Operation control method and device for converter under weak power grid of virtual power plant

Abstract

The invention provides an operation control method and device for a converter under a weak power grid of a virtual power plant, and belongs to the field of power grid control. The method comprises the steps that a plurality of controllers are constructed according to inner and outer ring control variables of a virtual power plant weak grid system, and the inner ring control variables comprise inductive current, capacitor voltage and capacitor current; constructing a small-signal mathematical model corresponding to each controller, training the small-signal mathematical model of each controller based on the actually measured impedance data, the actually measured inductive current, the actually measured capacitor voltage and the actually measured capacitor current data of the converter, and determining a control model; and controlling the output voltage of the converter based on the control model of each controller. According to the invention, multiple targets of power adjustment, harmonic suppression, resonance suppression, island detection and state switching, low voltage ride through, overvoltage or overcurrent protection and the like can be synchronously realized, so that the operation stability of a weak power grid is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of virtual power plant control, and particularly to an operating control method and device for a converter under a weak power grid of a virtual power plant. Background Art

[0002] Assume that the equivalent output impedance of the converter can be obtained through the small-signal mathematical model of the system. Then, according to the Middlebrook stability criterion, the grid connection stability of the converter can be judged by the ratio of the grid impedance to the converter output impedance. The loop gain contains important performance index information, such as the cut-off frequency, stability margin, etc. It can not only qualitatively judge the stability of the loop, but also quantitatively analyze the stability margin. The adaptive control of the converter can also be realized by online measuring the loop gain of the underlying controller.

[0003] The underlying controller of the grid-connected converter is responsible for controlling the self-variables of the converter system to realize the core functions of the converter. For an LCL-filtered converter, the controllable variables are: inductor current, capacitor voltage, capacitor current, and grid current. The underlying controller with inductor current or capacitor current closed-loop control has a certain resonance suppression ability and relatively strong adaptability to grid impedance changes.

[0004] In addition, in the aspect of new energy participating in power grid voltage regulation control, some theoretical studies have been carried out at home and abroad, and new energy reactive power support methods based on droop control, constant voltage control, virtual synchronous machine control, etc. have been proposed. In terms of frequency support, it mainly includes active power support methods such as new energy primary frequency modulation technology and virtual inertia control technology. These schemes have different theoretical bases but the same control objectives, which are to adaptively adjust the controller parameters to achieve the desired control performance indicators. They all have deficiencies in terms of dynamic performance and applicability, and lack a new converter weak grid operation control scheme for virtual power plants. Summary of the Invention

[0005] Embodiments of the present invention provide an operating control method and device for a converter under a weak power grid of a virtual power plant to solve the problem of how to improve the dynamic performance and applicability of the converter weak grid operation control scheme.

[0006] In a first aspect, embodiments of the present invention provide an operating control method for a converter under a weak power grid of a virtual power plant, including:

[0007] Constructing a plurality of controllers according to the inner and outer loop control variables of the virtual power plant weak grid system, where the inner loop control variables include: inductor current, capacitor voltage, and capacitor current;

[0008] Build a small-signal mathematical model for each controller respectively, and train the small-signal mathematical model of each controller based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine the control model;

[0009] Control the output voltage of the converter based on the control models of each controller.

[0010] In a possible implementation, the controller includes: v O -i G controller, i C -i G controller, i L -i G controller, i L -v O -i G controller and i C -v O -i G controller;

[0011] wherein, i L corresponds to the inductor current, v O corresponds to the capacitor voltage, and i C corresponds to the capacitor current.

[0012] In a possible implementation, before controlling the output voltage of the converter based on the control models of each controller, it further includes:

[0013] Inject a sinusoidal perturbation signal x p into the grid current outer loop, and extract the first voltage waveform x in and the second voltage waveform x out at the perturbation frequencies before and after the perturbation point;

[0014] Determine the loop gain according to the first voltage waveform x in and the second voltage waveform x out ;

[0015] Determine the cut-off frequency and phase margin of each controller according to the loop gain.

[0016] In a possible implementation, the determining the loop gain according to the first voltage waveform x in and the second voltage waveform x out includes:

[0017] Determine the loop gain according to the following formula:

[0018] T = -x out / x in .

[0019] In a possible implementation manner, determining the cut-off frequency and phase margin of each controller according to the loop gain includes:

[0020] Determining the frequency corresponding to the unit loop gain as the cut-off frequency of each controller;

[0021] Determining the phase angle corresponding to the unit loop gain as the phase margin of each controller.

[0022] In a possible implementation manner, when two converters are connected in parallel, it further includes:

[0023] Determining the operating parameters of the filter according to the cut-off frequencies corresponding to the converters.

[0024] In a possible implementation manner, determining the operating parameters of the filter according to the cut-off frequencies corresponding to the converters includes:

[0025] When the difference between the cut-off frequencies corresponding to the two converters is less than a set value, projecting the second voltage waveform signal at the perturbation point after the two converters are connected in parallel onto a rectangular coordinate system rotating at the perturbation frequency of the two converters to separate the interference frequencies;

[0026] Determining the suppression frequency of the filter according to the interference frequency separation result to achieve suppression of the interference frequencies.

[0027] In a possible implementation manner, projecting the second voltage waveform signal at the perturbation point after the two converters are connected in parallel onto a rectangular coordinate system rotating at the perturbation frequency of the two converters includes:

[0028] Projecting the second voltage waveform signal x at the perturbation point after the two converters are connected in parallel onto a rotating coordinate system with a frequency of ω out according to the following formula: est1 onto a rotating coordinate system with a frequency of ω

[0029]

[0030] where x out is the second voltage waveform signal at the perturbation point after the two converters are connected in parallel; ω est1 is the perturbation frequency of the first converter; ω est2 is the perturbation frequency of the second converter; x out1 is the second voltage waveform at the perturbation frequency before and after the perturbation point of the first converter; x out2 is the second voltage waveform at the perturbation frequency before and after the perturbation point of the second converter.

[0031] In a possible implementation manner, determining the operating parameters of the filter according to the cut-off frequencies corresponding to the converters includes:

[0032] When the difference between the cut-off frequencies corresponding to the two converters is greater than or equal to the set value, it is determined that the filter is a band-pass filter;

[0033] Determine the filtering frequency band of the band-pass filter according to the cut-off frequencies corresponding to the two converters and the difference.

[0034] In a second aspect, an embodiment of the present invention provides an operating control device for a converter under a weak grid of a virtual power plant, including:

[0035] A controller construction module, configured to construct a plurality of controllers according to the internal and external loop control variables of the virtual power plant weak grid system, where the internal loop control variables include: inductor current, capacitor voltage, and capacitor current;

[0036] A model construction module, configured to construct a small-signal mathematical model corresponding to each controller, and train the small-signal mathematical model of each controller based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine the control model;

[0037] A control module, configured to control the output voltage of the converter based on the control models of each controller.

[0038] An embodiment of the present invention provides an operating control method and device for a converter under a weak grid of a virtual power plant. By constructing a plurality of controllers according to the internal and external loop control variables of the virtual power plant weak grid system, namely inductor current, capacitor voltage, and capacitor current, different control requirements of different power grids can be met. A small-signal mathematical model is constructed corresponding to each controller, and the small-signal mathematical model of each controller is trained based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine the control model, so as to achieve precise control of different controllers. The control models of each controller are used to control the output voltage of the converter, synchronously realizing multiple objectives such as power regulation, harmonic suppression, resonance suppression, island detection and state switching, low voltage ride-through, overvoltage or overcurrent protection, etc., thereby improving the stability of the weak grid operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0040] Figure 1 It is a schematic structural diagram of a new energy grid-connected system;

[0041] Figure 2 It is a schematic structural diagram of a bottom-layer controller;

[0042] Figure 3 It is a schematic diagram of the online monitoring of performance indicators and the adaptive adjustment process;

[0043] Figure 4 It is a schematic diagram of the operation control method of the converter under a weak power grid of a virtual power plant provided by an embodiment of the present invention;

[0044] Figure 5 It is a schematic diagram of the structure of the experimental test platform provided by an embodiment of the present invention;

[0045] Figure 6 It is a schematic diagram of the structure of the operation control device of the converter under a weak power grid of a virtual power plant provided by an embodiment of the present invention. Detailed implementation manners

[0046] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are presented to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0047] The underlying controller of the grid-connected converter is responsible for controlling the self-variables of the converter system to achieve the core functions of the converter. As Figure 1 shown, for an LCL-filtered converter, the controllable variables are: inductor current i L , capacitor voltage v O , capacitor current i C and grid current i G , and the common underlying controllers are summarized in Table 1.

[0048] Table 1 Summary of the underlying control strategies of the grid-connected converter

[0049]

[0050] Among them, proportional-integral-derivative, PID; resonant regulator, Resonant, R; proportional-resonant, PR; dead-beat, DB; high-pass filter, HPF; hysteresis control, HC. "+" represents parallel connection, "-" represents series connection, and the loop form follows: inner loop - outer loop.

[0051] According to Figure 2It can be seen that the underlying controller with closed-loop control of inductor current \(i_L\) or capacitor current \(i_C\) has a certain resonance suppression ability and relatively strong adaptability to grid impedance changes. Figure 2 In Figure 2 , the second-order generalized integrator, Second-Order Generalized Integrator, SOGI; the high-pass filter, High-Pass Filter, HPF.

[0052] In addition, in the field of new energy participating in grid voltage regulation control, domestic and foreign scholars have proposed various reactive power support methods based on theoretical research, including new energy technologies based on droop control, constant voltage control, and virtual synchronous machine control. In terms of frequency support, it mainly involves active power support methods such as new energy primary frequency modulation and virtual inertia control technologies. The active support ability of the grid can be evaluated by comparing the ratio of the grid impedance to the converter output impedance. Therefore, by online measuring the grid impedance information, an impedance-based adaptive control strategy can be implemented to enhance the grid connection stability. For example, according to the online measured grid impedance information, the damping coefficient of the converter can be adaptively adjusted, or the control parameters of the underlying controller can be adaptively regulated to achieve the adaptive following of the converter output impedance to the grid impedance change, thereby improving the adaptability of the converter to the grid impedance change.

[0053] Although the impedance-based adaptive control performs poorly in terms of dynamic performance, in order to improve the control performance, various schemes for implementing adaptive control based on control performance indicators (such as bandwidth, phase margin, etc.) have been proposed. These schemes include relay feedback adaptive control, model reference adaptive control, and limit cycle oscillation adaptive control. Although their theoretical bases are different, their control objectives are the same, which is to adaptively adjust the controller parameters to achieve the desired control performance indicators.

[0054] This proposal aims to online measure the cut-off frequency and stability margin of the outer loop of the underlying controller through the small-signal perturbation method, realize the adaptive adjustment of the underlying controller parameters, ensure that the converter achieves the desired loop control performance, and improve the grid connection stability of the high-proportion new energy converter.

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will be described through specific embodiments with reference to the accompanying drawings.

[0056] Figure 3 It is the application scenario diagram of the operation control method of the converter under weak grid of the virtual power plant provided by the embodiment of the present invention. As Figure 3As shown, the closed-loop control of the grid current \(i_G\) serves as the outer loop of the underlying controller. Through the disturbance signal generator and the online measurer for the cut-off frequency and phase margin, the cut-off frequency and phase margin closed-loop regulators are adjusted according to the online monitoring results to improve the accuracy of the operation control of the converter in the inner loop of the weak grid.

[0057] Figure 4 This is the schematic flowchart of the operation control method for the converter under the weak grid of the virtual power plant provided by the embodiment of the present invention. As Figure 4 shown, the method includes the following steps:

[0058] S401. Construct multiple controllers according to the inner and outer loop control variables of the virtual power plant weak grid system, where the inner loop control variables include: inductor current, capacitor voltage, and capacitor current.

[0059] Among them, a high-performance underlying controller should implement all the core functions of the converter as much as possible: power regulation, harmonic suppression, resonance suppression, island detection and state switching, low voltage ride-through, overvoltage or overcurrent protection, etc., which determines the multi-loop attribute of the structure of the converter underlying controller.

[0060] The closed-loop control of the grid current \(i\) G has excellent performance in suppressing grid harmonics and power regulation and is most suitable as the outer loop of the underlying controller. Therefore, there are also three control variables that can be used as the inner loop: the inductor current \(i\) L , the capacitor voltage \(v\) O and the capacitor current \(i\) C . Although the inductor voltage on the converter side and the inductor voltage on the grid side are also controllable, in actual converters, these two signals are generally not measured, so they are not considered. Optionally, there are five structures of the underlying controller (inner loop - outer loop): (1) \(v\) O - \(i\) G ; (2) \(i\) C - \(i\) G ; (3) \(i\) L - \(i\) G ; (4) \(i\) L - \(v\) O - \(i\) G ; (5) \(i\) C - \(v\) O - \(i\) G .

[0061] S402. Respectively construct small-signal mathematical models for each controller, and train the small-signal mathematical models of each controller based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine the control models.

[0062] S403. Control the output voltage of the converter based on the control models of each controller.

[0063] For such a multi - input and multi - output link, first, design the control relationship between the output variables and the input variables. On this basis, conduct a necessity analysis of decoupling. If decoupling is required, design the decoupling algorithm. Deduce the open - loop transfer function of each performance index control loop and design their respective regulators.

[0064] The purpose of online measurement of performance indicators is to perform closed - loop control, adjust the control parameters of the underlying controller to adapt to the change of grid impedance, maintain the high control performance of the converter, and achieve the stable operation of the high - proportion new - energy converter in a weak grid for virtual power plants.

[0065] The fluctuation of grid impedance has a significant impact on the grid - connection stability of the converter, the resonance suppression ability, and the outer - loop control performance. These performance indicators are the key to evaluating the quality of the underlying controller.

[0066] In the embodiments of the present application, for the multiple controllers constructed in step S401, small - signal mathematical models are respectively constructed, and the expression of the equivalent output impedance of the converter is deduced. Then, the Nyquist diagram is used to analyze the grid - connection stability, thereby improving the grid control stability.

[0067] In addition, in the embodiments of the present application, the transfer function between the grid current of the underlying controller and the output voltage of the converter is deduced, and the resonance suppression effects of each underlying controller are compared through frequency - response analysis. At the same time, by deducing the open - loop transfer function of the underlying controller and using the Bode diagram to compare and analyze its cut - off frequency and stability margin, it is verified that the control model has a high equivalent output impedance of the converter, a strong resonance suppression ability, and excellent grid - current control performance.

[0068] In this embodiment, by constructing multiple controllers according to the inner - loop and outer - loop control variables of the virtual - power - plant weak - grid system, namely the inductor current, capacitor voltage, and capacitor current, different control requirements of different grids are met. Small - signal mathematical models are respectively constructed for each controller, and the small - signal mathematical models of each controller are trained based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine the control model, realizing the precise control of different controllers. Using the control models of each controller to control the output voltage of the converter, multiple objectives such as power regulation, harmonic suppression, resonance suppression, island detection and state switching, low - voltage ride - through, over - voltage or over - current protection are synchronously achieved, thereby improving the stability of weak - grid operation.

[0069] In different implementation manners, the types of controllers are different. Optionally, the controller includes v O -i G controller, i C -i G controller, i L -i GController, i L -v O -i G Controller and i C -v O -i G Any two or more of the controllers.

[0070] In a possible implementation, the controller includes: v O -i G Controller, i C -i G Controller, i L -i G Controller, i L -v O -i G Controller and i C -v O -i G Controller;

[0071] Wherein, i L corresponds to the inductor current, v O corresponds to the capacitor voltage and i C corresponds to the capacitor current.

[0072] In this embodiment, the controller includes five controllers constructed based on three inner-loop control variables of the inductor current, capacitor voltage, and capacitor current, which can simultaneously meet multiple requirements such as power regulation, harmonic suppression, resonance suppression, island detection and state switching, low-voltage ride-through, overvoltage or overcurrent protection, etc., and fully ensure the stability of the power grid operation.

[0073] To ensure the precise control of the converter output voltage, it is necessary to determine the cut-off frequency and phase margin of each controller before control.

[0074] In a possible implementation, before controlling the converter output voltage based on the control model of each controller, it further includes:

[0075] Inject a sinusoidal perturbation signal x p into the grid current outer loop, and extract the first voltage waveform x in and the second voltage waveform x out at the perturbation frequency before and after the perturbation point;

[0076] Determine the loop gain according to the first voltage waveform x in and the second voltage waveform x out ;

[0077] Determine the cut-off frequency and phase margin of each controller according to the loop gain.

[0078] Among them, before controlling the output voltage of the converter based on the control models of each controller, a sinusoidal perturbation signal x is first injected into the outer loop of the grid current. p The purpose is to introduce a controllable interference into the system so as to better observe and analyze the response of the system.

[0079] Secondly, after injecting the perturbation signal, the first voltage waveform x at the perturbation frequency before and after the perturbation point is measured and extracted. in and the second voltage waveform x out These two waveforms respectively represent the responses of the system at a specific frequency before and after the injection of the perturbation signal. By comparing these two waveforms, information about the dynamic characteristics of the system is obtained.

[0080] Then, based on the first voltage waveform x in and the second voltage waveform x out the loop gain that measures the system's response ability to the perturbation signal is determined, and the amplification or attenuation degree of the system at a specific frequency is determined. By calculating the loop gain, the stability and response speed of the system are evaluated.

[0081] Finally, based on the determined loop gain, the cut-off frequency and phase margin of each controller are further determined. The cut-off frequency refers to the highest frequency at which the system can effectively respond to signals, and the phase margin is another key index to measure the stability of the system. By reasonably setting these two parameters, it can be ensured that the system can maintain good stability and anti-interference ability while meeting the performance requirements.

[0082] In this embodiment, by injecting a sinusoidal perturbation signal x into the outer loop of the grid current p and extracting the first voltage waveform x at the perturbation frequency before and after the perturbation point in and the second voltage waveform x out the loop gain can be determined, and based on this, the cut-off frequency and phase margin of each controller are determined, providing a basis for the precise control of the converter output voltage and improving the control accuracy of the converter.

[0083] Based on the foregoing embodiment, in a possible implementation manner, determining the loop gain according to the first voltage waveform x in and the second voltage waveform x out includes:

[0084] Determine the loop gain according to the following formula:

[0085] T = -x out / x in .

[0086] In this embodiment, the loop gain is the gain obtained when the signal passes through the closed-loop path of the control system from the input to the output. It reflects the overall amplification or attenuation effect of the control system. Adjusting the loop gain according to the calculation result of the loop gain can improve the performance of the system, enhance the stability and response speed of the system.

[0087] In a possible implementation, determining the cut-off frequency and phase margin of each controller according to the loop gain includes:

[0088] Determining the frequency corresponding to the unit loop gain as the cut-off frequency of each controller;

[0089] Determining the phase angle corresponding to the unit loop gain as the phase margin of each controller.

[0090] Among them, the unit loop gain is |T| = 1. According to the frequency and phase angle corresponding to the unit loop gain, the actual cut-off frequency and phase margin of each controller are determined. For x in and x out perform closed-loop control on the amplitude to achieve autonomous search for the cut-off frequency, so that the system can dynamically adjust the cut-off frequency and phase margin according to the actual operating conditions, thereby achieving the best control effect, ensuring the stability and response speed of the system, and improving the performance of the entire system.

[0091] In a possible implementation, when two converters are connected in parallel, it further includes:

[0092] Determining the working parameters of the filter according to the cut-off frequency corresponding to each converter.

[0093] Analyze the interference mechanism of two converters (numbered #1 and #2 respectively) in parallel. When two adaptive regulators work simultaneously, due to the influence of the disturbance signal x p2 in converter #2, the expression of the disturbance output signal x out in converter #1 becomes:

[0094] x out (t) = |x out1 |cos(ω est1 t + ∠x out1 ) + |x out2 |cos(ω est2 t + ∠x out2 )

[0095] Among them, the subscripts 1 and 2 represent the converter numbers; x out1 is the second voltage waveform of converter #1; x out2 is the second voltage waveform of converter #2; ω est1 is the disturbance frequency of converter #1; ω est2 is the disturbance frequency of converter #1.

[0096] The system with two converters in parallel is considered in the following two cases: the difference between the cut-off frequencies corresponding to the two converters is less than the set value, and the difference between the cut-off frequencies corresponding to the two converters is greater than or equal to the set value.

[0097] In a possible implementation, according to the cut-off frequencies corresponding to each converter, the operating parameters of the filter are determined, including:

[0098] When the difference between the cut-off frequencies corresponding to the two converters is less than the set value, the second voltage waveform signal at the perturbation point after the two converters are connected in parallel is projected onto a rectangular coordinate system rotating at the perturbation frequency of the two converters to separate the interference frequencies.

[0099] Determine the suppression frequency of the filter according to the separation result of the interference frequencies to achieve the suppression of the interference frequencies.

[0100] Among them, when the difference between the cut-off frequencies corresponding to the two converters is less than the set value, the interference frequencies are separated by means of rectangular coordinate projection, and the components of each interference frequency can be more clearly identified. According to the separation result of the interference frequencies, the suppression frequency of the filter is further determined. By setting the suppression frequency of the filter, these interference frequencies can be suppressed targeted, thereby improving the stability and performance of the system.

[0101] In this embodiment, through this method for determining the filter parameters based on the converter cut-off frequency, the interference frequencies can be effectively separated and suppressed, ensuring the normal operation of the virtual power grid system and improving its performance.

[0102] In a possible implementation, projecting the second voltage waveform signal at the perturbation point after the two converters are connected in parallel onto a rectangular coordinate system rotating at the perturbation frequency of the two converters includes:

[0103] Project the second voltage waveform signal x at the perturbation point after the two converters are connected in parallel according to the following formula out onto the rotating coordinate system with a frequency of ω est1 :

[0104] 2x out (t)·sin(2ω est1 t)=|x out |·[sin(2ω est1 t+∠x out1 )-sin∠x out1 +|x out2 |·[sin((ω est1 +ω est2 )t+∠x out2 )-sin((ω est2 -ωest1 )t + ∠x out2 )]

[0105] 2x out (t)·cos(2ω est1 t) = |x out |·[cos(2ω est1 t + ∠x out1 ) - cos∠x out1 + |x out2 |·[0cos((ω est1 + ω est2 )t + ∠x out2 ) - cos((ω est2 - ω est1 )t + ∠x out2 )]

[0106] Wherein, x out is the second voltage waveform signal at the perturbation point after paralleling two converters; ω est1 is the perturbation frequency of the first converter; ω est2 is the perturbation frequency of the second converter; x out1 is the second voltage waveform at the perturbation frequency before and after the perturbation point of the first converter; x out2 is the second voltage waveform at the perturbation frequency before and after the perturbation point of the second converter.

[0107] Referring to the above formula, the harmonic components in x out that are close to the perturbation frequency ω est1 of the first converter are converted into: ① high-frequency harmonics (sin(2ω est1 t + ∠x out1 ), sin((ω est1 + ω est2 )t + ∠x out2 ) terms), ② low-frequency harmonics (sin((ω est2 - ω est1 )t + ∠x out2 ) terms). After extracting the DC component of the converted signal, the amplitude calculation of x out1 is performed. Combining with the known frequency information, the reshaping of the x out1 signal can be realized, and the purpose of anti-interference can be achieved.

[0108] In this embodiment, for the harmonic interference of similar frequencies, referring to the information engineering theory, the disturbed signal is first projected onto a rectangular coordinate system that rotates at the perturbation frequency of the converter to separate the interference frequency, and then a filter is designed specifically to suppress the separated harmonic interference.

[0109] In a possible implementation, according to the cut-off frequencies corresponding to each converter, the operating parameters of the filter are determined, including:

[0110] When the difference between the cut-off frequencies corresponding to the two converters is greater than or equal to a set value, it is determined that the filter is a band-pass filter;

[0111] According to the cut-off frequencies and the difference corresponding to the two converters, the filtering frequency band of the band-pass filter is determined.

[0112] In this case, effective suppression of interference can be achieved by reasonably designing the band-pass filter.

[0113] In this embodiment, when the difference between the cut-off frequencies corresponding to the two converters is greater than or equal to a preset threshold, it is determined that the filter should be set as a band-pass filter. According to the cut-off frequencies corresponding to the two converters and the difference between them, the specific filtering frequency band of the band-pass filter is determined. By reasonably designing the parameters of the band-pass filter, interference signals can be effectively suppressed, thereby ensuring the stable operation of the system and the clear transmission of signals.

[0114] In summary, this solution integrates inner-loop control variables such as inductor current, capacitor voltage, and capacitor current, constructs multiple underlying controllers, and improves the underlying controller solution for high-performance core functions. To verify the effectiveness of this solution, Matlab / Simulink simulation technology is adopted, and a comprehensive performance comparison and analysis is carried out with other types of underlying controllers.

[0115] In a specific embodiment, experimental equipment such as a bidirectional DC power supply (which can simulate photovoltaic power generation, power batteries, etc.), a three-phase grid-connected simulator, and a Yokogawa power analyzer provides hardware equipment for the grid connection and testing of the converter; having a hardware-in-the-loop simulation platform helps to verify the reliability of the low-cost and high-reliability converter prototype and improve the efficiency of practice.

[0116] Experimental equipment such as a bidirectional DC power supply (which can simulate photovoltaic power generation, power batteries, etc.), a three-phase grid-connected simulator, and a power analyzer provides solid hardware support for the grid connection operation and performance testing of the converter. In addition, equipping a hardware-in-the-loop simulation platform helps to verify the cost-effective and reliable converter prototype and can significantly improve the efficiency of experimental operations.

[0117] The implementation plan is divided into the following four steps:

[0118] The first step: Development and debugging of the converter device

[0119] ① Observe whether the observation device accurately evaluates the impedance threshold of the weak grid impedance and online detects the system performance indicators; ② Observe whether the device is stable under island operation; ③ Observe whether the device has an active support effect on the weak grid during grid disturbances. ④ Use a power analyzer to measure the overall efficiency of the converter and the power factor of the grid-side current respectively, and verify whether this method reduces the losses and whether the filter parameter design meets the power quality requirements.

[0120] Step 2: Verify the high control performance of the underlying controller

[0121] Build a weak grid experimental platform as shown in Figure 5 to simulate the grid impedance through a sliding rheostat, a variable inductor, and different types of PCC loads, and comprehensively test the performance of the underlying controller in aspects such as filter resonance suppression, converter / weak grid connection stability, and grid harmonic suppression under different grid impedance conditions, and verify the feasibility of the underlying control optimization scheme.

[0122] Step 3: Verify the effectiveness of the performance index adaptive regulator

[0123] Converter #1 and converter #2 (i.e., Figure 5 inverter #1 and inverter #2 in

[0124] ) are connected to the grid in parallel. The closed-loop regulator of the control performance index in converter #1 is enabled, and that in converter #2 is not enabled. Compare and analyze the differences in the control performance of the converters under conditions such as grid impedance change and load mutation, and verify the feasibility and effectiveness of the performance index adaptive closed-loop regulator for maintaining the high control performance of the converter. It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean 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 to the implementation process of the embodiments of the present invention.

[0125] The following is the device embodiment of the present invention. For the details not described in detail, reference can be made to the corresponding method embodiment above.

[0126] Figure 6 The structural schematic diagram of the operation control device of the converter under the weak grid of the virtual power plant provided by the embodiment of the present invention is shown. For the convenience of description, only the parts related to the embodiment of the present invention are shown and are described in detail as follows:

[0127] As shown in Figure 6 , the operation control device 6 of the converter under the weak grid of the virtual power plant includes: a controller construction module 601, a model construction module 602, and a control module 603.

[0128] A controller construction module 601, configured to construct a plurality of controllers according to the internal and external loop control variables of the virtual power plant weak grid system, where the internal loop control variables include: inductor current, capacitor voltage, and capacitor current;

[0129] A model construction module 602, configured to construct a small-signal mathematical model corresponding to each controller, and train the small-signal mathematical model of each controller based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine a control model;

[0130] A control module 603, configured to control the output voltage of the converter based on the control models of the respective controllers.

[0131] In a possible implementation, the controller includes: v O -i G controller, i C -i G controller, i L -i G controller, i L -v O -i G controller and i C -v O -i G controller;

[0132] wherein, i L corresponds to the inductor current, v O corresponds to the capacitor voltage, and i C corresponds to the capacitor current.

[0133] In a possible implementation, the device further includes: a determination module, configured to inject a sine wave disturbance signal x p into the outer loop of the grid current, and extract a first voltage waveform x in and a second voltage waveform x out at the disturbance frequencies before and after the disturbance point;

[0134] Determine the loop gain according to the first voltage waveform x in and the second voltage waveform x out ;

[0135] Determine the cut-off frequency and phase margin of each controller according to the loop gain.

[0136] In a possible implementation, the determination module is specifically configured to:

[0137] Determine the loop gain according to the following formula:

[0138] T = -x out / x in .

[0139] In a possible implementation, the determining module is specifically configured to:

[0140] Determine the frequency corresponding to the unit loop gain as the cut-off frequency of each controller;

[0141] Determine the phase angle corresponding to the unit loop gain as the phase margin of each controller.

[0142] In a possible implementation, when two converters are connected in parallel, the determining module is further configured to determine the operating parameters of the filter according to the cut-off frequencies corresponding to the converters.

[0143] In a possible implementation, the determining module is specifically configured to:

[0144] When the difference between the cut-off frequencies corresponding to the two converters is less than a set value, project the second voltage waveform signal at the perturbation point after the two converters are connected in parallel onto a rectangular coordinate system rotating at the perturbation frequency of the two converters to separate the interference frequencies;

[0145] Determine the suppression frequency of the filter according to the interference frequency separation result to achieve the suppression of the interference frequency.

[0146] In a possible implementation, the determining module is specifically configured to:

[0147] Project the second voltage waveform signal x at the perturbation point after the two converters are connected in parallel according to the following formula out onto a rotating coordinate system with a frequency of ω est1 :

[0148]

[0149] where x out is the second voltage waveform signal at the perturbation point after the two converters are connected in parallel; ω est1 is the perturbation frequency of the first converter; ω est2 is the perturbation frequency of the second converter; x out1 is the second voltage waveform at the perturbation frequencies before and after the perturbation point of the first converter; x out2 is the second voltage waveform at the perturbation frequencies before and after the perturbation point of the second converter.

[0150] In a possible implementation, the determining module is specifically configured to:

[0151] When the difference between the cut-off frequencies corresponding to the two converters is greater than or equal to the set value, determine that the filter is a band-pass filter;

[0152] Determine the filtering frequency band of the band-pass filter according to the cut-off frequencies and the difference corresponding to the two converters.

[0153] In this embodiment, multiple controllers are constructed based on the inductor current, capacitor voltage, and capacitor current of the inner and outer loop control variables of the virtual power plant weak grid system to meet the different control requirements of different power grids. Small-signal mathematical models are respectively constructed for each controller, and the small-signal mathematical models of each controller are trained based on the measured impedance data, measured inductor current, measured capacitor voltage, and measured capacitor current data of the converter to determine the control models and achieve precise control of different controllers. The control models of each controller are used to control the output voltage of the converter, synchronously achieving multiple objectives such as power regulation, harmonic suppression, resonance suppression, island detection and state switching, low voltage ride-through, overvoltage or overcurrent protection, etc., thereby improving the stability of the weak grid operation.

[0154] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed or recorded in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0155] Those of ordinary skill in the art can realize that the templates, units, and algorithm steps of the various examples described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0156] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, to implement all or part of the processes of the above method embodiments of the present invention, it can also be completed by a computer program instructing relevant hardware. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above method embodiments for controlling the operation of the converter under the virtual power plant weak grid can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0157] The above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements 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 method for operating and controlling a converter under a weak power grid of a virtual power plant, characterized in that, Including: Constructing a plurality of controllers according to the inner and outer loop control variables of the virtual power plant weak grid system, wherein the inner loop control variables include: inductor current, capacitor voltage and capacitor current; Respectively constructing a small-signal mathematical model for each controller, and training the small-signal mathematical model of each controller based on the measured impedance data, measured inductor current, measured capacitor voltage and measured capacitor current data of the converter to determine the control model; Controlling the output voltage of the converter based on the control models of the respective controllers.

2. The operating control method of the converter under a weak grid in a virtual power plant according to claim 1, characterized in that, The controller includes: v O -i G controller, i C -i G controller, i L -i G controller, i L -v O -i G controller and i C -v O -i G controller; where, i L corresponds to the inductor current, v O corresponds to the capacitor voltage and i C corresponds to the capacitor current.

3. The operating control method of the converter under a weak grid in a virtual power plant according to claim 1, characterized in that, Before controlling the output voltage of the converter based on the control models of the respective controllers, it further includes: Inject a sinusoidal disturbance signal x into the outer loop of the grid current p and extract the first voltage waveform x at the disturbance frequency before and after the disturbance point in and the second voltage waveform x out ; Based on the first voltage waveform x in and the second voltage waveform x out determine the loop gain; Determining the cut-off frequency and phase margin of each controller according to the loop gain.

4. The operating control method of the converter under a weak grid of a virtual power plant according to claim 3, characterized in that, The determining the loop gain according to the first voltage waveform x in and the second voltage waveform x out comprises: Determining the loop gain according to the following formula: T = -x out / x in 。 5. The operating control method of the converter under a weak power grid of a virtual power plant according to claim 4, characterized in that, The determining the cut-off frequency and phase margin of each controller according to the loop gain includes: Determining the frequency corresponding to the unit loop gain as the cut-off frequency of each controller; Determining the phase angle corresponding to the unit loop gain as the phase margin of each controller.

6. The operating control method of the converter under a weak power grid of a virtual power plant according to claim 3, characterized in that When two converters are connected in parallel, it further includes: Determining the operating parameters of the filter according to the cut-off frequencies corresponding to the respective converters.

7. The operating control method of the converter under a weak power grid of a virtual power plant according to claim 3, characterized in that The determining the operating parameters of the filter according to the cut-off frequencies corresponding to the respective converters includes: When the difference between the cut-off frequencies corresponding to the two converters is less than the set value, projecting the second voltage waveform signal at the disturbance point after the two converters are connected in parallel onto a rectangular coordinate system rotating at the disturbance frequency of the two converters to separate the interference frequencies; Determining the suppression frequency of the filter according to the interference frequency separation result to achieve the suppression of the interference frequency.

8. The operating control method of the converter under a weak power grid of a virtual power plant according to claim 7, characterized in that, The projecting the second voltage waveform signal at the disturbance point after the two converters are connected in parallel onto a rectangular coordinate system rotating at the disturbance frequency of the two converters includes: Project the second voltage waveform signal x at the perturbation point after paralleling two converters according to the following formula out onto the rotating coordinate system with a frequency of ω est1 : 2x out (t)·sin(2ω est1 t)=|x out |·[sin(2ω est1 t+∠x out1 )-sin∠x out1 +|x out2 |·[sin((ω est1 +ω est2 )t+∠x out2 )-sin((ω est2 -ω est1 )t+∠x out2 )] 2x out (t)·cos(2ω est1 t)=|x out |·[cos(2ω est1 t+∠x out1 )-cos∠x out1 +|x out2 |·[cos((ω est1 +ω est2 )t+∠x out2 )-cos((ω est2 -ω est1 )t+∠x out2 )] where x out is the second voltage waveform signal at the perturbation point after paralleling the two converters; ω est1 is the perturbation frequency of the first converter; ω est2 is the perturbation frequency of the second converter; x out1 is the second voltage waveform at the perturbation frequencies before and after the perturbation point of the first converter; x out2 is the second voltage waveform at the perturbation frequencies before and after the perturbation point of the second converter.

9. The operating control method of the converter under a weak grid of a virtual power plant according to claim 3, characterized in that, The determining the operating parameters of the filter according to the cut-off frequencies corresponding to the respective converters includes: When the difference between the cut-off frequencies corresponding to the two converters is greater than or equal to the set value, determining that the filter is a band-pass filter; Determining the filtering frequency band of the band-pass filter according to the cut-off frequencies corresponding to the two converters and the difference.

10. An operating control device for a converter under a weak power grid of a virtual power plant, characterized in that, Including: A controller construction module for constructing a plurality of controllers according to the inner and outer loop control variables of the virtual power plant weak grid system, wherein the inner loop control variables include: inductor current, capacitor voltage and capacitor current; A model construction module for respectively constructing a small-signal mathematical model for each controller, and training the small-signal mathematical model of each controller based on the measured impedance data, measured inductor current, measured capacitor voltage and measured capacitor current data of the converter to determine the control model; A control module for controlling the output voltage of the converter based on the control models of the respective controllers.

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