CN103337951A - Method for realizing MMC (Modular Multilevel Converter) redundancy protection strategy based on carrier phase shift modulation - Google Patents

Abstract

The invention provides a method for realizing an MMC redundancy protection strategy based on carrier phase shift modulation, which comprises the following steps: firstly, the state of a sub-module is divided into the normal operation state and redundant standby state according to bypass switch state of the MMC sub-module; then the start-up mode of precharging the redundant sub-module is adopted, and a corresponding carrier dynamic allocator is designed to solve the problem that when a sub-module in the state of normal operation fails, carrier assignment problem exists during the operation of a redundant standby sub-module; finally in full consideration of the influence on capacitance pressure balancing and circulation inhibition strategies when the redundant standby sub-module is put into operation, a trigger with the redundancy protection function is designed; the designed redundancy protection strategy can improve the reliability of operation of the system, ensures that the current converter can continuously perform normal operation when the sub-module fails, the purpose that the failure sub-module is replaced with the redundant sub-module can be realized quickly at the same time, and obvious perturbation of the system can not be caused.

Description

A kind of implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy

Technical field

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

Background technology

Development along with device for high-power power electronic, based on all-controlling power electronics device and pulse-width modulation (Pulse-width Modulation such as IGBT, PWM) (Voltage Source Converter VSC) becomes the new trend that direct current transportation develops to the voltage-source type converter of technology.High voltage direct current transmission (High Voltage Direct Current based on the voltage-source type converter, HVDC) system is because it is economical flexibly and high controlled advantage, is incorporated into the power networks in the large-scale wind electricity field, distributed power generation is incorporated into the power networks, isolated island power, asynchronous AC network is interconnected and field such as multiterminal direct current transportation has obtained application widely.

But general two level or the three-level voltage source type converter of adopting of conventional VSC-HVDC system exists switching frequency height, harmonic wave of output voltage is big, electric pressure is low, the current conversion station floor space is big shortcoming, has the problem of series connection device dynamic voltage balancing in addition.(modular multilevel converter MMC) is the most promising novel voltage source converter at present to the modular multilevel current transformer.The topological structure structure of its novel flexible modularization makes its extensibility strong, realize Redundant Control easily, and well overcome shortcomings such as there is the switching frequency height in traditional electrical potential source converter, harmonic wave of output voltage is big, electric pressure is low, the current conversion station floor space is big, dynamic voltage balancing difficulty, became in recent years the focus of research both at home and abroad.

The brachium pontis of MMC is that (sub-module SM) is composed in series, in case there is SM to break down, converter can't operate as normal, even may be out of service by the identical submodule of several structures.This will cause serious threat to the reliability of whole direct current system.Therefore, design submodule redundancy protecting strategy is very necessary.

The redundancy protecting strategy is according to the difference of the modulator approach that adopts and difference.The modulator approach commonly used of MMC mainly contains three kinds at present: space vector width pulse modulation method (space vector pulse-width modulation, SVPWM), nearest level modulation method (nearest level modulation, NLM) and the phase-shifting carrier wave modulator approach (carrier phase-shifted SPWM, CPS-SPWM).Each modulator approach is applicable to different application scenarios, and pluses and minuses are respectively arranged.Wherein, (carrier phase-shifted SPWM is CPS-SPWM) because its dynamic adjustments ability is strong for the phase-shifting carrier wave modulator approach, can be in conjunction with the additional control of capacitor voltage equalizing, reduce switching frequency, and have good harmonic characterisitic, obtained using widely in engineering.But the CPS-SPWM method is by the carrier wave of each submodule correspondence and the relatively generation triggering signal of modulating wave; do not carry out the electric capacity ordering; therefore CPS-SPWM can't be as the redundancy protecting strategy of the easy realization submodule of nearest level modulation method, and this is one of subject matter of running into of present CPS-SPWM.

Summary of the invention

The object of the invention is to overcome the prior art defective; a kind of implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy is provided; when submodule breaks down; handle the allocation of carriers problem when redundant sub puts into operation in the phase-shifting carrier wave modulation strategy; and can not produce tangible disturbance to system; have versatility, be easy to realize.

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

A kind of implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy may further comprise the steps:

Step 1: according to the MMC submodule by-pass switch state with control guarantor function submodule is classified, each submodule is divided into normal operation submodule and redundant standby submodule;

Step 2: on the basis of step 1, all submodules are carried out precharge MMC start strategy, all submodule electric capacity are carried out precharge;

Step 3: after step 2 finished, design carrier wave dynamic allocator broke down in the normal-sub module, when redundant sub puts into operation, the corresponding carrier wave of all submodules is reallocated.

Have control in the described step 1 and protect two insulated gate bipolar transistor IGBTs up and down that the submodule of function comprises series connection ₁And IGBT ₂, two insulated gate bipolar transistor IGBTs ₁And IGBT ₂Difference reverse parallel connection diode D ₁And D ₂, two insulated gate bipolar transistor IGBTs up and down ₁And IGBT ₂Be parallel with capacitor C after the series connection, following insulated gate bipolar transistor IGBT 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 redundant standby submodule; By-pass switch K closure then is redundant standby submodule, and it then is normal operation submodule that by-pass switch K disconnects.

It is as follows that described step 2 pair all submodule electric capacity carry out precharge concrete steps:

The stage of not controlling that step 201:MMC system starts, the by-pass switch of all submodules is all opened on each brachium pontis of MMC, the IGBT of all submodules all is in the state of cut-offfing, and AC system voltage charges to capacitor C by the diode of each submodule, and capacitor 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 redundant standby submodule number;

In the controlled stage that step 202:MMC system starts, the capacitance voltage of each submodule reaches the maximum U in the stage do not controlled _CmaxThe time, the trigger according to the design of phase-shifting carrier wave modulator approach switches to the input state by blocking, and system enters the controlled stage of startup, redundant standby submodule by-pass switch closure, the carrier wave of all redundant standby submodules is T _Cb, the equal locking of redundant standby submodule IGBT keeps voltage constant; Simultaneously, normally moving submodule electric capacity continuation charging back carrier wave is through the carrier wave T after the phase shift _Cps

Wherein, T _CpsBe the carrier wave of i element phase shift 2 π i/N, T _CbBe the carrier wave for generation of IGBT locking triggering level.

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

1) before the fault: when the submodule fault did not take place in system, the carrier wave that normally moves submodule was dephased carrier wave T _Cps, by-pass switch is all opened; The carrier wave of redundant standby submodule is T _Cb, by-pass switch is all closed;

2) during fault: the by-pass switch of closed fault submodule, the fault submodule is out of service, and the capacitance voltage discharge is 0, and its carrier wave is by original T _CpsBecome T _Cb, IGBT all is in blocking; Simultaneously, open the by-pass switch of the redundant standby submodule that substitutes the fault submodule, redundant sub puts into operation, and its carrier wave keeps original T _CbConstant, the electric capacity of this redundant sub continues charging;

3) after the fault: when the capacitance voltage of the redundant sub that puts into operation during near the rated value of capacitance voltage, the submodule carrier wave that puts into operation is changed into each submodule and is distributed dephased carrier wave T _Cps

Wherein, T _CpsBe the carrier wave of i element phase shift 2 π i/N, T _CbBe the carrier wave for generation of IGBT locking triggering level.

The trigger of described phase-shifting carrier wave modulator approach design, when not having redundant standby submodule to drop into, the modulating wave M of j submodule _UjBy common basic sinusoidal modulation wave U _uThe capacitor voltage equalizing controlling value U of corresponding submodule superposes _VbjSuppress controlling value U with circulation _CirForm; Capacitor voltage equalizing controlling value and circulation for redundant module suppress controlling value, the carrier wave that need judge whether this redundant module earlier is the carrier wave after the phase shift, if then calculate the modulating wave of this module according to the modulating wave composition mode of normal-sub module, otherwise, do not calculate;

The modulating wave M of j submodule _Uj:

M _uj＝U _u+U _cir+U _vbj

1) U _u: be the common basic sinusoidal modulation wave of being controlled each submodule that obtains by the dq decoupling zero, calculated by formula:

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

Wherein, U _DcBe dc voltage, u _rIt is the magnitude of voltage that converter valve top-cross stream voltage obtains through dq decoupling zero control;

2) U _Cir: be that circulation suppresses controlled quentity controlled variable, by at basic modulating wave U _uOn, stack circulation suppresses controller and obtains; The specific implementation process is: with the mean value U of whole submodule capacitance voltages _CavWith reference quantity U _CrefRelatively the back produces the circulation setting value by the PI controller, again and produce circulation i between the three-phase brachium pontis _CirProduce circulation through the PI controller relatively and suppress strategy controller output valve U _Cir

Wherein, produce circulation i between the three-phase brachium pontis _CirObtain by following formula:

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

Wherein, i _uWith i _lRefer to brachium pontis and following brachium pontis electric current respectively;

The mean value U of submodule capacitance voltage _CavObtain by following formula:

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

Wherein, U _CjBe the capacitance voltage of j submodule, K _jIt is the by-pass switch state of j submodule;

3) U _Vbi: the capacitor voltage equalizing controlled quentity controlled variable that is i submodule; Capacitance voltage U with j submodule _CjWith reference value U _CrefRelatively, through proportional component, judge the positive and negative of output valve by the brachium pontis sense of current again, obtain the A Pressure and Control value U of j submodule mutually at last _Vbj

Implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy of the present invention; when breaking down, module replaces with redundant sub; the total number of submodule of state of putting into operation does not change; system voltage is to be formed by stacking by the submodule capacitance voltage that puts into operation; electric parameters such as the voltage and current of system can't produce obvious variation along with the variation of each submodule carrier wave; can improve reliability of system operation; guarantee that converter can continue normal operation when the submodule fault; simultaneously; can realize redundant sub replacement fault submodule fast, can't cause tangible disturbance to system.

Description of drawings

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

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

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

Fig. 4 is submodule allocation of carriers process schematic diagram of the present invention; Carrier State figure when (a) not breaking down for system; Carrier State figure when (b) breaking down for submodule 3; Carrier State figure when (c) dropping into for redundant module;

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

Fig. 6 is the trigger realization flow figure that the present invention has redundancy protecting;

Fig. 7 is that circulation of the present invention suppresses controller;

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

A went up brachium pontis submodule capacitance voltage mutually when Fig. 9 was system provided by the invention startup;

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

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

Figure 12 is the carrier wave of each submodule before and after the fault provided by the invention; (a) be submodule carrier wave before the fault; (b) be submodule carrier wave after the fault;

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

Embodiment

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

A kind of implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy, described method specifically may further comprise the steps:

Step 1: according to the MMC submodule by-pass switch state with control guarantor function submodule is classified, each submodule is divided into normal operation submodule and redundant standby submodule;

As shown in Figure 1, have control and protect two insulated gate bipolar transistor IGBTs up and down that the submodule of function comprises series connection ₁And IGBT ₂, two insulated gate bipolar transistor IGBTs ₁And IGBT ₂Difference reverse parallel connection diode D ₁And D ₂, two insulated gate bipolar transistor IGBTs up and down ₁And IGBT ₂Be parallel with capacitor C after the series connection, following insulated gate bipolar transistor IGBT 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 redundant standby submodule; By-pass switch K closure then is redundant standby submodule, and it then is normal operation submodule that by-pass switch K disconnects.

(1) normal operating condition

When the by-pass switch of submodule disconnected, submodule was in normal operating condition.If the submodule of normal operation breaks down, closed its by-pass switch then, submodule is transferred to redundant stand-by state from normal operating condition.The group module failure is excluded, and connecting system keeps the by-pass switch closure, and is standby as redundant sub.

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

1) blocking: shown in Fig. 2 (a), work as IGBT ₁With IGBT ₂When all turn-offing, current i forward this moment (as the figure sense of current) is through inverse parallel diode D ₁, the capacitor C charging; Perhaps oppositely pass through D ₂, capacitor C is not charged and is not discharged yet;

2) input state: shown in Fig. 2 (b), work as IGBT ₁Conducting and IGBT ₂During shutoff, this moment, the electric current forward was through D ₁, the capacitor C charging; Perhaps oppositely pass through IGBT ₁, the capacitor C discharge;

3) bypass condition: shown in Fig. 2 (c), work as IGBT ₁Turn-off and IGBT ₂During conducting, this moment, the electric current forward was through IGBT ₂, perhaps oppositely pass through D ₂, capacitor C is not charged and is not discharged yet.

(2) the redundant stand-by state of SM

By-pass switch closure and IGBT when submodule ₁With IGBT ₂When all turn-offing, submodule is in redundant stand-by state, as shown in Figure 3.As just when the submodule of running status breaks down, the by-pass switch of redundant sub disconnects, and submodule just changes normal operating condition over to from redundant stand-by state.

In order to keep the capacitance voltage value of redundant module, redundant state adopts connected mode shown in Figure 3 usually.Be closes bypass switch K, IGBT ₁With IGBT ₂All turn-off, this moment, by-pass switch K was with the submodule short circuit, and capacitor C is not charged and do not discharged yet, and its voltage is constant.

Step 2: on the basis of step 1, all submodules are carried out precharge MMC start strategy, all submodule electric capacity are carried out precharge, guarantee the rapidity that redundant sub puts into operation;

It is as follows that all submodule electric capacity are carried out precharge concrete steps:

The stage of not controlling that step 201:MMC system starts.The not control stage refers to the trigger locking, and the IGBT of all submodules all is in the state of cut-offfing, and AC system voltage charges to electric capacity by the diode of each submodule.MMC system for the N+1 level, each brachium pontis has M redundant sub, and N normal operation submodule all opened the by-pass switch of N+M submodule on each brachium pontis of MMC, then AC system is charged to the electric capacity of the submodule of the N+M on the brachium pontis, 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 in the stage do not controlled _CmaxThe time, the trigger according to the design of phase-shifting carrier wave modulator approach switches to the input state by blocking, and system enters the controlled stage of startup.

For the dynamic assignment problem of clear description carrier wave when the normal operation of submodule and the fault, define 3 variablees that record carrier waves, as shown in table 1:

The variable of table 1 record carrier wave

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

T cps	Dimension is N, the carrier wave of i 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 that starts, with M redundant sub by-pass switch closure, the carrier wave of all redundant standby submodules is T _Cb, make the state of the equal locking of IGBT up and down, be in redundant stand-by state as shown in Figure 3, it is constant keeping voltage.The carrier wave of N submodule is the carrier wave T after the phase shift of N process simultaneously _Cps, be in normal operating condition shown in Figure 2.

Step 3: after the start-up course of step 2 finishes, design carrier wave dynamic allocator breaks down the problem of the carrier reallocation of correspondence when redundant sub puts into operation in order to solve the normal-sub module, and guarantee in this process, can not cause tangible disturbance to system;

The concrete steps that the corresponding carrier wave of the redundant sub that drops into is reallocated are as follows:

Start on the basis of finishing in step 2 precharge, N+1 level MMC system for M redundant sub of brachium pontis series connection, the carrier wave dynamic allocator of flexible design, break down in order to solve the normal-sub module, the problem of the carrier reallocation of correspondence when redundant sub puts into operation, and guarantee in this process, can not cause tangible disturbance to system, the realization flow of carrier wave dynamic allocator as shown in Figure 5, concrete steps are as follows:

In realization flow figure, define following significant variable:

1) the by-pass switch state variable K of submodule: its dimension is N+M.K _iThe by-pass switch state of representing i submodule, 1 expression by-pass switch disconnects, and this submodule is in normal operating condition; 0 expression by-pass switch closure, this submodule is in redundant stand-by state.

2) the capacitance voltage V of submodule _c: its dimension is N+M.V _CiThe capacitance voltage value of representing i submodule.

3) the rated value U of submodule capacitance voltage _Ref: its dimension is 1.By the dc voltage U of institute _DcDetermine that with the submodule number N that puts into operation employing formula (2) calculates:

U _ref＝U _dc/N (2)

4) i is the numbering of all submodules of brachium pontis, and establishing N is normally to move the submodule number, and M is the submodule number this patent that is in redundant state, then i＜=N+M; J is phase shift 2 π/N numbering of carrier wave afterwards, and j＜=N;

Realization flow step with reference to figure 5 carrier wave dynamic allocator is as follows:

Step 1): the folding condition of judging the by-pass switch of i submodule earlier; 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 that judges i 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): with the carrier wave T of locking submodule _CbAssignment is given the carrier wave T of i submodule _Ci

Step 4): judge whether to finish the distribution of the carrier wave after the phase shift, if j＜=N, unallocated the finishing of carrier wave after the phase shift be described, then carry out step 5; If j〉N, illustrate that the carrier wave after the phase shift distributes, then carry out step 3;

Step 5): with j dephased carrier wave T _CpsjAssignment is given the carrier wave T of i submodule _Ci, then with the carrier index j+1 after the phase shift, handle the carrier wave after the next phase shift; Carry out step 6;

Step 6): judge whether to finish the allocation of carriers of all submodules, if i 〉=N+M, then obtain the carrier wave of all N+M submodule; If i＜N+M then with the numbering i+1 of submodule, returns step 1, continue to distribute the carrier wave of next submodule.

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

1) before the fault: when the submodule fault did not take place in system, the allocation of carriers of each submodule correspondence was 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 redundant sub is T _Cb, by-pass switch is all closed;

2) during fault: when the 3rd submodule broke down, the allocation of carriers of each submodule correspondence was shown in Fig. 4 (b).At this moment, the by-pass switch of closed fault submodule 3, submodule 3 is out of service, and the capacitance voltage discharge is 0.Its carrier wave is by original T _Cps3Become T _Cb, IGBT all is in blocking, so that maintenance.Simultaneously, open the by-pass switch of redundant sub 7, redundant sub 7 puts into operation, and its carrier wave keeps original T _CbConstant, the capacitance voltage of this redundant sub continues charging.

3) after the fault: when the capacitance voltage of redundant sub 7 during near the rated value of capacitance voltage, corresponding allocation of carriers is shown in Fig. 4 (c).At this moment, all submodules that put into operation dynamically distribute dephased carrier wave T for each submodule by carrier wave distributor _Cps

By the assigning process of the (a) and (b) of Fig. 4, (c) three carrier waves as can be known, when replacing the submodule 3 of faults with redundant sub 7, the carrier wave of some (even may all) submodule changes (as the carrier wave of the 4th submodule 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 total number of the submodule of the state that puts into operation still is N, and system voltage is to be formed by stacking by this N sub-module capacitance voltage.Because capacitor voltage equalizing control and circulation suppress the effect of control strategy, make that when the submodule carrier wave changes electric parameters such as the voltage and current of system can't produce obvious variation along with the variation of each submodule carrier wave simultaneously.

No matter redundant sub be which, perhaps have simultaneously several submodules break down (under the enough situations of redundant module number) can carry out allocation of carriers according to the designed carrier wave dynamic allocator of the present invention.

On the basis of the designed carrier wave dynamic allocator of step 3; take into full account the redundant sub input suppresses control to capacitor voltage equalizing and circulation influence; and design has the trigger of function of redundancy protection accordingly; because the symmetry of upper and lower bridge arm and three-phase; it is example that the present invention goes up brachium pontis mutually with A; design has the trigger of function of redundancy protection accordingly, and realization flow is seen Fig. 6.

M _UaiBe the modulating wave of i submodule, all be superimposed with by common basic modulating wave and suppressed by the capacitor voltage equalizing controlling value of corresponding submodule and circulation that controlling value forms; All pressures and circulation for redundant module suppress control, and the carrier wave that need judge whether this redundant module earlier is the carrier wave after the phase shift, if, then form mode according to the modulating wave of normal-sub module, calculate the modulating wave of this module, otherwise, do not need to carry out this step calculating

Constitute M _UaiThree part explanations:

1) U _Ua: be the common basic sinusoidal modulation wave of being gone up each submodule of brachium pontis by the A that dq decoupling zero control obtains mutually, calculated by following formula:

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

Wherein, U _DcBe dc voltage, u _RaIt is the magnitude of voltage that converter valve side A cross streams voltage obtains through dq decoupling zero control.

2) U _Cira: the circulation that is the A phase suppresses controlled quentity controlled variable, suppresses controller by the circulation of Fig. 7 and obtains;

Going up the brachium pontis submodule mutually with A is example, can pass through at basic modulating wave U _UaOn, the circulation shown in the stack accompanying drawing 7 suppresses the resulting circulation of controller and suppresses controlling value U _CiraRealize.The specific implementation process is: with the mean value U of the whole submodule capacitance voltages of A phase upper and lower bridge arm _CavaWith reference quantity U _CrefRelatively the back produces the circulation setting value by the PI controller, again with i _CiraProduce circulation through the PI controller relatively and suppress strategy controller output valve U _Cira

Because the voltage between each brachium pontis can not be in full accord when steady operation for MMC, thereby cause homophase upper and lower bridge arm voltage asymmetric, can produce circulation between the three-phase brachium pontis of MMC, thereby sinusoidal brachium pontis 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 that respectively A goes up brachium pontis and following brachium pontis electric current mutually.

Wherein, because each brachium pontis has the existence of redundant sub, circulation suppresses the mean value U of the submodule capacitance voltage in the controller _CavaEmploying is calculated by following formula,

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

Wherein, U _CajBe the capacitance voltage of j submodule, K _jIt is the by-pass switch state of j submodule.

3) U _Vbai: be the capacitor voltage equalizing controlled quentity controlled variable of i submodule, obtained by the capacitor voltage equalizing controller of Fig. 8;

Going up the brachium pontis submodule mutually with A is example, can pass through at basic modulating wave U _UaOn, the Pressure and Control value U of resulting j the submodule of capacitor voltage equalizing controller shown in the stack accompanying drawing 8 _VbajRealize.The specific implementation process is: with the capacitance voltage U of j submodule of A phase _CajWith reference value U _CrefRelatively, through proportional component, judge the positive and negative of output valve by the brachium pontis sense of current again, obtain the A Pressure and Control value U of j submodule mutually at last _Vbaj

As shown in the formula as can be known, by the basic modulating wave U of j submodule of last brachium pontis _UaLast stack circulation suppresses controlled quentity controlled variable U _CiraWith capacitor voltage equalizing controlled quentity controlled variable U _Vbai, obtain the modulating wave M of j submodule of brachium pontis _Uaj:

M _uaj＝U _uaj+U _cira+U _vbaj

The trigger realization flow that has redundancy protecting referring to Fig. 6 is specific as follows:

In flow chart, F _P1iThe trigger impulse of the last IGBT of corresponding i submodule, F _P2iIt is the trigger impulse of IGBT under the corresponding submodule.

Step 1): the carrier wave T that judges i submodule earlier _CiWhether be the carrier wave T of locking submodule _CbIf 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 the upper and lower IGBT of submodule _P1iWith F _P2iAll assignment is 0, and namely submodule is in blocking, carry out step 7;

Step 3): with the capacitor voltage equalizing controlling value U of i submodule _VbaiSuppress controlling value U with circulation _Cira, be superimposed to basic modulating wave U _Ua, obtain the modulating wave M that capacitor voltage equalizing and circulation suppress control that has of i submodule _Uai, carry out step 4;

Step 4): the modulating wave M that judges i submodule _UaiModulating wave T with i submodule _CiSize, if M _UaiT _Ci, then carry out step 5; If M _Uai＜=T _CiThen carry out step 6;

Step 5): the triggering level F of i the upper and lower IGBT of submodule _P1i=1 and F _P2i=0 is 0, and namely submodule is in the input state;

Step 6): the triggering level F of i the 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 finishes the generation of the triggering level of all submodule IGBT, if i 〉=N+M, then produce the triggering level of all N+M the upper and lower IGBT of submodule; If i＜N+M then with the numbering i+1 of submodule, returns step 1, continue to produce the triggering level of next submodule;

Below function and the effect based on the phase-shifting carrier wave modulated M MC redundancy protecting strategy that propose of the present invention just; simulation example is elaborated the carrier wave dynamic allocator that has MMC submodule function of redundancy protection that checking this paper proposes and the validity of trigger.Should be emphasized that following explanation only is exemplary, rather than in order to limit the scope of the invention and to use.

At first, build 7 level both-end MMC DC transmission system simulation models in PSCAD/EMTDC, wherein each brachium pontis of MMC has submodule SM1～SM6 and 1 standby submodule SM7 of redundancy of 6 normal operations.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 the phase-shifting carrier wave modulator approach, and carrier frequency is 200Hz, and the rectification side adopts decides active power and decide Reactive Power Control, and the control reference value is respectively 10MW and 3Mvar.The inversion side adopts decides reactive power and decides direct voltage control, and the control reference value is respectively 5Mvar and 20kV.

(1) precharge starts strategy:

Employing is to the precharge Starting mode of redundant module, and every electric capacity charging voltage maximum that goes up 7 submodules of brachium pontis (comprising redundant standby submodule) mutually should be:

When the capacitance voltage value of submodule reached 2.02kV, the startup stage of entering control, trigger put into operation.The startup stage A go up the brachium pontis submodule mutually capacitance voltage as shown in Figure 9, wherein Vc1～Vc7 represents 7 sub-module capacitance voltages on the brachium pontis.

Supposing the system rectification side A when 1.5s goes up the 2nd submodule of brachium pontis mutually and breaks down, and this moment, the fault submodule was bypassed, and redundant standby submodule puts into operation.After an adjustment process, system enters steady operational status, as shown in figure 10.

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

If redundant module adopts not charging modes to start, then break down when being bypassed at submodule 2, redundant sub 7 will arrive the rated capacity magnitude of voltage through 0.13s, as shown in figure 11.

(2) dynamic allocation procedure of carrier wave:

Figure 12 is seen in the variation of the carrier wave of each submodule before and after the fault.When the 2nd submodule broke down, except the carrier wave of the 1st submodule did not change, variation had all taken place in the carrier wave of other submodules as Figure 12 (a).Carrier wave as Figure 12 (b) submodule 7 is T at the moment of fault retention value _Cb, through behind the 0.073s, the capacitance voltage of submodule 7 reaches rated value, and corresponding carrier wave switches to the carrier wave after the phase shift.

(3) to the perturbation analysis of system:

Although for each submodule, sudden change has taken place in carrier wave, system's brachium pontis electric current I _u, direct voltage U _Dc, the submodule output voltage V _SmauAnd the active power P of converting plant ₁Steady with the variation of reactive power Q 1, as shown in figure 13, the disturbance to system when carrier wave changes is not obvious.

More than experiment; fully verified when fault takes place; the MMC submodule redundancy protecting strategy based on the phase-shifting carrier wave modulator approach that adopts the present invention to propose can make redundant module steadily substitute malfunctioning module and put into operation, proves that redundancy protecting strategy in this paper is feasible effective.In addition, adopt precharge of the present invention to start scheme, can effectively reduce the voltage dip that when the standby submodule of redundancy puts into operation, produces, reduce the time that redundant module is charged to rated voltage; And designed carrier wave dynamic allocator can well handle the allocation of carriers problem when redundant sub puts into operation in the phase-shifting carrier wave modulation strategy, and should can not produce tangible disturbance to system by strategy, has versatility, is easy to realize.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation 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. implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy is characterized in that may further comprise the steps:

Step 1: according to the MMC submodule by-pass switch state with control guarantor function submodule is classified, each submodule is divided into normal operation submodule and redundant standby submodule;

Step 2: on the basis of step 1, all submodules are carried out precharge MMC start strategy, all submodule electric capacity are carried out precharge;

Step 3: after step 2 finished, design carrier wave dynamic allocator broke down in the normal-sub module, when redundant sub puts into operation, the corresponding carrier wave of all submodules is reallocated.

2. the implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy according to claim 1 is characterized in that: have control in the described step 1 and protect two insulated gate bipolar transistor IGBTs up and down that the submodule of function comprises series connection ₁And IGBT ₂, two insulated gate bipolar transistor IGBTs ₁And IGBT ₂Difference reverse parallel connection diode D ₁And D ₂, two insulated gate bipolar transistor IGBTs up and down ₁And IGBT ₂Be parallel with capacitor C after the series connection, following insulated gate bipolar transistor IGBT 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 redundant standby submodule; By-pass switch K closure then is redundant standby submodule, and it then is normal operation submodule that by-pass switch K disconnects.

3. the implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy according to claim 1 is characterized in that: it is as follows that described step 2 pair all submodule electric capacity carry out precharge concrete steps:

The stage of not controlling that step 201:MMC system starts, the by-pass switch of all submodules is all opened on each brachium pontis of MMC, the IGBT of all submodules all is in the state of cut-offfing, and AC system voltage charges to capacitor C by the diode of each submodule, and capacitor 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 redundant standby submodule number;

In the controlled stage that step 202:MMC system starts, the capacitance voltage of each submodule reaches the maximum U in the stage do not controlled _CmaxThe time, the trigger according to the design of phase-shifting carrier wave modulator approach switches to the input state by blocking, and system enters the controlled stage of startup, redundant standby submodule by-pass switch closure, the carrier wave of all redundant standby submodules is T _Cb, the equal locking of redundant standby submodule IGBT keeps voltage constant; Simultaneously, normally moving submodule electric capacity continuation charging back carrier wave is through the carrier wave T after the phase shift _Cps

Wherein, T _CpsBe the carrier wave of i element phase shift 2 π i/N, T _CbBe the carrier wave for generation of IGBT locking triggering level.

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

1) before the fault: when the submodule fault did not take place in system, the carrier wave that normally moves submodule was dephased carrier wave T _Cps, by-pass switch is all opened; The carrier wave of redundant standby submodule is T _Cb, by-pass switch is all closed;

2) during fault: the by-pass switch of closed fault submodule, the fault submodule is out of service, and the capacitance voltage discharge is 0, and its carrier wave is by original T _CpsBecome T _Cb, IGBT all is in blocking; Simultaneously, open the by-pass switch of the redundant standby submodule that substitutes the fault submodule, redundant sub puts into operation, and its carrier wave keeps original T _CbConstant, the electric capacity of this redundant sub continues charging;

3) after the fault: when the capacitance voltage of the redundant sub that puts into operation during near the rated value of capacitance voltage, the submodule carrier wave that puts into operation is changed into each submodule and is distributed dephased carrier wave T _Cps

Wherein, T _CpsBe the carrier wave of i element phase shift 2 π i/N, T _CbBe the carrier wave for generation of IGBT locking triggering level.

5. the implementation method based on phase-shifting carrier wave modulated M MC redundancy protecting strategy according to claim 3 is characterized in that: the trigger of described phase-shifting carrier wave modulator approach design, and when not having redundant standby submodule to drop into, the modulating wave M of j submodule _UjBy common basic sinusoidal modulation wave U _uThe capacitor voltage equalizing controlling value U of corresponding submodule superposes _VbjSuppress controlling value U with circulation _CirForm; Capacitor voltage equalizing controlling value and circulation for redundant module suppress controlling value, the carrier wave that need judge whether this redundant module earlier is the carrier wave after the phase shift, if then calculate the modulating wave of this module according to the modulating wave composition mode of normal-sub module, otherwise, do not calculate;

The modulating wave M of j submodule _Uj:

M _uj＝U _u+U _cir+U _vbj

1) U _u: be the common basic sinusoidal modulation wave of being controlled each submodule that obtains by the dq decoupling zero, calculated by formula:

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

Wherein, U _DcBe dc voltage, u _rIt is the magnitude of voltage that converter valve top-cross stream voltage obtains through dq decoupling zero control;

2) U _Cir: be that circulation suppresses controlled quentity controlled variable, by at basic modulating wave U _uOn, stack circulation suppresses controller and obtains; The specific implementation process is: with the mean value U of whole submodule capacitance voltages _CavWith reference quantity U _CrefRelatively the back produces the circulation setting value by the PI controller, again and produce circulation i between the three-phase brachium pontis _CirProduce circulation through the PI controller relatively and suppress strategy controller output valve U _Cir

Wherein, produce circulation i between the three-phase brachium pontis _CirObtain by following formula:

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

Wherein, i _uWith i _lRefer to brachium pontis and following brachium pontis electric current respectively;

The mean value U of submodule capacitance voltage _CavObtain by following formula:

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

Wherein, U _CjBe the capacitance voltage of j submodule, K _jIt is the by-pass switch state of j submodule;

3) U _Vbi: the capacitor voltage equalizing controlled quentity controlled variable that is i submodule; Capacitance voltage U with j submodule _CjWith reference value U _CrefRelatively, through proportional component, judge the positive and negative of output valve by the brachium pontis sense of current again, obtain the A Pressure and Control value U of j submodule mutually at last _Vbj

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