CN107834559B - Transformer integrated power quality intelligent adjusting system and control method thereof - Google Patents

Transformer integrated power quality intelligent adjusting system and control method thereof Download PDF

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CN107834559B
CN107834559B CN201711115102.8A CN201711115102A CN107834559B CN 107834559 B CN107834559 B CN 107834559B CN 201711115102 A CN201711115102 A CN 201711115102A CN 107834559 B CN107834559 B CN 107834559B
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voltage
transformer
impedance
harmonic
winding
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CN107834559A (en
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李勇
王绍阳
刘乾易
曹一家
罗隆福
王鹏程
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Hunan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • 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
    • Y02E40/40—Arrangements for reducing harmonics

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Abstract

The invention discloses a transformer integrated electric energy quality intelligent regulation system and a control method thereof, wherein the system comprises an industrial power distribution network, a transformer, an industrial rectification load and three intelligent impedance branches; the industrial power distribution network, the industrial rectification load and the three intelligent impedance branches are connected together through a transformer; the transformer network side winding adopts a star connection mode and is connected with an industrial power distribution network; a load winding in a secondary low-voltage winding of the transformer adopts a star connection mode and is connected with an industrial rectification load; the filter winding in the secondary low-voltage winding of the transformer adopts a triangular connection mode, and the three intelligent impedance branches are connected with the filter winding in a star connection mode. On the premise of realizing multi-target control, the invention reduces the design difficulty of the induction filter transformer, simplifies the physical tuning process of the traditional passive filter, simultaneously shields the load harmonic on the secondary side of the transformer, reduces the loss of the harmonic current to the transformer and has good environmental adaptability.

Description

Transformer integrated power quality intelligent adjusting system and control method thereof
Technical Field
The invention relates to the technical field of power quality control, in particular to a transformer integrated power quality intelligent adjusting system combining an intelligent impedance principle and an induction filtering technology and a control method thereof.
Background
With the further development of power electronics of a power system, various fully-controlled devices are widely applied to power loads, and due to the nonlinear characteristics of the devices, power quality problems such as reactive loss, system network side voltage and current distortion, local series-parallel resonance and the like are inevitably caused to a power grid.
The research on the comprehensive treatment of harmonic waves is a hot topic in the field of power electronics, and the current main methods can be divided into active treatment and passive treatment. The active management starts from the aspect of harmonic generation, and mainly aims at the improvement of equipment, the research and the development of an improved electric energy change device. The active treatment method has the disadvantages of high technical difficulty and high cost, and can not be easily adopted generally. The passive treatment mode is a method for inhibiting or isolating harmonic waves on the premise that the harmonic waves are generated, and is mainly realized by additionally arranging filtering devices such as a passive filter, an active filter or a hybrid active filter.
At present, the passive filter device occupies the main position of harmonic suppression by virtue of low cost, and is widely applied to the whole industrial rectification system. However, the passive filter is formed by combining a filter capacitor, a reactor, and a resistor in a certain ratio corresponding to different harmonics, and is only for harmonics of a fixed frequency, and cannot function when load harmonics dynamically change. The active filter can actively filter harmonic current in a tracking manner according to the designed characteristics of the active filter, and the reactive power required by the system is dynamically compensated. However, the active filter has high price, small capacity and large construction and maintenance operation investment, so that large-area popularization and use are difficult.
In recent times, related scholars have proposed a method of suppressing harmonic currents on the load side-inductive filtering. The induction filtering technology is based on a rectifier transformer, the winding parameters of the transformer are specially designed by researching the magnetic potential balance principle of the transformer, and the effect of a passive filtering branch circuit is added, so that harmonic waves are effectively restrained on the low-voltage side of the transformer, and the influence of the harmonic waves on a network side system is prevented. The method enables the harmonic current to flow through the harmonic tuning branch, and reduces the loss of the transformer. However, because the method is based on the passive filtering technology, the resonance is inevitably generated, and the passive filtering tuning branch can only fixedly compensate the reactive power consumed by part of the system. In addition, the inductive filtering technology also needs to meet the requirement of dual zero impedance, and as for the existing technology, the transformer winding and the monotonic tuning filtering branch have certain difficulty in realizing zero impedance.
Disclosure of Invention
In view of the above, the invention aims to solve the defects of the induction filtering technology in the application of the industrial rectification system, optimize the design structure, and innovatively provide an intelligent regulating system for the quality of the transformer integrated electric energy and a control method thereof by combining the induction filtering technology and the intelligent impedance principle on the basis of analyzing the current main technology for controlling the quality of the electric energy. The system carries out optimization design on the controller through an intelligent impedance principle, and can realize multi-target control of reactive dynamic compensation, bidirectional harmonic current suppression, resonance damping and the like. In addition, the novel tuning branch can be automatically adjusted through a control strategy, so that the physical tuning process of the traditional passive filter is simplified, and the novel tuning branch has good environmental adaptability.
The invention realizes the aim through the following technical scheme:
an intelligent transformer integrated power quality adjusting system comprises an industrial power distribution network, a transformer, an industrial rectification load and three intelligent impedance branches; the industrial power distribution network, the industrial rectification load and the three intelligent impedance branches are connected together through a transformer;
the transformer network side winding adopts a star connection mode and is connected with an industrial power distribution network; a load winding in a secondary low-voltage winding of the transformer adopts a star connection mode and is connected with an industrial rectification load; the filter winding in the secondary low-voltage winding of the transformer adopts a triangular connection mode, and the three intelligent impedance branches are connected with the filter winding in a star connection mode.
Furthermore, the intelligent impedance branch comprises a capacitor bank, a coupling transformer and a voltage source inverter, wherein the voltage source inverter is connected in series with a winding on one side of the coupling transformer, one end of a winding on the other side of the coupling transformer is connected with a filter winding of the transformer, the other end of the winding is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded.
Further, the transformer integrates an expression of the network side harmonic current of the power quality intelligent adjusting system:
Figure BDA0001466153270000031
wherein: n is a radical of1、N2、N3The number of turns of a net side winding, a load winding and a filter winding of the novel induction filter transformer are respectively; i isLhFor load side harmonic currents, UShIs the power grid background harmonic voltage; zShIs the side source impedance of the power grid under the condition of h harmonic wave, Z1hIs the network side impedance, Z, of the transformer under the condition of h harmonic3hFor the filter winding impedance under h harmonic conditions, ZACTIs the equivalent intelligent impedance of the active filter; ztIs a coupling transformer impedance; zCIs the capacitor bank impedance;
to prevent harmonic load current from flowing into the source, the equivalent impedance of the smart impedance loop must be very low, ideally if Z isACT+Z3h+Zt+ZCWhen the value is 0, then ILhAll the current flows through the intelligent impedance loop and does not flow into a power grid any more; the intelligent impedance loop must be U when considering the source side background harmonic voltageShInfinite impedance is provided, harmonic distortion of the voltage of the power grid is blocked, and meanwhile, harmonic current feedback control automatically provides resonance damping to avoid resonance between the intelligent impedance branch and the impedance of the power grid;
in the dynamic compensation of reactive power at fundamental frequency, ZACTThe impedance value is based on the fundamental current I of the power gridS1And fundamental wave voltage US1The smart impedance is automatically adjusted to maintain the phase of the fundamental voltage and current at a desired level.
A control method of a transformer integrated power quality intelligent regulation system specifically comprises the following steps:
s1, the control system suppresses multiple harmonic components;
s2, the control system dynamically compensates the reactive power in the power grid;
s3, the control system keeps the voltage of the direct current side stable;
and S4, superposing control signals obtained by the harmonic suppression part, the reactive compensation part and the direct current voltage stabilization part, and providing pulse signals for the main circuit through PWM modulation.
Further, the specific steps in step S1 are as follows:
s11, sampling three-phase current signals of a side a, a side b and a side c of the power grid, and obtaining all harmonic components except a fundamental wave signal through a notch filter;
s12, carrying out PR control algorithm on each subharmonic component to obtain the intelligent impedance terminal voltage U corresponding to each subharmonicafh；
S13, corresponding U to each harmonicafhThe control signals of the harmonic suppression part are obtained through integration.
Further, in step S11, the transfer function of the notch filter is as follows:
Figure BDA0001466153270000041
where s is a complex variable with zero real part and angular frequency imaginary part, ωcIs the bandwidth, ω, of the notch filter0Is the resonant frequency.
Further, in step S12, the control algorithm of the system for the harmonic component is based on the PR controller, which is mathematically transformed based on the PI control algorithm, and the expression is as follows:
Figure BDA0001466153270000042
where s is a complex variable with zero real part and angular frequency imaginary part, kpIs the proportional gain, krIs the resonance term gain, ω is the resonance frequency, and its high gain at the resonance frequency ω provides zero steady state error for the sinusoidal reference value;
in the suppression of multiple harmonics, a plurality of PR controllers are connected in parallel, the harmonics of a plurality of frequencies are compensated, and each harmonic of a specific frequency corresponds to a terminal voltage U which generates an intelligent impedanceafhVoltage corresponding to all frequenciesSum of (1) UafI.e. the required terminal voltage of the inverter.
Further, in step S2, the transformer integrated with the intelligent power quality regulation system obtains the fundamental voltage U of the power grid in the reactive power compensation control part by using the same harmonic component strategy as described aboveS1And fundamental current IS1Component, phase detection algorithms calculate the phase difference between the two signals once US1And IS1Is a pure sinusoidal signal and has no noise, the phase difference can be obtained from the zero crossing point, and the phase difference signal controls the voltage U at the end of the active filter which is connected with the capacitor bank in seriesaf1Amplitude of the capacitor bank voltage U at fundamental frequencyC1Given by:
UC1＝UF1-Uaf1
wherein U isF1For filtering winding terminal voltage, U, at fundamental frequencyC1Is the terminal voltage of the capacitor bank at fundamental frequency, Uaf1Is the active filter terminal voltage;
neglecting the voltage drop caused by the grid impedance under fundamental conditions, so UF1Is constant, maintains Uaf1And UC1In-phase alignment because the voltage drop at the fundamental frequency of the coupling transformer is very low UC1And UF1The phase difference between the two can be ignored, and the U is controlledaf1Thereby changing UC1And further reactive compensation is realized.
Further, the specific steps in step S2 are as follows:
s21, sampling three-phase current signals of a side a, b and c of the power grid, and obtaining a fundamental current of the three phases a, b and c after the signals pass through a notch filter and relevant changes;
s22, sampling three-phase voltage signals of a side a, b and c of the power grid, and obtaining a fundamental voltage of the three phases a, b and c after the signals pass through a notch filter and relevant changes;
s23, phase difference is obtained by phase detection of voltage and current signals of a phase, a phase and a phase under fundamental frequency;
and S24, comprehensively controlling the detected phase difference to obtain a control signal for reactive compensation.
Further, the specific steps in step S3 are as follows:
s31, sampling the voltage of the direct current capacitor of the inverter, subtracting the voltage from the reference voltage, and obtaining a voltage stabilization active control quantity through a PI controller;
s32, directly obtaining the fundamental frequency sine reference quantity of the current of the intelligent impedance branch circuit through a notch filter and operation;
and S33, multiplying the voltage stabilization active control quantity by the current fundamental frequency sine reference quantity to obtain a control signal of the direct current voltage stabilization.
Compared with the prior art, the invention has the following beneficial effects:
1) due to the application of the intelligent impedance, on one hand, the transformer does not need to meet the zero impedance condition like the original induction filter transformer, the design difficulty of the transformer is reduced, and the design cost is reduced; on the other hand, according to the magnetic potential balance principle of the transformer, load harmonic waves are shielded on the secondary side of the transformer, and the loss of harmonic current to the transformer is reduced.
2) The invention can regulate and control the voltage at two ends of the active inverter under the fundamental frequency to achieve the purpose of the reactive power required by the dynamic compensation system; meanwhile, under the harmonic condition, all harmonic currents generated by the load flow through the intelligent impedance branch by utilizing the integration of the control signals corresponding to the harmonic components, and meanwhile, the harmonic distortion of the voltage of the power grid is blocked. The harmonic current feedback control automatically provides resonance damping to avoid resonance between the filter and the grid impedance.
3) The system optimally designs the controller through an intelligent impedance principle, and the new intelligent impedance branch can be automatically adjusted through a control strategy, so that the physical tuning process of the traditional passive filter is simplified, and the system has good environmental adaptability.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic diagram of an integrated power quality intelligent regulation system of a transformer according to the present invention;
FIG. 2 is a single-phase equivalent circuit of the transformer integrated power quality intelligent regulation system of the present invention;
FIG. 3 is an equivalent circuit diagram of the transformer integrated power quality intelligent regulation system utilizing intelligent impedance to perform reactive power transmission;
FIG. 4 is a schematic diagram of the integrated power quality intelligent regulating system of the transformer according to the present invention;
fig. 5 is a schematic diagram of the transformer integrated power quality intelligent regulation system for controlling multiple harmonic components simultaneously.
Description of reference numerals:
1: industrial power distribution network, 2: mesh-side winding, 3: filter winding, 4: load winding, 5: industrial rectifying load, 6: intelligent impedance branch, 7: coupling transformer, 8: capacitor bank, 9: a voltage source inverter;
10: single-phase equivalent circuit of transformer, 11: industrial rectification load single-phase equivalent circuit, 12: the intelligent impedance branch single-phase equivalent circuit;
13: PR resonance control, 14: reactive compensation control, 15: and D, direct current voltage stabilization control.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art without any inventive work based on the embodiments of the present invention belong to the protection scope of the present invention.
As shown in fig. 1, the schematic diagram of an intelligent transformer-integrated power quality adjustment system is shown, and the system includes an industrial power distribution network 1, a transformer, an industrial rectification load 5, and three intelligent impedance branches 6. The industrial power distribution network 1, the industrial rectification load 5 and the three intelligent impedance branches 6 are connected together through a transformer.
The transformer network side winding 2 adopts a star connection mode and passes through system impedance ZSIs connected with an industrial power distribution network 1; a load winding 4 in the secondary low-voltage winding adopts a star connection mode and is connected with an industrial rectification load 5; the filter winding 3 in the secondary low-voltage winding adopts a triangular connection mode, and the three intelligent impedance branches 6 are connected with the filter winding 3 in a star connection mode. Through design adjustment of the system to the intelligent impedance, the equivalent impedance of the whole intelligent impedance filter loop including the filter winding in the secondary low-voltage winding can be close to 0.
The specific intelligent impedance filtering loop consists of an intelligent impedance branch circuit 6 and a filtering winding 3; the intelligent impedance branch circuit 6 is composed of a capacitor bank 8, a coupling transformer 7 and a voltage source type inverter 9, the voltage source type inverter 9 is connected in series on a winding on one side of the coupling transformer 7, one end of a winding on the other side of the coupling transformer 7 is connected with the transformer filter winding 3, the other end of the winding is connected with one end of the capacitor bank 8, and the other end of the capacitor bank 8 is grounded.
The working principle of suppressing multiple harmonic components in the present invention will be described in detail below.
Fig. 2 shows a single-phase equivalent circuit of the transformer integrated power quality intelligent regulation system, which comprises a transformer single-phase equivalent circuit 10, an industrial rectification load single-phase equivalent circuit 11 and an intelligent impedance branch single-phase equivalent circuit 12. In equivalent models Is、UsAnd ZsThe network side current, the network side voltage and the network side impedance are respectively; i isLAnd IfAre the load current and the filter branch current.
According to the transformer magnetic potential balance principle, a multi-winding transformer voltage transfer formula, kirchhoff current and voltage theorem, an expression of network side harmonic current can be deduced:
Figure BDA0001466153270000081
wherein: n is a radical of1、N2、N3Respectively, are novel inductive filtering transformersThe number of turns of the transformer network side winding, the load winding and the filter winding; i isLhFor load side harmonic currents, UShIs the power grid background harmonic voltage; zShIs the side source impedance of the power grid under the condition of h harmonic wave, Z1hIs the network side impedance, Z, of the transformer under the condition of h harmonic3hFor the filter winding impedance under h harmonic conditions, ZACTIs the equivalent intelligent impedance of the active filter; ztIs a coupling transformer impedance; zCIs the capacitor bank impedance.
As can be seen from equation (1), the equivalent impedance of the smart impedance loop must be very low in order to prevent the harmonic load current from flowing into the source. Ideally, if ZACT+Z3h+Zt+ZCWhen the value is 0, then ILhAll the current flows through the intelligent impedance loop and does not flow into a power grid any more; at this time ZACTMust be controlled to a value of ZACT＝-(Z3h+Zt+ZC) The passive impedance of the intelligent impedance loop is the impedance of the coupling transformer (Z)t＝rt+jωLt) And capacitor impedance (Z)c＝rc+1/j ω C) and smart impedance (Z)ACT＝ra+jωLa) And (4) forming. Therefore, the active inductance L should be adjustedaTo make the intelligent impedance of a specific frequency ω auto-tune:
Figure BDA0001466153270000082
the system can realize multiple frequency tuning simultaneously by equivalent of different active inductances for specific frequency harmonics. In addition, it produces an active resistance ra＝-(r3+rt+rc) So as to eliminate the internal resistance of the intelligent impedance loop and convert the internal resistance into an ideal filter under the specific subharmonic condition.
When the source side background harmonic voltage is considered, the intelligent impedance loop must be U as shown in the formula (1)ShProviding infinite impedance. Meanwhile, harmonic current feedback control automatically provides resonance damping to avoid resonance between the smart impedance branch and the grid impedance.
In the ideal supplementFor both cases, IShMust be zero and the equivalent impedance of the smart impedance loop for a particular subharmonic should be:
(1) for the harmonic current at the load side, the equivalent impedance of the intelligent impedance loop is 0;
(2) for the source side background harmonic voltage, the equivalent impedance of the intelligent impedance loop is ∞;
according to the superposition theorem, the voltage U is applied to the voltage type active inverter by considering the two equivalent conditionsafh:
Figure BDA0001466153270000091
When U is turnedafh＝U3hAnd no harmonic current flows into the intelligent impedance loop from the network, namely infinite impedance of the intelligent impedance loop. When U is turnedafh＝-(Z3+Zt+ZC)·IfhThe intelligent impedance loop is realized to realize zero impedance, and the superposition of the two equivalent impedances represents the characteristics of the intelligent impedance.
The reactive compensation principle is as follows:
at fundamental frequency, ZACTThe impedance value is based on the fundamental current I of the power gridS1And fundamental wave voltage US1The included angle theta between them. The smart impedance maintains the phase of the fundamental voltage and current at a desired level by automatic adjustment.
The reactive power provided by the smart impedance can be given by (without taking into account the fully tuned branch resistance r)c):
Figure BDA0001466153270000092
Wherein U isFFor filtering winding terminal voltage at fundamental frequency, XCIs the reactance of a capacitor bank, XACTIs a variable reactance equivalent to an active filter, the reactive power generated being represented by XCAnd XACTThe effect is obtained. FIG. 3 is a schematic diagram of a reactive power transfer equivalent circuit of a system, which can be controlled by controlling the active reactance according to the description of FIG. 3XACTThe method is suitable for different working requirements:
(1) overcomplete-when the reactive power produced by the capacitor bank exceeds the demand of the load. Then adjust XACTTo achieve the purpose of connecting another capacitor (-jX) in series with the capacitor bankACT) The effect of (3) is to increase the equivalent impedance of the branch and to reduce the reactive power delivered. As shown in fig. 3 (a).
(2) Under-compensation-when the reactive power produced by the capacitor bank is insufficient to meet the load requirements. Then XACTControlled as a series inductor (+ jX)ACT) The transferred reactive power is increased by lowering the equivalent impedance of the branches. As shown in fig. 3 (b). The topology of intelligent impedance can adapt to continuous change of reactive power.
The comprehensive control method of the transformer integrated power quality intelligent regulation system is specifically described as follows:
fig. 4 is a comprehensive control strategy diagram of the transformer integrated power quality intelligent regulation system, and the control method of the system is mainly divided into four parts: PR resonance control 13, reactive compensation control 14, direct current regulated voltage control 15 and signal modulation.
(1) PR resonance control
1) Sampling three-phase current signals of a side a, a side b and a side c of the power grid, and obtaining all harmonic components except a fundamental wave signal through a notch filter;
2) respectively carrying out PR control algorithm on each subharmonic component to obtain the intelligent impedance terminal voltage U corresponding to each subharmonicafh；
3) Corresponding the harmonics to UafhThe control signals of the harmonic suppression part are obtained through integration.
The method for detecting harmonic waves of the transformer integrated power quality intelligent regulation system uses a notch filter, and the transfer function of the notch filter is as follows:
Figure BDA0001466153270000101
where s is a complex variable with zero real part and angular frequency imaginary part, ωcIs the bandwidth, ω, of the notch filter0Is the resonant frequency.
The control algorithm of the system for harmonic components is based on a PR controller, and is obtained by mathematical transformation on the basis of a PI control algorithm, and the expression is as follows:
Figure BDA0001466153270000102
where s is a complex variable with zero real part and angular frequency imaginary part, kpIs the proportional gain, krIs the resonance term gain and ω is the resonance frequency. The high gain at its resonant frequency ω provides zero steady state error for the sinusoidal reference value. The method has the similar effect to the PI in the DC line analysis, and can directly reference the current sinusoidal signal, thereby eliminating the transformation of a reference system and the synchronous algorithm of PLL.
In the suppression of multiple harmonics, a plurality of resonance controllers (PR) are connected in parallel, and a plurality of harmonics with specific frequencies are compensated. Each harmonic of specific frequency corresponds to a terminal voltage U of intelligent impedanceafhThe sum U of the voltages for all specific subharmonic frequenciesafI.e. the required terminal voltage of the inverter.
(2) Reactive compensation control
1) Sampling three-phase current signals of a side a, b and c of the power grid, and obtaining a fundamental wave current of the three phases a, b and c after the three-phase current signals pass through a notch filter and relevant changes;
2) sampling three-phase voltage signals of a side a, b and c of the power grid, and obtaining a fundamental voltage of the three phases a, b and c after the three-phase voltage signals pass through a notch filter and relevant changes;
3) phase difference is obtained by phase detection of voltage and current signals of a phase, a phase and a phase under the fundamental frequency;
4) and comprehensively controlling the detected phase difference to obtain a control signal for reactive compensation.
The transformer integrated power quality intelligent regulation system obtains the fundamental wave voltage U of the power grid by using the same harmonic component strategy in the reactive power compensation control partS1And current IS1And (4) components. Phase detection algorithm calculates two signalsThe phase difference between them. Once U is turned onS1And IS1Is a pure sinusoidal signal and has no noise, the phase difference can be obtained from the zero crossings. Phase difference signal control and capacitor bank series active filter terminal voltage Uaf1The amplitude of (d). At fundamental frequency, the capacitor bank voltage UC1Given by:
UC1＝UF1-Uaf1
wherein U isF1For filtering winding terminal voltage, U, at fundamental frequencyC1Is the terminal voltage of the capacitor bank at fundamental frequency, Uaf1Is the active filter terminal voltage.
Neglecting the voltage drop caused by the grid impedance under fundamental conditions, so UF1Is constant. Holding Uaf1And UC1In-phase alignment because the voltage drop at the fundamental frequency of the coupling transformer is very low UC1And UF1The phase difference between the two can be ignored, and the U is controlledaf1Thereby changing UC1And further reactive compensation is realized.
(3) DC regulated control
1) Sampling the DC capacitor voltage of the inverter, subtracting the reference voltage, and obtaining a voltage stabilization active control quantity through a PI controller;
2) directly obtaining the fundamental frequency sine reference quantity of the current of the intelligent impedance branch circuit through a notch filter and operation;
3) and multiplying the voltage stabilization active control quantity by the current fundamental frequency sine reference quantity to obtain a control signal of the direct current voltage stabilization.
(4) Signal modulation
1) Superposing control signals obtained by the harmonic suppression part, the reactive compensation part and the direct current voltage stabilization part to obtain control signals;
2) and the control signal is modulated by PWM to provide a pulse signal for the main circuit.
Fig. 5 is a schematic diagram of the transformer integrated power quality intelligent regulation system of the present invention for simultaneously controlling multiple harmonic components, and it can be seen that a plurality of resonance controllers (PR) are connected in parallel and simultaneously compensate for harmonics of multiple frequencies.
The invention aims to solve the defects of the application of an inductive filtering technology in an industrial rectifying system, and provides an intelligent regulating system for the quality of integrated electric energy of a transformer by combining the inductive filtering technology and the thought of intelligent impedance. The system redesigns the filtering branch of the original induction regulation and control filtering system by an intelligent impedance principle, reduces the design difficulty of the transformer and simplifies the traditional full-tuning branch. The new tuning branch consists of a capacitor bank, a coupling transformer and an active inverter connected in series with the coupling transformer. The transformer is installed near the industrial rectifying load and has a three-winding structure. The main winding adopts a star-shaped connecting wire and is connected with the power grid side, the industrial rectification load is connected with the star-shaped winding used as a valve winding, and the filter winding is connected with the tuning branch and the active inverter by adopting a triangular connecting wire. On one hand, the purpose of reactive power required by a dynamic compensation system can be achieved by regulating and controlling the voltage at two ends of the active inverter under the fundamental frequency; on the other hand, the system can utilize the integration of the control signals corresponding to the harmonic components of each time, so that the load harmonic current can completely flow through the intelligent impedance branch, and meanwhile, the harmonic distortion of the voltage of the power grid is blocked. The harmonic current feedback control automatically provides resonance damping to avoid resonance between the smart impedance branch and the grid impedance.
Compared with the prior art, the invention has the following technical advantages:
1) due to the application of the intelligent impedance, on one hand, the transformer does not need to meet the zero impedance condition like the original induction filter transformer, the design difficulty of the transformer is reduced, and the design cost is reduced; on the other hand, according to the magnetic potential balance principle of the transformer, load harmonic waves are shielded on the secondary side of the transformer, and the loss of harmonic current to the transformer is reduced.
2) The invention can regulate and control the voltage at two ends of the active inverter under the fundamental frequency to achieve the purpose of the reactive power required by the dynamic compensation system; meanwhile, under the harmonic condition, all harmonic currents generated by the load flow through the intelligent impedance branch by utilizing the integration of the control signals corresponding to the harmonic components, and meanwhile, the harmonic distortion of the voltage of the power grid is blocked. The harmonic current feedback control automatically provides resonance damping to avoid resonance between the smart impedance branch and the grid impedance.
3) The system optimally designs the controller through an intelligent impedance principle, and the new intelligent impedance branch can be automatically adjusted through a control strategy, so that the physical tuning process of the traditional passive filter is simplified, and the system has good environmental adaptability.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (9)

1. The transformer integrated power quality intelligent regulation system is characterized by comprising an industrial power distribution network, a transformer, an industrial rectification load and three intelligent impedance branches; the industrial power distribution network, the industrial rectification load and the three intelligent impedance branches are connected together through a transformer;
the transformer network side winding adopts a star connection mode and is connected with an industrial power distribution network; a load winding in a secondary low-voltage winding of the transformer adopts a star connection mode and is connected with an industrial rectification load; the filter winding in the secondary low-voltage winding of the transformer adopts a triangular connection mode, and three intelligent impedance branches are connected with the filter winding in a star connection mode;
the transformer integrated power quality intelligent regulation system comprises an expression of network side harmonic current:
Figure FDA0002619423950000011
wherein: n is a radical of1、N2、N3The number of turns of a net side winding, a load winding and a filter winding of the novel induction filter transformer are respectively; i isLhFor load side harmonic currents, UShIs the power grid background harmonic voltage; zShIs the side source impedance of the power grid under the condition of h harmonic wave, Z1hIs the network side impedance, Z, of the transformer under the condition of h harmonic3hFor the filter winding impedance under h harmonic conditions, ZACTIs the equivalent intelligent impedance of the active filter; ztIs a coupling transformer impedance; zCIs the capacitor bank impedance;
to prevent harmonic load currents from flowing into the net side, the equivalent impedance of the smart impedance loop must be very low, ideally if Z isACT+Z3h+Zt+ZCWhen the value is 0, then ILhAll the current flows through the intelligent impedance loop and does not flow into a power grid any more; when the background harmonic voltage of the power grid is considered, the intelligent impedance loop is UShInfinite impedance is provided, harmonic distortion of the voltage of the power grid is blocked, and meanwhile, harmonic current feedback control automatically provides resonance damping to avoid resonance between the intelligent impedance branch and the impedance of the power grid;
in the dynamic compensation of reactive power at fundamental frequency, ZACTThe impedance value is based on the fundamental current I of the power gridS1And fundamental wave voltage US1The smart impedance is automatically adjusted to maintain the phase of the fundamental voltage and current at a desired level.
2. The transformer integrated power quality intelligent regulation system of claim 1, wherein the intelligent impedance branch comprises a capacitor bank, a coupling transformer, a voltage source inverter; the voltage source inverter is connected in series with a winding on one side of the coupling transformer, one end of a winding on the other side of the coupling transformer is connected with a filter winding of the transformer, the other end of the winding is connected with one end of the capacitor bank, and the other end of the capacitor bank is grounded.
3. The control method of the transformer integrated power quality intelligent regulation system according to any one of claims 1 to 2, characterized by comprising the following steps:
s1, the control system suppresses multiple harmonic components;
s2, the control system dynamically compensates the reactive power in the power grid;
s3, the control system keeps the voltage of the direct current side stable;
and S4, superposing control signals obtained by the harmonic suppression part, the reactive compensation part and the direct current voltage stabilization part, and providing pulse signals for the main circuit through PWM modulation.
4. The control method of the transformer integrated electric energy quality intelligent regulation system according to claim 3, characterized in that the specific steps in step S1 are as follows:
s11, sampling three-phase current signals of a side a, a side b and a side c of the power grid, and obtaining all harmonic components except a fundamental wave signal through a notch filter;
s12, carrying out PR control algorithm on each subharmonic component to obtain the intelligent impedance terminal voltage U corresponding to each subharmonicafh；
S13, corresponding U to each harmonicafhThe control signals of the harmonic suppression part are obtained through integration.
5. The method for controlling the transformer integrated power quality intelligent regulation system according to claim 4, wherein in step S11, the transfer function of the notch filter is as follows:
Figure FDA0002619423950000021
where s is a complex variable with zero real part and angular frequency imaginary part, ωcIs the bandwidth, ω, of the notch filter0Is the resonant frequency.
6. The method as claimed in claim 4, wherein in step S12, the control algorithm of the system for harmonic components is based on PR controller, which is obtained by mathematical transformation based on PI control algorithm, and its expression is as follows:
Figure FDA0002619423950000031
where s is a complex variable with zero real part and angular frequency imaginary part, kpIs the proportional gain, krIs the resonance term gain, ω is the resonance frequency, and its high gain at the resonance frequency ω provides zero steady state error for the sinusoidal reference value;
in the suppression of multiple harmonics, a plurality of PR controllers are connected in parallel, and simultaneously, a plurality of harmonics with specific frequencies are compensated, wherein each harmonic with specific frequency corresponds to a terminal voltage U of an intelligent impedanceafhThe sum of the voltages U corresponding to all particular timesafI.e. the required terminal voltage of the inverter.
7. The method as claimed in claim 3, wherein in step S2, the transformer-integrated power quality intelligent regulation system uses the grid-side initial sampling voltage and current signals to subtract the voltage and current harmonic components obtained after being processed by the notch filter to obtain the fundamental voltage Ufundamental in the reactive power compensation control partS1And fundamental current IS1Component, phase detection algorithms calculate the phase difference between the two signals once US1And IS1Is a pure sinusoidal signal and has no noise, the phase difference can be obtained from the zero crossing point, and the phase difference signal controls the voltage U at the end of the active filter which is connected with the capacitor bank in seriesaf1Amplitude of the capacitor bank voltage U at fundamental frequencyC1Given by:
UC1＝UF1-Uaf1
wherein U isF1For filtering winding terminal voltage, U, at fundamental frequencyC1Is the terminal voltage of the capacitor bank at fundamental frequency, Uaf1Is the active filter terminal voltage;
neglecting the voltage drop caused by the grid impedance under fundamental conditions, so UF1Is constant, maintains Uaf1And UC1In-phase alignment because the voltage drop at the fundamental frequency of the coupling transformer is very low UC1And UF1The phase difference between the two can be ignored, and the controlSystem Uaf1Thereby changing UC1And further reactive compensation is realized.
8. The control method of the transformer integrated electric energy quality intelligent regulation system according to claim 3, characterized in that the specific steps in step S2 are as follows:
s21, sampling three-phase current signals of a side a, b and c of the power grid, and obtaining a fundamental current of the three phases a, b and c after the signals pass through a notch filter and relevant changes;
s22, sampling three-phase voltage signals of a side a, b and c of the power grid, and obtaining a fundamental voltage of the three phases a, b and c after the signals pass through a notch filter and relevant changes;
s23, phase difference is obtained by phase detection of voltage and current signals of a phase, a phase and a phase under fundamental frequency;
and S24, comprehensively controlling the detected phase difference to obtain a control signal for reactive compensation.
9. The control method of the transformer integrated electric energy quality intelligent regulation system according to claim 3, characterized in that the specific steps in step S3 are as follows:
s31, sampling the voltage of the direct current capacitor of the inverter, subtracting the voltage from the reference voltage, and obtaining a voltage stabilization active control quantity through a PI controller;
s32, directly obtaining the fundamental frequency sine reference quantity of the current of the intelligent impedance branch circuit through a notch filter and operation;
and S33, multiplying the voltage stabilization active control quantity by the current fundamental frequency sine reference quantity to obtain a control signal of the direct current voltage stabilization.
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