CN102570864B - Online loss calculation method for modular multilevel converter - Google Patents

Abstract

The invention discloses an online loss calculation method for a modular multilevel converter (MMC), and belongs to the field of power transmission and distribution. The method comprises the following steps of: 1) calculating the conduction loss of two insulated gate bipolar transistors (LGBT) and two flywheel diodes in each sub-module (SM); 2) calculating the switching loss of the two IGBTs and the reverse recovery loss of the two flywheel diodes in each SM; and 3) calculating related loss by using a loss calculation module. The method has the advantages that: 1, the complexity of manual measurement and calculation is effectively avoided when the MMC has a great number of modules, workload is greatly reduced, and the method is fast and convenient; 2, the online calculation of the loss of the MMC is realized, and the method is wide in application range, and can be applied to the loss calculation of an MMC system in any operating state; and 3, modular packaging is facilitated, a floor area is saved, the utilization rate of resources is increased, and the output of a platform comprises various kinds of loss and loss ratios, so that the method is direct and clear, and staff can conveniently observe the running state of the system at any time.

Description

The online loss computing method of a kind of modularization multi-level converter

Technical field

The invention belongs to power transmission and distribution field, particularly the online loss computing method of a kind of modularization multi-level converter.

Background technology

In recent years, demand supply of electric power being increased day by day for meeting economic growth, can turn-off voltage source converter (the Voltage SourceConverter of power electronic device based on large power all-controlled type, be called for short VSC) be widely used in high voltage direct current transmission (High Voltage DirectCurrent, be called for short HVDC) in technology, and obtain good operational performance, be referred to as Technology of HVDC based Voltage Source Converter (VSC-HVDC).But, the loss of this system (employing Technology of HVDC based Voltage Source Converter) is far longer than the loss of traditional DC transmission system, this is mainly to cause because Technology of HVDC based Voltage Source Converter adopts larger converter loss, especially two level, three-level voltage source converter, although its topological structure, control strategy is comparatively simple, but switching frequency is high, converter loss is larger, this also becomes it and is applied to the major obstacle of high-power long-distance transmissions, so the damage measure of falling that the loss characteristic of voltage source converter is furtherd investigate and proposed to be correlated with will have important engineering significance.

A kind of Novel electric potential source converter topology---modularization multi-level converter (MMC), because of characteristics such as it are controlled flexibly, switching frequency is low, loss is little, is just progressively applied in flexible DC power transmission engineering.The loss characteristic research of modularization multi-level converter also becomes one of important research content of Technology of HVDC based Voltage Source Converter, existing loss computing method is mostly for two level voltage source converters, and the research of calculating about modularization multi-level converter loss is considerably less.Compared with two level converters, topological structure, control mode and the loss characteristic of modularization multi-level converter have very big-difference, and only some can apply in the loss calculating of modularization multi-level converter existing two level converter loss computing methods.

On the one hand, because of the particularity of modularization multi-level converter topological structure, operation mechanism and control mode, the electric current possibility that synchronization flows through upper and lower bridge arm IGBT module is different, though also can release the current value of modularization multi-level converter upper and lower bridge arm by the method for theory analysis and empirical equation, but along with the variation of running environment, during such as the variation of system modulation degree or the system failure, the applicability of these formula will reduce greatly.On the other hand, when the level number of modularization multi-level converter very high, when namely the upper and lower bridge arm of the every phase of modularization multi-level converter has a lot of SM modules, when computed losses, need to measure the electric current that flows in each SM module two IGBT devices and two fly-wheel diodes (FWD) device, also need to detect the conducting state of each device, if manually calculate converter loss, workload will be very huge, such as the U.S. Trans BayCable Project(TBC engineering having put into operation in 2010), this project adopts 199 level modularization multi-level converters, every phase upper and lower bridge arm has 216 SM modules, wherein 198 SM modules put into operation and form 199 level, other 18 SM module redundancies, if measure its loss, must measure acquisition 3 × 2 × 216 × 2=2592(and wherein 3 refer to MMC three-phase bridge, 2 × 216 is the number of the single-phase brachium pontis SM of MMC module, last 2 is IGBT device number or fly-wheel diode device number in each SM module) electric current of the electric current of individual IGBT and the fly-wheel diode of same number, if but adopt the online method detecting, increase corresponding electric parameters measuring point only need to each device the inside, build corresponding computing module, by certain algorithm, just can rely on computer, in very short simulation time, realize quickly and easily the real-time calculating of loss in emulation, can greatly reduce workload.So will find a kind of loss computing method that can be applicable to any situation, still do not have at present document to carry out systematic research to the online loss computing method of modularization multi-level converter, so, along with the extensive use of engineering reality, select suitable simulated environment PSCAD/EMTDC, do further investigation for the online loss computing method of modularization multi-level converter and have urgent demand property and necessity, this will not only have great theory innovation meaning, also has important Practical Project and is worth.

Summary of the invention

The present invention is directed to above-mentioned defect and disclose the online loss computing method of kind modularization multi-level converter.It comprises the following steps:

1) obtain A phase brachium pontis current i by measurement _a, B phase brachium pontis current i _b, C phase brachium pontis current i _cwith the working temperature t of current environment, then calculate the on-state loss of an IGBT in each SM module, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode;

2) calculate an IGBT and the switching loss of the 2nd IGBT and the reverse recovery loss of the first fly-wheel diode and the second fly-wheel diode in each SM module;

3) calculate the total on-state loss P of IGBT by loss computing module _tcon, the total on-state loss P of fly-wheel diode _dcon, IGBT master switch loss P _tsw, the total reverse recovery loss P of fly-wheel diode _drec, IGBT total losses P _t, fly-wheel diode total losses P _d, the total on-state loss P of modularization multi-level converter _con, modularization multi-level converter master switch loss P _sw, modularization multi-level converter total losses P _totwith modularization multi-level converter loss ratio K.

Described step 1) specifically comprises the following steps:

11) from product description, obtain following four articles of curves: the collection emitter voltage V ' of the one IGBT when temperature is 25 DEG C _cEwith collector current I _cthe collection emitter voltage V of relation curve, temperature the one IGBT while being 125 DEG C _cEwith collector current I _cthe forward conduction voltage V ' of relation curve, temperature the first fly-wheel diode while being 25 DEG C _f-DC Forward Current I _frelation curve and the forward conduction voltage V of temperature first fly-wheel diode while being 125 DEG C _f-DC Forward Current I _frelation curve;

12) the collection emitter voltage V of the one IGBT in the time that temperature is 125 DEG C _cEwith collector current I _crelation curve in, obtain following N group data by trace-point method: (I _c1, V _cE1), (I _c2, V _cE2) ... (I _cN, V _cEN), wherein, I _c1-I _cNbe the collector current value of an IGBT, V _cE1-V _cENan IGBT collector current value to be I _c1-I _cNtime the one IGBT collection emitter voltage value, 1≤N≤100; To (I _c1, V _cE1), (I _c2, V _cE2) ... (I _cN, V _cEN) this N group data carry out high order curve matching in MATLAB, the one IGBT collection emitter voltage V when obtaining temperature and being 125 DEG C _cEwith collector current I _crelationship;

According to following formula: R _t1=V _cE1/ I _c1, R _t2=V _cE2/ I _c2r _tN=V _cEN/ I _cNobtain: when an IGBT collector current value is I _c1-I _cNtime the one IGBT on state resistance value be R _t1-R _tN, and then obtain following N group data: (I _c1, R _t1), (I _c2, R _t2) ... (I _cN, R _tN); To (I _c1, R _t1), (I _c2, R _t2) ... (I _cN, R _tN) this N group data carry out high order curve matching in MATLAB, the on state resistance R of the one IGBT when obtaining temperature and being 125 DEG C _twith collector current I _crelationship;

13) the first fly-wheel diode forward conduction voltage V in the time that temperature is 125 DEG C _f-DC Forward Current I _frelation curve in, obtain following M group data by trace-point method: (I _f1, V _f1), (I _f2, V _f2) ... (I _fM, V _fM), wherein, I _f1-I _fMbe the DC Forward Current value of the first fly-wheel diode, V _f1-V _fMthat DC Forward Current value when the first fly-wheel diode is I _f1-I _fMtime the first fly-wheel diode forward conduction magnitude of voltage, 1≤M≤100; To (I _f1, V _f1), (I _f2, V _f2) ... (I _fM, V _fM) this M group data carry out high order curve matching in MATLAB, the first fly-wheel diode forward conduction voltage V when obtaining temperature and being 125 DEG C _fwith DC Forward Current I _frelationship;

According to following formula: R _d1=V _f1/ I _f1, R _d2=V _f2/ I _f2r _dM=V _cEM/ I _cMthe DC Forward Current value obtaining when the first fly-wheel diode is I _f1-I _fMtime the first fly-wheel diode on state resistance value R _d1-R _dM, and then obtain following M group data: (I _f1, R _d1), (I _f2, R _d2) ... (I _fM, R _dM); To (I _f1, R _d1), (I _f2, R _d2) ... (I _fM, R _dM) this M group data carry out high order curve matching in MATLAB, the first fly-wheel diode on state resistance R when obtaining temperature and being 125 DEG C _dwith DC Forward Current I _frelationship;

14) four curves in step 11) are carried out to interpolation arithmetic by following formula:

${\mathrm{\α}}_T=\frac{1}{V_{\mathrm{CE}}}[\frac{V_{\mathrm{CE}}-V_{\mathrm{CE}}^{\′}}{100}(t-25)+V_{\mathrm{CE}}^{\′}]$

${\mathrm{\α}}_D=\frac{1}{V_F^{\′}}[\frac{V_F^{\′}-V_F}{100}(t-25)+V_F]$

Obtain the junction temperature factor alpha of the on-state loss of an IGBT and the 2nd IGBT _tjunction temperature factor alpha with the on-state loss of the first fly-wheel diode and the second fly-wheel diode _d, in above-mentioned formula, the working temperature that t is current environment;

15) in curve fitting module, calculate the threshold voltage V such as the real-time on-state of an IGBT by following formula _cEX, the first fly-wheel diode the threshold voltage V such as real-time on-state _dX, an IGBT real-time on-state substitutional resistance R _tXreal-time on-state substitutional resistance R with the first fly-wheel diode _dX:

V _CEX＝α _T×V _CE

V _DX＝α _D×V _F

R _TX＝α _T×R _T

R _DX＝α _D×R _D

16) by V _cEXand R _tXthe following formula of substitution, draws the middle on-state loss P of an IGBT as calculated _eFS:

$\left\{\begin{array}{c}{V}_{\mathrm{EF}}=V_{\mathrm{CEX}}+R_{\mathrm{TX}}\·i\\ I_{\mathrm{EF}}=\sqrt{\stackrel{\‾}{\left|i\right|}\·\hat{i}}\\ P_{\mathrm{EFS}}=i\·V_{\mathrm{EF}}\end{array}\right.$

In above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, in A phase brachium pontis, and i=i _a, in B phase brachium pontis, i=i _b, in C phase brachium pontis, i=i _c, V _eFfor the threshold voltages such as the on-state of IGBT, I _eFfor the equivalent electric current of on-state of IGBT, the peak value of brachium pontis electric current, it is the arithmetic mean of brachium pontis electric current; In real work, I _c=i, integrating step 12)-step 15) finds out: V _cEXand R _tXbe the function of t and i, so, P _eFSfor the function of t and i;

By V _dXand R _dXthe following formula of substitution, draws the middle on-state loss P of the first fly-wheel diode as calculated _dFS:

$\left\{\begin{array}{c}{V}_{\mathrm{DF}}=V_{\mathrm{DX}}+R_{\mathrm{DX}}\·i\\ I_{\mathrm{DF}}=\sqrt{\stackrel{\‾}{\left|i\right|}\·\hat{i}}\\ P_{\mathrm{DFS}}=i\·V_{\mathrm{DF}}\end{array}\right.$

In above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, V _dFfor the threshold voltages such as the on-state of fly-wheel diode, I _dFfor the equivalent electric current of on-state of fly-wheel diode; In real work, I _f=i, integrating step 12)-step 15) finds out: V _dXand R _dXbe the function of t and i, so, P _dFSfor the function of t and i;

17) the middle on-state loss P ' of the 2nd IGBT _eFSmiddle on-state loss P with an IGBT _eFScomputational methods identical, by step 11)-step 16) draw the threshold voltage V ' such as the real-time on-state of the 2nd IGBT _cEX, the 2nd IGBT real-time on-state substitutional resistance R ' _tXmiddle on-state loss P ' with the 2nd IGBT _eFS;

The middle on-state loss P ' of the second fly-wheel diode _dFSmiddle on-state loss P with the first fly-wheel diode _dFScomputational methods identical, by step 11)-step 16) draw the threshold voltage V ' such as the real-time on-state of the second fly-wheel diode _dX, the second fly-wheel diode real-time on-state substitutional resistance R ' _dXmiddle on-state loss P ' with the second fly-wheel diode _dFS;

18) solve the mean value s4 of the duty ratio of the second fly-wheel diode in the mean value s3 of the duty ratio of the first fly-wheel diode in the mean value s2 of the duty ratio of the 2nd IGBT in the mean value s1 of the duty ratio of an IGBT in every all SM modules, all SM modules, all SM modules and all SM modules;

19) by the on-state loss P of following formula calculating the one IGBT _eF, the 2nd IGBT on-state loss P ' _eF, the first fly-wheel diode on-state loss P _dFon-state loss P ' with the second fly-wheel diode _dF:

P _EF＝s1×P _EFS

P′ _EF＝s2×P′ _EFS

P _DF＝s3×P _DFS

P′ _DF＝s4×P′ _DFS。

Described step 18) specifically comprise the following steps:

181) simulation time t1 and described point step-length h are inputed in duty ratio measuring module, duty ratio measuring module is by gathering the current signal that flows through an IGBT, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode in each SM module, off state is opened in judgement, obtains the duty ratio of an IGBT in each SM module, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode;

182) duty ratio mean value solves the module duty ratio to an IGBT in each SM module respectively, the duty ratio of the 2nd IGBT in each SM module, in each SM module, in the duty ratio of the first fly-wheel diode and each SM module, the duty ratio of the second fly-wheel diode is averaged, output is respectively the mean value s1 of the duty ratio of an IGBT in all SM modules, the mean value s2 of the duty ratio of the 2nd IGBT in all SM modules, the mean value s4 of the duty ratio of the second fly-wheel diode in the mean value s3 of the duty ratio of the first fly-wheel diode and all SM modules in all SM modules.

Described step 2) specifically comprise the following steps:

21) utilize interpolation to introduce the junction temperature coefficient ρ of the switching loss of an IGBT _tjunction temperature coefficient ρ with the first fly-wheel diode reverse recovery loss _d, calculate both variation with temperature, its computing formula is as follows:

${\mathrm{\ρ}}_T=\frac{1}{E_{\mathrm{SW}1}}[\frac{E_{\mathrm{SW}1}-E_{\mathrm{SW}2}}{100}(t-25)+E_{\mathrm{SW}2}]$

${\mathrm{\ρ}}_D=\frac{1}{E_{\mathrm{rec}1}}[\frac{E_{\mathrm{rec}1}-E_{\mathrm{rec}2}}{100}(t-25)+E_{\mathrm{rec}2}]$

In above-mentioned formula, E _sw1the energy loss in the switching process of an IGBT while meeting the following conditions: an IGBT supply voltage V _ccfor reference voltage u _ref, rated current electric current is reference current i _ref, junction temperature is 125 DEG C; E _sw2the energy loss in the switching process of an IGBT while meeting the following conditions: an IGBT supply voltage V _ccfor reference voltage u _ref, rated current is reference current i _ref, junction temperature is 25 DEG C; E _sw1and E _sw2all know by the product description of an IGBT;

E _rec1the reverse recovery energy loss of the first fly-wheel diode while meeting the following conditions: both end voltage is reference voltage u _ref, DC Forward Current is reference current i _ref, junction temperature is 125 DEG C; E _rec2the reverse recovery energy loss of the first fly-wheel diode while meeting the following conditions: both end voltage is reference voltage u _ref, DC Forward Current is reference current i _ref, junction temperature is 25 DEG C; E _rec1and E _rec2all know by the product description of the first fly-wheel diode;

22) switching frequency measurement module obtains the switching frequency f of an IGBT by the number of SM module trigger impulse in measurement unit's time _sT, the switching frequency f of the first fly-wheel diode _sDbe the switching frequency f of an IGBT _sThalf;

23) by the switching loss P of following formula calculating the one IGBT _swTreverse recovery loss P with the first fly-wheel diode _swD:

$\left\{\begin{array}{c}{P}_{\mathrm{swT}}={\mathrm{\ρ}}_T\·f_{\mathrm{sT}}\·\left(\frac{E_{\mathrm{on}}+E_{\mathrm{off}}}{u_{\mathrm{ref}}\·i_{\mathrm{ref}}}\right)\·U_C\·\stackrel{\‾}{\left|i\right|}\\ P_{\mathrm{swD}}={\mathrm{\ρ}}_D\·f_{\mathrm{sD}}\·\left(\frac{E_{\mathrm{rec}}}{u_{\mathrm{ref}}\·i_{\mathrm{ref}}}\right)\·U_C\·\stackrel{\‾}{\left|i\right|}\end{array}\right.$

In above-mentioned formula, U _cfor the average capacitor voltage of SM module, E _on, E _off, E _recbe respectively and be defined in an IGBT reference voltage u _ref, an IGBT reference current i _refoppositely recover energy loss with IGBT turn-on consumption, turn-off power loss and the first fly-wheel diode under maximum junction temperature; I is the upper and lower bridge arm electric current that flows into modularization multi-level converter, it is the arithmetic mean of brachium pontis electric current;

24) the switching loss P ' of the 2nd IGBT _swTswitching loss P with an IGBT _swTcomputational methods identical, by step 21)-step 23) obtain the switching loss P ' of the 2nd IGBT _swT;

The reverse recovery loss P ' of the second fly-wheel diode _swDreverse recovery loss P with a fly-wheel diode _swDcomputational methods identical, by step 21)-step 23) obtain the reverse recovery loss P ' of the second fly-wheel diode _swD;

The total on-state loss P of described IGBT _tconfor all SM module I GBT on-state loss sums of modularization multi-level converter, IGBT on-state loss is the on-state loss P of an IGBT _eFon-state loss P ' with the 2nd IGBT _eFsum;

The total on-state loss P of described fly-wheel diode _dconfor all SM module fly-wheel diode on-state loss sums of modularization multi-level converter, fly-wheel diode on-state loss is the on-state loss P of the first fly-wheel diode _dFon-state loss P ' with the second fly-wheel diode _dFsum;

Described IGBT master switch loss P _tswfor all SM module I GBT switching loss sums of modularization multi-level converter, IGBT switching loss is the switching loss P of an IGBT _swTswitching loss P ' with the 2nd IGBT _swTsum;

The total reverse recovery loss P of described fly-wheel diode _drecfor all SM module fly-wheel diode reverse recovery loss sums of modularization multi-level converter, fly-wheel diode reverse recovery loss is the reverse recovery loss P of the first fly-wheel diode _swDreverse recovery loss P ' with the second fly-wheel diode _swDsum;

Described IGBT total losses P _tfor the total on-state loss P of IGBT _tconwith IGBT master switch loss P _tswsum;

Described fly-wheel diode total losses P _dfor the total on-state loss P of fly-wheel diode _dconwith the total reverse recovery loss P of fly-wheel diode _drecsum;

The total on-state loss P of described modularization multi-level converter _confor the total on-state loss P of IGBT _tconwith the total on-state loss P of fly-wheel diode _dconsum;

Described modularization multi-level converter master switch loss P _swfor IGBT master switch loss P _tswwith the total reverse recovery loss P of fly-wheel diode _drecsum;

Described modularization multi-level converter total losses P _totfor IGBT total losses P _twith fly-wheel diode total losses P _dsum;

Described modularization multi-level converter loss ratio K is modularization multi-level converter total losses and the ratio of system total transmission capacity.

Beneficial effect of the present invention is: the first, and while effectively having avoided in MMC that number of modules is more, the complexity that manual measurement calculates, workload reduces greatly, efficient and convenient; The second, by the associated electrical tolerance of real-time measurement system, realized MMC loss in line computation, applied widely, calculate applicable to the loss of the MMC system under any operating state.The 3rd, self-defining module, in Practical Project, very convenient in modularized encapsulation, save floor space, improve resource utilization, and this platform is output as all kinds of losses and loss ratio, straightforward, facilitate staff's observing system running status at any time.

Brief description of the drawings

Fig. 1 is modularization multi-level converter topology diagram;

Fig. 2 is the each SM modular structure of modularization multi-level converter figure;

Fig. 3 is curve fitting module functional schematic;

Fig. 4 is switching frequency measurement module functional schematic;

Fig. 5 is duty ratio measuring functions of modules schematic diagram;

Fig. 6 is that duty ratio mean value solves functions of modules schematic diagram;

Fig. 7 is loss computing module functional schematic.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

Technical problem to be solved by this invention is while overcoming system running state change, during such as modulation degree change or the system failure, the deficiency that the modularization multi-level converter loss theory of computation and empirical equation applicability reduce, under PSCAD/EMTDC, provide the online loss computer general of a kind of effective, real-time modularization multi-level converter platform.

The present invention, under PSCAD/EMTDC, solves module and loss computing module by switching frequency measurement module, duty ratio measuring module, duty ratio mean value, realizes the online loss of modularization multi-level converter and calculates.

As shown in Figure 1, modularization multi-level converter is made up of A phase brachium pontis, B phase brachium pontis and C phase brachium pontis, A phase brachium pontis is gone up mutually brachium pontis by A and is descended mutually brachium pontis to form with A, B phase brachium pontis is gone up mutually brachium pontis by B and is descended mutually brachium pontis to form with B, C phase brachium pontis is gone up mutually brachium pontis by C and is descended mutually brachium pontis to form with C, and A goes up mutually brachium pontis, A and descends mutually brachium pontis, B to go up mutually brachium pontis, B to descend mutually brachium pontis, C to go up mutually brachium pontis to descend being mutually in series by n SM module of the 1st SM module to the of brachium pontis with C;

As shown in Figure 2, the structure of n SM module of the 1st SM module to the is identical, and the structure of each SM module is as follows: an IGBT who is parallel with the first fly-wheel diode connects with the 2nd IGBT that is parallel with the second fly-wheel diode, then connects with capacitor C.

The loss of each SM module is divided into an IGBT, the 2nd IGBT, the loss of the first fly-wheel diode and the second fly-wheel diode, the one IGBT loss is divided into again the steady-state loss of an IGBT and the switching loss of an IGBT, the 2nd IGBT loss is divided into again the steady-state loss of the 2nd IGBT and the switching loss of the 2nd IGBT, the steady-state loss of the one IGBT is divided into the driving loss of on-state loss and an IGBT of an IGBT, the steady-state loss of the 2nd IGBT is divided into the driving loss of on-state loss and the 2nd IGBT of the 2nd IGBT, the switching loss of the one IGBT is divided into the turn-on consumption of an IGBT and the turn-off power loss of an IGBT, the switching loss of the 2nd IGBT is divided into the turn-on consumption of the 2nd IGBT and the turn-off power loss of the 2nd IGBT.

The first fly-wheel diode loss is divided into the reverse recovery loss of on-state loss and first fly-wheel diode of the first fly-wheel diode, and the second fly-wheel diode loss is divided into the reverse recovery loss of on-state loss and second fly-wheel diode of the second fly-wheel diode.Wherein the driving loss of an IGBT and the 2nd IGBT is very little, negligible, so mainly the on-state loss to an IGBT, the on-state loss of the 2nd IGBT, the on-state loss of the first fly-wheel diode, the on-state loss of the second fly-wheel diode, the switching loss of an IGBT, the switching loss of the 2nd IGBT, the reverse recovery loss of the first fly-wheel diode, the reverse recovery loss of the second fly-wheel diode are calculated in the present invention.

The online loss computing method of a kind of modularization multi-level converter comprises the following steps:

1) obtain A phase brachium pontis current i by measurement _a, B phase brachium pontis current i _b, C phase brachium pontis current i _cwith the working temperature t of current environment, then calculate the on-state loss of an IGBT in each SM module, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode;

Step 1) specifically comprises the following steps:

11) from product description, obtain following four articles of curves: the collection emitter voltage V ' of the one IGBT when temperature is 25 DEG C _cEwith collector current I _cthe collection emitter voltage V of relation curve, temperature the one IGBT while being 125 DEG C _cEwith collector current I _cthe forward conduction voltage V ' of relation curve, temperature the first fly-wheel diode while being 25 DEG C _f-DC Forward Current I _frelation curve and the forward conduction voltage V of temperature first fly-wheel diode while being 125 DEG C _f-DC Forward Current I _frelation curve;

12) the collection emitter voltage V of the one IGBT in the time that temperature is 125 DEG C _cEwith collector current I _crelation curve in, obtain following N group data by trace-point method: (I _c1, V _cE1), (I _c2, V _cE2) ... (I _cN, V _cEN), wherein, I _c1-I _cNbe the collector current value of an IGBT, V _cE1-V _cENan IGBT collector current value to be I _c1-I _cNtime the one IGBT collection emitter voltage value, 1≤N≤100; To (I _c1, V _cE1), (I _c2, V _cE2) ... (I _cN, V _cEN) this N group data are the abbreviations of matrix experiment chamber (Matrix Laboratory) at MATLAB(MATLAB) and in carry out high order curve matching, the one IGBT collection emitter voltage V when obtaining temperature and being 125 DEG C _cEwith collector current I _crelationship;

According to following formula: R _t1=V _cE1/ I _c1, R _t2=V _cE2/ I _c2r _tN=V _cEN/ I _cNobtain: when an IGBT collector current value is I _c1-I _cNtime the one IGBT on state resistance value be R _t1-R _tN, and then obtain following N group data: (I _c1, R _t1), (I _c2, R _t2) ... (I _cN, R _tN); To (I _c1, R _t1), (I _c2, R _t2) ... (I _cN, R _tN) this N group data carry out high order curve matching in MATLAB, the on state resistance R of the one IGBT when obtaining temperature and being 125 DEG C _twith collector current I _crelationship;

13) the first fly-wheel diode forward conduction voltage V in the time that temperature is 125 DEG C _f-DC Forward Current I _frelation curve in, obtain following M group data by trace-point method: (I _f1, V _f1), (I _f2, V _f2) ... (I _fM, V _fM), wherein, I _f1-I _fMbe the DC Forward Current value of the first fly-wheel diode, V _f1-V _fMthat DC Forward Current value when the first fly-wheel diode is I _f1-I _fMtime the first fly-wheel diode forward conduction magnitude of voltage, 1≤M≤100; To (I _f1, V _f1), (I _f2, V _f2) ... (I _fM, V _fM) this M group data carry out high order curve matching in MATLAB, the first fly-wheel diode forward conduction voltage V when obtaining temperature and being 125 DEG C _fwith DC Forward Current I _frelationship;

According to following formula: R _d1=V _f1/ I _f1, R _d2=V _f2/ I _f2r _dM=V _cEM/ I _cMthe DC Forward Current value obtaining when the first fly-wheel diode is I _f1-I _fMtime the first fly-wheel diode on state resistance value R _d1-R _dM, and then obtain following M group data: (I _f1, R _d1), (I _f2, R _d2) ... (I _fM, R _dM); To (I _f1, R _d1), (I _f2, R _d2) ... (I _fM, R _dM) this M group data carry out high order curve matching in MATLAB, the first fly-wheel diode on state resistance R when obtaining temperature and being 125 DEG C _dwith DC Forward Current I _frelationship;

14) four curves in step 11) are carried out to interpolation arithmetic by following formula:

${\mathrm{\α}}_T=\frac{1}{V_{\mathrm{CE}}}[\frac{V_{\mathrm{CE}}-V_{\mathrm{CE}}^{\′}}{100}(t-25)+V_{\mathrm{CE}}^{\′}]$

${\mathrm{\α}}_D=\frac{1}{V_F^{\′}}[\frac{V_F^{\′}-V_F}{100}(t-25)+V_F]$

Obtain the junction temperature factor alpha of the on-state loss of an IGBT and the 2nd IGBT _tjunction temperature factor alpha with the on-state loss of the first fly-wheel diode and the second fly-wheel diode _d, in above-mentioned formula, the working temperature that t is current environment;

15) as shown in Figure 3, in curve fitting module, calculate the threshold voltage V such as the real-time on-state of an IGBT by following formula _cEX, the first fly-wheel diode the threshold voltage V such as real-time on-state _dX, an IGBT real-time on-state substitutional resistance R _tXreal-time on-state substitutional resistance R with the first fly-wheel diode _dX:

V _CEX＝α _T×V _CE

V _DX＝α _D×V _F

R _TX＝α _T×R _T

R _DX＝α _D×R _D

16) by V _cEXand R _tXthe following formula of substitution, draws the middle on-state loss P of an IGBT as calculated _eFS:

$\left\{\begin{array}{c}{V}_{\mathrm{EF}}=V_{\mathrm{CEX}}+R_{\mathrm{TX}}\·i\\ I_{\mathrm{EF}}=\sqrt{\stackrel{\‾}{\left|i\right|}\·\hat{i}}\\ P_{\mathrm{EFS}}=i\·V_{\mathrm{EF}}\end{array}\right.$

In above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, in A phase brachium pontis, and i=i _a, in B phase brachium pontis, i=i _b, in C phase brachium pontis, i=i _c, V _eFfor the threshold voltages such as the on-state of IGBT, I _eFfor the equivalent electric current of on-state of IGBT, the peak value of brachium pontis electric current, it is the arithmetic mean of brachium pontis electric current; In real work, I _c=i, integrating step 12)-step 15) finds out: V _cEXand R _tXbe the function of t and i, so, P _eFSfor the function of t and i;

By V _dXand R _dXthe following formula of substitution, draws the middle on-state loss P of the first fly-wheel diode as calculated _dFS:

$\left\{\begin{array}{c}{V}_{\mathrm{DF}}=V_{\mathrm{DX}}+R_{\mathrm{DX}}\·i\\ I_{\mathrm{DF}}=\sqrt{\stackrel{\‾}{\left|i\right|}\·\hat{i}}\\ P_{\mathrm{DFS}}=i\·V_{\mathrm{DF}}\end{array}\right.$

In above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, V _dFfor the threshold voltages such as the on-state of fly-wheel diode, I _dFfor the equivalent electric current of on-state of fly-wheel diode; In real work, I _f=i, integrating step 12)-step 15) finds out: V _dXand R _dXbe the function of t and i, so, P _dFSfor the function of t and i;

17) the middle on-state loss P ' of the 2nd IGBT _eFSmiddle on-state loss P with an IGBT _eFScomputational methods identical, by step 11)-step 16) draw the threshold voltage V ' such as the real-time on-state of the 2nd IGBT _cEX, the 2nd IGBT real-time on-state substitutional resistance R ' _tXmiddle on-state loss P ' with the 2nd IGBT _eFS;

The middle on-state loss P ' of the second fly-wheel diode _dFSmiddle on-state loss P with the first fly-wheel diode _dFScomputational methods identical, by step 11)-step 16) draw the threshold voltage V ' such as the real-time on-state of the second fly-wheel diode _dX, the second fly-wheel diode real-time on-state substitutional resistance R ' _dXmiddle on-state loss P ' with the second fly-wheel diode _dFS;

18) solve the mean value s4 of the duty ratio of the second fly-wheel diode in the mean value s3 of the duty ratio of the first fly-wheel diode in the mean value s2 of the duty ratio of the 2nd IGBT in the mean value s1 of the duty ratio of an IGBT in every all SM modules, all SM modules, all SM modules and all SM modules;

19) by the on-state loss P of following formula calculating the one IGBT _eF, the 2nd IGBT on-state loss P ' _eF, the first fly-wheel diode on-state loss P _dFon-state loss P ' with the second fly-wheel diode _dF:

P _EF＝s1×P _EFS

P′ _EF＝s2×P′ _EFS

P _DF＝s3×P _DFS

P′ _DF＝s4×P′ _DFS。

Step 18) specifically comprise the following steps:

181) as shown in Figure 5, simulation time t1 and described point step-length h are inputed in duty ratio measuring module, duty ratio measuring module is by gathering the current signal that flows through an IGBT, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode in each SM module, off state is opened in judgement, obtains the duty ratio of an IGBT in each SM module, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode;

182) as shown in Figure 6, duty ratio mean value solves the module duty ratio to an IGBT in each SM module respectively, the duty ratio of the 2nd IGBT in each SM module, in each SM module, in the duty ratio of the first fly-wheel diode and each SM module, the duty ratio of the second fly-wheel diode is averaged, output is respectively the mean value s1 of the duty ratio of an IGBT in all SM modules, the mean value s2 of the duty ratio of the 2nd IGBT in all SM modules, the mean value s4 of the duty ratio of the second fly-wheel diode in the mean value s3 of the duty ratio of the first fly-wheel diode and all SM modules in all SM modules.

The switching loss of IGBT and fly-wheel diode reverse recovery loss are the dynamic losss in break-over of device and turn off process, in theory can be by the product of electric current and voltage being asked to the assign to switching loss of calculating device of constant volume, but provide the function of time of the voltage and current of switching process, very difficult.The present invention is by step 2) calculate switching loss and the fly-wheel diode reverse recovery loss of IGBT.

2) calculate an IGBT and the switching loss of the 2nd IGBT and the reverse recovery loss of the first fly-wheel diode and the second fly-wheel diode in each SM module;

Step 2) specifically comprise the following steps

21) utilize interpolation to introduce the junction temperature coefficient ρ of the switching loss of an IGBT _tthe junction temperature coefficient ρ of (in the temperature range that can bear at an IGBT) and the first fly-wheel diode reverse recovery loss _d(in the temperature range that the first fly-wheel diode can bear), calculates both variation with temperature, and its computing formula is as follows:

${\mathrm{\ρ}}_T=\frac{1}{E_{\mathrm{SW}1}}[\frac{E_{\mathrm{SW}1}-E_{\mathrm{SW}2}}{100}(t-25)+E_{\mathrm{SW}2}]$

${\mathrm{\ρ}}_D=\frac{1}{E_{\mathrm{rec}1}}[\frac{E_{\mathrm{rec}1}-E_{\mathrm{rec}2}}{100}(t-25)+E_{\mathrm{rec}2}]$

In above-mentioned formula, E _sw1the energy loss in the switching process of an IGBT while meeting the following conditions: an IGBT supply voltage V _ccfor reference voltage u _ref, rated current electric current is reference current i _ref, junction temperature is 125 DEG C; E _sw2the energy loss in the switching process of an IGBT while meeting the following conditions: an IGBT supply voltage V _ccfor reference voltage u _ref, rated current is reference current i _ref, junction temperature is 25 DEG C; E _sw1and E _sw2all know by the product description of an IGBT; In reality, two IGBT of each SM module the inside adopt same model conventionally, so the relevant parameter such as reference voltage, reference current of the 2nd IGBT is all identical with an IGBT.

E _rec1the reverse recovery energy loss of the first fly-wheel diode while meeting the following conditions: both end voltage is reference voltage u _ref, DC Forward Current is reference current i _ref, junction temperature is 125 DEG C; E _rec2the reverse recovery energy loss of the first fly-wheel diode while meeting the following conditions: both end voltage is reference voltage u _ref, DC Forward Current is reference current i _ref, junction temperature is 25 DEG C; E _rec1and E _rec2all know by the product description of the first fly-wheel diode; In each SM module, the reference voltage of the first fly-wheel diode, reference current are identical with an IGBT, and reference voltage, the reference current of the second fly-wheel diode are identical with the 2nd IGBT.

22) as shown in Figure 4,, for the switching loss of computing module multilevel converter more accurately, need to measure in real time the switching frequency of an IGBT.For this reason, switching frequency measurement module obtains the switching frequency f of an IGBT by the number of SM module trigger impulse in measurement unit's time _sTwith the switching frequency (both equate) of the 2nd IGBT, but the switching frequency of the first fly-wheel diode cannot directly record.But when in each SM module, IGBT opens and has electric current to flow through, the first fly-wheel diode is in off state; When the first fly-wheel diode is opened and has electric current to flow through, an IGBT does not just have electric current to flow through in opening state yet, therefore, and the switching frequency f of an IGBT _sTthe first fly-wheel diode switching frequency f _sDtwice.

23) by the switching loss P of following formula calculating the one IGBT _swTreverse recovery loss P with the first fly-wheel diode _swD:

$\left\{\begin{array}{c}{P}_{\mathrm{swT}}={\mathrm{\ρ}}_T\·f_{\mathrm{sT}}\·\left(\frac{E_{\mathrm{on}}+E_{\mathrm{off}}}{u_{\mathrm{ref}}\·i_{\mathrm{ref}}}\right)\·U_C\·\stackrel{\‾}{\left|i\right|}\\ P_{\mathrm{swD}}={\mathrm{\ρ}}_D\·f_{\mathrm{sD}}\·\left(\frac{E_{\mathrm{rec}}}{u_{\mathrm{ref}}\·i_{\mathrm{ref}}}\right)\·U_C\·\stackrel{\‾}{\left|i\right|}\end{array}\right.$

In above-mentioned formula, U _cfor the average capacitor voltage of SM module, E _on, E _off, E _recbe respectively and be defined in an IGBT reference voltage u _ref, an IGBT reference current i _refoppositely recover energy loss with IGBT turn-on consumption, turn-off power loss and FWD under 125 DEG C of working junction temperatures; I is the upper and lower bridge arm electric current that flows into modularization multi-level converter, it is the arithmetic mean of brachium pontis electric current;

24) the switching loss P ' of the 2nd IGBT _swTswitching loss P with an IGBT _swTcomputational methods identical, by step 21)-step 23) obtain the switching loss P ' of the 2nd IGBT _swT;

The reverse recovery loss P ' of the second fly-wheel diode _swDreverse recovery loss P with a fly-wheel diode _swDcomputational methods identical, by step 21)-step 23) obtain the reverse recovery loss P ' of the second fly-wheel diode _swD.

3) as shown in Figure 7, by IGBT module parameter (V _cE, V _d, R _t, R _d, α _t, α _d, ρ _t, ρ _d), Uc, t, i _a, i _b, i _c, the switching frequency of two IGBT and two fly-wheel diodes inputs in loss computing module in s1, s2, s3, s4, each SM module, calculates the total on-state loss P of IGBT by loss computing module _tcon, the total on-state loss P of fly-wheel diode _dcon, IGBT master switch loss P _tsw, the total reverse recovery loss P of fly-wheel diode _drec, IGBT total losses P _t, fly-wheel diode total losses P _d, the total on-state loss P of modularization multi-level converter _con, modularization multi-level converter master switch loss P _sw, modularization multi-level converter total losses P _totwith modularization multi-level converter loss ratio K.

The total on-state loss P of IGBT _tconfor all SM module I GBT on-state loss sums of modularization multi-level converter, IGBT on-state loss is the on-state loss P of an IGBT _eFon-state loss P ' with the 2nd IGBT _eFsum;

The total on-state loss P of fly-wheel diode _dconfor all SM module fly-wheel diode on-state loss sums of modularization multi-level converter, fly-wheel diode on-state loss is the on-state loss P of the first fly-wheel diode _dFon-state loss P ' with the second fly-wheel diode _dFsum;

IGBT master switch loss P _tswfor all SM module I GBT switching loss sums of modularization multi-level converter, IGBT switching loss is the switching loss P of an IGBT _swTswitching loss P ' with the 2nd IGBT _swTsum;

The total reverse recovery loss P of fly-wheel diode _drecfor all SM module fly-wheel diode reverse recovery loss sums of modularization multi-level converter, fly-wheel diode reverse recovery loss is the reverse recovery loss P of the first fly-wheel diode _swDreverse recovery loss P ' with the second fly-wheel diode _swDsum;

IGBT total losses P _tfor the total on-state loss P of IGBT _tconwith IGBT master switch loss P _tswsum;

Fly-wheel diode total losses P _dfor the total on-state loss P of fly-wheel diode _dconwith the total reverse recovery loss P of fly-wheel diode _drecsum;

The total on-state loss P of modularization multi-level converter _confor the total on-state loss P of IGBT _tconwith the total on-state loss P of fly-wheel diode _dconsum;

Modularization multi-level converter master switch loss P _swfor IGBT master switch loss P _tswwith the total reverse recovery loss P of fly-wheel diode _drecsum;

Modularization multi-level converter total losses P _totfor IGBT total losses P _twith fly-wheel diode total losses P _dsum;

Described modularization multi-level converter loss ratio K is modularization multi-level converter total losses and the ratio of system total transmission capacity.System total transmission capacity, is the set point of a modularization multi-level converter, and for a fixing modularization multi-level converter, its capacity determines, can be by measuring.

Claims (3)

1. the online loss computing method of modularization multi-level converter, is characterized in that, it comprises the following steps:

1) obtain A phase brachium pontis current i by measurement _a, B phase brachium pontis current i _b, C phase brachium pontis current i _cwith the working temperature t of current environment, then calculate the on-state loss of an IGBT in each SM module, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode;

2) calculate an IGBT and the switching loss of the 2nd IGBT and the reverse recovery loss of the first fly-wheel diode and the second fly-wheel diode in each SM module;

3) calculate the total on-state loss P of IGBT by loss computing module _tcon, the total on-state loss P of fly-wheel diode _dcon, IGBT master switch loss P _tsw, the total reverse recovery loss P of fly-wheel diode _drec, IGBT total losses P _t, fly-wheel diode total losses P _d, the total on-state loss P of modularization multi-level converter _con, modularization multi-level converter master switch loss P _sw, modularization multi-level converter total losses P _totwith modularization multi-level converter loss ratio K;

The total on-state loss P of described IGBT _tconfor all SM module I GBT on-state loss sums of modularization multi-level converter, IGBT on-state loss is the on-state loss P of an IGBT _eFon-state loss P' with the 2nd IGBT _eFsum;

The total on-state loss P of described fly-wheel diode _dconfor all SM module fly-wheel diode on-state loss sums of modularization multi-level converter, fly-wheel diode on-state loss is the on-state loss P of the first fly-wheel diode _dFon-state loss P' with the second fly-wheel diode _dFsum;

Described IGBT master switch loss P _tswfor all SM module I GBT switching loss sums of modularization multi-level converter, IGBT switching loss is the switching loss P of an IGBT _swTswitching loss P' with the 2nd IGBT _swTsum;

The total reverse recovery loss P of described fly-wheel diode _drecfor all SM module fly-wheel diode reverse recovery loss sums of modularization multi-level converter, fly-wheel diode reverse recovery loss is the reverse recovery loss P of the first fly-wheel diode _swDreverse recovery loss P' with the second fly-wheel diode _swDsum;

Described IGBT total losses P _tfor the total on-state loss P of IGBT _tconwith IGBT master switch loss P _tswsum;

Described fly-wheel diode total losses P _dfor the total on-state loss P of fly-wheel diode _dconwith the total reverse recovery loss P of fly-wheel diode _drecsum;

The total on-state loss P of described modularization multi-level converter _confor the total on-state loss P of IGBT _tconwith the total on-state loss P of fly-wheel diode _dconsum;

Described modularization multi-level converter master switch loss P _swfor IGBT master switch loss P _tswwith the total reverse recovery loss P of fly-wheel diode _drecsum;

Described modularization multi-level converter total losses P _totfor IGBT total losses P _twith fly-wheel diode total losses P _dsum;

Described modularization multi-level converter loss ratio K is modularization multi-level converter total losses and the ratio of system total transmission capacity;

Described step 1) specifically comprise the following steps:

11) from product description, obtain following four articles of curves: the collection emitter voltage V' of the one IGBT when temperature is 25 DEG C _cEwith collector current I _cthe collection emitter voltage V of relation curve, temperature the one IGBT while being 125 DEG C _cEwith collector current I _cthe forward conduction voltage V' of relation curve, temperature the first fly-wheel diode while being 25 DEG C _f-DC Forward Current I _frelation curve and the forward conduction voltage V of temperature first fly-wheel diode while being 125 DEG C _f-DC Forward Current I _frelation curve;

12) the collection emitter voltage V of the one IGBT in the time that temperature is 125 DEG C _cEwith collector current I _crelation curve in, obtain following N group data by trace-point method: (I _c1, V _cE1), (I _c2, V _cE2) ... (I _cN, V _cEN), wherein, I _c1-I _cNbe the collector current value of an IGBT, V _cE1-V _cENan IGBT collector current value to be I _c1-I _cNtime the one IGBT collection emitter voltage value, 1≤N≤100; To (I _c1, V _cE1), (I _c2, V _cE2) ... (I _cN, V _cEN) this N group data carry out high order curve matching in MATLAB, the one IGBT collection emitter voltage V when obtaining temperature and being 125 DEG C _cEwith collector current I _crelationship;

According to following formula: R _t1=V _cE1/ I _c1, R _t2=V _cE2/ I _c2r _tN=V _cEN/ I _cNobtain: when an IGBT collector current value is I _c1-I _cNtime the one IGBT on state resistance value be R _t1-R _tN, and then obtain following N group data: (I _c1, R _t1), (I _c2, R _t2) ... (I _cN, R _tN); To (I _c1, R _t1), (I _c2, R _t2) ... (I _cN, R _tN) this N group data carry out high order curve matching in MATLAB, the on state resistance R of the one IGBT when obtaining temperature and being 125 DEG C _twith collector current I _crelationship;

13) the first fly-wheel diode forward conduction voltage V in the time that temperature is 125 DEG C _f-DC Forward Current I _frelation curve in, obtain following M group data by trace-point method: (I _f1, V _f1), (I _f2, V _f2) ... (I _fM, V _fM), wherein, I _f1-I _fMbe the DC Forward Current value of the first fly-wheel diode, V _f1-V _fMthat DC Forward Current value when the first fly-wheel diode is I _f1-I _fMtime the first fly-wheel diode forward conduction magnitude of voltage, 1≤M≤100; To (I _f1, V _f1), (I _f2, V _f2) ... (I _fM, V _fM) this M group data carry out high order curve matching in MATLAB, the first fly-wheel diode forward conduction voltage V when obtaining temperature and being 125 DEG C _fwith DC Forward Current I _frelationship;

According to following formula: R _d1=V _f1/ I _f1, R _d2=V _f2/ I _f2r _dM=V _cEM/ I _cMthe DC Forward Current value obtaining when the first fly-wheel diode is I _f1-I _fMtime the first fly-wheel diode on state resistance value R _d1-R _dM, and then obtain following M group data: (I _f1, R _d1), (I _f2, R _d2) ... (I _fM, R _dM); To (I _f1, R _d1), (I _f2, R _d2) ... (I _fM, R _dM) this M group data carry out high order curve matching in MATLAB, the first fly-wheel diode on state resistance R when obtaining temperature and being 125 DEG C _dwith DC Forward Current I _frelationship;

14) to step 11) in four curves carry out interpolation arithmetic by following formula:

${\mathrm{\α}}_T=\frac{1}{V_{\mathrm{CE}}}[\frac{V_{\mathrm{CE}}-V_{\mathrm{CE}}^{\′}}{100}(t-25)+V_{\mathrm{CE}}^{\′}]$

${\mathrm{\α}}_D=\frac{1}{V_F^{\′}}[\frac{V_F^{\′}-V_F}{100}(t-25)+V_F]$

Obtain the junction temperature factor alpha of the on-state loss of an IGBT and the 2nd IGBT _tjunction temperature factor alpha with the on-state loss of the first fly-wheel diode and the second fly-wheel diode _d, in above-mentioned formula, the working temperature that t is current environment;

15) in curve fitting module, calculate the threshold voltage V such as the real-time on-state of an IGBT by following formula _cEX, the first fly-wheel diode the threshold voltage V such as real-time on-state _dX, an IGBT real-time on-state substitutional resistance R _tXreal-time on-state substitutional resistance R with the first fly-wheel diode _dX:

V _CEX＝α _T×V _CE

V _DX＝α _D×V _F

R _TX＝α _T×R _T

R _DX＝α _D×R _D

16) by V _cEXand R _tXthe following formula of substitution, draws the middle on-state loss P of an IGBT as calculated _eFS:

$\left\{\begin{array}{c}{V}_{\mathrm{EF}}=V_{\mathrm{CEX}}+R_{\mathrm{TX}}\·i\\ I_{\mathrm{EF}}=\sqrt{\left|\stackrel{\‾}{i}\right|\·\hat{i}}\\ P_{\mathrm{EFS}}=i\·V_{\mathrm{EF}}\end{array}\right.$

In above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, in A phase brachium pontis, and i=i _a, in B phase brachium pontis, i=i _b, in C phase brachium pontis, i=i _c, V _eFfor the threshold voltages such as the on-state of IGBT, I _eFfor the equivalent electric current of on-state of IGBT, the peak value of brachium pontis electric current, it is the arithmetic mean of brachium pontis electric current; In real work, I _c=i, integrating step 12)-step 15) find out: V _cEXand R _tXbe the function of t and i, so, P _eFSfor the function of t and i;

By V _dXand R _dXthe following formula of substitution, draws the middle on-state loss P of the first fly-wheel diode as calculated _dFS:

$\left\{\begin{array}{c}{V}_{\mathrm{DF}}=V_{\mathrm{DX}}+R_{\mathrm{DX}}\·i\\ I_{\mathrm{DF}}=\sqrt{\left|\stackrel{\‾}{i}\right|\·\hat{i}}\\ P_{\mathrm{DFS}}=i\·V_{\mathrm{DF}}\end{array}\right.$

In above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, V _dFfor the threshold voltages such as the on-state of fly-wheel diode, I _dFfor the equivalent electric current of on-state of fly-wheel diode; In real work, I _f=i, integrating step 12)-step 15) find out: V _dXand R _dXbe the function of t and i, so, P _dFSfor the function of t and i;

17) the middle on-state loss P' of the 2nd IGBT _eFSmiddle on-state loss P with an IGBT _eFScomputational methods identical, by step 11)-step 16) draw the threshold voltage V ' such as the real-time on-state of the 2nd IGBT _cEX, the 2nd IGBT real-time on-state substitutional resistance R ' _tXmiddle on-state loss P' with the 2nd IGBT _eFS;

The middle on-state loss P' of the second fly-wheel diode _dFSmiddle on-state loss P with the first fly-wheel diode _dFScomputational methods identical, by step 11)-step 16) draw the threshold voltage V ' such as the real-time on-state of the second fly-wheel diode _dX, the second fly-wheel diode real-time on-state substitutional resistance R ' _dXmiddle on-state loss P' with the second fly-wheel diode _dFS;

18) solve the mean value s4 of the duty ratio of the second fly-wheel diode in the mean value s3 of the duty ratio of the first fly-wheel diode in the mean value s2 of the duty ratio of the 2nd IGBT in the mean value s1 of the duty ratio of an IGBT in all SM modules, all SM modules, all SM modules and all SM modules;

19) by the on-state loss P of following formula calculating the one IGBT _eF, the 2nd IGBT on-state loss P' _eF, the first fly-wheel diode on-state loss P _dFon-state loss P' with the second fly-wheel diode _dF:

P _EF＝s1×P _EFS

P' _EF＝s2×P' _EFS

P _DF＝s3×P _DFS

P' _DF＝s4×P' _DFS。

2. the online loss computing method of a kind of modularization multi-level converter according to claim 1, is characterized in that described step 18) specifically comprise the following steps:

181) simulation time t1 and described point step-length h are inputed in duty ratio measuring module, duty ratio measuring module is by gathering the current signal that flows through an IGBT, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode in each SM module, off state is opened in judgement, obtains the duty ratio of an IGBT in each SM module, the 2nd IGBT, the first fly-wheel diode and the second fly-wheel diode;

182) duty ratio mean value solves the module duty ratio to an IGBT in each SM module respectively, the duty ratio of the 2nd IGBT in each SM module, in each SM module, in the duty ratio of the first fly-wheel diode and each SM module, the duty ratio of the second fly-wheel diode is averaged, output is respectively the mean value s1 of the duty ratio of an IGBT in all SM modules, the mean value s2 of the duty ratio of the 2nd IGBT in all SM modules, the mean value s4 of the duty ratio of the second fly-wheel diode in the mean value s3 of the duty ratio of the first fly-wheel diode and all SM modules in all SM modules.

3. the online loss computing method of a kind of modularization multi-level converter according to claim 1, is characterized in that described step 2) specifically comprise the following steps:

21) utilize interpolation to introduce the junction temperature coefficient ρ of the switching loss of an IGBT _tjunction temperature coefficient ρ with the first fly-wheel diode reverse recovery loss _d, calculate both variation with temperature, its computing formula is as follows:

${\mathrm{\ρ}}_T=\frac{1}{E_{\mathrm{SW}1}}[\frac{E_{\mathrm{SW}1}-E_{\mathrm{SW}2}}{100}(t-25)+E_{\mathrm{SW}2}]$

${\mathrm{\ρ}}_D=\frac{1}{E_{\mathrm{rec}1}}[\frac{E_{\mathrm{rec}1}-E_{\mathrm{rec}2}}{100}(t-25)+E_{\mathrm{rec}2}]$

In above-mentioned formula, E _sw1the energy loss in the switching process of an IGBT while meeting the following conditions: an IGBT supply voltage V _ccfor reference voltage u _ref, rated current is reference current i _ref, junction temperature is 125 DEG C; E _sw2the energy loss in the switching process of an IGBT while meeting the following conditions: an IGBT supply voltage V _ccfor reference voltage u _ref, rated current is reference current i _ref, junction temperature is 25 DEG C; E _sw1and E _sw2all know by the product description of an IGBT;

E _rec1the reverse recovery energy loss of the first fly-wheel diode while meeting the following conditions: both end voltage is reference voltage u _ref, DC Forward Current is reference current i _ref, junction temperature is 125 DEG C; E _rec2the reverse recovery energy loss of the first fly-wheel diode while meeting the following conditions: both end voltage is reference voltage u _ref, DC Forward Current is reference current i _ref, junction temperature is 25 DEG C; E _rec1and E _rec2all know by the product description of the first fly-wheel diode;

22) switching frequency measurement module obtains the switching frequency f of an IGBT by the number of SM module trigger impulse in measurement unit's time _sT, the switching frequency f of the first fly-wheel diode _sDbe the switching frequency f of an IGBT _sThalf;

23) by the switching loss P of following formula calculating the one IGBT _swTreverse recovery loss P with the first fly-wheel diode _swD:

$\left\{\begin{array}{c}{P}_{\mathrm{swT}}={\mathrm{\ρ}}_T\·f_{\mathrm{sT}}\·\left(\frac{E_{\mathrm{on}}+E_{\mathrm{off}}}{u_{\mathrm{ref}}\·i_{\mathrm{ref}}}\right)\·U_C\·\left|\stackrel{\‾}{i}\right|\\ P_{\mathrm{swD}}={\mathrm{\ρ}}_D\·f_{\mathrm{sD}}\·\left(\frac{E_{\mathrm{rec}}}{u_{\mathrm{ref}}\·i_{\mathrm{ref}}}\right)\·U_C\·\left|\stackrel{\‾}{i}\right|\end{array}\right.$

In above-mentioned formula, U _cfor the average capacitor voltage of SM module, E _on, E _off, E _recbe respectively and be defined in an IGBT reference voltage u _ref, an IGBT reference current i _refoppositely recover energy loss with IGBT turn-on consumption, turn-off power loss and the first fly-wheel diode under maximum junction temperature; I is the upper and lower bridge arm electric current that flows into modularization multi-level converter, it is the arithmetic mean of brachium pontis electric current;

24) the switching loss P' of the 2nd IGBT _swTswitching loss P with an IGBT _swTcomputational methods identical, by step 21)-step 23) obtain the switching loss P' of the 2nd IGBT _swT;

The reverse recovery loss P' of the second fly-wheel diode _swDreverse recovery loss P with a fly-wheel diode _swDcomputational methods identical, by step 21)-step 23) obtain the reverse recovery loss P' of the second fly-wheel diode _swD.