CN105634258A - Virtual impedance-based AC side fault current suppression method for MMC - Google Patents
Virtual impedance-based AC side fault current suppression method for MMC Download PDFInfo
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Abstract
The invention relates to a virtual impedance-based AC side fault current suppression method for an MMC, and belongs to the technical field of power transmission and distribution. An AC side fault of the MMC causes an over-current of a switching device. On the basis of an existing control strategy, a virtual impedance shunt circuit in a primary system is mapped into a controller through a feedback function; and an impedance of a secondary side valve outlet circuit of a transformer is equivalently increased, so that the transient increase rate of a fault current when an AC side fault of the MMC appears is effectively suppressed; and the increase rates of other types of fault currents are not increased. According to the core technical scheme, the method comprises the following steps: firstly, measuring three-phase voltage and current, a reactive power and a DC side current of a PCC point of an MMC system in real time; secondly, supposing that a virtual impedance circuit is connected to the secondary side valve outlet circuit of the transformer in series, carrying out reactive power deviation calculation on D and Q-axis currents through the virtual impedance shunt circuit; and finally adding related deviation correction to a measurement value of reactive control quantity of a DQ decoupling controller for correction.
Description
Technical field
The invention belongs to power transmission and distribution technical field, particularly relate to a kind of MMC AC fault current suppressing method based on virtual impedance.
Background technology
Modularization multi-level converter (ModularMultilevelConverter, MMC) there is higher power transmission capacity, bear that voltage change ratio is low without a large amount of IGBT crimping series connection, device and the advantage such as harmonic characterisitic is better, be increasingly becoming the development trend of flexible DC power transmission.
AC (AC system side, the Circuit Fault on Secondary Transformer) fault of MMC can cause the rising of inverter alternating current, the charge and discharge of submodule, and then causes switching device to cross stream. The transient current size flowing through device under fault condition before the generation of switching device block action directly affects choosing of switching device parameter. The suppression of fault current during for MMC generation AC fault, has the suppression to negative-sequence current component when studying mostly for generation asymmetric fault; For AC fault, the suppression of the symmetrical fault generation moment of fault current rates of climb such as especially serious three-phase ground is short-circuit, existing research does not almost relate to.
Summary of the invention
The fault current of AC fault is occurred to suppress problem for above-mentioned background technology is mentioned MMC, the present invention adopts virtual impedance control strategy, based on existing DQ decoupling control policy, by increasing reactive power feedback element at Q axle, ssystem transfer function is modified, feedback control is mapped in primary system and forms virtual impedance parallel circuit, equivalence increases Circuit Fault on Secondary Transformer valve outlet port circuit impedance such that it is able to the instantaneous rate of climb of alternating current and bridge arm current when effectively suppressing MMC AC to break down.
The present invention is the mapping in primary system of the control system, and the steady state operating condition of system will not be produced impact by itself; And during other faults such as system generation DC side fault, the additional control designed by the present invention will not accelerate the rate of climb of its fault current. The feature of technical scheme comprises the following steps:
Step 1: utilize current sensor to measure MMC system PCC point three-phase current in real time, utilizes voltage sensor to measure MMC system PCC point three-phase voltage in real time, and by the electric current recorded, voltage transformation in the DQ coordinate system that Q shaft voltage is 0 of locking; Current sensor is utilized to measure MMC system dc bus current in real time.
Step 2: set the resistance value in virtual impedance circuit and reactance value according to MMC circuit parameter, it is connect in Circuit Fault on Secondary Transformer valve outlet port circuit after parallel connection that virtual resistance links system form with virtual reactance; According to the difference in MMC controller transmitting active power direction, D, Q shaft current is carried out reactive power deviation calculating through virtual impedance parallel circuit.
Step 3: according to the difference of the idle class controlled quentity controlled variable of MMC controller, step 2 gained reactive power drift correction amount is attached to DQ decoupling controller idle class controlled quentity controlled variable measured value on be modified, realize the in real time monitoring to AC fault electric current by suppressing that alternating voltage amplitude is changed and suppress.
The present invention passes through three steps, it is possible to realize realizing the rate of climb of AC fault electric current (alternating current, bridge arm current) when MMC system generation AC fault effectively suppressing.Accompanying drawing explanation
Fig. 1 is the virtual impedance circuit diagram being attached to Circuit Fault on Secondary Transformer valve outlet port circuit; Fig. 2 is reactive power deviation computing block diagram; Fig. 3 is the DQ decoupling controller of additional idle class controlled quentity controlled variable deviation.
Detailed description of the invention
A kind of MMC AC fault current suppressing method based on virtual impedance that the present invention relates to will be elaborated below. It is emphasized that the description below is merely exemplary, rather than in order to limit the scope of the present invention and application thereof.
The technical problem to be solved adopts virtual impedance control strategy, based on existing DQ decoupling control policy, by increasing the feedback element of idle controlled quentity controlled variable at Q axle, ssystem transfer function is modified, feedback control is mapped in primary system and forms virtual impedance parallel circuit, equivalence increases the impedance of Circuit Fault on Secondary Transformer valve outlet port circuit such that it is able to the instantaneous rate of climb of alternating current and bridge arm current when effectively suppressing MMC AC to break down. The present invention adopts the following technical scheme that realization:
Step 1: utilize voltage sensor to measure MMC system PCC point three-phase voltage in real time, be designated asu sa��u sb��u sc; Utilize current sensor to measure MMC system PCC point three-phase current in real time, be designated asi sa��i sb��i sc; By in the current-voltage conversion that records to the DQ coordinate system that Q shaft voltage is 0 of locking, it is transformed to D, Q shaft current of DC quantity, has been designated as respectivelyi d��i q; Utilize power-measuring device to measure MMC system PCC point place reactive power, be designated asQ s; Current sensor is utilized to measure MMC system dc bus current in real time, it is stipulated that flowing out current conversion station is just, is designated asI dc��
Step 2: according to the resistance value in MMC circuit system parameter setting virtual impedance circuitR virAnd reactance valueL vir,R virWithL virLinking system form is connect into Circuit Fault on Secondary Transformer valve outlet port circuit after parallel connection, as shown in Figure 1;
To D, Q shaft currenti d��i qCarry out reactive power deviation calculating through virtual impedance parallel circuit, have:
,
WhereinkValue determined by active power transfer direction, it is stipulated that for:
Controller realizes block diagram as shown in Figure 2.
Step 3: according to the difference of the idle class controlled quentity controlled variable of MMC controller, relevant drift correction amount is attached to DQ decoupling controller meritorious class controlled quentity controlled variable measured value on be modified, thus realizing the in real time monitoring to direct fault current and suppressing: if current conversion station is for determine Reactive Power Control station, then the calculating of use step 2 reactive power deviation value to wattless power measurement valueQ sBeing modified, controller outer loop feedback value is modified to:
;
If current conversion station is for determine alternating voltage control station, then carries out outer shroud by PI controller and control to obtainQ sref, control to be converted to determine Reactive Power Control by determining alternating voltage, still adopt said method to carry out drift correction.
Controller implements block diagram as shown in Figure 3.
It should be noted that step 1,2 and 3 entirety are as summary of the invention, and three steps are organic indivisible entirety.
The above; being only the present invention preferably detailed description of the invention, but protection scope of the present invention is not limited thereto, any those familiar with the art is in the technical scope that the invention discloses; the change that can readily occur in or replacement, all should be encompassed within protection scope of the present invention. Therefore, protection scope of the present invention should be as the criterion with scope of the claims.
Claims (2)
1. the MMC AC fault current suppressing method based on virtual impedance, it is characterized in that introducing the virtual impedance parallel circuit of Circuit Fault on Secondary Transformer valve outlet port circuit, comprise the following steps: step 1: measure MMC system PCC in real time and point out three-phase voltage, three-phase current, reactive power and DC bus current; Step 2: assume that virtual impedance circuit connected in series enters Circuit Fault on Secondary Transformer valve outlet port circuit, D, Q shaft current is carried out reactive power deviation calculating through virtual impedance parallel circuit; Step 3: relevant drift correction amount is attached to DQ decoupling controller idle class controlled quentity controlled variable measured value on be modified.
2. based on a kind of MMC AC fault current suppressing method based on virtual impedance described in claim 1, it is characterized in that step 1,2 and 3 entirety are as summary of the invention, make it possible to realize realizing the rate of climb of AC fault electric current (alternating current, bridge arm current) when MMC system generation AC fault effectively suppressing, and the fault current rate of climb of other types fault will not be accelerated, three steps are organic indivisible entirety.
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| CN107528495A (en) * | 2017-09-25 | 2017-12-29 | 中国电力科学研究院 | A kind of control method and system for improving PWM inverter impact resistance |
| CN108494261A (en) * | 2018-04-13 | 2018-09-04 | 东南大学 | A kind of active current-limiting method suitable for MMC type commutator transformer DC Line Fault |
| CN109950916A (en) * | 2019-04-11 | 2019-06-28 | 华北电力大学 | UPFC failure based on mixed type impedance gets over method |
| CN110112900A (en) * | 2019-06-25 | 2019-08-09 | 国网湖南省电力有限公司 | The quick suppressing method of electric current based on virtual impedance |
| CN110401206A (en) * | 2019-05-31 | 2019-11-01 | 北京交通大学 | Grid-connected converter low-frequency oscillation suppression method based on non-crossing feedback 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 |
| CN112928938A (en) * | 2021-03-25 | 2021-06-08 | 中国矿业大学 | Virtual reactance-based MMC direct current fault current limiting method |
| CN113067358A (en) * | 2021-03-25 | 2021-07-02 | 中国矿业大学 | Method for reducing direct current side current-limiting reactor of MMC type direct current network |
| CN113595123A (en) * | 2021-06-15 | 2021-11-02 | 中电普瑞电力工程有限公司 | High-frequency impedance calculation method and device of modular multilevel converter |
| CN114498584A (en) * | 2022-01-24 | 2022-05-13 | 四川大学 | Virtual impedance-based fault current suppression method for multi-drop point hybrid cascade direct current system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN107528495A (en) * | 2017-09-25 | 2017-12-29 | 中国电力科学研究院 | A kind of control method and system for improving PWM inverter impact resistance |
| CN108494261A (en) * | 2018-04-13 | 2018-09-04 | 东南大学 | A kind of active current-limiting method suitable for MMC type commutator transformer DC Line Fault |
| CN109950916B (en) * | 2019-04-11 | 2020-10-30 | 华北电力大学 | UPFC fault transition method based on mixed impedance |
| CN109950916A (en) * | 2019-04-11 | 2019-06-28 | 华北电力大学 | UPFC failure based on mixed type impedance gets over method |
| 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 |
| CN110401206A (en) * | 2019-05-31 | 2019-11-01 | 北京交通大学 | Grid-connected converter low-frequency oscillation suppression method based on non-crossing feedback virtual impedance |
| CN110112900A (en) * | 2019-06-25 | 2019-08-09 | 国网湖南省电力有限公司 | The quick suppressing method of electric current 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 |
| CN112928938A (en) * | 2021-03-25 | 2021-06-08 | 中国矿业大学 | Virtual reactance-based MMC direct current fault current limiting method |
| CN113067358A (en) * | 2021-03-25 | 2021-07-02 | 中国矿业大学 | Method for reducing direct current side current-limiting reactor of MMC type direct current network |
| CN112928938B (en) * | 2021-03-25 | 2022-12-02 | 中国矿业大学 | Virtual reactance-based MMC direct current fault current limiting method |
| CN113067358B (en) * | 2021-03-25 | 2024-09-27 | 中国矿业大学 | Method for reducing direct-current side current-limiting reactor of MMC type direct-current power grid |
| CN113595123A (en) * | 2021-06-15 | 2021-11-02 | 中电普瑞电力工程有限公司 | High-frequency impedance calculation method and device of modular multilevel converter |
| CN113595123B (en) * | 2021-06-15 | 2024-04-19 | 中电普瑞电力工程有限公司 | High-frequency impedance calculation method and device for modularized multi-level converter |
| CN114498584A (en) * | 2022-01-24 | 2022-05-13 | 四川大学 | Virtual impedance-based fault current suppression method for multi-drop point hybrid cascade direct current system |
| CN114498584B (en) * | 2022-01-24 | 2022-09-23 | 四川大学 | Virtual impedance-based fault current suppression method for multi-drop point hybrid cascade direct current system |
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