Load adaptive starting control method of off-grid energy storage system and off-grid energy storage system

Abstract

The application provides a load adaptive starting control method of an off-grid energy storage system and the off-grid energy storage system. The method comprises the following steps: in the off-grid operation mode, controlling an inverter to operate at a rated voltage amplitude and a rated voltage frequency; sampling an output current of the inverter and outputting a current signal in real time, and generating an overcurrent signal when a peak value of the current signal reaches a preset value; starting timing a first preset time length and detecting the overcurrent signal; in the first preset time length, accumulating the number of times of detecting the overcurrent signal; judging whether the accumulated value reaches a preset number of times, if yes, reducing the voltage amplitude and the voltage frequency of the inverter output, and if not, restarting timing the first preset time length when the first preset time length ends. The method of the application does not need to increase the overload capacity of the inverter, is suitable for the smooth starting of various loads, ensures the stable operation of the inverter, saves the frequency converter or the soft starter, reduces the system cost and price, reduces external elements, is simple in wiring, and is convenient to install and maintain.

Description

Technical Field

[0001] This invention relates to the field of energy storage systems, and in particular to a load adaptive start-up control method for an off-grid energy storage system and an off-grid energy storage system. Background Technology

[0002] As the core device of an energy storage system, the energy storage inverter has both grid-connected and off-grid modes. In grid-connected mode, the energy storage inverter supplies energy to the grid. In off-grid mode, the energy storage inverter needs to independently supply power to the load and maintain a stable voltage and frequency output. Typically, energy storage inverters are designed with a short-term overload capacity of 1.2 to 1.5 times the rated load for a duration of 3 to 30 seconds to meet the switching and short-term impact requirements of general loads.

[0003] However, in practical applications, off-grid energy storage systems typically need to power motor-type loads, such as water pumps, fans, or compressors. These loads exhibit two prominent characteristics when started directly: first, the starting current is extremely high, reaching 5-7 times the rated current; second, they require the absorption of a large amount of inductive reactive power during startup, easily causing a sudden drop in output voltage. When the power of the motor-type load reaches a certain value, the limited short-time overload capacity of the energy storage inverter cannot meet the startup requirements of the motor-type load, causing it to remain in a stalled or low-speed operating state. Ultimately, the energy storage inverter triggers overcurrent or overload protection due to insufficient short-time overload capacity, leading to the failure of the motor-type load to start. This not only affects the normal operation of the motor-type load but may also damage the motor-type load or the energy storage inverter itself.

[0004] To address this issue, traditional solutions typically involve adding a soft-start device, such as a frequency converter, between the output of the energy storage inverter and the motor load. When the motor load starts, the frequency converter slowly ramps up its voltage and frequency according to a preset start-up curve, limiting the starting current and thus preventing a large starting current from triggering the energy storage inverter's protection until it reaches rated operation. However, this traditional solution requires the additional purchase and installation of a frequency converter, increasing system cost and floor space requirements, as well as operational complexity, resulting in poor economic efficiency and applicability.

[0005] However, while this traditional solution is suitable for motor-type loads, it is not suitable for resistive loads or ordinary household loads. When the frequency converter is connected to a resistive load or ordinary household load, the frequency converter slowly ramps up at extremely low voltage and frequency according to a preset start-up curve. If the voltage and frequency provided by the frequency converter do not reach a certain value, the resistive load or ordinary household load cannot start normally. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a load adaptive start-up control method and an off-grid energy storage system, which can achieve uninterrupted power supply when resistive loads or ordinary household loads are less than the rated power of the energy storage system; and achieve stable start-up of motor loads when motor loads are greater than the rated power of the energy storage system, without the need for frequency converter assistance, and is quick to install and highly economical.

[0007] This application proposes a load adaptive start-up control method for an off-grid energy storage system. The energy storage system includes an inverter and a control device, wherein the inverter is connected to the load and the control device. The method includes the following steps:

[0008] S1: When the inverter enters the off-grid operation mode, the inverter is controlled to operate at the rated voltage amplitude and rated voltage frequency, so that the voltage amplitude output by the inverter is the rated voltage amplitude and the voltage frequency is the rated voltage frequency.

[0009] S2: Sample the output current of the inverter in real time and output a current signal, and generate an overcurrent signal when the peak value of the current signal reaches a preset value;

[0010] S3: Start timing for the first preset duration and detect the overcurrent signal;

[0011] S4: Within the first preset time period, the cumulative number of times the overcurrent signal is detected is accumulated, and a cumulative value is obtained;

[0012] S5: Determine whether the cumulative value has reached the preset number of times. If yes, proceed to step S6. If no, return to step S3 when the first preset time ends.

[0013] S6: Control the inverter to reduce the voltage amplitude and voltage frequency output by the inverter;

[0014] S7: Determine whether the reduced voltage amplitude has reached the minimum voltage value and whether the reduced voltage frequency has reached the minimum frequency value. If yes, control the inverter to operate at the minimum voltage value and the minimum frequency value and enter the protection state. If no, return to step S3.

[0015] Optionally, controlling the inverter in step S6 to reduce the voltage amplitude and voltage frequency output by the inverter includes controlling the inverter to reduce the voltage amplitude output by the inverter by a first voltage step and reduce the voltage frequency by a first frequency step.

[0016] Optionally, before step S3, the step-down flag bit is initialized by setting the step-down flag bit to 0;

[0017] Step S3, starting the timing for the first preset duration, includes timing the first preset duration using a timer counter;

[0018] In step S4, the cumulative number of times the overcurrent signal is detected within the first preset time period is accumulated to obtain the cumulative value, which includes the cumulative number of times the overcurrent signal is detected within the first preset time period and when the buck flag is 0.

[0019] Optionally, step S5 may return to step S3 at the end of the first preset duration, including clearing both the timer counter and the accumulated value to zero at the end of the first preset duration, and then returning to step S3.

[0020] Optionally, if the condition in step S5 is true, then step S6 is executed, including if the condition is true, setting the step-down flag to 1, executing step S6, and then clearing both the accumulated value and the timer counter to zero; or if the condition is true, setting the step-down flag to 1, clearing both the accumulated value and the timer counter to zero, and then executing step S6.

[0021] If no in step S7, return to step S3, including setting the voltage reduction flag to 0 and returning to step S3 if no.

[0022] Optionally, controlling the inverter in step S6 to reduce the voltage amplitude and voltage frequency output by the inverter includes starting a second preset time period and controlling the inverter to reduce the voltage amplitude and voltage frequency output by the inverter when the second preset time period ends.

[0023] Optionally, start timing for a second preset duration, including timing the second preset duration using a delay counter;

[0024] If the error in step S7 is not found, then return to step S3, including if the error is not found, then clear the delay counter and return to step S3.

[0025] Optionally, the minimum frequency value is the rated voltage frequency minus a preset frequency offset.

[0026] Optionally, the method further includes the following steps:

[0027] S8: When the overcurrent signal is not detected, start timing for a third preset duration, and determine whether the overcurrent signal is detected within the third preset duration;

[0028] S9: If the overcurrent signal is not detected at the end of the third preset time period, determine whether the voltage amplitude of the inverter output reaches the rated voltage amplitude and whether the voltage frequency reaches the rated voltage frequency. If yes, control the inverter to operate at the rated voltage amplitude and the rated voltage frequency. If no, control the inverter to increase the voltage amplitude and voltage frequency of the inverter and return to step S3.

[0029] Optionally, controlling the inverter in step S9 to increase the voltage amplitude and voltage frequency of the inverter includes controlling the inverter to increase the voltage amplitude output by the inverter by a second voltage step and increase the voltage frequency by a second frequency step.

[0030] Optionally, the start timing of the third preset duration in step S8 includes timing the third preset duration using a continuous counter;

[0031] The load adaptive start-up control method for the off-grid energy storage system further includes clearing the continuous counter to zero and returning to step S3 when the overcurrent signal is detected.

[0032] Optionally, step S9, which involves controlling the inverter to increase its voltage amplitude and frequency and then returning to step S3, includes controlling the inverter to increase its voltage amplitude and frequency, clearing the continuous counter, and then returning to step S3.

[0033] Optionally, step S2 involves sampling the inverter's output current in real time and outputting a current signal, and generating an overcurrent signal when the peak value of the current signal reaches a preset value. This specifically includes the following steps:

[0034] S21: Sample the output current of the inverter in real time and output a current signal representing the magnitude of the output current;

[0035] S22: Compare the current signal with the preset value, and generate the overcurrent signal when the peak value of the current signal reaches the preset value.

[0036] This application also proposes an off-grid energy storage system, comprising:

[0037] Inverter, connected to the load;

[0038] A control device, connected to the inverter, is used to execute the load adaptive start-up control method for an off-grid energy storage system as described in any embodiment of this application.

[0039] The beneficial effects of this application include at least the following:

[0040] The load adaptive start-up control method of the off-grid energy storage system in this embodiment starts timing for a first preset time and detects overcurrent signals. Within the first preset time, the number of times the overcurrent signal is detected is accumulated, and a cumulative value is obtained. The load weight is judged by detecting the overcurrent signal. When the cumulative value reaches a preset number, it indicates that the load is heavy, and the inverter is controlled to reduce its output voltage amplitude and voltage frequency. When no overcurrent signal is detected, it indicates that the load has started. Therefore, when the inverter's output voltage amplitude and voltage frequency have not reached the rated voltage amplitude and voltage frequency, its output voltage amplitude and voltage frequency are increased. When the cumulative value has not reached the preset number, the inverter's output voltage amplitude and voltage frequency remain unchanged. This method can adaptively handle motor loads, ordinary household loads, and resistive loads without the need for external frequency converters or soft starters, reducing system costs and prices. It integrates the drive function into a single device, achieving a high degree of integration, significantly reducing system size, reducing external components, simplifying wiring, and facilitating installation and maintenance. Furthermore, there is no need to increase the inverter's overload capacity, ensuring stable operation of the inverter in various complex load environments.

[0041] The features and technical advantages of this application have been broadly outlined above to facilitate a better understanding of the following detailed description. Additional features and advantages of this application, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily utilized as the basis for modifying or designing other structures or processes to achieve the same purpose as this application. Those skilled in the art will also recognize that such equivalent constructions do not depart from the spirit and scope of this application as set forth in the appended claims. Attached Figure Description

[0042] To gain a more comprehensive understanding of this application and its advantages, the following description is now taken in conjunction with the accompanying drawings, in which:

[0043] Figure 1 A schematic diagram of the structure of an off-grid energy storage system according to an embodiment of this application is shown;

[0044] Figure 2 A flowchart of the load adaptive start-up control method for an off-grid energy storage system according to an embodiment of this application is shown;

[0045] Figure 3 A flowchart of steps S3 and S4 in an embodiment of this application is shown;

[0046] Figure 4 The following is a detailed flowchart of steps S5 and S6 in an embodiment of this application;

[0047] Figure 5 A flowchart of step S7 in an embodiment of this application is shown;

[0048] Figure 6 The following is a detailed flowchart of steps S8 and S9 in an embodiment of this application.

[0049] Unless otherwise indicated, corresponding numbers and symbols in different figures generally refer to corresponding parts. The accompanying drawings are provided to clearly illustrate relevant aspects of various embodiments and are not necessarily drawn to scale. Detailed Implementation

[0050] Various exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0051] The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment illustrated herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments. The terms "first," "second," "third," etc. (if present) in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "coupled," "connected," and "linked" should be interpreted broadly. For example, they can refer to electrical connection or mutual communication; they can be a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0054] Please see Figure 1The schematic diagram of the off-grid energy storage system according to an embodiment of this application shows that the energy storage system includes an inverter 2 and a control device 1. The output terminal of the inverter 2 is connected to the load 3 through an inductor L. The first terminal of the capacitor C1 is connected to the inductor L, and the second terminal of the capacitor C1 is grounded to GND. The control device 1 is connected to the inverter 2 and is used to sample the output current of the inverter 2 in real time and control the operation of the inverter 2 according to the output current. When the inverter 2 operates in off-grid mode, it acts as an independent power supply to power the load. The inverter 2 needs to have an overload capacity of 1.2 to 1.5 times to meet the start-up requirements of the load. During the start-up process of various loads, the start-up current of different loads is different. By sampling the output current of the inverter 2 in real time, the weight of the load is determined. The heavier the load, the easier it is to trigger overcurrent. Different control strategies are used to control the inverter 2 according to the weight of the load, so that the load can start up smoothly, quickly and stably. In this embodiment, the inverter 2 can be a three-phase inverter, or it can be a single-phase inverter.

[0055] This application provides a load-adaptive start-up control method for an off-grid energy storage system, which operates in off-grid mode, such as... Figure 2 As shown, the method includes:

[0056] S1: When the inverter enters the off-grid operation mode, the inverter is controlled to operate at the rated voltage amplitude and rated voltage frequency, so that the voltage amplitude output by the inverter is the rated voltage amplitude and the voltage frequency is the rated voltage frequency.

[0057] S2: Sample the output current of the inverter in real time, and generate an overcurrent signal when the peak value of the output current reaches a preset value;

[0058] S3: Start timing for the first preset duration and detect the overcurrent signal;

[0059] S4: Within the first preset time period, the cumulative number of times the overcurrent signal is detected is accumulated, and a cumulative value is obtained;

[0060] S5: Determine whether the cumulative value has reached the preset number of times. If yes, proceed to step S6. If no, return to step S3 when the first preset time ends.

[0061] S6: Control the inverter to reduce the voltage amplitude and voltage frequency output by the inverter;

[0062] S7: Determine whether the reduced voltage amplitude has reached the minimum voltage value and whether the reduced voltage frequency has reached the minimum frequency value. If yes, control the inverter to operate at the minimum voltage value and the minimum frequency value and enter the protection state. If no, return to step S3.

[0063] like Figure 1 and Figure 2 As shown, when inverter 2 enters off-grid operation mode, control device 1 controls inverter 2 to operate at its rated voltage amplitude and rated voltage frequency, ensuring that the current output voltage amplitude and frequency of inverter 2 are the rated voltage amplitude and frequency. The rated voltage amplitude and frequency output by inverter 2 can directly start resistive loads or ordinary household loads. Since resistive loads or ordinary household loads are not inductive, there will be no load interruption or delayed start-up when these loads start. However, when the load is an impulsive load such as a motor, the starting current surge is large, reaching 5-7 times the rated current, which will trigger overcurrent. The rated voltage amplitude and frequency output by inverter 2 cannot directly start motor loads; the output voltage amplitude and frequency of inverter 2 need to be reduced to avoid triggering inverter protection due to the large inrush current.

[0064] Furthermore, in step S2, the output current of the inverter is sampled in real time and a current signal is output, and an overcurrent signal is generated when the peak value of the current signal reaches a preset value. Specifically, the steps are as follows: S21: The output current of the inverter is sampled in real time and a current signal representing the magnitude of the output current is output.

[0065] S22: Compare the current signal with the preset value, and generate the overcurrent signal when the peak value of the current signal reaches the preset value.

[0066] Please see Figure 1 The control device 1 includes a current sampling circuit 11, a current comparison circuit 12, and a controller 13. The current sampling circuit 11 samples the output current of the inverter 2 and outputs a current signal characterizing the magnitude of the output current. The current sampling circuit 11 may include a sensor and a signal conditioning circuit. The sensor is disposed on the output conductor of the inverter 2 to sense the output current, and the signal conditioning circuit conditions and amplifies the sensed output current to output a current signal. The current sampling circuit 11 may also include a sampling resistor and an operational amplifier circuit. The sampling resistor is disposed on the output conductor of the inverter 2, and the output current is sensed by detecting the voltage across the sampling resistor. The operational amplifier circuit amplifies the voltage across the sampling resistor to output a current signal. In this embodiment, the specific circuit of the current sampling circuit 11 is not limited to the two methods described above, and other circuits capable of real-time sampling of the output current are within the scope of protection of this application. When the inverter 3 is a three-phase inverter, it is necessary to simultaneously sample the output current on the three output conductors of the three-phase inverter in real time.

[0067] The current comparison circuit 12 compares the current signal with the preset value and generates an overcurrent signal when the peak value of the current signal reaches the preset value. Generating an overcurrent signal when the peak value of the current signal reaches the preset value can be understood as generating an overcurrent signal when the peak value of the current signal is greater than or equal to the preset value. The preset value is generally greater than the rated current value, and the selection of the preset value depends on the specific situation. The current comparison circuit 12 can be a comparator. When the peak value of the current signal reaches the preset value, the comparator outputs a flip signal, i.e., triggers an overcurrent event. This flip signal can be an overcurrent signal. By sampling the three-phase output current of the three-phase inverter in real time and outputting three current signals, the comparator will output a flip signal, i.e., trigger an overcurrent event, when the peak value of any one of the current signals reaches the preset value.

[0068] When the inverter enters off-grid operation mode, a large inrush current is generated the instant a motor-type load is connected. The current sampling circuit 11 samples the output current and outputs a current signal. The current comparison circuit 12 triggers a hardware overcurrent when the peak value of the current signal reaches the preset value, i.e., outputs an overcurrent signal. The current comparison circuit 12 feeds back the overcurrent signal to the controller 13.

[0069] In step S3, a timer counter is started to time a first preset duration and the overcurrent signal is detected. The first preset duration can be one or more power frequency cycles, selected according to actual needs. Specifically, controller 13 is used to detect the overcurrent signal. When controller 13 detects an overcurrent signal, it immediately forces the corresponding switch to turn off within the current switching cycle and remains off for the remainder of the cycle. When the next switching cycle arrives, the drive signal is turned on again. If the output current is still too high, it is turned off again within the cycle, and this process repeats continuously to achieve wave-by-wave current limiting. Each time controller 13 receives an overcurrent signal, the number of wave-by-wave current limiting operations increases by 1, i.e., the cumulative value increases by 1. Through a fast hardware-level protection mechanism, the current can be monitored and limited in real time within each switching cycle, ensuring that the current peak does not instantly break down the device, allowing the inverter to provide a large inrush current for a short period.

[0070] Furthermore, before step S3, the step-down flag bit is initialized by setting it to 0.

[0071] Please see Figure 1 , Figure 2 and Figure 3In step S4, the cumulative number of times the overcurrent signal is detected within the first preset duration is calculated to obtain a cumulative value. This includes the cumulative number of times the overcurrent signal is detected within the first preset duration and when the buck flag is 0. Each overcurrent event triggered by any phase of the three-phase inverter will increment the cumulative value by 1. Specifically, in step S4, it is first determined whether the first preset duration has ended. If so, both the cumulative value and the timer counter are cleared. Otherwise, it is determined whether the buck flag is 0. If so, the cumulative number of times the overcurrent signal is detected is calculated to obtain the cumulative value. If not, the process proceeds to step S6, controlling the inverter 12 to perform buck and frequency reduction operations. In this embodiment, determining whether the first preset duration has ended can be achieved by determining whether the count value of the timer counter has reached the first preset duration. If the count value of the timer counter is less than the first preset duration, the timer counter is still counting, indicating that the first preset duration has not ended. If the buck flag is 0 at this time, the cumulative number of times the overcurrent signal is detected is calculated to obtain the cumulative value. If the count value of the timer reaches the first preset duration, the timer stops counting, indicating that the first preset duration has ended. Before proceeding to step S3, both the accumulated value and the timer need to be cleared to restart timing the first preset duration and detecting the overcurrent signal.

[0072] Please see Figure 1 , Figure 2 and Figure 4 In step S5, it is determined whether the accumulated value has reached a preset number of times. If yes, step S6 is executed; otherwise, the process returns to step S3 at the end of the first preset duration. Specifically, when the accumulated value reaches the preset number of times, the step-down flag is set to 1, and both the accumulated value and the timer counter are cleared to zero before step S6 is executed. The preset number is selected according to actual needs. When the accumulated value is less than the preset number of times, the process returns to step S3 at the end of the first preset duration to proceed to the next first preset duration and re-determine the load weight. In other embodiments, when the accumulated value reaches the preset number of times, the step-down flag is set to 1, step S6 is executed, and both the accumulated value and the timer counter are cleared to zero. In another embodiment, when the accumulated value reaches the preset number of times, the step-down flag is set to 1, steps S6 and S7 are executed, and both the accumulated value and the timer counter are cleared to zero before returning to step S3. These embodiments are merely to illustrate that before returning to step S3, the accumulated value and the timer counter must be cleared to zero before the next first preset duration of timing and overcurrent signal detection can be performed.

[0073] In this embodiment, the severity of the load is determined by accumulating the number of overcurrent signal detections. A higher number of overcurrent signal detections indicates a higher trigger frequency, representing a heavier load, while a lower number of detections indicates a lighter load. By determining whether the cumulative value reaches a preset number, noise can be effectively filtered out, ensuring that the buck-frequency reduction operation is only initiated when a real and continuous overload occurs. This provides a fault-tolerant mechanism, guarantees system stability, and improves the system's anti-interference capability and lifespan. Furthermore, different control strategies are employed to activate the corresponding load based on its severity. When the load (e.g., resistive loads and ordinary household loads) is light, the inverter activates the load based on the rated voltage amplitude and frequency. When the load (e.g., motor loads) is heavy, the inverter activates based on the buck-frequency voltage amplitude and frequency, ensuring a smooth and reliable load start-up and stable inverter operation, thereby improving load adaptability.

[0074] Furthermore, in step S6, controlling the inverter to reduce the voltage amplitude and voltage frequency output by the inverter includes starting a second preset time period and, at the end of the second preset time period, controlling the inverter to reduce the voltage amplitude and voltage frequency output by the inverter.

[0075] In this embodiment, when the cumulative number of times the overcurrent signal is detected reaches a preset number, it indicates that the load is relatively heavy, and the controller performs a voltage reduction and frequency reduction operation. By repeatedly judging whether the cumulative number of times the overcurrent signal is detected has reached the preset number, the controller determines the number of times it will perform the voltage reduction and frequency reduction operation, that is, it determines how much the voltage amplitude and voltage frequency of the inverter output will be reduced, thereby achieving a smooth start-up of motor-type loads.

[0076] Furthermore, the timing of the second preset duration begins, including timing the second preset duration via a delay counter;

[0077] If the error in step S7 is not found, then return to step S3, including if the error is not found, then clear the delay counter and return to step S3.

[0078] For details, please refer to Figure 1 , Figure 2 , Figure 4 and Figure 5The system first determines whether the buck flag is 1. If yes, it proceeds to step S6. If no, it returns to step S3 and continues timing for the first preset duration and detecting the overcurrent signal. In step S6, a delay counter is started to time a second preset duration, which can be one power frequency cycle. The system then determines whether the second preset duration has ended. If yes, it controls the inverter to reduce the voltage amplitude and frequency output by the inverter. If no, it returns to step S3. Determining whether the second preset duration has ended can be achieved by checking if the delay counter's count value has reached the second preset duration. When the delay counter's count value is less than the second preset duration, it indicates that the second preset duration has not ended, and the delay counter continues counting. When the delay counter's count value reaches the second preset duration, it indicates that the second preset duration has ended, and the delay counter stops counting. This means that when the buck flag is 1, a second preset duration needs to be delayed before controlling the inverter to reduce the voltage amplitude and frequency output by the inverter.

[0079] In step S7, it is determined whether the reduced voltage amplitude and frequency have reached the minimum voltage value and minimum frequency value. If yes, the inverter is controlled to operate at the minimum voltage and frequency values ​​and enters the protection state. If not, the voltage reduction flag is set to 0, the delay counter is cleared, and the process returns to step S3. In this embodiment, the minimum voltage value is selected as needed, for example, 50V. The protection state refers to a fault shutdown to protect the inverter, but this may cause motor loads to fail to start.

[0080] Furthermore, the minimum frequency value is the rated voltage frequency minus a preset frequency offset. The preset frequency offset can be selected according to requirements, for example, 18Hz.

[0081] Furthermore, controlling the inverter in step S6 to reduce the voltage amplitude and frequency output by the inverter includes controlling the inverter to reduce the voltage amplitude by a first voltage step and the voltage frequency by a first frequency step. Specifically, within a first preset time period, when the cumulative value exceeds a preset number, the controller controls the inverter to perform a voltage and frequency reduction operation. In each voltage and frequency reduction operation, the voltage amplitude and voltage frequency output by the inverter are reduced by a first voltage step and a first frequency step, respectively. The first voltage step and the first frequency step can be selected as needed, for example, the first voltage step is 10V and the first frequency step is 1Hz.

[0082] In this embodiment, the load adaptive start-up control method is applicable to controlling the start-up of motor-type loads as well as non-inductive loads such as resistive loads and ordinary household loads. If the number of times the controller detects the overcurrent signal is less than a preset number, it indicates a relatively light load, such as a resistive load or ordinary household load. In this case, the inverter's current output voltage amplitude and frequency are the rated voltage amplitude and frequency. The inverter control starts the load based on the current output voltage amplitude and frequency, without interruption or delayed start-up. When the cumulative value reaches the preset number, it indicates a relatively heavy load, such as a motor-type load. The controller performs a voltage and frequency reduction operation. After the voltage and frequency reduction operation is completed, the inverter's current output voltage amplitude and frequency are the reduced voltage amplitude and frequency. The controller then checks if the cumulative value has reached the preset number. If the cumulative value still reaches the preset number, the voltage and frequency reduction operation continues, repeating this process until the cumulative value is less than the preset number. This load-adaptive start-up control method does not require increasing the inverter's overload capacity, nor does it require adding a frequency converter or soft starter. It can ensure smooth start-up and stable operation, and also reduce costs and size.

[0083] Furthermore, the method also includes the following steps:

[0084] S8: When the overcurrent signal is not detected, start timing for a third preset duration, and determine whether the overcurrent signal is detected within the third preset duration;

[0085] S9: If the overcurrent signal is not detected at the end of the third preset time period, determine whether the voltage amplitude of the inverter output reaches the rated voltage amplitude and whether the voltage frequency reaches the rated voltage frequency. If yes, control the inverter to operate at the rated voltage amplitude and the rated voltage frequency. If no, control the inverter to increase the voltage amplitude and voltage frequency of the inverter and return to step S3.

[0086] For details, please refer to Figure 1 , Figure 2 and Figure 6The system checks if the step-down flag is 1. If yes, proceed to step S6; otherwise, check if an overcurrent signal is detected. If no, start a continuous counter to begin timing for a third preset duration. If yes, clear the continuous counter and return to step S3. The third preset duration can be selected as needed. Checking for an overcurrent signal within the third preset duration means continuously checking for overcurrent signals as long as the continuous counter's count value is less than the third preset duration. The determination of whether the third preset duration has ended can be achieved by checking if the continuous counter's count value has reached the third preset duration. When the continuous counter's count value is less than the third preset duration, the continuous counter continues counting and returns to step S3 to detect an overcurrent signal again. When the count value of the continuous counter reaches the third preset duration, it is determined whether the voltage amplitude and voltage frequency output by the inverter have reached the rated voltage amplitude and rated voltage frequency. If yes, the inverter is controlled to operate at the rated voltage amplitude and rated voltage frequency. If not, the inverter is controlled to increase the voltage amplitude and voltage frequency, and the continuous counter is reset to zero, then the process returns to step S3. At this time, the current output voltage amplitude and voltage frequency of the inverter are the increased voltage amplitude and voltage frequency.

[0087] Further, step S9, controlling the inverter to increase its voltage amplitude and frequency, includes controlling the inverter to increase the output voltage amplitude by a second voltage step and the voltage frequency by a second frequency step. Specifically, if the controller does not detect an overcurrent signal within a third preset time period, it controls the inverter to perform a voltage boost and frequency boost operation. In each voltage boost and frequency boost operation, the output voltage amplitude and voltage frequency of the inverter increase by a second voltage step and a second frequency step, respectively. The second voltage step and the second frequency step can be selected as needed, for example, the second voltage step is 1V and the second frequency step is 0.1Hz.

[0088] In this embodiment, if no overcurrent signal is detected within the third preset time period, it is considered that the motor load has been started and the load has become lighter. By boosting the voltage and frequency, the voltage amplitude and frequency output by the inverter can be restored to the rated voltage amplitude and the rated voltage frequency, thereby achieving stable start-up of the motor load.

[0089] This application also provides an off-grid energy storage system, including an inverter and a control device, wherein the inverter is connected to the control device and a load, and is used to execute the load adaptive start-up control method of the off-grid energy storage system in any of the foregoing embodiments.

[0090] The off-grid energy storage system and its load adaptive start-up control method are disclosed in this application. When the number of times the controller detects the overcurrent signal is less than a preset number, it indicates a lighter load, such as a resistive load or a typical household load. The inverter's current output voltage amplitude and frequency are the rated voltage amplitude and frequency. The inverter controller starts the load based on the current output voltage amplitude and frequency without interruption or delayed start-up. When the accumulated value reaches the preset number, it indicates a heavier load, such as a motor load. The controller performs a voltage and frequency reduction operation. After the voltage and frequency reduction operation is completed, it continues to check if the accumulated value has reached the preset value. If the accumulated value still reaches the preset number, the voltage and frequency reduction operation continues, repeating this process until the accumulated value is less than the preset number. When the motor load becomes lighter and no overcurrent signal is detected within a third preset time period, a voltage and frequency boost operation is performed until the inverter's output voltage amplitude and frequency return to the rated voltage amplitude and frequency. This load adaptive start control method and off-grid energy storage system can adaptively and stably start motor loads, ordinary household loads and resistive loads without the need for external auxiliary equipment. It can ensure smooth and reliable start-up of various loads without increasing the inverter's overload capacity. In various complex load environments, it can ensure the stable operation of the inverter, thereby improving the load adaptability and economy of the energy storage system. It can also reduce external components, simplify wiring, and facilitate installation and maintenance.

[0091] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the present application as defined by the appended claims.

[0092] Furthermore, the scope of this application is not limited to the specific embodiments of the processes, machines, manufactures, compositions of matter, methods, and steps described herein. Those skilled in the art will readily understand from the disclosure of this application that, according to this application, currently existing or to be developed processes, machines, manufactures, compositions of matter, methods, or steps that perform substantially the same function or achieve substantially the same results as the corresponding embodiments described herein can be utilized. Therefore, it is intended that the appended claims encompass such processes, machines, manufactures, compositions of matter, methods, or steps within their scope.

Claims

1. A load adaptive start-up control method for an off-grid energy storage system, characterized in that, The energy storage system includes an inverter and a control device, wherein the inverter is connected to the load and the control device; The method includes the following steps: S1: When the inverter enters the off-grid operation mode, the inverter is controlled to operate at the rated voltage amplitude and rated voltage frequency, so that the voltage amplitude output by the inverter is the rated voltage amplitude and the voltage frequency is the rated voltage frequency. S2: Sample the output current of the inverter in real time and output a current signal, and generate an overcurrent signal when the peak value of the current signal reaches a preset value; S3: Start timing for the first preset duration and detect the overcurrent signal; S4: Within the first preset time period, the cumulative number of times the overcurrent signal is detected is accumulated, and a cumulative value is obtained; S5: Determine whether the cumulative value has reached the preset number of times. If yes, proceed to step S6. If no, return to step S3 when the first preset time ends. S6: Control the inverter to reduce the voltage amplitude and voltage frequency output by the inverter; S7: Determine whether the reduced voltage amplitude has reached the minimum voltage value and whether the reduced voltage frequency has reached the minimum frequency value. If yes, control the inverter to operate at the minimum voltage value and the minimum frequency value and enter the protection state. If no, return to step S3. Before step S3, the step-down flag bit is initialized by setting it to 0; Step S3, starting the timing for the first preset duration, includes timing the first preset duration using a timer counter; In step S4, the cumulative number of times the overcurrent signal is detected within the first preset time period is accumulated to obtain the cumulative value, including the cumulative number of times the overcurrent signal is detected within the first preset time period and when the buck flag is 0. If the condition in step S5 is true, then step S6 is executed, including setting the step-down flag to 1, executing step S6, and then clearing both the accumulated value and the timer counter; or setting the step-down flag to 1, clearing both the accumulated value and the timer counter, and then executing step S6. If no in step S7, return to step S3, including setting the voltage reduction flag to 0 and returning to step S3 if no.

2. The load adaptive start-up control method for off-grid energy storage systems according to claim 1, characterized in that, Step S6 involves controlling the inverter to reduce the voltage amplitude and frequency output by the inverter, including controlling the inverter to reduce the voltage amplitude by a first voltage step and the voltage frequency by a first frequency step.

3. The load adaptive start-up control method for off-grid energy storage systems according to claim 1, characterized in that, Step S5 involves returning to step S3 when the first preset duration ends, including resetting the timer and the accumulated value to zero when the first preset duration ends, and then returning to step S3.

4. The load adaptive start-up control method for off-grid energy storage systems according to claim 1, characterized in that, Step S6 involves controlling the inverter to reduce the voltage amplitude and frequency output by the inverter, including starting a second preset time period and controlling the inverter to reduce the voltage amplitude and frequency output by the inverter at the end of the second preset time period.

5. The load adaptive start-up control method for off-grid energy storage systems according to claim 4, characterized in that, Start timing for the second preset duration, including timing the second preset duration via a delay counter; If the error in step S7 is not found, then return to step S3, including if the error is not found, then clear the delay counter and return to step S3.

6. The load adaptive start-up control method for off-grid energy storage systems according to claim 1, characterized in that, The minimum frequency value is the rated voltage frequency minus the preset frequency offset.

7. The load adaptive start-up control method for off-grid energy storage systems according to claim 1, characterized in that, It also includes the following steps: S8: When the overcurrent signal is not detected, start timing for a third preset duration, and determine whether the overcurrent signal is detected within the third preset duration; S9: If the overcurrent signal is not detected at the end of the third preset time period, determine whether the voltage amplitude of the inverter output reaches the rated voltage amplitude and whether the voltage frequency reaches the rated voltage frequency. If yes, control the inverter to operate at the rated voltage amplitude and the rated voltage frequency. If no, control the inverter to increase the voltage amplitude and voltage frequency of the inverter and return to step S3.

8. The load adaptive start-up control method for off-grid energy storage systems according to claim 7, characterized in that, Step S9 involves controlling the inverter to increase its voltage amplitude and voltage frequency, including controlling the inverter to increase the voltage amplitude output by the inverter by a second voltage step and the voltage frequency by a second frequency step.

9. The load adaptive start-up control method for off-grid energy storage systems according to claim 7, characterized in that, The start of timing for the third preset duration in step S8 includes timing for the third preset duration using a continuous counter; The load adaptive start-up control method for the off-grid energy storage system further includes clearing the continuous counter to zero and returning to step S3 when the overcurrent signal is detected.

10. The load adaptive start-up control method for an off-grid energy storage system according to claim 9, characterized in that, Step S9 involves controlling the inverter to increase its voltage amplitude and frequency, and then returning to step S3. This includes controlling the inverter to increase its voltage amplitude and frequency, clearing the continuous counter, and then returning to step S3.

11. The load adaptive start-up control method for an off-grid energy storage system according to claim 1, characterized in that, Step S2 involves sampling the inverter's output current in real time and outputting a current signal, and generating an overcurrent signal when the peak value of the current signal reaches a preset value. Specifically, this includes the following steps: S21: Sample the output current of the inverter in real time and output a current signal representing the magnitude of the output current; S22: Compare the current signal with the preset value, and generate the overcurrent signal when the peak value of the current signal reaches the preset value.

12. An off-grid energy storage system, characterized in that, include: Inverter, connected to the load; A control device, connected to the inverter, is used to execute the load adaptive start-up control method for an off-grid energy storage system as described in any one of claims 1 to 11.

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