CN103346554B - A kind of circulation inhibition method being applied to flexible direct current power transmission system - Google Patents
A kind of circulation inhibition method being applied to flexible direct current power transmission system Download PDFInfo
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- CN103346554B CN103346554B CN201310244952.3A CN201310244952A CN103346554B CN 103346554 B CN103346554 B CN 103346554B CN 201310244952 A CN201310244952 A CN 201310244952A CN 103346554 B CN103346554 B CN 103346554B
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Abstract
The present invention relates to a kind of circulation inhibition method being applied to flexible direct current power transmission system, the bridge arm current signal that utilization detects obtains the additional control signals for suppressing circulation through a laggard row standardization of PI controller.Then by this Signal averaging on existing voltage reference signal, then obtain the Trig control signal of each brachium pontis of circulator through pulse-width modulation, thus make bridge arm voltage close to bridge arm voltage reference value.Adopt this kind of circulation inhibition method, can when not increasing brachium pontis inductance, by loop current suppression in very low level, and this kind of method calculates simple, is easy to Project Realization.
Description
Technical field
The present invention relates to power electronics and custom power field, be specifically related to a kind of novel circulation inhibition method being applied to flexible direct current power transmission system.
Background technology
Relative to traditional flexible direct current power transmission system (based on IGBT serial connection technology), based on modular multilevel circulator (modular multilevel converter, MMC) flexible direct current power transmission system is simple because of its structure, is easy to the features such as engineering construction and is causing the extensive concern of domestic and international experts and scholars in recent years.
In MMC topological structure important feature be storage capacitor has been put into series connection submodule in the middle of.This results in a series of problem, such as due to the existence of bridge arm current, make to be engraved in change during the capacitance voltage of each submodule, how to keep the capacitance voltage of each submodule to stablize and become technological difficulties, in addition, due to the fluctuation of capacitance voltage, make the voltage of upper and lower bridge arm in a phase and not identical with DC bus-bar voltage, cause the generation of circulation.The effect of circulation when rectification is for DC bus provides direct current, and the effect when inversion is for the submodule of upper and lower bridge arm charges.The effective value that circulation alternating current component increases bridge arm current makes the loss of this brachium pontis increase accordingly, and capacitance voltage also can fluctuate larger simultaneously, and the pressure drop of alternating current component on brachium pontis inductance can produce humorous wave interference to valve side output AC voltage in addition.Therefore be necessary to eliminate this alternating current component, to reduce circulation valve loss and to improve the waveform of the alternating voltage that valve side exports.
For in the Analysis on Running Mechanism process of flexible direct current power transmission system, a lot of researcher indicates the method for the mechanism that circulation produces and elimination, the people such as Xu Zheng in patent " a kind of three-phase modular multilevel circulator circulation inhibition method " by two frequency multiplication circulation are carried out dq conversion, additional set amount is provided by uneoupled control, thus realize the suppression of two frequency multiplication electric currents, but which is only applicable to steady state condition; The people such as Tang Guangfu control respectively for low-frequency oscillation and two harmonics in patent " a kind of valve current control method based on modular multilevel circulator ", but this kind of method complexity, and the bad adjustment of controller parameter.
Summary of the invention
The object of this invention is to provide a kind of simple and effective loop current suppression controller, it also has obvious inhibitory action to the electric current flowing through brachium pontis during DC side two-stage short trouble, is conducive to the loss of minimizing system.
For achieving the above object, the solution of the present invention is: a kind of circulation inhibition method being applied to flexible direct current power transmission system, and step is as follows:
1), measuring each phase upper and lower bridge arm electric current, is the inside circulation of corresponding phase divided by two with each phase upper and lower bridge arm electric current (ipj, inj) addition;
2) carry out standardization again after each mutually inner circulation, step 1) obtained and the difference of given circulation signal carry out proportion adjustment and obtain loop current suppression additional control signals;
3), respectively go up bridge arm voltage reference signal (Vpj_ref) mutually and add that described loop current suppression additional control signals obtains correspondence and goes up the final voltage reference signal of brachium pontis (Upj_ref) mutually; Described loop current suppression additional control signals obtains correspondence and descends the final voltage reference signal of brachium pontis (Unj_ref) mutually respectively to descend bridge arm voltage reference signal (Vnj_ref) to add mutually;
4) the final voltage reference signal of each phase upper and lower bridge arm is through pulse duration modulation method, generates the Trig control signal of each brachium pontis.
Because brachium pontis ideal current is DC bus 1/3rd, described step 2) in given circulation signal be 1/3rd of DC bus current.
The invention provides a kind of novel circulation inhibition method being applied to flexible direct current power transmission system, when not increasing brachium pontis inductance, mode only by additional suppression circulation control signal just can by inner for MMC loop current suppression in low-down level, and can effectively suppress two harmonics and also have obvious inhibitory action to the electric current flowing through brachium pontis during DC side two-stage short trouble, be conducive to the loss of minimizing system.
Accompanying drawing explanation
Fig. 1 is flexible DC power transmission basic structure;
Fig. 2 is control block diagram of the present invention;
Fig. 3 is loop current suppression controller architecture figure;
Fig. 4 adopts A phase circulation before and after circulation inhibition method of the present invention;
Fig. 5 (a), Fig. 5 (b) adopt the electric electric current of the upper brachium pontis of A phase before and after circulation inhibition method of the present invention.
Embodiment
Below in conjunction with accompanying drawing, the present invention will be further described in detail.
Flexible direct current power transmission system is made up of three-phase six brachium pontis, and each brachium pontis is by be coupled or uncoupled inductance and several identical submodule SM cascades are formed.Each submodule comprises two IGBT, two backward diodes and DC capacitor composition, structure as shown in Figure 1, direct current and upper and lower bridge arm electric current (Ipa, Ipb, Ipc, Ina, Inc, Inc), voltage (Upa, Upb, Upc, Una, Unc, Unc) as shown in Figure 1.Wherein j=a, b, c, represent abc three-phase respectively, p represents brachium pontis, and n represents lower brachium pontis, and Id, Vd are DC bus current and voltage.
Circulation inhibition method is as follows:
Measure each bridge arm current, calculate the inside circulation Idiffj of each phase: every mutually inner circulation obtains divided by two after being added by this phase upper and lower bridge arm electric current (ipj, inj).
Carry out standardization again after the difference of inside circulation signal (Idiffj) calculated and given circulation signal (Id/3) is carried out proportion adjustment and namely obtain loop current suppression additional control signals, as Fig. 3, given circulation signal gets Id/3.
Adopt ripe Direct Current Closed-loop Control Strategy herein, this control strategy comprises outer ring controller, interior ring controller.Outer ring controller is mainly used in response operator control instruction, and power instruction reference value, the power elevation rate of the power control mode that control system issues according to operations staff and correspondence, analytical calculation completes corresponding inner ring current reference instruction.Interior ring controller receives outer ring controller and calculates the active current reference value Idref and reactive current reference value Iqref that produce, and compare analysis with current actual active current Id, reactive current Iq, to between deviation carry out PI control, and add voltage feedforward control link, common analytical calculation completes converter bridge arm modulation voltage and calculates, and the upper bridge arm voltage reference signal (Vpj_ref) obtained adds that namely loop current suppression additional control signals obtains the final voltage reference signal of brachium pontis (Upj_ref) in j phase; Add that namely loop current suppression additional control signals obtains the final voltage reference signal of brachium pontis (Unj_ref) under j phase with the lower bridge arm voltage reference signal (Vnj_ref) that dual-loop controller obtains, Upj_ref, Unj_ref, through pulse duration modulation method, generate corresponding six brachium pontis Trig control signals, control turning on and off of IGBT in each submodule, thus ensure that bridge arm voltage actual value is identical with the reference value of bridge arm voltage, realize each phase voltage and control.
As Fig. 4, before 0.9s, circulation controller does not work, and after 0.9s, circulation controller starts the A phase circulation response wave shape figure after working.As can be seen from A phase circulation response condition, this controller is to bridge arm current, and current on line side and direct voltage all do not cause very large impact, and corresponding speed is very fast.The design of controller only have employed ratio (K) controller in addition, enormously simplify the complexity of control system, is conducive to the use of engineering.
When the DC side both positive and negative polarity generation direct short-circuit fault of rectifier, when making direct voltage become 0, under adopting control method situation of the present invention, bridge arm current, current on line side and direct current all can not be undergone mutation, and the maximum that fault reaches obviously reduces, this is that fault processes the time achieving preciousness further.Specifically see Fig. 5 (a) and (b).
Fig. 5 (a) is depicted as when not having this circulation controller, when when 0.8s, the DC side both positive and negative polarity of rectifier is short-circuited fault, and simulation waveform when making direct voltage become 0.When Fig. 5 (b) is for band stream controller, the situation of change of each physical quantity after 0.8s DC side fault.Two width figure do contrast known when there being circulation controller, bridge arm current, current on line side and direct current all can not be undergone mutation, and the maximum that fault reaches obviously reduces, this be fault process further achieve preciousness time.
Claims (1)
1. be applied to a circulation inhibition method for flexible direct current power transmission system, it is characterized in that, step is as follows:
1), measuring each phase upper and lower bridge arm electric current, is the inside circulation of corresponding phase divided by two with each phase upper and lower bridge arm electric current (ipj, inj) addition;
2), by step 1) difference of each mutually inner circulation of obtaining and given circulation signal carries out standardization again after carrying out proportion adjustment and obtains loop current suppression additional control signals; Described given circulation signal is 1/3rd of DC bus current;
3), respectively go up bridge arm voltage reference signal (Vpj_ref) mutually and add that described loop current suppression additional control signals obtains correspondence and goes up the final voltage reference signal of brachium pontis (Upj_ref) mutually; Described loop current suppression additional control signals obtains correspondence and descends the final voltage reference signal of brachium pontis (Unj_ref) mutually respectively to descend bridge arm voltage reference signal (Vnj_ref) to add mutually;
4) the final voltage reference signal of each phase upper and lower bridge arm is through pulse duration modulation method, generates the Trig control signal of each brachium pontis; The method effectively can suppress the electric current flowing through brachium pontis when two harmonics and DC side two-stage short trouble.
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Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104319801A (en) * | 2014-10-20 | 2015-01-28 | 许继电气股份有限公司 | Modular multi-level converter bridge arm circulation control method |
| CN104333032B (en) * | 2014-11-20 | 2016-09-07 | 北京荣信慧科科技有限公司 | Reduce the circulation control strategy of flexible direct current transmission converter valve current peak |
| CN105226927A (en) * | 2015-09-24 | 2016-01-06 | 南方电网科学研究院有限责任公司 | The circulation inhibition method of cascade connection multi-level converter and system |
| CN105356778B (en) * | 2015-12-10 | 2018-01-09 | 湖南大学 | A kind of modular multilevel inverter and its dead-beat control method |
| CN106546851B (en) * | 2016-11-01 | 2022-02-25 | 全球能源互联网研究院 | Stability control method and device for MMC converter valve operation test circuit |
| CN107196327B (en) * | 2017-07-12 | 2020-03-27 | 华北电力科学研究院有限责任公司 | Feedforward control method for restraining power oscillation of modular voltage source type converter valve |
| CN108173296A (en) * | 2018-01-22 | 2018-06-15 | 国网山西省电力公司客户服务中心 | A kind of zero sequence loop current suppression control method of alternating current-direct current mixing micro-capacitance sensor |
| CN108418239B (en) * | 2018-04-26 | 2021-02-02 | 南方电网科学研究院有限责任公司 | Power control method and device for flexible direct current transmission system |
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| CN101295877B (en) * | 2008-06-05 | 2011-11-16 | 上海交通大学 | Control system of offshore wind power flexible DC power transmission current transformer |
| CN101854061B (en) * | 2010-04-30 | 2012-04-25 | 浙江大学 | Circulating-current restraining method for three-phase modular multilevel convertor |
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