Microgrid stability determination method and device, storage medium and electronic equipment

Abstract

The invention discloses a microgrid stability determination method and device, a storage medium and electronic equipment. The method comprises the following steps: determining output impedance information corresponding to a power supply in a micro-grid and input impedance information corresponding to a plurality of loads powered by the power supply respectively; determining load difference information based on the input impedance information corresponding to the plurality of loads; and based on the load difference information and the output impedance information, determining a stability result of the microgrid accessing the plurality of loads. According to the method and the device, the technical problem of inaccurate judgment on the stability of the micro-grid in related technologies is solved.

Description

Technical Field

[0001] The present invention relates to the field of power system engineering, and in particular to a method, device, storage medium and electronic equipment for determining the stability of a microgrid. Background Art

[0002] The large-scale access of electric vehicles to DC microgrids will have many impacts. Since electric vehicles require a lot of electricity when charging, this may cause the voltage and frequency of the system to be in an abnormal state, which in turn causes equipment damage or system instability, thus posing a challenge to the safe and stable operation of the power system. As the scale of microgrid systems expands and the complexity of devices increases, the dynamic response caused by constant power loads becomes more and more significant, causing the system to gradually deviate from stability or even eventually lose stability. The resulting stability issues are becoming more and more important.

[0003] In the related technology, multiple constant power loads are aggregated into one constant power load, and the dynamic response of the system when multiple loads are connected in parallel is not considered. The impact of the increase in the number of aggregated loads is not included in the judgment of the stability of the microgrid, resulting in inaccurate judgment of the accuracy of the microgrid, which in turn causes the instability of the microgrid.

[0004] To address the above-mentioned problems, no effective solution has been proposed yet. Summary of the invention

[0005] The embodiments of the present invention provide a method, device, storage medium and electronic device for determining the stability of a microgrid, so as to at least solve the technical problem of inaccurate judgment on the stability of a microgrid in the related art.

[0006] According to one aspect of an embodiment of the present invention, a method for determining the stability of a microgrid is provided, comprising: determining output impedance information corresponding to a power source in the microgrid, and input impedance information corresponding to a plurality of loads powered by the power source; determining load difference information based on the input impedance information corresponding to the plurality of loads; and determining stability results of the microgrid connected to the plurality of loads based on the load difference information and the output impedance information.

[0007] Optionally, determining the load difference information based on the input impedance information respectively corresponding to the multiple loads includes: determining a target load among the multiple loads; determining a target impedance of the target load and a differential impedance between the target load and other loads based on the input impedance information respectively corresponding to the multiple loads, wherein the other loads are loads among the multiple loads other than the target load; determining the load difference information based on the differential impedance.

[0008] Optionally, determining the stability result of the microgrid accessing the multiple loads based on the load difference information and the output impedance information includes: adjusting the output impedance information based on the load difference information to determine the adjusted output impedance information; determining the source-load impedance ratio based on the number of loads among the multiple loads, the adjusted output impedance information, and the dynamic response information; and determining the stability result based on the equivalent curve of the source-load impedance ratio.

[0009] Optionally, determining the stability result based on the equivalent curve of the source-load impedance ratio includes: determining the intersection position with the real axis of the frequency-domain coordinate system based on the equivalent curve; determining the change trend between the stability of the microgrid and the number of loads based on the intersection position; and determining the stability result based on the change trend.

[0010] Optionally, determining the change trend between the stability of the microgrid and the number of loads based on the intersection position includes: determining that the change trend is that the stability of the microgrid is inversely proportional to the number of loads when the partial derivative of the real part at the intersection position is negative; and determining the stability result based on the change trend includes: determining the number of boundaries based on the intersection position, where the number of boundaries is the maximum number of loads that can be accessed while the microgrid remains stable; and determining the stability result based on the number of boundaries and the number of loads among the multiple loads.

[0011] Optionally, the method further includes: in response to an access signal of a newly added load, updating the multiple loads to determine the updated multiple loads and the input impedance information corresponding to the updated multiple loads respectively; determining new load difference information based on the input impedance information corresponding to the updated multiple loads respectively; and determining the new stability result of the microgrid accessing the newly added load based on the new load difference information and the output impedance information.

[0012] Optionally, the multiple loads are constant-power loads with load differences.

[0013] According to another aspect of the embodiments of the present invention, a microgrid stability determination device is provided, including: an acquisition module for determining the output impedance information corresponding to a power source in the microgrid and the input impedance information corresponding to multiple loads powered by the power source respectively; a difference analysis module for determining load difference information based on the input impedance information corresponding to the multiple loads respectively; and a stability evaluation module for determining the stability result of the microgrid accessing the multiple loads based on the load difference information and the output impedance information.

[0014] According to another aspect of the embodiments of the present invention, a non-volatile storage medium is provided. The non-volatile storage medium stores multiple instructions, and the instructions are adapted to be loaded and executed by a processor to perform any of the microgrid stability determination methods described above.

[0015] According to another aspect of the embodiments of the present invention, an electronic device is provided, including: one or more processors and a memory. The memory is used to store one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors are caused to implement any of the microgrid stability determination methods described above.

[0016] In the embodiments of the present invention, by determining the output impedance information corresponding to the power sources in the microgrid and the input impedance information corresponding to multiple loads powered by the power sources respectively; based on the input impedance information corresponding to the multiple loads respectively, determining the load difference information; based on the load difference information and the output impedance information, determining the stability result of the microgrid accessing the multiple loads. The purpose of improving the accuracy of the stability result based on the load difference information between multiple loads is achieved, and the technical effect of improving the accuracy of the microgrid stability result and increasing the stability of the microgrid operation is realized. Furthermore, the technical problem of inaccurate determination of the microgrid stability in the related art is solved. Description of the Drawings

[0017] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0018] Figure 1 is a flowchart of an optional microgrid stability determination method provided according to an embodiment of the present invention;

[0019] Figure 2 is a first curve graph of an optional microgrid stability determination method provided according to an embodiment of the present invention;

[0020] Figure 3 is a second curve graph of an optional microgrid stability determination method provided according to an embodiment of the present invention;

[0021] Figure 4 is a third curve graph of an optional microgrid stability determination method provided according to an embodiment of the present invention;

[0022] Figure 5 is a schematic diagram of an optional microgrid stability determination method provided according to an embodiment of the present invention;

[0023] Figure 6It is a schematic structural diagram of an optional method for determining the stability of a microgrid according to an embodiment of the present invention;

[0024] Figure 7 It is a schematic diagram of an optional device for determining the stability of a microgrid according to an embodiment of the present invention. Detailed implementation manners

[0025] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a 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 those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order different from those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0027] For the convenience of description, some nouns or terms related to the embodiments of the present application are described below:

[0028] Nyquist Theorem (Nyquist Theorem) is a mathematical tool used to evaluate the stability of a linear time-invariant system. By analyzing the frequency response of the system (i.e., the characteristics of the gain and phase of the system changing with frequency), especially by drawing the Nyquist diagram of the system to determine whether the system is stable. In the present application, the Nyquist Theorem is used to evaluate the stability after an electric vehicle is connected to a DC microgrid.

[0029] The stability of a DC microgrid refers to that in a DC microgrid, the interaction between the power supply and the load will not cause the voltage or frequency to continuously deviate from the normal operating range, so as to ensure the safe and reliable operation of the system.

[0030] IME (Impedance Multiplier Effect) refers to the phenomenon in the power system where due to changes in load characteristics or system parameters, the total impedance of the system significantly increases.

[0031] A constant power load is a type of load whose consumed power remains constant regardless of voltage changes.

[0032] The source-load impedance ratio is the ratio between the power source output impedance and the load input impedance in the power system. This ratio is one of the key parameters for evaluating system stability.

[0033] According to an embodiment of the present invention, there is provided an embodiment of a method for determining the stability of a microgrid. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. And although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0034] Figure 1 is a flowchart of an optional method for determining the stability of a microgrid according to an embodiment of the present invention, as Figure 1 shown, the method includes the following steps:

[0035] Step S102, determine the output impedance information corresponding to the power source in the microgrid, and the input impedance information corresponding to multiple loads powered by the power source respectively;

[0036] It can be understood that by measurement or calculation, the specific values of the power source output impedance and each load input impedance are obtained, the output impedance information of the power source in the microgrid system and the input impedance information of multiple loads powered by this power source are obtained. The information of the output impedance and the input impedance is the basis of the entire stability evaluation process.

[0037] In an optional embodiment, the multiple loads are constant power loads with load differences.

[0038] It can be understood that constant power loads have the characteristic of maintaining constant power output when the voltage changes, and when multiple such loads interact, they may exacerbate voltage fluctuations due to their negative impedance characteristics, thus affecting the microgrid characteristics. The matching relationship between the power source output impedance and the load input impedance is crucial for the stability of the system. By adjusting the output impedance of the power source, the impedance matching relationship between the source and the load can be optimized, thereby improving the stability of the system. For example, when the load has negative impedance characteristics, appropriately increasing the output impedance of the power source can offset this negative effect and reduce voltage fluctuations.

[0039] Optionally, in a microgrid, a Constant Power Load (CPL) has a negative impedance characteristic, that is, when the voltage drops, the load will try to draw more current from the power grid to maintain its constant power. In related technologies, multiple constant power loads are usually simply aggregated and equivalent to a single constant power load. During the whole process, only the impact of the increase in the total charging power on the stability of the microgrid system is considered, and the impact caused by the increase in the number of aggregated loads is not analyzed. When multiple such loads interact with each other, they may exacerbate voltage fluctuations and even lead to system instability. This is because each load tries to increase the current when the voltage drops, further reducing the voltage and forming a vicious cycle.

[0040] Step S104: Determine load difference information based on the input impedance information corresponding to multiple loads respectively.

[0041] It can be understood that based on the input impedance information of multiple loads respectively, by identifying and quantifying the differences between loads, a data basis is provided for subsequent microgrid stability discrimination. In this application, by avoiding simply aggregating multiple loads into a single constant power load, the adverse impact of impedance multiplication effect on system stability analysis is reduced.

[0042] In an optional embodiment, determining load difference information based on the input impedance information corresponding to multiple loads respectively includes: determining a target load among multiple loads; based on the input impedance information corresponding to multiple loads respectively, determining the target impedance of the target load and the difference impedance between the target load and other loads, where other loads are the loads other than the target load among multiple loads; and determining load difference information based on the difference impedance.

[0043] It can be understood that a target load is selected among multiple loads, and based on the input impedance information corresponding to multiple loads respectively, the target impedance of the target load and the difference impedance from other loads are calculated. Other loads refer to the loads other than the target load among multiple loads. By determining the impedance difference, the differences between each load in the microgrid can be accurately identified and quantified.

[0044] Optionally, taking multiple loads as constant power loads as an example, the constant power loads that need to be aggregated in the microgrid system are not exactly the same. The i-th constant power load among multiple loads (for example, there are N in total) is selected as the standard load, that is, the target load, denoted as Z inf as the i-th constant power load. After selecting the standard load, the input impedances of the remaining N - 1 constant power loads (i.e., other loads) are respectively represented by the input impedance of the standard load and the difference impedance. Z xk is the difference impedance between the k-th constant power load and the standard load, Zink The input impedance of the k-th constant power load among the remaining N - 1 constant power loads.

[0045] Optionally, a common node can be introduced, and the difference impedance between the N - 1 constant power loads (i.e., other loads) and the standard load (i.e., the target impedance) is connected in parallel with it. After the common node, a situation of N identical constant power loads connected in parallel is formed, which can be expressed in the following way:

[0046]

[0047] Among them, the load difference information is denoted as Z x .

[0048] Step S106, based on the load difference information and the output impedance information, determine the stability result of the microgrid accessing multiple loads.

[0049] It can be understood that according to the load difference information and the output impedance information, the stability result after the microgrid accesses multiple loads is determined. Introducing the above load difference information into the stability judgment is beneficial to determining whether the microgrid is stable after accessing multiple loads and improving the accuracy of the stability judgment.

[0050] In an alternative embodiment, based on the load difference information and the output impedance information, determining the stability result of the microgrid accessing multiple loads includes: adjusting the output impedance information based on the load difference information to determine the adjusted output impedance information; determining the source-load impedance ratio based on the number of loads of multiple loads, the adjusted output impedance information, and the dynamic response information; and determining the stability result based on the equivalent curve of the source-load impedance ratio.

[0051] It can be understood that the output impedance information of the power source is adjusted using the identified load difference information to obtain the adjusted output impedance information. Dynamically adjusting the output impedance information of the power source according to the load difference information is beneficial to improving the accuracy of the source-load impedance ratio. Combining the number of loads, the adjusted output impedance information, and the dynamic response information of the system to obtain the source-load impedance ratio. By generating the equivalent curve of the source-load impedance ratio, the stability of the microgrid can be effectively evaluated to obtain the stability result. It should be noted that the instability of the microgrid comes from the mismatch between the output impedance information of the power source and the input impedance information of multiple loads. Since the impedance mismatch will cause voltage fluctuations and harmonic problems in the microgrid. Therefore, using the load difference information to obtain more accurate adjusted output impedance information is beneficial to obtaining more accurate stability results.

[0052] Optionally, by introducing the difference impedance of the common node, the load is processed as a parallel connection of a standard impedance and a difference impedance, and the load difference information can be obtained and denoted as Z x. The load difference information is used to adjust the output impedance information of the power supply, and the above output impedance information is denoted as Z R , and the adjusted output impedance information is denoted as The adjustment can be carried out in the following way

[0053] Optionally, in this application, the constant-power load is simplified to a second-order model, which considers the characteristics of the input filter of the external line to simulate the influence of the load on the system stability. The source-load impedance ratio can be obtained in the following way

[0054]

[0055] where Z″ in represents the dynamic response information

[0056] The above dynamic response information can be obtained in the following way. For example, if the microgrid system parameter model is known, the output impedance information Z of the power supply can be calculated R , and the input impedance information Z of the load in , where Z R (s) is the series equivalent reactance of the common line and the power supply output impedance. If the specific model and parameters are unknown, the impedance values of the subsystems in the microgrid can be measured separately. The constant-power load is simplified to a second-order model, where the second-order model can represent the dynamic response information and is an ideal model that only considers the external line and the input filter. The model of its Z in is denoted as Z″ in (s), that is, the dynamic response information can be expressed as

[0057]

[0058] where R and L are the line resistance and inductance, L F and C F are the filter inductance and capacitance, and u F is the capacitance voltage

[0059] It should be noted that the second-order model of the constant-power load reflects the behavior characteristics of the load during the dynamic process in the microgrid, especially when the power demand of the load remains constant while the voltage or current changes. The core characteristic of the constant-power load is that its power demand remains constant within a certain range, that is, regardless of how the voltage or current changes, the load will try to maintain its power output unchanged. The second-order model describes the dynamic response process of the constant-power load when the voltage or current changes by introducing the dynamic characteristics of the external line and the input filter. This includes the roles of the line resistance R and inductance L, as well as the filter inductance L F and capacitance CF. The presence of the above components in the circuit will affect the voltage and current waveforms of the load, and thus affect its power output

[0060] Optionally, according to the microgrid system structure, the source-load impedance ratio with the number of constant power loads connected being N is obtained:

[0061]

[0062] The above is the Nyquist equivalent expression of the microgrid system and the equivalent curve of the source-load impedance ratio. The Nyquist curve is the representation of the locus of H(s) in the complex plane, which is plotted by calculating H(jω), where j is the imaginary unit and ω is the angular frequency. If the Nyquist curve encircles the point (-1, 0) but does not include the point (1, 0), the system is stable; if the Nyquist curve includes the point (1, 0), the system is unstable.

[0063] Figure 2 is the first curve diagram of an optional microgrid stability determination method provided according to an embodiment of the present invention. As Figure 2 shown, it shows that as the number of loads N increases from 2 to 5, the intersection position of the equivalent curves changes. Figure 2 The intersection situation at the intersection position is magnified in . It can be seen the relationship between the (-1, 0) indicated by the cross and the equivalent curves in two cases. In the case of N = 2, the curve does not include the (-1, 0) point and is in a stable state, while in the case of N = 5, the curve includes the (-1, 0) point and is in an unstable state.

[0064] In an optional embodiment, based on the equivalent curve of the source-load impedance ratio, the stability result is determined, including: determining the intersection position with the real axis of the frequency domain coordinate system based on the equivalent curve; determining the change trend between the stability of the microgrid and the number of loads based on the intersection position; and determining the stability result based on the change trend.

[0065] It can be understood that based on the intersection position of the Nyquist equivalent curve and the real axis of the frequency domain coordinate system, the change trend of the stability of the microgrid under different numbers of loads is evaluated. The maximum number of loads that the microgrid can access in a stable state, that is, the boundary number, can be determined through the intersection position. By defining and quantifying the boundary number to evaluate the stability of the microgrid, the relationship between the stability of the system and the number of loads is intuitively reflected by the change of the intersection position, which helps to obtain a more accurate microgrid stability result.

[0066] Figure 3 is the second curve diagram of an optional microgrid stability determination method provided according to an embodiment of the present invention. As Figure 3As shown, the relationship between different oscillation modes of the microgrid and the number of loads is illustrated. It can be seen that a similar changing trend is maintained according to the number of loads. As the number N of parallel connections increases, the amplitude of the input impedance gradually decreases. When N = 5, the amplitudes of the input and output impedances intersect, and there is a negative phase margin at the corresponding frequency, resulting in the instability of the microgrid system.

[0067] In an alternative embodiment, based on the intersection point position, determining the changing trend between the stability of the microgrid and the number of loads includes: when the partial derivative of the real part at the intersection point position is negative, determining that the changing trend is that the stability of the microgrid is inversely proportional to the number of loads; based on the changing trend, determining the stability result includes: based on the intersection point position, determining the boundary number, where the boundary number is the maximum number of loads that can be connected to the microgrid while maintaining stability; based on the boundary number and the number of loads of multiple loads, determining the stability result.

[0068] It can be understood that the intersection point of the above equivalent curve and the frequency domain coordinate system is associated with the dynamic response characteristics. The real part of the intersection point position can indicate the frequency, and the imaginary part indicates the gain or phase. When the partial derivative of the real part at the intersection point position is negative, the stability of the microgrid is inversely proportional to the number of loads, that is, when the partial derivative of the real part at the intersection point position is less than 0, increasing the number of loads will reduce the stability of the microgrid. The maximum number of loads that can be connected to the microgrid while maintaining a stable state is determined through the intersection point position, that is, the stability of the microgrid is determined by comparing the boundary number with the actual number of loads. The relationship between stability and the number of loads is judged by the positive or negative of the partial derivative of the real part, and the stability boundary of the microgrid is determined accordingly.

[0069] Optionally, the source-load impedance ratio The intersection point position with the real axis is related to the static stability of the microgrid system. Taking the angular frequency ω = ω0 and making the Nyquist curve (i.e., the equivalent curve) of the system intersect with the real axis, the intersection point position can be obtained. The real part of the impedance ratio at this frequency is denoted as When the partial derivative of the real part with respect to the number N of constant power load connections is less than 0, that is, At this time, the intersection point of the Nyquist curve and the real axis approaches the point (-1, 0), indicating that in this case, the stability degree of the microgrid system is relatively low or even unstable. In contrast, if the partial derivative of the real part of the intersection point is greater than 0, it means that as the number of constant power load connections increases, the stability of the microgrid system will be enhanced.

[0070] Figure 4 is the third curve graph of an alternative microgrid stability determination method provided according to an embodiment of the present invention. As Figure 4 shown, taking the number of loads of multiple loads connected to the microgrid as 2 and 5 as examples, it illustrates that as the number of connected loads increases, the amplitude and phase margin in the microgrid will also change. The frequency domain analysis results change with the number of parallel connections. Z LTo aggregate the input impedance information of multiple loads.

[0071] Optionally, based on a parametric model or measurement information, a quantization index I is defined ND , for determining the stability of the microgrid and determining the corresponding number of boundaries, which can be expressed in the following way:

[0072]

[0073] Quantization index I ND is only related to the microgrid system structure and the number of constant power loads in parallel. Therefore, the stability of the system can be accurately evaluated under different operating conditions. If I ND > 0, the Nyquist curve of the source-load impedance ratio does not contain the point (-1, 0), indicating that the microgrid system is in a stable operating state under this operating condition.

[0074] If I ND = 0, the number of parallel loads that make the microgrid in a critically stable state, that is, the number of boundaries, can be determined. When the number of boundaries is greater than the number of loads of the multiple loads connected to the microgrid, it indicates that the current connection action of the multiple loads will not cause the microgrid to become unstable. When the number of boundaries is less than the number of multiple loads connected to the microgrid, it indicates that too many loads are connected, resulting in the instability of the microgrid.

[0075] Through the quantization index I ND the maximum number of constant power loads that the microgrid system can accommodate, that is, the number of boundaries, can be calculated. Since it is not restricted by the microgrid structure and operating state, it effectively reduces the limitations of microgrid stability judgment and improves the judgment efficiency.

[0076] In an alternative embodiment, in response to the access signal of a newly added load, multiple loads are updated to determine the updated multiple loads and the input impedance information corresponding to the updated multiple loads respectively; based on the input impedance information corresponding to the updated multiple loads respectively, new load difference information is determined; based on the new load difference information and the output impedance information, the new stability result after the microgrid accesses the newly added load is determined.

[0077] It can be understood that when a new load is connected, the input impedance information corresponding to the multiple loads will be updated in real time, while the output impedance of the power supply does not update. Based on the input impedance information corresponding to the updated multiple loads and the output impedance of the power supply, the stability result after the microgrid accesses the newly added load is re-evaluated.

[0078] Through the above step S102, the output impedance information corresponding to the power sources in the microgrid and the input impedance information corresponding to multiple loads powered by the power sources are determined; in step S104, based on the input impedance information corresponding to the multiple loads respectively, the load difference information is determined; in step S106, based on the load difference information and the output impedance information, the stability result of the microgrid accessing multiple loads is determined. The purpose of improving the accuracy of the stability result based on the load difference information between multiple loads is achieved, the accuracy of the microgrid stability result is improved, and thus the technical problem of inaccurate judgment of the microgrid stability in the related art is solved.

[0079] Based on the above embodiments and alternative embodiments, the present invention proposes an alternative implementation manner. Figure 5 It is a schematic diagram of an alternative method for determining the stability of a microgrid provided according to an embodiment of the present invention. The following describes Figure 5 the processing manner shown therein.

[0080] Step S1, extraction of microgrid system information: The microgrid system containing multiple constant-power loads aggregated is partitioned, and the output impedance of the power source and the input impedance information of the loads are obtained through calculation or measurement.

[0081] Step S11, first, partition the microgrid system. The microgrid system containing N aggregated constant-power loads is divided into two subsystems, namely the power source and the load, according to the power flow direction.

[0082] Dividing the microgrid system into two subsystems, namely the power source and the load, and respectively managing and optimizing these two subsystems can achieve effective partitioning of the microgrid system, thereby improving the operation efficiency and stability of the system. In the power source subsystem, various energy resources inside the microgrid system are centrally managed, and the load subsystem is responsible for managing various constant-power loads inside the microgrid system. Subsequently, the real-time data of the power source and the load are collected and monitored to adjust and optimize the system operation in a timely manner.

[0083] Step S12, data preprocessing: If the parameter model of the microgrid system is known, the output impedance information Z R of the power source and the input impedance information Z in of the load can be calculated, where Z R (s) is the series equivalent reactance of the common line and the output impedance of the power source. If the specific model and parameters are unknown, the impedance values of the above subsystems can be measured respectively. It should be noted that the constant-power load is simplified to a second-order model, where the second-order model can represent the dynamic response information and is an ideal model that only considers the external line and the input filter. The model of Z in is denoted as Z″ in (s), that is, the dynamic response information can be expressed as:

[0084]

[0085] Among them, R and L are the line resistance and inductance, and L F and C F are the filter inductance and capacitance, and u F is the capacitor voltage.

[0086] Step S2: Equivalent modeling of the electric vehicle load. Introduce the difference impedance and equivalent the constant power load cluster in the microgrid system as a single load.

[0087] Step S21: In a generalized microgrid system, there are different types of loads, such as residential, commercial, industrial, etc. Their energy consumption patterns and power demands may vary greatly. And the loads in the microgrid system may also differ in scale. Some may be small loads, while some may be large loads, and their impacts on the power system are also different. Therefore, the constant power loads to be aggregated are not exactly the same. For the convenience of subsequent stability analysis, model and equivalent N constant power loads as a single load. First, select the i-th constant power load as the standard load (i.e., the target load), denoted as Z ini as the i-th constant power load, and its input impedance information is used as the reference value.

[0088] Step S22: After selecting the standard load, to simplify the processing and reduce the computational complexity, represent the input impedance of the remaining constant power loads using the combination of the input impedance information of the standard load and the difference impedance.

[0089] Z xk is the difference impedance between the k-th constant power load and the standard load, and Z ink represents the input impedance of the k-th constant power load among the remaining N - 1 constant power loads.

[0090] Step S23: After the input impedances of all the constant power loads are set, introduce a common node and connect the difference impedance between the remaining N - 1 constant power loads and the standard load in parallel to it. After the common node, a situation of N identical constant power loads in parallel is formed, which can be represented in the following way:

[0091]

[0092] Among them, the load difference information is denoted as Z x .

[0093] Step S24: By treating the load as a parallel combination of a standard impedance and a difference impedance, the load difference information denoted as Z x. The load difference information is used to adjust the output impedance information of the power supply, and the above output impedance information is denoted as Z R , and the adjusted output impedance information is denoted as The adjustment can be carried out in the following way By introducing the difference impedance of the common node, the difference impedance can be used to simulate the parallel structure at the load end of the microgrid system, which can more accurately reflect the actual situation. In addition, Z can be adjusted R to meet the specific requirements and conditions of the system. In this way, the dynamic characteristics and stability of the system can be more accurately described, providing strong support for subsequent system analysis and control design

[0094] Step - S3, Analysis of the stability of electric vehicle load aggregation

[0095] Step S31, According to the microgrid system structure, obtain the source - load impedance ratio, that is, the Nyquist equivalent expression of the system where, Z″ in represents the dynamic response information

[0096] The source - load impedance ratio The intersection position with the real axis is related to the static stability of the microgrid system. Taking the angular frequency ω = ω0 and making the Nyquist curve (i.e., the equivalent curve) of the system intersect with the real axis, the intersection position can be obtained, and the real part of the impedance ratio at this frequency is denoted as

[0097] When the partial derivative of the real part with respect to the number N of constant - power load accesses is less than 0, that is , the intersection of the Nyquist curve and the real axis approaches the point (-1, 0) continuously, indicating that the stability of the microgrid system is relatively low or even unstable in this case. On the contrary, if the partial derivative of the intersection real part is greater than 0, it means that with the increase in the number of constant - power load accesses, the stability of the microgrid system will be enhanced

[0098] Based on the parameter model or measurement information, define the quantization index I ND , which is used to determine the microgrid stability and determine the corresponding boundary quantity, and can be expressed in the following way

[0099]

[0100] The quantization index I ND is only related to the microgrid system structure and the number of constant - power load paralleling, so the stability of the system can be accurately evaluated under different working conditions. If I ND > 0, the Nyquist curve of the source - load impedance ratio does not contain the point (-1, 0), indicating that the microgrid system is in a stable operating state under this working condition

[0101] The equivalent order reduction technology and stability analysis processing described above provide a way to judge the stability of a microgrid system with multiple constant power loads connected, and through the quantization index I ND it is possible to calculate the maximum number of constant power loads that the microgrid system can accommodate. Since it is not restricted by the microgrid structure and operating conditions, it effectively reduces the limitations of microgrid stability judgment and improves the judgment efficiency.

[0102] Figure 6 is a schematic structural diagram of an optional microgrid stability determination method provided according to an embodiment of the present invention. As Figure 6 shown, taking the charging of electric vehicles in a charging station as an application scenario, the electric vehicle loads CPL-1 to CPL-N in the charging station charge at the same power p L = 50 kW, and the line resistance and conductance connecting each load to the point of common coupling (PCC) are both R = 8.3 mΩ and L = 45.5 mH. The common line resistance and inductance between the PCC node and the converter are R DC = 10.1 mΩ and L DC = 48.9 mH. And the rated charging voltage of the load is P is the active power injected into the AC system.

[0103] Based on the structure of electric vehicles connected in parallel to a DC microgrid, there are the following two situations: For situation 1, initially there are 2 identical electric vehicles charging aggregately, that is, N = 2. The quantization index I is determined in the following way ND

[0104]

[0105] When the quantization index I ND > 0, the preliminary judgment of stability indicates that the microgrid system is stable at this time.

[0106] For situation 2, the number of aggregately charging electric vehicles increases to N = 5. At this time the partial derivative with respect to N is less than zero, indicating that the increase in the number of aggregately constant power loads has an adverse effect on stability.

[0107] By setting I ND = 0, the parallel number N that makes the system critically stable can be obtained max= 4.37. It can be seen that the number of aggregated loads at this time has exceeded the maximum number given in the estimation method, and the system is small-signal unstable. The optional implementation modes described above achieve at least the following effects: Based on the parametric model or measurement information, the high-order DC microgrid with constant-power loads is equivalent to a reduced-order microgrid system with a single load connected, avoiding directly equivalenting the loads to a single constant-power load and reducing the system stability level. The Nyquist criterion adopted has excellent performance in analyzing the stability of the microgrid system, can be used to analyze the stability problems caused by multiple loads connected in parallel, and estimate the number of constant-power loads that the microgrid system can access according to the proposed quantitative index.

[0108] It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. And although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0109] In this embodiment, a microgrid stability determination device is also provided. This device is used to implement the above embodiments and preferred implementation modes, and those that have been described will not be repeated here. As used below, the terms "module" and "device" can be a combination of software and / or hardware that can achieve a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation in hardware, or a combination of software and hardware is also possible and contemplated.

[0110] According to an embodiment of the present invention, an apparatus embodiment for implementing the microgrid stability determination method is also provided. Figure 7 It is a schematic diagram of a microgrid stability determination device according to an embodiment of the present invention. As Figure 7 shown, the above microgrid stability determination device includes an acquisition module 702, a difference analysis module 704, and a stability evaluation module 706. The device will be described below.

[0111] The acquisition module 702 is used to determine the output impedance information corresponding to the power source in the microgrid, and the input impedance information corresponding to multiple loads powered by the power source respectively.

[0112] The difference analysis module 704 is connected to the acquisition module 702 and is used to determine the load difference information based on the input impedance information corresponding to multiple loads respectively.

[0113] The stability evaluation module 706 is connected to the difference analysis module 704 and is used to determine the stability result of the microgrid accessing multiple loads based on the load difference information and the output impedance information.

[0114] In a microgrid stability determination device provided by an embodiment of the present invention, an acquisition module 702 is provided to determine the output impedance information corresponding to a power source in the microgrid and the input impedance information corresponding to multiple loads powered by the power source respectively; a difference analysis module 704 is connected to the acquisition module 702 to determine load difference information based on the input impedance information corresponding to the multiple loads respectively; a stability evaluation module 706 is connected to the difference analysis module 704 to determine the stability result of the microgrid accessing multiple loads based on the load difference information and the output impedance information. The purpose of improving the accuracy of the stability result is achieved based on the load difference information between multiple loads, and the technical effects of improving the accuracy of the microgrid stability result and increasing the stability of the microgrid operation are realized, thereby solving the technical problem of inaccurate judgment of the microgrid stability in the related art.

[0115] It should be noted that the above-mentioned respective modules can be implemented by software or hardware. For example, for the latter, it can be implemented in the following manner: the above-mentioned respective modules can be located in the same processor; or, the above-mentioned respective modules are located in different processors in any combination.

[0116] It should be noted here that the above-mentioned acquisition module 702, difference analysis module 704, and stability evaluation module 706 correspond to steps S102 to S106 in the embodiment. The examples and application scenarios implemented by the above-mentioned modules and the corresponding steps are the same, but are not limited to the content disclosed in the above-mentioned embodiment. It should be noted that the above-mentioned modules, as a part of the device, can run in a computer terminal.

[0117] It should be noted that the optional or preferred implementation manners of this embodiment can be referred to the relevant descriptions in the embodiment, and will not be repeated here.

[0118] The above-mentioned microgrid stability determination device may further include a processor and a memory. The acquisition module 702, difference analysis module 704, stability evaluation module 706, etc. are all stored in the memory as program units, and the corresponding functions are implemented by the processor executing the above-mentioned program units stored in the memory.

[0119] The processor contains a kernel, and the kernel retrieves the corresponding program unit from the memory. One or more kernels can be set. The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of, for example, read-only memory (ROM) or flash memory (flash RAM), and the memory includes at least one storage chip.

[0120] An embodiment of the present invention provides a non-volatile storage medium, on which a program is stored, and when the program is executed by a processor, a microgrid stability determination method is implemented.

[0121] An embodiment of the present invention provides an electronic device, which includes a processor, a memory, and a program stored on the memory and executable on the processor. When the processor executes the program, the following steps are implemented: determining output impedance information corresponding to a power source in a microgrid, and input impedance information corresponding to a plurality of loads powered by the power source respectively; determining load difference information based on the input impedance information corresponding to the plurality of loads respectively; and determining a stability result of the microgrid accessing the plurality of loads based on the load difference information and the output impedance information. The device herein may be a server, a PC, etc.

[0122] The present invention also provides a computer program product, which, when executed on a data processing device, is adapted to execute a program initialized with the following method steps: determining output impedance information corresponding to a power source in a microgrid, and input impedance information corresponding to a plurality of loads powered by the power source respectively; determining load difference information based on the input impedance information corresponding to the plurality of loads respectively; and determining a stability result of the microgrid accessing the plurality of loads based on the load difference information and the output impedance information.

[0123] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0124] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0125] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means implements the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1The functions specified in one or more boxes.

[0126] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide for implementing the steps of the functions specified in one Figure 1 one process or more processes and / or boxes Figure 1 or more boxes.

[0127] In a typical configuration, a computing device includes one or more processors (CPUs), an input / output interface, a network interface, and memory.

[0128] The memory may include non-permanent memory in the computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of, for example, read-only memory (ROM) or flash memory (flash RAM). The memory is an example of a computer-readable medium.

[0129] Computer-readable media include permanent and non-permanent, removable and non-removable media, and information storage can be implemented by any method or technology. The information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette tapes, magnetic disk storage or other magnetic storage devices, or any other non-transmission media that can be used to store information accessible by a computing device. As defined herein, computer-readable media do not include transitory computer-readable media, such as modulated data signals and carrier waves.

[0130] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, commodity or device comprising the element.

[0131] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0132] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A method for determining the stability of a microgrid, characterized in that, Including: Determine the output impedance information corresponding to the power sources in the microgrid, and the input impedance information corresponding to multiple loads powered by the power sources respectively; Based on the input impedance information corresponding to the multiple loads respectively, determine the load difference information; Based on the load difference information and the output impedance information, determine the stability result of the microgrid accessing the multiple loads.

2. The method according to claim 1, wherein The determining the load difference information based on the input impedance information corresponding to the multiple loads respectively includes: Determine a target load among the multiple loads; Based on the input impedance information corresponding to the multiple loads respectively, determine the target impedance of the target load and the difference impedance between the target load and other loads, where the other loads are the loads other than the target load among the multiple loads; Based on the difference impedance, determine the load difference information.

3. The method according to claim 1, wherein The determining the stability result of the microgrid accessing the multiple loads based on the load difference information and the output impedance information includes: Based on the load difference information, adjust the output impedance information to determine the adjusted output impedance information; Based on the number of loads of the multiple loads, the adjusted output impedance information, and the dynamic response information, determine the source-load impedance ratio; Based on the equivalent curve of the source-load impedance ratio, determine the stability result.

4. The method according to claim 3, wherein The determining the stability result based on the equivalent curve of the source-load impedance ratio includes: Based on the equivalent curve, determine the intersection position with the real axis of the frequency domain coordinate system; Based on the intersection position, determine the change trend between the stability of the microgrid and the number of loads; Based on the change trend, determine the stability result.

5. The method according to claim 4, wherein the determining the change trend between the stability of the microgrid and the number of loads based on the intersection position includes: when the partial derivative of the real part at the intersection position is negative, determine that the change trend is that the stability of the microgrid is inversely proportional to the number of loads; the determining the stability result based on the change trend includes: based on the intersection position, determine the number of boundaries, where the number of boundaries is the maximum number of loads that the microgrid can access while remaining stable; based on the number of boundaries and the number of loads of the multiple loads, determine the stability result.

6. The method according to claim 5, wherein The method further includes: In response to the access signal of a newly added load, update the multiple loads to determine the updated multiple loads and the input impedance information corresponding to the updated multiple loads respectively; Based on the input impedance information corresponding to the updated multiple loads respectively, determine the new load difference information; Based on the new load difference information and the output impedance information, determine the new stability result of the microgrid after accessing the newly added load.

7. The method according to any one of claims 1 to 6, characterized in that The multiple loads are constant power loads with load differences.

8. A microgrid stability determination device, characterized in that Including: An acquisition module for determining the output impedance information corresponding to the power sources in the microgrid, and the input impedance information corresponding to multiple loads powered by the power sources respectively; A difference analysis module, configured to determine load difference information based on input impedance information respectively corresponding to the multiple loads; A stability evaluation module, configured to determine a stability result of the microgrid accessing the multiple loads based on the load difference information and the output impedance information.

9. A non-volatile storage medium, characterized in that, The non-volatile storage medium stores a plurality of instructions, and the instructions are adapted to be loaded and executed by a processor to perform the microgrid stability determination method according to any one of claims 1 to 7.

10. An electronic device, characterized in that, Comprising: One or more processors and a memory, the memory is used to store one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the microgrid stability determination method according to any one of claims 1 to 7.

Images