discharge power limit. This value aims to prevent irreversible chemical damage or thermal runaway caused by overcurrent discharge, high-rate discharge at low temperatures, or excessive deep discharge. This limiting condition directly determines the upper limit of energy that the inverter can extract from the battery under the current battery conditions.

[0065] The inverter's own temperature limit refers to the output power derating curve set based on the thermal stress characteristics of the inverter's internal power devices. During long-term operation, internal power switching devices such as Insulated Gate Bipolar Transistors (IGBTs) or Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) generate heat due to switching and conduction losses. By collecting inverter heatsink temperature or junction temperature data and combining it with a preset temperature-power derating strategy, the maximum allowable output power of the inverter in its current thermal state is calculated. When a temperature rise is detected, this limit decreases non-linearly to forcibly reduce the inverter output, ensuring that the power devices operate within a safe junction temperature range and preventing device overheating failure.

[0066] In practical engineering applications, the two constraints mentioned above are logically ANDed, and the smaller value is taken as the final power limit, thus determining the maximum allowable output power. This means that regardless of whether the battery management system tightens the power limit due to low battery temperature or low state of charge, or the inverter is derating due to high ambient temperature or limited heat dissipation, the final output power must simultaneously meet both types of safety constraints, thereby ensuring that the entire off-grid power supply system operates within the dual safety boundaries of the source and conversion ends. Through this fusion of multi-dimensional constraints, the calculated sustainable operating time can truly reflect the physical limits of the equipment under current operating conditions.

[0067] The calculation of the current sustainable operating time is based on the principle of energy conservation. For example, the theoretical maximum sustainable time can be obtained by directly dividing the current absolute remaining power of each inverter by its current maximum allowable output power. Alternatively, system efficiency losses can be considered, multiplying the absolute remaining power by a preset conversion efficiency coefficient and then dividing by the output power to obtain a more realistic estimated time. This calculation reflects the sustainable operating capability of each inverter under extreme full-load conditions, helping to identify weak links in the system and avoid excessive stress on the weakest inverters.

[0068] S3. Determine the system target operating time benchmark based on the current supported operating time of each inverter.

[0069] The system target operating time benchmark is a macroscopic time reference quantity that guides the power distribution strategy of the entire off-grid system, aiming to coordinate the output differences between inverters. There are various ways to select the system target operating time benchmark. For example, it can be the minimum current supported operating time of all inverters, ensuring that the overall system operating time is not lower than the limit capacity of the weakest device; alternatively, it can be the maximum or average current supported operating time of all inverters, aiming to maximize or equalize the overall system operating time.

[0070] In one specific implementation, the system target runtime benchmark includes at least one of the minimum sustainable runtime, the maximum sustainable runtime, and the average sustainable runtime.

[0071] Based on the current operating time of each inverter calculated in the aforementioned steps, key statistical features are extracted from this dataset as parameters for constructing the target operating time benchmark of the system.

[0072] The minimum sustainable operating time is the minimum among all the current sustainable operating times of all inverters. This value represents the endurance limit of the weakest battery cell in the current system. Setting it as the target operating time benchmark ensures that the system does not exceed the limit of the weakest link during overall operation, thereby strictly protecting the safety boundaries of all battery cells and effectively preventing the risk of system collapse caused by over-discharge of individual batteries.

[0073] The maximum supported operating time is the maximum value among all the inverters' current supported operating times. This value represents the longest theoretically achievable continuous power supply capability under the current battery conditions. Using this value as a benchmark for the system's target operating time is typically applicable to operating scenarios that pursue extreme load capacity or specific optimization goals.

[0074] The average sustainable operating time is the arithmetic mean of the sustainable operating times of each inverter. This value reflects the overall average energy storage level of the system. Using it as the benchmark for the system's target operating time allows for a balance between the depth of discharge of each battery and the system's output capacity, taking into account both operational efficiency and equipment health.

[0075] By configuring at least one of the above as the target operating time benchmark for the system, a flexible reference coordinate is provided for dynamically adjusting the power distribution strategy according to the load conditions, enabling the system to adaptively switch between robustness, load capacity and equalization speed according to the needs of actual application scenarios.

[0076] The process of determining this benchmark reflects the system's preferred configuration of its operating strategy. For example, in scenarios with extremely high requirements for power supply reliability, the system target operating time benchmark can be configured as the minimum sustainable operating time; conversely, in scenarios with high requirements for energy utilization efficiency, it can be configured as the average sustainable operating time. By setting a clear system target operating time benchmark, dispersed individual operating times can be transformed into a unified system control target, providing a quantitative basis for the subsequent back-calculation of target power.

[0077] S4. Calculate the target power corresponding to each inverter based on the current absolute remaining power of each inverter and the system target operating time reference.

[0078] The target power, based on the system's energy balance principle, is the desired output value allocated to each inverter and is a key control variable for achieving consistent operating times. This step involves reverse calculation, transforming the time-dimensional benchmark into a power-dimensional instruction. The calculation logic follows the fundamental physical relationship that energy equals power multiplied by time. For example, the current absolute remaining power of each inverter can be divided by the system's target operating time benchmark to directly obtain the target power that each inverter should handle. Alternatively, based on the above calculation results, the system load rate can be further introduced for weighted correction to adapt to changes in actual load demand.

[0079] In one specific implementation, the target power for each inverter is calculated based on the current absolute remaining power of each inverter and the system target operating time reference. Specifically, this includes at least one of the following three target power types:

[0080] Calculate the first target power for each inverter based on its current absolute remaining power and maximum operating time.

[0081] The first target power is based on the time index corresponding to the inverter with the longest possible operating time in the system, primarily applicable to control scenarios that aim to maximize the overall system operating time. This maximum possible operating time benchmark is derived from the statistical analysis results of the operating time of each inverter in the previous steps. The first target power for each inverter is obtained by dividing the current absolute remaining power of each inverter by this maximum possible operating time benchmark. This calculation logic aims to ensure that all inverters can maintain their maximum possible operating time. Under this constraint, inverters with more absolute remaining power are allocated higher output power, while those with less are allocated lower output power. This allocation method ensures that each inverter is power-planned according to a unified, longer time benchmark, effectively avoiding the risk of system paralysis due to a single unit prematurely exhausting its energy.

[0082] Calculate the second target power for each inverter based on its current absolute remaining power and minimum operating time.

[0083] The second target power is based on the time index corresponding to the inverter with the shortest supported operating time in the system. This is mainly applicable to control scenarios that require rapid response to high load demands or pursue maximum instantaneous load capacity. This minimum supported operating time benchmark is also provided by the statistical results of the previous steps. The second target power for each inverter is obtained by dividing the current absolute remaining power of each inverter by this minimum supported operating time benchmark. This calculation process aims to maximize the system's load capacity, and its core logic is that all inverters output power according to the lifespan standard of the shortest time bottleneck unit. In this allocation mode, each inverter tends to operate at higher power, which, although it shortens the overall system's supported time to a minimum, ensures that the total output power the system can provide reaches its peak within that time period.

[0084] Calculate the third target power for each inverter based on its current absolute remaining power and average operating time.

[0085] The third target power is based on the average operating time of all inverters in the system. First, the arithmetic mean of the operating time of each inverter is calculated, and this average is used as the baseline for the system's average operating time. Then, the current absolute remaining power of each inverter is divided by this average operating time baseline to obtain the third target power for each inverter. This calculation process strikes a balance between pursuing the longest operating time and the maximum load capacity, taking into account both the actual energy state of each inverter and the system's operating efficiency. The third target power, as a compromise, avoids both excessively low power output due to solely pursuing long operating times and excessively short operating times due to solely pursuing high power, thus providing a balanced power allocation strategy for the system.

[0086] The parallel calculation of the three target powers mentioned above provides multi-dimensional data support for the subsequent dynamic selection or weighted synthesis of the final control target power based on the actual load conditions.

[0087] The details are shown in the table below:

[0088] Pursue the longest possible runtime (balancing to the weakest machine lifespan). Ps_min_i = EBat_i / Max(Ti) Maximize total system time Pursue the system's maximum load-carrying capacity (in the shortest time). Ps_max_i = EBat_i / Min(Ti) The system has the largest load capacity. To achieve the desired average uptime (while taking into account the status of each machine). Ps_ave_i = EBat_i / Ave(Ti) Each machine is based on its average lifespan

[0089] S5. Adjust the droop control parameters of each inverter according to the target power of each inverter, so that each inverter outputs with different droop control parameters in parallel operation, so as to adjust the actual support time of each inverter to be consistent.

[0090] Droop control parameters are core adjustment variables for inverters to achieve autonomous power distribution during parallel operation, typically manifested as frequency droop coefficients or voltage droop coefficients. These parameters define the static slope relationship between inverter output power and electrical parameters, and are the core adjustment variables for power distribution in parallel operation of inverters. The physical nature of these parameters characterizes the sensitivity of the system's active power changes to frequency or voltage fluctuations. In inductive systems, the frequency droop coefficient controls active power distribution by adjusting the system output frequency; in resistive systems, the voltage droop coefficient controls active power distribution by adjusting the system output voltage. The selection of droop control parameters depends on the line impedance characteristics and load type of the off-grid power supply system, and is the direct execution target for power balancing regulation provided in the embodiments of this application.

[0091] In this embodiment, to achieve balanced operating time, differentiated droop control parameters need to be configured for each inverter. Essentially, this changes the inverter's output power response sensitivity to system frequency or voltage fluctuations. For example, for an inverter requiring reduced output power, its frequency droop coefficient can be increased, allowing it to reduce power output more significantly when the system frequency drops slightly; conversely, for an inverter requiring increased output power, its frequency droop coefficient can be decreased, enabling it to handle more load power.

[0092] The droop control parameters are derived from the configuration parameters of the inverter controller, and their values ​​are directly related to the target power of each inverter. In engineering implementation, the droop control parameters are dynamically determined based on the target power calculated according to the method provided in the embodiments of this application.

[0093] For example, when the system is an inductive system, the frequency droop coefficient is used, and its calculation logic is as follows: When the system is a resistive system, the voltage droop factor is used, and its calculation logic is as follows: .in, The preset frequency droop range (e.g., 0.5Hz). This is a preset voltage droop range (e.g., 10V). This represents the target power for each inverter.

[0094] Through the above calculation process, the abstract target power is transformed into specific control parameters.

[0095] Based on the above steps S1 to S5, this embodiment eliminates the evaluation deviation caused by differences in battery specifications by obtaining battery operating parameters and calculating the absolute remaining power; it coordinates the output differences of each inverter by calculating the supported operating time and determining the system target operating time benchmark; and it achieves consistency in the actual supported operating time of each inverter by reversely calculating the target power and adjusting the droop control parameters.

[0096] During system operation, the droop control parameters are adjusted by issuing new parameter configuration commands to the inverter control unit, allowing each inverter to output with different droop control parameters in parallel operation. By setting the frequency droop coefficient or voltage droop coefficient, the control dimension can be flexibly selected according to the specific line characteristics, ensuring that time-based balanced control can be achieved in different types of off-grid power supply systems. This parameter selection method allows each inverter to respond to different power commands with differentiated slopes, thereby adjusting the actual support time of each inverter to be more consistent and avoiding insufficient system adaptability due to a single parameter type.

[0097] This adjustment process ensures that, even when inverters are physically connected to the same bus and maintain consistent output frequency and voltage while operating in parallel, their actual output power is distributed according to the target power calculated in step S4 due to differences in their respective droop control parameters. This control strategy based on differentiated droop coefficients eliminates the need for complex centralized communication scheduling, achieving global power optimization solely through adjustments to local control parameters. As each inverter operates at the target power, their actual operating time gradually converges, preventing some inverters from prematurely shutting down due to prolonged overload, thus significantly improving the overall continuous operation capability and stability of the off-grid power supply system.

[0098] In one specific implementation, in order to adapt to changes in actual load demand, a step of dynamically adjusting the target power based on the load rate can be added to the calculation.

[0099] like Figure 2 As shown, step S4, which calculates the target power for each inverter based on the current absolute remaining power of each inverter and the system target operating time, includes:

[0100] Step S401: Obtain the current actual load power of the system, and determine the current load rate of the system based on the ratio of the actual load power to the sum of the third target power of each inverter.

[0101] The current actual load power of the system characterizes the real-time energy consumption level of the off-grid power supply system, reflecting the total power required by all load devices (such as lighting, home appliances, or industrial equipment) connected to the AC bus at the current moment. This data is obtained by collecting the current and voltage values ​​at the AC bus through the current sampling circuit and voltage sampling circuit inside the system, and calculating the active power value. The third target power of each inverter is calculated based on the average supportable operating time determined in the previous steps, representing the ideal power allocation value while taking into account the state of each inverter. The current load factor of the system is defined as the ratio of the current actual load power of the system to the sum of the third target power of all inverters. This parameter is used to measure the saturation degree of the current actual load relative to the average support capacity of the system. By calculating this ratio, the specific value of the load is normalized into a relative coefficient, which serves as the quantitative basis for subsequent weighted decision-making. The calculation process is expressed as follows:

[0102] Considering the issue of response speed under load in practical applications, we will use an actual load here. The summation of the characteristic load Ps_ave_i calculated with the average time Ave(Ti). In comparison, the weighting coefficients can be obtained. :

[0103]

[0104] The closer η is to 0, the smaller the system load; the closer η is to 1, the larger the system load.

[0105] In other words, when the system is under light load, the load factor approaches 0; when the system is under heavy load and close to the upper limit of its average support capacity, the load factor approaches 1. This process transforms complex power values ​​into weighting factors that facilitate logic control, achieving a quantitative mapping of load states.

[0106] Step S402: The first target power and the second target power are weighted and summed according to the load rate to obtain the final target power of each inverter, so as to determine the droop control parameters of each inverter.

[0107] The first and second target powers represent the power allocation benchmarks for the system when pursuing the longest operating time (conservative strategy) and the maximum load capacity (aggressive strategy), respectively. The weighted summation process dynamically adjusts the weight allocation based on the load rate calculated in the preceding steps, thereby determining the final target power for each inverter. This process uses the load rate as a bridge connecting the load state and the control strategy, allowing the final target power to adaptively adjust with changes in the actual load. The logic of the weighted calculation is as follows:

[0108] + (1- )*

[0109] When the load rate is low (e.g.) When the value is close to 0, the coefficient (1−η) approaches 1, and the final target power of each inverter is... trending toward the second target power This means that each inverter tends to output at its maximum capacity, thereby quickly leveling out the SOC and accelerating the power balancing process; when the load rate is high (e.g. When approaching 1), the final target power of each inverter tending towards the first target power This means that each inverter tends to derating its output to ensure the overall continuous operation of the system and avoid overloading of weak links.

[0110] Through this dynamic weighting mechanism, the final target power automatically switches the dominant strategy under different load conditions, achieving adaptive and smooth switching of the system under different load conditions. This allows for fine-grained control of power allocation without manual intervention. After determining the final target power, it is substituted into the calculation formula for the droop control parameters to obtain the updated droop coefficient. The actual output power of the inverter is then adjusted by changing the droop coefficient, achieving closed-loop control. This mechanism avoids system oscillations or control instability caused by sudden changes in power allocation strategy near the load rate critical point, effectively improving the stability and reliability of off-grid power supply systems.

[0111] In one specific implementation, the method further includes the steps of acquiring operating parameters, determining absolute remaining power, calculating the available operating time, determining the system target operating time reference, calculating the target power, and adjusting droop control parameters. These steps are continuously iterated after the system enters off-grid operation mode until the actual available operating time of each inverter tends to be consistent.

[0112] After the system switches to off-grid operation mode, a closed-loop control process based on real-time data feedback is initiated. This process executes cyclically according to a preset period, aiming to achieve energy balance in the multi-unit parallel system through dynamic adjustment. At the beginning of each iteration, real-time operating parameters of the energy storage units connected to each inverter are collected, including but not limited to the current battery voltage, rated ampere-hour capacity, and current state of charge (SOC). Given the time-varying characteristics of the energy storage unit state during discharge, especially the continuous decrease in state of charge (SOC) as the discharge progresses, this directly affects the current absolute remaining capacity of each energy storage unit. It exhibits a dynamic decay trend.

[0113] Based on the real-time collected operating parameters, the current absolute remaining power of each energy storage unit is recalculated, and the operating time that each inverter can sustain in the current state is derived accordingly. Combining this with the overall system's target operating time benchmark, the target power output value of each inverter is calculated. Based on the deviation between this target power and the current actual power, the droop control parameters of each inverter are corrected and updated. After the parameter adjustment is completed, the next iteration cycle begins immediately, and the latest operating parameters are acquired again, repeating the above calculation and adjustment process.

[0114] Through this high-frequency iterative adjustment, the droop control parameters can dynamically adapt to the state changes of the energy storage units. For inverters with low absolute remaining power and short operating time, their droop coefficient is adjusted to a larger value, thereby limiting their output power; conversely, for inverters with high absolute remaining power and long operating time, their droop coefficient is adjusted to a smaller value, allowing them to handle more load power. As the iteration process progresses, the differences in the actual operating time of each inverter gradually converge. When the actual operating time of each inverter tends to be consistent or falls within the preset error range, the system is determined to have reached an equilibrium state. At this point, maintaining the current droop control parameters or performing low-frequency sustaining iterations can achieve synchronous power consumption of each energy storage unit while ensuring power supply reliability, thereby maximizing the overall endurance of the off-grid power supply system.

[0115] The above steps are continuously executed iteratively after the system enters the off-grid operation state, which can respond to changes in battery status and load in real time and ensure dynamic balance throughout the entire operation cycle.

[0116] <Example 2>

[0117] This embodiment provides an off-grid system balancing control system for executing the off-grid system balancing control method described in Embodiment 1 above, so as to realize that the batteries connected to each inverter in an off-grid power supply system composed of multiple inverters connected in parallel can bear loads differently according to their own energy reserves and load-carrying capacity.

[0118] like Figure 3 As shown, the system includes: a parameter acquisition unit 101, a power calculation unit 102, a time calculation unit 103, a time reference determination unit 104, a power calculation unit 105, and a droop parameter adjustment unit 106. Specifically,

[0119] The parameter acquisition unit 101 is used to acquire the operating parameters of the batteries connected to each inverter. The operating parameters include at least the parameters used to characterize the current voltage, ampere-hour capacity and current state of charge of the battery.

[0120] The power calculation unit 102 is used to determine the current absolute remaining power of the batteries connected to each inverter based on the operating parameters.

[0121] The time calculation unit 103 is used to calculate the current operating time that each inverter can support based on its current absolute remaining power and its current maximum allowable output power.

[0122] The time base determination unit 104 is used to determine the system target operating time base based on the supportable operating time of each inverter.

[0123] The power calculation unit 105 is used to calculate the target power of each inverter based on the current absolute remaining power of each inverter and the system target operating time reference.

[0124] The droop parameter adjustment unit 106 is used to adjust the droop control parameters of each inverter according to the target power of each inverter, so that each inverter outputs with different droop control parameters in parallel operation, so as to adjust the actual support time of each inverter to be consistent.

[0125] In this embodiment, each unit module in the off-grid system equalization control system can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the operations corresponding to each module. Specifically, as shown... Figure 3As shown, the operation of each module can be controlled by the control unit 107. Furthermore, the steps performed by each of the above units are the same as those corresponding to the equalization control method in Embodiment 1, which can be referred to in Embodiment 1 and will not be repeated here.

[0126] Based on the functions of the parameter acquisition unit 101 to the droop parameter adjustment unit 106, this embodiment eliminates the evaluation deviation caused by differences in battery specifications by acquiring battery operating parameters and calculating the absolute remaining power; it coordinates the output differences of each inverter by calculating the supported operating time and determining the system target operating time benchmark; and it achieves a convergence of the actual supported operating time of each inverter by reversely calculating the target power and adjusting the droop control parameters, significantly improving the overall continuous operation capability and stability of the off-grid power supply system.

[0127] In another embodiment, such as Figure 3 As shown, to trigger the parameter acquisition unit 101 to start working when the system is detected to have entered off-grid operation mode, an off-grid status detection unit 108 can be added to the system. This off-grid status detection unit 108 serves as the system's startup enable module, and its core function is to monitor the grid connection status of the power supply system in real time. Once it is confirmed that the system is disconnected from the main grid, it immediately activates the subsequent balancing control logic. In specific implementation, this unit can determine whether the system has switched to off-grid mode by detecting whether the voltage amplitude and frequency on the grid side exceed the normal range, or by detecting the disconnection status signal of the grid connection switch. When the off-grid status detection unit 108 confirms that the system has entered off-grid operation mode, it outputs a trigger signal to the parameter acquisition unit, causing the parameter acquisition unit 101 to start collecting the battery operating parameters of each inverter. When no off-grid status is detected (such as when in grid-connected operation mode), this unit can keep the parameter acquisition unit 101 in a sleep or standby state, thereby avoiding invalid data collection and calculation. The above configuration ensures that the balancing control strategy is executed only in off-grid conditions, which not only reduces the system's standby power consumption but also avoids control conflicts that may occur in grid-connected conditions, thereby improving the operational reliability and response speed of the off-grid system's balancing control system.

[0128] The scope of protection of this invention is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its scope and spirit. If these modifications and variations fall within the scope of the claims of this invention and their equivalents, then the intent of this invention also includes these modifications and variations.

Claims

1. An off-grid system balancing control method, applied to an off-grid power supply system consisting of multiple inverters connected in parallel, each inverter being connected to a battery, characterized in that, Includes the following steps: The operating parameters of the batteries connected to each inverter are obtained, and the current absolute remaining capacity of the batteries connected to each inverter is determined based on the operating parameters. The operating parameters include at least the parameters used to characterize the current voltage, ampere-hour capacity and current state of charge of the batteries. Calculate the current operating time that each inverter can support based on its current absolute remaining power and its current maximum allowable output power. The system target operating time baseline is determined based on the current supported operating time of each inverter. The target power of each inverter is calculated based on the current absolute remaining power of each inverter and the target operating time of the system. Adjust the droop control parameters of each inverter according to the target power of each inverter, so that each inverter outputs with different droop control parameters in parallel operation, so as to adjust the actual supporting operating time of each inverter to be closer to the same.

2. The off-grid system equalization control method according to claim 1, characterized in that, The current absolute remaining power is the product of the current voltage, ampere-hour capacity, and current state of charge of the batteries connected to each inverter.

3. The off-grid system equalization control method according to claim 1, characterized in that, The maximum allowable output power of each inverter is determined by the limitations of the battery management system and / or the inverter's own temperature limitations.

4. The off-grid system equalization control method according to claim 1, characterized in that, The target operating time benchmark of the system includes at least one of the minimum supportable operating time, the maximum supportable operating time, and the average supportable operating time.

5. The off-grid system equalization control method according to claim 4, characterized in that, The calculation of the target power corresponding to each inverter based on the current absolute remaining power of each inverter and the system target operating time reference includes: Calculate the first target power for each inverter based on the current absolute remaining power of each inverter and the maximum supported operating time. And / or, calculate the second target power corresponding to each inverter based on the current absolute remaining power of each inverter and the minimum supportable operating time; And / or, calculate the third target power for each inverter based on the current absolute remaining power of each inverter and the average operating time that can be sustained.

6. The off-grid system equalization control method according to claim 5, characterized in that, The step of calculating the target power corresponding to each inverter based on the current absolute remaining power of each inverter and the system target operating time reference includes: Obtain the current actual load power of the system, and determine the current load rate of the system based on the ratio of the actual load power to the sum of the third target power of each inverter; The first target power and the second target power are weighted and summed according to the load rate to obtain the final target power of each inverter, so as to determine the droop control parameters of each inverter.

7. The off-grid system equalization control method according to claim 6, characterized in that, When the load rate approaches its minimum value, the final target power of each inverter approaches the second target power; when the load rate approaches its maximum value, the final target power of each inverter approaches the first target power.

8. The off-grid system equalization control method according to claim 1, characterized in that, The droop control parameter is either the frequency droop coefficient or the voltage droop coefficient.

9. The off-grid system equalization control method according to claim 1, characterized in that, The steps of acquiring operating parameters, determining absolute remaining power, calculating the available operating time, determining the system target operating time benchmark, calculating the target power, and adjusting the droop control parameters are continuously iterated after the system enters the off-grid operation state until the actual available operating time of each inverter tends to be consistent.

10. An off-grid system balancing control system, applied to an off-grid power supply system consisting of multiple inverters connected in parallel, each inverter being connected to a battery, characterized in that, include: The parameter acquisition unit is used to acquire the operating parameters of the batteries connected to each inverter. The operating parameters include at least the parameters characterizing the current voltage, ampere-hour capacity and current state of charge of the battery. The power calculation unit is used to determine the current absolute remaining power of the batteries connected to each inverter based on the operating parameters. The time calculation unit is used to calculate the current operating time that each inverter can support based on its current absolute remaining power and its current maximum allowable output power. The time base determination unit is used to determine the target operating time base of the system based on the supportable operating time of each inverter; The power calculation unit is used to calculate the target power of each inverter based on the current absolute remaining power of each inverter and the target operating time of the system. The droop parameter adjustment unit is used to adjust the droop control parameters of each inverter according to the target power of each inverter, so that each inverter outputs with different droop control parameters in parallel operation, so as to adjust the actual support time of each inverter to be consistent.

11. The off-grid system equalization control system according to claim 10, characterized in that, Also includes: The off-network status detection unit is used to trigger the parameter acquisition unit to start working when the system is detected to have entered an off-network operation state.

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