CN112086992A - Harmonic suppression method in flexible direct current transmission system - Google Patents
Harmonic suppression method in flexible direct current transmission system Download PDFInfo
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- CN112086992A CN112086992A CN202010914517.7A CN202010914517A CN112086992A CN 112086992 A CN112086992 A CN 112086992A CN 202010914517 A CN202010914517 A CN 202010914517A CN 112086992 A CN112086992 A CN 112086992A
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- 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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention discloses a harmonic suppression method in a flexible direct current transmission system, which is characterized in that a harmonic suppressor is arranged to sample upper and lower bridge arm currents of a modular multi-level converter, an output current signal passes through a proportional resonance controller to generate a harmonic suppression wave which is superposed on modulation waves of a converter level controller and a circulating current suppression controller to obtain a total modulation wave, the total modulation wave is sent to an FPGA, and the FPGA generates pulse information to be executed by an IGBT in a modular multi-level converter MMC according to capacitance voltage information, bridge arm currents and modulation wave information. The harmonic suppression method in the flexible direct current transmission system has the advantages of universality, simple control structure, suitability for different power operation modes and the like.
Description
Technical Field
The invention relates to a flexible direct current transmission system, in particular to a harmonic suppression method in the flexible direct current transmission system.
Background
MMC-HVDC (Modular Multilevel Converter, MMC; High Voltage Direct Current, HVDC) is a new generation of Direct Current transmission technology and develops very rapidly. The method has the characteristics of high modularization, easiness in expansion, good output voltage waveform and the like, and is particularly suitable for medium-high voltage high-power systems.
Harmonic waves and suppression thereof are important technical problems in high voltage direct current transmission. In the existing direct current transmission engineering case, the factors such as series compensation of a transmission system, wind power generation access, improper parameter setting of a conventional direct current converter and the like can cause subsynchronous oscillation or higher harmonic oscillation of the system. For a flexible direct current transmission system, the two harmonic waves are harmful that the harmonic content of bridge arm current and a power module is increased when oscillation current is injected into an MMC-HVDC system, on one hand, the loss and the current stress of an MMC power switch device are increased, on the other hand, the oscillation of direct current side current is caused, and the phenomena of continuous vibration, overcurrent tripping and the like of the system are caused when the system is serious. At present, a current converter level controller is mostly adopted to deal with harmonic suppression, for example, an additional damping controller and an active or reactive current loop control mode are adopted. However, the scheme has large calculation amount and complex structure, and cannot be universally used under the influence of the active or reactive outer loop control mode of the converter.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a harmonic suppression method in a flexible direct current transmission system.
The technical scheme is as follows: the invention provides a harmonic suppression method in a flexible direct-current transmission system, which is characterized in that a harmonic suppressor is arranged to sample and process upper and lower bridge arm currents of a modular multi-level converter, an output current signal passes through a proportional resonance controller to generate a harmonic suppression wave which is superposed on modulation waves of a converter level controller and a circulating current suppression controller to obtain a total modulation wave, the total modulation wave is sent to an FPGA, and the FPGA generates pulse information to be executed by an IGBT in a modular multi-level converter MMC according to capacitance voltage information, the bridge arm currents and the modulation wave information.
In the implementation, the operation of extracting the harmonic component by the harmonic suppressor is as follows:
firstly, current of an upper bridge arm and a lower bridge arm are sampled and then superposed;
secondly, reducing half of the superposed current to obtain iphx (x ═ a, b and c), and filtering out harmonic components through a first-order low-pass filter LPF to obtain direct-current components idcx (x ═ a, b and c);
and thirdly, subtracting the direct current component idcx (x ═ a, b, c) from the iphx (x ═ a, b, c) current to obtain a harmonic current component ihrx (x ═ a, b, c) in each phase.
The implementation of the first order low pass filter LPF in the second step is shown in formula (1), where ω iscAnd s is a variable of the Laplace transform commonly used in the control field.
Wherein the cut-off frequency is 10 Hz.
The current signal output by the LPF passes through the proportional resonant controller, and the implementation scheme is shown in formula (2), wherein k ispIs a proportionality coefficient, krAs proportional parameter of the resonant controller, omeganFor higher harmonic frequencies to be suppressed, omegacIs the bandwidth of harmonic wave, and s is the general Laplace transform variable in the control field.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the scheme directly inhibits the current harmonic waves of the bridge arm, can reduce the calculation amount of judging the power running mode, monitoring the harmonic waves and the like, and is easy to be applied to a large-scale and multi-valve-group complex flexible direct-current power transmission system. By restraining harmonic current, the loss and current stress of the MMC power switch device can be reduced, and the reliability and economy of system operation are improved.
Drawings
FIG. 1 is a converter valve topology diagram of a flexible DC power transmission system;
FIG. 2 is a block diagram of harmonic suppressor harmonic component extraction and processing;
FIG. 3 is a control block diagram of a proportional resonant controller;
fig. 4 is a block diagram of the integral modulation wave control of the converter valve.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in a converter valve topological diagram of a flexible direct-current transmission system shown in fig. 1, three phase units are connected in parallel to form a direct-current bus, each phase unit comprises an upper bridge arm and a lower bridge arm, each bridge arm is formed by connecting n Power Modules (PM) and a reactor in series, and the reactor provides loop current impedance and inhibits internal loop current. The circuit structure of each power module is the same, and the power module is composed of two IGBTs, two anti-parallel diodes and an energy storage capacitor.
The operation of extracting the harmonic component by using the harmonic suppressor is shown in fig. 2, and the steps are as follows:
firstly, current of an upper bridge arm and a lower bridge arm are sampled and then superposed;
secondly, reducing half of the superposed current to obtain iphx (x ═ a, b and c), and filtering out harmonic components through a first-order low-pass filter LPF to obtain direct-current components idcx (x ═ a, b and c);
and thirdly, subtracting the direct current component idcx (x ═ a, b, c) from the iphx (x ═ a, b, c) current to obtain a harmonic current component ihrx (x ═ a, b, c) in each phase.
A first order low pass filter LPF with a cut-off frequency of 10Hz, and is realized by formula (1), wherein omegacAnd s is a variable of the Laplace transform commonly used in the control field.
Considering that the direct current component of the three-phase bridge arm current has an unbalanced phenomenon when the power grid voltage is unbalanced, a static coordinate system is adopted to independently restrain the three-phase harmonic component, and corresponding amplitude limiting is added.
The harmonic current component in each phase extracted by the harmonic suppressor is ihrx (x ═ a, b, c), and ihrx _ ref (x ═ a, b, c) is set as the control purpose of the three-phase harmonicIn the standard, ihrx _ ref (x ═ a, b, c) is set to 0, and is input to the proportional resonant controller together with the harmonic current component ihrx (x ═ a, b, c), and the proportional resonant controller shown in fig. 3 is characterized in that for low-frequency harmonics, better suppression can be obtained by using the proportional controller; for higher harmonics, a suppression effect can be obtained with a suitable resonance controller. The implementation scheme is shown in formula (2), wherein kpIs a proportionality coefficient, krAs proportional parameter of the resonant controller, omeganFor higher harmonic frequencies to be suppressed, omegacIs the bandwidth of harmonic wave, and s is the general Laplace transform variable in the control field.
As shown in fig. 4, the proportional resonant controller outputs a harmonic suppression wave uhrx _ ref (x is a, b, c) which is superimposed on the modulation wave of the converter-level controller and the circulating current suppression modulation wave, and finally the harmonic suppression wave and the circulating current suppression modulation wave are sent to the FPGA, and the FPGA generates pulse information to be executed by the IGBT of the power module according to the capacitance voltage information, the bridge arm current and the modulation wave information.
Claims (5)
1. A harmonic suppression method in a flexible direct current transmission system is characterized in that a harmonic suppressor is arranged to sample upper and lower bridge arm currents of a modular multi-level converter, an output current signal passes through a proportional resonance controller to generate a harmonic suppression wave which is superposed on modulation waves of a converter level controller and a circulating current suppression controller to obtain a total modulation wave, the total modulation wave is sent to an FPGA, and the FPGA generates pulse information to be executed by an IGBT in a modular multi-level converter MMC according to capacitance voltage information, bridge arm currents and modulation wave information.
2. Method of harmonic suppression in a flexible direct current transmission system according to claim 1, characterized in that the operation of the harmonic suppressor to extract harmonic components is as follows:
firstly, current of an upper bridge arm and a lower bridge arm are sampled and then superposed;
secondly, reducing half of the superposed current to obtain iphx (x ═ a, b and c), and filtering out harmonic components through a first-order low-pass filter LPF to obtain direct-current components idcx (x ═ a, b and c);
and thirdly, subtracting the direct current component idcx (x ═ a, b, c) from the iphx (x ═ a, b, c) current to obtain a harmonic current component ihrx (x ═ a, b, c) in each phase.
3. Method of harmonic suppression in a flexible direct current transmission system according to claim 2, characterized in that the implementation of the first order low pass filter LPF in the second step is given in formula (1), where ω iscAnd s is a variable of the Laplace transform commonly used in the control field.
4. A method of harmonic suppression in a flexible direct current transmission system according to claim 3, characterized in that the cut-off frequency is 10 Hz.
5. The harmonic suppression method in a flexible direct current transmission system according to claim 1, wherein the implementation of the proportional resonant controller is shown in formula (2), wherein k ispIs a proportionality coefficient, krAs proportional parameter of the resonant controller, omeganFor higher harmonic frequencies to be suppressed, omegacIs the bandwidth of harmonic wave, and s is the general Laplace transform variable in the control field.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20140226373A1 (en) * | 2013-02-13 | 2014-08-14 | Korea Electrotechnology Research Institute | Method for Suppressing Circulating Current in Modular Multilevel Converter for High Voltage Direct-Current Transmission |
| CN105811748A (en) * | 2016-01-25 | 2016-07-27 | 杭州电子科技大学 | Modular multi-level converter circulating harmonic inhibition method |
| US20180302003A1 (en) * | 2015-11-04 | 2018-10-18 | Mitsubishi Electric Corporation | Power converter |
| WO2019140584A1 (en) * | 2018-01-18 | 2019-07-25 | 华北电力大学 | Method for online adaptive suppression of high-frequency oscillation caused by flexible direct current |
| CN110504853A (en) * | 2018-05-18 | 2019-11-26 | 南京理工大学 | Improvement circular current control method based on flexible DC transmission |
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2020
- 2020-09-03 CN CN202010914517.7A patent/CN112086992A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20140226373A1 (en) * | 2013-02-13 | 2014-08-14 | Korea Electrotechnology Research Institute | Method for Suppressing Circulating Current in Modular Multilevel Converter for High Voltage Direct-Current Transmission |
| US20180302003A1 (en) * | 2015-11-04 | 2018-10-18 | Mitsubishi Electric Corporation | Power converter |
| CN105811748A (en) * | 2016-01-25 | 2016-07-27 | 杭州电子科技大学 | Modular multi-level converter circulating harmonic inhibition method |
| WO2019140584A1 (en) * | 2018-01-18 | 2019-07-25 | 华北电力大学 | Method for online adaptive suppression of high-frequency oscillation caused by flexible direct current |
| CN110504853A (en) * | 2018-05-18 | 2019-11-26 | 南京理工大学 | Improvement circular current control method based on flexible DC transmission |
Non-Patent Citations (1)
| Title |
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| 樊道庆等: "模块化多电平的谐波补偿控制策略", 《自动化与仪表》 * |
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Application publication date: 20201215 |