CN105634258B - A kind of MMC exchange side fault current suppressing method based on virtual impedance - Google Patents

A kind of MMC exchange side fault current suppressing method based on virtual impedance Download PDF

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CN105634258B
CN105634258B CN201510046269.8A CN201510046269A CN105634258B CN 105634258 B CN105634258 B CN 105634258B CN 201510046269 A CN201510046269 A CN 201510046269A CN 105634258 B CN105634258 B CN 105634258B
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mmc
circuit
current
virtual impedance
fault
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CN105634258A (en
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赵成勇
张帆
许建中
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North China Electric Power University
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North China Electric Power University
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Abstract

The present invention relates to a kind of, and the MMC based on virtual impedance exchanges side fault current suppressing method, belongs to transmission & distribution electro-technical field.The exchange side failure of MMC causes switching device overcurrent, the present invention is based on existing control strategies, by the way that the virtual impedance parallel circuit in primary system is mapped in controller by feedback function, equivalent increase Circuit Fault on Secondary Transformer valve outlet circuit impedance, the instantaneous rate of climb of fault current when to effectively inhibit MMC exchange side failure, and the other types fault current rate of climb will not be accelerated.Core technology scheme of the present invention is: firstly, real-time measurement MMC system PCC points out three-phase voltage, electric current, reactive power and DC side electric current;Secondly, it is assumed that virtual impedance circuit is connected into Circuit Fault on Secondary Transformer valve outlet circuit, carries out carrying out the calculating of reactive power deviation by virtual impedance parallel circuit to D, Q shaft current;It is modified finally, relevant drift correction amount is attached on the measured value of the idle class control amount of DQ decoupling controller.

Description

A kind of MMC exchange side fault current suppressing method based on virtual impedance
Technical field
The invention belongs to transmission & distribution electro-technical fields more particularly to a kind of MMC based on virtual impedance to exchange side fault current Suppressing method.
Background technique
Modularization multi-level converter (Modular Multilevel Converter, MMC) is transmitted with higher power Capacity bears the advantages that voltage change ratio is low and harmonic characterisitic is preferable without a large amount of IGBT crimping series connection, device, is increasingly becoming The development trend of flexible DC transmission.
Exchange side (AC system side, Circuit Fault on Secondary Transformer) failure of MMC will lead to the raising of inverter alternating current, son The charge and discharge of module, and then cause switching device overcurrent.Fault condition lower switch device block action flows through device before occurring Transient current size directly affects the selection of switching device parameter.The suppression of fault current when occurring to exchange side failure for MMC System, existing research are directed to inhibition when asymmetric fault occurs to negative-sequence current component mostly;For exchanging side failure, especially The inhibition of the moment of fault current rate of climb occurs for the symmetrical faults such as serious three-phase ground short circuit, and existing research does not almost relate to And.
Summary of the invention
Inhibit problem for the fault current for mentioning MMC generation exchange side failure in above-mentioned background technique, the present invention uses Virtual impedance control strategy is based on existing DQ decoupling control policy, by increasing reactive power feedback element in Q axis, to system Transmission function is modified, and feedback control is mapped to formation virtual impedance parallel circuit, equivalent increase transformation in primary system Device secondary side valve outlet circuit impedance, alternating current and bridge arm current when so as to effectively inhibit MMC exchange side to break down The instantaneous rate of climb.
The present invention is mapping of the control system in primary system, itself will not generate shadow to the steady state operating condition of system It rings;And when other failures such as system generation DC side failure, additional control designed by the present invention will not accelerate its fault current The rate of climb.The feature of technical solution of the present invention the following steps are included:
Step 1: utilizing current sensor real-time measurement MMC system PCC point three-phase current, surveyed in real time using voltage sensor MMC system PCC point three-phase voltage is measured, and in the DQ coordinate system for being 0 by the Q shaft voltage of the electric current measured, voltage transformation to locking; Utilize current sensor real-time measurement MMC system dc bus current.Step 2: virtual impedance electricity is set according to MMC circuit parameter Resistance value and reactance value in road, virtual resistance are connected to system form with virtual reactance to connect after parallel connection into Circuit Fault on Secondary Transformer In valve outlet circuit;It is in parallel by virtual impedance to D, Q shaft current according to the difference in MMC controller transmitting active power direction Circuit carries out the calculating of reactive power deviation.Step 3: according to the difference of the idle class control amount of MMC controller, by step 2 gained nothing Function power deviation correction amount is attached on the measured value of the idle class control amount of DQ decoupling controller and is modified, by exchange Real-time monitoring and inhibition to AC fault electric current are realized in the inhibition of voltage magnitude variation.
The present invention can be realized and (be handed over when exchange side failure occurs for MMC system AC fault electric current by three steps Galvanic electricity stream, bridge arm current) the rate of climb realize effectively inhibit.
Detailed description of the invention
Fig. 1 is the virtual impedance circuit diagram for being attached to Circuit Fault on Secondary Transformer valve outlet circuit;Fig. 2 is that reactive power is inclined Poor computing block diagram;Fig. 3 is the DQ decoupling controller for adding idle class control amount deviation.
Specific embodiment
It below will be detailed to a kind of MMC exchange side fault current suppressing method work based on virtual impedance of the present invention Explanation.It is emphasized that following the description is only exemplary, the range and its application being not intended to be limiting of the invention.
The technical problems to be solved by the invention use virtual impedance control strategy, are based on existing DQ decoupling control policy, By increasing the feedback element of idle control amount in Q axis, ssystem transfer function is modified, feedback control is mapped to once Virtual impedance parallel circuit, the equivalent impedance for increasing Circuit Fault on Secondary Transformer valve outlet circuit, so as to effective are formed in system The instantaneous rate of climb of alternating current and bridge arm current when MMC exchange side being inhibited to break down.The present invention uses following technical side Case is realized:
Step 1: utilizing voltage sensor real-time measurement MMC system PCC point three-phase voltage, be denoted asu sau sbu sc;Utilize electricity Flow sensor real-time measurement MMC system PCC point three-phase current, is denoted asi sai sbi sc;By the current-voltage conversion measured to locking Q shaft voltage be 0 DQ coordinate system in, be transformed to D, Q shaft current of DC quantity, be denoted as respectivelyi sdi sq;Utilize function Rate measuring device measures reactive power at MMC system PCC point, is denoted asQ s;Utilize current sensor real-time measurement MMC system dc Bus current is positive, it is specified that flowing out converter station, is denoted asI dc.Step 2: according to MMC circuit system parameter setting virtual impedance circuit In resistance valueR virAnd reactance valueL vir,R virWithL virSystem form is connected to connect after parallel connection into Circuit Fault on Secondary Transformer valve outlet Circuit, as shown in Figure 1;To D, Q shaft currenti sdi sqThe calculating of reactive power deviation is carried out by virtual impedance parallel circuit, is had:, whereinsFor pull-type operator,kValue determined by active power transfer direction It is fixed, it is specified that are as follows:.Controller realizes that block diagram is as shown in Figure 2.Step 3: according to the idle class control of MMC controller Relevant drift correction amount is attached on the measured value of the active class control amount of DQ decoupling controller and repairs by the difference of amount Just, to realize the real-time monitoring and inhibition to AC fault electric current: if converter station is to determine Reactive Power Control station, using step It is rapid 2 calculate reactive power deviation to wattless power measurement valueQ sIt is modified, the amendment of controller outer loop feedback value are as follows:;If converter station is to determine alternating voltage control station, outer loop control is carried out by PI controller and is obtainedQ sref, will Determine alternating voltage control to be converted to and determine Reactive Power Control, drift correction is still carried out using the above method.Controller specific implementation Block diagram is as shown in Figure 3.It should be noted that step 1,2 and 3 is whole as summary of the invention, and three steps are organically indivisible Entirety.
The foregoing is only a preferred embodiment of the present invention, but scope of protection of the present invention is not limited thereto, In the technical scope disclosed by the present invention, any changes or substitutions that can be easily thought of by anyone skilled in the art, It should be covered by the protection scope of the present invention.Therefore, protection scope of the present invention should be with scope of protection of the claims Subject to.

Claims (1)

1. a kind of MMC based on virtual impedance exchanges side fault current suppressing method, it is characterized in that introducing Circuit Fault on Secondary Transformer The virtual impedance parallel circuit of valve outlet circuit, comprising the following steps:
Step 1: utilizing voltage sensor real-time measurement MMC system PCC point three-phase voltage, be denoted asu sau sbu sc;It is passed using electric current Sensor real-time measurement MMC system PCC point three-phase current, is denoted asi sai sbi sc;By the current-voltage conversion measured to the Q of locking In the DQ coordinate system that shaft voltage is 0, it is transformed to D, Q shaft current of DC quantity, has been denoted as respectivelyi sdi sq;It is surveyed using power Reactive power at device measurement MMC system PCC point is measured, is denoted asQ s;Utilize current sensor real-time measurement MMC system dc bus Electric current is positive, it is specified that flowing out converter station, is denoted asI dc
Step 2: according to the resistance value in MMC circuit system parameter setting virtual impedance parallel circuitR virAnd reactance valueL vir,R vir WithL virSystem form is connected to connect after parallel connection into Circuit Fault on Secondary Transformer valve outlet circuit;
To D, Q shaft currenti sdi sqThe calculating of reactive power deviation is carried out by virtual impedance parallel circuit, is had:
,
WhereinsFor pull-type operator,kValue determined by active power transfer direction, it is specified that are as follows:
Step 3: according to the difference of the idle class control amount of MMC controller, relevant drift correction amount being attached to DQ decoupling control It is modified on the measured value of the idle class control amount of device, to realize the real-time monitoring and inhibition to AC fault electric current: if Converter station is to determine Reactive Power Control station, then calculates resulting reactive power deviation to wattless power measurement value using step 2Q sIt is modified, the amendment of controller outer loop feedback value are as follows:
If converter station is to determine alternating voltage control station, outer loop control is carried out by PI controller and obtains reactive power reference qrefQ sref, alternating voltage control will be determined and be converted to and determine Reactive Power Control, drift correction is still carried out using the above method.
CN201510046269.8A 2015-01-30 2015-01-30 A kind of MMC exchange side fault current suppressing method based on virtual impedance Active CN105634258B (en)

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CN107528495B (en) * 2017-09-25 2019-11-08 中国电力科学研究院 A kind of control method and system improving PWM inverter impact resistance
CN108494261B (en) * 2018-04-13 2019-12-10 东南大学 active current limiting method suitable for direct current fault of MMC type direct current transformer
CN109950916B (en) * 2019-04-11 2020-10-30 华北电力大学 UPFC fault transition method based on mixed impedance
CN110401206B (en) * 2019-05-31 2020-11-13 北京交通大学 Grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance
CN110112900B (en) * 2019-06-25 2021-02-09 国网湖南省电力有限公司 Current rapid suppression method based on virtual impedance
CN111130080A (en) * 2020-01-17 2020-05-08 佛山科学技术学院 Photovoltaic system instantaneous fault overcurrent suppression method based on virtual impedance
CN111224409A (en) * 2020-01-17 2020-06-02 南方电网科学研究院有限责任公司 Virtual impedance-based over-current suppression method for direct current access device

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