Control method and system of energy storage converter under unbalanced power grid voltage

Abstract

The invention relates to the technical field of energy storage converter control, and particularly discloses a control method and system of an energy storage converter under an unbalanced power grid voltage, and the method comprises the steps: analyzing the stability characteristics of a power grid and the state of power grid energy storage equipment under the unbalanced power grid voltage; whether the energy storage converter needs to be controlled or not is judged, a power grid fault response threshold value is determined, whether the energy storage converter needs to be switched to a fault mode or not is judged, meanwhile, a three-phase voltage signal is converted into a direct-current component through synchronous coordinate transformation, and positive-sequence and negative-sequence components are separated out through the positive-sequence and negative-sequence component extraction technology; the method solves the problems that a traditional control method lacks robustness to uncertain factors and a dynamic environment, is often a fixed control strategy and is difficult to carry out self-adaptive adjustment according to the condition change of a power grid, ensures that the response of the energy storage converter adapts to the change condition of the power grid, and improves the stability of the power grid. The power quality of the power grid is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage converter control, and in particular to a control method and system for an energy storage converter under an unbalanced grid voltage. Background Art

[0002] The energy storage converter has a bidirectional power conversion function, that is, it can absorb electric energy from the grid to charge the energy storage system, and can also transmit the electric energy of the energy storage system to the grid. At the same time, the energy storage converter can realize independent control of active and reactive power. Under unbalanced grid conditions, by accurately controlling the active and reactive output of the energy storage converter, the three-phase voltage and current can be effectively balanced, and the impact of imbalance on the grid can be alleviated. With the large-scale access of renewable energy (such as wind power and photovoltaics), the imbalance problem of the grid has become increasingly serious. Renewable energy generation is intermittent and volatile, which can easily cause asymmetry of grid voltage and lead to three-phase imbalance in the grid. The randomness of the load and the asynchronous access of distributed energy may also cause grid imbalance. The imbalance of the grid will increase line losses, reduce grid efficiency, affect the safe operation of equipment, cause voltage fluctuations, and reduce power supply reliability. In severe cases, it will cause power outages. Through appropriate control strategies, the imbalance problem can be alleviated and the operation efficiency and stability of the grid can be improved.

[0003] Nowadays, there are still some deficiencies in the research on the control of energy storage inverters under unbalanced grid voltage. Specifically, the traditional control methods lack robustness to uncertain factors and dynamic environments. In practical applications, factors such as load fluctuations and distributed power supply fluctuations will cause the grid conditions to change continuously. Under these conditions, traditional control strategies show response lag or large errors. In addition, traditional control methods are often fixed control strategies, which are difficult to adaptively adjust according to changes in grid conditions, and have limited ability to improve power quality. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a control method and system for an energy storage converter under an unbalanced grid voltage, which can effectively solve the problems involved in the above-mentioned background technology.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A first aspect of the present invention provides a control method for an energy storage converter under an unbalanced grid voltage, comprising the following steps: Based on the power grid monitoring cycle stored in the database, the power grid stability characteristics under the unbalanced power grid voltage are analyzed to obtain the power grid stability characteristic determination factor; Based on the grid energy storage device status data and the grid stability characteristic determination factor, the grid energy storage device status under the unbalanced grid voltage is analyzed to obtain the energy converter control determination factor. According to the energy converter control determination factor, it is determined whether the energy storage converter needs to be controlled and the grid fault response threshold is determined: If the energy storage converter does not need to be controlled, it will enter the next cycle of grid monitoring; If the energy storage converter needs to be controlled, the grid fault characteristics under the unbalanced grid voltage are analyzed, and combined with the grid fault response threshold, it is determined whether the energy storage converter needs to be switched to the fault mode; In fault mode, the grid voltage under unbalanced grid voltage is monitored, the amplitude and phase of the grid voltage are obtained, the three-phase voltage signal is converted into DC component using synchronous coordinate transformation, the positive and negative sequence components are separated from the DC component using positive and negative sequence component extraction technology, and the positive and negative sequence component adjustment schemes are determined.

[0006] As a further method, the grid stability characteristics under unbalanced grid voltage are analyzed to obtain grid stability characteristic determination factors. The specific analysis process is: obtaining grid stability characteristic data, the grid stability characteristic data specifically includes grid voltage imbalance, grid voltage drop event frequency, and grid voltage fluctuation frequency; based on the acquired grid stability characteristic data, a comprehensive analysis is performed to obtain a grid stability characteristic determination factor, and the grid stability characteristic determination factor is used as an analysis basis for determining whether the energy storage converter needs to be controlled and determining the grid fault response threshold.

[0007] As a further method, the state of the grid energy storage device under the unbalanced grid voltage is analyzed based on the grid energy storage device state data and the grid stability characteristic determination factor to obtain the energy converter control determination factor, which specifically includes: Obtaining grid energy storage equipment status data, which specifically includes the ratio of battery capacity to rated capacity, the cumulative number of battery charge and discharge cycles, and the output power factor of the energy storage converter; Based on the acquisition of grid energy storage equipment status data and combined with the grid stability characteristic determination factor, a comprehensive analysis is conducted to obtain the energy storage converter control determination factor, which serves as the analysis basis for determining whether the energy storage converter needs to be controlled and determining the grid fault response threshold.

[0008] As a further method, the energy storage converter is judged whether it needs to be controlled and the grid fault response threshold is determined according to the energy converter control determination factor. The specific analysis process is: comparing the energy storage converter control determination factor with the energy storage converter control determination threshold stored in the database; If the energy storage converter control determination factor is not lower than the energy storage converter control determination threshold, the energy storage converter does not need to be controlled and enters the next cycle of grid monitoring; If the energy storage converter control determination factor is lower than the energy storage converter control determination threshold, the energy storage converter needs to be controlled, and the energy storage converter control determination factor is stored as a designated tag. The designated tag is compared one by one with each set tag stored in the database to determine the set tag that is the same as the designated tag, and the corresponding power grid fault response threshold stored in the database is obtained.

[0009] As a further method, the energy storage converter control determination factor, the specific analysis process is: ; In the formula, is the energy storage converter control decision factor, is the power grid stability characteristic determination factor, is the ratio of battery capacity to rated capacity, The cumulative number of battery charge and discharge cycles. is the output power factor of the energy storage converter, For setting The compensation factor, For setting The compensation factor, For setting compensation factor.

[0010] As a further method, the grid fault characteristics under unbalanced grid voltage are analyzed. The specific analysis process is: obtaining grid fault characteristic data, the grid fault characteristic data specifically includes the duration of grid voltage drop, the total harmonic distortion rate of the grid, and the ratio of the grid voltage swell value to the rated voltage; based on the obtained grid fault characteristic data, a comprehensive analysis is performed to obtain a grid fault response factor, and the grid fault response factor is used as an analysis basis for determining whether the energy storage converter needs to switch to the fault mode.

[0011] As a further method, combined with the grid fault response threshold, it is determined whether the energy storage converter needs to switch to the fault mode. The specific analysis process is: compare the grid fault response factor with the grid fault response threshold; if the grid fault response factor is not lower than the grid fault response threshold, the energy storage converter corresponding to the grid fault response factor does not need to switch to the fault mode; if the grid fault response factor is lower than the grid fault response threshold, the energy storage converter corresponding to the grid fault response factor needs to switch to the fault mode.

[0012] As a further method, the amplitude and phase of the grid voltage are obtained, and the three-phase voltage signal is converted into a DC component using synchronous coordinate transformation. The specific analysis process is: collect the three-phase voltage signal of the grid, obtain the instantaneous amplitude of the three-phase voltage and grid phase , Represents the instantaneous value of phase A voltage, represents the instantaneous value of phase B voltage, Represents the instantaneous value of phase C voltage, and the three-phase balance condition is: ; The three-phase voltage signal is transformed using Clarke transform and Park transform. Transform to the dq rotating coordinate system: Clarke transformation converts three-phase voltage signals into stationary Coordinate system; ; ; for The shaft voltage component, for Shaft voltage component; The Park transformation The voltage components in the coordinate system are converted to synchronously rotating Rotate the coordinate system; ; ; for The shaft voltage component, for Shaft voltage component; exist In the rotating coordinate system, the grid voltage signal is regarded as a DC component. Under balanced conditions and Shows a constant value.

[0013] As a further method, the positive and negative sequence components are separated by using the positive and negative sequence component extraction technology to determine the positive and negative sequence component adjustment schemes. The specific analysis process is as follows: In the rotating coordinate system, based on the low-pass filter and Perform low-pass filtering to extract the positive-sequence d-axis voltage component , positive sequence q-axis voltage component ; Will The rotating coordinate system is converted to the inverse synchronous rotating coordinate system, that is, based on the rotation frequency −𝜔 of the negative sequence component, the low-pass filter is used to transform the inverse synchronous rotating coordinate system and Perform low-pass filtering to extract the negative-sequence d-axis voltage component and the negative sequence q-axis voltage component ; The process of determining the positive sequence component regulation scheme is: Active power control: Get the active power reference value stored in the database ; ; is the positive sequence d-axis current reference value; Use the PI controller to convert the current d-axis current and Compare and generate d-axis current control signal To regulate active power output; Reactive power control: Get reactive power reference value stored in database ; ; is the positive sequence q-axis current reference value; Use the PI controller to convert the current q-axis current and Compare and generate q-axis current control signal To regulate reactive power output; The process of determining the negative sequence component regulation scheme is: Negative sequence current compensation: To balance the grid current, the negative sequence d-axis current component and the q-axis current component Set as a goal; Use the PI controller to convert the current negative sequence d-axis current component and the negative sequence q-axis current component Compared with the target, the control output negative sequence d-axis current control signal is obtained and negative sequence q-axis current control signal , generate compensation current and suppress negative sequence current; Negative sequence voltage compensation: To reduce the impact of negative sequence voltage, the negative sequence d-axis voltage component and the q-axis voltage component Set as a goal; Use the PI controller to convert the current negative sequence d-axis voltage component and the negative sequence q-axis voltage component Compared with the target, the control output negative sequence d-axis voltage control signal is obtained and negative sequence q-axis voltage control signal , adjust the output voltage to achieve voltage balance.

[0014] A second aspect of the present invention provides a control system for an energy storage converter under an unbalanced grid voltage, comprising a stability characteristic determination factor acquisition module, an energy storage converter control determination module, and a positive and negative sequence component adjustment scheme determination module, wherein: The stability characteristic determination factor acquisition module is used to analyze the grid stability characteristics under the unbalanced grid voltage based on the grid monitoring cycle stored in the database to obtain the grid stability characteristic determination factor; The energy storage converter control judgment module is used to analyze the state of the grid energy storage device under the unbalanced grid voltage based on the grid energy storage device state data and the grid stability characteristic judgment factor, obtain the energy converter control judgment factor, and judge whether the energy storage converter needs to be controlled and determine the grid fault response threshold according to the energy converter control judgment factor: If the energy storage converter does not need to be controlled, it will enter the next cycle of grid monitoring; If the energy storage converter needs to be controlled, the grid fault characteristics under the unbalanced grid voltage are analyzed, and combined with the grid fault response threshold, it is determined whether the energy storage converter needs to be switched to the fault mode; The positive- and negative-sequence component regulation scheme determination module is used to monitor the grid voltage under the unbalanced grid voltage in a fault mode, obtain the amplitude and phase of the grid voltage, use synchronous coordinate transformation to convert the three-phase voltage signal into a DC component, use the positive- and negative-sequence component extraction technology to separate the positive- and negative-sequence components from the DC component, and determine the positive- and negative-sequence component regulation schemes.

[0015] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: (1) The present invention provides a control method and system for energy storage converters under unbalanced grid voltage, periodically analyzes grid stability characteristics, extracts and analyzes grid stability characteristic data, and can timely identify voltage imbalance, voltage fluctuation and other problems in the grid. The grid stability characteristic determination factor can help quickly identify potential imbalance or fluctuation trends, thereby issuing early warnings. By analyzing the grid stability characteristics, a more accurate determination factor can be obtained. According to the actual fluctuation of the grid and the state of the energy storage device, the grid fault response threshold is adjusted in real time to ensure that the response of the energy storage converter adapts to the changes in the grid, enhance the flexibility of the control strategy, provide active and reactive power support by adjusting the positive sequence component, and stabilize the grid voltage; suppress the voltage imbalance of the grid by adjusting the negative sequence component and reduce the negative sequence component of the current. This can effectively improve the power quality of the grid and reduce the impact on electrical equipment.

[0016] (2) The present invention analyzes the state of the grid energy storage device under the unbalanced grid voltage, and combines the grid stability characteristic determination factor to determine whether the energy storage converter needs to be controlled and determine the grid fault response threshold. The state of the energy storage device directly affects its regulation capability. By analyzing the state of the energy storage device, the energy storage converter can more accurately determine when and to what extent to intervene in the control, avoid blind regulation, and ensure system stability. Combined with the grid stability characteristic determination factor, the energy storage converter can dynamically adjust the control requirements according to the actual imbalance degree of the grid, ensure fast and accurate regulation response, and help provide accurate support when the grid fluctuates. In combination with the energy storage device state and the grid characteristic determination factor, the grid fault response threshold can be dynamically adjusted, and the control requirements can be flexibly determined. The energy storage converter can more effectively regulate the grid voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is further described using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention. A person skilled in the art can obtain other drawings based on the following drawings without creative work.

[0018] Figure 1 It is a flow chart of a control method of the energy storage converter of the present invention under an unbalanced grid voltage.

[0019] Figure 2 The diagram is a schematic diagram of module connections of a control system of an energy storage converter of the present invention under an unbalanced grid voltage.

[0020] Figure 3 This is a flow chart for determining whether the energy storage converter needs to switch to a fault mode in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] Reference Figure 1 As shown, the first aspect of the present invention provides a control method for an energy storage converter under an unbalanced grid voltage, comprising: based on a grid monitoring cycle stored in a database, analyzing grid stability characteristics under an unbalanced grid voltage to obtain a grid stability characteristic determination factor.

[0023] The specific analysis process is as follows: obtaining grid stability characteristic data, which specifically includes grid voltage imbalance, grid voltage drop event frequency, and grid voltage fluctuation frequency; based on the obtained grid stability characteristic data, a comprehensive analysis is performed to obtain a grid stability characteristic determination factor, which is used as an analysis basis for determining whether the energy storage converter needs to be controlled and determining the grid fault response threshold.

[0024] Voltage imbalance refers to the degree of asymmetry of the three-phase voltage amplitude or phase in the power grid, expressed as the ratio of negative sequence voltage to positive sequence voltage. Voltage imbalance is generally obtained through power quality analyzers or smart substation monitoring equipment. Voltage sag refers to the phenomenon that the voltage drops to between 10% and 90% of the rated voltage in a short period of time. The frequency of voltage sag events indicates the number of times the voltage sag occurs in the power grid within a certain period of time. The frequency of voltage sag events can be obtained through voltage monitors, power quality monitoring devices or distribution automation terminals. Voltage fluctuation frequency indicates the number of periodic or non-periodic fluctuations of the power grid voltage near the rated voltage. The voltage fluctuation frequency is generally obtained by power quality monitors or flicker meters.

[0025] In a three-phase power grid, when the voltage imbalance is high, the voltage of one phase may be affected by excessive load or fault, causing the voltage to temporarily drop or fluctuate, thereby increasing the frequency of voltage drop events. When a voltage drop occurs in the power grid, especially a single-phase or two-phase voltage drop in a three-phase system, it is easy to cause three-phase asymmetry, resulting in an increase in voltage imbalance. Voltage imbalance can cause asymmetry in current and voltage, leading to increased volatility. For example, if the access and separation of loads in the power grid are asymmetric in the three phases, it will cause frequent voltage fluctuations. Therefore, when the voltage imbalance increases, the frequency of voltage fluctuations will also increase accordingly. The occurrence of voltage drop events will cause the voltage to drop and recover suddenly, causing short-term voltage fluctuations. When the voltage drop frequency is high, the voltage fluctuation frequency will also increase, which is manifested as increased voltage instability.

[0026] The grid voltage imbalance, the frequency of voltage drop events, and the frequency of voltage fluctuations reflect the true stability of the grid. The determination factors analyzed based on these characteristic data can accurately identify whether the grid is in an unstable state, thereby providing a reliable basis for whether the energy storage converter should be controlled. Through the comprehensive analysis of multi-dimensional data, it is possible to avoid misjudgments caused by fluctuations in a single indicator, improve the accuracy of identifying unstable grid conditions, and ensure that the energy storage converter intervenes only when necessary.

[0027] Based on comprehensive feature analysis, the control strategy of the energy storage converter can be intelligentized, the fault response threshold can be dynamically set according to the judgment factor, and the protection mechanism of the energy storage converter can be flexibly adjusted according to the severity and frequency of the fault. The judgment factor obtained based on the comprehensive feature data analysis can realize automatic judgment and control, which helps to simplify the operation process of the energy storage converter and improve the automation level of power grid dispatching and energy storage system management.

[0028] The specific analysis process of determining the grid stability characteristics is as follows: ; In the formula, is the power grid stability characteristic determination factor, is the grid voltage unbalance, is the frequency of grid voltage drop events, is the grid voltage fluctuation frequency, For setting The compensation factor, For setting The compensation factor, For setting The compensation factor, is a natural constant.

[0029] It should be explained that the above-mentioned grid stability characteristic determination factor is calculated through the grid voltage imbalance, grid voltage drop event frequency, and grid voltage fluctuation frequency. After normalization, the voltage imbalance, voltage drop frequency and voltage fluctuation frequency reflect the health of the power grid from the aspects of power grid symmetry, steady-state stability and transient stability, which can more comprehensively measure the overall stability of the power grid and avoid misjudgment caused by a single indicator. By integrating different power grid characteristic data to form a determination factor, a data-driven stability assessment method can be formed, which is helpful to realize the automated management of smart grids and reduce human intervention. The calculated power grid stability characteristic determination factor can be used as a decision-making basis for energy storage converter control, ensuring voltage stability and power grid stability, and improving power supply reliability.

[0030] It should be explained that the above setting The compensation factor is obtained from the database, and the historical measured grid voltage imbalance, grid voltage drop event frequency, grid voltage fluctuation frequency and The mapping set of compensation factors is obtained Corresponding compensation factor.

[0031] It should be noted that the following They are also obtained through a mapping set of historical data and compensation factors established in a database, that is, the corresponding compensation factors are obtained according to the current data.

[0032] Based on the grid energy storage device status data and the grid stability characteristic determination factor, the grid energy storage device status under the unbalanced grid voltage is analyzed to obtain the energy converter control determination factor. According to the energy converter control determination factor, it is determined whether the energy storage converter needs to be controlled and the grid fault response threshold is determined: if the energy storage converter does not need to be controlled, the grid monitoring of the next cycle is entered; if the energy storage converter needs to be controlled, the grid fault characteristics under the unbalanced grid voltage are analyzed, combined with the grid fault response threshold, such as Figure 3 As shown, it is determined whether the energy storage converter needs to be switched to a fault mode.

[0033] The specific analysis process is as follows: obtaining the status data of the grid energy storage equipment, which specifically includes the ratio of battery capacity to rated capacity, the cumulative number of battery charge and discharge cycles, and the output power factor of the energy storage converter; based on the acquisition of the grid energy storage equipment status data and the grid stability characteristic determination factor, a comprehensive analysis is performed to obtain the energy storage converter control determination factor, which is used as the analysis basis for determining whether the energy storage converter needs to be controlled and determining the grid fault response threshold.

[0034] The ratio of battery capacity to rated capacity indicates the percentage of the current remaining battery capacity to the rated capacity. It is used to evaluate the remaining life and health status of the battery and is obtained through the battery management system (BMS). The cumulative number of battery charge and discharge cycles indicates the cumulative number of charge and discharge times of the battery and is an important indicator of battery aging. It is obtained through the battery management system (BMS). The output power factor of the energy storage converter indicates the ratio of the active power and apparent power of the output current of the energy storage converter, indicating the output efficiency. It is obtained through the power converter control system (PCS) or power quality monitor.

[0035] After multiple charge and discharge cycles, the battery will gradually age, resulting in capacity decay. The more cycles, the lower the actual capacity of the battery (i.e., the current available capacity), which reduces the ratio of the battery capacity to the rated capacity. There is a negative correlation between the number of cycles and the capacity ratio. An increase in the number of cycles will lead to a decrease in the capacity ratio. The higher the ratio of the battery capacity to the rated capacity, the greater the available capacity of the battery. At this time, the energy storage system has a higher power output capacity, and the energy storage inverter can better control the output power factor and achieve a higher coordination of active power and reactive power. When the capacity ratio decreases, the available capacity of the battery is insufficient, and the energy storage inverter will be limited while meeting the active power output demand, which may lead to a decrease in the ability to compensate for reactive power, thereby affecting the power factor.

[0036] The output power factor of the energy storage converter can be used as a basis for judging its output characteristics. If the power factor is too low, it means that the reactive power output is high, which may affect the stability of the system. By combining the power factor data, it can be ensured that the output of the converter meets the needs of the power grid. In the case of low capacity or high number of cycles, the energy storage device can avoid unnecessary control, reduce the load of the equipment, effectively extend the battery life, and optimize the use of energy storage equipment. The output power factor combined with the grid characteristic determination factor can effectively help identify whether the grid needs reactive support. The energy storage converter can provide reactive power in a timely manner at low power factors, improve the voltage stability of the grid, and thus ensure the power supply quality of the grid. According to the fault response threshold set by the control determination factor, the energy storage converter can flexibly adjust and respond at multiple levels when different degrees of faults occur in the grid.

[0037] The energy storage converter control determination factor is compared with the energy storage converter control determination threshold stored in the database; if the energy storage converter control determination factor is not lower than the energy storage converter control determination threshold, the energy storage converter does not need to be controlled and enters the next cycle of power grid monitoring; if the energy storage converter control determination factor is lower than the energy storage converter control determination threshold, the energy storage converter needs to be controlled, and the energy storage converter control determination factor is stored as a designated label, and the designated label is compared one by one with each set label stored in the database to determine the set label that is the same as the designated label, and obtain the corresponding power grid fault response threshold stored in the database for the set label.

[0038] By comparing the energy storage converter control determination factor with the preset control determination threshold, it is possible to accurately determine whether the energy storage converter needs to intervene in the control, ensuring that the adjustment is only started when the grid is unbalanced or fluctuates beyond a certain level, avoiding unnecessary actions. By automatically judging and comparing the thresholds, the energy storage converter control is started only when necessary, avoiding frequent charging and discharging operations, reducing energy consumption and equipment wear, and extending the service life of the energy storage equipment. Each time the control determination factor is lower than the control determination threshold, the appropriate fault response threshold under the current conditions is automatically found through label comparison to ensure response accuracy and timeliness. The solution ensures that the control action of the energy storage converter is highly matched with the grid imbalance or fluctuation level, preventing grid voltage fluctuations caused by excessive response, and further improving the stability and power quality of the grid.

[0039] Specifically, the energy storage converter control determination factor, the specific analysis process is: ; In the formula, is the energy storage converter control decision factor, is the power grid stability characteristic determination factor, is the ratio of battery capacity to rated capacity, The cumulative number of battery charge and discharge cycles. is the output power factor of the energy storage converter, For setting The compensation factor, For setting The compensation factor, For setting compensation factor.

[0040] It should be explained that the above energy storage converter control determination factor is calculated by the ratio of battery capacity to rated capacity, the cumulative number of battery charge and discharge cycles, the output power factor of the energy storage converter and the grid stability characteristic determination factor. After normalization, the battery capacity ratio, cycle number and power factor represent the battery health status, service life and output efficiency respectively, while the grid stability characteristic determination factor reflects the operating status of the grid. By integrating these factors to calculate the determination factor, the energy storage inverter can obtain comprehensive information on the battery status and grid status, thereby making more accurate control decisions.

[0041] The battery capacity ratio and the cumulative number of charge and discharge cycles reflect the health of the battery. Combined with the determination factor of grid demand, it can help determine whether to reduce the frequency of use when the battery is in poor condition, avoid frequent operation when the battery is inefficient or seriously attenuated, and improve the overall work efficiency of the system. Combined with the determination factor of grid stability characteristics, the energy storage inverter control determination factor can flexibly adjust the control strategy of the energy storage system according to the fluctuation of the grid, and support the optimized scheduling of the smart grid.

[0042] The grid fault characteristic data is obtained, and the grid fault characteristic data specifically includes the duration of the grid voltage drop, the total harmonic distortion rate of the grid, and the ratio of the grid voltage surge value to the rated voltage. Based on the obtained grid fault characteristic data, a comprehensive analysis is performed to obtain the grid fault response factor, which is used as an analysis basis for determining whether the energy storage converter needs to switch to the fault mode.

[0043] The duration of voltage sag refers to the duration of the grid voltage being lower than a certain percentage of the rated voltage within a certain period of time. The duration of grid voltage sag is usually obtained by a power quality analyzer or voltage monitor. The total harmonic distortion rate of the grid (is an indicator to measure the ratio of harmonic components to fundamental components in voltage or current. The total harmonic distortion rate of voltage is defined as the ratio of the root mean square value of all harmonic components to the root mean square value of the fundamental component. The total harmonic distortion rate is obtained by a power quality monitor or harmonic analyzer. The ratio of the grid voltage swell value to the rated voltage refers to the ratio of the voltage to a certain multiple of the rated voltage, which is usually called voltage swell. The voltage swell ratio is usually obtained by power quality monitoring equipment or voltage monitors.

[0044] Voltage sags are usually accompanied by system load instability, especially when there are a large number of power electronic devices (such as inverters, rectifiers) or nonlinear loads in the power grid. Voltage sags can cause fluctuations in the operating state of power equipment, generate additional harmonic currents, and increase the total harmonic distortion rate. Voltage sags and voltage swells usually occur alternately after load switching, large load start / stop, or fault clearance. When a voltage sag occurs in one or more phases of the power grid (such as a short circuit fault), a short-term voltage swell may occur during the recovery process. If the voltage sag lasts for a long time, the possibility of voltage swell will also increase.

[0045] Characteristic data such as voltage drop duration, total harmonic distortion rate, and voltage surge value can reflect the extent of grid faults. Comprehensive analysis of these data and the resulting fault response factor can accurately determine the severity of the fault, thereby ensuring that the response decision of the energy storage converter is based on the actual grid conditions. When the grid fault reaches a certain level, the grid fault response factor can trigger the energy storage converter to enter fault mode, immediately reduce output or cut off the connection, avoid equipment overload or damage, and protect the safety of the energy storage system. Abnormalities in the total harmonic distortion rate and voltage surge of the grid usually affect the power quality. The energy storage converter can switch to fault mode according to the fault response factor when the harmonics and voltage are seriously abnormal, thereby avoiding the equipment from delivering bad power to the grid and reducing interference with other grid equipment. When a fault occurs, the fault response factor can help the energy storage converter quickly switch to fault mode, reduce response delays, ensure that protection measures are taken in the shortest time, and support automated fault identification and protection triggering.

[0046] Grid fault response factor, the specific analysis process is: ; In the formula, is the power grid fault response factor, is the duration of grid voltage drop, is the total harmonic distortion rate of the power grid, is the ratio of the grid voltage surge value to the rated voltage, For setting The compensation factor, For setting The compensation factor, For setting compensation factor.

[0047] It should be explained that the above-mentioned grid fault response factor is calculated by the duration of grid voltage drop, total harmonic distortion rate of grid, and the ratio of grid voltage surge value to rated voltage. After normalization, the voltage sag duration, voltage swell and total harmonic distortion rate reflect the instantaneous voltage anomaly and power quality status of the power grid respectively, which can comprehensively evaluate the fault degree of the power grid and avoid misjudgment caused by a single indicator. By calculating the fault response factor by combining multiple indicators, misjudgment can be avoided and the response factor can be made more stable and accurate.

[0048] When the fault response factor is lower than a certain threshold, the energy storage system can enter the fault protection mode. By judging the size of the factor, it is determined whether the protection response needs to be triggered, thereby ensuring the safety of the energy storage system and the power grid. The protection is triggered only when the comprehensive fault response factor exceeds the safety threshold, avoiding the energy storage converter from frequently switching to the fault mode, which helps to improve the stability and durability of the equipment. Voltage drops and sudden increases often cause shocks to power equipment. Through timely monitoring and response to the fault response factor, the energy storage system can be triggered to respond when the voltage is abnormal, reducing the voltage shock to the power equipment and extending the service life of the equipment.

[0049] The grid fault response factor is compared with the grid fault response threshold; if the grid fault response factor is not lower than the grid fault response threshold, the energy storage converter corresponding to the grid fault response factor does not need to be switched to the fault mode; if the grid fault response factor is lower than the grid fault response threshold, the energy storage converter corresponding to the grid fault response factor needs to be switched to the fault mode.

[0050] By setting the response threshold, it is possible to accurately determine whether the power grid is in a faulty or abnormal state, and avoid the energy storage converter from mistakenly entering the fault mode when the power grid fluctuation is not serious, thereby improving the accuracy of fault judgment and the response flexibility of the energy storage system. The comparison of the power grid fault response factor and the threshold enables the energy storage converter to dynamically adapt to different fault levels.

[0051] It does not enter fault mode in case of slight fluctuations, but quickly switches modes in case of serious faults, ensuring the intelligence and flexible response capabilities of the system. It switches to fault mode only when the grid fault response factor is lower than the threshold, avoiding frequent and unnecessary switching. Frequent switching of energy storage inverters will increase equipment wear and reduce its service life. Reasonable setting of the response factor can reduce the load on the equipment and increase its operating life. When the grid fault response factor is lower than the threshold, the energy storage inverter switches to fault mode and can respond immediately, providing the necessary support power to help the grid restore stability. For fault conditions such as voltage drops and overcurrents, the timely switching of energy storage inverters helps reduce the impact of fluctuations on the grid and improve the power quality and reliability of fault protection.

[0052] In fault mode, the grid voltage under unbalanced grid voltage is monitored, the amplitude and phase of the grid voltage are obtained, the three-phase voltage signal is converted into DC component using synchronous coordinate transformation, the positive and negative sequence components are separated using positive and negative sequence component extraction technology, and the positive and negative sequence component adjustment schemes are determined.

[0053] The specific analysis process is: collect the three-phase voltage signal of the power grid and obtain the instantaneous amplitude of the three-phase voltage and grid phase , Represents the instantaneous value of phase A voltage, represents the instantaneous value of phase B voltage, Represents the instantaneous value of phase C voltage, and the three-phase balance condition is: ; The three-phase voltage signal is transformed using Clarke transform and Park transform. Transform to the dq rotating coordinate system: Clarke transformation converts three-phase voltage signals into stationary Coordinate system; ; ; for The shaft voltage component, for Shaft voltage component; The Park transformation The voltage components in the coordinate system are converted to synchronously rotating Rotate the coordinate system; ; ; for The shaft voltage component, for Shaft voltage component; exist In the rotating coordinate system, the grid voltage signal is regarded as a DC component. Under balanced conditions and Shows a constant value.

[0054] In the dq rotating coordinate system, the three-phase voltage signal is converted into a constant DC component and ,The control and calculation of DC signals are simpler than those of AC signals, which facilitates the real-time power control of energy storage converters and simplifies the control process. The phase difference of the three-phase voltage signal is unified to the same coordinate system after coordinate transformation, so that the signal adjustment is no longer affected by the phase difference, which simplifies the calculation and improves the response speed and control accuracy. In the dq coordinate system, the d-axis and q-axis represent the active power component and reactive power component of the power grid respectively.

[0055] By controlling and , can realize independent regulation of active power and reactive power, under the condition of balanced power grid in dq rotating coordinate system and If the grid is unbalanced or disturbed, these components will fluctuate, which can be monitored and The voltage signal in the dq coordinate system shows a constant DC component in a balanced state. This characteristic can effectively suppress the influence of high-frequency harmonic components on power quality and improve the harmonic suppression capability of the system.

[0056] In the dq rotating coordinate system, the voltage signal becomes a DC component. The control system of the energy storage converter can respond more quickly to grid changes and achieve rapid dynamic control, meeting the requirements of smart grids for flexible control and rapid response. The dq coordinate system facilitates the extraction and separation of positive and negative sequence components in unbalanced grids, which provides a good foundation for advanced control strategies (such as unbalanced compensation and harmonic suppression).

[0057] exist In the rotating coordinate system, based on the low-pass filter and Perform low-pass filtering to extract the positive-sequence d-axis voltage component , positive sequence q-axis voltage component ; Will The rotating coordinate system is converted to the inverse synchronous rotating coordinate system, that is, based on the rotation frequency −𝜔 of the negative sequence component, the low-pass filter is used to transform the inverse synchronous rotating coordinate system and Perform low-pass filtering to extract the negative-sequence d-axis voltage component and the negative sequence q-axis voltage component .

[0058] The process of determining the positive sequence component regulation scheme is as follows: Active power control: Obtain the active power reference value stored in the database ; ; is the positive sequence d-axis current reference value; Use the PI controller to convert the current d-axis current and Compare and generate d-axis current control signal To regulate active power output; Reactive power control: Get reactive power reference value stored in database ; ; is the positive sequence q-axis current reference value; Use the PI controller to convert the current q-axis current and Compare and generate q-axis current control signal To adjust reactive power output.

[0059] The process of determining the negative sequence component regulation scheme is as follows: Negative sequence current compensation: In order to balance the grid current, the negative sequence d-axis current component and the q-axis current component Set as target; use PI controller to set the current negative sequence d-axis current component and the negative sequence q-axis current component Compared with the target, the control output negative sequence d-axis current control signal is obtained and negative sequence q-axis current control signal , generate compensation current and suppress negative sequence current; Negative sequence voltage compensation: In order to reduce the impact of negative sequence voltage, the negative sequence d-axis voltage component and the q-axis voltage component Set as target; use PI controller to set the current negative sequence d-axis voltage component and the negative sequence q-axis voltage component Compared with the target, the control output negative sequence d-axis voltage control signal is obtained and negative sequence q-axis voltage control signal , adjust the output voltage to achieve voltage balance.

[0060] Positive sequence component d-axis current Closely related to active power, by setting the positive sequence d-axis current reference value , which can accurately control the active power output. The PI controller compares the actual current with the reference value and generates a regulation signal , ensuring that the active power output meets the needs of the power grid and improving the stability and efficiency of power transmission.

[0061] Q-axis current of positive sequence component Used to adjust reactive power by setting reactive power reference value , which can meet the reactive power demand of the power grid and improve the stability of the power grid voltage. The reactive power regulation signal generated by the PI controller It helps to realize reactive power compensation and improve the voltage quality and power quality of the power grid. In the dq coordinate system, the negative sequence d-axis current reference value and q-axis current reference value , so that the negative sequence current disappears or is minimized.

[0062] The PI controller adjusts the signal and To suppress the negative sequence current, this reduces the asymmetric current in the power grid and effectively reduces the imbalance, thereby protecting the power equipment and improving the power quality. and q-axis voltage reference value The negative sequence voltage control signal generated by the PI controller is and It is used to eliminate the imbalance of negative sequence voltage, improve the voltage symmetry of the power grid, and make the electric energy more stable and reliable.

[0063] Negative sequence current and voltage will increase the loss of power equipment, causing additional heating and vibration in motors, transformers and other equipment, and accelerating the aging of equipment. By eliminating or suppressing the negative sequence component, the energy storage converter can reduce the additional loss of equipment, extend its service life, and reduce maintenance and replacement costs. Unbalanced power grids may cause current overload or voltage abnormalities in power equipment. Compensation for negative sequence current and voltage can prevent equipment from working in an unsafe state for a long time and ensure that power equipment operates stably within the rated parameter range.

[0064] Eliminating or reducing negative sequence current and voltage helps balance the power grid, especially under conditions of large-scale unbalanced loads. Compensation strategies can quickly restore the balance of the power grid and prevent further spread of fluctuations or instability in the power grid. When the power grid is unbalanced, negative sequence components will aggravate grid fluctuations and increase the risk of failure. By suppressing negative sequence components, these secondary faults can be prevented and the stable operation of the power grid can be ensured, especially for the power supply security of sensitive loads and important equipment. In the case of voltage fluctuations or sudden imbalances in the power grid, the energy storage converter can respond quickly based on the regulation scheme of positive and negative sequence components, provide stable active and reactive power support, realize timely compensation for the power grid, and improve the dynamic stability of the power grid.

[0065] Reference Figure 2 As shown, the second aspect of the present invention provides a control system for an energy storage converter under an unbalanced grid voltage, including a stability characteristic determination factor acquisition module, an energy storage converter control judgment module and a positive and negative sequence component adjustment scheme determination module.

[0066] The stability characteristic determination factor acquisition module is used to analyze the grid stability characteristics under the unbalanced grid voltage based on the grid monitoring cycle stored in the database to obtain the grid stability characteristic determination factor.

[0067] The energy storage converter control judgment module is used to analyze the state of the grid energy storage device under the unbalanced grid voltage based on the grid energy storage device state data and the grid stability characteristic judgment factor, obtain the energy converter control judgment factor, and judge whether the energy storage converter needs to be controlled and determine the grid fault response threshold according to the energy converter control judgment factor: if the energy storage converter does not need to be controlled, it enters the next cycle of grid monitoring; if the energy storage converter needs to be controlled, the grid fault characteristics under the unbalanced grid voltage are analyzed, and combined with the grid fault response threshold, it is judged whether the energy storage converter needs to switch to the fault mode.

[0068] The positive and negative sequence component regulation scheme determination module is used to monitor the grid voltage under unbalanced grid voltage in fault mode, obtain the amplitude and phase of the grid voltage, convert the three-phase voltage signal into a DC component using synchronous coordinate transformation, separate the positive and negative sequence components using positive and negative sequence component extraction technology, and determine the positive and negative sequence component regulation schemes.

[0069] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A control method for an energy storage converter under an unbalanced grid voltage, characterized in that: The following steps are involved: Based on the power grid monitoring cycle stored in the database, the power grid stability characteristics under the unbalanced power grid voltage are analyzed to obtain the power grid stability characteristic determination factor; Based on the grid energy storage device status data and the grid stability characteristic determination factor, the grid energy storage device status under the unbalanced grid voltage is analyzed to obtain the energy converter control determination factor. According to the energy converter control determination factor, it is determined whether the energy storage converter needs to be controlled and the grid fault response threshold is determined: If the energy storage converter does not need to be controlled, it will enter the next cycle of grid monitoring; If the energy storage converter needs to be controlled, the grid fault characteristics under the unbalanced grid voltage are analyzed, and combined with the grid fault response threshold, it is determined whether the energy storage converter needs to be switched to the fault mode; In fault mode, the grid voltage under unbalanced grid voltage is monitored, the amplitude and phase of the grid voltage are obtained, the three-phase voltage signal is converted into DC component using synchronous coordinate transformation, the positive and negative sequence components are separated from the DC component using positive and negative sequence component extraction technology, and the positive and negative sequence component adjustment schemes are determined.

2. The control method of the energy storage converter under unbalanced grid voltage according to claim 1, characterized in that: The grid stability characteristics under the unbalanced grid voltage are analyzed to obtain the grid stability characteristics determination factor. The specific analysis process is as follows: Obtaining grid stability characteristic data, the grid stability characteristic data specifically includes grid voltage imbalance, grid voltage drop event frequency, and grid voltage fluctuation frequency; Based on the acquired grid stability characteristic data, a grid stability characteristic determination factor is obtained through comprehensive analysis. The grid stability characteristic determination factor serves as an analysis basis for judging whether the energy storage converter needs to be controlled and determining the grid fault response threshold.

3. The control method of the energy storage converter under unbalanced grid voltage according to claim 1, characterized in that: The state of the grid energy storage device under the unbalanced grid voltage is analyzed based on the grid energy storage device state data and the grid stability characteristic determination factor to obtain the energy converter control determination factor, specifically including: Obtaining grid energy storage equipment status data, which specifically includes the ratio of battery capacity to rated capacity, the cumulative number of battery charge and discharge cycles, and the output power factor of the energy storage converter; Based on the acquisition of grid energy storage equipment status data and combined with the grid stability characteristic determination factor, a comprehensive analysis is conducted to obtain the energy storage converter control determination factor, which serves as the analysis basis for determining whether the energy storage converter needs to be controlled and determining the grid fault response threshold.

4. The control method of the energy storage converter under unbalanced grid voltage according to claim 1, characterized in that: The specific analysis process of judging whether the energy storage converter needs to be controlled and determining the grid fault response threshold according to the energy converter control determination factor is as follows: comparing the energy storage converter control determination factor with the energy storage converter control determination threshold stored in the database; If the energy storage converter control determination factor is not lower than the energy storage converter control determination threshold, the energy storage converter does not need to be controlled and enters the next cycle of grid monitoring; If the energy storage converter control determination factor is lower than the energy storage converter control determination threshold, the energy storage converter needs to be controlled, and the energy storage converter control determination factor is stored as a designated tag. The designated tag is compared one by one with each set tag stored in the database to determine the set tag that is the same as the designated tag, and the corresponding power grid fault response threshold stored in the database is obtained.

5. The control method of the energy storage converter under unbalanced grid voltage according to claim 4 is characterized in that: The specific analysis process of the energy storage converter control determination factor is as follows: ； In the formula, is the energy storage converter control decision factor, is the power grid stability characteristic determination factor, is the ratio of battery capacity to rated capacity, The cumulative number of battery charge and discharge cycles. is the output power factor of the energy storage converter, For setting The compensation factor, For setting The compensation factor, For setting compensation factor.

6. The control method of the energy storage converter under unbalanced grid voltage according to claim 1, characterized in that: The grid fault characteristics under unbalanced grid voltage are analyzed. The specific analysis process is as follows: Obtaining grid fault characteristic data, which specifically includes grid voltage drop duration, grid harmonic total distortion rate, and grid voltage surge value to rated voltage ratio; Based on the acquired grid fault characteristic data, a grid fault response factor is obtained through comprehensive analysis. The grid fault response factor is used as an analysis basis for determining whether the energy storage converter needs to switch to a fault mode.

7. The control method of the energy storage converter under unbalanced grid voltage according to claim 6 is characterized in that: The grid fault response threshold is combined to determine whether the energy storage converter needs to switch to the fault mode. The specific analysis process is as follows: comparing the power grid fault response factor with a power grid fault response threshold; If the grid fault response factor is not lower than the grid fault response threshold, the energy storage converter corresponding to the grid fault response factor does not need to switch to the fault mode; If the grid fault response factor is lower than the grid fault response threshold, the energy storage converter corresponding to the grid fault response factor needs to switch to the fault mode.

8. The control method of the energy storage converter under unbalanced grid voltage according to claim 1, characterized in that: The amplitude and phase of the grid voltage are obtained, and the three-phase voltage signal is converted into a DC component using synchronous coordinate transformation. The specific analysis process is as follows: Collect the three-phase voltage signal of the power grid and obtain the instantaneous amplitude of the three-phase voltage and grid phase , Represents the instantaneous value of phase A voltage, represents the instantaneous value of phase B voltage, Represents the instantaneous value of phase C voltage, and the three-phase balance condition is: ; The three-phase voltage signal is transformed using Clarke transform and Park transform. Transform to the dq rotating coordinate system: Clarke transformation converts three-phase voltage signals into stationary Coordinate system; ； ； for The shaft voltage component, for Shaft voltage component; The Park transformation The voltage components in the coordinate system are converted to synchronously rotating Rotate the coordinate system; ； ； for The shaft voltage component, for Shaft voltage component; exist In the rotating coordinate system, the grid voltage signal is regarded as a DC component. Under balanced conditions and Shows a constant value.

9. The control method of the energy storage converter under unbalanced grid voltage according to claim 8, characterized in that: The positive and negative sequence components are separated by using the positive and negative sequence component extraction technology, and the positive and negative sequence component adjustment schemes are determined. The specific analysis process is as follows: exist In the rotating coordinate system, based on the low-pass filter and Perform low-pass filtering to extract the positive-sequence d-axis voltage component , positive sequence q-axis voltage component ; Will The rotating coordinate system is converted to the inverse synchronous rotating coordinate system, that is, based on the rotation frequency −𝜔 of the negative sequence component, the low-pass filter is used to transform the inverse synchronous rotating coordinate system and Perform low-pass filtering to extract the negative-sequence d-axis voltage component and the negative sequence q-axis voltage component ; The process of determining the positive sequence component regulation scheme is: Active power control: Get the active power reference value stored in the database ; ； is the positive sequence d-axis current reference value; Use the PI controller to convert the current d-axis current and Compare and generate d-axis current control signal To regulate active power output; Reactive power control: Get reactive power reference value stored in database ; ； is the positive sequence q-axis current reference value; Use the PI controller to convert the current q-axis current and Compare and generate q-axis current control signal To regulate reactive power output; The process of determining the negative sequence component regulation scheme is: Negative sequence current compensation: To balance the grid current, the negative sequence d-axis current component and the q-axis current component Set as a goal; Use the PI controller to convert the current negative sequence d-axis current component and the negative sequence q-axis current component Compared with the target, the control output negative sequence d-axis current control signal is obtained and negative sequence q-axis current control signal , generate compensation current and suppress negative sequence current; Negative sequence voltage compensation: To reduce the impact of negative sequence voltage, the negative sequence d-axis voltage component and the q-axis voltage component Set as a goal; Use the PI controller to convert the current negative sequence d-axis voltage component and the negative sequence q-axis voltage component Compared with the target, the control output negative sequence d-axis voltage control signal is obtained and negative sequence q-axis voltage control signal , adjust the output voltage to achieve voltage balance.

10. A control system for an energy storage converter under an unbalanced grid voltage, applied to a control method for an energy storage converter under an unbalanced grid voltage as claimed in any one of claims 1 to 9, characterized in that: It includes a stability characteristic determination factor acquisition module, an energy storage converter control determination module and a positive and negative sequence component adjustment scheme determination module, wherein: The stability characteristic determination factor acquisition module is used to analyze the grid stability characteristics under the unbalanced grid voltage based on the grid monitoring cycle stored in the database to obtain the grid stability characteristic determination factor; The energy storage converter control judgment module is used to analyze the state of the grid energy storage device under the unbalanced grid voltage based on the grid energy storage device state data and the grid stability characteristic judgment factor, obtain the energy converter control judgment factor, and judge whether the energy storage converter needs to be controlled and determine the grid fault response threshold according to the energy converter control judgment factor: If the energy storage converter does not need to be controlled, it will enter the next cycle of grid monitoring; If the energy storage converter needs to be controlled, the grid fault characteristics under the unbalanced grid voltage are analyzed, and combined with the grid fault response threshold, it is determined whether the energy storage converter needs to be switched to the fault mode; The positive- and negative-sequence component regulation scheme determination module is used to monitor the grid voltage under the unbalanced grid voltage in a fault mode, obtain the amplitude and phase of the grid voltage, use synchronous coordinate transformation to convert the three-phase voltage signal into a DC component, use the positive- and negative-sequence component extraction technology to separate the positive- and negative-sequence components from the DC component, and determine the positive- and negative-sequence component regulation schemes.

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