CN114400719A - New energy grid-connected control circuit and SST control method based on virtual synchronous machine - Google Patents

New energy grid-connected control circuit and SST control method based on virtual synchronous machine Download PDF

Info

Publication number
CN114400719A
CN114400719A CN202210156141.7A CN202210156141A CN114400719A CN 114400719 A CN114400719 A CN 114400719A CN 202210156141 A CN202210156141 A CN 202210156141A CN 114400719 A CN114400719 A CN 114400719A
Authority
CN
China
Prior art keywords
voltage
current
control
reference value
grid
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202210156141.7A
Other languages
Chinese (zh)
Inventor
程静
王维庆
程志江
何山
赵振民
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Xinjiang University
Original Assignee
Xinjiang University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Xinjiang University filed Critical Xinjiang University
Priority to CN202210156141.7A priority Critical patent/CN114400719A/en
Publication of CN114400719A publication Critical patent/CN114400719A/en
Pending legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a new energy grid-connected control circuit and an SST control method based on a virtual synchronous machine, aiming at accessing a new energy grid into a three-stage SST consisting of an input stage, an isolation stage and an output stage, arranging a VSG-based new energy grid-connected control circuit at the output stage, carrying out constant control on current balance, active power and reactive power under unbalanced voltage through an SST control method based on the circuit, calculating a control strategy for realizing grid stability through the SST control method based on the virtual synchronous machine under the unbalanced voltage, thereby improving the power supply quality of the grid and improving the output grid-connected current, voltage and power quality of the SST output stage.

Description

New energy grid-connected control circuit and SST control method based on virtual synchronous machine
Technical Field
The invention belongs to the control technology of an electric power system, and particularly relates to a new energy grid-connected control circuit and an SST control method based on a virtual synchronous machine.
Background
In a low-voltage distribution network, the problem of electric energy quality of the low-voltage distribution network is more and more prominent due to the diversity and complexity of electricity utilization loads, particularly, the voltage quality of the low-voltage distribution network is aggravated due to the access of distributed new energy, the phenomenon of high-voltage and low-voltage unbalance occurs, and the existing control management technology is not obvious in effect; the power load of the low-voltage distribution network is mostly single-phase load, the three-phase imbalance problem exists objectively and in real time due to the influence of factors such as power utilization time difference and the like, the three-phase imbalance problem seriously restricts the output and voltage quality problems of the transformer, and the loss of the low-voltage distribution line is increased; and with economic development, nonlinear loads are more and more, harmonic and reactive problems are more and more prominent, and application limitations exist.
On the other hand, under unbalanced grid voltage, the inverter controlled by the traditional VSG control strategy faces the problems of unbalanced output current, active and reactive power fluctuation and the like, and most of the traditional strategies for processing three-phase voltage unbalance are not suitable for virtual synchronous generator control.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems of current imbalance, power oscillation, current quality and the like caused by an SST output stage in the traditional VSG control under the condition of three-phase imbalance of voltage of a low-voltage distribution network, the invention provides a VSG-based new energy grid-connected control circuit for the first purpose, and provides a virtual synchronous machine-based SST control method under the condition of unbalanced voltage for the second purpose based on the control circuit.
The technical scheme is as follows: a new energy grid-connected control circuit based on VSG, in the circuit, the new energy is connected to the isolation level of the three-level SST topological structure main circuit composed of the input level, the isolation level and the output level in a grid-connected mode, the circuit comprises an SST control circuit based on a virtual synchronous machine under unbalanced voltage, and the SST control circuit comprises a VSG controller, a current reference value generator, a positive and negative sequence current regulator based on PI and a midpoint potential balance controller;
in the SST control circuit, a VSG controller provides a voltage reference value for a current reference generator, and a modulation wave generator controls the current injected into a power grid by an output stage under the regulation output of a PI-based positive and negative sequence current regulator and a midpoint potential balance controller to only allow the current to contain a positive sequence component.
In the circuit, the input stage comprises a half-bridge type MMC submodule topological structure, the middle isolation stage comprises a double-active-bridge series resonance converter, and the output stage comprises a T-type three-level type inverter structure.
Furthermore, the input stage is connected with a medium-high voltage alternating current power grid through a half-bridge type MMC converter, and the number of MMC sub-modules is increased or decreased to adapt to different voltage levels;
the isolation stage comprises a double-active-bridge series resonance converter, so that the output direct-current voltage at the input side is modulated into high-frequency alternating-current voltage through a single-phase full-bridge inverter circuit, the high-frequency alternating-current voltage is coupled to the secondary side through a high-frequency transformer, the high-frequency alternating-current voltage is converted into direct current through a single-phase full-bridge rectifier circuit, the direct-current voltage conversion and the electrical isolation of the input and output stage are realized, and the power is allowed to flow in a two-way mode; the isolation level adopts a structure of input series connection/output parallel connection to realize input voltage division and output shunt, and a low-voltage direct-current bus of the isolation level provides a direct-current port for new energy grid connection or load;
the output stage comprises a T-shaped three-level inverter, the bridge arm output voltage is subjected to midpoint clamping through an IGBT which is reversely connected in series, and the output stage converts low-voltage direct current output by the isolation stage into stable three-phase power frequency voltage which is input to a low-voltage distribution network to supply power to users.
The SST control method is used for current balance control, active power constant control and reactive power constant control after new energy is connected to the grid, comprises the steps of extracting positive and negative sequence components of output current based on positive and negative sequence separation of a biquadratic generalized integrator, and comprises the following calculation and modulation processes:
(1) controller output voltage reference value u based on VSG* kCalculating a negative sequence current reference value through instantaneous active power and reactive power so that the SST controls the output stageThe current injected into the grid contains only positive sequence components;
(2) based on current balance control, calculating and solving voltage reference value u of VSG controller* kPositive sequence voltage u with the grid+ gdCurrent i+ iThe relationship of the component reference values, there is the following expression:
Figure BDA0003511515280000021
in the formula: u iskd、*ukqRespectively, the voltage reference value u of the VSG control module* kComponent i under d and q axes after Park transformation+ id、i+ iqRespectively, the positive sequence current i of the grid+ iAfter being subjected to Park transformation, the components under d and q axes are obtained;
(3) considering that in the active power constant control, a negative sequence current reference value of the active power constant control and a positive sequence current reference value of the current balance control are correlated with each other, and calculating the negative sequence current reference value, the following expression is present:
Figure BDA0003511515280000022
Figure BDA0003511515280000023
in the formula: u. ofg +、ug -Respectively, low-voltage distribution network voltage Ug +And Ug -Instantaneous value of (a); i.e. ii +、ii -Are respectively the output current Ii +And Ii -Instantaneous value of (a);
in the reactive power constant control, a positive sequence current reference value in the current balance control is correlated with a negative sequence current reference value in the active power constant control and the reactive power constant control, and is opposite to the negative sequence current reference value in the active power constant control;
(4) the method comprises the following steps of setting a current reference generator, controlling the output of negative sequence current reference values under the constant control of active power and the constant control of reactive power, introducing a flexible coefficient H, and realizing the stable control of the power grid by using the control coefficient H under the working condition of unbalanced voltage of the power grid, wherein the method comprises the following steps of:
when H is 0, current balance control is realized; when H is 1, realizing active constant control; when H is-1, reactive constant control is realized, and the expression thereof is as follows:
Figure BDA0003511515280000031
(5) the output current is regulated by setting a positive-negative sequence current regulator based on the PI, so that the positive-negative sequence current reference value is quickly tracked, and the regulation value is calculated by the following expression:
Figure BDA0003511515280000032
in the formula: e.g. of the type*Is the modulation voltage; kp and Ki are proportional integral coefficients;
(6) the voltage balance of the T-shaped three-level output stage and the two capacitors is carried out by a neutral point potential balance controller, wherein the generated zero sequence components are as follows:
Figure BDA0003511515280000033
in the formula: v. of0Is the zero sequence component, C is the capacitive reactance value of the voltage-dividing capacitor, inpavIs the midpoint current, inp0Is the midpoint current after the zero sequence component is superimposed, fsIs the carrier frequency.
Further, in the above method, in the positive-negative sequence separation based on the biquadratic generalized integrator, the transfer function of the quadratic generalized integrator is as follows:
Figure BDA0003511515280000041
Figure BDA0003511515280000042
in the formula: d(s), E(s) are band-pass and low-pass filters, respectively; omegarIs the resonant frequency; k is the damping coefficient.
In the method, the current injected into the power grid by the SST output stage is allowed to only contain a positive sequence component, a negative sequence current reference value is set to be zero, the positive sequence current reference value is calculated through a voltage reference value generated by the VSG control module and an output stage positive sequence circuit equation, and the SST output stage outputs a voltage stable value uikAnd VSG module output voltage reference value uk *Approximately equal, the relationship between the voltage reference value of the VSG control module and the grid positive sequence voltage and current component reference values can be obtained, and the following relationship exists:
Figure BDA0003511515280000043
in the formula: u. ofid、uiqAnd iid、iiqOutputting d and q axis components of the voltage and current for the output stage; u. ofgd、ugqIs the grid voltage dq axis component;
Figure BDA0003511515280000044
in the formula: u. ofkd、ukqThe components of the VSG controller voltage reference value in the d and q axes, respectively.
Further, the relationship is calculated according to the components of the voltage reference value of the VSG controller under d and q axes, the calculated relationship is converted into a positive sequence current reference value expression, and the positive sequence current reference value expression is transformed into a complex frequency domain through a laplace final value theorem, so that the following relationship is obtained:
Figure BDA0003511515280000045
in the formula: s is a differential operator; r is the total resistance of the inverter to the grid;
according to the Laplace final value theorem, the time domain expression is simplified and converted as follows:
Figure BDA0003511515280000046
setting the negative sequence current reference value to zero, and obtaining the double frequency power fluctuation component as follows:
Figure BDA0003511515280000051
from the above, the double frequency power fluctuation component is not completely eliminated; and the power oscillation is weakened, and the current balance control target is realized at the cost of active power oscillation and reactive power oscillation.
Furthermore, in the active power constant control, when the SST is used as a grid-connected interface of a photovoltaic system or an energy storage system, the active power needs to be constantly controlled, so that the double-frequency active power fluctuation component is zero, and only an average active power component is generated, wherein the expression is as follows:
Figure BDA0003511515280000052
from the above equation, the negative sequence current reference value for the constant work power control and the positive sequence current reference value for the current balance control are correlated with each other.
In the reactive power constant control, when a large-capacity power generation device is connected to a power grid through an SST and provides stable reactive power support, a double-frequency reactive power fluctuation component is made zero, and an expression for an output average reactive power component is as follows:
Figure BDA0003511515280000053
from the above equation, the negative sequence current reference value for the reactive power constant control and the positive sequence current reference value for the current balance control are correlated with each other.
Has the advantages that: compared with the prior art, firstly, the negative sequence component is not considered in the traditional VSG control strategy, so that active power and reactive power oscillate, the active loop and the reactive loop in VSG control are transmitted to the amplitude value and the phase angle of the output voltage reference value, so that the output current of the SST output stage is unbalanced, and the quality of the output power of the SST is poor. An output stage control strategy based on an improved VSG is provided, and output current balance and active or reactive power fluctuation are achieved on the premise of not changing the voltage source characteristics of the VSG by adding a control link i-f (uk).
The control circuit and the control method have the remarkable effects that:
(1) the improved VSG control strategy provided by the invention reserves the basic characteristics of a voltage source of VSG, a positive sequence current reference value is obtained through a positive sequence circuit of an SST output stage in VSG control, a negative sequence current reference value of different control targets is calculated by combining an instantaneous power theory, then a positive and negative sequence current regulation module is cascaded to realize grid-connected current balance, active/reactive power oscillation and grid-connected current harmonic content, and reliable switching of three control targets is realized by introducing flexible coefficients.
(2) The method comprises the proposed zero-sequence component injection midpoint potential balancing method, the VSG control strategy is jointly improved, the method is suitable for well balancing T-shaped three-level output stage voltage capacitance voltage under the unbalanced voltage working condition, injection of low-order harmonics is effectively reduced, and the output stage power quality is improved.
(3) When the control method and the control device realize the current balance VSG control or the active power constant VSG control, the frequency doubling fluctuation of SST low-voltage direct-current bus voltage is effectively inhibited, and the access adaptability of the direct-current micro-grid and the power supply reliability of a direct-current load are improved.
Drawings
FIG. 1 is a Solid State Transformer (SST) main circuit topology;
FIG. 2 is a circuit diagram of the new energy grid connection and controller connection according to the present invention;
FIG. 3 is a block diagram of the control circuit architecture and control strategy of the present invention;
FIG. 4 is a control block diagram of the VSG in the embodiment;
FIG. 5 is a block diagram of a current reference value generator control architecture in accordance with the present invention;
FIG. 6 is a block diagram of the positive and negative sequence current control and modulation strategy of the present invention;
FIG. 7 is a prior art VSG controlled SST output stage simulation result;
FIG. 8 is the simulation result of the VSG control output stage with constant reactive power for current balance switching in the embodiment;
FIG. 9 is the simulation result of VSG control output stage with constant switching power in current balance in the embodiment;
figure 10 is a simulation result of VSG control output stage target switching implemented in accordance with the present invention.
Detailed Description
In order to explain the technical solution of the present invention in detail, the following description is further made with reference to the accompanying drawings and specific embodiments.
The invention provides a new energy grid-connected control circuit and an SST control method based on a virtual synchronous machine.
In the development process of a power system, in order to adapt to the change of the characteristics of the power system after the high-proportion new energy is accessed and ensure the requirement of the power quality, a main circuit is formed by a three-stage SST topological structure and consists of an input stage, an isolation stage and an output stage, as shown in figure 1. In the invention, the input stage adopts a half-bridge type MMC submodule topological structure, the middle isolation stage adopts a double-active-bridge series resonance converter, and the output stage adopts a T-shaped three-level type inverter structure. The structure combination meets most of power grid regulation and control requirements, compared with the existing output stage which mostly adopts a three-phase two-level structure or a three-phase four-wire structure, the application of the T-type three-level inverter structure for the output stage is less, and the regulation and control requirements of high-quality new energy grid connection are met.
Referring to fig. 1 and 2, in the main circuit topology structure of the solid-state transformer, the input stage is connected to the medium-high voltage ac power grid through a half-bridge type MMC converter, and by increasing or decreasing the number of MMC submodules, the power transformer is adapted to different voltage levels, reduces the voltage withstand requirement of the power switching element, improves the power quality control capability and power density, and realizes unit power factor or constant power factor operation.
The isolation stage adopts a double-active-bridge series resonance converter, so that the output direct-current voltage at the input side is modulated into high-frequency alternating-current voltage through a single-phase full-bridge inverter circuit, the high-frequency alternating-current voltage is coupled to the secondary side through a high-frequency transformer, the high-frequency alternating-current voltage is converted into direct current through a single-phase full-bridge rectifier circuit, the direct-current voltage conversion and the electrical isolation of the input and output stage are realized, and the power is allowed to circulate in two directions. The isolation stage adopts a structure of input series connection/output parallel connection to realize input voltage division and output shunt, and a low-voltage direct-current bus of the isolation stage provides a direct-current port for new energy grid connection or load.
The output stage adopts a T-shaped three-level inverter, is an improvement of a NPC (neutral point clamped) three-level topological structure of a diode, and mainly has the function of realizing neutral point clamping of bridge arm output voltage through an IGBT (insulated gate bipolar transistor) which is reversely connected in series. The output stage converts the low-voltage direct current output by the isolation stage into stable three-phase power frequency voltage, and the stable three-phase power frequency voltage is input into a low-voltage distribution network to supply power to users.
After the new energy is accessed in the isolation stage, a control circuit is arranged at the output stage, namely the VSG-based new energy grid-connected control circuit provided by the invention, and the control circuit is installed as shown in fig. 2. The control logic of the control circuit is shown in fig. 3. Based on the control circuit, a control strategy based on a virtual synchronous machine is realized, a VSG-SST control strategy of double-sequence current is considered, and a controller controls and adjusts positive sequence and negative sequence components of output current of an SST (fixed transformer) output stage by measuring parameter values of a low-voltage distribution network, so that SVPWM modulation signals are adjusted in real time and added to 12 IGBTs of the output stage, various parameters of the low-voltage distribution network are changed, and the requirement on power quality is met. Aiming at the problems of current imbalance, power oscillation and current quality caused by SST output stage due to traditional VSG (synchronous virtual machine) control under the condition of three-phase imbalance of voltage of a low-voltage distribution network, an improved T-type three-level output stage combination control strategy based on VSG is provided, namely a virtual synchronous machine-based SST control strategy considering double-sequence current, and the output grid-connected current and power quality of the SST output stage are improved. According to the invention, a positive sequence current reference value is obtained by a VSG master control strategy output voltage reference value, and a negative sequence current reference value is calculated by an instantaneous power theory so as to realize current balance control and active/reactive constant control under unbalanced voltage.
With reference to fig. 3, the control circuit is mainly composed of a conventional VSG controller, a current reference value generator, a PI-based positive-negative sequence current regulator, and a midpoint potential balance controller. However, the T-type three-level inverter structure is used for an output stage, and compared with the existing three-phase two-level structure or three-phase four-wire structure which is mostly adopted, the T-type three-level inverter structure has stronger harmonic suppression capability, but introduces a new problem, namely that the neutral point is unbalanced, and the T-type three-level inverter structure is provided with a neutral point potential balancing link to solve the problem.
Based on the control circuit, the SST control method based on the virtual synchronous machine under the unbalanced voltage provided by the invention comprises the step of adopting a positive and negative sequence separation method based on a biquadratic and quadratic generalized integrator, and realizing good extraction effect of positive and negative sequence components of the grid voltage and the output current with a good filtering function. The second order generalized integrator transfer function is as in equation (1).
Figure BDA0003511515280000081
In the formula: d(s), E(s) are band-pass and low-pass filters, respectively; omegarIs the resonant frequency; k is the damping coefficient.
For the VSG controller, the circuit structure of the VSG controller is as shown in fig. 4, and for fig. 4, the following parameter correspondence exists:
Udc *representing a low-voltage direct-current bus voltage reference value; the reference value, i.e. the desired expected value, is set in the embodiment simulation by human. U shapedcLRepresenting the actual value of the DC bus voltage, the actual values being obtained by field measurement。PrefA reference value representing active power; qrefA reference value representing reactive power; peInstantaneous active power for output; the actual values are calculated from measurements: pe＝Uik_aIik_a+Uik_bIik_b+Uik_cIik_c。QeThe instantaneous reactive power, the actual value, representing the output is calculated from measurements:
Figure BDA0003511515280000082
Kqd, J are the integral gain coefficient, virtual damping coefficient, and inertial coefficient, respectively; the three parameters are based on debugging and empirical values, and the setting values in this embodiment are: the gain coefficient is 0.14, the virtual damping coefficient is 7, and the inertia coefficient is 0.1. Omega*Representing a rated angular velocity, i.e. a grid angular velocity; (50Hz power frequency AC, angular speed value omega)*＝2πf＝314rads-1I.e., 314 radians/second); E. theta is the VSG output voltage reference amplitude and phase angle respectively; voltage reference u* kThe amplitude phase angle form of E & lt theta can be written, UO represents VSG no-load electromotive force, and the given set value is 311V; u. of* kIs the output voltage reference value of the VSG controller.
The VSG control circuit structure is improved, and the stable value u of the output voltage of the SST output stage is obtainedikAnd VSG module output voltage reference value uk *Approximately equal, the relationship between the voltage reference value of the VSG control module and the grid positive sequence voltage and current component reference value can be obtained from equation (2), as shown in equation (3):
Figure BDA0003511515280000091
in the formula: u. ofid、uiqAnd iid、iiqOutputting d and q axis components of the voltage and current for the output stage; u. ofgd、ugqFor the dq-axis component of the mains voltage
Figure BDA0003511515280000092
In the formula: u. ofkd、ukqThe components of the VSG control module voltage reference value in the dq axis, respectively. Converting the formula (3) into a positive sequence current reference value expression and transforming the positive sequence current reference value expression into a complex frequency domain through Laplace final value theorem, wherein the formula (4) is as follows:
Figure BDA0003511515280000093
in the formula: s is a differential operator; r is the total resistance of the inverter to the grid.
Equation (4) can be simplified and transformed to the time domain according to the Laplace final theorem, as shown in equation (5):
Figure BDA0003511515280000094
the negative sequence current reference value is set to zero, and the frequency-doubled power fluctuation component can be obtained according to the formula (5), as shown in the following formula (6).
Figure BDA0003511515280000095
From equation (6), the double frequency power fluctuation component is not completely eliminated, but the power oscillation is greatly reduced. Thus, the current balance control objective is achieved at the expense of active and reactive power oscillations.
For the current reference value generator, the current reference value calculation module is the core of the control strategy, and the voltage reference value u is output by the VSG main control strategy* kAnd (4) solving a positive sequence current reference value, and calculating a negative sequence current reference value by an instantaneous power theory so as to realize current balance control and active/reactive constant control under unbalanced voltage.
The specific control strategy comprises three aspects of consideration, namely current balance control, active power constant control and reactive power constant control, and comprises the following derivation and calculation processes:
(1) current balance control
In order to obtain high-quality grid-connected current under the condition of unbalanced grid voltage, the current injected into the grid by the SST output stage is only allowed to contain a positive sequence component. Therefore, the negative sequence current reference value needs to be set to zero, and the positive sequence current reference value is calculated by the voltage reference value generated by the VSG control module and the output stage positive sequence circuit equation, as shown in fig. 5.
Derivation and calculation process: VSG control module voltage reference value u* kPositive sequence voltage u with the grid+ gdCurrent i+ iThe relationship of the component reference values is as follows:
Figure BDA0003511515280000101
in the formula: u iskd、*ukqRespectively, the voltage reference value u of the VSG control module* kAfter being subjected to Park transformation, the components under d and q axes are obtained; i.e. i+ id、i+ iqRespectively, the positive sequence current i of the grid+ iAnd after being subjected to Park transformation, the components under d and q axes are obtained.
And (4) converting the formula (6) into a positive sequence current reference value expression and converting the positive sequence current reference value expression into a complex frequency domain through Laplace transformation, wherein the complex frequency domain is represented by the formula (7).
Figure BDA0003511515280000102
In the formula: s is a differential operator; r represents the total resistance of the inverter to the low voltage distribution network.
According to the Laplace final theorem, equation (7) can be simplified and converted to the time domain, equation (8).
Figure BDA0003511515280000103
And (4) conclusion: the double frequency power fluctuation component is not completely eliminated, but the power oscillation is greatly weakened. Achieving the current balance control objective comes at the expense of active and reactive power oscillations.
(2) Active power constant control
When the SST is used as a grid-connected interface of a photovoltaic or energy storage system, the power is constantly controlled, so that the double-frequency active power fluctuation component P in the formula (9)s2And Pc2And (4) generating only the average active power component to obtain the formula (10) when the average active power component is zero.
Figure BDA0003511515280000111
In the formula: u. ofg +、ug -Respectively, low-voltage distribution network voltage Ug +And Ug -Instantaneous value of (a); i.e. ii +、ii -Are respectively the output current Ii +And Ii -Instantaneous value of (a).
Figure BDA0003511515280000112
As can be seen from equation (10), the negative sequence current reference value for active power constant control and the positive sequence current reference value for current balance control are correlated with each other, and the negative sequence current reference value, as shown in equation (12), is calculated using equation (8).
Figure BDA0003511515280000113
And (4) conclusion: the negative sequence current component is not eliminated, so that the active power constant control is larger than the reactive power oscillation in the current balance control, and the SST output stage is unbalanced in grid-connected current.
(3) Reactive power constant control
When a large-capacity power generation device is connected into a power grid through the SST and provides stable reactive power support, the frequency doubling reactive power fluctuation component Q in the formula (9) is mainly useds2And Qc2Is zero, only the average reactive power component is output, as(13)。
Figure BDA0003511515280000114
As can be seen from equation (13), the negative sequence current reference value for the reactive power constant control and the positive sequence current reference value for the current balance control are correlated with each other, and the negative sequence current reference value, as shown in equation (14), is calculated by using equation (8).
Figure BDA0003511515280000115
And (4) conclusion: the negative sequence current component is not eliminated, so that the reactive power constant control is larger than the active power oscillation in the current balance control, and the SST output stage is unbalanced in grid-connected current.
(4) Positive and negative sequence current regulator, modulation wave generator and neutral point potential balance controller based on PI
As can be seen from the expressions (8), (10) and (13), the positive-sequence current reference value in the current balance control and the negative-sequence current reference value in the active and reactive power constant control are correlated with each other, and the negative-sequence current reference values in the expressions (12) and (14) are opposite to each other. Therefore, a current reference generator is designed, a flexible coefficient H is introduced, and a control target is selected by the control coefficient H under the condition of unbalanced network voltage to meet different requirements, as shown in FIG. 6.
When H is 0, current balance control is realized; when H is 1, realizing active constant control; when H is-1, reactive constant control is realized.
In fig. 6, formula (15) and formula (16) in the block diagram:
Figure BDA0003511515280000121
Figure BDA0003511515280000122
in the formula: v. of0Is a zero sequence ofAn amount; c is capacitance reactance value of voltage-dividing capacitor, and two voltage-dividing capacitors are identical, i.e. C ═ C1＝C2；inpavIs the midpoint current; i.e. inp0Is the midpoint current after the zero sequence component is superimposed; f. ofsIs the carrier frequency, and takes 20000 Hz.
In order to realize the regulation of the output current and further quickly track the reference value of the positive-negative sequence current, a positive-negative sequence current regulation module based on PI is designed, as shown in the formula (17).
Figure BDA0003511515280000123
In the formula: e.g. of the type*Is the modulation voltage; kp and Ki are proportional-integral coefficients.
Three-phase cavel modulation waves are generated by adopting a three-level SVPWM (space vector pulse width modulation) strategy, so that a certain balance effect on the midpoint potential can be realized. However, since the current flows through the middle point of the two voltage-dividing capacitors on the dc side of the T-type three-level output stage, the voltage of the capacitors fluctuates or shifts, which affects the quality of the output power. Therefore, a zero-sequence component injection neutral-point potential balance method is adopted, and injected zero-sequence components participate in modulation, so that voltage balance of two capacitors of a T-shaped three-level output stage is effectively realized, and zero-sequence components are generated as shown in the following formula (18).
Figure BDA0003511515280000131
In the formula: v. of0Is a zero sequence component; c is the capacitance reactance value of the voltage-dividing capacitor; i.e. inpavIs the midpoint current; i.e. inp0Is the midpoint current after the zero sequence component is superimposed; f. ofsIs the carrier frequency.
Example 1
In order to verify the effectiveness of the control strategy, according to the topological structure shown in fig. 2, an SST system simulation model is built on a Matlab/simulink software platform for simulation analysis.
The effective value of the input-stage voltage is 10kV, the voltage of a high-voltage direct-current bus is 16kV, the voltage of a low-voltage direct-current bus is 750V, the grid-connected voltage of an output-stage alternating-current port is 380V, and simulation parameters of the SST output stage are set as shown in Table 1.
Table 1 output stage parameter set
Figure BDA0003511515280000132
Setting the operation condition: in the time period of 0s to 0.3s, the three phases of the grid voltage are balanced; in the time period of 0.3s to 0.9s, the three phases of the grid voltage are unbalanced, namely the A phase voltage is increased by 20%, the B phase voltage is kept unchanged, and the C phase voltage is decreased by 20%; midpoint potential balance control was added at 0.6 s. The results of the operation are shown in FIG. 7.
As can be seen from fig. 7: when the voltage of a power grid is balanced in a period of 0s to 0.3s, the SST output stage outputs grid-connected current which is balanced in three phases, the amplitude is 34.8A, and a low-voltage direct-current bus, an output active power and an output reactive power are stable;
in the period of 0.3s to 0.9s, when the voltage of a power grid is unbalanced, the SST output stage outputs grid-connected current to generate three-phase imbalance, the maximum peak value is 38.5A, the harmonic content is 6.92%, the low-voltage direct-current bus outputs double-frequency fluctuation of active power and reactive power, the voltage fluctuation amplitude of the low-voltage direct-current bus is 2.5V, the active power fluctuation amplitude is 5.2kW, and the reactive power fluctuation amplitude is 6.6 kvar;
before 0.6s is added into the neutral point potential balance control, the output stage DC side voltage-dividing capacitance voltage UC1And UC2The fluctuation peak values are 385V and 365V respectively; after the midpoint potential balance control is added for 0.6s, the voltage of the two voltage-dividing capacitors is kept balanced at the target potential 375V.
According to the control of the invention, the operation condition switching comprises the following three aspects:
(1) current balance control to reactive power constant control
Setting the operation condition: in the time period of 0s to 0.3s, the voltage of the power grid is balanced; in the time period of 0.3s to 0.9s, the three phases of the grid voltage are unbalanced; current balance is targeted 0.6s ago; after 0.6s the reactive power is targeted to be constant. The results of the operation are shown in FIG. 8.
As can be seen from fig. 8: when the three phases of the grid voltage are unbalanced, the SST output stage current under the control of the current balance VSG keeps three-phase balance, the amplitude is 35A, and the harmonic content is 1.49%. The fluctuation of the output active power and reactive power is reduced, but the voltage of the low-voltage direct-current bus and the output active/reactive power still have double frequency fluctuation, and the fluctuation amplitudes of the three are 1.5V, 3.9kW and 3.7kvar respectively.
Under the control of the reactive constant VSG, the fluctuation amplitude of the reactive power output by the SST output stage is reduced to 0.49kvar, but the three phases of the grid-connected current are unbalanced, the voltage of the low-voltage direct-current bus and the fluctuation of the output active power are increased, the fluctuation peak value of the grid-connected current is 38.5A, the harmonic content is 0.58%, and the fluctuation amplitudes of the low-voltage direct-current bus and the active power are respectively 3.1V and 7.6 kW.
The results show that VSG control with current balance as the target can ensure output grid-connected current balance, and the harmonic content and the output active/reactive power are reduced; VSG control targeting reactive power constancy can achieve output reactive power constancy, but results in current imbalance and large active power fluctuations.
(2) Current balance control to active constant control
Setting the operation condition: in the time period of 0s to 0.3s, the voltage of the power grid is balanced; in the time period of 0.3s to 0.9s, the three phases of the grid voltage are unbalanced; current balance is targeted 0.6s ago; after 0.6s, the active power is constant. The results of the operation are shown in FIG. 9.
As can be seen from fig. 9: when a voltage three-phase unbalance working condition occurs, under the control of an active constant VSG, the fluctuation amplitude of active power output by the SST output stage is reduced to 0.5kW, the fluctuation amplitude of low-voltage direct-current bus voltage is reduced to 0.4V, but the output grid-connected current is three-phase unbalanced, the fluctuation peak value is 37.5A, the harmonic content is 0.65%, the output reactive power fluctuation is increased, and the fluctuation amplitude is 7.54 kvar.
The above results indicate that VSG control targeting active power constancy can achieve output active power constancy, but results in current imbalance and large reactive power fluctuations.
(3) Flexible coefficient switching control target
Setting the operation condition: in the time period of 0s to 0.3s, the voltage of the power grid is balanced; in the time period of 0.3s to 0.9s, the three phases of the grid voltage are unbalanced; 0s to 0.5s, with current balance as the target; 0.5s to 0.7s, with the aim of constant reactive power; 0.7s to 0.9s, with the goal of active power constancy. The results of the operation are shown in FIG. 10.
As can be seen from fig. 10:
under the three-phase unbalanced working condition of the power grid voltage, the midpoint potential balance algorithm effectively controls the voltage U of the voltage-dividing capacitorC1And UC2Balancing;
when H is equal to 0, VSG control with current balance as a target is realized, the SST output stage outputs grid-connected current with three-phase balance, and the amplitude is 35A;
when H is 1, VSG control with the aim of constant reactive power is realized, and the fluctuation amplitude of the reactive power output by the SST output stage is 0.49 kvar;
when H is equal to-1, VSG control with the aim of constant active power is realized, and the active power fluctuation output by the SST output stage is 0.5 kW.
The above results show that the SST output stage based on the improved VSG can realize stable operation of different control targets, and change flexible parameters to smoothly switch three different control targets.

Claims (9)

1. The utility model provides a new forms of energy grid-connected control circuit based on VSG which characterized in that: in the circuit, new energy is connected to an isolation level of a three-level SST main circuit topological structure formed by an input level, an isolation level and an output level in a grid-connected mode, the circuit comprises an SST control circuit based on a virtual synchronous machine under unbalanced voltage for power grid stability regulation and control, and the SST control circuit comprises a VSG controller, a current reference value generator, a positive and negative sequence current regulator based on PI and a midpoint potential balance controller;
in the SST control circuit, a VSG controller provides a voltage reference value for a current reference generator, and a modulation wave generator controls the current injected into a power grid by an output stage under the regulation output of a PI-based positive and negative sequence current regulator and a midpoint potential balance controller to only allow the current to contain a positive sequence component.
2. The VSG-based new energy grid-connected control circuit according to claim 1, wherein: in the circuit, the input stage comprises a half-bridge type MMC submodule topological structure, the middle isolation stage comprises a double-active-bridge series resonance converter, and the output stage comprises a T-type three-level type inverter structure.
3. The VSG-based new energy grid-connected control circuit according to claim 2, wherein: the input stage is connected with a medium-high voltage alternating current power grid through a half-bridge type MMC converter, and is suitable for different voltage levels by increasing and decreasing the number of MMC sub-modules;
the isolation stage comprises a double-active-bridge series resonance converter, so that the output direct-current voltage at the input side is modulated into high-frequency alternating-current voltage through a single-phase full-bridge inverter circuit, the high-frequency alternating-current voltage is coupled to the secondary side through a high-frequency transformer, the high-frequency alternating-current voltage is converted into direct current through a single-phase full-bridge rectifier circuit, the direct-current voltage conversion and the electrical isolation of the input and output stage are realized, and the power is allowed to flow in a two-way mode; the isolation level adopts a structure of input series connection/output parallel connection to realize input voltage division and output shunt, and a low-voltage direct-current bus of the isolation level provides a direct-current port for new energy grid connection or load;
the output stage comprises a T-shaped three-level inverter, the bridge arm output voltage is subjected to midpoint clamping through an IGBT which is reversely connected in series, and the output stage converts low-voltage direct current output by the isolation stage into stable three-phase power frequency voltage which is input to a low-voltage distribution network to supply power to users.
4. The SST control method is used for current balance control, active power constant control and reactive power constant control after new energy is connected to the power grid, and is characterized in that: the method comprises the steps of extracting positive and negative sequence components of output current based on positive and negative sequence separation of a biquadratic generalized integrator, and comprises the following calculation and modulation processes:
(1) controller output voltage reference value u based on VSG* kCalculating a negative sequence current reference value through instantaneous active power and reactive power, so that the current injected into the power grid by the SST control output stage only contains a positive sequence component;
(2) based on current balance control, calculating and solving voltage reference value u of VSG controller* kPositive sequence voltage u with the grid+ gdCurrent i+ iThe relationship of the component reference values, there is the following expression:
Figure FDA0003511515270000021
in the formula: u. of* kd、*ukqRespectively, the voltage reference value u of the VSG control module* kComponent i under d and q axes after Park transformation+ id、i+ iqRespectively, the positive sequence current i of the grid+ iAfter being subjected to Park transformation, the components under d and q axes are obtained;
(3) considering that in the active power constant control, a negative sequence current reference value of the active power constant control and a positive sequence current reference value of the current balance control are correlated with each other, and calculating the negative sequence current reference value, the following expression is present:
Figure FDA0003511515270000022
Figure FDA0003511515270000023
in the formula: u. ofg +、ug -Respectively, low-voltage distribution network voltage Ug +And Ug -Instantaneous value of (a); i.e. ii +、ii -Are respectively the output current Ii +And Ii -Instantaneous value of (a);
in the reactive power constant control, a positive sequence current reference value in the current balance control is correlated with a negative sequence current reference value in the active power constant control and the reactive power constant control, and is opposite to the negative sequence current reference value in the active power constant control;
(4) the method comprises the following steps of setting a current reference generator, controlling the output of negative sequence current reference values under the constant control of active power and the constant control of reactive power, introducing a flexible coefficient H, and realizing the stable control of the power grid by using the control coefficient H under the working condition of unbalanced voltage of the power grid, wherein the method comprises the following steps of:
when H is 0, current balance control is realized; when H is 1, realizing active constant control; when H is-1, reactive constant control is realized, and the expression thereof is as follows:
Figure FDA0003511515270000024
(5) the output current is regulated by setting a positive-negative sequence current regulator based on the PI, so that the positive-negative sequence current reference value is quickly tracked, and the regulation value is calculated by the following expression:
Figure FDA0003511515270000031
in the formula: e.g. of the type*Is the modulation voltage; kp, KiIs a proportional-integral coefficient;
(6) the voltage balance of the T-shaped three-level output stage and the two capacitors is carried out by a neutral point potential balance controller, wherein the generated zero sequence components are as follows:
Figure FDA0003511515270000032
in the formula: v. of0Is the zero sequence component, C is the capacitive reactance value of the voltage-dividing capacitor, inpavIs the midpoint current, inp0Is the midpoint current after the zero sequence component is superimposed, fsIs the carrier frequency.
5. The virtual synchronous machine-based SST control method under unbalanced voltage according to claim 4, characterized in that: in the positive and negative sequence separation based on the biquadratic generalized integrator, the transfer function of the quadratic generalized integrator is as follows:
Figure FDA0003511515270000033
Figure FDA0003511515270000034
in the formula: d(s), E(s) are band-pass and low-pass filters, respectively; omegarIs the resonant frequency; k is the damping coefficient.
6. The virtual synchronous machine-based SST control method under unbalanced voltage according to claim 4, characterized in that: in the method, the current injected into the power grid by the SST output stage is allowed to only contain a positive sequence component, a negative sequence current reference value is set to be zero, the positive sequence current reference value is calculated through a voltage reference value generated by the VSG control module and an output stage positive sequence circuit equation, and the SST output stage outputs a voltage stable value uikAnd VSG module output voltage reference value uk *Approximately equal, the relationship between the voltage reference value of the VSG control module and the grid positive sequence voltage and current component reference values can be obtained, and the following relationship exists:
Figure FDA0003511515270000035
in the formula: u. ofid、uiqAnd iid、iiqOutputting d and q axis components of the voltage and current for the output stage; u. ofgd、ugqIs the grid voltage dq axis component;
Figure FDA0003511515270000041
in the formula: u. ofkd、ukqThe components of the VSG controller voltage reference value in the d and q axes, respectively.
7. The virtual synchronous machine-based SST control method under unbalanced voltage according to claim 6, characterized in that: according to the component calculation relationship of the VSG controller voltage reference value under d and q axes, converting the VSG controller voltage reference value into a positive sequence current reference value expression and converting the positive sequence current reference value expression into a complex frequency domain through Laplace final value theorem to obtain the following relationship:
Figure FDA0003511515270000042
in the formula: s is a differential operator; r is the total resistance of the inverter to the grid;
according to the Laplace final value theorem, the time domain expression is simplified and converted as follows:
Figure FDA0003511515270000043
setting the negative sequence current reference value to zero, and obtaining the double frequency power fluctuation component as follows:
Figure FDA0003511515270000044
from the above, the double frequency power fluctuation component is not completely eliminated; and the power oscillation is weakened, and the current balance control target is realized at the cost of active power oscillation and reactive power oscillation.
8. The virtual synchronous machine-based SST control method under unbalanced voltage according to claim 4, characterized in that: in active power constant control, when an SST is used as a grid-connected interface of a photovoltaic system or an energy storage system, active power needs to be constantly controlled, so that a double-frequency active power fluctuation component is zero, only an average active power component is generated, and the expression is as follows:
Figure FDA0003511515270000045
from the above equation, the negative sequence current reference value for the active power constant control and the positive sequence current reference value for the current balance control are correlated with each other.
9. The virtual synchronous machine-based SST control method under unbalanced voltage according to claim 4, characterized in that: in the reactive power constant control, when a large-capacity power generation device is connected to a power grid through an SST and provides stable reactive power support, a double-frequency reactive power fluctuation component is made zero, and an expression for an output average reactive power component is as follows:
Figure FDA0003511515270000051
from the above equation, the negative sequence current reference value for the reactive power constant control and the positive sequence current reference value for the current balance control are correlated with each other.
CN202210156141.7A 2022-02-19 2022-02-19 New energy grid-connected control circuit and SST control method based on virtual synchronous machine Pending CN114400719A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202210156141.7A CN114400719A (en) 2022-02-19 2022-02-19 New energy grid-connected control circuit and SST control method based on virtual synchronous machine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202210156141.7A CN114400719A (en) 2022-02-19 2022-02-19 New energy grid-connected control circuit and SST control method based on virtual synchronous machine

Publications (1)

Publication Number Publication Date
CN114400719A true CN114400719A (en) 2022-04-26

Family

ID=81234111

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202210156141.7A Pending CN114400719A (en) 2022-02-19 2022-02-19 New energy grid-connected control circuit and SST control method based on virtual synchronous machine

Country Status (1)

Country Link
CN (1) CN114400719A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116632925A (en) * 2023-06-06 2023-08-22 南京工程学院 Improved virtual synchronous control method of flexible multi-state switch under unbalanced power grid condition

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116632925A (en) * 2023-06-06 2023-08-22 南京工程学院 Improved virtual synchronous control method of flexible multi-state switch under unbalanced power grid condition

Similar Documents

Publication Publication Date Title
CN108280271B (en) Unified power flow controller equivalent modeling method based on switching period average principle
CN113839388B (en) Current double-loop control method of active power filter based on hybrid load
CN104218587A (en) Three-level four-leg active filter compensation distribution network neutral current control method
CN104410083B (en) Capacitance midpoint potential balancing device on SVG (Static VAR Generator) direct current side and control method of capacitance midpoint potential balancing device
Chennai et al. Unified power quality conditioner based on a three-level NPC inverter using fuzzy control techniques for all voltage disturbances compensation
Ding et al. Harmonic characteristics analysis of PWM-based electric vehicle chargers considering control strategy
CN114400719A (en) New energy grid-connected control circuit and SST control method based on virtual synchronous machine
Antar et al. Using seven-level cascade H-bridge inverter with HVDC system to improve power quality
CN111030131B (en) MMC-STATCOM circulating current suppression device based on negative sequence virtual impedance
Zheng et al. Control strategy for suppressing power oscillation of virtual synchronous generator under unbalanced grid voltage
CN104362759A (en) Final power quality regulating and controlling device for power distribution network and regulating and controlling method
CN204290329U (en) A kind of SVG DC bus capacitor neutral-point potential balance device
Coteli et al. Three-level cascaded inverter based D-STATCOM using decoupled indirect current control
Soomro et al. Optimal design of a single-phase APF based on PQ theory
Demirdelen et al. A modular cascaded multilevel inverter based shunt hybrid active power filter for selective harmonic and reactive power compensation under distorted/unbalanced grid voltage conditions
Liang et al. The simulation research of STATCOM based on cascaded multi-level converter
Fan et al. An improved control method for current-controlled VSG during transient voltage disturbance
Jin et al. Model predictive control for three-phase unbalance compensation under three-phase four-wire power system
CN104810830A (en) Three-phase four-wire system four-leg static synchronous compensator and control method
Baoan et al. Steinmetz theory applied to fundamental phase reference current calculation for a STATCOM with delta configuration
Liu et al. Capacitor Voltage Feedforward-based Voltage Loop Control for Grid-forming Modular Multilevel Converters Under Wide-range of Grid Strength
Zhu et al. DC-Link current optimal control of current source PWM converter
CN113890032B (en) Power electronic transformer control method and system for power quality control of transformer area
Li et al. Study of harmonic elimination in switching devices in STATCOM
Cheng et al. Single-phase bridgeless rectifier with capability of power quality management

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination