A kind of pre-charge method of the modularization multi-level converter of clamp Shuangzi module
Technical field
The invention belongs to electric system power transmission and distribution applied technical fields, and in particular to a kind of modularization of clamp Shuangzi module
The pre-charge method of multilevel converter.
Background technology
2001, A.Lesnicar et al. proposed the voltage source converter (modular of modular multilevel structure
Multilevel converter, MMC), MMC has defeated in addition to can realize active and idle independent control
It is few to go out voltage harmonic content, is not necessarily to filter, modular construction autgmentability is strong, a series of advantages such as Redundant Control easy to implement,
Thus rapidly become the research hotspot in transverter field.
MMC is made of a series of cascade submodules, and according to the difference of sub-module types, the performance of MMC is also not quite similar.
Wherein half-bridge submodule is had been widely used due to simple in structure, and existing MMC-HVDC engineerings are substantially based on half
Bridge submodule.However the MMC based on half-bridge submodule can not effectively be latched direct fault current, thus the DC Line Fault of system is worn
More can force difference, once occur DC side failure, generally require whole system stoppage in transit, reduce the reliability of system operation.In order to
Solve the problems, such as this, the existing MMC-HVDC engineering in general based on half-bridge submodule using direct current cables as transmission line of electricity,
To reduce the probability of DC side failure, but this can undoubtedly reduce the economy of system while limit in overhead line field of power transmission
Using.
To solve the defect of above-mentioned half-bridge submodule, academia has also been proposed many submodules with failure blocking ability
Type, to improve the DC Line Fault ride-through capability of system, clamp Shuangzi module is one of which.Based on clamp Shuangzi module
Other than the general advantage for remaining early stage MMC, maximum advantage is quickly to control using transverter MMC (C-MMC)
Realize DC Line Fault self-cleaning, and additional increased device and loss are little, thus the following flexible direct current based on C-MMC is defeated
Electric system has broad application prospects.As the MMC of other sub-module types, there are one each submodules of C-MMC contain
Flying capacitor, under high pressure scene, the need of work of submodule depends on self-energizing power supply, in the starting stage submodule of charging
Capacitance is not charged, and self-energizing power supply can not start, so being rank necessary to C-MMC normal operations to the precharge of submodule capacitance
Section.The mode of precharge is broadly divided into self-excitation precharge and it encourages two kinds of precharge, and it is additional auxiliary due to needing that it encourages precharge
DC charging power supply is helped, economy is poor, so the precharge mode of mainstream is plugged in using grid line voltage at present
Self-excitation precharge mode.
Due to submodule own structural characteristics, the pre-charge method of C-MMC and the MMC of other types submodule are not
Together, C-MMC own structural characteristics how are efficiently used, the effective pre-charge method of design safety is a problem to be solved.
Invention content
It is of the invention the present invention provides a kind of pre-charge method of the modularization multi-level converter of clamp Shuangzi module
It is designed to provide the pre-charge method of the modularization multi-level converter based on clamp Shuangzi module, according to the topology of C-MMC
Design feature, designs the two benches pre-charge method of " not controlling charging " and " controllable charging ", and is adopted in " not controlling charging " stage
A point method for bridge arm charging is taken, pre-charge process is safe, quick, effective, has stronger engineering practicability.
In order to achieve the above objectives, the precharge of the modularization multi-level converter of a kind of clamp Shuangzi module of the present invention
Method 1, a kind of pre-charge method of the modularization multi-level converter of clamp Shuangzi module, which is characterized in that including " not controlling and filling
Electricity " stage and " controllable charging " stage, the submodule on " not controlling charging " stage, all bridge arms of transverter are carried out at the same time preliminary filling
Electricity, until the voltage of the capacitance of all submodules reaches capacitance threshold value UCC, " controllable charging " stage in a manner of dividing bridge arm to charge,
Each bridge arm capacitance is charged into rated voltage U successivelyCR。
Further, include the following steps:
Step 1 connects transverter exchange side breaker, and transverter is under the effect of exchange side line voltage, and all bridge arms are simultaneously
Into line precharge, the capacitance voltage of all submodules reaches capacitance threshold value UCC;
Step 2, implement divide bridge arm charge by way of, each bridge arm capacitance is charged into rated voltage U successivelyCR;
Step 3, all bridge arm submodule capacitor voltages both be charged to rated voltage UCRLater, all submodules are latched, in advance
Charging process terminates.
Further, in step 2, all bridge arms are divided into two groups according to current direction, the identical bridge arm of current direction is
The capacitance of same group of bridge arm, all submodules on same group of bridge arm charges simultaneously, the capacitance wheel of the submodule on two groups of bridge arms
Current charge.
Further, note bridge arm current direction is positive direction by direct current common point to exchange side exit, works as bridge arm current
For negative direction when, so that all submodules of the bridge arm is worked in non-blocking mode, give all submodules of the bridge arm capacitor charging, work as bridge
When arm electric current is positive direction, all submodules of entire bridge arm are bypassed, after all submodules of certain bridge arm charge to rated voltage then
Bypass all submodules of entire bridge arm.
Further, in step 1, current-limiting resistance is accessed while connecting transverter exchange side breaker, in step 3, is closed
Current-limiting resistance is cut off after locking all submodules.
Further, capacitance voltage threshold value UCCTake the 30% of rated voltage.
Compared with prior art, it is the normal work of transverter that the present invention, which at least has technique effect beneficial below, the present invention,
Most important preparation pre-charge process providing method foundation before making, the present invention is based on modularization multi-level converter precharge
General feature, entire pre-charge process is divided into " not controlling charging " and " controllable charging " two stages, in " controllable charging "
Stage combines the design feature of clamp Shuangzi module, uses a control strategy for point bridge arm charging, can fast and accurately will be electric
Capacity charge provides a kind of method of highly effective to rated voltage, for transverter precharge.The controllable charging stage makes full use of
The design feature of clamp Shuangzi module has carried out grouping charging so that capacitance voltage in controllable charge circuit to bridge arm capacitance
The counter electromotive force of composition is minimum, thus charging process is quicker;Simultaneously because the controllable charging stage is directly by capacitance voltage
Rated value is charged to, thus charging result is more accurate.
Further, which is characterized in that in step 1, current-limiting resistance is accessed while connecting transverter exchange side breaker,
To limit charging current, prevent precharge initial period since capacitance voltage is relatively low, charging current is excessive and leads to the devices such as IGBT
The damage of part.
Further, capacitance voltage threshold value UCCThe 30% of rated voltage is taken, since the trigger circuit of submodule is typically logical
It crosses capacitance partial pressure and takes energy, research shows that submodule trigger circuit could work normally when capacitance voltage is not less than 30%, together
When do not control rising of later stage charging stage with submodule capacitor voltage, charging rate gradually slows down, for improve charge efficiency answer
It is transferred to the controllable charging stage as early as possible, therefore selects not control the voltage threshold that the charging stage terminates as the 30% of rated voltage.
Description of the drawings
Fig. 1 is clamp Shuangzi module topology structure chart;
Fig. 2 is flow chart of the present invention;
Fig. 3 is clamp Shuangzi module equivalent circuit diagram in the case of electric current positive direction;
Fig. 4 is the equivalent circuit diagram of Fig. 2;
Fig. 5 is clamp Shuangzi module equivalent circuit diagram in the case of electric current negative direction;
Fig. 6 is the equivalent circuit diagram of Fig. 4;
Fig. 7 is pre-charge current circuit diagram;
Thick line indicates the branch that electric current flows through in Fig. 2 and Fig. 4.
Specific implementation mode
The following describes the present invention in detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is the topology diagram for clamping Shuangzi module, 5 IGBT (Insulated Gate Bipolar Trans
Istor guides insulated gate bipolar transistor):T11,T12,T21,T22And T0, 2 capacitances:C1And C2And 7 diodes:
D11,D12,D21,D22,D0,Dc1And Dc2, wherein T0To guide IGBT, D0For T0Anti-paralleled diode, Dc1And Dc2For clamp
Diode, T0,D0,Dc1And Dc2Clamp Shuangzi module is divided into two groups.In the first set, D11For T11Anti-paralleled diode,
T 11Emitter connection clamp Shuangzi module interface A, T11Collector connection capacitance C1With clamp diode Dc1It is negative
Pole;D12For T12Anti-paralleled diode, T12Collector connection clamp Shuangzi module interface A, T12Emitter connection
Guide IGBT (T0) emitter, clamp diode Dc2Cathode, D12Anode and capacitance C1.In the second set, D22For T22Anti-paralleled diode, T22Emitter connection clamp Shuangzi module interface B, T22Collector connection guiding IGBT
(T0) collector, capacitance C2With clamp diode Dc1Anode;D21For T21Anti-paralleled diode, T21Collector
The interface B, T of connection clamp Shuangzi module21Emitter connection clamp diode Dc2Anode, D21Anode and capacitance C2。
Containing there are two capacitance in wherein each submodule as shown in Figure 1, clamp Shuangzi module can approximation regard two and half as
The specific works pattern of the series connection of bridge submodule, submodule is as shown in table 1, and in table 1,1 indicates trigger pulse, and 0 indicates do not have
Trigger pulse, UAOIndicate the output voltage of first half-bridge, UOBIndicate the output voltage of second half-bridge, USMIndicate entire pincers
The output voltage of position Shuangzi module, iSMIndicate the electric current of submodule, UcIndicate the load voltage value of each capacitance.
Table 1 clamps formula Shuangzi module operating mode
The specific works pattern of submodule is divided to two kinds of normal mode and non-blocking mode, pre-charge process mainly to utilize locking mould
The third situation under formula and normal mode.It is different according to submodule current direction wherein under non-blocking mode, the equivalent electricity of submodule
Road is also not exactly the same, in the case of electric current positive direction clamp Shuangzi module equivalent circuit diagram as shown in figure 3, Fig. 3 equivalent circuit
Figure as shown in figure 4, electric current from direct current common point followed by diode D11, capacitance C1, diode D0, capacitance C2And diode
D21, be then out, in the case of electric current positive direction clamp Shuangzi module equivalent circuit diagram as shown in figure 5, the equivalent circuit diagram of Fig. 5 such as
Shown in Fig. 6, electric current flows through diode D22After shunt, flow through diode D all the wayc1With capacitance C1, another way flows through Dc2Afterwards, two-way
Merging passes through capacitance C1, it is then out.
The pre-charge process for clamping the modularization multi-level converter of Shuangzi module is divided into " not controlling charging " and " controllable aerating
Two stages of electricity " after capacitance voltage is charged to corresponding threshold value by " not controlling charging " stage, are transferred to " controllable charging " stage by capacitance
Voltage is charged to rated value, in order to limit charging current in pre-charge process, needs additional current-limiting resistance, is limited after precharge
Leakage resistance is cut off.Due to the operation principle of modularization multi-level converter, too low in capacitance voltage, submodule can not
Control, so first carrying out " not controlling charging " stage, under grid line voltage effect, all bridge arm submodule capacitances charge to threshold simultaneously
Value (be set as rated voltage herein 30 percent) then continues at " controllable charging " stage, and " controllable charging " is with bridge arm current
Direction is foundation, using the strategy for dividing bridge arm to charge.
With reference to Fig. 2, the pre-charge method for clamping the modularization multi-level converter of Shuangzi module includes the following steps:
Step 1 connects transverter exchange side breaker, while accessing current-limiting resistance, under the conditions of capacitance voltage is too low, submodule
Block can not trigger, and be completely in blocking, transverter is under the effect of exchange side line voltage, and the submodule on all bridge arms is simultaneously
Into line precharge, until the capacitance voltage of all submodules reaches capacitance threshold value UCC, capacitance voltage threshold value takes rated voltage
30%.
Step 2, after step 1, the capacitance voltage of submodule reaches threshold value UCC, at this point, submodule IGBT is controllable, pass through
Implement the mode for dividing bridge arm to charge, each bridge arm capacitance is charged into rated voltage successively.Specially:Remember converter bridge arm electric current side
To being positive direction by direct current common point to exchange side exit, all bridge arms are divided into two groups according to current direction, current direction
Identical bridge arm is same group.According to fig. 3 to clamp Shuangzi modular structure feature in Fig. 6, when bridge arm current is negative direction, son
The equivalent capacity voltage of module is low, so the series capacitance voltage of entire bridge arm is also low, it directly will be electric convenient for exchange side line voltage
Capacity charge is to rated voltage.Therefore it when bridge arm current is negative direction, allows all submodules of the bridge arm to work in non-blocking mode, gives
The capacitor charging of all submodules of the bridge arm allows all submodules of the bridge arm to work in normally when bridge arm current is positive direction
The third situation of pattern bypasses all submodules of entire bridge arm, i.e., entire bridge arm submodule output voltage is 0.When certain bridge
All submodules of arm charge to after rated voltage and then bypass all submodules of entire bridge arm, a, b, and c tri- alternates charging, with a, b
For phase, pre-charge current circuit as shown in fig. 7, in Fig. 7 capacitance indicate, the equivalent capacity of entire bridge arm, wherein being bypassed
Bridge arm diode equivalent.
Step 3, after step 2, all bridge arm submodule capacitor voltages both be charged to after rated voltage, and locking is all
Then submodule cuts off current-limiting resistance, pre-charge process terminates, and transverter can be transferred to normal operating mode.