CN110571829B - Three-phase three-wire system converter power oscillation suppression method based on Fermat point - Google Patents

Three-phase three-wire system converter power oscillation suppression method based on Fermat point Download PDF

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CN110571829B
CN110571829B CN201910867457.5A CN201910867457A CN110571829B CN 110571829 B CN110571829 B CN 110571829B CN 201910867457 A CN201910867457 A CN 201910867457A CN 110571829 B CN110571829 B CN 110571829B
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power
current
voltage
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CN110571829A (en
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李晓涵
何晋伟
杜李扬
王秀瑞
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Tianjin 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage

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Abstract

The invention discloses a method for suppressing power oscillation of a three-phase three-wire system converter based on a Fermat point, which defines a triangular equiangular center (Fermat point) of a fault line voltage as a new neutral point and provides a novel method for suppressing power oscillation according to a new rule that power generated by positive and negative sequence voltages of a three-phase three-wire system is uniformly distributed in three phases and a system has no active oscillation. The method comprises the following steps: firstly, calculating the phase voltage under a Fermat point coordinate system according to the network side fault line voltage. And secondly, obtaining a three-phase reference current vector for realizing power oscillation suppression according to the obtained new rule of power distribution and power oscillation, and performing current tracking control. Thirdly, a signal obtained by current tracking control is used as a PWM reference signal to realize closed-loop control of the system. The invention realizes the simplification of the asymmetric fault problem by establishing a new neutral point, and the method breaks away from the complex coordinate transformation and sequence component calculation of the traditional method and greatly simplifies the control complexity.

Description

Three-phase three-wire system converter power oscillation suppression method based on Fermat point
Technical Field
The invention relates to the field of grid-connected control of three-phase three-wire system, in particular to a novel power oscillation suppression method of a three-phase three-wire system converter applied to power grid asymmetric faults.
Background
With the increase of the permeability of new energy loads such as photovoltaic and the like, the potential hazards of system load unbalance and short-circuit faults are greatly increased while clean and convenient energy is provided for people, and huge impact is brought to the structure and control of a modern power distribution network.
When the voltage asymmetry fault occurs in the power grid, the grid-side power can generate double frequency oscillation, which is caused by the products of positive sequence current and negative sequence voltage components and positive sequence voltage and negative sequence current components. The power fluctuation can cause severe pulsation of the dc side voltage of the inverter, which seriously jeopardizes the life of the dc bus capacitor and the stability of the system, and therefore must be suppressed. According to the traditional method, the asymmetric power grid voltage is subjected to abc-dq transformation, and the positive sequence and negative sequence components of a fundamental wave are separated through positive and negative sequence decoupling under a positive and negative sequence synchronous reference coordinate system. The method has a complex structure and large calculation amount, and the system bandwidth needs to be reduced for ensuring the system stability. Most of the existing methods for suppressing power oscillation are improved in a delay link on the basis, and the simplification of a control algorithm is not realized fundamentally.
Disclosure of Invention
In order to overcome the defects of the traditional grid-connected control method in the aspects of system power oscillation suppression control complexity and control effect, the invention provides a three-phase three-wire system converter power oscillation suppression method based on a Fermat point. The method defines the equiangular center (i.e. Fermat point O) of the triangle of the fault line voltage F ) The fault is a new neutral point, so that the voltage amplitude drop and phase angle shift asymmetric fault in the three-phase static coordinate system can be converted into the voltage amplitude fault in the Fermat point coordinate system. In addition, according to the rule between power distribution and power oscillation of the three-phase three-wire system obtained through mathematical derivation, a novel power oscillation suppression strategy is designed, complex coordinate transformation and sequence component calculation in the traditional control method are eliminated, the control complexity is greatly simplified, and a good oscillation suppression effect is achieved. In addition, in order to prevent the risk of system current out-of-limit, a current amplitude limiting control strategy is added, the three-phase current amplitude is ensured to be always within a safety threshold value on the premise of not influencing the power oscillation suppression effect, and guidance can be provided for selecting an actual system fault coping scheme.
The purpose of the invention is realized by the following technical scheme:
A three-phase three-wire system converter power oscillation suppression method based on a Fermat point is based on a three-phase three-wire system converter under the asymmetrical fault of a power grid, wherein the three-phase three-wire system converter is connected to a Point of Common Coupling (PCC) through a filter and then exchanges power with a three-phase independent power grid, the converter adopts a cascade H-bridge structure, and the method is characterized by comprising the following steps of:
step S1: three-phase three-wire system line voltage under power grid asymmetric fault obtained through voltage fault detection equipment
Figure BDA0002201677490000021
Amplitude a, line voltage
Figure BDA0002201677490000022
Amplitude b, line voltage
Figure BDA0002201677490000023
The amplitude c and the angular frequency omega of the power grid are converted into a new neutral point (Fermat point O) F ) Lower three-phase voltage vector
Figure BDA0002201677490000024
Therefore, voltage asymmetric faults of amplitude drop and phase angle shift in a three-phase static coordinate system can be converted into voltage amplitude faults in a Fermat point coordinate system;
step S2: instantaneous active power p of three-phase three-wire system asymmetric fault system abc_F Instantaneous reactive power q abc_F Respectively corresponding to given value P of DC power ref 、Q ref For comparison, P is generated by Proportional Integral (PI) regulation setting 、Q setting Forming a power tracking outer loop;
step S3: calculating to obtain the amplitude reference of the three-phase reference current meeting the power oscillation suppression condition according to the rule between the power distribution and the power oscillation of the three-phase three-wire system obtained by mathematical derivation;
Step S4: respectively extracting three-phase voltage phases under a Fermat point coordinate system, indirectly obtaining phase references of three-phase reference currents, and synthesizing three-phase reference current initial vectors by adopting a direct current control method
Figure BDA0002201677490000025
Step S5: the synthesized reference current initial vector may appear at this time
Figure BDA0002201677490000026
The method can not be directly applied to current tracking of a three-phase three-wire system, and a correction link of zero sequence current elimination is required; namely, on the premise of not destroying the power oscillation suppression effect, the redundant part of each phase of reference current is proportionally eliminated according to the amplitude of the three-phase current, and the three-phase reference current vector with the power oscillation suppression effect is obtained
Figure BDA0002201677490000027
Step S6: adding a current amplitude limiting controller, and when the detected three-phase current peak value is larger than the set safety threshold value
Figure BDA0002201677490000028
When the current is detected, the controller automatically adjusts the current amplitude to be reduced to a safe threshold value according to the proportion; at the moment, a three-phase reference current vector which meets the power oscillation suppression condition and has current amplitude not exceeding the limit is obtained
Figure BDA0002201677490000029
Step S7: obtained in the last step
Figure BDA00022016774900000210
As a reference vector, tracking control is carried out on the current at the network side by adopting a double-loop control method combining Proportional Resonance (PR) control and proportional control (P) control to form a current tracking control inner loop, and a voltage control signal is obtained
Figure BDA00022016774900000211
Step S8: the voltage signal obtained in the last step is used
Figure BDA00022016774900000212
And as a three-phase voltage reference wave, generating a duty ratio signal of a switching tube corresponding to the cascaded H bridge through a PWM generator, thereby controlling the switching-on and switching-off of the switching tube of the converter.
Further, in step S2, the instantaneous active power p of the three-phase three-wire system fault system abc_F Instantaneous reactive power q abc_F As defined below:
Figure BDA00022016774900000213
Figure BDA0002201677490000031
wherein p is aF 、p bF 、p cF Respectively represents three-phase instantaneous active power q under a Fermat point coordinate system aF 、q bF 、q cF Respectively representing three-phase instantaneous reactive power under a Fermat point coordinate system;
Figure BDA0002201677490000032
is the three-phase instantaneous phase voltage under the Fermat point coordinate system,
Figure BDA0002201677490000033
Figure BDA0002201677490000034
a set of voltage quadrature quantities lagging 90 degrees from the Fermat point instantaneous phase voltage;
Figure BDA0002201677490000035
the instantaneous network side current of the three-phase three-wire system fault system is obtained.
Further, the above-mentioned related current vector includes
Figure BDA0002201677490000036
The synthesis is carried out by adopting the mode shown in formula (3):
Figure BDA0002201677490000037
Figure BDA0002201677490000038
representing active components of three-phase currents, the phases of which and the corresponding phase voltages
Figure BDA0002201677490000039
The phases are the same;
Figure BDA00022016774900000310
representing reactive components of three-phase current, the phase of which is orthogonal to the corresponding phase voltage
Figure BDA00022016774900000311
Phase identity (j ═ a, b, c); therefore, the above-mentioned current vector can be written in the form shown in equation (4):
Figure BDA00022016774900000312
wherein
Figure BDA00022016774900000313
The magnitude of the three-phase current is represented,
Figure BDA00022016774900000314
the initial phase angle of the three-phase current is shown,
Figure BDA00022016774900000315
representing the magnitude of the real components of the three-phase current,
Figure BDA00022016774900000316
The amplitude (j ═ a, b, c) of the reactive component of the three-phase current is shown, ω shows the angular frequency of the power grid, and t shows the time.
Further, for a three-phase three-wire system, the instantaneous active power p of the asymmetric fault system at the traditional neutral point O abc_o Instantaneous reactive power q abc_o Can be expressed as:
Figure BDA00022016774900000317
Figure BDA00022016774900000318
wherein P is ao 、P bo 、P co Respectively represents three-phase instantaneous active power, Q, under the traditional neutral point O ao 、Q bo 、Q co Respectively representing three-phase instantaneous reactive power under the traditional neutral point O;
Figure BDA00022016774900000319
three-phase instantaneous phase voltage under the traditional neutral point O,
Figure BDA00022016774900000320
Figure BDA00022016774900000321
a set of voltage quadrature quantities lagging 90 degrees from the three-phase instantaneous phase voltages;
Figure BDA00022016774900000322
the instantaneous network side current of the three-phase three-wire system fault system is obtained.
For a three-phase three-wire system, the instantaneous power in the Fermat point coordinate system satisfies the following formula:
Figure BDA0002201677490000041
Figure BDA0002201677490000042
from the conventional neutral point O to the new neutral point O F Due to three-phase three-wire system
Figure BDA0002201677490000043
Figure BDA0002201677490000044
Therefore, for a three-phase three-wire system, the instantaneous active power calculated under the Fermat point coordinate system and the instantaneous active power calculated under the traditional neutral point have an equivalent relation, namely p abc_F ＝p abc_o Instantaneous reactive power q abc_F ＝q abc_o The same process is carried out; therefore, the instantaneous power of the three-phase three-wire system can be directly measured by measuring p under the Fermat point coordinate system abc_F 、q abc_F Thus obtaining the product.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
The method for suppressing the power oscillation of the three-phase three-wire system converter based on the Fermat point well solves two problems of neutral point ambiguity and power oscillation of the three-phase three-wire system when the asymmetric fault of a power grid occurs.
1. When the power grid has asymmetric faults, the three-phase voltage under the traditional neutral point no longer meets the conditions of equal amplitude and 120 degrees of phase difference. The value of the neutral point is not possessed any more when the neutral point is used for calculating the phase voltage and analyzing the voltage fault, and the reference significance is greatly reduced. In the traditional method, the fault is generally analyzed in a dq two-phase rotating coordinate system, although the influence of a fault neutral point can be eliminated, a delay link is introduced, and the intuitiveness of the actual fault system analysis is reduced. Therefore, the invention defines the equiangular center (namely the Fermat point) of the voltage triangle of the fault line as a new neutral point, can convert the asymmetric faults of voltage amplitude drop and phase angle shift under the three-phase static coordinate system into the voltage amplitude faults under the Fermat point coordinate system, does not need the calculation of sequence components, realizes the simplification of the asymmetric fault problem, and provides a more intuitive and effective solution for the asymmetric fault analysis of an actual system.
2. According to actual guess and mathematical demonstration, a rule between power distribution and power oscillation of the three-phase three-wire system is obtained, and a novel power oscillation suppression strategy is designed. The invention breaks away from complex coordinate transformation and sequence component calculation, can directly synthesize the three-phase reference current vector with the power oscillation suppression effect under different working conditions by setting the power distribution proportion, greatly simplifies the control complexity and has good oscillation suppression effect. The invention discovers a hidden action mechanism between power distribution and power oscillation of a three-phase three-wire system, provides a novel power oscillation suppression strategy based on the hidden action mechanism, solves the problem of power oscillation suppression in a brand-new angle, and can provide guidance for selecting an actual system fault coping scheme.
Drawings
Fig. 1 is a schematic diagram of a topology of a cascaded H-bridge converter in an embodiment of the present invention.
Fig. 2 shows a fmann point coordinate system vector diagram.
FIG. 3 is a schematic diagram of reference current generation for the method of the present invention.
Fig. 4 is a three-phase current limiting control flow chart.
FIG. 5 is a block diagram of the overall control of the system.
FIG. 6 is a comparison graph of simulation of the control method provided by the invention and an ideal control effect under the asymmetric fault of the three-phase power grid.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The control method of the invention is based on the topological structure of the cascaded H-bridge converter, as shown in figure 1. Three-phase three-wire systems are often accompanied by voltage amplitude sags and phase angle shifts when the grid experiences asymmetric faults. At this time, the three-phase voltage under the neutral point in the traditional sense no longer meets the conditions of equal amplitude and 120 degrees of phase difference. Therefore, for simple analysis, the equiangular center (i.e. the mathematical Fermat point O) satisfying the mutual difference of the included angles of three vertexes of 120 degrees (the mutual difference of phase angles of three phase voltages of 120 degrees) in the line voltage triangle under the fault system is defined F ) Is the "new neutral point". Fermat point O F Can be obtained by making equilateral triangles on three sides of the line voltage triangle and calculating the intersection points of line segments AA ', BB ' and CC ', as shown in FIG. 2. Mathematics can prove that there is one and only one Fermat point per given voltage triangle.
Because the three-phase voltage under the Fermat point coordinate system meets the condition that the phase angles are mutually different by 120 degrees, the asymmetric faults of voltage amplitude drop and phase angle deviation under the three-phase static coordinate system can be converted into the voltage amplitude fault under the Fermat point coordinate system, and the problem of asymmetric faults is simplified.
Since the zero sequence voltage component of the three-phase three-wire system has no path, the zero sequence voltage component can be ignored as 0. According to analysis and research of instantaneous current and instantaneous power in the traditional power oscillation suppression method, a rule between power distribution and power oscillation of the three-phase three-wire system is obtained through mathematical demonstration. The control method is based on the rule.
The invention discloses a Fermat point-based three-phase three-wire system converter power oscillation suppression method, which comprises the following specific steps:
step S1: three-phase three-wire system line voltage under power grid asymmetric fault obtained through voltage fault detection equipment
Figure BDA0002201677490000051
Amplitude a, line voltage
Figure BDA0002201677490000052
Amplitude b, line voltage
Figure BDA0002201677490000053
The amplitude c and the power grid angular frequency omega obtain a new neutral point (Fermat point O) according to the conversion formulas (1) and (2) F ) Lower three-phase voltage vector
Figure BDA0002201677490000054
And accordingly, establishing a Fermat point coordinate system as shown in FIG. 2;
Figure BDA0002201677490000055
wherein:
Figure BDA0002201677490000061
Figure BDA0002201677490000062
the amplitudes of the three-phase voltages under the Fermat point coordinate system are respectively. Wherein the intermediate variable
Figure BDA0002201677490000063
Figure BDA0002201677490000064
h has no actual physical meaning. S is the area of a triangle formed by the three-phase line voltage under the Fermat point according to HelenThe formula can be found:
Figure BDA0002201677490000065
ω is the grid angular frequency and t represents time.
Step S2: instantaneous active power p of three-phase three-wire system asymmetric fault system abc_F Instantaneous reactive power q abc_F Respectively corresponding to given value P of DC power ref 、Q ref For comparison, P was generated by PI regulation setting 、Q setting Forming a power tracking outer loop. Referring to Akagi instantaneous reactive power theory, instantaneous active power p of three-phase three-wire system fault system abc_F Instantaneous reactive power q abc_F As defined below:
Figure BDA0002201677490000066
Figure BDA0002201677490000067
wherein p is aF 、p bF 、P cF Respectively represents three-phase instantaneous active power q under a Fermat point coordinate system aF 、q bF 、q cF Respectively representing three-phase instantaneous reactive power under a Fermat point coordinate system;
Figure BDA0002201677490000068
is the three-phase instantaneous phase voltage under the Fermat point coordinate system,
Figure BDA0002201677490000069
Figure BDA00022016774900000610
a set of voltage quadrature quantities lagging 90 degrees from the instantaneous phase voltage at the fermat point, as shown in equation (5);
Figure BDA00022016774900000611
Figure BDA00022016774900000612
the instantaneous network side current of the three-phase three-wire system fault system is obtained. The current vector (including) according to the invention
Figure BDA00022016774900000613
Figure BDA00022016774900000614
) Are synthesized and defined in the manner shown in formulas (6) to (7).
Figure BDA00022016774900000615
Figure BDA00022016774900000616
Representing active components of three-phase currents, the phases of which and the corresponding phase voltages
Figure BDA00022016774900000617
The phases are the same;
Figure BDA00022016774900000618
representing reactive components of three-phase current, the phase of which is orthogonal to the corresponding phase voltage
Figure BDA00022016774900000619
Phase identity (j ═ a, b, c); thus, the current vector referred to herein can be written in the form shown in equation (7):
Figure BDA0002201677490000071
wherein
Figure BDA0002201677490000072
The magnitude of the three-phase current is represented,
Figure BDA0002201677490000073
the initial phase angle of the three-phase current is shown,
Figure BDA0002201677490000074
representing the magnitude of the real components of the three-phase current,
Figure BDA0002201677490000075
the amplitude (j ═ a, b, c) of the reactive component of the three-phase current is shown, ω shows the angular frequency of the power grid, and t shows the time.
Step S3: according to mathematical demonstration, in order to suppress active power oscillation, a system needs to satisfy a certain power distribution relation, so that the amplitude reference of the three-phase reference current is obtained by setting a distribution proportion:
Figure BDA0002201677490000076
therefore, the method comprises the following steps:
Figure BDA0002201677490000077
equation (9) is an amplitude reference expression of the active component and the reactive component of the reference current satisfying the three-phase power uniform distribution, where P is setting 、Q setting The resulting control signal is adjusted for the PI of the power outer loop in step S2,
Figure BDA0002201677490000078
representing the magnitude of the real component of the three-phase reference current,
Figure BDA0002201677490000079
representing the magnitude of the reactive component of the three-phase reference current,
Figure BDA00022016774900000710
representing three-phase voltage under a Fermat point coordinate system
Figure BDA00022016774900000711
The amplitude of (a) of (b) is,
Figure BDA00022016774900000712
representing the three-phase voltage orthogonal quantity under the Fermat point coordinate system
Figure BDA00022016774900000713
Thus, satisfies
Figure BDA00022016774900000714
Step S4: by adopting a direct current control method, the active components of the initial three-phase reference current are determined on the basis of obtaining the three-phase current amplitude reference
Figure BDA00022016774900000715
And a reactive component
Figure BDA00022016774900000716
By extracting the three-phase voltages in the Fermat point coordinate system separately
Figure BDA00022016774900000717
And
Figure BDA00022016774900000718
the reference current synthesis diagram of (2) is shown in fig. 3. The three-phase reference current vector after synthesis is shown in equation (10):
Figure BDA0002201677490000081
step S5: initial three-phase reference current vector synthesized at this time
Figure BDA0002201677490000082
May appear
Figure BDA0002201677490000083
The condition (2) can not be directly applied to current tracking of a three-phase three-wire system, and needs to be carried out And eliminating the zero sequence current. On the premise of not destroying the power oscillation suppression effect, the redundant parts of the reference currents of all phases are proportionally eliminated according to the amplitude of the three-phase current, and the three-phase reference current vector with the power oscillation suppression effect is obtained
Figure BDA0002201677490000084
Figure BDA0002201677490000085
Step S6: considering that the system current may have out-of-limit risk, a current limiting link needs to be added, and when the system automatically detects that the three-phase current peak value is larger than the set safety threshold value
Figure BDA0002201677490000086
And the current out-of-limit controller can automatically adjust the current amplitude to be reduced to a safe range in proportion. The control flow is shown in fig. 4. Reference current signal generated at this time
Figure BDA0002201677490000087
The three-phase current reference vector not only meets the requirements of double frequency suppression of active power and current amplitude, but also cannot exceed a safety threshold.
Step S7: the three-phase current signals obtained in the previous step are processed
Figure BDA0002201677490000088
Tracking and controlling the system network side current as a reference vector to obtain a voltage control signal
Figure BDA0002201677490000089
The stability of the system can be improved by adopting a double-loop control method combining Proportional Resonance (PR) control and proportional control (P) control. The overall control block diagram of the system is shown in FIG. 5, wherein I gj1 And I gj2 All of which are shown in figure 5.
Step S8: the voltage signal obtained in the last step is used
Figure BDA00022016774900000810
And as a three-phase voltage reference wave, a duty ratio signal of a corresponding switching tube of the cascaded H-bridge is formed by the PWM generator, so that the switching tube of the converter is controlled to be switched on and off.
Fig. 6 is a simulation comparison diagram when a three-phase voltage asymmetric fault occurs in the cascaded H-bridge grid-connected system. The circuit topology shown in fig. 5 is employed. Wherein L is 1 ＝0.2mH，L 2 ＝1mH，
Figure BDA00022016774900000811
C 1 ＝40μF，
Figure BDA00022016774900000812
V dc 130V, switching frequency f switch 1.2 kHz. The set fault working conditions are as follows: the a phase voltage is raised to k a 1.2, the initial phase angle is shifted by-0.2 pi, i.e. theta a -0.2 pi; drop k of b-phase voltage b 0.5, the initial phase angle is shifted by 0.1 pi, i.e.
Figure BDA00022016774900000813
c-phase voltage drops to k c 0.3, the initial phase angle is shifted by-0.2 pi, i.e.
Figure BDA00022016774900000814
The active power dc is given at 20kW with a power factor of 0.8. It can be seen from the simulation waveform that, because of the serious asymmetric fault of the voltage at 0.1s, the system power before the power oscillation suppression measure is not added has double frequency oscillation to a great extent, and the system is greatly damaged. At the moment, the asymmetric fault voltage of the voltage amplitude and the phase angle can be converted into the voltage amplitude fault in the Fermat point coordinate system, and the problem of the asymmetric fault system is simplified. After the power oscillation suppression method is adopted for 0.2s, the power oscillation starts to be reduced, the direct current quantity of the power is stabilized near a given value, and compared with the reference current which is directly calculated and solved by adopting theoretical calculation for 0.3s, the control effect is not greatly different.
The power oscillation suppression method provided by the invention is based on analysis and research of instantaneous current and instantaneous power in the traditional oscillation suppression method, and provides relevant proof about the correctness of the method:
power oscillation suppression mechanism of one-phase and three-phase three-wire system
When the three-phase three-wire system has asymmetric fault, because the Y/delta transformer exists between the cascade converter and the alternating current system and cuts off the path of the zero sequence component of the voltage and the current on the network side, the zero sequence component is not considered under the general condition, and only the positive sequence component and the negative sequence component are considered. The output instantaneous voltage and output instantaneous current at the ac side of the cascaded converter can be decomposed into:
Figure BDA0002201677490000091
wherein U is + 、U - 、I + 、I - Respectively positive and negative sequence voltage and current amplitude under a Fermat point coordinate system; theta + 、θ - 、
Figure BDA0002201677490000092
The initial phase angle of positive and negative sequence voltage and current under a Fermat point coordinate system; omega is the angular frequency of the power grid; gamma is the phase difference between the voltage and the current in three phases under the Fermat point coordinate system, and the three phases a, b and c are respectively corresponding to 0 degree, -120 degrees and 120 degrees.
Substituting equation (12) into equation (3) yields:
Figure BDA0002201677490000093
in the formula: p is a radical of 0 And q is 0 The direct current components in the instantaneous active power and the reactive power are respectively; p is a radical of c2 、p s2 、q c2 、q s2 The second harmonic component in the instantaneous active power and the reactive power respectively. Wherein:
Figure BDA0002201677490000094
Figure BDA0002201677490000101
From the equations (14) and (15), the double frequency oscillation in the instantaneous active and reactive power of the cascaded converters is represented by U + I - And U - I + The double-frequency oscillation of instantaneous reactive power generated by interaction does not cause serious influence on an actual system, but the double-frequency oscillation of instantaneous active power can cause direct-current bus voltage pulsation to influence the safety and stability of the system, so that the double-frequency oscillation of the active power is the key point of the system to be inhibited. To suppress this, p is required to be c2 +p s2 When the value is 0, the following conditions are satisfied:
Figure BDA0002201677490000102
the following can be obtained in a simultaneous manner:
Figure BDA0002201677490000103
or
Figure BDA0002201677490000104
Equations (17) and (18) are conditions for suppressing the active power frequency doubling oscillation, and the two satisfy one set of conditions, so that the system realizes the active power oscillation suppression.
Novel power oscillation suppression strategy mechanism of two-phase and three-phase three-wire system
The Fermat point coordinate system provided by the invention is used as a reference to analyze an asymmetric fault system, and a voltage asymmetric system with amplitude drop and phase angle shift in a three-phase static coordinate system can be converted into an amplitude drop fault system in the Fermat point coordinate system. The three-phase voltage under the Fermat point coordinate system meets the following expression:
Figure BDA0002201677490000105
k a 、k b 、k c respectively under the Fermat point coordinate system
Figure BDA0002201677490000106
The degree of the drop of the three-phase voltage,
Figure BDA0002201677490000107
For the phase voltage amplitude in the non-fault condition, take
Figure BDA0002201677490000108
When k is a 、k b 、k c A value of 1 indicates no drop, the closer the value is
Figure BDA0002201677490000109
Indicating a deeper drop. ω denotes the grid angular frequency and t denotes time.
The a, b, c three-phase voltages can be expressed as:
Figure BDA0002201677490000111
according to the symmetrical component rule, the positive and negative sequence components of the three-phase voltage in (20) can be solved, wherein the positive and negative sequence components of the a-phase voltage are as follows:
Figure BDA0002201677490000112
the positive and negative sequence component amplitude U of the three-phase voltage under the Fermat point coordinate system can be obtained by the same method + And U - Comprises the following steps:
Figure BDA0002201677490000113
the positive sequence instantaneous voltage of a phase can be obtained by simultaneous equations (20), (21) and (22):
Figure BDA0002201677490000114
from (23), no matter what asymmetric fault occurs to the grid voltage, the positive sequence voltage initial phase angle theta after the Fermat point coordinate system is resolved + 0 ° always holds. According to the negative sequence voltage expression obtained from the formula (21), the initial phase angle theta of the negative sequence voltage can be found - And three-phase drop depth k a 、k b 、k c Are all related to
Figure BDA0002201677490000115
The phase fall depths are the same (0 < k) a ＜1，k b ＝k c ) When theta is greater than theta - 0 or pi.
The reference current vector used by the invention can be synthesized according to the following formula:
Figure BDA0002201677490000116
Figure BDA0002201677490000117
representing the real component of the reference current;
Figure BDA0002201677490000118
a reactive component (j ═ a, b, c) representing a reference current; as used herein, the active component of a reference current can be expressed in the form of a vector as shown in (25):
Figure BDA0002201677490000121
The positive and negative sequence components of the active component of the a-phase reference current are as follows:
Figure BDA0002201677490000122
the positive and negative sequence amplitude I of the active component of the three-phase current under the Fermat point coordinate system can be obtained in the same way + And I - Can be expressed as:
Figure BDA0002201677490000123
by combining the above formulas, the positive sequence component of the active component of the a-phase current can be obtained as follows:
Figure BDA0002201677490000124
compared with the formula (28), under the novel power oscillation suppression strategy provided by the invention, no matter what asymmetric faults occur to the grid voltage, the positive sequence active current phase angle
Figure BDA0002201677490000125
This is always true. Negative sequence current phase angle
Figure BDA0002201677490000126
And three-phase drop depth k a 、k b 、k c All relate to when the a-phase single-phase falls (0 < k) a ＜1，k b ＝k c ) When the temperature of the water is higher than the set temperature,
Figure BDA0002201677490000127
or 0.
According to the analysis, the amplitudes of the positive and negative sequence components of the three-phase voltage and current under the novel power oscillation suppression strategy can be compared, as shown in table 1.
Table 1 comparison of three-phase voltage current positive and negative sequence component amplitudes (j ═ a, b, c) under the novel power oscillation suppression strategy of the present invention
Figure BDA0002201677490000128
From table 1, it can be seen that the actual network side current can realize the novel power oscillation suppression strategy provided by the present inventionWhen the slightly lower reference current vector is subjected to no-difference tracking, the condition that U is satisfied + I - ＝U - I + I.e. to suppress the amplitude condition of the power doubling oscillation.
Table 2 comparison of positive and negative sequence components of a-phase voltage current under the novel power oscillation suppression strategy of the present invention (j ═ a, b, c)
Figure BDA0002201677490000131
As can be seen from Table 2, when the actual grid-side current can realize the error-free tracking of the reference current vector under the novel power oscillation suppression strategy provided by the invention, theta is satisfied + ＝0，
Figure BDA0002201677490000132
The real parts and the imaginary parts of the negative sequence components of the a-phase voltage current are opposite numbers to each other, so that the requirements of the real parts and the imaginary parts of the negative sequence components of the a-phase voltage current are met
Figure BDA0002201677490000133
bc works the same way. The two conditions for restraining the power double-frequency oscillation satisfy an amplitude condition and a second phase angle condition, and prove that the suppression of the power double-frequency oscillation can be realized when the power generated by the positive and negative sequence components of the three-phase alternating voltage is the same. Reactive current
Figure BDA0002201677490000134
Similarly, the system power oscillation suppression condition can also be satisfied.
To sum up: the three-phase three-wire system converter power oscillation suppression method based on the Fermat point defines a fault line voltage triangle equiangular center (namely the Fermat point) as a new neutral point, and converts the asymmetric faults of voltage amplitude drop and phase angle shift in a three-phase static coordinate system into voltage amplitude faults in a Fermat point coordinate system. In addition, through analysis of the relation between power distribution and power oscillation of the asymmetric fault system, a hidden rule that the system has no active power double frequency fluctuation when the power generated by the positive and negative sequence voltages of the three-phase three-wire system is uniformly distributed in three phases is obtained, and a novel power oscillation suppression strategy is designed according to the hidden rule, so that complex coordinate transformation and sequence component calculation are separated, the control complexity is greatly simplified, and a good oscillation suppression effect is achieved. In addition, a current amplitude limiting control strategy is added to ensure that the amplitude of the three-phase current is always within a safety threshold. The invention avoids the complex difficulty of analyzing the variable under the traditional neutral point of the asymmetric fault system, simplifies the asymmetric fault problem by establishing a new neutral point, provides a novel power oscillation suppression strategy based on the discovered system power oscillation rule, solves the power oscillation suppression problem in a brand-new angle, and can provide guidance for selecting the actual system fault coping scheme.
The present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (3)

1. A three-phase three-wire system converter power oscillation suppression method based on a Fermat point is based on a three-phase three-wire system converter under the asymmetrical fault of a power grid, wherein the three-phase three-wire system converter is connected to a Point of Common Coupling (PCC) through a filter and then exchanges power with a three-phase independent power grid, the converter adopts a cascade H-bridge structure, and the method is characterized by comprising the following steps of:
step S1: three-phase three-wire system line voltage under power grid asymmetric fault obtained through voltage fault detection equipment
Figure FDA0003591613640000011
Amplitude a, line voltage
Figure FDA0003591613640000012
Amplitude b, line voltage
Figure FDA0003591613640000013
The amplitude c and the grid angular frequency omega are converted into a new neutral point, namely a Fermat point O F Lower three-phase voltage vector
Figure FDA0003591613640000014
Therefore, voltage asymmetric faults of amplitude drop and phase angle shift in a three-phase static coordinate system can be converted into voltage amplitude faults in a Fermat point coordinate system;
Step S2: instantaneous active power p of three-phase three-wire system asymmetric fault system abc_F Instantaneous reactive power q abc_F Respectively corresponding to given value P of DC power ref 、Q ref Comparing, and generating control signal P via proportional-integral PI regulation setting 、Q setting Forming a power tracking outer loop;
instantaneous active power p of three-phase three-wire system fault system abc_F Instantaneous reactive power q abc_F The definition is as follows:
Figure FDA0003591613640000015
Figure FDA0003591613640000016
wherein p is aF 、p bF 、p cF Respectively represents three-phase instantaneous active power q under a Fermat point coordinate system aF 、q bF 、q cF Respectively representing three-phase instantaneous reactive power under a Fermat point coordinate system;
Figure FDA00035916136400000114
is the three-phase instantaneous phase voltage under the Fermat point coordinate system,
Figure FDA0003591613640000018
Figure FDA0003591613640000019
a set of voltage quadrature quantities lagging 90 degrees from the Fermat point instantaneous phase voltage;
Figure FDA00035916136400000110
instantaneous network side current of a three-phase three-wire system fault system;
step S3: calculating to obtain the amplitude reference of the three-phase reference current meeting the power oscillation suppression condition according to the rule between the power distribution and the power oscillation of the three-phase three-wire system obtained by mathematical derivation; control signal P setting The amplitude of the active component of the three-phase current is in positive correlation with the control signal Q setting Positive correlation with the amplitude of the reactive component of the three-phase current;
step S4: respectively extracting three-phase voltage phases under a Fermat point coordinate system, indirectly obtaining phase references of three-phase reference currents, and synthesizing three-phase reference current initial vectors by adopting a direct current control method
Figure FDA00035916136400000111
Step S5: the synthesized reference current initial vector may appear at this time
Figure FDA00035916136400000112
The method can not be directly applied to current tracking of a three-phase three-wire system, and a correction link of zero sequence current elimination is required; namely, on the premise of not destroying the power oscillation suppression effect, the redundant part of each phase of reference current is proportionally eliminated according to the amplitude of the three-phase current, and the three-phase reference current vector with the power oscillation suppression effect is obtained
Figure FDA00035916136400000113
Step S6: adding a current amplitude limiting controller, and when the detected three-phase current peak value is larger than the set safety threshold value
Figure FDA00035916136400000218
When the current is detected, the controller automatically adjusts the current amplitude to be reduced to a safe threshold value according to the proportion; at the moment, a three-phase reference current vector which meets the power oscillation suppression condition and has current amplitude not exceeding the limit is obtained
Figure FDA0003591613640000021
Step S7: obtained in the last step
Figure FDA0003591613640000022
As a reference vector, tracking control is carried out on the current at the network side by adopting a double-loop control method combining Proportional Resonance (PR) control and proportional control (P) control to form a current tracking control inner loop, and a voltage control signal is obtained
Figure FDA0003591613640000023
Step S8: the voltage signal obtained in the last step is used
Figure FDA0003591613640000024
And as a three-phase voltage reference wave, generating a duty ratio signal of a switching tube corresponding to the cascaded H bridge through a PWM generator, thereby controlling the switching-on and switching-off of the switching tube of the converter.
2. A fermat point based three-phase three-wire converter power oscillation suppression method as claimed in claim 1 wherein said current vector of interest comprises
Figure FDA0003591613640000025
The synthesis is carried out by adopting the mode shown in formula (3):
Figure FDA0003591613640000026
Figure FDA0003591613640000027
representing active components of three-phase currents, the phases of which and the corresponding phase voltages
Figure FDA0003591613640000028
The phases are the same;
Figure FDA0003591613640000029
representing reactive components of three-phase current, the phase of which is orthogonal to the corresponding phase voltage
Figure FDA00035916136400000210
Phase identity (j ═ a, b, c); therefore, the above-mentioned current vector can be written in the form shown in equation (4):
Figure FDA00035916136400000211
wherein
Figure FDA00035916136400000212
The magnitude of the three-phase current is represented,
Figure FDA00035916136400000213
the initial phase angle of the three-phase current is shown,
Figure FDA00035916136400000214
representing the magnitude of the real components of the three-phase current,
Figure FDA00035916136400000215
the amplitude (j ═ a, b, c) of the reactive component of the three-phase current is shown, ω shows the angular frequency of the power grid, and t shows the time.
3. The Fermat point-based three-phase three-wire converter power oscillation suppression method according to claim 1, characterized in that for a three-phase three-wire system, the traditional neutral point is O belowInstantaneous active power p of asymmetric fault system abc_o Instantaneous reactive power q abc_o Can be expressed as:
Figure FDA00035916136400000216
Figure FDA00035916136400000217
wherein P is ao 、P bo 、P co Respectively represents three-phase instantaneous active power, Q, under the traditional neutral point O ao 、Q bo 、Q co Respectively representing three-phase instantaneous reactive power under the traditional neutral point O;
Figure FDA0003591613640000031
Is three-phase instantaneous phase voltage under the traditional neutral point O,
Figure FDA0003591613640000032
Figure FDA0003591613640000033
a set of voltage quadrature quantities lagging 90 degrees from the three-phase instantaneous phase voltages;
Figure FDA0003591613640000034
instantaneous network side current of a three-phase three-wire system fault system;
for a three-phase three-wire system, the instantaneous power in the Fermat point coordinate system satisfies the following formula:
Figure FDA0003591613640000035
Figure FDA0003591613640000036
is a traditionNeutral point O to new neutral point O F Due to three-phase three-wire system
Figure FDA0003591613640000037
Figure FDA0003591613640000038
Therefore, for a three-phase three-wire system, the instantaneous active power calculated by converting into the Fermat point coordinate system has an equivalent relation with the instantaneous active power calculated by the traditional neutral point, namely p abc_F ＝p abc_o Instantaneous reactive power q abc_F ＝q abc_o The same process is carried out; therefore, the instantaneous power of the three-phase three-wire system can be directly measured by measuring p under the Fermat point coordinate system abc_F 、q abc_F Thus obtaining the product.
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103326609A (en) * 2012-03-22 2013-09-25 张家港智电柔性输配电技术研究所有限公司 Controlling method for three-phase voltage type grid inverter
CN105182177A (en) * 2015-07-15 2015-12-23 深圳市华沃表计科技有限公司 Method for detecting actual power grid power supply state in three-phase meter zero line breaking condition
CN107196327A (en) * 2017-07-12 2017-09-22 华北电力科学研究院有限责任公司 The feed forward control method of suppression module voltage-source type converter valve oscillation of power

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103326609A (en) * 2012-03-22 2013-09-25 张家港智电柔性输配电技术研究所有限公司 Controlling method for three-phase voltage type grid inverter
CN105182177A (en) * 2015-07-15 2015-12-23 深圳市华沃表计科技有限公司 Method for detecting actual power grid power supply state in three-phase meter zero line breaking condition
CN107196327A (en) * 2017-07-12 2017-09-22 华北电力科学研究院有限责任公司 The feed forward control method of suppression module voltage-source type converter valve oscillation of power

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