CN113193560A - Method for equally dividing harmonic power in island micro-grid - Google Patents

Method for equally dividing harmonic power in island micro-grid Download PDF

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CN113193560A
CN113193560A CN202110492104.9A CN202110492104A CN113193560A CN 113193560 A CN113193560 A CN 113193560A CN 202110492104 A CN202110492104 A CN 202110492104A CN 113193560 A CN113193560 A CN 113193560A
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harmonic
voltage
power supply
fundamental
distributed power
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CN113193560B (en
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李山林
楼冠男
顾伟
杨权
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Southeast University
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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
    • H02J3/01—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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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

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Abstract

The invention relates to the technical field of micro-grid operation control, and discloses a method for equally dividing harmonic power in an island micro-grid. Firstly, collecting local voltage and current information, obtaining a fundamental voltage reference value through droop control, and then obtaining fundamental voltage recovery and reactive power average compensation quantity; obtaining a fundamental voltage modulation wave through a fundamental control voltage current double ring; extracting each frequency harmonic in the local voltage and current based on MHSCO, and calculating each harmonic power; then, through a parallel harmonic control link, obtaining compensation quantities meeting harmonic current equalization and harmonic voltage recovery through a distributed average consistency algorithm and a containment method, and adding the harmonic compensation quantities to obtain a harmonic compensation total quantity; and superposing the fundamental voltage modulation wave and the total harmonic compensation quantity, and obtaining an SPWM control signal of the inverter through SPWM modulation. The method can accurately distribute the harmonic power among the distributed power supplies, effectively inhibit the output harmonic voltage, and has good precision and dynamic performance.

Description

Method for equally dividing harmonic power in island micro-grid
Technical Field
The invention relates to the technical field of micro-grid operation control, in particular to a method for equally dividing harmonic power in an island micro-grid.
Background
With the gradual depletion of fossil energy sources such as coal and petroleum, the world enters a key period of large-scale development and utilization of new energy. However, these renewable energy sources have limitations in land area, with significant dispersibility and instability. Most of these dispersed new energy sources are connected to the distribution grid through distributed generation. The micro-grid is an area autonomous grid system formed by various distributed power sources, distributed energy storage, loads and related monitoring and protecting devices. The method provides a new mode for the use of new energy distributed power generation. The micro-grid can be divided into a grid-connected micro-grid and an island micro-grid. And the grid-connected micro-grid is connected with the large power grid through a single point to transmit power. And the island-type micro-grid has small equivalent inertia due to the loss of the support of the voltage and the frequency of the large grid, is easily influenced by disturbance and is difficult to control.
Generally, distributed power supplies with power electronic interfaces are operated in parallel in a microgrid, and one of the main problems faced in microgrid applications is harmonic waves caused by nonlinear loads and inverter pulse width modulation, which have a great influence on the quality of electric energy. Droop control has traditionally been employed to improve flexibility, redundancy and scalability in microgrid systems, but it also has some significant limitations: 1) even if the distributed power sources are identical, the reactive and harmonic power distributions are poor due to the inconsistency of line impedance; 2) the frequency and voltage amplitude deviate from nominal values. Furthermore, the widespread use of non-linear loads inevitably produces voltage distortions that degrade system performance, especially when critical loads are present in the microgrid.
Several methods for harmonic power averaging and distortion reduction have been proposed, but most of them suffer from voltage quality degradation, high parameter dependence or complex control loops. Moreover, most distortion suppression in the field is based on the voltage of the PCC, and the corresponding research on the local output voltage of the distributed power supply is insufficient. Harmonic attenuation in PCC voltages may reduce output voltage distortion to some extent, but may not guarantee a total harmonic distortion of the output voltage below 5%. And because the contradiction exists between the complete suppression of the local harmonic voltage and the harmonic power sharing, no strategy can simultaneously solve the problems of accurate harmonic power sharing and output distortion compensation. Therefore, there is a need for a control scheme to improve these power quality issues of parallel distributed power supplies in a flexible, simple and efficient manner.
Disclosure of Invention
The invention aims to solve the technical problems of accurately sharing harmonic power according to capacity between distributed power supplies under the condition that nonlinear loads exist on the output sides of the distributed power supplies, effectively inhibiting harmonic waves of output voltage, and completing reactive power sharing and voltage amplitude recovery, thereby improving the electric energy quality of a micro-grid.
The invention adopts the following technical scheme for solving the technical problems: the invention designs a method for equally dividing harmonic power in an island micro-grid, which comprises the following steps:
step A: acquiring local voltage and current information through a local controller of the distributed power supply, obtaining a fundamental voltage reference value through droop control, and calculating to obtain compensation quantity required by reactive power sharing according to capacity and compensation quantity required by restoring global average voltage to a normal value of each distributed power supply based on a distributed communication network and a consistency algorithm;
and B: obtaining a fundamental wave voltage modulation wave through calculation of a fundamental wave control loop, a voltage outer ring and a current inner ring;
and C: based on a multi-harmonic observer, through a harmonic control link connected in parallel, obtaining compensation quantity meeting harmonic power average and harmonic voltage recovery compensation quantity through a distributed average consistency algorithm and a containment method, and adding the harmonic compensation quantities to obtain the total harmonic compensation quantity;
step D: and superposing the fundamental voltage modulation wave and the total harmonic compensation quantity, and obtaining the SPWM control signal of the inverter by an SPWM modulation method.
Further, a fundamental voltage reference value V is obtained in the step Ai fThe method comprises the following steps:
step A01: according to the following control method, the angular frequency reference value omega of the fundamental wave of the output voltage of the distributed power supply is calculatediAnd an amplitude reference value Vi：
Figure BDA0003052811880000021
Wherein, subscript i represents the ith distributed power supply; omegaiAnd ViThe reference value of the angular frequency and the reference value of the amplitude of the fundamental wave of the output voltage of the distributed power supply are respectively; omeganiAnd VniRespectively a rated voltage angular frequency and a rated amplitude; piAnd QiThe active power and the reactive power output by the inverter are respectively obtained through local voltage and current calculation; m isiAnd niThe droop coefficients for frequency and voltage, respectively.
Step A02: based on the distributed communication network, the compensation amount u required by the reactive power capacity sharing of each distributed power supply is calculated by using a consistency algorithmQi：
Figure BDA0003052811880000022
Wherein a isijIs a contiguous element of the distributed communication topology, aij>0 denotes DGiCan receive data from DGjOtherwise aij＝0；kQpAnd kQiProportional term and integral term of PI controller; cQIs the coupling gain; n is a radical ofiRepresenting the set of connections to the ith station distributed power supply.
Step A03: calculating the compensation amount u required for restoring the global average voltage to a normal value based on a dynamic consistency observervi：
Figure BDA0003052811880000023
Wherein the content of the first and second substances,
Figure BDA0003052811880000031
is the global average voltage; vioIs the distributed power supply output voltage amplitude; cEIs the gain factor; k is a radical ofViIs a voltage integral term; vrefIs the reference voltage for which convergence is expected.
Step A04: equally dividing reactive power of each distributed power supply by the compensation amount u required by capacityQiAnd the compensation amount u required to restore the global average voltage to a normal valueviAdding the compensation quantity required by the fundamental wave to obtain a reference value V of fundamental wave voltagei fCan be expressed as:
Vi f＝Vni-niQi+uQi+uViformula (4)
Further, a fundamental voltage modulated wave u is obtained in the step Bi fThe method comprises the following steps:
step B01: establishing a voltage outer loop control model in a fundamental wave control loop:
Figure BDA0003052811880000032
wherein the content of the first and second substances,
Figure BDA0003052811880000033
and
Figure BDA0003052811880000034
respectively representing reference values of the output current of the distributed power supply in a dq coordinate system; k is a radical ofupAnd kuiRespectively representing PI controller parameters of the voltage outer ring; viodAnd VioqRespectively representing reference values of the output voltage of the distributed power supply in a dq coordinate system; cfRepresenting the capacitance value of the LC filter of the distributed power supply connection.
Step B02: establishing a current inner loop control model in a fundamental wave control loop:
Figure BDA0003052811880000035
wherein the content of the first and second substances,
Figure BDA0003052811880000036
and
Figure BDA0003052811880000037
respectively representing the values of the fundamental wave voltage modulation waves of the distributed power supply in a dq coordinate system; k is a radical ofipAnd kiiPI controller parameters respectively representing current inner loops; i.e. iiodAnd iioqRespectively representing reference values of the output current of the distributed power supply in a dq coordinate system; l isfRepresenting the inductance value of the LC filter of the distributed power supply connection.
Step B03: will be provided with
Figure BDA0003052811880000038
And
Figure BDA0003052811880000039
obtaining a fundamental voltage modulation wave u under a three-phase coordinate system through inverse Park transformationi f。
Further, the harmonic power average compensation quantity obtained in the step C
Figure BDA00030528118800000310
The method comprises the following steps:
step C01: extracting harmonic components in output voltage and current of the distributed power supply based on a multiple harmonic observer (MHSCO):
Figure BDA00030528118800000311
wherein the content of the first and second substances,
Figure BDA00030528118800000312
is the current or voltage under investigationObserved values of the h-th harmonic of (a); v. ofkIs an input variable; omega and omegacThe fundamental frequency and the cut-off frequency, respectively; ts is the sampling period; m is the estimated number of major harmonics.
Step C02: calculating the harmonic power through the extracted accurate harmonic component:
Figure BDA0003052811880000041
wherein the content of the first and second substances,
Figure BDA0003052811880000042
and
Figure BDA0003052811880000043
are the true values of the fundamental voltage and the harmonic output current;
Figure BDA0003052811880000044
and
Figure BDA0003052811880000045
the h harmonic currents are extracted on the d and q axes, respectively.
Step C03: according to the consistency principle, harmonic power equalization can be achieved by comparing local harmonic power information of distributed power sources and adjacent nodes thereof, and compensation quantity meeting h-th harmonic power equalization is calculated according to the following formula:
Figure BDA0003052811880000046
wherein, ciAnd cjIs a parameter inversely proportional to the capacity of the ith and jth distributed power supplies; k is a radical ofHpAnd kHiIs the proportional and integral terms of the harmonic power averaging controller.
Further, in the step C, the harmonic voltage recovery compensation amount is calculated by the following formula
Figure BDA0003052811880000047
Figure BDA0003052811880000048
Figure BDA0003052811880000049
Wherein the content of the first and second substances,
Figure BDA00030528118800000410
is a harmonic voltage reference of h frequency; vi fAnd Vi hIs the fundamental and h-th harmonic voltage obtained by the MHSCO;
Figure BDA00030528118800000413
is a reference value for the selected h-th harmonic distortion; HDmaxIs the maximum allowable variation of harmonic distortion, typically chosen to be 5%; giIndicating whether the ith DG takes precedence, gi1 indicates that a critical load has been connected to DGiOtherwise gi＝0；khviIs the integral term of the harmonic voltage controller. It is noted that,
Figure BDA00030528118800000414
the choice of (a) is crucial. In general, for buses where critical loads are present,
Figure BDA00030528118800000415
select 0% if all HD are in HDmaxWithin the range, harmonic voltage control can be achieved. If a non-critical bus deviates from the limit, then
Figure BDA00030528118800000416
Will be relaxed so that the HD on all lines is at HDmaxWithin the range. In equation (10), the power quality of the bus containing the critical load is first guaranteed and all the voltage THD can be kept at [0, HDmax]Within.
Further, theIn step C, all the sub-distributed harmonic controllers are operated in parallel, and all the sub-harmonic compensation quantities are superposed through current loops to obtain the total harmonic compensation quantity
Figure BDA00030528118800000417
Figure BDA00030528118800000418
Wherein the content of the first and second substances,
Figure BDA00030528118800000419
is a current inner loop transfer function at different frequencies with filtered inductor current feedback for fast response.
Further, in the step D, the fundamental voltage modulation wave and the total harmonic compensation amount are added, and then the control signal of the inverter is obtained through SPWM modulation.
Has the advantages that: the invention discloses a method for equally dividing harmonic power in an island micro-grid, which has the following beneficial effects compared with the prior art: the method for distributed uniform distribution of harmonic power in the island microgrid provided by the invention considers the contradiction between harmonic power uniform distribution and harmonic voltage suppression, and provides a control scheme which can ensure accurate distribution of harmonic load power and can compensate local voltage distortion within a required range; the invention introduces a plurality of harmonic sequence component observers, so that each harmonic can be simultaneously processed in parallel; the invention provides convenience for flexible plug and play operation of the micro-grid based on a consistency algorithm. The control performance of the island micro-grid is improved, and the power quality is improved.
Drawings
FIG. 1 is a flow chart of a distributed harmonic power sharing and harmonic voltage suppressing method for an island micro-grid designed by the invention;
FIG. 2 is a microgrid simulation system employed in embodiments of the present invention;
FIG. 3 is a diagram of the effect of controlling the output voltage of each distributed power supply in the micro-grid;
FIG. 4 is a diagram of the effect of reactive power control output by each distributed power source in the microgrid;
FIG. 5 is a graph of the control effect of each distributed power source outputting fifth harmonic power in the micro-grid;
FIG. 6 is a graph of the effect of controlling the output of the seventh harmonic power of each distributed power source in the microgrid;
fig. 7a is an output voltage waveform when there is only droop control of the distributed power supply 1;
fig. 7b is the output voltage waveform when there is only droop control for the distributed power supply 2;
fig. 7c is the output voltage waveform when there is only droop control for the distributed power supply 3;
fig. 8a is an output voltage waveform of the distributed power supply 1 when harmonic voltage suppression is put into operation;
fig. 8b is an output voltage waveform of the distributed power supply 2 when harmonic voltage suppression is engaged;
fig. 8c is an output voltage waveform of the distributed power supply 3 when harmonic voltage suppression is put into operation;
fig. 9a is an output voltage waveform of the distributed power supply 1 when put into the proposed control strategy;
fig. 9b is an output voltage waveform of the distributed power supply 2 when put into the proposed control strategy;
fig. 9c is an output voltage waveform of the distributed power supply 3 when the proposed control strategy is engaged;
Detailed Description
The following description will explain embodiments of the present invention in further detail with reference to the accompanying drawings.
The invention designs a method for equally dividing harmonic power in an island micro-grid, which in practical application, as shown in figure 1, specifically comprises the following steps:
step A: acquiring local voltage and current information through a local controller of the distributed power supply, obtaining a fundamental voltage reference value through droop control, calculating to obtain compensation quantity meeting the requirement that fundamental voltage is restored to a normal value and reactive power of each distributed power supply is equally divided according to capacity based on a distributed communication network and a consistency algorithm, and then entering the step B;
in the step a, the reference value of the fundamental voltage is calculated according to the following steps a01 to a 04:
step A01: the control method comprises the following steps:
Figure BDA0003052811880000061
calculating to obtain the amplitude and the frequency reference value of the output voltage of the distributed power supply; wherein, subscript i represents the ith distributed power supply; omegaiAnd ViThe reference value of the angular frequency and the reference value of the amplitude of the fundamental wave of the output voltage of the distributed power supply are respectively; omeganiAnd VniRespectively a rated voltage angular frequency and a rated amplitude; piAnd QiThe active power and the reactive power output by the inverter are respectively obtained through local voltage and current calculation; m isiAnd niThe droop coefficients for frequency and voltage, respectively.
Step A02: based on a distributed communication network and a consistency algorithm:
Figure BDA0003052811880000062
calculating compensation amount u required by reactive power sharing of each distributed power supplyQi(ii) a Wherein a isijIs a contiguous element of the distributed communication topology, aij>0 denotes DGiCan receive data from DGjOtherwise aij＝0；kQpAnd kQiProportional term and integral term of PI controller; cQIs the coupling gain; n is a radical ofiRepresenting the set of connections to the ith station distributed power supply.
Step A03: based on a dynamic consistency observer:
Figure BDA0003052811880000063
calculating the compensation u needed to restore the global average voltageVi(ii) a Wherein the content of the first and second substances,
Figure BDA0003052811880000064
is the global average voltage; vioIs the distributed power supply output voltage amplitude; cEIs the gain factor; k is a radical ofViIs a voltage integral term; vrefIs the reference voltage for which convergence is expected.
Step A04: the compensation amount required by the fundamental wave is obtained by adding the reactive power average compensation amount and the global voltage recovery compensation amount, and the reference value of the fundamental wave voltage of the droop link is represented as follows:
Vi f＝Vni-niQi+uQi+uViformula (4)
And B: c, calculating a fundamental wave control loop, a voltage outer ring and a current inner ring to obtain a fundamental wave voltage modulation wave, and then entering the step C;
in the step B, the modulated wave of the fundamental voltage is calculated according to the following steps B01 to B03:
step B01: establishing a voltage outer loop control model in a fundamental wave control loop:
Figure BDA0003052811880000065
wherein the content of the first and second substances,
Figure BDA0003052811880000071
and
Figure BDA0003052811880000072
respectively representing reference values of the output current of the distributed power supply in a dq coordinate system; k is a radical ofupAnd kuiRespectively representing PI controller parameters of the voltage outer ring; viodAnd VioqRespectively representing reference values of the output voltage of the distributed power supply in a dq coordinate system; cfRepresenting the capacitance value of the LC filter of the distributed power supply connection.
Step B02: establishing a current inner loop control model in a fundamental wave control loop:
Figure BDA0003052811880000073
wherein the content of the first and second substances,
Figure BDA0003052811880000074
and
Figure BDA0003052811880000075
respectively representing the values of the fundamental wave voltage modulation waves of the distributed power supply in a dq coordinate system; k is a radical ofipAnd kiiPI controller parameters respectively representing current inner loops; i.e. iiodAnd iioqRespectively representing reference values of the output current of the distributed power supply in a dq coordinate system; l isfRepresenting the inductance value of the LC filter of the distributed power supply connection.
Step B03: will be provided with
Figure BDA0003052811880000076
And
Figure BDA0003052811880000077
obtaining a modulation wave u under a three-phase coordinate system through inverse Park transformationi f。
And C: on the basis of a multi-harmonic observer, through a harmonic control link connected in parallel, compensation quantities meeting harmonic power equalization and harmonic voltage recovery are obtained through a distributed average consistency algorithm and a containment method, harmonic compensation quantities of each time are added to obtain a harmonic compensation total quantity, and then the step D is carried out;
in the step C, the harmonic power average compensation amount is calculated according to the following steps C01 to C03:
step C01: extracting harmonic components in output voltage and current of the distributed power supply based on a multiple harmonic observer (MHSCO):
Figure BDA0003052811880000078
wherein the content of the first and second substances,
Figure BDA0003052811880000079
is an observed value of the h harmonic of the current or voltage under study; v. ofkIs an input variable; omega and omegacThe fundamental frequency and the cut-off frequency, respectively; ts is the sampling period; m is the estimated number of major harmonics.
Step C02: calculating the harmonic power through the extracted accurate harmonic component:
Figure BDA00030528118800000710
wherein the content of the first and second substances,
Figure BDA00030528118800000711
and
Figure BDA00030528118800000712
are the true values of the fundamental voltage and the harmonic output current;
Figure BDA00030528118800000713
and
Figure BDA00030528118800000714
the h harmonic currents are extracted on the d and q axes, respectively.
Step C03: following the consistency principle, the harmonic power equalization can be achieved by comparing the local harmonic power information of the distributed power sources and the adjacent nodes thereof according to the following formula:
Figure BDA00030528118800000715
calculating compensation quantity meeting h-th harmonic power average; wherein, ciAnd cjIs a parameter inversely proportional to the capacity of the ith and jth distributed power supplies; k is a radical ofHpAnd kHiIs the proportional and integral terms of the harmonic power averaging controller.
For local harmonic voltages, according to the following formula:
Figure BDA0003052811880000081
Figure BDA0003052811880000082
obtaining a compensation quantity of harmonic voltage suppression; wherein the content of the first and second substances,
Figure BDA0003052811880000083
is a harmonic voltage reference of h frequency; vi fAnd Vi hIs the fundamental and h-th harmonic voltage obtained by the MHSCO;
Figure BDA0003052811880000086
is a reference value for the selected h-th harmonic distortion; HDmaxIs the maximum allowable variation of harmonic distortion, typically chosen to be 5%; giIndicating whether the ith DG takes precedence, gi1 indicates that a critical load has been connected to DGiOtherwise gi＝0；khviIs the integral term of the harmonic voltage controller. It is noted that,
Figure BDA0003052811880000087
the choice of (a) is crucial. In general, for buses where critical loads are present,
Figure BDA0003052811880000088
select 0% if all HD are in HDmaxWithin the range, harmonic voltage control can be achieved. If a non-critical bus deviates from the limit, then
Figure BDA0003052811880000089
Will be relaxed so that the HD on all lines is at HDmaxWithin the range. In equation (10), the power quality of the bus containing the critical load is first guaranteed and all the voltage THD can be kept at [0, HDmax]Within.
Aiming at each distributed harmonic controller which runs in parallel, each harmonic compensation quantity passes through a current control loop and is superposed according to the following formula:
Figure BDA00030528118800000810
obtaining the total harmonic compensation amount; wherein the content of the first and second substances,
Figure BDA00030528118800000811
is a current inner loop transfer function at different frequencies with filtered inductor current feedback for fast response.
Step D: and superposing the fundamental voltage modulation wave and the total harmonic compensation quantity, and obtaining the SPWM control signal of the inverter by an SPWM modulation method.
Applying the designed technical scheme to the practice, as shown in fig. 2, the simulation system is that the microgrid is composed of three distributed power sources, DG1, DG2 and DG3 are connected to a common terminal (PCC) through respective connection impedances, wherein the three DGs have local nonlinear loads with different sizes. The rated active and reactive capacities of the three distributed power supplies are equal, and the load at the common end adopts an impedance type load. According to the island microgrid distributed harmonic power sharing and harmonic voltage suppression method, a simulation microgrid model is built based on an MATLAB/Simulink platform, and the control effect of the method is verified.
Fig. 3 to 9 show simulation results of the microgrid control in the present embodiment. At the beginning of operation, each distributed power supply operates in a droop control mode. To show the contradiction between harmonic power averaging and local harmonic suppression, only the harmonic voltage suppression strategy was applied at 4s, and then the proposed strategy was applied at 7 s. The simulation results are shown in fig. 3 to fig. 9, where fig. 3 is a graph of the control effect of the output voltage of each distributed power supply in the microgrid, and the abscissa represents time, unit: second, ordinate represents output voltage, unit: volts. As can be seen from fig. 3, each distributed power source initially deviates from the rated value by the droop control, and the average value of the output voltage is raised to the rated voltage value by the fundamental voltage recovery control after 7 seconds. Fig. 4 is a diagram of reactive power control effect of each distributed power supply output in the microgrid, and the abscissa represents time in unit: second, the ordinate represents the reactive power, in units: it is used for treating chronic hepatitis B. As shown in fig. 4, initially, the reactive power output by each distributed power source does not reach the capacity sharing, and after 7s, the reactive power output by each distributed power source reaches the uniform value under the control of the reactive power sharing. Fig. 5 is a control effect graph of five harmonic power output by each distributed power supply in the microgrid, wherein an abscissa represents time in units of: second, the ordinate represents the reactive power, in units: and (4) tile. And 4s, after the harmonic voltage complete suppression strategy is put into operation, the harmonic power output by each distributed power supply is greatly increased and is not equally divided according to the capacity, and 7s, after the harmonic power equal division strategy is put into operation, the fifth harmonic power output by each distributed power supply reaches a consistent value. Fig. 6 is a diagram of the control effect of each distributed power source outputting seventh harmonic power in the microgrid, and the abscissa represents time in units: second, the ordinate represents the reactive power, in units: and (4) tile. And 4s, after the harmonic voltage complete suppression strategy is put into use, the harmonic power output by each distributed power supply is greatly increased and is not evenly divided according to the capacity, and 7s, after the harmonic power evenly dividing strategy is put into use, the seventh harmonic power output by each distributed power supply reaches a consistent value.
As can be seen from fig. 3 to 6, at the start of operation, the voltage amplitude, reactive and harmonic power averaging all failed. Fig. 7 shows output voltage waveforms when only droop control is present in each distributed power supply, and the abscissa represents time in units of: second, ordinate represents voltage, unit: volts. As shown in fig. 7, prior to running the harmonic rejection scheme, the output voltage of each distributed power supply is distorted by 6.7%, 7.8%, and 6.93%, respectively, of Total Harmonic Distortion (THD), 5% above the standard limit. In the second stage, fig. 8 shows the output voltage waveform of each distributed power supply when harmonic voltage suppression is applied, and the abscissa represents time in units of: second, ordinate represents voltage, unit: volts. As shown in fig. 8, the harmonic waves output by each distributed power supply are greatly suppressed, which are 1.44%, 1.81% and 2.01%, respectively, and theoretically, the voltage THD can be reduced to zero; however, only the 5 and 7 th harmonic voltage controllers are considered in this embodiment, excluding all harmonic controllers. Meanwhile, during [4s, 7s ], the poor harmonic power distribution is severely exacerbated, as shown in fig. 5 and 6, which shows the contradiction between harmonic power averaging and local harmonic voltage suppression. For the third stage after 7s, fig. 9 is a graph of the output voltage waveform of each distributed power supply when put into the proposed control strategy, with the abscissa representing time in units: second, ordinate represents voltage, unit: volts. As shown in fig. 3-6, after a brief transient duration, the output voltage increases with the average to the nominal value and the harmonic power distribution error is eliminated. Taking the voltage THD of the distributed power supply 3 as a priority bus, and then the voltages of the distributed power supplies 1 and 2 are close to each other, the output voltages THD of the distributed power supplies 1 and 2 are increased from 1.44% to 2.08% and from 1.81% to 3.62%, respectively, which is still within an acceptable range. Thus, the effectiveness of the proposed harmonic control scheme is verified.
The control method for the distributed equalization of the harmonic power and the suppression of the harmonic voltage of the island micro-grid, provided by the invention, considers the contradiction between the harmonic power equalization and the harmonic voltage suppression, provides a control scheme which can ensure the accurate distribution of the harmonic load power and can compensate the local voltage distortion within the required range, and provides a comprehensive method for the harmonic power equalization and the local harmonic voltage suppression; the invention introduces a plurality of harmonic sequence component observers, so that each harmonic can be simultaneously processed in parallel; the invention provides convenience for flexible plug and play operation of the micro-grid based on a consistency algorithm. The control performance of the island micro-grid is improved, and the power quality is improved.
The embodiments of the present invention are described in detail above with reference to the accompanying drawings. It will be understood by those skilled in the art that the present invention is not limited by the foregoing examples, which are provided to illustrate the principles of the invention, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is also within the scope of the invention as claimed.

Claims (7)

1. A method for equally dividing harmonic power in an island micro-grid is characterized by comprising the following steps:
step A: acquiring local voltage and current information through a local controller of the distributed power supply, obtaining a fundamental voltage reference value through droop control, and calculating to obtain compensation quantity required by reactive power sharing according to capacity and compensation quantity required by restoring global average voltage to a normal value of each distributed power supply based on a distributed communication network and a consistency algorithm;
and B: obtaining a fundamental wave voltage modulation wave through calculation of a fundamental wave control loop, a voltage outer ring and a current inner ring;
and C: based on a multi-harmonic observer, through a harmonic control link connected in parallel, obtaining compensation quantity meeting harmonic power average and harmonic voltage recovery compensation quantity through a distributed average consistency algorithm and a containment method, and adding the harmonic compensation quantities to obtain the total harmonic compensation quantity;
step D: and superposing the fundamental voltage modulation wave and the total harmonic compensation quantity, and obtaining the SPWM control signal of the inverter by an SPWM modulation method.
2. The method for sharing harmonic power in an island micro-grid according to claim 1, wherein the fundamental voltage reference value V obtained in the step A is obtainedi fThe method comprises the following steps:
step A01: according to the following control method, the angular frequency reference value omega of the fundamental wave of the output voltage of the distributed power supply is calculatediAnd an amplitude reference value Vi：
Figure FDA0003052811870000011
Wherein, subscript i represents the ith distributed power supply; omegaiAnd ViThe reference value of the angular frequency and the reference value of the amplitude of the fundamental wave of the output voltage of the distributed power supply are respectively; omeganiAnd VniRespectively a rated voltage angular frequency and a rated amplitude; piAnd QiActive power and reactive power of inverter output calculated by local voltage and currentWork power; m isiAnd niThe droop coefficients for frequency and voltage, respectively.
Step A02: based on the distributed communication network, the compensation amount u required by the reactive power capacity sharing of each distributed power supply is calculated by using a consistency algorithmQi：
Figure FDA0003052811870000012
Wherein a isijIs a contiguous element of the distributed communication topology, aij>0 denotes DGiCan receive data from DGjOtherwise aij＝0；kQpAnd kQiProportional term and integral term of PI controller; cQIs the coupling gain; n is a radical ofiRepresenting the set of connections to the ith station distributed power supply.
Step A03: calculating the compensation amount u required for restoring the global average voltage to a normal value based on a dynamic consistency observervi：
Figure FDA0003052811870000021
Wherein the content of the first and second substances,
Figure FDA0003052811870000022
is the global average voltage; vioIs the distributed power supply output voltage amplitude; cEIs the gain factor; k is a radical ofViIs a voltage integral term; vrefIs the reference voltage for which convergence is expected.
Step A04: equally dividing reactive power of each distributed power supply by the compensation amount u required by capacityQiAnd the compensation amount u required to restore the global average voltage to a normal valueviAdding the compensation quantity required by the fundamental wave to obtain a reference value V of fundamental wave voltagei fCan be expressed as:
Vi f＝Vni-niQi+uQi+uViformula (II)(4)
3. The method according to claim 1, wherein the fundamental voltage modulation wave u obtained in the step B is a fundamental voltage modulation wave ui fThe method comprises the following steps:
step B01: establishing a voltage outer loop control model in a fundamental wave control loop:
Figure FDA0003052811870000023
wherein the content of the first and second substances,
Figure FDA0003052811870000024
and
Figure FDA0003052811870000025
respectively representing reference values of the output current of the distributed power supply in a dq coordinate system; k is a radical ofupAnd kuiRespectively representing PI controller parameters of the voltage outer ring; viodAnd VioqRespectively representing reference values of the output voltage of the distributed power supply in a dq coordinate system; cfRepresenting the capacitance value of the LC filter of the distributed power supply connection.
Step B02: establishing a current inner loop control model in a fundamental wave control loop:
Figure FDA0003052811870000026
wherein the content of the first and second substances,
Figure FDA0003052811870000027
and
Figure FDA0003052811870000028
respectively representing the values of the fundamental wave voltage modulation waves of the distributed power supply in a dq coordinate system; k is a radical ofipAnd kiiPI controller parameters representing the current inner loop, respectively；iiodAnd iioqRespectively representing reference values of the output current of the distributed power supply in a dq coordinate system; l isfRepresenting the inductance value of the LC filter of the distributed power supply connection.
Step B03: will be provided with
Figure FDA0003052811870000029
And
Figure FDA00030528118700000210
obtaining a fundamental voltage modulation wave u under a three-phase coordinate system through inverse Park transformationi f。
4. The method for sharing harmonic power in an island micro-grid according to claim 1, wherein the harmonic power sharing compensation quantity obtained in the step C is obtained
Figure FDA00030528118700000211
The method comprises the following steps:
step C01: extracting harmonic components in output voltage and current of the distributed power supply based on a multiple harmonic observer (MHSCO):
Figure FDA0003052811870000031
wherein the content of the first and second substances,
Figure FDA0003052811870000032
is an observed value of the h harmonic of the current or voltage under study; v. ofkIs an input variable; omega and omegacThe fundamental frequency and the cut-off frequency, respectively; ts is the sampling period; m is the estimated number of major harmonics.
Step C02: calculating the harmonic power through the extracted accurate harmonic component:
Figure FDA0003052811870000033
wherein the content of the first and second substances,
Figure FDA0003052811870000034
and
Figure FDA0003052811870000035
are the true values of the fundamental voltage and the harmonic output current;
Figure FDA0003052811870000036
and
Figure FDA0003052811870000037
the h harmonic currents are extracted on the d and q axes, respectively.
Step C03: according to the consistency principle, harmonic power equalization can be achieved by comparing local harmonic power information of distributed power sources and adjacent nodes thereof, and compensation quantity meeting h-th harmonic power equalization is calculated according to the following formula:
Figure FDA0003052811870000038
wherein, ciAnd cjIs a parameter inversely proportional to the capacity of the ith and jth distributed power supplies; k is a radical ofHpAnd kHiIs the proportional and integral terms of the harmonic power averaging controller.
5. The method for sharing harmonic power in an island micro-grid according to claim 1, wherein in the step C, the harmonic voltage recovery compensation amount is calculated by the following formula
Figure FDA0003052811870000039
Figure FDA00030528118700000310
Figure FDA00030528118700000311
Wherein the content of the first and second substances,
Figure FDA00030528118700000312
is a harmonic voltage reference of h frequency;
Figure FDA00030528118700000313
and
Figure FDA00030528118700000314
is the fundamental and h-th harmonic voltage obtained by the MHSCO;
Figure FDA00030528118700000315
is a reference value for the selected h-th harmonic distortion; HDmaxIs the maximum allowable variation of harmonic distortion, typically chosen to be 5%; giIndicating whether the ith DG takes precedence, gi1 indicates that a critical load has been connected to DGiOtherwise gi＝0；khviIs the integral term of the harmonic voltage controller. It is noted that,
Figure FDA00030528118700000316
the choice of (a) is crucial. In general, for buses where critical loads are present,
Figure FDA00030528118700000317
select 0% if all HD are in HDmaxWithin the range, harmonic voltage control can be achieved. If a non-critical bus deviates from the limit, then
Figure FDA00030528118700000318
Will be relaxed so that the HD on all lines is at HDmaxWithin the range. In the formula (10), the power quality of the bus including the critical load is first ensured, andand all the voltage THD can be kept at 0, HDmax]Within.
6. The method according to claim 1, wherein in step C, the sub-distributed harmonic controllers are operated in parallel, and the sub-harmonic compensation quantities are obtained by current loop and superposition to obtain a total harmonic compensation quantity
Figure FDA0003052811870000041
Figure FDA0003052811870000042
Wherein the content of the first and second substances,
Figure FDA0003052811870000043
is a current inner loop transfer function at different frequencies with filtered inductor current feedback for fast response.
7. The method for sharing harmonic power in an island micro-grid according to claim 1, wherein in step D, the fundamental voltage modulation wave and the total harmonic compensation amount are added, and then the control signal of the inverter is obtained through SPWM modulation.
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