CN110676878A - Multi-target current reference instruction calculation method and system suitable for non-ideal power grid - Google Patents

Multi-target current reference instruction calculation method and system suitable for non-ideal power grid Download PDF

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CN110676878A
CN110676878A CN201910983403.5A CN201910983403A CN110676878A CN 110676878 A CN110676878 A CN 110676878A CN 201910983403 A CN201910983403 A CN 201910983403A CN 110676878 A CN110676878 A CN 110676878A
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power grid
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闫涵
王新杰
芮苏媛
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Nanjing Tech 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • 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
    • Y02E40/30—Reactive power compensation
    • 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

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Abstract

The invention discloses a multi-target current reference instruction calculation method and system suitable for a non-ideal power grid. The system comprises a three-phase three-level grid-connected inverter and a digital calculation processing module, wherein the digital calculation processing module comprises a sampling unit, a phase locking unit, a harmonic component extraction unit and a current reference instruction calculation unit. The method comprises the following steps: the sampling unit collects three-phase power grid voltage information, the phase-locking unit obtains power grid voltage phase information, the harmonic component extraction unit extracts harmonic component information in non-ideal power grid voltage, and then the current reference instruction calculation unit calculates current reference instructions under three power and current control targets respectively based on an instantaneous reactive power theory. The method has low hardware cost, can realize the current reference calculation of various control targets of the NPC three-phase three-level inverter under the non-ideal power grid condition, is suitable for various power application occasions, and improves the network access electric energy quality of the inverter.

Description

Multi-target current reference instruction calculation method and system suitable for non-ideal power grid
Technical Field
The invention relates to the technical field of direct current-alternating current converters of electric energy conversion devices, in particular to a multi-target current reference instruction calculation method and system suitable for a non-ideal power grid.
Background
The NPC (neutral Point clamped) three-phase three-level grid-connected inverter plays a role of an energy conversion interface in a distributed grid-connected power generation system, and the working state of the three-phase three-level grid-connected inverter has a great influence on the quality of electric energy entering a power grid. Under ideal grid conditions, the grid voltage only contains a fundamental frequency positive sequence, and the existing current reference instruction is generally given by directly using sinusoidal current.
However, most of the actual grid conditions are non-ideal, and common non-ideal grid voltages contain fundamental frequency negative sequence components, 5 frequency multiplication negative sequence components, 7 frequency multiplication positive sequence components and the like besides fundamental frequency positive sequence components, so that pulsation of various frequencies occurs in active power and reactive power, and at the moment, the sinusoidal current setting cannot meet the requirement of suppressing power pulsation. In order to adapt to different power control application occasions under the non-ideal power grid condition, a current reference instruction calculation method which is suitable for the non-ideal power grid and has various control targets needs to be adopted.
Disclosure of Invention
The invention aims to provide a multi-target current reference instruction calculation method and a multi-target current reference instruction calculation system which are suitable for three-phase non-ideal power grid conditions and can perform good grid-connected control on an NPC three-phase inverter, so that the quality of power energy entering a grid is improved, and low-frequency pulsation of active power and reactive power can be effectively inhibited.
The technical solution for realizing the purpose of the invention is as follows: a multi-target current reference instruction calculation method suitable for a non-ideal power grid comprises the following steps:
step 1, sampling a three-phase non-ideal grid voltage signal e at the AC side of a three-phase three-level grid-connected invertera、eb、ecAnd performing Clark conversion on the three-phase non-ideal power grid voltage to obtain a three-phase non-ideal power grid voltage signal e under an alpha beta coordinate systemα、eβ；
Step 2, obtaining fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage;
step 3, performing different frequency multiplication and different direction rotation transformation on the three-phase non-ideal power grid voltage by using the fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage, and filtering alternating current components by using traps with different frequencies to obtain harmonic component information in the three-phase non-ideal power grid voltage;
and 4, respectively calculating current reference instructions under three control targets of networking current sine, active power pulsation suppression and reactive power pulsation suppression based on an instantaneous reactive power theory according to the harmonic component information.
Further, the step 1 is to sample a three-phase non-ideal grid voltage signal e at the alternating current side of the three-phase three-level grid-connected invertera、eb、ecSpecifically, the following are defined:
Figure BDA0002235943480000021
Figure BDA0002235943480000022
Figure BDA0002235943480000023
in the formula, e+、e-、e5-、e7+The three-phase non-ideal power grid voltage respectively comprises a fundamental frequency positive sequence component, a fundamental frequency negative sequence component, a 5 frequency multiplication negative sequence component and a 7 frequency multiplication positive sequence component; wherein subscripts a, b, c represent a phase a, b phase, c phase, respectively;
clark conversion is carried out on the three-phase non-ideal power grid voltage to obtain a three-phase non-ideal power grid voltage signal e under an alpha beta coordinate systemα、eβComprises the following steps:
Figure BDA0002235943480000024
further, step 3, performing different frequency multiplication and different direction rotation transformation on the three-phase non-ideal grid voltage by using the fundamental frequency positive sequence phase information of the three-phase non-ideal grid voltage, and then respectively filtering the alternating current components by using traps with different frequencies to obtain harmonic component information in the three-phase non-ideal grid voltage, wherein the process specifically comprises the following steps:
for three-phase non-ideal network voltage signal eα、eβCarrying out fundamental frequency positive sequence rotation transformation, and respectively filtering 2-time and 6-time alternating current components by using a wave trap to obtain three-phase non-ideal power grid voltage fundamental frequency positive sequence components
Figure BDA0002235943480000025
Respectively at dq+Projection of a coordinate system
Figure BDA0002235943480000026
For three-phase non-ideal network voltage signal eα、eβCarrying out fundamental frequency negative sequence rotation transformation, and respectively filtering out 2-time, 4-time and 8-time alternating current components by using a wave trap to obtain a power grid voltage fundamental frequency negative sequence componentRespectively at dq-Projection of a coordinate system
Figure BDA0002235943480000028
For three-phase non-ideal network voltage signal eα、eβCarrying out 5-time frequency negative sequence rotation transformation, and respectively filtering 4 times, 6 times and 8 times of alternating current components by using a wave trap to obtain 5-time frequency negative sequence components of the grid voltage
Figure BDA0002235943480000029
Respectively at dq5-Projection of a coordinate system
Figure BDA00022359434800000210
For three-phase non-ideal network voltage signal eα、eβCarrying out 7-time frequency positive sequence rotation conversion, and respectively filtering 6-time, 8-time and 12-time alternating current components by using a wave trap to obtain a power grid voltage 7-time frequency positive sequence component
Figure BDA00022359434800000211
Respectively at dq7+Projection of a coordinate system
Figure BDA00022359434800000212
Further, step 4, according to the harmonic component information, based on the instantaneous reactive power theory, calculating current reference commands under three control targets of network access current sine, active power pulsation suppression and reactive power pulsation suppression, respectively, and the process specifically includes:
(1) under the condition of a three-phase non-ideal power grid, establishing a grid-connected current expression under an alpha and beta coordinate system as follows:
Figure BDA0002235943480000031
in the formula i+、i-、i5-、i7+Respectively a fundamental frequency positive sequence component, a fundamental frequency negative sequence component, a 5 frequency multiplication negative sequence component and a 7 frequency multiplication positive sequence component contained in the network access current;
the sequential components of the network current are similar to the three-phase non-ideal network voltage
Figure BDA0002235943480000032
Figure BDA0002235943480000033
The projections of the rotating coordinate system in their corresponding order are respectively
Figure BDA0002235943480000034
(2) According to the instantaneous reactive theory, active power and reactive power respectively contain power pulsation of 2-frequency multiplication, 4-frequency multiplication, 6-frequency multiplication, 8-frequency multiplication and 12-frequency multiplication generated by cross multiplication of three-phase non-ideal grid voltage and grid-connected current, and current reference value calculation formulas under different control targets can be obtained by selectively inhibiting the power pulsation of different frequency multiplications:
aiming at a grid-connected control target I: three-phase network access current is sinusoidal and balanced;
under the condition of a three-phase non-ideal power grid, reference values of each harmonic and positive-negative sequence components of the grid-connected current are as follows:
Figure BDA0002235943480000035
in the formula (I), the compound is shown in the specification,respectively representing projection reference values of each sequence component of the network access current in a corresponding sequence rotation coordinate system;
Figure BDA0002235943480000037
and
Figure BDA0002235943480000038
respectively representing the direct current reference values of active power and reactive power;
aiming at a grid-connected control target II: inhibiting the fluctuation of active power frequency multiplication 2, 4 and 6;
under the condition of a three-phase non-ideal power grid, reference values of each harmonic and positive-negative sequence components of the grid-connected current are as follows:
Figure BDA0002235943480000041
aiming at a grid-connected control target III: reactive power 2 frequency multiplication, 4 frequency multiplication and 6 frequency multiplication fluctuation are inhibited;
under the condition of a three-phase non-ideal power grid, reference values of each harmonic and positive-negative sequence components of the grid-connected current are as follows:
Figure BDA0002235943480000042
wherein A, B, C are respectively:
Figure BDA0002235943480000051
a multi-target current reference instruction computing system suitable for a non-ideal power grid comprises a three-phase three-level grid-connected inverter and a digital computing processing module, wherein the digital computing processing module comprises a sampling unit, a phase locking unit, a harmonic component extraction unit and a current reference instruction computing unit;
the sampling unit is used for collecting a three-phase non-ideal power grid voltage signal at the AC side of the three-phase three-level grid-connected inverter and sending the signal to the phase-locking unit;
the phase locking unit is used for acquiring fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage according to the three-phase non-ideal power grid voltage signal obtained by sampling and sending the information to the harmonic component extraction unit;
the harmonic component extraction unit is used for extracting harmonic component information in the three-phase non-ideal power grid voltage according to the power grid voltage fundamental frequency positive sequence phase information and sending the harmonic component information to the current reference instruction calculation unit;
and the current reference instruction calculating unit is used for calculating current reference instructions under three power and current control targets respectively based on an instantaneous reactive power theory according to the harmonic component information.
Compared with the prior art, the invention has the following remarkable advantages: 1) the method can be suitable for non-ideal power grid conditions, improves the quality of the power energy of the power grid, and effectively inhibits power pulsation at the same time; 2) the method is simple and reliable, is easy to realize digitally, and can realize various different grid-connected control targets only by correspondingly modifying a software algorithm.
The present invention is described in further detail below with reference to the attached drawing figures.
Drawings
FIG. 1 is a schematic diagram of a multi-target current reference command calculation system suitable for a non-ideal power grid according to the present invention.
Fig. 2 is a schematic diagram of a main power circuit of the NPC three-phase three-level grid-connected inverter.
FIG. 3 is a schematic diagram of a harmonic component extracting unit according to the present invention.
Fig. 4 is a simulation result diagram of embodiment 1 of the present invention, in which (a) is a schematic diagram of a reference network access current and an actual network access current, (b) is a schematic diagram of a network access current FFT analysis, (c) is a schematic diagram of a network access instantaneous active power, and (d) is a schematic diagram of a network access instantaneous reactive power.
Fig. 5 is a simulation result diagram of embodiment 2 of the present invention, in which (a) is a schematic diagram of a reference network access current and an actual network access current, (b) is a schematic diagram of a network access instantaneous active power, (c) is a schematic diagram of a network access instantaneous active power FFT analysis, and (d) is a schematic diagram of a network access instantaneous reactive power.
Fig. 6 is a simulation result diagram of embodiment 3 of the present invention, in which (a) is a schematic diagram of a reference network access current and an actual network access current, (b) is a schematic diagram of a network access instantaneous active power, (c) is a schematic diagram of a network access instantaneous reactive power, and (d) is a schematic diagram of a network access instantaneous reactive power FFT analysis.
Detailed Description
The invention provides a multi-target current reference instruction calculation method suitable for a non-ideal power grid, which comprises the following steps of:
step 1, sampling a three-phase non-ideal grid voltage signal e at the AC side of a three-phase three-level grid-connected invertera、eb、ecAnd performing Clark conversion on the three-phase non-ideal power grid voltage to obtain a three-phase non-ideal power grid voltage signal e under an alpha beta coordinate systemα、eβ；
Step 2, obtaining fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage;
step 3, performing different frequency multiplication and different direction rotation transformation on the three-phase non-ideal power grid voltage by using the fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage, and filtering alternating current components by using traps with different frequencies to obtain harmonic component information in the three-phase non-ideal power grid voltage;
and 4, respectively calculating current reference instructions under three control targets of networking current sine, active power pulsation suppression and reactive power pulsation suppression based on an instantaneous reactive power theory according to the harmonic component information.
Further, in the step 1, a three-phase non-ideal grid voltage signal e at the alternating current side of the three-phase three-level grid-connected inverter is sampleda、eb、ecSpecifically, the following are defined:
Figure BDA0002235943480000061
Figure BDA0002235943480000062
in the formula, e+、e-、e5-、e7+The three-phase non-ideal power grid voltage respectively comprises a fundamental frequency positive sequence component, a fundamental frequency negative sequence component, a 5 frequency multiplication negative sequence component and a 7 frequency multiplication positive sequence component; wherein subscripts a, b, c represent a phase a, b phase, c phase, respectively;
clark conversion is carried out on the three-phase non-ideal power grid voltage to obtain a three-phase non-ideal power grid voltage signal e under an alpha beta coordinate systemα、eβComprises the following steps:
Figure BDA0002235943480000064
further preferably, the three-phase non-ideal power grid voltage fundamental frequency positive sequence phase information is acquired in step 2, and specifically, the three-phase non-ideal power grid voltage fundamental frequency positive sequence phase information is acquired by using a bi-quad generalized integral software phase-locked loop.
Further, step 3 utilizes the fundamental frequency positive sequence phase information of the three-phase non-ideal grid voltage to perform different frequency multiplication and rotation transformation in different directions on the three-phase non-ideal grid voltage, and then respectively utilizes wave traps with different frequencies to filter alternating current components to obtain harmonic component information in the three-phase non-ideal grid voltage, and in combination with fig. 3, the process specifically comprises:
for three-phase non-ideal network voltage signal eα、eβCarrying out fundamental frequency positive sequence rotation transformation, and respectively filtering 2-time and 6-time alternating current components by using a wave trap to obtain three-phase non-ideal power grid voltage fundamental frequency positive sequence components
Figure BDA0002235943480000071
Respectively at dq+Projection of a coordinate system
Figure BDA0002235943480000072
For three-phase non-ideal network voltage signal eα、eβCarrying out fundamental frequency negative sequence rotation transformation, and respectively filtering out 2-time, 4-time and 8-time alternating current components by using a wave trap to obtain a power grid voltage fundamental frequency negative sequence component
Figure BDA0002235943480000073
Respectively at dq-Projection of a coordinate system
Figure BDA0002235943480000074
For three-phase non-ideal network voltage signal eα、eβCarrying out 5-time frequency negative sequence rotation transformation, and respectively filtering 4 times, 6 times and 8 times of alternating current components by using a wave trap to obtain 5-time frequency negative sequence components of the grid voltageRespectively at dq5-Projection of a coordinate system
Figure BDA0002235943480000076
For three-phase non-ideal network voltage signal eα、eβCarrying out 7-time frequency positive sequence rotation conversion, and respectively filtering 6-time, 8-time and 12-time alternating current components by using a wave trap to obtain a power grid voltage 7-time frequency positive sequence componentRespectively at dq7+Projection of a coordinate system
Further, step 4, according to the harmonic component information, respectively calculating current reference instructions under three control targets of network-access current sine, active power pulsation suppression and reactive power pulsation suppression based on an instantaneous reactive power theory, wherein the process specifically comprises the following steps:
(1) under the condition of a three-phase non-ideal power grid, establishing a grid-connected current expression under an alpha and beta coordinate system as follows:
in the formula i+、i-、i5-、i7+Respectively a fundamental frequency positive sequence component, a fundamental frequency negative sequence component, a 5 frequency multiplication negative sequence component and a 7 frequency multiplication positive sequence component contained in the network access current;
the sequential components of the network current are similar to the three-phase non-ideal network voltage
Figure BDA0002235943480000081
The projections of the rotating coordinate system in their corresponding order are respectively
Figure BDA0002235943480000083
(2) According to the instantaneous reactive power theory, the network-access instantaneous complex powerComprises the following steps:
Figure BDA0002235943480000085
wherein j is a complex unit, p(t)For instantaneous active power of network access, q(t)The instantaneous reactive power is the network access reactive power.
The network access instantaneous active power p can be obtained according to the formula(t)Network-access instantaneous reactive power q(t)Are respectively:
p(t)＝P0+Pc2cos(2ωt)+Ps2sin(2ωt)+Pc4cos(4ωt)+Ps4sin(4ωt)
+Pc6cos(6ωt)+Ps6sin(6ωt)+Pc8cos(8ωt)+Ps8sin(8ωt)
+Pc12cos(12ωt)+Ps12sin(12ωt)
q(t)＝Q0+Qc2cos(2ωt)+Qs2sin(2ωt)+Qc4cos(4ωt)+Qs4sin(4ωt)
+Qc6cos(6ωt)+Qs6sin(6ωt)+Qc8cos(8ωt)+Qs8sin(8ωt)
+Qc12cos(12ωt)+Qs12sin(12ωt)
in the formula, Pc2、Ps2、Pc4、Ps4、Pc6、Ps6、Pc8、Ps8、Pc12、Ps12Respectively corresponding to the frequency multiplication active power pulsation in the network-accessing instantaneous active power0The direct current component in the network-access instantaneous active power is obtained; qc2、Qs2、Qc4、Qs4、Qc6、Qs6、Qc8、Qs8、Qc12、Qs12Respectively corresponding to the frequency multiplication reactive power pulsation in the network-accessing instantaneous reactive power, Q0Is a direct current component in the network access instantaneous reactive power;
the active power ripple coefficient, the reactive power ripple coefficient, the power grid voltage harmonic component and the network access current harmonic component have the following relations:
Figure BDA0002235943480000086
Figure BDA0002235943480000091
it can be seen from the above that, the active power and the reactive power respectively contain power ripples of 2 frequency multiplication, 4 frequency multiplication, 6 frequency multiplication, 8 frequency multiplication and 12 frequency multiplication generated by cross multiplication of three-phase non-ideal grid voltage and grid-connected current, and by selectively suppressing the power ripples of different frequency multiplications, current reference value calculation formulas under different control targets can be obtained:
aiming at a grid-connected control target I: three-phase network access current is sinusoidal and balanced;
under the condition of a three-phase non-ideal power grid, harmonic waves and negative sequence components in the network current need to be eliminated, so that reference values corresponding to the non-fundamental frequency harmonic waves and the negative sequence components of the network current are set to be 0, and the reference values of each sub-harmonic wave and the positive and negative sequence components of the network current are as follows:
Figure BDA0002235943480000092
in the formula (I), the compound is shown in the specification,respectively representing projection reference values of each sequence component of the network access current in a corresponding sequence rotation coordinate system;
Figure BDA0002235943480000094
andrespectively representing the direct current reference values of active power and reactive power;
aiming at a grid-connected control target II: inhibiting the fluctuation of active power frequency multiplication 2, 4 and 6;
the control target is to suppress 2, 4 and 6 frequency multiplication components in active power, the corresponding 2, 4 and 6 active power pulsation coefficients are taken as 0, and the reference values of each subharmonic and positive and negative sequence components of the network access current under the control target are obtained by solving the following steps:
Figure BDA0002235943480000101
aiming at a grid-connected control target III: reactive power 2 frequency multiplication, 4 frequency multiplication and 6 frequency multiplication fluctuation are inhibited;
the control target is to suppress 2, 4 and 6 frequency multiplication components in active power, corresponding 2, 4 and 6 times of reactive power pulsation coefficients are taken as 0, and reference values of each subharmonic and positive and negative sequence components of the network access current are obtained by solving the following steps:
Figure BDA0002235943480000102
wherein A, B, C are respectively:
with reference to fig. 1, the multi-target current reference instruction calculation system applicable to a non-ideal power grid, provided by the invention, comprises a three-phase three-level grid-connected inverter and a digital calculation processing module, wherein the digital calculation processing module comprises a sampling unit, a phase locking unit, a harmonic component extraction unit and a current reference instruction calculation unit;
the sampling unit is used for collecting a three-phase non-ideal power grid voltage signal at the AC side of a three-phase three-level grid-connected inverter (the NPC three-phase three-level grid-connected inverter main power circuit is shown in figure 2), and sending the signal to the phase-locking unit;
the phase locking unit is used for acquiring fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage according to the sampled three-phase non-ideal power grid voltage signal and sending the information to the harmonic component extraction unit;
the harmonic component extracting unit, as shown in fig. 3, is configured to extract harmonic component information in the three-phase non-ideal grid voltage according to the grid voltage fundamental frequency positive sequence phase information, and send the harmonic component information to the current reference instruction calculating unit;
and the current reference instruction calculating unit is used for calculating current reference instructions under three power and current control targets respectively based on an instantaneous reactive power theory according to the harmonic component information.
Further, the three power and current control objectives include network-entry current sinusoidization, active power ripple rejection, and reactive power ripple rejection.
Illustratively, the digital computation processing module employs TMS320F2808 and EPM1270T chips.
The present invention will be described in further detail with reference to examples.
Example 1
In the embodiment, a simulation model of the multi-target current reference instruction computing system suitable for the non-ideal power grid as shown in fig. 1 is established, and a finite set model is selected for predictive control in the control method. The grid-connected control target of the embodiment 1 is three-phase grid-connected current which is sinusoidal and balanced, and specific parameters are shown in the following table 1. The active power reference value P in this example* 010(kW), reactive power reference Q* 00 (Var). The simulation result of the embodiment 1 is shown in fig. 4, and fig. 4(a) to (d) are the simulation results of the three-phase reference current and the network access current, the network access current FFT analysis, the network access instantaneous active power, and the network access instantaneous reactive power, respectively, and it can be seen from fig. 4 that the current reference instruction calculation system suitable for the non-ideal power grid can give the current reference meeting the control target, the network access current can follow the current reference value under the adopted model predictive control, and the three-phase network access current is sinusoidal and balanced to achieve the control target.
TABLE 1 simulation parameters
Amplitude of fundamental frequency positive sequence component: 320V Amplitude of the fundamental frequency negative sequence component: 30V
5 frequency multiplication negative sequence component amplitude: 20V 7 frequency multiplication positive sequence component amplitude: 10V
Fundamental frequency 50Hz
Vdc 400(V)
C1(＝C2) 500e-6(F)
λdc 1
Ts 25e-6(s)
R 1(Ω)
L 5e-3(H)
Example 2
In the embodiment, a simulation model of the multi-target current reference instruction computing system suitable for the non-ideal power grid as shown in FIG. 3 is established, and the control method adopts the finite set model for prediction control. The grid-connected control target of the embodiment 2 is to eliminate the idle 2, 4 and 6 times of fluctuation, and specific parameters are shown in the table 1. The active power reference value P in this example* 010(kW), reactive power reference Q* 00 (Var). The simulation result of the embodiment 2 is shown in fig. 5, and fig. 5(a) to (d) are the simulation results of the three-phase reference current and the network access current, the network access instantaneous active power FFT analysis, and the network access instantaneous reactive power, respectively, and it can be seen from fig. 5 that the current reference instruction calculation system suitable for the non-ideal power grid can give a current reference meeting the control target, the grid-connected current can follow the current reference value under the adopted model prediction control, and the network access reactive 2, 4, and 6 times of fluctuation can be effectively eliminated, so as to achieve the control target.
Example 3
In the embodiment, a simulation model of the multi-target current reference instruction computing system suitable for the non-ideal power grid as shown in FIG. 3 is established, and the control method adopts the finite set model for prediction control. The grid-connection control object of embodiment 3 isAnd eliminating the idle work for 2, 4 and 6 times of fluctuation, wherein the specific parameters are shown in the table 1. The active power reference value P in this example* 00(W), reactive power reference Q* 010 (kVar). The simulation result of the embodiment 3 is shown in fig. 6, and fig. 6(a) to (d) are the simulation results of FFT analysis of three-phase reference current and network access current, network access instantaneous active power, network access instantaneous reactive power, and network access instantaneous reactive power, respectively, and it can be seen from fig. 6 that the current reference instruction calculation system suitable for the non-ideal power grid can give a current reference conforming to the control target, the grid-connected current can follow the current reference value under the adopted model predictive control, and 2, 4, and 6-time fluctuations of network access reactive power can be effectively eliminated, so as to achieve the control target.
In summary, according to the multi-target current reference instruction calculation method suitable for the non-ideal power grid, the obtained current reference instruction can be applied to grid-connected control of the NPC three-phase three-level inverter under the non-ideal power grid condition, and an ideal control effect is achieved.

Claims (7)

1. A multi-target current reference instruction calculation method suitable for a non-ideal power grid is characterized by comprising the following steps:
step 1, sampling a three-phase non-ideal grid voltage signal e at the AC side of a three-phase three-level grid-connected invertera、eb、ecAnd performing Clark conversion on the three-phase non-ideal power grid voltage to obtain a three-phase non-ideal power grid voltage signal e under an alpha beta coordinate systemα、eβ；
Step 2, obtaining fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage;
step 3, performing different frequency multiplication and different direction rotation transformation on the three-phase non-ideal power grid voltage by using the fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage, and filtering alternating current components by using traps with different frequencies to obtain harmonic component information in the three-phase non-ideal power grid voltage;
and 4, respectively calculating current reference instructions under three control targets of networking current sine, active power pulsation suppression and reactive power pulsation suppression based on an instantaneous reactive power theory according to the harmonic component information.
2. The method for calculating the multi-target current reference command applicable to the non-ideal power grid according to claim 1, wherein the step 1 is used for sampling a three-phase non-ideal grid voltage signal e at the AC side of the three-phase three-level grid-connected invertera、eb、ecSpecifically, the following are defined:
Figure FDA0002235943470000011
Figure FDA0002235943470000012
Figure FDA0002235943470000013
in the formula, e+、e-、e5-、e7+The three-phase non-ideal power grid voltage respectively comprises a fundamental frequency positive sequence component, a fundamental frequency negative sequence component, a 5 frequency multiplication negative sequence component and a 7 frequency multiplication positive sequence component; wherein subscripts a, b, c represent a phase a, b phase, c phase, respectively;
clark conversion is carried out on the three-phase non-ideal power grid voltage to obtain a three-phase non-ideal power grid voltage signal e under an alpha beta coordinate systemα、eβComprises the following steps:
Figure FDA0002235943470000014
3. the method for calculating the multi-target current reference command applicable to the non-ideal power grid according to claim 1, wherein the step 2 is to acquire the fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage, and specifically, the fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage is acquired by using a biquadratic generalized integral software phase-locked loop.
4. The method for calculating the multi-target current reference command applicable to the non-ideal power grid according to claim 1, wherein step 3 is to perform different frequency multiplication and different direction rotation transformation on the three-phase non-ideal power grid voltage by using the fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage, and then obtain harmonic component information in the three-phase non-ideal power grid voltage after filtering out alternating current components by using wave traps with different frequencies, and the method specifically comprises the following steps:
for three-phase non-ideal network voltage signal eα、eβCarrying out fundamental frequency positive sequence rotation transformation, and respectively filtering 2-time and 6-time alternating current components by using a wave trap to obtain three-phase non-ideal power grid voltage fundamental frequency positive sequence componentsRespectively at dq+Projection of a coordinate system
For three-phase non-ideal network voltage signal eα、eβCarrying out fundamental frequency negative sequence rotation transformation, and respectively filtering out 2-time, 4-time and 8-time alternating current components by using a wave trap to obtain a power grid voltage fundamental frequency negative sequence component
Figure FDA0002235943470000023
Projection in dq coordinate system respectively
Figure FDA0002235943470000024
For three-phase non-ideal network voltage signal eα、eβCarrying out 5-time frequency negative sequence rotation transformation, and respectively filtering 4 times, 6 times and 8 times of alternating current components by using a wave trap to obtain 5-time frequency negative sequence components of the grid voltage
Figure FDA0002235943470000025
Respectively at dq5Projection of a coordinate system
Figure FDA0002235943470000026
For three-phase non-ideal network voltage signal eα、eβCarrying out 7-time frequency positive sequence rotation conversion, and respectively filtering 6-time, 8-time and 12-time alternating current components by using a wave trap to obtain a power grid voltage 7-time frequency positive sequence component
Figure FDA0002235943470000027
Respectively at dq7+Projection of a coordinate system
Figure FDA0002235943470000028
5. The method for calculating the multi-target current reference command suitable for the non-ideal power grid according to claim 1 or 4, wherein the step 4 is to calculate the current reference commands under three control targets of networking current sine, active power pulsation suppression and reactive power pulsation suppression respectively based on an instantaneous reactive power theory according to the harmonic component information, and the process specifically comprises the following steps:
(1) under the condition of a three-phase non-ideal power grid, establishing a grid-connected current expression under an alpha and beta coordinate system as follows:
Figure FDA0002235943470000029
in the formula i+、i-、i5-、i7+Respectively a fundamental frequency positive sequence component, a fundamental frequency negative sequence component, a 5 frequency multiplication negative sequence component and a 7 frequency multiplication positive sequence component contained in the network access current;
the sequential components of the network current are similar to the three-phase non-ideal network voltage
Figure FDA0002235943470000032
In its correspondence withThe projections of the sequentially rotated coordinate system are respectively
(2) According to the instantaneous reactive theory, active power and reactive power respectively contain power ripples of 2 frequency multiplication, 4 frequency multiplication, 6 frequency multiplication, 8 frequency multiplication and 12 frequency multiplication generated by cross multiplication of three-phase non-ideal grid voltage and grid-connected current, and current reference value calculation formulas under different control targets are obtained by selectively inhibiting the power ripples of different frequency multiplications:
aiming at a grid-connected control target I: three-phase network access current is sinusoidal and balanced;
under the condition of a three-phase non-ideal power grid, reference values of each harmonic and positive-negative sequence components of the grid-connected current are as follows:
in the formula (I), the compound is shown in the specification,
Figure FDA0002235943470000035
respectively representing projection reference values of each sequence component of the network access current in a corresponding sequence rotation coordinate system;
Figure FDA0002235943470000036
and
Figure FDA0002235943470000037
respectively representing the direct current reference values of active power and reactive power;
aiming at a grid-connected control target II: inhibiting the fluctuation of active power frequency multiplication 2, 4 and 6;
under the condition of a three-phase non-ideal power grid, reference values of each harmonic and positive-negative sequence components of the grid-connected current are as follows:
Figure FDA0002235943470000041
aiming at a grid-connected control target III: reactive power 2 frequency multiplication, 4 frequency multiplication and 6 frequency multiplication fluctuation are inhibited;
under the condition of a three-phase non-ideal power grid, reference values of each harmonic and positive-negative sequence components of the grid-connected current are as follows:
Figure FDA0002235943470000042
wherein A, B, C are respectively:
Figure FDA0002235943470000051
6. a multi-target current reference instruction calculation system suitable for a non-ideal power grid is characterized by comprising a three-phase three-level grid-connected inverter and a digital calculation processing module, wherein the digital calculation processing module comprises a sampling unit, a phase locking unit, a harmonic component extraction unit and a current reference instruction calculation unit;
the sampling unit is used for collecting a three-phase non-ideal power grid voltage signal at the AC side of the three-phase three-level grid-connected inverter and sending the signal to the phase-locking unit;
the phase locking unit is used for acquiring fundamental frequency positive sequence phase information of the three-phase non-ideal power grid voltage according to the three-phase non-ideal power grid voltage signal obtained by sampling and sending the information to the harmonic component extraction unit;
the harmonic component extraction unit is used for extracting harmonic component information in the three-phase non-ideal power grid voltage according to the power grid voltage fundamental frequency positive sequence phase information and sending the harmonic component information to the current reference instruction calculation unit;
and the current reference instruction calculating unit is used for calculating current reference instructions under three power and current control targets respectively based on an instantaneous reactive power theory according to the harmonic component information.
7. The system of claim 6, wherein the three power and current control objectives include net-entry current sinusoid, active power ripple rejection, and reactive power ripple rejection.
CN201910983403.5A 2019-10-16 2019-10-16 Multi-target current reference instruction calculation method and system suitable for non-ideal power grid Pending CN110676878A (en)

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