Novel networking control method for improving synchronous stability of current converter

Abstract

The invention relates to the technical field of power electronic equipment stability and optimization control research, and provides a novel networking control method for improving the synchronous stability of a current converter. The method comprises the following steps: acquiring an active power measurement value output by a common coupling point converter, inputting the active power measurement value into an active synchronization ring, and generating a common coupling point voltage phase reference value; obtaining an active power difference value between the output active power measurement value and the active power reference value, and inputting the active power difference value into a proportional controller to obtain an output current d-axis component reference value; obtaining a reactive power difference value between a reactive power measurement value output by the common coupling point converter and a reactive power reference value, and inputting the reactive power difference value into a proportional-integral controller to obtain an output current q-axis component reference value; acquiring a d-axis component measured value and a q-axis component measured value of the output current, and inputting a d-axis component reference value and a q-axis component reference value of the output current of the converter into a vector current controller, so as to obtain a d-axis component reference value and a q-axis component reference value of the output voltage of the converter; and performing Parker inverse transformation on the d-axis component reference value of the output voltage and the q-axis component reference value of the output voltage to generate a modulation signal, and finally generating a PWM signal of the converter through a triangular carrier modulation mode.

Description

Technical Field

[0001] This invention relates to the field of power electronic equipment stability and optimization control research technology, and in particular to a novel grid control method for improving converter synchronization stability. Background Technology

[0002] With the large-scale integration of renewable energy sources such as wind and solar power into the power grid via power electronic converters, the construction of a new power system with a high proportion of new energy sources has become an inevitable trend. Against this backdrop, grid-based control technology, capable of autonomously establishing grid voltage and frequency and providing stable support for the system, is considered crucial for enhancing grid resilience and stability, and has attracted widespread attention from researchers both domestically and internationally.

[0003] The core idea of ​​grid-based control is to enable the converter to simulate the characteristics of a traditional synchronous generator, maintaining stable operation with the power grid through its inherent synchronization mechanism. Traditional grid-based control strategies, such as those based on virtual synchronous machines, primarily establish the phase and frequency of the port voltage by simulating the rotor motion equations of a synchronous machine. However, existing research shows that the synchronization mechanism of such traditional grid-based control is highly dependent on system strength, making it prone to synchronization instability when dealing with grid disturbances, thus limiting its stable operating boundary under different short-circuit ratios. Furthermore, traditional methods have limited damping effects on system oscillations during dynamic processes, require strict parameter design, and struggle to achieve the optimal balance between maintaining synchronization stability and providing rapid voltage / frequency support, while lacking flexible power regulation capabilities. Therefore, although existing grid-based control technologies can simulate the external characteristics of synchronous machines, their synchronization stability and dynamic performance under different grid environments still need further improvement. A novel grid-based control method is urgently needed to enhance its adaptability and robustness to grid disturbances, thereby broadening its stable operating range under various grid conditions and providing technical support for building a safer and more stable new power system. Summary of the Invention

[0004] In view of this, the present invention provides a novel grid control method to improve the synchronization stability of converters, in order to solve the technical problem that existing grid technologies are prone to synchronization instability when dealing with grid disturbances and changes in operating conditions (especially after the grid short-circuit ratio fluctuates over a wide range and transient faults occur).

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a novel grid control method for improving converter synchronization stability, comprising the following steps:

[0007] S1. Obtain the measured value of the active power output of the converter at the common coupling point and the active power reference value, input the two into the active power synchronization loop, and generate the voltage phase reference value at the common coupling point;

[0008] S2. Obtain the active power difference between the measured value of the output active power and the reference value of the active power, input the active power difference into the proportional controller, and obtain the reference value of the d-axis component of the output current;

[0009] S3. Obtain the reactive power difference between the measured reactive power value and the reactive power reference value of the converter output at the common coupling point, and input the reactive power difference into the proportional-integral controller to obtain the reference value of the q-axis component of the output current;

[0010] S4. Obtain the measured values ​​of the d-axis and q-axis components of the converter output current, and input them into the vector current controller in combination with the reference values ​​of the d-axis and q-axis components of the converter output current to obtain the reference values ​​of the d-axis and q-axis components of the converter output voltage.

[0011] S5. Combine the reference values ​​of the d-axis component and q-axis component of the output voltage with the phase reference value of the common coupling point voltage generated by the active power synchronization loop to perform Parker inverse transformation to generate a modulation signal. Finally, the PWM signal of the converter is generated by triangular carrier modulation.

[0012] Further, in step S1, the process of obtaining the common coupling point voltage phase reference value by outputting the active power measurement value and the active power reference value can be expressed as:

[0013]

[0014] in, This represents the phase reference value of the common coupling point voltage output by the active power synchronization loop controlled by a virtual synchronous machine. The value represents the rated angular frequency of the power grid, J represents the inertia coefficient of the virtual synchronous machine, and D represents the rated angular frequency of the power grid. p P represents the damping coefficient. ref These represent the measured and reference values ​​of the converter output power, respectively. "s" represents the Laplace operator.

[0015] Further, in step S2, the reference value of the d-axis component of the output current is obtained by inputting the active power difference between the measured active power value and the active power reference value into the proportional controller, which can be specifically expressed as:

[0016]

[0017] Among them, i cdref k represents the reference value of the d-axis component of the converter output current. pP This is the active power ratio control coefficient.

[0018] Further, in step S3, the reference value of the q-axis component of the output current is obtained by inputting the reactive power difference between the reactive power measurement value and the reactive power reference value into the proportional-integral controller, and can be expressed as:

[0019]

[0020] Among them, i cqref k represents the reference value for the q-axis component of the converter output current. pQ k is the reactive power proportional control coefficient. iQ This is the reactive power integral control coefficient.

[0021] Further, in step S4, the reference values ​​of the d-axis component of the converter output voltage and the reference values ​​of the q-axis component of the output voltage are obtained by acquiring the measured values ​​of the d-axis and q-axis components of the converter output current, and combining them with the reference values ​​of the d-axis and q-axis components of the converter output current, which are then input into the vector current controller. This can be expressed as:

[0022]

[0023] Among them, v cdref This represents the reference value for the d-axis component of the converter output voltage, v. cqref k represents the reference value for the q-axis component of the converter output voltage. pI For the proportional gain of the current controller, k iI This is the integral gain of the current controller.

[0024] Furthermore, step S5 specifically includes the following steps:

[0025] S51. Generate a modulation signal to control the grid-connected converter based on the reference values ​​of the d-axis component of the converter output voltage and the reference values ​​of the q-axis component of the converter output voltage;

[0026] S52. The modulation signal of the converter is transmitted to the PWM generator, and the drive signal of the converter is generated by carrier modulation.

[0027] The advantages of this invention compared to the prior art are:

[0028] 1. The present invention proposes a novel grid control method to improve the synchronous stability of converters. It improves the voltage and current dual inner loop of traditional grid converters, eliminates the reverse resonance peak of its impedance characteristics near the fundamental frequency, and improves the small-signal stability of the system.

[0029] 2. This invention uses power synchronization, which retains the frequency support capability and damping inertia characteristics similar to traditional synchronous machines.

[0030] 3. This invention employs an outer loop for active and reactive power control, which can be extended to constant power control scenarios to improve the steady-state power regulation capability of traditional grid-connected equipment.

[0031] 4. The active and reactive power control outer loop adopted in this invention can quantitatively adjust the active and reactive power output according to grid connection requirements during system faults, thereby improving the transient stability of the system.

[0032] 5. The method of the present invention has a simple structure, is easy to apply in engineering practice, and has good results under different inertia and damping parameter conditions. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this invention, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a flowchart of a novel grid control method for improving converter synchronization stability provided by an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the control principle of an existing grid converter based on virtual synchronous machine control;

[0036] Figure 3 This is a schematic diagram of a novel network control method based on network fusion control provided in an embodiment of the present invention.

[0037] Figure 4 It is the equivalent single-input single-output impedance and grid impedance Bode plot of a traditional grid converter under strong grid conditions before applying the new grid control.

[0038] Figure 5 The equivalent single-input single-output impedance and grid impedance Bode plot of the converter under different grid strengths after applying the novel grid control are provided in the embodiments of the present invention.

[0039] Figure 6 The waveforms of simulated voltage, current, and power of a conventional grid converter under strong grid conditions before applying the novel grid control provided in this embodiment of the invention are shown.

[0040] Figure 7 The waveforms of simulated voltage, current, and power of the converter under a strong grid after applying the novel grid control provided in this embodiment of the invention are shown.

[0041] Figure 8 The waveforms of simulated voltage, current, and power of the converter under weak grid conditions after applying the novel grid control provided in this embodiment of the invention are shown.

[0042] Figure 9 The waveforms of the simulated voltage, current, and power of the converter under a three-phase short-circuit fault after applying the novel grid control provided in this embodiment of the invention are shown. Detailed Implementation

[0043] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0044] The following will describe in detail, with reference to the accompanying drawings, a novel grid control method for improving the synchronization stability of converters according to the present invention.

[0045] Figure 1 This is a flowchart of a novel grid control method for improving converter synchronization stability provided by an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the control principle of an existing grid converter based on virtual synchronous machine control;

[0047] Figure 3 This is a schematic diagram of a novel network control method based on network fusion control provided in an embodiment of the present invention.

[0048] like Figure 1 As shown, this novel network control method includes:

[0049] S1. Obtain the measured value of the active power output of the converter at the common coupling point and the active power reference value, input the two into the active power synchronization loop, and generate the voltage phase reference value at the common coupling point;

[0050] S2. Obtain the active power difference between the measured value of the output active power and the reference value of the active power, input the active power difference into the proportional controller, and obtain the reference value of the d-axis component of the output current;

[0051] S3. Obtain the reactive power difference between the measured reactive power value and the reactive power reference value of the converter output at the common coupling point, and input the reactive power difference into the proportional-integral controller to obtain the reference value of the q-axis component of the output current;

[0052] S4. Obtain the measured values ​​of the d-axis and q-axis components of the converter output current, and input them into the vector current controller in combination with the reference values ​​of the d-axis and q-axis components of the converter output current to obtain the reference values ​​of the d-axis and q-axis components of the converter output voltage.

[0053] S5. Combine the reference values ​​of the d-axis component and q-axis component of the output voltage with the phase reference value of the common coupling point voltage generated by the active power synchronization loop, perform inverse Parker transformation to generate a modulation signal, and finally generate the PWM signal of the converter through triangular carrier modulation.

[0054] Further, in step S1, the process of obtaining the common coupling point voltage phase reference value by outputting the active power measurement value and the active power reference value can be expressed as:

[0055]

[0056] in, This represents the phase reference value of the common coupling point voltage output of the active power loop controlled by a virtual synchronous machine. The value represents the rated angular frequency of the power grid, J represents the inertia coefficient of the virtual synchronous machine, and D represents the rated angular frequency of the power grid. p P represents the damping coefficient. ref These represent the measured and reference values ​​of the converter output power, respectively. "s" represents the Laplace operator.

[0057] Further, in step S2, the reference value of the d-axis component of the output current is obtained by inputting the active power difference between the measured active power value and the active power reference value into the proportional controller, which can be specifically expressed as:

[0058]

[0059] Among them, i cdref k represents the reference value of the d-axis component of the converter output current. pP This is the active power ratio control coefficient.

[0060] Further, in step S3, the reference value of the q-axis component of the output current is obtained by inputting the reactive power difference between the reactive power measurement value and the reactive power reference value into the proportional-integral controller, and can be expressed as:

[0061]

[0062] Among them, i cqref k represents the reference value for the q-axis component of the converter output current. pQ k is the reactive power proportional control coefficient. iQ This is the reactive power integral control coefficient.

[0063] Further, in step S4, the reference values ​​of the d-axis component of the converter output voltage and the reference values ​​of the q-axis component of the output voltage are obtained by acquiring the measured values ​​of the d-axis and q-axis components of the converter output current, and combining them with the reference values ​​of the d-axis and q-axis components of the converter output current, which are then input into the vector current controller. This can be expressed as:

[0064]

[0065] Among them, v cdref This represents the reference value for the d-axis component of the converter output voltage, v. cqref k represents the reference value for the q-axis component of the converter output voltage. pI For the proportional gain of the current controller, k iI This is the integral gain of the current controller.

[0066] Furthermore, step S5 specifically includes the following steps:

[0067] S51. Generate a modulation signal to control the grid-connected converter based on the reference values ​​of the d-axis component of the converter output voltage and the reference values ​​of the q-axis component of the converter output voltage;

[0068] S52. The modulation signal of the converter is transmitted to the PWM generator, and the drive signal of the converter is generated by carrier modulation.

[0069] Figure 4 This is a Bode plot of the equivalent single-input single-output impedance and grid impedance of a traditional grid converter under strong grid conditions before applying the novel grid control, provided in an embodiment of the present invention.

[0070] Figure 5 The equivalent single-input single-output impedance and grid impedance Bode plot of the converter under different grid strengths after applying the novel grid control are provided in the embodiments of the present invention.

[0071] Figure 6 The waveforms of simulated voltage, current, and power of a conventional grid converter under strong grid conditions before applying the novel grid control provided in this embodiment of the invention are shown.

[0072] Figure 7 The waveforms of simulated voltage, current, and power of the converter under a strong grid after applying the novel grid control provided in this embodiment of the invention are shown.

[0073] Figure 8 The waveforms of simulated voltage, current, and power of the converter under weak grid conditions after applying the novel grid control provided in this embodiment of the invention are shown.

[0074] Figure 9 The waveforms of the simulated voltage, current, and power of the converter under a three-phase short-circuit fault after applying the novel grid control provided in this embodiment of the invention are shown.

[0075] like Figures 4 to 5 As shown, Figure 4Bode plots of equivalent single-input single-output impedance and grid impedance of traditional grid-connected converters under strong grid conditions before applying new grid control are shown. The solid line represents the equivalent single-input single-output impedance of the traditional grid-connected converter, and the dashed line represents the grid impedance. Figure 5 The Bode plots of the equivalent single-input single-output impedance and grid impedance of the converter under different grid intensities after applying the novel grid control of this invention are shown. The dashed line represents the equivalent single-input single-output impedance of the converter under different grid intensities, and the solid line represents the grid impedance.

[0076] like Figures 6 to 9 As shown, Figure 6 The waveforms of simulated voltage, current, and power of a conventional grid converter under strong grid conditions before applying the novel grid control provided in this embodiment of the invention are shown. Figure 7 The waveforms of simulated voltage, current, and power of the converter under a strong grid after applying the novel grid control provided in this embodiment of the invention are shown. Figure 8 The waveforms of simulated voltage, current, and power of the converter under weak grid conditions after applying the novel grid control provided in this embodiment of the invention are shown. Figure 9 The waveforms of the simulated voltage, current, and power of the converter under a three-phase short-circuit fault after applying the novel grid control provided in this embodiment of the invention are shown. Figures 6 to 9 In the x-axis, t represents time, in seconds (s). In the y-axis: v abc The three-phase voltage vector at the common coupling point is represented by the per-unit value [pu]; abc The three-phase current vector at the common coupling point is represented by the per-unit value [pu]; P and Q are the active and reactive power injected into the grid at the common coupling point, respectively, and are also represented by the per-unit value [pu].

[0077] Before and after adopting the novel network control method of the present invention, from Figure 4 and Figure 5 The following conclusions can be drawn: Figure 4 In the case of a strong power grid (taking a short-circuit ratio SCR = 8 as an example), the amplitude-frequency characteristic curves of the equivalent single-input single-output impedance and the grid impedance of a traditional grid-connected converter intersect at 49.8 Hz and 51.2 Hz, with phase differences of 13° and -54° at the intersection point, respectively. At this point, the Nyquist curve of the system will encircle (-1, j0), indicating that the system has the risk of oscillation. Figure 5 After using the novel grid control strategy of this invention, regardless of whether it is a strong grid (SCR = 8) or a weak grid (SCR = 1), the phase difference corresponding to the intersection of the amplitude-frequency characteristic curves of the converter's equivalent single-input single-output impedance and the grid impedance is much less than 180°, indicating that the stability margin of the converter grid-connected system has been greatly improved.

[0078] Figure 6Simulation waveforms of a conventional grid-connected converter system under strong grid conditions without using this invention are presented, where the grid short-circuit ratio is set to 8, indicating a high grid strength. As shown in the figure, at t = 4s, the converter output power increases to the rated value, indicating that the system gradually loses stability and oscillates, demonstrating the risk of synchronous oscillation for conventional grid-connected converters under strong grid conditions. Figure 7 Using the novel grid control strategy proposed in this invention under a strong grid with a short-circuit ratio of 8, the converter output power is increased to the rated value in 2 seconds by modifying the converter power reference value. It can be seen that after using the novel grid control strategy, the converter can operate stably under a strong grid, and the system synchronization stability is greatly improved. Figure 8 The waveforms of the converter grid-connected system using the novel grid control under weak grid conditions are presented. It can be seen that the system also does not oscillate, indicating that the novel grid control strategy proposed in this invention can ensure the synchronous and stable operation of the converter under a wide short-circuit ratio range. Figure 9 The operation performance of the novel grid control strategy proposed in this invention under grid fault conditions was further verified. As shown in the figure, a three-phase short-circuit fault occurred in the system at t=6s, and the voltage drop depth was 80%. According to the grid connection guidelines, the converter needs to support the grid connection point voltage by injecting pure reactive power at this time. It can be seen that the novel grid control strategy proposed in this invention can achieve this function and ensure the transient stability of the system.

[0079] The method employed in this invention reduces the risk of oscillations when traditional grid-connected converters are interconnected with the AC grid, thus improving the synchronous stability of the system. By using this novel grid control strategy, the reverse resonance peak near the fundamental frequency of the traditional grid-connected converter is significantly eliminated, improving the stability margin. Simultaneously, the active and reactive power control outer loop employed in this invention can quantitatively adjust the active and reactive power output according to grid connection guidelines during system faults, improving the transient stability of the system. The structure is simple, facilitating practical engineering applications, and exhibits good performance under changing system operating conditions.

[0080] All of the above-mentioned optional technical solutions can be combined in any way to form the optional embodiments of this application, and will not be described in detail here.

[0081] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A novel grid control method for improving converter synchronization stability, characterized in that, include: S1. Obtain the measured value of the active power output of the converter at the common coupling point and the active power reference value, input the two into the active power synchronization control loop, and generate the voltage phase reference value at the common coupling point; S2. Obtain the active power difference between the measured value of the output active power and the reference value of the active power, input the active power difference into the proportional controller, and obtain the reference value of the d-axis component of the output current; S3. Obtain the reactive power difference between the measured reactive power value and the reactive power reference value of the converter output at the common coupling point, and input the reactive power difference into the proportional-integral controller to obtain the reference value of the q-axis component of the output current; S4. Obtain the measured values ​​of the d-axis and q-axis components of the converter output current, and input them into the vector current controller in combination with the reference values ​​of the d-axis and q-axis components of the converter output current to obtain the reference values ​​of the d-axis and q-axis components of the converter output voltage. S5. Combine the reference values ​​of the d-axis component and q-axis component of the output voltage with the phase reference value of the common coupling point voltage to perform inverse Parker transformation to generate a modulation signal. Finally, the PWM signal of the converter is generated by triangular carrier modulation.

2. The novel grid control method for improving converter synchronization stability according to claim 1, characterized in that, In step S1, the process of generating a common coupling point voltage phase reference value by outputting the active power measurement value and the active power reference value can be expressed as follows: in, This represents the phase reference value of the common coupling point voltage output by the active power synchronization loop controlled by a virtual synchronous machine. The value represents the rated angular frequency of the power grid, J represents the inertia coefficient of the virtual synchronous machine, and D represents the rated angular frequency of the power grid. p P represents the damping coefficient. ref These represent the measured and reference values ​​of the converter output power, respectively. "s" represents the Laplace operator.

3. The method according to claim 1, characterized in that, In step S2, the reference value of the d-axis component of the output current is obtained by inputting the active power difference between the measured active power value and the active power reference value into the proportional controller, and can be expressed as: Among them, i cdref k represents the reference value of the d-axis component of the converter output current. pP This is the active power ratio control coefficient.

4. The method according to claim 1, characterized in that, In step S3, the reference value of the q-axis component of the output current is obtained by inputting the reactive power difference between the reactive power measurement value and the reactive power reference value into the proportional-integral controller, which can be expressed as: Among them, i cqref k represents the reference value for the q-axis component of the converter output current. pQ k is the reactive power proportional control coefficient. iQ This is the reactive power integral control coefficient.

5. The method according to claim 1, characterized in that, In step S4, the reference values ​​for the d-axis component of the converter output voltage and the reference values ​​for the q-axis component of the output voltage are obtained by acquiring the measured values ​​of the d-axis and q-axis components of the converter output current, and combining them with the reference values ​​for the d-axis and q-axis components of the converter output current, which are then input into the vector current controller. This can be expressed as: Among them, v cdref This represents the reference value for the d-axis component of the converter output voltage, v. cqref k represents the reference value for the q-axis component of the converter output voltage. pI For the proportional gain of the current controller, k iI This is the integral gain of the current controller.

6. The novel grid control method for improving converter synchronization stability according to claim 1, characterized in that, Step S5 specifically includes the following steps: S51. Generate a modulation signal to control the grid-connected converter based on the reference values ​​of the d-axis component of the converter output voltage and the reference values ​​of the q-axis component of the converter output voltage; S52. The modulation signal of the converter is transmitted to the PWM generator, and the drive signal of the converter is generated by carrier modulation.

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