CN104953571A - Improved MMC (modular multi-level converter) structure with direct current fault clearing capacity - Google Patents

Abstract

The invention discloses an improved MMC (modular multi-level converter) structure with direct current fault clearing capacity. The improved MMC structure is characterized in that on the basis of a double-thyristor method, an accelerating current-limiting module is connected in series into each arm of an MMC; during normal operation of a system, all thyristors are in a disconnected state, an IGBT (insulated gate bipolar transistor) in each accelerating current-limiting module is in a connected state, and a current-limiting resistor Rc is in a bypass state all along; when a fault occurs on the direct current side of the system, all the IGBTs Ta and Tb in each MMC sub-module are disconnected and all the thyristors are connected, fault current is prevented from being fed into the direct current fault point by a direct current side power supply, meanwhile, all the IGBTs in the accelerating current-limiting modules of six arms are disconnected simultaneously, the accelerating current-limiting resistor Rc is added, and the fault isolation speed is increased and overcurrent on the direct current side is prevented. The improved MMC structure is applicable to all the direct current fault types, and the protection range is enlarged; meanwhile, the fault current attenuation speed is increased, and time for fault isolation is shortened greatly; overcurrent on the direct current side is reduced, and overcurrent harm on the direct current side is reduced greatly.

Description

There is the modularization multi-level converter modified node method of DC Line Fault Scavenging activity

Technical field

The present invention relates to protecting electrical power system control field, particularly relate to a kind of DC Line Fault processing method.

Background technology

Fast-speed direct current Fault Isolation is the key technology of flexible direct current system development.During flexible direct current system generation DC Line Fault, TSD total system down electric current sharply rises, and seriously jeopardizes the safety of system, reliability service.But existing converter all cannot realize the self-cleaning of DC Line Fault, excision faulty line of must taking measures on customs clearance.But because fault current during DC Line Fault is without natural zero-crossing point, cause DC circuit breaker blow-out comparatively difficult, therefore jumbo DC circuit breaker technology also reaches far away business application level.So both at home and abroad a large amount of scholar's primary study has the converter structure of fault clearance ability and corresponding control program.Wherein, double-thyristor method, owing to having advantage in isolation effect, cost of investment, control complexity etc., has good application prospect in Practical Project.Namely double-thyristor method adds antiparallel double-thyristor in each MMC submodule, this double-thyristor and the 2nd IGBTT in parallel _bwith the second sustained diode _bform in parallel.When systems are functioning properly, only have in each MMC submodule one group of IGBT and fly-wheel diode open-minded, double-thyristor all turns off; When breaking down in system dc side, all IGBTT in MMC submodule _a, T _bturn off, and all thyristors are open-minded, stop AC power supply to DC Line Fault point feed-in fault current.But, because DC side Conversion fault to be become the three phase short circuit fault of AC by double-thyristor method, the long-term overcurrent of AC therefore can be caused; Simultaneous faults electric current realizes Natural Attenuation according to the resistive component in DC Line Fault loop, therefore its Fault Isolation speed can slow down along with the close of abort situation, when especially there is metallicity fault near converter outlet, long time is needed to realize Fault Isolation.Corresponding corrective measure must be taked in practical engineering application to solve above-mentioned deficiency.

During flexible direct current system generation DC Line Fault, fault overcurrent will have a strong impact on the safe and reliable operation that whole direct current system comprises AC, DC side and converter.Therefore, during DC Line Fault, requirement can excise faulty line fast, and certain failure separation method namely must be taked to isolate DC Line Fault circuit.

Double-thyristor method, due to the advantage in isolation effect, cost of investment, control complexity etc., has good application prospect in Practical Project.But, because DC side Conversion fault to be become the three phase short circuit fault of AC by double-thyristor method, the long-term overcurrent of AC therefore can be caused; Simultaneous faults electric current realizes Natural Attenuation according to the resistive component in DC Line Fault loop, therefore its Fault Isolation speed can slow down along with the close of abort situation, when especially there is metallicity fault near converter outlet, long time is needed to realize Fault Isolation.To sum up state double-thyristor method and there is the limited shortcoming of protection range fault type that is not enough and protection, corresponding corrective measure therefore must be taked in practical engineering application to solve above-mentioned deficiency.

Summary of the invention

In order to overcome above-mentioned prior art Problems existing, the present invention proposes a kind of modularization multi-level converter (modular multilevel converter with DC Line Fault Scavenging activity, MMC) modified node method, in MMC submodule, arrange double-thyristor, there is Fault Isolation speed for double-thyristor method affects larger by abort situation, fault type; And AC bears the deficiencies such as long-time overcurrent, add in each brachium pontis and accelerate current limliting module, realize DC system fault process.

The present invention proposes a kind of MMC modified node method with DC Line Fault Scavenging activity, comprise multiple MMC converter be made up of MMC submodule; Described MMC submodule comprises first, second IGBTT _a, T _b, first, second sustained diode _a, D _bwith DC capacitor C, connected mode is: an IGBTT of one group of parallel connection _awith the first sustained diode _a, organize the 2nd IGBTT in parallel with another _bwith the second sustained diode _bform series connection; This cascaded structure forms in parallel with DC capacitor C again; Antiparallel double-thyristor is added, this double-thyristor and the 2nd IGBTT in parallel in each MMC submodule _bwith the second sustained diode _bform in parallel; Wherein, current limliting module is accelerated in access one of connecting in each brachium pontis of converter, and this acceleration current limliting module is by two first, second current limliting IGBTT antiparallel ₁, T ₂and the current-limiting resistance R of parallel connection with it _cform;

When system is normally run, in each MMC submodule only one group of IGBT and fly-wheel diode open-minded; The all IGBT accelerated in current limliting module are open-minded, and double-thyristor all turns off, current-limiting resistance R _cbe in the state of being bypassed always;

Time breaking down in system dc side, all IGBTT in MMC submodule _a, T _bturn off, and all thyristors are open-minded, stop AC power supply to DC Line Fault point feed-in fault current; All IGBT simultaneously in six brachium pontis acceleration current limliting modules turn off.

Compared with prior art, the present invention has the implementation result after following improvement:

(1), acceleration disturbance current attenuation speed, the greatly time of shortening needed for Fault Isolation;

(2), simultaneously, improvement project is applicable to all DC Line Fault types, further increases protection range;

(3), by increasing the equivalent short circuit impedance of AC during Failure elimination, reducing the overcurrent that AC bears, greatly reducing the harm of AC overcurrent.

Accompanying drawing explanation

Fig. 1 is DC Line Fault processing method schematic diagram;

Fig. 2 is that DC Line Fault removes stage equivalent circuit diagram.In figure: u _sabcfor the alternating voltage of AC A, B, C phase; i _sabcfor the alternating current of AC A, B, C phase; i _la, i _lb, i _lcthe brachium pontis reactance that representative is corresponding with A, B, C phase respectively continues electric current; L _rand R _rrepresent inductance value and the resistance value of brachium pontis reactor; R _cthe resistance value in current limliting module is accelerated in representative; L _kand R _kthe equivalent inductance value of representing fault circuit and equivalent resistance; i _dcfor DC line fault electric current.

Embodiment

Below in conjunction with the drawings and the specific embodiments, be described in further detail technical scheme of the present invention.

To modularization multi-level converter (the Modular Multilevel Converter based on double-thyristor method, MMC) topological structure carries out certain improvement, as shown in Fig. 1 (a): double-thyristor method adds antiparallel double-thyristor in each MMC submodule of MMC converter, on this basis, current limliting module is accelerated in the present invention's access one of connecting in each brachium pontis of MMC, and this module is by two antiparallel IGBT and resistance R in parallel with it _cform.In figure: T ₁, T ₂for the IGBT of reverse parallel connection, R _cfor the resistance sealed in converter bridge arm after fault generation.

When direct current system is normally run, in each brachium pontis, the IGBT of the acceleration current limliting module of series connection is all in opening state.Now, the circulation path of bridge arm current as shown in Fig. 1 (b), resistance R _cbe in the state of being bypassed, system can normally be run and can not produce added power dissipation always.

Time breaking down in system dc side, turn off all IGBT in MMC submodule immediately, and open all thyristors, stop AC power supply to DC Line Fault point feed-in fault current; Turn off all IGBT in six brachium pontis acceleration current limliting modules immediately simultaneously.Now, fault current (comprise alternating current source supply electric current and brachium pontis reactance continues electric current) circulation path in module is as shown in Fig. 1 (c).According to the working mechanism of fault current circulation path and double-thyristor method, the equivalent electric circuit at the now interconnected place of alternating current-direct current can be obtained as shown in Figure 2.

Current-limiting resistance R _cinput the DC side fault current rate of decay is accelerated, therefore fault current will decay to zero rapidly, and its isolation speed will no longer be subject to abort situation impact.R simultaneously _cinput AC equivalent short circuit impedance is increased greatly, reduce the over-current level of AC during fault clearance.

Consider system and the ability of overcurrent and the withstand voltage upper limit of electronic power switch device are born to the isolation requirement of speed, AC, obtain the R be shown below _cchoosing value the standard: (relation that formula (1), (2), (3) are "AND", and the common factor separated when formula (1), (2), (3) is for time empty, pays the utmost attention to the solution of formula (3).)

$R_c\≥\frac{5L_r}{t_{\max }}---\left(1\right)$

$R_c\≥\sqrt{{\left(\frac{2U_m}{I_{m\_\max }}\right)}^2-0.25{L_r}^2}---\left(2\right)$

$R_c\≤\frac{3U_{\max }}{I_{dc0}}---\left(3\right)$

Above-mentioned formula (1) ~ (3), t _maxfor the higher limit that system requires DC Line Fault isolation operation time limit, I _{m_max}for the overcurrent amplitude allowed, U _maxfor the IGBT withstand voltage upper limit, L _rfor brachium pontis reactance value, U _mfor AC phase voltage amplitude, I _dc0for entering fault clearance moment DC line electric current initial value.

Claims (3)

1. there is a modularization multi-level converter modified node method for DC Line Fault Scavenging activity, comprise multiple MMC submodule and accelerate current limliting module; Described MMC submodule comprises first, second IGBTT _a, T _b, first, second sustained diode _a, D _bwith DC capacitor C, connected mode is: an IGBTT of one group of parallel connection _awith the first sustained diode _a, organize the 2nd IGBTT in parallel with another _bwith the second sustained diode _bform series connection; This cascaded structure forms in parallel with DC capacitor C again; Add antiparallel double-thyristor, this double-thyristor and the 2nd IGBTT in parallel in each MMC submodule simultaneously _bwith the second sustained diode _bform in parallel; It is characterized in that, in each brachium pontis of MMC, series connection has accessed one and has accelerated current limliting module, and this acceleration current limliting module is by two first, second current limliting IGBTT antiparallel ₁, T ₂and the current-limiting resistance R of parallel connection with it _cform;

When system is normally run, only have in each MMC submodule one group of IGBT and fly-wheel diode open-minded; The all IGBT accelerated in current limliting module are open-minded, and double-thyristor all turns off, current-limiting resistance R _cbe in the state of being bypassed always;

Time breaking down in system dc side, all IGBTT in MMC submodule _a, T _bturn off, and all thyristors are open-minded, stop AC power supply to DC Line Fault point feed-in fault current; Turn off all IGBT in the acceleration current limliting module on converter six brachium pontis simultaneously, drop into and accelerate current-limiting resistance R _c, the speed of acceleration disturbance isolation, simultaneously limiting AC side overcurrent.

2. there is the modularization multi-level converter modified node method of DC Line Fault Scavenging activity as claimed in claim 1, it is characterized in that, described current-limiting resistance R _cchoosing value be the common factor of solution of formula (1), formula (2), formula (3):

$R_c\≥\frac{5L_r}{t_{\max }}---\left(1\right)$

$R_c\≥\sqrt{{\left(\frac{2U_m}{I_{m\_\max }}\right)}^2-0.25{L_r}^2}---\left(2\right)$

$R_c\≤\frac{3U_{\max }}{I_{dc0}}---\left(3\right)$

In above-mentioned formula (1) ~ (3), t _maxfor the higher limit that system requires DC Line Fault isolation operation time limit, I _{m_max}for the overcurrent amplitude allowed, U _maxfor the IGBT withstand voltage upper limit, Lr is brachium pontis reactance value, U _mfor AC phase voltage amplitude, I _dc0for entering fault clearance moment DC line electric current initial value.

3. there is the modularization multi-level converter modified node method of DC Line Fault Scavenging activity as claimed in claim 1, it is characterized in that, when the common factor that described formula (1), formula (2), formula (3) are separated is empty, described current-limiting resistance R _cchoosing value pay the utmost attention to the solution of formula (3).