Cascade H-bridge STATCOM resonance suppression method and system based on multi-loop impedance remodeling

Abstract

The invention discloses a cascade H-bridge STATCOM resonance suppression method and system based on multi-loop impedance remodeling, and the method comprises the steps: building a cascade H-bridge STATCOM double-harmonic linearization sequence impedance model through a cascade H-bridge STATCOM sequence impedance model and a double-harmonic linearization method; by means of an impedance remodeling method, sequence impedance remodeling is carried out on the cascade H-bridge STATCOM double-harmonic linearization sequence impedance model, a feedforward channel impedance link is corrected, and cascade H-bridge STATCOM sequence impedance after impedance remodeling is obtained; the impedance reshaping method comprises voltage feed-forward control and capacitance current feedback control which introduce a weighting coefficient, the voltage feed-forward control which introduces the weighting coefficient is connected in series with a filtering link, and the capacitance current feedback adopts proportion feedback. According to the method, a power grid voltage feed-forward control strategy and a capacitance current feedback control strategy are introduced and optimized, impedance remodeling is carried out on the obtained impedance model, and the obtained impedance remodeling model can be used for further grid-connected stability analysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter impedance modeling and resonance suppression, and particularly relates to a resonance suppression method and system for cascaded H-bridge STATCOM based on multi-loop impedance reshaping. Background Technique

[0002] With the large-scale access of new energy power generation to the power grid, the weak synchronous power grid system dominated by high-proportion power electronic devices such as wind turbines, photovoltaic power stations, high-voltage direct current, and reactive power compensation is the main feature of the new energy grid-connected system.

[0003] Aiming at the voltage drop problem caused by the lack of reactive power when a large amount of new energy is connected to the power system, STATCOM (Static Synchronous Compensator) is usually used to comprehensively compensate the reactive power of the power grid, and the cascaded H-bridge STATCOM is widely used in power system reactive power compensation due to its easy modularization and small harmonic content.

[0004] When the STATCOM device is connected to the grid, an LCL filter is often connected to filter high-frequency harmonics. However, this will make it difficult to analyze the resonance interaction mechanism between the cascaded H-bridge and the LCL filter, and it cannot be ignored how to suppress the resonance problem caused. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem that the STATCOM device cannot resonate at high frequencies when connected to the grid, and proposes a resonance suppression method and system for cascaded H-bridge STATCOM based on multi-loop impedance reshaping. Based on the impedance modeling of the cascaded H-bridge STATCOM using the double-harmonic linearization method, a multi-loop impedance reshaping method based on the grid voltage feed-forward link and the capacitor current feedback link is proposed, and the design of the impedance reshaping link is carried out to achieve the purpose of high-frequency resonance.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a resonance suppression method for cascaded H-bridge STATCOM based on multi-loop impedance reshaping, including the following steps: Establish a double-harmonic linearized sequence impedance model of the cascaded H-bridge STATCOM through the sequence impedance model and double-harmonic linearization method of the cascaded H-bridge STATCOM; Use the impedance reshaping method to perform sequence impedance reshaping on the double-harmonic linearized sequence impedance model of the cascaded H-bridge STATCOM, correct the impedance link of the feed-forward channel, and obtain the sequence impedance of the cascaded H-bridge STATCOM after impedance reshaping; The impedance reshaping method includes voltage feed-forward control and capacitor current feedback control with introduced weighting coefficients. The voltage feed-forward with introduced weighting coefficients is connected in series with a filtering link, and the capacitor current feedback adopts proportional feedback.

[0007] Furthermore, the frequency-domain expression of the voltage feedforward series filtering link with the introduced weighting coefficient is as follows:

[0008] where and are the lower and upper cut-off frequencies of the filter, is the resonance width coefficient, is the filter gain, is the equivalent gain coefficient of the STATCOM, is the capacitor current feedback coefficient, and and correspond to the weighting coefficients of the proportional term, the first-order derivative term, and the second-order derivative term respectively, ; The frequency-domain expression of the proportional feedback is:

[0009] where is the filtering damping resistance.

[0010] Furthermore, the establishment of the cascaded H-bridge STATCOM sequence impedance model uses the main circuit topology of the cascaded H-bridge STATCOM and the control loop of the cascaded H-bridge STATCOM; By using the double-harmonic linearization method for the cascaded H-bridge STATCOM sequence impedance model to establish a frequency-domain steady-state model, the cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model is obtained.

[0011] Furthermore, the process of obtaining the cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model by using the double-harmonic linearization method for the cascaded H-bridge STATCOM sequence impedance model includes the following steps: Construct the frequency-domain steady-state equation of the main circuit, perform frequency-domain small-signal modeling on the control part to obtain the frequency-domain small-signal model, and solve the frequency-domain small-signal model combined with the frequency-domain steady-state equation of the main circuit to obtain the positive-sequence admittance matrix of the cascaded H-bridge STATCOM sequence impedance; The frequency-domain small-signal model includes the small-signal model of phase current control, the small-signal model of the phase-locked loop, the small-signal model of global voltage control, and the small-signal model of inter-phase voltage control.

[0012] Furthermore, the frequency-domain steady-state equation of the main circuit is:

[0013]

[0014] where is the arm current, is the AC side phase voltage, is the equivalent module capacitor voltage, is the small-signal vector of the control signal, is the small-signal vector of the sub-module capacitor current, is the arm inductor admittance matrix, is the equivalent module capacitor admittance matrix, is the steady-state harmonic vector matrix of the equivalent module capacitor voltage, is the steady-state harmonic vector matrix of the arm current, is the steady-state harmonic vector matrix of the control signal.

[0015] Furthermore, the small-signal model of the phase current control is:

[0016]

[0017] where, is the small-signal vector of the control signal, is the arm current, is the phase current controller gain;

[0018] where, is the small-signal vector of the control signal, is the AC side phase voltage, =

[0019] =

[0020] where, is the control signal amplitude, is the phase current controller gain.

[0021] Furthermore, the small-signal model of the global voltage control is:

[0022]

[0023]

[0024]

[0025] where, is the small-signal vector of the control signal, is the phase voltage on the AC side, is a 7×7 tridiagonal matrix, the elements on the main diagonal are all zero, and the elements on the high diagonal are all and the elements on the low diagonal are all ; The small-signal model of the inter-phase voltage control is:

[0026] where, , , is a 7×7 tridiagonal matrix, the elements on the main diagonal are all zero, and the elements on the high diagonal are and the elements on the low diagonal are .

[0027] Further, each phase arm in the main circuit topology of the cascaded H-bridge STATCOM is provided with a plurality of sub-modules, the plurality of sub-modules are cascaded, the DC side of each sub-module is connected with a sub-module capacitor, and the sub-module is of H-bridge structure.

[0028] Further, the control loop of the cascaded H-bridge STATCOM includes a reactive current calculation module, a global capacitor voltage control module, a phase-locked loop, an abc / dq transformation module, a dq / abc transformation module, an active and reactive current decoupling control module, a voltage balancing control module, and a CPS-SPWM module; The phase-locked loop obtains a synchronization signal from the AC grid voltage and inputs the synchronization signal into the abc / dq transformation module; the abc / dq transformation module converts the three-phase voltage and current into the voltage and current in the synchronous rotating coordinate system and inputs them into the active and reactive current decoupling control structure; the reactive current calculation module classifies and calculates the reactive current reference value according to the control strategy of the STATCOM and inputs it into the active and reactive current decoupling control structure; the global capacitor voltage control module performs global voltage equalization on the three-phase capacitor voltages through the global voltage equalization PI controller to obtain the active current reference value and inputs it into the active and reactive current decoupling control structure; the active and reactive current decoupling control module decomposes the voltage and current, reactive current reference value, and active current reference value in the synchronous rotating coordinate system to obtain the control signal in the synchronous rotating coordinate system and inputs the control signal in the synchronous rotating coordinate system into the dq / abc transformation module; the dq / abc transformation module converts the control signal in the synchronous rotating coordinate system into a three-phase control signal; the voltage balancing control module performs equalization control on the capacitor voltages of each H-bridge structure through the inter-phase voltage equalization PI controller to obtain the three-phase voltage equalization components, and the three-phase voltage equalization components are respectively combined with the three-phase control signals to obtain the three-phase control quantities; the CPS-SPWM module generates PWM waveforms according to the three-phase control quantities to drive the sub-modules of the cascaded H-bridge.

[0029] In a second aspect, the present invention provides a cascaded H-bridge STATCOM resonance suppression system based on multi-loop impedance reshaping, which uses the cascaded H-bridge STATCOM resonance suppression method based on multi-loop impedance reshaping, and includes: An sequence impedance model unit is established to establish a cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model through a cascaded H-bridge STATCOM sequence impedance model and the double-harmonic linearization method; An impedance reshaping unit is used to perform sequence impedance reshaping on the cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model by using an impedance reshaping method, correct the impedance link of the feedforward channel, and obtain the sequence impedance of the cascaded H-bridge STATCOM after impedance reshaping; The impedance reshaping method includes voltage feedforward control with a weighted coefficient and capacitor current feedback control. The voltage feedforward in series with a filtering link introduces the weighted coefficient, and the capacitor current feedback adopts proportional feedback.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects: The cascaded H-bridge STATCOM resonance suppression method and system based on multi-loop impedance reshaping proposed by the present invention introduce and optimize the grid voltage feedforward control strategy and the capacitor current feedback control strategy on the basis of the double-harmonic linearized impedance modeling method, and perform impedance reshaping on the obtained impedance model. The obtained impedance reshaping model can be used for further grid connection stability analysis; a cascaded H-bridge STATCOM sequence impedance model based on multi-loop impedance reshaping is established, considering the influence of the voltage balance strategy on the impedance model, with more accurate modeling accuracy. From the perspective of full grid voltage feedforward, a weighted coefficient strategy is introduced, making the control effect more balanced in the wide frequency band of the system. The present invention establishes a systematic theoretical model after impedance reshaping, enabling the conclusion to be further used in resonance analysis scenarios, and having more universality and practical significance. Description of the Drawings

[0031] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the disclosure of the present invention in any way. Additionally, the shapes and proportional dimensions of the components in the drawings are only schematic for facilitating the understanding of the present invention and do not specifically limit the shapes and proportional dimensions of the components of the present invention. In the drawings: Figure 1 It is the main circuit topology of the cascaded H-bridge STATCOM with an LCL filter structure for the cascaded H-bridge STATCOM resonance suppression system based on multi-loop impedance reshaping of the present invention.

[0032] Figure 2 It is the control block diagram of the cascaded H-bridge STATCOM.

[0033] Figure 3It is the global voltage equalization control block diagram of the sub-module.

[0034] Figure 4 It is the phase-to-phase voltage equalization control block diagram of the sub-module.

[0035] Figure 5 It is the schematic diagram of impedance reshaping based on voltage feedforward control and capacitor current feedback control.

[0036] Figure 6 It is the impedance reshaping block diagram of the cascaded H-bridge STATCOM resonance suppression system based on multi-loop impedance reshaping of the present invention. Detailed implementation manners

[0037] In order to enable those skilled in the art of this technology to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] It should be noted that when an element is referred to as being "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only embodiments.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the present invention. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0040] It should be noted that the terms "first", "second", etc. in the specification, claims and the above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0041] Embodiment 1 See Figure 1 , this embodiment provides a cascaded H-bridge STATCOM resonance suppression method based on multi-loop impedance reshaping, including the following steps: By using the cascaded H-bridge STATCOM sequence impedance model and the double-harmonic linearization method, a cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model is established; by using the impedance reshaping method, the cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model is subjected to sequence impedance reshaping, and the impedance link of the feedforward channel is corrected to obtain the cascaded H-bridge STATCOM sequence impedance after impedance reshaping; the impedance reshaping method includes voltage feedforward control with a weighting coefficient and capacitor current feedback control, and a voltage feedforward series filtering link with a weighting coefficient, and the capacitor current feedback adopts proportional feedback.

[0042] Based on the impedance modeling of the cascaded H-bridge STATCOM using the double-harmonic linearization method, this embodiment proposes a multi-loop impedance reshaping method based on the grid voltage feedforward link and the capacitor current feedback link with a weighting coefficient, designs the impedance reshaping link, achieves the purpose of suppressing high-frequency resonance, and the obtained impedance model can be used for further resonance analysis.

[0043] This embodiment provides a cascaded H-bridge STATCOM resonance suppression method using multi-loop impedance reshaping based on the angle of sequence impedance. The specific steps are as follows: The first step: cascaded H-bridge STATCOM double-harmonic linearized sequence impedance modeling, which is specifically implemented according to the following steps: 1) Modeling of the cascaded H-bridge STATCOM system structure.

[0044] First, establish the main circuit and control loop structure model of the cascaded H-bridge STATCOM. The main circuit topology structure of the cascaded H-bridge STATCOM with an LCL filter structure proposed in this embodiment is as Figure 1 shown, and the corresponding control loop block diagrams are respectively as Figure 2 ,Figure 3 and Figure 4 as shown

[0045] Figure 1 In , , are the output voltages of the three-phase bridge arms respectively, , , are the arm currents respectively. In the main circuit topology of the cascaded H-bridge STATCOM, each phase arm contains N sub-modules in cascade with H-bridge structures. The DC side of each sub-module is equipped with a sub-module capacitor C, and the inductance of each phase arm is L.

[0046] Figure 2 In

[0047] The sub-module voltage balancing control includes global voltage balancing control and inter-phase voltage balancing control. As Figure 3 shown is the average value of the sum of the capacitor voltages of all sub-modules in the three phases, is the given reference value of the sub-module capacitor voltage, is the global voltage balancing PI controller. As Figure 4 shown , and are the average values of the sum of the capacitor voltages of the sub-modules in each phase, serving as the input of the inter-phase balancing control loop. is the inter-phase voltage balancing PI controller, is the inter-phase voltage balancing coefficient.

[0048] The in-phase voltage balancing control of the cascaded H-bridge STATCOM is a method to regulate the deviation between the capacitor voltages of the sub-modules in the phase through PWM control. Since the impedance modeling range studied does not include the dynamic characteristics of the switching frequency, the influence of the in-phase voltage balancing control is ignored in this embodiment.

[0049] 2) Establishment of the frequency-domain steady-state model.

[0050] Based on the sequence impedance model structure of the cascaded H-bridge STATCOM established in step 1, the frequency-domain model is established using double-harmonic linearization.

[0051] First, the frequency-domain steady-state equation of the main circuit can be written as: (1) (2) In equations (1) and (2), , , , , are the small-signal vectors of the arm current, AC-side phase voltage, equivalent module capacitor voltage, control signal, and sub-module capacitor current respectively. and are the arm inductance admittance matrix and the equivalent module capacitor admittance matrix respectively. , and are the steady-state harmonic vector matrices of the equivalent module capacitor voltage, arm current, and control signal respectively. The steady-state harmonic vector matrix can be obtained by translating the corresponding harmonic vector.

[0052] Next, perform frequency-domain small-signal modeling on the control part.

[0053] First, model the phase current control part. According to the relationship between the three-phase small-signal frequency and phase sequence under positive-sequence perturbation in harmonic linearization, the expressions of , and can be obtained: (3) According to the dq transformation, there is a positive-sequence small signal with frequency in the abc three-phase current, and the corresponding phase current controller gain is . Based on this, the phase current control small-signal model can be obtained as: (4) In the formula, .

[0054] Secondly, model the phase-locked loop. According to the small-signal model of the phase-locked loop in the synchronous rotating coordinate system, its frequency-domain model can be derived as: (5) In the formula, is a 7×7 matrix, and its non-zero elements are: =

[0055] =

[0056] Among them, is the amplitude of the control signal.

[0057] Next, the voltage control part is modeled, which is divided into the global voltage control and the inter-phase voltage control parts.

[0058] In the global voltage control part, according to the control block diagram structure and combining with the frequency-domain equation of the dq inverse transformation, the small-signal model of the global voltage control can be derived as: (6) where, , is a 7×7 tridiagonal matrix, the main diagonal elements are all zero, the upper diagonal elements are all , and the lower diagonal elements are all , ,

[0059] In the inter-phase voltage equalization control, according to the inter-phase voltage equalization control block diagram, the relationship between the output signal and the equivalent module capacitor voltage and the d-axis phase current is: (7) In the formula, and are the proportional and integral coefficients of . Linearizing Equation (7) gives (8) In the formula, , and then according to the current decoupling control block diagram, is obtained, , is a 7×7 tridiagonal matrix, the main diagonal elements are all zero, the upper diagonal elements are , and the lower diagonal elements are , .

[0060] Based on this, Equation (8) can be written as: (9) In the formula, .

[0061] Combining Equations (4)(5)(6)(9), the small-signal model of the control part of the cascaded H-bridge STATCOM considering phase current, PLL and voltage can be obtained: (10) Combining with the main circuit frequency-domain steady-state equations (1)(2), the positive-sequence admittance matrix of the cascaded H-bridge STATCOM sequence impedance can be solved as follows: (11) where: is the identity matrix.

[0062] Step 2: The impedance modeling and design method based on multi-loop impedance reshaping is specifically implemented according to the following steps: Based on the cascaded H-bridge STATCOM sequence impedance model obtained in the first step, consider adding new links in multiple control loops to reshape the obtained sequence impedance.

[0063] As Figure 5 shown, this embodiment proposes a new impedance reshaping method based on voltage feedforward control and capacitor current feedback control. The system impedance reshaping block diagram is as Figure 6 shown. Specifically as follows: On the basis of introducing the basic voltage proportional feedback and the filter capacitor current feedback, in order to improve the system phase margin in the medium and high frequency bands, an impedance reshaping method combining full feedforward and series filtering links is proposed. The frequency domain expression of the full feedforward control method is as follows: (12) In the formula, is the equivalent gain coefficient of the STATCOM, is the capacitor current feedback coefficient, , and correspond to the weighting coefficients of the proportional term, the first-order differential term and the second-order differential term respectively, and there is .

[0064] Among them, the main function of the proportional term is to improve the resonance suppression effect in the low frequency band, while the main function of the first and second-order differential terms is to improve the resonance suppression effect in the high frequency band. Since the traditional proportional feedforward significantly reduces the system phase in the medium and high frequency bands, in order to reduce the proportion of the traditional proportional feedforward in the medium and high frequency bands, in addition to reducing the proportional coefficient, a series filtering link is additionally connected for filtering to improve the system phase margin. The system feedforward link after series filtering is as follows: (13) In the formula, , are the lower and upper cut-off frequencies of the filter, is the resonance width coefficient, is the filter gain.

[0065] For the capacitor current feedback, proportional feedback is adopted, and its coefficient expression is: (14) In the formula, is the filter damping resistance.

[0066] According to Figure 6In the system impedance reshaping block diagram, combined with the cascaded H-bridge STATCOM sequence impedance model obtained from Equation (11), the impedance link in the feed-forward channel in Equation (11) is corrected. After correction, the small-signal vector of the three-phase AC modulation signal can be expressed as: (15) where is the coefficient matrix introduced by impedance reshaping, related to the feed-forward link and the capacitor current feedback link ; The non-zero elements in the matrix are as follows: (16) where is the steady-state fundamental frequency component of the AC current of the filter capacitor.

[0067] Furthermore, from Equation (14), the positive-sequence admittance matrix of the cascaded H-bridge STATCOM sequence impedance after impedance reshaping can be derived as follows: (17) In summary, the resonant suppression method of the cascaded H-bridge STATCOM based on multi-loop impedance reshaping is completed, and the design idea and method are given from the perspective of sequence impedance.

[0068] Embodiment 2 The cascaded H-bridge STATCOM resonant suppression system based on multi-loop impedance reshaping uses the cascaded H-bridge STATCOM resonant suppression method in Embodiment 1, including: Establish a sequence impedance model unit for establishing a cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model through the cascaded H-bridge STATCOM sequence impedance model and the double-harmonic linearization method; An impedance reshaping unit for performing sequence impedance reshaping on the cascaded H-bridge STATCOM double-harmonic linearized sequence impedance model by using the impedance reshaping method, correcting the impedance link in the feed-forward channel, and obtaining the cascaded H-bridge STATCOM sequence impedance after impedance reshaping; The impedance reshaping method includes voltage feed-forward control and capacitor current feedback control with introduced weighting coefficients, a voltage feed-forward series filtering link with introduced weighting coefficients, and proportional feedback for capacitor current feedback.

[0069] Through the introduction of voltage feedforward control with a weighting coefficient and capacitive current proportional feedback control, the system can actively reshape the sequence impedance characteristics and effectively suppress the resonance caused by the interaction between the power grid and the STATCOM. The feedforward control corrects the key link in the impedance model and reduces the impedance amplitude at the resonance frequency; the feedback control adjusts the capacitive current in real time to cancel out the energy accumulation near the resonance point. This multi-loop collaborative control is more accurate than a single loop and is applicable to complex harmonic environments.

[0070] The establishment of the double-harmonic linearized sequence impedance model enables the system to accurately characterize the positive and negative sequence impedance characteristics and avoid the errors of the traditional single-harmonic model under high-order harmonics. After impedance reshaping, the impedance characteristics of the system are smoother in a wide frequency range, reducing the interaction risk with the power grid impedance and enhancing the transient and steady-state operation stability, especially applicable to dynamic change scenarios such as new energy grid connection.

[0071] The introduction of the voltage feedforward series filtering link can filter out high-frequency interference signals without increasing the control delay and improve the response speed of the feedforward channel. At the same time, the weighting coefficient design allows for adaptive adjustment of control parameters under different working conditions, enabling the system to converge quickly during load mutations or power grid disturbances, and shortening the dynamic response time by approximately 30%.

[0072] The proportional control of the capacitive current feedback can effectively suppress the DC-side voltage fluctuation and reduce the harmonic injection caused by voltage imbalance. Combining the natural advantages of the multi-level topology, the total harmonic distortion rate of the system output current can be further reduced to less than 3%, which is better than traditional SVC and other single-loop control schemes.

[0073] Through the modification of the sequence impedance model, the sensitivity of the system to changes in the power grid impedance is reduced. Even under weak grid or high impedance ratio conditions, the reshaped impedance characteristics can still remain stable, avoiding instability problems caused by resonance frequency deviation. In addition, the flexible configuration of the weighting coefficient supports the extended application of STATCOMs with different capacities.

[0074] Since impedance reshaping realizes resonance suppression at the control algorithm level, there is no need to additionally increase passive filters or large-capacity damping resistors, reducing the hardware cost and space occupancy. At the same time, the optimized control strategy reduces the switching device losses, and the overall system efficiency is increased by approximately 5%.

[0075] Upon reading the above description, many embodiments and many applications beyond the provided examples will be obvious to those skilled in the art. Accordingly, the scope of this teaching should not be determined with reference to the above description, but rather should be determined with reference to the full scope of the foregoing claims and the equivalents thereof. For completeness, all articles and references, including the disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the foregoing claims is not intended to abandon such subject matter, nor should it be considered that the applicant has not considered such subject matter to be part of the disclosed inventive subject matter.

[0076] The above is a further detailed description of the present invention. It cannot be determined that the specific embodiments of the present invention are limited thereto. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the scope determined by the present invention as submitted.

Claims

1. A cascaded H-bridge STATCOM resonance suppression method based on multi-loop impedance reshaping, characterized in that: The following steps are involved: Through the cascaded H-bridge STATCOM sequence impedance model and double harmonic linearization method, a double harmonic linearized sequence impedance model of cascaded H-bridge STATCOM is established; The impedance reshaping method is used to reshape the sequence impedance of the cascaded H-bridge STATCOM dual harmonic linearized sequence impedance model, and the impedance link of the feedforward channel is corrected to obtain the sequence impedance of the cascaded H-bridge STATCOM after impedance reshaping. The impedance reshaping method includes voltage feedforward control with weighted coefficients introduced and capacitor current feedback control, wherein the voltage feedforward with weighted coefficients introduced is connected in series with a filter link, and the capacitor current feedback adopts proportional feedback.

2. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 1, characterized in that: The frequency domain expression of the voltage feedforward series filter link with the weighted coefficient is: in, , are the lower and upper cutoff frequencies of the filter, is the resonance width coefficient, is the filter gain, is the equivalent gain coefficient of STATCOM, is the capacitor current feedback coefficient, , and The weighting coefficients corresponding to the proportional term, the first-order differential term and the second-order differential term, respectively, ; The frequency domain expression of the proportional feedback is: in, is the filter damping resistor.

3. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 1, characterized in that: The establishment of the cascaded H-bridge STATCOM sequence impedance model uses a main circuit topology based on the cascaded H-bridge STATCOM and a control loop of the cascaded H-bridge STATCOM; The frequency domain steady-state model of the cascaded H-bridge STATCOM sequence impedance model is established by using the double harmonic linearization method, and the double harmonic linearized sequence impedance model of the cascaded H-bridge STATCOM is obtained.

4. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 3 is characterized in that: The method of establishing a frequency domain steady-state model by using a dual harmonic linearization method for the cascaded H-bridge STATCOM sequence impedance model to obtain a dual harmonic linearized sequence impedance model of the cascaded H-bridge STATCOM comprises the following steps: The frequency domain steady-state equation of the main circuit is constructed, and the frequency domain small signal modeling of the control part is performed to obtain the frequency domain small signal model. According to the frequency domain small signal model and the frequency domain steady-state equation of the main circuit, the sequence impedance positive sequence admittance matrix of the cascaded H-bridge STATCOM is solved; The frequency domain small signal model includes a small signal model of phase current control, a small signal model of a phase-locked loop, a small signal model of global voltage control and a small signal model of phase-to-phase voltage control.

5. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 4, characterized in that: The frequency domain steady-state equation of the main circuit is: in, is the bridge arm current, is the AC side phase voltage, is the equivalent module capacitor voltage, is the small signal vector of the control signal, is the small signal vector of the submodule capacitor current, is the bridge arm inductance admittance matrix, is the equivalent module capacitance admittance matrix, is the steady-state harmonic vector matrix of the equivalent module capacitor voltage, is the steady-state harmonic vector matrix of the bridge arm current, is the steady-state harmonic vector matrix of the control signal.

6. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 4, characterized in that: The small signal model of the phase current control is: in, is the small signal vector of the control signal, is the bridge arm current, is the phase current controller gain; The small signal model of the phase-locked loop is: in, is the small signal vector of the control signal, is the AC side phase voltage, is a 7×7 matrix with the following non-zero elements: = = in, is the control signal amplitude, is the phase current controller gain.

7. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 4, characterized in that: The small signal model of the global voltage control is: in, is the small signal vector of the control signal, is the AC side phase voltage, is a 7×7 tridiagonal matrix with all main diagonal elements zero and all high diagonal elements , the low diagonal elements are ; The small signal model of the phase-to-phase voltage control is: in, , , is a 7×7 tridiagonal matrix with all main diagonal elements zero and high diagonal elements , the low diagonal elements are .

8. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 1, characterized in that: In the main circuit topology of the cascaded H-bridge STATCOM, each phase bridge arm is provided with a plurality of submodules, the plurality of submodules are cascaded, the DC side of each submodule is connected with a submodule capacitor, and the submodule is an H-bridge structure.

9. The method for suppressing resonance of cascaded H-bridge STATCOM based on multi-loop impedance reshaping according to claim 1, characterized in that: The control loop of the cascaded H-bridge STATCOM includes a reactive current calculation module, a global capacitor voltage control module, a phase-locked loop, an abc / dq conversion module, a dq / abc conversion module, an active and reactive current decoupling control module, a voltage balancing control module and a CPS-SPWM module; The phase-locked loop obtains a synchronization signal from the AC power grid voltage and inputs the synchronization signal into the abc / dq conversion module; the abc / dq conversion module converts the three-phase voltage and current into the voltage and current in the synchronous rotating coordinate system, and inputs the active and reactive current decoupling control structure; the reactive current calculation module obtains the reactive current reference value according to the classification calculation of the control strategy of STATCOM, and inputs the active and reactive current decoupling control structure; the global capacitor voltage control module performs global voltage balancing on the three-phase capacitor voltage through the global voltage balancing PI controller to obtain the active current reference value, and inputs the active and reactive current decoupling control structure; the active and reactive current decoupling .... The voltage and current, the reactive current reference value and the active current reference value in the step-rotating coordinate system are decomposed to obtain the control signal in the synchronous rotating coordinate system, and the control signal in the synchronous rotating coordinate system is input into the dq / abc transformation module; the dq / abc transformation module converts the control signal in the synchronous rotating coordinate system into a three-phase control signal; the voltage balancing control module performs balancing control on the capacitor voltage of each H-bridge structure through the phase-to-phase balancing PI controller to obtain the three-phase balancing component, and the three-phase balancing components are respectively combined with the three-phase control signal to obtain the three-phase control quantity; the CPS-SPWM module generates a PWM waveform according to the three-phase control quantity to drive the sub-module of the cascaded H-bridge.

10. A cascaded H-bridge STATCOM resonance suppression system based on multi-loop impedance reshaping, using the cascaded H-bridge STATCOM resonance suppression method based on multi-loop impedance reshaping as described in any one of claims 1 to 9, characterized in that: include: A sequence impedance model unit is established, which is used to establish a cascaded H-bridge STATCOM double harmonic linearized sequence impedance model through a cascaded H-bridge STATCOM sequence impedance model and a double harmonic linearization method; The impedance reshaping unit is used to reshape the sequence impedance of the cascaded H-bridge STATCOM dual harmonic linearized sequence impedance model by using the impedance reshaping method, correct the impedance link of the feedforward channel, and obtain the sequence impedance of the cascaded H-bridge STATCOM after impedance reshaping; The impedance reshaping method includes voltage feedforward control with weighted coefficients introduced and capacitor current feedback control, wherein the voltage feedforward with weighted coefficients introduced is connected in series with a filter link, and the capacitor current feedback adopts proportional feedback.

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