An adaptive virtual inertia control system and method for upqc

Abstract

The application discloses a kind of adaptive virtual inertia control system and method for UPQC, it is related to power distribution network technical field, frequency voltage droop unit is used to exert active droop frequency control and reactive droop voltage control to adaptive virtual synchronous machine;Adaptive virtual inertia calculation unit is used to determine the small disturbance corresponding to actual active power, the small disturbance corresponding to actual reactive power and the small disturbance corresponding to actual frequency of adaptive virtual synchronous machine output based on virtual synchronous machine algorithm, active droop frequency control and reactive droop voltage control, and determine the adaptive adjustment model of virtual inertia based on the small disturbance corresponding to actual active power, the small disturbance corresponding to actual reactive power and the small disturbance corresponding to actual frequency.This application effectively solves the power fluctuation and overcurrent problem of traditional VSG control in transient process, has better dynamic response, improves the stability of independent microgrid frequency and voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, and can also be used in the technical field of virtual synchronous generator control, and particularly relates to an adaptive virtual inertia control system and method for UPQC. BACKGROUND

[0002] With the increasing proportion of distributed new energy in power grid generation, the virtual synchronous generator technology (VSG) capable of realizing "friendly" grid connection and droop inertia control of wind and light distributed new energy will be an inevitable development trend of future distributed new energy grid connection, and therefore has become one of the research hotspots of high-proportion distributed new energy grid connection. At the same time, as the most excellent representative in the field of flexible AC power transmission, the unified power quality conditioner (UPQC) can adjust line flow, voltage support and system damping, and improve steady-state and transient stability by controlling multiple electrical parameters such as voltage amplitude and phase.

[0003] At present, the control strategy research on VSG mainly aims at the operating conditions of a single converter, but if the VSG algorithm is introduced into UPQC, more attention needs to be paid to the coordinated operation control problem of the series and parallel converters in UPQC, and the research on this aspect is still in the blank.

[0004] This section aims to provide background or context for the embodiments of the application stated in the claims. The description herein does not admit to be prior art because it is included in this section. SUMMARY

[0005] To solve at least one technical problem mentioned in the background section, the present application provides an adaptive virtual inertia control system and method for UPQC, which makes the new energy power generation device have the frequency and voltage support capability of traditional synchronous generators without changing the original control of the new energy power generation device.

[0006] In a first aspect, an adaptive virtual inertia control system for UPQC is provided, the UPQC comprising a series voltage source converter and a parallel voltage source converter, and the adaptive virtual inertia control system comprising a frequency and voltage droop unit, an adaptive virtual synchronous machine and an adaptive virtual inertia calculation unit, wherein:

[0007] The frequency and voltage droop unit is configured to apply active droop frequency control and reactive droop voltage control to the adaptive virtual synchronous machine.

[0008] The adaptive virtual inertia calculation unit is configured to determine actual active power corresponding small disturbance quantity, actual reactive power corresponding small disturbance quantity, and actual frequency corresponding small disturbance quantity of the adaptive virtual synchronous machine output based on a virtual synchronous machine algorithm corresponding to the adaptive virtual synchronous machine, the active power droop frequency control, and the reactive power droop voltage control, and determine an adaptive adjustment model of virtual inertia based on the actual active power corresponding small disturbance quantity, the actual reactive power corresponding small disturbance quantity, and the actual frequency corresponding small disturbance quantity, wherein the adaptive adjustment model of virtual inertia is as follows:

[0009]

[0010]

[0011] wherein, is a steady-state virtual inertia; is an active power adaptive virtual inertia; is a reactive power adaptive virtual inertia; is the actual active power corresponding small disturbance quantity; is the actual frequency corresponding small disturbance quantity; is a maximum deviation value of the actual frequency and a rated frequency; is the actual reactive power corresponding small disturbance quantity; is a terminal rated voltage of the adaptive virtual synchronous machine; is a maximum deviation value of the terminal actual voltage and the terminal rated voltage.

[0012] In some optional manners of the embodiment, the frequency and voltage droop unit comprises a frequency droop sub-unit and a voltage droop sub-unit, wherein:

[0013] The frequency droop sub-unit is configured to apply the active power droop frequency control on the adaptive virtual synchronous machine based on a grid reference frequency, an actual frequency of a port of the parallel voltage source type converter, an active power-frequency characteristic coefficient, an active power reference value of the parallel voltage source type converter output, and active power transmitted by the UPQC through the parallel voltage source type converter.

[0014] The voltage droop sub-unit is configured to apply the reactive power droop voltage control on the adaptive virtual synchronous machine based on a rated voltage amplitude of a grid, a voltage amplitude of a port of the parallel voltage source type converter, a reactive power-voltage amplitude characteristic coefficient, a reactive power reference value of the parallel voltage source type converter output, and reactive power transmitted by the UPQC through the parallel voltage source type converter.

[0015] In some alternative manners of the embodiment, the virtual synchronous machine algorithm adopts a second-order model of a synchronous generator to establish a mathematical model for simulating motion characteristics of a rotor, and an expression corresponding to the virtual synchronous machine algorithm is as follows:

[0016]

[0017] wherein, is a virtual inertia of the rotor; , are an actual frequency and a rated frequency of the adaptive virtual synchronous machine, respectively; is a deviation value of the actual frequency and the rated frequency of the adaptive virtual synchronous machine; , are an actual output torque and a torque given value of the adaptive virtual synchronous machine, respectively; is an active damping coefficient; , are an actual active power and an active power given value output by the adaptive virtual synchronous machine, respectively; represents an angle of power.

[0018] In some alternative manners of the embodiment, the adaptive virtual inertia calculation unit is further configured to:

[0019] determine an expression of a virtual electromotive force output by the adaptive virtual synchronous machine based on the voltage control of the reactive droop;

[0020] determine a steady-state equation of the adaptive virtual synchronous machine based on the frequency control of the active droop, the expression of the virtual synchronous machine algorithm, the expression of the virtual electromotive force, the expression of the actual active power output by the adaptive virtual synchronous machine, and the expression of the actual reactive power;

[0021] superimpose a disturbance on the steady-state equation, perform disturbance separation and linearization, and then perform Laplace transform to determine a small-signal model corresponding to the adaptive virtual synchronous machine, wherein an expression of the small-signal model includes a small disturbance function corresponding to the actual active power output by the adaptive virtual synchronous machine, a small disturbance function corresponding to the actual reactive power, a small disturbance function corresponding to the actual frequency, and a small disturbance function corresponding to the virtual electromotive force.

[0022] In some alternative manners of the embodiment, the expression of the virtual electromotive force is as follows:

[0023]

[0024] wherein, is a virtual electromotive force of the adaptive virtual synchronous machine; a no-load electromotive force of the adaptive virtual synchronous machine; a reactive voltage droop adjustment part of the virtual electromotive force; a terminal voltage deviation of the adaptive virtual synchronous machine; a reactive damping coefficient; 、 respectively, an actual reactive power and a reactive power given value output by the adaptive virtual synchronous machine; a voltage excitation adjustment coefficient; an actual terminal voltage of the adaptive virtual synchronous machine.

[0025] In some optional modes of the embodiment, the expression of the steady-state equation of the adaptive virtual synchronous machine is as follows:

[0026]

[0027] wherein, a port voltage of the adaptive virtual synchronous machine; a synchronous reactance of the adaptive virtual synchronous machine.

[0028] In some optional modes of the embodiment, the expression of the small-signal model is as follows:

[0029]

[0030] wherein, respectively, a small disturbance quantity function corresponding to an actual active power output by the adaptive virtual synchronous machine, a small disturbance quantity function corresponding to an actual reactive power, a small disturbance quantity function corresponding to an actual frequency, a small disturbance quantity function corresponding to a virtual electromotive force, and a small disturbance quantity function corresponding to a power angle; 、 respectively, an active given control quantity and a reactive given control quantity of the adaptive virtual synchronous machine; a complex variable.

[0031] In some optional modes of the embodiment, the adaptive virtual synchronous machine is connected with a control port of the parallel voltage source type converter, and is configured to determine a voltage reference value and a phase angle reference value of the parallel voltage source type converter based on the frequency voltage droop unit and the adaptive virtual inertia calculation unit, wherein the parallel voltage source type converter is configured in a virtual synchronous generator control mode.

[0032] The adaptive virtual inertia control system further comprises an SVPWM modulation unit configured to determine a pulse control signal of the parallel voltage source type converter based on the voltage reference value and the phase angle reference value.

[0033] In some optional aspects of this embodiment, the UPQC further includes a bidirectional DC / DC converter and a battery energy storage device, wherein the battery energy storage device is connected in parallel with a DC capacitor of a common DC bus through the bidirectional DC / DC converter;

[0034] When the AC side frequency of the UPQC drops, the adaptive virtual synchronous machine extracts energy from the DC capacitor to provide inertia response, causing the voltage of the common DC bus to drop instantaneously. The bidirectional DC / DC converter adjusts the inductor current in real time through the voltage outer loop to control the charge and discharge power of the battery energy storage device, thereby providing voltage support for the DC capacitor.

[0035] The adaptive virtual inertia calculation unit is further configured to:

[0036] Based on the maximum current ramp rate of the ramp limiter in the battery energy storage device, the power synchronization coefficient, and the rated frequency of the adaptive virtual synchronous machine, a frequency step amplitude boundary required to trigger the ramp limiter is determined, wherein the frequency step amplitude boundary is expressed as follows:

[0037]

[0038] Based on the frequency step amplitude boundary, it is determined that the active adaptive virtual inertia satisfies the following constraints:

[0039]

[0040] Where, is the frequency step amplitude boundary; is the maximum current ramp rate; is the power synchronization coefficient; is the rated frequency of the adaptive virtual synchronous machine.

[0041] In a second aspect, an embodiment of the present application provides an adaptive virtual inertia control method for UPQC, comprising:

[0042] Constructing a UPQC system and a control model of an adaptive virtual synchronous machine in the UPQC system, wherein the UPQC system includes a series voltage source converter and a shunt voltage source converter, the adaptive virtual synchronous machine is connected to a port of the shunt voltage source converter, and is configured to configure the shunt voltage source converter to a virtual synchronous generator control mode;

[0043] Applying frequency control of active power droop and voltage control of reactive power droop to the adaptive virtual synchronous machine;

[0044] determine a small disturbance quantity corresponding to actual active power output by the adaptive virtual synchronous machine, a small disturbance quantity corresponding to actual reactive power, and a small disturbance quantity corresponding to actual frequency based on the frequency control of the active droop and the voltage control of the reactive droop, and determine that an adaptive adjustment model of virtual inertia satisfies the following equation based on the small disturbance quantity corresponding to actual active power, the small disturbance quantity corresponding to actual reactive power, and the small disturbance quantity corresponding to actual frequency:

[0045]

[0046]

[0047] wherein, is a steady-state virtual inertia; is an active adaptive virtual inertia; is a reactive adaptive virtual inertia; is the small disturbance quantity corresponding to actual active power; is the small disturbance quantity corresponding to actual frequency; is a maximum deviation value of the actual frequency from a rated frequency; is the small disturbance quantity corresponding to actual reactive power; is a terminal rated voltage of the adaptive virtual synchronous machine; is a maximum deviation value of the terminal actual voltage from the terminal rated voltage.

[0048] The adaptive virtual inertia control system and method for UPQC provided by the embodiments of the present application can increase the rotational inertia under the same conditions through adaptive control, effectively solve the power fluctuation and overcurrent problem of the traditional VSG control in the transient process, have better dynamic response, improve the stability of the independent microgrid frequency and voltage, and make the new energy power generation device have the frequency and voltage support capability of the traditional synchronous generator without changing the original control of the new energy power generation device. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. In the drawings:

[0050] Figure 1 is a structural schematic diagram of the adaptive virtual inertia control system for UPQC in the embodiments of the present application;

[0051] Figure 2Schematic diagram of the structure of a UPQC with energy storage capability in an embodiment of the present invention;

[0052] Figure 3 A simplified schematic diagram of a UPQC-BESS power transmission system according to an embodiment of the present invention;

[0053] Figure 4 This is a schematic diagram of the harmonic voltage detection principle in an embodiment of the present invention;

[0054] Figure 5 SEC active filter control block diagram in an embodiment of the present invention;

[0055] Figure 6 This is a block diagram of a virtual synchronous generator control system applicable to UPQC in an embodiment of the present invention;

[0056] Figure 7 4 is a flow chart of an adaptive virtual inertia control method for UPQC in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0058] Virtual synchronous generators can be divided into two types: power station type and unit type. The power station type refers to connecting to the power system at the power station grid connection point, simulating the synchronous external characteristics of the entire power station. Currently, it only refers to energy storage virtual synchronous machines; the unit type is mainly used for distributed energy such as photovoltaics and wind turbines to connect to the power grid. In recent years, research has focused on the field of distributed and unitized virtual synchronous generators, and few scholars have studied the power station type.

[0059] For wind turbines, leveraging rotor kinetic energy or reserving spare capacity can achieve system inertial stability. However, the former relies on rotor kinetic energy and can only increase active power output for a limited time, while the latter can result in significant power generation losses, resulting in poor economic efficiency and failing to meet current grid requirements for fully accommodating distributed renewable energy while ensuring power supply security. Currently, the most common virtual synchronous machine algorithms for photovoltaic and wind turbines mostly add energy storage (electrochemical energy storage or supercapacitors) to the DC bus between their converters to provide inertial support for the power system, adjust the voltage amplitude and frequency at the grid connection point, and achieve virtual synchronous control of individual distributed renewable energy units. However, upgrading the "unit-based virtual synchronous machine" algorithm for current wind turbines or photovoltaic power plants according to the proposed solution requires shutting down each individual generating unit and adding energy storage units on a "one-by-one" basis. This modification is cumbersome and costly. Therefore, a "station-based virtual synchronous machine" solution for large-scale wind and photovoltaic power plants is urgently needed to achieve "friendly" grid connection of distributed renewable energy.

[0060] It is recommended to add energy storage devices, primarily batteries, to the UPQC's common DC bus. This would achieve a wider range of transmission capacity and network control capabilities at a relatively low cost, increasing the UPQC's appeal to power companies, transmission companies, and distributed renewable energy operators. Furthermore, by fully leveraging the controllable and adjustable voltage amplitude and phase of the UPQC's series and parallel outputs, and upgrading the virtual synchronous generator algorithm on a traditional UPQC, the drawbacks of unit-type virtual synchronous generator retrofits could be avoided, further reducing the cost of distributed renewable energy retrofits. Furthermore, due to the UPQC's isolation, the voltage at the distributed renewable energy access point remains relatively stable, reducing the requirements for grid adaptability and fault ride-through capability.

[0061] Based on this, an embodiment of the present invention provides an adaptive virtual inertia control method for UPQC, including:

[0062] Constructing a UPQC system and a control model of an adaptive virtual synchronous machine in the UPQC system, wherein the UPQC system includes a series voltage source converter, a parallel voltage source converter, and an adaptive virtual inertia control system, wherein the adaptive virtual synchronous machine is connected to a port of the parallel voltage source converter to configure the parallel voltage source converter in a virtual synchronous generator control mode;

[0063] Among them, such as Figure 1 As shown, the adaptive virtual inertia control system includes: a frequency and voltage droop unit, an adaptive virtual synchronous machine and an adaptive virtual inertia calculation unit, wherein:

[0064] The frequency and voltage droop unit is used to apply frequency control of active power droop and voltage control of reactive power droop to the adaptive virtual synchronous machine;

[0065] The adaptive virtual inertia calculation unit is used to determine a small disturbance amount corresponding to the actual active power output by the adaptive virtual synchronous machine, a small disturbance amount corresponding to the actual reactive power, and a small disturbance amount corresponding to the actual frequency based on a virtual synchronous machine algorithm corresponding to the adaptive virtual synchronous machine, the frequency control of the active power droop, and the voltage control of the reactive power droop, and based on the small disturbance amount corresponding to the actual active power, the small disturbance amount corresponding to the actual reactive power, and the small disturbance amount corresponding to the actual frequency, determine that an adaptive adjustment model of the virtual inertia satisfies the following equation:

[0066]

[0067]

[0068] Where, is the steady-state virtual inertia; It is the active adaptive virtual inertia; is the reactive adaptive virtual inertia; is the small disturbance corresponding to the actual active power; is the small disturbance amount corresponding to the actual frequency; is the maximum deviation between the actual frequency and the rated frequency; is the small disturbance corresponding to the actual reactive power; is the rated voltage of the machine end of the adaptive virtual synchronous machine; It is the maximum deviation between the actual voltage at the machine end and the rated voltage at the machine end.

[0069] It should be noted that the operating architecture of the UPQC system equipped with energy storage function is as follows Figure 2The UPQC system is composed of three core components: series converter (SEC), shunt converter (SHC) and battery energy storage system (BESS) integrated in the common DC bus. Specifically, the SEC is connected in series between M1 and M2 nodes through a transformer, and the SHC is directly connected in parallel to the M2 node. The energy storage system is connected in parallel to the support capacitor of the common DC bus through a bidirectional DC / DC converter, and its core functions include maintaining the stability of the bus voltage and realizing the charge and discharge control of the energy storage device. This topology structure not only ensures the power quality regulation capability, but also realizes the dynamic energy balance management.

[0070] After detecting and extracting the harmonic voltage of node M1, the UPQC can generate a harmonic voltage with the same size and opposite direction as the SEC to offset the harmonic voltage generated by the harmonic source, ensuring the voltage quality of the power grid. The SHC is controlled as a sinusoidal voltage source, so that the output voltage of the distributed new energy is a standard sinusoidal value. Since the voltage source has a small impedance to harmonic current, the grid harmonic current flows into the parallel converter, thereby achieving the purpose of canceling the harmonic current and making the current flowing to the grid close to sinusoidal. The voltage amplitude, phase and frequency at the parallel connection of UPQC can be used as controllable electrical quantities to control the coordination of UPQC and distributed new energy, simulate the dynamic response ability of traditional synchronous generators to grid voltage and frequency, and provide a research approach for station-type virtual synchronous generators. It does not need to stop and modify the existing wind turbine, and can independently maintain the stability and power quality of the power grid.

[0071] Considering the harmonic suppression effect of system filter devices, the simplified model of UPQC-BESS power transmission system under the power frequency component of AC voltage and current is as shown in Figure 3 . represents the line impedance between the output end of the series side of UPQC and the distribution network; represents the line impedance between its parallel output end and the distributed new energy plant and the equivalent output impedance of its grid-connected inverter. 、 respectively represent the voltage amplitudes of the distribution network and the distributed new energy; 、 respectively represent the voltage phases thereof; 、 , 、 respectively represent the voltage amplitudes and phases of nodes M1 and M2; , , 、 Represent the output voltage amplitude and phase of SEC and SHC respectively; Indicates the equivalent impedance of the UPQC series part, including the equivalent impedance of the series transformer , the line impedance between the UPQC series and parallel ports And the output impedance of SEC ; The equivalent impedance of the UPQC parallel part is represented by the output impedance of the SHC. For the Lord; Represents the apparent power transmitted to the distribution network; Represents the output apparent power of distributed renewable energy; 、 Represent the output apparent power of SEC and SHC respectively. Output power S from node M2 ​​through the main feeder line M2 There are two destinations: one is the power exchanged with the UPQC series part , and the other part is transmitted to the distribution network through transmission lines , including impedance losses on long transmission lines .like Figure 3 As shown, the UPQC series unit can be equivalent to a controllable voltage source and a dynamic output impedance in the steady state. An equivalent model of the voltage source, in which the amplitude-phase parameters of the voltage source are all controlled by the control.

[0072] Once the DC bus voltage is stabilized, the DC / DC converter and battery can be used as ideal energy storage sources to balance power differentials. Therefore, the DC / DC component is not further analyzed, and only its basic power model is presented. The bidirectional DC / DC power converter, SEC, and SHC in the battery energy storage system are electrically coupled via a shared DC bus. This architecture not only fulfills the core function of maintaining DC-side voltage stability for the UPQC but also provides the necessary real-time active power compensation for the two parallel-connected converter units. This energy interaction hub structure achieves dynamic power balancing within the system through a coordinated control strategy.

[0073] It should also be noted that in this application, when the series active filter is working, it is first necessary to accurately detect the harmonic voltage to be compensated, and then, by controlling the SEC, generate a compensation signal of equal magnitude and opposite direction to the harmonic voltage to offset the harmonic voltage, so that the harmonics in the network are finally compensated and the voltage and current waveforms are close to sine waves.

[0074] This device detects the three-phase grid voltage and obtains the grid voltage phase angle through phase-locked loop control. The transformation is converted into a direct current, the harmonics are filtered out after passing through a low-pass filter, the fundamental component is obtained, and then the three-phase fundamental voltage is restored after the coordinate inverse transformation. The fundamental principle is shown in Figure 4 .

[0075] The capacitor voltage and the filtered inductor current output by the SEC are taken as feedback quantities. The voltage outer loop adopts a proportional link to track the harmonic voltage, and the inner loop adopts a proportional link to improve the dynamic response of the active filter system. The control block diagram of the SEC active filter is shown in Figure 5 . The voltage outer loop gain, the current inner loop gain, and the PWM gain are represented by Kp, KI, and Kpwm, respectively.

[0076] In some embodiments of the present embodiment, the frequency and voltage droop unit comprises a frequency droop sub-unit and a voltage droop sub-unit, wherein:

[0077] The frequency droop sub-unit is configured to apply the active droop frequency control to a virtual synchronous generator (i.e., an adaptive virtual synchronous machine) based on a grid reference frequency, an actual frequency of a port of the parallel voltage source type converter, an active power-frequency characteristic coefficient, an active power reference value output by the parallel voltage source type converter, and an active power transmitted by the UPQC through the parallel voltage source type converter.

[0078] The voltage droop sub-unit is configured to apply the reactive droop voltage control to the virtual synchronous generator (i.e., the adaptive virtual synchronous machine) based on a rated voltage amplitude of the grid, a voltage amplitude of the port of the parallel voltage source type converter, a reactive power-voltage amplitude characteristic coefficient, a reactive power reference value output by the parallel voltage source type converter, and a reactive power transmitted by the UPQC through the parallel voltage source type converter.

[0079] Specifically, a control model of the VSG is constructed in the UPQC, and the mechanical-electrical coupling dynamic characteristics of the synchronous generator are accurately reproduced at the grid interface end. In the UPQC architecture integrated with the energy storage configuration, the parallel compensation port needs to face the distributed new energy grid connection point to build an alternating voltage stability support. In view of this topology constraint, the SHC should be configured in the virtual synchronous generator control mode, and the control block diagram of the virtual synchronous generator suitable for the UPQC is shown in Figure 6 .

[0080] Figure 6 , , represent the active and reactive power reference values output by the SHC, respectively. , ​​P and Q represent the active power and the reactive power transmitted by the SHC, respectively; 、 ωgrid and ωSHC represent the grid reference frequency and the actual frequency of the SHC port, respectively; 、 Ugrid and USHC represent the rated voltage amplitude of the grid and the voltage amplitude of the parallel port, respectively; Kp is the active-power-frequency characteristic coefficient, Kq is the reactive-power-voltage amplitude characteristic coefficient; 、 ωgrid and USHC represent the grid voltage angular frequency and the output voltage amplitude of the parallel converter, respectively; Kp is the active-power-damping coefficient; 、 θ and USHC represent the phase obtained by the virtual synchronous machine algorithm and the voltage amplitude instruction of the SHC, respectively; Kp is the integral element.

[0081] In some embodiments of the present embodiment, the virtual synchronous machine algorithm adopts a 2nd order model of a conventional synchronous generator, and the virtual synchronous machine algorithm corresponding to the virtual synchronous machine satisfies the following formula to simulate the motion characteristics of the rotor:

[0082]

[0083] In the formula, J is the virtual inertia of the rotor; ωgrid and ωSHC represent the grid voltage angular frequency and the output voltage amplitude of the parallel converter, respectively; 、 ωgrid and ωSHC represent the grid voltage angular frequency and the output voltage amplitude of the parallel converter, respectively; ωgrid and ωSHC represent the grid voltage angular frequency and the output voltage amplitude of the parallel converter, respectively; 、 ωgrid and ωSHC represent the grid voltage angular frequency and the output voltage amplitude of the parallel converter, respectively; Kp is the active-power-damping coefficient; P and P set ωgrid and ωSHC represent the grid voltage angular frequency and the output voltage amplitude of the parallel converter, respectively; θ represents the power angle.

[0084] It should be noted that, in the present application, the active-power-given value of the adaptive virtual synchronous machine P is the active-power reference value of the SHC output ; the reactive-power-given value of the adaptive virtual synchronous machine Q is the reactive-power reference value of the SHC output ; the actual active power P output by the adaptive virtual synchronous machine is the active power transmitted by the SHC ; and the actual reactive power Q output by the adaptive virtual synchronous machine is the reactive power transmitted by the SHC .

[0085] In some embodiments of the present embodiment, the adaptive virtual inertia calculation unit is further configured to:

[0086] determine an expression of a virtual electromotive force of the adaptive virtual synchronous machine output based on the reactive voltage droop control;

[0087] determine a steady-state equation of the adaptive virtual synchronous machine based on the expression of the virtual synchronous machine algorithm, the expression of the virtual electromotive force, the expression of the actual active power and the expression of the actual reactive power of the adaptive virtual synchronous machine output based on the active frequency droop control;

[0088] superimpose a disturbance on the steady-state equation, perform disturbance separation and linearization, and then perform Laplace transform to determine a small-signal model corresponding to the adaptive virtual synchronous machine, wherein an expression of the small-signal model includes a small-disturbance function corresponding to the actual active power, a small-disturbance function corresponding to the actual reactive power, a small-disturbance function corresponding to the actual frequency, and a small-disturbance function corresponding to the virtual electromotive force of the adaptive virtual synchronous machine output.

[0089] Specifically, the virtual electromotive force of the VSG output is adjusted through the reactive voltage droop relationship wherein the virtual electromotive force satisfies the following formula:

[0090]

[0091] wherein, is the virtual electromotive force of the adaptive virtual synchronous machine; is the no-load electromotive force of the adaptive virtual synchronous machine; is the reactive voltage droop adjustment part of the virtual electromotive force; is a terminal voltage deviation of the adaptive virtual synchronous machine; is a reactive damping coefficient; , are the actual reactive power and the given value of the reactive power of the adaptive virtual synchronous machine output, respectively; is a voltage excitation adjustment coefficient; is an actual terminal voltage of the adaptive virtual synchronous machine.

[0092] Further, in combination with the expressions of the active power and the reactive power of the terminal output of the hidden pole generator, the steady-state equation of the VSG is determined as follows:

[0093]

[0094] wherein, a port voltage of the adaptive virtual synchronous machine; a synchronous reactance of the adaptive virtual synchronous machine.

[0095] Further, superimposing a disturbance on the steady-state equation, performing disturbance separation and linearization, and performing Laplace transform, and from the power angle characteristics of the synchronous machine, is very small in normal operation, so the following approximate relationship can be obtained: , , Meanwhile, from the small signal assumption, Thus, the small signal model of the system in which active power and reactive power are relatively independent can be obtained from the small signal assumption:

[0096]

[0097] In the formula, are respectively a small disturbance quantity function corresponding to the actual active power output by the adaptive virtual synchronous machine, a small disturbance quantity function corresponding to the actual reactive power, a small disturbance quantity function corresponding to the actual frequency, a small disturbance quantity function corresponding to the virtual electromotive force, and a small disturbance quantity function corresponding to the power angle; , are respectively the active power given control quantity and the reactive power given control quantity of the adaptive virtual synchronous machine; is a complex variable.

[0098] The overshoot and oscillation of the system are weakened through automatic adjustment of the moment of inertia. When the grid fluctuation is too large, the moment of inertia is adjusted to increase the damping ratio of the system, reduce the overshoot of power, and shorten the oscillation period, so that the frequency of the VSG system is always within the allowed range, wherein, when the grid fluctuation is too large, , the moment of inertia is adjusted to increase the damping ratio of the system, reduce the overshoot of power, and shorten the oscillation period, so that the frequency of the VSG system is always within the allowed range, wherein, when the grid fluctuation is too large, does not exceed the threshold , and when the grid fluctuation is too large, , the moment of inertia is adjusted to increase the damping ratio of the system, reduce the overshoot of power, and shorten the oscillation period, so that the frequency of the VSG system is always within the allowed range, wherein, when the grid fluctuation is too large, does not exceed the threshold , the moment of inertia can be changed, that is, the following equation is satisfied:

[0099]

[0100]

[0101] Further, the adaptive adjustment model of the virtual inertia is determined to satisfy the following equation, that is, the expression of the adaptive virtual inertia is:

[0102]

[0103]

[0104] In the formula, is a steady-state virtual inertia; is an active adaptive virtual inertia; is a reactive adaptive virtual inertia; is a small disturbance quantity corresponding to the actual active power; is a small disturbance quantity corresponding to the actual frequency; is a maximum deviation value of the actual frequency from the rated frequency; is a small disturbance quantity corresponding to the actual reactive power; is a terminal rated voltage of the adaptive virtual synchronous machine; is a maximum deviation value of the terminal actual voltage from the terminal rated voltage.

[0105] In some embodiments of the present embodiment, the adaptive virtual synchronous machine is connected to a control port of the parallel voltage source type converter, and is configured to determine, based on the frequency voltage droop unit and the adaptive virtual inertia calculation unit, a voltage reference value and a phase angle reference value of the parallel voltage source type converter, wherein the parallel voltage source type converter is configured in a virtual synchronous generator control mode.

[0106] The adaptive virtual inertia control system further comprises an SVPWM modulation unit configured to determine, based on the voltage reference value and the phase angle reference value, a pulse control signal for the parallel voltage source type converter.

[0107] The UPQC further comprises a bidirectional DC / DC converter and a battery energy storage device, wherein the battery energy storage device is connected in parallel to a DC capacitor of a common DC bus through the bidirectional DC / DC converter.

[0108] When the AC side frequency of the UPQC drops, the adaptive virtual synchronous machine extracts energy from the DC capacitor to provide inertia response, the voltage of the common DC bus instantaneously drops, the bidirectional DC / DC converter adjusts the inductance current in real time through a voltage outer loop to control the charge and discharge power of the battery energy storage device, thereby achieving voltage support for the DC capacitor.

[0109] The adaptive virtual inertia calculation unit is further configured to:

[0110] determine, based on a maximum current ramp rate of a ramp limiter in the battery energy storage device, a power synchronization coefficient, and a rated frequency of the adaptive virtual synchronous machine, a frequency step amplitude boundary required for triggering the ramp limiter, wherein an expression of the frequency step amplitude boundary is as follows:

[0111]

[0112] Based on the frequency step amplitude boundary, it is determined that the active adaptive virtual inertia meets the following constraints:

[0113]

[0114] In the formula, is the frequency step amplitude boundary; the is the maximum current ramp rate; is the power synchronization coefficient; is the rated frequency of the adaptive virtual synchronous machine.

[0115] Specifically, when the frequency of the AC side of the UPQC system drops, the VSG prioritizes extracting energy from the DC capacitor to provide inertia response, resulting in a transient drop in the DC bus voltage. At this time, the DC / DC converter on the DC side adjusts the inductor current in real time through the voltage outer loop, controls the battery charging and discharging power, and realizes the rapid support of the DC capacitor voltage.

[0116] In some embodiments of the present embodiment, the VSG inertia frequency modulation power requirement meets the following formula:

[0117]

[0118] In the formula, is the VSG inertia frequency modulation power requirement, is the battery charging and discharging power, is the DC capacitor charging and discharging power, is the power transmission loss of the battery and the DC / DC converter;

[0119] In the system dynamic analysis, the charging and discharging current during the battery ramping period can be considered as:

[0120]

[0121] In the formula, is the initial charging and discharging current of the battery, is the maximum current ramp rate of the ramping limiter.

[0122] In some embodiments of the present embodiment, the SOC change of the battery during the ramping period meets the following formula:

[0123]

[0124] In the formula, is the initial value of the SOC, is the rated capacity of the battery, is the battery charging and discharging current;

[0125] The power output of the energy storage system to the front stage of the DC / DC converter during the ramping period meets the following formula:

[0126]

[0127] In the formula, is the DC / DC converter front stage voltage, 0 at the beginning of the battery ramp-up moment, is a certain moment after the ramp-up moment.

[0128] When the charge-discharge rate of the battery is high, the SOC changes significantly during single inertia frequency adjustment, especially at the end of charge-discharge, the battery terminal voltage will fluctuate obviously with the rapid change of SOC. The fluctuation range of the DC bus capacitor voltage is mainly constrained by the rated withstand voltage level of the power electronic device and the modulation ratio of the pulse width modulation strategy. The fluctuation range of the DC side voltage of the inverter is usually controlled within ±15% of the rated voltage, and the boundary of the frequency step amplitude required for triggering the ramp-up limiter is:

[0129]

[0130] Considering the frequency step boundary, the constraint of the active adaptive inertia coefficient is determined as:

[0131]

[0132] In the formula, is the power synchronization coefficient; is the rated frequency of the adaptive virtual synchronous machine.

[0133] The embodiment of the application also provides an adaptive virtual inertia control method for UPQC, as described in the following embodiment. Since the principle of solving the problem of the method is similar to the system, the implementation of the method can be referred to the implementation of the system, and the repeated parts will not be described.

[0134] As Figure 7 shown, the adaptive virtual inertia control method for UPQC comprises:

[0135] Step 10, constructing a UPQC system and a control model of an adaptive virtual synchronous machine in the UPQC system, wherein the UPQC system comprises a series voltage source type converter and a parallel voltage source type converter, the adaptive virtual synchronous machine is connected with a port of the parallel voltage source type converter, and is used for configuring the parallel voltage source type converter into a virtual synchronous generator control mode;

[0136] Step 20, applying active droop frequency control and reactive droop voltage control to the adaptive virtual synchronous machine;

[0137] Step 30, determining the small disturbance quantity corresponding to the actual active power, the small disturbance quantity corresponding to the actual reactive power and the small disturbance quantity corresponding to the actual frequency of the adaptive virtual synchronous machine output based on the virtual synchronous machine algorithm corresponding to the adaptive virtual synchronous machine, the active power droop frequency control and the reactive power droop voltage control.

[0138] Step 40, determining that the adaptive adjustment model of the virtual inertia satisfies the following equation based on the small disturbance quantity corresponding to the actual active power, the small disturbance quantity corresponding to the actual reactive power and the small disturbance quantity corresponding to the actual frequency.

[0139]

[0140]

[0141] In the formula, is a steady-state virtual inertia; is an active adaptive virtual inertia; is a reactive adaptive virtual inertia; is the small disturbance quantity corresponding to the actual active power; is the small disturbance quantity corresponding to the actual frequency; is the maximum deviation value of the actual frequency and the rated frequency; is the small disturbance quantity corresponding to the actual reactive power; is the terminal rated voltage of the adaptive virtual synchronous machine; is the maximum deviation value of the terminal actual voltage and the terminal rated voltage.

[0142] In some optional modes of the embodiment, the active power droop frequency control and the reactive power droop voltage control are applied to the adaptive virtual synchronous machine, including:

[0143] The active power droop frequency control is applied to the adaptive virtual synchronous machine based on the grid reference frequency, the actual frequency of the port of the parallel voltage source type converter, the active power-frequency characteristic coefficient, the active power reference value output by the parallel voltage source type converter and the active power transmitted by the UPQC through the parallel voltage source type converter.

[0144] The reactive power droop voltage control is applied to the adaptive virtual synchronous machine based on the rated voltage amplitude of the grid, the voltage amplitude of the port of the parallel voltage source type converter, the reactive power-voltage amplitude characteristic coefficient, the reactive power reference value output by the parallel voltage source type converter and the reactive power transmitted by the UPQC through the parallel voltage source type converter.

[0145] The virtual synchronous machine algorithm adopts a second-order model of a synchronous generator to establish a mathematical model for simulating motion characteristics of a rotor, and an expression corresponding to the virtual synchronous machine algorithm is as follows:

[0146]

[0147] wherein, is a virtual inertia of the rotor; respectively, are an actual frequency and a rated frequency of the adaptive virtual synchronous machine; is a deviation value of the actual frequency and the rated frequency of the adaptive virtual synchronous machine; respectively, are an actual output torque and a torque given value of the adaptive virtual synchronous machine; is an active damping coefficient; respectively, are an actual active power and an active power given value output by the adaptive virtual synchronous machine; represents an angle of attack.

[0148] In some optional manners of the embodiment, based on the virtual synchronous machine algorithm corresponding to the adaptive virtual synchronous machine, the frequency control of the active droop, and the voltage control of the reactive droop, determining small disturbance amounts corresponding to actual active power, actual reactive power, and actual frequency output by the adaptive virtual synchronous machine, comprises:

[0149] based on the voltage control of the reactive droop, determining an expression of a virtual electromotive force output by the adaptive virtual synchronous machine;

[0150] based on the frequency control of the active droop, the expression of the virtual synchronous machine algorithm, the expression of the virtual electromotive force, the expression of the actual active power, and the expression of the actual reactive power output by the adaptive virtual synchronous machine, determining a steady-state equation of the adaptive virtual synchronous machine;

[0151] superimposing a disturbance on the steady-state equation, and after disturbance separation and linearization, performing Laplace transform to determine a small-signal model corresponding to the adaptive virtual synchronous machine, wherein an expression of the small-signal model comprises a small disturbance amount function corresponding to the actual active power, a small disturbance amount function corresponding to the actual reactive power, a small disturbance amount function corresponding to the actual frequency, and a small disturbance amount function corresponding to the virtual electromotive force output by the adaptive virtual synchronous machine.

[0152] In some optional manners of the embodiment, the expression of the virtual electromotive force is as follows:

[0153] ​​​

[0154] wherein, is a virtual electromotive force of the adaptive virtual synchronous machine; is an open-circuit electromotive force of the adaptive virtual synchronous machine; is a reactive voltage droop adjustment part of the virtual electromotive force; is a terminal voltage deviation of the adaptive virtual synchronous machine; is a reactive damping coefficient; , are actual reactive power and reactive power given value output by the adaptive virtual synchronous machine, respectively; is a voltage excitation adjustment coefficient; is an actual terminal voltage of the adaptive virtual synchronous machine.

[0155] In some optional modes of the embodiment, the expression of the steady-state equation of the adaptive virtual synchronous machine is as follows:

[0156]

[0157] wherein, is a port voltage of the adaptive virtual synchronous machine; is a synchronous reactance of the adaptive virtual synchronous machine.

[0158] In some optional modes of the embodiment, the expression of the small-signal model is as follows:

[0159]

[0160] wherein, are small perturbation quantity functions corresponding to actual active power, actual reactive power, actual frequency, virtual electromotive force and power angle output by the adaptive virtual synchronous machine, respectively; , are active given control quantity and reactive given control quantity of the adaptive virtual synchronous machine, respectively; is a complex variable.

[0161] In some optional modes of the embodiment, the UPQC further comprises a bidirectional DC / DC converter and a battery energy storage device, wherein the battery energy storage device is connected in parallel with a DC capacitor of the common DC bus through the bidirectional DC / DC converter;

[0162] When the AC side frequency of the UPQC drops, the adaptive virtual synchronous machine extracts energy from the DC capacitor to provide inertia response, the voltage of the common DC bus instantaneously drops, the bidirectional DC / DC converter adjusts the inductor current in real time through the voltage outer loop, controls the charge and discharge power of the battery energy storage device, and realizes voltage support for the DC capacitor;

[0163] The adaptive virtual inertia control method further comprises:

[0164] Based on the maximum current ramp rate of the ramp limiter in the battery energy storage device, the power synchronization coefficient and the rated frequency of the adaptive virtual synchronous machine, a frequency step amplitude boundary required for triggering the ramp limiter is determined, wherein the expression of the frequency step amplitude boundary is as follows:

[0165]

[0166] Based on the frequency step amplitude boundary, it is determined that the active adaptive virtual inertia satisfies the following constraint:

[0167]

[0168] In the formula, The frequency step amplitude boundary is the frequency step amplitude boundary; the The maximum current ramp rate is the maximum current ramp rate; The power synchronization coefficient is the power synchronization coefficient; The rated frequency of the adaptive virtual synchronous machine is the rated frequency of the adaptive virtual synchronous machine.

[0169] So far, for the coordinated operation control problem of series and parallel converters in UPQC, the application proposes an adaptive virtual inertia control method, which makes the new energy power generation device have the frequency and voltage support capability of traditional synchronous generators without changing the original control of the new energy power generation device. Combined with the verification of the simulation experiment, the following conclusions are obtained:

[0170] 1) Analyze the mathematical model of the UPQC system with energy storage capability in the steady state, explain the power flow mechanism inside the UPQC, and design a virtual synchronous generator control strategy suitable for UPQC.

[0171] 2) For the virtual synchronization control strategy of the unified power quality conditioner, based on the UPQC system operation scheme with energy storage capability, the UPQC power mathematical model is established, the traditional synchronous generator set is simulated, without external modification, only the original converter control of the new energy power generation is modified, and the virtual synchronization control strategy suitable for UPQC is realized.

[0172] 3) Based on the small signal model of VSG, a strategy of inertia adaptive control is proposed to automatically adjust the inertia to weaken the overshoot and oscillation of the system, and improve the stability of active power and frequency of the distribution network.

[0173] It can be understood that the above examples are only examples for better understanding the technical solutions of the embodiments of the present application, and are not the only limitation of the embodiments of the present application.

[0174] It should be noted that in the description of the present application, the terms "upper", "lower", etc. indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0175] It should also be noted that in the description of the present application, relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0176] In the embodiments of the present application, the singular form "one", "the" and the like includes the plural form, and should be broadly understood as "one kind" or "a kind of", rather than limited to the meaning of "one"; in addition, the term "said" should be understood to include both singular and plural forms, unless the context clearly indicates otherwise. In addition, the term "according to" should be understood as "at least partially according to", and the term "based on" should be understood as "at least partially based on", unless the context clearly indicates otherwise.

[0177] It should be understood that the various forms of flow shown above can be reordered, added or deleted. For example, the steps described in the present disclosure can be executed in parallel, sequentially or in different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, which is not limited herein.

[0178] The foregoing detailed description has set forth various embodiments of the application via illustrative examples and / or implementation contexts. It is to be understood, however, that the breadth and scope of the present application are not limited to those specific embodiments, but rather include all changes, modifications and alternatives that fall within the spirit and principles of the present application. Thus, the scope of the present application should be determined by the appended claims and equivalents thereof.

[0179] The above detailed description has set forth various embodiments of the application via illustrative examples and / or implementation contexts. It is to be understood, however, that the breadth and scope of the present application are not limited to those specific embodiments, but rather include all changes, modifications and alternatives that fall within the spirit and principles of the present application. Thus, the scope of the present application should be determined by the appended claims and equivalents thereof.

Claims

1. An adaptive virtual inertia control system for an UPQC, wherein the UPQC comprises a series voltage source converter and a parallel voltage source converter, characterized in that: The adaptive virtual inertia control system includes: a frequency and voltage droop unit, an adaptive virtual synchronous machine, and an adaptive virtual inertia calculation unit, wherein: The frequency and voltage droop unit is used to apply frequency control of active power droop and voltage control of reactive power droop to the adaptive virtual synchronous machine; The adaptive virtual inertia calculation unit is used to determine, based on a virtual synchronous machine algorithm corresponding to the adaptive virtual synchronous machine, the frequency control of the active power droop, and the voltage control of the reactive power droop, a small disturbance amount corresponding to the actual active power output by the adaptive virtual synchronous machine, a small disturbance amount corresponding to the actual reactive power, and a small disturbance amount corresponding to the actual frequency, and determine an adaptive adjustment model of the virtual inertia based on the small disturbance amount corresponding to the actual active power, the small disturbance amount corresponding to the actual reactive power, and the small disturbance amount corresponding to the actual frequency. The adaptive adjustment model of the virtual inertia is as follows: Where, is the steady-state virtual inertia; It is the active adaptive virtual inertia; is the reactive adaptive virtual inertia; is a small disturbance function corresponding to the actual active power; is a small disturbance function corresponding to the actual frequency; is the maximum deviation between the actual frequency and the rated frequency; is a small disturbance function corresponding to the actual reactive power; is the rated voltage of the machine end of the adaptive virtual synchronous machine; The maximum deviation between the actual voltage at the machine end and the rated voltage at the machine end; is the active damping coefficient; is the rated frequency of the adaptive virtual synchronous machine.

2. The adaptive virtual inertia control system according to claim 1, characterized in that: The frequency and voltage droop unit includes a frequency droop subunit and a voltage droop subunit, wherein: The frequency droop subunit is configured to apply the active power droop frequency control to the adaptive virtual synchronous machine based on the grid reference frequency, the actual frequency of the parallel voltage source converter port, the active power-frequency characteristic coefficient, the active power reference value output by the parallel voltage source converter, and the active power transmitted by the UPQC through the parallel voltage source converter; The voltage droop subunit is used to apply reactive droop voltage control to the adaptive virtual synchronous machine based on the rated voltage amplitude of the power grid, the voltage amplitude of the port of the parallel voltage source converter, the reactive power-voltage amplitude characteristic coefficient, the reactive power reference value output by the parallel voltage source converter, and the reactive power transmitted by UPQC through the parallel voltage source converter.

3. The adaptive virtual inertia control system according to claim 2, characterized in that: The virtual synchronous machine algorithm uses the second-order model of the synchronous generator to establish a mathematical model for simulating the motion characteristics of the rotor. The model corresponding to the virtual synchronous machine algorithm is: Where, is the virtual inertia of the rotor; is the actual frequency of the adaptive virtual synchronous machine; is the deviation between the actual frequency and the rated frequency of the adaptive virtual synchronous machine; 、 are respectively the actual output torque and torque given value of the adaptive virtual synchronous machine; 、 are respectively the actual active power and the active power given value output by the adaptive virtual synchronous machine; Indicates the power angle.

4. The adaptive virtual inertia control system according to claim 3, characterized in that: The adaptive virtual inertia calculation unit is further configured to: Determining a model of a virtual electromotive force output by the adaptive virtual synchronous machine based on the voltage control of the reactive power droop; Determining a steady-state model of the adaptive virtual synchronous machine based on the frequency control of the active power droop, the model of the virtual synchronous machine algorithm, the model of the virtual electromotive force, the model of the actual active power output by the adaptive virtual synchronous machine, and the model of the actual reactive power; A disturbance is superimposed on the steady-state model, and a Laplace transform is performed after disturbance separation and linearization to determine a small signal model corresponding to the adaptive virtual synchronous machine, wherein the small signal model includes a small disturbance function corresponding to the actual active power output by the adaptive virtual synchronous machine, a small disturbance function corresponding to the actual reactive power, a small disturbance function corresponding to the actual frequency, and a small disturbance function corresponding to the virtual electromotive force.

5. The adaptive virtual inertia control system according to claim 4, characterized in that: The model of the virtual electromotive force is as follows: Where, is the virtual electromotive force of the adaptive virtual synchronous machine; is the no-load electromotive force of the adaptive virtual synchronous machine; is the reactive voltage droop regulating part of the virtual electromotive force; is the terminal voltage deviation of the adaptive virtual synchronous machine; is the reactive damping coefficient; 、 are respectively the actual reactive power and the reactive power set value output by the adaptive virtual synchronous machine; is the voltage excitation regulation coefficient; is the actual voltage at the machine end of the adaptive virtual synchronous machine.

6. The adaptive virtual inertia control system according to claim 4, characterized in that: The steady-state model of the adaptive virtual synchronous machine is as follows: Where, is the port voltage of the adaptive virtual synchronous machine; is the synchronous reactance of the adaptive virtual synchronous machine.

7. The adaptive virtual inertia control system according to claim 4, characterized in that: The small signal model is as follows: Where, They are respectively the small disturbance function corresponding to the virtual electromotive force of the adaptive virtual synchronous machine and the small disturbance function corresponding to the power angle; They are respectively the active power given control quantity and reactive power given control quantity of the adaptive virtual synchronous machine; is a complex variable.

8. The adaptive virtual inertia control system according to claim 1, characterized in that: The adaptive virtual synchronous machine is connected to a control port of the parallel voltage source converter and is configured to determine a voltage reference value and a phase angle reference value of the parallel voltage source converter based on the frequency voltage droop unit and the adaptive virtual inertia calculation unit, wherein the parallel voltage source converter is configured in a virtual synchronous generator control mode; The adaptive virtual inertia control system further includes an SVPWM modulation unit for determining a pulse control signal for the parallel voltage source converter based on the voltage reference value and the phase angle reference value.

9. The adaptive virtual inertia control system according to claim 1, characterized in that: The UPQC further includes a bidirectional DC / DC converter and a battery energy storage device, wherein the battery energy storage device is connected in parallel with a DC capacitor of a common DC bus through the bidirectional DC / DC converter; When the AC side frequency of the UPQC drops, the adaptive virtual synchronous machine extracts energy from the DC capacitor to provide inertia response, causing the voltage of the common DC bus to drop instantaneously. The bidirectional DC / DC converter adjusts the inductor current in real time through the voltage outer loop to control the charge and discharge power of the battery energy storage device, thereby providing voltage support for the DC capacitor. The adaptive virtual inertia calculation unit is further configured to: Based on the maximum current ramp rate of the ramp limiter in the battery energy storage device, the power synchronization coefficient, and the rated frequency of the adaptive virtual synchronous machine, a frequency step amplitude boundary required to trigger the ramp limiter is determined, wherein the frequency step amplitude boundary is expressed as follows: Based on the frequency step amplitude boundary, it is determined that the active adaptive virtual inertia satisfies the following constraints: Where, is the frequency step amplitude boundary; is the maximum current ramp rate; is the power synchronization coefficient.

10. An adaptive virtual inertia control method for UPQC, characterized in that: include: Constructing a UPQC system and a control model of an adaptive virtual synchronous machine in the UPQC system, wherein the UPQC system includes a series voltage source converter and a shunt voltage source converter, the adaptive virtual synchronous machine is connected to a port of the shunt voltage source converter, and is configured to configure the shunt voltage source converter to a virtual synchronous generator control mode; Applying frequency control of active power droop and voltage control of reactive power droop to the adaptive virtual synchronous machine; Determining a small disturbance amount corresponding to actual active power, actual reactive power, and actual frequency output by the adaptive virtual synchronous machine based on a virtual synchronous machine algorithm corresponding to the adaptive virtual synchronous machine, frequency control of the active power droop, and voltage control of the reactive power droop; Based on the small disturbance amount corresponding to the actual active power, the small disturbance amount corresponding to the actual reactive power, and the small disturbance amount corresponding to the actual frequency, an adaptive adjustment model of the virtual inertia is determined, wherein the adaptive adjustment model of the virtual inertia is as follows: Where, is the steady-state virtual inertia; It is the active adaptive virtual inertia; is the reactive adaptive virtual inertia; is the small disturbance corresponding to the actual active power; is the small disturbance amount corresponding to the actual frequency; is the maximum deviation between the actual frequency and the rated frequency; is the small disturbance corresponding to the actual reactive power; is the rated voltage of the machine end of the adaptive virtual synchronous machine; The maximum deviation between the actual voltage at the machine end and the rated voltage at the machine end; is the active damping coefficient; is the rated frequency of the adaptive virtual synchronous machine.

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