A system parameter normalization method suitable for new energy grid-connected stability analysis

Abstract

The application provides a system parameter unitization method suitable for new energy grid connection stability analysis, is applied to a multi-power form interconnected and power electronicized power system, and expands the application range of the unitization method.The method comprises the following steps: step 1, selecting voltage and current reference values according to the maximum stress of a switching device of a new energy converter; step 2, obtaining power reference values and impedance reference values based on the voltage and current reference values; step 3, calculating voltage, current and impedance reference values of each stage; step 4, calculating voltage, current and power unit values of key nodes and impedance unit values of key elements; step 5, obtaining converter control parameter reference values according to a frequency domain impedance model; and step 6, calculating converter control parameter unit values.

Description

Technical Field

[0001] This invention relates to the field of stability analysis technology for high-proportion renewable energy power systems, and in particular to a per-unit method for system parameters applicable to the stability analysis of renewable energy grid connection. Background Technology

[0002] In recent years, the proportion of new energy sources, represented by wind power and photovoltaics, in the power system has been continuously increasing. Compared with conventional generator sets and traditional power installations, new energy sources are connected to the system after being converted and controlled by power electronic devices. Power electronic devices have complex and flexible control structures and parameters. Under the action of a precision control system, they replace mechanical switches with semiconductor switching devices at different time scales, rapidly switching on and off. Through various topology transformations, they change the operating functions and electrical performance of the power system. Traditional AC power systems based on synchronous generators are transforming into interconnected systems with multiple power sources, multiple energy conversions, and multiple power forms. Power flows bidirectionally between multiple complex networks, exhibiting characteristics such as strong nonlinearity, high sensitivity, large impact, and AC / DC coupling.

[0003] In power systems with large-scale integration of power electronic devices, circuits may experience excessive voltage and current stress, leading to device damage and reduced system reliability. The dynamic interaction between converters and the grid can easily induce resonance and broadband resonance phenomena different from those in traditional grids, jeopardizing power quality and system stability. Furthermore, the stability problems of traditional power systems are equivalent to the synchronization stability problems of generator sets, while the stability assessment of next-generation power systems requires comprehensive consideration of generation equipment, transmission and distribution networks, and load characteristics. In terms of planning and design, unlike the precisely customizable equipment in classic power systems, the semiconductor devices of power electronic devices are difficult to manufacture to design specifications. In summary, power systems with large-scale integration of power electronic devices become increasingly complex in terms of steady-state characteristic analysis, stability assessment, and device design, posing new challenges to safe and reliable operation.

[0004] Per-unit scaling is a commonly used numerical notation method in engineering calculations, maturely applied to the steady-state characteristics, transient stability analysis, and transmission and distribution network design of classical power systems. When analyzing steady-state characteristics, large power plants are treated as ideal AC voltage sources, and per-unit scaling methods are used to construct equivalent circuits for multi-voltage-level power systems, thereby enabling power flow calculations. In transient stability analysis, per-unit values ​​can simplify the dynamic equations of synchronous generator units. Similarly, per-unit values, when applied to the parameter design of transmission and distribution networks, can effectively reduce the computational workload in the parameter design process of transformers, reactors, and other devices. However, the classical per-unit scaling method has certain limitations. First, the default frequency for parameter per-unit scaling is the power frequency, which is unsuitable for interconnected systems with multiple power modes such as AC and DC. Second, it does not consider the stress of switching devices or involve the reduction of control parameters, making it difficult to reflect the operating characteristics of power electronic devices, resulting in a lack of physical meaning. Finally, this method cannot adapt to the changes in stability analysis methods in new-generation power systems and is difficult to apply to stability assessment. Summary of the Invention

[0005] To adapt to the trend of large-scale grid connection of new energy sources and the electrification of power systems, and to make up for the shortcomings of the classic per-unit method, this invention proposes a per-unit method for system parameters applicable to the stability analysis of grid connection of new energy sources.

[0006] The present invention specifically adopts the following technical solution:

[0007] A per-unit method for system parameters applicable to grid-connected stability analysis of new energy sources, characterized by the following steps:

[0008] Step 1: Select the voltage and current reference values ​​based on the maximum stress of the switching devices in the new energy converter;

[0009] Step 2: Obtain the power reference value and impedance reference value based on the voltage and current reference values;

[0010] Step 3: Calculate the reference values ​​for voltage, current, and impedance at each stage;

[0011] Step 4: Calculate the per-unit values ​​of voltage, current, and power at critical nodes, and the per-unit values ​​of impedance for critical components;

[0012] Step 5: Obtain the reference values ​​of the converter control parameters based on the frequency domain impedance model;

[0013] Step 6: Calculate the per-unit values ​​of the control parameters for each converter.

[0014] Furthermore, in step 1, the maximum voltage stress P of the device is... MV Maximum current stress P MI Set as voltage reference value U respectively B1 and current reference value I B1This ensures that the per-unit values ​​of the maximum voltage stress and maximum current stress of the switching device are both 1.

[0015] Furthermore, consider the following in step 2:

[0016] In a three-phase system, the power reference value S B Voltage reference value U B1 Current reference value I B1 Power reference value Z B1 The relationship between them is:

[0017]

[0018]

[0019] The power reference value and impedance reference value are obtained based on the above relationship.

[0020] Furthermore, in step 3, let the line corresponding to the voltage, current, and impedance reference values ​​to be calculated be line 1. If there is a line 2 with a different voltage level connected to line 1 via a transformer, let the transformer ratio be N; the voltage reference value of line 2 is U. B2 Current reference value I B2 Impedance reference value Z B2 Represented as:

[0021] U B2 =U B1 / N

[0022] I B2 =N·I B1

[0023]

[0024] Further introducing the concept of equivalent turns ratio of a converter, the input terminal of the converter is equivalent to the primary side of a voltage transformer, while the output terminal of the converter is considered as the secondary side of a transformer. The ratio of the input voltage to the output voltage of the converter is the equivalent turns ratio M of the converter. This extends the method of calculating the reference value for line sections with different voltage levels to line sections with different power configurations in AC / DC hybrid configurations, namely:

[0025] U B2 =U B1 / M

[0026] I B2 =M·I B1

[0027]

[0028] Further, in step 4, based on the power reference value and the voltage, current, and impedance reference values ​​obtained in steps 1-3 for each voltage level, the nominal values ​​of voltage, current, and power of each key node are divided by the voltage, current, and power reference values ​​of the corresponding voltage level to obtain the per-unit values ​​of voltage / current / power of the key node; the nominal values ​​of impedance of each key component are divided by the impedance reference values ​​of the corresponding voltage level to obtain the per-unit values ​​of impedance of the key component.

[0029] Furthermore, in step 5, given the converter circuit structure and control structure, the impedance expression Z of the converter in the s-domain is... c Depends on the steady-state operating point voltage U, current I, and each controller g c1 ,g c2 …g cn

[0030] Z c (s)=f(U,I,g c1 ,g c2 ...g cn )

[0031] The frequency domain expression corresponding to the above equation is:

[0032] Z c (ω)=f(ω,U,I,g c1 ,g c2 ...g cn )

[0033] Select the baseline value for the impedance calculation control parameters when the angular frequency w = 1, i.e., s = jw = j; assuming the converter uses PI control, the expression for the PI controller is:

[0034]

[0035] K P With K I The ratio T represents the corner frequency of the controller, which determines the phase characteristics of the controller; when T is constant and the integral coefficient K... I When the frequency response curve of the controller changes, it shifts vertically on the Bode plot while the phase characteristic remains unchanged. Considering that only the amplitude is normalized and not the phase during impedance normalization, and that T remains constant by default during control parameter normalization, the normalization of PI control parameters only requires normalizing the integral coefficient K. I Impedance, voltage, current reference values ​​and required control parameter reference values: K IB1 ,K IB2 …K IBn The relation is:

[0036] Z B =|f(ω,U B ,I B,K IB1 ,K IB2 ...K IBn ) ω＝1

[0037] The baseline values ​​of the control parameters are solved by substituting the expression obtained from the impedance modeling of the converter into the above equation.

[0038] Furthermore, in step 6, assuming there are n PI control parameters to be normalized in the converter, the normalization result of the control parameters is:

[0039]

[0040] Compared with existing technologies, the present invention and its preferred embodiments are suitable for power systems with interconnected power modes and power electronics, especially for stability analysis of high proportion of new energy grid connection, thus expanding the application scope of the per-unit method. Attached Figure Description

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0042] Figure 1 This is a schematic diagram of the circuit and control structure of a new energy inverter grid-connected system according to an embodiment of the present invention;

[0043] Figure 2 This is the equivalent circuit of a new energy inverter grid-connected system according to an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the key steps of the per-unit method proposed in this invention. Detailed Implementation

[0045] In the following, specific embodiments of this application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand and implement this application. Without departing from the principles of this application, features from various embodiments can be combined to obtain new implementations, or certain features from some embodiments can be substituted to obtain other preferred implementations.

[0046] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0047] To make the features and advantages of this patent more apparent and understandable, specific embodiments are provided below for detailed explanation:

[0048] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0049] The per-unit method for system parameters applicable to grid-connected stability analysis of new energy sources provided in this embodiment of the invention specifically includes the following steps:

[0050] Step 1: Select the voltage and current reference values ​​based on the maximum stress of the switching devices in the new energy converter;

[0051] Classical per-unit scaling methods typically select the rated power and rated voltage of representative equipment or buses at a certain voltage level as benchmark values, and use these as the first step in per-unit scaling. It can be seen that classical per-unit scaling methods only consider the influence of topology on system operating characteristics, while the integration of large-scale power electronic devices means that semiconductor devices and converter control strategies also play a decisive role in the safe and stable operation of the power system. Therefore, the first step of the improved per-unit scaling method proposed in this invention focuses on semiconductor device parameters, and sets the maximum voltage stress P of the device as the benchmark. MV Maximum current stress P MI Set as voltage reference value U respectively B1 and current reference value I B1 Therefore, the significant feature of the improved per-unit method is that the per-unit values ​​of the maximum voltage stress and maximum current stress of the switching device are both 1.

[0052] Step 2: Obtain the power reference value and impedance reference value based on the voltage and current reference values;

[0053] In a three-phase system, the power reference value S B Voltage reference value U B1 Current reference value I B1 Power reference value Z B1 The relationship between them is:

[0054]

[0055]

[0056] The power reference value and impedance reference value can be obtained based on the above relationship.

[0057] Step 3: Calculate the reference values ​​for voltage, current, and impedance at each stage;

[0058] Let the line corresponding to the above reference value be line 1. If there is a line 2 with a different voltage level connected to the high-voltage line 1 in the above formula via a transformer, and the transformer ratio is N; similar to the classic per-unit method, the voltage reference value U of line 2 is... B2 Current reference value I B2 Impedance reference value Z B2 It can be represented as:

[0059] U B2 =U B1 / N

[0060] I B2 =N·I B1

[0061]

[0062] However, in power systems where new energy converters and other power electronic devices are connected, in addition to transformers coupling different levels of lines, the converters connect to different power configurations, typically manifesting as the evolution from classic pure AC power systems to AC / DC hybrid systems. Therefore, this invention introduces the concept of the equivalent turns ratio of the converter in its improved per-unit method, treating the converter's input as equivalent to the primary side of a transformer, and the converter's output as the secondary side of a transformer. The ratio of the converter's input to its output voltage is the converter's equivalent turns ratio M. Thus, the above method for calculating the reference value for line segments at different voltage levels can be extended to line segments with different power configurations in AC / DC hybrid systems, i.e.:

[0063] U B2 =U B1 / M

[0064] I B2 =M·I B1

[0065]

[0066] Step 4: Calculate the per-unit values ​​of voltage / current / power at critical nodes and the per-unit values ​​of impedance for critical components;

[0067] Based on the power reference value and the voltage, current, and impedance reference values ​​obtained in the first three steps for each voltage level, the per-unit values ​​of the voltage / current / power of each critical node can be obtained by dividing the nominal values ​​of the voltage / current / power of each critical node by the voltage / current / power reference values ​​of the corresponding voltage level. Similarly, the per-unit values ​​of the impedance of each critical component can be obtained by dividing the nominal values ​​of the impedance of each critical component by the impedance reference values ​​of the corresponding voltage level.

[0068] Step 5: Obtain the reference values ​​of the converter control parameters based on the frequency domain impedance model;

[0069] Given the converter circuit structure and control structure, the impedance expression Z of the converter in the s-domain (Laplace domain) is... c Depends on the steady-state operating point voltage U, current I, and each controller g c1 ,g c2 …g cn

[0070] Z c (s)=f(U,I,g c1 ,g c2 ...g cn )

[0071] The corresponding frequency domain expression is:

[0072] Z c (ω)=f(ω,U,I,g c1 ,g c2 ...g cn )

[0073] For ease of calculation, this invention selects the baseline value for the impedance calculation control parameter when the angular frequency w = 1, i.e., s = jw = j. Converters generally employ PI control, and the expression for a PI controller is:

[0074]

[0075] K P With K I The ratio T represents the corner frequency of the controller and determines its phase characteristics; when T remains constant while the integral coefficient K... I When the frequency response curve of the controller changes, it shifts vertically on the Bode plot while the phase characteristic remains unchanged. Considering that only the amplitude is normalized and not the phase during impedance normalization, T can be assumed to remain constant during control parameter normalization. Therefore, a key feature of this invention is that only the integral coefficient K needs to be normalized during PI control parameter normalization. I Impedance, voltage, current reference values ​​and required control parameter reference values ​​(K) IB1 ,K IB2 …K IBn The relation is:

[0076] Z B =|f(ω,U B ,I B ,K IB1 ,K IB2 ...K IBn )| ω＝1

[0077] Therefore, by substituting the expression obtained from the impedance modeling of the converter into the above equation, the reference values ​​of the control parameters can be solved.

[0078] Step 6: Calculate the per-unit values ​​of the control parameters for each converter;

[0079] Suppose there are n PI control parameters to be normalized in the converter, then the normalization result of the control parameters is:

[0080]

[0081] The following is a specific application example to further illustrate the solution of the present invention:

[0082] An embodiment of the present invention (a 500kW power-level new energy inverter grid-connected system) is as follows: Figure 1 As shown, the main circuit output current is filtered by an LC filter and boosted by a 630kVA transformer before being connected to the grid. The grid-connected inverter is controlled using the inverter-side inductor current as the feedback signal. The current control loop employs a PI algorithm in a synchronous rotating coordinate system. The input voltage of the phase-locked loop is the low-voltage side voltage of the transformer, and a PI algorithm is also used to achieve grid phase tracking. In the construction of the inverter's wideband impedance model, the transformer leakage reactance and grid-side impedance are referred to the low-voltage side. The equivalent circuit is as follows: Figure 2 As shown; considering the right side of the filter inductor in the figure as the point of common coupling (PCC), the equivalent inverter impedance Z can be obtained by looking from the PCC point towards the inverter side. i The equivalent grid impedance Z can be obtained by looking from point PCC towards the grid side. g Z can be obtained by combining the grid impedance and transformer leakage reactance. g The equivalent inductance component L g and equivalent resistance component R g .

[0083] Before standardization, the key parameters (with nominal values) of this new energy inverter grid-connected system are as follows: Rated effective value of grid voltage V g The voltage is 315V, and the rated effective value of the grid-connected current is I. g The rated power is 916A, the rated grid-connected power S is 500kW, and the filter inductance L is... f The filter capacitor C is 150μH. f The equivalent inductance on the grid side is 80μF. gThe maximum voltage stress P of the IGBT power electronic switching device used in the inverter bridge arm is 0.3mH. MV The voltage is 1200V, and the maximum current stress P of the device is... MI It is 1400A, DC voltage V dc 700V, current loop proportionality coefficient K P1 The integral coefficient K of the current loop is 0.64. I1 The proportional gain K of the phase-locked loop is 100. P2 The integral coefficient K of the phase-locked loop is 1.7. I2 The value is 300. The improved per-unit method proposed according to this invention has the following flowchart. Figure 3 As shown, the specific per-unit transformation process is analyzed as follows:

[0084] Step 1: Select the voltage and current reference values ​​based on the maximum stress of the switching devices in the new energy converter;

[0085] Classical per-unit scaling methods typically select the rated power and rated voltage of representative equipment or buses at a certain voltage level as benchmark values, and use these as the first step in per-unit scaling. It can be seen that classical per-unit scaling methods only consider the influence of topology on system operating characteristics, while the integration of large-scale power electronic devices means that semiconductor devices and converter control strategies also play a decisive role in the safe and stable operation of the power system. Therefore, the first step of the improved per-unit scaling method proposed in this invention focuses on semiconductor device parameters, and sets the maximum voltage stress P of the device as the benchmark. MV Maximum current stress P MI Set as voltage reference value U respectively B1 and current reference value I B1 Therefore, the voltage reference value U B1 Selected as 1200V, current reference value I B1 1400A was selected.

[0086] Step 2: Obtain the power reference value and impedance reference value based on the voltage and current reference values;

[0087] In a three-phase system, the power reference value S B Voltage reference value U B1 Current reference value I B1 Power reference value Z B1 The relationship between them is:

[0088]

[0089]

[0090] Based on the above relationships, the power reference value and impedance reference value can be obtained, where the power reference value is S. B1 It is 2909kW, and the impedance reference value ZB1 It is 0.495Ω.

[0091] Step 3: Calculate the reference values ​​for voltage, current, and impedance at each stage;

[0092] Let the line corresponding to the above reference value be line 1. If there is a line 2 with a different voltage level connected to the high-voltage line 1 in the above formula via a transformer, and the transformer ratio is N; similar to the classic per-unit method, the voltage reference value U of line 2 is... B2 Current reference value I B2 Impedance reference value Z B2 It can be represented as:

[0093] U B2 =U B1 / N

[0094] I B2 =N·I B1

[0095]

[0096] Based on the equivalent circuit Figure 2 Since the relevant parameters of the high-voltage side of the transformer have been converted to the low-voltage side in advance, there is no need to calculate the reference values ​​of the high-voltage side of the transformer in this case.

[0097] In power systems where new energy converters and other power electronic devices are connected, in addition to transformers coupling different levels of lines, converters connect to different power configurations, typically manifesting as the evolution from classic pure AC power systems to AC / DC hybrid systems. Therefore, this invention introduces the concept of the equivalent turns ratio of the converter in its improved per-unit method. The input terminal of the converter is equivalent to the primary side of a transformer, while the output terminal is considered the secondary side of a transformer. The ratio of the input to the output voltage of the converter is the equivalent turns ratio M. Thus, the above method for calculating the reference value for line segments at different voltage levels can be extended to line segments with different power configurations in AC / DC hybrid systems, i.e.:

[0098] U B2 =U B1 / M

[0099] I B2 =M·I B1

[0100]

[0101] In this embodiment, the inverter bridge arm realizes the conversion of DC to AC. Based on the relationship between the rated DC voltage and the rated AC voltage, the turns ratio M is 0.45, and the reference voltage value U on the DC side is... B2 It is 2667V.

[0102] Step 4: Calculate the per-unit values ​​of voltage / current / power at critical nodes and the per-unit values ​​of impedance for critical components;

[0103] Based on the power reference value and the voltage, current, and impedance reference values ​​obtained in the first three steps for each voltage level, the per-unit values ​​of the voltage / current / power of each critical node can be obtained by dividing the nominal values ​​of the voltage / current / power of each critical node by the voltage / current / power reference values ​​of the corresponding voltage level. Similarly, the per-unit values ​​of the impedance of each critical component can be obtained by dividing the nominal values ​​of the impedance of each critical component by the impedance reference values ​​of the corresponding voltage level.

[0104] In this embodiment, the maximum voltage stress P of the IGBT power electronic switching device used in the inverter bridge arm is... MV Standardized to 1, the maximum current stress P of the device MI Per-unit normalized to 1, the rated effective value of the grid voltage V g Standardized to 0.2625, the rated effective value of the grid-connected current I g The per-unit value is 0.6543, the rated grid-connected power S is per-unit value 0.1719, and the filter inductance L... f Per-unit normalized to j0.0952, filter capacitor C f Per-unit normalized to -j80.38, the grid-side equivalent resistance R g Per-unit normalized to 0.202, the equivalent inductance L on the grid side. g Per-unit normalized to j0.1904, DC voltage V dc The per-unit value is 0.2625.

[0105] Step 5: Obtain the reference values ​​of the converter control parameters based on the frequency domain impedance model;

[0106] Given the converter circuit structure and control structure, the impedance expression Z of the converter in the s-domain (Laplace domain) is... c Depends on the steady-state operating point voltage U, current I, and each controller g c1 ,g c2 …g cn

[0107] Z c (s)=f(U,I,g c1 ,g c2 ...g cn )

[0108] The corresponding frequency domain expression is:

[0109] Z c (ω)=f(ω,U,I,g c1 ,g c2 ...g cn )

[0110] For ease of calculation, this invention selects the baseline value for the impedance calculation control parameter when the angular frequency w = 1, i.e., s = jw = j. Converters generally employ PI control, and the expression for a PI controller is:

[0111]

[0112] K P With K I The ratio T represents the corner frequency of the controller and determines its phase characteristics; when T remains constant while the integral coefficient K... I When the frequency response curve of the controller changes, it shifts vertically on the Bode plot while the phase characteristic remains unchanged. Considering that only the amplitude is normalized and not the phase during impedance normalization, T can be assumed to remain constant during control parameter normalization. Therefore, a key feature of this invention is that only the integral coefficient K needs to be normalized during PI control parameter normalization. I Impedance, voltage, current reference values ​​and required control parameter reference values ​​(K) IB1 ,K IB2 …K IBn The relation is:

[0113] Z B =|f(ω,U B ,I B ,K IB1 ,K IB2 ...K IBn )| ω＝1

[0114] Therefore, substituting the expression obtained from the impedance modeling of the converter into the above equation yields the baseline value of the control parameter. In this embodiment, it is necessary to determine the baseline value K of the current loop control parameter. IB1 and the reference value K of the phase-locked loop control parameters IB2 Due to the inverter impedance Z dd The frequency response curve in the low-frequency range basically coincides with the frequency response curve of the current loop controller, that is, the relationship between impedance and controller is:

[0115]

[0116] Current loop control parameter reference value K IB1 The calculation formula is:

[0117]

[0118] In the formula, T1 is 0.0064, K IB1 The calculation result is 0.495.

[0119] Inverter impedance Z qq The low-frequency characteristics depend on the voltage, current stable operating point, and phase-locked loop control parameters, and can be approximated as:

[0120]

[0121] According to the constant amplitude PARK transformation formula, where I d V is the peak value of the phase current. d For the peak phase voltage, g pll This refers to the s-domain expression of the phase-locked loop (PLL) controller. To calculate the reference values ​​for the PLL integral coefficients, the relationship between voltage, current, impedance, and control parameter reference values ​​can be obtained from the above formula:

[0122]

[0123] In the formula, T2 is 0.0057, K IB2 The calculation result is 0.00051.

[0124] Step 6: Calculate the per-unit values ​​of the control parameters for each converter;

[0125] This new energy grid-connected inverter has two PI control parameters that need to be normalized. Combining the original values ​​of the current loop and phase-locked loop control parameters, the normalized result of the current loop control parameter is 202.02, and the normalized result of the phase-locked loop control parameter is 588240.

[0126] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

[0127] The system and method provided in this embodiment can be stored in a computer-readable storage medium in the form of code, implemented as a computer program, and the basic parameter information required for calculation can be input through computer hardware, and the calculation results can be output.

[0128] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied 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.

[0129] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0130] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0131] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

[0133] This patent is not limited to the above-described preferred embodiments. Anyone can derive other methods for standardizing system parameters applicable to the grid connection stability analysis of new energy sources based on the guidance of this patent. All equivalent changes and modifications made within the scope of this patent application shall fall within the scope of this patent.

Claims

1. A method for standardizing system parameters suitable for grid-connected stability analysis of new energy sources, characterized in that, Includes the following steps: Step 1: Select the voltage and current reference values ​​based on the maximum stress of the switching devices in the new energy converter; Step 2: Obtain the power reference value and impedance reference value based on the voltage and current reference values; Step 3: Calculate the reference values ​​for voltage, current, and impedance at each stage; Step 4: Calculate the per-unit values ​​of voltage, current, and power at critical nodes, and the per-unit values ​​of impedance for critical components; Step 5: Obtain the reference values ​​of the converter control parameters based on the frequency domain impedance model; Step 6: Calculate the per-unit values ​​of the control parameters for each converter; In step 5, given the converter circuit structure and control structure, the impedance expression Z of the converter in the s-domain is... c Depends on the steady-state operating point voltage U, current I, and each controller g c1 ,g c2 …g cn : The frequency domain expression corresponding to the above equation is: Select the baseline value for the impedance calculation control parameters when the angular frequency w=1, i.e., s=jw=j; assuming the converter uses PI control, the expression for the PI controller is: K P With K I The ratio T represents the corner frequency of the controller, which determines the phase characteristics of the controller; when T is constant and the integral coefficient K... I When the frequency response curve of the controller changes, it shifts vertically on the Bode plot while the phase characteristic remains unchanged. Considering that only the amplitude is normalized and not the phase during impedance normalization, and that T remains constant by default during control parameter normalization, the normalization of PI control parameters only requires normalizing the integral coefficient K. I Impedance, voltage, current reference values ​​and required control parameter reference values: K IB1 ,K IB2 …K IBn The relation is: The baseline values ​​of the control parameters are solved by substituting the expression obtained from the impedance modeling of the converter into the above equation. In step 6, assuming there are n PI control parameters to be normalized in the converter, the normalization result of the control parameters is: 。 2. The system parameter per-unit method for grid-connected stability analysis of new energy sources according to claim 1, characterized in that: In step 1, the maximum voltage stress P of the device is... MV Maximum current stress P MI Set as voltage reference value U respectively B1 and current reference value I B1 This ensures that the per-unit values ​​of the maximum voltage stress and maximum current stress of the switching device are both 1.

3. The system parameter standardization method for grid-connected stability analysis of new energy sources according to claim 2, characterized in that: Consider the following in step 2: In a three-phase system, the power reference value S B Voltage reference value U B1 Current reference value I B1 Power reference value Z B1 The relationship between them is: The power reference value and impedance reference value are obtained based on the above relationship.

4. The system parameter standardization method for grid-connected stability analysis of new energy sources according to claim 3, characterized in that: In step 3, let the line corresponding to the reference values ​​of voltage, current and impedance of each level be calculated be line 1. If there is a line 2 with a different voltage level connected to line 1 through a transformer, let the transformer ratio be N. Line 2 voltage reference value U B2 Current reference value I B2 Impedance reference value Z B2 Represented as: Further introducing the concept of equivalent turns ratio of a converter, the input terminal of the converter is equivalent to the primary side of a voltage transformer, while the output terminal of the converter is considered as the secondary side of a transformer. The ratio of the input voltage to the output voltage of the converter is the equivalent turns ratio M of the converter. This extends the method of calculating the reference value for line sections with different voltage levels to line sections with different power configurations in AC / DC hybrid configurations, namely: 。 5. A method for standardizing system parameters suitable for grid-connected stability analysis of new energy sources according to claim 4, characterized in that: In step 4, based on the power reference value and the voltage, current, and impedance reference values ​​obtained in steps 1-3 for each voltage level, the nominal values ​​of voltage, current, and power of each key node are divided by the voltage, current, and power reference values ​​of the corresponding voltage level to obtain the per-unit values ​​of voltage / current / power of the key node; the nominal values ​​of impedance of each key component are divided by the impedance reference values ​​of the corresponding voltage level to obtain the per-unit values ​​of impedance of the key component.

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