CN103337951B - A kind of implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation - Google Patents

Abstract

The invention provides a kind of implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation, first according to the by-pass switch state of MMC submodule, submodule is divided into normal operation and redundancy two states for subsequent use; Then adopt to the Starting mode of redundancy submodule precharge, and design corresponding carrier wave dynamic allocator, normally ought run sub-module fault, allocation of carriers problem when redundancy spare module puts into operation in order to solve; Finally take into full account and the impact that redundancy spare module puts into operation on capacitor voltage equalizing and loop current suppression strategy designed the trigger with function of redundancy protection; Designed redundancy protecting strategy, can improve the reliability of system cloud gray model, ensures that converter can continue normal operation when sub-module fault, meanwhile, can realize redundancy submodule fast and replace fault submodule, can't cause obvious disturbance to system.

Description

A kind of implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation

Technical field

The invention belongs to power system operation and control technology field, relate to a kind of implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation.

Background technology

Along with the development of device for high-power power electronic, based on the all-controlling power electronics devices such as IGBT and pulse-width modulation (Pulse-width Modulation, PWM) voltage source converter (Voltage SourceConverter, VSC) of technology becomes the new trend of direct current transportation development.Based on high voltage direct current transmission (the High Voltage Direct Current of voltage source converter, HVDC) system is economical flexibly and the controlled advantage of height due to it, grid-connected at Large Scale Wind Farm Integration, distributed power generation is grid-connected, island with power, asynchronous AC network are interconnected and the field such as multi-terminal HVDC transmission is widely used.

But the VSC-HVDC system of routine generally adopts two level or three-level voltage source type converter, there is the shortcoming that switching frequency is high, harmonic wave of output voltage is large, electric pressure is low, current conversion station floor space is large, there is the problem of Tandem devices dynamic voltage balancing in addition.Modular multi-level converter (modular multilevelconverter, MMC) is the most promising current Novel electric Source Con-verters.The topological structure structure of its novel flexible modular makes its extensibility strong, easily realize Redundant Control, and well overcome traditional electrical Source Con-verters and there is the shortcomings such as switching frequency is high, harmonic wave of output voltage is large, electric pressure is low, current conversion station floor space is large, dynamic voltage balancing is difficult, become the focus of research both at home and abroad in recent years.

The brachium pontis of MMC is composed in series by the submodule (sub-module, SM) that several structures are identical, once there be SM to break down, converter cannot normally work, even may be out of service.This will cause serious threat to the reliability of whole direct current system.Therefore, it is very necessary for designing submodule redundancy protecting strategy.

Redundancy protecting strategy is different according to the difference of adopted modulator approach.The conventional modulator approach of current MMC mainly contains three kinds: space vector width pulse modulation method (space vector pulse-widthmodulation, SVPWM), nearest Level modulation scheme (nearest level modulation, and phase-shifting carrier wave modulator approach (carrier phase-shifted SPWM, CPS-SPWM) NLM).Each modulator approach is applicable to different application scenarios, respectively has pluses and minuses.Wherein, phase-shifting carrier wave modulator approach (carrier phase-shiftedSPWM, CPS-SPWM) due to its dynamic adjustments ability strong, can control in conjunction with capacitor voltage equalizing is additional, reduce switching frequency, and there is good harmonic characterisitic, engineering is widely used.But CPS-SPWM method produces triggering signal by the carrier wave that each submodule is corresponding with comparing of modulating wave; do not carry out electric capacity sequence; therefore CPS-SPWM cannot as nearest Level modulation scheme the easy redundancy protecting strategy realizing submodule, this is one of subject matter of running into of current CPS-SPWM.

Summary of the invention

The object of the invention is to overcome prior art defect; a kind of implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation is provided; when submodule breaks down; allocation of carriers problem when redundancy submodule puts into operation in process phase-shifting carrier wave modulation strategy; and obvious disturbance can not be produced to system; there is versatility, be easy to realize.

For achieving the above object, the present invention is by the following technical solutions:

Based on an implementation method for the MMC redundancy protecting strategy of phase-shifting carrier wave modulation, comprise the following steps:

Step 1: the MMC submodule by-pass switch state according to having control guarantor function is classified to submodule, each submodule is divided into normal operation submodule and redundancy spare module;

Step 2: on the basis of step 1, the MMC all submodules being carried out to precharge starts strategy, carries out precharge to all submodule electric capacity;

Step 3: after step 2 terminates, when design carrier wave dynamic allocator breaks down in normal-sub module, redundancy submodule puts into operation, reallocates to the corresponding carrier wave of all submodules.

The submodule in described step 1 with control guarantor function comprises two insulated gate bipolar transistor IGBTs up and down of series connection ₁and IGBT ₂, two insulated gate bipolar transistor IGBTs ₁and IGBT ₂anti-parallel diodes D respectively ₁and D ₂, upper and lower two insulated gate bipolar transistor IGBTs ₁and IGBT ₂electric capacity C is parallel with, lower insulated gate bipolar transistor IGBT after series connection ₂be parallel with by-pass switch K and bypass thyristor T, according to the state of by-pass switch K, each submodule be divided into normal operation submodule and redundancy spare module; By-pass switch K is closed is then redundancy spare module, and by-pass switch K disconnects then for normally to run submodule.

The concrete steps that described step 2 carries out precharge to all submodule electric capacity are as follows:

What step 201:MMC system started does not control the stage, on each brachium pontis of MMC, the by-pass switch of all submodules is all opened, the IGBT of all submodules is all in the state of cut-offfing, and AC system voltage is charged to electric capacity C by the diode of each submodule, and electric capacity C voltage can reach maximum U _cmax:

U _cmax＝1.414U _s/(N+M)

Wherein, U _sbe the effective value of AC system voltage, N is normal operation submodule number, and M is redundancy spare number of modules;

In the controlled stage that step 202:MMC system starts, the capacitance voltage of each submodule reaches the maximum U not controlling the stage _cmaxtime, according to the trigger of phase-shifting carrier wave modulator approach design, be switched to input state by blocking, system enters the controlled stage of startup, and redundancy spare module bypass switch closes, and the carrier wave of all redundancy spare modules is T _cb, the equal locking of redundancy spare module I GBT keeps voltage constant; Meanwhile, after normal operation submodule electric capacity continues charging, carrier wave is the carrier wave T after phase shift _cps;

Wherein, T _cpsbe the carrier wave of i-th element phase shift 2 π i/N, T _cbfor the carrier wave for generation of IGBT locking triggering level.

The concrete steps that described step 3 is reallocated to the corresponding carrier wave of all submodules are as follows:

1), before fault: when sub-module fault does not occur system, the normal carrier wave running submodule is dephased carrier wave T _cps, by-pass switch is all opened; The carrier wave of redundancy spare module is T _cb, by-pass switch is all closed;

2) during fault: the by-pass switch of closed fault submodule, fault submodule is out of service, and capacitance voltage electric discharge is 0, and its carrier wave is by original T _cpsbecome T _cb, IGBT is all in blocking; Meanwhile, open the by-pass switch of the redundancy spare module of alternative fault submodule, redundancy submodule puts into operation, and its carrier wave keeps original T _cbconstant, the electric capacity of this redundancy submodule continues charging;

3) after fault: when rated value close to capacitance voltage of the capacitance voltage of the redundancy submodule put into operation, the submodule carrier wave put into operation is changed into each submodule and distributed dephased carrier wave T _cps;

Wherein, T _cpsbe the carrier wave of i-th element phase shift 2 π i/N, T _cbfor the carrier wave for generation of IGBT locking triggering level.

The trigger of described phase-shifting carrier wave modulator approach design, when not having redundancy spare module to drop into, the modulating wave M of a jth submodule _ujby common basic sinusoidal modulation wave U _usuperpose the capacitor voltage equalizing controlling value U of corresponding submodule _vbjwith loop current suppression controlling value U _circomposition; For capacitor voltage equalizing controlling value and the loop current suppression controlling value of redundant module, need the carrier wave first judging whether this redundant module to be carrier wave after phase shift, if so, then calculate the modulating wave of this module according to the modulating wave building form of normal-sub module, otherwise, do not calculate;

The modulating wave M of a jth submodule _uj:

M _uj＝U _u+U _cir+U _vbj

1) U _u: the common basic sinusoidal modulation wave being each submodule obtained by dq uneoupled control, is calculated by formula:

$U_u=\frac{U_{\mathrm{dc}}}{2N}-\frac{u_r}{N}$

Wherein, U _dcdC voltage, u _rit is the magnitude of voltage that converter valve side alternating voltage obtains through dq uneoupled control;

2) U _cir: be loop current suppression controlled quentity controlled variable, by basic modulating wave U _uon, superposition circulation inhibitory control device obtains; Specific implementation process is: by the mean value U of whole submodule capacitor voltage _cavwith reference quantity U _crefproduce circulation setting value by PI controller more afterwards, then and three-phase brachium pontis between produce circulation i _cirloop current suppression strategy controller output valve U is produced more afterwards through PI controller _cir;

Wherein, circulation i is produced between three-phase brachium pontis _cirobtained by following formula:

$i_{\mathrm{cir}}=\frac{1}{2}(i_u+i_l)$

Wherein, i _uwith i _lrefer to brachium pontis and lower bridge arm current respectively;

The mean value U of submodule capacitor voltage _cavobtained by following formula:

$U_{\mathrm{cav}}=\underset{j=1}{\overset{j=N+M}{\mathrm{\Σ}}}{K}_j\·U_{\mathrm{cj}}$

Wherein, U _cjthe capacitance voltage of a jth submodule, K _jit is the by-pass switch state of a jth submodule;

3) U _vbj: the capacitor voltage equalizing controlled quentity controlled variable being a jth submodule; By the capacitance voltage U of a jth submodule _cjwith reference value U _crefrelatively, through proportional component, then judge the positive and negative of output valve by bridge arm current direction, finally obtain the Pressure and Control value U of an A phase jth submodule _vbj.

The implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation of the present invention, replace by redundancy submodule when there being module to break down, total number of the submodule of the state that puts into operation does not change, system voltage is formed by stacking by the submodule capacitor voltage put into operation, the electric parameters such as the voltage and current of system can't produce obvious change along with the change of each submodule carrier wave, the reliability of system cloud gray model can be improved, ensure that converter can continue normal operation when sub-module fault, simultaneously, redundancy submodule can be realized fast and replace fault submodule, obvious disturbance can't be caused to system.

Accompanying drawing explanation

Fig. 1 is the submodule topology diagram that the present invention has that function is protected in control;

Fig. 2 is the normal operating condition structure chart of submodule of the present invention; A () is blocking: (b) is input state: (c) is bypass condition;

Fig. 3 is the redundancy stand-by state structure chart of submodule of the present invention;

Fig. 4 is submodule allocation of carriers process schematic of the present invention; A () is Carrier State figure when system does not break down; B () is Carrier State figure when submodule 3 breaks down; C () is Carrier State figure when redundant module drops into;

Fig. 5 is the flow chart of carrier wave dynamic allocator of the present invention;

Fig. 6 is the trigger realization flow figure of the present invention with redundancy protecting;

Fig. 7 is loop current suppression controller of the present invention;

Fig. 8 is capacitor voltage equalizing controller of the present invention;

Brachium pontis submodule capacitor voltage in A phase when Fig. 9 is system provided by the invention startup;

Figure 10 is provided by the invention under precharge Starting mode, each submodule capacitor voltage before and after fault;

Figure 11 is provided by the invention under not precharge Starting mode, each submodule capacitor voltage before and after fault;

Figure 12 is the carrier wave of each submodule before and after fault provided by the invention; A () is submodule carrier wave before fault; B () is submodule carrier wave after fault;

Figure 13 is the waveform of each electrical variable before and after fault provided by the invention.

Embodiment

Below in conjunction with drawings and Examples, the present invention is elaborated.

Based on an implementation method for the MMC redundancy protecting strategy of phase-shifting carrier wave modulation, described method specifically comprises the following steps:

Step 1: the MMC submodule by-pass switch state according to having control guarantor function is classified to submodule, each submodule is divided into normal operation submodule and redundancy spare module;

As shown in Figure 1, the submodule with control guarantor function comprises two insulated gate bipolar transistor IGBTs up and down of series connection ₁and IGBT ₂, two insulated gate bipolar transistor IGBTs ₁and IGBT ₂anti-parallel diodes D respectively ₁and D ₂, upper and lower two insulated gate bipolar transistor IGBTs ₁and IGBT ₂electric capacity C is parallel with, lower insulated gate bipolar transistor IGBT after series connection ₂be parallel with by-pass switch K and bypass thyristor T, according to the state of by-pass switch K, each submodule be divided into normal operation submodule and redundancy spare module; By-pass switch K is closed is then redundancy spare module, and by-pass switch K disconnects then for normally to run submodule.

(1) normal operating condition

When the by-pass switch of submodule disconnects, submodule is in normal operating condition.If the normal submodule run breaks down, then its by-pass switch closed, submodule is transferred to redundancy stand-by state from normal operating condition.When sub-module fault is excluded, connecting system, keeps by-pass switch to close, for subsequent use as redundancy submodule.

Under normal operating conditions, according to IGBT ₁and IGBT ₂conducting situation, submodule can be subdivided into again locking, input and excision three basic running statuses.

1) blocking: as shown in Fig. 2 (a), works as IGBT ₁with IGBT ₂when all turning off, now current i forward (as the figure sense of current) is through anti-paralleled diode D ₁, electric capacity C charges; Or reverses through D ₂, electric capacity C does not charge and does not discharge yet;

2) state is dropped into: as shown in Fig. 2 (b), work as IGBT ₁conducting and IGBT ₂during shutoff, now electric current forward is through D ₁, electric capacity C charges; Or reverses through IGBT ₁, electric capacity C discharges;

3) bypass condition: as shown in Fig. 2 (c), works as IGBT ₁turn off and IGBT ₂during conducting, now electric current forward is through IGBT ₂, or reverses through D ₂, electric capacity C does not charge and does not discharge yet.

(2) SM redundancy stand-by state

When the by-pass switch of submodule closes and IGBT ₁with IGBT ₂when all turning off, submodule is in redundancy stand-by state, as shown in Figure 3.When have just break down at the submodule of running status time, the by-pass switch of redundancy submodule disconnects, and submodule just proceeds to normal operating condition from redundancy stand-by state.

In order to maintain the capacitance voltage value of redundant module, redundant state adopts the connected mode shown in Fig. 3 usually.I.e. closes bypass switch K, IGBT ₁with IGBT ₂all turn off, now by-pass switch K is by submodule short circuit, and electric capacity C does not charge and do not discharge yet, and its voltage is constant.

Step 2: on the basis of step 1, the MMC all submodules being carried out to precharge starts strategy, carries out precharge, ensure the rapidity that redundancy submodule puts into operation to all submodule electric capacity;

The concrete steps of carrying out precharge to all submodule electric capacity are as follows:

What step 201:MMC system started does not control the stage.Stage of not controlling refers to flip-flop latch, and the IGBT of all submodules is all in the state of cut-offfing, and AC system voltage passes through the diode of each submodule to capacitor charging.For the MMC system of N+1 level, each brachium pontis has M redundancy submodule, N number of normal operation submodule, is all opened by the by-pass switch of N+M submodule on each for MMC brachium pontis, then the electric capacity of AC system to the submodule of the N+M on brachium pontis charges, its accessible maximum U _cmaxfor:

U _cmax＝1.414U _s/(N+M) (1)

Wherein, U _sit is the effective value of ac line voltage.

The controlled stage that step 202:MMC system starts.The controlled stage refers to that the capacitance voltage when each submodule reaches the maximum U not controlling the stage _cmaxtime, according to the trigger of phase-shifting carrier wave modulator approach design, be switched to input state by blocking, system enters the controlled stage of startup.

In order to clear description carrier wave normally runs and dynamic assignment problem during fault at submodule, define the variable of 3 record carrier waves, as shown in table 1:

Table 1 records the variable of carrier wave

Variable	Describe
		T c	Dimension is N+M, the carrier wave of i-th element representation submodule i

T cps	Dimension is N, the carrier wave of i-th element representation phase shift 2 π i/N
		T cb	Dimension is 1, for generation of the carrier wave of IGBT locking triggering level

In the controlled stage started, closed by M redundancy submodule by-pass switch, the carrier wave of all redundancy spare modules is T _cb, make the state of the equal locking of upper and lower IGBT, be in redundancy stand-by state as shown in Figure 3, keep voltage to be constant.The carrier wave of N number of submodule is N number of carrier wave T after phase shift simultaneously _cps, be in the normal operating condition shown in Fig. 2.

Step 3: after the start-up course of step 2 terminates, design carrier wave dynamic allocator, breaks down in order to solve normal-sub module, the problem of carrier reallocation corresponding when redundancy submodule puts into operation, and ensure in the process, obvious disturbance to be caused to system;

The concrete steps of reallocating to the corresponding carrier wave of the redundancy submodule dropped into are as follows:

Start in step 2 precharge on the basis of terminating, for the N+1 level MMC system of brachium pontis series connection M redundancy submodule, the carrier wave dynamic allocator of flexible design, break down in order to solve normal-sub module, the problem of carrier reallocation corresponding when redundancy submodule puts into operation, and ensure in the process, obvious disturbance to be caused to system, as shown in Figure 5, concrete steps are as follows for the realization flow of carrier wave dynamic allocator:

In realization flow figure, define following significant variable:

1) the by-pass switch state variable K of submodule: its dimension is N+M.K _irepresent the by-pass switch state of i-th submodule, 1 represents that by-pass switch disconnects, and this submodule is in normal operating condition; 0 represents that by-pass switch closes, and this submodule is in redundancy stand-by state.

2) the capacitance voltage V of submodule _c: its dimension is N+M.V _cirepresent the capacitance voltage value of i-th submodule.

3) the rated value U of submodule capacitor voltage _ref: its dimension is 1.By institute DC voltage U _dcdetermine with the submodule number N put into operation, adopt formula (2) to calculate:

U _ref＝U _dc/N (2)

4) i is the numbering of all submodules of brachium pontis, if N normally runs submodule number, M is the submodule number this patent being in redundant state, then i<=N+M; J be phase shift 2 π/N after the numbering of carrier wave, and j<=N;

With reference to figure 5 carrier wave dynamic allocator to realize flow step as follows:

Step 1): the folding condition first judging the by-pass switch of i-th submodule; If K _i=1, then by-pass switch is opened; Then carry out step 2; If K _i=0, then by-pass switch is closed; Carry out step 3;

Step 2): the capacitance voltage V judging i-th submodule _ciwith capacitance voltage rated value U _refrelation; If V _ci<U _ref, then carry out step 3; If V _ci>=U _ref, then carry out step 4;

Step 3): by the carrier wave T of locking submodule _cbassignment gives the carrier wave T of i-th submodule _ci;

Step 4): the distribution having judged whether the carrier wave after phase shift, if j<=N, illustrates that the carrier wave after phase shift is unallocated complete, then carry out step 5; If j>N, illustrate that the carrier wave after phase shift distributes, then carry out step 3;

Step 5): by a jth dephased carrier wave T _cpsjassignment gives the carrier wave T of i-th submodule _ci, then by the carrier index j+1 after phase shift, process the carrier wave after next phase shift; Carry out step 6;

Step 6): the allocation of carriers having judged whether all submodules, if i>=N+M, then obtains the carrier wave of the submodule of all N+M; If i<N+M, then by the numbering i+1 of submodule, return step 1, continue the carrier wave distributing next submodule.

With reference to figure 4, in order to the redistribution process of directviewing description carrier wave, the present invention is for 7 level and each brachium pontis has the MMC (N=6 and M=1) of 1 redundancy, as shown in Fig. 4 (a), wherein 1,2,3,4,5,6 is the submodule of normal operating condition, and 7 is redundancy spare module (the expression submodule by-pass switch of band shade closes).

1), before fault: when sub-module fault does not occur system, allocation of carriers corresponding to each submodule is as shown in Fig. 4 (a), and namely the carrier wave of normal-sub module is dephased carrier wave T _cps, by-pass switch is all opened; The carrier wave of redundancy submodule is T _cb, by-pass switch is all closed;

2), during fault: when the 3rd submodule breaks down, allocation of carriers corresponding to each submodule is as shown in Fig. 4 (b).Now, the by-pass switch of closed fault submodule 3, submodule 3 is out of service, and capacitance voltage electric discharge is 0.Its carrier wave is by original T _cps3become T _cb, IGBT is all in blocking, to overhaul.Meanwhile, open the by-pass switch of redundancy submodule 7, redundancy submodule 7 puts into operation, and its carrier wave keeps original T _cbconstant, the capacitance voltage of this redundancy submodule continues charging.

3) after fault: when rated value close to capacitance voltage of the capacitance voltage of redundancy submodule 7, corresponding allocation of carriers is as shown in Fig. 4 (c).Now, all submodules put into operation dynamically distribute dephased carrier wave T for each submodule by carrier wave distributor _cps.

From the assigning process of (a), (b), (c) three carrier waves of Fig. 4, when replacing the submodule 3 of fault by redundancy submodule 7, the carrier wave of some (even may be whole) submodule changes (if the carrier wave of the 4th submodule is by original carrier wave T _cps4become carrier wave T _cps3, etc.).Although the running status of this moment submodule can change along with the sudden change of carrier wave, this can't produce obvious disturbance to the output voltage of brachium pontis.This is because put into operation, total number of the submodule of state is still N, and system voltage is formed by stacking by this N number of submodule capacitor voltage.Simultaneously because capacitor voltage equalizing controls the effect with loop current suppression control strategy, make when submodule carrier wave changes, the electric parameters such as the voltage and current of system can't produce obvious change along with the change of each submodule carrier wave.

No matter redundancy submodule be which, or have simultaneously several submodule break down (in the enough situations of redundant module number) allocation of carriers can be carried out according to the carrier wave dynamic allocator designed by the present invention.

On the basis of the carrier wave dynamic allocator designed by step 3; take into full account that redundancy submodule drops into the impact controlled capacitor voltage equalizing and loop current suppression; and design is accordingly with the trigger of function of redundancy protection; due to the symmetry of upper and lower bridge arm and three-phase; the present invention is for brachium pontis in A phase; design is accordingly with the trigger of function of redundancy protection, and realization flow is shown in Fig. 6.

M _uaibe the modulating wave of i-th submodule, be all superimposed with by common fundamental modulation ripple and be made up of the capacitor voltage equalizing controlling value of corresponding submodule and loop current suppression controlling value; All pressures of redundant module and loop current suppression are controlled, needs the carrier wave first judging whether this redundant module to be carrier wave after phase shift, if, then according to the modulating wave building form of normal-sub module, calculate the modulating wave of this module, otherwise, do not need to carry out this step calculating

Form M _uaithree part illustrate:

1) U _ua: the common basic sinusoidal modulation wave being each submodule of brachium pontis in the A phase that obtained by dq uneoupled control, is calculated by following formula:

$U_{\mathrm{ua}}=\frac{U_{\mathrm{dc}}}{2N}-\frac{u_{\mathrm{ra}}}{N}---\left(3\right)$

Wherein, U _dcdC voltage, u _rait is the magnitude of voltage that converter valve side A cross streams voltage obtains through dq uneoupled control.

2) U _cira: the loop current suppression controlled quentity controlled variable being A phase, is obtained by the loop current suppression controller of Fig. 7;

For brachium pontis submodule in A phase, can pass through at basic modulating wave U _uaon, the loop current suppression controlling value U that the loop current suppression controller of superposition shown in accompanying drawing 7 obtains _cirarealize.Specific implementation process is: by the mean value U of the whole submodule capacitor voltage of A phase upper and lower bridge arm _cavawith reference quantity U _crefproduce circulation setting value by PI controller more afterwards, then with i _ciraloop current suppression strategy controller output valve U is produced more afterwards through PI controller _cira;

Because the voltage of MMC when steady operation between each brachium pontis can not be completely the same, thus cause homophase upper and lower bridge arm asymmetrical voltage, circulation can be produced between the three-phase brachium pontis of MMC, thus sinusoidal bridge arm current waveform is distorted.Produce circulation i _cirasize be:

$i_{\mathrm{cira}}=\frac{1}{2}(i_{\mathrm{ua}}+i_{\mathrm{la}})---\left(4\right)$

Wherein, i _uawith i _larefer to brachium pontis and lower bridge arm current in A phase respectively.

Wherein, because each brachium pontis has the existence of redundancy submodule, the mean value U of the submodule capacitor voltage in loop current suppression controller _cavaadopt and calculated by following formula,

$U_{\mathrm{cava}}=\underset{j=1}{\overset{j=N+M}{\mathrm{\&Sigma;}}}{K}_j\&CenterDot;U_{\mathrm{caj}}---\left(5\right)$

Wherein, U _cajthe capacitance voltage of a jth submodule, K _jit is the by-pass switch state of a jth submodule.

3) U _vbaj: the capacitor voltage equalizing controlled quentity controlled variable being a jth submodule, is obtained by the capacitor voltage equalizing controller of Fig. 8;

For brachium pontis submodule in A phase, can pass through at basic modulating wave U _uaon, the Pressure and Control value U of the jth submodule that the capacitor voltage equalizing controller of superposition shown in accompanying drawing 8 obtains _vbajrealize.Specific implementation process is: by the capacitance voltage U of an A phase jth submodule _cajwith reference value U _crefrelatively, through proportional component, then judge the positive and negative of output valve by bridge arm current direction, finally obtain the Pressure and Control value U of an A phase jth submodule _vbaj.

As shown in the formula known, by the basic modulating wave U of a upper brachium pontis jth submodule _uaupper superposition circulation inhibitory control amount U _cirawith capacitor voltage equalizing controlled quentity controlled variable U _vbai, obtain the modulating wave M of a brachium pontis jth submodule _uaj:

M _uaj＝U _uaj+U _cira+U _vbaj

Specific as follows with the trigger realization flow of redundancy protecting see Fig. 6:

In flow charts, F _p1ithe trigger impulse of the upper IGBT of corresponding i-th submodule, F _p2iit is the trigger impulse of IGBT under corresponding submodule.

Step 1): the carrier wave T first judging i-th submodule _cibe whether the carrier wave T of locking submodule _cb; If T _ci=T _cb, then carry out step 2; If T _ci≠ T _cb, then carry out step 3;

Step 2): the triggering level F of i-th upper and lower IGBT of submodule _p1iwith F _p2iequal assignment is 0, and namely submodule is in blocking, carry out step 7;

Step 3): by the capacitor voltage equalizing controlling value U of i-th submodule _vbaiwith loop current suppression controlling value U _cira, be superimposed to fundamental modulation ripple U _ua, obtain the modulating wave M controlled with capacitor voltage equalizing and loop current suppression of i-th submodule _uai, carry out step 4;

Step 4): the modulating wave M judging i-th submodule _uaiwith the modulating wave T of i-th submodule _cisize, if M _uai>T _ci, then carry out step 5; If M _uai<=T _ci; Then carry out step 6;

Step 5): the triggering level F of i-th upper and lower IGBT of submodule _p1i=1 and F _p2i=0 is 0, and namely submodule is in input state;

Step 6): the triggering level F of i-th upper and lower IGBT of submodule _p1i=0 and F _p2i=1 is 0, and namely submodule is in bypass condition;

Step 7): judge whether trigger completes the generation of the triggering level of all submodule IGBT, if i>=N+M, then produce the triggering level of the upper and lower IGBT of submodule of all N+M; If i<N+M, then by the numbering i+1 of submodule, return step 1, continue the triggering level producing next submodule;

Below with regard to function and the effect of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation of the present invention's proposition; simulation example is described in detail, verifies proposed with the carrier wave dynamic allocator of MMC submodule function of redundancy protection and the validity of trigger.It is emphasized that following explanation is only exemplary, instead of in order to limit the scope of the invention and apply.

First, in PSCAD/EMTDC, build 7 level both-end MMC DC transmission system simulation models, wherein each brachium pontis of MMC has 6 submodule SM1 ~ SM6 and 1 redundancy spare module SM7 normally run.And the system parameters of this simulation model is set, as shown in table 2:

Table 2 simulation system parameters

Then, simulation example of the present invention adopts phase-shifting carrier wave modulator approach, and carrier frequency is 200Hz, and rectification side adopts determines active power and determines Reactive Power Control, controls reference value and is respectively 10MW and 3Mvar.Inverter side adopts determines reactive power and constant DC voltage control, controls reference value and is respectively 5Mvar and 20kV.

(1) precharge starts strategy:

Adopt the Starting mode to redundant module precharge, the capacitor charging voltage max often going up brachium pontis 7 submodules (comprising redundancy spare module) mutually should be:

U _cmax＝1.414·10/(6+1)＝2.02kV

When the capacitance voltage value of submodule reaches 2.02kV, the startup stage of entering control, trigger puts into operation.Startup stage A phase on brachium pontis submodule capacitance voltage as shown in Figure 9, wherein Vc1 ~ Vc7 represents 7 submodule capacitor voltage on brachium pontis.

Supposing the system when 1.5s in rectification side A phase brachium pontis the 2nd submodule break down, now fault submodule is bypassed, and redundancy spare module puts into operation.After an adjustment process, system enters steady operational status, as shown in Figure 10.

During 1.5s, the 2nd submodule breaks down and is bypassed, and redundancy submodule 7 puts into operation.Submodule 7 reaches near rated capacity magnitude of voltage through 0.073s.

If redundant module adopt not charging modes start, then submodule 2 break down be bypassed time, redundancy submodule 7 will arrive rated capacity magnitude of voltage through 0.13s, as shown in figure 11.

(2) dynamic allocation procedure of carrier wave:

Before and after fault, Figure 12 is shown in the change of the carrier wave of each submodule.If Figure 12 (a) is when the 2nd submodule breaks down, except the carrier wave of the 1st submodule does not change, the carrier wave of other submodules all there occurs change.If the carrier wave of Figure 12 (b) submodule 7 is T at the moment retention value of fault _cb, after 0.073s, the capacitance voltage of submodule 7 reaches rated value, and corresponding carrier switch becomes the carrier wave after phase shift.

(3) to the perturbation analysis of system:

Although for each submodule, carrier wave there occurs sudden change, system brachium pontis electric current I _u, direct voltage U _dc, submodule output voltage V _smauand the active-power P of converting plant ₁steady, as shown in figure 13, not obvious to the disturbance of system when carrier wave changes with the change of reactive power Q 1.

More than test; fully demonstrate when fault occurs; the MMC submodule redundancy protecting strategy based on phase-shifting carrier wave modulator approach adopting the present invention to propose, can make redundant module steadily substitute malfunctioning module and put into operation, prove that redundancy protecting strategy in this paper is effectively feasible.In addition, adopt precharge of the present invention to start scheme, the voltage dip produced when redundancy spare module puts into operation can be effectively reduced, reduce the time that redundant module is charged to rated voltage; And the allocation of carriers problem of designed carrier wave dynamic allocator when can well process that in phase-shifting carrier wave modulation strategy, redundancy submodule puts into operation, and this strategy can not produce obvious disturbance to system, has versatility, is easy to realize.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily 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 the protection range of claim.

Claims (5)

1., based on an implementation method for the MMC redundancy protecting strategy of phase-shifting carrier wave modulation, it is characterized in that comprising the following steps:

Step 1: the MMC submodule by-pass switch state according to having control guarantor function is classified to submodule, each submodule is divided into normal operation submodule and redundancy spare module;

Step 2: on the basis of step 1, the MMC all submodules being carried out to precharge starts strategy, carries out precharge to all submodule electric capacity;

Step 3: after step 2 terminates, when design carrier wave dynamic allocator breaks down in normal-sub module, redundancy submodule puts into operation, reallocates to the corresponding carrier wave of all submodules.

2. the implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation according to claim 1, is characterized in that: the submodule in described step 1 with control guarantor function comprises two insulated gate bipolar transistor IGBTs up and down of series connection ₁and IGBT ₂, two insulated gate bipolar transistor IGBTs ₁and IGBT ₂anti-parallel diodes D respectively ₁and D ₂, upper and lower two insulated gate bipolar transistor IGBTs ₁and IGBT ₂electric capacity C is parallel with, lower insulated gate bipolar transistor IGBT after series connection ₂be parallel with by-pass switch K and bypass thyristor T, according to the state of by-pass switch K, each submodule be divided into normal operation submodule and redundancy spare module; By-pass switch K is closed is then redundancy spare module, and by-pass switch K disconnects then for normally to run submodule.

3. the implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation according to claim 1, is characterized in that: the concrete steps that described step 2 carries out precharge to all submodule electric capacity are as follows:

What step 201:MMC system started does not control the stage, on each brachium pontis of MMC, the by-pass switch of all submodules is all opened, the IGBT of all submodules is all in the state of cut-offfing, and AC system voltage is charged to electric capacity C by the diode of each submodule, and electric capacity C voltage can reach maximum U _cmax:

U _{c max}＝1.414U _s/(N+M)

Wherein, U _sbe the effective value of AC system voltage, N is normal operation submodule number, and M is redundancy spare number of modules;

In the controlled stage that step 202:MMC system starts, the capacitance voltage of each submodule reaches the maximum U not controlling the stage _cmaxtime, according to the trigger of phase-shifting carrier wave modulator approach design, be switched to input state by blocking, system enters the controlled stage of startup, and redundancy spare module bypass switch closes, and the carrier wave of all redundancy spare modules is T _cb, the equal locking of redundancy spare module I GBT keeps voltage constant; Meanwhile, after normal operation submodule electric capacity continues charging, carrier wave is the carrier wave T after phase shift _cps;

Wherein, T _cpsbe the carrier wave of i-th element phase shift 2 π i/N, T _cbfor the carrier wave for generation of IGBT locking triggering level.

4. the implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation according to claim 1, is characterized in that: the concrete steps that described step 3 is reallocated to the corresponding carrier wave of all submodules are as follows:

1), before fault: when sub-module fault does not occur system, the normal carrier wave running submodule is dephased carrier wave T _cps, by-pass switch is all opened; The carrier wave of redundancy spare module is T _cb, by-pass switch is all closed;

2) during fault: the by-pass switch of closed fault submodule, fault submodule is out of service, and capacitance voltage electric discharge is 0, and its carrier wave is by original T _cpsbecome T _cb, IGBT is all in blocking; Meanwhile, open the by-pass switch of the redundancy spare module of alternative fault submodule, redundancy submodule puts into operation, and its carrier wave keeps original T _cbconstant, the electric capacity of this redundancy submodule continues charging;

3) after fault: when rated value close to capacitance voltage of the capacitance voltage of the redundancy submodule put into operation, the submodule carrier wave put into operation is changed into each submodule and distributed dephased carrier wave T _cps;

Wherein, T _cpsbe the carrier wave of i-th element phase shift 2 π i/N, T _cbfor the carrier wave for generation of IGBT locking triggering level.

5. the implementation method of the MMC redundancy protecting strategy based on phase-shifting carrier wave modulation according to claim 3, is characterized in that: the trigger of described phase-shifting carrier wave modulator approach design, when not having redundancy spare module to drop into, and the modulating wave M of a jth submodule _ujby common basic sinusoidal modulation wave U _usuperpose the capacitor voltage equalizing controlling value U of corresponding submodule _vbjwith loop current suppression controlling value U _circomposition; For capacitor voltage equalizing controlling value and the loop current suppression controlling value of redundant module, need the carrier wave first judging whether this redundant module to be carrier wave after phase shift, if so, then calculate the modulating wave of this module according to the modulating wave building form of normal-sub module, otherwise, do not calculate;

The modulating wave M of a jth submodule _uj:

M _uj＝U _u+U _cir+U _vbj

1) U _u: the common basic sinusoidal modulation wave being each submodule obtained by dq uneoupled control, is calculated by formula:

$U_u=\frac{U_{\mathrm{dc}}}{2N}-\frac{u_r}{N}$

Wherein, U _dcdC voltage, u _rit is the magnitude of voltage that converter valve side alternating voltage obtains through dq uneoupled control;

2) U _cir: be loop current suppression controlled quentity controlled variable, by basic modulating wave U _uon, superposition circulation inhibitory control device obtains; Specific implementation process is: by the mean value U of whole submodule capacitor voltage _cavwith reference quantity U _crefproduce circulation setting value by PI controller more afterwards, then and three-phase brachium pontis between produce circulation i _cirloop current suppression strategy controller output valve U is produced more afterwards through PI controller _cir;

Wherein, circulation i is produced between three-phase brachium pontis _cirobtained by following formula:

$i_{\mathrm{cir}}=\frac{1}{2}(i_u+i_l)$

Wherein, i _uwith i _lrefer to brachium pontis and lower bridge arm current respectively;

The mean value U of submodule capacitor voltage _cavobtained by following formula:

$U_{\mathrm{cav}}=\underset{j=1}{\overset{j=N+M}{\mathrm{\&Sigma;}}}{K}_j\&CenterDot;U_{\mathrm{cj}}$

Wherein, U _cjthe capacitance voltage of a jth submodule, K _jit is the by-pass switch state of a jth submodule;

3) U _vbj: the capacitor voltage equalizing controlled quentity controlled variable being a jth submodule; By the capacitance voltage U of a jth submodule _cjwith reference value U _crefrelatively, through proportional component, then judge the positive and negative of output valve by bridge arm current direction, finally obtain the Pressure and Control value U of an A phase jth submodule _vbj.