CN111509725A - Voltage recovery control method for parallel common coupling point of three-phase four-wire system converter - Google Patents

Voltage recovery control method for parallel common coupling point of three-phase four-wire system converter Download PDF

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CN111509725A
CN111509725A CN202010385765.7A CN202010385765A CN111509725A CN 111509725 A CN111509725 A CN 111509725A CN 202010385765 A CN202010385765 A CN 202010385765A CN 111509725 A CN111509725 A CN 111509725A
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voltage
axis
sequence
zero
component
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CN111509725B (en
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罗恩博
党军朋
陆海
张旭东
苏适
杨洋
何婕
袁兴宇
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Electric Power Research Institute of Yunnan Power Grid Co Ltd
Yuxi Power Supply Bureau of Yunnan Power Grid Co Ltd
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Electric Power Research Institute of Yunnan Power Grid Co Ltd
Yuxi Power Supply Bureau of Yunnan Power Grid Co Ltd
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    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • 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
    • 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

Abstract

The application relates to the technical field of operation and control of a microgrid, and particularly discloses a three-phase four-wire system converter parallel public coupling point voltage recovery control method, which is used for respectively compensating positive sequence, negative sequence and zero-axis voltage reference values in each three-phase four-wire system converter, so that the voltage of a public coupling point keeps a rated amplitude value and three-phase symmetry under different load conditions.

Description

Voltage recovery control method for parallel common coupling point of three-phase four-wire system converter
Technical Field
The application relates to the technical field of operation and control of a micro-grid, in particular to a voltage recovery control method for a parallel common coupling point of a three-phase four-wire system converter.
Background
The micro-grid refers to a small autonomous power system formed by fusing a distributed power supply, a power electronic technology, an energy storage device, a monitoring group, a protection device, an energy management system, a load and the like. The micro-grid has a grid-connected mode and an island mode. In order to improve the rated capacity and reliability of a micro-grid and realize access management of single-phase and nonlinear loads, a scheme that three-phase four-wire system converters are operated in parallel is generally adopted at present.
In a microgrid formed by parallel operation of three-phase four-wire converters, a phenomenon of three-phase imbalance generally exists, and the requirement of the microgrid on energy operation supply and demand balance is very strict, so how to realize current sharing among the converters under unbalanced load, improve the electric energy quality of a Point of Common Coupling (PCC), ensure stable operation of the microgrid, and become a problem to be solved urgently.
In order to solve the above problems, in the prior art, a microgrid control strategy based on an adaptive virtual impedance is disclosed, which includes adding a negative sequence virtual impedance, adjusting an output impedance of a microgrid, and compensating a public coupling point and a key node voltage imbalance degree through adaptation of the virtual impedance. Although virtual impedance self-adaptation can realize compensation of voltage unbalance of a common coupling point and a key node, the average accuracy of negative sequence current and zero sequence current is reduced. Therefore, a method for realizing the voltage recovery control of the pcc under the condition of maintaining the current sharing accuracy is needed.
Disclosure of Invention
The application provides a voltage recovery control method for a parallel common coupling point of a three-phase four-wire system current converter, which aims to solve the problem that in the prior art, the voltage unbalance compensation of the common coupling point and a key node is realized by using virtual impedance self-adaption, but the negative sequence and zero sequence current sharing precision is reduced.
In a first aspect, the embodiment of the present application provides a method for controlling voltage recovery at a parallel common coupling point of three-phase four-wire converters, where the method is applied to a system, where the system includes a local controller and a microgrid central controller, where the local controller is connected by low-bandwidth communication, the local controller is disposed at each three-phase four-wire converter, and the microgrid central controller is disposed at the common coupling point;
the method comprises the following steps:
the microgrid central controller sequentially uses a second-order general integral orthogonal signal generator and a positive-negative sequence calculator to extract voltage components of the common coupling point, wherein the voltage components comprise a first voltage positive sequence component, a first voltage negative sequence component and a first voltage zero sequence component;
the microgrid central controller is used for carrying out phase locking on the first voltage positive sequence component to obtain a first phase angle of the first voltage positive sequence component;
the microgrid central controller performs dq transformation on the first voltage positive sequence component in a rotating coordinate system determined by the first phase angle to obtain a second voltage positive sequence component, and performs dq transformation on the first voltage negative sequence component in a rotating coordinate system with the same frequency and opposite direction as the first voltage positive sequence component to obtain a second voltage negative sequence component; carrying out dq transformation on the first voltage zero-sequence component in a rotating coordinate system determined by the first phase angle to obtain a second voltage zero-sequence component;
the microgrid central controller respectively performs proportional integral control and low-pass filtering on the second voltage positive sequence component, the second voltage negative sequence component and the second voltage zero sequence component in corresponding rotating coordinate systems to obtain a positive sequence voltage compensation quantity, a negative sequence voltage compensation quantity and a zero sequence voltage compensation quantity;
the microgrid central controller sends the positive sequence voltage compensation quantity, the negative sequence voltage compensation quantity and the zero sequence voltage compensation quantity to the local controller;
the local controller obtains a second phase angle, performs inverse dq transformation on the positive sequence voltage compensation quantity according to a second phase angle to obtain α axis positive sequence voltage compensation quantity and β axis positive sequence voltage compensation quantity, performs inverse dq transformation on the negative sequence voltage compensation quantity according to the second phase angle to obtain α axis negative sequence voltage compensation quantity and β axis negative sequence voltage compensation quantity, synthesizes α axis positive sequence voltage compensation quantity and α axis negative sequence voltage compensation quantity to obtain α axis voltage compensation quantity, synthesizes β axis positive sequence voltage compensation quantity and β axis negative sequence voltage compensation quantity to obtain β axis voltage compensation quantity, performs inverse dq transformation on the zero sequence voltage compensation quantity according to the second phase angle, and obtains a zero axis voltage compensation quantity under a β 00 coordinate system after synthesis;
the local controller adds the α shaft voltage compensation quantity to the first α shaft voltage reference added with the virtual impedance, adds the β shaft voltage compensation quantity to the first β shaft voltage reference added with the virtual impedance, and adds the zero shaft voltage compensation quantity to the first zero shaft voltage reference added with the virtual impedance, so that voltage and current control is realized, and further, the compensation of voltage amplitude deviation and unbalance of a common coupling point is realized.
Optionally, a specific method for the local controller to acquire the second phase angle includes:
calculating three-phase instantaneous active power and instantaneous reactive power under an αβ coordinate system;
after the instantaneous active power and the instantaneous reactive power are subjected to low-pass filtering, extracting an active component and a reactive component;
and the active component is subjected to power droop to obtain a voltage angular frequency, and the voltage angular frequency is subjected to integration and 2 pi residue taking to generate a second phase angle.
Optionally, the method for the local controller to add a virtual impedance in the first α -axis voltage reference, the first β -axis voltage reference, and the first zero-axis voltage reference includes:
acquiring a second α axis voltage reference, and acquiring a first α axis voltage reference added with virtual impedance according to a second α axis voltage reference, a positive sequence virtual inductor, a positive sequence virtual resistor, a negative sequence virtual inductor, a negative sequence virtual resistor, a current positive sequence component and a current negative sequence component;
acquiring a second β axis voltage reference, and acquiring a first β axis voltage reference added with virtual impedance according to a second β axis voltage reference, a positive sequence virtual inductor, a positive sequence virtual resistor, a negative sequence virtual inductor, a negative sequence virtual resistor, a current positive sequence component and a current negative sequence component;
and obtaining the first zero-axis voltage reference added with the virtual impedance according to the zero-sequence virtual resistance and the zero-sequence current component.
Optionally, the obtaining of the second α -axis voltage reference and the second β -axis voltage reference comprises:
the local controller obtains a voltage amplitude value by using the reactive power through power droop, and obtains a second α -axis voltage reference and a second β -axis voltage reference after the first phase angle and the voltage amplitude value are subjected to dq conversion.
Optionally, the method for obtaining the current positive sequence component, the current negative sequence component, and the zero sequence current component includes:
the local controller converts three-phase current into α -axis current component, β -axis current component and zero-sequence current component through Clark conversion, extracts the α -axis current component sequentially through a second-order general integral orthogonal signal generator and a positive-negative sequence calculator to obtain a current positive-sequence component, and extracts the β -axis current component sequentially through the second-order general integral orthogonal signal generator and the positive-negative sequence calculator to obtain a current negative-sequence component.
Optionally, the method for controlling the voltage and the current by the local controller includes:
obtaining a α axis voltage outer ring according to the first α axis voltage reference and α axis voltage compensation quantity, controlling the α axis voltage outer ring by adopting quasi-proportional resonance, then subtracting a α axis current component, and obtaining a α axis modulation voltage reference by adopting a proportional control α axis current inner ring;
obtaining a β axis voltage outer ring according to the first β axis voltage reference and β axis voltage compensation quantity, controlling the β axis voltage outer ring by adopting quasi-proportional resonance, then subtracting a β axis current component, and obtaining a β axis modulation voltage reference by adopting a proportional control β axis current inner ring;
obtaining a zero-axis voltage outer ring according to the first zero-axis voltage reference and the zero-axis voltage compensation quantity, controlling the zero-axis voltage outer ring by adopting quasi-proportional resonance integral, then subtracting a zero-axis current component, and obtaining a zero-axis modulation voltage reference by adopting a proportional control zero-axis current inner ring;
and generating a driving signal by using the α axis modulation voltage reference, the β axis modulation voltage reference and the zero axis modulation voltage reference by using a sine pulse width modulation module, and controlling voltage and current according to the driving signal.
The application discloses a three-phase four-wire system converter parallel common coupling point voltage recovery control method, which compensates positive sequence, negative sequence and zero-axis voltage reference values in each three-phase four-wire system converter respectively, and realizes that the voltage of the common coupling point keeps a rated amplitude and three-phase symmetry under different load conditions.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a system configuration diagram of a parallel common coupling point of a three-phase four-wire system converter according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a PCC voltage extraction link in one embodiment of the present application;
FIG. 3 is a diagram illustrating a voltage compensation amount generation process for a PCC voltage according to an embodiment of the present application;
FIG. 4 is a schematic diagram of voltage recovery control in a local controller according to an embodiment of the present application;
FIG. 5 is a schematic diagram of a power droop link in one embodiment of the present application;
FIG. 6 is a schematic diagram of a current extraction stage according to an embodiment of the present application;
FIG. 7 is a schematic diagram of adding a dummy impedance element in one embodiment of the present application;
FIG. 8 is a schematic diagram of a voltage-current control link according to an embodiment of the present application;
FIG. 9 shows simulation results of magnitude variations of negative-sequence and zero-sequence currents and voltage unbalances in an embodiment of the present application;
fig. 10 is a simulation result of the pcc three-phase voltage and the inverter current in one embodiment of the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.
When the three-phase four-wire system converter is connected with the parallel system, the influence of unmatched line impedance can be reduced by reasonably designing the positive sequence virtual impedance, the negative sequence virtual impedance and the zero sequence virtual impedance, the uniform distribution of symmetrical and asymmetrical current in a steady state is realized, and the stability margin and the transient response capability of the system are ensured. However, the positive, negative and zero sequence virtual impedances all result in the pcc voltage distortion level increasing with load, with amplitude offset and asymmetric components. Aiming at the problem, the invention provides a voltage recovery control method based on low bandwidth communication, which is used for respectively compensating positive sequence, negative sequence and zero-axis voltage reference values in each three-phase four-wire system converter and realizing that the voltage of a public coupling point keeps the rated amplitude and three-phase symmetry under different load conditions.
As shown in fig. 1, in this embodiment, a parallel system formed by two converters is taken as an example, a local controller is disposed at each three-phase four-wire converter, the local controller implements control and protection functions of a single converter, and is connected to a microgrid central controller through low-bandwidth communication, for example, Controller Area Network (CAN) communication, the microgrid central controller is disposed at a common coupling point, collects voltages of the common coupling point and performs related processing to obtain positive-sequence, negative-sequence and zero-sequence voltage compensation signals, and transmits the signals to each local controller through CAN communication, and the local controller receives a recovery control instruction to implement recovery control of the voltages of the common coupling point, in fig. 1, an ac-side filter circuit in the three-phase four-wire converter employs L C L structure (L)1、L2、C、Rd) The filter capacitor midpoint and the DC bus midpoint pass through an inductor LnConnection of, Zline_1、Zline_2Is line impedance, Zload_aIs an alternating a-phase load.
The parallel common coupling point voltage recovery control method for the three-phase four-wire system converter disclosed by the embodiment comprises the following steps of:
and step S1, the microgrid central controller sequentially uses a second-order general quadrature signal generator (SOGI-QSG) and a positive-negative sequence calculator (PNSC) to extract voltage components of the point of common coupling, wherein the voltage components comprise a first voltage positive sequence component, a first voltage negative sequence component and a first voltage zero sequence component.
Step S2, the microgrid central controller performs phase locking on the first voltage positive sequence component to obtain a first phase angle of the first voltage positive sequence component.
Step S3, the microgrid central controller performs dq transformation on the first voltage positive sequence component in a rotating coordinate system determined by the first phase angle to obtain a second voltage positive sequence component, and performs dq transformation on the first voltage negative sequence component in a rotating coordinate system with the same frequency and opposite direction as the first voltage positive sequence component to obtain a second voltage negative sequence component; and carrying out dq transformation on the first voltage zero-sequence component in a rotating coordinate system determined by the first phase angle to obtain a second voltage zero-sequence component.
Referring to fig. 2, fig. 2 is a process of extracting and acquiring a voltage component from the pcc voltage by the microgrid central controller, where u in fig. 2abcIs the three-phase voltage at the point of common coupling, and generates αβ 0 voltage u under the coordinate system after transforming the matrix Tαβ0α Axis Voltage uαThe first voltage positive sequence component u _, is extracted by sequentially passing through SOGI-QSG (α) and PNSCα +And u \β +(u in the figure)αβ +) Then for the first voltage positive sequence component u _ \α +And u \β +Performing phase locking (P LL-pos) to obtain the frequency omega of the first voltage positive sequence componentPCC(ω in the figure) and a first phase angle θPCC(theta in the figure), and then the first voltage positive sequence component u _ \, is appliedα +And u \β +At the first phase angle thetaPCCDq transformation is carried out in the determined rotating coordinate system to obtain a second voltage positive sequence component uPCC_d +(u in the figure)d +) At the same time, β axis voltage u is appliedβThe first voltage negative sequence component u _, is extracted by sequentially passing through SOGI-QSG (β) and PNSCα -And u \β -(u in the figure)αβ -) The first voltage negative sequence component u _ \/is addedα -And u \β -At a rotating coordinate system (i.e., -theta) of same frequency and opposite direction to the first voltage positive sequence componentPCCDetermined rotating coordinate system) to obtain a second voltage negative sequence component uPCC_d -And uPCC_q -(u in the figure)dq -) (ii) a Finally, zero axis voltage u0Extracting by SOGI-QSG (0) to obtain a first voltage zero-sequence component u0(not shown in the figure), and converting the first voltage zero sequence component u0At a first phase angle thetaPCCDq transformation is carried out in the determined rotating coordinate system to obtain a second voltage zero sequence component uPCC_d_0And uPCC_q_0(u in the figure)dq_0). U in the figureα'，quα'，uβ'，quβ'，u0'，qu0' both are signal parameters generated by a second-order general quadrature signal generator (SOGI-QSG), and the specific method can refer to the prior art, and the application is not limited in detail.
And step S4, the microgrid central controller respectively performs proportional integral control and low-pass filtering on the second voltage positive sequence component, the second voltage negative sequence component and the second voltage zero sequence component in corresponding rotating coordinate systems to obtain a positive sequence voltage compensation quantity, a negative sequence voltage compensation quantity and a zero sequence voltage compensation quantity.
Referring to fig. 3, fig. 3 is a voltage compensation amount generating process, and in fig. 3, at a first phase angle θPCCThe determined rotation coordinate system corresponds to the second voltage positive sequence component u obtained in FIG. 2PCC_d +Proportional integral control (G) is performed in sequencesec) And low-pass filtering (L PF) to obtain a positive sequence voltage compensation ucomp_d +(ii) a At-theta of same frequency opposite to the first phase anglePCCThe determined rotation coordinate system corresponds to the second voltage negative sequence component u obtained in FIG. 2PCC_d -And uPCC_q -(u in the figure)PCC_dq -) Proportional integral control (G) is performed in sequencesec) And low-pass filtering (L PF) to obtain the negative-sequence voltage compensation ucomp_d -And ucomp_q -(u in the figure)comp_dq -) (ii) a At a first phase angle thetaPCCDetermining the zero sequence component u of the second voltage obtained in FIG. 2 in the rotating coordinate systemPCC_d_0And uPCC_q_0(u in the figure)PCC_dq_0) Proportional integral control (G) is performed in sequencesec) And low-pass filtering (L PF) to obtain zero-sequence voltage compensation ucomp_d_0And ucomp_q_0(u in the figure)comp_dp_0) Wherein, the reference value of the positive sequence d-axis component is the rated voltage amplitude U*And the reference values of the components of the negative sequence dq axis and the zero sequence dq axis are zero.
And step S5, the microgrid central controller sends the positive sequence voltage compensation quantity, the negative sequence voltage compensation quantity and the zero sequence voltage compensation quantity to the local controller.
In this step, the microgrid central controller transmits the positive sequence voltage compensation amount u obtained in step S4 through CAN communicationcomp_d -And ucomp_q -Negative sequence voltage compensation amount ucomp_d -And ucomp_q -And zero sequence voltage compensation ucomp_d_0And ucomp_q_0And sending the data to each local controller.
And step S6, the local controller acquires a second phase angle, performs inverse dq transformation on the positive sequence voltage compensation quantity according to a second phase angle to obtain a α axis positive sequence voltage compensation quantity and a β axis positive sequence voltage compensation quantity, performs inverse dq transformation on the negative sequence voltage compensation quantity according to the second phase angle to obtain a α axis negative sequence voltage compensation quantity and a β axis negative sequence voltage compensation quantity, synthesizes a α axis positive sequence voltage compensation quantity and a α axis negative sequence voltage compensation quantity to obtain a α axis voltage compensation quantity, synthesizes a β axis positive sequence voltage compensation quantity and an β axis negative sequence voltage compensation quantity to obtain a β axis voltage compensation quantity, performs inverse dq transformation on the zero sequence voltage compensation quantity according to the second phase angle, and obtains a zero axis voltage compensation quantity in a β 00 coordinate system after synthesis.
Referring to fig. 4, fig. 4 is a structural diagram of an algorithm of a voltage recovery control in a local controller, and in fig. 4, a positive sequence voltage compensation amount u obtained in fig. 3comp_d +Carrying out inverse dq transformation according to the second phase angle theta, namely dq transformation into αβ 0 coordinate system to obtain α axis positive sequence voltage compensation amount ucomp_α +And β axis positive sequence voltage compensation ucomp_β +The negative sequence voltage compensation u obtained in FIG. 3comp_dq -Carrying out inverse dq conversion according to-theta to obtain α axis negative sequence voltage compensation quantity ucomp_α -And β axis negative sequence voltage compensation ucomp_β -Zero sequence voltage compensation u obtained in FIG. 3comp_dp_0Performing inverse dq transformation according to the second phase angle theta to obtain ucomp_α_0And ucomp_β_0Finally, the α axis component α axis positive sequence voltage compensation quantity ucomp_α +And α Axis negative sequence Voltage Compensationucomp_α -The compensation values are combined to obtain α axis voltage compensation ucomp_αThe β axis component β axis positive sequence voltage compensation quantity ucomp_β +And β axis negative sequence voltage compensation ucomp_β -The compensation values are combined to obtain β axis voltage compensation ucomp_βCombining the zero-axis components to obtain the zero-axis voltage compensation ucomp_0。
Alternatively, the method for acquiring the second phase angle in step S6 may be obtained by:
calculating three-phase instantaneous active power and instantaneous reactive power under an αβ coordinate system;
after the instantaneous active power and the instantaneous reactive power are subjected to low-pass filtering, extracting an active component and a reactive component;
and the active component is subjected to power droop to obtain a voltage angular frequency, and the voltage angular frequency is subjected to integration and 2 pi residue taking to generate a second phase angle.
As shown in fig. 5, three-phase instantaneous active power P and instantaneous reactive power q are calculated under an αβ coordinate system, and the instantaneous active power P passes through a low-pass filtering link (L PF in the figure), so as to decouple the bandwidth of a power loop and a voltage-current loop, extract an active component P, and the active component P passes through a droop link (pfdrop) to obtain a voltage angular frequency ω, which is specifically obtained by using the following formula:
ω＝ω*+kPf(Pref-P) (1)；
wherein, ω is*To reference angular frequency, kPfFor Pf droop gain, PrefIs a reference active power.
After the voltage angular frequency omega rate is integrated (1/s) and 2 pi is subjected to residue taking (Mod (0-2 pi) in the graph), a second phase angle theta is generated; in this embodiment, since the phase angle deviation between the output of the inverter and the voltage at the pcc is small, it is considered that the second phase angle is approximately equal to the first phase angle, i.e. θ ≈ θPCCI.e. the rotational coordinate system defined by theta and thetaPCCThe determined rotational coordinate system remains coincident, -theta is determined as the rotational coordinate system and-thetaPCCThe determined rotational coordinate system remains consistent.
In addition, in fig. 5, the local controller obtains the voltage amplitude U through power droop (qudrop) by using the reactive power Q, and specifically obtains the voltage amplitude by using the following formula:
U＝U*+kQU(Qref-Q) (2)；
wherein, U*For voltage amplitude reference, kQUIs QU droop gain, QrefIs a reactive power reference.
The second phase angle theta and the voltage amplitude U are subjected to dq conversion to obtain a second α axis voltage reference Uα_refA second β axis voltage reference uβ_ref。
Optionally, this embodiment further discloses a link for the local controller to extract current to filter the inductor L2For example, referring to FIG. 6, the filter inductor L is first introduced2Three-phase current iL2_a、iL2_bAnd iL2_0Obtaining α axis current component i through Clark transformation (T is a transformation matrix in the figure)L2_αβ Axis Current component iL2_βAnd zero axis current component iL2_0Sequentially adopting a second-order general quadrature signal generator (SOGI-QSG (α)) and a positive-negative sequence calculator (PNSC) to extract the α axis current component to obtain a current positive sequence component iL2_α +And iL2_β +Sequentially adopting a second-order general quadrature signal generator (SOGI-QSG (β)) and a positive-negative sequence calculator (PNSC) to extract the β -axis current positive sequence component to obtain a current negative sequence component iL2_α -And iL2_β -. I in the figureL2α'，qiL2α'，iL2β'，qiL2β' both are signal parameters generated by a second-order general quadrature signal generator (SOGI-QSG), and the specific method can refer to the prior art, and the application is not limited in detail. Of course, other current extraction of the filter inductor may be extracted by the method disclosed with reference to fig. 6, and will not be described in detail herein.
Optionally, an embodiment of the present application further discloses that a method for adding a virtual impedance in the first α -axis voltage reference, the first β -axis voltage reference, and the first zero-axis voltage reference by using the local controller includes:
acquiring a second α axis voltage reference, and acquiring a first α axis voltage reference added with virtual impedance according to a second α axis voltage reference, a positive sequence virtual inductor, a positive sequence virtual resistor, a negative sequence virtual inductor, a negative sequence virtual resistor, a current positive sequence component and a current negative sequence component;
acquiring a second β axis voltage reference, and acquiring a first α axis voltage reference added with virtual impedance according to a second β axis voltage reference, a positive sequence virtual inductor, a positive sequence virtual resistor, a negative sequence virtual inductor, a negative sequence virtual resistor, a current positive sequence component and a current negative sequence component;
and obtaining the first zero-axis voltage reference added with the virtual impedance according to the zero-sequence virtual resistance and the zero-sequence current component.
In order to realize the equipartition of positive sequence, negative sequence and zero sequence currents when the impedance of the converter circuit is mismatched, a virtual impedance link is designed, referring to fig. 7, and a second α -axis voltage reference u in fig. 7α_refAnd a second β axis voltage reference uβ_refObtained in fig. 5, Lv +Is a positive sequence virtual inductor, Rv +Is a positive sequence virtual resistor Lv -Is a negative sequence virtual inductor, Rv -Is a negative sequence virtual resistance; rv_0Is a zero sequence virtual resistance, iL2_α +And iL2_β +Is the current positive sequence component, i, obtained in FIG. 6L2_α -And iL2_β -For the negative sequence component of the current obtained in fig. 6, according to the adding method in the figure, the first α -axis voltage reference u is finally obtainedα_ref', a first β axis voltage reference uβ_ref' and first zero-axis voltage reference u0_ref'。
Step S7, the local controller adds the α axis voltage compensation amount to the first α axis voltage reference after adding the virtual impedance, adds the β axis voltage compensation amount to the first β axis voltage reference after adding the virtual impedance, and adds the zero axis voltage compensation amount to the first zero axis voltage reference after adding the virtual impedance, so as to implement voltage and current control, and further implement compensation of voltage amplitude deviation and unbalance of the common coupling point.
Specifically, referring to fig. 8, fig. 8 is a structural diagram of a voltage and current control link, and optionally, the method for controlling the voltage and the current by the local controller includes:
as shown in FIG. 8, first α -axis voltage reference u added with virtual impedance is inputα_ref' and α Axis Voltage Compensation amount u obtained in FIG. 4comp_α(u in FIG. 8)c_α) Quasi-proportional resonant controller Gv_PRSubtracting the filter inductor L in the inverter from the output parameter1Component i of current at axis αL1_αThen, the signal is inputted to a proportional controller GiProportional controller GiThe output parameter is added with α shaft voltage compensation amount uc_αTo obtain α axis modulation voltage reference eα。
Similarly, a first β -axis voltage reference u added with a virtual impedance is inputβ_ref' and β Axis Voltage Compensation amount u obtained in FIG. 4comp_β(u in FIG. 8)c_β) Quasi-proportional resonant controller Gv_PRSubtracting the filter inductor L in the inverter from the output parameter1Component i of current at axis βL1_βThen, the signal is inputted to a proportional controller GiProportional controller GiThe output parameter is added with β shaft voltage compensation amount uc_βTo obtain β axis modulation voltage reference eβ。
Similarly, the first zero-axis voltage reference u added with the virtual impedance is input0_ref' and a zero-axis voltage compensation amount ucomp_0(u in FIG. 8)c_0) Quasi-proportional resonance integral control Gv_PIRSubtracting the filter inductor L in the inverter from the output parameter1Component i of the current in the zero axisL1_0Then, the signal is inputted to a proportional controller GiProportional controller GiThe output parameter is added with a zero-axis voltage compensation quantity uc_0Obtaining the zero-axis modulation voltage reference e0。
Finally, the α axis modulation voltage obtained above is referenced to eαβ Axis modulated Voltage reference eβAnd a zero-axis modulation voltage reference e0Input to a sinusoidal pulse width modulation module SPWM to obtain a conversionAnd the current transformer controls the voltage and the current according to the driving signal of each switching tube.
The application provides a method for realizing voltage recovery control of a common coupling point under the condition of maintaining current sharing precision, and the method for voltage recovery control of the parallel common coupling point of the three-phase four-wire system converter has the following beneficial effects:
1) the voltage compensation signal is converted into direct current for transmission, so that the reasonable utilization of low-bandwidth communication is ensured;
2) the voltage amplitude of the point of common coupling and three-phase symmetry recovery are realized, and the current sharing precision is not influenced.
3) The voltage recovery control method has good dynamic characteristics for voltage recovery control when unbalanced load is put into use.
The embodiment of the application also discloses a voltage recovery control method for the parallel common coupling point of the three-phase four-wire system converter through simulation verification, wherein a hardware loop and control parameters are shown in a table 1:
TABLE 1
Figure BDA0002483870210000081
First, the system positive sequence virtual reactance L is setv +1mH, negative sequence virtual resistance Rv -0.5 omega, zero sequence virtual resistance Rv_0The load of a phase is 10kW, the load of b phase is 13kW, and the load of c phase is 16kW, which are set to 1 omega. Simulation results are shown in FIG. 9, where the first graph from top to bottom in FIG. 9 is a graph of the magnitude of the negative-sequence current over time, I1 -And I2 -Respectively representing the negative sequence current amplitudes of the two converters; the second graph is a graph of the amplitude of the zero sequence current as a function of time, I1-0And I2-0Respectively representing zero sequence current amplitudes of the two converters; the third graph is a plot of the voltage amplitude at the point of common coupling versus time, VUF-Indicating the negative sequence voltage of the point of common coupling, VUF0Representing the pcc zero sequence voltage, it can be seen in fig. 9 that voltage recovery control is not enabled at time 0.5s and enabled at time 1 s. Voltage recovery controlDistribution error of negative sequence current before and after the enable is 0.13A and 0.14A, distribution error of zero sequence current is 0.31A and 0.34A, voltage VUF of point of common coupling-From 1.1% down to 0.56%, VUF0From 1.9% down to 0.3%. FIG. 10 is a simulation result of the three-phase voltage at the point of common coupling and the inverter current, and in FIG. 10, the first graph from the top to the bottom is a graph of the amplitude of the three-phase voltage at the point of common coupling with time before the voltage recovery control is enabled, uPCC-aRepresenting the amplitude of the phase voltage u at the point of common coupling aPCC-bRepresenting the b-phase voltage amplitude, u, of the point of common couplingPCC-cRepresenting the c phase voltage amplitude of the common coupling point; the second graph is a graph of the change of the amplitude of the three-phase voltage of the point of common coupling with time after the voltage recovery control is enabled, uPCC-aRepresenting the amplitude of the phase voltage u at the point of common coupling aPCC-bRepresenting the b-phase voltage amplitude, u, of the point of common couplingPCC-cRepresenting the c phase voltage amplitude of the common coupling point; the third graph is a graph of the time-dependent change in the three-phase current of the converter 1, iL2-1-aShowing phase a current, i, of the converter 1L2-1-bRepresenting the b-phase current, i, of the converter 1L2-1-cReferring to the c-phase current of the inverter 1, as shown in fig. 10, the three-phase voltage amplitudes at the pcc are 311/305/298V before the voltage recovery control is enabled, and the three-phase voltage amplitudes at the pcc are 311/313/309V after the voltage recovery control is enabled. Wherein, the evaluation indexes of the introduced voltage negative sequence content and zero sequence content are shown as formula (3), and | u in formula 3)+I is the positive sequence voltage amplitude, u-I is the negative sequence voltage amplitude, u0And | is zero sequence voltage amplitude:
Figure BDA0002483870210000091
the simulation results show that the voltage recovery control method for the common coupling point can realize the compensation of the voltage amplitude and the unbalance of the common coupling point under the unbalanced load, and hardly influences the current sharing precision.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.

Claims (6)

1. A three-phase four-wire system converter parallel common coupling point voltage recovery control method is applied to a system, the system comprises a local controller and a microgrid central controller which are connected in a low-broadband communication mode, the local controller is arranged at each three-phase four-wire system converter, and the microgrid central controller is arranged at a common coupling point;
the method comprises the following steps:
the microgrid central controller sequentially uses a second-order general integral orthogonal signal generator and a positive-negative sequence calculator to extract voltage components of the common coupling point, wherein the voltage components comprise a first voltage positive sequence component, a first voltage negative sequence component and a first voltage zero sequence component;
the microgrid central controller is used for carrying out phase locking on the first voltage positive sequence component to obtain a first phase angle of the first voltage positive sequence component;
the microgrid central controller performs dq transformation on the first voltage positive sequence component in a rotating coordinate system determined by the first phase angle to obtain a second voltage positive sequence component, and performs dq transformation on the first voltage negative sequence component in a rotating coordinate system with the same frequency and opposite direction as the first voltage positive sequence component to obtain a second voltage negative sequence component; carrying out dq transformation on the first voltage zero-sequence component in a rotating coordinate system determined by the first phase angle to obtain a second voltage zero-sequence component;
the microgrid central controller respectively performs proportional integral control and low-pass filtering on the second voltage positive sequence component, the second voltage negative sequence component and the second voltage zero sequence component in corresponding rotating coordinate systems to obtain a positive sequence voltage compensation quantity, a negative sequence voltage compensation quantity and a zero sequence voltage compensation quantity;
the microgrid central controller sends the positive sequence voltage compensation quantity, the negative sequence voltage compensation quantity and the zero sequence voltage compensation quantity to the local controller;
the local controller obtains a second phase angle, performs inverse dq transformation on the positive sequence voltage compensation quantity according to a second phase angle to obtain α axis positive sequence voltage compensation quantity and β axis positive sequence voltage compensation quantity, performs inverse dq transformation on the negative sequence voltage compensation quantity according to the second phase angle to obtain α axis negative sequence voltage compensation quantity and β axis negative sequence voltage compensation quantity, synthesizes α axis positive sequence voltage compensation quantity and α axis negative sequence voltage compensation quantity to obtain α axis voltage compensation quantity, synthesizes β axis positive sequence voltage compensation quantity and β axis negative sequence voltage compensation quantity to obtain β axis voltage compensation quantity, performs inverse dq transformation on the zero sequence voltage compensation quantity according to the second phase angle, and obtains a zero axis voltage compensation quantity under a β 00 coordinate system after synthesis;
the local controller adds the α shaft voltage compensation quantity to the first α shaft voltage reference added with the virtual impedance, adds the β shaft voltage compensation quantity to the first β shaft voltage reference added with the virtual impedance, and adds the zero shaft voltage compensation quantity to the first zero shaft voltage reference added with the virtual impedance, so that voltage and current control is realized, and further, the compensation of voltage amplitude deviation and unbalance of a common coupling point is realized.
2. The control method according to claim 1, wherein the specific method for the local controller to acquire the second phase angle comprises:
calculating three-phase instantaneous active power and instantaneous reactive power under an αβ coordinate system;
after the instantaneous active power and the instantaneous reactive power are subjected to low-pass filtering, extracting an active component and a reactive component;
and the active component is subjected to power droop to obtain a voltage angular frequency, and the voltage angular frequency is subjected to integration and 2 pi residue taking to generate a second phase angle.
3. The method of claim 2, wherein the method of the local controller adding a virtual impedance in the first α axis voltage reference, the first β axis voltage reference, and the first zero axis voltage reference comprises:
acquiring a second α axis voltage reference, and acquiring a first α axis voltage reference added with virtual impedance according to a second α axis voltage reference, a positive sequence virtual inductor, a positive sequence virtual resistor, a negative sequence virtual inductor, a negative sequence virtual resistor, a current positive sequence component and a current negative sequence component;
acquiring a second β axis voltage reference, and acquiring a first β axis voltage reference added with virtual impedance according to a second β axis voltage reference, a positive sequence virtual inductor, a positive sequence virtual resistor, a negative sequence virtual inductor, a negative sequence virtual resistor, a current positive sequence component and a current negative sequence component;
and obtaining the first zero-axis voltage reference added with the virtual impedance according to the zero-sequence virtual resistance and the zero-sequence current component.
4. The control method of claim 3, wherein the obtaining of the second α -axis voltage reference and the second β -axis voltage reference comprises:
the local controller obtains a voltage amplitude value by using the reactive power through power droop, and obtains a second α -axis voltage reference and a second β -axis voltage reference after the first phase angle and the voltage amplitude value are subjected to dq conversion.
5. The control method according to claim 3, wherein the method for obtaining the current positive sequence component, the current negative sequence component and the zero sequence current component comprises:
the local controller converts three-phase current into α -axis current component, β -axis current component and zero-sequence current component through Clark conversion, extracts the α -axis current component sequentially through a second-order general integral orthogonal signal generator and a positive-negative sequence calculator to obtain a current positive-sequence component, and extracts the β -axis current component sequentially through the second-order general integral orthogonal signal generator and the positive-negative sequence calculator to obtain a current negative-sequence component.
6. The control method of claim 3, wherein the method for controlling the voltage and current by the local controller comprises:
obtaining a α axis voltage outer ring according to the first α axis voltage reference and α axis voltage compensation quantity, controlling the α axis voltage outer ring by adopting quasi-proportional resonance, then subtracting a α axis current component, and obtaining a α axis modulation voltage reference by adopting a proportional control α axis current inner ring;
obtaining a β axis voltage outer ring according to the first β axis voltage reference and β axis voltage compensation quantity, controlling the β axis voltage outer ring by adopting quasi-proportional resonance, then subtracting a β axis current component, and obtaining a β axis modulation voltage reference by adopting a proportional control β axis current inner ring;
obtaining a zero-axis voltage outer ring according to the first zero-axis voltage reference and the zero-axis voltage compensation quantity, controlling the zero-axis voltage outer ring by adopting quasi-proportional resonance integral, then subtracting a zero-axis current component, and obtaining a zero-axis modulation voltage reference by adopting a proportional control zero-axis current inner ring;
and generating a driving signal by using the α axis modulation voltage reference, the β axis modulation voltage reference and the zero axis modulation voltage reference by using a sine pulse width modulation module, and controlling voltage and current according to the driving signal.
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