Grid-connected converter optimization control method and system based on dynamic virtual impedance

Abstract

The invention belongs to the technical field of grid-connected converters, and particularly discloses a grid-connected converter optimization control method and system based on dynamic virtual impedance, and the method comprises the steps: calculating the output voltage reference values of a # imgabs0 # axis and a # imgabs1 # axis, and the output phase angle of a converter; performing coordinate transformation on the output voltage reference values to obtain output voltage reference values of a d axis and a q axis; the method comprises the following steps: acquiring instantaneous current measurement values of a d axis and a q axis of a grid-connected converter, combining the instantaneous current measurement values with output voltage reference values of the d axis and the q axis, virtual resistance and virtual inductance to obtain a modulation signal, combining the modulation signal with an output phase angle of the converter, and performing coordinate transformation and PWM modulation to obtain a grid-connected converter switch control signal. And optimal control of the grid-connected converter is realized. According to the invention, through dynamic adjustment of the virtual impedance, rapid and accurate tracking of the output power of the converter to the power reference value can be realized, so that accurate control of the output active power and the output reactive power is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected converters, and in particular 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 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 generation increases, in order to meet the load requirements, converters often operate in parallel. In 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 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. New energy power generation with high penetration has intermittency, randomness, and output volatility, and the grid impedance often has a problem of 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 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, which is more stable in weak grids but unstable in strong grids. At the same time, 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 new energy power generation under high penetration, hoping to provide stable voltage and frequency outputs in both strong grids and weak grids. However, in this way, there is an inherent coupling between active and reactive power regulation, and it is impossible to independently track the power command, which may lead to a significant deviation between the actual output power of the converter and the reference command, triggering a series of hazards such as frequency / voltage instability, a decrease in power generation revenue, 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: An optimized control method for a grid-connected converter based on dynamic virtual impedance, comprising: Calculating The output voltage reference values of the axis and the 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 the q-axis;

[0008] 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.

[0009] As an optional solution, 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; Making the output active power equal to the active power reference value, the output reactive power equal to the reactive power reference value, and the modulus of the output voltage of the converter equal to the modulus of the grid voltage; Performing joint iterative solution on the above formulas by the Newton-Raphson iterative method to obtain the final adapted resistance and adapted inductance.

[0010] 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: ; Wherein, ; ; Wherein, , , , respectively represent the modulus of the output voltage of the converter, the modulus of the grid voltage, the modulus of the grid impedance, and the grid impedance angle, and are respectively the actual output active power and reactive power of the grid-connected converter system, and are respectively the adapted resistance and the adapted inductance.

[0011] As an alternative, the process of joint iterative solution by the Newton-Raphson iterative method is specifically as follows: Given the initial values of the adaptive resistance and the adaptive inductance 、 ; Bring the th iteration result and into the residual function F , and calculate ; Take the partial derivatives of with respect to 、 to obtain 、 ; Use the Newton iteration formula to update the th iteration result; When is less than the preset tolerance in absolute value, terminate the iteration.

[0012] As an alternative, calculate the output voltage reference values of the axis and the axis, as well as the output phase angle of the converter, specifically as follows: Based on the given active power reference value and reactive power reference value, calculate the output current reference values of the axis and the axis; The axis and the axis output current reference values are respectively subtracted from the instantaneous current measurement values of the axis and the 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; Based on the intermediate variables, obtain the output voltage reference values of the axis and the axis, and based on the output voltage reference values, obtain the output phase angle of the converter.

[0013] As an alternative, the instantaneous current measurement values are combined with the output voltage reference values of the d-axis and q-axis, the virtual resistance, and the virtual inductance to obtain the modulation signal, specifically as follows: ; Among them, 、 are respectively the instantaneous current measurement values of the d-axis and q-axis, 、 are respectively the virtual resistance and the virtual inductance, is the output angular frequency of the converter, and the modulation signal of the dq-axis 。

[0014] In some other embodiments, the following technical solutions are adopted: An optimized control system for a grid-connected converter based on dynamic virtual impedance, comprising: 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; A voltage reference value transformation module for performing coordinate transformation on the output voltage reference values to obtain the output voltage reference values of the d-axis and q-axis;

[0015] In some other embodiments, the following technical solutions are adopted: A terminal device, comprising a processor and a memory, the processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are adapted to be loaded and executed by the processor to perform the above-mentioned optimized control method for a grid-connected converter based on dynamic virtual impedance.

[0016] In some other embodiments, the following technical solutions are adopted: A computer-readable storage medium, in which multiple instructions are stored, 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.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention uses the instantaneous current measurement values in combination with the output voltage reference values of the d-axis and q-axis, virtual resistance and 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 inductance and the output power, when the grid strength changes, or the active power reference value or reactive power reference value changes, it can quickly adapt to the new virtual resistance and inductance, and through the dynamic adjustment of the virtual impedance, it can realize 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.

[0018] (2) When the reference value of active power or the reference value of reactive power changes in the method of the present invention, the corresponding adaptive impedance can be accurately calculated, so that the output values of active power or reactive power can be adjusted in real time, ensuring that the output active power and reactive power can follow the reference value, 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 in 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.

[0019] Other features and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of this aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of a converter grid-connected system in an embodiment of the present invention; 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; Figure 3 It is a schematic structural diagram of an optimized control of a grid-connected converter based on dynamic virtual impedance in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] It should be noted that the following detailed description is illustrative and is intended 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 the present application belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments 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 form is also intended to include the plural form. In addition, 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.

[0023] Embodiment 1 The main improvement of the present invention is to introduce a dynamic virtual impedance adjustment mechanism on the basis of the AHO control architecture to realize the fast and accurate tracking of the converter output power to the reference value.

[0024] 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 filter capacitors the LC filter composed of the grid-side inductor

[0025] Assume ~ represent the 6 switching elements of the inverter, and define the switching states of the inverter 、 、 as follows: ; ; 。

[0026] Then the switching synthesis vector of the inverter is: ; wherein, is the natural logarithm, is the imaginary unit.

[0027] 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 it is impossible to achieve independent tracking and control of the power command, resulting in a deviation in the output power.

[0028] Based on this, in one or more embodiments, an optimized control method for a grid-connected converter based on dynamic virtual impedance is disclosed, combining Figure 2 and Figure 3 specifically including the following process: S101: Calculate the output voltage reference values of the axis and the

[0029] axis, and the output phase angle of the converter. The specific implementation process of this step is as follows: S1011: Based on the given active power reference value and reactive power reference value calculate the output current reference values and of the axis; the calculation formula is as follows: ; wherein, , 、 are respectively the output voltage reference values of the axis and the axis, 。

[0030] S1012: Subtract the output current reference values of the axis and the axis respectively from the instantaneous current measurement values of the axis and the axis, multiply the deviation values by the scaling factor axis and the axis, and then multiply the result by the rotation angle matrix axis and the axis to obtain a set of intermediate variables axis and the axis, and define axis and the axis. .

[0031] S1013: Based on the intermediate variables, obtain the output voltage reference values of the axis and the axis, and based on the output voltage reference values, obtain the output phase angle of the converter.

[0032] Establish a relationship between axis and the axis, specifically: ; wherein, , , , , respectively represent the differential of the output voltage reference value of the axis, the convergence speed constant, the voltage reference value, the output voltage amplitude, and the angular frequency reference value. axis.

[0033] The output phase angle of the converter axis, and the output angular frequency of the converter is the differential of axis.

[0034] S102: Perform -dq coordinate transformation on the output voltage reference values to obtain the output voltage reference values of the d-axis and q-axis axis and the axis.

[0035] S103: Obtain 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 the modulation signal; S104: 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, thereby achieving optimal control of the grid-connected converter.

[0036] Specifically, the instantaneous current measurement value is combined with the output voltage reference value of the d-axis and q-axis, the virtual resistance and the virtual inductance to obtain the modulation signal and , specifically: ; in, , are the instantaneous current measurements of the d-axis and q-axis respectively, , are virtual resistance and virtual inductance respectively, is the inverter output angular frequency, the modulation signal of the dq axis .

[0037] The converter switch control signal is obtained through dq-abc coordinate transformation and PWM modulation. .

[0038] The virtual resistor and virtual inductance The specific calculation process is explained as follows: In the grid-connected converter system, the actual output active power The actual output reactive power The formula is: ; in, , , , , Respectively represent the modulus of the converter output voltage, the modulus of the grid voltage, the phase angle of the converter output voltage relative to the grid voltage, the modulus of the grid impedance and the grid impedance angle; , ; is the grid side resistance, is the grid side inductance.

[0039] Lian Li , The calculation formula can be transformed into the following form: ; Impedance parameters to be matched and , should be The above equation is satisfied under the condition.

[0040] Solving the matching resistance by Newton-Raphson iteration method And matching inductor , the matching resistance and matching inductance can be quickly solved; the specific process is as follows: First, given the initial value , ; Subsequently, the iteration result of the th time , is substituted into the residual function: ; Calculate ; For , find the partial derivatives with respect to , as , ; Using 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.

[0041] After calculating the adapted resistance and the adapted inductance , combining the detected actual grid resistance and the inductance , the calculation formulas for the virtual resistance and the virtual inductance are: .

[0042] It should be noted that the detection of the actual grid resistance and inductance can be achieved by existing technical methods (such as: injecting non - characteristic harmonics, injecting wide - frequency signals, etc.), which will not be elaborated here.

[0043] In this embodiment, the modulation signal is obtained by combining the instantaneous current measurement value 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, new adapted impedance parameters can be quickly obtained, thus achieving dynamic power tracking; or, when the grid strength fluctuates, that is, the actual grid resistance and the inductance change, the virtual impedance will also change accordingly, achieving accurate tracking of active power and reactive power.

[0044] Through the control method of this embodiment, regardless of whether the active power reference value or the reactive power reference value No matter how it changes, the corresponding adaptive impedance can be calculated to ensure that both the output active power and reactive power can follow the reference values, achieving power decoupling.

[0045] Embodiment 2 In one or more embodiments, an optimized control system for a grid-connected converter based on dynamic virtual impedance is disclosed, specifically including: A voltage reference value calculation module for calculating the output voltage reference values of the d-axis and q-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 values to obtain the output voltage reference values of the d-axis and q-axis;

[0046] It should be noted that the specific implementation manners of the above modules are exactly the same as those in Embodiment 1 and will not be elaborated here.

[0047] Embodiment 3 In one or more embodiments, a terminal device is disclosed, which 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 adapted to be loaded and executed by the processor to perform the optimized control method for a grid-connected converter based on dynamic virtual impedance described in Embodiment 1.

[0048] 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 DSP, application-specific integrated circuits ASIC, field-programmable gate arrays FPGA 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.

[0049] 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.

[0050] During implementation, the steps of the above method may be completed by the integrated logic circuit in the hardware of the processor or the instructions in software form.

[0051] Embodiment 4 In one or more embodiments, a computer-readable storage medium is disclosed, in which multiple instructions are stored, and the instructions are adapted to be loaded and executed by a processor of a terminal device to implement the optimized control method for a grid-connected converter based on dynamic virtual impedance described in the first embodiment.

[0052] Although the specific embodiments of the present invention are described above in conjunction with the accompanying drawings, they do not limit 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 labor on the basis of the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A grid-connected converter optimization control method based on dynamic virtual impedance, characterized in that: include: calculate Axis and The output voltage reference value of the shaft, and the output phase angle of the converter; Performing coordinate transformation on the output voltage reference value to obtain output voltage reference values ​​of the d-axis and the q-axis; The instantaneous current measurement values ​​of the d-axis and q-axis of the grid-connected converter are obtained, and the instantaneous current measurement values ​​are combined with the output voltage reference values, virtual resistance and virtual inductance of the d-axis and q-axis to obtain a modulation signal. The modulation signal is combined with the output phase angle of the converter, and after coordinate transformation and PWM modulation, a grid-connected converter switch control signal is obtained to achieve optimized control of the grid-connected converter.

2. A method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance according to claim 1, characterized in that: The value of the virtual resistance is equal to the difference between the adaptation resistance and the actual grid resistance; the value of the virtual inductance is equal to the difference between the adaptation inductance and the actual grid inductance.

3. A method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance according to claim 2, characterized in that: The calculation method of the adaptation resistance and the adaptation inductance is: Establish a mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adaptive resistor and adaptive inductor; Set the output active power to be equal to the active power reference value, the output reactive power to be equal to the reactive power reference value, and the output voltage modulus of the converter to be equal to the grid voltage modulus; The above formulas are jointly iterated and solved by the Newton-Raphson iteration method to obtain the final adapted resistance and adapted inductance.

4. The method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance according to claim 3, characterized in that: The mapping relationship between the actual output active power and reactive power of the grid-connected converter system and the adaptation resistor and the adaptation inductor is established, specifically: ； in, ； ； in, , , , They represent the output voltage modulus of the converter, the grid voltage modulus, the grid impedance modulus and the grid impedance angle respectively. and are respectively the actual output active power and reactive power of the grid-connected converter system, and They are respectively the adaptation resistor and the adaptation inductor.

5. The method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance according to claim 3, characterized in that: The specific process of joint iterative solution by Newton-Raphson iteration method is as follows: Given the initial values ​​of the adaptation resistor and the adaptation inductor , ; The first The result of the iteration and Substitute the residual function F ,calculate ; right Ask about , The partial derivative of , ; Use Newton's iteration formula to update The iteration results; when The iteration is terminated when the absolute value of is less than the preset tolerance.

6. The method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance according to claim 1, characterized in that: calculate Axis and The output voltage reference value of the shaft and the output phase angle of the converter are as follows: Based on the given active power reference and reactive power reference, calculate Axis and Output current reference value of the axis; Said Axis and The output current reference value of the axis is Axis and The instantaneous current measurement values ​​of the axis are respectively subtracted, the deviation value and the scaling factor Multiply them together, and then multiply them with the rotation angle matrix to get a set of intermediate variables; Based on the intermediate variables Axis and An output voltage reference value of the shaft is used to obtain an output phase angle of the converter based on the output voltage reference value.

7. The method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance according to claim 1, characterized in that: The instantaneous current measurement value is combined with the output voltage reference value of the d-axis and q-axis, the virtual resistance and the virtual inductance to obtain a modulation signal, specifically: ； in, , are the instantaneous current measurements of the d-axis and q-axis respectively, , are virtual resistance and virtual inductance respectively, is the converter output angular frequency, the modulation signal of the dq axis .

8. A grid-connected converter optimization control system based on dynamic virtual impedance, characterized in that: include: Voltage reference value calculation module, used to calculate Axis and The output voltage reference value of the shaft, and the output phase angle of the converter; A voltage reference value conversion module, used for performing coordinate conversion on the output voltage reference value to obtain output voltage reference values ​​of the d-axis and the q-axis; The converter optimization module is used to 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, virtual resistance and virtual inductance of the d-axis and q-axis to obtain a modulation signal. The modulation signal is combined with the output phase angle of the converter, and after coordinate transformation and PWM modulation, a grid-connected converter switch control signal is obtained to achieve optimized control of the grid-connected converter.

9. A terminal device, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions, characterized in that: The instructions are suitable for being loaded by a processor and executing the grid-connected converter optimization control method based on dynamic virtual impedance as described in any one of claims 1-7.

10. A computer-readable storage medium storing a plurality of instructions, characterized in that: The instructions are suitable for being loaded by a processor of a terminal device and executing the method for optimizing and controlling a grid-connected converter based on dynamic virtual impedance as described in any one of claims 1 to 7.

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