Transformer area voltage autonomous flexible management system based on virtual phase modulation control

Abstract

The invention provides a transformer area voltage autonomous flexible treatment system based on virtual phase modulation control, and belongs to the technical field of transformer area voltage treatment. Comprising a cascaded H-bridge chain type static synchronous compensator. The control system of the static synchronous compensator comprises a reactive voltage outer loop control unit, a reactive current inner loop control unit and a virtual phase modulation control module. The virtual phase modulation control module is used for obtaining phase information generated by the direct-current voltage; the reactive voltage outer loop control unit is used for obtaining a reactive voltage reference value; the reactive current inner loop control unit is used for generating a voltage instruction according to the reactive voltage reference value; and the control system of the static synchronous compensator generates a switching signal of each H-bridge module according to the voltage instruction and the phase information. The running characteristics of the synchronous phase modifier are simulated, the rotor inertia of the synchronous generator is simulated by using the direct current capacitor voltage of each unit of the chain-type STATCOM, positive damping is injected to the system, and the system stability is improved, so that the autonomous flexible management of the voltage of the transformer area is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of transformer area voltage management, and particularly relates to a transformer area voltage autonomous flexible management system based on virtual phase modulation control. BACKGROUND

[0002] With the global energy transformation advancing, large-scale grid connection of new energy makes the power system present the characteristics of "double high", that is, high proportion of grid connection of new energy and high proportion of penetration of power electronic equipment, and the composition and operation characteristics of the power system are undergoing profound changes. Under this background, a large number of non-traditional loads such as photovoltaic and charging piles flow into the distribution transformer area, making the power supply and demand balance of the transformer area face great challenges.

[0003] In terms of control compensation, the traditional transformer area voltage regulation method adopts tap switch regulation and reactive power compensation device, but the tap switch regulation has slow speed and low regulation accuracy, and cannot track the changes of transformer area voltage in real time; and the conventional reactive power compensation device is mostly fixed compensation or grouping compensation, which is difficult to realize continuous and smooth adjustment of reactive power, and has problems such as switching oscillation and response lag, and is difficult to adapt to the current frequent and complex transformer area voltage fluctuations. Therefore, it is urgent to explore a flexible management strategy that can autonomously, quickly and flexibly regulate the transformer area voltage, adapt to high proportion of distributed energy access and diversified load characteristics. SUMMARY

[0004] The application provides a transformer area voltage autonomous flexible management system based on virtual phase modulation control to solve the problems in the prior art.

[0005] To solve one or part or all of the above technical problems, the application adopts the following technical scheme: A transformer area voltage autonomous flexible management system based on virtual phase modulation control, comprising a cascaded H-bridge chain static synchronous compensator; the control system of the static synchronous compensator comprises a reactive voltage outer loop control unit, a reactive current inner loop control unit and a virtual phase modulation control module; The virtual phase modulation control module is used to obtain phase information generated by a direct current voltage according to an average direct current voltage of an H-bridge module of the static synchronous compensator, a direct current voltage set value and a grid fundamental frequency; The reactive voltage outer loop control unit is used to obtain a reactive voltage reference value according to the average direct current voltage of the H-bridge module of the static synchronous compensator, a reactive voltage rated value, a reference value and an actual value of reactive power; The reactive current inner loop control unit is used to generate a voltage instruction according to the reactive voltage reference value, dq components of output voltage and current of the static synchronous compensator, an alternating current end angular frequency of the converter, and an inductance value of the connected filter reactor; The control system of the static synchronous compensator generates a switching signal of each H-bridge module according to the voltage instruction and the phase information.

[0006] Further, the reactive voltage outer loop control unit comprises a damping control module and a reactive power control module, and the reactive current inner loop control unit comprises a virtual impedance control module and a current decoupling control module. The damping control module is configured to generate a damping term according to a DC voltage of the static synchronous compensator and output the damping term to the reactive power control module; the reactive power control module is configured to generate the reactive voltage reference value in combination with the damping term and output the reactive voltage reference value to the virtual impedance control module; the virtual impedance control module is configured to generate a current reference value in combination with the reactive voltage reference value and output the current reference value to the current decoupling control module; and the current decoupling control module is configured to generate the voltage instruction in combination with the current reference value.

[0007] Further, an algorithm formula of the virtual phase modulation control module is where θ is the phase information, , and are an average DC voltage of an H-bridge module of the static synchronous compensator, a DC voltage set value, and a grid fundamental frequency, respectively.

[0008] Further, the damping control module is configured to pass the average DC voltage of the H-bridge module of the static synchronous compensator through a low-pass filter with a time constant T and a differential element, and then multiply the average DC voltage by a damping coefficient to obtain the damping term ζ, where s is a Laplace operator.

[0009] Further, an algorithm formula of the reactive power control module is , is the reactive voltage reference value, ζ is the damping term, , and are a reactive voltage rated value of the static synchronous compensator, a reference value and an actual value of the reactive power, and are a proportional parameter and an integral parameter of a PI controller in the reactive power control module, and s is a Laplace operator.

[0010] Further, the virtual impedance control module obtains the current reference value by solving a state equation and where is the reactive voltage reference value, is an active voltage reference value, and the value is 0,​ and are the dq components of the output voltage of the static synchronous compensator, respectively, , and are the grid fundamental frequency, virtual inductance and virtual resistance, respectively.

[0011] Further, the algorithm formula of the current decoupling control module is wherein and are the voltage instructions, , , and are the dq components of the output voltage and current of the static synchronous compensator, respectively, and are the current reference values, and ω and L are the angular frequency of the AC side of the converter of the static synchronous compensator and the inductance value of the connected filter reactor, respectively, and are the proportional and integral parameters of the PI controller in the current decoupling control module, respectively.

[0012] At present, some existing technologies apply energy storage systems to distribution voltage regulation, using the charge and discharge characteristics of the energy storage system to suppress distribution voltage fluctuations. However, the cost of the energy storage system is relatively high and complex problems such as capacity configuration and coordinated control of the energy storage system need to be solved. In addition, some existing technologies propose to use adjustable reactive power of distributed power to assist distribution voltage regulation, but due to the uncertainty of the output of the distributed power, the support effect on the distribution voltage is volatile.

[0013] The flexible interconnection device based on power electronic equipment also helps to complete the power balance between different transformer areas, and part of the existing technology proposes to apply chain static synchronous compensator (STATCOM) to the autonomous flexible management of transformer area voltage, and the traditional grid-connected chain STATCOM relies on phase-locked loop control, lacks the ability to actively support the grid frequency and voltage, and is difficult to cope with the inertia loss problem of the system under high proportion of new energy access. The virtual synchronous generator (VSG) technology can simulate the external characteristics of synchronous machines through the construction of inertia forward channel and damping closed loop structure, and the transient response effect is good, but the active ring design is usually involved in the control strategy and the direct current voltage is not involved, so the VSG technology is difficult to be directly used for network control of chain STATCOM. In view of the above problems, the present application establishes the frequency and voltage dynamic relationship by matching control, applies the network STATCOM to the autonomous flexible management of transformer area voltage, simulates the operating characteristics of the synchronous phase modifier, combines the split-phase control advantage of the chain topology, and realizes the active support and oscillation suppression of the transformer area voltage.

[0014] The present application proposes a kind of transformer area voltage autonomous flexible management system based on virtual phase modulation control, by simulating the operating characteristics of the synchronous phase modifier, using the direct current capacitor voltage of each unit of chain STATCOM simulates the rotor inertia of synchronous generator, injects positive damping for system, can effectively suppress system voltage oscillation, improve system stability, realizes the network control without energy storage support, realizes the autonomous flexible management of transformer area voltage.

[0015] The present application does not need to additionally increase battery or super capacitor to provide active support, significantly reduces cost and system complexity.The present application can actively set and support AC frequency, enhance grid stability.The present application uses the inertia of direct current capacitor voltage, converts the dynamic change of direct current side into reactive regulation instruction of network side by the way of damping control, improves the stability and dynamic response speed of system under power disturbance. BRIEF DESCRIPTION OF DRAWINGS

[0016] The present application will be further described in detail below in combination with the drawings.

[0017] Figure 1 The structural schematic diagram of the present application; Figure 2 The equivalent circuit of H bridge chain link cascade module of chain STATCOM of the present application; Figure 3 The characteristic root trajectory graph when analyzing the stability of network type chain STATCOM; Figure 4Fault condition diagram for verifying stability of grid-connected chain STATCOM Figure 5 Phase angle waveform diagram of AC terminal of converter for verifying effectiveness of grid-connected control of grid-connected chain STATCOM Figure 6 Frequency waveform diagram of AC terminal of converter for verifying effectiveness of grid-connected control of grid-connected chain STATCOM Figure 7 Voltage waveform diagram of point of common coupling for verifying voltage damping property of grid-connected chain STATCOM Figure 8 Average DC voltage waveform for verifying DC voltage equalization effect of grid-connected chain STATCOM DETAILED DESCRIPTION

[0018] In order to better understand the present application, the content of the present application is further clearly set forth below in conjunction with embodiments and drawings, but the protection scope of the present application is not limited to the following embodiments. In the following description, a large number of specific details are given in order to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details.

[0019] Embodiment 1: refer to Figure 1 The purpose of the present embodiment is to provide a transformer area voltage autonomous flexible management system based on virtual phase modulation control. The management system comprises a cascaded H-bridge chain static synchronous compensator (STATCOM). Each phase of the chain STATCOM is composed of n structurally identical H-bridge chain modules, each H-bridge unit is powered by an independent DC voltage source, each phase adopts star connection mode, and is connected to the power grid system through a filter reactor L.

[0020] Figure 1 Among the related parameters of is the three-phase output voltage of the power grid; and are the three-phase voltage and current at the load end, respectively; , and are the three-phase output voltages of the chain STATCOM; , and are the three-phase output currents of the chain STATCOM; the DC voltages of the three-phase H-bridge modules are respectively denoted as , and , where j=1...N; the DC voltages of the H-bridge modules in the three phases are added and averaged to obtain the average DC voltage ; , and , are the d-axis and q-axis components of the three-phase output voltage and three-phase output current of the chain STATCOM via dq transformation, respectively; is the output reactive power of the chain STATCOM; is a damping control coefficient; and represent a virtual resistance and a virtual inductance; and θ is the phase angle of the AC end of the chain STATCOM converter. The " * " in the upper right corner of the above electrical quantities represents a reference value.

[0021] The control system of the chain STATCOM includes a reactive voltage outer loop control unit, a reactive current inner loop control unit, and a virtual phase modulation control module. The reactive voltage outer loop control unit includes a damping control module and a reactive power control module. The reactive current inner loop control unit includes a virtual impedance control module and a current decoupling control module.

[0022] Virtual phase modulation control is one of the core control technologies of the chain STATCOM. It mainly simulates the operating characteristics of a synchronous phase modulator to actively support the voltage of the transformer area. In a traditional power system, when the power grid is disturbed, the frequency of the synchronous generator will not change abruptly due to the physical inertia of the rotor. By utilizing the similar characteristic that the DC capacitor voltage of each unit of the chain STATCOM will not change abruptly when disturbed, the virtual phase modulation control module of the present application simulates the rotor inertia of the synchronous generator by the DC capacitor of each unit, and establishes a matching relationship between the DC voltage and the angular frequency of the AC end of the converter: (1) wherein is the average DC voltage of each module in the three-phase, is the DC voltage set value of the chain STATCOM, ω is the angular frequency of the AC end of the converter of the chain STATCOM, is the fundamental frequency of the power grid.

[0023] The angular frequency of the AC end of the converter is transformed by an integral transformer to obtain the phase information θ: (2) The phase information θ generated by the DC voltage is introduced into the control system to realize the grid operation of the chain STATCOM.

[0024] In summary, the virtual phase modulation control module is used to obtain the phase information θ generated by the DC voltage according to the average DC voltage of the H-bridge module of the chain STATCOM , the DC voltage set value of the chain STATCOM , and the fundamental frequency of the power grid . .

[0025] The main purpose of the reactive voltage outer loop control unit is to regulate the reactive power of the grid connection point to maintain the stability of the system voltage. The reactive power control module is used to adjust the output of the reactive power through a PI controller according to the difference between the reference value and the actual value of the reactive power, generate a reactive voltage reference value , so as to realize the control of the voltage. The damping control module is used to take the DC voltage fluctuation into the reactive voltage reference value generation link, and provide positive damping for the system through a differential link with a gain of Dp to suppress oscillation. Since the inertia energy that can be matched by the capacitance value is relatively small, the damping control can improve the inertia of the DC side, so as to complete the adaptive adjustment of the power and improve the active response to the grid frequency fluctuation when the DC voltage changes caused by the grid side power change.

[0026] The calculation formula of the reactive voltage reference value is: (3) Wherein is the rated value of the output reactive voltage of the chain STATCOM; and are the proportional and integral parameters of the PI controller in the reactive power control module. ζ is the damping term output by the damping control module, T represents the time constant of the low-pass filter; s is the Laplace operator.

[0027] In summary, the reactive voltage outer loop control unit is used to obtain the reactive voltage reference value according to the average DC voltage of the H-bridge module of the chain STATCOM, the rated value of the reactive voltage , and the reference value and the actual value of the reactive power. Specifically, the damping control module is used to pass the average DC voltage of the H-bridge module of the chain STATCOM through a low-pass filter with a time constant of T and a differential link, and then multiply it by the damping coefficient Dp to obtain the damping term ζ and output it to the reactive power control module. The reactive power control module is used to process the reference value and the actual value of the reactive power of the chain STATCOM by using the PI controller, and obtain the reactive voltage reference value after superimposing the damping term ζ and the rated value of the output reactive voltage of the chain STATCOM.

[0028] The virtual impedance control module is additionally added in the reactive current inner loop control unit, and is used for simulating the impedance characteristics of the synchronous generator in the device control loop. The core is to adjust the equivalent output impedance of the device through the current or voltage feedback, so as to change the dynamic response of the system, introduce positive damping in the key frequency band, offset the negative damping characteristics of the system, and realize wide frequency coverage. The state equation of the virtual impedance control module is: (4) Wherein is the active voltage reference value, and the value is set to 0. According to the state equation, the current reference value and can be solved, and the current reference value is input into the current decoupling control module.

[0029] The voltage instruction output by the current decoupling control module is , : (5) Wherein and are the proportional and integral parameters of the PI controller in the current decoupling control module, and L is the inductance value of the filter reactor.

[0030] In summary, the reactive current inner loop control unit is used for generating the voltage instruction , and according to the reactive voltage reference value , the dq components of the three-phase output voltage of the chain STATCOM , the dq components of the three-phase output current , , the alternating current end angular frequency ω of the converter, and the inductance value L of the filter reactor. The virtual impedance control module is used for obtaining the reference value and of the three-phase output current dq components of the chain STATCOM according to the reactive voltage reference value obtained by the reactive power control module, the dq components of the three-phase output voltage of the chain STATCOM , the grid fundamental frequency , the virtual resistance and the virtual inductance , and outputs to the current decoupling control module. The current decoupling control module is used for generating the current reference value and according to the current reference value , the dq components of the three-phase output current of the chain STATCOM and , and the dq components of the three-phase output voltage of the chain STATCOM . The AC terminal angular frequency ω of the cascaded STATCOM converter, the inductance value L of the filter reactor, and the output voltage command. , , Finally, the chain-type STATCOM control system responds to the voltage command. , The phase information θ is used to generate three-phase voltage commands through coordinate transformation (such as inverse Park transformation + inverse Clarke transformation), and finally generate switching signals that act on each H-bridge module of the chained STATCOM.

[0031] This invention simulates the operating characteristics of a synchronous condenser and uses the DC capacitor voltage of each unit of a chain-type STATCOM to simulate the rotor inertia of a synchronous generator, establishing a matching relationship between the DC voltage and the angular frequency of the AC terminal of the converter, thus realizing the grid-connected operation of the chain-type STATCOM. As a grid-connected chain-type STATCOM, it can actively set the frequency and voltage of the AC port, providing voltage and frequency support to the power grid, instead of passively following the grid.

[0032] The feasibility and effectiveness of the governance system provided by this invention will be analyzed below through theoretical derivation and experimental simulation.

[0033] 1. Damping characteristics analysis of a network-type chain STATCOM The equivalent circuit of the H-bridge cascade module of a chained STATCOM is as follows: Figure 2 The system output is equivalent to an AC voltage source, with R connected in series with it. S The losses are related to current, such as the conduction losses of components; the resistor R connected in parallel with the DC capacitor C represents the losses affected by the DC side voltage, such as the capacitor's own losses; the controlled current source connected in parallel with the DC capacitor C represents the losses that are affected by both the DC side voltage and the device current, such as switching losses.

[0034] The corresponding output voltage of the chain-type STATCOM for: (6) Where N is the number of chain units and M is the modulation ratio.

[0035] Neglecting resistance, the current flowing into the system from the chained STATCOM in the αβ stationary coordinate system can be expressed as: (7) The electromagnetic power of the generator is: (8) in and Let dq be the component of the magnetic flux linkage.

[0036] Ignoring changes in the main flux linkage, we obtain the linearized electromagnetic power expression for the generator when the chained STATCOM exists: (9) Rearrange equation (9) as follows In the form of. Among them This reflects the system's response characteristics to changes in angular velocity. Damping coefficient. The larger the value, the stronger the damping effect of the system on changes in angular velocity.

[0037] (10) Equation (10) is the damping model of the chain STATCOM. It can be seen that the chain STATCOM can provide electrical damping to the system.

[0038] 2. Stability Analysis of Networked Chain-Type STATCOM By linearizing the system output equation, the small-signal model and the characteristic equation of the system are obtained. The stability of the network-type chain STATCOM is then analyzed by solving the characteristic equation.

[0039] Based on the preceding text, the state equations and modulation voltage equations of the network-type chained STATCOM system are as follows: (11) The chained STATCOM only performs reactive power compensation, therefore its d-axis voltage ( Since the current is 0, it is not considered. The inner current loop can be approximated as a proportional element, and the system output equation can be obtained: (12) in This is the modulation voltage output by the chained STATCOM.

[0040] (13) After linearizing the system model, a small-signal model is obtained: (14) Due to ΔQ g It satisfies the following relationship with Δθ: (15) According to equation (13): (16) Substituting equations (15) and (16) into equation (14) yields the characteristic equation of the system: As can be seen from the above equation, the system's characteristic equation is a second-order equation, and the real parts of the system's characteristic roots are negative, meaning the system remains stable. Furthermore, it can be known that... This will affect system stability. For different damping coefficients... Solving the characteristic equation yields the characteristic root locus diagram, as shown below. Figure 3 As shown, other coefficients in the equation are listed in the table below. The eigenvalue distribution is symmetric about the real axis; therefore, the eigenvalue locus only shows the portion where the imaginary part is greater than 0. From the eigenvalue locus, it can be seen that when... As the value increases, the negative real part of the characteristic root is further away from the imaginary axis, which means the system stability is enhanced.

[0041] To verify the proposed control strategy, based on Figure 1 The simulation model was built using MATLAB / Simulink, and the parameters are shown in the table above. Two fault conditions were set for the simulation: (1) the voltage amplitude of phase C of the power grid drops by 30% for 0.2s; (2) the frequency of the three-phase voltage of the power grid drops to 49.8Hz for 0.2s. The two fault conditions are as follows: Figure 4 As shown.

[0042] 3. Verification of the effectiveness of network control in a network-structured chain-type STATCOM system Under this control strategy, when the amplitude of phase C voltage and the frequency of the three-phase voltage drop, the simulation yields the waveforms of phase angle and frequency changes at the AC terminal of the converter, as follows: Figure 5 and Figure 6 As shown in the figure. The simulation results show that when the system frequency or voltage changes, the phase angle of the AC terminal of the converter is not affected and changes periodically between 0 and 2π. Moreover, after the initial oscillation, the AC terminal frequency of the converter quickly stabilizes at the rated frequency of 50Hz, which reflects the voltage source nature of the grid-type STATCOM and verifies the effectiveness of the grid control.

[0043] 4. Verification of voltage damping properties of a network-type chain-type STATCOM system Under this control strategy, when the amplitude of phase C voltage and the frequency of the three-phase voltage drop, the simulated voltage waveform at the point of common junction is as follows: Figure 7 As shown, when the voltage drops, the point of common access voltage decreases rapidly, but under the action of the grid-type STATCOM, the voltage quickly stabilizes. When the frequency drops, the point of common access voltage gradually increases and becomes unstable, but under the action of the grid-type chain STATCOM, the voltage quickly stabilizes. This indicates that the grid-type chain STATCOM scheme based on virtual phase modulation control can effectively dampen voltage oscillations and manage voltage fluctuations in the distribution area.

[0044] 5. Verification of DC voltage equalization effect of network-type chain STATCOM system Under this control strategy, when the amplitude of the C-phase voltage and the frequency of the three-phase voltage drop, the simulation yields the average DC voltage waveform of the chain-type STATCOM as follows: Figure 8 As shown, when the amplitude of phase C voltage and the frequency of the three-phase voltage drop, the DC voltage stabilizes at 120V after a brief oscillation. This result verifies the effectiveness of the control strategy for DC voltage equalization and also demonstrates the effectiveness of the matching control.

[0045] This invention proposes an autonomous and flexible voltage management system for distribution transformer areas based on virtual phase modulation control. This system simulates the operating characteristics of a synchronous condenser and utilizes the DC capacitor voltages of each unit of a chain-type STATCOM to simulate the rotor inertia of a synchronous generator, injecting positive damping into the system to improve system stability, thereby achieving autonomous and flexible voltage management of distribution transformer areas. Theoretical analysis and simulation verification yield the following conclusions: By using the DC capacitor of the converter to simulate the rotor inertia of the synchronous condenser and incorporating the DC voltage fluctuation into the reactive current reference value generation process, the network operation of a chain-type STATCOM can be realized.

[0046] Damping control can enhance the system's inertia, injecting positive damping into the system, and the damping coefficient D p The larger the value, the stronger the system stability.

[0047] Simulation results show that the present invention can effectively suppress system voltage oscillations, maintain system frequency stability, and improve system dynamic stability.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A transformer area voltage autonomous flexible management system based on virtual phase modulation control, characterized in that, The static synchronous compensator comprises a cascade H-bridge chain; a control system of the static synchronous compensator comprises a reactive voltage outer loop control unit, a reactive current inner loop control unit and a virtual phase modulation control module; The virtual phase modulation control module is used for obtaining phase information of a direct current voltage according to an average direct current voltage of an H-bridge module of the static synchronous compensator, a direct current voltage set value and a power grid fundamental frequency; The reactive voltage outer loop control unit is used for obtaining a reactive voltage reference value according to the average direct current voltage of the H-bridge module of the static synchronous compensator, a reactive voltage rated value, a reference value and an actual value of reactive power; The reactive current inner loop control unit is used for generating a voltage instruction according to the reactive voltage reference value, dq components of output voltage and current of the static synchronous compensator, an alternating current end angular frequency of a converter, and an inductance value of a connected filter reactor; The control system of the static synchronous compensator generates a switching signal of each H-bridge module according to the voltage instruction and the phase information.

2. The virtual regulation control based autonomous flexible governance system for transformer area voltage according to claim 1, characterized in that, The reactive voltage outer loop control unit comprises a damping control module and a reactive power control module, and the reactive current inner loop control unit comprises a virtual impedance control module and a current decoupling control module; The damping control module is used for generating a damping term according to a direct current voltage of the static synchronous compensator and outputting to the reactive power control module; the reactive power control module is used for generating the reactive voltage reference value in combination with the damping term and outputting to the virtual impedance control module; The virtual impedance control module is used for generating a current reference value in combination with the reactive voltage reference value and outputting to the current decoupling control module, and the current decoupling control module is used for generating the voltage instruction in combination with the current reference value.

3. The virtual phase modulation control based autonomous flexible governance system for transformer area voltage according to claim 1, characterized in that, The algorithm formula of the virtual phase modulation control module is Wherein θ is the phase information, , and are the average DC voltage, DC voltage set value and grid fundamental frequency of the H-bridge module of the static synchronous compensator, respectively.

4. The virtual phase modulation control based autonomous flexible governance system for transformer area voltage according to claim 2, characterized in that, The damping control module is used for averaging the H-bridge module direct current voltage of the static synchronous compensator through a low-pass filter with a time constant T and a differential element, multiplied by a damping factor , obtaining the damping term ζ, , s is the Laplace operator.

5. The virtual phase modulation control based autonomous flexible governance system for transformer area voltage of claim 2, wherein, The algorithm formula of the reactive power control module is , is the reactive voltage reference value, and ζ is the damping term, , and are respectively a reactive voltage rated value, a reference value and an actual value of the reactive power of the static synchronous compensator, and are respectively a proportional parameter and an integral parameter of the PI controller in the reactive power control module, and s is a Laplace operator.

6. The virtual phase modulation control based autonomous flexible governance system for transformer area voltage of claim 2, wherein, The virtual impedance control module obtains the current reference value by solving state equations obtaining the current reference value and wherein is the reactive voltage reference value, is the active voltage reference value, the value being 0, and are the dq components of the output voltage of the static synchronous compensator, respectively, , and are the grid fundamental frequency, the virtual inductance and the virtual resistance, respectively.

7. The virtual phase modulation control based autonomous flexible governance system for transformer area voltage according to claim 2, characterized in that, The algorithm formula of the current decoupling control module is wherein and is the voltage instruction, , , and are respectively the dq components of the output voltage and current of the static synchronous compensator, and are the current reference values, ω and L are respectively the angular frequency of the converter AC terminal of the static synchronous compensator and the inductance value of the connected filter reactor, and are respectively the proportional and integral parameters of the PI controller in the current decoupling control module.

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