Optimization Control Method and System of Grid-Connected Inverters Based on Dynamic Virtual Impedance

Abstract

The present invention belongs to the technical field of grid-connected converters, and specifically discloses an optimized control method and system for grid-connected converters based on dynamic virtual impedance. The method includes: calculating the output voltage reference values of the d-axis and q-axis, and the output phase angle of the converter; performing coordinate transformation on the output voltage reference values to obtain the output voltage reference values of the d-axis and q-axis; acquiring the instantaneous current measurement values of the d-axis and q-axis of the grid-connected converter, and combining the instantaneous current measurement values with the output voltage reference values of the d-axis and q-axis, the virtual resistance, and the virtual inductance to obtain a modulation signal. The modulation signal is combined with the output phase angle of the converter, and through coordinate transformation and PWM modulation, a switching control signal for the grid-connected converter is obtained, realizing the optimized control of the grid-connected converter. Through the dynamic adjustment of the virtual impedance, the present invention can achieve the fast and accurate tracking of the converter output power to the power reference value, thereby realizing the precise control of the output active power and output reactive power.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected converters, and particularly to an optimized control method and system for grid-connected converters based on dynamic virtual impedance. Background Art

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Since distributed power generation is mostly located in remote areas with long transmission lines and many transformers, the power grid exhibits weak grid characteristics; as the proportion of distributed power generation increases, in order to meet the load requirements, converters often operate in parallel. Under this condition, the equivalent grid impedance of a single converter increases, and the weak grid characteristics of the power grid are significant. The frequent curtailment of wind and light and power grid failures caused by the weak grid have seriously threatened the safe and stable operation of the power grid and new energy power generation systems. High-penetration new energy power generation is intermittent, random, and has fluctuating power output, and the grid impedance often has large fluctuations.

[0004] Grid-connected converters play a key role in new energy power generation and are widely used in systems such as micro energy, distributed power generation, energy storage, AC-DC microgrids, etc. Traditional grid-connected converters mainly adopt grid-following control or grid-forming control: Grid-following control adjusts the active and reactive power outputs based on the grid phase and is suitable for strong grids, but the stability margin decreases in weak grids, which may cause harmonic resonance or even instability; Grid-forming control directly realizes the output power regulation by controlling the phase of the output voltage vector, is more stable under weak grids, but is unstable in strong grids, and there are also power tracking problems, which may lead to a decrease in the efficiency of the new energy grid-connected system and the risk of grid instability under dynamic conditions.

[0005] The prior art has proposed an AHO (Adaptive Heuristic Optimization) control strategy for grid-connected converters in high-penetration new energy power generation, hoping to provide stable voltage and frequency outputs in both strong and weak grids. However, there is an inherent coupling between active and reactive power regulation in this way, and independent tracking of power commands cannot be achieved, which may lead to significant deviations between the actual output power of the converter and the reference command, triggering a series of hazards such as frequency / voltage instability, reduced power generation benefits, and limited new energy consumption. Summary of the Invention

[0006] In order to solve the above problems, the present invention proposes an optimized control method and system for grid-connected converters based on dynamic virtual impedance. On the basis of the AHO architecture, a dynamic virtual impedance adjustment mechanism is introduced. By adapting impedance calculation and real-time identification of grid parameters, the virtual impedance parameters are dynamically reconstructed, and the mapping relationship between impedance and output power is used to achieve fast and accurate tracking of the converter output power to the reference value.

[0007] In some embodiments, the following technical solutions are adopted:

[0008] An optimized control method for a grid-connected converter based on dynamic virtual impedance, comprising:

[0009] Calculating the output voltage reference values of the axis and the

[0010] axis, and the output phase angle of the converter;

[0011] Performing coordinate transformation on the output voltage reference values to obtain the output voltage reference values of the d-axis and q-axis;

[0012] Obtaining the instantaneous current measurement values of the d-axis and q-axis of the grid-connected converter, combining the instantaneous current measurement values with the output voltage reference values of the d-axis and q-axis, the virtual resistance and the virtual inductance to obtain a modulation signal, and combining the modulation signal with the output phase angle of the converter, and through coordinate transformation and PWM modulation, obtaining the switching control signal of the grid-connected converter to realize the optimized control of the grid-connected converter.

[0013] As an optional solution, the value of the virtual resistance is equal to the difference between the adapted resistance and the actual grid resistance; the value of the virtual inductance is equal to the difference between the adapted inductance and the actual grid inductance.

[0014] As an optional solution, the calculation methods of the adapted resistance and the adapted inductance are:

[0015] Establishing a mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adapted resistance and the adapted inductance;

[0016] Letting the output active power be equal to the active power reference value, the output reactive power be equal to the reactive power reference value, and the modulus of the output voltage of the converter be equal to the modulus of the grid voltage;

[0017] As an optional solution, establishing a mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adapted resistance and the adapted inductance, specifically:

[0018] ;

[0019] Wherein,

[0020] ;

[0021] ;

[0022] Wherein, , , , respectively represent the output voltage magnitude, grid voltage magnitude, grid impedance magnitude, and grid impedance angle of the converter, and are respectively the actual output active power and reactive power of the grid-connected converter system, and are respectively the adaptive resistance and adaptive inductance.

[0023] As an alternative solution, the process of joint iterative solution by the Newton-Raphson iterative method is specifically as follows:

[0024] Given the initial values of the adaptive resistance and adaptive inductance , ;

[0025] Substitute the iteration result of the and into the residual function F , and calculate ;

[0026] Take the partial derivatives of with respect to , ; , ;

[0027] Use the Newton iteration formula to update the iteration result;

[0028] When the absolute value of is less than the preset tolerance, terminate the iteration.

[0029] As an alternative solution, calculate the output voltage reference values of the axis and axis, and the output phase angle of the converter, specifically as follows:

[0030] Based on the given active power reference value and reactive power reference value, calculate the output current reference values of the axis and axis;

[0031] The axis and axis output current reference values are respectively subtracted from the instantaneous current measurement values of the axis and axis. The deviation values are multiplied by the scaling factor , and then multiplied by the rotation angle matrix to obtain a set of intermediate variables;

[0032] Based on the intermediate variables, obtain the axis and The output voltage reference value of the axis, and based on the output voltage reference value, the output phase angle of the converter is obtained.

[0033] As an alternative solution, the instantaneous current measurement value combines the output voltage reference values of the d-axis and q-axis, a virtual resistance, and a virtual inductance to obtain a modulation signal, specifically:

[0034] ;

[0035] Among them, and are the instantaneous current measurement values of the d-axis and q-axis respectively, and are the virtual resistance and virtual inductance respectively, is the output angular frequency of the converter, and the modulation signal of the dq-axis .

[0036] In some other embodiments, the following technical solution is adopted:

[0037] An optimized control system for a grid-connected converter based on dynamic virtual impedance, including:

[0038] A voltage reference value calculation module for calculating the output voltage reference values of the axis and the axis, as well as the output phase angle of the converter;

[0039] A voltage reference value transformation module for performing coordinate transformation on the output voltage reference value to obtain the output voltage reference values of the d-axis and q-axis;

[0040] A converter optimization module for obtaining the instantaneous current measurement values of the d-axis and q-axis of the grid-connected converter. The instantaneous current measurement value combines the output voltage reference values of the d-axis and q-axis, a virtual resistance, and a virtual inductance to obtain a modulation signal. The modulation signal combines the output phase angle of the converter, and through coordinate transformation and PWM modulation, a switching control signal for the grid-connected converter is obtained to achieve optimized control of the grid-connected converter.

[0041] In some other embodiments, the following technical solution is adopted:

[0042] A terminal device includes a processor and a memory. The processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are suitable for being loaded and executed by the processor to perform the above-mentioned optimized control method for a grid-connected converter based on dynamic virtual impedance.

[0043] In some other embodiments, the following technical solution is adopted:

[0044] A computer-readable storage medium stores multiple instructions, and the instructions are adapted to be loaded and executed by a processor of a terminal device to perform the above-mentioned optimized control method for a grid-connected converter based on dynamic virtual impedance.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] (1) The present invention uses the instantaneous current measurement value in combination with the output voltage reference values of the d-axis and q-axis, the virtual resistance, and the virtual inductance to obtain a modulation signal, thereby realizing the optimized control of the grid-connected converter; based on the mapping relationship between the virtual resistance and virtual inductance and the output power, when the grid strength changes, or when the active power reference value or the reactive power reference value changes, it can quickly adapt to the new virtual resistance and virtual inductance. Through the dynamic adjustment of the virtual impedance, it can achieve fast and accurate tracking of the converter output power to the power reference value, thereby realizing precise control of the output active power and output reactive power.

[0047] (2) When the active power reference value or the reactive power reference value changes in the method of the present invention, the corresponding adapted impedance can be accurately calculated, so that the output values of the active power or reactive power can be adjusted in real time, ensuring that the output active power and reactive power can keep up with the reference values, realizing the decoupling of power; breaking through the tracking deviation limitation caused by power coupling in traditional AHO control, significantly improving the energy conversion efficiency of the new energy grid-connected system within a wide impedance fluctuation range, providing a converter control solution with strong robustness and engineering practicability for high-penetration new energy scenarios, and effectively solving the problem of coordinated optimization of stability and economy under the condition of variable grid strength.

[0048] Other features and advantages of the additional aspects of the present invention will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of this aspect. Description of the Drawings

[0049] Figure 1 It is a schematic structural diagram of a converter grid-connected system in an embodiment of the present invention;

[0050] Figure 2 It is a flowchart of an optimized control method for a grid-connected converter based on dynamic virtual impedance in an embodiment of the present invention;

[0051] Figure 3 It is a schematic structural diagram of an optimized control for a grid-connected converter based on dynamic virtual impedance in an embodiment of the present invention. Detailed Embodiments

[0052] It should be noted that the following detailed description is illustrative and aims to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0053] It should be noted that the terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0054] Embodiment 1

[0055] The main improvement of the present invention is to introduce a dynamic virtual impedance regulation mechanism on the basis of the AHO control architecture to achieve fast and accurate tracking of the converter output power to the reference value.

[0056] The structure of the converter grid-connected system is as Figure 1 shown, including a DC source , a three-phase bridge PWM inverter, a filter inductor and a filter capacitor to form an LC filter, a grid-side inductor and an AC grid.

[0057] Assume ~ represent the 6 switching elements of the inverter, and define the switching states , , of the inverter as follows:

[0058] ; ; .

[0059] Then the switching synthesis vector of the inverter is:

[0060] ;

[0061] where is the natural logarithm, is the imaginary unit.

[0062] In the traditional AHO control architecture, the output voltage reference values of the d-axis and q-axis are directly used as modulation signals. However, in this way, there is an inherent coupling in the active and reactive power regulation, and the independent tracking and control of the power command cannot be achieved, resulting in a deviation in the output power.

[0063] Based on this, in one or more embodiments, an optimized control method for grid-connected converters based on dynamic virtual impedance is disclosed, which combines Figure 2 and Figure 3 , and specifically includes the following process:

[0064] S101: Calculate the axis and axis output voltage reference values, and the output phase angle of the converter.

[0065] The specific implementation process of this step is as follows:

[0066] S1011: Based on the given active power reference value and the reactive power reference value , calculate the axis and axis output current reference values and ; The calculation formula is as follows:

[0067] ;

[0068] Among them, , , are respectively the axis and axis output voltage reference values, .

[0069] S1012: Subtract the axis and axis output current reference values and from the axis and axis instantaneous current measurement values and respectively, multiply the deviation value by the scaling factor , and then multiply by the rotation angle matrix to obtain a set of intermediate variables and , and define .

[0070] S1013: Obtain the axis and axis output voltage reference values based on the intermediate variables, and obtain the output phase angle of the converter based on the output voltage reference values.

[0071] Establish the relationship between and , specifically:

[0072] ;

[0073] Among them, 、 、 、 、 respectively represent the output voltage reference value of the axis differential, convergence speed constant, voltage reference value, output voltage amplitude, and angular frequency reference value.

[0074] The converter output phase angle , the converter output angular frequency is the differential of.

[0075] S102: Perform -dq coordinate transformation on the output voltage reference value to obtain the output voltage reference values and of the d-axis and q-axis.

[0076] S103: Obtain the instantaneous current measurement values of the d-axis and q-axis of the grid-connected converter. The instantaneous current measurement values are combined with the output voltage reference values of the d-axis and q-axis, virtual resistance, and virtual inductance to obtain the modulation signal;

[0077] S104: The modulation signal is combined with the output phase angle of the converter, and through coordinate transformation and PWM modulation, the switch control signal of the grid-connected converter is obtained to achieve the optimal control of the grid-connected converter.

[0078] Specifically, the instantaneous current measurement values are combined with the output voltage reference values of the d-axis and q-axis, virtual resistance, and virtual inductance to obtain the modulation signal and , specifically:

[0079] ;

[0080] Among them, 、 are respectively the instantaneous current measurement values of the d-axis and q-axis, 、 are respectively the virtual resistance and virtual inductance, is the converter output angular frequency, and the modulation signal of the dq-axis .

[0081] The converter switch control signal is obtained through dq-abc coordinate transformation and PWM modulation.

[0082] Next, the specific calculation process of the virtual resistance and the virtual inductance will be described:

[0083] In the grid-connected converter system, the actual output active power and the actual output reactive power are calculated by the following formulas:

[0084] ;

[0085] where , , , , represent the magnitude of the converter output voltage, the magnitude of the grid voltage, the phase angle of the converter output voltage relative to the grid voltage, the magnitude of the grid impedance, and the grid impedance angle, respectively; , ; is the grid-side resistance, is the grid-side inductance.

[0086] By combining the calculation formulas of and , it can be transformed into the following form:

[0087] ;

[0088] The impedance parameters and to be solved should satisfy the above equation under the condition of

[0089] By using the Newton-Raphson iteration method to solve the adaptive resistance and the adaptive inductance , the rapid solution of the adaptive resistance and the adaptive inductance can be achieved; the specific process is as follows:

[0090] First, initial values , are given;

[0091] Subsequently, the iteration results of the th time , are substituted into the residual function:

[0092] ;

[0093] Calculate ;

[0094] Take the partial derivatives of , with respect to , ;

[0095] Use the Newton iteration formula , update the iteration result of the th time; when the absolute value of is less than the preset tolerance, terminate the iteration.

[0096] Calculate the adapted resistance and the adapted inductance After that, combine the actually measured power grid resistance with the inductance , the virtual resistance and the virtual inductance , the calculation formula is:

[0097] .

[0098] It should be noted that the detection of the actual power grid resistance and inductance can be realized by existing technical methods (such as: injecting non-characteristic harmonics, injecting wide-frequency signals, etc.), which will not be elaborated here.

[0099] In this embodiment, the modulation signal is obtained by using the instantaneous current measurement value in combination with the output voltage reference values of the d-axis and q-axis, the virtual resistance and the virtual inductance; using the mapping relationship between the virtual impedance and the output power, when the upper-layer control issues an instruction to the converter, that is, the given active power reference value or the given reactive power reference value changes, the virtual impedance changes with the power reference. Through the method of this embodiment, the new adapted impedance parameters can be quickly obtained, so as to realize dynamic power tracking; or, when the grid strength fluctuates, that is, the actual power grid resistance and the inductance change, the virtual impedance will also change accordingly, realizing accurate tracking of active power and reactive power.

[0100] Through the control method of this embodiment, regardless of the active power reference value or the reactive power reference value how it changes, the corresponding adapted impedance can be calculated to ensure that the output active power and reactive power can follow the reference values, realizing power decoupling.

[0101] Embodiment Two

[0102] In one or more embodiments, an optimized control system for a grid-connected converter based on dynamic virtual impedance is disclosed, specifically including:

[0103] A voltage reference value calculation module, used to calculate the output voltage reference values of the axis and the

[0104] A voltage reference value transformation module is used to perform coordinate transformation on the output voltage reference value to obtain the output voltage reference values of the d-axis and q-axis.

[0105] A converter optimization module is used to obtain the measured values of the instantaneous currents of the d-axis and q-axis of the grid-connected converter. The measured values of the instantaneous currents, combined with the output voltage reference values of the d-axis and q-axis, a virtual resistor, and a virtual inductor, are used to obtain a modulation signal. The modulation signal, combined with the output phase angle of the converter, undergoes coordinate transformation and PWM modulation to obtain the switch control signal of the grid-connected converter, thereby achieving the optimized control of the grid-connected converter.

[0106] It should be noted that the specific implementation manners of the above-mentioned modules are exactly the same as those in Embodiment 1 and will not be elaborated here.

[0107] Embodiment 3

[0108] In one or more embodiments, a terminal device is disclosed, which includes a processor and a memory. The processor is used to implement instructions, and the memory is used to store multiple instructions. The instructions are adapted to be loaded and executed by the processor to perform the optimized control method of the grid-connected converter based on dynamic virtual impedance described in Embodiment 1.

[0109] It should be understood that in this embodiment, the processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor, or the processor may also be any conventional processor, etc.

[0110] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0111] During the implementation process, each step of the above method may be completed by the integrated logic circuit in the hardware of the processor or the instructions in the form of software.

[0112] Embodiment 4

[0113] In one or more embodiments, a computer-readable storage medium is disclosed, in which multiple instructions are stored. The instructions are adapted to be loaded and executed by the processor of the terminal device to perform the optimized control method of the grid-connected converter based on dynamic virtual impedance described in Embodiment 1.

[0114] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative efforts on the basis of the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. An optimized control method for grid-connected converters based on dynamic virtual impedance, characterized in that, Including: Calculation axis and the output voltage reference value of the axis and the output phase angle of the converter; Performing coordinate transformation on the output voltage reference value to obtain the output voltage reference values of the d-axis and q-axis; Obtaining the instantaneous current measurement values of the d-axis and q-axis of the grid-connected converter. The instantaneous current measurement values, combined with the output voltage reference values of the d-axis and q-axis, the virtual resistance, and the virtual inductor, are used to obtain a modulation signal. The modulation signal, combined with the output phase angle of the converter, undergoes coordinate transformation and PWM modulation to obtain the switching control signal of the grid-connected converter, realizing the optimal control of the grid-connected converter; Wherein, the value of the virtual resistance is equal to the difference between the adapted resistance and the actual grid resistance; the value of the virtual inductor is equal to the difference between the adapted inductance and the actual grid inductance; The calculation methods of the adapted resistance and the adapted inductance are as follows: Establishing a mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adapted resistance and the adapted inductance; Setting the output active power equal to the active power reference value, the output reactive power equal to the reactive power reference value, and the output voltage modulus of the converter equal to the grid voltage modulus; Performing joint iterative solution through the Newton-Raphson iterative method to obtain the final adapted resistance and adapted inductance.

2. The optimized control method for a grid-connected converter based on dynamic virtual impedance according to claim 1, characterized in that, Establishing a mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adapted resistance and the adapted inductance, specifically: ； Wherein, ； ； Among them, , , , respectively represent the output voltage magnitude, grid voltage magnitude, grid impedance magnitude, and grid impedance angle of the converter, and are respectively the actual output active power and reactive power of the grid-connected converter system, and are respectively the matching resistor and the matching inductor.

3. The optimized control method for a grid-connected converter based on dynamic virtual impedance according to claim 1, wherein, The process of performing joint iterative solution through the Newton-Raphson iterative method is specifically: Given the initial values of the adaptive resistor and the adaptive inductor , ; Bring the iteration result of the th into the residual function F , and calculate ; For Find the partial derivatives with respect to , ; , ; Update the iteration result of the th iteration using the Newton iteration formula; Terminate the iteration when the absolute value of is less than a preset tolerance.

4. The optimized control method for grid-connected converters based on dynamic virtual impedance according to claim 1, characterized in that Calculation shaft and the output voltage reference value of the shaft, and the output phase angle of the converter, specifically: Calculate the reference values of the output currents of the axis and the axis based on the given reference values of the active power and the reactive power; The axis and the output current reference value of the axis are respectively subtracted from axis and the instantaneous current measured value of the axis, the deviation value is multiplied by the scaling factor and then multiplied by the rotation angle matrix to obtain a set of intermediate variables; Obtained based on the intermediate variable axis and the output voltage reference value of the axis, and obtain the output phase angle of the converter based on the output voltage reference value.

5. The optimized control method of a grid-connected converter based on dynamic virtual impedance according to claim 1, wherein The instantaneous current measurement values, combined with the output voltage reference values of the d-axis and q-axis, the virtual resistance, and the virtual inductor, are used to obtain a modulation signal, specifically: ； Among them, , are the measured values of the instantaneous currents on the d-axis and q-axis respectively, , are the virtual resistance and virtual inductance respectively, is the output angular frequency of the converter, and the modulation signals on the dq axes are .

6. An optimized control system for a grid-connected converter based on dynamic virtual impedance, characterized in that, Including: A voltage reference value calculation module for calculating the axis and the output voltage reference value of the axis, as well as the output phase angle of the converter; A voltage reference value transformation module for performing coordinate transformation on the output voltage reference value to obtain the output voltage reference values of the d-axis and q-axis; A converter optimization module for obtaining the instantaneous current measurement values of the d-axis and q-axis of the grid-connected converter. The instantaneous current measurement values, combined with the output voltage reference values of the d-axis and q-axis, the virtual resistance, and the virtual inductor, are used to obtain a modulation signal. The modulation signal, combined with the output phase angle of the converter, undergoes coordinate transformation and PWM modulation to obtain the switching control signal of the grid-connected converter, realizing the optimal control of the grid-connected converter; Wherein, the value of the virtual resistance is equal to the difference between the adapted resistance and the actual grid resistance; the value of the virtual inductor is equal to the difference between the adapted inductance and the actual grid inductance; The calculation methods of the adapted resistance and the adapted inductance are as follows: Establishing a mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adapted resistance and the adapted inductance; Setting the output active power equal to the active power reference value, the output reactive power equal to the reactive power reference value, and the output voltage modulus of the converter equal to the grid voltage modulus; Performing joint iterative solution through the Newton-Raphson iterative method to obtain the final adapted resistance and adapted inductance.

7. A terminal device, comprising a processor and a memory, the processor being configured to implement instructions; the memory being configured to store a plurality of instructions, characterized in that, The instruction is suitable for being loaded and executed by a processor to perform the optimal control method of the grid-connected converter based on dynamic virtual impedance according to any one of claims 1-5.

8. A computer-readable storage medium storing multiple instructions, characterized in that, The instruction is suitable for being loaded and executed by a processor of a terminal device to perform the optimal control method of the grid-connected converter based on dynamic virtual impedance according to any one of claims 1-5.

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