CN105048488B - A kind of flexible direct current network DC short trouble traversing method - Google Patents

Abstract

Coordinate the method that control realization flexible direct current network DC short trouble is passed through the invention discloses a kind of MMC for possessing negative level fan-out capability and mechanical type dc circuit breaker, belong to flexible direct current network DC error protection field.In the prior art, the means of processing DC Line Fault mainly have three kinds：Disconnected by alternating current equipment and carry out DC Line Fault removing in itself with the connection of straight-flow system, by transverter, isolate by DC equipment progress DC Line Fault, but three of the above method all can not effectively realize flexible direct current network DC error protection.MMC in the present invention includes the submodule for possessing negative level fan-out capability, pass through the upper and lower bridge arm output voltage of flexible modulation, make transverter DC port voltage that negative level is presented, so as to reach that direct-current short circuit fault current is controllable and quickly be reduced to zero purpose, mechanical dc circuit breaker is set to meet the demand of isolated DC failure.

Description

A kind of flexible direct current network DC short trouble traversing method

Technical field

The invention belongs to flexible direct current network DC error protection field, it is based on possessing negative electricity more particularly, to one kind The module Multilevel Inverters MMC (Modular Multilevel Converter) of flat fan-out capability and mechanical dc circuit breaker Coordinate the method that control realization flexible direct current network DC short trouble is passed through.

Background technology

In recent years, the generation of electricity by new energy of offshore wind farm and remote districts is rapidly progressed.

Transmitted electricity compared to ac transmission and Traditional DC, Technology of HVDC based Voltage Source Converter can independent control be active, reactive power, right The defensive ability/resistance ability of voltage disturbance is strong, and the power network of composition can realize the decoupling of voltage problem and the branch of frequency issues between interacted system Support, is an active and controllable power network, is the optimal selection for realizing many drop point new energy interconnections.But, direct-current short circuit failure is The unavoidable problem of flexible DC power transmission.Compared to Traditional DC transmission system, the direct-current short circuit in flexible direct current power transmission system Failure has the characteristics of fault current is big, the rate of climb is fast, especially in flexible direct current network, and single-point DC Line Fault is easily developed For multiple spot AC fault, the safe operation of serious threat power network.Flexible direct current network based on trolley line, impermanency short circuit event Hinder probability of happening high, therefore above mentioned problem is especially prominent.At present, the means of processing DC Line Fault mainly have three kinds：

1) connection with straight-flow system is disconnected by alternating current equipment (such as AC circuit breaker).This method is needed not rely on directly Breaker is flowed, by converter blocking, AC circuit breaker acts to remove DC Line Fault.After faulty line is isolated, change Device unblock is flowed, AC circuit breaker reclosing, system recovers power transmission.But it is due to AC circuit breaker actuation time length (≈ 100ms), and active and reactive power can not be adjusted for current conversion station during failure, therefore big is influenceed on AC system.

2) DC Line Fault removing is carried out by transverter (modularization multi-level converter MMC) itself, i.e., based on full-bridge MMC Direct current lock-out scheme.However, the program needs block IGBT drivings, the controllability of current conversion station is sacrificed, and during failure Can not be to active and reactive power flexible modulation.

3) DC Line Fault isolation is carried out by DC equipment (such as dc circuit breaker).At present, dc circuit breaker can be divided into three Class：Mechanical type, solid-state version and mixed type.Mechanical type Circuit breaker technology is more ripe, but the breaker has poor (oneself of cutout abilities Induced Oscillation 30~40ms of ≈, precharge type ≈ 10ms), response speed slow (self-oscillation≤4kA, precharge type≤8kA) no Foot.Solid-state version breaker fast response time (≈ 1ms), but there is the deficiency that dynamic voltage balancing is difficult and steady-state operation loss is high, at present Only applied in low pressure, middle pressure field.Mixed type primary cut-out has good response speed (3~5ms of ≈) and cutout Ability (≤9kA), it is considered to be the most high voltage DC breaker of application prospect.But, the technology is not yet in Practical Project It is verified, and with current research speed, the breaker is difficult to break through to the field more than 500kV in 10 years futures.Therefore, High voltage DC breaker at this stage is difficult to be applied directly to flexible direct current network.At present, the protection based on dc circuit breaker Scheme is to increase smoothing reactor in DC line, is reduced by suppressing the fault current rate of climb and responds speed to breaker Degree, the demand of cutout abilities.But, this method inevitably increases loss (institute's band of smoothing reactor of DC line The loss come).

In summary, above-mentioned three kinds of schemes all can not effectively realize that multiterminal flexible high pressure DC transmission system DC failure is protected Shield.

The content of the invention

For problems of the prior art, the application provides a kind of based on possessing negative level fan-out capability MMC coordinates the method that control realization flexible direct current network DC short trouble is passed through with mechanical dc circuit breaker, wherein by right The control of current conversion station DC port negative level output voltage, realizes the purpose that reduction direct fault current rapidly drops to zero.

To achieve the above object, according to one aspect of the present invention, there is provided a kind of radial flexible direct current network DC Short trouble traversing method, the flexible direct current network includes n change of current station port, is changed wherein each port corresponds to one respectively Stream station, a DC power transmission line and a mechanical dc circuit breaker, during normal work, one of current conversion station is used to determine directly Voltage is flowed, remaining current conversion station is used to determine active power, and the current conversion station includes A, B, C three-phase, per by upper and lower two bridge arms Composition, it is characterised in that this method comprises the following steps：

(1) each current conversion station detection judges whether DC side is short-circuited failure, is then order execution step (2), otherwise Proceed detection；

(2) electrical quantity detected according to each current conversion station DC port carries out fault location；

(3) in the flexible direct current network, each current conversion station is switched to and determines active power controller, active power Instruction is set to zero, and reactive power keeps constant when instructing relative normal work, is obtained according to the instruction calculating of active and reactive power The alternating voltage reference value e of MMC outputs needed for per phase during failure_vij；

Remaining all current conversion station in addition to circuit correspondence current conversion station where fault location, refer to according to the reference of direct fault current Make valueThe detected value direct fault current i that the current conversion station DC port is checked_dciWith DC port voltage U'_dciCalculate The negative level voltage U of output needed for obtaining the DC port of non-fault line correspondence current conversion station_zi, and the non-faulting line that is added to The upper and lower bridge arm reference voltage u of road correspondence current conversion station_pij、u_nijIn common mode operation part, through the stack plus after reference voltage u_pij、u_nijModulation obtain upper and lower bridge arm submodule triggering and conducting signal；The corresponding current conversion station of faulty line does static var compensation Device STATCOM operations are repaid, reduce the influence to connected AC network；The final fault current caused in faulty line is decayed to Zero, wherein, i=1,2..., n represent current conversion station 1,2..., n in the flexible direct current network, subscript j=a, b, c respectively, point Biao Shi not a, b, c three-phase；

(4) all mechanical dc circuit breakers obtain the fault current in circuit by detection, suitable if decaying to zero Sequence performs step (5), otherwise proceeds detection；

(5) the corresponding mechanical dc circuit breaker of tripping zero failure current circuit；

(6) remaining described all current conversion station wait for a period of time after coordinating control, the corresponding change of current of non-fault line Station is switched to normal control mode and completes to pass through.

Preferably, in the step (3), the reference instruction value i of the direct fault current_d ^* _ciObtained according to below equation Arrive

In which it is assumed that failure occurs in kth bar circuit, i_{dci_rated}Specified electricity during for non-faulty line i normal works Stream, whereinRepresent the reference instruction value for being used to determine the direct fault current of the current conversion station of DC voltage.

Preferably, in the step (3), the negative level voltage U of the DC port output of remaining all current conversion station_zi Obtained according to below equation

Wherein, U'_dciFor current conversion station DC port voltage detecting value, K_p、K_iRespectively PI parameters of fault current controllers.

Preferably, in the step (3), the upper and lower bridge arm reference voltage u_pij、u_nijObtained according to below equation

Wherein, U'_dciFor current conversion station DC port voltage detecting value, e_vijThe alternating voltage ginseng exported for needed for MMC per phase Examine value, U_ziFor the negative level voltage of all current conversion station DC ports output in addition to circuit correspondence current conversion station where fault location.

It is another aspect of this invention to provide that there is provided a kind of looped network shape flexible direct current network DC short trouble side of passing through Method, the flexible direct current network includes several change of current station ports and several mechanical choppers, wherein each port pair A current conversion station and some circuits are answered, every circuit two ends are respectively comprising a breaker, during normal work, one of them Current conversion station is used to determine DC voltage, and remaining current conversion station is used to determine active power, and the current conversion station includes A, B, C three-phase, often It is made up of upper and lower two bridge arms, it is characterised in that this method comprises the following steps：

(1) each current conversion station detection judges whether DC side is short-circuited failure, is then order execution step (2), otherwise Proceed detection；

(2) electrical quantity that each current conversion station DC port is detected carries out fault location；

(3) in the flexible direct current network, each current conversion station is switched to and determines active power controller, active power Instruction is set to zero, and reactive power keeps constant when instructing relative normal work, is obtained according to the instruction calculating of active and reactive power The alternating voltage reference value e of MMC outputs needed for per phase during failure_vij；

By adjusting the upper and lower bridge arm output voltage so that direct-current short circuit fault current is controllable and is reduced to zero；

(4) all mechanical dc circuit breakers obtain the fault current in circuit by detection, suitable if decaying to zero Sequence performs step (5), otherwise proceeds detection；

(5) the mechanical dc circuit breaker at tripping zero failure current circuit two ends；

(6) each current conversion station is waited for a period of time after coordinating control, and the corresponding current conversion station of non-fault line is cut Normal control mode is changed to complete to pass through.

In general, according to the above-mentioned technical concept of the present invention, to possess following technology compared with prior art, mainly excellent Point：

1st, exported by the negative level of transverter itself, make direct fault current flexibly controllable, utilize mechanical direct current interruption Device is the demand that disclosure satisfy that isolated DC failure, it is ensured that non-faulty line is continuously run during failure；

2nd, coordinate control period, transverter is non-latching, can continue to provide reactive power support to AC system, reduce to handing over The influence of streaming system.

Brief description of the drawings

Fig. 1 is the flexible direct current schematic network structure of the present invention；

Fig. 2 is full-bridge MMC structural representations；

Fig. 3 is the direct fault current controller closed loop configuration block diagram of the present invention；

Fig. 4 be failure during MMC1 and any one mutually upper and lower bridge arm output voltage reference values of MMC2；

Fig. 5 is the present invention based on the MMC for possessing negative level fan-out capability and mechanical dc circuit breaker cooperation control Flow chart；

Fig. 6 be failure during current conversion station MMC1 and MMC2 overall control block diagram；

Fig. 7 is the three end DC transmission system embodiment schematic diagrams of the present invention；

Fig. 8 is the Case Simulation figure of the present invention.Wherein, (a) flows through CB₃Fault current I_faultChange with time figure, (b) transverter MMC1 port voltages are changed with time figure, and (c) transverter MMC2 port voltages are changed with time figure, and (d) is changed Stream device MMC3 port voltages change with time figure, and the active and reactive power of (e) transverter MMC1 transmission changes over time figure, (f) the active and reactive power of transverter MMC2 transmission changes over time figure, the active and idle work(of (g) transverter MMC3 transmission Rate changes over time figure.

Embodiment

In order to make the purpose , technical scheme and advantage of the present invention be clearer, it is right below in conjunction with drawings and Examples The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and It is not used in the restriction present invention.As long as in addition, technical characteristic involved in each embodiment of invention described below Not constituting conflict each other can just be mutually combined.

The MMC for possessing negative level fan-out capability not only includes what is be made up of a kind of submodule for possessing negative level fan-out capability MMC (such as full-bridge MMC), also including mixing what is constituted by possessing the submodule of negative level fan-out capability and remaining type submodule MMC (such as half-bridge and full-bridge mixed type MMC).Mechanical dc circuit breaker technology is more ripe, but the breaker has cutout abilities Poor (self-oscillation 30~40ms of ≈, precharge type ≈ 10ms), response speed are slow (self-oscillation≤4kA, precharge type≤8kA) Deficiency, it is difficult to directly meet the demand of flexible direct current power transmission system isolated DC failure.

The MMC for possessing negative level fan-out capability of the embodiment of the present invention and the scheme of mechanical dc circuit breaker cooperation In, each port of the radial n ports flexible direct current network correspond to respectively a current conversion station, a DC power transmission line and One mechanical dc circuit breaker, as shown in Figure 1.During normal work, it is assumed that the constant DC voltage control of current conversion station 1, remaining current conversion station Determine active power controller, this method comprises the following steps：

(1) detection of each current conversion station judges whether DC side is short-circuited failure, is then order execution step (2)；Otherwise after It is continuous to be detected；

(2) electrical quantity detected according to current conversion station DC port carries out fault location；

(3) in flexible direct current network described in example, all current conversion stations is switched to and determine active power controller, active power Instruction is set to zero, and reactive power keeps constant when instructing relative normal work.Obtained according to the instruction calculating of active and reactive power The alternating voltage reference value e of MMC outputs needed for per phase during failure_vij；

As shown in figure 3, all current conversion stations in addition to the circuit correspondence current conversion station where the fault location, according to direct fault current Reference instruction valueThe detected value direct fault current i that the current conversion station DC port is checked_dciWith DC port voltage U'_dciThe negative level voltage U of output needed for calculating the DC port for obtaining non-fault line correspondence current conversion station_zi, and it is described to be added to The upper and lower bridge arm reference voltage u of non-fault line correspondence current conversion station_pij、u_nijIn common mode operation part, as shown in figure 4, passing through To reference voltage u after superposition_pij、u_nijModulation obtain upper and lower bridge arm submodule triggering and conducting signal, faulty line is corresponding to be changed SVC STATCOM operations are done at stream station, reduce the influence to connected AC network；Finally cause in faulty line Fault current decay to zero, wherein, subscript i=1,2..., n, represent respectively current conversion station 1 in the flexible direct current network, 2..., n, subscript j=a, b, c, represent a, b, c three-phase respectively；

(4) all mechanical dc circuit breakers obtain the fault current in circuit by detection, suitable if decaying to zero Sequence performs step (5), otherwise proceeds detection；

(5) the corresponding mechanical dc circuit breaker of tripping zero failure current circuit；

(6) current conversion station is waited for a period of time after coordinating control, and the corresponding current conversion station of non-fault line is switched to normally Control model completes to pass through.

In embodiments of the invention,

In which it is assumed that failure occurs in kth bar circuit.i_{dci_rated}Specified electricity during for non-faulty line i normal works Stream,Represent the reference instruction value for being used to determine the direct fault current of the current conversion station of DC voltage, U'_dciFor current conversion station DC port voltage detecting value, K_p、K_iRespectively the PI parameters of fault current controllers, e_vijFor the friendship calculated in step 3 Flow voltage reference value.Secondly, it is necessary to which explanation, due to the randomness of trouble point, (becomes so a values are uncertain in figure 3 from 0 Change to 1), therefore in controller PI parameter designings, make a=0.

To make those skilled in the art more fully understand the present invention, with reference to specific embodiment, possess to the present invention The MMC of negative level fan-out capability and the scheme of mechanical dc circuit breaker cooperation are described in detail.

In following examples, possesses the MMC of negative level fan-out capability by taking full-bridge MMC as an example, as shown in Figure 2.Three ends are flexible straight Flow Network Construction of Power Transmission as shown in Figure 7.AC phase voltage virtual value 10kV, DC bus-bar voltage is 20kV, each bridge arm bag Containing 8 full-bridge submodules.Submodule electric capacity 15mF, bridge arm inductance 5.5mH, the Ω of bridge arm inductance equivalent resistance 0.2.Normal work When, MMC1 constant DC voltage controls, MMC2, MMC3 determine active power controller, the active, reactive power that each current conversion station is transmitted with And trend positive direction has been indicated in figure.

As shown in Figure 7, it is assumed that failure occurs at F points (the corresponding transmission lines of electricity of MMC3), and DC voltage is 0kV.Transverter Detect after failure, be switched to active power controller, and active power instruction is zero, when Reactive Power Control is relatively normal Keep constant；MMC1 and MMC2 carries out direct fault current control, and its instruction isDirect fault current control The output U of device processed_zi, it is added in the common mode component of upper and lower bridge arm reference signal；MMC3 does STATCOM operations.Work as DC-isolation Switch CB₃Detect fault current I_faultWhen being zero, operation is cut-off in execution.MMC1 and MMC2 is switched to normally after waiting 30ms Mode of operation.

Coordinate control period, flow through CB₃Fault current change over time as shown in Fig. 8 (a), as a result show fault current It is controllable, and within 15ms rapid decay to zero, CB₃Occur to detect zero failure electric current, tripping after general 20ms in failure Mechanical dc circuit breaker, isolated DC failure；Transverter MMC1 DC port voltage is changed over time as shown in Fig. 8 (b), knot Fruit shows, puts into negative level immediately after current conversion station detects DC Line Fault, direct fault current is declined rapidly, waits (ensure mechanical dc circuit breaker CB after 30ms₃Reliable isolated DC failure) MMC1 recovery normal mode of operation, DC port Voltage recovers normal；Transverter MMC2 DC port voltage is changed over time as shown in Fig. 8 (c), is as a result shown, in current conversion station Detect and also put into negative level immediately after DC Line Fault, direct fault current is declined rapidly, MMC2 is extensive after waiting 30ms Multiple normal mode of operation, DC port voltage recovers normal；Transverter MMC3 DC port voltage is changed over time such as Fig. 8 (d) shown in, as a result show, drag down DC port voltage immediately after current conversion station detects DC Line Fault, do STATCOM fortune OK；The active and reactive power of transverter MMC1 transmission is changed over time as shown in figure (e), is as a result shown, coordinates control period MMC1 can continue to provide reactive power support to AC system, and after DC Line Fault is isolated, active power transfer is quickly extensive It is multiple；The active and reactive power of transverter MMC2 transmission is changed over time as shown in figure (f), is as a result shown, coordinates control period MMC2 still can continue to provide reactive power support to AC system, and after DC Line Fault is isolated, active power transfer is quick Recover normal；The active and reactive power of transverter MMC3 transmission is changed over time as shown in figure (g), is as a result shown, MMC3 is done STATCOM is run, and can continue to provide reactive power support to AC system, active power maintains zero.

The cooperation scheme is applicable in high, medium and low voltage flexible direct-current transmission field.

As it will be easily appreciated by one skilled in the art that the foregoing is only presently preferred embodiments of the present invention, it is not used to The limitation present invention, any modification, equivalent and the improvement made within the spirit and principles of the invention etc., it all should include Within protection scope of the present invention.

Claims (4)

1. a kind of radial flexible direct current network DC short trouble traversing method, the flexible direct current network includes the n change of current Station port, wherein each port corresponds to a current conversion station, a DC power transmission line and a mechanical dc circuit breaker respectively, just Often during work, one of current conversion station is used to determine DC voltage, and remaining current conversion station is used to determine active power, the current conversion station It is every to be made up of upper and lower two bridge arms, it is characterised in that this method comprises the following steps comprising A, B, C three-phase：

(1) each current conversion station detection judges whether DC side is short-circuited failure, is then order execution step (2), otherwise continues Detected；

(2) electrical quantity detected according to each current conversion station DC port carries out fault location；

(3) in the flexible direct current network, each current conversion station is switched to and determines active power controller, active power instruction It is set to zero, reactive power keeps constant when instructing relative normal work, failure is obtained according to the instruction calculating of active and reactive power The alternating voltage reference value e of period MMC outputs needed for per phase_vij；

Remaining all current conversion station in addition to circuit correspondence current conversion station where fault location, according to the reference instruction value of direct fault currentThe direct fault current i that the current conversion station DC port is detected_dciWith DC port voltage U'_dciCalculating obtains non-faulting The negative level voltage U of output needed for the DC port of circuit correspondence current conversion station_zi, and the non-fault line correspondence change of current that is added to The upper and lower bridge arm reference voltage u stood_pij、u_nijIn common mode operation part, through the stack plus after reference voltage u_pij、u_nijTune Upper and lower bridge arm submodule triggering and conducting signal is made；The corresponding current conversion station of faulty line is SVC STATCOM Operation, reduces the influence to connected AC network；The final fault current caused in faulty line decays to zero, wherein, i= 1st, 2..., n, represent current conversion station 1,2..., n in the flexible direct current network, subscript j=a, b, c respectively, and a, b, c are represented respectively Three-phase；

The upper and lower bridge arm reference voltage u_pij、u_nijObtained according to below equation

$\left\{\begin{array}{c}{u}_{pij}=\frac{1}{2}{U}_{dci}^{\′}-\frac{1}{2}{U}_{zi}-e_{vij}\\ u_{nij}=\frac{1}{2}{U}_{dci}^{\′}-\frac{1}{2}{U}_{zi}+e_{vij}\end{array}\right.$

Wherein, U'_dciFor current conversion station DC port voltage detecting value, e_vijThe alternating voltage reference value exported for needed for MMC per phase, U_ziFor the negative level voltage of all current conversion station DC ports output in addition to circuit correspondence current conversion station where fault location；

(4) all mechanical dc circuit breakers obtain the fault current in circuit by detection, are sequentially held if decaying to zero Row step (5), otherwise proceeds detection；

(5) the corresponding mechanical dc circuit breaker of tripping zero failure current circuit；

(6) remaining described all current conversion station are waited for a period of time after coordinating control, and the corresponding current conversion station of non-fault line is cut Normal control mode is changed to complete to pass through.

2. the method as described in claim 1, it is characterised in that in the step (3), the reference of the direct fault current Command valueObtained according to below equation

$\left\{\begin{array}{c}\begin{array}{cc}{i}_{dci}^{*}=i_{dci\_rated}& \left(i\≠1\right)\end{array}\\ i_{dc1}^{*}=\underset{i=2}{\overset{k-1}{\mathrm{\Σ}}}{i}_{dci\_rated}+\underset{i=k+1}{\overset{n}{\mathrm{\Σ}}}{i}_{dci\_rated}\end{array}\right.$

In which it is assumed that failure occurs in kth bar circuit, i_{dci_rated}Rated current during for non-faulty line i normal works, its InRepresent the reference instruction value of the direct fault current of current conversion station for determining DC voltage.

3. method as claimed in claim 1 or 2, it is characterised in that in the step (3), remaining described all current conversion station DC port output negative level voltage U_ziObtained according to below equation

$U_{zi}=U_{dci}^{\′}-\[K_p(i_{dci}^{*}-i_{dci})+K_I\∫(i_{dci}^{*}-i_{dci})dt\]$

Wherein, U'_dciFor current conversion station DC port voltage detecting value, K_p、K_IRespectively PI parameters of fault current controllers.

4. a kind of looped network shape flexible direct current network DC short trouble traversing method, the flexible direct current network is changed including several Station port and several mechanical dc circuit breakers are flowed, wherein each port one current conversion station of correspondence and some circuits, often Circuit two ends described in bar are respectively comprising a mechanical dc circuit breaker, and during normal work, one of current conversion station is used to determine direct current Voltage, remaining current conversion station is used to determine active power, and the current conversion station includes A, B, C three-phase, per by upper and lower two bridge arm groups Into, it is characterised in that this method comprises the following steps：

(1) each current conversion station detection judges whether DC side is short-circuited failure, is then order execution step (2), otherwise continues Detected；

(2) electrical quantity detected according to each current conversion station DC port carries out fault location；

(3) in the flexible direct current network, each current conversion station is switched to and determines active power controller, active power instruction It is set to zero, reactive power keeps constant when instructing relative normal work, failure is obtained according to the instruction calculating of active and reactive power The alternating voltage reference value e of period MMC outputs needed for per phase_vij；

By adjusting the upper and lower bridge arm output voltage so that direct-current short circuit fault current is controllable and is reduced to zero；

(4) all mechanical dc circuit breakers obtain the fault current in circuit by detection, are sequentially held if decaying to zero Row step (5), otherwise proceeds detection；

(5) the mechanical dc circuit breaker at tripping zero failure current circuit two ends；

(6) each current conversion station is waited for a period of time after coordinating control, and the corresponding current conversion station of non-fault line is switched to Normal control mode completes to pass through.